Sequential oxidations of phenylchalcogenides by H2O2: insights into the redox behavior of selenium via DFT analysis

The biological activity of sulfur and selenium, despite their similarity, shows some remarkable differences that have been recognized in many different scenarios. However, the underlying cause has not been completely clarified yet. The difference in the redox behavior of these two chalcogens has lately been addressed as justification of the presence of selenium in some essential biological systems. In particular, selenium is found in some peroxidases,i.e.glutathione peroxidases (GPx), whose redox activity relies on a fast-reacting selenocysteine and is fundamental in metabolizing harmful peroxides. In this work, a systematicin silicoinvestigation on model systems,i.e.phenylchalcogenides, containing sulfur, selenium and tellurium is presented. Sequential oxidation reactions of these chalcogen-based substrates by hydrogen peroxide are carried out spanning the range of the biologically relevant chalcogen oxidation numbers [Advances in Molecular Toxicology, ed. J. C. Fishbein, Elsevier, 2010, vol. 4, pp. 183-222.] (2−, 0, 2+ and 4+) and analyzed through the calculation of intrinsic reaction coordinate paths and the application of the activation strain model. The results allowed us to highlight the different behaviors of S, Se and Te in highly oxidizing environments.