Organic Peroxides Research Articles

Selenium catalysis enables negative feedback organic oscillators.

The construction of materials regulated by chemical reaction networks requires regulatory motifs that can be stacked together into systems with desired properties. Multiple autocatalytic reactions producing thiols are known. However, negative feedback loop motifs are unavailable for thiol chemistry. Here, we develop a negative feedback loop based on the selenocarbonates. In this system, thiols induce the release of aromatic selenols that catalyze the oxidation of thiols by organic peroxides. This negative feedback loop has two important features. First, catalytic oxidation of thiols follows Michaelis-Menten-like kinetics, thus increasing nonlinearity for the negative feedback. Second, the strength of the negative feedback can be tuned by varying substituents in selenocarbonates. When combined with the autocatalytic production of thiols in a flow reactor, this negative feedback loop induces sustained oscillations. The availability of this negative feedback motif enables the future construction of oscillatory, homeostatic, adaptive, and other regulatory circuits in life-inspired systems and materials.

Peroxiredoxin 6 suppresses ferroptosis in lung endothelial cells

Peroxiredoxin 6 (Prdx6) repairs peroxidized membranes by reducing oxidized phospholipids, and by replacing oxidized sn-2 fatty acyl groups through hydrolysis/reacylation by its phospholipase A2 (aiPLA2) and lysophosphatidylcholine acyltransferase activities. Prdx6 is highly expressed in the lung, and intact lungs and cells null for Prdx6 or with single-point mutations that inactivate either Prdx6-peroxidase or aiPLA2 activity alone exhibit decreased viability, increased lipid peroxidation, and incomplete repair when exposed to paraquat, hyperoxia, or organic peroxides. Ferroptosis is form of cell death driven by the accumulation of phospholipid hydroperoxides. We studied the role of Prdx6 as a ferroptosis suppressor in the lung. We first compared the expression Prdx6 and glutathione peroxidase 4 (GPx4) and visualized Prdx6 and GPx4 within the lung. Lung Prdx6 mRNA levels were five times higher than GPx4 levels. Both Prdx6 and GPx4 localized to epithelial and endothelial cells. Prdx6 knockout or knockdown sensitized lung endothelial cells to erastin-induced ferroptosis. Cells with genetic inactivation of either aiPLA2 or Prdx6-peroxidase were more sensitive to ferroptosis than WT cells, but less sensitive than KO cells. We then conducted RNA-seq analyses in Prdx6-depleted cells to further explore how the loss of Prdx6 sensitizes lung endothelial cells to ferroptosis. Prdx6 KD upregulated transcriptional signatures associated with selenoamino acid metabolism and mitochondrial function. Accordingly, Prdx6 deficiency blunted mitochondrial function and increased GPx4 abundance whereas GPx4 KD had the opposite effect on Prdx6. Moreover, we detected Prdx6 and GPx4 interactions in intact cells, suggesting that both enzymes cooperate to suppress lipid peroxidation. Notably, Prdx6-depleted cells remained sensitive to erastin-induced ferroptosis despite the compensatory increase in GPx4. These results show that Prdx6 suppresses ferroptosis in lung endothelial cells and that both aiPLA2 and Prdx6-peroxidase contribute to this effect. These results also show that Prdx6 supports mitochondrial function and modulates several coordinated cytoprotective pathways in the pulmonary endothelium.

Hydrolysis reactivity reveals significant seasonal variation in the composition of organic peroxides in ambient PM2.5

Atmospheric organic peroxides (POs) play a key role in the formation of O3 and secondary organic aerosol (SOA), impacting both air quality and human health. However, there still remain technical challenges in investigating the reactivity of POs in ambient aerosols due to the instability and lack of standards for POs, impeding accurate evaluation of their environmental impacts. In the present study, we conducted the first attempt to categorize and quantify POs in ambient PM2.5 through hydrolysis, which is an important transformation pathway for POs, thus revealing the reactivities of various POs. POs were generally categorized into hydrolyzable POs (HPO) and unhydrolyzable POs (UPO). HPO were further categorized into three groups: short-lifetime HPO (S-HPO), intermediate-lifetime HPO (I-HPO), and long-lifetime HPO (L-HPO). S-HPO and L-HPO are typically formed from Criegee intermediate (CI) and RO2 radical reactions, respectively. Results show that L-HPO are the most abundant HPO, indicating the dominant role of RO2 pathway in HPO formation. Despite their lower concentration compared to L-HPO, S-HPO make a major contribution to the HPO hydrolysis rate due to their faster rate constants. The hydrolysis of PM2.5 POs accounts for 19 % of the nighttime gas-phase H2O2 growth during the summer observation, constituting a noteworthy source of gas-phase H2O2 and contributing to the atmospheric oxidation capacity. Seasonal and weather conditions significantly impact the composition of POs, with HPO concentrations in summer being significantly higher than those in winter and elevated under rainy and nighttime conditions. POs are mainly composed of HPO in summer, while in winter, POs are dominated by UPO.

The long-chain flavodoxin FldX1 improves the biodegradation of 4-hydroxyphenylacetate and 3-hydroxyphenylacetate and counteracts the oxidative stress associated to aromatic catabolism in Paraburkholderia xenovorans

BackgroundBacterial aromatic degradation may cause oxidative stress. The long-chain flavodoxin FldX1 of Paraburkholderia xenovorans LB400 counteracts reactive oxygen species (ROS). The aim of this study was to evaluate the protective role of FldX1 in P. xenovorans LB400 during the degradation of 4-hydroxyphenylacetate (4-HPA) and 3-hydroxyphenylacetate (3-HPA).MethodsThe functionality of FldX1 was evaluated in P. xenovorans p2-fldX1 that overexpresses FldX1. The effects of FldX1 on P. xenovorans were studied measuring growth on hydroxyphenylacetates, degradation of 4-HPA and 3-HPA, and ROS formation. The effects of hydroxyphenylacetates (HPAs) on the proteome (LC–MS/MS) and gene expression (qRT-PCR) were quantified. Bioaugmentation with strain p2-fldX1 of 4-HPA-polluted soil was assessed, measuring aromatic degradation (HPLC), 4-HPA-degrading bacteria, and plasmid stability.ResultsThe exposure of P. xenovorans to 4-HPA increased the formation of ROS compared to 3-HPA or glucose. P. xenovorans p2-fldX1 showed an increased growth on 4-HPA and 3-HPA compared to the control strain WT-p2. Strain p2-fldX1 degraded faster 4-HPA and 3-HPA than strain WT-p2. Both WT-p2 and p2-fldX1 cells grown on 4-HPA displayed more changes in the proteome than cells grown on 3-HPA in comparison to glucose-grown cells. Several enzymes involved in ROS detoxification, including AhpC2, AhpF, AhpD3, KatA, Bcp, CpoF1, Prx1 and Prx2, were upregulated by hydroxyphenylacetates. Downregulation of organic hydroperoxide resistance (Ohr) and DpsA proteins was observed. A downregulation of the genes encoding scavenging enzymes (katE and sodB), and gstA and trxB was observed in p2-fldX1 cells, suggesting that FldX1 prevents the antioxidant response. More than 20 membrane proteins, including porins and transporters, showed changes in expression during the growth of both strains on hydroxyphenylacetates. An increased 4-HPA degradation by recombinant strain p2-fldX1 in soil microcosms was observed. In soil, the strain overexpressing the flavodoxin FldX1 showed a lower plasmid loss, compared to WT-p2 strain, suggesting that FldX1 contributes to bacterial fitness. Overall, these results suggest that recombinant strain p2-fldX1 is an attractive bacterium for its application in bioremediation processes of aromatic compounds.ConclusionsThe long-chain flavodoxin FldX1 improved the capability of P. xenovorans to degrade 4-HPA in liquid culture and soil microcosms by protecting cells against the degradation-associated oxidative stress.

Calorimetric and kinetic evaluation of thermal stability and process safety in tert-butyl peroxy-2-ethylhexanoate and tert-butyl peroxybenzoate

This study evaluated the thermal stability and process safety of tert-butyl peroxybenzoate (TBPB), tert-butyl peroxy-2-ethylhexanoate (TBPO), and their mixture. Thermogravimetric (TG) analysis, differential scanning calorimetry (DSC), and accelerated rate calorimetry were used to elucidate the thermal behavior and breakdown kinetics. The TG results indicated moderate to low breakdown temperatures for all samples, demonstrating their thermal stability. DSC revealed onset temperatures for exothermic disintegration between 66.66 °C and 104.23 °C. The mixture had two distinct exothermic peaks, signifying the thermal decomposition of the mixture was such that the characteristic temperature and heat of the reaction were between those of TBPB and TBPO. Using Heat–Wait–Search methodology, the study identified thermal runaway exothermically. Under pseudoadiabatic conditions, the mixture exhibited greater increases in temperature and pressure—of 115.06 °C and 28.77 bar, respectively—compared with the individual compounds. To elucidate the apparent activation energy (Ea) and reaction kinetics, the study applied models developed by Arrhenius, Flynn-Wall-Ozawa, Friedman, Kissinger, and Starink. The Ea values obtained based on the TG, DSC, and ARC experiments were approximately 50.47, 98.19, and 99.71 kJ/mol, respectively, and were lower than those of TBPB and TBPO pure substances. The self-accelerating decomposition temperature of TBPB/TBPO decreased from 34 to 32 °C as the packaging of TBPB/TBPO was increased from 25 to 100 kg and was more than 10 °C lower than that of the individual substance. These findings offer a framework for evaluating the thermal risks associated with TBPB and TBPO, particularly when mixed. They contribute to the safe transit, storage, and handling of industrial organic peroxides, enriching our collective understanding of the stability and safety of these compounds.

8-OxoG-Dependent Regulation of Global Protein Responses Leads to Mutagenesis and Stress Survival in Bacillus subtilis.

The guanine oxidized (GO) system of Bacillus subtilis, composed of the YtkD (MutT), MutM and MutY proteins, counteracts the cytotoxic and genotoxic effects of the oxidized nucleobase 8-OxoG. Here, we report that in growing B. subtilis cells, the genetic inactivation of GO system potentiated mutagenesis (HPM), and subsequent hyperresistance, contributes to the damaging effects of hydrogen peroxide (H2O2) (HPHR). The mechanism(s) that connect the accumulation of the mutagenic lesion 8-OxoG with the ability of B. subtilis to evolve and survive the noxious effects of oxidative stress were dissected. Genetic and biochemical evidence indicated that the synthesis of KatA was exacerbated, in a PerR-independent manner, and the transcriptional coupling repair factor, Mfd, contributed to HPHR and HPM of the ΔGO strain. Moreover, these phenotypes are associated with wider pleiotropic effects, as revealed by a global proteome analysis. The inactivation of the GO system results in the upregulated production of KatA, and it reprograms the synthesis of the proteins involved in distinct types of cellular stress; this has a direct impact on (i) cysteine catabolism, (ii) the synthesis of iron-sulfur clusters, (iii) the reorganization of cell wall architecture, (iv) the activation of AhpC/AhpF-independent organic peroxide resistance, and (v) increased resistance to transcription-acting antibiotics. Therefore, to contend with the cytotoxic and genotoxic effects derived from the accumulation of 8-OxoG, B. subtilis activates the synthesis of proteins belonging to transcriptional regulons that respond to a wide, diverse range of cell stressors.

Direct aqueous photochemistry of methylglyoxal and its effect on sulfate formation

In recent years, among many oxidation pathways studied for atmospheric sulfate formation, the aqueous phase oxidation pathways of H2O2 and organic hydroperoxides (ROOHs) have attracted great scientific attention. Higher concentrations of H2O2 and ubiquitous ROOHs have been observed in atmospheric aqueous phase environments (cloud water, fog droplets, etc.). However, there are still some gaps in the study of their aqueous phase generation and their influences on sulfate formation. In this study, the aqueous phase photochemical reaction of methylglyoxal, a ubiquitous organic substance in the atmospheric aqueous phase, was studied under UV irradiation, and the generation of H2O2 and ROOHs in this system was investigated. It is found for the first time that the aqueous phase photolysis of methylglyoxal not only produces H2O2 but also produces ROOHs, and UV light and O2 are necessary for the formation of H2O2 and ROOHs. Based on the experimental results, the possible mechanism of aqueous phase photochemistry of methylglyoxal and the generation of H2O2 and ROOHs were proposed. The effect of aqueous phase photolysis of methylglyoxal on sulfate formation under different conditions was also investigated. The results show that the aqueous phase photolysis of methylglyoxal significantly promoted SO2 oxidation and sulfate formation, in which SO2 oxidation was realized by the generated H2O2, ROOHs and •OH radicals, and the importance of the formed ROOHs cannot be ignored. These results fill some gaps in the field of aqueous phase H2O2 and ROOHs production, and to a certain extent confirm the important roles of the aqueous phase photolysis of methylglyoxal and the formed H2O2 and ROOHs in the production of sulfate. The study reveals the new sources of H2O2 and ROOHs, and provides a new insight into the heterogeneous aqueous phase oxidation pathways and mechanisms of SO2 in cloud and fog droplets and haze particles.

Reactive Oxygen Species Formation and Peroxide and Carbonyl Decomposition in Aqueous Photolysis of Secondary Organic Aerosols.

The mechanism and kinetics of reactive oxygen species (ROS) formation when atmospheric secondary organic aerosol (SOA) is exposed to solar radiation are poorly understood. In this study, we combined an in situ UV-vis irradiation system with electron paramagnetic resonance (EPR) spectroscopy to characterize the photolytic formation of ROS in aqueous extracts of SOA formed by the oxidation of isoprene, α-pinene, α-terpineol, and toluene. We observed substantial formation of free radicals, including •OH, superoxide (HO2•), and organic radicals (R•/RO•) upon irradiation. Compared to dark conditions, the radical yield was enhanced by a factor of ∼30 for •OH and by a factor of 2-10 for superoxide radicals, and we observed the emergence of organic radicals. Total peroxide measurements showed substantial decreases of peroxide contents after photoirradiation, indicating that organic peroxides can be an important source of the observed radicals. A liquid chromatography interfaced with high-resolution mass spectrometry was used to detect a number of organic radicals in the form of adducts with a spin trap, BMPO. The types of detected radicals and aqueous photolysis of model compounds indicated that photolysis of carbonyls by Norrish type I mechanisms plays an important role in the organic radical formation. The photolytic ROS formation serves as the driving force for cloud and fog processing of SOA.

Role of Hydroperoxyl Radicals in Heterogeneous Oxidation of Oxygenated Organic Aerosols.

Heterogeneous oxidative aging of organic aerosols (OA) occurs ubiquitously in the atmosphere, initiated by oxidants, such as the hydroxyl radicals (•OH). Hydroperoxyl radicals (HO2•) are also an important oxidant in the troposphere, and its gas-phase chemistry has been well studied. However, the role of HO2• in heterogeneous OA oxidation remains elusive. Here, we carry out •OH-initiated heterogeneous oxidation of several OA model systems under different HO2• conditions in a flow tube reactor and characterize the molecular oxidation products using a suite of mass spectrometry instrumentation. By using hydrogen-deuterium exchange (HDX) with thermal desorption iodide-adduct chemical ionization mass spectrometry, we provide direct observation of organic hydroperoxide (ROOH) formation from heterogeneous HO2• and peroxy radicals (RO2•) reactions for the first time. The ROOH may contribute substantially to the oxidation products, varied with the parent OA chemical structure. Furthermore, by regulating RO2• reaction pathways, HO2• also greatly influence the overall composition of the oxidized OA. Last, we suggest that the RO2• + HO2• reactions readily occur at the OA particle interface rather than in the particle bulk. These findings provide new mechanistic insights into the heterogeneous OA oxidation chemistry and help fill the critical knowledge gap in understanding atmospheric OA oxidative aging.

PH regulates the formation of organosulfates and inorganic sulfate from organic peroxide reaction with dissolved SO2 in aquatic media

Abstract. Organic peroxides (OPs) are an important component of dissolved organic matter (DOM), detected in various aquatic media. Despite their unique functions as redox agents in water ecosystems, the complete mechanisms and factors controlling their transformation are not explicitly established. Here, we evaluate the pH effect on the aqueous-phase reaction of three selected OPs (methyl hydroperoxide (MHP), peracetic acid (PAA), and benzoyl peroxide (BZP)) with dissolved SO2. Results show that due to the presence of the hydroperoxyl group in their structures, MHP and PAA are susceptible to forming inorganic sulfate and organosulfate (methyl sulfate for MHP and acetyl sulfate for PAA) depending on the pH, while BZP exclusively forms organosulfate (benzoyl sulfate) in the pH range investigated. Moreover, it is seen that the ability of PAA to form inorganic sulfate relative to organosulfate is more pronounced, which is supported by a previous experimental observation. The effective rate constants of the transformation of these peroxides within the pH 1–10 and 240–340 K ranges exhibit positive pH and temperature dependencies, and BZP is seen to degrade more effectively than MHP and PAA. In addition to the pH impact, it is highlighted that the formation of organic and/or inorganic sulfate strongly depends on the nature of the substituents on the peroxy function. Namely, PAA and BZP are more reactive than MHP, which may be attributed to the electron-withdrawing effects of -C(O)R (R = -CH3 and -C6H5 for PAA and BZP, respectively) substituents that activate the peroxy function. The results further indicate that the aqueous-phase degradation of OPs can adequately drive the change in the chemical composition of DOM, both in terms of organic and inorganic sulfate mass fractions.

Synthesis and Characterization of Organic Peroxides from Monoterpene-Derived Criegee Intermediates in Secondary Organic Aerosol.

Ozonolysis of alkenes is known to produce reactive intermediates─stabilized Criegee intermediates (SCIs), and their subsequent bimolecular reactions with various carboxylic acids can form α-acyloxyalkyl hydroperoxides (AAHPs), which is considered a major class of organic peroxides in secondary organic aerosol (SOA). Despite their atmospheric and health importance, the molecular-level identification of organic peroxides in atmospheric aerosols is highly challenging, preventing further assessment of their environmental fate. Here, we synthesize 20 atmospherically relevant AAHPs through liquid-phase ozonolysis, in which two types of monoterpene-derived SCIs from either α-pinene or 3-carene are scavenged by 10 different carboxylic acids to form AAHPs with diverse structures. These AAHPs are identified individually by liquid chromatography coupled with high-resolution mass spectrometry. AAHPs were previously thought to decompose quickly in an aqueous environment such as cloud droplets, but we demonstrate here that AAHPs hydrolysis rates are highly compound-dependent with rate constants differing by 2 orders of magnitude. In contrast, the aqueous-phase formation rate constants between SCI and various carboxylic acids vary only within a factor of 2-3. Finally, we identified two of the 20 synthesized AAHPs in α-pinene SOA and two in 3-carene SOA, contributing ∼0.3% to the total SOA mass. Our results improve the current molecular-level understanding of organic peroxides and are useful for a more accurate assessment of their environmental fate and health impact.

Human Milk-Derived Enterococcus faecalis HM20: A Potential Alternative Agent of Antimicrobial Effect against Methicillin-Resistant Staphylococcus aureus (MRSA).

The increasing global impact of skin diseases, fueled by methicillin-resistant Staphylococcus aureus (MRSA), emphasizes the necessity for alternative therapies with lower toxicity, such as lactic acid bacteria (LAB). This study aims to isolate potential LAB from human milk and evaluate their efficacy against MRSA using various methods, including well diffusion, microdilution, crystal violet assay, enzymatic characterization, SDS-PAGE, and scanning electron microscopy (SEM). Among the 26 LAB screened, the human milk-derived strain HM20 exhibited significant antimicrobial activity against S. aureus CCARM 3089 (MRSA), which is a highly resistant skin pathogen. Through 16S rRNA sequencing, strain HM20 was identified as closely related to Enterococcus faecalis ATCC 19433T, which was subsequently designated as Enterococcus faecalis HM20. The minimum inhibitory concentration (MIC) of the cell-free supernatant (CFS) of HM20 against S. aureus KCTC 3881 and S. aureus CCARM 3089 was determined to be 6.25% and 12.5%, respectively. Furthermore, the effective inhibition of biofilm formation in S. aureus KCTC 3881 and S. aureus CCARM 3089 was observed at concentrations of 12.5% and 25% or higher, respectively. The antibacterial effect of the CFS was attributed to the presence of organic acids, hydrogen peroxide, and bacteriocins. Additionally, the antimicrobial peptides produced by HM20 were found to be stable under heat treatment and analyzed to have a size below 5 kDa. SEM image observations confirmed that the CFS of HM20 caused damage to the cell wall, forming pores and wrinkles on S. aureus KCTC 3881 and S. aureus CCARM 3089. This comprehensive investigation on strain HM20 conducted in this study provides foundational data for potential developments in functional materials aimed at addressing skin infections and antibiotic-resistant strains in the future.

Development of extrusion blown films of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) blends for flexible packaging

AbstractPoly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) is a biodegradable polymer with significant potential for use in food packaging. However, its limited melt strength poses a challenge when employing film‐blowing techniques to produce flexible packaging. To overcome this obstacle, we developed blends consisting of 70 wt% PHBV and 30 wt% poly(butylene‐co‐succinate‐co‐adipate) (PBSA). Organic peroxides such as dicumyl peroxide and 2,5‐dimethyl‐2,5‐di‐(tert‐butylperoxy)hexane, were utilized as reactive compatibilizers to enhance the interfacial adhesion between the polymers. Additionally, acetyl tributyl citrate (ATBC) was employed as a plasticizer to improve processability and ductility. The inclusion of organic peroxides resulted in the formation of long‐branched structures, as confirmed by the van‐Gurp‐Palmen plot. The melt flow index decreased from 30 to 9.8 g/10 min without ATBC and 15.5 g/10 min with ATBC. Successful production of blown PHBV/PBSA films was achieved on a pilot scale (bubble height 180 cm). These films exhibited heat‐sealing capability and increased impact strength (7.7 kJ/m2). Moreover, the films maintained a maximum elongation at break of 4% during a 3‐month storage experiment with frozen food. Food safety was assessed through overall migration experiments, and the non‐plasticized films received approval. In conclusion, the compatibilized PHBV/PBSA blends demonstrate great potential as materials for manufacturing film‐blown flexible packaging.

Effect and mechanism of iron-carbon micro-electrolysis pretreatment of organic peroxide production wastewater.

The wastewater from organic peroxide production has high chemical oxygen demand (COD) concentration and poor biodegradability, so it is necessary to find a cost-effective treatment method. The iron-carbon microelectrolysis (IC-ME) technology was used to pretreat the organic peroxide production wastewater, and the influence of reaction conditions on the removal effect of pollutants and the degradation mechanism were studied. The effects of initial pH, iron filings, iron-carbon ratio, and reaction time on the wastewater treatment were investigated by single-factor and response surface optimization experiments, and the degradation mechanism was analyzed by three-dimensional fluorescence spectroscopy, UV-Vis, and gas chromatography mass spectrometry (GC-MS). The experimental results showed that the COD removal efficiency was 35.67% and the biodegradability of wastewater was increased from 0.113 to 0.173 under the conditions of initial pH of 3.1, the dosage of iron filings of 30.5g/L, the ratio of iron-carbon of 1.01, and the reaction time of 122.8min, and the process of IC-ME for degrading COD of wastewater from the production of organic peroxide was consistent with the secondary reaction. The IC-ME process could decompose macromolecular organic compounds such as tyrosine proteins and aromatic proteins, and improve the biodegradability of wastewater. It provides a theoretical reference for the practical application of IC-ME to treat this type of wastewater.

Carotenoid-dependent singlet oxygen photogeneration in light-harvesting complex 2 of Ectothiorhodospira haloalkaliphila leads to the formation of organic hydroperoxides and damage to both pigments and protein matrix.

Earlier, it was suggested that carotenoids in light-harvesting complexes 2 (LH2) can generate singlet oxygen, further oxidizing bacteriochlorophyll to 3-acetyl-chlorophyll. In the present work, it was found that illumination of isolated LH2 preparations of purple sulfur bacterium Ectothiorhodospira haloalkaliphila with light in the carotenoid absorption region leads to the photoconsumption of molecular oxygen, which is accompanied by the formation of hydroperoxides of organic molecules in the complexes. Photoformation of two types of organic hydroperoxides were revealed: highly lipophilic (12 molecules per one LH2) and relatively hydrophobic (68 per one LH2). It has been shown that illumination leads to damage to light-harvesting complexes. On the one hand, photobleaching of bacteriochlorophyll and a decrease in its fluorescence intensity are observed. On the other hand, the photoinduced increase in the hydrodynamic radius of the complexes, the reduction in their thermal stability, and the change in fluorescence intensity indicate conformational changes occurring in the protein molecules of the LH2 preparations. Inhibition of the processes described above upon the addition of singlet oxygen quenchers (L-histidine, Trolox, sodium L-ascorbate) may support the hypothesis that carotenoids in LH2 preparations are capable of generating singlet oxygen, which, in turn, damage to protein molecules.

Synthesis of selenium and fluorine co-doped graphitic carbon nitride for photodegradation of toxic organic pollutants and hydrogen peroxide photoproduction

Science is developing every day to race against the factual growth of industrial pollution in order to redeem the environment. In this study, modification of graphitic carbon nitride via selenium and fluoride doping was successfully conducted. Specifically, the process of co-calcination was conscripted using organic precursors, whilst the foreign elements were obtained from ammonium fluoride and selenium dioxide. The morphological assessment revealed the treated-graphitic carbon nitride possessed a flaky sheet form with high porosity and great crystalline uniformity. Photochemical investigation showed the co-doping of selenium and fluorine elevated the optical properties, including the decrement of bandgap and diminishing the recombination rate of electrons and holes. With interesting improvement in photocatalytic activity, the material was applied in persistent organic compound degradation and hydrogen peroxide production. The treatment improved the degradation percentage, in which the methylene blue removal achieved 99.96 % while the tetracycline removal reached 86.38 %. Moreover, high compatibility and great reusability over 4 cycles were also recorded. When applying the material for the generation of hydrogen peroxide, the co-doped material performance was observed to reach 3307 μM/g.h. The results concluded the advancement in material modification with great application in various aspects.

Polypropylene nanocomposites produced by in‐situ grafting of maleic anhydride using different mixing procedures

AbstractNanocomposites (NC) of polypropylene (PP) and organophilic montmorillonite (oMt) are produced by reactive mixing with simultaneous grafting of maleic anhydride (MA) onto PP using organic peroxide as initiator. Five different strategies of incorporating reactants and clay into a laboratory mixer are used. The structure of composites is examined by FT‐IR spectroscopy, x‐ray diffraction and scanning electron microscopy. Rotational rheometry, thermogravimetry and oxygen permeability are used to evaluate properties. The preparation method has a remarkable influence on NC's structure. Simultaneous addition of peroxide and MA to molten PP followed by incorporation of clay 20 minutes later produces the best degree of clay exfoliation/disaggregation. The NCs obtained using this procedure are highly transparent and have very thin tactoids with interlayer spacing more than 50% larger than the original oMt. The incorporation of just 2 wt% of clay gives place to more than 30% reduction in PP oxygen permeability. Additionally, the temperature at the maximum thermal degradation rate in nitrogen reduces in about 60°C while the temperature at which the thermal degradation process begins is not affected.Highlights Highly intercalated/exfoliated PP/oMt nanocomposites are synthesized Reactive mixing procedure affects the quality of nanocomposite's structure A initial period of grafting before clay addition is the most effective method Highly transparent materials with small tactoids of d001>4 nm is generated PP oxygen permeability is highly reduced by the use of just 2 wt% of nanoclay

Metal-catalyzed asymmetric reactions enabled by organic peroxides.

As a class of multifunctional reagents, organic peroxides play vital roles in the chemical industry, pharmaceutical synthesis and polymerization reactions. Metal-catalyzed asymmetric catalysis has emerged as one of the most straightforward and efficient strategies to construct enantioenriched molecules, and an increasing number of metal-catalyzed asymmetric reactions enabled by organic peroxides have been disclosed by researchers in recent years. Despite remarkable progress, the types of asymmetric reactions facilitated by organic peroxides remain limited and the catalysis systems need to be further broadened. To the best of our knowledge, there is still no review devoted to summarizing the reactions from this perspective. In this review, we will endeavor to highlight the advances in metal-catalyzed asymmetric reactions enabled by organic peroxides. We hope that this survey will summarize the functions of organic peroxides in catalytic reactions, improve the understanding of these compounds and inspire future developments in this area.

Vibrational spectroscopy and dissociation dynamics of cyclohexyl hydroperoxide.

Organic hydroperoxides (ROOH) are ubiquitous in the atmospheric oxidation of volatile organic compounds (VOCs) as well as in low-temperature oxidation of hydrocarbon fuels. The present work focuses on a prototypical cyclic hydroperoxide, cyclohexyl hydroperoxide (CHHP). The overtone OH stretch (2νOH) spectrum of jet-cooled CHHP is recorded by IR multiphoton excitation with UV laser-induced fluorescence detection of the resulting OH products. A distinctive IR feature is observed at 7012.5 cm-1. Two conformers of CHHP are predicted to have similar stabilities (within 0.2 kcal mol-1) and overtone OH stretch transitions (2νOH), yet are separated by a significant interconversion barrier. The IR power dependence indicates that absorption of three or more IR photons is required for dissociation of CHHP to cyclohexoxy (RO) and OH radical products. Accompanying high-level single- and multi-reference electronic structure calculations quantitatively support the experimental results. Calculations are extended to a range of organic hydroperoxides to examine trends in bond dissociation energies associated with RO + OH formation and compared with prior theoretical results.

Dioxygen-halogen bonding exemplified by crystalline peroxosolvates of N,N'-bis(haloacetyl) bispidines.

The halogen bonding in molecular crystals and supramolecular assemblies has been widely investigated. Special attention is given to the molecular structures capable of simultaneously exhibiting different types of non-covalent interactions, including conventional hydrogen bonds and halogen bonds. This paper systematically analyzes crystalline peroxosolvates of bispidine-based bis-amide derivatives, containing haloacetic acid residues, namely previously reported 1,1'-(1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonane-3,7-diyl)bis(2-iodooethanone) peroxosolvate C13H20I2N2O2·H2O2 (1) and four new crystalline compounds, 1,1'-(1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonane-3,7-diyl)bis(2-bromoethanone) peroxosolvate C13H20Br2N2O2·H2O2 (2), 1,1'-(9-hydroperoxy-9-hydroxy-1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonane-3,7-diyl)bis(2-iodoethanone) peroxosolvate C13H20I2N2O5·0.5H2O2 (3), 1,1'-(9-hydroperoxy-9-hydroxy-1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonane-3,7-diyl)bis(2-bromoethanone) peroxosolvate C13H20Br2N2O5·H2O2 (4), and 1,1'-(9-hydroperoxy-9-hydroxy-1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonane-3,7-diyl)bis(2-chloroethanone) peroxosolvate C13H20Cl2N2O5·H2O2 (5). Compounds 2-5 were synthesized for the first time and their crystal structures were determined by single-crystal X-ray diffractometry (SCXRD). To the best of our knowledge, 3-5 are unprecedented crystalline hydrogen peroxide adducts of organic hydroperoxides (R-OOH). Short intermolecular contacts between halogen and hydroperoxo oxygen atoms were found in 1-3. The halogen bonding of C-I(Br) fragments with dioxygen species in compounds 1-3 as well as in the previously reported cocrystal of diacetone diperoxide with triodotrinitrobenzene (6) was identified through reduced density gradient analysis, Hirshfeld surface analysis, and Bader analysis of crystalline electron density. The interactions were quantified using the electron density topological properties acquired from the periodic DFT calculations and evaluated to lie in the range of 9-19 kJ mol-1. A distinctive spectral feature was revealed for this type of interaction, involving a red shift of the characteristic O-O stretching vibration by about 6 cm-1, which appeared in IR spectra as a narrow low-intensity band in the region 837-872 cm-1.