New aspects of anthocyanin complexation. Intramolecular copigmentation as a means for colour loss?
Two series of structurally related anthocyanins, extracted from the blue flowers of Evolvulus pilosus cv. Blue Daze and from the blue-purple flowers of Eichhornia crassipes, exhibit remarkable colour stabilities in aqueous solution at mildly acidic pH values. All the pigments possess the same chromophore (delphinidin), but a different pattern of glycosylation and acylation. Moreover, one of the pigments has an apigenin 7-glucoside molecule (a flavone) attached to the glycosidic chain by two ester bonds with malonic acid, instead of an aromatic acid and is 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 constant when compared with the parent delphinidin 3-glucoside or 3,5-diglucoside molecules, which supports the existence of intramolecular hydrophobic interactions between the chromophoric skeleton and the acyl or flavonoid groups. The role played by the sugar units on the hydrophobicity/hydrophilicity of the pigments is also discussed.
Figueiredo
P
P
Laboratoire de Chimie des Polyphénols, Associé au CNRS, Université Louis Pasteur, Institut de Chimie, Strasbourg, France.
Elhabiri
M
M
Toki
K
K
Saito
N
N
Dangles
O
O
Brouillard
R
R
D000872:Anthocyanins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D003116:Color; D007700:Kinetics; D008969:Molecular Sequence Data; D015394:Molecular Structure; D018521:Plant Physiological Phenomena
D000872:Anthocyanins