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  • Articles  (1,101)
  • Chemistry  (1,037)
  • Condensed Matter: Electronic Properties, etc.  (64)
  • 2015-2019  (69)
  • 1995-1999  (626)
  • 1980-1984  (320)
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  • Articles  (1,101)
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  • 1
    Electronic Resource
    Electronic Resource
    A CP-MAS NMR study of some deactivation methods in capillary gas chromatography (1984)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 7 (1984), S. 607-614 
    Details
    ISSN: 0935-6304
    Keywords: Gas chromatography, GC ; Fused silica capillary columns ; CP-MAS NMR ; Silylation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of temperature, water content, and the type of reagent on the silylation of fused silica capillaries was studied by 29Si and 13C CP-MAS NMR. Fumed silica (Cab-O-Sil M5), which is essentially a highly dispersed vitreous quartz with a surface comparable to that of fused silica capillary columns, was selected as a model material.Hexamethyldisilazane (HMDS) and 1,2-diphenyl-1,1,3,3-tetraphenyldisilazane (DPTMDS), which were used as silylation reagents, yielded trimethyl- and dimethylphenylsilyl surface groups respectively at lower temperatures (〈 350°C and 〈250°C respectively). At higher temperatures, increasingly more dimethylsilyl groups are formed, with the silicon bound to two oxygen atoms. This process occurs for DPTMDS at a considerably lower temperature than for HMDS. The formation of silyl groups on the surface and the disappearance of hydroxyl groups are followed independently. The 13C NMR and GC-MS of the reaction products showed that with DPTMDS, the formation of two Si-O-Si links is accompanied by a loss of phenyl groups rather than of methyl groups.After the Cab-O-Sil had been dried over P2O5, the formation of these double links occurred for HMDS only at temperatures above 460°C and for DPTMDS at 400°C. Thus we concluded that water supplies oxygen atoms for double Si-O-Si links (possibly crosslinks) necessary for efficient deactivation. This may explain the less successful silanization of fused silica capillaries because their water content is lower than that of glass capillaries.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240071102
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  • 2
    Electronic Resource
    Electronic Resource
    Untersuchung von Elektronentransferprozessen mit neuartigen, spaltenbildenden PorphyrinenWir danken Prof. J.-P. Sauvage und Prof. A. Harriman für wertvolle Diskussionen. (1997)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 109 (1997), S. 396-399 
    Details
    ISSN: 0044-8249
    Keywords: Elektronentransfer ; Porphyrinoide ; Supramolekulare Chemie ; Wirt-Gast-Chemie ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19971090422
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  • 3
    Electronic Resource
    Electronic Resource
    Novel Cleft-Containing Porphyrins as Models for Studying Electron Transfer ProcessesWe would like to thank Prof. J.P. Sauvage and Prof. A. Harriman for fruitful discussions. (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 36 (1997), S. 361-363 
    Details
    ISSN: 0570-0833
    Keywords: electron transfer ; host-guest chemistry ; porphyrinoids ; supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199703611
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  • 4
    Electronic Resource
    Electronic Resource
    Small effect on the rate of complexation of some dialkyl-2,2′-bipyridyl-5,5′-dicarboxylates with the ion of Ni(II) in methanol (1982)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 14 (1982), S. 599-603 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of formation of the 1:1 complexes of some dialkyl-2,2′-bipyridyl-5,5′-dicarboxylates with the ion of Ni(II) have been determined by the stopped-flow spectrophotometric method. Second-order formation rate constants have been correlated with the Taft modification of the Hammett equation. A linear regression has been found (P = 0.95 confidence) with the following characteristics: slope = -0.6 ± 0.1; intercept = 1.32 ± 0.02 (log k0). An inductive effect of the alkyl groups upon the reaction of the complexation is proposed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550140515
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  • 5
    Electronic Resource
    Electronic Resource
    Stereoselective polymerization of butadiene by a new dicationic nickel complex (1996)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 239 (1996), S. 33-41 
    Details
    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: Der neuartige dikationische Komplex [dppfNi(MeCN)4][BF4]2 (dppf = 1,1′-Bis(diphenylphosphin)ferrocen) zeigte in Anwesenheit von Diethylaluminiumchlorid (AIEt2CI) hohe Aktivität für die Polymerisation von 1,3-Butadien. Reaktionsdauer, Temperatur und das Aluminium/Nickel-Verhältnis wurden auf maximale Aktivität und Selektivität optimiert. Umsätze über 90% konnten erreicht werden. Im Vergleich zu Polybutadienen, die mit anderen Nickel-Phosphin-Systemen hergestellt wurden, zeigten die synthetisierten Polybutadiene höhere cis-1,4-Anteile (〈80%) und eine geringe Bildung von 1,2-Einheiten (2%). Alle Polymeren hatten niedrige mittlere Molekulargewichte (Mw 〉 11 800).
    Notes: The new dicationic nickel complex [dppfNi(MeCN)4][BF4]2 (dppf = 1,1′-bis(diphenylphosphino)ferrocene) in the presence of diethylaluminium chloride (AIEt2CI) exhibited high activity on the 1,3-butadiene polymerization. Reaction time, temperature and aluminium/nickel molar ratio were optimized in order to achieve maximum activity and selectivity. Conversions higher than 90% were obtained in contrast to other nickel-based systems using phosphine ligands, the resulting polybutadiene showed high cis-1,4 (〈80%) content and only small amount of 1,2-units (2%). All polymers presented low molecular weights (Mw 〉 11 800).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1996.052390104
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  • 6
    Electronic Resource
    Electronic Resource
    Relationship between proton-proton nmr coupling constants and substituent electronegativities. III. Conformational analysis of proline rings in solution using a generalized Karplus equation (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1211-1245 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The relationship between published vicinal proton-proton coupling constants and the pseudorotation properties of the pyrrolidine ring in L-proline, 4-hydroxy-L-proline, 4-fluoro-L-proline, and several linear and cyclic model proline peptides is investigated. Compared to earlier studies, several important improvements are incorporated: (1) a new empirical generalization of the classical Karplus equation is utilized, which allows a valid correction for the effects of electronegativity and orientation of substitutents on 3JHH; (2) an empirical correlation between proton-proton torsion angles and the pseudorotational parameters P and τm is derived; and (3) the best fit of the conformational parameters to the experimental coupling constants is obtained by means of a computerized iterative least-squares procedure. Two pseudorotation ranges were considered, classified as type N (χ2 positive sign) and type S (χ2 negative sign). The conformational equilibrium is fully described in terms of four geometrical parameters (PN, τN, PS, τS) and the equilibrium constant K. The present results indicate that, in general, the geometrical properties found in x-ray studies of proline and hydroxyproline residues are well preserved in solution. Several novel features are encountered, however. It is demonstrated that the proline ring occurs in a practically 1:1 conformational equilibrium between well-defined N- and S-type forms. Introduction of an amide group at the C-terminal end has no observable effect on this equilibrium, but the formation of a peptide bond at the imino nitrogen site results in a pronounced, but not exclusive, preference for an S-type form which is roughly 1.1 kcal/mol more stable than its N-type counterpart. The hydroxyproline ring system in neutral or acidic medium displays a pure N-type state, but N-acetylation results in the appearance of a minor (S-type) conformation. Cyclic proline dipeptides similarly exist in a biased conformational equilibrium. The major form (77-88%) corresponds to the N-type conformer observed in the solid state; the minor S-form has not been observed before. In contrast, cyclic hydroxyproline dipeptides display complete conformational purity. Ranges of endocyclic torsion angles deduced for the various classes of pyrrolidine derivatives in solution are presented. Each torsion appears confined to a surprisingly narrow range, comprising about 4°-8° in most cases. In all, the proline ring is far less “floppy” than hitherto assumed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1981.360200610
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  • 7
    Electronic Resource
    Electronic Resource
    Synthesis of α-Cyanoenamines by Cyanation of α-Bromoimmonium Bromides and Dehydrobromination of β-bromo-α-(dialkylamino)nitriles (1983)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 116 (1983), S. 3846-3857 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthese von α-Cyanenaminen durch Cyanierung von α-Bromimmonium-bromiden und Dehydrobromierung von β-Brom-α-(dialkylamino)nitrilenDie Reaktion der α-Bromimmonium-bromide 4 mit Kaliumcyanid in Dimethylformamid gibt β-Brom-α-(dialkylamino)nitrile 5, die in verschiedenen Base-Lösungsmittel-Systemen zu (E)- und (Z)-α-Cyanenaminen 2 dehydrobromiert werden. Eine Modifizierung einer kürzlich veröffentlichten Synthese von α-Cyanenaminen 2 aus Aldehyden über Enamine führte zu einer verbesserten und schnellen Methode für die Darstellung der Titelverbindungen.
    Notes: The reaction of α-bromoimmonium bromides 4 with potassium cyanide in dimethylformamide gave rise to β-bromo-α-(dialkylamino)nitriles 5, which were dehydrobrominated in various basesolvent systems to afford (E)- and (Z)-α-cyanoenamines 2. An adaption of a previously published preparation of α-cyanoenamines starting from aldehydes via enamines led to an improved, efficient and fast synthesis of the title compounds.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19831161208
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  • 8
    Electronic Resource
    Electronic Resource
    Synthesis of 2′-Deoxy-5-(isothiazol-5-yl)uridine and Its Interaction with the HSV-1 Thymidine Kinase (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1462-1474 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2′-Deoxy-5-(isothiazol-5-yl)uridine (12) was synthesized starting from 2′-deoxy-5-iodouridine using a Pd-catalysed cross-coupling reaction with propiolaldehyde diethyl acetal followed by deprotection and ring closure using thiosulfate. 2′-Deoxyuridine 12 has a particular place among the 5-heteroaryl-substituted 2′-deoxyuridines in that it has a high affinity for herpes simplex virus type 1 (HSV-1)-encoded thymidine kinase (TK) without antiviral activity. Biochemical studies revealed that 12 is a substrate for viral TK. We further investigated the interaction of 12 with the HSV-1 thymidine kinase. The conformation of 12 in solution was established by NMR spectroscopy. The most stable conformer 12A has the S-atom of the isothiazole ring placed in the neighbourhood of the C(4)=O group of the pyrimidine moiety. The compound was docked in its most stable conformation in the active site of HSV-1 TK and subjected to energy minimization. This demonstrated that the isothiazole moiety binds in a cavity lined by the side chains of Tyr-132, Arg-163, Ala-167, and Ala-168 and that the C(3) atom of the isothiazole moiety is located in close proximity of the phenolic O-atom of Tyr-132 and the aliphatic part of the Arg-163 side chain.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790519
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  • 9
    Electronic Resource
    Electronic Resource
    Facile Synthesis of 2-Alkoxy-2-aryloxiranes (1983)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 116 (1983), S. 3631-3636 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Eine einfache Darstellung von 2-Alkoxy-2-aryloxiranenTertiäre (α-Bromalkyl)arylketone 1 reagierten mit überschüssigem Kaliumcarbonat in trockenem Alkohol ausschließlich zu den entsprechenden 2-Alkoxy-2-aryloxiranen 4. Silbercarbonat in trockenem Alkohol führte in einer Konkurrenzreaktion zur Bildung von 4 und zu einer semibenzilischen Favorskii-Umlagerung (→5). Dagegen trat mit Silber-hexafluoroantimonat ausschließlich die letztere Umlagerungsreaktion ein.
    Notes: Tertiary α-bromoalkyl aryl ketones 1 were converted into 2-alkoxy-2-aryloxiranes 4 exclusively by reaction with excess potassium carbonate in the corresponding dry alcohol. Silver carbonate in a dry alcohol with these α-bromo ketones yielded competitively formation of 2-alkoxyoxiranes and semi-benzilic Favorskii rearrangement (→5), while silver hexafluoroantimonate in the same medium afforded the latter rearrangement reaction exclusively.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19831161112
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  • 10
    Electronic Resource
    Electronic Resource
    Synthesis, Characterization and Dynamic Behavior of (π-Allyl)palladium Complexes with Polydentate Nitrogen Ligands, Evidence of a Dissociative Mechanism (1996)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 129 (1996), S. 589-594 
    Details
    ISSN: 0009-2940
    Keywords: Fluxionality ; Heterocyclic ligands ; Palladium complexes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New examples of the fluxional behavior of (η3-allyl)palla-dium complexes are described. Variable-temperature experiments and line-shape analysis of two (η3-allyl)palladium complexes containing 2-(1H-pyrazol-1-yl)azine ligands were performed in order to determine the activation free energies, enthalpies and entropies of the process. A dissociative mechanism pointing to a selective Pd-N cleavage is proposed on the basis of these results and NOE experiments above and below the coalescence temperature.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19961290519
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