One-electron redox potentials of RSSR+˙–RSSR couples from dimethyl disulphide and lipoic acid

Abstract

One-electron redox potentials have been measured for three (RSSR)+˙/RSSR couples by reference to (SCN)2–˙/2 SCN– and/or I2–˙/2 I– in pulse radiolysis experiments: E°(CH3SSCH3+˙/CH3SSCH3)+(1.391 ± 0.003) V; E°[lip(SS)COOH+˙/lip(SS)COOH]+(1.13 ± 0.01) V; and E°[lip(SS)COO–+˙/lip(SS)COO–]+(1.10 ± 0.01) V [lip(SS)= lipoic acid]. The paper also includes equilibrium constants for the underlying RSSR + X2–˙⇄ RSSR+˙+ 2 X– equilibria (X = SCN or I), and rate constants for the respective back and/or forward reactions. The results are discussed in the light of structural considerations and in relation to other redox couples involving sulphur-centred radical species.