A synthetic precedent for the [FeIV2(μ-O) 2] diamond core proposed for methane monooxygenase intermediate Q

Genqiang Xue; Dong Wang; Raymond De Hont; Adam T. Fiedler; Xiaopeng Shan; Eckard Münck; Lawrence Que

doi:10.1073/pnas.0708516105

A synthetic precedent for the [Fe^IV₂(μ-O) ₂] diamond core proposed for methane monooxygenase intermediate Q

Genqiang Xue, Dong Wang, Raymond De Hont, Adam T. Fiedler, Xiaopeng Shan, Eckard Münck, Lawrence Que

Chemistry (Twin Cities)

Research output: Contribution to journal › Article › peer-review

151 Scopus citations

Abstract

Intermediate Q, the methane-oxidizing species of soluble methane monooxygenase, is proposed to have an [Fe^IV₂(μ-O) ₂] diamond core. In an effort to obtain a synthetic precedent for such a core, bulk electrolysis at 900 mV (versus Fc^+/0) has been performed in MeCN at -40° C on a valence-delocalized [Fe ^IIIFe^IV(μ-O)₂(L^b) ₂]³⁺ complex (1b) (E_1/2 = 760 mV versus Fc ^+/0). Oxidation of 1b results in the near-quantitative formation of a deep red complex, designated 2b, that exhibits a visible spectrum with max at 485 nm (9,800 M^-1·cm^-1) and 875 nm (2,200 M ^-1·cm^-1). The 4.2 K Mössbauer spectrum of 2b exhibits a quadrupole doublet with δ = -0.04(1) mm·s^-1 and ΔEQ = 2.09(2) mm·s^-1, parameters typical of an iron(IV) center. The Mössbauer patterns observed in strong applied fields show that 2b is an antiferromagnetically coupled diiron(IV) center. Resonance Raman studies reveal the diagnostic vibration mode of the [Fe ₂(μ-O)₂] core at 674 cm^-1, downshifting 30 cm^-1 upon ¹⁸O labeling. Extended x-ray absorption fine structure (EXAFS) analysis shows two O/N scatterers at 1.78 Å and an Fe scatterer at 2.73 Å. Based on the accumulated spectroscopic evidence, 2b thus can be formulated as [Fe^IV₂(μ-O) ₂(L^b)₂]⁴⁺, the first synthetic complex with an [Fe^IV₂(μ-O)₂] core. A comparison of 2b and its mononuclear analog [Fe^IV(O)(L ^b)(NCMe)]²⁺ (4b) reveals that 4b is 100-fold more reactive than 2b in oxidizing weak C - H bonds. This surprising observation may shed further light on how intermediate Q carries out the hydroxylation of methane.

Original language	English (US)
Pages (from-to)	20713-20718
Number of pages	6
Journal	Proceedings of the National Academy of Sciences of the United States of America
Volume	104
Issue number	52
DOIs	https://doi.org/10.1073/pnas.0708516105
State	Published - Dec 26 2007

Keywords

Diiron(IV)
Electrochemistry
Iron-oxo
Nonheme
Oxygen activation

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10.1073/pnas.0708516105

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@article{dd7d0584866d486b9dedaf94dc8d3ede,

title = "A synthetic precedent for the [FeIV2(μ-O) 2] diamond core proposed for methane monooxygenase intermediate Q",

abstract = "Intermediate Q, the methane-oxidizing species of soluble methane monooxygenase, is proposed to have an [FeIV2(μ-O) 2] diamond core. In an effort to obtain a synthetic precedent for such a core, bulk electrolysis at 900 mV (versus Fc+/0) has been performed in MeCN at -40° C on a valence-delocalized [Fe IIIFeIV(μ-O)2(Lb) 2]3+ complex (1b) (E1/2 = 760 mV versus Fc +/0). Oxidation of 1b results in the near-quantitative formation of a deep red complex, designated 2b, that exhibits a visible spectrum with max at 485 nm (9,800 M-1·cm-1) and 875 nm (2,200 M -1·cm-1). The 4.2 K M{\"o}ssbauer spectrum of 2b exhibits a quadrupole doublet with δ = -0.04(1) mm·s-1 and ΔEQ = 2.09(2) mm·s-1, parameters typical of an iron(IV) center. The M{\"o}ssbauer patterns observed in strong applied fields show that 2b is an antiferromagnetically coupled diiron(IV) center. Resonance Raman studies reveal the diagnostic vibration mode of the [Fe 2(μ-O)2] core at 674 cm-1, downshifting 30 cm-1 upon 18O labeling. Extended x-ray absorption fine structure (EXAFS) analysis shows two O/N scatterers at 1.78 {\AA} and an Fe scatterer at 2.73 {\AA}. Based on the accumulated spectroscopic evidence, 2b thus can be formulated as [FeIV2(μ-O) 2(Lb)2]4+, the first synthetic complex with an [FeIV2(μ-O)2] core. A comparison of 2b and its mononuclear analog [FeIV(O)(L b)(NCMe)]2+ (4b) reveals that 4b is 100-fold more reactive than 2b in oxidizing weak C - H bonds. This surprising observation may shed further light on how intermediate Q carries out the hydroxylation of methane.",

keywords = "Diiron(IV), Electrochemistry, Iron-oxo, Nonheme, Oxygen activation",

author = "Genqiang Xue and Dong Wang and {De Hont}, Raymond and Fiedler, {Adam T.} and Xiaopeng Shan and Eckard M{\"u}nck and Lawrence Que",

year = "2007",

month = dec,

day = "26",

doi = "10.1073/pnas.0708516105",

language = "English (US)",

volume = "104",

pages = "20713--20718",

journal = "Proceedings of the National Academy of Sciences of the United States of America",

issn = "0027-8424",

publisher = "National Academy of Sciences",

number = "52",

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TY - JOUR

T1 - A synthetic precedent for the [FeIV2(μ-O) 2] diamond core proposed for methane monooxygenase intermediate Q

AU - Xue, Genqiang

AU - Wang, Dong

AU - De Hont, Raymond

AU - Fiedler, Adam T.

AU - Shan, Xiaopeng

AU - Münck, Eckard

AU - Que, Lawrence

PY - 2007/12/26

Y1 - 2007/12/26

N2 - Intermediate Q, the methane-oxidizing species of soluble methane monooxygenase, is proposed to have an [FeIV2(μ-O) 2] diamond core. In an effort to obtain a synthetic precedent for such a core, bulk electrolysis at 900 mV (versus Fc+/0) has been performed in MeCN at -40° C on a valence-delocalized [Fe IIIFeIV(μ-O)2(Lb) 2]3+ complex (1b) (E1/2 = 760 mV versus Fc +/0). Oxidation of 1b results in the near-quantitative formation of a deep red complex, designated 2b, that exhibits a visible spectrum with max at 485 nm (9,800 M-1·cm-1) and 875 nm (2,200 M -1·cm-1). The 4.2 K Mössbauer spectrum of 2b exhibits a quadrupole doublet with δ = -0.04(1) mm·s-1 and ΔEQ = 2.09(2) mm·s-1, parameters typical of an iron(IV) center. The Mössbauer patterns observed in strong applied fields show that 2b is an antiferromagnetically coupled diiron(IV) center. Resonance Raman studies reveal the diagnostic vibration mode of the [Fe 2(μ-O)2] core at 674 cm-1, downshifting 30 cm-1 upon 18O labeling. Extended x-ray absorption fine structure (EXAFS) analysis shows two O/N scatterers at 1.78 Å and an Fe scatterer at 2.73 Å. Based on the accumulated spectroscopic evidence, 2b thus can be formulated as [FeIV2(μ-O) 2(Lb)2]4+, the first synthetic complex with an [FeIV2(μ-O)2] core. A comparison of 2b and its mononuclear analog [FeIV(O)(L b)(NCMe)]2+ (4b) reveals that 4b is 100-fold more reactive than 2b in oxidizing weak C - H bonds. This surprising observation may shed further light on how intermediate Q carries out the hydroxylation of methane.

AB - Intermediate Q, the methane-oxidizing species of soluble methane monooxygenase, is proposed to have an [FeIV2(μ-O) 2] diamond core. In an effort to obtain a synthetic precedent for such a core, bulk electrolysis at 900 mV (versus Fc+/0) has been performed in MeCN at -40° C on a valence-delocalized [Fe IIIFeIV(μ-O)2(Lb) 2]3+ complex (1b) (E1/2 = 760 mV versus Fc +/0). Oxidation of 1b results in the near-quantitative formation of a deep red complex, designated 2b, that exhibits a visible spectrum with max at 485 nm (9,800 M-1·cm-1) and 875 nm (2,200 M -1·cm-1). The 4.2 K Mössbauer spectrum of 2b exhibits a quadrupole doublet with δ = -0.04(1) mm·s-1 and ΔEQ = 2.09(2) mm·s-1, parameters typical of an iron(IV) center. The Mössbauer patterns observed in strong applied fields show that 2b is an antiferromagnetically coupled diiron(IV) center. Resonance Raman studies reveal the diagnostic vibration mode of the [Fe 2(μ-O)2] core at 674 cm-1, downshifting 30 cm-1 upon 18O labeling. Extended x-ray absorption fine structure (EXAFS) analysis shows two O/N scatterers at 1.78 Å and an Fe scatterer at 2.73 Å. Based on the accumulated spectroscopic evidence, 2b thus can be formulated as [FeIV2(μ-O) 2(Lb)2]4+, the first synthetic complex with an [FeIV2(μ-O)2] core. A comparison of 2b and its mononuclear analog [FeIV(O)(L b)(NCMe)]2+ (4b) reveals that 4b is 100-fold more reactive than 2b in oxidizing weak C - H bonds. This surprising observation may shed further light on how intermediate Q carries out the hydroxylation of methane.

KW - Diiron(IV)

KW - Electrochemistry

KW - Iron-oxo

KW - Nonheme

KW - Oxygen activation

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DO - 10.1073/pnas.0708516105

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C2 - 18093922

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EP - 20718

JO - Proceedings of the National Academy of Sciences of the United States of America

JF - Proceedings of the National Academy of Sciences of the United States of America

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