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

Nitrite reductase (NiR) catalyzes nitrite (NO 2 - ) 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 2 - , in the presence of H + , generates NO with a H 2 O 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 2 - reduction, we report the acid-induced NO 2 - reduction chemistry of a nonheme Fe II -nitrito complex, [(12TMC)Fe II (NO 2 - )] + (Fe II -NO 2 - , 2), with variable amounts of H + . Fe II -NO 2 - upon reaction with one-equiv. of acid (H + ) generates [(12TMC)Fe(NO)] 2+ , {FeNO} 7 (3) with H 2 O 2 rather than H 2 O. However, the amount of H 2 O 2 decreases with increasing equivalents of H + and entirely disappears when H + reaches ≅ two-equiv. and shows H 2 O formation. Furthermore, we have spectroscopically characterized and followed the formation of H 2 O 2 (H + = one-equiv.) and H 2 O (H + ≅ two-equiv.) and explained why bio-driven NiR reactions end with NO and H 2 O. Mechanistic investigations, using 15 N-labeled- 15 NO 2 - and 2 H-labeled-CF 3 SO 3 D (D + source), revealed that the N atom in the {Fe 14/15 NO} 7 is derived from the NO 2 - ligand and the H atom in H 2 O or H 2 O 2 is derived from the H + source, respectively.