Non-Bornian Theory of the Gibbs Energy of Ion Transfer between Two Immiscible Liquids

Abstract

A non-Bornian theory has been proposed for the standard Gibbs free energy of ion transfer at the organic solvent (O)/water (W) interface. In this theory the ionic charge (z)-dependent term of , which has so far been considered as describing electrostatic (i.e., long-range) ion−solvent interactions, is treated as describing the specific (short-range) interactions. A quantum chemical consideration has shown that the short-range interaction energy can be given by a quadratic function of the surface field strength (E) of an ion. In the present theory it should also be noted that a hydrophilic ion, being preferentially hydrated in the O phase, is assumed to transfer across the interface as the hydrated ion. The new, non-Bornian theory has been applied to 34 ions in the nitrobenzene (NB)/W system. In the data analyses the ions have been classified into five groups, including hydrated cations, nonhydrated cations, hydrated anions, nonhydrated anions, and polyoxometalate anions (nonhydrated), where “hydrated” or “nonhydrated” means that the ion is associated with some water molecules in NB or not. Regression analyses have shown that in accord with the theory, the z-dependent term of can be given by a quadratic function of E for each group of ions. Furthermore, the present theory has been found to be useful for the prediction of for some hydrophilic ions.