Free-radical probes of condensed-phase aspects of radiation damage mechanisms in DNA constituents: 5-halouracils

Employing free radicals as structural and quantitative monitors for radiation-induced alterations, some aspects of condensed- phase damage mechanisms in organic material are discussed using DNA and its constituents as target example. Specifically, reactions in low-temperature glasses are compared with those in aqueous solutions exemplified for the natural nucleic acid constituents uracil and thymine and their 5-halogen substituted derivatives which modify the radiation response. In addition, the topic of energy transfer in solid-state radiation chemistry is outlined and discussed emphasizing again the group of 5-halouracils. A difference in transfer mechanisms between aquated and dry solid systems is outlined and the role of structural water is tentatively implied. The findings are discussed in the context of electron microscopy at low temperatures.