Configurational studies of complexes of various tea catechins and caffeine in crystal state.

Crystals of the complexes of (+)-catechin (CA) of non-galloylated catechin and (-)-catechin-3-O-gallate (Cg) of galloylated catechin with caffeine were prepared, and their stereochemical structures and intermolecular interactions were determined by X-ray crystallographic analysis. CA formed a 1 : 1 complex with caffeine by intermolecular hydrogen bonds, whereas Cg formed a 1 : 2 complex with caffeine, which was formed by face-to-face and offset π-π interactions and intermolecular hydrogen bonds. A solution of two kinds of non-galloylated catechin, CA and (-)-epicatechin (EC), and caffeine (molar ratio 1 : 1 : 2) in water afforded a 1 : 1 : 2 complex, the crystal structure of which had two layers, one layer in which CA and caffeine formed alternate lines and an other layer in which EC and caffeine formed alternate lines. The 1 : 1 : 2 complex was formed by offset π-π and CH-π interactions and intermolecular hydrogen bonds.