Reactions of e−aq, co2•−, ho, o2•− and o2(1δg) with a dendro[60]fullerene and c60[c(cooh)2]n (n = 2–6)

Using pulse radiolysis and laser flash photolysis, we have investigated the reactions of the deleterious species, e−aq, HO, O2•− and O2(1Δg) with 10 water-soluble cyclopropyl-fused C60 derivatives including a mono-adduct dendro[60]fullerene (d) and C60 derivatives based on C60[C(COOH)2]n=2–6, some of which are known to be neuroprotective in vivo. The rate constants for reactions of e−aq and HO lie in the range 0.5–3.3 × 1010 M−1 s−1. The d and bis-adduct monoanion radicals display sharp absorption peaks around 1000 nm (ϵ = 7 000–11 500 M−1 cm−1); the anions of the tris-, tetra-, and penta-adduct derivatives have broader, weaker absorptions. The monohydroxylated radicals have their most intense absorption maxima around 390–440 nm (ϵ = 1000–3000 M−1 cm−1). The anion and hydroxylated radical absorption spectra display a blue-shift as the number of addends increases. The radical anions react with oxygen (k ∼ 107–109 M−1 s−1). The reaction of O2•− with the C60 derivatives does not occur via an electron transfer. The rate constants for singlet oxygen reaction with the dendrofullerene and eee-derivative in D2O at pH 7.4 are k ∼ 7 × 107 and ∼ 2 × 107 M−1 s−1 respectively, in contrast to ∼ 1.2 × 105 M−1 s−1 for the reaction with C60 in C6D6. The large acceleration of the rates for electron reduction and singlet oxygen reactions in water is due to a solvophobic process.