Effect of β-cyclodextrin on the chemistry of 3′,4′,7-trihydroxyflavylium

The pH dependence of the network of chemical reactions involving 3′,4′,7-trihydroxyflavylium was studied and all the rate and equilibrium constants were determined in the presence and absence of β-cyclodextrin. The β-cyclodextrin increases the rate constant of the flavylium cation hydration to give the hemiketal and decreases the reverse rate constant (de-hydration). The quantum yield of the flavylium cation formation from irradiation of the trans-chalcone increases from 0.023 to 0.055, respectively, in the absence and presence of β-cyclodextrin. NMR spectral characterization of the inclusion complex between 3′,4′,7-trihydroxyflavylium and β-cyclodextrin was performed by ROESY and suggests a structure in which the hydroxyl substituents at positions 3′ and 4′ interact with the internal surface of the β-cyclodextrin.