PROTON NUCLEAR-MAGNETIC-RESONANCE STUDIES OF MONOACYLATED ANTHOCYANINS FROM THE WILD CARROT - PART 1 - INTERMOLECULAR AND INTRAMOLECULAR INTERACTIONS IN SOLUTION

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.