Rate Of H2O2 Generation Research Articles

Iodide-Induced Fragmentation of Polymerized Hydrophilic Carbon Nitride for High-Performance Quasi-Homogeneous Photocatalytic H2 O2 Production.

Polymeric carbon nitride (PCN) as a class of two-electron oxygen reduction reaction (2 e- ORR) photocatalyst has attracted much attention for H2 O2 production. However, the low activity and inferior selectivity of 2 e- ORR greatly restrict the H2 O2 production efficiency. Herein, we develop a new strategy to synthesize hydrophilic, fragmented PCN photocatalyst by the terminating polymerization (TP-PCN) effect of iodide ions. The obtained TP-PCN with abundant edge active sites (AEASs), which can form quasi-homogeneous photocatalytic system, exhibits superior H2 O2 generation rate (3265.4 μM h-1 ), far surpassing PCN and other PCN-based photocatalysts. DFT calculations further indicate that TP-PCN is more favorable for electron transiting from β spin-orbital to the π* orbitals of O2 , which optimizes O2 activation and reduces the energy barrier of H2 O2 formation. This work provides a new concept for designing functional photocatalysts and understanding the mechanism of O2 activation in ORR for H2 O2 production.

Iodide‐Induced Fragmentation of Polymerized Hydrophilic Carbon Nitride for High‐Performance Quasi‐Homogeneous Photocatalytic H2O2 Production

AbstractPolymeric carbon nitride (PCN) as a class of two‐electron oxygen reduction reaction (2 e− ORR) photocatalyst has attracted much attention for H2O2 production. However, the low activity and inferior selectivity of 2 e− ORR greatly restrict the H2O2 production efficiency. Herein, we develop a new strategy to synthesize hydrophilic, fragmented PCN photocatalyst by the terminating polymerization (TP‐PCN) effect of iodide ions. The obtained TP‐PCN with abundant edge active sites (AEASs), which can form quasi‐homogeneous photocatalytic system, exhibits superior H2O2 generation rate (3265.4 μM h−1), far surpassing PCN and other PCN‐based photocatalysts. DFT calculations further indicate that TP‐PCN is more favorable for electron transiting from β spin‐orbital to the π* orbitals of O2, which optimizes O2 activation and reduces the energy barrier of H2O2 formation. This work provides a new concept for designing functional photocatalysts and understanding the mechanism of O2 activation in ORR for H2O2 production.

Palmitoyl-CoA effect on cytochrome c release, a key process of apoptosis, from liver mitochondria of rat with sucrose diet-induced obesity

Cytochrome c (cyt-c) release from the mitochondria to the cytosol is a key process in the initiation of hepatocyte apoptosis involved in the progression of non-alcoholic fatty liver disease (NAFLD) to fibrosis, cirrhosis and hepatocellular carcinoma. Hepatocyte apoptosis may be related to lipotoxicity due to the accumulation of palmitic acid and palmitoyl-CoA (Pal-CoA). Therefore, the aim of this study is to examine whether Pal-CoA induces cyt-c release from liver mitochondria of sucrose-fed rat (SF). Pal-CoA-induced cyt-c release was sensitive to cyclosporine A indicating the involvement of the mitochondrial membrane permeability transition (mMPT). In addition, cyt-c release from SF mitochondria remains significantly lower than C mitochondria despite the increased rate of H2O2 generation in SF mitochondria. The decreased cyt-c release from SF may be also related to the increased proportion of the palmitic acid-enriched cardiolipin, due to the high availibilty of palmitic acid in SF liver. The enrichment of cardiolipin molecular species with palmitic acid makes cardiolipin more resistant to peroxidation, a mechanism involved in the dissociation of cyt-c from mitochondrial inner membrane. These results suggest that Pal-CoA may participate in the progression of NAFLD to more severe disease through mechanisms involving cyt-c release and mMPT, a key process of apoptosis.

Graphene quantum dots piecing together into graphene on nano Au for overall water splitting

Utilizing photocatalysts to split water into H2 and H2O2 simultaneously is an ideal but challenging process to obtain clean H2 energy and high valuable H2O2. Most of the photocatalysts currently studied for the overall water splitting are converting water into H2 and O2, resulting in further need of gas separation. Here, we reported a photocatalyst which can utilize the nano-Au based localized surface plasmonic resonance (LSPR) effect to produce H2 and H2O2 simultaneously. Nitrogen doped graphene quantum dots (N-GQDs) pieced together into large graphene through a catalytic process by chloroauric acid, in which dodecahedron nano-Au particles can also be obtained concurrently. Then Au wrapped up by graphene can be in situ formed with good interfaces. Photocatalytic activity tests revealed that the as prepared graphene@Au catalysts show efficient photocatalytic overall water splitting activity with a H2 evolution rate of 65.6 μmol g−1 h−1 and H2O2 generation rate of 49.7 μmol g−1 h−1. This work provides a feasible route for the facile fabrication of graphene through the bottom-up polycondensation of N-GQDs by amide bonds and new insights into the synthesis of photocatalysts for overall water splitting into H2 and H2O2.

Ferric iron reduction reaction electro-Fenton with gas diffusion device: A novel strategy for improvement of comprehensive efficiency in electro-Fenton

Applying the optimal 2-electron oxygen reduction reaction potential in electro-Fenton (2e-ORR-EF) for degradation has become a common strategy because of the highest H2O2 generation rate in such condition. However, in 2e-ORR-EF system, the Fe(III) ions crystallize on the surface of cathode and form a layer of film according to SEM, XPS, XRD and Mössbauer spectrum resulting in poor reaction rate of EF. Hence, we propose FRR-EF, which is operated by applying the optimal potential of ferric iron reduction reaction (FRR) rather than that of 2e-ORR on cathode for EF. Gas diffusion device was also carried out to ensure the H2O2 generation rate. In this novel strategy, only − 0.1 V was applied on cathode. High H2O2 production rate (0.021 ± 0.002 mmol L−1 min−1 cm−2), and slow Fe(II) consumption rate (0.03 min−1) were achieved. The EIS result showed that at this potential, the formation of the Fe film was effectively alleviated, thus prolonging the degradation life of the cathode. This new strategy can balance both 2e-ORR and FRR, thus improving the comprehensive efficiency of EF, which provides essential references to the EF not only in potential operation but also in the design of reaction device.

The bionic sunflower: a bio-inspired autonomous light tracking photocatalytic system

Inspired by sunflowers, a bionic sunflower based on a photo-responsive smart hydrogel was used as a photocatalytic reactor and always exhibited a relatively stable and high H2O2 generation rate at any random angle of irradiation.

Kinetic modeling of H2O2 dynamics in the mitochondria of HeLa cells.

Hydrogen peroxide (H2O2) promotes a range of phenotypes depending on its intracellular concentration and dosing kinetics, including cell death. While this qualitative relationship has been well established, the quantitative and mechanistic aspects of H2O2 signaling are still being elucidated. Mitochondria, a putative source of intracellular H2O2, have recently been demonstrated to be particularly vulnerable to localized H2O2 perturbations, eliciting a dramatic cell death response in comparison to similar cytosolic perturbations. We sought to improve our dynamic and mechanistic understanding of the mitochondrial H2O2 reaction network in HeLa cells by creating a kinetic model of this system and using it to explore basal and perturbed conditions. The model uses the most current quantitative proteomic and kinetic data available to predict reaction rates and steady-state concentrations of H2O2 and its reaction partners within individual mitochondria. Time scales ranging from milliseconds to one hour were simulated. We predict that basal, steady-state mitochondrial H2O2 will be in the low nM range (2–4 nM) and will be inversely dependent on the total pool of peroxiredoxin-3 (Prx3). Neglecting efflux of H2O2 to the cytosol, the mitochondrial reaction network is expected to control perturbations well up to H2O2 generation rates ~50 μM/s (0.25 nmol/mg-protein/s), above which point the Prx3 system would be expected to collapse. Comparison of these results with redox Western blots of Prx3 and Prx2 oxidation states demonstrated reasonable trend agreement at short times (≤ 15 min) for a range of experimentally perturbed H2O2 generation rates. At longer times, substantial efflux of H2O2 from the mitochondria to the cytosol was evidenced by peroxiredoxin-2 (Prx2) oxidation, and Prx3 collapse was not observed. A refined model using Monte Carlo parameter sampling was used to explore rates of H2O2 efflux that could reconcile model predictions of Prx3 oxidation states with the experimental observations.

Mitochondrial Costs of Being Hot: Effects of Acute Thermal Change on Liver Bioenergetics in Toads (Bufo bufo).

Global climatic warming is predicted to drive extreme thermal events, especially in temperate terrestrial environments. Hence, describing how physiological parameters are affected by acute temperature changes would allow us to understand the energy management of organisms facing such non-predictable and constraining events. As mitochondria play a key role in the conversion of energy from food into ATP but also produce harmful reactive oxygen species, the understanding of its functioning is crucial to determine the proximal causes of potential decline in an animal’s performance. Here we studied the effects of acute temperature changes (between 20 and 30°C) on mitochondrial respiration, ATP synthesis rate, oxidative phosphorylation efficiency (ATP/O), and H2O2 generation in isolated liver mitochondria of a terrestrial ectotherm, the common toad (Bufo bufo). Using succinate as the respiratory substrate, we found that the mitochondrial rates of oxygen consumption, ATP synthesis, and H2O2 generation increased as the temperature increased, being 65, 52, and 66% higher at 30°C than at 20°C, respectively. We also found that the mitochondrial coupling efficiency (ATP/O) decreased, while the oxidative cost of ATP production (H2O2/ATP ratio) increased. The present results further indicate that between 40 and 60% of temperature effects on mitochondrial ATP production and H2O2 generation was at minima driven by an action on the oxidative capacity of the mitochondria. These results suggest that B. bufo may need to allocate extra energy to maintain ATP production and protect cells from oxidative stress, reducing the energy allocable performances.

Wettability controlled photocatalytic reactive oxygen generation and Klebsiella pneumoniae inactivation over triphase systems

Antibacterial technology based on photo-generated reactive oxygen species (ROS) represents a promising strategy for antibiotic-resistant bacteria inactivation, but often results in poor activity due to the limited O2 solubility in traditional water-catalyst diphase system. In this work, we develop an air-water-catalyst triphase system to explore the superiority of air phase-supplied O2 for the enhancement of ROS generation and Klebsiella pneumoniae (KPN) inactivation efficiencies. Using P25-TiO2 as model photocatalysts, we demonstrate that Wenzel-Cassie coexistent wetting state is the most conducive for photocatalytic ROS generation, offering a H2O2 generation rate of 1003 ± 52 μM h−1, which is 18 times higher than corresponding diphase system. It also affords an over two orders of magnitude reduced KPN colony concentration within 30 min irradiation, achieving over 99 % light-triggered removal efficiency. The advantages of triphase system for photocatalytic bacterial inactivation will inspire the development of efficient photocatalytic antibacterial systems in atmosphere-connected water bodies.

Constructing efficient WO3-FPC system for photoelectrochemical H2O2 production and organic pollutants degradation

Photoelectrochemical (PEC) reduction of O2 to H2O2 not only provides great potential for solar energy conversion but also produces an eco-friendly oxidant. Exploring an efficient PEC system for this reaction is desirable but challenging. In this work, by applying anodic potential to a WO3 photoanode in order to accelerate photogenerated charge separation and employing F-doped porous carbon (FPC) as a cathode to selectively activate the reduction of O2 to H2O2, we report an elaborate WO3/FPC system with an efficient PEC H2O2 generation rate of 0.87 mmol L−1 h−1 and a Faradaic efficiency (FE) of 75%. This improved performance arises from the moderate reduction potential, superior charge separation on the WO3 photoanode and high selectivity H2O2 generation on the FPC cathode. After adding Fe2+ to catalyze H2O2 in order to generate OH and considering phenol, bisphenol A and atrazine as target pollutants, the degradation property of this PEC system was tested. The pollutants were more than 90% degraded and 40% mineralized within 60 min. This work provides new insights into the development of a PEC system for H2O2 generation and pollutant degradation.

Influence of discharge types on hydrogen peroxide generation in water with/without PI film barrier

Discharge types in water have great differences in morphology and physical properties which can play significant roles in active species production. The characteristics of different discharge types (streamer and spark discharge) and their influences on hydrogen peroxide (H2O2) generation are investigated in this paper. Three discharge regions i.e., streamer, streamer-to-spark and spark regions are divided according to the breakdown probability. The experimental results show that the discharges in streamer-to-spark region gain the highest production rate and energy yield of H2O2 generation. While we find that the streamer discharges just below the threshold of streamer and streamer-to-spark regions are more suitable for H2O2 generation considering the quick corrosion of electrodes caused by sparks. A layer of 0.1 mm polyimide (PI) film is introduced in the experiment, which efficiently inhibits the streamer-to-spark transition and proves to further promote the maximum production rate of H2O2 in streamer discharge from 2.6 to 3.5 μmol/(L·min) with 8% loss in energy yield.

Which Antioxidant System Shapes Intracellular H2O2 Gradients?

Cellular antioxidant systems control the levels of hydrogen peroxide (H2O2) within cells. Multiple theoretical models exist that predict the diffusion properties of H2O2 depending on the rate of H2O2 generation and amount and reaction rates of antioxidant machinery components. Despite these theoretical predictions, it has remained unknown how antioxidant systems shape intracellular H2O2 gradients. The relative role of thioredoxin (Trx) and glutathione systems in H2O2 pattern formation and maintenance is another disputed question. Here, we visualized cellular antioxidant activity and H2O2 gradients formation by exploiting chemogenetic approaches to generate compartmentalized intracellular H2O2 and using the H2O2 biosensor HyPer to analyze the resulting H2O2 distribution in specific subcellular compartments. Using human HeLa cells as a model system, we propose that the Trx system, but not the glutathione system, regulates intracellular H2O2 gradients. Antioxid. Redox Signal. 31, 664-670.

The exceptional longevity of the naked mole-rat may be explained by mitochondrial antioxidant defenses.

Naked mole‐rats (NMRs) are mouse‐sized mammals that exhibit an exceptionally long lifespan (>30 vs. <4 years for mice), and resist aging‐related pathologies such as cardiovascular and pulmonary diseases, cancer, and neurodegeneration. However, the mechanisms underlying this exceptional longevity and disease resistance remain poorly understood. The oxidative stress theory of aging posits that (a) senescence results from the accumulation of oxidative damage inflicted by reactive oxygen species (ROS) of mitochondrial origin, and (b) mitochondria of long‐lived species produce less ROS than do mitochondria of short‐lived species. However, comparative studies over the past 28 years have produced equivocal results supporting this latter prediction. We hypothesized that, rather than differences in ROS generation, the capacity of mitochondria to consume ROS might distinguish long‐lived species from short‐lived species. To test this hypothesis, we compared mitochondrial production and consumption of hydrogen peroxide (H2O2; as a proxy of overall ROS metabolism) between NMR and mouse skeletal muscle and heart. We found that the two species had comparable rates of mitochondrial H2O2 generation in both tissues; however, the capacity of mitochondria to consume ROS was markedly greater in NMRs. Specifically, maximal observed consumption rates were approximately two and fivefold greater in NMRs than in mice, for skeletal muscle and heart, respectively. Our results indicate that differences in matrix ROS detoxification capacity between species may contribute to their divergence in lifespan.

Electrochemical catalytic mechanism of N-doped graphene for enhanced H2O2 yield and in-situ degradation of organic pollutant

Highly efficient electrochemical advanced oxidation processes (EAOPs) based on carbon catalysts are promising and green technologies for environmental remediation. Herein, for the purpose of cost-effectiveness, wide pH suitability and excellent reusability, graphite felt modified with regulatable N-doped graphene was developed as a cathode to electrochemically generate H2O2 with high yield and selectivity, and efficiently catalyze H2O2 to form OH for organic pollutants degradation by in-situ metal-free EAOPs. Particularly, the catalytic mechanism of N-doped graphene for enhanced performance was explored. Optimized N-doped graphene showed a very high H2O2 generation rate of 8.6 mg/h/cm2, low electric energy consumption (9.8 kW h/kg) and high H2O2 selectivity of 78.02% in neutral pH solution. Compared with electro-Fenton (EF), this in-situ metal-free EAOPs on N-doped graphene displayed significant improvement on the degradation performance of organic pollutants in neutral and alkaline solutions, and was certified to be less affected by initial pH. The pyridinic N and CC in N-doped graphene enhanced the onset potential while graphite N determined the disk current of oxygen reduction reaction (ORR) process. Most importantly, it proved that the introduction of graphite N could promote the 2e- ORR process for H2O2 generation, and the presence of pyridinic N could catalyze H2O2 to the production of OH. Taken phenol as target pollutant, OH generated by N-doped graphene accounted for 80.72% while O2− contributed 19.28% to its degradation, based on which a possible mechanism for phenol degradation was proposed. Moreover, in-situ metal-free EAOPs showed excellent stability, reusability and performance for various organic pollutants degradation. This work would shed light on the catalytic mechanism for metal-free EAOPs, and thus promote its application for organic pollutants degradation.

Exogenous glutathione attenuates lead-induced oxidative stress in wheat by improving antioxidant defense and physiological mechanisms

ABSTRACTThis study aims at investigate how exogenous glutathione (GSH, 1.0 mM) affects the oxidative stress and antioxidant defense in wheat seedlings under lead (Pb) stress [0.5 and 1.0 mM Pb(NO3)2]. Lead treatment decreased growth, leaf relative water content, and chlorophyll (chl) content whereas raised proline (Pro) level. Lead stress increased H2O2 content, generation rate, and membrane lipid peroxidation. Addition of Pb also disrupted antioxidant enzyme activities and status of endogenous ascorbate and GSH pool. The increase of methylglyoxal was evident under Pb stress. Glutathione supplementation under Pb stress increased antioxidant redox pool and augmented the activities of antioxidant enzymes, and decreased ROS production. Exogenous supplementation of GSH reverted the increase in the methylglyoxal level due to Pb stress due to increased activities of glyoxalase enzymes. Exogenous GSH also regulated Pro, well-maintained tissue water status and prevented chl degradation and increased plant growth and biomass. Abbreviations: AO- ascorbate oxidase; APX- ascorbate peroxidase; AsA- ascorbic acid (ascorbate); BSA- bovine serum albumin; CAT- catalase; CDNB-1-chloro-2, 4-dinitrobenzene; chl- chlorophyll; DHA- dehydroascorbate; DHAR- dehydroascorbate reductase; DTNB- 5,5′-dithio-bis (2-nitrobenzoic acid); EDTA- ethylenediaminetetraacetic acid; Gly I- glyoxalase I; Gly II- glyoxalase II; GR- glutathione reductase; GSH- reduced glutathione; GSSG- oxidized glutathione; GPX- glutathione peroxidase; GST- glutathione S-transferase; MDA- malondialdehyde; MDHA- monodehydroascorbate; MDHAR- monodehydroascorbate reductase; MG- methylglyoxal; NADPH- nicotinamide adenine dinucleotide phosphate; NBT- nitroblue tetrazolium chloride; Pb- lead; PEG- polyethylene glycol; Pro- proline, ROS- reactive oxygen species; RWC- relative water content; SLG- S-d-lactoylglutathione; SOD- superoxide dismutase; TBA- thiobarbituric acid; TCA- trichloroacetic acid.

Krebs cycle metabolites and preferential succinate oxidation following neonatal hypoxic-ischemic brain injury in mice.

BackgroundReverse electron transport (RET) driven by the oxidation of succinate has been proposed as the mechanism of accelerated production of reactive oxygen species (ROS) in post-ischemic mitochondria. However, it remains unclear whether upon reperfusion, mitochondria preferentially oxidase succinate.MethodsNeonatal mice were subjected to Rice-Vannucci model of hypoxicischemic brain injury (HI) followed by assessment of Krebs cycle metabolites, mitochondrial substrate preference, and H2O2 generation rate in the ischemic brain.ResultsWhile brain mitochondria from control mice exhibited a rotenonesensitive complex-I-dependent respiration, HI-brain mitochondria, at the initiation of reperfusion, demonstrated complex-II-dependent respiration, as rotenone minimally affected, but inhibition of complex-II ceased respiration. This was associated with a 30-fold increase of cerebral succinate concentration and significantly elevated H2O2 emission rate in HI-mice compared to controls. At sixty minutes of reperfusion, cerebral succinate content and the mitochondrial response to rotenone did not differ from that in controls.ConclusionThese data are the first ex-vivo evidence, that at the initiation of reperfusion, brain mitochondria transiently shift their metabolism from complex-I-dependent oxidation of NADH toward complex II-linked oxidation of succinate. Our study provides a critical piece of support for existence of the RET-dependent mechanism of elevated ROS production in reperfusion.

Ascorbate ameliorates Echis coloratus venom-induced oxidative stress in human fibroblasts.

Reports related to the effects of Echis coloratus venom (EcV) on the antioxidant capacity of human tissues is very scarce. The present study was undertaken to investigate the activities and gene expression levels of glutathione peroxidase (GPx), glutathione reductase (GR), glutathione S-transferase (GST), superoxide dismutase (SOD) and catalase (CAT), as well as the levels of reduced glutathione (GSH), oxidized glutathione (GSSG) and the generation rates of superoxide anions (SOA), hydrogen peroxide (H2O2) and lipid peroxides (LPO) in cultured human fibroblasts incubated with EcV, ascorbate (Asc) and EcV plus Asc at concentrations and incubation periods that maintained cell viability. Results indicated that the activities of all antioxidant enzymes and their corresponding transcripts underwent highly significant decreases and downregulation in EcV-treated cultures (0.5 µg/ml medium for 4 h) compared to venom-free controls (P<0.001). Additionally, there were concurrent equally significant increases in SOA, H2O2 and LPO generation rates in the venom-incubated cultures compared to controls (P<0.001). Results also indicated very significant decreases and parallel equally significant increases in GSH and GSSG levels respectively in the envenomed cultures compared to controls (P<0.001) leading to a drastically lower GSH/GSSG ratio. However, further incubation of the EcV-treated cultures with Asc (400 µM for 12 h) restored the activities and levels of all investigated parameters including the expression levels of the antioxidant genes to control venom-free values. It is concluded that Asc acted to neutralize the increased reactive oxygen species generation, thus ameliorating the EcV-induced oxidative stress and alleviating the downregulation of antioxidant genes.

Energetic, oxidative and ionic exchange in rat brain and liver mitochondria at experimental audiogenic epilepsy (Krushinsky-Molodkina model).

The role of brain and liver mitochondria at epileptic seizure was studied on Krushinsky-Molodkina (KM) rats which respond to sound with an intensive epileptic seizure (audiogenic epilepsy). We didn't find significant changes in respiration rats of brain and liver mitochondria of KM and control rats; however the efficiency of АТР synthesis in the KM rat mitochondria was 10% lower. In rats with audiogenic epilepsy the concentration of oxidative stress marker malondialdehyde in mitochondria of the brain (but not liver) was 2-fold higher than that in the control rats. The rate of H2O2 generation in brain mitochondria of КМ rats was twofold higher than in the control animals when using NAD-dependent substrates. This difference was less pronounced in liver mitochondria. In KM rats, the activity of mitochondrial ATP-dependent potassium channel was lower than in liver mitochondria of control rats. The comparative study of the mitochondria ability to retain calcium ions revealed that in the case of using the complex I and complex II substrates, permeability transition pore is easier to trigger in brain and liver mitochondria of KM and КМs rats than in the control ones. The role of the changes in the energetic, oxidative, and ionic exchange in the mechanism of audiogenic epilepsy generation in rats and the possible correction of the epilepsy seizures are discussed.

The effect of Echis coloratus venom on biochemical and molecular markers of the antioxidant capacity in human fibroblasts

ABSTRACTThis study was undertaken to examine the activities and levels of major antioxidants/oxidants in cultured human fibroblasts incubated with a sublethal dose of Echis coloratus venom (EcV).Glutathione peroxidase (GPx), catalase (CAT), superoxide dismutase (SOD) and glutathione reductase (GR) activities and gene expression levels as well as reduced glutathione (GSH) levels, and the concurrent hydrogen peroxide (H2O2), superoxide anions (SOA), lipid peroxides (LPO) and oxidized glutathione (GSSG) generation rates were assayed in fibroblast cultures and sonicates incubated with 0.5 µg ml–1 medium EcV for 4 h at 37°C.Data indicated that the activities of all antioxidant enzymes were significantly decreased and their corresponding transcripts downregulated in EcV-incubated cells compared to controls (p < 0.001). In contrast, there were parallel equally significant increases in H2O2, SOA and LPO generation rates in venom-incubated cells compared to controls (p < 0.001). Additionally, GSH levels were significantly decreased and those of GSSG were equally significantly increased in venom-incubated cultures compared to controls (p < 0.001) leading to a lowered GSH/GSSG ratio.In conclusion, incubation of fibroblast cultures with EcV resulted in a shift towards oxidative metabolism causing severe OS. This correlated with significant downregulation in the expression levels of all investigated antioxidant genes.

Reaction Mechanism of the Multiple-Electron Oxygen Reduction Reaction on the Surfaces of Gold and Platinum Nanoparticles Loaded on Titanium(IV) Oxide.

Au and Pt nanoparticles with varying mean particle size and comparable loading amounts were loaded on the surface of TiO2 (Au/TiO2 and Pt/TiO2, respectively). The photocatalytic activities of Au/TiO2 and Pt/TiO2 for the oxygen reduction reaction (ORR) in an aerated aqueous solution containing 4% ethanol were compared under ultraviolet-light irradiation at 298 K. The initial rate of H2O2 generation (or H2O2 formation rate) in the Au/TiO2 system is much greater than that in the Pt/TiO2 system regardless of the metal particle size. To clarify the origin for the striking difference in the activity, the photocatalytic ORR on the model slabs (M28/(TiO2)32 and M50/(TiO2)96, M = Au and Pt) was simulated by density functional theory (DFT) calculations taking the solvation effect into consideration. The DFT calculations clearly show that regardless of the cluster size, H2O2 formation more easily occurs structurally and energetically for the Au/TiO2 system, whereas H2O is generated with the O-O bond cleavage in the Pt/TiO2 system.