Characterization of creaming precipitate of tea catechins and caffeine in aqueous solution.

The content of a crude precipitate formed by creaming, which was made from a catechin mixture and caffeine, was investigated by an integral volume of H-2 proton signals of tea catechins in the (1)H-NMR spectrum. Gallated catechins formed a crude precipitate more predominantly than non-gallated catechins. The 2,3-cis-non-gallated catechin (-)-epicatechin (EC) formed a 1:1 complex with caffeine, and 2,3-cis-gallated catechin (-)-epicatechin gallate (ECg) formed a 2:4 complex with caffeine.

Configurational studies of complexes of tea catechins with caffeine and various cyclodextrins.

A suspension of an equimolecular amount of ENT-gallocatechin-3-O-gallate ( ENTGCg) and caffeine in water afforded two kinds of crystals, which were 1 : 2 and 2 : 2 complexes of ENTGCg and caffeine. The stereochemical structures and intermolecular interactions between ENTGCg and caffeine were determined by X-ray crystallographic analysis. The crystal structure of ENTGCg was determined and compared with those of the 1 : 2 and 2 : 2 complexes.

NMR spectroscopic characterization of inclusion complexes comprising cyclodextrins and gallated catechins in aqueous solution: cavity size dependency.

The structure of inclusion complexes of gamma-cyclodextrin (gamma-CD), (-)-gallocatechin gallate (GCg), and (-)-epigallocatechin gallate (EGCg) in D(2)O was investigated using several NMR techniques. GCg formed a 1:1 inclusion complex with gamma-CD in which the A and C rings of GCg were inserted deep at the head of the A ring into the gamma-CD cavity from the wide secondary hydroxyl group side. In the 1:1 inclusion complex with GCg and gamma-CD, the GCg moiety maintained a conformation in which the B and B' rings of GCg took both pseudoequatorial positions with respect to the C ring.

Diastereomeric difference of inclusion modes between (-)-epicatechin gallate, (-)-epigallocatechin gallate and (+)-gallocatechin gallate, with beta-cyclodextrin in aqueous solvent.

Inclusion complexes of (-)-epicatechin gallate (ECg) as well as (+)-gallocatechin gallate (GCg) and beta-cyclodextrin (beta-CD) in an aqueous solution were investigated using several NMR techniques and a computational method. ECg and EGCg formed a 1:1 complex with beta-CD, in which the A ring and a portion of the C ring were included from the wide secondary hydroxyl group side of the beta-CD cavity, and the B and B' rings were left outside the cavity. GCg formed a 1:2 complex with beta-CD, in which the A and B rings of GCg were included by two molecules of beta-CD.

Structure and intramolecular flexibility of beta-cyclodextrin complex with (-)-epigallocatechin gallate in aqueous solvent.

The probable structure of the inclusion complex of beta-cyclodextrin (beta-CD) and (-)-epigallocatechin gallate (EGCg) in D2O was investigated using several NMR techniques. EGCg formed a 1:1 complex with beta-CD, in which the A ring and a portion of the C ring of EGCg were included at the head of the phenolic hydroxyl group attached to C7 of EGCg in the beta-CD cavity from the wide secondary hydroxyl group side. In the 1:1 complex with beta-CD, EGCg maintained the conformation in which the B and B' rings of EGCg took pseudoequatorial and pseudoaxial positions with respect to the C ring, respectively.