On the polarity of buckminsterfullerene with a water molecule inside

Since the recent achievement of Kurotobi and Murata to capture a water molecule in a C60 fullerene (Science2011, 333, 613), there has been a debate about the properties of this H2O@C60 complex. In particular, the polarity of the complex, which is thought to be underlying the easy separation of H2O@C60 from the empty fullerene by HPLC, was calculated and found to be almost equal to that of an isolated water molecule. Here we present our detailed analysis of the charge distribution of the water-encapsulated C60 complex, which shows that the polarity of the complex is, with 0.5 ± 0.1 D, indeed substantial, but significantly smaller than that of H2O. This may have important implications for the aim to design water-soluble and biocompatible fullerenes.