Discrete charge patterns, Coulomb correlations and interactions in protein solutions

¹ Institut für Theoretische Physik II, Heinrich-Heine-Universität Düsseldorf D-40225 Düsseldorf, Germany
² Department of Chemistry, Lensfield Rd - Cambridge CB2 1EW, UK

Received: 27 September 2001
Accepted: 5 December 2001

Abstract

The effective Coulomb interaction between globular proteins is calculated as a function of monovalent salt concentration c_s, by explicit Molecular Dynamics simulations of pairs of model proteins in the presence of microscopic co and counterions. For discrete charge patterns of monovalent sites on the surface, the resulting osmotic virial coefficient B₂ is found to be a strikingly non-monotonic function of c_s. The non-monotonicity follows from a subtle Coulomb correlation effect which is completely missed by conventional non-linear Poisson-Boltzmann theory and explains various experimental findings.