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Graham N George - One of the best experts on this subject based on the ideXlab platform.
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spectroscopic studies of Molybdenum and tungsten enzymes
Coordination Chemistry Reviews, 2011Co-Authors: Jake M Pushie, Graham N GeorgeAbstract:Abstract Molybdenum and tungsten are the only second and third-row transition elements with a known function in living systems. Molybdenum fulfills functional roles in enzyme systems in almost all living creatures, from bacteria through plants to invertebrates and mammals, while tungsten takes the place of Molybdenum in some prokaryotes, especially the hyperthermophilic archaea. The enzymes contain the metal bound by an unusual sulfur-containing cofactor. Despite possessing common structural elements, the enzymes are remarkable in the range of different chemical reactions that are catalyzed, although almost all are two-electron oxidation–reduction reactions in which an oxygen atom is transferred to or from the Molybdenum. The functional roles filled by Molybdenum enzymes are equally diverse; for example, they play essential roles in microbial respiration, in the uptake of nitrogen in green plants, in controlling insect eye color, and in human health. Spectroscopic studies, in particular electron paramagnetic resonance and X-ray absorption spectroscopy, have played an essential role in our understanding of the active site structures and catalytic mechanisms of the Molybdenum and tungsten enzymes. This review summarizes the role spectroscopy has played in the state of our knowledge of the Molybdenum and tungsten enzymes, with particular regard to structural information on the Molybdenum sites.
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The Active Site of Arsenite Oxidase from Alcaligenes faecalis
Journal of the American Chemical Society, 2002Co-Authors: Thomas P. Conrads, Graham N George, Craig Hemann, Ingrid J. Pickering, Roger C. Prince, Russ HilleAbstract:Arsenite oxidase, a member of the DMSO reductase family of Molybdenum enzymes, has two molecules of guanosine dinucleotide Molybdenum cofactor coordinating the Molybdenum at the active site. X-ray ...
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Observation of ligand-based redox chemistry at the active site of a Molybdenum enzyme
Journal of the American Chemical Society, 1999Co-Authors: Graham N George, José J. G. Moura, Cristina Costa, Isabel MouraAbstract:The mononuclear Molybdenum enzymes all possess one or two molybdopterin cofactors coordinated to the Molybdenum through the ditholene motif. Despite this common feature, they exhibit quite diverse functionality. The Molybdenum enzymes previously have been described as all involving two-electron redox chemistry at Molybdenum, coupled with the transfer of an oxygen atom from water via Molybdenum to substrate, or the reverse. While these rules still appear to hold for most Molybdenum enzymes, and for their close relatives the tungsten enzymes, it now seems that there are at least some exceptions. The recently discovered tungsten enzyme acetylene hydratase catalyzes a net hydration reaction, rather than a redox one. Very recently it has been shown that formate oxidation to CO{sub 2} by Eschericia coli formate dehydrogenase H (FDH{sub H}) does not involve oxygen atom transfer. This enzyme has also been shown to possess a potentially redox-active selenosulfide ligand to Molybdenum, with the selenosulfide sulfur probably being one of the sulfurs of the cofactor dithiolene. The authors present an extended X-ray absorption fine structure (EXAFS) spectroscopic study of the Molybdenum site of Desulfovibrio desulfuricans ATCC 27774 formate dehydrogenase (FDH) and show that under reducing conditions the selenosulfide group can be reduced. This is themore » first observation of ligand-based redox chemistry in a Molybdenum enzyme.« less
Brian M. Leonard - One of the best experts on this subject based on the ideXlab platform.
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Iron-Doped Molybdenum Carbide Catalyst with High Activity and Stability for the Hydrogen Evolution Reaction
Chemistry of Materials, 2015Co-Authors: Brian M. LeonardAbstract:Molybdenum-based materials have been widely investigated recently as promising alternatives to platinum for catalyzing the hydrogen evolution reaction (HER). Molybdenum carbide is one of the most studied transition-metal carbides because of its cheap price, high abundance, good conductivity, and catalytic activity. In order to further improve the catalytic activity of Molybdenum carbide, some modifications have been applied. In this paper, a wide range of magnetic iron-doped Molybdenum carbide (Mo2–xFexC) nanomaterials were synthesized by a unique amine–metal oxide composite method. The amount of iron dopants was controlled by setting different iron/Molybdenum ratios in the precursors. Iron-doped Molybdenum carbide nanomaterials were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, Raman microscopy, and X-ray photoelectron spectroscopy. Electrocatalytic HER tests were used to demonstrate the catalytic activity upon addition ...
Hideki Sugimoto - One of the best experts on this subject based on the ideXlab platform.
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oxido alcoholato thiolato Molybdenum vi complexes with a dithiolene ligand generated by oxygen atom transfer to the Molybdenum iv complexes
Inorganica Chimica Acta, 2019Co-Authors: Hideki Sugimoto, Masanori Sato, Kaoru Asano, Takeyuki Suzuki, Takashi Ogura, Shinobu ItohAbstract:Abstract Oxido-alcoholato- and oxido-thiolato-Molybdenum(VI) complexes bearing two ene-1,2-dithiolate ligands (cyclohexene-1,2-dithiolate) are prepared as synthetic models of Molybdenum(VI) reaction centers of dimethyl sulfoxide reductase family of Molybdenum enzymes. These complexes are prepared by oxygen atom transfer from tertiary amine N-oxide (trimethylamine N-oxide and N,N-dimethylaniline N-oxide) to the five-coordinate alcoholato- and thiolato-Molybdenum(IV) complexes, and are characterized by UV–vis, cold-spray-ionization mass, resonance Raman, and 1H NMR spectroscopies. The oxygen atom transfer reactions are studied kinetically at a low temperature (−40 °C) to demonstrate that the reactivity of the thiolato-Molybdenum(IV) complex is higher than that of alcoholato-Molybdenum(IV) complex by about 7 times, and that the oxygen atom transfer reactivity increases with increasing the electron withdrawing ability of the p-substituent of N,N-dimethylaniline N-oxide derivatives. Mechanistic details are discussed based on the reactivity studies.
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A Model for the Active-Site Formation Process in DMSO Reductase Family Molybdenum Enzymes Involving Oxido−Alcoholato and Oxido−Thiolato Molybdenum(VI) Core Structures
2016Co-Authors: Hideki Sugimoto, Masanori Sato, Takeyuki Suzuki, Takashi Ogura, Kaori Asano, Kaoru Mieda, Takashi Matsumoto, Logan J. Giles, Amrit Pokhrel, Martin L. KirkAbstract:New bis(ene-1,2-dithiolato)-oxido–alcoholato Molybdenum(VI) and -oxido–thiolato Molybdenum(VI) anionic complexes, denoted as [MoVIO(ER)L2]– (E = O, S; L = dimethoxycarboxylate-1,2-ethylenedithiolate), were obtained from the reaction of the corresponding dioxido-Molybdenum(VI) precursor complex with either an alcohol or a thiol in the presence of an organic acid (e.g., 10-camphorsulfonic acid) at low temperature. The [MoVIO(ER)L2]– complexes were isolated and characterized, and the structure of [MoVIO(OEt)L2]– was determined by X-ray crystallography. The Mo(VI) center in [MoVIO(OEt)L2]– exhibits a distorted octahedral geometry with the two ene-1,2-dithiolate ligands being symmetry inequivalent. The computed structure of [MoVIO(SR)L2]– is essentially identical to that of [MoVIO(OR)L2]–. The electronic structures of the resulting Molybdenum(VI) complexes were evaluated using electronic absorption spectroscopy and bonding calculations. The nature of the distorted Oh geometry in these [MoVIO(EEt)L2]– complexes results in a lowest unoccupied molecular orbital wave function that possesses strong π* interactions between the Mo(dxy) orbital and the cis S(pz) orbital localized on one sulfur donor from a single ene-1,2-dithiolate ligand. The presence of a covalent Mo–Sdithiolene bonding interaction in these monooxido Mo(VI) compounds contributes to their low-energy ligand-to-metal charge transfer transitions. A second important d–p π bonding interaction derives from the ∼180° Ooxo–Mo–E–C dihedral angle involving the alcoholate and thiolate donors, and this contributes to ancillary ligand contributions to the electronic structure of these species. The formation of [MoVIO(OEt)L2]– and [MoVIO(SEt)L2]– from the dioxidoMolybdenum(VI) precursor may be regarded as a model for the active-site formation process that occurs in the dimethyl sulfoxide reductase family of pyranopterin Molybdenum enzymes
Shinobu Itoh - One of the best experts on this subject based on the ideXlab platform.
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oxido alcoholato thiolato Molybdenum vi complexes with a dithiolene ligand generated by oxygen atom transfer to the Molybdenum iv complexes
Inorganica Chimica Acta, 2019Co-Authors: Hideki Sugimoto, Masanori Sato, Kaoru Asano, Takeyuki Suzuki, Takashi Ogura, Shinobu ItohAbstract:Abstract Oxido-alcoholato- and oxido-thiolato-Molybdenum(VI) complexes bearing two ene-1,2-dithiolate ligands (cyclohexene-1,2-dithiolate) are prepared as synthetic models of Molybdenum(VI) reaction centers of dimethyl sulfoxide reductase family of Molybdenum enzymes. These complexes are prepared by oxygen atom transfer from tertiary amine N-oxide (trimethylamine N-oxide and N,N-dimethylaniline N-oxide) to the five-coordinate alcoholato- and thiolato-Molybdenum(IV) complexes, and are characterized by UV–vis, cold-spray-ionization mass, resonance Raman, and 1H NMR spectroscopies. The oxygen atom transfer reactions are studied kinetically at a low temperature (−40 °C) to demonstrate that the reactivity of the thiolato-Molybdenum(IV) complex is higher than that of alcoholato-Molybdenum(IV) complex by about 7 times, and that the oxygen atom transfer reactivity increases with increasing the electron withdrawing ability of the p-substituent of N,N-dimethylaniline N-oxide derivatives. Mechanistic details are discussed based on the reactivity studies.
Russ Hille - One of the best experts on this subject based on the ideXlab platform.
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spectroscopic and kinetic properties of the Molybdenum containing nad dependent formate dehydrogenase from ralstonia eutropha
Journal of Biological Chemistry, 2016Co-Authors: Dimitri Niks, Jayant Duvvuru, Miguel Escalona, Russ HilleAbstract:We have examined the rapid reaction kinetics and spectroscopic properties of the Molybdenum-containing, NAD(+)-dependent FdsABG formate dehydrogenase from Ralstonia eutropha. We confirm previous steady-state studies of the enzyme and extend its characterization to a rapid kinetic study of the reductive half-reaction (the reaction of formate with oxidized enzyme). We have also characterized the electron paramagnetic resonance signal of the Molybdenum center in its Mo(V) state and demonstrated the direct transfer of the substrate Cα hydrogen to the Molybdenum center in the course of the reaction. Varying temperature, microwave power, and level of enzyme reduction, we are able to clearly identify the electron paramagnetic resonance signals for four of the iron/sulfur clusters of the enzyme and find suggestive evidence for two others; we observe a magnetic interaction between the Molybdenum center and one of the iron/sulfur centers, permitting assignment of this signal to a specific iron/sulfur cluster in the enzyme. In light of recent advances in our understanding of the structure of the Molybdenum center, we propose a reaction mechanism involving direct hydride transfer from formate to a Molybdenum-sulfur group of the Molybdenum center.
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The Active Site of Arsenite Oxidase from Alcaligenes faecalis
Journal of the American Chemical Society, 2002Co-Authors: Thomas P. Conrads, Graham N George, Craig Hemann, Ingrid J. Pickering, Roger C. Prince, Russ HilleAbstract:Arsenite oxidase, a member of the DMSO reductase family of Molybdenum enzymes, has two molecules of guanosine dinucleotide Molybdenum cofactor coordinating the Molybdenum at the active site. X-ray ...
