Phosphatides

Phosphatides, substances from the group of lipoids, in structure are complex esters of polyhydric alcohols (glycerol or sphingosine) with fatty acids and phosphoric acid; the latter is connected with a residue of a nitrogenous base: choline or colamine (aminoethyl alcohol). Of the fatty acids contained in phosphatides, the following have been found: stearic, palmitic, oleic, arachidonic, lignoceric, linolenic, linoleic, an unsaturated acid with a chain of 22 carbon atoms and 4 ethylene linkages (Klenk), and others. Substances of the phosphatide group are still little studied in regard to properties and structure, since their isolation in pure form and identification present great difficulties. All of them dissolve with greater or lesser ease in fat solvents: ether, carbon disulfide, alcohol, benzene, petroleum ether, etc. In mixtures, phosphatides influence each other's solubility. With water, phosphatides give colloidal solutions (of the emulsoid type). According to the ratio of N and P, phosphatides are subdivided into monoaminophosphatides (if the ratio N : P = 1 : 1) and diaminophosphatides (N : P = 2 : 1). The most studied of the monoaminophosphatides are lecithin (see) and cephalin. Recent works have established the existence of natural lecithins containing in the molecule residues of two unsaturated fatty acids, as well as forms containing residues of two saturated fatty acids. Close in structure to lecithins are alpha- and beta-diglycerophosphoric acids, isolated from cabbage and spinach leaves and apparently being intermediate products in the transformation of phosphatides. Substances of the sphingomyelin group belong to the diaminophosphatides, constructed on the type of lecithins with the difference that instead of glycerol they contain the two-valent unsaturated amino alcohol-sphingosine CH₃(CH₂)₁₂CH : CH CHNH₂ CHOH CH₂OH (sphingosine is insoluble in water, dissolves in alcohol, crystallizes in the form of long needles). The structure of sphingomyelins can apparently be expressed by the following formula: fatty acid NH-OC-R', "J", "phosphoric J", "|", "\CH₃ acid \ 0=P-O-CH-CH₂-N⁺(CH₃)₃ choline From fatty acids in sphingomyelins, stearic, lignoceric, and nervonic acids have been found, which indicates the possibility of the existence of 3 sphingomyelins. Sphingomyelin was first isolated by Thudicum as a component of protagon. It is found in the adrenal glands, kidneys, liver, egg yolk, heart, fish sperm, and possibly in all other tissues and organs. Sphingomyelin represents a crystalline mass, not hygroscopic and not changing in light and air. It dissolves in warm pyridine, does not dissolve in acetone and ether; with water it gives an emulsion. Its solution in a mixture of methyl alcohol and chloroform rotates to the right: [a]_D° = +7.5 to +8.7. From various organs and tissues, as well as from tubercle bacilli, other phosphatides have been isolated, but their chemical structure has not yet been clarified. Phosphatides also formerly included kephalin, a substance extracted by cold alcohol from the liver of horses, dolphins, and other organs of various animals; kephalin is not an individual chemical substance, but represents a mixture of phosphatides (mainly cephalin), carbohydrates, and inorganic salts. Regarding sulfur-containing phosphosulfatides, see Sulfamides. Phosphatides form compounds with proteins, which apparently play a significant role in regulating the passage of water into and out of tissues, influence the precipitation of proteins, forming with proteins in the presence of free acid insoluble complexes. Phosphatides are an essential component of animal and plant cells. On the biological significance of phosphatides and their synthesis in the organism, see Lecithin, Lipoids, Metabolism, lipoid metabolism. Methods for the quantitative determination of phosphatides have been poorly developed and are mainly based on the determination of phosphorus content. As for individual representatives of phosphatides, in recent years the method of Lintzel for the quantitative determination of lecithin has appeared, based on the presence in the lecithin molecule of a choline residue; the latter upon oxidation with permanganate gives volatile trimethylamine, which after distillation is titrated; other volatile bases (NH₃, methyl-, dimethylamine) are previously converted by formaldehyde into non-volatile compounds.

M. Karyagina.