The First μ(OH)‐Bridged Model Complex for the Mixed‐Valent Fe<sup>II</sup>Fe<sup>III</sup> Form of Hemerythrin

Bossek, Ursula; Hummel, Helga; Weyhermüller, Thomas; Bili, Eckhard; Wieghardt, Karl

doi:10.1002/anie.199526421

Cited by 66 publications

(59 citation statements)

References 29 publications

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“…Concomitant with the contraction in Fe-Fe distance was an increase in the angle formed by these two iron ions and the bridging density, from 113.0 to 116.7°. Both of these changes are consistent with those observed for oxidation of a hydroxy-bridged mixed-valent Fe 2+ /Fe 3+ model complex to an oxo-bridged di-Fe 3+ state (16), suggesting that the unexpectedly long Fe-Fe (19). (D) As in B, other than the soaking time for the crystal was increased to 20 min and the anomalous difference map contoured at 10σ (PDB entry 6GKA; ref.…”

Section: Resultssupporting

confidence: 77%

Reaction of O ₂ with a diiron protein generates a mixed-valent Fe ²⁺ /Fe ³⁺ center and peroxide

Bradley

Svistunenko

Pullin

et al. 2019

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

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The gene encoding the cyanobacterial ferritinSynFtn is up-regulated in response to copper stress. Here, we show that, whileSynFtn does not interact directly with copper, it is highly unusual in several ways. First, its catalytic diiron ferroxidase center is unlike those of all other characterized prokaryotic ferritins and instead resembles an animal H-chain ferritin center. Second, as demonstrated by kinetic, spectroscopic, and high-resolution X-ray crystallographic data, reaction of O2with the di-Fe2+center results in a direct, one-electron oxidation to a mixed-valent Fe2+/Fe3+form. Iron–O2chemistry of this type is currently unknown among the growing family of proteins that bind a diiron site within a four α-helical bundle in general and ferritins in particular. The mixed-valent form, which slowly oxidized to the more usual di-Fe3+form, is an intermediate that is continually generated during mineralization. Peroxide, rather than superoxide, is shown to be the product of O2reduction, implying that ferroxidase centers function in pairs via long-range electron transfer through the protein resulting in reduction of O2bound at only one of the centers. We show that electron transfer is mediated by the transient formation of a radical on Tyr40, which lies ∼4 Å from the diiron center. As well as demonstrating an expansion of the iron–O2chemistry known to occur in nature, these data are also highly relevant to the question of whether all ferritins mineralize iron via a common mechanism, providing unequivocal proof that they do not.

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Section: Resultssupporting

confidence: 77%

Reaction of O ₂ with a diiron protein generates a mixed-valent Fe ²⁺ /Fe ³⁺ center and peroxide

Bradley

Svistunenko

Pullin

et al. 2019

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

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“…The asymmetric coordination pattern observed for metal centers in 1 and 2 is uncommon for symmetric binucleating ligands which tend to bind two metal centers in a similar fashion. 43,44 It is unclear to us at this point why one isomer is favored over another.…”

Section: Resultsmentioning

confidence: 99%

Structural, EPR, and Mössbauer Characterization of (μ-Alkoxo)(μ-Carboxylato)Diiron(II,III) Model Complexes for the Active Sites of Mixed-Valent Diiron Enzymes

Chakrabarti

Dong

et al. 2012

Inorg. Chem.

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To obtain structural and spectroscopic models for the diiron(II,III) centers in the active sites of diiron enzymes, the (μ-alkoxo)(μ-carboxylato)diiron(II,III) complexes [FeIIFeIII(N-Et-HPTB)(O2CPh)(NCCH3)2](ClO4)3 (1) and [FeIIFeIII(N-Et-HPTB)(O2CPh) (Cl)(HOCH3)](ClO4)2 (2) (N-Et-HPTB = N,N,N′,N′-tetrakis(2-(1-ethyl-benzimidazolylmethyl))-2-hydroxy-1,3-diamino propane), have been prepared and characterized by X-ray crystallography, EPR, and Mössbauer spectroscopy. The Fe1-Fe2 separations are 3.60 Å and 3.63 Å and the Fe1-O1-Fe2 bond angles are 128.0° and 129.4° for 1 and 2, respectively. Mössbauer and EPR studies of 1 show that the FeIII (SA = 5/2) and FeII (SB = 2) sites are antiferromagnetically coupled to yield a ground state with S = 1/2 (g = 1.75, 1.88, 1.96); Mössbauer analysis of solid 1 yields J = 22.5 ± 2 cm−1 for the exchange coupling constant ( = JSA•SB convention). In addition to the S = 1/2 ground state spectrum of 1, the EPR signal for the S = 3/2 excited state of the spin ladder can also be observed, the first time such a signal has been detected for an antiferromagnetically coupled diiron(II,III) complex. The anisotropy of the 57Fe magnetic hyperfine interactions at the FeIII site is larger than normally observed in mononuclear complexes and arises from admixing S > 1/2 excited states into the S = 1/2 ground state by zero-field splittings at the two Fe sites. Analysis of the “D/J” mixing has allowed us to extract the zero-field splitting parameters, local g values, and magnetic hyperfine structural parameters for the individual Fe sites. The methodology developed and followed in this analysis is presented in detail. The spin Hamiltonian parameters of 1 are related to the molecular structure with the help of DFT calculations. Contrary to what was assumed in previous studies, our analysis demonstrates that the deviations of the g-values from the free electron value (g = 2) for the antiferromagnetically coupled diiron(II,III) core in complex 1 are predominantly determined by the anisotropy of the effective g-values of the ferrous ion, and only to a lesser extent by the admixture of excited states into ground state ZFS terms (D/J mixing). The results for 1 are discussed in the context of the data available for diiron(II,III) clusters in proteins and synthetic diiron(II,III) complexes.

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“…The combination of two redox‐active iron centers in close proximity confers advantages for catalysis, including cooperative binding and activation of substrates, and the use of both metal ions for multi‐electron processes. Many biomimetic diiron complexes have been generated as spectroscopic and mechanistic probes for the enzymes, and as synthetic catalysts for related chemistry . A notable feature among several of the aforementioned enzyme active sites is the asymmetric coordination environment.…”

Section: Introductionmentioning

confidence: 99%

Structural Differences and Redox Properties of Unsymmetric Diiron PDIxCy Complexes

2020

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We present two bimetallic iron complexes, [Fe 2 (PDIeCy)(OTf ) 4 ] (1) and [Fe 2 (PDIpCy)(THF)(OTf ) 4 ] (2) coordinated by an unsymmetric ligand. The new ligand, PDIeCy (PDI = pyridyldiimine; e = ethyl; Cy = cyclam), is a variant of the previously reported PDIpCy (p = propyl) ligand, featuring a shorter linker between the two metal coordination sites. The structural and electronic properties of 1 and 2, both in the solid and solution state, were analyzed by means of X-ray crystallography, and spectroscopic methods, including 19 F-NMR. The two ligand platforms yield markedly different diiron structures: the PDIeCy ligand permits formation of a bridged, μ-OTf complex, while the [a] 499 two iron centers of the PDIpCy-based 2 remain unconnected, directly, under all conditions examined. Both compounds contain electronically non-coupled high-spin (S = 2) ferrous centers, as established by Mössbauer spectroscopy and magnetic susceptibility studies. Cyclic voltammetry demonstrates the rich redox chemistry of the compounds, involving both ligand and metal-centered redox processes. Moreover, we synthesized the two-electron reduced [Fe 2 (PDIeCy)] 2+ form of 1, which contains the dianionic PDI 2ligand, and represents a two-electron charge localized complex.group, to support dinuclear complexes thereof (Scheme 1). [29] We reported the synthesis of non-coupled homo-and heterobimetallic Ni-and Zn-containing PDIpCy complexes. We now have focused our attention on diiron compounds. Iron offers Scheme 1. Synthesis of 1 and 2.

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The First μ(OH)‐Bridged Model Complex for the Mixed‐Valent Fe^IIFe^III Form of Hemerythrin

Cited by 66 publications

References 29 publications

Reaction of O ₂ with a diiron protein generates a mixed-valent Fe ²⁺ /Fe ³⁺ center and peroxide

Reaction of O ₂ with a diiron protein generates a mixed-valent Fe ²⁺ /Fe ³⁺ center and peroxide

Structural, EPR, and Mössbauer Characterization of (μ-Alkoxo)(μ-Carboxylato)Diiron(II,III) Model Complexes for the Active Sites of Mixed-Valent Diiron Enzymes

Structural Differences and Redox Properties of Unsymmetric Diiron PDIxCy Complexes

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The First μ(OH)‐Bridged Model Complex for the Mixed‐Valent FeIIFeIII Form of Hemerythrin

Cited by 66 publications

References 29 publications

Reaction of O 2 with a diiron protein generates a mixed-valent Fe 2+ /Fe 3+ center and peroxide

Reaction of O 2 with a diiron protein generates a mixed-valent Fe 2+ /Fe 3+ center and peroxide

Structural, EPR, and Mössbauer Characterization of (μ-Alkoxo)(μ-Carboxylato)Diiron(II,III) Model Complexes for the Active Sites of Mixed-Valent Diiron Enzymes

Structural Differences and Redox Properties of Unsymmetric Diiron PDIxCy Complexes

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The First μ(OH)‐Bridged Model Complex for the Mixed‐Valent Fe^IIFe^III Form of Hemerythrin

Reaction of O ₂ with a diiron protein generates a mixed-valent Fe ²⁺ /Fe ³⁺ center and peroxide

Reaction of O ₂ with a diiron protein generates a mixed-valent Fe ²⁺ /Fe ³⁺ center and peroxide