Département de chimie moléculaire

Disulfides are involved in a broad range of radical-based synthetic organic and biochemical transformations. In particular{,} the reduction of a disulfide to the corresponding radical anion{,} followed by S–S bond cleavage to yield a thiyl radical and a thiolate anion plays critical roles in radical-based photoredox transformations and the disulfide radical anion in conjunction with a proton donor{,} mediates the enzymatic synthesis of deoxynucleotides from nucleotides within the active site of the enzyme{,} ribonucleotide reductase (RNR). To gain fundamental thermodynamic insight into these reactions{,} we have performed experimental measurements to furnish the transfer coefficient from which the standard E0(RSSR/RSSR˙−) reduction potential has been determined for a homologous series of disulfides. The electrochemical potentials are found to be strongly dependent on the structures and electronic properties of the substituents of the disulfides. In the case of cysteine{,} a standard potential of E0(RSSR/RSSR˙−) = −1.38 V vs. NHE is determined{,} making the disulfide radical anion of cysteine one of the most reducing cofactors in biology.