60 



LIGHT AND LIFE 



50.000 



o 



o 



2000 



WAVENUMBERS, CM'' 

 45,000 40,000 35,000 



2400 



2800 



WAVELENGTH. A 



31,250 



3200 



Fig. 19. Near ultraviolet absorption curves of 9-methylpurine at room temperature, 

 after Mason (25). Curve a, in cvclohexane; curve b, in water; pH 5.05. 



(curve a) strongly blue-shifts, but is probably still present in the 2900 

 A region. Mason (25) has established by a study of the substitution 

 of groups along different axes of the pinine molecule that the absorp- 

 tion region from 2300 to 2750 consists of two tt —^ tt* transitions, 

 one polarized along the long axis (y) of the molecule, and one along 

 the intermediate axis (z) . 



VJI. DioxvRUiONi'ci.Kic Acid and CHLORorHVLL 



A. Hypochromism in DNA 



It is -well known that DNA, upon undergoing a random-coil to 

 helix transformation, exhibits a diminution of 30 per cent to 50 



