action ob^ ultraviolet light on viruses 149 



Absorption by Some Definite Molecules 



iVbsorption spectra of simple substances such as benzene 

 vapor are very sharp. In solution, or in the liquid state, the lines 

 are broadened. When a simple substitution is made on a molecule 

 such as anthracene, the relatively simple spectrum becomes 

 changed, in general because certain resonant electronic con- 

 figurations are no longer possible. 



Samples of various spectra are given in Fig. ii.'i. An excellent 

 review is given by Beavan and Holiday (1952). Of some interest 

 is the sharpening of the absorption spectra of some organic com- 

 })ounds at low temperatures. This has been applied to molecules 

 of biological interest by Sinsheimer, Scott, and Loofbourow 

 (1950) and by Brown and Randall (1949). In general, one would 

 expect a sharpening at low temperatures because of less 

 molecular agitation. This is not found in practice. For example, 

 purines show no sharpening, but pyrimidines definitely do. The 

 absorption spectra of thymine and cytosine are shown in Fig. 

 6.2a and clearly have many distinct bands. 



The effect of the nature of the solvent on the absorption of 

 tryptophane and tyrosine can be seen in Fig. 6.2b where data 

 due to Holiday (1936) are plotted. Although the general shape 

 is not changed, the details of the peaks are considerably altered. 

 The effect of substitution is shown in Fig. 6.2c where data of 

 Jones (1947) are plotted for anthracene and anthraldehyde in 

 ethanol. The substitution of the aldehyde group for the hydrogen 

 removes many possible absorption modes, as can be seen from 

 the figure. 



The absorption spectrum of the pneumococcus transforming 

 factor, a form of desoxyribose nucleic acid, taken by Fluke, is 

 shown in Fig. 6.3. The absorption by the purines and pyrimi- 

 dines causes the broad band at 2,600 A. The rise at 2,200 A is 

 more doubtful. 



In Fig. 6.4, the absorption spectrum of insulin, taken by 

 Suprynowicz is shown. This is representative of protein absorp- 

 tion. A broad maximum occurs at 2,750 A, but in this particular 

 substance six peaks [previously reported by Beaven and Holiday 



