The bacterial enzyme nitric oxide reductase can protect bacteria from the toxic effects of human-produced nitric oxide (NO). It contains one heme and one non-heme iron center, has been studied using model systems, however there is current debate concerning the role of each iron atom in binding and reducing NO. Speelman and Lehnert have successfully utilized a high-spin non-heme iron model complex to probe the feasibility of NO coordination and reduction at the non-heme site. Our approach builds on this precedent and uses a tetradentate ligand called DIG3tren. DIG3tren has a secondary coordination sphere with three opportunities for internal H-bonding to the NO, and steric protection, both of which we hypothesize will facilitate stability of reduced NO. We have demonstrated successful coordination of NO to an iron(II) DIG3tren complex, spectroscopically detectable effects of our ligand’s secondary coordination sphere, and a reversible reduction of the initially-formed {FeNO}7 species that appears to furnish a reactive {FeNO}8 species. We have recently obtained a crystal structure of the {FeNO}7 complex. Our findings support a hypothesis that the non-heme site in nitric oxide reductase may be involved in the binding and reduction of NO suggesting that inhibitors of this site may prove useful as new antimicrobial agents.

Synthesis and characterization of a high-spin Fe-NO enzyme model complex with H-bond donors

255th National Meeting (2018)

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