Theoretical investigations on the conversions of cyclic polysulfides to acyclic polysulfide diradicals and subsequent reactions of biological interest

Sulfur is one of the most necessary biogenic elements in nature that must be assimilated by all organisms; it is an essential macronutrient for living organisms and has multiple roles in plant development. The oxidation of elemental sulfur is a complex process involving the contact of cells with sulfur particles, the oxidation of sulfur to sulfite, and the oxidation of sulfite to sulfate. To provide hypothesis concerning the most probable processes in the early states, we determined, by quantum-chemical calculations, the energies of some allotropic forms containing up to 32–40 sulfur atoms and energetics of their reactions with triplet dioxygen. The most probable reactions occurred with methylpolysulfane anions with an electron transfer to give the superoxide anion radical (and thiyls radicals) and especially the formation of peroxydic polysulfane anions. Calculations confirmed that the triplet diradical is more stable than the singlet one for acyclic polysulfide chains.