Fluorescence study on the inclusion complexes of rutin with beta-cyclodextrin, hydroxypropyl-beta-cyclodextrin and gamma-cyclodextrin

The interaction of beta-cyclodextrin(CD), hydroxypropyl-beta-cyclodextrin(HP-beta-CD) and gamma-cyclodextrin(gamma-CD) with the drug rutin has been investigated by using fluorescence spectroscopy. The stoichiometry of the complexes and their apparent formation constants have been estimated. The thermodynamic parameters(Delta H, Delta S) for the formation of complexes were obtained from the van't Hoff equation. The results show that the formation constants of rutin with several cyclodextrins exhibit the order HP-beta-CD>beta-CD>gamma-CD with the same stoichiometry of the complexes 1:1. Rutin has no measurable fluorescence enhancement in alpha-CD system. The thermodynamics of the complex formation displays an enthalpy-entropy compensation effect. The complexing ability of HP-beta-CD is remarkble stronger than beta-CD and gamma-CD.