Interaction between macroions mediated by divalent rod-like ions

¹ Faculty of Electrical Engineering, Tržaška 25, University of Ljubljana 1000 Ljubljana, Slovenia
² University College for Health Care, Poljanska 26a, University of Ljubljana 1000 Ljubljana, Slovenia
³ Research Group “Lipid Membranes”, Friedrich-Schiller University Neugasse. 25, Jena 07743, Germany

Received: 22 July 2004
Accepted: 28 September 2004

Abstract

Attractive interactions between identical like-charged macroions in aqueous multivalent salt solution arise due to ion-ion correlations. The mean-field level Poisson-Boltzmann (PB) theory does not predict such behavior for point-like structureless ions. Various multivalent ions, such as certain DNA condensing agents or short stiff polyelectrolytes, do have an internal, often rod-like, structure. Applying PB theory to the generic case of divalent rod-like salt ions, we find attraction between like-charged macroions above a critical distance between the two individual charges of the rod-like ions. We calculate this distance analytically within linearized PB theory. Numerical results for the non-linear PB theory indicate strong enhancement of the tendency to mediate attractive interactions.