Theoretical study of the addition and abstraction reactions of hydroxyl radical with uracil

Abstract

The addition as well as abstraction reactions of hydroxyl radical(dOH) with the nucleic acid base,uracil(U), in the gasphasehasbeenexploredattheB3LYP/6-31þG(d,p)level of density functional theory (DFT). The energy barrier of the dOH addition to both the C5 and C6 positions of the uracil is less than 1 kcal/mol while the hydrogen abstractions(H abstractions)from either the N1 or the N3 positions are 9.5 kcal/mol. Further the energetics of these reactions are assessed by applying the effect of aqueous medium through the polarizable continuummodel(PCM).Both the gas and the solution phase data established that the thermodynamic and kinetic factors are more favorable for the dOH addition to either C5orC6 positions of the uracil than the H-abstraction reactions.Moreover,calculation sat the MPW1K/6-31þG(d,p),CCSD(T)/6-31þG(d,p)//B3LYP/6-31þG(d,p)andCCSD(T)/6-31þG(d,p)// MPW1K/6-31þG(d,p) levels of theoretical methods qualitatively supported the B3LYP/6-31 þG(d,p)results