The effect of 3-O-β-glucosylation on structural transformations of anthocyanidins

In this study the effect of 3-O-β-glucosylation on the experimentally determined pKa and pKh values of cyanidin, malvidin, delphinidin were investigated using pH dependent UV-Vis spectroscopy. Structural transformations of cyanidin-type pigments from flavylium cation through the colorless chemiacetal and chalcone forms to the mixture of quinoidal-bases, were characterized on the basis of thermochemical parameters calculated by functional theory B3LYP method. The most stable molecular structures of cyanidin 3-O-β-glucoside and the role of intramolecular hydrogen bondings in stabilization of its different forms are discussed. The results explain how the stabilization of cyanidin 3-O-β-glucoside flavylium cation by the net of intramolecular H-bondings within sugar moiety and between sugar and anthocyanin molecule affects its structural transformations.