The mechanism of methane and dioxygen activation in the catalytic cycle of methane monooxygenase

Shteinman, A. A.

doi:10.1016/0014-5793(95)00195-f

Cited by 40 publications

(12 citation statements)

References 29 publications

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“…The catalytic centers responsible for the activity of Fe zeolites were also proposed as various binuclear Fe-oxo cores comprising mono- and bis-(μ-oxo) and (μ-peroxo) species stabilized in the zeolite channels. Although some of the structural features of the Cu and Fe cores, such as the arrangements of oxygen bridge atoms, bond lengths, and positions in three-dimensional (3D) space, may be similar for both zeolites and enzymes, selectivity in partial oxidation of methane is ensured in the enzymes by a complex mechanism including specific ligand fields and the exactly defined environment of the active site, which allow desorption of the product but do not allow further subsequent reactions. − The chemical behavior of the active site is uniquely suited to methane oxidation in monooxygenases, in contrast to the nonspecific activity of the zeolitic centers. As such complex local structures and functionality are principally lacking in the zeolites, sufficient selectivity can be achieved only in a pseudocatalytic cyclic process with separate sequential steps of (i) oxidation of the di- or trinuclear active centers by molecular oxygen, (ii) oxidation of a hydrocarbon molecule by the activated oxygen bound in the active site, and (iii) desorption of the product, where the hydrocarbon and molecular oxygen are not simultaneously present over the catalyst in any of the steps of the cyclic process.…”

Section: Introductionmentioning

confidence: 99%

Effect of the Nuclearity and Coordination of Cu and Fe Sites in β Zeolites on the Oxidation of Hydrocarbons

et al. 2020

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Cu and Fe zeolites can activate oxygen for oxidative reactions of methane and stable hydrocarbon molecules. Here, we analyzed the activity of Cu and Fe sites with various nuclearities and coordinations in *BEA zeolites toward complete oxidation of methane, toluene, and ethanol by molecular oxygen. Spectral analysis of the interaction of methane with the individual Cu and Fe sites and a kinetic study show that the oxidation of methane is catalyzed by different active sites with different activation energies. In the low-temperature region (225–325 °C), the activity is primarily caused by reactive bridging oxygen atoms in dimeric Cu and Fe clusters. Isolated Fe3+-oxo ions in the octahedral coordination and Cu2+ partially charge-balanced by the framework with less rigid redox states contribute to the activity at higher temperatures of ≥350 °C. The isolated Fe3+-oxo ions tetrahedrally coordinated to the framework oxygen and the bare Cu2+ ions charge-balanced exclusively by the framework are strongly stabilized and cannot act as active sites. Oxidation of the hydrocarbons over both the dimeric and isolated Cu and Fe active sites is nonspecific with practically barrierless consecutive reactions of already activated molecules and therefore fully CO2-selective for all of the hydrocarbons in an excess of oxygen.

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Section: Introductionmentioning

confidence: 99%

Effect of the Nuclearity and Coordination of Cu and Fe Sites in β Zeolites on the Oxidation of Hydrocarbons

et al. 2020

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“…3,14 Determining the mechanism of C-H bond activation in biological systems is of great interest currently. 15,16 To this end, the mechanism of sMMO-mediated hydroxylation has been studied with radical spin-traps 17 as well as radical clock substrate probes. 18 Several mechanisms, which have been suggested to account for the observations, invoke alkyl free radical and/or carbocation structures as potential intermediate species 13,[18][19][20] or a concerted process involving direct oxygen insertion into a substrate carbon-iron bond.…”

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confidence: 99%

Regio- and Stereoselectivity of Particulate Methane Monooxygenase from Methylococcus capsulatus (Bath)

et al. 1997

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The regiospecificity and stereoselectivity of alkane hydroxylation and alkene epoxidation by the particulate methane monooxygenase from Methylococcus capsulatus (Bath) was evaluated over a range of substrates. Oxidation products were identified by conventional GC analysis, and the stereoselectivity of oxidation was determined by a combination of chiral GC and HPLC methods, as well as 1H NMR analysis of the corresponding (R)-2-acetoxy-2-phenylethanoate ester derivatives in the case of alkanol products. Alkane hydroxylation was found to proceed favoring attack at the C-2 position in all cases, and the stereoselectivity for n-butane and n-pentane was characterized by an enantiomeric excess of 46% and 80%, respectively, with preference for the (R)-alcohol noted for both substrates. Epoxides were formed with smaller stereoselectivities. Together, the regio- and stereoselectivity results suggest that an equilibrium of competing substrate binding modes exists. A simple substrate-binding model that incorporates preferential C-2 oxidation with the observed stereoselectivity of alkane hydroxylation is proposed, and hypotheses for the general mechanism are suggested and discussed.

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“…[13][14][15][16][17][18] The catalytic cycle of sMMO can formally be divided into two steps: dioxygen activation and substrate oxidation (Figure 1 The final steps of the mechanism, in which a hydrogen is abstracted from substrate, followed by recombination of the substrate with the resulting OH moiety in the core to produce hydroxylated product (methanol, in the case of a methane substrate) have been discussed extensively in previous work. 5,8,14,[33][34][35][36][37][38][39][40] In ref. [ 42 ], this reaction is modeled using quantum dynamical methods, and both concerted and "radical rebound" mechanisms (the latter involving a very short lived bound radical species) are shown to contribute to the reaction pathway.…”

Section: Introductionmentioning

confidence: 99%

Intermediates in Dioxygen Activation by Methane Monooxygenase: A QM/MM Study

et al. 2007

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Protein effects in the activation of dioxygen by methane monooxygenase (MMO) were investigated by using combined QM/MM and broken-symmetry Density Functional Theory (DFT) methods. The effects of a novel empirical scheme recently developed by our group on the relative DFT energies of the various intermediates in the catalytic cycle are investigated. Inclusion of the protein leads to much better agreement between the experimental and computed geometric structures for the reduced form (MMOH red ). Analysis of the electronic structure of MMOH red reveals that the two iron atoms have distinct environments. Different coordination geometries tested for the MMOH peroxo intermediate reveal that, in the protein environment, the μ-η 2 ,η 2 structure is more stable than the others. Our analysis also shows that the protein helps to drive reactants towards products along the reaction path. Furthermore, these results demonstrate the importance of including the protein environment in our models and the usefulness of the QM/MM approach for accurate modeling of enzymatic reactions. A discrepancy remains in our calculation of the Fe-Fe distance in our model of H Q as compared to EXAFS data obtained several years ago, for which we currently do not have an explanation.

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The mechanism of methane and dioxygen activation in the catalytic cycle of methane monooxygenase

Cited by 40 publications

References 29 publications

Effect of the Nuclearity and Coordination of Cu and Fe Sites in β Zeolites on the Oxidation of Hydrocarbons

Effect of the Nuclearity and Coordination of Cu and Fe Sites in β Zeolites on the Oxidation of Hydrocarbons

Regio- and Stereoselectivity of Particulate Methane Monooxygenase from Methylococcus capsulatus (Bath)

Intermediates in Dioxygen Activation by Methane Monooxygenase: A QM/MM Study

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