Nitrite Formation at a Diiron Dinitrosyl Complex.

Pathogenic bacteria employ iron-containing enzymes to detoxify nitric oxide (NO) produced by mammals as part of their immune response. Two classes of diiron proteins, flavodiiron nitric oxide reductases (FNORs) and the hemerythrin-like proteins from mycobacteria (HLPs), are upregulated in bacteria in response to an increased local NO concentration. While FNORs reduce NO to nitrous oxide (NO), the HLPs have been found to either reduce nitrite to NO (YtfE), or oxidize NO to nitrite (-HLP). Various structural and functional models of the diiron site in FNORs have been developed over the years. However, the NO oxidation reactivity of -HLP has yet to be replicated with a synthetic complex. Compared to the FNORs, the coordination environment of the diiron site in -HLP contains one less carboxylate ligand and, therefore, is expected to be more electron-poor. Herein, we synthesized a new diiron complex that models the electron-poor coordination environment of the -HLP diiron site. The diferrous precursor reacts with NO to form a diiron dinitrosyl species (), which is in equilibrium with a mononitrosyl diiron species () in solution. Both complexes can be isolated and fully characterized. However, only oxidation of produced nitrite in high yield (71%). Our study provides the first model that reproduces the NO oxidase reactivity of -HLP and suggests intermediacy of an species.