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{{short description|Carboxylic acid}} | {{short description|Carboxylic acid}} | ||
{{Fats}} | {{Fats}} | ||
[[Image:rasyslami.jpg|thumb | [[Image:rasyslami.jpg|thumb|Three-dimensional representations of several fatty acids. [[Saturated and unsaturated compounds|Saturated]] fatty acids have perfectly straight chain structure. [[Unsaturated compound|Unsaturated]] ones are typically bent, unless they have a [[#Unsaturated fatty acids|trans]] configuration.]] | ||
In [[chemistry]], particularly in [[biochemistry]], a '''fatty acid''' is a [[carboxylic acid]] with an [[aliphatic]] chain, which is either [[saturated and unsaturated compounds#Organic chemistry|saturated or unsaturated]]. Most naturally occurring fatty acids have an [[Branched chain fatty acids|unbranched chain]] of an even number of carbon atoms, from 4 to 28.<ref name="iupac">{{cite journal |url=http://goldbook.iupac.org/F02330.html|title=IUPAC Compendium of Chemical Terminology|journal=Pure and Applied Chemistry|volume=67|issue=8–9|publisher=International Union of Pure and Applied Chemistry|year=1997 |pages=1307–1375|doi=10.1351/pac199567081307|access-date=2007-10-31|last1=Moss|first1=G. P.|last2=Smith|first2=P. A. S.|last3=Tavernier|first3=D.|s2cid=95004254|doi-access=free}}</ref> Fatty acids are a major component of the lipids (up to 70% by weight) in some species such as microalgae<ref>{{cite journal |last1=Chen |first1=Lin |title=Biodiesel production from algae oil high in free fatty acids by two-step catalytic conversion |journal=Bioresource Technology |date=2012 |volume=111 |pages=208–214 |doi=10.1016/j.biortech.2012.02.033 |pmid=22401712 |bibcode=2012BiTec.111..208C }}</ref> but in some other organisms are not found in their standalone form, but instead exist as three main classes of [[ester]]s: [[triglyceride]]s, [[phospholipid]]s, and [[cholesteryl ester]]s. In any of these forms, fatty acids are both important [[diet (nutrition)|dietary]] sources of fuel for animals and important structural components for [[cell (biology)|cells]]. | In [[chemistry]], particularly in [[biochemistry]], a '''fatty acid''' is a [[carboxylic acid]] with an [[aliphatic]] chain, which is either [[saturated and unsaturated compounds#Organic chemistry|saturated or unsaturated]]. Most naturally occurring fatty acids have an [[Branched chain fatty acids|unbranched chain]] of an even number of carbon atoms, from 4 to 28.<ref name="iupac">{{cite journal |url=http://goldbook.iupac.org/F02330.html|title=IUPAC Compendium of Chemical Terminology|journal=Pure and Applied Chemistry|volume=67|issue=8–9|publisher=International Union of Pure and Applied Chemistry|year=1997 |pages=1307–1375|doi=10.1351/pac199567081307|access-date=2007-10-31|last1=Moss|first1=G. P.|last2=Smith|first2=P. A. S.|last3=Tavernier|first3=D.|s2cid=95004254|doi-access=free}}</ref> Fatty acids are a major component of the lipids (up to 70% by weight) in some species such as microalgae<ref>{{cite journal |last1=Chen |first1=Lin |title=Biodiesel production from algae oil high in free fatty acids by two-step catalytic conversion |journal=Bioresource Technology |date=2012 |volume=111 |pages=208–214 |doi=10.1016/j.biortech.2012.02.033 |pmid=22401712 |bibcode=2012BiTec.111..208C }}</ref> but in some other organisms are not found in their standalone form, but instead exist as three main classes of [[ester]]s: [[triglyceride]]s, [[phospholipid]]s, and [[cholesteryl ester]]s. In any of these forms, fatty acids are both important [[diet (nutrition)|dietary]] sources of fuel for animals and important structural components for [[cell (biology)|cells]]. | ||
==History== | ==History== | ||
The concept of fatty acid (''acide gras'') was introduced in 1813 by [[Michel Eugène Chevreul]],<ref>{{cite journal |last=Chevreul |first=M. E. |date=1813 |title=Sur plusieurs corps gras, et particulièrement sur leurs combinaisons avec les alcalis |journal=Annales de Chimie |volume=88 |pages=225–261 |publisher=H. Perronneau |location=Paris |url=http://gallica.bnf.fr/ark:/12148/bpt6k65741176/f225.item |via=Gallica}}</ref><ref>{{cite book |last=Chevreul |first=M. E. |title=Recherches chimiques sur les corps gras d'origine animale |publisher=Levrault |location=Paris |date=1823 |url=https://archive.org/details/rechercheschimi00chevgoog |via=Internet Archive}}</ref><ref>{{cite web |last=Leray |first=Claude |title=Chronological history of lipid science |website=Cyberlipid Center |date=11 November 2017 |url=http://www.cyberlipid.org/history/history1.htm | The concept of fatty acid (''acide gras'') was introduced in 1813 by [[Michel Eugène Chevreul]],<ref>{{cite journal |last=Chevreul |first=M. E. |date=1813 |title=Sur plusieurs corps gras, et particulièrement sur leurs combinaisons avec les alcalis |journal=Annales de Chimie |volume=88 |pages=225–261 |publisher=H. Perronneau |location=Paris |url=http://gallica.bnf.fr/ark:/12148/bpt6k65741176/f225.item |via=Gallica}}</ref><ref>{{cite book |last=Chevreul |first=M. E. |title=Recherches chimiques sur les corps gras d'origine animale |publisher=Levrault |location=Paris |date=1823 |url=https://archive.org/details/rechercheschimi00chevgoog |via=Internet Archive}}</ref><ref>{{cite web |last=Leray |first=Claude |title=Chronological history of lipid science |website=Cyberlipid Center |date=11 November 2017 |url=http://www.cyberlipid.org/history/history1.htm |archive-url=https://web.archive.org/web/20171006012012/http://www.cyberlipid.org/history/history1.htm |archive-date=2017-10-06 }}</ref> though he initially used some variant terms: ''graisse acide'' and ''acide huileux'' ("acid fat" and "oily acid").<ref>{{cite encyclopedia |editor-last=Menten |editor-first=P. |title=Dictionnaire de chimie: Une approche étymologique et historique |publisher=De Boeck |location=Bruxelles |date=2013 |isbn=978-2-8041-8175-8 |url=https://books.google.com/books?id=NKTKDgAAQBAJ}}</ref> | ||
==Types of fatty acids== | ==Types of fatty acids== | ||
[[Image:Isomers of oleic acid.svg|thumb | [[Image:Isomers of oleic acid.svg|thumb|Comparison of the [[Cis–trans isomerism|''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. | Fatty acids are classified in many ways: by length, by saturation vs unsaturation, by even vs odd carbon content, and by linear vs branched. | ||
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Saturated fatty acids have no C=C double bonds. They have the formula CH{{sub|3}}(CH{{sub|2}}){{sub|n}}COOH, where ''n'' is some positive integer. An important saturated fatty acid is [[stearic acid]] (''n'' = 16), which when neutralized with [[sodium hydroxide]] is the most common form of [[soap]]. | Saturated fatty acids have no C=C double bonds. They have the formula CH{{sub|3}}(CH{{sub|2}}){{sub|n}}COOH, where ''n'' is some positive integer. An important saturated fatty acid is [[stearic acid]] (''n'' = 16), which when neutralized with [[sodium hydroxide]] is the most common form of [[soap]]. | ||
[[File:Arachidic formula representation.svg|thumb | [[File:Arachidic formula representation.svg|thumb|[[Arachidic acid]], a saturated fatty acid]] | ||
{| class="wikitable" | {| class="wikitable" | ||
|+ Examples of saturated fatty acids | |+ Examples of saturated fatty acids | ||
|- | |- | ||
! Common name || Chemical structure || ''C'':''D''{{efn|name=c:d}} | ! Common name || Chemical structure || ''C'' :''D'' {{efn|name=c:d}} | ||
|- | |- | ||
|[[Propionic acid]] | |[[Propionic acid]] | ||
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{| class="wikitable" | {| class="wikitable" | ||
|+ Examples of | |+ Examples of unsaturated fatty acids | ||
|- | |- | ||
! Common name || Chemical structure || Δ{{sup|''x''}}{{efn|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.}} || ''C'':''D''{{efn|name=c:d|1="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).}} || IUPAC<ref name="IUPAClipid"/> || ''n''−''x''{{efn|name=omega-x|1=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.}} | ! Common name || Chemical structure || Δ{{sup|''x''}}{{efn|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.}} || ''C'':''D''{{efn|name=c:d|1="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).}} || IUPAC<ref name="IUPAClipid"/> || ''n''−''x''{{efn|name=omega-x|1=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.}} | ||
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|- | |- | ||
|[[Arachidonic acid]] | |[[Arachidonic acid]] | ||
|CH{{sub|3}}(CH{{sub|2}}){{sub|4}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''(CH{{sub|2}}){{sub|3}}COOH<sup>[http://webbook.nist.gov/cgi/cbook.cgi?Name=Arachidonic+Acid&Units=SI NIST]</sup> | |CH{{sub|3}}(CH{{sub|2}}){{sub|4}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''(CH{{sub|2}}){{sub|3}}COOH<sup>[http://webbook.nist.gov/cgi/cbook.cgi?Name=Arachidonic+Acid&Units=SI NIST] {{Webarchive|url=https://web.archive.org/web/20090304154551/http://webbook.nist.gov/cgi/cbook.cgi?Name=Arachidonic+Acid&Units=SI |date=2009-03-04 }}</sup> | ||
|''cis'',''cis'',''cis'',''cis''-Δ{{sup|5}}Δ{{sup|8}},Δ{{sup|11}},Δ{{sup|14}} | |''cis'',''cis'',''cis'',''cis''-Δ{{sup|5}}Δ{{sup|8}},Δ{{sup|11}},Δ{{sup|14}} | ||
|20:4 | |20:4 | ||
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|[[omega-6 fatty acid|''n''−6]] | |[[omega-6 fatty acid|''n''−6]] | ||
|- | |- | ||
|[[ | |[[Linolelaidic acid]] | ||
|CH{{sub|3}}(CH{{sub|2}}){{sub|4}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''(CH{{sub|2}}){{sub|7}}COOH | |CH{{sub|3}}(CH{{sub|2}}){{sub|4}}'''CH=CH'''CH{{sub|2}}'''CH=CH'''(CH{{sub|2}}){{sub|7}}COOH | ||
|''trans'',''trans''-Δ{{sup|9}},Δ{{sup|12}} | |''trans'',''trans''-Δ{{sup|9}},Δ{{sup|12}} | ||
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===Even- vs odd-chained fatty acids=== | ===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 | Most naturally occurring fatty acids are even-chained, e.g. [[Stearic acid|stearic]] (C18) and [[Oleic acid|oleic]] (C18), meaning they are composed of an even number of carbon atoms; [[Odd-chain fatty acid|odd-chained fatty acids]] (OCFA) also occur, albeit far less frequently. The most common OCFA are the saturated C15 and C17 derivatives, [[pentadecanoic acid]] and [[heptadecanoic acid]] respectively, which are found in dairy products.<ref>{{cite journal|doi=10.3945/an.115.011387|pmid=27422507|pmc=4942867|title=Pentadecanoic and Heptadecanoic Acids: Multifaceted Odd-Chain Fatty Acids|year=2016|last1=Pfeuffer|first1=Maria|last2=Jaudszus|first2=Anke|journal=Advances in Nutrition|volume=7|issue=4|pages=730–734}}</ref><ref>{{cite journal|doi=10.1096/fasebj.8.15.8001737|title=The Animal Fatty Acid Synthase: One Gene, One Polypeptide, Seven Enzymes|year=1994|last1=Smith|first1=S.|journal=The FASEB Journal|volume=8|issue=15|pages=1248–1259|doi-access=free |pmid=8001737|s2cid=22853095}}</ref> On a molecular level, OCFAs are biosynthesized and metabolized slightly differently from the even-chained relatives. | ||
===Branching=== | ===Branching=== | ||
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===Decarboxylation=== | ===Decarboxylation=== | ||
[[Ketonic decarboxylation]] is a method useful for producing symmetrical ketones from carboxylic acids. The process involves reactions of the carboxylic acid with an inorganic base. Stearone is prepared by heating [[magnesium stearate]].<ref>{{cite journal |author=A. G. Dobson | [[Ketonic decarboxylation]] is a method useful for producing symmetrical ketones from carboxylic acids. The process involves reactions of the carboxylic acid with an inorganic base. Stearone is prepared by heating [[magnesium stearate]].<ref>{{cite journal |author-first1=A. G. |author-last1=Dobson |author-first2= H. H. |author-last2=Hatt|doi=10.15227/orgsyn.033.0084|title=Stearone |journal=Organic Syntheses |year=1953 |volume=33 |page=84}}</ref> | ||
===Chemistry of saturated vs unsaturated acids=== | ===Chemistry of saturated vs unsaturated acids=== | ||
The reactivity of saturated fatty acids is usually associated with the carboxylic acid or the adjacent methylene group By conversion to their acid chlorides, they can be converted to the symmetrical fatty ketone laurone ({{chem2|O\dC(C_{n}H_{(2n+1)})2}}).<ref>{{cite journal |author=J. C. Sauer|doi=10.15227/orgsyn.031.0068 |title=Laurone |journal=Organic Syntheses |date=1951 |volume=31 |page=68 }}</ref> Treatment with [[sulfur trioxide]] gives the α-sulfonic acids.<ref>{{cite journal |doi=10.15227/orgsyn.036.0083 |title=α-Sulfopalmitic Acid |journal=Organic Syntheses |date=1956 |volume=36 |page=83 |first1=J. K. |last1=Weil |first2=R. G. |last2=Bistline, Jr. |first3=A. J. |last3=Stirton}}</ref> | The reactivity of saturated fatty acids is usually associated with the carboxylic acid or the adjacent methylene group By conversion to their acid chlorides, they can be converted to the symmetrical fatty ketone laurone ({{chem2|O\dC(C_{n}H_{(2n+1)})2}}).<ref>{{cite journal |author-first1=J. C. |author-last1=Sauer|doi=10.15227/orgsyn.031.0068 |title=Laurone |journal=Organic Syntheses |date=1951 |volume=31 |page=68 }}</ref> Treatment with [[sulfur trioxide]] gives the α-sulfonic acids.<ref>{{cite journal |doi=10.15227/orgsyn.036.0083 |title=α-Sulfopalmitic Acid |journal=Organic Syntheses |date=1956 |volume=36 |page=83 |first1=J. K. |last1=Weil |first2=R. G. |last2=Bistline, Jr. |first3=A. J. |last3=Stirton}}</ref> | ||
The reactivity of unsaturated fatty acids is often dominated by the site of unsaturation. These reactions are the basis of ozonolysis, hydrogenation, and the iodine number. Ozonolysis (degradation by ozone) is practiced in the production of [[azelaic acid]] ((CH{{sub|2}}){{sub|7}}(CO{{sub|2}}H){{sub|2}}) from [[oleic acid]].<ref name="Ullmann Fatty Acids"/> | The reactivity of unsaturated fatty acids is often dominated by the site of unsaturation. These reactions are the basis of ozonolysis, hydrogenation, and the iodine number. Ozonolysis (degradation by ozone) is practiced in the production of [[azelaic acid]] ((CH{{sub|2}}){{sub|7}}(CO{{sub|2}}H){{sub|2}}) from [[oleic acid]].<ref name="Ullmann Fatty Acids"/> | ||
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==Skin== | ==Skin== | ||
The [[stratum corneum]] {{ndash}} the outermost layer of the [[epidermis]] {{ndash}} is composed of terminally [[Cellular differentiation|differentiated]] and [[Enucleation (microbiology)|enucleated]] [[corneocyte]]s within a lipid matrix.<ref name=":0">{{cite journal | last1=Knox | first1=Sophie | last2=O'Boyle | first2=Niamh M. | title=Skin lipids in health and disease: A review | journal=Chemistry and Physics of Lipids | volume=236 | year=2021 | issn=0009-3084 | pmid=33561467 | doi=10.1016/j.chemphyslip.2021.105055 | article-number=105055| s2cid=231864420 | doi-access=free }}</ref> Together with [[cholesterol]] and [[ceramide]]s, free fatty acids form a water-impermeable barrier that prevents [[evaporation|evaporative water loss]].<ref name=":0"/> Generally, the epidermal lipid matrix is composed of an equimolar mixture of ceramides (about 50% by weight), cholesterol (25%), and free fatty acids (15%).<ref name=":0"/> Saturated fatty acids 16 and 18 carbons in length are the dominant types in the epidermis,<ref name=":0"/><ref name=":1">{{Cite journal|display-authors=3 |last1=Merleev |first1=Alexander A. |last2=Le |first2=Stephanie T. |last3=Alexanian |first3=Claire |last4=Toussi |first4=Atrin |last5=Xie |first5=Yixuan |last6=Marusina |first6=Alina I. |last7=Watkins |first7=Steven M. |last8=Patel |first8=Forum |last9=Billi |first9=Allison C. |last10=Wiedemann |first10=Julie |last11=Izumiya |first11=Yoshihiro |last12=Kumar |first12=Ashish |last13=Uppala |first13=Ranjitha |last14=Kahlenberg |first14=J. Michelle |last15=Liu |first15=Fu-Tong |date=2022-08-22 |title=Biogeographic and disease-specific alterations in epidermal lipid composition and single-cell analysis of acral keratinocytes |journal=JCI Insight |volume=7 |issue=16 | | The [[stratum corneum]] {{ndash}} the outermost layer of the [[epidermis]] {{ndash}} is composed of terminally [[Cellular differentiation|differentiated]] and [[Enucleation (microbiology)|enucleated]] [[corneocyte]]s within a lipid matrix.<ref name=":0">{{cite journal | last1=Knox | first1=Sophie | last2=O'Boyle | first2=Niamh M. | title=Skin lipids in health and disease: A review | journal=Chemistry and Physics of Lipids | volume=236 | year=2021 | issn=0009-3084 | pmid=33561467 | doi=10.1016/j.chemphyslip.2021.105055 | article-number=105055| s2cid=231864420 | doi-access=free }}</ref> Together with [[cholesterol]] and [[ceramide]]s, free fatty acids form a water-impermeable barrier that prevents [[evaporation|evaporative water loss]].<ref name=":0"/> Generally, the epidermal lipid matrix is composed of an equimolar mixture of ceramides (about 50% by weight), cholesterol (25%), and free fatty acids (15%).<ref name=":0"/> Saturated fatty acids 16 and 18 carbons in length are the dominant types in the epidermis,<ref name=":0"/><ref name=":1">{{Cite journal|display-authors=3 |last1=Merleev |first1=Alexander A. |last2=Le |first2=Stephanie T. |last3=Alexanian |first3=Claire |last4=Toussi |first4=Atrin |last5=Xie |first5=Yixuan |last6=Marusina |first6=Alina I. |last7=Watkins |first7=Steven M. |last8=Patel |first8=Forum |last9=Billi |first9=Allison C. |last10=Wiedemann |first10=Julie |last11=Izumiya |first11=Yoshihiro |last12=Kumar |first12=Ashish |last13=Uppala |first13=Ranjitha |last14=Kahlenberg |first14=J. Michelle |last15=Liu |first15=Fu-Tong |date=2022-08-22 |title=Biogeographic and disease-specific alterations in epidermal lipid composition and single-cell analysis of acral keratinocytes |journal=JCI Insight |volume=7 |issue=16 |article-number=e159762 |doi=10.1172/jci.insight.159762 |issn=2379-3708 |pmc=9462509 |pmid=35900871}}</ref> while unsaturated fatty acids and saturated fatty acids of various other lengths are also present.<ref name=":0"/><ref name=":1" /> The relative abundance of the different fatty acids in the epidermis is dependent on the body site the skin is covering.<ref name=":1" /> There are also characteristic epidermal fatty acid alterations that occur in [[psoriasis]], [[atopic dermatitis]], and other [[inflammation|inflammatory conditions]].<ref name=":0"/><ref name=":1" /> | ||
==Analysis== | ==Analysis== | ||
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==References== | ==References== | ||
{{notelist}} | {{notelist}} | ||
<references> | |||
<ref name=rayn1991>{{cite journal | vauthors = Raynard RS, Cossins AR | title = Homeoviscous adaptation and thermal compensation of sodium pump of trout erythrocytes | journal = The American Journal of Physiology | volume = 260 | issue = 5 Pt 2 | pages = R916–24 | date = May 1991 | pmid = 2035703 | doi = 10.1152/ajpregu.1991.260.5.R916 | s2cid = 24441498 }}</ref> | <ref name=rayn1991>{{cite journal | vauthors = Raynard RS, Cossins AR | title = Homeoviscous adaptation and thermal compensation of sodium pump of trout erythrocytes | journal = The American Journal of Physiology | volume = 260 | issue = 5 Pt 2 | pages = R916–24 | date = May 1991 | pmid = 2035703 | doi = 10.1152/ajpregu.1991.260.5.R916 | s2cid = 24441498 }}</ref> | ||
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<ref name=hulb2003xa>{{cite journal | vauthors = Hulbert AJ | title = Life, death and membrane bilayers | journal = The Journal of Experimental Biology | volume = 206 | issue = Pt 14 | pages = 2303–11 | date = July 2003 | pmid = 12796449 | doi = 10.1242/jeb.00399 | doi-access = free | bibcode = 2003JExpB.206.2303H }}</ref> | <ref name=hulb2003xa>{{cite journal | vauthors = Hulbert AJ | title = Life, death and membrane bilayers | journal = The Journal of Experimental Biology | volume = 206 | issue = Pt 14 | pages = 2303–11 | date = July 2003 | pmid = 12796449 | doi = 10.1242/jeb.00399 | doi-access = free | bibcode = 2003JExpB.206.2303H }}</ref> | ||
</references> | |||
==External links== | ==External links== | ||