480 V. CHEMISTRY OF PHOSPHATIDES AND CEREBROSIDES 



Several tests have been employed to detect phrenosine, all of which 

 depend upon the carbohydrate group. These reactions are not specific for 

 phrenosine, however, but will be given by all cerebrosides. These include 

 the reaction with concentrated sulfuric acid (yellow, then purple colora- 

 tion), ^^^ which depends upon the presence of galactose and sphingosine, the 

 Molisch reaction (violet coloration when pure concentrated sulfuric acid is 

 added to an a-naphthol solution of cerebroside), and the orcin test (green- 

 blue-green coloration on the addition of orcin and hydrochloric acid con- 

 taining ferric chloride), which depends upon the galactose/^^ 



(2) Cerasine 



The solubility of cerasines is similar in all cases to that of the phrenosines, 

 except that in most instances it is somewhat greater. This differential solu- 

 bility, particularly that obtained in acetone containing 10% water, and in a 

 3:2 acetic acid-chloroform mixture, has been widely employed for the 

 separation of phrenosine from cerasine. The phrenosines will almost com- 

 pletely precipitate when the solution is maintained at a temperature of 

 37 °C., while the cerasines remain in solution. AVhen the temperature is 

 lowered, cerasine will precipitate. 



Cerasine forms liquid crystals, in the same way as does phrenosine; 

 these crystals melt with further heating at 180°C. (clearing point)*"® or 

 185-187°C.*^' Myelin formation occurs less readily with cerasine than 

 with phrenosine.*"^® 



In contradistinction to phrenosine, which is dextro-rotatory, cerasine 

 preparations have uniformly been found to be levo-rotatory. The values 

 reported in the several solvents are quite variable. Thus, in pyridine, the 

 following specific rotations have been reported: -9.03° (18°C.)*='9; -2.78°, 

 -2.50° (18°C.), -2.74° (20°C.), -3.71°, -3.78° (25°C.y'''; and -9.12° 

 (15°C.).^" The value found in a 1:1 pyridine-acetone mixture was 

 -4.58° (50°C.),3*2 ^^.^iie j^ chloroform with 10% pyridine the following 

 specific rotations have been noted: -10.99° (57°C.)**"; -9.18° (57°C.)*»3; 

 -8.76° (57°C.)=*"; and -5.08° (50°C.).3*- In chloroform solution rota- 

 tions of -11.59° (56°C.)*39 and -9.18° (57°C.),''='9 have been reported, 

 while the results in absolute alcohol at 59°C. are given as —3.89°**^ and 

 -4.52°.***' The iodme value, 31.3, is quite similar to that for phrenosine. 

 It is unchanged by heating for one hour with saturated barium hydroxide. 



Cerasine forms several derivatives which correspond to those of phreno- 

 sine. Cerasine dibromide has been investigated by Kossel and Freytag'*' 

 and also by Levene and Jacobs.*^® Cerasine forms a pentacetyl derivative 

 instead of the hexaacetyl derivative yielded by phrenosine. The solubility 



^38 S. Frankel and K. Linnert, Biochem. Z., 26, 41-43 (1910). 



"9 H. Lieb and I\I. Mladenovic, Z. physiol. Chetn., ISl, 208-220 (1929). 



"» 11. Lieb, Z. vhysiol. Cliem., I40, 305-3i:i (1924). 



