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

Abstract

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.