Molecular dynamics simulations of a charged dendrimer in multivalent salt solution.

The multivalent salt dependent behaviors of a charged dendrimer in solution are investigated by molecular dynamics simulations with explicit free ions. We find that the charged dendrimers show a dense-core conformation together with the back-folding of terminal monomers to the interior under all the conditions studied. We also observe an interesting ion exchange phenomenon, the replacement of the condensed monovalent counterions by multivalent salt ions due to a strong electrostatic attraction. Furthermore, we find that the dendrimer adopts an extended conformation in the absence of salt. Upon addition of salt, the dendrimer collapses as a result of a drop in the osmotic pressure inside the dendrimer. With an additional increase in the salt concentration, the dendrimer weakly swells due to an enhanced excluded volume effect of the adsorbed salt ions. The overcharge phenomenon also appears in our system. Consequently, our findings show a strong dependence of the conformation of charged dendrimers on salt concentration and give valuable insight into their behaviors at various salt concentrations at the molecular level.