Isoprene

Chembox new
Name = Isoprene
ImageFileL1 = Isoprene.svg
ImageSizeL1 = 100px
ImageFileR1 = Isoprene-3d.png ImageSizeR1 = 120px
IUPACName = 2-Methyl-buta-1,3-diene
OtherNames = isoprene
Section1 = Chembox Identifiers
CASNo = 78-79-5
SMILES = C=C(C)C=C
Section2 = Chembox Properties
Formula = C₅H₈
MolarMass = 68.11 g/mol
Density = 0.681 g/cm³
MeltingPt = -145.95 °C
BoilingPt = 34.067 °C

Isoprene is a common synonym for the chemical compound 2-methylbuta-1,3-diene. It is commonly used in industry, is an important biological material, and can be a harmful environmental pollutant and toxicant when present in excess quantities.

At room temperature, isoprene is a colorless liquid which is highly flammable and easily ignited. It can form explosive mixtures in air and is highly reactive, capable of polymerizing explosively when heated. The United States Department of Transportation considers isoprene a hazardous material and requires special marking, labeling, and transportation for it.

It is most readily available industrially as a by-product of the thermal cracking of naphtha or oil. About 95% of isoprene production is used to produce cis-1,4-polyisoprene - a synthetic version of natural rubber.

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 which has similar, but not identical properties.

Biological roles and effects

Isoprene is formed naturally in animals and plants and is generally the most common hydrocarbon found in the human body. The estimated production rate of isoprene in the human body is .15 µmol/kg/h, equivalent to approximately 17 mg/day for a 70 kg person. 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. 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 while daytime emissions are expected to be substantial (~5-20 mg/m²/h) during hot and sunny days.

With a global biogenic production in the range of 400–600 Tg of carbon/year, isoprene has a large impact on atmospheric processes and is thus an important compound in the field of Atmospheric Chemistry. Isoprene affects the oxidative state of large air masses, is an important precursor for ozone, and is a pollutant in the lower atmosphere. Furthermore, isoprene forms secondary organic aerosols through photooxidation with OH radicals, however this has been questioned by some researchers due to the atmospherically irrelevant isoprene and OH concentrations used in these experiments. Therefore, further work is needed due to the possible wide-ranging health effects, particularly for the respiratory tract, and reduced visibility due to light scattering effects. Because of its atmospheric importance, much work has been devoted to emission studies from isoprene-emitting vegetation, and, kinetic and mechanistic studies of isoprene oxidation via OH radicals, ozone, and NO₃ radicals.

It 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. 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 synthetised by the HMG-CoA reductase pathway. Addition of these chains to proteins is termed isoprenylation.

According to the United States Department of Health and Human Services Eleventh Edition Report on Carcinogens, isoprene is reasonably expected to be a human carcinogen. Tumors have been observed in multiple locations in multiple test species exposed to isoprene vapor. No adequate human studies of the relationship between isoprene exposure and human cancer have been reported.

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 [http://www.cholesterol-and-health.com/Synthesis-Of-Cholesterol.html flow chart] shows the biosynthesis of isoprenes, and the point at which statins act to inhibit this process.

References

External links

* [http://ntp.niehs.nih.gov/ntp/roc/toc11.html Report on Carcinogens, Eleventh Edition; U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program]

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isoprène — [ izɔprɛn ] n. m. • v. 1868; probablt de iso et pr(opyl)ène 1 ♦ Chim. Liquide volatil, de formule C5H8, qui peut se polymériser en une substance analogue au caoutchouc (⇒ élastomère). Adj. ISOPRÉNIQUE . 2 ♦ Biochim. Unité constitutive des… … Encyclopédie Universelle
Isoprene — I so*prene, n. [Etymol. uncertain.] (Chem.) An oily, volatile unsaturated hydrocarbon ({C5H8}), obtained by the distillation of caoutchouc or gutta percha, and used to make synthetic rubber by polymerization. In organic chemistry, it is viewed… … The Collaborative International Dictionary of English
isoprene — [ī sōprēn΄, ī səprēn΄] n. [coined (1860) by C. G. Williams (1829 1910), Brit chemist < ISO + PR(OPYL) + ENE] a colorless, volatile liquid, CH2:C(CH3)CH:CH2, prepared by the dry distillation of raw rubber or synthetically: when heated with… … English World dictionary
isoprene — /uy seuh preen /, n. Chem. a colorless, volatile, water insoluble liquid, C5H8, of the terpene class, usually obtained from rubber or from oil of turpentine by pyrolysis: used chiefly in the manufacture of synthetic rubber by polymerization.… … Universalium
Isoprene — One of the major components that makes up natural rubber and is used to make synthetic rubbers. It is also emitted from plants and trees, has been detected in tobacco smoke and automobile exhaust. Isoprene is a possible carcinogen (cancer causing … Medical dictionary
isoprene — i·so·prè·ne s.m. TS chim. idrocarburo dei dieni a cinque atomi di carbonio, liquido incolore e volatile, la cui molecola è l unità costitutiva del caucciù e di altre sostanze naturali {{line}} {{/line}} DATA: 1869. ETIMO: der. di iso e… … Dizionario italiano
isoprene — izoprenas statusas T sritis chemija formulė CH₂=C(CH₃)CH=CH₂ atitikmenys: angl. isoprene rus. изопрен ryšiai: sinonimas – 2 metil 1,3 butadienas … Chemijos terminų aiškinamasis žodynas

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