Acid-induced nitrite reduction of nonheme iron(ii)-nitrite: mimicking biological Fe-NiR reactions.

Nitrite reductase (NiR) catalyzes nitrite (NO ) to nitric oxide (NO) transformation in the presence of an acid (H ions/pH) and serves as a critical step in NO biosynthesis. In addition to the NiR enzyme, NO synthases (NOSs) participate in NO production. The chemistry involved in the catalytic reduction of NO , in the presence of H, generates NO with a HO molecule utilizing two H + one electron from cytochromes and is believed to be affected by the pH. Here, to understand the effect of H ions on NO reduction, we report the acid-induced NO reduction chemistry of a nonheme Fe-nitrito complex, [(12TMC)Fe(NO )] (Fe-NO , 2), with variable amounts of H. Fe-NO upon reaction with one-equiv. of acid (H) generates [(12TMC)Fe(NO)], {FeNO} (3) with HO rather than HO. However, the amount of HO decreases with increasing equivalents of H and entirely disappears when H reaches ≅ two-equiv. and shows HO formation. Furthermore, we have spectroscopically characterized and followed the formation of HO (H = one-equiv.) and HO (H ≅ two-equiv.) and explained why bio-driven NiR reactions end with NO and HO. Mechanistic investigations, using N-labeled-NO and H-labeled-CFSOD (D source), revealed that the N atom in the {FeNO} is derived from the NO ligand and the H atom in HO or HO is derived from the H source, respectively.