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  • Wiley-Blackwell  (2)
  • 1995-1999  (2)
  • 1
    ISSN: 0947-6539
    Keywords: electronic structure ; frontier orbitals ; metalloporphyrins ; radical cations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of magnesium and zinc tetraarylporphyrins and their porphyrinoxidized derivatives were studied by UV/Vis, ESR, and resonance Raman spectroscopy at various temperatures. The series included tetra(meta-dichlorophenyl)porphyrinatozinc (5), tetra(ortho-dichlorophenyl)porphyrinatozinc (6), tetra(ortho-difluorophenyl)porphyrinatozinc and -magnesium (9 and 10), and tetra(pentafluorophenyl)porphyrinatozinc and -magnesium (7 and 8). The radical cations (3a-10a) were isolated by chemical one-electron oxidation of their neutral precursors (3-10). Despite the structural similarity of all these radicals, their electronic ground state varied within the series. The position of the chloro groups was found to play a key role. While the radical cation of the meta-dichloro-substituted derivative 5a exhibited A2u spectroscopic features, the ortho-dichlorophenyl derivative (6a) showed A1u spectral features. Radicals of the fluoro-substituted porphyrins, especially that of 10, were found to have state-admixed (A1u/A2u) electronic structures, and the relative contributions of the two states was found to vary with temperature and to depend on the axial ligand. The results indicate that the fluoro-substituted porphyrins are primarily A2u at low temperature, even though their room temperature spectroscopic features resemble those of A1u cations. The elucidation of factors that affect the electronic structures of the radicals in the present series is helpful in providing a greater understanding of the spin-spin interactions in the intermediates of heme-dependant enzymatic reactions and their synthetic analogues.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    BioEssays 17 (1995), S. 713-719 
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The DNA of all species is constantly under threat from both endogenous and exogenous factors, which damage its chemical structure. Probably the most common lesion that arises in cellular DNA is the loss of a base to generate an abasic site, which is usually referred to as an apurinic or apyrimidinic (AP) site. Since these lesions are potentially both cytotoxic and mutagenic, cells of all organisms express dedicated repair enzymes, termed AP endonucleases, to counteract their damaging effects. Indeed, many organisms consider it necessary to express two or more of these lesion-specific endonucleases, underscoring the requirement that exists to remove AP sites for the maintenance of genome integrity and cell viability. Most AP endonucleases are very versatile enzymes, capable of performing numerous additional repair roles. In this article, we review the AP endonuclease class of repair enzymes, with emphasis on the evolutionary conservation of structural features, not only between prokaryotic and eukaryotic homologues, but also between these enzymes and the RNase H domain of one class of reverse transcriptase.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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