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.
β-Cyclodextrin encapsulation elevates antioxidant capacity of tea: A closing chapter on non-epicatechins, atomistic insights from X-ray analysis, DFT calculation and DPPH assay.
Polyphenolic catechins prevalent in tea are powerful antioxidants for therapeutics of various free radical-related diseases. The non-epicatechins are thermally obtained from the naturally abundant epicatechins. In our study series on the structure-antioxidant property relationship of the CD inclusion complexes with tea catechins, this closing chapter presents the β-CD encapsulation of three non-epicatechins, i.e., (-)-gallocatechin (GC) 1, (-)-catechin gallate (GC) 2, and (-)-gallocatechin gallate (GCG) 3 investigated by means of single-crystal X-ray diffraction, DFT calculation and DPPH radical scavenging activity assay. Detailed structural comparisons of the β-CD inclusion complexes with both non-epi and epi type catechins reveal that a common host-guest hydrogen bonding scheme and the shielding of catechin OH groups inside the host circular wall play a prime role in flourishing antioxidant capacities in the order of 3 > 2 > 1. This is consistent with the relative thermodynamic stabilities derived from DFT energy minimization.
Plant apparency and chemical defense
A major objective of insect ecology is to explain observed patterns of interaction between plants and herbivorous insects. We would like to understand both how such patterns are maintained in ecological time and also how they have come about in evolutionary time. A test of how far such understanding has progressed will be our ability to predict how patterns vary from one kind of community to another and how they will change when subjected to natural or human disturbance.