Host-Guest Complexation of Apple Antioxidant Quercetin By Linked b-Cyclodextrin Dimer

Abstract

In aqueous phosphate buffer at pH 7.0 (3.3 % ethanol, I = 0.10 mol dm^-3 at 298.2 K) quercetin forms host-guest complexes with b-cyclodextrin (bCD) and N,N'-bis(6^A-deoxy-6^A-b- cyclodextrinyl)urea (66bCD₂ur) of stoichiometry bCD.Qc and 66bCD₂ur.Qc, the analogous K₁ = 537 and 1901 dm³ mol^-1, respectively, showing a good cooperative binding of two annuli of the dimer to the guest. The complexation of quercetin (Qc) by b-cyclodextrin (bCD) and N,N'- bis(6^A-deoxy-6^A-b-cyclodextrin)urea (66bCD₂ur) in D₂O was studied by 2D ROESY ¹H NMR provided evidence for complexation of quercetin into bCD annuli. The models of complexes were constructed and energy minimized.