13C-Nuclear magnetic resonance spectroscopic studies of triacylglycerols of type AAA containing ( Z)- and ( E)-monoethylenic acyl groups

Abstract

The 13C-NMR properties of a total of 22 synthetic ( Z)-ethylenic and ( E)-ethylenic triacylglycerols of type AAA (containing isomeric positional unsaturated fatty acid homologues with the ethylenic bond located at Δ 2 to Δ 12 position) have been studied. The results show that the shifts of the glyceryl carbon atoms are only significantly affected when the unsaturated center is located at either the Δ 2 or Δ 3 position of the acyl chains. The ethylenic carbon atoms in the α- and β-acyl chains are fully resolved except in two cases, viz. 12:1(3 Z)/12:1(3 Z)/12:1(3 Z) and 15:1(6 E)/15:1(6 E)/15:1(6 E), where the shifts of the C-4 and C-7 ethylenic carbon atoms in the α- and β-acyl chains, respectively, remain unresolved. From the carbon chemical shift values of the ethylenic carbons and the difference between the shift values of these nuclei in the same acyl chain, it is possible to determine the position of the unsaturated center by this technique. Using the signal pattern displayed by the ethylenic carbon nuclei in the spectra, the positional distribution of short-chain fatty acid moieties in the glycerol ‘backbone’ can be determined. Methylene carbon atoms in the α- and β-acyl chain, which are located close to the acyl function are resolved up to the C-6 carbon atom. It is possible to locate the position of the unsaturated center in the acyl chains as remote as the Δ 12 position and the position (α- or β-acyl) of the unsaturated acyl chains on the glyceryl backbone of these triacylglycerol molecules by 13C-NMR spectroscopy.