First Direct In Situ EPR Spectroelectrochemical Evidence of the Superoxide Anion Radical

Abstract

For the first time, the superoxide anion radical was formed by electrochemical reduction of oxygen and detected in situ by EPR spectroscopy without changing the temperature. The spin susceptibilities of solid superoxide solutions were measured between 280 and 4 K showing Curie behavior. The EPR results were explained in the frame of an ion association and support the formation of a loose ion pair between the superoxide anion radical and the potassium crown ether complex. An alternative explanation for the large EPR line width of the superoxide anion radical at higher temperatures is given.

Highly Characteristic Adsorption Based on Single Crystal {001}-TiO2 Surface Molecular Recognition Promotes Enhanced Oxidation

“…The EPR spectrum consists of four spectral peaks with an intensity ratio of 1:2:2:1 responding to the typical EPR spectrum of DMPO–OH which is obtained by the reaction of DMPO and • OH . The characteristic peaks of other radicals were not observed. , When MI-TiO 2 was used as photocatalyst, the signal of DMPO–OH adduct was very weak, indicating that ordinary polycrystalline TiO 2 nanoparticles can only produce very small amount of • OH. But when single crystal 001-MI-TiO 2 nanosheets were used as photocatalyst, the signal of DMPO–OH adduct became very significant.…”

Transformation of Formazanate at Nickel(II) Centers to Give a Singly Reduced Nickel Complex with Azoiminate Radical Ligands and Its Reactivity toward Dioxygen

“…As mentioned above, after the reaction between 2 and O 2 , the observed signal had a g zz value of 2.045, that is, lower than one should expect, which may be a consequence of the additional presence of 18-c-6 and a solvent. Indeed, in 2011, Büchner and co-workers found that 18-c-6 leads to a line broadening of the EPR spectrum of the superoxide radical anion and also changes of the g anisotropy …”

“…Indeed, in 2011, Buchner and co-workers found that 18-c-6 leads to a line broadening of the EPR spectrum of the superoxide radical anion and also changes of the g anisotropy. 40 Apparently, binding of the superoxide radical anion to the nickel center is not favorable, likely because of the relatively stable square-planar coordination environment of the nickel-(II) center in 3. However, this is the basis on which many catalysts employed industrially for oxidation reactions with O 2 work.…”

Critical Comparison of the Superoxide Dismutase-like Activity of Carbon Antioxidant Nanozymes by Direct Superoxide Consumption Kinetic Measurements

“…] as frozen samples at μM to mM concentrations. 31,32,35 for its fast kinetic change 22,36−38 and are therefore advantageous over FQ-EPR or RFQ-EPR.…”

“…On the other hand, electron paramagnetic resonance (EPR) can be used to monitor the EPR signal of SO, allows for a temporally sufficient supply of SO, and is free of optical interference due to nanozymes. SO anion radical exhibits easily distinguishable EPR features of axial symmetry, and the EPR method has been used to successfully characterize the kinetics of [SO] in elucidating the reaction mechanism of alternative function as SO synthase of nitric oxide synthase. − Recently the steady-state kinetics of nanozyme PEG-HCCs and its simplified analogue, perylene diimide, , were quantified using manual freeze or rapid-freeze quench combined with EPR (FQ-EPR or RFQ-EPR) to directly measure [O 2 –• ] as frozen samples at μM to mM concentrations. ,, However, FQ-EPR or RFQ-EPR requires a substantial amount of sample and is extremely time-consuming in building a kinetic curve. Alternatively, stopped-flow kinetic measurements allow for mixing of sufficient SO with SO-quenching catalysts to directly follow the UV absorbance of SO for its fast kinetic change ,− and are therefore advantageous over FQ-EPR or RFQ-EPR.…”