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.
Molecular interactions between caffeine and catechins in green tea.
Migration of green tea components from an active packaging material containing green tea extract was performed in water and 3% acetic acid in water. The migration values for acid simulant were much higher than the values obtained in water. The influence of the acidic media in solutions of catechin standards and green tea extract was evaluated by liquid chromatography. Catechin, epicatechin, and caffeine from the green tea extract exhibited major variation in their concentrations values, with increases of 29.90, 20.75, and 15.95%, respectively, in acidic medium. The results suggested that catechins and caffeine form complexes through intermolecular interactions in neutral media and that these interactions are broken in acidic media. The continuous variation method was also performed to confirm the stoichiometry of the complexes between catechins and caffeine. Finally, a computer simulation was applied by Chem Pro 12.0, and the energies involved were calculated to confirm the experimental results obtained.
SECONDARY COMPOUNDS AS PROTECTIVE AGENTS
INTRODUCTION ........ ...... ...... ....... ... ....... ......... 479 THE NATURE OF SECONDARY COMPOUNDS .. ... ..... 480 Introduction 480 Distribution of Secondary Compounds in Space and Time 481 Function of Secondary Compounds 483 Secondary Compounds as Waste Products 483 Secondary Compounds as Protective Agents 484 SECONDARY COMPOUNDS AND PLANT DISEASES .... ..... ... .. ........ .. 485 Introduction 485 Defenses on the Surface of Plants 485 Defensive Function of the Cell Wall ........ ...... ...... ........ 486 Che"1ical Defenses within the Cell .... ...... ...... ........ ........ 486 The Role of Tannins 487 The Role of Phytoalexins 488 SECONDARY COMPOUNDS AND ALLELOPATHY ......... ... ..... ....... ..... ..... ......... 489 Introduction 489 The Complexity of Allelopathy 489 Allelopathic Activity of Secondary Compounds 490 Nonprotein Amino Acids and Allelopathy 490 SECONDARY COMPOUNDS AS INSECT DETERRENTS .. ... .. ... ....... 490 Introduction 490 Insect Chemoreceptors 491 Insect-deterrent Properties of Secondary Compounds 492