FORMATION OF ANTHOCYANIN ION-PAIRS - A COPIGMENTATION EFFECT

The influence of the addition of ionic salts (NaCl, NaBr. Nal, NaClO4) on anthocyanin equilibria is studied in this work. The effect of thei r addition is a colour enhancement through the formation of an ion-pai r between the charged flavylium cation and the anion. which displaces the equilibria towards the coloured flavylium form. The ion-pair forma tion is an alternative model to that which suggests a preferable hydra tion of salt anions instead of the flavylium cation. Throughout this w ork two natural anthocyanins are studied (malvidin 3,5-diglucoside and malvidin 3-glucoside) as well as one anthocyanidin (malvidin). The th ermal and photochemical stability of the ion-pairs formed is also exam ined. Experiments with a synthetic anthocyanin analogue (4'.7-dihydrox yflavylium chloride) which has photochromic properties are also descri bed for comparison purposes.