Inclusion Complexes of Cyclodextrins with Galangin: a Thermodynamic and Reactivity Study

The formation of the complexes of galangin (GAL) with native beta-cyclodextrin (beta CD), and with its substituted counterparts such as dimethyl-beta CD (DM beta CD) and hydroxypropyl-beta CD (HP beta CD), was studied by fluorescence spectra in aqueous medium. The binding association constants (K (a)) of the complexes were determined at different temperatures. The formation constants obtained have the following trend upon complex formation at the three temperatures studied: HP beta CD > DM beta CD > beta CD. The thermodynamic data for the inclusion of GAL in DM beta CD and HP beta CD indicated that is mainly enthalpy driven whereas for beta CD it is an entropy-driven process. The antioxidant ability studies of GAL and CD complexes showed practically no change in its activity when the beta-cyclodextrin complex is formed. The decrease in the T (eq) observed for GAL-DM beta CD and GAL-HP beta CD in comparison with GAL-beta CD could be due to effective protection of the phenol group in the cyclodextrin cavity, which is in agreement with molecular modeling studies.