A theoretical study on structures of an epigallocatechin-3-O-gallate/caffeine complex in aqueous solution

Abstract

Complexations between aromatic compounds often affect food quality. For example, it is well-known that catechins form complexes with caffeine. Both are major compounds in green tea but the structures of their complexes in aqueous solution have not been clarified. In this study, we elucidated the structure of the epigallocatechin-3-O-gallate (EGCg)/caffeine complex in aqueous solution by DFT calculations and NMR experiments. A detailed analysis of 1H NMR titration data revealed that EGCg forms a 1:1 complex with caffeine, and our combination of the DFT calculations and NOESY experiments showed that EGCg binds with caffeine in the space surrounded by the axial galloyloxy group and the A-ring. Aromatic/aromatic and CH/π interactions are the major intermolecular forces in the complex. Furthermore, calculations using an explicit solvent model suggested that water molecules stabilize the EGCg/caffeine complex by hydration and intermolecular cross-linking.