- 70 



As a rule, large scale preparations of chlorophylls a^ and b con- 

 tain the a' and b' isomers. The presence of these isomers may be at- 

 tributed to the relatively long time required for the isolation of the 

 pigments and also to the fact that the preparation procedures usually 

 employed do not separate the natural chlorophylls from their isomers-^' >'. 



Isomerization of Chlorophylls a and b by Heat and Alkalies 



■fflhen n-propanol or dioxane solutions of chlorophylls a^ and _b are 

 heated to 100" for an hour, the pigments are converted to an equilib- 

 rium mixture with their respective isomerso If the isomers a^' and b^* 

 ere separated by adsorption, recovered and heated again in solution, 

 they are reconverted into the same equilibrium mixture obtained by 

 heating a and b as illustrated by Figure III,13o And if the reformed 

 a and b are separated, recovered and reheated, they again yield &^ and 

 V, 



The isomerization of chlorophylls a and b in n-propanol yielding 

 about 20 per cent of a» and b' occurs almost instantly at room tempera- 

 ture when traces of potassiimi hydroxide are added to the solution »^o 

 The a' and b' formed by alkalies and isolated by adsorption are recon- 

 verted to the mixture of isomers by retreatment with alkalies o 



Isomerization of Chlorophyll d 



TOien solutions of chlorophyll d are permitted to stand for a few 

 hours at room temperature, small amounts of a less sorbed isomer, 

 chlorophyll d' , are formedo Upon longer standing or upon heating the 

 solution, two additional, less sorbed isomers, isochlorophyll d and 

 isochlorophyll d' appear. All these isomers are separable in columns 

 of powdered sugar with petrolexmi ether plus Oo5 P®r cent n-propanol 



