Overcharging of a spherical macroion by an oppositely charged polyelectrolyte

¹ Department of Physics, University of California - Santa Barbara, CA 93106, USA
² Materials Research Laboratory, University of California Santa Barbara, CA 93106, USA
³ Materials Department, University of California - Santa Barbara, CA 93106, USA

Received: 4 May 1998
Accepted: 1 March 1999

Abstract

We consider the electrostatic interaction between a spherical macroion of charge Qq and an oppositely, highly charged polyelectrolyte of charge (N,Q > 0). For the polyelectrolyte fully collapses on the macroion, while for N>Q only a partial collapse (up to neutralization of the macroion) is expected. We show, however, that for N>Q, the amount of collapsed polyelectrolyte can be bigger than that required to neutralize the macroion, i.e. the macroion can be overcharged. The overcharging increases with the diameter of the macroion (continuously or through multiple first-order transitions), until a total collapse of the polyelectrolyte takes place. The predictions of this model are then compared with Monte Carlo simulations and a possible mechanism is suggested for the overcharging of the octameric histone in the nucleosome.