The addition of an aqueous solution of diketopiperazine cyclo(Pro-Xxx) (Xxx: amino acid residue) to an aqueous solution of (−)-epigallocatechin-3-O-gallate (EGCg) led to precipitation of the complex of EGCg and cyclo(Pro-Xxx). The molecular capture abilities of cyclo(Pro-Xxx) using EGCg were evaluated by the ratio of the amount of cyclo(Pro-Xxx) included in the precipitates of the complex with EGCg to that of the total cyclo(Pro-Xxx) used. Stronger hydrophobicity of the side chain of the amino acid residue of cyclo(Pro-Xxx) led to a higher molecular capture ability. Furthermore, the molecular capture ability decreased when the side chain of the amino acid residue had a hydrophilic hydroxyl group. When diketopiperazine cyclo(Pro-Xxx), excluding cyclo(D-Pro-L-Ala), was taken into the hydrophobic space formed by the three aromatic A, B, and B′ rings of EGCg, and formed a complex, their conformation was maintained in the hydrophobic space. Based on nuclear Overhauser effect (NOE) measurement, the 3-position methyl group of cyclo(D-Pro-L-Ala) in D₂O was axial, whereas that of cyclo(L-Pro-L-Ala) was equatorial. When cyclo(D-Pro-L-Ala) was taken into the hydrophobic space of EGCg and formed a 2 : 2 complex, its 3-position methyl group changed from the axial position to the equatorial position due to steric hindrance by EGCg.

将二酮哌嗪环（Pro-Xxx）（Xxx：氨基酸残基）的水溶液添加到（-）-表没食子儿茶素-3- O的水溶液中-gallate (EGCg) 导致 EGCg 和环 (Pro-Xxx) 的复合物沉淀。使用 EGCg 的环 (Pro-Xxx) 的分子捕获能力通过与 EGCg 复合物的沉淀物中包含的环 (Pro-Xxx) 的量与所用的总环 (Pro-Xxx) 的量之比来评估。cyclo(Pro-Xxx) 氨基酸残基侧链的更强疏水性导致更高的分子捕获能力。此外，当氨基酸残基的侧链具有亲水性羟基时，分子捕获能力降低。当不包括环(D-Pro-L-Ala)的二酮哌嗪环(Pro-Xxx)被带入EGCg的三个芳香A、B和B'环形成的疏水空间中，形成复合物时，它们的构象保持在疏水空间中。基于核奥弗豪泽效应 (NOE) 测量，₂ O 是轴向的，而环（L-Pro-L-Ala）是赤道的。当环(D-Pro-L-Ala)进入EGCg的疏水空间并形成2:2复合物时，由于EGCg的空间位阻，其3位甲基从轴向位置变为赤道位置。