Metal substitution in the active site of nitrogenase MFe7S9 (M = Mo4+, V3+, Fe3+)

Timothy Lovell, Rhonda A. Torres, Wen Ge Han, Tiqing Liu, David Case, Louis Noodleman

Research output: Contribution to journalArticle

40 Citations (Scopus)

Abstract

The unifying view that molybdenum is the essential component in nitrogenase has changed over the past few years with the discovery of a vanadium-containing nitrogenase and an iron-only nitrogenase. The principal question that has arisen for the alternative nitrogenases concerns the structures of their corresponding cofactors and their metal valence assignments and whether there are significant differences with that of the more widely known molybdenum-iron cofactor (FeMoco). Spin-polarized broken-symmetry (BS) density functional theory (DFT) calculations are used to assess which of the two possible metal-ion valence assignments (4Fe2+4Fe3+ or 6Fe2+-2Fe3+) for the iron-only cofactor (FeFeco) best represents the resting state. For the 6Fe2+2Fe3+ oxidation state, the spin coupling pattern for several spin state alignments compatible with S = 0 were generated and assessed by energy criteria. The most likely BS spin state is composed of a 4Fe cluster with spin Sa = 7/2 antiferromagnetically coupled to a 4Fe′ cluster with spin Sb = 7/2. This state has the lowest DFT energy for the isolated FeFeco cluster and displays calculated Mössbauer isomer shifts consistent with experiment. Although the S = 0 resting state of FeFeco has recently been proposed to have metal-ion valencies of 4Fe2+4Fe3+ (derived from experimental Mössbauer isomer shifts), our isomer shift calculations for the 4Fe2+4Fe3+ oxidation state are in poorer agreement with experiment. Using the Mo4+6Fe2+Fe3+ oxidation level of the cofactor as a starting point, the structural consequences of replacement of molybdenum (Mo4+) with vanadium (V3+) or iron (Fe3+) in the cofactor have been investigated. The size of the cofactor cluster shows a dependency on the nature of the heterometal and increases in the order FeMoco < FeVco < FeFeco.

Original languageEnglish (US)
Pages (from-to)5744-5753
Number of pages10
JournalInorganic Chemistry
Volume41
Issue number22
DOIs
StatePublished - Nov 4 2002
Externally publishedYes

Fingerprint

Nitrogenase
Substitution reactions
Metals
Isomers
substitutes
Vanadium
Molybdenum
Iron
Oxidation
metals
molybdenum
Density functional theory
Metal ions
iron
isomers
Molybdoferredoxin
vanadium
oxidation
shift
metal ions

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

Cite this

Lovell, Timothy ; Torres, Rhonda A. ; Han, Wen Ge ; Liu, Tiqing ; Case, David ; Noodleman, Louis. / Metal substitution in the active site of nitrogenase MFe7S9 (M = Mo4+, V3+, Fe3+). In: Inorganic Chemistry. 2002 ; Vol. 41, No. 22. pp. 5744-5753.
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abstract = "The unifying view that molybdenum is the essential component in nitrogenase has changed over the past few years with the discovery of a vanadium-containing nitrogenase and an iron-only nitrogenase. The principal question that has arisen for the alternative nitrogenases concerns the structures of their corresponding cofactors and their metal valence assignments and whether there are significant differences with that of the more widely known molybdenum-iron cofactor (FeMoco). Spin-polarized broken-symmetry (BS) density functional theory (DFT) calculations are used to assess which of the two possible metal-ion valence assignments (4Fe2+4Fe3+ or 6Fe2+-2Fe3+) for the iron-only cofactor (FeFeco) best represents the resting state. For the 6Fe2+2Fe3+ oxidation state, the spin coupling pattern for several spin state alignments compatible with S = 0 were generated and assessed by energy criteria. The most likely BS spin state is composed of a 4Fe cluster with spin Sa = 7/2 antiferromagnetically coupled to a 4Fe′ cluster with spin Sb = 7/2. This state has the lowest DFT energy for the isolated FeFeco cluster and displays calculated M{\"o}ssbauer isomer shifts consistent with experiment. Although the S = 0 resting state of FeFeco has recently been proposed to have metal-ion valencies of 4Fe2+4Fe3+ (derived from experimental M{\"o}ssbauer isomer shifts), our isomer shift calculations for the 4Fe2+4Fe3+ oxidation state are in poorer agreement with experiment. Using the Mo4+6Fe2+Fe3+ oxidation level of the cofactor as a starting point, the structural consequences of replacement of molybdenum (Mo4+) with vanadium (V3+) or iron (Fe3+) in the cofactor have been investigated. The size of the cofactor cluster shows a dependency on the nature of the heterometal and increases in the order FeMoco < FeVco < FeFeco.",
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Lovell, T, Torres, RA, Han, WG, Liu, T, Case, D & Noodleman, L 2002, 'Metal substitution in the active site of nitrogenase MFe7S9 (M = Mo4+, V3+, Fe3+)', Inorganic Chemistry, vol. 41, no. 22, pp. 5744-5753. https://doi.org/10.1021/ic020474u

Metal substitution in the active site of nitrogenase MFe7S9 (M = Mo4+, V3+, Fe3+). / Lovell, Timothy; Torres, Rhonda A.; Han, Wen Ge; Liu, Tiqing; Case, David; Noodleman, Louis.

In: Inorganic Chemistry, Vol. 41, No. 22, 04.11.2002, p. 5744-5753.

Research output: Contribution to journalArticle

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