OPTICAL PROPERTIES OF NUCLEIC ACIDS 



507 



210 



230 250 270 



Wavelength, rriM 

 Fig. 10. Uracil (Shugar and Fox'*). 



290 



data on p^'rimidine nucleosides have been published by Hotchkiss,-" Loring 

 et al.,''^ and Lampen and co-workers." 



The ionization in the pH 12-13 region observed in the free pyrimidine 

 bases is probably attributable to the acidic dissociation of the 2-hydroxyl 

 group, and in the purines to the acidic dissociation of the iminazole NH 

 group. In the nucleosides both of these are blocked, and the spectroscopic 

 changes in the same pH region can in this case be attributed to a sugar 

 hydroxyl dissociation. (See Jordan^ and Shugar and Fox^^'^^.) 



The first demonstration that the sugar group in the naturally occurriiig nucleosides 

 was attached to the purine nucleus in the 9-position rather than in the 7- was carried 



« H. S. Loring. H. W. Bortner, L. W. Levy, and M. L. Hammell, J. Biol. Chem. 196, 



807 (1952). 

 " T. P. Wang, H. Z. Sable, and J. O. Lampen, J. Biol. Chem. 184, 17 (1950). 



