Molecular Dynamics Simulations Predict a Favorable and Unique Mode of Interaction between Lithium (Li+) Ions and Hydrophobic Molecules in Aqueous Solution

We report the results of molecular dynamics simulations of the interaction thermodynamics of group I cations with hydrophobic molecules in water using a variety of nonpolarizable force fields. Surprisingly, we find that the Li+ ion is predicted to form thermodynamically favorable interactions with methane and neopentane using a new mode of recognition that is intermediate between a direct contact and a solvent-separated complex. Further simulations show that this favorable interaction is only predicted by ion parameter sets that correctly reproduce Li+’s experimental hydration number.