2-2-dimethyl-5-hydroxy-1-pyrrolidinyloxy and 2-chlorophenol

Additional experimental evidence is presented for in vitro generation of hydroxyl radicals because of redox cycling of environmentally persistent free radicals (EPFRs) produced after adsorption of 2-monochlorophenol at 230 °C (2-MCP-230) on copper oxide supported by silica, 5% Cu(II)O/silica (3.9% Cu). A chemical spin trapping agent, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), in conjunction with electron paramagnetic resonance (EPR) spectroscopy was employed. Experiments in spiked O(17) water have shown that ∼15% of hydroxyl radicals formed as a result of redox cycling. This amount of hydroxyl radicals arises from an exogenous Fenton reaction and may stay either partially trapped on the surface of particulate matter (physisorbed or chemisorbed) or transferred into solution as free OH. Computational work confirms the highly stable nature of the DMPO-OH adduct, as an intermediate produced by interaction of DMPO with physisorbed/chemisorbed OH (at the interface of solid catalyst/solution). All reaction pathways have been supported by ab initio calculations.

Topics: Adsorption; Chlorophenols; Copper; Cyclic N-Oxides; Electron Spin Resonance Spectroscopy; Hydroxyl Radical; Particulate Matter; Silicon Dioxide; Solutions

Reactive oxygen species (ROS) generated by environmentally persistent free radicals (EPFRs) of 2-monochlorophenol, associated with CuO/silica particles, were detected using the chemical spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), in conjunction with electron paramagnetic resonance (EPR) spectroscopy. Yields of hydroxyl radical ((•)OH), superoxide anion radical (O(2)(•-)), and hydrogen peroxide (H(2)O(2)) generated by EPFR-particle systems were reported. Failure to trap superoxide radicals in aqueous solvent, formed from reaction of EPFRs with molecular oxygen, results from fast transformation of the superoxide to hydrogen peroxide. However, formation of superoxide as an intermediate product in hydroxyl radical formation in aprotic solutions of dimethyl sulfoxide (DMSO) and acetonitrile (AcN) was observed. Experiments with superoxide dismutase (SOD) and catalase (CAT) confirmed formation of superoxide and hydrogen peroxide, respectively, in the presence of EPFRs. The large number of hydroxyl radicals formed per EPFR and monotonic increase of the DMPO-OH spin adduct concentration with incubation time suggest a catalytic cycle of ROS formation.

Topics: Animals; Catalase; Cattle; Chlorophenols; Cyclic N-Oxides; Electron Spin Resonance Spectroscopy; Environmental Pollutants; Hydrogen Peroxide; Hydroxyl Radical; Iron; Oxidation-Reduction; Reactive Oxygen Species; Solutions; Solvents; Superoxide Dismutase; Superoxides; Water