Investigation Of [emim][Gly]/H₂O Mixture Systems: A DFT Study And A Polarizable Charge Model

In the search for alternatives to conventional solvents partly driven by the need for"green"chemistry and sustainable technology, but primarily because of the potential for novel synthetic routes and process designs, a number of environmentally benign media have been explored recently. Room-temperature ionic liquids (ILs) are one such class of solvents. To expand the utility of ionic liquids, IL-based mixed solvents have come into focus. In particular the solubility of water is an important factor for the industrial use of ILs in synthesis, electrochemistry, catalysis, industrial cleaning, solvent extraction and separations. It has been demonstrated that the addition of water can strongly affect the physical and chemical properties of ILs, such as viscosity, electrical conductivity, reactivity, polarity, surface characters, as well as solvation and solubility properties. Hence, information on the structures of ILs and their interactions with water are important not only in the fundamental research but also in practical applications. In this paper, the interaction bwtween water molecules and novel amino acid ionic liquids (AAILs) with 1-ethyl-3-methyl-imidazolium cation ([emim]+) and glycine anions ([Gly]-) has been firstly systematically investigated by molecular dynamics simulation.To predict the effect of water molecules on the macroscopical properties of AAILs, the adjusted Amber99 force fields have been applied to molecular dynamics simulations by Tinker program. Various thermodynamics and dynamics properties of [emim][Gly] and [emim][Gly]/(H2O) mixture system (the mole fraction of H2O and ionic liquid are 1:3, 1:2, 1:1, 2:1, 3:1 respectively) at the temperature of 300K have been simulated in the isothermal-isobaric (NPT) ensemble and canonical ensemble(NVT). The microstructure, H-bond network of AAILs in the liquid state have been fully discussed, and the physicochemical properties, such as density, vapor enthalpy, self-diffusion and radial distribution function have been explored.In the available models of ILs, most force fields are use fixed charges that depend only on atom type. Obviously such force fields do not produce charges that depend on geometry or respond to an exteral potential, especially, the charge distributions and polarility are very imported to ILs. Therefore, it is desirable to develop models with increased accuracy to describe different thermodynamic states and heterogeneous systems of ILs. Thus, a transferable intermolecular approach including fluctuaing charges is introduced by the combination of electronegativity equalization method (EEM) and molecular mechanics (MM). We adjust and establish a series of practical parameters, and use this model to make some preliminary molecular dynamics simulations. The results are well consistent with the fixed charge model and avaliable experimental results.The investigation on the polarization charge model of AAILs, and the interaction between AAILs and water can explore the micromechanism of the water state in ILs, and the effect of water on the properties of AAILs, such as viscosity, conductivity, reaction activity polarity and solubility, and so on. This dissertation builds some theoretical foundation for the application of ionic liquids on chemical synthesis, chemical separation, electrochemistry, etc.