Electron transfer: A primary step in the reactions of sodium hydrosulphide, an H2S/HS− donor

Endogenously produced H2S/HS−, a newly found gasotransmitter, is well represented by NaHS. In deoxygenated media it terminated semi-stable oxidant radicals up to stoichiometric ratios of 1:1. In the presence of oxygen the antioxidant activities of NaHS were impaired considerably due to its competitive reactions with molecular oxygen. The primary reaction steps of NaHS were investigated using two different spin traps, 5,5-dimethylpyrroline-N-oxide and sodium 3,5-dibromo-4-nitrosobenzenesulphonate (DBNBS), in protolytic and aprotic solvents (water and dimethylsulphoxide, DMSO) under argon and oxygen. Sulphhydryl radicals (HS*/S* −) were primarily formed (S* − in water and HS* in DMSO), probably coupled to the formation of superoxide radical anions. The DBNBS spin trap acted also as an electron acceptor and formed its radical anions in the presence of NaHS. Hence, one of the primary steps in the reactions of sulphides is the electron transfer from H2S/HS− species to a suitable acceptor, which may play a fundamental role in their biological functions.