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  • Azobenzene  (1)
  • Life and Medical Sciences  (1)
  • 1995-1999  (2)
  • 1
    ISSN: 1434-193X
    Keywords: UV spectroscopy ; Poly(maleic acid-co-alkyl vinyl ether)s ; Azobenzene ; (Cyanobiphenylyl)oxy ; Cooperative binding ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The interaction of poly(maleic acid-co-alkyl vinyl ether)s and poly(sulfonylethyl maleic acid monoamide-co-alkyl vinyl ether)s with and without (cyanobiphenylyl)oxy chromophores with N-[ω-(substituted azobenzoxy)alkyl]-N,N-dimethyl-N-hydroxyethylammonium bromide surfactants has been studied by UV spectroscopy. The azobenzene unit is functionalized at the 4′-position with a cyano or fluoro substituent and is connected to the surfactant headgroup via a decyl or dodecyl spacer. Upon addition of surfactants to poly(maleic acid-co-butyl vinyl ether) the absorption maxima (λmax) of the azobenzene chromophores immediately show their maximum blue shift. This indicates cooperative binding of surfactant to this polymer, and the formation of micelle-like aggregates surrounded by polyelectrolyte is assumed. Upon addition of the surfactants to the other polyelectrolytes λmax values of the azobenzoxy chromophores gradually shift to lower values indicating a lower cooperativity of surfactant binding. This is attributed to the formation of microdomains by the polyelectrolytes themselves. For these systems the formation of mixed micelles is assumed. The compactness of the microdomains of the maleic acid copolymers is influenced by the pH and binding with surfactants is also influenced by pH. The sulfonylethyl maleic acid monoamide copolymers show no pH dependence in binding above neutral pH. For these polyelectrolytes the cooperativity also becomes less with a longer spacer between backbone and chromophore. Upon elongation of the surfactant spacer or changing the end group from a cyano to the more hydrophobic fluoro substituent a lower λmaxis observed for the chromophores upon initial binding to the polyelectrolytes indicating more cooperative binding. When surfactants and polyelectrolytes are both labelled with chromophores, binding proceeds noncooperatively and the formation of mixed micelles is assumed.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    BioEssays 17 (1995), S. 287-290 
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Ethylene (C2H4) is a gaseous plant hormone produced by higher and lower (green) plants and, when grown on appropriate substrates, also by fungi, yeasts and bacteria. Ethylene is involved in many developmental processes in plants and is biologically active in trace amounts (10 - 100 nl/I of air) that may be present in the outside air due to industrial air pollution(1). Fruit ripening and flower senescence especially, in a variety of commercially important crops, are dramatically stimulated by ethylene. Following characterization of the genes coding for the key enzymes in ethylene biosynthesis, i.e. ACC synthase and ACC oxidase, it has become clear that their expression is regulated in a complex manner involving developmental, hormonal and tissue-specific factors. This was recently very elegantly demonstrated for the expression of ACC oxidase genes in developing petunia flowers by Tang et al.(2). The spatial and temporal expression patterns, especially in the reproductive organs, suggest a hitherto unknown role for ethylene in reproductive processes such as the self-incompatible response and the secretion of cellular exudate by the stigma and nectary.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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