Powders and films of variably hydrated poly(U), poly(A) and poly(A):poly(U) were X-irradiated at 4 K. Spectra and free radical yields wer acquired at 4 K using Q-band EPR spectroscopy. Evidence for electron transfer from the hydration layer to the RNA bases, supporting in part the damage transfer hypothesis of Gregoli et al. (Radiat. Res. 89, 238-254, 1985), is presented. Based on measurements of radical yield as a function of hydration, we propose that intermolecular packing and polymer conformation are dominant factors in determining free radical trapping ability in these polymers. Our annealing results indicate that increasing hydration facilitates intercluster combination reactions.

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