Nuclear magnetic relaxation of water in ionic-liquid solutions: Determining the kosmotropicity of ionic liquids and its relationship with the enzyme enantioselectivity

The nuclear magnetic relaxations of water in ionic-liquid (IL) solutions were examined at various IL concentrations in order to better understand their hydration behaviors (in terms of nuclear magnetic resonance (NMR) B′-coefficients). From these B′-values of ILs, the individual ion's B′-coefficients were further calculated based on the additivity. These coefficients represent the hydration behavior ('kosmotropicity') of ILs in aqueous solutions. Using these data, a linear correlation was found between enzyme enantioselectivity in aqueous solution and the δ′ parameter (difference in NMR B′-coefficients of anion and cation). In general, high enzyme enantiomeric ratios (E) could be achieved in solutions of ILs with high δ′ values.