Electronic and infrared vibrational analysis of cyanidin–quercetin copigment complex

Abstract

Copigment complex formation between cyanidin and quercetin, in aqueous buffered solutions, was studied by electronic absorption and infrared vibrational spectroscopies. It was found that the association of cyanidin with quercetin occurred at pH 3.0 and pH 5.0 including cyanidin flavylium ion and anhydrobase transformation forms, respectively. Obtained copigmentation constant values of K = 2726.7 (pH 3.0) and K = 1093.1 (pH 5.0) indicated good association ability of the investigated molecules. Infrared spectra revealed the existence of hydrogen bonds in the copigment complexes structures. The analysis of the deconvoluted infrared spectra indicated several types of hydrogen bonds, differently formed: the H O ⋯ H bonds with the corresponding bands around 3500 cm −1 and bonds formed via H 3O +, oxonium, ion of the molecules with the corresponding bands below 3000 cm −1.