Carboxyfullerenes eliminate superoxide faster at lower pH. C3 exhibits an order of magnitude faster rate of superoxide elimination as compared to D3, compare (A) and (B). Both drugs showed an inverse relationship between the efficiency of superoxide removal and pH; a trend that was more pronounced in the hexa isomers as shown in (C). Superoxide was generated by HX/XO metabolism at pH 7.4, or through thermal decomposition of SIN-1 at pH values of 8.5, 9.0, 9.5, and 10, see experimental section for details.