Thionitrous Acid/Thionitrite and Perthionitrite Intermediates in the ?Crosstalk? of NO and H2S

Abstract

The chemistry of aqueous NO and H2S as redox regulators of cellular and physiological responses in cardiovascular, immune or neurological tissues has raised the question of the overlapping pathophysiological functions often involving similar molecular targets. The interactions of NO with H2S may functionally influence each other and focus has been directed to new N/S hybrid species eventually determining signaling capabilities. Besides the well-studied nitrosothiols, RSNOs, the eruption of H2S in the mechanistic scene has stimulated increased interest in thionitrous acid, HSNO, and thionitrite, NOS−, as well as in perthionitrite (nitrosopersulfide), S2NO−. We discuss the elusive chemistry of the latter molecules as intermediates in selected reactions in aqueous solution, either as free species or as bound to iron metal centers. The coordination chemistry involves mainly an updating on the “Gmelin” reaction proceeding upon mixing nitroprusside [Fe(CN)5(NO)]2 − and H2S, with controversial and still unsolved mechanistic issues related to the onset of NO, HNO/N2O, polysulfides HSn − (n = 2–7), together with bound thionitrous acid/thionitrite/perthionitrite and other intermediates and products.