68 



of powdered augaro They form yellow or gray colored zones that precede 



2 



the green zones of the chlorophylls . 



Like the chlorophylls, the methyl chlorophyllides and the pheophy- 

 tins yield additional pigments vihen the solutions are heated-^ ■'■» *o In 

 columns of powdered sugar, these heat-formed substances are less sorbed 

 that the parent pigments o They are reconverted to the parent compounds 

 by heating their solutions^. By analogy with the chlorophylls, they 

 are isomers of the parent pigments. 



Some of the xanthophylls, such as violaxanthin, are extremely 

 sensitive to acid„ An acid as weak as acetic acid in organic solvents 

 soon converts these xanthophylls into several pigments that exhibit 

 spectral absorption maxima at wave lengths shorter than those of the 

 maxima of the parent pigments^ »^o 



Isomerization of the Chlorophylls by Heating Leaves 



TOien leaves are scalded or blanched with boiling water for only 

 5 to 10 minutes, relatively large amounts of the chlorophyll isomers 

 a'' and b' are formed *^o Separation of the extracted pigments in a 

 column of powdered sugar yielded a series of zones like that shown in 

 Figure III, 12, 



IsomerizatijOn of Chlorophylls a and b in Solution at Room Temperature 



When petroleum ether solutions of the chloroplast pigments are 

 permitted to stand at room temperature for only an hour or two, de- 

 tectable quantities of chlorophylls a' and b' are formedo These iso- 

 mers separate readily in the sugar columns as already indicated in 

 Figure III,12o Solutions that have stood for longer periods contain 

 much more of the a' and b' isomers, which increase to 10 to 20 per cent 

 of the a and bo 



