Complexation between a semiflexible polyelectrolyte and an oppositely charged sphere

We study theoretically the interaction of a charged, semiflexible polymer w ith an oppositely charged sphere. Both the effects of added salt (leading t o a finite screening length) and of a bare stiffness of the polymer are tak en into account. For intermediate salt concentration and high enough sphere charge we obtain a strongly bound complex where the polymer completely wra ps around the sphere. The complex may or may not exhibit charge reversal, d epending on the sphere charge and salt concentration. The low-salt regime i s dominated by the polymer-polymer repulsion and leads to a characteristic hump shape: the polymer partially wraps around the sphere, and the two poly mer arms extend parallel and in opposite directions from the sphere. In the high-salt regime we find bent solutions, where the polymer partially wraps the sphere and the polymer ends extend in arbitrary directions from the sp here; in this regime, the wrapping transition is strongly discontinuous. Th is wrapping behavior agrees qualitatively well with the salt-induced releas e of DNA from nucleosomal core particles. The salt dependence of the wrappi ng transition for large salt concentrations agrees with experimental result s for the complexation of synthetic polyelectrolytes with charged micelles. Other applications include the complexation of polyelectrolytes with charg ed colloids or multivalent ions. In our analysis we calculate the classical or optimal path of the polymer, using a perturbational scheme. This calcul ation is confirmed and augmented by scaling arguments, which in addition al low us to consider the effect of polymer fluctuations.