The distribution functions of cations relative to Ubiquitin are shown in Figure , for solutions with different anions, at the reference concentration of 1 mol L -1 . This concentration will serve as an illustrative framework for examining the hydrophobic influence of cations on protein solvation by IL ions throughout the paper. Similar results were obtained with different concentrations, and when notable differences are present the results are discussed independently. : The anions form localized interactions with the protein surface atoms. For the case of [Cl] -, in Figure , the first peak is smaller in comparison to the other anions and displaced to larger distances, and corresponds to ionic interactions of Cl -ions with basic residues . The most distinct of all interactions are hydrogen bonds, which in Figure -D are observed as sharp peaks at ∼1.9 Å 7,30 . Among the anions, [DCA] -and [NO3] -exhibit the greatest interactions with the protein surface via hydrogen bonding . The choice of cation does not alter the qualitative shapes of the protein-anion