Nonlinear conductivity of fullerenol aqueous solutions.

Fullerenols have been a subject of intense research in many fields with the claim of possible applications in biomedicine such as free-radical sponges, antioxidants, and photosensitizers. However, its transport characteristics, important in determining the feasibility of many applications, have not been studied yet. In this work, electrochemical impedance of aqueous solutions of two types of fullerenols (C(60)(OH)(22-26) and C(60)(OH)(18-22)(OK)(4)) was measured. Sample conductivity was extracted from impedance data, and a nonlinear concentration-dependent conductivity was found for one of two types (C(60)(OH)(18-22)(OK)(4)). A concentration-dependent mobility that accounts electrophoretic and relaxation effects could explain experimental data. As a result, we obtained some fullerenol parameters, relevant to transport phenomena: its hydrodynamic radius, the number of attached hydroxides, and the number of counterions solvated into solution. In addition, an important result for pharmaceutical applications has been discussed, which is the change of pH in water induced by the different concentrations of fullerenol, indicating it behaves as a weak acid.