INTERACTION OF ORGANIC MOLECULES WITH PROTEINS 



103 



The first tendency, I think, would be to say that the interaction of the pro- 

 tein must involve the azo group in some way. By having the sulfonic acid in the 

 ortho position we are blocking access to this azo group. Perhaps I should also men- 

 tion that the same thing happens with the carboxyl group and the same thing 

 happens with the phosphonic acid group. We have not tried the arsonic acids 

 simply because we did not have the ortho one to use. Using the sulfonate or 

 carboxylate as an example, if we put the anionic substituent in the ortho position, 

 we get an effect very different from the para position and it may indicate, then, 

 that access to the azo group is blocked. If that were true, then we can reason 

 from models shown in the next illustrations (Fig. 12). B represents the meta 



Top: 



Fig. 12. Molecular model of 



(CH3)oN— 



^_N=N-^ 



-O— C 



\ 



o 



Bottom: 



(CH3)2N- 



^ 



-N=N— 



C=0 



-o 



