In an organic chemistry general sense, an ether lipid implies an ether bridge between an alkyl group and an unspecified alkyl or aryl group, not necessarily glycerol. If glycerol is involved, the compound is called a glyceryl ether, which may take the form of an alkylglycerol, an alkyl acyl glycerol, or in combination with a phosphatide group, a phospholipid.
Hopanoids are a diverse subclass of triterpenoids with the same hydrocarbon skeleton as the compound hopane. This group of pentacyclic molecules therefore refers to simple hopenes, hopanols and hopanes, but also to extensively functionalized derivatives such as bacteriohopanepolyols (BHPs) and hopanoids covalently attached to lipid A.
TEX86 is an organic paleothermometer based upon the membrane lipids of mesophilic marine Nitrososphaerota (formerly Marine Group 1 Crenarchaeota).
Cholestane is a saturated tetracyclic triterpene. This 27-carbon biomarker is produced by diagenesis of cholesterol and is one of the most abundant biomarkers in the rock record. Presence of cholestane, its derivatives and related chemical compounds in environmental samples is commonly interpreted as an indicator of animal life and/or traces of O2, as animals are known for exclusively producing cholesterol, and thus has been used to draw evolutionary relationships between ancient organisms of unknown phylogenetic origin and modern metazoan taxa. Cholesterol is made in low abundance by other organisms (e.g., rhodophytes, land plants), but because these other organisms produce a variety of sterols it cannot be used as a conclusive indicator of any one taxon. It is often found in analysis of organic compounds in petroleum.
Phytane is the isoprenoid alkane formed when phytol, a chemical substituent of chlorophyll, loses its hydroxyl group. When phytol loses one carbon atom, it yields pristane. Other sources of phytane and pristane have also been proposed than phytol.
Caldarchaeol is a membrane-spanning lipid of the glycerol dialkyl glycerol tetraether class. It is found in hyperthermophilic archaea. Membranes made up of caldarchaeol are more stable since the hydrophobic chains are linked together, allowing the microorganisms to withstand high temperatures. It is also known as dibiphytanyldiglycerol tetraether. Two glycerol units are linked together by two strains which consist of two phytanes linked together to form a linear chain of 32 carbon atoms.
Archaeol is composed of two phytanyl chains linked to the sn-2 and sn-3 positions of glycerol. As its phosphate ester, it is a common component of the membranes of archaea.
Desmosterol (Cholesta-5,24-dien-3β-ol) is a lipid present in the membrane of phytoplankton. Structurally, desmosterol has a similar backbone to cholesterol, with the exception of an additional double bond in the structure of desmosterol.
Isorenieratene /ˌaɪsoʊrəˈnɪərətiːn/ is a carotenoid light harvesting pigment produced exclusively by the genus Chlorobium. Chlorobium are the brown-colored strains of the family of green sulfur bacteria (Chlorobiaceae). Green sulfur bacteria are anaerobic photoautotrophic organisms meaning they perform photosynthesis in the absence of oxygen using hydrogen sulfide in the following reaction:
Dinosterol (4α,23,24-trimethyl-5α-cholest-22E-en-3β-ol) is a 4α-methyl sterol that is produced by several genera of dinoflagellates and is rarely found in other classes of protists. The steroidal alkane, dinosterane, is the 'molecular fossil' of dinosterol, meaning that dinosterane has the same carbon skeleton as dinosterol, but lacks dinosterol's hydroxyl group and olefin functionality. As such, dinosterane is often used as a biomarker to identify the presence of dinoflagelletes in sediments.
Taraxerol is a naturally-occurring pentacyclic triterpenoid. It exists in various higher plants, including Taraxacum officinale (Asteraceae), Alnus glutinosa (Betulaceae), Litsea dealbata (Lauraceae), Skimmia spp. (Rutaceae), Dorstenia spp. (Moraceae), Maytenus spp. (Celastraceae), and Alchornea latifolia (Euphobiaceae). Taraxerol was named "alnulin" when it was first isolated in 1923 from the bark of the grey alder by Zellner and Röglsperger. It also had the name "skimmiol" when Takeda and Yosiki isolated it from Skimmia (Rutaceae). A large number of medicinal plants are known to have this compound in their leaves, roots or seed oil.
Crocetane, or 2,6,11,15-tetramethylhexadecane, is an isoprenoid hydrocarbon compound. Unlike its isomer phytane, crocetane has a tail-to-tail linked isoprenoid skeleton. Crocetane has been detected in modern sediments and geological records as a biomarker, often associated with anaerobic methane oxidation.
Jessica E. Tierney (born 1982) is an American paleoclimatologist who has worked with geochemical proxies such as marine sediments, mud, and TEX86, to study past climate in East Africa. Her papers have been cited more than 2,500 times; her most cited work is Northern Hemisphere Controls on Tropical Southeast African Climate During the Past 60,000 Years. Tierney is currently an associate professor of geosciences and the Thomas R. Brown Distinguished Chair in Integrative Science at the University of Arizona and faculty affiliate in the University of Arizona School of Geography, Development and Environment Tierney is the first climatologist to win NSF's Alan T Waterman Award (2022) since its inception in 1975.
24-Norcholestane, a steroid derivative, is used as a biomarker to constrain the source age of sediments and petroleum through the ratio between 24-norcholestane and 27-norcholestane, especially when used with other age diagnostic biomarkers, like oleanane. While the origins of this compound are still unknown, it is thought that they are derived from diatoms due to their identification in diatom rich sediments and environments. In addition, it was found that 24-norcholestane levels increased in correlation with diatom evolution. Another possible source of 24-norcholestane is from dinoflagellates, albeit to a much lower extent.
Crenarchaeol is a glycerol biphytanes glycerol tetraether (GDGT) biological membrane lipid. Together with archaeol, crenarcheol comprises a major component of archaeal membranes. Archaeal membranes are distinct from those of bacteria and eukaryotes because they contain isoprenoid GDGTs instead of diacyl lipids, which are found in the other domains. It has been proposed that GDGT membrane lipids are an adaptation to the high temperatures present in the environments that are home to extremophile archaea
Paula Veronica Welander is a microbiologist and professor at Stanford University who is known for her research using lipid biomarkers to investigate how life evolved on Earth.
Highly branched isoprenoids (HBIs) are long-chain alkenes produced by a small number of marine diatoms. There are a variety of highly branched isoprenoid structures, but C25 Highly branched isoprenoids containing 1 to 3 double bonds are the most common in the sedimentary record. Highly branched isoprenoids have been used as environmental proxies for sea ice conditions in the Arctic and Antarctic throughout the Holocene, and more recently, are being used to reconstruct more ancient ice records.
Lycopane (C40H82; 2,6,10,14,19,23,27,31-octamethyldotriacontane), a 40 carbon alkane isoprenoid, is a widely present biomarker that is often found in anoxic settings. It has been identified in anoxically deposited lacustrine sediments (such as the Messel formation and the Condor oil shale deposit). It has been found in sulfidic and anoxic hypersaline environments (such as the Sdom Formation). It has been widely identified in modern marine sediments, including the Peru upwelling zone, the Black Sea, and the Cariaco Trench. It has been found only rarely in crude oils.
Hydroxyarchaeol is a core lipid unique to archaea, similar to archaeol, with a hydroxide functional group at the carbon-3 position of one of its ether side chains. It is found exclusively in certain taxa of methanogenic archaea, and is a common biomarker for methanogenesis and methane-oxidation. Isotopic analysis of hydroxyarchaeol can be informative about the environment and substrates for methanogenesis.
Glycerol dialkyl glycerol tetraether lipids (GDGTs) are a class of membrane lipids synthesized by archaea and some bacteria, making them useful biomarkers for these organisms in the geological record. Their presence, structure, and relative abundances in natural materials can be useful as proxies for temperature, terrestrial organic matter input, and soil pH for past periods in Earth history. Some structural forms of GDGT form the basis for the TEX86 paleothermometer. Isoprenoid GDGTs, now known to be synthesized by many archaeal classes, were first discovered in extremophilic archaea cultures. Branched GDGTs, likely synthesized by acidobacteriota, were first discovered in a natural Dutch peat sample in 2000.
