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 Transportationconsiders 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
naphthaor oil. About 95% of isoprene production is used to produce cis-1,4-polyisoprene - a synthetic version of natural rubber.
rubberis a polymerof 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 perchaare composed of trans-1,4-polyisoprene, a structural isomerwhich has similar, but not identical properties.
Biological roles and effects
Isoprene is formed naturally in animals and plants and is generally the most common
hydrocarbonfound 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 DMAPPpathway; 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. HemeA has an isoprenoid tail, and lanosterol, the sterol precursor in animals, is derived from squaleneand 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 ServicesEleventh 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. Statinsare 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.
Merck Index: an encyclopedia of chemicals, drugs, and biologicals, Susan Budavari (ed.), 11th Edition, Rahway, NJ : Merck, 1989, ISBN 0-911910-28-X
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