The influence of formamide (model of protein unit) on the intramolecular proton transfer in the DNA simple base guanine: A density functional theory study

For the purpose of investigating the influence of protein unit on the intramolecular proton transfer (IPT) reactions in the simple base guanine, a simple model (formamide) of peptides is designed to biological system investigations, and five complexes of formamide–guanine (FG1, FG2, FG3, FG4, and FG5) are determined at the B3LYP/6‐311++G(d,p) level of theory. For comparison, HF and MP2 methods are also used in this paper. The proton transfer (PT) reaction processes of guanine and FGs have been investigated employing the B3LYP/6‐311++G(d,p) level of theory. The selected thermodynamic and kinetic parameters, such as the activation energies (E_a), changes of enthalpy (ΔH) and changes of free energies (ΔG), as well as the equilibrium constants (K_p) for those reaction processes, have also been obtained by calculational means. The calculated results indicate that the assisted and protected effects of formamide on IPT in guanine are site‐dependent. CH1 is the lowest activation energy needed PT process no matter where the formamide molecule is located in. The activation energy of CH1 with formamide in S2 is the lowest one (153.3 KJ/mol), whereas the one of CH5 with formamide in S5 is the highest (318.3 KJ/mol). © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008