title: Revisiting the Mössbauer Isomer Shifts of the FeMoco Cluster of Nitrogenase and the Cofactor Charge.
abstract: Despite decades of research, the structure-activity relationship of nitrogenase is still not understood. Only recently was the full molecular structure of the FeMo cofactor (FeMoco) revealed, but the charge and metal oxidation states of FeMoco have been controversial. With the recent identification of the interstitial atom as a carbide and the more recent revised oxidation-state assignment of the molybdenum atom as Mo(III), here we revisit the Mössbauer properties of FeMoco. By a detailed error analysis of density functional theory-computed isomer shifts and computing isomer shifts relative to the P-cluster, we find that only the charge of [MoFe7S9C]1-fits the experimental data. In view of the recent Mo(III) identification, the charge of [MoFe7S9C]1-corresponds to a formal oxidation-state assignment of Mo(III)3Fe(II)4Fe(III), although due to spin delocalization, the physical oxidation state distribution might also be interpreted as Mo(III)1Fe(II)4Fe(2.5)2Fe(III), according to a localized orbital analysis of the MS= 3/2 broken symmetry solution. These results can be reconciled with the recent spatially resolved anomalous dispersion study by Einsle et al. that suggests the Mo(III)3Fe(II)4Fe(III) distribution, if some spin localization (either through interactions with the protein environment or through vibronic coupling) were to take place.
authors.affiliation: Max Planck Institute for Chemical Energy Conversion , Stiftstr. 34-36, 45470 Mülheim an der Ruhr, Germany.|Science Institute, University of Iceland , Dunhagi 3, 107 Reykjavik, Iceland.
authors.forename: Ragnar
authors.identifier: http://orcid.org/0000-0003-2167-8374
authors.initials: R
authors.lastname: Bjornsson
authors.affiliation: Max Planck Institute for Chemical Energy Conversion , Stiftstr. 34-36, 45470 Mülheim an der Ruhr, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Neese
authors.affiliation: Max Planck Institute for Chemical Energy Conversion , Stiftstr. 34-36, 45470 Mülheim an der Ruhr, Germany.|Department of Chemistry and Chemical Biology, Cornell University , Ithaca, New York 14853, United States.
authors.forename: Serena
authors.initials: S
authors.lastname: DeBeer
mesh_terms: D008983:Molybdoferredoxin / Q000737:chemistry* / Q000378:metabolism; D009591:Nitrogenase / Q000737:chemistry* / Q000378:metabolism; D011789:Quantum Theory; D013237:Stereoisomerism
chemical_list: D008983:Molybdoferredoxin; D009591:Nitrogenase