Transformation of the {Fe(NO)2}9 dinitrosyl iron complexes (DNICs) into S-nitrosothiols (RSNOs) triggered by acid-base pairs.

S-nitrosation of the coordinated thiolate of dinitrosyl iron complexes (DNICs) to generate S-nitrosothiols (RSNOs) was demonstrated. Transformation of [{(NO)(2)Fe(μ-StBu)}(2)] (1-tBuS) into the {Fe(NO)(2)}(9) DNIC [(NO)(2)Fe(StBu)(MeIm)] (2-MeIm) occurs under addition of 20 equiv of 1-methylimidazole (MeIm) into a solution of 1-tBuS in THF. The dynamic interconversion between {Fe(NO)(2)}(9) [(NO)(2)Fe(S-NAP)(dmso)] (2-dmso) (NAP = N-acetyl-D-penicillamine) and [{(NO)(2)Fe(μ-S-NAP)}(2)] (1-NAP) was also observed in a solution of complex 1-NAP in DMSO. In contrast to the reaction of complex 2-MeIm and bis(dimethylthiocarbamoyl) disulfide ((DTC)(2)) to yield {Fe(NO)}(7)[(NO)Fe(DTC)(2)] (3) (DTC = S(2)CNMe(2)) accompanied by (tBuS)(2) and NO(g), transformation of {Fe(NO)(2)}(9) 2-MeIm (2-dmso) into RSNOs (RS = tBuS, NAP-S) along with complex 3 induced by the Brønsted acid solution of (DTC)(2) demonstrated that Brønsted acid may play a critical role in triggering S-nitrosation of the coordinated thiolate of DNICs 2-MeIm (or 2-dmso) to produce RSNOs. That is, DNIC-mediated S-nitrosation requires a Brønsted acid-Lewis base pair to produce RSNO. Transformation of DNICs into RSNOs may only occur on the one-thiolate-containing {Fe(NO)(2)}(9) DNICs, in contrast to protonation of the two-thiolate-containing DNICs (NO)(2)Fe(SR)(2) by Brønsted acid to yield [{(NO)(2)Fe(μ-SR)}(2)]. These results might rationalize that the known protein-Cys-SNO sites derived from DNICs were located adjacent to acid and base motifs, and no protein-bound SNO characterized to date has been directly derived from [protein-(cysteine)(2)Fe(NO)(2)] in biology.