Dependence of gamma-irradiated Y-peak and melting of DNA on concentration and ionic environment.

Y-peak is found to be a function of ionic strength and concentrations of DNA. The Y-peak reveals close dynamic interaction between DNA and solvent system. Electronic transitions responsible for Y-peak are not the same transitions that are responsible for X-peak. Y-peak's electronic transitions are indicative of charge transfer complex formation between DNA and solvent system. gamma-Irradiation induces hyperchromicity due to strand separation at lower doses. A-T base pairs are first to undergo coiled state as shown by delta Tm spread. Strand chopping and saturation of double bonds of the exposed bases by free radicals (H degrees and OH degrees) give rise to hypochromic regions at X-peak. Rise in ionic strength and the concentration of DNA has protective effect against gamma-damage. Y-peak is found to be a function of solvent, whereas, X-peak is independent of solvent nature.