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  • 1
  • 2
    Publikationsdatum: 1995-04-01
    Print ISSN: 0265-9247
    Digitale ISSN: 1521-1878
    Thema: Biologie , Medizin
    Publiziert von Wiley
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    ISSN: 0947-3440
    Schlagwort(e): Thermotropic and lyotropic phase behavior ; Amphotropes ; Surfactants ; Liquid crystals ; Chromophores ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: New ammonium amphiphiles having a N,N-dimethyl-N-hydroxyethylammonium headgroup and various azobenzene mesogenic units connected by a decyl or dodecyl spacer have been synthesized. The azobenzene unit is functionalized at the 4-position with a cyano, methoxy or fluoro substituent. For the cyano-substituted amphotropes and the fluoro compound with a dodecyl spacer a smectic phase is formed as was observed by differential scanning calorimetry and polarization microscopy. Complexation with sodium dodecyl sulfate, SDS, in a 1:1 molar ratio induces the formation of a smectic phase for the compounds with a decyl spacer. The compounds with a dodecyl spacer showed rather complex behavior attributed to different crystal morphologies. The ammonium amphotropes form aggregates in water when heated above their Krafft temperature. However, these aggregates are not stable and crystallize upon cooling. The ion pair amphiphiles with SDS as second component form vesicles in water as observed by optical and electron microscopy. The observed blue shift in the UV absorption maximum of the amphotropes upon addition of SDS indicates π-π stacking between mesogenic units resulting from aggregation.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    ISSN: 1434-193X
    Schlagwort(e): UV spectroscopy ; Poly(maleic acid-co-alkyl vinyl ether)s ; Azobenzene ; (Cyanobiphenylyl)oxy ; Cooperative binding ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -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.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    ISSN: 1434-193X
    Schlagwort(e): Surfactants ; H aggregates ; Ion pairs ; Copper(II) binding ; Copper ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -A novel, single-chained ammonium amphiphile that carries an o-hydroxyazobenzene unit at the terminus of its hydrophobic chain has been synthesized. This compound forms ordered thread-like aggregates upon dispersion in water. These aggregates exhibit a phase transition at 56 °C. The o-hydroxyazobenzene unit binds several transition-metal ions in a 2:1 stoichiometry. Binding of these metal ions results in a lowering of the critical aggregation concentration. From the changes in the UV absorption spectrum it is concluded that the Cu2+ complex forms more tightly packed aggregates in water than the Zn2+ and Ni2+ complexes.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    ISSN: 1022-1352
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A new series of rigid polymers was synthesized via radical copolymerization of N-phenylmaleimides, bearing pendant chromophores, with 4-vinylpyridine or styrene. Structural characterization was achieved by 1H NMR and 13C NMR spectroscopy, gel permeation chromatography (GPC), elemental analysis and differential scanning calorimetry (DSC). The thermal properties as well as the morphology of the investigated polymers at the air-water interface appear to be related to their rigidity. In spite of the presence of excellent mesogenic units, the polymers do not exhibit liquid crystalline behaviour. The 4-vinylpyridine copolymers form stable monolayers at the air-water interface. The attached chromophores electronically behave as monomers, as shown with in situ UVVIS absorption spectroscopy. Brewster angle microscopy shows a spontaneous aggregation of these polymers into domains on a neutral subphase, whereas on an acidic subphase a more homogeneous monolayer is formed. The monolayers give Z-type transfer onto hydrophilic quartz. However, the chromophores seem to be oriented randomly at the substrate surface. The styrene copolymers do not form stable monolayers as a result of crystallization at the air-water interface.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    ISSN: 0947-3440
    Schlagwort(e): Mesogenic unit ; Monomer exchange ; “Gel-to-liquid crystalline” phase transition ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Novel double-chained ammonium amphiphiles carrying one azobenzene moiety (I) have been synthesized. The bilayer-stabilizing effect of different azobenzenes (ABs) has been investigated by measuring the “gel-to-liquid crystalline” phase transition temperatures of the formed bilayers in water using differential scanning calorimetry. It is found that the stabilizing effect of the azobenzenes strongly depends on the substituents at the aromatic ring. The stabilizing effect increases in the sequence F 〈 H 〈 NO2 〈 CN 〈 OCH3 〈 N=N-Ph, which cannot be correlated with the electron-withdrawing or -donating properties of the substituents. It is concluded that dipole-dipole interactions between the ABs are of minor importance for the overall stabilization of the bilayer. Instead, other factors determine the strength of the van der Waals interactions between the ABs. In the bilayers the ABs form H-aggregates as is observed by the blue shift of the UV absorption maximum. This blue shift is not affected by the “gel-to-liquid crystalline” phase transition. Bilayers of I-N=N-Ph do not exchange monomers with vesicles of didodecyldimethylammonium bromide, whereas all other investigated bilayers do. Compound I-N=N-Ph forms monolayers at the water-air interface, which are much more stable than the monolayers of the other investigated compounds.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    BioEssays 17 (1995), S. 287-290 
    ISSN: 0265-9247
    Schlagwort(e): Life and Medical Sciences ; Cell & Developmental Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Medizin
    Notizen: 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.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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