Stanford Advisors

All Publications

  • Photon catalysis of deuterium iodide photodissociation. Physical chemistry chemical physics : PCCP Hilsabeck, K. I., Meiser, J. L., Sneha, M., Balakrishnan, N., Zare, R. N. 2018


    A catalyst enhances a reaction pathway without itself being consumed or changed. Recently, there has been growing interest in the concept of "photon catalysis" in which nonresonant photons, which are neither absorbed nor scattered, promote reactions. The driving force behind this effect is the interaction between the strong electric field associated with a pulsed, focused laser and the polarizability of the reacting system. In this study, the effect of near-infrared, nonresonant radiation on the photodissociation of deuterium iodide is demonstrated. We use nanosecond pulses rather than time-resolved spectroscopy to investigate the average effect of the electric field on the branching ratio for forming D + I(2P3/2) and D + I(2P1/2). Changes in the measured D-atom speeds between field-free and strong-field conditions confirm substantial differences in dissociation dynamics. Both the magnitude and direction of change in the branching ratios are dependent upon the photodissociation wavelength. Experiments and theoretical calculations confirm that the mechanism for photon catalysis under these conditions is dynamic Stark shifting of potential energy surfaces rather than electric-field-induced alignment of reagent molecules.

    View details for PubMedID 30516765

  • Nonresonant photons catalyze photodissociation of phenol. Journal of the American Chemical Society Hilsabeck, K. I., Meiser, J. L., Sneha, M., Harrison, J. A., Zare, R. N. 2018


    Phenol represents an ideal polyatomic system for demonstrating photon catalysis because of its large polarizability, well-characterized excited-state potential energy surfaces, and nonadiabatic dissociation dynamics. A nonresonant IR pulse (1064 nm) supplies a strong electric field (εo = 4 x 107 V/cm) during the photolysis of isolated phenol (C6H5OH) molecules to yield C6H5O + H near two known energetic thresholds: the S1/S2 conical intersection and the S1 - S0 origin. H-atom speed distributions show marked changes in the relative contributions of dissociative pathways in both cases, compared to the absence of the nonresonant IR pulse. Results indicate that nonresonant photons lower the activation barrier for some pathways relative to others by dynamically Stark shifting the excited-state potential energy surfaces rather than aligning molecules in the strong electric field. Theoretical calculations offer support for the experimental interpretation.

    View details for PubMedID 30571915

  • Polypyrrole nanoparticles for tunable, pH-sensitive and sustained drug release NANOSCALE Samanta, D., Meiser, J. L., Zare, R. N. 2015; 7 (21): 9497-9504


    We report the development of a generalized pH-sensitive drug delivery system that can release any charged drug preferentially at the pH range of interest. Our system is based on polypyrrole nanoparticles (PPy NPs), synthesized via a simple one-step microemulsion technique. These nanoparticles are highly monodisperse, stable in solution over the period of a month, and have good drug loading capacity (∼15 wt%). We show that PPy NPs can be tuned to release drugs at both acidic and basic pH by varying the pH, the charge of the drug, as well as by adding small amounts of charged amphiphiles. Moreover, these NPs may be delivered locally by immobilizing them in a hydrogel. Our studies show encapsulation within a calcium alginate hydrogel results in sustained release of the incorporated drug for more than 21 days. Such a nanoparticle-hydrogel composite drug delivery system is promising for treatment of long-lasting conditions such as cancer and chronic pain which require controlled, localized, and sustained drug release.

    View details for DOI 10.1039/c5nr02196k

    View details for Web of Science ID 000354983100021

    View details for PubMedID 25931037