Perhydroxyl Anion Research Articles

Biofilm Degradation by Seashell-Derived Calcium Hydroxide and Hydrogen Peroxide.

Microbial cells and self-produced extracellular polymeric substances assembled to form biofilms that are difficult to remove from surfaces, causing problems in various fields. Seashell-derived calcium hydroxide, a sustainable inorganic material, has shown high bactericidal activity even for biofilms due to its alkalinity. However, its biofilm removal efficacy is relatively low. Herein, we report a biofilm degradation strategy that includes two environmentally friendly reagents: seashell-derived calcium hydroxide and hydrogen peroxide. A biofilm model of Escherichia coli was prepared in vitro, treated with calcium hydroxide–hydrogen peroxide solutions, and semi-quantified by the crystal violet stain method. The treatment significantly improved biofilm removal efficacy compared with treatments by calcium hydroxide alone and hydrogen peroxide alone. The mechanism was elucidated from calcium hydroxide–hydrogen peroxide solutions, which suggested that perhydroxyl anion and hydroxyl radical generated from hydrogen peroxide, as well as the alkalinity of calcium hydroxide, enhanced biofilm degradation. This study showed that concurrent use of other reagents, such as hydrogen peroxide, is a promising strategy for improving the biofilm degradation activity of seashell-derived calcium hydroxide and will contribute to developing efficient biofilm removal methods.

Molecular dynamics simulations of singlet oxygen atoms reactions with water leading to hydrogen peroxide

The formation mechanisms of hydrogen peroxide due to the interaction of oxygen atom from the cold atmospheric plasmas in contact with water are not fully understood. Previous work on molecular dynamics (MD) simulations of interactions of O atoms in bulk water based on reactive force field and density-functional tight-binding method did not observe the formation of . In this work we applied density functional theory in MD simulations of 192 trajectories considering system to explore the reaction mechanisms for atomic oxygen radical in water. Our calculations revealed that triplet (ground) state oxygen was not reactive. Oxywater-similar structure was a transient product. Perhydroxyl anion and its counterpart hydronium were formed. In most of simulated cases, hydrogen peroxide was observed as a final product. The formation pathways of hydrogen peroxide exhibited large complexities for the simple hydrogen bonded system. According to the sources and pathways of the hydrogen atom being bonded in hydrogen peroxide molecule, mechanisms can be classified into (1) hydrogen-abstraction, (2) hydrogen-transfer n (n = 3, 4, 5, 6, 7, 8), (3) proton-delivery n = 2, 3, (4) proton-transfer. It was confirmed that for correct prediction of reaction mechanisms is better to use quantum molecular dynamic simulations.

Selective Oxidation of Lignin into Aromatic Aldehydes Using Niobium Oxalate

Abstract. There is a strong interest in using lignin as a precursor for synthesis of value-added chemicals such as aromatic aldehydes. Among the existing processes for converting lignin into aromatic aldehydes, catalytic oxidation appears to be most promising. In this research, we explored niobium oxalate as a selective oxidation catalyst and hydrogen peroxide as an oxidant for oxidizing lignin into vanillin and syringaldehyde. Research objectives were to (1) determine the effect of catalyst mass, lignin concentration, and H 2 O 2 concentration on synthesis of aromatic aldehydes; (2) study the effect of reaction temperature; and (3) optimize the reaction parameters. Batch experiments were performed via central composite design at 95°C using 4 to 12 g of lignin per 100 mL, 3 to 7 mL of H 2 O 2 per 100 mL, and 0.5 to 1.0 g of catalyst per 100 mL. Results indicated that under optimum conditions (3 mL of H 2 O 2 , 0.5 g of catalyst, and 7.26 g of lignin), 65.58 mg g -1 of vanillin and 23.12 mg g -1 of syringaldehyde were produced. In addition, production of aldehydes showed dependency on temperature in the range of 85°C to 100°C, with 100°C producing the highest product concentrations. It is theorized that perhydroxyl anion (HOO - ), being a strong nucleophile and the most active agent in alkaline hydrogen peroxide, breaks the I± and I²-aryl ether bonds of lignin to produce corresponding aldehydes. It is suggested that niobium is a potential catalyst for selective oxidation of lignin.

H2O2 oxidation of lignin model dimers catalyzed by copper(II)– phenanthroline

This work aims at elucidating some of the key steps of the oxidation pathways of lignin model compounds by hydrogen peroxide under alkaline conditions (0.05M NaOH) in the presence of copper(II)-phenanthroline complex. Phenolic and non-phenolic βO4 dimeric phenyl propane structures were selected as lignin models since they represent the most abundant structures in lignin: 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy) propane-1-ol and 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy) propane-1-one, and their methylated counterparts. After 3h at 80°C the main products in the reaction medium were analyzed by HPLC. The results suggested that the first step was the oxidation of the benzylic OH group to a ketone group. This step would be catalyzed by the copper (II)-phenanthroline complex and favored by the presence of dissolved oxygen. The second step would be the cleavage of the βO4 linkage by a series of nucleophilic attacks initiated by the reaction of the perhydroxyl anion on the carbonyl group which would not be influenced by the presence of the copper complex. This mechanism is in accordance with the formation of acetaldehyde, veratric or vanillic acid, and guaiacol which were identified as the main reaction products of the models oxidation.

<b>Dyeing Behavior of Keratin Fibers with Oxidative Dyeing System:Mechanism for the Respective Effects of Each EDTA and Ascorbic Acid</b>

The effects of EDTA and ascorbic acid on the oxidative dyeing behavior of wool fibers dyed with the couple systems of p-phenilenediamine/p-amino-o-cresol (pPDA/pAOC) and p-aminophenol/p-amino-o-cresol (pAP/pAOC) were investigated by means of analyzing dyeing rate curve which was expressed in relation to the surface dye concentration (K/S) and the dyeing time. The effects of these additives on the dye uptake behavior were dependent on the reactivity of the oxidative dye intermediate, hydrogen peroxide concentration, and the additive concentration. In pAP/pAOC dyeing system, the amount of dye uptake in dying system with EDTA was reduced compared with that of non-additive dyeing system. This is due to the fact that oxidative coupling reaction is inhibited by chelating metal ions present on the fiber surface. However, the amount of dye uptake increased with increasing of the added amount of EDTA. This finding implies that there is another effect of EDTA. This effect was believed to arise from that the oxidative decomposition of the oxidation dye generated in the fiber-liquid interface is suppressed by the reduction in the perhydroxyl anion concentration. On the other hand, ascorbic acid exerted the effect in both dyeing system and brought on the action similar to EDTA; the inhibiting action of oxidative coupling reaction and the suppressing action of the oxidative decomposition of the generated dye. These actions are due to the fact that ascorbic acid preferentially reacts with the active oxygen species. The former is primarily caused by the decrease in the amount of hydroxyl radical, and the latter is due to the decrease in the perhydroxyl anion. In addition, ascorbic acid acted as a pro-oxidant and resulted in decomposition of the dye that adsorbed into the fiber.

Effects of Urea on Hydrogen Peroxide Bleaching of Cotton Fabrics

In order to establish the bleaching process for cotton fabrics under the neutral condition, cotton fabrics were bleached by hydrogen peroxide with urea. It was revealed that hydrogen peroxide bleaching with urea showed the higher whiteness of bleached fabrics than that without urea at more than 70 degrees Celsius. Tensile strength did not decrease after bleaching. Some radicals were observed by ESR measurement when urea was added into hydrogen peroxide aqueous solution. The effects of urea on hydrogen peroxide bleaching seems to be caused by active oxygen ; hydroxyl radical, perhydroxyl radical and superoxide anion radical as well as perhydroxyl anion. The residual hydrogen peroxide concentrations in bleaching baths were measured. When urea is added to the bleaching baths, the decomposition of hydrogen peroxide is accelerated even in the neutral bath.

Effects of the Dyeing Conditions on Dyeing of Wool Fiber with Oxidation Dyes

Dyeing behavior for wool fibers from the couple system of p-phenilendiamine/p-amino-o-cresol and p-aminophenol/p-amino-o-cresol in use in current hair dye formulation was investigated. This paper describes the variation of dye uptake with factors such as pH in the bath solution, concentration of hydrogen peroxide, dyeing temperature and liquor ratio. Generally, the apparent dye uptakes increased with increasing of dyeing time, hydrogen peroxide concentration, dye temperature, and liquor ratio. However, indo dye decomposition by excess hydrogen peroxide is a competitive process in both couple systems. Particularly, the following fact was definitely observed above pH10.0: the higher dyeing temperature and the higher concentration of hydrogen peroxide led to the increase of the rate of dye formation reaction and the extent of dye decomposition. On the other hand, below pH10.0, the dye decomposition was also decreased due to the suppressing hydrolysis of hydrogen peroxide to perhydroxyl anion. Ultimately, it could be verified that the dyeing behavior of oxidation dye into wool fibers was subjected to a certain balance between dye formation and dye loss by hydrogen peroxide.

Kinetic investigation of an azo dye oxidation by hydrogen peroxide in aqueous surfactant solution

In this study, the oxidation of resorcinol based an azo dye, 5-methyl-4-(2-thiazolylazo)resorcinol (5-Me-TAR) by hydrogen peroxide has been investigated from kinetic, spectroscopic and thermodynamic point of view to examine the influence of a cationic surfactant such as cetylpyridiniumchloride (CPC). Activation energy (298.15–313.15 K) and entropy (298.15 K) of the reaction were calculated as 67 kJ/mol and −72 J mol −1 K −1 in borate buffer, respectively. However, the addition of CPC into 5-Me-TAR solutions at different pH values always reduced the intensity of its azo form, the intensity of its hydrazone form increased. The oxidation of dye proceeds via perhydroxyl anion and hydrazone tautomeric form and oxidation rate was accelerated by the presence of CPC either in micellar or premicellar regions.

Alkaline hydrogen peroxide bleaching of cellulose

A closed system bleaching apparatus was designed to determine the kinetics and effects of various factors on alkaline hydrogen peroxide bleaching of textile cellulose fabrics. It was confirmed that perhydroxyl anion is the primary bleaching moiety in alkaline hydrogen peroxide systems. The use of the apparatus in the measurement of fabric color, waste oxygen, and the subsequent calculation of hydroxyl ion, and molecular hydrogen peroxide confirmed that pH and titration of 'free' hydrogen peroxide in alkaline bleaching systems are not good indicators of bleaching mechanism. The role of the cellulose itself in the chemical bleaching system was determined. The rate of bleaching on cotton fabric was shown to be a first order reaction in concentration of perhydroxyl anion at 60 and 90 °C. An activation energy of 17 kcal/mole was estimated. Decomposition of H2O2 into waste oxygen was found to be second order kinetics.

Kinetic investigations of azo dye oxidation in aqueous media

A detailed kinetic and spectroscopic investigation has been made of the oxidation of 4-(4-sulfophenylazo)-1-naphthol (Orange I, 4) and 1-(4-sulfophenylazo)-2-naphthol (Orange II, 5) and a series of specially synthesised, substituted 1-arylazo-2-naphthol dyes (6a, 6b) by hypochlorite, peracids and hydrogen peroxide in aqueous media. In all cases, observed second-order rate constants exhibit maxima in alkaline media at a pH equal to the midpoint of the pKA values of dye and oxidant. It is found that substituents upon the aryl ring ortho to the azo group suppress dye reactivity towards hypochlorite and, in addition, it is shown that peracids exhibit similar trends. In contrast, oxidation by hydrogen peroxide is enhanced by ortho substituents, suggesting that it functions via a different mechanism. Surprisingly, the dye common anion has been identified as the form of the dye most susceptible to oxidation by peracids and hypochlorite, with the undissociated oxidant molecules acting as electrophiles. In contrast, dye oxidation by hydrogen peroxide proceeds via the perhydroxyl anion and the hydrazone tautomeric form of the dye. The main function of ortho substituents is to increase the dye pKA, thereby influencing observed rates (k2obs) by changing the equilibrium concentration of reactive species. Substituents also exert an electronic effect on absolute rate constants, k2, giving good Hammett plots for both ortho and para substituents. Reactive oxygen species, e.g. singlet oxygen, superoxide or hydroxyl radicals, are not implicated in the rate-controlling step of the reaction.

The oxidation of cinnamaldehyde with alkaline hydrogen peroxide

AbstractThe oxidation of cinnamaldehyde (3‐phenyl‐2‐propenal) by alkaline peroxide results in epoxidation of the double bond to form cinnamaldehyde epoxide (3‐phenyl‐2,3‐epoxy‐propanal) which undergoes further reaction by ring opening and side chain cleavage to yield benzaldehyde and acidic fragments. The reactions are first‐order in the organic substrates and perhydroxyl anion and second‐order overall. In the presence of alkali alone, two further reactions take place in which cinnamaldehyde and cinnamaldehyde epoxide side chains are cleaved by reaction with hydroxide ion to form benzaldehyde and side chain fragments. These reactions are first‐order in the organic substrates and hydroxide ion and second‐order overall. Increasing solvent polarity accelerates the rates of reaction and reaction mechanisms have been proposed to describe the observed kinetic behavior. The stereoselectivity of the epoxidation reaction has been examined in terms of an existing model for epoxidation of α, β‐unsaturated ketones by alkaline peroxide. © 1993 John Wiley & Sons, Inc.

Mechanism of bleaching by peroxides. Part 1.—Kinetics of bleaching of phenolphthalein by hydrogen peroxide at high pH

The kinetics of the oxidation of phenolphthalein by alkaline hydrogen peroxide have been studied in aqueous solution over a range of pH, ionic strength and temperature. The rate of reaction was found to be first order in both phenolphthalein and hydrogen peroxide. Use of free radical and singlet oxygen trapping agents have ruled out the involvement of these species in the reaction. The variation of the rate constant with pH and ionic strength has shown that at pH 11 the main reaction is that between the pink bisphenolate form of phenolphthalein and the perhydroxyl anion, HO2–. At pH 9, epoxidation by the hydrogen peroxide molecule contributed most to the overall rate constant. Borate-buffered solutions gave a faster rate of reaction than those in hydrogencarbonate or ammonia buffers. Experiments over the temperature range 21.0–45.0 °C lead to activation energies of 43.3 and 48.4 kJ mol–1 and entropies of activation of –149 and –131 J K–1 mol–1 at 298 K, in carbonate and borate buffers, respectively. A mechanism for the reaction is proposed.

Mechanism of bleaching by peroxides. Part 2.—Kinetics of bleaching of alizarin and crocetin by hydrogen peroxide at high pH

The kinetics of the oxidation of alizarin (1,2-dihydroxyanthraquinone) and crocetin (8,8-diapo-ψ,ψ-carotenedioic acid) by alkaline hydrogen peroxide have been studied in aqueous solution over a range of pH, ionic strength and temperature. In each case the rates of the reactions were found to be first order both in the organic colourant and in hydrogen peroxide. Use of free radical and singlet oxygen trapping agents have ruled out the involvement of these species in both reactions. Analysis of the kinetics of oxidation of alizarin has shown that over the pH range 10–12 the predominant reaction is that between the mono-ionised form of alizarin and the perhydroxyl anion, HOO–. The kinetic experiments with crocetin, coupled with spectrophotometric determination of its second ionisation constant, showed that the largest rate constant was that for reaction between HOO– and the doubly ionised form of crocetin. Experiments over the temperature range 21.0–45.0 °C led to activation energies of 68.8 and 69.9 kJ mol–1, and entropies of activation of –95 and –92 J K–1 mol–1 for the alizarin and crocetin reactions, respectively, at 298 K in hydrogencarbonate buffers. Mechanisms for both reactions are proposed.

Peroxide Bleaching Reactions Under Alkaline and Acidic Conditions

Abstract An examination of previously reported kinetic expressions describing peroxide bleaching of wood pulp under alkaline conditions reveals that the overall process can be considered as a combination of two parallel reaction routes. The first route corresponds to a reaction involving direct participation of the perhydroxyl anion in chromophore elimination. This mechanism can be identified with the classical explanation for peroxide bleaching. The second route can be associated with reactions in which chromophores are eliminated through the action of free radical intermediate species. New experimental evidence is presented to show that processes catalysed by transition metal ions can lead to enhancement of bleaching. A two stage peroxide bleaching sequence, initially under acidic conditions in the presence of chromium, followed by alkaline conditions produces an acceleration in bleaching rate, without significant additional consumption of peroxide.

The decomposition of hydrogen peroxide catalysed by palladium-gold alloy wires

The decomposition of hydrogen peroxide has been examined on a range of PdAu alloy compositions in a grease-free high-vacuum apparatus. The catalytic activity per cm 2 at 8.15M and 250°C varies little with the alloy composition, from 100 Pd0 Au to 10 Pd90 Au, where there is an increase by a factor 3 to 0 Pd100 Au. Much larger differences in activity, however, appear to be brought about by differences in surface pretreatment, attributed to the formation of a monolayer of adsorbed oxygen, which it is postulated may react with the perhydroxyl anion by the mechanism MO+O 2H −→M+OH −+O 2 To a first approximation this mechanism accounts for the effects of pH and the apparent frequency factor of the reaction and the absence of any correlation with holes in the d bands of the alloy.