Spirazines 29 



Of the various geometric forms which chemical 

 structures might exhibit, the helical spiral ap- 

 pears to be about the only one which possesses 

 characteristics similar to those mentioned above, 

 and it appears that the helical spiral is also the 

 only configuration, besides rings and chains, 

 which the polypeptide molecule can be made to 

 assume. The ease with which diketopiperazine 

 rings are formed from dipeptides, and the diffi- 

 culty of splitting such rings, seems to indicate 

 that the valencies of the successive carbon and 

 nitrogen atoms in dipeptides are at such angles 

 to one another as to give them a natural tendency 

 to form six-atom rings ; and if dipeptides tend to 

 form six-atom rings, then polypeptides would 

 tend to form spirals with six-atom convolutions, 

 which will be referred to, briefly, as "spirazines." 



It will be observed that one of the valencies of 

 the alpha carbon atom in these amino acids is 

 always occupied by hydrogen. Chemically it 

 would be possible to attach more complex groups 

 in this position, but it will be found upon experi- 

 mentation with atomic models that the presence 

 of more complex groups in^this position would 

 render the spirazine structure impossible, and it 

 will be observed that complex groups never occur 

 in this position in the decomposition products of 

 natural proteins. 



