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Nitrogen Reduction to Ammonia on a Biomimetic Mononuclear Iron Centre: Insights into the Nitrogenase Enzyme

Nitrogenases catalyse 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 u...

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Autores principales: Kaczmarek, Monika A., Malhotra, Abheek, Balan, G. Alex, Timmins, Amy, de Visser, Sam P.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: John Wiley and Sons Inc. 2017
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5915742/
https://www.ncbi.nlm.nih.gov/pubmed/29165842
http://dx.doi.org/10.1002/chem.201704688
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author Kaczmarek, Monika A.
Malhotra, Abheek
Balan, G. Alex
Timmins, Amy
de Visser, Sam P.
author_facet Kaczmarek, Monika A.
Malhotra, Abheek
Balan, G. Alex
Timmins, Amy
de Visser, Sam P.
author_sort Kaczmarek, Monika A.
collection PubMed
description Nitrogenases catalyse 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 N(2) into NH(3). Herein, we present a computational study on the [(TPB)FeN(2)](−) complex and describe its conversion into 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 pK (a) values of biomimetic mononuclear nitrogenase intermediates vary little with iron oxidation states. As such, the model gives several possible NH(3) formation pathways depending on the order of electron/proton transfer, and 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.
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spelling pubmed-59157422018-05-02 Nitrogen Reduction to Ammonia on a Biomimetic Mononuclear Iron Centre: Insights into the Nitrogenase Enzyme Kaczmarek, Monika A. Malhotra, Abheek Balan, G. Alex Timmins, Amy de Visser, Sam P. Chemistry Full Papers Nitrogenases catalyse 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 N(2) into NH(3). Herein, we present a computational study on the [(TPB)FeN(2)](−) complex and describe its conversion into 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 pK (a) values of biomimetic mononuclear nitrogenase intermediates vary little with iron oxidation states. As such, the model gives several possible NH(3) formation pathways depending on the order of electron/proton transfer, and 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. John Wiley and Sons Inc. 2017-12-14 2018-04-06 /pmc/articles/PMC5915742/ /pubmed/29165842 http://dx.doi.org/10.1002/chem.201704688 Text en © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
spellingShingle Full Papers
Kaczmarek, Monika A.
Malhotra, Abheek
Balan, G. Alex
Timmins, Amy
de Visser, Sam P.
Nitrogen Reduction to Ammonia on a Biomimetic Mononuclear Iron Centre: Insights into the Nitrogenase Enzyme
title Nitrogen Reduction to Ammonia on a Biomimetic Mononuclear Iron Centre: Insights into the Nitrogenase Enzyme
title_full Nitrogen Reduction to Ammonia on a Biomimetic Mononuclear Iron Centre: Insights into the Nitrogenase Enzyme
title_fullStr Nitrogen Reduction to Ammonia on a Biomimetic Mononuclear Iron Centre: Insights into the Nitrogenase Enzyme
title_full_unstemmed Nitrogen Reduction to Ammonia on a Biomimetic Mononuclear Iron Centre: Insights into the Nitrogenase Enzyme
title_short Nitrogen Reduction to Ammonia on a Biomimetic Mononuclear Iron Centre: Insights into the Nitrogenase Enzyme
title_sort nitrogen reduction to ammonia on a biomimetic mononuclear iron centre: insights into the nitrogenase enzyme
topic Full Papers
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5915742/
https://www.ncbi.nlm.nih.gov/pubmed/29165842
http://dx.doi.org/10.1002/chem.201704688
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