New aspects of anthocyanin complexation. Intramolecular copigmentation as a means for colour loss?

Abstract

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.

Molar Absorptivity and Color Characteristics of Acylated and Non-Acylated Pelargonidin-Based Anthocyanins

“…It has been reported as a general characteristic that an increase in the number of substitutions is accompanied by an increase in the molar absorptivity of the flavylium cation form when compared to their parent mono-and diglucosides (Figueiredo et al, 1996b). Our results showed a general hyperchromic effect of acylation of pg derivatives as compared to the parent pg-3-soph-5-glu, in particular, when 2 acylating groups were present.…”

Vegetable-based dye-sensitized solar cells

“…407 Dyrby et al 408 investigated acylated anthocyanins from red cabbage that have shown low sensitivity to photo-degradation in the 3-7 pH range and thermal stability, with respect to other non-acylated anthocyanins obtained from red grape, 409 black currant 410 and elderberry. 401,402,413,414 Molecular co-pigmentation between anthocyanin and other compounds (co-pigments) is an important stabilizing mechanism of chromophores. 408 In the past years, many of the aforementioned vegetables and many others were identified as potential natural source of stable anthocyanins.…”

Phenetics in Tree Peony Species from China by Flower Pigment Cluster Analysis

“…lishizhenii was the lowest. The copigment indices (Cl) varied among species (Robinson and Robinson 1931, Asen et al 1972, Figueiredo et a/. 1996, Wang et a/.…”