High Concentrations Of Hydrogen Peroxide Research Articles

Hydrogen Peroxide Production in an Electrochemical Flow-by Reactor using Gas Diffusion Electrodes Modified with Organic Redox Catalysts

This paper presents a proposal to use an electrochemical flow-by reactor for hydrogen peroxide electrogeneration using cathodes formed from the incorporation of organic redox catalysts (2-ethylanthraquinone, 2-tert-butylanthraquinone, alizarin, and azobenzene) in the structure of gas diffusion electrodes. These electrodes help circumvent the low solubility of oxygen in aqueous solutions. Organic redox catalysts, which typically contain quinone or azo groups in their structure, were added to the electrode mass in a 10% proportion. The electrodes were used to study the electrogeneration of hydrogen peroxide in situ, in an acid medium (0.1 mol L-1 H2SO4 and 0.1 mol L-1 K2SO4, pH 1), inside an electrochemical flow-by reactor. Comparative analysis among the different catalysts indicated that the best electrode for hydrogen peroxide electrogeneration was the gas diffusion electrode modified with 10% of 2-ethylanthraquinone. With an underflow rate of 200 L h-1, hydrogen peroxide was formed with a maximum yield of 998.12 mg L-1 after 2 h at -2.0 V vs Pt//Ag/AgCl, for which the energy consumption was 11.21 kWh kg-1. The use of the electrochemical flow-by reactor was much more efficient, in that it yielded higher concentrations of hydrogen peroxide with extremely low energy consumption, compared to that obtained when using an electrochemical cell. In addition, for ensuring appropriate usage of the electrodes, optimizing their potential for the maximum generation of hydrogen peroxide, and obtaining the highest efficiency for the reduction of oxygen, a fuzzy algorithm was developed to help support the user’s decision.

Enhanced electrochemical oxidation process with hydrogen peroxide pretreatment for removal of high strength ammonia from semiconductor wastewater

Electrochemical oxidation (EO) process was investigated for decomposing ammonia in wastewater from semiconductor industry. This wastewater typically contains high concentration of hydrogen peroxide as well as ammonia in nature. As results of lab test, the presence of hydrogen peroxide exhibited a significant negative effect on ammonia removal efficiency, which was described by an oxidant-scavenging reaction pathway with recurrence relationship. Hydrogen peroxide removal by activated carbon was proposed as a pretreatment of EO process not only for the enhancement of reaction rate but also for the stability of effluent quality. As results of pilot test, ammonia removal rates were enhanced 2 ∼ 3.5 times after pretreatment. In addition, economic analysis results indicated that operating expense with pretreatment was about 60 % of that without pretreatment, which was about 30 % less than that in conventional chlorination without addition of hazardous chemicals. The suggested process has great potential for alternative to conventional chlorination in treatment of high strength ammonia wastewater from semiconductor industry.

Outstanding self-lubrication of SiC ceramic with porous surface/AlCoCrFeNiTi0.5 high-entropy alloy tribol-pair under 90 wt% H2O2 harsh environment

High-concentration hydrogen peroxide solution (HCHP) was regard as potential fuel resources. However, mechanical wear of moving parts under HCHP was energy-wasteful and dangerous. This work designed a novel SiC ceramic/AlCoCrFeNiTi0.5 high-entropy alloy tribo-pair, which successfully achieved outstanding self-lubrication under HCHP. The lubrication behavior of the proposed tribo-pair mainly benefitted from three aspects: (i) oxidation and hydrolysis reactions of SiC ceramic, (ii) hydrodynamic and secondary lubrication effects of surface pores, (iii) inhibited adhesion behaviors between SiC ceramic and AlCoCrFeNiTi0.5 alloy. Rounding the pore edges of SiC ceramic further improved the load-carrying capacity of self-lubrication. The wear bottleneck problem under harsh HCHP was solved in this work.

Peracetic acid-induced kraft lignin solubilization and its characterization for selective production of macromolecular biopolymers

This study was conducted to investigate the degradation characteristics of kraft lignin (KL) during peracetic acid (PAA) treatment, and to produce potentially valuable polymers of low molecular weight lignin by controlling the reaction conditions. For the peracetic acid treatment, acetic acid (AA) and hydrogen peroxide (HP) were directly mixed at ratios of 4:1, 1:1, and 1:4 (v/v) and employed as reaction media. After PAA treatment of kraft lignin at 80 °C, complete dissolution of the lignin and reduction in the molecular weight were observed. When the PAA reaction was performed at high HP concentration (1:4, v/v), the aromatic lignin skeleton opened and converted to a structure containing large amounts of carboxyl groups. On the other hand, the treatment at high AA concentration (4:1, v/v) decomposed lignin while maintaining its aromatic structure. Hence, we demonstrated that the selective production of lignin-derived polymers can be controlled depending on PAA and HP concentrations.

Sulfadimethoxine photodegradation in UV-C/H2O2 system: Reaction kinetics, degradation pathways, and toxicity

Sulfonamide antibiotics in water have raised public concern, owing to their stability and capacity to induce microbial resistance. We investigated the degradation efficiencies of photolysis by ultraviolet light and photolysis combined with hydrogen peroxide treatment. Combining ultraviolet light irradiation with hydrogen peroxide treatment was more effective at removing sulfadimethoxine than irradiation alone or UV/persulfate system. We also assessed the effects of hydrogen peroxide concentrations, reaction time, and the composition of the water matrix. The removing efficiency of sulfadimethoxine was negatively affected by high concentrations of hydrogen peroxide and with increasing alkalinity (pH 7.5–9.0). A tentative degradation pathway was proposed, involving the initial one-electron oxidation of sulfadimethoxine by ·OH and further reactions of the formed cation intermediate. We assessed the acute toxicity of the transformation products to Vibrio fischeri, and found that combining ultraviolet light irradiation with hydrogen peroxide treatment exerted lower toxicity to the bacterium than irradiation alone.

Relationship Between Main Channel Structure of Catalases and the Evolutionary Direction in Cold-Adapted Hydrogen Peroxide-Tolerant Exiguobacteium and Psychrobacter.

Catalase has crucial role in adaptive response to H2O2. Main channel structure responsible for substrate selectivity was estimated to understand the relationship between the evolutionary direction of catalases from Exiguobacterium oxidotolerans and Psychrobacter piscatorii which survive in cold and high concentration of hydrogen peroxide, and their catalytic property. E. oxidotolerans catalase (EKTA) exhibited a higher ratio of compound I formation rate using peracetic acid (a substrate lager than H2O2)/catalase activity using H2O2 as the substrate than P. piscatori catalase (PKTA). It was considered that the ratio was attributed to the size of the amino acid residues locating at the bottle neck structure in the main channel. The differences in the ratio of the compound I formation rate with peracetic acid to catalase activity with H2O2 between the deeper branches in the phylogenetic tree in both EKTA and PKTA were large. This indicates that catalases from the hydrogen peroxide-tolerant bacteria have evolved in different directions, exhibiting effective catalytic activity and allowing broader substrates size or H2O2-specific substrate acceptability in EKTA and PKTA, respectively. It is considered that the main channel structure reflected the difference in the evolutionary direction of clade 1 and clade 3 catalases.

Effect of Bleaching Gel Concentration on Tooth Color and Sensitivity: A Systematic Review and Meta-analysis.

The aim of this systematic review and meta-analysis was to evaluate a high concentration of hydrogen peroxide (35%) regarding tooth sensitivity and color change in tooth bleaching in comparison to low concentrations (6% to 20%). This review was conducted using the criteria of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses and is registered on the Prospective Register of Systematic Reviews (CRD42017064493). The PICO question was "Does a concentration of hydrogen peroxide ≥35% using in-office bleaching procedure contribute to greater tooth sensitivity?" A search was made in PubMed/MEDLINE, Scopus, and the Cochrane Library. Fourteen studies were selected for the qualitative analysis and seven for quantitative analysis. A total of 649 patients were evaluated (mean age: 36.32 years; range: 13.9 to 31 years), and the follow-up period ranged from one week to 12 months. The meta-analysis demonstrated that tooth sensitivity was higher in the patients submitted to treatment involving a high concentration of hydrogen peroxide (0.67; 95% confidence interval [CI]: 0.44 to 1.03; p=0.04; I 2 : 56%), and a significant difference was found regarding objective color ΔE (1.53; 95% CI: 2.99 to 0.08; p<0.0001; I 2 : 82%) but no significant difference was found regarding subjective color ΔSGU (0.24; CI: 0.75 to 1.23; p<0.00001; I 2 : 89%). This study indicated that a lower concentration of hydrogen peroxide causes less tooth sensitivity and better effectiveness in objective color change (ΔE); however, there is no difference between them related to subjective color (ΔSGU).

Conjoint Effects of Chemical and Mechanical Stresses on Fuel Cell PFSA Membranes

During fuel cell operation, proton-exchange membranes (PEMs) are subjected to aggressive chemical environment and mechanical fatigue that alter their properties and may lead to performance loss or, in the worst cases, fuel cell shutdown due to membrane failure. Membrane degradation due to chemical and mechanical stresses remains one of the main factors limiting PEM fuel cell lifetime [1]. Chemical damages are mostly due to radical attacks leading to the scission of the polymer chains (backbone or/and side chains), while mechanical stress comes from repeated swelling/shrinkage cycles caused by the membrane water-uptake. Despite quantities of works focusing independently on chemical (most often) or mechanical (more rarely) degradations, only a few studies were published on the effect of both combined [2]–[4]. Among them, Kusoglu et al. demonstrated that a static compression affects its microstructure and accelerates the chemical decomposition of the polymer chains in Nafion® membranes [2].In this study, we investigate the impact of both chemical and mechanical degradations on the morphology and physicochemical properties of Nafion® membranes: chemical structure, as well as water transport and sorption. The membrane degradation process was induced by a custom-made device that mimics the operating conditions of the fuel cell by exposing the membrane simultaneously to a free radical environment and cyclic compression. The generation of free radical environment is based on the circulation of a continuous flow of hydrogen peroxide or Fenton’s solution (i.e. hydrogen peroxide and ferrous ions), while mechanical fatigue is induced by a cyclic compression to reproduce the swelling/shrinkage sequences entailed by the membrane water-uptake during transient fuel cell operation.Preliminary studies were necessary to determine the appropriate experimental conditions, both from a chemical and a mechanical point of view. Firstly, an investigation similar to the one of Frensch et al. was performed to determine the effect of Fenton’s reagent concentrations on membrane degradation [5]: fluoride emission measurements showed that a higher degradation rate was obtained at a low iron ions concentration. Moreover, at low iron concentration, the degradation rate depended also significantly on the hydrogen peroxide concentration. On the other hand, high hydrogen peroxide concentration (≈ 30 %vol) entailed strong membrane morphology modification with the appearance of many bubbles - with a diameter varying from some micrometers to several millimeters- at the surface of both membranes [6]. Such morphology evolutions cannot be considered as representative of the degradations occurring during fuel cell operation.The first mechanical and chemical degradation tests were carried out using a 0.0503 cm3.s-1 flow of either pure water or 3%vol diluted H2O2 through two thermostated (80°C) half-cells. The half-cells and the membrane were inserted between the clamps of an electromechanical testing machine (MTS load frame model 312.21) and the mechanical stress consisted in a sinusoidal constraint between 0 and 5 MPa at 0.1 Hz. As expected, the application of this sinusoidal constraint increased significantly the degradation rate (Figure): the fluoride emissions were 5 to 7 times higher than under chemical stress only. Indeed, Nafion® XL’s degradation rate increases from 11 µg/h/gNafion to 68 µg/h/gNafion when mechanical stress was applied in addition to chemical stress. Likewise, the values increased from 11 to 54 µg/h/gNafion with NR-211. Moreover, with the combination of cyclic compression and H2O2 solution exposure, the degradation rates approached the values obtained with a Fenton’s reagents exposure.[1] R. Borup et al., Chem. Rev., 107 (10), 3904–3951, 2007.[2] A. Kusoglu et al., ECS Electrochem. Lett., 3 (5), F33–F36, 2014.[3] S. velan Venkatesan et al., J. Electrochem. Soc., 163 (7), F637–F643, 2016.[4] V. M. Ehlinger et al., 166 (7), F3255–F3267, 2019.[5] S. H. Frensch et al., J. Power Sources, 420, 54–62, 2019.[6] S. Mu et al., J. Appl. Polym. Sci., 129 (3), 1586–1592, 2013. Figure 1

Glutaredoxin-like protein (GLP)-a novel bacteria sulfurtransferase that protects cells against cyanide and oxidative stresses.

The pathogen Xylella fastidiosa belongs to the Xanthomonadaceae family, a large group of Gram-negative bacteria that cause diseases in many economically important crops. A predicted gene, annotated as glutaredoxin-like protein (glp), was found to be highly conserved among the genomes of different genera within this family and highly expressed in X. fastidiosa. Analysis of the GLP protein sequences revealed three protein domains: one similar to monothiol glutaredoxins (Grx), an Fe-S cluster and a thiosulfate sulfurtransferase/rhodanese domain (Tst/Rho), which is generally involved in sulfur metabolism and cyanide detoxification. To characterize the biochemical properties of GLP, we expressed and purified the X. fastidiosa recombinant GLP enzyme. Grx activity and Fe-S cluster formation were not observed, while an evaluation of Tst/Rho enzymatic activity revealed that GLP can detoxify cyanide and transfer inorganic sulfur to acceptor molecules in vitro. The biological activity of GLP relies on the cysteine residues in the Grx and Tst/Rho domains (Cys33 and Cys266, respectively), and structural analysis showed that GLP and GLPC266S were able to form high molecular weight oligomers (> 600kDa), while replacement of Cys33 with Ser destabilized the quaternary structure. In vivo heterologous enzyme expression experiments in Escherichia coli revealed that GLP can protect bacteria against high concentrations of cyanide and hydrogen peroxide. Finally, phylogenetic analysis showed that homologous glp genes are distributed across Gram-negative bacterial families with conservation of the N- to C-domain order. However, no eukaryotic organism contains this enzyme. Altogether, these results suggest that GLP is an important enzyme with cyanide-decomposing and sulfurtransferase functions in bacteria, whose presence in eukaryotes we could not observe, representing a promising biological target for new pharmaceuticals.

Initial and pulp chamber concentration of hydrogen peroxide using different bleaching products

Objective: This study’s aim was to quantify the hydrogen peroxide (HP) penetration into the pulp chamber of teeth submitted to different protocols of bleaching. Material and Methods: Ninety premolars were randomly divided into nine groups according to the bleaching agent protocol (n = 10): control (no bleaching), carbamide peroxide 10% [10% CP], carbamide peroxide 16% [16% CP], carbamide peroxide 22% [22% CP], hydrogen peroxide 4% [4% HP], hydrogen peroxide 6% [6% HP], hydrogen peroxide 7.5% [7.5% HP], hydrogen peroxide 10% [10% HP] and hydrogen peroxide 35% [35% HP]. The penetration of HP was measured via spectrophotometric analysis of the acetate buffer solution from the pulp chamber. The absorbance of the resulting solution was determined in a spectrophotometer and converted into equivalent concentration of HP (?g/ mL). To analyze the concentration of HP, the titration of bleaching agents with potassium permanganate was used. Data were subjected to ANOVA and Tukey’s test for pairwise comparison (? = 0.05). Results: Higher concentration of HP in the pulp chamber was found in the HP 35% group (p &lt; 0.0001). No significant difference between at-home protocols were observed (p = 0.64). Titration values showed that the concentration of the products was similar to that claimed by the manufacturer. Conclusion: It follows that the amount of HP that reaches the pulp chamber is not proportional to the concentration of whitening gels, but depends on the application time recommended by the manufacturers.KEYWORDSAt-home bleaching; Dental enamel permeability; Inoffice bleaching; Tooth bleaching.

Differential Sensitivity of Two Endothelial Cell Lines to Hydrogen Peroxide Toxicity: Relevance for In Vitro Studies of the Blood-Brain Barrier.

Oxidative stress (OS) has been linked to blood–brain barrier (BBB) dysfunction which in turn has been implicated in the initiation and propagation of some neurological diseases. In this study, we profiled, for the first time, two endothelioma cell lines of mouse brain origin, commonly used as in vitro models of the blood–brain barrier, for their resistance against oxidative stress using viability measures and glutathione contents as markers. OS was induced by exposing cultured cells to varying concentrations of hydrogen peroxide and fluorescence microscopy/spectrometry was used to detect and estimate cellular glutathione contents. A colorimetric viability assay was used to determine changes in the viability of OS-exposed cells. Both the b.End5 and bEnd.3 cell lines investigated showed demonstrable content of glutathione with a statistically insignificant difference in glutathione quantity per unit cell, but with a statistically significant higher capacity for the b.End5 cell line for de novo glutathione synthesis. Furthermore, the b.End5 cells demonstrated greater oxidant buffering capacity to higher concentrations of hydrogen peroxide than the bEnd.3 cells. We concluded that mouse brain endothelial cells, derived from different types of cell lines, differ enormously in their antioxidant characteristics. We hereby recommend caution in making comparisons across BBB models utilizing distinctly different cell lines and require further prerequisites to ensure that in vitro BBB models involving these cell lines are reliable and reproducible.

Redox requirements for ubiquitin-like urmylation of Ahp1, a 2-Cys peroxiredoxin from yeast

The yeast peroxiredoxin Ahp1, like related anti-oxidant enzymes in other species, undergoes urmylation, a lysine-directed conjugation to ubiquitin-like modifier Urm1. Ahp1 assembles into a homodimer that detoxifies peroxides via forming intersubunit disulfides between peroxidatic and resolving cysteines that are subsequently reduced by the thioredoxin system. Although urmylation coincides with oxidative stress, it is unclear how this modification happens on a molecular level and whether it affects peroxiredoxin activity. Here, we report that thioredoxin mutants decrease Ahp1 urmylation in yeast and each subunit of the oxidized Ahp1 dimer is modified by Urm1 suggesting coupling of urmylation to dimerization. Consistently, Ahp1 mutants unable to form dimers, fail to be urmylated as do mutants that lack the peroxidatic cysteine. Moreover, Ahp1 urmylation involves at least two lysine residues close to the catalytic cysteines and can be prevented in yeast cells exposed to high organic peroxide concentrations. Our results elucidate redox requirements and molecular determinants critical for Ahp1 urmylation, thus providing insights into a potential link between oxidant defense and Urm1 utilization in cells.

Seminal plasma has limited counteracting effects following induction of oxidative stress in donkey spermatozoa.

The aim of this study was to evaluate the response of donkey spermatozoa to oxidative stress induced by hydrogen peroxide, and to determine whether the presence of seminal plasma modulates the sperm response to that stress. Nine ejaculates were collected, extended in skim milk extender and split into two aliquots. Seminal plasma was removed from the first but not second aliquot. Samples were subsequently split into four aliquots supplemented with different concentrations of commercial hydrogen peroxide (0, 100 and 250µM and 50mM). Aliquots were incubated at 37°C under aerobic conditions and several sperm parameters, namely motility, viability, intracellular levels of peroxides and superoxides and mitochondrial membrane potential, were evaluated at 0, 1 and 3h. Exposure to hydrogen peroxide markedly decreased sperm motility but had much less of an effect on sperm viability, mitochondrial membrane potential and intracellular reactive oxygen species levels. A protective effect of seminal plasma against the loss of sperm motility was not apparent, but some kinetic parameters and relative levels of superoxides were better maintained when seminal plasma was present together with high concentration of hydrogen peroxide. In conclusion, oxidative stress induced by hydrogen peroxide reduces donkey sperm motility and has a less apparent effect on other sperm parameters. Finally, seminal plasma is only able to partially ameliorate the detrimental effect of this induced stress.

Molecular domino reactor built by automated modular synthesis for cancer treatment.

Rationale: A cascade, or domino, reaction consists of two, or more, consecutive reactions such that subsequent reactions occur only if some chemical functionality has first been established in the prior step. However, while construction of predesigned and desired molecular domino reactors in a tailored manner is a valuable endeavor, it is still challenging.Methods: To address this challenge, we herein report an aptamer-based photodynamic domino reactor built through automated modular synthesis. The engineering of this reactor takes advantage of the well-established solid-phase synthesis platform to incorporate a photosensitizer into G-quadruplex/ hemin DNAzyme at the molecular level.Results: As a proof of concept, our photodynamic domino reactor, termed AS1411/hemin- pyrochlorophyll A, achieves in vivo photodynamic domino reaction for efficient cancer treatment by using a high concentration of hydrogen peroxide (H2O2) in the tumor microenvironment (TME) to produce O2, followed by consecutive generation of singlet oxygen (1O2) using the pre-produced O2. More specifically, phosphoramidite PA (pyrochlorophyll A) is coupled to aptamer AS1411 to form AS1411-PA ApDC able to simultaneously perform in vivo targeted imaging and photodynamic therapy (PDT). The insertion of hemin into the AS1411 G-quadruplex was demonstrated to alleviate tumor hypoxia by decomposition of H2O2 to produce O2. This was followed by the generation of 1O2 by PA to trigger cascading amplified PDT.Conclusion: Therefore, this study provides a general strategy for building an aptamer-based molecular domino reactor through automated modular synthesis. By proof of concept, we further demonstrate a novel method of achieving enhanced PDT, as well as alleviating TME hypoxia at the molecular level.

A mitochondrial-targetable dual functional near-infrared fluorescent probe to monitor pH and H2O2 in living cells and mice.

A lower pH level and high hydrogen peroxide (H2O2) concentration in mitochondria is closely associated with a variety of diseases including cancer and inflammation. Thus, determination of changes in the level of acidic pH and H2O2 is of great importance and could provide new insights into the key functions under both physiological and pathological conditions. Herein, we present a novel mitochondria-targetable probe NIR-pH-H2O2, as the first near infrared (NIR) fluorescent small molecule, to monitor changes of endogenous pH (pka = 6.17) and H2O2 with high sensitivity, good compatibility and low cytotoxicity. Futhermore, it was successfully employed to monitor pH and H2O2 in a mouse acute inflammation model. These results demonstrate that NIR-pH-H2O2 is a novel bifunctional mitochondrial-targeted NIR probe to sense acidic pH and H2O2in vitro and in vivo, indicating its huge potential for the diagnosis of pH and H2O2-related diseases.

Chemical signature detection of groundwater and geothermal waters for evidence of crustal deformation along fault zones

Common crustal igneous and high grade metamorphic rocks contain peroxy defects which remain dormant until the rock experiences stress upon deformation. Stress activated peroxy defects form highly reactive oxygen species (ROS) at the rock-water interface observed in both terrestrial and extraterrestrial rock samples. The ROS complex is formed upon rock fluid interaction when groundwater combines with the ROS to produce hydrogen peroxide giving an indirect measure of the underlying rock stress and crustal deformation along active faults. The average concentration of hydrogen peroxide from the Sohna thermal spring water falling along the active Sohna fault and geothermal field was measured to be ~ 0.53 ± 0.014 mg/l. Similar average concentration was also recorded from borewell sample north of the spring (~0.56 ± 0.017 mg/l) within the same geothermal field. Lower concentration of hydrogen peroxide was recorded within samples collected from hard rock aquifers outside the geothermal field and the active fault zone (~0.138 ± 0.095 mg/l). The detailed analysis suggests that the presence of hydrogen peroxide is largely dependent on the circulation pattern through the interconnected fractures/joints within the quartzite bedrock lying adjacent to the fault plane. Laboratory analysis results also show high hydrogen peroxide concentration within two borewell samples falling adjacent to the epicentre of a shallow microtremor event within the hard rock region falling alongside a lineament along the Delhi hard rock mega fold. Rock water interaction post stress activation of peroxy defects and formation of ROS has therefore been inferred to be responsible for the formation of hydrogen peroxide at the rock water interface within these zones. This pilot study provides scientific field evidence that hydrogen peroxide concentrations within groundwaters might offer prospects for seismic stress estimation and crustal deformation along seismically active zones.

Presence of X-ray Induced High Concentrated Hydrogen Peroxide Clusters

Presence of X-ray Induced High Concentrated Hydrogen Peroxide Clusters

INFLUENCE OF DIFFERENT METHODS OF WHITENING ON THE STRUCTURE OF HARD TISSUES OF TEETH

Nowadays 74% of people believe that an imperfect smile has a negative impact on their careers, and 92% believe that it is one that contributes to success in their personal lives. The desire of patients to have an aesthetically perfect smile has always aroused great interest from dentists and has led to the active development of such a trend in aesthetic dentistry, such as teeth whitening. The color of the crowns of teeth and the inherent color characteristics play an important role in the perception of the appearance of the person, the formation of his image and self-esteem. Therefore, they affect the quality of life of a person due to his dental health. There are 5 main treatments for altered teeth: microabrasion, teeth whitening, direct restoration of composites, veneering, restoration of ceramic and metal-ceramic crowns. In recent years, conservative treatments, which include different types of whitening, have been favored to achieve maximum aesthetic results in the correction of altered teeth. For whitening, a considerable number of different remedies are offered that allow the tooth color to change relatively quickly. Nowadays, the world of dental practice is increasingly paying attention to the development of more cost-effective methods that meet the aesthetic needs of patients. The most common procedure for improving the color of the crowns of teeth today is whitening, which does not affect the reduction of the volume of hard tissues of the tooth. Teeth whitening is a restoration of the natural color of the teeth with the application of a chemical agent that oxidizes the organic pigments of the hard tissues of the tooth. Bleaching process is possible due to the ability of the active chemical components ( carbamide peroxide, hydrogen peroxide) to penetrate into enamel and dentin to all parts of the tooth. These substances break down into oxygen radicals, which destroy the colored pigments, the formation of which leads to discoloration of the teeth. The structure of the tooth does not change. Nowadays, home, professional and combined teeth whitening are widely used. The effect of bleaching is analyzed using a scanning electron microscope. Most studies did not report significant changes in the surface morphology of enamel after bleaching with low concentrations of urea peroxide and hydrogen peroxide. Similarly, studies evaluating the effects of higher concentrations of hydrogen peroxide (35%) and carbamidee peroxide (35%) have also reported no significant changes in the morphology of the enamel surface. In general, it is obvious that tooth sensitivity is a common clinical side effect after a teeth whitening procedure. However, the sensitivity is transient and disappears shortly after the bleaching procedure has been stopped.

Fenton\u2019s reaction-based chemical oxidation in suboptimal conditions can lead to mobilization of oil hydrocarbons but also contribute to the total removal of volatile compounds

Fenton’s reaction-based chemical oxidation is in principle a method that can be utilized for all organic fuel residues thus making it a potential all-purpose, multi-contaminant, in situ application for cases in which storage and distribution of different types of fuels have resulted in contamination of soil or groundwater. Since peroxide breakdown reactions are also expected to lead to a physical transport of the target compound, this secondary physical removal, or rebound concentrations related to it, is prone to be affected by the chemical properties of the target compound. Also, since soil conditions are seldom optimal for Fenton’s reaction, the balance between chemical oxidation and transport may vary. In this study, it was found that, with a high enough hydrogen peroxide concentration (5 M), methyl tert-butyl ether–spiked groundwater could be treated even under suboptimal conditions for chemical mineralization. In these cases, volatilization was not only contributing to the total removal but also leading to rebound effects similar to those associated with air sparging techniques. Likewise for diesel, temporal transport from soil to the aqueous phase was found to lead to false positives that outweighed the actual remediation effect through chemical mineralization.

In vitro bleaching effect of hydrogen peroxide with different time of exposition and concentration on shear bond strength of orthodontic brackets to human enamel: A meta-analysis of in vitro studies

Controversy exists regarding the effect of bleaching on shear bond strength (SBS) of orthodontic brackets to enamel. This study aims to do a review and meta-analysis on the effect of bleaching with hydrogen peroxide on SBS according to the interval between bleaching and bonding to human enamel and the concentration of Hydrogen Peroxide. An electronic search of the literature was performed in Scopus, PubMed and Cochrane databases including CENTRAL and Cochrane library for relevant in vitro studies on the effect of bleaching with hydrogen peroxide on shear bond strength of human enamel, published until June 2018. Modified Cochrane Risk of Bias tool was used to assess the quality of the individual studies. AMSTAR tool was used for assessing the quality of the study. Nineteen studies were included in the qualitative analysis. Regardless of the interval between bleaching and bonding, reduction in SBS was not statistically significant when the hydrogen peroxide of less than 35% is used. Bleaching with 35% hydrogen reduces SBS when the bonding is conducted immediately (P<0.0001) or the time interval was shorter than one day (P<0.0005). On the other hand, use of high dose hydrogen peroxide resulted in a statistically significant reduction in SBS irrespective of the time interval between the procedures (P<0.05 for all categories of time interval). Bleaching with hydrogen peroxide decreases the SBS of brackets in patients undergoing orthodontic treatment especially if the time interval between bleaching and bonding procedures is short and a high concentration of hydrogen peroxide is used.