The reaction of sulfenic acids with OH and HO2 radicals in different environments

Abstract

Sulfenic acids are involved in major chemical processes occurring in the atmosphere, in food chemistry and in biological systems. In these diverse environments, oxidation reactions caused by reactive oxygen species, especially hydroxyl (OH) and hydroperoxyl (HO₂) radicals, are very important, but their mechanisms remain poorly understood. To address this question, in this paper we present high-level theoretical results on selected reactions in gas phase and in aqueous solution. The study shows that the abstraction of the acidic hydrogen by OH or HO₂ is the most important process in all cases. It leads to the formation of sulfinyl radicals and H₂O or H₂O₂, respectively, following a proton-coupled electron transfer (pcet) mechanism. The associated rate constants depend on sulfenic acid derivative when the oxidizing species is HO₂, but all processes are diffusion controlled in the case of reaction with OH. From structurally simple systems to a cysteine-derived model peptide, this work provides a systematic study that contributes to a comprehensive understanding of the reactivity of sulfenic acids with radicals.