C60 and water-soluble fullerene derivatives as antioxidants against radical-initiated lipid peroxidation

C-60, vitamin E, and three C-60 derivatives (polar 1 and water-soluble C-3/D(3)C(60)s) were examined for their antioxidant effects on prevention of lipid peroxidation induced by superoxide and hydroxyl radicals. The protection effect on lipid peroxidation was found to be in the sequence: C-60 greater than or equal to vitamin E > 1 > none, for liposoluble antioxidants, and C3C60 much greater than D3C60 > none, for water-soluble ones. Fluorescence quenching of PyCH2COOH (Py = pyrene) by both C-3-. and D(3)C(60)s shows that the Stern-Volmer constant, K-SV, is about the same for both quenchers in aqueous solution. Upon addition of liposomes, the fluorescence quenching becomes more efficient: 5-fold higher in K-SV for C3C60 than for D3C60. When Py(CH2)(n)COOH (n = 1, 3, 5, 9, or 15) was incorporated in lipid membranes, the K(SV)s all were small and nearly equal for D3C60 but were quite large and different for C3C60 with the sequence: n = 1 < 3 < 5 < 9 < 15. The better protection effect of C3C60 on lipid peroxidation than that of D3C60 is attributed to its stranger interaction with membranes. Overall, the antioxidation abilities of the compounds examined were rationalized in terms of the number of reactive sites, the location of antioxidant in lipid membranes, and the strength of interactions between antioxidants and membranes.