Acylglycerols structure

SOURCES, FATTY ACID CONTENT, AND ACYLGLYCEROL STRUCTURE... 

Olid carbon is asymmetric. The various acylglycerols are normally soluble in benzene, chloroform, ether, and hot ethanol. Although triacylglycerols are insoluble in water, mono- and diacylglycerols readily form organized structures in water (discussed later), owing to the polarity of their free hydroxyl groups. 

In some polysaccharides, the reducing terminal is linked, through a phosphoric diester linkage, to O-1 of a 2,3-di-6 -acylglycerol. This structural feature has been demonstrated for some capsular polysaccharides from E. coli and Neisseria species, - but is probably more common than that. Non-covalent linkage between the lipid part and the cell membrane may explain why extracellular polysaccharides often occur as capsules, and the high (apparent) molecular weight observed for these polysaccharides may be due to micelle formation in aqueous solution. 

B 1. If you wished to determine the complete structure of the isolated tri-acylglycerol, what experimental approach would you follow ... 

Lipids are made up of many classes of very different molecules that all show solubility properties in organic solvents. Mass spectrometry plays a key role in the biochemistry of lipids. Indeed, mass spectrometry allows not only the detection and determination of the structure of these molecules but also their quantification. For practical reasons, only the fatty acids, acylglycerols and bile acids are discussed here, although other types of lipids such as phospholipids, [253-256] steroids, [257-259] prostaglandins, [260] ceramides, [261,262] sphingolipids [263,264] and leukotrienes [265,266] have been analysed successfully by mass spectrometry. Moreover, the described methods will be limited to those that are based only on mass spectrometry, even if the majority of these methods generally are coupled directly or indirectly with separation techniques such as GC or HPLC. A book on the mass spectrometry of lipids was published in 1993. [267]... 

This method can be applied directly to acylglycerols present in a mixture, as is illustrated by the mass spectrometric analysis of natural cocoa butter. [299] This analysis (Figure 8.65) allowed the determination of the complete structure of the predominant acylglycerols in the cocoa (Table 8.10). 

As expected from fatty acid composition, the main triacylglycerols contain linolenic acid in their molecules and 84% of all triacylglycerols have this acid in their structure (Table 3). Among them, 21% of total acylglycerols contained three ALA in molecule, second by contribution were acylglycerols with two ALA, and linoleic acid had the second-most abundant fatty acid present in the flax oil (17). 

EFFECTS OF STEREOSPECIFIC STRUCTURE OF DIETARY ACYLGLYCEROLS ON CHYLOMICRON CLEARING AND TISSUE TARGETING... 

The stereospecific numbering of acylglycerols has been introduced by H. Hirschmann (J. Biol. Chem. 235 (1960) 2762) and is widely accepted, although its application is limited. See H. Hauser. G. Poupart, in The Structure of Biological Membranes. P. Yeagle (Ed.), CRC Press, Boca Raton, Florida, 1992. 

Figure 6-3. The structures of fatty acids, glycerol, and the acylglycerols. R indicates a linear aliphatic chain. Fatty acids are identified by the number of carbons and the number of double bonds and their position (e.g., 18 1,A9).

Figure 26-13 Structure and classification of glycerol esters (acylglycerols). R, Ka, and R3 are fatty acid(s) of varying chain length.

The employment of 1,3-selective lipases leads to structured TAG where specific acyl groups are confined to either the l-(3-) or 2-acylglycerol position. One of the earliest examples is cocoa butter substitute formed by 1,3-selective lipase-catalyzed acidolysis (reaction 1 of Fig. 3) of palm oil midfraction by palmitic acid (resulting in the replacement of 1-, 3-dipalmityl, 2-oleyl TAG by l-(3-) palmityl, 2-oleyl, 3- (1-) steryl TAG and 1-, 3-disteryl, 2-oleyl TAG, both of which are abundant in cocoa butter). The product... 

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