Spectroscopic and computational insight into the intermolecular interactions between Zwitter-type ionic liquids and water molecules.

Geometric and conformational changes of zwitter-type ionic liquids (ZILs) due to hydrogen-bonding interactions with water molecules are investigated by density functional theory (DFT), two-dimensional IR correlation spectroscopy (2D IR COS), and pulsed-gradient spin-echo NMR (PGSE NMR). Simulation results indicate that molecular structures in the optimized states are strongly influenced by hydrogen bonding of water molecules with the sulfonate group or imidazolium and pyrrolidinium rings of 3-(1-methyl-3-imidazolio)propanesulfonate (1) and 3-(1-methyl-1-pyrrolidinio)propanesulfonate (2), respectively. Concentration-dependent 2D IR COS reveals kinetic conformational changes of the two ZIL-H(2)O systems attributable to intermolecular interactions, as well as the interactions of sulfonate groups and imidazolium or pyrrolidinium rings with water molecules.