PHOTOSYNTHETIC PIGMENTS IQ 



combines the two procedures: a partial purification by par- 

 tition with solvents followed by adsorption on a suitable 

 column (Rothemund, 1944). When obtained in pure form 

 both chlorophylls are nearly black, wax-like solids which do 

 not show any tendency to crystallize in bulk. 



The chlorophylls (Fig. 3.1) are methyl phytol esters of 

 the parent dicarboxylic acids, the chlorophyllins. Phytol 

 (C20H39OH) is a long chain alcohol, containing one double 

 bond, which is related to the carotenoids and can be re- 

 garded as derivable from vitamin A by hydrogenation. 



CH3 CH2 CH2 CH2 CHo CH2 CH2 CH 



CH CH2 CH CH2 CH CH2 C CH2OH 



I III 



CH3 CH3 CH3 CHj 



Phytol (C20H39OH) 



The enzyme chlorophyllase hydrolyses the phytol group 

 from chlorophyll. In acetone the resulting green product is 

 chlorophyllin, whilst in ethanol or methanol the phytyl is 

 replaced by ethyl or methyl to give ethyl or methyl chloro- 

 phyllide. These esters crystallize easily and were the first 

 chlorophyll derivatives to be obtained in crystalline form. 

 With excess phytol chlorophyll is synthesized from chloro- 

 phyllin in the presence of the enzyme, i.e. the reaction is 

 reversible. Chlorophyllase has not been obtained in a soluble 

 form; it is present in the insoluble residue of the chloroplast 

 fraction after acetone treatment; it has also been found in 

 roots. Some plants show little chlorophyllase activity, e.g. 

 Urtica and the grasses; others show good activity, e.g. 

 Datura, Heracleum, and Galeopsis. It follows that in the 

 preparation of chlorophyll it is desirable to use plants which 

 contain little chlorophyllase. 



The chlorophylls are remarkable in being a group of 

 natural substances in which magnesium is^ present in a non- 

 ionic form. Treatment with dilute acid results in the solu- 

 tion in alcohol becoming brown and a dark precipitate of 

 the corresponding magnesium-free compound, the phaeo- 

 phytin, is obtained. In organic solvents containing water 

 under neutral conditions chlorophyll cannot be reformed 



