[Investigation of Mechanism of Creming-down Phenomenon and Development of High-order Functions Using Tea Catechins]

An aqueous solution of 2,3-cis gallate type catechin (-)-epigallocatechin-3-O-gallate (EGCg) and caffeine afforded a precipitate of Creaming-down Phenomenon, which crystallized slowly for about three months to give a colorless block crystal. By X-ray crystallographic analysis, the crystal was determined to be a 2 : 2 complex of EGCg and caffeine, in which caffeine molecules were captured in a hydrophobic space formed with three aromatic A, B, and B' rings of EGCg. It was considered that the solubility of the 2 : 2 complex in water rapidly decreased and the 2 : 2 complex precipitated from aqueous solution. The hydrophobic spaces of EGCg captured a variety of heterocyclic compounds, and the molecular capture abilities of heterocyclic compounds using EGCg from the aqueous solutions were evaluated. Since the C ring of EGCg has two chiral carbon atoms, C₂ and C₃, the hydrophobic space of EGCg was a chiral space. EGCg captured diketopiperazine cyclo(Pro-Xxx) (Xxx=Phe, Tyr) and pharmaceuticals with a xanthine skeleton, proxyphylline and diprophylline, in the hydrophobic space, and recognized their chirality.