30. PHOTOCHEMISTRY OF NUCLEIC ACIDS 51 



Buell and Hansen 48 report details for the construction of an instrument 

 suitable for measurements in the range 230-190 niju, based on the use of a 

 ' ' solar-blind ' ' photomultiplier . 



Of great interest to most laboratories is the development by Beckman 

 of its photomultiplier attachment which increases sensitivity over the entire 

 spectral range and makes possible measurements to 190 mp. A similar goal 

 has been achieved by Unicam through the use of a fused quartz prism with 

 improved transmission characteristics and which is said to extend the useful 

 working range to 186 mp, the region of maximum absorption of the peptide 

 bond 49 and most likely of nucleoproteins. 



With the use of proper precautions for checking the absence of, or cor- 

 recting for, stray light, these new instruments should considerably extend 

 the potentialities of spectral techniques to structural studies upon, and the 

 analytical chemistry of, nucleic acids and their derivatives. An analytical 

 procedure for serum proteins has already been described, based on peptide 

 bond absorption at. 210 ran. 50 Many nucleic acid derivatives possess an 

 absorption maximum in the region 190-210 mp which the new instruments 

 define clearly 51 • 52 (Fig. 4) while others, such as some dihydropyrimidines 

 and photoproducts of uracil derivatives, possess a maximum at neutral pH 

 only in this region. 



2. Aqueous Solution Infrared Spectroscopy 



Most infrared investigations in the past have involved the use of films, 

 mulls or solutions in nonaqueous solvents (Volume I, Chapter 14). The 

 appearance on the market of thin cells using a variety of water-resistant 

 window materials, 53 together with the use of D 2 as solvent in the 3-m and 

 6-/x regions of the spectrum where H 2 strongly absorbs, now makes possible 

 routine infrared spectroscopy of nucleic acids and their derivatives in 

 aqueous medium. 53 " 55 Several laboratories have already begun to exploit 

 this powerful technique in structural studies on pyrimidine nucleosides and 

 nucleotides, 56, 57 as well as on nucleic acids and nucleoproteins. 54 ' 58 Atten- 



48 M. V. Buell and R. E. Hansen, Science 126, 842 (1957); Anal. Chem., 31, 878 

 (1959). 



49 A. R. Goldfarb, L. J. Saidel, and E. Mosowitch, /. Biol. Chem. 193, 397 (1951); 

 J. S. Ham and J. R. Piatt, /. Chem. Phys. 20, 335 (1952). 



50 M. P. Tombs, F. Sonter, and N. F. McLagan, Biochem. J. 71, 13P (1959); ibid. 73, 

 167 (1959). 



61 A. Rorsch, R. Beukers, J. Ijlstra, and W. Berends, Rec. trav. chim. 77, 423 (1958). 



62 M. V. Buell and R. E. Hansen, J. Biol. Chem. in press (1960). 

 53 H. Sternglanz, Appl. Spectroscopy 10, 77 (1956). 



" E. R. Blout, Ann. N. Y. Acad. Sci. 69, 84 (1957). 



55 W. J. Potts, Jr., and N. W. Wright, Anal. Chem. 28, 1255 (1956). 



56 H. T. Miles, Biochim. et Biophys. Acta 22, 247 (1956); 27, 46 (1958); 30, 324 (1958). 



57 R. L. Sinsheimer, R. L. Nutter, and G. R. Hopkins, Biochim. et Biophys. Acta 18, 

 13 (1955). 



