584 VI. CAROTENOIDS AND RELATED fOMPOT^NDS 



hydroxyl group. As yet no one has succeeded in preparing an acetyl deriva- 

 tive. Rhodopin forms dark red ciystals from a carbon disulfide-petroleum 

 ether mixture. These appear as small clusters of prisms and needles. 

 They melt at 171°C. 



b. Rhodovibrin. Rhodovibrin can be separated from rhodopin chro- 

 matograi)liicHlly, since it is adsorbed more readily on calcium hydroxide 

 than is rhodopin. Its structure is unknown, but presumably pure crystals 

 have been shown to melt at 168°C. 



c. Rhodopurpurin. Rhodopurpurin is a fourth distinct pigment pres- 

 ent in the extracts from Rhodovihrio. It is probably a hydrocarbon with an 

 empirical formula of C40H56 or C40H58. 



(18) Aphanin and Aphandcene 



Several carotenoid pigments are present in blue algae. Although a num- 

 ber of investigations have recently been made in this field, the results are 

 still somewhat confusing. In 1927, Kylin^*^ was able to demonstrate three 

 new pigments in the blue alga (Calothrix scopulorum) , in addition to caro- 

 tene, but these were not further characterized. Sometime later, 

 Tischer^^^'^*^ separated four new pigments from another fresh-water blue- 

 green alga (Aphanizomenon flos-aquae) , as well as /3-carotene. These new 

 substances were called aphanin, aphanacene, flavacene, and aphanizophyll. 

 The pigments have not been demonstrated elsewhere. 



Aphanin is a monoketone having an empirical formula of C40H54O. 

 Tischer^*^ proved that it has 12 double bonds and forms an oxime. Since it 

 is active as a provitamin A, ^** it is necessary that there be one intact unsub- 

 stituted /3-ionone ring. The probable formula'^ is given here. Although 



H3C C Hj H jC CHj 



/\ hhIhhhIhhhhIhhhIhh /\ 

 hzc c-c:c-c:c-c:c'c:c'c:c'c:c'c:c-c:c'c:c'c ghz 



I II II I 



HsC c c c=o 



\ / \ • / \ / 



C CH3 H3C c 



Hz Hz 



Aphanin 



the principal pigment of the blue alga is /3-carotene, 50 mg. of aphanin and 

 20 mg. of aphanacene were obtained per kilogram of dried alga. 



Aphanacene is one of the pigments which Tischer^^^ isolated from 

 Aphanizomenon flos-aquae. It was considered to be a dicarotenoid made up 

 of tw^o molecules of aphanin joined by an oxygen bridge and having a com- 

 position of CsoHioeOs. Aphanacene forms an oxime which demonstrates 

 the presence of at least one carbonyl group. The provitamin A activity is 



3" J. Tischer, Z. physiol. Chem., 260, 257-271 (1939). 



388 A. Scheunert and K. H. Wagner, Z. physiol. Chem., 260, 272-275 (1939). 



