Stereochemical structure and intermolecular interaction of complexes of (-)-Gallocatechin-3-O-gallate and caffeine.

A suspension containing an equimolecular amount of (-)-gallocatechin-3-O-gallate (GCg) and caffeine in water was heated at 90 °C for 30 min to give a 1 : 2 complex of GCg and caffeine. X-Ray crystallographic analysis of crystal of the 1 : 2 complex showed that π-π interactions formed between the A, B' rings of GCg and the two six-membered rings of caffeine. Whereas, the same suspension was heated at 90 °C for 30 s to give a sticky substance, which contained GCg, caffeine, and water at a molar ratio of 1 : 1 : 22 based on measurement of the integral volume of (1)H-NMR signals. The sticky substance crystallized slowly to give a 2 : 2 complex of GCg and caffeine. X-Ray crystallographic analysis of crystal of the 2 : 2 complex showed that the A and C rings of GCg moieties faced each other, and face-to-face π-π interactions formed between the B ring of GCg and caffeine, the B' ring of GCg and caffeine.