4in V. f'TTEMTSTRY OF PHOSPHATIDES AND CERKBEOSTDES 



Lecithin forms a colloidal solution with water from which it may be 

 precipitated by acetone. Leathes^^ demonstrated that, when a lecithin 

 surface comes into contact with water, peculiar finger-like growths of 

 lecithin result. Such myelin forms are inhibited by calcium ions, except 

 when cholesterol is present. These irregular growths on the surface pre- 

 sumably occur liecause of the very considerable surface area occupied by a 

 film of lecithin; the extent of this film exceeds that of the component fatty 

 acids, apparently because the other groups in the lecithin molecule separate 

 the fatty acid chains, thus preventing any close packing. 



Aqueous solutions of lecithin can be prepared in the presence of bile 

 salts up to 80% of the weight of the salts, and only part of the solute in this 

 case is precipitable by acetone. The presence of many inorganic salts, 

 such as barium chloride, accelerates the solubility of lecithin under such 

 conditions.™ On the other hand, it has been stated that lecithin prevents 

 the precipitation of bile salts from their alcoholic solutions by ether. 

 Hammarsten'^^ believes that this may be explained by the assumption that 

 a lecithin-bile salt combination is formed which is soluble in ether, chloro- 

 form, and benzene. 



In addition to its possible combination with bile salts, lecithin combines 

 with inorganic salts, sugars, and possibly also with protein. It for As a 

 loose combination with sodium chloride which is soluble in ether, but which 

 dissolves with difficulty in alcohol, and is insoluble in acetone.''^ Strecker^^ 

 first proved that lecithin can be completely precipitated from an alcohol 

 solution by cadmium chloride as a white flocculent precipitate. However, 

 the proportions of lecithin and cadmium were found to be variable, •'"'•'^^•''* 

 and it is now believed that cephalin is also precipitated by the same salt. 

 After remo\'al of cephalin, however, the precipitation as the cadmium 

 chloride salt is ^■ery useful in the preparation of pure lecithin. Lecithin 

 precipitates as a double salt, on the addition of an alcoholic solution of 

 platinum chloride to an alcohol solution of lecithin." This platinum salt 

 dissolves readily in ether, carbon disulfide, chloroform, and benzene, and 

 corresponds to the empirical formula (C42H83NP08Cl)2-PtCl4. Discrep- 

 ancies in the composition of this salt reported by several workers can 

 probably be traced to the fact that it may also contain cephalin in amounts 

 which, in one preparation, were as high as 30%.''^ Bing^^ and Mayer" have 



69 J. B. Leathes, Lancet, 1925, I, 803-807, 853-856, 957-962, 1019-1022. 



'" J. H. Long and F. Gephart, /. Am. Chem. Soc, 30, 1312-1319 (1908). 



'1 O. Hammarsten, Ergeb. Physiol, 4, 1-22 (1905). 



'2 H. J. Bing, Skand. Arch. Physiol, 11, 166-175 (1901). 



" A. Erlandsen, Z. physiol Chem., 51, 71-155 (1907). 



->' J. E. Eppler, Z. physiol Chem., 87, 233-254 (1913). 



^6 S. Frankel and A. Kasz, Biochem. Z., 124, 216-227 (1921). 



'6 H. J. Bing, Skand. Arch. Physiol, 9, 336-411 (1899). 



" P. Mayer, Biochem. Z., 1, 81-107 (1906). 



