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  • 1
    ISSN: 0935-9648
    Keywords: Sensors ; ISFETs and CHEMFETs ; Polysiloxanes ; Reference FETs ; Polymer Membranes ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Synthetic receptor molecules that selectively bind charged guests can store chemical information. The transduction of this information into electronic signals connects the chemical and electronic domains. Field effect transistors (FETs) are attractive transducing elements because these microdevices are able to register and amplify chemical changes at the gate oxide surface of the semiconductor chip.Integration of molecular receptors and field effect transistors into one chemical system gives a device that can communicate-changes of substrate activities in aqueous solution. Simulations of a system in which the receptor molecules are directly attached to the FET gate oxide indicate serious limitations with respect to sensitivity, dynamic range and extreme requirements for complex stability. Therefore we have concentrated on the integration of covalently attached thin membranes.The problem of the thermodynamically ill-defined oxidemembrane ipterface has been solved by applying a covalently linked hydrophilic polyhydroxyethylmethacrylate (polyHEMA) gel between the sensing membrane and the silylated gate oxide. A buffered aqueous electrolyte solution in the hydrogel renders the surface potential at the gate oxide constant via the dissociation equilibrium of the residual silanol groups. The subsequent attachment of a polysiloxane membrane that has the required dielectric constant, glass transition temperature Tg, and receptor molecule, provides a stable chemical system that transduces the complexation of cationic species into electronic signals (CHEMFET).The response to changing K⊕ concentrations in a solution of 0.1 M NaCl is fast (〈1 sec) and linear in the concentration range of 10-5-1.0 M (55-58 mV /decade). A reference FET (REFET) based on the same technology is obtained when the intrinsic sensitivity to changes in ion concentration is eliminated by the addition of 2.10-5 mol g-1 of didodecyldimethyl ammonium bromide to the ACE membrane. Differential measurements with a REFET/CHEMFET combination showed excellent linear K⊕ response over long periods of time.All chemical reactions used are compatible with planar IC technology and allow fabrication on wafer scale.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0947-3440
    Keywords: Thermotropic and lyotropic phase behavior ; Amphotropes ; Surfactants ; Liquid crystals ; Chromophores ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-193X
    Keywords: Surfactants ; H aggregates ; Ion pairs ; Copper(II) binding ; Copper ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -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.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 5
    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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  • 6
    ISSN: 0947-3440
    Keywords: Mesogenic unit ; Monomer exchange ; “Gel-to-liquid crystalline” phase transition ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 17 (1973), S. 1449-1454 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A computer program has been devised for routine use which processes raw data such as polymer sample weight, moisture content, solution volume, and viscometer flow times to calculate a least-squares-derived intrinsic viscosity. In addition to eliminating errors inherent in graphic solutions and freeing technicians from tedious calculation, the computer output provides the 95% confidence interval of the intrinsic viscosity.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 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.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 92 (1980), S. 429-444 
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Glykogen-Phosphorylasen katalysieren den Abbau von Glykogen durch Phosphat (oder Arsenat) zu Glucose-1-phosphat (bzw. Glucose + Arsenat). Alle Glykogen-Phosphorylasen enthalten Pyridoxal-5′-phosphat, ein Vitamin-B6-Derivat, als Cofaktor. Es ist im Enzym durch eine Doppelbindung mit der ∊-Aminogruppe eines Lysinrestes verbunden. Wird der Cofaktor vom Enzymprotein abgetrennt, erhält man inaktives Apoenzym. Das Enzym bleibt jedoch aktiv, wenn man die Doppelbindung mit NaBH4 reduziert. Sollte daher Pyridoxalphosphat an der Katalyse der Glykogen-Phosphorylasen beteiligt sein, so müßte es eine andere Funktion als in allen anderen „klassischen“ Pyridoxalphosphat-abhängigen Enzymen haben, denn diese werden durch Reduktion inaktiviert. Die 31P-NMR-Spektroskopie hat gezeigt, daß die Phosphatgruppe von Pyridoxalphosphat in den katalytisch aktiven Formen der Glykogen-Phosphorylasen als Dianion in einer hydrophoben Umgebung vorliegt. Die kovalente und allosterische Aktivierung der Muskel-Glykogen-Phosphorylasen wird von der Umwandlung der monoprotonierten Form der Phosphatgruppe des Cofaktors in die dianionische Form begleitet. Wir fanden nun derartige Ionisierungsänderungen auch bei den nichtregulierten aktiven Kartoffel- und E. -coli-Maltodextrin-Phosphorylasen, und zwar bei der Bindung von Glucose und Oligosacchariden sowie bei katalytischem Umsatz, d. h. Arsenolyse der α-1,4-glykosidischen Bindungen. (Maltodextrin-Phosphorylasen gehören wie Glykogen-Phosphorylasen zur Klasse der α-Glucan-Phosphorylasen.) Versuche unserer Gruppe sowie neuere Befunde über die Raumstruktur der kristallinen Muskel-Glykogen-Phosphorylase legen es nahe, die dianionische Phosphatgruppe als Protonenacceptor beim Glucosyltransfer vom und zum Glucosylacceptor anzusehen. Wenn dies auch nicht die einzige Erklärung der Befunde sein mag, so kann doch nicht mehr daran gezweifelt werden, daß die dianionische Phosphatgruppe des Cofaktors der Glykogen-Phosphorylasen eine katalytische Funktion ausübt.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 95 (1983), S. 336-337 
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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