THE CHLOROPLAST PIGMENTS 



47i 



magnesium content and were also very 

 similar in the composition of their basic 

 nuclei. 



Willstatter and Stoll are of the opinion 

 that further investigation is necessary to 

 fix and strengthen our conception of the 

 chlorophyll molecule. It is well to note 

 here that by the most drastic treatment 

 with acids and alkalies nitrogen always 

 remains in the decomposition products. 

 It is interesting too to note that there are 

 ■four nitrogens and that each is bound in 

 the form of pyrrole. Etioporphyrin, the 

 parent substance of blood and chlorophyll, 

 is composed of four pyrrole nuclei. 

 Reduction of the porphyrins yields hemo- 

 pyrrole, which is also known as the reduc- 

 tion product of blood dyes tuff. 



Nencki and Marchlewski were the first 

 to obtain it from a chlorophyll derivative. 

 Willstatter and Asahina have shown that 

 hemopyrrole has a surprisingly compli- 

 cated composition, being a mixture of at 

 least three components. Phyllopyrrole, 

 a tetra-substituted pyrrole, has been iso- 

 lated from the mixture. Phyllopyrrole, 

 isohemopyrrole and cryptopyrrole are now 

 known as components of chlorophyll 

 because of the work of Fischer and Bartho- 

 lomaeus and Piloty and Knorr. Other 

 pyrrole constituents also are present. 

 Phyllopyrrole is distinguished from the 

 pyrrole bases with eight carbon atoms 

 principally by the absence of the pine 

 splinter reaction and of the color reaction 

 with dimethylamino-benzaldehyde. Also, 

 it is not precipitated in an acid solution by 

 a diazonium salt. It was considered a 

 pyrrole, for it took up four atoms of 

 hydrogen and produced a saturated hydro- 

 derivative. The pine shaving reaction is, 

 analogously to the dimethylamino-benzal- 

 dehyde reaction, to be understood as a 

 condensation of the aldehydes of the wood 

 with the pyrrole nucleus. Feist has 

 shown that pyrroles substituted at all four 



carbon atoms cannot condense with alde- 

 hydes, and Fischer had noticed that 

 pyrroles similarly substituted do not give 

 the Ehrlich reaction. Also phyllopyrrole 

 is not precipitated by an aqueous mercuric 

 chloride solution, which is contrary to 

 statements in the literature. 



When chlorophyll, as well as when 

 hemin, is reduced a mixture of different 

 pyrroles is always formed. A review of 

 the literature will easily convince one that 

 our knowledge regarding pyrroles is very 

 elementary and that there is much need for 

 further work on these decomposition 

 products of chlorophyll and of the blood 

 pigment. 



Those who have never worked with 

 chlorophyll do not realize some of the 

 difficulties involved in its preparation. 

 Chlorophyll as a pure chemical substance 

 was not isolated in an undamaged condi- 

 tion and free from accompanying materials 

 until all of its physical and chemical 

 properties were known. Colorless accom- 

 panying materials, fats, waxes and salts of 

 fatty acids accompany the pigment and 

 distribute themselves among the different 

 solvents in much the same ratio as chloro- 

 phyll does. Because the pigment was so 

 easily soluble in all solvents its purifica- 

 tion was very difficult. Chlorophyll of a 

 certain degree of purity is no longer soluble 

 in petroleum ether which is free of alcohol. 

 After this fact was known the preparation 

 of chlorophyll was soon accomplished. 

 At first the yields were very small but now 

 8 to 10 grams of pure chlorophyll may be 

 obtained from each kilogram of dry nettle 

 leaves. At the present time, pure chloro- 

 phyll, crude chlorophyll, pheophytin and 

 the copper salts of chlorophyll may be 

 easily prepared and some are now being 

 prepared by the ton. Let us now turn our 

 attention to some of the factors affecting 

 chlorophyll. The effect of light will be 

 considered first. 



