Intermolecular copigmentation, anthocyanins

Eiro, M.J. and Heinonen, M., Anthocyanin color behavior and stability during storage effect of intermolecular copigmentation, J. Agric. Food Chem., 50, 7461, 2002. 

The poor stability of anthocyanins with simple stractures can be overcome by intermolecular copigmentation reaction, that is, an association with different compounds, especially polyphenolic ones, stabilized by n-n intermolecular and hydrogen bonds. However, this complex dissociates at high temperatures. ... 

It involves, on one hand an anthocyanin under its flavylium or quinonoidal base form, and on the other hand another planar hydrophobic structure that can be another anthocyanin unit (self-association), or another colorless species (copigment), covalently bound (intramolecular copigmentation) or not (intermolecular copigmentation) to the anthocyanin pigment. 

MALIEN-AUBERT c, DANGLES o and AMIOT M J (2001), Color Stability of commercial anthocyanin-based extracts in relation to the phenolic composition. Protective effects by into and intermolecular copigmentation , J Agric Food Chem, 49, 170-176. 

Malien-Aubert, C., Dangles, O., Amiot, M. J. Color Stability of Commercial Anthocyanin-Based Extracts in Relation to the Phenolic Composition. Protective Effects by Intra- and Intermolecular Copigmentation. J. Agric. Food Chem. 49, 170-176, 2001. 

Fig. 57.12 Schematic representation of the intermolecular copigmentation between anthocyanins and flavonoids. (—), anthocyanin (—), flavonoids [170]...

At the plants pH values (3-7), anthocyanins are mostly present as colorless structures. But a stabilizing mechanism takes place. Such effects are provided by complexation of the color form with other species present in the solution, which can be either an identical anthocyanin molecule (self-association), one of its aromatic acyl groups substituents (intramolecular copigmentation) or another molecule (intermolecular copigmentation). 

One of the best-established functions of anthocyanins is in the production of flower color and the provision of colors attractive to plant pollinators. Considerable effort has been made to give explanations for the color variations expressed by anthocyanins in plants. Various factors including concentration and nature of the anthocyanidin, anthocyanidin equilibrium forms, the extent of anthocyanin glycosidation and acylation, the nature and concentration of copigmentation, metal complexes, intra- and intermolecular association mechanisms, and influence of external factors like pH, salts, etc. have been found to have impact on anthocyanin colors. ... 

Finally, one may note that the variations in the beautiful colours of flowers due to anthocyanins result from supramolecular effects, namely copigmentation, intramolecular sandwich-type stacking and intermolecular association [8.61]. 

Copigmentation is usually classified in (a) intermolecular anthocyanin-anthocyanin self-association, (b) intermolecular anthocyanin-copigment (i.e., flavonoids, phenolic acids) association, (c) intermolecular anthocyanin-copigment-metal ion association or (d) intramolecular self-association of acylated anthocyanins. 

---