Identification of individual diacylglycerols by adsorption thin-layer chromatography of their coordination complexes

Abstract

Diacylglycerols (DAGs) obtained by glycerolysis of a mixture of cocoa butter, poppy seed and linseed oils were separated by preparative thin-layer chromatography (TLC) into their positional isomers. An isomerically pure model mixture of rac-1,2-DAGs was further separated into eleven fractions using adsorption TLC of coordination complexes of unsaturated DAGspecies with silver ions on an analytical scale. The mobility of the separate TLC zones of this mixture, which included residues of stearic (St), palmitic (P), oleic (O), linoleic (L) and linolenic (Le) acids, was compared with that of standard rac-1,2-DAG zones. The comparison demonstrated that the model mixture was composed of the following individual DAG species: StO-, PO-, OO-, OL-, LL-, OLe-, LLe- and LeLe-glycerols, in addition to SS-, SL- and SLe-glycerols in which S is St or P. The different mobilities of these DAG species can be accounted for by the differences in the relative polarities of the Ag + complexes of O, L and Le, which were found to be 1.03, 2.46 and 5.45, respectively. There was a strong negative correlation between the mobility and the polarity of the DAG species.