(13)C nuclear magnetic resonance spectra of natural undiluted lipids: docosahexaenoic-rich phospholipid and triacylglycerol from fish.

In the (13)C NMR spectra of natural, unenriched docosahexaenoic acid-rich sardine oil and cod muscle glycerophosphocholine significant signal intensity differences across the 1D spectrum between undiluted and diluted samples were observed. In undiluted samples (13)C-(13)C 2D nuclear Overhauser enhancement spectroscopy (NOESY) interchain cross-peaks for CH, CH(2), CH(3), and C=C structures were observed. Results indicate that in undiluted natural lipids, NMR signal intensity is influenced by polarization transfer from the extended lipid structure. The NOE enhancement of specific molecular sites especially in unsaturated lipids is evidence that some natural lipids remain oriented relative to each other and in an orderly arrangement at the molecular level long enough for the effect to be detected by the NMR experiment. The presence of polyunsaturated fatty acids in mixtures of natural lipids could stabilize specific local molecular conformations within the remaining less saturated lipids.