The influence of isolated and penta-hydrated Zn(2+) on some of the intramolecular proton-transfer processes of thymine: a quantum chemical study

Zinc cation (Zn(2+)) plays an important role in the chemistry of DNA base pairs. In this work, the influence of isolated and penta-hydrated Zn(2+) 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(2+) and T are exothermic in vacuum. Compared to T, Zn(2+) increases the stability of tautomer T′ by 28.7 kcal mol(−1), promoting the intramolecular proton transfer of T. But in a micro-water environment, the attachment processes of Zn(2+) to T hydrates, penta-hydrated Zn(2+) to T, and penta-hydrated Zn(2+) 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(2+) is much reduced and the proton transfer is thermodynamically unfavored. The detailed characterization is helpful to understand the genotoxicity of zinc ions.