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3′‐(β‐D‐Glycopyranosyloxy)flavylium Ions: Synthesis and investigation of their properties in aqueous solution. Hydrogen bonding as a mean of colour variation
Author(s) -
Hajji Hakima El,
Dangles Olivier,
Figueiredo Paulo,
Brouillard Raymond
Publication year - 1997
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19970800206
Subject(s) - chemistry , aqueous solution , chromophore , intramolecular force , hydrogen bond , pigment , glycosyl , ion , chalcone , stereochemistry , organic chemistry , molecule
This work describes a straightforward synthesis of two 3′‐(β‐D‐glycopyranosyloxy)flavylium ions thought to be good models of natural anthocyanins (pigments). For both pigments and for the non‐glycosylated flavylium ion taken as a reference, H 2 O addition and proton‐transfer reactions as well as formation of molecular complexes with chlorogenic acid and caffeine (copigmentation) are quantitatively investigated in mildly acidic aqueous solution. A remarkable affinity of caffeine for the trans ‐chalcone form of the pigments is demonstrated. Moreover, the differences in the flavylium p K a values are interpreted in terms of possible intramolecular H‐bonding between the glycosyl residue and the chromophore. The discussion is then extended to a series of malonylated anthocyanins recently reported for their unusual pigmentation properties. A possible role for the malonyl group (frequently encountered in the structure of naturally occurring anthocyanins) in plant colour expression is outlined for the first time.