Liquid molecular model explains discontinuity between site uniformity among three N-3 fatty acids and their 13C and 1H NMR spectra

Numerous health benefits of seafoods are attributed to their n-3 long-chain polyunsaturated fatty acid content. especially eicosapentaenoic arid (EPA; 20:5n-3) and docosahexaenoic acid (DHA: 22:6n-3). EPA. DHA and their precursor alpha-linolenic add (ALA; 18:3n-3) differ vastly biochemically, but from a physical chemical standpoint are close structural analogs. There remains, for example, no satisfactory explanation why only DHA can be utilized in fast signal processing tissues such as neuronal, retinal and cardiac. Recently, gradient temperature Raman spectroscopy has identified key lipid structural differences that require further NMR elucidation. H-1 and C-13 1D experiments were performed on neat EPA. DHA, and ALA and 4 different 2D experiments on EPA. The methine( 13)C spectra show six chemical shifts for ALA: 10 for an EPA, and 12 for DNA. The chemical shift of the first -C=closest to the Cl carbonyl site is always the most upfield; that of the last - C= closest to the methyl end is always the most downfield. H-1 chemical shift of almost none of the methine protons match. The C-13 paired molecular sites identified as conformationally redundant are not identical to the H-1 molecular sites identified as con forrnationally paired. For EPA, long-range coupling is stronger and extends longer at the methyl-ended Cl 8 to C10H(2) section and is shorter at C5 to C7H(2); also C18= and =C17 coupling differ. Repeating (H-C=C-H)-CH2 moieties are planar: unequal torsion alters both curvature and twist both ends of the lipids. The methyl end is the most elastic. Asymmetry in twist between the two ends results in torque at the methylene site near the geometric center, resulting in unusually strong electron C-13 and H-1 shielding. Published by Elsevier B.V.