Dipalmitoyl-lecithin: assignment of the 1H and 13C nuclear magnetic resonance spectra, and conformational studies

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Abstract
The 13C resonances of the glycerol and choline groups of dipalmitoyl-lecithin in CD3OD, CDCl3, and D2O have been assigned from the 14N–13C and 31P–13C coupling constants, and proton decoupling studies on the assigned 1H spectra. Well-defined solvent effects are observed, but the chemical shifts for dipalmitoyl-lecithin in bilayers in D2O are very similar to the shifts of the corresponding resonances in biological membranes. From an analysis of the 1H spectrum of the CH2 multiplet in the CH–CH2OCOR fragment, the two vicinal coupling constants were extracted and used to calculate rotamer populations from a Karplus treatment. In a high proportion of the molecules of dipalmitoyl-lecithin in CD3OD and in CDCl3 the fatty acid chains are arranged gauche to each other, suggesting the presence of strong hydrophobic interactions. From an AA′BB′ analysis of the choline –CH2·CH2–fragment in dipalmitoyl-lecithin observed vicinal coupling constants indicate a similar conformation to that found in choline derivatives where an electrostatic interaction between the N+ and the O atoms leads to the conformation being exclusively in the gauche+N/O form.

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