@article { ISI:000381384300031, title = {Composition dependence of the glass forming ability in binary mixtures: the role of demixing entropy}, journal = {Journal of Chemical Physics}, volume = {145}, number = {3}, year = {2016}, month = {JUL}, pages = {Article Number: 034503}, publisher = {AMER INST PHYSICS}, address = {1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA}, abstract = {

We present a comparative study of the glass forming ability of binary systems with varying composition, where the systems have similar global crystalline structure (CsCl+fcc). Biased Monte Carlo simulations using umbrella sampling technique show that the free energy cost to create a CsCl nucleus increases as the composition of the smaller particles is decreased. We find that systems with comparatively lower free energy cost to form CsCl nucleus exhibit more pronounced pre-crystalline demixing near the liquid/crystal interface. The structural frustration between the CsCl and fcc crystal demands this demixing. We show that closer to the equimolar mixture, the entropic penalty for demixing is lower and a glass forming system may crystallize when seeded with a nucleus. This entropic penalty as a function of composition shows a non-monotonic behaviour with a maximum at a composition similar to the well known Kob-Anderson (KA) model. Although the KA model shows the maximum entropic penalty and thus maximum frustration against CsCl formation, it also shows a strong tendency towards crystallization into fcc lattice of the larger {\textquoteleft}{\textquoteleft}A{\textquoteright}{\textquoteright} particles which can be explained from the study of the energetics. Thus for systems closer to the equimolar mixture although it is the requirement of demixing which provides their stability against crystallization, for KA model it is not demixing but slow dynamics and the presence of the {\textquoteleft}{\textquoteleft}B{\textquoteright}{\textquoteright} particles make it a good glass former. The locally favoured structure around {\textquoteleft}{\textquoteleft}B{\textquoteright}{\textquoteright} particles is quite similar to the CsCl structure and the incompatibility of CsCl and fcc hinders the fcc structure growth in the KA model. Although the glass forming binary systems studied here are quite similar, differing only in composition, we find that their glass forming ability cannot be attributed to a single phenomenon. Published by AIP Publishing.

}, issn = {0021-9606}, doi = {10.1063/1.4958630}, author = {Nandi, Ujjwal Kumar and Banerjee, Atreyee and Chakrabarty, Suman and Bhattacharyya, Sarika Maitra} } @article { ISI:000375631300006, title = {Correlating Nitrile IR frequencies to local electrostatics quantifies noncovalent interactions of peptides and proteins}, journal = {Journal of Physical Chemistry B}, volume = {120}, number = {17}, year = {2016}, month = {MAY}, pages = {4034-4046}, publisher = {AMER CHEMICAL SOC}, type = {Article}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Noncovalent interactions, in particular the hydrogen bonds and nonspecific long-range electrostatic interactions are fundamental to biomolecular functions. A molecular understanding of the local electrostatic environment, consistently for both specific (hydrogen-bonding) and nonspecific electrostatic (local polarity) interactions, is essential for a detailed understanding of these processes. Vibrational Stark Effect (VSE) has proven to be an extremely useful method to measure the local electric field using infrared spectroscopy of carbonyl and nitrile based probes. The nitrile chemical group would be an ideal choice because of its absorption in an infrared spectral window transparent to biomolecules, ease of site-specific incorporation into proteins, and common occurrence as a substituent in various drug molecules. However, the inability of VSE to describe the dependence of IR frequency on electric field for hydrogen-bonded nitriles to date has severely limited nitrile{\textquoteright}s utility to probe the noncovalent interactions. In this work, using infrared spectroscopy and atomistic molecular dynamics simulations, we have reported for the first time a linear correlation between nitrile frequencies and electric fields in a wide range of hydrogen-bonding environments that may bridge the existing gap between VSE and H-bonding interactions. We have demonstrated the robustness of this field-frequency correlation for both aromatic nitriles and sulfur-based nitriles in a wide range of molecules of varying size and compactness, including small molecules in complex solvation environments, an amino acid, disordered peptides, and structured proteins. This correlation, when coupled to VSE, can be used to quantify noncovalent interactions, specific or nonspecific, in a consistent manner.

}, issn = {1520-6106}, doi = {10.1021/acs.jpcb.6b02732}, author = {Deb, Pranab and Haldar, Tapas and Kashid, Somnath M. and Banerjee, Subhrashis and Chakrabarty, Suman and Bagchi, Sayan} } @article {46204, title = {Charge transfer liquid: a stable donor-acceptor interaction in the solvent-free liquid state}, journal = {Chemical Communications}, volume = {55}, year = {2019}, month = {AUG}, pages = {9371-9374}, type = {Article}, abstract = {

Charge-transfer complexes have been an inspiration to develop many functional soft materials. However, most of those studies have focused on solution based assemblies wherein the explicit control of solvents and their polarity are crucial. In this context, we explore an efficient and stable charge transfer liquid using a solvent-free liquid dialkoxynaphthalene donor and a naphthalenediimide acceptor. It has been observed that irrespective of the donor-acceptor ratio, the charge-transfer liquid exhibited an unprecedented stability and retained characteristic features even at increased temperatures. The underlying intermolecular interactions leading to efficient CT have been examined by NMR techniques together with theoretical modelling studies. The concept of charge transfer liquid will be highly beneficial for the development of processable optoelectronically active materials.

}, doi = {10.1039/c9cc03671g}, author = {Wakchaure, Vivek Chandrakant and Pillai, Lekshmi, V and Goudappagouda and Ranjeesh, Kayaramkodath Chandran and Chakrabarty, Suman and Ravindranathan, Sapna and Rajamohanan, Pattuparambil R and Babu, Sukumaran Santhosh} } @article {45521, title = {Comparison of different water models for melting point calculation of methane hydrate using molecular dynamics simulations}, journal = {Chemical Physics}, volume = {516}, year = {2019}, month = {JAN }, pages = {6-14}, type = {Article}, abstract = {

Molecular dynamics simulation is a powerful tool to understand the gas hydrate nucleation, growth, and dissociation at molecular level. Prerequisite of super-cooling during gas hydrate formation and a certain degree of super-healing during melting shows significant hysteresis in the transition between solid and liquid state due to large nucleation barrier. Different water models quantitatively differ in their prediction of thermodynamic and kinetic properties of bulk water, including phase behaviour. The present work carries out a systematic investigation of the effect of the chosen water model on the phase behaviour, in particular, the decomposition of methane hydrate. Void-induced melting has been used to predict the melting point of methane hydrate using TIP4P/Ice, TIP4P/2005, TIP4P, and SPC/E water models. This method avoids the need for a predetermined interface for melting point calculations and thus may have its importance in identifying dissociation kinetics of bulk hydrate.

}, keywords = {decomposition, Gas hydrates, Void-induced melting, Water models}, issn = {0301-0104}, doi = {10.1016/j.chemphys.2018.08.036}, author = {Choudhary, Nilesh and Chakrabarty, Suman and Roy, Sudip and Kumar, Rajnish} }