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  • 1
    Electronic Resource
    Electronic Resource
    On the tautomerism of 2,4-disubstituted 3,4,5,6-tetrahydrobenzo[h]quinazolines (1991)
    Springer
    Monatshefte für Chemie 122 (1991), S. 209-213 
    Details
    ISSN: 1434-4475
    Keywords: Benzo[h]quinazolines ; 13C-NMR spectroscopy ; Tautomerism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Tautomerie von 2,4-disubstituierten 3,4,5,6-Tetrahydrobenzo[h]chinazolinen wurde durch1H-,13C-NMR- und UV-Spektroskopie untersucht. Der Vergleich der Spektren von5 und der Modellverbindungen1,3,4 und6 legt nahe, daß für5 das Tautomere5A dominiert.
    Notes: Summary The tautomerism of the title compounds was investigated by1H-,13C-NMR and UV spectroscopy. Compound5 was compared with respect to its spectra with those of appropriate model compounds1,3,4, and6. This gave evidence that5 predominates in the tautomeric from5A.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00809366
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  • 2
    Electronic Resource
    Electronic Resource
    Investigation of association in purine - pyrimidine aqueous systems by 1H NMR chemical shift (1987)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 25 (1987), S. 892-896 
    Details
    ISSN: 0749-1581
    Keywords: 1H NMR chemical shifts ; Purine-pyrimidine aqueous systems ; Self-association ; Hetero-association ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The association behaviour of purine and pyrimidine has been studied in deuterium oxide at 35°C by measuring the concentration-dependent selective changes in the chemical shifts of the CH protons. A satisfactory interpretation of the cross-interaction, i.e. the mutually induced upfield shifts in mixed solution, required the extension of the 1:1 hetero-association model by taking into account the self-association of both compounds. The self-association and the hetero-association parameters have been determined on the basis of two-state and three-state models. The equilibrium constants give a decreasing tendency for association within the series purine-purine (0.82 ± 0.08 1 mol-1) 〉 purine-pyrimidine (0.54 ± 0.06 1 mol-1) 〉 pyrimidine-pyrimidine (0.050 ± 0.002 1 mol-1), and the values of the dimer upfield shifts suggest that the association processes are dominated by the interaction of the six-membered rings.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260251013
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  • 3
    Electronic Resource
    Electronic Resource
    Equilibrium constants for association of caffeine and theophylline with aromatic salts in aqueous solutions studied by 1H NMR chemical shift measurements (1985)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 23 (1985), S. 375-378 
    Details
    ISSN: 0749-1581
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction of caffeine and theophylline with sodium benzoate and sodium salicylate has been studied in deuterium oxide at 35 °C by measuring the aromatic salt-induced changes in the chemical shifts of the N-methyl protons. Taking into account the self-association of the N-methylxanthines, on the basis of a 1:1 complexation model the association constants for caffeine-sodium benzoate, theophylline-sodium benzoate, caffeine-sodium salicylate and theophylline-sodium salicylate were found to be 2.1 ± 0.1, 1.5 ± 0.2, 7.8 ± 0.2 and 5.0 ± 0.21 mol-1, respectively.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260230518
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of methylation on the association ability of purine and pyrimidine in aqueous solutions. A 1H NMR chemical shift study (1989)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 27 (1989), S. 592-598 
    Details
    ISSN: 0749-1581
    Keywords: 1H NMR chemical shift ; Association ; 6-methylpurine ; 4-methylpyrimidine ; Caffeine ; Theophylline ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The self-association of 6-methylpurine and 4-methylpyrimidine and their hetero-association with caffeine and theophylline in deuterium oxide at 35°C were studied by measuring the concentration-dependent changes in proton chemical shift. The association parameters were calculated using simple and competitive dimer models. The self-association constants for 6-methylpurine and 4-methylpyrimidine were found to be 2.24 ± 0.07 and 0.200 ± 0.007 1 mol-1, respectively, and the hetero-association constants could be ordered in the decreasing series caffeine-6-methylpurine (4.85 ± 0.12 1 mol-1) 〉 theophylline-6-methylpurine (4.11 ± 0.15 1 mol-1) 〉 caffeine-4-methylpyrimidine (1.45 ± 0.13 1 mol-1) 〉 theophylline-4-methylpyrimidine (0.98 ± 0.10 1 mol-1). The equilibrium constants imply that methylation enhances the association ability and the upfield dimer shifts can be interpreted in terms of a stacking-like interaction.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260270613
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  • 5
    Electronic Resource
    Electronic Resource
    Study of the self-association of methylated pyrimidines in aqueous solutions by 1H NMR chemical shifts (1990)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 28 (1990), S. 246-249 
    Details
    ISSN: 0749-1581
    Keywords: 1H NMR chemical shift ; Self-association ; Stacking ; Methylation ; Pyrimidine ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The self-association of pyrimidine and its methylated derivatives was studied by measuring the concentration-dependent changes in proton chemical shifts in deuterium oxide at 35°C. The data were analysed by a dimer model with two parameters. The equilibrium constants give an increasing tendency for self-association within the series pyrimidine (0.091 ° 0.006 l mol-1) 〈 5-methylpyrimidine (0.165 ° 0.006 l mol-1) ≈ 4-methylpyrimidine (0.183 ± 0.005 l mol-1) 〈 4,6-dimethylpyrimidine (0.410 ± 0.011 l mol-1), and the values of the dimer shifts suggest a stacking-like arrangement for the associated molecules.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260280310
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  • 6
    Electronic Resource
    Electronic Resource
    Hetero-association of caffeine and theophylline with purine and pyrimidine in aqueous solutions studied by 1H NMR chemical shift measurements (1989)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 27 (1989), S. 249-252 
    Details
    ISSN: 0749-1581
    Keywords: 1H NMR chemical shift ; Caffeine ; Theophylline ; Purine ; Pyrimidine ; Hetero-association ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction of caffeine and theophylline with purine and pyrimidine was studied in deuterium oxide at 35°C by measuring the concentration-dependent selective changes in the chemical shifts of the N-methyl protons of the xanthine derivatives. Using a competitive dimer model, the equilibrium constants give a decreasing tendency for hetero-association within the series caffeine-purine (2.97 ± 0.15 1 mol-1) 〉 theophylline-purine (2.44 ± 0.10 1 mol-1) 〉 caffeine-pyrimidine (1.18 ± 0.20 1 mol-1) 〉 theophylline-pyrimidine (0.70 ± 0.08 1 mol-1), and the upfield dimer shifts suggest a plane-to-plane arrangement.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260270311
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  • 7
    Electronic Resource
    Electronic Resource
    1H NMR chemical shift study on the stacking interaction between purine and 6-methylpurine (1990)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 28 (1990), S. 1040-1044 
    Details
    ISSN: 0749-1581
    Keywords: 1H NMR chemical shift ; Stacking interaction ; Association ; Purine ; 6-Methylpurine ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mutually induced proton chemical shift changes were measured for purine-6-methylpurine solutions in deuterium oxide at 35° C. The chemical shift vs. concentration profiles were analysed using a three-state decomposition model based on simultaneous, competitive dimer equilibria. The association parameters for purine-6-methylpurine hetero-association provide some additional information about the effect of methylation on the stacking interaction between nucleic acid bases. The equilibrium constant (2.54 ± 0.17 and 2.57 ± 0.29 I mol-1, calculated from the experimental data on purine and 6-methylpurine, respectively) suggests the dominant role of the methylated counterpart in the association. The upfield dimer shifts indicate that the methyl group perturbs the plane-to-plane or stacking-like arrangement in the associated state.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260281209
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  • 8
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    Correlations between Cytotoxicity and Topography of Some 2-Arylidenebenzocycloalkanones Determined by X-ray Crystallography (2002)
    American Chemical Society
    Details
    Publication Date: 2002-06-04
    Print ISSN: 0022-2623
    Electronic ISSN: 1520-4804
    Topics: Chemistry and Pharmacology , Medicine
    Published by American Chemical Society
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