Hopanoic Acids Research Articles

The stereochemistry of bound and extractable pentacyclic triterpenoids during closed system pyrolysis

The distributions of hopanoic acids, ranging from C30 to C34, in the Messel oil shale were characterized in both the free and bound states. The bound acids were released by thermochemolysis in the presence of tetramethylammonium hydroxide (TMAH). These were compared with the distributions of the hopanoic acids and hopanes released or generated from Messel oil shale kerogen following closed system microscale pyrolysis. This comparison revealed that epimerization had occurred at C-17, C-21 and C-22 during heating. It was also clear that the residual bound hopanoic acids had undergone configurational isomerization. During the pyrolysis there is a large loss of hopanoic acids following their rapid release from the kerogen into the free fraction even at 250 °C. In these particular experiments this loss does not appear to result in exclusive formation of hopanes, by way of decarboxylation or reduction reactions, unless the resulting hopanes are either themselves rapidly transformed into other compounds or the reaction rates are a function of the total number of carbon atoms in each hopanoic acid precursor.

Formation of carboxylic acids during aerobic biodegradation of crude oil and evidence of microbial oxidation of hopanes

During the biodegradation of crude oil in the laboratory, significant amounts of carboxylic acids were produced. Medium molecular weight (C 10–C 20) carboxylic acids were rapidly produced, which coincided with the removal of the n-alkanes but these acids were then also rapidly biodegraded. After extensive biodegradation of the hydrocarbons there was an increase in the concentration of higher (>C 20) molecular weight branched and cyclic carboxylic acids which appeared as an unresolved complex mixture (UCM) in the gas chromatograms of these acid fractions. These latter acids appeared recalcitrant to further biodegradation during the experiment. The presence of hopanoic acids with the 17α(H),21β(H) configuration in the most degraded laboratory samples, indicated that biodegradation of hopane hydrocarbons had also taken place, with side chain oxidation.

Hopanoic acids in Mesozoic sedimentary rocks: their origin and relationship with hopanes

Hopanoic acids were found in all but the two most mature of a suite of 30 Triassic to Cretaceous sedimentary rocks. Their carbon number distributions generally maximise at C 32, consistent with hopanoic acids found in modern sediments. The extent of isomerisation (measured by %ββ and %22S αβ parameters) is less for the acids than for associated hopanes, possibly due to increased isomerisation of hopanes in association with their generation from macromolecules and functionalised precursors. In immature samples the hopane carbon number distributions are consistent with an origin from defunctionalisation of hopanoic acids and other early diagenetically-formed hopanoids, whilst hopanes in more mature samples exhibit broader carbon number distributions indicative of side-chain cleavage during generation of macromolecularly-bound hopanoids.

Kerogen-bound and free hopanoic acids in the Messel oil shale kerogen

Kerogen-bound and free hopanoic acids in the Messel oil shale kerogen

Lipids as indicators of eutrophication in marine coastal sediments

Total organic carbon (TOC) and sedimentary lipid contents were investigated in the Bunnefjord, the most inner part of the Oslofjord (Norway). The Bunnefjord is an intermittent anoxic basin and has undergone major eutrophication since the early 1800s. A core from this fjord was collected at 100 m depths under anoxic remnant waters. The first 15 cm corresponding to deposits from 1500 to present were considered for analysis. Lipid classes were quantified by TLC–FID and the molecular composition of selected lipid classes was investigated by GC and GC–MS. Lipids were dominated by two main classes, phospholipids and hydrocarbons. The hydrocarbons represented up to 7.4% of total lipids in the sediment layers covering the period when the most extensive cultural eutrophication took place (1900 to 1970). The higher fluxes of organic carbon produced during this period may have controlled hydrocarbon inputs into the sediments, due to the hydrophobic character of these pollutants. The hydrocarbon concentration reversed toward pre-industrial levels in the more recent layers, which suggests an improvement of the water quality, possibly in response to improved treatment of the sewage in the cities around Bunnefjord. The second most abundant pool of lipids consists in phospholipids, mostly contributed by bacteria. Even though the concentration decreased with depth, their relative proportions to total lipids remained high, mainly in the deepest layers (>80% of total lipids). A rapid decrease of the polyunsaturated fatty acid methyl esters (FAME) from the phospholipid fraction in the upper 4 cm suggests a rapid biodegradation of planktonic inputs and meiofauna. Odd branched fatty acids were more probably contributed by bacteria linked to the high sedimentary hydrocarbon content. The down core distribution of 16:1ω7, 18:1ω7, 18:1ω5 esterified to phospholipids suggests a vertical zonation of the microbial community in relation to redox conditions and available organic matter. In addition to bacterial sulphur biomass, the presence of hopanoic acids in the phospholipids fraction suggests the contribution of bacteria growing on methane. According to the sterol composition, dominated by 4α(H)-methylsterols, dinoflagellates represent the major contributors to the organic matter produced in the water column, particularly during the period of extensive eutrophication. Long-chain diols (1,13-C 26, 1,15-C 30 and 1,15-C 32) and long-chain keto-ols (1,15-C 30 and 1,15-C 32) are reported for the first time at high latitudes. Their relative distributions (diol and keto-ol indexes of Versteegh et al. [Org. Geochem. 27 (1997)]) have allowed depicting a particular event during the eutrophication period, a freshwater intrusion with inputs of land-derived organic matter. This is in accordance with the downcore distribution of freshwater/terrestrial markers as sitosterol, dehydroabietic acid and iso- and anteiso-pimaric acids. The diol and keto-ol indexes have also underlined the general transition trend from marine to more brackish waters in the Bunnefjord. These last observations provide confidence into the use of these compounds in paleoenvironmental reconstruction.

Structural study of the Moroccan Timahdit (Y-layer) oil shale kerogen using chemical degradations

This paper deals with the structural characterization of the Moroccan Timahdit (Y-layer) oil shale kerogen. For this purpose, the kerogen concentrate was submitted to stepwise hydrolysis under phase transfer catalysis conditions. The results show that aliphatic and aromatic dicarboxylic acids are involved in the cross-linking of the kerogen matrix, acting as bridges, while aliphatic and aromatic monocarboxylic acids, and alcohols represent monosubstituents of the matrix. Aliphatic mono- and dicarboxylic acids are produced on ruthenium tetroxide oxidation of the kerogen. These acids arise from a variety of reactions including cleavage of ester linkages. 17α(H),21β(H)- and 17β(H),21α(H)-hopanoic acids, probably bound to the kerogen by ether groups, were identified in the oxidation products.

Kerogen-bound and free hopanoic acids in the messel oil shale kerogen.

The distribution of the free and bound hopanoic acids in both unheated and heated (350 degrees C for 50 h) kerogens, isolated from the Messel oil shale, were analyzed by GC-MS. The bound acids were released by subjecting the kerogen to three different treatments, namely, thermochemolysis in the presence of tetramethylammonium hydroxide (TMAH), as well as basic and acidic hydrolyses. All of these methods gave a series of hopanoic acids ranging from C(30) to C(34), in which the biological 17beta, 21beta(H) configuration is prominent. Both 22R and 22S epimers are present for the C(30) acid, whereas the others are dominated by the sidechain 22R-configuration. Thermochemolysis in the presence of TMAH was the most efficient in releasing kerogen-bound hopanoids. Following pyrolysis, the acids are generated and released into the free fraction with apparent epimerization occurring at C-17, C-21, and C-22. The bound hopanoic acids may be both chemically bonded as well as possibly being physically encapsulated within the macromolecular fraction of sedimentary organic matter. They are therefore either generated by breaking the bonds which bind them to the kerogen or they are released as a result of the macromolecular cage being broken apart.

Influence of biodegradation on crude oil acidity and carboxylic acid composition

Quantitative analysis of separated carboxylic acid fractions of 33 crude oils from the UK, Italy and California, showed that the carboxylic acid fraction is a major factor responsible for the acidity in these oils. It was apparent that biodegradation is the main process that produces high concentrations of carboxylic acids in these crude oils with the extent of biodegradation, as measured from their hydrocarbon compositions, being clearly correlated with their total acid number (TAN). Although probably not important in influencing oil TAN, the distribution of C30–C32 hopanoic acids was also seen to be controlled by biodegradation, increasing in concentration for all but the most biodegraded oils. Hopanoic acids with the 17β(H),21β(H) stereochemistry were found in many of the biodegraded oils, and were thought to be mainly derived from the bacteria that were responsible for the biodegradation of the oil. This may have implications for the timing and mechanisms of the biodegradation involved. The role of C0–C3 alkylphenols in determining oil acidity was investigated and shown not to be a significant factor in the sample set studied. However, a number of undegraded oils, with low carboxylic acid contents were seen to have relatively high acidities, showing that factors other than biodegradation, possibly related to high sulphur content can control oil acidity in certain oil types.

Carboxylic acids of marine evaporitic oils from Sergipe-Alagoas Basin, Brazil

A suite of 10 different marine evaporitic oil samples from Sergipe-Alagoas Basin, Brazil was studied for its biomarker content, in particular its acidic constituents. The oils showed different molecular distributions and relative abundances of n-alkanoic, isoprenoid and hopanoic acids. The observed differences were assigned to the incorporation of immature organic matter in the oils and fractionation along the migration pathway. The diagenetic precursor functionality (alcohol/ether or acid) was proposed based on the comparison of the relative abundances of the neutral and acidic biomarkers (hopanoids, isoprenoids, alkyl-steranes, monoaromatic alkyl-steroids). In the acidic fraction, 3 series of steroid-alkanoic acids and monoaromatic steroid-alkanoic acids (steroid-methanoic, ethanoic and propanoic acids and monoaromatic steroid-methanoic, ethanoic and propanoic acids) were detected, while in the neutral fraction only 2 series of each corresponding class could be observed (methyl and ethyl-steranes and monoaromatic methyl and ethyl-steroids). These carbon shifts suggest that decarboxylation is an important process in the formation of the alkyl-steranes and monoaromatic alkyl-steroids, and we infer that carboxylic acids are the diagenetic precursors of these classes of compounds. When alcohol or ether are the diagenetic precursors (isoprenoids and hopanoids), no significant differences in the molecular distributions between neutral and acidic fractions were observed.

Composition and early diagenesis of fatty acids in lacustrine sediments, lake Aydat (France)

The organic acids from recent sediments from lake Aydat, a small eutrophic lake located in the French Massif Central, have been analysed to determine their possible source(s) and their fate during early diagenesis. The analytical procedure yields three groups of acids — free, H +-labile and OH −-labile — , successively obtained by solvent extraction, acid hydrolysis and saponification in toluene, in the presence of a phase transfer catalyst (PTC). The free components are relatively minor except for the presence of amounts of ββ-hopanoic acids (C 32>>C 30). The H +-labile components, assumed to be mostly of bacterial origin, disappear very rapidly at depth. In contrast, notable proportions of OH −-labile compounds, mostly derived from algae and terrestrial plants, survive in the deepest samples analysed, i.e. >40 cm. The various fatty acids (FA) identified comprise normal saturated FA (with a strong C 20- dominance), monounsaturated FA ( cis and trans C 16:1, C 18:1, C 24:1 with ω5, ω7 and ω9 double bond position), branched ( iso, anteiso) FA, 3-hydroxy FA and 3-methoxy FA, α,ω- dicarboxylic acids, as well as hopanoic acids and a few lignin-derived aromatic acids. A notable part of the most unusual of these various compound types are classically attributed to methanotrophs, which implies that markers from other micro-organisms are already destroyed in the water column. A distinctive acid composition at 20 cm depth might be explained by intensive microbial activity induced by unusual climatic conditions (i.e. an exceptional drought).

A natural pyrolysis experiment — hopanes from hopanoic acids?

The formation or generation of hopanes are important processes during both the natural heating of organic-rich sediments and laboratory pyrolysis experiments. Molecular maturity parameters as well as the amounts (ng/g rock) of the C 31 hopanes and C 30–C 32 hopanoic acids were quantified in a Jurassic silty shale horizon (Isle of Skye, Scotland) as a function of distance from an igneous intrusion. The maturity profiles of the homohopanes and the hopanoic acids are comparable. There is also a correlation between the decreasing amounts of C 30–C 32 hopanoic acids and concomitant increases in C 29–C 31 hopanes suggesting that free hopanoic acids could be one potential source of hopanes in this particular horizon. Other possible sources could include hopanoic acids that are bound into the macromolecular fraction.

Product distribution from oxidative degradation of sulphur-rich kerogens from the Nördlinger Ries (southern Germany)

The distributions of carboxylic acids generated by mild Na 2Cr 2O 7/AcOH oxidation of sulphur-rich kerogens from the Nördlinger Ries, southern Germany, were studied by gas chromatography and combined gas chromatography/mass spectrometry. Major oxidation products were saturated normal monocarboxylic acids (C 8C 31), saturated normal α,ω-dicarboxylic acids (C 8C 29), and isoprenoid acids (C 14C 21, except C 18). Less dominant were iso- and anteiso-acids (C 11C 18), oxo-acids (mainly 10-oxo- n-octadecanoic acid), n-monoenoic acids (C 16:1 and C 18:1), series of 3β-carboxysteroids, hopanoic acids, isoprenoid and steroid ketones, maleimides (1 H-pyrrole-2,5-diones), and aromatic acids. The lipid composition of the kerogens is consistent with a major contribution from planktonic and microbial organisms in sample from NR-10, and mixed autochthonous and allochthonous sources in samples from well NR-30 located closer to the rim of the basin. Furthermore, the data indicate a predominantly open-chain cross-linked structure for the Nördlinger Ries kerogens and point toward a mild thermal history for these samples. The results further confirm the presence of tetrapyrrole pigments which are most likely entrapped in the molecular sieve-type network of kerogens.

Organic geochemical studies of soils from the Rothamsted Classical Experiments—II, Soils from the Hoosfield Spring Barley Experiment treated with different quantities of manure

Total lipid extracts (TLEs) were obtained from soil samples taken in the years 1882, 1913, 1946, 1965 and 1995 from three treatments of the Hoosfield Spring Barley Experiment at Rothamsted Experimental Station, Harpenden, Hertfordshire, U.K. The extracts were fractionated and molecular analyses performed using gas chromatography (GC) and gas chromatography-mass spectrometry (GC/MS). In addition to the soil samples (contemporary and archived), the two primary organic inputs, barley and farmyard manure (FYM), were studied so that the composition and diagenetic behaviour of extractable lipids from the two inputs could be assessed. The major aliphatic soil lipids exhibited variable dominance with respect to the expression of barley and FYM derived lipids. Wax esters were of low abundance and too strongly affected by degradation and transesterification processes to identify a dominant input whilst the composition of soil n-alkanols was largely determined by FYM with a minor pedogenic input. n-Alkanoic acids increased in overall abundance in soils with a continual FYM input and showed appreciable degradation in soils receiving no manure. C 32 ββ hopanoic acid was detected in two plots and appeared to degrade at a rate similar to 5 β-stanols with the most likely source of this compound being the FYM. Measurements of absolute concentrations of 5 β-stanols, biomarkers characteristic of manuring, revealed that a manuring signal persisted for >120 years within the soil which had been intensively cultivated annually and had received no manure since 1871. The persistence of a manure signal in soils has important implications for archaeological studies of agricultural practices based on 5 β-stanols.

Bacterial and algal markers in sedimentary organic matter deposited under natural sulphurization conditions (Lorca Basin, Murcia, Spain)

Free lipids, sulphur-bound lipids present in macromolecular fractions and kerogen pyrolysis products have been studied in shales and early diagenetic carbonates replacing gypsum from a Messinian sequence of Lorca Basin. The high abundance of phytane, 2,3-dimethyl-5-(2,6,10-trimethylundecyl)thiophene, mid-chain C 20 isoprenoid thiophenes and bithiophenes and bis-O-phytanyl and O-phytanyl-O-sesterterpanyl glycerol ethers indicates that the organic matter in all these samples was deposited under hypersaline conditions. The isopranyl glycerol ethers are essentially found in the sulphur-bound macromolecular matter which contrasts with the low concentrations of these compounds as free lipids. However, the distributions of these isopranyl glycerols is paralleled by the occurrence of free phytanic acid (shales and laminated carbonate) and 3,7,11,15,19-pentamethyleicosanoic acid (only in the laminated carbonate). The bacterial inputs are represented by 2-hydroxytetracosanoic acid, n-octadec-11-enoic acid, hopanoic acids and the distributions of iso- and anteiso-C 15 and C 17 homologues and minor amounts of iso-C 16 and anteiso-C 14. These branched fatty acids are characteristic of sulphate-reducing bacteria. The relative proportions of the iso- and anteiso-compounds in the total fatty acid distributions are correlated with the proportion of reduced sulphur in the sediments.

5587202 Repulpable hot melt polymer/fatty acid compositions for fibrous products: Sandvick Paul E; Verbrugge Calvin J Racine, WI, United States assigned to S C Johnson & Son Inc

The distributions of carboxylic acids generated by mild Na2Cr2O7/AcOH oxidation of sulphur-rich kerogens from the Nördlinger Ries, southern Germany, were studied by gas chromatography and combined gas chromatography/mass spectrometry. Major oxidation products were saturated normal monocarboxylic acids (C8C31), saturated normal α,ω-dicarboxylic acids (C8C29), and isoprenoid acids (C14C21, except C18). Less dominant were iso- and anteiso-acids (C11C18), oxo-acids (mainly 10-oxo-n-octadecanoic acid), n-monoenoic acids (C16:1 and C18:1), series of 3β-carboxysteroids, hopanoic acids, isoprenoid and steroid ketones, maleimides (1H-pyrrole-2,5-diones), and aromatic acids. The lipid composition of the kerogens is consistent with a major contribution from planktonic and microbial organisms in sample from NR-10, and mixed autochthonous and allochthonous sources in samples from well NR-30 located closer to the rim of the basin. Furthermore, the data indicate a predominantly open-chain cross-linked structure for the Nördlinger Ries kerogens and point toward a mild thermal history for these samples. The results further confirm the presence of tetrapyrrole pigments which are most likely entrapped in the molecular sieve-type network of kerogens.

5587317 Chemical-biological process for dehalogenation of halogenated organic compounds: Odom James M Avondale, PA, United States assigned to E I Du Pont de Memours & Company

The distributions of carboxylic acids generated by mild Na2Cr2O7/AcOH oxidation of sulphur-rich kerogens from the Nördlinger Ries, southern Germany, were studied by gas chromatography and combined gas chromatography/mass spectrometry. Major oxidation products were saturated normal monocarboxylic acids (C8C31), saturated normal α,ω-dicarboxylic acids (C8C29), and isoprenoid acids (C14C21, except C18). Less dominant were iso- and anteiso-acids (C11C18), oxo-acids (mainly 10-oxo-n-octadecanoic acid), n-monoenoic acids (C16:1 and C18:1), series of 3β-carboxysteroids, hopanoic acids, isoprenoid and steroid ketones, maleimides (1H-pyrrole-2,5-diones), and aromatic acids. The lipid composition of the kerogens is consistent with a major contribution from planktonic and microbial organisms in sample from NR-10, and mixed autochthonous and allochthonous sources in samples from well NR-30 located closer to the rim of the basin. Furthermore, the data indicate a predominantly open-chain cross-linked structure for the Nördlinger Ries kerogens and point toward a mild thermal history for these samples. The results further confirm the presence of tetrapyrrole pigments which are most likely entrapped in the molecular sieve-type network of kerogens.

Differentiation of palaeomarine and modern seawater intruded salinities in coastal groundwaters (of Karaikal and Tanjavur, India) based on inorganic chemistry, organic biomarker fingerprints and radiocarbon dating

Hydrosalinity evolution is examined in the Karaikal and Tanjavur coastal aquifers situated about 300 km south of Madras, Tamil Nadu, India. Ancient and modern sources of solutes in groundwaters have been differentiated using hydro-geochemical data, environmental radioisotope dates and organic biomarkers. Results from different techniques show consistently that the Pliocene aquifer possesses characteristic palmitoleic and oleic acid biomarkers, apparent 14C ages of more than 20 000 years and high I/Cl ratio; the modern marine-estuarine intruded groundwaters in the alluvial aquifer display relatively younger apparent 14C ages (modern to 3000 years), enriched potassium ion, low I/Cl ratio and contain vaccenic and hopanoic acid biomarkers, and they also tend to display transient changes in chemical characteristics. These results have practical importance with regard to identifying and controlling seawater intrusion in coastal areas.

Extractable and bound fatty acids in core sediments from the Nördlinger Ries, southern Germany

Gas chromatography (g.c.) and gas chromatography-mass spectrometry (g.c.-m.s.) analyses of fatty acids directly extracted by organic solvents from five sulfur-rich lacustrine sediments in the Nördlinger Ries comprise several homologous series. Saturated normal monocarboxylic acids (C 9C 33) were the dominant series, while isoprenoid acids (C 14C 21, except C 18), iso- ( i) and anteiso ( ai)-acids (C 11C 18), hopanoic acids (C 30C 33) and monounsaturated acids (C 16:1 and C 18:1) were minor constituents. Moreover, 10-oxoacids ( n-C 16 and n-C 18) were identified in abnormally high amounts in the three samples from well NR-10. Base hydrolysis of kerogen concentrates and extractable polar fractions liberated, in addition to the fatty acid constituents belonging to the compound classes mentioned above, steroidal acids (C 28C 31) and α,ω-dicarboxylic acids (C 7C 28). The results are discussed in terms of qualitative and quantitative variations of the fatty acids in the free and bound lipid fractions. The high concentrations of fatty acids in the bitumens are attributed to early diagenesis. The carbon number distributions of n-alkanoic acids in the free and bound fractions indicate a major contribution of autochthonous sources in samples from well NR-10, and a mixed contribution of both autochthonous and allochthonous sources in samples from well NR-30. Bacterial biomarkers, including extended hopanoic acids and i-/ai-branched acids are more significant in the bound lipid fractions. The results further support previous suggestions of a broad similarity between the structure of asphaltenes and kerogen derived from the same source rock. Finally, the data confirm the extremely mild thermal history of the Nördlinger Ries sediments.

Free Aliphatic Acids in Sulfur-Rich Lacustrine Sediments: Their Origin and Relation to Hydrocarbons

Free fatty and hopanoic acids, and hydrocarbons of five organic- and sulfur-rich lacustrine sediments from Nordlinger Ries black shales (southern Germany), have been studied by gas chomatography and computerized GC-MS. The results indicate that Nordlinger Ries sediments contain abnormally high concentrations of those free acids (up to 57% of total extractable bitumen). Besides n-alkanoic, monomethyl, and isoprenoid acids common to any other immature sediments, high concentrations of C 16 and C 18 10-oxoalkanoic acids are unusual constituents of these sediments. The high concentrations of fatty acids in the bitumens are attributed to early diagenesis. The carbon distributions of the acids are consistent with an origin mainly from planktonic and microbial organisms

Application of carboxylic acid biomarkers as indicators of biodegradation and migration of crude oils from the Maracaibo Basin, Western Venezuela

The acid fractions of 15 crude oils of different degrees of maturity, biodegradation, and origin, from the Maracaibo Basin, western Venezuela, were analyzed by high-resolution gas chromatography/ mass spectrometry (GC/MS) to determine their usefulness as indicators of biodegradation and oil migration. Acyclic as well as tri- and pentacyclic (hopanoic) monocarboxylic acids were identified and quantified for this purpose. The total acidity as well as the ratio of tricyclic to pentacyclic acids were good parameters of biodegradation in these oils. When used in conjunction, they differentiated “mixed” oils (biodegraded with non-biograded) and early generated oils from others. Contrary to previous reports, hopanoic acids (HAs) were found to be morre resistant to biodegradation than their alkane counterparts. The isomeric distribution of the HAs as well as the carbon preference index (CPI) and the C 28/C 18 ratio of the n-acids were found to be useful in determining the migration histories of the oils.