Highly efficient conversion of superoxide to oxygen using hydrophilic carbon clusters

Proc Natl Acad Sci U S A. 2015 Feb 24;112(8):2343-8. doi: 10.1073/pnas.1417047112. Epub 2015 Feb 9.


Many diseases are associated with oxidative stress, which occurs when the production of reactive oxygen species (ROS) overwhelms the scavenging ability of an organism. Here, we evaluated the carbon nanoparticle antioxidant properties of poly(ethylene glycolated) hydrophilic carbon clusters (PEG-HCCs) by electron paramagnetic resonance (EPR) spectroscopy, oxygen electrode, and spectrophotometric assays. These carbon nanoparticles have 1 equivalent of stable radical and showed superoxide (O2 (•-)) dismutase-like properties yet were inert to nitric oxide (NO(•)) as well as peroxynitrite (ONOO(-)). Thus, PEG-HCCs can act as selective antioxidants that do not require regeneration by enzymes. Our steady-state kinetic assay using KO2 and direct freeze-trap EPR to follow its decay removed the rate-limiting substrate provision, thus enabling determination of the remarkable intrinsic turnover numbers of O2 (•-) to O2 by PEG-HCCs at >20,000 s(-1). The major products of this catalytic turnover are O2 and H2O2, making the PEG-HCCs a biomimetic superoxide dismutase.

Keywords: antioxidant; carbon nanoparticles; hydrophilic carbon clusters; superoxide; superoxide dismutase mimetic.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carbon / chemistry*
  • Catalysis
  • Electron Spin Resonance Spectroscopy
  • Hydrogen Peroxide / metabolism
  • Hydrogen-Ion Concentration
  • Hydrophobic and Hydrophilic Interactions*
  • Hydroxyl Radical / chemistry
  • Oxygen / chemistry*
  • Polyethylene Glycols / chemistry
  • Sodium Hydroxide / chemistry
  • Superoxide Dismutase / metabolism
  • Superoxides / chemistry*


  • Superoxides
  • Hydroxyl Radical
  • Polyethylene Glycols
  • Sodium Hydroxide
  • Carbon
  • Hydrogen Peroxide
  • Superoxide Dismutase
  • Oxygen