Light-Independent Reactive Oxygen Species (ROS) Formation through Electron Transfer from Carboxylated Single-Walled Carbon Nanotubes in Water

Abstract

Promising developments in application of carbon nanotubes (CNTs) have raised concern regarding potential biological and environmental effects upon their inevitable release to the environment. Although some CNTs have been reported to generate reactive oxygen species (ROS) under light, limited information exists on ROS generation by these materials in the dark. In this study, generation of ROS was examined, initiated by electron transfer from biological electron donors through carboxylated single-walled carbon nanotubes (C-SWCNT) to molecular oxygen in water in the dark. In the presence of C-SWCNT, the oxidation of NADH (β-nicotinamide adenine dinucleotide, reduced form) and DTTre (DL-dithiothreitol, reduced form) was confirmed by light absorbance shifts (340 nm to 260 nm during oxidation of NADH to NAD(+), and increased light absorbance at 280 nm during oxidation of DTTre). Production of superoxide anion (O2(•-)) was detected by its selective reaction with a tetrazolium salt (NBT(2+)), forming a formazan product that is visible at 530 nm. A modified acid-quenched N,N-diethyl-p-phenylenediamine (DPD) assay was used to measure the accumulation of H2O2 in C-SWCNT suspensions containing O2 and NADH. In the same suspensions (i.e., containing C-SWCNT, NADH, and O2), pBR322 DNA plasmid was cleaved, although •OH was not detected when using •OH scavenging molecular probes. These results indicate that the oxidation of electron donors by C-SWCNT can be a light-independent source of ROS in water, and that electron shuttling through CNTs to molecular oxygen may be a potential mechanism for DNA damage by this specific CNT and potentially other carbon-based nanomaterials.

Biomolecular Interactions and Biological Responses of Emerging Two-Dimensional Materials and Aromatic Amino Acid Complexes

“…It is well known that the presenceπ bonds in nanocarbons can promote electron-transfer reactions (which is also evident in our electrochemistry results described in Fig. 4) in biomolecules and can generate ROS by acting as redox mediators 37 . The DCF fluorescence intensity showed only slight changes in ROS levels for graphene and its associated amino acid complexes.…”

Reduced graphene oxide-catalyzed oxidative coupling reaction of 4-methoxyphenol in aerobic aqueous solution

“…This result gave us an implication that H 2 O 2 should not be the final reductive product and can be reduced further in the following reaction. Indeed, it had been reported that rGO can promote the decomposition of H 2 O 2 in the dark [20]. As mentioned above, OH was also found to take part in the oxidative coupling reaction of MOP.…”

Electricity-induced catalytic oxidation of RhB by O2 at a graphite anode

“…Firstly, the carbon atoms in carbon materials are either sp 2 or sp 3 hybridized, while the sp 2 hybridized carbon atoms are able to participate in electro-transfer reactions. The singlewalled carbon nanotube is known to act as redox mediator in some biological systems which uses the large array of conjugated C¼C bonds to shuttle electrons from biological electron donors to electron acceptors [20,21]. Secondly, since nearly all carbon surfaces are prone to reactions with O 2 and H 2 O, oxygencontaining groups are present on a vast majority of carbon materials [5].…”

“…Specifically, in the presence of O 2 this process is dominated by the anode-catalyzed O 2 -oxidation mechanism in which the O 2 performs as the oxidant and the unsaturated functional groups in graphite play a catalyzing role. Such a catalytic reaction is analogue to that happens on the carbon nanotubes, in which the O 2 is firstly absorbed on the carbon nanotubes and then added across the C¼C bond to form transition species with reaction characteristics resemble to that of the peroxyl radical [21,25]. Since the RhB is partially degraded rather than totally mineralized, the anode-catalyzed O 2 -oxidation mechanism presents lower oxidation power than the OH oxidation mechanism.…”