Occurrence and biomarker potential of 23-methyl steroids in diatoms and sediments |
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| Authors: | Sebastiaan W Rampen Stefan Schouten Ellen C Hopmans Ben Abbas Anna AM Noordeloos Jan AJ Geenevasen J Michael Moldowan Peter Denisevich Jaap S Sinninghe Damsté |
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| Institution: | 1. NIOZ Royal Netherlands Institute for Sea Research, Departments of Marine Organic Biogeochemistry and Biological Oceanography, P.O. Box 59, 1790 AB Den Burg, The Netherlands;2. University of Amsterdam, Van’t Hoff Institute for Molecular Sciences, Nieuwe Achtergracht 129, 1018 WS Amsterdam, The Netherlands;3. Stanford University, Department of Geological and Environmental Sciences, Stanford, CA 94305-2115, USA |
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| Abstract: | 23-Methyl sterols have been reported to be synthesized by a few marine algae, but unambiguous identification of 23-methyl steroids in sediments and petroleum is lacking. We report the presence of 23-methylcholesta-5,22E-dien-3β-ol in 14 out of 106 diatom cultures, thereby showing that diatoms, together with dinoflagellates, may be an important environmental source for such steroids. Synthesis of authentic 23-methylcholestanes showed that their mass spectra are identical to those of 24-methylcholestanes, but that they elute earlier on apolar stationary phases during gas chromatography (GC) analysis. Co-injection of the authentic standards with sediment extracts revealed the presence of these compounds in the Skole unit of the Oligocene Menelite Formation, the Miocene Monterey Formation and the Messinian Vena del Gesso Formation. In addition, we tentatively identified 23,24-dimethyl-27-norcholestanes in some of these sediments. Molecular clock calculations suggest that diatoms are a possible source for 23-methyl steroids in sediments and petroleum from the late Jurassic onwards. |
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