Monoacylglycerols ethers

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... 

Typical thin-layer chromatogram of lipids. The solvent system, hexane-diethyl ether-acetic acid (90 10 1). (1) cholesterol, (2) fatty acid, (3) triacylglycerol, (4) fatty acid methyl ester, (5) cholesterol ester, (6) glycerophosphatide, (7) sphingolipid, (8) 1,3- or 1,2-diacylglycerol, (9) 1 - or 2-monoacylglycerol. The Rf for (5), cholesterol ester, is calculated as follows ... 

Mobile phases of hexane or light petroleum ether as main components and acetone or diethyl ether as polar modifiers are used for the separation of simple lipids. Acetic or formic acid is often added to keep the free fatty acids in the fully protonated form. The retention of simple lipids increases in the order waxes, sterol esters, methyl esters, triacylglycerols, free fatty acid, sterols, dia-cylglyerols, and monoacylglycerols (see Fig. la). If no acid is present in the mobile phase, the free fatty acids migrate between diacylglyerols and monoacylglycerols. The... 

A) Reference mixture of simple lipid classes, silica gel TLC, mobile phase hexane-ethyl ether-acetic acid, 80 20 2 (v/v/v) SE, sterol esters ME, fatty acid methyl esters TG, triacylglycerols EEA, free fatty acids S, sterols 1,3-DG, 1,3-diacylgly-cerols 1,2-DG, 1,2-diacylglycerols MG, monoacylglycerols C, complex lipids detection by spraying with 5% ethanolic phosphomolibdic acid and heating for several minutes at 180°C. 

Fig. 1. Structures of lipids covalently attached to proteins. Panel A shows proteins that are lipidated on cytoplasmi-cally exposed amino acids, whereas panel B shows lipidated proteins in the extracellular leaflet. (A) iV-myristoyl glycine, palmitate thioester-linked to cysteine, farnesyl, or geranylgeranyl (prenyl) thioether-linked to cysteine. (B) A/-palmitoyl cysteine, cholesterol ester-linked to glycine, and a minimal GPI anchor linked to the to amino acid in a GPI-anchored protein. The GPI structure is shown with a diacylglycerol moiety containing two ester-linked fatty acids. Other GPI anchors are based on ceramide, while yet others have monoacylglycerol, a fatty acid ether-linked to glycerol, and/or a fatty acid ester-linked to inositol.

The polarity of a lipid affects its volatility, solubility, and nonspecific binding to other polar compounds. Lipids are often functionally classified as neutral or polar on the basis of their mobility on thin-layer chromatography using a neutral or polar solvent system. Neutral lipids such as wax esters, steryl esters, ether lipids, and TAG are chemically neutral while other neutral lipids, such as free FA, fatty alcohols, and monoacylglycerols, are actually slightly polar due to the presence of hydroxyl or carboxyl groups. Table 3.8 lists the relative polarities of some common lipid classes. 

The monoacylglycerol band is removed with a spatula and transferred to a conical flask of 50 ml. The monoacylglycerols are dissolved in diethyl ether. The filtrate is collected in a round-bottomed flask of 25 ml for the preparation of the methyl esters (see Section 6.2.16). The methyl esters thus obtained are examined by gas chromatography as described in Section 6.2.16. 

Monoacylglycerols and diacylglycerols. The early GC/MS methods of analysis of MGs and DGs utilized TMS ethers, which were unstable and could... 

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... 

Trifluoroacetate derivatives of hydroxy acids, monoacylglycerols and glycerol ethers are... 

Isopropylidene derivatives of vicinal diols, for example glycerol ethers, 1-monoacylglycerols or dihydroxy acids, are prepared by reacting the diol with acetone in the presence of a small amount of an acidic catalyst (Figure 4.1(d)). Anhydrous copper sulfate is probably the mildest catalyst and is used as follows ... 

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