Fatty acid

In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with a long aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, from 4 to 28.[1] Fatty acids are usually not found in organisms in their standalone form, but instead exist as three main classes of esters: triglycerides, phospholipids, and cholesteryl esters. In any of these forms, fatty acids are both important dietary sources of fuel for animals and they are important structural components for cells.

Types of fats in food
See also
Three-dimensional representations of several fatty acids. Saturated fatty acids have perfectly straight chain structure. Unsaturated ones are typically bent, unless they have a trans configuration.

History

The concept of fatty acid (acide gras) was introduced in 1813 by Michel Eugène Chevreul,[2][3][4] though he initially used some variant terms: graisse acide and acide huileux ("acid fat" and "oily acid").[5]

Types of fatty acids
Comparison of the trans isomer Elaidic acid (top) and the cis isomer oleic acid (bottom).

Fatty acids are classified in many ways: by length, by saturation vs unsaturation, by even vs odd carbon content, and by linear vs branched.

Length of fatty acids

Saturated fatty acids
Main article: Saturated fat
For a more comprehensive list, see List of saturated fatty acids.

Saturated fatty acids have no C=C double bonds. They have the same formula CH3(CH2)nCOOH, with variations in "n". An important saturated fatty acid is stearic acid (n = 16), which when neutralized with lye is the most common form of soap.

Arachidic acid, a saturated fatty acid.
Examples of saturated fatty acids
Common nameChemical structureC:D[9]
Caprylic acidCH3(CH2)6COOH8:0
Capric acidCH3(CH2)8COOH10:0
Lauric acidCH3(CH2)10COOH12:0
Myristic acidCH3(CH2)12COOH14:0
Palmitic acidCH3(CH2)14COOH16:0
Stearic acidCH3(CH2)16COOH18:0
Arachidic acidCH3(CH2)18COOH20:0
Behenic acidCH3(CH2)20COOH22:0
Lignoceric acidCH3(CH2)22COOH24:0
Cerotic acidCH3(CH2)24COOH26:0

Unsaturated fatty acids
Main article: Unsaturated fat

Unsaturated fatty acids have one or more C=C double bonds. The C=C double bonds can give either cis or trans isomers.

cis
A cis configuration means that the two hydrogen atoms adjacent to the double bond stick out on the same side of the chain. The rigidity of the double bond freezes its conformation and, in the case of the cis isomer, causes the chain to bend and restricts the conformational freedom of the fatty acid. The more double bonds the chain has in the cis configuration, the less flexibility it has. When a chain has many cis bonds, it becomes quite curved in its most accessible conformations. For example, oleic acid, with one double bond, has a "kink" in it, whereas linoleic acid, with two double bonds, has a more pronounced bend. α-Linolenic acid, with three double bonds, favors a hooked shape. The effect of this is that, in restricted environments, such as when fatty acids are part of a phospholipid in a lipid bilayer, or triglycerides in lipid droplets, cis bonds limit the ability of fatty acids to be closely packed, and therefore can affect the melting temperature of the membrane or of the fat. Cis unsaturated fatty acids, however, increase cellular membrane fluidity, whereas trans unsaturated fatty acids do not.
trans
A trans configuration, by contrast, means that the adjacent two hydrogen atoms lie on opposite sides of the chain. As a result, they do not cause the chain to bend much, and their shape is similar to straight saturated fatty acids.

In most naturally occurring unsaturated fatty acids, each double bond has three (n-3), six (n-6), or nine (n-9) carbon atoms after it, and all double bonds have a cis configuration. Most fatty acids in the trans configuration (trans fats) are not found in nature and are the result of human processing (e.g., hydrogenation). Some trans fatty acids also occur naturally in the milk and meat of ruminants (such as cattle and sheep). They are produced, by fermentation, in the rumen of these animals. They are also found in dairy products from milk of ruminants, and may be also found in breast milk of women who obtained them from their diet.

The geometric differences between the various types of unsaturated fatty acids, as well as between saturated and unsaturated fatty acids, play an important role in biological processes, and in the construction of biological structures (such as cell membranes).

Examples of Unsaturated Fatty Acids
Common nameChemical structureΔx[10]C:D[9]IUPAC[11]n−x[12]
Myristoleic acidCH3(CH2)3CH=CH(CH2)7COOHcis-Δ914:114:1(9)n−5
Palmitoleic acidCH3(CH2)5CH=CH(CH2)7COOHcis-Δ916:116:1(9)n−7
Sapienic acidCH3(CH2)8CH=CH(CH2)4COOHcis-Δ616:116:1(6)n−10
Oleic acidCH3(CH2)7CH=CH(CH2)7COOHcis-Δ918:118:1(9)n−9
Elaidic acidCH3(CH2)7CH=CH(CH2)7COOHtrans-Δ918:1n−9
Vaccenic acidCH3(CH2)5CH=CH(CH2)9COOHtrans-Δ1118:1n−7
Linoleic acidCH3(CH2)4CH=CHCH2CH=CH(CH2)7COOHcis,cis-Δ9,Δ1218:218:2(9,12)n−6
Linoelaidic acidCH3(CH2)4CH=CHCH2CH=CH(CH2)7COOHtrans,trans-Δ9,Δ1218:2n−6
α-Linolenic acidCH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOHcis,cis,cis-Δ9,Δ12,Δ1518:318:3(9,12,15)n−3
Arachidonic acidCH3(CH2)4CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)3COOHNISTcis,cis,cis,cis-Δ5Δ8,Δ11,Δ1420:420:4(5,8,11,14)n−6
Eicosapentaenoic acidCH3CH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)3COOHcis,cis,cis,cis,cis-Δ5,Δ8,Δ11,Δ14,Δ1720:520:5(5,8,11,14,17)n−3
Erucic acidCH3(CH2)7CH=CH(CH2)11COOHcis-Δ1322:122:1(13)n−9
Docosahexaenoic acidCH3CH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)2COOHcis,cis,cis,cis,cis,cis-Δ4,Δ7,Δ10,Δ13,Δ16,Δ1922:622:6(4,7,10,13,16,19)n−3

Even- vs odd-chained fatty acids

Most fatty acids are even-chained, e.g. stearic (C18) and oleic (C18), meaning they are composed of an even number of carbon atoms. Some fatty acids have odd numbers of carbon atoms; they are referred to as odd-chained fatty acids (OCFA). The most common OCFA are the saturated C15 and C17 derivatives, pentadecanoic acid and heptadecanoic acid respectively, which are found in dairy products.[13][14] On a molecular level, OCFAs are biosynthesized and metabolized slightly differently from the even-chained relatives.

Nomenclature

Carbon atom numbering
See also: Essential fatty acid § Nomenclature and terminology
Numbering of carbon atoms. The systematic (IUPAC) C-x numbers are in blue. The omega-minus "ω−x" labels are in red. The Greek letter labels are in green.[15]

Most naturally occurring fatty acids have an unbranched chain of carbon atoms, with a carboxyl group (–COOH) at one end, and a methyl group (–CH3) at the other end.

The position of the carbon atoms in the backbone of a fatty acid are usually indicated by counting from 1 at the −COOH end. Carbon number x is often abbreviated or C-x (or sometimes Cx), with x=1, 2, 3, etc. This is the numbering scheme recommended by the IUPAC.

Another convention uses letters of the Greek alphabet in sequence, starting with the first carbon after the carboxyl. Thus carbon α (alpha) is C-2, carbon β (beta) is C-3, and so forth.

Although fatty acids can be of diverse lengths, in this second convention the last carbon in the chain is always labelled as ω (omega), which is the last letter in the Greek alphabet. A third numbering convention counts the carbons from that end, using the labels "ω", "ω−1", "ω−2". Alternatively, the label "ω−x" is written "n−x", where the "n" is meant to represent the number of carbons in the chain.[15]

In either numbering scheme, the position of a double bond in a fatty acid chain is always specified by giving the label of the carbon closest to the carboxyl end.[15] Thus, in an 18 carbon fatty acid, a double bond between C-12 (or ω−6) and C-13 (or ω−5) is said to be "at" position C-12 or ω−6. The IUPAC naming of the acid, such as "octadec-12-enoic acid" (or the more pronounceable variant "12-octadecanoic acid") is always based on the "C" numbering.

The notation Δx,y,... is traditionally used to specify a fatty acid with double bonds at positions x,y,.... (The capital Greek letter "Δ" (delta) corresponds to Roman "D", for Double bond). Thus, for example, the 20-carbon arachidonic acid is Δ5,8,11,14, meaning that it has double bonds between carbons 5 and 6, 8 and 9, 11 and 12, and 14 and 15.

In the context of human diet and fat metabolism, unsaturated fatty acids are often classified by the position of the double bond closest to the ω carbon (only), even in the case of multiple double bonds such as the essential fatty acids. Thus arachidonic acid, linoleic acid (18 carbons, Δ9,12), and myristoleic acid (14-carbon, Δ8) are all classified as "ω−3" fatty acids; meaning that their formula ends with –CH=CH–CH
2–CH
3.

Fatty acids with an odd number of carbon atoms are called odd-chain fatty acids, whereas the rest are even-chain fatty acids. The difference is relevant to gluconeogenesis.

Naming of fatty acids

The following table describes the most common systems of naming fatty acids.

Nomenclature Examples Explanation
Trivial Palmitoleic acid Trivial names (or common names) are non-systematic historical names, which are the most frequent naming system used in literature. Most common fatty acids have trivial names in addition to their systematic names (see below). These names frequently do not follow any pattern, but they are concise and often unambiguous.
Systematic cis-9-octadec-9-enoic acid
(9Z)-octadec-9-enoic acid		 Systematic names (or IUPAC names) derive from the standard IUPAC Rules for the Nomenclature of Organic Chemistry, published in 1979,[16] along with a recommendation published specifically for lipids in 1977.[17] Carbon atom numbering begins from the carboxylic end of the molecule backbone. Double bonds are labelled with cis-/trans- notation or E-/Z- notation, where appropriate. This notation is generally more verbose than common nomenclature, but has the advantage of being more technically clear and descriptive.
Δx cis-Δ9, cis-Δ12 octadecadienoic acid In Δx (or delta-x) nomenclature, each double bond is indicated by Δx, where the double bond begins at the xth carbon–carbon bond, counting from carboxylic end of the molecule backbone. Each double bond is preceded by a cis- or trans- prefix, indicating the configuration of the molecule around the bond. For example, linoleic acid is designated "cis-Δ9, cis-Δ12 octadecadienoic acid". This nomenclature has the advantage of being less verbose than systematic nomenclature, but is no more technically clear or descriptive.
n−x
(or ω−x)		 n−3
(or ω−3)		 n−x (n minus x; also ω−x or omega-x) nomenclature both provides names for individual compounds and classifies them by their likely biosynthetic properties in animals. A double bond is located on the xth carbon–carbon bond, counting from the methyl end of the molecule backbone. For example, α-Linolenic acid is classified as a n−3 or omega-3 fatty acid, and so it is likely to share a biosynthetic pathway with other compounds of this type. The ω−x, omega-x, or "omega" notation is common in popular nutritional literature, but IUPAC has deprecated it in favor of n−x notation in technical documents.[16] The most commonly researched fatty acid biosynthetic pathways are n−3 and n−6.
Lipid numbers 18:3
18:3n3
18:3, cis,cis,cis-Δ9,Δ12,Δ15
18:3(9,12,15)		 Lipid numbers take the form C:D,[9] where C is the number of carbon atoms in the fatty acid and D is the number of double bonds in the fatty acid. If D is more than one, the double bonds are assumed to be interrupted by CH
2 units, i.e., at intervals of 3 carbon atoms along the chain. For instance, α-Linolenic acid is an 18:3 fatty acid and its three double bonds are located at positions Δ9, Δ12, and Δ15. This notation can be ambiguous, as some different fatty acids can have the same C:D numbers. Consequently, when ambiguity exists this notation is usually paired with either a Δx or n−x term.[16] For instance, although α-Linolenic acid and γ-Linolenic acid are both 18:3, they may be unabiguously described as 18:3n3 and 18:3n6 fatty acids, respectively. For the same purpose, IUPAC recommends using a list of double bond positions in parentheses, appended to the C:D notation.[11] For instance, IUPAC recommended notations for α-and γ-Linolenic acid are 18:3(9,12,15) and 18:3(6,9,12), respectively.

Free fatty acids

When circulating in the plasma (plasma fatty acids), not in their ester, fatty acids are known as non-esterified fatty acids (NEFAs) or free fatty acids (FFAs). FFAs are always bound to a transport protein, such as albumin.[18]

Production

Industrial

Fatty acids are usually produced industrially by the hydrolysis of triglycerides, with the removal of glycerol (see oleochemicals). Phospholipids represent another source. Some fatty acids are produced synthetically by hydrocarboxylation of alkenes.[19]

Hyper-oxygenated fatty acids

Hyper-oxygenated fatty acids are produced by a specific industrial processes for topical skin creams. The process is based on the introduction or saturation of peroxides into fatty acid esters via the presence of ultraviolet light and gaseous oxygen bubbling under controlled temperatures. Specifically linolenic acids have been shown to play an important role in maintaining the moisture barrier function of the skin (preventing water loss and skin dehydration).[20] A study in Spain reported in the Journal of Wound Care in March 2005 compared a commercial product with a greasy placebo and that specific product was more effective and also cost-effective.[21] A range of such OTC medical products is now widely available. However, topically applied olive oil was not found to be inferior in a "randomised triple-blind controlled non-inferiority" trial conducted in Spain during 2015.[22][23] Commercial products are likely to be less messy to handle and more washable than either olive oil or petroleum jelly, both of which, if applied topically may stain clothing and bedding.

By animals
Main article: Fatty acid synthesis

In animals, fatty acids are formed from carbohydrates predominantly in the liver, adipose tissue, and the mammary glands during lactation.[24]

Carbohydrates are converted into pyruvate by glycolysis as the first important step in the conversion of carbohydrates into fatty acids.[24] Pyruvate is then decarboxylated to form acetyl-CoA in the mitochondrion. However, this acetyl CoA needs to be transported into cytosol where the synthesis of fatty acids occurs. This cannot occur directly. To obtain cytosolic acetyl-CoA, citrate (produced by the condensation of acetyl-CoA with oxaloacetate) is removed from the citric acid cycle and carried across the inner mitochondrial membrane into the cytosol.[24] There it is cleaved by ATP citrate lyase into acetyl-CoA and oxaloacetate. The oxaloacetate is returned to the mitochondrion as malate.[25] The cytosolic acetyl-CoA is carboxylated by acetyl CoA carboxylase into malonyl-CoA, the first committed step in the synthesis of fatty acids.[25][26]

Malonyl-CoA is then involved in a repeating series of reactions that lengthens the growing fatty acid chain by two carbons at a time. Almost all natural fatty acids, therefore, have even numbers of carbon atoms. When synthesis is complete the free fatty acids are nearly always combined with glycerol (three fatty acids to one glycerol molecule) to form triglycerides, the main storage form of fatty acids, and thus of energy in animals. However, fatty acids are also important components of the phospholipids that form the phospholipid bilayers out of which all the membranes of the cell are constructed (the cell wall, and the membranes that enclose all the organelles within the cells, such as the nucleus, the mitochondria, endoplasmic reticulum, and the Golgi apparatus).[24]

The "uncombined fatty acids" or "free fatty acids" found in the circulation of animals come from the breakdown (or lipolysis) of stored triglycerides.[24][27] Because they are insoluble in water, these fatty acids are transported bound to plasma albumin. The levels of "free fatty acids" in the blood are limited by the availability of albumin binding sites. They can be taken up from the blood by all cells that have mitochondria (with the exception of the cells of the central nervous system). Fatty acids can only be broken down in mitochondria, by means of beta-oxidation followed by further combustion in the citric acid cycle to CO2 and water. Cells in the central nervous system, although they possess mitochondria, cannot take free fatty acids up from the blood, as the blood-brain barrier is impervious to most free fatty acids, excluding short-chain fatty acids and medium-chain fatty acids.[28][29] These cells have to manufacture their own fatty acids from carbohydrates, as described above, in order to produce and maintain the phospholipids of their cell membranes, and those of their organelles.[24]

Variation between animal species

Studies on the cell membranes of mammals and reptiles discovered that mammalian cell membranes are composed of a higher proportion of polyunsaturated fatty acids (DHA, omega-3 fatty acid) than reptiles.[30] Studies on bird fatty acid composition have noted similar proportions to mammals but with 1/3rd less omega-3 fatty acids as compared to omega-6 for a given body size.[31] This fatty acid composition results in a more fluid cell membrane but also one that is permeable to various ions (H+
 & Na+
), resulting in cell membranes that are more costly to maintain. This maintenance cost has been argued to be one of the key causes for the high metabolic rates and concomitant warm-bloodedness of mammals and birds.[30] However polyunsaturation of cell membranes may also occur in response to chronic cold temperatures as well. In fish increasingly cold environments lead to increasingly high cell membrane content of both monounsaturated and polyunsaturated fatty acids, to maintain greater membrane fluidity (and functionality) at the lower temperatures.[32][33]

Fatty acids in dietary fats

The following table gives the fatty acid, vitamin E and cholesterol composition of some common dietary fats.[34][35]

SaturatedMonounsaturatedPolyunsaturatedCholesterolVitamin E
g/100gg/100gg/100gmg/100gmg/100g
Animal fats
Duck fat[36]33.249.312.91002.70
Lard[36]40.843.89.6930.60
Tallow[36]49.841.84.01092.70
Butter54.019.82.62302.00
Vegetable fats
Coconut oil85.26.61.70.66
Cocoa butter60.032.93.001.8
Palm kernel oil81.511.41.603.80
Palm oil45.341.68.3033.12
Cottonseed oil25.521.348.1042.77
Wheat germ oil18.815.960.70136.65
Soybean oil14.523.256.5016.29
Olive oil14.069.711.205.10
Corn oil12.724.757.8017.24
Sunflower oil11.920.263.0049.00
Safflower oil10.212.672.1040.68
Hemp oil101575012.34
Canola/Rapeseed oil5.364.324.8022.21

Reactions of fatty acids

Fatty acids exhibit reactions like other carboxylic acids, i.e. they undergo esterification and acid-base reactions.

Acidity

Fatty acids do not show a great variation in their acidities, as indicated by their respective pKa. Nonanoic acid, for example, has a pKa of 4.96, being only slightly weaker than acetic acid (4.76). As the chain length increases, the solubility of the fatty acids in water decreases, so that the longer-chain fatty acids have minimal effect on the pH of an aqueous solution. Even those fatty acids that are insoluble in water will dissolve in warm ethanol, and can be titrated with sodium hydroxide solution using phenolphthalein as an indicator. This analysis is used to determine the free fatty acid content of fats; i.e., the proportion of the triglycerides that have been hydrolyzed.

Neutralization of fatty acids, i.e. saponification, is a widely practiced route to metallic soaps.[37]

Hydrogenation and hardening

Hydrogenation of unsaturated fatty acids is widely practiced. Typical conditions involve 2.0–3.0 MPa of H2 pressure, 150 °C, and nickel supported on silica as a catalyst. This treatment affords saturated fatty acids. The extent of hydrogenation is indicated by the iodine number. Hydrogenated fatty acids are less prone toward rancidification. Since the saturated fatty acids are higher melting than the unsaturated precursors, the process is called hardening. Related technology is used to convert vegetable oils into margarine. The hydrogenation of triglycerides (vs fatty acids) is advantageous because the carboxylic acids degrade the nickel catalysts, affording nickel soaps. During partial hydrogenation, unsaturated fatty acids can be isomerized from cis to trans configuration.[38]

More forcing hydrogenation, i.e. using higher pressures of H2 and higher temperatures, converts fatty acids into fatty alcohols. Fatty alcohols are, however, more easily produced from fatty acid esters.

In the Varrentrapp reaction certain unsaturated fatty acids are cleaved in molten alkali, a reaction which was, at one point of time, relevant to structure elucidation.

Auto-oxidation and rancidity
Main article: Rancidification

Unsaturated fatty acids undergo a chemical change known as auto-oxidation. The process requires oxygen (air) and is accelerated by the presence of trace metals. Vegetable oils resist this process to a small degree because they contain antioxidants, such as tocopherol. Fats and oils often are treated with chelating agents such as citric acid to remove the metal catalysts.

Ozonolysis

Unsaturated fatty acids are susceptible to degradation by ozone. This reaction is practiced in the production of azelaic acid ((CH2)7(CO2H)2) from oleic acid.[38]

Circulation

Digestion and intake
Main article: Digestion § Fat digestion

Short- and medium-chain fatty acids are absorbed directly into the blood via intestine capillaries and travel through the portal vein just as other absorbed nutrients do. However, long-chain fatty acids are not directly released into the intestinal capillaries. Instead they are absorbed into the fatty walls of the intestine villi and reassemble again into triglycerides. The triglycerides are coated with cholesterol and protein (protein coat) into a compound called a chylomicron.

From within the cell, the chylomicron is released into a lymphatic capillary called a lacteal, which merges into larger lymphatic vessels. It is transported via the lymphatic system and the thoracic duct up to a location near the heart (where the arteries and veins are larger). The thoracic duct empties the chylomicrons into the bloodstream via the left subclavian vein. At this point the chylomicrons can transport the triglycerides to tissues where they are stored or metabolized for energy.

Metabolism
Main article: Fatty acid metabolism

When metabolized, fatty acids yield large quantities of ATP. Many cell types can use either glucose or fatty acids for this purpose. Fatty acids (provided either by ingestion or by drawing on triglycerides stored in fatty tissues) are distributed to cells to serve as a fuel for muscular contraction and general metabolism. They are broken down to CO2 and water by the intra-cellular mitochondria, releasing large amounts of energy, captured in the form of ATP through beta oxidation and the citric acid cycle.

Essential fatty acids
Main article: Essential fatty acid

Fatty acids that are required for good health but cannot be made in sufficient quantity from other substrates, and therefore must be obtained from food, are called essential fatty acids. There are two series of essential fatty acids: one has a double bond three carbon atoms away from the methyl end; the other has a double bond six carbon atoms away from the methyl end. Humans lack the ability to introduce double bonds in fatty acids beyond carbons 9 and 10, as counted from the carboxylic acid side.[39] Two essential fatty acids are linoleic acid (LA) and alpha-linolenic acid (ALA). These fatty acids are widely distributed in plant oils. The human body has a limited ability to convert ALA into the longer-chain omega-3 fatty acids — eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which can also be obtained from fish. Omega-3 and omega-6 fatty acids are biosynthetic precursors to endocannabinoids with antinociceptive, anxiolytic, and neurogenic properties.[40]

Distribution
Main article: Blood fatty acids

Blood fatty acids adopt distinct forms in different stages in the blood circulation. They are taken in through the intestine in chylomicrons, but also exist in very low density lipoproteins (VLDL) and low density lipoproteins (LDL) after processing in the liver. In addition, when released from adipocytes, fatty acids exist in the blood as free fatty acids.

It is proposed that the blend of fatty acids exuded by mammalian skin, together with lactic acid and pyruvic acid, is distinctive and enables animals with a keen sense of smell to differentiate individuals.[41]

Analysis

The chemical analysis of fatty acids in lipids typically begins with an interesterification step that breaks down their original esters (triglycerides, waxes, phospholipids etc) and converts them to methyl esters, which are then separated by gas chromatography.[42] or analyzed by gas chromatography and mid-infrared spectroscopy.

Separation of unsaturated isomers is possible by silver ion (argentation) thin-layer chromatography.[43][44] Other separation techniques include high-performance liquid chromatography (with short columns packed with silica gel with bonded phenylsulfonic acid groups whose hydrogen atoms have been exchanged for silver ions). The role of silver lies in its ability to form complexes with unsaturated compounds.

Industrial uses

Fatty acids are mainly used in the production of soap, both for cosmetic purposes and, in the case of metallic soaps, as lubricants. Fatty acids are also converted, via their methyl esters, to fatty alcohols and fatty amines, which are precursors to surfactants, detergents, and lubricants.[38] Other applications include their use as emulsifiers, texturizing agents, wetting agents, anti-foam agents, or stabilizing agents.[45]

Esters of fatty acids with simpler alcohols (such as methyl-, ethyl-, n-propyl-, isopropyl- and butyl esters) are used as emollients in cosmetics and other personal care products and as synthetic lubricants. Esters of fatty acids with more complex alcohols, such as sorbitol, ethylene glycol, diethylene glycol, and polyethylene glycol are consumed in food, or used for personal care and water treatment, or used as synthetic lubricants or fluids for metal working.

See also

References
  1. Moss, G. P.; Smith, P. A. S.; Tavernier, D. (1997). IUPAC Compendium of Chemical Terminology. Pure and Applied Chemistry. 67 (2nd ed.). International Union of Pure and Applied Chemistry. pp. 1307–1375. doi:10.1351/pac199567081307. ISBN 978-0-521-51150-6. S2CID 95004254. Retrieved 2007-10-31.
  2. Chevreul, M. E. (1813). Sur plusieurs corps gras, et particulièrement sur leurs combinaisons avec les alcalis. Annales de Chimie, t. 88, p. 225-261. link (Gallica), link (Google).
  3. Chevreul, M. E. Recherches sur les corps gras d'origine animale. Levrault, Paris, 1823. link.
  4. Leray, C. Chronological history of lipid center. Cyberlipid Center. Last updated on 11 November 2017. link Archived 2017-10-13 at the Wayback Machine.
  5. Menten, P. Dictionnaire de chimie: Une approche étymologique et historique. De Boeck, Bruxelles. link.
  6. Cifuentes, Alejandro, ed. (2013-03-18). "Microbial Metabolites in the Human Gut". Foodomics: Advanced Mass Spectrometry in Modern Food Science and Nutrition. John Wiley & Sons, 2013. ISBN 9781118169452.
  7. Roth, Karl S. (2013-12-19). "Medium-Chain Acyl-CoA Dehydrogenase Deficiency". Medscape.
  8. Beermann, C.; Jelinek, J.; Reinecker, T.; Hauenschild, A.; Boehm, G.; Klör, H.-U. (2003). "Short term effects of dietary medium-chain fatty acids and n−3 long-chain polyunsaturated fatty acids on the fat metabolism of healthy volunteers". Lipids in Health and Disease. 2: 10. doi:10.1186/1476-511X-2-10. PMC 317357. PMID 14622442.
  9. “C:D“ is the numerical symbol: total amount of (C)arbon atoms of the fatty acid, and the number of (D)ouble (unsaturated) bonds in it; if D > 1 it is assumed that the double bonds are separated by one or more methylene bridge(s).
  10. Each double bond in the fatty acid is indicated by Δx, where the double bond is located on the xth carbon–carbon bond, counting from the carboxylic acid end.
  11. "IUPAC Lipid nomenclature: Appendix A: names of and symbols for higher fatty acids". www.sbcs.qmul.ac.uk.
  12. In n minus x (also ω−x or omega-x) nomenclature a double bond of the fatty acid is located on the xth carbon–carbon bond, counting from the terminal methyl carbon (designated as n or ω) toward the carbonyl carbon.
  13. Pfeuffer, Maria; Jaudszus, Anke (2016). "Pentadecanoic and Heptadecanoic Acids: Multifaceted Odd-Chain Fatty Acids". Advances in Nutrition: An International Review Journal. 7 (4): 730–734. doi:10.3945/an.115.011387. PMC 4942867. PMID 27422507.
  14. Smith, S. (1994). "The Animal Fatty Acid Synthase: One Gene, One Polypeptide, Seven Enzymes". The FASEB Journal. 8 (15): 1248–1259. doi:10.1096/fasebj.8.15.8001737. PMID 8001737. S2CID 22853095.
  15. A common mistake is to say that the last carbon is "ω−1".
    Another common mistake is to say that the position of a bond in omega-notation is the number of the carbon closest to the END.
    For double bonds, these two mistakes happen to compensate each other; so that a "ω−3" fatty acid indeed has the double bond between the 3rd and 4th carbons from the end, counting the methyl as 1.
    However, for substitutions and other purposes, they don't: a hydroxyl "at ω−3" is on carbon 15 (4th from the end), not 16. See for example this article. doi:10.1016/0005-2760(75)90089-2
    Note also that the "−" in the omega-notation is a minus sign, and "ω−3" should in principle be read "omega minus three". However, it is very common (especially in non-scientific literature) to write it "ω-3" (with a hyphen/dash) and read it as "omega-three". See for example Karen Dooley (2008), Omega-three fatty acids and diabetes.
  16. Rigaudy, J.; Klesney, S. P. (1979). Nomenclature of Organic Chemistry. Pergamon. ISBN 978-0-08-022369-8. OCLC 5008199.
  17. "The Nomenclature of Lipids. Recommendations, 1976". European Journal of Biochemistry. 79 (1): 11–21. 1977. doi:10.1111/j.1432-1033.1977.tb11778.x.
  18. Dorland's Illustrated Medical Dictionary. Elsevier.
  19. Anneken, David J.; Both, Sabine; Christoph, Ralf; Fieg, Georg; Steinberner, Udo; Westfechtel, Alfred (2006). "Fatty Acids". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a10_245.pub2.
  20. Essential fatty-acids lubricate skin prevent pressure sores (see "suggested reading at end)
  21. The effectiveness of a hyper-oxygenated fatty acid compound in preventing pressure ulcers
  22. Lupiañez-Perez, I.; Uttumchandani, S. K.; Morilla-Herrera, J. C.; Martin-Santos, F. J.; Fernandez-Gallego, M. C.; Navarro-Moya, F. J.; Lupiañez-Perez, Y.; Contreras-Fernandez, E.; Morales-Asencio, J. M. (2015). "Topical Olive Oil is Not Inferior to Hyperoxygenated Fatty Aids to Prevent Pressure Ulcers in High-Risk Immobilised Patients in Home Care. Results of a Multicentre Randomised Triple-Blind Controlled Non-Inferiority Trial". PLOS ONE. 10 (4): e0122238. Bibcode:2015PLoSO..1022238L. doi:10.1371/journal.pone.0122238. PMC 4401455. PMID 25886152.
  23. Clinical trial number NCT01595347 for "Olive Oil's Cream Effectiveness in Prevention of Pressure Ulcers in Immobilized Patients in Primary Care (PrevenUP)" at ClinicalTrials.gov
  24. Stryer, Lubert (1995). "Fatty acid metabolism.". Biochemistry (4th ed.). New York: W. H. Freeman and Company. pp. 603–628. ISBN 978-0-7167-2009-6.
  25. Ferre, P.; Foufelle, F. (2007). "SREBP-1c Transcription Factor and Lipid Homeostasis: Clinical Perspective". Hormone Research. 68 (2): 72–82. doi:10.1159/000100426. PMID 17344645. this process is outlined graphically in page 73
  26. Voet, Donald; Voet, Judith G.; Pratt, Charlotte W. (2006). Fundamentals of Biochemistry (2nd ed.). John Wiley and Sons. pp. 547, 556. ISBN 978-0-471-21495-3.
  27. Zechner, R.; Strauss, J. G.; Haemmerle, G.; Lass, A.; Zimmermann, R. (2005). "Lipolysis: pathway under construction". Curr. Opin. Lipidol. 16 (3): 333–340. doi:10.1097/01.mol.0000169354.20395.1c. PMID 15891395. S2CID 35349649.
  28. Tsuji A (2005). "Small molecular drug transfer across the blood-brain barrier via carrier-mediated transport systems". NeuroRx. 2 (1): 54–62. doi:10.1602/neurorx.2.1.54. PMC 539320. PMID 15717057. Uptake of valproic acid was reduced in the presence of medium-chain fatty acids such as hexanoate, octanoate, and decanoate, but not propionate or butyrate, indicating that valproic acid is taken up into the brain via a transport system for medium-chain fatty acids, not short-chain fatty acids. ... Based on these reports, valproic acid is thought to be transported bidirectionally between blood and brain across the BBB via two distinct mechanisms, monocarboxylic acid-sensitive and medium-chain fatty acid-sensitive transporters, for efflux and uptake, respectively.
  29. Vijay N, Morris ME (2014). "Role of monocarboxylate transporters in drug delivery to the brain". Curr. Pharm. Des. 20 (10): 1487–98. doi:10.2174/13816128113199990462. PMC 4084603. PMID 23789956. Monocarboxylate transporters (MCTs) are known to mediate the transport of short chain monocarboxylates such as lactate, pyruvate and butyrate. ... MCT1 and MCT4 have also been associated with the transport of short chain fatty acids such as acetate and formate which are then metabolized in the astrocytes [78].
  30. Hulbert AJ, Else PL (August 1999). "Membranes as possible pacemakers of metabolism". Journal of Theoretical Biology. 199 (3): 257–74. doi:10.1006/jtbi.1999.0955. PMID 10433891.
  31. Hulbert AJ, Faulks S, Buttemer WA, Else PL (November 2002). "Acyl composition of muscle membranes varies with body size in birds". The Journal of Experimental Biology. 205 (Pt 22): 3561–9. PMID 12364409.
  32. Hulbert AJ (July 2003). "Life, death and membrane bilayers". The Journal of Experimental Biology. 206 (Pt 14): 2303–11. doi:10.1242/jeb.00399. PMID 12796449.
  33. Raynard RS, Cossins AR (May 1991). "Homeoviscous adaptation and thermal compensation of sodium pump of trout erythrocytes". The American Journal of Physiology. 260 (5 Pt 2): R916–24. doi:10.1152/ajpregu.1991.260.5.R916. PMID 2035703.
  34. McCann; Widdowson; Food Standards Agency (1991). "Fats and Oils". The Composition of Foods. Royal Society of Chemistry.
  35. Altar, Ted. "More Than You Wanted To Know About Fats/Oils". Sundance Natural Foods. Retrieved 2006-08-31.
  36. "USDA National Nutrient Database for Standard Reference". U.S. Department of Agriculture. Archived from the original on 2015-03-03. Retrieved 2010-02-17.
  37. Klaus Schumann, Kurt Siekmann (2005). "Soaps". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a24_247. ISBN 978-3527306732.CS1 maint: uses authors parameter (link)
  38. Anneken, David J.; et al. "Fatty Acids". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH.
  39. Bolsover, Stephen R.; et al. (15 February 2004). Cell Biology: A Short Course. John Wiley & Sons. pp. 42ff. ISBN 978-0-471-46159-3.
  40. Ramsden, Christopher E.; Zamora, Daisy; Makriyannis, Alexandros; Wood, JodiAnne T.; Mann, J. Douglas; Faurot, Keturah R.; MacIntosh, Beth A.; Majchrzak-Hong, Sharon F.; Gross, Jacklyn R. (August 2015). "Diet-induced changes in n-3 and n-6 derived endocannabinoids and reductions in headache pain and psychological distress". The Journal of Pain. 16 (8): 707–716. doi:10.1016/j.jpain.2015.04.007. ISSN 1526-5900. PMC 4522350. PMID 25958314.
  41. "Electronic Nose Created To Detect Skin Vapors". Science Daily. July 21, 2009. Retrieved 2010-05-18.
  42. Aizpurua-Olaizola O, Ormazabal M, Vallejo A, Olivares M, Navarro P, Etxebarria N, et al. (January 2015). "Optimization of supercritical fluid consecutive extractions of fatty acids and polyphenols from Vitis vinifera grape wastes". Journal of Food Science. 80 (1): E101-7. doi:10.1111/1750-3841.12715. PMID 25471637.
  43. Breuer B, Stuhlfauth T, Fock HP (July 1987). "Separation of fatty acids or methyl esters including positional and geometric isomers by alumina argentation thin-layer chromatography". Journal of Chromatographic Science. 25 (7): 302–6. doi:10.1093/chromsci/25.7.302. PMID 3611285.
  44. Breuer, B.; Stuhlfauth, T.; Fock, H. P. (1987). "Separation of Fatty Acids or Methyl Esters Including Positional and Geometric Isomers by Alumina Argentation Thin-Layer Chromatography". Journal of Chromatographic Science. 25 (7): 302–6. doi:10.1093/chromsci/25.7.302. PMID 3611285.
  45. "Fatty Acids: Building Blocks for Industry" (PDF). aciscience.org. American Cleaning Institute. Retrieved 22 Apr 2018.
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