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  • 1990-1994  (25)
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Materialart
Erscheinungszeitraum
Jahr
  • 11
    Digitale Medien
    Digitale Medien
    Spectroscopic and structural investigations of the ferrous and ferric high-spin state of a “picket—fence” porphyrinato acetato iron complex. A refined model for the P460 center of hydroxylamine oxidoreductase (1992)
    Springer
    Hyperfine interactions 71 (1992), S. 1295-1298 
    Details
    ISSN: 1572-9540
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Mössbauer investigations were performed in the ferrous and ferric form of the ‘picket-fence’ porphyrinato acetato iron complex |Fe(CH3CO2) (TPpivP)|1−,0 at temperatures varying from 1.5–200K and in fields of 0–6.2T. The ferrous complex has an unusually large quadrupole splitting, ΔEQ=+4.25mms−1. The quadrupole splitting in the ferric species, ΔEQ=+1.1mms−1, is as normally found in ferric high-spin iron porphyrins. Spin-Hamiltonian analysis of the magnetic spectra yields zero-field parameters D=−0.9mms−1, E/D=0.33 and magnetic hyperfine parameters Ax,y=−17T, Az=−13.3T in the ferrous high-spin (S=2) complex, and D=7.5cm−1, E/D≈0 and Ax,y,z=20T in the ferric high-spin (S=5/2) species.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02397321
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  • 12
    Digitale Medien
    Digitale Medien
    Mössbauer study of a novel binuclear Fe(II/III) delocalized-valence compound (1990)
    Springer
    Hyperfine interactions 53 (1990), S. 311-315 
    Details
    ISSN: 1572-9540
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract In this paper, we briefly summarize the main conclusions of the Mössbauer analysis of [L2Fe2(μ-OH)3] (ClO4)2·2CH3OH·2H2O with L=N,N',N"-trimethyl-1,4,7-triazacyclononane, a novel dimeric iron compound, which possesses a central exchange-coupled delocalized-valence Fe(II/III) unit. The complete delocalization of the excess electron in the dimeric iron center is concluded from the indistinguishability of the two iron sites in Mössbauer spectroscopy. The magnetic Mössbauer spectra imply a system spinS t=9/2 for the dimer in its ground state. The values for hyperfine and spin-Hamiltonian parameters, obtained from simulations of the Mössbauer spectra, are δ=0.74 mms−1, ΔE Q=−2.14 mms−1,A ⊥=−10.6 T,A ∥=−13.5 T andD=1.8 cm−1. The system spinS t=9/2 is interpreted to be a consequence of double-exchange coupling.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02101058
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  • 13
    Digitale Medien
    Digitale Medien
    Modulations of exchange coupling in oxoferrylporphyrin cation radical complexes detected by Mössbauer and EPR measurements (1992)
    Springer
    Hyperfine interactions 71 (1992), S. 1299-1302 
    Details
    ISSN: 1572-9540
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Oxoferrylporphyrin cation radical complexes were generated using the prophyrin dianions: tetrakis 2,6-dichlorophenyl (TDCPP) and tetrakis 2,4,6-trimethoxyphenyl (TTMPP). Spin coupling between ferryl iron (S=1) and porphyrin radical S′=1/2), ligand field interaction and hyperfine parameters of iron were studied by Mössbauer and EPR measurements and corresponding spin Hamiltonian analyses. Samples of [FeIV=0 TDCPP], which had to be prepared in CH2Cl2, were “vacuum dried” in order to obtain Mössbauer spectra.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02397322
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  • 14
    Digitale Medien
    Digitale Medien
    The association between the antineoplastic drug daunomycin and iron. evidence for polynuclear aggregates (1992)
    Springer
    Hyperfine interactions 71 (1992), S. 1263-1266 
    Details
    ISSN: 1572-9540
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract In contrast to literature data, at millimolar iron and daunomycin (DN) concentrations no solitary Fe(DN)3 complexes are formed in appreciable amounts. The Mössbauer spectroscopic analysis revealed severe dependencies on temperature and on the metal ligand ratio. Two species can be discerned: exchange-coupled polynuclear aggregates, which are magnetically highly anisotropic and another superparamagnetic system, exhibiting much less magnetic anisotropy. The cooperative phenomena observed are attributed to stacking effects of daunomycin.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02397313
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  • 15
    Digitale Medien
    Digitale Medien
    Mössbauer study of iron-doped lithium niobate (1994)
    Springer
    Hyperfine interactions 94 (1994), S. 2005-2010 
    Details
    ISSN: 1572-9540
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract From Mössbauer spectra of LiNbO3∶57Fe(III) single crystals under external fields of 4.92 and 6.2 T, the crystal field and hyperfine parameters are determined. Transmission integral fits indicate a Boltzmann population of the Fe(III) electronic levels with a spin temperature equal to the sample temperature. Spectra at external fields of 0 T and 19 mT can be satisfactorily simulated using an effective spin 1/2,g-factors calculated from spin-expectation values and an internal averaged dipole field of 5.5 mT inclined 20
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02063731
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  • 16
    Digitale Medien
    Digitale Medien
    Exchange interaction in trinuclear transition-metal complexes (1992)
    Springer
    Hyperfine interactions 68 (1992), S. 229-232 
    Details
    ISSN: 1572-9540
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Heterotrinuclear transition-metal complexes are of interest for the study of long-range magnetic interactions and as model compounds for the investigation of biological electron transport chains. The systems under study here contain paramagnetic Fe111-containing terminal units and a bridging unit with M11=Zn, Cu, Ni, Co, Fe, Mn. The spectroscopic methods applied include Mössbauer, — EPR- and magnetic susceptibility investigations. The spin-Hamiltonian analysis of the measured results yields information about the intramolecular super-exchange interactions among the various magnetic transmition-metal sites. In view of the 7Å separation between the two terminal Fe111 sites, the Fe111...Fe111 exchange coupling of the order −10cm−1 is large.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02396478
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  • 17
    Digitale Medien
    Digitale Medien
    Spin coupling in iron-containing proteins and model complexes (1992)
    Springer
    Hyperfine interactions 68 (1992), S. 39-46 
    Details
    ISSN: 1572-9540
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract In the field of transition metals in biology we are concerned with a variety of homo- and hetero-polynuclear metal clusters which exhibit spin coupling. A further example for spin coupling in this field is provided by mononuclear transition metal complexes, with the paramagnetic metal site and an additional nonmetallic site forming a spin-coupled system. For both types of spin-coupled systems we present examples here, and we discuss the influence of localized and delocalized mixed-valence states, and the strength of superexchange, spin-dipolar and double-exchange contributions to spin coupling.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02396450
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  • 18
    Digitale Medien
    Digitale Medien
    High oxidation states of iron in biological and biomimetical systems: Complementary Mössbauer, EPR and magnetic susceptibility studies (1994)
    Springer
    Hyperfine interactions 90 (1994), S. 143-158 
    Details
    ISSN: 1572-9540
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Compound I and compound II of heme peroxidases represent high-valent iron complexes with iron in the formal oxidation state IV. Reliable information about their magnetic and electronic properties requires the applications of complementary techniques like Mössbauer and EPR spectroscopy, magnetic susceptibility measurements and theoretical calculations. In order to study the physical properties of the high-valent iron moiety, a series of novel porphyrin-like complexes has been investigated, obtained with the planar N4-donating ligand L=pentane-2,4-dion-bis(S-alkylisothiosemicarbazonate). Due to their symmetry and their ability of binding a variety of axial ligands of biological relevance, these complexes can serve as biomimetic models for high-valent iron-porphyrin complexes. 5-coordinated and 6-coordinated complexes differ significantly in their spin states (5=1 versusS=0), whereas Mössbauer and XAS spectra are similar. MO calculations based on experimental molecular structures provide deeper understanding of theelectronic structure of these compounds. They reveal the formal nature of the concept of oxidation number in descriptions of high-valent complexes, in the sense that these numbers cannot be correlated with empirical data.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02069124
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  • 19
    Digitale Medien
    Digitale Medien
    Mössbauer, magnetic susceptibility, EPR, and EXAFS investigations of the vibrationally-induced low-spin/high-spin transition in a biomimetic Fe(III) complex (1994)
    Springer
    Hyperfine interactions 90 (1994), S. 453-457 
    Details
    ISSN: 1572-9540
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Magnetic susceptibility measurements from 2 to 520 K, Mössbauer measurements from 1.2 to 450 K, and EPR measurements at 10 K have been performed on the monomeric FeIII complex (1,4,7-tris(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triaza-cyclononan)Fe. The complex exhibits a low-spin/high-spin transition at temperatures above 250 K. This behavior is quantitatively explained on the basis of a crystal-field model, which explicitly includes the vibrational properties of iron ligands. The EPR spectrum at 10 K yields a pure FeIII low-spin signal withg values 2.58(5), 2.12(5), 1.45(5). The values are consistently described by a crystal-field model, which explicitly includes spin-orbit coupling within the t2g subspace. The temperature dependence of the quadrupole splitting indicates a phase transition at approximately 100 K. The existence of the phase transition is corroborated by the temperature dependence of the effective thickness. The observation of only one quadrupole doublet up to 450 K indicates that the relaxation time between the high-spin and the low-spin configurations is shorter than the quadrupole precession time. X-ray structure analysis on single crystals at RT and temperature-dependent EXAFS investigation of powder material between 30 and 200 K indicate that the observed phase transition induces only changes of bond angles, while the low-spin/high-spin transition most likely induces changes of metal-ligand bond distances.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02069155
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  • 20
    Digitale Medien
    Digitale Medien
    Mössbauer studies on yeast metallothionein (1994)
    Springer
    Hyperfine interactions 91 (1994), S. 791-795 
    Details
    ISSN: 1572-9540
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Iron-substituted yeast metallothionein, Fe(II)-yeast-MT, has been studied by Mössbauer spectroscopy. The iron in the protein is in the high-spin ferrous state. As maximum metal content, 4 Fe(II)/molecule has been determined, with the 4 metal ions forming a diamagnetic cluster due to the antiferromagnetic exchange interaction between the Fe(II) ions via bridging thiolates. In case the iron titration is less than 4 Fe(II)/apoprotein, the ions are magnetically noninteracting, with each individual Fe(II) behaving similar to Fe(II) in reduced rubredoxin.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02064608
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