Increasing H2O2 Concentration Research Articles

Oxidation and Destruction of Polyvinyl Alcohol under the Combined Action of Ozone–Oxygen Mixture and Hydrogen Peroxide

The oxidative transformations of a polyvinyl alcohol in aqueous solutions are studied under the simultaneous action of the two oxidizing agents, an ozone–oxygen mixture and a hydrogen peroxide. Effective parameters a and b, which characterize the first and second channels of carboxyl group accumulation, respectively, grow linearly upon an increase in the initial concentration of H2O2. After the temperature dependence of a and b parameters (331–363 K) in a PVA + O3 + O2 + H2O2 + H2O reaction system is studied, the parameters of the activation of COOH group accumulation are found (where PVA is a polyvinyl alcohol). New data on the effect process conditions (length of oxidation, temperature, and hydrogen peroxide concentration) have on the degree of destructive transformations of polyvinyl alcohol in the investigated reaction system are obtained.

Concentration-dependent effect of bleaching agents on the immunolabelling of interleukin-6, interleukin-17 and CD5-positive cells in the dental pulp.

To evaluate lymphocyte-like cell activation (CD5-positive cells) and the expression of interleukin (IL)-6 and IL-17 in the pulp after tooth bleaching with two concentrations of hydrogen peroxide (H2 O2 ). The right and left maxillary molars from 40 rats were treated randomly with bleaching gel with 20% H2 O2 (BLUE group, 1 application of 50min), 35% H2 O2 (MAXX group, three applications of 15min), or placebo gel (control). After 2 and 30days, the rats were killed (n=10), and the jaws were processed for histological and immunohistochemistry analysis of the pulp tissue. The scores of inflammation and immunolabelling (IL-6/IL-17) were submitted to Mann-Whitney and Kruskal-Wallis followed Dunn tests, respectively; anova tests were used for comparisons of number of CD5-positive cells and pulp chamber area values (P<0.05). At 2days, 60% of specimens of the BLUE group were associated with moderate inflammation in pulp horns, and in the MAXX group with necrosis (P<0.05). At 30days, the pulp was organized, and tertiary dentine was formed. The MAXX group had superior immunolabelling of IL-17 at 2days differing significantly from other groups (P<0.05). At 2days, 90% of the specimens of the BLUE group had moderate immunolabelling of IL-6, and 50% of the MAXX group had severe immunolabelling, both significantly different from the control (P<0.05). There was no significant difference between the groups at 30days (P>0.05). CD5-positive cells were present at 2 and 30days, particularly in the bleached groups (P<0.05), without significant difference between time periods (P>0.05). IL-6 and IL-17 participated in inflammation in the pulp tissue of rats after tooth bleaching, particularly at 2days. The immunolabelling was greater with increasing H2 O2 concentration. This process was accompanied by the prolonged activation of CD5-positive cells.

Combined effect of copper and hydrodynamic conditions on Myriophyllum alterniflorum biomarkers

The aim of this study is to determine the combined effect of copper and hydrodynamic conditions on the response of certain biomarkers of an aquatic macrophyte, namely Myriophyllum alterniflorum. Watermilfoil biomarkers are monitored in a synthetic medium enriched or not with copper (100 μg.L−1) for 21 days in aquarium systems (150 L), under three hydrodynamic conditions: laminar, turbulent, and calm. The studied biomarkers are: respiratory and photosynthetic activities; concentrations of chlorophyll a, b and carotenoids; osmotic potential; hydrogen peroxide content; and growth. In addition, Cu contents in water and in Myriophyllum alterniflorum (roots and shoots) are investigated. The hydrodynamic conditions only affect watermilfoil morphology. Copper accumulates less in turbulent zones; moreover, it is more likely to accumulate in shoots than in roots, except within the calm zone. Cu leads to: i) a significant increase in H2O2 content, ii) a decrease in root growth, pigment content, osmotic potential, photosynthesis and respiration rates, and iii) an inhibition of shoot branching. Differential effects are also observed between younger and older parts, thus indicating the benefit of considering these two plant parts separately in water quality biomonitoring.

Oxidative stress response to aluminum oxide (Al2O3) nanoparticles in Triticum aestivum

The development of nanotechnologies has increased the amount of manufactured metal oxide nanoparticles in the environment. In the view of nanoparticle dispersion to the environment, assessment of their toxicity becomes very crucial. Aluminum oxide (Al2O3) nanoparticles have wide range of use in industry as well as personal care products. The aim of this study was to evaluate the dose dependent effects of 13-nm-sized Al2O3 nanoparticles on wheat correlating with the appearance of enzymatic and non-enzymatic antioxidant defense response. Wheat roots were exposed to different concentrations of Al2O3 nanoparticles (5, 25 and 50 mg mL−1) for 96 h. The effects of Al2O3 nanoparticles were studied using different parameters such as H2O2 content, superoxide dismutase and catalase activity, lipid peroxidation, total proline, photosynthetic pigment and anthocyanin content. The results indicated that while Al2O3 nanoparticles caused a dose dependent increase in H2O2 content, superoxide dismutase activity, lipid peroxidation and proline contents, the catalase activity was decreased in compare the control. Moreover, total chlorophyll, chlorophyll a, carotenoids and anthocyanin contents reduced in the highest concentration 50 mg mL−1. In conclusion, Al2O3 nanoparticles caused oxidative stress in wheat after 96 h.

Enhanced photocatalytic activity of Fe3O4-WO3-APTES for azo dye removal from aqueous solutions in the presence of visible irradiation

ABSTRACTDevelopment of highly active photocatalysts for treatment of dye-laden wastewaters is vital. The photocatalytic removal of azo dye Reactive Black 5 was investigated by Fe3O4-WO3-3-aminopropyltriethoxysilane (APTES) nanoparticles in the presence of visible light. The Fe3O4-WO3-APTES nanoparticles were synthesized via a facile coprecipitation method. The photocatalyst was characterized by XRD, FT-IR, SEM, EDX, VSM, UV–Vis, and pHPZC techniques. The effects of some operational parameters such as solution pH, nanophotocatalyst dosage, initial RB5 concentration, H2O2 concentration, different purging gases, and type of organic compounds on the removal efficiency were studied by the Fe3O4-WO3-APTES nanoparticles as a photocatalyst. Maximum phtocatalytic activity was obtained at pH 3. The photocatalytic removal of RB5 increased with increasing H2O2 concentration up to 5 mM. The removal efficiency declined in the presence of different purging gases and all types of organic compounds. First-order rate constant (kobs) decreased from 0.027 to 0.0022 min−1 and electrical energy per order (EEo) increased from 21.33 to 261.82 (kWh/m3) with increasing RB5 concentration from 10 to 100 mg/L, respectively. The efficiency of LED/Fe3O4-WO3-APTES process for RB5 removal was approximately 89.9%, which was more effective than the LED/Fe3O4-WO3 process (60.72%). Also, photocatalytic activity decreased after five successive cycles.

Degradation behavior of triclosan by co-exposure to chlorine dioxide and UV irradiation: influencing factors and toxicity changes.

This study investigated the transformation of triclosan (TCS) following co-exposure to UV irradiation and ClO2. Special attention was given to understand the influencing of water quality parameters and toxicity changes during the co-exposure process. The results show that the co-exposure process prompted TCS elimination quickly and effectively, with more than 99% of TCS degraded under the experimental conditions. The molar yield ratios of 2,4-dichlorophenol/TCS (2,4-DCP/TCS) were calculated to be 35.81-74.49%; however, the by-product of 2,8-dichlorodibenzop-dioxin (2,8-Cl2DD) was not detected. The TCS degradation was sensitive to ClO2 dosage, pH, H2O2, and natural organic matter (NOM), but not to the carbonate (CO32-) concentration. Neutral and slightly alkaline condition were favorable to TCS elimination. The TCS removal rate increased from 85.33 to 99.75% when the ClO2 concentration increased from 0.25 to 1.5mgL-1. TCS degradation can be promoted at low NOM level (1, 3, and 5mgL-1), whereas was inhibited at high NOM concentrations of 7 and 9mgL-1. While adding H2O2, the degradation rate of TCS increased with increasing H2O2 concentration from 1 to 3mgL-1; however, too low or overdosed H2O2 (0.5 and 5mgL-1) hindered TCS degradation. Based on the results of a microtox bioassay, the toxicity did not change following the co-exposure process.

Antioxidant potential in Stevia rebaudiana callus in response to polyethylene glycol, paclobutrazol and gibberellin treatments.

The study on Stevia callus has the potential to advance the knowledge of antioxidant mechanisms involved in unorganized cells response to drought stress. The effects of polyethylene glycol (PEG; 0 and 4% w/v) in combination with paclobutrazol (PBZ; 0 and 2mgl-1) and gibberellin (GA; 0 and 2mgl-1) were studied on Stevia rebaudiana callus. PEG treatment led to an oxidative stress, as indicated by increased H2O2 contentwhose accumulation was prevented with PBZ and GA treatments. All treatments of PEG, PBZ and GA increased the total antioxidant capacity, with the highest antioxidant power in PBZ and GA treatments without PEG. The activity of superoxide dismutase, catalase and ascorbate peroxidase significantly increased in PEG treatment alone or in combination with PBZ and GA. All treatments of PEG, PBZ and GA significantly increased proteins, amino acids and proline contents, with the highest increase in presence of PBZ in medium culture. In contrary to proline, the activity of pyrroline-5-carboxylate synthetase and proline dehydrogenase did not change in response to any of thetreatments. Collectively, our results demonstrated that PBZ and GA increased reactive oxygen species scavenging and osmolytes in PEG-treated calli more than PEG treatment alone to alleviate negative effects of PEG on Stevia calli. These findings will enable us to design effective genetic engineering strategies in callus culture to generate some somaclonal variation that may be useful in enhancing drought resistance in Stevia.

H2O2 and NADPH oxidases involve in regulation of 2-(2-phenylethyl)chromones accumulation during salt stress in Aquilaria sinensis calli

2-(2-Phenylethyl)chromones are the main compounds responsible for the quality of agarwood, which is widely used in traditional medicines, incenses and perfumes. H2O2 and NADPH oxidases (also known as respiratory burst oxidase homologs, Rbohs) mediate diverse physiological and biochemical processes in environmental stress responses. However, little is known about the function of H2O2 and NADPH oxidases in 2-(2-phenylethyl)chromones accumulation. In this study, we found that salt stress induced a transient increase in content of H2O2 and 2-(2-phenylethyl)chromones accumulation in Aquilaria sinensis calli. Exogenous H2O2 remarkably decreased the production of 2-(2-phenylethyl)chromones, while dimethylthiourea (DMTU), a scavenger of H2O2, significantly increased 2-(2-phenylethyl)chromones accumulation in salt treated calli. Three new H2O2-generating genes, named AsRbohA-C, were isolated and characterized from A. sinensis. Salt stress also induced a transient increase in AsRbohA-C expression and NADPH oxidase activity. Furthermore, exogenous H2O2 increased AsRbohA-C expression and NADPH oxidase activity, while DMTU inhibited AsRbohA-C expression and NADPH oxidase activity under salt stress. Moreover, diphenylene iodonium (DPI), the inhibitor of NADPH oxidases, reduced AsRbohA-C expression and NADPH oxidase activity, but significantly induced 2-(2-phenylethyl)chromones accumulation during salt stress. These results clearly demonstrated the central role of H2O2 and NADPH oxidases in regulation of salt-induced 2-(2-phenylethyl)chromones accumulation in A. sinensis calli.

Heterotrophic cultivation of Euglena gracilis on chemically pretreated media

Abstract In this research, the impact of chemical agents on the growth of Euglena gracilis and contaminants (S. cerevisiae and B. subtilis) in different cultivation media was studied. E. gracilis was cultivated on modified Hutner and complex medium in Erlenmeyer flasks and a stirred tank bioreactor. H2O2 and antimycin were used as suppressors of contaminant growth activities during algae cultivation. The use of antimycin as a chemical suppressor of contaminants is not recommendable because of its significant impact on the E. gracilis growth. At a H2O2 concentration of 5 mg L-1 contaminant growth activities were almost completely suppressed. In these conditions, E. gracilis is capable to grow, but a further increase of H2O2 concentration is related to significant reduction of algae growth. H2O2 as a suppressor of contaminants has great potential for industrial application, but its optimal concentration for a particular bioprocess has to be determined in order to obtain the maximal bioprocess efficiency.

Removal of organic pollutants from produced water using Fenton oxidation

Produced water (PW) is the largest stream of wastewater from oil and gas exploration. It is highly polluted and requires proper treatment before disposal. The main objective of this study was to investigate the effectiveness of Fenton oxidation in degradation of organic matter in PW. The role of operating factors viz., H2O2 concentration (0.12 × 10-3 moles/L to 3 moles/L), [H2O2]/[Fe2+] molar ratio (2 to 75), and reaction time (30 to 200 minutes), on COD removal was determined through a series of batch experiments conducted in acidic environment at room temperature. The experiments were conducted with 500 mL PW samples in 1L glass beakers covered on the outside with aluminum foil to protect them from sunlight. Pre-decided amounts of ferrous sulfate heptahydrate (FeSO4.7H2O) and hydrogen peroxide (H2O2) were added to initiate the Fenton reaction. An increase in COD removal was observed with increase in reaction time and [H2O2]/[Fe2+] molar ratio. COD removal also increased with H2O2 concentration up to 0.01 moles/L; further increase in H2O2 concentration decreased the COD removal efficiency. Over 90% COD removal was achieved under optimum reaction conditions. The study indicates that Fenton oxidation is effective for remediation of PW in terms of organic matter removal.

Reaction control of metal-assisted chemical etching for silicon-based zone plate nanostructures.

Metal-assisted chemical etching (MACE) reaction parameters were investigated for the fabrication of specially designed silicon-based X-ray zone plate nanostructures using a gold catalyst pattern and etching solutions composed of HF and H2O2. Etching depth, zone verticality and zone roughness were studied as a function of etching solution composition, temperature and processing time. Homogeneous, vertical etching with increasing depth is observed at increasing H2O2 concentrations and elevated processing temperatures, implying a balance in the hole injection and silica dissolution kinetics at the gold–silicon interface. The etching depth decreases and zone roughness increases at the highest investigated H2O2 concentration and temperature. Possible reasons for these observations are discussed based on reaction chemistry and zone plate design. Optimum MACE conditions are found at HF : H2O2 concentrations of 4.7 M : 0.68 M and room temperature with an etching rate of ≈0.7 μm min−1, which is about an order of magnitude higher than previous reports. Moreover, our results show that a grid catalyst design is important for successful fabrication of vertical high aspect ratio silicon nanostructures.

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

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

Bleaching and enamel surface interactions resulting from the use of highly-concentrated bleaching gels

Tooth bleaching is considered a non-invasive treatment, although the use of highly-concentrated products may provoke increased surface roughness and enamel demineralization, as well as postoperative sensitivity. Thus, the aim of this study was to investigate whether hydrogen peroxide (H2O2) concentration would affect tooth bleaching effectiveness and the enamel surface properties. Enamel/dentin bovine specimens (6 × 4 mm) were immersed in coffee solution for 7 days and evaluated with a spectrophotometer (Easyshade; baseline), using the CIEL*a*b* color parameters. Hardness was measured using a hardness tester. The specimens were randomly assigned into four groups: one negative control, in which the specimens were not bleached, but they were irradiated with a laser-light source (Whitening Lase II, DMC Equipments); and three groups using distinct H2O2 concentration, namely LP15% (15% Lase Peroxide Lite), LP25% (25% Lase Peroxide Sensy), and LP35% (35% Lase Peroxide Sensy), all products from DMC. The bleached specimens were also irradiated with the laser-light source. After bleaching, all specimens were evaluated using scanning electron microscopy (SEM). pH kinetics and rate was monitored during bleaching. The data were analyzed using ANOVA and Tukey’s test (p < 0.05). All bleaching gels produced similar color change (p > 0.05). Concerning hardness, only the LP25% and LP35% significantly reduced hardness after bleaching; also, there was a progressive tendency for a greater percentage reduction in hardness with increased H2O2 concentration of the gel (R2 = 0.9973, p < 0.001). SEM showed that LP25% and LP35% produced an etching pattern on enamel with prism rods exposure. In conclusion, H2O2 concentration above the 15% level does not increase bleaching effectiveness, and may increase the possibility for alteration of enamel hardness, surface morphology, and acidity of the medium. When using H2O2-based bleaching agents, dental practitioners should choose for less concentrated gels, e.g., around the 15% level.

Crystal growth mechanism of calcium phosphate coatings on titanium by electrochemical deposition

The pulsed current electrochemical deposition of calcium phosphate (Ca-P) coatings on a titanium substrate was investigated in this study. The effects of applied voltage and H2O2 concentration in the electrolyte solution on the phase composition and coating morphology were studied using X-ray diffraction and scanning electron microscopy. At lower concentrations of H2O2, the coating consists of mixed phases of dicalcium phosphate dehydrate, octa-calcium phosphate, and hydroxyapatite, whereas increased H2O2 concentrations results in a dual phase of octa-calcium phosphate and hydroxyapatite being deposited. Furthermore, with increasing H2O2 concentration, the voltage must be reduced in order to avoid H2 evolution. The best conditions for Ca-P deposition were achieved at −1.4V and 1.5wt% H2O2. The morphological changes at different deposition times as well as the crystallographic orientation of deposited crystals were studied using scanning electron microscopy and transmission electron microscopy. It was found that the crystal growth of Ca-P coatings is a time-dependent process. During the first stage of deposition (t=1min), the electrolyte is supersaturated and randomly oriented polycrystals of Ca-P nucleate and form nanoplates. During the second stage (t=3min), crystals grow slightly in a more oriented fashion and form micro-sized plates. During the third stage (t>10min), the deposited crystals grow in a highly directional manner and the morphology of the coating consists of elongated ribbon-like single crystals.

PTCA (1H-pyrrole-2,3,5-tricarboxylic acid) as a marker for oxidative hair treatment.

Hair analysis for the assessment of alcohol or drug abstinence has become a routine procedure in forensic toxicology. Hair coloration leading to loss of incorporated xenobiotics and to false negative results has turned out to be a major problem. Currently only colored extracts provide hints of manipulations but not bleaching. A liquid chromatographic-tandem mass spectrometric (LC-MS/MS) method was developed and validated to determine 1H-pyrrole-2,3,5-tricarboxylic acid (PTCA), a major oxidation product of melanin. PTCA was determined in natural hair samples (n=21) after treatment with 3% hydrogen peroxide (H2 O2 ) for 30 or 40minutes with concentrations up to 12% for 40minutes. In another series, 12 natural hair samples were submitted to different coloration procedures (henna, tinting, semi-permanent and permanent dyeing, bleaching) and the changes in PTCA content were determined. A significant increase in the PTCA content was found for both incubation times and increasing H2 O2 concentrations. Coloration with henna or tinting had no influence on PTCA levels detected, but a significant increase was observed after semi-permanent and permanent dyeing and bleaching. As PTCA concentrations in natural hair were found to be in a range of <2.1-16.4ng/mg (8.4±3.8ng/mg, mean±SD, n=33), a cut-off of 20ng/mg is recommended for the distinction between natural vs. excessively oxidized hair. In case of naturally low melanin content (light-blond or white hair), no marked increase in PTCA may occur. The present study demonstrated that PTCA is formed during oxidative treatment of melanin in hair, which can be used to detect previous hair coloration including oxidation.

Nitric oxide acts downstream of hydrogen peroxide in regulating aluminum-induced antioxidant defense that enhances aluminum resistance in wheat seedlings

In response to aluminum (Al) stress, various plants increase their antioxidant defense system. In wheat, Al tolerance is a complex phenomenon, and whether this Al-induced response eventually enhances the ability of wheat to tolerate Al or not is still unclear and evidence is also scarce about the signals triggering it. After Al exposure, an increase in the intracellular concentration of H2O2 occurred within 2h in tolerant genotype, but was not observed in sensitive genotype. Stimulating rapid H2O2 accumulation in the root tips of Yang-5 with H2O2 donor relieved Al-induced root inhibition. In addition, pretreatment with H2O2 donor enhanced the activity of nitrate reductase (NR), which, in turn, induced accumulation of endogenous NO in both genotypes; whereas H2O2 scavenger or inhibitor blocked NO burst in roots of tolerant genotype. Conversely, Al-induced transient H2O2 generation was not sensitive to NO scavenger. Scavenging or inhibition of NO burst aggravated H2O2-relieved Al-induced root inhibition as well as oxidative damage. Elevated antioxidant enzyme activities induced by H2O2 donor were also suppressed by NO scavenger or NR inhibitor. These results suggest a novel signaling pathway where Al-induced transient H2O2 production mediates NO burst in regulating Al-induced antioxidant defense that enhances Al resistance in wheat seedlings.

Structural and Functional Properties Changes of β-Conglycinin Exposed to Hydroxyl Radical-Generating Systems.

The objective of the present study was to examine the structural and functional changes of β-conglycinin exposed to oxidizing radicals produced by FeCl3/H2O2/ascorbic acid hydroxyl radical-generating system (HRGS) for 3 h at room temperature. Increasing H2O2 concentrations resulted in a loss of histidine residues, lysine residues, and available lysine, which was accompanied by the formation of protein carbonyls and disulphide bonds (p < 0.05). Changes in secondary structure, surface hydrophobicity, and intrinsic fluorescence indicated that hydroxyl radicals had induced protein unfolding and conformational alterations. Results from SDS-PAGE implied that a small amount of protein cross-linkages produced by oxidative incubation. The emulsifying properties of β-conglycinin were gradually improved with the increasing extent of oxidation. The structural changes above contributed to the reduction of potential allergenicity of β-conglycinin, as verified by specific ELISA analysis. These results suggest that moderate oxidation could partially improve the protein functional properties and reduced the potential allergy of protein, providing guidance for effective use of moderately oxidized soy protein in the industry.

Preparation and antioxidant properties of low molecular holothurian glycosaminoglycans by H2O2/ascorbic acid degradation

An effective method of free radical degradation induced by H2O2/ascorbic acid, which was different from previously reported H2O2/Cu2+ method, was developed to depolymerize a novel glycosaminoglycan from Holothuria mexicana (HmG). The results indicated that the degradation efficiency increased with the reduced solution concentration, increased H2O2 concentration and ascorbic acid concentration. The chemical composition and structure of different molecular HmG were analyzed. The results showed that the primary structure and sulfate esters were well reserved during the degradation. Two dimension nuclear magnetic resonance of a low molecular product (DHmG-2) indicate that it contained chondroitin sulfate backbone and major 4-O-sulfated fucose branches. The antioxidant assays of HmG and DHmG-3 showed a fine scavenging abilities on 1,1-diphenyl-2-picrylhydrazyl (DPPH), superoxide and hydroxyl radicals in concentration dependent manner. Besides, molecular weight did not obviously affect the antioxidant activities of HmG.

Insights into nuclear DNA content, hydrogen peroxide and antioxidative enzyme activities during transverse thin cell layer organogenesis and ex vitro acclimatization of Malaxis wallichii, a threatened medicinal orchid.

Malaxis wallichii (Lindl.) Deb, a small, perennial, monopodial, terrestrial orchid, is endemic to tropical Himalayas at an altitude of 1200-2000m asl. The pseudobulbs are important ingredients of century old drug 'Ashtavarga' and a polyherbal energetic tonic 'Chyavanprash'. An efficient genetically stable in vitro propagation protocol using transverse thin cell layer culture system was established for M. wallichii. In the present report, meta-topolin alone proved to be three times more beneficial compared to other routinely used cytokinins in inducing highest number of shoot buds, plant height and growth of regenerated shoots. The highest regeneration frequency (89%) along with maximum number of adventitious shoots per explant (22.5±0.6) was observed in MS medium supplemented with 1.0mg/l meta-topolin and 0.5mg/l α-naphthalene acetic acid. Highest rooting frequency with highest number of roots (8.66±0.3) was achieved in half-strength MS medium fortified with 1.0mg/l indole acetic acid. Clonal stability of in vitro-derived plantlets was evaluated and compared to donor plant using intron splice junction (ISJ) markers and flow cytometry. ISJ markers revealed 4.76% clonal variability indicating high degree of genetic stability amongst the in vitro-derived regenerants. The nuclear DNA content of M. wallichii (2n) was found to be 2C=2.760±0.02pg and therefore, 1349.64Mbp (1C). Flow cytometry analysis of actively growing young and mature leaves from donor as well as in vitro-derived plantlets revealed presence of three peaks corresponding to 2C, 4C and 8C, while 2C was the most abundant. In the present investigation, there was no significant difference in the 2C DNA content between the mother and in vitro-derived plants; however, the frequency of endopolyploid cells varied in young and adult plants. An increased H2O2 content as well as lipid peroxidation activities were observed during early stages of acclimatization which declined afterwards. The enhanced activities of antioxidant enzymes like superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase in acclimatized plantlets as compared to in vitro-grown ones revealed their active involvement in growth and development against oxidative stress under external adverse environment.

Leaching of yttrium from cathode ray tube fluorescent powder: Kinetic study and empirical models

In this paper, leaching kinetics of yttrium from cathode ray tubes in sulphuric acid and hydrogen peroxide solution was investigated. It was found that hydrogen peroxide concentration, followed by temperature, has the greatest influence on leaching rate. Leaching rate is clearly enhanced by the increase in H2O2 concentration. The leaching process without hydrogen peroxide follows the kinetic model controlled by the chemical regime, whereas in presence of H2O2 it follows the kinetic model controlled by diffusion through the product layer. The apparent activation energy was determined to be 40.0kJ/mol and 90.3kJ/mol with and without hydrogen peroxide in solution, respectively. Moreover, the experimental data were used to describe empirical mathematical models in order to predict the yttrium extraction as a function of sulphuric acid concentration, hydrogen peroxide concentration, temperature and time. From the analysis of the results and models, the optimal conditions to maximize the extraction of yttrium were inferred: 40°C, 10%vol hydrogen peroxide, 15min of reaction with 15%wt/vol pulp density, or alternatively at higher temperature (80°C) 15%wt/vol pulp density, 120–180min with 0% or 5%vol hydrogen peroxide in solution. Hence, yttrium is easily leached from CRTs powder at low temperature (40°C) with higher concentration of hydrogen peroxide, or by means of higher temperature (80°C) and lower concentration, even null, of hydrogen peroxide.