Calculations of the Energetics of Oxidation of Aqueous Nucleosides and the Effects of Prototropic Equilibria

Recently the calculated standard reduction potentials of the radical-cations of N-methyl substituted DNA bases have been reported that agree fairly well with the experimental results. However, there are issues reflecting the fact that the experimental results usually relate, to the couple E degrees(Nuc center dot,H+/NucH(+)), whereas the calculated results are for the E degrees(Nuc(center dot+)/Nuc) couple. To calculate the midpoint reduction potential at PH 7 (E-m7), it is important to have accurate acid dissociation constants (pKs) for both,ground-state bases and their radicals, and the effects of uncertainty in some of these values (e.g., that of the adenosine radical) must be considered. Calculations of the pKs of the radicals of the nucleic acid bases (as nucleosides) have been performed to explore the effects the various pKs have on calculating the Values of E-m7 and to see what improvements Can be made with the accuracy of the calculations.