Binding energy of tea catechin/caffeine complexes in water evaluated by titration experiments with 1H-NMR

Evaluating the binding energy of a catechin/caffeine complex in water is important in order to elucidate the ability for molecular recognition of tea catechins. The results of this study revealed that the stoichiometric ratio of the complexation between tea chatechins (EGCg, ECg, EGC, and EC) and caffeine was 1:1 at least up to a concentration of 5.O mm. The free energy (-DeltaG) values for binding in water at 301K were evaluated to be 2.7, 2.6, 2.2, and 2.0 kcal/mol for EGCg, ECg, EGC, and EC, respectively, by the titration method with H-1-NMR. An investigation of the (HNMR)-H-1 chemical shift change and NOESY spectra in the catechin/caffeine solutions showed the participation of the A-rings of the catechins in complexation, as well as that of the galloyl groups or beta-rings.