We studied the (PA) 1 (Na + ) 0-1 (Cl -) 0-1 (w) 0-5 cluster systems to investigate the influence of ions on the PA-containing clusters. Figure shows clusters with sodium ion, with chloride ion, and with both ions simultaneously. Generally, we observe no proton transfers in these clusters. For the (PA) 1 (Na + ) 1-5 clusters in Figure , PA prefers the Ct conformer. This can be ascribed to the bifurcated ion-dipole interactions between the adjacent carbonyl oxygens of PA and Na + . The water molecules are generally observed to reside on the other side of Na + for the (PA) 1 (Na + ) 1 (w) 1-4 clusters thus building up a hydrogen-bonded water network solely interacting with the Na + ion. However, for the (PA) 1 (Na + ) 1 (w) 5 cluster, we observe that the Na + ion is "solvated" by the water molecules, thus residing more remotely from the PA monomer.