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

Despite a comprehensive study on the biosynthesis and function of nitric oxide, biological metabolism of nitric oxide, especially when its concentration exceeds the cytotoxic level, remains elusive. Oxidation of nitric oxide by O in aqueous solution has been known to yield NO. On the other hand, a biomimetic study on the metal-mediated conversion of NO to NO/NO via O reactivity disclosed a conceivable pathway for aerobic metabolism of NO. During the NO-to-NO conversion, transient formation of metal-bound peroxynitrite and subsequent release of NO via O-O bond cleavage were evidenced by nitration of tyrosine residue or 2,4-di--butylphenol (DTBP). However, the synthetic/catalytic/enzymatic cycle for conversion of nitric oxide into a nitrite pool is not reported. In this study, sequential reaction of the ferrous complex [(PMDTA)Fe(κ-,'-NO)(κ--NO)] (; PMDTA = pentamethyldiethylenetriamine) with NO, KC, and O established a synthetic cycle, complex → {Fe(NO)} DNIC [(PMDTA)Fe(NO)][NO] () → {Fe(NO)} DNIC [(PMDTA)Fe(NO)] () → [(PMDTA)(NO)Fe(κ-,-ONOO)] () → complex , for the transformation of nitric oxide into nitrite. In contrast to the reported reactivity of metal-bound peroxynitrite toward nitration of DTBP, peroxynitrite-bound MNIC lacks phenol nitration reactivity toward DTBP. Presumably, the [(PMDTA)Fe] core in {Fe(NO)} MNIC provides a mononuclear template for intramolecular interaction between Fe-bound peroxynitrite and Fe-bound NO, yielding Fe-bound nitrite stabilized in the form of complex . This [(PMDTA)Fe]-core-mediated concerted peroxynitrite homolytic O-O bond cleavage and combination of the O atom with Fe-bound NO reveals a novel and effective pathway for NO-to-NO transformation. Regarding the reported assembly of the dinitrosyliron unit (DNIU) [Fe(NO)] in the biological system, this synthetic cycle highlights DNIU as a potential intermediate for nitric oxide monooxygenation activity in a nonheme iron system.