NEW ASPECTS OF ANTHOCYANIN COMPLEXATION - INTRAMOLECULAR COPIGMENTATION AS A MEANS FOR COLOR LOSS

Two series of structurally related anthocyanins, extracted from the bl ue flowers of Evolvulus pilosus cv. Blue Daze and from the blue-purple flowers of Eichhornia crassipes, exhibit remarkable colour stabilitie s in aqueous solution at mildly acidic pH values. All the pigments pos sess the same chromophore (delphinidin), but a different pattern of gl ycosylation and acylation. Moreover, one of the pigments has an apigen in 7-glucoside molecule (a flavone) attached to the glycosidic chain b y two ester bonds with malonic acid, instead of an aromatic acid and i s the only known anthocyanin with such a structure. All the molecules studied, except one which has only a 3-gentiobioside (a disaccharide) as substituent, denote an effect of reduction in the hydration constan t when compared with the parent delphinidin 3-glucoside or 3,5-digluco side molecules, which supports the existence of intramolecular hydroph obic interactions between the chromophoric skeleton and the acyl or fl avonoid groups. The role played by the sugar units on the hydrophobici ty/hydrophilicity of the pigments is also discussed.