Hydrated Magnesium\nIon–Uracil and Magnesium\nChloride–Uracil Clusters Revealed by Ab Initio Study

The study focuses on the interaction between canonical\nuracil and\nits rare tautomers with Mg<sup>2+</sup> and MgCl<sub>2</sub> in the\nmicrocosmic water environment and aims to elucidate how ions interact\nwith nucleobase and the cation–anion correlation effect involved\nusing density functional theory calculations. The structures of the\nUra–Mg<sup>2+</sup>(H<sub>2</sub>O)<sub>0–6</sub> and\nUra–MgCl<sub>2</sub>(H<sub>2</sub>O)<sub>0–6</sub> clusters\nare characterized and show that the water molecules preferentially\ninteract with Mg<sup>2+</sup>/MgCl<sub>2</sub>, and Mg<sup>2+</sup> adopts a hexacoordination pattern in both Ura–Mg<sup>2+</sup>(H<sub>2</sub>O)<sub>0–6</sub> and Ura–MgCl<sub>2</sub>(H<sub>2</sub>O)<sub>0–6</sub> clusters. When uracil interacts\nwith Mg<sup>2+</sup> in (H<sub>2</sub>O)<sub>0–6</sub> environments,\nit tends to favor the formation of keto–enol structures. However,\nin the presence of Cl<sup>–</sup> cooperating with Mg<sup>2+</sup>, the Ura–MgCl<sub>2</sub>(H<sub>2</sub>O)<sub>0–6</sub> complexes prefer to form diketo structures. The proton transfer\nmechanism shows that the initial solvation can promote the change\nfrom the keto–enol structure to the diketo structure, which\nis strengthened by the analysis of the Ura–Mg<sup>2+</sup>(H<sub>2</sub>O)<sub>6</sub> and Ura–MgCl<sub>2</sub>(H<sub>2</sub>O)<sub>6</sub> structures in the aqueous phase using the PCM model.\nAdditionally, reduced density gradient, atom in molecules, and energy\ndecomposition analysis combined with charge transfer analysis were\ncarried out to obtain the variation law of the interactions between\nMg<sup>2+</sup> and Ura with the water number increasing, thereby\nrevealing the interaction mechanism of uracil with magnesium ion and\nthe effect of Cl<sup>–</sup> on the interaction between Mg<sup>2+</sup> and uracil.