摘要
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 2 in aqueous solution has been known to yield NO 2 - . On the other hand, a biomimetic study on the metal-mediated conversion of NO to NO 2 - /NO 3 - via O 2 reactivity disclosed a conceivable pathway for aerobic metabolism of NO. During the NO-to-NO 3 - conversion, transient formation of metal-bound peroxynitrite and subsequent release of • NO 2 via O-O bond cleavage were evidenced by nitration of tyrosine residue or 2,4-di-tert-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 2 -O,O′-NO 2 )(κ 1 -O-NO 2 )] (3; PMDTA = pentamethyldiethylenetriamine) with NO (g) , KC 8 , and O 2 established a synthetic cycle, complex 3 → {Fe(NO) 2 } 9 DNIC [(PMDTA)Fe(NO) 2 ][NO 2 ] (4) → {Fe(NO) 2 } 10 DNIC [(PMDTA)Fe(NO) 2 ] (1) → [(PMDTA)(NO)Fe(κ 2 -O,N-ONOO)] (2) → complex 3, 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 2 lacks phenol nitration reactivity toward DTBP. Presumably, the [(PMDTA)Fe] core in {Fe(NO)} 8 MNIC 2 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 3. 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 2 - transformation. Regarding the reported assembly of the dinitrosyliron unit (DNIU) [Fe(NO) 2 ] in the biological system, this synthetic cycle highlights DNIU as a potential intermediate for nitric oxide monooxygenation activity in a nonheme iron system.