212 CHEMISTRY OF THE PROTEIDS CHAP. 



the fact that asparagin is a considerably stronger acid than is glycocoll, 

 Winkelblech concludes that asparagin has the constitutional formula : 



H H 



-C.CONH 2 C-CH 2 .CONH 2 



NH 3 rather than 00 



OC - 



How the constitution of a molecule affects its acid and its basic 

 character is not as yet fully understood. The author has for a con- 

 siderable time investigated the problems of intramolecular coagulation 

 in mono- and in di-amino acids, and hopes before long to be able to 

 communicate definite facts bearing on this matter. 



The last point to be considered is the relative strength of the acid 

 and the basic radicals in the amphoteric amino-acids. If the carboxyl- 

 group COOH is replaced by the much more strongly acid sulphonic 

 radical S0 3 , then the basic character of the NH 2 -group may be 

 diminished to such an extent as practically not to make itself felt at 

 all. This holds good, for example, in the case of sulphanilic acid, 

 C 6 H 4 (NH 3 )(S0 2 0). On the other hand, the basic character of the 

 NH 2 -group may be strengthened by the introduction of alkyl-radicals 

 (methyl, CH 3 ; ethyl, C 2 H 5 ) till it is 1 to 20 times stronger than ammonia 

 (Winkelblech). The acid character of the COOH radical may hereby 

 be overcome so completely as to prevent the latter from acting as 

 an acid radical, at least at the ordinary room -temperature. Thus 

 betain develops acid characters only at zero -temperature (Davidson). 1 

 Glycocoll, sarcosin, and betain are in descending order less and less 

 acid : 



CH 2 CH CH 



< 



Glycocoll. Sarcosin. Betain. 



The great inhibiting effect of the amino-group NH 2 on the carboxyl- 

 group COOH is well seen by comparing acetic acid with amino-acetk 

 acid or glycocoll. Thus fa normal acetic acid, dissociating only tc 

 the extent of 2 per cent, is 500,000 times more strongly acid than is 

 amino-acetic acid. 



As amino-acids are too feeble to allow of their dissociation- 

 constant being determined at the ordinary temperature, e.g. by eithei 

 measuring their electrical conductivity or their rate of sugar-inversior 



1 Davidson, Uber Diazonium und normale Diazotate, Dissertation, Wiirzburg, 1898. 



