Fatty Acids

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Name: Hilal Ahmed Class: B. pharma (3 rd year) Roll no: 112

INTRODUCTION::

INTRODUCTION: Naturally occurring fatty acids mostly have even number of carbon atoms, and except for those of bacterial origin, they might be highly unsaturated. As all the fats contain glycerol, their properties have been found to differ according to the nature of fatty acids present in them. Fatty acids occurring in higher animals tend to have chain lengths of 16, 18 or 20 carbon atoms except in milk fat, where the saturated fatty acids, C 10 – C 14 make up 10% of the molar total.

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Oleic acid is the most abundant fatty acid in humans, both in depot fat and in milk. Butyric acid with four carbon atoms is normally the shortest fatty acids found in human fat. The general formula of fatty acids is CH 3 (CH 2 ) n COOH or RCOOH, where R is a hydrocarbon chain. The CH 3 (CH 2 ) n CO-chain is termed as an acyl radical. The value of ‘n’ varies from zero in acetic acid to 86 in mycolic acid.

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The carboxylic acid (-COOH) group of a fatty acid is strongly polar. It ionizes in water at intracellular pH by the loss of a proton. The hydrocarbon chain is insoluble in water and is nonpolar . Fatty acids therefore possess hydrophilic as well as hydrophobic character. At physiological pH fatty acids exist in solution as the ionized alkyl carboxylates, R-COO - , e.g., stearate : CH3(CH2)18 –COO - .

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The fatty acids can be divided into two groups: saturated and unsaturated. Saturated fatty acids have only single bonds in the hydrocarbon chain. Unsaturated fatty acids have at least one C = C double bond in the chains. Saturated fatty acids are solids at room temperature because the regular nature of their aliphatic chains allows the molecules to be packed in a close, parallel alignment.

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The interactions (van der Walls forces) between neighboring chains are weak, but the regular packing allows these forces to operate over a large portion of the chain so that a considerable amount of energy is needed in order to melt them. In contrast, unsaturated fatty acids are all liquids at room temperature because the cis double bond interrupt the regular packing of the chains.

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Thus much less energy is required to melt them. The greater the degree of unsaturation, the lower the melting point because each double bond introduces more disorder into the packing of the molecules. A Saturated fatty acid is having maximum possible number of attached hydrogen's. Each carbon atom has two hydrogen atoms attached to it. One of the terminal carbon atom is having three hydrogen atoms while the other is having a carboxyl (-COOH) group. The hydrocarbon portions of saturated fatty acids have only single bonds.

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Name Formula Common Source Butyric acid CH 3 (CH 2 ) 2 COOH Butter Caproic acid CH 3 (CH 2 ) 4 COOH Butter Caprylic acid CH 3 (CH 2 ) 6 COOH Cocunut oil, palm oil Lauric acid CH 3 (CH 2 ) 10 COOH Laurel kernel oil Myristic acid CH 3 (CH 2 ) 12 COOH Nutmeg oil Palmitic acid CH 3 (CH 2 ) 14 COOH Palm oil, animal fat Stearic acid CH 3 (CH 2 ) 16 COOH Cocoa butter Arachidic acid CH 3 (CH 2 ) 18 COOH Peanut oil Major Saturated Fatty Acids found in plants and animals:

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Unsaturated fatty acids have one or more double bonds. The general formula for these fatty acid is R-CH=CH(CH 2 ) n COOH . Generally the double bonds range between 1 to 6 and occur after 9, 12, 15, 18, etc carbon atoms. Monounsaturated fatty acids usually contain a cis olefinic bond in a limited number of preferred positions in the carbon chain. Some of the unsaturated acids like linolenic acid, linoleic acid & arachidonic acid are required for the normal health of animals & have to be supplied to the organism in the diet. Such acids are known as essential fatty acids.

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Name Formula Common Source Palmitoleic acid CH 3 (CH 2 ) 5 CH = CH(CH 2 ) 7 COOH Milk fat, sardine oil Oleic acid CH 3 (CH 2 ) 7 CH = CH(CH 2 ) 7 COOH Olive oil, pork fat Linoleic acid CH 3 (CH 2 ) 4 CH = CHCH 2 CH = CH(CH 2 ) 7 COOH Linseed oil, soyabean oil Linolenic acid CH 3 CH 2 CH = CHCH 2 CH = CHCH 2 CH = CH(CH 2 ) 7 COOH Linseed and hempseed oil Erucic acid CH 3 (CH 2 ) 7 CH = CH(CH 2 ) 11 COOH Mustard oil Major Unsaturated Fatty Acids in Plants and Animals:

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Fatty acids having more than one double bond are termed as polyunsaturated fatty aids. According to the number of double bonds, fatty acids are termed as monoenoic (1 double bond), dienoic (2 double bonds), trienoic (3 double bonds), tetraenoic (4 double bonds), etc Unsaturated fats have been found to be more common in living organisms than saturated fats. Unsaturated fats may have an odd or an even number of carbon atoms.

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Odd-numbered acids occur in all cells as minor components of total fatty acids. They are morecommon in plants, but are also found in animals. Most of the fatty acids in animals are even-numbered. This is to be expected because animal cells synthesize fatty acids by polymerization of 2-C units. Increase in the number of double bonds progressively decreases the melting point. In general, the melting points of unsaturated fatty acids are lower than saturated fatty acids and are oils rather than solids at room temperature .

Nomenclature of Fatty Acids::

Nomenclature of Fatty Acids: The systematic name for a fatty acid is derived from the name of its parent hydrocarbon by replacing its final ‘e’ by oic acid. Thus the names of the saturated fatty acids end with the suffix – anoic and those of unsaturated acids with the suffux – enoic . Thus the C 18 saturated fatty acid is called octadecanoic acid (from the hydrocarbon octadecane ) ; a C 18 fatty acid with one double bond is called octadecadienoic acid; and with three double bonds octadecatrienoic acid.

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Numbering of carbon atoms in fatty acids is started at the carboxyl terminus, i.e. In one of the numbering, carbon atom adjacent to the carboxyl carbon i.e., C2 is known as α -carbon atom, carbon atom 3 is known as β -carbon atom and the end methyl carbon is known as the ω -carbon atom.

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Various conventions are adopted for indicating the position of the double bond(s). The most widely used one involves the use of the symbol ∆ followed by a superscript number. For example, ∆ 9 means that there is a double bond between carbon atoms 9 and 10. Alternatively, the position of the double bond is indicated by the numerals as in case of simple alkenes. Lastly, mote that the total number of carbon atoms, and number and position(s) of the double bond(s) is again indicated by a convention. For example,

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The symbol 18: 0 denotes a C 18 fatty acid with no double bond. The symbol 18: 1 ; 9 denotes a C 18 fatty acid with a double bond between carbon atoms 9 and 10. The symbol 18: 2 ; 9, 12 denotes a C 18 fatty acid with two double bonds between C 9 and C 10 , and between C 12 and C 13 .

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