P-24 1:2及び2:2 (-)-ガロカテキンガレート・カフェイン錯体の結晶構造及び相互作用の解明(ポスター発表の部)

抄録

Catechins included in the certain species of plants such as tea (Camellia sinensis, Camelliaceae) show various physiologically modulating effects such as anti-oxidative, anti-carcinogenic and anti-hypercholesterolemic. Interstingly, it is known that catechins form complexes with caffeine, especially in black tea and coffee. Such complexation is not only and interesting chemical phenomenon, but also may show intersting unique biological activities. Then various studies on the complexes of catechins and caffeine in solution state have been performed. In this study, the crystal structure of the complex of (-)-gallocatechin gallate (GCg) and caffeine was determined fully, and the interaction between GCg and caffeine moieties in the complex was also investigated. A suspension of GCg and caffeine in water afforded two kinds of complex, the 1:2 and 2:2 complexes of GCf and caffeine. The crystal structures of the two complexes were determined by X-ray crystallography. A remarkable difference in the layer structure between the crystal structures of the 1:2 and 2:2 complexes and GCg alone was observed (Figure 7). The units of the 1:2 complex piled up in the same direction almost vertically against the b-c plane, as shown in Figure 7a. The driving force for the formation of the 1:2 complex was thought to be mainly π-π interactions between the A, B' rings of GCg and the six-membered rings of caffeines. GCg molecules in the 2:2 complex piled up as shown in Figure 7b, and A and C rings of GCgs faced each other. The π-π interactions between the B ring of GCg and caffeine, the B' ring of GCg and caffeine, and the A rings of GCgs were formed in the 2:2 comples, whereas GCg molecules in the layer of GCg alone piled up in the same direction as shown in Figure 7c, and no π-π interaction was observed.