32 Carbon Assimilation. 



little 20% hydrochloric acid and then washed with water in a separat- 

 ing funnel.. In this way is produced in ether solution, a magnesium 

 free chlorophyll derivative, phasophytin. The solution is evaporated 

 down on a water hath and the residue dissolved in 5 c.c. alcohol. 

 Note the olive green colour of the solution. This is heated and a 

 grain of copper acetate is added. The colour changes back to a 

 brilliant green, but without the chlorophyll fluorescence. A copper 

 compound of chlorophyll has been produced very similar to the 

 magnesium compound, but much more stable. 



For spectroscopic examination of this substance, see Experi- 

 ment 15. 



Phseophytin combines very easily with acetates of some metals to 

 form intensely coloured stable compounds. Ferric acetate gives, even 

 in the cold, a greenish blue solution with a weak fluorescence. 

 Zinc acetate gives a blue green solution with strong fluorescence. 



Not only phseophytin but all the chlorophyll derivatives devoid 

 of magnesium, such as ph^ophorbide, phytochlorin, phytorhodin 

 and the various porphyrins behave similarly towards the salts of 

 certain metals (copper, zinc and iron) and form complex compounds 

 all very stable in acid and alkaline media. The formation of these 

 complex compounds is accompanied by such noticeable changes in 

 colour that even the smallest traces of certain metals can be 

 discovered in this way. Hence it is very difficult to prepare the 

 magnesium free chlorophyll derivatives absolutely pure, as even the 

 zinc from the walls of glass vessels may disturb the molecule ; for 

 the same reason spatulas of ignoble metals must not be used. 



Also solvents may disturb the molecules of these derivatives 

 owing to the impurities in them. Thus ' pure ' methyl alcohol often 

 contains a small quantity of copper which would be sufficient to 

 affect the magnesium free derivatives. Willstatter uses this 

 property in order to test the purity of methyl alcohol as regards 

 copper, by dissolving some phytochlorin e in the methyl alcohol. 

 After standing for some time, the chlorophyll derivative is carried 

 over into ether and the excess of phytochlorin removed by washing 

 with 10% hydrochloric acid. As the copper compound of phyto- 

 chlorin e is stable in presence of this strength of acid, it remains in 

 the ether layer to which it gives an intense blue-green colouration. 

 The spectrum of these derivatives is also quite distinct from 

 the metal free substances and more like the chlorophyll spectrum. 

 See Experiment 15, b and c. 



