Polarization Charge Model And Thermodynamic Properties Of Amino Acid Ionic Liquids: A Theoretical Study

Recent years, alternatives to conventional solvents are sought because of thedemand for “green” chemistry and sustainable technology. Given the potential fornovel synthesis routes and process designs, a number of environmentally benignmedia have been recently explored. Amino acid-based functionalized ionic liquids(AAILs) are one such class of solvents. The most interesting features of these AAILsare their strong hydrogen bonding abilities and chiral centers. Their physicochemicalproperties can be easily adjusted for a wide range of tasks. Thus, these AAILs pavethe way for various applications, such as intermediates for peptide syntheses, chiralsolvents, functional materials, and biodegradable ionic liquids (ILs). AAILs are,therefore, ideal candidates to act as a platform for “task-specific ILs”.In this work, EEM/MM is applied to an AAIL system containing1-ethyl-3-methylimidazolium ([Emim]+) and Glycine ([Gly]) are explored and testedin this study. A consistent integration of EEM with MM requires the input of theEEM charges of all atoms into the MM intermolecular electrostatic interaction term.Compared with previous ionic liquid (IL) force fields, the EEM/MM model has twooutstanding features: the EEM/MM model not only presents the electrostaticinteraction of atoms and their changes in respond to different ambient environmentsbut also introduces “the H-bond interaction region” in which a new parameterkHB(RHB) is used to describe the electrostatic interaction of hydrogen atoms in[Emim]+and the oxygen atoms in [Gly]–; a nonrigid [Emim][Gly] body model, whichpermits vibration of [Emim][Gly] body permitting the vibration of the bond lengthand angle is allowed due to the combination of EEM and MM. The EEM/MM modelgives quite accurate predictions for gas-phase state properties of [Emim]+,[Gly]–, andion pairs, such as optimized geometries, dipole moments, vibrational frequencies, andcluster interaction energies. Due to its explicit description of charges and hydrogenbonds, the EEM/MM model also performs well for the liquid-phase properties of[Emim][Gly] under ambient conditions. The calculated properties, such as density, heat of vaporization, self-diffusion coefficient, and ionic conductivity, are fairlyconsistent with available experimental results.We systematically studied the relationship between properties and structures of[Emim][AA], which were formed by20natural amino acid anions [AA]–and1-ethyl-3-methyl imidazole cation [Emim]+by the DFT method. And combine withmolecular dynamic simulation, we simulate the thermodynamic and kinetic propertiesof liquid-phase [Emim][AA] systems at300K by Tinker program. The calculateddensities, molar volumes, enthalpies of vaporization of amino acid ionic liquids are inagreement with the experimental values. Combined with the Born-Haber cycle,further use of phase-change cycle predicted amino acid ionic liquid enthalpy offormation...