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Title: A Six-Coordinate Peroxynitrite Low-Spin Iron(III) Porphyrinate Complex—The Product of the Reaction of Nitrogen Monoxide (·NO (g)) with a Ferric-Superoxide Species

Peroxynitrite ( OON=O, PN) is a reactive nitrogen species (RNS) which can effect deleterious nitrative or oxidative (bio)chemistry. It may derive from reaction of superoxide anion (O 2 •–) with nitric oxide (·NO) and has been suggested to form an as-yet unobserved bound heme-iron-PN intermediate in the catalytic cycle of nitric oxide dioxygenase (NOD) enzymes, which facilitate a ·NO homeostatic process, i.e., its oxidation to the nitrate anion. Here, a discrete six-coordinate low-spin porphyrinate-Fe III complex [(P Im)Fe III( OON=O)] (P Im; a porphyrin moiety with a covalently tethered imidazole axial “base” donor ligand) has been identified and characterized by various spectroscopies (UV–vis, NMR, EPR, XAS, resonance Raman) and DFT calculations, following its formation at –80 °C by addition of ·NO (g) to the heme-superoxo species, [(P Im)Fe III(O 2 •–)]. DFT calculations confirm that is a six-coordinate low-spin species with the PN ligand coordinated to iron via its terminal peroxidic anionic O atom with the overall geometry being in a cis-configuration. Complex thermally transforms to its isomeric low-spin nitrato form [(P Im)Fe III(NO 3 )]. While previous (bio)chemical studies show that phenolic substrates undergo nitration in the presence of PN or PN-metal complexes, in the present system, addition ofmore » 2,4-di- tert-butylphenol ( 2,4DTBP) to complex does not lead to nitrated phenol; the nitrate complex still forms. Furthermore, DFT calculations reveal that the phenolic H atom approaches the terminal PN O atom (farthest from the metal center and ring core), effecting O–O cleavage, giving nitrogen dioxide (·NO 2) plus a ferryl compound [(P Im)Fe IV=O] (7); this rebounds to give [(P Im)Fe III(NO 3 )].The generation and characterization of the long sought after ferriheme peroxynitrite complex has been accomplished.« less
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  1. Johns Hopkins Univ., Baltimore, MD (United States)
  2. Stanford Univ., Stanford, CA (United States)
  3. Oregon Health & Science Univ., Portland, OR (United States)
  4. SLAC National Accelerator Lab., Menlo Park, CA (United States)
  5. Stanford Univ., Stanford, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)
Publication Date:
Grant/Contract Number:
24221005; GM118030; GM40392; AC02-76SF00515
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 139; Journal Issue: 48; Journal ID: ISSN 0002-7863
American Chemical Society (ACS)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
Country of Publication:
United States
OSTI Identifier: