Quantum Mechanical Calculations of Redox Potentials of the Metal Clusters in Nitrogenase
(2023) In Molecules 28(1). Abstract
 We have calculated redox potentials of the two metal clusters in Monitrogenase with quantum mechanical (QM) calculations. We employ an approach calibrated for iron–sulfur clusters with 1–4 Fe ions, involving QMcluster calculations in continuum solvent and large QM systems (400–500 atoms), based on structures from combined QM and molecular mechanics (QM/MM) geometry optimisations. Calculations on the Pcluster show that we can reproduce the experimental redox potentials within 0.33 V. This is similar to the accuracy obtained for the smaller clusters, although two of the redox reactions involve also proton transfer. The calculated P^{1+}/P^{N} redox potential is nearly the same independently of whether P^{1+} is... (More)
 We have calculated redox potentials of the two metal clusters in Monitrogenase with quantum mechanical (QM) calculations. We employ an approach calibrated for iron–sulfur clusters with 1–4 Fe ions, involving QMcluster calculations in continuum solvent and large QM systems (400–500 atoms), based on structures from combined QM and molecular mechanics (QM/MM) geometry optimisations. Calculations on the Pcluster show that we can reproduce the experimental redox potentials within 0.33 V. This is similar to the accuracy obtained for the smaller clusters, although two of the redox reactions involve also proton transfer. The calculated P^{1+}/P^{N} redox potential is nearly the same independently of whether P^{1+} is protonated or deprotonated, explaining why redox titrations do not show any pH dependence. For the FeMo cluster, the calculations clearly show that the formal oxidation state of the cluster in the resting E_{0} state is MoIIIFeII3FeIII4, in agreement with previous experimental studies and QM calculations. Moreover, the redox potentials of the first five E_{0}–E_{4} states are nearly constant, as is expected if the electrons are delivered by the same site (the Pcluster). However, the redox potentials are insensitive to the formal oxidation states of the Fe ion (i.e., whether the added protons bind to sulfide or Fe ions). Finally, we show that the later (E_{4}–E_{8}) states of the reaction mechanism have redox potential that are more positive (i.e., more exothermic) than that of the E_{0}/E_{1} couple. (Less)
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https://lup.lub.lu.se/record/242e35dae3274f3ca808c75495d29d10
 author
 Jiang, Hao ^{LU} ; Svensson, Oskar K. G. ^{LU} and Ryde, Ulf ^{LU}
 organization
 publishing date
 2023
 type
 Contribution to journal
 publication status
 published
 subject
 keywords
 nitrogenase, redox potential, formal oxidation states, FeMo cluster, Pcluster
 in
 Molecules
 volume
 28
 issue
 1
 article number
 65
 pages
 16 pages
 publisher
 MDPI AG
 external identifiers

 scopus:85145696816
 pmid:36615260
 ISSN
 14203049
 DOI
 10.3390/molecules28010065
 language
 English
 LU publication?
 yes
 id
 242e35dae3274f3ca808c75495d29d10
 date added to LUP
 20221222 10:40:56
 date last changed
 20230406 04:15:32
@article{242e35dae3274f3ca808c75495d29d10, abstract = {{We have calculated redox potentials of the two metal clusters in Monitrogenase with quantum mechanical (QM) calculations. We employ an approach calibrated for iron–sulfur clusters with 1–4 Fe ions, involving QMcluster calculations in continuum solvent and large QM systems (400–500 atoms), based on structures from combined QM and molecular mechanics (QM/MM) geometry optimisations. Calculations on the Pcluster show that we can reproduce the experimental redox potentials within 0.33 V. This is similar to the accuracy obtained for the smaller clusters, although two of the redox reactions involve also proton transfer. The calculated P<sup>1+</sup>/P<sup>N</sup> redox potential is nearly the same independently of whether P<sup>1+</sup> is protonated or deprotonated, explaining why redox titrations do not show any pH dependence. For the FeMo cluster, the calculations clearly show that the formal oxidation state of the cluster in the resting E<sub>0</sub> state is MoIIIFeII3FeIII4, in agreement with previous experimental studies and QM calculations. Moreover, the redox potentials of the first five E<sub>0</sub>–E<sub>4</sub> states are nearly constant, as is expected if the electrons are delivered by the same site (the Pcluster). However, the redox potentials are insensitive to the formal oxidation states of the Fe ion (i.e., whether the added protons bind to sulfide or Fe ions). Finally, we show that the later (E<sub>4</sub>–E<sub>8</sub>) states of the reaction mechanism have redox potential that are more positive (i.e., more exothermic) than that of the E<sub>0</sub>/E<sub>1</sub> couple.}}, author = {{Jiang, Hao and Svensson, Oskar K. G. and Ryde, Ulf}}, issn = {{14203049}}, keywords = {{nitrogenase; redox potential; formal oxidation states; FeMo cluster; Pcluster}}, language = {{eng}}, number = {{1}}, publisher = {{MDPI AG}}, series = {{Molecules}}, title = {{Quantum Mechanical Calculations of Redox Potentials of the Metal Clusters in Nitrogenase}}, url = {{http://dx.doi.org/10.3390/molecules28010065}}, doi = {{10.3390/molecules28010065}}, volume = {{28}}, year = {{2023}}, }