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  • 1
    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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  • 2
    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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