496 



G. H. BEAVEN, E. R. HOLIDAY, AND E. A. JOHNSON 



^ 6 



220 



240 



300 



320 



260 280 



Wavelength, idm 



Fig. 1. Isomeric cytidylic acids (Cohn, unpublished) 



5'- and deoxy- 



3'- 



Pqx1*i6 is a good illustration of the application of such methods, and is 

 noteworthy for the excellent style of publication of the spectral data. 



The absorption characteristics of a given compound in aqueous solution 

 can therefore be given as a series of spectra of the individual ionic species, 

 together with a list of the corresponding pi^ values preferably as deter- 

 mined spectroscopically. 



The pK value for a given ionization can be determined from the follow- 

 ing expression (see Hammett and co-workers'^ and Edwards'^) : 



pKa = pH — log 



1^ D. Shugar and J. J. Fox, Biochim. et Biophys. Acta 9, 199 (1952). 



i« J. J. Fox and D. Shugar, Biochim. et Biophys. Acta 9, 369 (1952). 



" L. A. Flexser, L. P. Hammett, and A. Dingwall, J. Am. Chem. Soc. 57, 2103 (1935). 



" L. J. Edwards, Trans. Faraday Soc. 46, 723 (1950). 



