The influence of isolated and penta-hydrated Zn on some of the intramolecular proton-transfer processes of thymine: a quantum chemical study.

Zinc cation (Zn) plays an important role in the chemistry of DNA base pairs. In this work, the influence of isolated and penta-hydrated Zn on some of the intramolecular proton-transfer processes of thymine (T) is investigated by the density functional theory method. It is shown that the calculated binding energies between Zn and T are exothermic in vacuum. Compared to T, Zn increases the stability of tautomer T' by 28.7 kcal mol, promoting the intramolecular proton transfer of T. But in a micro-water environment, the attachment processes of Zn to T hydrates, penta-hydrated Zn to T, and penta-hydrated Zn to T hydrates lead to the rearrangement of molecules and the redistribution of charges. The conventional T is still the most stable form and the influence of Zn is much reduced and the proton transfer is thermodynamically unfavored. The detailed characterization is helpful to understand the genotoxicity of zinc ions.