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.

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