Ether lipids, synthetic

Milk fat contains small amounts of ether lipids. Synthetic ether lipids at low concentrations are potent anti-neoplastic agents. Cell culture studies showed that they inhibited cell growth, induced differentiation, promoted apoptosis and showed anti-metastatic activity. In human chemoprevention trials ether lipids have been administered parenterally. Although the ether bond is preserved when these lipids are delivered orally, no cancer chemoprevention studies have utilized dietary ether lipids (Parodi, 2004). 

Finally, besides conventional liposomes that are made from natural (e.g., egg yolk and soybean) or synthetic phospholipids, novel liposomes called archaeosomes that are prepared from the polar ether lipids extracted from various archaeobacteria proved also interesting for the design of vaccines as peptide antigen carriers (71) and as powerful self-adjuvanting vaccine delivery vesicles that promote both humoral and cell-mediated immunity (72). Related to this, one can mention that pseudopeptides, which are less prone to proteolysis when conjugated to liposomes, were also competent in triggering a humoral immune response (73). 

Alkyl glyceryl ethers are now being viewed as C-3 building blocks in lipid chemistry. The presence of two free OH groups allows the introduction of much functionality for specific synthetic surfactants and specialty lipids. Their use in newer synthetic approaches has been reviewed [43-45]. 

Glasses exist that fnnction as selective electrodes for many different monovalent and some divalent cations. Alternatively, a hydrophobic membrane can be made semiper-meable if a hydrophobic molecnle called an ionophore that selectively binds an ion is dissolved in it. The selectivity of the membrane is determined by the structnre of the ionophore. Some ionophores are natnral products, such as gramicidin, which is highly specific for K+, whereas others such as crown ethers and cryptands are synthetic. Ions such as, 1, Br, and N03 can be detected using quaternary ammonium cationic surfactants as a lipid-soluble counterion. ISEs are generally sensitive in the 10 to 10 M range, but are not perfectly selective. The most typical membrane material used in ISEs is polyvinyl chloride plasticized with dialkylsebacate or other hydrophobic chemicals. 

For some foods, incomplete extraction of color is obtained, probably due to the high binding affinity of dyes to the bulk of the food matrix, especially to proteins, lipids, and carbohydrates (156,161,162). This problem can be overcome by the use of selected solvents or enzymes to digest the food prior to extraction. Petroleum ether can be used to extract lipids (163). Acetone can be used to remove lipids and coagulate protein (164). Enzymes, such as amyloglucosidase (165,166), papain (167), lipase, pectinase, cellulase, and phospholipase, added to the sample and incubated under optimum pH and temperature conditions release synthetic colors bound to or associated with the food matrix. Furthermore, enzyme digestion can solubilize some foods, enabling analysis to be continued (156). 

Came and coworkers have described a toxic lipid extracted from Coryne-bacterium ovis, a pathogen which, in sheep, causes a wide-spread disease known as caseous lymphadenitis. The lipid extracted from living C. ovis with petroleum ether is toxic for leucocytes in vitro. A preliminary chemical investigation of this lipid fraction, kindly prepared by Dr. Came, has not yet yielded definite information about the chemical nature of the active fraction. A synthetic 6,6 -dicorynomycolate of trehalose, prepared by Diara and Pudles, has been found devoid of leucotoxic action. 

Other lipid compositions with synthetic lipids, hydrogenated SPC (HSPC) and PEG-modified phospholipids are often used, especially for liposome formulations intended for parenteral applications use (long circulating or stealth liposomes) (41). Several analytical methods to follow loss of lipids during the preparation steps are available. Radioactively labeled lipids ( H-DPPC, C-DPPC) or cholesterol ( H-cholesterol) or H-cholesteryl hexadecyl ether (NEN Life Science Products, Boston, MA, USA) or lipophilic fluorescence dyes (e.g. lipophilic BODIPy derivatives. Molecular Probes) are added at appropriate amounts to the initial lipid mixtures. 

Behavior of iron-sulfur proteins in particles after phylloquinone removal. According to the electron-carrier sequence presented above, removal of A] from the chain is expected to block forward electron transfer to succeeding carriers. This area of research, however, has been somewhat controversial. For instance, Itoh et a/initially found that, contrary to expectation, in particles whose phylloquinone was nearly quantitatively extracted, FeS-A/B could still be photochemically reduced at both 10 K and at room temperature. These authors also demonstrated photoaccumulation ofFeS-X . Meanwhile, Mansfield, Hubbard, Nugent and Evans performed ether extraction on PS-I particles prepared from pea chloro-plasts and obtained a similar correlation between phylloquinone extraction and the development of iron-sulfur-protein EPR signals, showing that the iron-sulfur proteins were retained. However, these authors found that the iron sulfur centers could only be reduced chemically, not photochemically. Furthermore, they also reported that addition of synthetic vitamin Kj to the extracted particles did not restore electron transfer to the iron-sulfur proteins. The authors explained that ether not only extracted phylloquinone and pigment molecules but also lipids, whose removal could possibly have affected the structure of the reaction center and consequently electron-transfer behavior. 

Stabilization of a lipid membrane onto a solid support by covalent attachment also provides the physical stability necessary for the development of practical sensors. An oriented membrane can be prepared by allowing self-assembly of individual amphiphilic molecules onto a solid surface through either the reaction of terminal silane moieties with a hydroxylated surface to form a silyl ether [33,34], or by the reaction of sulfur-terminated compounds (alkylthiols or disulfides) with gold surfaces [35,36]. A variety of species, both with and without polar head groups, have been deposited onto surfaces such as glass, quartz, silicon, and gold [37-39]. These include phospholipids, fatty acids, and fatty amines which were synthetically altered so as to contain either a silyl chloride or a thiol moiety at the terminus of the acyl chain [40]. Both monolayers... 

Extraction of dissolved hydrocarbons from sea water Most of the methods used are based on the liquid—liquid extraction of lipids by a solvent various solvents such as CH2CI2, CHCI3, CQ4, nCeHn, nCsHi2, petroleum ether and ethyl acetate have been tested for the recovery and employed (Table I). Recovery of a synthetic mixture of saturated hydrocarbons by extraction with petroleum ether and ethyl acetate is about 97% (Jeffrey et al., 1964). Blumer (1970) demonstrated that the extraction of dissolved lipids at pH 2 using pentane as the solvent was quantitative after four extraction steps. Parker et al. (1972), using a technique for the continuous extraction from sea water with hexane, found in control experi-... 

The synthetic compound, l,2-di-0-9 -octadecenyl-3-0-/3-D-galactopyranosyl-5n-glycerol, which is an ether analogue of mono-D-galactosyldiacylglycerol, can be converted by plant enzymes into the 6-O-acyl derivative.The availability of the 9-octadecenyl compound can provide a substrate for studies on the direct desaturation of lipid-linked acyl or alkyl chains. 

Smith et al. (1960) made comparisons of the lipids of 72 strains of mycobacteria including virulent and avirulent strains of Mycobacterium tuberculosis, and M. bovis. They also studied M. avium, M. phlei, M. smegmatis, and representatives of the atypical acid-fast group. The cultures were grown on synthetic medium and were extracted with ether-ethanol. The lipids were separated by chromatography on magnesium silicate-Celite and were identified by means of their infrared spectra. 

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