lt is generally agreed that the biological consequences of ionizing radiation originates with effects of the radiation on DNA. lt is also generally agreed that the indirect effect of attack by hydroxyl radicals from water radiolysis is responsible for a significant portion of the consequences. However, less agreement exists on the identities of the significant products of direct DNA ionization. Since existing evidence indicates that direct effects are roughly as important as indirect ones, the long-range objectives of this work are to identify the mechanisms, and to help clarify the importance, of direct ionization effects in DNA. The specific aims for this project, derived from existing evidence and models reported in the literature, are: (1) to continue the effort to identify and characterize the primary products of purine derivatives, and to characterize their subsequent products: (2) to investigate the character (variability of methyl coupling, protonation state, and effect of hydration) of thymine anions in a variety of systems; (3) to investigate factors which may control the elementary protonation and deprotonation reactions of the primary ions; (4) to investigate the role of "bound" water in determining the identity and chemical behavior of the primary ionic products; (5) to investigate systems in which more than one base is present in order to clarify mechanisms in which anions and cations may appear preferentially among the constituents of a system. To meet these aims, a variety of experiments will be performed using well characterized molecular systems (single crystals), and focusing on the radical (paramagnetic) products of ionization events. The main experimental procedures will be those of high resolution magnetic resonance spectroscopy (ENDOR), associated with temperature control (below 10 K to 300 K).