THE AMPHOTERIC PROPERTIES OF SOME AMINO-ACIDS 



AND PEPTIDES. 



By HERBERT ECKWEILER, HELEN MILLER NOYES, and K. GEORGE FALK. 

 {From the Harriman Research Laboratory, the Roosevelt Hospital, New York.) 



(Received for publication, October 27, 1920.) 

 INTRODUCTION. 



The change in the hydrogen ion concentration of a solution upon 

 the addition of acid or alkali has been used to follow the changes 

 characteristic of certain dissolved substances. Thus, the progressive 

 neutralization of polybasic acids and of polyacid bases has been studied 

 in this way.^ Amphoteric electrolytes lend themselves readily to this 

 method of investigation. Recently, the results obtained with a num- 

 ber of proteins have been presented in the form of titration curves in 

 which amounts of standard acid and alkali were plotted along one 

 axis and the resulting pH values of the protein solution along the other 

 axis.^ Such titration curves may be expected to be more or less 

 characteristic for the acid- and base-combining properties or groups of 

 such substances. In view of the importance and value of such studies 

 in protein chemistry, the titration curves of some of the simple amino- 

 acids and dipeptides are presented here as a necessary preliminary to 

 a more satisfactory understanding of the more complex bodies. 



Experimental Methods. 



The following substances were studied; glycine, alanine, a-amino- 

 butyric acid, leucine, glycyl-glycine, alanyl-glycine, and alanyl-alanine. 

 Data were obtained also for solutions of sodium chloride, acetone, 



^ Hildebrand, J. H., /. Am. Chem. Soc, 1913, xxxv, 847. 



2 CJ. Cohn, E. J., Gross, J., and Johnson, O. C, /. Gen. Physiol, 1919-20, ii, 

 145. Cohn, E. J., Wolbach, S. B., Henderson, L. J., and Cathcart, P. H., /. Gen. 

 Physiol, 1918-19, i, 221. Sorensen, S. P. L., Compt. rend. lab. Carlsberg, 1915-17, 

 xii. Clark, W. M,, The determination of hydrogen ions, Baltimore, 1920, espe- 

 cially pp. 34 and 211, for general discussion and references. 



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