Nanoscale Aggregation Properties of Neuroprotective Carboxyfullerene (C3) in Aqueous Solution

Water-soluble malonic acid derivatives of C 60 are known to have potent antioxidant activity with potential medical applications as neuroprotective agents. It is commonly assumed that e,e,e tris-malonic acid-C 60 (or C 3 ) exists as discrete molecules solubilized in aqueous solution. In this work, C 3 is revealed to aggregate in water. The aggregation properties have been studied as a function of concentration, temperature, and pH by dynamic light scattering (DLS). The C 3 aggregates are polydisperse under physiological conditions, do not vary much in size as a function of concentration or temperature, and tend to larger sizes at low pH values. Transmission electron microscopy (TEM) and cryo-TEM have been used to visualize the morphology of the nanocrystalline aggregates. The results suggest that 40−80 nm aggregates of C 3, not individual C 3 molecules, are responsible for their neuroprotective action in cells.