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., O-2(.-) and O-2((1)Delta(g)) With 10 water-soluble cyclopropyl-fused C-60 derivatives including a mono-adduct dendro[60]fullerene (d) and C-60 derivatives based on C-60[C(COOH)(2)](n=2-6), some of which are known to be neuro-protective in vivo. The rate constants for reactions of e(aq)(-) and HO. lie in the range 0.5-3.3 x 10(10) M-1 s(-1). The d and bis-adduct monoanion radicals display sharp absorption peaks around 1000 nm (epsilon = 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 (epsilon = 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 similar to 10(7)-10(9) M-1 s(-1)). The reaction of O-2(.-) with the C-60 derivatives does not occur via an electron transfer. The rate constants for singlet oxygen reaction with the dendrofullerene and ece-derivative in D2O at pH 7.4 are k similar to 7 x 10(7) and similar to 2 x 10(7) M-1 s-(1) respectively, in contrast to similar to 1.2 x 10(5) M-1 s(-1) for the reaction with C-60 in C6D6. The large acceleration of the rates for electron reduction and singlet oxygen reactions in water is due to a solvophobic process. (C) 2000 Elsevier Science Inc.