2013
Volume 13, Number 1, pp. 30–35
The hetero-association of caffeine with 5-caffeoylquinic acid and ethidium bromide
Abebe Belay
Department of Physics, School of Natural Sciences, Adama Science and Technology University, P.O. Box 1888, Adama, Ethiopia
The hetero-association of caffeine with 5-caffeoyl quinic acid (5-CQA) and ethidium bromide (EB) in aqueous solution was investigated. The association was analysed by the modified Benesi–Hildebrand model. Nonlinear numerical curve-fitting of the model to the experimental data was based on the Levenberg–Marquardt algorithm. From the analysis of the dynamical equilibrium of the interacting molecules, the hetero-association of caffeine with 5-CQA and EB reduces the monomer concentration of the compounds in the solution. The calculated hetero-association constants of 5-CQA–CA and EB–CA were K = 30 ± 17 M–1 and K = 41 ± 2 M–1, respectively. The heterocomplexation is presumably stabilized by the interactions of the cyclic chromophores of these molecules. In view of the extensive worldwide consumption of coffee and caffeinated beverages and the consequent possible physiological effects, as well as a direct interaction with aromatic drugs, investigations of the association constants of 5-CQA–CA, EB–CA and structural features of the complex are necessary and timely.
Keywords: Benesi–Hildebrand model, caffeine, 5-caffeoylquinic acid, ethidium bromide, hetero-association