Electronic properties of single- and double-MoFe3S4 cubane-type clusters

Mascharak, P. K.; Papaefthymiou, Georgia C.; Armstrong, William H.; Foner, S.; Frankel, Richard B.; Holm, R. H.

doi:10.1021/ic00162a017

Cited by 45 publications

(45 citation statements)

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“…The iron atoms with the calculated higher d and DE Q values are the irons forming the mixed-valence delocalized pair. Magnetic Mössbauer measurements of similar [MoFe 3 S 4 ] 3+ core compounds have additionally revealed antiparallel alignment of the two iron species, 29,30 in agreement with the brokensymmetry solution.…”

Section: Resultssupporting

confidence: 57%

Identification of a spin-coupled Mo(iii) in the nitrogenase iron–molybdenum cofactor

et al. 2014

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Section: Resultssupporting

confidence: 57%

Identification of a spin-coupled Mo(iii) in the nitrogenase iron–molybdenum cofactor

et al. 2014

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“…Treatment of NifQ with DTH gave rise to a different EPRactive species resembling spectra of chemically synthesized compounds comprising S ϭ 3/2 [Mo-3Fe-4S] 3ϩ clusters (28)(29)(30) (data not shown). This new EPR signal did not arise from reduction of the [3Fe-4S] ϩ cluster to the [3Fe-4S] 0 state (S ϭ 2), because such a species would be EPR silent in the perpen- In conclusion, CW-EPR and ESE field sweep EPR analysis, combined with Fe and Mo determinations, indicate that NifQ is able to coordinate a redox responsive [Mo-3Fe-4S] cluster.…”

Section: Resultsmentioning

confidence: 92%

Metal trafficking for nitrogen fixation: NifQ donates molybdenum to NifEN/NifH for the biosynthesis of the nitrogenase FeMo-cofactor

Hernández

Curatti

Aznar

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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The molybdenum nitrogenase, present in a diverse group of bacteria and archea, is the major contributor to biological nitrogen fixation. The nitrogenase active site contains an iron-molybdenum cofactor (FeMo-co) composed of 7Fe, 9S, 1Mo, one unidentified light atom, and homocitrate. The nifQ gene was known to be involved in the incorporation of molybdenum into nitrogenase. Here we show direct biochemical evidence for the role of NifQ in FeMo-co biosynthesis. As-isolated NifQ was found to carry a molybdenum-iron-sulfur cluster that serves as a specific molybdenum donor for FeMo-co biosynthesis. Purified NifQ supported in vitro FeMo-co synthesis in the absence of an additional molybdenum source. The mobilization of molybdenum from NifQ required the simultaneous participation of NifH and NifEN in the in vitro FeMo-co synthesis assay, suggesting that NifQ would be the physiological molybdenum donor to a hypothetical NifEN/NifH complex.nif ͉ iron-sulfur cluster ͉ Azotobacter vinelandii B iological nitrogen fixation performed by microorganisms that have nitrogenase(s) accounts for roughly two-thirds of the nitrogen fixed globally. Most nitrogen fixation is carried out by the activity of molybdenum nitrogenase (1), which is widely distributed in nature (2). The molybdenum-nitrogenase enzyme is composed of two proteins (3): a heterotetrameric NifDKprotein component (a 2 ␤ 2 dinitrogenase) and a homodimeric NifH-protein component (dinitrogenase reductase). NifDK contains one iron-molybdenum cofactor (FeMo-co) within the active site of each ␣-subunit (NifD), and one [8Fe-7S] P-cluster at the interface of the ␣-and ␤-subunits in each ␣␤ pair (4). NifH contains a [4Fe-4S] cluster bridging the two subunits and one site for Mg-ATP binding and hydrolysis in each subunit (5).FeMo-co is a unique cofactor ʈ composed of a [Mo-3Fe-3S] partial cubane bridged to a [4Fe-3S] partial cubane by three sulfur ligands and one unidentified light atom in the center of the cofactor (6). The molybdenum atom is also coordinated to the organic acid homocitrate. The biosynthesis of FeMo-co is a complex process that involves the activities of several nitrogen fixation (nif ) gene products that function as molecular scaffolds, enzymes, or escort proteins that carry FeMo-co precursors between assembly sites in the pathway (7,8). Following assembly, FeMo-co is inserted into apo-NifDK, a P-cluster-containing but FeMo-co-deficient form of NifDK that is matured into functional NifDK simply by FeMo-co insertion, to generate the mature dinitrogenase enzyme that is competent for nitrogen fixation.The NifEN scaffold protein is believed to function in the pathway as a central node to which an [Fe-S]-containing FeMo-co precursor, molybdenum, and homocitrate might converge to complete the assembly of FeMo-co (9-12). In this model, the [Fe-S]-containing FeMo-co precursor, NifB-co**, would be initially assembled by NifB and then transferred to NifEN for its conversion into the [Fe-S] VK-cluster (13,14). Homocitrate would be provided by the homocitrate-synthase ac...

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“…Magnetic and Mössbauer spectroscopic properties for four representative polycrystalline clusters and two others reported earlier 24,25 are provided in Figure 5 and Table 3. Clusters 3 and 4 exhibit Curie-type behavior at 2-20 K with Curie constants close to C = 3 emu K/mol for an S = 2 ground state (g = 2).…”

Section: Resultsmentioning

confidence: 97%

The [MoFe₃S₄]²⁺ Oxidation State: Synthesis, Substitution Reactions, and Structures of Phosphine-Ligated Cubane-Type Clusters with the S = 2 Ground State

Holm

2011

Inorg. Chem.

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The cluster [(Tp)MoFe3S4(PEt3)3]1+ containing the cubane-type [MoFe3(μ3-S)4]2+ reduced core undergoes facile ligand substitution reactions at the iron sites leading to an extensive set of mono- and disubstituted species [(Tp)MoFe3S4(PEt3)3-nLn]1-n with L = halide, N3-, PhS-, PhSe-, R3SiO-, and R3SiS- and n = 1 and 2. Structures of 10 members of the set are reported. For two representative clusters, Curie behavior at 2-20 K indicates a spin-quintet ground state. Zero-field Mössbauer spectra consist of two doublets in a 2:1 intensity ratio. 57Fe isomer shifts are consistent with the mean oxidation state Fe32.33+ arising from electron delocalization of the mixed-valence oxidation state description [Mo3+Fe3+Fe2+2]. Reaction of [(Tp)MoFe3S4(PEt3)2Cl] with (Me3Si)2S affords [(Tp)MoFe3S4(PEt3)2(SSiMe3)], a likely first intermediate in the formation of the tricluster compound {[(Tp)MoFe3S4(PEt)2]3S}(BPh4) from the reaction of [(Tp)MoFe3S4(PEt3)3](BPh4) and NaSSiMe3 in THF. The tricluster consists of three cluster units bound to a central μ3-S atom in a species of overall C3 symmetry. Relatively few clusters in the [MoFe3S4]2+ oxidation state have been prepared compared to the abundance of clusters in the oxidized [MoFe3S4]3+ state. This work is the first comprehensive study of the [MoFe3S4]2+ state, one conspicuous feature of which is its ability to bind hard and soft σ-donors and strong to weak π-acid ligands. (Tp = tris(pyrazolyl)hydroborate(1-))

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Electronic properties of single- and double-MoFe3S4 cubane-type clusters

Cited by 45 publications

References 3 publications

Identification of a spin-coupled Mo(iii) in the nitrogenase iron–molybdenum cofactor

Identification of a spin-coupled Mo(iii) in the nitrogenase iron–molybdenum cofactor

Metal trafficking for nitrogen fixation: NifQ donates molybdenum to NifEN/NifH for the biosynthesis of the nitrogenase FeMo-cofactor

The [MoFe₃S₄]²⁺ Oxidation State: Synthesis, Substitution Reactions, and Structures of Phosphine-Ligated Cubane-Type Clusters with the S = 2 Ground State

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Electronic properties of single- and double-MoFe3S4 cubane-type clusters

Cited by 45 publications

References 3 publications

Identification of a spin-coupled Mo(iii) in the nitrogenase iron–molybdenum cofactor

Identification of a spin-coupled Mo(iii) in the nitrogenase iron–molybdenum cofactor

Metal trafficking for nitrogen fixation: NifQ donates molybdenum to NifEN/NifH for the biosynthesis of the nitrogenase FeMo-cofactor

The [MoFe3S4]2+ Oxidation State: Synthesis, Substitution Reactions, and Structures of Phosphine-Ligated Cubane-Type Clusters with the S = 2 Ground State

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The [MoFe₃S₄]²⁺ Oxidation State: Synthesis, Substitution Reactions, and Structures of Phosphine-Ligated Cubane-Type Clusters with the S = 2 Ground State