Comparative analysis of ionic and hydrophobic hydration effects

Abstract

Abstract The results of neutron scattering experiments on LiCl, CsCl, [CH 3 ] 4 NCl (2M) and [C 4 H 9 ] 4 NCl (1M) aqueous solutions are presented. The main difference between the effects of ionic (LiCl and CsCl solutions) and hydrophobic ([C 4 H 9 ] 4 NCl) hydration is observed in the generalized frequency distribution (GFD) of hydration water molecules. In the case of Li + and Cs + solutions the decreasing of the weight of the first translation mode (at the lowest frequency), corresponding to the deformation of the tetrahedral angle OOO, is detected. This result may be considered as an evidence of network disruption of hydrogen bonds (HB) in the hydration shell. For the hydrophobic hydration, in contrast to ionic hydration, the low frequency mode shows no significant changes. On the basis of this result we may conclude that the water HB structure in the solution of [C 4 H 9 ] 4 NCl has no alterations when compared to pure water and this conclusion is in agreement with neutron diffraction data.