A COMPREHENSIVE STUDY OF SUGAR RADICALS IN IRRADIATED DNA

Density functional theory is used to study the energetics, geometries, and hyperfine couplings in sugar radicals which are generated through irradiation of DNA. The C4'-S and the C3'-S radicals are determined t o be the lowest lying species of the radicals formed through abstracti on of a hydrogen or a hydroxyl group from a model of the sugar present in DNA, respectively. The C2' radical has the highest energy and the smallest degree of ring puckering of all possible carbon-centered radi cals formed via hydrogen abstraction. In addition to the possible dehy drogenated and dehydroxylated products, various radicals which lead to substantial ring alterations, such as ring breaks or flattening of th e ring, are also studied. In most cases, the calculated hyperfine coup ling constants directly support the assignment of the experimentally o bserved couplings to the specific radicals. The effects of rotation ab out the C5'C4' bond on the HFCCs in the C5' and O5' radicals are exami ned in order to compare the experimental and theoretical results. In c ases where experiment and theory differ, the calculated results facili tate the assignment of the experimental couplings to alternative radic als.