Intramolecular copigmentation

Keepers, J.W. and James, T.L., A theoretical smdy of distance determinations from NMR two-dimensional nuclear Overhauser effect spectra, J. Mag. Resort, 57, 404, 1984. Kemp, W., Organic Spectroscopy, 3rd ed., W.H. Ereeman, New York, 1991. Figueiredo, P. et al., New aspects of anthocyanin complexation intramolecular copigmentation as a means for colour loss Phytochemistry, 41, 301, 1996. 

Figueiredo, P. et al., New aspects of anthocyanin complexation. Intramolecular copigmentation as a means for colour loss Phytochemistry, 41, 301, 1996. 

It is known that polyacylated anthocyanins are very stable in neutral or weakly acidic aqueous solutions, whereas simple anthocyanins are quickly decolorized by hydration at the 2-position of the anthocyanidin nucleus. The shift to blue colors and increased anthocyanin stability are in many cases simply achieved by intramolecular copigmentation involving... 

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. 

Figueiredo, P, George, R, Tatsuzawa, R, Toki, K., Saito, N., Brouillard, R. (1999). New features of intramolecular copigmentation by acylated anthocyanins. Phytochemistry, 51, 125-132. 

The red-violet color of malvidin-3-glucoside - (+)-catechin condensation products (via acetaldehyde), which some authors have suggested is an intramolecular copigmentation effect (Escribano-Baildn et al., 1996), is more pH-stable and SO2 discoloration-stable than are free anthocyanins (Escribano-Bail6n et al., 2001). However, these adducts are also less stable in aqueous solution because of the breakage of the ethyl bridge that joins the anthocyanin to the catechin (Escribano-Bail6n et al., 2001). 

Flower pigments. Term for a subgroup of plant pigments responsible for the manifold colors of flowers. The most important F. p. are the anthocyanins, flav-onoids, carotinoids, and betalains. Yellow colors are caused by flavonoids, carotenoids, and betaxanthins while anthocyans and betacyans (see betalains) are responsible for red, violet, and blue colors. The many color tones result on the one hand from the simultaneous presence of flavonoids and anthocyans (intermo-lecular copigmentation) and on the other hand from intramolecular copigmentation and the formation of chelates between metal salts and anthocyans. 

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). 

Five delphinidin-based anthocyanins, isolated from the flowers of the above mentioned Evolvulus cultivar, were integrated in physicochemical studies on intramolecular copigmentation (Figueiredo et al. 1996) and complexation with alu-mininm and gallinm ions (Elhabiri et al. 1997), respectively. 

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