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GuannanDong/PhytaneSandbox
Skeletal formula of phytane
Names
IUPAC name
2,6,10,14-Tetramethylhexadecane[1]
Identifiers
3D model (JSmol)
1744639
ChEBI
ChemSpider
EC Number
  • 211-332-2
MeSH phytane
UNII
  • InChI=1S/C20H42/c1-7-18(4)12-9-14-20(6)16-10-15-19(5)13-8-11-17(2)3/h17-20H,7-16H2,1-6H3 ☒N
    Key: GGYKPYDKXLHNTI-UHFFFAOYSA-N ☒N
  • CCC(C)CCCC(C)CCCC(C)CCCC(C)C
Properties
C20H42
Molar mass 282.556 g·mol−1
Appearance Colorless liquid
Odor Odorless
Density 0.791 g mL-1 (at 20 °C)
Boiling point 301.41 °C (574.54 °F; 574.56 K) at 760 mmHg
Related compounds
Related alkanes
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Phytane is a type of isoprenoid alkane that is mostly formed from dehydroxylation of phytol[2]. Phytol is part of the chlorophyll molecule. Similarly, pristane is also mainly formed from phytol but has one less carbon. Pristane and phytane are common constituents in petroleum and have been used as a biomarker for indicating depositional conditions and correlating oil and its source rock (from where oil formed). In environmental studies, pristane and phytane are target compounds for investigating oil spill.

Chemistry

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Phytane is a clear and colorless liquid at room temperature. It is a head-to-tail linked regular isoprenoid, a non-polar compound[2].

Phytane has many structural isomers with chemical formula C20H42, 366319 to be exact. Among them, crocetane is a tail-to-tail linked isoprenoid and often co-elutes with phytane on GC/MS due to the structural similarity.

The substituent of phytane is phytanyl. Phytanyl groups are frequently found in archaeal membrane lipids of methanogen and halophilic archaea[3], for example, in archaeol.

Phytene is the singly unsaturated version of phytane. Phytene is also found as the functional group phytyl in many organic molecules of biological importance such as chlorophyll, tocopherol (Vitamin E) and phylloquinone (Vitamin K1). Phytene's corresponding alcohol is phytol.

Geranylgeranene is the fully unsaturated form of phytane. The corresponding substituent is geranylgeranyl.

Sources

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Structure of chlorophyll a, with a side chain containing a phytyl group.

The major source of phytane and pristane is thought to be chlorophyll[4]. Chlorophyll is one of the most important photosynthesis pigments in plants, algae, and cyanobacteria, and is the most abundant tetrapyrrole in the biosphere[5]. Hydrolysis of chlorophyll a, b, d, and f during invertebrate feeding[6], or in marine sediment, releases phytol from the side chain, which is then converted to phytane or pristane.

Another possible source of phytane and pristane is archaeal ether lipids. Laboratory studies show that thermal maturation of methanogenic archaea generates pristane and phytane from diphytanyl glyceryl ethers (archaeols)[7][8][9].

In addition, pristane can be possibly originated from tocopherols[10] and methyltrimethyltridecylchromans (MMTCs)[11].

Preservation

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In suitable environment, biomolecules like chlorophyll can be converted and preserved in recognizable form as biomarker. Conversion during diagenesis often causes the chemical loss of functional groups like double bonds and hydroxyl groups.

Pristane and phytane are formed by diagenesis of phytol under oxic and anoxic conditions, respectively.

Early studies suggested that pristane and phytane are diagenetic products of phytol under different redox conditions. Pristane can be formed in oxidizing conditions by phytol oxidation to phytenic acid, which may then undergo decarboxylation to pristene, before finally being reduced to pristane. In contrast, phytane is likely from reduction and dehydration of phytol (via dihydrophytol or phytene) under relatively anoxic conditions[12].

However, different biotic and abiotic processes may play a significant role during the diagenesis of chlorophyll and phytol, and the exact reactions are more complicated and not well-correlated to redox conditions[3][13].

Geochemical parameter

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Pristane/Phytane ratio

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Pristane/Phytane, or Pr/Ph, is an indicator for redox conditions in the depositional environment. This index is based on the assumption that pristane is formed from phytol by an oxidative pathway, while phytane is generated through various reductive pathways[12][14]. In non-biodegraded crude oil, Pr/Ph less than 0.8 indicates saline to hypersaline conditions associated with evaporite and carbonate deposition; whereas organic-lean terrigenous, fluvial, and deltaic sediments under oxic to suboxic conditions usually generate crude oil with Pr/Ph above 3[15]. Pr/Ph is commonly applied because pristane and phytane are measured easily using gas chromatography.

However, the index should be used very cautiously: pristane and phytane may not result from degradation of the same precursor (chlorophyll phytyl chain and ether lipids of archaea[7] for both pristane and phytane, α-tocopherols[10] and MMTCs[11] only for pristane). Also, pristane, but not phytane, can be produced in reducing environments by clay-catalysed degradation of phytol and subsequent reduction[16]. Additionally, during catagenesis, Pr/Ph tends to increase[17]. This variation may be due to preferential release of sulfur-bound phytols from source rocks during early maturation[18].

Pristane/nC17 and phytane/nC18 ratios

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Pristane/n-heptadecane (or Pr/nC17) and phytane/n-octadecane (or Ph/C18) are sometimes used in petroleum correlation studies. Oils from rocks deposited under open-ocean conditions showed Pr/nC17 < 0.5, while those from inland peat swamp had ratios greater than 1[19].

The ratios should be used with caution for several reasons. Both Pr/nC17 and Ph/nC18 decrease with thermal maturity of petroleum because isprenoids are less thermal stable than linear ones. However, biodegradation increases these ratios because aerobic bacteria generally attack linear alkanes before the isprenoids. Therefore, biodegraded oil is similar to low-maturity non-degraded oil in the sense of low n-alkane relative to pristane and phytane[15].

Biodegradation scale

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Pristane and phytane are more resistant to biodegradation than n-alkanes, but less so than steranes and hopanes. The presence or depletion of pristane and phytane can be used to determine the level of biodegradation.

Compound specific isotopes analysis

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Carbon isotopes

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Carbon isotope composition of pristane and phytane generally reflects the kinetic isotope fractionation in photosynthesis. For example, δ13C (PDB) of pristane and phytane in gilsonites from the Uinta Basin, Utah is -33 to -34‰, suggesting an origin from photic zone organism. The isotopic ratios match those in the proposed Mahogany Ledge oil shale source rocks.

Carbon isotope compositions of pristane and phytane in crude oil can help to constrain their source. Pristane and phytane from a common precursor should have δ13C values differing by no more than 0.3 ‰[20].

Hydrogen isotopes

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Hydrogen isotope composition of phytol in marine phytoplankton and algae is highly depleted, with δD (VSMOW) from -360 to -280‰[21]. Thermal maturation preferentially releases light isotopes and pristane and phytane becomes progressively heavier with maturation.

Case study: limitation of Pr/Ph as a redox indicator

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Inferences from Pr/Ph on the redox potential of the source sediments should always be supported by other geochemical and geological data, such as sulfur content or the C35 homohopane index. The Baghewala-1 oil from India has low Pr/Ph (0.9), high sulfur (1.2 wt.%) and high C35 homohopane index (12), consistent with anoxia during deposition of the source rock[22].

However, drawing conclusion on the oxicity of depositional environment from Pr/Ph alone can be misleading because salinity effect seems to control the Pr/Ph in hypersaline environments. The decrease in Pr/Ph during deposition of the Permian Kupferschiefer sequence in Germany, which is in coincidence with an increase in trimethylated 2-methyl-2-(4,8,12-trimethyltridecyl)chromans, aromatic compounds believed to be markers of salinity[23].

See also

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Reference

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  1. ^ "phytane - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 27 March 2005. Identification and Related Records. Retrieved 14 March 2012.
  2. ^ a b Moldowan, J. M.; Walters, C. C.; Peters, K. E. (December 2004). "Organic chemistry". The Biomarker Guide. Retrieved 2019-06-01.
  3. ^ a b Rontani, Jean-François; Bonin, Patricia (November 2011). "Production of pristane and phytane in the marine environment: role of prokaryotes". Research in Microbiology. 162 (9): 923–933. doi:10.1016/j.resmic.2011.01.012. PMID 21288485.
  4. ^ Dean, R. A.; Whitehead, E. V. (1961-01-01). "The occurrence of phytane in petroleum". Tetrahedron Letters. 2 (21): 768–770. doi:10.1016/S0040-4039(01)99264-0. ISSN 0040-4039.
  5. ^ Baker, E.W.; Louda, J.W. (1986). "Porphyrins in the geological record". In Johns, R.B. (ed.). Biological Markers in the Sedimentary Record. Elsevier. pp. 125–224.
  6. ^ Blumer, Max; Avigan, Joel (1968-05-01). "On the origin of pristane in marine organisms". Journal of Lipid Research. 9 (3): 350–352. doi:10.1016/S0022-2275(20)43103-7. ISSN 0022-2275. PMID 5646185.
  7. ^ a b Rowland, S. J. (1990-01-01). "Production of acyclic isoprenoid hydrocarbons by laboratory maturation of methanogenic bacteria". Organic Geochemistry. 15 (1): 9–16. doi:10.1016/0146-6380(90)90181-X. ISSN 0146-6380.
  8. ^ Navale, Vivek (1994-06-01). "Comparative study of low and high temperature hydrous pyrolysis products of monoglycerol diether lipid from archaebacteria". Journal of Analytical and Applied Pyrolysis. 29 (1): 33–43. doi:10.1016/0165-2370(93)00786-M. ISSN 0165-2370.
  9. ^ Pease, T. K.; Van Vleet, E. S.; Barre, J. S.; Dickins, H. D. (1998-01-01). "Simulated degradation of glyceryl ethers by hydrous and flash pyrolysis". Organic Geochemistry. 29 (4): 979–988. doi:10.1016/S0146-6380(98)00047-3. ISSN 0146-6380.
  10. ^ a b Brassell, S. C.; P. A. Schenck; de Leeuw, J. W.; Goossens, H. (November 1984). "Tocopherols as likely precursors of pristane in ancient sediments and crude oils". Nature. 312 (5993): 440–442. doi:10.1038/312440a0. ISSN 1476-4687. S2CID 4329068.
  11. ^ a b Li, Maowen; Larter, Steve R.; Taylor, Paul; Jones, D. Martin; Bowler, Bernard; Bjorøy, Malvin (1995-02-01). "Biomarkers or not biomarkers? A new hypothesis for the origin of pristane involving derivation from methyltrimethyltridecylchromans (MTTCs) formed during diagenesis from chlorophyll and alkylphenols". Organic Geochemistry. 23 (2): 159–167. doi:10.1016/0146-6380(94)00112-E. ISSN 0146-6380.
  12. ^ a b Eglinton, G.; S. C. Brassell; Simoneit, B. R. T.; Didyk, B. M. (March 1978). "Organic geochemical indicators of palaeoenvironmental conditions of sedimentation". Nature. 272 (5650): 216–222. doi:10.1038/272216a0. ISSN 1476-4687. S2CID 128737515.
  13. ^ Rontani, Jean-François; Volkman, John K. (2003-01-01). "Phytol degradation products as biogeochemical tracers in aquatic environments". Organic Geochemistry. 34 (1): 1–35. doi:10.1016/S0146-6380(02)00185-7. ISSN 0146-6380.
  14. ^ D. M. McKIRDY; Powell, T. G. (May 1973). "Relationship between Ratio of Pristane to Phytane, Crude Oil Composition and Geological Environment in Australia". Nature Physical Science. 243 (124): 37–39. doi:10.1038/physci243037a0. ISSN 2058-1106.
  15. ^ a b Peters, K. E.; Walters, C. C.; Moldowan, J. M. (2004), "Source- and age-related biomarker parameters", The Biomarker Guide, Cambridge University Press, pp. 483–607, doi:10.1017/cbo9781107326040.004, ISBN 9781107326040, retrieved 2019-06-01
  16. ^ Schenck, P. A.; Lange, F. de; Boon, J. J.; Rijpstra, C.; Irene, W.; Leeuw, J. W. de (1977). "relationship between lipids from Fontinalis antipyretica , its detritus and the underlying sediment: the fate of waxesters and sterolesters". Interactions Between Sediments and Fresh Water; Proceedings of an International Symposium.
  17. ^ VOLKMAN, J. K. (1986). "Acyclic isoprenoids as biological markers". Biological Markers in the Sedimentary Record.: 1817–1828.
  18. ^ De Graaf, Wim; Damsté, Jaap S. Sinninghe; de Leeuw, Jan W (1992-12-01). "Laboratory simulation of natural sulphurization: I. Formation of monomeric and oligomeric isoprenoid polysulphides by low-temperature reactions of inorganic polysulphides with phytol and phytadienes". Geochimica et Cosmochimica Acta. 56 (12): 4321–4328. doi:10.1016/0016-7037(92)90275-N. ISSN 0016-7037.
  19. ^ Lijmbach, W. M. (1975-01-01). "SP (1) On the Origin of Petroleum". World Petroleum Congress. {{cite journal}}: Cite journal requires |journal= (help)
  20. ^ Hayes, J. M.; Freeman, Katherine H.; Popp, Brian N.; Hoham, Christopher H. (1990-01-01). "Compound-specific isotopic analyses: A novel tool for reconstruction of ancient biogeochemical processes". Organic Geochemistry. Proceedings of the 14th International Meeting on Organic Geochemistry. 16 (4): 1115–1128. doi:10.1016/0146-6380(90)90147-R. ISSN 0146-6380. PMID 11540919.
  21. ^ Sessions, Alex L.; Burgoyne, Thomas W.; Schimmelmann, Arndt; Hayes, John M. (1999-09-01). "Fractionation of hydrogen isotopes in lipid biosynthesis". Organic Geochemistry. 30 (9): 1193–1200. doi:10.1016/S0146-6380(99)00094-7. ISSN 0146-6380.
  22. ^ K. E. Peters (2), M. E. Clark (3) (1995). "Recognition of an Infracambrian Source Rock Based on Biomarkers in the Baghewala-1 Oil, India". AAPG Bulletin. 79 (10). doi:10.1306/7834da12-1721-11d7-8645000102c1865d. ISSN 0149-1423.{{cite journal}}: CS1 maint: numeric names: authors list (link)
  23. ^ Schwark, L; Vliex, M; Schaeffer, P (1998-12-01). "Geochemical characterization of Malm Zeta laminated carbonates from the Franconian Alb, SW-Germany (II)". Organic Geochemistry. 29 (8): 1921–1952. doi:10.1016/S0146-6380(98)00192-2. ISSN 0146-6380.
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