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  • 76  (1)
  • Hydroxylation  (1)
  • Iron-sulfur  (1)
  • Key words Carbonmonoxy-Myoglobin  (1)
  • 1
    Digitale Medien
    Digitale Medien
    Low temperature study of myoglobin-ligand rebinding kinetics with Mössbauer spectroscopy (1997)
    Springer
    European biophysics journal 26 (1997), S. 227-237 
    Details
    ISSN: 1432-1017
    Schlagwort(e): Key words Carbonmonoxy-Myoglobin ; Recombination kinetics ; Mössbauer spectroscopy ; Scaling law ; Activated tunneling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Physik
    Notizen: Abstract We have studied the recombination kinetics of carboxymyoglobin (after photodissociation of the CO ligand) by Mössbauer spectroscopy for temperatures in the range 4.2 – 60 K. The observed kinetics display non-exponential behaviour which was monitored over periods of a few days. It is shown that the time dependence of the kinetics can be reduced to a single universal function of the temperature-dependent variable (t/τ 1/2(T)) β(T) . The half-decay time τ 1/2(T) and the scaling parameter β(T) are analysed for the presence of tunneling effects. The non-Arrhenius temperature dependence of the half-decay time below 60 K is interpreted as activated tunneling in models with an Eckart barrier or a fluctuating barrier.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002490050075
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): Key words High-valent iron porphyrins ; Molecular orbital calculations ; Hydroxylation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s007750050043
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Iron-sulfur interconversions in the anaerobic ribonucleotide reductase from Escherichia coli (1999)
    Springer
    JBIC 4 (1999), S. 614-620 
    Details
    ISSN: 1432-1327
    Schlagwort(e): Key words Ribonucleotide reductase ; Anaerobiosis ; Iron-sulfur ; Oxidation ; Interconversions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s007750050385
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Magnetic measurements on stable Fe(0) microclusters. Part 2 (1986)
    Springer
    The European physical journal 3 (1986), S. 303-308 
    Details
    ISSN: 1434-6079
    Schlagwort(e): 75 ; 76 ; 81
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Zero valent iron microclusters were stabilized inside the pore structure ofA-type zeolites. The cage diameter of the matrix was 1.1 nm. Mößbauer spectra show superparamagnetic behaviour down to at least 77 K. Below 10 K, slow relaxation of most of the superparamagnetic moments was observed. Information on the magnetic properties was obtained from the Mößbauer spectra below 4.2 K and from measurements in an external magnetic field applied parallel to the gamma beam. Evidence has been found for both bulk-like and non-crystalline iron clusters.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01384820
    Standort Signatur Einschränkungen Verfügbarkeit
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