Flavodiiron NO reductases (FNORs) are enzymes involved in microbial pathogenesis. Pathogens equipped with these enzymes have resistance towards nitric oxide (NO), which is a human immune defense agent. These FNOR enzymes utilize a non-heme diiron active site to reduce NO to nitrous oxide (N2O), allowing for microbial proliferation. Despite significant efforts, intermediates that provide insight into how the non-heme diiron active sites of FNORs reduce NO to N2O have not been observed. Computational studies predict that the key species involved in N-N coupling of the two NO units to form N2O are iron-hyponitrite species. However, the exact coordination chemistry of non-heme iron centers with hyponitrite remains largely unknown. In synthetic complexes, hyponitrite binding has been observed primarily at nickel, ruthenium, platinum, and copper metal centers. Only two iron-hyponitrite species have been structurally characterized in the literature thus far, one heme complex and one dinitrosyl iron complex (DNIC). Herein, we describe the structural and electronic characterization of non-heme iron complexes with pre-formed hyponitrite. Utilizing derivatives of the tris(2-pyridylmethyl)amine (TPA) ligand, we were able to study the coordination chemistry of hyponitrite with non-heme iron centers. Our work provides us the opportunity, for the first time, to obtain structures of non-heme iron-hyponitrite complexes and study their reactivity.

Synthesis and characterization of non-heme iron hyponitrite complexes

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