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Hetero‐association of caffeine and theophylline with purine and pyrimidine in aqueous solutions studied by 1 H NMR chemical shift measurements
Author(s) -
Aradi Ferenc,
Földesi András
Publication year - 1989
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260270311
Subject(s) - theophylline , chemistry , pyrimidine , purine , caffeine , xanthine , dimer , chemical shift , stereochemistry , aqueous solution , medicinal chemistry , organic chemistry , medicine , enzyme , endocrinology
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.