The Scaled-Charge Additive Force Field for Amino Acid Based Ionic Liquids

Abstract. Ionic liquids (ILs) constitute an emerging field of research. New ILs are continuously introduced involving more and more organic and inorganic ions. Amino acid based ILs (AAILs) represent a specific interest due to their evolutional connection to proteins. We report a new non- polarizable force field (FF) for the eight AAILs comprising 1-ethyl-3-methylimidazolium cation and amino acid anions. The anions were obtained via deprotonation of carboxyl group. Specific cation-anion non-covalent interactions have been taken into account by computing electrostatic potential for ion pairs, in contrast to isolated ions. The van der Waals interactions have been transferred from the CHARMM36 FF with minor modifications. Therefore, compatibility between our parameters and CHARMM36 parameters is preserved. Our FF can be easily implemented using a variety of popular molecular dynamics programs. It will find broad applications in computational investigation of ILs

Exploding Nitromethane in silico, in real time

Nitromethane (NM) is widely applied in chemical technology as a solvent for extraction, cleaning and chemical synthesis. NM was considered safe for a long time, until a railroad tanker car exploded in 1958. We investigate detonation kinetics and reaction mechanisms in a variety of systems consisting of NM, molecular oxygen and water vapor. State-of-the-art reactive molecular dynamics allows us to simulate reactions in time-domain, as they occur in real life. High polarity of the NM molecule is shown to play an important role, driving the first exothermic step of the reaction. Presence of oxygen is important for faster oxidation, whereas its optimal concentration is in agreement with the proposed reaction mechanism. Addition of water (50 mol%) inhibits detonation; however, water does not prevent detonation entirely. The reported results provide important insights for improving applications of NM and preserving safety of industrial processes.Comment: arXiv admin note: text overlap with arXiv:1408.372

Imidazolium Ionic Liquid Mediates Black Phosphorus Exfoliation while Preventing Phosphorene Decomposition

Forthcoming applications in electronics and optoelectronics make phosphorene a subject of vigorous research efforts. Solvent-assisted exfoliation of phosphorene promises affordable delivery in industrial quantities for future applications. We demonstrate, using equilibrium, steered and umbrella sampling molecular dynamics, that the 1-ethyl-3- methylimidazolium tetrafluoroborate [EMIM][BF4] ionic liquid is an excellent solvent for phosphorene exfoliation. The presence of both hydrophobic and hydrophilic moieties, as well as substantial shear viscosity, allows [EMIM][BF4] simultaneously to facilitate separation of phosphorene sheets and to protect them from getting in direct contact with moisture and oxygen. The exfoliation thermodynamics is moderately unfavorable, indicating that an external stimulus is necessary. Unexpectedly, [EMIM][BF4] does not coordinates phosphorene by p-electron stacking with the imidazole ring. Instead, the solvation proceeds via hydrophobic side chains, while polar imidazole rings form an electrostatically stabilized protective layer. The simulations suggest that further efforts in solvent engineering for phosphorene exfoliation should concentrate on use of weakly coordinating ions and grafting groups that promote stronger dispersion interactions, and on elongation of nonpolar chains