Effect of highly concentrated sucrose and urea in aqueous solution on the ion transfer at the aqueous|organic solution interface

Abstract

Voltammograms for transfers of various ions from an aqueous solution, W, to 1,2-dichloroethane, DCE, in the presence of highly concentrated sucrose (up to 2.4 mol dm⁻³) or urea (up to 9.8 mol dm⁻³) in W were successfully recorded by employing a micro W|DCE interface. It was found based on the analysis of voltammograms observed that the highly concentrated sucrose or urea gave considerable influences on the diffusion of alkylsulfonate, alkali metal, alkaline earth metal or halide ions and the long-distance interaction between an ion and water. This result could be attributed to the effect of sucrose or urea on the viscosity and the relative dielectric constant of W. On the other hand, the Stokes radius of an ion in W, the formation energy of a cavity to dissolve a neutral molecule in W and the short-distance interaction between an ion and water molecules were not significantly influenced by sucrose or urea added in W, which does not support the view that sucrose or urea works as a structure-forming or -breaking agent, respectively. It was also found that the effect of urea on the denaturation of a protein in W was similar to that on the formation energy of a cavity in W.