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  • 1
    ISSN: 1572-8927
    Keywords: Quadrupole relaxation ; 23Na+,87Rb+, and14N NMR ; ion-solvent interaction ; asymmetry effects ; preferential solvation ; acetonitrile-water mixtures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Nuclear magnetic relaxation rates of23Na+,87Rb+, and14N in acetonitrile-water mixtures have been measured over the complete mixture range. The interaction of the quadrupole moment of ionic nuclei with electric field gradients is an excellent short ranged probe for the direct neighborhood of ions in solution. Thus the23Na+ and87Rb+ relaxation contains information about dynamics composition and symmetry of the inner solvation sphere in the mixed solvent. It was found that the relaxation rate of both ionic nuclei has an unexpected marked maximum in the acetonitrile (AN) rich region. The14N and2H relaxation rates of the solvent molecules revealed that the maximum could not be explained by dynamic effects. Further experimental results showed that it is caused by local symmetry changes. By measuring 1/T1 of the cationic nuclei in AN-H2O and AN-D2O it was possible for the first time to separate quantitatively asymmetry effects from selective solvation effects. It turned out that both cations are strongly preferentially hydrated. Comparison of the results of two approaches for the evaluation of the D2O-H2O isotope effect led to interesting hints concerning the location of the electric point dipole in acetonitrile molecules having contact with cations.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Langenbeck's archives of surgery 355 (1981), S. 517-517 
    ISSN: 1435-2451
    Keywords: Polyurethane graft ; Microporosity ; Control angiography ; Scanning electronic microscopy ; Polyurethanprothesen ; Mikroporosität ; Kontrollangiographie ; Rasterelektronenmikroskopie
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Die neuen Kunststoffprothesen bestehen aus Polyúrethan, das nach einem speziellen Sprühverfahren verarbeitet wird. Die Prothesen sind längs- und querelastisch sowie mikroporös. In tierexperimentellen Untersuchungen wurden 20mal die terminale Aorta, 24mal die arteria carotis communis und 12mal die arteria femoralis superficialis ersetzt. Die Tiere wurden in regelmäßigen Abst↭den angiographiert. Nach Tötung erfolgten rasterelektronenmikroskopische und histologische Untersuchungen. Von 20 Aortentransplantaten blieben 18 bis zum Zeitpunkt der Tötung, bzw. bis heute offen. In Carotisposition scheinen sich die Transplantate nicht zu bewähren.
    Notes: Summary The new plastic graft consists of polyurethane manufactured in a special spray process. These grafts are elastic both transversally and longitudinally and are microporous. In experiments on animals, the abdominal aorta was substituted 20 times, the common carotid artery 24 times, and the superficial femoral artery 12 times. The animals were regularly subjected to angiographical examinations. After they were killed, they were examined histologically and by means of a scanning electronic microscope. Of the 20 abdominal grafts, 18 have remained open to date. Carotis grafts, however, seemed to fail.
    Type of Medium: Electronic Resource
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