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  • Hydroxylation  (1)
  • Interconversions  (1)
  • Springer  (2)
  • International Union of Crystallography (IUCr)
  • 1
    Electronic Resource
    Electronic Resource
    Molecular orbital study of the hydroxylation of benzene and monofluorobenzene catalysed by iron-oxo porphyrin π cation radical complexes (1996)
    Springer
    JBIC 1 (1996), S. 192-204 
    Details
    ISSN: 1432-1327
    Keywords: Key words High-valent iron porphyrins ; Molecular orbital calculations ; Hydroxylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  The reaction mechanism for the hydroxylation of benzene and monofluorobenzene, catalysed by a ferryl-oxo porphyrin cation radical complex (compound) is described by electronic structure calculations in local spin density approximation. The active site of the enzyme is modelled as a six-coordinated (Por+)Fe(IV)O a2u complex with imidazole or H3CS– as the axial ligand. The substrates under study are benzene and fluorobenzene, with the site of attack in para, meta and ortho position with respect to F. Two reaction pathways are investigated, with direct oxygen attack leading to a tetrahedral intermediate and arene oxide formation as a primary reaction step. The calculations show that the arene oxide pathway is distinctly less probable, that hydroxylation by an H3CS––coordinated complex is energetically favoured compared with imidazole, and that the para position with respect to F is the preferred site for hydroxylation. A partial electron transfer from the substrate to the porphyrin during the reaction is obtained in all cases. The resulting charge distribution and spin density of the substrates reveal the transition state as a combination of a cation and a radical σ-adduct intermediate with slightly more radical character in the case of H3CS– as axial ligand. A detailed analysis of the orbital interactions along the reaction pathway yields basically different mechanisms for the modes of substrate–porphyrin electron transfer and rupture of the Fe–O bond. In the imidazole-coordinated complex an antibonding π*(Fe–O) orbital is populated, whereas in the H3CS––coordinated system a shift of electron density occurs from the Fe–O bond region into the Fe–S bond.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050043
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  • 2
    Electronic Resource
    Electronic Resource
    Iron-sulfur interconversions in the anaerobic ribonucleotide reductase from Escherichia coli (1999)
    Springer
    JBIC 4 (1999), S. 614-620 
    Details
    ISSN: 1432-1327
    Keywords: Key words Ribonucleotide reductase ; Anaerobiosis ; Iron-sulfur ; Oxidation ; Interconversions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  The anaerobic ribonucleotide reductase from Escherichia coli contains an iron-sulfur cluster which, in the reduced [4Fe-4S]+ form, serves to reduce S-adenosylmethionine and to generate a catalytically essential glycyl radical. The reaction of the reduced cluster with oxygen was studied by UV-visible, EPR, NMR, and Mössbauer spectroscopies. The [4Fe-4S]+ form is shown to be extremely sensitive to oxygen and converted to [4Fe-4S]2+, [3Fe-4S]+/0, and to the stable [2Fe-2S]2+ form. It is remarkable that the oxidized protein retains full activity. This is probably due to the fact that during reduction, required for activity, the iron atoms, from 2Fe and 3Fe clusters, readily reassemble to generate an active [4Fe-4S] center. This property is discussed as a possible protective mechanism of the enzyme during transient exposure to air. Futhermore, the [2Fe-2S] form of the protein can be converted into a [3Fe-4S] form during chromatography on dATP-Sepharose, explaining why previous preparations of the enzyme were shown to contain large amounts of such a 3Fe cluster. This is the first report of a 2Fe to 3Fe cluster conversion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050385
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    Paper (German National Licenses)
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