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The low solubility of fullerenes in aqueous solution limits their applications in biology. By appropriate substitution, the fullerenes can be transformed into stabilized anions that are water soluble and can form large aggregated structures. A laser light scattering study of the association behavior of the potassium salt of pentaphenyl fullerene (Ph₅C₆₀K) in water revealed that the hydrocarbon anions Ph₅C₆₀ ⁻ associate into bilayers, forming stable spherical vesicles with an average hydrodynamic radius and a radius of gyration of about 17 nanometers at a very low critical aggregation concentration of less than 10⁻⁷ moles per liter. The average aggregation number of associated particles in these large spherical vesicles is about 1.2 × 10⁴.