548 



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



4000 3000 



2000 



Frequency, cm.'i 

 1500 1200 1000 900 



800 



700 



2 4 6 8 10 12 14 



Wavelength, m 

 Fig. 28. Infrared absorption spectrum of cast film of DNA sodium salt (Rowen^^^). 



relation to the specific interactions between base substituent groups en- 

 visaged in the Watson and Crick structure for DNA." 



With regard to infrared absorption studies on nucleic acids proper there 

 is as yet very little to add to Fraser's excellent account/^" which deals also 

 with proteins and polysaccharides. The following frequency ranges are 

 listed by him for the fundamental vibrations that may be readily recognized 

 in the spectra of nucleic acids (e.g., Fig. 28). 



(1) Vibrations involving hydrogen atoms: 



Bond stretching O— H 3000-3700 cm.-i 



N— H 3000-3500 



C— H 2800-3100 

 Bond bending O— H ca. 1100 



N— H 1500-1600 



C— H 1300-1500 



(2) Multiple-bond stretching: 



C=0 1600-1800 cm.-i 

 C=N ca. 1650 

 C=C ca. 1650 

 P=0 1250-1300 " 



(3) Skeletal frequencies involving many linked atoms: 



\ / 



— C— O— C— ca. 1100 cm.-i 



163 J. W. Rowen, Biochim. et Biophys. Acta 10, 391 (1953). 



