1
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Tucci FJ, Rosenzweig AC. Direct Methane Oxidation by Copper- and Iron-Dependent Methane Monooxygenases. Chem Rev 2024; 124:1288-1320. [PMID: 38305159 PMCID: PMC10923174 DOI: 10.1021/acs.chemrev.3c00727] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2024]
Abstract
Methane is a potent greenhouse gas that contributes significantly to climate change and is primarily regulated in Nature by methanotrophic bacteria, which consume methane gas as their source of energy and carbon, first by oxidizing it to methanol. The direct oxidation of methane to methanol is a chemically difficult transformation, accomplished in methanotrophs by complex methane monooxygenase (MMO) enzyme systems. These enzymes use iron or copper metallocofactors and have been the subject of detailed investigation. While the structure, function, and active site architecture of the copper-dependent particulate methane monooxygenase (pMMO) have been investigated extensively, its putative quaternary interactions, regulation, requisite cofactors, and mechanism remain enigmatic. The iron-dependent soluble methane monooxygenase (sMMO) has been characterized biochemically, structurally, spectroscopically, and, for the most part, mechanistically. Here, we review the history of MMO research, focusing on recent developments and providing an outlook for future directions of the field. Engineered biological catalysis systems and bioinspired synthetic catalysts may continue to emerge along with a deeper understanding of the molecular mechanisms of biological methane oxidation. Harnessing the power of these enzymes will necessitate combined efforts in biochemistry, structural biology, inorganic chemistry, microbiology, computational biology, and engineering.
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Affiliation(s)
- Frank J Tucci
- Departments of Molecular Biosciences and of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Amy C Rosenzweig
- Departments of Molecular Biosciences and of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
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2
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Yang B, Song X, Wang B. DFT mechanistic study of biomimetic diiron complex catalyzed dehydrogenation: Unexpected Fe(III)Fe(III)-1,1-μ-hydroperoxy active species for hydride abstraction. J Inorg Biochem 2024; 251:112426. [PMID: 37980877 DOI: 10.1016/j.jinorgbio.2023.112426] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2023] [Revised: 11/03/2023] [Accepted: 11/07/2023] [Indexed: 11/21/2023]
Abstract
The diiron active site is pivotal in catalyzing transformations in both biological and chemical systems. Recently, a range of biomimetic diiron catalysts have been synthesized, drawing inspiration from the active architecture of soluble methane monooxygenase (sMMO). These catalysts have been successfully deployed for the dehydrogenation of indolines, marking a significant advancement in the field. Using density functional theory (DFT) calculations, we have identified a novel mechanistic pathway that governs the dehydrogenation of indolines catalyzed by a biomimetic diiron complex. Specifically, this reaction is facilitated by the transfer of a hybrid atom from the C1 position of the substrate to the distal oxygen atom of the Fe(III)Fe(III)-1,1-μ-hydroperoxy active species. This transfer serves as the rate-limiting step for the heterolytic cleavage of the OO bond, ultimately generating the substrate cation. The mechanism we propose aligns well with mechanistic investigations incorporating both kinetic isotope effect (KIE) measurements and evaluations of stereochemical selectivity. This research contributes to the broader scientific understanding of catalysis involving biomimetic diiron complexes and offers valuable insights into the catalytic behaviors of non-heme diiron metalloenzymes.
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Affiliation(s)
- Boxuan Yang
- Key Laboratory of Chemical Biology of Fujian Province, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Xitong Song
- Fujian Provincial Key Laboratory of Ecology-Toxicological Effects & Control for Emerging Contaminants, College of Environmental and Biological Engineering, Putian University, Putian 351100, China; Key Laboratory of Ecological Environment and Information Atlas, Fujian Provincial University (Putian University), Putian 351100, China
| | - Binju Wang
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
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3
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Kumar R, Ansari A, Comba P, Rajaraman G. Rebound or Cage Escape? The Role of the Rebound Barrier for the Reactivity of Non-Heme High-Valent Fe IV =O Species. Chemistry 2024; 30:e202303300. [PMID: 37929771 DOI: 10.1002/chem.202303300] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2023] [Revised: 11/03/2023] [Accepted: 11/06/2023] [Indexed: 11/07/2023]
Abstract
Owing to their high reactivity and selectivity, variations in the spin ground state and a range of possible pathways, high-valent FeIV =O species are popular models with potential bioinspired applications. An interesting example of a structure-reactivity pattern is the detailed study with five nonheme amine-pyridine pentadentate ligand FeIV =O species, including N4py: [(L1 )FeIV =O]2+ (1), bntpen: [(L2 )FeIV =O]2+ (2), py2 tacn: [(L3 )FeIV =O]2+ (3), and two isomeric bispidine derivatives: [(L4 )FeIV =O]2+ (4) and [(L5 )FeIV =O]2+ (5). In this set, the order of increasing reactivity in the hydroxylation of cyclohexane differs from that with cyclohexadiene as substrate. A comprehensive DFT, ab initio CASSCF/NEVPT2 and DLPNO-CCSD(T) study is presented to untangle the observed patterns. These are well reproduced when both activation barriers for the C-H abstraction and the OH rebound are taken into account. An MO, NBO and deformation energy analysis reveals the importance of π(pyr) → π*xz (FeIII -OH) electron donation for weakening the FeIII -OH bond and thus reducing the rebound barrier. This requires that pyridine rings are oriented perpendicularly to the FeIII -OH bond and this is a subtle but crucial point in ligand design for non-heme iron alkane hydroxylation.
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Affiliation(s)
- Ravi Kumar
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai, Powai, 400076, India
| | - Azaj Ansari
- Department of Chemistry, Central University of Haryana, Haryana, 123031, India
| | - Peter Comba
- Institute of Inorganic Chemistry &, Interdisciplinary Center for Scientific Computing, Heidelberg University, 69120, Heidelberg, Germany
| | - Gopalan Rajaraman
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai, Powai, 400076, India
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4
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Britto NJ, Sen A, Rajaraman G. Unravelling the Effect of Acid-Driven Electron Transfer in High-Valent Fe IV =O/Mn IV =O Species and Its Implications for Reactivity. Chem Asian J 2023; 18:e202300773. [PMID: 37855305 DOI: 10.1002/asia.202300773] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 10/12/2023] [Accepted: 10/16/2023] [Indexed: 10/20/2023]
Abstract
The electron transfer (ET) step is one of the crucial processes in biochemical redox reactions that occur in nature and has been established as a key step in dictating the reactivity of high-valent metal-oxo species. Although metalloenzymes possessing metal-oxo units at their active site are typically associated with outer-sphere electron transfer (OSET) processes, biomimetic models, in contrast, have been found to manifest either an inner-sphere electron transfer (ISET) or OSET mechanism. This distinction is clearly illustrated through the behaviour of [(N4Py)MnIV (O)]2+ (1) and [(N4Py)FeIV (O)]2+ (2) complexes, where complex 1 showcases an OSET mechanism, while complex 2 exhibits an ISET mechanism, especially evident in their reactions involving C-H bond activation and oxygen atom transfer reactions in the presence of a Lewis/Bronsted acid. However, the precise reason for this puzzling difference remains elusive. This work unveils the origin of the perplexing inner-sphere vs outer-sphere electron transfer process (ISET vs OSET) in [(N4Py)MnIV (O)]2+ (1) and [(N4Py)FeIV (O)]2+ (2) species in the presence of Bronsted acid. The calculations indicate that when the substrate (toluene) approaches both 1 and 2 that is hydrogen bonded with two HOTf molecules (denoted as 1-HOTf and 2-HOTf, respectively), proton transfer from one of the HOTf molecules to the metal-oxo unit is triggered and a simultaneous electron transfer occurs from toluene to the metal centre. Interestingly, the preference for OSET by 1-HOTf is found to originate from the choice of MnIV =O centre to abstract spin-down (β) electron from toluene to its δ(dxy ) orbital. On the other hand, in 2-HOTf, a spin state inversion from triplet to quintet state takes place during the proton (from HOTf) coupled electron transfer (from toluene) preferring a spin-up (α) electron abstraction to its σ* (dz 2 ) orbital mediated by HOTf giving rise to ISET. In addition, 2-HOTf was calculated to possess a larger reorganisation energy, which facilitates the ISET process via the acid. The absence of spin-inversion and smaller reorganisation energy switch the mechanism to OSET for 1-HOTf. Therefore, for the first time, the significance of spin-state and spin-inversion in the electron transfer process has been identified and demonstrated within the realm of high-valent metal-oxo chemistry. This discovery holds implications for the potential involvement of high-valent Mn-oxo species in performing similar transformative processes within Photosystem II.
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Affiliation(s)
| | - Asmita Sen
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, 400 076, India
| | - Gopalan Rajaraman
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, 400 076, India
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5
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Jacobs AB, Banerjee R, Deweese DE, Braun A, Babicz JT, Gee LB, Sutherlin KD, Böttger LH, Yoda Y, Saito M, Kitao S, Kobayashi Y, Seto M, Tamasaku K, Lipscomb JD, Park K, Solomon EI. Nuclear Resonance Vibrational Spectroscopic Definition of the Fe(IV) 2 Intermediate Q in Methane Monooxygenase and Its Reactivity. J Am Chem Soc 2021; 143:16007-16029. [PMID: 34570980 PMCID: PMC8631202 DOI: 10.1021/jacs.1c05436] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Methanotrophic bacteria utilize the nonheme diiron enzyme soluble methane monooxygenase (sMMO) to convert methane to methanol in the first step of their metabolic cycle under copper-limiting conditions. The structure of the sMMO Fe(IV)2 intermediate Q responsible for activating the inert C-H bond of methane (BDE = 104 kcal/mol) remains controversial, with recent studies suggesting both "open" and "closed" core geometries for its active site. In this study, we employ nuclear resonance vibrational spectroscopy (NRVS) to probe the geometric and electronic structure of intermediate Q at cryogenic temperatures. These data demonstrate that Q decays rapidly during the NRVS experiment. Combining data from several years of measurements, we derive the NRVS vibrational features of intermediate Q as well as its cryoreduced decay product. A library of 90 open and closed core models of intermediate Q is generated using density functional theory to analyze the NRVS data of Q and its cryoreduced product as well as prior spectroscopic data on Q. Our analysis reveals that a subset of closed core models reproduce these newly acquired NRVS data as well as prior data. The reaction coordinate with methane is also evaluated using both closed and open core models of Q. These studies show that the potent reactivity of Q toward methane resides in the "spectator oxo" of its Fe(IV)2O2 core, in contrast to nonheme mononuclear Fe(IV)═O enzyme intermediates that H atoms abstract from weaker C-H bonds.
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Affiliation(s)
- Ariel B. Jacobs
- Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California, 94305, United States
| | - Rahul Banerjee
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55391 U.S.A
| | - Dory E. Deweese
- Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California, 94305, United States
| | - Augustin Braun
- Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California, 94305, United States
| | - Jeffrey T. Babicz
- Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California, 94305, United States
| | - Leland B. Gee
- Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California, 94305, United States
| | - Kyle D. Sutherlin
- Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California, 94305, United States
| | - Lars H. Böttger
- Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California, 94305, United States
| | - Yoshitaka Yoda
- Japan Synchrotron Radiation Research Institute, Hyogo 679-5198, Japan
| | - Makina Saito
- Department of Physics, Graduate School of Science, Tohoku University, Sendai, Miyagi 980-8578 Japan
| | - Shinji Kitao
- Institute for Integrated Radiation and Nuclear Science, Kyoto University, Osaka, 590-0494
| | - Yasuhiro Kobayashi
- Institute for Integrated Radiation and Nuclear Science, Kyoto University, Osaka, 590-0494
| | - Makoto Seto
- Institute for Integrated Radiation and Nuclear Science, Kyoto University, Osaka, 590-0494
| | - Kenji Tamasaku
- RIKEN SPring-8 Center, RIKEN, Sayo, Hyogo, 679-5148, Japan
| | - John D. Lipscomb
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55391 U.S.A
| | - Kiyoung Park
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
| | - Edward I. Solomon
- Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California, 94305, United States,Stanford Synchrotron Radiation Light Source, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California, 94025, United States
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6
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Shteinman AA, Mitra M. Nonheme mono- and dinuclear iron complexes in bio-inspired C H and C C bond hydroxylation reactions: Mechanistic insight. Inorganica Chim Acta 2021. [DOI: 10.1016/j.ica.2021.120388] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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7
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Schulz C, Castillo RG, Pantazis DA, DeBeer S, Neese F. Structure-Spectroscopy Correlations for Intermediate Q of Soluble Methane Monooxygenase: Insights from QM/MM Calculations. J Am Chem Soc 2021; 143:6560-6577. [PMID: 33884874 PMCID: PMC8154522 DOI: 10.1021/jacs.1c01180] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2021] [Indexed: 12/22/2022]
Abstract
The determination of the diiron core intermediate structures involved in the catalytic cycle of soluble methane monooxygenase (sMMO), the enzyme that selectively catalyzes the conversion of methane to methanol, has been a subject of intense interest within the bioinorganic scientific community. Particularly, the specific geometry and electronic structure of the intermediate that precedes methane binding, known as intermediate Q (or MMOHQ), has been debated for over 30 years. Some reported studies support a bis-μ-oxo-bridged Fe(IV)2O2 closed-core conformation Fe(IV)2O2 core, whereas others favor an open-core geometry, with a longer Fe-Fe distance. The lack of consensus calls for a thorough re-examination and reinterpretation of the spectroscopic data available on the MMOHQ intermediate. Herein, we report extensive simulations based on a hybrid quantum mechanics/molecular mechanics approach (QM/MM) approach that takes into account the complete enzyme to explore possible conformations for intermediates MMOHox and MMOHQ of the sMMOH catalytic cycle. High-level quantum chemical approaches are used to correlate specific structural motifs with geometric parameters for comparison with crystallographic and EXAFS data, as well as with spectroscopic data from Mössbauer spectroscopy, Fe K-edge high-energy resolution X-ray absorption spectroscopy (HERFD XAS), and resonance Raman 16O-18O difference spectroscopy. The results provide strong support for an open-core-type configuration in MMOHQ, with the most likely topology involving mono-oxo-bridged Fe ions and alternate terminal Fe-oxo and Fe-hydroxo groups that interact via intramolecular hydrogen bonding. The implications of an open-core intermediate Q on the reaction mechanism of sMMO are discussed.
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Affiliation(s)
- Christine
E. Schulz
- Max-Planck-Institut
für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
| | - Rebeca G. Castillo
- Max
Planck Institute for Chemical Energy Conversion, Stiftstr. 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Dimitrios A. Pantazis
- Max-Planck-Institut
für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
| | - Serena DeBeer
- Max
Planck Institute for Chemical Energy Conversion, Stiftstr. 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Frank Neese
- Max-Planck-Institut
für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
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8
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Barona M, Gaggioli CA, Gagliardi L, Snurr RQ. DFT Study on the Catalytic Activity of ALD-Grown Diiron Oxide Nanoclusters for Partial Oxidation of Methane to Methanol. J Phys Chem A 2020; 124:1580-1592. [PMID: 32017850 DOI: 10.1021/acs.jpca.9b11835] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Using density functional theory (DFT), we studied the catalytic activity of iron oxide nanoclusters that mimic the structure of the active site in the soluble form of methane monooxygenase (sMMO) for the partial oxidation of methane to methanol. Using N2O as the oxidant, we consider a radical-rebound mechanism and a concerted mechanism for the oxidation of methane on either a bridging oxygen (Ob) or a terminal oxygen (Ot) active site. We find that the radical-rebound pathway is preferred over the concerted pathway by 40-50 kJ/mol, but the desorption of methanol and the regeneration of the oxygen site are found to be the highest barriers for the direct conversion of methane to methanol with these catalysts. As demonstrated by a population analysis, the Ox (x = b or t) site behaves as an oxygen radical during the H abstraction, and the [Fe+-Ox-] site behaves as a Lewis acid-base pair during the concerted C-H cleavage. Molecular orbital decomposition analysis further demonstrates electron transfer during the oxidation and reduction steps of the reaction. High-level multireference calculations were also carried out to further assess the DFT results. Understanding how these systems behave during the proposed reaction pathways provides new insights into how they can be tuned for methane partial oxidation.
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Affiliation(s)
- Melissa Barona
- Department of Chemical and Biological Engineering , Northwestern University , Evanston , Illinois 60208 , United States
| | - Carlo Alberto Gaggioli
- Department of Chemistry, Chemical Theory Center, and Supercomputing Institute , University of Minnesota-Twin Cities , Minneapolis , Minnesota 55455 , United States
| | - Laura Gagliardi
- Department of Chemistry, Chemical Theory Center, and Supercomputing Institute , University of Minnesota-Twin Cities , Minneapolis , Minnesota 55455 , United States
| | - Randall Q Snurr
- Department of Chemical and Biological Engineering , Northwestern University , Evanston , Illinois 60208 , United States
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9
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Ahn S, Hong M, Sundararajan M, Ess DH, Baik MH. Design and Optimization of Catalysts Based on Mechanistic Insights Derived from Quantum Chemical Reaction Modeling. Chem Rev 2019; 119:6509-6560. [DOI: 10.1021/acs.chemrev.9b00073] [Citation(s) in RCA: 85] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Seihwan Ahn
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
- Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon, 34141, Republic of Korea
| | - Mannkyu Hong
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
- Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon, 34141, Republic of Korea
| | - Mahesh Sundararajan
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
- Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon, 34141, Republic of Korea
| | - Daniel H. Ess
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, United States
| | - Mu-Hyun Baik
- Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
- Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon, 34141, Republic of Korea
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10
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Abstract
Aerobic life is possible because the molecular structure of oxygen (O2) makes direct reaction with most organic materials at ambient temperatures an exceptionally slow process. Of course, these reactions are inherently very favorable, and they occur rapidly with the release of a great deal of energy at high temperature. Nature has been able to tap this sequestered reservoir of energy with great spatial and temporal selectivity at ambient temperatures through the evolution of oxidase and oxygenase enzymes. One mechanism used by these enzymes for O2 activation has been studied in detail for the soluble form of the enzyme methane monooxygenase. These studies have revealed the step-by-step process of O2 activation and insertion into the ultimately stable C-H bond of methane. Additionally, an elegant regulatory mechanism has been defined that enlists size selection and quantum tunneling to allow methane oxidation to occur specifically in the presence of more easily oxidized substrates.
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Affiliation(s)
- Rahul Banerjee
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA; , ,
| | - Jason C Jones
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA; , ,
| | - John D Lipscomb
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA; , ,
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11
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Snyder BER, Bols ML, Schoonheydt RA, Sels BF, Solomon EI. Iron and Copper Active Sites in Zeolites and Their Correlation to Metalloenzymes. Chem Rev 2017; 118:2718-2768. [DOI: 10.1021/acs.chemrev.7b00344] [Citation(s) in RCA: 193] [Impact Index Per Article: 27.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Benjamin E. R. Snyder
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Max L. Bols
- Department of Microbial and Molecular Systems, Centre for Surface Chemistry and Catalysis, KU Leuven—University of Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium
| | - Robert A. Schoonheydt
- Department of Microbial and Molecular Systems, Centre for Surface Chemistry and Catalysis, KU Leuven—University of Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium
| | - Bert F. Sels
- Department of Microbial and Molecular Systems, Centre for Surface Chemistry and Catalysis, KU Leuven—University of Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium
| | - Edward I. Solomon
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
- Photon Science, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
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12
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Localized orbital corrections for density functional calculations on transition metal containing systems. Coord Chem Rev 2017. [DOI: 10.1016/j.ccr.2017.02.014] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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13
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Wang VCC, Maji S, Chen PPY, Lee HK, Yu SSF, Chan SI. Alkane Oxidation: Methane Monooxygenases, Related Enzymes, and Their Biomimetics. Chem Rev 2017; 117:8574-8621. [PMID: 28206744 DOI: 10.1021/acs.chemrev.6b00624] [Citation(s) in RCA: 249] [Impact Index Per Article: 35.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Methane monooxygenases (MMOs) mediate the facile conversion of methane into methanol in methanotrophic bacteria with high efficiency under ambient conditions. Because the selective oxidation of methane is extremely challenging, there is considerable interest in understanding how these enzymes carry out this difficult chemistry. The impetus of these efforts is to learn from the microbes to develop a biomimetic catalyst to accomplish the same chemical transformation. Here, we review the progress made over the past two to three decades toward delineating the structures and functions of the catalytic sites in two MMOs: soluble methane monooxygenase (sMMO) and particulate methane monooxygenase (pMMO). sMMO is a water-soluble three-component protein complex consisting of a hydroxylase with a nonheme diiron catalytic site; pMMO is a membrane-bound metalloenzyme with a unique tricopper cluster as the site of hydroxylation. The metal cluster in each of these MMOs harnesses O2 to functionalize the C-H bond using different chemistry. We highlight some of the common basic principles that they share. Finally, the development of functional models of the catalytic sites of MMOs is described. These efforts have culminated in the first successful biomimetic catalyst capable of efficient methane oxidation without overoxidation at room temperature.
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Affiliation(s)
- Vincent C-C Wang
- Institute of Chemistry, Academia Sinica , 128, Section 2, Academia Road, Nankang, Taipei 11529, Taiwan
| | - Suman Maji
- School of Chemical Engineering and Physical Sciences, Lovely Professional University , Jalandhar-Delhi G. T. Road (NH-1), Phagwara, Punjab India 144411
| | - Peter P-Y Chen
- Department of Chemistry, National Chung Hsing University , 250 Kuo Kuang Road, Taichung 402, Taiwan
| | - Hung Kay Lee
- Department of Chemistry, The Chinese University of Hong Kong , Shatin, New Territories, Hong Kong
| | - Steve S-F Yu
- Institute of Chemistry, Academia Sinica , 128, Section 2, Academia Road, Nankang, Taipei 11529, Taiwan
| | - Sunney I Chan
- Institute of Chemistry, Academia Sinica , 128, Section 2, Academia Road, Nankang, Taipei 11529, Taiwan.,Department of Chemistry, National Taiwan University , No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan.,Noyes Laboratory, 127-72, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States
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14
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Kim Y, Mai BK, Park S. VTST/MT studies of the catalytic mechanism of C-H activation by transition metal complexes with [Cu 2(μ-O 2)], [Fe 2(μ-O 2)] and Fe(IV)-O cores based on DFT potential energy surfaces. J Biol Inorg Chem 2017; 22:321-338. [PMID: 28091753 DOI: 10.1007/s00775-017-1441-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2016] [Accepted: 01/04/2017] [Indexed: 01/21/2023]
Abstract
High-valent Cu and Fe species, which are generated from dioxygen activation in metalloenzymes, carry out the functionalization of strong C-H bonds. Understanding the atomic details of the catalytic mechanism has long been one of the main objectives of bioinorganic chemistry. Large H/D kinetic isotope effects (KIEs) were observed in the C-H activation by high-valent non-heme Cu or Fe complexes in enzymes and their synthetic models. The H/D KIE depends significantly on the transition state properties, such as structure, energies, frequencies, and shape of the potential energy surface, when the tunneling effect is large. Therefore, theoretical predictions of kinetic parameters such as rate constants and KIEs can provide a reliable link between atomic-level quantum mechanical mechanisms and experiments. The accurate prediction of the tunneling effect is essential to reproduce the kinetic parameters. The rate constants and HD/KIE have been calculated using the variational transition-state theory including multidimensional tunneling based on DFT potential energy surfaces along the reaction coordinate. Excellent agreement was observed between the predicted and experimental results, which assures the validity of the DFT potential energy surfaces and, therefore, the proposed atomic-level mechanisms. The [Cu2(μ-O)2], [Fe2(μ-O)2], and Fe(IV)-oxo species were employed for C-H activation, and their role as catalysts was discussed at an atomic level.
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Affiliation(s)
- Yongho Kim
- Department of Applied Chemistry and Institute of Natural Sciences, Kyung Hee University, 1 Seochun-Dong, Giheung-Gu, Yongin-Si, Gyeonggi-Do, 446-701, Korea.
| | - Binh Khanh Mai
- Department of Applied Chemistry and Institute of Natural Sciences, Kyung Hee University, 1 Seochun-Dong, Giheung-Gu, Yongin-Si, Gyeonggi-Do, 446-701, Korea
| | - Sumin Park
- Department of Applied Chemistry and Institute of Natural Sciences, Kyung Hee University, 1 Seochun-Dong, Giheung-Gu, Yongin-Si, Gyeonggi-Do, 446-701, Korea
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15
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Rokob TA. Pathways for Arene Oxidation in Non-Heme Diiron Enzymes: Lessons from Computational Studies on Benzoyl Coenzyme A Epoxidase. J Am Chem Soc 2016; 138:14623-14638. [PMID: 27682344 DOI: 10.1021/jacs.6b06987] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Oxygenation of aromatic rings using O2 is catalyzed by several non-heme carboxylate-bridged diiron enzymes. In order to provide a general mechanistic description for these reactions, computational studies were carried out at the ONIOM(B3LYP/BP86/Amber) level on the non-heme diiron enzyme benzoyl coenzyme A epoxidase, BoxB. The calculations revealed four possible pathways for attacking the aromatic ring: (a) electrophilic (2e-) attack by a bis(μ-oxo)-diiron(IV) species (Q pathway); (b) electrophilic (2e-) attack via the σ* orbital of a μ-η2:η2-peroxo-diiron(III) intermediate (Pσ* pathway); (c) radical (1e-) attack via the π*-orbital of a superoxo-diiron(II,III) species (Pπ* pathway); (d) radical (1e-) attack of a partially quenched bis(μ-oxo)-diiron(IV) intermediate (Q' pathway). The results allowed earlier work of de Visser on olefin epoxidation by diiron complexes and QM-cluster studies of Liao and Siegbahn on BoxB to be put into a broader perspective. Parallels with epoxidation using organic peracids were also examined. Specifically for the BoxB enzyme, the Q pathway was found to be the most preferred, but the corresponding bis(μ-oxo)-diiron(IV) species is significantly destabilized and not expected to be directly observable. Epoxidation via the Pσ* pathway represents an energetically somewhat higher lying alternative; possible strategies for experimental discrimination are discussed. The selectivity toward epoxidation is shown to stem from a combination of inherent electronic properties of the thioacyl substituent and enzymatic constraints. Possible implications of the results for toluene monooxygenases are considered as well.
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Affiliation(s)
- Tibor András Rokob
- Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences , Magyar Tudósok körútja 2, 1117 Budapest, Hungary
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16
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Bilyachenko AN, Levitsky MM, Yalymov AI, Korlyukov AA, Vologzhanina AV, Kozlov YN, Shul'pina LS, Nesterov DS, Pombeiro AJL, Lamaty F, Bantreil X, Fetre A, Liu D, Martinez J, Long J, Larionova J, Guari Y, Trigub AL, Zubavichus YV, Golub IE, Filippov OA, Shubina ES, Shul'pin GB. A heterometallic (Fe6Na8) cage-like silsesquioxane: synthesis, structure, spin glass behavior and high catalytic activity. RSC Adv 2016. [DOI: 10.1039/c6ra07081g] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The exotic “Asian Lantern” heterometallic cage silsesquioxane [(PhSiO1.5)20(FeO1.5)6(NaO0.5)8(n-BuOH)9.6(C7H8)] (I) was obtained and characterized by X-ray diffraction, EXAFS, topological analyses and DFT calculation.
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17
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Jerome SV, Hughes TF, Friesner RA. Successful application of the DBLOC method to the hydroxylation of camphor by cytochrome p450. Protein Sci 2016; 25:277-85. [PMID: 26441133 PMCID: PMC4815313 DOI: 10.1002/pro.2819] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2015] [Revised: 10/01/2015] [Accepted: 10/02/2015] [Indexed: 01/19/2023]
Abstract
The activation barrier for the hydroxylation of camphor by cytochrome P450 was computed using a mixed quantum mechanics/molecular mechanics (QM/MM) model of the full protein-ligand system and a fully QM calculation using a cluster model of the active site at the B3LYP/LACVP*/LACV3P** level of theory, which consisted of B3LYP/LACV3P** single point energies computed at B3LYP/LACVP* optimized geometries. From the QM/MM calculation, a barrier height of 17.5 kcal/mol was obtained, while the experimental value was known to be less than or equal to 10 kcal/mol. This process was repeated using the D3 correction for hybrid DFT in order to investigate whether the inadequate treatment of dispersion interaction was responsible for the overestimation of the barrier. While the D3 correction does reduce the computed barrier to 13.3 kcal/mol, it was still in disagreement with experiment. After application of a series of transition metal optimized localized orbital corrections (DBLOC) and without any refitting of parameters, the barrier was further reduced to 10.0 kcal/mol, which was consistent with the experimental results. The DBLOC method to CH bond activation in methane monooxygenase (MMO) was also applied, as a second, independent test. The barrier in MMO was known, by experiment, to be 15.4 kcal/mol. After application of the DBLOC corrections to the MMO barrier compute by B3LYP, in a previous study, and accounting for dispersion with Grimme's D3 method, the unsigned deviation from experiment was improved from 3.2 to 2.3 kcal/mol. These results suggested that the combination of dispersion plus localized orbital corrections could yield significant quantitative improvements in modeling the catalytic chemistry of transition-metal containing enzymes, within the limitations of the statistical errors of the model, which appear to be on the order of approximately 2 kcal/mole.
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Affiliation(s)
- Steven V Jerome
- Department of Chemistry, Columbia University, New York, New York, 10027
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18
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Chatterjee S, Sengupta K, Samanta S, Das PK, Dey A. Concerted Proton–Electron Transfer in Electrocatalytic O2 Reduction by Iron Porphyrin Complexes: Axial Ligands Tuning H/D Isotope Effect. Inorg Chem 2015; 54:2383-92. [DOI: 10.1021/ic5029959] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Sudipta Chatterjee
- Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700032, India
| | - Kushal Sengupta
- Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700032, India
| | - Subhra Samanta
- Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700032, India
| | - Pradip Kumar Das
- Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700032, India
| | - Abhishek Dey
- Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700032, India
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19
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Mai BK, Kim Y. Substrate-dependent H/D kinetic isotope effects and the role of the di(μ-oxo)diiron(IV) core in soluble methane monooxygenase: a theoretical study. Chemistry 2014; 20:6532-41. [PMID: 24715359 DOI: 10.1002/chem.201303466] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2013] [Revised: 01/28/2014] [Indexed: 11/07/2022]
Abstract
Soluble methane monooxygenase (sMMO) is an enzyme that converts alkanes to alcohols using a di(μ-oxo)diiron(IV) intermediate Q at the active site. Very large kinetic isotope effects (KIEs) indicative of significant tunneling are observed for the hydrogen transfer (H-transfer) of CH4 and CH3 CN; however, a relatively small KIE is observed for CH3NO2. The detailed mechanism of the enzymatic H-transfer responsible for the diverse range of KIEs is not yet fully understood. In this study, variational transition-state theory including the multidimensional tunneling approximation is used to calculate rate constants to predict KIEs based on the quantum-mechanically generated intrinsic reaction coordinates of the H-transfer by the di(μ-oxo)diiron(IV) complex. The results of our study reveal that the role of the di(μ-oxo)diiron(IV) core and the H-transfer mechanism are dependent on the substrate. For CH4 , substrate binding induces an electron transfer from the oxygen to one Fe(IV) center, which in turn makes the μ-O ligand more electrophilic and assists the H-transfer by abstracting an electron from the C-H σ orbital. For CH3CN, the reduction of Fe(IV) to Fe(III) occurs gradually with substrate binding and H-transfer. The charge density and electrophilicity of the μ-O ligand hardly change upon substrate binding; however, for CH3NO2, there seems to be no electron movement from μ-O to Fe(IV) during the H-transfer. Thus, the μ-O ligand appears to abstract a proton without an electron from the C-H σ orbital. The calculated KIEs for CH4, CH3CN, and CH3NO2 are 24.4, 49.0, and 8.27, respectively, at 293 K, in remarkably good agreement with the experimental values. This study reveals that diverse KIE values originate mainly from tunneling to the same di(μ-oxo)diiron(IV) core for all substrates, and demonstrate that the reaction dynamics are essential for reproducing experimental results and understanding the role of the diiron core for methane oxidation in sMMO.
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Affiliation(s)
- Binh Khanh Mai
- Department of Applied Chemistry, Kyung Hee University, 1 Seochun-Dong, Giheung-Gu, Yongin-Si, Gyeonggi-Do, 446-701 (Korea), Fax: (+82) 31-203-5773
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20
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Huang SP, Shiota Y, Yoshizawa K. DFT study of the mechanism for methane hydroxylation by soluble methane monooxygenase (sMMO): effects of oxidation state, spin state, and coordination number. Dalton Trans 2013; 42:1011-23. [PMID: 23108153 DOI: 10.1039/c2dt31304a] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The exact structure of the active site of intermediate Q, the methane-oxidizing species of soluble methane monooxygenase (sMMO), and the reaction mechanism of Q with methane molecule are still not fully clear. To gain further insights into the structure and reaction mechanism, five diiron models of Q that differ in shape, oxidation state, spin state, and coordination number of the two iron centers are studied. Different mechanisms in different spin states were explored. Density functional theory (DFT) calculations show that Fe(III)Fe(IV)(μ-O)(μ-OH) is more reactive than Fe(IV)(2)(μ-O)(2) in the oxygen-rich environment and that the reactivity of the active core of sMMO-Q is not enhanced by converting its oxo bridge into a terminal ligand. A four-coordinated diiron model is the most effective for methane hydroxylation. Both radical and non-radical intermediates are involved in the reactions for the four-coordinated diiron model.
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Affiliation(s)
- Shu-Ping Huang
- Institute for Materials Chemistry and Engineering, and International Research Center for Molecular Systems, Kyushu University, Fukuoka 819-0395, Japan
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21
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Li Y, Myae Soe CM, Wilson JJ, Tuang SL, Apfel UP, Lippard SJ. Triptycene-based Bis(benzimidazole) Carboxylate-Bridged Biomimetic Diiron(II) Complexes. Eur J Inorg Chem 2013; 2013:2011-2019. [PMID: 23585728 PMCID: PMC3625018 DOI: 10.1002/ejic.201201387] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2012] [Indexed: 11/06/2022]
Abstract
A triptycene-based bis(benzimidazole) ester ligand, L3, was designed to enhance the electron donating ability of the heterocyclic nitrogen atoms relative to those of the first generation bis(benzoxazole) analogs, L1 and L2. A convergent synthesis of L3 was designed and executed. Three-component titration experiments using UV-visible spectroscopy revealed that the desired diiron(II) complex could be obtained with a 1:2:1 ratio of L3:Fe(OTf)2(MeCN)2:external carboxylate reactants. X-ray crystallographic studies of two diiron complexes derived in this manner from L3 revealed their formulas to be [Fe2L3(μ-OH)(μ-O2CR)(OTf)2], where R = 2,6-bis(p-tolyl)benzoate (7) or triphenylacetate (8). The structures are similar to that of a diiron complex derived from L1, [Fe2L1(μ-OH)(μ-O2CArTol)(OTf)2] (9) with a notable difference being that, in 7 and 8, the geometry at iron more closely resembles square-pyramidal than trigonal-bipyramidal. Mössbauer spectroscopic analyses of 7 and 8 indicate the presence of high-spin diiron(II) cores. These results demonstrate the importance of substituting benzimidazole for benzoxazole for assembling biomimetic diiron complexes with syn disposition of two N-donor ligands, as found in O2-activating carboxylate-bridged diiron centers in biology.
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Affiliation(s)
- Yang Li
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
| | - Chan Myae Myae Soe
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
| | - Justin J. Wilson
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
| | - Suan Lian Tuang
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
| | - Ulf-Peter Apfel
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
| | - Stephen J. Lippard
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
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22
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Nuclear resonance vibrational spectroscopic and computational study of high-valent diiron complexes relevant to enzyme intermediates. Proc Natl Acad Sci U S A 2013; 110:6275-80. [PMID: 23576760 DOI: 10.1073/pnas.1304238110] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
High-valent intermediates of binuclear nonheme iron enzymes are structurally unknown despite their importance for understanding enzyme reactivity. Nuclear resonance vibrational spectroscopy combined with density functional theory calculations has been applied to structurally well-characterized high-valent mono- and di-oxo bridged binuclear Fe model complexes. Low-frequency vibrational modes of these high-valent diiron complexes involving Fe motion have been observed and assigned. These are independent of Fe oxidation state and show a strong dependence on spin state. It is important to note that they are sensitive to the nature of the Fe2 core bridges and provide the basis for interpreting parallel nuclear resonance vibrational spectroscopy data on the high-valent oxo intermediates in the binuclear nonheme iron enzymes.
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23
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Khanh Mai B, Kim Y. Theoretical studies for large tunneling and the hydrogen-transfer mechanism in the C-H activation of CH3CN by a di(μ-oxo)diiron(IV) complex: a model for intermediate Q in soluble methane monooxygenase. Chemistry 2013; 19:3568-72. [PMID: 23400929 DOI: 10.1002/chem.201204488] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2013] [Indexed: 11/11/2022]
Affiliation(s)
- Binh Khanh Mai
- Department of Applied Chemistry, Kyung Hee University, 1 Seochun-Dong, Giheung-Gu, Yongin-Si, Gyeonggi-Do, 446-701, Korea
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24
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Bikas R, Hosseini-Monfared H, Zoppellaro G, Herchel R, Tucek J, Owczarzak AM, Kubicki M, Zboril R. Synthesis, structure, magnetic properties and theoretical calculations of methoxy bridged dinuclear iron(iii) complex with hydrazone based O,N,N-donor ligand. Dalton Trans 2013; 42:2803-12. [DOI: 10.1039/c2dt31751f] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
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25
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Lyakin OY, Shteinman AA. Oxo complexes of high-valence iron in oxidation catalysis. KINETICS AND CATALYSIS 2012. [DOI: 10.1134/s0023158412050084] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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26
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Gopakumar G, Belanzoni P, Baerends EJ. Hydroxylation catalysis by mononuclear and dinuclear iron oxo catalysts: a methane monooxygenase model system versus the Fenton reagent Fe(IV)O(H2O)5(2+). Inorg Chem 2011; 51:63-75. [PMID: 22221279 DOI: 10.1021/ic200754w] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Hydroxylation of aliphatic C-H bonds is a chemically and biologically important reaction, which is catalyzed by the oxidoiron group FeO(2+) in both mononuclear (heme and nonheme) and dinuclear complexes. We investigate the similarities and dissimilarities of the action of the FeO(2+) group in these two configurations, using the Fenton-type reagent [FeO(2+) in a water solution, FeO(H(2)O)(5)(2+)] and a model system for the methane monooxygenase (MMO) enzyme as representatives. The high-valent iron oxo intermediate MMOH(Q) (compound Q) is regarded as the active species in methane oxidation. We show that the electronic structure of compound Q can be understood as a dimer of two Fe(IV)O(2+) units. This implies that the insights from the past years in the oxidative action of this ubiquitous moiety in oxidation catalysis can be applied immediately to MMOH(Q). Electronically the dinuclear system is not fundamentally different from the mononuclear system. However, there is an important difference of MMOH(Q) from FeO(H(2)O)(5)(2+): the largest contribution to the transition state (TS) barrier in the case of MMOH(Q) is not the activation strain (which is in this case the energy for the C-H bond lengthening to the TS value), but it is the steric hindrance of the incoming CH(4) with the ligands representing glutamate residues. The importance of the steric factor in the dinuclear system suggests that it may be exploited, through variation in the ligand framework, to build a synthetic oxidation catalyst with the desired selectivity for the methane substrate.
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Affiliation(s)
- G Gopakumar
- Theoretische Chemie, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
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27
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Do LH, Lippard SJ. Evolution of strategies to prepare synthetic mimics of carboxylate-bridged diiron protein active sites. J Inorg Biochem 2011; 105:1774-85. [PMID: 22113107 PMCID: PMC3232320 DOI: 10.1016/j.jinorgbio.2011.08.025] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2011] [Revised: 08/08/2011] [Accepted: 08/11/2011] [Indexed: 10/17/2022]
Abstract
We present a comprehensive review of research conducted in our laboratory in pursuit of the long-term goal of reproducing the structures and reactivity of carboxylate-bridged diiron centers used in biology to activate dioxygen for the conversion of hydrocarbons to alcohols and related products. This article describes the evolution of strategies devised to achieve these goals and illustrates the challenges in getting there. Particular emphasis is placed on controlling the geometry and coordination environment of the diiron core, preventing formation of polynuclear iron clusters, maintaining the structural integrity of model complexes during reactions with dioxygen, and tuning the ligand framework to stabilize desired oxygenated diiron species. Studies of the various model systems have improved our understanding of the electronic and physical characteristics of carboxylate-bridged diiron units and their reactivity toward molecular oxygen and organic moieties. The principles and lessons that have emerged from these investigations will guide future efforts to develop more sophisticated diiron protein model complexes.
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Affiliation(s)
- Loi H. Do
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139. U.S.A
| | - Stephen J. Lippard
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139. U.S.A
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28
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Roos K, Siegbahn PEM. A comparison of two-electron chemistry performed by the manganese and iron heterodimer and homodimers. J Biol Inorg Chem 2011; 17:363-73. [DOI: 10.1007/s00775-011-0858-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2011] [Accepted: 11/02/2011] [Indexed: 10/15/2022]
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29
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Do LH, Wang H, Tinberg CE, Dowty E, Yoda Y, Cramer SP, Lippard SJ. Characterization of a synthetic peroxodiiron(III) protein model complex by nuclear resonance vibrational spectroscopy. Chem Commun (Camb) 2011; 47:10945-7. [PMID: 21897991 DOI: 10.1039/c1cc13836g] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The vibrational spectrum of an η(1),η(1)-1,2-peroxodiiron(III) complex was measured by nuclear resonance vibrational spectroscopy and fit using an empirical force field analysis. Isotopic (18)O(2) labelling studies revealed a feature involving motion of the {Fe(2)(O(2))}(4+) core that was not previously observed by resonance Raman spectroscopy.
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Affiliation(s)
- Loi H Do
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
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30
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Song WJ, Lippard SJ. Mechanistic studies of reactions of peroxodiiron(III) intermediates in T201 variants of toluene/o-xylene monooxygenase hydroxylase. Biochemistry 2011; 50:5391-9. [PMID: 21595439 PMCID: PMC3116272 DOI: 10.1021/bi200340f] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Site-directed mutagenesis studies of a strictly conserved T201 residue in the active site of toluene/o-xylene monooxygenase hydroxylase (ToMOH) revealed that a single mutation can facilitate kinetic isolation of two distinctive peroxodiiron(III) species, designated T201(peroxo) and ToMOH(peroxo), during dioxygen activation. Previously, we characterized both oxygenated intermediates by UV-vis and Mössbauer spectroscopy, proposed structures from DFT and QM/MM computational studies, and elucidated chemical steps involved in dioxygen activation through the kinetic studies of T201(peroxo) formation. In this study, we investigate the kinetics of T201(peroxo) decay to explore the reaction mechanism of the oxygenated intermediates following O(2) activation. The decay rates of T201(peroxo) were monitored in the absence and presence of external (phenol) or internal (tryptophan residue in an I100W variant) substrates under pre-steady-state conditions. Three possible reaction models for the formation and decay of T201(peroxo) were evaluated, and the results demonstrate that this species is on the pathway of arene oxidation and appears to be in equilibrium with ToMOH(peroxo).
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Affiliation(s)
- Woon Ju Song
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
| | - Stephen J. Lippard
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
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31
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Gordon JC, Kubas GJ. Perspectives on How Nature Employs the Principles of Organometallic Chemistry in Dihydrogen Activation in Hydrogenases. Organometallics 2010. [DOI: 10.1021/om100436c] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- John C. Gordon
- Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Gregory J. Kubas
- Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
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32
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Tinberg CE, Lippard SJ. Oxidation reactions performed by soluble methane monooxygenase hydroxylase intermediates H(peroxo) and Q proceed by distinct mechanisms. Biochemistry 2010; 49:7902-12. [PMID: 20681546 PMCID: PMC2935519 DOI: 10.1021/bi1009375] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Soluble methane monooxygenase is a bacterial enzyme that converts methane to methanol at a carboxylate-bridged diiron center with exquisite control. Because the oxidizing power required for this transformation is demanding, it is not surprising that the enzyme is also capable of hydroxylating and epoxidizing a broad range of hydrocarbon substrates in addition to methane. In this work we took advantage of this promiscuity of the enzyme to gain insight into the mechanisms of action of H(peroxo) and Q, two oxidants that are generated sequentially during the reaction of reduced protein with O(2). Using double-mixing stopped-flow spectroscopy, we investigated the reactions of the two intermediate species with a panel of substrates of varying C-H bond strength. Three classes of substrates were identified according to the rate-determining step in the reaction. We show for the first time that an inverse trend exists between the rate constant of reaction with H(peroxo) and the C-H bond strength of the hydrocarbon examined for those substrates in which C-H bond activation is rate-determining. Deuterium kinetic isotope effects revealed that reactions performed by Q, but probably not H(peroxo), involve extensive quantum mechanical tunneling. This difference sheds light on the observation that H(peroxo) is not a sufficiently potent oxidant to hydroxylate methane, whereas Q can perform this reaction in a facile manner. In addition, the reaction of H(peroxo) with acetonitrile appears to proceed by a distinct mechanism in which a cyanomethide anionic intermediate is generated, bolstering the argument that H(peroxo) is an electrophilic oxidant that operates via two-electron transfer chemistry.
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Affiliation(s)
- Christine E. Tinberg
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
| | - Stephen J. Lippard
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
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33
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Friedle S, Reisner E, Lippard SJ. Current challenges of modeling diiron enzyme active sites for dioxygen activation by biomimetic synthetic complexes. Chem Soc Rev 2010; 39:2768-79. [PMID: 20485834 DOI: 10.1039/c003079c] [Citation(s) in RCA: 221] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This tutorial review describes recent progress in modeling the active sites of carboxylate-rich non-heme diiron enzymes that activate dioxygen to carry out several key reactions in Nature. The chemistry of soluble methane monooxygenase, which catalyzes the selective oxidation of methane to methanol, is of particular interest for (bio)technological applications. Novel synthetic diiron complexes that mimic structural, and, to a lesser extent, functional features of these diiron enzymes are discussed. The chemistry of the enzymes is also briefly summarized. A particular focus of this review is on models that mimic characteristics of the diiron systems that were previously not emphasized, including systems that contain (i) aqua ligands, (ii) different substrates tethered to the ligand framework, (iii) dendrimers attached to carboxylates to mimic the protein environment, (iv) two N-donors in a syn-orientation with respect to the iron-iron vector, and (v) a N-rich ligand environment capable of accessing oxygenated high-valent diiron intermediates.
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Affiliation(s)
- Simone Friedle
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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34
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Roithová J, Schröder D. Selective activation of alkanes by gas-phase metal ions. Chem Rev 2010; 110:1170-211. [PMID: 20041696 DOI: 10.1021/cr900183p] [Citation(s) in RCA: 377] [Impact Index Per Article: 26.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Jana Roithová
- Department of Organic Chemistry, Charles University in Prague, Faculty of Sciences, Hlavova 8, 12843 Prague 2, Czech Republic.
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35
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Balcells D, Clot E, Eisenstein O. C—H Bond Activation in Transition Metal Species from a Computational Perspective. Chem Rev 2010; 110:749-823. [PMID: 20067255 DOI: 10.1021/cr900315k] [Citation(s) in RCA: 843] [Impact Index Per Article: 60.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- David Balcells
- Institut Charles Gerhardt, Université Montpellier 2, CNRS 5253, cc 1501, Place Eugène Bataillon, 34000 Montpellier, France
| | - Eric Clot
- Institut Charles Gerhardt, Université Montpellier 2, CNRS 5253, cc 1501, Place Eugène Bataillon, 34000 Montpellier, France
| | - Odile Eisenstein
- Institut Charles Gerhardt, Université Montpellier 2, CNRS 5253, cc 1501, Place Eugène Bataillon, 34000 Montpellier, France
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Tinberg CE, Lippard SJ. Revisiting the mechanism of dioxygen activation in soluble methane monooxygenase from M. capsulatus (Bath): evidence for a multi-step, proton-dependent reaction pathway. Biochemistry 2009; 48:12145-58. [PMID: 19921958 PMCID: PMC2797563 DOI: 10.1021/bi901672n] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Stopped-flow kinetic investigations of soluble methane monooxygenase (sMMO) from M. capsulatus (Bath) have clarified discrepancies that exist in the literature regarding several aspects of catalysis by this enzyme. The development of thorough kinetic analytical techniques has led to the discovery of two novel oxygenated iron species that accumulate in addition to the well-established intermediates H(peroxo) and Q. The first intermediate, P*, is a precursor to H(peroxo) and was identified when the reaction of reduced MMOH and MMOB with O(2) was carried out in the presence of >or=540 microM methane to suppress the dominating absorbance signal due to Q. The optical properties of P* are similar to those of H(peroxo), with epsilon(420) = 3500 M(-1) cm(-1) and epsilon(720) = 1250 M(-1) cm(-1). These values are suggestive of a peroxo-to-iron(III) charge-transfer transition and resemble those of peroxodiiron(III) intermediates characterized in other carboxylate-bridged diiron proteins and synthetic model complexes. The second identified intermediate, Q*, forms on the pathway of Q decay when reactions are performed in the absence of hydrocarbon substrate. Q* does not react with methane, forms independently of buffer composition, and displays a unique shoulder at 455 nm in its optical spectrum. Studies conducted at different pH values reveal that rate constants corresponding to P* decay/H(peroxo) formation and H(peroxo) decay/Q formation are both significantly retarded at high pH and indicate that both events require proton transfer. The processes exhibit normal kinetic solvent isotope effects (KSIEs) of 2.0 and 1.8, respectively, when the reactions are performed in D(2)O. Mechanisms are proposed to account for the observations of these novel intermediates and the proton dependencies of P* to H(peroxo) and H(peroxo) to Q conversion.
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Affiliation(s)
| | - Stephen J. Lippard
- To whom correspondence should be addressed.
. Telephone: (617) 253-1892. Fax: (617)
258-8150
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37
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Friedle S, Kodanko JJ, Morys AJ, Hayashi T, Moënne-Loccoz P, Lippard SJ. Modeling the syn disposition of nitrogen donors in non-heme diiron enzymes. Synthesis, characterization, and hydrogen peroxide reactivity of diiron(III) complexes with the syn N-donor ligand H2BPG2DEV. J Am Chem Soc 2009; 131:14508-20. [PMID: 19757795 DOI: 10.1021/ja906137y] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In order to model the syn disposition of histidine residues in carboxylate-bridged non-heme diiron enzymes, we prepared a new dinucleating ligand, H(2)BPG(2)DEV, that provides this geometric feature. The ligand incorporates biologically relevant carboxylate functionalities, which have not been explored as extensively as nitrogen-only analogues. Three novel oxo-bridged diiron(III) complexes, [Fe(2)(mu-O)(H(2)O)(2)(BPG(2)DEV)](ClO(4))(2) (6), [Fe(2)(mu-O)(mu-O(2)CAr(iPrO))(BPG(2)DEV)](ClO(4)) (7), and [Fe(2)(mu-O)(mu-CO(3))(BPG(2)DEV)] (8), were prepared. Single-crystal X-ray structural characterization confirms that two pyridyl groups are bound syn with respect to the Fe-Fe vector in these compounds. The carbonato-bridged complex 8 forms quantitatively from 6 in a rapid reaction with gaseous CO(2) in organic solvents. A common maroon-colored intermediate (lambda(max) = 490 nm; epsilon = 1500 M(-1) cm(-1)) forms in reactions of 6, 7, or 8 with H(2)O(2) and NEt(3) in CH(3)CN/H(2)O solutions. Mass spectrometric analyses of this species, formed using (18)O-labeled H(2)O(2), indicate the presence of a peroxide ligand bound to the oxo-bridged diiron(III) center. The Mossbauer spectrum at 90 K of the EPR-silent intermediate exhibits a quadrupole doublet with delta = 0.58 mm/s and DeltaE(Q) = 0.58 mm/s. The isomer shift is typical for a peroxodiiron(III) species, but the quadrupole splitting parameter is unusually small compared to those of related complexes. These Mossbauer parameters are comparable to those observed for a peroxo intermediate formed in the reaction of reduced toluene/o-xylene monooxygenase hydroxylase with dioxygen. Resonance Raman studies reveal an unusually low-energy O-O stretching mode in the peroxo intermediate that is consistent with a short diiron distance. Although peroxodiiron(III) intermediates generated from 6, 7, and 8 are poor O-atom-transfer catalysts, they display highly efficient catalase activity, with turnover numbers up to 10,000. In contrast to hydrogen peroxide reactions of diiron(III) complexes that lack a dinucleating ligand, the intermediates generated here could be re-formed in significant quantities after a second addition of H(2)O(2), as observed spectroscopically and by mass spectrometry.
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Affiliation(s)
- Simone Friedle
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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38
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Chanda A, de Oliveira FT, Collins TJ, Münck E, Bominaar EL. Density Functional Theory Study of the Structural, Electronic, and Magnetic Properties of a μ-oxo Bridged Dinuclear FeIV Complex Based on a Tetra-Amido Macrocyclic Ligand. Inorg Chem 2008; 47:9372-9. [DOI: 10.1021/ic800881p] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Arani Chanda
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania, 15213
| | | | - Terrence J. Collins
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania, 15213
| | - Eckard Münck
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania, 15213
| | - Emile L. Bominaar
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania, 15213
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Puerta L, Franco HJ, Murgich J, Gonzalez C, Simón-Manso Y, Mujica V. Dipole Orientation and Surface Cluster Size Effects on Chemisorption-Induced Magnetism: A DFT Study of the Interaction of Gold−Thiopolypeptide. J Phys Chem A 2008; 112:9771-83. [DOI: 10.1021/jp710748h] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Luis Puerta
- Departamento de Química, FACYT, Universidad de Carabobo, Apartado 2005, Valencia, Edo. Carabobo, Venezuela, Escuela de Química, Universidad Central de Venezuela, Apartado 47102, Caracas 1041-A, Venezuela, Centro de Química, IVIC, Apartado 21827, Caracas 1020A, Venezuela, Physical and Chemical Properties Division, Building 221, Room A111, NIST, Gaithersburg, Maryland 20899, Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, and Center for Nanoscale
| | - Héctor J. Franco
- Departamento de Química, FACYT, Universidad de Carabobo, Apartado 2005, Valencia, Edo. Carabobo, Venezuela, Escuela de Química, Universidad Central de Venezuela, Apartado 47102, Caracas 1041-A, Venezuela, Centro de Química, IVIC, Apartado 21827, Caracas 1020A, Venezuela, Physical and Chemical Properties Division, Building 221, Room A111, NIST, Gaithersburg, Maryland 20899, Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, and Center for Nanoscale
| | - Juan Murgich
- Departamento de Química, FACYT, Universidad de Carabobo, Apartado 2005, Valencia, Edo. Carabobo, Venezuela, Escuela de Química, Universidad Central de Venezuela, Apartado 47102, Caracas 1041-A, Venezuela, Centro de Química, IVIC, Apartado 21827, Caracas 1020A, Venezuela, Physical and Chemical Properties Division, Building 221, Room A111, NIST, Gaithersburg, Maryland 20899, Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, and Center for Nanoscale
| | - Carlos Gonzalez
- Departamento de Química, FACYT, Universidad de Carabobo, Apartado 2005, Valencia, Edo. Carabobo, Venezuela, Escuela de Química, Universidad Central de Venezuela, Apartado 47102, Caracas 1041-A, Venezuela, Centro de Química, IVIC, Apartado 21827, Caracas 1020A, Venezuela, Physical and Chemical Properties Division, Building 221, Room A111, NIST, Gaithersburg, Maryland 20899, Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, and Center for Nanoscale
| | - Yamil Simón-Manso
- Departamento de Química, FACYT, Universidad de Carabobo, Apartado 2005, Valencia, Edo. Carabobo, Venezuela, Escuela de Química, Universidad Central de Venezuela, Apartado 47102, Caracas 1041-A, Venezuela, Centro de Química, IVIC, Apartado 21827, Caracas 1020A, Venezuela, Physical and Chemical Properties Division, Building 221, Room A111, NIST, Gaithersburg, Maryland 20899, Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, and Center for Nanoscale
| | - Vladimiro Mujica
- Departamento de Química, FACYT, Universidad de Carabobo, Apartado 2005, Valencia, Edo. Carabobo, Venezuela, Escuela de Química, Universidad Central de Venezuela, Apartado 47102, Caracas 1041-A, Venezuela, Centro de Química, IVIC, Apartado 21827, Caracas 1020A, Venezuela, Physical and Chemical Properties Division, Building 221, Room A111, NIST, Gaithersburg, Maryland 20899, Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, and Center for Nanoscale
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Hurst JK, Cape JL, Clark AE, Das S, Qin C. Mechanisms of water oxidation catalyzed by ruthenium diimine complexes. Inorg Chem 2008; 47:1753-64. [PMID: 18330967 DOI: 10.1021/ic700724h] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
(18)O-isotope-labeling studies have led to the conclusion that there exist two major pathways for water oxidation catalyzed by dimeric ruthenium ions of the general type cis, cis-[L2Ru(III)(OH2)]2O(4+). We have proposed that both pathways involve concerted addition of H and OH fragments derived from H 2O to the complexes in their four-electron-oxidized states, i.e., [L2Ru(V)(O)]2O(4+), ultimately generating bound peroxy intermediates that decay with the evolution of O2. The pathways differ primarily in the site of addition of the OH fragment, which is either a ruthenyl O atom or a bipyridine ligand. In the former case, water addition is thought to give rise to a critical intermediate whose structure is L2Ru(IV)(OH)ORu(IV)(OOH)L2(4+); the structures of intermediates involved in the other pathway are less well defined but may involve bipyridine OH adducts of the type L2Ru(V)(O)ORu(IV)(OH)(L(*)OH)L(4+), which could react further to generate unstable dioxetanes or similar endoperoxides. Published experimental and theoretical support for these pathways is reviewed within the broader context of water oxidation catalysis and related reactions reported for other diruthenium and group 8 monomeric diimine-based catalysts. New experiments that are designed to probe the issue of bipyridine ligand "noninnocence" in catalysis are described. Specifically, the relative contributions of the two pathways have been shown to correlate with substituent effects in 4,4'- and 5,5'-substituted bipyridine complexes in a manner consistent with the formation of a reactive OH-adduct intermediate in one of the pathways, and the formation of OH-bipyridine adducts during catalytic turnover has been directly confirmed by optical spectroscopy. Finally, a photosensitized system for catalyzed water oxidation has been developed that allows assessment of the catalytic efficiencies of the complex ions under neutral and alkaline conditions; these studies show that the ions are far better catalysts than had previously been assumed based upon reported catalytic parameters obtained with strong oxidants in acidic media.
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Affiliation(s)
- James K Hurst
- Department of Chemistry, Washington State University, Pullman, Washington 99164-4630, USA.
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41
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Han WG, Noodleman L. Structural Model Studies for the High-Valent Intermediate Q of Methane Monooxygenase from Broken-Symmetry Density Functional Calculations. Inorganica Chim Acta 2008; 361:973-986. [PMID: 19262682 PMCID: PMC2391136 DOI: 10.1016/j.ica.2007.06.007] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Mössbauer isomer shift parameters have been obtained for both density functional theory (DFT) OPBE and OLYP functionals by linear regressions between the measured isomer shifts and calculated electron densities at Fe nuclei for a number of Fe(2+,2.5+) and Fe(2.5+,3+,3.5+,4+) complexes grouped separately. The calculated isomer shifts and quadrupole splittings on the sample Fe complexes from OPBE and OLYP functionals are similar to those of PW91 calculations (J. Comput. Chem. 27 (2006) 1292), however the fit parameters from the linear regressions differ between PW91 and OPBE, OLYP. Four models for the active site structure of the hydroxylase component of soluble methane monooxygenase (MMOH) have been studied, using three DFT functionals OPBE, OLYP, and PW91, incorporated with broken-symmetry methodology and the conductor-like screening (COSMO) solvation model. The calculated properties, including optimized geometries, electronic energies, pK(a)'s, Fe net spin populations, and Mössbauer isomer shifts and quadrupole splittings, have been reported and compared with available experimental values. The high-spin antiferromagnetically (AF) coupled Fe(4+) sites are correctly predicted by OPBE and OLYP methods for all active site models. PW91 potential overestimates the Fe-ligand covalencies for some of the models because of spin crossover. Our calculations and data analysis support the structure (our current model II shown in Figure 8) proposed by Friesner and Lippard's group (J. Am. Chem. Soc. 123 (2001) 3836-3837), which contains an Fe(4+)(μ-O)(2)Fe(4+) center, one axial water which also H-bonds to both side chains of Glu243 and Glu114, and one bidentate carboxylate group from the side chain of Glu144, which is likely to represent the active site of MMOH-Q. A new model structure (model IV shown in Figure 9), which has a terminal hydroxo and a protonated His147 which is dissociated from a nearby Fe, is more asymmetric in its Fe(μ-O)(2)Fe diamond core, and is another very good candidate for intermediate Q.
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Affiliation(s)
- Wen-Ge Han
- Department of Molecular Biology TPC15 The Scripps Research Institute 10550 N. Torrey Pines Rd. La Jolla, California 92037
| | - Louis Noodleman
- Department of Molecular Biology TPC15 The Scripps Research Institute 10550 N. Torrey Pines Rd. La Jolla, California 92037
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42
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Reisner E, Lippard SJ. Synthesis of Dicarboxylate “C-Clamp” 1,2-Diethynylarene Compounds as Potential Transition-Metal Ion Hosts. European J Org Chem 2008. [DOI: 10.1002/ejoc.200700816] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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43
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A synthetic precedent for the [FeIV2(mu-O)2] diamond core proposed for methane monooxygenase intermediate Q. Proc Natl Acad Sci U S A 2007; 104:20713-8. [PMID: 18093922 DOI: 10.1073/pnas.0708516105] [Citation(s) in RCA: 137] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Intermediate Q, the methane-oxidizing species of soluble methane monooxygenase, is proposed to have an [Fe(IV)(2)(mu-O)(2)] diamond core. In an effort to obtain a synthetic precedent for such a core, bulk electrolysis at 900 mV (versus Fc(+/0)) has been performed in MeCN at -40 degrees C on a valence-delocalized [Fe(III)Fe(IV)(mu-O)(2)(L(b))(2)](3+) complex (1b) (E(1/2) = 760 mV versus Fc(+/0)). Oxidation of 1b results in the near-quantitative formation of a deep red complex, designated 2b, that exhibits a visible spectrum with lambda(max) at 485 nm (9,800 M(-1).cm(-1)) and 875 nm (2,200 M(-1).cm(-1)). The 4.2 K Mössbauer spectrum of 2b exhibits a quadrupole doublet with delta = -0.04(1) mm.s(-1) and DeltaE(Q) = 2.09(2) mm.s(-1), parameters typical of an iron(IV) center. The Mössbauer patterns observed in strong applied fields show that 2b is an antiferromagnetically coupled diiron(IV) center. Resonance Raman studies reveal the diagnostic vibration mode of the [Fe(2)(mu-O)(2)] core at 674 cm(-1), downshifting 30 cm(-1) upon (18)O labeling. Extended x-ray absorption fine structure (EXAFS) analysis shows two O/N scatterers at 1.78 A and an Fe scatterer at 2.73 A. Based on the accumulated spectroscopic evidence, 2b thus can be formulated as [Fe(IV)(2)(mu-O)(2)(L(b))(2)](4+), the first synthetic complex with an [Fe(IV)(2)(mu-O)(2)] core. A comparison of 2b and its mononuclear analog [Fe(IV)(O)(L(b))(NCMe)](2+) (4b) reveals that 4b is 100-fold more reactive than 2b in oxidizing weak C H bonds. This surprising observation may shed further light on how intermediate Q carries out the hydroxylation of methane.
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Rinaldo D, Philipp DM, Lippard SJ, Friesner RA. Intermediates in dioxygen activation by methane monooxygenase: a QM/MM study. J Am Chem Soc 2007; 129:3135-47. [PMID: 17326634 PMCID: PMC2517126 DOI: 10.1021/ja0654074] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Protein effects in the activation of dioxygen by methane monooxygenase (MMO) were investigated by using combined QM/MM and broken-symmetry Density Functional Theory (DFT) methods. The effects of a novel empirical scheme recently developed by our group on the relative DFT energies of the various intermediates in the catalytic cycle are investigated. Inclusion of the protein leads to much better agreement between the experimental and computed geometric structures for the reduced form (MMOH(red)). Analysis of the electronic structure of MMOH(red) reveals that the two iron atoms have distinct environments. Different coordination geometries tested for the MMOH(peroxo) intermediate reveal that, in the protein environment, the mu-eta2,eta2 structure is more stable than the others. Our analysis also shows that the protein helps to drive reactants toward products along the reaction path. Furthermore, these results demonstrate the importance of including the protein environment in our models and the usefulness of the QM/MM approach for accurate modeling of enzymatic reactions. A discrepancy remains in our calculation of the Fe-Fe distance in our model of HQ as compared to EXAFS data obtained several years ago, for which we currently do not have an explanation.
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45
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Stone KL, Behan RK, Green MT. Resonance Raman spectroscopy of chloroperoxidase compound II provides direct evidence for the existence of an iron(IV)-hydroxide. Proc Natl Acad Sci U S A 2006; 103:12307-10. [PMID: 16895990 PMCID: PMC1567876 DOI: 10.1073/pnas.0603159103] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We report direct evidence for the existence of an iron(IV)-hydroxide. Resonance Raman measurements on chloroperoxidase compound II (CPO-II) reveal an isotope ((18)O and (2)H)-sensitive band at nu(Fe-O) = 565 cm(-1). Preparation of CPO-II in H(2)O using H(2)(18)O(2) results in a red-shift of 22 cm(-1), while preparation of CPO-II in (2)H(2)O using H(2)O(2) results in a red-shift of 13 cm(-1). These values are in good agreement with the isotopic shifts predicted (23 and 12 cm(-1), respectively) for an Fe-OH harmonic oscillator. The measured Fe-O stretching frequency is also in good agreement with the 1.82-A Fe-O bond reported for CPO-II. A Badger's rule analysis of this distance provides an Fe-O stretching frequency of nu(Badger) = 563 cm(-1). We also present X-band electron nuclear double resonance (ENDOR) data for cryoreduced CPO-II. Cryogenic reduction (77 K) of the EPR-silent Fe(IV)OH center in CPO-II results in an EPR-active Fe(III)OH species with a strongly coupled (13.4 MHz) exchangeable proton. Based on comparisons with alkaline myoglobin, we assign this resonance to the hydroxide proton of cryoreduced CPO-II.
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Affiliation(s)
- Kari L Stone
- Department of Chemistry, Pennsylvania State University, University Park, PA 16802, USA
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46
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Chen PPY, Chan SI. Theoretical modeling of the hydroxylation of methane as mediated by the particulate methane monooxygenase. J Inorg Biochem 2006; 100:801-9. [PMID: 16494948 DOI: 10.1016/j.jinorgbio.2005.12.014] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2005] [Accepted: 12/13/2005] [Indexed: 11/22/2022]
Abstract
We present here the results of density functional theory (DFT) calculations directed toward elucidation of the CH bond activation mechanism that might be adopted by the particulate methane monooxygenase (pMMO) in the hydroxylation of methane and related small alkanes. In these calculations, we considered three of the most probable models for the transition metal active site mediating the "oxo-transfer": (i) the trinuclear copper cluster bis(mu(3)-oxo)trinuclear copper(II, II, III) complex 1, recently proposed by Chan et al. [S.I. Chan, K.H.-C. Chen, S.S.-F. Yu, C.-L. Chen, S.S.-J. Kuo, Biochemistry 43 (2004) 4421-4430.]; (ii) the most frequently used model complex, bis(mu-oxo)Cu(III)(2) complex 2; and (iii) the mixed-valence bis(mu-oxo)Cu(II)Cu(III) complex 3. The results obtained indicate that the methane hydroxylation chemistry mediated by the trinuclear copper cluster bis(mu(3)-oxo)trinuclear copper(II, II, III) complex 1 offers the most facile pathway for methane hydroxylation, and this model yields KIE values that are in good agreement with experiment. In this mechanism, the reaction proceeds along a "singlet" potential surface and a "singlet oxene" is directly inserted across a CH bond in a concerted manner. Kinetic isotope effects (k(H)/k(D) or KIE) associated with the concerted oxene insertion process mediated by complex 1 are calculated to be 5.2 at 300K when tunneling effects are included. Overall rate constants for the methane hydroxylation by the three models have been calculated as a function of temperature, and the rates are at least 5-6 orders of magnitude more facile when the chemistry is mediated by complex 1 compared to complex 2 or complex 3.
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Affiliation(s)
- Peter P-Y Chen
- Institute of Chemistry, Academia Sinica, 128 Section 2, Academia Road, Nankang, Taipei 115, Taiwan, ROC
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Abreu IA, Rodriguez JA, Cabelli DE. Theoretical Studies of Manganese and Iron Superoxide Dismutases: Superoxide Binding and Superoxide Oxidation. J Phys Chem B 2005; 109:24502-9. [PMID: 16375454 DOI: 10.1021/jp052368u] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Density-functional calculations indicate that the second sphere of coordination around the metal centers of manganese and iron superoxide dismutases (MnSODs and FeSODs) plays an important role in the binding of O2(-). In these systems, O2(-) prefers to bind to Mn or Fe in end-on configurations. For human and E. coli MnSODs, the bound O2(-) forms hydrogen bonds with the tyrosine and glutamine amino acid residues in the second sphere of coordination. In the cases of E. coli and T. elongates FeSODs, hydrogen bonding occurs between the bound O2(-) and the tyrosine amino acid only because the glutamine is too far away for an effective bonding interaction. The manner in which the O2(-) binds to the metal center in MnSODs and FeSODs can affect the rate of subsequent protonation and determine the mechanism for the formation of H2O2. Both Mn- and Fe-containing superoxide dismutases contain a metal-bound solvent molecule that has been suggested to be involved in the uptake of a H+ upon reduction of the metal center [Bull, C.; Fee, J. A. J. Am. Chem. Soc. 1985, 107, 3295; Miller, A.-F.; Padmakumar, K.; Sorkin, D. L.; Karapetian, A.; Vance, C. K. J. Inorg. Biochem. 2003, 93, 71]. Using density-functional theory, we confirm this suggestion and show the involvement of the second sphere of coordination in the process. We show that the oxidation of superoxide by Mn- or Fe-containing superoxide dismutases is facilitated by a cooperative effect between superoxide binding, protonation of the OH- bound to the metal, and electron transfer from the superoxide molecule to the oxidized metal. In particular, proton transfer through tyrosine-34 on the absence of a bound superoxide is uphill while, once superoxide is bound, the energetic barrier is lowered. It is this barrier that likely keeps the resting state (Mn(III)SOD) of the enzyme with a bound hydroxide, instead of a water. This work provides a model for the mechanism of reaction of superoxide with the oxidized form of the metal within Mn- and FeSODs.
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Affiliation(s)
- Isabel A Abreu
- Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, USA
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Abstract
[reaction: see text] An efficient route to a new family of dinucleating ligands has been developed. A convergent strategy to these ligands involved dual Sonogashira cross-coupling of 2,3-diethynyltriptycene with a variety of functionally diverse 5-bromopyridines. The resultant ligands were accessed in four steps and 40-50% overall yield from 1,2,4,5-tetrabromobenzene. Synthesis of an imidazole and a quinoline derivative by this method is also described.
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Affiliation(s)
- Jeremy J. Kodanko
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
| | - Anna J. Morys
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
| | - Stephen J. Lippard
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
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Friesner RA, Guallar V. AB INITIO QUANTUM CHEMICAL AND MIXED QUANTUM MECHANICS/MOLECULAR MECHANICS (QM/MM) METHODS FOR STUDYING ENZYMATIC CATALYSIS. Annu Rev Phys Chem 2005; 56:389-427. [PMID: 15796706 DOI: 10.1146/annurev.physchem.55.091602.094410] [Citation(s) in RCA: 445] [Impact Index Per Article: 23.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We describe large scale ab initio quantum chemical and mixed quantum mechanics/molecular mechanics (QM/MM) methods for studying enzymatic reactions. First, technical aspects of the methodology are reviewed, including the hybrid density functional theory (DFT) methods that are typically employed for the QM aspect of the calculations, and various approaches to defining the interface between the QM and MM regions in QM/MM approaches. The modeling of the enzymatic catalytic cycle for three examples--methane monooxygenase, cytochrome P450, and triose phosphate isomerase--are discussed in some depth, followed by a brief summary of other systems that have been investigated by ab initio methods over the past several years. Finally, a discussion of the qualitative and quantitative conclusions concerning enzymatic catalysis that are available from modern ab initio approaches is presented, followed by a conclusion briefly summarizing future prospects.
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Affiliation(s)
- Richard A Friesner
- Department of Chemistry, Columbia University, New York, New York 10027, USA.
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Lippard SJ. Hydroxylation of C-H bonds at carboxylate-bridged diiron centres. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2005; 363:861-77; discussion 1035-40. [PMID: 15901540 DOI: 10.1098/rsta.2004.1532] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Nature uses carboxylate-bridged diiron centres at the active sites of enzymes that catalyse the selective hydroxylation of hydrocarbons to alcohols. The resting diiron(III) state of the hydroxylase component of soluble methane monooxygenase enzyme is converted by two-electron transfer from an NADH-requiring reductase into the active diiron(II) form, which subsequently reacts with O2 to generate a high-valent diiron(IV) oxo species (Q) that converts CH4 into CH3OH. In this step, C-H bond activation is achieved through a transition state having a linear C...H...O unit involving a bound methyl radical. Kinetic studies of the reaction of Q with substrates CH3X, where X=H, D, CH3, NO2, CN or OH, reveal two classes of reactivity depending upon whether binding to the enzyme or C-H bond activation is rate-limiting. Access of substrates to the carboxylate-bridged diiron active site in the hydroxylase (MMOH) occurs through a series of hydrophobic pockets. In the hydroxylase component of the closely related enzyme toluene/o-xylene monooxygenase (ToMOH), substrates enter through a wide channel in the alpha-subunit of the protein that tracks a course identical to that found in the structurally homologous MMOH. Synthetic models for the carboxylate-bridged diiron centres in MMOH and ToMOH have been prepared that reproduce the stoichiometry and key geometric and physical properties of the reduced and oxidized forms of the proteins. Reactions of the diiron(II) model complexes with dioxygen similarly generate reactive intermediates, including high-valent species capable not only of hydroxylating pendant C-H bonds but also of oxidizing phosphine and sulphide groups.
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Affiliation(s)
- Stephen J Lippard
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
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