Spin‐State Rationale for the Peroxo‐Stabilizing Role of the Thiolate Ligand in Superoxide Reductase

Bukowski, Michael R.; Halfen, Heather L.; Berg, Tieme A. van den; Halfen, Jason A.; Que, Lawrence

doi:10.1002/anie.200461527

Cited by 59 publications

(61 citation statements)

References 21 publications

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“…Such trans ligand donation effects have been observed for Fe 3ϩ -alkylperoxo species in SOR model complexes for which decreased Lewis basicity (i.e. decreased electron density donation from the trans ligand) was correlated with increased Fe™O bond strength and stability (33).…”

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confidence: 63%

“…However, at the difference of the P450 enzymes that favor the heterolytic cleavage of the O™O bond of the peroxide intermediate to form the high valent iron oxo species (34), our previous RR experiments demonstrated that the SOR active site can accommodate unusual Fe 3ϩ -peroxo species with particularly weak Fe™O bond and strong O™O bond, which, in addition to the spin state of the iron (33), clearly favors the Fe™O bond cleavage to form its reaction product H 2 O 2 . Our present work further shows that the strength of the S™Fe bond, which is finely tuned by the cysteine environment, significantly contributes to this unusual weak Fe™O bond in SOR.…”

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confidence: 99%

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Assessing the Role of the Active-site Cysteine Ligand in the Superoxide Reductase from Desulfoarculus baarsii

Mathé

Weill

Mattioli

et al. 2007

Journal of Biological Chemistry

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confidence: 63%

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confidence: 99%

Assessing the Role of the Active-site Cysteine Ligand in the Superoxide Reductase from Desulfoarculus baarsii

Mathé

Weill

Mattioli

et al. 2007

Journal of Biological Chemistry

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“…The remaining topology not represented in the bpmen family until very recently [26,27] is the trans topology, with all four ligating atoms of the tetradentate N4 ligand approximately arrayed in the equatorial plane. To fill this gap, we initially designed the L 8 py 2 ligand, [26] in which two propylene straps connecting the two 2-pyridylmethylamine units serve to enforce the desired topology.…”

Section: Resultsmentioning

confidence: 99%

“…To fill this gap, we initially designed the L 8 py 2 ligand, [26] in which two propylene straps connecting the two 2-pyridylmethylamine units serve to enforce the desired topology. In the recently reported structure of [Fe II - (9), the iron center in fact adopts a square-pyramidal arrangement with only one bound triflate occupying the apical position, leaving a free coordination site trans to the triflate anion.…”

Section: Resultsmentioning

confidence: 99%

“…The Fe III ÀOOH intermediate proposed in the nwa pathway is a plausible candidate for 9, as the related Fe III À OOR species has been observed and characterized in its low-temperature reaction with tBuOOH. [26] cis-a Complexes 6 and 7: Complexes with cis-a topology (6 and 7) are efficient catalysts for highly stereoselective olefin epoxidation with diol/epoxide (D/E) ratios of 0.1:1 (see Figure 3). [14,25] Under the same conditions, 6 and 7 generally afford about twice as much epoxide product as 9 and 10, suggesting that the cis-a topology provides a superior ligand arrangement for activating H 2 O 2 for epoxidation.…”

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Ligand Topology Effects on Olefin Oxidations by Bio‐Inspired [Fe^II(N₂Py₂)] Catalysts

Mas‐Ballesté

Costas

Berg

et al. 2006

Chemistry A European J

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Linear tetradentate N2Py2 ligands can coordinate to an octahedral FeII center in three possible topologies (cis-alpha, cis-beta, and trans). While for the N,N'-bis(2-pyridylmethyl)-1,2-diaminoethane (bpmen) complex, only the cis-alpha topology has been observed, for N,N'-bis(2-pyridylmethyl)-1,2-diaminocyclohexane (bpmcn) both cis-alpha and cis-beta isomers have been reported. To date, no facile interconversion between cis-alpha and cis-beta topologies has been observed for ironII complexes even at high temperatures. However, this work provides evidence for facile interconversion in solution of cis-alpha, cis-beta, and trans topologies for [Fe(bpmpn)X2] (bpmpn=N,N'-bis(2-pyridylmethyl)-1,3-diaminopropane; X=triflate, CH3CN) complexes. As reported previously, the catalytic behavior of cis-alpha and cis-beta isomers of [Fe(bpmcn)(OTf)2] with respect to olefin oxidation depends dramatically on the geometry adopted by the iron complex. To establish a general pattern of the catalysis/topology dependence, this work presents an extended comparison of the catalytic behavior for oxidation of olefins of a family of [Fe(N2py2)] complexes that present different topologies. 18O labeling experiments provide evidence for a complex mechanistic landscape in which several pathways should be considered. Complexes with a trans topology catalyze only non-water-assisted epoxidation. In contrast, complexes with a cis-alpha topology, such as [Fe(bpmen)X2] and [Fe(alpha-bpmcn)(OTf)2], can catalyze both epoxidation and cis-dihydroxylation through a water-assisted mechanism. Surprisingly, [Fe(bpmpn)X2] and [Fe(beta-bpmcn)(OTf)2] catalyze epoxidation via a water-assisted pathway and cis-dihydroxylation via a non-water-assisted mechanism, a result that requires two independent and distinct oxidants.

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Superoxide Reductase

Nivière¹,

Bonnot²,

Bourgeois³

2004

Handbook of Metalloproteins

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Superoxide reductase (SOR) is a small bacterial metalloprotein, which is present in the cytoplasm of some anaerobic or microaerophilic microorganisms. SOR is involved in the detoxification of the superoxide radical and catalyzes its one‐electron reduction into hydrogen peroxide. Three different classes of SOR have been identified and structurally characterized. They all contain a similar active site, which consists of an unusual nonheme iron center, coordinated in a square‐pyramidal geometry to four nitrogens from four histidine side chains in the equatorial plane and the sulfur of one cysteine residue along the fifth axial position. In the reduced state, the sixth axial coordinating site of the iron is vacant, suggesting the most obvious site for initial binding of the superoxide substrate. The reaction mechanism of SOR has been studied by pulse radiolysis. SOR reacts specifically at a nearly diffusion‐controlled rate with O 2 •− , generating H 2 O 2 and the oxidized Fe 3+ active site. Reaction intermediates have been observed and proposed to be Fe 3+ ‐(hydro)peroxo species, resulting from the fast electron transfer from the ferrous iron to the superoxide anion and from protonation step. Formation of Fe 3+ ‐(hydro)peroxo intermediate species in the active site of SOR has been supported by resonance Raman spectroscopy and X‐ray structures of iron(III) peroxide species in the SOR from Desulfoarculus baarsii .

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Spin‐State Rationale for the Peroxo‐Stabilizing Role of the Thiolate Ligand in Superoxide Reductase

Cited by 59 publications

References 21 publications

Assessing the Role of the Active-site Cysteine Ligand in the Superoxide Reductase from Desulfoarculus baarsii

Assessing the Role of the Active-site Cysteine Ligand in the Superoxide Reductase from Desulfoarculus baarsii

Ligand Topology Effects on Olefin Oxidations by Bio‐Inspired [Fe^II(N₂Py₂)] Catalysts

Superoxide Reductase

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Spin‐State Rationale for the Peroxo‐Stabilizing Role of the Thiolate Ligand in Superoxide Reductase

Cited by 59 publications

References 21 publications

Assessing the Role of the Active-site Cysteine Ligand in the Superoxide Reductase from Desulfoarculus baarsii

Assessing the Role of the Active-site Cysteine Ligand in the Superoxide Reductase from Desulfoarculus baarsii

Ligand Topology Effects on Olefin Oxidations by Bio‐Inspired [FeII(N2Py2)] Catalysts

Superoxide Reductase

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Ligand Topology Effects on Olefin Oxidations by Bio‐Inspired [Fe^II(N₂Py₂)] Catalysts