Delineating oxidative processes of aqueous C ₆₀ preparations: Role of THF peroxide

The oxidative reactivity of THF derivatives formed during THF/nC ₆₀ synthesis was evaluated with indigo dye as a model compound. The results showed that the formation of previously undetected oxidizing agents during THF/nC ₆₀ synthesis accounted for the degradation of indigo dye by THF/nC ₆₀ (THF/nC ₆₀/unwashed), while THF/nC ₆₀ after vigorous washing (THF/ nC ₆₀/washed) and nC ₆₀ prepared without the use of THFwere not reactive. γ-Butyrolactone (GBL) was detected by GC-MS in the THF/nC ₆₀/unwashed as one of THF derivatives, but showed no reactivity with indigo dye. An organic peroxide was detected in the THF/nC ₆₀/unwashed by HPLC,and was reactive with indigo dye. This compound was found to also account for the elevated antibacterial and bactericidal activities of THF/ nC ₆₀/unwashed on E. coli. Analysis by LC/(+ESI)MS and ¹H NMR showed that the detected THF peroxide was tetrahydro-2-(tetrahydrofuran-2- ylperoxy)furan. The formation of THF peroxide during the preparation of aqueous stable C ₆₀ aggregates provides another potential explanation for the reactivity and oxidative stress mechanisms of THF/nC ₆₀ system reported in the literature, although it does not exclude the potential reactivity and toxicity of nC ₆₀ itself.