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

Abstract

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