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Charles G. Young - One of the best experts on this subject based on the ideXlab platform.

  • chemical systems modeling the d1 mo v states of Molybdenum Enzymes
    Journal of Inorganic Biochemistry, 2016
    Co-Authors: Charles G. Young
    Abstract:

    This review focuses on the synthesis, properties and electron paramagnetic resonance (EPR), electron spin echo envelope modulation (ESEEM) and electron-nuclear double resonance (ENDOR) spectroscopy of mononuclear d1 oxo- and sulfido-Mo(V) complexes relevant to the understanding of the EPR-active Mo(V) forms of pterin-containing Molybdenum Enzymes.

  • Chemical systems modeling the d(1) Mo(V) states of Molybdenum Enzymes.
    Journal of Inorganic Biochemistry, 2016
    Co-Authors: Charles G. Young
    Abstract:

    This review focuses on the synthesis, properties and electron paramagnetic resonance (EPR), electron spin echo envelope modulation (ESEEM) and electron-nuclear double resonance (ENDOR) spectroscopy of mononuclear d1 oxo- and sulfido-Mo(V) complexes relevant to the understanding of the EPR-active Mo(V) forms of pterin-containing Molybdenum Enzymes.

  • scorpionate complexes as models for Molybdenum Enzymes
    European Journal of Inorganic Chemistry, 2016
    Co-Authors: Charles G. Young
    Abstract:

    Scorpionate ligands have supported the development of a number of important synthetic models for pterin-containing Molybdenum Enzymes. These ligands stabilize biologically relevant mononuclear oxido- and sulfido-Mo(VI,V,IV) complexes capable of sustaining a wide range of biomimetic reactions, including oxygen atom, sulfur atom and coupled electron-proton transfer reactions. Studies of scorpionate-Mo compounds have also provided key insights into the bonding in oxido-Mo dithiolene moieties, the orbital control of enzymatic reactions and the synthesis and behavior of biologically relevant Mo-pterindithiolene complexes. This microreview covers advances in the synthesis and study of scorpionate complexes as models for Molybdenum Enzymes in the second half of the field's 30-year history, i.e., from around 2000, the turn of the century, onwards.

  • Molybdenum mpt containing Enzymes
    Encyclopedia of Inorganic and Bioinorganic Chemistry, 2011
    Co-Authors: Charles G. Young
    Abstract:

    Molybdenum, an essential trace element for all forms of life, is found in a wide range of Mo-MPT Enzymes important in the metabolism of small molecules and anions of nitrogen, sulfur, carbon, chlorine, selenium, and arsenic, and in the global biogeochemical cycles of these elements. These Enzymes feature active sites composed of a single (mononuclear) Mo atom coordinated by one or two MPT-based ligands, L (MPT = ‘molybdopterin′ or Metal-binding Pterin ene-1,2-diThiolate). These ligands contain a pyranopterin or simple pterin nucleus, an ene-1,2-dithiolate (dithiolene) unit, and a pendant phosphate group; in Enzymes from prokaryotes, the phosphate is generally attached to a nucleotide, giving ‘dinucleotide’ forms of MPT. The dithiolene moiety functions as a bidentate S2-donor ligand to Mo. The Mo-MPT Enzymes are classified into two broad functional types: oxotransferases and hydroxylases. The oxotransferases generally catalyze oxygen atom transfer reactions and fall into two families: the sulfite oxidase and dimethyl sulfoxide (DMSO) reductase families. Enzymes from these families contain square-pyramidal cis-[MoVIO2L(cysteinate)]− and distorted trigonal prismatic [MoVIO(AA)L2]− (AA = serinate, cysteinate, selenocysteinate, etc.) oxidized active sites, respectively. The hydroxylases all belong to the xanthine oxidase family and generally catalyze net insertion of oxygen into the CH bonds of heterocyclic aromatic compounds and aldehydes. They contain biologically unique, square-pyramidal [MoVIOS(OH)L]− oxidized active sites featuring a catalytically essential terminal sulfido ligand. The sulfido ligand can act in a bridging capacity to Cu, as recently demonstrated for CO dehydrogenase. In most reactions catalyzed by Mo-MPT Enzymes, an oxygen atom is exchanged between substrate and water with concomitant consumption (for reductases) or production (for oxidases) of reducing equivalents (2e−, 2H+). Synthetic analogue (model) studies have produced complexes replicating or informing the composition, structures, spectroscopy, and chemistry of the Enzymes. This account focuses on the Mo bioinorganic chemistry of the Mo-MPT Enzymes and selected synthetic analogues. It is divided into two main parts. Part 1 provides an overview of the enzyme systems, their distribution, roles, and essential chemistry, as well as a discussion of consensus structures and likely mechanisms. The genes and proteins involved in Mo trafficking and Mo-cofactor biosynthesis are also briefly described. Part 2 summarizes important developments in the production of synthetic analogues, with a focus on new dithiolene, scorpionate, and other complexes sharing the structural, spectroscopic, or chemical attributes of the Enzymes. Keywords: Molybdenum Enzymes; oxygen atom transfer (OAT); coupled electron-proton transfer (CEPT); pterin-dithiolene ligands; sulfite oxidase; nitrate reductase; DMSO reductase; xanthine oxidase/dehydrogenase; dithiolene complexes; trispyrazolylborate complexes

  • insights into the nature of mo v species in solution modeling catalytic cycles for Molybdenum Enzymes
    Inorganica Chimica Acta, 2009
    Co-Authors: Asha Rajapakshe, Charles G. Young, Andrei V Astashkin, Rae Ana Snyder, Pablo Bernardson, David J Evans, Dennis H Evans, John H. Enemark
    Abstract:

    Abstract The tris(pyrazolyl)borate and related tripodal N-donor ligands originally developed by Trofimenko stabilize mononuclear compounds containing MoVIO2, MoVIO, MoVO, and MoIVO units and effectively inhibit their polynucleation in organic solvents. Dioxo-Mo(VI) complexes of the type LMoO2(SPh), where L = hydrotris(3,5-dimethylpyrazol-1-yl)borate (Tp∗), hydrotris(3-isopropylpyrazol-1-yl)borate (TpiPr), and hydrotris(3,5-dimethyl-1,2,4-triazol-1-yl)borate (Tz) and related derivatives are the only model systems that mimic the complete reaction sequence of sulfite oxidase, in which oxygen from water is ultimately incorporated into product. The quasi-reversible, one-electron reduction of Tp∗MoO2(SPh) in acetonitrile exhibits a positive potential shift upon addition of a hydroxylic proton donor, and the magnitude of the shift correlates with the acidity of the proton donor. These reductions produce two Mo(V) species, [Tp∗MoVO2(SPh)]− and Tp∗MoVO(OH)(SPh), that are related by protonation. Measurement of the relative amounts of these two Mo(V) species by EPR spectroscopy enabled the pKa of the MoV(OH) unit in acetonitrile to be determined and showed it to be several pKa units smaller than that for water in acetonitrile. Similar electrochemical-EPR experiments for TpiPrMoO2(SPh) indicated that the pKa for its MoV(OH) unit was ∼1.7 units smaller than that for Tp∗MoVO(OH)(SPh). Density functional theory calculations also predict a smaller pKa for TpiPrMoVO(OH)(SPh) compared to Tp∗MoVO(OH)(SPh). Analysis of these results indicates that coupled electron–proton transfer (CEPT) is thermodynamically favored over the indirect process of metal reduction followed by protonation. The crystal structure of TpiPrMoO2(SPh) is also presented.

John H. Enemark - One of the best experts on this subject based on the ideXlab platform.

  • vibrational control of covalency effects related to the active sites of Molybdenum Enzymes
    Journal of the American Chemical Society, 2018
    Co-Authors: John H. Enemark, Benjamin W Stein, Jing Yang, Regina P Mtei, Nicholas J Wiebelhaus, Dominic K Kersi, Jesse Lepluart, Dennis L Lichtenberger, M.l. Kirk
    Abstract:

    A multitechnique spectroscopic and theoretical study of the Cp2M(benzenedithiolato) (M = Ti, V, Mo; Cp = η5-C5H5) series provides deep insight into dithiolene electronic structure contributions to electron transfer reactivity and reduction potential modulation in pyranopterin Molybdenum Enzymes. This work explains the magnitude of the dithiolene folding distortion and the concomitant changes in metal-ligand covalency that are sensitive to electronic structure changes as a function of d-electron occupancy in the redox orbital. It is shown that the large fold angle differences correlate with covalency, and the fold angle distortion is due to a pseudo-Jahn–Teller (PJT) effect. The PJT effect in these and related transition metal dithiolene systems arises from the small energy differences between metal and sulfur valence molecular orbitals, which uniquely poise these systems for dramatic geometric and electronic structure changes as the oxidation state changes. Herein, we have used a combination of resonance ...

  • Sulfite-oxidizing Enzymes
    Journal of Biological Inorganic Chemistry, 2014
    Co-Authors: Ulrike Kappler, John H. Enemark
    Abstract:

    Sulfite-oxidizing Enzymes (SOEs) are Molybdenum Enzymes that exist in almost all forms of life where they carry out important functions in protecting cells and organisms against sulfite-induced damage. Due to their nearly ubiquitous presence in living cells, these Enzymes can be assumed to be evolutionarily ancient, and this is reflected in the fact that the basic domain architecture and fold structure of all sulfite-oxidizing Enzymes studied so far are similar. The Mo centers of all SOEs have five-coordinate square pyramidal coordination geometry, which incorporates a pyranopterin dithiolene cofactor. However, significant differences exist in the quaternary structure of the Enzymes, as well as in the kinetic properties and the nature of the electron acceptors used. In addition, some SOEs also contain an integral heme group that participates in the overall catalytic cycle. Catalytic turnover involves the paramagnetic Mo(V) oxidation state, and EPR spectroscopy, especially high-resolution pulsed EPR spectroscopy, provides detailed information about the molecular and electronic structure of the Mo center and the Mo-based sulfite oxidation reaction.

  • insights into the nature of mo v species in solution modeling catalytic cycles for Molybdenum Enzymes
    Inorganica Chimica Acta, 2009
    Co-Authors: Asha Rajapakshe, Charles G. Young, Andrei V Astashkin, Rae Ana Snyder, Pablo Bernardson, David J Evans, Dennis H Evans, John H. Enemark
    Abstract:

    Abstract The tris(pyrazolyl)borate and related tripodal N-donor ligands originally developed by Trofimenko stabilize mononuclear compounds containing MoVIO2, MoVIO, MoVO, and MoIVO units and effectively inhibit their polynucleation in organic solvents. Dioxo-Mo(VI) complexes of the type LMoO2(SPh), where L = hydrotris(3,5-dimethylpyrazol-1-yl)borate (Tp∗), hydrotris(3-isopropylpyrazol-1-yl)borate (TpiPr), and hydrotris(3,5-dimethyl-1,2,4-triazol-1-yl)borate (Tz) and related derivatives are the only model systems that mimic the complete reaction sequence of sulfite oxidase, in which oxygen from water is ultimately incorporated into product. The quasi-reversible, one-electron reduction of Tp∗MoO2(SPh) in acetonitrile exhibits a positive potential shift upon addition of a hydroxylic proton donor, and the magnitude of the shift correlates with the acidity of the proton donor. These reductions produce two Mo(V) species, [Tp∗MoVO2(SPh)]− and Tp∗MoVO(OH)(SPh), that are related by protonation. Measurement of the relative amounts of these two Mo(V) species by EPR spectroscopy enabled the pKa of the MoV(OH) unit in acetonitrile to be determined and showed it to be several pKa units smaller than that for water in acetonitrile. Similar electrochemical-EPR experiments for TpiPrMoO2(SPh) indicated that the pKa for its MoV(OH) unit was ∼1.7 units smaller than that for Tp∗MoVO(OH)(SPh). Density functional theory calculations also predict a smaller pKa for TpiPrMoVO(OH)(SPh) compared to Tp∗MoVO(OH)(SPh). Analysis of these results indicates that coupled electron–proton transfer (CEPT) is thermodynamically favored over the indirect process of metal reduction followed by protonation. The crystal structure of TpiPrMoO2(SPh) is also presented.

  • pulsed epr investigations of systems modeling Molybdenum Enzymes hyperfine and quadrupole parameters of oxo 17o in mo17o sph 4
    Journal of the American Chemical Society, 2005
    Co-Authors: Andrei V Astashkin, Jon J A Cooney, Frank Neese, Arnold M Raitsimring, Eric Bultman, John H. Enemark
    Abstract:

    Ka band ESEEM spectroscopy was used to determine the hyperfine (hfi) and nuclear quadrupole (nqi) interaction parameters for the oxo-17O ligand in [Mo17O(SPh)4]-, a spectroscopic model of the oxo-Mo(V) centers of Enzymes. The isotropic hfi constant of 6.5 MHz found for the oxo-17O is much smaller than the values of ∼20−40 MHz typical for the 17O nucleus of an equatorial OH(2) ligand in Molybdenum Enzymes. The 17O nqi parameter (e2qQ/h = 1.45 MHz, η ≈ 0) is the first to be obtained for an oxo group in a metal complex. The parameters of the oxo-17O ligand, as well as other magnetic resonance parameters of [Mo17O(SPh)4]- predicted by quasi-relativistic DFT calculations, were in good agreement with those obtained in experiment. From the electronic structure of the complex revealed by DFT, it follows that the SOMO is almost entirely Molybdenum dxy and sulfur p, while the spin density on the oxo-17O is negative, determined by spin polarization mechanisms. The results of this work will enable direct experimental...

  • new oxovanadium bis 1 2 dithiolate compounds that mimic the hydrogen bonding interactions at the active sites of mononuclear Molybdenum Enzymes
    Inorganic Chemistry, 2002
    Co-Authors: Jon J A Cooney, Michael D Carducci, Anne E Mcelhaney, Hugh D Selby, John H. Enemark
    Abstract:

    Reaction of VO(acac)2 with 1,2-dithiols in the presence of triethylamine gives pentacoordinate oxovanadium complexes [HNEt3]2[VO(bdt)2] (1), [HNEt3]2[VO(tdt)2] (2), and [HNEt3]2[VO(bdtCl2)2] (3) (where H2bdt = 1,2-benzenedithiol, H2tdt = 3,4-toluenedithiol, and H2bdtCl2 = 3,6-dichloro-1,2-benzenedithiol). Compounds 1−3 have been characterized by IR, UV/visible, EPR, and mass spectroscopies. The X-ray crystal stuctures of 1 and 2 show hydrogen-bonding interactions between the terminal oxo atom and triethylammonium counterions and between ligand sulfur atoms and the counterions. These interactions are comparable with those found at the active sites of mononuclear Molybdenum Enzymes.

M.l. Kirk - One of the best experts on this subject based on the ideXlab platform.

  • 3.11 – Molybdenum Enzymes
    Comprehensive Inorganic Chemistry II, 2020
    Co-Authors: M.l. Kirk, B. Stein
    Abstract:

    This chapter on Molybdenum Enzymes primarily focuses on recent advances in the knowledge base over the last decade regarding the inorganic chemistry of Molybdenum Enzymes, which include the large pyranopterin Molybdenum enzyme class and Molybdenum-containing nitrogenase. This is not a comprehensive coverage of relevant small model chemistry or the more biological aspects of Molybdenum Enzymes. Specifically, the scope of this chapter focuses on recent advances in our understanding of enzyme geometric structure, electronic structure, and the reaction coordinates of pyranopterin Molybdenum Enzymes and nitrogenase since ca.2000.

  • remote charge effects on the oxygen atom transfer reactivity and their relationship to Molybdenum Enzymes
    Inorganic Chemistry, 2019
    Co-Authors: Jaya Paudel, M.l. Kirk, Amrit Pokhrel, Feifei Li
    Abstract:

    We report the syntheses, crystal structures, and characterization of the novel cis-dioxoMolybdenum(VI) complexes [Tpm*MoVIO2Cl](MoO2Cl3) (1) and [Tpm*MoVIO2Cl](ClO4) (2), which are supported by the charge-neutral tris(3,5-dimethyl-1-pyrazolyl)methane (Tpm*) ligand. A comparison between isostructural [Tpm*MoVIO2Cl]+ and Tp*MoVIO2Cl [Tp* = hydrotris(3,5-dimethyl-1-pyrazolyl)borate] reveals the effects of one unit of overall charge difference on their spectroscopic and electrochemical properties, geometric and electronic structures, and O-atom-transfer (OAT) reactivities, providing new insight into pyranopterin molybdoenzyme OAT reactivity. Computational studies of these molecules indicate that the delocalized positive charge lowers the lowest unoccupied molecular orbital (LUMO) energy of cationic [Tpm*MoO2Cl]+ relative to Tp*MoO2Cl. Despite their virtually identical geometric structures revealed by crystal structures, the MoVI/MoV redox potential of 2 is increased by 350 mV relative to that of Tp*MoVIO2Cl. ...

  • vibrational control of covalency effects related to the active sites of Molybdenum Enzymes
    Journal of the American Chemical Society, 2018
    Co-Authors: John H. Enemark, Benjamin W Stein, Jing Yang, Regina P Mtei, Nicholas J Wiebelhaus, Dominic K Kersi, Jesse Lepluart, Dennis L Lichtenberger, M.l. Kirk
    Abstract:

    A multitechnique spectroscopic and theoretical study of the Cp2M(benzenedithiolato) (M = Ti, V, Mo; Cp = η5-C5H5) series provides deep insight into dithiolene electronic structure contributions to electron transfer reactivity and reduction potential modulation in pyranopterin Molybdenum Enzymes. This work explains the magnitude of the dithiolene folding distortion and the concomitant changes in metal-ligand covalency that are sensitive to electronic structure changes as a function of d-electron occupancy in the redox orbital. It is shown that the large fold angle differences correlate with covalency, and the fold angle distortion is due to a pseudo-Jahn–Teller (PJT) effect. The PJT effect in these and related transition metal dithiolene systems arises from the small energy differences between metal and sulfur valence molecular orbitals, which uniquely poise these systems for dramatic geometric and electronic structure changes as the oxidation state changes. Herein, we have used a combination of resonance ...

  • a model for the active site formation process in dmso reductase family Molybdenum Enzymes involving oxido alcoholato and oxido thiolato Molybdenum vi core structures
    Inorganic Chemistry, 2016
    Co-Authors: Hideki Sugimoto, Amrit Pokhrel, Masanori Sato, Kaori Asano, Takeyuki Suzuki, Kaoru Mieda, Takashi Ogura, Takashi Matsumoto, Logan J Giles, M.l. Kirk
    Abstract:

    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...

  • Electronic structure contributions to reactivity in xanthine oxidase family Enzymes
    JBIC Journal of Biological Inorganic Chemistry, 2015
    Co-Authors: Benjamin W Stein, M.l. Kirk
    Abstract:

    We review the xanthine oxidase (XO) family of pyranopterin Molybdenum Enzymes with a specific emphasis on electronic structure contributions to reactivity. In addition to xanthine and aldehyde oxidoreductases, which catalyze the two-electron oxidation of aromatic heterocycles and aldehyde substrates, this mini-review highlights recent work on the closely related carbon monoxide dehydrogenase (CODH) that catalyzes the oxidation of CO using a unique Mo–Cu heterobimetallic active site. A primary focus of this mini-review relates to how spectroscopy and computational methods have been used to develop an understanding of critical relationships between geometric structure, electronic structure, and catalytic function.

Partha Basu - One of the best experts on this subject based on the ideXlab platform.

  • Functional mononuclear Molybdenum Enzymes: challenges and triumphs in molecular cloning, expression, and isolation
    JBIC Journal of Biological Inorganic Chemistry, 2020
    Co-Authors: Breeanna Mintmier, Samih Nassif, John F. Stolz, Partha Basu
    Abstract:

    Mononuclear Molybdenum Enzymes catalyze a variety of reactions that are essential in the cycling of nitrogen, carbon, arsenic, and sulfur. For decades, the structure and function of these crucial Enzymes have been investigated to develop a fundamental knowledge for this vast family of Enzymes and the chemistries they carry out. Therefore, obtaining abundant quantities of active enzyme is necessary for exploring this family’s biochemical capability. This mini-review summarizes the methods for overexpressing mononuclear Molybdenum Enzymes in the context of the challenges encountered in the process. Effective methods for Molybdenum cofactor synthesis and incorporation, optimization of expression conditions, improving isolation of active vs. inactive enzyme, incorporation of additional prosthetic groups, and inclusion of redox enzyme maturation protein chaperones are discussed in relation to the current Molybdenum enzyme literature. This article summarizes the heterologous and homologous expression studies providing underlying patterns and potential future directions. Graphic abstract

  • CHAPTER 2:Pterin-Inspired Model Compounds of Molybdenum Enzymes
    Molybdenum and Tungsten Enzymes, 2016
    Co-Authors: Sharon J. Nieter Burgmayer, Benjamin R. Williams, Partha Basu
    Abstract:

    The Molybdenum cofactor at the catalytic heart of mononuclear molybdoEnzymes comprises a Molybdenum ion coordinated by one or two dithiolene ligands containing an N-heterocyclic structure known as pterin. Understanding the details of the unusual combination of Molybdenum with pterin and dithiolene is the impetus behind employing model chemistry to investigate the cofactor’s broad redox capabilities. This chapter highlights the major efforts to synthesize pterin-containing models and study their chemical properties. The history of identification of the cofactor’s pyranopterin dithiolene ligand and the details of pterin redox chemistry are reviewed, followed by an account of the synthesis and analysis of pterin-inspired chemical models. The implications of these models’ chemical reactivity and redox features that provide a fundamental basis for understanding the Molybdenum cofactor are included. In addition, we highlight the potential directions of the field.

  • Recent developments in the study of molybdoenzyme models
    Journal of Biological Inorganic Chemistry, 2015
    Co-Authors: Partha Basu, Sharon J. Nieter Burgmayer
    Abstract:

    Over the past two decades, a plethora of crystal structures of Molybdenum Enzymes has appeared in the literature providing a clearer picture of the enzymatic active sites and increasing the challenge to chemists to develop accurate models for those sites. In this minireview we discuss the most recent model studies aimed to reproduce detailed features of the pterin–dithiolene ligand, both as the uncoordinated form and as a chelate coordinated to Molybdenum.

  • oxygen atom transfer in models for Molybdenum Enzymes isolation and structural spectroscopic and computational studies of intermediates in oxygen atom transfer from Molybdenum vi to phosphorus iii
    Chemistry: A European Journal, 2005
    Co-Authors: Andrew J Millar, Partha Basu, Christian J. Doonan, Paul D Smith, Victor N Nemykin, Charles G. Young
    Abstract:

    Intermediates in the oxygen atom transfer from Mo V I to P I I I , [Tp i P r MoOX(OPR 3 )] (Tp i P r =hydrotris(3-isopropylpyrazol-l-yl)borate; X= Cl - , phenolates, thiolates), have been isolated from the reactions of [Tp i P r -MoO 2 X] with phosphines (PEt 3 , PMePh 2 , PPh 3 ). The green, diamagnetic oxoMolybdenum(iv) complexes possess local C 1 symmetry (by NMR spectroscopy) and exhibit IR bands assigned to ν(Mo=O) (approximately 950 cm - 1 ) and ν(P=O) (1140-1083 cm - 1 ) vibrations. The X-ray crystal structures of [Tp i P r MoOX(OPEt 3 )] (X=OC 6 H 4 -2-sBu, SnBu), [Tp i P r MoO(OPh)-(OPMePh 2 )], and [Tp i P r MoOCl-(OPPh 3 )] have been determined. The monomeric complexes exhibit distorted octahedral geometries, with coordination spheres composed of tridentate fac-Tp i P r and mutually cis monodentate terminal oxo, phosphoryl (phosphine oxide), and monoanionic X ligands. The electronic structures and stabilities of the complexes have been probed by computational methods, with the three-dimensional energy surfaces confirming the existence of a low-energy steric pocket that restricts the conformational freedom of the phosphoryl ligand and inhibits complete oxygen atom transfer. The reactivity of the complexes is also briefly described.

  • a coordination chemist s view of the active sites of mononuclear Molybdenum Enzymes
    Current Science, 2003
    Co-Authors: Partha Basu, John F. Stolz, Michael T Smiths
    Abstract:

    A comparison of the coordination environment of twelve structurally characterized mononuclear Molybdenum-containing Enzymes revealed many similarities that helped define specific features of the active sites. Using bond distances and angles, the types of bonds and terminal groups of significance were identified. For example, a distance between Molybdenum and oxygen atoms ranging from 1.6 to 1.8 A was considered as a Mo=O bond. The dithiolene sulphur to Molybdenum single bond distances fluctuated around 2.40 A. In most cases, the sulphur-sulphur interaction within the co-factors is weak, with distances above 3.00 A, but both trimethylamine N-oxide and dissimilatory nitrate reductase (i.e. NapA) show strong sulphur-sulphur interactions with distances closer to 2.80 A. In addition, the dithiolene bite angle (S-Mo-S) was observed to be directly affected by the distance of the sulphurs from the metal centre. The bite angle is very small for co-factors that are further away from the Molybdenum atom, as observed in TMAOR. A small bite angle is suggestive of ligand dissociation.

Isabel Moura - One of the best experts on this subject based on the ideXlab platform.

  • Incorporation of Molybdenum in rubredoxin: models for mononuclear Molybdenum Enzymes
    Journal of Biological Inorganic Chemistry, 2015
    Co-Authors: Biplab K. Maiti, Isabel Moura, Luisa B. Maia, Célia M. Silveira, Smilja Todorovic, Cíntia Carreira, Marta S. P. Carepo, Raquel Grazina, Sofia R. Pauleta, José J. G. Moura
    Abstract:

    Molybdenum is found in the active site of Enzymes usually coordinated by one or two pyranopterin molecules. Here, we mimic an enzyme with a mononuclear Molybdenum-bis pyranopterin center by incorporating Molybdenum in rubredoxin. In the Molybdenum-substituted rubredoxin, the metal ion is coordinated by four sulfurs from conserved cysteine residues of the apo-rubredoxin and two other exogenous ligands, oxygen and thiol, forming a Mo(VI)-(S-Cys)4(O)(X) complex, where X represents –OH or –SR. The rubredoxin Molybdenum center is stabilized in a Mo(VI) oxidation state, but can be reduced to Mo(IV) via Mo(V) by dithionite, being a suitable model for the spectroscopic properties of resting and reduced forms of Molybdenum-bis pyranopterin-containing Enzymes. Preliminary experiments indicate that the Molybdenum site built in rubredoxin can promote oxo transfer reactions, as exemplified with the oxidation of arsenite to arsenate.

  • structural and electron paramagnetic resonance epr studies of mononuclear Molybdenum Enzymes from sulfate reducing bacteria
    Accounts of Chemical Research, 2006
    Co-Authors: Carlos D. Brondino, José J. G. Moura, M J Romao, Maria G Rivas, Isabel Moura
    Abstract:

    Molybdenum and tungsten are found in biological systems in a mononuclear form in the active site of a diverse group of Enzymes that generally catalyze oxygen-atom-transfer reactions. The metal atom (Mo or W) is coordinated to one or two pyranopterin molecules and to a variable number of ligands such as oxygen (oxo, hydroxo, water, serine, aspartic acid), sulfur (cysteines), and selenium (selenocysteines) atoms. In addition, these proteins contain redox cofactors such as iron-sulfur clusters and heme groups. All of these metal cofactors are along an electron-transfer pathway that mediates the electron exchange between substrate and an external electron acceptor (for oxidative reactions) or donor (for reductive reactions). We describe in this Account a combination of structural and electronic paramagnetic resonance studies that were used to reveal distinct aspects of these Enzymes.

  • Handbook of Metalloproteins - Dissimilatory Nitrate Reductase
    Handbook of Metalloproteins, 2006
    Co-Authors: Maria João Romão, João M. Dias, Isabel Moura
    Abstract:

    The dissimilatory nitrate reductase (NAP) from Desulfovibrio desulfuricans ATCC 27774 catalyses the reduction of nitrate to nitrite for respiration. It belongs to the DMSO reductase family of molybdoEnzymes and contains one single subunit of 755 amino acids with one Molybdenum cofactor and one [4Fe–4S] cluster. The Mo atom is coordinated by two cis-dithiolene groups of two molybdopterin guanine dinucleotides (MGD), by the sulfur atom of Cys140 and by one OH/OH2 ligand. One of the MGD cofactors is directly involved in the electron transfer between the Molybdenum center and the [4Fe–4S] cluster. 3D Structure Keywords: Molybdenum Enzymes; molybdopterin; nitrate reductase; [4Fe–4S]; desulfovibrio desulfuricans

  • analysis of the electron paramagnetic resonance properties of the 2fe 2s 1 centers in Molybdenum Enzymes of the xanthine oxidase family assignment of signals i and ii
    Biochemistry, 2000
    Co-Authors: Jorge Caldeira, José J. G. Moura, Isabel Moura, Bruno Guigliarelli, Valerie Belle, Marcel Asso, Patrick Bertrand
    Abstract:

    : MolybdoEnzymes of the xanthine oxidase family contain two [2Fe-2S](1+,2+) clusters that are bound to the protein by very different cysteine motifs. In the X-ray crystal structure of Desulfovibrio gigas aldehyde oxidoreductase, the cluster ligated by a ferredoxin-type motif is close to the protein surface, whereas that ligated by an unusual cysteine motif is in contact with the molybdopterin [Romao, M. J., Archer, M., Moura, I., Moura, J. J. G., LeGall, J., Engh, R., Schneider, M., Hof, P., and Huber, R. (1995) Science 270, 1170-1176]. These two clusters display distinct electron paramagnetic resonance (EPR) signals: the less anisotropic one, called signal I, is generally similar to the g(av) approximately 1.96-type signals given by ferredoxins, whereas signal II often exhibits anomalous properties such as very large g values, broad lines, and very fast relaxation properties. A detailed comparison of the temperature dependence of the spin-lattice relaxation time and of the intensity of these signals in D. gigas aldehyde oxidoreductase and in milk xanthine oxidase strongly suggests that the peculiar EPR properties of signal II arise from the presence of low-lying excited levels reflecting significant double exchange interactions. The issue raised by the assignment of signals I and II to the two [2Fe-2S](1+) clusters was solved by using the EPR signal of the Mo(V) center as a probe. The temperature dependence of this signal could be quantitatively reproduced by assuming that the Mo(V) center is coupled to the cluster giving signal I in xanthine oxidase as well as in D. gigas aldehyde oxidoreductase. This demonstrates unambiguously that, in both Enzymes, signal I arises from the center which is closest to the Molybdenum cofactor.

  • Observation of ligand-based redox chemistry at the active site of a Molybdenum enzyme
    Journal of the American Chemical Society, 1999
    Co-Authors: Graham N. George, José J. G. Moura, Cristina Costa, Isabel Moura
    Abstract:

    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