Molecular Capture Using Hydrophobic Space Formed By Tea Gallated Catechins in Water

Ishizu T

Published on: 2022-01-13

Abstract

The component of a precipitate resulted by creaming down, which was made from a catechin mixture and caffeine, was determined by an integrated value of a proton signals for H₂ of tea catechins in the quantitative ¹H NMR spectrum. The results showed that gallated catechins formed a precipitate by creaming down more predominantly than non-gallated catechins.

X-ray crystallographic analysis showed that the gallated catechin (-)-epigallocatechin-3-O-gallate (EGCg) formed 2:2 complex with caffeine, in which the caffeine moieties were located in the strong hydrophobic space surrounded by the bottom and top walls of the B’ rings of EGCg moieties and left and right walls of A and B rings of EGCg moieties. Therefore, the solubility of the 2:2 complex of EGCg and caffeine in water reduced rapidly, causing precipitation due to the creaming-down phenomenon.

The precipitates of the 2:2 complex occurred when aqueous solution of the heterocyclic compounds (Table 3) was poured into an aqueous solution of EGCg. The molecular capture abilities of the heterocyclic compounds were evaluated with the ratios of the amount of the heterocyclic compounds included in the precipitates to that of the total heterocyclic compounds used.

Furthermore, the molecular capture abilities of diketopiperazine cyclo(Pro-Xxx) (Xxx: amino acid residue) were evaluated, and the correlation between the chemical structures of cyclo(Pro-Xxx) and their molecular capture abilities was investigated.

When cyclo(Pro-Xxx) was taken into the hydrophobic space formed by EGCg to form the 2:2 complex of EGCg, conformation of cyclo(Pro-Xxx) other than cyclo(D-Pro-L-Ala) still maintained. And conformation of cyclo(D-Pro-L-Ala) changed, that is, its 3-position methyl group changed from the axial position to the equatorial position due to steric hindrance by EGCg moieties.