Abstract: The theoretical studies on the mechanisms of ring-opening reaction of 8-hydroxyguanine radical were performed by the experimentally calibrated theoretical method of B3LYP/DZP++. All of the computational results revealed that the ring-opening reaction occured through a pathway including two elementary reactions, the C8—N9 bond-broken step followed by a transfer step of cation-like hydrogen atom of the hydroxyl moiety. The high activation energy in the transfer reaction of hydrogen atom in the absence of water led this reaction to be somewhat difficult; on the contrary, the hydrogen transfer might occur feasibly with assistance of one water molecule due to the formation of a six-member ring transition state which was beneficial to lower the reaction activation energy. The difference of the activation energies of two elementary reactions demonstrated that the rate-limiting steps of ring-opening reaction in the absence of water and in the presence of water were the hydrogen transfer step and C8—N9 bond-broken process, respectively.

Key words: 8-Hydroxyguanine radical, Ring-opening reaction, H-transfer reaction, Catalytic action of water