Phospholipids chemical structures

SPHINGOSINE-CONTAINING PHOSPHOLIPIDES— INOSITOL-CONTAINING PHOSPHOLIPIDES—(Chemical structures of compounds in this group are as yet incomplete.)... 

Seki and Tirrell [436] studied the pH-dependent complexation of poly(acrylic acid) derivatives with phospholipid vesicle membranes. These authors found that polyfacrylic acid), poly(methacrylic arid) and poly(ethacrylic acid) modify the properties of a phospholipid vesicle membrane. At or below a critical pH the polymers complex with the membrane, resulting in broadening of the melting transition. The value of the critical pH depends on the chemical structure and tacticity of the polymer and increases with polymer hydro-phobicity from approximately 4.6 for poly(acrylic acid) to approximately 8 for poly(ethacrylic acid). Subsequent photophysical and calorimetric experiments [437] and kinetic studies [398] support the hypothesis that these transitions are caused by pH dependent adsorption of hydrophobic polymeric carboxylic acids... 

Fig I. Chemical structure nf phosphatidylcholine (PC) (I) and other related phospholipids. o represents falls acid residues. The choline frag-... 

The ELS detector was previously also referred to as a mass detector, pointing to the fact that the response is (mainly) determined by the mass of the sample rather than by its chemical structure. Van der Meeren et al., though, demonstrated that the ELSD calibration curves of phospholipid classes were also dependent on the fatty acid composition (52). The dependence on the fatty acid composition is, however, completely different in nature and much less pronounced than for UV detection. The reason for this behavior is to be found in the partial resolution of molecular species, even during normal-phase chromatography. Thus, the peak shape depends not only on the chromatographic system but also on the fatty acid composition and molecular species distribution of the PL sample (47). Because it was shown before, based on both theoretical considerations and practical experiments, that the ELS detector response is generally inversely proportional to peak width (62,104), it follows that the molecular species distribution of the PL standards used should be similar to the sample components to be quantified. It was shown that up to 20% error may be induced if an inappropriate standard is used (52). 

FIGURE 14.2 Chemical structures of two representative classes of phospholipids. 

The initial event in the entry of viruses into cells is the attachment of the virus to specific receptors on the cell membrane. The chemical structures of most receptors for animal viruses are poorly defined. Cell surface glycoprotein, glycolipids, and phospholipids have been implicated. Very recently Helenius et al. (29) could identify human HLA and murine H-2 histocompatibility antigens as receptors for Semliki Forest virus these antigens are well-defined membrane glycoproteins. 

Local delivery of bevacizumab at the vessel wall can be performed by dedicated stents coated with PC. The PC polymer mimics the chemical structure of the PC headgroup, which makes up 90% of phospholipids in the outer membrane of a red blood cell. PC has been shown to decrease protein absorption and platelet adhesion thereby we can expect that the PC coating reduces the thrombus formation of the stainless steel stent, allowing the prevention of subacute thrombosis. Both in vitro and in vivo researches have demonstrated that PC-based polymers are effective in improving the biocompatibility of inert materials (60-62). 

Figure 9.6 Chemical structure of complex lipids (e.g., phospholipids and glycolipids) which differ in that they contain additional elements (e.g., P, S, and N) or small hydrophilic compounds (e.g., sugars and certain amino acids).

Unfortunately, the impact of the Hokins observations was not im-mmediately felt. At that point in time, phospholipids were viewed mainly as semipermeable membrane structures whose main function was to regulate the ion content of the cell. In addition, another deterrent was the limited information on the chemical structure of the mammalian cell phospholipids. Hence... 

This brief historical sketch serves as an introduction to the main goal of this book, which is to describe in some detail the chemical nature of phospholipids present in mammalian cells. It is hoped that there will be sufficient information for the reader to appreciate the uniqueness of many of these compounds, develop some rapport with their chemical structure, and become familiar with their isolation and identification. 

As underscored above, there is one other area of specificity of chemical structural patterns in cellular membrane phospholipids that is perplexing yet fascinating and also a consistent characteristic of particular phospholipids. This concerns the distribution of alkylacyl and alkenylacyl types of phospho-glycerides found in many cells. Table 1-7 provides data on such a distribution in human eosinophils. 

As a first approach, one must undertake to isolate these substances from a cell, purify them to apparent homogeneity, and then determine their chemical structure. Only with such an approach can one hope to interpret their exact role in cellular reactions. The next chapter will center on the isolation, purification, and initial characterization of cellular phospholipids. 

Dorfler HD. Relationships between miscibility behavior and chemical structure of phospholipids in pseudobinary systems. Colloid Polym. Sci. 2000 278 130-136. 

Eicosanoids, also referred to as icosanoids, are so named because of the 20-carbon constituency that identifies this class of oxygenated lipid molecules. A primary synthetic pathway for these molecules involves the phospholipase-mediated cleavage of a membrane phospholipid to produce arachidonic acid [(all-Z)-ik osa-5,8,ll,14-tetraenoic acid]. From this biologically essential intermediate fatty acid, two major subclasses of eicosanoids can be produced 1) leukotrienes, via the action of lipooxygenases, and 2) prostanoids, via the action of cyclooxygenases (COX-1 and COX-2). Examples of chemical structures for a leukotriene (Fig. la) and three types of prostanoids (Fig. Ib-d) underscore their shared arachidonate origin. 

The simplest method for modifying natural (crude) lecithin is the addition of a non-reactive substance. Plastic lecithins are converted to fluid forms by adding 2% to 5% fatty acids and/or carriers such as soybean oil. If the additives react with the lecithin to alter the chemical structure of one or more of the phospholipid components, the resulting product is referred to as a chemically modified lecithin. Modification can also be achieved by subjecting lecithin to partial controlled enzymatic hydrolysis. Finally, refined lecithin products can be obtained by fractionating the various phospholipid components. 

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