O
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            Activation by Nonheme Iron Complexes: A Monomeric Fe(III)-Oxo Complex Derived From O
            <sub>2</sub>

MacBeth, Cora E.; Golombek, Adina; Young, Victor G.; Yang, Cheng; Kuczera, Krzysztof; Hendrich, Michael P.; Borovik, A. S.

doi:10.1126/science.289.5481.938

Cited by 438 publications

(345 citation statements)

References 30 publications

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“…3). This mode is consistent with the calculated ν Fe─O of tripodal Fe III ─O − (19) but is lower than the ν Fe─O (671 cm −1 ) of the only reported nonheme Fe III ─O − model complex (20). This frequency is at the high end of calculated ν Fe─OH values (19) and distinct from those of most experimentally measured hydroxyl modes, but it is very close to the ν FeðIVÞ─OH mode of protonated compound II of chloroperoxidase (CPO) at 565 cm −1 (21) and the ν FeðIIIÞ─OH modes of di-iron hydroxomethemerythrin at 565 cm −1 (22) and a synthetic Fe III ─OH model at 574 cm −1 (23).…”

Section: Discussionsupporting

confidence: 79%

Insight into the mechanism of an iron dioxygenase by resolution of steps following the Fe ^IV ═O species

Grzyska

Appelman

Hausinger

et al. 2010

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

124

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Iron oxygenases generate elusive transient oxygen species to catalyze substrate oxygenation in a wide range of metabolic processes. Here we resolve the reaction sequence and structures of such intermediates for the archetypal non-heme Fe II and α-ketoglutarate-dependent dioxygenase TauD. Time-resolved Raman spectra of the initial species with 16 O 18 O oxygen unequivocally establish the Fe IV ═O structure. 1 H∕ 2 H substitution reveals direct interaction between the oxo group and the C1 proton of substrate taurine. Two new transient species were resolved following Fe IV ═O; one is assigned to the ν FeO mode of an Fe III ─OðHÞ species, and a second is likely to arise from the vibration of a metal-coordinated oxygenated product, such as Fe II ─O─C 1 or Fe II ─OOCR. These results provide direct insight into the mechanism of substrate oxygenation and suggest an alternative to the hydroxyl radical rebinding paradigm.ferric-oxo | ferryl | non-heme iron | oxygenation | transient Raman I nterest in the mechanism of iron oxygenases arises from their roles in an array of critical biological functions ranging from bacterial biodegradation of xenobiotics and recalcitrant compounds to human drug metabolism and cellular regulation. Many heme and non-heme iron oxygenases are believed to share highly oxidized iron-oxo species as central elements in their reaction mechanisms (1, 2). Several transient oxygen intermediates have been studied extensively in heme enzymes, including compound I-type species of cytochrome P450s (3), but the intermediates occurring during substrate oxygenation have not been directly observed. Even less is known about the transient species in the non-heme Fe oxygenases. An Fe IV -oxo intermediate was observed in the Fe II and α-ketoglutarate-dependent dioxygenase TauD (4-6), the archetype of this enzyme family (7), and in the related prolyl 4-hydroxylase (8) or the chlorinating enzymes CytC3 and SyrB2 (9, 10). The Fe-oxygen vibration in TauD at 821 cm −1 was assigned to an Fe IV ═O stretching mode, whereas an additional oxygen vibration at 583 cm −1 was not assigned (6). Here, through the use of substrate and media isotopes and varying reaction times, we resolve vibrations associated with three distinct transient oxygen-containing species during TauD catalysis that lead us to propose an alternative to the hydroxyl radical rebinding step that is central to the traditionally accepted mechanism (Fig. 1). ResultsTransient Oxygen Species Detected by Difference Raman Spectroscopy. The time dependence of the TauD reaction with 1 H-and 2 H-taurine was examined by cryogenic continuous-flow Raman spectroscopy (Fig. 2 and Fig. S1). The previously reported oxygen vibrations (6) can be seen as shifts at 825∕788 and 578∕555 cm −1 between the 16 O and 18 O derivatives (for 1 H-taurine, Fig. 2A). Intensities of the isotopic shifts diminished rapidly at longer delay times, although the decay of both species was significantly slower and overall intensities were greater with 2 H-taurine.The 16 O∕ 18 O difference spectra aro...

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Section: Discussionsupporting

confidence: 79%

Insight into the mechanism of an iron dioxygenase by resolution of steps following the Fe ^IV ═O species

Grzyska

Appelman

Hausinger

et al. 2010

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

124

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“…46 Their relative bond strengths are also reflected in their Fe-X bond energies (calculated from fragment dissociation in CH 2 -Cl 2 solvent), which show that the Fe III -O bond energy is about -102 kcal/mol, significantly higher than the Fe III -S bonding energy of -62 kcal/ mol. 47 Note that, although the coefficients (46) Note that the force constant for Fe-O is expected to be higher than that of Fe-S by a factor of 1.44 due to higher mass of S (32) relative to O (16). However, here the ratio is 1.9 which indicates that the Fe-O bond is stronger than the Fe-S bond.…”

Section: A Evaluation Of Dft Calculations Using Xasmentioning

confidence: 90%

X-ray Absorption Spectroscopy and Density Functional Theory Studies of [(H₃buea)Fe^III^-X]ⁿ^- (X = S^2-, O^2-, OH^-): Comparison of Bonding and Hydrogen Bonding in Oxo and Sulfido Complexes

et al. 2006

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Iron L-edge, iron K-edge, and sulfur K-edge X-ray absorption spectroscopy was performed on a series of compounds [Fe III H3buea(X)] n-(X ) S 2-, O 2-, OH -). The experimentally determined electronic structures were used to correlate to density functional theory calculations. Calculations supported by the data were then used to compare the metal-ligand bonding and to evaluate the effects of H-bonding in Fe III-O vs Fe III-S complexes. It was found that the Fe III-O bond, while less covalent, is stronger than the Fe III-S bond. This dominantly reflects the larger ionic contribution to the Fe III-O bond. The H-bonding energy (for three H-bonds) was estimated to be -25 kcal/mol for the oxo as compared to -12 kcal/mol for the sulfide ligand. This difference is attributed to the larger charge density on the oxo ligand resulting from the lower covalency of the Fe-O bond. These results were extended to consider an Fe IV-O complex with the same ligand environment. It was found that hydrogen bonding to Fe IV-O is less energetically favorable than that to Fe III-O, which reflects the highly covalent nature of the Fe IV-O bond.

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“…This link has recently been identified independently by the groups of Li et al 56 and Cho et al, who generated a high-spin Fe III -OOH complex supported by the Me 4 cy ligand via protonation of the side-on peroxoiron(III) conjugate base 56,57 . This hydroperoxo complex was shown to convert quantitatively to the corresponding S = 1 oxoiron(IV) complex either through acid-mediated O-O bond heterolysis, followed by the reduction of the transient oxoiron(V) intermediate 56 46, also reacts with O 2 to yield an oxoiron(III) intermediate, which is proposed to derive from the reduction of an initially formed oxoiron(IV) species. Although the oxoiron(IV) species on the way to the generation of the oxoiron(III) complex could not be trapped, it has recently been synthesized by the one-electron oxidation of the preformed [(H 3 buea)Fe III (Fig.…”

mentioning

confidence: 99%

The biology and chemistry of high-valent iron–oxo and iron–nitrido complexes

2012

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selective functionalization of unactivated c-H bonds and ammonia production are extremely important industrial processes. a range of metalloenyzmes achieve these challenging tasks in biology by activating dioxygen and dinitrogen using cheap and abundant transition metals, such as iron, copper and manganese. High-valent iron-oxo and -nitrido complexes act as active intermediates in many of these processes. the generation of well-described model compounds can provide vital insights into the mechanism of such enzymatic reactions. advances in the chemistry of model high-valent iron-oxo and -nitrido systems can be related to our understanding of the biological systems.H igh-valent oxoiron(IV) and formally oxoiron(V) species have been spectroscopically identified as active intermediates in the catalytic cycles of a number of enzymatic systems 1-10 . Haem and non-haem proteins use these reactive intermediates to couple the activation of dioxygen to the oxidation of their substrates. In most cases, an oxygen atom is inserted into an unactivated C-H bond of the substrate; for example, in hydroxylation reactions [1][2][3][4][5][6][7][8][9][10] . However, many other reactions, including halogenation, desaturation, cyclization, epoxidation and decarboxylation, are also known to involve oxoiron species 1,3 . Superoxidized iron complexes with (valence) isoelectronic imido and nitrido ligands, as well as 'surface nitrides' , have also been implicated as key intermediates in the nitrogen atom transfer reactions 11 , the biological synthesis of ammonia by the nitrogenase enzyme 12-16 and the industrial Haber-Bosch process 17 .The generation of well-described model compounds can provide vital insights into the mechanism of such enzymatic reactions. Consequently, considerable effort has been made by synthetic chemists to prepare viable models for the putative reaction intermediates in the catalytic cycles of O 2 and N 2 activating enzymes. In this review, we provide an overview of all high-valent oxoiron and nitridoiron species that have been either identified or proposed as reactive intermediates in biology. Subsequently, we summarize some of the recent advances in bioinorganic chemistry that have led to the identification and isolation of iron complexes in unusually high formal oxidation states, containing iron-oxygen or iron-nitrogen multiple bonds. The spectroscopic characterization and the reactivity studies of these model complexes provide vital insights into the mechanism that nature uses to induce the reductive cleavage of dioxygen or dinitrogen in carrying out a number of important biochemical oxidative transformations. Moreover, the comparative review of the electronic structures of the isoelectronic oxoiron and nitridoiron functionalities reveals that the Fe-N bonds are intrinsically more covalent than the Fe-O bonds.

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O ₂ Activation by Nonheme Iron Complexes: A Monomeric Fe(III)-Oxo Complex Derived From O ₂

Cited by 438 publications

References 30 publications

Insight into the mechanism of an iron dioxygenase by resolution of steps following the Fe ^IV ═O species

Insight into the mechanism of an iron dioxygenase by resolution of steps following the Fe ^IV ═O species

X-ray Absorption Spectroscopy and Density Functional Theory Studies of [(H₃buea)Fe^III^-X]ⁿ^- (X = S^2-, O^2-, OH^-): Comparison of Bonding and Hydrogen Bonding in Oxo and Sulfido Complexes

The biology and chemistry of high-valent iron–oxo and iron–nitrido complexes

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O 2 Activation by Nonheme Iron Complexes: A Monomeric Fe(III)-Oxo Complex Derived From O 2

Cited by 438 publications

References 30 publications

Insight into the mechanism of an iron dioxygenase by resolution of steps following the Fe IV ═O species

Insight into the mechanism of an iron dioxygenase by resolution of steps following the Fe IV ═O species

X-ray Absorption Spectroscopy and Density Functional Theory Studies of [(H3buea)FeIII-X]n- (X = S2-, O2-, OH-): Comparison of Bonding and Hydrogen Bonding in Oxo and Sulfido Complexes

The biology and chemistry of high-valent iron–oxo and iron–nitrido complexes

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Product

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O ₂ Activation by Nonheme Iron Complexes: A Monomeric Fe(III)-Oxo Complex Derived From O ₂

Insight into the mechanism of an iron dioxygenase by resolution of steps following the Fe ^IV ═O species

Insight into the mechanism of an iron dioxygenase by resolution of steps following the Fe ^IV ═O species

X-ray Absorption Spectroscopy and Density Functional Theory Studies of [(H₃buea)Fe^III^-X]ⁿ^- (X = S^2-, O^2-, OH^-): Comparison of Bonding and Hydrogen Bonding in Oxo and Sulfido Complexes