Theoretical studies of the 1-ethyl-3-methylimidazolium glycine, [EMIM][Gly], ionic liquid – water mixture — I. Prediction of the solvation and structural properties

Abstract

Gaussian-based HF/MP2 and DFT/B3LYP methods have been explored to study the microsolvation of glycine anion with water, [Gly]–(W)n, and 1-ethyl-3-methylimidazolium glycine ionic liquid (IL) with water, [EMIM][Gly](W)n, n = 1–6 and 12. The water molecules are either isolated or aggregated around [Gly]– and [EMIM][Gly]. Their electronic structures have been calculated clearly to verify the molecular state of H2O and the results were used to compare with experiments. The water effect on the interaction energies and local packing of [EMIM][Gly] is considered. We identified an important factor: the variation of [EMIM][Gly](W)n polarity with the different numbers of H2O. As the amount of H2O increases, the polar network is continuously broken up. The dipole moments are changed to be lowest when the H-bonding ability of [Gly]– is almost saturated. Meanwhile, the nonpolar groups of the cation form an enhanced aggregation. Such observation can provide initial insights for the experimental nanostructural evolution in the IL–water mixtures.