Computational evaluation of relevant species in inorganic sulfur biochemistry

The role of inorganic sulfur species in biological systems has gained considerable interest since the recognition of sulfanes, particularly dihydrogen sulfide or sulfane, H2S, disulfane, HSSH, trisulfane, HSSSH, and their conjugate bases, as endogenous species and mediators of signaling functions in different tissues. The one-electron oxidation of H2S/HS− has been assigned as the onset of signaling processes or oxidative detoxification mechanisms. These varied sulfur containing inorganic species are, together with organic counterparts, reunited as reactive sulfur species (RSS). In order to shed light on this rich and still not completely explored chemistry, we have performed electronic structure calculations at different levels of theory, to provide estimations and the molecular basis of the pKa values of the polysulfides HSSH and HSSSH and of the radical HS•. In addition, we also reported the characterization of selected inorganic RSS including both radical and non-radical species with different protonation states with the intention of assisting the interpretation of chemical/biochemical experiments involving these species.