Towards Understanding the Methylation Effect on the Aqueous Photoionization Energy of DNA Components

Abstract

Much of biochemistry and biophysics of DNA relies on the electronic structure of nucleotides. Nucleotide ionization plays an important role in mechanisms resulting in DNA damage caused by high-energy photons. However there is little information on the effects of methylation and hydration on the energetics of ionization of DNA bases. Employment of ab initio quantum mechanical calculations at the Hartree-Fock self consistent field (SCF) and in density functional theory (DFT) levels of theory provide evidence that methylation of guanine and cytosine stabilize the electronic structure of their radical cations and lower the ionization threshold energy in aqueous solution and at different ionic strengths.