Host-guest complexation of apple antioxidant quercetin by linked β-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 β-cyclodextrin (βCD) and N,N'-bis(6A-deoxy-6 A-β-cyclodextrinyl)urea (66βCD2ur) of stoichiometry βCD.Qc and 66βCD2ur.Qc, the analogous K 1 = 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 β-cyclodextrin (βCD) and N,N'-bis(6A-deoxy-6A-b-cyclodextrin) urea (66βCD2ur) in D2O was studied by 2D ROESY 1H NMR provided evidence for complexation of quercetin into βCD annuli. The models of complexes were constructed and energy minimized.