title: Antioxidant deactivation on graphenic nanocarbon surfaces.
abstract: This article reports a direct chemical pathway for antioxidant deactivation on the surfaces of carbon nanomaterials. In the absence of cells, carbon nanotubes are shown to deplete the key physiological antioxidant glutathione (GSH) in a reaction involving dissolved dioxygen that yields the oxidized dimer, GSSG, as the primary product. In both chemical and electrochemical experiments, oxygen is only consumed at a significant steady-state rate in the presence of both nanotubes and GSH. GSH deactivation occurs for single- and multi-walled nanotubes, graphene oxide, nanohorns, and carbon black at varying rates that are characteristic of the material. The GSH depletion rates can be partially unified by surface area normalization, are accelerated by nitrogen doping, and suppressed by defect annealing or addition of proteins or surfactants. It is proposed that dioxygen reacts with active sites on graphenic carbon surfaces to produce surface-bound oxygen intermediates that react heterogeneously with glutathione to restore the carbon surface and complete a catalytic cycle. The direct catalytic reaction between nanomaterial surfaces and antioxidants may contribute to oxidative stress pathways in nanotoxicity, and the dependence on surface area and structural defects suggest strategies for safe material design.
authors.affiliation: Department of Chemistry, Brown University, Providence, RI, 02912, USA.
authors.forename: Xinyuan
authors.initials: X
authors.lastname: Liu
authors.forename: Sujat
authors.initials: S
authors.lastname: Sen
authors.forename: Jingyu
authors.initials: J
authors.lastname: Liu
authors.forename: Indrek
authors.initials: I
authors.lastname: Kulaots
authors.forename: David
authors.initials: D
authors.lastname: Geohegan
authors.forename: Agnes
authors.initials: A
authors.lastname: Kane
authors.forename: Alex A
authors.initials: AA
authors.lastname: Puretzky
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Rouleau
authors.forename: Karren L
authors.initials: KL
authors.lastname: More
authors.forename: G Tayhas R
authors.initials: GT
authors.lastname: Palmore
authors.forename: Robert H
authors.initials: RH
authors.lastname: Hurt
mesh_terms: D000975:Antioxidants / Q000737:chemistry / Q000378:metabolism*; D002374:Catalase / Q000378:metabolism; D002384:Catalysis; D055664:Electrochemical Techniques; D004566:Electrodes; D019803:Glutathione Disulfide / Q000737:chemistry; D006108:Graphite / Q000737:chemistry*; D037742:Nanotubes, Carbon / Q000737:chemistry* / Q000648:ultrastructure; D009584:Nitrogen / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D013482:Superoxide Dismutase / Q000378:metabolism; D013499:Surface Properties
chemical_list: D000975:Antioxidants; D037742:Nanotubes, Carbon; D006108:Graphite; D002374:Catalase; D013482:Superoxide Dismutase; D009584:Nitrogen; D010100:Oxygen; D019803:Glutathione Disulfide