Abstract
The demonstration of complex formation between riboflavin and caffeine by previous workers suggested that xanthines and related compounds might be suitable as solubilizing agents for the vitamin. Caffeine, theophylline, and dimethyluracil were investigated and were found to increase the apparent water solubility of riboflavin. The effect was presumably due to the formation of 1:1 complexes. Apparent dissociation constants were determined to be: caffeine, 34.5 × 10 −3 mole/L.; theophylline, 52.6 × 10 −3 mole/L.; dimethyluracil, 182 × 10 −3 mole/L. The marked difference in complexing tendencies between caffeine and dimethyluracil suggested that the imidazole ring of the xanthine nucleus was strongly involved in the interaction. Quenching of fluorescence experiments were also conducted for comparative purposes.
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