PROTON NUCLEAR-MAGNETIC-RESONANCE STUDIES OF MONOACYLATED ANTHOCYANINS FROM THE WILD CARROT - PART 1 - INTERMOLECULAR AND INTRAMOLECULAR INTERACTIONS IN SOLUTION
Eg. Gakh et al., PROTON NUCLEAR-MAGNETIC-RESONANCE STUDIES OF MONOACYLATED ANTHOCYANINS FROM THE WILD CARROT - PART 1 - INTERMOLECULAR AND INTRAMOLECULAR INTERACTIONS IN SOLUTION, Phytochemical analysis, 9(1), 1998, pp. 28-34
Inter- and intra-molecular interactions of five anthocyanins (one non-
acylated and four acylated with either sinapic acid or 4-methylated si
napic acid) obtained from cell culture of the wild carrot (Daucus caro
ta ssp, carota) have been studied by one-and two-dimensional proton nu
clear magnetic resonance (NMR) spectroscopy, Temperature and concentra
tion dependencies of proton chemical shifts show that self-association
of non-acylated anthocyanins depends upon the number and position of
the sugar units, It was found for the first time that there were non-a
cylated anthocyanins that were not protected by self-association. Both
intra-and inter-molecular interactions were found in the acylated ant
hocyanins under study, These compounds form strong intra-molecular pi-
complexes between the sinapoyl group and the anthocyanidin nucleus, th
e double bond of sinapic acid being involved as well as its aromatic r
ing, Upon increasing the concentration of the anthocyanins or lowering
the temperature of the NMR sample, the pi-complexes form multinuclear
complexes as shown by the resultant negative nuclear Overhauser effec
t (NOE) values, Spin diffusion was observed in the acylated anthocyani
ns for temperatures below -40 degrees C. It was also concluded that, b
ecause anthocyanins fall in the range of medium-size molecules with NO
Es of small magnitude, and because they readily form complexes, two-di
mensional NOE experiments are more reliable for structural elucidation
of the anthocyanins than are one-dimensional steady-state NOE experim
ents. (C) 1998 John Wiley & Sons, Ltd.