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Mechanistic Study of Nitrite Reduction on Iron(II) Complexes of Methylated N-Confused Porphyrins

Abstract

Proton delivery to the prosthetic group is a crucial step to sustain the activity of nitrite reductase. Iron N-confused porphyrin (NCP) complex, which is capable of relaying protons from the outer pyrrolic nitrogen (NoutH) of the inverted pyrrole ring to the axial coordinated ligand, has been demonstrated to facilitate facile nitrite reduction. The time-dependent FTIR studies on the reaction between [FeII(HCTPPMe)Br] (1) and a nitrite anion revealed a two-step process involving conversion of starting complex 1 to a {Fe(NO)}7 intermediate, [Fe(CTPPMe)(NO)] (5), before the detection of [Fe(CTPPCH2)(NO)] (3), a {Fe(NO)}6 end product. Moreover, spectroscopic data confirms that NoutH on NCP core is indispensable to the proceeding of nitrite reduction reaction. Mass spectra have detected the coordination of a nitrite to the iron center while DFT theoretical calculations suggeste that subsequent intramolecular proton transfer to nitro group to form [Fe(CTPPMe)(HNO2)] (6a) evokes a homolytic N-OH bond fission on axial nitrous acid due to an enhanced π-backbonding to produce {Fe(NO)}7 intermediate and to release a hydroxyl radical. The subsequent oxidation of {Fe(NO)}7 intermediate by hydroxyl radical obtained the final {Fe(NO)}6 [Fe(CTPPCH2)(NO)] (3). This study illustrates a proton assisted small molecule activation on the iron N-confused porphyrin coordination sphere and provides complemental insights into the mechanism of enzymatic nitrite reduction reactions.

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Publication details

The article was received on 04 Aug 2017, accepted on 06 Oct 2017 and first published on 06 Oct 2017


Article type: Paper
DOI: 10.1039/C7DT02869E
Citation: Dalton Trans., 2017, Accepted Manuscript
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    Mechanistic Study of Nitrite Reduction on Iron(II) Complexes of Methylated N-Confused Porphyrins

    W. Ching, P. P. Chen and C. Hung, Dalton Trans., 2017, Accepted Manuscript , DOI: 10.1039/C7DT02869E

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