Linoleic acid

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Linoleic acid
LAnumbering.png
Linoleic-acid-from-xtal-1979-3D-balls.png
Linoleic-acid-from-xtal-1979-3D-vdW.png
Names
Preferred IUPAC name
(9Z,12Z)-Octadeca-9,12-dienoic acid
Other names
cis,cis-9,12-Octadecadienoic acid
C18:2 (Lipid numbers)
Identifiers
3D model (JSmol)
3DMet
1727101
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.000.428 Edit this at Wikidata
EC Number
  • 200-470-9
57557
KEGG
UNII
  • InChI=1S/C18H32O2/c1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16-17-18(19)20/h6-7,9-10H,2-5,8,11-17H2,1H3,(H,19,20)/b7-6-,10-9- checkY
    Key: OYHQOLUKZRVURQ-HZJYTTRNSA-N checkY
  • InChI=1/C18H32O2/c1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16-17-18(19)20/h6-7,9-10H,2-5,8,11-17H2,1H3,(H,19,20)/b7-6-,10-9-
    Key: OYHQOLUKZRVURQ-HZJYTTRNBX
  • CCCCC/C=C\C/C=C\CCCCCCCC(=O)O
Properties
C18H32O2
Molar mass 280.452 g·mol−1
Appearance Colorless oil
Density 0.9 g/cm3[1]
Melting point −12 °C (10 °F)[1]
−6.9 °C (19.6 °F)[2]
−5 °C (23 °F)[3]
Boiling point 229 °C (444 °F) at 16 mmHg[2]
230 °C (446 °F) at 21 mbar[3]
230 °C (446 °F) at 16 mmHg[1]
0.139 mg/L[3]
Vapor pressure 16 Torr at 229 °C[citation needed]
Hazards
NFPA 704 (fire diamond)
2
1
0
Flash point 112 °C (234 °F)[3]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Linoleic acid is an organic compound with the formula COOH(CH2)7CH=CHCH2CH=CH(CH2)4CH3. 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.[4]

Linoleic acid is a polyunsaturated omega-6 fatty acid. It is a colorless or white liquid that is virtually insoluble in water but soluble in many organic solvents.[2] It typically occurs in nature as a triglyceride (ester of glycerin) rather than as a free fatty acid.[5] It is one of two essential fatty acids for humans, who must obtain it through their diet.[6]

The word "linoleic" derives from the Latin linum "flax" + oleum "oil", reflecting the fact that it was first isolated from linseed oil.

History[edit]

In 1844, F. Sacc, working at the laboratory of Justus von Liebig, isolated linoleic acid from linseed oil.[7][8] In 1886, K. Peters determined the existence of two double bonds.[9] Its essential role in human diet was discovered by G. O. Burr and others in 1930.[10] 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.[11]

In physiology[edit]

The consumption of linoleic acid is vital to proper health, as it is an essential fatty acid.[12]

Metabolism and eicosanoids[edit]

Linoleic Acid Metabolism.gif

Linoleic acid is a precursor to arachidonic acid (AA) with elongation and saturation.[12] AA is the precursor to some prostaglandins,[13] leukotrienes (LTA, LTB, LTC), and thromboxane (TXA).[14]

The metabolism of LA to AA begins with the conversion of LA into gamma-linolenic acid (GLA), effected by Δ6desaturase.[15] GLA is converted to dihomo-γ-linolenic acid (DGLA), the immediate precursor to AA.

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, catalyze oxidation of LA to epoxide products viz., its 12,13-epoxide, Vernolic acid, and its 9,10-epoxide, Coronaric acid. These linoleic acid products are implicated in human physiology and pathology.[16]

Uses and reactions[edit]

Linoleic acid is a component of quick-drying oils, which are useful in oil paints and varnishes. These applications exploit the lability of the doubly allylic C-H groups (-CH=CH-CH2-CH=CH-) toward oxygen in air (autoxidation). Addition of oxygen leads to crosslinking and formation of a stable film.[17]

Reduction of the carboxylic acid group of linoleic acid yields linoleyl alcohol.[18]

Linoleic acid is a surfactant with a critical micelle concentration of 1.5 x 10−4 M @ pH 7.5.[citation needed]

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.[19][20][21][22]

Linoleic acid is also used in some bar of soap products.

Dietary sources[edit]

It is abundant in safflower, and corn oil, and comprises over half their composition by weight. It is present in medium quantities in soybean oils, sesame, and almonds.[23][24]

Name % LA ref.
Salicornia oil 75%
Evening Primrose oil 65-80% [25]
Melon seed oil 70%
Poppyseed oil 70%
Grape seed oil 69.6%
Prickly Pear seed oil 63%
Artichoke oil 60%
Hemp oil 54.3% [26]
Wheat germ oil 55%
Cottonseed oil 54%
Corn oil 51.9% [27]
Walnut oil 51%
Soybean oil 50.9% [28]
Sesame oil 45%
Rice bran oil 39%
Argan oil 37%
Pistachio oil 32.7%
Peach oil 29% [29]
Almonds 24%
Canola oil 17.8% [30]
Sunflower oil 20.5% [31]
Chicken fat 18-23% [32]
Peanut oil 19.6% [33]
Egg yolk 16%
Linseed oil (flax), cold pressed 14.2% [34]
Safflower oil 72-78% [35]
Lard 10%
Palm oil 10%
Olive oil 8.4 [36]
Durio graveolens 4.95% [37]
Cocoa butter 3%
Macadamia oil 2%
Butter 2%
Coconut oil 2%
  average val

Other occurrences[edit]

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.[38]

Health effects[edit]

Consumption of linoleic acid has been associated with lowering the risk of cardiovascular disease and premature death.[39]

See also[edit]

References[edit]

  1. ^ a b c The Merck Index, 11th Edition, 5382
  2. ^ a b c William M. Haynes (2016). CRC Handbook of Chemistry and Physics (97th ed.). Boca Raton: CRC Press. pp. 3–338. ISBN 978-1-4987-5429-3.
  3. ^ a b c d Record of CAS RN 60-33-3 in the GESTIS Substance Database of the Institute for Occupational Safety and Health
  4. ^ "Fatty Acids". Cyber Lipid. Archived from the original on 28 October 2018. Retrieved 31 July 2017.
  5. ^ Mattes, RD (2009). "Is there a fatty acid taste?". Annu. Rev. Nutr. 29: 305–27. doi:10.1146/annurev-nutr-080508-141108. PMC 2843518. PMID 19400700.
  6. ^ Simopoulos, Artemis P. (2008). "The importance of the omega-6/omega-3 fatty acid ratio in cardiovascular disease and other chronic diseases". Experimental Biology and Medicine. 233 (6): 674–688. doi:10.3181/0711-mr-311. PMID 18408140. S2CID 9044197.
  7. ^ F. Sacc (1844) "Ueber das Leinöl, seine physicalischen und chemischen Eigenscharften und seine Oxydationsproducte". Liebig Annalen, volume 51, pages 213-230.
  8. ^ F. Sacc (1845): "Expériences sur les propriétés physiques et chimiques de l'huile de Lin". SChweizer. Gesell. N. Dekschr., volume 7
  9. ^ (1886), Monatsch., volume 7, pages 522-
  10. ^ (1930: J Biol Chem, volume 86, pages 587-
  11. ^ R. A. Raphael and Franz Sondheimer (1950): "The synthesis of long-chain aliphatic acids from acetylenic compounds. Part III. The synthesis of linoleic acid". Journal of the Chemical Society (Resumed), article 432, doi:10.1039/jr9500002100
  12. ^ a b Whelan, Jay; Fritsche, Kevin (May 2013). "Linoleic Acid". Advances in Nutrition. 4 (3): 311–312. doi:10.3945/an.113.003772. PMC 3650500. PMID 23674797.
  13. ^ Wlodawer, Paulina; Samuelsson, Bengt (25 August 1973). "On the organization and mechanism of prostaglandin synthetase". The Journal of Biological Chemistry. 248 (16): 5673–5678. doi:10.1016/S0021-9258(19)43558-8. PMID 4723909.
  14. ^ Terano, Takashi; Salmon, John A.; Moncada, Salvador (February 1984). "Biosynthesis and biological activity of leukotriene B5". Prostaglandins. 27 (2): 217–232. doi:10.1016/0090-6980(84)90075-3. PMID 6326200.
  15. ^ Evidence suggests that infants must acquire Δ6desaturase breast milk. Breast-milk fed babies have higher concentrations of GLA than formula-fed babies, while formula-fed babies have elevated concentrations of LA. David F. Horrobin (1993). "Fatty acid metabolism in health and disease: the role of Δ-6-desaturase". American Journal of Clinical Nutrition. 57 (5 Suppl): 732S–737S. doi:10.1093/ajcn/57.5.732S. PMID 8386433.
  16. ^ Jandacek, Ronald J. (20 May 2017). "Linoleic Acid: A Nutritional Quandary". Healthcare. 5 (2): 25. doi:10.3390/healthcare5020025. ISSN 2227-9032. PMC 5492028. PMID 28531128.
  17. ^ Ulrich Poth (2002). "Drying Oils and Related Products". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a09_055.
  18. ^ Adkins, Homer; Gillespie, R. H. (1949). "Oleyl Alcohol". Organic Syntheses. 29: 80. doi:10.15227/orgsyn.029.0080.
  19. ^ Diezel, W.E.; Schulz, E.; Skanks, M.; Heise, H. (1993). "Plant oils: Topical application and anti-inflammatory effects (croton oil test)". Dermatologische Monatsschrift. 179: 173.
  20. ^ Letawe, C; Boone, M; Pierard, GE (March 1998). "Digital image analysis of the effect of topically applied linoleic acid on acne microcomedones". Clinical and Experimental Dermatology. 23 (2): 56–58. doi:10.1046/j.1365-2230.1998.00315.x. PMID 9692305. S2CID 28594076.
  21. ^ Ando, H; Ryu, A; Hashimoto, A; Oka, M; Ichihashi, M (March 1998). "Linoleic acid and α-linolenic acid lightens ultraviolet-induced hyperpigmentation of the skin". Archives of Dermatological Research. 290 (7): 375–381. doi:10.1007/s004030050320. PMID 9749992. S2CID 23036319.
  22. ^ Darmstadt, GL; Mao-Qiang, M; Chi, E; Saha, SK; Ziboh, VA; Black, RE; Santosham, M; Elias, PM (2002). "Impact of topical oils on the skin barrier: possible implications for neonatal health in developing countries". Acta Paediatrica. 91 (5): 546–554. CiteSeerX 10.1.1.475.1064. doi:10.1080/080352502753711678. PMID 12113324.
  23. ^ "Nutrient Data Laboratory Home Page". USDA National Nutrient Database for Standard Reference, Release 20. U.S. Department of Agriculture, Agricultural Research Service. 2007. Archived from the original on 14 April 2016.
  24. ^ Kaur, Narinder; Chugh, Vishal; Gupta, Anil K. (October 2014). "Essential fatty acids as functional components of foods- a review". Journal of Food Science and Technology. 51 (10): 2289–2303. doi:10.1007/s13197-012-0677-0. PMC 4190204. PMID 25328170.
  25. ^ "Evening Primrose Oil for Menopause does it help". 26 January 2018.
  26. ^ Oomah, B. Dave; Busson, Muriel; Godfrey, David V; Drover, John C. G (1 January 2002). "Characteristics of hemp (Cannabis sativa L.) seed oil". Food Chemistry. 76 (1): 33–43. doi:10.1016/S0308-8146(01)00245-X.
  27. ^ "FoodData Central". fdc.nal.usda.gov.
  28. ^ "FoodData Central". fdc.nal.usda.gov.
  29. ^ Wu, Hao; Shi, John; Xue, Sophia; Kakuda, Yukio; Wang, Dongfeng; Jiang, Yueming; Ye, Xingqian; Li, Yanjun; Subramanian, Jayasankar (2011). "Essential oil extracted from peach (Prunus persica) kernel and its physicochemical and antioxidant properties". LWT - Food Science and Technology. 44 (10): 2032–2039. doi:10.1016/j.lwt.2011.05.012.
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  32. ^ M. K. Nutter, E. E. Lockhart and R. S. Harris (1943). "The chemical composition of depot fats in chickens and turkeys". Journal of the American Oil Chemists' Society. 20 (11): 231–234. doi:10.1007/BF02630880. S2CID 84893770.
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  34. ^ "FoodData Central". fdc.nal.usda.gov.
  35. ^ Hall III, C. (2015). Wrigley, Colin W.; Corke, Harold; Seetharaman, Koushik; Faubion, Jonathan (eds.). Encyclopedia of Food Grains. Academic Press. ISBN 978-0-12-394786-4.
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  37. ^ Nasaruddin, Mohd Hanif; Noor, Noor Qhairul Izzreen Mohd; Mamat, Hasmadi (2013). "Komposisi Proksimat dan Komponen Asid Lemak Durian Kuning (Durio graveolens) Sabah" [Proximate and Fatty Acid Composition of Sabah Yellow Durian (Durio graveolens)] (PDF). Sains Malaysiana (in Malay). 42 (9): 1283–1288. ISSN 0126-6039. OCLC 857479186. Retrieved 28 November 2017.
  38. ^ "Earth News: Ancient 'smell of death' revealed". BBC. 9 September 2009.
  39. ^ Li J, Guasch-Ferré M, Li Y, Hu FB. (2020). "Dietary intake and biomarkers of linoleic acid and mortality: systematic review and meta-analysis of prospective cohort studies". The American Journal of Clinical Nutrition. 112 (1): 150–167. doi:10.1093/ajcn/nqz349. PMC 7326588. PMID 32020162.{{cite journal}}: CS1 maint: multiple names: authors list (link)

Further reading[edit]

External links[edit]