The effect of ionization and deprotonation of guanine on the formation of base pairs

The effect of the ionization of the guanine on the formation of base pairs is investigated using the B3LYP method with 6-31++G∗∗ basis set. The base pairing with neutral DNA base lowers the adiabatic ionization potential of guanine, while the base pairing with protonated DNA base increases the ionization potential of guanine. The proton transfer can occur in the Watson–Crick GC and GA base pairs when an electron is lost. The effect of the deprotonation of the guanine cation on the formation of base pairs is also explored. From an energy point of view, the ionization of guanine cannot result in the Watson–Crick mispair formation, but the deprotonation from the guanine cation is in favor of the combination of the G(−H) and guanine. In the Hoogsteen base pairs, the ionization of guanine slightly affects the interaction mode, but it may result in the dissociation of the Hoogsteen base pairs if the DNA bases pairing with guanine are the protonated A, T and C. The deprotonation from guanine cation slightly affects the base pairing energies of the Hoogsteen base pairs.