Properties of disulfide radical anions and their reactions in chemistry and biology

Abstract

Disulfide radical anions (RSSR^•−) derive both from the direct electron attachment to disulfide-containing compounds and the reaction of thiyl radicals with thiolate, being also reversible (RS^• + RS⁻ ⇆ RSSR^•−). The investigation of these reactive intermediates started in 1960s by pulse radiolysis (PR) technique and electron spin resonance (ESR) spectroscopy, and more recently, their generation was studied in organic chemistry and biological mechanisms. The present review addresses a compendium on structural, chemical and spectroscopical properties of disulfide radical anions, as well as their involvement in synthetical and biological processes. Particular emphasis is given to disulfide moieties as reactive sites in proteins, and to the generation of small sulfur-centered radicals, connected to the discovery of a mechanism of tandem protein-lipid damage. Other important biologically related processes involving disulfide radical anions are treated in the review, such as: its formation from the glutathione thiyl radical GS^• (GS^• + GS⁻ ⇆ GSSG^•−), resulting from the antioxidant reactivity of glutathione (GSH/GS^–), and the reduction of a ketone moiety by the disulfide radical anion at the active site of the enzymes ribonucleotide reductase (RNRs), the latter used for establishing a bioinspired reduction process in organic synthesis.