OPTICAL PROPERTIES OF NUCLEIC ACIDS 



505 



210 



230 



290 



250 270 



Wavelength, rriM 

 Fig. 8. 5-MethyIcytosine (Shugar and Fox'"). 



310 



hypoxaiithine, thymine, and cytosine at neutral pH, and GuUand and 

 Story^^ compared guanosine and guanine deoxyriboside. For purine ribosides 

 Hotchkiss'" gives data for adenosine and guanosine, although in a form 

 quite unsuitable for general use without extensive arithmetical conversion, 

 and Kalckar^^ includes data for these two and for inosine. The differences 

 between ribo- and the corresponding deoxyribo- derivatives may be expected 

 to be very small (compare curves given by MacNutt^^ for guanine and 

 hypoxaiithine deoxyribosides with Figs. 12 and 13), but Fox and Shugar^® 

 have shown that, at least for pyrimidine derivatives, real distinctions can 

 be detected. The realization of the precision obtainable by the use of photo- 

 electric spectrophotometers has come very recently in some quarters, since 



" J. M. Gulland and L. F. Story, J. Chem. Soc. 1938, 692. 

 38 H. M. Kalckar, /. Biol. Chem. 167, 429, 445 (1947). 



