Monomeric Carboxylate Ferrous Complexes as Models for the Dioxygen Binding Sites in Non-Heme Iron Proteins. The Reversible Formation and Characterization of .mu.-Peroxo Diferric Complexes

Kitajima, Nobumasa; Tamura, Nobuchika; Amagai, Hironobu; Fukui, Hideno; Moro‐oka, Yoshihiko; Mizutani, Yasuhisa; Kitagawa, Teizo; Mathur, Rajeev S.; Heerwegh, Kristel

doi:10.1021/ja00099a025

Cited by 159 publications

(152 citation statements)

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“…Particularly, EXAFS investigation of F peroxo has revealed a very short Fe-Fe distance of 2.53 Å , suggesting a Fe-O-O angle of 107° [18], while the spectroscopic properties of R2 peroxo are very similar to those of a structurally known peroxodiferric complex having a Fe-Fe distance of 4.0 Å and a Fe-O-O angle of 129° [15,25]. The resonance Raman data of F peroxo and R2 peroxo are consistent with these angular assignments [18,26].…”

Section: Discussionmentioning

confidence: 91%

Section: Discussionmentioning

confidence: 99%

“…One compound is the peroxide complex mentioned above with a l-1,2-peroxide and two l-1,3-benzoate ligands [15,25]. Its J value was determined by temperature-dependent magnetization measurements to be 66 cm -1 [25], comparable to that of F peroxo and R2 peroxo . The other peroxodiferric complex was generated by oxygenation of a l-alkoxo-l-1,3-benzoato bridged diferrous compound at low temperatures and was proposed to have a l-alkoxo-l-1,2-peroxo-l-1,3-benzoato-Fe 2 core [32].…”

Section: Discussionmentioning

confidence: 99%

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Exchange coupling constant J of peroxodiferric reaction intermediates determined by Mössbauer spectroscopy

Krebs

Bollinger

Theil³

et al. 2002

J Biol Inorg Chem

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Oxygen activation at a carboxylate-bridged diiron cluster is employed by a number of enzymes for diverse biological functions. The mechanisms by which O(2) is activated at the diferrous clusters have been studied in detail and peroxodiferric reaction intermediates have been observed in several of these diiron proteins. To understand further the magnetic properties of this common reaction intermediate, we have used Mössbauer spectroscopy to determine the magnitude and sign of the exchange coupling constant J (in the exchange Hamiltonian J S(1) x S(2)) of the peroxodiferric intermediates generated during the reactions of O(2) with two different proteins, the recombinant M ferritin from frog and the site-directed variant W48F/D84E of the R2 subunit of ribonucleotide reductase from Escherichia coli. Both intermediates are antiferromagnetically coupled with a moderate coupling constant J of 50+/-10 cm(-1) for R2-W48F/D84E and 75+/-10 cm(-1) for M ferritin. This work demonstrates the capability of Mössbauer spectroscopy to determine exchange coupling constants of diiron complexes, including reaction intermediates. The approach and its limitations are described.

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Section: Discussionmentioning

confidence: 91%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Exchange coupling constant J of peroxodiferric reaction intermediates determined by Mössbauer spectroscopy

Krebs

Bollinger

Theil³

et al. 2002

J Biol Inorg Chem

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“…6.7) [16], while Kitajima used a monomeric Fe(II) complex composed of a bidentate carboxylate and a hindered hydrotris(3,5-i Pr-pyrazolyl)borate (Tp iPr ) ligand that assembled into an iron dimer ( Fig. 6.8) [17]. In studies with both systems, the dioxygen binding to the Fe(II) complexes was monitored at temperatures less than -20 8C, which was necessary to assist in stabilizing the peroxo adducts and prevent iron-oxo species that are formed at room temperature.…”

Section: Synthetic L-peroxo Diiron Complexesmentioning

confidence: 99%

Dioxygen Binding and Activation: Reactive Intermediates

Borovik

Zinn

Zart

2006

Activation of Small Molecules

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“…Very often, the presence of non-innocent ligands such as (a-ceto) carboxylates, thiolates, or catecholates proved to be crucial. [18][19][20][21][22][23][24] In some cases, examples of formation of m-oxo dinuclear complexes were reported, and a mechanism that parallels what is described in porphyrin chemistry was discussed. [20,21,23] Recently, Fe II complexes with amide-containing macrocycles were shown to react with dioxygen.…”

Section: Introductionmentioning

confidence: 99%

Reactivity of Molecular Dioxygen towards a Series of Isostructural Dichloroiron(III) Complexes with Tripodal Tetraamine Ligands: General Access to μ‐Oxodiiron(III) Complexes and Effect of α‐Fluorination on the Reaction Kinetics

Thallaj

Rotthaus

Benhamou

et al. 2008

Chemistry A European J

101

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We have synthesized the mono, di-, and tri-alpha-fluoro ligands in the tris(2-pyridylmethyl)amine (TPA) series, namely, FTPA, F(2)TPA and F(3)TPA, respectively. Fluorination at the alpha-position of these nitrogen-containing tripods shifts the oxidation potential of the ligand by 45-70 mV per added fluorine atom. The crystal structures of the dichloroiron(II) complexes with FTPA and F(2)TPA reveal that the iron center lies in a distorted octahedral geometry comparable to that already found in TPAFeCl(2). All spectroscopic data indicate that the geometry is retained in solution. These three isostructural complexes all react with molecular dioxygen to yield stable mu-oxodiiron(III) complexes. Crystal structure analyses are reported for each of these three mu-oxo compounds. With TPA, a symmetrical structure is obtained for a dicationic compound with the tripod coordinated in the kappa(4)N coordination mode. With FTPA, the compound is a neutral mu-oxodiiron(III) complex with a kappa(3)N coordination mode of the ligand. Oxygenation of the F(2)TPA complex gave a neutral unsymmetrical compound, the structure of which is reminiscent of that already found with the trifluorinated ligand. On reduction, all mu-oxodiiron(III) complexes revert to the starting iron(II) species. The oxygenation reaction parallels the well-known formation of mu-oxo derivatives from dioxygen in the chemistry of porphyrins reported almost three decades ago. The striking feature of the series of iron(II) precursors is the effect of the ligand on the kinetics of oxygenation of the complexes. Whereas the parent complex undergoes 90 % conversion over 40 h, the monofluorinated ligand provides a complex that has fully reacted after 30 h, whereas the reaction time for the complex with the difluorinated ligand is only 10 h. Analysis of the spectroscopic data reveals that formation of the mu-oxo complexes proceeds in two distinct reversible kinetic steps with k(1) approximately 10 k(2). For TPAFeCl(2) and FTPAFeCl(2) only small variations in the k(1) and k(2) values are observed. By contrast, F(2)TPAFeCl(2) exhibits k(1) and k(2) values that are ten times higher. These differences in kinetics are interpreted in the light of structural and electronic effects, especially the Lewis acidity at the metal center. Our results suggest coordination of dioxygen as an initial step in the process leading to formation of mu-oxodiiron(III) compounds, by contrast with an unlikely outer-sphere reduction of dioxygen, which generally occurs at negative potentials.

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Monomeric Carboxylate Ferrous Complexes as Models for the Dioxygen Binding Sites in Non-Heme Iron Proteins. The Reversible Formation and Characterization of .mu.-Peroxo Diferric Complexes

Cited by 159 publications

References 2 publications

Exchange coupling constant J of peroxodiferric reaction intermediates determined by Mössbauer spectroscopy

Exchange coupling constant J of peroxodiferric reaction intermediates determined by Mössbauer spectroscopy

Dioxygen Binding and Activation: Reactive Intermediates

Reactivity of Molecular Dioxygen towards a Series of Isostructural Dichloroiron(III) Complexes with Tripodal Tetraamine Ligands: General Access to μ‐Oxodiiron(III) Complexes and Effect of α‐Fluorination on the Reaction Kinetics

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