Increasing H2O2 Concentration Research Articles

High temporal resolution of hydrogen peroxide (H2O2) dynamics during heat stress does not support a causative role in coral bleaching

Human-induced climate change is causing ocean warming that triggers the breakdown of the coral–algal symbiosis. The proximate cause of this phenomenon, known as coral bleaching, is commonly attributed to the overproduction of reactive oxygen species (ROS) by the thermally stressed photosynthetic algal symbionts. However, direct evidence that algal ROS production (e.g., in the form of H2O2) and coral physiological stress are the ultimate cause of bleaching remains ambiguous. Here, we investigated the temporal dynamics of H2O2 and oxygen (O2) concentrations during thermally induced coral bleaching to disentangle cause from consequence. Microsensors at the tissue interface of Pocillopora damicornis measured H2O2 and O2 concentrations while exposing single nubbins to baseline temperatures (30 °C) and to minor (33 °C), moderate (36 °C), and high (39 °C) levels of acute heat stress using the Coral Bleaching Automated Stress System (CBASS). We show that a temporary decline in O2 concentration, accompanied by a declining photosynthetic efficiency and loss of Symbiodiniaceae and pigmentation, is the initial response to moderate thermal stress. This response was neither provoked nor followed by an increased H2O2 concentration at the coral tissue interface. A steady light-independent increase of H2O2 was only detected during high heat stress, resulting in the complete and permanent loss of photosynthetic activity. Our findings do not support a direct connection between algal photodamage and an increase in H2O2 concentration during thermally induced bleaching and suggest that more research on the function of H2O2 is warranted. This notion is further substantiated by the observation of an additional source of H2O2, likely oxidative bursts, that were common at the baseline temperature and under minor heat stress, while their occurrence decreased at moderate and high heat stress. Resolving the multifaceted and dynamic roles of H2O2 in coral bleaching is critical to better understand the response of the coral holobiont to thermal stress and identifying the processes underlying the breakdown of the coral–algal symbiosis.

Insight into the biodegradation behavior of pure molybdenum under simulated inflammatory condition

The study explores the impact of simulated inflammation on the corrosion behavior of pure Mo, a potential biodegradable metal for biomedical applications for the first time. Under simulated inflammatory conditions, Mo exhibits altered electrochemical properties, such as increased open circuit potential, higher corrosion rates, and reduced impedance as H2O2 concentration rises. Immersion test confirm the higher corrosion rates with increases in H2O2 concentration. Interestingly, pure Mo exhibit uniform corrosion behavior under aggressive simulated inflammation which is beneficial to maintain biomedical devices’ mechanical integrity. Furthermore, the underlying biodegradation mechanism and the mechanism of inflammatory cell-released inflammation species induced corrosion were discussed.

SmRAV1, an AP2 and B3 Transcription Factor, Positively Regulates Eggplant's Response to Salt Stress.

Salt stress is a lethal abiotic stress threatening global food security on a consistent basis. In this study, we identified an AP2 and B3 domain-containing transcription factor (TF) named SmRAV1, and its expression levels were significantly up-regulated by NaCl, abscisic acid (ABA), and hydrogen peroxide (H2O2) treatment. High expression of SmRAV1 was observed in the roots and sepal of mature plants. The transient expression assay in Nicotiana benthamiana leaves revealed that SmRAV1 was localized in the nucleus. Silencing of SmRAV1 via virus-induced gene silencing (VIGS) decreased the tolerance of eggplant to salt stress. Significant down-regulation of salt stress marker genes, including SmGSTU10 and SmNCED1, was observed. Additionally, increased H2O2 content and decreased catalase (CAT) enzyme activity were recorded in the SmRAV1-silenced plants compared to the TRV:00 plants. Our findings elucidate the functions of SmRAV1 and provide opportunities for generating salt-tolerant lines of eggplant.

Effects of Hydrogen Peroxide on the Hydrogen Bonding Structure and Dynamics of Water and Its Influence on the Aqueous Solvation of the Insulin Monomer.

The hydrogen bond structure and dynamics of water and hydrogen peroxide (H2O2) in their binary mixtures have been studied at 298 K by classical molecular dynamics simulations. Twelve different concentrations of aqueous-H2O2 solutions are considered for this study. We have analyzed the interactions between water and H2O2 by site-site pair correlation functions and observed that the probability of formation of OW···HP hydrogen bonds are higher compared to OP···HW. The second solvation shell of water is strongly affected by increasing H2O2 concentrations (XP > 0.50), which signifies the destruction of the tetrahedral network structure of water. The translational and rotational dynamics of water and H2O2 do not significantly change up to 25% of H2O2 in aqueous mixtures. The hydrogen bond lifetime of water-water, water-H2O2, and H2O2-H2O2 in the aqueous-H2O2 solutions shows a very minimal change with increasing H2O2 concentrations. In addition to this, we also investigated the effect of H2O2 on the insulin monomer and observed that higher concentrations of H2O2 (XP = 0.10) change the secondary structure. The influence of H2O2 is more on chain-B than that on chain-A in the insulin monomer. The H2O2 occupancy at the protein surface is higher for negatively charged (GLU) and polar (ASN and THR) amino acid residues compared with that for positively charged and neutral residues in the solutions.

Genome-wide identification of ascorbate peroxidase (APX) gene family and the function of SmAPX2 under high temperature stress in eggplant

Ascorbate peroxidase (APX) plays pivotal roles in regulating diverse biological processes in plants against biotic and abiotic stresses by eliminating hydrogen peroxide (H2O2). However, the function and information of APX gene family members in eggplant's response to high temperature stress remain largely unclear. Herein, we have identified nine APXs in the eggplant genome (SmAPXs), which were classified into three clades and the members of each clade exhibited similar gene structures and motifs. SmAPXs were distributed on seven chromosomes and contained phytohormone responsiveness-, defense and stress-related, and transcription factors binding cis-elements within their promoters. Transcript expressions of some SmAPXs, especially SmAPX2 that localize in cytomembrane and cytoplasm, were up-regulated by high temperature and ABA treatment. SmAPX2 exhibits APX enzyme activity, which enables to catalyze oxidation of ascorbic acid by H2O2in vitro and alleviate the H2O2 accumulation under high temperature stress by SmAPX2 transient expression in vivo. SmAPX2 silencing decreased eggplant's tolerance to high temperature stress, accompanied by transcript expression down-regulation of high temperature defense-related and ABA-response-related genes, reduction of APX enzyme activity, and increase of H2O2 content. These data provide comprehensive overview of SmAPX gene family, and indicate that SmAPX2 positively functions in eggplant response to high temperature stress.

Genome-Wide Identification of Catalase Gene Family and the Function of SmCAT4 in Eggplant Response to Salt Stress

Salinity is an important abiotic stress, damaging plant tissues by causing a burst of reactive oxygen species (ROS). Catalase (CAT) enzyme coded by Catalase (CAT) genes are potent in reducing harmful ROS and hydrogen peroxide (H2O2) produced. Herein, we performed bioinformatics and functional characterization of four SmCAT genes, retrieved from the eggplant genome database. Evolutionary analysis CAT genes revealed that they are divided into subgroups I and II. The RT-qPCR analysis of SmCAT displayed a differential expression pattern in response to abiotic stresses. All the CAT proteins of eggplant were localized in the peroxisome, except for SmCAT4, which localized in the cytomembrane and nucleus. Silencing of SmCAT4 compromised the tolerance of eggplant to salt stress. Suppressed expression levels of salt stress defense related genes SmTAS14 and SmDHN1, as well as increase of H2O2 content and decrease of CAT enzyme activity was observed in the SmCAT4 silenced eggplants. Our data provided insightful knowledge of CAT gene family in eggplant. Positive regulation of eggplant response to salinity by SmCAT4 provides resource for future breeding programs.

The effect of spermine on Tetranychus urticae-Cucumis sativus interaction

BackgroundTwo spotted spider mite, Tetranychus urticae (Acari: Tetranychidae) is one of the most important plant pests in the world. Due to increased resistance of mites to acaricides, it is necessary to use other methods such as inducing resistance in plants by natural compounds for pests' management. Polyamins such as spermine are effective in increasing plant resistance to biotic and abiotic stressors. In this research, the effect of spermine treatments in cucumber plants on life table parameters of T. urticae was investigated. Also, top-down effect of spermine and T. urticae on cucumber biochemical parameters was measured. In the experiments, 1, 2 and 3 mM spermine concentrations were used.ResultsAmongst the spermine treatments, those mites that fed on cucumbers which received 1 mM spermine showed the shortest protonymphal period and higher ovipositon period, fecundity, gross and net reproductive rates and life expectancy compare to control. Treatment with 2 mM spermine lead to the longest teleochrysalis period and shortest range of age-stage-specific fecundity period. In addition, 2 mM spermine lowered intrinsic and finite rate of population increase in T. urticae. The longest larval period of T. urticae was observed in 3 mM spermine. Feeding of T. urticae from cucumber plants increased hydrogen peroxide (H2O2), malondialdehyde (MDA) content, electrolyte leakage (EL) level and ascorbate peroxidase (APX) activity but inhibited catalase (CAT) activity in this plant. Infested cucumber plants treated with 2 mM spermine showed lower H2O2 and MDA content and highest activity of APX and CAT on day 1 and 3 compare to the others. The 3 mM spermine increased H2O2 content in infested plants during the whole experiment as well as non-infested plants in day 5 and 9 only. This treatment induced the highest MDA content and lowest catalase activity on day1, 3 and 5 of experiment in infested plants.ConclusionThis study showed that 2 mM spermine was the only effective concentration that reduce cucumber sensitivity to T. urticae. The trend of changes in biochemical parameters, especially H2O2, in 3 mM spermine was abnormal, and this concentration could be considered toxic.

The Growth, Leaf Antioxidant Enzymes and Amino Acid Content of Tomato as Affected by Grafting on Wild Tomato Rootstocks 1 (S. Pimpinellifolium and S. Habrochaites) Under Salt Stress

Salinity in soil or water is a serious threat to plant growth, which reduces yields and threatens food security. It is possible to reduce the negative effects of salinity on tomato scions through grafting. To evaluate the effects of salt stress on graft combinations in hydroponic conditions, SP3, SP4, SP5 (S. pimpinellifolium), SH1, SH3, SH5 (S. habrochaites) and two hybrids L × SP5 (S. lycopersicum L. × S. pimpinellifolium) and L × SH3 (S. lycopersicum L. × S. habrochaites) were used as rootstock and two varieties Galaxy and H2274 (S. lycopersicum L.) were used as scion. Plants were evaluated in terms of biomass parameters and antioxidant enzyme activities and amino acid contents in leaf tissues under control and salt stress conditions. Salt stress decreased the fresh weight of shoots and roots by 68.71 and 23.59, respectively, and increased H2O2 content (93.90 %) and MDA content (63.71 %). In addition, salt stress in leaf tissues POD (204.49 %), CAT (83.87 %), SOD (204.49 %), GR (88.23 %), GST (100.16 %), G6PD (32.85 %), 6GPD (46.19 %), APX (157.29 %) caused an increase in enzymes and total amino acid content (160.57 %). In salt stress conditions, SH5/Galaxy and L × SP5/Galaxy are the graft combinations with the highest fresh shoot and root weight, leaf number and root volume. These graft combinations contain the most isoleucine, proline lysine, alanine arginine, sucrosine leucine, methionine, hydroxyproline glutamate, glutamine and histidine amino acids in leaf tissues and have the lowest MDA content. Ungrafted H2274 and Galaxy plants have the highest MDA and content under salt stress conditions, these ungrafted plants have the least other amino acids and enzymes other than theonine amino acid in their leaf tissues. Furthermore, ungrafted plants under saline conditions had the lowest shoot and root fresh weight, leaf number and root volume. MDA content correlated negatively with shoot and root fresh weight, leaf number and root volume. H2O2 correlated positively with CAT, SOD, GST and peroxidase enzymes and negatively with APX, GR and G6PD enzymes. It seems that the antioxidant enzyme activity and amino acid content in leaf tissues influence salinity response and the appropriate rootstock/scion combination could be a viable method for tomato cultivation in saline conditions.

MD simulation of chemically enhanced polishing of 6H-SiC in aqueous H2O2

Chemical enhanced polishing (CEP) is a widely employed final process for achieving precise surface shaping and planarization of semiconductor wafers. However, determining the chemical effect involved in material removal through experimental means is extremely challenging. In this study, we conducted reactive force field (ReaxFF) molecular dynamics (MD) simulations to gain insight into the chemical effects of CEP using an aqueous hydrogen peroxide (H2O2) diamond suspension as a polishing medium for 6H-SiC single crystals. The inclusion of aqueous H2O2 resulted in the formation of SiOH and COH species, which are comparatively easier to remove through mechanical abrasion. Furthermore, an increase in H2O2 concentration was found to enhance the material removal. The MD simulations also revealed that the chemical effects on the Si-face of 6H-SiC were more pronounced than those on the C-face due to the generation of a greater number of SiO species and the favourable atomic structure of the Si-face for chemical removal. The results showed that the material remove rate on the Si-face is greater than that on the C-face during polishing, aligning with the findings from MD simulation. Furthermore, a systematic experimental study was carried out to examine the influence of various conditions on material removal rate and surface quality in both polishing and lapping processes.

Synergistic effects of hydrogen peroxide and phosphate on uranium(VI) immobilization: implications for the remediation of groundwater at decommissioned in situ leaching uranium mine.

The processes of acid in situ leaching (ISL) uranium (U) mines cause the pollution of groundwater. Phosphate (PO43-) has the potential to immobilize U in groundwater through forming highly insoluble phosphate minerals, but the performance is highly restricted by low pH and high sulfate concentration. In this study, hydrogen peroxide (H2O2) and PO43- were synergistically used for immobilizing U based on the specific properties of groundwater from a decommissioned acid ISL U mine. The removal mechanisms of U and the stability of U on the formed minerals were elucidated by employing X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and kinetic experiments. Our results indicated that the removal of U by simultaneously adding H2O2 and PO43- was significantly higher than the removal of U by individually adding H2O2 or PO43-. The removal of U increased with increasing PO43- concentration from 20 to 200 mg L-1 while decreased with increasing H2O2 concentration from 0.003 to 0.3%. Specifically, the removal efficiency of U from groundwater reached 98% after the application of 0.003% H2O2 and 200 mg L-1 PO43-. Amorphous iron phosphate that preferentially formed at low H2O2 and high PO43- concentrations played a dominant role in U removal, while the formations of schwertmannite and crystalline iron phosphates may be also contributed to the removal of U. This was significantly different from the immobilization mechanism of U through the formation of uranyl phosphate minerals after adding phosphate. The kinetic experimental results suggested that the immobilized U had a good stability. Our research may provide a promising method for in situ remediating U-contaminated groundwater at the decommissioned acid ISL U mines.

Capturing Cu2+ and recycling spent Cu-adsorbents as catalyst for eliminating Rhodamine B: reactivity and mechanism.

The thorny problem of adsorption is the disposing of spent adsorbent. In this manuscript, the exhaust adsorbent of efficient capture Cu(II) over ZSM-5 that supported zero-valent iron (nZVI) was reused as a catalyst for eliminating Rhodamine B (RhB). Batch experiments were used to evaluate the removal performance of Cu2+ and RhB. The results demonstrated that the Cu2+ adsorption process obeyed pseudo-second-order kinetics, and the adsorption performance was dependent on solution pH. The maximum adsorption capacity at the optimal pH 4.0 was 375.9 mg/g; equilibrium was reached rapidly within 35 min. From XPS, the reduction-oxidation between Fe0 and Cu2+ was occurred in the adsorption process, and Fe2+, Fe3+, and Cu0 was formed. In the recycling experiments, RhB was removed by the spent Cu adsorbent, with the removal performance being dependent on the initial Cu concentration, in the order of 5 mg/L > 20 mg/L > 0 mg/L > 100 mg/L > 500 mg/L. RhB removal also improved with increasing H2O2 concentration. More than 99.9% of the RhB was degraded within 8 min using 1.75 mM H2O2, which was a large improvement over the previously used catalyst. The hydroxyl radical was found to be the main free radical responsible for RhB degradation.

Phosphorus removal by porous aggregate from aerated concrete waste residues：Simulating porous structure, performance optimisation, adsorption mechanisms

In order to reveal the action mechanism of porous structure of aerated concrete waste residues as aggregate on its working performance and phosphorus removal performance, the porous aggregate is prepared by adjusting the of hydrogen peroxide (H2O2) content to simulate the pore structure of aerated concrete. The results show that with the increase of H2O2 content, the porosity and pore diameter of porous aggregate increases, which causes that the loose bulk density, cylinder compressive strength and softening coefficient decrease and the water absorption through time increases. The correlation coefficients between the four performances and total porosity exceeds 0.95. With the increase of H2O2 content, the pH value decreases and TP removal rate increases. The better fitting of the pseudo-second-order model and Elovich model confirms the key existence of chemical adsorption. In the fitting curve of Intraparticle diffusion model the second stage of rapid absorption becomes the main control step due to calcium and aluminum ions from capillary pores and gel pores and the hydration of unreacted particles. The Ca/Si and Al/Si decreases by 57.7% and 46.6% in EDS maps after phosphorus removal, and CaO/SiO2 and Al2O3/SiO2 in XRF results decrease. The hydration of unreacted C4A3Š and dissolution of Ca2+ and Al3+ during phosphorus removal promote the chemical absorption of porous aggregate. P/Si increases by 631.9% and P2O5/SiO2 increases from 0.01 to 0.11. The fluffy substances appears on the smooth inner wall of the porous aggregate in SEM morphology is phosphate mineral.

Seed nano-priming using silica nanoparticles: effects in seed germination and physiological properties of Stevia Rebaudiana Bertoni

BackgroundThis study aimed to assess the effects of different concentrations of silicon (Si) nutrient sources, including bulk silicon dioxide (bSiO2) and two types of silica nanoparticles, nSiO2 (I) and nSiO2 (II) at different concentrations of 1, 5, 10, 25, 50, and 100 ppm in the germination process of stevia. The priming experiment was conducted using a completely randomized design with three replicates to ensure the reliability of the results.ResultsAll stevia seedlings subjected to nano-priming significantly improved the germination parameters. The germination percentage increased by 106%, reaching 68% in nano-primed seedlings. Similarly, the germination rate showed a remarkable increase of 128.12% at 7.3 day−1. Additionally, the root, shoot, and seedling dry weight increased by 283%, 168.9%, and 220% and determined 0.092, 0.078, and 0.17 g plant−1, respectively, compared to the control. Furthermore, seed priming with nSiO2 (I) at a concentration of 10 ppm resulted in an increased catalase (CAT) activity (36.15 Umg−1 protein) and peroxidase (POX) activity (approximately 0.057 U.mg−1 protein). Also, the highest sucrose amount was observed in the root (equal to 160.4 μg g−1 DW) and shoot (equal to 247 μg g−1 DW) of seedlings primed with 10 ppm of nSiO2 (I). However, it should be noted that nano-priming at the highest concentration led to oxidative damage indicated by an increase in H2O2 concentration. Conversely, bSiO2 demonstrated a lesser effect on improving germination, seedling growth, antioxidant activities, and biochemical attributes compared to nSiO2 (I), and nSiO2 (II).ConclusionsThis study established that seed priming with nSiO2 (I) at a concentration of 10 ppm was the most effective in enhancing germination percentage and rate, root/shoot/dry weight, biochemical attributes, and enzyme activities (such as α-amylase, CAT, and POX). The results suggested that seed priming with nSiO2 (I) at the optimal concentration could improve the seed germination by enhancing the antioxidant system, starch metabolism, and ultimately protecting plants from oxidative damage.Graphical

Effect of H2O2 Concentration on Morphology, Reflectivity and Wettability of Si Nanowalls Prepared by Metal Assisted Chemical Etching

A facile and low cost method, metal assisted chemical etching was used to prepare silicon (Si) nanowalls atop the Si wafer, where the effect of etchant solution concentration (H2O2 concentration) on the morphology, reflectivity and wettability of the fabricated Si nanowalls is investigated. The morphological and structural studies by scanning and transmission electron microscopy revealed the Si nanowalls prepared at both low and high H2O2 concentration are smooth, nonporous and single crystalline, where the increase of H2O2 concentration only changes the morphology from isolated nanowall structure to agglomerated nanowall structure. The height of nanowalls also increases with increase in H2O2 concentration and follows a linear behaviour with an etching rate of 5697 nm/M. The reflectance study shows that the reflectance is extremely low over broad wavelength range (300-1100 nm) for Si nanowalls, compared to that of planar Si wafer. The increase of H2O2 concentration significantly changes the wavelength dependence of the reflectance spectrum. The wettability studies show that SiNWs prepared at low H2O2 concentration exhibit hydrophobicity in contrast to the hydrophilicity of planar Si wafer, where the increase of H2O2 concentration to very high value changes the hydrophobicity of SiNWs to hydrophilicity as similar to planar Si wafer.

ROS-mediated waterlogging memory, induced by priming, mitigates photosynthesis inhibition in tomato under waterlogging stress.

With global climate change, the frequency and intensity of waterlogging events are increasing due to frequent and heavy precipitation. Little is known however about the response of plants to repeated waterlogging stress events. The aim is to clarify physiological regulation mechanisms of tomato plants under repeated waterlogging stress, and whether Trichoderma harzianum can alleviate waterlogging injury. We identified two genotypes of tomato, 'MIX-002' and 'LA4440', as waterlogging tolerant and sensitive genotypes, respectively, based on plant biomass accumulation. The two tomato genotypes were subjected to a waterlogging priming treatment for 2 days (excess water for 1cm above substrate surface) followed by a recovery stage for 2 days, and then a second waterlogging stress for 5 days (excess water for 1cm above substrate surface) followed by a second recovery stage for 3 days. Leaf physiological, plant growth parameters, and the expression of five key genes were investigated. We found that the two genotypes responded differently to waterlogging priming and stress in terms of photosynthesis, reactive oxygen species (ROS), and osmotic regulatory mechanisms. Waterlogging stress significantly increased H2O2 content of 'MIX-002', while that of 'LA4440' had no significant change. Under waterlogging stress, photosynthesis of the two genotypes treated with waterlogging priming returned to the control level. However, Trichoderma harzianum treatment during the second recovery stage did not show positive mitigative effects. The plants of 'LA4440' with priming showed lower peroxidase (POD) activity and proline content but higher H2O2 content than that without priming under waterlogging stress. Under waterlogging stress with priming as compared to without priming, SODCC2 was downregulated in two tomatoes, and AGR2 and X92888 were upregulated in 'MIX-002' but downregulated in 'LA4440'. Overall, the two tomato genotypes exhibited distinct photosynthetic, ROS and osmotic regulatory mechanisms responding to the waterlogging stress. Waterlogging priming can induce stress memory by adjusting stomatal conductance, sustaining ROS homeostasis, regulating osmotic regulatory substances and key gene expressions mediated by H2O2, and thus alleviate the damage on tomato photosynthesis when waterlogging reoccurred.

Tuning active sites in MoS2-based catalysts via H2O2 etching to enhance hydrodesulfurization performance

A H2O2 etching strategy was adopted to introduce coordinatively unsaturated sites (CUS) on MoS2-based catalysts for dibenzothiophene (DBT) hydrodesulfurization (HDS). The CUS concentrations on MoS2 slabs were finely regulated by changing the concentrations of H2O2 solution. With the increasing H2O2 concentrations (0.1–0.3 mol/L), The CUS concentrations on MoS2 slabs increased gradually. However, the high-concentration H2O2 etching (0.5 mol/L) increased the MoOxSy and MoO3 contents on MoS2 slabs compared to etching with the H2O2 concentration of 0.3 mol/L, which led to the less CUS concentration in the sulfided Mo–H-0.5 catalyst than in the sulfided Mo–H-0.3 catalyst. A microstructure-activity correlation indicated that the CUS introduced by H2O2 etching on MoS2 slabs significantly enhanced DBT HDS. Different Co loadings were further introduced into Mo–H-0.3, which had the most CUS concentration, and the corresponding 0.2-CoMo catalyst with the highest CoMoS content (3.853 wt%) exhibited the highest reaction rate constant of 6.95 × 10−6 mol g−1 s−1 among these CoMo catalysts.

Decolorization of azo Direct Blue 71 dye in aqueous solutions using sequential upflow anaerobic sludge blanket reactor and UV/H2O2 process

In this research, decolorization of synthetic textile wastewater was investigated by upflow anaerobic sludge blanket (UASB) reactor and advanced oxidation UV/H2O2. In the acclimation phase, an 18 L UASB reactor with a discharge of 18 cm3/min was fed with a colorless synthetic wastewater for 40 days. Then the reactor was fed with wastewater containing Direct Blue 71 as the coloring agent at 6 consecutive steps with concentrations of 10, 50, 100, 200, 300 and 400 mg/L. In the first step, the removal efficiency was the least due to the low inflow dye concentration. However, by further increment of dye concentration in the influent to greater than 200 mg/L, the removal efficiency gradually increased and reached above 80 %. Since the treated effluent from steps 4–6 did not meet regulations, it was discharged into a UV/H2O2 reactor for further treatment. The results showed that with increasing H2O2 concentration, the removal efficiency increased, although excessive increase in H2O2 concentration reduced the removal efficiency. The pseudo-first order kinetic model was in good agreement with the degradation data with the optimal reaction rate constant at a concentration of 2225 mg/L of H2O2.

Antifungal and elicitor activities of p-hydroxybenzoic acid for the control of aflatoxigenic Aspergillus flavus in kiwifruit

Aspergillus flavus not only reduces kiwifruit production but also synthesizes carcinogenic aflatoxins, resulting in a relevant threat to human health. p-Hydroxybenzoic acid (pHBA) is one of the most abundant phenolics in kiwifruit. In this study, pHBA was found to reduce A. flavus mycelial growth by blocking the fungal mitotic exit network (MEN) and cytokinesis and to inhibit the biosynthesis of aflatoxins B1 and B2. The application of pHBA promoted the accumulation of endogenous pHBA and induced oxidative stress in A. flavus-infected kiwifruit, resulting in an increase in H2O2 content and catalase (CAT) and superoxide dismutase (SOD) activities. Preventive and curative treatments with 5 mM pHBA reduced A. flavus advancement by 46.1% and 68.0%, respectively. Collectively, the antifungal and elicitor properties of pHBA were examined for the first time, revealing new insights into the role of pHBA in the defense response of kiwifruit against A. flavus infection.

Resolving the Mechanism for H2O2 Decomposition over Zr(IV)-Substituted Lindqvist Tungstate: Evidence of Singlet Oxygen Intermediacy.

The decomposition of hydrogen peroxide (H2O2) is the main undesired side reaction in catalytic oxidation processes of industrial interest that make use of H2O2 as a terminal oxidant, such as the epoxidation of alkenes. However, the mechanism responsible for this reaction is still poorly understood, thus hindering the development of design rules to maximize the efficiency of catalytic oxidations in terms of product selectivity and oxidant utilization efficiency. Here, we thoroughly investigated the H2O2 decomposition mechanism using a Zr-monosubstituted dimeric Lindqvist tungstate, (Bu4N)6[{W5O18Zr(μ-OH)}2] ({ZrW5}2), which revealed high activity for this reaction in acetonitrile. The mechanism of the {ZrW5}2-catalyzed H2O2 degradation in the absence of an organic substrate was investigated using kinetic, spectroscopic, and computational tools. The reaction is first order in the Zr catalyst and shows saturation behavior with increasing H2O2 concentration. The apparent activation energy is 11.5 kcal·mol-1, which is significantly lower than the values previously found for Ti- and Nb-substituted Lindqvist tungstates (14.6 and 16.7 kcal·mol-1, respectively). EPR spectroscopic studies indicated the formation of superoxide radicals, while EPR with a specific singlet oxygen trap, 2,2,6,6-tetramethylpiperidone (4-oxo-TEMP), revealed the generation of 1O2. The interaction of test substrates, α-terpinene and tetramethylethylene, with H2O2 in the presence of {ZrW5}2 corroborated the formation of products typical of the oxidation processes that engage 1O2 (endoperoxide ascaridole and 2,3-dimethyl-3-butene-2-hydroperoxide, respectively). While radical scavengers tBuOH and p-benzoquinone produced no effect on the peroxide product yield, the addition of 4-oxo-TEMP significantly reduced it. After optimization of the reaction conditions, a 90% yield of ascaridole was attained. DFT calculations provided an atomistic description of the H2O2 decomposition mechanism by Zr-substituted Lindqvist tungstate catalysts. Calculations showed that the reaction proceeds through a Zr-trioxidane [Zr-η2-OO(OH)] key intermediate, whose formation is the rate-determining step. The Zr-substituted POM activates heterolytically a first H2O2 molecule to generate a Zr-peroxo species, which attacks nucleophilically to a second H2O2, causing its heterolytic O-O cleavage to yield the Zr-trioxidane complex. In agreement with spectroscopic and kinetic studies, the lowest-energy pathway involves dimeric Zr species and an inner-sphere mechanism. Still, we also found monomeric inner- and outer-sphere pathways that are close in energy and could coexist with the dimeric one. The highly reactive Zr-trioxidane intermediate can evolve heterolytically to release singlet oxygen and also decompose homolytically, producing superoxide as the predominant radical species. For H2O2 decomposition by Ti- and Nb-substituted POMs, we also propose the formation of the TM-trioxidane key intermediate, finding good agreement with the observed trends in apparent activation energies.

An Assessment of the Effects of Light Intensities and Temperature Changes on Cyanobacteria’s Oxidative Stress via the Use of Hydrogen Peroxide as an Indicator

Humans and other organisms are adversely affected by cyanobacterial blooming. This study aims to investigate the long-term effects of light intensities and different temperatures on Phormidium ambiguum and Pseudanabaena foetida. Enough P. ambiguum and P. foetida cells were acclimated for 24 days at 30 °C, 20 °C, and 10 °C in separate incubators. The starting day sample was collected after 24 days of acclimatization, and a second sample was collected seven days later at light intensities of 10, 30, 50, 200, and 600 µmol m−2 s−1 for each temperature. The optical density (OD730), hydrogen peroxide (H2O2) concentration, protein content, chlorophyll-a (Chl-a) concentration, and catalase (CAT) activity were measured. Light intensity changes soon after collection resulted in nearly identical starting day samples at each individual temperature. The H2O2 concentration and algal biomass increased until a light intensity of 200 µmol m−2 s−1 was reached and decreased afterward in each temperature for both species after seven days. In association with an increasing H2O2 concentration, the Chl-a concentration decreased after 50 µmol m−2s−1 of light intensity, affecting the protein content. The algal biomass was significantly lower at 10 °C compared to 30 °C. The CAT activity increased proportionately with the H2O2 concentration and algal biomass. Therefore, water bodies in the field can be illuminated with long-term high light intensities in different temperatures to reduce algal biomass.