512 VI. CAROTENOIDS AND RELATED COMPOUNDS 



erythrophyll, .solanoriibin, vitellorubin, hematochrome, chlororufin, bac- 

 teriopurpurin, hemohitein, and tetronerythrin. It was realized that these 

 pigments formed a homologous group of substances even if they were not 

 completely identical, and Schrotter-Kristelli believed that the term "lipo- 

 xanthin" \\as a satisfactory designation. The chief characteristics were 

 defined as an affinity for fats, insolubility in water, a blue color reaction 

 with sulfuric acid, absorption at the violet end of the spectrum, lack of 

 fluorescence in solution, and finally their ready destruction by light and 

 oxygen. Palmer'- states that the lipoxanthins thus comprise a more or 

 less indefinite group of pigments which can be classified together under the 

 heading of "lipochromes." 



Czapek^^ has suggested the name chromolipoids as a more satisfactory 

 designation for such pigments. This terminology is based upon the idea 

 that lipochromes, at least in plants, should be classed as lipoids because of 

 their fat-like behavior as regards solubility and their common distribution 

 in the cell. Another property which is similar in the lipochromes and the 

 phosphatides (as well as in unsaturated neutral fats) is the readiness with 

 which they absorb oxygen. The word chromolipoids would automatically 

 place these pigments as a sub-group of the lipids. 



However, a more specific term was desirable to designate the fat-soluble 

 yellow pigments than the general designation of chromolipoids. The term 

 carotinoids was ultimately suggested^'' as the one to cover the yellow pig- 

 ments which comprised a group of substances related genetically to caro- 

 tene and to similar compounds. The term carotin was first assigned to the 

 pigment now known as j3-carotene, which Wachenroder^ separated from 

 the carrot (Daucus carota) in 1826. The term carotinen was used to cover 

 the related pigments which were referred to as the carotin group. The 

 present spelling, i.e., carotene, was first proposed by Arnaud*" in 1886, after 

 it was demonstrated that the substance was a hydrocarbon. However, the 

 earlier spelling, namely, carotin, was retained l)y many workers until quite 

 recently""; the proposal of Arnaud has now been almost universally 

 adopted. Zopf^-^^ suggested that the carotene group be divided into true 

 carotenes (eucarotines) and carotinines, which contain oxygen as well as 

 carbon and hydrogen. The latter substances were believed to be acids, 

 and did not include the real oxygen-containing members of the carotenoids, 

 such as the alcohols and ketones. 



'8 F. Czapek, Biochemie der Pflanzen, 2nd ed., Vol. /, Jena, 1913, p. 803. 



38 M. Tswett, Ber. dent, botan. Ges., 29, 630-636 (1911). 



« A. Arnaud, Compt. rend., 102, 1119-1122 (1886). 



^1 The earlier spelling was used as recently as 1922 in the monograph of L. S. Palmer, 

 Carotinoids and Related Pigments, Chemical Catalog Co., New York, 1922. 



^2 W. Zopf, Beitr. Physiol. Morphol. niederer Organismen, 3, 26-47 (1893). Cited 

 by L. S. Palmer, p. 19. 



" W. Zopf, Biol. Zentr., 15, 417-427 (1895). 



