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PACLIVA Informe resumido

Project ID: EVK2-CT-2002-00143
Financiado con arreglo a: FP5-EESD
País: Spain

Method to characterise alkenone composition

Alkenones are produced by algae and, extracted from marine sediments, are used as a proxy for sea surface temperature. This work improves the characterisation of the chemical composition of alkenones. A method for the location of the double bonds in these compounds was developed. Cyclopropylamine was used as derivatisation reagent for the first time. It was found to give high reaction yields, high GC retention time differences between derivatives and precursor compounds, and virtual absence of by-products. Examination of a large group of alkenones from cultures of Emiliania huxleyi, recent and ancient sediments with cyclopropylamine derivatization showed that in all cases the double bonds were located at the same carbon atom distance from the carbonyl group and spaced in intervals of five methylene groups either from the carbonyl or between them, e.g. at sites 7, 14, 21 and 28. This result corrects previous assumptions in which double bond positions were situated by reference to the methyl end.

4,4-Dimethyloxazoline derivatization of hexatriacontenoates present in the same samples showed that these compounds have also their unsaturations with seven carbon atom spacing and counting by reference to the carboxyl group. The concurrence of both series of isomers in compounds of different oxygen functionalities indicates that the precursor hapthophycean algal species have a major biosynthetic pathway leading to the formation of these lipids. The data presented in this work unify the structures of the known alkenones in the present and the recent past under a common metabolic pathway.

For the first time the scientific community has a robust method for the determination of double bond positions in alkenone mixtures of interest for paleoclimatic studies. The application of this method to all types of alkenone distributions know to date has shown that all isomers have the double bond locations in the same position relative to the carbonyl group. This finding is important for paleoceanographic studies because it reveals a strong uniformity in the alkenone mixtures used for paleotemperature estimations in all sorts of marine environments and time periods. The relationship between alkenone distributions and sea surface temperature estimates is therefore reinforced.


Joan GRIMALT, (Vice-director)
Tel.: +34-934-006118
Fax: +34-932-045904
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