Double bonds in unsaturated fatty acids

In addition to unsaturated fatty acids, several other modified fatty acids are found in nature. Microorganisms, for example, often contain branched-chain fatty acids, such as tuberculostearic acid (Figure 8.2). When these fatty acids are incorporated in membranes, the methyl group constitutes a local structural perturbation in a manner similar to the double bonds in unsaturated fatty acids (see Chapter 9). Some bacteria also synthesize fatty acids containing cyclic structures such as cyclopropane, cyclopropene, and even cyclopentane rings. 

If a fatty acid already has a double bond in it, the scheme by which the fatty acid is oxidized depends on where the double bond ends up after several of the C-2 fragments have been removed by normal p oxidation. With a double bond already present, the enzyme that catalyzes the first step (insertion of the double bond at C-2) gets confused when there is already a double bond at C-2 or at C-3. The fact that the double bonds in unsaturated fatty acids are invariably cis also complicates life since the double bond introduced at C-2 by the desaturating enzyme of p oxidation is a trans double bond. 

The presence of cis rather than trans double bonds in unsaturated fatty acids ensures that lipids containing fatty acids have low melting points and are therefore fluid at physiological temperatures. 

The presence of an unsaturation within a fatty acid is indicated and its position is established by the absence of fragments derived from cleavages of this unsaturated bond and the adjacent ones. This corresponds, on the spectrum, to a four-carbon atom hole , i.e. by two peaks in the series separated by 54 Th (Figure 8.60). [282] This absence of ions results from the fact that cleaving a vinylic bond or a double bond is not energetically favoured. The localization of double bonds in unsaturated fatty acids is made more difficult and even impossible as the number of unsaturations increases because the process of losing alkanes is hidden by the loss of 45 Da ( COOH). 

In the hydrogenation process, unsaturated fatty acids are reacted with hydrogen gas with the help of nickel catalyst. In this process, two hydrogen atoms are attached to the double bond in unsaturated fatty acids. Complete hydrogenation of vegetable oils converts essentially all of the unsaturated fatty acids to stearic acid. 

The determination of the sites of the C—C double bonds in unsaturated fatty acid derivatives and other lipids plays an outstanding role in the analytical application of mass spectrometry. Much work has been published on the localization of double bonds in... 

The determination of the sites of the C—C double bonds in unsaturated fatty acid derivatives and other lipids plays an outstanding role in the analytical application of mass spectrometry. Much work has been published on the localization of double bonds in monoolefins, and a number of extensive reviews has appeared on the topic . Two major methodologies have been employed. In the first one, unsaturated C—C bonds are converted to appropriate derivatives by synthesis in the liquid phase, which are then subjected to mass spectrometric analysis mostly by using standard El techniques. These methods will be mentioned only briefly in the next section, including some recent work which has not yet been mentioned in the reviews. The second methodology takes advantage of the bimolecular reactivity of neutral olefins with ionic reagents in the gas phase,... 

Naturally occuring fatty acids have a cis geometry. This cis-structure decreases the melting points of the acids and hence increasing the number of double bonds in unsaturated fatty acids decreases the melting point. 

The double bonds in unsaturated fatty acids generally have the cis configuration. This configuration produces a bend in the molecules, which prevents them from packing together as tightly as fully saturated fatty acids. As a result, unsaturated fatty acids have... 

The aim of further research should be the development of robust catalysts, which activate oxygen in a nonradical manner, probably via biomimetic cascades, and which are also able to provide an oxidative cleavage of unactivated internal double bonds in unsaturated fatty acids. 

Hydroxy fatty acids may be intermediates of F. a.b which have been diverted (3-hydroxy fatty acids with D-configuration). They may also arise by oxygenation catalysed by cytochrome P-450 systems (especially (fl-oxidation in eukaryotes see Fatty acid degradation). Hydroxy fatty acids can also be biosynthesized by hydration of double bonds in unsaturated fatty acids specific fatty acid hydratase systems catalysing this reaction have been characterized in bacter-... 

The nutritional value of nut and seed oil is not affected by slight rancidity (replacement of the double-bond in unsaturated fatty acids with an atom of oxygen). However, the cosmetic characteristics (color, flavor, odor and total acceptability) may be greatly degraded. 

In nature, the more prevalent structure of the double bonds in unsaturated fatty acids is the cis structure, which means that the hydrogen atoms are on one side of the double bond and the carbon chains attached to the double bond are on the other side. During the process of hydrogenation of vegetable oils, some of the cis double... 

The double bonds in unsaturated fatty acids will react with hydrogen to produce saturated fatty acids. For example, when hydrogen is added to glyceryl trioleate (triolein) using a nickel catalyst, the product is the saturated fat glyceryl tristearate (tristearin). 

The effect of canolol on the storage stability was confirmed by storing canola oil at 60°C over 168 h. The parameters used to monitor the oxidative state of the oil were diene absorption as well as the hexanal content. An increase of absorption at 240 nm was found as a resnlt of a shift of the double bond in unsaturated fatty acids during oxidation. Hexanal, a key compound of the oxidation of fats and oil can be used as an indicator to follow the extent of oxidation. 

Shantha, N.C. and Kaimal, T.N.B. (1984) Mass spectrometric location of double bonds in unsaturated fatty acids including conjugated acids as their methoxy-bromo derivatives. Lipids, 19 (12), 971-974. 

The chemical reactions of the triacylglycerols (fats and oils) are similar to the hydrogenation of aUcenes and the hydrolysis and saponification of esters. The double bonds in unsaturated fatty acids of a triacylglycerol will react with hydrogen to produce saturated (single bonds) fatty acids. 

The double bonds in unsaturated fatty acids are almost always cis. 

The double bonds in unsaturated fatty acids are almost always cis. Example State the number of carbon atoms, saturated or unsaturated, and name of the following ... 

The number and location of the double bonds in unsaturated fatty acids are important to their role in nutrition and biological function. 

Von Rudloff, E., Periodate-permanganate oxidations. IV Determination of the position of double bonds in unsaturated fatty acids and esters, 7. Am. Oil Chem. Soc., 1956,33, 126-128. Boyer, J. L., J. P. Canselier, V. Castro, Analysis of S03-sulfonation products of 1-alkenes by spectrometric methods, J. Am. Oil Chem. Soc., 1982,59,458-464. 

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