Phospholipids nitrogen-free

Some 40 years ago in the halcyon days of study of the then new technique of silicic acid column chromatography of lipids, it was apparent to several investigators that there were nitrogen-free phospholipids in these samples. Also, these unique, acidic phospholipids did not contain inositol. In the usual protocol, lipids were applied to a silicic acid column in a nonpolar solvent such as hexane (or petroleum ether, b.p. 30-60°C), and elution continued with increasing amounts of diethyl ether. These solvent mixtures would elute the... 

Nitrogen-free Phospholipids.—Mycobacterial phospholipids differ from those of other organisms by the absence of choline and colamine (for a review on bacterial phospholipids in general, see Ref. 36) the latter has only once been found—in a small fraction, after careful chromatography of a phospholipid of M. marianum. - ... 

The chloroform solution of lipids (Solution A) is placed in a 50-mL round-bottomed spherical Quick-fit flask. Following evaporation of the solvent in a rotary evaporator at about 37°C, a thin lipid film is formed on the walls of the flask. The film is flushed for about 60 seconds with oxygen-free nitrogen (N2) to ensure complete solvent removal and to replace air. Two milliliters of distilled water and a few glass beads are added into the flask, the stopper is replaced, and the flask shaken vigorously by hand or mechanically until the lipid film has been transformed into a milky suspension. This process is carried out above the liquid-crystalline transition temperature (7/) of the phospholipid component of liposomes (> 7/) by prewarming the water... 

Next, the removal of any suspected contaminants—such as carbohydrates (e.g., glucose), free amino acids, nucleotides and so on—can be accomplished by the procedure of Wells and Dittmer (1963). The lipid sample, dissolved in a mixture of chloroform-methanol-water (60 30 4.5, v/v), is passed through a previously washed column of Sephadex G-25, the effluent is collected and saved, and the column is then washed with a mixture of chloroform-methanol (2 1, v/v). The second eluent is collected and combined with the first and will contain all the phospholipid, free of contaminants. The two eluates are combined, phased by the addition of water, and then the chloroform-rich layer is removed and evaporated to dryness under nitrogen. The residue is dissolved in chloroform-methanol (2 1, v/v) and made to volume in a glass-stoppered volumetric flask. 

Free radicals may also be formed by (a) homolysis of covalent bonds, (b) addition of an electron to a neutral atom, or (c) loss of a single electron from a neutral atom. These radicals, especially if they are of low molecular weight, are usually extremely reactive hence, they are short-lived. Since they have an unpaired electron, they are highly electrophilic (i.e., electron loving ) and attack sites of increased electron density, as in compounds with nitrogen atoms (e.g., proteins, amino acids, DNA, RNA) and carbon-carbon double bonds (i.e., polyuunsaturated fatty acids and phospholipids which make up bilipid cell membranes). 

However, the nitrogenous bases of phospholipids can be identified by their IR absorption spectra in the region of 900-1100 cm Free amine groups as... 

Both the relative potencies of the free-add and anionic forms of barbiturates and also the possible interference by barbiturates in the binding of calcium to phospholipids are subject to considerable controversy. In consequence, various derivatives and salts of barbituric add have been extensively investigated. The analysis of calcium 5,5-diethylbarbiturate trihydrate (41) reveals that the deprotonated nitrogen atoms are co-... 

Fig. 1. Possible theoretical exchanges of free nitrogenous bases (X) with membrane-bound endogenous phospholipids (Ptd-Etn, Ptd-Cho, Ptd-Ser, Ptd-Thr). See the text, for abbreviations X = ethanola-mine, choline or L-serine...

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