STACKING INTERACTIONS BETWEEN CAFFEINE AND METHYL GALLATE

The self-association of caffeine and methyl gallate (a simple polyphen ol) has been studied by NMR in the solvent mixture H2O-[H-2(6)]-dimeth ylsulfoxide (9:1, by volume) at 288 K, using the isodesmic model (also known as the indefinite noncooperative model). The chemical shift cha nges observed suggest that caffeine molecules in a stack are associate d in a head-to-tail (antiparallel) manner. The interaction between mon omeric caffeine and methyl gallate stacks has also been investigated a nd the results indicate that caffeine prefers to bind at the ends of m ethyl gallate stacks rather than intercalating into the stacks. Compar ison of the association constants suggests that in a mixture df methyl gallate and caffeine, heterostacks are formed in preference to self-a ssociated solutes, which has an obvious bearing on the bioavailability of aromatic and phenolic species.