H2O2 Consumption Research Articles

Simultaneous removal of NOx and SO2 from coal-fired flue gas based on the catalytic decomposition of H2O2 over Fe2(MoO4)3

The purification of flue gas has drawn the increasing attention in recent years. In the present study, a novel oxidation-absorption process was proposed for simultaneous removal of NOx and SO2 from coal-fired flue gas based on the catalytic decomposition of H2O2 over Fe2(MoO4)3, in which gaseous pollutants were first oxidized by OH radicals and then absorbed with ammonia solution. The effects of H2O2 dosage, temperature, gas hourly space velocity (GHSV) and flue gas component on simultaneous removal efficiency were systematically investigated. The results indicated that the removal efficiencies of 91.4% for NOx and 100% for SO2 could be achieved under the optimal conditions. The signal of OH radical was verified by fluorescence test. The OH radicals were essential for NO oxidation and the subsequent NOx removal, while SO2 was primarily removed in absorption process. Moreover, the presence of SO2 was favorable for NOx removal, mainly because the existence of SO2 promoted NO oxidation. X-ray photoelectron spectroscopy (XPS) analysis further confirmed that SO2 could reduce part of Fe3+ to Fe2+ on catalyst surface, thereby reducing the consumption of H2O2 by Fe3+ and promoting the majority of H2O2 to generate OH. The continuity test revealed that the synthesized Fe2(MoO4)3 showed satisfactory stability. The surface morphology and crystal structure of the catalyst exhibit negligible change after 15 h of reaction. Products analysis indicated that NH4NO3 and (NH4)2SO4 were the primary products after removal of NOx and SO2. A three-step mechanism was preliminarily developed to interpret the simultaneous removal process in H2O2/Fe2(MoO4)3 system.

In situ generation and efficient activation of H2O2 for pollutant degradation over CoMoS2 nanosphere-embedded rGO nanosheets and its interfacial reaction mechanism

Consumption of additional H2O2 is necessary in classical Fenton catalysis. Herein, we report a novel and special nanocatalyst consisting of CoMoS2 nanosphere-embedded, reduced graphene oxide (rGO) nanosheets (CMS-rGO NSs). This nanocatalyst was discovered to have an impressive reactivity for in situ generation and synchronistical activation of H2O2 in different active centers, yielding fast and efficient degradation of the pollutants. The reaction rate is ∼21 times higher than that of conventional Fenton catalysts. The characterization shows that countless flower-like CoMoS2 nanospheres are uniformly embedded in the rGO nanosheets through MoSC bonding bridges in CMS-rGO NSs, which leads to activation of the π electrons and their transfer from rGO to the metal centers (π → M). The formed MoOCo further leads to a distribution of orientations of the electrons around the metal centers due to the different electronegativity of Mo and Co. During the reaction, the dissolved O2 is efficiently reduced to HO2/O2− around the electron-rich Mo center, and HO2/O2− is further reduced to H2O2 around the Co center. The generated H2O2 is finally reduced to OH for degrading dyes in the electron-rich metal (Mo or Co) centers of CMS-rGO NSs. The dye pollutants also act as electron donors, and they are directly degraded in the electron-poor π-center of CMS-rGO NSs, which promote the electron transfer cycle and achieve electron gain-loss balance. This discovery provides a new strategy for H2O2 generation-activation and pollutant degradation through constructing electron transfer bridges over the surface of catalysts.

Synthesis, structure-activity relationship studies and biological characterization of new [1,2,4]triazolo[1,5-a]pyrimidine-based LSD1/KDM1A inhibitors

The histone lysine specific demethylase 1 (LSD1/KDM1A) is implicated in the development of cancers, targeting LSD1 has been recognized as a promising strategy for cancer therapy. To date, some small-molecule inhibitors are currently being investigated in clinical trials. Herein we report the design, synthesis and biochemical characterization of [1,2,4]triazolo[1,5-a]pyrimidine derivatives as new LSD1 inhibitors. Of these compounds, compound C26 inhibited LSD1 in a reversible manner (IC50 = 1.72 μM) and showed selectivity to LSD1 over MAO-A/B. Besides, compound C26 displayed FAD-competitive binding to LSD1. Interestingly, C26 did not inhibit horseradish peroxidase (HRP) and quench H2O2, thus excluding the possibility that LSD1 inhibition by C26 was due to the HRP inhibition and consumption of H2O2. In LSD1 overexpressed A549 cells, compound C26 concentration-dependently induced accumulation of H3K4me1/me2 and H3K9me2 and showed cellular target engagement to LSD1. Additionally, compound C26 significantly inhibited migration of A549 cells in a concentration-dependent manner, further western blot analysis showed that C26 increased expression levels of epithelial cell markers E-Cadherin and Claudin-1, down-regulated mesenchymal cell marker N-Cadherin and the upstream transcription factors Snail and Slug. Docking studies were also performed to rationalize the potency of C26 toward LSD1. To conclude, the [1,2,4]triazolo[1,5-a]pyrimidine could serve as a promising scaffold for the development of new LSD1 inhibitors.

Electrochemical Assays and Immunoassays of the Myeloperoxidase/SCN-/H2O2 System.

Strategies to detect and characterize myeloperoxidase (MPO) are needed, given that this "split personality" enzyme kills harmful microorganisms but also damages a host tissue. Here, we describe electrochemical approaches to measure MPO by using the pseudohalogenation (MPO/SCN-/H2O2) and catalase-like (MPO/H2O2) cycles. Their kinetics were determined by monitoring the consumption of H2O2 with a nitrogen-doped carbon nanotubes (N-CNT) electrode, which could detect 0.50 μM H2O2 at -0.20 V. The unique design of internally calibrated electrochemical continuous enzyme assay (ICECEA) and electrode stability allowed use of one N-CNT electrode for over half a year to reliably determine MPO. The kinetic measurements showed that (a) SCN- did not affect the affinity of MPO for H2O2, (b) catalase-like cycle was slower, and (c) MPO retained enzymatically active conformation after complexation with its antibody Ab both in a solution and on the surface of an antibody dipstick (d/Ab). The homogeneous assays could detect 5.2 μg L-1 MPO (35 pM) via a faster cycle. The heterogeneous immunoassays with the capture of MPO on d/Ab could detect 60 μg L-1, which was suitable for the accurate detection of MPO in human saliva (101% recovery). Replacing a detection antibody of ELISA with ICECEA as a signal transducer for immunoassays offers a rapid method for the selective determination of enzymes; for example, time of MPO quantification was cut from 3-4 h (sandwich ELISA) to ∼20 min (ICECEA-dipstick).

TiO2/Schwertmannite nanocomposites as superior co-catalysts in heterogeneous photo-Fenton process

The heterogeneous photo-Fenton reaction is an effective technique in combating organic contaminants for both soil and water remediation, and extensive studies have focused on enhancing its efficiency and reducing its costs. In this work, we developed novel photo-Fenton catalysts by simply milling commercially available TiO2 (P25) with Schwertmannite (Sh), a natural iron-oxyhydroxysulfate nanomineral. We expect that the photo-generated electrons from TiO2 could continuously migrate to Sh, which then could enhance the separation of electron-hole pairs on TiO2 and accelerate the reduction of Fe(III) to Fe(II) on Sh, leading to high degradation efficiency of the target organic contaminants. SEM and TEM results showed the distribution of TiO2 on Sh surface for the nanocomposites (TiO2/Sh). Under simulated sunlight irradiation, the much higher content of Fe(II) was determined on TiO2/Sh than on Sh via a common method in the iron ore, and the consumption of H2O2 and the production of •OH were more significant in the TiO2/Sh system than those in the TiO2 and Sh systems. These results well support our hypothesis that the photo-generated electrons could migrate from TiO2 to Sh on the composites, and can also explain the much higher degradation efficiency of Rhodamine B (RhB) in the TiO2/Sh system. Besides, TiO2/Sh had lower Fe dissolution as compared with Sh, and retained high catalytic stability after four repeated cycles. Above merits of the TiO2/Sh composites, in combining with their simple synthesis method and low-cost property, indicated that they should have promising applications as heterogeneous photo-Fenton catalysts.

Modified hydrogen peroxide bleaching of bamboo chemo-mechanical pulp using aqueous alcohol media

The brightness of bleached bamboo chemo-mechanical pulp (CMP) is often too low to be used as a furnish in value-added paper products. In this study, preliminary optimization of various parameters of a modified hydrogen peroxide (H2O2) bleaching procedure for bamboo CMP pulps was performed using the inclusion of ethanol in the bleaching medium (IEBM). Compared with a conventional bleaching method, this modified process is aimed at improving bleaching efficiency and brightness ceiling of bamboo CMP with the proper usage of chemicals. The CMP was bleached to a brightness of 74.2% ISO at the usage level of 12% H2O2, which shows it increased by 7.4% ISO compared with the conventional method. For a brightness target of 72.0% ISO, bleaching with the IEBM method reduced the H2O2 consumption by approximately 60%. In addition, a higher activation energy of H2O2 for the IEBM method was calculated to be 23.3 kJ/mol, which was increased by 3.3 kJ/mol compared with the conventional method.

Mitochondria can act as energy-sensing regulators of hydrogen peroxide availability

Mitochondria are widely recognized as sources of reactive oxygen species in animal cells, with H2O2 being of particular note because it can act not only in oxidative stress but also is important to several signalling pathways. Lesser recognized is that mitochondria can have far greater capacity to consume H2O2 than to produce it; however, the consumption of H2O2 may be kinetically constrained by H2O2 availability especially at the low nanomolar (or lower) concentrations that occur in vivo. The production of H2O2 is a function of many factors, not the least of which are respiratory substrate availability and the protonmotive force (Δp). The Δp, which is predominantly membrane potential (ΔΨ), can be a strong indicator of mitochondrial energy status, particularly if respiratory substrate supply is either not meeting or exceeding demand. The notion that mitochondria may functionally act in regulating H2O2 concentrations may be somewhat implicit but little evidence demonstrating this is available. Here we demonstrate key assumptions that are required for mitochondria to act as regulators of H2O2 by an integrated system of production and concomitant consumption. In particular we show the steady-state level of H2O2 mitochondria approach is a function of both mitochondrial H2O2 consumption and production capacity, the latter of which is strongly influenced by ΔΨ. Our results are consistent with mitochondria being able to manipulate extramitochondrial H2O2 as a means of signalling mitochondrial energetic status, in particular the Δp or ΔΨ. Such a redox-based signal could operate with some independence from other energy sensing mechanisms such as those that transmit information using the cytosolic adenylate pool.

The Correlation Between the Cytotoxicity of Cold Atmospheric Plasma and the Extracellular H2O2-Scavenging Rate

Cold atmospheric plasma (CAP) has shown its promising capability in cancer treatment both in vitro and in vivo . However, the anti-cancer mechanism is still largely unknown. CAP may kill cancer cells via triggering the rise of intracellular reactive oxygen species, DNA damage, mitochondrial damage, or cellular membrane damage. While the specific vulnerability of cancer cells to CAP has been observed, the underlying mechanism of such cell-based specific vulnerability to CAP is completely unknown. Here, through the comparison of CAP treatment and H2O2 treatment on ten different cancer cell lines in vitro , we observed that the H2O2 consumption rate by cancer cells was strongly correlated to the cytotoxicity of CAP treatment on cancer cells. Cancer cells that clear extracellular H2O2 more quickly are more resistant to the cytotoxicity of CAP treatment. This finding strongly indicates that the anti-oxidant system in cancer cells play a key role in the specific vulnerability of cancer cells to CAP treatment in vitro .

Heterogeneous and non-acid process for production of epoxidized soybean oil from soybean oil using hydrogen peroxide as clean oxidant over TS-1 catalysts

Abstract In order to develop an efficient and environmental friendly approach for epoxidation of soybean oil (SO), a series of hetero-catalysts, titanium silicalite-1 (TS-1) with different Si/Ti ratio (TS-1-x, x = 40, 70, 80), mesoporous TS-1-40 (MTS-1-40) and anatase TiO2, were prepared under controlled conditions. These different catalysts were characterized by various characterization methods like XRD, IR, UV–Vis, TGA, ICP, SEM, TEM and N2-adsorption, respectively, and the catalytic reaction experiments of the SO epoxidation were studied systematically using hydrogen peroxide (H2O2) as clean oxidant over the different catalysts. The results reveal that the TS-1-x catalysts exhibit higher epoxidation catalytic activity and less consumption of H2O2 than anatase TiO2, and the number of framework Ti sites in TS-1 structure played a very important role in their catalytic performance of the epoxidation reaction, which is attributed to the unique nature and coordination geometry of the Ti sites in TS-1 framework. Furthermore, the reusability and regeneration behaviors of TS-1-40 catalyst were also studied.

Glutathione and H2O2 consumption promoted photodynamic and chemotherapy based on biodegradable MnO2–Pt@Au25 nanosheets

Photodynamic therapy (PDT) has become a significant anticancer method by making full use of reactive oxygen species (ROS) to kill cancer cells. However, high concentration of reductive glutathione (GSH) in tumor site is an enemy, which can decrease the PDT efficacy due to ROS consumption property of reductive GSH. To overcome the problem, here we design an innovative nanoplatform, which could integrate PDT, chemotherapy and magnetic resonance imaging (MRI) in one nanosystem. In this platform, MnO2 nanosheets were employed as the carrier by conjugating photosensitizer (Au25 nanoclusters) with platinum(IV) (Pt(IV)) prodrugs for synergistic PDT and chemotherapy. Interestingly, GSH can reduce MnO2 nanosheets and Pt(IV) prodrugs simultaneously. Consequently, the concentration of intercellular GSH has been greatly decreased. More importantly, Mn2+ reduced from MnO2 nanosheets remarkably improves both T1– and T2–weighted MRI owing to high level of GSH and H2O2 in acidic tumor microenvironment, and Pt(II) reduced from Pt(IV) gives rise to high chemotoxicity to cancer cells. Combined with high PDT efficiency by consuming large amount of intercellular GSH, this nanoplatform has successfully achieved the MRI guided synergistic therapy, which is promising for potential clinic applications in cancer therapy.

Fluorene oxidation by solar-driven photo-Fenton process: toward mild pH conditions.

Polycyclic aromatic hydrocarbons (PAHs) are on the list of priority pollutants to be eliminated from the environment due to their carcinogenic and mutagenic action, chemical stability, and resistance to biodegradation. The aim of this study was to evaluate the degradation of fluorene, a well-known PAH, in aqueous solutions (0.03 and 0.08mgL-1), by means of a solar-driven conventional (PF) and modified photo-Fenton mediated by ferrioxalate complexes (PFF). Photolysis was also employed for comparison purposes. PF reaction was evaluated at different pH values (2.8, 3.5, and 4.0) and iron concentrations (2, 5, 10, and 20mgL-1). On the other hand, PFF studies were conducted at mild pH conditions (4.0, 5.0, and 6.0) and iron content of 2mgL-1, keeping initial iron/oxalate molar ratio at 1:3. In both PF and PFF, the initial hydrogen peroxide/iron molar ratio was maintained at 5. In the presence of methanol as cosolvent for fluorene dissolution, the PF reaction was hampered and no consumption of H2O2 was observed during the reaction carried out at constant pH (2.8). This led to low degradation rates, similar to those achieved by photolysis. Under the same pH but using acetonitrile as cosolvent for fluorene dissolution, fluorene degradation was found to be proportional to the iron content used in the PF experiments. On the other hand, at an invariable iron concentration of 5mg Fe2+ L-1, the increase in pH was accompanied by a decrease in the molar fraction of the most photoactive iron complex (FeOH2+) and ferric hydroxides precipitation, leading to a reduction in the fluorene degradation rate. With regard to the PFF tests, similar fluorene degradation performance was achieved at pH 4 and 5, while at pH 6 iron precipitation became relevant and the degradation rate was slightly slower. PFF has shown to be more efficient than the PF under the same pH (4) and iron concentration (2mgL-1). Moreover, even at near neutral pH (6), fluorine degradation was shown to be feasible by using ferrioxalate complexes.

Comparing Electron Leak in Vertebrate Muscle Mitochondria.

Mitochondrial electron transfer for oxidative ATP regeneration is linked to reactive oxygen species (ROS) production in aerobic eukaryotic cells. Because they can contribute to signaling as well as oxidative damage in cells, these ROS have profound impact for the physiology and survival of the organism. Although mitochondria have been recognized as a potential source for ROS for about 50years, the mechanistic understanding on molecular sites and processes has advanced recently. Most experimental approaches neglect thermal variability among species although temperature impacts mitochondrial processes significantly. Here we delineate the importance of temperature by comparing muscle mitochondrial ROS formation across species. Measuring the thermal sensitivity of respiration, electron leak rate (ROS formation), and the antioxidant capacity (measured as H2O2 consumption) in intact mitochondria of representative ectothermic and endothermic vertebrate species, our results suggest that using a common assay temperature is inappropriate for comparisons of organisms with differing body temperatures. Moreover, we propose that measuring electron leak relative to the mitochondrial antioxidant capacity (the oxidant ratio) may be superior to normalizing relative to respiration rates or mitochondrial protein for comparisons of mitochondrial metabolism of ROS across species of varying mitochondrial respiratory capacities.

Mechanisms of hydroxyl radicals production from pyrite oxidation by hydrogen peroxide: Surface versus aqueous reactions

Pyrite oxidation by hydrogen peroxide (H2O2) occurs in both natural and engineered systems. Hydroxyl radical (OH) is a key reactive intermediate for pyrite and coexisting substances oxidation. In acidic H2O2/pyrite systems, H2O2 decomposition by aqueous Fe2+ is documented to predominate for OH production, whereas here we show that H2O2 decomposition by surface Fe(II) sites contributes considerably to OH production under certain conditions. Pyrite oxidation by H2O2 under anoxic conditions was performed under different conditions (2–12 g/L pyrite, 0.025–1 mM H2O2 and pH 2–4), and OH and aqueous Fe2+/Fe3+ production as well as H2O2 consumption were measured during the oxidation. In order to evaluate the contribution of surface reaction to OH production, 1 mM 2, 2′-bipyridine (BPY) was added to inhibit H2O2 decomposition by aqueous Fe2+. The rate constants of OH production decreased by 44.4–65.6% with addition of 1 mM BPY, which suggests that both surface and aqueous reactions contributed to OH production. Regarding the surface reaction, density functional theory (DFT) calculation reveals that H2O2 was adsorbed onto the Fe(II) sites on pyrite surface and transformed to surface adsorbed OH which desorbed subsequently into the aqueous solution. On the basis of mechanistic understanding, a kinetic model was developed to assess the relative contributions of surface and aqueous reactions to OH production. The relative contribution of surface reaction is dependent on the ratio of pyrite surface concentration to aqueous Fe2+ concentration, which decreases with the progress of pyrite oxidation due to the increase in aqueous Fe2+. When the ratio is higher than the threshold value of 1.6 × 103 m2/mM, surface reaction becomes predominant for OH production. Typical systems necessitating consideration of surface reaction involve pyritic rocks and shale leaching and pollutants treatment by H2O2/pyrite. The mechanisms unraveled in this study supplement the fundamental of OH production from pyrite oxidation by both H2O2 and O2 in natural and engineered systems.

A chemiluminescence-based catalase assay using H2O2-sensitive CdTe quantum dots.

A method is described for the chemiluminescence based determination of the activity of catalase (CAT) using H2O2-sensitive CdTe quantum dots (QDs). It is based on the finding that the chemiluminescence (CL) of the CdTe/H2O2 system is reduced due to the consumption of H2O2 by the catalytic action of CAT. The Michaelis constant is calculated to be 519 ± 27mM, showing the potential of the method to accurately measure the Km compared to the standard method. The method does not require QDs to be conjugated to biological/organic molecules and therefore is considered to be a rapid and convenient method for determination of CAT in real samples. At an incubation time of 2s, the LOD was calculated to be 4.5 unit/mL, with a linear range from 6 to 400 unit/mL. The assay is sensitive, simple, and suitable for practical applications. Graphical abstract Schematic representation of chemiluminescence-based catalase U(CAT) assay using the CdSe QD/H2O2 system. The reduction of H2O2 is reflected by the chemiluminescence of theQDs. A mechanism is put forward based on the changes in chemiluminescence intensity of the QDs by the consumption of H2O2 due to the catalyticaction of CAT.

How does intensification influence the operational and environmental performance of photo-Fenton processes at acidic and circumneutral pH.

This study evaluates the technical, economical, and environmental impact of sodium persulfate (Na2S2O8) as an enhancing agent in a photo-Fenton process within a solar-pond type reactor (SPR). Photo-Fenton (PF) and photo-Fenton intensified with the addition of persulfate (PFPS) processes decolorize 97% the azo dye direct blue 71 (DB71) and allow producing a highly biodegradable effluent. Intensification with persulfate allowed reducing treatment time in 33% (from 120 to 80min) and the consumption of chemical auxiliaries needed for pH adjustment. Energy, reagents, and chemical auxiliaries are still and environmental hotspot for PF and PFPS; however, it is worth mentioning that their environmental footprint is lower than that observed for compound parabolic concentrator (CPC)-type reactors. A life-cycle assessment (LCA) confirms that H2O2, NaOH, and energy consumption are the variables with the highest impact from an environmental standpoint. The use of persulfate reduced the relative impact in 1.2 to 12% in 12 of the 18 environmental categories studied using the ReCiPe method. The PFPS process emits 1.23kg CO2 (CO2-Eqv/m3 treated water). On the other hand, the PF process emits 1.28kg CO2 (CO2-Eqv/m3 treated water). Process intensification, chemometric techniques, and the use of SPRs minimize the impact of some barriers (reagent and energy consumption, technical complexity of reactors, pressure drops, dirt on the reflecting surfaces, fragility of reactor materials), limiting the application of advanced oxidation systems at an industrial level, and decrease treatment cost as well as potential environmental impacts associated with energy and reagents consumption. Treatment costs for PF processes (US$0.78/m3) and PFPS processes (US$0.63/m3) were 20 times lower than those reported for photo-Fenton processes in CPC-type reactors.

Adsorption-depended Fenton-like reaction kinetics in CeO2-H2O2 system for salicylic acid degradation

Degradation of salicylic acid (SA) was employed to investigate the Fenton-like reaction in CeO2-H2O2 system. The adsorption and degradation behaviors of adsorbates (eg. SA, H2O2) on CeO2 were observed through the kinetics tracks. It is found that SA follows Langmuir isothermal secondary adsorption and its adsorption capacity plays a significant role in promoting Fenton-like process. The enhanced adsorption of SA in acidic environment not only benefits the degradation of SA, but also depresses the H2O2 consumption. When surface Ce3+ sites are over-occupied with highly concentrated H2O2, the reactivity of interfacial peroxide species would suffer significant decline. Photoabsorption of CeO2 in visible region emerges due to the complexation of surface cerium ions with adsorbed species. Accordingly, a visible light sensitization process initiates electrons transfer from interface species to the ceria; and therefore, the degradation of SA in CeO2-H2O2 system was promoted by visible light (λ > 420 nm) irradiation. The enhanced Fenton-like reactivity under visible light was also confirmed with DMPO-trapping EPR spectroscopy.

H2O2 metabolism in liver and heart mitochondria: Low emitting-high scavenging and high emitting-low scavenging systems

Although mitochondria are presumed to emit and consume reactive oxygen species (ROS), the quantitative interplay between the two processes in ROS regulation is not well understood. Here, we probed the role of mitochondrial bioenergetics in H2O2 metabolism using rainbow trout liver and heart mitochondria. Both liver and heart mitochondria emitted H2O2 at rates that depended on their metabolic state, with the emission rates (free radical leak) constituting 0.8–2.9% and 0.2–2.5% of the respiration rate in liver and heart mitochondria, respectively. When presented with exogenous H2O2, liver and heart mitochondria consumed it by first order reactions with half-lives (s) of 117 and 210, and rate constants of 5.96 and 3.37 (× 10−3 s−1), respectively. The mitochondrial bioenergetic status greatly affected the rate of H2O2 consumption in heart but not liver mitochondria. Moreover, the activities and contribution of H2O2 scavenging systems varied between liver and heart mitochondria. The significance of the scavenging systems ranked by the magnitude (%) of inhibition of H2O2 removal after correcting for emission were, liver (un-energized and energized): catalase > glutathione (GSH) ≥ thioredoxin reductase (TrxR); un-energized heart mitochondria: catalase > TrxR > GSH and energized heart mitochondria: GSH > TrxR > catalase. Notably, depletion of GSH evoked a massive surge in H2O2 emission that grossly masked the contribution of this pathway to H2O2 scavenging in heart mitochondria. Irrespective of the organ of their origin, mitochondria behaved as H2O2 regulators that emitted or consumed it depending on the ambient H2O2 concentration, mitochondrial bioenergetic state and activity of the scavenging enzyme systems. Indeed, manipulation of mitochondrial bioenergetics and H2O2 scavenging systems caused mitochondria to switch from being net consumers to net emitters of H2O2. Overall, our data suggest that the low levels of H2O2 typically present in cells would favor emission of this metabolite but the scavenging systems would prevent its accumulation.

Highly dispersed Fe3+-Al2O3 for the Fenton-like oxidation of phenol in a continuous up-flow fixed bed reactor. Enhancing catalyst stability through operating conditions

A highly dispersed Fe3+-Al2O3 catalyst (6 wt% Fe) was used for the catalytic wet hydrogen peroxide oxidation of phenol (1 g/L) in an up-flow fixed bed reactor (UFBR) under continuous operation. To enhance catalytic performance, three simple synthesis strategies were combined: two-stage impregnation of iron citrate, acid washing with CH3COOH and thermal treatment at 900 °C. Solid samples were characterized in depth by several techniques: N2 Physisorption, XRD, SEM–EDAX, TEM, TGA, PZC, TPD of pyridine, XPS and Mössbauer. Peroxidation experiments were performed in an UFBR over a wide range of operating parameters in order to evaluate their influence on phenol mineralization and catalyst stability. Under selected operating condition (T = 90 °C, Wcat = 20 g, QL = 1.2 mL/min and [H2O2]:[Phenol] = 16.8), complete phenol conversion and remarkable TOC reduction of 90% were achieved, with a high H2O2 consumption efficiency (η = 76%) and low Fe leaching (< 3 mg/L). After 70 h of usage at different steady state conditions, the catalyst retained high mineralization levels (XTOC> 70%) but the cumulative iron loss was calculated to be c.a. 20% of the initial Fe loaded in the UFBR. The catalyst was susceptible to leaching due to the accumulation of complexing intermediates such as carboxylic acids. However, acceptable iron leaching values (< 10 mg/L) were achieved when the reactor operating conditions were properly set (55% < XTOC> 80%). The presence of chelating by-products favored also the Fe redistribution inside the catalyst pellets. Nevertheless, catalyst decay in the long-term operation was mainly due to the occurrence and permanence of chelating organic acids. This process was specially promoted by the amphoteric character of the alumina-based catalyst. However, adsorbed species were promptly eliminated by calcination at 500 °C, recovering steady state conversion profiles.

Kinetic and stoichiometric constraints determine the pathway of H2O2 consumption by red blood cells.

Red blood cells (RBC) are considered as a circulating sink of H2O2, but a significant debate remains over the role of the different intraerythocyte peroxidases. Herein we examined the kinetic of decomposition of exogenous H2O2 by human RBC at different cell densities, using fluorescent and oxymetric methods, contrasting the results against a mathematical model. Fluorescent measurements as well as oxygen production experiments showed that catalase was responsible for most of the decomposition of H2O2 at cell densities suitable for both experimental settings (0.1-10 × 1010 cell L-1), since sodium azide but not N-ethylmaleimide (NEM) inhibited H2O2 consumption. Oxygen production decreased at high cell densities until none was detected above 1.1 × 1012 cell L-1, being recovered after inhibition of the thiol dependent systems by NEM. This result underlined that the consumption of H2O2 by catalase prevail at RBC densities regularly used for research, while the thiol dependent systems predominate when the cell density increases, approaching the normal number in blood (5 × 1012 cell L-1). The mathematical model successfully reproduced experimental results and at low cell number it showed a time sequence involving Prx as the first line of defense, followed by catalase, with a minor role by Gpx. The turning points were given by the total consumption of reduced Prx in first place and reduced GSH after that. However, Prx alone was able to account for the added H2O2 (50 µM) at physiological RBC density, calling attention to the importance of cell density in defining the pathway of H2O2 consumption and offering an explanation to current apparently conflicting results in the literature.

The role of surface-bound hydroxyl radicals in the reaction between H2O2 and UO2

In this work, we have studied the reaction between H2O2 and UO2 with particular focus on the nature of the hydroxyl radical formed as an intermediate. Experiments were performed to study the kinetics of H2O2 consumption and uranium dissolution at different initial H2O2 concentrations. The results show that the consumption rates at a given H2O2 concentration are different depending on the initial H2O2 concentration. This is attributed to an alteration of the reactive interface, likely caused by blocking of surface sites by oxidized U/surface-bound hydroxyl radicals. The dissolution yield given by the amount of dissolved uranium divided by the amount of consumed hydrogen peroxide was used to compare the different cases. For all initial H2O2 concentrations, the dissolution yield increases with reaction time. The final dissolution yield decreases with increasing initial H2O2 concentration. This is expected from the mechanism of catalytic decomposition of H2O2 on oxide surfaces. As the experiments were performed in solutions containing 10 mM and a strong concentration dependence was observed in the 0.2–2.0 mM H2O2 concentration range, we conclude that the intermediate hydroxyl radical is surface bound rather than free.