1
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Panda S, Phan H, Karlin KD. Heme-copper and Heme O 2-derived synthetic (bioinorganic) chemistry toward an understanding of cytochrome c oxidase dioxygen chemistry. J Inorg Biochem 2023; 249:112367. [PMID: 37742491 PMCID: PMC10615892 DOI: 10.1016/j.jinorgbio.2023.112367] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Revised: 08/22/2023] [Accepted: 09/07/2023] [Indexed: 09/26/2023]
Abstract
Cytochrome c oxidase (CcO), also widely known as mitochondrial electron-transport-chain complex IV, is a multi-subunit transmembrane protein responsible for catalyzing the last step of the electron transport chain, dioxygen reduction to water, which is essential to the establishment and maintenance of the membrane proton gradient that drives ATP synthesis. Although many intermediates in the CcO catalytic cycle have been spectroscopically and/or computationally authenticated, the specifics regarding the IP intermediate, hypothesized to be a heme-Cu (hydro)peroxo species whose O-O bond homolysis is supported by a hydrogen-bonding network of water molecules, are largely obscured by the fast kinetics of the A (FeIII-O2•-/CuI/Tyr) → PM (FeIV=O/CuII-OH/Tyr•) step. In this review, we have focused on the recent advancements in the design, development, and characterization of synthetic heme-peroxo‑copper model complexes, which can circumvent the abovementioned limitation, for the investigation of the formation of IP and its O-O cleavage chemistry. Novel findings regarding (a) proton and electron transfer (PT/ET) processes, together with their contributions to exogenous phenol induced O-O cleavage, (b) the stereo-electronic tunability of the secondary coordination sphere (especially hydrogen-bonding) on the geometric and spin state alteration of the heme-peroxo‑copper unit, and (c) a plausible mechanism for the Tyr-His cofactor biogenesis, are discussed in great detail. Additionally, since the ferric-superoxide and the ferryl-oxo (Compound II) species are critically involved in the CcO catalytic cycle, this review also highlights a few fundamental aspects of these heme-only (i.e., without copper) species, including the structural and reactivity influences of electron-donating trans-axial ligands and Lewis acid-promoted H-bonding.
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Affiliation(s)
- Sanjib Panda
- Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218, USA
| | - Hai Phan
- Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218, USA
| | - Kenneth D Karlin
- Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218, USA.
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2
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Domergue J, Guinard P, Douillard M, Pécaut J, Hostachy S, Proux O, Lebrun C, Le Goff A, Maldivi P, Duboc C, Delangle P. A Series of Ni Complexes Based on a Versatile ATCUN-Like Tripeptide Scaffold to Decipher Key Parameters for Superoxide Dismutase Activity. Inorg Chem 2023. [PMID: 37247425 DOI: 10.1021/acs.inorgchem.3c00766] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The cellular level of reactive oxygen species (ROS) has to be controlled to avoid some pathologies, especially those linked to oxidative stress. One strategy for designing antioxidants consists of modeling natural enzymes involved in ROS degradation. Among them, nickel superoxide dismutase (NiSOD) catalyzes the dismutation of the superoxide radical anion, O2•-, into O2 and H2O2. We report here Ni complexes with tripeptides derived from the amino-terminal CuII- and NiII-binding (ATCUN) motif that mimics some structural features found in the active site of the NiSOD. A series of six mononuclear NiII complexes were investigated in water at physiological pH with different first coordination spheres, from compounds with a N3S to N2S2 set, and also complexes that are in equilibrium between the N-coordination (N3S) and S-coordination (N2S2). They were fully characterized by a combination of spectroscopic techniques, including 1H NMR, UV-vis, circular dichroism, and X-ray absorption spectroscopy, together with theoretical calculations and their redox properties studied by cyclic voltammetry. They all display SOD-like activity, with a kcat ranging between 0.5 and 2.0 × 106 M-1 s-1. The complexes in which the two coordination modes are in equilibrium are the most efficient, suggesting a beneficial effect of a nearby proton relay.
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Affiliation(s)
- Jérémy Domergue
- Univ. Grenoble Alpes, CNRS, DCM, 38000 Grenoble, France
- IRIG, SyMMES, Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, 38000 Grenoble, France
| | - Pawel Guinard
- Univ. Grenoble Alpes, CNRS, DCM, 38000 Grenoble, France
- IRIG, SyMMES, Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, 38000 Grenoble, France
| | - Magali Douillard
- Univ. Grenoble Alpes, CNRS, DCM, 38000 Grenoble, France
- IRIG, SyMMES, Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, 38000 Grenoble, France
| | - Jacques Pécaut
- IRIG, SyMMES, Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, 38000 Grenoble, France
| | - Sarah Hostachy
- IRIG, SyMMES, Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, 38000 Grenoble, France
| | - Olivier Proux
- CNRS, OSUG, Université Grenoble Alpes, 38000 Grenoble, France
| | - Colette Lebrun
- IRIG, SyMMES, Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, 38000 Grenoble, France
| | - Alan Le Goff
- Univ. Grenoble Alpes, CNRS, DCM, 38000 Grenoble, France
| | - Pascale Maldivi
- IRIG, SyMMES, Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, 38000 Grenoble, France
| | - Carole Duboc
- Univ. Grenoble Alpes, CNRS, DCM, 38000 Grenoble, France
| | - Pascale Delangle
- IRIG, SyMMES, Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, 38000 Grenoble, France
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3
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Sarkar P, Sarmah A, Mukherjee C. Where is the unpaired electron density? A combined experimental and theoretical finding on the geometric and electronic structures of the Co( iii) and Mn( iv) complexes of the unsymmetrical non-innocent pincer ONS ligand. Dalton Trans 2022; 51:16723-16732. [DOI: 10.1039/d2dt01868c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The geometry and electronic structures of the Co and Mn complexes of the pincer H3LONS ligand composed of both hard and soft donor atoms at the coordinating sites are reported.
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Affiliation(s)
- Prasenjit Sarkar
- Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati, 781039, Assam, India
| | - Amrit Sarmah
- Department of Molecular Modelling, Institute of Organic Chemistry and Biochemistry ASCR, v.v.i. Flemingovo nám. 2, CZ-166 10 Prague 6, Czech Republic
- Regional Centre of Advanced Technologies and Materials, Faculty of Science, Palacký University Olomouc, 78371 Olomouc, Czech Republic
| | - Chandan Mukherjee
- Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati, 781039, Assam, India
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4
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Dedushko MA, Pikul JH, Kovacs JA. Superoxide Oxidation by a Thiolate-Ligated Iron Complex and Anion Inhibition. Inorg Chem 2021; 60:7250-7261. [PMID: 33900756 DOI: 10.1021/acs.inorgchem.1c00336] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Superoxide (O2•-) is a toxic radical, generated via the adventitious reduction of dioxygen (O2), which has been implicated in a number of human disease states. Nonheme iron enzymes, superoxide reductase (SOR) and superoxide dismutase (SOD), detoxify O2•- via reduction to afford H2O2 and disproportionation to afford O2 and H2O2, respectively. The former contains a thiolate in the coordination sphere, which has been proposed to prevent O2•- oxidation to O2. The work described herein shows that, in contrast to this, oxidized thiolate-ligated [FeIII(SMe2N4(tren)(THF)]2+ (1ox-THF) is capable of oxidizing O2•- to O2. Coordinating anions, Cl- and OAc-, are shown to inhibit dioxygen evolution, implicating an inner-sphere mechanism. Previously we showed that the reduced thiolate-ligated [FeII(SMe2N4(tren))]+ (1) is capable of reducing O2•- via a proton-dependent inner-sphere mechanism involving a transient Fe(III)-OOH intermediate. A transient ferric-superoxo intermediate, [FeIII(SMe2N4(tren))(O2)]+ (3), is detected by electronic absorption spectroscopy at -130 °C in the reaction between 1ox-THF and KO2 and shown to evolve O2 upon slight warming to -115 °C. The DFT calculated O-O (1.306 Å) and Fe-O (1.943 Å) bond lengths of 3 are typical of ferric-superoxo complexes, and the time-dependent DFT calculated electronic absorption spectrum of 3 reproduces the experimental spectrum. The electronic structure of 3 is shown to consist of two antiferromagnetically coupled (Jcalc = -180 cm-1) unpaired electrons, one in a superoxo π*(O-O) orbital and the other in an antibonding π*(Fe(dyz)-S(py)) orbital.
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Affiliation(s)
- Maksym A Dedushko
- The Department of Chemistry, University of Washington: Box 351700, Seattle, Washington 98195-1700, United States
| | - Jessica H Pikul
- The Department of Chemistry, University of Washington: Box 351700, Seattle, Washington 98195-1700, United States
| | - Julie A Kovacs
- The Department of Chemistry, University of Washington: Box 351700, Seattle, Washington 98195-1700, United States
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5
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Ekanayake DM, Fischer AA, Elwood ME, Guzek AM, Lindeman SV, Popescu CV, Fiedler AT. Nonheme iron-thiolate complexes as structural models of sulfoxide synthase active sites. Dalton Trans 2020; 49:17745-17757. [PMID: 33241840 PMCID: PMC7781232 DOI: 10.1039/d0dt03403g] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Two mononuclear iron(ii)-thiolate complexes have been prepared that represent structural models of the nonheme iron enzymes EgtB and OvoA, which catalyze the O2-dependent formation of carbon-sulfur bonds in the biosynthesis of thiohistidine compounds. The series of Fe(ii) complexes reported here feature tripodal N4 chelates (LA and LB) that contain both pyridyl and imidazolyl donors (LA = (1H-imidazol-4-yl)-N,N-bis((pyridin-2-yl)methyl)methanamine; LB = N,N-bis((1-methylimidazol-2-yl)methyl)-2-pyridylmethylamine). Further coordination with monodentate aromatic or aliphatic thiolate ligands yielded the five-coordinate, high-spin Fe(ii) complexes [FeII(LA)(SMes)]BPh4 (1) and [FeII(LB)(SCy)]BPh4 (2), where SMes = 2,4,6-trimethylthiophenolate and SCy = cyclohexanethiolate. X-ray crystal structures revealed that 1 and 2 possess trigonal bipyramidal geometries formed by the N4S ligand set. In each case, the thiolate ligand is positioned cis to an imidazole donor, replicating the arrangement of Cys- and His-based substrates in the active site of EgtB. The geometric and electronic structures of 1 and 2 were analyzed with UV-vis absorption and Mössbauer spectroscopies in tandem with density functional theory (DFT) calculations. Exposure of 1 and 2 to nitric oxide (NO) yielded six-coordinate FeNO adducts that were characterized with infrared and electron paramagnetic resonance (EPR) spectroscopies, confirming that these complexes are capable of binding diatomic molecules. Reaction of 1 and 2 with O2 causes oxidation of the thiolate ligands to disulfide products. The implications of these results for the development of functional models of EgtB and OvoA are discussed.
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6
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Park H, Lee D. Ligand Taxonomy for Bioinorganic Modeling of Dioxygen-Activating Non-Heme Iron Enzymes. Chemistry 2020; 26:5916-5926. [PMID: 31909506 DOI: 10.1002/chem.201904975] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Revised: 01/04/2020] [Indexed: 12/15/2022]
Abstract
Novel functions emerge from novel structures. To develop efficient catalytic systems for challenging chemical transformations, chemists often seek inspirations from enzymatic catalysis. A large number of iron complexes supported by nitrogen-rich multidentate ligands have thus been developed to mimic oxo-transfer reactivity of dioxygen-activating metalloenzymes. Such efforts have significantly advanced our understanding of the reaction mechanisms by trapping key intermediates and elucidating their geometric and electronic properties. Critical to the success of this biomimetic approach is the design and synthesis of elaborate ligand systems to balance the thermodynamic stability, structural adaptability, and chemical reactivity. In this Concept article, representative design strategies for biomimetic atom-transfer chemistry are discussed from the perspectives of "ligand builders". Emphasis is placed on how the primary coordination sphere is constructed, and how it can be elaborated further by rational design for desired functions.
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Affiliation(s)
- Hyunchang Park
- Department of Chemistry, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Korea
| | - Dongwhan Lee
- Department of Chemistry, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Korea
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7
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Fischer AA, Miller JR, Jodts RJ, Ekanayake DM, Lindeman SV, Brunold TC, Fiedler AT. Spectroscopic and Computational Comparisons of Thiolate-Ligated Ferric Nonheme Complexes to Cysteine Dioxygenase: Second-Sphere Effects on Substrate (Analogue) Positioning. Inorg Chem 2019; 58:16487-16499. [PMID: 31789510 DOI: 10.1021/acs.inorgchem.9b02432] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Parallel spectroscopic and computational studies of iron(III) cysteine dioxygenase (CDO) and synthetic models are presented. The synthetic complexes utilize the ligand tris(4,5-diphenyl-1-methylimidazol-2-yl)phosphine (Ph2TIP), which mimics the facial three-histidine triad of CDO and other thiol dioxygenases. In addition to the previously reported [FeII(CysOEt)(Ph2TIP)]BPh4 (1; CysOEt is the ethyl ester of anionic l-cysteine), the formation and crystallographic characterization of [FeII(2-MTS)(Ph2TIP)]BPh4 (2) is reported, where the methyl 2-thiosalicylate anion (2-MTS) resembles the substrate of 3-mercaptopropionate dioxygenase (MDO). One-electron chemical oxidation of 1 and 2 yields ferric species that bind cyanide and azide anions, which have been used as spectroscopic probes of O2 binding in prior studies of FeIII-CDO. The six-coordinate FeIII-CN and FeIII-N3 adducts are examined with UV-vis absorption, electron paramagnetic resonance (EPR), and resonance Raman (rRaman) spectroscopies. In addition, UV-vis and rRaman studies of cysteine- and cyanide-bound FeIII-CDO are reported for both the wild-type (WT) enzyme and C93G variant, which lacks the Cys-Tyr cross-link that is present in the second coordination sphere of the WT active site. Density functional theory (DFT) and ab initio calculations are employed to provide geometric and electronic structure descriptions of the synthetic and enzymatic FeIII adducts. In particular, it is shown that the complete active space self-consistent field (CASSCF) method, in tandem with n-electron valence state second-order perturbation theory (NEVPT2), is capable of elucidating the structural basis of subtle shifts in EPR g values for low-spin FeIII species.
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Affiliation(s)
- Anne A Fischer
- Department of Chemistry , Marquette University , Milwaukee , Wisconsin 53201 , United States
| | - Joshua R Miller
- Department of Chemistry , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States
| | - Richard J Jodts
- Department of Chemistry , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States
| | - Danushka M Ekanayake
- Department of Chemistry , Marquette University , Milwaukee , Wisconsin 53201 , United States
| | - Sergey V Lindeman
- Department of Chemistry , Marquette University , Milwaukee , Wisconsin 53201 , United States
| | - Thomas C Brunold
- Department of Chemistry , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States
| | - Adam T Fiedler
- Department of Chemistry , Marquette University , Milwaukee , Wisconsin 53201 , United States
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8
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Gordon JB, McGale JP, Prendergast JR, Shirani-Sarmazeh Z, Siegler MA, Jameson GNL, Goldberg DP. Structures, Spectroscopic Properties, and Dioxygen Reactivity of 5- and 6-Coordinate Nonheme Iron(II) Complexes: A Combined Enzyme/Model Study of Thiol Dioxygenases. J Am Chem Soc 2018; 140:14807-14822. [PMID: 30346746 PMCID: PMC6596423 DOI: 10.1021/jacs.8b08349] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The synthesis of four new FeII(N4S(thiolate)) complexes as models of the thiol dioxygenases are described. They are composed of derivatives of the neutral, tridentate ligand triazacyclononane (R3TACN; R = Me, iPr) and 2-aminobenzenethiolate (abtx; X = H, CF3), a non-native substrate for thiol dioxygenases. The coordination number of these complexes depends on the identity of the TACN derivative, giving 6-coordinate (6-coord) complexes for FeII(Me3TACN)(abtx)(OTf) (1: X = H; 2: X = CF3) and 5-coordinate (5-coord) complexes for [FeII(iPr3TACN)(abtx)](OTf) (3: X = H; 4: X = CF3). Complexes 1-4 were examined by UV-vis, 1H/19F NMR, and Mössbauer spectroscopies, and density functional theory (DFT) calculations were employed to support the data. Mössbauer spectroscopy reveals that the 6-coord 1-2 and 5-coord 3- 4 exhibit distinct spectra, and these data are compared with that for cysteine-bound CDO, helping to clarify the coordination environment of the cys-bound FeII active site. Reaction of 1 or 2 with O2 at -95 °C leads to S-oxygenation of the abt ligand, and in the case of 2, a rare di(sulfinato)-bridged complex, [Fe2III(μ-O)((2-NH2) p-CF3C6H3SO2)2](OTf)2 ( 5), was obtained. Parallel enzymatic studies on the CDO variant C93G were carried out with the abt substrate and show that reaction with O2 leads to disulfide formation, as opposed to S-oxygenation. The combined model and enzyme studies show that the thiol dioxygenases can operate via a 6-coord FeII center, in contrast to the accepted mechanism for nonheme iron dioxygenases, and that proper substrate chelation to Fe appears to be critical for S-oxygenation.
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Affiliation(s)
- Jesse B Gordon
- Department of Chemistry , The Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States
- School of Chemistry , Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne , 30 Flemington Road , Parkville , Victoria 3010 , Australia
| | - Jeremy P McGale
- Department of Chemistry , The Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States
- School of Chemistry , Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne , 30 Flemington Road , Parkville , Victoria 3010 , Australia
| | - Joshua R Prendergast
- Department of Chemistry , The Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States
- School of Chemistry , Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne , 30 Flemington Road , Parkville , Victoria 3010 , Australia
| | - Zahra Shirani-Sarmazeh
- Department of Chemistry , The Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States
- School of Chemistry , Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne , 30 Flemington Road , Parkville , Victoria 3010 , Australia
| | - Maxime A Siegler
- Department of Chemistry , The Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States
- School of Chemistry , Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne , 30 Flemington Road , Parkville , Victoria 3010 , Australia
| | - Guy N L Jameson
- Department of Chemistry , The Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States
- School of Chemistry , Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne , 30 Flemington Road , Parkville , Victoria 3010 , Australia
| | - David P Goldberg
- Department of Chemistry , The Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States
- School of Chemistry , Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne , 30 Flemington Road , Parkville , Victoria 3010 , Australia
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9
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Klein JEMN, Mandal D, Ching WM, Mallick D, Que L, Shaik S. Privileged Role of Thiolate as the Axial Ligand in Hydrogen Atom Transfer Reactions by Oxoiron(IV) Complexes in Shaping the Potential Energy Surface and Inducing Significant H-Atom Tunneling. J Am Chem Soc 2017; 139:18705-18713. [PMID: 29179544 DOI: 10.1021/jacs.7b11300] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
An H/D kinetic isotope effect (KIE) of 80 is found at -20 °C for the oxidation of 9,10-dihydroanthracene by [FeIV(O)(TMCS)]+, a complex supported by the tetramethylcyclam (TMC) macrocycle with a tethered thiolate. This KIE value approaches that previously predicted by DFT calculations. Other [FeIV(O)(TMC)(anion)] complexes exhibit values of 20, suggesting that the thiolate ligand of [FeIV(O)(TMCS)]+ plays a unique role in facilitating tunneling. Calculations show that tunneling is most enhanced (a) when the bond asymmetry between C-H bond breaking and O-H bond formation in the transition state is minimized, and (b) when the electrostatic interactions in the O---H---C moiety are maximal. These two factors-which peak for the best electron donor, the thiolate ligand-afford a slim and narrow barrier through which the H-atom can tunnel most effectively.
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Affiliation(s)
- Johannes E M N Klein
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Debasish Mandal
- Institute of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem , 91904 Jerusalem, Israel
| | - Wei-Min Ching
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Dibyendu Mallick
- Institute of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem , 91904 Jerusalem, Israel
| | - Lawrence Que
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Sason Shaik
- Institute of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem , 91904 Jerusalem, Israel
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10
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Ching WM, Zhou A, Klein JEMN, Fan R, Knizia G, Cramer CJ, Guo Y, Que L. Characterization of the Fleeting Hydroxoiron(III) Complex of the Pentadentate TMC-py Ligand. Inorg Chem 2017; 56:11129-11140. [DOI: 10.1021/acs.inorgchem.7b01459] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
| | | | | | - Ruixi Fan
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Gerald Knizia
- Department
of Chemistry, Pennsylvania State University, 401A Chemistry Bldg; University Park, Pennsylvania 16802, United States
| | | | - Yisong Guo
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
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11
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Bigelow JO, England J, Klein JEMN, Farquhar ER, Frisch JR, Martinho M, Mandal D, Münck E, Shaik S, Que L. Oxoiron(IV) Tetramethylcyclam Complexes with Axial Carboxylate Ligands: Effect of Tethering the Carboxylate on Reactivity. Inorg Chem 2017; 56:3287-3301. [DOI: 10.1021/acs.inorgchem.6b02659] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jennifer O. Bigelow
- Department of Chemistry
and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Jason England
- Department of Chemistry
and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Johannes E. M. N. Klein
- Department of Chemistry
and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Erik R. Farquhar
- Department of Chemistry
and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Jonathan R. Frisch
- Department of Chemistry
and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Marlène Martinho
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Debasish Mandal
- Institute of Chemistry and the Lise Meitner-Minerva
Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel
| | - Eckard Münck
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Sason Shaik
- Institute of Chemistry and the Lise Meitner-Minerva
Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel
| | - Lawrence Que
- Department of Chemistry
and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, United States
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12
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Zhou A, Prakash J, Rohde GT, Klein JEMN, Kleespies ST, Draksharapu A, Fan R, Guo Y, Cramer CJ, Que L. The Two Faces of Tetramethylcyclam in Iron Chemistry: Distinct Fe-O-M Complexes Derived from [Fe IV(O anti/syn)(TMC)] 2+ Isomers. Inorg Chem 2017; 56:518-527. [PMID: 28001379 PMCID: PMC5293164 DOI: 10.1021/acs.inorgchem.6b02417] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Tetramethylcyclam (TMC, 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) exhibits two faces in supporting an oxoiron(IV) moiety, as exemplified by the prototypical [(TMC)FeIV(Oanti)(NCCH3)](OTf)2, where anti indicates that the O atom is located on the face opposite all four methyl groups, and the recently reported syn isomer [(TMC)FeIV(Osyn)(OTf)](OTf). The ability to access two isomers of [(TMC)FeIV(Oanti/syn)] raises the fundamental question of how ligand topology can affect the properties of the metal center. Previously, we have reported the formation of [(CH3CN)(TMC)FeIII-Oanti-CrIII(OTf)4(NCCH3)] (1) by inner-sphere electron transfer between Cr(OTf)2 and [(TMC)FeIV(Oanti)(NCCH3)](OTf)2. Herein we demonstrate that a new species 2 is generated from the reaction between Cr(OTf)2 and [(TMC)FeIV(Osyn)(NCCH3)](OTf)2, which is formulated as [(TMC)FeIII-Osyn-CrIII(OTf)4(NCCH3)] based on its characterization by UV-vis, resonance Raman, Mössbauer, and X-ray absorption spectroscopic methods, as well as electrospray mass spectrometry. Its pre-edge area (30 units) and Fe-O distance (1.77 Å) determined by X-ray absorption spectroscopy are distinctly different from those of 1 (11-unit pre-edge area and 1.81 Å Fe-O distance) but more closely resemble the values reported for [(TMC)FeIII-Osyn-ScIII(OTf)4(NCCH3)] (3, 32-unit pre-edge area and 1.75 Å Fe-O distance). This comparison suggests that 2 has a square pyramidal iron center like 3, rather than the six-coordinate center deduced for 1. Density functional theory calculations further validate the structures for 1 and 2. The influence of the distinct TMC topologies on the coordination geometries is further confirmed by the crystal structures of [(Cl)(TMC)FeIII-Oanti-FeIIICl3] (4Cl) and [(TMC)FeIII-Osyn-FeIIICl3](OTf) (5). Complexes 1-5 thus constitute a set of complexes that shed light on ligand topology effects on the coordination chemistry of the oxoiron moiety.
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Affiliation(s)
- Ang Zhou
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant Street Southeast, Minneapolis, Minnesota 55455, United States
| | - Jai Prakash
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant Street Southeast, Minneapolis, Minnesota 55455, United States
| | - Gregory T. Rohde
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant Street Southeast, Minneapolis, Minnesota 55455, United States
| | - Johannes E. M. N. Klein
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant Street Southeast, Minneapolis, Minnesota 55455, United States
| | - Scott T. Kleespies
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant Street Southeast, Minneapolis, Minnesota 55455, United States
| | - Apparao Draksharapu
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant Street Southeast, Minneapolis, Minnesota 55455, United States
| | - Ruixi Fan
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Yisong Guo
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Christopher J. Cramer
- Department of Chemistry, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota, 207 Pleasant Street Southeast, Minneapolis, Minnesota 55455, United States
| | - Lawrence Que
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant Street Southeast, Minneapolis, Minnesota 55455, United States
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Prakash J, Que L. Formation of the syn isomer of [FeIV(Oanti)(TMC)(NCMe)]2+ in the reaction of Lewis acids with the side-on bound peroxo ligand in [FeIII(η2-O2)(TMC)]+. Chem Commun (Camb) 2016; 52:8146-8. [DOI: 10.1039/c6cc01660j] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We demonstrate that the reactions of [FeIII(η2-O2)(TMC)]+ (TMC = tetramethylcyclam) with Lewis acids (H+ and NO+) afford the recently described syn isomer of [FeIV(O)(TMC)(NCMe)]2+ (and not the anti isomer as had been tacitly assumed).
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Affiliation(s)
- Jai Prakash
- Department of Chemistry and Centre for Metals in Biocatalysis
- University of Minnesota
- Minneapolis
- USA
| | - Lawrence Que
- Department of Chemistry and Centre for Metals in Biocatalysis
- University of Minnesota
- Minneapolis
- USA
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Prakash J, Rohde GT, Meier KK, Münck E, Que L. Upside Down! Crystallographic and Spectroscopic Characterization of an [Fe IV(O syn)(TMC)]2+ Complex. Inorg Chem 2015; 54:11055-7. [PMID: 26615667 DOI: 10.1021/acs.inorgchem.5b02011] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Fe(II)(TMC)(OTf)2 reacts with 2-(t)BuSO2-C6H4IO to afford an oxoiron(IV) product, 2, distinct from the previously reported [Fe(IV)(Oanti)(TMC)(NCMe)](2+). In MeCN, 2 has a blue-shifted near-IR band, a higher ν(Fe═O), a larger Mössbauer quadrupole splitting, and quite a distinct (1)H NMR spectrum. Structural analysis of crystals grown from CH2Cl2 reveals a complex with the formulation of [Fe(IV)(Osyn)(TMC)(OTf)](OTf) and the shortest Fe(IV)═O bond [1.625(4) Å] found to date.
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Affiliation(s)
- Jai Prakash
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Gregory T Rohde
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Katlyn K Meier
- Department of Chemistry, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
| | - Eckard Münck
- Department of Chemistry, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
| | - Lawrence Que
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota , Minneapolis, Minnesota 55455, United States
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Widger LR, Jiang Y, Siegler M, Kumar D, Latifi R, de Visser SP, Jameson GN, Goldberg DP. Synthesis and ligand non-innocence of thiolate-ligated (N4S) Iron(II) and nickel(II) bis(imino)pyridine complexes. Inorg Chem 2013; 52:10467-80. [PMID: 23992096 PMCID: PMC3827697 DOI: 10.1021/ic4013558] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The known iron(II) complex [Fe(II)(LN3S)(OTf)] (1) was used as starting material to prepare the new biomimetic (N4S(thiolate)) iron(II) complexes [Fe(II)(LN3S)(py)](OTf) (2) and [Fe(II)(LN3S)(DMAP)](OTf) (3), where LN3S is a tetradentate bis(imino)pyridine (BIP) derivative with a covalently tethered phenylthiolate donor. These complexes were characterized by X-ray crystallography, ultraviolet-visible (UV-vis) spectroscopic analysis, (1)H nuclear magnetic resonance (NMR), and Mössbauer spectroscopy, as well as electrochemistry. A nickel(II) analogue, [Ni(II)(LN3S)](BF4) (5), was also synthesized and characterized by structural and spectroscopic methods. Cyclic voltammetric studies showed 1-3 and 5 undergo a single reduction process with E(1/2) between -0.9 V to -1.2 V versus Fc(+)/Fc. Treatment of 3 with 0.5% Na/Hg amalgam gave the monoreduced complex [Fe(LN3S)(DMAP)](0) (4), which was characterized by X-ray crystallography, UV-vis spectroscopic analysis, electron paramagnetic resonance (EPR) spectroscopy (g = [2.155, 2.057, 2.038]), and Mössbauer (δ = 0.33 mm s(-1); ΔE(Q) = 2.04 mm s(-1)) spectroscopy. Computational methods (DFT) were employed to model complexes 3-5. The combined experimental and computational studies show that 1-3 are 5-coordinate, high-spin (S = 2) Fe(II) complexes, whereas 4 is best described as a 5-coordinate, intermediate-spin (S = 1) Fe(II) complex antiferromagnetically coupled to a ligand radical. This unique electronic configuration leads to an overall doublet spin (S(total) = 1/2) ground state. Complexes 2 and 3 are shown to react with O2 to give S-oxygenated products, as previously reported for 1. In contrast, the monoreduced 4 appears to react with O2 to give a mixture of sulfur oxygenates and iron oxygenates. The nickel(II) complex 5 does not react with O2, and even when the monoreduced nickel complex is produced, it appears to undergo only outer-sphere oxidation with O2.
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Affiliation(s)
- Leland R. Widger
- Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
| | - Yunbo Jiang
- Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
| | - Maxime Siegler
- Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
| | - Devesh Kumar
- Department of Applied Physics, School for Physical Sciences, Babasaheb Bhimrao Ambedkar University, Vidya Vihar, Rae Bareilly Road, Lucknow (U. P.) 226 025, India
| | - Reza Latifi
- Manchester Institute of Biotechnology and School of Chemical Engineering and Analytical Science, The University of Manchester, 131 Princess Street, Manchester M1 7DN, United Kingdom
| | - Sam P. de Visser
- Manchester Institute of Biotechnology and School of Chemical Engineering and Analytical Science, The University of Manchester, 131 Princess Street, Manchester M1 7DN, United Kingdom
| | - Guy N.L. Jameson
- Department of Chemistry & MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Otago, PO Box 56, Dunedin 9054, New Zealand
| | - David P. Goldberg
- Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
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Metal vs. chalcogen competition in the catalytic mechanism of cysteine dioxygenase. J Inorg Biochem 2013; 122:1-7. [DOI: 10.1016/j.jinorgbio.2013.01.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2012] [Revised: 12/25/2012] [Accepted: 01/11/2013] [Indexed: 11/18/2022]
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McDonald AR, Van Heuvelen KM, Guo Y, Li F, Bominaar EL, Münck E, Que L. Characterization of a thiolato iron(III) Peroxy dianion complex. Angew Chem Int Ed Engl 2012; 51:9132-6. [PMID: 22888066 PMCID: PMC3448492 DOI: 10.1002/anie.201203602] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2012] [Revised: 06/19/2012] [Indexed: 11/09/2022]
Abstract
Nucleophilic oxidant: The reaction between a thiolato iron(II) complex 1 and superoxide in aprotic solvent at -90 °C yields a novel thiolato iron(III) peroxide intermediate 2, which exhibits unusually high nucleophilic reactivity. Compound 2 is an isomer of the thiolato iron(II) superoxide intermediate that is invoked in the reaction between superoxide reductase and superoxide.
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Affiliation(s)
- Aidan R. McDonald
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, MN 55455, USA
| | - Katherine M. Van Heuvelen
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, MN 55455, USA
| | - Yisong Guo
- Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA 15213, USA
| | - Feifei Li
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, MN 55455, USA
| | - Emile L. Bominaar
- Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA 15213, USA
| | - Eckard Münck
- Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA 15213, USA
| | - Lawrence Que
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, MN 55455, USA
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18
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McDonald AR, Van Heuvelen KM, Guo Y, Li F, Bominaar EL, Münck E, Que L. Characterization of a Thiolato Iron(III) Peroxy Dianion Complex. Angew Chem Int Ed Engl 2012. [DOI: 10.1002/ange.201203602] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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19
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Wilson SA, Chen J, Hong S, Lee YM, Clémancey M, Garcia-Serres R, Nomura T, Ogura T, Latour JM, Hedman B, Hodgson KO, Nam W, Solomon EI. [Fe(IV)═O(TBC)(CH3CN)]2+: comparative reactivity of iron(IV)-oxo species with constrained equatorial cyclam ligation. J Am Chem Soc 2012; 134:11791-806. [PMID: 22708532 DOI: 10.1021/ja3046298] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
[Fe(IV)═O(TBC)(CH(3)CN)](2+) (TBC = 1,4,8,11-tetrabenzyl-1,4,8,11-tetraazacyclotetradecane) is characterized, and its reactivity differences relative to [Fe(IV)═O(TMC)(CH(3)CN)](2+) (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) are evaluated in hydrogen atom (H-atom) abstraction and oxo-transfer reactions. Structural differences are defined using X-ray absorption spectroscopy and correlated to reactivities using density functional theory. The S = 1 ground states are highly similar and result in large activation barriers (~25 kcal/mol) due to steric interactions between the cyclam chelate and the substrate (e.g., ethylbenzene) associated with the equatorial π-attack required by this spin state. Conversely, H-atom abstraction reactivity on an S = 2 surface allows for a σ-attack with an axial substrate approach. This results in decreased steric interactions with the cyclam and a lower barrier (~9 kcal/mol). For [Fe(IV)═O(TBC)(CH(3)CN)](2+), the S = 2 excited state in the reactant is lower in energy and therefore more accessible at the transition state due to a weaker ligand field associated with the steric interactions of the benzyl substituents with the trans-axial ligand. This study is further extended to the oxo-transfer reaction, which is a two-electron process requiring both σ- and π-electron transfer and thus a nonlinear transition state. In oxo-transfer, the S = 2 has a lower barrier due to sequential vs concerted (S = 1) two electron transfer which gives a high-spin ferric intermediate at the transition state. The [Fe(IV)═O(TBC)(CH(3)CN)](2+) complex is more distorted at the transition state, with the iron farther out of the equatorial plane due to the steric interaction of the benzyl groups with the trans-axial ligand. This allows for better orbital overlap with the substrate, a lower barrier, and an increased rate of oxo-transfer.
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Affiliation(s)
- Samuel A Wilson
- Department of Chemistry, Stanford University, Stanford, California 94305, USA
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Rearrangement of the Tris(2-pyridylthio)methanido Ligand in an Iron(II) Complex Containing an Fe−C Bond. Inorg Chem 2010; 50:708-10. [DOI: 10.1021/ic101913p] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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21
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McDonald AR, Bukowski MR, Farquhar ER, Jackson TA, Koehntop KD, Seo MS, De Hont RF, Stubna A, Halfen JA, Münck E, Nam W, Que L. Sulfur versus iron oxidation in an iron-thiolate model complex. J Am Chem Soc 2010; 132:17118-29. [PMID: 21070030 DOI: 10.1021/ja1045428] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In the absence of base, the reaction of [Fe(II)(TMCS)]PF6 (1, TMCS = 1-(2-mercaptoethyl)-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane) with peracid in methanol at -20 °C did not yield the oxoiron(IV) complex (2, [Fe(IV)(O)(TMCS)]PF6), as previously observed in the presence of strong base (KO(t)Bu). Instead, the addition of 1 equiv of peracid resulted in 50% consumption of 1. The addition of a second equivalent of peracid resulted in the complete consumption of 1 and the formation of a new species 3, as monitored by UV-vis, ESI-MS, and Mössbauer spectroscopies. ESI-MS showed 3 to be formulated as [Fe(II)(TMCS) + 2O](+), while EXAFS analysis suggested that 3 was an O-bound iron(II)-sulfinate complex (Fe-O = 1.95 Å, Fe-S = 3.26 Å). The addition of a third equivalent of peracid resulted in the formation of yet another compound, 4, which showed electronic absorption properties typical of an oxoiron(IV) species. Mössbauer spectroscopy confirmed 4 to be a novel iron(IV) compound, different from 2, and EXAFS (Fe═O = 1.64 Å) and resonance Raman (ν(Fe═O) = 831 cm(-1)) showed that indeed an oxoiron(IV) unit had been generated in 4. Furthermore, both infrared and Raman spectroscopy gave indications that 4 contains a metal-bound sulfinate moiety (ν(s)(SO2) ≈ 1000 cm (-1), ν(as)(SO2) ≈ 1150 cm (-1)). Investigations into the reactivity of 1 and 2 toward H(+) and oxygen atom transfer reagents have led to a mechanism for sulfur oxidation in which 2 could form even in the absence of base but is rapidly protonated to yield an oxoiron(IV) species with an uncoordinated thiol moiety that acts as both oxidant and substrate in the conversion of 2 to 3.
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Affiliation(s)
- Aidan R McDonald
- Department of Chemistry and Center for Metals in Biocatalysis, 207 Pleasant Street SE, University of Minnesota, Minneapolis, Minnesota 55455, USA
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Li F, England J, Que L. Near-stoichiometric conversion of H(2)O(2) to Fe(IV)=O at a nonheme iron(II) center. Insights into the O-O bond cleavage step. J Am Chem Soc 2010; 132:2134-5. [PMID: 20121136 DOI: 10.1021/ja9101908] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Near-quantitative formation of an oxoiron(IV) intermediate [Fe(IV)(O)(TMC)(CH(3)CN)](2+) (2) from stoichiometric H(2)O(2) was achieved with [Fe(II)(TMC)](2+) (1) (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraaza-cyclotetradecane). This important outcome is best rationalized by invoking a direct reaction between 1 and H(2)O(2) followed by a heterolytic O-O bond cleavage facilitated by an acid-base catalyst (2,6-lutidine in our case). A sizable H/D KIE of 3.7 was observed for the formation of 2, emphasizing the importance of proton transfer in the cleavage step. Pyridines with different pK(a) values were also investigated, and less basic pyridines were found to function less effectively than 2,6-lutidine. This study demonstrates that the reaction of Fe(II) with H(2)O(2) to form Fe(IV)= O can be quite facile. Two factors promote the near-stoichiometric conversion of H(2)O(2) to Fe(IV)=O in this case: (a) the low reactivity between 1 and 2 and (b) the poor H-atom abstracting ability of 2, which inhibits subsequent reaction with residual H(2)O(2). Both factors inhibit formation of the Fe(III) byproduct commonly found in reactions of Fe(II) complexes with H(2)O(2). These results may shed light into the nature of the O-O bond cleaving step in the activation of dioxygen by nonheme iron enzymes and in the first step of the Fenton reaction.
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Affiliation(s)
- Feifei Li
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, USA
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Namuswe F, Hayashi T, Jiang Y, Kasper GD, Sarjeant AAN, Moënne-Loccoz P, Goldberg DP. Influence of the nitrogen donors on nonheme iron models of superoxide reductase: high-spin Fe(III)-OOR complexes. J Am Chem Soc 2010; 132:157-67. [PMID: 20000711 DOI: 10.1021/ja904818z] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A new five-coordinate, (N(4)S(thiolate))Fe(II) complex, containing tertiary amine donors, [Fe(II)(Me(4)[15]aneN(4))(SPh)]BPh(4) (2), was synthesized and structurally characterized as a model of the reduced active site of superoxide reductase (SOR). Reaction of 2 with tert-butyl hydroperoxide (tBuOOH) at -78 degrees C led to the generation of the alkylperoxo-iron(III) complex [Fe(III)(Me(4)[15]aneN(4))(SPh)(OOtBu)](+) (2a). The nonthiolate-ligated complex, [Fe(II)(Me(4)[15]aneN(4))(OTf)(2)] (3), was also reacted with tBuOOH and yielded the corresponding alkylperoxo complex [Fe(III)(Me(4)[15]aneN(4))(OTf)(OOtBu)](+) (3a) at an elevated temperature of -23 degrees C. These species were characterized by low-temperature UV-vis, EPR, and resonance Raman spectroscopies. Complexes 2a and 3a exhibit distinctly different spectroscopic signatures than the analogous alkylperoxo complexes [Fe(III)([15]aneN(4))(SAr)(OOR)](+), which contain secondary amine donors. Importantly, alkylation at nitrogen leads to a change from low-spin (S = 1/2) to high-spin (S = 5/2) of the iron(III) center. The resonance Raman data reveal that this change in spin state has a large effect on the nu(Fe-O) and nu(O-O) vibrations, and a comparison between 2a and the nonthiolate-ligated complex 3a shows that axial ligation has an additional significant impact on these vibrations. To our knowledge this study is the first in which the influence of a ligand trans to a peroxo moiety has been evaluated for a structurally equivalent pair of high-spin/low-spin peroxo-iron(III) complexes. The implications of spin state and thiolate ligation are discussed with regard to the functioning of SOR.
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Affiliation(s)
- Frances Namuswe
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA
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Ray K, England J, Fiedler AT, Martinho M, Münck E, Que L. An inverted and more oxidizing isomer of [Fe(IV)(O)(tmc)(NCCH3)]2+. Angew Chem Int Ed Engl 2008; 47:8068-71. [PMID: 18798182 DOI: 10.1002/anie.200802219] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Kallol Ray
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, MN 55455, USA
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Namuswe F, Kasper GD, Sarjeant AAN, Hayashi T, Krest CM, Green MT, Moënne-Loccoz P, Goldberg DP. Rational tuning of the thiolate donor in model complexes of superoxide reductase: direct evidence for a trans influence in Fe(III)-OOR complexes. J Am Chem Soc 2008; 130:14189-200. [PMID: 18837497 DOI: 10.1021/ja8031828] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Iron peroxide species have been identified as important intermediates in a number of nonheme iron as well as heme-containing enzymes, yet there are only a few examples of such species either synthetic or biological that have been well characterized. We describe the synthesis and structural characterization of a new series of five-coordinate (N4S(thiolate))Fe(II) complexes that react with tert-butyl hydroperoxide ((t)BuOOH) or cumenyl hydroperoxide (CmOOH) to give metastable alkylperoxo-iron(III) species (N4S(thiolate)Fe(III)-OOR) at low temperature. These complexes were designed specifically to mimic the nonheme iron active site of superoxide reductase, which contains a five-coordinate iron(II) center bound by one Cys and four His residues in the active form of the protein. The structures of the Fe(II) complexes are analyzed by X-ray crystallography, and their electrochemical properties are assessed by cyclic voltammetry. For the Fe(III)-OOR species, low-temperature UV-vis spectra reveal intense peaks between 500-550 nm that are typical of peroxide to iron(III) ligand-to-metal charge-transfer (LMCT) transitions, and EPR spectroscopy shows that these alkylperoxo species are all low-spin iron(III) complexes. Identification of the vibrational modes of the Fe(III)-OOR unit comes from resonance Raman (RR) spectroscopy, which shows nu(Fe-O) modes between 600-635 cm(-1) and nu(O-O) bands near 800 cm(-1). These Fe-O stretching frequencies are significantly lower than those found in other low-spin Fe(III)-OOR complexes. Trends in the data conclusively show that this weakening of the Fe-O bond arises from a trans influence of the thiolate donor, and density functional theory (DFT) calculations support these findings. These results suggest a role for the cysteine ligand in SOR, and are discussed in light of the recent assessments of the function of the cysteine ligand in this enzyme.
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Affiliation(s)
- Frances Namuswe
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA
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27
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Ray K, England J, Fiedler A, Martinho M, Münck E, Que L. An Inverted and More Oxidizing Isomer of [FeIV(O)(tmc)(NCCH3)]2+. Angew Chem Int Ed Engl 2008. [DOI: 10.1002/ange.200802219] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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28
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Ganyushin D, Neese F. First-principles calculations of magnetic circular dichroism spectra. J Chem Phys 2008; 128:114117. [DOI: 10.1063/1.2894297] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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29
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Axial ligand tuning of a nonheme iron(IV)-oxo unit for hydrogen atom abstraction. Proc Natl Acad Sci U S A 2007; 104:19181-6. [PMID: 18048327 DOI: 10.1073/pnas.0709471104] [Citation(s) in RCA: 343] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The reactivities of mononuclear nonheme iron(IV)-oxo complexes bearing different axial ligands, [Fe(IV)(O)(TMC)(X)](n+) [where TMC is 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane and X is NCCH(3) (1-NCCH(3)), CF(3)COO(-) (1-OOCCF(3)), or N(3)(-) (1-N(3))], and [Fe(IV)(O)(TMCS)](+) (1'-SR) (where TMCS is 1-mercaptoethyl-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane), have been investigated with respect to oxo-transfer to PPh(3) and hydrogen atom abstraction from phenol O H and alkylaromatic C H bonds. These reactivities were significantly affected by the identity of the axial ligands, but the reactivity trends differed markedly. In the oxidation of PPh(3), the reactivity order of 1-NCCH(3) > 1-OOCCF(3) > 1-N(3) > 1'-SR was observed, reflecting a decrease in the electrophilicity of iron(IV)-oxo unit upon replacement of CH(3)CN with an anionic axial ligand. Surprisingly, the reactivity order was inverted in the oxidation of alkylaromatic C H and phenol O H bonds, i.e., 1'-SR > 1-N(3) > 1-OOCCF(3) > 1-NCCH(3). Furthermore, a good correlation was observed between the reactivities of iron(IV)-oxo species in H atom abstraction reactions and their reduction potentials, E(p,c), with the most reactive 1'-SR complex exhibiting the lowest potential. In other words, the more electron-donating the axial ligand is, the more reactive the iron(IV)-oxo species becomes in H atom abstraction. Quantum mechanical calculations show that a two-state reactivity model applies to this series of complexes, in which a triplet ground state and a nearby quintet excited-state both contribute to the reactivity of the complexes. The inverted reactivity order in H atom abstraction can be rationalized by a decreased triplet-quintet gap with the more electron-donating axial ligand, which increases the contribution of the much more reactive quintet state and enhances the overall reactivity.
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Kitagawa T, Dey A, Lugo-Mas P, Benedict JB, Kaminsky W, Solomon E, Kovacs JA. A functional model for the cysteinate-ligated non-heme iron enzyme superoxide reductase (SOR). J Am Chem Soc 2007; 128:14448-9. [PMID: 17090014 PMCID: PMC2532059 DOI: 10.1021/ja064870d] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Superoxide reductases (SORs) are cysteine-ligated, non-heme iron enzymes that reduce toxic superoxide radicals (O2-). The functional role of the trans cysteinate, as well as the mechanism by which SOR reduces O2-, is unknown. Herein is described a rare example of a functional metalloenzyme analogue, which catalytically reduces superoxide in a proton-dependent mechanism, via a trans thiolate-ligated iron-peroxo intermediate, the first example of its type. Acetic-acid-promoted H2O2 release, followed by Cp2Co reduction, regenerates the active Fe(II) catalyst. The thiolate ligand and its trans positioning relative to the substrate are shown to contribute significantly to the catalyst's function, by lowering the redox potential, changing the spin state, and dramatically lowering the nuFe-O stretching frequency well-below that of any other reported iron-peroxo, while leaving nuO-O high, so as to favor superoxide reduction and Fe-O, as opposed to O-O, bond cleavage. Thus we provide critical insight into the relationship between the SOR structure and its function, as well as important benchmark parameters for characterizing highly unstable thiolate-ligated iron-peroxo intermediates.
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Electronic structure of dinuclear iron nitrosyl complexes with different ligands at two iron centers. Polyhedron 2007. [DOI: 10.1016/j.poly.2007.03.021] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Kovacs JA, Brines LM. Understanding how the thiolate sulfur contributes to the function of the non-heme iron enzyme superoxide reductase. Acc Chem Res 2007; 40:501-9. [PMID: 17536780 PMCID: PMC3703784 DOI: 10.1021/ar600059h] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Toxic superoxide radicals, generated via adventitious reduction of dioxygen, have been implicated in a number of disease states. The cysteinate-ligated non-heme iron enzyme superoxide reductase (SOR) degrades superoxide via reduction. Biomimetic analogues which provide insight into why nature utilizes a trans-thiolate to promote SOR function are described. Spectroscopic and/or structural characterization of the first examples of thiolate-ligated Fe (III)-peroxo complexes provides important benchmark parameters for the identification of biological intermediates. Oxidative addition of superoxide is favored by low redox potentials. The trans influence of the thiolate appears to significantly weaken the Fe-O peroxo bond, favoring proton-induced release of H 2O 2 from a high-spin Fe(III)-OOH complex.
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Affiliation(s)
- Julie A Kovacs
- The Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195-1700, USA
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Abstract
Oxoiron(IV) species are often implicated in the catalytic cycles of oxygen-activating non-heme iron enzymes. The paucity of suitable model complexes stimulated us to fill this void, and our synthetic efforts have afforded a number of oxoiron(IV) complexes. This Account provides a chronological perspective of the observations that contributed to the generation of the first non-heme iron(IV)-oxo complexes in high yield and summarizes their salient properties to date.
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Affiliation(s)
- Lawrence Que
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, USA
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Fiedler AT, Brunold TC. Spectroscopic and Computational Studies of Ni3+ Complexes with Mixed S/N Ligation: Implications for the Active Site of Nickel Superoxide Dismutase. Inorg Chem 2007; 46:8511-23. [PMID: 17305331 DOI: 10.1021/ic061237k] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Both Ni-containing superoxide dismutase (NiSOD) and NiFe hydrogenases feature thiolate-rich active sites that are capable of stabilizing the Ni3+ oxidation state in catalytically relevant species. In an effort to better understand the role of Ni(3+)-S bonding interactions in these metalloenzymes, we have employed various spectroscopic and computational methods to probe the geometric and electronic structures of three Ni(3+) complexes with mixed S/N ligation: [Ni(3+)(pdtc)(2)]- (1), [Ni(3+)(emb)]- (2), and [Ni(3+)(ema)]- (3) [where pdtc is pyridine-2,6-bis(monothiocarboxylate) and emb and ema are the tetraanions of N,N'-ethylenebis(o-mercaptobenzamide) and N,N'-ethylenebis(2-mercaptoacetamide), respectively]. Each complex has been examined with electronic absorption, magnetic circular dichroism, electron paramagnetic resonance, and resonance Raman (rR) spectroscopies. Detailed assignments of the features observed in the corresponding spectra have been established within the framework of density functional theory calculations that provide remarkably accurate reproductions of the absorption spectra, g values, and vibrational frequencies. Collectively, our spectroscopic and computational studies have yielded experimentally validated electronic-structure descriptions for 1-3 that provide significant insights into the nature of the Ni(3+)-S bonding interactions. Additionally, the results obtained in these studies reveal that the thermochromism observed for 2 is due to the formation of a dimeric species at reduced temperatures, the structure of which has been determined through computational analysis of viable dimer models. Finally, we have employed the framework established in our spectroscopic and computational studies of the Ni(3+) models to carry out a detailed analysis of our rR data of NiSOD obtained previously. Our results indicate that the Ni(3+)-S bonds in oxidized NiSOD are significantly stronger than those in 1-3 due to the unique mixed amine/amide ligation that is present at the enzyme active site.
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Affiliation(s)
- Adam T Fiedler
- Department of Chemistry, University of Wisconsin-Madison, 1101 W. University Avenue, Madison, Wisconsin 53706, USA
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Brines LM, Kovacs JA. Understanding the Mechanism of Superoxide Reductase Promoted Reduction of Superoxide. Eur J Inorg Chem 2006. [DOI: 10.1002/ejic.200600461] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Lisa M. Brines
- Department of Chemistry, University of Washington, Box 351700, Seattle, WA 98195, USA, Fax: +1‐206‐685‐8665
| | - Julie A. Kovacs
- Department of Chemistry, University of Washington, Box 351700, Seattle, WA 98195, USA, Fax: +1‐206‐685‐8665
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Synthesis and Characterization of Mononuclear Octahedral Fe(III) Complex Containing a Biomimetic Tripodal Ligand, N-(Benzimidazol-2-ylmethyl)iminodiacetic Acid. B KOREAN CHEM SOC 2006. [DOI: 10.5012/bkcs.2006.27.10.1597] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Suh Y, Seo MS, Kim KM, Kim YS, Jang HG, Tosha T, Kitagawa T, Kim J, Nam W. Nonheme iron(II) complexes of macrocyclic ligands in the generation of oxoiron(IV) complexes and the catalytic epoxidation of olefins. J Inorg Biochem 2006; 100:627-33. [PMID: 16458358 DOI: 10.1016/j.jinorgbio.2005.12.013] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2005] [Accepted: 12/13/2005] [Indexed: 11/22/2022]
Abstract
Mononuclear nonheme oxoiron(IV) complexes bearing 15-membered macrocyclic ligands were generated from the reactions of their corresponding iron(II) complexes and iodosylbenzene (PhIO) in CH(3)CN. The oxoiron(IV) species were characterized with various spectroscopic techniques such as UV-vis spectrophotometer, electron paramagnetic resonance, electrospray ionization mass spectrometer, and resonance Raman spectroscopy. The oxoiron(IV) complexes were inactive in olefin epoxidation. In contrast, when iron(II) or oxoiron(IV) complexes were combined with PhIO in the presence of olefins, high yields of epoxide products were obtained. These results indicate that in addition to the oxoiron(IV) species, there must be at least one more active oxidant (e.g., Fe(IV)-OIPh adduct or oxoiron(V) species) that effects the olefin epoxidation. We have also demonstrated that the ligand environment of iron catalysts is an important factor in controlling the catalytic activity as well as the product selectivity in the epoxidation of olefins by PhIO.
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Affiliation(s)
- Yumi Suh
- Department of Chemistry, Division of Nano Sciences, and Center for Biomimetic Systems, Ewha Womans University, Seoul 120-750, Republic of Korea
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Maganas D, Staniland SS, Grigoropoulos A, White F, Parsons S, Robertson N, Kyritsis P, Pneumatikakis G. Structural, spectroscopic and magnetic properties of M[R2P(E)NP(E)R′2]2complexes, M = Co, Mn, E = S, Se and R, R′ = Ph oriPr. Covalency of M–S bonds from experimental data and theoretical calculations. Dalton Trans 2006:2301-15. [PMID: 16688318 DOI: 10.1039/b517938f] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The S/Se-containing bidentate ligands LH of the type R2P(E)NHP(E)R'2, E = S, Se and R, R' = Ph or iPr have been employed to synthesize ML2 (M = Mn, Co) complexes which contain the biologically important MS4 core. Theoretical calculations on the LH and L- forms of the ligands probe the geometric and electronic changes induced by the deprotonation of the LH form, which are correlated with structural data from X-ray crystallography. These results reflect the flexibility of the ligands, which enables them to be rather versatile with respect to the formation of ML2 complexes with varied geometries and MEPNPE metallacycle conformations. A series of old and new ML2 complexes have been synthesized and their structural, spectroscopic and magnetic properties characterized in detail. The nephelauxetic ratio beta of the CoL2 complexes provides evidence of covalent interactions, whereas the EPR properties of the MnL2 complexes are interpreted on the basis of predominant ionic interactions, between the metal center and the ligands, respectively. Additional evidence for the existence of covalent interactions in the CoL2 complexes (R = Ph, iPr, or mixed Ph/iPr), is offered by comparisons between their 31P NMR. The aforementioned notations are supported by extensive theoretical calculations on the ML2 (E = S, R = Me) modelled structures, which probe the covalent and ionic character of the M-S bonds when M = Co or Mn. Wider implications of the findings of the present study on the M-S covalency and its importance in the active sites of various metalloenzymes are also discussed.
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Affiliation(s)
- Dimitrios Maganas
- Inorganic Chemistry Laboratory, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis, GR-157 71 Athens, Greece
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Krishnamurthy D, Sarjeant AN, Goldberg DP, Caneschi A, Totti F, Zakharov LN, Rheingold AL. Mononuclear, Dinuclear, and Pentanuclear [{N,S(thiolate)}Iron(II)] Complexes: Nuclearity Control, Incorporation of Hydroxide Bridging Ligands, and Magnetic Behavior. Chemistry 2005; 11:7328-41. [PMID: 16144021 DOI: 10.1002/chem.200500156] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The mixed N3S(thiolate) ligand 1-[bis[2-(pyridin-2-yl)ethyl]amino]-2-methylpropane-2-thiol (Py2SH) was used in the synthesis of four iron(II) complexes: [(Py2S)FeCl] (1), [(Py2S)FeBr] (2), [(Py2S)4Fe5II(mu-OH)2](BF4)4 (3), and [(Py2S)2Fe2II(mu-OH)]BF4 (4). The X-ray structures of 1 and 2 revealed monomeric iron(II)-alkylthiolate complexes with distorted trigonal-bipyramidal geometries. The paramagnetic 1H NMR spectra of 1 and 2 display resonances from delta = -25 ppm to +100 ppm, consistent with a high-spin iron(II) ion (S = 2). Spectral assignments were made on the basis of chemical shift information and T1 measurements and show the monomeric structures are intact in solution. To provide entry into hydroxide-containing complexes, a novel synthetic method was developed involving strict aprotic conditions and limiting amounts of H2O. Reaction of Py2SH with NaH and Fe(BF4)2.6 H2O under aprotic conditions led to the isolation of the pentanuclear, mu-OH complex 3, which has a novel dimer-of-dimers type structure connected by a central iron atom. Conductivity data on 3 show this structure is retained in CH2Cl2. Rational modification of the ligand-to-metal ratio allows control over the nuclearity of the product, yielding the dinuclear complex 4. The X-ray structure of 4 reveals an unprecedented face-sharing, biooctahedral complex with an [S2O] bridging arrangement. The magnetic properties of 3 and 4 in the range 1.9-300 K were successfully modeled. Dinuclear 4 is antiferromagnetically coupled [J = -18.8(2) cm(-1)]. Pentanuclear 3 exhibits ferrimagnetic behavior, with a high-spin ground state of S(T) = 6, and was best modeled with three different exchange parameters [J = -15.3(2), J' = -24.7(3), and J'' = -5.36(7) cm(-1)]. DFT calculations provided good support for the interpretation of the magnetic properties.
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Affiliation(s)
- Divya Krishnamurthy
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA
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Bukowski MR, Koehntop KD, Stubna A, Bominaar EL, Halfen JA, Münck E, Nam W, Que L. A Thiolate-Ligated Nonheme Oxoiron(IV) Complex Relevant to Cytochrome P450. Science 2005; 310:1000-2. [PMID: 16254150 DOI: 10.1126/science.1119092] [Citation(s) in RCA: 219] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Thiolate-ligated oxoiron(IV) centers are postulated to be the key oxidants in the catalytic cycles of oxygen-activating cytochrome P450 and related enzymes. Despite considerable synthetic efforts, chemists have not succeeded in preparing an appropriate model complex. Here we report the synthesis and spectroscopic characterization of [FeIV(O)(TMCS)]+ where TMCS is a pentadentate ligand that provides a square pyramidal N4(SR)apical, where SR is thiolate, ligand environment about the iron center, which is similar to that of cytochrome P450. The rigidity of the ligand framework stabilizes the thiolate in an oxidizing environment. Reactivity studies suggest that thiolate coordination favors hydrogen-atom abstraction chemistry over oxygen-atom transfer pathways in the presence of reducing substrates.
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Affiliation(s)
- Michael R Bukowski
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, MN 55455, USA
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