Comparison of the aggregation behavior of water-soluble hexa(sulfobutyl)fullerenes and polyhydroxylated fullerenes for their free-radical scavenging activity

We study the aggregation behavior of two highly water-soluble fullerene derivatives, hexa(sulfobutyl)fullerenes (FC4S) and polyhydroxylated fullerenes (fullerenols) [C-60(OH)(18)] using small-angle x-ray scattering. We found that FC4S forms spheroidal aggregates having a similar radius of gyration R-g approximate to 19 Angstrom, in a wide concentration range from 0.4 to 26 mM in water solutions, whereas the mean sizes observed for C-60(OH)(18) aggregates in water solutions grow nearly two-fold from R-g = 20 Angstrom to R-g = 40 Angstrom as the concentration increases from 0.7 to 50 mM. The implication of the structural differences between the two fullerene derivatives on their free-radical scavenging activity is discussed.