CHAPTER II 



CHLOROPHYLL 



If green leaves are pounded in alcohol, the liquid soon turns 

 green, while the leaves become discoloured. This solution of 

 chlorophyll contains a mixture of a number of substances, 

 including all the secondary pigments. 



Various methods may be used to separate the pigments 

 from one another, but the simplest is that of chromatography. 

 There is a red pigment (carotene) and several yellow pigments 

 (xanthophylls) beside the green pigment, chlorophyll proper. 

 The last is divided into two pigments, a and b. They have very 

 similar properties but can be easily separated, not only by 

 chromatography, but particularly by petroleum ether, in 

 which chlorophyll-Z? is insoluble. 



A kilogramme of fresh leaves contains on an average 

 2 grammes of chlorophyll-a, 0-75 of chlorophyll-Z? and 0-5 of 

 carotenoids — xanthophylls and carotene. 



Chemical Properties 



The chemical formula for chlorophyll was gradually 

 defined through the work of Willstater and of H. Fischer. 

 It was not difficult to find the overall formula, CgsH^gN^OgMg, 

 but the nature and place of all the elements of this molecule 

 were determined by long and patient research and the structural 

 formula can now be written fairly certainly as opposite. 



We notice immediately the tetrapyrrol central nucleus 

 centred on an atom of magnesium and bearing on two 

 carboxyls and two alcohols — phytol (C20H39OH) and methyl 

 alcohol. 



As a result of the presence of magnesium, burnt chlorophyll 

 leaves a residue composed uniquely of magnesia and repre- 



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