Synthesis of a new bluish pigment from the reaction of a methylpyranoanthocyanin with sinapaldehyde

Abstract

The synthesis of a new pigment with a bluish color was obtained from the reaction of methylpyranomalvidin-3-glucoside with sinapaldehyde and its formation mechanism seems to involve a charge-transfer reaction pathway. The structure of this compound was fully characterized by LC/DAD-MS and NMR. Its equilibrium forms present in water at different pH values and the respective ionization constants were determined by UV-visible spectroscopy. The results revealed the presence of three equilibria involving only deprotonation reactions at the 7-OH and 4′-OH positions of the pyranoanthocyanin moiety and at the 4′″-OH of the syringol moiety (pKa1 = 3.64 ± 0.01; pKa2 = 8.02 ± 0.01; pKa3 = 11.19 ± 0.01). © 2011 Elsevier Ltd. All rights reserved.