Oxidation Of Oxalate Research Articles

Reductive Electrosynthesis Initiated By Mediated Oxalate Oxidation

Reductive electrosynthesis often requires large negative potentials, air-sensitive electrocatalysts, precious metal electrode surfaces, dry solvent, and/or a sacrificial anode. As a result, electroorganic reduction reactions remain relatively underdeveloped compared to oxidative electroorganic methods. This work introduces a novel reductive electrosynthetic method, wherein the mediated oxidation of oxalate (C2O4 2–) at a carbon electrode facilitates the homogeneous reduction of aryl halides. Specifically, the homogeneous oxidation of C2O4 2– in mixed organic/aqueous solutions by electrochemically generated 1,1-dimethylferrocenium (E 0 (DiMeFc+/DiMeFc) = 0.35 V vs Ag/AgCl) produces the strongly reducing CO2 ·– (E 0 (CO2/ CO2 ·–) = –2.17 V vs Ag/AgCl), capable of reducing species whose reduction potential exceeds –2.0 V. Thus, strongly reducing conditions are achieved under mild applied potentials (0.4 V vs Ag/AgCl) at a carbon electrode, thereby eliminating the need for large negative potentials, air-sensitive homogeneous electrocatalysts, and precious metal heterogeneous electrocatalysts. Additionally, the hydrogen evolution reaction serves as a convenient counter-electrode reaction eliminating the need for a sacrificial anode/oxidant. Furthermore, additions of H2O can be used to tune the reaction efficiency. Overall, this method demonstrates that reduction reactions that typically require potentials of approximately –2.0 V vs Ag/AgCl can be carried out at 0.4 V vs Ag/AgCl using an inexpensive, commercially available iron-based electrocatalyst at a carbon electrode. Figure 1

Water film-mediated photocatalytic oxidation of oxalate on TiO2

Water films on minerals under humid environment can be photocatalytic hotspots when exposed to sunlight or artificial sources of ultraviolet (and visible) radiation. In this study, we resolved the water film-mediated photocatalysis of oxalate adsorbed on TiO2 using in situ infrared spectroscopy. We found that 0.5 to 4 monolayer- (ML) thick water films enhanced the photodecomposition rates of oxalate under 21 kPa O2. We explained this through the combined actions of direct hole transfer, ligand-to-metal-charge transfer, as well as the production of hydroxyl radicals and reactive oxygen species. Rates were, however, substantially slower in the absence of O2 because charge recombination, together with water film-mediated charge localization, disrupted hole transfer and hydroxyl radical production. Our work adds insight into the impact of humidity on controlling important photocatalytic processes in nature (drying soils, atmospheric aerosols), and technology (water and air treatment).

Cooperative NHC/Photoredox Catalysis: Three‐Component Reaction of Aroyl Fluorides, Styrenes and Oxalates

Comprehensive SummaryCooperative NHC/photoredox catalysis has emerged as an important research field in recent years. Herein, this article describes the use of cesium salt derivatives of tert‐alcohols as alkyl radical precursors in a three‐component reaction with styrene and aromatic acyl fluorides to synthesize α‐arylalkyl aryl ketones. The aroyl fluoride reacts with the NHC catalyst, leading to the formation of an acyl azolium ion. This acyl azolium ion can then be reduced by the photoredox catalyst, generating the corresponding ketyl radical anion. The C‐radical generated from oxalate oxidation undergoes an addition reaction with the styrene derivative, followed by cross‐coupling of the addition radical with the ketone radical, which is fragmented by NHC to give the target ketone.

Two-dimensional modeling of CO2 mineral trapping through the oxalate‑carbonate pathway: Influence of the root system model

Two-dimensional reactive transport models, one with a simplified root system and the other accounting for dynamically evolving root architecture, were constructed to examine the influence of model complexity on capturing the effect of soil-root dynamics relating to the Oxalate Carbonate Pathway (OCP) of the Iroko tree over 170 years. Oxidation of oxalate from fallen tree tissue by soil bacteria enables local soil pH increase, leading to the sequestration of atmospheric carbon in carbonate minerals (calcite) in the shallow soil surrounding the tree. Simulations of both root models corroborate previous one-dimensional models of the OCP focused on Ca and C mass balance, where high weathering rates of Ca-containing silicate minerals in bedrock, along with contributions from groundwater, provided sufficient Ca for precipitation of observed quantities of calcite. Both simulations demonstrate the development of a distinct high pH zone where oxalate is oxidized, Ca accumulates, and calcite precipitates (OCP zone); and a low pH zone where roots collect Ca, later returned to the top soil as calcium oxalate (Total Root Extent/TRE zone) via litterfall. While the extent of OCP zone development near the ground surface was very similar between simulations, differences in localized root water uptake between the two approaches resulted in variation in water and solute transport and influenced the geometry of the OCP zone at depth, with implications for calcite precipitation in the soil. Trends in CO2 and O2 partial pressures in the OCP zone were mirrored in the TRE zone, suggesting linkage between the two zones with regard to gas transport. Near the end of the tree's lifespan, results indicate that soil permeability decreases due to calcite precipitation may limit O2 ingress and availability in the shallow soil, while trapping CO2 released from the oxidation of organics in the shallow soil, with implications for the long-term sustainability of the OCP itself.

Kinetic Modeling-Assisted Optimization of the Peroxone (O3/H2O2) Water Treatment Process

In this work, we investigate the influence of H2O2 dosage, H2O2 dosing method, and electron-rich dissolved organic matter (DOM) on the performance of the peroxone (O3/H2O2) process using oxalate (OA) as the target organic compound. Our results show that the method used for H2O2 dosing (i.e., single, multiple, and/or continuous injection(s)) has a significant influence on OA removal after 1 h with nearly 100% of OA oxidized by continuous injection of a total of 1 mM H2O2, but only 48 and 80% OA were removed when the same amount of H2O2 (1 mM) is applied in single and multiple injection(s), respectively. Inhibition of futile scavenging of •OH by H2O2 when H2O2 is dosed in smaller amounts either frequently or continuously throughout the process results in a higher efficiency of organic oxidation compared to that achieved with a single injection of a high concentration of H2O2 at the outset. Our results further show that the presence of high concentrations of humic acids (HA, a representative electron-rich DOM) promotes O3 decay and concomitant •OH generation rates and, as a result, significantly enhances the oxidation rate of OA by ozone alone. As such, any enhancement in •OH generation and associated OA oxidation that might be achieved by H2O2 addition in the presence of HA will be dependent on the extent of •OH generation that results from HA-promoted O3 decay. Based on our results, we have developed a mathematical model that can be used to predict •OH generation and OA oxidation by the peroxone process over a range of conditions. The model provides a good description of the influence of various operating parameters (including ozone dosage, H2O2 dosage, H2O2 dosing method, and the presence of HA) on OA oxidation and, potentially, can be used to optimize the choice of operating conditions in full-scale peroxone systems.

Electroorganic synthesis in aqueous solution via generation of strongly oxidizing and reducing intermediates.

Water is the ideal green solvent for organic electrosynthesis. However, a majority of electroorganic processes require potentials that lie beyond the electrochemical window for water. In general, water oxidation and reduction lead to poor synthetic yields and selectivity or altogether prohibit carrying out a desired reaction. Herein, we report several electroorganic reactions in water using synthetic strategies referred to as reductive oxidation and oxidative reduction. Reductive oxidation involves the homogeneous reduction of peroxydisulfate (S2O82-) via electrogenerated Ru(NH3)62+ at potential of -0.2 V vs. Ag/AgCl (3.5 M KCl) to form the highly oxidizing sulfate radical anion (E0' (SO4˙-/SO42-) = 2.21 V vs. Ag/AgCl), which is capable of oxidizing species beyond the water oxidation potential. Electrochemically generated SO4˙- then efficiently abstracts a hydrogen atom from a variety of organic compounds such as benzyl alcohol and toluene to yield product in water. The reverse analogue of reductive oxidation is oxidative reduction. In this case, the homogeneous oxidation of oxalate (C2O42-) by electrochemically generated Ru(bpy)33+ produces the strongly reducing carbon dioxide radical anion (E0' (CO2˙-/CO2) = -2.1 V vs. Ag/AgCl), which can reduce species at potential beyond the water or proton reduction potential. In preliminary studies, the CO2˙- has been used to homogeneously reduce the C-Br moiety belonging to benzyl bromide at an oxidizing potential in aqueous solution.

ISOLATION, SCREENING, AND PARTIAL CHARACTERIZATION OF OXALATE OXIDASE ENZYME FROM PSEUDOMONAS STRAIN UNDER INDUCED OXALATE STRESS CONDITION

Oxalate oxidase (OxO), a manganese dependent enzyme, is involved in the catalysis of oxalate oxidation to carbon dioxide with the formation of hydrogen peroxide. OxO is present in the cell wall of plants. It increases the resistivity against diseases and external stress. Oxalate is found as waste metabolites in mammals, excess accumulation of oxalate results in hyperoxaluria and urolithiasis in humans. These disorders can be diagnosed by the help of OxO in many analytical methods. The present study is aimed on isolation of OxO enzyme from Pseudomonas strain under high salt stress. The OxO enzyme was produced in bulk under selected salt stress. It was partially purified by ammonium sulphate precipitation method, dialysis and ion-exchange chromatography. The OxO enzyme on enzymatic analysis showed potent activity concerning oxalic acid substrate. The microtiter plate analysis confirmed the ability of OxO enzyme purified from Pseudomonas strain in the diagnosis of oxalate-related disorders and in the future could be used to prepare the diagnostic biosensors.

ISOLATION, SCREENING, AND PARTIAL CHARACTERIZATION OF OXALATE OXIDASE ENZYME FROM PSEUDOMONAS STRAIN UNDER INDUCED OXALATE STRESS CONDITION

Oxalate oxidase (OxO), a manganese dependent enzyme, is involved in the catalysis of oxalate oxidation to carbon dioxide with the formation of hydrogen peroxide. OxO is present in the cell wall of plants. It increases the resistivity against diseases and external stress. Oxalate is found as waste metabolites in mammals, excess accumulation of oxalate results in hyperoxaluria and urolithiasis in humans. These disorders can be diagnosed by the help of OxO in many analytical methods. The present study is aimed on isolation of OxO enzyme from Pseudomonas strain under high salt stress. The OxO enzyme was produced in bulk under selected salt stress. It was partially purified by ammonium sulphate precipitation method, dialysis and ion-exchange chromatography. The OxO enzyme on enzymatic analysis showed potent activity concerning oxalic acid substrate. The microtiter plate analysis confirmed the ability of OxO enzyme purified from Pseudomonas strain in the diagnosis of oxalate-related disorders and in the future could be used to prepare the diagnostic biosensors.

Key Considerations When Assessing Novel Fenton Catalysts: Iron Oxychloride (FeOCl) as a Case Study.

Iron oxychloride (FeOCl) has been reported to be a highly efficient heterogeneous Fenton catalyst over a wide pH range. In order to determine the true catalytic performance of FeOCl, we simultaneously quantified the adsorptive and oxidative removal of formate, oxalate, and rhodamine-B (RhB) and the formation of RhB oxidation products at both pH 4.0 and 7.0. FeOCl was found to be a poor Fenton catalyst at either pH, as gauged by the oxidation of formate, oxalate, and rhodamine B and the decomposition of H2O2, in comparison with ferrihydrite (Fhy), one of the most common Fe-containing Fenton catalysts. The adsorption of target contaminants to FeOCl and homogeneous Fenton processes, induced by dissolved iron, resulted in overevaluation of the catalytic performance of FeOCl, especially for (i) the use of strongly adsorbing target compounds, without consideration of the role of adsorption in their removal and (ii) exceedingly high concentrations of H2O2 to remove trace quantities of target contaminants. Overall, this study highlights that the systematic quantification of H2O2 decomposition, target compound adsorption, and oxidation as well as the concentrations of oxidized products formed are prerequisites for unequivocal elucidation of the catalytic nature and reaction mechanism of solid Fenton catalysts.

Kinetic Modeling-Assisted Mechanistic Understanding of the Catalytic Ozonation Process Using Cu-Al Layered Double Hydroxides and Copper Oxide Catalysts.

In this study, copper aluminum layered hydroxides (Cu-Al LDHs) and copper oxide (CuO) were utilized as catalysts for heterogeneous catalytic ozonation (HCO). Target compounds oxalate and formate were used with removal by adsorption and oxidation quantified to elucidate the role of the catalyst in contaminant removal. Oxidation of oxalate mostly occurred on the catalyst surface via interaction of surface oxalate complexes with surface-located oxidants. In contrast, the oxidation of formate occurred in the bulk solution as well as on the surface of the catalyst. Measurement of O3 decay kinetics coupled with fluorescence microscopy image analysis corresponding to 7-hydroxycoumarin formation indicates that while surface hydroxyl groups in Cu-Al LDHs facilitate slow decay of O3 resulting in the formation of hydroxyl radicals on the surface, CuO rapidly transforms O3 into surface-located hydroxyl radicals and/or other oxidants. Futile consumption of surface-located oxidants via interaction with the catalyst surface was minimal for Cu-Al-LDHs; however, it becomes significant in the presence of higher CuO dosages. A mechanistic kinetic model has been developed which adequately describes the experimental results obtained and can be used to optimize the process conditions for the application of HCO.

Interfacial photoreactions of Cr(VI) and oxalate on lepidocrocite surface under oxic and acidic conditions: Reaction mechanism and potential implications for contaminant degradation in surface waters

The transformation of contaminants by photocatalysts under light illumination has been extensively studied in engineered water systems. However, the interfacial photoreaction mechanism for the reduction of chromium (Cr(VI)) on natural iron (Fe) oxides in acidic and oxic surface waters associated with soil remain unclear. Herein, the photochemical behavior of Cr(VI) and oxalate on lepidocrocite surfaces was investigated to disclose the natural detoxification process of Cr(VI). Kinetic results showed that Cr(VI) was quickly reduced in the system with lepidocrocite and oxalate under light illumination, while no Cr(VI) reduction was observed in the dark. No obvious secondary Fe oxides and Cr-containing precipitates were found, but the newly generated Cr(III) was evenly distributed on the lepidocrocite surface or entered into the lepidocrocite defects. Cr(VI) and oxalate can form ternary complexes with lepidocrocite, and Cr(VI) reduction and the oxidation of oxalate to carbon dioxide occurred simultaneously on the lepidocrocite surface. Amongst the reactions involving lepidocrocite, oxalate, and Cr(VI), the oxidation of oxalate was attributed to reactive oxygen species such as H2O2, OH, and ·O2−, while Cr(VI) reduction was mainly caused by photogenerated electrons, CO2−, H2O2, Fe(II), and through the direct electron transfer in the Cr(VI)-oxalate complex. The findings of the Cr(VI) molecular-scale photoreduction mechanism on mineral surfaces would have implications for interpreting the natural attenuation of Cr(VI) toxicity in natural surface waters associated with soil.

Heterogeneous Fenton Chemistry Revisited: Mechanistic Insights from Ferrihydrite-Mediated Oxidation of Formate and Oxalate.

The heterogeneous Fenton process has been widely applied though some aspects of this process are still poorly understood. In this study, we simultaneously quantify the adsorption and decomposition of formate and H2O2 at pH 4.0 in the presence of freshly formed ferrihydrite and provide new insights into the ferrihydrite-induced heterogeneous Fenton mechanism with the aid of kinetic and reactive-transport modeling. Our results show that the decomposition of H2O2 and formate is controlled by surface-initiated reactions. Adsorbed formate occupies the surface sites otherwise available for reaction with H2O2 and therefore hampers the surface Fenton reactions despite the negligible accumulation of H2O2 on the surface. The minimal impact of methanol (an effective HO• scavenger) on formate oxidation as well as the poor oxidation of fully adsorbed oxalate compared with the ready oxidation of partially adsorbed formate demonstrates that oxidation mainly occurs in the solid-liquid boundary layer, rather than in bulk or on the surface. This is suggested to be due to the diffusion of surface-generated HO•, rather than surface Fe(II), to the boundary layer with the results of kinetic and reactive-transport modeling supporting this conclusion. The new findings are critical to our understanding of the removal behavior of more complex organic target species and to the design of more effective heterogeneous Fenton technologies.

Functional Diversity of the Litter-Associated Fungi from an Oxalate-Carbonate Pathway Ecosystem in Madagascar.

The oxalate-carbonate pathway (OCP) is a biogeochemical process linking oxalate oxidation and carbonate precipitation. Currently, this pathway is described as a tripartite association involving oxalogenic plants, oxalogenic fungi, and oxalotrophic bacteria. While the OCP has recently received increasing interest given its potential for capturing carbon in soils, there are still many unknowns, especially regarding the taxonomic and functional diversity of the fungi involved in this pathway. To fill this gap, we described an active OCP site in Madagascar, under the influence of the oxalogenic tree Tamarindus indica, and isolated, identified, and characterized 50 fungal strains from the leaf litter. The fungal diversity encompassed three phyla, namely Mucoromycota, Ascomycota, and Basidiomycota, and 23 genera. Using various media, we further investigated their functional potential. Most of the fungal strains produced siderophores and presented proteolytic activities. The majority were also able to decompose cellulose and xylan, but only a few were able to solubilize inorganic phosphate. Regarding oxalate metabolism, several strains were able to produce calcium oxalate crystals while others decomposed calcium oxalate. These results challenge the current view of the OCP by indicating that fungi are both oxalate producers and degraders. Moreover, they strengthen the importance of the role of fungi in C, N, Ca, and Fe cycles.

Effects of persulfate and hydrogen peroxide on oxidation of oxalate by pulsed corona discharge

Application of gas-phase pulsed corona discharge (PCD) to oxidation of aqueous pollutants shows unequalled energy efficiency among advanced oxidation processes (AOPs). Improved AOPs often activate extrinsic oxidants. Experimental research was undertaken into sodium persulfate and hydrogen peroxide activation by PCD in oxidation of 1.11 mM oxalate. Oxidant and target compound concentration ratios, pH, gas-liquid contact surface and pulse repetition frequency were studied as control parameters. Results implicated a beneficial effect at oxalate/persulfate molar ratios from 1:0.1 to 1:1 in acidic medium with the optimum at 1:0.5, moderate contact surface and lower frequency. However, the observed synergism of PCD/PS combination decreased with increasing the initial pH of the treated solution. Hydrogen peroxide exhibited negative or neutral impact in all media. Non-assisted PCD proved the most energy efficient approach towards water treatment at neutral and alkaline conditions.

Ultrasensitive Electrochemistry by Radical Annihilation Amplification in a Solid-Liquid Microgap.

We report a technique to amplify the electrochemical signal within micro- and nanodroplets via radical annihilation amplification. Toluene droplets filled with decamethylferrocene (DmFc) are suspended in an aqueous solution containing 10 mM NaClO4 and 10 μM Na2C2O4. When a toluene droplet irreversibly collides with an ultramicroelectrode biased sufficiently positive for concurrent oxidation of DmFc and oxalate (C2O42-), blip-type responses are observed in the amperometric i-t trace even when the concentration of DmFc is 50 nM. The toluene droplet wetting the ultramicroelectrode effectively creates a microgap, where DmFc molecules are oxidized to DmFc+. In the continuous phase, the oxidation of oxalate (C2O42-) produces a strong reducing agent, CO2•-. Regeneration of DmFc via radical annihilation amplifies the current, similar to conventional nanogap experiments. This experiment allows one to observe the electrochemistry of hundreds to thousands of molecules trapped in a femtoliter droplet, enhancing the sensitivity of droplet-based electrochemistry by 5 orders of magnitude. Finite element simulations validate our experimental results and indicate the importance of the droplet geometry to amplification.

Infuence of chemically synthesized copper nanoparticles and cupric ions on oxalate oxidation system in germinating Sorghum grain

We have earlier reported the effects of chemically synthesized copper nanoparticles (CuNPs) on oxalate oxidase (OxOx) activity, extracted from the shoot tissue of germinating grain sorghum i.e. in vitro. Here, we tried to study this effect in vivo and compare it with those of Cu2+. We describe herein, characterization of CuNPs and their effects on oxalate oxidation system i.e. OxOx activity, total oxalate and H2O2 content in vivo i.e. in shoot tissues/leaves of germinating grain Sorghum (Sorghum vulgare L). To achieve it, grain sorghum seeds were grown up to 10 days in laboratory, irrigated with Hoagland’s solution containing either CuNPs (1.0 ppm) or Cu2+ (1.0 ppm) after 4 days of germination. Control were irrigated with Hoagland solution only. The shoot/leaves of the seedling plants were harvested at 4, 6, 8 and 10 day of germination and analysed quantitatively for OxOx activity, soluble protein, H2O2 and total oxalate. The growth of the Sorghum seedling plants supplemented with CuNPs and Cu2+ was decreased significantly (P <0.1) at all growth stages compared to control. This inhibitory effect of CuNPs was higher than Cu2+. CuNPs decreased the activity of OxOx but Cu2+ had no effect at day 10. Both CuNPs and Cu2+ decreased the specific activity of OxOx and H2O2 content but increased total oxalate content at day 10. The decrease in H2O2 content in both CuNPs and Cu2+ supplemented shoot tissues with concomitant increase in oxalate content confirmed the decreased activity of OxOx in CuNPs and Cu2+ supplemented seedling plants.

Distinct response patterns of soil bacteria to oxalate imply their role in buffering soil acidification: Evidence from red soils with long‐term fertilisation regimes

AbstractLong‐term chemical‐only fertilisation (NPK) decreases soil pH, but this soil acidification is rarely reported with manure fertilisation (M). Soil acidification always leads to a negative effect on sustainable development. As oxalate oxidation is accompanied by soil alkalisation, it is still unknown how and to what extent bacterial oxalate oxidation in soils with different fertilisation regimes contributes to buffering of soil acidification. To assess the potential role of oxalotrophy in buffering soil acidification, two soils that underwent contrasted fertilisation regimes for over 30 years were used. The oxalotrophic communities were characterised based on a biomarker of oxalotrophic taxa (the frc gene), and their responsiveness to calcium oxalate (CaOx) addition was assessed. In addition, stable isotope probing was employed to explore the active bacteria responding to CaOx addition. Despite similar abundances of oxalotrophic bacteria between NPK and M soils before microcosm incubation, the M soil harboured more oxalotrophic bacteria belonging to Deltaproteobacteria, and the NPK soil was colonised by more oxalotrophic bacteria affiliated with Actinobacteria, Alphaproteobacteria, and Betaproteobacteria. In the incubation experiments, the M soil took half of the time that the NPK soil needed to deplete the added CaOx. The faster CaOx consumption rate could be explained by the higher functional redundancy and higher proportion of fast‐response oxalotrophic taxa in M soil. The most dominant active oxalotrophic taxa were Oxalicibacterium and Burkholderia in the M and NPK soils, respectively. Furthermore, the better performance of oxalate oxidation was conjectured to contribute to a higher soil acidification buffering ability. This study obtained an important cue to the feasibility of active oxalotrophic taxa in buffering acidification in soils with different fertilisation regimes, which provides valuable evidence for exploring alternative ways for alleviating soil acidification.

Direct Observation of C2O4•- and CO2•- by Oxidation of Oxalate within Nanogap of Scanning Electrochemical Microscope.

Oxalate oxidation in the presence of different oxidized luminophores leads to the emission of light and has been studied extensively in electrogenerated chemiluminescence (ECL). The proposed mechanism involves the initial formation of the oxalate radical anion, C2O4•-. The ensuing decomposition of C2O4•- produces a very strong reductant, CO2•-, which reacts with the oxidized luminophores to generate excited states that emit light. Although the mechanism has been proposed for decades, the experimental demonstration is still lacking, because of the complexity of the system and the short lifetimes of both radical anions. To address these issues, we studied oxalate oxidation at platinum ultramicroelectrodes (UMEs) in anhydrous N, N-dimethylformamide (DMF) solution by nanoscale scanning electrochemical microscopy (SECM) with the tip generation/substrate collection (TG/SC) mode. A Pt nanoelectrode was utilized as the SECM generator for oxalate oxidation, while another Pt UME served as the SECM collector and was used to capture the generated intermediates. We studied the influence of the gap distance, d, on the substrate current ( is). The results indicate that, when 73 nm < d < 500 nm, the species captured by the substrate were primarily CO2•-, while C2O4•- was the predominant intermediate measured when d was below 73 nm. A half-life of 1.3 μs for C2O4•- was obtained, which indicates a stepwise mechanism for oxalate oxidation. The relevance of these observations to the use of oxalate as the coreactant in ECL systems is also discussed.

Large Magneto-Current Effect in the Electrochemical Detection of Oxalate in Aqueous Solution

Herein, we first report an interesting observation of a large magneto-current (MC) of nearly 30% based on the electrochemical oxidation of oxalate in aqueous solution at room temperature. The large MC is ascribed to spin-dependent oxidation of oxalate. Both singlet and triplet radical pairs are generated during the electrochemical oxidation of oxalate. An applied magnetic field could accelerate the spin evolution of a singlet radical pair into its triplet state. The triplet radical pair has a much larger dissociation probability than the singlet radical pair because of the Pauli exclusion principle. Thus, enhancing the triplet yield could largely increase the oxidation rate of oxalate and generate significant MC. The significant MC effect provides a new approach to study spin evolution of radical pairs in electrochemical cells. Furthermore, an effective analytical method for oxalate determination can be developed based on the significant MC effect.

Immobilised Electrocatalysts: Nafion Particles Doped with Ruthenium(II) Tris(2,2'-bipyridyl).

Nafion particles doped with ruthenium(II) tris(2,2'-bipyridyl) are synthesized by using a re-precipitation method. Characterization including SEM sizing and quantification of Ru(bpy)32+ in the Nafion particles using UV/Vis spectroscopy was conducted. The synthesized Ru-Nafion particles were investigated electrochemically at both ensemble and single particle levels. Voltammetry of the drop-cast Ru-Nafion particles evidences the successful incorporation of Ru(bpy)32+ into the Nafion particle but only a small fraction of the incorporated Ru(bpy)32+ was detected due at least in part to the formation of the likely agglomerated and irregular "mat" associated with the dropcast technique. In contrast, nano-impact experiments provided a quantitative determination of the amount of Ru(bpy)32+ in single Ru-Nafion particles. Finally, oxidation of solution-phase oxalate mediated by Ru(bpy)32+ within individual Nafion particles was observed, showing the electrocatalytic properties of the Ru-Nafion particles.