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  • 1
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 11 (1972), S. 1181-1207 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The optical and conformational properties of certain 7-ribosyl purines have been studied using several experimental and theoretical methods. The CD, MCD, and absorption spectra of the 7-ribosyl purines and their cations have been determined experimentally with some solvent effects being noted. Theoretically we have used the SCF-CI and CNDO molecular orbital calculations to determine the optical properties of the bases; Simpson's bond exciton theory to determine the optical properties of the bases; Simpson's bond exciton theory to determine the optical properties of the ribose moiety; the optical activity was determined by the dipole coupling and electricmagnetic coupling equations; and the conformational energy calculations are included as a basis for excluding highly improbable conformations. On the basis of these calculations, we concluded that the oxy derivatives and the amino derivatives are predominately in the “extreme anti” conformation and “standard anti” conformation, respectively. However, the conclusions are tentative since at the present time the band assignments are not unequivocal. At least one n-π* transition has been identified in the spectra which is not notably sensitive to pH and solvent effects. Several implications of this observation are discussed.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 25 (1990), S. 3-8 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The first negative-ion fast atom bombardment mass spectra of a related series of monosubstituted Group VIB transition metal pentacarbonyls, M(CO)5L (M = Cr), Mo or W and L = P(Ph)3, As(Ph)3 or Sb(PH)3), have been obtained. Instead of molecular ion radicals, pseudomolecular adduct ions, [M + H]- and [M + 15]-, were detected, with the hydride species being much more abundant. High-resolution measurements and comparison of observed isotope clusters with computer-generated theoretical isotope patterns confirmed that ionization occurred by several mechanisms, including electron capture, charge dissociation and formation of adducts with charged species. Fragmentation consisted primarily of elimination of neutral ligands, i.e. ([MH - L]-, [MH - CO]-, [MH - 2CO]-, etc. B/E and constant neutral loss linked scanning with collisional activation were used to confirm fragmentation pathways and characterize the site of hydride attachment on the transition metal complex. The information obtained demonstrates the utility of fast atom bombardment mass Spectrometry in the analysis of metal carbonyls.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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