Spring 2020 Shires Graduate Research Seminar Series

Date(s) - Fri 02/21/20
1:30 pm - 2:20 pm

Jett Hall (JH) 259 Watkins Connected Learning Classroom


Advances in Computing Mechanisms of Specific Anion Binding: F vs Cl

Dr. Susan Rempe

Distinguished member of the Technical Staff at Sandia National Laboratories               

A. Muralidharan1, L. R. Pratt1, M. I. Chaudhari2, and S. B. Rempe2

1Department of Chemical and Biomolecular Engineering, Tulane University, New Orleans, LA 70118

2Department of Computational Biology and Biophysics, Sandia National Laboratories, Albuquerque, NM  87185

Ion hydration typically defines the reference state for the binding of specific ions to a mineral-water interface, and transport of ions through cellular and synthetic membranes. Thus, binding and transport mechanisms include mechanisms of ion hydration. Anion hydration is difficult to predict because it is complicated by H-bond donation between neighboring water molecules. This situation can lead to competing structures and anharmonic vibrational motions in chemically simple clusters like (H2O)nCl. Here, we apply a specialized free energy theory, called quasi-chemical theory, and exploit dynamics calculations on isolated (H2O)nCl clusters to account for anharmonicity. Comparing singly hydrated F and Cl clusters, classic OH-bond donation to the anion occurs for F, while Cl clusters exhibit more flexible, but dipole-dominated, interactions between ligand and ion. The predicted Cl — F- hydration free energy difference agrees well with experiment, a significant theoretical step for addressing issues like Hofmeister ranking, selectivity of ion binding to mineral-water interfaces, and selective ion transport across cellular and synthetic membranes for ion/water separations [1]. 

[1] Muralidharan, A; Chaudhari, MI; Pratt, LR; and SB Rempe. 2019. Quasi-chemical theory for anion hydration and specific ion effects: Cl(aq) vs. F(aq). Chem. Phys. Lett.: X (Frontiers article) 4:100037.