β-Cyclodextrin encapsulation elevates antioxidant capacity of tea: A closing chapter on non-epicatechins, atomistic insights from X-ray analysis, DFT calculation and DPPH assay.

Polyphenolic catechins prevalent in tea are powerful antioxidants for therapeutics of various free radical-related diseases. The non-epicatechins are thermally obtained from the naturally abundant epicatechins. In our study series on the structure-antioxidant property relationship of the CD inclusion complexes with tea catechins, this closing chapter presents the β-CD encapsulation of three non-epicatechins, i.e., (-)-gallocatechin (GC) 1, (-)-catechin gallate (GC) 2, and (-)-gallocatechin gallate (GCG) 3 investigated by means of single-crystal X-ray diffraction, DFT calculation and DPPH radical scavenging activity assay. Detailed structural comparisons of the β-CD inclusion complexes with both non-epi and epi type catechins reveal that a common host-guest hydrogen bonding scheme and the shielding of catechin OH groups inside the host circular wall play a prime role in flourishing antioxidant capacities in the order of 3 > 2 > 1. This is consistent with the relative thermodynamic stabilities derived from DFT energy minimization.