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Concept: Peroxide


In-office tooth whitening using hydrogen peroxide (H2O2) has been practised in dentistry without significant safety concerns for more than a century. While few disputes exist regarding the efficacy of peroxide-based at-home whitening since its first introduction in 1989, its safety has been the cause of controversy and concern. This article reviews and discusses safety issues of tooth whitening using peroxide-based materials, including biological properties and toxicology of H2O2, use of chlorine dioxide, safety studies on tooth whitening, and clinical considerations of its use. Data accumulated during the last two decades demonstrate that, when used properly, peroxide-based tooth whitening is safe and effective. The most commonly seen side effects are tooth sensitivity and gingival irritation, which are usually mild to moderate and transient. So far there is no evidence of significant health risks associated with tooth whitening; however, potential adverse effects can occur with inappropriate application, abuse, or the use of inappropriate whitening products. With the knowledge on peroxide-based whitening materials and the recognition of potential adverse effects associated with the procedure, dental professionals are able to formulate an effective and safe tooth whitening regimen for individual patients to achieve maximal benefits while minimising potential risks.

Concepts: Immune system, Oxygen, Effectiveness, Hydrogen peroxide, Oxide, Chlorine, Patient safety, Peroxide


A polyethylene based packaging material containing nano-Ag, nano-TiO2, nano-SiO2, and attapulgite has been prepared. The effect of nanocomposite packaging material (Nano-PM) on the senescence of Flammulina velutipes during 15 days of postharvest storage at 4 °C and a relative humidity of 90% were analyzed. The results showed that compared with normal packaging material (Normal-PM) and no packaging (No-PM), Nano-PM improved the appearance quality, reduced weight loss and cap opening. The degree of maturity and increase in molecular weight of F. velutipes polysaccharides (FVP) were delayed. The content loss of proteoglycan protein was less and degree of oxidation was lower. The storage with Nano-PM reduced the fibrosis of texture, cellulase activity, the accumulation of hydrogen peroxide (H2O2) and superoxide radical (O2-) by 18.9%, 48.3%, 26.6% and 27.8%, respectively (P < .05). The Nano-PM effectively delayed the postharvest senescence of F. velutipes, hence prolonged its shelf life and increased its preservation quality.

Concepts: Oxygen, Redox, Radical, Hydrogen peroxide, Oxide, Superoxide, Packaging, Peroxide


Ionized radiations trigger thoughtful adverse hazards through multiple organ dysfunctions. Recently, antioxidant-based biodrugs are used to prevent and treat ionizing radiation hazards. The present study aimed to investigate the prospective ameliorative effect of Cicer arietinum extract (CAE) against γ-irradiation and the pathway of this amelioration in male albino rats. Twenty four rats were allocated into four groups; (i) control group, (ii) CAE group in which rats treated with a dosage of 500 mg CAE/kg b.wt, (iii) γ-irradiated group in which rats exposed to 6Gy γ-irradiation, (iv) γ-irradiated+CAE group; rats of this group treated with CAE 1 h post exposure. All rats treated for 21 days. Liver, kidney and femoral bone were rapidly excised and homogenized for the biochemical analysis. Energy dispersive X-ray (EDX) and inductively coupled plasma emission spectrometer (ICP) analyses exhibit that γ-irradiation elicits significant change in the essential trace elements content in liver, kidney, and bone. Further, significant increases in TBARS and H2O2 contents accompanied by significant decreases in GSH, SOD, CAT, and GPx activities in liver, kidney and bone tissues were recorded in the γ-irradiated rats compared to control group. Additionally, marked reduction in the thickness of cortical bone was recorded in rats exposed to γ-irradiation. Conversely, CAE (500 mg/kg b.wt, p.o) administration for 21 days to γ-irradiated rats effectively reverses most of the altered parameters of the γ-irradiated rats. In conclusion, the present findings suggested that CAE is a potential agent that can be used against radiation hazards. This effect may be owing to its antioxidant mechanism, as CAE has an inhibitory effect against hydrogen peroxide (H2O2) and superoxide radical (O2·-) beside its ferric reducing antioxidant power (FRAP). This finding recommended that CAE can be utilized clinically to mitigate ionized radiation-induced hazard effects.

Concepts: Bone, Ionizing radiation, Redox, Radiation therapy, Hydrogen peroxide, Osseous tissue, Superoxide, Peroxide


Oxygen and nitric oxide are small hydrophobic molecules that usually need to diffuse a considerable distance to accomplish their biological functions and necessarily need to traverse several lipid membranes. Different methods have been used to study the diffusion of these molecules in membranes and herein we focus in the quenching of fluorescence of pyrenes inserted in the membrane. The pyrene derivatives have long fluorescence lifetimes (around 200 ns) that make them very sensitive to fluorescence quenching by nitric oxide, oxygen and other paramagnetic species. Results show that the apparent diffusion coefficients in membranes are similar to those in water, indicating that diffusion of these molecules in membranes is not considerably limited by the lipids. This high apparent diffusion in membranes is a consequence of both a favorable partition of these molecules in the hydrophobic interior of membranes and a high diffusion coefficient. Altering the composition of the membrane results in slight changes in diffusion, indicating that in most cases the lipid membranes will not hinder the passage of oxygen or nitric oxide. The diffusion of nitric oxide in the lipid core of low density lipoprotein is also very high, supporting its role as an antioxidant. In contrast to the high permeability of membranes to nitric oxide and oxygen, the permeability to other reactive species such as hydrogen peroxide and peroxynitrous acid is nearly five orders of magnitude lower.

Concepts: Fluorescence, Oxygen, Water, Lipoprotein, Paramagnetism, Lipid, Lipid bilayer, Peroxide


Ultrasound (US)-triggered sonodynamic therapy (SDT) can solve the critical issue of low tissue-penetrating depth of traditional photo-triggered therapies, but the SDT efficacy is still not satisfactorily high on combating cancer at current stage. Here we report on augmenting the SDT efficacy based on catalytic nanomedicine, which takes the efficient catalytic features of nanoenzymes to modulate the tumor microenvironment (TME). The multifunctional nanosonosensitizers have been successfully constructed by the integration of MnOx component with biocompatible/biodegradable hollow mesoporous organosilica nanoparticles (HMONs), followed by the conjugation with protoporphyrin (PpIX, as the sonosensitizer) and cyclic arginine-glycine-aspartic pentapeptide c(RGDyC) (as the targeting peptide). The MnOx component in composite nanosonosensitizer acts as the inorganic nanoenzyme for converting the tumor-overexpressed hydrogen peroxide (H2O2) molecules into oxygen and enhancing the tumor oxygen level subsequently, which has been demonstrated to facilitate the SDT-induced reactive oxygen species production and enhance the SDT efficacy subsequently. The targeted accumulation of these composite nanosonosensitizers efficiently suppressed the growth of U87 tumor xenograft on nude mice after the US-triggered SDT treatment. The high in vivo biocompatibility and easy excretion-out of these multifunctional nanosonosensitizers from the body have also been evaluated and demonstrated to guarantee their future clinical translation, and their TME-responsive T1-weighted magnetic resonance imaging capability provides the potential for therapeutic guidance and monitoring during SDT.

Concepts: Oxygen, Oxidative stress, Reactive oxygen species, Brain tumor, Therapy, Magnetic resonance imaging, Hydrogen peroxide, Peroxide


Cerium oxide nanoparticles are known to catalyze the decomposition of reactive oxygen species such as the superoxide radical and hydrogen peroxide. Herein, we examine the superoxide dismutase (SOD) and catalase (CAT) mimetic catalytic activities of nanoceria and demonstrate the existence of generic behaviors. For particles of sizes 4.5, 7.8, 23 and 28 nm, the SOD and CAT catalytic activities exhibit the characteristic shape of a Langmuir isotherm as a function of cerium concentration. The results show that the catalytic effects are enhanced for smaller particles and for the particles with the largest Ce3+ fraction. The SOD-like activity obtained from the different samples is found to superimpose on a single master curve using the Ce3+ surface area concentration as a new variable, indicating the existence of particle independent redox mechanisms. For the CAT assays, the adsorption of H2O2 molecules at the particle surface modulates the efficacy of the decomposition process and must be taken into account. We design an amperometry-based experiment to evaluate the H2O2 adsorption at nanoceria surfaces, leading to the renormalization of the particle specific area. Depending on the particle type the amount of adsorbed H2O2 molecules varies from 2 to 20 nm-2. The proposed scalings are predictive and allow the determination of the SOD and CAT catalytic properties of cerium oxide solely from physicochemical features.

Concepts: Oxygen, Superoxide dismutase, Catalysis, Nitrogen, Hydrogen peroxide, Adsorption, Superoxide, Peroxide


[Fe(β-BPMCN)(CH3CN)2]2+(1, BPMCN = N,N'-bis(pyridyl-2-methyl)- N,N'-dimethyl-trans-1,2-diaminocyclo-hexane) is a relatively poor catalyst for cyclohexane hydroxylation by H2O2and cannot perform benzene hydroxylation. However, addition of Sc3+activates the 1/H2O2reaction mixture to be able to hydroxylate cyclohexane and benzene within seconds at -40 °C. A metastable S = ½ FeIII-(η1-OOH) intermediate 2 is trapped at -40 °C that undergoes rapid decay upon addition of Sc3+at rates independent of [substrate] but linearly dependent on [Sc3+]. HClO4elicits comparable reactivity as Sc3+at the same concentration. We thus postulate that these additives facilitate O-O bond heterolysis of 2 to form a highly electrophilic FeV=O oxidant (Ox) that is comparably reactive to the fastest nonheme high-valent iron-oxo oxidants found to date.

Concepts: Oxygen, Antioxidant, Oxidizing agent, Electrochemistry, Solvent, Peroxide, Hydroxylation, Intermediate 2


Collagen IV is a major component of the basement membrane in epithelial tissues. The NC1 domains of collagen IV protomers are covalently linked together through sulfilimine bonds, the formation of which is catalyzed by peroxidasin. Although hydrogen peroxide is essential for this reaction, the exact source of the oxidant remains elusive. Members of the NOX/DUOX NADPH oxidase family are specifically devoted to the production of superoxide and hydrogen peroxide. Our aim in this study was to find out if NADPH oxidases contribute in vivo to the formation of collagen IV sulfilimine crosslinks. We used multiple genetically modified in vivo model systems to provide a detailed assessment of this question. Our data indicate that in various peroxidasin-expressing tissues sulfilimine crosslinks between the NC1 domains of collagen IV can be readily detected in the absence of functioning NADPH oxidases. We also analyzed how subatmospheric oxygen levels influence the collagen IV network in collagen-producing cultured cells with rapid matrix turnover. We showed that collagen IV crosslinks remain intact even under strongly hypoxic conditions. Our hypothesis is that during collagen IV network formation PXDN cooperates with a NOX/DUOX-independent H2O2source that is functional also at very low ambient oxygen levels.

Concepts: Oxygen, Redox, Epithelium, Hydrogen peroxide, NADPH oxidase, Oxidase, Superoxide, Peroxide


It has been unclear whether superoxide and/or hydrogen peroxide play important roles in the phenomenon of obligate anaerobiosis. This question was explored using Bacteroides thetaiotaomicron, a major fermentative bacterium in the human gastrointestinal tract. Aeration inactivated two enzyme families-[4Fe-4S] dehydratases and nonredox mononuclear iron enzymes-whose homologs, in contrast, remain active in aerobic Escherichia coli Inactivation-rate measurements of one such enzyme, B. thetaiotaomicron fumarase, showed that it is no more intrinsically sensitive to oxidants than is an E. coli fumarase. Indeed, when the E. coli enzymes were expressed in B. thetaiotaomicron, they no longer could tolerate aeration; conversely, the B. thetaiotaomicron enzymes maintained full activity when expressed in aerobic E. coli Thus, the aerobic inactivation of the B. thetaiotaomicron enzymes is a feature of their intracellular environment rather than of the enzymes themselves. B. thetaiotaomicron possesses superoxide dismutase and peroxidases, and it can repair damaged enzymes. However, measurements confirmed that the rate of reactive oxygen species production inside aerated B. thetaiotaomicron is far higher than in E. coli Analysis of the damaged enzymes recovered from aerated B. thetaiotaomicron suggested that they had been inactivated by superoxide rather than by hydrogen peroxide. Accordingly, overproduction of superoxide dismutase substantially protected the enzymes from aeration. We conclude that when this anaerobe encounters oxygen, its internal superoxide levels rise high enough to inactivate key catabolic and biosynthetic enzymes. Superoxide thus comprises a major element of the oxygen sensitivity of this anaerobe. The extent to which molecular oxygen exerts additional direct effects remains to be determined.

Concepts: Protein, Oxygen, Bacteria, Reactive oxygen species, Superoxide dismutase, Hydrogen peroxide, Peroxide, Anaerobic organism


Two transition-metal-free methods to access substituted phenols via the arylation of silanols or hydrogen peroxide with diaryliodonium salts are presented. The complementary reactivity of the two nucleophiles allows synthesis of a broad range of phenols without competing aryne formation, as illustrated by the synthesis of the anesthetic Propofol. Furthermore, silyl-protected phenols can easily be obtained, which are suitable for further transformations.

Concepts: Oxygen, Ammonia, Hydrogen peroxide, Functional groups, Aryl, Phenols, Alkyl, Peroxide