The influence of packing on free radical yields in solid-state DNA: film compared to lyophilized frozen solution.

Radiation-induced free radical damage in solid-state DNA arises from direct-type damage mechanisms. In the present study, free radical yields in film and lyophilized Na DNA model systems are compared. The free radical yields in lyophilized samples are significantly greater than those in films. Since DNA conformation cannot account for the differences in free radical yields between different DNA preparations, it is proposed that the intermolecular spacing of DNA is a critical variable. The differences in the hydration dependence of free radical yields between the film and lyophilized DNA model systems are consistent with this thesis. The relatively large free radical yields observed in lyophilized DNA emphasize the fact that DNA is an extremely effective electron and hole scavenger, more so than previously thought.