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To oxidize trace concentrations of organic contaminants under conditions relevant to surface- and groundwater, air-diffusion cathodes were coupled to stainless-steel cathodes that convert atmospheric O2 into hydrogen peroxide (H2O2), which then was activated to produce hydroxyl radicals (·OH). By separating H2O2 generation from its activation and employing a flow-through electrode consisting of stainless-steel fibers, the two processes could be operated efficiently in a manner that overcame mass-transfer limitations for O2, H2O2, and trace organic contaminants. The flexibility resulting from separate control of the two processes made it possible to avoid both the accumulation of excess H2O2 and the energy losses that take place after H2O2 has been depleted. The decrease in treatment efficacy occurring in the presence of natural organic matter was substantially lower than that typically observed in homogeneous advanced oxidation processes. Experiments conducted with ionized and neutral compounds indicated that electrostatic repulsion prevented negatively charged ·OH scavengers from interfering with the oxidation of neutral contaminants. Energy consumption by the dual-cathode system was lower than values reported for other technologies intended for small-scale drinking water treatment systems. The coordinated operation of these two cathodes has the potential to provide a practical, inexpensive way for point-of-use drinking water treatment.

Bisphenol A (BPA), extensively used in the production of polycarbonate plastic and epoxy resin, poses significant threats to aquatic ecosystems and human health. Advanced oxidation processes (AOPs), which generate reactive species in situ, offer promising alternatives for wastewater treatment. Among these, the Fenton process, generating OH radicals, stands out. This study aims to explore the oxidative degradation of BPA by detecting its intermediates and elucidating its degradation pathway. Our findings reveal the existence of two interconnected degradation pathways. This study underscores the importance of advanced oxidation processes in mitigating the detrimental effects of BPA contamination, emphasizing the need for further research to optimize wastewater treatment methods and safeguard both ecosystems and human health.

Peroxymonosulfate (PMS) as an oxidant has been extensively applied to remove organic pollutants, but the molecular interaction mechanism of PMS and organic pollutants under the electrochemical process remains unclear. This work unraveled the interaction relationship of PMS on ofloxacin (OFN) degradation by PMS-based electrochemical oxidation. The results showed that hydroxyl and sulfate radicals generated from the electrochemical reaction could effectively degrade OFN. Under the electrochemical oxidation process, 100% or 12.1 ± 2.1% of OFN was degraded within 15 min in the presence or absence of PMS, respectively. Quantum chemical calculations and molecular dynamics simulations indicated that the hydrogen bonds and van der Waals force were the primary interaction force between PMS and OFN. Besides, the PMS-OFN binding process was a stable dynamic process, and its stability was dependent on the number of hydrogen bonds generated. The structure-activity relationship suggested that OFN was transformed into short-chain intermediates with lower toxicity within 15 min. Additionally, this electrochemical system for degrading OFN retained excellent reusability and recyclability, affording high oxidation ability during successive cycles. More importantly, this electrochemical process could highly efficiently degrade various organic pollutants (4-chlorophenol, methyl orange, sulfamethoxazole, and perfluorooctanoic acid). This study provided a new possibility for the application of the electrochemical system in large-scale wastewater treatment. © 2024 American Chemical Society.

Pharmaceutical and industrial utilization of synthetic chemicals has an immerse impact on the environment. In that sense, novel chemicals with potential for industrial application should be investigated for their behavior in reactions with hydroxyl radical, simulating AOPs (Advanced Oxidation Processes). AOPs are known for being highly effective in wastewater management and natural water remediation. In this paper, exhaustive research on the radical scavenging activity of a newly synthesized coumarin derivative (4HCBH), as a representative of the series of coumarin- benzohydrazides with high antioxidative potential was conducted. This study took into consideration the pH value range significant for practically all living organisms (pH=7.0- 8.5). According to the experimentally obtained results, the 4HCBH showed an increase in radical scavenging activity, following the slight increase in pH values, which suggested that the formation of anionic form of 4HCBH is responsible for its antiradical activity. Further investigations led to the postulation of a novel mechanistic approach called Sequential Proton Loss Electron Transfer – Radical-Radical Coupling (SPLET- RRC), in which, by a series of steps, a new, stable compound was formed. Furthermore, it was demonstrated that the product generated through SPLET-RRC showed lower toxicity than the parent molecule.

The total oxidizable precursor (TOP) assay has been extensively used for detecting PFAS pollutants that do not have analytical standards. It uses hydroxyl radicals (HO•) from the heat activation of persulfate under alkaline pH to convert H-containing precursors to perfluoroalkyl carboxylates (PFCAs) for target analysis. However, the current TOP assay oxidation method does not apply to emerging PFAS because (i) many structures do not contain C-H bonds for HO• attack and (ii) the transformation products are not necessarily PFCAs. In this study, we explored the use of classic acidic persulfate digestion, which generates sulfate radicals (SO4-•), to extend the capability of the TOP assay. We examined the oxidation of Nafion-related ether sulfonates that contain C-H or -COO-, characterized the oxidation products, and quantified the F atom balance. The SO4-• oxidation greatly expanded the scope of oxidizable precursors. The transformation was initiated by decarboxylation, followed by various spontaneous steps, such as HF elimination and ester hydrolysis. We further compared the oxidation of legacy fluorotelomers using SO4-• versus HO•. The results suggest novel product distribution patterns, depending on the functional group and oxidant dose. The general trends and strategies were also validated by analyzing a mixture of 100000- or 10000-fold diluted aqueous film-forming foam (containing various fluorotelomer surfactants and organics) and a spiked Nafion precursor. Therefore, (1) the combined use of SO4-• and HO• oxidation, (2) the expanded list of standard chemicals, and (3) further elucidation of SO4-• oxidation mechanisms will provide more critical information to probe emerging PFAS pollutants.

The photochemical degradation pathways of 6PPD-quinone (6PPDQ, 6PPD-Q), a toxic transformation product of the tire antiozonant 6PPD, were determined under simulated sunlight conditions typical of high-latitude surface waters. Direct photochemical degradation resulted in 6PPDQ half-lives ranging from 17.5 h at 20 °C to no observable degradation over 48 h at 4 °C. Sensitization of excited triplet-state pathways using Cs+ and Ar purging demonstrated that 6PPDQ does not decompose significantly from a triplet state relative to a singlet state. However, assessment of processes involving reactive oxygen species (ROS) quenchers and sensitizers indicated that singlet oxygen and hydroxyl radical do significantly contribute to the degradation of 6PPDQ. Investigation of these processes in natural lake waters indicated no difference in attenuation rates for direct photochemical processes at 20 °C. This suggests that direct photochemical degradation will dominate in warm waters, while indirect photochemical pathways will dominate in cold waters, involving ROS mediated by chromophoric dissolved organic matter (CDOM). Overall, the aquatic photodegradation rate of 6PPDQ will be strongly influenced by the compounding effects of environmental factors such as light screening and temperature on both direct and indirect photochemical processes. Transformation products were identified via UHPLC-Orbitrap mass spectrometry, revealing four major processes: (1) oxidation and cleavage of the quinone ring in the presence of ROS, (2) dealkylation, (3) rearrangement, and (4) deamination. These data indicate that 6PPDQ can photodegrade in cool, sunlit waters under the appropriate conditions: t1/2 = 17.4 h tono observable decrease (direct); t1/2 = 5.2-11.2 h (indirect, CDOM).

Over the last decades, scientific research is focused on the development of green technologies which would be effectively used for the purification of aquatic environment pollution. Among the various electrochemical technologies, the electrochemical advanced oxidation processes (EAOPs) are promising option that may be applied to remove organic pollutants from wastewater. These methods are based on the electrochemical generation of very powerful oxidizing species, such as the hydroxyl radical (•OH) at the anode surface or in the bulk solutions, which is then able to destroy organics partially or to their total mineralization. This article reviews currently most promising approach of EAOPs technology, introduces its basic principles, and describes the research progress in that field. Both technics of production OH radical are considered, and the role of electrode materials is discussed together with the author’s laboratory experiments.

When air pollution particles encounter water, whether in clouds or in the lungs, they partly dissolve, which starts a cascade of reactions. In clouds, this chemistry can change the mass concentration, chemical composition, and size distribution of particulate matter (PM) left behind when the cloud re-evaporates, making it an important process impacting the earth’s climate. In the lungs, particles induce health impacts via mechanisms that are areas of active research. While these two environments are distinct, both are mediated by the reactions of reactive oxygen species (ROS). Excess amounts of ROS formation triggered by the inhalation of PM is believed to be one of the causes of PM-induced diseases. I utilized different oxidative potential (OP) metrics in my research to quantify aerosol particles’ ability to generate ROS. I further combined lab measurements with statistical analysis and kinetics models to determine the most toxic components in PM and dominant emission sources contributing to OP. In this dissertation, I first delved into the chemistry of ascorbate, one of the most abundant antioxidants in the lung. Ascorbate plays a vital role in the mechanism by which particulate air pollution initiates biological responses. I synthesized the literature on ascorbate, trace metals, and ROS interactions. Recognizing the large disagreements on the ascorbate reactions with iron or copper, I developed a chemical kinetics model to constrain the mechanisms and derive key rate constants. The modeling results suggest trace metals iron and copper are efficient sinks for ascorbate. Secondly, I investigated the interactions of PM and ROS with two other OP metrics – the hydroxyl radical (OH) and dithiothreitol (DTT) assays. The source apportionment analysis on OP indicates that vehicular exhaust and brake and tire wear are primary contributors to OP. I further linked the measured PM mass and OP with the CalEnviroScreen database. This is the first study in the US to uncover a di

The hydroxyl radical (OH) is the dominant oxidant in the outdoor environment, controlling the lifetimes of volatile organic compounds (VOCs) and contributing to the growth of secondary organic aerosols. Despite its importance outdoors, there have been relatively few measurements of the OH radical in indoor environments. During the House Observations of Microbial and Environmental Chemistry (HOMEChem) campaign, elevated concentrations of OH were observed near a window during cooking events, in addition to elevated mixing ratios of nitrous acid (HONO), VOCs, and nitrogen oxides (NOX). Particularly high concentrations were measured during the preparation of a traditional American Thanksgiving dinner, which required the use of a gas stove and oven almost continually for 6 h. A zero-dimensional chemical model underpredicted the measured OH concentrations even during periods when direct sunlight illuminated the area near the window, which increases the rate of OH production by photolysis of HONO. Interferences with measurements of nitrogen dioxide (NO2) and ozone (O3) suggest that unmeasured photolytic VOCs were emitted during cooking events. The addition of a VOC that photolyzes to produce peroxy radicals (RO2), similar to pyruvic acid, into the model results in better agreement with the OH measurements. These results highlight our incomplete understanding of the nature of oxidation in indoor environments.

Atmospheric brown carbon (BrC) can impact the radiative balance of the earth and form photooxidants. However, the light absorption and photochemical properties of BrC from different sources remain poorly understood. To address this gap, dilute water extracts of particulate matter (PM) samples collected at Davis, CA over one year were analyzed using high resolution aerosol mass spectrometry (HR-AMS) and UV-vis spectroscopy. Positive matrix factorization (PMF) on combined AMS and UV-vis data resolved five water-soluble organic aerosol (WSOA) factors with distinct mass spectra and UV-vis spectra: a fresh and an aged water-soluble biomass burning OA (WSBBOAfresh and WSBBOAaged) and three oxygenated OA (WSOOAs). WSBBOAfresh is the most light-absorbing, with a mass absorption coefficient (MAC365 nm) of 1.1 m2 g-1, while the WSOOAs are the least (MAC365 nm = 0.01-0.1 m2 g-1). These results, together with the high abundance of WSBBOAs (∼52% of the WSOA mass), indicate that biomass burning activities such as residential wood burning and wildfires are an important source of BrC in northern California. The concentrations of aqueous-phase photooxidants, i.e., hydroxyl radical (·OH), singlet molecular oxygen (1O2*), and oxidizing triplet excited states of organic carbon (3C*), were also measured in the PM extracts during illumination. Oxidant production potentials (PPOX) of the five WSOA factors were explored. The photoexcitation of BrC chromophores from BB emissions and in OOAs is a significant source of 1O2* and 3C*. By applying our PPOX values to archived AMS data at dozens of sites, we found that oxygenated organic species play an important role in photooxidant formation in atmospheric waters.

A combined kinetic and diffusion model with an accurate alpha-dose rate profile was used to model radiation induced dissolution of UO 2 . Previous experimental data were used to fit the surface site reaction system involving the surface bound hydroxyl radical as an intermediate species for both UO 2 oxidation and surface catalysed decomposition of H 2 O 2 . The performance of the model was explored in terms of sensitivity to spatial and temporal resolution as well as simplifications in the models describing the surface reactions and the reactions in solution. As a result, optimal conditions for running the numerical simulations were identified., QC 20230414

Coumarins represent a broad class of compounds with pronounced pharmacological properties and therapeutic potential. The pursuit of the commercialization of these compounds requires the establishment of controlled and highly efficient degradation processes, such as advanced oxidation processes (AOPs). Application of this methodology necessitates a comprehensive understanding of the degradation mechanisms of these compounds. For this reason, possible reaction routes between HO• and recently synthesized aminophenol 4,7-dihydroxycoumarin derivatives, as model systems, were examined using electron paramagnetic resonance (EPR) spectroscopy and a quantum mechanical approach (a QM-ORSA methodology) based on density functional theory (DFT). The EPR results indicated that all compounds had significantly reduced amounts of HO• radicals present in the reaction system under physiological conditions. The kinetic DFT study showed that all investigated compounds reacted with HO• via HAT/PCET and SPLET mechanisms. The estimated overall rate constants (koverall) correlated with the EPR results satisfactorily. Unlike HO• radicals, the newly formed radicals did not show (or showed negligible) activity towards biomolecule models representing biological targets. Inactivation of the formed radical species through the synergistic action of O2/NOx or the subsequent reaction with HO• was thermodynamically favored. The ecotoxicity assessment of the starting compounds and oxidation products, formed in multistage reactions with O2/NOx and HO•, indicated that the formed products showed lower acute and chronic toxicity effects on aquatic organisms than the starting compounds, which is a prerequisite for the application of AOPs procedures in the degradation of compounds.

In this paper, reaction kinetics, degradation mechanisms and associated toxicity have been assessed in detail concerning the abatement of neonicotinoid insecticide clothianidin (CLO) by ozone-based oxidation in water. The second-order rate constants for the reaction of CLO with molecular ozone (O3) and hydroxyl radical ([rad]OH) were determined by the direct and competition kinetics (with UV/H2O2 system as the radical source) methods, respectively, and estimated to be 103 M−1 s−1 and 3.7·109 M−1 s−1. This suggested a (potential) higher contribution of the indirect mechanism rather than the direct degradative pathway in the CLO ozonation process. Additionally, CLO oxidation was studied through an O3 and O3/H2O2 system for three complex real water matrices with distinct characteristics. DOC content was found to be the main parameter responsible for making difficult the achievement of high CLO degradations, whereas carbonate alkalinity did not exert a great impact on the process efficiency. Results indicated that typical ozone doses (up to 1 mg O3/mg DOC) were not enough for the complete removal of this micropollutant, ranging only from 50 to 80%. The study concerning the transformation products (TPs), performed by means of high-resolution mass spectrometry, allowed to suggest potential degradation routes based on the five major CLO-TPs identified. It was inferred that [rad]OH was involved in the formation of all TPs, whereas O3 was only involved in the formation of two of them. A preliminary toxicity assessment concerning CLO and its TPs during ozonation was conducted at three different trophic levels via the ECOSAR software. Results showed that none of the compounds was classified as very toxic for aquatic organisms, and all TPs exhibited minor toxicity than the parent compound. Changes in molecular structure, such as chlorothiazole ring breakdown, could be the main reason for this considerable decrease in toxicity. Overall, the present study demonstrates that ozonat

IntroductionOxidative stress mediated by reactive oxygen species (ROS) is a key process for adverse aerosol health effects. Secondary organic aerosols (SOA) account for a major fraction of particulate matter with aerodynamic diameter ≤2.5 µm (PM2.5). PM2.5 inhalation and deposition into the respiratory tract causes the formation of ROS by chemical reactions and phagocytosis of macrophages in the epithelial lining fluid (ELF), but their relative contributions are not well quantified and their link to oxidative stress remains uncertain. The specific aims of this project were (1) elucidating the chemical mechanism and quantifying the formation kinetics of ROS in the ELF by SOA; (2) quantifying the relative importance of ROS formation by chemical reactions and macrophages in the ELF.MethodsSOA particles were generated using reaction chambers from oxidation of various precursors including isoprene, terpenes, and aromatic compounds with or without nitrogen oxides (NOx). We collected size-segregated PM at two highway sites in Anaheim, CA, and Long Beach, CA, and at an urban site in Irvine, CA, during two wildfire events. The collected particles were extracted into water or surrogate ELF that contained lung antioxidants. ROS generation was quantified using electron paramagnetic resonance (EPR) spectroscopy with a spin-trapping technique. PM oxidative potential (OP) was also quantified using the dithiothreitol assay. In addition, kinetic modeling was applied for analysis and interpretation of experimental data. Finally, we quantified cellular superoxide release by RAW264.7 macrophage cells upon exposure to quinones and isoprene SOA using a chemiluminescence assay as calibrated with an EPR spin-probing technique. We also applied cellular imaging techniques to study the cellular mechanism of superoxide release and oxidative damage on cell membranes.ResultsSuperoxide radicals (·O2-) were formed from aqueous reactions of biogenic SOA generated by hydroxy radical (·OH) photooxida

We present OH observations made in Amazonas, Brazil during the Green Ocean Amazon campaign (GoAmazon2014/5) from February to March of 2014. The average diurnal variation of OH peaked with a midday (10:00–15:00) average of 1.0 × 106 (±0.6 × 106) molecules cm−3. This was substantially lower than previously reported in other tropical forest photochemical environments (2–5 × 106 molecules cm−3) while the simulated OH reactivity was lower. The observational data set was used to constrain a box model to examine how well current photochemical reaction mechanisms can simulate observed OH. We used one near-explicit mechanism (MCM v3.3.1) and four condensed mechanisms (i.e., RACM2, MOZART-T1, CB05, CB6r2) to simulate OH. A total of 14 days of analysis shows that all five chemical mechanisms were able to explain the measured OH within instrumental uncertainty of 40% during the campaign in the Amazonian rainforest environment. Future studies are required using more reliable NOx and VOC measurements to further investigate discrepancies in our understanding of the radical chemistry in the tropical rainforest. © 2021. American Geophysical Union. All Rights Reserved.

We present OH observations made in Amazonas, Brazil during the Green Ocean Amazon campaign (GoAmazon2014/5) from February to March of 2014. The average diurnal variation of OH peaked with a midday (10:00–15:00) average of 1.0 × 106 (±0.6 × 106) molecules cm−3. This was substantially lower than previously reported in other tropical forest photochemical environments (2–5 × 106 molecules cm−3) while the simulated OH reactivity was lower. The observational data set was used to constrain a box model to examine how well current photochemical reaction mechanisms can simulate observed OH. We used one near-explicit mechanism (MCM v3.3.1) and four condensed mechanisms (i.e., RACM2, MOZART-T1, CB05, CB6r2) to simulate OH. A total of 14 days of analysis shows that all five chemical mechanisms were able to explain the measured OH within instrumental uncertainty of 40% during the campaign in the Amazonian rainforest environment. Future studies are required using more reliable NOx and VOC measurements to further investigate discrepancies in our understanding of the radical chemistry in the tropical rainforest. © 2021. American Geophysical Union. All Rights Reserved.

The hydroxyl radical (OH) is the most important oxidant on global and local scales in the troposphere. Urban OH controls the removal rate of primary pollutants and triggers the production of ozone. Interannual trends of OH in urban areas are not well documented or understood due to the short lifetime and high spatial heterogeneity of OH. We utilize machine learning with observational inputs emphasizing satellite remote sensing observations to predict surface OH in 49 North American cities from 2005 to 2014. We observe changes in the summertime OH over one decade, with wide variation among different cities. In 2014, compared to the summertime OH in 2005, 3 cities show a significant increase of OH, whereas, in 27 cities, OH decreases in 2014. The year-to-year variation of OH is mapped to the decline of the NO2 column. We conclude that these cities in this analysis are either in the NOx-limited regime or at the transition from a NOx suppressed regime to a NOx-limited regime. The result emphasizes that, in the future, controlling NOx emissions will be most effective in regulating the ozone pollution in these cities.

While many mechanisms governing bacterial envelope homeostasis have been identified, others remain poorly understood. To decipher these processes, we previously developed an assay in the Gram-negative model Escherichia coli to identify genes involved in maintenance of envelope integrity. One such gene was ElyC, which was shown to be required for envelope integrity and peptidoglycan synthesis at room temperature. ElyC is predicted to be an integral inner membrane protein with a highly conserved domain of unknown function (DUF218). In this study, and stemming from a further characterization of the role of ElyC in maintaining cell envelope integrity, we serendipitously discovered an unappreciated form of oxidative stress in the bacterial envelope. We found that cells lacking ElyC overproduce hydroxyl radicals (HO) in their envelope compartment and that HO overproduction is directly or indirectly responsible for the peptidoglycan synthesis arrest, cell envelope integrity defects, and cell lysis of the DelyC mutant. Consistent with these observations, we show that the DelyC mutant defect is suppressed during anaerobiosis. HOis known to cause DNA damage but to our knowledge has not been shown to interfere with peptidoglycan synthesis. Thus, our work implicates oxidative stress as an important stressor in the bacterial cell envelope and opens the door to future studies deciphering the mechanisms that render peptidoglycan synthesis sensitive to oxidative stress.

While many mechanisms governing bacterial envelope homeostasis have been identified, others remain poorly understood. To decipher these processes, we previously developed an assay in the Gram-negative model Escherichia coli to identify genes involved in maintenance of envelope integrity. One such gene was ElyC, which was shown to be required for envelope integrity and peptidoglycan synthesis at room temperature. ElyC is predicted to be an integral inner membrane protein with a highly conserved domain of unknown function (DUF218). In this study, and stemming from a further characterization of the role of ElyC in maintaining cell envelope integrity, we serendipitously discovered an unappreciated form of oxidative stress in the bacterial envelope. We found that cells lacking ElyC overproduce hydroxyl radicals (HO) in their envelope compartment and that HO overproduction is directly or indirectly responsible for the peptidoglycan synthesis arrest, cell envelope integrity defects, and cell lysis of the DelyC mutant. Consistent with these observations, we show that the DelyC mutant defect is suppressed during anaerobiosis. HOis known to cause DNA damage but to our knowledge has not been shown to interfere with peptidoglycan synthesis. Thus, our work implicates oxidative stress as an important stressor in the bacterial cell envelope and opens the door to future studies deciphering the mechanisms that render peptidoglycan synthesis sensitive to oxidative stress.

While many mechanisms governing bacterial envelope homeostasis have been identified, others remain poorly understood. To decipher these processes, we previously developed an assay in the Gram-negative model Escherichia coli to identify genes involved in maintenance of envelope integrity. One such gene was ElyC, which was shown to be required for envelope integrity and peptidoglycan synthesis at room temperature. ElyC is predicted to be an integral inner membrane protein with a highly conserved domain of unknown function (DUF218). In this study, and stemming from a further characterization of the role of ElyC in maintaining cell envelope integrity, we serendipitously discovered an unappreciated form of oxidative stress in the bacterial envelope. We found that cells lacking ElyC overproduce hydroxyl radicals (HO) in their envelope compartment and that HO overproduction is directly or indirectly responsible for the peptidoglycan synthesis arrest, cell envelope integrity defects, and cell lysis of the DelyC mutant. Consistent with these observations, we show that the DelyC mutant defect is suppressed during anaerobiosis. HOis known to cause DNA damage but to our knowledge has not been shown to interfere with peptidoglycan synthesis. Thus, our work implicates oxidative stress as an important stressor in the bacterial cell envelope and opens the door to future studies deciphering the mechanisms that render peptidoglycan synthesis sensitive to oxidative stress.

The oxidative capacity of the troposphere – primarily characterized by the burden of the most abundant and reactive of oxidants, the hydroxyl radical (OH) – determines the lifetime of many trace gases of importance to climate and human health, including air pollutants and the greenhouse gas methane. In the upper troposphere, there is large uncertainty in the oxidative capacity associated with the lightning NOx production, for which reported results range from 16-700 mol NO flash-1. I implemented a lightning parameterization which significantly improves the representation of lightning in one chemical transport and and showed that this parameterization should be more effective in any model. I combined the model simulations configured with this new lightning parameterization with the satellite observations of NO2 column to yield a better estimate of lightning NOx production over the continental US. In cities, urban OH controls the removal rate of primary pollutants and triggers the production of ozone. Interannual trends of OH in urban areas are not well documented or understood due to the short lifetime and high spatial heterogeneity of OH and of OH precursors. Here I synthesized a machine learning technique, satellite observations and simulations from a state-of-art chemical transport model to estimate OH trends between 2005 and 2014 in 49 North American cities. I described trends in the summertime OH with wide variation among different cities. The variation of OH is explained by the shift in chemical regime from one where additional NOx slows chemistry to one where additional NOx speeds chemistry over the years. The identification of chemical regime, in turn, sheds light on the effective policy for controlling ozone.

The hydroxyl radical (OH) is the most important oxidant on global and local scales in the troposphere. Urban OH controls the removal rate of primary pollutants and triggers the production of ozone. Interannual trends of OH in urban areas are not well documented or understood due to the short lifetime and high spatial heterogeneity of OH. We utilize machine learning with observational inputs emphasizing satellite remote sensing observations to predict surface OH in 49 North American cities from 2005 to 2014. We observe changes in the summertime OH over one decade, with wide variation among different cities. In 2014, compared to the summertime OH in 2005, 3 cities show a significant increase of OH, whereas, in 27 cities, OH decreases in 2014. The year-to-year variation of OH is mapped to the decline of the NO2 column. We conclude that these cities in this analysis are either in the NOx-limited regime or at the transition from a NOx suppressed regime to a NOx-limited regime. The result emphasizes that, in the future, controlling NOx emissions will be most effective in regulating the ozone pollution in these cities.

X-ray radiolytic labeling uses broadband X-rays for in situ hydroxyl radical labeling to map protein interactions and conformation. High flux density beams are essential to overcome radical scavengers. However, conventional sample delivery environments, such as capillary flow, limit the use of a fully unattenuated focused broadband beam. An alternative is to use a liquid jet, and we have previously demonstrated that use of this form of sample delivery can increase labeling by tenfold at an unfocused X-ray source. Here we report the first use of a liquid jet for automated inline quantitative fluorescence dosage characterization and sample exposure at a high flux density microfocused synchrotron beamline. Our approach enables exposure times in single-digit microseconds while retaining a high level of side-chain labeling. This development significantly boosts the method's overall effectiveness and efficiency, generates high-quality data, and opens up the arena for high throughput and ultrafast time-resolved in situ hydroxyl radical labeling.

Ethylene is an invisible, colorless and odorless gas, which has no known dangerous effect in humans, on concentrations found within the storage chain and sale of fruits and vegetables. The ethylene molecule is relatively small and simple: it consists of two carbon atoms associated with four hydrogen atoms. The molecular weight of ethylene is 28.05 gmol-1 and fruits and vegetables produce different amounts of ethylene as they mature. Usually, ethylene cannot be detected by humans, although sometimes only people with well-developed olfactory ability can smell large amounts, but to this fact other volatile organic compounds of fruits and vegetables also contribute. Since its specific weight (1,178 kgm-3 to 15oC) is similar to that of air (1,225 kgm-3 to 15oC), ethylene freely diffuses to any other adjacent fruit or vegetables and to the spaces in which they are stored. In addition to CO2 and O2, ethylene is the most important gas to be monitored and controlled in the fruit and vegetable supply chain. Less than one part per million (1 ppm) in volume of ethylene gas, is enough to trigger the maturation process of the climatic fruit (which can continue to mature, once collected). Ethylene is considered a plant hormone that controls a wide range of physiological processes. During storage, after harvesting fruits and vegetables, ethylene may induce effects including senescence, over-maturation, accelerated quality loss, increased susceptibility to fruit pathogens and affecting different physiological processes. In addition to the endogenous production of ethylene by plant tissues, there are also external sources such as contaminants and the own metabolism of plants and fungi., Peer Reviewed, Postprint (published version)

Bisphenols are important industrial materials for example for the production of plastics, but are also well known for their adverse health effects, in particular bisphenol A (BPA) is an endocrine disruptor. The widespread use of plastics has raised concerns. Therefore, the removal of bisphenols from wastewater has sparked the interest of the scientific community. This work introduces a novel hybrid technique of micro-nano bubbles assisted laccase (MNB-Lac) to degrade bisphenols in water. The feasibility of MNB-Lac using BPA as a model contaminant was evaluated by comparing with MNB, Lac, ultrasound (UL), UL-Lac, and UL-MNB-Lac. Comprehensive investigations were carried out to understand the specific influences of key process parameters including the initial pollutant concentration, temperature, air intake, pH, outlet pipe length, and Lac concentration on BPA degradation. The alkaline environment and extended length of outlet pipe could improve the degradation efficiency further. MNB-Lac exhibited 2.3–6.2 folds higher BPA degradation and less time than the other above process under the optimal parameters. The mechanism of MNB-Lac revealed that the generation of hydroxyl radical, high O2 solubility, and high mass transfer efficiency induced by MNB play important roles on enhancing the degradation catalyzed by Lac. MNB-Lac was successfully used for treating bisphenol B, bisphenol C, and the mixture of three bisphenols with high removal efficiency. Subsequently, these degradation products were analyzed by GC–MS. MNB-Lac potentially represents an innovative technology with considerable advantages in contaminant cleanup and time efficiency for treating phenolic contaminated water. Furthermore, the findings provide new insights into the enhancement of the performance of an oxidizing enzyme by introducing MNB technology., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., BT/Biocatalysis

Persulfate (PS, S2O82−) activation through transition metal sulfides (TMS) has gained increasing attention since it can decompose a wide variety of refractory halogenated organic compounds in groundwater and wastewater. However, the processes of PS activation by TMS and particularly the formation of •OH radical under anoxic and acidic conditions (pH ∼2.8) remain elusive. Herein, by employing mixed redox-couple-involved chalcopyrite (CuFeS2) (150 mg/L) nanoparticles for PS (3.0 mM) activation, 96% of trichloroethylene was degraded within 120 min at pH 6.8 under visible light irradiation. The combination of experimental studies and theoretical calculations suggested that the Cu(I)/Fe(III) mixed redox-couple in CuFeS2 plays a crucial role to activate PS. Cu(I) acted as an electron donor to transfer electron to Fe(III), then Fe(III) served as an electron transfer bridge as well as a catalytic center to further donate this received electron to the O–O bond of PS, thus yielding SO4•− for trichloroethylene oxidation. Moreover, for the first time, •OH radicals were found to form from the catalytic hydrolysis of PS onto CuFeS2 surface, where S2O82− anion was hydrolyzed to yield H2O2 and these ensuing H2O2 were further transformed into •OH radicals via photoelectron-assisted O–O bond cleavage step. Our findings offer valuable insights for understanding the mechanisms of PS activation by redox-couple- involved TMS, which could promote the design of effective activators toward PS decomposition for environmental remediation. © 2022 Elsevier Ltd

The electrochemical oxidation method is a promising technology for the degradation of perfluorooctane sulfonate (PFOS). However, the elimination processes of PFOS are still unknown, including the electron transfer pathway, key reactive sites, and degradation mechanism. Here, we fabricated diatomite and cerium (Ce) co-modified Sb2O3 (D-Ce/Sb2O3) anode to realize efficient degradation of PFOS via peroxymonosulfate (PMS) activation. The transferred electron and the generated hydroxyl radical (•OH) can high-effectively decompose PFOS. The electron can be rapidly transferred from the highest occupied molecular orbital of the PFOS to the lowest unoccupied molecular orbital of the PMS via the D-Ce/Sb2O3 driven by a potential energy difference under electrochemical process. The active site of Ce-O in the D-Ce/Sb2O3 can greatly reduce the migration distance of the electron and the •OH, and thus improving the catalytic activity for degrading various organic micropollutants with high stability. In addition, the electrochemical process shows strong resistance and tolerance to the changing pH, inorganic ions, and organic matter. This study offers insights into the electron transfer pathway and PMS activation mechanism in PFOS removal via electrochemical oxidation, paving the way for its potential application in water purification. © 2022

We present OH observations made in Amazonas, Brazil during the Green Ocean Amazon campaign (GoAmazon2014/5) from February to March of 2014. The average diurnal variation of OH peaked with a midday (10:00–15:00) average of 1.0 × 106 (±0.6 × 106) molecules cm−3. This was substantially lower than previously reported in other tropical forest photochemical environments (2–5 × 106 molecules cm−3) while the simulated OH reactivity was lower. The observational data set was used to constrain a box model to examine how well current photochemical reaction mechanisms can simulate observed OH. We used one near-explicit mechanism (MCM v3.3.1) and four condensed mechanisms (i.e., RACM2, MOZART-T1, CB05, CB6r2) to simulate OH. A total of 14 days of analysis shows that all five chemical mechanisms were able to explain the measured OH within instrumental uncertainty of 40% during the campaign in the Amazonian rainforest environment. Future studies are required using more reliable NOx and VOC measurements to further investigate discrepancies in our understanding of the radical chemistry in the tropical rainforest. © 2021. American Geophysical Union. All Rights Reserved.

While many mechanisms governing bacterial envelope homeostasis have been identified, others remain poorly understood. To decipher these processes, we previously developed an assay in the Gram-negative model Escherichia coli to identify genes involved in maintenance of envelope integrity. One such gene was ElyC, which was shown to be required for envelope integrity and peptidoglycan synthesis at room temperature. ElyC is predicted to be an integral inner membrane protein with a highly conserved domain of unknown function (DUF218). In this study, and stemming from a further characterization of the role of ElyC in maintaining cell envelope integrity, we serendipitously discovered an unappreciated form of oxidative stress in the bacterial envelope. We found that cells lacking ElyC overproduce hydroxyl radicals (HO) in their envelope compartment and that HO overproduction is directly or indirectly responsible for the peptidoglycan synthesis arrest, cell envelope integrity defects, and cell lysis of the DelyC mutant. Consistent with these observations, we show that the DelyC mutant defect is suppressed during anaerobiosis. HOis known to cause DNA damage but to our knowledge has not been shown to interfere with peptidoglycan synthesis. Thus, our work implicates oxidative stress as an important stressor in the bacterial cell envelope and opens the door to future studies deciphering the mechanisms that render peptidoglycan synthesis sensitive to oxidative stress.

While many mechanisms governing bacterial envelope homeostasis have been identified, others remain poorly understood. To decipher these processes, we previously developed an assay in the Gram-negative model Escherichia coli to identify genes involved in maintenance of envelope integrity. One such gene was ElyC, which was shown to be required for envelope integrity and peptidoglycan synthesis at room temperature. ElyC is predicted to be an integral inner membrane protein with a highly conserved domain of unknown function (DUF218). In this study, and stemming from a further characterization of the role of ElyC in maintaining cell envelope integrity, we serendipitously discovered an unappreciated form of oxidative stress in the bacterial envelope. We found that cells lacking ElyC overproduce hydroxyl radicals (HO) in their envelope compartment and that HO overproduction is directly or indirectly responsible for the peptidoglycan synthesis arrest, cell envelope integrity defects, and cell lysis of the DelyC mutant. Consistent with these observations, we show that the DelyC mutant defect is suppressed during anaerobiosis. HOis known to cause DNA damage but to our knowledge has not been shown to interfere with peptidoglycan synthesis. Thus, our work implicates oxidative stress as an important stressor in the bacterial cell envelope and opens the door to future studies deciphering the mechanisms that render peptidoglycan synthesis sensitive to oxidative stress.

The UV-sulfite reductive treatment using hydrated electrons (eaq-) is a promising technology for destroying perfluorocarboxylates (PFCAs, CnF2n+1COO-) in any chain length. However, the C-H bonds formed in the transformation products strengthen the residual C-F bonds and thus prevent complete defluorination. Reductive treatments of fluorotelomer carboxylates (FTCAs, CnF2n+1-CH2CH2-COO-) and sulfonates (FTSAs, CnF2n+1-CH2CH2-SO3-) are also sluggish because the ethylene linker separates the fluoroalkyl chain from the end functional group. In this work, we used oxidation (Ox) with hydroxyl radicals (HO•) to convert FTCAs and FTSAs to a mixture of PFCAs. This process also cleaved 35-95% of C-F bonds depending on the fluoroalkyl chain length. We probed the stoichiometry and mechanism for the oxidative defluorination of fluorotelomers. The subsequent reduction (Red) with UV-sulfite achieved deep defluorination of the PFCA mixture for up to 90%. The following use of HO• to oxidize the H-rich residues led to the cleavage of the remaining C-F bonds. We examined the efficacy of integrated oxidative and reductive treatment of n = 1-8 PFCAs, n = 4,6,8 perfluorosulfonates (PFSAs, CnF2n+1-SO3-), n = 1-8 FTCAs, and n = 4,6,8 FTSAs. A majority of structures yielded near-quantitative overall defluorination (97-103%), except for n = 7,8 fluorotelomers (85-89%), n = 4 PFSA (94%), and n = 4 FTSA (93%). The results show the feasibility of complete defluorination of legacy PFAS pollutants and will advance both remediation technology design and water sample analysis.

In the method of X-ray footprinting mass spectrometry (XFMS), proteins at micromolar concentration in solution are irradiated with a broadband X-ray source, and the resulting hydroxyl radical modifications are characterized using liquid chromatography mass spectrometry to determine sites of solvent accessibility. These data are used to infer structural changes in proteins upon interaction with other proteins, folding, or ligand binding. XFMS is typically performed under aerobic conditions; dissolved molecular oxygen in solution is necessary in many, if not all, the hydroxyl radical modifications that are generally reported. In this study we investigated the result of X-ray induced modifications to three different proteins under aerobic versus low oxygen conditions, and correlated the extent of damage with dose calculations. We observed a concentration-dependent protecting effect at higher protein concentration for a given X-ray dose. For the typical doses used in XFMS experiments there was minimal X-ray induced aggregation and fragmentation, but for higher doses we observed formation of covalent higher molecular weight oligomers, as well as fragmentation, which was affected by the amount of dissolved oxygen in solution. The higher molecular weight products in the form of dimers, trimers, and tetramers were present in all sample preparations, and, upon X-ray irradiation, these oligomers became non-reducible as seen in SDS-PAGE. The results provide an important contribution to the large body of X-ray radiation damage literature in structural biology research, and will specifically help inform the future planning of XFMS, and well as X-ray crystallography and small-angle X-ray scattering experiments.

Pollutants such as pharmaceutical products and pesticides are still present in treated water. Several of these compounds are photoactive. The photodegradation of eight organic pollutants was studied using listed advanced oxidation processes: UV/H2O2, UV/persulfate, Fenton, photo-Fenton and UV/TiO2. The results show that photodegradation is most effective in the first 10 min of treatments in simulated urban wastewater collected from the local Nišava River. To identify the correlation between applied degradation processes as well as the relationship among the structure of investigated compounds and efficiency of degradation, Pearson’s correlation coefficient analysis and principal component analysis (PCA) were performed. The established correlations between the applied processes, as well as the determination of the influence of the structure on the efficiency of degradation, enable a more efficient choice of the degradation procedure, especially in the case of interference. Additionally, process electrical energy consumption and treatment costs for simulated urban wastewater with different pharmaceuticals and pesticides were determined.

Pollutants such as pharmaceutical products and pesticides are still present in treated water. Several of these compounds are photoactive. The photodegradation of eight organic pollutants was studied using listed advanced oxidation processes: UV/H2O2, UV/persulfate, Fenton, photo-Fenton and UV/TiO2. The results show that photodegradation is most effective in the first 10 min of treatments in simulated urban wastewater collected from the local Nišava River. To identify the correlation between applied degradation processes as well as the relationship among the structure of investigated compounds and efficiency of degradation, Pearson’s correlation coefficient analysis and principal component analysis (PCA) were performed. The established correlations between the applied processes, as well as the determination of the influence of the structure on the efficiency of degradation, enable a more efficient choice of the degradation procedure, especially in the case of interference. Additionally, process electrical energy consumption and treatment costs for simulated urban wastewater with different pharmaceuticals and pesticides were determined.

We investigated the ability of graphene quantum dot (GQD) nanoparticles to protect SH-SY5Y human neuroblastoma cells from oxidative/nitrosative stress induced by iron-nitrosyl complex sodium nitroprusside (SNP).GQD reduced SNP cytotoxicity by preventing mitochondrial depolarization, caspase-2 activation, and subsequent apoptotic death. Although GQD diminished the levels of nitric oxide (NO) in SNP-exposed cells, NO scavengers displayed only a slight protective effect, suggesting that NO quenching was not the main protective mechanism of GQD. GQD also reduced SNP-triggered increase in the intracellular levels of hydroxyl radical (•OH), superoxide anion (O2•- ), and lipid peroxidation. Nonselective antioxidants, •OH scavenging, and iron chelators, but not superoxide dismutase, mimicked GQD cytoprotective activity, indicating that GQD protect cells by neutralizing •OH generated in the presence of SNP-released iron. Cellular internalization of GQD was required for optimal protection, since a removal of extracellular GQD by extensive washing only partly diminished their protective effect. Moreover, GQD cooperated with SNP to induce autophagy, as confirmed by the inhibition of autophagylimiting Akt/PRAS40/mTOR signaling and increase in autophagy gene transcription, protein levels of proautophagic beclin-1 and LC3-II, formation of autophagic vesicles, and degradation of autophagic target p62. The antioxidant activity of GQD was not involved in autophagy induction, as antioxidants N-acetylcysteine and dimethyl sulfoxide failed to stimulate autophagy in SNP-exposed cells. Pharmacological inhibitors of early (wortmannin, 3-methyladenine) or late stages of autophagy (NH4Cl) efficiently reduced the protective effect of GQD. Therefore, the ability of GQD to prevent the in vitro neurotoxicity of SNP depends on both •OH/NO scavenging and induction of cytoprotective autophagy.

We investigated the ability of graphene quantum dot (GQD) nanoparticles to protect SH-SY5Y human neuroblastoma cells from oxidative/nitrosative stress induced by iron-nitrosyl complex sodium nitroprusside (SNP).GQD reduced SNP cytotoxicity by preventing mitochondrial depolarization, caspase-2 activation, and subsequent apoptotic death. Although GQD diminished the levels of nitric oxide (NO) in SNP-exposed cells, NO scavengers displayed only a slight protective effect, suggesting that NO quenching was not the main protective mechanism of GQD. GQD also reduced SNP-triggered increase in the intracellular levels of hydroxyl radical (•OH), superoxide anion (O2•- ), and lipid peroxidation. Nonselective antioxidants, •OH scavenging, and iron chelators, but not superoxide dismutase, mimicked GQD cytoprotective activity, indicating that GQD protect cells by neutralizing •OH generated in the presence of SNP-released iron. Cellular internalization of GQD was required for optimal protection, since a removal of extracellular GQD by extensive washing only partly diminished their protective effect. Moreover, GQD cooperated with SNP to induce autophagy, as confirmed by the inhibition of autophagylimiting Akt/PRAS40/mTOR signaling and increase in autophagy gene transcription, protein levels of proautophagic beclin-1 and LC3-II, formation of autophagic vesicles, and degradation of autophagic target p62. The antioxidant activity of GQD was not involved in autophagy induction, as antioxidants N-acetylcysteine and dimethyl sulfoxide failed to stimulate autophagy in SNP-exposed cells. Pharmacological inhibitors of early (wortmannin, 3-methyladenine) or late stages of autophagy (NH4Cl) efficiently reduced the protective effect of GQD. Therefore, the ability of GQD to prevent the in vitro neurotoxicity of SNP depends on both •OH/NO scavenging and induction of cytoprotective autophagy.

We investigated the ability of graphene quantum dot (GQD) nanoparticles to protect SH-SY5Y human neuroblastoma cells from oxidative/nitrosative stress induced by iron-nitrosyl complex sodium nitroprusside (SNP). GQD reduced SNP cytotoxicity by preventing mitochondrial depolarization, caspase-2 activation, and subsequent apoptotic death. Although GQD diminished the levels of nitric oxide (NO) in SNP-exposed cells, NO scavengers displayed only a slight protective effect, suggesting that NO quenching was not the main protective mechanism of GQD. GQD also reduced SNP-triggered increase in the intracellular levels of hydroxyl radical (•OH), superoxide anion (O2•- ), and lipid peroxidation. Nonselective antioxidants, •OH scavenging, and iron chelators, but not superoxide dismutase, mimicked GQD cytoprotective activity, indicating that GQD protect cells by neutralizing •OH generated in the presence of SNP-released iron. Cellular internalization of GQD was required for optimal protection, since a removal of extracellular GQD by extensive washing only partly diminished their protective effect. Moreover, GQD cooperated with SNP to induce autophagy, as confirmed by the inhibition of autophagylimiting Akt/PRAS40/mTOR signaling and increase in autophagy gene transcription, protein levels of proautophagic beclin-1 and LC3-II, formation of autophagic vesicles, and degradation of autophagic target p62. The antioxidant activity of GQD was not involved in autophagy induction, as antioxidants N-acetylcysteine and dimethyl sulfoxide failed to stimulate autophagy in SNP-exposed cells. Pharmacological inhibitors of early (wortmannin, 3-methyladenine) or late stages of autophagy (NH4Cl) efficiently reduced the protective effect of GQD. Therefore, the ability of GQD to prevent the in vitro neurotoxicity of SNP depends on both •OH/NO scavenging and induction of cytoprotective autophagy.

We investigated the ability of graphene quantum dot (GQD) nanoparticles to protect SH-SY5Y human neuro blastoma cells from oxidative/nitrosative stress induced by iron-nitrosyl complex sodium nitroprusside (SNP). GQD reduced SNP cytotoxicity by preventing mitochondrial depolarization, caspase-2 activation, and subsequent apoptotic death. Although GQD diminished the levels of nitric oxide (NO) in SNP-exposed cells, NO scavengers displayed only a slight protective effect, suggesting that NO quenching was not the main protective mechanism of GQD. GQD also reduced SNP-triggered increase in the intracellular levels of hydroxyl radical ( • OH), superoxide anion (O2 •− ), and lipid peroxidation. Nonselective antioxidants, • OH scavenging, and iron chelators, but not superoxide dismutase, mimicked GQD cytoprotective activity, indicating that GQD protect cells by neutralizing • OH generated in the presence of SNP-released iron. Cellular internalization of GQD was required for optimal protection, since a removal of extracellular GQD by extensive washing only partly diminished their protective effect. Moreover, GQD cooperated with SNP to induce autophagy, as confirmed by the inhibition of autophagy limiting Akt/PRAS40/mTOR signaling and increase in autophagy gene transcription, protein levels of proauto phagic beclin-1 and LC3-II, formation of autophagic vesicles, and degradation of autophagic target p62. The antioxidant activity of GQD was not involved in autophagy induction, as antioxidants N-acetylcysteine and dimethyl sulfoxide failed to stimulate autophagy in SNP-exposed cells. Pharmacological inhibitors of early (wortmannin, 3-methyladenine) or late stages of autophagy (NH4Cl) efficiently reduced the protective effect of GQD. Therefore, the ability of GQD to prevent the in vitro neurotoxicity of SNP depends on both • OH/NO scavenging and induction of cytoprotective autophagy.

The UV-sulfite reductive treatment using hydrated electrons (eaq-) is a promising technology for destroying perfluorocarboxylates (PFCAs, CnF2n+1COO-) in any chain length. However, the C-H bonds formed in the transformation products strengthen the residual C-F bonds and thus prevent complete defluorination. Reductive treatments of fluorotelomer carboxylates (FTCAs, CnF2n+1-CH2CH2-COO-) and sulfonates (FTSAs, CnF2n+1-CH2CH2-SO3-) are also sluggish because the ethylene linker separates the fluoroalkyl chain from the end functional group. In this work, we used oxidation (Ox) with hydroxyl radicals (HO•) to convert FTCAs and FTSAs to a mixture of PFCAs. This process also cleaved 35-95% of C-F bonds depending on the fluoroalkyl chain length. We probed the stoichiometry and mechanism for the oxidative defluorination of fluorotelomers. The subsequent reduction (Red) with UV-sulfite achieved deep defluorination of the PFCA mixture for up to 90%. The following use of HO• to oxidize the H-rich residues led to the cleavage of the remaining C-F bonds. We examined the efficacy of integrated oxidative and reductive treatment of n = 1-8 PFCAs, n = 4,6,8 perfluorosulfonates (PFSAs, CnF2n+1-SO3-), n = 1-8 FTCAs, and n = 4,6,8 FTSAs. A majority of structures yielded near-quantitative overall defluorination (97-103%), except for n = 7,8 fluorotelomers (85-89%), n = 4 PFSA (94%), and n = 4 FTSA (93%). The results show the feasibility of complete defluorination of legacy PFAS pollutants and will advance both remediation technology design and water sample analysis.

In the method of X-ray footprinting mass spectrometry (XFMS), proteins at micromolar concentration in solution are irradiated with a broadband X-ray source, and the resulting hydroxyl radical modifications are characterized using liquid chromatography mass spectrometry to determine sites of solvent accessibility. These data are used to infer structural changes in proteins upon interaction with other proteins, folding, or ligand binding. XFMS is typically performed under aerobic conditions; dissolved molecular oxygen in solution is necessary in many, if not all, the hydroxyl radical modifications that are generally reported. In this study we investigated the result of X-ray induced modifications to three different proteins under aerobic versus low oxygen conditions, and correlated the extent of damage with dose calculations. We observed a concentration-dependent protecting effect at higher protein concentration for a given X-ray dose. For the typical doses used in XFMS experiments there was minimal X-ray induced aggregation and fragmentation, but for higher doses we observed formation of covalent higher molecular weight oligomers, as well as fragmentation, which was affected by the amount of dissolved oxygen in solution. The higher molecular weight products in the form of dimers, trimers, and tetramers were present in all sample preparations, and, upon X-ray irradiation, these oligomers became non-reducible as seen in SDS-PAGE. The results provide an important contribution to the large body of X-ray radiation damage literature in structural biology research, and will specifically help inform the future planning of XFMS, and well as X-ray crystallography and small-angle X-ray scattering experiments.

Pollutants such as pharmaceutical products and pesticides are still present in treated water. Several of these compounds are photoactive. The photodegradation of eight organic pollutants was studied using listed advanced oxidation processes: UV/H2O2, UV/persulfate, Fenton, photo-Fenton and UV/TiO2. The results show that photodegradation is most effective in the first 10 min of treatments in simulated urban wastewater collected from the local Nišava River. To identify the correlation between applied degradation processes as well as the relationship among the structure of investigated compounds and efficiency of degradation, Pearson’s correlation coefficient analysis and principal component analysis (PCA) were performed. The established correlations between the applied processes, as well as the determination of the influence of the structure on the efficiency of degradation, enable a more efficient choice of the degradation procedure, especially in the case of interference. Additionally, process electrical energy consumption and treatment costs for simulated urban wastewater with different pharmaceuticals and pesticides were determined.

We investigated the ability of graphene quantum dot (GQD) nanoparticles to protect SH-SY5Y human neuro blastoma cells from oxidative/nitrosative stress induced by iron-nitrosyl complex sodium nitroprusside (SNP). GQD reduced SNP cytotoxicity by preventing mitochondrial depolarization, caspase-2 activation, and subsequent apoptotic death. Although GQD diminished the levels of nitric oxide (NO) in SNP-exposed cells, NO scavengers displayed only a slight protective effect, suggesting that NO quenching was not the main protective mechanism of GQD. GQD also reduced SNP-triggered increase in the intracellular levels of hydroxyl radical ( • OH), superoxide anion (O2 •− ), and lipid peroxidation. Nonselective antioxidants, • OH scavenging, and iron chelators, but not superoxide dismutase, mimicked GQD cytoprotective activity, indicating that GQD protect cells by neutralizing • OH generated in the presence of SNP-released iron. Cellular internalization of GQD was required for optimal protection, since a removal of extracellular GQD by extensive washing only partly diminished their protective effect. Moreover, GQD cooperated with SNP to induce autophagy, as confirmed by the inhibition of autophagy limiting Akt/PRAS40/mTOR signaling and increase in autophagy gene transcription, protein levels of proauto phagic beclin-1 and LC3-II, formation of autophagic vesicles, and degradation of autophagic target p62. The antioxidant activity of GQD was not involved in autophagy induction, as antioxidants N-acetylcysteine and dimethyl sulfoxide failed to stimulate autophagy in SNP-exposed cells. Pharmacological inhibitors of early (wortmannin, 3-methyladenine) or late stages of autophagy (NH4Cl) efficiently reduced the protective effect of GQD. Therefore, the ability of GQD to prevent the in vitro neurotoxicity of SNP depends on both • OH/NO scavenging and induction of cytoprotective autophagy.

We investigated the ability of graphene quantum dot (GQD) nanoparticles to protect SH-SY5Y human neuroblastoma cells from oxidative/nitrosative stress induced by iron-nitrosyl complex sodium nitroprusside (SNP).GQD reduced SNP cytotoxicity by preventing mitochondrial depolarization, caspase-2 activation, and subsequent apoptotic death. Although GQD diminished the levels of nitric oxide (NO) in SNP-exposed cells, NO scavengers displayed only a slight protective effect, suggesting that NO quenching was not the main protective mechanism of GQD. GQD also reduced SNP-triggered increase in the intracellular levels of hydroxyl radical (•OH), superoxide anion (O2•- ), and lipid peroxidation. Nonselective antioxidants, •OH scavenging, and iron chelators, but not superoxide dismutase, mimicked GQD cytoprotective activity, indicating that GQD protect cells by neutralizing •OH generated in the presence of SNP-released iron. Cellular internalization of GQD was required for optimal protection, since a removal of extracellular GQD by extensive washing only partly diminished their protective effect. Moreover, GQD cooperated with SNP to induce autophagy, as confirmed by the inhibition of autophagylimiting Akt/PRAS40/mTOR signaling and increase in autophagy gene transcription, protein levels of proautophagic beclin-1 and LC3-II, formation of autophagic vesicles, and degradation of autophagic target p62. The antioxidant activity of GQD was not involved in autophagy induction, as antioxidants N-acetylcysteine and dimethyl sulfoxide failed to stimulate autophagy in SNP-exposed cells. Pharmacological inhibitors of early (wortmannin, 3-methyladenine) or late stages of autophagy (NH4Cl) efficiently reduced the protective effect of GQD. Therefore, the ability of GQD to prevent the in vitro neurotoxicity of SNP depends on both •OH/NO scavenging and induction of cytoprotective autophagy.

We investigated the ability of graphene quantum dot (GQD) nanoparticles to protect SH-SY5Y human neuroblastoma cells from oxidative/nitrosative stress induced by iron-nitrosyl complex sodium nitroprusside (SNP). GQD reduced SNP cytotoxicity by preventing mitochondrial depolarization, caspase-2 activation, and subsequent apoptotic death. Although GQD diminished the levels of nitric oxide (NO) in SNP-exposed cells, NO scavengers displayed only a slight protective effect, suggesting that NO quenching was not the main protective mechanism of GQD. GQD also reduced SNP-triggered increase in the intracellular levels of hydroxyl radical (•OH), superoxide anion (O2•- ), and lipid peroxidation. Nonselective antioxidants, •OH scavenging, and iron chelators, but not superoxide dismutase, mimicked GQD cytoprotective activity, indicating that GQD protect cells by neutralizing •OH generated in the presence of SNP-released iron. Cellular internalization of GQD was required for optimal protection, since a removal of extracellular GQD by extensive washing only partly diminished their protective effect. Moreover, GQD cooperated with SNP to induce autophagy, as confirmed by the inhibition of autophagylimiting Akt/PRAS40/mTOR signaling and increase in autophagy gene transcription, protein levels of proautophagic beclin-1 and LC3-II, formation of autophagic vesicles, and degradation of autophagic target p62. The antioxidant activity of GQD was not involved in autophagy induction, as antioxidants N-acetylcysteine and dimethyl sulfoxide failed to stimulate autophagy in SNP-exposed cells. Pharmacological inhibitors of early (wortmannin, 3-methyladenine) or late stages of autophagy (NH4Cl) efficiently reduced the protective effect of GQD. Therefore, the ability of GQD to prevent the in vitro neurotoxicity of SNP depends on both •OH/NO scavenging and induction of cytoprotective autophagy.

We investigated the ability of graphene quantum dot (GQD) nanoparticles to protect SH-SY5Y human neuroblastoma cells from oxidative/nitrosative stress induced by iron-nitrosyl complex sodium nitroprusside (SNP).GQD reduced SNP cytotoxicity by preventing mitochondrial depolarization, caspase-2 activation, and subsequent apoptotic death. Although GQD diminished the levels of nitric oxide (NO) in SNP-exposed cells, NO scavengers displayed only a slight protective effect, suggesting that NO quenching was not the main protective mechanism of GQD. GQD also reduced SNP-triggered increase in the intracellular levels of hydroxyl radical (•OH), superoxide anion (O2•- ), and lipid peroxidation. Nonselective antioxidants, •OH scavenging, and iron chelators, but not superoxide dismutase, mimicked GQD cytoprotective activity, indicating that GQD protect cells by neutralizing •OH generated in the presence of SNP-released iron. Cellular internalization of GQD was required for optimal protection, since a removal of extracellular GQD by extensive washing only partly diminished their protective effect. Moreover, GQD cooperated with SNP to induce autophagy, as confirmed by the inhibition of autophagylimiting Akt/PRAS40/mTOR signaling and increase in autophagy gene transcription, protein levels of proautophagic beclin-1 and LC3-II, formation of autophagic vesicles, and degradation of autophagic target p62. The antioxidant activity of GQD was not involved in autophagy induction, as antioxidants N-acetylcysteine and dimethyl sulfoxide failed to stimulate autophagy in SNP-exposed cells. Pharmacological inhibitors of early (wortmannin, 3-methyladenine) or late stages of autophagy (NH4Cl) efficiently reduced the protective effect of GQD. Therefore, the ability of GQD to prevent the in vitro neurotoxicity of SNP depends on both •OH/NO scavenging and induction of cytoprotective autophagy.

Fibrous chrysotile has been the most commonly applied asbestos mineral in a range of technical applications. However, it is toxic and carcinogenic upon inhalation. The chemical reactivity of chrysotile fiber surfaces contributes to its adverse health effects by catalyzing the formation of highly reactive hydroxyl radicals (HO•) from H2O2. In this Haber-Weiss cycle, Fe on the fiber surface acts as a catalyst: Fe3+ decomposes H2O2 to reductants that reduce surface Fe3+ to Fe2+, which is back-oxidized by H2O2 (Fenton-oxidation) to yield HO•. Chrysotile contains three structural Fe species: ferrous and ferric octahedral Fe and ferric tetrahedral Fe (Fe3+tet). Also, external Fe may adsorb or precipitate onto fiber surfaces. The goal of this study was to identify the Fe species on chrysotile surfaces that catalyze H2O2 decomposition and HO• generation.