16 CAROTINOIDS AND RELATED PIGMENTS 



Lipochromes 



Krukenberg (1882k, 1886), a number of years after Thudichum, 

 proposed the name lipochrome to cover all the animal and plant pig- 

 ments which had previously been known as luteins, carotins, zoonery- 

 thrin, tetronen r thrin, chlorophan, xanthophan and rhodophan. The 

 name lipochrome has been widely adopted and due to the very broad 

 basis upon which the name was founded it has been applied to numer- 

 ous plant and animal pigments not mentioned by Krukenberg, or 

 unknown to him. Krukenberg believed that all the pigments which 

 he proposed to designate as lipochromes were associated with fat in 

 their natural state, and the name suggests this supposition as well as 

 their capability of existing in association with fats and oils. 



It was obviously the intention of the originator of the name lipo- 

 chrome to limit it to pigments of yellow or reddish tints, but the name 

 itself is applicable to pigments of many other colors, such as chloro- 

 phyll and many vegetable dyes of various colors, which have a marked 

 affinity for fat. Numerous workers object to the use of the name lipo- 

 chrome on this account. Kohl (1902a), for example, in his extensive 

 monograph on carotin, objects to designating this pigment as a lipo- 

 chrome because of the numerous cases in which it is known to occur 

 free from fat, and also because he believes that where carotin is 

 actually found associated with fat it is in combination with the fat 

 and not merely in solution. 



The particular properties by which Krukenberg (1886) proposed to 

 judge whether a pigment should be classified as a lipochrome are, in 

 general, as follows: They are soluble in alcohols (methyl, ethyl and 

 amyl), ether, chloroform, benzene, carbon disulfide, petroleum ether 

 and acetone; in the solid state they are colored blue-green to blue by 

 concentrated sulphuric and nitric acids and generally blue-green with 

 iodine in potassium iodide ; they show two and sometimes three absorp- 

 tion bands in the blue and violet region of the spectrum; they are not 

 destroyed on boiling with alcoholic caustic alkalies; in the solid state 

 they are greenish-yellow, yellow, orange or red, and their solutions are 

 yellow; they are very sensitive to light and readily bleach, the 

 bleached pigments being similar to cholesterol. 



Subsequent investigations of the lipochromes, using the class char- 

 acteristics defined by Krukenberg, have added very little to our knowl- 

 edge of the properties of these pigments considered as a group, but 

 have served merely to define more closely certain of the criteria enu- 



