Characterisation of monounsaturated fatty acids from an estuarine sediment

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PREVIOUS investigations of fatty acids in marine sediments have primarily been concerned with the concentrations of the individual acids rather than their chemical configuration1-4. Brown and Swidler5 have demonstrated the ability of clay to catalyse the conversion of oleic acid (18:1Δ9 cis) to elaidic acid (18:1Δ9 trans) accompanied by extensive rearrangement of the double bond position. (18:1= normal carbon chain length: Number of double bonds). As most biologically produced olefinic acids are believed to be in the cis configuration, diagenetic changes in the sediment may alter the cis isomers to the more stable trans isomers, as well as cause migration of the double bond. Consequently, investigations of the monounsaturated fatty acid cis/trans ratio and position of the double bonds, with depth in the sediment, may yield significant information on diagenetic pathways of these acids. We have determined the presence of small amounts of palmitelaidic acid (16:1Δ9 trans) and elaidic acid (18:1Δ9 trans), as well as other positional isomers of these trans acids, in a Recent estuarine sediment. In addition, we have also confirmed that the major monounsaturated fatty acids are palmitoleic acid (16:1 Δ9 cis) and oleic acid (18:1Δ9 cis). We give here the methods for isolating these acids and confirming their structures, and their geochemical significance is discussed. © 1976 Nature Publishing Group.

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