The probable structures of the inclusion complexes of β-cyclodextrin (β-CD) with (+)-catechin (CA) and (−)-epicatechin (EC) in D2O at 35 °C were investigated using NMR. In the β-CD·CA inclusion complex, a large portion of the flavonoid skeleton was included in the β-CD cavity and the axis of C1 ‘−C4 ‘ of the B ring inclined to the molecular axis of β-CD, and the CA molecule fitted tightly with β-CD. In the β-CD·EC inclusion complex, the B ring was included deeply in the β-CD cavity from the secondary hydroxyl group side and the A ring was left outside the cavity near the secondary hydroxyl group side and EC molecule fitted loosely.

The probable structure of the inclusion complex of beta-cyclodextrin (beta-CD) and (-)-epigallocatechin gallate (EGCg) in D2O was investigated using several NMR techniques. EGCg formed a 1:1 complex with beta-CD, in which the A ring and a portion of the C ring of EGCg were included at the head of the phenolic hydroxyl group attached to C7 of EGCg in the beta-CD cavity from the wide secondary hydroxyl group side. In the 1:1 complex with beta-CD, EGCg maintained the conformation in which the B and B' rings of EGCg took pseudoequatorial and pseudoaxial positions with respect to the C ring, respectively. The structure of the inclusion complexes of beta-CD and EGCg obtained from NMR experiments supported those determined from AM1 semiempirical SCF MO calculations well.

Inclusion complexes of (-)-epicatechin gallate (ECg) as well as (+)-gallocatechin gallate (GCg) and beta-cyclodextrin (beta-CD) in an aqueous solution were investigated using several NMR techniques and a computational method. ECg and EGCg formed a 1:1 complex with beta-CD, in which the A ring and a portion of the C ring were included from the wide secondary hydroxyl group side of the beta-CD cavity, and the B and B' rings were left outside the cavity. GCg formed a 1:2 complex with beta-CD, in which the A and B rings of GCg were included by two molecules of beta-CD. The difference between the two modes of inclusion of the 1:1 complex of ECg, EGCg.beta-CD and the 1:2 complex of GCg.beta-CD might have resulted from the size of the space between the B and B' rings in aqueous solution. As a result of nuclear Overhauser effect (NOE) experiments, GCg was considered to have a large enough space between the B and B' rings to include the B ring in the beta-CD cavity; on the other hand, ECg and EGCg have no such large space.

Stereochemical structures of a 1:1 complex of (−)-epicatechin (EC) and caffeine, and a 2:4 complex of (−)-epicatechin gallate (ECg) and caffeine were determined by X-ray crystallographic analysis, and noncovalent interactions forming between EC, ECg and caffeine moieties were also elucidate.

A merohedrally twinned crystal of the complex of (−)-gallocatechin gallate and caffeine was prepared in aqueous solution, and X-ray crystallographic analysis was performed. The driving force for the formation of the complex was thought to be mainly the π–π interaction between the B′ ring of GCg and caffeine, the B ring of GCg and caffeine.