1
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Atta S, Mandal A, Saha R, Majumdar A. Reduction of nitrite to nitric oxide and generation of reactive chalcogen species by mononuclear Fe(II) and Zn(II) complexes of thiolate and selenolate. Dalton Trans 2024; 53:949-965. [PMID: 38126213 DOI: 10.1039/d3dt03768a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2023]
Abstract
Comparative reactivity of a series of new Zn(II) and Fe(II) compounds, [(Py2ald)M(ER)] (E = S, R = Ph: M = Zn, 1aZn; M = Fe, 1aFe; E = S, R = 2,6-Me2-C6H3: M = Zn, 1bZn; M = Fe, 1bFe; E = Se, R = Ph: M = Zn, 2Zn; M = Fe, 2Fe), and [(Py2ald)M]22+ (M = Zn, 5Zn; M = Fe, 5Fe) is presented. Compound 1aZn could react with nitrite (NO2-) to produce [(Py2ald)Zn(ONO)] (3Zn), which, upon treatment with thiols and PhSeH (proton source), could regenerate either 1aZn/5Zn and 2Zn respectively, along with the production of nitric oxide (NO) where the yield of NO increases in the order tBuSH ≪ PhCH2SH < PhSH < PhSeH. In contrast to this, 1aFe, 2Fe and 5Fe could affect the direct reduction of NO2- in the absence of protons to generate NO and [{(Py2ald)(ONO)Fe}2-μ2-O] (8Fe). Moreover, 8Fe could regenerate 5Fe and 1aFe/2Fe upon treatment with 4 and 6 equiv. of PhEH (E = S/Se), respectively, along with the generation of NO. Finally, a comparative study of the mononuclear Zn(II) and Fe(II) compounds for the transfer of the coordinated thiolate/selenolate and the generation and transfer of reactive sulfur/selenium species (RES-, E = Se, S) to a series of organic substrates has been provided.
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Affiliation(s)
- Sayan Atta
- School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Kolkata 700032, West Bengal, India.
| | - Amit Mandal
- School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Kolkata 700032, West Bengal, India.
| | - Rahul Saha
- School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Kolkata 700032, West Bengal, India.
| | - Amit Majumdar
- School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Kolkata 700032, West Bengal, India.
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2
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Dedushko MA, Greiner MB, Downing AN, Coggins M, Kovacs JA. Electronic Structure and Reactivity of Dioxygen-Derived Aliphatic Thiolate-Ligated Fe-Peroxo and Fe(IV) Oxo Compounds. J Am Chem Soc 2022; 144:8515-8528. [PMID: 35522532 DOI: 10.1021/jacs.1c07656] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Herein, we examine the electronic and geometric structural properties of O2-derived aliphatic thiolate-ligated Fe-peroxo, Fe-hydroxo, and Fe(IV) oxo compounds. The latter cleaves strong C-H bonds (96 kcal mol-1) on par with the valine C-H bond cleaved by isopencillin N synthase (IPNS). Stopped-flow kinetics studies indicate that the barrier to O2 binding to [FeII(SMe2N4(tren))]+ (3) is extremely low (Ea = 36(2) kJ mol-1), as theoretically predicted for IPNS. Dioxygen binding to 3 is shown to be reversible, and a superoxo intermediate, [FeIII(SMe2N4(tren))(O2)]+ (6), forms in the first 25 ms of the reaction at -40 °C prior to the rate-determining (Ea = 46(2) kJ mol-1) formation of peroxo-bridged [(SMe2N4(tren))Fe(III)]2(μ-O2)2+ (7). A log(kobs) vs log([Fe]) plot for the formation of 7 is consistent with the second-order dependence on iron, and H2O2 assays are consistent with a 2:1 ratio of Fe/H2O2. Peroxo 7 is shown to convert to ferric-hydroxo [FeIII(SMe2N(tren))(OH)]+ (9, g⊥ = 2.24, g∥ = 1.96), the identity of which was determined via its independent synthesis. Rates of the conversion 7 → 9 are shown to be dependent on the X-H bond strength of the H-atom donor, with a kH/kD = 4 when CD3OD is used in place of CH3OH as a solvent. A crystallographically characterized cis thiolate-ligated high-valent iron oxo, [FeIV(O)(SMe2N4(tren))]+ (11), is shown to form en route to hydroxo 9. Electronic structure calculations were shown to be consistent with 11 being an S = 1 Fe(IV)═O with an unusually high νFe-O stretching frequency at 918 cm-1 in line with the extremely short Fe-O bond (1.603(7) Å).
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Affiliation(s)
- Maksym A Dedushko
- Department of Chemistry, University of Washington, Campus Box 351700, Seattle, Washington 98195-1700, United States
| | - Maria B Greiner
- Department of Chemistry, University of Washington, Campus Box 351700, Seattle, Washington 98195-1700, United States
| | - Alexandra N Downing
- Department of Chemistry, University of Washington, Campus Box 351700, Seattle, Washington 98195-1700, United States
| | - Michael Coggins
- Department of Chemistry, University of Washington, Campus Box 351700, Seattle, Washington 98195-1700, United States
| | - Julie A Kovacs
- Department of Chemistry, University of Washington, Campus Box 351700, Seattle, Washington 98195-1700, United States
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3
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Ekanayake DM, Pham D, Probst AL, Miller JR, Popescu CV, Fiedler AT. Electronic structures and spectroscopic signatures of diiron intermediates generated by O 2 activation of nonheme iron(II)-thiolate complexes. Dalton Trans 2021; 50:14432-14443. [PMID: 34570147 PMCID: PMC8721859 DOI: 10.1039/d1dt02286e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The activation of O2 at thiolate-ligated iron(II) sites is essential to the function of numerous metalloenzymes and synthetic catalysts. Iron-thiolate bonds in the active sites of nonheme iron enzymes arise from either coordination of an endogenous cysteinate residue or binding of a deprotonated thiol-containing substrate. Examples of the latter include sulfoxide synthases, such as EgtB and OvoA, that utilize O2 to catalyze tandem S-C bond formation and S-oxygenation steps in thiohistidine biosyntheses. We recently reported the preparation of two mononuclear nonheme iron-thiolate complexes (1 and 2) that serve as structural active-site models of substrate-bound EgtB and OvoA (Dalton Trans. 2020, 49, 17745-17757). These models feature monodentate thiolate ligands and tripodal N4 ligands with mixed pyridyl/imidazolyl donors. Here, we describe the reactivity of 1 and 2 with O2 at low temperatures to give metastable intermediates (3 and 4, respectively). Characterization with multiple spectroscopic techniques (UV-vis absorption, NMR, variable-field and -temperature Mössbauer, and resonance Raman) revealed that these intermediates are thiolate-ligated iron(III) dimers with a bridging oxo ligand derived from the four-electron reduction of O2. Structural models of 3 and 4 consistent with the experimental data were generated via density functional theory (DFT) calculations. The combined experimental and computational results illuminate the geometric and electronic origins of the unique spectral features of diiron(III)-μ-oxo complexes with thiolate ligands, and the spectroscopic signatures of 3 and 4 are compared to those of closely-related diiron(III)-μ-peroxo species. Collectively, these results will assist in the identification of intermediates that appear on the O2 reaction landscapes of iron-thiolate species in both biological and synthetic environments.
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Affiliation(s)
| | - Dao Pham
- Department of Chemistry, The College of Arts and Sciences, University of St. Thomas, St. Paul, Minnesota 55105, USA.
| | - Andrew L Probst
- Department of Chemistry, The College of Arts and Sciences, University of St. Thomas, St. Paul, Minnesota 55105, USA.
| | - Joshua R Miller
- Department of Chemistry, University of Wisconsin - Madison, Madison, Wisconsin 53706, USA
| | - Codrina V Popescu
- Department of Chemistry, The College of Arts and Sciences, University of St. Thomas, St. Paul, Minnesota 55105, USA.
| | - Adam T Fiedler
- Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53233, USA.
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4
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Toledo S, Yan Poon PC, Gleaves M, Rees J, Rogers DM, Kaminsky W, Kovacs JA. Increasing reactivity by incorporating π-acceptor ligands into coordinatively unsaturated thiolate-ligated iron(II) complexes. Inorganica Chim Acta 2021; 524. [PMID: 34305163 DOI: 10.1016/j.ica.2021.120422] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Reported herein is the structural, spectroscopic, redox, and reactivity properties of a series of iron complexes containing both a π-donating thiolate, and π-accepting N-heterocycles in the coordination sphere, in which we systematically vary the substituents on the N-heterocycle, the size of the N-heterocycle, and the linker between the imine nitrogen and tertiary amine nitrogen. In contrast to our primary amine/thiolate-ligated Fe(II) complex, [FeII(SMe2N4(tren))]+ (1), the Fe(II) complexes reported herein are intensely colored, allowing us to visually monitor reactivity. Ferrous complexes with R = H substituents in the 6-position of the pyridines, [FeII(SMe2N4(6-H-DPPN)]+ (6) and [FeII(SMe2N4(6-H-DPEN))(MeOH)]+ (8-MeOH) are shown to readily bind neutral ligands, and all of the Fe(II) complexes are shown to bind anionic ligands regardless of steric congestion. This reactivity is in contrast to 1 and is attributed to an increased metal ion Lewis acidity assessed via aniodic redox potentials, Ep,a, caused by the π-acid ligands. Thermodynamic parameters (ΔH, ΔS) for neutral ligand binding were obtained from T-dependent equilibrium constants. All but the most sterically congested complex, [FeII(SMe2N4(6-Me-DPPN)]+ (5), react with O2. In contrast to our Mn(II)-analogues, dioxygen intermediates are not observed. Rates of formation of the final mono oxo-bridged products were assessed via kinetics and shown to be inversely dependent on redox potentials, Ep,a, consistent with a mechanism involving electron transfer.
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Affiliation(s)
- Santiago Toledo
- The Department of Chemistry, University of Washington, Box 351700 Seattle, WA 98195-1700, United States
| | - Penny Chaau Yan Poon
- The Department of Chemistry, University of Washington, Box 351700 Seattle, WA 98195-1700, United States
| | - Morgan Gleaves
- The Department of Chemistry, University of Washington, Box 351700 Seattle, WA 98195-1700, United States
| | - Julian Rees
- The Department of Chemistry, University of Washington, Box 351700 Seattle, WA 98195-1700, United States
| | - Dylan M Rogers
- The Department of Chemistry, University of Washington, Box 351700 Seattle, WA 98195-1700, United States
| | - Werner Kaminsky
- The Department of Chemistry, University of Washington, Box 351700 Seattle, WA 98195-1700, United States
| | - Julie A Kovacs
- The Department of Chemistry, University of Washington, Box 351700 Seattle, WA 98195-1700, United States
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5
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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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6
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Gordon JB, McGale JP, Siegler MA, Goldberg DP. Proton-Coupled Electron-Transfer Reactivity Controls Iron versus Sulfur Oxidation in Nonheme Iron-Thiolate Complexes. Inorg Chem 2021; 60:6255-6265. [PMID: 33872005 DOI: 10.1021/acs.inorgchem.0c03779] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Reaction of the five-coordinate FeII(N4S) complexes, [FeII(iPr3TACN)(abtX)](OTf) (abt = aminobenzenethiolate, X = H, CF3), with a one-electron oxidant and an appropriate base leads to net H atom loss, generating new FeIII(iminobenzenethiolate) complexes that were characterized by single-crystal X-ray diffraction (XRD), as well as UV-vis, EPR, and Mössbauer spectroscopies. The spectroscopic data indicate that the iminobenzenethiolate complexes have S = 3/2 ground states. In the absence of a base, oxidation of the FeII(abt) complexes leads to disulfide formation instead of oxidation at the metal center. Bracketing studies with separated proton-coupled electron-transfer (PCET) reagents show that the FeII(aminobenzenethiolate) and FeIII(iminobenzenethiolate) forms are readily interconvertible by H+/e- transfer and provide a measure of the bond dissociation free energy (BDFE) for the coordinated N-H bond between 64 and 69 kcal mol-1. This work shows that coordination to the iron center causes a dramatic weakening of the N-H bond and that Fe- versus S-oxidation in a nonheme iron complex can be controlled by the protonation state of an ancillary amino donor.
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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
| | - Jeremy P McGale
- Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Maxime A Siegler
- Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - David P Goldberg
- Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
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7
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Wang L, Gennari M, Cantú Reinhard FG, Padamati SK, Philouze C, Flot D, Demeshko S, Browne WR, Meyer F, de Visser SP, Duboc C. O2 Activation by Non-Heme Thiolate-Based Dinuclear Fe Complexes. Inorg Chem 2020; 59:3249-3259. [DOI: 10.1021/acs.inorgchem.9b03633] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Affiliation(s)
- Lianke Wang
- Institutes of Physical Science and Information Technology, Anhui University, 230601 Hefei, Anhui, P. R. China
- Univ. Grenoble Alpes, CNRS UMR 5250, DCM, F-38000 Grenoble, France
| | - Marcello Gennari
- Univ. Grenoble Alpes, CNRS UMR 5250, DCM, F-38000 Grenoble, France
| | - Fabián G. Cantú Reinhard
- Manchester Institute of Biotechnology and Department of Chemical Engineering and Analytical Science, The University of Manchester, 131 Princess Street, Manchester M1 7DN, United Kingdom
| | - Sandeep K. Padamati
- Univ. Grenoble Alpes, CNRS UMR 5250, DCM, F-38000 Grenoble, France
- Molecular Inorganic Chemistry, Stratingh Institute for Chemistry, Faculty of Science and Engineering, University of Groningen, Nijenborgh 4, 9747AG Groningen, The Netherlands
| | | | - David Flot
- ESRF European Synchrotron 71, Ave Martyrs Grenoble, 38000 Grenoble, France
| | - Serhiy Demeshko
- Institute of Inorganic Chemistry, University of Göttingen, Tammannstrasse 4, D-37077 Göttingen, Germany
| | - Wesley R. Browne
- Molecular Inorganic Chemistry, Stratingh Institute for Chemistry, Faculty of Science and Engineering, University of Groningen, Nijenborgh 4, 9747AG Groningen, The Netherlands
| | - Franc Meyer
- Institute of Inorganic Chemistry, University of Göttingen, Tammannstrasse 4, D-37077 Göttingen, Germany
| | - Sam P. de Visser
- Manchester Institute of Biotechnology and Department of Chemical Engineering and Analytical Science, The University of Manchester, 131 Princess Street, Manchester M1 7DN, United Kingdom
| | - Carole Duboc
- Univ. Grenoble Alpes, CNRS UMR 5250, DCM, F-38000 Grenoble, France
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8
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Gordon JB, Vilbert AC, DiMucci IM, MacMillan SN, Lancaster KM, Moënne-Loccoz P, Goldberg DP. Activation of Dioxygen by a Mononuclear Nonheme Iron Complex: Sequential Peroxo, Oxo, and Hydroxo Intermediates. J Am Chem Soc 2019; 141:17533-17547. [PMID: 31647656 DOI: 10.1021/jacs.9b05274] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The activation of dioxygen by FeII(Me3TACN)(S2SiMe2) (1) is reported. Reaction of 1 with O2 at -135 °C in 2-MeTHF generates a thiolate-ligated (peroxo)diiron complex FeIII2(O2)(Me3TACN)2(S2SiMe2)2 (2) that was characterized by UV-vis (λmax = 300, 390, 530, 723 nm), Mössbauer (δ = 0.53, |ΔEQ| = 0.76 mm s-1), resonance Raman (RR) (ν(O-O) = 849 cm-1), and X-ray absorption (XAS) spectroscopies. Complex 2 is distinct from the outer-sphere oxidation product 1ox (UV-vis (λmax = 435, 520, 600 nm), Mössbauer (δ = 0.45, |ΔEQ| = 3.6 mm s-1), and EPR (S = 5/2, g = [6.38, 5.53, 1.99])), obtained by one-electron oxidation of 1. Cleavage of the peroxo O-O bond can be initiated either photochemically or thermally to produce a new species assigned as an FeIV(O) complex, FeIV(O)(Me3TACN)(S2SiMe2) (3), which was identified by UV-vis (λmax = 385, 460, 890 nm), Mössbauer (δ = 0.21, |ΔEQ| = 1.57 mm s-1), RR (ν(FeIV═O) = 735 cm-1), and X-ray absorption spectroscopies, as well as reactivity patterns. Reaction of 3 at low temperature with H atom donors gives a new species, FeIII(OH)(Me3TACN)(S2SiMe2) (4). Complex 4 was independently synthesized from 1 by the stoichiometric addition of a one-electron oxidant and a hydroxide source. This work provides a rare example of dioxygen activation at a mononuclear nonheme iron(II) complex that produces both FeIII-O-O-FeIII and FeIV(O) species in the same reaction with O2. It also demonstrates the feasibility of forming Fe/O2 intermediates with strongly donating sulfur ligands while avoiding immediate sulfur oxidation.
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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
| | - Avery C Vilbert
- Department of Chemistry and Chemical Biology, Baker Laboratory , Cornell University , Ithaca , New York 14853 , United States
| | - Ida M DiMucci
- Department of Chemistry and Chemical Biology, Baker Laboratory , Cornell University , Ithaca , New York 14853 , United States
| | - Samantha N MacMillan
- Department of Chemistry and Chemical Biology, Baker Laboratory , Cornell University , Ithaca , New York 14853 , United States
| | - Kyle M Lancaster
- Department of Chemistry and Chemical Biology, Baker Laboratory , Cornell University , Ithaca , New York 14853 , United States
| | - Pierre Moënne-Loccoz
- Department of Chemical Physiology and Biochemistry , Oregon Health & Science University , Portland , Oregon 97239 , United States
| | - David P Goldberg
- Department of Chemistry , The Johns Hopkins University , 3400 North Charles Street , Baltimore , Maryland 21218 , United States
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9
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Johnson EJ, Kleinlein C, Musgrave RA, Betley TA. Diiron oxo reactivity in a weak-field environment. Chem Sci 2019; 10:6304-6310. [PMID: 31341583 PMCID: PMC6598509 DOI: 10.1039/c9sc00605b] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2019] [Accepted: 05/08/2019] [Indexed: 11/21/2022] Open
Abstract
Concomitant deprotonation and metalation of a dinucleating cofacial Pacman dipyrrin ligand platform tBudmxH2 with Fe2(Mes)4 results in formation of a diiron complex ( tBudmx)Fe2(Mes)2. Treatment of ( tBudmx)Fe2(Mes)2 with one equivalent of water yields the diiron μ-oxo complex ( tBudmx)Fe2(μ-O) and free mesitylene. A two-electron oxidation of ( tBudmx)Fe2(μ-O) gives rise to the diferric complex ( tBudmx)Fe2(μ-O)Cl2, and one-electron reduction from this FeIIIFeIII state allows for isolation of a mixed-valent species [Cp2Co][( tBudmx)Fe2(μ-O)Cl2]. Both ( tBudmx)Fe2(μ-O) and [Cp2Co][( tBudmx)Fe2(μ-O)Cl2] exhibit basic character at the bridging oxygen atom and can be protonated using weak acids to form bridging diferrous hydroxide species. The basicity of the diferrous oxo ( tBudmx)Fe2(μ-O) is quantified through studies of the pK a of its conjugate acid, [( tBudmx)Fe2(μ-OH)]+, which is determined to be 15.3(6); interestingly, upon coordination of neutral solvent ligands to yield ( tBudmx)Fe2(μ-O)(thf)2, the basicity is increased as observed through an increase in the pK a of the conjugate acid [( tBudmx)Fe2(μ-OH)(thf)2]+ to 26.8(6). In contrast, attempts to synthesize a diferric bridging hydroxide by two-electron oxidation of [( tBudmx)Fe2(μ-OH)(thf)2]+ resulted in isolation of ( tBudmx)Fe2(μ-O)Cl2 with concomitant loss of a proton, consistent with the pK a of the conjugate acid [( tBudmx)Fe2(μ-OH)Cl2]+ determined computationally to be -1.8(6). The foregoing results highlight the intricate interplay between oxidation state and reactivity in diiron μ-oxo units.
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Affiliation(s)
- Elizabeth J Johnson
- Department of Chemistry and Chemical Biology , Harvard University , Cambridge , MA 02138 , USA .
| | - Claudia Kleinlein
- Department of Chemistry and Chemical Biology , Harvard University , Cambridge , MA 02138 , USA .
| | - Rebecca A Musgrave
- Department of Chemistry and Chemical Biology , Harvard University , Cambridge , MA 02138 , USA .
| | - Theodore A Betley
- Department of Chemistry and Chemical Biology , Harvard University , Cambridge , MA 02138 , USA .
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10
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Hsieh CC, Liu YC, Tseng MC, Chiang MH, Horng YC. Dioxygen activation by a dinuclear thiolate-ligated Fe(ii) complex. Dalton Trans 2019; 48:379-386. [PMID: 30516213 DOI: 10.1039/c8dt04491k] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Dioxygen activation by FeII thiolate complexes is relatively rare in biological and chemical systems because the sulfur site is at least as vulnerable as the iron site to oxidative modification. O2 activation by FeII-SR complexes with thiolate bound trans to the O2 binding site generally affords the FeIV[double bond, length as m-dash]O intermediate and oxidized thiolate. On the other hand, O2 activation by Fe(ii)-SR complexes with thiolate bound cis to the O2 binding site generates FeIII-O-FeIII or S-oxygenated complexes. The postulated FeIV[double bond, length as m-dash]O intermediate has only been identified in isopenicillin N synthase recently. We demonstrated here that O2 activation by a dinuclear FeII thiolate-rich complex produces a mononuclear FeIII complex and water with a supply of electron donors. The thiolate is bound cis to the postulated dioxygen binding site, and no FeIII-O-FeIII or S-oxygenated complex was observed. Although we have not detected the transient intermediate by spectroscopic measurements, the FeIV[double bond, length as m-dash]O intermediate is suggested to exist by theoretical calculation, and P-oxidation and hydride-transfer experiments. In addition, an unprecedented FeIII-O2-FeIII complex supported by thiolates was observed during the reaction by using a coldspray ionization time-of-flight mass (CSI-TOF MS) instrument. This is also supported by low-temperature UV-vis measurements. The intramolecular NHO[double bond, length as m-dash]FeIV hydrogen bonding, calculated by DFT, probably fine tunes the O2-activation process for intramolecular hydrogen abstraction, avoiding the S-oxygenation at cis-thiolate.
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Affiliation(s)
- Chang-Chih Hsieh
- Department of Chemistry, National Changhua University of Education, Changhua 50058, Taiwan.
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11
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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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12
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Clares MP, Acosta-Rueda L, Castillo CE, Blasco S, Jiménez HR, García-España E, Basallote MG. Iron(II) Complexes with Scorpiand-Like Macrocyclic Polyamines: Kinetico-Mechanistic Aspects of Complex Formation and Oxidative Dehydrogenation of Coordinated Amines. Inorg Chem 2017; 56:4400-4412. [DOI: 10.1021/acs.inorgchem.6b03070] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- M. Paz Clares
- Departamento
de Química Inorgánica, Universidad de Valencia, Instituto de Ciencia Molecular, Edificio de Institutos de Paterna, C/Catedrático
José Beltrán 2, 46980 Paterna, Valencia, Spain
| | - Laura Acosta-Rueda
- Departamento
de Ciencia de los Materiales e Ingeniería Metalúrgica
y Química Inorgánica, Instituto de Biomoléculas
(INBIO), Facultad de Ciencias, Universidad de Cádiz, Avda República Saharahui s/n, Puerto Real, 11510 Cádiz, Spain
| | - Carmen E. Castillo
- Departamento
de Ciencia de los Materiales e Ingeniería Metalúrgica
y Química Inorgánica, Instituto de Biomoléculas
(INBIO), Facultad de Ciencias, Universidad de Cádiz, Avda República Saharahui s/n, Puerto Real, 11510 Cádiz, Spain
| | - Salvador Blasco
- Departamento
de Química Inorgánica, Universidad de Valencia, Instituto de Ciencia Molecular, Edificio de Institutos de Paterna, C/Catedrático
José Beltrán 2, 46980 Paterna, Valencia, Spain
| | - Hermas R. Jiménez
- Departamento
de Química Inorgánica, Facultad de Química, Universidad de Valencia, C/Dr. Moliner 50, 46100 Burjasot, Valencia, Spain
| | - Enrique García-España
- Departamento
de Química Inorgánica, Universidad de Valencia, Instituto de Ciencia Molecular, Edificio de Institutos de Paterna, C/Catedrático
José Beltrán 2, 46980 Paterna, Valencia, Spain
| | - Manuel G. Basallote
- Departamento
de Ciencia de los Materiales e Ingeniería Metalúrgica
y Química Inorgánica, Instituto de Biomoléculas
(INBIO), Facultad de Ciencias, Universidad de Cádiz, Avda República Saharahui s/n, Puerto Real, 11510 Cádiz, Spain
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13
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Villar-Acevedo G, Lugo-Mas P, Blakely MN, Rees JA, Ganas AS, Hanada EM, Kaminsky W, Kovacs JA. Metal-Assisted Oxo Atom Addition to an Fe(III) Thiolate. J Am Chem Soc 2016; 139:119-129. [PMID: 28033001 DOI: 10.1021/jacs.6b03512] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Cysteinate oxygenation is intimately tied to the function of both cysteine dioxygenases (CDOs) and nitrile hydratases (NHases), and yet the mechanisms by which sulfurs are oxidized by these enzymes are unknown, in part because intermediates have yet to be observed. Herein, we report a five-coordinate bis-thiolate ligated Fe(III) complex, [FeIII(S2Me2N3(Pr,Pr))]+ (2), that reacts with oxo atom donors (PhIO, IBX-ester, and H2O2) to afford a rare example of a singly oxygenated sulfenate, [FeIII(η2-SMe2O)(SMe2)N3(Pr,Pr)]+ (5), resembling both a proposed intermediate in the CDO catalytic cycle and the essential NHase Fe-S(O)Cys114 proposed to be intimately involved in nitrile hydrolysis. Comparison of the reactivity of 2 with that of a more electron-rich, crystallographically characterized derivative, [FeIIIS2Me2NMeN2amide(Pr,Pr)]- (8), shows that oxo atom donor reactivity correlates with the metal ion's ability to bind exogenous ligands. Density functional theory calculations suggest that the mechanism of S-oxygenation does not proceed via direct attack at the thiolate sulfurs; the average spin-density on the thiolate sulfurs is approximately the same for 2 and 8, and Mulliken charges on the sulfurs of 8 are roughly twice those of 2, implying that 8 should be more susceptible to sulfur oxidation. Carboxamide-ligated 8 is shown to be unreactive towards oxo atom donors, in contrast to imine-ligated 2. Azide (N3-) is shown to inhibit sulfur oxidation with 2, and a green intermediate is observed, which then slowly converts to sulfenate-ligated 5. This suggests that the mechanism of sulfur oxidation involves initial coordination of the oxo atom donor to the metal ion. Whether the green intermediate is an oxo atom donor adduct, Fe-O═I-Ph, or an Fe(V)═O remains to be determined.
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Affiliation(s)
- Gloria Villar-Acevedo
- The Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195-1700, United States
| | - Priscilla Lugo-Mas
- The Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195-1700, United States
| | - Maike N Blakely
- The Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195-1700, United States
| | - Julian A Rees
- The Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195-1700, United States
| | - Abbie S Ganas
- The Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195-1700, United States
| | - Erin M Hanada
- The Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195-1700, United States
| | - Werner Kaminsky
- 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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14
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Attia AAA, Cioloboc D, Lupan A, Silaghi-Dumitrescu R. Multiconfigurational and DFT analyses of the electromeric formulation and UV-vis absorption spectra of the superoxide adduct of ferrous superoxide reductase. J Inorg Biochem 2016; 165:49-53. [PMID: 27768962 DOI: 10.1016/j.jinorgbio.2016.09.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2016] [Revised: 09/14/2016] [Accepted: 09/29/2016] [Indexed: 11/29/2022]
Abstract
The putative initial adduct of ferrous superoxide reductase (SOR) with superoxide has been alternatively formulated as ferric-peroxo or ferrous-superoxo. The ~600-nm UV-vis absorption band proposed to be assigned to this adduct (either as sole intermediate in the SOR catalytic cycle, or as one of the two intermediates) has recently been interpreted as due to a ligand-to-metal charge transfer, involving thiolate and superoxide in a ferrous complex, contrary to an alternative assignment as a predominantly cysteine thiolate-to-ferric charge transfer in a ferric-peroxo electromer. In an attempt to clarify the electromeric formulation of this adduct, we report a computational study using a multiconfigurational complete active space self-consistent field (MC-CASSCF) wave function approach as well as modelling the UV-vis absorption spectra with time-dependent density functional theory (TD-DFT). The MC-CASSCF calculations disclose a weak interaction between iron and the dioxygenic ligand and a dominant configuration with an essentially ferrous-superoxo character. The computed UV-vis absorption spectra reveal a marked dependence on the choice of density functional - both in terms of location of bands and in terms of orbital contributors. For the main band in the visible region, besides the recently reported thiolate-to-superoxide charge transfer, a more salient, and less functional-dependent, feature is a thiolate-to-ferric iron charge transfer, consistent with a ferric-peroxo electromer. By contrast, the computed UV-vis spectra of a ferric-hydroperoxo SOR model match distinctly better (and with no qualitative dependence on the DFT methodology) the 600-nm band as due to a mainly thiolate-to-ferric character - supporting the assignment of the SOR "600-nm intermediate" as a S=5/2 ferric-hydroperoxo species.
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Affiliation(s)
- Amr A A Attia
- Department of Chemistry, Faculty of Chemistry and Chemical Engineering, Babeş-Bolyai University, Cluj-Napoca, Romania
| | - Daniela Cioloboc
- Department of Chemistry, University of Texas at San Antonio, San Antonio, TX 78249, United States
| | - Alexandru Lupan
- Department of Chemistry, Faculty of Chemistry and Chemical Engineering, Babeş-Bolyai University, Cluj-Napoca, Romania
| | - Radu Silaghi-Dumitrescu
- Department of Chemistry, Faculty of Chemistry and Chemical Engineering, Babeş-Bolyai University, Cluj-Napoca, Romania.
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15
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Iovan DA, Betley TA. Characterization of Iron-Imido Species Relevant for N-Group Transfer Chemistry. J Am Chem Soc 2016; 138:1983-93. [PMID: 26788747 DOI: 10.1021/jacs.5b12582] [Citation(s) in RCA: 135] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
A sterically accessible tert-butyl-substituted dipyrrinato di-iron(II) complex [((tBu)L)FeCl]2 possessing two bridging chloride atoms was synthesized from the previously reported solvento adduct. Upon treatment with aryl azides, the formation of high-spin Fe(III) species was confirmed by (57)Fe Mössbauer spectroscopy. Crystallographic characterization revealed two possible oxidation products: (1) a terminal iron iminyl from aryl azides bearing ortho isopropyl substituents, ((tBu)L)FeCl((•)NC6H3-2,6-(i)Pr2); or (2) a bridging di-iron imido arising from reaction with 3,5-bis(trifluoromethyl)aryl azide, [((tBu)L)FeCl]2(μ-NC6H3-3,5-(CF3)2). Similar to the previously reported ((Ar)L)FeCl((•)NC6H4-4-(t)Bu), the monomeric iron imido is best described as a high-spin Fe(III) antiferromagnetically coupled to an iminyl radical, affording an S = 2 spin state as confirmed by SQUID magnetometry. The di-iron imido possesses an S = 0 ground state, arising from two high-spin Fe(III) centers weakly antiferromagnetically coupled through the bridging imido ligand. The terminal iron iminyl complex undergoes facile decomposition via intra- or intermolecular hydrogen-atom abstraction (HAA) from an imido aryl ortho isopropyl group, or from 1,4-cyclohexadiene, respectively. The bridging di-iron imido is a competent N-group transfer reagent to cyclic internal olefins as well as styrene. Although solid-state magnetometry indicates an antiferromagnetic interaction between the two iron centers (J = -108.7 cm(-1)) in [((tBu)L)FeCl]2(μ-NC6H3-3,5-(CF3)2), we demonstrate that in solution the bridging imido can facilitate HAA as well as dissociate into a terminal iminyl species, which then can promote HAA. In situ monitoring reveals the di-iron bridging imido is a catalytically competent intermediate, one of several iron complexes observed in the amination of C-H bond substrates or styrene aziridination.
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Affiliation(s)
- Diana A Iovan
- Department of Chemistry and Chemical Biology, Harvard University , 12 Oxford Street, Cambridge, Massachusetts 02138, United States
| | - Theodore A Betley
- Department of Chemistry and Chemical Biology, Harvard University , 12 Oxford Street, Cambridge, Massachusetts 02138, United States
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16
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Coggins MK, Toledo S, Kovacs JA. Isolation and characterization of a dihydroxo-bridged iron(III,III)(μ-OH)2 diamond core derived from dioxygen. Inorg Chem 2013; 52:13325-31. [PMID: 24229319 PMCID: PMC3885352 DOI: 10.1021/ic4010906] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Dioxygen addition to coordinatively unsaturated [Fe(II)(O(Me2)N4(6-Me-DPEN))](PF6) (1) is shown to afford a complex containing a dihydroxo-bridged Fe(III)2(μ-OH)2 diamond core, [Fe(III)(O(Me2)N4(6-Me-DPEN))]2(μ-OH)2(PF6)2·(CH3CH2CN)2 (2). The diamond core of 2 resembles the oxidized methane monooxygenase (MMOox) resting state, as well as the active site product formed following H-atom abstraction from Tyr-OH by ribonucleotide reductase (RNR). The Fe-OH bond lengths of 2 are comparable with those of the MMOHox suggesting that MMOHox contains a Fe(III)2(μ-OH)2 as opposed to Fe(III)2(μ-OH)(μ-OH2) diamond core as had been suggested. Isotopic labeling experiments with (18)O2 and CD3CN indicate that the oxygen and proton of the μ-OH bridges of 2 are derived from dioxygen and acetonitrile. Deuterium incorporation (from CD3CN) suggests that an unobserved intermediate capable of abstracting a H-atom from CH3CN forms en route to 2. Given the high C-H bond dissociation energy (BDE = 97 kcal/mol) of acetonitrile, this indicates that this intermediate is a potent oxidant, possibly a high-valent iron oxo. Consistent with this, iodosylbenzene (PhIO) also reacts with 1 in CD3CN to afford the deuterated Fe(III)2(μ-OD)2 derivative of 2. Intermediates are not spectroscopically observed in either reaction (O2 and PhIO) even at low-temperatures (-80 °C), indicating that this intermediate has a very short lifetime, likely due to its highly reactive nature. Hydroxo-bridged 2 was found to stoichiometrically abstract hydrogen atoms from 9,10-dihydroanthracene (C-H BDE = 76 kcal/mol) at ambient temperatures.
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Affiliation(s)
| | | | - Julie A. Kovacs
- The Department of Chemistry, University of Washington: Box 351700 Seattle, WA 98195-1700
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17
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Coggins MK, Brines LM, Kovacs JA. Synthesis and structural characterization of a series of Mn(III)OR complexes, including a water-soluble Mn(III)OH that promotes aerobic hydrogen-atom transfer. Inorg Chem 2013; 52:12383-93. [PMID: 24156315 DOI: 10.1021/ic401234t] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Hydrogen-atom-transfer (HAT) reactions are a class of proton-coupled electron-transfer (PCET) reactions used in biology to promote substrate oxidation. The driving force for such reactions depends on both the oxidation potential of the catalyst and the pKa value of the proton-acceptor site. Both high-valent transition-metal oxo M(IV)═O (M = Fe, Mn) and lower-valent transition-metal hydroxo compounds M(III)OH (M = Fe, Mn) have been shown to promote these reactions. Herein we describe the synthesis, structure, and reactivity properties of a series of Mn(III)OR compounds [R = (p)NO2Ph (5), Ph (6), Me (7), H (8)], some of which abstract H atoms. The Mn(III)OH complex 8 is water-soluble and represents a rare example of a stable mononuclear Mn(III)OH. In water, the redox potential of 8 was found to be pH-dependent and the Pourbaix (E(p,c) vs pH) diagram has a slope (52 mV pH(-1)) that is indicative of the transfer a single proton with each electron (i.e., PCET). The two compounds with the lowest oxidation potential, hydroxide- and methoxide-bound 7 and 8, are found to oxidize 2,2',6,6'-tetramethylpiperidin-1-ol (TEMPOH), whereas the compounds with the highest oxidation potential, phenol-ligated 5 and 6, are shown to be unreactive. Hydroxide-bound 8 reacts with TEMPOH an order of magnitude faster than methoxide-bound 7. Kinetic data [kH/kD = 3.1 (8); kH/kD = 2.1 (7)] are consistent with concerted H-atom abstraction. The reactive species 8 can be aerobically regenerated in H2O, and at least 10 turnovers can be achieved without significant degradation of the "catalyst". The linear correlation between the redox potential and pH, obtained from the Pourbaix diagram, was used to calculate the bond dissociation free energy (BDFE) = 74.0 ± 0.5 kcal mol(-1) for Mn(II)OH2 in water, and in MeCN, its BDFE was estimated to be 70.1 kcal mol(-1). The reduced protonated derivative of 8, [Mn(II)(S(Me2)N4(tren))(H2O)](+) (9), was estimated to have a pKa of 21.2 in MeCN. The ability (7) and inability (5 and 6) of the other members of the series to abstract a H atom from TEMPOH was used to estimate either an upper or lower limit to the Mn(II)O(H)R pKa based on their experimentally determined redox potentials. The trend in pKa [21.2 (R = H) > 16.2 (R = Me) > 13.5 (R = Ph) > 12.2 (R = (p)NO2Ph)] is shown to oppose that of the oxidation potential E(p,c) [-220 (R = (p)NO2Ph) > -300 (R = Ph) > -410 (R = Me) > -600 (R = H) mV vs Fc(+/0)] for this particular series.
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Affiliation(s)
- Michael K Coggins
- Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195-1700, United States
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18
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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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Notash B, Amani V, Safari N, Ostad SN, Abedi A, Dehnavi MZ. The influence of steric effects on intramolecular secondary bonding interactions; cytotoxicity in gold(iii) bithiazole complexes. Dalton Trans 2013; 42:6852-8. [DOI: 10.1039/c3dt00073g] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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20
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Abstract
The S-oxygenation of cysteine with dioxygen to give cysteine sulfinic acid occurs at the non-heme iron active site of cysteine dioxygenase. Similar S-oxygenation events occur in other non-heme iron enzymes, including nitrile hydratase and isopenicillin N synthase, and these enzymes have inspired the development of a class of [N(x)S(y)]-Fe model complexes. Certain members of this class have provided some intriguing examples of S-oxygenation, and this article summarizes these results, focusing on the non-heme iron(II/III)-thiolate model complexes that are known to react with O(2) or other O-atom transfer oxidants to yield sulfur oxygenates. Key aspects of the synthesis, structure, and reactivity of these systems are presented, along with any mechanistic information available on the oxygenation reactions. A number of iron(III)-thiolate complexes react with O(2) to give S-oxygenates, and the degree to which the thiolate sulfur donors are oxidized varies among the different complexes, depending upon the nature of the ligand, metal geometry, and spin state. The first examples of iron(II)-thiolate complexes that react with O(2) to give selective S-oxygenation are just emerging. Mechanistic information on these transformations is limited, with isotope labeling studies providing much of the current mechanistic data. The many questions that remain unanswered for both models and enzymes provide strong motivation for future work in this area.
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Affiliation(s)
- Alison C. McQuilken
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - David P. Goldberg
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, USA
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21
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Coggins MK, Toledo S, Shaffer E, Kaminsky W, Shearer J, Kovacs JA. Characterization and dioxygen reactivity of a new series of coordinatively unsaturated thiolate-ligated manganese(II) complexes. Inorg Chem 2012; 51:6633-44. [PMID: 22642272 DOI: 10.1021/ic300192q] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The synthesis, structural, and spectroscopic characterization of four new coordinatively unsaturated mononuclear thiolate-ligated manganese(II) complexes ([Mn(II)(S(Me2)N(4)(6-Me-DPEN))](BF(4)) (1), [Mn(II)(S(Me2)N(4)(6-Me-DPPN))](BPh(4))·MeCN (3), [Mn(II)(S(Me2)N(4)(2-QuinoPN))](PF(6))·MeCN·Et(2)O (4), and [Mn(II)(S(Me2)N(4)(6-H-DPEN)(MeOH)](BPh(4)) (5)) is described, along with their magnetic, redox, and reactivity properties. These complexes are structurally related to recently reported [Mn(II)(S(Me2)N(4)(2-QuinoEN))](PF(6)) (2) (Coggins, M. K.; Kovacs, J. A. J. Am. Chem. Soc.2011, 133, 12470). Dioxygen addition to complexes 1-5 is shown to result in the formation of five new rare examples of Mn(III) dimers containing a single, unsupported oxo bridge: [Mn(III)(S(Me2)N(4)(6-Me-DPEN)](2)-(μ-O)(BF(4))(2)·2MeOH (6), [Mn(III)(S(Me2)N(4)(QuinoEN)](2)-(μ-O)(PF(6))(2)·Et(2)O (7), [Mn(III)(S(Me2)N(4)(6-Me-DPPN)](2)-(μ-O)(BPh(4))(2) (8), [Mn(III)(S(Me2)N(4)(QuinoPN)](2)-(μ-O)(BPh(4))(2) (9), and [Mn(III)(S(Me2)N(4)(6-H-DPEN)](2)-(μ-O)(PF(6))(2)·2MeCN (10). Labeling studies show that the oxo atom is derived from (18)O(2). Ligand modifications, involving either the insertion of a methylene into the backbone or the placement of an ortho substituent on the N-heterocyclic amine, are shown to noticeably modulate the magnetic and reactivity properties. Fits to solid-state magnetic susceptibility data show that the Mn(III) ions of μ-oxo dimers 6-10 are moderately antiferromagnetically coupled, with coupling constants (2J) that fall within the expected range. Metastable intermediates, which ultimately convert to μ-oxo bridged 6 and 7, are observed in low-temperature reactions between 1 and 2 and dioxygen. Complexes 3-5, on the other hand, do not form observable intermediates, thus illustrating the effect that relatively minor ligand modifications have upon the stability of metastable dioxygen-derived species.
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Affiliation(s)
- Michael K Coggins
- The Department of Chemistry, University of Washington, Campus Box 351700, Seattle, Washington 98195-1700, USA
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Sallmann M, Siewert I, Fohlmeister L, Limberg C, Knispel C. Ein Trispyrazolylborato-Eisen-Cysteinato-Komplex als funktionelles Modell für die Cystein-Dioxygenase. Angew Chem Int Ed Engl 2012. [DOI: 10.1002/ange.201107345] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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23
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Sallmann M, Siewert I, Fohlmeister L, Limberg C, Knispel C. A trispyrazolylborato iron cysteinato complex as a functional model for the cysteine dioxygenase. Angew Chem Int Ed Engl 2012; 51:2234-7. [PMID: 22287034 DOI: 10.1002/anie.201107345] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2011] [Indexed: 11/07/2022]
Affiliation(s)
- Madleen Sallmann
- Humboldt-Universität zu Berlin, Institut für Chemie, Berlin, Germany
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24
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Zhang D, Hernandez B, Selke M. Photooxidation of metal-bound thiolates: reactivity of sulfur containing peroxidic intermediates. J Sulphur Chem 2011; 29:377-388. [PMID: 22379490 DOI: 10.1080/17415990802146980] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
A variety of reactions of singlet oxygen with metal-bound thiolates are described, and contrasted with the photooxidation of organic sulfides. Superficially, these two processes appear to involve similar mechanisms, but there are important differences: unlike the photooxidation of organic sulfides, the rate of the initial reaction of metal-thiolates with singlet oxygen (k(t)) appears to be affected by protic solvents and acids. The nucleophilicity of the thiolate moiety is reduced by addition of acids or in protic solvents, leading to significantly lower k(t) values. The primary intermediate in the photooxidation of organic sulfides is a nucleophilic persulfoxide, which can be stabilized by protic solvents or by addition of acid. However, the primary intermediate in the photooxidation of metal thiolates cannot be trapped with phosphite, suggesting that it may be less nucleophilic than its organic counterpart. Support for this hypothesis is also derived from the rather modest (compared with organic sulfides) acceleration of the rate of product formation by addition of acid.
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Affiliation(s)
- Dong Zhang
- Department of Chemistry and Biochemistry, California State University Los Angeles, Los Angeles, CA, USA
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25
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Villar-Acevedo G, Nam E, Fitch S, Benedict J, Freudenthal J, Kaminsky W, Kovacs JA. Influence of thiolate ligands on reductive N-O bond activation. Probing the O2(-) binding site of a biomimetic superoxide reductase analogue and examining the proton-dependent reduction of nitrite. J Am Chem Soc 2011; 133:1419-27. [PMID: 21207999 PMCID: PMC3178331 DOI: 10.1021/ja107551u] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Nitric oxide (NO) is frequently used to probe the substrate-binding site of "spectroscopically silent" non-heme Fe(2+) sites of metalloenzymes, such as superoxide reductase (SOR). Herein we use NO to probe the superoxide binding site of our thiolate-ligated biomimetic SOR model [Fe(II)(S(Me(2))N(4)(tren))](+) (1). Like NO-bound trans-cysteinate-ligated SOR (SOR-NO), the rhombic S = 3/2 EPR signal of NO-bound cis-thiolate-ligated [Fe(S(Me(2))N(4)(tren)(NO)](+) (2; g = 4.44, 3.54, 1.97), the isotopically sensitive ν(NO)(ν((15)NO)) stretching frequency (1685(1640) cm(-1)), and the 0.05 Å decrease in Fe-S bond length are shown to be consistent with the oxidative addition of NO to Fe(II) to afford an Fe(III)-NO(-) {FeNO}(7) species containing high-spin (S = 5/2) Fe(III) antiferromagnetically coupled to NO(-) (S = 1). The cis versus trans positioning of the thiolate does not appear to influence these properties. Although it has yet to be crystallographically characterized, SOR-NO is presumed to possess a bent Fe-NO similar to that of 2 (Fe-N-O = 151.7(4)°). The N-O bond is shown to be more activated in 2 relative to N- and O-ligated {FeNO}(7) complexes, and this is attributed to the electron-donating properties of the thiolate ligand. Hydrogen-bonding to the cysteinate sulfur attenuates N-O bond activation in SOR, as shown by its higher ν(NO) frequency (1721 cm(-1)). In contrast, the ν(O-O) frequency of the SOR peroxo intermediate and its analogues is not affected by H-bonds to the cysteinate sulfur or other factors influencing the Fe-SR bond strength; these only influence the ν(Fe-O) frequency. Reactions between 1 and NO(2)(-) are shown to result in the proton-dependent heterolytic cleavage of an N-O bond. The mechanism of this reaction is proposed to involve both Fe(II)-NO(2)(-) and {FeNO}(6) intermediates similar to those implicated in the mechanism of NiR-promoted NO(2)(-) reduction.
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Affiliation(s)
| | - Elaine Nam
- Department of Chemistry, University of Washington, Seattle, WA 98195
| | - Sarah Fitch
- Department of Chemistry, University of Washington, Seattle, WA 98195
| | | | | | | | - Julie A. Kovacs
- Department of Chemistry, University of Washington, Seattle, WA 98195
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26
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Badiei YM, Siegler MA, Goldberg DP. O2 activation by bis(imino)pyridine iron(II)-thiolate complexes. J Am Chem Soc 2011; 133:1274-7. [PMID: 21207980 DOI: 10.1021/ja109923a] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The new iron(II)-thiolate complexes [((iPr)BIP)Fe(II)(SPh)(Cl)] (1) and [((iPr)BIP)Fe(II)(SPh)(OTf)] (2) [BIP = bis(imino)pyridine] were prepared as models for cysteine dioxygenase (CDO), which converts Cys to Cys-SO(2)H at a (His)(3)Fe(II) center. Reaction of 1 and 2 with O(2) leads to Fe-oxygenation and S-oxygenation, respectively. For 1 + O(2), the spectroscopic and reactivity data, including (18)O isotope studies, are consistent with an assignment of an iron(IV)-oxo complex, [((iPr)BIP)Fe(IV)(O)(Cl)](+) (3), as the product of oxygenation. In contrast, 2 + O(2) results in direct S-oxygenation to give a sulfonato product, PhSO(3)(-). The positioning of the thiolate ligand in 1 versus 2 appears to play a critical role in determining the outcome of O(2) activation. The thiolate ligands in 1 and 2 are essential for O(2) reactivity and exhibit an important influence over the Fe(III)/Fe(II) redox potential.
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Affiliation(s)
- Yosra M Badiei
- Department of Chemistry, Johns Hopkins University , Baltimore, Maryland 21212, United States
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27
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Jiang Y, Widger LR, Kasper GD, Siegler MA, Goldberg DP. Iron(II)-thiolate S-oxygenation by O2: synthetic models of cysteine dioxygenase. J Am Chem Soc 2010; 132:12214-5. [PMID: 20712312 DOI: 10.1021/ja105591q] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The synthesis of structural and functional models of the active site of the nonheme iron enzyme cysteine dioxygenase (CDO) is reported. A bis(imino)pyridine ligand scaffold was employed to synthesize a mononuclear ferrous complex, Fe(II)(LN(3)S)(OTf) (1), which contains three neutral nitrogen donors and one anionic thiolato donor. Complex 1 is a good structural model of the Cys-bound active site of CDO. Reaction of 1 with O(2) results in oxygenation of the thiolato sulfur, affording the sulfonato complex Fe(II)(LN(3)SO(3))(OTf) (2) under mild conditions. Isotope labeling studies show that O(2) is the sole source of O atoms in the product and that the reaction proceeds via a dioxygenase-type mechanism for two out of three O atoms added, analogous to the dioxygenase reaction of CDO. The zinc(II) analog, Zn(LN(3)S)(OTf) (4), was prepared and found to be completely unreactive toward O(2), suggesting a critical role for Fe(II) in the oxygenation chemistry observed for 1. To our knowledge, S-oxygenation mediated by an Fe(II)-SR complex and O(2) is unprecedented.
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Affiliation(s)
- Yunbo Jiang
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21212, USA
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28
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Wane A, Thallaj N, Mandon D. Biomimetic Interaction between FeIIand O2: Effect of the Second Coordination Sphere on O2Binding to FeIIComplexes: Evidence of Coordination at the Metal Centre by a Dissociative Mechanism in the Formation of μ-Oxo Diferric Complexes. Chemistry 2009; 15:10593-602. [DOI: 10.1002/chem.200901350] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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29
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Schröder K, Enthaler S, Bitterlich B, Schulz T, Spannenberg A, Tse MK, Junge K, Beller M. Design of and Mechanistic Studies on a Biomimetic Iron-Imidazole Catalyst System for Epoxidation of Olefins with Hydrogen Peroxide. Chemistry 2009; 15:5471-81. [DOI: 10.1002/chem.200802731] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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30
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Lugo-Mas P, Taylor W, Schweitzer D, Theisen RM, Xu L, Shearer J, Swartz RD, Gleaves MC, Dipasquale A, Kaminsky W, Kovacs JA. Properties of square-pyramidal alkyl-thiolate Fe(III) complexes, including an analogue of the unmodified form of nitrile hydratase. Inorg Chem 2008; 47:11228-36. [PMID: 18989922 PMCID: PMC2659597 DOI: 10.1021/ic801704n] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The syntheses and structures of three new coordinatively unsaturated, monomeric, square-pyramidal thiolate-ligated Fe(III) complexes are described, [Fe(III)((tame-N(3))S(2)(Me2))](+) (1), [Fe(III)(Et-N(2)S(2)(Me2))(py)](1-) (3), and [Fe(III)((tame-N(2)S)S(2)(Me2))](2-) (15). The anionic bis-carboxamide, tris-thiolate N(2)S(3) coordination sphere of 15 is potentially similar to that of the yet-to-be characterized unmodified form of NHase. Comparison of the magnetic and reactivity properties of these reveals how anionic charge build up (from cationic 1 to anionic 3 and dianionic 15) and spin-state influence apical ligand affinity. For all of the ligand-field combinations examined, an intermediate S = 3/2 spin state was shown to be favored by a strong N(2)S(2) basal plane ligand field, and this was found to reduce the affinity for apical ligands, even when they are built in. This is in contrast to the post-translationally modified NHase active site, which is low spin and displays a higher affinity for apical ligands. Cationic 1 and its reduced Fe(II) precursor are shown to bind NO and CO, respectively, to afford [Fe(III)((tame-N(3))S(2)(Me))(NO)](+) (18, nu(NuO) = 1865 cm(-1)), an analogue of NO-inactivated NHase, and [Fe(II)((tame-N(3))S(2)(Me))(CO)] (16; nu(CO) stretch (1895 cm(-1)). Anions (N(3)(-), CN(-)) are shown to be unreactive toward 1, 3, and 15 and neutral ligands unreactive toward 3 and 15, even when present in 100-fold excess and at low temperatures. The curtailed reactivity of 15, an analogue of the unmodified form of NHase, and its apical-oxygenated S = 3/2 derivative [Fe(III)((tame-N(2)SO(2))S(2)(Me2))](2-) (20) suggests that regioselective post-translational oxygenation of the basal plane NHase cysteinate sulfurs plays an important role in promoting substrate binding. This is supported by previously reported theoretical (DFT) calculations.
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Affiliation(s)
- Priscilla Lugo-Mas
- The Department of Chemistry, University of Washington, Box 351700 Seattle, Washington 98195-1700, USA
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31
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Thallaj N, Rotthaus O, Benhamou L, Humbert N, Elhabiri M, Lachkar M, Welter R, Albrecht-Gary AM, Mandon D. Reactivity of Molecular Dioxygen towards a Series of Isostructural Dichloroiron(III) Complexes with Tripodal Tetraamine Ligands: General Access to μ-Oxodiiron(III) Complexes and Effect of α-Fluorination on the Reaction Kinetics. Chemistry 2008; 14:6742-53. [DOI: 10.1002/chem.200701967] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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32
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Schwedhelm KF, Horstmann M, Faber JH, Reichert Y, Bringmann G, Faber C. The novel antimalarial compound dioncophylline C forms a complex with heme in solution. ChemMedChem 2008; 2:541-8. [PMID: 17315144 DOI: 10.1002/cmdc.200600263] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A structural model of the complex formed between the novel antimalarial compound dioncophylline C (DioC) and its presumed target ferriprotoporphyrin IX heme (FPIX) is presented. The complex structure was calculated with molecular dynamics (MD) simulations using intermolecular distance restraints between DioC and the iron center in FPIX, determined from NMR paramagnetic relaxation. Besides the spin state of the iron and longitudinal relaxation rates of hydrogen nuclei in DioC, the effective correlation time of paramagnetic relaxation was determined from NMR measurements at three different magnetic field strengths. The derived structural model shows high similarity to complexes formed by FPIX and antimalarials of the quinoline family (chloroquine, quinine, quinidine, and amodiaquine). The conformation of DioC is sterically stabilized by a water molecule coordinated to iron in FPIX. This structural feature may provide an important hint at possibilities for a further optimization of novel naphthylisoquinoline alkaloid (NIQ) antimalarial drugs.
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Affiliation(s)
- Kai F Schwedhelm
- Department of Experimental Physics 5, University of Würzburg, Am Hubland, 97074 Würzburg, Germany
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33
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Brines LM, Villar-Acevedo G, Kitagawa T, Swartz RD, Lugo-Mas P, Kaminsky W, Benedict JB, Kovacs JA. Comparison of Structurally-Related Alkoxide, Amine, and Thiolate-Ligated M (M= Fe, Co) Complexes: the Influence of Thiolates on the Properties of Biologically Relevant Metal Complexes. Inorganica Chim Acta 2008; 361:1070-1078. [PMID: 21731109 DOI: 10.1016/j.ica.2007.07.038] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Mechanistic pathways of metalloenzymes are controlled by the metal ion's electronic and magnetic properties, which are tuned by the coordinated ligands. The functional advantage gained by incorporating cysteinates into the active site of non-heme iron enzymes such as superoxide reductase (SOR) is not entirely understood. Herein we compare the structural and redox properties of a series of structurally-related thiolate, alkoxide, and amine-ligated Fe(II) complexes in order to determine how the thiolate influences properties critical to function. Thiolates are shown to reduce metal ion Lewis acidity relative to alkoxides and amines, and have a strong trans influence thereby helping to maintain an open coordination site. Comparison of the redox potentials of the structurally analogous compounds described herein indicates that alkoxide ligands favor the higher-valent Fe(3+) oxidation state, amine ligands favor the reduced Fe(2+) oxidation state, and thiolates fall somewhere in between. These properties provide a functional advantange for substrate reducing enzymes in that they provide a site at the metal ion for substrate to bind, and a moderate potential that facilitates both substrate reduction, and regeneration of the catalytically active reduced state. Redox potentials for structurally-related Co(II) complexes are shown to be cathodically-shifted relative to their Fe(II) analogues, making them ineffective reducing agents for substrates such as superoxide.
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Affiliation(s)
- Lisa M Brines
- The Department of Chemistry, University of Washington: Box 351700 Seattle, WA 98195-1700
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34
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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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35
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Straganz GD, Nidetzky B. Variations of the 2-His-1-carboxylate theme in mononuclear non-heme FeII oxygenases. Chembiochem 2007; 7:1536-48. [PMID: 16858718 DOI: 10.1002/cbic.200600152] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
A facial triad of two histidine side chains and one aspartate or glutamate side chain forms the canonical metal-coordinating motif in the catalytic centers of various mononuclear non-heme Fe(II) enzymes. Although these active sites are based on totally unrelated protein folds and bring about a wide range of chemical transformations, most of them share the ability to couple dioxygen reduction with the oxygenation of an organic substrate. With the increasing number of protein structures now solved, it has become clear that the 2-His-1-carboxylate signature is less of a paradigm for non-heme Fe(II) active sites than had long been thought and that it can be replaced by alternative metal centers in various oxygenases, the structure-function relationships and proposed catalytic mechanisms of which are reviewed here. Metal coordination through three histidines and one glutamate constitutes the classical motif described for enzyme members of the cupin protein superfamily, such as aci-reductone dioxygenase and quercetin dioxygenase, multiple metal forms of which (including the Fe(II) type) are found in nature. Cysteine dioxygenase and diketone dioxygenase, which are strictly Fe(II)-dependent oxygenases based on the cupin fold, bind the catalytic metal through the homologous triad of histidines, but lack the fourth glutamate ligand. An alpha-ketoglutarate-dependent Fe(II) halogenase shows metal coordination by two histidines as the only protein-derived ligands, whilst carotene oxygenase, from a different protein fold family, features an Fe(II) site consisting of four histidine side chains. These recently discovered metallocenters are discussed with respect to their metal-binding properties and the reaction coordinates of the O(2)-dependent conversions they catalyze.
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Affiliation(s)
- G D Straganz
- Institute of Biotechnology and Biochemical Engineering Graz University of Technology Petersgasse 12/I, 8010 Graz, Austria.
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36
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Grapperhaus CA, O’Toole MG, Mashuta MS. Synthesis and structure of the tetradeca-iron(III) oxide–alkoxide cluster [Bu4N]2[Fe14O8(OCH2CH3)20Cl8]. INORG CHEM COMMUN 2006. [DOI: 10.1016/j.inoche.2006.07.027] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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37
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McCoy JG, Bailey LJ, Bitto E, Bingman CA, Aceti DJ, Fox BG, Phillips GN. Structure and mechanism of mouse cysteine dioxygenase. Proc Natl Acad Sci U S A 2006; 103:3084-9. [PMID: 16492780 PMCID: PMC1413891 DOI: 10.1073/pnas.0509262103] [Citation(s) in RCA: 154] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2005] [Indexed: 11/18/2022] Open
Abstract
Cysteine dioxygenase (CDO) catalyzes the oxidation of l-cysteine to cysteine sulfinic acid. Deficiencies in this enzyme have been linked to autoimmune diseases and neurological disorders. The x-ray crystal structure of CDO from Mus musculus was solved to a nominal resolution of 1.75 Angstroms. The sequence is 91% identical to that of a human homolog. The structure reveals that CDO adopts the typical beta-barrel fold of the cupin superfamily. The NE2 atoms of His-86, -88, and -140 provide the metal binding site. The structure further revealed a covalent linkage between the side chains of Cys-93 and Tyr-157, the cysteine of which is conserved only in eukaryotic proteins. Metal analysis showed that the recombinant enzyme contained a mixture of iron, nickel, and zinc, with increased iron content associated with increased catalytic activity. Details of the predicted active site are used to present and discuss a plausible mechanism of action for the enzyme.
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Affiliation(s)
- Jason G. McCoy
- Center for Eukaryotic Structural Genomics and Department of Biochemistry, University of Wisconsin, Madison, WI 53706-1544
| | - Lucas J. Bailey
- Center for Eukaryotic Structural Genomics and Department of Biochemistry, University of Wisconsin, Madison, WI 53706-1544
| | - Eduard Bitto
- Center for Eukaryotic Structural Genomics and Department of Biochemistry, University of Wisconsin, Madison, WI 53706-1544
| | - Craig A. Bingman
- Center for Eukaryotic Structural Genomics and Department of Biochemistry, University of Wisconsin, Madison, WI 53706-1544
| | - David J. Aceti
- Center for Eukaryotic Structural Genomics and Department of Biochemistry, University of Wisconsin, Madison, WI 53706-1544
| | - Brian G. Fox
- Center for Eukaryotic Structural Genomics and Department of Biochemistry, University of Wisconsin, Madison, WI 53706-1544
| | - George N. Phillips
- Center for Eukaryotic Structural Genomics and Department of Biochemistry, University of Wisconsin, Madison, WI 53706-1544
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Mathé C, Nivière V, Mattioli TA. Fe3+-Hydroxide Ligation in the Superoxide Reductase from Desulfoarculus baarsii Is Associated with pH Dependent Spectral Changes. J Am Chem Soc 2005; 127:16436-41. [PMID: 16305229 DOI: 10.1021/ja053808y] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Superoxide reductase (SOR) catalyzes the reduction of O2*- to H2O2. Its active site consists of a non-heme Fe2+ center in an unusual square-pyramidal [His4 Cys] coordination. Like many SORs, the electronic absorption band corresponding to the oxidized active site of the SOR from Desulfoarculus baarsii exhibits a pH-dependent alkaline transition changing from ca. 644 to 560 nm as the pH increases and with an apparent pKa of 9.0. Variants in which the conserved amino acids glutamate 47 and lysine 48 were replaced by the neutral residues alanine (E47A) and isoleucine (K48I), respectively, exhibited the same alkaline transition but at lower apparent pKa values of 6.7 and 7.6, respectively. Previous work [Nivière, V.; Asso, M.; Weill, C. O.; Lombard, M.; Guigliarelli, B.; Favaudon, V.; Houée-Levin, C. Biochemistry 2004, 43, 808-818] has shown that this alkaline transition is associated with the protonation/deprotonation of an unidentified base, B-, which is neither E47 nor K48. In this work, we show by resonance Raman spectroscopy that at basic pH a high-spin Fe3+-OH species is formed at the active site. The presence of the HO- ligand was directly associated with an absorption band maximum at 560 nm, whereas upon protonation, the band shifts to 644 nm. With respect to our previous work, B- can be identified with this high-spin Fe3+-OH species, which upon protonation results in a water molecule at the active site. Implications for the SOR catalytic cycle are proposed.
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Affiliation(s)
- Christelle Mathé
- Laboratoire de Biophysique du Stress Oxydant, SBE/DBJC and CNRS URA 2096, CEA/Saclay, 91191 Gif-sur-Yvette Cedex, France
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