STRUCTURAL ASPECTS OF ANTHOCYANIN-FLAVONOID COMPLEX FORMATION AND ITS ROLE IN PLANT COLOR

Article abstract of DOI:10.1016/0031-9422(81)85111-4

Key Word Index - Anthocyanin; flavonoid glycosides; synthesis; complex formation; plant color; spectral properties. The complex formation of flavonoids with anthocyanins, resulting in increase in both absorbance and in a bathochromic shift of the visible absorption maximum of the latter, is based mainly on hydrogen bond formation between the carbonyl group of the anthocyanin anhydrobase and aromatic hydroxyl groups of the complex-forming flavonoids.The larger the number of hydroxyl groups in the flavonoid molecule, the strongr the complex formation.The presence of a 3-hydroxyl group in the flavonoid molecule has little effect on the complex-forming ability.The nature of the sugar substituent of the complex-forming flavonoid compound has no influence on the reaction.The 5-hydroxyl group of flavonoids is strongly bound by intramolecular hydrogen bond to the 4-carbonyl and does not participate in the complex formation.The most important hydroxyl group in the flavonoid molecule is one in the 7-position.Unsaturation at C2-C3 in the heterocyclic ring is an important factor for complex formation.Aromatic hydroxyl groups in the flavonoid system alone cannot account for all the complex-forming ability, suggesting additional involvment by electrostatic forces and configurational or steric effects.