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. Epigallocatechin-3-O-gallate (EGCg) formed a 1 : 1 complex with β-cyclodextrin (CD), in which the aromatic A ring and a part of the heterocyclic C ring were included from the wide secondary hydroxyl group side of the β-CD cavity in aqueous solution, while the B rings and 3-O-gallate groups (B' rings) were left outside the cavity. In contrast, ENTGCg formed a 1 : 2 complex with β-CD, in which the aromatic A and B rings of ENTGCg were included by two molecules of β-CD.
A novel capsule-like structure of micro-sized particles formed by phytosterol ester and γ-cyclodextrin in water.
The composite material formed by phytosterol ester (PSE) and γ-cyclodextrin (γ-CD) disperses readily in water and has been used to mask undesirable flavours. This paper elucidates the structure of the PSE/γ-CD particle. Cryogenic scanning electron microscopy and contact angle measurements showed that the PSE/γ-CD particles formed a capsule-like structure with a hydrophilic surface. A phase-solubility study using cholesteryl oleate (ChO), one of the components of PSE, showed that ChO formed a hydrophilic and stoichiometric inclusion complex with γ-CD at a molar ratio of 2:5. The structure of the PSE/γ-CD inclusion complex was similar to that of ChO/γ-CD, based on differential scanning calorimetry and powder X-ray diffractometry results. Thus, we propose that the PSE/γ-CD particle has a capsule-like structure wherein a hydrophobic PSE droplet is surrounded by an outer layer of the hydrophilic PSE/γ-CD inclusion complex.
Plant polyphenols ― Secondary metabolism and chemical defence: some observations
Abstract Secondary metabolism and theories of plant-animal co-evolution are briefly discussed. Current ideas concerning the role of polyphenols as mediators of a general form of chemical defence in plants are outlined. Studies are described of the association of a group of biosynthetically inter-related polyphenols based on gallic acid and D -glucose with the protein bovine serum albumin. The results are interpreted in terms of structure-activity relationships in protein-polyphenol complexation and are used to comment on the co-evolution theory and the position of plant polyphenols in higher plant secondary metabolism and defence.