Increasing H2O2 Concentration Research Articles

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.

The removal of NO from flue gas by Fe/NaOH/H2O2 system

NO emitted from coal combustion was harmful to the environment. For most current wet denitrification technologies, obtaining the desired removal efficiency was always dependent on the contact time of NO with the reaction solution. In this paper, a novel Fe/NaOH/H2O2 technology was proposed to remove NO, which could obtain 90% NO removal efficiency when the flue gas residence time in solution was 3 s. The mechanism of H2O2 decomposition and NO removal were analyzed. Results demonstrated that Fe and NaOH together catalyzed H2O2 to produce radicals, and ⋅O2− radicals took the main responsibility in the process of NO removal. NO3− and NO2− were the final forms of NO. In addition, the effects of several common experimental parameters were investigated on the NO removal performance. The increase of H2O2 concentration, Fe concentration, solution pH and reaction temperature all had a positive effect on NO removal, but this process was also accompanied by an intensification of the useless decomposition of H2O2 (consumption of H2O2 in the form of O2). The addition of SO2 to the flue gas had a slight effect on the NO removal and the useless decomposition of H2O2.

Synergistic Removal of Ciprofloxacin and Sulfamethoxazole by Lemna minor and Salvinia molesta in Mixed Culture: Implications for Phytoremediation of Antibiotic-Contaminated Water

Aquatic macrophytes have been used for the removal of antibiotics from contaminated water. Here, we have studied the capacity of Lemna minor and Salvinia molesta to reclaim ciprofloxacin (1.5 µg Cipro L−1) and/or sulfamethoxazole (0.3 µg Sulfa L−1) from artificially contaminated waters when plants were exposed in monoculture (L. minor or S. molesta) or in mixed culture (L. minor + S. molesta). Neither Cipro nor Sulfa alone induced negative effects on plants. As shown by the Abbot modelling, Cipro and Sulfa displayed antagonistic effects on plants. In both species, increased H2O2 concentrations and antioxidant enzyme activities were observed in plants when grown together. Although the antibiotics showed natural degradation, their concentration in water from treatments with plants was significantly lower, indicating the ability of the plants to uptake the compounds. When in co-culture, greater growth rates were observed for both plant species, which resulted in greater Cipro and Sulfa removal in the mixed system when compared with those with plants in monoculture. Both plants showed tolerance to the studied concentrations of antibiotics, with greater antibiotic uptake being reported for S. molesta. Although at the tested concentrations the antibiotics did not induce negative effects on plants, exposure to Cipro changed the relative yield of S. molesta, which may result in effects on community structure. The use of both L. minor and S. molesta in artificial wetlands may increase the phytoremediation capacity of systems.

Soluble and supported hematin as a catalyst for decolourization of anthraquinone textile dyes: A kinetic modelling validation study

Hematin-catalysed decolourizations of alizarin red S solutions were carried out in order to validate a peroxidatic model in competition with pseudo-catalatic routes. Absorbance and dissolved oxygen were followed with time and hematin was used in solution or immobilized onto chitosan. Initial rates decreased with increasing dye concentration. Modelled dye concentration profiles properly reproduced experimental data. Optimized rate constants indicated that immobilization reduced hematin activity, emphasized dye inhibition and promoted the pseudo-catalatic pathway. The increase in H2O2 concentration increased oxygen evolution rates whereas the increase of dye concentration depleted them, which agree with the kinetic model proposal. These findings were also discussed considering some additional reactions which consume or evolve oxygen. UV–visible stack spectra of reacting systems allowed to propose some degradation products, whose molecular weights decreased with the increase of hydrogen peroxide to dye molar ratio. This is consistent with accumulation of inorganic radicalsproposed by the pseudo-catalatic mechanism.

Effective nitric oxide removal from flue gas using UV/H2O2 solution catalyzed by Fe3O4@FeEDTA

AbstractBACKGROUNDHow to control NOx emission in flue gas economically and efficiently is the focus in the field of energy and environment in the world. In this work, Fe3O4‐magnetic microspheres were employed as the matrix with loading FeEDTA (where EDTA is ethylenediaminetetraacetic acid) to prepare magnetic denitrification absorbent Fe3O4@FeEDTA. The performance of nitric oxide (NO) removal using Fe3O4@FeEDTA dispersed in H2O2 solution with ultraviolet (UV) was first investigated.RESULTSThe results showed that Fe3O4@FeEDTA could be used as a good catalytic oxidation denitrification agent. Increasing H2O2 concentration and O2 concentration could promote NO absorption. NO removal efficiency increased as pH value increased from 1.5 to 3.0, then decreased when pH continued to increase. The elevated temperature was conducive to NO removal. CO2 hardly affected the removal of NO, while SO2 with high concentration was not conducive to NO absorption. In addition, the NO removal mechanism was preliminarily analyzed with X‐ray photoelectron spectrometry, electron spin resonance and ion chromatography. The mechanism study indicated that NO removal by Fe3O4@FeEDTA/H2O2 was a catalysis–complexation–oxidation–absorption process, in which •OH was determined to be the main oxidizing species, and NO captured by Fe(II)EDTA was mainly oxidized by •OH to NO3−.CONCLUSIONThe catalytic activity of Fe3O4@FeEDTA could maintain stability during the repeat experiment, realizing the recycling and reuse of Fe3O4@FeEDTA. The UV‐Fe3O4@FeEDTA‐activated H2O2 advanced oxidation technology is suitable for wet denitrification. © 2023 Society of Chemical Industry (SCI).

Gas Flow-Dependent Modification of Plasma Chemistry in μAPP Jet-Generated Cold Atmospheric Plasma and Its Impact on Human Skin Fibroblasts.

The micro-scaled Atmospheric Pressure Plasma Jet (µAPPJ) is operated with low carrier gas flows (0.25-1.4 slm), preventing excessive dehydration and osmotic effects in the exposed area. A higher yield of reactive oxygen or nitrogen species (ROS or RNS) in the µAAPJ-generated plasmas (CAP) was achieved, due to atmospheric impurities in the working gas. With CAPs generated at different gas flows, we characterized their impact on physical/chemical changes of buffers and on biological parameters of human skin fibroblasts (hsFB). CAP treatments of buffer at 0.25 slm led to increased concentrations of nitrate (~352 µM), hydrogen peroxide (H2O2; ~124 µM) and nitrite (~161 µM). With 1.40 slm, significantly lower concentrations of nitrate (~10 µM) and nitrite (~44 µM) but a strongly increased H2O2 concentration (~1265 µM) was achieved. CAP-induced toxicity of hsFB cultures correlated with the accumulated H2O2 concentrations (20% at 0.25 slm vs. ~49% at 1.40 slm). Adverse biological consequences of CAP exposure could be reversed by exogenously applied catalase. Due to the possibility of being able to influence the plasma chemistry solely by modulating the gas flow, the therapeutic use of the µAPPJ represents an interesting option for clinical use.

The phytoremediation capacity of Lemna minor prevents deleterious effects of anti-HIV drugs to nontarget organisms

We investigated physiological responses of Lemna minor plants and their capacity to remove tenofovir (TNF; 412 ng l−1), lamivudine (LMV; 5428 ng l−1) and/or efavirenz (EFV; 4000 ng l−1) from water through phytoremediation. In addition, the toxicological safety of water contaminated with these drugs after treatment with L. minor plants to photosynthetic microorganisms (Synechococcus elongatus and Chlorococcum infusionum) was evaluated. The tested environmental representative concentrations of drugs did not have a toxic effect on L. minor, and their tolerance mechanisms involved an increase in the activity of P450 and antioxidant enzymes (catalase and ascorbate peroxidase). L. minor accumulated significant quantities of TNF, LMV and EFV from the media (>70%), and the interactive effect of LMV and EFV increased EFV uptake by plants submitted to binary or tertiary mixture of drugs. Photosynthetic microorganisms exposed to TNF + LMV + EFV showed toxicological symptoms which were not observed when exposed to contaminated water previously treated with L. minor. An increased H2O2 concentrations but no oxidative damage in S. elongatus cells exposed to non-contaminated water treated with L. minor was observed. Due to its capacity to tolerate and reclaim anti-HIV drugs, L. minor plants must be considered in phytoremediation programs. They constitute a natural-based solution to decrease environmental contamination by anti-HIV drugs and toxicological effects of these pharmaceuticals to nontarget organisms.

Molecular Cloning and Expression Analysis of the Typical Class III Chitinase Genes from Three Mangrove Species under Heavy Metal Stress.

Chitinases are considered to act as defense proteins when plants are exposed to heavy metal stresses. Typical class III chitinase genes were cloned from Kandelia obovate, Bruguiera gymnorrhiza, and Rhizophora stylosa by using RT-PCR and RACE and named KoCHI III, BgCHI III, and RsCHI III. Bioinformatics analysis revealed that the three genes encoding proteins were all typical class III chitinases with the characteristic catalytic structure belonging to the family GH18 and located outside the cell. In addition, there are heavy metal binding sites in the three-dimensional spatial structure of the type III chitinase gene. Phylogenetic tree analysis indicated that CHI had the closest relationship with chitinase in Rhizophora apiculata. In mangrove plants, the balance of the oxidative system in the body is disrupted under heavy metal stress, resulting in increased H2O2 content. Real-time PCR illustrated that the expression level under heavy metal stress was significantly higher than that in the control group. Expression levels of CHI III were higher in K. obovate than in B. gymnorrhiza and R. stylosa. With the increase in heavy metal stress time, the expression level increased continuously. These results suggest that chitinase plays an important role in improving the heavy metal tolerance of mangrove plants.

Use of hydrogen peroxide to prime the autohydrolysis and enzymatic hydrolysis efficiency of wheat straw pulp residues

Exogenous ash penalties cause straw pulp residues to exhibit low autohydrolysis performance due to an organic–inorganic colloid medium. In this study, H2O2 was applied following the soil organism to oxidize the organic components playing a role in the buffer system by increasing the negative charge on the surface of the particulate ash, thus reducing the acid buffer and cation exchange capacity of the pretreated wheat straw pulp residue (WSPR). The results showed that with the enzymatic efficiency increasing concentrations (0–3%) of H2O2, the enzymatic efficiencies of pretreated WSPR improved significantly with increasing H2O2 concentration (0–3%) from 49.73 to 88.27%. A linear correlation was observed between these increases and the accessibility of the substrate to the enzymes, the substrate's surface charge, and the lignin's available surface area. The addition of 2% H2O2 in WSPR autohydrolysis was able to increase the production of glucose and xylooligosaccharides by 1.58 and 2.38 times, respectively. This work demonstrated an innovative option for producing fermentable sugars from WSPR by effectively abolishing the self-buffering effects during autohydrolysis.

Uncovering the Role of PdePrx12 Peroxidase in Enhancing Disease Resistance in Poplar Trees.

Peroxidase (Prx)-related genes are reported to be involved in the metabolism of hydrogen peroxide (H2O2) in plants. Here, we found that the expression of the PdePrx12 gene was upregulated in wild-type (WT) poplar line NL895 infected with the pathogens Botryosphaeria dothidea strain 3C and Alternaria alternata strain 3E. The PdePrx12 gene was cloned in the poplar line NL895 and its overexpression (OE) and reduced-expression (RE) vectors were constructed. OE and RE transgenic lines were then generated. The H2O2 content in the leaves was measured by DAB staining and spectrophotometric analysis, and the data revealed that the OE line had a reduced H2O2 content, whereas the RE line had an increased H2O2 content. These transgenic and WT plants were also inoculated with the 3C/3E pathogens. The leaf area infected by pathogen 3C/3E was determined and the OE line was found to have a larger area of infection, whereas the RE line was found to have a smaller area of infection. This result suggested PdePRX12 is involved in disease resistance in poplar. Given these results, this study demonstrated that when poplar is infected by pathogens, the expression of PdePrx12 is inhibited, leading to an increase in H2O2 content, thereby enhancing disease resistance.

MAPK cascade and ROS metabolism are involved in GABA-induced disease resistance in red pitaya fruit

This study investigates the effects of γ-Aminobutyric acid (GABA) and mitogen-activated protein kinase (MAPK) inhibitor (PD98059) in disease resistance in red pitaya fruit. Results demonstrated that GABA treatment suppressed the growth of Gilbertella persicaria; increased H2O2 content and O2•- production rate; enhanced reduced glutathione and ascorbic acid contents, as well as increased the activities and transcripts of catalase (CAT), NADPH oxidase (NOX), peroxidise (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR), and up-regulated HcMYB111/24 expressions. Furthermore, GABA promoted the expressions of HcMAPKKK1-HcMAPKK2/4-HcMAPK1/7 cascades. However, PD98059 +GABA treatment decreased the disease resistance against G. persicaria and reduced H2O2 content; inhibited the activities and gene expressions of NOX, CAT, SOD, POD, GR and APX, and down-regulated the expressions of HcMAPK1/7. These findings suggest that GABA induces disease resistance by regulating ROS metabolism and MAPK cascades in red pitaya fruit.

The distribution of submerged macrophytes in response to intense solar radiation and salinity reveals hydrogen peroxide as an abiotic stress indicator

The feasible condition for submerged macrophyte growth is hard to understand as many environmental factors contribute to establishing macrophyte distribution with different intensities generating excess reactive oxygen species (ROS). Among various kinds of ROS, hydrogen peroxide (H2O2) is relatively stable and can be measured accurately. Thus, for the quantification of submerged macrophyte species, H2O2 can be used to evaluate their distribution in a lake. Submerged macrophytes, such as Potamogeton anguillanus, were abundant in Lake Shinji. The largest biomass distribution was around 1.35 m deep, under low solar radiation intensity, and nearly no biomass was found less than 0.3 m deep, where solar radiation was high. Tissue H2O2 concentrations varied in response to the diurnal photosynthetically active radiation (PAR) intensity, which was followed by antioxidant activities, though slightly delayed. Laboratory experiments were conducted with different PAR intensities or salinity concentrations. A stable level of H2O2 was maintained up to about 200 μmol m−2 s−1 of PAR for 30 days, followed by a gradual increase as PAR increased. The H2O2 concentration increased with higher salinity. A change in Chlorophyll a (Chl-a) concentration is associated with an altering H2O2 concentration, following a unique negative relationship with H2O2 concentration. If H2O2 exceeded 45 μmol/gFW, the homeostasis collapsed, and H2O2 and Chl-a significantly declined afterward. The above findings indicate that H2O2 has a negative effect on the physiological condition of the plant. The increase in H2O2 concentration was prevented by antioxidant activities, which elevated with increasing H2O2 concentration.

Cobalt ferrite as an electromagnetically boosted metal oxide hetero-Fenton catalyst for water treatment

The cobalt ferrite Fenton catalysts were obtained by the flow co-precipitation method. FTIR, XRD, and Mössbauer spectroscopy confirmed the spinel structure. The crystallite size of the as-synthesized sample is 12 nm, while the samples annealed at 400 and 600 °C have crystallite sizes of 16 and 18 nm, respectively. The as-synthesized sample has a grain size of 0.1–5.0 μm in size, while the annealed samples have grain sizes of 0.5 μm–15 μm. The degree of structure inversion ranges from 0.87 to 0.97. The catalytic activity of cobalt ferrites has been tested in the decomposition of hydrogen peroxide and the oxidation of caffeine. The annealing of the CoFe2O4 increases its catalytic activity in both model reactions, with the optimal annealing temperature being 400 °C. The reaction order has been found to increase with increasing H2O2 concentration. Electromagnetic heating accelerates the catalytic reaction more than 2 times. As a result, the degree of caffeine decomposition increases from 40% to 85%. The used catalysts have insignificant changes in crystallite size and distribution of cations. Thus, the electromagnetically heated cobalt ferrite can be a controlled catalyst in water purification technology.

Effect of Salicylic Acid on the Growth and Development of Sweet Pepper (Capsicum annum L.) under Standard and High EC Nutrient Solution in Aeroponic Cultivation

High electrical conductivity (EC) in cultivation systems with the recirculating nutrient solutions can affect plant growth and development. This study aimed to investigate the effect of salicylic acid (SA) on the selected physiological and biochemical parameters of sweet pepper (Capsicum annum L.) growing aeroponically at standard and high concentrations of nutritive solutions. Four experimental variants were tested: (1) plants cultivated under low EC conditions, (2) plants cultivated under low EC conditions and treated with foliar SA, (3) plants cultivated under high EC conditions, (4) plants cultivated under high EC conditions and treated with SA on leaves and roots. The obtained results revealed that exogenous SA, regardless of EC, reduced the formation of fruits with calcium deficiency symptoms. Furthermore, SA helps plants to cope with high EC nutrient stress through an increase in leaf SPAD index, maximum light-adapted chlorophyll fluorescence and PSII viability. Exogenous SA reduced the number of soluble proteins both under low and high EC; however, increased H2O2 content induced a defence mechanism reflected by the upregulation of antioxidant enzyme activity. The results of the study provide valuable information on the role of SA in the alleviation of the harmful effect of salinity under aeroponic cultivation.

A Mechanistic Study of Goethite-Based Fenton-Like Reactions for Imidacloprid Degradation

Biotic transformation of imidacloprid (IMD) has been widely investigated in the environments. However, little was known about IMD degradation via abiotic pathways, such as reactive oxygen species (ROS)-based oxidation processes. Here we systematically investigated the mechanism of hydroxyl radical (•OH) production and the associated IMD degradation in the goethite (α-FeOOH)-based Fenton-like systems. Results showed that IMD can be efficiently degraded in the α-FeOOH/H2O2 systems, with degradation rate exceeded 80% within 48h. Based on the examination of electron paramagnetic resonance (EPR) and chemical probes, •OH was identified as the key ROS that responsible for IMD degradation. IMD can be decomposed via hydroxylation or removal of -N-NO2 to produce hydroxylated IMD, cyclic urea and 6-chloronicotinic acid, with the associated toxicities also evaluated. In addition, the increasing H2O2 concentration and decreasing solution pH both significantly increased IMD degradation. This study provides theoretical understanding for the implications of soil mineral-based Fenton-like reactions in the abiotic transformation of pesticide pollutants.

Modulations in protein phosphorylation explain the physiological responses of barley (Hordeum vulgare) to nanoplastics and ZnO nanoparticles.

To address the knowledge gap on the effects of the co-existence of nanomaterials on plant growth, barley (Hordeum vulgare L.) plants were irrigated with zinc oxide nanoparticles (0.5gL-1), nanoplastics (1gL-1), and the combination of these two nanomaterials for 10 days. The co-existence of nanoplastics and ZnO nanoparticles increased H2O2 concentration by 12.76% and 38.30%, compared with the ZnO nanoparticles and nanoplastics exposure. The concentration of abscisic acid (ABA) in plants under the co-existence of nanoplastics and ZnO nanoparticles was 29.53% and 10.42% higher than that in ZnO nanoparticles treated plants and nanoplastics treated plants. The global analysis of phosphoproteomics identified 132 phosphorylated proteins and 173 phosphorylation sites in barley leaves exposed to the nanomaterial combination, which were related to photosynthesis, carbon fixation, nitrogen metabolism, and arginine and proline metabolisms. Further physiological analysis indicated that the combination of ZnO nanoparticles and nanoplastics caused larger damage to the systems of antioxidant and carbohydrate metabolisms as exemplified by decreased activities of apoplastic peroxidases (25.10%-48.60%), glutathione reductase (91.07%-94.94%), and sucrose synthase (53.59%-61.19%) in roots and increased cell wall invertase activity (12.97%-17.61%) in leaves, compared with the single nanomaterial treatments. These results indicate that the modulations in protein phosphorylation were closely related to the physiological responses to nanomaterial exposure, suggesting that the co-existence of nanomaterials may lead to greater impacts than single ones.

Catalytic Oxidation of Benzoins by Hydrogen Peroxide on Nanosized HKUST-1: Influence of Substituents on the Reaction Rates and DFT Modeling of the Reaction Path

In this research, the oxidation of a series of benzoins, R-C(=O)-CH(OH)-R, where R = phenyl, 4-methoxyphenyl, 4-bromophenyl, and 2-naphthyl, by hydrogen peroxide in the presence of nanostructured HKUST-1 (suspension in acetonitrile/water mixture) was studied. The respective benzoic acids were the only products of the reactions. The initial average reaction rates were experimentally determined at different concentrations of benzoin, H2O2 and an effective concentration of HKUST-1. The sorption of the isotherms of benzoin, dimethoxybenzoin and benzoic acid on HKUST-1, as well as their sorption kinetic curves, were measured. The increase in H2O2 concentration expectedly led to an acceleration of the reaction. The dependencies of the benzoin oxidation rates on the concentrations of both benzoin and HKUST-1 passed through the maxima. This finding could be explained by a counterplay between the increasing reaction rate and increasing benzoin sorption on the catalyst with the increase in the concentration. The electronic effect of the substituent in benzoin had a significant influence on the reaction rate, while no relation between the size of the substrate molecule and the rate of its oxidation was found. It was confirmed by DFT modeling that the reaction could pass through the Baeyer-Villiger mechanism, involving an attack by the HOO- anion on the C atom of the activated C=O group.

Effects of polyethylene and biodegradable microplastics on photosynthesis, antioxidant defense systems, and arsenic accumulation in maize (Zea mays L.) seedlings grown in arsenic-contaminated soils

Arsenic (As) and microplastic (MP) co-exposure is a major environmental problem in terrestrial ecosystems. Polyethylene and biodegradable plastics decompose into MP particles under microbial-mediated and weathering conditions. However, the effects of MP particles on physiological responses and As accumulation in maize have not been thoroughly explored. In this study, the effects of polyethylene microplastic particles (PEMPs) and biodegradable microplastic particles (BPMPs) on As accumulation, growth and physio-biochemical performance of maize seedlings (Zea mays L.) in As-contaminated soil were investigated. Our study showed that 10 % PE reduced As content in maize seedlings leaves (roots) by 41.19(34.53) μg kg−1, compared to the control. The 10 % BP reduced As content in maize seedlings leaves (roots) by 64.24 (57.27) μg kg−1. 10 % PE (10 % BP) reduced maize seedlings leaf area, total chlorophyll content and photosynthetic rate by 5.05 % (21.68 %), 44.98 % (57.12 %) and 65.29 % (77.89 %) and increased H2O2 content by 38.04 % (179.6 %), respectively. The antioxidant defense system of maize seedlings leaves was damaged by PEMPs and As co-exposure. Maize seedlings has adapted to stress by regulating antioxidant enzyme activity and the AsA-GSH cycle under BPMPs and As co-exposure. This study provides new insights into the effects of PEMPs and BPMPs on phytotoxicity and As accumulation in As-contaminated soils. Preliminarily data suggests that BPMPs may exhibit greater toxic effects on maize seedlings than PEMPs, which warrants further exploration.

Role of oxidative stress in the physiology of sensitive and resistant Amaranthus palmeri populations treated with herbicides inhibiting acetolactate synthase.

The aim of the present study was to elucidate the role of oxidative stress in the mode of action of acetolactate synthase (ALS) inhibiting herbicides. Two populations of Amaranthus palmeri S. Watson from Spain (sensitive and resistant to nicosulfuron, due to mutated ALS) were grown hydroponically and treated with different rates of the ALS inhibitor nicosulfuron (one time and three times the field recommended rate). Seven days later, various oxidative stress markers were measured in the leaves: H2O2, MDA, ascorbate and glutathione contents, antioxidant enzyme activities and gene expression levels. Under control conditions, most of the analysed parameters were very similar between sensitive and resistant plants, meaning that resistance is not accompanied by a different basal oxidative metabolism. Nicosulfuron-treated sensitive plants died after a few weeks, while the resistant ones survived, independently of the rate. Seven days after herbicide application, the sensitive plants that had received the highest nicosulfuron rate showed an increase in H2O2 content, lipid peroxidation and antioxidant enzymatic activities, while resistant plants did not show these responses, meaning that oxidative stress is linked to ALS inhibition. A supralethal nicosulfuron rate was needed to induce a significant oxidative stress response in the sensitive population, providing evidence that the lethality elicited by ALS inhibitors is not entirely dependent on oxidative stress.