Modeling specific-ion effects in aqueous solutions and ion channels

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Thomas Beck of the University of Cincinnati is supported by an award from the Theoretical and Computational Chemistry program for research to develop theoretical methodology for modeling specific-ion effects in aqueous solutions and ion channels. The work is focused on determining a quantitative understanding of the specific-ion, or Hofmeister, effect in which a strong dependence on ion type, particularly the anion identity, is seen in salting-out of proteins, basic colloidal interactions, properties of polyelectrolytes, and other related topics. Beck and his coworkers address this problem by performing accurate quantum chemical calculations for interactions between ions and their neighboring solvation shells. The inner shell solvation is then coupled to a continuum or classical molecular dynamics approximation for the outer shell contribution to the free energy. The conceptual link that allows the physical partitioning is the Potential Distribution Theorem (PDT) which allows for exact partitioning of free energy contributions of the various components. The work is having a broader impact on our understanding of biophysical systems, particularly membranes and ion channels.