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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