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  • Analytical Chemistry and Spectroscopy  (3)
  • Adaptation  (1)
  • Biochemistry  (1)
  • 1
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Double-charge-transfer spectroscopy is routinely used to measure double-ionization energies of molecules to singlet and triplet electronic states of dications, but is experimentally difficult to apply because the yield of negative ions generated in the double-electron-capture reactions is low. The use of a data-acquisition system and repetitive scanning of a spectrum can increase signal-to-noise ratios, but the number of scans that can be acquired is limited by drifting in the spectrum position, which results in spectral-peak broadening. This limitation has been overcome in the present investigation by the application of a computer enhancement program that effectively superimposes successive spectra which are subject to slight drift. Spectra obtained for H+ projectile ions reacting with hexafluorobenzene (C6F6) molecules are presented; use of the program with such spectra reveals features in the computer-enhanced spectrum which are not clearly evident in the individual spectra.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab initio calculations employing a standard double-zeta basis set augmented with various polarization functions have been used to investigate the lowest energy region of the ground-state potential energy surface of the formamide molecule. Hartree-Fock calculations with only d polarization functions on the nonhydrogen atoms located two stable minima, that with geometry distorted from planarity having slightly lower energy; only one stable minimum with planar structure is found when p polarization functions on the hydrogens are included. In contrast optimizations, which account approximately for the correlation energy using second-order Møller-Plesset perturbation theory consistently favor a single slightly nonplanar minimum energy geometry.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Double ionization of the 1,1-dimethyl allene molecule to triplet electronic states of the dication has been studied using theoretical and experimental methods. Although the calculated data indicate a high density of states, suitable groupings of calculated double-ionization energies to those states agree well with values measured by double-charge-transfer spectroscopy. This indicates that the theoretical predictions provide an accurate indication of the composition of the triplet-state manifold for the 1,1-dimethyl allene dication between 25.2 eV and 39.6 eV.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Vertical double-ionization energies of ethylamine, propylamine and butylamine molecules to triplet electronic states of their dications were measured by double-charge-transfer spectroscopy. The energies to the lowest states of the dications were calculated using an ab initio method with four basis sets. The calculated values predicted fairly well the reduction in the lowest energy observed when the length of the substituted alkyl group increased. Double-ionization energies to the lowest and higher lying triplet states of the dications were calculated by application of a semi-empirical form of the multiple scattering Xα method. Even though several spectral peaks may only be identified with transitions to groups of closely lying states, the calculated data gave an insight into the electronic transitions which take place to give the double-charge-transfer spectra.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-2013
    Keywords: Adaptation ; Hypertrophy ; Irradiation ; Myosin heavy chain ; Satellite cells ; Skeletal muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The right extensor digitorum longus (EDL) muscle of growing male rats was overloaded by ablation of its synergist tibialis anterior (TA) muscle. Four weeks later, the overloaded muscle was heavier and contained larger type IIA, IIX and IIB fibres than either untreated contralateral muscle or control muscle from an untreated animal. The myonuclear-to-myoplasmic volume ratio was maintained in the overloaded muscle. Overloaded EDL muscle, previously subjected to a dose of irradiation sufficient to sterilise satellite cells, and EDL muscle which had been only irradiated, were significantly lighter and contained significantly smaller fibres than controls, though a significant amount of normal EDL muscle growth did occur following either treatment. The myonuclear-to-myoplasmic volume ratio of the irradiated muscles was smaller than in controls. Overloaded muscle, with or without prior irradiation, possessed a smaller proportion of fibres containing IIB myosin heavy chain (MHC) and a larger proportion of fibres containing IIA and IIX MHC; a significant percentage of these fibres coexpressed either type IIA and IIX MHC or type IIX and IIB MHC. Thus in the absence of satellite cell mitosis, muscles of young rats possess a limited capacity for normal growth but not for compensatory hypertrophy. Adaptations in MHC gene expression to chronic overload are completely independent of satellite cell activity.
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