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  • 1990-1994  (6)
  • 1990  (6)
Material
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  • 1990-1994  (6)
Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Mineralium deposita 25 (1990), S. 271-271 
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 332 (1990), S. 367-374 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Investigations on Regioselectivity of Wittig-Horner and Reformatsky-Reactions on Selected 3,17-Dioxo SteroidsThe Reformatsky synthesis and the Wittig-Horner olefination of 3,17-dioxo steroids like androsta-1,4-diene-3,17-dione (ADD) 1 and androst-4-ene-3,17-dione (AD) 2 is described. There are differences in the regioselective introduction of identical substructures with these two methods resulting from different nucleophilicity and stereoelectronical relations of these two reagents. In Reformatsky synthesis the oxo group in 3-position predominantly reacts, whereas in the Wittig-Horner olefination (in the case of 1) the reaction occurs mainly in the 17-position.The structures of all new compounds has been confirmed by spectroscopical data.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Beads of aluminium carboxymethyl cellulose gel are prepared by dropping aqueous solution of 2 to 15% sodium carboxymethyl cellulose with a degree of polymerization ranging from 140 to 950 into a solution of Al2(SO4)3. Spherical carriers can be obtained by partial drying of the gels. The swelling of the xerogel particles in water depends on the type of initial polymer and on washing processes. The particles show a regular distribution of Al3+ ions. On the other hand porous and reactive polymer beads with a relatively smooth surface characterized by SEM are prepared if the water in the gels is stepwisely exchanged by organic solvents.
    Notes: Durch Elintropfen von 2- bis 15%iger wäßriger Natriumcarboxymethylcellulose mit Polymerisationsgraden im Bereich von 140 bis 950 in eine Al2(SO4)3-Lösung lassen sich sphärische Aluminiumcarboxymethylcellulose-Gele herstellen. Die partielle Trocknung dieser Gele führt zu sphärishchen Trägermaterialien, die in Abhängigkeit vom Ausgangspolymertyp und von Waschprozessen unterschiedlich stark in Wasser quellen und eine gleichmäßige Al3+-Verteilung aufweisen. Erfolgt die Entwässerung durch schrittweisen Lösungsmittelaustausch, erhält man poröse und reaktive Polymerkugeln, die in REM eine relativ obene Oberfläche zeigen.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Investigations on the introduction of reactive functional groups into cellulose at heterogeneous conditions of reaction are reviewed. From the organic chemist's point of view the survey considers reactions characterized by yielding a high degree of substitution, a selective course of functionalisation, or the use of modern preparation techniques and new reagents.
    Notes: Die vorliegende Übersicht enthält eine zusammenfassende Darstellung von Untersuchungen zur Einführung reaktiver funktioneller Gruppen in die Cellulose. Unter synthesechemischen Gesichtspunkten werden heterogen verlaufende Reaktionen betrachtet, die sich vor allem durch die Erzielung eines möglichst hohen durchschnittlichen Substitutionsgrades, einen weitgehend selektiven Verlauf oder die Anwendung neuer präparativer Techniken und Reagenzien auszeichnen.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 41 (1990), S. 259-269 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: This review covers the formation, the structure and some areas of application of ionotropic gels obtained from natural, biotechnologically produced and chemically modified polysaccharides containing carboxy functions as anionic groups. Special points of interest are the interaction between the carboxylic groups and polyvalent metal cations and the selectivity of this interaction, the morphology of ionotropic capillary gels inclusive of model considerations on structure formation, and the application of these gels for cell immobilization and for the controlled release of bioactive compounds.
    Notes: Die vorliegende Übersichtsarbeit behandelt die Bildungsweise, die chemische und morphologische Struktur und die wesentlichen Anwendungsmöglichkeiten von ionotropen Gelen auf Basis natürlicher, biotechnologisch gewonnener und chemisch modifizierter Polysaccharide mit Carboxyfunktionen als anionischen Gruppen. Schwerpunkte sind dabei die Wechselwirkung zwischen den Carboxygruppen und den mehrwertigen Metallkationen und die Selektivität dieser Wechselwirkung, die Morphologie ionotroper Kapillargele einschließlich der Modellvorstellungen zu ihrer Bildung sowie die Anwendung solcher Gele zur Zell-Immobilisierung und kontrollierten Wirkstoff-Freisetzung.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 41 (1990), S. 333-338 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Comparing a C-6-substituted carboxy cellulose and carboxy methyl cellulose samples differing in substituent distribution, the acidity of the COOH-group and the symplex formation of these polymers are investigated. The acidity of the COOH-group is inversely correlated to the average distance between the anionic charge centre and the anhydroglucose ring. Obviously, no significant effect of the regioselectivity of substitution on symplex formation exists.
    Notes: Es wird über vergleichende Untersuchungen zur Acidität der Carboxygruppe und zur Symplexbildung bei einer C-6-substituierten Carboxycellulose einerseits, Carboxymethylcellulosen mit unterschiedlicher Substituentenverteilung andererseits berichtet. Die Acidität der Carboxygruppe korreliert invers zum mittleren Abstand zwischen anionischem Ladungszentrum und Anhydroglucosering. Ein signifikanter Einfluß der Regioselektivität der Substitution auf die Symplexbildung besteht offensichtlich nicht.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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