Michael Fayer
David Mulvane Ehrsam and Edward Curtis Franklin Professor of Chemistry
Web page: http://web.stanford.edu/group/fayer/
Bio
My research group studies complex molecular systems by using ultrafast multi-dimensional infrared and non-linear UV/Vis methods. A basic theme is to understand the role of mesoscopic structure on the properties of molecular systems. Many systems have structure on length scales large compare to molecules but small compared to macroscopic dimensions. The mesoscopic structures occur on distance scales of a few nanometers to a few tens of nanometers. The properties of systems, such as water in nanoscopic environments, room temperature ionic liquids, functionalized surfaces, liquid crystals, metal organic frameworks, water and other liquids in nanoporous silica, polyelectrolyte fuel cell membranes, vesicles, and micelles depend on molecular level dynamics and intermolecular interactions. Our ultrafast measurements provide direct observables for understanding the relationships among dynamics, structure, and intermolecular interactions.
Bulk properties are frequently a very poor guide to understanding the molecular level details that determine the nature of a chemical process and its dynamics. Because molecules are small, molecular motions are inherently very fast. Recent advances in methodology developed in our labs make it possible for us to observe important processes as they occur. These measurements act like stop-action photography. To focus on a particular aspect of a time evolving system, we employ sequences of ultrashort pulses of light as the basis for non-linear methods such as ultrafast infrared two dimensional vibrational echoes, optical Kerr effect methods, and ultrafast IR transient absorption experiments.
We are using ultrafast 2D IR vibrational echo spectroscopy and other multi-dimensional IR methods, which we have pioneered, to study dynamics of molecular complexes, water confined on nm lengths scales with a variety of topographies, molecules bound to surfaces, ionic liquids, and materials such as metal organic frameworks and porous silica. We can probe the dynamic structures these systems. The methods are somewhat akin to multidimensional NMR, but they probe molecular structural evolution in real time on the relevant fast time scales, eight to ten orders of magnitude faster than NMR. We are obtaining direct information on how nanoscopic confinement of water changes its properties, a topic of great importance in chemistry, biology, geology, and materials. For the first time, we are observing the motions of molecular bound to surfaces. In biological membranes, we are using the vibrational echo methods to study dynamics and the relationship among dynamics, structure, and function. We are also developing and applying theory to these problems frequently in collaboration with top theoreticians.
We are studying dynamics in complex liquids, in particular room temperature ionic liquids, liquid crystals, supercooled liquids, as well as in influence of small quantities of water on liquid dynamics. Using ultrafast optical heterodyne detected optical Kerr effect methods, we can follow processes from tens of femtoseconds to ten microseconds. Our ability to look over such a wide range of time scales is unprecedented. The change in molecular dynamics when a system undergoes a phase change is of fundamental and practical importance. We are developing detailed theory as the companion to the experiments.
We are studying photo-induced proton transfer in nanoscopic water environments such as polyelectrolyte fuel cell membranes, using ultrafast UV/Vis fluorescence and multidimensional IR measurements to understand the proton transfer and other processes and how they are influenced by nanoscopic confinement. We want to understand the role of the solvent and the systems topology on proton transfer dynamics.
Administrative Appointments
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David Mulvane Ehrsam and Edward Curtis Franklin Professor of Chemistry, Stanford University (2000 - Present)
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Professor of Chemistry, Stanford University (1984 - 2000)
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Associate Professor of Chemistry, Stanford University (1980 - 1984)
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Assistant Professor of Chemistry, Stanford University (1974 - 1980)
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Professor of Physics, University of Grenoble (1982 - 1982)
Honors & Awards
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Peter Debye Award in Physical Chemistry, American Chemical Society (2021)
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Pittsburgh Spectroscopy Award, Spectroscopy Society of Pittsburgh (2018)
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Ahmed Zewail Award in Ultrafast Science and Technology, American Chemical Society (2014)
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Arthur L. Schawlow Prize in Laser Science, American Physical Society (2012)
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Ellis R. Lippincott Award, Optical Society of America (2009)
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Fellow, Optical Society of America (2009)
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Fellow, Royal Society of Chemistry (2008)
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E. Bright Wilson Award for Spectroscopy, American Chemical Society (2007)
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Member, National Academy of Sciences (2007)
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Earl K. Plyler Prize for Molecular Spectroscopy, American Physical Society (2000)
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Member, American Academy of Arts and Sciences (1999)
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Dean's Award for Distinguished Teaching, Stanford University (1986)
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Fellow, Guggenheim Foundation (1983)
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Fellow, American Physical Society (1982)
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Dreyfus Teacher-Scholar Award, Camille & Henry Dreyfus Foundation (1977)
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Fellow, Camille & Henry Dreyfus Foundation (1977)
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Fellow, Alfred P. Sloan Foundation (1977)
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Phi Beta Kappa, University of California at Berkeley (1969)
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Fellow, National Science Foundation (1966-1967)
Boards, Advisory Committees, Professional Organizations
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Member, Editorial Board, Journal of Chemical Physics (1987 - 1990)
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Member, Advisory Board, Journal of Physical Chemistry (1986 - 1989)
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Associate Editor, Journal of Luminescence (1988 - Present)
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Advisory Editor, Chemical Physics (1985 - Present)
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Advisory Editor, Chemical Physics Letters (1984 - 2006)
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Chairman, Awards Committee, Earl K. Plyler Prize for Molecular Spectroscopy (2006 - 2006)
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Chairman, 7th International Conference on Unconventional Photoactive Systems, Stanford University (1995 - 1995)
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Chairman, Fourth International Conference on Dynamical Processes, Stanford University (1983 - 1983)
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Member, American Chemical Society
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Member, American Optical Society
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Member, American Physical Society
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Member, Royal Society of Chemistry
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Member, Sigma Xi
Professional Education
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Ph.D., University of California at Berkeley, Chemistry (1974)
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B.S., University of California at Berkeley, Chemistry (1969)
2024-25 Courses
- Quantum mechanics with spectroscopy examples
CHEM 275 (Spr) - Spectroscopy Laboratory
CHEM 176 (Win) -
Independent Studies (4)
- Advanced Undergraduate Research
CHEM 190 (Aut, Win, Spr, Sum) - Directed Instruction/Reading
CHEM 90 (Aut, Win, Spr, Sum) - Research and Special Advanced Work
CHEM 200 (Aut, Win, Spr, Sum) - Research in Chemistry
CHEM 301 (Aut, Win, Spr, Sum)
- Advanced Undergraduate Research
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Prior Year Courses
2023-24 Courses
- Quantum mechanics with spectroscopy examples
CHEM 275 (Spr) - Spectroscopy Laboratory
CHEM 176 (Win)
2022-23 Courses
- Advanced Physical Chemistry
CHEM 271 (Aut) - Physical Chemistry II
CHEM 173 (Aut) - Spectroscopy Laboratory
CHEM 176 (Win)
2021-22 Courses
- Advanced Physical Chemistry
CHEM 271 (Aut) - Spectroscopy Laboratory
CHEM 176 (Win)
- Quantum mechanics with spectroscopy examples
Stanford Advisees
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Doctoral Dissertation Reader (AC)
Christina Deschene, Dashiel Grusky, Ashley Saunders, Sunny Wang -
Doctoral Dissertation Advisor (AC)
Aaron Charnay, Tristan Heck, Laura Leibfried, Max Moncada Cohen, Junkun Pan, Jordyn Smith, Xiangyu Xing
All Publications
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Effects of Nanoconfinement on Dynamics in Concentrated Aqueous Magnesium Chloride Solutions.
The journal of physical chemistry. B
2024
Abstract
Water behavior in various natural and manufactured settings is influenced by confinement in organic or inorganic frameworks and the presence of solutes. Here, the effects on dynamics from both confinement and the addition of solutes are examined. Specifically, water and ion dynamics in concentrated (2.5-4.2 m) aqueous magnesium chloride solutions confined in mesoporous silica (2.8 nm pore diameter) were investigated using polarization selective pump-probe and 2D infrared spectroscopies. Fitting the rotational and spectral diffusion dynamics measured by the vibrational probe, selenocyanate, with a previously developed two-state model revealed distinct behaviors at the interior of the silica pores (core state) and near the wall of the confining framework (shell state). The shell dynamics are noticeably slower than the bulk, or core, dynamics. The concentration-dependent slowing of the dynamics aligns with behavior in the bulk solutions, but the spectrally separated water-associated and Mg2+-associated forms of the selenocyanate probe exhibit different responses to confinement. The disparity in the complete reorientation times is larger upon confinement, but the spectral diffusion dynamics become more similar near the silica surface. The length scales that characterize the transition from surface-influenced to bulk-like behavior for the salt solutions in the pores are discussed and compared to those of pure water and an organic solvent confined in the same pores. These comparisons offer insights into how confinement modulates the properties of different liquids.
View details for DOI 10.1021/acs.jpcb.4c01639
View details for PubMedID 38787935
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Pendant Group Functionalization of Cyclic Olefin for High Temperature and High-Density Energy Storage.
Advanced materials (Deerfield Beach, Fla.)
2024: e2402133
Abstract
High-temperature flexible polymer dielectrics are critical for high-power-density energy storage and conversion under harsh operating conditions. These types of dielectrics will need to simultaneously possess a high bandgap, dielectric constant and glass transition temperature - a substantial challenge when designing novel dielectric polymers. In this work, by varying halogen substituents of an aromatic pendant hanging off a bicyclic mainchain polymer, a class of high-temperature olefins with adjustable thermal stability are obtained, all with uncompromised large bandgaps. Halogens substitution of the pendant groups at para or ortho position of polyoxanorborneneimides (PONB) imparts it with tunable high glass transition temperature from ∼220 to 245 °C, while with also moderate dielectric constant of ∼ 2.8-3.0 and high breakdown strength of ∼625-800 MV/m. A high energy density of 7.1 J/cc at 200 °C is achieved with p-POClNB, representing the highest reported energy density among all-organic homo-polymer dielectrics. Molecular dynamic simulations and ultrafast infrared spectroscopy were used to probe the free volume element distribution and chain relaxations of the polymers to provide insights to the dielectric thermal properties. An increase in free volume element is observed with the change in the pendant group from fluorine to bromine at the para position; however, a decrease in free volume element is observed as we change the pendant group from fluorine to chlorine at the ortho position because of the steric hindrance. Overall, the dielectric constant and band gap remain stable while the glass transition temperature changes more obviously. Consequently, by proper designing the pendant groups, the thermal stability of PONB can be improved for harsh condition electrification. This article is protected by copyright. All rights reserved.
View details for DOI 10.1002/adma.202402133
View details for PubMedID 38767177
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Fast Structural Dynamics in Concentrated HCl Solutions: From Proton Hopping to the Bulk Viscosity.
Journal of the American Chemical Society
2024
Abstract
Concentrated acid solutions, particularly HCl, have been studied extensively to examine the proton hopping and infrared spectral signatures of hydronium ions. Much less attention has been given to the structural dynamics of concentrated HCl solutions. Here, we apply optical heterodyne detected-optical Kerr effect (OHD-OKE) measurements to examine HCl concentration-dependent dynamics from moderate (0.8 m) to very high (15.5 m) concentrations and compare the results to the dynamics of NaCl solutions, as Na+ is similar in size to the hydronium cation. Both HCl and NaCl OHD-OKE signals decay as triexponentials at all concentrations, in contrast to pure water, which decays as a biexponential. Two remarkable features of the HCl dynamics are the following: (1) the bulk viscosity is linearly related to the slowest decay constant, t3, and (2) the concentration-dependent proton hopping times, determined by ab initio MD simulations and 2D IR chemical exchange experiments, both obtained from the literature, fall on the same line as the slowest structural dynamics relaxation time, t3, within experimental error. The structural dynamics of hydronium/chloride/water clusters, with relaxation times t3, are responsible for the concentration dependence of microscopic property of proton hopping and the macroscopic bulk viscosity. The slowest time constant (t3), which does not have a counterpart in pure water, is 3 ps at 0.8 m and increases by a factor of ∼2 by 15.5 m. The two fastest HCl decay constants, t1 and t2, are similar to those of pure water and increase mildly with the concentration.
View details for DOI 10.1021/jacs.3c11620
View details for PubMedID 38682723
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Restricted Orientation Anisotropy Method for FVE Radii Characterization: Confirmed and Refined via the Study of Six Vibrational Probes
MACROMOLECULES
2024; 57 (3): 903-915
View details for DOI 10.1021/acs.macromol.3c02093
View details for Web of Science ID 001161247700001
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Influence of Internal Bond Rotation on Ultrafast IR Anisotropy Measurements and the Internal Rotational Potential.
The journal of physical chemistry. B
2023
Abstract
Measurement of molecular orientation relaxation using ultrafast infrared (IR) pump-probe experiments is widely used to understand the properties of liquids and other systems. In the simplest situation, the anisotropy decay is a single exponential reflecting diffusive orientational relaxation. However, the anisotropy decay is frequently biexponential. The faster component is caused by solvent caging restricting angular sampling until constraint release permits all angles to be sampled. Here, we describe another mechanism that limits the range of sampling, i.e., sampling of a restricted range of angles via internal bond reorientation on a rotational potential surface with barriers. If the internal angular sampling occurs faster than the entire molecule's diffusive orientational relaxation, it will produce a fast component of anisotropy decay with a cone angle determined by the shape of the internal rotation potential. We studied four molecules to illustrate the effects of internal bond rotations on anisotropy decay. The molecules are p-chlorobenzonitrile, phenylselenocyanate, phenylthiocyanate, and 2-nitrophenylselenocyante in the solvent N,N-dimethylformamide. The CN stretch is used as the IR chromophore. p-Chlorobenzonitrile does not have internal rotation; its anisotropy decays as a single exponential. The other three have bent geometries and internal rotation of the moieties containing the CN occurs; the anisotropies decay as biexponentials. The faster of the two decays can be understood in terms of motions on the rotational potential surface. A method is developed for extracting the intramolecular rotational potential surface by employing a modification of the harmonic cone model, and the results are compared to density functional theory calculations.
View details for DOI 10.1021/acs.jpcb.3c07080
View details for PubMedID 38150550
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Water-in-Salt: Fast Dynamics, Structure, Thermodynamics, and Bulk Properties.
The journal of physical chemistry. B
2023
Abstract
We present concentration-dependent dynamics of highly concentrated LiBr solutions and LiCl temperature-dependent dynamics for two high concentrations and compare the results to those of prior LiCl concentration-dependent data. The dynamical data are obtained using ultrafast optical heterodyne-detected optical Kerr effect (OHD-OKE). The OHD-OKE decays are composed of two pairs of biexponentials, i.e., tetra-exponentials. The fastest decay (t1) is the same as pure water's at all concentrations within error, while the second component (t2) slows slightly with concentration. The slower components (t3 and t4), not present in pure water, slow substantially, and their contributions to the decays increase significantly with increasing concentration, similar to LiCl solutions. Simulations of LiCl solutions from the literature show that the slow components arise from large ion/water clusters, while the fast components are from ion/water structures that are not part of large clusters. Temperature-dependent studies (15-95 °C) of two high LiCl concentrations show that decreasing the temperature is equivalent to increasing the room temperature concentration. The LiBr and LiCl concentration dependences and the two LiCl concentrations' temperature dependences all have bulk viscosities that are linearly dependent on τcslow, the correlation time of the slow dynamics (weighted averages of t3 and t4). Remarkably, all four viscosity vs 1/τCslow plots fall on the same line. Application of transition state theory to the temperature-dependent data yields the activation enthalpies and entropies for the dynamics of the large ion/water clusters, which underpin the bulk viscosity.
View details for DOI 10.1021/acs.jpcb.3c07711
View details for PubMedID 38118403
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Structural Dynamics of a Novel Pseudohalide Perovskite Cs2Pb(SeCN)(2)Br-2 Investigated with Nonlinear Infrared Spectroscopy
JOURNAL OF PHYSICAL CHEMISTRY C
2023
View details for DOI 10.1021/acs.jpcc.3c02251
View details for Web of Science ID 001030464100001
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Synthetically tunable polymers, free volume element size distributions, and dielectric breakdown field strengths
MATERIALS TODAY
2023; 67: 57-67
View details for DOI 10.1016/j.mattod.2023.05.010
View details for Web of Science ID 001071986900001
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Long-Range Interface Effects in Room Temperature Ionic Liquids: Vibrational Lifetime Studies of Thin Films.
The journal of physical chemistry. B
2023
Abstract
Interface effects in the room temperature ionic liquids (RTILs) 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF4) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BmimNTf2) were investigated using ultrafast infrared polarization selective pump-probe (PSPP) spectroscopy. The CN stretch mode of SCN- dissolved in the RTILs was used as the vibrational probe. The vibrational lifetime of the SCN- was the experimental observable. Quite similar single SCN- lifetimes were observed: 59.5 ± 0.4 ps in bulk BmimBF4 and 56.4 ± 0.4 ps in bulk BmimNTf2. Thin films of both RTILs with thicknesses in the range of 15-300 nm were prepared by spin coating on functionalized substrates. PSPP experiments were performed in a small-incidence reflection geometry. In the thin films, a second, shorter lifetime was observed in addition to the bulk lifetime, with the amplitude of the shorter lifetime increasing with decreasing film thickness. By modeling the thickness dependence of the lifetime amplitudes, the correlation length of the interface effect (constant for exponential falloff of the influence of the interface) was determined to be 44.6 ± 0.6 nm for BmimBF4 and 48.3 ± 2.2 nm for BmimNTf2. The values for the shorter film lifetimes were 12.6 ± 0.1 ps for BmimBF4 and 20.2 ± 0.6 ps for BmimNTf2; the substantial differences from the bulk lifetimes showed that some of the SCN- anions near the interface experience an environment distinct from that of the bulk. It was also found that for the BmimNTf2 sample only, some of the SCN- anions reside in the surface functionalized layer with two distinct environments having distinct lifetimes.
View details for DOI 10.1021/acs.jpcb.3c02948
View details for PubMedID 37381928
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Ion/Water Network Structural Dynamics in Highly Concentrated Lithium Chloride and Lithium Bromide Solutions Probed with Ultrafast Infrared Spectroscopy.
The journal of physical chemistry. B
2023
Abstract
The structural dynamics of highly concentrated LiCl and LiBr aqueous solutions were observed from 1-4 to 1-16 water molecules per ion pair using ultrafast polarization-selective pump-probe (PSPP) experiments on the OD stretch of dilute HOD. At these high salt concentrations, an extended ion/water network exists with complex structural dynamics. Population decays from PSPP experiments highlight two distinct water components. From the frequency-dependent amplitudes of the decays, the spectra of hydroxyls bound to halides and to water oxygens are obtained, which are not observable in the FT-IR spectra. PSPP experiments also measure frequency-dependent water orientational relaxation. At short times, wobbling dynamics within a restricted angular cone occurs. At high concentrations, the cone angles are dependent on frequency (hydrogen bond strength), but at higher water concentrations (>10 waters per ion pair), there is no frequency dependence. The average cone angle increases as the ion concentration decreases. The slow time constant for complete HOD orientational relaxation is independent of concentration but slower in LiCl than in LiBr. Comparison to structural MD simulations of LiCl from the literature indicates that the loss of the cone angle wavelength dependence and the increase in the cone angles as the concentration decreases occur as the prevalence of large ion/water clusters gives way to contact ion pairs.
View details for DOI 10.1021/acs.jpcb.2c08792
View details for PubMedID 37172191
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Dynamics of Concentrated Aqueous Lithium Chloride Solutions Investigated with Optical Kerr Effect Experiments.
The journal of physical chemistry. B
2023
Abstract
We report the dynamics of concentrated lithium chloride aqueous solutions over a range of moderate to high concentrations. Concentrations (1-29 to 1-3.3 LiCl-water) were studied in which, at the highest concentrations, there are far too few water molecules to solvate the ions. The measurements were made with optically heterodyne-detected optical Kerr effect experiments, a non-resonant technique able to observe dynamics over a wide range of time scales and signal amplitudes. While the pure water decay is a biexponential, the LiCl-water decays are tetra-exponentials at all concentrations. The faster two decays arise from water dynamics, while the slower two decays reflect the dynamics of the ion-water network. The fastest decay (t1) is the same as pure water at all concentrations. The second decay (t2) is also the same as that of pure water at the lower concentrations, and then, it slows with increasing concentration. The slower dynamics (t3 and t4), which do not have counterparts in pure water, arise from ion-water complexes and, at the highest concentrations, an extended ion-water network. Comparisons are made between the concentration dependence of the observed dynamics and simulations of structural changes from the literature, which enable the assignment of dynamics to specific ion-water structures. The concentration dependences of the bulk viscosity and the ion-water network dynamics are directly correlated. The correlation provides an atomistic-level understanding of the viscosity.
View details for DOI 10.1021/acs.jpcb.3c01702
View details for PubMedID 37018545
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Concentration Dependence of Dynamics and Structure among Hydrated Magnesium Ions: An Ultrafast Infrared Study.
The journal of physical chemistry. B
2023
Abstract
The dynamics of aqueous magnesium chloride solutions, from relatively dilute (0.5 m) to near saturated (4.2 m) concentrations, were investigated using ultrafast two dimensional infrared and polarization selective pump-probe spectroscopies. The experiments were performed on two spectrally distinct nitrile stretch frequencies of the selenocyanate vibrational probe, corresponding to the CN nitrogen lone pair being associated with water and with Mg2+. No chemical exchange of the two species was observed over the experimental time scale (∼100 ps), enabling straightforward analysis of their dynamics. The dynamics reported by the Mg2+-associated peak are slower than those of the water-associated peak, suggesting that the immediate environment of the hydrated Mg2+ is different from the rest of the solution. Notably, the Mg2+-associated peak displays three spectral diffusion time scales, the slowest being ∼30 ps, while the water-associated peak decays as a faster biexponential. From the complete orientational relaxation time and hydrodynamic theory, a magnesium hydration number of six was obtained, which is in good agreement with NMR and X-ray diffraction studies. This hydration number holds for all concentrations until near saturation, when the linewidths and the dynamics deviate from linear trends, indicative of Mg2+ solvation structure changes resulting from a shortage of water molecules needed for full solvation.
View details for DOI 10.1021/acs.jpcb.3c00300
View details for PubMedID 36995831
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Dynamics of Acrylamide Hydrogels, Polymers, and Monomers in Water Measured with Optical Heterodyne-Detected Optical Kerr Effect Spectroscopy.
The journal of physical chemistry. B
2023
Abstract
The ultrafast dynamics of acrylamide monomers (AAm), polyacrylamide (PAAm), and polyacrylamide hydrogels (PAAm-HG) in water were studied using optical heterodyne-detected optical Kerr effect (OHD-OKE) spectroscopy. Previous ultrafast infrared (IR) measurements of the water dynamics showed that at the same concentration of the acrylamide moiety, AAm, PAAm, and PAAm-HG exhibited identical water dynamics and that these dynamics slowed with increasing concentration. In contrast to the IR measurements, OHD-OKE experiments measure the dynamics of both the water and the acrylamide species, which occur on different time scales. In this study, the dynamics of all the acrylamide systems slowed with increasing concentration. We found that AAm exhibits tetraexponential decays, the longest component of which followed Debye-Stokes-Einstein behavior except for the highest concentration, 40% (w/v). Low concentrations of PAAm followed a single power law decay, while high concentrations of PAAm and all concentrations of PAAm-HG decayed with two power laws. The highest concentrations, 25% and 40%, of PAAm and PAAm-HG showed nearly identical dynamics. We interpreted this result as reflecting a similar extent of chain-chain interactions. At low concentrations, PAAm displays non-Markovian, single-chain dynamics (single power law), but PAAm displays entangled chain-chain interactions at high concentrations (two power laws). PAAm-HG has chain-chain interactions at all concentrations that arise from the cross-linking. At high concentrations, the dynamics of the entangled of PAAm become identical within error as those of the cross-linked PAAm-HG.
View details for DOI 10.1021/acs.jpcb.2c08164
View details for PubMedID 36706351
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Water Dynamics in Aqueous Poly-N-Isopropylacrylamide Below and Through the Lower Critical Solution Temperature.
The journal of physical chemistry. B
2022
Abstract
Poly-N-isopropylacrylamide (PNIPAM) is a thermo-responsive polymer that exhibits a reversible structural change from extended chains to aggregates in aqueous solution above its lower critical solution temperature (LCST). Using polarization-selective IR pump-probe spectroscopy, the water orientational dynamics in PNIPAM from below to above the LCST were examined and compared to those of its monomer solution, N-isopropylacrylamide (NIPAM), polyacrylamide, and an acrylamide monomer solution, which are not thermo-responsive. The OD stretch of dilute HOD in H2O is used as a vibrational probe of water orientational dynamics. Below the LCST of the polymer, NIPAM and PNIPAM solutions exhibited identical water dynamics that were significantly different from those of bulk water, containing both faster and slower components due to solute-water interactions. Therefore, there is no difference in the nature of water interactions with a single NIPAM moiety and a long polymer chain. For all systems, including PNIPAM below and above the LCST, the orientational dynamics were modeled with a bulk water component and a polymer/monomer-associated component based on previous experimental and computational findings. Above the LCST, PNIPAM showed fast water orientational relaxation but much slower long-time dynamics compared to those of NIPAM. The slow component in PNIPAM, which was too slow to be accurately measured due to the limited OD vibrational lifetime, is ascribed to water confined in small voids (<2 nm in diameter) of PNIPAM globules. These results highlight important details about thermo-responsive polymers and the dynamics of their solvation water as they undergo a significant structural change.
View details for DOI 10.1021/acs.jpcb.2c05506
View details for PubMedID 36067498
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Probing Lattice Dynamics in Two-Dimensional InorganicPseudohalide Perovskites with Ultrafast Infrared Spectroscopy br
JOURNAL OF PHYSICAL CHEMISTRY C
2022; 126 (24): 10145-10158
View details for DOI 10.1021/acs.jpcc.2c03516
View details for Web of Science ID 000821434300001
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Water Dynamics and Structure of Highly Concentrated LiCl Solutions Investigated Using Ultrafast Infrared Spectroscopy.
Journal of the American Chemical Society
2022
Abstract
In highly concentrated salt solutions, the water hydrogen bond (H-bond) network is completely disrupted by the presence of ions. Water is forced to restructure as dictated by the water-ion and ion-ion interactions. Using ultrafast polarization-selective pump-probe (PSPP) spectroscopy measurements of the OD stretch of dilute HOD, we demonstrate that the limited water-water H-bonding present in concentrated lithium chloride solutions (up to four waters per ion pair) is, on average, stronger than that occurring in bulk water. Furthermore, information on the orientational dynamics and the angular restriction of water H-bonded to both water oxygens and chloride anions was obtained through analysis of the frequency-dependent anisotropy decays. It was found that, when the salt concentration increased, the water showed increasing restriction and slowing at frequencies correlated with strong H-bonding. The angular restriction of the water molecules and strengthening of water-water H-bonds are due to the formation of a water-ion network not present in bulk water and dilute salt solutions. The structural evolution of the ionic medium was also observed through spectral diffusion of the OD stretch using 2D IR spectroscopy. Compared to bulk water, there is significant slowing of the biexponential spectral diffusion dynamics. The slowest component of the spectral diffusion (13 ps) is virtually identical to the time for complete reorientation of HOD measured with the PSPP experiments. This result suggests that the slowest component of the spectral diffusion reflects rearrangement of water molecules in the water-ion network.
View details for DOI 10.1021/jacs.2c00616
View details for PubMedID 35226487
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Proton Transfer from a Photoacid to a Water Wire: First Principles Simulations and Fast Fluorescence Spectroscopy.
The journal of physical chemistry. B
2021
Abstract
Proton transfer reactions are ubiquitous in chemistry, especially in aqueous solutions. We investigate photoinduced proton transfer between the photoacid 8-hydroxypyrene-1,3,6-trisulfonate (HPTS) and water using fast fluorescence spectroscopy and ab initio molecular dynamics simulations. Photoexcitation causes rapid proton release from the HPTS hydroxyl. Previous experiments on HPTS/water described the progress from photoexcitation to proton diffusion using kinetic equations with two time constants. The shortest time constant has been interpreted as protonated and photoexcited HPTS evolving into an "associated" state, where the proton is "shared" between the HPTS hydroxyl and an originally hydrogen bonded water. The longer time constant has been interpreted as indicating evolution to a "solvent separated" state where the shared proton undergoes long distance diffusion. In this work, we refine the previous experimental results using very pure HPTS. We then use excited state ab initio molecular dynamics to elucidate the detailed molecular mechanism of aqueous excited state proton transfer in HPTS. We find that the initial excitation results in rapid rearrangement of water, forming a strong hydrogen bonded network (a "water wire") around HPTS. HPTS then deprotonates in ≤3 ps, resulting in a proton that migrates back and forth along the wire before localizing on a single water molecule. We find a near linear relationship between the emission wavelength and proton-HPTS distance over the simulated time scale, suggesting that the emission wavelength can be used as a ruler for the proton distance. Our simulations reveal that the "associated" state corresponds to a water wire with a mobile proton and that the diffusion of the proton away from this water wire (to a generalized "solvent-separated" state) corresponds to the longest experimental time constant.
View details for DOI 10.1021/acs.jpcb.1c07254
View details for PubMedID 34743512
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The Influence of Cholesterol on Fast Dynamics Inside of Vesicle and Planar Phospholipid Bilayers Measured with 2D IR Spectroscopy
JOURNAL OF PHYSICAL CHEMISTRY B
2015; 119 (29): 8852-8862
Abstract
Phospholipid bilayers are frequently used as models for cell membranes. Here the influence of cholesterol on the structural dynamics in the interior of 1,2-dilauroyl-sn-glycero-3-phosphocholine (dilauroylphosphatidylcholine, DLPC) vesicles and DLPC planar bilayers are investigated as a function of cholesterol concentration. 2D IR vibrational echo spectroscopy was performed on the antisymmetric CO stretch of the vibrational probe molecule tungsten hexacarbonyl, which is located in the interior alkyl regions of the bilayers. The 2D IR experiments measure spectral diffusion, which is caused by the structural fluctuations of the bilayers. The 2D IR measurements show that the bilayer interior alkyl region dynamics occur on time scales ranging from a few picoseconds to many tens of picoseconds. These are the time scales of the bilayers' structural dynamics, which act as the dynamic solvent bath for chemical processes of membrane biomolecules. The results suggest that at least a significant fraction of the dynamics arise from density fluctuations. Samples are studied in which the cholesterol concentration is varied from 0% to 40% in both the vesicles (72 nm diameter) and fully hydrated planar bilayers in the form of aligned multibilayers. At all cholesterol concentrations, the structural dynamics are faster in the curved vesicle bilayers than in the planar bilayers. As the cholesterol concentration is increased, at a certain concentration there is a sudden change in the dynamics, that is, the dynamics abruptly slow down. However, this change occurs at a lower concentration in the vesicles (between 10% and 15% cholesterol) than in the planar bilayers (between 25% and 30% cholesterol). The sudden change in the dynamics, in addition to other IR observables, indicates a structural transition. However, the results show that the cholesterol concentration at which the transition occurs is influenced by the curvature of the bilayers.
View details for DOI 10.1021/jp503940k
View details for Web of Science ID 000358623900004
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Structural Influences on the Fast Dynamics of Alkylsiloxane Monolayers on SiO2 Surfaces Measured with 2D IR Spectroscopy
JOURNAL OF PHYSICAL CHEMISTRY C
2015; 119 (29): 16811-16823
View details for DOI 10.1021/acs.jpcc.5b05641
View details for Web of Science ID 000358624000045
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Dynamics of water, methanol, and ethanol in a room temperature ionic liquid.
journal of chemical physics
2015; 142 (21): 212408-?
Abstract
The dynamics of a series of small molecule probes with increasing alkyl chain length: water, methanol, and ethanol, diluted to low concentration in the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, was investigated with 2D infrared vibrational echo (2D IR) spectroscopy and polarization resolved pump-probe (PP) experiments on the deuterated hydroxyl (O-D) stretching mode of each of the solutes. The long timescale spectral diffusion observed by 2D IR, capturing complete loss of vibrational frequency correlation through structural fluctuation of the medium, shows a clear but not dramatic slowing as the probe alkyl chain length is increased: 23 ps for water, 28 ps for methanol, and 34 ps for ethanol. Although in each case, only a single population of hydroxyl oscillators contributes to the infrared line shapes, the isotropic pump-probe decays (normally caused by population relaxation) are markedly nonexponential at short times. The early time features correspond to the timescales of the fast spectral diffusion measured with 2D IR. These fast isotropic pump-probe decays are produced by unequal pumping of the OD absorption band to a nonequilibrium frequency dependent population distribution caused by significant non-Condon effects. Orientational correlation functions for these three systems, obtained from pump-probe anisotropy decays, display several periods of restricted angular motion (wobbling-in-a-cone) followed by complete orientational randomization. The cone half-angles, which characterize the angular potential, become larger as the experimental frequency moves to the blue. These results indicate weakening of the angular potential with decreasing hydrogen bond strength. The slowest components of the orientational anisotropy decays are frequency-independent and correspond to the complete orientational randomization of the solute molecule. These components slow appreciably with increasing chain length: 25 ps for water, 42 ps for methanol, and 88 ps for ethanol. The shape and volume of the probe, therefore, impact reorientation far more severely than they do spectral diffusion at long times, though these two processes occur on similar timescales at earlier times.
View details for DOI 10.1063/1.4914156
View details for PubMedID 26049428
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Proton Transfer in Ionic and Neutral Reverse Micelles
JOURNAL OF PHYSICAL CHEMISTRY B
2015; 119 (19): 6024-6034
Abstract
Proton-transfer kinetics in both ionic and neutral reverse micelles were studied by time-correlated single-photon counting investigations of the fluorescent photoacid 8-hydroxypyrene-1,3,6-trisulfonate (HPTS). Orientational dynamics of dissolved probe molecules in the water pools of the reverse micelles were also investigated by time-dependent fluorescence anisotropy measurements of MPTS, the methoxy derivative of HPTS. These experiments were compared to the same experiments in bulk water. It was found that in ionic reverse micelles (surfactant Aerosol OT, AOT), orientational motion (fluorescence anisotropy decay) of MPTS was relatively unhindered, consistent with MPTS being located in the water core of the reverse micelle away from the water-surfactant interface. In nonionic reverse micelles (surfactant Igepal CO-520, Igepal), however, orientational anisotropy displayed a slow multiexponential decay consistent with wobbling-in-a-cone behavior, indicating MPTS is located at the water-surfactant interface. HPTS proton transfer in ionic reverse micelles followed kinetics qualitatively like those in bulk water, albeit slower, with the long-time power law time dependence associated with recombination of the proton with the dissociated photoacid, suggesting a modified diffusion-controlled process. However, the power law exponents in the ionic reverse micelles are smaller (∼ -0.55) than that in bulk water (-1.1). In neutral reverse micelles, proton-transfer kinetics did not show discernible power law behavior and were best represented by a two-component model with one relatively waterlike population and a population with a faster fluorescence lifetime and negligible proton transfer. We explain the Igepal results on the basis of close association between the probe and the neutral water-surfactant interface, with the probe experiencing a distribution of more and less waterlike environments. In addition, the observation in bulk water of a power law t(-1.1) for diffusion-controlled recombination is in contrast to the theoretical prediction of t(-1.5) and previously reported observations. The difference from prior experimental results is discussed.
View details for DOI 10.1021/acs.jpcb.5b02753
View details for Web of Science ID 000354911300010
View details for PubMedID 25913559
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Structural dynamics inside a functionalized metal-organic framework probed by ultrafast 2D IR spectroscopy.
Proceedings of the National Academy of Sciences of the United States of America
2014; 111 (52): 18442-18447
Abstract
The structural elasticity of metal-organic frameworks (MOFs) is a key property for their functionality. Here, we show that 2D IR spectroscopy with pulse-shaping techniques can probe the ultrafast structural fluctuations of MOFs. 2D IR data, obtained from a vibrational probe attached to the linkers of UiO-66 MOF in low concentration, revealed that the structural fluctuations have time constants of 7 and 670 ps with no solvent. Filling the MOF pores with dimethylformamide (DMF) slows the structural fluctuations by reducing the ability of the MOF to undergo deformations, and the dynamics of the DMF molecules are also greatly restricted. Methodology advances were required to remove the severe light scattering caused by the macroscopic-sized MOF particles, eliminate interfering oscillatory components from the 2D IR data, and address Förster vibrational excitation transfer.
View details for DOI 10.1073/pnas.1422194112
View details for PubMedID 25512539
View details for PubMedCentralID PMC4284562
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New divergent dynamics in the isotropic to nematic phase transition of liquid crystals measured with 2D IR vibrational echo spectroscopy
JOURNAL OF CHEMICAL PHYSICS
2014; 141 (19)
Abstract
The isotropic phase of nematogenic liquid crystals has nanometer length scale domains with pseudonematic ordering. As the isotropic to nematic phase transition temperature (TNI) is approached from above, the orientational correlation length, ξ, of the pseudonematic domains grows as (T - T(*))(-1/2), where T(*) is 0.5-1 K below TNI. The orientational relaxation, which is a collective property of the pseudonematic domains, was measured with optical heterodyne detected-optical Kerr effect (OHD-OKE). The orientational relaxation obeys Landau-de Gennes theory, as has been shown previously. To examine the environmental evolution experienced by molecules in the pseudonematic domains, two-dimensional infrared (2D IR) vibrational echo experiments on the CN stretching mode of the non-perturbative vibrational probes 4-pentyl-4(')-selenocyanobiphenyl (5SeCB) and 4-pentyl-4(')-thiocyanobiphenyl (5SCB) in the nematogen 4-cyano-4(')-pentylbiphenyl (5CB) were performed. The 2D IR experiments measure spectral diffusion, which is caused by structural fluctuations that couple to the CN vibrational frequency. Temperature dependent studies were performed just above TNI, where the correlation length of pseudonematic domains is large and changing rapidly with temperature. These studies were compared to 2D IR experiments on 4-pentylbiphenyl (5B), a non-mesogenic liquid that is very similar in structure to 5CB. The time constants of spectral diffusion in 5CB and 5B are practically identical at temperatures ≥5 K above TNI. As the temperature is lowered, spectral diffusion in 5B slows gradually. However, the time constants for spectral diffusion in 5CB slow dramatically and diverge as T(*) is approached. This divergence has temperature dependence proportional to (T - T(*))(-1/2), precisely the same as seen for the correlation length of pseudonematic domains, but different from the observed orientational relaxation times, which are given by the Landau-de Gennes theory. The data and previous results show that spectral diffusion in 5CB has no contributions from orientational relaxation, and the structural dynamics responsible for the spectral diffusion are likely a result of density fluctuations. The results suggest that the correlation length of the density fluctuations is diverging with the same temperature dependence as the pseudonematic domain correlation length, ξ. The isotropic-nematic phase transition in liquid crystals is described in the context of the slowing of orientational relaxation associated with divergent growth of the orientational correlation length. The results presented here show that there is another divergent dynamical process, likely associated with density fluctuations.
View details for DOI 10.1063/1.4901081
View details for Web of Science ID 000345514700026
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Orientational Dynamics in a Lyotropic Room Temperature Ionic Liquid
JOURNAL OF PHYSICAL CHEMISTRY B
2013; 117 (47): 14775-14784
Abstract
In a previous study of room temperature ionic liquid/water mixtures, the first clearly observed biexponential decays in optical heterodyne-detected optical Kerr effect (OHD-OKE) experiments on a liquid were reported, (Sturlaugson, A. L.; Fruchey, K. S.; Fayer, M. D. J. Phys. Chem. B 2012, 116, 1777), and it was suggested that the biexponential behavior is indicative of the approach to gelation. Here, new OHD-OKE experiments on mixtures of the room temperature ionic liquid 1-methyl-3-octylimidazolium chloride (OmimCl) with water are presented. The OmimCl/water system is shown to gel over the water mole fraction range of 0.69-0.81. In the OHD-OKE decays, the biexponential behavior becomes more distinct as the gelling concentration range is approached from either high or low water concentrations. The biexponential decays are analyzed in terms of the wobbling-in-a-cone model, and the resulting diffusion constants and "relative" order parameters and cone angles are reported. Comparison of the OmimCl/water data with the previously reported room temperature ionic liquid/water OHD-OKE decays supports the previous hypothesis that the biexponential dynamics are due to the approach to the liquid-gel transition and suggests that the order of the concentration-dependent phase transition can be tuned by the choice of anion.
View details for DOI 10.1021/jp407325b
View details for Web of Science ID 000330160100020
View details for PubMedID 24171452
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Dynamics of isolated water molecules in a sea of ions in a room temperature ionic liquid.
journal of physical chemistry. B
2013; 117 (2): 623-635
Abstract
The vibrational dynamics of the antisymmetric and symmetric stretching modes of very low concentration spatially isolated D(2)O molecules in the room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium hexafluorophosphate (BmImPF(6)) were examined using two-dimensional infrared (2D IR) vibrational echo spectroscopy and infrared pump-probe experiments. In BmImPF(6), D(2)O's antisymmetric and symmetric stretching modes are well resolved in the IR absorption spectrum in spite of the fact that the D(2)O is surrounded by a sea of ions, making it is possible to study inter- and intramolecular dynamics. Both population exchange between the modes and excited-state relaxation to the ground state contribute to the population dynamics. The kinetics for the incoherent population exchange (scattering) between the two modes was determined by the time dependence of the exchange peaks in the 2D IR spectrum. In addition, coherent quantum beats were observed at short time in both the amplitudes and 2D IR band shapes of the modes. The quantum beat decay is caused by dephasing due to both inhomogeneous and homogeneous broadening of the spectral lines. Analysis of the oscillations of the 2D line shapes demonstrates that there is some degree of anticorrelation in the inhomogeneous broadening of the two modes. It is proposed that a distribution in the coupling strength between the local modes that give rise to symmetric and antisymmetric eigenstates is responsible for the anticorrelation. Spectral diffusion, caused by structural evolution of the medium, occurs on multiple time scales and is identical for the two modes within experimental error. The spectral diffusion is fast compared to the time scale for complete orientational randomization of the RTIL. Spectral diffusion of the OD stretch of HOD in BmImPF(6) was also measured, and is essentially the same as that of the D(2)O modes. Orientational anisotropy measurements of HOD in BmImPF(6) determined the orientational relaxation dynamics of the isolated HOD molecules.
View details for DOI 10.1021/jp310086s
View details for PubMedID 23276306
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Protein Dynamics Studied with Ultrafast Two-Dimensional Infrared Vibrational Echo Spectroscopy
ACCOUNTS OF CHEMICAL RESEARCH
2012; 45 (11): 1866-1874
Abstract
Proteins, enzymes, and other biological molecules undergo structural dynamics as an intrinsic part of their biological functions. While many biological processes occur on the millisecond, second, and even longer time scales, the fundamental structural dynamics that eventually give rise to such processes occur on much faster time scales. Many decades ago, chemical kineticists focused on the inverse of the reaction rate constant as the important time scale for a chemical reaction. However, through transition state theory and a vast amount of experimental evidence, we now know that the key events in a chemical reaction can involve structural fluctuations that take a system of reactants to its transition state, the crossing of a barrier, and the eventual relaxation to product states. Such dynamics occur on very fast time scales. Today researchers would like to investigate the fast structural fluctuations of biological molecules to gain an understanding of how biological processes proceed from simple structural changes in biomolecules to the final, complex biological function. The study of the fast structural dynamics of biological molecules requires experiments that operate on the appropriate time scales, and in this Account, we discuss the application of ultrafast two-dimensional infrared (2D IR) vibrational echo spectroscopy to the study of protein dynamics. The 2D IR vibrational echo experiment is akin to 2D NMR, but it operates on time scales many orders of magnitude faster. In the experiments, a particular vibrational oscillator serves as a vibrational dynamics probe. As the structure of the protein evolves in time, the structural changes are manifested as time-dependent changes in the frequency of the vibrational dynamics probe. The 2D IR vibrational echo experiments can track the vibrational frequency evolution, which we then relate to the time evolution of the protein structure. In particular, we measured protein substate interconversion for mutants of myoglobin using 2D IR chemical exchange spectroscopy and observed well-defined substate interconversion on a sub-100 ps time scale. In another study, we investigated the influence of binding five different substrates to the enzyme cytochrome P450(cam). The various substrates affect the enzyme dynamics differently, and the observed dynamics are correlated with the enzyme's selectivity of hydroxylation of the substrates and with the substrate binding affinity.
View details for DOI 10.1021/ar200275k
View details for PubMedID 22433178
View details for PubMedCentralID PMC3389584
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Analysis of Water in Confined Geometries and at Interfaces
ANNUAL REVIEW OF ANALYTICAL CHEMISTRY, VOL 3
2010; 3: 89-107
Abstract
The properties of water depend on its extended hydrogen bond network and the continual picosecond-time scale structural evolution of the network. Water molecules in confined environments with pools a few nanometers in diameter or at interfaces undergo hydrogen bond structural dynamics that differ drastically from the dynamics they undergo in bulk water. Orientational motions of water require hydrogen bond network rearrangement. Therefore, observations of orientational relaxation in nanoscopic water systems provide information about the influence of confinement and interfaces on hydrogen bond dynamics. Ultrafast infrared polarization- and wavelength-selective pump-probe experiments can measure the orientational relaxation of water and distinguish water at an interface from water removed from an interface. These experiments can be applied to water in reverse micelles (spherical nanopools). The results provide quantitative determination of the dynamics of water as a function of the size and nature of the confining structure.
View details for DOI 10.1146/annurev-anchem-070109-103410
View details for Web of Science ID 000280599500005
View details for PubMedID 20636035
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Ultrafast dynamics of solute-solvent complexation observed at thermal equilibrium in real time
SCIENCE
2005; 309 (5739): 1338-1343
Abstract
In general, the formation and dissociation of solute-solvent complexes have been too rapid to measure without disturbing the thermal equilibrium. We were able to do so with the use of two-dimensional infrared vibrational echo spectroscopy, an ultrafast vibrational analog of two-dimensional nuclear magnetic resonance spectroscopy. The equilibrium dynamics of phenol complexation to benzene in a benzene-carbon tetrachloride solvent mixture were measured in real time by the appearance of off-diagonal peaks in the two-dimensional vibrational echo spectrum of the phenol hydroxyl stretch. The dissociation time constant tau(d) for the phenol-benzene complex was 8 picoseconds. Adding two electron-donating methyl groups to the benzene nearly tripled the value of tau(d) and stabilized the complex, whereas bromobenzene, with an electron-withdrawing bromo group, formed a slightly weaker complex with a slightly lower tau(d). The spectroscopic method holds promise for studying a wide variety of other fast chemical exchange processes.
View details for DOI 10.1126/science.1116213
View details for Web of Science ID 000231543300034
View details for PubMedID 16081697
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Rethinking Vibrational Stark Spectroscopy: Peak Shifts, Line Widths, and the Role of Non-Stark Solvent Coupling.
The journal of physical chemistry. B
2023
Abstract
A vibration's transition frequency is partly determined by the first-order Stark effect, which accounts for the electric field experienced by the mode. Using ultrafast infrared pump-probe and FT-IR spectroscopies, we characterized both the 0 1 and 1 2 vibrational transitions' field-dependent peak positions and line widths of the CN stretching mode of benzonitrile (BZN) and phenyl selenocyanate (PhSeCN) in ten solvents. We present a theoretical model that decomposes the observed line width into a field-dependent Stark contribution and a field-independent non-Stark solvent coupling contribution (NSC). The model demonstrates that the field-dependent peak position is independent of the line width, even when the NSC dominates the latter. Experiments show that when the Stark tuning rate is large compared to the NSC (PhSeCN), the line width has a field dependence, albeit with major NSC-induced excursions from linearity. When the Stark tuning rate is small relative to the NSC (BZN), the line width is field-independent. BZN's line widths are substantially larger for the 1 2 transition, indicating a 1 2 transition enhancement of the NSC. Additionally, we examine, theoretically and experimentally, the difference in the 0 1 and 1 2 transitions' Stark tuning rates. Second-order perturbation theory combined with density functional theory explain the difference and show that the 1 2 transition's Stark tuning rate is 10% larger. The Stark tuning rate of PhSeCN is larger than BZN's for both transitions, consistent with the theoretical calculations. This study provides new insights into vibrational line shape components and a more general understanding of the vibrational response to external electric fields.
View details for DOI 10.1021/acs.jpcb.2c06071
View details for PubMedID 36629314
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Identical Water Dynamics in Acrylamide Hydrogels, Polymers, and Monomers in Solution: Ultrafast IR Spectroscopy and Molecular Dynamics Simulations.
Journal of the American Chemical Society
2021
Abstract
The dynamics and structure of water in polyacrylamide hydrogels (PAAm-HG), polyacrylamide, and acrylamide solutions are investigated using ultrafast infrared experiments on the OD stretch of dilute HOD/H2O and molecular dynamics simulations. The amide moiety of the monomer/polymers interacts strongly with water through hydrogen bonding (H-bonding). The FT-IR spectra of the three systems indicate that the range of H-bond strengths is relatively unchanged from bulk water. Vibrational population relaxation measurements show that the amide/water H-bonds are somewhat weaker but fall within the range of water/water H-bond strengths. A previous study of water dynamics in PAAm-HG suggested that the slowing observed was due to increasing confinement with concentration. Here, for the same concentrations of the amide moiety, the experimental results demonstrate that the reorientational dynamics (infrared pump-probe experiments) and structural dynamics (two-dimensional infrared spectroscopy) are identical in the three acrylamide systems studied. Molecular dynamics simulations of the water orientational relaxation in aqueous solutions of the acrylamide monomer, trimer, and pentamer are in good agreement with the experimental results and are essentially chain length independent. The simulations show that there is a slower, low-amplitude (<7%) decay component not accessible by the experiments. The simulations examine the dynamics and structure of water H-bonded to acrylamide, in the first solvent shell, and beyond for acrylamide monomers and short chains. The experiments and simulations show that the slowing of water dynamics in PAAm-HG is not caused by confinement in the polymer network but rather by interactions with individual acrylamide moieties.
View details for DOI 10.1021/jacs.1c07151
View details for PubMedID 34491037
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Ultrafast Dynamics and Liquid Structure in Mesoporous Silica: Propagation of Surface Effects in a Polar Aprotic Solvent.
The journal of physical chemistry. B
2021
Abstract
Enhancement of processes ranging from gas sorption to ion conduction in a liquid can be substantial upon nanoconfinement. Here, the dynamics of a polar aprotic solvent, 1-methylimidazole (MeIm), in mesoporous silica (2.8, 5.4, and 8.3 nm pore diameters) were examined using femtosecond infrared vibrational spectroscopy and molecular dynamics simulations of a dilute probe, the selenocyanate (SeCN-) anion. The long vibrational lifetime and sensitivity of the CN stretch enabled a comprehensive investigation of the relatively slow time scales and subnanometer distance dependences of the confined dynamics. Because MeIm does not readily donate hydrogen bonds, its interactions in the hydrophilic silanol pores differ more from the bulk than those of water confined in the same mesopores, resulting in greater structural order and more dramatic slowing of dynamics. The extent of surface effects was quantified by modified two-state models used to fit three spatially averaged experimental observables: vibrational lifetime, orientational relaxation, and spectral diffusion. The length scales and the models (smoothed step, exponential decay, and simple step) describing the transitions between the distinctive shell behavior at the surface and the bulk-like behavior at the pore interior were compared to those of water. The highly nonuniform distributions of the SeCN- probe and antiparallel layering of MeIm revealed by the simulations guided the interpretation of the results and development of the analytical models. The results illustrate the importance of electrostatic effects and H-bonding interactions in the behavior of confined liquids.
View details for DOI 10.1021/acs.jpcb.1c04798
View details for PubMedID 34450013
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Long Vibrational Lifetime R-Selenocyanate Probes for Ultrafast Infrared Spectroscopy: Properties and Synthesis.
The journal of physical chemistry. B
2021
Abstract
Ultrafast infrared vibrational spectroscopy is widely used for the investigation of dynamics in systems from water to model membranes. Because the experimental observation window is limited to a few times the probe's vibrational lifetime, a frequent obstacle for the measurement of a broad time range is short molecular vibrational lifetimes (typically a few to tens of picoseconds). Five new long-lifetime aromatic selenocyanate vibrational probes have been synthesized and their vibrational properties characterized. These probes are compared to commercial phenyl selenocyanate. The vibrational lifetimes range between 400 and 500 ps in complex solvents, which are some of the longest room-temperature vibrational lifetimes reported to date. In contrast to vibrations that are long-lived in simple solvents such as CCl4, but become much shorter in complex solvents, the probes discussed here have 400 ps lifetimes in complex solvents and even longer in simple solvents. One of them has a remarkable lifetime of 1235 ps in CCl4. These probes have a range of molecular sizes and geometries that can make them useful for placement into different complex materials due to steric reasons, and some of them have functionalities that enable their synthetic incorporation into larger molecules, such as industrial polymers. We investigated the effect of a range of electron-donating and electron-withdrawing para-substituents on the vibrational properties of the CN stretch. The probes have a solvent-independent linear relationship to the Hammett substituent parameter when evaluated with respect to the CN vibrational frequency and the ipso 13C NMR chemical shift.
View details for DOI 10.1021/acs.jpcb.1c04939
View details for PubMedID 34339200
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Distinguishing steric and electrostatic molecular probe orientational ordering via their effects on reorientation-induced spectral diffusion.
The Journal of chemical physics
2021; 154 (24): 244104
Abstract
The theoretical framework for reorientation-induced spectral diffusion (RISD) describes the polarization dependence of spectral diffusion dynamics as measured with two-dimensional (2D) correlation spectroscopy and related techniques. Generally, RISD relates to the orientational dynamics of the molecular chromophore relative to local electric fields of the medium. The predictions of RISD have been shown to be very sensitive to both restricted orientational dynamics (generally arising from steric hindrance) and the distribution of local electric fields relative to the probe (electrostatic ordering). Here, a theory that combines the two effects is developed analytically and supported with numerical calculations. The combined effects can smoothly vary the polarization dependence of spectral diffusion from the purely steric case (least polarization dependence) to the purely electrostatic case (greatest polarization dependence). Analytic approximations of the modified RISD equations were also developed using the orientational dynamics of the molecular probe and two order parameters describing the degree of electrostatic ordering. It was found that frequency-dependent orientational dynamics are a possible consequence of the combined electrostatic and steric effects, providing a test for the applicability of this model to experimental systems. The modified RISD equations were then used to successfully describe the anomalous polarization-dependent spectral diffusion seen in 2D infrared spectroscopy in a polystyrene oligomer system that exhibits frequency-dependent orientational dynamics. The degree of polarization-dependent spectral diffusion enables the extent of electrostatic ordering in a chemical system to be quantified and distinguished from steric ordering.
View details for DOI 10.1063/5.0053308
View details for PubMedID 34241361
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Complex Formation and Dissociation Dynamics on Amorphous Silica Surfaces.
The journal of physical chemistry. B
2021
Abstract
Benzene complex formation and dissociation dynamics with silanols on the amorphous silica surfaces of nanoporous SiO2, from a benzene/carbon tetrachloride solution, were measured by the growth of off-diagonal peaks in the two-dimensional infrared (2D IR) chemical exchange spectrum of the isolated Si-OD stretch. The presence of two types of isolated silanols, termed type I and II, was revealed, with dissociation time constants of 82 and 4.0 ps, respectively. The type I silanols are associated with the main IR absorption feature in the Si-OD stretching region, while the type II silanols give rise to a broader shoulder to lower frequency. Polarization selective pump-probe (PSPP) measurements provided the vibrational lifetimes and orientational relaxation rates of the two silanols in the CCl4 (free) and benzene (complex) environments. The type II silanols constitute roughly 30% of the isolated silanol population and exhibit a substantially faster rate of vibrational relaxation, making the type I dynamics the dominant contribution to the PSPP and 2D IR signals. From the measured dissociation times, the enthalpies of formation for the two surface complexes were obtained, with the formation of the type I complex being significantly more exothermic. As the type II site is preferentially removed from the amorphous silica surface with increasing activation temperature, the results provide a reasonable explanation for the increased exothermicity of benzene adsorption on silica with increasing activation temperature in previous calorimetry experiments.
View details for DOI 10.1021/acs.jpcb.1c01225
View details for PubMedID 33890776
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Orientational Pair Correlations and Local Structure of Benzonitrile from Molecular Dynamics Simulations with Comparisons to Experiments.
The journal of physical chemistry. B
2021
Abstract
We present an experimentally parametrized molecular dynamics study of single-molecule and collective orientational relaxation in neat benzonitrile through the analysis of the reorientational anisotropy and polarizability anisotropy time correlation function (PA-TCF). The simulations show that the PA-TCF is dominated by collective reorientation after 20 ps. Collective reorientation is found to be slower than single-molecule reorientation by a factor of 1.67, consistent with recent experiments. The simulations provide direct evidence of local antiparallel benzonitrile configurations. These structures, which have been the center of some debate, are responsible for the slower rate of collective versus single-molecule reorientation in the liquid. Further structural analysis indicates that significant Coulombic interactions between the nitrile group and hydrogen atoms on adjacent molecules play a role in the formation of the antiparallel structures. The single-molecule dynamics reflected in the anisotropy are complex and consist of a ballistic regime, restricted angular diffusion, and spatially anisotropic free diffusion. The principal components of the rotational diffusion tensor are independently obtained and shown to reproduce the free diffusion regime of the anisotropy for each principal axis according to the predictions of a previous theory.
View details for DOI 10.1021/acs.jpcb.0c11148
View details for PubMedID 33730488
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Free Volume Element Sizes and Dynamics in Polystyrene and Poly(methyl methacrylate) Measured with Ultrafast Infrared Spectroscopy.
Journal of the American Chemical Society
2021
Abstract
The size, size distribution, dynamics, and electrostatic properties of free volume elements (FVEs) in polystyrene (PS) and poly(methyl methacrylate) (PMMA) were investigated using the Restricted Orientation Anisotropy Method (ROAM), an ultrafast infrared spectroscopic technique. The restricted orientational dynamics of a vibrational probe embedded in the polymer matrix provides detailed information on FVE sizes and their probability distribution. The probe's orientational dynamics vary as a function of its frequency within the inhomogeneously broadened vibrational absorption spectrum. By characterizing the degree of orientational restriction at different probe frequencies, FVE radii and their probability distribution were determined. PS has larger FVEs and a broader FVE size distribution than PMMA. The average FVE radii in PS and PMMA are 3.4 and 3.0 A, respectively. The FVE radius probability distribution shows that the PS distribution is non-Gaussian, with a tail to larger radii, whereas in PMMA, the distribution is closer to Gaussian. FVE structural dynamics, previously unavailable through other techniques, occur on a 150 ps time scale in both polymers. The dynamics involve FVE shape fluctuations which, on average, conserve the FVE size. FVE radii were associated with corresponding electric field strengths through the first-order vibrational Stark effect of the CN stretch of the vibrational probe, phenyl selenocyanate (PhSeCN). PMMA displayed unique measured FVE radii for each electric field strength. By contrast, PS showed that, while larger radii correspond to unique and relatively weak electric fields, the smallest measured radii map onto a broad distribution of strong electric fields.
View details for DOI 10.1021/jacs.0c13397
View details for PubMedID 33630576
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Pulse-shaped chopping: Eliminating and characterizing heat effects in ultrafast infrared spectroscopy.
The Journal of chemical physics
2020; 153 (20): 204201
Abstract
The infrared pulses used to generate nonlinear signals from a vibrational probe can cause heating via solvent absorption. Solvent absorption followed by rapid vibrational relaxation produces unwanted heat signals by creating spectral shifts of the solvent and probe absorptions. The signals are often isolated by "chopping," i.e., alternately blocking one of the incident pulses. This method is standard in pump-probe transient absorption experiments. As less heat is deposited into the sample when an incident pulse is blocked, the heat-induced spectral shifts give rise to artificial signals. Here, we demonstrate a new method that eliminates heat induced signals using pulse shaping to control pulse spectra. This method is useful if the absorption spectrum of the vibrational probe is narrow compared to the laser bandwidth. By using a pulse shaper to selectively eliminate only frequencies of light resonant with the probe absorption during the "off" shot, part of the pulse energy, and the resulting heat, is delivered to the solvent without generating the nonlinear signal. This partial heating reduces the difference heat signal between the on and off shots. The remaining solvent heat signal can be eliminated by reducing the wings of the on shot spectrum while still resonantly exciting the probe; the heat deposition from the on shot can be matched with that from the off shot, eliminating the solvent heat contribution to the signal. Modification of the pulse sequence makes it possible to measure only the heat signal, permitting the kinetics of heating to be studied.
View details for DOI 10.1063/5.0031581
View details for PubMedID 33261482
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Proton Transfer Dynamics in the Aprotic Proton Accepting Solvent 1-Methylimidazole.
The journal of physical chemistry. B
2020
Abstract
The dynamics of proton transfer to the aprotic solvent 1-methylimidazole (MeIm, proton acceptor) from the photoacid 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) was investigated using fast fluorescence measurements. The closely related molecule, 8-methoxypyrene-1,3,6-trisulfonic acid trisodium salt (MPTS), which is not a photoacid, was also studied for comparison. Following optical excitation, the wavelength-dependent population dynamics of HPTS in MeIm resulting from the deprotonation process were collected over the entire fluorescence emission window. Analysis of the time-dependent fluorescence spectra revealed four distinct fluorescence bands that appear and decay on different time scales. We label these four states as protonated (P), associated I (AI), associated II (AII), and deprotonated (D). We find that the simple kinetic scheme of P AI AII D is not consistent with the data. Instead, the kinetic scheme that describes the data has P decaying into AI, which mainly goes on to deprotonation (D), but AI can also feed into AII. AII can return to AI or decay to the ground state, but does not deprotonate within experimental error. Quantum chemistry and excited state QM/MM Born-Oppenheimer molecular dynamics simulations indicate that AI and AII are two H-bonding conformations of MeIm to the HPTS hydroxyl, axial, and equatorial, respectively.
View details for DOI 10.1021/acs.jpcb.0c05525
View details for PubMedID 32790382
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Amorphous polymer dynamics and free volume element size distributions from ultrafast IR spectroscopy.
Proceedings of the National Academy of Sciences of the United States of America
2020
Abstract
A method for measuring the size and size probability distribution of free volume regions in polymeric materials using ultrafast infrared (IR) polarization-selective pump-probe experiments is presented. Measurements of the ultrafast dynamics of a vibrational probe (the CN stretch of phenyl selenocyanate) in poly(methyl methacrylate) show that the probe dynamics are highly confined. The degree of confinement was found to be both time-dependent and dependent on the vibrational frequency of the probe molecule. The experiments demonstrate that different vibrational frequencies correspond to distinct subensembles of probe molecules that have different dynamic properties determined by their local structural environments. By combining the degree of dynamical confinement with the molecular size of the probe molecule, the free volume element size probability distribution was determined and found to be in good agreement with the best established experimental measure of free volume. The relative probability of a free volume element size is determined by the amplitude of the nitrile absorption spectrum at the frequency of the measurement. The inhomogeneous broadening of the spectrum was linked to the vibrational Stark effect, which permits site selectivity. The observed dynamics at each frequency were then associated with a different size free volume element and distinct local electric field. The multiple timescales observed in the pump-probe experiments were connected to local structural fluctuations of the free volume elements.
View details for DOI 10.1073/pnas.2003225117
View details for PubMedID 32513742
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Effects of pore size on water dynamics in mesoporous silica.
The Journal of chemical physics
2020; 152 (15): 154704
Abstract
Water confined in mesoporous silica plays a central role in its many uses ranging from gas sorption to nanoconfined chemical reactions. Here, the influence of pore diameter (2.5-5.4 nm) on water hydrogen bond (H-bond) dynamics in MCM41 and SBA15 mesoporous silicas is investigated using femtosecond infrared vibrational spectroscopy and molecular dynamics simulations on selenocyanate (SeCN-) anions dissolved in the pores. As shown recently, SeCN- spectral diffusion is a reliable probe of surrounding water H-bond structural motions. Additionally, the long CN stretch vibrational lifetime facilitates measurement of the full range of confined dynamics, which are much slower than in bulk water. The simulations shed light on quantitative details that are inaccessible from the spatially averaged observables. The dependence of SeCN- orientational relaxation and that of spectral diffusion on the distance from the silica interface are quantitatively described with an exponential decay and a smoothed step-function, respectively. The distance-dependence of both quantities is found to be independent of the diameter of the pores, and the spatial distribution of SeCN- is markedly non-uniform, reaching a maximum between the interface and the pore center. The results indicate that the commonly invoked two-state, or core-shell, model is a more appropriate description of spectral diffusion. Using these insights, we model the full time-dependence of the measured dynamics for all pore sizes and extract the "core" and "shell" dynamical correlation functions and SeCN- spatial probability distributions. The results are critically compared to those for water confined in reverse micelles.
View details for DOI 10.1063/1.5145326
View details for PubMedID 32321257
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Microstructural and Dynamical Heterogeneities in Ionic Liquids.
Chemical reviews
2020
Abstract
Ionic liquids (ILs) are a special category of molten salts solely composed of ions with varied molecular symmetry and charge delocalization. The versatility in combining varied cation-anion moieties and in functionalizing ions with different atoms and molecular groups contributes to their peculiar interactions ranging from weak isotropic associations to strong, specific, and anisotropic forces. A delicate interplay among intra- and intermolecular interactions facilitates the formation of heterogeneous microstructures and liquid morphologies, which further contributes to their striking dynamical properties. Microstructural and dynamical heterogeneities of ILs lead to their multifaceted properties described by an inherent designer feature, which makes ILs important candidates for novel solvents, electrolytes, and functional materials in academia and industrial applications. Due to a massive number of combinations of ion pairs with ion species having distinct molecular structures and IL mixtures containing varied molecular solvents, a comprehensive understanding of their hierarchical structural and dynamical quantities is of great significance for a rational selection of ILs with appropriate properties and thereafter advancing their macroscopic functionalities in applications. In this review, we comprehensively trace recent advances in understanding delicate interplay of strong and weak interactions that underpin their complex phase behaviors with a particular emphasis on understanding heterogeneous microstructures and dynamics of ILs in bulk liquids, in mixtures with cosolvents, and in interfacial regions.
View details for DOI 10.1021/acs.chemrev.9b00693
View details for PubMedID 32292036
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Enhanced Menshutkin SN2 Reactivity in Mesoporous Silica: The Influence of Surface Catalysis and Confinement.
Journal of the American Chemical Society
2020
Abstract
A significant enhancement in the Menshutkin SN2 reaction between 1-methylimidazole (MeIm) and methyl thiocyanate (MeSCN) is observed when the reaction is confined in the nanoscale silica pores of MCM41 and SBA15. The experiments in the silica pores are conducted without the surrounding bulk reaction mixture. The influences of temperature, pore radius, and surface chemistry on the kinetics of the confined reaction are analyzed with time-dependent infrared spectroscopy, molecular dynamics simulations, and ab initio calculations. The rate constant of the pseudo-first order reaction increases with decreasing pore size, and the activation energy is found to decrease by 5.6 kJ/mol in the smallest pore studied (2.8 nm) relative to the bulk reaction. The rate constant dependence on pore size is accurately described by a two-state model in which molecules within the 4.6 A interfacial layer experience a 2.4-fold rate constant increase relative to those reacting at the bulk rate further away from the interface. The removal of polar silanol groups from the silica surface via passivation with trimethylsilyl chloride results in bulk-like kinetics despite a reduction in the pore diameter, demonstrating the role of silanols as catalytic sites. Electronic structure calculations of the energy profile on a model silica surface confirm that silanol groups, particularly those of the vicinal type, can reduce the activation energy and reaction endothermicity through the donation of hydrogen bonds to the reactant, transition state, and product complexes.
View details for DOI 10.1021/jacs.9b12666
View details for PubMedID 32077695
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Structural Dynamics in Ionic Liquid Thin Films: The Effect of Cation Chain Length
JOURNAL OF PHYSICAL CHEMISTRY C
2020; 124 (7): 4179–89
View details for DOI 10.1021/acs.jpcc.9b11871
View details for Web of Science ID 000515216500028
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Controlling the Dynamics of Ionic Liquid Thin Films via Multilayer Surface Functionalization.
Journal of the American Chemical Society
2020
Abstract
The structural dynamics of planar thin films of an ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BmimNTf2) as a function of surface charge density and thickness were investigated using two-dimensional infrared (2D IR) spectroscopy. The films were made by spin coating a methanol solution of the IL on silica substrates that were functionalized with alkyl chains containing head groups that mimic the IL cation. The thicknesses of the ionic liquid films ranged from ∼50 to ∼250 nm. The dynamics of the films are slower than those in the bulk IL, becoming increasingly slow as the films become thinner. Control of the dynamics of the IL films can be achieved by adjusting the charge density on substrates through multilayer network surface functionalization. The charge density of the surface (number of positively charged groups in the network bound to the surface per unit area) is controlled by the duration of the functionalization reaction. As the charge density is increased, the IL dynamics become slower. For comparison, the surface was functionalized with three different neutral groups. Dynamics of the IL films on the functionalized neutral surfaces are faster than on any of the ionic surfaces but still slower than the bulk IL, even for the thickest films. These results can have implications in applications that employ ILs that have electrodes, such as batteries, as the electrode surface charge density will influence properties like diffusion close to the surface.
View details for DOI 10.1021/jacs.0c03044
View details for PubMedID 32349470
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Single Ensemble Non-exponential Photoluminescent Population Decays from a Broadband White-Light-Emitting Perovskite.
Journal of the American Chemical Society
2020
Abstract
The mechanism of white-light emission from layered Pb-X (X = Cl or Br) perovskites following UV excitation has generated considerable interest. Prior time-dependent studies indicated that the broadband photoluminescence (PL) from (110) perovskites arises from a distribution of self-trapped excitonic sites emitting in different regions of the visible spectrum with different decay dynamics. Here, using time-correlated single photon counting to study single crystals, we show that the white-light emission decay from the (110) perovskite (EDBE)PbBr4 (EDBE = 2,2'-(ethylenedioxy)bis(ethylammonium)) behaves as a single ensemble. Following the rapid decay (0.6 ns) of a small spectral side band, the broad emission line shape is constant to 100 ns. We propose that rapid local structural fluctuations cause the self-trapped excitons (STEs) to experience a wide range of energies, resulting in the very broad PL. The STEs sample fluctuating local environments on time scales fast compared to the PL, which averages the PL decay at all emission wavelengths, yielding single ensemble PL dynamics. Although emission occurs from a very wide, inhomogeneously broadened spectral line with time-averaged single ensemble luminescence dynamics, the decay is tri-exponential. Two heuristic models for the tri-exponential decay involving defects are discussed. Spin-coated films show faster non-exponential decays with the slowest component of the crystal PL absent. Like the crystals, the film PL decays as a single ensemble. These results demonstrate that the broadband emission decay of (EDBE)PbBr4 arises from a time-averaged single ensemble and not from a set of excited states emitting with distinct luminescence decays at different wavelengths.
View details for DOI 10.1021/jacs.0c05636
View details for PubMedID 32909430
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CLS Next Gen: Accurate Frequency-Frequency Correlation Functions from Center Line Slope Analysis of 2D Correlation Spectra Using Artificial Neural Networks.
The journal of physical chemistry. A
2020
Abstract
The center line slope (CLS) observable has become a popular method for characterizing spectral diffusion dynamics in two-dimensional (2D) correlation spectroscopy because of its ease of implementation, robustness, and clear theoretical relationship to the frequency-frequency correlation function (FFCF). The FFCF relates the frequency fluctuations of an ensemble of chromophores to coupled bath modes of the chemical system and is used for comparison to molecular dynamics simulations and for calculating 2D spectra. While in the appropriate limits, the CLS can be shown to be the normalized FFCF, from which the full FFCF can be obtained, in practice the assumptions that relate the CLS to the normalized FFCF are frequently violated. These violations are due to the presence of homogeneous broadening and motional narrowing. The generalized problem of relating the CLS to the FFCF is reanalyzed by introducing a new set of dimensionless parameters for both the CLS and FFCF. A large data set was generated of CLS parameters derived from numerically modeled 2D line shapes with known FFCF parameters. This data set was used to train feedforward artificial neural networks that act as functions, which take the CLS parameters as inputs and return FFCF parameters. These neural networks were deployed in an algorithm that is able to quickly and accurately determine FFCF parameters from experimental CLS parameters and the fwhm of the absorption line shape. The method and necessary inputs to accurately obtain the FFCF from the CLS are presented.
View details for DOI 10.1021/acs.jpca.0c04313
View details for PubMedID 32551669
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Dynamical properties of a room temperature ionic liquid: Using molecular dynamics simulations to implement a dynamic ion cage model.
The Journal of chemical physics
2019; 151 (15): 154502
Abstract
The transport behavior of ionic liquids (ILs) is pivotal for a variety of applications, especially when ILs are used as electrolytes. Many aspects of the transport dynamics of ILs remain to be understood. Here, a common ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BmimNTf2), was studied with molecular dynamics simulations. The results show that BmimNTf2 displays typical structural relaxation, subdiffusive behavior, and a breakdown of the Stokes-Einstein diffusion relation as in glass-forming liquids. In addition, the simulations show that the translational dynamics, reorientation dynamics, and structural relaxation dynamics are well described by the Vogel-Fulcher-Tammann equation like fragile glass forming liquids. Building on previous work that employed ion cage models, it was found that the diffusion dynamics of the cations and anions were well described by a hopping process random walk where the step time is the ion cage lifetime obtained from the cage correlation function. Detailed analysis of the ion cage structures indicated that the electrostatic potential energy of the ion cage dominates the diffusion dynamics of the caged ion. The ion orientational relaxation dynamics showed that ion reorientation is a necessary step for ion cage restructuring. The dynamic ion cage model description of ion diffusion presented here may have implications for designing ILs to control their transport behavior.
View details for DOI 10.1063/1.5126231
View details for PubMedID 31640381
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Direct observation of proton hopping in water/HCl solutions by 2D IR spectroscopy and ab initio simulations
AMER CHEMICAL SOC. 2019
View details for Web of Science ID 000525061503740
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Dynamics of organic molecule-ion and water-ion complexes in concentrated aqueous salt solutions: 2D IR chemical exchange spectroscopy
AMER CHEMICAL SOC. 2019
View details for Web of Science ID 000525061502446
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Tracking Aqueous Proton Transfer by Two-Dimensional Infrared Spectroscopy and ab Initio Molecular Dynamics Simulations
ACS CENTRAL SCIENCE
2019; 5 (7): 1269–77
View details for DOI 10.1021/acscentsci.9b00447
View details for Web of Science ID 000476928300020
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Tracking Aqueous Proton Transfer by Two-Dimensional Infrared Spectroscopy and ab Initio Molecular Dynamics Simulations.
ACS central science
2019; 5 (7): 1269-1277
Abstract
Proton transfer in water is ubiquitous and a critical elementary event that, via proton hopping between water molecules, enables protons to diffuse much faster than other ions. The problem of the anomalous nature of proton transport in water was first identified by Grotthuss over 200 years ago. In spite of a vast amount of modern research effort, there are still many unanswered questions about proton transport in water. An experimental determination of the proton hopping time has remained elusive due to its ultrafast nature and the lack of direct experimental observables. Here, we use two-dimensional infrared spectroscopy to extract the chemical exchange rates between hydronium and water in acid solutions using a vibrational probe, methyl thiocyanate. Ab initio molecular dynamics (AIMD) simulations demonstrate that the chemical exchange is dominated by proton hopping. The observed experimental and simulated acid concentration dependence then allow us to extrapolate the measured single step proton hopping time to the dilute limit, which, within error, gives the same value as inferred from measurements of the proton mobility and NMR line width analysis. In addition to obtaining the proton hopping time in the dilute limit from direct measurements and AIMD simulations, the results indicate that proton hopping in dilute acid solutions is induced by the concerted multi-water molecule hydrogen bond rearrangement that occurs in pure water. This proposition on the dynamics that drive proton hopping is confirmed by a combination of experimental results from the literature.
View details for DOI 10.1021/acscentsci.9b00447
View details for PubMedID 31403075
View details for PubMedCentralID PMC6661862
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Reorientation-induced Stokes shifts caused by directional interactions in electronic spectroscopy: Fast dynamics of poly(methyl methacrylate).
The Journal of chemical physics
2019; 150 (19): 194201
Abstract
Dynamic Stokes shift measurements report on structural relaxation, driven by a dipole created in a chromophore by its excitation from the ground electronic state to the S1 state. Here, we demonstrate that it is also possible to have an additional contribution from orientational relaxation of the Stokes shift chromophore. This effect, called reorientation-induced Stokes shift (RISS), can be observed when the reorientation of the chromophore and the solvent structural relaxation occur on similar time scales. Through a vector interaction, the electronic transition of the chromophore couples to its environment. The orientational diffusive motions of the chromophores will have a slight bias toward reducing the transition energy (red shift) as do the solvent structural diffusive motions. RISS is manifested in the polarization-dependence of the fluorescence Stokes shift using coumarin 153 (C153) in poly(methyl methacrylate) (PMMA). A similar phenomenon, reorientation-induced spectral diffusion (RISD), has been observed and theoretically explicated in the context of two dimensional infrared (2D IR) experiments. Here, we generalize the existing RISD theory to include properties of electronic transitions that generally are not present in vibrational transitions. Expressions are derived that permit determination of the structural dynamics by accounting for the RISS contributions. Using these generalized equations, the structural dynamics of the medium can be measured for any system in which the directional interaction is well represented by a first order Stark effect and RISS or RISD is observed. The theoretical results are applied to the PMMA data, and the structural dynamics are obtained and discussed.
View details for DOI 10.1063/1.5094806
View details for PubMedID 31117782
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Direct determination of proton transfer rate by 2D IR chemical exchange spectroscopy and ab initio molecular dynamics simulation
AMER CHEMICAL SOC. 2019
View details for Web of Science ID 000478861204162
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Fast dynamics of a hydrogen-bonding glass forming liquid: Chemical exchange-induced spectral diffusion in 2D IR spectroscopy.
The Journal of chemical physics
2019; 150 (12): 124507
Abstract
Polarization-selective Two Dimensional Infrared (2D IR) and IR pump-probe spectroscopies have been performed on the hydrogen bonding glass forming liquid 2-biphenylmethanol doped with the long-lived vibrational probe phenylselenocyanate over a wide range of temperatures. The spectral diffusion seen in the 2D spectra was found to have a large polarization dependence, in large excess of what is predicted by standard theory. This anomaly was explained by decomposing the 2D spectra into hydrogen-bonding and non-bonding components, which exchange through large-angle orientational motion. By adapting chemical exchange theories, parameters for the component peaks were then calculated by fitting the polarization-dependent spectral diffusion and the pump-probe anisotropy. A model of highly heterogeneous exchange and orientational dynamics was used to explain the observed time dependences as a function of temperature on fast time scales. The experimental observations, the kinetic modeling, and physical arguments lead to the determination of the times for interconversion of slow dynamics structural domains to fast dynamics structural domains in the supercooled liquid as a function of temperature. The slow to fast domain interconversion times range from 40 ps at 355 K to 5000 ps at 270 K.
View details for PubMedID 30927894
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Fast dynamics of a hydrogen-bonding glass forming liquid: Chemical exchange-induced spectral diffusion in 2D IR spectroscopy
JOURNAL OF CHEMICAL PHYSICS
2019; 150 (12)
View details for DOI 10.1063/1.5088499
View details for Web of Science ID 000462914300030
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Water Dynamics in Nanoporous Silica: Ultrafast Vibrational Spectroscopy and Molecular Dynamics Simulations
JOURNAL OF PHYSICAL CHEMISTRY C
2019; 123 (9): 5790–5803
View details for DOI 10.1021/acs.jpcc.9b00593
View details for Web of Science ID 000460996000073
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Imidazole and 1-Methylimidazole Hydrogen Bonding and Nonhydrogen Bonding Liquid Dynamics: Ultrafast IR Experiments
JOURNAL OF PHYSICAL CHEMISTRY B
2019; 123 (9): 2094–2105
View details for DOI 10.1021/acs.jpcb.8b11299
View details for Web of Science ID 000460996400022
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Imidazole and 1-Methylimidazole Hydrogen Bonding and Nonhydrogen Bonding Liquid Dynamics: Ultrafast IR Experiments.
The journal of physical chemistry. B
2019
Abstract
The dynamics of imidazole (IM) and 1-methylimidazole (1-MeIM) in the liquid phase at 95 °C were studied by IR polarization selective pump-probe and two-dimensional IR (2D IR) spectroscopies. The two molecules are very similar structurally except that IM can be simultaneously a hydrogen bond donor and acceptor and therefore forms extended hydrogen-bonded networks. The broader IR absorption spectrum and a shorter vibrational lifetime of the vibrational probe, selenocyanate anion (SeCN-), in IM vs 1-MeIM indicate that stronger hydrogen bonding exists between SeCN- and IM. Molecular dynamics (MD) simulations support the strong hydrogen bond formation between SeCN- and IM via the HN moiety. SeCN- makes two H-bonds with IM; it is inserted in the IM H-bonded chains rather than being a chain terminator. The strong hydrogen bonding influenced the reorientation dynamics of SeCN- in IM, leading to a more restricted short time angular sampling (wobbling-in-a-cone). The complete orientational diffusion time in IM is 1.7 times slower than in 1-MeIM, but the slow down is less than expected, considering the 3-fold larger viscosity of IM. The jump reorientation mechanism accounts for the anomalously fast orientational relaxation in IM, and the MD simulations determined the average jump angle of the probe between hydrogen bonding sites. Spectral diffusion time constants obtained from the 2D IR experiments are only modestly slower in IM than in 1-MeIM in spite of the significant increase in viscosity. The results indicate that the spectral diffusion sensed by the SeCN- has IM hydrogen bond dynamics contributions not present in 1-MeIM.
View details for PubMedID 30727725
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Dynamics of Water Molecules and Ions in Concentrated Lithium Chloride Solutions Probed with Ultrafast 2D IR Spectroscopy.
The journal of physical chemistry. B
2019
Abstract
Water and ion dynamics in concentrated LiCl solutions were studied using ultrafast 2D IR spectroscopy with the methyl thiocyanate (MeSCN) CN stretch as the vibrational probe. The IR absorption spectrum of MeSCN has two peaks, one peak for water associated with the nitrogen lone pair of MeSCN (W) and the other peak corresponding to Li+ associated with the lone pair (L). To extract the spectral diffusion (structural dynamics) of W and L species, we developed a method that isolates the peak of interest by subtracting the 2D Gaussian proxies of multiple interfering peaks. Center line slope data (normalized frequency-frequency correlation function) for 2D bands from the W and L are fit with triexponential functions. The fastest component (1.1-1.6 ps) is assigned to local hydrogen bond length fluctuations. The intermediate timescale (∼4.0 ps) corresponds to the hydrogen bond network rearrangement. The slowest component decays in ∼40 ps and corresponds to ion pair and ion cluster dynamics. The very similar W and L spectral diffusion indicates that the motions of the water and ions are strongly coupled. Orientational relaxations of the W and L species were extracted using a new method to eliminate the effects of overlapping peaks. The results show that MeSCN bound to water undergoes orientational relaxation significantly faster than MeSCN bound to Li+. The orientational and spectral diffusion results are compared. A Stark coupling model is used to extract the root mean square average electric field caused by the ion clouds along the CN moiety as a function of concentration.
View details for DOI 10.1021/acs.jpcb.9b06038
View details for PubMedID 31402658
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Bulk-like and Interfacial Water Dynamics in Nafion Fuel Cell Membranes Investigated with Ultrafast Nonlinear IR Spectroscopy.
The journal of physical chemistry. B
2019
Abstract
The water confined in the hydrophilic domains of Nafion fuel cell membranes is central to its primary function of ion transport. Water dynamics are intimately linked to proton transfer and are sensitive to the structural features and length scales of confinement. Here, ultrafast polarization-selective pump-probe and two-dimensional infrared vibrational echo (2D IR) experiments were performed on fully hydrated Nafion membranes with sodium counterions to explicate the water dynamics. Like aerosol-OT reverse micelles (AOT RMs), the water dynamics in Nafion are attributed to bulk-like core water in the central region of the hydrophilic domains and much slower interfacial water. Population and orientational dynamics of water in Nafion are slowed by polymer confinement. Comparison of the observed dynamics to those of AOT RMs helps identify local interactions between water and sulfonate anions at the interface and among water molecules in the core. This comparison also demonstrates that the well-known spherical cluster morphology of Nafion is not appropriate. Spectral diffusion of the interfacial water, which arises from structural dynamics, was obtained from the 2D IR experiments taking the core water to have dynamics similar to bulk water. Like the orientational dynamics, spectral diffusion was found to be much slower at the interface compared to bulk water. Together, the dynamics indicate slow reorganization of weakly hydrogen-bonded water molecules at the interface of Nafion. These results provide insights into proton transport mechanisms in fuel cell membranes, and more generally, water dynamics near the interface of confining systems.
View details for DOI 10.1021/acs.jpcb.9b07592
View details for PubMedID 31580076
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Orientational Pair Correlations in a Dipolar Molecular Liquid: Time-Resolved Resonant and Nonresonant Pump-Probe Spectroscopies
JOURNAL OF PHYSICAL CHEMISTRY B
2018; 122 (50): 12147-12153
View details for DOI 10.1021/acs.jpcb.8b10711
View details for Web of Science ID 000454566600032
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Orientational Pair Correlations in a Dipolar Molecular Liquid: Time-Resolved Resonant and Nonresonant Pump-Probe Spectroscopies.
The journal of physical chemistry. B
2018
Abstract
Orientational pair correlations (OPCs), when they are sufficiently strong in a liquid, contain information on the interplay between structure and dynamics that arise from intermolecular interactions. Consequently, the quantification of OPCs remains a subject of substantial interest in current experimental and theoretical works. In the case of benzonitrile, the importance of OPCs remains ambiguous, owing to the use of model-dependent analyses or reliance on a single spectroscopic technique. Here, IR polarization-selective pump-probe (PSPP) and optical heterodyne-detected optical Kerr effect (OHD-OKE) experiments were used to quantify OPCs in benzonitrile. These methods measure single molecule and collective orientational relaxation dynamics, respectively. A comparison of the orientational correlation function (PSPP) of the naturally abundant 13CN stretching mode and the polarizability anisotropy relaxation (OHD-OKE) of the liquid revealed that the collective reorientation time was a factor of 1.56 ± 0.08 slower than the single molecule reorientation time. The two types of measurements on dilute benzonitrile in carbon tetrachloride were the same within experimental error. These results support the proposition that OPCs exist and arise from the formation of parallel-aligned intermolecular structures in the neat liquid.
View details for PubMedID 30411625
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Ion-Molecule Complex Dissociation and Formation Dynamics in LiCl Aqueous Solutions from 2D IR Spectroscopy
JOURNAL OF PHYSICAL CHEMISTRY B
2018; 122 (46): 10582-10592
View details for DOI 10.1021/acs.jpcb.8b08743
View details for Web of Science ID 000451495900016
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Ion-Molecule Complex Dissociation and Formation Dynamics in LiCl Aqueous Solutions from 2D IR Spectroscopy.
The journal of physical chemistry. B
2018
Abstract
Ion-molecule complex dynamics as well as water dynamics in concentrated lithium chloride (LiCl) solutions are examined using ultrafast two-dimensional infrared (2D IR) spectroscopy with the CN stretching mode of methyl thiocyanate (MeSCN) as the vibrational probe. In pure water, MeSCN has a narrow symmetric absorption line shape. 2D IR spectral diffusion measurements of the CN stretch give the identical time dependence of water dynamics, as previously observed using the OD stretch of HOD in H2O. In concentrated LiCl solutions, the IR absorption spectrum of MeSCN displays two distinct peaks, one corresponding to water H-bonded to the N lone pair of MeSCN (W) and the other corresponding to Li+ associated with the N (L). These two species are in equilibrium, and switching of the CN bonding partner from Li+ to H2O and vice versa was observed and explicated with 2D IR chemical exchange spectroscopy. The MeSCN·Li+ complex dissociation time constant, tauLW, and the MeSCN·H2O dissociation time constant, tauWL, were determined. The observed tauLW chemical exchange dissociation time constant changes from 60 to 40 ps as the LiCl concentration decreases from 10.7 to 7.7 M, mainly due to the increase of the water concentration as the LiCl concentration is reduced. The observed time constants are independent of the model for the chemical reaction. With the assumption of a simple chemical equation, MeSCN·Li+ + H2O ⇄ MeSCN·H2O + Li+, the equilibrium equation rate constants were obtained from the observed chemical exchange time constants. It was determined that the equilibrium rate constants barely change even though the viscosity changes by a factor of 2 and the ionic strength changes by a factor of 1.4. Extrapolation to dilute LiCl solution estimates the tauLW to be 30 ps. The orientational relaxation (anisotropy decay) of both the W and L complexes was measured using polarization selective 2D IR experiments. The lithium-bonded species undergoes orientational relaxation 3 times slower than the water-bonded species in each LiCl solution studied. The difference demonstrates the distinct interactions with the medium experienced by the neutral and charged species in the concentrated salt solutions.
View details for PubMedID 30365321
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Dynamics and Microstructures of Nicotine/Water Binary Mixtures near the Lower Critical Solution Temperature
JOURNAL OF PHYSICAL CHEMISTRY B
2018; 122 (41): 9538–48
View details for DOI 10.1021/acs.jpcb.8b06205
View details for Web of Science ID 000448087800012
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Dynamics and Microstructures of Nicotine/Water Binary Mixtures near the Lower Critical Solution Temperature.
The journal of physical chemistry. B
2018
Abstract
The orientational dynamics and microscopic structures of nicotine/water binary mixtures near the system's lower critical solution temperature (LCST) were elucidated using optical heterodyne-detected optical Kerr effect (OHD-OKE) spectroscopy, nuclear magnetic resonance correlation spectroscopy (NMR COSY), first-principles calculations, and molecular dynamics simulations. Water concentrations were investigated from zero to close to pure water. At temperatures below the LCST, OHD-OKE experiments measured an anomalous slowing as the phase transition concentration was approached. At moderate concentrations and low temperatures, intermolecular cross-peaks between nicotine and water molecules were observed in the COSY spectra, demonstrating the formation of structures that persist for milliseconds. These results suggest that pair correlations contribute to the slowdown in the OHD-OKE data at moderate water concentrations. First-principles calculations revealed that intermolecular hydrogen bonding coordination between nitrogen atoms in pyridine moieties and water lowers the energy barriers for the reorientations of the two nicotine rings. Atomistic simulations demonstrate that with increasing water concentration, hydrogen bonding interactions between pyridine moieties and water molecules first increase and then decrease with a maximum at moderate water concentrations. These experimental and computational characterizations of the dynamics of nicotine molecules are attributed to the distinct configurations of water molecules around the pyridine ring moieties in nicotine molecules.
View details for PubMedID 30229656
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Extraordinary Slowing of Structural Dynamics in Thin Films of a Room Temperature Ionic Liquid.
ACS central science
2018; 4 (8): 1065–73
Abstract
The role that interfaces play in the dynamics of liquids is a fundamental scientific problem with vast importance in technological applications. From material science to biology, e.g., batteries to cell membranes, liquid properties at interfaces are frequently determinant in the nature of chemical processes. For most liquids, like water, the influence of an interface falls off on a 1 nm distance scale. Room temperature ionic liquids (RTILs) are a vast class of unusual liquids composed of complex cations and anions that are liquid salts at room temperature. They are unusual liquids with properties that can be finely tuned by selecting the structure of the cation and anion. RTILs are being used or developed in applications such as batteries, CO2 capture, and liquids for biological processes. Here, it is demonstrated quantitatively that the influence of an interface on RTIL properties is profoundly different from that observed in other classes of liquids. The dynamics of planar thin films of the room temperature ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BmimNTf2), were investigated using two-dimensional infrared spectroscopy (2D IR) with the CN stretch of SeCN- as the vibrational probe. The structural dynamics (spectral diffusion) of the thin films with controlled nanometer thicknesses were measured and compared to the dynamics of the bulk liquid. The samples were prepared by spin coating the RTIL, together with the vibrational probe, onto a surface functionalized with an ionic monolayer that mimics the structure of the BmimNTf2. Near-Brewster's angle reflection pump-probe geometry 2D IR facilitated the detection of the exceedingly small signals from the films, some of which were only 14 nm thick. Even in quarter micron (250 nm) thick films, the observed dynamics were much slower than those of the bulk liquid. Using a new theoretical description, the correlation length (exponential falloff of the influence of the interfaces) was found to be 28 ± 5 nm. This very long correlation length, 30 times greater than that of water, has major implications for the use of RTILs in devices and other applications.
View details for PubMedID 30159404
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Extraordinary Slowing of Structural Dynamics in Thin Films of a Room Temperature Ionic Liquid
ACS CENTRAL SCIENCE
2018; 4 (8): 1065-1073
View details for DOI 10.1021/acscentsci.8b00353
View details for Web of Science ID 000442445700018
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Dynamically Disordered Lattice in a Layered Pb-I-SCN Perovskite Thin Film Probed by Two-Dimensional Infrared Spectroscopy
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2018; 140 (31): 9882-9890
View details for DOI 10.1021/jacs.8b03787
View details for Web of Science ID 000441475800015
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Water Dynamics in Polyacrylamide Hydrogels
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2018; 140 (30): 9466-9477
View details for DOI 10.1021/jacs.8b03547
View details for Web of Science ID 000440877000026
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Dynamically Disordered Lattice in a Layered Pb-I-SCN Perovskite Thin Film Probed by Two-Dimensional Infrared Spectroscopy.
Journal of the American Chemical Society
2018
Abstract
The dynamically flexible lattices in lead halide perovskites may play important roles in extending carrier recombination lifetime in 3D perovskite solar-cell absorbers and in exciton self-trapping in 2D perovskite white-light phosphors. Two-dimensional infrared (2D IR) spectroscopy was applied to study a recently reported Pb-I-SCN layered perovskite. The Pb-I-SCN perovskite was spin-coated on a SiO2 surface as a thin film, with a thickness of 100 nm, where the S12CN- anions were isotopically diluted with the ratio of S12CN:S13CN = 5:95 to avoid vibrational coupling and excitation transfer between adjacent SCN- anions. The 12CN stretch mode of the minor S12CN- component was the principal vibrational probe that reported on the structural evolution through 2D IR spectroscopy. Spectral diffusion was observed with a time constant of 4.1 ± 0.3 ps. Spectral diffusion arises from small structural changes that result in sampling of frequencies within the distribution of frequencies comprising the inhomogeneously broadened infrared absorption band. These transitions among discrete local structures are distinct from oscillatory phonon motions of the lattice. To accurately evaluate the structural dynamics through measurement of spectral diffusion, the vibrational coupling between adjacent SCN- anions had to be carefully treated. Although the inorganic layers of typical 2D perovskites are structurally isolated from each other, the 2D IR data demonstrated that the layers of the Pb-I-SCN perovskite are vibrationally coupled. When both S12CN- and S13CN- were pumped simultaneously, cross-peaks between S12CN and S13CN vibrations and an oscillating 2D band shape of the S12CN- vibration were observed. Both observables demonstrate vibrational coupling between the closest SCN- anions, which reside in different inorganic layers. The thin films and the isotopic dilution produced exceedingly small vibrational echo signal fields; measurements were made possible using the near-Brewster's angle reflection pump-probe geometry.
View details for PubMedID 30024160
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The influence of hydrophilicity on the orientational dynamics and structures of imidazolium-based ionic liquid/water binary mixtures.
The Journal of chemical physics
2018; 149 (4): 044501
Abstract
The orientational dynamics and microscopic structures of imidazolium-based ionic liquids of varying hydrophilicity were investigated using optical heterodyne-detected optical Kerr effect (OHD-OKE) spectroscopy and atomistic simulations. Hydrophilicity was tuned via anion selection, cation alkyl chain length, and the addition of a strong hydrogen bond donor on the cation (protic ionic liquid). In the hydrophobic samples, which saturate at relatively low water concentration, OHD-OKE data display Debye Stokes Einstein (DSE) behavior as a function of water concentration. The DSE behavior indicates that the microstructures of the hydrophobic ionic liquid/water mixtures do not fundamentally change as a function of water concentration. The hydrophilic samples have two regimes of different DSE behaviors demonstrating the presence of two structural regimes depending on water concentration. These experimental results indicate that in hydrophilic ionic liquid/water samples, significant structural changes occur to accommodate high water concentrations, while hydrophobic samples become water saturated because the restructuring of local ionic structures is unfavorable. Atomistic simulations show that the local ionic microstructures experience distinct changes in these hydrophilic ionic liquid/water binary samples because of the delicate interplay of intermolecular interactions among imidazolium cations, hydrophilic anions, and water molecules.
View details for PubMedID 30068204
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The influence of hydrophilicity on the orientational dynamics and structures of imidazolium-based ionic liquid/water binary mixtures
JOURNAL OF CHEMICAL PHYSICS
2018; 149 (4)
View details for DOI 10.1063/1.5038563
View details for Web of Science ID 000440586200036
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Water Dynamics in Polyacrylamide Hydrogels.
Journal of the American Chemical Society
2018
Abstract
Polymeric hydrogels have wide applications including electrophoresis, biocompatible materials, water superadsorbents, and contact lenses. The properties of hydrogels involve the poorly characterized molecular dynamics of water and solutes trapped within the three-dimensional cross-linked polymer networks. Here we apply ultrafast two-dimensional infrared (2D IR) vibrational echo and polarization-selective pump-probe (PSPP) spectroscopies to investigate the ultrafast molecular dynamics of water and a small molecular anion solute, selenocyanate (SeCN-), in polyacrylamide hydrogels. For all mass concentrations of polymer studied (5% and above), the hydrogen-bonding network reorganization (spectral diffusion) dynamics and reorientation dynamics reported by both water and SeCN- solvated by water are significantly slower than in bulk water. As the polymer mass concentration increases, molecular dynamics in the hydrogels slow further. The magnitudes of the slowing, measured with both water and SeCN-, are similar. However, the entire hydrogen-bonding network of water molecules appears to slow down as a single ensemble, without a difference between the core water population and the interface water population at the polymer-water surface. In contrast, the dissolved SeCN- do exhibit two-component dynamics, where the major component is assigned to the anions fully solvated in the confined water nanopools. The slower component has a small amplitude which is correlated with the polymer mass concentration and is assigned to adsorbed anions strongly interacting with the polymer fiber networks.
View details for PubMedID 29985609
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Preface: Special Topic on Chemical Physics of Ionic Liquids
JOURNAL OF CHEMICAL PHYSICS
2018; 148 (19)
View details for DOI 10.1063/1.5039492
View details for Web of Science ID 000432853800003
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Preface: Special Topic on Chemical Physics of Ionic Liquids.
The Journal of chemical physics
2018; 148 (19): 193501
View details for DOI 10.1063/1.5039492
View details for PubMedID 30307194
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Monolayer dynamics at the air/ water interface: From ultrafast to ultraslow dynamics
AMER CHEMICAL SOC. 2018
View details for Web of Science ID 000435537700540
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Influence of mesoscopic confinement on the dynamics of room temperature ionic liquids
AMER CHEMICAL SOC. 2018
View details for Web of Science ID 000435539905553
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Influence of Water on Carbon Dioxide and Room Temperature Ionic Liquid Dynamics: Supported Ionic Liquid Membrane vs the Bulk Liquid
JOURNAL OF PHYSICAL CHEMISTRY B
2018; 122 (8): 2389–95
Abstract
The influence of water on the dynamics of a room temperature ionic liquid (RTIL), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimNTf2), and CO2 in the RTIL was studied in the bulk liquid and a supported ionic liquid membrane (SILM) using two-dimensional infrared (IR) and IR polarization selective pump-probe spectroscopies. In the water-saturated bulk EmimNTf2, the complete orientational randomization and structural spectral diffusion (SSD) of CO2 became faster than in the dry EmimNTf2. In the poly(ether sulfone) SILM, only the longer time components of the SSD became faster in the water-saturated RTIL; the complete orientational randomization remained similar to the dry RTIL in the SILM. The implication is that the presence of water in EmimNTf2 contained in the SILM facilitates the fluctuation of globally modified RTIL structure in the pores, but the local RTIL environments are relatively unaffected.
View details for PubMedID 29412666
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Ultrafast to Ultraslow Dynamics of a Langmuir Monolayer at the Air/Water Interface Observed with Reflection Enhanced 2D IR Spectroscopy
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2017; 139 (46): 16518–27
Abstract
Monolayers play important roles in naturally occurring phenomena and technological processes. Monolayers at the air/water interface have received considerable attention, yet it has proven difficult to measure monolayer and interfacial molecular dynamics. Here we employ a new technique, reflection enhanced two-dimensional infrared (2D IR) spectroscopy, on a carbonyl stretching mode of tricarbonylchloro-9-octadecylamino-4,5-diazafluorenerhenium(I) (TReF18) monolayers at two surface densities. Comparison to experiments on a water-soluble version of the metal carbonyl headgroup shows that water hydrogen bond rearrangement dynamics slow from 1.5 ps in bulk water to 3.1 ps for interfacial water. Longer time scale fluctuations were also observed and attributed to fluctuations of the number of hydrogen bonds formed between water and the three carbonyls of TReF18. At the higher surface density, two types of TReF18 minor structures are observed in addition to the main structure. The reflection method can take usable 2D IR spectra on the monolayer within 8 s, enabling us to track the fluctuating minor structures' appearance and disappearance on a tens of seconds time scale. 2D IR chemical exchange spectroscopy further shows these structures interconvert in 30 ps. Finally, 2D spectral line shape evolution reveals that it takes the monolayers hours to reach macroscopic structural equilibrium.
View details for PubMedID 29072913
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The influence of mesoscopic confinement on the dynamics of imidazolium-based room temperature ionic liquids in polyether sulfone membranes
JOURNAL OF CHEMICAL PHYSICS
2017; 147 (19): 194502
Abstract
The structural dynamics of a series of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (CnmimNTf2, n = 2, 4, 6, 10: ethyl-Emim; butyl-Bmim; hexyl-Hmim; decyl-Dmim) room temperature ionic liquids confined in the pores of polyether sulfone (PES 200) membranes with an average pore size of ∼350 nm and in the bulk liquids were studied. Time correlated single photon counting measurements of the fluorescence of the fluorophore coumarin 153 (C153) were used to observe the time-dependent Stokes shift (solvation dynamics). The solvation dynamics of C153 in the ionic liquids are multiexponential decays. The multiexponential functional form of the decays was confirmed as the slowest decay component of each bulk liquid matches the slowest component of the liquid dynamics measured by optical heterodyne-detected optical Kerr effect (OHD-OKE) experiments, which is single exponential. The fact that the slowest component of the Stokes shift matches the OHD-OKE data in all four liquids identifies this component of the solvation dynamics as arising from the complete structural randomization of the liquids. Although the pores in the PES membranes are large, confinement on the mesoscopic length scale results in substantial slowing of the dynamics, a factor of ∼4, for EmimNTf2, with the effect decreasing as the chain length increases. By DmimNTf2, the dynamics are virtually indistinguishable from those in the bulk liquid. The rotation relaxation of C153 in the four bulk liquids was also measured and showed strong coupling between the C153 probe and its environment.
View details for PubMedID 29166092
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Discontinuity in Fast Dynamics at the Glass Transition of ortho-Terphenyl
JOURNAL OF PHYSICAL CHEMISTRY B
2017; 121 (45): 10417–28
Abstract
The dynamics of the molecular glass former ortho-terphenyl through the glass transition were observed with two-dimensional infrared vibrational spectroscopy measurements of spectral diffusion using the small probe molecule phenylselenocyanate. Although the slow diffusive motions were not visible on the experimental time scale, a picosecond-scale exponential relaxation was observed at temperatures from above to well below the glass transition temperature. The characteristic time scale has a smooth temperature dependence from the liquid into the glass phase, but the range of vibrational frequencies the probe samples displayed a discontinuity at the glass transition temperature. Complementary pump-probe experiments associate the observed motion with density fluctuations. The key features of the dynamics are reproduced with a simple corrugated well potential energy surface model. In addition, the temperature dependence of the homogeneous vibrational dephasing was found to have a T2 functional form, where T is the absolute temperature.
View details for PubMedID 29039665
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Guest Hydrogen Bond Dynamics and Interactions in the Metal-Organic Framework MIL-53(AI) Measured with Ultrafast Infrared Spectroscopy
JOURNAL OF PHYSICAL CHEMISTRY C
2017; 121 (21): 11880-11890
View details for DOI 10.1021/acs.jpcc.7b02458
View details for Web of Science ID 000402775200098
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Proton Transfer in Perfluorosulfonic Acid Fuel Cell Membranes with Differing Pendant Chains and Equivalent Weights
JOURNAL OF PHYSICAL CHEMISTRY B
2017; 121 (17): 4544-4553
Abstract
Proton transfer in the nanoscopic water channels of polyelectrolyte fuel cell membranes was studied using a photoacid, 8-hydroxypyrene-1,3,6-trisulfonic acid sodium salt (HPTS), in the channels. The local environment of the probe was determined using 8-methoxypyrene-1,3,6-trisulfonic acid sodium salt (MPTS), which is not a photoacid. Three fully hydrated membranes, Nafion (DuPont) and two 3M membranes, were studied to determine the impact of different pendant chains and equivalent weights on proton transfer. Fluorescence anisotropy and excited state population decay data that characterize the local environment of the fluorescent probes and proton transfer dynamics were measured. The MPTS lifetime and anisotropy results show that most of the fluorescent probes have a bulk-like water environment with a relatively small fraction interacting with the channel wall. Measurements of the HPTS protonated and deprotonated fluorescent bands' population decays provided information on the proton transport dynamics. The decay of the protonated band from ∼0.5 ns to tens of nanoseconds is in part determined by dissociation and recombination with the HPTS, providing information on the ability of protons to move in the channels. The dissociation and recombination is manifested as a power law component in the protonated band fluorescence decay. The results show that equivalent weight differences between two 3M membranes resulted in a small difference in proton transfer. However, differences in pendant chain structure did significantly influence the proton transfer ability, with the 3M membranes displaying more facile transfer than Nafion.
View details for DOI 10.1021/acs.jpcb.7b01764
View details for Web of Science ID 000400881300024
View details for PubMedID 28398064
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Dynamics in a Water Interfacial Boundary Layer Investigated with IR Polarization-Selective Pump-Probe Experiments
JOURNAL OF PHYSICAL CHEMISTRY B
2017; 121 (17): 4530-4537
Abstract
The dynamics of water molecules near the surfactant interface in large Aerosol-OT reverse micelles (RMs) (w0 = 16-25) was investigated with IR polarization-selective pump-probe experiments using the SeCN(-) anion as a vibrational probe. Linear absorption spectra of RMs (w0 = 25-2) can be decomposed into the weighted sum of the SeCN(-) spectra in bulk water and the spectrum of the SeCN(-) anion interacting with the interfacial sulfonate head groups (w0 = 1). The spectra of the large RMs, w0 ≥ 16, are overwhelmingly dominated by the bulk water component. Anisotropy decays (orientational relaxation) of the anion for w0 ≥ 16 displayed bulk water relaxation (1.4 and 4.5 ps) plus an additional slow decay with a time constant of ∼13 ps. The amplitude of the slow decay was too large to be associated with SeCN(-) in contact with the interface on the basis of the linear spectrum decomposition. The results indicate that the observed slow components arise from SeCN(-) in a water boundary layer, in which water molecules are perturbed by the interface but are not directly associated with it. This layer is the transition between water in direct contact with the interface and bulk water in the large RM cores. In the boundary layer, the water dynamics is slow compared to that in bulk water.
View details for DOI 10.1021/acs.jpcb.7b01028
View details for Web of Science ID 000400881300022
View details for PubMedID 28379003
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Molecular origins of superacidity in sulfated MOF-808
AMER CHEMICAL SOC. 2017
View details for Web of Science ID 000430569103507
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Dynamics of room temperature ionic liquids measured with two dimensional infrared spectroscopy: The influence of electric fields on observables
AMER CHEMICAL SOC. 2017
View details for Web of Science ID 000430569106448
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Carbon dioxide dynamics in room temperature ionic liquids and supported ionic liquid membranes: 2D IR and polarization selective pump-prove experiments
AMER CHEMICAL SOC. 2017
View details for Web of Science ID 000430569106303
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Dynamics of functionalized alkyl monolayers on gold: Two dimensional infrared experiments and molecular dynamics simulations
AMER CHEMICAL SOC. 2017
View details for Web of Science ID 000430568500331
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Direct observation of dynamic crossover in fragile molecular glass formers with 2D IR vibrational echo spectroscopy
JOURNAL OF CHEMICAL PHYSICS
2017; 146 (12)
Abstract
The dynamics of supercooled liquids of the molecular glass formers benzophenone and ortho-terphenyl were investigated with 2D IR spectroscopy using long-lived vibrational probes. The long lifetimes of the probes enabled structural dynamics of the liquids to be studied from a few hundred femtoseconds to a nanosecond. 2D IR experiments measured spectraldiffusion of a vibrational probe, which reports on structural fluctuations of the liquid. Analysis of the 2D IR data provides the frequency-frequency correlation function (FFCF). Two vibrational probes were examined with equivalent results, demonstrating the observed liquid dynamics are not significantly influenced by the probe molecules. At higher temperatures, the FFCF is a biexponential decay. However, at mild supercooling, the biexponential decay is no longer sufficient, indicating a dynamic crossover. The crossover occurs at a temperature well above the mode-coupling theory critical temperature for the given liquid, indicating dynamic heterogeneity above the critical temperature. Examination of the low temperature data with lifetime density analysis shows that the change is best described as an additional, distinct relaxation that shows behavior consistent with a slow β-process.
View details for DOI 10.1063/1.4978852
View details for Web of Science ID 000397929300058
View details for PubMedID 28388155
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Enhanced nonlinear spectroscopy for monolayers and thin films in near-Brewster's angle reflection pump-probe geometry
JOURNAL OF CHEMICAL PHYSICS
2017; 146 (9)
View details for DOI 10.1063/1.4977508
View details for Web of Science ID 000397312800042
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Dynamics in a Room-Temperature Ionic Liquid from the Cation Perspective: 2D IR Vibrational Echo Spectroscopy.
Journal of the American Chemical Society
2017; 139 (6): 2408-2420
Abstract
The dynamics of the room-temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BmimNTf2) were investigated with two-dimensional infrared (2D IR) vibrational echo spectroscopy and polarization selective pump-probe (PSPP) experiments. The CN stretch frequency of a modified Bmim(+) cation (2-SeCN-Bmim(+)), in which a SeCN moiety was substituted onto the C-2 position of the imidazolium ring, was used as a vibrational probe. A major result of the 2D IR experiments is the observation of a long time scale structural spectral diffusion component of 600 ps in addition to short and intermediate time scales similar to those measured for selenocyanate anion (SeCN(-)) dissolved in BmimNTf2. In contrast to 2-SeCN-Bmim(+), SeCN(-) samples its inhomogeneous line width nearly an order of magnitude faster than the complete structural randomization time of neat BmimNTf2 liquid (870 ± 20 ps) measured with optical heterodyne-detected optical Kerr effect (OHD-OKE) experiments. The orientational correlation function obtained from PSPP experiments on 2-SeCN-Bmim(+) exhibits two periods of restricted angular diffusion (wobbling-in-a-cone) followed by complete orientational randomization on a time scale of 900 ± 20 ps, significantly slower than observed for SeCN(-) but identical within experimental error to the complete structural randomization time of BmimNTf2. The experiments indicate that 2-SeCN-Bmim(+) is sensitive to local motions of the ionic region that influence the spectral diffusion and reorientation of small, anionic, and neutral molecules as well as significantly slower, longer-range fluctuations that are responsible for complete randomization of the liquid structure.
View details for DOI 10.1021/jacs.6b12011
View details for PubMedID 28099808
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Dynamics of a Room Temperature Ionic Liquid in Supported Ionic Liquid Membranes vs the Bulk Liquid: 2D IR and Polarized IR Pump-Probe Experiments
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2017; 139 (1): 311-323
Abstract
Supported ionic liquid membranes (SILMs) are membranes that have ionic liquids impregnated in their pores. SILMs have been proposed for advanced carbon capture materials. Two-dimensional infrared (2D IR) and polarization selective IR pump-probe (PSPP) techniques were used to investigate the dynamics of reorientation and spectral diffusion of the linear triatomic anion, SeCN(-), in poly(ether sulfone) (PES) membranes and room-temperature ionic liquid (RTIL), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimNTf2). The dynamics in the bulk EmimNTf2 were compared to its dynamics in the SILM samples. Two PES membranes, PES200 and PES30, have pores with average sizes, ∼300 nm and ∼100 nm, respectively. Despite the relatively large pore sizes, the measurements reveal that the reorientation of SeCN(-) and the RTIL structural fluctuations are substantially slower in the SILMs than in the bulk liquid. The complete orientational randomization, slows from 136 ps in the bulk to 513 ps in the PES30. 2D IR measurements yield three time scales for structural spectral diffusion (SSD), that is, the time evolution of the liquid structure. The slowest decay constant increases from 140 ps in the bulk to 504 ps in the PES200 and increases further to 1660 ps in the PES30. The results suggest that changes at the interface propagate out and influence the RTIL structural dynamics even more than a hundred nanometers from the polymer surface. The differences between the IL dynamics in the bulk and in the membranes suggest that studies of bulk RTIL properties may be poor guides to their use in SILMs in carbon capture applications.
View details for DOI 10.1021/jacs.6b10695
View details for Web of Science ID 000392036900049
View details for PubMedID 27973786
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Water-anion hydrogen bonding dynamics: Ultrafast IR experiments and simulations.
The Journal of chemical physics
2017; 146 (23): 234501
Abstract
Many of water's remarkable properties arise from its tendency to form an intricate and robust hydrogen bond network. Understanding the dynamics that govern this network is fundamental to elucidating the behavior of pure water and water in biological and physical systems. In ultrafast nonlinear infrared experiments, the accessible time scales are limited by water's rapid vibrational relaxation (1.8 ps for dilute HOD in H2O), precluding interrogation of slow hydrogen bond evolution in non-bulk systems. Here, hydrogen bonding dynamics in bulk D2O were studied from the perspective of the much longer lived (36.2 ps) CN stretch mode of selenocyanate (SeCN(-)) using polarization selective pump-probe (PSPP) experiments, two-dimensional infrared (2D IR) vibrational echo spectroscopy, and molecular dynamics simulations. The simulations make use of the empirical frequency mapping approach, applied to SeCN(-) for the first time. The PSPP experiments and simulations show that the orientational correlation function decays via fast (2.0 ps) restricted angular diffusion (wobbling-in-a-cone) and complete orientational diffusive randomization (4.5 ps). Spectral diffusion, quantified in terms of the frequency-frequency correlation function, occurs on two time scales. The initial 0.6 ps time scale is attributed to small length and angle fluctuations of the hydrogen bonds between water and SeCN(-). The second 1.4 ps measured time scale, identical to that for HOD in bulk D2O, reports on the collective reorganization of the water hydrogen bond network around the anion. The experiments and simulations provide details of the anion-water hydrogen bonding and demonstrate that SeCN(-) is a reliable vibrational probe of the ultrafast spectroscopy of water.
View details for PubMedID 28641416
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Hydrogen Bonding versus π-π Stacking Interactions in Imidazolium-Oxalatoborate Ionic Liquid.
The journal of physical chemistry. B
2017; 121 (29): 7173–79
Abstract
Intermolecular features like hydrogen bonding and π-type interactions play pivotal roles in stabilizing molecular structures in ionic liquids with planar rings and hydrogen-bond donors and acceptors. However, the delicate interplay among these interactions is complicated and depends on specific ion types. In this work, ab initio molecular dynamics simulations were performed to reveal competitive and cooperative characteristics among hydrogen bonding and π-type interactions in a typical imidazolium-oxalatoborate ionic liquid. Imidazolium rings take preferential on-top parallel orientations, leading to their particular π-π stacking distributions at short distances. Intermolecular interactions between imidazolium and oxalato rings are manifested by short-range on-top parallel orientations and in-plane hydrogen bonding interactions, promoting their parallel displaced offset stacking arrangements. However, on an intermediate distance scale, attractive Coulombic interactions between imidazolium and oxalato rings dominate and contribute to their perpendicular orientations. Spatial coordination patterns between intermolecular oxalato rings are balanced by repulsive electrostatic interactions and steric hindrance effects, leading to their tilted orientations in local environments.
View details for PubMedID 28691812
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Impact of Hydrogen Bonding on the Dynamics and Structure of Protic Ionic Liquid/Water Binary Mixtures.
The journal of physical chemistry. B
2017; 121 (36): 8564–76
Abstract
The orientational dynamics and microscopic liquid structure of a protic ionic liquid, 1-ethylimidazolium bis(trifluoromethylsulfonyl)imide (EhimNTf2), and its aprotic analogue, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimNTf2), were studied at various water concentrations using optical heterodyne-detected optical Kerr effect (OHD-OKE) spectroscopy, linear infrared spectroscopy, and atomistic simulations. The OHD-OKE experiments essentially measure the orientational relaxation of the Ehim+ and Emim+ cations. The experiments and simulations show a significant dynamical and structural change in EhimNTf2 between the 2:1 ion pair:water and the 1:1 ion pair:water concentrations. The OHD-OKE data show that EmimNTf2/water mixtures exhibit hydrodynamic behavior at all water concentrations up to saturation. In contrast, EhimNTf2/water mixtures deviate from hydrodynamic behavior at water concentrations above 2:1. At the 1:1 concentration, the orientational randomization of the Ehim+ cation is slower than that predicted using viscosity data. Atomistic simulation results reveal the microscopic ionic structures of dry liquids and the preferential hydrogen bonding of water to the H atom of the N-H of Ehim+ over other sites on the Ehim+ and Emim+ cations. Atomistic simulation results demonstrate that in EhimNTf2 RTIL/water mixtures there is a substantial jump in the formation of water-water hydrogen bonds in addition to N-H-water hydrogen bonds upon increasing the water concentration from 2:1 to 1:1. Water-water hydrogen bonding strengthens the spatial coordination of the H atom of the N-H moiety of Ehim+ to neighboring water molecules through preferential hydrogen bonding. The jump in the concentration of water-water hydrogen bonds occurs at the Ehim+/water concentration at which the orientational relaxation deviates from hydrodynamic behavior. This structural observation is confirmed with FT-IR spectra that show asymmetry in the peak for the O-D stretch that is indicative of water clusters. The formation of water clusters and the strengthening of the N-H···OH2 hydrogen bonds slow the orientational relaxation of Ehim+ cations as observed by the OHD-OKE experiments.
View details for PubMedID 28810731
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Carbon Dioxide in a Supported Ionic Liquid Membrane: Structural and Rotational Dynamics Measured with 2D IR and Pump-Probe Experiments.
Journal of the American Chemical Society
2017
Abstract
Supported ionic liquid membranes (SILMs) are porous membranes impregnated with ionic liquids (ILs) and used as advanced carbon capture materials. Here, two-dimensional infrared (2D IR) and IR polarization selective pump-probe (PSPP) spectroscopies were used to investigate CO2 reorientation and spectral diffusion dynamics in SILMs. The SILM contained 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonly)imide in the poly(ether sulfone) membrane with average pore size of ~350 nm. Two ensembles of CO2 were observed in the SILM, one in the IL phase in the membrane pores and the other in the supporting membrane polymer. CO2 in the polymer displayed a red-shifted IR absorption spectrum and a shorter vibrational lifetime of the asymmetric stretch mode compared to the IL phase. Despite the relatively large pore sizes, the complete orientational randomization of CO2 and structural fluctuations of the IL (spectral diffusion) in the pores are slower than in the bulk IL by ~2-fold. The implication is that the IL structural change induced by the polymer interface can propagate out from the interface more than a hundred nanometers, influencing the dynamics. The dynamics in the polymer are even slower. This study demonstrates that there are significant differences in the dynamics of ILs in SILMs on a molecular level compared to the bulk IL, and the study of dynamics in SILMs can provide important information for the design of SILMs for CO2 capture.
View details for PubMedID 28723129
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Water Dynamics in 1-Alkyl-3-methylimidazolium Tetrafluoroborate Ionic Liquids
JOURNAL OF PHYSICAL CHEMISTRY B
2016; 120 (44): 11523-11538
Abstract
The effects of water concentration and varying alkyl chain length on the dynamics of water in 1-alkyl-3-methylimidazolium tetrafluoroborate room-temperature ionic liquids (RTILs) were characterized using two-dimensional infrared (2D IR) vibrational echo spectroscopy and polarization-selective IR pump-probe experiments to study the water hydroxyl (OD) stretching mode of dilute HOD in H2O. Three imidazolium cation alkyl chain lengths, ethyl (Emim(+)), butyl (Bmim(+)), and decyl (Dmim(+)), were investigated. Both Bmim(+) and Dmim(+) cations have sufficiently long chains that the liquids exhibit polar-apolar segregation, whereas the Emim(+) IL has no significant apolar aggregation. Although the OD absorption spectra are independent of the chain length, the measured reorientation and spectral diffusion dynamics are chain length dependent and tend to slow when the alkyl chain is long enough for polar-apolar segregation. As the water concentration is increased, a water-associated water population forms, absorbing in a new spectral region red-shifted from the isolated, anion-associated, water population. Furthermore, the anion-associated water dynamics are accelerated. At sufficiently high water concentrations, water in all of the RTILs experiences similar dynamics, the solvent structures having been fluidized by the addition of water. The water concentration at which the dilute water dynamics changes to fluidized dynamics depends on the alkyl chain length, which determines the extent and ordering of the apolar regions. Increases in both water concentration and alkyl chain length serve to modify the ordering of the RTIL, but with opposite and competing effects on the dissolved water dynamics.
View details for DOI 10.1021/acs.jpcb.6b08410
View details for Web of Science ID 000387738300019
View details for PubMedID 27726398
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Orientational Dynamics of a Functionalized Alkyl Planar Monolayer Probed by Polarization-Selective Angle-Resolved Infrared Pump-Probe Spectroscopy.
Journal of the American Chemical Society
2016: -?
Abstract
Polarization-selective angle-resolved infrared pump-probe spectroscopy was developed and used to study the orientational dynamics of a planar alkylsiloxane monolayer functionalized with a rhenium metal carbonyl headgroup on an SiO2 surface. The technique, together with a time-averaged infrared linear dichroism measurement, characterized picosecond orientational relaxation of the headgroup occurring at the monolayer-air interface by employing several sets of incident angles of the infrared pulses relative to the sample surface. By application of this method and using a recently developed theory, it was possible to extract both the out-of-plane and "mainly"-in-plane orientational correlation functions in a model-independent manner. The observed correlation functions were compared with theoretically derived correlation functions based on several dynamical models. The out-of-plane correlation function reveals the highly restricted out-of-plane motions of the head groups and also suggests that the angular distribution of the transition dipole moments is bimodal. The mainly-in-plane correlation function, for the sample studied here with the strongly restricted out-of-plane motions, essentially arises from the purely in-plane dynamics. In contrast to the out-of-plane dynamics, significant in-plane motions occurring over various time scales were observed including an inertial motion, a restricted wobbling motion of ∼3 ps, and complete randomization occurring in ∼25 ps.
View details for PubMedID 27668512
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The Influence of Water on the Alkyl Region Structure in Variable Chain Length Imidazolium-Based Ionic Liquid/Water Mixtures
JOURNAL OF PHYSICAL CHEMISTRY B
2016; 120 (39): 10350-10357
Abstract
Solutions of room temperature ionic liquids (RTILs) and water were studied by observing the reorientational dynamics of the fluorescent probe perylene. Perylene is solvated in the alkyl regions of the RTILs. Its D2h symmetry made it possible to extract dynamical information on both in-plane and out-of-plane reorientation from time-resolved fluorescence anisotropy measurements. Perylene reorientation reports on its interactions with the alkyl chains. The RTILs were a series of 1-alkyl-3-methylimidazolium tetrafluoroborates (CnmimBF4, where n is the number of carbons in the alkyl chain), and the effects on perylene's dynamics were observed when varying the alkyl chain length of the cation (n = 4, 6, 8, and 10; butyl, hexyl, octyl, decyl) and varying the water content from pure RTIL to roughly three water molecules per RTIL ion pair. Time correlated single photon counting was used to measure the fluorescence anisotropy decays to determine the orientational dynamics. The friction coefficients for both the in-plane and out-of-plane reorientation were determined to eliminate the influence of changes in viscosity caused by both the addition of water and the different alkyl chain lengths. The friction coefficients provided information on the interactions of the perylene with the alkyl environment and how these interactions changed with chain length and water content. As the chain length increased, the addition of water had less of an effect on the local alkyl environment surrounding the perylene. The friction coefficients generally increased with higher water contents; the in-plane orientational motion was hindered significantly more than the out-of-plane motion. The restructuring of the alkyl regions is likely a consequence of a rearrangement of the ionic imidazolium head groups to accommodate partial solvation by water, which results in a change in the arrangement of the alkyl chains. At very high water content, BmimBF4 broke this general trend, with both in-plane and out-of-plane rotational friction decreasing above a water content of one water per ion pair. This decrease indicates a major reorganization of the overall liquid structure in high water content mixtures. In contrast to BmimBF4, the longer chain length RTILs are not infinitely miscible with water, and do not show evidence of a major reorganization before reaching saturation and phase-separating. The results suggest that phase separation in longer chain length BF4 RTILs is a consequence of their inability to undergo the reorganization of the alkyl regions necessary to accommodate high water concentrations.
View details for DOI 10.1021/acs.jpcb.6b07853
View details for Web of Science ID 000384959200018
View details for PubMedID 27643808
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Ionic Liquid versus Li+ Aqueous Solutions: Water Dynamics near Bistriflimide Anions
JOURNAL OF PHYSICAL CHEMISTRY B
2016; 120 (37): 9997-10009
Abstract
The ultrafast dynamics of concentrated aqueous solutions of the salt lithium bistriflimide and ionic liquid (IL) 1-ethyl-3-methylimidazolium bistriflimide was studied using two-dimensional infrared (2D IR) vibrational echo and polarization-selective IR pump-probe techniques to monitor water's hydroxyl stretch. Two distinct populations of hydroxyl groups, with differing vibrational lifetimes, are detected in solution: those engaged in hydrogen bonding with other water molecules and those engaged in hydrogen bonding with the bistriflimide anion. Water molecules with the same hydrogen bond partner exhibit similar vibrational lifetimes in the two solutions. The reorientation dynamics of the anion-associated waters is also similar in form in the two solutions, showing a restricted wobbling-in-a-cone motion followed by a slower diffusive orientational randomization. However, the wobbling motions are much more angularly restricted in the IL solution. Spectral diffusion dynamics, which tracks the structural fluctuations of water's hydrogen bonds, is very different in the two solutions. Water in the IL solution experiences much faster fluctuations overall and shows a greater extent of motional narrowing, resulting in a larger homogeneously broadened component in the spectral line, compared to those in the aqueous lithium salt. Thus, even when the hydroxyls of water associate with the same anion in solution, the cation identity and extent of ionic ordering (i.e., salt solution vs IL) can play an important role in determining the structural fluctuations experienced by a small hydrogen-bonded solute.
View details for DOI 10.1021/acs.jpcb.6b07145
View details for Web of Science ID 000384034100017
View details for PubMedID 27580210
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Alkyl Chain Length Dependence of the Dynamics and Structure in the Ionic Regions of Room-Temperature Ionic Liquids.
journal of physical chemistry. B
2016; 120 (30): 7488-7501
Abstract
The dynamics of four 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide room-temperature ionic liquids (RTILs) with carbon chain lengths of 2, 4, 6, and 10 were studied by measuring the orientational and spectral diffusion dynamics of the vibrational probe SeCN(-). Vibrational absorption spectra, two-dimensional infrared (2D IR), and polarization-selective pump-probe (PSPP) experiments were performed on the CN stretch. In addition, optical heterodyne-detected optical Kerr effect (OHD-OKE) experiments were performed on the bulk liquids. The PSPP experiments yielded triexponential anisotropy decays, which were analyzed with the wobbling-in-a-cone model. The slowest decay, the complete orientational randomization, slows with increasing chain length in a hydrodynamic trend consistent with the increasing viscosity. The shortest time scale wobbling motions are insensitive to chain length, while the intermediate time scale wobbling slows mildly as the chain length increases. The 2D IR spectra measured in parallel (⟨XXXX⟩) and perpendicular (⟨XXYY⟩) polarization configurations gave different decays, showing that reorientation-induced spectral diffusion (RISD) contributes to the dynamics. The spectral diffusion caused by the RTIL structural fluctuations was obtained by removing the RISD contributions. The faster structural fluctuations are relatively insensitive to chain length. The slowest structural fluctuations slow substantially when going from Emim (2 carbon chain) to Bmim (4 carbon chain) and slow further, but more gradually, as the chain length is increased. It was shown previously that K(+) causes local ion clustering in the Emim RTIL. The K(+) effect increases with increasing chain length. The OHD-OKE measured complete structural randomization times slow substantially with increasing chain length and are much slower than the dynamics experienced by the SeCN(-) located in the ionic regions of the RTILs.
View details for DOI 10.1021/acs.jpcb.6b05397
View details for PubMedID 27388422
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Water of Hydration Dynamics in Minerals Gypsum and Bassanite: Ultrafast 2D IR Spectroscopy of Rocks.
Journal of the American Chemical Society
2016; 138 (30): 9694-9703
Abstract
Water of hydration plays an important role in minerals, determining their crystal structures and physical properties. Here ultrafast nonlinear infrared (IR) techniques, two-dimensional infrared (2D IR) and polarization selective pump-probe (PSPP) spectroscopies, were used to measure the dynamics and disorder of water of hydration in two minerals, gypsum (CaSO4·2H2O) and bassanite (CaSO4·0.5H2O). 2D IR spectra revealed that water arrangement in freshly precipitated gypsum contained a small amount of inhomogeneity. Following annealing at 348 K, water molecules became highly ordered; the 2D IR spectrum became homogeneously broadened (motional narrowed). PSPP measurements observed only inertial orientational relaxation. In contrast, water in bassanite's tubular channels is dynamically disordered. 2D IR spectra showed a significant amount of inhomogeneous broadening caused by a range of water configurations. At 298 K, water dynamics cause spectral diffusion that sampled a portion of the inhomogeneous line width on the time scale of ∼30 ps, while the rest of inhomogeneity is static on the time scale of the measurements. At higher temperature, the dynamics become faster. Spectral diffusion accelerates, and a portion of the lower temperature spectral diffusion became motionally narrowed. At sufficiently high temperature, all of the dynamics that produced spectral diffusion at lower temperatures became motionally narrowed, and only homogeneous broadening and static inhomogeneity were observed. Water angular motions in bassanite exhibit temperature-dependent diffusive orientational relaxation in a restricted cone of angles. The experiments were made possible by eliminating the vast amount of scattered light produced by the granulated powder samples using phase cycling methods.
View details for DOI 10.1021/jacs.6b05589
View details for PubMedID 27385320
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Critical Slowing of Density Fluctuations Approaching the Isotropic-Nematic Transition in Liquid Crystals: 2D IR Measurements and Mode Coupling Theory.
journal of physical chemistry. B
2016; 120 (28): 7003-7015
Abstract
Two-dimensional infrared (2D IR) data are presented for a vibrational probe in three nematogens: 4-cyano-4'-pentylbiphenyl, 4-cyano-4'-octylbiphenyl, and 4-(trans-4-amylcyclohexyl)-benzonitrile. The spectral diffusion time constants in all three liquids in the isotropic phase are proportional to [T*/(T - T*)](1/2), where T* is 0.5-1 K below the isotropic-nematic phase transition temperature (TNI). Rescaling to a reduced temperature shows that the decays of the frequency-frequency correlation function (FFCF) for all three nematogens fall on the same curve, suggesting a universal dynamic behavior of nematogens above TNI. Spectral diffusion is complete before significant orientational relaxation in the liquid, as measured by optically heterodyne detected-optical Kerr effect (OHD-OKE) spectroscopy, and before any significant orientational randomization of the probe measured by polarization selective IR pump-probe experiments. To interpret the OHD-OKE and FFCF data, we constructed a mode coupling theory (MCT) schematic model for the relationships among three correlation functions: ϕ1, a correlator for large wave vector density fluctuations; ϕ2, the orientational correlation function whose time derivative is the observable in the OHD-OKE experiment; and ϕ3, the FFCF for the 2D IR experiment. The equations for ϕ1 and ϕ2 match those in the previous MCT schematic model for nematogens, and ϕ3 is coupled to the first two correlators in a straightforward manner. Resulting models fit the data very well. Across liquid crystals, the temperature dependences of the coupling constants show consistent, nonmonotonic behavior. A remarkable change in coupling occurs at ∼5 K above TNI, precisely where the rate of spectral diffusion in 5CB was observed to deviate from that of a similar nonmesogenic liquid.
View details for DOI 10.1021/acs.jpcb.6b04997
View details for PubMedID 27363680
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Structural and Rotational Dynamics of Carbon Dioxide in 1-Alkyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquids: The Effect of Chain Length
JOURNAL OF PHYSICAL CHEMISTRY B
2016; 120 (27): 6698-6711
Abstract
Ionic liquids (ILs) have been proposed as possible carbon dioxide (CO2) capture media; thus, it is useful to understand the dynamics of both the dissolved gas and its IL environment as well as how altering an IL affects these dynamics. With increasing alkyl chain length, it is well-established that ILs obtain a mesoscopic structural feature assigned to polar-apolar segregation, and the change in structure with chain length affects the dynamics. Here, the dynamics of CO2 in a series of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ILs, in which the alkyl group is ethyl, butyl, hexyl, or decyl, were investigated using ultrafast infrared spectroscopy by measuring the reorientation and spectral diffusion of carbon dioxide in the ILs. It was found that reorientation of the carbon dioxide occurs on three time scales, which correspond to two different time scales of restricted wobbling-in-a-cone motions and a long-time complete diffusive reorientation. Complete reorientation slows with increasing chain length but less than the increases in viscosity of the bulk liquids. Spectral diffusion, measured with two-dimensional IR spectroscopy, is caused by a combination of the liquids' structural fluctuations and reorientation of the CO2. The data were analyzed using a recent theory that takes into account both contributions to spectral diffusion and extracts the structural spectral diffusion. Different components of the structural fluctuations have distinct dependences on the alkyl chain length. All of the dynamics are fast compared to the complete orientational randomization of the bulk ILs, as measured with optical heterodyne-detected optical Kerr effect measurements. The results indicate a hierarchy of constraint releases in the liquids that give rise to increasingly slower dynamics.
View details for DOI 10.1021/acs.jpcb.6b03971
View details for Web of Science ID 000379991000024
View details for PubMedID 27264965
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Ionic Liquid Dynamics Measured with 2D IR and IR Pump-Probe Experiments on a Linear Anion and the Influence of Potassium Cations
JOURNAL OF PHYSICAL CHEMISTRY B
2016; 120 (26): 5842-5854
Abstract
The room-temperature ionic liquid EmimNTf2 (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) was studied with two-dimensional infrared (2D IR) spectroscopy and polarization selective pump-probe (PSPP) experiments using low-concentration selenocyanate (SeCN(-)) as the vibrational probe. SeCN(-) was added as EmimSeCN, which keeps the cation the same. KSeCN was also used, so K(+) was added. Two 2D IR polarization configurations were employed: ⟨XXXX⟩ (all pulses have the same polarization) and ⟨XXYY⟩ (the first two pulse polarizations are perpendicular to that of the third pulse and the echo). The spectral diffusion differs for the two configurations, demonstrating that reorientation-induced spectral diffusion, in addition to structural spectral diffusion (SSD), plays a role in the observed dynamics. The SSD was extracted from the 2D IR time-dependent data. The samples with EmimSeCN have dynamics on several fast time scales; however, when KSeCN is used, both the PPSP anisotropy decay and the 2D IR decays have low amplitude offsets (nondecaying values at long times). The size of the offsets increased with increased K(+) concentration. These results are explained in terms of a two-ensemble model. A small fraction of the SeCN(-) is located in the regions modified by the presence of K(+), causing a substantial slowing of the SeCN(-) orientational relaxation and spectral diffusion. Having a small ensemble of SeCN(-) that undergoes very slow dynamics is sufficient to explain the offsets. For the major ensemble, the dynamics with and without K(+) are the same.
View details for DOI 10.1021/acs.jpcb.6b00409
View details for Web of Science ID 000379457200008
View details for PubMedID 26872207
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Quasi-rotating frame: accurate line shape determination with increased efficiency in noncollinear 2D optical spectroscopy
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS
2016; 33 (6): 1143-1156
View details for DOI 10.1364/JOSAB.33.001143
View details for Web of Science ID 000377512600017
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Unraveling the dynamics and structure of functionalized self-assembled monolayers on gold using 2D IR spectroscopy and MD simulations
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2016; 113 (18): 4929-4934
Abstract
Functionalized self-assembled monolayers (SAMs) are the focus of ongoing investigations because they can be chemically tuned to control their structure and dynamics for a wide variety of applications, including electrochemistry, catalysis, and as models of biological interfaces. Here we combine reflection 2D infrared vibrational echo spectroscopy (R-2D IR) and molecular dynamics simulations to determine the relationship between the structures of functionalized alkanethiol SAMs on gold surfaces and their underlying molecular motions on timescales of tens to hundreds of picoseconds. We find that at higher head group density, the monolayers have more disorder in the alkyl chain packing and faster dynamics. The dynamics of alkanethiol SAMs on gold are much slower than the dynamics of alkylsiloxane SAMs on silica. Using the simulations, we assess how the different molecular motions of the alkyl chain monolayers give rise to the dynamics observed in the experiments.
View details for DOI 10.1073/pnas.1603080113
View details for Web of Science ID 000375395700026
View details for PubMedID 27044113
View details for PubMedCentralID PMC4983838
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Carbon dioxide in an ionic liquid: Structural and rotational dynamics
JOURNAL OF CHEMICAL PHYSICS
2016; 144 (10)
Abstract
Ionic liquids (ILs), which have widely tunable structural motifs and intermolecular interactions with solutes, have been proposed as possible carbon capture media. To inform the choice of an optimal ionic liquid system, it can be useful to understand the details of dynamics and interactions on fundamental time scales (femtoseconds to picoseconds) of dissolved gases, particularly carbon dioxide (CO2), within the complex solvation structures present in these uniquely organized materials. The rotational and local structural fluctuation dynamics of CO2 in the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimNTf2) were investigated by using ultrafast infrared spectroscopy to interrogate the CO2 asymmetric stretch. Polarization-selective pump probe measurements yielded the orientational correlation function of the CO2 vibrational transition dipole. It was found that reorientation of the carbon dioxide occurs on 3 time scales: 0.91 ± 0.03, 8.3 ± 0.1, 54 ± 1 ps. The initial two are attributed to restricted wobbling motions originating from a gating of CO2 motions by the IL cations and anions. The final (slowest) decay corresponds to complete orientational randomization. Two-dimensional infrared vibrational echo (2D IR) spectroscopy provided information on structural rearrangements, which cause spectral diffusion, through the time dependence of the 2D line shape. Analysis of the time-dependent 2D IR spectra yields the frequency-frequency correlation function (FFCF). Polarization-selective 2D IR experiments conducted on the CO2 asymmetric stretch in the parallel- and perpendicular-pumped geometries yield significantly different FFCFs due to a phenomenon known as reorientation-induced spectral diffusion (RISD), revealing strong vector interactions with the liquid structures that evolve slowly on the (independently measured) rotation time scales. To separate the RISD contribution to the FFCF from the structural spectral diffusion contribution, the previously developed first order Stark effect RISD model is reformulated to describe the second order (quadratic) Stark effect-the first order Stark effect vanishes because CO2 does not have a permanent dipole moment. Through this analysis, we characterize the structural fluctuations of CO2 in the ionic liquid solvation environment, which separate into magnitude-only and combined magnitude and directional correlations of the liquid's time dependent electric field. This new methodology will enable highly incisive comparisons between CO2 dynamics in a variety of ionic liquid systems.
View details for DOI 10.1063/1.4943390
View details for Web of Science ID 000372974600024
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Carbon dioxide in an ionic liquid: Structural and rotational dynamics.
journal of chemical physics
2016; 144 (10): 104506-?
Abstract
Ionic liquids (ILs), which have widely tunable structural motifs and intermolecular interactions with solutes, have been proposed as possible carbon capture media. To inform the choice of an optimal ionic liquid system, it can be useful to understand the details of dynamics and interactions on fundamental time scales (femtoseconds to picoseconds) of dissolved gases, particularly carbon dioxide (CO2), within the complex solvation structures present in these uniquely organized materials. The rotational and local structural fluctuation dynamics of CO2 in the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimNTf2) were investigated by using ultrafast infrared spectroscopy to interrogate the CO2 asymmetric stretch. Polarization-selective pump probe measurements yielded the orientational correlation function of the CO2 vibrational transition dipole. It was found that reorientation of the carbon dioxide occurs on 3 time scales: 0.91 ± 0.03, 8.3 ± 0.1, 54 ± 1 ps. The initial two are attributed to restricted wobbling motions originating from a gating of CO2 motions by the IL cations and anions. The final (slowest) decay corresponds to complete orientational randomization. Two-dimensional infrared vibrational echo (2D IR) spectroscopy provided information on structural rearrangements, which cause spectral diffusion, through the time dependence of the 2D line shape. Analysis of the time-dependent 2D IR spectra yields the frequency-frequency correlation function (FFCF). Polarization-selective 2D IR experiments conducted on the CO2 asymmetric stretch in the parallel- and perpendicular-pumped geometries yield significantly different FFCFs due to a phenomenon known as reorientation-induced spectral diffusion (RISD), revealing strong vector interactions with the liquid structures that evolve slowly on the (independently measured) rotation time scales. To separate the RISD contribution to the FFCF from the structural spectral diffusion contribution, the previously developed first order Stark effect RISD model is reformulated to describe the second order (quadratic) Stark effect-the first order Stark effect vanishes because CO2 does not have a permanent dipole moment. Through this analysis, we characterize the structural fluctuations of CO2 in the ionic liquid solvation environment, which separate into magnitude-only and combined magnitude and directional correlations of the liquid's time dependent electric field. This new methodology will enable highly incisive comparisons between CO2 dynamics in a variety of ionic liquid systems.
View details for DOI 10.1063/1.4943390
View details for PubMedID 26979696
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Coupling of Carbon Dioxide Stretch and Bend Vibrations Reveals Thermal Population Dynamics in an Ionic Liquid.
journal of physical chemistry. B
2016; 120 (3): 549-556
Abstract
The population relaxation of carbon dioxide dissolved in the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimNTf2) was investigated using polarization-selective ultrafast infrared pump-probe spectroscopy and two-dimensional infrared (2D IR) spectroscopy. Due to the coupling of the bend with the asymmetric stretch, excitation of the asymmetric stretch of a molecule with a thermally populated bend leads to an additional peak, a hot band, which is red-shifted from the main asymmetric absorption band by the combination band shift. This hot band peak exchanges population with the main peak through the gain and loss of bend excitation quanta. The isotropic pump-probe signal originating from the unexcited bend state displays a fast, relatively small amplitude, initial growth followed by a longer time scale exponential decay. The signal is analyzed over its full time range using a kinetic model to determine both the vibrational lifetime (the final decay) and rate constant for the loss of the bend energy. This bend relaxation manifests as the fast initial growth of the stretch/no bend signal because the hot band (stretch with bend) is "over pumped" relative to the ground state equilibrium. The nonequilibrium pumping occurs because the hot band has a larger transition dipole moment than the stretch/no bend peak. The system is then prepared, utilizing an acousto-optic mid-infrared pulse shaper to cut a hole in the excitation pulse spectrum, such that the hot band is not pumped. The isotropic pump-probe signal from the stretch/no bend state is altered because the initial excited state population ratio has changed. Instead of a growth due to relaxation of bend quanta, a fast initial decay is observed because of thermal excitation of the bend. Fitting this curve gives the rate constant for thermal excitation of the bend and the lifetime, which agree with those determined in the pump-probe experiments without frequency-selective pumping.
View details for DOI 10.1021/acs.jpcb.5b11454
View details for PubMedID 26731088
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Molecular Anion Hydrogen Bonding Dynamics in Aqueous Solution.
journal of physical chemistry. B
2015; 119 (42): 13407-13415
Abstract
The dynamic nature of hydrogen bonding between a molecular anion, selenocyanate (SeCN(-)), and water in aqueous solution (D2O) is addressed using FT-IR spectroscopy, two-dimensional infrared (2D IR) vibrational echo spectroscopy, and polarization selective IR pump-probe (PSPP) experiments performed on the CN stretching mode. The CN absorption spectrum is asymmetric with a wing on the low frequency (red) side of the line in contrast to the spectrum in the absence of hydrogen bonding. It is shown that the red wing is the result of an increase in the CN stretch transition dipole moment due to the effect of hydrogen bonding (non-Condon effect). This non-Condon effect is similar in nature to observations on pure water and other nonionic systems where hydrogen bonding enhances the extinction coefficient. The 2D IR measurements of spectral diffusion (solvent structural evolution) yield a time constant of 1.5 ps, which is within error the same as that of the OH stretch of HOD in D2O (1.4 ps). The orientational relaxation of SeCN(-) measured by PSPP experiments is long (4.04 ps) compared to the spectral diffusion time. The population decay at or near the absorption line center is a single-exponential decay of 37.4 ± 0.3 ps, the vibrational lifetime. However, on the red side of the line the decay is biexponential with a low amplitude, fast component; on the blue side of the line there is a low amplitude, fast growth followed by the lifetime decay. Both of the fast components have 1.5 ps time constants, which is the spectral diffusion time. The fast components of the population decays are the results of the non-Condon effect that causes the red side of the line to be over pumped by the pump pulse. Spectral diffusion then produces the fast decay component on the red side of the line and the growth on the blue side of the line as the excess initial population on the red side produces a net population flow from red to blue.
View details for DOI 10.1021/acs.jpcb.5b08168
View details for PubMedID 26434772
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Separation of experimental 2D IR frequency-frequency correlation functions into structural and reorientation-induced contributions.
journal of chemical physics
2015; 143 (12): 124505-?
Abstract
A vibrational transition frequency can couple to its environment through a directional vector interaction. In such cases, reorientation of the vibrational transition dipole (molecular orientational relaxation) and its frequency fluctuations can be strongly coupled. It was recently shown [Kramer et al., J. Chem. Phys. 142, 184505 (2015)] that differing frequency-frequency correlation function (FFCF) decays, due to reorientation-induced spectral diffusion (RISD), are observed with different two-dimensional infrared polarization configurations when such strong coupling is present. The FFC functional forms were derived for the situation in which all spectral diffusion is due to reorientational motion. We extend the previous theory to include vibrational frequency evolution (spectral diffusion) caused by structural fluctuations of the medium. Model systems with diffusive reorientation and several regimes of structural spectral diffusion rates are analyzed for first order Stark effect interactions. Additionally, the transition dipole reorientational motion in complex environments is frequently not completely diffusive. Several periods of restricted angular motion (wobbling-in-a-cone) may precede the final diffusive orientational randomization. The polarization-weighted FFCF decays are presented in this case of restricted transition dipole wobbling. With these extensions to the polarization-dependent FFCF expressions, the structural spectral diffusion dynamics of methanol in the room temperature ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate can be separated quantitatively from RISD using the experimental center line slope data. In addition, prior results on the spectral diffusion of water, methanol, and ethanol in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide are re-examined to elucidate the influence of reorientation on the data, which were interpreted in terms of structural fluctuations.
View details for DOI 10.1063/1.4931402
View details for PubMedID 26429022
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Separation of experimental 2D IR frequency-frequency correlation functions into structural and reorientation-induced contributions.
journal of chemical physics
2015; 143 (12): 124505-?
Abstract
A vibrational transition frequency can couple to its environment through a directional vector interaction. In such cases, reorientation of the vibrational transition dipole (molecular orientational relaxation) and its frequency fluctuations can be strongly coupled. It was recently shown [Kramer et al., J. Chem. Phys. 142, 184505 (2015)] that differing frequency-frequency correlation function (FFCF) decays, due to reorientation-induced spectral diffusion (RISD), are observed with different two-dimensional infrared polarization configurations when such strong coupling is present. The FFC functional forms were derived for the situation in which all spectral diffusion is due to reorientational motion. We extend the previous theory to include vibrational frequency evolution (spectral diffusion) caused by structural fluctuations of the medium. Model systems with diffusive reorientation and several regimes of structural spectral diffusion rates are analyzed for first order Stark effect interactions. Additionally, the transition dipole reorientational motion in complex environments is frequently not completely diffusive. Several periods of restricted angular motion (wobbling-in-a-cone) may precede the final diffusive orientational randomization. The polarization-weighted FFCF decays are presented in this case of restricted transition dipole wobbling. With these extensions to the polarization-dependent FFCF expressions, the structural spectral diffusion dynamics of methanol in the room temperature ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate can be separated quantitatively from RISD using the experimental center line slope data. In addition, prior results on the spectral diffusion of water, methanol, and ethanol in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide are re-examined to elucidate the influence of reorientation on the data, which were interpreted in terms of structural fluctuations.
View details for DOI 10.1063/1.4931402
View details for PubMedID 26429022
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Dynamics in the isotropic phase of liquid crystals-2D IR experiments and mode coupling theory
AMER CHEMICAL SOC. 2015
View details for Web of Science ID 000432475702789
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The Influence of Cholesterol on Fast Dynamics Inside of Vesicle and Planar Phospholipid Bilayers Measured with 2D IR Spectroscopy.
journal of physical chemistry. B
2015; 119 (29): 8852-8862
Abstract
Phospholipid bilayers are frequently used as models for cell membranes. Here the influence of cholesterol on the structural dynamics in the interior of 1,2-dilauroyl-sn-glycero-3-phosphocholine (dilauroylphosphatidylcholine, DLPC) vesicles and DLPC planar bilayers are investigated as a function of cholesterol concentration. 2D IR vibrational echo spectroscopy was performed on the antisymmetric CO stretch of the vibrational probe molecule tungsten hexacarbonyl, which is located in the interior alkyl regions of the bilayers. The 2D IR experiments measure spectral diffusion, which is caused by the structural fluctuations of the bilayers. The 2D IR measurements show that the bilayer interior alkyl region dynamics occur on time scales ranging from a few picoseconds to many tens of picoseconds. These are the time scales of the bilayers' structural dynamics, which act as the dynamic solvent bath for chemical processes of membrane biomolecules. The results suggest that at least a significant fraction of the dynamics arise from density fluctuations. Samples are studied in which the cholesterol concentration is varied from 0% to 40% in both the vesicles (72 nm diameter) and fully hydrated planar bilayers in the form of aligned multibilayers. At all cholesterol concentrations, the structural dynamics are faster in the curved vesicle bilayers than in the planar bilayers. As the cholesterol concentration is increased, at a certain concentration there is a sudden change in the dynamics, that is, the dynamics abruptly slow down. However, this change occurs at a lower concentration in the vesicles (between 10% and 15% cholesterol) than in the planar bilayers (between 25% and 30% cholesterol). The sudden change in the dynamics, in addition to other IR observables, indicates a structural transition. However, the results show that the cholesterol concentration at which the transition occurs is influenced by the curvature of the bilayers.
View details for DOI 10.1021/jp503940k
View details for PubMedID 24901902
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Dynamics of water, methanol, and ethanol in a room temperature ionic liquid
JOURNAL OF CHEMICAL PHYSICS
2015; 142 (21)
Abstract
The dynamics of a series of small molecule probes with increasing alkyl chain length: water, methanol, and ethanol, diluted to low concentration in the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, was investigated with 2D infrared vibrational echo (2D IR) spectroscopy and polarization resolved pump-probe (PP) experiments on the deuterated hydroxyl (O-D) stretching mode of each of the solutes. The long timescale spectral diffusion observed by 2D IR, capturing complete loss of vibrational frequency correlation through structural fluctuation of the medium, shows a clear but not dramatic slowing as the probe alkyl chain length is increased: 23 ps for water, 28 ps for methanol, and 34 ps for ethanol. Although in each case, only a single population of hydroxyl oscillators contributes to the infrared line shapes, the isotropic pump-probe decays (normally caused by population relaxation) are markedly nonexponential at short times. The early time features correspond to the timescales of the fast spectral diffusion measured with 2D IR. These fast isotropic pump-probe decays are produced by unequal pumping of the OD absorption band to a nonequilibrium frequency dependent population distribution caused by significant non-Condon effects. Orientational correlation functions for these three systems, obtained from pump-probe anisotropy decays, display several periods of restricted angular motion (wobbling-in-a-cone) followed by complete orientational randomization. The cone half-angles, which characterize the angular potential, become larger as the experimental frequency moves to the blue. These results indicate weakening of the angular potential with decreasing hydrogen bond strength. The slowest components of the orientational anisotropy decays are frequency-independent and correspond to the complete orientational randomization of the solute molecule. These components slow appreciably with increasing chain length: 25 ps for water, 42 ps for methanol, and 88 ps for ethanol. The shape and volume of the probe, therefore, impact reorientation far more severely than they do spectral diffusion at long times, though these two processes occur on similar timescales at earlier times.
View details for DOI 10.1063/1.4914156
View details for Web of Science ID 000355931800012
View details for PubMedID 26049428
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Observation and theory of reorientation-induced spectral diffusion in polarization-selective 2D IR spectroscopy.
journal of chemical physics
2015; 142 (18): 184505-?
Abstract
In nearly all applications of ultrafast multidimensional infrared spectroscopy, the spectral degrees of freedom (e.g., transition frequency) and the orientation of the transition dipole are assumed to be decoupled. We present experimental results which confirm that frequency fluctuations can be caused by rotational motion and observed under appropriate conditions. A theory of the frequency-frequency correlation function (FFCF) observable under various polarization conditions is introduced, and model calculations are found to reproduce the qualitative trends in FFCF rates. The FFCF determined with polarization-selective two-dimensional infrared (2D IR) spectroscopy is a direct reporter of the frequency-rotational coupling. For the solute methanol in a room temperature ionic liquid, the FFCF of the hydroxyl (O-D) stretch decays due to spectral diffusion with different rates depending on the polarization of the excitation pulses. The 2D IR vibrational echo pulse sequence consists of three excitation pulses that generate the vibrational echo, a fourth pulse. A faster FFCF decay is observed when the first two excitation pulses are polarized perpendicular to the third pulse and the echo, 〈XXY Y〉, than in the standard all parallel configuration, 〈XXXX〉, in which all four pulses have the same polarization. The 2D IR experiment with polarizations 〈XY XY〉 ("polarization grating" configuration) gives a FFCF that decays even more slowly than in the 〈XXXX〉 configuration. Polarization-selective 2D IR spectra of bulk water do not exhibit polarization-dependent FFCF decays; spectral diffusion is effectively decoupled from reorientation in the water system.
View details for DOI 10.1063/1.4920949
View details for PubMedID 25978898
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Observation and theory of reorientation-induced spectral diffusion in polarization-selective 2D IR spectroscopy
JOURNAL OF CHEMICAL PHYSICS
2015; 142 (18)
Abstract
In nearly all applications of ultrafast multidimensional infrared spectroscopy, the spectral degrees of freedom (e.g., transition frequency) and the orientation of the transition dipole are assumed to be decoupled. We present experimental results which confirm that frequency fluctuations can be caused by rotational motion and observed under appropriate conditions. A theory of the frequency-frequency correlation function (FFCF) observable under various polarization conditions is introduced, and model calculations are found to reproduce the qualitative trends in FFCF rates. The FFCF determined with polarization-selective two-dimensional infrared (2D IR) spectroscopy is a direct reporter of the frequency-rotational coupling. For the solute methanol in a room temperature ionic liquid, the FFCF of the hydroxyl (O-D) stretch decays due to spectral diffusion with different rates depending on the polarization of the excitation pulses. The 2D IR vibrational echo pulse sequence consists of three excitation pulses that generate the vibrational echo, a fourth pulse. A faster FFCF decay is observed when the first two excitation pulses are polarized perpendicular to the third pulse and the echo, 〈XXY Y〉, than in the standard all parallel configuration, 〈XXXX〉, in which all four pulses have the same polarization. The 2D IR experiment with polarizations 〈XY XY〉 ("polarization grating" configuration) gives a FFCF that decays even more slowly than in the 〈XXXX〉 configuration. Polarization-selective 2D IR spectra of bulk water do not exhibit polarization-dependent FFCF decays; spectral diffusion is effectively decoupled from reorientation in the water system.
View details for DOI 10.1063/1.4920949
View details for Web of Science ID 000354775800023
View details for PubMedID 25978898
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Dynamics of dihydrogen bonding in aqueous solutions of sodium borohydride.
journal of physical chemistry. B
2015; 119 (8): 3546-3559
View details for DOI 10.1021/jp512426y
View details for PubMedID 25635342
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Dynamics of dihydrogen bonding in aqueous solutions of sodium borohydride.
journal of physical chemistry. B
2015; 119 (8): 3546-3559
View details for DOI 10.1021/jp512426y
View details for PubMedID 25635342
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Dynamics and structure of room temperature ionic liquids
CHEMICAL PHYSICS LETTERS
2014; 616: 259-274
View details for DOI 10.1016/j.cplett.2014.09.062
View details for Web of Science ID 000345397700047
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New divergent dynamics in the isotropic to nematic phase transition of liquid crystals measured with 2D IR vibrational echo spectroscopy.
The Journal of chemical physics
2014; 141 (19): 194502
Abstract
The isotropic phase of nematogenic liquid crystals has nanometer length scale domains with pseudonematic ordering. As the isotropic to nematic phase transition temperature (TNI) is approached from above, the orientational correlation length, ξ, of the pseudonematic domains grows as (T - T(*))(-1/2), where T(*) is 0.5-1 K below TNI. The orientational relaxation, which is a collective property of the pseudonematic domains, was measured with optical heterodyne detected-optical Kerr effect (OHD-OKE). The orientational relaxation obeys Landau-de Gennes theory, as has been shown previously. To examine the environmental evolution experienced by molecules in the pseudonematic domains, two-dimensional infrared (2D IR) vibrational echo experiments on the CN stretching mode of the non-perturbative vibrational probes 4-pentyl-4(')-selenocyanobiphenyl (5SeCB) and 4-pentyl-4(')-thiocyanobiphenyl (5SCB) in the nematogen 4-cyano-4(')-pentylbiphenyl (5CB) were performed. The 2D IR experiments measure spectral diffusion, which is caused by structural fluctuations that couple to the CN vibrational frequency. Temperature dependent studies were performed just above TNI, where the correlation length of pseudonematic domains is large and changing rapidly with temperature. These studies were compared to 2D IR experiments on 4-pentylbiphenyl (5B), a non-mesogenic liquid that is very similar in structure to 5CB. The time constants of spectral diffusion in 5CB and 5B are practically identical at temperatures ≥5 K above TNI. As the temperature is lowered, spectral diffusion in 5B slows gradually. However, the time constants for spectral diffusion in 5CB slow dramatically and diverge as T(*) is approached. This divergence has temperature dependence proportional to (T - T(*))(-1/2), precisely the same as seen for the correlation length of pseudonematic domains, but different from the observed orientational relaxation times, which are given by the Landau-de Gennes theory. The data and previous results show that spectral diffusion in 5CB has no contributions from orientational relaxation, and the structural dynamics responsible for the spectral diffusion are likely a result of density fluctuations. The results suggest that the correlation length of the density fluctuations is diverging with the same temperature dependence as the pseudonematic domain correlation length, ξ. The isotropic-nematic phase transition in liquid crystals is described in the context of the slowing of orientational relaxation associated with divergent growth of the orientational correlation length. The results presented here show that there is another divergent dynamical process, likely associated with density fluctuations.
View details for DOI 10.1063/1.4901081
View details for PubMedID 25416893
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Dynamics of dihydrogen bonding: Spectral diffusion of borohydride in water
AMER CHEMICAL SOC. 2014
View details for Web of Science ID 000349167404255
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Investigations of functionalized surface monolayer molecular dynamics with ultrafast 2D IR experiments
AMER CHEMICAL SOC. 2014
View details for Web of Science ID 000349165101614
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Probing the ultrafast dynamics of pure and binary functionalized monolayers with heterodyne-detected 2D IR vibrational echo spectroscopy
AMER CHEMICAL SOC. 2014
View details for Web of Science ID 000349167404259
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Ultrafast molecular dynamics at functionalized interfaces probed by nonlinear infrared spectroscopy
AMER CHEMICAL SOC. 2014
View details for Web of Science ID 000349167404256
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Pseudonematic domain effects on the dynamics and spectral diffusion of a nematogen in the isotropic phase: An optical Kerr effect and 2D IR vibrational echo study
AMER CHEMICAL SOC. 2014
View details for Web of Science ID 000349167404257
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Influence of alkyl chain length on the dynamics and structure of alkylmethylimidazolium room temperature ionic liquids
AMER CHEMICAL SOC. 2014
View details for Web of Science ID 000349167404363
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Ultrafast hydrogen bonding dynamics of water and alcohols in ionic liquids
AMER CHEMICAL SOC. 2014
View details for Web of Science ID 000349167404151
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Length Scales and Structural Dynamics in Nematogen Pseudonematic Domains Measured with 2D IR Vibrational Echoes and Optical Kerr Effect Experiments.
journal of physical chemistry. B
2014; 118 (28): 7856-7868
Abstract
Nematogen liquids in the isotropic phase are macroscopically homogeneous but on multinanometer length scales have pseudonematic domains with correlation lengths that grow as the isotropic to nematic phase transition temperature (TNI) is approached from above. Orientational relaxation of nematogens in the isotropic phase manifests as two fast power laws and a slow exponential decay when measured by optical heterodyne detected optical Kerr effect (OHD-OKE) experiments. The long time exponential relaxation is associated with complete randomization of pseudonematic domains. We examine the effect of local orientational correlation on spectral diffusion (structural evolution) experienced by a vibrational probe molecule within the pseudonematic domains of 4-cyano-4'-pentylbiphenyl (5CB) using two-dimensional infrared (2D IR) vibrational echo spectroscopy. The addition of low concentration 4-pentyl-4'-thiocyanobiphenyl (5SCB) as a long-lived vibrational probe to 5CB is shown to lower TNI of the sample slightly, but the fast power law dynamics and exponential decays observed by OHD-OKE spectroscopy are unchanged. We compare the complete orientational relaxation and spectral diffusion for samples of 5SCB in 5CB to 5SCB in 4-pentylbiphenyl (5B) at four temperatures above TNI. 5B has a molecular structure similar to 5CB but is not a nematogen. At all but the lowest temperature, the spectral diffusion in 5CB and 5B is described well as a triexponential decay with very similar time constants. The results demonstrate that the presence of local orientational order at temperatures well above TNI does not affect the spectral diffusion (structural evolution) within pseudonematic domains when the correlation lengths are short. However, when the temperature of the sample is held very close to TNI, the spectral diffusion in 5CB slows dramatically while that in 5B does not. It is only as the correlation length becomes very long that its presence impacts the spectral diffusion (structural fluctuations) sensed by the vibrational probes located in pseudonematic domains. The orientational relaxation is modeled with schematic mode coupling theory (MCT). Fitting with MCT provides density and orientational correlation functions. The density correlation decays are similar for 5B and 5CB, but the orientational correlation decays are much slower for 5CB. Additionally, the time dependence of the spectral diffusion in 5CB is strikingly similar to that of the density correlation function decay, while the orientational correlation function decay is far too slow to contribute to the spectral diffusion. Therefore, density fluctuations are likely the source of spectral diffusion at temperatures at least 5 K above TNI.
View details for DOI 10.1021/jp500144p
View details for PubMedID 24521155
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Theory of third-order spectroscopic methods to extract detailed molecular orientational dynamics for planar surfaces and other uniaxial systems.
journal of chemical physics
2014; 140 (14): 144702-?
Abstract
Functionalized organic monolayers deposited on planar two-dimensional surfaces are important systems for studying ultrafast orientational motions and structures of interfacial molecules. Several studies have successfully observed the orientational relaxation of functionalized monolayers by fluorescence depolarization experiments and recently by polarization-resolved heterodyne detected vibrational transient grating (HDTG) experiments. In this article we provide a model-independent theory to extract orientational correlation functions unique to interfacial molecules and other uniaxial systems based on polarization-resolved resonant third-order spectroscopies, such as pump-probe spectroscopy, HDTG spectroscopy, and fluorescence depolarization experiment. It will be shown (in the small beam-crossing angle limit) that five measurements are necessary to completely characterize the monolayer's motions: I(∥)(t) and I(⊥)(t) with the incident beams normal to the surface, I(∥)(t) and I(⊥)(t) with a non-zero incident angle, and a time averaged linear dichroism measurement. Once these measurements are performed, two orientational correlation functions corresponding to in-plane and out-of-plane motions are obtained. The procedure is applicable not only for monolayers on flat surfaces, but any samples with uniaxial symmetry such as uniaxial liquid crystals and aligned planar bilayers. The theory is valid regardless of the nature of the actual molecular motions on interface. We then apply the general results to wobbling-in-a-cone model, in which molecular motions are restricted to a limited range of angles. Within the context of the model, the cone angle, the tilt of the cone relative to the surface normal, and the orientational diffusion constant can be determined. The results are extended to describe analysis of experiments where the beams are not crossing in the small angle limit.
View details for DOI 10.1063/1.4870436
View details for PubMedID 24735308
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Theory of third-order spectroscopic methods to extract detailed molecular orientational dynamics for planar surfaces and other uniaxial systems
JOURNAL OF CHEMICAL PHYSICS
2014; 140 (14)
Abstract
Functionalized organic monolayers deposited on planar two-dimensional surfaces are important systems for studying ultrafast orientational motions and structures of interfacial molecules. Several studies have successfully observed the orientational relaxation of functionalized monolayers by fluorescence depolarization experiments and recently by polarization-resolved heterodyne detected vibrational transient grating (HDTG) experiments. In this article we provide a model-independent theory to extract orientational correlation functions unique to interfacial molecules and other uniaxial systems based on polarization-resolved resonant third-order spectroscopies, such as pump-probe spectroscopy, HDTG spectroscopy, and fluorescence depolarization experiment. It will be shown (in the small beam-crossing angle limit) that five measurements are necessary to completely characterize the monolayer's motions: I(∥)(t) and I(⊥)(t) with the incident beams normal to the surface, I(∥)(t) and I(⊥)(t) with a non-zero incident angle, and a time averaged linear dichroism measurement. Once these measurements are performed, two orientational correlation functions corresponding to in-plane and out-of-plane motions are obtained. The procedure is applicable not only for monolayers on flat surfaces, but any samples with uniaxial symmetry such as uniaxial liquid crystals and aligned planar bilayers. The theory is valid regardless of the nature of the actual molecular motions on interface. We then apply the general results to wobbling-in-a-cone model, in which molecular motions are restricted to a limited range of angles. Within the context of the model, the cone angle, the tilt of the cone relative to the surface normal, and the orientational diffusion constant can be determined. The results are extended to describe analysis of experiments where the beams are not crossing in the small angle limit.
View details for DOI 10.1063/1.4870436
View details for Web of Science ID 000334836600028
View details for PubMedID 24735308
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Award Address (Ahmed Zewail Award in Ultrafast Science and Technology sponsored by the Ahmed Zewail Endowment Fund established by the Newport Corporation (Newport)). Ultrafast 2D IR vibrational echo spectroscopy
AMER CHEMICAL SOC. 2014
View details for Web of Science ID 000348457603588
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Size-dependent ultrafast structural dynamics inside phospholipid vesicle bilayers measured with 2D IR vibrational echoes
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2014; 111 (3): 918-923
Abstract
The ultrafast structural dynamics inside the bilayers of dilauroylphosphatidylcholine (DLPC) and dipalmitoylphosphatidylcholine vesicles with 70, 90, and 125 nm diameters were directly measured with 2D IR vibrational echo spectroscopy. The antisymmetric CO stretch of tungsten hexacarbonyl was used as a vibrational probe and provided information on spectral diffusion (structural dynamics) in the alkyl region of the bilayers. Although the CO stretch absorption spectra remain the same, the interior structural dynamics become faster as the size of the vesicles decrease, with the size dependence greater for dipalmitoylphosphatidylcholine than for DLPC. As DLPC vesicles become larger, the interior dynamics approach those of the planar bilayer.
View details for DOI 10.1073/pnas.1323110111
View details for Web of Science ID 000329928400026
View details for PubMedID 24395796
View details for PubMedCentralID PMC3903213
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Dynamics of Molecular Monolayers with Different Chain Lengths in Air and Solvents Probed by Ultrafast 2D IR Spectroscopy
JOURNAL OF PHYSICAL CHEMISTRY C
2014; 118 (1): 523-532
View details for DOI 10.1021/jp410683h
View details for Web of Science ID 000329678200056
- The Influence of Cholesterol on Fast Dynamics Inside of Vesicle and Planar Phospholipid Bilayers Measured with 2D IR Spectroscopy J. Phys. Chem B. 2014
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Dynamics in the Isotropic Phase of Nematogens Using 2D IR Vibrational Echo Measurements on Natural-Abundance (CN)-C-13 and Extended Lifetime Probes
JOURNAL OF PHYSICAL CHEMISTRY B
2013; 117 (48): 15060-15071
Abstract
The long time scale orientational relaxation of nematogens in the isotropic phase is associated with the randomization of pseudonematic domains, which have a correlation length that grows as the isotropic-to-nematic phase transition temperature is approached from above. Here we begin to address the fast dynamics of the nematogen molecules within the domains using two-dimensional infrared (2D IR) vibrational echo experiments. The problems of performing ultrafast IR experiments in pure liquids are discussed, and solutions are presented. In addition, the issue of short vibrational lifetimes, which limit the ability of 2D IR experiments to examine dynamics over a wide range of times, is addressed. The experiments were performed on the nematogen 4-cyano-4'-pentylbiphenyl (5CB), with the CN stretch initially used as the vibrational probe. Although the CN stretch has a small transition dipole, because the sample is a pure liquid it is necessary to use an exceedingly thin sample to perform the experiments. The small sample volume leads to massive heating effects that distort the results. In addition, the high concentration in the pure liquid can result in vibrational excitation transfer that interferes with the measurements of structural dynamics, and the CN vibrational lifetime is very short (3.6 ps). These problems were overcome by performing the experiments on the natural-abundance (13)CN stretch (5(13)CB), which greatly reduced the absorbance, eliminating the heating problems; also, this stretch has a longer lifetime (7.9 ps). Experiments were also performed on benzonitrile, which showed that the heating problems associated with pure liquids are not unique to 5CB. Again, the problems were eliminated by conducting measurements on the (13)CN stretch, which has an even longer lifetime (20.2 ps) compared with the (12)CN stretch (5.6 ps). Finally, to extend the range of the dynamical measurements, 4-pentyl-4'-thiocyanobiphenyl (5SCB) was synthesized and studied as a dilute solute in 5CB. The CN stretch of 5SCB has a vibrational lifetime of 103 ps, which permits dynamical measurements to 200 ps, revealing the full range of fast structural dynamics in the isotropic phase of 5CB. It is shown that the 5SCB probe reports essentially the same dynamics as 5(13)CB on the short time scale that is observable with the 5(13)CB vibrational probe.
View details for DOI 10.1021/jp4071955
View details for Web of Science ID 000328101100019
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Dynamics in the isotropic phase of nematogens using 2D IR vibrational echo measurements on natural-abundance 13CN and extended lifetime probes.
journal of physical chemistry. B
2013; 117 (48): 15060-15071
Abstract
The long time scale orientational relaxation of nematogens in the isotropic phase is associated with the randomization of pseudonematic domains, which have a correlation length that grows as the isotropic-to-nematic phase transition temperature is approached from above. Here we begin to address the fast dynamics of the nematogen molecules within the domains using two-dimensional infrared (2D IR) vibrational echo experiments. The problems of performing ultrafast IR experiments in pure liquids are discussed, and solutions are presented. In addition, the issue of short vibrational lifetimes, which limit the ability of 2D IR experiments to examine dynamics over a wide range of times, is addressed. The experiments were performed on the nematogen 4-cyano-4'-pentylbiphenyl (5CB), with the CN stretch initially used as the vibrational probe. Although the CN stretch has a small transition dipole, because the sample is a pure liquid it is necessary to use an exceedingly thin sample to perform the experiments. The small sample volume leads to massive heating effects that distort the results. In addition, the high concentration in the pure liquid can result in vibrational excitation transfer that interferes with the measurements of structural dynamics, and the CN vibrational lifetime is very short (3.6 ps). These problems were overcome by performing the experiments on the natural-abundance (13)CN stretch (5(13)CB), which greatly reduced the absorbance, eliminating the heating problems; also, this stretch has a longer lifetime (7.9 ps). Experiments were also performed on benzonitrile, which showed that the heating problems associated with pure liquids are not unique to 5CB. Again, the problems were eliminated by conducting measurements on the (13)CN stretch, which has an even longer lifetime (20.2 ps) compared with the (12)CN stretch (5.6 ps). Finally, to extend the range of the dynamical measurements, 4-pentyl-4'-thiocyanobiphenyl (5SCB) was synthesized and studied as a dilute solute in 5CB. The CN stretch of 5SCB has a vibrational lifetime of 103 ps, which permits dynamical measurements to 200 ps, revealing the full range of fast structural dynamics in the isotropic phase of 5CB. It is shown that the 5SCB probe reports essentially the same dynamics as 5(13)CB on the short time scale that is observable with the 5(13)CB vibrational probe.
View details for DOI 10.1021/jp4071955
View details for PubMedID 24156524
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Orientational dynamics in a lyotropic room temperature ionic liquid.
journal of physical chemistry. B
2013; 117 (47): 14775-14784
Abstract
In a previous study of room temperature ionic liquid/water mixtures, the first clearly observed biexponential decays in optical heterodyne-detected optical Kerr effect (OHD-OKE) experiments on a liquid were reported, (Sturlaugson, A. L.; Fruchey, K. S.; Fayer, M. D. J. Phys. Chem. B 2012, 116, 1777), and it was suggested that the biexponential behavior is indicative of the approach to gelation. Here, new OHD-OKE experiments on mixtures of the room temperature ionic liquid 1-methyl-3-octylimidazolium chloride (OmimCl) with water are presented. The OmimCl/water system is shown to gel over the water mole fraction range of 0.69-0.81. In the OHD-OKE decays, the biexponential behavior becomes more distinct as the gelling concentration range is approached from either high or low water concentrations. The biexponential decays are analyzed in terms of the wobbling-in-a-cone model, and the resulting diffusion constants and "relative" order parameters and cone angles are reported. Comparison of the OmimCl/water data with the previously reported room temperature ionic liquid/water OHD-OKE decays supports the previous hypothesis that the biexponential dynamics are due to the approach to the liquid-gel transition and suggests that the order of the concentration-dependent phase transition can be tuned by the choice of anion.
View details for DOI 10.1021/jp407325b
View details for PubMedID 24171452
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Water and room temperature ionic liquids
AMER CHEMICAL SOC. 2013
View details for Web of Science ID 000329618405808
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Theoretical examination of picosecond phenol migration dynamics in phenylacetylene solution
CHEMICAL PHYSICS
2013; 422: 175-183
View details for DOI 10.1016/j.chemphys.2013.04.015
View details for Web of Science ID 000324309600022
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The influence of lithium cations on dynamics and structure of room temperature ionic liquids.
journal of physical chemistry. B
2013; 117 (33): 9768-9774
Abstract
The orientational relaxation dynamics of perylene in the room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium bis(trifluoromethyl)sulfonyl imide were studied as a function of lithium ion concentration. Perylene is nonpolar and locates in the alkyl regions of the RTIL. The lithium cation was added as lithium bis(trifluoromethyl)sulfonyl imide, so the addition of Li(+) did not change the anion. The Li(+) concentration ranged from 0 to 0.4 mol fraction. The dynamics were measured by observing the fluorescence anisotropy decay using time correlated single photon counting. The anisotropy experiments and viscosity measurements were performed as a function of temperature for each Li(+) concentration sample. Because perylene has high symmetry, it was possible to independently determine the in-plane and out-of-plane diffusion constants and friction coefficients. With increasing concentration of lithium salt the viscosity increases and both the in-plane and out-of-plane orientational relaxations of perylene become slower. However, the corresponding molecular friction coefficients decreased, with the in-plane coefficient decreasing to a greater extent than the out-of-plane coefficient. The decrease in the friction coefficients demonstrates that lithium ions, which are located in the ionic regions of the RTILs, change the structure of the alkyl regions of the RTIL.
View details for DOI 10.1021/jp405752q
View details for PubMedID 23879633
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The Influence of Lithium Cations on Dynamics and Structure of Room Temperature Ionic Liquids
JOURNAL OF PHYSICAL CHEMISTRY B
2013; 117 (33): 9768-9774
Abstract
The orientational relaxation dynamics of perylene in the room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium bis(trifluoromethyl)sulfonyl imide were studied as a function of lithium ion concentration. Perylene is nonpolar and locates in the alkyl regions of the RTIL. The lithium cation was added as lithium bis(trifluoromethyl)sulfonyl imide, so the addition of Li(+) did not change the anion. The Li(+) concentration ranged from 0 to 0.4 mol fraction. The dynamics were measured by observing the fluorescence anisotropy decay using time correlated single photon counting. The anisotropy experiments and viscosity measurements were performed as a function of temperature for each Li(+) concentration sample. Because perylene has high symmetry, it was possible to independently determine the in-plane and out-of-plane diffusion constants and friction coefficients. With increasing concentration of lithium salt the viscosity increases and both the in-plane and out-of-plane orientational relaxations of perylene become slower. However, the corresponding molecular friction coefficients decreased, with the in-plane coefficient decreasing to a greater extent than the out-of-plane coefficient. The decrease in the friction coefficients demonstrates that lithium ions, which are located in the ionic regions of the RTILs, change the structure of the alkyl regions of the RTIL.
View details for DOI 10.1021/jp405752q
View details for Web of Science ID 000323593500020
View details for PubMedID 23879633
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Ultrafast Structural Dynamics Inside Planar Phospholipid Multibilayer Model Cell Membranes Measured with 2D IR Spectroscopy.
Journal of the American Chemical Society
2013; 135 (30): 11063-11074
Abstract
The ultrafast dynamics in the interior of planar aligned multibilayers of 1,2-dilauroyl-sn-glycero-3-phosphocholine (dilauroylphosphatidylcholine, DLPC) are investigated using 2D IR vibrational echo spectroscopy. The nonpolar and water insoluble vibrational dynamics probe, tungsten hexacarbonyl (W(CO)6), is located in the alkane interior of the membranes. The 2D IR experiments conducted on the antisymmetric CO stretching mode measure spectral diffusion caused by the structural dynamics of the membrane from ∼200 fs to ∼200 ps as a function of the number of water molecules hydrating the head groups and as a function of cholesterol content for a fixed hydration level. FT-IR studies of the lipid bilayers and the model liquids, hexadecane and bis(2-ethylhexyl) succinate, indicate that as the number of hydrating water molecules increases from 2 to 16, there are structural changes in the membrane that partition some of the W(CO)6 into the ester region of DLPC. However, the 2D IR measurements, which are made solely on the W(CO)6 in the alkane regions, show that the level of hydration has no observable impact on the interior membrane dynamics. FT-IR spectra and 2D IR experiments on samples with cholesterol concentrations from 0 to 60% demonstrate that there is a change in the membrane structure and an abrupt change in dynamics at 35% cholesterol. The dynamics are independent of cholesterol content from 10 to 35%. At 35%, the dynamics become slower and remain unchanged from 35 to 60% cholesterol.
View details for DOI 10.1021/ja403675x
View details for PubMedID 23837718
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Dynamics in the interior of AOT lamellae investigated with two-dimensional infrared spectroscopy.
Journal of the American Chemical Society
2013; 135 (13): 5118-5126
Abstract
The dynamics inside the organic regions of aerosol-OT (AOT)/water mixtures in the lamellar mesophase, bicontinuous cubic (BC) phase, and in an analogous molecule without the charged sulfonate headgroup are investigated by observing spectral diffusion, orientational relaxation and population relaxation using ultrafast two-dimensional infrared (2D IR) vibrational echo spectroscopy and IR pump-probe experiments on the asymmetric CO stretch of a vibrational probe, tungsten hexacarbonyl (W(CO)6). The water layer thickness between the bilayer planes in the lamellar phase was varied. For comparison, the dynamics of W(CO)6 in the normal liquid bis(2-ethylhexyl) succinate (EHS), which is analogous to AOT but has no charged sulfonate headgroup, were also studied. The 2D IR experiments measure spectral diffusion, which results from the structural evolution of the system. Spectral diffusion is quantified by the frequency-frequency correlation function (FFCF). In addition to a homogeneous component, the FFCFs are biexponential decays with fast and slow time components of ∼12.5 and ∼150 ps in the lamellar phase. Both components of the FFCF are independent of the number of water molecules per headgroup for the lamellae, but they slow somewhat in the BC phase. The dynamics in the ordered phases are in sharp contrast to the dynamics in EHS, which displays fast and slow components of the FFCF of 5 and 80 ps, respectively. As the hydration level of AOT increases, vibrational lifetime decreases, suggesting some change in the local environment of W(CO)6 with water content.
View details for DOI 10.1021/ja312676e
View details for PubMedID 23465101
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Dynamics in the Interior of AOT Lamellae Investigated with Two-Dimensional Infrared Spectroscopy
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2013; 135 (13): 5118-5126
Abstract
The dynamics inside the organic regions of aerosol-OT (AOT)/water mixtures in the lamellar mesophase, bicontinuous cubic (BC) phase, and in an analogous molecule without the charged sulfonate headgroup are investigated by observing spectral diffusion, orientational relaxation and population relaxation using ultrafast two-dimensional infrared (2D IR) vibrational echo spectroscopy and IR pump-probe experiments on the asymmetric CO stretch of a vibrational probe, tungsten hexacarbonyl (W(CO)6). The water layer thickness between the bilayer planes in the lamellar phase was varied. For comparison, the dynamics of W(CO)6 in the normal liquid bis(2-ethylhexyl) succinate (EHS), which is analogous to AOT but has no charged sulfonate headgroup, were also studied. The 2D IR experiments measure spectral diffusion, which results from the structural evolution of the system. Spectral diffusion is quantified by the frequency-frequency correlation function (FFCF). In addition to a homogeneous component, the FFCFs are biexponential decays with fast and slow time components of ∼12.5 and ∼150 ps in the lamellar phase. Both components of the FFCF are independent of the number of water molecules per headgroup for the lamellae, but they slow somewhat in the BC phase. The dynamics in the ordered phases are in sharp contrast to the dynamics in EHS, which displays fast and slow components of the FFCF of 5 and 80 ps, respectively. As the hydration level of AOT increases, vibrational lifetime decreases, suggesting some change in the local environment of W(CO)6 with water content.
View details for DOI 10.1021/ja312676e
View details for Web of Science ID 000317259300042
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Structural Dynamics at Monolayer-Liquid Interfaces Probed by 2D IR Spectroscopy
JOURNAL OF PHYSICAL CHEMISTRY C
2013; 117 (3): 1409-1420
View details for DOI 10.1021/jp311144b
View details for Web of Science ID 000314205100023
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Dynamics of Isolated Water Molecules in a Sea of Ions in a Room Temperature Ionic Liquid
JOURNAL OF PHYSICAL CHEMISTRY B
2013; 117 (2): 623-635
Abstract
The vibrational dynamics of the antisymmetric and symmetric stretching modes of very low concentration spatially isolated D(2)O molecules in the room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium hexafluorophosphate (BmImPF(6)) were examined using two-dimensional infrared (2D IR) vibrational echo spectroscopy and infrared pump-probe experiments. In BmImPF(6), D(2)O's antisymmetric and symmetric stretching modes are well resolved in the IR absorption spectrum in spite of the fact that the D(2)O is surrounded by a sea of ions, making it is possible to study inter- and intramolecular dynamics. Both population exchange between the modes and excited-state relaxation to the ground state contribute to the population dynamics. The kinetics for the incoherent population exchange (scattering) between the two modes was determined by the time dependence of the exchange peaks in the 2D IR spectrum. In addition, coherent quantum beats were observed at short time in both the amplitudes and 2D IR band shapes of the modes. The quantum beat decay is caused by dephasing due to both inhomogeneous and homogeneous broadening of the spectral lines. Analysis of the oscillations of the 2D line shapes demonstrates that there is some degree of anticorrelation in the inhomogeneous broadening of the two modes. It is proposed that a distribution in the coupling strength between the local modes that give rise to symmetric and antisymmetric eigenstates is responsible for the anticorrelation. Spectral diffusion, caused by structural evolution of the medium, occurs on multiple time scales and is identical for the two modes within experimental error. The spectral diffusion is fast compared to the time scale for complete orientational randomization of the RTIL. Spectral diffusion of the OD stretch of HOD in BmImPF(6) was also measured, and is essentially the same as that of the D(2)O modes. Orientational anisotropy measurements of HOD in BmImPF(6) determined the orientational relaxation dynamics of the isolated HOD molecules.
View details for DOI 10.1021/jp310086s
View details for Web of Science ID 000313920300016
View details for PubMedID 23276306
- Ultrafast Infrared Vibrational Spectroscopy edited by Fayer, M. D. Francis & Taylor Group, LLC. 2013
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Water Hydrogen Bonding Dynamics at Charged Interfaces Observed with Ultrafast Nonlinear Vibrational Spectroscopy
VIBRATIONAL SPECTROSCOPY AT ELECTRIFIED INTERFACES
2013: 3-47
View details for Web of Science ID 000324485100004
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Vibrational Echo Chemical Exchange Spectroscopy
ULTRAFAST INFRARED VIBRATIONAL SPECTROSCOPY
2013: 1-33
View details for Web of Science ID 000368015900002
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Water Dynamics in Divalent and Monovalent Concentrated Salt Solutions
JOURNAL OF PHYSICAL CHEMISTRY B
2012; 116 (46): 13781-13792
Abstract
Water hydrogen bond dynamics in concentrated salt solutions are studied using polarization-selective IR pump-probe spectroscopy and 2D IR vibrational echo spectroscopy performed on the OD hydroxyl stretching mode of dilute HOD in H(2)O/salt solutions. The OD stretch is studied to eliminate vibrational excitation transfer, which interferes with the dynamical measurements. Though previous research suggested that only the anion affected dynamics in solution, here it is shown that the cation plays a role as well. From FT-IR spectra of the OD stretch, it is seen that replacing either ion of the salt pair causes a shift in absorption frequency relative to that of the OD stretch absorption in bulk pure water. This shift becomes pronounced with larger, more polarizable anions or smaller, high charge-density cations. The vibrational lifetime of the OD hydroxyl stretch in these solutions is a local property and is primarily dependent on the nature of the anion and whether the OD is hydrogen bonded to the anion or to the oxygen of another water molecule. However, the cation still has a small effect. Time dependent anisotropy measurements show that reorientation dynamics in these concentrated solutions is a highly concerted process. While the lifetime, a local probe, displays an ion-associated and a bulk-like component in concentrated solutions, the orientational relaxation does not have two subensemble dynamics, as demonstrated by the lack of a wavelength dependence. The orientational relaxation of the single ensemble is dependent on the identity of both the cation and anion. The 2D IR vibrational echo experiments measure spectral diffusion that is caused by structural evolution of the system. The vibrational echo measurements yield the frequency-frequency correlation function (FFCF). The results also show that the structural dynamics are dependent on the cation as well as the anion.
View details for DOI 10.1021/jp3095402
View details for Web of Science ID 000311461000023
View details for PubMedID 23113682
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Comparisons of 2D IR measured spectral diffusion in rotating frames using pulse shaping and in the stationary frame using the standard method
JOURNAL OF CHEMICAL PHYSICS
2012; 137 (18)
Abstract
Multidimensional visible spectroscopy using pulse shaping to produce pulses with stable controllable phases and delays has emerged as an elegant tool to acquire electronic spectra faster and with greatly reduced instrumental and data processing errors. Recent migration of this approach using acousto-optic modulator (AOM) pulse shaping to the mid-infrared region has proved useful for acquiring two dimensional infrared (2D IR) vibrational echo spectra. The measurement of spectral diffusion in 2D IR experiments hinges on obtaining accurate 2D line shapes. To date, pulse shaping 2D IR has not been used to study the time-dependent spectral diffusion of a vibrational chromophore. Here we compare the spectral diffusion data obtained from a standard non-collinear 2D IR spectrometer using delay lines to the data obtained from an AOM pulse shaper based 2D IR spectrometer. The pulse shaping experiments are performed in stationary, partially rotating, and fully rotating reference frames and are the first in the infrared to produce 2D spectra collected in a fully rotating frame using a phase controlled pulse sequence. Rotating frame experiments provide a dramatic reduction in the number of time points that must be measured to obtain a 2D IR spectrum, with the fully rotating frame giving the greatest reduction. Experiments were conducted on the transition metal carbonyl complex tricarbonylchloro(1,10-phenanthroline)rhenium(I) in chloroform. The time dependent data obtained from the different techniques and with different reference frames are shown to be in agreement.
View details for DOI 10.1063/1.4764470
View details for Web of Science ID 000311317800007
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Comparisons of 2D IR measured spectral diffusion in rotating frames using pulse shaping and in the stationary frame using the standard method.
journal of chemical physics
2012; 137 (18): 184201-?
Abstract
Multidimensional visible spectroscopy using pulse shaping to produce pulses with stable controllable phases and delays has emerged as an elegant tool to acquire electronic spectra faster and with greatly reduced instrumental and data processing errors. Recent migration of this approach using acousto-optic modulator (AOM) pulse shaping to the mid-infrared region has proved useful for acquiring two dimensional infrared (2D IR) vibrational echo spectra. The measurement of spectral diffusion in 2D IR experiments hinges on obtaining accurate 2D line shapes. To date, pulse shaping 2D IR has not been used to study the time-dependent spectral diffusion of a vibrational chromophore. Here we compare the spectral diffusion data obtained from a standard non-collinear 2D IR spectrometer using delay lines to the data obtained from an AOM pulse shaper based 2D IR spectrometer. The pulse shaping experiments are performed in stationary, partially rotating, and fully rotating reference frames and are the first in the infrared to produce 2D spectra collected in a fully rotating frame using a phase controlled pulse sequence. Rotating frame experiments provide a dramatic reduction in the number of time points that must be measured to obtain a 2D IR spectrum, with the fully rotating frame giving the greatest reduction. Experiments were conducted on the transition metal carbonyl complex tricarbonylchloro(1,10-phenanthroline)rhenium(I) in chloroform. The time dependent data obtained from the different techniques and with different reference frames are shown to be in agreement.
View details for DOI 10.1063/1.4764470
View details for PubMedID 23163363
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Dynamics of Functionalized Surface Molecular Monolayers Studied with Ultrafast Infrared Vibrational Spectroscopy
JOURNAL OF PHYSICAL CHEMISTRY C
2012; 116 (44): 23428-23440
Abstract
The structural dynamics of thin films consisting of tricarbonyl (1,10-phenanthroline)rhenium chloride (RePhen(CO)(3)Cl) linked to an alkyl silane monolayer through a triazole linker synthesized on silica-on-calcium-fluoride substrates are investigated using ultrafast infrared (IR) techniques. Ultrafast 2D IR vibrational echo experiments and polarization selective heterodyne detected transient grating (HDTG) measurements, as well as polarization dependent FT-IR and AFM experiments are employed to study the samples. The vibrational echo experiments measure spectral diffusion, while the HDTG experiments measure the vibrational excited state population relaxation and investigate the vibrational transition dipole orientational anisotropy decay. To investigate the anticipated impact of vibrational excitation transfer, which can be caused by the high concentration of RePhen(CO)(3)Cl in the monolayer, a concentration dependence of the spectral diffusion is measured. To generate a range of concentrations, mixed monolayers consisting of both hydrogen terminated and triazole/RePhen(CO)(3)Cl terminated alkyl silanes are synthesized. It is found that the measured rate of spectral diffusion is independent of concentration, with all samples showing spectral diffusion of 37 ± 6 ps. To definitively test for vibrational excitation transfer, polarization selective HDTG experiments are conducted. Excitation transfer will cause anisotropy decay. Polarization resolved heterodyne detected transient grating spectroscopy is sensitive to anisotropy decay (depolarization) caused by excitation transfer and molecular reorientation. The HDTG experiments show no evidence of anisotropy decay on the appropriate time scale, demonstrating the absence of excitation transfer the RePhen(CO)(3)Cl. Therefore the influence of excitation transfer on spectral diffusion is inconsequential in these samples, and the vibrational echo measurements of spectral diffusion report solely on structural dynamics. A small amount of very fast (~2 ps time scale) anisotropy decay is observed. The decay is concentration independent, and is assigned to wobbling-in-a-cone orientational motions of the RePhen(CO)(3)Cl. Theoretical calculations reported previously for experiments on a single concentration of the same type of sample suggested the presence of some vibrational excitation transfer and excitation transfer induced spectral diffusion. Possible reasons for the experimentally observed lack of excitation transfer in these high concentration samples are discussed.
View details for DOI 10.1021/jp307677b
View details for Web of Science ID 000310769300031
View details for PubMedCentralID PMC3523711
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Dynamics of Functionalized Surface Molecular Monolayers Studied with Ultrafast Infrared Vibrational Spectroscopy.
The journal of physical chemistry. C, Nanomaterials and interfaces
2012; 116 (44): 23428-23440
Abstract
The structural dynamics of thin films consisting of tricarbonyl (1,10-phenanthroline)rhenium chloride (RePhen(CO)(3)Cl) linked to an alkyl silane monolayer through a triazole linker synthesized on silica-on-calcium-fluoride substrates are investigated using ultrafast infrared (IR) techniques. Ultrafast 2D IR vibrational echo experiments and polarization selective heterodyne detected transient grating (HDTG) measurements, as well as polarization dependent FT-IR and AFM experiments are employed to study the samples. The vibrational echo experiments measure spectral diffusion, while the HDTG experiments measure the vibrational excited state population relaxation and investigate the vibrational transition dipole orientational anisotropy decay. To investigate the anticipated impact of vibrational excitation transfer, which can be caused by the high concentration of RePhen(CO)(3)Cl in the monolayer, a concentration dependence of the spectral diffusion is measured. To generate a range of concentrations, mixed monolayers consisting of both hydrogen terminated and triazole/RePhen(CO)(3)Cl terminated alkyl silanes are synthesized. It is found that the measured rate of spectral diffusion is independent of concentration, with all samples showing spectral diffusion of 37 ± 6 ps. To definitively test for vibrational excitation transfer, polarization selective HDTG experiments are conducted. Excitation transfer will cause anisotropy decay. Polarization resolved heterodyne detected transient grating spectroscopy is sensitive to anisotropy decay (depolarization) caused by excitation transfer and molecular reorientation. The HDTG experiments show no evidence of anisotropy decay on the appropriate time scale, demonstrating the absence of excitation transfer the RePhen(CO)(3)Cl. Therefore the influence of excitation transfer on spectral diffusion is inconsequential in these samples, and the vibrational echo measurements of spectral diffusion report solely on structural dynamics. A small amount of very fast (~2 ps time scale) anisotropy decay is observed. The decay is concentration independent, and is assigned to wobbling-in-a-cone orientational motions of the RePhen(CO)(3)Cl. Theoretical calculations reported previously for experiments on a single concentration of the same type of sample suggested the presence of some vibrational excitation transfer and excitation transfer induced spectral diffusion. Possible reasons for the experimentally observed lack of excitation transfer in these high concentration samples are discussed.
View details for DOI 10.1021/jp307677b
View details for PubMedID 23259027
View details for PubMedCentralID PMC3523711
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Fast Dynamics of HP35 for Folded and Urea-Unfolded Conditions
JOURNAL OF PHYSICAL CHEMISTRY B
2012; 116 (36): 11024-11031
Abstract
The changes in fast dynamics of HP35 with a double CN vibrational dynamics label (HP35-P(2)) as a function of the extent of denaturation by urea were investigated with two-dimensional infrared (2D IR) vibrational echo spectroscopy. Cyanophenylalanine (PheCN) replaces the native phenylalanine at two residues in the hydrophobic core of HP35, providing vibrational probes. NMR data show that HP35-P(2) maintains the native folded structure similar to wild type and that both PheCN residues share essentially the same environment within the peptide. A series of time-dependent 2D IR vibrational echo spectra were obtained for the folded peptide and the increasingly unfolded peptide. Analysis of the time dependence of the 2D spectra yields the system's spectral diffusion, which is caused by the sampling of accessible structures of the peptide under thermal equilibrium conditions. The structural dynamics become faster as the degree of unfolding is increased.
View details for DOI 10.1021/jp304058x
View details for Web of Science ID 000308631200007
View details for PubMedID 22909017
View details for PubMedCentralID PMC3475495
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Water in a crowd
AMER CHEMICAL SOC. 2012
View details for Web of Science ID 000324621807263
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Dynamics of water interacting with ions
AMER CHEMICAL SOC. 2012
View details for Web of Science ID 000324621802677
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Dynamics of a heterogeneous catalyst studied with ultrafast 2D IR vibrational echo spectroscopy
AMER CHEMICAL SOC. 2012
View details for Web of Science ID 000324621803104
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Excitation transfer induced spectral diffusion and the influence of structural spectral diffusion
JOURNAL OF CHEMICAL PHYSICS
2012; 137 (6)
Abstract
The theory of vibrational excitation transfer, which causes spectral diffusion and is also influenced by structural spectral diffusion, is developed and applied to systems consisting of vibrational chromophores. Excitation transfer induced spectral diffusion is the time-dependent change in vibrational frequency induced by an excitation on an initially excited molecule jumping to other molecules that have different vibrational frequencies within the inhomogeneously broadened vibrational absorption line. The excitation transfer process is modeled as Förster resonant transfer, which depends on the overlap of the homogeneous spectra of the donating and accepting vibrational chromophores. Because the absorption line is inhomogeneously broadened, two molecules in close proximity can have overlaps of their homogeneous lines that range from substantial to very little. In the absence of structural dynamics, the overlap of the homogeneous lines of the donating and accepting vibrational chromophores would be fixed. However, dynamics of the medium that contains the vibrational chromophores, e.g., a liquid solvent or a surrounding protein, produce spectral diffusion. Spectral diffusion causes the position of a molecule's homogeneous line within the inhomogeneous spectrum to change with time. Therefore, the overlap of donating and accepting molecules' homogeneous lines is time dependent, which must be taken into account in the excitation transfer theory. The excitation transfer problem is solved for inhomogeneous lines with fluctuating homogeneous line frequencies. The method allows the simultaneous treatment of both excitation transfer induced spectral diffusion and structural fluctuation induced spectral diffusion. It is found that the excitation transfer process is enhanced by the stochastic fluctuations in frequencies. It is shown how a measurement of spectral diffusion can be separated into the two types of spectral diffusion, which permits the structural spectral diffusion to be determined in the presence of excitation transfer spectral diffusion. Various approximations and computational methodologies are explored.
View details for DOI 10.1063/1.4742762
View details for Web of Science ID 000308048700009
View details for PubMedID 22897257
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Conformational Dynamics and Stability of HP35 Studied with 2D IR Vibrational Echoes
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2012; 134 (29): 12118-12124
Abstract
Two-dimensional infrared (2D IR) vibrational echo spectroscopy was used to measure the fast dynamics of two variants of chicken villin headpiece 35 (HP35). The CN of cyanophenylalanine residues inserted in the hydrophobic core were used as a vibrational probe. Experiments were performed on both singly (HP35-P) and doubly CN-labeled peptide (HP35-P(2)) within the wild-type sequence, as well as on HP-35 containing a singly labeled cyanophenylalanine and two norleucine mutations (HP35-P NleNle). There is a remarkable similarity between the dynamics measured in singly and doubly CN-labeled HP35, demonstrating that the presence of an additional CN vibrational probe does not significantly alter the dynamics of the small peptide. The substitution of two lysine residues by norleucines markedly improves the stability of HP35 by replacing charged with nonpolar residues, stabilizing the hydrophobic core. The results of the 2D IR experiments reveal that the dynamics of HP35-P are significantly faster than those of HP35-P NleNle. These observations suggest that the slower structural fluctuations in the hydrophobic core, indicating a more tightly structured core, may be an important contributing factor to HP35-P NleNle's increased stability.
View details for DOI 10.1021/ja303017d
View details for Web of Science ID 000306724500059
View details for PubMedID 22764745
View details for PubMedCentralID PMC3487692
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Water Dynamics in Water/DMSO Binary Mixtures
JOURNAL OF PHYSICAL CHEMISTRY B
2012; 116 (18): 5479-5490
Abstract
The dynamics of dimethyl sulfoxide (DMSO)/water solutions with a wide range of water concentrations are studied using polarization selective infrared pump-probe experiments, two-dimensional infrared (2D IR) vibrational echo spectroscopy, optical heterodyne detected optical Kerr effect (OHD-OKE) experiments, and IR absorption spectroscopy. Vibrational population relaxation of the OD stretch of dilute HOD in H(2)O displays two vibrational lifetimes even at very low water concentrations that are associated with water-water and water-DMSO hydrogen bonds. The IR absorption spectra also show characteristics of both water-DMSO and water-water hydrogen bonding. Although two populations are observed, water anisotropy decays (orientational relaxation) exhibit single ensemble behavior, indicative of concerted reorientation involving water and DMSO molecules. OHD-OKE experiments, which measure the orientational relaxation of DMSO, reveal that the DMSO orientational relaxation times are the same as orientational relaxation times found for water over a wide range of water concentrations within experimental error. The fact that the reorientation times of water and DMSO are basically the same shows that the reorientation of water is coupled to the reorientation of DMSO itself. These observations are discussed in terms of a jump reorientation model. Frequency-frequency correlation functions determined from the 2D IR experiments on the OD stretch show both fast and slow spectral diffusion. In analogy to bulk water, the fast component is assigned to very local hydrogen bond fluctuations. The slow component, which is similar to the slow water reorientation time at each water concentration, is associated with global hydrogen bond structural randomization.
View details for DOI 10.1021/jp301967e
View details for Web of Science ID 000303786500017
View details for PubMedID 22510039
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Ribonuclease S Dynamics Measured Using a Nitrile Label with 2D IR Vibrational Echo Spectroscopy
JOURNAL OF PHYSICAL CHEMISTRY B
2012; 116 (13): 4034-4042
Abstract
A nitrile-labeled amino acid, p-cyanophenylalanine, is introduced near the active site of the semisynthetic enzyme ribonuclease S to serve as a probe of protein dynamics and fluctuations. Ribonuclease S is the limited proteolysis product of subtilisin acting on ribonuclease A, and consists of a small fragment including amino acids 1-20, the S-peptide, and a larger fragment including residues 21-124, the S-protein. A series of two-dimensional vibrational echo experiments performed on the nitrile-labeled S-peptide and the RNase S are described. The time-dependent changes in the two-dimensional infrared vibrational echo line shapes are analyzed using the center line slope method to obtain the frequency-frequency correlation function (FFCF). The observations show that the nitrile probe in the S-peptide has dynamics that are similar to, but faster than, those of the single amino acid p-cyanophenylalanine in water. In contrast, the dynamics of the nitrile label when the peptide is bound to form ribonuclease S are dominated by homogeneous dephasing (motionally narrowed) contributions with only a small contribution from very fast inhomogeneous structural dynamics. The results provide insights into the nature of the structural dynamics of the ribonuclease S complex. The equilibrium dynamics of the nitrile labeled S-peptide and the ribonuclease S complex are also investigated by molecular dynamics simulations. The experimentally determined FFCFs are compared to the FFCFs obtained from the molecular dynamics simulations, thereby testing the capacity of simulations to determine the amplitudes and time scales of protein structural fluctuations on fast time scales under thermal equilibrium conditions.
View details for DOI 10.1021/jp2122856
View details for Web of Science ID 000302337000015
View details for PubMedID 22417088
View details for PubMedCentralID PMC3354990
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Investigation of Nanostructure in Room Temperature Ionic Liquids using Electronic Excitation Transfer
JOURNAL OF PHYSICAL CHEMISTRY B
2012; 116 (10): 3054-3064
Abstract
Donor-donor electronic excitation transfer among 9-phenylanthracene (9PA) chromophores was measured in the room temperature ionic liquid (RTIL) 1-methyl-3-octylimidazolium chloride using time dependent fluorescence depolarization. 9PA, which is uncharged and nonpolar, will partition into the organic regions of the RTIL. The excitation transfer rate, which is sensitive to the distribution of chromophores in the RTIL, is modeled using different spatial configurations of 9PA molecules in the RTIL solution. The models are an isotropic distribution (random distribution) and a clustered sphere model to represent hydrophobic regions of a nanostructured environment. Model calculations were performed to demonstrate the sensitivity of excitation transfer to different distributions of chromophores. When compared to the experiment, the isotropic model can adequately match the data. From a Bayesian analysis of the sensitivity of the excitation transfer to the models for the spatial distribution of chromophores, an upper limit of 6 Å radius is placed on the size of hydrophobic domains in the RTIL.
View details for DOI 10.1021/jp207757r
View details for Web of Science ID 000301509500002
View details for PubMedID 22313385
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Orientational Dynamics of Room Temperature Ionic Liquid/Water Mixtures: Water-Induced Structure
JOURNAL OF PHYSICAL CHEMISTRY B
2012; 116 (6): 1777-1787
Abstract
Optical heterodyne detected optical Kerr effect (OHD-OKE) measurements on a series of 1-alkyl-3-methylimidazolium tetrafluoroborate room-temperature ionic liquids (RTILs) as a function of chain length and water concentration are presented. The pure RTIL reorientational dynamics are identical in form to those of other molecular liquids studied previously by OHD-OKE (two power laws followed by a single exponential decay at long times), but are much slower at room temperature. In contrast, the addition of water to the longer alkyl chain RTILs causes the emergence of a long time biexponential orientational anisotropy decay. Such distinctly biexponential decays have not been seen previously in OHD-OKE experiments on any type of liquid and are analyzed here using a wobbling-in-a-cone model. The slow component for the longer chain RTILs does not obey the Debye-Stokes-Einstein (DSE) equation across the range of solutions, and thus we attribute it to slow cation reorientational diffusion caused by a stiffening of cation alkyl tail-tail associations. The fast component of the decay is assigned to the motions (wobbling) of the tethered imidazolium head groups. The wobbling-in-a-cone analysis provides estimates of the range of angles sampled by the imidazolium head group prior to the long time scale complete orientational randomization. The heterogeneous dynamics and non-DSE behavior observed here should have a significant effect on reaction rates in RTIL/water cosolvent mixtures.
View details for DOI 10.1021/jp209942r
View details for Web of Science ID 000300274900005
View details for PubMedID 22224942
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Dynamics at Specific Sites in Proteins Studied by 2D IR Vibrational Echo Spectroscopy
CELL PRESS. 2012: 224A-225A
View details for DOI 10.1016/j.bpj.2011.11.1233
View details for Web of Science ID 000321561201436
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Dynamics of Water Interacting with Interfaces, Molecules, and Ions.
ACCOUNTS OF CHEMICAL RESEARCH
2012; 45 (1): 3-14
Abstract
Water is a critical component of many chemical processes, in fields as diverse as biology and geology. Water in chemical, biological, and other systems frequently occurs in very crowded situations: the confined water must interact with a variety of interfaces and molecular groups, often on a characteristic length scale of nanometers. Water's behavior in diverse environments is an important contributor to the functioning of chemical systems. In biology, water is found in cells, where it hydrates membranes and large biomolecules. In geology, interfacial water molecules can control ion adsorption and mineral dissolution. Embedded water molecules can change the structure of zeolites. In chemistry, water is an important polar solvent that is often in contact with interfaces, for example, in ion-exchange resin systems. Water is a very small molecule; its unusual properties for its size are attributable to the formation of extended hydrogen bond networks. A water molecule is similar in mass and volume to methane, but methane is a gas at room temperature, with melting and boiling points of 91 and 112 K, respectively. This is in contrast to water, with melting and boiling points of 273 and 373 K, respectively. The difference is that water forms up to four hydrogen bonds with approximately tetrahedral geometry. Water's hydrogen bond network is not static. Hydrogen bonds are constantly forming and breaking. In bulk water, the time scale for hydrogen bond randomization through concerted formation and dissociation of hydrogen bonds is approximately 2 ps. Water's rapid hydrogen bond rearrangement makes possible many of the processes that occur in water, such as protein folding and ion solvation. However, many processes involving water do not take place in pure bulk water, and water's hydrogen bond structural dynamics can be substantially influenced by the presence of, for example, interfaces, ions, and large molecules. In this Account, spectroscopic studies that have been used to explore the details of these influences are discussed. Because rearrangements of water molecules occur so quickly, ultrafast infrared experiments that probe water's hydroxyl stretching mode are useful in providing direct information about water dynamics on the appropriate time scales. Infrared polarization-selective pump-probe experiments and two-dimensional infrared (2D IR) vibrational echo experiments have been used to study the hydrogen bond dynamics of water. Water orientational relaxation, which requires hydrogen bond rearrangements, has been studied at spherical interfaces of ionic reverse micelles and compared with planar interfaces of lamellar structures composed of the same surfactants. Water orientational relaxation slows considerably at interfaces. It is found that the geometry of the interface is less important than the presence of the interface. The influence of ions is shown to slow hydrogen bond rearrangements. However, comparing an ionic interface to a neutral interface demonstrates that the chemical nature of the interface is less important than the presence of the interface. Finally, it is found that the dynamics of water at an organic interface is very similar to water molecules interacting with a large polyether.
View details for DOI 10.1021/ar2000088
View details for Web of Science ID 000301083400002
View details for PubMedID 21417263
View details for PubMedCentralID PMC3151308
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Water in a Crowd
PHYSIOLOGY
2011; 26 (6): 381-392
Abstract
In many situations, form biology to geology, water occurs not as the pure bulk liquid but rather in nanoscopic environments, in contact with interfaces, interacting with ionic species, and interacting with large organic molecules. In such situations, water does not behave in the same manner as it does in the pure bulk liquid. Water dynamics are fundamental to many processes such as protein folding and proton transport. Such processes depend on the dynamics of water's hydrogen bonding network. Here, the results of ultrafast infrared experiments are described that shed light on the influences of nanoconfinement, interfaces, ions, and organic molecules on water hydrogen bond dynamics.
View details for DOI 10.1152/physiol.00021.2011
View details for Web of Science ID 000298377300002
View details for PubMedID 22170957
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Structural Dynamics of a Catalytic Monolayer Probed by Ultrafast 2D IR Vibrational Echoes
SCIENCE
2011; 334 (6056): 634-639
Abstract
Ultrafast two-dimensional infrared (2D IR) vibrational echo spectroscopy has proven broadly useful for studying molecular dynamics in solutions. Here, we extend the technique to probing the interfacial dynamics and structure of a silica surface-tethered transition metal carbonyl complex--tricarbonyl (1,10-phenanthroline)rhenium chloride--of interest as a photoreduction catalyst. We interpret the data using a theoretical framework devised to separate the roles of structural evolution and excitation transfer in inducing spectral diffusion. The structural dynamics, as reported on by a carbonyl stretch vibration of the surface-bound complex, have a characteristic time of ~150 picoseconds in the absence of solvent, decrease in duration by a factor of three upon addition of chloroform, and decrease another order of magnitude for the bulk solution. Conversely, solvent-complex interactions increase the lifetime of the probed vibration by 160% when solvent is applied to the monolayer.
View details for DOI 10.1126/science.1211350
View details for Web of Science ID 000296494700045
View details for PubMedID 22021674
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Dynamics of Water at the Interface in Reverse Micelles: Measurements of Spectral Diffusion with Two-Dimensional Infrared Vibrational Echoes
JOURNAL OF PHYSICAL CHEMISTRY B
2011; 115 (40): 11658-11670
Abstract
Water dynamics inside of reverse micelles made from the surfactant Aerosol-OT (AOT) were investigated by observing spectral diffusion, orientational relaxation, and population relaxation using two-dimensional infrared (2D IR) vibrational echo spectroscopy and pump-probe experiments. The water pool sizes of the reverse micelles studied ranged in size from 5.8 to 1.7 nm in diameter. It is found that spectral diffusion, characterized by the frequency-frequency correlation function (FFCF), significantly changes as the water pool size decreases. For the larger reverse micelles (diameter 4.6 nm and larger), the 2D IR signal is composed of two spectral components: a signal from bulk-like core water, and a signal from water at the headgroup interface. Each of these signals (core water and interfacial water) is associated with a distinct FFCF. The FFCF of the interfacial water layer can be obtained using a modified center line slope (CLS) method that has been recently developed. The interfacial FFCFs for large reverse micelles have a single exponential decay (∼1.6 ps) to an offset plus a fast homogeneous component and are nearly identical for all large sizes. The observed ∼1.6 ps interfacial decay component is approximately the same as that found for bulk water and may reflect hydrogen bond rearrangement of bulk-like water molecules hydrogen bonded to the interfacial water molecules. The long time offset arises from dynamics that are too slow to be measured on the accessible experimental time scale. The influence of the chemical nature of the interface on spectral diffusion was explored by comparing data for water inside reverse micelles (5.8 nm water pool diameter) made from the surfactants AOT and Igepal CO-520. AOT has charged, sulfonate head groups, while Igepal CO-520 has neutral, hydroxyl head groups. It is found that spectral diffusion on the observable time scales is not overly sensitive to the chemical makeup of the interface. An intermediate-sized AOT reverse micelle (water pool diameter of 3.3 nm) is analyzed as a large reverse micelle because it has distinct core and interface regions, but its core region is more constrained than bulk water. The interfacial FFCF for this intermediate-sized reverse micelle is somewhat slower than those found for the larger reverse micelles. The water nanopools in the smaller reverse micelles cannot be separated into core and interface regions. In the small reverse micelles, the FFCFs are biexponential decays to an offset plus a fast homogeneous component. Each small reverse micelle exhibits an ∼1 ps decay time, which may arise from local hydrogen bond fluctuations and a slower, ∼6-10 ps decay, which is possibly due to slow hydrogen bond rearrangement of noninterfacial water molecules or topography fluctuations at the interface.
View details for DOI 10.1021/jp206903k
View details for Web of Science ID 000295545900014
View details for PubMedID 21899355
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Two-Dimensional IR Spectroscopy of Protein Dynamics Using Two Vibrational Labels: A Site-Specific Genetically Encoded Unnatural Amino Acid and an Active Site Ligand
JOURNAL OF PHYSICAL CHEMISTRY B
2011; 115 (38): 11294-11304
Abstract
Protein dynamics and interactions in myoglobin (Mb) were characterized via two vibrational dynamics labels (VDLs): a genetically incorporated site-specific azide (Az) bearing unnatural amino acid (AzPhe43) and an active site CO ligand. The Az-labeled protein was studied using ultrafast two-dimensional infrared (2D IR) vibrational echo spectroscopy. CO bound at the active site of the heme serves as a second VDL located nearby. Therefore, it was possible to use Fourier transform infrared (FT-IR) and 2D IR spectroscopic experiments on the Az in unligated Mb and in Mb bound to CO (MbAzCO) and on the CO in MbCO and MbAzCO to investigate the environment and motions of different states of one protein from the perspective of two spectrally resolved VDLs. A very broad bandwidth 2D IR spectrum, encompassing both the Az and CO spectral regions, found no evidence of direct coupling between the two VDLs. In MbAzCO, both VDLs reported similar time scale motions: very fast homogeneous dynamics, fast, ∼1 ps dynamics, and dynamics on a much slower time scale. Therefore, each VDL reports independently on the protein dynamics and interactions, and the measured dynamics are reflective of the protein motions rather than intrinsic to the chemical nature of the VDL. The AzPhe VDL also permitted study of oxidized Mb dynamics, which could not be accessed previously with 2D IR spectroscopy. The experiments demonstrate that the combined application of 2D IR spectroscopy and site-specific incorporation of VDLs can provide information on dynamics, structure, and interactions at virtually any site throughout any protein.
View details for DOI 10.1021/jp206986v
View details for Web of Science ID 000295057900029
View details for PubMedID 21823631
View details for PubMedCentralID PMC3261801
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Time-Dependent Fifth-Order Bands in Nominally Third-Order 2D IR Vibrational Echo Spectra
JOURNAL OF PHYSICAL CHEMISTRY A
2011; 115 (34): 9714-9723
Abstract
Progress in the field of 2D IR vibrational spectroscopy has been bolstered by the production of intense mid-IR laser pulses. As higher-energy pulses are employed, a concomitant increase occurs in the likelihood of fifth-order contributions to the 2D IR spectra. We report the appearance of fifth-order signals in 2D IR spectra of CO bound to the active site of the enzyme cytochrome P450(cam) with the substrate norcamphor. Two bands with novel time dependences, one on the diagonal and one off-diagonal, are not accounted for by normal third-order interactions. These bands are associated with a ν = 1-2 vibrational transition frequency. Both bands decay to 0 and then grow back in with opposite sign. The diagonal band is positive at short time, decays to 0, reappears with negative sign, before eventually decaying to 0. The off-diagonal band is negative at short time, decays to 0, reappears positive, and then decays to 0. The appearance and time dependence of these bands are characterized. Understanding these fifth-order bands is useful because they may be misidentified with time-dependent bands that arise from other processes, such as chemical exchange, vibrational coupling, or energy transfer. The presence and unusual time dependences of the fifth-order bands are reproduced with model calculations that account for the fact that vibrational relaxation from the ν = 2 to 1 level is approximately a factor of 2 faster than that from the ν = 1 to 0 level.
View details for DOI 10.1021/jp201516s
View details for Web of Science ID 000294146400046
View details for PubMedID 21648438
View details for PubMedCentralID PMC3162047
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Extracting 2D IR frequency-frequency correlation functions from two component systems
JOURNAL OF CHEMICAL PHYSICS
2011; 135 (7)
Abstract
The center line slope (CLS) method is often used to extract the frequency-frequency correlation function (FFCF) from 2D IR spectra to delineate dynamics and to identify homogeneous and inhomogeneous contributions to the absorption line shape of a system. While the CLS method is extremely efficient, quite accurate, and immune to many experimental artifacts, it has only been developed and properly applied to systems that have a single vibrational band, or to systems of two species that have spectrally resolved absorption bands. In many cases, the constituent spectra of multiple component systems overlap and cannot be distinguished from each other. This situation creates ambiguity when analyzing 2D IR spectra because dynamics for different species cannot be separated. Here a mathematical formulation is presented that extends the CLS method for a system consisting of two components (chemically distinct uncoupled oscillators). In a single component system, the CLS corresponds to the time-dependent portion of the normalized FFCF. This is not the case for a two component system, as a much more complicated expression arises. The CLS method yields a series of peak locations originating from slices taken through the 2D spectra. The slope through these peak locations yields the CLS value for the 2D spectra at a given T(w). We derive analytically that for two component systems, the peak location of the system can be decomposed into a weighted combination of the peak locations of the constituent spectra. The weighting depends upon the fractional contribution of each species at each wavelength and also on the vibrational lifetimes of both components. It is found that an unknown FFCF for one species can be determined as long as the peak locations (referred to as center line data) of one of the components are known, as well as the vibrational lifetimes, absorption spectra, and other spectral information for both components. This situation can arise when a second species is introduced into a well characterized single species system. An example is a system in which water exists in bulk form and also as water interacting with an interface. An algorithm is presented for back-calculating the unknown FFCF of the second component. The accuracy of the algorithm is tested with a variety of model cases in which all components are initially known. The algorithm successfully reproduces the FFCF for the second component within a reasonable degree of error.
View details for DOI 10.1063/1.3625278
View details for Web of Science ID 000294065200026
View details for PubMedID 21861571
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Influence of Histidine Tag Attachment on Picosecond Protein Dynamics
BIOCHEMISTRY
2011; 50 (25): 5799-5805
Abstract
Polyhistidine affinity tags are routinely employed as a convenient means of purifying recombinantly expressed proteins. A tacit assumption is commonly made that His tags have little influence on protein structure and function. Attachment of a His tag to the N-terminus of the robust globular protein myoglobin leads to only minor changes to the electrostatic environment of the heme pocket, as evinced by the nearly unchanged Fourier transform infrared spectrum of CO bound to the heme of His-tagged myoglobin. Experiments employing two-dimensional infrared vibrational echo spectroscopy of the heme-bound CO, however, find that significant changes occur to the short time scale (picoseconds) dynamics of myoglobin as a result of His tag incorporation. The His tag mainly reduces the dynamics on the 1.4 ps time scale and also alters protein motions of myoglobin on the slower, >100 ps time scale, as demonstrated by the His tag's influence on the fluctuations of the CO vibrational frequency, which reports on protein structural dynamics. The results suggest that affinity tags may have effects on protein function and indicate that investigators of affinity-tagged proteins should take this into consideration when investigating the dynamics and other properties of such proteins.
View details for DOI 10.1021/bi2003923
View details for Web of Science ID 000291897000023
View details for PubMedID 21619030
View details for PubMedCentralID PMC3133630
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Temperature Dependent Equilibrium Native to Unfolded Protein Dynamics and Properties Observed with IR Absorption and 2D IR Vibrational Echo Experiments
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2011; 133 (17): 6681-6691
Abstract
Dynamic and structural properties of carbonmonoxy (CO)-coordinated cytochrome c(552) from Hydrogenobacter thermophilus (Ht-M61A) at different temperatures under thermal equilibrium conditions were studied with infrared absorption spectroscopy and ultrafast two-dimensional infrared (2D IR) vibrational echo experiments using the heme-bound CO as the vibrational probe. Depending on the temperature, the stretching mode of CO shows two distinct bands corresponding to the native and unfolded proteins. As the temperature is increased from low temperature, a new absorption band for the unfolded protein grows in and the native band decreases in amplitude. Both the temperature-dependent circular dichroism and the IR absorption area ratio R(A)(T), defined as the ratio of the area under the unfolded band to the sum of the areas of the native and unfolded bands, suggest a two-state transition from the native to the unfolded protein. However, it is found that the absorption spectrum of the unfolded protein increases its inhomogeneous line width and the center frequency shifts as the temperature is increased. The changes in line width and center frequency demonstrate that the unfolding does not follow simple two-state behavior. The temperature-dependent 2D IR vibrational echo experiments show that the fast dynamics of the native protein are virtually temperature independent. In contrast, the fast dynamics of the unfolded protein are slower than those of the native protein, and the unfolded protein fast dynamics and at least a portion of the slower dynamics of the unfolded protein change significantly, becoming faster as the temperature is raised. The temperature dependence of the absorption spectrum and the changes in dynamics measured with the 2D IR experiments confirm that the unfolded ensemble of conformers continuously changes its nature as unfolding proceeds, in contrast to the native state, which displays a temperature-independent distribution of structures.
View details for DOI 10.1021/ja111009s
View details for Web of Science ID 000290363400036
View details for PubMedID 21469666
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Protein Dynamics in Cytochrome P450 Molecular Recognition and Substrate Specificity Using 2D IR Vibrational Echo Spectroscopy
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2011; 133 (11): 3995-4004
Abstract
Cytochrome (cyt) P450s hydroxylate a variety of substrates that can differ widely in their chemical structure. The importance of these enzymes in drug metabolism and other biological processes has motivated the study of the factors that enable their activity on diverse classes of molecules. Protein dynamics have been implicated in cyt P450 substrate specificity. Here, 2D IR vibrational echo spectroscopy is employed to measure the dynamics of cyt P450(cam) from Pseudomonas putida on fast time scales using CO bound at the active site as a vibrational probe. The substrate-free enzyme and the enzyme bound to both its natural substrate, camphor, and a series of related substrates are investigated to explicate the role of dynamics in molecular recognition in cyt P450(cam) and to delineate how the motions may contribute to hydroxylation specificity. In substrate-free cyt P450(cam), three conformational states are populated, and the structural fluctuations within a conformational state are relatively slow. Substrate binding selectively stabilizes one conformational state, and the dynamics become faster. Correlations in the observed dynamics with the specificity of hydroxylation of the substrates, the binding affinity, and the substrates' molecular volume suggest that motions on the hundreds of picosecond time scale contribute to the variation in activity of cyt P450(cam) toward different substrates.
View details for DOI 10.1021/ja109168h
View details for Web of Science ID 000288889900058
View details for PubMedID 21348488
View details for PubMedCentralID PMC3063108
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Dynamics of the folded and unfolded villin headpiece (HP35) measured with ultrafast 2D IR vibrational echo spectroscopy
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2011; 108 (9): 3578-3583
Abstract
A series of two-dimensional infrared vibrational echo experiments performed on nitrile-labeled villin headpiece [HP35-(CN)(2)] is described. HP35 is a small peptide composed of three alpha helices in the folded configuration. The dynamics of the folded HP35-(CN)(2) are compared to that of the guanidine-induced unfolded peptide, as well as the nitrile-functionalized phenylalanine (PheCN), which is used to differentiate the peptide dynamic contributions to the observables from those of the water solvent. Because the viscosity of solvent has a significant effect on fast dynamics, the viscosity of the solvent is held constant by adding glycerol. For the folded peptide, the addition of glycerol to the water solvent causes observable slowing of the peptide's dynamics. Holding the viscosity constant as GuHCl is added, the dynamics of unfolded peptide are much faster than those of the folded peptide, and they are very similar to that of PheCN. These observations indicate that the local environment of the nitrile in the unfolded peptide resembles that of PheCN, and the dynamics probed by the CN are dominated by the fluctuations of the solvent molecules, in contrast to the observations on the folded peptide.
View details for DOI 10.1073/pnas.1100587108
View details for Web of Science ID 000287844400029
View details for PubMedID 21321226
View details for PubMedCentralID PMC3048147
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Temperature and Hydration-Dependent Rotational and Translational Dynamics of a Polyether Oligomer
JOURNAL OF PHYSICAL CHEMISTRY B
2011; 115 (5): 945-950
Abstract
Temperature-dependent rotational diffusion of tetraethylene glycol dimethyl ether (TEGDE) is measured by optical heterodyne-detected optical Kerr effect (OHD-OKE) spectroscopy and compared to previous measurements of rotational diffusion as a function of water content. Both types of data, temperature-dependent and hydration-dependent, follow the Debye-Stokes-Einstein (DSE) equation and agree quantitatively with hydrodynamic calculations. Of particular importance is the result that both types of data show nearly identical dependence on the viscosity divided by the temperature (η/T). We also compare the translational diffusion constants as previously measured by pulsed field gradient spin-echo (PFG-SE) NMR as a function of both temperature and water content. The temperature-dependent data follow the Stokes-Einstein (SE) equation. Similar to the rotation, the low water content mixtures obey the SE equation and show the same proportionality to η/T as the temperature-dependent data. At higher water fractions, the data do not obey the SE equation. The principal results are that the influence of temperature on dry TEGDE orientational relaxation is the same as the influence of water content at fixed temperature, and that the influence of temperature on translational diffusion of dry TEGDE is the same as the influence of water content over a range of relatively low water concentrations. The results demonstrate that there are no large TEGDE structural changes or specific, long-lived water-polyether interactions in the solutions over the entire concentration range.
View details for DOI 10.1021/jp110487j
View details for Web of Science ID 000286797700020
View details for PubMedID 21222441
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Water dynamics in small reverse micelles in two solvents: Two-dimensional infrared vibrational echoes with two-dimensional background subtraction
JOURNAL OF CHEMICAL PHYSICS
2011; 134 (5)
Abstract
Water dynamics as reflected by the spectral diffusion of the water hydroxyl stretch were measured in w(0) = 2 (1.7 nm diameter) Aerosol-OT (AOT)/water reverse micelles in carbon tetrachloride and in isooctane solvents using ultrafast 2D IR vibrational echo spectroscopy. Orientational relaxation and population relaxation are observed for w(0) = 2, 4, and 7.5 in both solvents using IR pump-probe measurements. It is found that the pump-probe observables are sensitive to w(0), but not to the solvent. However, initial analysis of the vibrational echo data from the water nanopool in the reverse micelles in the isooctane solvent seems to yield different dynamics than the CCl(4) system in spite of the fact that the spectra, vibrational lifetimes, and orientational relaxation are the same in the two systems. It is found that there are beat patterns in the interferograms with isooctane as the solvent. The beats are observed from a signal generated by the AOT/isooctane system even when there is no water in the system. A beat subtraction data processing procedure does a reasonable job of removing the distortions in the isooctane data, showing that the reverse micelle dynamics are the same within experimental error regardless of whether isooctane or carbon tetrachloride is used as the organic phase. Two time scales are observed in the vibrational echo data, ~1 and ~10 ps. The slower component contains a significant amount of the total inhomogeneous broadening. Physical arguments indicate that there is a much slower component of spectral diffusion that is too slow to observe within the experimental window, which is limited by the OD stretch vibrational lifetime.
View details for DOI 10.1063/1.3532542
View details for Web of Science ID 000287095500059
View details for PubMedID 21303143
- Water Dynamics in Small AOT Reverse Micelles in Two Solvents: 2D IR Vibrational Echoes with 2D Background Subtraction J. Chem. Phys. 2011; 134 (054512)
- Time-Dependent 5th Order Bands in Nominally 3rd Order 2D IR Vibrational Echo Spectra J. Phys. Chem. A 2011; 115: 9714-9723
- The Influence of Histidine Tag Attachment on Protein Dynamics Biochemistry 2011; 50: 5799-5805
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Conformational Switching between Protein Substates Studied with 2D IR Vibrational Echo Spectroscopy and Molecular Dynamics Simulations
JOURNAL OF PHYSICAL CHEMISTRY B
2010; 114 (51): 17187-17193
Abstract
Myoglobin is an important protein for the study of structure and dynamics. Three conformational substates have been identified for the carbonmonoxy form of myoglobin (MbCO). These are manifested as distinct peaks in the IR absorption spectrum of the CO stretching mode. Ultrafast 2D IR vibrational echo chemical exchange experiments are used to observed switching between two of these substates, A(1) and A(3), on a time scale of <100 ps for two mutants of wild-type Mb. The two mutants are a single mutation of Mb, L29I, and a double mutation, T67R/S92D. Molecular dynamics (MD) simulations are used to model the structural differences between the substates of the two MbCO mutants. The MD simulations are also employed to examine the substate switching in the two mutants as a test of the ability of MD simulations to predict protein dynamics correctly for a system in which there is a well-defined transition over a significant potential barrier between two substates. For one mutant, L29I, the simulations show that translation of the His64 backbone may differentiate the two substates. The simulations accurately reproduce the experimentally observed interconversion time for the L29I mutant. However, MD simulations exploring the same His64 backbone coordinate fail to display substate interconversion for the other mutant, T67R/S92D, thus pointing to the likely complexity of the underlying protein interactions. We anticipate that understanding conformational dynamics in MbCO via ultrafast 2D IR vibrational echo chemical exchange experiments can help to elucidate fast conformational switching processes in other proteins.
View details for DOI 10.1021/jp109203b
View details for Web of Science ID 000285560100022
View details for PubMedID 21128650
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Dynamics of a Myoglobin Mutant Enzyme: 2D IR Vibrational Echo Experiments and Simulations
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2010; 132 (51): 18367-18376
Abstract
Myoglobin (Mb) double mutant T67R/S92D displays peroxidase enzymatic activity in contrast to the wild type protein. The CO adduct of T67R/S92D shows two CO absorption bands corresponding to the A(1) and A(3) substates. The equilibrium protein dynamics for the two distinct substates of the Mb double mutant are investigated by using two-dimensional infrared (2D IR) vibrational echo spectroscopy and molecular dynamics (MD) simulations. The time-dependent changes in the 2D IR vibrational echo line shapes for both of the substates are analyzed using the center line slope (CLS) method to obtain the frequency-frequency correlation function (FFCF). The results for the double mutant are compared to those from the wild type Mb. The experimentally determined FFCF is compared to the FFCF obtained from molecular dynamics simulations, thereby testing the capacity of a force field to determine the amplitudes and time scales of protein structural fluctuations on fast time scales. The results provide insights into the nature of the energy landscape around the free energy minimum of the folded protein structure.
View details for DOI 10.1021/ja108491t
View details for Web of Science ID 000285818700056
View details for PubMedID 21142083
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Room Temperature Ionic Liquid-Lithium Salt Mixtures: Optical Kerr Effect Dynamical Measurements
JOURNAL OF PHYSICAL CHEMISTRY B
2010; 114 (25): 8350-8356
Abstract
The addition of lithium salts to ionic liquids causes an increase in viscosity and a decrease in ionic mobility that hinders their possible application as an alternative solvent in lithium ion batteries. Optically heterodyne-detected optical Kerr effect spectroscopy was used to study the change in dynamics, principally orientational relaxation, caused by the addition of lithium bis(trifluoromethylsulfonyl)imide to the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Over the time scales studied (1 ps-16 ns) for the pure ionic liquid, two temperature-independent power laws were observed: the intermediate power law (1 ps to approximately 1 ns), followed by the von Schweidler power law. The von Schweidler power law is followed by the final complete exponential relaxation, which is highly sensitive to temperature. The lithium salt concentration, however, was found to affect both power laws, and a discontinuity could be found in the trend observed for the intermediate power law when the concentration (mole fraction) of lithium salt is close to chi(LiTf(2)N) = 0.2. A mode coupling theory (MCT) schematic model was also used to fit the data for both the pure ionic liquid and the different salt concentration mixtures. It was found that dynamics in both types of liquids are described very well by MCT.
View details for DOI 10.1021/jp103810r
View details for Web of Science ID 000278982200008
View details for PubMedID 20527943
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Theory of interfacial orientational relaxation spectroscopic observables
JOURNAL OF CHEMICAL PHYSICS
2010; 132 (24)
Abstract
The orientational correlation functions measured in the time-resolved second-harmonic generation (TRSHG) and time-resolved sum-frequency generation (TRSFG) experiments are derived. In the laboratory coordinate system, the Y(l) (m)(Omega(lab)(t))Y(2) (m)(Omega(lab)(0)) (l=1,3 and m=0,2) correlation functions, where the Y(l) (m) are spherical harmonics, describe the orientational relaxation observables of molecules at interfaces. A wobbling-in-a-cone model is used to evaluate the correlation functions. The theory demonstrates that the orientational relaxation diffusion constant is not directly obtained from an experimental decay time in contrast to the situation for a bulk liquid. Model calculations of the correlation functions are presented to demonstrate how the diffusion constant and cone half-angle affect the time-dependence of the signals in TRSHG and TRSFG experiments. Calculations for the TRSHG experiments on Coumarin C314 molecules at air-water and air-water-surfactant interfaces are presented and used to examine the implications of published experimental results for these systems.
View details for DOI 10.1063/1.3442446
View details for Web of Science ID 000279740200041
View details for PubMedID 20590210
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Orientational and Translational Dynamics of Polyether/Water Solutions
JOURNAL OF PHYSICAL CHEMISTRY B
2010; 114 (16): 5350-5358
Abstract
Optical heterodyne-detected optical Kerr effect (OHD-OKE) experiments and pulsed field-gradient spin-echo NMR (PFGSE-NMR) experiments were performed to measure the rotational and translational diffusion constants of a polyether, tetraethylene glycol dimethyl ether (TEGDE), in binary mixtures with water over concentrations ranging from pure TEGDE to approaching infinite dilution. In addition, hydrodynamic calculations of the rotational and translational diffusion constants for several rigid TEGDE conformations in the neat liquid and in the infinitely dilute solution were performed to supplement the experimental data. The rotational relaxation data follow the Debye-Stokes-Einstein (DSE) equation within experimental error over the entire water concentration range. The agreement with the DSE equation indicates that there is no significant structural change of the polyether as the water content is changed. In contrast to the rotational dynamics, the translational diffusion data show a distinct deviation from Stokes-Einstein (SE) behavior. As the water content of the mixture is reduced, the translational diffusion rate decreases less rapidly than the increase in viscosity alone predicts until the water/TEGDE mole ratio of 7:1 is reached. Upon further reduction of water content, the translational diffusion tracks the viscosity. Comparison of the translational data with the rotational data and the hydrodynamic computations shows that the translational dynamics cannot be explained by a molecular shape change and that the low water fraction solutions are the ones that deviate from hydrodynamic behavior. A conjecture is presented as a possible explanation for the different behaviors of the rotational and translational dynamics.
View details for DOI 10.1021/jp101369e
View details for Web of Science ID 000276889100018
View details for PubMedID 20373773
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Water and proton dynamics in fuel cell membranes
AMER CHEMICAL SOC. 2010
View details for Web of Science ID 000208189304289
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Dynamics in Organic Ionic Liquids in Distinct Regions Using Charged and Uncharged Orientational Relaxation Probes
JOURNAL OF PHYSICAL CHEMISTRY B
2010; 114 (8): 2840-2845
Abstract
The temperature-dependent fluorescence anisotropy decay (orientational relaxation) of perylene and sodium 8-methoxypyrene-1,3,6-sulfonate (MPTS) were measured in a series of 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (alkyl = ethyl, butyl, hexyl, octyl) organic room temperature ionic liquids (RTIL). The two fluorescent probe molecules display markedly different rotational dynamics when analyzed using Stokes-Einstein-Debye theory, demonstrating that they are located in distinct environments within the RTILs and have very different interactions with their surroundings. Perylene rotates with subslip behavior, becoming increasingly subslip as the length of ionic liquid alkyl chain is increased. The dynamics approach those of perylene in an organic oil. In contrast, MPTS shows superstick behavior, likely reflecting very strong coordination with the RTIL cations. These results are consistent with different elements of rotational friction within the ionic liquid structure, which are available to solutes depending on their chemical functionality.
View details for DOI 10.1021/jp911123v
View details for Web of Science ID 000274842600036
View details for PubMedID 20136068
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Hydrogen Bond Migration between Molecular Sites Observed with Ultrafast 2D IR Chemical Exchange Spectroscopy
JOURNAL OF PHYSICAL CHEMISTRY B
2010; 114 (7): 2383-2389
Abstract
Hydrogen-bonded complexes between phenol and phenylacetylene are studied using ultrafast two-dimensional infrared (2D IR) chemical exchange spectroscopy. Phenylacetylene has two possible pi hydrogen bonding acceptor sites (phenyl or acetylene) that compete for hydrogen bond donors in solution at room temperature. The OD stretch frequency of deuterated phenol is sensitive to which acceptor site it is bound. The appearance of off-diagonal peaks between the two vibrational frequencies in the 2D IR spectrum reports on the exchange process between the two competitive hydrogen-bonding sites of phenol-phenylacetylene complexes in the neat phenylacetylene solvent. The chemical exchange process occurs in approximately 5 ps and is assigned to direct hydrogen bond migration along the phenylacetylene molecule. Other nonmigration mechanisms are ruled out by performing 2D IR experiments on phenol dissolved in the phenylacetylene/carbon tetrachloride mixed solvent. The observation of direct hydrogen bond migration can have implications for macromolecular systems.
View details for DOI 10.1021/jp911452z
View details for Web of Science ID 000274578500008
View details for PubMedID 20121275
- Absolutely Small - How Quantum Theory Explains Our Everyday World AMACOM, New York. 2010
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The Contribution of Fast Protein Dynamics to Cytochrome P450 Molecular Recognition Characterized by Two-Dimensional Infrared Spectroscopy
CELL PRESS. 2010: 234A
View details for DOI 10.1016/j.bpj.2009.12.1270
View details for Web of Science ID 000208762002170
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Ultrafast Dynamics of Thermal Denaturation of Cytochrome-C with Two Dimensional Infrared Spectroscopy
CELL PRESS. 2010: 441A
View details for DOI 10.1016/j.bpj.2009.12.2398
View details for Web of Science ID 000208762004207
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Ultrafast Interconversion between Protein Conformational Substates: Directly Observed by 2D IR Vibrational Echo Spectroscopy
CELL PRESS. 2010: 743A
View details for DOI 10.1016/j.bpj.2009.12.4073
View details for Web of Science ID 000208762007206
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Solvent Control of the Soft Angular Potential in Hydroxyl-pi Hydrogen Bonds: Inertial Orientational Dynamics
JOURNAL OF PHYSICAL CHEMISTRY B
2009; 113 (40): 13300-13307
Abstract
Ultrafast polarization and wavelength selective IR pump-probe spectroscopy is used to measure the inertial and long time orientational dynamics of pi-hydrogen bonding complexes. Inertial orientational relaxation is sensitive to the angular potential associated with the hydrogen bond. The complexes studied are composed of phenol-OD (hydroxyl hydrogen replaced by deuterium) and various pi-base solvents with different electron donating or withdrawing substituents (chlorobenzene, bromobenzene, benzene, toluene, p-xylene, mesitylene, 1-pentyne). The different substituents provide experimental control of the hydrogen bond strength. The inertial orientational relaxation of the complexes, measured at the center frequency of each line, is independent of the hydrogen bond strength, demonstrating the insensitivity of the OD inertial dynamics, and therefore the H-bond angular potential, to the hydrogen bond strength. OD stretch absorption bands are inhomogeneously broadened through interactions with the solvent. The hydrogen bonding complexes all have similar wavelength dependent inertial orientational relaxation across their inhomogeneously broadened OD stretch absorption lines. The wavelength dependence of the inertial reorientation across each line arises because of a correlation between local solvent structure and the angular potential. These two results imply that local solvent structure acts as the controlling influence in determining the extent of inertial orientational relaxation, and therefore the angular potential, and that variation in the pi-hydrogen bond strength is of secondary importance.
View details for DOI 10.1021/jp907616x
View details for Web of Science ID 000270363500023
View details for PubMedID 19746960
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Water dynamics at neutral and ionic interfaces
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2009; 106 (36): 15243-15248
Abstract
The orientational dynamics of water at a neutral surfactant reverse micelle interface are measured with ultrafast infrared spectroscopy of the hydroxyl stretch, and the results are compared to orientational relaxation of water interacting with an ionic interface. The comparison provides insights into the influence of a neutral vs. ionic interface on hydrogen bond dynamics. Measurements are made and analyzed for large nonionic surfactant Igepal CO-520reverse micelles (water nanopool with a 9-nm diameter). The results are compared with those from a previous study of reverse micelles of the same size formed with the ionic surfactant Aerosol-OT (AOT). The results demonstrate that the orientational relaxation times for interfacial water molecules in the two types of reverse micelles are very similar (13 ps for Igepal and 18 ps for AOT) and are significantly slower than that of bulk water (2.6 ps). The comparison of water orientational relaxation at neutral and ionic interfaces shows that the presence of an interface plays the dominant role in determining the hydrogen bond dynamics, whereas the chemical nature of the interface plays a secondary role.
View details for DOI 10.1073/pnas.0907875106
View details for Web of Science ID 000269632400030
View details for PubMedID 19706895
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Water Dynamics in Salt Solutions Studied with Ultrafast Two-Dimensional Infrared (2D IR) Vibrational Echo Spectroscopy
ACCOUNTS OF CHEMICAL RESEARCH
2009; 42 (9): 1210-1219
Abstract
Water is ubiquitous in nature, but it exists as pure water infrequently. From the ocean to biology, water molecules interact with a wide variety of dissolved species. Many of these species are charged. In the ocean, water interacts with dissolved salts. In biological systems, water interacts with dissolved salts as well as charged amino acids, the zwitterionic head groups of membranes, and other biological groups that carry charges. Water plays a central role in a vast number of chemical processes because of its dynamic hydrogen-bond network. A water molecule can form up to four hydrogen bonds in an approximately tetrahedral arrangement. These hydrogen bonds are continually being broken, and new bonds are being formed on a picosecond time scale. The ability of the hydrogen-bond network of water to rapidly reconfigure enables water to accommodate and facilitate chemical processes. Therefore, the influence of charged species on water hydrogen-bond dynamics is important. Recent advances in ultrafast coherent infrared spectroscopy have greatly expanded our understanding of water dynamics. Two-dimensional infrared (2D IR) vibrational echo spectroscopy is providing new observables that yield direct information on the fast dynamics of molecules in their ground electronic state under thermal equilibrium conditions. The 2D IR vibrational echoes are akin to 2D nuclear magnetic resonance (NMR) but operate on time scales that are many orders of magnitude shorter. In a 2D IR vibrational echo experiment (see the Conspectus figure), three IR pulses are tuned to the vibrational frequency of interest, which in this case is the frequency of the hydroxyl stretching mode of water. The first two pulses "label" the initial molecular structures by their vibrational frequencies. The system evolves between pulses two and three, and the third pulse stimulates the emission of the vibrational echo pulse, which is the signal. The vibrational echo pulse is heterodyne, detected by combining it with another pulse, the local oscillator. Heterodyne detection provides phase and amplitude information, which are both necessary to perform the two Fourier transforms that take the data from the time domain to a two-dimensional frequency domain spectrum. The time dependence of a series of 2D IR vibrational echo spectra provides direct information on system dynamics. Here, we use two types of 2D IR vibrational echo experiments to examine the influence that charged species have on water hydrogen-bond dynamics. Solutions of NaBr and NaBF(4) are studied. The NaBr solutions are studied as a function of the concentration using vibrational echo measurements of spectral diffusion and polarization-selective IR pump-probe measurements of orientational relaxation. Both types of measurements show the slowing of hydrogen-bond network structural evolution with an increasing salt concentration. NaBF(4) is studied using vibrational echo chemical-exchange spectroscopy. In these experiments, it is possible to directly observe the chemical exchange of water molecules switching their hydrogen-bond partners between BF(4)(-) and other water molecules. The results demonstrate that water interacting with ions has slower hydrogen-bond dynamics than pure water, but the slowing is a factor of 3 or 4 rather than orders of magnitude.
View details for DOI 10.1021/ar900043h
View details for Web of Science ID 000269861400002
View details for PubMedID 19378969
View details for PubMedCentralID PMC2745496
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Proton Transfer and Proton Concentrations in Protonated Nafion Fuel Cell Membranes
JOURNAL OF PHYSICAL CHEMISTRY B
2009; 113 (30): 10210-10221
Abstract
Proton transfer in protonated Nafion fuel cell membranes is studied using several pyrene derivative photoacids. Proton transfer in the center of the Nafion nanoscopic water channels is probed with the highly charged photoacid 8-hydroxypyrene-1,3,6-trisulfonate (HPTS). At high hydration levels, both the time-integrated fluorescence spectrum and the fluorescence kinetics of HPTS permit the determination of hydronium concentration of the interior of the water pools in Nafion. The proton transfer kinetics of HPTS in protonated Nafion at maximum hydration are identical to the kinetics displayed by HPTS in a 0.5 M HCl solution. The hydronium concentration near the water interface in Nafion is estimated with rhodamine-6G to be 1.4 M. Excited state proton transfer (ESPT) is followed in the nonpolar side chain regions of Nafion with the photoacid 8-hydroxy-N,N,N',N',N'',N''-hexamethylpyrene-1,3,6-trisulfonamide (HPTA). Excited state proton transfer of HPTA is possible in protonated Nafion only at the highest hydration level due to a relatively high local pH.
View details for DOI 10.1021/jp9036777
View details for Web of Science ID 000268231000025
View details for PubMedID 19572659
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Water dynamics in large and small reverse micelles: From two ensembles to collective behavior
JOURNAL OF CHEMICAL PHYSICS
2009; 131 (1)
Abstract
The dynamics of water in Aerosol-OT reverse micelles are investigated with ultrafast infrared spectroscopy of the hydroxyl stretch. In large reverse micelles, the dynamics of water are separable into two ensembles: slow interfacial water and bulklike core water. As the reverse micelle size decreases, the slowing effect of the interface and the collective nature of water reorientation begin to slow the dynamics of the core water molecules. In the smallest reverse micelles, these effects dominate and all water molecules have the same long time reorientational dynamics. To understand and characterize the transition in the water dynamics from two ensembles to collective reorientation, polarization and frequency selective infrared pump-probe experiments are conducted on the complete range of reverse micelle sizes from a diameter of 1.6-20 nm. The crossover between two ensemble and collective reorientation occurs near a reverse micelle diameter of 4 nm. Below this size, the small number of confined water molecules and structural changes in the reverse micelle interface leads to homogeneous long time reorientation.
View details for DOI 10.1063/1.3159779
View details for Web of Science ID 000267799100026
View details for PubMedID 19586114
View details for PubMedCentralID PMC2721765
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Water Dynamics at the Interface in AOT Reverse Micelles
JOURNAL OF PHYSICAL CHEMISTRY B
2009; 113 (25): 8560-8568
Abstract
The orientational dynamics of water molecules at the interface in large Aerosol-OT (AOT) reverse micelles are investigated using ultrafast infrared spectroscopy of the OD stretch of dilute HOD in H(2)O. In large reverse micelles ( approximately 9 nm diameter or larger), a significant amount of the nanoscopic water is sufficiently distant from the interface that it displays bulk-like characteristics. However, some water molecules interact with the interface and have vibrational absorption spectra and dynamics distinct from bulk water. The different characteristics of these interfacial waters allow their contribution to the data to be separated from the bulk. The infrared absorption spectrum of the OD stretch is analyzed to show that the interfacial water molecules have a spectrum that peaks near 2565 cm(-1) in contrast to 2509 cm(-1) in bulk water. A two-component model is developed that simultaneously describes the population relaxation and orientational dynamics of the OD stretch in the spectral region of the interfacial water. The model provides a consistent description of both observables and demonstrates that water interacting with the interface has slower vibrational relaxation and orientational dynamics. The orientational relaxation of interfacial water molecules occurs in 18 +/- 3 ps, in contrast to the bulk water value of 2.6 ps.
View details for DOI 10.1021/jp902004r
View details for Web of Science ID 000267205600023
View details for PubMedID 19485407
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Geometry and Nanolength Scales versus Interface Interactions: Water Dynamics in AOT Lamellar Structures and Reverse Micelles
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2009; 131 (23): 8318-8328
Abstract
To determine the relative importance of the confining geometry and nanoscopic length scale versus water/interface interactions, the dynamic interactions between water and interfaces are studied with ultrafast infrared spectroscopy. Aerosol OT (AOT) is a surfactant that can form two-dimensional lamellar structures with known water layer thickness as well as well-defined monodispersed spherical reverse micelles of known water nanopool diameter. Lamellar structures and reverse micelles are compared based on two criteria: surface-to-surface dimensions to study the effect of confining length scales, and water-to-surfactant ratio to study water/interface interactions. We show that the water-to-surfactant ratio is the dominant factor governing the nature of water interacting with an interface, not the characteristic nanoscopic distance. The detailed structure of the interface and the specific interactions between water and the interface also play a critical role in the fraction of water molecules influenced by the surface. A two-component model in which water is separated into bulk-like water in the center of the lamellar structure or reverse micelle and interfacial water is used to quantitatively extract the interfacial dynamics. A greater number of perturbed water molecules are present in the lamellar structures as compared to the reverse micelles due to the larger surface area per AOT molecule and the greater penetration of water molecules past the sulfonate head groups in the lamellar structures.
View details for DOI 10.1021/ja901950b
View details for Web of Science ID 000267623100054
View details for PubMedID 19449867
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Water Dynamics and Interactions in Water-Polyether Binary Mixtures
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2009; 131 (15): 5530-5539
Abstract
Poly(ethylene) oxide (PEO) is a technologically important polymer with a wide range of applications including ion-exchange membranes, protein crystallization, and medical devices. PEO's versatility arises from its special interactions with water. Water molecules may form hydrogen-bond bridges between the ether oxygens of the backbone. While steady-state measurements and theoretical studies of PEO's interactions with water abound, experiments measuring dynamic observables are quite sparse. A major question is the nature of the interactions of water with the ether oxygens as opposed to the highly hydrophilic PEO terminal hydroxyls. Here, we examine a wide range of mixtures of water and tetraethylene glycol dimethyl ether (TEGDE), a methyl-terminated derivative of PEO with 4 repeat units (5 ether oxygens), using ultrafast infrared polarization selective pump-probe measurements on water's hydroxyl stretching mode to determine vibrational relaxation and orientational relaxation dynamics. The experiments focus on the dynamical interactions of water with the ether backbone because TEGDE does not have the PEO terminal hydroxyls. The experiments observe two distinct subensembles of water molecules: those that are hydrogen bonded to other waters and those that are associated with TEGDE molecules. The water orientational relaxation has a fast component of a few picoseconds (water-like) followed by much slower decay of approximately 20 ps (TEGDE associated). The two decay times vary only mildly with the water concentration. The two subensembles are evident even in very low water content samples, indicating pooling of water molecules. Structural change as water content is lowered through either conformational changes in the backbone or increasing hydrophobic interactions is discussed.
View details for DOI 10.1021/ja809261d
View details for Web of Science ID 000265268100036
View details for PubMedID 19323522
View details for PubMedCentralID PMC2889155
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PHYS 430-Enzyme dynamical changes upon substrate binding and structural interconversions measured with ultrafast 2-D IR vibrational echo spectroscopy
AMER CHEMICAL SOC. 2009
View details for Web of Science ID 000207857808011
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Ion-water hydrogen-bond switching observed with 2D IR vibrational echo chemical exchange spectroscopy
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2009; 106 (2): 375-380
Abstract
The exchange of water hydroxyl hydrogen bonds between anions and water oxygens is observed directly with ultrafast 2D IR vibrational echo chemical exchange spectroscopy (CES). The OD hydroxyl stretch of dilute HOD in H(2)O in concentrated (5.5 M) aqueous solutions of sodium tetrafluoroborate (NaBF(4)) displays a spectrum with a broad water-like band (hydroxyl bound to water oxygen) and a resolved, blue shifted band (hydroxyl bound to BF(4)(-)). At short time (200 fs), the 2D IR vibrational echo spectrum has 4 peaks, 2 on the diagonal and 2 off-diagonal. The 2 diagonal peaks are the 0-1 transitions of the water-like band and the hydroxyl-anion band. Vibrational echo emissions at the 1-2 transition frequencies give rise to 2 off-diagonal peaks. On a picosecond time scale, additional off-diagonal peaks grow in. These new peaks arise from chemical exchange between water hydroxyls bound to anions and hydroxyls bound to water oxygens. The growth of the chemical exchange peaks yields the time dependence of anion-water hydroxyl hydrogen bond switching under thermal equilibrium conditions as T(aw) = 7 +/- 1 ps. Pump-probe measurements of the orientational relaxation rates and vibrational lifetimes are used in the CES data analysis. The pump-probe measurements are shown to have the correct functional form for a system undergoing exchange.
View details for DOI 10.1073/pnas.0811489106
View details for Web of Science ID 000262804000006
View details for PubMedID 19106293
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Dynamics of Liquids, Molecules, and Proteins Measured with Ultrafast 2D IR Vibrational Echo Chemical Exchange Spectroscopy
ANNUAL REVIEW OF PHYSICAL CHEMISTRY
2009; 60: 21-38
Abstract
A wide variety of molecular systems undergo fast structural changes under thermal equilibrium conditions. Such transformations are involved in a vast array of chemical problems. Experimentally measuring equilibrium dynamics is a challenging problem that is at the forefront of chemical research. This review describes ultrafast 2D IR vibrational echo chemical exchange experiments and applies them to several types of molecular systems. The formation and dissociation of organic solute-solvent complexes are directly observed. The dissociation times of 13 complexes, ranging from 4 ps to 140 ps, are shown to obey a relationship that depends on the complex's formation enthalpy. The rate of rotational gauche-trans isomerization around a carbon-carbon single bond is determined for a substituted ethane at room temperature in a low viscosity solvent. The results are used to obtain an approximate isomerization rate for ethane. Finally, the time dependence of a well-defined single structural transformation of a protein is measured.
View details for DOI 10.1146/annurev-physchem-073108-112712
View details for Web of Science ID 000268071200003
View details for PubMedID 18851709
- Water Dynamics at Neutral and Ionic Interfaces in Reverse Micelles 2009: 15243–48
- Ultrafast 2D-IR Vibration Echo Spectroscopy of Proteins Biological and Biomedical Infrared Spectroscopy edited by Barth, A., Harris, P. I. IOS Press BV, Amsterdam. 2009
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Solute-Solvent Complex Switching Dynamics of Chloroform between Acetone and Dimethylsulfoxide-Two-Dimensional IR Chemical Exchange Spectroscopy
JOURNAL OF PHYSICAL CHEMISTRY B
2008; 112 (44): 13906-13915
Abstract
Hydrogen bonds formed between C-H and various hydrogen bond acceptors play important roles in the structure of proteins and organic crystals, and the mechanisms of C-H bond cleavage reactions. Chloroform, a C-H hydrogen bond donor, can form weak hydrogen-bonded complexes with acetone and with dimethylsulfoxide (DMSO). When chloroform is dissolved in a mixed solvent consisting of acetone and DMSO, both types of hydrogen-bonded complexes exist. The two complexes, chloroform-acetone and chloroform-DMSO, are in equilibrium, and they rapidly interconvert by chloroform exchanging hydrogen bond acceptors. This fast hydrogen bond acceptor substitution reaction is probed using ultrafast two-dimensional infrared (2D-IR) vibrational echo chemical exchange spectroscopy. Deuterated chloroform is used in the experiments, and the 2D-IR spectrum of the C-D stretching mode is measured. The chemical exchange of the chloroform hydrogen bonding partners is tracked by observing the time-dependent growth of off-diagonal peaks in the 2D-IR spectra. The measured substitution rate is 1/30 ps for an acetone molecule to replace a DMSO molecule in a chloroform-DMSO complex and 1/45 ps for a DMSO molecule to replace an acetone molecule in a chloroform-acetone complex. Free chloroform exists in the mixed solvent, and it acts as a reactive intermediate in the substitution reaction, analogous to a SN1 type reaction. From the measured rates and the equilibrium concentrations of acetone and DMSO, the dissociation rates for the chloroform-DMSO and chloroform-acetone complexes are found to be 1/24 ps and 1/5.5 ps, respectively. The difference between the measured rate for the complete substitution reaction and the rate for complex dissociation corresponds to the diffusion limited rate. The estimated diffusion limited rate agrees well with the result from a Smoluchowski treatment of diffusive reactions.
View details for DOI 10.1021/jp806035w
View details for Web of Science ID 000260533100027
View details for PubMedID 18855462
View details for PubMedCentralID PMC2646412
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Water at the surfaces of aligned phospholipid multibilayer model membranes probed with ultrafast vibrational spectroscopy
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2008; 130 (42): 13927-13937
Abstract
The dynamics of water at the surface of artificial membranes composed of aligned multibilayers of the phospholipid dilauroyl phosphatidylcholine (DLPC) are probed with ultrafast polarization selective vibrational pump-probe spectroscopy. The experiments are performed at various hydration levels, x = 2 - 16 water molecules per lipid at 37 degrees C. The water molecules are approximately 1 nm above or below the membrane surface. The experiments are conducted on the OD stretching mode of dilute HOD in H 2O to eliminate vibrational excitation transfer. The FT-IR absorption spectra of the OD stretch in the DLPC bilayer system at low hydration levels shows a red-shift in frequency relative to bulk water, which is in contrast to the blue-shift often observed in systems such as water nanopools in reverse micelles. The spectra for x = 4 - 16 can be reproduced by a superposition of the spectra for x = 2 and bulk water. IR Pump-probe measurements reveal that the vibrational population decays (lifetimes) become longer as the hydration level is decreased. The population decays are fit well by biexponential functions. The population decays, measured as a function of the OD stretch frequency, suggest the existence of two major types of water molecules in the interfacial region of the lipid bilayers. One component may be a clathrate-like water cluster near the hydrophobic choline group and the other may be related to the hydration water molecules mainly associated with the phosphate group. As the hydration level increases, the vibrational lifetimes of these two components decrease, suggesting a continuous evolution of the hydration structures in the two components associated with the swelling of the bilayers. The agreement of the magnitudes of the two components obtained from IR spectra with those from vibrational lifetime measurements further supports the two-component model. The vibrational population decay fitting also gives an estimation of the number of phosphate-associated water molecules and choline-associated water molecules, which range from 1 to 4 and 1 to 12, respectively, as x increases from 2 to 16. Time-dependent anisotropy measurements yield the rate of orientational relaxation as a function of x. The anisotropy decay is biexponential. The fast component is almost independent of x, and is interpreted as small orientational fluctuations that occur without hydrogen-bond rearrangement. The slower component becomes very long as the hydration level decreases. This component is a measure of the rate of complete orientational randomization, which requires H-bond rearrangement and is discussed in terms of a jump reorientation model.
View details for DOI 10.1021/ja803252y
View details for Web of Science ID 000260047700037
View details for PubMedID 18823116
View details for PubMedCentralID PMC2648527
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Charge Transfer in Photoacids Observed by Stark Spectroscopy
JOURNAL OF PHYSICAL CHEMISTRY A
2008; 112 (41): 10244-10249
Abstract
The charge redistribution upon photoexcitation is investigated for a series of pyrene photoacids to better understand the driving force behind excited-state proton-transfer processes. The changes in electric dipole for the lowest two electronic transitions ( (1)L b and (1)L a) are measured by Stark spectroscopy, and the magnitudes of charge transfer of the protonated and deprotonated states are compared. For neutral photoacids studied here, the results show that the amount of charge transfer depends more upon the electronic state that is excited than the protonation state. Transitions from the ground state to the (1)L b state result in a much smaller change in electric dipole than transitions to the (1)L a state. Conversely, for the cationic (ammonium) photoacid studied, photoexcitation of a particular electronic state results in much smaller charge transfer for the protonated state than for the deprotonated state.
View details for DOI 10.1021/jp805189u
View details for Web of Science ID 000259943100022
View details for PubMedID 18798602
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Solute-solvent complex kinetics and thermodynamics probed by 2D-IR vibrational echo chemical exchange Spectroscopy
JOURNAL OF PHYSICAL CHEMISTRY B
2008; 112 (33): 10221-10227
Abstract
The formation and dissociation kinetics of a series of triethylsilanol/solvent weakly hydrogen bonding complexes with enthalpies of formation ranging from -1.4 to -3.3 kcal/mol are measured with ultrafast two-dimensional infrared (2D IR) chemical exchange spectroscopy in liquid solutions at room temperature. The correlation between the complex enthalpies of formation and dissociation rate constants can be expressed with an equation similar to the Arrhenius equation. The experimental results are in accord with previous observations on eight phenol/solvent complexes with enthalpies of formation from -0.6 to -2.5 kcal/mol. It was found that the inverse of the solute-solvent complex dissociation rate constant is linearly related to exp(-DeltaH0/RT) where DeltaH0 is the complex enthalpy of formation. It is shown here, that the triethylsilanol-solvent complexes obey the same relationship with the identical proportionality constant, that is, all 13 points, five silanol complexes and eight phenol complexes, fall on the same line. In addition, features of 2D IR chemical exchange spectra at long reaction times (spectral diffusion complete) are explicated using the triethylsilanol systems. It is shown that the off-diagonal chemical exchange peaks have shapes that are a combination (outer product) of the absorption line shapes of the species that give rise to the diagonal peaks.
View details for DOI 10.1021/jp804087v
View details for Web of Science ID 000258460400022
View details for PubMedID 18665635
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PHYS 286-Dynamics of native and unfolded cytochrome c using 2-D-IR vibrational echo spectroscopy
236th National Meeting of the American-Chemical-Society
AMER CHEMICAL SOC. 2008
View details for Web of Science ID 000270256307032
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PHYS 110-Water dynamics and the influence of nanoconfinement
AMER CHEMICAL SOC. 2008
View details for Web of Science ID 000270256307019
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Native and unfolded cytochrome c-comparison of dynamics using 2D-IR vibrational echo spectroscopy
JOURNAL OF PHYSICAL CHEMISTRY B
2008; 112 (32): 10054-10063
Abstract
Unfolded vs native CO-coordinated horse heart cytochrome c (h-cyt c) and a heme axial methionine mutant cyt c552 from Hydrogenobacter thermophilus ( Ht-M61A) are studied by IR absorption spectroscopy and ultrafast 2D-IR vibrational echo spectroscopy of the CO stretching mode. The unfolding is induced by guanidinium hydrochloride (GuHCl). The CO IR absorption spectra for both h-cyt c and Ht-M61A shift to the red as the GuHCl concentration is increased through the concentration region over which unfolding occurs. The spectra for the unfolded state are substantially broader than the spectra for the native proteins. A plot of the CO peak position vs GuHCl concentration produces a sigmoidal curve that overlays the concentration-dependent circular dichroism (CD) data of the CO-coordinated forms of both Ht-M61A and h-cyt c within experimental error. The coincidence of the CO peak shift curve with the CD curves demonstrates that the CO vibrational frequency is sensitive to the structural changes induced by the denaturant. 2D-IR vibrational echo experiments are performed on native Ht-M61A and on the protein in low- and high-concentration GuHCl solutions. The 2D-IR vibrational echo is sensitive to the global protein structural dynamics on time scales from subpicosecond to greater than 100 ps through the change in the shape of the 2D spectrum with time (spectral diffusion). At the high GuHCl concentration (5.1 M), at which Ht-M61A is essentially fully denatured as judged by CD, a very large reduction in dynamics is observed compared to the native protein within the approximately 100 ps time window of the experiment. The results suggest the denatured protein may be in a glassy-like state involving hydrophobic collapse around the heme.
View details for DOI 10.1021/jp802246h
View details for Web of Science ID 000258290000060
View details for PubMedID 18646797
View details for PubMedCentralID PMC2671645
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Direct observation of fast protein conformational switching
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2008; 105 (25): 8619-8624
Abstract
Folded proteins can exist in multiple conformational substates. Each substate reflects a local minimum on the free-energy landscape with a distinct structure. By using ultrafast 2D-IR vibrational echo chemical-exchange spectroscopy, conformational switching between two well defined substates of a myoglobin mutant is observed on the approximately 50-ps time scale. The conformational dynamics are directly measured through the growth of cross peaks in the 2D-IR spectra of CO bound to the heme active site. The conformational switching involves motion of the distal histidine/E helix that changes the location of the imidazole side group of the histidine. The exchange between substates changes the frequency of the CO, which is detected by the time dependence of the 2D-IR vibrational echo spectrum. These results demonstrate that interconversion between protein conformational substates can occur on very fast time scales. The implications for larger structural changes that occur on much longer time scales are discussed.
View details for DOI 10.1073/pnas.0803764105
View details for Web of Science ID 000257185700026
View details for PubMedID 18562286
View details for PubMedCentralID PMC2438383
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Taking apart the two-dimensional infrared vibrational echo spectra: More information and elimination of distortions
JOURNAL OF CHEMICAL PHYSICS
2008; 128 (20)
Abstract
Ultrafast two-dimensional infrared (2D-IR) vibrational echo spectroscopy can probe the fast structural evolution of molecular systems under thermal equilibrium conditions. Structural dynamics are tracked by observing the time evolution of the 2D-IR spectrum, which is caused by frequency fluctuations of vibrational mode(s) excited during the experiment. However, there are a variety of effects that can produce line shape distortions and prevent the correct determination of the frequency-frequency correlation function (FFCF), which describes the frequency fluctuations and connects the experimental observables to a molecular level depiction of dynamics. In addition, it can be useful to analyze different parts of the 2D spectrum to determine if dynamics are different for subensembles of molecules that have different initial absorption frequencies in the inhomogeneously broadened absorption line. Here, an important extension to a theoretical method for extraction of the FFCF from 2D-IR spectra is described. The experimental observable is the center line slope (CLSomega(m)) of the 2D-IR spectrum. The CLSomega(m) is obtained by taking slices through the 2D spectrum parallel to the detection frequency axis (omega(m)). Each slice is a spectrum. The slope of the line connecting the frequencies of the maxima of the sliced spectra is the CLSomega(m). The change in slope of the CLSomega(m) as a function of time is directly related to the FFCF and can be used to obtain the complete FFCF. CLSomega(m) is immune to line shape distortions caused by destructive interference between bands arising from vibrational echo emission, from the 0-1 vibrational transition (positive), and from the 1-2 vibrational transition (negative) in the 2D-IR spectrum. The immunity to the destructive interference enables the CLSomega(m) method to compare different parts of the bands as well as comparing the 0-1 and 1-2 bands. Also, line shape distortions caused by solvent background absorption and finite pulse durations do not affect the determination of the FFCF with the CLSomega(m) method. The CLSomega(m) can also provide information on the cross correlation between frequency fluctuations of the 0-1 and 1-2 vibrational transitions.
View details for DOI 10.1063/1.2927906
View details for Web of Science ID 000256304200031
View details for PubMedID 18513030
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Water dynamics - The effects of ions and nanoconfinement
JOURNAL OF PHYSICAL CHEMISTRY B
2008; 112 (17): 5279-5290
Abstract
Hydrogen bond dynamics of water in highly concentrated NaBr salt solutions and reverse micelles are studied using ultrafast 2D-IR vibrational echo spectroscopy and polarization-selective IR pump-probe experiments performed on the OD hydroxyl stretch of dilute HOD in H(2)O. The vibrational echo experiments measure spectral diffusion, and the pump-probe experiments measure orientational relaxation. Both experimental observables are directly related to the structural dynamics of water's hydrogen bond network. The measurements performed on NaBr solutions as a function of concentration show that the hydrogen bond dynamics slow as the NaBr concentration increases. The most pronounced change is in the longest time scale dynamics which are related to the global rearrangement of the hydrogen bond structure. Complete hydrogen bond network randomization slows by a factor of approximately 3 in approximately 6 M NaBr solution compared to that in bulk water. The hydrogen bond dynamics of water in nanoscopically confined environments are studied by encapsulating water molecules in ionic head group (AOT) and nonionic head group (Igepal CO 520) reverse micelles. Water dynamics in the nanopools of AOT reverse micelles are studied as a function of size by observing orientational relaxation. Orientational relaxation dynamics deviate significantly from bulk water when the size of the reverse micelles is smaller than several nm and become nonexponential and slower as the size of the reverse micelles decreases. In the smallest reverse micelles, orientational relaxation (hydrogen bond structural randomization) is almost 20 times slower than that in bulk water. To determine if the changes in dynamics from bulk water are caused by the influence of the ionic head groups of AOT or the nanoconfinement, the water dynamics in 4 nm nanopools in AOT reverse micelles (ionic) and Igepal reverse micelles (nonionic) are compared. It is found that the water orientational relaxation in the 4 nm diameter nanopools of the two types of reverse micelles is almost identical, which indicates that confinement by an interface to form a nanoscopic water pool is a primary factor governing the dynamics of nanoscopic water rather than the presence of charged groups at the interface.
View details for DOI 10.1021/jp7121856
View details for Web of Science ID 000255292300005
View details for PubMedID 18370431
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Water dynamics and proton transfer in Nafion fuel cell membranes
LANGMUIR
2008; 24 (8): 3690-3698
Abstract
The dynamics of water and its effect on proton transport kinetics in Nafion membranes are compared at several hydration levels. Nafion is the most widely used polyelectrolyte membrane in fuel cells. Ultrafast infrared spectroscopy of the O-D stretch of dilute HOD in H2O provides a probe of the local environment and hydrogen bond network dynamics of water confined in the hydrophilic regions of Nafion. The kinetics of proton transfer in Nafion are tracked by following the excited-state proton transfer and recombination kinetics of a molecular probe, pyranine (HPTS). The hydrophilic domains of Nafion grow with increased hydration, and the interfacial regions reorganize, leading to a changing local environment for water near the interface. Swelling is not uniform throughout the membrane, and heterogeneity is observed in the fluorescence anisotropy decays of the methoxy derivative of pyranine. Measurements of the time-dependent anisotropy of water in Nafion provide a direct probe of the hydrogen bond network dynamics. These dynamics, as well as the rate of proton transport over nanoscopic distances, are observed to slow significantly as the hydration level of the membrane decreases. The results provide insights into the influence of changes in the dynamics of water on the proton-transfer processes.
View details for DOI 10.1021/la703358a
View details for Web of Science ID 000254647400003
View details for PubMedID 18220436
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Water inertial reorientation: Hydrogen bond strength and the angular potential
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2008; 105 (14): 5295-5300
Abstract
The short-time orientational relaxation of water is studied by ultrafast infrared pump-probe spectroscopy of the hydroxyl stretching mode (OD of dilute HOD in H(2)O). The anisotropy decay displays a sharp drop at very short times caused by inertial orientational motion, followed by a much slower decay that fully randomizes the orientation. Investigation of temperatures from 1 degrees C to 65 degrees C shows that the amplitude of the inertial component (extent of inertial angular displacement) depends strongly on the stretching frequency of the OD oscillator at higher temperatures, although the slow component is frequency-independent. The inertial component becomes frequency-independent at low temperatures. At high temperatures there is a correlation between the amplitude of the inertial decay and the strength of the O-D O hydrogen bond, but at low temperatures the correlation disappears, showing that a single hydrogen bond (OD O) is no longer a significant determinant of the inertial angular motion. It is suggested that the loss of correlation at lower temperatures is caused by the increased importance of collective effects of the extended hydrogen bonding network. By using a new harmonic cone model, the experimentally measured amplitudes of the inertial decays yield estimates of the characteristic frequencies of the intermolecular angular potential for various strengths of hydrogen bonds. The frequencies are in the range of approximately 400 cm(-1). A comparison with recent molecular dynamics simulations employing the simple point charge-extended water model at room temperature shows that the simulations qualitatively reflect the correlation between the inertial decay and the OD stretching frequency.
View details for DOI 10.1073/pnas.0801554105
View details for Web of Science ID 000254893600004
View details for PubMedID 18381817
View details for PubMedCentralID PMC2291089
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Charge redistribution and photoacidity: Neutral versus cationic photoacids
JOURNAL OF CHEMICAL PHYSICS
2008; 128 (8)
Abstract
A series of pyrene photoacids is used to investigate excited-state proton transfer with time-dependent pump-probe spectroscopy. The deprotonation dynamics of a cationic photoacid, 8-aminopyrene-1,3,6-trisulfonic acid trisodium salt (APTS), shows single exponential dynamics( approximately 30 ps) in water. This is in contrast to what is observed for the neutral photoacids 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) and 8-hydroxy-N,N,N',N',N",N"-hexamethylpyrene-1,3,6-trisulfonamide, which display biexponential dynamics. For the cationic photoacid, the vast majority of the intramolecular charge redistribution does not occur in the protonated state. Instead, the charge redistribution, which is responsible for the photoacidity and the observed spectroscopic changes, occurs primarily following the excited-state proton transfer. The lack of charge redistribution prior to proton transfer causes APTS to display single exponential kinetics. In contrast, the dynamics for the neutral photoacids are multiexponential because major charge redistribution precedes proton transfer followed by additional charge redistribution that accompanies proton transfer. Previous studies of HPTS in water are discussed in terms of the results presented here.
View details for DOI 10.1063/1.2825297
View details for Web of Science ID 000254047200036
View details for PubMedID 18315062
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Disulfide bond influence on protein structural dynamics probed with 2D-IR vibrational echo spectroscopy
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2007; 104 (49): 19309-19314
Abstract
Intramolecular disulfide bonds are understood to play a role in regulating protein stability and activity. Because disulfide bonds covalently link different components of a protein, they influence protein structure. However, the effects of disulfide bonds on fast (subpicosecond to approximately 100 ps) protein equilibrium structural fluctuations have not been characterized experimentally. Here, ultrafast 2D-IR vibrational echo spectroscopy is used to examine the constraints an intramolecular disulfide bond places on the structural fluctuations of the protein neuroglobin (Ngb). Ngb is a globin family protein found in vertebrate brains that binds oxygen reversibly. Like myoglobin (Mb), Ngb has the classical globin fold and key residues around the heme are conserved. Furthermore, the heme-ligated CO vibrational spectra of Mb (Mb-CO) and Ngb (Ngb-CO) are virtually identical. However, in contrast to Mb, human Ngb has an intramolecular disulfide bond that affects its oxygen affinity and protein stability. By using 2D-IR vibrational echo spectroscopy, we investigated the equilibrium protein dynamics of Ngb-CO by observing the CO spectral diffusion (time dependence of the 2D-IR line shapes) with and without the disulfide bond. Despite the similarity of the linear FTIR spectra of Ngb-CO with and without the disulfide bond, 2D-IR measurements reveal that the equilibrium sampling of different protein configurations is accelerated by disruption of the disulfide bond. The observations indicate that the intramolecular disulfide bond in Ngb acts as an inhibitor of fast protein dynamics even though eliminating it does not produce significant conformational change in the protein's structure.
View details for DOI 10.1073/pnas.0709760104
View details for Web of Science ID 000251525800028
View details for PubMedID 18042705
View details for PubMedCentralID PMC2148286
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Observation of slow charge redistribution preceding excited-state proton transfer
JOURNAL OF CHEMICAL PHYSICS
2007; 127 (20)
Abstract
The photoacid 8-hydroxy-N,N,N',N',N',N'-hexamethylpyrene-1,3,6-trisulfonamide (HPTA) and related compounds are used to investigate the steps involved in excited-state deprotonation in polar solvents using pump-probe spectroscopy and time correlated single photon counting fluorescence spectroscopy. The dynamics show a clear two-step process leading to excited-state proton transfer. The first step after electronic excitation is charge redistribution occurring on a tens of picoseconds time scale followed by proton transfer on a nanosecond time scale. The three states observed in the experiments (initial excited state, charge redistributed state, and proton transfer state) are recognized by distinct features in the time dependence of the pump-probe spectrum and fluorescence spectra. In the charge redistributed state, charge density has transferred from the hydroxyl oxygen to the pyrene ring, but the OH sigma bond is still intact. The experiments indicate that the charge redistribution step is controlled by a specific hydrogen bond donation from HPTA to the accepting base molecule. The second step is the full deprotonation of the photoacid. The full deprotonation is clearly marked by the growth of stimulated emission spectral band in the pump-probe spectrum that is identical to the fluorescence spectrum of the anion.
View details for DOI 10.1063/1.2803188
View details for Web of Science ID 000251325100025
View details for PubMedID 18052436
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Confinement or the nature of the interface? Dynamics of nanoscopic water
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2007; 129 (46): 14311-14318
Abstract
The dynamics of water confined in two different types of reverse micelles are studied using ultrafast infrared pump-probe spectroscopy of the hydroxyl OD stretch of HOD in H2O. Reverse micelles of the surfactant Aerosol-OT (ionic head group) in isooctane and the surfactant Igepal CO 520 (nonionic head group) in 50/50 wt % cyclohexane/hexane are prepared to have the same diameter water nanopools. Measurements of the IR spectra and vibrational lifetimes show that the identity of the surfactant head groups affects the local environment experienced by the water molecules inside the reverse micelles. The orientational dynamics (time-dependent anisotropy), which is a measure of the hydrogen bond network rearrangement, are very similar for the confined water in the two types of reverse micelles. The results demonstrate that confinement by an interface to form a nanoscopic water pool is a primary factor governing the dynamics of nanoscopic water rather than the presence of charged groups at the interface.
View details for DOI 10.1021/ja073977d
View details for Web of Science ID 000251182000056
View details for PubMedID 17958424
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Are water simulation models consistent with steady-state and ultrafast vibrational spectroscopy experiments?
CHEMICAL PHYSICS
2007; 341 (1-3): 143-157
View details for DOI 10.1016/j.chemphys.2007.06.043
View details for Web of Science ID 000251573300016
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Hydrogen bond dynamics in aqueous NaBr solutions
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2007; 104 (43): 16731-16738
Abstract
Hydrogen bond dynamics of water in NaBr solutions are studied by using ultrafast 2D IR vibrational echo spectroscopy and polarization-selective IR pump-probe experiments. The hydrogen bond structural dynamics are observed by measuring spectral diffusion of the OD stretching mode of dilute HOD in H(2)O in a series of high concentration aqueous NaBr solutions with 2D IR vibrational echo spectroscopy. The time evolution of the 2D IR spectra yields frequency-frequency correlation functions, which permit quantitative comparisons of the influence of NaBr concentration on the hydrogen bond dynamics. The results show that the global rearrangement of the hydrogen bond structure, which is represented by the slowest component of the spectral diffusion, slows, and its time constant increases from 1.7 to 4.8 ps as the NaBr concentration increases from pure water to approximately 6 M NaBr. Orientational relaxation is analyzed with a wobbling-in-a-cone model describing restricted orientational diffusion that is followed by complete orientational randomization described as jump reorientation. The slowest component of the orientational relaxation increases from 2.6 ps (pure water) to 6.7 ps (approximately equal to 6 M NaBr). Vibrational population relaxation of the OD stretch also slows significantly as the NaBr concentration increases.
View details for Web of Science ID 000250487600005
View details for PubMedID 17940023
View details for PubMedCentralID PMC2040434
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Neuroglobin dynamics observed with ultrafast 2D-IR vibrational echo spectroscopy
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2007; 104 (41): 16116-16121
Abstract
Neuroglobin (Ngb), a protein in the globin family, is found in vertebrate brains. It binds oxygen reversibly. Compared with myoglobin (Mb), the amino acid sequence has limited similarity, but key residues around the heme and the classical globin fold are conserved in Ngb. The CO adduct of Ngb displays two CO absorption bands in the IR spectrum, referred to as N(3) (distal histidine in the pocket) and N(0) (distal histidine swung out of the pocket), which have absorption spectra that are almost identical with the Mb mutants L29F and H64V, respectively. The Mb mutants mimic the heme pocket structures of the corresponding Ngb conformers. The equilibrium protein dynamics for the CO adduct of Ngb are investigated by using ultrafast 2D-IR vibrational echo spectroscopy by observing the CO vibration's spectral diffusion (2D-IR spectra time dependence) and comparing the results with those for the Mb mutants. Although the heme pocket structure and the CO FTIR peak positions of Ngb are similar to those of the mutant Mb proteins, the 2D-IR results demonstrate that the fast structural fluctuations of Ngb are significantly slower than those of the mutant Mbs. The results may also provide some insights into the nature of the energy landscape in the vicinity of the folded protein free energy minimum.
View details for DOI 10.1073/pnas.0707718104
View details for Web of Science ID 000250128800028
View details for PubMedID 17916624
View details for PubMedCentralID PMC2042171
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Ultrafast 2D-IR vibrational echo spectroscopy: a probe of molecular dynamics
LASER PHYSICS LETTERS
2007; 4 (10): 704-718
View details for DOI 10.1002/lapl.200710046
View details for Web of Science ID 000250301700001
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Frequency-frequency correlation functions and apodization in two-dimensional infrared vibrational echo spectroscopy: A new approach
JOURNAL OF CHEMICAL PHYSICS
2007; 127 (12)
Abstract
Ultrafast two-dimensional infrared (2D-IR) vibrational echo spectroscopy can probe structural dynamics under thermal equilibrium conditions on time scales ranging from femtoseconds to approximately 100 ps and longer. One of the important uses of 2D-IR spectroscopy is to monitor the dynamical evolution of a molecular system by reporting the time dependent frequency fluctuations of an ensemble of vibrational probes. The vibrational frequency-frequency correlation function (FFCF) is the connection between the experimental observables and the microscopic molecular dynamics and is thus the central object of interest in studying dynamics with 2D-IR vibrational echo spectroscopy. A new observable is presented that greatly simplifies the extraction of the FFCF from experimental data. The observable is the inverse of the center line slope (CLS) of the 2D spectrum. The CLS is the inverse of the slope of the line that connects the maxima of the peaks of a series of cuts through the 2D spectrum that are parallel to the frequency axis associated with the first electric field-matter interaction. The CLS varies from a maximum of 1 to 0 as spectral diffusion proceeds. It is shown analytically to second order in time that the CLS is the T(w) (time between pulses 2 and 3) dependent part of the FFCF. The procedure to extract the FFCF from the CLS is described, and it is shown that the T(w) independent homogeneous contribution to the FFCF can also be recovered to yield the full FFCF. The method is demonstrated by extracting FFCFs from families of calculated 2D-IR spectra and the linear absorption spectra produced from known FFCFs. Sources and magnitudes of errors in the procedure are quantified, and it is shown that in most circumstances, they are negligible. It is also demonstrated that the CLS is essentially unaffected by Fourier filtering methods (apodization), which can significantly increase the efficiency of data acquisition and spectral resolution, when the apodization is applied along the axis used for obtaining the CLS and is symmetrical about tau=0. The CLS is also unchanged by finite pulse durations that broaden 2D spectra.
View details for DOI 10.1063/1.2772269
View details for Web of Science ID 000249787300033
View details for PubMedID 17902917
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Dynamics around solutes and solute-solvent complexes in mixed solvents
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2007; 104 (36): 14221-14226
Abstract
Ultrafast 2D-IR vibrational echo experiments, IR pump-probe experiments, and FT-IR spectroscopy of the hydroxyl stretch of phenol-OD in three solvents, CCl4, mesitylene (1, 3, 5 trimethylbenzene), and the mixed solvent of mesitylene and CCl4 (0.83 mole fraction CCl4), are used to study solute-solvent dynamics via observation of spectral diffusion. Phenol forms a complex with Mesitylene. In the mesitylene solution, there is only complexed phenol; in the CCl4 solution, there is only uncomplexed phenol; and in the mixed solvent, both phenol species are present. Dynamics of the free phenol in CCl4 or the mixed solvent are very similar, and dynamics of the complex in mesitylene and in the mixed solvent are very similar. However, there are differences in the slowest time scale dynamics between the pure solvents and the mixed solvents. The mixed solvent produces slower dynamics that are attributed to first solvent shell solvent composition variations. The composition variations require a longer time to randomize than is required in the pure solvents, where only density variations occur. The experimental results and recent MD simulations indicate that the solvent structure around the solute may be different from the mixed solvent's mole fraction.
View details for DOI 10.1073/pnas.0701710104
View details for Web of Science ID 000249333600010
View details for PubMedID 17581876
View details for PubMedCentralID PMC1964852
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Water Dynamics in Nafion Fuel Cell Membranes: the Effects of Confinement and Structural Changes on the Hydrogen Bond Network.
The journal of physical chemistry. C, Nanomaterials and interfaces
2007; 111 (25): 8884-8891
Abstract
The complex environments experienced by water molecules in the hydrophilic channels of Nafion membranes are studied by ultrafast infrared pump-probe spectroscopy. A wavelength dependent study of the vibrational lifetime of the O-D stretch of dilute HOD in H(2)O confined in Nafion membranes provides evidence of two distinct ensembles of water molecules. While only two ensembles are present at each level of membrane hydration studied, the characteristics of the two ensembles change as the water content of the membrane changes. Time dependent anisotropy measurements show that the orientational motions of water molecules in Nafion membranes are significantly slower than in bulk water and that lower hydration levels result in slower orientational relaxation. Initial wavelength dependent results for the anisotropy show no clear variation in the time scale for orientational motion across a broad range of frequencies. The anisotropy decay is analyzed using a model based on restricted orientational diffusion within a hydrogen bond configuration followed by total reorientation through jump diffusion.
View details for DOI 10.1021/jp067460k
View details for PubMedID 18728757
View details for PubMedCentralID PMC2523265
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Dynamics of nanoscopic water
AMER CHEMICAL SOC. 2007
View details for Web of Science ID 000207593907021
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Proton transport and the water environment in nafion fuel cell membranes and AOT reverse micelles
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2007; 129 (26): 8122-8130
Abstract
The properties of confined water and diffusive proton-transfer kinetics in the nanoscopic water channels of Nafion fuel cell membranes at various hydration levels are compared to water in a series of well-characterized AOT reverse micelles with known water nanopool sizes using the photoacid pyranine as a molecular probe. The side chains of Nafion are terminated by sulfonate groups with sodium counterions that are arrayed along the water channels. AOT has sulfonate head groups with sodium counterions that form the interface with the reverse micelle's water nanopool. The extent of excited-state deprotonation is observed by steady-state fluorescence measurements. Proton-transfer kinetics and orientational relaxation are measured by time-dependent fluorescence using time-correlated single photon counting. The time dependence of deprotonation is related to diffusive proton transport away from the photoacid. The fluorescence reflecting the long time scale proton transport has an approximately t-0.8 power law decay in contrast to bulk water, which has a t-3/2 power law. For a given hydration level of Nafion, the excited-state proton transfer and the orientational relaxation are similar to those observed for a related size AOT water nanopool. The effective size of the Nafion water channels at various hydration levels are estimated by the known size of the AOT reverse micelles that display the corresponding proton-transfer kinetics and orientational relaxation.
View details for DOI 10.1021/ja071939o
View details for Web of Science ID 000247563700025
View details for PubMedID 17567012
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Water dynamics in nafion fuel cell membranes: The effects of confinement and structural changes on the hydrogen bond network
JOURNAL OF PHYSICAL CHEMISTRY C
2007; 111 (25): 8884-8891
Abstract
The complex environments experienced by water molecules in the hydrophilic channels of Nafion membranes are studied by ultrafast infrared pump-probe spectroscopy. A wavelength dependent study of the vibrational lifetime of the O-D stretch of dilute HOD in H(2)O confined in Nafion membranes provides evidence of two distinct ensembles of water molecules. While only two ensembles are present at each level of membrane hydration studied, the characteristics of the two ensembles change as the water content of the membrane changes. Time dependent anisotropy measurements show that the orientational motions of water molecules in Nafion membranes are significantly slower than in bulk water and that lower hydration levels result in slower orientational relaxation. Initial wavelength dependent results for the anisotropy show no clear variation in the time scale for orientational motion across a broad range of frequencies. The anisotropy decay is analyzed using a model based on restricted orientational diffusion within a hydrogen bond configuration followed by total reorientation through jump diffusion.
View details for DOI 10.1021/jp067460k
View details for Web of Science ID 000247601900022
View details for PubMedCentralID PMC2523265
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Viscosity-dependent protein dynamics
BIOPHYSICAL JOURNAL
2007; 92 (10): 3652-3662
Abstract
Spectrally resolved stimulated vibrational echo spectroscopy is used to investigate the dependence of fast protein dynamics on bulk solution viscosity at room temperature in four heme proteins: hemoglobin, myoglobin, a myoglobin mutant with the distal histidine replaced by a valine (H64V), and a cytochrome c552 mutant with the distal methionine replaced by an alanine (M61A). Fructose is added to increase the viscosity of the aqueous protein solutions over many orders of magnitude. The fast dynamics of the four globular proteins were found to be sensitive to solution viscosity and asymptotically approached the dynamical behavior that was previously observed in room temperature sugar glasses. The viscosity-dependent protein dynamics are analyzed in the context of a viscoelastic relaxation model that treats the protein as a deformable breathing sphere. The viscoelastic model is in qualitative agreement with the experimental data but does not capture sufficient system detail to offer a quantitative description of the underlying fluctuation amplitudes and relaxation rates. A calibration method based on the near-infrared spectrum of water overtones was constructed to accurately determine the viscosity of small volumes of protein solutions.
View details for DOI 10.1529/biophysj.106.093708
View details for Web of Science ID 000245852600029
View details for PubMedID 17446536
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Hydrogen bond lifetimes and energetics for solute/solvent complexes studied with 2D-IR vibrational echo spectroscopy
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2007; 129 (14): 4328-4335
Abstract
Weak pi hydrogen-bonded solute/solvent complexes are studied with ultrafast two-dimensional infrared (2D-IR) vibrational echo chemical exchange spectroscopy, temperature-dependent IR absorption spectroscopy, and density functional theory calculations. Eight solute/solvent complexes composed of a number of phenol derivatives and various benzene derivatives are investigated. The complexes are formed between the phenol derivative (solute) in a mixed solvent of the benzene derivative and CCl4. The time dependence of the 2D-IR vibrational echo spectra of the phenol hydroxyl stretch is used to directly determine the dissociation and formation rates of the hydrogen-bonded complexes. The dissociation rates of the weak hydrogen bonds are found to be strongly correlated with their formation enthalpies. The correlation can be described with an equation similar to the Arrhenius equation. The results are discussed in terms of transition state theory.
View details for DOI 10.1021/ja067760f
View details for Web of Science ID 000245723800048
View details for PubMedID 17373792
View details for PubMedCentralID PMC2522382
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Ultrafast 2-D infrared vibrational echo chemical exchange spectroscopy studies of chemical processes
AMER CHEMICAL SOC. 2007
View details for Web of Science ID 000207722807353
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Influence of environment and substrate binding on the dynamics of heme proteins
AMER CHEMICAL SOC. 2007
View details for Web of Science ID 000207722807351
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Substrate binding and protein conformational dynamics measured by 2D-IR vibrational echo spectroscopy
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2007; 104 (8): 2637-2642
Abstract
Enzyme structural dynamics play a pivotal role in substrate binding and biological function, but the influence of substrate binding on enzyme dynamics has not been examined on fast time scales. In this work, picosecond dynamics of horseradish peroxidase (HRP) isoenzyme C in the free form and when ligated to a variety of small organic molecule substrates is studied by using 2D-IR vibrational echo spectroscopy. Carbon monoxide bound at the heme active site of HRP serves as a spectroscopic marker that is sensitive to the structural dynamics of the protein. In the free form, HRP assumes two distinct spectroscopic conformations that undergo fluctuations on a tens-of-picoseconds time scale. After substrate binding, HRP is locked into a single conformation that exhibits reduced amplitudes and slower time-scale structural dynamics. The decrease in carbon monoxide frequency fluctuations is attributed to reduced dynamic freedom of the distal histidine and the distal arginine, which are key residues in modulating substrate binding affinity. It is suggested that dynamic quenching caused by substrate binding can cause the protein to be locked into a conformation suitable for downstream steps in the enzymatic cycle of HRP.
View details for DOI 10.1073/pnas.0610027104
View details for Web of Science ID 000244511200016
View details for PubMedID 17296942
View details for PubMedCentralID PMC1815234
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Deprotonation dynamics and stokes shift of pyranine (HPTS)
JOURNAL OF PHYSICAL CHEMISTRY A
2007; 111 (2): 230-237
Abstract
The short and intermediate time scale dynamics of the photoacid pyranine (1-hydroxy-3,6,8-pyrenetrisulfonic acid, commonly referred to as HPTS) are studied with visible pump-probe spectroscopy in various solvents to elucidate the nature of its proton-transfer kinetics in water. The observed time dependences of HPTS are compared with those of the methoxy derivative, MPTS. A global fitting procedure is employed to model both the spectral shift (Stokes shift) caused by solvent reorganization and deprotonation of pyranine in water. Three distinct time-dependent features can be clearly identified. They are the Stokes shift (1 ps in H(2)O and 1.5 ps in D(2)O), followed by the deprotonation processes, which gives rise to a biexponential decay of the protonated species with time constants (in H(2)O) of 3 and 88 ps. By the use of a model previously discussed in the literature, the biexponential process can be interpreted as an initial deprotonation step followed by the longer time scale process which separates the resulting ion pair. The results presented here are consistent with some of the previous reports but unambiguously identify and quantitatively measure the Stokes shift as a separate and distinct phenomenon from the deprotonation process, in contrast to other reports that have suggested that all short time (a few picoseconds) dynamics are merely a Stokes shift.
View details for DOI 10.1021/jp066041k
View details for Web of Science ID 000243388500006
View details for PubMedID 17214458
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Ultrafast 2D IR vibrational echo spectroscopy
ACCOUNTS OF CHEMICAL RESEARCH
2007; 40 (1): 75-83
Abstract
The experimental technique and applications of ultrafast two-dimensional infrared (2D IR) vibrational echo spectroscopy are presented. Using ultrashort infrared pulses and optical heterodyne detection to provide phase information, unique information can be obtained about the dynamics, interactions, and structures of molecular systems. The form and time evolution of the 2D IR spectrum permits examination of processes that cannot be studied with linear infrared absorption experiments. Three examples are given: organic solute-solvent complex chemical exchange, dynamics of the hydrogen-bond network of water, and assigning peaks in an IR spectrum of a mixture of species.
View details for DOI 10.1021/ar068010d
View details for Web of Science ID 000243683700008
View details for PubMedID 17226947
- Confinement or Properties of the Interface? Dynamics of Nanoscopic Water in Reverse Micelles J. Am. Chem. Soc. 2007; 129: 14311 - 14318
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Ultrafast chemical exchange 2D IR spectroscopy
15th International Conference on Ultrafast Phenomena
SPRINGER-VERLAG BERLIN. 2007: 323–325
View details for Web of Science ID 000250104700104
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Probing dynamics of complex molecular systems with ultrafast 2D IR vibrational echo spectroscopy
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
2007; 9 (13): 1533-1549
Abstract
Ultrafast 2D IR vibrational echo spectroscopy is described and a number of experimental examples are given. Details of the experimental method including the pulse sequence, heterodyne detection, and determination of the absorptive component of the 2D spectrum are outlined. As an initial example, the 2D spectrum of the stretching mode of CO bound to the protein myoglobin (MbCO) is presented. The time dependence of the 2D spectrum of MbCO, which is caused by protein structural evolution, is presented and its relationship to the frequency-frequency correlation function is described and used to make protein structural assignments based on comparisons to molecular dynamics simulations. The 2D vibrational echo experiments on the protein horseradish peroxidase are presented. The time dependence of the 2D spectra of the enzyme in the free form and with a substrate bound at the active site are compared and used to examine the influence of substrate binding on the protein's structural dynamics. The application of 2D vibrational echo spectroscopy to the study of chemical exchange under thermal equilibrium conditions is described. 2D vibrational echo chemical exchange spectroscopy is applied to the study of formation and dissociation of organic solute-solvent complexes and to the isomerization around a carbon-carbon single bond of an ethane derivative.
View details for DOI 10.1039/b618158a
View details for Web of Science ID 000245633400002
View details for PubMedID 17429547
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Phenol-benzene complexation dynamics: Quantum chemistry calculation, molecular dynamics simulations, and two dimensional IR spectroscopy
JOURNAL OF CHEMICAL PHYSICS
2006; 125 (24)
Abstract
Molecular dynamics (MD) simulations and quantum mechanical electronic structure calculations are used to investigate the nature and dynamics of the phenol-benzene complex in the mixed solvent, benzene/CCl4. Under thermal equilibrium conditions, the complexes are continuously dissociating and forming. The MD simulations are used to calculate the experimental observables related to the phenol hydroxyl stretching mode, i.e., the two dimensional infrared vibrational echo spectrum as a function of time, which directly displays the formation and dissociation of the complex through the growth of off-diagonal peaks, and the linear absorption spectrum, which displays two hydroxyl stretch peaks, one for the complex and one for the free phenol. The results of the simulations are compared to previously reported experimental data and are found to be in quite reasonable agreement. The electronic structure calculations show that the complex is T shaped. The classical potential used for the phenol-benzene interaction in the MD simulations is in good accord with the highest level of the electronic structure calculations. A variety of other features is extracted from the simulations including the relationship between the structure and the projection of the electric field on the hydroxyl group. The fluctuating electric field is used to determine the hydroxyl stretch frequency-frequency correlation function (FFCF). The simulations are also used to examine the number distribution of benzene and CCl4 molecules in the first solvent shell around the phenol. It is found that the distribution is not that of the solvent mole fraction of benzene. There are substantial probabilities of finding a phenol in either a pure benzene environment or a pure CCl4 environment. A conjecture is made that relates the FFCF to the local number of benzene molecules in phenol's first solvent shell.
View details for DOI 10.1063/1.2403132
View details for Web of Science ID 000243158000025
View details for PubMedID 17199356
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Dynamics of a discotic liquid crystal in the isotropic phase
JOURNAL OF CHEMICAL PHYSICS
2006; 125 (19)
Abstract
Optically heterodyne-detected optical Kerr effect (OHD-OKE) experiments are conducted to study the orientational dynamics of a discotic liquid crystal 2,3,6,7,10,11-hexakis(pentyloxy)triphenylene (HPT) in the isotropic phase near the columnar-isotropic (C-I) phase transition. The OHD-OKE signal of HPT is characterized by an intermediate power law t(-0.76+/-0.02) at short times (a few picoseconds), a von Schweidler power law t(-0.26+/-0.01) at intermediate times (hundreds of picoseconds), and an exponential decay at long times (tens of nanoseconds). The exponential decay has Arrhenius temperature dependence. The functional form of the total time dependent decay is identical to the one observed previously for a large number of molecular supercooled liquids. The mode coupling theory schematic model based on the Sjogren [Phys. Rev. A 33, 1254 (1986)] model is able to reproduce the HPT data over a wide range of times from <1 ps to tens of nanoseconds. The studies indicate that the HPT C-I phase transition is a strong first order transition, and the dynamics in the isotropic phase display a complex time dependent profile that is common to other molecular liquids that lack mesoscopic structure.
View details for DOI 10.1063/1.2378623
View details for Web of Science ID 000242181800081
View details for PubMedID 17129161
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Identification and properties of the L-1(a) and L-1(b) states of pyranine
JOURNAL OF CHEMICAL PHYSICS
2006; 125 (14)
Abstract
The spectroscopic locations of the 1La and 1Lb electronic states of pyranine (1-hydroxy-3,6,8-pyrenetrisulfonic acid, commonly referred to as HPTS), as well as several related compounds, are found using magnetic circular dichroism spectroscopy as well as absorption and fluorescence spectroscopies. These electronic states have been discussed in connection with the photoacid properties of HPTS. Polarization selective fluorescence spectroscopy is used to identify the transition dipole directions of the electronic states of the compounds studied. The issue of the origin for the changes in vibronic structure of HPTS in different solvents is addressed. It is demonstrated that a Brownian oscillator model, in which the strength of the coupling of the electronic states to the solvent changes with solvent, is sufficient to reproduce the trends in the shapes of the vibronic structure.
View details for DOI 10.1063/1.2358685
View details for Web of Science ID 000241248400047
View details for PubMedID 17042616
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Ultrafast two-dimensional infrared vibrational echo chemical exchange experiments and theory
JOURNAL OF PHYSICAL CHEMISTRY B
2006; 110 (40): 19998-20013
Abstract
Ultrafast two-dimensional (2D) infrared vibrational echo experiments and theory are used to examine chemical exchange between solute-solvent complexes and the free solute for the solute phenol and three solvent complex partners, p-xylene, benzene, and bromobenzene, in mixed solvents of the partner and CCl4. The experiments measure the time evolution of the 2D spectra of the hydroxyl (OD) stretching mode of the phenol. The time-dependent 2D spectra are analyzed using time-dependent diagrammatic perturbation theory with a model that includes the chemical exchange (formation and dissociation of the complexes), spectral diffusion of both the complex and the free phenol, orientational relaxation of the complexes and free phenol, and the vibrational lifetimes. The detailed calculations are able to reproduce the experimental results and demonstrate that a method employed previously that used a kinetic model for the volumes of the peaks is adequate to extract the exchange kinetics. The current analysis also yields the spectral diffusion (time evolution of the dynamic line widths) and shows that the spectral diffusion is significantly different for phenol complexes and free phenol.
View details for DOI 10.1021/jp0624808
View details for Web of Science ID 000241053400033
View details for PubMedID 17020388
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Ultrafast carbon-carbon single-bond rotational isomerization in room-temperature solution
SCIENCE
2006; 313 (5795): 1951-1955
Abstract
Generally, rotational isomerization about the carbon-carbon single bond in simple ethane derivatives in room-temperature solution under thermal equilibrium conditions has been too fast to measure. We achieved this goal using two-dimensional infrared vibrational echo spectroscopy to observe isomerization between the gauche and trans conformations of an ethane derivative, 1-fluoro-2-isocyanato-ethane (1), in a CCl4 solution at room temperature. The isomerization time constant is 43 picoseconds (ps, 10(-12) s). Based on this value and on density functional theory calculations of the barrier heights of 1, n-butane, and ethane, the time constants for n-butane and ethane internal rotation under the same conditions are approximately 40 and approximately 12 ps, respectively.
View details for DOI 10.1126/science.1132178
View details for Web of Science ID 000240832200048
View details for PubMedID 17008529
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Cytochrome c(552) mutants: Structure and dynamics at the active site probed by multidimensional NMR and vibration echo spectroscopy
Festschrift in honor of the 65th Birthday of Robert J Silbey
AMER CHEMICAL SOC. 2006: 18803–10
Abstract
Spectrally resolved infrared stimulated vibrational echo experiments are used to measure the vibrational dephasing of a CO ligand bound to the heme cofactor in two mutated forms of the cytochrome c552 from Hydrogenobacter thermophilus. The first mutant (Ht-M61A) is characterized by a single mutation of Met61 to an Ala (Ht-M61A), while the second variant is doubly modified to have Gln64 replaced by an Asn in addition to the M61A mutation (Ht-M61A/Q64N). Multidimensional NMR experiments determined that the geometry of residue 64 in the two mutants is consistent with a non-hydrogen-bonding and hydrogen-bonding interaction with the CO ligand for Ht-M61A and Ht-M61A/Q64N, respectively. The vibrational echo experiments reveal that the shortest time scale vibrational dephasing of the CO is faster in the Ht-M61A/Q64N mutant than that in Ht-M61A. Longer time scale dynamics, measured as spectral diffusion, are unchanged by the Q64N modification. Frequency-frequency correlation functions (FFCFs) of the CO are extracted from the vibrational echo data to confirm that the dynamical difference induced by the Q64N mutation is primarily an increase in the fast (hundreds of femtoseconds) frequency fluctuations, while the slower (tens of picoseconds) dynamics are nearly unaffected. We conclude that the faster dynamics in Ht-M61A/Q64N are due to the location of Asn64, which is a hydrogen bond donor, above the heme-bound CO. A similar difference in CO ligand dynamics has been observed in the comparison of the CO derivative of myoglobin (MbCO) and its H64V variant, which is caused by the difference in axial residue interactions with the CO ligand. The results suggest a general trend for rapid ligand vibrational dynamics in the presence of a hydrogen bond donor.
View details for DOI 10.1021/jp054959q
View details for Web of Science ID 000240654900010
View details for PubMedID 16986870
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PHYS 237-Orientational dynamics of supercooled ionic organic liquids studied over a wide range of temperatures and times
AMER CHEMICAL SOC. 2006
View details for Web of Science ID 000207781609171
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COLL 148-Structural changes and water dynamics in Nafion fuel cell membranes
AMER CHEMICAL SOC. 2006
View details for Web of Science ID 000207781603386
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COLL 147-Marking the interaction of water with interfaces in reverse micelles using steady-state and time-resolved IR spectroscopy
AMER CHEMICAL SOC. 2006
View details for Web of Science ID 000207781603520
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PHYS 32-Stimulated vibrational echo experiments and MD simulations reveal the nature of ultrafast protein fluctuations in confinement
AMER CHEMICAL SOC. 2006
View details for Web of Science ID 000207781609061
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Dynamics in supercooled ionic organic liquids and mode coupling theory analysis
JOURNAL OF PHYSICAL CHEMISTRY A
2006; 110 (35): 10384-10391
Abstract
Optically heterodyne-detected optical Kerr effect experiments are applied to study the orientational dynamics of the supercooled ionic organic liquids N-propyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide (PMPIm) and 1-ethyl-3-methylimidazolium tosylate (EMImTOS). The orientational dynamics are complex with relaxation involving several power law decays followed by a final exponential decay. A mode coupling theory (MCT) schematic model, the Sjögren model, was able to reproduce the PMPIm data very successfully over a wide range of times from 1 ps to hundreds of ns for all temperatures studied. Over the temperature range from room temperature down to the critical temperature Tc of 231 K, the OHD-OKE signal of PMPIm is characterized by the intermediate power law t(-1.00+/-0.04) at short times, a von Schweidler power law t(-0.51+/-0.03) at intermediate times, and a highly temperature-dependent exponential (alpha relaxation) at long times. This form of the decay is identical to the form observed previously for a large number of organic van der Waals liquids. MCT analysis indicates that the theory can explain the experimental data very well for a range of temperatures above Tc, but as might be expected, there are some deviations from the theoretical modeling at temperatures close to Tc. For EMImTOS, the orientational dynamics were studied on the ps time scale in the deeply supercooled region near its glass transition temperature. The orientational relaxation of EMImTOS clearly displays the feature associated with the boson peak at approximately 2 ps, which is the first time domain evidence of the boson peak in ionic organic liquids. Overall, all the dynamical features observed earlier for organic van der Waals liquids using the same experimental technique are also observed for organic ionic liquids.
View details for DOI 10.1021/jp0637476
View details for Web of Science ID 000240149200003
View details for PubMedID 16942043
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What nonlinear-IR experiments can tell you about water that the IR spectrum cannot
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2006; 128 (32): 10366-10367
Abstract
Frequently, the IR spectrum of water is used to characterize the structure and strength of the associated hydrogen bond network. Here, we use nonlinear-IR spectroscopy to investigate the dynamics of four aqueous systems that have very similar absorption spectra. We address the question: to what extent can the dynamics of water vary in systems with very similar absorption spectra? The results illustrate that the vibrational lifetimes and orientational relaxation time scales vary dramatically between the four samples and do not correlate with the amount of water relative to surfactant or solute in solution. Nonlinear-IR spectroscopies are therefore important for providing detailed information necessary to understand hydrogen bonded systems.
View details for DOI 10.1021/ja062549p
View details for Web of Science ID 000239618700010
View details for PubMedID 16895392
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Photoinduced electron transfer and geminate recombination in the group head region of micelles
JOURNAL OF CHEMICAL PHYSICS
2006; 125 (5)
Abstract
A pump-probe spectroscopic study of photoinduced forward electron transfer and geminate recombination between donors and acceptors located in the head group regions of micelles is presented. The hole donor is octadecyl-rhodamine B (ODRB) and the hole acceptor is N,N-dimethyl-aniline (DMA). The experiments are conducted as a function of the DMA concentration in the dodecyltrimethylammonium bromide and tetradecyltrimethylammonium bromide micelles. In spite of the fact that the absorptions of both the ODRB radical and ground state bleach spectrally overlap with the ODRB excited state absorption, a procedure that makes it possible to determine the geminate recombination dynamics is presented. These experiments are the first to measure the dynamics of geminate recombination in micelles, and the experiments have two orders of magnitude better time resolution than previous studies of forward transfer. The experimental data are compared to statistical mechanics theoretical calculations of both the forward transfer and the geminate recombination. The theory includes important aspects of the topology of the micelle and the diffusion of the donor-acceptors in the micelle head group region. A semiquantitative but nonquantitative agreement between theory and experiments is achieved.
View details for DOI 10.1063/1.2227392
View details for Web of Science ID 000239573100051
View details for PubMedID 16942246
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Tracking water's response to structural changes in Nafion membranes
JOURNAL OF PHYSICAL CHEMISTRY A
2006; 110 (29): 9084-9088
Abstract
As the water content of Nafion membranes increases, the local environments of water molecules change due to reorganization of the pendant side chains in the hydrophilic domains. Changes in local structure as a function of water content are studied by measuring the IR spectra and the vibrational lifetimes of the hydroxyl stretch of dilute HOD in H(2)O. The main features of the IR spectra are fit well by a weighted sum of the spectra of bulk water and almost dry Nafion, suggesting a two-environment model. An additional small peak on the high frequency side of the main band associated with non-hydrogen-bonded water embedded in the polymer near the interface is analyzed quantitatively as a function of the membrane water content. The spectra of this peak show that a significant reorganization of the interfacial region occurs when the water content of the membrane exceeds the threshold for ion conduction. Vibrational excited state population relaxation times (lifetimes) of the main band lengthen substantially as the water content of the membrane is decreased. The population decays are not single exponentials and indicate that multiple ensembles of water molecules exist, and the characteristics of the individual ensembles change with water content. This is in contrast to the spectra of the main water absorption band, which is only sensitive to two classes of water molecules.
View details for DOI 10.1021/jp0623084
View details for Web of Science ID 000239141600009
View details for PubMedID 16854019
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Testing the core/shell model of nanoconfined water in reverse micelles using linear and nonlinear IR spectroscopy
JOURNAL OF PHYSICAL CHEMISTRY A
2006; 110 (15): 4985-4999
Abstract
A core/shell model has often been used to describe water confined to the interior of reverse micelles. The validity of this model for water encapsulated in AOT/isooctane reverse micelles ranging in diameter from 1.7 to 28 nm (w0 = 2-60) and bulk water is investigated using four experimental observables: the hydroxyl stretch absorption spectra, vibrational population relaxation times, orientational relaxation rates, and spectral diffusion dynamics. The time dependent observables are measured with ultrafast infrared spectrally resolved pump-probe and vibrational echo spectroscopies. Major progressive changes appear in all observables as the system moves from bulk water to the smallest water nanopool, w0 = 2. The dynamics are readily distinguishable for reverse micelle sizes smaller than 7 nm in diameter (w0 = 20) compared to the response of bulk water. The results also demonstrate that the size dependent absorption spectra and population relaxation times can be quantitatively predicted using a core-shell model in which the properties of the core (interior of the nanopool) are taken to be those of bulk water and the properties of the shell (water associated with the headgroups) are taken to be those of w0 = 2. A weighted sum of the core and shell components reproduces the size dependent spectra and the nonexponential population relaxation dynamics. However, the same model does not reproduce the spectral diffusion and the orientational relaxation experiments. It is proposed that, when hydrogen bond structural rearrangement is involved (orientational relaxation and spectral diffusion), dynamical coupling between the shell and the core cause the water nanopool to display more homogeneous dynamics. Therefore, the absorption spectra and vibrational lifetime decays can discern different hydrogen bonding environments whereas orientational and spectral diffusion correlation functions predict that the dynamics are size dependent but not as strongly spatially dependent within a reverse micelle.
View details for DOI 10.1021/jp061065c
View details for Web of Science ID 000236991900006
View details for PubMedID 16610816
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Dynamics of proteins encapsulated in silica sol-gel glasses studied with IR vibrational echo spectroscopy
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2006; 128 (12): 3990-3997
Abstract
Spectrally resolved infrared stimulated vibrational echo spectroscopy is used to measure the fast dynamics of heme-bound CO in carbonmonoxy-myoglobin (MbCO) and -hemoglobin (HbCO) embedded in silica sol-gel glasses. On the time scale of approximately 100 fs to several picoseconds, the vibrational dephasing of the heme-bound CO is measurably slower for both MbCO and HbCO relative to that of aqueous protein solutions. The fast structural dynamics of MbCO, as sensed by the heme-bound CO, are influenced more by the sol-gel environment than those of HbCO. Longer time scale structural dynamics (tens of picoseconds), as measured by the extent of spectral diffusion, are the same for both proteins encapsulated in sol-gel glasses compared to that in aqueous solutions. A comparison of the sol-gel experimental results to viscosity-dependent vibrational echo data taken on various mixtures of water and fructose shows that the sol-gel-encapsulated MbCO exhibits dynamics that are the equivalent of the protein in a solution that is nearly 20 times more viscous than bulk water. In contrast, the HbCO dephasing in the sol-gel reflects only a 2-fold increase in viscosity. Attempts to alter the encapsulating pore size by varying the molar ratio of silane precursor to water (R value) used to prepare the sol-gel glasses were found to have no effect on the fast or steady-state spectroscopic results. The vibrational echo data are discussed in the context of solvent confinement and protein-pore wall interactions to provide insights into the influence of a confined environment on the fast structural dynamics experienced by a biomolecule.
View details for DOI 10.1021/ja058745y
View details for Web of Science ID 000236401600049
View details for PubMedID 16551107
View details for PubMedCentralID PMC2532503
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Ultrafast chemical exchange 2-D infrared spectroscopy of complexes in solution
231st National Meeting of the American-Chemical-Society
AMER CHEMICAL SOC. 2006
View details for Web of Science ID 000238125908342
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Formation and dissociation of intra-intermolecular hydrogen-bonded solute-solvent complexes: Chemical exchange two-dimensional infrared vibrational echo spectroscopy
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2006; 128 (9): 2977-2987
Abstract
2-Methoxyphenol (2MP) solutes form weak complexes with toluene solvent molecules. The complexes are unusual in that the 2MP hydroxyl has an intramolecular hydrogen bond and simultaneously forms an intermolecular hydrogen bond with toluene and other aromatic solvents. In the equilibrated solute-solvent solution, there exists approximately the same concentration of 2MP-toluene complex and free 2MP. The very fast formation and dissociation (chemical exchange) of this type of three-centered hydrogen bond complex were observed in real time under thermal equilibrium conditions with two-dimensional (2D) infrared vibrational echo spectroscopy. Chemical exchange is manifested in the 2D spectrum by the growth of off-diagonal peaks. Both the formation and dissociation can be characterized in terms of the dissociation time constant, which was determined to be 3 ps for the 2MP-toluene complex. The intra-intermolecular hydrogen bond formation is influenced by subtle details of the molecular structure. Although 2MP forms a complex with toluene, it is demonstrated that 2-ethoxyphenol (2EP) does not form complexes to any significant extent. Density functional calculations at the B3LYP/6-31+G(d,p) level suggest that steric effects caused by the extra methyl group in 2EP are responsible for the difference.
View details for DOI 10.1021/ja057084
View details for Web of Science ID 000235942000050
View details for PubMedID 16506778
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Photoinduced electron transfer and geminate recombination in liquids on short time scales: Experiments and theory
JOURNAL OF CHEMICAL PHYSICS
2006; 124 (8)
Abstract
The coupled processes of intermolecular photoinduced forward electron transfer and geminate recombination between the (hole) donor (Rhodamine 3B) and (hole) acceptors (N,N-dimethylaniline) are studied in three molecular liquids: acetonitrile, butyronitrile, and benzonitrile. Two color pump-probe experiments on time scales from approximately 100 fs to hundreds of picoseconds give information about the depletion of the donor excited state due to forward electron transfer and the survival kinetics of the radicals produced by forward electron transfer. The data are analyzed with a model presented previously that includes distance dependent forward and back electron transfer rates, donor and acceptor diffusion, solvent structure, and the hydrodynamic effect in a mean-field theory of through solvent electron transfer. The forward electron transfer is in the normal regime, and the Marcus equation for the distance dependence of the transfer rate is used. The forward electron transfer data for several concentrations in the three solvents are fitted to the theory with a single adjustable parameter, the electronic coupling matrix element Jf at contact. Within experimental error all concentrations in all three solvents are fitted with the same value of Jf. The geminate recombination (back transfer) is in the inverted region, and semiclassical treatment developed by Jortner [J. Chem. Phys. 64, 4860 (1976)] is used to describe the distance dependence of the back electron transfer. The data are fitted with the single adjustable parameter Jb. It is found that the value of Jb decreases as the solvent viscosity increases. Possible explanations are discussed.
View details for DOI 10.1063/1.2174009
View details for Web of Science ID 000235663300032
View details for PubMedID 16512726
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Three homeotropically aligned nematic liquid crystals: Comparison of ultrafast to slow time-scale dynamics
JOURNAL OF CHEMICAL PHYSICS
2006; 124 (4)
Abstract
The dynamics of two nematic liquid crystals, 4-(trans-4(')-n-octylcyclohexyl)isothiocyanatobenzene and 4-(4-pentyl-cyclohexyl)-benzonitrile, are investigated as a function of temperature both in the homeotropically aligned nematic phase and in the isotropic phase using optical heterodyne-detected optical Kerr effect experiments, which measures the time derivative of the polarizability-polarizability-correlation function (orientational relaxation). Data are presented over a time range of 500 fs-70 micros for the nematic phase and 500 fs to a few hundred nanoseconds for the isotropic phase. The nematic dynamics are compared with a previously studied liquid crystal in the nematic phase. All three liquid crystals have very similar dynamics in the nematic phase that are very different from the isotropic phase. On the slowest time scale (20 ns-70 micros), a temperature-independent power law, the final power law, t(-f) with f approximately 0.5, is observed. On short time scales (approximately 3 ps to approximately 1 ns), a temperature-dependent intermediate power law is observed with an exponent that displays a linear dependence on the nematic order parameter. Between the intermediate power law and the final power law, there is a crossover region that has an inflection point. For times that are short compared to the intermediate power law (approximately <2 ps), the data decay much faster, and can be described as a third power law, although this functional form is not definitive. The isotopic phase data have the same features as found in previous studies of nematogens in the isotropic phase, i.e., the temperature-independent intermediate power law and von Schweidler power law at short to intermediate times, and a highly temperature-dependent long time exponential decay that is well described by the Landau-de Gennes theory. The results show that liquid-crystal dynamics in the nematic phase exhibit universal behavior.
View details for DOI 10.1063/1.2149867
View details for Web of Science ID 000234979300070
View details for PubMedID 16460211
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A mode coupling theory description of the short- and long-time dynamics of nematogens in the isotropic phase
JOURNAL OF CHEMICAL PHYSICS
2006; 124 (1)
Abstract
Optical heterodyne-detected optical Kerr effect (OHD-OKE) experimental data are pre-sented on nematogens 4-(trans-4-n-octylcyclohexyl)isothiocyanatobenzene (8-CHBT), and 4-(4-pentyl-cyclohexyl)-benzonitrile (5-PCH) in the isotropic phase. The 8-CHBT and 5-PCH data and previously published data on 4-pentyl-4-biphenylcarbonitrile (5-CB) are analyzed using a modification of a schematic mode coupling theory (MCT) that has been successful in describing the dynamics of supercooled liquids. At long time, the OHD-OKE data (orientational relaxation) are well described with the standard Landau-de Gennes (LdG) theory. The data decay as a single exponential. The decay time diverges as the isotropic to nematic phase transition is approached from above. Previously there has been no theory that can describe the complex dynamics that occur at times short compared to the LdG exponential decay. Earlier, it has been noted that the short-time nematogen dynamics, which consist of several power laws, have a functional form identical to that observed for the short time behavior of the orientational relaxation of supercooled liquids. The temperature-dependent orientational dynamics of supercooled liquids have recently been successfully described using a schematic mode coupling theory. The schematic MCT theory that fits the supercooled liquid data does not reproduce the nematogen data within experimental error. The similarities of the nematogen data to the supercooled liquid data are the motivation for applying a modification of the successful MCT theory to nematogen dynamics in the isotropic phase. The results presented below show that the new schematic MCT theory does an excellent job of reproducing the nematogen isotropic phase OHD-OKE data on all time scales and at all temperatures.
View details for DOI 10.1063/1.2145679
View details for Web of Science ID 000234428900043
View details for PubMedID 16409058
- Comparisons of the Orientational Dynamics of Three Homeotropically Aligned Nematic Liquid Crystals J. Chem. Phys 2006; 124
- Vibrational Echo and Pump-Probe Spectroscopic Studies of the Dynamics of Water Molecules Confined to Nanoscopic Dimensions Femtochemistry VII: Fundamental Ultrafast Processes in Chemistry, Physics, and Biology 2006: 195 - 203
- Identification and Properties of the 1La and 1Lb States of Pyranine (HPTS) J. Chem. Phys. 2006; 125
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Dynamics of nanoscopic water: Vibrational echo and infrared pump-probe studies of reverse micelles
JOURNAL OF PHYSICAL CHEMISTRY B
2005; 109 (45): 21273-21284
Abstract
The dynamics of water in nanoscopic pools 1.7-4.0 nm in diameter in AOT reverse micelles were studied with ultrafast infrared spectrally resolved stimulated vibrational echo and pump-probe spectroscopies. The experiments were conducted on the OD hydroxyl stretch of low-concentration HOD in the H2O, providing a direct examination of the hydrogen-bond network dynamics. Pump-probe experiments show that the vibrational lifetime of the OD stretch mode increases as the size of the reverse micelle decreases. These experiments are also sensitive to hydrogen-bond dissociation and reformation dynamics, which are observed to change with reverse micelle size. Spectrally resolved vibrational echo data were obtained at several frequencies. The vibrational echo data are compared to data taken on bulk water and on a 6 M NaCl solution, which is used to examine the role of ionic strength on the water dynamics in reverse micelles. Two types of vibrational echo measurements are presented: the vibrational echo decays and the vibrational echo peak shifts. As the water nanopool size decreases, the vibrational echo decays become slower. Even the largest nanopool (4 nm, approximately 1000 water molecules) has dynamics that are substantially slower than bulk water. It is demonstrated that the slow dynamics in the reverse micelle water nanopools are a result of confinement rather than ionic strength. The data are fit using time-dependent diagrammatic perturbation theory to obtain the frequency-frequency correlation function (FFCF) for each reverse micelle. The results are compared to the FFCF of water and show that the largest differences are in the slowest time scale dynamics. In bulk water, the slowest time scale dynamics are caused by hydrogen-bond network equilibration, i.e., the making and breaking of hydrogen bonds. For the smallest nanopools, the longest time scale component of the water dynamics is approximately 10 times longer than the dynamics in bulk water. The vibrational echo data for the smallest reverse micelle displays a dependence on the detection wavelength, which may indicate that multiple ensembles of water molecules are being observed.
View details for DOI 10.1021/jp051837p
View details for Web of Science ID 000233280600006
View details for PubMedID 16853758
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Photoinduced electron transfer in the head group region of sodium dodecyl sulfate micelles
JOURNAL OF LUMINESCENCE
2005; 115 (3-4): 138-146
View details for Web of Science ID 000232171400009
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Accidental vibrational degeneracy in vibrational excited states observed with ultrafast two-dimensional IR vibrational echo spectroscopy
JOURNAL OF CHEMICAL PHYSICS
2005; 123 (16)
Abstract
The coupling between the OD stretch v=2 level and benzene-ring modes in 2-methoxyphenol-OD (hydroxyl H replaced by D) is observed with ultrafast two-dimensional (2D) IR vibrational echo spectroscopy. Because of this coupling, the 1-2 transition peak in the 2D spectrum is split into a doublet with peaks of approximately equal amplitudes. Several molecules and solvents were used to study this phenomenon. Near-IR (NIR) spectroscopy measurements and density-functional theory calculations (B3LYP6-31+G(d,p) level) were also applied. Experimental results and calculations show that the OD stretch 1-2 transition is coupled to a combination band related to the benzene-ring motions. A simple quantum-mechanical model indicates that the combination band has a frequency of 5172 and 5176.5 cm(-1) in CCl4 and hexane, respectively. The transition between this combination band and the ground state is too weak to detect by NIR. The transition between this band and the OD stretch first excited state is also so weak that most of the intensity of the doublet comes from the oscillator strength produced by coupling to the OD stretch. The model gives the coupling strengths as 6.5 and 7 cm(-1) in CCl4 and hexane, respectively.
View details for DOI 10.1063/1.2071967
View details for Web of Science ID 000232855700022
View details for PubMedID 16268691
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The influence of aqueous versus glassy solvents on protein dynamics: Vibrational echo experiments and molecular dynamics simulations
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2005; 127 (41): 14279-14289
Abstract
Spectrally resolved infrared stimulated vibrational echo measurements are used to measure the vibrational dephasing of the CO stretching mode of carbonmonoxy-hemoglobin (HbCO), a myoglobin mutant (H64V), and a bacterial cytochrome c(552) mutant (Ht-M61A) in aqueous solution and trehalose glasses. The vibrational dephasing of the heme-bound CO is significantly slower for all three proteins embedded in trehalose glasses compared to that of aqueous protein solutions. All three proteins exhibit persistent but notably slower spectral diffusion when the protein surface is fixed by the glassy solvent. Frequency-frequency correlation functions (FFCFs) of the CO are extracted from the vibrational echo data to reveal that the structural dynamics, as sensed by the CO, of the three proteins in trehalose and aqueous solution are dominated by fast (tens of femtoseconds), motionally narrowed fluctuations. MD simulations of H64V in dynamic and "static" water are presented as models of the aqueous and glassy environments. FFCFs are calculated from the H64V simulations and qualitatively reproduce the important features of the experimentally extracted FFCFs. The suppression of long time scale (picoseconds to tens of picoseconds) frequency fluctuations (spectral diffusion) in the glassy solvent is the result of a damping of atomic displacements throughout the protein structure and is not limited to structural dynamics that occur only at the protein surface. The analysis provides evidence that some dynamics are coupled to the hydration shell of water, supporting the idea that the bioprotection offered by trehalose is due to its ability to immobilize the protein surface through a thin, constrained layer of water.
View details for DOI 10.1021/ja053627w
View details for Web of Science ID 000232605600051
View details for PubMedID 16218622
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Ultrafast dynamics of myoglobin without the distal histidine: Stimulated vibrational echo experiments and molecular dynamics simulations
JOURNAL OF PHYSICAL CHEMISTRY B
2005; 109 (35): 16959-16966
Abstract
Ultrafast protein dynamics of the CO adduct of a myoglobin mutant with the polar distal histidine replaced by a nonpolar valine (H64V) have been investigated by spectrally resolved infrared stimulated vibrational echo experiments and molecular dynamics (MD) simulations. In aqueous solution at room temperature, the vibrational dephasing rate of CO in the mutant is reduced by approximately 50% relative to the native protein. This finding confirms that the dephasing of the CO vibration in the native protein is sensitive to the interaction between the ligand and the distal histidine. The stimulated vibrational echo observable is calculated from MD simulations of H64V within a model in which vibrational dephasing is driven by electrostatic forces. In agreement with experiment, calculated vibrational echoes show slower dephasing for the mutant than for the native protein. However, vibrational echoes calculated for H64V do not show the quantitative agreement with measurements demonstrated previously for the native protein.
View details for DOI 10.1021/jp0517201
View details for Web of Science ID 000231687400054
View details for PubMedID 16853158
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Polarization selective spectroscopy experiments: methodology and pitfalls
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS
2005; 22 (9): 2009-2017
View details for Web of Science ID 000231790500023
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Photoinduced electron transfer and geminate recombination in micellar systems
AMER CHEMICAL SOC. 2005: U2776
View details for Web of Science ID 000236797305472
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Boson peak in supercooled liquids: Time domain observations and mode coupling theory
JOURNAL OF CHEMICAL PHYSICS
2005; 123 (6)
Abstract
Optical heterodyne-detected optical Kerr effect (OHD-OKE) experiments are presented for the supercooled liquid acetylsalicylic acid (aspirin - ASP). The ASP data and previously published OHD-OKE data on supercooled dibutylphthalate (DBP) display highly damped oscillations with a periods of approximately 2 ps as the temperature is reduced to and below the mode coupling theory (MCT) temperature T(C). The oscillations become more pronounced below T(C). The oscillations can be interpreted as the time domain signature of the boson peak. Recently a schematic MCT model, the Sjogren model, was used to describe the OHD-OKE data for a number of supercooled liquids by Gotze and Sperl [W. Gotze and M. Sperl, Phys. Rev. E 92, 105701 (2004)] , but the short-time and low-temperature behaviors were not addressed. Franosch et al. [T. Franosch, W. Gotze, M. R. Mayr, and A. P. Singh, Phys. Rev. E 55, 3183 (1997)] found that the Sjogren model could describe the boson peak observed by depolarized light-scattering (DLS) experiments on glycerol. The OHD-OKE experiment measures a susceptibility that is a time domain equivalent of the spectrum measured in DLS. Here we present a detailed analysis of the ASP and DBP data over a broad range of times and temperatures using the Sjogren model. The MCT schematic model is able to describe the data very well at all temperatures and relevant time scales. The trajectory of MCT parameters that fit the high-temperature data (no short-time oscillations) when continued below T(C) results in calculations that reproduce the oscillations seen in the data. The results indicate that increasing translational-rotational coupling is responsible for the appearance of the boson peak as the temperature approaches and drops below T(C).
View details for DOI 10.1063/1.2000235
View details for Web of Science ID 000231310500043
View details for PubMedID 16122327
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Orientational dynamics of water confined on a nanometer length scale in reverse micelles
JOURNAL OF CHEMICAL PHYSICS
2005; 122 (17)
Abstract
The time-resolved orientational anisotropies of the OD hydroxyl stretch of dilute HOD in H(2)O confined on a nanometer length scale in sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles are studied using ultrafast infrared polarization and spectrally resolved pump-probe spectroscopy, and the results are compared to the same experiments on bulk water. The orientational anisotropy data for three water nanopool sizes (4.0, 2.4, and 1.7 nm) can be fitted well with biexponential decays. The biexponential decays are analyzed using a wobbling-in-a-cone model that involves fast orientational diffusion within a cone followed by slower, full orientational relaxation. The data provide the cone angles, the diffusion constants for motion within the cones, and the final diffusion constants as a function of the nanopool size. The two processes can be interpreted as a local angular fluctuation of the OD and a global hydrogen bond network rearrangement process. The trend in the relative amplitudes of the long and short exponential decays suggest an increasing rigidity as the nanopool size decreases. The trend in the long decay constants indicates a longer hydrogen bond network rearrangement time with decreasing reverse micelle size. The anisotropy measurements for the reverse micelles studied extrapolate to approximately 0.33 rather than the ideal value of 0.4, suggesting the presence of an initial inertial component in the anisotropy decay that is too fast to resolve. The very fast decay component is consistent with initial inertial orientational motion that is seen in published molecular-dynamics simulations of water in AOT reverse micelles. The angle over which the inertial orientational motion occurs is determined. The results are in semiquantitative agreement with the molecular-dynamics simulations.
View details for DOI 10.1063/1.1883605
View details for Web of Science ID 000229064600025
View details for PubMedID 15910039
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Ultrafast to slow orientational dynamics of a homeotropically aligned nematic liquid crystal
JOURNAL OF PHYSICAL CHEMISTRY B
2005; 109 (14): 6514-6519
Abstract
The orientational dynamics of a homeotropically aligned nematic liquid crystal, 4'-pentyl-4-biphenylcarbonitrile (5-CB), is studied over more than six decades of time (500 fs to 2 mus) using optical heterodyne detected optical Kerr effect experiments. In contrast to the dynamics of nematogens in the isotropic phase, the data do not decay as a highly temperature-dependent exponential on the longest time scale, but rather, a temperature-independent power law spanning more than two decades of time, the final power law, is observed. On short time scales (approximately 3 ps to approximately 1 ns) another power law, the intermediate power law, is observed that is temperature dependent. The power law exponent of the correlation function associated with the intermediate power law displays a linear dependence on the change in the nematic order parameter with temperature. Between the intermediate power law and the final power law, there is a crossover region that displays an inflection point. The temperature-dependent orientational dynamics in the nematic phase are shown to be very different than those observed in the isotropic phase.
View details for DOI 10.1021/jp0459581
View details for Web of Science ID 000228231200009
View details for PubMedID 16851731
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Dynamics of water confined on a nanometer length scale in reverse micelles: Ultrafast infrared vibrational echo spectroscopy
PHYSICAL REVIEW LETTERS
2005; 94 (5)
Abstract
The dynamics of water, confined on a nanometer length scale (1.7 to 4.0 nm) in sodium bis-(2-ethylhexyl) sulfosuccinate reverse micelles, is directly investigated using frequency resolved infrared vibrational echo experiments. The data are compared to bulk water and salt solution data. The experimentally determined frequency-frequency correlation functions show that the confined water dynamics is substantially slower than bulk water dynamics and is size dependent. The fastest dynamics (approximately 50 fs) is more similar to bulk water, while the slowest time scale dynamics is much slower than water, and, in analogy to bulk water, reflects the making and breaking of hydrogen bonds.
View details for DOI 10.1103/PhysRevLett.94.057405
View details for Web of Science ID 000226941500083
View details for PubMedID 15783696
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Dynamics of water probed with vibrational echo correlation spectroscopy
JOURNAL OF CHEMICAL PHYSICS
2004; 121 (24): 12431-12446
Abstract
Vibrational echo correlation spectroscopy experiments on the OD stretch of dilute HOD in H(2)O are used to probe the structural dynamics of water. A method is demonstrated for combining correlation spectra taken with different infrared pulse bandwidths (pulse durations), making it possible to use data collected from many experiments in which the laser pulse properties are not identical. Accurate measurements of the OD stretch anharmonicity (162 cm(-1)) are presented and used in the data analysis. In addition, the recent accurate determination of the OD vibrational lifetime (1.45 ps) and the time scale for the production of vibrational relaxation induced broken hydrogen bond "photoproducts" ( approximately 2 ps) aid in the data analysis. The data are analyzed using time dependent diagrammatic perturbation theory to obtain the frequency time correlation function (FTCF). The results are an improved FTCF compared to that obtained previously with vibrational echo correlation spectroscopy. The experimental data and the experimentally determined FTCF are compared to calculations that employ a polarizable water model (SPC-FQ) to calculate the FTCF. The SPC-FQ derived FTCF is much closer to the experimental results than previously tested nonpolarizable water models which are also presented for comparison.
View details for DOI 10.1063/1.1818107
View details for Web of Science ID 000225714500036
View details for PubMedID 15606264
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Watching hydrogen bonds break: A transient absorption study of water
JOURNAL OF PHYSICAL CHEMISTRY A
2004; 108 (50): 10957-10964
View details for DOI 10.1021/jp046711r
View details for Web of Science ID 000225694900006
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Dynamics of hemoglobin in human erythrocytes and in solution: Influence of viscosity studied by ultrafast vibrational echo experiments
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2004; 126 (48): 15702-15710
Abstract
Ultrafast spectrally resolved stimulated vibrational echo experiments are used to measure the vibrational dephasing of the CO stretching mode of hemoglobin-CO (HbCO) inside living human erythrocytes (red blood cells), in liquid solutions, and in a glassy matrix. A method is presented to overcome the adverse impact on the vibrational echo signal from the strong light scattering caused by the cells. The results from the cytoplasmic HbCO are compared to experiments on aqueous HbCO samples prepared in different buffers, solutions containing low and high concentrations of glycerol, and in a solid trehalose matrix. Measurements are also presented that provide an accurate determination of the viscosity at the very high Hb concentration that is found inside the cells. It is demonstrated that the dynamics of the protein, as sensed by the CO ligand, are the same inside the erythrocytes and in aqueous solution and are independent of the viscosity. In solutions that are predominantly glycerol, the dynamics are modified somewhat but are still independent of viscosity. The experiments in trehalose give the dynamics at infinite viscosity and are used to separate the viscosity-dependent dynamics from the viscosity-independent dynamics. Although the HbCO dynamics are the same in the red blood cell and in the equivalent aqueous solutions, differences in the absorption spectra show that the distribution of a protein's equilibrium substates is sensitive to small pH differences.
View details for DOI 10.1021/ja0454790
View details for Web of Science ID 000225505700020
View details for PubMedID 15571392
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Spectral diffusion in a fluctuating charge model of water
JOURNAL OF CHEMICAL PHYSICS
2004; 121 (18): 8897-8900
Abstract
We apply the combined electronic structure/molecular dynamics approach of Corcelli, Lawrence, and Skinner [J. Chem. Phys. 120, 8107 (2004)] to the fluctuating charge (SPC-FQ) model of liquid water developed by Rick, Stuart, and Berne [J. Chem. Phys. 101, 6141 (1994)]. For HOD in H(2)O the time scale for the long-time decay of the OD stretch frequency time-correlation function, which corresponds to the time scale for hydrogen-bond rearrangement in the liquid, is about 1.5 ps. This result is significantly longer than the 0.9 ps decay previously calculated for the nonpolarizable SPC/E water model. Our results for the SPC-FQ model are in better agreement with recent vibrational echo experiments.
View details for DOI 10.1063/1.1803532
View details for Web of Science ID 000224798900026
View details for PubMedID 15527354
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Photoinduced intermolecular electron transfer in liquid solutions
JOURNAL OF PHYSICAL CHEMISTRY A
2004; 108 (32): 6696-6703
View details for DOI 10.1021/jp049391k
View details for Web of Science ID 000223182700012
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Vibrational echo experiments on red blood cells: Comparison of the dynamics of cytoplasmic and aqueous hemoglobin
CHEMICAL PHYSICS LETTERS
2004; 392 (4-6): 324-329
View details for DOI 10.1016/j.cplett.2004.05.080
View details for Web of Science ID 000222553100008
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Fifth-order contributions to ultrafast spectrally resolved vibrational echoes: Heme-CO proteins
JOURNAL OF CHEMICAL PHYSICS
2004; 121 (2): 877-885
Abstract
The fifth order contributions to the signals of ultrafast infrared spectrally resolved stimulated vibrational echoes at high intensities have been investigated in carbonmonoxy heme proteins. High intensities are often required to obtain good data. Intensity dependent measurements are presented on hemoglobin-CO (Hb-CO) and a mutant of myoglobin, H64V-CO. The spectrally resolved vibrational echoes demonstrate that fifth order effects arise at both the 1-0 and the 2-1 emission frequencies of the stretching mode of the CO chromophore bound at the active site of heme proteins. Unlike one-dimensional experiments, in which the signal is integrated over all emission frequencies, spectrally resolving the signal shows that the fifth order contributions have a much more pronounced influence on the 2-1 transition than on the 1-0 transition. By spectrally isolating the 1-0 transition, the influence of fifth order contributions to vibrational echo data can be substantially reduced. Analysis of fifth order Feynman diagrams that contribute in the vibrational echo phase-matched direction demonstrates the reason for the greater influence of fifth order processes on the 1-2 transition, and that the fifth order contributions are heterodyne amplified by the third order signal. Finally, it is shown that the anharmonic oscillations in vibrational echo data of Hb-CO that previous work had attributed strictly to fifth order effects arise even without fifth order contributions.
View details for DOI 10.1063/1.1758940
View details for Web of Science ID 000222265600033
View details for PubMedID 15260618
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Hydrogen bond networks: Structure and evolution after hydrogen bond breaking
JOURNAL OF PHYSICAL CHEMISTRY B
2004; 108 (21): 6544-6554
View details for DOI 10.1021/jp036600c
View details for Web of Science ID 000221546200005
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Photoinduced electron transfer and geminate recombination for photoexcited acceptors in a pure donor solvent
JOURNAL OF CHEMICAL PHYSICS
2004; 120 (20): 9601-9611
Abstract
Photoinduced electron transfer and geminate recombination are studied for the systems rhodamine 3B (R3B(+)) and rhodamine 6G (R6G(+)), which are cations, in neat neutral N,N-dimethylaniline (DMA). Following photoexcitation of R3B(+) or R6G(+) (abbreviated as R(+)), an electron is transferred from DMA to give the neutral radical R and the cation DMA(+). Because the DMA hole acceptor is the neat solvent, the forward transfer rate is very large, approximately 5x10(12) s(-1). The forward transfer is followed by geminate recombination, which displays a long-lived component suggesting several percent of the radicals escape geminate recombination. Spectrally resolved pump-probe experiments are used in which the probe is a "white" light continuum, and the full time-dependent spectrum is recorded with a spectrometer/charge-coupled device. Observations of stimulated emission (excited state decay-forward electron transfer), the R neutral radical spectrum, and the DMA(+) radical cation spectrum as well as the ground-state bleach recovery (geminate recombination) make it possible to unambiguously follow the electron transfer kinetics. Theoretical modeling shows that the long-lived component can be explained without invoking hole hopping or spin-forbidden transitions.
View details for DOI 10.1063/1.1712826
View details for Web of Science ID 000221268300020
View details for PubMedID 15267972
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Vibrational echo correlation spectroscopy probes of hydrogen bond dynamics in water and methanol
8th International Meeting on Hole Burning Single Molecule, and Related Spectroscopies
ELSEVIER SCIENCE BV. 2004: 271–86
View details for DOI 10.1016/j.jlumin.2003.12.035
View details for Web of Science ID 000220706100038
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Water dynamics: dependence on local structure probed with vibrational echo correlation spectroscopy
CHEMICAL PHYSICS LETTERS
2004; 386 (4-6): 295-300
View details for DOI 10.1016/j.cplett.2004.01.042
View details for Web of Science ID 000220124700014
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Water dynamics: Vibrational echo correlation spectroscopy and comparison to molecular dynamics simulations
JOURNAL OF PHYSICAL CHEMISTRY A
2004; 108 (7): 1107-1119
View details for DOI 10.1021/jp036266k
View details for Web of Science ID 000188957600002
- Vibrational Echo Correlation Spectroscopy: a New Probe of Hydrogen Bond Dynamics in Water and Methanol Femtosecond Laser Spectroscopy: Progress in Lasers edited by Hannaford, P. Kluwer, Brussells. 2004
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Hydrogen bond breaking probed with multidimensional stimulated vibrational echo correlation spectroscopy
JOURNAL OF CHEMICAL PHYSICS
2003; 119 (24): 12981-12997
View details for DOI 10.1063/1.1627762
View details for Web of Science ID 000187576300033
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Orientational dynamics of the ionic organic liquid 1-ethyl-3-methylimidazolium nitrate
JOURNAL OF CHEMICAL PHYSICS
2003; 119 (24): 13017-13023
View details for DOI 10.1063/1.1628668
View details for Web of Science ID 000187576300037
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Hydrogen bond dynamics probed with ultrafast infrared heterodyne-detected multidimensional vibrational stimulated echoes
PHYSICAL REVIEW LETTERS
2003; 91 (23)
Abstract
Hydrogen bond dynamics are explicated with exceptional detail using multidimensional infrared vibrational echo correlation spectroscopy with full phase information. Probing the hydroxyl stretch of methanol-OD oligomers in CCl4, the dynamics of the evolving hydrogen bonded network are measured with ultrashort (<50 fs) pulses. The data along with detailed model calculations demonstrate that vibrational relaxation leads to selective hydrogen bond breaking on the red side of the spectrum (strongest hydrogen bonds) and the production of singly hydrogen bonded photoproducts.
View details for DOI 10.1103/PhysRevLett.91.237402
View details for Web of Science ID 000187004500053
View details for PubMedID 14683215
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Dynamical signature of two "ideal glass transitions" in nematic liquid crystals
JOURNAL OF CHEMICAL PHYSICS
2003; 119 (19): 10421-10427
View details for DOI 10.1063/1.1618215
View details for Web of Science ID 000186273200053
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Myoglobin-CO substate structures and dynamics: Multidimensional vibrational echoes and molecular dynamics simulations
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2003; 125 (45): 13804-13818
Abstract
Spectrally resolved infrared stimulated vibrational echo data were obtained for sperm whale carbonmonoxymyoglobin (MbCO) at 300 K. The measured dephasing dynamics of the CO ligand are in agreement with dephasing dynamics calculated with molecular dynamics (MD) simulations for MbCO with the residue histidine-64 (His64) having its imidazole epsilon nitrogen protonated (N(epsilon)-H). The two conformational substate structures B(epsilon) and R(epsilon) observed in the MD simulations are assigned to the spectroscopic A(1) and A(3) conformational substates of MbCO, respectively, based on the agreement between the experimentally measured and calculated dephasing dynamics for these substates. In the A(1) substate, the N(epsilon)-H proton and N(delta) of His64 are approximately equidistant from the CO ligand, while in the A(3) substate, the N(epsilon)-H of His64 is oriented toward the CO, and the N(delta) is on the surface of the protein. The MD simulations show that dynamics of His64 represent the major source of vibrational dephasing of the CO ligand in the A(3) state on both femtosecond and picosecond time scales. Dephasing in the A(1) state is controlled by His64 on femtosecond time scales, and by the rest of the protein and the water solvent on longer time scales.
View details for DOI 10.1021/ja035654x
View details for Web of Science ID 000186424800045
View details for PubMedID 14599220
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Using ultrafast infrared multidimensional correlation spectroscopy to aid in vibrational spectral peak assignments
CHEMICAL PHYSICS LETTERS
2003; 381 (1-2): 139-146
View details for DOI 10.1016/j.cplett.2003.09.113
View details for Web of Science ID 000186450600020
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Structural dynamics of hydrogen bonded methanol oligomers: Vibrational transient hole burning studies of spectral diffusion
JOURNAL OF CHEMICAL PHYSICS
2003; 119 (1): 423-434
View details for DOI 10.1063/1.1578058
View details for Web of Science ID 000183585400049
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Ultrafast heterodyne detected infrared multidimensional vibrational stimulated echo studies of hydrogen bond dynamics
CHEMICAL PHYSICS LETTERS
2003; 374 (3-4): 362-371
View details for DOI 10.1016/S0009-2614(03)00643-2
View details for Web of Science ID 000183518100025
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Dynamics in supercooled liquids and in the isotropic phase of liquid crystals: A comparison
JOURNAL OF CHEMICAL PHYSICS
2003; 118 (20): 9303-9311
View details for DOI 10.1063/1.1568338
View details for Web of Science ID 000182794300030
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Experimental observation of a nearly logarithmic decay of the orientational correlation function in supercooled liquids on the picosecond-to-nanosecond time scales
PHYSICAL REVIEW LETTERS
2003; 90 (19)
Abstract
Dynamics of five supercooled molecular liquids have been studied using optical heterodyne detected optical Kerr effect experiments. "Intermediate" time scale power law decays (approximately 2 ps to 1-10 ns) with temperature independent exponents close to -1 have been observed in all five samples from high temperature to approximately T(c), the mode-coupling theory (MCT) critical temperature. The amplitude of the intermediate power law increases with temperature as [(T-T(c))/T(c)](1/2). The results cannot be explained by standard MCT, and one possible explanation within MCT would require the higher order singularity scenario, thought to be highly improbable, to be virtually universal.
View details for DOI 10.1103/PhysRevLett.90.197401
View details for Web of Science ID 000182928300050
View details for PubMedID 12785982
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Hydrogen bond dynamics in alcohols.
225th National Meeting of the American-Chemical-Society
AMER CHEMICAL SOC. 2003: U467–U467
View details for Web of Science ID 000187918002403
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Logarithmic decay of the orientational correlation function in supercooled liquids on the Ps to Ns time scale
JOURNAL OF CHEMICAL PHYSICS
2003; 118 (6): 2800-2807
View details for DOI 10.1063/1.1536612
View details for Web of Science ID 000180564800038
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Orientational relaxation and vibrational excitation transfer in methanol-carbon tetrachloride solutions
JOURNAL OF CHEMICAL PHYSICS
2003; 118 (5): 2270-2278
View details for DOI 10.1063/1.1534580
View details for Web of Science ID 000180579900030
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Isomerization and intermolecular solute-solvent interactions of ethyl isocyanate: Ultrafast infrared vibrational echoes and linear vibrational spectroscopy
JOURNAL OF CHEMICAL PHYSICS
2003; 118 (3): 1312-1326
View details for DOI 10.1063/1.1527926
View details for Web of Science ID 000180316700037
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Structural assignments and dynamics of the A substates of MbCO: Spectrally resolved vibrational echo experiments and molecular dynamics simulations
JOURNAL OF PHYSICAL CHEMISTRY B
2003; 107 (1): 4-7
View details for DOI 10.1021/jp026793o
View details for Web of Science ID 000180254900002
- Experimental Observation of Nearly Logarithmic Decay of the Orientational Correlation Function in Supercooled Liquids on the Ps to Ns Time Scale Phys. Rev. Lett. 2003; 90 (197401)
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Hydrogen bond dissociation and reformation in methanol oligomers following hydroxyl stretch relaxation
JOURNAL OF PHYSICAL CHEMISTRY A
2002; 106 (50): 12012-12023
View details for DOI 10.1021/jp.021696g
View details for Web of Science ID 000179921000004
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Short time dynamics in the isotropic phase of liquid crystals: the aspect ratio and the power law decay
CHEMICAL PHYSICS LETTERS
2002; 366 (1-2): 82-87
View details for Web of Science ID 000179253000013
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Hydrogen bond breaking and reformation in alcohol oligomers following vibrational relaxation of a non-hydrogen-bond donating hydroxyl stretch
JOURNAL OF PHYSICAL CHEMISTRY A
2002; 106 (41): 9428-9435
View details for DOI 10.1021/jp021170w
View details for Web of Science ID 000178548500007
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Frequency selected ultrafast infrared vibrational echo studies of liquids, glasses, and proteins
JOURNAL OF PHYSICAL CHEMISTRY A
2002; 106 (38): 8839-8849
View details for DOI 10.1021/jp021145q
View details for Web of Science ID 000178106300002
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Temperature-dependent vibrational dephasing: Comparison of liquid and glassy solvents using frequency-selected vibrational echoes
JOURNAL OF CHEMICAL PHYSICS
2002; 117 (6): 2732-2740
View details for DOI 10.1063/1.1492280
View details for Web of Science ID 000177042800032
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Vibrational dynamics of a metalloporphyrin carbonyl in liquid and glass solutions: Ultrafast 1-D and frequency-selected vibrational echo experiments
LASER PHYSICS
2002; 12 (8): 1104-1113
View details for Web of Science ID 000177820400007
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Influence of diffusion on the kinetics of donor-acceptor electron transfer monitored by the quenching of donor fluorescence
JOURNAL OF PHYSICAL CHEMISTRY A
2002; 106 (30): 6982-6990
View details for DOI 10.1021/jp0207228
View details for Web of Science ID 000177104700010
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Myoglobin-CO conformational substate dynamics: 2D vibrational echoes and MD simulations
BIOPHYSICAL JOURNAL
2002; 82 (6): 3277-3288
Abstract
Two-dimensional (2D) infrared vibrational echoes were performed on horse heart carbonmonoxymyoglobin (MbCO) in water over a range of temperatures. The A(1) and A(3) conformational substates of MbCO are found to have different dephasing rates with different temperature dependences. A frequency-frequency correlation function derived from molecular dynamics simulations on MbCO at 298 K is used to calculate the vibrational echo decay. The calculated decay shows substantial agreement with the experimentally measured decays. The 2D vibrational echo probes protein dynamics and provides an observable that can be used to test structural assignments for the MbCO conformational substates.
View details for PubMedID 12023251
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Comparison of the ultrafast to slow time scale dynamics of three liquid crystals in the isotropic phase
JOURNAL OF CHEMICAL PHYSICS
2002; 116 (14): 6339-6347
View details for DOI 10.1063/1.1462039
View details for Web of Science ID 000174634200048
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Exploring relaxation and hydrogen bond breaking in methanol-d oligomers in carbon tetrachloride.
AMER CHEMICAL SOC. 2002: C62–C62
View details for Web of Science ID 000176296801735
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Separation of contributions to the third-order signal: ultrafast frequency-selected vibrational echo experiments on a metalloporphyrin-CO
CHEMICAL PHYSICS LETTERS
2002; 355 (1-2): 139-146
View details for Web of Science ID 000174847500022
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Vibrational dynamics of large hot molecules in the collisionless gas phase
JOURNAL OF CHEMICAL PHYSICS
2002; 116 (9): 3540-3553
View details for DOI 10.1063/1.1446850
View details for Web of Science ID 000173888400004
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Thermal, structural, and orientational relaxation of supercooled salol studied by polarization-dependent impulsive stimulated scattering
JOURNAL OF CHEMICAL PHYSICS
2002; 116 (8): 3384-3395
View details for DOI 10.1063/1.1445749
View details for Web of Science ID 000173853600026
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Accidental degeneracy beats: A distinct type of beat phenomenon in nonlinear optical spectroscopy
PHYSICAL REVIEW A
2002; 65 (2)
View details for DOI 10.1103/PhysRevA.65.023817
View details for Web of Science ID 000173879500114
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Orientational dynamics of the glass forming liquid, dibutylphthalate: Time domain experiments and comparison to mode coupling theory
JOURNAL OF CHEMICAL PHYSICS
2002; 116 (4): 1598-1606
View details for Web of Science ID 000173384200042
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Liquid crystal dynamics in the isotropic phase
JOURNAL OF CHEMICAL PHYSICS
2002; 116 (1): 360-367
View details for Web of Science ID 000172784700041
- Comparison of the Ultrafast to Slow Timescale Dynamics of Three Liquid Crystals in the Isotropic Phase J. Chem. Phys. 2002; 116: 6339-6347
- Separation of Contributions to the Third-Order Vibrational Echo Signal: Ultrafast Frequency-Selected Experiments on a Metalloporphyrin-CO Chem. Phys. Lett. 2002; 355: 139-146
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Vibrational relaxation of the free terminal hydroxyl stretch in methanol oligomers: Indirect pathway to hydrogen bond breaking
JOURNAL OF CHEMICAL PHYSICS
2001; 115 (20): 9352-9360
View details for Web of Science ID 000172129300026
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Dynamic partitioning of an aromatic probe between the headgroup and core regions of cationic micelles
JOURNAL OF PHYSICAL CHEMISTRY B
2001; 105 (41): 10007-10015
View details for DOI 10.1021/jp0113127
View details for Web of Science ID 000171614900016
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Photoinduced intermolecular electron transfer in micelles: Dielectric and structural properties of micelle headgroup regions
JOURNAL OF PHYSICAL CHEMISTRY A
2001; 105 (39): 8944-8957
View details for DOI 10.1021/jp0106597
View details for Web of Science ID 000171401200016
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Temperature and density dependent solute vibrational relaxation in supercritical fluoroform
JOURNAL OF CHEMICAL PHYSICS
2001; 115 (10): 4689-4695
View details for Web of Science ID 000170647600032
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Two-dimensional ultrafast infrared vibrational echo studies of solute-solvent interactions and dynamics
JOURNAL OF CHEMICAL PHYSICS
2001; 115 (1): 317-330
View details for Web of Science ID 000169385300037
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Solute-solvent interactions: two-dimensional ultrafast infrared vibrational echo experiments
CHEMICAL PHYSICS LETTERS
2001; 340 (3-4): 267-274
View details for Web of Science ID 000169234100012
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Vibrational dephasing of carbonmonoxy myoglobin
JOURNAL OF PHYSICAL CHEMISTRY B
2001; 105 (19): 4068-4071
View details for DOI 10.1021/jp010798o
View details for Web of Science ID 000168803800005
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Two-dimensional time-frequency ultrafast infrared vibrational echo spectroscopy
PHYSICAL REVIEW LETTERS
2001; 86 (17): 3899-3902
Abstract
2D spectrally resolved ultrafast (<200 fs) IR vibrational echo experiments were performed on Rh(CO)(2)acac [(acetylacetonato)dicarbonylrhodium (I)]. The 2D spectra display features that reflect the 0-1 and 1-2 transitions and the combination band transition of the symmetric (S) and antisymmetric (A) CO stretching modes. Three oscillations in the data arise from the frequency difference between the S and A modes (quantum beats) and the S and A anharmonicities. A new explanation is given for these "anharmonic" oscillations. Calculations show that spectral resolution enables the 0-1 and 1-2 dephasing to be measured independently.
View details for Web of Science ID 000168338300051
View details for PubMedID 11329352
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Solute-solute spatial distribution in hydrogen bonding liquids probed with time-dependent intermolecular electron transfer
JOURNAL OF CHEMICAL PHYSICS
2001; 114 (10): 4552-4564
View details for Web of Science ID 000167367800023
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Effects of solvent viscosity on protein dynamics: Infrared vibrational echo experiments and theory
JOURNAL OF PHYSICAL CHEMISTRY B
2001; 105 (5): 1081-1092
View details for Web of Science ID 000166846100023
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Time domain optical studies of dynamics in supercooled o-terphenyl: Comparison to mode coupling theory on fast and slow time scales
JOURNAL OF PHYSICAL CHEMISTRY B
2001; 105 (1): 238-245
View details for Web of Science ID 000166324400035
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Fast protein dynamics probed with infrared vibrational echo experiments
ANNUAL REVIEW OF PHYSICAL CHEMISTRY
2001; 52: 315-356
Abstract
IR vibrational echo experiments are used to study dynamics in myoglobin (Mb) by investigating the dephasing of the CO-stretching mode of CO bound at the active site of the protein (Mb-CO). The temperature dependence and the viscosity dependence of Mb-CO pure dephasing have been measured in several solvents. In low-temperature, glassy solvents, the pure dephasing has a power law temperature dependence, T(1.3), that reflects glasslike protein dynamics. In liquids, the temperature dependence is much steeper and arises from a combination of pure temperature dependence and the influence of decreasing solvent viscosity with increasing temperature. As the solvent viscosity decreases, the ability of the protein's surface to undergo topological fluctuations increases, which in turn increases the internal protein-structural fluctuations. The protein-structural motions are coupled to the CO bound at the active site by electric field fluctuations that accompany movements of polar residues. The dynamic electric field-coupling mechanism is tested by observing differences in the temperature dependence of the pure dephasing of Mb-CO mutations.
View details for Web of Science ID 000169246500014
View details for PubMedID 11326068
- Dynamic Partitioning of an Aromatic Probe Between the Head Group and Core Regions of Cationic Micelles J. Phys. Chem. B 2001; 105: 10007-10015
- Photoinduced Intermolecular Electron Transfer in Micelles: Dielectric and Structural Properties of Micelle Head Group Regions J. Phys. Chem. A 2001; 105: 8944-8957
- Time Domain Optical Studies of Dynamics in Supercooled Ortho-terphenyl: Comparison to Mode Coupling Theory on Fast and Slow Time Scales J. Phys. Chem. 2001; 105: 238-245
- Infrared Vibrational Echo Experiments Ultrafast Infrared and Raman Spectroscopy, edited by Fayer, M. D. Marcel Dekker: New York. 2001: 227–272
- Ultrafast Infrared and Raman Spectroscopy Marcel Dekker, New York. 2001
- Elements of Quantum Mechanics Oxford University Press, New York. 2001
- Vibrational Relaxation of Polyatomic Molecules in Supercritical Fluids and the Gas Phase Ultrafast Infrared and Raman Spectroscopy edited by Fayer, M. D. Marcel Dekker: New York. 2001: 625–674
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Photoinduced intermolecular electron transfer in complex liquids: Experiment and theory
JOURNAL OF CHEMICAL PHYSICS
2000; 113 (22): 10191-10201
View details for Web of Science ID 000165584900039
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Distance dependence of electron transfer in DNA: The role of the reorganization energy and free energy
JOURNAL OF PHYSICAL CHEMISTRY B
2000; 104 (48): 11541-11550
View details for DOI 10.1021/jp001362w
View details for Web of Science ID 000165725700015
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A detailed test of mode-coupling theory on all time scales: Time domain studies of structural relaxation in a supercooled liquid
JOURNAL OF CHEMICAL PHYSICS
2000; 113 (9): 3723-3733
View details for Web of Science ID 000088878400029
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Two-pulse echo experiments in the spectral diffusion regime
JOURNAL OF CHEMICAL PHYSICS
2000; 113 (8): 3233-3242
View details for Web of Science ID 000088792800037
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Temperature dependence of solute vibrational relaxation in supercritical fluids: experiment and theory
CHEMICAL PHYSICS LETTERS
2000; 325 (5-6): 619-626
View details for Web of Science ID 000088612600021
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Vibrational lifetimes and spectral shifts in supercritical fluids as a function of density: Experiments and theory
JOURNAL OF PHYSICAL CHEMISTRY B
2000; 104 (10): 2402-2414
View details for Web of Science ID 000085902600026
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Orientational dynamics in supercooled liquids near T(c) and comparison with ideal mode-coupling theory
Physical review letters
2000; 84 (11): 2437-40
Abstract
Orientational dynamics in supercooled salol and ortho-terphenyl were measured near their critical temperatures, T(c), with optical Kerr effect experiments spanning a very broad range of times. Above T(c), the decays are shown to be in excellent agreement with the master curve predicted by ideal mode-coupling theory when higher order terms are included. Between the critical decay and the von Schweidler power laws, the intermediate time range of the data can be modeled by a power law. This intermediate power law, located at 2
View details for PubMedID 11018904
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Orientational dynamics in supercooled liquids near T-c and comparison with ideal mode-coupling theory
PHYSICAL REVIEW LETTERS
2000; 84 (11): 2437-2440
View details for Web of Science ID 000085791900039
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Dynamics in globular proteins: vibrational echo experiments
CHEMICAL PHYSICS LETTERS
2000; 316 (1-2): 122-128
View details for Web of Science ID 000084839600019
- Orientational Dynamics in Supercooled Liquids Near Tc and Comparison to Ideal Mode Coupling Theory Phys. Rev. Lett. 2000; 84: 2437-2440
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Density dependent vibrational relaxation in supercritical fluids
CHEMICAL PHYSICS LETTERS
1999; 313 (3-4): 592-599
View details for Web of Science ID 000083977700031
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Non-exponential relaxation of a single quantum vibrational excitation of a large molecule in collision free gas phase at elevated temperature
CHEMICAL PHYSICS LETTERS
1999; 312 (5-6): 399-406
View details for Web of Science ID 000083955200008
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Phase separation in binary and ternary polymer composites studied with electronic excitation transport
MACROMOLECULES
1999; 32 (20): 6638-6645
View details for Web of Science ID 000083003300034
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Translational-rotational coupling in supercooled liquids: Heterodyne detected density induced molecular alignment
JOURNAL OF CHEMICAL PHYSICS
1999; 111 (6): 2710-2719
View details for Web of Science ID 000081711200039
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T-2 selective scanning vibrational echo spectroscopy
CHEMICAL PHYSICS LETTERS
1999; 305 (1-2): 51-56
View details for Web of Science ID 000080307200009
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Density-induced heterodyne-amplified rotational dynamics: a new technique for studying orientational relaxation
CHEMICAL PHYSICS LETTERS
1999; 304 (1-2): 28-34
View details for Web of Science ID 000079956000005
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A dynamical transition in the protein myoglobin observed by infrared vibrational echo experiments
JOURNAL OF PHYSICAL CHEMISTRY A
1999; 103 (14): 2381-2387
View details for Web of Science ID 000079837600027
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Crack propagation induced heating in crystalline energetic materials
JOURNAL OF CHEMICAL PHYSICS
1999; 110 (7): 3576-3583
View details for Web of Science ID 000078446100035
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Nitro group asymmetric stretching mode lifetimes of molecules used in energetic materials
CHEMICAL PHYSICS LETTERS
1999; 299 (1): 84-90
View details for Web of Science ID 000077850200012
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Myoglobin dynamics measured with vibrational echo experiments
8th International Conference on Time-Resolved Vibrational Spectroscopy
TAYLOR & FRANCIS LTD. 1999: 19–34
View details for Web of Science ID 000081370000004
- T2 Selective Scanning Vibrational Echo Spectroscopy Chem. Phys. Lett. 1999; 305: 51-56
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Monte Carlo simulations of electronic excitation transfer in polymer composites and comparison to theory
JOURNAL OF CHEMICAL PHYSICS
1998; 109 (19): 8708-8718
View details for Web of Science ID 000077005000064
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Temperature dependent vibrational lifetimes in supercritical fluids near the critical point
JOURNAL OF CHEMICAL PHYSICS
1998; 109 (14): 5971-5979
View details for Web of Science ID 000076216900033
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Vibrational echo spectroscopy: Spectral selectivity from vibrational coherence
JOURNAL OF CHEMICAL PHYSICS
1998; 109 (13): 5455-5465
View details for Web of Science ID 000076152700034
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Fluorescent probe solubilization in the headgroup and core regions of micelles: Fluorescence lifetime and orientational relaxation measurements
JOURNAL OF PHYSICAL CHEMISTRY B
1998; 102 (37): 7216-7224
View details for Web of Science ID 000076219600023
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Polystyrene size determination in polystyrene and poly(vinyl methyl ether) using electronic excitation transport
JOURNAL OF PHYSICAL CHEMISTRY B
1998; 102 (37): 7112-7119
View details for Web of Science ID 000076219600008
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Myoglobin's ultrafast dynamics measured with vibrational echo experiments
International Symposium on Free Electron Laser Facilities and Applications (FELFA 98)
ELSEVIER SCIENCE BV. 1998: 218–24
View details for Web of Science ID 000076020700033
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Solvent reorganization energy and free energy change for donor/acceptor electron transfer at micelle surfaces: Theory and experiment
JOURNAL OF PHYSICAL CHEMISTRY B
1998; 102 (31): 6078-6088
View details for Web of Science ID 000075277400022
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Vibrational echoes: a new approach to condensed-matter vibrational spectroscopy
INTERNATIONAL REVIEWS IN PHYSICAL CHEMISTRY
1998; 17 (3): 261-306
View details for Web of Science ID 000075551700001
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Vibrational dynamics of polyatomic molecules in polyatomic supercritical fluids near the critical point.
AMER CHEMICAL SOC. 1998: U148–U148
View details for Web of Science ID 000072414500490
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Vibrational dephasing mechanisms in liquids and glasses: Vibrational echo experiments
JOURNAL OF CHEMICAL PHYSICS
1998; 108 (5): 1794-1803
View details for Web of Science ID 000071748000007
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Dynamics of myoglobin-CO with the proximal histidine removed: Vibrational echo experiments
JOURNAL OF PHYSICAL CHEMISTRY B
1998; 102 (2): 331-333
View details for Web of Science ID 000071542300002
- Vibrational Echoes: A New Approach to Condensed Mater Vibrational Spectroscopy Internat. Rev. Phys. Chem. 1998; 17: 261-306
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Vibrational echo studies of proteins, liquids, and glasses
Conference on Laser Techniques for Condensed-Phase and Biological Systems
SPIE-INT SOC OPTICAL ENGINEERING. 1998: 34–45
View details for Web of Science ID 000074381300004
- Polystyrene Size Determination in Polystyrene and Polyvinylmethylether Using Electronic Excitation Transport J. Phys. Chem. B 1998; 102: 7112-7119
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Temperature dependence of vibrational lifetimes at the critical density in supercritical mixtures
JOURNAL OF CHEMICAL PHYSICS
1997; 107 (23): 9741-9748
View details for Web of Science ID A1997YK98200003
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Vibrational relaxation in supercritical fluids near the critical point
JOURNAL OF CHEMICAL PHYSICS
1997; 107 (19): 7642-7650
View details for Web of Science ID A1997YG65500006
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Photoinduced electron transfer on the surfaces of micelles
JOURNAL OF PHYSICAL CHEMISTRY B
1997; 101 (45): 9352-9361
View details for Web of Science ID A1997YF25500030
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Photoinduced electron transfer between donors and acceptors on micelle surfaces
CHEMICAL PHYSICS LETTERS
1997; 276 (5-6): 309-315
View details for Web of Science ID A1997XZ47800003
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Vibrational echo studies of pure dephasing: Mechanisms in liquids and glasses
CHEMICAL PHYSICS LETTERS
1997; 276 (3-4): 217-223
View details for Web of Science ID A1997XY27700007
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Effect of chromophore diffusion on electronic excitation transfer in micellar systems
CHEMICAL PHYSICS LETTERS
1997; 276 (3-4): 274-281
View details for Web of Science ID A1997XY27700017
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Vibrational lifetimes and vibrational line positions in polyatomic supercritical fluids near the critical point
JOURNAL OF CHEMICAL PHYSICS
1997; 107 (10): 3747-3757
View details for Web of Science ID A1997XV75600001
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Vibrational anharmonicity and multilevel vibrational dephasing from vibrational echo beats
JOURNAL OF CHEMICAL PHYSICS
1997; 106 (24): 10027-10036
View details for Web of Science ID A1997XE59300005
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Electronic dephasing in nonpolar room temperature liquids: UV photon echo pulse duration dependent measurements
JOURNAL OF CHEMICAL PHYSICS
1997; 106 (18): 7498-7511
View details for Web of Science ID A1997WX28900004
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Temperature-dependent vibrational and orientational relaxation of monocarbonyls in polyatomic solvents.
AMER CHEMICAL SOC. 1997: 117-PHYS
View details for Web of Science ID A1997WP18702376
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Photoinduced electron transfer and geminate recombination in liquids
JOURNAL OF PHYSICAL CHEMISTRY A
1997; 101 (10): 1887-1902
View details for Web of Science ID A1997WL76900017
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Mutant and wild-type myoglobin-CO protein dynamics: Vibrational echo experiments
JOURNAL OF PHYSICAL CHEMISTRY B
1997; 101 (8): 1468-1475
View details for Web of Science ID A1997WL11700029
- Vibrational Echo Studies of Heme Protein Dynamics ACS Symp. Ser. edited by Foukas, J. T., Kivelson, D., Mohanty, U., Nelson, K. A. 1997: 337–50
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Vibrational echo studies of heme-protein dynamics
Symposium on Supercooled Liquids - Advances and Novel Applications, at the 212th National Meeting of the American-Chemical-Society
AMER CHEMICAL SOC. 1997: 324–337
View details for Web of Science ID A1997BJ91B00023
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Electronic excitation transfer as a probe of phase behavior in polymer composites
Conference on Advances in Fluorescence Sensing Technology III
SPIE - INT SOC OPTICAL ENGINEERING. 1997: 446–452
View details for Web of Science ID A1997BH84B00050
- Electronic Dephasing of a Non-polar Solute in Non-polar Liquids: UV Femtosecond Photon Echo Pulse Duration Dependent Measurements J. Chem. Phys. 1997; 106: 7498-7511
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Vibrational relaxation of a polyatomic solute in a polyatomic supercritical fluid near the critical point
JOURNAL OF CHEMICAL PHYSICS
1996; 105 (19): 8973-8976
View details for Web of Science ID A1996VT10200054
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Tuning the vibrational relaxation of CO bound to heme and metalloporphyrin complexes
JOURNAL OF PHYSICAL CHEMISTRY
1996; 100 (46): 18023-18032
View details for Web of Science ID A1996VT70800004
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Vibrational echo studies of myoglobin-CO
JOURNAL OF PHYSICAL CHEMISTRY
1996; 100 (38): 15620-15629
View details for Web of Science ID A1996VH46300044
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Vibrational relaxation in metalloporphyrin CO complexes
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
1996; 118 (33): 7853-7854
View details for Web of Science ID A1996VD32800031
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Vibrational echo studies of protein dynamics
PHYSICAL REVIEW LETTERS
1996; 77 (8): 1648-1651
View details for Web of Science ID A1996VC33600060
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Vibrational dynamics of carbon monoxide at the active sites of mutant heme proteins
JOURNAL OF PHYSICAL CHEMISTRY
1996; 100 (29): 12100-12107
View details for Web of Science ID A1996UX96100035
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Photophysical studies of probes bound to cross-link junctions in poly(dimethyl siloxane) elastomers and nanocomposites
3rd International Symposium on Functional Dyes (FUNCTIONAL DYE 95)
INT UNION PURE APPLIED CHEMISTRY. 1996: 1381–88
View details for Web of Science ID A1996VA06500005
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Calculations of electronic excitation transfer: Applications to ordered phases in polymeric materials
JOURNAL OF PHYSICAL CHEMISTRY
1996; 100 (24): 10257-10264
View details for Web of Science ID A1996UQ84400037
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Experimental and theoretical analysis of photoinduced electron transfer: Including the role of liquid structure
JOURNAL OF PHYSICAL CHEMISTRY
1996; 100 (20): 8106-8117
View details for Web of Science ID A1996UL28200013
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Rotational dynamics of naphthalene-labeled cross-link junctions in poly(dimethylsiloxane) elastomers
JOURNAL OF PHYSICAL CHEMISTRY
1996; 100 (18): 7646-7655
View details for Web of Science ID A1996UJ11700046
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Electronic spectral diffusion in glasses: The influence of coupling to the medium on experimental observables
JOURNAL OF CHEMICAL PHYSICS
1996; 104 (11): 3865-3875
View details for Web of Science ID A1996TY72800001
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Role of diffusion in photoinduced electron transfer on a micelle surface: Theoretical and Monte Carlo investigations
JOURNAL OF PHYSICAL CHEMISTRY
1996; 100 (9): 3767-3774
View details for Web of Science ID A1996TX76600066
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Solvent structure and hydrodynamic effects in photoinduced electron transfer
JOURNAL OF CHEMICAL PHYSICS
1996; 104 (8): 2976-2986
View details for Web of Science ID A1996TV78700026
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Ultrafast infrared spectroscopy in biomolecules: Active site dynamics of heme proteins
7th International Conference on Time Resolved Vibrational Spectroscopy (TRVS-7)
JOHN WILEY & SONS LTD. 1996: 277–99
View details for Web of Science ID A1996VM55100003
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Chromophore rich nanodomains in bulk and ultra thin film polymer blends
7th International Conference on Unconventional Photoactive Systems
GORDON BREACH PUBLISHING, TAYLOR & FRANCIS GROUP. 1996: 31–35
View details for Web of Science ID A1996UU78900006
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Temperature-dependent vibrational dynamics and inhomogeneous broadening in glass-forming liquids studied with infrared photon echoes
9th International Symposium on Ultrafast Processes in Spectroscopy (UPS 95)
PLENUM PRESS DIV PLENUM PUBLISHING CORP. 1996: 123–125
View details for Web of Science ID A1996BH05B00027
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Vibrational population dynamics in liquids and glasses - IR pump-probe experiments from 10 K to 300 K
9th International Symposium on Ultrafast Processes in Spectroscopy (UPS 95)
PLENUM PRESS DIV PLENUM PUBLISHING CORP. 1996: 115–117
View details for Web of Science ID A1996BH05B00025
- Rotational Dynamics of Naphthalene-Labeled Cross-link Junctions of Varying Functionality in Poly(dimethylsiloxane) Elastomers J. Phys. Chem. 1996; 100: 7646-7655
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Theory of electronic excitation transfer in polymer micelles and lamellae
7th International Conference on Unconventional Photoactive Systems
GORDON BREACH PUBLISHING, TAYLOR & FRANCIS GROUP. 1996: 173–177
View details for Web of Science ID A1996UU78900028
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Nanodomain formation and phase separation in polymer blends
Fluorescence Detection IV Conference
SPIE - INT SOC OPTICAL ENGINEERING. 1996: 136–142
View details for Web of Science ID A1996BF25C00015
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Liquid, glass, and protein vibrational dynamics: Infrared vibrational echo experiments
Proceedings of the Fifth International Meeting on Hole Burning and Related Spectroscopies (HBRS'96) - Science and Applications
GORDON BREACH PUBLISHING, TAYLOR & FRANCIS GROUP. 1996: 1–9
View details for Web of Science ID A1996WE58000002
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PHOTOINDUCED ELECTRON-TRANSFER AND GEMINATE RECOMBINATION IN LIQUIDS - ANALYTICAL THEORY AND MONTE-CARLO SIMULATIONS
JOURNAL OF CHEMICAL PHYSICS
1995; 103 (20): 8864-8872
View details for Web of Science ID A1995TF29800009
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NANODOMAIN FORMATION IN A LIQUID POLYMER BLEND - THE INITIAL-STAGES OF PHASE-SEPARATION
JOURNAL OF CHEMICAL PHYSICS
1995; 103 (18): 8189-8200
View details for Web of Science ID A1995TC85400054
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INFRARED PHOTON-ECHO EXPERIMENTS - EXPLORING VIBRATIONAL DYNAMICS IN LIQUIDS AND GLASSES
ACCOUNTS OF CHEMICAL RESEARCH
1995; 28 (11): 437-445
View details for Web of Science ID A1995TE93600001
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VIBRATIONAL-RELAXATION OF CARBON-MONOXIDE IN MODEL HEME COMPOUNDS - 6-COORDINATE METALLOPORPHYRINS (M=FE, RU, OS)
CHEMICAL PHYSICS LETTERS
1995; 244 (3-4): 218-223
View details for Web of Science ID A1995RY33200005
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INFRARED VIBRATIONAL PHOTON-ECHO EXPERIMENTS IN LIQUIDS AND GLASSES
JOURNAL OF PHYSICAL CHEMISTRY
1995; 99 (36): 13310-13320
View details for Web of Science ID A1995RU47600003
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THE LOW-FREQUENCY DENSITY-OF-STATES AND VIBRATIONAL POPULATION-DYNAMICS OF POLYATOMIC-MOLECULES IN LIQUIDS
JOURNAL OF CHEMICAL PHYSICS
1995; 103 (9): 3325-3334
View details for Web of Science ID A1995RT92300006
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HOMOGENEOUS VIBRATIONAL DYNAMICS AND INHOMOGENEOUS BROADENING IN GLASS-FORMING LIQUIDS - INFRARED PHOTON-ECHO EXPERIMENTS FROM ROOM-TEMPERATURE TO 10 K
JOURNAL OF CHEMICAL PHYSICS
1995; 103 (8): 2810-2826
View details for Web of Science ID A1995RP71500005
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VIBRATIONAL DYNAMICS OF LIQUIDS AND GLASSES PROBED WITH IR PHOTON-ECHOES
International Workshop on Laser Physics (LPHYS-94)
INTERPERIODICA. 1995: 652–55
View details for Web of Science ID A1995RE19300038
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VIBRATIONAL DYNAMICS IN CONDENSED MATTER PROBED WITH LINAC BASED FELS
16th International Free Electron Laser Conference
ELSEVIER SCIENCE BV. 1995: 540–43
View details for Web of Science ID A1995QR44300145
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MULTILEVEL VIBRATIONAL DEPHASING AND VIBRATIONAL ANHARMONICITY FROM INFRARED PHOTON-ECHO BEATS
CHEMICAL PHYSICS LETTERS
1995; 234 (4-6): 289-295
View details for Web of Science ID A1995QK79900004
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VIBRATIONAL SPECTRAL DIFFUSION AND POPULATION-DYNAMICS IN A GLASS-FORMING LIQUID - VARIABLE BANDWIDTH PICOSECOND INFRARED-SPECTROSCOPY
JOURNAL OF CHEMICAL PHYSICS
1995; 102 (10): 3919-3931
View details for Web of Science ID A1995QL73400003
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THEORY OF UNIVERSAL FAST ORIENTATIONAL DYNAMICS IN THE ISOTROPIC-PHASE OF LIQUID-CRYSTALS
JOURNAL OF CHEMICAL PHYSICS
1995; 102 (10): 4193-4202
View details for Web of Science ID A1995QL73400033
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PHOTOINDUCED ELECTRON-TRANSFER AND GEMINATE RECOMBINATION ON A MICELLE SURFACE - ANALYTICAL THEORY AND MONTE-CARLO SIMULATIONS
JOURNAL OF CHEMICAL PHYSICS
1995; 102 (9): 3820-3829
View details for Web of Science ID A1995QH96800033
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EXCLUDED-VOLUME EFFECTS IN PHOTOINDUCED ELECTRON-TRANSFER AND GEMINATE RECOMBINATION - ANALYTICAL THEORY AND SIMULATIONS
JOURNAL OF PHYSICAL CHEMISTRY
1995; 99 (7): 1856-1866
View details for Web of Science ID A1995QG92400012
- Vibrational Dynamics in Liquids and Glasses Probed with Infrared Photon Echoes Using a Free Electron Laser edited by Barbara, P. F., Knox, W. H., Mourou, G. A., Zewail, A. H., 1995: 58–62
- Vibrational Dynamics at the Active Site of Myoglobin: Picosecond Infrared Free Electron Laser Experiments edited by Barbara, P. F., Knox, W. H., Mourou, G. A., Zewail, A. H. 1995: 445–47
- Local Order and Ultrafast Molecular Dynamics in Liquids: Subpicosecond Transient Grating Optical Kerr Effect Experiments edited by Barbara, P. F., Knox, W. H., Mourou, G. A., Zewail, A. H. 1995: 97–98
- Vibrational Dynamics in Condensed Matter Probed with Linac Based FELs Nuclear Instruments & Methods in Physics Research A 1995; 358: 550-553
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THEORY OF VIBRATIONAL-RELAXATION OF POLYATOMIC-MOLECULES IN LIQUIDS
JOURNAL OF CHEMICAL PHYSICS
1994; 101 (12): 10618-10629
View details for Web of Science ID A1994QJ59200043
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VIBRATIONAL DYNAMICS OF CARBON-MONOXIDE AT THE ACTIVE-SITE OF MYOGLOBIN - PICOSECOND INFRARED FREE-ELECTRON LASER PUMP-PROBE EXPERIMENTS
JOURNAL OF PHYSICAL CHEMISTRY
1994; 98 (43): 11213-11219
View details for Web of Science ID A1994PN85800032
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VIBRATIONAL PHOTON-ECHOES IN A LIQUID AND GLASS - ROOM-TEMPERATURE TO 10-K
JOURNAL OF CHEMICAL PHYSICS
1994; 101 (2): 1741-1744
View details for Web of Science ID A1994NW97900092
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INTERMOLECULAR STRUCTURE IN A SINGLE-COMPONENT POLYMER GLASS - TOWARDS HIGH-RESOLUTION MEASUREMENTS OF THE SIDE-CHAIN PAIR CORRELATION-FUNCTION
JOURNAL OF CHEMICAL PHYSICS
1994; 100 (12): 9156-9169
View details for Web of Science ID A1994NR28400066
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TEMPERATURE-DEPENDENT VIBRATIONAL-RELAXATION IN POLYATOMIC LIQUIDS - PICOSECOND INFRARED PUMP-PROBE EXPERIMENTS
JOURNAL OF CHEMICAL PHYSICS
1994; 100 (12): 9035-9043
View details for Web of Science ID A1994NR28400053
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PHONON-INDUCED SCATTERING BETWEEN VIBRATIONS AND MULTIPHOTON VIBRATIONAL UP-PUMPING IN LIQUID SOLUTION
CHEMICAL PHYSICS LETTERS
1994; 221 (5-6): 412-418
View details for Web of Science ID A1994NJ12000014
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DYNAMICS IN POLYDIMETHYLSILOXANE - THE EFFECT OF SOLUTE POLARITY
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
1994; 116 (3): 1027-1032
View details for Web of Science ID A1994MW99000025
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ULTRAFAST NONEXPONENTIAL DYNAMICS IN A POLYMER GLASS-FORMING LIQUID
JOURNAL OF CHEMICAL PHYSICS
1994; 100 (2): 1673-1683
View details for Web of Science ID A1994MT00700100
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EFFECTS OF LOCAL LIQUID STRUCTURE ON ORIENTATIONAL RELAXATION - 2-ETHYLNAPHTHALENE, NEAT AND IN SOLUTION
JOURNAL OF PHYSICAL CHEMISTRY
1994; 98 (1): 313-320
View details for Web of Science ID A1994MR06800052
- Local Order and Ultrafast dynamics in Liquids Transient Grating Optical Kerr Effect Experiments edited by Rizzo, T., Myers, A. John Wiley & Sons, New York. 1994: 211–282
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PICOSECOND VIBRATIONAL PHOTON-ECHO EXPERIMENTS IN LIQUIDS AND GLASSES
Conference on Longer Wavelength Lasers and Applications
SPIE - INT SOC OPTICAL ENGINEERING. 1994: 26–34
View details for Web of Science ID A1994BB27G00004
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MOLECULAR-ENERGY TRANSFER IN CONDENSED MATTER STUDIED BY ULTRAFAST VIBRATIONAL SPECTROSCOPY
Conference on Longer Wavelength Lasers and Applications
SPIE - INT SOC OPTICAL ENGINEERING. 1994: 75–84
View details for Web of Science ID A1994BB27G00010
- Electron Transfer in Solution: Theory and Experiment Ultrafast Spectroscopy of Chemical Systems edited by John, S. Kluwer Academic Publishers. 1994: 37–80
- Phonon Induced Scattering Between Vibrations and Multiphoton Up-pumping in Liquid Solution Chem. Phys. Lett. 1994; 221: 412-418
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STRUCTURE OF COMPLEX-SYSTEMS USING ELECTRONIC EXCITATION TRANSPORT - THEORY, MONTE-CARLO SIMULATIONS, AND EXPERIMENTS ON MICELLE SOLUTIONS
JOURNAL OF CHEMICAL PHYSICS
1994; 100 (1): 271-286
View details for Web of Science ID A1994MN42600030
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INFLUENCE OF LOCAL LIQUID STRUCTURE ON ORIENTATIONAL DYNAMICS - ISOTROPIC-PHASE OF LIQUID-CRYSTALS
JOURNAL OF PHYSICAL CHEMISTRY
1993; 97 (37): 9478-9487
View details for Web of Science ID A1993LY47200036
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OPTICAL PARAMETRIC AMPLIFICATION OF 1-KHZ HIGH-ENERGY PICOSECOND MIDINFRARED PULSES AND APPLICATION TO INFRARED TRANSIENT-GRATING EXPERIMENTS ON DIAMOND
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS
1993; 10 (9): 1785-1791
View details for Web of Science ID A1993LV98600036
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INTERMOLECULAR STRUCTURE IN A POLYMER GLASS - ELECTRONIC EXCITATION TRANSFER STUDIES
MACROMOLECULES
1993; 26 (12): 3041-3048
View details for Web of Science ID A1993LG45300008
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TRANSIENT GRATING DIFFRACTION FROM AN INTERFACE BETWEEN 2 MATERIALS - THEORY AND EXPERIMENTAL APPLICATION
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS
1993; 10 (6): 1006-1016
View details for Web of Science ID A1993LF37400008
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DYNAMICS OF IONIC LIPOPHILIC PROBES IN MICELLES - PICOSECOND FLUORESCENCE DEPOLARIZATION MEASUREMENTS
JOURNAL OF PHYSICAL CHEMISTRY
1993; 97 (21): 5762-5769
View details for Web of Science ID A1993LE40100049
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EXTRA RESONANCES IN TIME-DOMAIN 4-WAVE-MIXING
OPTICS LETTERS
1993; 18 (10): 781-783
Abstract
We show that extra resonances, such as those caused in frequency-domain nonlinear wave mixing by pure dephasing or laser fluctuations, can also be induced by operation in the time domain. These pulse-length-induced extra resonances arise in transient-grating experiments when the laser pulses are short enough that a steady state cannot be achieved during the excitation process. We show theoretically that these resonances increase in strength with decreasing excitation pulse length until the pulse length becomes shorter than the dephasing time of the medium and quote an experimental example to support this interpretation.
View details for Web of Science ID A1993LA94700009
View details for PubMedID 19802271
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PICOSECOND INFRARED VIBRATIONAL PHOTON-ECHOES IN A LIQUID AND GLASS USING A FREE-ELECTRON LASER
PHYSICAL REVIEW LETTERS
1993; 70 (18): 2718-2721
View details for Web of Science ID A1993KZ98900015
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CHEMICAL-REACTION INITIATION AND HOT-SPOT FORMATION IN SHOCKED ENERGETIC MOLECULAR MATERIALS
JOURNAL OF PHYSICAL CHEMISTRY
1993; 97 (9): 1901-1913
View details for Web of Science ID A1993KQ33900031
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FLAME TEMPERATURE-MEASUREMENT USING PICOSECOND TRANSIENT GRATING EXPERIMENTS
CHEMICAL PHYSICS LETTERS
1993; 203 (4): 344-348
View details for Web of Science ID A1993KN04700005
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PHOTOINDUCED ELECTRON-TRANSFER AND GEMINATE RECOMBINATION IN SOLUTION
JOURNAL OF PHYSICAL CHEMISTRY
1993; 97 (7): 1374-1382
View details for Web of Science ID A1993KM69400021
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THERMAL-BOUNDARY RESISTANCE AND DIFFUSIVITY MEASUREMENTS ON THIN YBA2CU3O7-X FILMS WITH MGO AND SRTIO3 SUBSTRATES USING THE TRANSIENT GRATING METHOD
JOURNAL OF APPLIED PHYSICS
1993; 73 (2): 850-857
View details for Web of Science ID A1993KG47600051
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PICOSECOND INFRARED VIBRATIONAL PHOTON-ECHOES AND LIFETIME MEASUREMENTS USING THE STANFORD SUPERCONDUCTING-ACCELERATOR-PUMPED FREE-ELECTRON LASER
CONF ON FREE-ELECTRON LASER SPECTROSCOPY IN BIOLOGY, MEDICINE, AND MATERIALS SCIENCE
SPIE - INT SOC OPTICAL ENGINEERING. 1993: 86–93
View details for Web of Science ID A1993BY82X00011
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SHOCKED ENERGETIC MOLECULAR MATERIALS - CHEMICAL-REACTION INITIATION AND HOT-SPOT FORMATION
SYMP ON STRUCTURE AND PROPERTIES OF ENERGETIC MATERIALS, AT THE 1992 FALL MEETING OF THE MATERIALS RESEARCH SOC
MATERIALS RESEARCH SOC. 1993: 379–384
View details for Web of Science ID A1993BY43U00048
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ULTRAFAST DYNAMICS OF NEMATIC LIQUID-CRYSTALS IN THE ISOTROPIC-PHASE
CONF ON ULTRAFAST PULSE GENERATION AND SPECTROSCOPY
SPIE - INT SOC OPTICAL ENGINEERING. 1993: 263–274
View details for Web of Science ID A1993BY83B00028
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FEL-MICROSCOPY FOR THE INVESTIGATION OF TRANSIENT LOCAL HEATING IN SINGLE LIVING CELLS
CONF ON FREE-ELECTRON LASER SPECTROSCOPY IN BIOLOGY, MEDICINE, AND MATERIALS SCIENCE
SPIE - INT SOC OPTICAL ENGINEERING. 1993: 154–161
View details for Web of Science ID A1993BY82X00018
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INTERFACE SELECTIVE TRANSIENT GRATING SPECTROSCOPY - THEORY AND APPLICATIONS TO THERMAL FLOW AND ACOUSTIC PROPAGATION IN SUPERCONDUCTING THIN-FILMS
CONF ON ULTRAFAST PULSE GENERATION AND SPECTROSCOPY
SPIE - INT SOC OPTICAL ENGINEERING. 1993: 302–313
View details for Web of Science ID A1993BY83B00032
- Optical Parametric Generation of 1 kHz, High Energy, Picosecond Infrared Pulses and Application to Infrared Transient Grating Experiments on Diamond J.O.S.A. B 1993; 10: 1785-1791
- Extra Resonances in Time-Domain Four-Wave Mixing Experiments Optics Letters 1993; 18: 781-783
- Thermal Diffusivity Measurement of Natural and Isotopically Enriched Diamond by Picosecond Infrared Transient Grating Experiments Applied Physics A 1993; 56: 87-90
- Shocked Energetic Molecular Materials: Chemical Reaction Initiation and Hot Spot Formation Materials Research Society edited by Liebenberg, D. H., Armstrong, R. W., Gilman, J. J. 1993: 379–84
- Dynamics in Complex Liquids: Optical Nonlinear Experiments Femtosecond Spectroscopy of Chemical Reactions 1993: 271-286
- The Influence of Local Liquid Structure on Orientational Dynamics: The Isotropic Phase of Liquid Crystals J. Phys. Chem. 1993; 97: 9478-9487
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ELECTRONIC EXCITATION TRANSFER IN CONCENTRATED MICELLE SOLUTIONS
JOURNAL OF PHYSICAL CHEMISTRY
1992; 96 (22): 8930-8937
View details for Web of Science ID A1992JW46400043
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ULTRAFAST SIDE GROUP MOTIONS OF POLYMERS
JOURNAL OF PHYSICAL CHEMISTRY
1992; 96 (21): 8619-8626
View details for Web of Science ID A1992JU55500075
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SPECTRAL DIFFUSION IN LIQUIDS
JOURNAL OF CHEMICAL PHYSICS
1992; 97 (5): 2948-2962
View details for Web of Science ID A1992JL37200012
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THE GRATING DECOMPOSITION METHOD - A NEW APPROACH FOR UNDERSTANDING POLARIZATION-SELECTIVE TRANSIENT GRATING EXPERIMENTS .1. THEORY
JOURNAL OF CHEMICAL PHYSICS
1992; 97 (1): 69-77
View details for Web of Science ID A1992JA79200009
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THE GRATING DECOMPOSITION METHOD - A NEW APPROACH FOR UNDERSTANDING POLARIZATION-SELECTIVE TRANSIENT GRATING EXPERIMENTS .2. APPLICATIONS
JOURNAL OF CHEMICAL PHYSICS
1992; 97 (1): 78-85
View details for Web of Science ID A1992JA79200010
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NANOSECOND TIME SCALE DYNAMICS OF PSEUDO-NEMATIC DOMAINS IN THE ISOTROPIC-PHASE OF LIQUID-CRYSTALS
CHEMICAL PHYSICS LETTERS
1992; 194 (3): 213-216
View details for Web of Science ID A1992JB82000014
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DYNAMICS IN POLY(DIMETHYLSILOXANE) MELTS - FLUORESCENCE DEPOLARIZATION MEASUREMENTS OF PROBE CHROMOPHORE ORIENTATIONAL RELAXATION
JOURNAL OF PHYSICAL CHEMISTRY
1992; 96 (13): 5255-5263
View details for Web of Science ID A1992JB26400017
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LOCAL-STRUCTURE DYNAMICS IN LIQUIDS - NONHYDRODYNAMIC ORIENTATIONAL RELAXATION OF 2-ETHYL NAPHTHALENE
CHEMICAL PHYSICS LETTERS
1992; 193 (1-3): 49-54
View details for Web of Science ID A1992HW68300008
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THE INFLUENCE OF DIFFUSION ON PHOTOINDUCED ELECTRON-TRANSFER AND GEMINATE RECOMBINATION
JOURNAL OF CHEMICAL PHYSICS
1992; 96 (10): 7410-7422
View details for Web of Science ID A1992HU55700021
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THE TRANSIENT GRATING - A HOLOGRAPHIC WINDOW TO DYNAMIC PROCESSES
ACCOUNTS OF CHEMICAL RESEARCH
1992; 25 (5): 227-233
View details for Web of Science ID A1992HU24800004
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THERMAL-DIFFUSION, INTERFACIAL THERMAL BARRIER, AND ULTRASONIC PROPAGATION IN YBA2CU3O7-X THIN-FILMS - SURFACE-SELECTIVE TRANSIENT-GRATING EXPERIMENTS
PHYSICAL REVIEW B
1992; 45 (17): 10009-10021
View details for Web of Science ID A1992HR54300055
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DYNAMICS IN A LOW-TEMPERATURE GLASS - FAST GENERATION AND DETECTION OF OPTICAL HOLES
JOURNAL OF CHEMICAL PHYSICS
1992; 96 (5): 3484-3494
View details for Web of Science ID A1992HG95300016
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REORIENTATIONAL MOTION OF A CROSS-LINK JUNCTION IN A POLY(DIMETHYLSILOXANE) NETWORK MEASURED BY TIME-RESOLVED FLUORESCENCE DEPOLARIZATION
JOURNAL OF CHEMICAL PHYSICS
1992; 96 (4): 3269-3278
View details for Web of Science ID A1992HE74300090
- Reorientational Motion of a Crosslink Junction in a Poly(dimethylsiloxane) Network Measured by Time-resolved Fluorescence Depolarization J. Chem. Phys. 1992; 96: 3269-3278
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APPLICATIONS OF INFRARED FREE-ELECTRON LASERS - BASIC RESEARCH ON THE DYNAMICS OF MOLECULAR-SYSTEMS
IEEE JOURNAL OF QUANTUM ELECTRONICS
1991; 27 (12): 2697-2713
View details for Web of Science ID A1991GR21700027
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PICOSECOND POLARIZATION-SELECTIVE TRANSIENT GRATING EXPERIMENTS IN SODIUM-SEEDED FLAMES
JOURNAL OF CHEMICAL PHYSICS
1991; 95 (8): 5775-5784
View details for Web of Science ID A1991GJ59200028
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SURFACE SELECTIVITY IN 4-WAVE-MIXING - TRANSIENT GRATINGS AS A THEORETICAL AND EXPERIMENTAL EXAMPLE
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS
1991; 8 (9): 1880-1888
View details for Web of Science ID A1991GD76600014
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PICOSECOND PHOTON-ECHO EXPERIMENTS USING A SUPERCONDUCTING ACCELERATOR-PUMPED FREE-ELECTRON LASER
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS
1991; 8 (8): 1652-1662
View details for Web of Science ID A1991GA28100014
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TEMPERATURE-DEPENDENT INTERSYSTEM CROSSING AND TRIPLET TRIPLET ABSORPTION OF RUBRENE IN SOLID-SOLUTION
JOURNAL OF LUMINESCENCE
1991; 50 (2): 75-81
View details for Web of Science ID A1991GD76200002
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PICOSECOND FEL EXPERIMENTS ON CONDENSED MATTER SYSTEMS
12TH INTERNATIONAL CONF ON FREE ELECTRON LASER ( FEL 90 )
ELSEVIER SCIENCE BV. 1991: 797–97
View details for Web of Science ID A1991FV59500171
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INFLUENCE OF DIFFUSION ON PHOTOINDUCED ELECTRON-TRANSFER
JOURNAL OF PHYSICAL CHEMISTRY
1991; 95 (9): 3454-3457
View details for Web of Science ID A1991FK32200003
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ELECTRONIC EXCITATION TRANSFER IN CLUSTERED CHROMOPHORE SYSTEMS - CALCULATION OF TIME-RESOLVED OBSERVABLES FOR INTERCLUSTER TRANSFER
JOURNAL OF CHEMICAL PHYSICS
1991; 94 (8): 5622-5630
View details for Web of Science ID A1991FH07600043
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FORWARD AND BACK PHOTOINDUCED ELECTRON-TRANSFER IN SOLID-SOLUTIONS - A COMPARISON OF THEORETICAL METHODS
CHEMICAL PHYSICS LETTERS
1991; 179 (1-2): 152-158
View details for Web of Science ID A1991FH14300026
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PHOTORESPONSE OF NB FILMS - OBSERVATION OF BIEXPONENTIAL RECOVERY TIMES OF THE SUPERCONDUCTING STATE
1990 APPLIED SUPERCONDUCTIVITY CONF
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. 1991: 1523–27
View details for Web of Science ID A1991EY65200174
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SUPERCONDUCTING, TRANSITION, AND NORMAL STATE PHOTORESPONSE IN YBCO OBSERVED AT DIFFERENT TEMPERATURES
1990 APPLIED SUPERCONDUCTIVITY CONF
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. 1991: 1519–22
View details for Web of Science ID A1991EY65200173
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ANOMALOUS PHOTORESPONSE OF METAL-FILMS
APPLIED PHYSICS LETTERS
1991; 58 (6): 568-570
View details for Web of Science ID A1991EX18700007
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PICOSECOND TIME-RESOLVED 4-WAVE-MIXING EXPERIMENTS IN SODIUM-SEEDED FLAMES
OPTICS LETTERS
1991; 16 (3): 177-179
Abstract
Picosecond four-wave mixing experiments have been used to study collisions in a Na-seeded, premixed, methane-air flame. Population gratings are used to measure Na excited-state quenching collision rates, while polarization gratings are used to measure Na ground-state hyperfine coherence randomizing collision rates and overall Na diffusion rates, even though these processes are slower than the excited-state quenching rate.
View details for Web of Science ID A1991EV19700021
View details for PubMedID 19773874
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PROBING LOW-TEMPERATURE GLASS DYNAMICS BY FAST GENERATION AND DETECTION OF OPTICAL HOLES
CHEMICAL PHYSICS LETTERS
1991; 176 (6): 551-558
View details for Web of Science ID A1991EX46800011
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ULTRASONIC WAVE-PROPAGATION AND BARRIER-LIMITED HEAT-FLOW IN THIN-FILMS OF YBA2CU3O7-X
PHYSICAL REVIEW B
1991; 43 (4): 2696-2699
View details for Web of Science ID A1991FF08300027
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OBSERVATION OF FAST TIME SCALE SPECTRAL DIFFUSION IN A LOW-TEMPERATURE GLASS - COMPARISON OF PICOSECOND PHOTON AND STIMULATED ECHOES
CHEMICAL PHYSICS LETTERS
1991; 176 (3-4): 335-342
View details for Web of Science ID A1991EY53200015
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SOLVENT RELAXATION EFFECTS ON THE KINETICS OF PHOTOINDUCED ELECTRON-TRANSFER REACTIONS
JOURNAL OF CHEMICAL PHYSICS
1991; 94 (2): 1081-1092
View details for Web of Science ID A1991EU59200028
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NANOSECOND TIMESCALE OPTICAL INHOMOGENEOUS BROADENING OF DYE MOLECULES IN LIQUIDS AT AND NEAR ROOM-TEMPERATURE
CHEMICAL PHYSICS LETTERS
1991; 176 (2): 159-166
View details for Web of Science ID A1991EV68500003
- Excitation Transport in Polymeric Solids Laser Optics of Condensed Matter edited by Maradudin, M., Garmine, G., Rebane, R. Plenum Press. 1991: 157–163
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THERMAL HISTORY AND TEMPERATURE-DEPENDENT PHOTON-ECHO AND HOLE BURNING LINEWIDTHS IN LOW-TEMPERATURE GLYCEROL GLASSES
CHEMICAL PHYSICS LETTERS
1990; 175 (3): 149-155
View details for Web of Science ID A1990EM55500001
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PHOTOINDUCED ELECTRON-TRANSFER, GEMINATE RECOMBINATION, AND DIFFUSION IN LIQUID SOLUTION
JOURNAL OF PHYSICAL CHEMISTRY
1990; 94 (21): 8007-8009
View details for Web of Science ID A1990EE48600003
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SOLVENT RELAXATION AND ELECTRON BACK TRANSFER FOLLOWING PHOTOINDUCED ELECTRON-TRANSFER IN AN ENSEMBLE OF RANDOMLY DISTRIBUTED DONORS AND ACCEPTORS
JOURNAL OF CHEMICAL PHYSICS
1990; 93 (5): 3550-3561
View details for Web of Science ID A1990DW34200062
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NONHYDRODYNAMIC MOLECULAR MOTIONS IN A COMPLEX LIQUID - TEMPERATURE-DEPENDENT DYNAMICS IN PENTYLCYANOBIPHENYL
JOURNAL OF CHEMICAL PHYSICS
1990; 93 (5): 3503-3514
View details for Web of Science ID A1990DW34200057
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HIGH-TEMPERATURE OPTICAL DEPHASING MECHANISM FOR DYE MOLECULES IN PMMA GLASS
CHEMICAL PHYSICS LETTERS
1990; 171 (1-2): 19-24
View details for Web of Science ID A1990DT29400005
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OPTICAL DEPHASING OF A NEAR-INFRARED DYE IN PMMA - PHOTON-ECHOES USING THE SUPERCONDUCTING ACCELERATOR PUMPED FREE-ELECTRON LASER
CHEMICAL PHYSICS LETTERS
1990; 170 (2-3): 133-138
View details for Web of Science ID A1990DQ15900001
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HOLE BURNING LINE-SHAPES IN A 2-DIMENSIONAL GLASS - A MODEL FOR HOLE BURNING LINE-SHAPES OF MOLECULES ON SURFACES
CHEMICAL PHYSICS LETTERS
1990; 168 (3-4): 371-378
View details for Web of Science ID A1990DE08800026
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DISPERSIVE EXCITATION TRANSPORT AT ELEVATED-TEMPERATURES (50-K-298-K) - EXPERIMENTS AND THEORY
JOURNAL OF CHEMICAL PHYSICS
1990; 92 (9): 5622-5635
View details for Web of Science ID A1990DB61200046
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PROBING ORGANIC GLASSES AT LOW-TEMPERATURE WITH VARIABLE TIME SCALE OPTICAL DEPHASING MEASUREMENTS
CHEMICAL REVIEWS
1990; 90 (3): 439-457
View details for Web of Science ID A1990DE48000002
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DYNAMICS IN THE PRETRANSITIONAL ISOTROPIC-PHASE OF PENTYLCYANOBIPHENYL STUDIED WITH SUBPICOSECOND TRANSIENT GRATING EXPERIMENTS
CHEMICAL PHYSICS LETTERS
1990; 167 (6): 527-534
View details for Web of Science ID A1990CZ55700006
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2-LEVEL SYSTEMS AND LOW-TEMPERATURE GLASS DYNAMICS - SPECTRAL DIFFUSION AND THERMAL REVERSIBILITY OF HOLE-BURNING LINEWIDTHS
JOURNAL OF CHEMICAL PHYSICS
1990; 92 (7): 4145-4158
View details for Web of Science ID A1990DC48300014
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AN EXAMINATION OF RADIATIVE AND NONRADIATIVE EXCITATION TRANSPORT IN THIN ANTHRACENE-CRYSTALS - TRANSIENT GRATING EXPERIMENTS
SOLID STATE COMMUNICATIONS
1990; 74 (4): 281-284
View details for Web of Science ID A1990CV72700013
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SOLVATION SHELL EFFECTS AND SPECTRAL DIFFUSION - PHOTON-ECHO AND OPTICAL HOLE BURNING EXPERIMENTS ON IONIC DYES IN ETHANOL GLASS
JOURNAL OF CHEMICAL PHYSICS
1990; 92 (7): 4125-4138
View details for Web of Science ID A1990DC48300012
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EXPERIMENTAL AND THEORETICAL-ANALYSIS OF TRANSIENT GRATING GENERATION AND DETECTION OF ACOUSTIC WAVE-GUIDE MODES IN ULTRATHIN SOLIDS
JOURNAL OF APPLIED PHYSICS
1990; 67 (7): 3362-3377
View details for Web of Science ID A1990CV63900023
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SHOCKED MOLECULAR-SOLIDS - VIBRATIONAL UP PUMPING, DEFECT HOT SPOT FORMATION, AND THE ONSET OF CHEMISTRY
JOURNAL OF CHEMICAL PHYSICS
1990; 92 (6): 3798-3812
View details for Web of Science ID A1990CU65800057
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PSEUDOLOCAL MODES OF GUEST MOLECULES IN MIXED MOLECULAR-CRYSTALS - PHOTON-ECHO EXPERIMENTS AND COMPUTER-SIMULATIONS
JOURNAL OF CHEMICAL PHYSICS
1990; 92 (6): 3323-3334
View details for Web of Science ID A1990CU65800008
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TRANSIENT GRATING OPTICAL KERR EFFECT MEASUREMENTS OF REORIENTATIONAL DYNAMICS IN LIQUIDS AND LIQUID-CRYSTALLINE SAMPLES
19TH EUROPEAN CONGRESS ON MOLECULAR SPECTROSCOPY ( EUCMOS 19 )
ELSEVIER SCIENCE BV. 1990: 19–24
View details for Web of Science ID A1990CZ85700005
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QUANTITATIVE MEASUREMENT OF CHAIN CONTRACTION IN A SOLID BLEND OF 2 INCOMPATIBLE POLYMERS - POLY(METHYL METHACRYLATE) POLY(VINYL ACETATE)
MACROMOLECULES
1990; 23 (1): 111-120
View details for Web of Science ID A1990CH78600020
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LOW-TEMPERATURE GLASS DYNAMICS PROBED BY OPTICAL DEPHASING MEASUREMENTS
JOURNAL OF LUMINESCENCE
1990; 45 (1-6): 49-53
View details for Web of Science ID A1990CV17300015
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MULTITIMESCALE DYNAMICS IN GLASSES - OPTICAL DEPHASING AND SOLUTE-SOLVENT INTERACTIONS
CONF ON PICOSECOND AND FEMTOSECOND SPECTROSCOPY FROM LABORATORY TO REAL WORLD
SPIE - INT SOC OPTICAL ENGINEERING. 1990: 43–52
View details for Web of Science ID A1990BR24B00004
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ROTATIONAL-DYNAMICS IN SIMPLE AND NEMATOGENIC LIQUIDS - TRANSIENT GRATING OPTICAL KERR EFFECT INVESTIGATIONS
7TH INTERNATIONAL CONF ON ULTRAFAST PHENOMENA
SPRINGER-VERLAG BERLIN. 1990: 447–449
View details for Web of Science ID A1990BS05F00134
- Photoinduced Electron Transfer, Geminate Recombination, and Diffusion in Liquid Solutions J. Phys. Chem. 1990; 94: 8007-8009
- Dispersive Excitation Transport at Elevated Temperatures (50-298 K): Experiments and Theory J. Chem. Phys. 1990; 92: 5622-5635
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THE NATURE OF GLASS DYNAMICS - THERMAL REVERSIBILITY OF SPECTRAL DIFFUSION IN A LOW-TEMPERATURE GLASS
CHEMICAL PHYSICS LETTERS
1989; 162 (6): 449-454
View details for Web of Science ID A1989AY91000006
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GENERATION AND DETECTION OF ACOUSTIC WAVE-GUIDE MODES IN ULTRATHIN CRYSTALS USING THE TRANSIENT GRATING TECHNIQUE
CHEMICAL PHYSICS LETTERS
1989; 162 (4-5): 306-312
View details for Web of Science ID A1989AX21000010
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PICOSECOND TIME-SCALE PHASE-RELATED OPTICAL PULSES - MEASUREMENT OF SODIUM OPTICAL COHERENCE DECAY BY OBSERVATION OF INCOHERENT FLUORESCENCE
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS
1989; 6 (10): 1905-1910
View details for Web of Science ID A1989AV08300020
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DISPERSIVE ELECTRONIC EXCITATION TRANSPORT IN POLYMERIC SOLIDS AT AND NEAR ROOM-TEMPERATURE
CHEMICAL PHYSICS LETTERS
1989; 161 (1): 16-22
View details for Web of Science ID A1989AN06300004
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EXPERIMENTAL INVESTIGATION OF DONOR-ACCEPTOR ELECTRON-TRANSFER AND BACK TRANSFER IN SOLID-SOLUTIONS
JOURNAL OF PHYSICAL CHEMISTRY
1989; 93 (17): 6388-6396
View details for Web of Science ID A1989AM55000023
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ANALYSIS OF COMPLEX MOLECULAR-DYNAMICS IN AN ORGANIC LIQUID BY POLARIZATION SELECTIVE SUBPICOSECOND TRANSIENT GRATING EXPERIMENTS
JOURNAL OF CHEMICAL PHYSICS
1989; 91 (4): 2269-2279
View details for Web of Science ID A1989AK29300036
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TIME EVOLUTION OF NON-PHOTOCHEMICAL HOLE BURNING LINEWIDTHS - OBSERVATION OF SPECTRAL DIFFUSION AT LONG TIMES
CHEMICAL PHYSICS LETTERS
1989; 159 (1): 1-6
View details for Web of Science ID A1989AF05000001
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ANISOTROPIC REORIENTATIONAL RELAXATION OF BIPHENYL - TRANSIENT GRATING OPTICAL KERR EFFECT MEASUREMENTS
JOURNAL OF CHEMICAL PHYSICS
1989; 90 (12): 6893-6902
View details for Web of Science ID A1989U950100012
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TIME SCALES AND OPTICAL DEPHASING MEASUREMENTS - INVESTIGATION OF DYNAMICS IN COMPLEX-SYSTEMS
PHYSICAL REVIEW B
1989; 39 (15): 11066-11084
View details for Web of Science ID A1989U836700065
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APPLICATION OF A 2-COLOR FREE-ELECTRON LASER TO CONDENSED-MATTER MOLECULAR-DYNAMICS
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS
1989; 6 (5): 977-994
View details for Web of Science ID A1989U557300016
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FLUORESCENCE DEPOLARIZATION OF CHROMOPHORES IN POLYMERIC SOLIDS
MACROMOLECULES
1989; 22 (2): 874-879
View details for Web of Science ID A1989T340200060
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TUNABLE SUBPICOSECOND DYE-LASER AMPLIFIED AT 1 KHZ BY A CAVITY-DUMPED, Q-SWITCHED, AND MODE-LOCKED ND-YAG LASER
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS
1989; 6 (2): 257-263
View details for Web of Science ID A1989T170200018
- Polymers in Solids: Structure and Interactions Measured by Electronic Excitation Transport Optical Techniques to Characterizing Polymer Systems Elsevier Science Publishers, B.V., The Netherlands. 1989: 277–324
- A New Approach to the Nonlinear Spectroscopic Investigation of Dynamics in Complex Solids: Theory and Experiments Comments on Condensed Matter Physics 1989; 14: 243-364
- Electronic Excitation Transport in Restricted Geometries Molecular Dynamics in Restricted Geometries edited by Klafter, J., Drake, J. M. John Wiley & Sons, New York. 1989: 39–75
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TIME-DEPENDENCE OF DONOR-ACCEPTOR ELECTRON-TRANSFER AND BACK TRANSFER IN SOLID-SOLUTION
JOURNAL OF CHEMICAL PHYSICS
1989; 90 (1): 159-170
View details for Web of Science ID A1989R629500023
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OPTICAL DEPHASING IN GLASSES - THEORETICAL COMPARISON OF THE INCOHERENT PHOTON-ECHO, ACCUMULATED GRATING ECHO, AND 2-PULSE PHOTON-ECHO EXPERIMENTS
CHEMICAL PHYSICS
1988; 128 (1): 135-155
View details for Web of Science ID A1988U461900011
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SOLUTE SOLVENT DYNAMICS AND INTERACTIONS IN GLASSY MEDIA - PHOTON-ECHO AND OPTICAL HOLE BURNING STUDIES OF CRESYL VIOLET IN ETHANOL GLASS
CHEMICAL PHYSICS LETTERS
1988; 152 (4-5): 287-293
View details for Web of Science ID A1988R152700003
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PHOTOINDUCED ELECTRON-TRANSFER AND BACK TRANSFER IN SYSTEMS OF RANDOMLY DISTRIBUTED DONORS AND ACCEPTORS - PICOSECOND TRANSIENT GRATING EXPERIMENTS
JOURNAL OF PHYSICAL CHEMISTRY
1988; 92 (15): 4258-4260
View details for Web of Science ID A1988P528300002
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EFFECTS OF SPECTRAL DIFFUSION IN INCOHERENT PHOTON-ECHO EXPERIMENTS
PHYSICAL REVIEW B
1988; 37 (17): 10440-10443
View details for Web of Science ID A1988N946900082
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POLARITON EFFECTS IN TRANSIENT GRATING EXPERIMENTS PERFORMED ON ANTHRACENE SINGLE-CRYSTALS
CHEMICAL PHYSICS LETTERS
1988; 145 (5): 475-480
View details for Web of Science ID A1988N154600023
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SHORT POLYMER-CHAIN STATISTICS AND THE RELATIONSHIP TO END TO END ELECTRONIC EXCITATION TRANSPORT - RANDOM-WALKS WITH VARIABLE STEP LENGTHS
MACROMOLECULES
1988; 21 (4): 1145-1154
View details for Web of Science ID A1988N052200049
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THEORY OF THE PHONON PERTURBED PHOTON-ECHO EXPERIMENT - DIRECT DETERMINATION OF ELECTRONIC EXCITATION PHONON COUPLING
JOURNAL OF CHEMICAL PHYSICS
1988; 88 (6): 3407-3416
View details for Web of Science ID A1988M666800001
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DYNAMICS IN LOW-TEMPERATURE GLASSES - THEORY AND EXPERIMENTS ON OPTICAL DEPHASING, SPECTRAL DIFFUSION, AND HYDROGEN TUNNELING
JOURNAL OF CHEMICAL PHYSICS
1988; 88 (3): 1564-1587
View details for Web of Science ID A1988L898300011
- An Investigation of the Mechanism of Nonphotochemical Hole Burning of Resorufin in Ethanol Glass Chem. Phys. Lett. 1988; 143: 1-5
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AN INVESTIGATION OF THE MECHANISM OF NON-PHOTOCHEMICAL HOLE BURNING OF RESORUFIN IN ETHANOL GLASS
CHEMICAL PHYSICS LETTERS
1988; 143 (1): 1-5
View details for Web of Science ID A1988L560100001
- Picosecond Transient Grating Experiments on Hydrogenated Amorphous Silicon International Conference on Unconventional Photoactive Solids 1988: 225–236
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EFFECT OF HYDROGEN-BOND STRENGTH ON RESORUFIN NONPHOTOCHEMICAL HOLE BURNING IN ETHANOL-2,2,2-TRIFLUOROETHANOL GLASSES
CHEMICAL PHYSICS LETTERS
1987; 142 (5): 371-375
View details for Web of Science ID A1987L138900015
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PICOSECOND PHOTON-ECHO AND OPTICAL HOLE BURNING STUDIES OF CHROMOPHORES IN ORGANIC GLASSES
JOURNAL OF LUMINESCENCE
1987; 38 (1-6): 9-14
View details for Web of Science ID A1987L337600005
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OPTICAL HOMOGENEOUS LINEWIDTHS OF RESORUFIN IN ETHANOL GLASS - AN APPARENT CONTRADICTION BETWEEN HOLE-BURNING AND PHOTON-ECHO RESULTS - COMMENT
CHEMICAL PHYSICS LETTERS
1987; 139 (5): 485-490
View details for Web of Science ID A1987K321300021
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IMPURITY PERTURBED DOMAINS - RESONANT ENHANCEMENT OF BULK MODE CARS BY COUPLING TO THE ELECTRONIC STATES OF DILUTE IMPURITIES
JOURNAL OF CHEMICAL PHYSICS
1987; 87 (5): 2498-2504
View details for Web of Science ID A1987J808000012
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HOMOGENEOUS OPTICAL DEPHASING AND LINE BROADENING PROCESSES IN AN ORGANIC GLASS - COMPARISON OF THE TEMPERATURE DEPENDENCES OF PICOSECOND PHOTON-ECHO AND HOLE BURNING EXPERIMENTS
CHEMICAL PHYSICS LETTERS
1987; 139 (1): 66-71
View details for Web of Science ID A1987J772500013
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GAS-PHASE DYNAMICS AND SPECTROSCOPY PROBED WITH PICOSECOND TRANSIENT GRATING EXPERIMENTS
JOURNAL OF CHEMICAL PHYSICS
1987; 86 (10): 5370-5391
View details for Web of Science ID A1987H434600019
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PICOSECOND TRANSIENT GRATING EXPERIMENTS IN SODIUM VAPOR - VELOCITY AND POLARIZATION EFFECTS
JOURNAL OF PHYSICAL CHEMISTRY
1987; 91 (7): 1704-1707
View details for Web of Science ID A1987G585600006
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PROBING INTERMOLECULAR INTERACTIONS WITH PICOSECOND PHOTON-ECHO EXPERIMENTS
ACCOUNTS OF CHEMICAL RESEARCH
1987; 20 (3): 120-126
View details for Web of Science ID A1987G658500007
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ULTRAFAST OPTICAL DEPHASING IN A LOW-TEMPERATURE ORGANIC GLASS
CHEMICAL PHYSICS LETTERS
1987; 134 (3): 268-272
View details for Web of Science ID A1987G381400013
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A PICOSECOND PHOTON-ECHO STUDY OF A CHROMOPHORE IN AN ORGANIC GLASS - TEMPERATURE-DEPENDENCE AND COMPARISON TO NONPHOTOCHEMICAL HOLE BURNING
JOURNAL OF CHEMICAL PHYSICS
1987; 86 (1): 77-87
View details for Web of Science ID A1987F432600010
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ENSEMBLE AVERAGE CONFORMATION OF ISOLATED POLYMER COILS IN SOLID BLENDS USING ELECTRONIC EXCITATION TRANSPORT
ACS SYMPOSIUM SERIES
1987; 358: 323-342
View details for Web of Science ID A1987L817300025
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QUANTITATIVE-DETERMINATION OF THE RADIUS OF GYRATION OF POLY(METHYL METHACRYLATE) IN THE AMORPHOUS SOLID-STATE BY TIME-RESOLVED FLUORESCENCE DEPOLARIZATION MEASUREMENTS OF EXCITATION TRANSPORT
MACROMOLECULES
1987; 20 (1): 168-175
View details for Web of Science ID A1987F707700028
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ELECTRONIC EXCITATION TRANSPORT ON ISOLATED, FLEXIBLE POLYMER-CHAINS IN THE AMORPHOUS SOLID-STATE RANDOMLY TAGGED OR END TAGGED WITH CHROMOPHORES
JOURNAL OF CHEMICAL PHYSICS
1986; 85 (8): 4702-4711
View details for Web of Science ID A1986E294400062
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INFLUENCE OF ORIENTATIONAL FLUCTUATIONS ON ELECTRON-TRANSFER IN SYSTEMS OF DONOR-ACCEPTOR PAIRS
JOURNAL OF PHYSICAL CHEMISTRY
1986; 90 (21): 5141-5146
View details for Web of Science ID A1986E347100050
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EXCITATION TRANSFER IN DISORDERED TWO-DIMENSIONAL AND ANISOTROPIC 3-DIMENSIONAL SYSTEMS - EFFECTS OF SPATIAL GEOMETRY ON TIME-RESOLVED OBSERVABLES
JOURNAL OF CHEMICAL PHYSICS
1986; 85 (7): 4087-4107
View details for Web of Science ID A1986E095400048
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OPTICAL DEPHASING OF CHROMOPHORES IN AN ORGANIC GLASS - PICOSECOND PHOTON-ECHO AND HOLE BURNING EXPERIMENTS
CHEMICAL PHYSICS LETTERS
1986; 130 (1-2): 6-11
View details for Web of Science ID A1986E263700002
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EFFECT OF CHOLESTEROL ON VISCOELASTIC PROPERTIES OF DIPALMITOYLPHOSPHATIDYLCHOLINE MULTIBILAYERS AS MEASURED BY A LASER-INDUCED ULTRASONIC PROBE
BIOCHEMISTRY
1986; 25 (17): 4825-4832
Abstract
Using a novel laser-induced ultrasonic probe, we have examined the bulk viscoelastic properties of fully hydrated dipalmitoylphosphatidylcholine (DPPC) aligned multibilayers in terms of the anisotropic in-plane elastic stiffness (C11) and viscosity (eta 11). Our measurements of C11 are in accord with those reported on Brillouin light scattering on a similar system. Our measurements on viscosity are the first of their kind and are, on the average, a factor of 10 lower than microviscosities estimated by spectroscopic techniques. We report the first comprehensive study of the effects of cholesterol on the bulk mechanical properties of DPPC multibilayers. At temperatures above the phase transition temperature of DPPC (Tc), an increase in both C11 and eta 11 is noticed when cholesterol is incorporated in the multibilayers. However, at temperatures below Tc, no measurable changes are detected in either C11 or eta 11. These results, reflecting changes in the bulk viscoelastic properties of the multibilayers, differ from the changes reported by local fluidity parameters in that the latter indicate a decrease in the bilayer fluidity in the presence of cholesterol above Tc and an increase below Tc ("dual effect" of cholesterol). Our data suggest that the "dual effect" of cholesterol is noticeable only on a molecular scale. Increasing cholesterol concentrations higher than 20 mol % cease to further affect C11 or eta 11 of the DPPC multibilayers. This agrees with various results reported in the literature, by techniques measuring the local effects of cholesterol, and supports the changes in molecular organization postulated to occur when cholesterol concentration reaches 20 mol % in the lipid bilayers.
View details for Web of Science ID A1986D754500016
View details for PubMedID 3768316
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PICOSECOND HOLOGRAPHIC GRATING GENERATION OF ULTRASONIC-WAVES
IEEE JOURNAL OF QUANTUM ELECTRONICS
1986; 22 (8): 1437-1452
View details for Web of Science ID A1986D667700034
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OPTICAL DEPHASING OF THE ELECTRONIC-TRANSITIONS OF DELOCALIZED MOLECULAR DIMER STATES
JOURNAL OF CHEMICAL PHYSICS
1986; 84 (10): 5463-5478
View details for Web of Science ID A1986C330800025
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DELOCALIZATION OF ELECTRONIC EXCITATIONS IN DISORDERED MOLECULAR-SYSTEMS
CHEMICAL PHYSICS LETTERS
1986; 125 (5-6): 507-513
View details for Web of Science ID A1986C169900019
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NONPHOTOCHEMICAL HOLE BURNING AND INTERSYSTEM CROSSING IN THE PENTACENE BENZOIC-ACID SYSTEM - DEUTERIUM EFFECTS
JOURNAL OF LUMINESCENCE
1985; 34 (1-2): 37-45
View details for Web of Science ID A1985ANT2200005
- Electronic Excitation Transport in Disordered Infinite Volume Systems Int. Rev. Phys. Chem. 1985; 4: 207-235
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DETERMINATION OF THE GUEST RADIUS OF GYRATION IN POLYMER BLENDS - TIME-RESOLVED MEASUREMENTS OF EXCITATION TRANSPORT INDUCED FLUORESCENCE DEPOLARIZATION
MACROMOLECULES
1985; 18 (6): 1182-1190
View details for Web of Science ID A1985ALG9200024
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SURFACE QUENCHING OF OPTICALLY GENERATED CARRIERS IN THIN-FILM HYDROGENATED AMORPHOUS-SILICON - PICOSECOND TRANSIENT-GRATING EXPERIMENTS
PHYSICAL REVIEW B
1985; 32 (12): 8035-8040
View details for Web of Science ID A1985AWE9100050
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TRANSIENT PROPERTIES OF TRIPLET BOTTLENECK HOLEBURNING IN AN OPTICALLY THICK SAMPLE
CHEMICAL PHYSICS
1985; 94 (1-2): 265-271
View details for Web of Science ID A1985AEE2000023
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A LASER-INDUCED ULTRASONIC PROBE OF THE MECHANICAL-PROPERTIES OF ALIGNED LIPID MULTIBILAYERS
BIOPHYSICAL JOURNAL
1985; 47 (1): 37-42
Abstract
The recently developed laser-induced phonon spectroscopy (LIPS) technique is applied to the determination of dynamic mechanical properties of aligned dilauroylphosphatidylcholine (DLPC) multibilayer arrays containing 2 and 20% water by weight. Sample excitation by two crossed 100-ps laser pulses generates a longitudinal ultrasonic wave whose wavelength depends on the crossing angle. In these experiments, the acoustic wave propagates parallel to the bilayer planes. The ultrasonic velocity and attenuation are monitored through the diffraction of a variably delayed probe pulse by the acoustic grating. The velocity measures the lateral area compressibility of the bilayers, while the attenuation is related to the viscosity. Velocities obtained in the gel and liquid crystal phases are compared with those found previously using Brillouin scattering. The acoustic attenuation is shown to be an order of magnitude more sensitive to the gel-liquid crystal phase transition than the velocity. The lipid area compressibility and viscosity of DLPC-20% water multilayers with and without 100 mM CaCl2 are found to be identical within our experimental error.
View details for Web of Science ID A1985TZ82100005
View details for PubMedID 3978188
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INHOMOGENEOUS BROADENING OF ELECTRONIC-TRANSITIONS OF CHROMOPHORES IN CRYSTALS AND GLASSES - ANALYSIS OF HOLE BURNING AND FLUORESCENCE LINE NARROWING EXPERIMENTS
JOURNAL OF CHEMICAL PHYSICS
1985; 82 (9): 3948-3958
View details for Web of Science ID A1985AHT6800010
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ELECTRON-TRANSFER BETWEEN MOLECULES RANDOMLY DISTRIBUTED IN A GLASS
JOURNAL OF CHEMICAL PHYSICS
1985; 83 (5): 2242-2251
View details for Web of Science ID A1985AQG3700028
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PROBING GAS-PHASE DYNAMICS WITH PICOSECOND TRANSIENT GRATING SPECTROSCOPY
CHEMICAL PHYSICS LETTERS
1985; 117 (1): 12-17
View details for Web of Science ID A1985AJY6100003
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EXCITATION TRANSPORT AND TRAPPING IN A SYNTHETIC CHLOROPHYLLIDE SUBSTITUTED HEMOGLOBIN - ORIENTATION OF THE CHLOROPHYLL-S1 TRANSITION DIPOLE
BIOCHEMISTRY
1984; 23 (7): 1564-1571
Abstract
Excitation transport in synthetic zinc chlorophyllide substituted hemoglobin has been observed by pico -second time-resolved fluorescence depolarization experiments. In this hybrid molecular system, two zinc chlorophyllide molecules are substituted into the beta-chains of hemoglobin, while deoxy hemes remain in the alpha-chains. The rate of excitation transfer between the two chlorophyllides is analyzed in terms of the distance and orientation dependences predicted by the F orster dipole-dipole theory. In this analysis, the beta-beta interchromophore geometry is assumed to be that of the deoxyhemoglobin crystal structure. When combined with steady-state fluorescence depolarization data of the complementary hybrid containing zinc chlorophyllide in the alpha-chains, these experiments provide the necessary information to determine the orientation of the S1 transition dipole moment in the zinc chlorophyllide molecule. We also find that the fluorescence lifetime of the zinc chlorophyllide is 1.42 ns when the heme is in the deoxy state but 3.75 ns when the heme is ligated to carbon monoxide. This is explained by irreversible excitation transfer from the S1 state of the zinc chlorophyllide to the lower energy excited states present in deoxy heme.
View details for Web of Science ID A1984SK48400034
View details for PubMedID 6722108
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OPTICAL DEPHASING OF MOLECULAR DIMERS IN MIXED-CRYSTALS - PICOSECOND PHOTON-ECHO EXPERIMENTS
CHEMICAL PHYSICS LETTERS
1984; 110 (1): 7-13
View details for Web of Science ID A1984TJ93600002
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PICOSECOND TRANSIENT GRATING MEASUREMENTS OF SINGLET EXCITON TRANSPORT IN ANTHRACENE SINGLE-CRYSTALS
CHEMICAL PHYSICS LETTERS
1984; 106 (1-2): 13-19
View details for Web of Science ID A1984SN85700003
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A PICOSECOND HOLOGRAPHIC GRATING APPROACH TO MOLECULAR-DYNAMICS IN ORIENTED LIQUID-CRYSTAL FILMS
JOURNAL OF CHEMICAL PHYSICS
1984; 81 (10): 4314-4321
View details for Web of Science ID A1984TV20700020
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HOPPING TRANSPORT ON A RANDOMLY SUBSTITUTED LATTICE FOR LONG-RANGE AND NEAREST NEIGHBOR INTERACTIONS
JOURNAL OF CHEMICAL PHYSICS
1984; 80 (11): 5731-5744
View details for Web of Science ID A1984SV51900052
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HOPPING TRANSPORT ON A RANDOMLY SUBSTITUTED LATTICE IN THE PRESENCE OF DILUTE DEEP TRAPS
CHEMICAL PHYSICS
1984; 85 (1): 149-164
View details for Web of Science ID A1984SH34000014
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A COHERENT PHOTOACOUSTIC APPROACH TO EXCITED-STATE-EXCITED-STATE ABSORPTION-SPECTROSCOPY - APPLICATION TO THE INVESTIGATION OF A NEAR-RESONANT CONTRIBUTION TO ULTRASONIC DIFFRACTION
JOURNAL OF PHYSICAL CHEMISTRY
1984; 88 (14): 3021-3025
View details for Web of Science ID A1984SY47300019
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THEORY OF PHOTON-ECHOES FROM INTERACTING IMPURITIES IN CRYSTALS WITH INHOMOGENEOUSLY BROADENED ABSORPTION-SPECTRA
JOURNAL OF CHEMICAL PHYSICS
1984; 81 (12): 5395-5404
View details for Web of Science ID A1984AAM6800026
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INTERSYSTEM CROSSING FROM SINGLET-STATES OF MOLECULAR DIMERS AND MONOMERS IN MIXED MOLECULAR-CRYSTALS - PICOSECOND STIMULATED PHOTON-ECHO EXPERIMENTS
CHEMICAL PHYSICS
1984; 84 (1): 51-60
View details for Web of Science ID A1984SE74600005
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PICOSECOND STUDIES OF EXCITATION TRANSPORT IN A FINITE VOLUME - THE CLUSTERED TRANSPORT-SYSTEM OCTADECYL RHODAMINE-B IN TRITON X-100 MICELLES
JOURNAL OF CHEMICAL PHYSICS
1984; 80 (3): 1246-1253
View details for Web of Science ID A1984SC59400039
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LASER-INDUCED PHENOMENA AT LIQUID-GLASS INTERFACES - PARTICLE DEPOSITION AND HOLOGRAPHIC BUBBLE GRATING FORMATION
JOURNAL OF APPLIED PHYSICS
1984; 55 (11): 4072-4080
View details for Web of Science ID A1984SS85000024
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EXCITATION TRANSPORT AND DYNAMICS IN SOLID-STATE SYSTEMS
JOURNAL OF LUMINESCENCE
1984; 31-2 (DEC): 525-529
View details for Web of Science ID A1984ACU8500002
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ELECTRONIC EXCITATION TRANSPORT IN DISORDERED FINITE VOLUME SYSTEMS
JOURNAL OF PHYSICAL CHEMISTRY
1984; 88 (25): 6108-6116
View details for Web of Science ID A1984TY05000012
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NEW APPROACH TO PROBING POLYMER AND POLYMER BLEND STRUCTURE USING ELECTRONIC EXCITATION TRANSPORT
MACROMOLECULES
1983; 16 (12): 1839-1844
View details for Web of Science ID A1983RW27100008
- Exciton Coherence Spectroscopy and Excitation Dynamics of Condensed Molecular Systems edited by Agranovich, V. M., Hochstrasser, M. R. North Holland. 1983: 185–248
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EXCITATION TRANSPORT ON SUBSTITUTIONALLY DISORDERED LATTICES
AMER INST PHYSICS. 1983: 1389–89
View details for Web of Science ID A1983RL10600060
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HOLOGRAPHIC GENERATION OF BUBBLE GRATINGS AT LIQUID-GLASS INTERFACES AND THE DYNAMICS OF BUBBLES ON SURFACES
CHEMICAL PHYSICS LETTERS
1983; 98 (5): 428-432
View details for Web of Science ID A1983RA50300005
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ELECTRONIC EXCITED-STATE TRANSPORT AMONG MOLECULES DISTRIBUTED RANDOMLY IN A FINITE VOLUME
JOURNAL OF CHEMICAL PHYSICS
1983; 78 (5): 2518-2524
View details for Web of Science ID A1983QE87800055
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ELECTRONIC EXCITED-STATE TRANSPORT AND TRAPPING IN DISORDERED-SYSTEMS - PICOSECOND FLUORESCENCE MIXING, TRANSIENT GRATING, AND PROBE PULSE EXPERIMENTS
JOURNAL OF CHEMICAL PHYSICS
1983; 78 (8): 5138-5146
View details for Web of Science ID A1983QL72600045
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EXCITATION TRANSPORT ON SUBSTITUTIONALLY DISORDERED LATTICES
PHYSICAL REVIEW LETTERS
1983; 50 (17): 1324-1327
View details for Web of Science ID A1983QL86700027
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PICOSECOND TRANSIENT GRATING GENERATION OF TUNABLE ULTRASONIC-WAVES
PROCEEDINGS OF THE SOCIETY OF PHOTO-OPTICAL INSTRUMENTATION ENGINEERS
1982; 322: 68-74
View details for Web of Science ID A1982PA80400011
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VISCOSITY DEPENDENCE OF THE ROTATIONAL REORIENTATION OF RHODAMINE-B IN MONO-ALCOHOL AND POLY-ALCOHOL - PICOSECOND TRANSIENT GRATING EXPERIMENTS
JOURNAL OF PHYSICAL CHEMISTRY
1982; 86 (24): 4694-4700
View details for Web of Science ID A1982PS59400011
- Picosecond Holographic Grating Experiments on Molecular Condensed Phases Picosecond Phenomena III. 1982: 82-86
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LASER-INDUCED ULTRASONICS - A DYNAMIC HOLOGRAPHIC APPROACH TO THE MEASUREMENT OF WEAK ABSORPTIONS, OPTOELASTIC CONSTANTS AND ACOUSTIC ATTENUATION
CHEMICAL PHYSICS
1982; 72 (3): 371-379
View details for Web of Science ID A1982PV11400016
- Electronic Excited State Transport and Trapping in One and Two Dimensional Disordered Systems Chem. Phys. 1982; 70: 139-147
- Viscosity Dependence of the Rotational Reorientation of Rhodamine B in Mono- and Polyalcohol. Picosecond Transient Grating Experiments J. Phys. Chem 1982; 86: 4694-4700
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ON THE REFRACTIVE-INDEX CORRECTION IN LUMINESCENCE SPECTROSCOPY - COMMENT
CHEMICAL PHYSICS LETTERS
1982; 88 (1): 123-127
View details for Web of Science ID A1982NQ10600026
- Nonphotochemical Hole Burning and Antihole Production in the Mixed Molecular Crystal Pentacene in Benzoic Acid J. Chem. Phys. 1982; 77: 2283-2289
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NON-PHOTOCHEMICAL HOLE BURNING AND ANTI-HOLE PRODUCTION IN THE MIXED MOLECULAR-CRYSTAL PENTACENE IN BENZOIC-ACID
JOURNAL OF CHEMICAL PHYSICS
1982; 77 (5): 2283-2289
View details for Web of Science ID A1982PF44900009
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TEMPERATURE-DEPENDENT DEPHASING OF DELOCALIZED DIMER STATES OF PENTACENE IN PARA-TERPHENYL - PICOSECOND PHOTON-ECHO EXPERIMENTS
CHEMICAL PHYSICS LETTERS
1982; 90 (3): 172-177
View details for Web of Science ID A1982PC37900002
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LASER-INDUCED EXCITED-STATE AND ULTRASONIC WAVE GRATINGS - AMPLITUDE AND PHASE GRATING CONTRIBUTIONS TO DIFFRACTION
JOURNAL OF CHEMICAL PHYSICS
1982; 77 (3): 1144-1152
View details for Web of Science ID A1982NZ84000009
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OPTICAL-DENSITY EFFECTS IN PHOTON-ECHO EXPERIMENTS
JOURNAL OF CHEMICAL PHYSICS
1982; 76 (1): 31-39
View details for Web of Science ID A1982MW46500007
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ELECTRONIC EXCITED-STATE TRANSPORT AND TRAPPING IN ONE-DIMENSIONAL AND TWO-DIMENSIONAL DISORDERED-SYSTEMS
CHEMICAL PHYSICS
1982; 70 (1-2): 139-147
View details for Web of Science ID A1982PF56700016
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DYNAMICS OF MOLECULES IN CONDENSED PHASES - PICOSECOND HOLOGRAPHIC GRATING EXPERIMENTS
ANNUAL REVIEW OF PHYSICAL CHEMISTRY
1982; 33: 63-87
View details for Web of Science ID A1982PP03300004
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ELECTRONIC EXCITED-STATE TRANSPORT AND TRAPPING IN SOLUTION
JOURNAL OF CHEMICAL PHYSICS
1982; 76 (4): 2015-2027
View details for Web of Science ID A1982NB26300051
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OPTICAL-GENERATION OF TUNABLE ULTRASONIC-WAVES
JOURNAL OF APPLIED PHYSICS
1982; 53 (2): 1144-1149
View details for Web of Science ID A1982NA59100057
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ELECTRONIC EXCITED-STATE TRANSPORT IN RANDOM-SYSTEMS - TIME-RESOLVED FLUORESCENCE DEPOLARIZATION MEASUREMENTS
JOURNAL OF PHYSICAL CHEMISTRY
1981; 85 (14): 1989-1994
View details for Web of Science ID A1981LX12500008
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LUMINESCENT SOLAR CONCENTRATORS AND THE REABSORPTION PROBLEM
APPLIED OPTICS
1981; 20 (17): 2934-2940
Abstract
The problem of reabsorption in luminescent solar concentrators (LSC) is discussed. A mathematical development is presented which enables the LSC gain to be calculated based on the optical properties of the materials and a random walk formalism. Two- and three-dimensional analyses are used. A detailed set of calculations for a common dye (rhodamine 6G) is used to examine the practicality of employing a single dye. The effects of diameter, thickness, and quantum yield on the LSC output are presented. The spectrum of the LSC output as a function of concentration is calculated. It is suggested that LSCs can be made more efficient with a system which utilizes radiationless electronic excited state transport and trapping as intermediate steps between absorption and reemission. Trap emission substantially avoids the reabsorption problem.
View details for Web of Science ID A1981MD89800020
View details for PubMedID 20333077
- Correlation Function Analysis of Coherent Optical Transients and Fluorescence from a Quasi Two Level System Phys. Rev. A 1981; 24: 1994-2008
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DELOCALIZED ELECTRONIC EXCITATIONS OF PENTACENE DIMERS IN A PARA-TERPHENYL HOST - PICOSECOND PHOTON-ECHO EXPERIMENTS
CHEMICAL PHYSICS LETTERS
1981; 79 (3): 403-407
View details for Web of Science ID A1981LP68700002
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THEORY OF PHOTON-ECHOES FROM A PAIR OF COUPLED 2 LEVEL SYSTEMS - IMPURITY DIMERS AND ENERGY-TRANSFER IN MOLECULAR-CRYSTALS
JOURNAL OF CHEMICAL PHYSICS
1981; 75 (7): 3195-3202
View details for Web of Science ID A1981MF63600004
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CORRELATION-FUNCTION ANALYSIS OF COHERENT OPTICAL TRANSIENTS AND FLUORESCENCE FROM A QUASI-2-LEVEL SYSTEM
PHYSICAL REVIEW A
1981; 24 (4): 1994-2008
View details for Web of Science ID A1981ML75100038
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NON-PHOTOCHEMICAL HOLE BURNING IN THE MIXED MOLECULAR-CRYSTAL PENTACENE IN BENZOIC-ACID
CHEMICAL PHYSICS LETTERS
1981; 84 (1): 59-63
View details for Web of Science ID A1981MS63900014
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ELECTRONIC EXCITED-STATE ENERGY-TRANSFER, TRAPPING BY DIMERS AND FLUORESCENCE QUENCHING IN CONCENTRATED DYE SOLUTIONS - PICOSECOND TRANSIENT GRATING EXPERIMENTS
CHEMICAL PHYSICS
1981; 58 (3): 325-334
View details for Web of Science ID A1981LX72100004
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LASER-INDUCED PHONON SPECTROSCOPY - OPTICAL-GENERATION OF ULTRASONIC-WAVES AND INVESTIGATION OF ELECTRONIC EXCITED-STATE INTERACTIONS IN SOLIDS
PHYSICAL REVIEW B
1981; 24 (6): 3261-3275
View details for Web of Science ID A1981MK31500044
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LASER-INDUCED PHONONS - A PROBE OF INTERMOLECULAR INTERACTIONS IN MOLECULAR-SOLIDS
JOURNAL OF CHEMICAL PHYSICS
1980; 72 (9): 5202-5218
View details for Web of Science ID A1980JS98300069
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SITE-DEPENDENT VIBRONIC LINE WIDTHS AND RELAXATION IN THE MIXED MOLECULAR-CRYSTAL PENTACENE IN PARA-TERPHENYL
JOURNAL OF PHYSICAL CHEMISTRY
1980; 84 (16): 2001-2004
View details for Web of Science ID A1980KC48300002
- Exciton Scattering and the Dephasing of ESR and Optical Absorption Lines: The 1,2,4,5-tetrachlorobenzene Triplet Exciton Problem Chem. Phys. 1980; 73: 744-748
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INTERMOLECULAR INTERACTION DYNAMICS AND OPTICAL DEPHASING - PICOSECOND PHOTON-ECHO MEASUREMENTS IN MIXED MOLECULAR-CRYSTALS
JOURNAL OF CHEMICAL PHYSICS
1980; 72 (4): 2332-2339
View details for Web of Science ID A1980JK06800020
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EXCITON SCATTERING AND THE DEPHASING OF ELECTRON-SPIN-RESONANCE AND OPTICAL-ABSORPTION LINES - THE 1,2,4,5-TETRACHLOROBENZENE TRIPLET EXCITON PROBLEM
JOURNAL OF CHEMICAL PHYSICS
1980; 73 (2): 744-748
View details for Web of Science ID A1980KD11500020
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ELECTRONIC EXCITED-STATE TRANSPORT IN SOLUTION
JOURNAL OF CHEMICAL PHYSICS
1979; 70 (9): 4254-4271
View details for Web of Science ID A1979GU87400035
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EXCITED-STATE DYNAMICS IN PURE MOLECULAR-CRYSTALS - PERYLENE AND THE EXCIMER PROBLEM
CHEMICAL PHYSICS LETTERS
1979; 64 (1): 88-93
View details for Web of Science ID A1979HD86000020
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PICOSECOND TIME SCALE OPTICAL COHERENCE EXPERIMENTS IN MIXED MOLECULAR-CRYSTALS - PENTACENE IN NAPHTHALENE
CHEMICAL PHYSICS LETTERS
1979; 67 (1): 41-47
View details for Web of Science ID A1979HU20600010
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SPIN-ORBIT-COUPLING IN EXCITON BANDS OF MOLECULAR-CRYSTALS
JOURNAL OF CHEMICAL PHYSICS
1978; 68 (1): 229-235
View details for Web of Science ID A1978EK35400028
- Energy Transport in Molecular Solids: Application of the Picosecond Transient Grating Technique Picosecond Phenomena edited by Shank, C. V., Ippen, E. P. Springer-Verlag, Berlin Heidelberg New York. 1978: 240
- Dynamics of Energy Transport in Molecular Crystals: The Picosecond Transient- Grating Method Phys. Rev. Lett. 1978; 41: 131-134
- Effects of Impurity Scattering and Transport Topology on Exciton Migration and Trapping: An Experimental Study of Quasi-One-Dimensional Molecular Crystals J. Chem. Phys. 1978; 69: 2752-2762
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SPIN-LATTICE RELAXATION IN TRIPLET-STATES OF ISOLATED MOLECULES AND PURE CRYSTALS IN ZERO-FIELD
JOURNAL OF CHEMICAL PHYSICS
1978; 69 (9): 4319-4321
View details for Web of Science ID A1978FW04100061
- The Effects of Impurity Scattering and Transport Topology on Trapping in Quasi-One-Dimensional Transport Systems: Application to Excitons in Molecular Crystals J. Chem. Phys. 1978; 69: 1996-2000
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EFFECTS OF IMPURITY SCATTERING AND TRANSPORT TOPOLOGY ON TRAPPING IN QUASI-ONE-DIMENSIONAL SYSTEMS - APPLICATION TO EXCITONS IN MOLECULAR-CRYSTALS
JOURNAL OF CHEMICAL PHYSICS
1978; 69 (5): 1996-2010
View details for Web of Science ID A1978FQ69500031
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EFFECTS OF IMPURITY SCATTERING AND TRANSPORT TOPOLOGY ON EXCITON MIGRATION AND TRAPPING - EXPERIMENTAL-STUDY OF QUASI-ONE-DIMENSIONAL MOLECULAR-CRYSTALS
JOURNAL OF CHEMICAL PHYSICS
1978; 69 (6): 2752-2762
View details for Web of Science ID A1978FS43400065
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DYNAMICS OF ENERGY-TRANSPORT IN MOLECULAR-CRYSTALS - PICOSECOND TRANSIENT-GRATING METHOD
PHYSICAL REVIEW LETTERS
1978; 41 (2): 131-134
View details for Web of Science ID A1978FE88100020
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COHERENT ONE-DIMENSIONAL EXCITON TRANSPORT AND IMPURITY SCATTERING
JOURNAL OF CHEMICAL PHYSICS
1977; 67 (8): 3808-3817
View details for Web of Science ID A1977EA83900054
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TRIPLET EXCITON SPECTRAL-LINE SHAPES IN MOLECULAR-CRYSTALS - 1,2,4,5-TETRACHLOROBENZENE
CHEMICAL PHYSICS LETTERS
1977; 52 (2): 279-284
View details for Web of Science ID A1977EE23500019
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EXPERIMENTAL-DETERMINATION OF TRIPLET EXCITON INTERMOLECULAR INTERACTION MATRIX ELEMENT AND EXCITON-PHONON SCATTERING RATE IN MOLECULAR-CRYSTALS
CHEMICAL PHYSICS LETTERS
1976; 41 (2): 305-310
View details for Web of Science ID A1976BZ53100025
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COHERENCE IN MULTILEVEL SYSTEMS .2. DESCRIPTION OF A MULTILEVEL SYSTEM AS 2 LEVELS IN CONTACT WITH A POPULATION RESERVOIR
PHYSICAL REVIEW A
1976; 13 (1): 383-395
View details for Web of Science ID A1976BC06000042
- Experimental Determination of the Triplet Exciton Intermolecular Interaction Matrix Element and the Exciton-Phonon Scattering Rate in Molecular Crystals Chem. Phys. Lett. 1976; 41: 305-310
- Coherence in Multilevel Systems. II. Description of a Multilevel System as Two Levels in Contact with a Population Reservoir Phys. Rev. A 1976; 13: 383
- On the Temperature Dependence of Excited Triplet State Spin Sublevel Populations of Shallow Traps in Molecular Crystals J. Chem. Phys. 1976; 65`: 2472-2473
- Direct Measurement of the Quantum Yield for the Creation of Mobile Excitons from Localized States Using Optically Detected Electron Spin Coherence Chem. Phys. Lett. 1975; 33: 471-476
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DIRECT MEASUREMENT OF QUANTUM YIELD FOR CREATION OF MOBILE EXCITONS FROM LOCALIZED STATES USING OPTICALLY DETECTED ELECTRON-SPIN COHERENCE
CHEMICAL PHYSICS LETTERS
1975; 33 (3): 471-476
View details for Web of Science ID A1975AJ81100016
- Coherent Energy Migration in Solids I. Band-Trap Equilibria at Boltzmann and Non-Boltzmann Temperatures Phys. Rev. B 1974; 9: 748-796
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COHERENT ENERGY MIGRATION IN SOLIDS .2. SPIN-RESONANCE ABSORPTION IN COHERENT-WAVE-PACKET STATES AND EFFECTS OF PHONON-EXCITON SCATTERING
PHYSICAL REVIEW B
1974; 10 (5): 1784-1800
View details for Web of Science ID A1974U068300003
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DECAY OF LOCALIZED STATES INTO DELOCALIZED BAND STATES - THEORY AND PRELIMINARY EXPERIMENTAL INVESTIGATIONS USING OPTICALLY DETECTED ELECTRON-SPIN COHERENCE
CHEMICAL PHYSICS LETTERS
1974; 25 (2): 149-157
View details for Web of Science ID A1974S548600001
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COHERENT ENERGY MIGRATION IN SOLIDS .1. BAND-TRAP EQUILIBRIA AT BOLTZMANN AND NONBOLTZMANN TEMPERATURES
PHYSICAL REVIEW B
1974; 9 (2): 748-769
View details for Web of Science ID A1974S232600046
- Coherent Energy Migration in Solids II. Spin Resonance Absorption in Coherent Wave Packet States and the Effects of Phonon-Exciton Scattering Phys. Rev. B 1974; 9 (2): 748-769
- The Decay of Localized States Into Delocalized Band States. Theory and Preliminary Experimental Investigations Using Optically Detected Electron Spin Coherence Chem. Phys. Lett. 1974; 25: 149-157
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OPTICALLY DETECTED NUCLEAR QUADRUPOLE RESONANCE AND TRANSFERRED HYPERFINE COUPLING VIA GUEST-HOST INTERACTIONS IN MOLECULAR CRYSTALS
JOURNAL OF CHEMICAL PHYSICS
1970; 53 (12): 4719-?
View details for Web of Science ID A1970I026800043
- Transition Metal Nuclear Quadrupole Resonance IV. Manganese--55 Nuclear Quadrupole Resonance in π-Pyrrolenylmanganese Tricarbonyl and π-Cyclopentadienylmanganese Tricarbonyl and π-Pyrrolenyl-Metal Bonds Inorganic Chemistry 1969; 8: 2792-2796
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TRANSITION METAL NUCLEAR QUADRUPOLE RESONANCE .4. MANGANESE-55 NUCLEAR QUADRUPOLE RESONANCE IN PI-PYRROLENYLMANGANESE TRICARBONYL AND PI-CYCLOPENTADIENYLMANGANESE TRICARBONYL AND PI-PYRROLENYL-METAL BONDS
INORGANIC CHEMISTRY
1969; 8 (12): 2792-?
View details for Web of Science ID A1969E758300051