The Force Field for Amino Acid Based Ionic Liquids: Polar Residues

Abstract: Ionic liquids (ILs) constitute one of the most active fields of research nowadays. Many organic and inorganic molecules can be converted into ions via relatively simple procedures. These ions can be combined into ILs. Amino acid based ILs (AAILs) represent a specific interest due to solubilization of biological species, participation in enzymatic catalysis, and capturing toxic gases. We develop a new force field (FF) for the seven selected AAILs comprising 1-ethyl-3-methylimidazolium cation and amino acid anions with polar residues. The anions were obtained via deprotonation of carboxyl group. We account for peculiar interactions between the anion and the cation by fitting electrostatic potential for an ion pair, in contrast to isolated ions. The van der Waals interactions were transferred from the CHARMM36 FF with minor modifications, as suggested by hybrid density functional theory. Compatibility between our parameters and CHARMM36 parameters is preserved. The developed interaction model fosters computational investigation of ionic liquids.