Charge transfer between two immiscible electrolyte solutions: Part IX. Kinetics of the transfer of choline and acetylcholine cations across the water/nitrobenzene interface

Abstract

Kinetic and thermodynamic parameters of the transfer of choline and acetylcholine cations across the water/nitrobenzen interface were evaluated using convolution potential sweep voltammetry. In order to trace the factors which control the ion-transfer kinetics the semi-phenomenological theory was used, assuming that: (1) the temperature dependence of the rate constant has the form of the Arrhenius equation; (2) the reaction site is located in the outer Helmholtz plane (oHp); (3) there exists a Brønsted-type relationship between the true activation Gibbs energy and the reaction Gibbs energy for the ion transfer from the oHp in water to that in the organic solvent phase. The apparent rate constants were corrected for the double-layer effect using the capacity data and the Gouy-Chapman theory. It is concluded that the observed potential dependence of the apparent rate constants arises largely from the effect of the potential on the concentration of the transferred ions at the reaction planes. The correlation of the true (corrected) rate constant with the reaction Gibbs energy for a series of the ions with similar structure indicates that the true charge-transfer coefficient α 1≅0.3, which would correspond to the asymmetric potential energy barrier for the ion-transfer step.