COMPUTATIONAL MODELING OF LOW-ENERGY ELECTRON-INDUCED DNA-DAMAGE BY EARLY PHYSICAL AND CHEMICAL EVENTS

Modelling and calculations are presented as a first step towards mecha nistic interpretation and prediction of radiation effects based on the spectrum of initial DNA damage produced by low energy electrons (100e V-4.5keV) that can be compared with experimental information. Relative yields of single and clustered strand breaks are presented in terms o f complexity and source of damage, either by direct energy deposition or by reaction of OH radicals, and dependence on the activation probab ility of OH radicals and the amount of energy required to give a singl e strand break (ssb). Data show that the majority of interactions in D NA do not lead to damage in the form of strand breaks and when they do occur, they are most frequently simple ssb. However, for double-stran d breaks (dsb), a high proportion (similar to 30%) are of more complex forms, even without considering additional complexity from base damag e. The greater contribution is from direct interactions in the DNA but reactions of OH radicals add substantially to this, both in terms of the total number of breaks and in increasing the complexity within a c luster. It has been shown that the lengths of damaged segments of DNA from individual electron tracks tend to be short, indicating that cons equent deletion length (simply by loss of a fragment between nearby ds b) would be short, very seldom exceeding a few tens of base pairs.