Steroid Hydrocarbons Research Articles

Short-chain A-ring methylated steroidal hydrocarbons

The distribution of steroids bearing short side-chains on the D-ring, with particular emphasis on the A-ring methylated series, is investigated over the late diagenesis-early catagenesis maturity range, by GC–MS analysis of a range of oils and selected immature source rock bitumens. A number of C19 steranes are commonly observed in oils, including 5α,14β-androstane and a compound tentatively identified as 4α-methyl-5α,14β-androstane. C21 and C22 desmethyl steranes, along with minor amounts of C23–C25 homologues, are ubiquitous, among which, by oil-window maturity, the 5α,14β,17β (diginane) isomers dominate, based on high m/z 218/217 ratios. The previously identified and commonly occurring C21 and C22 13β,17α-diapregnanes are accompanied by lesser amounts of their later-eluting 13α,17β isomers. 3-Methyl steranes appear limited to 5α,14β,17β isomers, primarily the C22 and C23 members, with no detectable corresponding diasteranes. Although relatively minor components overall, they are the main, if not only, methyl steranes in pre-Mesozoic samples. These distributions are consistent with the previously proposed mostly catagenetic generation from sterols bound to kerogen via their 3-hydroxy group with concomitant methylation at C-3 (in competition with reduction yielding desmethyl species). 4-Methyl steranes seem to be confined to post-Paleozoic samples, although trace amounts in older samples cannot be excluded. C22 components dominate, comprising 4α-methyldiginane and a compound suggested to be 4β-methyl-13β,17α-diapregnane, the latter identification being supported by close covariance of its abundance with that of the corresponding desmethyl 13β,17α-diapregnane. A much smaller amount of what appears to be 4β-methyl-13α,17β-diapregnane is present; again, its relative abundance closely covaries with that of its desmethyl analogue. In addition, the relative abundances of these proposed 4-methyldiapregnanes correlate negatively with 4-methyl diasterene and positively with diapregnane contents in immature bitumen, further supporting the proposed identifications. The reason for the meagre amounts of C23 4-methyl steranes is unclear, some possibilities are considered. Unlike their saturated counterparts, triaromatic pregnoids consistently exhibit methylation at C-2, C-3, C-4 and C-6, regardless of geological age, with C-3 and C-4 being most abundant, as also observed among C27+ homologues. We suggest it reflects a degree of random, geochemical methylation/transmethylation of aromatic pregnoids, as recognized for methylphenanthrenes. It is most obvious in oils from pre-Mesozoic marine sources, but is concealed in oils from younger sources by abundant biological contributions of 4-methyl steroids, resulting in a broadly linear positive correlation of the 4-methyl/3-methyl ratios for saturated and triaromatic pregnoids.

The La Luna Formation, Venezuela: A prospective unconventional reservoir

Since the early 2000s, the exploitation of unconventional reservoirs has become very important to the oil and gas industry because of their high potential source of energy and economic value. Venezuela possesses a world-class hydrocarbon source rock in one of the most prolific hydrocarbon basins in the world, namely the Cretaceous La Luna Formation in the Maracaibo Basin. Outcrop and core samples collected from the northwestern Maracaibo Basin provide the database for this study. A comprehensive multiscale characterization of the samples is undertaken to unravel the stratigraphic properties of the petroleum system. In addition, a geochemical approach is taken to evaluate the prospectivity of the La Luna Formation as an unconventional resource in the Maracaibo Basin. Rock-Eval pyrolysis and biomarker data indicate that the La Luna Formation is dominated by type II kerogen, indicating an oil-prone marine organic matter origin. Total organic carbon values range between 3.85 wt% and 9.10 wt%. Distributions of isoprenoids, steranes, and terpanes including gammacerane and monoaromatic steroid hydrocarbons indicate a hypersaline, marine carbonate anoxic depositional environment. Thermal maturity parameters indicate that most of the cores are currently in the oil window. This combined stratigraphic geochemical study indicates that the La Luna Formation has excellent potential as an unconventional reservoir for oil and gas in the study area.

The diagenetic continuum of steroid hydrocarbon transformation from early diagenesis into the oil window

Steroids and their derivatives are ubiquitous in the sedimentary rock record, where they are widely applied as biological or geochemical markers to determine organic facies as well as thermal maturation of bitumen and oils covering the diagenetic to catagenetic stages. The diagenetic continuum from early diagenesis into catagenesis of steroids has not been extensively studied despite the importance of these reactions in influencing the successive continuum of late diagenetic transformations.This study utilizes a stratigraphically constrained transect of 9 wells from the Upper Cretaceous Second White Specks and Belle Fourche formations of south-central Alberta, Canada ranging in thermal maturity from 0.2 %VRE to 0.8 %VRE. Biomarkers were examined from 69 samples from 8 wells and thermal maturity was determined from 87 samples from 9 wells using HAWK programmed pyrolysis analysis. Relative and absolute abundances of regular sterane, diasterene, diasterane, monoaromatic steroid, and triaromatic steroid biomarkers and changes in the proportions of steroid compound classes were determined and evaluated for thermal maturity. Additionally, isomerization ratios within each of the compound classes were examined with increasing thermal maturation.Rearranged diasterenes initially dominate the steroidal hydrocarbons, followed by diasteranes in the late diagenetic and catagenetic stages and at peak oil maturity (0.8 %VRE) diasteranes were most abundant. The relative abundance of a steroid is initially controlled by its rate of production or isomerization from a biological precursor, but at higher thermal maturities selective catagenetic destruction alters the relative abundance of steroid classes, with aromatic steroids and regular steranes being degraded or expelled earliest. Thermal maturity parameters based on the isomerization of regular steranes, and the aromatization of monoaromatic steroids are effective thermal maturity indicators in specific but overlapping ranges beginning at 0.2 %VRE. This work represents a novel examination of a natural thermal maturity transect and helps to consolidate our understanding and application of the diagenetic transformations of steroid compounds.

Permian and Triassic hydrocarbon migration and accumulation in the Cainan area, Junggar Basin, China

Gas Chromatography-Mass Spectrometer (GC-MS), chloroform asphalt “A”, and carbon isotope measurements were used to determine hydrocarbon migration pathways. This study focused on hydrocarbon migration pathways and accumulation distribution in the Wucaiwan region, Junggar Basin, China. The biometric parameters were used to compare oil sources. Type and distribution characteristics of natural gas were determined in order to study the different strata. Quantitative grain fluorescence (QGF) and quantitative grain fluorescence on extract (QGF-E) were analyzed to determine the hydrocarbon migration and charging periods. Geochemical indexes, such as, n-alkane, triterpenoids, sterane, and hopane, were utilized to investigate the pathways of hydrocarbon migration. Recent studies on petroleum maturity have focused on comparison of source rocks and reported that the maturity effects of source rock and reservoir oil are weak, while those effects are high in the Liuchu area. Analysis of triterpenoid and steroid hydrocarbon biomarkers elucidate the underground petroleum migration pathways to the reservoirs. Geochemical analyses of hopane and cholestanes were used. The ααα C29 (20 S)/(20 S + 20 R), C29ββ/(αα + ββ), and C31 hopane 22R/C30 hoopane ratios, and C19/C21 tricyclic terpane ratio, C19/C21 tricyclic terpenes, C31 (22 S)/(22 S + 22 R), and C29 (20 S)/(20 S + 20 R) ratios were analyzed to determine the maturity of crude oil. Petroleum migrated along fault, sandbody, and unconformity, which suggest vertical and lateral migration occurred. Reservoir sandstone porosity and mudstone content of the thick caprock are likely to limit lateral hydrocarbon migration. Petroleum migration and accumulation primarily occurred by vertical migration and lateral migration was weak. The study offers an improved understanding of uncertain hydrocarbon migration pathways and further developed the hydrocarbon migration and accumulation models.

Aromatic hydrocarbons as parameters of oil formation conditions

Aromatic hydrocarbons in the oils of Absheron and Baku archipelago, as well as in coastal zones have been identified via the method of chromato-mass-spectrometry. Geochemical estimation of distribution character of main biomarkers and their correlations as well is presented. The similarity in the distribution of monoaromatic and triaromatic steroid hydrocarbons, as well as benzogopane and sekabenzogopans has been specified, which suggests that studied oils are associated with one source rock or organic facies. The varieties observed in the distribution of saturated steranes are most likely the result of differences in the values of thermal maturity or the processes of secondary alterations.

Mixing scenario of a vagarious oil in the Dongying Depression, Bohai Bay Basin

An oil from the third Member of Shahejie Formation (Es3) in well C104 from the Dongying Depression, Bohai Bay Basin, exhibits a vagarious mixing scenario of considerably distinctive maturities. Detailed molecular geochemical analysis was performed on eight oil samples and ten source rock samples from the Paleogene Shahejie Formation and Mesozoic strata by gas chromatography–mass spectrometry analysis. Biomarkers such as terpanes, steranes and aromatic steroid hydrocarbons are abundantly preserved in the C104 oil, with the predominance of high-molecular-weight biomarkers for each class of components, such as pentacyclic terpanes and tricyclic terpanes, regular steranes and pregnanes, suggesting that the C104 oil is “immature”. However, the high values of maturity parameters derived from aromatic hydrocarbons consisting of MNR, DNR, TMNr, TNR1, TNR2, MPI-3 and MBPI indicate that the C104 oil has been highly mature. Hence, the C104 oil from the Es3 reservoir in the Dongying Depression witnessed multiple episodic charges of distinctive maturities and sources with highly mature source interfused into the immature fractions. Based on oil-oil and oil-source correlations, the “immature” fractions of the C104 oil are mainly from the source rocks of the Es4 Member in the Shahejie Formation, while the “highly mature” fractions of the C104 oil possess the possibility of Mesozoic sources. Potential highly mature source rocks in the Mesozoic strata probably remain undiscovered in the Dongying Depression, Bohai Bay Basin.

Oil-source and oil-oil correlations and the origin of the heavy oil and bitumen accumulations in Northern Alberta, Canada

The saturated and aromatic hydrocarbon compositions of potential source rock samples from the Devonian/Carboniferous Duvernay, Exshaw, and Lower Banff formations, the Triassic Doig Formation, and the Jurassic Gordondale (Nordegg) and Poker Chip Shale formations in the Western Canada Sedimentary Basin (WCSB) were investigated by gas chromatography–mass spectrometry (GC–MS). The study also included produced oils from the Cretaceous Clearwater play at Marten Hills and Peace River, oil sands cores from Athabasca and Cold Lake areas, and bitumen hosted in the Grosmont carbonate deposits.Oil-oil and oil-source correlation based on the aromatic steroid hydrocarbon compounds is enabled by their strong resistance to biodegradation and their presence in all reservoir samples analyzed. In addition, of the aromatic steroids hydrocarbons, triaromatic-dimethylcholesteroids (TA-DMC) and triaromatic dinosteroids represent age-diagnostic biomarkers that distinguish Paleozoic versus Jurassic sources. The Duvernay, Exshaw, and Lower Banff extracts lack TA-DMC and triaromatic dinosteroids, whereas extracts from the Gordondale and Poker Chip Shale display appreciable quantities of TA-DMC and triaromatic dinosteroids. Meanwhile, the Doig falls between the Gordondale/Poker Chip Shale and Duvernay/Exshaw source types in terms of the distribution of these triaromatic steroids. The compositions of TA-DMC and triaromatic dinosteroids in the oil sands and Grosmont bitumen are remarkably similar, confirming that these oil deposits are genetically related. The aromatic steroid hydrocarbon compositions of the oil sands and Grosmont bitumen most strongly resemble those for the Gordondale and Poker Chip Shale. Saturated biomarker features of the oil sands and Grosmont carbonate bitumen including 28,30-bisnorhopane and high diasteranes relative to regular steranes, although lacking in the Gordondale extracts, may be introduced through mixing with oil generated from the Poker Chip Shale. However, plots based on aromatic steroids and source-specific biomarkers such as aryl and diaryl isoprenoids indicate some degree of mixing with Duvernay and/or Exshaw contributions. This is also supported by a mixing model employing the averaged concentrations of methyltriaromatic steroids from endmember Gordondale and Exshaw extracts. These findings along with additional biomarker evidence support a strong Jurassic contribution to the studied oil sands and call for re-evaluation of the petroleum systematics of the WCSB.

Petroleum migration and accumulation in the Liuchu area of Raoyang Sag, Bohai Bay Basin, China

This study focused on vertical migration of petroleum in the Liuchu area, China. The physical properties of petroleum and changes in the geochemical characteristics of the study area were also investigated. Biomarkers such as, nitrogen compounds, n-alkanes, triterpenoids, steroids, hopanes, and cholestanes were analyzed in this regard. Petro-physical characteristics, such as, density, viscosity, concentrations of wax, resin, and sulfur of oil were studied. The rNa+/rCl− ratio of Ed2 formation water ranged from 0.25 to 5.7, oil density of Ed2 formation ranged from 0.85 to 0.95 g/cm3, and oil resin concentration 10–50%, oil wax content in Ed2 formation ranged from 2 to 29% were lower than that of Es1. The rNa+/rCl− ratio and mineralization of formation water data were examined to demonstrate the migration pathways. Geochemical and crude oil physical indexes were utilized to investigate the relationship between petroleum migration and seismic data. Cholestane αββ, ααα cholestane, diacholestane, steroid, and low ring terpenes in the formation were utilized to trace petroleum migration. Recent studies on petroleum maturity of have focused on comparison of source rocks and have reported that the maturity effects of source rock and reservoir oil are weak while those effects are high in the Liuchu aera. Analysis of triterpenoid and steroid hydrocarbon biomarkers elucidate the underground petroleum migration pathways to the reservoirs. Geochemical analyses of hopane and cholestanes were used. The ααα C29 (20S)/(20S + 20R) and C29 (ββ)/αα + ββ) ratios ranged from 0.2 to 0.35 Further, C31 (22S)/(22S + 22R), C32(22S)/(22S + 22R), and C29 (20S)/(20S + 20R) ratios ranged from 0.3 to 0.8, and 0.131 and 0.81, respectively. Petroleum migrated along migration channels. This suggested that vertical migration occurred after formation of the source rock fault and lateral migration occurred along the sandbody. Reservoir sandstone content, overlying mudstone content, and thickness of caprock are likely limited lateral petroleum migration. Petroleum migration and accumulation primarily occurred by vertical migration and lateral migration was weak. The results of this study enabled optimization of uncertain petroleum migration pathways and improved the petroleum migration and accumulation model.

Geochemical characterization of the Upper Mississippian Goddard Formation, Noble Ranch Group, and related oils in the Anadarko Basin of Oklahoma

The Woodford Shale is anecdotally assumed to be the major source of oil for plays in the Anadarko Basin, including the stacked oil and condensate play in the southcentral Oklahoma oil province (SCOOP). However, there is little published geochemical work to confirm this assumption. This study set out to identify a characteristic geochemical fingerprint for the Goddard Formation, another potential source rock in the SCOOP, to determine if the Goddard is contributing to oil accumulations within the SCOOP. The Upper Mississippian Goddard Formation has been a target for unconventional production in SCOOP since 2012. Published geochemical interpretations for the Goddard Formation are still limited, and this study represents the first detailed oil–source rock correlation for the Goddard in the SCOOP area. The most characteristic geochemical signature of the Goddard extracts is a predominance of tricyclic terpanes relative to the hopanes in the mass-to-charge ratio 191 chromatogram, possibly related to enrichment via thermal stress or a unique source signature. Additional distinctive signatures were also identified for the triaromatic steroid hydrocarbons, sesquiterpenoids, and steranes. The biomarker fingerprints of SCOOP oils are nearly identical with those of the Goddard extracts in this study. Oils in the SCOOP, therefore, appear to originate from a Mississippian source, such as the Goddard rather than the Woodford. This observation demonstrates the value of oil–source rock correlation studies and suggests that there may be effective source rocks in the Anadarko Basin that have been overlooked in the past and should be re-evaluated in detail.

Formation of 5α-Sitostan-3-one, 5α-Campestan-3-one, and Steroidal Hydrocarbons in Edible Oils during Catalytic Hydrogenation.

Targeted analysis confirmed the presence of new phytosterol degradation products in fully hydrogenated commercial samples. EI-MS, APCI-MS, and 1D-NMR experiments led to the identification of 10 novel markers of catalytic hydrogenation, among which 5α-sitostan-3-one and 5α-campestan-3-one, isomers of saturated and monounsaturated steroidal hydrocarbons, were reported in edible oils for the first time. Examination of the phytosterol degradation mechanism was done by the catalytic transfer deuteration technique. The mitigation strategy of potentially detrimental compounds included optimization of processing parameters. The effect of catalyst dosage (≤0.1% based on Ni basis) and temperature region (>180 °C) were the most crucial factors in phytosterol degradation control.

Universal Biomarker Analysis: Aromatic hydrocarbons

Universal Biomarker Analysis is a GC×GC-ToFMS method that provides absolute quantification and non-targeted pseudo MS-MS for all resolved hydrocarbon components in petroleum and rock extracts. This is achieved by merging two chromatographic datasets obtained under field ionization (FI), which provides molecular ions, and electron impact (EI), which provides diagnostic fragment ions. We recently demonstrated this technique for the analysis of saturated biomarkers (Walters et al., 2018). Here, we show its application to aromatic biomarkers. Universal Biomarker Analysis is compared to conventional GC–MS for frequently analyzed aromatic hydrocarbons, such as the alkylated naphthalenes and biphenyls, mono- and tri-aromatic steroidal hydrocarbons to illustrate where this new method provides demonstrated advantages. The technique is well suited for the analysis of rare species not commonly analyzed in targeted GC–MS/MS analyses. This is illustrated by the tentative identification of A/B-ring C26-C29 diaromatic steroidal hydrocarbons in a crude oil, compounds that have been previously identified as minor components of immature rock extracts, and indications of previously unknown C26 methyl-triaromatic steroidal hydrocarbons.

Severe biodegradation of polycyclic aromatic hydrocarbons in reservoired crude oils from the Miaoxi Depression, Bohai Bay Basin

Aromatic hydrocarbons are major components in crude oil. Biodegradation of polycyclic aromatic hydrocarbons, such as biphenyls, naphthalenes, phenanthrenes and aromatic steroid hydrocarbons have been well studied. However, little is known about the relative susceptibilities to biodegradation of fluorene, dibenzofuran, dibenzothiophene, chrysene and pyrene, and their alkylated homologues. In this study, gas chromatography–mass spectrometry analyses of aromatic fractions of a suite of severely biodegraded crude oils from the Bohai Bay Basin have been performed to investigate the fate and relative susceptibilities of these polycyclic aromatic hydrocarbons during severe biodegradation under geological conditions.Changes in concentrations of varying PAH classes with increasing biodegradation suggest their relative susceptibilities to microbial alteration are in the order biphenyls>naphthalenes>dibenzofurans>phenanthrenes∼fluorenes>dibenzothiophenes>chrysenes>pyrenes>C26–28 triaromatic steroid hydrocarbons. The relative susceptibilities to biodegradation of individual isomers of chrysenes, dibenzothiophenes, dibenzofurans, fluorenes, pyrenes and triaromatic steroid hydrocarbons were determined based on their compositional changes. The susceptibility to biodegradation of PAHs is not directed related to the number of aromatic rings, but may be controlled by the shapes of the substrate molecules which control the ability to penetrate the cell membrane and to fit the active site of the microbial enzyme. Sulfur-containing compounds, such as dibenzothiphenes, are more resistant to biodegradation than those non-sulfur-containing components with similar molecular structure, which is likely due to their relatively greater biotoxicity. PAHs with more alkyl substituents are generally more resistant to biodegradation, but exceptions were also observed, and this observation may due to demethylation of a substituted compound. Undoubtedly, the positions of alkyl substituents control the susceptibilities to biodegradation of PAH isomers. However, the observation that PAH isomers with β-substituents are more readily biodegraded is not universal, suggesting that the susceptibility of PAH isomers is not controlled by thermodynamic stability, but may be related to their stereochemical structures.

Paleoproterozoic sterol biosynthesis and the rise of oxygen

Natural products preserved in the geological record can function as 'molecular fossils', providing insight into organisms and physiologies that existed in the deep past. One important group of molecular fossils is the steroidal hydrocarbons (steranes), which are the diagenetic remains of sterol lipids. Complex sterols with modified side chains are unique to eukaryotes, although simpler sterols can also be synthesized by a few bacteria. Sterol biosynthesis is an oxygen-intensive process; thus, the presence of complex steranes in ancient rocks not only signals the presence of eukaryotes, but also aerobic metabolic processes. In 1999, steranes were reported in 2.7 billion year (Gyr)-old rocks from the Pilbara Craton in Australia, suggesting a long delay between photosynthetic oxygen production and its accumulation in the atmosphere (also known as the Great Oxidation Event) 2.45-2.32 Gyr ago. However, the recent reappraisal and rejection of these steranes as contaminants pushes the oldest reported steranes forward to around 1.64 Gyr ago (ref. 6). Here we use a molecular clock approach to improve constraints on the evolution of sterol biosynthesis. We infer that stem eukaryotes shared functionally modern sterol biosynthesis genes with bacteria via horizontal gene transfer. Comparing multiple molecular clock analyses, we find that the maximum marginal probability for the divergence time of bacterial and eukaryal sterol biosynthesis genes is around 2.31 Gyr ago, concurrent with the most recent geochemical evidence for the Great Oxidation Event. Our results therefore indicate that simple sterol biosynthesis existed well before the diversification of living eukaryotes, substantially predating the oldest detected sterane biomarkers (approximately 1.64 Gyr ago), and furthermore, that the evolutionary history of sterol biosynthesis is tied to the first widespread availability of molecular oxygen in the ocean-atmosphere system.

Molecular composition assessment of biodegradation influence at extreme levels – A case study from oilsand bitumen in the Junggar Basin, NW China

In order to understand the effects of extreme biodegradation on petroleum molecular compositions, a series of shallow buried oilsands from the northwestern margin of the Junggar Basin, NW China has been investigated using geochemical methods. Most samples have experienced at least level 8 biodegradation on the scale of Peters and Moldowan, but their molecular compositions still show dramatic variations. The bi- and tricyclic aromatic compounds are almost completely removed with aromatic steroid hydrocarbons being the only visible molecules in the aromatic hydrocarbon fraction. However, aromatic steroids are not sensitive to the assessment of biodegradation extent possibly due to mixed effects with water washing. At an extreme level of biodegradation after diasteranes were attacked, pregnanes, tri- and tetracyclic terpanes, non-hopane pentacyclic terpanes such as 18α-30-norneohopane, C30 diahopane and gammacerane remain prominent. The post extreme level of biodegradation can be further differentiated on the basis of the presence and absence of these ‘refractory’ components together with 25-norhopanes (NHs), 17-nortricyclic terpanes (NTTs) and C23 demethylated tetracyclic terpane (C23NTeT). These NHs, NTTs and C23NTeT are produced from corresponding hopanes, tri- and tetracyclic terpanes during biodegradation but they are biodegradable as well. Extreme plus 1 level of biodegradation is characterized by the attack of pregnanes and tricyclic terpanes. Extreme plus 2 level of biodegradation is characterized by the attack of tetracyclic terpanes and non-hopane pentacyclic terpanes. When biodegradation level reaches to extreme plus 3, NHs and NTTs are largely depleted. At extreme plus 4 level, the only traceable components are C23NTeT and C29NH. While different basins or reservoirs may have their unique features of the biodegradation process, relative rates of biodegradation of the different hydrocarbon classes that occur in the Junggar Basin may provide a protocol for intensity assessment after the extreme level of biodegradation is reached.

Uncommon steranes in Brazilian marginal crude oils: Dinoflagellate molecular fossils in the Sergipe-Alagoas Basin, Brazil

Comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GC×GC–TOFMS) was used to identify unusual steranes in branched-cyclic hydrocarbon fractions of crude oils from Sergipe-Alagoas Basin, Brazil and infer the geochemical settings of their Cretaceous source rocks. Hopane/sterane and sterane ratios, and the presence of gammacerane and β-carotane in the oil samples indicates a saline source rock depositional environment and predominantly marine organic matter (OM) input. Steroidal hydrocarbons were represented by alkyl steranes and several sterane series, including abundant short-chain steranes (C21 and C22), regular steranes (C27–C29), and diasteranes (C21–C23, C27–C29). The ring-A methyl sterane series contained 3β-methyl steranes (C22 and C23, C28–C30), abundant 3β-methyldiginane (C22), and 3β-methyldiacholestanes (C28), including 4-methyl steranes with abundant C30 4α,23,24-trimethylcholestanes in the branched-cyclic fraction of these crude oils. The C29 sterane isomers, 23,24-dimethylcholestane and 24-ethylcholestanes, were resolved by GC×GC–TOFMS, and a C29 dinosterane derivative was identified for the first time in Brazilian crude oils. The 23,24-dimethyl and 4,23,24-trimethyl steroids can be related to dinoflagellate OM and abundant dinosteranes suggests dinoflagellate blooms during source rock deposition in this Brazilian marginal basin. Additionally, the detection of C28–C32 3β-alkyl cholestanes, C29–C33 3β-alkyl 24-methylcholestanes, and C30–C34 3β-alkyl 24-ethylcholestane with ethyl to pentyl groups at C-3 resulted in a complex sterane fingerprint, as expected for petroleum generated from source rocks deposited under predominantly marine saline conditions with high microalgal input. These biomarker results provide additional insight into the character and geologic processes responsible for the source rocks of crude oils in the Brazilian marginal basins. This information will be a valuable exploration tool that can be used to constrain the distribution of different oil types in these basins.

Steroid hydroxylation by basidiomycete peroxygenases: a combined experimental and computational study.

The goal of this study is the selective oxyfunctionalization of steroids under mild and environmentally friendly conditions using fungal enzymes. With this purpose, peroxygenases from three basidiomycete species were tested for the hydroxylation of a variety of steroidal compounds, using H2O2 as the only cosubstrate. Two of them are wild-type enzymes from Agrocybe aegerita and Marasmius rotula, and the third one is a recombinant enzyme from Coprinopsis cinerea. The enzymatic reactions on free and esterified sterols, steroid hydrocarbons, and ketones were monitored by gas chromatography, and the products were identified by mass spectrometry. Hydroxylation at the side chain over the steroidal rings was preferred, with the 25-hydroxyderivatives predominating. Interestingly, antiviral and other biological activities of 25-hydroxycholesterol have been reported recently (M. Blanc et al., Immunity 38:106-118, 2013, http://dx.doi.org/10.1016/j.immuni.2012.11.004). However, hydroxylation in the ring moiety and terminal hydroxylation at the side chain also was observed in some steroids, the former favored by the absence of oxygenated groups at C-3 and by the presence of conjugated double bonds in the rings. To understand the yield and selectivity differences between the different steroids, a computational study was performed using Protein Energy Landscape Exploration (PELE) software for dynamic ligand diffusion. These simulations showed that the active-site geometry and hydrophobicity favors the entrance of the steroid side chain, while the entrance of the ring is energetically penalized. Also, a direct correlation between the conversion rate and the side chain entrance ratio could be established that explains the various reaction yields observed.

Pregnanes as molecular indicators for depositional environments of sediments and petroleum source rocks

Steroids with unconventional side chains have increasingly been applied as diagnostic markers for geological source and age assessments. However, one of the most distinctive characteristics, the abnormal abundance of pregnane and homopregnane in ancient sediments and petroleum, remains unresolved. Higher pregnane and homopregnane, as well as C23–C26 20-n-alkylpregnanes, relative to the regular steranes were observed in samples collected from different petroleum basins in China. These included Precambrian marine carbonate-derived petroleum (NW Sichuan Basin), Lower Paleozoic marine marl derived crude oils (Tarim Basin), and Eocene hypersaline lacustrine carbonate source rocks and associated petroleum (Bohai Bay Basin). However, all of the samples have many common biomarker characteristics, such as pristane/phytane ratios<1, low amounts of diasteranes and high C29/C30 hopane (∼0.6–1), C35/C34 hopane (mostly⩾1) and dibenzothiophene/phenanthrene (DBT/PHEN, mostly 0.5–1) ratios revealing a contribution from anoxic carbonate/marl source rocks deposited in restricted, clastic-starved settings. We suggest that 5α,l4β,l7β-pregnane and homopregnane, as well as their higher C23–C26 homologues, are geological products derived from steroids bound to the kerogen by a sulfurized side chain. Carbon or carbonate minerals are considered to be natural catalysts for this cracking reaction via preferential cleavage of the bond between C-20 and C-22. Similar distributions occur in the short chain analogues of 4-methylsterane, triaromatic steroid and methyltriaromatic steroid hydrocarbons, providing circumstantial evidence for this proposal. The ratio of pregnane and homopregnane to the total regular steranes and the ratio of C27 diasteranes to cholestanes can be sensitive indicators of sedimentary environments and facies. In general, high diasteranes and low pregnanes (with homologues) indicate an oxic water column or significant input of terrigenous organic matter in clay rich source rocks and some organic lean carbonate rocks. Low diasteranes with high pregnanes implies restricted, sulfur rich conditions, typical of anoxic carbonate source rocks. Furthermore, the two ratios may be useful to assess the variation of mineralogy and openness of source rock depositional settings.

Study of weathering effects on the distribution of aromatic steroid hydrocarbons in crude oils and oil residues.

The composition and distribution of triaromatic steroid hydrocarbons in oil residues after biodegradation and photo-oxidation processes were detected, and the diagnostic ratios for oil spill identification were developed and evaluated based on the relative standard deviation (RSD) and the repeatability limit. The preferential loss of C27 methyl triaromatic steranes (MTAS) relative to C28 MTAS and C29 MTAS was shown during the photo-oxidation process. In contrast to the photochemical degradation, the MTAS with the original 20R biological configuration was preferentially degraded during the biodegradation process. The RSD of most of the diagnostic ratios of MTAS ranged from 9 to 84% during the photo-oxidation process. However, the RSDs of such ratios derived from MTAS were all <5% even in high biodegradation, and such parameters may also provide new methods on oil spill identification. The parameters of monoaromatic sterane and monoaromatic sterane are not used well for oil spill identification after photo-oxidation. The triaromatic steroid hydrocarbons retained their molecular compositions after biodegradation and photo-oxidation and most of the diagnostic ratios derived from them could be efficiently used in oil spill identification.

Geochemical Evaluation of Thermal Maturity of the Cretaceous Sediments in the Calabar Flank based on the Distribution of the Polynuclear Aromatic Hydrocarbons

The thermal maturity parameter used in the evaluation of the hydrocarbon generative potential of the sedimentary organic matter is based largely on the extent of molecular transformation of the biological markers due to geothermal stress which is a function of depth or burial history. In particular the transformations leading to the formation of Polynuclear Aromatics usually occur at the end of diagenesis up to the onset of catagenesis. . An in-depth study of the transformation leading to the formation of polynuclear aromatic steroidal hydrocarbons revealed a step by step thermally mediated aromatization of the non-aromatic biogenic species during diagenetic/catagenetic evolution of organic matter in an anoxic environment. Since the formation of PAHs is a heat mediated process which increases with depth, then its concentration or the amount per unit mass of the rock sample can be used to estimate the thermal maturity of organic matter in the sediment .In light of the above, this work has evaluated the distribution profile of the PAHs in the Cretaceous sediments of the Calabar Flank using Gas Chromatograph interfaced to a Mass Spectrometer (GC-MS),an analytical tool combination widely used in the study of petroleum geochemistry. The results of the study based on the most dominant polynucear aromatic species namely, anthracene and phenanthrene revealed that Nkporo Shale(NS)samples from various locations in the Basin had a average PAH of 0.05mg/Kg (anthracene) and 0.06mg/Kg (phenanthrene).While the PAH value of Ekenkpon Shale(ES) samples was on the average 0.01mg/Kg and 0.02mg/Kg for anthracene and phenanthrene respectively. New Netim Marl(NNM) however gave the PAH value of only 0.001mg/Kg for phenanthrene and nil for anthracene .On the other hand Awi Sandstone (AS), Mfamosing Limestone (ML) and Nkporo Mudstone(NM) all fell within the non-detectable range. Based on the foregoing, PAH values can be used to evaluate the maturation level of organic matter in the sediments.

Chemical composition of lipids in brewer's spent grain: A promising source of valuable phytochemicals

Brewer's spent grain (BSG) is an important by-product from the brewing process produced in high amounts worldwide. BSG is rich in carbohydrates, lignin, proteins and lipids. In this work, the chemical composition of the lipids in BSG was studied in detail by gas chromatography and mass spectrometry. The predominant lipids were triglycerides (67% of total extract), followed by a series of free fatty acids (18%). Lower amounts of monoglycerides (1.6%) and diglycerides (7.7%) were also identified among the lipids in BSG, together with minor amounts of other aliphatic series such as n-alkanes and alkylresorcinols. Steroid compounds (steroid hydrocarbons, steroid ketones, free sterols, sterol esters and sterol glycosides) were also found in important amounts in BSG (ca. 5%), with free and conjugated sterols being the most abundant steroids. BSG can thus be regarded as a valuable source of phytochemicals of interest for the pharmaceutical, cosmetic, food or other industries.