Effects of ionic liquid constituent cations, tetraalkylammoniums, on water studied by means of the “1-propanol probing methodology”

We characterized the effects of tetrapropylammonium and tetrabutylammonium cations, typical constituent cations of ionic liquids, on the molecular organization of liquid water by using the 1-propanol probing methodology developed by us earlier. Of late, much attention has been paid to the properties of aqueous solutions of ionic liquids. Our results indicated that both ions gained hydrophobicity considerably. There is a remarkable difference in hydrophobicity between tetramethyl- and tetraethyl-ammonium cations we studied earlier using the same methodology. The hydrophobicity of tetrabutylammonium cation was twice stronger than that of tetrapropylammonium. We point out that the present methodology describes strictly at the equilibrium situation. Nevertheless, the resulting hydration numbers of these cations are close to the conclusions given by spectroscopic studies, which provides information of transient situation.