Higher Hydrogen Peroxide Production Research Articles

Electrolyte design for high hydrogen peroxide production rates utilizing commercial carbon gas diffusion electrodes

Electrolyte design for high hydrogen peroxide production rates utilizing commercial carbon gas diffusion electrodes

Rice resistance against Bipolaris oryzae infection is mediated by lower foliar potassium concentration

AbstractBrown spot, caused by Bipolaris oryzae, is a very important disease of rice. This study investigated the effect of potassium (K) on rice resistance to brown spot. The working hypothesis tested was that higher foliar K concentration could allow plants to respond more efficiently against fungal infection. Plants were grown in nutrient solution amended with three K rates (0.5, 1.0 and 2.5 mM) and noninoculated or inoculated with B. oryzae. The photosynthetic performance of plants, activities of defence and antioxidant enzymes and the concentrations of reactive oxygen species, phenolics and lignin were determined. Foliar K concentration was significantly higher by 38% and 91% for plants supplied with 1.0 and 2.5 mM K, respectively, compared to plants supplied with 0.5 mM K. Brown spot severity was significantly higher (≥20%) for plants supplied with 1.0 and 2.5 mM K than those supplied with 0.5 mM K (≤15%). Higher brown spot severity for plants supplied with 2.5 mM K resulted in changes in the photosynthetic apparatus, reduced chlorophyll a + b and carotenoids concentrations, and higher production of hydrogen peroxide and superoxide anion radical. In contrast, higher activities of defence and antioxidant enzymes and more production of phenolics for plants supplied with 0.5 mM K helped them to cope with B. oryzae infection more efficiently. In conclusion, rice resistance against brown spot was achieved by keeping a lower foliar K concentration linked to more active defence reactions, a robust antioxidative system and less damage to the photosynthetic apparatus.

Morpho-Physiological and Biochemical Responses of Field Pea Genotypes under Terminal Heat Stress.

Field pea is one of the important short-duration cool season pulse crops which contributes significantly towards food and nutritional security. Two heat-susceptible (HS) and two heat-tolerant (HT) genotypes were selected from the previous study for further characterization. A significant variation was observed for morpho-physiological traits studied. Principal component analysis explained that first two principal components, i.e., PC1 and PC2 showed 76.5% of the total variance in optimal condition, whereas 91.2% of the total variance was covered by the first two PCs in heat stress environment. The seed yield per plant determined significant and positive association with superoxide dismutase and number of seeds per pod under optimal conditions, whereas under heat stress condition, it was positively associated with number of effective pods per plant, biological yield per plant, proline, pod length, number of seeds per pod, superoxide dismutase, and peroxidase. The significant reduction was noticed in the susceptible genotypes, whereas tolerant genotypes showed stable and non-significant reduction in chlorophyll content. Further, minimum cell damage and higher hydrogen peroxide production was noticed in the susceptible genotypes. In addition, the biochemical characterization of HS and HT genotypes revealed that the higher expression of peroxidase, superoxide dismutase, and catalase modulates the tolerant responses in HT genotypes. These genotypes were further used in developing heat-tolerant field pea genotypes.

Applicability and antibacterial activity of polycyclic aromatic compound derivatives used as photocatalysts for water oxidation

Water is oxidized using 5,8-dicyano[5]phenacene, a thin-film catalyst supported on a silica plate by vacuum deposition; hydrogen peroxide is produced under visible-light irradiation. Despite the high hydrogen peroxide production rate during the initial reaction stage, the rate decreases after 12 h, and the reaction is almost terminated after 24 h, possibly because hydrogen peroxide undergoes self-decomposition. The self-decomposition rate of hydrogen peroxide increases with increasing concentration, and attains equilibrium. Additionally, Escherichia coli is efficiently sterilized using this catalyst under visible-light; the antibacterial effect is exhibited even under indoor light. Among several polycyclic aromatic derivatives, 9,10-dicyanoanthracene exhibits the highest hydrogen peroxide production rate and antibacterial activity against E. coli. Its antibacterial efficiency is approximately 16 times higher than that of 5,8-dicyano[5]phenacene. The oxygen species causing these antibacterial effects is investigated using trapping reagents. superoxide anion radicals and hydroxyl radicals induce antibacterial effects; hydroxyl radicals are particularly effective.

Folate receptor-targetable and tumor microenvironment-responsive manganese dioxide-based nano-photosensitizer for enhancing hypoxia alleviation-triggered phototherapeutic effects

Hypoxia in the tumor microenvironment (TME) is a major barrier to photodynamic cancer therapy (PCT) that entails oxygen-dependent cell killing. TME-responsive manganese dioxide (MnO2) nanoparticles have been used to alleviate hypoxia as well as improve the efficacy of PCT. However, many types of MnO2 nanoparticles do not have sufficient colloidal dispersity and stability as well as tumor targeting ability. To solve these problems, we developed a novel well-dispersible, tumor targetable-, TME-responsive-, and hypoxia alleviating-MnO2 nano-photosensitizer through the reaction of folate-polyethylene glycol-tetraethylenepentamine-chlorin e6 (Ce6) (FAPTEC) with Mn2+ under alkaline pH conditions to produce FAPTEC/MnO2 nanoparticles. The prepared FAPTEC/MnO2 nanoparticles exhibited good colloidal dispersity and stability under biological conditions, and they significantly increased oxygen production in situ following their degradation in the hypoxic TME, leading to enhancing singlet oxygen generation after laser irradiation. Moreover, after folate receptor-mediated cellular uptake, cytocompatible FAPTEC/MnO2 nanoparticles effectively alleviated hypoxia inside 4T1 cells with high hydrogen peroxide production under hypoxic conditions. Importantly, they also exerted more potent phototherapeutic effects under normoxic and even hypoxic conditions after laser irradiation compared to other photosensitizers (free Ce6 and FAPTEC). Therefore, our results suggest that FAPTEC/MnO2 nanoparticles provide promising nano-photosensitization for enhancing hypoxia alleviation-triggered phototherapeutic effects on hypoxic tumor cells.

Phosphorous Supplementation Alleviates Drought-Induced Physio-Biochemical Damages in Calligonum mongolicum.

Calligonum mongolicum is a phreatophyte playing an important role in sand dune fixation, but little is known about its responses to drought and P fertilization. In the present study, we performed a pot experiment to investigate the effects of P fertilization under drought or well-watered conditions on multiple morpho-physio-biochemical attributes of C. mongolicum seedlings. Drought stress leads to a higher production of hydrogen peroxide (H2O2) and malondialdehyde (MDA), leading to impaired growth and metabolism. However, C. mongolicum exhibited effective drought tolerance strategies, including a higher accumulation of soluble sugars, starch, soluble protein, proline, and significantly higheractivities of peroxidase (POD) and catalase (CAT) enzymes. P fertilization increased the productivity of drought-stressed seedlings by increasing their growth, assimilative shoots relative water content, photosynthetic pigments, osmolytes accumulation, mineral nutrition, N assimilation, and reduced lipid peroxidation. Our findings suggest the presence of soil high P depletion and C. mongolicum high P requirements during the initial growth stage. Thus, P can be utilized as a fertilizer to enhance the growth and productivity of Calligonum vegetation and to reduce the fragility of the hyper-arid desert of Taklamakan in the context of future climate change.

Sexual dimorphisms in renal mitochondrial bioenergetics

BackgroundStudies have shown that men have higher incidences of end‐stage renal disease than women at every point across the lifespan. Animal models for various renal diseases have similar occurrence with males being affected more frequently. Recent efforts have been heavily focused on delineating the mechanisms behind these sex‐based differences from various angles, with the mitochondria being highlighted as a target for sex difference‐related renal pathologies. The goal of this study is to investigate the sexual dimorphisms of renal mitochondria and their dependency on renal hemodynamics before disease onset.MethodsMitochondria were isolated from PBS‐flushed kidneys of Sprague Dawley male (SDM) and female (SDF) rats at 11 weeks of age using differential centrifugation. Renal cortex (SDMC vs SDFC) and medulla (SDMMvs SDFM) were separated for individual measurements. Mitochondrial membrane potential and hydrogen peroxide production were measured in spectrofluorimetry using the fluorescent dyes TMRM and Amplex Red, respectively. A portion of mitochondria were submitted to a histology core for electron microscopy. Additionally, mitochondrial oxygen consumption rate (OCR) was also assessed using Seahorse assay. Lipid peroxide radical formation was detected using electron paramagnetic resonance (EPR) with in vivo spin trapping. As a measure of renal function, GFR was assessed using FITC‐Inulin in conscious animals.ResultsElectron microscopy revealed similar yield of mainly round‐shaped isolated mitochondria with retained cristae and membrane structures in all groups. SDFM showed a higher membrane potential than SDMM (238.1±12.4 vs 162.0±8.8 au, p<0.001; respectively). Both SDFC and SDFM had higher hydrogen peroxide production in comparison to their male counterparts (cortex: 99443.7±3061.7 vs 69943.4±1708.6 au/protein, p<0.001; respectively. medulla: 113366.7±5430.7 vs 60613±2297.1 au/protein, p<0.001; respectively). Overall female mitochondria exhibited decreases in their basal, ATP‐linked, leaked OCRs as well as spare capacity compared to males (spare capacity: cortex: 5.9±0.6 vs 14.3±1.3, p<0.001; respectively. medulla: 4.9±0.6 vs 11.6±0.7 pmol/min/protein, p<0.001; respectively). EPR showed similar lipid peroxide radical levels in both sexes and sections of kidney. In the next part of the study, we explored if renal mitochondrial bioenergetics correlated with the GFR of the animal. Our data show the following GFR values for male and female rats as normalized to two kidney weights (2KW) and 2KW/ total body weight (2KW/TBW), respectively: 1.4±0.2 vs 0.8±0.1 mL/min/2KW, p=0.1416 and 0.5±0.1 vs 0.2±0.02 mL/min/2KW/TBW, p=0.0143. We did not observe any correlation between mitochondrial membrane potential and ROS production (measured in the isolated renal cortical mitochondria) with GFR in male or female rats (n= 5 in each group).ConclusionsOverall, we show here that female renal mitochondria exhibit lower oxygen consumption, higher ROS emission, and membrane potential vs males; however, lipid peroxidation is similar. Currently, we do not see a correlation between mitochondrial bioenergetics and GFR. More studies designed with higher statistical power are required to further elucidate the relationship between renal blood flow and mitochondrial bioenergetics.

Tuning oxygen-containing groups of pyrene for high hydrogen peroxide production selectivity

Oxygen-containing groups (OCGs) modified carbon materials can affect the microstructure and chemical composition, which is important for oxygen reduction to hydrogen peroxide (ORHP). Thus, exploring the relationship between structure and activity of OCG-containing electrodes is of great significance. In this work, we synthesized OCGs modified pyrene-based organic molecules as electrocatalysts for ORHP. Their electrocatalytic performance are correlated with types and locations of the modified OCGs. Particularly, the Pyr-2OMe with better absorption of O2 exhibits high H2O2 selectivity. DFT calculations reveal that the carbon atoms attached OCGs are the catalytic active sites. More importantly, the groups on one side of the molecules (Pyr-2OMe, Pyr-2OH, and Pyr-2CO) with large dipole moments exhibit superior catalytic activity. Thus, for the first time we find that the asymmetrically local charge redistribution of these catalysts can promote ORHP process. This work paves an alternative way to supply constructive information for understanding the structure and selectivity correlations.

Towards a more realistic heterogeneous electro-Fenton

• Mechanical design of the cell as a key issue in the scale-up. • Successful scaling-up of the heterogeneous electro-Fenton process. • Clofibric acid abatement was achieved regardless of the cell. • Higher hydrogen peroxide production & clofibric acid removal with improved design. With the aim of bringing the heterogeneous electro-Fenton (EF) treatment one step closer to a more realistic operation, the scaling-up of that technology was evaluated. Assays were performed firstly at lab scale in a stirred-tank reactor and then at bench scale in a flow setup including a jet aerator and a microfluidic flow-through electrochemical cell. A fluidized-bed reactor was added to the bench-scale installation in order to retain the solid catalyst, iron-containing alginate beads. To the best of the authors’ knowledge, there are no precedent studies reporting a heterogeneous EF treatment in a similar bench scale-configuration. Hydrogen peroxide generation and clofibric acid removal were assessed at both scales at current intensities of 0.12 and 0.25 A. Results showed that the scaled-up treatment was more efficient and cost-effective: at bench scale 18 times more volume was treated, the mass production of hydrogen peroxide was 28 higher and the specific cost for the removal of clofibric acid was cut by more than half. The most efficient treatment turned out to be the EF performed at 0.12 A at bench scale. Those results highlighted the importance of the reactor design in the scaling-up process. Additionally, aromatic intermediates were detected by liquid chromatography-mass spectrometry (LC-MS) and a degradation route was suggested. Carboxylic acids were also measured by HPLC confirming that the pollutant is mineralizing.

New insights into the hormonal regulation of silicon-supplied sorghum plants challenged with Colletotrichum sublineolum

Importance of sorghum as staple food worldwide is unquestionable and silicon (Si) supply has decreased the foliar symptoms of anthracnose, caused by Colletotrichum sublineolum, through potentiation of defense responses and preservation of photosynthetic apparatus. This study investigated the role of Si in cytological changes as well as in the expression of genes involved in auxin metabolism (GH3.1) and in signaling pathways mediated by salicylic acid (SA) (BTHip), jasmonic acid (JA)/ethylene (ET) (LOX), and JA (Jar, AOS 1, and ACCox) by real-time polymerase chain reaction in the leaves of plants non-supplied (-Si) or supplied (+Si) with Si and non-inoculated or inoculated with C. sublineolum. Sheath cells from +Si plants were less colonized by fungal hyphae due to intense phenolics and lignin deposition and high hydrogen peroxide production. Foliar lesions for +Si plants sprayed with an ET signaling inhibitor, ET biosynthesis inhibitor, and JA biosynthesis inhibitor were bigger compared to +Si plants sprayed with water. For +Si plants sprayed with ET and JA signaling inhibitors, foliar lesions were smaller compared to -Si plants sprayed with these same compounds. Suppression of auxin biosynthesis, transporter, and signaling by specific inhibitors resulted in smaller lesions. Expressions of GH3.1, BRHip, LOX, Jar, AOS 1, and ACCox were greater for +Si plants compared to -Si plants during the infection process of C. sublineolum. This study highlighted the potential of Si to boost sorghum resistance to anthracnose through a multistep process involving hormone-signaling pathways, especially regarding auxin metabolism and homeostasis, hydrogen peroxide generation, and plant cell wall strengthening.

A comparison between flow-through cathode and mixed tank cells for the electro-Fenton process with conductive diamond anode

This work focusses on the production of hydrogen peroxide and in the removal of bromacil by the electro-Fenton process using two different electrochemical cells: mixed tank cell (MTC) and flow-through cell (FTC). Both cells use boron doped diamond (BDD) as anode and carbon felt as cathode to promote the formation of hydrogen peroxide. In the case of the MTC, two surface area ratios, Acathode/Aanode, have been used. Results show that the H2O2 produced by MTC and FTCPSC increases with the time until a stabilization state. For the FTCPSC, the average hydrogen peroxide concentration produced increases progressively with the current, while for MTC the maximum values are found in applying very low current densities. In addition, the FTCPSC provides higher concentrations of hydrogen peroxide for the same current density applied. Regarding the MTC, it can be stated that the higher the area of the cathode, the higher is the amount of H2O2 produced and the lower is the cell voltage (because of a more efficient current lines distribution). The initial oxidation of bromacil is very efficiently attained being rapidly depleted from wastewater. However, the higher production of hydrogen peroxide obtained by the FTCPSC cell does not reflect on a better performance of the electro-Fenton process. Thus, bromacil is better mineralized using the MTC cell with the lowest cathode area. This observation has been explained because larger concentrations of produced hydrogen peroxide seems to benefit the oxidation of intermediates and not the mineralization.

Application of three-dimensional electrofenton process using MWCNTs-Fe3O4 nanocomposite for removal of diclofenac

Abstract The electrochemical removal of diclofenac (DCF) in aqueous solution was investigated by three-dimensional electrofenton (3DEF) process using Ti/TiO2-RuO2 anode electrode in the presence of composites of multi-walled carbon nanotubes (MWCNTs) and magnetite (Fe3O4) nanoparticle. The response surface methodology (RSM) coupled with central composite design (CCD) was used to evaluate the effects of different variables on the removal of DCF. Based on the experimental results, an empirical relationship between response and independent variables was obtained and expressed by a quadratic polynomial equation. Maximum DCF removal was 98.52% in optimum conditions at initial pH of 5.56, DCF concentration of 6.71 mg/L, the current density of 19.74 mA/cm2, MWCNTs-Fe3O4 concentration of 58.33 mg/L, and electrolysis time of 82.24 min. The chemical oxygen demand (COD) removal efficiency and H2O2 production in the 3DEF system were much higher than other electrocatalytic processes. This is related to the presence of MWCNTs-Fe3O4 as a particle electrode that can activate the molecular oxygen for higher production of hydrogen peroxide (H2O2) and hydroxyl radical (•OH). The MWCNTs-Fe3O4 nanocomposite indicated a high degree of stability and reusability. Additionally, 1-(2,6-dichlorophenyl) indolin-2-one, 2,6- dicholoaniline, 2,4- dichlorophenol, and 1,2- benzene dicarboxylic acid were identified as main oxidation products after 60 min reaction. Based on the reaction intermediate identified, a possible pathway for the electrochemical oxidation of DCF by the 3DEF process was proposed. Eventually, the 3DEF system with MWCNTs-Fe3O4 particle electrodes can be considered as a viable alternative for DCF removal from aqueous solution.

CfPDIP1, a novel secreted protein of Colletotrichum falcatum, elicits defense responses in sugarcane and triggers hypersensitive response in tobacco.

Colletotrichum falcatum, a hemibiotrophic fungal pathogen, causes one of the major devastating diseases of sugarcane-red rot. C. falcatum secretes a plethora of molecular signatures that might play a crucial role during its interaction with sugarcane. Here, we report the purification and characterization of a novel secreted protein of C. falcatum that elicits defense responses in sugarcane and triggers hypersensitive response (HR) in tobacco. The novel protein purified from the culture filtrate of C. falcatum was identified by MALDI TOF/TOF MS and designated as C. falcatum plant defense-inducing protein 1 (CfPDIP1). Temporal transcriptional profiling showed that the level of CfPDIP1 expression was greater in incompatible interaction than the compatible interaction until 120h post-inoculation (hpi). EffectorP, an in silico tool, has predicted CfPDIP1 as a potential effector. Functional characterization of full length and two other domain deletional variants (CfPDIP1ΔN1-21 and CfPDIP1ΔN1-45) of recombinant CfPDIP1 proteins has indicated that CfPDIP1ΔN1-21 variant elicited rapid alkalinization and induced a relatively higher production of hydrogen peroxide (H2O2) in sugarcane suspension culture. However, in Nicotiana tabacum, all the three forms of recombinant CfPDIP1 proteins triggered HR along with the induction of H2O2 production and callose deposition. Further characterization using detached leaf bioassay in sugarcane revealed that foliar priming with CfPDIP1∆1-21 has suppressed the extent of lesion development, even though the co-infiltration of CfPDIP1∆1-21 with C. falcatum on unprimed leaves increased the extent of lesion development than control. Besides, the foliar priming has induced systemic expression of major defense-related genes with the concomitant reduction of pathogen biomass and thereby suppression of red rot severity in sugarcane. Comprehensively, the results have suggested that the novel protein, CfPDIP1, has the potential to trigger a multitude of defense responses in sugarcane and tobacco upon priming and might play a potential role during plant-pathogen interactions.

High hydrogen peroxide production and antioxidative enzymes expression in the Chlamydomonas reinhardtii cia3 mutant with an increased tolerance to cadmium and anthracene

SUMMARYChlamydomonas reinhardtii cia3 mutant is deficient in activity of CAH3, a carbonic anhydrase isoform necessary for proper functioning of photosystem II (PS II). We used cia3 to verify the hypothesis that despite high concentration of external CO2, deficiency in CAH3 activity results in slight disorder of photosynthesis, which leads to mild but permanent overproduction of reactive oxygen species (ROS). As a consequence, cia3 should possess high ability to rebalance ROS homeostasis to overcome the oxidative stress induced by environmental factors, including chemical contaminations. We have found that in control conditions cia3 had a larger fraction of active PS II reaction centers but their efficiency was lower as compared with the wild type (WT), while H2O2 production by cia3 was significantly higher than in WT. In regard to ROS‐scavenging enzymes, the transcript level for superoxide dismutase (SOD) isoforms and the isoenzymes activity in cia3 were higher than in WT. There were no significant differences in the transcript level of ascorbate peroxidase (APX) and catalase (CAT) genes in both strains, and slightly elevated activity of the enzymes was observed in the cia3‐cells. Comparing the sensitivity of WT and cia3 to chemically‐induced stress we have found that the growth, photosynthesis and H2O2 production in WT were more strongly affected by cadmium and anthracene as compared with cia3. SODs expression and activity in the treated WT were higher than those in cia3, but APX and CAT activities were similar in both strains. Our results indicate that the CAH3‐deficiency is associated with markedly elevated H2O2 production and with a relatively higher initial transcript level and the activity of ROS‐scavenging enzymes. In consequence, cia3 revealed a higher tolerance to cadmium and anthracene compared with WT.

Electron shuttling catalytic effect of mellitic acid in zero-valent iron induced oxidative degradation

The enhanced oxidation capacity of zero-valent iron (ZVI) using mellitic acid (MA) as an electron shuttle catalyst was investigated using 4-chlorophenol (4-CP) as a model pollutant. In the presence of MA, enhanced electron transfer from ZVI surface to molecular oxygen resulted in higher production of hydrogen peroxide (H2O2), which subsequently increased the effective concentration of hydroxyl radical (HO) generated through the Fenton-type reaction. The possible role of MA as an efficient electron shuttle was supported by cyclic voltammetric estimation of MA reduction potential (E0=−0.184VNHE) and corroborated with photocurrent measurements in the ZVI suspension. Control experiments using Fe(II) ions instead of ZVI demonstrated that the presence of MA in the Fe(II)/H2O2 homogeneous system had no significant effect on the 4-CP oxidation efficiency. This indicates that the formation of a Fe(II)-MA complex does not contribute to the 4-CP oxidation pathway. The primary role of MA in the ZVI/O2 system seems to mediate the electron transfer from the ZVI surface to dioxygen. It implies that organic species containing multiple carboxylic ligands (species like MA or its structural analogues) may function as an electron shuttle in the ZVI/O2 catalytic system.

Electrocogeneration of hydrogen peroxide: Confocal and potentiostatic investigations of hydrogen peroxide formation in a direct methanol fuel cell

This work aims to fulfil some of the critical challenges associated with the electrochemical processes in commercialisation of an electrocogeneration direct methanol fuel cell: the understanding of the formation, decomposition and removal of hydrogen peroxide at the cathodic chamber. The better understanding of operating conditions on improving the electrocogeneration performance is also valuable for developing an optimal operating condition that enhances electrocogeneration activity. The production and removal of hydrogen peroxide are investigated by sensing the fluorescence signal in the cathodic chamber using confocal microscopy. It is found that the higher production of hydrogen peroxide promotes the intensity but reduces the cell potential due to the depletion of fresh reactant and the accumulation of hydrogen peroxide. Consequently, hydrogen peroxide should be removed efficiently in order to maintain the cell performance. The three-dimensional distribution and concentration of hydrogen peroxide are quantified at various operating potentials using fluorescence mapping, which is a correlation between the fluorescence signal and the concentration of hydrogen peroxide. The simultaneous fluorescence and potentiostatic investigations indicate that the electrocogeneration process is improved significantly by decreasing the cell potentials; the current efficiencies of 85.00, 64.78 and 51.13% are obtained at the operating potentials of 300, 400 and 550 mV respectively.

Oxygen reduction reaction catalyzed by ɛ-MnO2: Influence of the crystalline structure on the reaction mechanism

The oxygen reduction reaction (ORR) was studied in KOH electrolyte on carbon supported epsilon-manganese dioxide (ɛ-MnO2/C). The ɛ-MnO2/C catalyst was prepared via thermal decomposition of manganese nitrate and carbon powder (Vulcan XC-72) mixtures. X-ray powder diffraction (XRD) measurements were performed in order to determine the crystalline structure of the resulting composite, while energy dispersive X-ray analysis (EDX) was used to evaluate the chemical composition of the synthesized material. The electrochemical studies were conducted using cyclic voltammetry (CV) and quasi-steady state polarization measurements carried out with an ultra thin layer rotating ring/disk electrode (RRDE) configuration. The electrocatalytic results obtained for 20% (w/w) Pt/C (E-TEK Inc., USA) and α-MnO2/C for the ORR, considered as one of the most active manganese oxide based catalyst for the ORR in alkaline media, were included for comparison. The RRDE results revealed that the ORR on the MnO2 catalysts proceeds preferentially through the complete 4e− reduction pathway via a 2 plus 2e− reduction process involving hydrogen peroxide as an intermediate. A benchmark close to the performance of 20% (w/w) Pt/C (E-TEK Inc., USA) was observed for the ɛ-MnO2/C material in the kinetic control region, superior to the performance of α-MnO2/C, but a higher amount of HO2− was obtained when ɛ-MnO2/C was used as catalyst. The higher production of hydrogen peroxide on ɛ-MnO2/C was related to the presence of structural defects, typical of this oxide, while the better catalytic performance in the kinetic control region compared to α-MnO2/C was related with the higher electrochemical activity for the proton insertion kinetics, which is a structure sensitive process.

De-etiolation causes a phytochrome-mediated increase of polyamine oxidase expression in outer tissues of the maize mesocotyl: a role in the photomodulation of growth and cell wall differentiation

The photomodulation of polyamine oxidase (PAO) expression during de-etiolation of the maize (Zea mays L.) mesocotyl was used as the experimental model to investigate a possible correlation with the photomodulation of growth and with wall differentiation and stiffening. The accumulation of PAO transcript and enzyme activity were enhanced by light treatment in cortical and epidermal (outer) tissues of the mesocotyl. Histochemical analysis revealed that this phenomenon is mostly due to the increased level of PAO activity in epidermal and sub-epidermal tissues. The photomodulation of PAO activity upon de-etiolation in outer tissues is mediated by phytochrome. A close correlation was found between the time course of red-light-elicited increase of PAO activity and that of growth inhibition in the outer tissues of the apical, growing zone of the mesocotyl. Light exposure of etiolated, sub-apical mesocotyl segments resulted in a higher production of hydrogen peroxide (H2O2) in the incubation medium compared with segments incubated in the dark. The latter phenomenon was inhibited by the specific PAO inhibitor guazatine. A short pre-treatment of mesocotyl and coleoptile segments with 1 mM spermidine inhibited IAA-induced elongation growth, this phenomenon being reversed by catalase. Pre-treatment with catalase alone resulted in a higher extent of IAA-induced elongation. Moreover, pre-incubation with 1,3-diaminopropane, a product of spermidine oxidation catalysed by PAO, had no effect on IAA-induced elongation growth of either coleoptile or mesocotyl segments, while H2O2 pre-treatment was effective. These results indicate that PAO activity is important in producing H2O2 in vivo for peroxidase-catalysed wall-stiffening reactions and may be involved in the modulation of growth and cell wall differentiation in the maize mesocotyl.

Chemical Reactions of Organic Compounds with X-Ray Activated Water

Gas free solutions of carbon monoxide, alcohols, aldehydes, ketones and acids were irradiated in the concentration range 10 μM to 1 M, between pH=1 to 13 and the reactions studied principally by gas analysis and potentiometric acid analysis. One organic component systems and, to a more limited extent, two organic component systems were investigated. To obtain significant results, foreign organic matter must be strictly excluded from the low concentration solutions and the methods used to accomplish this are described. Organic impurities in the water can be detected by irradiating the water with x-rays and measuring the evolved hydrogen and carbon dioxide. The reactions cannot be briefly abstracted, but oxidation and condensation reactions with the evolvement of gaseous hydrogen are important in the effect of the rays. Carbon dioxide was produced from certain acids, particularly strongly from those having an oxygen containing group in the α-position. No liberation of carbon monoxide, hydrocarbons or oxygen was found. The effect of the rays on all the compounds studied depends on the hydrogen ion concentration, this factor affecting reaction rates as well as the nature of the reactions. The relation of reaction rate to pH can in some cases be represented by [P]=A(1+10−pH+α/1+10−pH+α).The rates of the reactions are in many cases independent of concentration, at high concentrations, but generally the rates decrease at low concentrations. The reason for this decrease may be the deactivation of the activated water, although this interpretation would, because of the form of the reaction product concentration curves, lead to the conclusion that the deactivation is approximately monomolecular (rather than bimolecular) during its initial stage. The same conclusion is indicated since the reaction rates are independent of x-ray intensity down to the lowest concentrations used. The x-ray reactions show some similarity to, but they are generally more complex than, the reactions produced by water activated with light inside the absorption band at 1900A. The irradiation of formic acid in the presence of oxygen at pH=3, results in a smaller decomposition of the formic acid than is produced in the absence of oxygen and a higher production of hydrogen peroxide than is obtained when oxygen is irradiated alone. This increased hydrogen peroxide production can be accounted for as resulting from the reaction of the oxygen with the nascent hydrogen liberated in the organic reaction.