Effect of Cations on Monolayer-protected Nanoclusters Aggregation

We studied the effect of metal and molecular cations in the aggregation of atomically precise monolayer-protected nanoclusters (MPCs) in explicit solvent using atomistic molecular dynamics simulations. While divalent cations such as Zn$^{2+}$ and Cd$^{2+}$ promote aggregation by forming ligand-cation-ligand bridges between the MPCs, the molecular cations such as tetraethylammonium and cholinium inhibit their aggregation by getting adsorbed into the MPC's ligand shell and reducing the ligands motion. Here we studied the aggregation of Au$_{25}$(SR)$_{18}$ nanoclusters with two types of ligands - para-amino benzoic Acid and d-penicillamine as prototypical examples.