Penetration of 35% hydrogen peroxide into the pulp chamber in bovine teeth after LED or Nd:YAG laser activation

This aim of the present study was to evaluate the pulp chamber penetration of 35% hydrogen peroxide activated by LED (light-emitting diode) or Nd:YAG laser in bovine teeth, after an in-office bleaching technique. Forty-eight bovine lateral incisors were divided into four groups, acetate buffer was placed into the pulp chamber and bleaching agent was applied as follows: for group A (n = 12), activation was performed by LED; for group B (n = 12), activation was performed by Nd:YAG laser (60 mJ, 20 Hz); group C (n = 12) received no light or laser activation; and the control group (n = 12) received no bleaching gel application or light or laser activation. The acetate buffer solution was transferred to a glass tube and Leuco Crystal Violet and horseradish peroxidase were added, producing a blue solution. The optical density of this solution was determined spectrophotometrically and converted into microgram equivalents of hydrogen peroxide. The results were analysed using ANOVA and Tukey's test (5%). It was verified that the effect of activation was significant, as groups activated by LED or laser presented greater hydrogen peroxide penetration into the pulp chamber (0.499 +/- 0.622 microg) compared with groups that were not (0.198 +/- 0.218 microg). There was no statistically significant difference in the penetration of hydrogen peroxide into the pulp chamber between the two types of activation (LED or laser). The results suggest that activation by laser or LED caused an increase in hydrogen peroxide penetration into the pulp chamber.

DEVELOPMENT OF POROUS CONCRETE GEOPOLYMER USING HYDROGEN PEROXIDE AS BLOWING AGENT.

Metakaolin and volcanic ashes respectively called MK and ZG were used as aluminosilicate raw materials for the synthesis of porous geopolymers. The hydrogen peroxide was used as a blowing agent. The geopolymer prepared were characterized by Spectroscopy Fourier Transform Infrared (SFTI), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and the determination of some physical properties such as bulk density, total porosity, volume shrinkage, compressive strength and thermal conductivity was also carried out. The presence of pores in the geopolymer obtained is function of the percentage of hydrogen peroxide added, causing the concomitantly decrease in compressive strength, apparent density and thermal conductivity. The use of hydrogen peroxide as a blowing agent gave some thermal insulation properties to these geopolymers which could be close to the properties of some commercial insulation materials.

Regulation of the OxyR transcription factor by hydrogen peroxide and the cellular thiol—disulfide status

The Escherichia coli transcription factor OxyR is activated by the formation of an intramolecular disulfide bond and subsequently is deactivated by enzymatic reduction of the disulfide bond. Here we show that OxyR can be activated by two possible pathways. In mutants defective in the cellular disulfide-reducing systems, OxyR is constitutively activated by a change in the thiol—disulfide redox status in the absence of added oxidants. In wild-type cells, OxyR is activated by hydrogen peroxide. By monitoring the presence of the OxyR disulfide bond after exposure to hydrogen peroxide in vivo and in vitro, we also show that the kinetics of OxyR oxidation by low concentrations of hydrogen peroxide is significantly faster than the kinetics of OxyR reduction, allowing for transient activation in an overall reducing environment. We propose that the activity of OxyR in vivo is determined by the balance between hydrogen peroxide levels and the cellular redox environment.

Ruthenium oxide hexacyanoferrate modified electrode for hydrogen peroxide detection

A sensor for H2O2 amperometric detection based on a Prussian blue (PB) analogue was developed. The electrocatalytic process allows the determination of hydrogen peroxide at 0.0 V with a limit of detection of 1.3 mu mol L-1 in a flow injection analysis (FIA) configuration. Studies on the optimization of the FIA parameters were performed and under optimal FIA operational conditions the linear response of the method was extended up to 500 mu mol L-1 hydrogen peroxide with good stability. The possibility of using the developed sensor in medium containing sodium ions and the increased operational stability constitute advantages in comparison with PB-based amperometric sensors. The usefulness of the methodology was demonstrated by addition-recovery experiments with rainwater samples and values were in the 98.8 to 103% range.

A Chloro-Bridged Linear Chain Imine-Copper(II) Complex and Its Application as an Enzyme-Free Amperometric Biosensor for Hydrogen Peroxide

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Lichen metabolites modulate hydrogen peroxide and nitric oxide in mouse macrophages

The activities of perlatolic acid (1), atranorin (2), and lecanoric acid (3) and their derivatives, such as orsellinates and β-methyl orsellinates obtained by alcoholysis, were assessed for stimulation of the release of hydrogen peroxide and nitric oxide in cultures of peritoneal macrophage cells from mice. The hydrogen peroxide production was estimated by oxidation of phenol red, while the Griess reagent was used to determine the nitric oxide production. 1 and 4-methoxy-ethyl orsellinate (XVII) were the compounds that induced the greatest release of H 2O 2, whereas n-pentyl orsellinate (IV), iso-propyl orsellinate (V), sec-butyl orsellinate (VI), and XVII induced a small release of NO. These results indicate that lichen products and their derivatives have potential immune-modulating activities. © 2009 Verlag der Zeitschrift für Naturforschung, Tübingen.

Toward pH-controllable bioelectrocatalysis for hydrogen peroxide based on polymer brushes

In the present work, a biosensor was built with smart material based on polymer brushes. The biosensor demonstrated a pH-sensitive on-off property, and it was further used to control or modulate the electrochemical responses of the biosensor. This property could be used to realize pH-controlled electrochemical reaction of hydrogen peroxide and HRP immobilized on polymer brushes. The composite film also showed excellent amperometric i-t response toward hydrogen peroxide in the concentration range of 0-13 μM. In future, this platform might be used for self-regulating targeted diagnostic, drug delivery and biofuel cell based on controllable bioelectrocatalysis. © 2013 Elsevier B.V.

Influence of the preparation method and the support on H2O 2electrogeneration using cerium oxide nanoparticles

This work describes the influence of the preparation method and the carbon support using a low contentof cerium oxide nanoparticles (CeO2/C 4%) on H2O2electrogeneration via the oxygen reduction reac-tion (ORR). For this purpose, the polymeric precursor (PPM) and sol-gel (SGM) methods with Vulcan XC72R (V) and Printex L6 (P) supports were employed. The materials were characterized by X-ray diffrac-tion (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). TheXRD analysis identified two phases comprising CeO2and CeO 2-x. The smallest mean crystallite size wasexhibited for the 4% CeO2/C PPM P material, which was estimated using the Debye-Scherrer equation tobe 6 nm and 4 nm for the CeO2and the CeO 2-xphases, respectively, and was determined by TEM to be5.9 nm. XPS analysis was utilized to compare the oxygen content of the 4% CeO2/C PPM P to Printex L6.The electrochemical analysis was accomplished using a rotating ring-disk electrode. The results showedthat the 4% CeO2/C specimen, prepared by PPM and supported on Printex L6, was the best electrocatalystfor H2O2production in 1 mol L -1NaOH. This material showed the highest ring current, producing 88%H2O2and transferring 2.2 electrons per O 2molecule via the ORR at the lowest onset potential. Addition-ally, the ring-current of the 4% CeO2/C PPM P material was higher than that of Vulcan XC 72R and PrintexL6, the reference materials for H2O 2production, indicating the highest electrocatalytic activity for the 4%CeO2/C PPM P material. © 2013 Elsevier Ltd. All rights reserved.

Hydrogen peroxide monitoring in Fenton reaction by using a ruthenium oxide hexacyanoferrate/multiwalled carbon nanotubes modified electrode

A novel amperometric sensor based on the incorporation of ruthenium oxide hexacyanoferrate (RuOHCF) into multiwalled carbon nanotubes (MWCNTs) immobilized on a glassy carbon electrode is described. Cyclic voltammetry experiments indicated that the cathodic reduction of hydrogen peroxide at the RuOHCF/MWCNTs100/GC modified electrode is facilitated, occurring at 0.0 V vs. Ag/AgCl/KCl(sat). Following the optimization of the experimental conditions, the proposed sensor presented excellent analytical properties for hydrogen peroxide determination, with a low limit of detection (4.7 mu mol L-1), a large dynamic concentration range (0.1-10 mmol L-1) and a sensitivity of 1280 mu A mmol(-1) L cm(-2). The usefulness of the RuOHCF/MWCNTs100/GC electrochemical sensor was confirmed by monitoring the consumption of hydrogen peroxide during the degradation of phenol by the Fenton reaction. (C) 2012 Elsevier B.V. All rights reserved.

Hydrogen peroxide-mediated neuronal cell death induced by an endogenous neurotoxin, 3-hydroxykynurenine.

3-Hydroxykynurenine (3-HK) is a tryptophan metabolite whose level in the brain is markedly elevated under several pathological conditions, including Huntington disease and human immunodeficiency virus infection. Here we demonstrate that micromolar concentrations (1-100 microM) of 3-HK cause cell death in primary neuronal cultures prepared from rat striatum. The neurotoxicity of 3-HK was blocked by catalase and desferrioxamine but not by superoxide dismutase, indicating that the generation of hydrogen peroxide and hydroxyl radical is involved in the toxicity. Measurement of peroxide levels revealed that 3-HK caused intracellular accumulation of peroxide, which was largely attenuated by application of catalase. The peroxide accumulation and cell death caused by 1-10 microM 3-HK were also blocked by pretreatment with allopurinol or oxypurinol, suggesting that endogenous xanthine oxidase activity is involved in exacerbation of 3-HK neurotoxicity. Furthermore, NADPH diaphorase-containing neurons were spared from toxicity of these concentrations of 3-HK, a finding reminiscent of the pathological characteristics of several neurodegenerative disorders such as Huntington disease. These results suggest that 3-HK at pathologically relevant concentrations renders neuronal cells subject to oxidative stress leading to cell death, and therefore that this endogenous compound should be regarded as an important factor in pathogenesis of neurodegenerative disorders.

Hydrogen Peroxide in Biocatalysis. A Dangerous Liaison

Hydrogen peroxide is a substrate or side-product in many enzyme-catalyzed reactions. For example, it is a side-product of oxidases, resulting from the re-oxidation of FAD with molecular oxygen, and it is a substrate for peroxidases and other enzymes. However, hydrogen peroxide is able to chemically modify the peptide core of the enzymes it interacts with, and also to produce the oxidation of some cofactors and prostetic groups (e.g., the hemo group). Thus, the development of strategies that may permit to increase the stability of enzymes in the presence of this deleterious reagent is an interesting target. This enhancement in enzyme stability has been attempted following almost all available strategies: site-directed mutagenesis (eliminating the most reactive moieties), medium engineering (using stabilizers), immobilization and chemical modification (trying to generate hydrophobic environments surrounding the enzyme, to confer higher rigidity to the protein or to generate oxidation-resistant groups), or the use of systems capable of decomposing hydrogen peroxide under very mild conditions. If hydrogen peroxide is just a side-product, its immediate removal has been reported to be the best solution. In some cases, when hydrogen peroxide is the substrate and its decomposition is not a sensible solution, researchers coupled one enzyme generating hydrogen peroxide “in situ” to the target enzyme resulting in a continuous supply of this reagent at low concentrations thus preventing enzyme inactivation. This review will focus on the general role of hydrogen peroxide in biocatalysis, the main mechanisms of enzyme inactivation produced by this reactive and the different strategies used to prevent enzyme inactivation caused by this “dangerous liaison”.

Permeability of different groups of maxillary teeth after 38% hydrogen peroxide internal bleaching

This study evaluated the influence of internal tooth bleaching with 38% hydrogen peroxide (H2O2) on the permeability of the coronal dentin in maxillary anterior teeth and premolars. Seventy teeth (14 per group) were used: central incisors (CI), lateral incisor (LI), canines (C), first premolars (1PM) and second premolars (2PM). Pulp chamber access and transversal sectioning at 2 mm from the cementoenamel junction were performed and the specimens were divided into 2 groups (n= 7): a) no treatment and b) bleaching with 38% H2O2. The bleaching agent was applied to the buccal surface and to the pulp chamber for 10 min. This procedure was repeated 3 times. The specimens were processed histochemically with copper sulfate and rubeanic acid, sectioned longitudinally, and digitalized in a scanner. The area of stained dentin was measured using Image Tool software. Data were analyzed statistically by ANOVA and Tukey's HSD test (?=0.05). There was statistically significant difference (p<0.001) among the untreated groups, CI (0.23 ± 0.26) having the lowest permeability and LI (10.14 ± 1.89) the highest permeability. Among the bleached groups, dentin permeability was increased in all groups of teeth except for 2PM. It may be concluded that bleaching with 38% H2O2 affected dentin permeability near the pulp chamber in maxillary anterior teeth and in first and second premolars.

Hydrogen peroxide bleaching of cellulose pulps obtained from brewer`s spent grain

Brewer`s spent grain (BSG) was evaluated for bleached pulp production. Two cellulose pulps with different chemical compositions were produced by soda pulping: one from the original raw material and the other from material pretreated by dilute acid. Both of them were bleached by a totally chlorine-free sequence performed in three stages, using 5% hydrogen peroxide in the two initial, and a 0.25 N NaOH solution in the last one. Chemical composition, kappa number, viscosity, brightness and yield of bleached and unbleached pulps were evaluated. The high hemicellulose (28.4% w/w) and extractives (5.8% w/w) contents in original BSG affected the pulping and bleaching processes. However, soda pulping of acid pretreated BSG gave a cellulose-rich pulp (90.4% w/w) with low hemicellulose and extractives contents (7.9% w/w and < 3.4% w/w, respectively), which was easily bleached achieving a kappa number of 11.21, viscosity of 3.12 cp, brightness of 71.3%, cellulose content of 95.7% w/w, and residual lignin of 3.4% w/w. Alkaline and oxidative delignification of acid pretreated BSG was found as an attractive approach for producing high-purity, chlorine-free cellulose pulp.

Treatment of industrial effluents of recalcitrant nature using ozone, hydrogen peroxide and ultraviolet radiation

Currently diverse industries have high pollution potential because their productive processes generate great volumes of refractory effluents. These effluents are problematic, mainly due to the presence of recalcitrant compounds that are detrimental in wastewater treatment plants using biological systems in their processes. In general, biological treatments do not remove refractory elements. Also, in most cases these compounds can inhibit the yield or are toxic for biota responsible to remove the polluting agents. The Advanced Oxidative Processes (AOPs) represent a technological alternative with a great potential for treatment of no biodegradable effluents. In this paper a review of the use of advanced oxidatives processes: Ozone (O(3)), peroxide of hydrogen (H(2)O(2)) and ultraviolet radiation (UV) is presented applied to the treatment of recalcitrant effluents.