THE CATIOTENOIDS — ^INTRODUCTION 511 



The classification was based upon the similarity of such properties as 

 solubility, the presence of three absorption bands in the blue, indigo, and 

 violet region of the spectrum, the ability of these pigments to be crystal- 

 lized in rhombic plates, and especially upon their ready combination with 

 protein, from which they could be extracted only with difficulty. It is now- 

 recognized that the luteins, as defined by Thudichum, represent a number 

 of different types of pigment. Since 1912, the name "lutein" has been 

 specifically applied to one of the pigments which can be prepared in crystal- 

 line form from egg-yolk. ^^ 



The term lipochrome was proposed l)y Krukenberg^^-*® to cover a number 

 of animal and plant pigments whi(;h had been known by such diverse names 

 as luteins, carotin, zoonerythrin, tetronerythrin, chlorophane, xanthophane. 

 and rhodophane. Although this designation was originally limited to pig- 

 ments with yellow or reddish tints, by implication it obviously should in- 

 clude any fat-soluble pigment such as chlorophjdl. However, the yellow 

 pigments were frequently found to be free from appreciable amounts of 

 fat, while the name would suggest their association with fat in the natural 

 state. Krukenberg^^ used a number of properties as a basis for inclusion 

 into the lipochrome group ; these included solubility in a number of organic 

 solvents, the development of a blue-green to blue color when the solid was 

 treated with concentrated sulfuric or nitric acid, the presence of two or 

 three absorption bands in the violet end of the spectrum, and a stability 

 toward boiling alcoholic potash. INIoreover, in the solid state, the lipo- 

 chromes are greenish yellow, yellow, or orange to red, while their solutions 

 are yellow ; they are defined as being sensitive to light, and can be bleached 

 to colorless compounds which appear to be similar to cholesterol. Kruken- 

 berg believed that all lipochromes contain oxygen as well as carbon and 

 hydrogen, although he recognized that nitrogen was absent. He therefore 

 failed to note the essential differences between the hydrocarbons with the 

 empirical formula C40H58 and the group of carotenols and other oxyhydro- 

 carbons which contain one or more oxygens. 



Lipoxanthin is another designation which has been used to include all 

 the animal and plant pigments. Schrotter-Kristelli^'' proposed that this 

 term be used to include pigments previously referred to by the following 

 names: eriolin, chlorophyll yellow, xanthin, anthoxanthin, phylloxanthin, 

 phycoxanthin, lipoxanthin, lutein, xanthophyll, carotin, chrj'sophyll, 



" R. Willstatter and H. H. Esoher, Z. physwi. Chem., 76, 214-225 (1912). 



'* C F. W. Ivrukenberg, Zur Kenntnis der Verhreitung der Lipochrome im Thierreiche. 

 Vergleichend-phyaiologische Studien, [2], Part 3, 92-107 (1886). Cited by L. S. Palmer, 

 Carotinoids and Related Pigments, Chemical Catalog Co., New York, 1922, pp. 16, 17. 



'* C. F. W. Krukenberg, Grundziige einer vergleichenden Physiologic der Farbstoffe 

 und der Farhen. Vergleichend-physiologische Vortrdge, Part 3, 85-104 (1886). Cited by 

 L. S. Palmer, pp. 16, 17, ff. 



^ H. R. Schrotter-Kristelli, Botan. Centr., 61, 33-46 (1895). 



