C18:2 (Lipid numbers)
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||280.452 g·mol−1|
|Melting point||−12 °C (10 °F)|
−6.9 °C (19.6 °F)
−5 °C (23 °F)
|Boiling point||229 °C (444 °F) at 16 mmHg|
230 °C (446 °F) at 21 mbar
230 °C (446 °F) at 16 mmHg
|Vapor pressure||16 Torr at 229 °C|
|NFPA 704 (fire diamond)|
|Flash point||112 °C (234 °F)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Linoleic acid is an organic compound with the formula HO2C(CH2)7CH=CHCH2CH=CH(CH2)3CH3. Both alkene groups are cis. It is a fatty acid sometimes denoted 18:2 (n-6) or 18:2 cis-9,12. A linoleate is a salt or ester of this acid.
Linoleic acid is a polyunsaturated omega-6 fatty acid. It is a colorless or white oil that is virtually insoluble in water but soluble in many organic solvents. It typically occurs in nature as a triglyceride (ester of glycerin) rather than as a free fatty acid. It is one of two essential fatty acids for humans, who must obtain it through their diet.
The consumption of linoleic acid is vital to proper health, as it is an essential fatty acid. In rats, a diet deficient in linoleate (the salt form of the acid) has been shown to cause mild skin scaling, hair loss, and poor wound healing.
Metabolism and eicosanoids
The metabolism of LA to AA begins with the conversion of LA into gamma-Linolenic acid (GLA), effected by Δ6desaturase. GLA is converted to dihomo-γ-linolenic acid (DGLA), the immediate precursor to AA. One of the possible fates of AA is to be transformed into a group of metabolites called eicosanoids during the inflammatory response and during physical activity; eicosanoids are a class of paracrine hormones. The three types of eicosanoids are prostaglandins, thromboxanes, and leukotrienes. Eicosanoids produced from AA tend to promote (not cause) inflammation and promote growth during and after physical activity in healthy humans. For example, both AA-derived thrombaxane and leukotrieneB4 are proaggregatory and vasoconstrictive eicosanoids during inflammation. The oxidized metabolic products of linoleic acid, such as 9-hydroxyoctadecanoic acid and 13-hydroxyoctadecanoic acid, have also been shown to activate TRPV1, the capsaicin receptor, and through this might play a major role in hyperalgesia and allodynia.
LA is also converted by various lipoxygenases, cyclooxygenases, cytochrome P450 enzymes (the CYP monooxygenases), and non-enzymatic autoxidation mechanisms to mono-hydroxyl products viz., 13-Hydroxyoctadecadienoic acid, and 9-Hydroxyoctadecadienoic acid; these two hydroxy metabolites are enzymatically oxidized to their keto metabolites, 13-oxo-octadecadienoic acid and 9-oxo-octadecdienoic acid. Certain cytochrome P450 enzymes, the CYP epoxygenases, metabolize LA to epoxide products viz., its 12,13-epoxide, Vernolic acid, and its 9,10-epoxide, Coronaric acid. These linoleic acid products have bioactivity and are implicated in human physiology and pathology.
Linoleic acid is used in making quick-drying oils, which are useful in oil paints and varnishes. These applications exploit the easy reaction of the linoleic acid with oxygen in air (autoxidation), which leads to crosslinking and formation of a stable film called linoxyn.
Linoleic acid has become increasingly popular in the beauty products industry because of its beneficial properties on the skin. Research points to linoleic acid's anti-inflammatory, acne reductive, skin-lightening and moisture retentive properties when applied topically on the skin.
Use in research
Linoleic acid lipid radicals can be used to show the antioxidant effect of polyphenols and natural phenols. Experiments on linoleic acid subjected to AAPH induced oxidation of linoleic acid, thus producing lipid radicals; the use of different combinations of phenolics then show that binary mixtures can lead to either a synergetic antioxidant effect, or to an antagonistic effect towards the lipid radicals. Research like this is useful in discovering which phenols prevent the autoxidation of vegetable oils.
|Evening Primrose oil||65-80%|||
|Melon seed oil||70%|
|Grape seed oil||69.6%|
|Prickly Pear seed oil||62.3%|
|Barbary Fig seed oil||65%|
|Wheat germ oil||55%|
|Rice bran oil||39%|
|Linseed oil (flax)||15%|
|Olive oil||10% (3.5 - 21%)|||
Cockroaches release oleic and linoleic acid upon death, which discourages other roaches from entering the area. This is similar to the mechanism found in ants and bees, which release oleic acid upon death.
In 1844, F. Sacc, working at the laboratory of Justus von Liebig, isolated linoleic acid from linseed oil. In 1886, K. Peters determined the existence of two double bonds. Its essential role in human diet was discovered by G. O. Burr and others in 1930. Its chemical structure was determined by T.P. Hilditch and others in 1939, and it was synthesized by R. A. Raphael and F. Sondheimer in 1950.
- Conjugated linoleic acid
- Omega-6 fatty acid: Negative health effects
- Essential fatty acids
- Essential fatty acid interactions
- Essential nutrients
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