OPTICAL PROPERTIES OF NUCLEIC ACIDS 553 



Infrared Absorption Spectra 



Blout and Lenormant'''^ have obtained infrared absorption spectra of 

 concentrated solutions of RNA, DNA, and DNP in both water and deu- 

 terium oxide, using very thin cells to reduce the solvent absorption. Under 

 these conditions the absorption bands are sharper than those given by 

 dried films. The characteristic 1020-cm.~^ band of DNA is retained in solu- 

 tion with a slight shift in wavelength, and DNA and RNA can be clearly 

 differentiated. 



Frick and Rosenberg"^ have obtained some infrared absorption evidence 

 for the existence of hydrogen bonds in native highly polymeric DNA. Work- 

 ing with pressed KBr sample plates^^* and a calcium fluoride prism, they 

 find that a small maximum at ca. 3.1 n, ascribed to hydrogen-bonded NH 

 stretching, is reduced to an inflection by prior exposure of the sample to pH 

 12, the remainder of the spectrum being unaltered. 



"8 E. R. Blout and H. Lenormant, /. Opt. Soc. Amcr. 43, 1093 (1953). 

 "' G. Frick and A. Rosenberg, Biochim. et Bio-phys. Ada 13, 455 (1954). 



