MP2 and DFT studies of the DNA rare base pairs: The molecular mechanism of the spontaneous substitution mutations conditioned by tautomerism of bases

We investigated structures and electronic properties of DNA base pairs containing the lactim forms of guanine (G*) or thymine (T*) as well as the imino forms of cytosine (C*) or adenine (A*) by ab initio MP2 and DFT methods. The found stable structures of G*–T and G–T* base pairs are the nonplanar ones. The obtained formation energies indicate that G*–T and A–C* are more favorable than G–T* and A*–C. The nature of their hydrogen bonding was discussed based on the energy decomposition analysis of Morokuma–Kitaura and the reduced-variational-space methods to elucidate the possibility of the tautomerization of DNA base pairs.