Honors & Awards
Winston Chen Stanford Graduate Fellowship, Stanford University (2015-2017)
CMAD Graduate Fellowship, Center for Molecular Analysis and Design, Stanford University (2013-2015)
Education & Certifications
B.Sc. (hons.), St. Xavier's College, Kolkata, Chemistry (2010)
M.S., Virginia Commonwealth University, Chemistry (2012)
Richard Zare, Doctoral Dissertation Advisor (AC)
dancing, singing, badminton
Electroresponsive nanoparticles for drug delivery on demand
2016; 8 (17): 9310-9317
The potential of electroresponsive conducting polymer nanoparticles to be used as general drug delivery systems that allow electrically pulsed, linearly scalable, and on demand release of incorporated drugs is demonstrated. As examples, facile release from polypyrrole nanoparticles is shown for fluorescein, a highly water-soluble model compound, piroxicam, a lipophilic small molecule drug, and insulin, a large hydrophilic peptide hormone. The drug loading is about 13 wt% and release is accomplished in a few seconds by applying a weak constant current or voltage. To identify the parameters that should be finely tuned to tailor the carrier system for the release of the therapeutic molecule of interest, a systematic study of the factors that affect drug delivery is performed, using fluorescein as a model compound. The parameters studied include current, time, voltage, pH, temperature, particle concentration, and ionic strength. Results indicate that there are several degrees of freedom that can be optimized for efficient drug delivery. The ability to modulate linearly drug release from conducting polymers with the applied stimulus can be utilized to design programmable and minimally invasive drug delivery devices.
View details for DOI 10.1039/c6nr01884j
View details for Web of Science ID 000375285800029
View details for PubMedID 27088543
Polypyrrole nanoparticles for tunable, pH-sensitive and sustained drug release
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
- Receptor-Ligand Interaction at 5-HT3 Serotonin Receptors: A Cluster Approach JOURNAL OF PHYSICAL CHEMISTRY A 2014; 118 (37): 8471-8476
- Prediction of Superhalogen-Stabilized Noble Gas Compounds JOURNAL OF PHYSICAL CHEMISTRY LETTERS 2014; 5 (18): 3151-3156
Potential of ZrO clusters as replacement Pd catalyst.
journal of chemical physics
2014; 141 (3): 034301-?
Atomic clusters with specific size and composition and mimicking the chemistry of elements in the periodic table are commonly known as superatoms. It has been suggested that superatoms could be used to replace elements that are either scarce or expensive. Based on a photoelectron spectroscopy experiment of negatively charged ions, Castleman and co-workers [Proc. Natl. Acad. Sci. U.S.A. 107, 975 (2010)] have recently shown that atoms of Ni, Pd, and Pt which are well known for their catalytic properties, have the same electronic structure as their counterpart isovalent diatomic species, TiO, ZrO, and WC, respectively. Based on this similarity they have suggested that ZrO, for example, could be a replacement catalyst for Pd. Since catalysts are seldom single isolated atoms, one has to demonstrate that clusters of ZrO also have the same electronic structure as same sized Pd clusters. To examine if this is indeed the case, we have calculated the geometries, electronic structure, electron affinity, ionization potential, and hardness of Pdn and (ZrO)n clusters (n = 1-5). We further studied the reaction of these clusters in neutral and charged forms with H2, O2, and CO and found it to be qualitatively different in most cases. These results obtained using density functional theory with hybrid B3LYP functional do not support the view that ZrO clusters can replace Pd as a catalyst.
View details for DOI 10.1063/1.4887086
View details for PubMedID 25053314
- Synthesis, Characterization, and Atomistic Modeling of Stabilized Highly Pyrophoric Al(BH4)(3) via the Formation of the Hypersalt K[Al(BH4)(4)] JOURNAL OF PHYSICAL CHEMISTRY C 2013; 117 (39): 19905-19915
Nitrate Superhalogens as Building Blocks of Hypersalts
JOURNAL OF PHYSICAL CHEMISTRY A
2013; 117 (26): 5428-5434
Using density functional theory (DFT) with a generalized gradient approximation for the exchange and correlation potential, we have studied the geometrical structure and electronic properties of NOx (x = 1-3), Li(NO3)x (x = 1,2), Mg(NO3)x (x = 1-3), and Al(NO3)x (x = 1-4) clusters. To validate the accuracy of the DFT-based method, calculations were also performed on small clusters using coupled cluster method with singles and doubles and noniterative inclusion of triples (CCSD(T)). With an electron affinity of 4.03 eV, NO3 behaves as a superhalogen molecule and forms the building block of hyperhalogens when interacting with metal atoms such as Li, Mg, and Al. This is confirmed by calculating the adiabatic detachment energies (ADEs) of Li(NO3)2, Mg(NO3)3, and Al(NO3)4, which are 5.69, 6.64, and 6.42 eV, respectively. We also demonstrate that these hyperhalogens can form salts when counter balanced by a cation such as K.
View details for DOI 10.1021/jp405201r
View details for Web of Science ID 000321542500005
View details for PubMedID 23750654
Zn in the +III Oxidation State
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2012; 134 (20): 8400-8403
The possibility that the group 12 elements Zn, Cd, and Hg can exist in an oxidation state of +III or higher has fascinated chemists for decades. It took nearly 20 years before experiments could confirm the theoretical prediction that Hg indeed can exist in the +IV oxidation state. While this unusual property of Hg is attributed to relativistic effects, Zn, which is much less massive than Hg, has not been expected to have an oxidation state higher than +II. Using density functional theory, we have shown that an oxidation state of +III for Zn can be realized by choosing specific ligands with large electron affinities. We demonstrate this by a systematic study of the interaction of Zn with the ligands F, BO(2), and AuF(6), whose electron affinities are progressively higher (3.4, 4.5, and 8.4 eV, respectively). The discovery of higher oxidation states of elements can help in the formulation of new reactions and hence in the development of new chemistry.
View details for DOI 10.1021/ja3029119
View details for Web of Science ID 000304285700029
View details for PubMedID 22559713
- Unique Spectroscopic Signature of Nearly Degenerate Isomers of Au(CN)(3) Anion JOURNAL OF PHYSICAL CHEMISTRY LETTERS 2011; 2 (24): 3027-3031
Au(CN)(n) Complexes: Superhalogens with Pseudohalogen as Building Blocks
2011; 50 (18): 8918-8925
Electron affinity (EA) is one of the most important factors that govern reactivity of atoms and molecules. Chlorine, with the highest electron affinity (3.6 eV) of all elements in the periodic table, is a classic example of reactive elements. Over past thirty years, much research has been done to expand the scope of molecules with electron affinities even larger than that of Cl. These molecules, called superhalogens, have the general formula MX(n+1) where M is a metal atom, X is a halogen atom, and n is the valency of the metal. In this paper we explore the potential of pseudohalogens such as CN, which mimic the chemistry of halogens, to serve as building blocks of new superhalogens. Using calculations based on density functional theory, we show that when a central Au atom is surrounded by CN moieties, superhalogens can be created with electron detachment energies as high as 8.4 eV. However, there is a stark contrast between the stability of these superhalogens and that of conventional AuF(n) superhalogens. Whereas AuF(n) complexes are stable up to n = 5 for neutrals and n = 6 for anions, Au(CN)(n) complexes (with CN moieties attached individually) are metastable beyond n = 1 for neutrals and n = 3 for anions. We investigate the nature and origin of these differences. In addition, we elucidate important distinctions between electron affinity (EA) and adiabatic detachment energy (ADE), two terms that are often used synonymously in literature.
View details for DOI 10.1021/ic201040c
View details for Web of Science ID 000294699700027
View details for PubMedID 21842842
Borane Derivatives: A New Class of Super- and Hyperhalogens
2011; 12 (13): 2423-2428
Super- and hyperhalogens are a class of highly electronegative species whose electron affinities far exceed those of halogen atoms and are important to the chemical industry as oxidizing agents, biocatalysts, and building blocks of salts. Using the well-known Wade-Mingos rule for describing the stability of closo-boranes B(n)H(n)(2-) and state-of-the-art theoretical methods, we show that a new class of super- and hyperhalogens, guided by this rule, can be formed by tailoring the size and composition of borane derivatives. Unlike conventional superhalogens, in which a central metal atom is surrounded by halogen atoms, the superhalogens formed according to the Wade-Mingos rule do not have to have either halogen or metal atoms. We demonstrate this by using B(12)H(13) and its isoelectronic cluster CB(11)H(12) as examples. We also show that while conventional superhalogens containing alkali atoms require at least two halogen atoms, a single borane-like moiety is sufficient to give M(B(12)H(12)) clusters (M=Li, Na, K, Rb, Cs) superhalogen properties. In addition, hyperhalogens can be formed by using the above superhalogens as building blocks. Examples include M(B(12)H(13))(2) and M(CB(11)H(12))(2) (M=Li-Cs). This finding opens the door to an untapped source of superhalogens and weakly coordinating anions with potential applications.
View details for DOI 10.1002/cphc.201100320
View details for Web of Science ID 000295235000015
View details for PubMedID 21796754