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Schüren AO, Ridgway BM, Di Salvo F, Carella LM, Gramm VK, Metzger E, Doctorovich F, Rentschler E, Schünemann V, Ruschewitz U, Klein A. Structural insight into halide-coordinated [Fe 4S 4X nY 4-n] 2- clusters (X, Y = Cl, Br, I) by XRD and Mössbauer spectroscopy. Dalton Trans 2023; 52:1277-1290. [PMID: 36621931 DOI: 10.1039/d2dt03203a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Iron sulphur halide clusters [Fe4S4Br4]2- and [Fe4S4X2Y2]2- (X, Y = Cl, Br, I) were obtained in excellent yields (77 to 78%) and purity from [Fe(CO)5], elemental sulphur, I2 and benzyltrimethylammonium (BTMA+) iodide, bromide and chloride. Single crystals of (BTMA)2[Fe4S4Br4] (1), (BTMA)2[Fe4S4Br2Cl2] (2), (BTMA)2[Fe4S4Cl2I2] (3), and (BTMA)2[Fe4S4Br2I2] (4) were isostructural to the previously reported (BTMA)2[Fe4S4I4] (5) (monoclinic, Cc). Instead of the chloride cubane cluster [Fe4S4Cl4]2-, we found the prismane-shaped cluster (BTMA)3[Fe6S6Cl6] (6) (P1̄). 57Fe Mössbauer spectroscopy indicates complete delocalisation with Fe2.5+ oxidation states for all iron atoms. Magnetic measurements showed small χMT values at 298 K ranging from 1.12 to 1.54 cm3 K mol-1, indicating the dominant antiferromagnetic exchange interactions. With decreasing temperature, the χMT values decreased to reach a plateau at around 100 K. From about 20 K, the values drop significantly. Fitting the data in the Heisenberg-Dirac-van Vleck (HDvV) as well as the Heisenberg Double Exchange (HDE) formalism confirmed the delocalisation and antiferromagnetic coupling assumed from Mössbauer spectroscopy.
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Affiliation(s)
- Andreas O Schüren
- Universität zu Köln, Mathematisch-Naturwissenschaftliche Fakultät, Department für Chemie, Institut für Anorganische Chemie, Greinstraße 6, D-50939 Köln, Germany. .,INQUIMAE-CONICET-Universidad de Buenos Aires, Intendente Güiraldes 2160, Pabellón 2, Piso 3, C1428EGA, Buenos Aires, Argentina
| | - Benjamin M Ridgway
- INQUIMAE-CONICET-Universidad de Buenos Aires, Intendente Güiraldes 2160, Pabellón 2, Piso 3, C1428EGA, Buenos Aires, Argentina
| | - Florencia Di Salvo
- INQUIMAE-CONICET-Universidad de Buenos Aires, Intendente Güiraldes 2160, Pabellón 2, Piso 3, C1428EGA, Buenos Aires, Argentina.,Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Química Inorgánica, Analítica y Química Física, Intendente Güiraldes 2160, Pabellón 2, Piso 3, C1428EGA, Buenos Aires, Argentina
| | - Luca M Carella
- Johannes Gutenberg Universität Mainz, Department Chemie, Duesbergweg 10-14, 55128 Mainz, Germany
| | - Verena K Gramm
- Universität zu Köln, Mathematisch-Naturwissenschaftliche Fakultät, Department für Chemie, Institut für Anorganische Chemie, Greinstraße 6, D-50939 Köln, Germany.
| | - Elisa Metzger
- TU Kaiserlautern Department of Physics, 67663 Kaiserlautern, Germany
| | - Fabio Doctorovich
- INQUIMAE-CONICET-Universidad de Buenos Aires, Intendente Güiraldes 2160, Pabellón 2, Piso 3, C1428EGA, Buenos Aires, Argentina.,Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Química Inorgánica, Analítica y Química Física, Intendente Güiraldes 2160, Pabellón 2, Piso 3, C1428EGA, Buenos Aires, Argentina
| | - Eva Rentschler
- Johannes Gutenberg Universität Mainz, Department Chemie, Duesbergweg 10-14, 55128 Mainz, Germany
| | - Volker Schünemann
- TU Kaiserlautern Department of Physics, 67663 Kaiserlautern, Germany
| | - Uwe Ruschewitz
- Universität zu Köln, Mathematisch-Naturwissenschaftliche Fakultät, Department für Chemie, Institut für Anorganische Chemie, Greinstraße 6, D-50939 Köln, Germany.
| | - Axel Klein
- Universität zu Köln, Mathematisch-Naturwissenschaftliche Fakultät, Department für Chemie, Institut für Anorganische Chemie, Greinstraße 6, D-50939 Köln, Germany.
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Senger M, Mebs S, Duan J, Shulenina O, Laun K, Kertess L, Wittkamp F, Apfel UP, Happe T, Winkler M, Haumann M, Stripp ST. Protonation/reduction dynamics at the [4Fe-4S] cluster of the hydrogen-forming cofactor in [FeFe]-hydrogenases. Phys Chem Chem Phys 2018; 20:3128-3140. [PMID: 28884175 DOI: 10.1039/c7cp04757f] [Citation(s) in RCA: 62] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The [FeFe]-hydrogenases of bacteria and algae are the most efficient hydrogen conversion catalysts in nature. Their active-site cofactor (H-cluster) comprises a [4Fe-4S] cluster linked to a unique diiron site that binds three carbon monoxide (CO) and two cyanide (CN-) ligands. Understanding microbial hydrogen conversion requires elucidation of the interplay of proton and electron transfer events at the H-cluster. We performed real-time spectroscopy on [FeFe]-hydrogenase protein films under controlled variation of atmospheric gas composition, sample pH, and reductant concentration. Attenuated total reflection Fourier-transform infrared spectroscopy was used to monitor shifts of the CO/CN- vibrational bands in response to redox and protonation changes. Three different [FeFe]-hydrogenases and several protein and cofactor variants were compared, including element and isotopic exchange studies. A protonated equivalent (HoxH) of the oxidized state (Hox) was found, which preferentially accumulated at acidic pH and under reducing conditions. We show that the one-electron reduced state Hred' represents an intrinsically protonated species. Interestingly, the formation of HoxH and Hred' was independent of the established proton pathway to the diiron site. Quantum chemical calculations of the respective CO/CN- infrared band patterns favored a cysteine ligand of the [4Fe-4S] cluster as the protonation site in HoxH and Hred'. We propose that proton-coupled electron transfer facilitates reduction of the [4Fe-4S] cluster and prevents premature formation of a hydride at the catalytic diiron site. Our findings imply that protonation events both at the [4Fe-4S] cluster and at the diiron site of the H-cluster are important in the hydrogen conversion reaction of [FeFe]-hydrogenases.
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Affiliation(s)
- Moritz Senger
- Department of Physics, Experimental Molecular Biophysics, Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany.
| | - Stefan Mebs
- Department of Physics, Biophysics of Metalloenzymes, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.
| | - Jifu Duan
- Faculty of Biology and Biotechnology, Photobiotechnology, Ruhr-Universität Bochum, 44801 Bochum, Germany.
| | - Olga Shulenina
- Faculty of Physics, St. Petersburg State University, 198504 St. Petersburg, Russian Federation
| | - Konstantin Laun
- Department of Physics, Experimental Molecular Biophysics, Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany.
| | - Leonie Kertess
- Faculty of Biology and Biotechnology, Photobiotechnology, Ruhr-Universität Bochum, 44801 Bochum, Germany.
| | - Florian Wittkamp
- Faculty of Chemistry and Biochemistry, Inorganic Chemistry I, Ruhr-Universität Bochum, 44801 Bochum, Germany
| | - Ulf-Peter Apfel
- Faculty of Chemistry and Biochemistry, Inorganic Chemistry I, Ruhr-Universität Bochum, 44801 Bochum, Germany
| | - Thomas Happe
- Faculty of Biology and Biotechnology, Photobiotechnology, Ruhr-Universität Bochum, 44801 Bochum, Germany.
| | - Martin Winkler
- Faculty of Biology and Biotechnology, Photobiotechnology, Ruhr-Universität Bochum, 44801 Bochum, Germany.
| | - Michael Haumann
- Department of Physics, Biophysics of Metalloenzymes, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.
| | - Sven T Stripp
- Department of Physics, Experimental Molecular Biophysics, Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany.
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Čorić I, Holland PL. Insight into the Iron-Molybdenum Cofactor of Nitrogenase from Synthetic Iron Complexes with Sulfur, Carbon, and Hydride Ligands. J Am Chem Soc 2016; 138:7200-11. [PMID: 27171599 PMCID: PMC5508211 DOI: 10.1021/jacs.6b00747] [Citation(s) in RCA: 118] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Nitrogenase enzymes are used by microorganisms for converting atmospheric N2 to ammonia, which provides an essential source of N atoms for higher organisms. The active site of the molybdenum-dependent nitrogenase is the unique carbide-containing iron-sulfur cluster called the iron-molybdenum cofactor (FeMoco). On the FeMoco, N2 binding is suggested to occur at one or more iron atoms, but the structures of the catalytic intermediates are not clear. In order to establish the feasibility of different potential mechanistic steps during biological N2 reduction, chemists have prepared iron complexes that mimic various structural aspects of the iron sites in the FeMoco. This reductionist approach gives mechanistic insight, and also uncovers fundamental principles that could be used more broadly for small-molecule activation. Here, we discuss recent results and highlight directions for future research. In one direction, synthetic iron complexes have now been shown to bind N2, break the N-N triple bond, and produce ammonia catalytically. Carbon- and sulfur-based donors have been incorporated into the ligand spheres of Fe-N2 complexes to show how these atoms may influence the structure and reactivity of the FeMoco. Hydrides have been incorporated into synthetic systems, which can bind N2, reduce some nitrogenase substrates, and/or reductively eliminate H2 to generate reduced iron centers. Though some carbide-containing iron clusters are known, none yet have sulfide bridges or high-spin iron atoms like the FeMoco.
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Affiliation(s)
- Ilija Čorić
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Patrick L. Holland
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
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X-ray crystal structures of [NHR3]2[Fe4S4X4] (X = PhS, R = Et or n Bu; X = Cl, R = n Bu): implications for sites of protonation in Fe–S clusters. TRANSIT METAL CHEM 2016. [DOI: 10.1007/s11243-016-0052-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Al-Rammahi TMM, Henderson RA. Binding small molecules and ions to [Fe4S4Cl4](2-) modulates rate of protonation of the cluster. Dalton Trans 2016; 45:1373-81. [PMID: 26661750 DOI: 10.1039/c5dt04523a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The mechanism of the acid-catalyzed substitution reaction of the terminal chloro-ligands in [Fe4S4Cl4](2-) by PhS(-) in the presence of NHBu(n)3(+) involves rate-limiting proton transfer from NHBu(n)3(+) to the cluster (k0 = 490 ± 20 dm(3) mol(-1) s(-1)). A variety of small molecules and ions (L = substrate = Cl(-), Br(-), I(-), RNHNH2 (R = Me or Ph), Me2NNH2, HCN, NCS(-), N3(-), Bu(t)NC or pyridine) bind to [Fe4S4Cl4](2-) and this affects the rate of subsequent protonation of [Fe4S4Cl4(L)](n-). Where the kinetics allow, the equilibrium constants for the substrates binding to [Fe4S4Cl4](2-) (K(L)) and the rates of proton transfer from NHBu(n)3(+) to [Fe4S4Cl4(L)](n-) (k) have been determined. The results indicate the following general features. (i) Bound substrates increase the rate of protonation of the cluster, but the rate increase is modest (k/k0 = 1.6 to ≥72). (ii) When K(L) is small, so is k/k0. (iii) Binding substrates which are good σ-donors or good π-acceptors lead to the largest k/k0. This behaviour is discussed in terms of the recent proposal that protonation of [Fe4S4Cl4](2-) at a μ3-S, is coupled to concomitant Fe-(μ3-SH) bond elongation/cleavage.
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Affiliation(s)
- Thaer M M Al-Rammahi
- School of Chemistry, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK. and Department of Chemistry, College of Science, University of Kerbala, Kerbala, Iraq
| | - Richard A Henderson
- School of Chemistry, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK.
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6
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Schüren AO, Gramm VK, Dürr M, Foi A, Ivanović-Burmazović I, Doctorovich F, Ruschewitz U, Klein A. Halide coordinated homoleptic [Fe4S4X4](2-) and heteroleptic [Fe4S4X2Y2](2-) clusters (X, Y = Cl, Br, I)--alternative preparations, structural analogies and spectroscopic properties in solution and solid state. Dalton Trans 2016; 45:361-75. [PMID: 26618565 DOI: 10.1039/c5dt02769a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
New facile methods to prepare iron sulphur halide clusters [Fe4S4X4](2-) from [Fe(CO)5] and elemental sulphur were elaborated. Reactions of ferrous precursors like tetrahalidoferrates(ii) or simple ferrous halides with [Fe(CO)5] and sulphur turned out to be efficient methods to prepare homoleptic [Fe4S4X4](2-) (X = Cl, Br) and heteroleptic clusters [Fe4S4X4-nYn](2-) (X = Cl, Br; Y = Br, I). Solid materials were obtained as salts of BTMA(+) (= benzyltrimethylammonium); the new compounds containing [Fe4S4Br4](2-) and [Fe4S4X2Y2](2-) (X, Y = Cl, Br, I) were all isostructural to (BTMA)2[Fe4S4I4] (monoclinic, Cc) as inferred from synchrotron X-ray powder diffraction. While the solid materials contain defined heteroleptic clusters with a halide X : Y ratio of 2 : 2, dissolving these compounds leads to rapid scrambling of the halide ligands forming mixtures of all five possible [Fe4S4X4-nYn](2-) clusters as could be shown by UHR-ESI MS. The variation of X and Y allowed assignment of the absorption bands in the visible and NIR; the long-wavelength bands around 1100 nm were tentatively assigned to intervalence charge transfer (IVCT) transitions.
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Affiliation(s)
- Andreas O Schüren
- Department für Chemie, Institut für Anorganische Chemie, Universität zu Köln, Greinstraße 6, 50939 Köln, Germany. and Departamento de Química Inorgánica, Analítica, y Química Física, Facultad de Ciencias Exactas y Naturales, INQUIMAE-CONICET, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón 2, Piso 3, C1428EHA Buenos Aires, Argentina
| | - Verena K Gramm
- Department für Chemie, Institut für Anorganische Chemie, Universität zu Köln, Greinstraße 6, 50939 Köln, Germany.
| | - Maximilian Dürr
- Department Chemie und Pharmazie, Lehrstuhl für Bioanorgansiche Chemie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 1, 91058 Erlangen, Germany
| | - Ana Foi
- Departamento de Química Inorgánica, Analítica, y Química Física, Facultad de Ciencias Exactas y Naturales, INQUIMAE-CONICET, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón 2, Piso 3, C1428EHA Buenos Aires, Argentina
| | - Ivana Ivanović-Burmazović
- Department Chemie und Pharmazie, Lehrstuhl für Bioanorgansiche Chemie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 1, 91058 Erlangen, Germany
| | - Fabio Doctorovich
- Departamento de Química Inorgánica, Analítica, y Química Física, Facultad de Ciencias Exactas y Naturales, INQUIMAE-CONICET, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón 2, Piso 3, C1428EHA Buenos Aires, Argentina
| | - Uwe Ruschewitz
- Department für Chemie, Institut für Anorganische Chemie, Universität zu Köln, Greinstraße 6, 50939 Köln, Germany.
| | - Axel Klein
- Department für Chemie, Institut für Anorganische Chemie, Universität zu Köln, Greinstraße 6, 50939 Köln, Germany.
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7
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Al-Rammahi TMM, Henderson RA. Exploring the acid-catalyzed substitution mechanism of [Fe4S4Cl4]2−. Dalton Trans 2016; 45:307-14. [DOI: 10.1039/c5dt04008f] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Kinetic studies focussing on either the protonation or substitution step of the acid catalyzed substitution reactions of [Fe4S4Cl4]2− support a mechanism involving concomitant cluster protonation and Fe–(μ3-SH) bond cleavage.
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8
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Čorić I, Mercado BQ, Bill E, Vinyard DJ, Holland PL. Binding of dinitrogen to an iron-sulfur-carbon site. Nature 2015; 526:96-9. [PMID: 26416755 PMCID: PMC4592811 DOI: 10.1038/nature15246] [Citation(s) in RCA: 143] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Accepted: 07/24/2015] [Indexed: 01/25/2023]
Abstract
Nitrogenases are the enzymes by which certain microorganisms convert atmospheric dinitrogen (N2) to ammonia, thereby providing essential nitrogen atoms for higher organisms. The most common nitrogenases reduce atmospheric N2 at the FeMo cofactor, a sulfur-rich iron-molybdenum cluster (FeMoco). The central iron sites that are coordinated to sulfur and carbon atoms in FeMoco have been proposed to be the substrate binding sites, on the basis of kinetic and spectroscopic studies. In the resting state, the central iron sites each have bonds to three sulfur atoms and one carbon atom. Addition of electrons to the resting state causes the FeMoco to react with N2, but the geometry and bonding environment of N2-bound species remain unknown. Here we describe a synthetic complex with a sulfur-rich coordination sphere that, upon reduction, breaks an Fe-S bond and binds N2. The product is the first synthetic Fe-N2 complex in which iron has bonds to sulfur and carbon atoms, providing a model for N2 coordination in the FeMoco. Our results demonstrate that breaking an Fe-S bond is a chemically reasonable route to N2 binding in the FeMoco, and show structural and spectroscopic details for weakened N2 on a sulfur-rich iron site.
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Affiliation(s)
- Ilija Čorić
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, USA
| | - Brandon Q Mercado
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, USA
| | - Eckhard Bill
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany
| | - David J Vinyard
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, USA
| | - Patrick L Holland
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, USA
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9
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Saouma CT, Morris WD, Darcy JW, Mayer JM. Protonation and Proton-Coupled Electron Transfer at S-Ligated [4Fe-4S] Clusters. Chemistry 2015; 21:9256-60. [PMID: 25965413 DOI: 10.1002/chem.201500152] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2015] [Indexed: 11/12/2022]
Abstract
Biological [Fe-S] clusters are increasingly recognized to undergo proton-coupled electron transfer (PCET), but the site of protonation, mechanism, and role for PCET remains largely unknown. Here we explore this reactivity with synthetic model clusters. Protonation of the arylthiolate-ligated [4Fe-4S] cluster [Fe4 S4 (SAr)4 ](2-) (1, SAr=S-2,4-6-(iPr)3 C6 H2 ) leads to thiol dissociation, reversibly forming [Fe4 S4 (SAr)3 L](1-) (2) and ArSH (L=solvent, and/or conjugate base). Solutions of 2+ArSH react with the nitroxyl radical TEMPO to give [Fe4 S4 (SAr)4 ](1-) (1ox ) and TEMPOH. This reaction involves PCET coupled to thiolate association and may proceed via the unobserved protonated cluster [Fe4 S4 (SAr)3 (HSAr)](1-) (1-H). Similar reactions with this and related clusters proceed comparably. An understanding of the PCET thermochemistry of this cluster system has been developed, encompassing three different redox levels and two protonation states.
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Affiliation(s)
- Caroline T Saouma
- Department of Chemistry, University of Washington, Box 351700, Seattle, WA 98195 (USA). .,Department of Chemistry, University of Utah, 315 S 1400 E Room 2020, Salt Lake City, UT 84112 (USA).
| | - Wesley D Morris
- Department of Chemistry, Yale University, 225 Prospect St., PO Box 208107, New Haven, CT 06520 (USA)
| | - Julia W Darcy
- Department of Chemistry, Yale University, 225 Prospect St., PO Box 208107, New Haven, CT 06520 (USA)
| | - James M Mayer
- Department of Chemistry, University of Washington, Box 351700, Seattle, WA 98195 (USA). .,Department of Chemistry, Yale University, 225 Prospect St., PO Box 208107, New Haven, CT 06520 (USA).
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10
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Dance I. Misconception of reductive elimination of H2, in the context of the mechanism of nitrogenase. Dalton Trans 2015; 44:9027-37. [DOI: 10.1039/c5dt00771b] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Calculated atom partial charges reveal misconceptions of reductive elimination of H2.
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Affiliation(s)
- Ian Dance
- School of Chemistry
- University of New South Wales
- Sydney 2052
- Australia
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11
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Dance I. Protonation of bridging sulfur in cubanoid Fe4S4 clusters causes large geometric changes: the theory of geometric and electronic structure. Dalton Trans 2015; 44:4707-17. [DOI: 10.1039/c4dt03681f] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Density functional calculations indicate that protonation of a μ3-S atom in cubanoid clusters [Fe4S4X4]2− leads to a large extension of one Fe–S(H) bond such that the SH ligand is doubly-bridging, μ-SH.
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Affiliation(s)
- Ian Dance
- School of Chemistry
- University of New South Wales
- Sydney 2052
- Australia
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12
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Dance I. What is the trigger mechanism for the reversal of electron flow in oxygen-tolerant [NiFe] hydrogenases? Chem Sci 2014; 6:1433-1443. [PMID: 29560232 PMCID: PMC5811149 DOI: 10.1039/c4sc03223c] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2014] [Accepted: 12/08/2014] [Indexed: 11/21/2022] Open
Abstract
A new mechanistic model is developed for the sequence of events by which oxygen-tolerant [NiFe] hydrogenase enzymes respond to O2.
The [NiFe] hydrogenases use an electron transfer relay of three FeS clusters – proximal, medial and distal – to release the electrons from the principal reaction, H2 → 2H+ + 2e–, that occurs at the Ni–Fe catalytic site. This site is normally inactivated by O2, but the subclass of O2-tolerant [NiFe] hydrogenases are able to counter this inactivation through the agency of an unusual and unprecedented proximal cluster, with composition [Fe4S3(Scys)6], that is able to transfer two electrons back to the Ni–Fe site and effect crucial reduction of O2-derived species and thereby reactivate the Ni–Fe site. This proximal cluster gates both the direction and the number of electrons flowing through it, and can reverse the normal flow during O2 attack. The unusual structures and redox potentials of the proximal cluster are known: a structural change in the proximal cluster causes changes in its electron-transfer potentials. Using protein structure analysis and density functional simulations, this paper identifies a closed protonic system comprising the proximal cluster, some contiguous residues, and a proton reservoir, and proposes that it is activated by O2-induced conformational change at the Ni–Fe site. This change is linked to a key histidine residue which then causes protonation of the proximal cluster, and migration of this proton to a key μ3-S atom. The resulting SH group causes the required structural change at the proximal cluster, modifying its redox potentials, and leads to the reversed electron flow back to the Ni–Fe site. This cycle is reversible, and the protons involved are independent of those used or produced in reactions at the active site. Existing experimental support for this model is cited, and new testing experiments are suggested.
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Affiliation(s)
- Ian Dance
- School of Chemistry , University of New South Wales , Sydney 2052 , Australia .
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13
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Dance I, Henderson RA. Large structural changes upon protonation of Fe4S4 clusters: the consequences for reactivity. Dalton Trans 2014; 43:16213-26. [DOI: 10.1039/c4dt01687d] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Recognition that protonation of μ3-S in [Fe4S4X4]2− clusters causes breaking of an S–Fe bond provides a kinetically consistent general mechanism for the acid-catalysed substitution reactions of [Fe4S4X4]2− clusters.
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Affiliation(s)
- Ian Dance
- School of Chemistry
- University of New South Wales
- Sydney 2052, Australia
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