Formation of hydroxyl radical from the photolysis of frozen hydrogen peroxide

Hydrogen peroxide (HOOH) in ice and snow is an important chemical tracer for the oxidative capacities of past atmospheres. However, photolysis in ice and snow will destroy HOOH and form the hydroxyl radical (*OH), which can react with snowpack trace species. Reactions of *OH in snow and ice will affect the composition of both the overlying atmosphere (e.g., by the release of volatile species such as formaldehyde to the boundary layer) and the snow and ice (e.g., by the *OH-mediated destruction of trace organics). To help understand these impacts, we have measured the quantum yield of *OH from the photolysis of HOOH on ice. Our measured quantum yields (Phi(HOOH --> *OH)) are independent of ionic strength, pH, and wavelength, but are dependent upon temperature. This temperature dependence for both solution and ice data is best described by the relationship ln(Phi(HOOH --> *OH)) = -(684 +/- 17)(1/T) + (2.27 +/- 0.064) (where errors represent 1 standard error). The corresponding activation energy (Ea) for HOOH (5.7 kJ mol(-1)) is much smaller than that for nitrate photolysis, indicating that the photochemistry of HOOH is less affected by changes in temperature. Using our measured quantum yields, we calculate that the photolytic lifetimes of HOOH in surface snow grains under midday, summer solstice sunlight are approximately 140 h at representative sites on the Greenland and Antarctic ice sheets. In addition, our calculations reveal that the majority of *OH radicals formed on polar snow grains are from HOOH photolysis, while nitrate photolysis is only a minor contributor. Similarly, HOOH appears to be much more important than nitrate as a photochemical source of *OH on cirrus ice clouds, where reactions of the photochemically formed hydroxyl radical could lead to the release of oxygenated volatile organic compounds to the upper troposphere.     

Self‐immolative nanoparticles triggered by hydrogen peroxide and pH

The azomethine‐based oligomers bearing boronate groups and imine moieties in the main chain were synthesized from a dialdehyde monomer and an aromatic (oligomer 4 ) diamine or an aliphatic diamine (oligomer 5 ). Based on the oligomers, the nanoparticles with hydrogen peroxide (H₂O₂) and pH dual‐responsive properties were constructed and encapsulated nile red inside. The nanoparticles disassembled either by the trigger of H₂O₂ or by the attack of H⁺, thus leading to the release of loaded species. Compared to oligomer 4 , oligomer 5 showed a faster degradation rate in the presence of H₂O₂, especially in a weak acidic environment. No significant cytotoxicity was observed as HeLa cells incubated in the nanoparticles with the concentration up to 200 μg/mL evidenced by cytotoxicity assay in vitro. Such a system capable of dual response of H₂O₂ and H⁺ may have potential application as a carrier for drug delivery. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1962–1969     

Removal of proteinaceous soils using hydroxyl radicals generated by the electrolysis of hydrogen peroxide

We have developed here for the first time a novel method to generate hydroxyl radicals, *OH, by applying slightly negative electric potentials (-0.2--0.8 V vs Ag/AgCl) to the surface of a metal (or metal oxide) that is in contact with hydrogen peroxide solution containing a supporting electrolyte. Namely, *OH radicals were generated at the surface by the electrolysis of hydrogen peroxide according to the equation, H2O2+e- --> *OH+OH-. This method was used to clean a stainless steel fouled with a model protein, beta-lactoglobulin. The *OHs generated at the surface were effective in removing beta-lactoglobulin that had been irreversibly adsorbed, by several minutes of treatment at room temperature (22+/-2 degrees C). The removal rates measured for various concentrations of H2O2 and supporting electrolyte and different potentials were determined exclusively by the electric current.     

Hydroxyl radical induced from hydrogen peroxide by cobalt manganese oxides for ciprofloxacin degradation

Advanced oxidation processes (AOPs) are promising technology to remove organic pollutant in water. However, the main problem in the AOPs is the low generation of hydroxyl radical (^?OH) owing to the low decomposition efficiency of hydrogen peroxide (H₂O₂). Herein, the spinel type cobalt acid manganese (MnCo₂O₄) with flower morphology was fabricated through a co-precipitation method. In situ Fourier transform infrared spectroscopy confirms that the MnCo₂O₄ with the optimal molar ratio of Co and Mn precursors (CM3, Co:Mn = 3) has more Lewis acid sites compared with single metal oxide catalysts (Co₃O₄ and Mn₂O₃), leading to the excellent performances for H₂O₂ decomposition rate constant on CM3, which is about 15.03 and 4.21 times higher than those of Co₃O₄ and Mn₂O₃, respectively. As a result, the obtained CM3 shows a higher ciprofloxacin degradation ratio than that of Co₃O₄ and Mn₂O₃. Furthermore, CM3 shows an excellent stability during several cycles. This work proposes effective catalysts for ciprofloxacin decomposition and provides feasible route for treating practical environmental problems.     

The formation of hydrogen peroxide in metallic reductors

The formation of hydrogen peroxide in various types of metallic reductors both in the presence and absence of oxygen has been studied. Only when oxygen is rigorously excluded is peroxide undetectable. The oxidimetric determination of iron is seriously affected by this peroxide when the test solution and reductor are open to atmospheric oxygen. Systems which are completely oxygen-free give satisfactory results.     

Theoretical study on the oxidation mechanism of thiourea by hydrogen peroxide with water and hydroxyl assistance

This article presents a theoretical study on the oxidation reaction of thiourea by hydrogen peroxide in water or alkaline solutions using density functional and ab initio theories. This work also focuses on the analysis of the thermodynamic and kinetic properties of the predicted oxidation mechanism of thiourea using density functional and ab initio theories. The calculated results show that the activation energies, activation enthalpies, and activation Gibbs free energies of the reaction decreased and the releasable reaction energies, enthalpies and Gibbs free energies increased with the cooperation of water or hydroxyl anion. We conclude that the oxidation reaction of thiourea by hydrogen peroxide in water or alkaline solutions was easier and more completed than that in the gas state. The calculated results are consistent with the experiments.     

Modifications of boronic ester pro-chelators triggered by hydrogen peroxide tune reactivity to inhibit metal-promoted oxidative stress

Several new analogs of salicylaldehyde isonicotinoyl hydrazone (SIH) and salicylaldehyde benzoyl hydrazone (SBH) that contain an aryl boronic ester (BSIH, BSBH) or acid (BASIH) in place of an aryl hydroxide have been synthesized and characterized as masked metal ion chelators. These pro-chelators show negligible interaction with iron(III), although the boronic acid versions exhibit some interaction with copper(II), zinc(II) and nickel(II). Hydrogen peroxide oxidizes the aryl boronate to phenol, thus converting the pro-chelators to tridentate ligands with high affinity metal binding properties. An X-ray crystal structure of a bis-ligated iron(III) complex, [Fe(SBH(m-OMe)(3))(2)]NO(3), confirms the meridonal binding mode of these ligands. Modifications of the aroyl ring of the chelators tune their iron affinity, whereas modifications on the boron-containing ring of the pro-chelators attenuate their reaction rates with hydrogen peroxide. Thus, the methoxy derivative pro-chelator (p-OMe)BASIH reacts with hydrogen peroxide nearly 5 times faster than the chloro derivative (m-Cl)BASIH. Both the rate of pro-chelator to chelator conversion as well as the metal binding affinity of the chelator influence the overall ability of these molecules to inhibit hydroxyl radical formation catalyzed by iron or copper in the presence of hydrogen peroxide and ascorbic acid. This pro-chelator strategy has the potential to improve the efficacy of medicinal chelators for inhibiting metal-promoted oxidative stress.     

Theoretical study of reaction of trifluoromethyl radical with hydroxyl and hydrogen radicals

Ab initio molecular orbital theory and density functional theory calculations have been carried out on the reactions of the trifluoromethyl radical with the hydroxyl and the hydrogen radicals. These reactions are key reactions that underlie a new fire extinguishing mechanism of non-bromine-containing halon replacements. The activation energies calculated by the MP2 and QCISD methods are in good agreement with the experimental values. The B3LYP, as well as MP2 and QCISD, give good results for the calculations of the heats of reactions. The GAUSSIAN-1 and GAUSSIAN-2 theory calculations present the most acxcurate results on both the activation energies and the heats of reactions. The effects of the scaling factors on the activation energies and the heats of reactions are also evaluated. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 277–289, 1998     

Hydroxylation of 3-nitrotyrosine by hydroxyl radical

Hydroxylation of 3-nitrotyrosine (3-NT) and 3-NT containing peptide Gly-nitroTyr-Gly in aqueous solution by hydroxyl radical were investigated with gamma irradiation. The structures of the hydroxylated products were confirmed by electrospray ionization mass spectrometry and 1H NMR spectrometry. The reactivity of 3-nitrotyrosine has been investigated using density functional theory (DFT) calculation.     

Troilite oxidation by hydrogen peroxide

The kinetics and mechanism of troilite oxidation by H(2)O(2) was studied at temperatures of 25 and 45 degrees C. Solutions within the range 0.1-0.85 mol L(-1) H(2)O(2) in HClO(4) (0.01-0.1 mol L(-1)) were used as dissolution media. The experimental amount of dissolved iron was plotted versus t(n), with n ranging from 0.25 to 1.55. The theoretical interpretation of this dependence suggests that the troilite oxidation involves several processes: Both experimental results and theoretical considerations illustrate the importance of temperature, pH, and [H(2)O(2)] for the kinetics and mechanisms of troilite oxidation. The amounts of dissolved iron strongly increase with temperature and [H(+)], whereas an increase of H(2)O(2) concentration seems to reduce the troilite oxidation. The reaction orders with respect to [H(+)] are variable, pointing out notable modifications of reaction mechanism with experimental conditions. The estimated value E(a)=25.4+/-0.9 k J mol(-1) ([H(2)O(2)]=0.4 mol L(-1) and pH 1) points to dissolution kinetics controlled by a mix regime of surface reaction and diffusion.     

On the formation of hydrogen peroxide in water microdroplets

Recent reports on the formation of hydrogen peroxide (H₂O₂) in water microdroplets produced via pneumatic spraying or capillary condensation have garnered significant attention. How covalent bonds in water could break under such mild conditions challenges our textbook understanding of physical chemistry and water. While there is no definitive answer, it has been speculated that ultrahigh electric fields at the air–water interface are responsible for this chemical transformation. Here, we report on our comprehensive experimental investigation of H₂O₂ formation in (i) water microdroplets sprayed over a range of liquid flow-rates, (shearing) air flow rates, and air composition, and (ii) water microdroplets condensed on hydrophobic substrates formed via hot water or humidifier under controlled air composition. Specifically, we assessed the contributions of the evaporative concentration and shock waves in sprays and the effects of trace O₃(g) on the H₂O₂ formation. Glovebox experiments revealed that the H₂O₂ formation in water microdroplets was most sensitive to the air–borne ozone (O₃) concentration. In the absence of O₃(g), we could not detect H₂O₂(aq) in sprays or condensates (detection limit ≥250 nM). In contrast, microdroplets exposed to atmospherically relevant O₃(g) concentration (10–100 ppb) formed 2–30 µM H₂O₂(aq), increasing with the gas–liquid surface area, mixing, and contact duration. Thus, the water surface area facilitates the O₃(g) mass transfer, which is followed by the chemical transformation of O₃(aq) into H₂O₂(aq). These findings should also help us understand the implications of this chemistry in natural and applied contexts.

A. Gallo Jr, H. Mishra et al., pinpoint the origins of the spontaneous H₂O₂ formation in water microdroplets formed via spraying or condensation, i.e., without the addition of electrical energy, catalyst, or co-solvent.     

Determination of hydroxyl radical by capillary electrophoresis and studies on hydroxyl radical scavenging activities of Chinese herbs

High-performance capillary electrophoresis (CE) with electrochemical detection (ED) was employed to determine hydroxyl radicals in the Fenton reaction. Hydroxyl radicals can react with salicylic acid to produce 2,3-dihydroxy benzoic acid and 2,5-dihydroxy benzoic acid, which can be analyzed by CE-ED. Based on this principle, hydroxyl radicals were determined indirectly. In a 20 mmol/L phosphate running buffer (pH 7.4), 2,3-dihydroxy benzoic acid and 2,5-dihydroxy benzoic acid would elute simultaneously from the capillary within 6 min. As the working electrode, a 300 m diameter carbon-disk electrode exhibits good responses at +0.60 V (vs. SCE) for the two analytes. Peak currents of the two analytes are additive. Excellent linearity was obtained in the concentration range from 1.0×10^-3 mol/L to 5.0×10^-6 mol/L for 2,3-dihydroxy benzoic acid. The detection limit (S/N=3) was 2.0×10^-6 mol/L. This method was successfully applied for studying hydroxyl radical scavenging activities of Chinese herbs. It is testified that Apocynum Venetum L., Jinkgo bibola L., Morus alba L. and Rhododendron dauricum L. have strong hydroxyl radical scavenging activities.     

Mechanism of hydrogen peroxide formation in electrolytic-cathode atmospheric-pressure direct-current discharge

The kinetics of buildup of hydrogen peroxide in an atmospheric pressure direct-current discharge with a distilled-water cathode has been experimentally measured. A kinetic reaction scheme has been proposed and analyzed to calculate peroxide concentrations in accordance with experimental data.     

Electrocatalytic hydrogen peroxide formation on mesoporous non-metal nitrogen-doped carbon catalyst

Direct electrochemical formation of hydrogen peroxide(H2O2) from pure O2 and H2on cheap metal-free earth abundant catalysts has emerged as the highest atom-efficient and environmentally friendly reaction pathway and is therefore of great interest from an academic and industrial point of view. Very recently,novel metal-free mesoporous nitrogen-doped carbon catalysts have attracted large attention due to the unique reactivity and selectivity for the electrochemical hydrogen peroxide formation [1–3]. In this work,we provide deeper insights into the electrocatalytic activity, selectivity and durability of novel metal-free mesoporous nitrogen-doped carbon catalyst for the peroxide formation with a particular emphasis on the influence of experimental reaction parameters such as p H value and electrode potential for three different electrolytes. We used two independent approaches for the investigation of electrochemical hydrogen peroxide formation, namely rotating ring-disk electrode(RRDE) technique and photometric UV–VIS technique. Our electrochemical and photometric results clearly revealed a considerable peroxide formation activity as well as high catalyst durability for the metal-free nitrogen-doped carbon catalyst material in both acidic as well as neutral medium at the same electrode potential under ambient temperature and pressure. In addition, the obtained electrochemical reactivity and selectivity indicate that the mechanisms for the electrochemical formation and decomposition of peroxide are strongly dependent on the p H value and electrode potential.     

Hydrogen peroxide and dioxygen activation by dinuclear copper complexes in aqueous solution: hydroxyl radical production initiated by internal electron transfer

Dinuclear Cu(II) complexes, CuII2Nn (n = 4 or 5), were recently found to specifically cleave DNA in the presence of a reducing thiol and O2 or in the presence of H2O2 alone. However, CuII2N3 and a closely related mononuclear Cu(II) complex exhibited no selective reaction under either condition. Spectroscopic studies indicate an intermediate is generated from CuII2Nn (n = 4 or 5) and mononuclear Cu(II) solutions in the presence of H2O2 or from CuI2Nn (n = 4 or 5) in the presence of O2. This intermediate decays to generate OH radicals and ligand degradation products at room temperature. The lack of reactivity of the intermediate with a series of added electron donors suggests the intermediate discharges through a rate-limiting intramolecular electron transfer from the ligand to the metal peroxo center to produce an OH radical and a ligand-based radical. These results imply that DNA cleavage does not result from direct reaction with a metal-peroxo intermediate but instead arises from reaction with either OH radicals or ligand-based radicals.     

Fluorinated alcohol directed formation of dispiro-1,2,4,5-tetraoxanes by hydrogen peroxide under acid conditions

The oxidative system MTO/30%H₂O₂/HBF₄/fluorous alcohol is promising for the selective synthesis of biologically important antimalarial dispiro-1,2,4,5-tetraoxanes by direct acid-catalysed cyclisation of various 4-substituted cyclohexanones (1, R=Me, Et, tBu, Ph, COOEt, CF₃). The role of the substitutent at the 4-position was important in the selectivity of formation of tetraoxane (2, TO) with respect to hexaoxonane (3, HO). By the use of fluorinated alcohols and under the right reaction conditions, tetraoxanes 2 were selectively formed and synthesised in 46-86% isolated yield from 4-substituted cyclohexanones 1.     

Bleaching of cellulose by hydrogen peroxide

Peroxides are important bleaching agents, industrially, for cellulosic products. They are also used in detergents. Peroxides can degrade cellulose as well as decolorize it and remove stains. Both free radicals and perhydroxyl anions have been suggested as the intermediates in the reactions occurring between cellulosic products and hydrogen peroxide. The proposed mechanisms are reviewed with emphasis primarily on cotton cellulose. Further work is required to establish unequivocally the mechanism of degradation and decolorization of cellulose products.