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  • Conference proceedings  (3)
  • Chemistry  (1)
  • Electron spin echo envelope modulation spectroscopy  (1)
  • Interconversions  (1)
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  • 1
    ISSN: 0392-6737
    Keywords: Mössbauer effect ; other γ-ray spectroscopy ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Sediment cores with different sub-bottom depths (I: 45 cm and II: 700 cm) from the Peru Basin have been investigated. From the depth profile of the relative amount of Fe(II) a redox zone is obtained which correlates with the organic carbon flux into the sediment (core I). Mössbauer parameters suggest that the iron in the sediments is mainly contained in clay minerals and to varying extent also in goethite.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 353-357 
    ISSN: 0392-6737
    Keywords: Mössbauer spectra ; Spectra ; photodissociation and photoionization of biomolecules ; bioluminescence ; Measurement of rate constants ; reaction cross-sections and activation energy ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Partial photodissociation of two carbonmonoxy-porphyrin complexes, a bridged and a fenced one, has been achieved. The results from monitoring the recombination point to an important influence of the solvent matrix on the recombination rates.
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  • 3
    ISSN: 0392-6737
    Keywords: Phonons and vibrations in crystal lattices ; Solid-liquid transitions ; Thermodynamic properties and entropy ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Dynamic properties of ultrafine clusters of γ-Fe2O3 (ferric oxide, FO) were studied by Mössbauer spectroscopy and by thermodynamic analysis. The data obtained for FO clusters allowed the conclusion that dynamic properties of clusters as well as the decrease of melting point and the appearance of a gap between freezing and melting points depend on intracluster atomic mobility. Intracluster atomic mobility in FO clusters was shown to increase by the action of surfactants which decrease intercluster interactions. The increase in intracluster atomic mobility was suggested to proceed via formation of a solid-liquid state.
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  • 4
    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.
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  • 5
    ISSN: 1432-1327
    Keywords: Key words g-Tensor determination of ferriheme model compound ; Electron spin echo envelope modulation spectroscopy ; Mössbauer spectroscopy ; Electron paramagnetic resonance spectroscopy ; Electronic ground state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  A model heme complex, bis(3-aminopyrazole)tetraphenylporphinatoiron(III) chloride, [TPPFe (NH2PzH)2]Cl, for which the EPR g-values lead to a rhombicity V/Δ=1.2 if g zz is the largest g-value, have been investigated by electron spin echo envelope modulation (ESEEM) and Mössbauer spectroscopies. The ESEEM studies focus on the proton sum frequency peaks at near twice the proton Larmor frequency. Analysis of the distant proton peak (mainly due to the pyrrole-H) at exactly twice the proton Larmor frequency shows conclusively that g zz is aligned along the normal to the porphyrin plane, and thus the electron configuration is (d xy )2(d xz ,d yz )3, with g zz 〉g yy 〉g xx . This system is thus another violation to Taylor's "proper axis system" rule. The near proton (the α-H and N-H of the axial ligands) peaks provide distance information for those protons from the metal. Magnetic Mössbauer studies of the same complex confirm the (d xy )2(d xz ,d yz )3 ground state and indicate that, as is the case for cytochrome P450cam, A xx is the largest magnitude A-value, and is negative in sign. Other low-spin iron(III) porphyrinates also have A xx of negative sign, but usually the magnitude is only about half that of A zz , which is always positive in sign.
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  • 6
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Preparation of Metal-Sulfur-Clusters by Simple Reaction of Metal-Salts with H2S: R2(NH4) [Cu3S12], R2[Cu4S12] · CH3CN, R2[Cu4S12,8], R2[Fe2S2(S5)2], R2[Fe4S4Br4], R2[Fe4S4Br2Cl2], R2[Fe4S4Cl4], R2[Fe2S2Cl4] (R = PPh4) and [Fe(DMF)6][Fe2S2Cl4]Simple preparation methods for metal sulfur clusters from simple metal salts and H2S in solution are reported (for the systems Cum+/H2S and Fen+/H2S). The compounds R2(NH4)[Cu3S12], R2[Cu4S12] · CH3CN, R2[Cu4S12,8], R2[Fe2S2(S5)2], R2[Fe4S4Br4], R2[Fe4S4Br2Cl2], R2[Fe4S4Cl4], R2[Fe2S2Cl4] (R = PPh4) and [Fe(DMF)6][Fe2S2Cl4] were characterized spectroscopically (IR, Raman, Fe-Mössbauer) and by complete crystal structure analyses (except R2[Fe2S2(S5)2] and R2[Fe2S2Cl4]).For structural data see Inhaltsübersicht.
    Notes: Es wird über eine einfache Darstellungsmöglichkeit von Metall-Schwefel-Clustern aus einfachen Metall-Salzen und H2S in Lösung berichtet und zwar für die Systeme Cum+/H2S und Fen+/H2S. Die Verbindungen R2(NH4)[Cu3S12], R2[Cu4S12] · CH3CN, R2[Cu4S12,8], R2[Fe2S2(S5)2], R2[Fe4S4Br4], R2[Fe4S4Br2Cl2], R2[Fe4S4Cl4], R2[Fe2S2Cl4] (R = PPh4) und [Fe(DMF)6][Fe2S2Cl4] wurden spektroskopisch (IR, Raman, Fe-Mößbauer) sowie durch vollständige Kristallstrukturanalyse charakterisiert (mit Ausnahme von R2[Fe2S2(S5)2]).(PPh4)2(NH4)[Cu4S12]: P1, a = 1266,0(5), b = 1 489,6(6), c = 1 493,6(6) pm, α = 74,72(3), β = 86,40(3), γ = 77,52(3)°, V = 2 652,9 · 106 pm3, Z = 2; R = 0,057 für 8377 unabhängige Reflexe (Fo 〉 3,92 σ(Fo)).(PPh4)2(NH4)[Cu4S12] · CH3CN: P1, a = 1 062,2(3), b = 1 336,2(4), c = 2 137,8(6) pm, α = 102,42(2), β = 90,60(2), γ = 110,16(2)°, V = 2 769,8 · 106 pm3, Z = 2; R = 0,076 für 4312 unabhängige Reflexe (Fo 〉 3,92 σ(Fo)).(PPh4)2[Cu4S12,8]: P21/n, a = 1 245,2(8), b = 1 306,9(10), c = 3348,7(22) pm, β = 98,90(5°), V = 5383,9 · 106 pm3, Z = 4; R = 0,094 für 4814 unabhängige Reflexe (Fo 〉 3,92 σ(Fo)).(PPh4)2[Fe4S4Br4]: C2/c, a = 1585,8(6), b = 1440,6(4), c = 2419,7(9) pm, β = 112,74(3)°, V = 5 098,1 · 106 pm3, Z = 4; R = 0,068 für 3 247 unabhängige Reflexe (Fo 〉 3,92 σ(Fo)).(PPh4)2[Fe4S4Br2Cl2]: C2/c, a = 1592,3(3), b = 1432,9(3), c = 2325,0(5) pm, β = 106,43(2)°, V = 5 088,1 · 106 pm3, Z = 4; R = 0,084 für 1982 unabhängige Reflexe (Fo 〉 3,92 σ(Fo)).(PPh4)2[Fe4S4Cl4]: C2/c, a = 1593,9(3), b = 1420,8(2), c = 2316,9(4) pm, β = 106,65(1)°, V = 5026,9 · 106 pm3, Z = 4; R = 0,069 für 3 902 unabhängige Reflexe (Fo 〉 3,92 σ(Fo)).[Fe(DMF)6][Fe2S2Cl4]: P1, a = 923,5(4), b = 941,4(4), c = 1123,9(5) pm, α = 75,29(4), β = 71,17(3), γ = 87,27(4)°, V = 893,9 · 106 pm3, Z = 1; R = 0,067 für 1832 unabhängige Reflexe (Fo 〉 3,92 σ(Fo)).
    Additional Material: 11 Ill.
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