NMR studies on the interaction between (-)-epigallocatechin gallate and cyclodextrins, free and bonded to silica gels.

The interaction between (-)-epigallocatechin-3-gallate (EGCG) and beta- or gamma-cyclodextrin (CD), in free solution and bonded to silica beads, has been studied by (1)H HR-MAS NMR spectroscopy. The chromatographic retardation of EGCG on columns packed with CD-silica beads was shown to be due to the interaction of EGCG with the CD ligands because no nonspecific interaction with the silica gel could be observed. EGCG forms a tighter complex with beta-CD than with gamma-CD and NMR data obtained from hydroxy protons together with MM2 calculations suggest that for beta-CD intermolecular hydrogen bonding, in addition to hydrophobic interaction, stabilizes the complex.