Separation and purification of fullerenols for improved biocompatibility

Isoelectric focusing was used to separate the different components of fullerenols based on their different electronegativities induced by the surface chemical functionalities and structures. Purified fractions of fullerenols were analyzed and characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results showed that four fractions of fullerenols could be separated by isoelectric focusing, and all fractions had a general formula of C-60(OH)(m)(O)(n) where the values of m and n might vary with their isoelectric points. Results from the capillary electrophoresis studies showed that the negative surface charge densities were different among the fractions of fullerenols, which indicated that the net surface negative charge was determined by the degree of C=O functionalization. In vitro cytotoxicity assays were also performed to determine the effect of purified fullerenols on cytotoxicity and DNA stability in Raw 264.7 cells. Although the fullerenols had low cytotoxicity, the composition of fullerenols with the highest negative charge density (-1.913 +/- 0.008 x 10(-4) C) and smaller size (3.92 +/- 0.71 nm) was found to induce DNA damage. Therefore, crude fullerenols must be separated and purified in order to obtain fullerenols with low degree of C=O functionalization and good biocompatibility. (C) 2011 Elsevier Ltd. All rights reserved.