Inclusion complexes of quercetin with three β-cyclodextrins derivatives at physiological pH: Spectroscopic study and antioxidant activity

Properties of the inclusion complexes of quercetin (QUE) with sulfobutyl ether-beta-cyclodextrin (SBE-beta-CD), hydroxypropyl-beta-cyclodextrin (HP-beta-CD), and methylated-beta-cyclodextrin (M-beta-CD) in tris-HCl buffer solutions of pH 7.40 were investigated. The stoichiometry and thermodynamic parameters for the complexation process (stability constants K, Gibbs free energy change Delta G, enthalpy change Delta H and entropy change Delta S) were determined using phase-solubility and fluorescence spectra analysis. The thermodynamic studies indicated that the inclusion reactions between QUE and the three beta-CDs are enthalpy-driven processes. Proton nuclear magnetic resonance spectroscopy indicated that B-ring, C-ring, and part of A-ring of QUE interact with the cavity of beta-CDs. The antioxidant activity of QUE and its inclusion complexes were determined by the scavenging of stable radical DPPH*. The results showed that the complexed QUE/CDs were more effective than free QUE, with the QUE/SBE-beta-CD complex as the best form. (C) 2013 Elsevier B.V. All rights reserved.