Isoprene
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| Names | |||
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| IUPAC name
2-methyl-1,3-butadiene
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| Other names
isoprene
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| Identifiers | |||
3D model (JSmol)
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| ECHA InfoCard | 100.001.040 | ||
CompTox Dashboard (EPA)
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| Properties | |||
| C5H8 | |||
| Molar mass | 68.12 g/mol | ||
| Density | 0.681 g/cm³ | ||
| Melting point | −145.95 °C | ||
| Boiling point | 34.067 °C | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Isoprene (short for isoterpene[1]), or 2-methyl-1,3-butadiene, is a common organic compound with the formula CH2=C(CH3)CH=CH2. It is present under standard conditions as a colorless liquid. It is the monomer of natural rubber and is a precursor to an immense variety of other naturally occurring compounds.
Occurrence and production
Natural rubber is a polymer 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 are composed of trans-1,4-polyisoprene, a structural isomer 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 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, hydroperoxides, organic nitrates and epoxides, which mix into water droplets and help create aerosols and 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.[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 of naphtha or oil, as a side product in the production of ethylene. About 20,000 tonnes are produced annually.[2] About 95% of isoprene production is used to produce cis-1,4-polyisoprene—a synthetic version of natural rubber.
Biological roles and effects
In general, it is the most common hydrocarbon found in the human body.[citation needed] The estimated production rate of isoprene in the human body is 0.15 µmol/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 (for example, the carotenes are tetraterpenes) are derived from isoprene, as are the terpenoids and coenzyme Q.[citation needed] Also derived from isoprene are phytol, retinol (vitamin A), tocopherol (vitamin E), dolichols, and squalene. Heme A has an isoprenoid tail, and lanosterol, the sterol precursor in animals, is derived from squalene 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, inhibit the synthesis of mevalonate. Mevalonate is a precursor to isopentenyl pyrophosphate, which combines with its isomer dimethylallyl pyrophosphate in repeating alternations to form isoprene (or polyprenyl) chains.
Statins are used to lower cholesterol, which is synthesized from the 15-carbon isoprenoid farnesyl pyrophosphate, but also inhibit all other isoprenes, including coenzyme Q10. This flow chart shows the biosynthesis of isoprenes, and the point at which statins act to inhibit this process.
See also
- Merck Index: an encyclopedia of chemicals, drugs, and biologicals, Susan Budavari (ed.), 11th Edition, Rahway, NJ : Merck, 1989, ISBN 0-911910-28-X
- Poisson, N. (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:10.1023/A:1006300616544. ISSN 0167-7764.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - Claeys, M. (2004). "Formation of secondary organic aerosols through photooxidation of isoprene". Science. 303 (5661): 1173–1176. doi:10.1126/science.1092805. ISSN 0036-8075. PMID 14976309.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - Pier, P. A. (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:10.1029/96JD03786. ISSN 0148-0227.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - Poschl, U. (2000). "Development and intercomparison of condensed isoprene oxidation mechanisms for global atmospheric modeling". Journal of Atmospheric Chemistry. 37 (1): 29–52. doi:10.1023/A:1006391009798. ISSN 0167-7764.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - Monson, R. K. (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.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help)
References
- ^ NIKLITSCHEK, M. (2008). "Genomic organization of the structural genes controlling the astaxanthin biosynthesis pathway of Xanthophyllomyces dendrorhous" (PDF). Biol Res (41): 393–108.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help); line feed character in|coauthors=at position 39 (help) - ^ 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
- ^ Guenther, A. (2006). "Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature)" (PDF). Atmos. Chem. Phys. 6: 3181–3210.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ 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
- ^ Organic Carbon Compounds Emitted By Trees Affect Air Quality, ScienceDaily, Aug. 7, 2009|url=http://www.sciencedaily.com/releases/2009/08/090806141518.htm
- ^ A source of haze, ScienceNews, August 6th, 2009|url=http://www.sciencenews.org/view/generic/id/46200/title/A_source_of_haze
- ^ a b Sharkey, TD (2007). "Isoprene Emission from Plants: Why and How". Annals of Botany. 101 (1): 5–18. doi:10.1093/aob/mcm240. PMID 17921528.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ C. G. Williams, Proceedings of the Royal Society 1860 10.