First-principles Studies of the Energetics and the Electronic Structures of Methylguanine

Abstract

We calculate the total energies, the equilibrium geometries, and the HOMO-LUMO energy gaps of keto 9-H guanine (N9H), keto 7-H guanine (N7H), and various guanine, methylguanine, and dimethylguanine molecules related to N9H and N7H. Bond orders are found to be crucial in determining the HOMO-LUMO energy gaps. The impact of structural changes such as methylation and the rearrangement of the hydrogen atoms of guanine molecules on the geometries and the electronic properties can be understood in terms of the bond orders, the steric effects, and the specific molecular topologies.