Triacylglycerols common fatty acids

Various combinations of hexane or light petroleum (40-60°C, bp) and diethyl ether, usually with a small amount of acetic acid (e.g. 90 10 1) or diisopropyl ether and acetic acid (98.5 1.5) are commonly used. The greater mobility is demonstrated by cholesterol esters followed by triacylglycerols, free fatty acids, cholestorol, diacylglycerols and monoacylglycerols, with complex polar lipids remaining unmoved. Double development in two solvents, e.g. diisopropyl... 

Simple triacylglycerols are composed of three identical fatty acid side chains, whereas mixed triacylglycerols have two or three different fatty acids. Table 29.2 lists the most common fatty acids used to form triacylglycerols. 

Available literature solubility data of pure lipids belonging to major (fatty acids, mono-, di- and triacylglycerols, and fatty acid esters) and minor lipid classes (pigments, sterols, vitamins, and hydrocarbons) in SCCO2 were compiled (26, 27). These references (26, 27) contain exhaustive bibliography on lipid + SCCO2 binary systems. Literature data were correlated using Chrastil s equation, which is an empirical model used quite commonly to correlate the solubility of lipid components (30). This model is based on the formation of a solute-solvent complex on association of the solute and solvent molecules and establishes a linear relationship between In(solubility) and In(density) as follows ... 

As previously described (see p. 13), fatty acids are monocarboxylic acids that typically contain hydrocarbon chains of variable lengths (between 12 and 20 carbons). The structures and names of several common fatty acids are illustrated in Table ILL Fatty acids are important components of several types of lipid molecules. They occur primarily in triacylglycerols and several types of membrane-bound lipid molecules. 

Figure 35.10 Triacylglycerd (TAG or triglyceride). TAG consists of three fatty acyl groups esterified with a glycerol backbone, hence the name triacylglycerol. The fatty acids can vary, but in the example shown all three arc stearic add so tins TAG is called tristearin . (In clinical circles the term triglyceride is commonly used This incorrectly suggests that the molecule comprises three glycerols" and so has been rejected by chemists.)...

The most common substituted fatty acids found in plants are the monohy droxy derivatives, though polyhydroxy acids, keto acids, epoxy acids, di-carboxylic acids and even to-fluoro acids (Ward et al., 1964) are known. The 2-hydroxy derivatives of common fatty acids are found esterified in cerebro-sides, ceramides, and phytoglycolipid in high amounts. In seed oils they occur in triacylglycerol. All known 2-hydroxy acids are d isomers. The 3-hydroxy acids, which are important intermediates in both fatty acid synthetase and )8-oxidation pathways, rarely accumulate. However, ricinoleic (12-hydroxyoleic) acid accounts for 90% of the fatty acids of commercial... 

Triacylglycerols I (cf. Fig. 1) of traditional oil seed crops contain a limited number of different fatty acids eight of these common fatty acids contribute more than 97% of the world production of edible vegetable oils [5]. Fatty acids such as palmitic and stearic acids are formed by fatty acid synthase in the plastids of plant cells. 

Common fatty acid compounds a.TWgIyceride or triacylglycerol Three... 

TLC procedures with silica gel G layers (containing calcium sulfate as binder) have been employed most frequently for lipid class separations. Commonly, the solvent elution system used is hexane- diethyl ether-formic acid (80 20 2 by volume), and this gives the separations shown in Figure 2.6. Cholesterol esters migrate to the solvent front, and they are followed by triacylglycerols, free fatty acids, cholesterol, diacylglycerols, monoacylglycerols and phospholipids (with other polar lipids). For small-scale preparative... 

An overview of the occurrence of saturated fatty acids in fats and oils is given in Table 3.7. Generally, the most common fatty acid is palmitic add, which occurs in virtually aU animal and plant hpids, bound in triacylglycerols and phosphohpids. 

The moss Ceratodon purpureas (Hedw.) Brid. contains large amounts of the acetylenic fatty acids 9,12-octadecadien-6-ynoic acid [18 2A] and 6,9,12-octadecatrien-6-ynoic acid [18 3A], which are in close structural relationship to the common fatty acids lino-leic acid [18 2(n-6)] and oc-linolenic acid [18 3(n-3)], and which are obviously restricted to the triacylglycerol fraction [2]. 

The language used will be the Queen s English or that subset of it as approved by the Royal Society of Chemistry (RSC). Where chemical names are concerned there are some lost causes, such as caustic soda, where little would be gained if those who clean factories called this substance sodium hydroxide. Arguably, the name caustic soda conveys more useful information. Similar lost causes are spirits of wine (ethyl alcohol or ethanol) and spirits of salts (hydrochloric acid). While lipid chemists may insist on referring to triacylglycerols many people in industry continue to refer to triglycerides. Similarly trivial names for fatty acids such as lauric will continue to be used. The principle in all of this is to use the proper name but to mention other names that are in common use. 

Gas chromatography (GC or, less commonly, GLC) is the most widely used separation technique for volatile samples. The resolution is sufficient to routinely separate components, such as homologous series, saturated from unsaturated fatty acids, terpenoids, triacylglycerols, etc. The use of a mass spectrometer to identify the separated components (GC-MS) is discussed in Section 8.4. 

Triacylglycerols, commonly refered to as fats and oils, consist of three fatty acids linked to a molecule of glycerol, a three-carbon alcohol. Fatty acids are long-carbon-chain molecules, each with a single carboxyl functional group. Common examples are stearic acid and palmitic acid, shown in Figure 16.3. 

We introduce here the structures and nomenclature of the fatty acids most commonly found in living organisms. Two types of fatty acid-containing compounds, triacylglycerols and waxes, are described to illustrate the diversity of structure and physical properties in this family of compounds. 

The first steps of glycerophospholipid synthesis are shared with the pathway to triacylglycerols (Fig. 21-17) two fatty acyl groups are esterified to C-l and C-2 of L-glycerol 3-phosphate to form phosphatidic acid. Commonly but not invariably, the fatty acid at C-l is saturated and that at C-2 is unsaturated. A second route to phosphatidic acid is the phosphorylation of a diacyl-glycerol by a specific kinase. 

All of the described procedures use emulsified substrate. Although the p-nitrophenyl laurate assay cocktail is stable for 3 days at 4°C, the emulsified olive oil substrates (or other triacylglycerol-based substrate systems) should be made fresh daily and rehomogenized periodically and when separation is visually evident. Use of day-old emulsion substrate will yield increased blank values for titratable acidity, and this effectively compromises the limit of detection of activity. Emulsified substrates should be in liquid form at common assay conditions (20° to 50°C), and partially solidified substrates (those rich in long-chain saturated fatty acids) will cause interfacial irregularities and confound the assessment of lipases in ways that cannot be accounted for. 

The structures of common lipids, (a) The structures of saturated and unsaturated fatty acids, represented here by stearic acid and oleic acid, (b) Three fatty acids covalently linked to glycerol by ester bonds form a triacylglycerol. (c) The general structure for a phospholipid consists of two fatty acids esterified to glycerol, which is linked through phosphate to a polar head group. The polar head group may be any one of several different compounds—for example, choline, serine, or ethanolamine. 

These lipids are then packaged into spherical lipoproteins, particles of lipids and proteins, known as chylomicrons, which are secreted into lymphatic vessels and subsequently enter the blood stream. Once in the circulatory system the triacylglycerol components of the chylomicrons are degraded to fatty acids and glycerol by the enzyme lipoprotein lipase, which is attached to the luminal (inner) side of capillary vessels in heart, muscle, adipose (commonly... 

While the hydrocarbon fraction of insect cuticular lipids is certainly the most studied and has been shown to play a key role in a wide range of chemical communication, other lipids are often present on the surface of insects. The most common cuticular lipids in addition to hydrocarbons include a variety of types of esters, free fatty acids, primary and secondary alcohols, ketones and sterols. Triacylglycerols and the more polar phospholipids are not common components of insect cuticular lipids. In some cases, hydrocarbons are hydroxylated and metabolized to oxygenated components, and these products include some of the short range and contact pheromones of the housefly (Blomquist, 2003) and the German cockroach (Schal et al., 2003). The oxygenated cuticular lipids are discussed in Chapter 9 (Buckner, this book). 

Lipases can be classified into groups that reflect their specificity. The common lipases include non-specific lipases that do not discriminate between the position or the type of the fatty acid on the triacylglycerol (e.g., lipase from Candida cylindracea) and 1,3-specific lipases that act only at the sn-l and sn-3 positions of the triacylglycerol (e.g., lipases from Aspergillus niger and Rhizopus species). In addition, some lipases are specific for a specific fatty acid type (e.g., lipase from Geotrichum candidum). 

Scheme 7.1. Base-catalyzed transesterification of triacylglycerols (TAGs) to produce fatty acid esters (biodiesel). Methyl esters (shown) are the most common but others, such as ethyl esters, can be produced depending on the alcohol used in the reaction. Ri, R2 and R3 represent unique fatty acids attached to the glycerol backbone of the TAG.

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