Plant lipids, polar

Possible Mechanism of Allelopathlc Action of Water-Insoluble Plant Lipids. Many non-polar natural products with germination and growth regulation activities In laboratory tests are In pure form not sufficiently water soluble to account for their allelopathlc activities observed In the field. For this reason the notion exists that sterols and other non-polar plant constituents are not likely to play a role In allelopathlc actions, and It Is generally concluded that the bioactivity data observed In the laboratory are therefore coincidental. 

When plant or animal tissues are extracted with nonpolar solvents, a portion of the material dissolves. The components of this soluble fraction are called lipids and include fatty acids, triacylglycerols, waxes, terpenes, postagladins, and steroids. The insoluble portion contains the more polar plant components including carbohydrates, lignin, proteins, and nucleic acids. 

Up until now, most of the published work on the SFE of natural products has been concerned primarily with nonpolar substances such as essential oils, lipids, flavor, and fragrance ingredients. However, recent reports have shown that some polar plant constituents (e.g. flavonoid glycosides, proteins, and steroidal glycosides) can be extracted by SFE as effectively as conventional organic solvent extraction. Examples of SFE applications for natural products are well reviewed in several literature sources [19-22]. 

Normal-phase sorbents such as silica and Florisil are used to isolate low to moderate polarity species from nonaqueous solutions. Examples of applications include lipid classification, plant pigment separations, and separations of fat-soluble vitamins from lipid extracts, as well as the clean-up of organic solvent concentrates obtained from a previous SPE method or liquid-liquid extraction. Alumina is used to remove polar species from nonaqueous solutions. Examples include vitamins in feeds and food and antibiotics and other additives from feed. Normal-phase chromatography has been used for a number of years, and most applications for normal-phase column chromatography may be easily transferred over to normal-phase SPE. 

Synthesis of polar and non-polar lipids in plants as well as animals is via the glycerol phosphate or Kennedy pathway (5). In this pathway 3-sn-glycerol phosphate, formed by reduction of dihydroxyacetone phpsphqte, is, acy.late(L by. acyl CoA in the 1- and... 

Polar Plant Lipids. The best known phosphatides can be fractionated into classes with the help of TLC this is shown in Fig. 139. Even extracts of green plant parts which contain many polar lipids, can be satisfactorily... 

Raison, J.K. and Wright, L.C. (1983) Thermal phase transitions in the polar lipids of plant membranes. Their induction by disaturated phospholipids and their possible relation to chilling injury. Biochim. Biophys. Acta 731, 69-78... 

At the end of each week, lipids of plant leaves were extracted according to a modified method of (7) and polar glycerolipid classes were separated by thin layer chromatography according to the method of (8). Fatty acids were analyzed by gas chromatography (9). 

Phospholipids are found widely in both plant and animal tissues and make up approximately 50% to 60% of cell membranes. Because they are like soaps in having a long, nonpolar hydrocarbon tail bound to a polar ionic head, phospholipids in the cell membrane organize into a lipid bilayer about 5.0 nm (50 A) thick. As shown in Figure 27.2, the nonpolar tails aggregate in the center of the bilayer in much the same way that soap tails aggregate in the center of a micelle. This bilayer serves as an effective barrier to the passage of water, ions, and other components into and out of cells. 

Isooctane, AOT and HAuCl4-3H20 were acquired from Sigma-Aldrich, lecithin (L-a-phosphatidylcholine, 95% Plant Soy) from Avanti Polar lipids. 

The extraction procedure used to isolate lipids from biological tissue depends on the class of lipid desired and the nature of the biological source (animal tissue, plant leaf, plant seed, bacteria, cell membranes, etc.). Because lipids are generally less polar than other cell constituents, they may be selectively extracted with the use of organic solvents. Early studies of lipids used ether, acetone, hexane, and other organic solvents for extraction however, these solvents extract only lipids bound in a nonpolar or hydrophobic manner. In the 1950s, Folch s group reported the use of chloroform and methanol (2 1) in... 

However, NP-HPLC has been criticized because of the apparent similarity in polarity between many OPPs, and the lipids of both animal and plant origin precluded the development of... 

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