Properties of precipitate of creaming down by (-)-epigallocatechin-3-O-gallate and caffeine.

An aqueous solution of equimolecular amounts of gallated catechin (-)-epigallocatechin-3-O-gallate (EGCg) and caffeine afforded a crude precipitate by creaming, which crystallized slowly for about three months at 10°C to give a colorless block crystal. The crystal was determined to be a 2 : 2 complex of EGCg and caffeine by X-ray crystallographic analysis. The 2 : 2 complex was formed with the cooperative effect of three intermolecular interactions, π-π and CH-π interactions, and intermolecular hydrogen bonds. Upon formation of the 2 : 2 complex, a caffeine molecule was captured by a hydrophobic space formed by the aromatic rings A, B, and B' rings of two EGCg molecules. Judging from the entropy value, the shift value in the chemical shift of proton signals in (1)H-NMR spectra, the NT1 value, and nuclear Overhauser effects (NOEs), it was thought that the structure of complexes of EGCg and caffeine in aqueous solution were the same as their crystal structure.