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  • 1980-1984  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 470 (1980), S. 118-130 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Acidity of Crystalline Silicic AcidsCrystalline silicic acids are strong solid acids with surface acidities ranging from H0 〈 -3 (H2Si14O29 · 5.4 H2O) to HO ≍ 2.3(H2Si2O5), measured with Hammett indicators. Thermal dehydration reduces the surface acidity to 2.3-3.3 only. The high acidity probably results from regular, extended hydrogen bonding systems including the surface water molecules. By disturbing the regular array of hydrogen bonds the acidity decreases to Ho = 5-6 which is considered to be the characteristic acidity of isolated silanol groups not involved in regular hydrogen bonding systems. The surface acidity is not directly related to the ease with which the protons are exchanged by alkali ions because of the cooperative nature of the cation exchange.
    Notes: Kristalline Kieselsäuren sind starke feste Säuren, deren Acidität zwischen H0 〈 -3(H2Si14O29 · 5,4 H2O) und Ho = 2,3(H2Si205) liegt. Sie wurde mit Hammettindikatoren gemessen. Thermische Wasserabspaltung erniedrigt die Acidität nur auf Ho = 2,3-3,3. Es wird vermutet, daß die hohe Acidität auf die Ausbildung regelmäßiger, ausgedehnter Wasserstoffbrückensysteme mit dem Oberflächenwasser beruht. Wird die regelmäßige Anordnung gestört, sinkt die Acidität auf die für isolierte Oberflächensilanolgruppen charakteristischen Werte von Ho = 5-6. Wegen der kooperativen Natur des Kationenaustausches verschiebt eine erhöhte Oberflächenacidität den Austausch der Silanolprotonen nicht zwanggsläufig zu kleineren pH-Werten.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1831
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Staining of lymphocytes from scrapie-infected STU mice with FITC-labelled anti-mouse Ig revealed disturbances in the capping process when compared with lymphocytes from mock-infected animals. Quantitative evaluation indicates that 10–15% of cells from scrapie-infected animals show an altered capping behaviour. These phenomena are discussed with special reference to the role of the lymphoreticular system in early scrapie agent replication.
    Type of Medium: Electronic Resource
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