Benzohopane Series, Their Novel Di-, Tri-, and Tetraaromatic

Article pubs.acs.org/EF

Benzohopane Series, Their Novel Di‑, Tri‑, and Tetraaromatic Derivatives, and Diaromatic 23- and 24-Norbenzohopanes from the Lower Jurassic Blanowice Formation, Southern Poland Maciej Rybicki,*,† Leszek Marynowski,† and Bernd R. T. Simoneit‡ †

Faculty of Earth Sciences, University of Silesia, Będzińska Street 60, 41-200 Sosnowiec, Poland Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, United States

‡

ABSTRACT: A total of 17 novel di-, tri-, and tetraaromatic derivatives of the benzohopane series cyclized at C-16 or C-20 as well as 4 diaromatic 23- and 24-norbenzohopanes have been identified in the coal and surrounding sandstone samples from the Lower Jurassic Blanowice Formation of southern Poland using gas chromatography−mass spectrometry. Their possible structures and formation pathway have been proposed on the basis of mass spectra and retention times. Bulk geochemical data and the presence of unsaturated benzohopane derivatives indicate low maturation of the Blanowice coals, characteristic for lignites. The diverse distributions of the benzohopane derivatives in the coals and surrounding sandstones showed differences in the extent of biodegradation. Our observations suggest that the di-, tri-, and tetraaromatic derivatives of benzohopanes cyclized at C-16 may be more resistant to biodegradation than regular benzohopanes.

1. INTRODUCTION Bacteriohopanepolyols are lipid membrane constituents of many bacterial groups.1 During diagenesis, these compounds (e.g., bacteriohopanetetrol) undergo chemical reactions, such as cyclization and aromatization, leading to an extensive series of structurally modified hopanoids2 in sedimentary organic matter (OM) and crude oils.3 Bacteriohopanetetrol can be cyclized at the C-20 or C-16 position. The benzohopanes formed by sidechain cyclization at C-20 were described by Hussler et al.4 and are widespread in sediments and crude oils.3,5−8 A second series of benzohopanes cyclized at C-16 was identified by Schaeffer et al.8 and commonly occurs in immature sediments.7,9 Recently, Cong et al.2 identified other benzohopanes in the Chinese Shengli lignite and proposed a novel type of cyclization of the hopanoid polyols at C-30, while Nytoft et al.9 reported additional previously unknown C33−C35 benzohopanes cyclized at C-20. Some benzohopanes identified in biodegraded bitumen as 25-norbenzohopanes may be C-10 demethylation products of C32 and C33 benzohopanes.10 Other benzohopane-like aromatic compounds include 8,14secohopanoids, bearing a fluorene moiety, isolated from the solvent extract of an immature sediment from the Jurassic Kimmeridge Clay Formation11 and diaromatic 8,14-secohopanoids from Mexican crude oils.12 Moreover, fully saturated compounds (hexahydrobenzohopanes) were also identified by Connan and Dessort.13 In the present study, we describe a novel series of di-, tri-, and tetraaromatic derivatives of the benzohopanes cyclized at C-16 and triaromatic derivatives of the benzohopanes cyclized at C-20 in the Blanowice Formation from southern Poland. We also propose their possible formation pathway as well as their inferred structures based on mass spectra and gas chromatographic retention times. The lithology, bulk properties, and biomolecular composition of the Blanowice Formation have been described elsewhere.14 © XXXX American Chemical Society

2. MATERIALS AND METHODS 2.1. Materials. The sample material was collected from an abandoned clay pit in Mrzygłód, Silesian−Cracow Upland, southern Poland (three sub-bituminous coal samples: MR7, MRW2, and MRW4), and four boreholes located about 10 km north of the Mrzygłód clay pit: Wysoka Lelowska 47Ż , Ż arki 90Ż , Jaworznik 124Ż (one sub-bituminous coal sample from each borehole: WL47W80, Z90W181, and J124W127, respectively), and Jaworznik 144Ż (one organic-rich sandstone sample: J144P197). All samples come from the Blanowice Formation of Late Pliensbachian−earliest Toarcian age (Lower Jurassic).15 Details about the samples and their location have been presented elsewhere.14 2.2. Methods. The crushed samples were extracted using a dichloromethane (DCM)/methanol mixture (5:1, v/v) with an accelerated Dionex ASE 350 solvent extractor. Extracts were separated into aliphatic, aromatic, and polar fractions by modified column chromatography.16 Silica gel was first activated at 110 °C for 24 h and then put into Pasteur pipettes. The eluents used for collection of the fractions were n-pentane (aliphatic), n-pentane and DCM (7:3, aromatic), and DCM and methanol (1:1, polar). All solvents were spectroscopically pure and of super-dehydrated grade. A blank sample (silica gel) was analyzed using the same procedure (including extraction and separation). In that sample, only trace amounts of phthalates, fatty acids (FAs), and n-alkanols were detected. The gas chromatography−mass spectrometry (GC−MS) analyses were carried out with an Agilent Technologies 7890A gas chromatograph and Agilent 5975C network mass spectrometer with triple-axis detector (MSD) at the Faculty of Earth Sciences, Sosnowiec, Poland. He (6.0 grade) was used as the carrier gas at a constant flow of 2.6 mL/min. Separation was on either of two different fused silica capillary columns: (1) J&W HP5-MS (60 m × 0.32 mm inner diameter, 0.25 μm film thickness) coated with a chemically bonded phase (5% phenyl and 95% methylsiloxane), with the GC oven temperature programmed from 45 °C (1 min) to 100 °C at 20 °C/min and then to 300 °C (held for 60 min) at 3 °C/min, with a solvent delay of 10 min, and (2) J&W Received: November 28, 2016 Revised: January 29, 2017 Published: February 7, 2017 A

DOI: 10.1021/acs.energyfuels.6b03154 Energy Fuels XXXX, XXX, XXX−XXX

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Energy & Fuels Table 1. Bulk Geochemical Data, Percentage Yields of Fractions, and Basic Molecular Parameters fractions sample

TOCa (%)

TSb (%)

EOMc (%)

ALd (%)

ARe (%)

POLf (%)

MR7 MRW2 MRW4 J124W127 WL47W80 Z90W181 J144P197

61.85 48.5 30.33 60.49 52.06 59.64 9.24

0.05 0.26 0.18 1.32 0.61 2.78 0.43

1.32 0.24 0.08 2.60 1.73 1.31 0.59

4 1 18 8 1 5 8

11 6 1 3 4 4 5

85 93 81 89 95 91 87

C31αβS/(S + R)g ββ-hopanesh 0.14 0.12 0.13 0.13 0.08 0.12 ndj

+ ++ ++ ++ ++ ++ −

∑BHs (cyclized at C-16)/∑BHs (cyclized at C-20)i 2.34 0.49 0.59 0.73 0.70 0.48 nd

a

TOC = total organic carbon (%). bTS = total sulfur (%). cEOM = extractable organic matter (%). dAL = aliphatic fraction (%). eAR = aromatic fraction (%). fPOL = polar fraction (%). gC31αβS/(S + R) = C31-homohopane 22S/(C31-homohopane 22S + C31-homohopane 22R). hββ-hopanes = 17β,21β(H)-hopane relative content: +, low/medium content of 17β,21β(H)-hopanes; ++, high content of 17β,21β(H)-hopanes; and −, absence of 17β,21β(H)-hopanes. i∑BHs (cyclized at C-16)/∑BHs (cyclized at C-20) = sum of benzohopanes cyclized at C-16/sum of benzohopanes cyclized at C-20. jnd = not detected. DB35-MS (60 m × 0.25 mm inner diameter, 0.25 μm film thickness) coated with a chemically bonded phase (35% phenyl and 65% methylsiloxane), with the GC oven temperature programmed from 50 °C (1 min) to 120 °C at 20 °C/min and then to 300 °C (held for 60 min) at 3 °C/min, with a solvent delay of 15 min. The GC column outlet was connected directly to the ion source of the MSD. The GC−MS interface was at 280 °C, while the ion source and quadrupole analyzer were at 230 and 150 °C, respectively. Mass spectra were recorded from 45 to 550 Da (0−40 min) and from 50 to 700 Da (>40 min). The mass spectrometer was operated in the electron impact mode (ionization energy of 70 eV). An Agilent Technologies MSD ChemStation E.02.01.1177 and Wiley Registry of Mass Spectral Data (9th edition) software were used for data collection and spectra processing. Abundances were calculated by comparison of peak areas for the internal standard (9-phenylindene for the aromatic fraction, added before separation) to that of the peak areas of the individual hydrocarbons obtained from the GC−MS total ion chromatograms. Compound assignment was aided by comparison to published mass spectra and by interpretation of MS fragmentation patterns. Abundances of total carbon, total sulfur (TS), and total inorganic carbon were determined using an Eltra CS-500 infrared (IR) analyzer with a total inorganic carbon module. Total organic carbon (TOC) was calculated as the difference between total carbon and total inorganic carbon. Calibration was made by means of the Eltra standards.

Figure 1. Mass fragmentogram (m/z 191) showing hopane distributions in sample J124W127. 29ene = C29 neohop-13(18)-ene. 30ene = C30 hop-13(18)-ene. The J&W HP5-MS column was used.

The homohopane 17α(H),21β(H)-S/(S + R) ratios are small, ranging from 0.08 to 0.14 in all samples (Table 1), confirming the low range of coalification of the Blanowice coals. High concentrations of 17β(H)-22,29,30-trisnorhopane also support the immaturity of the coal. 3.3. Benzohopane Distributions. A series of peaks of benzohopanes and their aromatic derivatives elute in the highretention time region in the total ion current (TIC) chromatograms of the aromatic hydrocarbon fractions (panels A and B of Figure 2 and Figure 3A). Their concentrations are given in Table 2. To systematize the nomenclature of the two benzohopane series as they progress to the multi-unsaturated derivatives, we propose the following names (Table 2): For the C-16 cyclized benzohopanes, we suggest 16,31-cyclohomohopa16,21,30-triene rather than 4′-methylbenzo[16,17,21]-22,29,30trisnorhop-16-ene, as originally given by Schaeffer et al.8 For the C-20 cyclized benzohopanes, we suggest 20,32-cyclo-17α(H)bishomohopa-20,22(30),31-triene, as given by Hussler et al.4,5 Benzohopanes cyclized at the C-16 position are present in the samples in relatively high amounts (Figure 2A and Table 2). These C31H46 and C32H48 benzohopanes with molecular ions at 418 and 432 Da, respectively, have the aromatic ring condensed to the D and E rings of hopane.3,8 The base peaks at m/z 197 and 211 originate from cleavage of the C ring in the terpenoid structure only when the benzene ring is bonded to the D and E

3. RESULTS AND DISCUSSION 3.1. General Bulk Data. The bulk geochemical parameters, including TOC and TS contents and extractable organic matter (EOM), are given in Table 1. The TOC and TS values indicate that studied samples are rich in organic matter (OM), with TOC between 30.33 and 61.85% for coals and with 9.24% TOC for the sandstone sample. The TS content is relatively low, not exceeding 0.26% for samples from the Mrzygłód outcrop, while in the drill core samples, values are higher, varying between 0.43 and 2.78% (Table 1). The contents of EOM range from 0.08 to 2.6%, with an average of 1.18% (Table 1). The polar fractions clearly dominate over the aromatic and aliphatic fractions in all samples, with contents higher than 80% (Table 1), as is characteristic for immature OM. 3.2. Hopane Distributions. Hopane hydrocarbons are present in all samples, except the OM-rich sandstone (J144P197). All have a similar distribution, with 17β(H)-22,29,30-trisnorhopane, 17β(H),21β(H)-30-norhopane (C29ββ), and 17β(H),21β(H)-hopane (C30ββ) as the most abundant compounds (Figure 1). The distribution of the extended homohopanes (C31−C33) is characterized by the 17α(H),21β(H)-22R homologues predominance, with the C31 17α(H),21β(H)-homohopane homologue as major, which is typical for coals (Figure 1). B


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Figure 2. Total ion current (TIC) chromatograms of aromatic hydrocarbon fractions of (A) sample Z90W181 and (B) sample J144P197. The J&W HP5-MS column was used.

Figure 3. (A) TIC chromatogram of the aromatic hydrocarbon fraction of sample J124W127 and (B) m/z 394 + 408 + 420 + 422 mass fragmentogram showing distributions of the di- and triaromatic benzohopanes. The J&W HP5-MS column was used.

A possible homologue, C31H40 with M• + at m/z 412, with an additional ethyl group is marked as compound 2 in Figures 2−4 and Table 2. All of the mass spectra of these aromatic compounds (Figures 5−7) have intense molecular and/or M−CH3 ions, with, in some cases, doubly charged molecular ions, typical of aromatic hydrocarbons and similar to the mass spectra of aromatized oleananes and ursanes.17−19 The acenaphthylene moiety as observed for the monoaromatic benzohopane is not found for any polyaromatic benzohopane. Compound 3 with M• + at m/z 382 (compound 3 in Figures 2−5 and Table 2) is

rings, respectively, as further supported by retro-Diels−Alder ions at m/z 158 and 172, respectively.7 A possible formation pathway of C31 benzohopane (Figures 2A and 4 and Table 2) to a series of polyaromatic derivatives is shown in Figure 4. The compound with M• + at m/z 384 (compound 1 in Figures 2, 4, and 5 and Table 2) is interpreted as a diaromatic benzohopane (C29H36) from the aromatization of the D and E rings of C31 benzohopane, producing an acenaphthylene moiety. This is supported by acenaphthyl tropylium ion at m/z 177 from C-ring cleavage and the A-ring fragment after loss of M−CH3 at m/z 133. C


a

compound

D

nd = not detected.

Benzohopanes Cyclized at C-16 16,31-cyclohomohopa-16,21,30-triene (or 4′-methylbenzo[16,17,21]-22,29,30-trisnorhop-16-ene) 16,31-cyclobishomohopa-16,21,30-triene (or 4′,6′-dimethylbenzo[16,17,21]-22,29,30-trisnorhop-16-ene) Benzohopanes Cyclized at C-20 20,32-cyclo-17α(H)-bishomohopa-20,22(30),30-triene 20,32-cyclo-17α(H)-trishomohopa-20,22(30),31-triene 20,32-cyclo-17α(H)-tetrakishomohopa-20,22(30),31-triene 20,32-cyclo-31-methyl-17α(H)-trishomohopane-20,22(30),31-triene 20,32-cyclo-17α(H)-pentakishomohopa-20,22(30),31-triene Polyaromatic Benzohopane Derivatives 16,31-cyclo-27,28-bisnorhomohopa-13,15,17,19,21,30-hexaene (1) 16,31-cyclo-27,28-bisnortrishomohopa-13,15,17,19,21,30-hexaene (2) 16,31-cyclo-27,28-bisnorhomohopa-11,13,15,17,19,21,30-heptaene (3) 16,31-cyclo-27,28-bisnorhomohopa-6,11,13,15,17,19,21,30-octaene (4) 16,31-cyclo-26,27,28-trisnorhomohopa-8,11,13,15,17,19,21,30-octaene (5) 16,31-cyclo-26,27,28-trisnorbishomohopa-8,11,13,15,17,19,21,30-octaene (6) 16,31-cyclo-26,27,28-trisnorhomohopa-6,8,11,13,15,17,19,21,30-nonaene (7) 16,31-cyclo-26,27,28-trisnorhomohopa-2,6,8,11,13,15,17,19,21,30-decaene (8) 16,31-cyclo-25,26,27,28-tetrakisnorbishomohopa-5,7,9,11,13,15,17,19,21,30-decaene (9) 16,31-cyclo-25,26,27,28-tetrakisnortrishomohopa-5,7,9,11,13,15,17,19,21,30-decaene (10) 16,31-cyclo-26,27,28-trisnor-30-methyl-bishomohopa-8,11,13,15,17,19,21,30-octaene (11) 16,31-cyclo-26,27,28-trisnortrishomohopa-8,11,13,15,17,19,21,30-octaene (12) 16,31-cyclo-26,27,28-trisnorpentakishomohopa-6,8,11,13,15,17,19,21,30-nonaene (13) 20,32-cyclo-26,27,28-trisnortrishomohopa-8,11,13,15,17,20,22(30),31-octaene (14) 20,32-cyclo-26,27,28-trisnortetrakishomohopa-8,11,13,15,17,20,22(30),31-octaene (15) 20,32-cyclo-26,27,28-trisnorpentakishomohopa-8,11,13,15,17,20,22(30),31-octaene (16) 20,32-cyclo-27,28-bisnortrishomohopa-13,15,17,20,22(30),31-hexaene (17) Diaromatic 23- and 24-Norbenzohopanes 16,31-cyclo-23,27,28-trisnorhomohopa-13,15,17,19,21,30-hexaene (18) 16,31-cyclo-24,27,28-trisnorhomohopa-13,15,17,19,21,30-hexaene (19) 20,32-cyclo-23,27,28,29-tetrakisnorbishomohopa-13,15,17,20,22,31-hexaene (20) 20,32-cyclo-24,27,28,29-tetrakisnorbishomohopa-13,15,17,20,22,31-hexaene (21) 418 432 432 446 460 460 474 384 412 382 380 366 380 364 362 362 376 394 394 420 394 408 422 412 370 370 370 370

C32H48 C33H50 C34H52 C34H52 C35H54 C29H36 C31H40 C29H34 C29H32 C28H30 C29H32 C28H28 C28H26 C28H26 C29H28 C30H34 C30H34 C32H36 C30H34 C31H36 C32H38 C31H40 C28H34 C28H34 C28H34 C28H34

MW

C31H46 C32H48

composition

nd nd nd nd

0.054 nd 0.002 nd 0.104 0.021 0.025 nd 0.002 0.004 nd nd nd nd nd nd 0.007

0.002 0.004 0.003 0.004 nd

0.002 0.001

MR7

nd nd nd nd

0.008 nd nd nd 0.006 0.010 0.005 nd nd nd nd nd nd nd 0.017 nd 0.017

0.018 0.029 0.011 0.010 nd

0.009 0.005

MRW2

nd nd nd nd

0.115 nd 0.056 nd 0.096 0.029 0.309 nd 0.002 0.002 nd nd nd nd nd nd 0.004

0.039 0.053 0.021 0.019 nd

0.022 0.011

MRW4

nd nd nd nd

0.406 0.369 0.177 nd 0.344 0.149 1.008 nd 0.019 0.016 0.189 0.150 0.474 0.197 0.495 0.355 0.138

0.093 0.112 0.032 0.036 0.006

0.102 0.025

J124W127

samples (μg/g of TOC)

nd nd nd nd

0.191 0.035 0.055 nd 0.452 0.016 0.612 nd 0.003 0.007 nd nd nd nd 0.006 nd nd

0.021 0.032 0.011 0.007 nd

0.018 0.005

WL47W80

Table 2. Concentrations of Benzohopanes, Their Polyaromatic Derivatives and Diaromatic 23- and 24-Norbenzohopanes in the Samples (μg/g of TOC)

nd nd nd nd

0.553 1.072 0.192 nd 0.941 0.277 2.409 nd 0.033 0.044 nd nd nd 1.021 1.080 0.992 0.188

0.470 0.819 0.205 0.230 0.062

0.183 0.101

Z90W181

2.641 4.742 7.306 7.383

1.114 nd 2.361 0.664 1.804 0.587 74.492 0.704 0.015 0.083 0.765 0.351 nd nd nd nd nd

nd nd nd nd nd

nda nd

J144P197

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Figure 4. Possible formation pathway of the polyaromatic derivatives of benzohopane cyclized at C-16 (compounds 1−10).

Figure 5. Mass spectra of di-, tri-, and tetraaromatic derivatives of benzohopanes cyclized at C-16. E


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Figure 6. Mass spectra of tri- and tetraaromatic derivatives of benzohopanes cyclized at C-16 and cyclized at C-20.

assigned as a diaromatic benzohopane (C29H34) derived from further aromatization at C-11−C-12. Compound 4 occurs as a trace component in the OM-rich sandstone sample (J144P197) with M• + at m/z 380, but we have no definitive mass spectrum; therefore, its structure is speculative as C29H32 (compound 4 in Figures 2 and 4 and Table 2), with tentative double bonds between C-6 and C-7 as well as between C-11 and C-12. Compound 5 is interpreted as a triaromatic benzohopane with M• + at m/z 366 (compound 5 in Figures 2−5 and Table 2) and assigned as C28H30 derived from aromatization of the C ring of the C31 benzohopane structure. A minor amount of its homologue is also found as C29H32 with M• + at m/z 380 (compound 6 in Figures 2 and 4 and Table 2). Compound 7 with M• + at m/z 364 is interpreted as C28H28 by loss of hydrogen to the double bond between positions C-6 and C-7 of compound 5. Furthermore, a small amount of a compound with M• + at m/z 362 has been assigned as another triaromatic benzohopane (C28H26) with two double bonds between positions C-2 and C-3 as well as between C-6 and C-7 (compound 8 in Figures 2B and 4 and Table 2). Some polyaromatic benzohopanes with an additional methyl group at C-31 are observed as traces, with two exceptions

of compounds 9 and 10 proposed as tetraaromatic benzohopanes. They have M• + at m/z 362 and 376, respectively, with relatively short retention times compared to the other polyaromatic benzohopanes and are interpreted as C28H26 and C29H28, respectively (compounds 9 and 10 in Figures 2 and 4−6 and Table 2). Further aromatic derivatives of benzohopane cyclized at C-16 include compounds with M• + at m/z 394 and 420 and assigned as triaromatic benzohopanes, C30H34 and C32H36, respectively, with differing alkyl substituents (compounds 11−13 in Figures 3 and 6 and Table 2). In addition, we observe minor amounts of analogues with successive degrees of aromatization to the tetraaromatic analogues, but the mass spectra only show M• +, M−CH3, and sometimes M2+ buried among ions from other compounds. The fully aromatic derivatives, 1,9,11-trimethylindeno[1,7-ab]chrysene and homologues, were not detectable. The full elucidation of these aromatic hydrocarbons would require further separation and confirmation by other methods. The benzohopanes cyclized at the C-20 position are more abundant compared to those cyclized at C-16 (Figures 2A and 3 and Tables 1 and 2). These compounds have the benzene ring F


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Figure 7. Mass spectra of di- and triaromatic derivatives of benzohopanes cyclized at C-20 and diaromatic 23- and 24-norbenzohopanes.

diaromatic 23- and 24-norbenzohopanes (compounds 18−21 in Figures 2B and 7 and Table 2). On the basis of their GC retention indices, the first two are assigned as cyclized at C-16 and the second two are assigned as cyclized at C-20. Furthermore, the axial 4β-methyl isomers for both elute prior to the equatorial 4α-methyl isomers as found for diterpane standards. It needs to be highlighted that all compounds discussed above have been identified using a J&W HP5-MS column. The J&W DB35-MS column is not recommended for benzohopane analysis as a result of its higher polarity compared to HP5-MS. On the DB35-MS column, only C31H46 C-16 benzohopane, its nine polyaromatic derivatives, and four diaromatic 23- and 24-norbenzohopanes (compounds 1−6, 9, 10, and 17−21 in the figures and tables) with shortest retention times were identifiable and the other compounds were not detected as a result of their longer retention times (over 130 min) on this column. 3.4. Benzohopane Resistance to Biodegradation. It is well-known that benzohopanes usually display a strong resistance to biodegradation.10,20−22 Liao et al.7 showed that the benzohopanes cyclized at C-20 are more stable than those

condensed to the E ring of a hopane skeleton, resulting in the occurrence of two groups of ions at m/z 144 + 14n and 156 + 14n.4,5,9 The presence of m/z 191 indicates the A and B rings of a hopanoid skeleton, whereas the key ions at m/z 211 + 14n are characteristic of fragments containing the benzene ring.9 Thus, M• + at m/z 432, 446, 460, and 474 indicates C32−C35 benzohopanes7,9 (Table 2). Besides the benzohopanes cyclized at the C-20 position, a series of their triaromatic derivatives have been observed in the samples. These compounds are characterized by strong M• + at m/z 394, 408, and 422, M+−CH3, and minor ions within m/z 167−211, including M • 2+ (compounds 14−16 in Figures 2A, 3, 6, and 7 and Table 2), with compositions of C30H34, C31H36, and C32H38, respectively. The proposed structures are given on the mass spectra (Figures 6 and 7). Interestingly, the compound with the highest molecular weight has the shortest retention time (Figures 2A and 3). A minor diaromatic analogue, C31H40 with M• + at m/z 412, is also found (compound 17 in Figures 3A and 7 and Table 2). In one sample (J144P197), we observe four essentially identical mass spectra with M• + at m/z 370 (C28H34), interpreted as G


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(9) Nytoft, H. P.; Vuković, N. S.; Kildahl-Andersen, G.; Rise, F.; Ž ivotić, D. R.; Stojanović, K. A. Energy Fuels 2016, 30, 5563−5575. (10) Bennett, B.; Jiang, C.; Larter, S. R. Org. Geochem. 2009, 40, 667− 670. (11) Sinninghe Damsté, J. S.; Schouten, S.; van Vliet, N. H.; Geenevasen, J. A. J. Tetrahedron Lett. 1998, 39, 3021−3024. (12) Carrillo-Hernández, T.; Schaeffer, P.; Albrecht, P. Chem. Commun. 2001, 1976−1977. (13) Connan, J.; Dessort, D. Org. Geochem. 1987, 11, 103−113. (14) Rybicki, M.; Marynowski, L.; Misz-Kennan, M.; Simoneit, B. R. T. Org. Geochem. 2016, 102, 77−92. (15) Gedl, P. Ann. Soc. Geol. Polym. 2007, 77, 147−159. (16) Bastow, T. P.; van Aarssen, B. G. K.; Lang, D. Org. Geochem. 2007, 38, 1235−1250. (17) Greiner, A. C.; Spyckerelle, C.; Albrecht, P. Tetrahedron 1976, 32, 257−260. (18) LaFlamme, R. E.; Hites, R. A. Geochim. Cosmochim. Acta 1979, 43, 1687−1691. (19) Freeman, K. H.; Boreham, C. J.; Summons, R. E.; Hayes, J. M. Org. Geochem. 1994, 21, 1037−1049. (20) Bennett, B.; Fustic, M.; Farrimond, P.; Huang, H.; Larter, S. R. Org. Geochem. 2006, 37, 787−797. (21) Tian, H.; Cheng, P.; Zhou, Q.; Xiao, X.; Wilkins, R. W. T. Org. Geochem. 2012, 45, 1−6. (22) Wang, G.; Wang, T. G.; Simoneit, B. R. T.; Zhang, L. Org. Geochem. 2013, 55, 72−84.

cyclized at C-16. The ratio of the sums of these two types of benzohopanes with cyclization at C-16 versus C-20 ranges from 0.48 to 0.73 in our samples (with one exception for sample MR7), indicating that the C-20 cyclized benzohopanes are more abundant (Table 1). However, in the sandstone sample J144P197, regular benzohopanes cyclized at the C-20 or C-16 positions are absent (Table 2 and Figure 2B), whereas the di-, tri-, and tetraaromatic derivatives of benzohopane cyclized at C-16 far exceed the other aromatic compounds (only small amounts of cadalene and benzo[b]fluoranthene were detected). The aliphatic fraction of this OM-rich sandstone sample contains an unresolved compound mixture (“hump”) and traces of hopanes and steranes, indicating that this sample is heavily biodegraded. This implies that the polyaromatic derivatives are more resistant to biodegradation than the regular benzohopanes cyclized at C-16 and can remain behind in biodegraded samples, even when their precursors are already absent.

4. CONCLUSION A novel series of di-, tri-, and tetraaromatic derivatives of benzohopanes cyclized at C-16 or C-20 were identified in the Lower Jurassic Blanowice Formation of southern Poland. Their possible structures and formation pathway have been proposed on the basis of their mass spectra and gas chromatographic retention times. The diverse distribution of benzohopane derivatives in these coals and surrounding sandstones reflected differences in the degree of biodegradation. The polyaromatic derivatives of benzohopane cyclized at C-16 appear to be more resistant to biodegradation than the regular benzohopanes. The general geochemical data and the occurrence of unsaturated benzohopane derivatives suggest a low coalification range of the Blanowice coals, a characteristic for lignites.

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Corresponding Author

*Telephone: +48-32-3689824. Fax: +48-32-2915865. E-mail: [email protected]. ORCID

Maciej Rybicki: 0000-0001-5735-7746 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by Narodowe Centrum Nauki (NCN) Grant DEC-2012/05/N/ST10/00486 to Maciej Rybicki.

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