Activity of water-soluble fullerenes towards OH-radicals and molecular oxygen

bis-functionalized C60 carrying negatively charged carboxyl groups, C60[C(CO−2)2]2, or positively charged quaternary ammonium groups, C60(C4H10N+)2, have been shown to exhibit high water-solubility without cluster formation. This renders them excellent targets for free radical attack and energy transfer reactions in aqueous environment. Absolute rate constants on the order of 8×109 M−1 s−1 and 1.5×109 M−1 s−1 have been measured for the addition of OH radicals to the fullerene core and for the formation of 1O2 through triplet excited states of the fullerenes, respectively, for a variety of bis-functionalized stereoisomers. Comparatively lower rates have been observed for the corresponding energy transfer reactions with γ-cyclodextrin-encapsulated (C60/γ-CD, C60C(CO−2)2/γ-CD, and C60[C(OCH2CH2)3CH3]2/γ-CD), and water-soluble poly-functionalized fullerenes (e,e,e-C60[C(CO−2)2]3, C60[(CH2)4SO3H]6, and C60(OH)18). The latter three also exhibited a lower reactivity towards OH radicals. In case of the γ-CD complexes, OH reacted exclusively with the macromolecular host.