CHAPTER XIV 

 Carotenoids of partly or completely unknown structure 



I. RHODOVIOLASCIN C42HgQ02 



History 



1873 Lankester^ is the first to investigate the pigments of purple bacteria, 



subsequent^ studied by other workers^. 

 1905 Archichovskji^ succeeds in separating a green pigment not identical 



with chlorophyll from the red pigments of purple bacteria. 

 1907 MoLiscH* carries out a detailed investigation of the red pigments. 

 1935-40 Karrer and co-workers^ investigate the pigment mixture from 



rhodovibrio-bacteria and thiocystis-bacteria. They isolate a number of 



different polyene pigments and partly elucidate the constitution of 



rhodoviolascin. 



Occurrence 



Rhodoviolascin has hitherto been found only in rhodovibrio-bacteria^ and 

 in thiocystis-bacteria^. (According to Zechmeister and co-workers', spirillo- 

 xanthin from rhodospirillum rubrum^ is identical with rhodoviolascin) . 



Preparation^- ^° 



For the method of growing rhodovibrio-bacteria, compare the communication 

 by Karrer and Solmssen*. The bacteria are dehydrated with ethanol and ex- 

 haustively extracted with carbon disulphide. After removal of the solvent by 

 distillation, an almost black residue remains which still contains much elementary 

 sulphur. (The latter is formed by reduction processes during the growth of the 

 bacteria in the magnesium sulphate-containing nutrient solution). The black 

 residue is dissolved in a ligroin-methanol mixture, the solution is decanted from 

 sulphur and diluted with a little water. Rhodoviolascin is precipitated as a dark- 

 red crystalline powder at the boundary between the ligroin and methanol. It is 

 filtered off and sealed in evacuated ampoules. The ligroin solution, which contains 

 the other carotenoids and also some more rhodoviolascin, is extracted several times 

 with methanol to remove the bacterio-chlorophyll, washed with water, dried over 

 sodium sulphate and concentrated by distillation. The residue is dissolved in a little 

 References p. 341-343. 



