415 J. Electroanal. Chem, 300 (1991) 415-429 Elsevier Sequoia S.A., Lausatme Kinetics of the transfer of acetylcholine across the water/ nitrobenzene-tetrachloromethane interface The Gibbs energy of transfer dependence of the standard rate constant Y. Shao *, J.A. Campbell and H.H. Girault Department of Chemistry, Universiq of Edinburgh, West Mains Road Edinburgh EH9 3JJ, Scoiland (UK) (Received 16 May 1990; in revised form 28 June 1990) Abstract The transfer of acetylcholine across the water/mtrobenzene-tetrachloromethane interface has been studied as a function of the composition of the organic phase. The potential dependence of the rate of ion transfer follows the Butler-Volmer equation. A new expression for the standard rate constant is proposed. The nature of the activated ion transfer reaction is discussed. INTRODUCTION Although modem electrochemical methodology has been applied for more than twenty years to the study of the kinetics of ion transfer across a liquid/ liquid interface, it is only very recently that reliable data on series of ions [l-3] or solvent properties [4] have been obtained. Most of the results suggest that the potential dependence of the ion transfer reaction follows a Butler-Volmer relationship. It has also emerged from the experimental results that the standard activation energy is related to the Gibbs energy of transfer. Indeed, Samec et al. [l-3] found that for a series of ions the standard rate constant kS can be expressed as k” = k” exp( a,AGF/RT) (1) where AGp is the standard Gibbs energy of transfer and OL, is equivalent to a Bronsted coefficient. l On leave from Wuhan University, People’s Republic of China. 0022-0728/91/$03.50 0 1991 - Elsevier Sequoia S.A.