Non-polar lipids

Recently, a quantitative electrospray ionization/mass spectrometry method (ESI/MS) has been developed to analyze the molecular profile, or hpidome of different lipid classes in very small samples. In this method, total lipid extracts from tissues or cultured cells can be directly analyzed. By manipulating the ionization method, the mass spectrographs of polar or even non-polar lipids can be obtained [8]. This method and the use of lipid arrays allow precise and quantitative identification of the lipid profile of a given tissue, and map functional changes that occur. 

At the beginning of the experiment the oil is present in the form of TG. During the reaction, the lipase splits the individual fatty acids from the glycerol backbone to form EE (a non-polar lipid component) as well as DG and MG (more polar lipid... 

Analysis of non-polar lipids by HPLC is best carried out using normal phase columns. However, for mixed phases with polar drug or drug within an aqueous phase some compromise may be necessary. Good separation of polar and neutral lipids with a C8 column and a four-solvent mobile phase has been reported. Elution of neutral lipids like triglycerides from C18 columns is slow, however, good resolution can been achieved. Mobile-phase development is usually necessary to effect... 

It is natural to classify lipids as polar or non-polar according to their interaction with water. Non-polar lipids, for example triglyceride oils, do not form aqueous phases, whereas polar lipids do. Except for cholesterol, membrane-forming lipids form aqueous phases and have polar head groups. Within membranes there are also trace amounts of lipids in membranes that do not interact with water, for example diacylglycerols. The structural formulae of two common membrane lipids, phosphatidylcholine (PC) and phosphatidylethanolamine (PE) are shown above. 

There are two important functions of the pore system, beside the provision of an acceptable texture. One is the heat transfer during baking, which takes place by evaporation and condensation over the pore network. The pore curvature will directly influence this process. The second function is the accumulation of flavour compounds formed by Maillard (browning) reactions during the final period in the oven. Non-polar lipids form a surface film in the pore system, where these flavour compounds are absorbed - just as porous inorganic materials such as zeolites adsorb incoming species. (The relation between absorption and curvature was discussed in Chapter 2.)... 

Ion Exchange Adsorption Process. Supercritical fluid extracts of Crotalaria spectabilis contain monocrotaline, a basic alkaloid, and non-polar lipid material. In the separation of caffeine from coffee, Zosel (3) recommended separation of the caffeine from the fluid phase by either adsorption onto activated carbon or absorption into liquid water. Activated carbon adsorption would be undesirable in the present case because the lipids would also be adsorbed and because desorption from activated carbon is quite difficult. Liquid water would absorb... 

The selective hydrophobicity or amphiphilicity of some lipid molecular species play a most important biological role for the living cell, because it forces lipid molecules to accumulate, thus minimizing their contact to water. The non- polar lipid assemblies formatting in this way are the boundary of the living cell, separating it from its water environment. 

Their retention factor (Rf) to various solvent mixtures (non polar lipids or polar lipids)... 

The cholesterol activity on lipid bilayers has been subjected to extensive studies. As described above, cholesterol belongs to the class of neutral (non-polar) lipids and can be characterized as an amphiphilic molecule having a hydroxyl group at the C-3 position and a non-polar region. Frequently, cholesterol is incorporated into lipid membranes and studies concerning the influence on the phase transition between gel and liquid crystalline phases of the lipid bilayers hav been published [26, 27]. 

Vereshchagin, A. G. The partition of polar and non-polar lipids in a reversed-phase chromatography system. J. Chromatogr. [Amsterdam] 14, 184 (1964). 

The relative polarity of a POP appears to determine whether it partitions preferentially into polar or non-polar lipid classes62,95 and may explain, at least in part, deviations from predicted values based on single, homogenous-compartment models. 

Lead, like mercury, causes neurological diseases. The organolead compounds are more toxic than mineral lead salts, since they are non-polar, lipid-soluble, and more readily cross the blood-brain barrier. This disease is related to mental retardation is children, lower performance on I.Q. tests, and hyperactivity. Severe exposure in adults causes irritability, sleeplessness, and irrational behavior. Some have gone as far as to blame anti-social behavior and criminality on sub-clinical Pb poisoning. A correlation between Pb in blood and Pb in air, dust and soils has been observed in many studies. The U.S. Centers for Disease Control has proclaimed a goal of reducing blood lead contents in children below 10 jag/lOOmL. 

Drug molecules are transported across cell membranes. Because of the lipid bilayer construction of the membrane (Appendix 2), non-polar (lipid-soluble) molecules are able to diffuse and penetrate the cell membrane. Polar molecules, however, cannot penetrate cell membrane readily via passive diffusion and rely on other transport mechanisms. 

In an earlier review [3], mixed micelles formed by bile salts were classified into those with (i) non-polar lipids (e.g., linear or cyclic hydrocarbons) (ii) insoluble amphiphiles (e.g., cholesterol, protonated fatty acids, etc.) (iii) insoluble swelling amphiphiles (e.g., phospholipids, monoglycerides, acid soaps ) and (iv) soluble amphiphiles (e.g., mixtures of bile salts with themselves, with soaps and with detergents) and the literature up to that date (1970) was critically summarized. Much recent work has appeared in all of these areas, but the most significant is the dramatic advances that have taken place in our understanding of the structure, size, shape, equilibria, and thermodynamics of bile salt-lecithin [16,18,28,29,99-102,127, 144,218,223,231-238] and bile salt-lecithin-cholesterol [238,239] micelles which are of crucial importance to the solubihty of cholesterol in bile [1]. This section briefly surveys recent results on the above subclasses. Information on solubilization, solubilization capacities or phase equilibria of binary, ternary or quaternary systems or structures of liquid crystalline phases can be found in several excellent reviews [5,85,207,208,210,211,213,216,217] and, where relevant, have been referred to earlier. 

In contrast to phospholipids, non-polar lipids such as DG behave differently. 

Thus, studies with model membranes provide clear evidence that the transbilayer movement of phospholipids is a very slow process in this system, whereas the process appears to be rapid for non-polar lipids. The results imply that if transbilayer movement of phospholipids does occur in biological membranes, it must be a facilitated process. 

Fairly large (but relatively non-polar) lipids such as triglycerides and cholesterol esters can be directly chromatographed in the gas phase. Such separations need... 

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... 

Table 3.180 Distribution of polar and non-polar lipids in cod, hake, trout, pilchard and wrasse ... 

Ion-exchange chromatography is a useful technique for the initial separation of lipids from crude mixtures. Separation of lipids on columns packed with adsorbants like DEAE-cellulose depends partly on ion-exchange with the ionic parts of polar lipids and partly on adsorption of highly polar non-ionic moieties such as the hydroxyl groups of inositol or carbohydrates. Non-polar lipids are eluted with solvents such as chloroform and polar non-ionic lipids and non-acidic lipids are partly resolved by increasing concentrations of methanol in chloroform. Weakly acidic lipids can then be eluted by inclusion of acetic acid in the solvent while strongly acidic lipids... 

When a non-polar lipid is also introduced the phase behaviour gets quite complex. An example of such a ternary lipid system (Lindstrom et al, 1981) is shown in Fig. 8.14. The triglyceride component, as well as the monoglyceride component, contain numerous compounds with different chains and both behave as one component with respect to the phase rule. It... 

The evidence for the relations between L2-, LS-and 5-phases and three-dimensional crystal forms is quite convincing. Lundqvist (1978) has reported extensive comparisons between condensed mono-layer phases and polymorphic forms in the crystalline state of non-polar lipids and a summary of this work, together with additional data on polar lipids, will be given below. 

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