Theoretical study of the pre- and post-translational effects of adenine and thymine tautomers and methyl derivatives

The study of pre-translational effects (ionization, tautomerization) and post-translational effects (methylation) of adenine and thymine has only recently been the focus of some studies. These effects can potentially help regulate gene expression as well as potentially disrupt normal gene function. Because of this wide array of roles, greater insight into these effects in deoxyribonucleic acids (DNA) are paramount. There has been considerable research of each phenomenon (tautomerization, methylation and ionization) individually. In this work, we attempt to shed light upon the pre-translational effects and post translational effects of adenine and thymine by investigating the electron affinities (EAs) and ionization potentials (IPs) of the major and minor tautomers and their methyl derivatives. We performed all calculations using the density functional theory (DFT) B3LYP functional accompanied with 6-311G(d,p), 6-311+G(d,p) and 6-311++G(df,pd) basis sets. Our results reveal that the thymine tautomer has a higher EA and IP than the adenine tautomers. The higher EA suggests that an electron that attaches to the AT base pair would predominately attach to the thymine instead of adenine. The higher IP would suggest that an electron that is removed from the AT base pair would be predominately removed from the adenine within the base pair. Understanding how tautomerization, ionization and methylation differences change effects, discourages, or promotes one another is lacking. In this work, we begin the steps of integrating these effects with one another, to gain a greater understanding of molecular changes in DNA bases.