Nitrogen reduction to ammonia on a biomimetic mononuclear iron centre: Insights into the nitrogenase enzyme

Monika A. Kaczmarek, Abheek Malhotra, Alex Balan, Amy Timmins, Samuel De Visser

    Research output: Contribution to journalArticlepeer-review


    Nitrogenases catalyze the nitrogen fixation to ammonia on a multinuclear Fe-Mo centre, but their mechanism and particularly the order of proton and electron transfer processes that happen during the catalytic cycle is still unresolved. Recently, a unique biomimetic mononuclear iron model was developed using tris(phosphine)borate (TPB) ligands that was shown to convert N2 into NH3. Herein, we present a computational study on the [(TPB)FeN2]– complex and its conversion to ammonia through the addition of electrons and protons. In particular, we tested the consecutive proton transfer on only the distal nitrogen atom or alternated protonation of the distal/proximal nitrogen. It is found that the lowest energy pathway is consecutive addition of three protons to the same site, which forms ammonia and an iron-nitrido complex. In addition, the proton transfer step of complexes with the metal in various oxidation and spin states were tested and show that the pKa values of biomimetic mononuclear nitrogenase intermediates vary little with iron oxidation states. As such, the model gives several possible NH3 formation pathways depending on the order of electron/proton transfer that all should be physically accessible in the natural system. These results may have implications for enzymatic nitrogenases and give insight into the catalytic properties of mononuclear iron centres.
    Original languageEnglish
    Pages (from-to)5293-5302
    Number of pages10
    JournalChemistry: A European Journal
    Issue number20
    Publication statusPublished - 22 Dec 2017

    Research Beacons, Institutes and Platforms

    • Manchester Institute of Biotechnology


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