364 



CH. — C 



PHOTOSYNTHESIS 



CH=CH 

 I I 



c — c 



CH5 — c — c 



CH 

 \ 



/ 



N 



N 



C2H5 — C = C 



\ 

 C 



\ 



/ 



C — CH 



-C 



\ 



\ 



C = C — C2H1 



NH 



HN 



/ 



CH3 — C = 



/ 



c 



I 



CH. 



\ 



c = c 



I 



CH3 



CH, 



^tioporphyrin C31H36N4 



These formulae indicate that the compounds under discussion are com- 

 plex aggregates of substituted pyrrole. The efforts to determine whether 

 there exists a chemical relationship between the chlorophyll and blood pig- 

 ments have been directed largely toward establishing the structure of these 

 complex compounds containing several pyrrole rings. (See page 365.) 



The photo-oxidation of solutions of chlorophyll and consequent change 

 of color is, as far as we know, the only effect which light has on these 

 substances. The red rays seem to exert the most powerful effect.** 

 Light which has been filtered through a solution of chlorophyll has very 

 little effect on a second solution of chlorophyll. Wager ^^ and Warner *^ 

 have reported that chlorophyll is oxidized in the light with the forma- 

 tion of aldehyde. It is doubtful, however, whether this reaction can be 

 interpreted as constituting a step in the course of photosynthesis. In 

 fact, Willstatter and Stoll are of the opinion that no aldehyde is formed 

 in the photo-oxidation of chlorophyll, but rather that the aldehyde which 

 was found arose from the oxidation of impurities in the chlorophyll 

 preparations. 



Wurmser *^ studied the rate of decolorization of chlorophyll solutions 

 in light of ^ = 680 [i[i. He found that colloidal substances such as 

 gelatine, gum arable and casein, when added to the chlorophyll solutions, 

 greatly retard the rate of their decolorization ; starch did not produce a 

 retardation. Wurmser demonstrated that the decolorization of chloro- 

 phyll solutions is due to the presence of oxygen; solutions from which 

 the last traces of oxygen have been removed remained unchanged after 



^Dangerard, Compt. rend., 151, 1386 (1910). 



^"^ Wager, Proc. Rov. Soc, 87 B, 386 (1914). 



*« Warner, jfcirf., 378 (1914). 



"Wurmser, "Recherches sur rassimilation chlorophylienne," Paris, 1921, p. 52. 



