Effects of protonation on proton-transfer processes in guanine–cytosine Watson–Crick base pairs

Intermolecular proton-transfer processes in guanine–cytosine Watson–Crick base pairs have been studied using the B3LYP density functional method. Protonation of the base pair was carried out both at the N7 and at the O6 atoms of guanine. It is found that protonation induces a strengthening of the base pair and facilitates the N1–N3 single-proton-transfer reaction. The double-proton-transfer reaction, however, turns out to be unfeasible when the system is protonated at these sites. Mutagenic implications of these proton-transfer processes are discussed.