Phosphatides

PHOSPHATIDES, substances from the group of lipoids, by their structure are complex esters of polyhydric alcohols (glycerol or sphingosine) with fatty acids and phosphoric acid; the latter combines with the residue of a nitrogenous base: choline or colamine (aminoethyl alcohol). Among the fatty acids entering into the composition of 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 bonds (Klenk), and others. Substances of the phosphatide group are still poorly studied regarding their properties and structure, since isolating them in a pure form and identifying them present great difficulties. All of them dissolve with greater or lesser ease in fatty solvents: ether, carbon disulfide, alcohol, benzene, petroleum ether, etc. In mixtures, phosphatides affect each other's solubility. With water, phosphatides yield colloidal solutions (of the emulsoid type). According to the ratio of nitrogen to phosphorus, phosphatides are subdivided into monoaminophosphatides (if the ratio of N : P = 1 : 1) and diaminophosphatides (N : P = 2 : 1). The most studied among 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 α- and β-diglyceridophosphoric acids, isolated from cabbage and spinach leaves and apparently being intermediate products of phosphatide transformation. Diaminophosphatides include substances of the sphingomyelin group, constructed on the type of lecithins with the difference that instead of glycerol they contain a dihydric unsaturated amino alcohol—sphingosine CH₃(CH₂)₁₂ CH : CH CHNH₂ CHOH CH₂ OH (sphingosine is insoluble in water, dissolves in alcohol, crystallizes in the form of long needles). The structure of sphingomyelin can apparently be expressed by the following formula: fatty acid NH-OC-R

phosphoric J

/CH₃ acid \ O=P-O-CH₂-CH₂-N-CH₃ choline. Among the fatty acids in sphingomyelins, stearic, lignoceric, and nervonic acids were found, which points to the possibility of the existence of 3 sphingomyelins. Sphingomyelin was first isolated by Thudichum as a component part of protagon. It is part of the adrenal glands, kidneys, liver, egg yolk, heart, fish sperm, and possibly all other tissues and organs. Sphingomyelin represents a crystalline mass, non-hygroscopic and unchanging 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]_D⁰ = + 7.5 to + 8.7. From various organs and tissues, as well as from tubercle bacilli, other phosphatides have also been isolated, but their chemical structure has not yet been elucidated. Iecorin was formerly classified among phosphatides—a substance extracted with cold alcohol from the liver of a horse, dolphin, and other organs of various animals; iecorin is not an individual chemical substance, but represents a mixture of phosphatides (predominantly cephalin), carbohydrates, and inorganic salts. Regarding sulfur-containing phosphosulfatides, see Sulfamides. Phosphatides yield compounds with proteins that apparently play an essential role in regulating the passage of water into and out of tissues, and influence the precipitation of proteins by forming insoluble complexes with them in the presence of free acid. Phosphatides are an indispensable component part 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 are still poorly developed and are based mainly on determining the phosphorus content. As for individual representatives of phosphatides, in recent years Lintzel's method has appeared for the quantitative determination of lecithin, based on the presence of a choline residue in the lecithin molecule; the latter upon oxidation with permanganate yields volatile trimethylamine, which is titrated after distillation; other volatile bases (NH₃, methyl-, dimethylamine) are preliminarily converted by formaldehyde into non-volatile compounds.

M. Karyagin.