Dinitrosyliron Complex [(PMDTA)Fe(NO)₂]: Intermediate for Nitric Oxide Monooxygenation Activity in Nonheme Iron...

Area of Science:

• Bioinorganic Chemistry
• Nitric Oxide Metabolism
• Coordination Chemistry

Background:

• Biological metabolism of nitric oxide (NO) at cytotoxic levels remains poorly understood.
• Previous biomimetic studies suggested metal-mediated NO conversion to nitrite/nitrate via oxygen reactivity.
• A synthetic/catalytic/enzymatic cycle for NO to nitrite conversion was previously unreported.

Purpose of the Study:

• To establish a synthetic cycle for the aerobic metabolism of nitric oxide (NO) to nitrite (NO2-).
• To investigate the role of a ferrous complex in mediating this transformation.
• To explore the potential of the dinitrosyliron unit (DNIU) as a biological intermediate.

Main Methods:

• Sequential reaction of a ferrous complex, [(PMDTA)Fe(κ2-O,O'-NO2)(κ1-O-NO2)] (3), with gaseous NO, KC8, and O2.
• Characterization of intermediate complexes, including dinitrosyliron species (DNIC) and metal-bound peroxynitrite.
• Evaluation of peroxynitrite reactivity in nitration assays using DTBP.

Main Results:

• A synthetic cycle was established for the transformation of NO to nitrite, involving transient dinitrosyliron and peroxynitrite intermediates.
• The ferrous complex facilitates a novel pathway for NO-to-NO2- transformation via concerted peroxynitrite homolytic O-O bond cleavage.
• Metal-bound peroxynitrite in complex 2 lacked phenol nitration reactivity, suggesting intramolecular interactions within the [(PMDTA)Fe] core.

Conclusions:

• The study presents a novel synthetic pathway for NO monooxygenation mediated by a mononuclear iron complex.
• The dinitrosyliron unit (DNIU) is highlighted as a potential intermediate for NO metabolism in nonheme iron systems.
• This work provides insights into the elusive aerobic metabolism of nitric oxide at high concentrations.