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  • Articles  (4)
  • Chemistry  (1)
  • Electron spin echo envelope modulation spectroscopy  (1)
  • Key words Carbonmonoxy-Myoglobin  (1)
  • Key words High-valent iron porphyrins  (1)
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  • Articles  (4)
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  • 1
    Electronic Resource
    Electronic Resource
    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
    Keywords: Key words Carbonmonoxy-Myoglobin ; Recombination kinetics ; Mössbauer spectroscopy ; Scaling law ; Activated tunneling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002490050075
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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    ESEEM and Mössbauer studies of the ferriheme model compound bis(3-aminopyrazole)tetraphenylporphyrinatoiron(III) chloride, [TPPFe(NH2PzH)2]Cl (1999)
    Springer
    JBIC 4 (1999), S. 708-716 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050343
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  • 4
    Electronic Resource
    Electronic Resource
    Darstellung von Metall-Schwefel-Clustern durch einfache Reaktion von Metallsalzen mit H2S: 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]Professor Friedo Huber zum 60. Geburtstage am 4. Juni 1989 gewidmet (1989)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 570 (1989), S. 7-36 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19895700102
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