Effect of solvation on ion binding to imidazole and methylimidazole.

Quantum chemical [MP2(FULL)/6-311++G-(d,p)] calculations are done on the binding of hydrated Li(+), Na(+), K(+), Mg(2+), Cu(+), and Zn(2+) metal ions with biologically relevant heteroaromatics such as imidazole and methylimidazole. The computed interaction energies are found to be in good agreement with the available experimental data. The effect of hydration on hydrogen bonding has been studied in detail and it shows that the hydrogen bond strength between H(2)O···H-N(1) substantially increases in the presence of metal ions. The present study quantifies the cooperativity between M···imidazole (M = Li(+), Na(+), K(+), Mg(2+), Cu(+), and Zn(2+)) and N(1)-H···OH(2) interactions. Topological atoms in molecules (AIM) analysis and charge analysis support the variation in hydrogen-bonding strength and the variation in M···imidazole binding strength. Effect of hydration on N(1)-H stretching frequency is studied, and it shows a clear shift in the stretching frequency after sequential hydration of metal ion as well as the N(1) of imidazole. The present study provides a detailed account on the biologically important M-histidine motif interaction with metal ions, where histidine is modeled by imidazole and methylimidazole.