Dresden 2014 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 44: Charged Soft Matter I

CPP 44.8: Talk

Thursday, April 3, 2014, 11:30–11:45, ZEU 118

Specific Ion Binding to Amphiprotic Surface Groups and the pH Dependence of the Hofmeister Series — •Nadine Schwierz¹ and Roland R. Netz² — ¹Physik Department, Technische Universität München, Germany — ²Physik Department, Freie Universität Berlin, Germany

Ion binding to amphiprotic surface groups is one of the central mechanisms for ion-specificity if ionizable groups are present on the surface of a macromolecule. To gain insight into the microscopic mechanism, we use a combination of atomistic simulations and Poisson-Boltzmann theory and bridge from computational results to macroscopic experimentally accessible properties.

In our modeling approach, we first extract single-ion surface interaction potentials at atomistically resolved surfaces composed of uncharged carboxyl-groups and of charged carboxylate-groups. The surface affinity of single ions depends strongly on whether the carboxyl group is dissociated or not and is even reversed for cations.

Phase diagrams, based on long-ranged forces between two heterogeneous surfaces containing carboxyl and carboxylate groups interacting across electrolyte solutions, feature direct, reversed and altered Hofmeister series in dependence of the salt concentration and pH. The results provide a microscopic explanation for the pH dependence of the Hofmeister series due to specific and diverse ion binding to carboxyl and carboxylate surface groups.