A growing family of O2 activating dinuclear iron enzymes with key catalytic diiron(III)-peroxo intermediates: Biological systems and chemical models

Trehoux, Alexandre; Mahy, Jean‐Pierre; Avenier, Frédéric

doi:10.1016/j.ccr.2016.05.014

Cited by 67 publications

(54 citation statements)

References 170 publications

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“…The observation that the rate constants decrease with the increase of the C−H BDE of the substrate supports an H-atom transfer as the rate determining step for the oxidation. [5] This conclusion is consistent with the observation of a kinetic isotope effect k H / k D =2.8 for the competitive oxidation of xanthene and xanthene- d 2 at −40°C. These observations strongly suggest that 2 may either react directly with the substrate or be in equilibrium with a high-valent derivative that actually cleaves the C–H bond.…”

Section: Resultssupporting

confidence: 89%

“…[3] A wealth of information concerning the nature and reactivity of the active species involved in the action of various metalloenzymes with mononuclear and dinuclear iron active sites has been uncovered from synthetic complexes. [4,5] Bioinspired iron catalysts have also been developed that use H 2 O 2 as oxidant and are capable of selective oxidation of aliphatic C–H bonds. [6] …”

Section: Introductionmentioning

confidence: 99%

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Hydrogen‐Atom Transfer Oxidation with H₂O₂ Catalyzed by [FeII(1,2‐bis(2,2′‐bipyridyl‐6‐yl)ethane(H₂O)₂]²⁺: Likely Involvement of a (μ‐Hydroxo)(μ‐1,2‐peroxo)diiron(III) Intermediate

Khenkin

Madhu

Shimon

et al. 2017

Israel Journal of Chemistry

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The iron(II) triflate complex (1) of 1,2-bis(2,2′-bipyridyl-6-yl)ethane, with two bipyridine moieties connected by an ethane bridge, was prepared. Addition of aqueous 30% H2O2 to an acetonitrile solution of 1 yielded 2, a green compound with λmax=710 nm. Moessbauer measurements on 2 showed a doublet with an isomer shift (δ) of 0.35 mm/s and a quadrupole splitting (ΔEQ) of 0.86 mm/s, indicative of an antiferromagnetically coupled diferric complex. Resonance Raman spectra showed peaks at 883, 556 and 451 cm−1 that downshifted to 832, 540 and 441 cm−1 when 1 was treated with H218O2. All the spectroscopic data support the initial formation of a (μ-hydroxo)(μ-1,2-peroxo)diiron(III) complex that oxidizes carbon-hydrogen bonds. At 0°C 2 reacted with cyclohexene to yield allylic oxidation products but not epoxide. Weak benzylic C−H bonds of alkylarenes were also oxidized. A plot of the logarithms of the second order rate constants versus the bond dissociation energies of the cleaved C−H bond showed an excellent linear correlation. Along with the observation that oxidation of the probe substrate 2,2-dimethyl-1-phenylpropan-1-ol yielded the corresponding ketone but no benzaldehyde, and the kinetic isotope effect, kH/kD, of 2.8 found for the oxidation of xanthene, the results support the hypothesis for a metal-based H-atom abstraction mechanism. Complex 2 is a rare example of a (μ-hydroxo)(μ-1,2-peroxo)diiron(III) complex that can elicit the oxidation of carbon-hydrogen bonds.

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Section: Resultssupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Hydrogen‐Atom Transfer Oxidation with H₂O₂ Catalyzed by [FeII(1,2‐bis(2,2′‐bipyridyl‐6‐yl)ethane(H₂O)₂]²⁺: Likely Involvement of a (μ‐Hydroxo)(μ‐1,2‐peroxo)diiron(III) Intermediate

Khenkin

Madhu

Shimon

et al. 2017

Israel Journal of Chemistry

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“…The first kinetically resolvable intermediate exhibits optical absorption features in the visible region of the spectrum, reminiscent of the low energy ligand-to-metal charge transfer transitions found in ( μ -peroxo)–Fe III /Fe III species. 26,29,31–34 Similar intermediates have been isolated in a number of nonheme diiron carboxylate proteins, including MMO, D Δ 9 D, RNR, CmlI and hDOHH. These species generally feature broad absorption bands centered around 700 nm with extinction coefficients of ~1500 M −1 cm −1 ; often accompanying these low-energy transitions are similarly or more intense bands at higher energies (400–500 nm).…”

Section: Discussionmentioning

confidence: 77%

“…Extinction coefficients for conversion of absorbance data were selected based on representative literature values, with ε 620, peroxo = 1500 M −1 cm −1 used for formation and decay of I 1 at 620 nm, and ε 390, IV/IV = 1500 M −1 cm −1 for decay of I 2 at 390 nm. 26,27 Experimental concentration values were then “assigned” in KinTek to the proposed observable species discussed above, and the model was fit to the data for determination of reaction rate constants. Spin quantitation based on a Cu II Az standard was used to obtain product concentration in the 20-minute EPR sample, which was calculated to be ~40 μ M. Concentrations of product at t < 20 min were obtained using the EPR intensity at 374 mT, scaled with respect to the intensity at that field position of the 20-minute sample.…”

Section: Methodsmentioning

confidence: 99%

Time-Resolved Investigations of Heterobimetallic Cofactor Assembly in R2lox Reveal Distinct Mn/Fe Intermediates

Miller¹,

Trivelas²,

Maugeri³

et al. 2017

Biochemistry

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The assembly mechanism of the Mn/Fe ligand-binding oxidases (R2lox), a family of proteins that are homologous to the nonheme diiron carboxylate enzymes, has been investigated using time-resolved techniques. Multiple heterobimetallic intermediates are observed through optical and magnetic resonance spectroscopies that exhibit unique spectral features, including visible absorption bands and exceptionally broad EPR signatures. On the basis of comparison to known diiron species and model compounds, the spectra have been attributed to (μ-peroxo)-MnIII/FeIII and high-valent Mn/Fe species. Global spectral analysis coupled with isotopic substitution and kinetic modeling reveals elementary rate constants for the assembly of Mn/Fe R2lox under aerobic conditions. A complete reaction mechanism for cofactor maturation that is consistent with experimental data has been developed. These results suggest that the Mn/Fe cofactor can perform direct C–H bond abstraction, demonstrating the potential for potent chemical reactivity that remains unexplored.

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“…103 CmlI P is proposed here to have a μ -oxo bridge as well as a μ -1,1-peroxo ligand that interacts with protein-derived ligands in the CmlI active site. It is the only example of a μ -1,1-peroxo species in diiron chemistry.…”

Section: Resultsmentioning

confidence: 99%

Unprecedented (μ-1,1-Peroxo)diferric Structure for the Ambiphilic Orange Peroxo Intermediate of the Nonheme N-Oxygenase CmlI

et al. 2017

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The final step in the biosynthesis of the antibiotic chloramphenicol is the oxidation of an aryl-amine substrate to an aryl-nitro product catalyzed by the N-oxygenase CmlI in three two-electron steps. The CmlI active site contains a diiron cluster ligated by three histidine and four glutamate residues, and activates dioxygen to perform its role in the biosynthetic pathway. It was previously shown that the active oxidant used by CmlI to facilitate this chemistry is a peroxo-diferric intermediate (CmlIP). Spectroscopic characterization demonstrated that the peroxo binding geometry of CmlIP is not consistent with the μ-1,2 mode commonly observed in nonheme diiron systems. Its geometry was tentatively assigned as μ- η2: η1 based on comparison with resonance Raman (rR) features of mixed-metal model complexes in the absence of appropriate diiron models. Here, X-ray absorption spectroscopy (XAS) and rR studies have been used to establish a refined structure for the diferric cluster of CmlIP. The rR experiments carried out with isotopically labeled water identified the symmetric and asymmetric vibrations of an Fe–O–Fe unit in the active site at 485 and 780 cm−1, respectively, which was confirmed by the 1.83-Å Fe–O bond observed by XAS. In addition, a unique Fe•••O scatterer at 2.82 Å observed from XAS analysis is assigned as arising from the distal O atom of a μ-1,1-peroxo ligand that is bound symmetrically between the irons. The (μ-oxo)(μ-1,1-peroxo)diferric core structure associated with CmlIP is unprecedented among diiron cluster-containing enzymes and corresponding biomimetic complexes. Importantly, it allows the peroxo-diferric intermediate to be ambiphilic, acting as an electrophilic oxidant in the initial N-hydroxylation of an arylamine and then becoming a nucleophilic oxidant in the final oxidation of an aryl-nitroso intermediate to the aryl-nitro product.

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A growing family of O2 activating dinuclear iron enzymes with key catalytic diiron(III)-peroxo intermediates: Biological systems and chemical models

Cited by 67 publications

References 170 publications

Hydrogen‐Atom Transfer Oxidation with H₂O₂ Catalyzed by [FeII(1,2‐bis(2,2′‐bipyridyl‐6‐yl)ethane(H₂O)₂]²⁺: Likely Involvement of a (μ‐Hydroxo)(μ‐1,2‐peroxo)diiron(III) Intermediate

Hydrogen‐Atom Transfer Oxidation with H₂O₂ Catalyzed by [FeII(1,2‐bis(2,2′‐bipyridyl‐6‐yl)ethane(H₂O)₂]²⁺: Likely Involvement of a (μ‐Hydroxo)(μ‐1,2‐peroxo)diiron(III) Intermediate

Time-Resolved Investigations of Heterobimetallic Cofactor Assembly in R2lox Reveal Distinct Mn/Fe Intermediates

Unprecedented (μ-1,1-Peroxo)diferric Structure for the Ambiphilic Orange Peroxo Intermediate of the Nonheme N-Oxygenase CmlI

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A growing family of O2 activating dinuclear iron enzymes with key catalytic diiron(III)-peroxo intermediates: Biological systems and chemical models

Cited by 67 publications

References 170 publications

Hydrogen‐Atom Transfer Oxidation with H2O2 Catalyzed by [FeII(1,2‐bis(2,2′‐bipyridyl‐6‐yl)ethane(H2O)2]2+: Likely Involvement of a (μ‐Hydroxo)(μ‐1,2‐peroxo)diiron(III) Intermediate

Hydrogen‐Atom Transfer Oxidation with H2O2 Catalyzed by [FeII(1,2‐bis(2,2′‐bipyridyl‐6‐yl)ethane(H2O)2]2+: Likely Involvement of a (μ‐Hydroxo)(μ‐1,2‐peroxo)diiron(III) Intermediate

Time-Resolved Investigations of Heterobimetallic Cofactor Assembly in R2lox Reveal Distinct Mn/Fe Intermediates

Unprecedented (μ-1,1-Peroxo)diferric Structure for the Ambiphilic Orange Peroxo Intermediate of the Nonheme N-Oxygenase CmlI

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Hydrogen‐Atom Transfer Oxidation with H₂O₂ Catalyzed by [FeII(1,2‐bis(2,2′‐bipyridyl‐6‐yl)ethane(H₂O)₂]²⁺: Likely Involvement of a (μ‐Hydroxo)(μ‐1,2‐peroxo)diiron(III) Intermediate

Hydrogen‐Atom Transfer Oxidation with H₂O₂ Catalyzed by [FeII(1,2‐bis(2,2′‐bipyridyl‐6‐yl)ethane(H₂O)₂]²⁺: Likely Involvement of a (μ‐Hydroxo)(μ‐1,2‐peroxo)diiron(III) Intermediate