1
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Robinson AL, Rebilly J, Guillot R, Herrero C, Maisonneuve H, Banse F. A Tale of Two Complexes: Electro‐Assisted Oxidation of Thioanisole by an “O
2
Activator/Oxidizing Species” Tandem System of Non‐Heme Iron Complexes. Chemistry 2022; 28:e202200217. [DOI: 10.1002/chem.202200217] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2022] [Indexed: 11/07/2022]
Affiliation(s)
- Amanda Lyn Robinson
- Institut de Chimie Moléculaire et des Matériaux d'Orsay Université Paris-Saclay CNRS 91405 Orsay cedex France
| | - Jean‐Noël Rebilly
- Institut de Chimie Moléculaire et des Matériaux d'Orsay Université Paris-Saclay CNRS 91405 Orsay cedex France
| | - Régis Guillot
- Institut de Chimie Moléculaire et des Matériaux d'Orsay Université Paris-Saclay CNRS 91405 Orsay cedex France
| | - Christian Herrero
- Institut de Chimie Moléculaire et des Matériaux d'Orsay Université Paris-Saclay CNRS 91405 Orsay cedex France
| | - Hélène Maisonneuve
- Institut de Chimie Moléculaire et des Matériaux d'Orsay Université Paris-Saclay CNRS 91405 Orsay cedex France
| | - Frédéric Banse
- Institut de Chimie Moléculaire et des Matériaux d'Orsay Université Paris-Saclay CNRS 91405 Orsay cedex France
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2
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Lo FC, Hsieh CC, Maestre-Reyna M, Chen CY, Ko TP, Horng YC, Lai YC, Chiang YW, Chou CM, Chiang CH, Huang WN, Lin YH, Bohle DS, Liaw WF. Crystal Structure Analysis of the Repair of Iron Centers Protein YtfE and Its Interaction with NO. Chemistry 2016; 22:9768-76. [DOI: 10.1002/chem.201600990] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2016] [Indexed: 11/07/2022]
Affiliation(s)
- Feng-Chun Lo
- Department of Chemistry; National Tsing Hua University; Hsinchu 30013 Taiwan
| | - Chang-Chih Hsieh
- Department of Chemistry; National Tsing Hua University; Hsinchu 30013 Taiwan
| | | | - Chin-Yu Chen
- Department of Life Sciences; National Central University; Taoyuan Taiwan
| | - Tzu-Ping Ko
- Institute of Biological Chemistry; Academia Sinica; Taipei Taiwan
| | - Yih-Chern Horng
- Department of Chemistry; National Changhua University of Education; Changhua Taiwan
| | - Yei-Chen Lai
- Department of Chemistry; National Tsing Hua University; Hsinchu 30013 Taiwan
| | - Yun-Wei Chiang
- Department of Chemistry; National Tsing Hua University; Hsinchu 30013 Taiwan
| | - Chih-Mao Chou
- Department of Life Sciences; National Central University; Taoyuan Taiwan
| | | | - Wei-Ning Huang
- Department of Biotechnology; Yuanpei University; Hsinchu Taiwan
| | - Yi-Hung Lin
- National Synchrotron Radiation Research Center Hsinchu; Taiwan
| | - D. Scott Bohle
- Department of Chemistry; McGill University; 801 Sherbrooke Street West Montreal QC H3A2K6 Canada
| | - Wen-Feng Liaw
- Department of Chemistry; National Tsing Hua University; Hsinchu 30013 Taiwan
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3
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Falkenhagen JP, Braun B, Bill E, Sattler D, Limberg C. A cubic Fe4Mo4 oxo framework and its reversible four-electron redox chemistry. Inorg Chem 2014; 53:7294-308. [PMID: 24981960 DOI: 10.1021/ic500584a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The potential of iron molybdates as catalysts in the Formox process stimulates research on aggregated but molecular iron-molybdenum oxo compounds. In this context, [(Me3TACN)Fe](OTf)2 was reacted with (nBu4N)2[MoO4], which led to an oxo cluster, [[(Me3TACN)Fe][μ-(MoO4-κ(3)O,O',O″)]]4 (1, Fe4Mo4) with a distorted cubic structure, where the corners are occupied by (Me3TACN)Fe(2+) and [Mo═O](4+) units in an alternating fashion, being bridged by oxido ligands. The cyclic voltammogram revealed four reversible oxidation waves that are assigned to four consecutive Fe(II) → Fe(III) transfers and motivated attempts to isolate compounds containing the respective cations. Indeed, a salt with a Fe(II)2Fe(III)2Mo(VI)4 constellation, [Fe4Mo4](TCNQ)2 (2), could be isolated after treatment with TCNQ. The Fe(II)Fe(III)3Mo(VI)4 stage could be reached via oxidation with DDQ or 3 equiv of thianthrenium hexafluorophosphate (ThPF6), giving [Fe4Mo4](DDQ)3 (4) or [Fe4Mo4](PF6)3 (5), respectively. The fully oxidized Fe(III)4Mo(VI)4 state was generated through oxidation with 4 equiv of ThPF6, leading to [Fe4Mo4](PF6)4, which showed a unique behavior: upon storage, one of the [Mo═O](4+) corners inverts, so that the terminal oxido ligand is located in the interior of the cage, leading to the formation of [[(Me3TACN)Fe]4[μ-([MoO4]3[MoO4(MeCN-κN)])-κ(3)O,O',O″)](PF6)4 (7). In this form, the compound could no longer be employed to enter the cyclic voltammogram recorded for 1, 3, and 5 from the oxidized side; no discrete redox events were observed. Compounds 1-3 and 7 were characterized structurally and 1, 3, and 7 additionally by SQUID measurements and Mössbauer spectroscopy. The data reveal a high degree of charge delocalization. (16)O/(18)O exchange experiments with labeled water performed with 1 revealed an interesting parallel with the Formox catalyst: water-(18)O exchanges its label with all of the oxido ligands (bridging and terminal). This property relates to the ion mobility being held responsible for the activity of iron molybdate catalysts compared to neat MoO3 or Fe2O3.
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Affiliation(s)
- Jan P Falkenhagen
- Institut für Chemie, Humboldt-Universität zu Berlin , Brook-Taylor-Straße 2, 12489 Berlin, Germany
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4
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Falkenhagen JP, Limberg C, Demeshko S, Horn S, Haumann M, Braun B, Mebs S. Iron-molybdenum-oxo complexes as initiators for olefin autoxidation with O2. Dalton Trans 2014; 43:806-16. [PMID: 24154868 DOI: 10.1039/c3dt52349g] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The reaction between [(TPA)Fe(MeCN)2](OTf)2 and [nBu4N](Cp*MoO3) yields the novel tetranuclear complex [(TPA)Fe(μ-Cp*MoO3)]2(OTf)2, 1, with a rectangular [Mo-O-Fe-O-]2 core containing high-spin iron(ii) centres. 1 proved to be an efficient initiator/(pre)catalyst for the autoxidation of cis-cyclooctene with O2 to give cyclooctene epoxide. To test, which features of 1 are essential in this regard, analogues with zinc(ii) and cobalt(ii) central atoms, namely [(TPA)Zn(Cp*MoO3)](OTf), 3, and [(TPA)Co(Cp*MoO3)](OTf), 4, were prepared, which proved to be inactive. The precursor compounds of 1, [(TPA)Fe(MeCN)2](OTf)2 and [nBu4N](Cp*MoO3) as well as Cp2*Mo2O5, were found to be inactive, too. Reactivity studies in the absence of cyclooctene revealed that 1 reacts both with O2 and PhIO via loss of the Cp* ligands to give the triflate salt 2 of the known cation [((TPA)Fe)2(μ-O)(μ-MoO4)](2+). The cobalt analogue 4 reacts with O2 in a different way yielding [((TPA)Co)2(μ-Mo2O8)](OTf)2, 5, featuring a Mo2O8(4-) structural unit which is novel in coordination chemistry. The compound [(TPA)Fe(μ-MoO4)]2, 6, being related to 1, but lacking Cp* ligands failed to trigger autoxidation of cyclooctene. However, initiation of autoxidation by Cp* radicals was excluded via experiments including thermal dissociation of Cp2*.
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Affiliation(s)
- Jan P Falkenhagen
- Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489, Berlin, Germany.
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5
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Li F, Chakrabarti M, Dong Y, Kauffmann K, Bominaar EL, Münck E, Que L. Structural, EPR, and Mössbauer characterization of (μ-alkoxo)(μ-carboxylato)diiron(II,III) model complexes for the active sites of mixed-valent diiron enzymes. Inorg Chem 2012; 51:2917-29. [PMID: 22360600 PMCID: PMC3298377 DOI: 10.1021/ic2021726] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
To obtain structural and spectroscopic models for the diiron(II,III) centers in the active sites of diiron enzymes, the (μ-alkoxo)(μ-carboxylato)diiron(II,III) complexes [Fe(II)Fe(III)(N-Et-HPTB)(O(2)CPh)(NCCH(3))(2)](ClO(4))(3) (1) and [Fe(II)Fe(III)(N-Et-HPTB)(O(2)CPh)(Cl)(HOCH(3))](ClO(4))(2) (2) (N-Et-HPTB = N,N,N',N'-tetrakis(2-(1-ethyl-benzimidazolylmethyl))-2-hydroxy-1,3-diaminopropane) have been prepared and characterized by X-ray crystallography, UV-visible absorption, EPR, and Mössbauer spectroscopies. Fe1-Fe2 separations are 3.60 and 3.63 Å, and Fe1-O1-Fe2 bond angles are 128.0° and 129.4° for 1 and 2, respectively. Mössbauer and EPR studies of 1 show that the Fe(III) (S(A) = 5/2) and Fe(II) (S(B) = 2) sites are antiferromagnetically coupled to yield a ground state with S = 1/2 (g= 1.75, 1.88, 1.96); Mössbauer analysis of solid 1 yields J = 22.5 ± 2 cm(-1) for the exchange coupling constant (H = JS(A)·S(B) convention). In addition to the S = 1/2 ground-state spectrum of 1, the EPR signal for the S = 3/2 excited state of the spin ladder can also be observed, the first time such a signal has been detected for an antiferromagnetically coupled diiron(II,III) complex. The anisotropy of the (57)Fe magnetic hyperfine interactions at the Fe(III) site is larger than normally observed in mononuclear complexes and arises from admixing S > 1/2 excited states into the S = 1/2 ground state by zero-field splittings at the two Fe sites. Analysis of the "D/J" mixing has allowed us to extract the zero-field splitting parameters, local g values, and magnetic hyperfine structural parameters for the individual Fe sites. The methodology developed and followed in this analysis is presented in detail. The spin Hamiltonian parameters of 1 are related to the molecular structure with the help of DFT calculations. Contrary to what was assumed in previous studies, our analysis demonstrates that the deviations of the g values from the free electron value (g = 2) for the antiferromagnetically coupled diiron(II,III) core in complex 1 are predominantly determined by the anisotropy of the effective g values of the ferrous ion and only to a lesser extent by the admixture of excited states into ground-state ZFS terms (D/J mixing). The results for 1 are discussed in the context of the data available for diiron(II,III) clusters in proteins and synthetic diiron(II,III) complexes.
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Affiliation(s)
- Feifei Li
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, MN 55455
| | | | - Yanhong Dong
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, MN 55455
| | - Karl Kauffmann
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213
| | - Emile L. Bominaar
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213
| | - Eckard Münck
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213
| | - Lawrence Que
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, MN 55455
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6
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Smith SJ, Peralta RA, Jovito R, Horn A, Bortoluzzi AJ, Noble CJ, Hanson GR, Stranger R, Jayaratne V, Cavigliasso G, Gahan LR, Schenk G, Nascimento OR, Cavalett A, Bortolotto T, Razzera G, Terenzi H, Neves A, Riley MJ. Spectroscopic and Catalytic Characterization of a Functional FeIIIFeII Biomimetic for the Active Site of Uteroferrin and Protein Cleavage. Inorg Chem 2012; 51:2065-78. [DOI: 10.1021/ic201711p] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Affiliation(s)
| | | | | | | | | | | | | | - Robert Stranger
- Research School of Chemistry, Australian National University, Canberra 0200, Australia
| | - Vidura Jayaratne
- Research School of Chemistry, Australian National University, Canberra 0200, Australia
| | - Germán Cavigliasso
- Research School of Chemistry, Australian National University, Canberra 0200, Australia
| | | | - Gerhard Schenk
- Department of Chemistry, National University of Ireland—Maynooth, Maynooth County, Kildare, Ireland
| | - Otaciro R. Nascimento
- Instituto de Física, Universidade de São Paulo, 13560-970 São
Carlos, São Paulo, Brazil
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7
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De Hont RF, Xue G, Hendrich MP, Que L, Bominaar EL, Münck E. Mössbauer, electron paramagnetic resonance, and density functional theory studies of synthetic S = 1/2 Fe(III)-O-Fe(IV)═O complexes. Superexchange-mediated spin transition at the Fe(IV)═O site. Inorg Chem 2011; 49:8310-22. [PMID: 20795646 DOI: 10.1021/ic100870v] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Previously we have characterized two high-valent complexes [LFe(IV)(μ-O)(2)Fe(III)L], 1, and [LFe(IV)(O)(μ-O)(OH) Fe(IV)L], 4. Addition of hydroxide or fluoride to 1 produces two new complexes, 1-OH and 1-F. Electron paramagnetic resonance (EPR) and Mössbauer studies show that both complexes have an S = 1/2 ground state which results from antiferromagnetic coupling of the spins of a high-spin (S(a) = 5/2) Fe(III) and a high-spin (S(b) = 2) Fe(IV) site. 1-OH can also be obtained by a 1-electron reduction of 4, which has been shown to have an Fe(IV)═O site. Radiolytic reduction of 4 at 77 K yields a Mössbauer spectrum identical to that observed for 1-OH, showing that the latter contains an Fe(IV)═O. Interestingly, the Fe(IV)═O moiety has S(b) = 1 in 4 and S(b) = 2 in 1-OH and 1-F. From the temperature dependence of the S = 1/2 signal we have determined the exchange coupling constant J (ℋ = JS(a)·S(b) convention) to be 90 ± 20 cm(-1) for both 1-OH and 1-F. Broken-symmetry density functional theory (DFT) calculations yield J = 135 cm(-1) for 1-OH and J = 104 cm(-1) for 1-F, in good agreement with the experiments. DFT analysis shows that the S(b) = 1 → S(b) = 2 transition of the Fe(IV)═O site upon reduction of the Fe(IV)-OH site to high-spin Fe(III) is driven primarily by the strong antiferromagnetic exchange in the (S(a) = 5/2, S(b) = 2) couple.
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Affiliation(s)
- Raymond F De Hont
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
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8
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9
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Ghosh A, Mitchell DA, Chanda A, Ryabov AD, Popescu DL, Upham EC, Collins GJ, Collins TJ. Catalase-peroxidase activity of iron(III)-TAML activators of hydrogen peroxide. J Am Chem Soc 2008; 130:15116-26. [PMID: 18928252 DOI: 10.1021/ja8043689] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Exceptionally high peroxidase-like and catalase-like activities of iron(III)-TAML activators of H 2O 2 ( 1: Tetra-Amidato-Macrocyclic-Ligand Fe (III) complexes [ F e{1,2-X 2C 6H 2-4,5-( NCOCMe 2 NCO) 2CR 2}(OH 2)] (-)) are reported from pH 6-12.4 and 25-45 degrees C. Oxidation of the cyclometalated 2-phenylpyridine organometallic complex, [Ru (II)( o-C 6H 4py)(phen) 2]PF 6 ( 2) or "ruthenium dye", occurs via the equation [ Ru II ] + 1/2 H 2 O 2 + H +-->(Fe III - TAML) [ Ru III ] + H 2 O, following a simple rate law rate = k obs (per)[ 1][H 2O 2], that is, the rate is independent of the concentration of 2 at all pHs and temperatures studied. The kinetics of the catalase-like activity (H 2 O 2 -->(Fe III - TAML) H 2 O + 1/2 O 2) obeys a similar rate law: rate = k obs (cat)[ 1][H 2O 2]). The rate constants, k obs (per) and k obs (cat), are strongly and similarly pH dependent, with a maximum around pH 10. Both bell-shaped pH profiles are quantitatively accounted for in terms of a common mechanism based on the known speciation of 1 and H 2O 2 in this pH range. Complexes 1 exist as axial diaqua species [FeL(H 2O) 2] (-) ( 1 aqua) which are deprotonated to afford [FeL(OH)(H 2O)] (2-) ( 1 OH) at pH 9-10. The pathways 1 aqua + H 2O 2 ( k 1), 1 OH + H 2O 2 ( k 2), and 1 OH + HO 2 (-) ( k 4) afford one or more oxidized Fe-TAML species that further rapidly oxidize the dye (peroxidase-like activity) or a second H 2O 2 molecule (catalase-like activity). This mechanism is supported by the observations that (i) the catalase-like activity of 1 is controllably retarded by addition of reducing agents into solution and (ii) second order kinetics in H 2O 2 has been observed when the rate of O 2 evolution was monitored in the presence of added reducing agents. The performances of the 1 complexes in catalyzing H 2O 2 oxidations are shown to compare favorably with the peroxidases further establishing Fe (III)-TAML activators as miniaturized enzyme replicas with the potential to greatly expand the technological utility of hydrogen peroxide.
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Affiliation(s)
- Anindya Ghosh
- Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA
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10
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Bitterlich B, Anilkumar G, Gelalcha FG, Spilker B, Grotevendt A, Jackstell R, Tse MK, Beller M. Development of a General and Efficient Iron-Catalyzed Epoxidation with Hydrogen Peroxide as Oxidant. Chem Asian J 2007; 2:521-9. [PMID: 17441190 DOI: 10.1002/asia.200600407] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The development of inexpensive and practical iron catalysts for the environmentally benign epoxidation of olefins with hydrogen peroxide as terminal oxidant is described. By systematic variation of ligands, metal sources, and reaction conditions, it was discovered that FeCl3 x 6 H2O in combination with pyridine-2,6-dicarboxylic acid and different amines shows high reactivity and excellent selectivity towards the epoxidation of aromatic olefins and moderate reactivity towards that of aliphatic olefins.
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Affiliation(s)
- Bianca Bitterlich
- Leibniz-Institut für Katalyse, Albert-Einstein-Str. 29a, D-18059 Rostock, Germany
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11
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Davydov R, Satterlee JD, Fujii H, Sauer-Masarwa A, Busch DH, Hoffman BM. A superoxo-ferrous state in a reduced oxy-ferrous hemoprotein and model compounds. J Am Chem Soc 2004; 125:16340-6. [PMID: 14692776 DOI: 10.1021/ja037037e] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cryoreduction of the [FeO2]6 (n = 6 is the number of electrons in 3d orbitals on Fe and pi* orbitals on O2) dioxygen-bound ferroheme through irradiation at 77 K generates an [FeO2]7 reduced oxy-heme. Numerous investigations have examined [FeO2]7 centers that have been characterized as peroxo-ferric centers, denoted [FeO2]per7, in which a ferriheme binds a dianionic peroxo-ligand. The generation of such an intermediate can be understood heuristically if the [FeO2]6 parent is viewed as a superoxo-ferric center and the injected electron localizes on the O-O moiety. We here report EPR/ENDOR experiments which show quite different properties for the [FeO2]7 centers produced by cryoreduction of monomeric oxy-hemoglobin (oxy-GMH3) from Glycera dibranchiata, which is unlike mammalian "globins" in having a leucine in place of the distal histidine; of frozen aprotic solutions of oxy-ferrous octaethyl porphyrin; and of the oxy-ferrous complex of the heme model, cyclidene. These [FeO2]7 centers are characterized as "superoxo-ferrous" centers ([FeO2]sup7), with nearly unit spin density localized on a superoxo moiety which is end-on coordinated to a low-spin ferrous ion. This assignment is based on their g tensors and 17O hyperfine couplings, which are characteristic of the superoxide ion coordinated to a diamagnetic metal ion, and on the absence of detectable ENDOR signals either from the in-plane 14N ligands or from an exchangeable H-bond proton. Such a center would arise if the electron that adds to the [FeO2]6 superoxo-ferric parent localizes on the Fe ion, to make a superoxo-ferrous moiety. Upon annealing to T > 150 K, the [FeO2]sup7 species converts to peroxo/hydroperoxo-ferric ([FeO2H]7) intermediates. These experiments suggest that the primary reduction product is [FeO2]sup7 and that the internal redox transition to [FeO2]per7/[FeO2H]7 states is driven at least in part by H-bonding/proton donation by the environment.
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Affiliation(s)
- Roman Davydov
- Department of Chemistry, Northwestern University, 2156 Sheridan Road, Evanston, Illinois 60208-3113, USA
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12
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Smoukov SK, Davydov RM, Doan PE, Sturgeon B, Kung IY, Hoffman BM, Kurtz DM. EPR and ENDOR evidence for a 1-His, hydroxo-bridged mixed-valent diiron site in Desulfovibrio vulgaris rubrerythrin. Biochemistry 2003; 42:6201-8. [PMID: 12755623 DOI: 10.1021/bi0300027] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Key features differentiating the coordination environment of the two irons in the mixed-valent (Fe(2+),Fe(3+)) diiron site of Desulfovibrio vulgaris rubrerythrin (Rbr(mv)) were determined by continuous wave (CW) and pulsed ENDOR spectroscopy at 35GHz. (14)N ENDOR evidence indicates that a nitrogen is bound only to the Fe(2+) ion of the mixed-valent site. Assuming that this nitrogen is from His131Ndelta, the same one that furnishes an iron ligand in the crystal structure of the diferric site, the ENDOR data allow us to specify the Fe(2+) and Fe(3+) positions within the molecular reference frame. In addition, the (1,2)H ENDOR on Rbr(mv) indicates the presence of a solvent-derived aqua/hydroxo ligand bound either terminally or in a bridging mode to Fe(3+) in the mixed-valent site. The relatively large g anisotropy of Rbr(mv) and weak antiferromagnetic coupling, J approximately -8 cm(-)(1) (in the 2JS(1)*S(2) formalism), between the irons is more consistent with a bridging than terminal hydroxo ligand. gamma-Irradiation was used to cryoreduce Rbr at 77 K, thereby producing a mixed-valent diiron site [(Rbr(ox))(mv)] that retains the structure of the diferric site. The EPR spectrum of (Rbr(ox))(mv) was nearly identical to that of the as-isolated or chemically reduced samples. This near identity implies that the structure of the mixed-valent Rbr diiron site is essentially identical to that of the diferric site, except for protonation of the oxo bridge, which apparently occurred via a proton jump from hydrogen-bonded solvent at 77 K. The EPR spectrum of (Rbr(ox))(mv) thus supports the (14)N ENDOR-assigned His131 ligation to Fe(2+) and assignment of the solvent-derived ligand observed in the (1,2)H ENDOR to a hydroxo bridge between the irons of the mixed-valent diiron site.
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Affiliation(s)
- Stoyan K Smoukov
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA
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13
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Berthold DA, Voevodskaya N, Stenmark P, Gräslund A, Nordlund P. EPR studies of the mitochondrial alternative oxidase. Evidence for a diiron carboxylate center. J Biol Chem 2002; 277:43608-14. [PMID: 12215444 DOI: 10.1074/jbc.m206724200] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The alternative oxidase (AOX) is a ubiquinol oxidase found in the mitochondrial respiratory chain of plants as well as some fungi and protists. It has been predicted to contain a coupled diiron center on the basis of a conserved sequence motif consisting of the proposed iron ligands, four glutamate and two histidine residues. However, this prediction has not been experimentally verified. Here we report the high level expression of the Arabidopsis thaliana alternative oxidase AOX1a as a maltose-binding protein fusion in Escherichia coli. Reduction and reoxidation of a sample of isolated E. coli membranes containing the alternative oxidase generated an EPR signal characteristic of a mixed-valent Fe(II)/Fe(III) binuclear iron center. The high anisotropy of the signal, the low value of the g-average tensor, and a small exchange coupling (-J) suggest that the iron center is hydroxo-bridged. A reduced membrane preparation yielded a parallel mode EPR signal with a g-value of about 15. In AOX containing a mutation of a putative glutamate ligand of the diiron center (E222A or E273A) the EPR signals are absent. These data provide evidence for an antiferromagnetic-coupled binuclear iron center, and together with the conserved sequence motif, identify the alternative oxidase as belonging to the growing family of diiron carboxylate proteins. The alternative oxidase is the first integral membrane protein in this family, and adds a new catalytic activity (ubiquinol oxidation) to this group of enzymatically diverse proteins.
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Affiliation(s)
- Deborah A Berthold
- Department of Biochemistry and Biophysics, Stockholm University Svante Arrhenius väg 16, Sweden.
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14
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Merkx M, Kopp DA, Sazinsky MH, Blazyk JL, Müller J, Lippard SJ. Dioxygen Activation and Methane Hydroxylation by Soluble Methane Monooxygenase: A Tale of Two Irons and Three Proteins. Angew Chem Int Ed Engl 2001. [DOI: 10.1002/1521-3773(20010803)40:15%3c2782::aid-anie2782%3e3.0.co;2-p] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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15
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Merkx M, Kopp DA, Sazinsky MH, Blazyk JL, Müller J, Lippard SJ. Aktivierung von Disauerstoff und Hydroxylierung von Methan durch lösliche Methan-Monooxygenase: eine Geschichte von zwei Eisenatomen und drei Proteinen. Angew Chem Int Ed Engl 2001. [DOI: 10.1002/1521-3757(20010803)113:15<2860::aid-ange2860>3.0.co;2-2] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Merkx M, Kopp DA, Sazinsky MH, Blazyk JL, Müller J, Lippard SJ. Dioxygen Activation and Methane Hydroxylation by Soluble Methane Monooxygenase: A Tale of Two Irons and Three Proteins. Angew Chem Int Ed Engl 2001; 40:2782-2807. [PMID: 29711993 DOI: 10.1002/1521-3773(20010803)40:15<2782::aid-anie2782>3.0.co;2-p] [Citation(s) in RCA: 461] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2001] [Revised: 05/03/2001] [Indexed: 11/11/2022]
Affiliation(s)
- Maarten Merkx
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue 18-590 Cambridge, MA 02139 (USA) Fax: (+1) 617-258-8150
| | - Daniel A Kopp
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue 18-590 Cambridge, MA 02139 (USA) Fax: (+1) 617-258-8150
| | - Matthew H Sazinsky
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue 18-590 Cambridge, MA 02139 (USA) Fax: (+1) 617-258-8150
| | - Jessica L Blazyk
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue 18-590 Cambridge, MA 02139 (USA) Fax: (+1) 617-258-8150
| | - Jens Müller
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue 18-590 Cambridge, MA 02139 (USA) Fax: (+1) 617-258-8150
| | - Stephen J Lippard
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue 18-590 Cambridge, MA 02139 (USA) Fax: (+1) 617-258-8150
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Krebs C, Davydov R, Baldwin J, Hoffman BM, Bollinger, JM, Huynh BH. Mössbauer and EPR Characterization of the S = 9/2 Mixed-Valence Fe(II)Fe(III) Cluster in the Cryoreduced R2 Subunit of Escherichia coli Ribonucleotide Reductase. J Am Chem Soc 2000. [DOI: 10.1021/ja000317z] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Carsten Krebs
- Contributions from the Department of Physics, Rollins Research Center, Emory University, Atlanta, Georgia 30322, Department of Chemistry, Northwestern University, Evanston, Illinois 60208, and Departments of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania 16802
| | - Roman Davydov
- Contributions from the Department of Physics, Rollins Research Center, Emory University, Atlanta, Georgia 30322, Department of Chemistry, Northwestern University, Evanston, Illinois 60208, and Departments of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania 16802
| | - Jeff Baldwin
- Contributions from the Department of Physics, Rollins Research Center, Emory University, Atlanta, Georgia 30322, Department of Chemistry, Northwestern University, Evanston, Illinois 60208, and Departments of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania 16802
| | - Brian M. Hoffman
- Contributions from the Department of Physics, Rollins Research Center, Emory University, Atlanta, Georgia 30322, Department of Chemistry, Northwestern University, Evanston, Illinois 60208, and Departments of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania 16802
| | - J. Martin Bollinger,
- Contributions from the Department of Physics, Rollins Research Center, Emory University, Atlanta, Georgia 30322, Department of Chemistry, Northwestern University, Evanston, Illinois 60208, and Departments of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania 16802
| | - Boi Hanh Huynh
- Contributions from the Department of Physics, Rollins Research Center, Emory University, Atlanta, Georgia 30322, Department of Chemistry, Northwestern University, Evanston, Illinois 60208, and Departments of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania 16802
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18
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Abstract
The past year has seen significant advances in the understanding of the dioxygen-activating chemistry of non-heme diiron enzymes, such as methane monooxygenase. Recent spectroscopic and structural studies on various biomimetic model compounds have provided new and valuable insights into this enzyme's mechanism of action and the important dioxygen-activation process.
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Affiliation(s)
- L Westerheide
- Anorganisch-Chemisches Institut, Universität Münster, Münster, D-48149, Germany
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