A molecular dynamics study of the Gibbs free energy of solvation of fullerene particles in octanol and water

The Gibbs free energy of solvation (ΔGsolv) for C60, and six other idealized, non-functionalized, fullerene particles of differing size and shape has been determined in octanol and water solvents from molecular dynamics simulations using thermodynamic integration. In particular, we have studied Buckminster fullerene (C60) and open and capped carbon nanotubes of different aspect ratios and solvent accessible surface areas. Knowledge of the ΔGsolv of a molecule in octanol and water can be used to understand the partitioning of the molecule between organic and aqueous phases and is one of several parameters used to model the fate of chemicals in the natural environment. The simulations were performed at ambient conditions, i.e., a temperature of 25 °C and a pressure of 1 bar. The fullerene molecules are all found to have a very high ΔGsolv in water, and a very low ΔGsolv in octanol, suggesting a strong preference for the organic phase. From a comparison of the results for capped and uncapped carbon nanotubes we found that the uncapped tubes exhibit significantly higher ΔGsolv than capped tubes. Furthermore, for capped carbon nanotubes, hydrophobic/organophilic shifts are observed with increasing excluded volume and solvent accessible surface area.