Sonderseminar SFB 1032 - Prof. Drew Parsons

Title: "Hofmeister Specific Ion Effects, Buffer Effects and theory of colloidal interactions"

Location: Seminar room N110 (old Physics building)

Host: Prof. Joachim Rädler (B01)

Abstract:

Specific ion effects refer to variations in the behaviour of a system that deviate from the behavior expected in generic salt solutions characterized solely by salt concentration. They are frequently reported in terms of a Hofmeister series which describes the strength of the deviation with respect to the cation or anion in the salt. Hofmeister effects, affecting for instance zeta potential, diffusion of colloidal particles or enzyme activity, are observed in pharmaceutical or industrial contexts where it is desirable to maintain a consistent pH through the use of buffer solutions. Hofmeister effects in such systems are typically reported with respect to background salts, while the buffer itself is ignored. And yet the buffer solution itself is an electrolyte which exhibits its own specific ion effect, that is, a specific buffer effect. We have conducted experimental measurements demonstrating that buffer specific effects are significant and cannot be ignored, both in inorganic porous silica, lysozyme protein interactions and DNA melting. One observation is that buffers, configured at the same buffer strength for the same pH, not only shift the value of the measurement but may even invert the sign of the lysozyme zeta potential or lysozyme diffusion coefficient. This talk presents mean field theory modifying the Poisson-Boltzmann model to explain these ion-specific and buffer-specific buffer. A core component is the van der Waals dispersion interaction of ion species with particles, inducing adsorption of ion beyond that expected from electrostatic interactions [1].

[1] Buffer-specific effects arise from ionic dispersion forces. Drew F. Parsons, Cristina Carucci and Andrea Salis. Phys. Chem. Chem. Phys., 2022, 24, 6544. doi:10.1039/d2cp00223j