Production and consumption of reactive oxygen species by fullerenes

Abstract

Reactive oxygen species (ROS) are one of the most important intermediates in chemical, photochemical, and biological processes. To understand the environmental exposure and toxicity of fullerenes better, the production and consumption of ROS (singlet oxygen, superoxide, hydrogen peroxide, and hydroxyl radicals) by Buckminster fullerene (C(60) ) and fullerenol were investigated in aqueous systems. Fullerenol exhibits higher photoproduction efficiency of singlet oxygen and superoxide than aqueous suspensions of C(60) aggregates (aqu/nC(60) ), and this higher efficiency results in higher steady-state concentrations of these two ROS. Transmission electron microscopy indicates that the C(60) molecules in aqu/nC(60) are much more closely packed than the C(60) cages in fullerenol. These observations provide additional evidence that the lower ROS production efficiency of aqu/nC(60) is attributable primarily to efficient self-quenching of C(60) triplet states. Production of singlet oxygen by aqu/nC(60) is accelerated by increasing oxygen concentration and in part is sensitized by fluorescent photoproducts that accumulate during irradiation. The fullerenes react slowly with singlet oxygen (second-order rate constant <4 × 10(5) M(-1) s(-1) ), but react rapidly with hydroxyl radicals (second-order rate constants of 5.4 × 10(9) and 4 × 10(8) M(-1) s(-1) for aqu/nC(60) and fullerenol, respectively). These results show that environmental conditions, including light exposure and oxygen concentration, have the potential to impact the generation of toxic ROS by fullerenes.

Long-Lifetime and Asymmetric Singlet Oxygen Photoluminescence from Aqueous Fullerene Suspensions

“…Thus, the O 2 (a 1 Δ) generated within the suspended nC 60 aggregates should not react with FFA dissolved in water and cannot be detected via FFA, which seems to, similar to the results by Bilski et al, 21 also conflict with the reports by Hou et al 19 and Kong et al 20 However, different from the report by Bilski et al, our measured lifetime for O 2 (a 1 Δ) within the nC 60 aggregates is ∼10 3 times longer than their value, which results in that a small quantity of O 2 (a 1 Δ) generated within the nC 60 aggregates can diffuse out of the aggregates within their lifetimes to form the unrestricted O 2 (a 1 Δ) in the bulk phase. Of course, it is clear that these bulkphase O 2 (a 1 Δ) can be detected by FFA, especially when the nC 60 suspensions are continuously irradiated for a very long time, which was respectively up to 20 and 100 h in the reports by Hou et al 19 and Kong et al 20 On the other hand, in contrast to the O 2 (a 1 Δ) trapped within the nC 60 aggregates, these bulk-phase O 2 (a 1 Δ) are completely negligible for our spectral and lifetime measurement owing to their small quantity and short lifetime of ∼4 μs in water, 25 which can also be further confirmed by our measured PL spectra from several C 60 -ethanol suspensions (see Figure S5). 32 Significantly, considering C 60 is nearly insoluble in water, our results actually imply that the bulk-phase O 2 60 should mainly take place in the interior of nC 60 , which can change in some extent our general understanding of the O 2 (a 1 Δ) formation mechanism in aqueous nC 60 suspensions and will influence one's estimation on the fate, transport, and toxicity of fullerenes in the aqueous environment.…”

Methylmercury Photodegradation in Surface Water of the Florida Everglades: Importance of Dissolved Organic Matter-Methylmercury Complexation

“…In addition, the photodegradation of MeHg−DOM complexes may also be driven by free radicals/reactive oxygen species (pathway 2) (e.g., organic radicals, ·OH and Figure S2) (Figure 2a and b). As the production of free radicals/reactive oxygen species is expected to increase under oxic conditions and decrease under anoxic conditions, 34,35 these results indicate that free radicals/reactive oxygen species may not play an important role in MeHg photodegradation in Everglades water. As this critical factor was often omitted in previous studies, the conclusion that free radicals/reactive oxygen species are the dominant factor (Figure 3d) was very slow (approximately 10% of that in Everglades water under solar radiation), indicating that 1 O 2 should not be a primary driver of MeHg photodegradation.…”

Novel interfaces for light directed neuronal stimulation: advances and challenges

“…The use of pure P3HT may reduce material toxicity during light exposure, as fullerene photoexcitation has been reported to produce ROS. 129 An ITO substrate was spin-coated with the polymer, followed by poly-L-lysine coating. Viability staining assays and patch-clamp recordings were used to validate biocompatibility.…”