Structural and Functional Models of the Dioxygen-Activating Centers of Non-Heme Diiron Enzymes Ribonucleotide Reductase and Soluble Methane Monooxygenase

Lee, Dongwhan; Lippard, Stephen J.

doi:10.1021/ja9831094

Cited by 104 publications

(136 citation statements)

References 22 publications

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“…In addition, the slightly lower rate for 6-SiO 2 (450) relative to 6-SiO 2 (800) suggests that a high degree of silica dehydroxylation may promote monodentate attachment of open precursors to the silica surface, because bidentate grafting is expected to synthesize MPV-inactive sites within a closed configuration. A monodentate mode of attachment of the open Al(III) sites to silica within catalyst 6 is consistent with studies of previous investigators who have grafted Me 3 Al on silica (23)(24)(25), and a recent detailed 27 Al NMR spectroscopic analysis of the binding of Et 3 Al on silica, which shows the predominant grafted species to contain two ethyl ligands on aluminum (40). Scott et al have notably shown within this regard that a silica dehydroxylation temperature of 800°C promotes greater monodentate grafting of organometallic complexes relative to a lower temperature of 500°C (23, 24).…”

Section: Resultssupporting

confidence: 89%

Catalytic consequences of open and closed grafted Al(III)-calix[4]arene complexes for hydride and oxo transfer reactions

Nandi

Tang

Okrut

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Section: Resultssupporting

confidence: 89%

Catalytic consequences of open and closed grafted Al(III)-calix[4]arene complexes for hydride and oxo transfer reactions

Nandi

Tang

Okrut

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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“…Radical traps are claimed to be able to intercept the C-OH bond as it forms in the transition state. The presence of terminal FeϭO bonds in Q remains a viable possibility, although it is not supported by extended x-ray absorption fine structure spectroscopy (46) and modeling chemistry (35). Perhaps Q is in dynamic equilibrium with such a species, as we have previously suggested (3).…”

Section: Mechanistic Implications and Comparisons With Literaturementioning

confidence: 95%

Oxidation of Ultrafast Radical Clock Substrate Probes by the Soluble Methane Monooxygenase from Methylococcus capsulatus(Bath)

Valentine

LeTadic-Biadatti

Toy

et al. 1999

Journal of Biological Chemistry

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Radical clock substrate probes were used to assess the viability of a discrete substrate radical species in the mechanism of hydrocarbon oxidation by the soluble methane monooxygenase (sMMO) from Methylococcus capsulatus (Bath). New substituted cyclopropane probes were used with very fast ring-opening rate constants and other desirable attributes, such as the ability to discriminate between radical and cationic intermediates. Oxidation of these substrates by a reconstituted sMMO system resulted in no rearranged products, allowing an upper limit of 150 fs to be placed on the lifetime of a putative radical species. This limit strongly suggests that there is no such substrate radical intermediate. The two enantiomers of trans-1-methyl-2-phenylcyclopropane were prepared, and the regioselectivity of their oxidation to the corresponding cyclopropylmethanol and cyclopropylphenol products was determined. The results are consistent with selective orientation of the two enantiomeric substrates in the hydrophobic cavity at the active site of sMMO, specific models for which were examined by molecular modeling.The soluble methane monooxygenase (sMMO) 1 from Methylococcus capsulatus (Bath), the hydroxylase component of which contains a dinuclear nonheme iron center, effects the mixed function oxidation of substrate,Equation 1 (1-3). In methanotrophic bacteria from which sMMO is isolated, methane is the natural substrate, providing both carbon and energy for the growth of the cell. The kinetically difficult selective transformation of methane to methanol is carried out at the active site of a 251-kDa hydroxylase enzyme (MMOH) (4 -7), the structure of which has been determined by x-ray crystallography. Electrons are supplied from NADH via a 38.5-kDa reductase protein (MMOR) (4,8), and the reactivity of the system is modulated by a 15.8-kDa coupling protein (MMOB) (9, 10). 2In addition to methane, sMMO can oxidize a wide variety of substrates (12)(13)(14)(15). This property has allowed the use of radical clock substrate probes to derive mechanistic information about the hydroxylation step in the enzyme mechanism. Radical clocks were first described in 1980 (16) and calibrated (17) for use in mechanistic studies of proteins (18,19) and related model compounds (20,21). Specifically, these substrates can reveal whether radical intermediates are formed during a reaction and, if so, can establish their lifetime and the rate constant for radical rebound. Fig. 1 depicts the oxidation of a radical clock substrate probe, which uses the ring opening of a cyclopropylcarbinyl radical. If hydrogen atom abstraction from the probe occurs, the resulting radical can either rebound to form the unrearranged alcohol or undergo ring opening before rebound to afford the rearranged alcohol. If the ring opening rate is known (17), the rebound rate, k oxidation , can be calculated according to Equation 2. k oxidation ϭ k ring opening ͑unrearranged alcohol / rearranged alcohol) (Eq. 2)The hypothesis that substrate radical intermediates form in the sMMO s...

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“…15,16 The introduction of m-terphenyl-based carboxylates, depicted in Chart 1, has facilitated the assembly of the desired dinuclear cores. [16][17][18][19][20] The protective pocket of aromatic rings prevents bimolecular decomposition reactions but can also block access of substrate to the O 2 -activated diiron center. To address this concern, substrates have been incorporated into the ancillary Ndonor ligands coordinated to the iron atoms, as illustrated by the formation of benzaldehyde from a benzyl moiety following exposure to O 2 In the present study we have expanded the family of substrate-tethered carboxylate-bridged diiron(II) compounds having benzyl-or ethyl-derivatized pyridine or aniline donor auxiliary ligands.…”

Section: Introductionmentioning

confidence: 99%

Synthesis, Characterization, and Preliminary Oxygenation Studies of Benzyl- and Ethyl-Substituted Pyridine Ligands of Carboxylate-Rich Diiron(II) Complexes

Carson

Lippard

2005

Inorg. Chem.

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Structural and Functional Models of the Dioxygen-Activating Centers of Non-Heme Diiron Enzymes Ribonucleotide Reductase and Soluble Methane Monooxygenase

Cited by 104 publications

References 22 publications

Catalytic consequences of open and closed grafted Al(III)-calix[4]arene complexes for hydride and oxo transfer reactions

Catalytic consequences of open and closed grafted Al(III)-calix[4]arene complexes for hydride and oxo transfer reactions

Oxidation of Ultrafast Radical Clock Substrate Probes by the Soluble Methane Monooxygenase from Methylococcus capsulatus(Bath)

Synthesis, Characterization, and Preliminary Oxygenation Studies of Benzyl- and Ethyl-Substituted Pyridine Ligands of Carboxylate-Rich Diiron(II) Complexes

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