376 



PHOTOSYNTHESIS 



phytin and magnesium carbonate or bicarbonate (the usual reaction of 

 acids on chlorophyll). 



From these facts Willstatter and Stoll conclude that chlorophyll, which 

 in their opinion is also in a colloidal state in the leaf, may, as the first 

 step in photosynthesis, unite with carbon dioxide, and thus also play a 

 chemical role. It is possible, however, that carbon dioxide first reacts 

 with some other substance in the leaf which acts as an absorbent, thus 

 producing a high concentration of carbon dioxide in the chloroplast which 

 then enables the chlorophyll to take up the carbon dioxide. The next 

 step in the photosynthetic reaction, as suggested by Willstatter and 

 Stoll is the rearrangement of the chlorophyll-carbonic acid, through the 

 action of light, into chlorophyll- formaldehyde peroxide and the splitting 

 off of an oxygen atom from the latter. This latter step has already been 

 described in the chapter on the Chemistry of Photosynthesis. 



Maquenne '■* has made some further theoretical deductions on the basis 

 of Willstatter and Stoll's theory. He also assumes that in the leaf the 

 chlorophyll is in a colloidal state, and that in this state the chlorophyll 

 molecules are held together in aggregates by "supplementary valencies." 

 These valencies are so feeble that they are easily broken and as a con- 

 sequence the chlorophyll passes into the molecularly dispersed state. These 

 valencies are secondary valencies of magnesium or of nitrogen; for illus- 

 tration Maquenne assumes that in the colloidal state three chlorophyll 

 molecules are linked through the secondary valencies of the magnesium. 

 The same reactions occur with this trichlorophyll which Willstatter and 

 Stoll assume to take place between chlorophyll and carbonic acid. The 

 difiference is that instead of a single chlorophyll molecule and one carbonic 

 acid molecule being involved, three (or more) of each are involved. We 

 thus have the following steps showing the reactions between three chloro- 

 phyll molecules and three molecules of carbonic acid ; only the magnesium 

 and two of the nitrogen atoms of the chlorophyll are given in the formulae : 



>N 



>N 

 >N 



>N 

 >N 



\ 



] 



/ 



I 



I 

 \ 



O 



Mg HO — C — OH 



O 

 Mg -f HO — C — OH 



>NH 



>N 

 >NH 



\ 



O 



II 

 Mg HO — C — OH 



>N 

 >NH 



O 



II 

 Mg — O — C — OH 



O 



Mg — O — C — OH 



/ 



Mg — O 



O 



II 



c 



OH 



>N >N 



"Maquenne, Bull. soc. chim. (4), 35-36, 649 (1924). 



