Furthermore, a significant degree of solvation of the Na + ion by water in the gas-phase is also thermodynamically favorable for stabilizing the clusters. Deprotonation of PA leading to PA -could lead to more stable clusters. The left panel of Figure presents the binding free energies normalized to the dry clusters of PA -with Na + and Cl -. Generally, the hydration profiles are similar to the PA-containing clusters described above. We observe the energies of the (PA -) 1 (w) 0-5 , (PA -) 1 (Na + ) 1 (w) 0-5 and (PA -) 1 (Na + ) 1 (Cl -) 1 (w) 0-5 to decrease with increasing water content. This leads to negative binding free energies in all cases. Hence, pyruvate hydration is favorable and, in general, seems to be enhanced by other ions.