Electron Gain and Electron Loss Radicals Stabilized on the Purine and Pyrimidine of a Cocrystal Exhibiting Base-Base Interstacking: ESR-ENDOR of X-Irradiated Adenosine:5-Bromouracil

KAR L., AND BERNHARD, W. A. Electron Gain and Electron Loss Radicals Stabilized on the Purine and Pyrimidine of a Cocrystal Exhibiting Base-Base Interstacking: ESR-ENDOR of XIrradiated Adenosine:5-Bromouracil. Radiat. Res. 93, 232-253 (1982). The predominant free radicals trapped in cocrystals of adenosine:5-bromouracil X-irradiated at 12?K were identified by ESR-ENDOR spectroscopy and the radical reactions were followed upon annealing to 480?K. The dominant electron abstraction and electron addition products stabilized on the bases at 12?K are observed to be the bromouracil 7r-cation and the adenine rcation and 7r-anion. The formation of an anion on bromouracil is inferred from the presence of a radical formed by deuterium addition to C6 of bromouracil at higher temperatures. Above 40?K the bromouracil 7r-cation appears to decay by recombination and is reduced to undetectable levels at - 170?K. Both adenine ir-ions are also observed to decay within the same temperature range. Above 200?K hydrogen adducts are stabilized on the bases. Experiments using partially deuterated cocrystals indicate that the H-adducts are formed via both hydrogen addition and protonation of the respective anions. Two hydrogen abstraction radicals stabilized on the sugar residue are detectable at temperatures above 200?K, but these may be present at much lower temperatures. The results presented here question the generally accepted hypothesis that, in the presence of purine:pyrimidine stacking interactions, holes are predominantly transferred to the purines while electrons are predominantly transferred to the pyrimidines.