Isoprene (short for isoterpene Terpenes are a large and varied class of hydrocarbons, produced primarily by a wide variety of plants, particularly conifers, though also by some insects such as termites or swallowtail butterflies, which emit terpenes from their osmeterium^[1]), or 2-methyl-1,3-butadiene, is a common organic compound An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered inorganic. The distinction between "organic" and " with the formula CH₂=C(CH₃)CH=CH₂. It is present under standard conditions as a colorless liquid. It is the monomer A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer. The most common natural monomer is glucose, which is linked by glycosidic bonds into polymers such as cellulose and starch, and is over 76% of the weight of all plant matter. Most often the term monomer refers to the organic molecules which form of natural rubber Natural rubber is an elastomer that was originally derived from a milky colloidal suspension, or latex, found in the sap of some plants. The purified form of natural rubber is the chemical polyisoprene, which can also be produced synthetically. Natural rubber is used extensively in many applications and products, as is synthetic rubber and is a precursor to an immense variety of other naturally occurring compounds.

Occurrence and production

Natural rubber Natural rubber is an elastomer that was originally derived from latex, a milky colloid found in the sap of some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the latex sap collected and refined into a usable rubber. The purified form of natural rubber is the chemical polyisoprene, which can also is a polymer A polymer is a large molecule composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a wide variety of properties of isoprene—most often cis-1,4-polyisoprene—with a molecular weight of 100,000 to 1,000,000. Typically, a few percent of other materials, such as proteins, fatty acids, resins, and inorganic materials are found in high-quality natural rubber. Some natural rubber sources called gutta percha Gutta-percha is a genus of tropical trees native to Southeast Asia and northern Australasia, from Taiwan south to the Malay Peninsula and east to the Solomon Islands. It is also an inelastic natural latex produced from the sap of these trees, particularly from the species Palaquium gutta. Chemically, gutta-percha is a polyterpene, a polymer of are composed of trans-1,4-polyisoprene, a structural isomer In chemistry, isomers are compounds with the same molecular formula but different structural formulas. The word is derived from the Greek ισομερης, isomerès; isos = "equal", méros = "part". There are many different classes of isomers, like stereoisomers, enantiomers, geometrical isomers, et cetera . Isomers do not that has similar, but not identical, properties.^[2]

Isoprene is produced and emitted by many species of trees into the atmosphere (major producers are oak An Oak is a tree or shrub in the genus Quercus , of which about 600 species exist on earth. "Oak" may also appear in the names of species in related genera, notably Lithocarpus. The genus is native to the northern hemisphere, and includes deciduous and evergreen species extending from cold latitudes to tropical Asia and the Americas trees). The yearly production of isoprene emissions by vegetation is around 600 Tg, with half that coming from tropical broadleaf trees and the remainder coming from shrubs.^[3] After release, isoprene is converted by free radicals (like the hydroxyl (OH) radical) and to a lesser extent by ozone ^[4] into various species, such as aldehydes An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl centre bonded to hydrogen and an R group. The group without R is called the aldehyde group or formyl group. Aldehydes differ from ketones in that the carbonyl is placed at the end of a carbon skeleton rather than, hydroperoxides, organic nitrates and epoxides An epoxide is a cyclic ether with three ring atoms. This ring approximately defines an equilateral triangle, which makes it highly strained. The strained ring makes epoxides more reactive than other ethers. Simple epoxides are named from the parent compound ethylene oxide or oxirane, such as in chloromethyloxirane. As a functional group epoxides, which mix into water droplets and help create aerosols and haze Haze is traditionally an atmospheric phenomenon where dust, smoke and other dry particles obscure the clarity of the sky. The World Meteorological Organization manual of codes includes a classification of horizontal obscuration into categories of fog, ice fog, steam fog, mist, haze, smoke, volcanic ash, dust, sand and snow. Sources for haze.^{[5] [6]} This appears to be a mechanism that trees use not only to overcome the overheating of leaves caused by the Sun but also to fight against free radicals, especially ozone Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope (O2). Ozone in the lower atmosphere is an air pollutant with harmful effects on the respiratory systems of animals and will burn sensitive plants; however, the ozone layer in the upper.^[7]

Isoprene was first isolated by thermal decomposition of natural rubber.^[8] It is most readily available industrially as a byproduct of the thermal cracking In petroleum geology and chemistry, cracking is the process whereby complex organic molecules such as kerogens or heavy hydrocarbons are broken down into simpler molecules by the breaking of carbon-carbon bonds in the precursors. The rate of cracking and the end products are strongly dependent on the temperature and presence of any catalysts of naphtha Naphtha normally refers to a number of different flammable liquid mixtures of hydrocarbons, i.e. a distillation product from petroleum or coal tar boiling in a certain range and containing certain hydrocarbons. It is a broad term covering the lightest and most volatile fraction of the liquid hydrocarbons in petroleum or oil, as a side product in the production of ethylene Ethylene is a gaseous organic compound with the formula C2H4. It is the simplest alkene (older name: olefin from its oil-forming property). Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and also has a role in biology as a hormone. Ethylene is the most. About 20,000 tonnes are produced annually.^[2] About 95% of isoprene production is used to produce cis-1,4-polyisoprene—a synthetic Synthetic rubber is any type of artificial elastomer, invariably a polymer. An elastomer is a material with the mechanical property that it can undergo much more elastic deformation under stress than most materials and still return to its previous size without permanent deformation. Synthetic rubber serves as a substitute for natural rubber in version of natural rubber Natural rubber is an elastomer that was originally derived from latex, a milky colloid found in the sap of some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the latex sap collected and refined into a usable rubber. The purified form of natural rubber is the chemical polyisoprene, which can also.

Biological roles and effects

In general, it is the most common hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls. Aromatic hydrocarbons , alkanes, alkenes, cycloalkanes and alkyne-based compounds are different types of hydrocarbons found in the human body.^{[citation needed]} The estimated production rate of isoprene in the human body is 0.15 µmol The mole is the SI base unit of amount of substance; one of a few units used to measure this physical quantity. The name "mole" is an 1897 translation of the German Mol, coined by Wilhelm Ostwald in 1893, although the related concept of equivalent mass had been in use at least a century earlier. The name is assumed to be derived from the/kg/h, equivalent to approximately 17 mg/day for a person weighing 70 kg. Isoprene is also common in low concentrations in many foods.

Isoprene is produced in the chloroplasts of leaves of certain tree species through the DMAPP pathway; the enzyme isoprene synthase is responsible for its biosynthesis. Isoprene is incorporated into and helps stabilize cell membranes in response to heat stress, conferring some tolerance to heat spikes. Isoprene may also confer some resistance to reactive oxygen species.^[7] The amount of isoprene released from isoprene-emitting vegetation depends on leaf mass, leaf area, light (particularly photosynthetic photon flux density, or PPFD), and leaf temperature. Thus, during the night, little isoprene is emitted from tree leaves, whereas daytime emissions are expected to be substantial (~5–20 mg/m²/h)^{[citation needed]} during hot and sunny days.

Isoprene is a common structural motif in biological systems. The terpenes Terpenes are a large and varied class of hydrocarbons, produced primarily by a wide variety of plants, particularly conifers, though also by some insects such as termites or swallowtail butterflies, which emit terpenes from their osmeterium (for example, the carotenes The term carotene is used for several related hydrocarbon substances having the formula C40Hx, which are synthesized by plants but cannot be made by animals. Carotene is an orange photosynthetic pigment important for photosynthesis. Carotenes are all coloured to the human eye. They are responsible for the orange colour of the carrot, for which are tetraterpenes) are derived from isoprene, as are the terpenoids The terpenoids , sometimes called isoprenoids, are a large and diverse class of naturally-occurring organic chemicals similar to terpenes, derived from five-carbon isoprene units assembled and modified in thousands of ways. Most are multicyclic structures that differ from one another not only in functional groups but also in their basic carbon and coenzyme Q Coenzyme Q10 is a 1,4-benzoquinone, where Q refers to the quinone chemical group, and 10 refers to the number of isoprenyl chemical subunits.^{[citation needed]} Also derived from isoprene are phytol, retinol Retinol, is one of the animal forms of vitamin A. It is a diterpenoid and an alcohol. It is convertable to other forms of vitamin A, but as retinol it is thought to serve an irreplaceable vitamin function in the reproductive tracts of male and female mammals. The retinyl ester derivative of the alcohol serves as the storage form of the vitamin in (vitamin A Vitamin A is a vitamin that is needed by the retina of the eye in the form of a specific metabolite, the light-absorbing molecule retinal. This molecule is absolutely necessary for both scotopic and color vision. In another version the vitamin is necessary for the function of the reproductive systems of both male and female mammals. Vitamin A also), tocopherol Tocopherols are a class of chemical compounds of which many have vitamin E activity. It is a series of organic compounds consisting of various methylated phenols. Because the vitamin activity was first identified in 1936 from a dietary fertility factor in rats, it was given the name "tocopherol" from the Greek words “τόκος” [ (vitamin E Vitamin E is a generic term for tocopherols and tocotrienols. Vitamin E is a family of α-, β-, γ-, and δ- tocopherols and corresponding four tocotrienols. Vitamin E is a fat-soluble antioxidant that stops the production of reactive oxygen species formed when fat undergoes oxidation. Of these, α-tocopherol (also written as alpha-tocopherol)), dolichols Dolichol refers to any of a group of long-chain mostly unsaturated organic compounds which are made up of varying numbers of isoprene units terminating in an α-saturated isoprenoid group, containing an alcohol functional group, and squalene Squalene is a natural organic compound originally obtained for commercial purposes primarily from shark liver oil, though plant sources are used as well, including amaranth seed, rice bran, wheat germ, and olives. All plants and animals produce squalene, including humans. Squalene has been proposed to be an important part of the Mediterranean diet. Heme A heme or haem (British English) is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as their prosthetic group; these are known as hemoproteins. Hemes are A has an isoprenoid tail, and lanosterol, the sterol precursor in animals, is derived from squalene Squalene is a natural organic compound originally obtained for commercial purposes primarily from shark liver oil, though plant sources are used as well, including amaranth seed, rice bran, wheat germ, and olives. All plants and animals produce squalene, including humans. Squalene has been proposed to be an important part of the Mediterranean diet and hence from isoprene. The functional isoprene units in biological systems are dimethylallyl pyrophosphate (DMAPP) and its isomer isopentenyl pyrophosphate (IPP), which are used in the biosynthesis of terpenes and lanosterol derivatives.

In virtually all organisms, isoprene derivatives are synthesized by the HMG-CoA reductase pathway. Addition of these chains to proteins is termed isoprenylation.

Biosynthesis and its inhibition by statins

HMG-CoA reductase inhibitors, also known as the group of cholesterol-lowering drugs called statins They lower cholesterol by inhibiting the enzyme HMG-CoA reductase, which is the rate-limiting enzyme of the mevalonate pathway of cholesterol synthesis. Inhibition of this enzyme in the liver results in decreased cholesterol synthesis as well as increased synthesis of LDL receptors, resulting in an increased clearance of low-density lipoprotein, inhibit the synthesis of mevalonate. Mevalonate is a precursor to isopentenyl pyrophosphate Isopentenyl pyrophosphate is an intermediate in the classical, HMG-CoA reductase pathway used by organisms in the biosynthesis of terpenes and terpenoids. IPP is formed from acetyl-CoA via mevalonic acid. IPP can then be isomerized to dimethylallyl pyrophosphate by the enzyme isopentenyl pyrophosphate isomerase, which combines with its isomer dimethylallyl pyrophosphate Dimethylallyl pyrophosphate (DMAPP) is an intermediate product of both mevalonic acid (MVA) pathway and DOXP/MEP pathway. It is an isomer of isopentenyl pyrophosphate (IPP) and exists in virtually all life forms in repeating alternations to form isoprene (or polyprenyl) chains.

Statins They lower cholesterol by inhibiting the enzyme HMG-CoA reductase, which is the rate-limiting enzyme of the mevalonate pathway of cholesterol synthesis. Inhibition of this enzyme in the liver results in decreased cholesterol synthesis as well as increased synthesis of LDL receptors, resulting in an increased clearance of low-density lipoprotein are used to lower cholesterol Cholesterol is a waxy steroid metabolite found in the cell membranes and transported in the blood plasma of all animals. It is an essential structural component of mammalian cell membranes, where it is required to establish proper membrane permeability and fluidity. In addition, cholesterol is an important component for the manufacture of bile, which is synthesized from the 15-carbon isoprenoid farnesyl pyrophosphate Farnesyl pyrophosphate is an intermediate in the HMG-CoA reductase pathway used by organisms in the biosynthesis of terpenes, terpenoids, and sterols, but also inhibit all other isoprenes, including coenzyme Q10 Coenzyme Q10 (also known as ubiquinone, ubidecarenone, coenzyme Q, and abbreviated at times to CoQ10 , CoQ, Q10, or Q) is a 1,4-benzoquinone, where Q refers to the quinone chemical group, and 10 refers to the number of isoprenyl chemical subunits. This flow chart shows the biosynthesis of isoprenes, and the point at which statins act to inhibit this process.

See also

• Merck Index The Merck Index is an encyclopedia of chemicals, drugs and biologicals with over 10,000 monographs on single substances or groups of related compounds. It also includes an appendix with monographs on organic name reactions. It is published by the United States pharmaceutical company Merck & Co. The Merck Index is also available by subscription: an encyclopedia of chemicals, drugs, and biologicals, Susan Budavari (ed.), 11th Edition, Rahway, NJ : Merck, 1989, ISBN 0-911910-28-X
• Poisson, N.; M. Kanakidou, and P. J. Crutzen Paul Jozef Crutzen is a Dutch Nobel prize winning atmospheric chemist (2000). "Impact of nonmethanehydrocarbons on tropospheric chemistry and the oxidizing power of the global troposphere: 3-dimensional modelling results". Journal of Atmospheric Chemistry 36 (2): 157–230. doi A digital object identifier is a character string used to uniquely identify an electronic document or other object. Metadata about the object is stored in association with the DOI name and this metadata may include a location, such as a URL, where the object can be found. The DOI for a document is permanent, whereas its location and other metadata:10.1023/A:1006300616544. ISSN An International Standard Serial Number is a unique eight-digit number used to identify a print or electronic periodical publication. The ISSN system was adopted as international standard ISO 3297 in 2007. The ISO subcommittee TC 46/SC 9 is responsible for the standard 0167-7764.
• Claeys, M.; B. Graham, G. Vas, W. Wang, R. Vermeylen, V. Pashynska, J. Cafmeyer, P. Guyon, M. O. Andreae, P. Artaxo, and W. Maenhaut (2004). "Formation of secondary organic aerosols through photooxidation of isoprene". Science 303 (5661): 1173–1176. doi A digital object identifier is a character string used to uniquely identify an electronic document or other object. Metadata about the object is stored in association with the DOI name and this metadata may include a location, such as a URL, where the object can be found. The DOI for a document is permanent, whereas its location and other metadata:10.1126/science.1092805. ISSN An International Standard Serial Number is a unique eight-digit number used to identify a print or electronic periodical publication. The ISSN system was adopted as international standard ISO 3297 in 2007. The ISO subcommittee TC 46/SC 9 is responsible for the standard 0036-8075. PMID A PMID is a unique number assigned to each PubMed citation of life sciences and biomedical scientific journal articles. The related Pubmed Central archive may additionally assign a separate number, a PMCID (PubMed Central Identifier), normally written with a PMC prefix 14976309.
• Pier, P. A.; and C. McDuffie (1997). "Seasonal isoprene emission rates and model comparisons using whole-tree emissions from white oak". Journal of Geophysical Research 102 (D20): 23,963–23,971. doi A digital object identifier is a character string used to uniquely identify an electronic document or other object. Metadata about the object is stored in association with the DOI name and this metadata may include a location, such as a URL, where the object can be found. The DOI for a document is permanent, whereas its location and other metadata:10.1029/96JD03786. ISSN An International Standard Serial Number is a unique eight-digit number used to identify a print or electronic periodical publication. The ISSN system was adopted as international standard ISO 3297 in 2007. The ISO subcommittee TC 46/SC 9 is responsible for the standard 0148-0227.
• Poschl, U.; R. von Kuhlmann, N. Poisson, and P. J. Crutzen Paul Jozef Crutzen is a Dutch Nobel prize winning atmospheric chemist (2000). "Development and intercomparison of condensed isoprene oxidation mechanisms for global atmospheric modeling". Journal of Atmospheric Chemistry 37 (1): 29–52. doi A digital object identifier is a character string used to uniquely identify an electronic document or other object. Metadata about the object is stored in association with the DOI name and this metadata may include a location, such as a URL, where the object can be found. The DOI for a document is permanent, whereas its location and other metadata:10.1023/A:1006391009798. ISSN 0167-7764.
• Monson, R. K.; and E. A. Holland (2001). "Biospheric trace gas fluxes and their control over tropospheric chemistry". Annual Review of Ecology and Systematics 32: 547–576. doi:10.1146/annurev.ecolsys.32.081501.114136.

References

1. ^ NIKLITSCHEK, M.; JENNIFER ALCAÍNO , SALVADOR BARAHONA , DIONISIA SEPÚLVEDA, CARLA LOZANO, MARISELA CARMONA, ANDRÉS MARCOLETA, CLAUDIO MARTÍNEZ2, PATRICIA LODATO, MARCELO BAEZA, and VÍCTOR CIFUENTES (2008). "Genomic organization of the structural genes controlling the astaxanthin biosynthesis pathway of Xanthophyllomyces dendrorhous". Biol Res (41): 393–108. http://www.scielo.cl/pdf/bres/v41n1/art11.pdf.
2. ^ ^{a b} Hans Martin Weitz and Eckhard Loser “Isoprene” in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a14_627
3. ^ Guenther, A.; T. Karl, P. Harley, C. Wiedinmyer, P. I. Palmer and C. Geron (2006). "Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature)". Atmos. Chem. Phys. 6: 3181–3210. doi:10.5194/acp-6-3181-2006. http://www.atmos-chem-phys.net/6/3181/2006/acp-6-3181-2006.pdf.
4. ^ IUPAC Subcommittee on Gas Kinetic Data Evaluation – Data Sheet Ox_VOC7, 2007|url= http://www.iupac-kinetic.ch.cam.ac.uk/datasheets/pdf/Ox_VOC7_O3_CH2C%28CH3%29CHCH2.pdf
5. ^ Organic Carbon Compounds Emitted By Trees Affect Air Quality, ScienceDaily, Aug. 7, 2009|url=http://www.sciencedaily.com/releases/2009/08/090806141518.htm
6. ^ A source of haze, ScienceNews, August 6th, 2009|url=http://www.sciencenews.org/view/generic/id/46200/title/A_source_of_haze
7. ^ ^{a b} Sharkey, TD; AE Wiberley, and AR Donohue (2007). "Isoprene Emission from Plants: Why and How". Annals of Botany 101 (1): 5–18. doi:10.1093/aob/mcm240. PMID 17921528. PMC 2701830. http://aob.oxfordjournals.org/cgi/content/full/101/1/5.
8. ^ C. G. Williams, Proceedings of the Royal Society 1860 10.

External links

• Report on Carcinogens, Eleventh Edition; U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program
• Science News article describing how isoprene released by plants is converted to light-scattering aerosols

Categories: Dienes | Monomers | IARC Group 2B carcinogens | Hemiterpenes

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