Armand Buchs

Novel triterpene-derived hydrocarbons of the arborane/fernane series in sediments: Part II

Two ring-B aromatized triterpenes related to the arborane/fernane series were isolated from an Italian Triassic black shale (4 and 7) and a French Jurassic laminated bituminous limestone (7). They were identified by MS and NMR spectroscopy. These compounds, 25-norferna-5,7,9-triene 7 (C29) and 22,25,29,30-tetranor-18β-ferna-5,7,9-triene 4 (C26), in the case of the Italian sediment, belong to a family which extends to at least C32 as shown by GC-MS. The presence of higher homologs and ring-A methylated structures in the Italian Triassic shale is analogous with the hopane series, which together with carbon isotopic data obtained by gas chromatography-isotope ratio mass spectrometry (GC-IRMS), strongly support a bacterial origin for most of these compounds. This suggests that 4 and 7 may result from a yet unrecognized rearrangement of sedimentary hopenes which have subsequently undergone ring-B aromatization. As an alternative, the C29 compound 7 could arise from C30 precursors not necessarily of bacterial origin (fernenes?). This hypothesis would apply particularly to the case of the Jurassic limestone, which does not show any trace of 4 nor of compounds with an extended side chain or a methyl group on ring A. Related structures also bearing an isopropyl group could derive by microbiological transformations from the corresponding fernen-3β-ols or isoarborinol as can be deduced from the occurrence of ring-A degraded monoaromatic hydrocarbons 3 and 5.

Steroidal ketones in the early diagenetic transformations of Δ5 sterols in different types of sediments

Incubation experiments of cholesterol labelled with various isotopes (2H, 3H and 14C) were performed in two different types of sediment, one highly oxygenated and the other completely anoxic, to ascertain the presence and the role of steroidal ketones in the early diagenesis of unsaturated sterols. Two different pathways for the hydrogenation of cholesterol have been observed, depending on the oxygenation rate of the sediment. If the intermediacy of steroidal ketones is evident in the oxic sediments of Lake Leman (Switzerland), a direct reduction of the Δ5 double bond also occurs in the anoxic sediments of Motte Lake (France).

Comparison of extraction techniques for bound carboxylic acids in Recent sediments: 2. β-Hydroxyacids

Abstract Various multi-step extraction procedures were used in order to determine the β-hydroxyacid content of a Recent lacustrine sediment. Similar distribution but important quantitative differences were noted. All the β-hydroxyacids are derived from the same origin but the commonly used methanolic saponification is inappropriate for the release of bound β-hydroxyacids. All the extraction techniques produce either 3 -methoxy or 3 -chloro and Δ 2 -unsaturated carboxylic acids as artifacts from the 3 -substituted fatty acids. A two-step procedure is recommended for the extraction of the maximum amount of β-hydroxyacids with the minimum formation of artifacts.

Extraction of biomarkers from sediments with supercritical carbon dioxide : a comparative study with solvent extraction and thermodesorption methods

Supercritical fluid extraction of rocks with CO2 (SFE-CO2) can advantageously replace the organic solvent extraction technique (SE) which is generally used for the analysis of the biomarkers. The powdered rock is extracted by carbon dioxide supercritical fluid at 55°C and a pressure of 31 MPa. After decompression in a capillary restrictor, the CO2 is volatilized and the extracted compounds are trapped in hexane. An aliquot can then be directly injected into a dual GC-FID-FPD or GC-MS system. The total extraction procedure takes only 45 min and the results obtained for hopanes and steranes are in very good agreement with those of liquid solvent extraction, which requires several hours. A comparison with thermodesorption is also presented.

A novel sedimentary lacustrine chlorin: Characterisation and geochemical significance

We report the isolation and the characterisation by D/MS, HR-MS and 1H-NMR of a new sedimentary lacustrine chlorin with a seven membered ring. A geochemical degradation pathway is proposed on the basis of the seven membered ring resistance to degradation.

Several unexpected marine sterols in a freshwater sediment

Abstract Some unexpected stanols, 22,23-methylene-23,24-dimethyl-5α(H)-cholestan-3β-ol (gorgostanol and the related stenol), 24,26-dimethyl-5α(H)-cholestan-3β-ol (aplystanol) and most probably 24-isopropyl-5α(H)-cholest-22-en-3β-ol, have been found in the sediment of a eutrophic pond. These compounds possess side chains which have until now been considered to belong exclusively to sterols of marine origin. The presence of these stanols in a freshwater sediment suggests that considering their side chain structures as specific marine input markers can lead to erroneous conclusions. The vertical distribution of these compounds along a 6 m core shows that they arise from organisms which still exist except for aplystanol which was found only in the sections below 5 m.

Capillary gas chromatography-mass spectrometry and identification of substituted carboxylic acids in lipids extracted from a 4000-year-old nubian burial

Polar carboxylic acid fractions of lipids extracted from samples from a 4000-year-old Nubian mummy were investigated by capillary gas chromatography mass spectrometry. They contain series of alpha,omega-dicarboxy, monohydroxy, dihydroxy and keto fatty acids, some of which were found for the first time outside the synthetic laboratory. Their chromatographic and mass spectrometric characteristic properties are reported.

Comparison of extraction techniques for bound carboxylic acids in Recent sediments: 1. Unsubstituted monocarboxylic acids

Abstract After the solvent extraction of the unbound lipids contained in a Recent lacustrine sediment, the remaining bound monocarboxylic acids were released by applying multi-step hydrolysis procedures. The relative and absolute abundances of these acids in the various hydrolysates differ greatly, thus clearly demonstrating that reliable comparisons of the fatty acid contents and distributions in various sediments require identical extraction methods. Systematic investigations show that after mild hydrolysis using either 5% KOH - methanol or 2 N HCl, the sediment still retains a large part of its fatty acids, which can be extracted after either hydrolysis in 6 N HCl or thermal treatment in 2 N KOH. The hydrolysis in HCl is much more efficient, but produces artifacts. The amounts of tightly bound fatty acids released by such treatments are important with respect to the total acid content and most of these acids are of bacterial origin. Their incomplete extraction would thus lead to greatly underestimating the microbial contribution to the sedimentary fatty acids.

A mass spectrometry and optical spectroscopy investigation of gas-phase ion formation in electrospray

To determine the limitations of electrospray mass spectrometry for the study of condensed-phase chemistry, it is important to understand the origin of cases for which the electrospray mass spectra, which are a measure of the relative abundances of gas-phase ions, do not reflect the equilibrium ion abundances in the solution electrosprayed. One such divergent case is that of free-base octaethylporphyrin. Under conditions for which this porphyrin is present in solution predominantly as the doubly charged, diprotonated molecule, the predominant ionic species observed in the electrospray mass spectrum is the singly charged, monoprotonated molecule. In this paper, direct optical spectroscopic measurements of the ions in solution (absorption spectra) and in the electrospray plume (fluorescence excitation spectra) are correlated with the ion distribution observed in the gas-phase (as reflected in the electrospray mass spectra) to determine at what point in the electrospray process and by what mechanism(s) the transformation from dication to monocation occurs. The data indicate that the major portion of the doubly protonated porphyrin species originally present in solution are converted to singly protonated species relatively late in the electrospray process, during the latter stages of droplet desolvation in the atmospheric/vacuum interface of the mass spectrometer, via the loss of a charged solvent molecule/cluster.

Unsubstituted and Hydroxy Substituted Fatty Acids in a Recent Lacustrine Sediment: (Lake Léman, Geneva, Switzerland)

Abstract Unsubstituted as well as α-, β- and (ω-1)-hydroxy substituted fatty acids were analyzed in a 5 m long sediment core taken from Lake Leman (Switzerland). All these acids occur in three forms: unbound, bound and tightly bound and our results show that there is no conversion from one form to another. The fact that below a burial depth of 30 cm the abundance profiles show no decreasing trend indicates that the diagenetic reactions do not operate below that depth. On the basis of our results, compared with other published data, source correlations are postulated for each of the acid classes. The presence of unsubstituted monounsaturated acids in the C20 to C32 range probably indicates that long chain fatty acids cannot be considered only as indicators of inputs from higher plants. Finally, C27, C29 and C31 (ω-1)-hydroxyacids with unusual structures have also been found in these sediments, as well as 2-methyl nonacosanoic acid; their origin has not yet been established.