Experimental Studies of Plant Pigments. 9 



to a leuco-base, which in turn, by exposure to air or, more rapidly, 

 by addition of an oxidizing agent, is reconverted into anthocyanin, 

 thus possibly explaining the facts observed by the Armstrongs: 



+ H + H 



Flavone -> Anthocyanin -> Leuco-base 



+ 0 

 <— 



We have also succeeded in oxidizing anthocyanin to flavone. 

 This was done most effectively by first isolating anthocyanin in 

 a fairly pure condition, by Willstatter's method. The only oxi- 

 dizing agent we have been able to use with success thus far is 

 hydrogen peroxide. Oxidase from potato, as well as oxidase from 

 Crimson King tulip, could not be used as a substitute for hydro- 

 gen peroxide. 



Flavone thus obtained from anthocyanin can be reduced back 

 again to anthocyanin: 



+ 0 



Anthocyanin — > Flavone 

 + H 

 <- 



The chemical relationship between flavones and anthocyanins 

 may be expressed thus (Willstatter) : 



Cl 



ty^ +H * i II 1 1 r p 



\/\ c Ah YV(° h N/VAm 



OH II OH H OH OH I 



O H 



Quercetin Cyanidin 

 (a flavone) (an anthocyanin) 



Anthocyanin as an indicator. — Anthocyanin (tulip, Crimson 

 King), when extracted with absolute alcohol made anhydrous 

 with copper sulfate, yields a red extract, whereas if extraction is 

 made with absolute alcohol rendered anhydrous with calcium oxid, 

 a green solution is obtained. The red extract can be changed to 

 green by the addition of calcium oxide, or soluble alkali, whereas, 

 vice-versa, the green extract can be changed to red by the addi- 

 tion of anhydrous copper sulfate or soluble acid. 



