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  • Chemistry  (25)
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  • 1
    ISSN: 0009-2940
    Keywords: Bis(iminophosphoranes) ; Guanidines, bicyclic ; Aza Wittig reaction ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A one-pot synthesis of [5 + 6]-, [6 + 6]-, and [6 + 7]-rigid bicyclic guanidines (6, 8, 19, 21, 23) based on a bis(iminophosphorane)-mediated annulation strategy is reported. The crystal and molecular structure of the parent [5 + 6]-bicyclic guanidine 8 has been established by X-ray diffraction. The crystallographically independent molecule forms dimers through a centre of symmetry by N-H-N hydrogen bonds. The molecule, and therefore the dimer, is statistically disordered in a 65/35 ratio. A statistical study of N-H-N hydrogen bonds of this kind of dimers has been carried out by using the Cambridge Structural Database.
    Additional Material: 3 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 1219-1227 
    ISSN: 0887-624X
    Keywords: 1,2,4-benzenetricarboxylic acid monoesters ; poly(amide-imide) structural regularity ; poly(amide-imide) “one-pot” synthesis ; 13C-NMR spectra of poly(amide-imide) ; phosphorylation reaction ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aromatic processable poly(amide-imide)s have been prepared according to the Yamazaki and Higashi phosphorylation reaction from flexible aromatic diamines and a mixture of isomeric 1,2,4-benzenetricarboxylic acid monoethylesters following a novel “one-pot” procedure. The polymerization was performed in 1-methyl-2-pyrrolidone/LiCl solutions using triphenylphosphite and pyridine as condensing agents to form amide bonds. Cyclization of the intermediate poly(amide-amic ethylester) occurred by eliminating ethanol under the polymerization conditions used, thus leading to the formation of imide rings. The influence of several parameters which regulate the degree of polymerization and the formation of the imide rings, such as reaction temperature, triphenylphosphite/monomers molar ratio, and pyridine concentration was carefully investigated. In particular, the catalytic activity of pyridine in the imidization reaction has been demonstrated. 13C-NMR spectroscopy has been used to show the absence of constitutional regularity in the prepared PAIs thus indicating equal reactivity toward polycondensation of the two different carboxyl groups of the 1,2,4-benzenetricarboxylic acid monoethylesters. © 1996 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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  • 3
    ISSN: 0935-9648
    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
    Additional Material: 4 Ill.
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  • 4
    ISSN: 0935-9648
    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
    Additional Material: 5 Ill.
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  • 5
    ISSN: 0935-9648
    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
    Additional Material: 4 Ill.
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  • 6
    ISSN: 0899-0042
    Keywords: Circular dichroism ; helicity rule ; X-ray structure determination ; ultraviolet spectra ; n - π* and π - π* bands ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiroptical properties of a series of 3 and/or 4-heterosubstituted 2(5H)-furanones were investigated with respect to correlation with absolute configuration. The n - π* and π - π* Cotton effects have been assigned on the basis of comparison with the UV spectra in solvents of varying polarity. It is demonstrated that the n - π* transition in 4-amino substituted 2(5H)-furanones appears at shorter wavelength with respect to the π - π* transition. With the exception of 4-pyrrolidino and 4-benzylamino substituted 2(5H)-furanones, other heterosubstituted 2(5H)-furanones follow the butenolide configurational rule (Gawronski et al. J. Org. Chem. 61:1513-1515, 1996). Absolute configuration of 2(5H)-furanone derivatives can also be assigned according to the sign of the Cotton effect (of unknown origin) at 200-230 nm. The structure of four representative sulfur and nitrogen substituted 2(5H)-furanones has been analyzed by X-ray diffraction. The results indicate planarity of the furanone ring and extended conjugation in 4-amino substituted 2(5H)-furanones. Chirality 9:537-544, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 217 (1994), S. 107-117 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Das Verhalten von mit primären Boramingruppen modifizierten Silikat-Füllstoffen wurde unter verschiedenen Reaktionsbedingungen untersucht. Der Füllstoff mit den besten Verstärkungseigenschaften wurde eingesetzt, um zwei unterschiedliche Vulkanisationssysteme zu vergleichen: ein wirksames Vulkanisationsverfahren (EV), das nach ISO als Methode zur Untersuchung des Verstärkungsverhaltens neuer Silikate empfohlen wird, sowie ein konventionelles Verfahren. Die besten Ergebnisse werden mit Silikat erhalten, welches 3 h bei 500°C behandelt wurde; unter diesen Bedingungen werden die meisten der primären Boramingruppen fixiert. Die Eigenschaften des nach dem EV-Verfahren modifizierten Silikats ähneln denen von mit Silan modifizierten Silikaten und sind in einigen Fallen besser als jene, welche nach dem konventionellen Verfahren erhalten werden. In allen Fallen wird die verstarkende Wirkung von gefällten Silikat-Füllstoffen durch die Boraminbehandlung verbessert.
    Notes: The behaviour of silica fillers modified with primary boron-amine groups has been studied under different reaction conditions. The filler with the best reinforcing properties was used to compare two different vulcanization systems: an efficient vulcanization system, EV, which is the recommended ISO Standards method to study the reinforcing behaviour of new silicas, and a conventional vulcanization system.The results indicate that the best properties are obtained with silica treated for 3 h at 500°C, reaction conditions which fix most of the primary boron-amine groups. Using the EV system, the properties of this modified silica are similar to those of silane-modified silica, and in some cases better than those obtained with a conventional vulcanization system. In all cases, the boron-amination treatment significantly improves the behaviour of precipitated silica as a reinforcing filler.
    Additional Material: 2 Ill.
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  • 8
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Kinetik der Vulkanisation sowie die Vernetzungsdichte von Styrol-Butadien-Kautschukmischungen wurden mit zwei Vulkanisationssystemen, einem wirksamen (EV) und einem konventionellen (CV), untersucht. Ein oberflächenmodifiziertes Silikat mit Boramingruppen (Si—O—B—(NH2)2) wurde als Füllstoff eingesetzt. Unbehandeltes und mit zwei Silanen (γ-Mercaptopropyl-trimethoxysilan und γ-Aminopropyl-triethoxysilan) modifiziertes Silikat wurden zum Vergleich eingesetzt. Die bestenkinetischen Parameter, wie die höchste Vulkanisierungsgeschwindigkeit, die längste Induktionszeit und die kleinste Aktivierungsenergie, wurden für die Mischung mit boraminiertem Silikat erhalten. Die Vernetzungsdichte, die mit dieser Mischung erreicht wurde, ist ähnlich der von mit Silan modifiziertem Silikat erzielten, da wahrscheinlich die Boramingruppen auf der Silikatoberfläche besser verteilt sind. Diese Fakten führen zu wichtigen technologischen Verbesserungen: größere Verarbeitungssicherheit, schnellere Vulkanisierungsgeschwindigkeit und verbesserte physikalische Eigenschaften.
    Notes: Vulcanization kinetics and crosslink density of styrene-butadiene rubber compounds have been studied with two vulcanization systems, an efficient (EV) and a conventional (CV) one. A surface-modified silica with boron-amine groups (Si—O—B—(NH2)2) was employed as filler. Untreated and modified silica with two silanes (γ-mercaptopropyl-trimethoxysilane and γ-aminopropyl-triethoxysilane) have been used as reference.The best kinetic parameters, such as highest vulcanization rate, longest induction time and lowest activation energy, were obtained for the compound with boronaminated silica. The crosslink density, achieved with this compound, is similar to that with silane-modified silica, probably because of the better surface distribution of boron-amine groups on the silica. These facts lead to important technological improvements: better processing safety, faster vulcanization rate and improved physical properties.
    Additional Material: 4 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Bioluminescence and Chemiluminescence 13 (1998), S. 371-378 
    ISSN: 0884-3996
    Keywords: bioluminescence ; luciferase ; ATP ; immobilization ; glass ; poly-L-lysine ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: The bioluminescent reaction catalysed by firefly luciferase has become widely established as an outstanding analytical system for assay of ATP. When used in solution, luciferase is unstable and cannot be re-used, a problem that can be partially circumvented by immobilizing the enzyme on solid substrates. Transparent glass is especially advantageous over alternative immobilizing matrices, since it allows most of the emitted photons to be detected. We report a new method for luciferase immobilization on glass which does not require prior silanization and glutaraldehyde activation, thus saving preparation time and minimizing enzyme inactivation. Our method is based on the co-immobilization by adsorption of luciferase (from a firefly lantern extract) and poly-L-lysine (PL) on non-porous glass strips. Luciferase immobilized in this way exhibits minimal variations in intersample activity, high sensitivity for ATP detection (linear luminescence responses down to 50 nmol/L) and good stability (full activity for at least 60 days when stored at -80°C). PL-mediated immobilization of luciferase on glass strips provides an attractive strategy for the design of specific ATP biosensors, with potential in industry, environmental screening, medicine and biological research. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
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  • 10
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The homopolymerization of styrene and its copolymerization with ethylene in the presence of a vanadium-based supported catalyst, {VCI3, 1 AICI3}, associated to triethylaluminium is examined. As indicated by means of 13C nuclear magnetic resoance and differential scanning calorimetry analysis, the homopolystyrenes obtained present a highly isotactic microstructure and are semicrystalline (melting temperature 220°C).In the case of styrene/ethylene random copolymerization, the formation of both, polyethylene blocks and isotactic polystyrene sequences was identified by analysis of the crude polymer. Solubility characteristics and structural characteristics from nuclear magnetic resonance spectra of these products support the formation of copolymers with ethylene and isotactic styrene blocks rather than that of two distinct homopolymers.
    Additional Material: 6 Ill.
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