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

bis-functionalized C-60 carrying negatively charged carboxyl groups, C-60[C(CO2-)(2)](2), or positively charged quaternary ammonium groups, C-60(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 x 10(9) M-1 s(-1) and 1.5 x 10(9) M-1 s(-1) have been measured for the addition of (OH)-O-.. radicals to the fullerene core and for the formation of O-1(2) 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 gamma-cyclodextrin-encapsulated (C-60/gamma-CD, C60C(CO2-)(2)/gamma-CD, and C-60[C(OCH2CH2)(3)CH3](2)/gamma-CD), and water-soluble poly-functionalized fullerenes (e,e,e-C-60[C(CO2-)(2)](3), C-60[(CH2)(4)SO3H](6), and C-60(OH)(18)). The latter three also exhibited a lower reactivity towards (OH)-O-. radicals. In case of the gamma-CD complexes,(OH)-O-.. reacted exclusively with the macromolecular host. (C) 1999 Elsevier Science Ltd. All rights reserved.