Raman Excitation Profiles of Purine and Pyrimidine Nucleic Acid Bases

Raman excitation profiles for the monophosphates of guanosine, cytidine, and thymidine have been obtained experimentally using tunable ultraviolet radiation. These data were then fit to a single state, preresonance enhancement equation in order to determine the effective absorption wavelength. In all cases these band origins agreed quite well with the electronic spectral maxima. For two of the bases these studies were performed at drastically varying pH's. A neutral-to-alkaline change produced only minor differences in the spectral data for guanosine, whereas a neutral-to-acidic change had a marked effect on both the spectrum and band origin for cytidine.