C-13 cross-polarization and magic-angle spinning nuclear magnetic resonance of polymorphic forms of three triacylglycerols

The cross-polarization and magic-angle spinning nuclear magnetic resonance (CP/MAS-NMR) technique has been used to analyze the polymorphic forms of three triacylglycerols, 1,3-dipalmitoyl-2-oleoyl glycerol (POP), 1,3-rac-palmitoyl-stearoyl-2-oleoyl glycerol (POS), and 1,3-distearoyl-2-oleoyl glycerol (SOS). Specific attention has been paid to glycerol, carbonyl, olefinic, and methyl end carbon resonances. Many distinct differences were observed in each polymorphic form of SOS. In the alpha form, the saturated and unsaturated acyl chains exhibit liquid state-like conformations. However, olefinic conformations of the gamma and beta' forms were asymmetric with respect to the cis double bond. Spectral difference between beta(2) and beta(1) was observed only for the methylene carbon, and not in the other regions. Spectra of corresponding polymorphic forms oi POP and POS were almost identical to those of SOS. However, some spectral differences were observed in the glycerol and methyl regions or gamma and beta'. From the chemical shifts of the methylene carbons, the crystal structures of the polymorphic form have been discussed, particularly in terms of the sub-cell structures.