SPECTROFLUOROMETRIC STUDY ON THE INCLUSION REACTION OF FLAVONOLS WITH BETA-CYCLODEXTRIN

Kinetics and thermodynamics of the inclusion reaction of flavonols with beta-cyclodextrin have been studied fluorometrically in 30%v/v methanolic aqueous solution. The equilibrium constants of this reaction were determined for flavonol and its 12 different hydroxy and methoxy derivatives in acidic and alkaline media where each flavonol is present quantitatively as fully protonated or deprotonated species. A thermodynamic consideration on the substituent effects reflected in these constants leads to a model for the present inclusion complex. With the inclusion constants for a monoprotic flavonol and its conjugate base, the effect of beta-cyclodextrin on the acid dissociation equilibrium of the flavonol is quantitatively described. Kinetic aspects of this inclusion reaction are also discussed.