Modulation of hydrogen bonding upon ion binding: Insights into cooperativity

The impact due to the of presence of ions, such as Mg²⁺, Na⁺, H⁺, Cl^?, and OH^? on hydrogen bonded clusters of increasing size (water, formamide, and acetamide n = 1–10]) in the context of associated cooperativity has been explored using density functinal theory (DFT) calculations. Sequential binding energies (SBE) rise on addition of monomer in case of parent clusters. SBE for ionic clusters are several times higher than that of parent clusters initially. This behavior is more dramatic on addition of either Mg²⁺ or H⁺ compared to other ions. Interestingly, SBE of both parent and ionic clusters approach nearly uniform values beyond n = 6 irrespective of kind of ion present in the cluster with the exception of magnesium. © 2013 Wiley Periodicals, Inc.