ANTHOCYANIN INTRAMOLECULAR INTERACTIONS - A NEW MATHEMATICAL APPROACHTO ACCOUNT FOR THE REMARKABLE COLORANT PROPERTIES OF THE PIGMENTS EXTRACTED FROM MATTHIOLA-INCANA

Citation
P. Figueiredo et al., ANTHOCYANIN INTRAMOLECULAR INTERACTIONS - A NEW MATHEMATICAL APPROACHTO ACCOUNT FOR THE REMARKABLE COLORANT PROPERTIES OF THE PIGMENTS EXTRACTED FROM MATTHIOLA-INCANA, Journal of the American Chemical Society, 118(20), 1996, pp. 4788-4793
Citations number
32
Categorie Soggetti
Chemistry
ISSN journal
00027863
Volume
118
Issue
20
Year of publication
1996
Pages
4788 - 4793
Database
ISI
SICI code
0002-7863(1996)118:20<4788:AII-AN>2.0.ZU;2-8
Abstract
In the last few years, a series of investigations has brought to light a mechanism of stabilization of the colorant properties of certain an thocyanins. Intramolecular interactions take place between the chromop hore moiety of the anthocyanin and one of its aromatic acid residues, which folds over the chromophore and thus confers protection against h ydration and subsequent formation of colorless forms. In our continuin g study of the physicochemical properties exhibited by acylated natura l anthocyanins, we report here on a series of five structurally relate d pigments extracted from the violet flowers of Matthiola incana. Thes e pigments all bear the same chromophore moiety, i.e., the cyanidin ag lycon, but differ in the degree of glycosylation and acylation. Acidit y constants for the deprotonation and hydration equilibria of the flav ylium cation, together with rate constants for the hydration step alon e were determined from UV-visible absorption measurements. The data su pport the existence of intramolecular, noncovalent interactions that s trongly stabilize the colored forms of the pigments. However, none of the four more heavily substituted anthocyanins follows the above-menti oned mechanism that was previously successfully applied to the study o f acylated anthocyanins. Consequently, a new mechanism with a differen t mathematical treatment is here developed to account for the differen t behavior exhibited by these distinctive pigments.