H2O2 Stability Research Articles

Coupling nitrogen/oxygen self-doped biomass porous carbon cathode catalyst with CuFeO2/biochar particle catalyst for the heterogeneous visible-light driven photo-electro-Fenton degradation of tetracycline

The heterogeneous visible-light driven photo-electro-Fenton (H-VL-PEF) system was built to degrade tetracycline using nitrogen/oxygen biomass self-doped porous carbon (NO/PC) cathode catalyst coupling CuFeO2/biochar particle catalyst. The NO/PC possessed the H2O2 selectivity of 85.3%, and the gas diffusion electrode with NO/PC as cathode catalyst (NO/PC-GDE) exhibited fine H2O2 electrogeneration performance and stability. The generated electrons on CuFeO2/biochar by electrostatic induction and light excitation promoted Fe3+/Fe2+ and Cu2+/Cu+ redox cycle, which was beneficial for HO•/O2•- formation and tetracycline degradation. The introduction of CuFeO2/biochar catalyst and visible light could reduce energy consumption and promote tetracycline mineralization. The CuFeO2/biochar loads, initial pH and current density of H-VL-PEF system were optimized. The degradation pathway of tetracycline was speculated based on the intermediates identified by HPLC/MS. Escherichia coli growth inhibition experiments and toxicity prediction analysis demonstrated that the comprehensive toxicity of tetracycline was alleviated due to the catalytic degradation of H-VL-PEF system.

Simple modulation of Fe-based single atoms/clusters catalyst with acidic microenvironment for ultrafast Fenton-like reaction

Single atom catalysts (SACs) are emerging as efficient peroxide activators to eliminate water contaminants, yet the correlation between structure and catalytic activity remains elusive. Here we moderated the Fe sites on the carbon nitride and obtained a combination of single atoms and clusters sites on FeCN5 with the recorded methylene blue oxidation rate of 59.43 mg/L min−1 via direct ultrafast H2O2 activation. The excellent performance was mainly ascribed to the high active sites exposure, self-creating acidic microenvironment, and assistance of leaching Fe. Nevertheless, excessive exposure of the catalyst at high pH may destroy the surface environment and inhibit H2O2 activation. To solve this issue, we developed a flow-through filter that reached nearly 100% pollutant degradation and H2O2 utilization and stability over 320 h when treating actual wastewater treatment. These findings provide profound insights into catalyst manipulation at atomic scales and the development of viable catalytic systems toward real-world application.

Meta-studtite stability in aqueous solutions. Impact of HCO3-, H2O2 and ionizing radiation on dissolution and speciation.

Two uranyl peroxides meta-studtite and studtite exist in nature and can form as alteration phases on the surface of spent nuclear fuel upon water intrusion in a geological repository. Meta-studtite and studtite have very low solubility and could therefore reduce the reactivity of spent nuclear fuel toward radiolytic oxidants. This would inhibit the dissolution of the fuel matrix and thereby also the spreading of radionuclides. It is therefore important to investigate the stability of meta-studtite and studtite under conditions that may influence their stability. In the present work, we have studied the dissolution kinetics of meta-studtite in aqueous solution containing 10 mM HCO3-. In addition, the influence of the added H2O2 and the impact of γ-irradiation on the dissolution kinetics of meta-studtite were studied. The results are compared to previously published data for studtite studied under the same conditions. 13C NMR experiments were performed to identify the species present in aqueous solution (i.e., carbonate containing complexes). The speciation studies are compared to calculations based on published equilibrium constants. In addition to the dissolution experiments, experiments focussing on the stability of H2O2 in aqueous solutions containing UO22+ and HCO3- were conducted. The rationale for this is that H2O2 was consumed relatively fast in some of the dissolution experiments.

Influence of a Polycarboxylate Based Solution on Stability of Hydrogen Peroxide and Application to E-waste Leaching

Hydrogen peroxide with its high oxidising potential is commonly used in hydrometallurgical extraction of metals from ores, anode slimes and waste materials (e.g. WEEE) and treatment of cyanidation effluents. Main detraction to H2O2 is its rapid catalytic decomposition leading to prohibitively high consumption. Effect of pH (0-4), Cu(II) (0-10 g.l-1) and temperature (20-80°C) on H2O2 stability was investigated using response surface methodology. Influence of neutral-alkaline conditions (pH 7.3-11.8) and presence of solids (1-20% w/v) was also tested. A polycarboxylate based solution (PBS) was utilised to improve H2O2 stabilisation. The significance order of parameters on H2O2 decomposition was temperature > pH > Cu(II). Elevating the level of these parameters increased H2O2 decomposition. The activation energy (60.7±2.5 kJ.mol-1) indicated a chemically controlled process. Alkaline conditions (up to pH 11.8) led to higher H2O2 decomposition. Presence of solids adversely affected H2O2 stability under certain conditions. The addition of PBS significantly improved (up to 54%) H2O2 stability in the presence of copper. The presence of PBS in H2SO4-H2O2 leaching of waste of printed circuit boards (WPCBs) enhanced copper extraction by up to 19%. PBS can be suitably utilised to stabilise and hence reduce H2O2 consumption in aqueous solutions particularly in the presence of copper.

A novel fluorescent glycopolymer for endogenous hydrogen peroxide imaging in living cells in a fully aqueous environment

The development of H2O2-responsive fluorescent glycopolymers with high specificity, sensitivity, and water solubility is a promising strategy for developing probes to detect the production and delivery of endogenous H2O2. Herein, two series of fluorescent glycopolymers (boronic acid derivatives, PG-PFE, and borate derivatives, PG-PFW) were synthesized through esterification and the Williamson reaction, respectively. To increase the sensitivity of the fluorescent glycopolymers, the effect of the reaction conditions on the grafting ratio was investigated in detail. Compared with the PG-PFE samples, the PG-PFW samples had a higher grafting ratio due to the highly efficient Williamson reaction. The structure and properties of the fluorescent glycopolymers were characterized by using nuclear magnetic resonance spectroscopy, gel permeation chromatography, ultraviolet spectroscopy, and photoluminescent spectroscopy. The obtained results showed that all of these fluorescent glycopolymers had good water solubility, low cytotoxicity, and selective responsiveness toward H2O2. HPG-PFW-5, with the highest grafting ratio, displayed a higher sensitivity toward H2O2 and higher stability during hydrolysis than the other materials. In confocal laser scanning microscope images, all of the fluorescent glycopolymers were observed only in cellular mitochondria, and HPG-PFW-5 exhibited a high degree of overlap with Mitotracker Red because of its high sensitivity. Two series of fluorescent glycopolymers (boronic acid derivatives, PG-PFE, and borate derivatives, PG-PFW) were synthesized through different methods. Compared with the PG-PFE samples, the PG-PFW samples had a higher grafting ratio due to the highly efficient Williamson reaction. The fluorescent glycopolymers possessed good water solubility, low cytotoxicity and selective responsiveness toward H2O2. Meantime, the fluorescent glycopolymers were imaged only in cellular mitochondria based on the fact that endogenous H2O2 is mainly distributed in cellular mitochondria.

Aluminium stress modulates the osmolytes and enzyme defense system in Fagopyrum species

The present investigation describes aluminum-induced changes in the leaves of two buckwheat species using both physiological and biochemical indices. With increasing levels of Al (viz. 100, 200 and 300 μM), the mean length of root, shoot as well as their biomass accumulation decreased linearly with respect to control. Tolerance test of F. kashmirianum revealed that it was more tolerant to Al-stress than F. tataricum as revealed by higher accumulation of Al in its roots without any significant damage. Translocation factor (TF) values of both species were found to be < 1, indicating more Al is restrained in roots. Total chlorophyll showed a non-significant increase in F. tataricum while as decreased in F. kashmirianum at 300 μM concentration besides, the carotenoid content exhibited inclined trend in F. tataricum and showed a concomitant decrease in F. kashmirianum. The anthocyanin level showed a non-significant decline in F. kashmirianum. Exposure to different Al-treatments enhances malondialdehyde (MDA), H2O2 and membrane stability index (MSI) in both species, with increases being greater in F. kashmirianum than F. tataricum as also revealed by DAB-mediated in vivo histo-chemical detection method. The osmolyte level in general were elevated in both buckwheat species however, enhancement was more in F. tataricum than F. kashmirianum. The activities of antioxidant enzymes viz. superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (POD), glutathione reductase (GR), glutathione-S-transferase (GST) were positively correlated with Al-treatment except catalase (CAT) which exhibits a reverse outcome in F. kashmirianum. The present investigation could play an essential role to better understand the detoxification mechanisms of Al in plants.

In Vitro Anticancer Efficacy of Six Different Clinically Approved Types of Liquids Exposed to Physical Plasma

Colorectal cancer metastasis often occurs before clinical diagnosis and leads to diffuse spread of tumor nodules in the peritoneal cavity and peritoneal carcinomatosis. These small lesions are difficult to remove surgically and poor prognosis. Current options in palliation include ionizing radiation and hyperthermic intraperitoneal chemotherapy that lead to severe side effects. In previous research, oxidant-enriched solutions, like physical plasma-treated cell culture medium, showed therapeutic potential in diminishing cancer growth of peritoneal lesions. However, the applicability of cell culture medium in clinical settings is limited. To this end, we compared the tumor-toxic activity of six clinically approved liquids following plasma treatment in vitro in murine CT26 colorectal cancer cells. Changes and stability of pH-value and hydrogen peroxide (H2O2) were assessed. Exposing colorectal cancer cells to these physical plasma-treated liquids reduced their metabolic activity, and created a distinct morphological alterations and a reduction in cell motility. While some solutions such as Ringer’s lactate show good effects, we found plasma-treated sodium chloride (NaCl) to perform consistently well in terms of H2O2 stability and cytotoxicity. In conclusion, several of the investigated liquids may be suitable as plasma-treated liquid for anticancer peritoneal lavage with NaCl giving the best in vitro results in our hands.

The preparation of hollow AgPt@Pt core-shell nanoparticles loaded on polypyrrole nanosheet modified electrode and its application in immunosensor

The designed synthesis of efficient materials can significantly enhance the performance of electrochemical immunoassay in the detection of diseases, pesticide residues and environmental pollutants. The hollow AgPt@Pt core-shell nanoparticles (AgPt@Pt HNs) have exhibited high catalytic efficiency to the hydrogen peroxide (H2O2) reduction for its high mass activity from their hollow structure. Their limitation of instability can be overcome by loading on polypyrrole nanosheet (PPy NS). Besides, PPy NS exhibits good conductivity, and there exists environmentally-friendly method for its synthetic. Thus, AgPt@Pt HNs loaded on PPy NS (AgPt@Pt HNs/PPy NS) exhibits high catalytic efficiency to the reduction of H2O2 and good stability. Furthermore, the quick electron transfer of AgPt@Pt HNs/PPy NS modified glassy carbon electrode has been evidenced by the finding that the large constant of apparent electron transfer rate has also enlarged the current signal when the amount of electron is invariant. The modified electrode has fabricated a label-free amperometric immunosensor to detect sensitively prostate-specific antigen (PSA) with H2O2 as the electroactive material. The immunosensor in hollow core-shell nanosheet structure exhibiting good detection performance of PSA shows its promising applications in the clinical diagnosis.

High-efficiency electrogeneration of hydrogen peroxide from oxygen reduction by carbon xerogels derived from glucose

Developing highly active and selective, and low cost electrocatalysts for the 2e− oxygen reduction from environmentally friendly precursors is attractive to industrial production and environmental remediation. In this study, carbon xerogels (CXs) were synthesized by the hydrothermal carbonization of glucose and polyaniline (PANI) and then used as catalysts for electrochemical generation of H2O2 from O2. It was found that the H2O2 production performance could be easily tunable by polymerization temperature of PANI (0–80 °C), in which onset potential (−0.45 V to −0.29 V) decreased while the catalytic activity and H2O2 selectivity (47%–94%) increased with the polymerization temperature. CX-80 (prepared at 80 °C) exhibited the best catalytic activity with excellent H2O2 selectivity of 94% in neutral condition, better than most reported electrocatalysts. The H2O2 production was also tested using gas diffusion electrodes modified by CXs, showing a high H2O2 yield (5.1 mg h−1 cm−2) and stability with low energy consumption (7.2 kWh kg−1) at cathode potential of −1.0 V and pH 7. The excellent performance of CX-80 was attributed to large volume of meso-/macropores and high content of C=O. We believed that CX-80 would be a promising metal-free electrocatalyst for sustainable and in-situ H2O2 generation from O2 in energy and environmental fields.

Direct synthesis of H2O2 on PdZn nanoparticles: The impact of electronic modifications and heterogeneity of active sites

The direct synthesis of H2O2 (H2 + O2 → H2O2) would reduce the cost of H2O2, but few catalytic materials demonstrably provide the necessary combination of high H2O2 selectivity and stability over long periods of continuous reaction. Here, we show that silica supported PdZnx nanoparticles (where x indicates the bulk composition, 0 ≤ x ≤ 30) are stable and selective catalysts for the continuous production of H2O2 in the absence of liquid-phase promoters. Increasing the ratio of Zn to Pd precursors in the synthesis lead to distributions of nanoparticles that contain greater fractions of β1-Pd1Zn1 and lower fractions of face-centered cubic (fcc) Pd nanoparticles. A combination of the measured functional dependence of steady-state H2O2 and H2O formation rates on H2 and O2 pressures and the need for protic solvents indicate that H2O2 forms on all members of the PdZnx series by proton-electron transfer steps to dioxygen and hydroperoxy surface intermediates that saturate active sites during catalysis. Primary H2O2 selectivities increase systematically with the Zn to Pd ratio and range from 26% on fcc Pd nanoparticles to 69% on PdZn30 catalysts, which contains β1-Pd1Zn1 nanoparticles and lacks detectable amounts of fcc Pd. The differences in H2O2 selectivities among the PdZnx catalysts reflect changes in activation enthalpies (ΔH‡) for H2O2 (from -3 to 14 kJ mol−1) and H2O (11 to 44 kJ mol−1) formation. These results demonstrate that pathways for H2O2 formation are less sensitive than H2O formation to electronic differences between active sites on fcc Pd and intermetallic β1-Pd1Zn1 nanoparticles, whose densities of states differ significantly near the Fermi level. Comparisons of the ratios of H2O2 and H2O formation rates to ΔH‡ values among Pd and PdZnx catalysts show that the increases in H2O2 selectivities are less than predicted from the differences in ΔH‡ values alone. This analysis shows that the current synthesis method introduces at least two distinguishable catalytically active sites, and a portion of the sites formed predominantly cleave O-O bonds in primary and secondary reaction pathways that form H2O and lead to lower H2O2 selectivities than would be achieved in their absence. These findings demonstrate that differences in electronic structure of active sites cause β-Pd1Zn1 nanoparticles to give greater H2O2 selectivities than Pd catalysts and suggest that a synthesis procedure that uniformly creates β-Pd1Zn1 and alloys all Pd on the support may lead to increasingly selective conversion of O2 and H2 to H2O2.

A novel hydrogen peroxide stabilizer in descaling process of metal surface

A recently developed descaling process for metal surface, which utilizes sulphuric, hydrofluoric acid and hydrogen peroxide (H2O2), has attracted great attention in consideration of eco-friendly sustainable process development. However, the intrinsic presence of metal ions, especially Fe(III), dramatically accelerates H2O2 decomposition, resulting in undesirable economic losses and even paralysis of operation. In this study, the stability of H2O2 in aqueous descaling acid was assessed by varying the ferric content from 0 to 30 g/L and the temperature from 32 to 45 °C. The results showed that any minor fluctuation in either factors causes a big attenuation in the life span of H2O2, necessitating the addition of a stabilizer. Thereby, a comprehensive screening test for potential stabilizers was carried out for an attempt to decelerate the H2O2 decomposition. Among all prospects, 2-anilinoethanol (AE, 100 mg/L) showed the most prominent stabilizing potential by successfully extending the half-life of peroxide by a factor of 2.66 compared to a controlled condition. The feasibility of AE as a stabilizer was further explored by elucidating its fate with GC-MS and IC analyses. A series of aromatics and short-chain organic acids was identified as the reaction intermediates. Aniline, with great H2O2 stabilizing capacity, was a predominant byproduct, which could help explain the superb positive effect of AE.

In Situ Encapsulation of Hydrogen Peroxide in a Silica Matrix in the Presence of Divalent Metal Ions (Mg2+ and Ca2+)

Encapsulating hydrogen peroxide (H2O2) in silica hydrogels is a simple, environmentally friendly, and cost-effective method that is easy to scale up. Sodium silicate is the most commonly used aqueous silicate in sol–gel chemistry. Previously, we studied the effects of Na+ and K+ ions in the starting silicate precursor on the structure of hydrogels and the stability of entrapped H2O2. In the present study, we present the results obtained when divalent ions, Mg2+ and Ca2+, were introduced in the sol. The use of divalent metal ions resulted in hydrogel structures that are different from those previously obtained. H2O2 stability increased with the addition of Mg2+ and Ca2+ ions and with decreasing pH. At low pH values, 93% of the peroxide was retained at the end of 10 days with Mg2+-containing hydrogels, compared to 91% retention with Ca2+-containing hydrogels, 87% retention with K+-containing hydrogels, and 68% retention with a unmodified sodium silicate precursor. The results show that the structure of the ...

Effect of hydrogen peroxide on improving the heat stability of whey protein isolate solutions

Whey protein isolate (WPI) solutions (12.8%w/w protein) were treated with varying concentrations of H2O2 in the range of 0-0.144 H2O2 to protein ratios (HTPR) by the addition of the required quantity of H2O2 and deionized water. The samples were analyzed for heat stability, rheological properties, denaturation level of β-lactoglobulin (β-LG) and α-lactalbumin (α-LA). The samples treated with H2O2 concentration >0.072 (HTPR) showed significant improvement in the heat stability, and decreased whey protein denaturation and aggregation. The WPI solution treated with H2O2 (>0.072 HTPR) remained in the liquid state after heat treatment at 120°C, whereas the control samples formed gel upon heat treatment. Detailed analysis of these samples suggested that the improvement in the heat stability of H2O2 treated WPI solution was attributed to the significant reduction in the sulfhydryl-disulfide interchange reaction during denaturation of β-LG and α-LA.

Tailoring Microbial Electrochemical Cells for Production of Hydrogen Peroxide at High Concentrations and Efficiencies.

A microbial peroxide producing cell (MPPC) for H2 O2 production at the cathode was systematically optimized with minimal energy input. First, the stability of H2 O2 was evaluated using different catholytes, membranes, and catalyst materials. On the basis of these results, a flat-plate MPPC fed continuously using 200 mm NaCl catholyte at a 4 h hydraulic retention time was designed and operated, producing H2 O2 for 18 days. H2 O2 concentration of 3.1 g L-1 H2 O2 with 1.1 Wh g-1 H2 O2 power input was achieved in the MPPC. The high H2 O2 concentration was a result of the optimum materials selected. The small energy input was largely the result of the 0.5 cm distance between the anode and cathode, which reduced ionic transport losses. However, >50 % of operational overpotentials were due to the 4.5-5 pH unit difference between the anode and cathode chambers. The results demonstrate that a MPPC can continuously produce H2 O2 at high concentration by selecting compatible materials and appropriate operating conditions.

Thick silica foam films through combined catalytic decomposition of H2O2 and sol–gel processes

A novel method for the preparation of thick silica foam films is reported that combines an alkoxide-based hydrolytic sol–gel process and in situ catalytic decomposition of hydrogen peroxide on a catalyst-coated support. A hydrogen peroxide/nitric acid aqueous solution was used to carry out acid-catalysed hydrolysis of tetramethoxysilane. Complete stability of H2O2 in the resulting silica sols over extended periods (>120min) was demonstrated by in situ Raman spectroscopy. The H2O2-loaded sols were sprayed on MnO2-coated substrates, resulting in heterogeneous catalytic decomposition of H2O2 and effective foaming and simultaneous gel formation due to oxygen gas and water formation. Silica foam films with a well-defined closed-cell porosity were annealed at 600°C without any damage to the closed-cell porous film morphology. Up to 530μm thick films were prepared with macropore sizes in the range of 29–47μm, exceptionally thin macropore wall thicknesses of 16–50nm and a bulk density as low as 64kg/m3, comparable to that of the aerogels. The lowest measured thermal conductivity of the prepared foams was 0.018±0.001W/(m∗K), which is also similar to silica aerogels, enabling the prepared foams to be used as efficient thermal insulation materials.

Effect of potassium ion on the stability and release rate of hydrogen peroxide encapsulated in silica hydrogels

Hydrogen peroxide (H2O2) is encapsulated in silica hydrogels using sol‐gel method and the effects of the K+ : Na+ ion ratio on gelation time, hydrogel structure, stability, and release rate of H2O2 were investigated. As the amount of K+ ions increased relative to the amount of Na+ ions at the same pH, the gel structure became less compact and the pore diameter increased. Hydrogen peroxide retention values up to 90 and 80% were observed at the end of 7 and 20 days, respectively, in the presence of K+ ions at low pH values when the initial H2O2 concentration was 19.9 wt %. Release rate of hydrogen peroxide decreased with decreasing pH for the two K+ : Na+ ion ratios studied. This work presents an environmentally friendly, low cost, and easy to scale up method to increase the stability of high initial concentrations of H2O2 at room temperature and customize the release rate. © 2016 American Institute of Chemical Engineers AIChE J, 63: 409–417, 2017

Catalyzed hydrogen peroxide combined with CO2 sparging for the treatment of contaminated groundwater

In this work we propose and investigate an innovative groundwater remediation option based on the combination of catalyzed hydrogen peroxide (H2O2) with CO2 sparging. The effectiveness of this new process was evaluated by carrying out lab-scale tests on a soil–water system spiked with Methyl Tertiary Butyl Ether (MtBE). The results achieved with the combined process, evaluated in terms of H2O2 lifetime and MtBE residual concentration in the liquid phase, were then compared with those obtained using H2O2 only or amended with KH2PO4 as stabilizing agent. The experimental results showed that the combined H2O2–CO2 process has basically two beneficial effects. On the one hand, fluxing CO2 into the oxidizing solution can lead to a pH decrease to acidic values that enhance the H2O2 stability. Indeed, from the results obtained in the stability tests carried out, it was observed that the hydrogen peroxide lifetime in the combined H2O2–CO2 process proved to be longer than the one achieved in the tests carried out with H2O2 only, although slightly lower than the one achieved using KH2PO4 as stabilizing agent. On the other hand, it was observed that with respect to a traditional chemical oxidation application, the CO2 sparging can further enhance the overall effectiveness of the process as a result of contaminant stripping by CO2. Indeed, the residual MtBE concentration observed after application of the combined H2O2–CO2 process was slightly lower than the ones obtained using H2O2 only or comparable to the one achieved using H2O2 amended with KH2PO4. Overall, these results showed that the combined H2O2–CO2 process could represent a promising alternative to traditional formulations, avoiding the use of chemical amendments, while leading to comparable residual contaminant’s concentration.

Characterization and application of a novel class II thermophilic peroxidase from Myceliophthora thermophila in biosynthesis of polycatechol

A peroxidase from the thermophilic fungus Myceliophthora thermophila that belongs to ascomycete Class II based on PeroxiBase classification was functionally expressed in methylotrophic yeast Pichia pastoris. The putative peroxidase from the genomic DNA was successfully cloned in P. pastoris X-33 under the transcriptional control of the alcohol oxidase (AOX1) promoter. The heterologous production was greatly enhanced by the addition of hemin with a titer of 0.41UmL−1 peroxidase activity at the second day of incubation. The recombinant enzyme was purified to homogeneity (50kDa) and characterized using a series of phenolic substrates that indicated similar characteristics with those of generic peroxidases. In addition, the enzyme was found thermostable, retaining its activity for temperatures up to 60°C after eight hours incubation. Moreover, the enzyme displayed remarkable H2O2 stability, retaining more than 80% of its initial activity after 24h incubation in 5000-fold molar excess of H2O2. The ability of the peroxidase to polymerize catechol at high superoxide concentrations, together with its high thermostability and substrate specificity, indicate a potential commercial significance of the enzyme.

Improving the oxidative stability of a high redox potential fungal peroxidase by rational design.

Ligninolytic peroxidases are enzymes of biotechnological interest due to their ability to oxidize high redox potential aromatic compounds, including the recalcitrant lignin polymer. However, different obstacles prevent their use in industrial and environmental applications, including low stability towards their natural oxidizing-substrate H2O2. In this work, versatile peroxidase was taken as a model ligninolytic peroxidase, its oxidative inactivation by H2O2 was studied and different strategies were evaluated with the aim of improving H2O2 stability. Oxidation of the methionine residues was produced during enzyme inactivation by H2O2 excess. Substitution of these residues, located near the heme cofactor and the catalytic tryptophan, rendered a variant with a 7.8-fold decreased oxidative inactivation rate. A second strategy consisted in mutating two residues (Thr45 and Ile103) near the catalytic distal histidine with the aim of modifying the reactivity of the enzyme with H2O2. The T45A/I103T variant showed a 2.9-fold slower reaction rate with H2O2 and 2.8-fold enhanced oxidative stability. Finally, both strategies were combined in the T45A/I103T/M152F/M262F/M265L variant, whose stability in the presence of H2O2 was improved 11.7-fold. This variant showed an increased half-life, over 30 min compared with 3.4 min of the native enzyme, under an excess of 2000 equivalents of H2O2. Interestingly, the stability improvement achieved was related with slower formation, subsequent stabilization and slower bleaching of the enzyme Compound III, a peroxidase intermediate that is not part of the catalytic cycle and leads to the inactivation of the enzyme.

Hydrogen Peroxide Stability in Silica Hydrogels

Hydrogen peroxide (H2O2) entrapment in silica hydrogels has potential to be used in various industrially important applications to increase H2O2 stability. In this study, optimum conditions for hydrogel formation and H2O2 stability were determined by varying the sodium content and initial H2O2 concentration. Higher retention and better stability of H2O2 were achieved with hydrogels at room temperature at low sodium concentration. Retention values of 89% were obtained with initial H2O2 concentrations up to 10 wt %. H2O2 decomposition in hydrogels followed a first-order reaction. Hydrogels were characterized by measuring their surface area, pore size, and pore size distribution by Brunauer–Emmett–Teller analysis and scanning electron microscopy. Mesoporous (3–24 nm) hydrogels with high surface area (1000–1400 m2/g) were obtained. In addition, the melting point of the entrapped H2O2-water mixture in the hydrogels was studied by low temperature differential scanning calorimetry.