i8 



PHOTOSYNTHESIS 



carotene removed from this by repeated washing with petrol 

 ether. A mixture of two chlorophylls, chlorophyll a and 

 chlorophyll h, now remains, and these can be separated since 

 chlorophyll a is the more soluble in petrol ether whilst h is 

 the more soluble in methyl alcohol. Many fractionations are 

 necessary to remove chlorophyll a from chlorophyll h. The 

 second method of separation was devised by Tswett. If the 



H2C=CH CH3 



H3C-C I 



/ 



\ 



N- 



HCd Mg 



C = N N 



r 



c 



BCH 



/ 

 \ 



■C2H5 



'^?4^ c c' " >=-^"' 



H^ \/^ %«/ \«X 



H 



CH2 



HC 



10 



V 



FIG. 3.1 



H39C20OOC-CH2 COOCH3 



J... Structural formula of chlorophyll a. Note the methyl 

 group attached to carbon atom 3 which becomes a formyl 

 group in chlorophyll b; the phytol group attached to the chain 

 at carbon atom 7; the cyclopentanone ring V. 



petrol ether extract is dehydrated and then filtered through 

 a column of powdered sucrose or calcium carbonate the 

 various pigments are adsorbed in different bands along the 

 column. The major bands are easily identified by their 

 colours, the blue-green of chlorophyll a, the neutral green of 

 chlorophyll b, the various yellow xanthophyll bands, and the 

 yellow carotene which is not adsorbed on the column but 

 comes through in solution. The best method of isolation 



