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Two novel compounds isolated from an amber sample from the Santonian of Piolenc (Vaucluse, SE France) were identified using nuclear magnetic resonance and high-resolution mass spectrometry as sulfurized analogues of diterpenic acids from the isopimaric series originating from ancient conifers possibly related to the Cupressaceae family. These two compounds are members of a diterpenoid series corresponding to early diagenetic transformation products of resin diterpenoids. They were likely formed once plant resin comes into contact with reduced sulfur species originating from bacterial sulfate reduction occurring in anaerobic settings such as mangroves or marshes. They represent the first evidence of sulfurization processes affecting plant resin prior to diagenetic transformation into amber. Given their mode of formation, these compounds may be used as indicators of sulfate-reducing processes in past depositional environments.

Summary The constitution of Baltic amber, the role of succinic acid and, more generally, of ester bonds in the constitution of macromolecular components of amber has been further investigated by chemical degradation of the solvent insoluble part of Baltic amber using butanolysis (BuOH/HCl). Succinic acid derivatives were the sole compounds released upon butanolysis whereas other compounds which could correspond to the alcohol counterparts of succinates could not be detected by GC-MS. This result indicate that these counterparts are all located on high molecular weight structural moieties. Succinic acid thus plays a key role as cross-linking agent between oligomeric structural moieties based on diterpenoids necessarily bound by at least one non-hydrolysable C-O or C-C bond.

The widely distributed aromatic di- and triterpenoids from higher plants occurring in sediments are formed by diagenetic microbial processes affecting their precursor plant lipids. These compounds and their stable isotopic composition (δ13C and δ2H) have the potential to be used for palaeoenvironmental and palaeoclimatic studies. In the present study, the isotopic composition of di- and triterpenoids aromatized to different extents has been measured to specifically examine the isotopic effects associated with the aromatization reaction. To overcome the possibility of multiple higher plant sources, as is generally the case with sedimentary lipids, the δ13C and δ2H values of aromatized di- and triterpenoids from lipid extracts recovered from conifer and angiosperm buried wood have been determined, allowing an unambiguous substrate/product relationship along the aromatization pathway to be assured. The results show that the δ13C compositions of both di- and triterpenes do not seem to be significantly affected by progressive aromatization, whereas the situation is different for δ2H values. In the case of diterpenoids related to abietic acid, a significant increase of the δ2H values by up to 86‰ with ongoing aromatization was measured. This is in contrast to what is expected for dehydrogenated compounds which should be globally more 2H-depleted than their precursor molecules (e.g., biosynthesized unsaturated fatty acids vs. their saturated precursors). This 2H enrichment of aromatized diterpenoids could indicate that they represent only minor residual intermediates, the majority having been further degraded by processes favoring the degradation of the 1H-containing substrates and having a moderately pronounced 12C/13C selectivity. With triterpenoids, preservation of the δ2H values was observed whatever the nature and extent of the aromatization process considered, which may be related to enzymatic reactions showing a limited influence on the hydrogen stable isotopic composition of the aromatized compounds.

A recent article (Said-Ahmad, W., Amrani, A., Aizenshtat, Z., 2013. The action of elemental sulfur plus water on 1-octene at low temperatures. Organic Geochemistry 59, 82–86) is commented on in this discussion. Radical mechanisms proposed by Said-Ahmad et al. (2013) for the formation of sulfurized and oxidized organic compounds in experiments involving elemental sulfur and 1-octene under aqueous conditions, aimed at investigating the interaction of organic matter and sulfur compounds under geological conditions, are not compatible with their experimental results and other studies. In addition, results from the experiments aimed at demonstrating the role of HO radicals in the formation of oxidized organic compounds were incorrectly interpreted by the authors. In this discussion, alternative mechanisms for the formation of the sulfurized and oxygenated products reported by Said-Ahmad et al. (2013) are proposed.

Euphorbia species are characterized by a net of laticifers producing large amounts of triterpenes. These hydrocarbon-like metabolites can be converted into fuel by the methods of the oil industry. Euphorbia lathyris is easily grown at an industrial scale. In an attempt to increase its triterpene production, the metabolic pathways leading to isoprenoid were investigated by incorporation of 13C labeled glucose and mevalonate and 2H labeled deoxyxylulose as well as by natural abundance isotope ratio GC-MS. Latex triterpenes are exclusively synthesized via the mevalonate (MVA) pathway: this may orient future search for improving the triterpene production in E. lathyris. Phytosterols and their precursors are mainly derived from MVA pathway with a slight contribution of the methylerythritol phosphate (MEP) pathway, whereas phytol is issued from MEP pathway with a minor contribution of the MVA pathway: this is in accordance with the metabolic cross-talk between cytosolic and plastidial compartments in plants. In addition, hopenol B behaved differently from the other latex triterpenes. Its 13C isotope abundance after incorporation of 13C labeled glucose and its natural abundance &delta, 2H signature clearly differed from those of the other latex triterpenes indicating another metabolic origin and suggesting that it may be synthesized by an endophytic fungus.

The article entitled “Ozonation of triterpenoids: Implications for early diagenesis of biomarkers in oxic environments” (Tay, K.S., Rahman, N.A., Abas, M.R.B, Simoneit, B.R.T., 2013. Organic Geochemistry 57, 34–40) deals with an investigation of the early diagenetic transformations undergone by higher plant triterpenoids under oxic conditions by means of laboratory experiments involving various triterpenes in the presence of ozone. Several aspects of the publication by Tay et al. (2013) are questionable, and are discussed in detail here. These comprise (i) the analytical procedure (based mainly on gas chromatography–mass spectrometry, GC–MS) used for the investigation of reaction mixtures likely to contain thermally labile (poly)oxygenated triterpenoids, (ii) the proposed mechanisms involving the hydroxyl radical as the key oxidizing species, (iii) the interpretation of mass spectra of the products and the structural assignments therefrom, and (iv) the geochemical relevance of the experiments with respect to non-biological oxidative alteration undergone by higher plant triterpenes in sediments.

International audience; Resinous material from conifers from the Pinaceae family is frequently found in an archaeological context. The material was used, notably, as waterproofing agent, as adhesive or for the caulking of boats. Two main types of material can be distinguished: resin, the exudate of conifer trees, and wood tar obtained by dry distillation of wood. Molecular investigation of such material aims, notably, at developing new molecular tools for the determination of the biological and geographical origin or of the manufacturing techniques, and for the discrimination between resin and wood tar. In this context, we report the identification by synthesis of alkyl guaiacyl dehydroabietates, which occur in a series of recent and archaeological conifer wood tar samples from shipwrecks and Gallo-Roman tar preparation sites. They most likely result from the reaction of dehydroabietic acid and alkyl guaiacols, the latter being typical wood pyrolysis products formed during the preparation of wood tar. Alkyl guaiacyl dehydroabietates are therefore proposed to be specific molecular markers for conifer wood tar, allowing a clear molecular distinction between this material and resin to be made. They are also more resistant to the alteration undergone by archaeological samples than other compounds previously proposed as markers of conifer wood tar such as anhydrosugars or alkyl guaiacols.

We report here a novel reductive coupling reaction of conjugated, non- or poorly enolizable aldehydes induced by H(2) S and operative in aqueous solutions under prebiotically relevant conditions. This reaction leads from retinal to β-carotene, and from benzylic aldehydes to the corresponding diarylethylenes. This novel reaction also opens a new potentially prebiotic pathway leading from glyoxylic acid to various compounds that are involved in the reductive tricarboxylic acid cycle. This C--C bond forming reaction of prebiotic interest might have been operative, notably, in the sulfide-rich environments of hydrothermal vents, which have been postulated as possible sites for the first steps of organic chemical evolution.

Laboratory experiments carried out under plausible prebiotic conditions (under conditions that might have occurred at primitive deep-sea hydrothermal vents) in water and involving constituents that occur in the vicinity of submarine hydrothermal vents (e.g., CO, H(2)S, NiS) have disclosed an iterative Ni-catalyzed pathway of C-C bond formation. This pathway leads from CO to various organic molecules that comprise, notably, thiols, alkylmono- and disulfides, carboxylic acids, and related thioesters containing up to four carbon atoms. Furthermore, similar experiments with organic compounds containing various functionalities, such as thiols, carboxylic acids, thioesters, and alcohols, gave clues to the mechanisms of this novel synthetic process in which reduced metal species, in particular Ni(0), appear to be the key catalysts. Moreover, the formation of aldehydes (and ketones) as labile intermediates via a hydroformylation-related process proved to be at the core of the chain elongation process. Since this process can potentially lead to organic compounds with any chain length, it could have played a significant role in the prebiotic formation of lipidic amphiphilic molecules such as fatty acids, potential precursors of membrane constituents.

The hypothesis of a low temperature natural “vulcanization” process as a potential mechanism for the formation of insoluble bitumen and H2S in reservoirs which have not undergone biodegradation, high thermal stress, or thermochemical sulfate reduction (TSR) has been investigated using laboratory simulation experiments. The experiments, involving elemental sulfur (32S and 34S), a low maturity oil and water at 200 °C in sealed gold tubes, clearly showed that elemental sulfur is able to induce the formation of H2S, polar compounds (resins and asphaltenes) and insoluble bitumen most likely by way of sulfur cross-linking processes. Specific organic sulfur compounds (thiophenes, dithiophenes and thienothiophenes) formed by the reaction of sulfur and hydrocarbons may be potential markers of such a process, but remain to be detected in natural samples.

The desulfurization of fuels (for example,diese loil) is a major concern of the petroleum industry worldwide because of the consequences for human health and the environment of high levels of sulfur dioxide emissions. In this context, a major problem encountered in refineries is the elimination of organosulfur components resistant to hydrodesulfurization processes. Although it has been shown that a substantial fraction of the organic sulfur compounds remaining after hydrodesulfurization is composed of mono-andpolyalkylated dibenzothiophenes (mainly 4,6-dialkyldibenzothiophenes),[1] the lack of knowledge concerning the structures of residual highly resistant organic sulfur compounds still appears to be the greatest handicap in progressing towards higher degrees of hydrodesulfurization.We report here the identification of a series of novel, terpenoid-derived, non-dibenzothiophenic polycyclic sulfides from highly desulfurized diesel oils. These 1,1,4a,6-tetramethyl-9-alkyl-1,2,3,4,4a,9b-hexahydrodibenzothiophenes1(9-alkylHDBT) were isolated from the aromatic fraction after oxidation to the corresponding sulfones 2 (9alkyl-HDBTO2).[2–4] The 9-ethyl homologue was unambiguously identified by mass spectrometry and NMR studies.

The reduction of allylic thiols to alkenes by hydrogen sulfide in aqueous solutions, a novel reaction that may explain reduction processes widely occurring in natural environments, has been discovered. Its mechanism has been studied and suggested to follow an S(RN)1-like pathway involving radical intermediates undergoing 1,4 hydrogen shifts. [reaction: see text]

The biodegradability of macromolecular organic structures of geological origin was investigated by performing in vitro studies. Cultures of the common Nocardioides simplex were grown, first, on a high molecular weight, asymmetric thioether (1-(phytanylsulfanyl)-octadecane 1) and then on macromolecular fractions isolated from a sulfur-rich oil. Gross data indicate that bacteria convert macromolecular substances to material of higher polarity by oxidizing the abundant thioethers to sulfones and sulfoxides and by introducing new functionalities, such as carboxylic acid, keto or hydroxyl groups. Furthermore, bacteria remineralize the macromolecular structures. Bacterially induced alterations were also studied on a molecular level after chemical desulfurization of the macromolecular structure. Thus, it could be established that the amounts of linear hydrocarbons in the macromolecular structure are decreased relative to branched and cyclic structures due to a preferential bacterial attack of the linear moieties bound to the macromolecules. This is further supported by the detection of S-bound fatty acids resulting from the bacterial oxidation of S-bound n-alkanes. Moreover, N. simplex also degraded sulfur-bound steranes by oxidation of the steroid side-chain leading to S-bound steroid acids.

Macromolecular fractions, isolated from the solvent extract of sulfur-rich Recent (Siders Pond, USA; Lake Cadagno, Switzerland; Walvis Bay, Namibia) and immature sediments (Gibellina, Messinian of Sicily; Vena del Gesso, Messinian of Italy), were investigated by chemical degradation using sodium ethanethiolate/methyliodide. This mild reagent which cleaves polysulfide bonds to yield methylsulfides has the advantage over other methods of leaving intact other functionalities (like double bonds) and preserving sulfur atoms at their incorporation site. The method is, therefore, well-suited to the molecular level investigation of sulfur-rich macromolecules from Recent sediments containing highly functionalized polysulfide-bound subunits. In Recent anoxic sulfur-rich sediments, the release of various methylthioethers clearly demonstrates that intermolecular sulfurization of organic matter does occur at the earliest stages of diagenesis. Steroids and phytane derivatives are the major sulfurized lipids, a feature also observed in more mature sulfur-rich sediments. Several phytene derivatives, such as cis and trans 1-methylthiophyt-2-enes, as well as methylthiosteroids, including 5α- and 5β-3-(methylthio)-cholest-2-enes, were identified by comparison with synthesized standards. Steroid methylthioenolethers are released from polysulfide-bound steroid enethiols present in the macromolecular fractions. The latter, which correspond to thioketones, can be considered as intermediates in the reductive sulfurization pathway leading from steroid ketones to polysulfide-bound saturated steroid skeletons and are characterized for the first time in the present study. Thus, it could be shown that the major part of the polysulfide-bound lipids occurring in Recent sediments is apparently the result of sulfurization processes affecting carbonyls (aldehydes and ketones). The unsaturated methylthioethers obtained from Recent sediments were not present in more mature evaporitic samples, which suggests that polysulfide-bound unsaturated thiols are intermediates formed during the first sulfurization steps occurring soon after deposition and that they are rapidly transformed by various processes taking place during early diagenesis, notably to yield their saturated counterparts.

Substantial amounts of alcohols occur in the desulfurization products of sulfur-rich nonpolar macromolecular fractions (NPMF) isolated from two crude oils and a sediment extract. These macromolecularly bound oxygenated compounds have been investigated in detail. Released straight chain components may have a hydroxy functionality at any position of the carbon skeleton and without any isomer predominance. Furthermore, the carbon-number distributions are very similar for the different alcohol isomers in each case and resemble those of the aliphatic hydrocarbons released by desulfurization. Thus, released hydrocarbons and alcohols likely originate from common functionalized precursors, most probably from polyunsaturated lipids of biological origin. Furthermore, they may derive from polyunsaturated components formed by elimination reactions on functionalized precursors which incorporated oxygen in free or already bound form at an early stage of diagenesis. The presence of hydroxyl functionalities at every position in the carbon skeleton suggests that double bond isomerization probably occurred in linear components prior to oxygen incorporation. Similarly, 2-hydroxy stanols released by desulfurization most likely result from oxygen uptake into Δ 2 -sterenes during diagenesis. The presence of mid-chain hydroxylated phytanols in the degradation products with OH-group mainly at the tertiary positions indicates that they result (at least partially) from oxygen incorporation into unsaturated phytane skeletons. Additional functionalities in the oxygenated substances, such as double bonds, aldehydes or allylic alcohols, may have served as substrates for reactions with sulfur species, resulting in sulfur-rich cross-linked macromolecular structures. The type of oxygen groups present in the macromolecules could be partially assigned by sequential chemical degradation experiments. The results indicate that free OH-functions are not abundant. Part of the oxygen is present as carboxylic acid, ester and ketone functions. However, the nature of a substantial part of the oxygen species remains unclear.

A novel series of di- to pentacyclic polyprenoid sulfides ( 6, 7, 15, 16 ) which are structurally related to the recently identified highly cyclised regular polyprenoid aromatic ( 1, 2, 3 ) and saturated hydrocarbons (5) and to the widely distributed tricyclopolyprenanes (e.g., 10 ) have been characterized in a wide range of sediments. Their distributions, extending from C 13 to C 30 , are clearly dominated by the C 15 , C 20 , C 25 and C 30 homologues, each being represented by several isomers. Two C 30 isomers ( 6a and 6b ), which are generally predominant, were isolated from a sample from Semecourt (Paris basin, France) and their structure established by NMR studies. Interestingly, these two isomers are the sole sulfides present in several samples. The structure of two C 20 isomers ( 7a, 7b ) was confirmed by synthesis of standards. These new sulfides clearly derive from precursors resulting from the incomplete cyclization of regular polyprenoids (e.g., 4 ). The presence of functionalities both on the side chain and, probably in the last ring, allowed intramolecular sulfur incorporation by a process similar to that leading to the formation of low molecular weight sulfides in sediments. Detection of these new polyprenoid sulfides in recent sediments indicates that the sulfurization step occurs at an early stage of diagenesis. The hydrocarbon skeletons of the lower di-, tri- and tetracyclic sulfides may derive from widespread terpenoids present in various organisms. The predominant pentacyclic homologues, however, have a rare and specific carbon skeleton which can not be related to any known biological precursor. The fact that these lower homologues always co-occur with the pentacyclic sulfides points to a common and specific origin for the whole series. Their origin seems, however, distinct from that of the related monoaromatic and saturated regular polycyclic polyprenoid hydrocarbons ( 1-3, 5 ) which are absent from the samples where sulfides occur. The carbon isotopic composition of two C 30 pentacyclic homologues ( 6a, 6b ) could be determined in two samples and suggests that their polyprenoid precursors originate either from primary producers or from heterotrophic organisms living in the oxic part of the water column.

Thioketones have been shown to be likely intermediates in the reduction of ketones and aldehydes to thiols by hydrogen sulfide ions, a reaction which plays an important role in the natural sulfurization of organic matter in sediments. The reduction proceeds by a thiophilic addition of HS− on the thioketone most likely via a single electron transfer mechanism.

A tetracyclic compound tentatively assigned as A -nor-friedel-8-en-10-one was recently reported by Bakar et al. (2011) [Bakar, N.A., Tay, K.S., Omar, N.Y.M.J., Abas, M.R.B., Simoneit, B.R.T., 2011. Applied Geochemistry 26, 1433–1445] from a Malaysian lake sediment. It was postulated to derive from friedelin via a sequence of diagenetic transformations involving the unprecedented removal of ring A and several hypothetical intermediates. We considered that this structural assignment needed to be reassessed, notably because we could detect the compound in wood samples devoid of friedelin-related triterpenes. Firm identification was also needed since the compound is becoming used as a proxy in recent publications and its occurrence interpreted in terms of palaeoenvironmental reconstruction. In the course of archaeometric studies of ancient buried wood, the presence of the compound as a predominant constituent of the lipid extract of a buried alder wood sample gave us the opportunity to firmly establish its structure. We report here its unambiguous identification using 1D and 2D nuclear magnetic resonance (NMR) spectroscopy after its isolation. Based on its structure, geochemical distribution and stable carbon isotopic composition, it appears that the compound likely does not derive from triterpenoids biosynthesized by higher plants, but might derive from a precursor terpenoid synthesized by microorganisms (bacteria, fungi) living within the buried wood, and possibly involved in the degradation of plant organic matter (wood, notably).

Novel aromatic carotenoid derivatives 7 and 8 have been identified by synthesis of reference compounds in a H2/PtO2-hydrogenated fraction from the organic extract of a lake sediment (lake Cadagno, Switzerland). They derive from unreported carotenoids presumably biosynthesized by purple sulfur photosynthetic bacteria (Chromatiaceae) and represent potential biomarkers to establish the occurrence of photic zone anoxia in ancient ecosystems.

A novel series of unusual A/B diaromatic 14-methylsteroids was identified by total synthesis of reference compound 1a . They constitute the major aromatic hydrocarbon components from Pakistani biodegraded crude oil seeps. They probably derive from the aromatization of ring A functionalized 14-methyl steroid precursors present in green algae.

Several oleanane-related triterpenoids bearing a unique C-2 oxygenated functionality have been identified as the predominant triterpenoids from a 4900 year old oak wood sample buried in a freshwater sediment. They likely represent specific molecular tools that can be used as markers to reconstruct past vegetation assemblages, or to recognise severely altered oak wood at archaeological sites.

A novel hexane-soluble nonpolar macromolecular fraction (NPMF) has been found to occur in substantial amounts (up to 32%) in sulfur-rich crude oils and a rock extract. It is highly aliphatic and has a molecular weight culminating at several thousand mass units, as proven by spectroscopic and molecular weight studies. C-S bond hydrogenolysis of NPMF with Raney nickel as a catalyst yields high proportions of aliphatic hydrocarbons in which long linear, acyclic polyisoprenoid and carotenoid chains usually predominate (except in one case) over polycyclic structures, such as steroids and hopanoids. Hence, NPMF consists mainly of macromolecules composed of low molecular weight hydrocarbon subunits cross-linked with sulfide bridges. Use of deuterated Raney nickel indicated in one case (Rozel Point oil) that the long chains and some hopanoids are multiattached to the macromolecular network, whereas other structural subunits, such as steroids or gammacerane, are essentially monoattached. Detailed structural determinations of the hydrocarbon “building blocks” of NPMF give information on their origin and the mode of formation of these macromolecules in the subsurface. Indeed, most of the building blocks can be related to algal (e.g., long linear chains, steroids, β-carotene, and related carotenoids) or bacterial (e.g., acyclic and monocyclic carotenoids, long-chain acyclic isoprenoids) precursors which essentially exist in living organisms as monounsaturated or polyunsaturated species or are easily transformed into such species by diagenetic processes (e.g., steroids). It appears that these alkenes or polyenes become selectively trapped into a macromolecular network by reaction with inorganic sulfur species produced by bacteria in a kind of natural, low-temperature, vulcanization process. This process could start at early diagenesis already in the water column or eventually continue in the bottom sediment. Although its exact nature is yet unknown, it seems likely that the cross-linking reaction can be initiated by the cleavage of sulfur species in a radical type mechanism. The alkanes formed upon desulfurization of NPMF usually represent much higher amounts than the free alkanes of the samples and show a dramatically different composition. They may deliver very useful, complementary information in studies related to source and palaeoenvironment.

A novel series of unusual A/B diaromatic 14-methylsteroids was identified by total synthesis of reference compound 1a . They constitute the major aromatic hydrocarbon components from Pakistani biodegraded crude oil seeps. They probably derive from the aromatization of ring A functionalized 14-methyl steroid precursors present in green algae.

International audience; Four oleanane-related triterpenoid ketones and phenols isolated from an archaeological piece of oak wood have been identified by NMR studies. Their structures give clue to the diagenetic transformation of 2,3-oxygenated higher plant triterpenoids in the environment

A novel thiophene 1 derived from higher plant triterpenoids of the oleanane series was detected in sediments deposited in evaporitic environments and identified by synthesis.

Polycyclic polyprenoid hydrocarbons and related demethylated compounds have been identified in severely altered bitumen from oil stained rocks of Upper Jurassic/Lower Cretaceous age. They occur as three series, one homologue of which has been isolated and structurally characterized from nuclear magnetic resonance (NMR) studies. They comprise hydrocarbons demethylated at the A/B ring junction, compounds demethylated at rings E/F/G and a novel series of compounds demethylated at both the ring A/B junction and the ring E/F/G junction, identified for the first time. The occurrence in a number of unaltered and biodegraded oils and source rocks of Upper Jurassic/Lower Cretaceous age, of non-demethylated hydrocarbons, together with related series demethylated at rings E/F/G, indicates that the demethylation process is unlikely to be related to a late degradation process, but rather results from the early transformation of precursors bearing functionalised methyl groups on rings E/F/G. In contrast, polycyclic polyprenoid hydrocarbons demethylated at the A/B ring junction occur only in the most biodegraded samples, suggesting that this demethylated series is formed at later stages of alteration by further demethylation of both non-demethylated compounds and compounds demethylated at rings E/F/G. In addition, a novel series of carboxylic acids related to the polycyclic polyprenoids has been tentatively identified using gas chromatography–mass spectrometry (GC–MS) and comprises both non-demethylated and demethylated structures at rings E/F/G. It is proposed that the acids represent alteration products of polyprenoids bound to aromatic sub-units from macromolecular material that have been released upon severe oxidation during exposure to biodegradation/weathering.

Two bridgehead-alkylated 2-thiaadamantanes (1,5-dimethyl and 1-methyl) have been identified in petroleum; these compounds give clues to sulfurisation processes affecting petroleum which has undergone high thermal stress.

We report here on the identification of two novel hexacyclic alkanes (C33 and C35) occurring in bitumen. The C35 compound 1 was identified by comparison with a standard obtained by synthesis involving a biomimetic proton-induced extensive cyclisation of an acyclic heptaprenoid. This cascade cyclisation allows the formation of eleven asymmetric centres present in the natural compound in only one step. The C33 analogue 2 was identified by NMR studies after isolation from the saturated hydrocarbon fraction of a bituminous rock. Both compounds are “orphan” molecular fossils of biological lipids of unknown origin formed by the extensive cyclisation of higher regular polyprenoids.

Five series of crude oil samples exposed to atmospheric conditions have been analysed at the molecular level, each series comprising several samples originating from the same crude oil but altered to different extents. The aim of our investigation was to compare the specific impact of abiotic oxidation to other alteration processes such as biodegradation, evaporation and water washing. Bulk analyses revealed that increasing alteration is accompanied by an increase in oxygen content which parallels a relative increase of the proportions, as well as of the molecular weights of the macromolecular constituents of the bitumens. Gas chromatographic–mass spectrometric analyses of polar fractions showed the presence of oxygen-containing compounds (steroid ketones, benzothiophenic acids and sulfones) which result from oxidation of petroleum lipids. The hypothesis that part of these oxygenated compounds results from abiotic oxidation processes rather than from biodegradation is supported, notably, by the fact that oxygen incorporation generally occurred without any diastereomeric discrimination. This is also supported by simulation experiments performed on petroleum lipids, which showed that abiotic oxidation induces cleavage reactions affecting C–C and C–S bonds which may intervene in the transformation of geomacromolecules in the environment by degradation (“depolymerization”). Thus abiotic oxidation may play a major role in the fate of petroleum pollutants in the environment by transforming lipidic organic matter from petroleum into more water soluble and, therefore, more biodegradable constituents. However, these can be more toxic to the environment as the water-soluble fraction may be easily taken up by biota.

A novel heptacyclic C37 alkane presenting a regular polyprenoid structure has been isolated from a biodegraded bituminous rock and identified by NMR; this hydrocarbon is the most highly cyclized polyprenoid alkane ever completely identified; the absence of specific methyl groups give clues to unprecedented biological precursor lipids resulting from the extensive cyclization of regular octaprenoids.