ASSOCIATION OF URACIL WITH Zn2+ AND THE HYDRATED Zn2+: A DFT INVESTIGATION

Abstract

The association behaviors between Uracil and Zn 2+ in vacuum and in the presence of extra water molecules have been investigated systematically using the density functional theory (DFT). In these systems, the interaction of Zn 2+ with the carbonyl oxygen O 4 is systematically favored relative to O 2. For Uracil- Zn 2+ complexes, the more stable coordination mode among the possible complexes corresponds to the bidentate one, where the monodentate coordination mode is about 37 kcal/mol higher in energy relative to the bidentate case. Correspondingly, the stabilities of these structures are enhanced due to the formations of the four-membered chelate ring in the bidentate coordination processes. In the monodentate coordination complexes, the hydration effects are larger than those in the bidentate coordination complexes. The most basic center in the Uracil remains the same regardless of whether introducing the water molecules to Zn 2+ or not. The calculated Zn 2+ bonding energies in Uracil- Zn 2+( H 2 O ) complexes are reduced in comparison to those of the unhydrated Uracil- Zn 2+ complexes. Moreover, investigations of stepwise hydration of Zn 2+ in the most stable Uracil- Zn 2+ complex suggest that the successive hydration effect on the Zn 2+ site can enhance the strength of C = O bond in the Uracil- Zn 2+ complexes and reduce the association interaction of Uracil with Zn 2+. Additionally, the most acidic site of Uracil has been changed from N 1- to N 3– H group before and after introducing the Zn 2+ and there is a significant increase in the overall acidity of the system.