A revisit to the non-Bornian theory of the Gibbs energy of ion transfer between two immiscible liquids

• The non-Bornian theory for the ion-transfer energy has been revised.
• The transfer energy is formulated based on short-range ion–solvent interactions.
• The Uhlig formula is not used for evaluating the cavity formation energy.
• The transfer energy is a simple function of the surface field strength of the ion.

Previously, Osakai and Ebina (1998) proposed a non-Bornian theory for the Gibbs energy (ΔGtr°,W→O) of ion transfer at the organic solvent/water interface. In a conventional manner, however, ΔGtr°,W→O was divided into ionic charge-dependent and -independent terms. The former was formulated based on non-Bornian, short-range interactions of an ion with primary solvent molecules, while the latter was evaluated as the energy of cavity formation by using the Uhlig formula. In this study, we have successfully shown that the above two terms can be brought together in the context of short-range ion–solvent interactions, and that the ΔGtr°,W→O scaled by the ionic surface area can be given by a quadratic function of the surface field strength of the ion. The obtained semiempirical equation of ΔGtr°,W→O is very simple, and would be useful for the prediction of ΔGtr°,W→O.

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