Solvent polarity considerations are unable to describe fullerene solvation behavior

Atomistic molecular dynamics simulations were employed to investigate the solvation properties of the fullerene C60 in binary water/dimethyl sulfoxide (DMSO) mixtures. Structural analysis indicates a preferential solvation with the predominance of DMSO molecules in the first solvation shell for the solutions with low concentrations of DMSO. PMF calculations indicate a maximization of the hydrophobic interaction at low concentrations of DMSO. The contact minima indicate a tendency of aggregation of these nanostructures in water/DMSO mixtures and in the both pure solvents. The free energy of solvation suggests that the hydrophobicity of the fullerene increases monotonically with the increase of DMSO concentration. This result is incompatible with the polarity of DMSO, since it was expected that increasing the concentration of DMSO entailed an increase of C60 solubility.