Upon visual inspection of the (PA) 1 (Cl -) 1 (w) 0-5 in Figure , we observe a much broader variation in the preferred PA conformer across the hydrated clusters. PA prefers the Cc conformer in the (PA) 1 (Cl -) 1 dimer cluster. For the (PA) 1 (Cl -) 1 (w) 1 cluster, the C-C bond rotation between the carbonyl groups of PA has occurred and the Tc conformer is now preferred. The relative geometry between the carboxylic O-H and the α-carbonyl group is not completely planar as it is in the ordinary Tc conformer, which can be ascribed to better steric access of Cl -and the water molecule to engage in hydrogen bond interactions with the carboxylic O-H and the α-carbonyl group, respectively. In the (PA) 1 (Cl -) 1 (w) 2 cluster, the C-C bond has rotated further, and thus PA adopts the Ct form thereby interacting with Cl -through the carboxylic O-H and water through the carboxylic carbonyl group.