Rate and equilibrium constants for the dehydration and deprotonation reactions of some monoacylated and glycosylated cyanidin derivatives

The rate and equilibrium constants for the pH-dependent hydration of a seri es of monoacylated anthocyanins semi-biosynthesized using a wild carrot sus pension culture have been measured. The features of the acyl groups that de crease the hydration and thus decrease the loss of color of these anthocyan ins are the presence of the side-chain double bond of the cinnamic acids an d the presence of electron-donating substituents at the para-position of th e acyl group. Methoxyl groups in the meta-position of the acyl groups have a greater effect than can be explained by their effects on the electron den sity in the acyl group. The data also suggest that there may be additional features of the acyl groups which contribute to the color retention in anth ocyanins.