Hydroxyl Radicals In Solution Research Articles

Directed electron regulation promoted sandwich-like CoO@FeBTC/NF with p-n heterojunctions by gel electrodeposition for oxygen evolution reaction

Metal organic framework (MOF) is currently-one of the key catalysts for oxygen evolution reaction (OER), but its catalytic performance is severely limited by electronic configuration. In this study, cobalt oxide (CoO) on nickel foam (NF) was first prepared, which then wrapped it with FeBTC synthesized by ligating isophthalic acid (BTC) with iron ions by electrodeposition to obtain CoO@FeBTC/NF p-n heterojunction structure. The catalyst requires only 255 mV overpotential to reach a current density of 100 mA cm−2, and can maintain 100 h long time stability at 500 mA cm−2 high current density. The catalytic properties are mainly related to the strong induced modulation of electrons in FeBTC by holes in the p-type CoO, which results in stronger bonding and faster electron transfer between FeBTC and hydroxide. At the same time, the uncoordinated BTC at the solid–liquid interface ionizes acidic radicals which form hydrogen bonds with the hydroxyl radicals in solution, capturing them onto the catalyst surface for the catalytic reaction. In addition, CoO@FeBTC/NF also has strong application prospects in alkaline electrolyzers, which only needs 1.78 V to reach a current density of 1 A cm−2, and it can maintain long-term stability for 12 h at this current. This study provides a new convenient and efficient approach for the control design of the electronic structure of MOF, leading to a more efficient electrocatalytic process.

Removal of contaminants of emerging concern by solar photo electro-Fenton process in a solar electrochemical raceway pond reactor

This work proposes the degradation of different contaminants of emerging concern (CECs) present in a secondary effluent from a municipal wastewater treatment plant in a solar electrochemical raceway pond reactor (SEC-RPR), applying the solar photo electro-Fenton (SPFE) process. Tap water and a secondary effluent were enriched with 100 µg L−1 of 7 CECs to study the degradation of these compounds by the SPEF process in a SEC-RPR. Among the results obtained, an elimination over 96% and 90% of 5 CECs (progesterone, estradiol, ibuprofen, diclofenac and estrone) was achieved, while sulfamethazine and carbamazepine were eliminated by 73, 37% and 80, 66% after 1 h of treatment, respectively. In turn, a secondary effluent that already achieved the minimum organic load standards established by Chilean regulations was treated in a SEC-RPR by applying different electrochemical advanced oxidation processes (EAOPs). However, regardless of the applied treatment (SPEF, electro-Fenton and electro-oxidation/H2O2), it was possible to further reduce the organic content and even mineralize it. These experiments were performed at pH 3, with Na2SO4 0.05 mM, Fe2+ 0.05 mM and applying a current density of 20 mA cm−2. The SPEF process implemented in a SEC-RPR is presented as an excellent alternative for the treatment of municipal wastewater, due to the large contact area between the effluent and UV radiation, in addition to the continuous and homogeneous generation of H2O2, which allows for the production of hydroxyl radicals in solution, favoring the degradation and mineralization of pollutants.

Electrochemical Formation and Activation of Hydrogen Peroxide from Water on Fluorinated Tin Oxide for Baeyer–Villiger Oxidation Reactions

The two-electron oxidation of water (2e-WOR) has been studied in the past as a possible method for the alternative preparation of hydrogen peroxide. Often, fluorinated tin oxide (FTO) is used as an anode and FTO itself was found also to be active for 2e-WOR. Because one use of H2O2 is as an oxygen donor for Baeyer–Villiger oxidation of ketones catalyzed by tin compounds and materials, presently we were interested in studying the use of in situ formed H2O2 for these reactions. First, the formation of H2O2 was verified in an acetonitrile/water solvent in a 2e-WOR reaction, which is more efficient than a comparable reaction in water in terms of the H2O2 concentration attained and faradaic efficiency at comparable potentials, that is, ∼3 V vs SHE. Second, initial studies on oxygenation of reactive substrates such as sulfides showed normalized reaction rates (NRRs) for two-electron oxidation reactions that were about 3 times higher than the NRR for H2O2 formation, indicating the formation of an active oxygen-donating or oxidizing species on the electrode surface prior to the formation and release of H2O2 into solution. Third, the Baeyer–Villiger oxygenation of 2-adamantanone at 2.1 V versus SHE in acetonitrile/water showed both the formation of the expected lactone product and hydroxylation at both tertiary and secondary C–H bonds. Hydroxylation is most easily explained by the presence of hydroxyl radical species as supported by the formation of a spin adduct and its identification by electron paramagnetic resonance. However, the potential used, 2.1 V versus SHE, is an underpotential for the formation of a solvated hydroxyl radical in solution, thereby leading to the conclusion that surface-bound hydroxyl species, OH*, are those that are reactive for the apparent one-electron water oxygenation reaction. Fourth, it was shown that although H2O2 can be thermally activated on FTO as a catalyst to a minor degree, electrochemical activation is by far more significant, leading to the use of FTO as an electrochemical catalyst for activation of H2O2 for the Baeyer–Villiger oxygenation and also alkene epoxidation.

UV-C Peroxymonosulfate Activation for Wastewater Regeneration: Simultaneous Inactivation of Pathogens and Degradation of Contaminants of Emerging Concern.

This study explores the capability of Sulfate Radical-based Advanced Oxidation Processes (SR-AOPs) for the simultaneous disinfection and decontamination of urban wastewater. Sulfate and hydroxyl radicals in solution were generated activating peroxymonosulfate (PMS) under UV-C irradiation at pilot plant scale. The efficiency of the process was assessed toward the removal of three CECs (Trimethoprim (TMP), Sulfamethoxazole (SMX), and Diclofenac (DCF)) and three bacteria (Escherichia coli, Enterococcus spp., and Pseudomonas spp.) in actual urban wastewater (UWW), obtaining the optimal value of PMS at 0.5 mmol/L. Under such experimental conditions, bacterial concentration ≤ 10 CFU/100 mL was reached after 15 min of UV-C treatment (0.03 kJ/L of accumulative UV-C radiation) for natural occurring bacteria, no bacterial regrowth was observed after 24 and 48 h, and 80% removal of total CECs was achieved after 12 min (0.03 kJ/L), with a release of sulfate ions far from the limit established in wastewater discharge. Moreover, the inactivation of Ampicillin (AMP), Ciprofloxacin (CPX), and Trimethoprim (TMP) antibiotic-resistant bacteria (ARB) and reduction of target genes (ARGs) were successfully achieved. Finally, a harmful effect toward the receiving aquatic environment was not observed according to Aliivibrio fischeri toxicity tests, while a slightly toxic effect toward plant growth (phytotoxicity tests) was detected. As a conclusion, a cost analysis demonstrated that the process could be feasible and a promising alternative to successfully address wastewater reuse challenges.

Exposure hazards of oxidative stress in environmental pollutants and application of plant antioxidants

Environmental chemical pollutants are diverse and have complex and varied exposure forms. The release of these pollutants into the environment will cause oxidative stress reaction, which is caused by excessive and uncontrolled reactive oxygen species damage to proteins, lipids and DNA. To protect the health of humans and other species, the crack problem of environmental protection, through continuous exploration, found in acid medium, rhodamine B can produce characteristic fluorescence, Feton system to produce hydroxyl radicals can rapid oxidation of rhodamine B fluorescence quenching, and many natural antioxidants can partially remove hydroxyl radicals in solution, reduce the degree of fluorescence quenching. Based on this principle, a new method for the determination of the antioxidant activity of oligosaccharide proanthocyanidins was established, which provides a new way to solve the problem of environmental pollution.

Co-carbonization of red mud and waste sawdust for functional application as Fenton catalyst: Evaluation of catalytic activity and mechanism

Synthesis of red mud/biochar (RMBC) composite was conducted by facile co-carbonization of red mud and waste sawdust. Multiple characterizations verify the reduction of ferric oxide and the formation of graphitic biochar with defects. Hydrogen peroxide activation by RMBC was investigated for Rhodamine B (RhB) oxidation. RMBC displays both adsorption and catalytic effects for RhB removal. Catalytic oxidation of RhB is effectively obtained at pH below 2.2. RhB oxidation is slightly improved with growing temperature. RhB oxidation in RMBC/H2O2 system obeys the pseudo first-order kinetic, and the low activation energy of 56 kJ/mol implies the effective hydrogen peroxide activation by RMBC. Associated with the determinations of radical and iron leaching, the dominant role of hydroxyl radical in solution is verified for RhB oxidation. The limitation of RMBC for heterogenous catalysis may be solved by the regulation of alkaline feature. RMBC processes special properties of red mud and biochar, and its application to wastewater treatment provides a green and sustainable approach obeying the “waste treating waste” concept.

Quantification of Plasma-Produced Hydroxyl Radicals in Solution and their Dependence on the pH

HO radicals are the most important reactive species generated during water treatment by non-thermal plasma devices. In this letter, we report the first quantification of the steady-state concentration and lifetime of plasma-produced hydroxyl radicals in water solutions at pH 3 and 7, and we discuss the differences based on their reactivity with other plasma-generated species. Finally, we show to what extent the use of chemical probes to quantify short-lived reactive species has an influence on the results and that it should be taken into account.

Photoactivity under visible light of defective ZnO investigated by EPR spectroscopy and photoluminescence

The photochemical and photophysical properties of a defective zinc oxide prepared by precipitation have been investigated using mainly electron paramagnetic resonance (EPR) and photoluminescence (PL) spectroscopy. As already reported in the literature the band gap of the oxide contains intra band gap states related to the presence of point defects (mainly cation vacancies) in the structure. The concentration and the energy levels of such defects, a fraction of them being paramagnetic, are the basis of a mechanisms of double and multiple excitations allowing visible photons with energy lower than the band gap value (hν <Eg) to promote electrons from the valence band (VB) to the conduction band (CB) similarly, though less efficiently, to what done by UV light with hν >Eg. Remarkably, some of the paramagnetic defects present in the bulk of the as prepared materials derive from excitation of VB electrons induced by ambient light illumination.The electron excitation from VB to CB has been observed upon irradiation under vacuum at 77 K with polychromatic light and applying four different filters to the emitted radiation with cut-off in the range between 400 nm and 495 nm. The process has been monitored by EPR as the photoexcitation ends up in the formation of trapped electron centers (signal at g = 1.96) and trapped hole centers (signal in the range 2.021 >g > 2.003) both clearly detected by this technique. A scheme of the energy state distribution in the band gap of the defective oxide, obtained coupling EPR and photoluminescence results, is proposed. Finally, a non-negligible fraction of the visible light generated carriers reach the surface of the nanocrystals, entailing the typical redox reactions of photocatalysis as indicated by the detection of hydroxyl radicals in solution performed by spin-trapping. For this reason, the wet chemistry prepared zinc oxide can be considered a visible light active (VLA) system.

Hydrogen plasma treated nanodiamonds lead to an overproduction of hydroxyl radicals and solvated electrons in solution under ionizing radiation

In numerous fields of application (environmental remediation, catalysis, nanomedicine), production of hydroxyl radicals and solvated electrons by nanomaterials is a cornerstone. Through a very sensitive, nanoparticle-compatible, coumarin-based protocol, we quantified hydroxyl radicals in solution when hydrogenated (H-ND) and oxidized (Ox-ND) detonation nanodiamonds were irradiated by MeV photons. We highlighted a blatant difference between the two surface chemistries as only H-ND led to 50% more radicals, for irradiation doses and ND concentrations relevant in nanomedicine. For the first time, we also quantified solvated electrons after keV irradiation of both suspensions and showed that in the presence of H-ND, hydroxyl radicals and solvated electrons were available in solution in equivalent and higher amounts than in water only. This asks the question of the mechanisms at stage and beside the negative/positive electron affinity hypothesis usually mentioned, we proposed, as for other nanomaterials, that interfacial water could play an essential role in radicals’ production in solution when detonation H-ND are irradiated.

Ligand enhanced pharmaceutical wastewater treatment with Fenton process using pyrite as the catalyst: Column experiments

Advanced oxidation processes offer practical and cost effective solutions for the treatment of poorly biodegradable industrial wastewaters. Here, column experiments were performed to understand the role of a complexing agent, citrate, on Fenton-treatment of an actual pharmaceutical wastewater with pyrite as the catalyst under dynamic flow conditions. Our results suggest that the pharmaceutical wastewater treatment with Fenton reaction using pyrite as the catalyst was mainly regulated by the extent of Fe dissolution from pyrite, which, in turn, resulted in formation of hydroxyl radicals in solution. The Fenton treatment efficiency was much lower in the absence of citrate compared to citric acid containing systems due to clogging of column pores with oxidized Fe species. On the other hand, the addition of citrate to wastewater significantly improved Fenton process efficacy, and prolonged the lifecycle of pyrite-packed columns depending on solution pH. Low pH values were favorable for better Fenton efficiency in systems containing citrate due to combined effect of proton and ligand promoted dissolution and mobilization of oxidized Fe species.

(Invited) Hydrogen Peroxide Electrochemical Sensing Based on a TiO2 nanotubes Electrode Modified with Hibiscus Sabdariffa L. Anthocyanins

The antioxidant properties of the alcoholic extract obtained from the calix of Hibiscus sabdariffa L. (H.s.), mostly referred in the literature as jamaica or rozelle, have been used in the present research to build an electrode with hydrogen peroxide sensing activity. This plant belongs to the malvaceae family and originates from tropical Africa but nowadays its cultivation spreads widely through Mexico, Central and South America and Southeast Asia1. The calyx of H.s. contains the most valuable nutritional components, that at the same time are responsible for the pigmentation (anthocyanins) and the quality of the flavor and its aroma (organic acids). Hence, the dried flower of jamaica has been used as a flavoring additive for soft drinks, as a significant source of fiber and as a tool to fight inflammatory processes2-3. As anthocyanins are widely consumed and cultivated in Latin America, gaining insights about further biological activities is of great interest. The anthocyanins found in H.s.have a strong scavenging effect on reactive oxygen and free radicals2. Some studies about the two main anthocyanins present in H.s. (delphinidin and cyanidin) demonstrated that both, the oxidation and the antioxidant activity, break the same O–H bond4-5. In addition, a widely used nanomaterial to build working electrodes is TiO2 nanotubes6, because they can be produced at low expense and have shown an excellent chemical stability in their anatase phase7. Furthermore, TiO2 nanotubes can be characterized by their effective electron transfer behavior and their high adsorptive property of organic compounds due to abundant active sites6. Therefore, this research project presents the methodology and results of a highly sensitive and selective electrochemical system, composed only by a titanium dioxide nanostructured electrode functionalized with a purified extract of jamaica. This technique establishes a new method to detect and quantify hydroxyl radicals in solution with a quantification limit of 3.91x10-6 M and a detection limit of 2.39 x10-6 M, that also have proven to be selective against other radicals (ABTS). In combination with the low cost in manufacturing and the eco-friendly nature of the materials, the novel electrode provides a significant enhancement when compared with other sensing materials available nowadays.

Piezo-electrochemical coupling of AgNbO3 piezoelectric nanomaterials

In this work, the AgNbO3 piezoelectric nanomaterials are hydrothermally synthesized, and they have an average particle size of~1 m, which is obtained from scanning electron microscopy pattern. The AgNbO3 nanomaterial possesses an orthorhombic crystal structure with an mm2 point group symmetry, indicated by the X-ray powder diffraction analysis result. The piezo-electrochemical coupling of AgNbO3 is characterized, and its physical mechanism is discussed. Under an external mechanical vibration, the surfaces of the piezoelectric AgNbO3 nanomaterials will generate a large number of positive and negative electric charges. Due to the existence of spontaneous polarization, these positive and negative electrical carriers are respectively distributed on the top surface and bottom surface of AgNbO3 and can further induce the generation of some strong oxidation middle active species such as hydroxyl radicals in solution on the basis of some special chemical redox reactions, realizing the piezo-electrochemical coupling. Therefore, we can consider the piezo-electrochemical coupling as the product of the piezoelectric effect and the electrochemical redox effect. Utilizing the strong piezo-electrochemical coupling, a practical application in mechano-catalysis is further developed to decompose dye solution under a driven vibration. After experiencing~60 min vibration with AgNbO3 nanomaterial as mechano-catalyst,~70% rhodamine B (~5 mg/L) is decomposed. Prior to the vibration, the rhodamine B solution with the addition of AgNbO3 catalyst is slowly stirred for 30 min to ensure the establishment of the physical adsorptiondesorption equilibrium between catalyst and dye. It is difficult to directly exert a mechanical stress on the micro/nanoparticles. Here, an ultrasonic source with a vibration frequency of~40 kHz is employed to exert a stress to compress and stretch the AgNbO3 particles through utilizing micro-bubble collapse forces during ultrasonic cavitations, which needs the AgNbO3 particle size to be roughly identical with the diameter (~m) of micro-bubble. Our mechanocatalytic dye decomposition experiment is conducted at room-temperature and in a dark environment to avoid the influence of photocatalysis. The slight increase of temperature of the dye solution in the ultrasonic vibration process has no obvious influence on the dye decomposition efficiency, which has been confirmed from our experiment. Through a technology of fluorescence spectrum trapping, the intermediate active product in the piezo-electrochemical coupling process-the strongly oxidized hydroxyl radicals, is successfully observed. With the increase of vibration time, the number of hydroxyl radicals obviously increases, which proves that the piezo-electrochemical coupling plays a key role in our mechano-catalytic process. After using AgNbO3 catalyst in cyclic decomposition of rhodamine B 5 times, no obvious reduction in the piezo-electrochemical coupling performance occurs. The AgNbO3 nanomaterial possesses an efficient piezo-electrochemical coupling for mechano-catalysis, and it has the advantages of high decomposition efficiency and reusability, and potential applications in vibration decomposing dye.

Ultrasound-enhanced nanosized zero-valent copper activation of hydrogen peroxide for the degradation of norfloxacin

Commercial nanosized zero-valent copper (nZVC) was used as hydrogen peroxide (H2O2) activator in conjunction with ultrasonic irradiation (US) for the oxidative degradation of norfloxacin (NOR) in this study. Compared with silent degradation system, a significantly enhanced NOR removal was obtained in sono-advanced Fenton process, which involved a synergistic effect between sonolysis and Fenton-like reaction. Almost complete removal of NOR was achieved at 30min when the operating conditions were 0.25g/L nZVC and 10mM H2O2 with ultrasound power of 240W at 20kHz. The released Cu+ during the nZVC dissolution was the predominant copper species to activate H2O2 and yield hydroxyl radicals (OH) in US/nZVC/H2O2 system. According to the radical quenching experiments and electron paramagnetic resonance technique, hydroxyl radicals in solution (OHfree) were verified as the primary reactive species, and superoxide anion radicals (O2−) were regarded as the mediator for the copper cycling by reduction of Cu2+ to Cu+. NOR removal efficiencies were improved in various degrees when increased nZVC dosage, ultrasound power, hydrogen-ion amount and H2O2 concentration. Moreover, the inhibitory effect of different inorganic salts on NOR degradation followed the sequence of Na2SO4>NaNO3≈no salt>NaCl>NaHCO3. Finally, eleven intermediates were identified and five oxidation pathways were proposed, the cleavage of piperazine ring and transformation of quinolone group seemed to be the major pathway.

Cyanide removal with a copper/active carbon fiber Cathode via a combined oxidation of a Fenton-like reaction and in situ generated copper oxides at anode

Cyanide is widely present in electroplating wastewater or metallurgical effluents. In the present study, the electrochemical destruction of cyanide with copper/active carbon fiber (Cu/ACF) composite cathode and Dimensionless Stable Anode (DSA) under alkaline conditions was investigated. Firstly, various cathode materials including stainless steel, ACF, copper plate and Cu/ACF were compared for cyanide removal. Cyanide removal efficiencies by the individual H2O2 oxidation generated using ACF cathode or individual DSAs anodic oxidation using stainless steel cathode were less than 20%. Using Cu/ACF as the cathode, the removal efficiency of cyanide was largely improved compared with other cathodes. At the current density of 50.01A/m2 and the geometric area ratio of Cu/ACF=1:2, the concentration of cyanide was lowered from 1.50 to 0.07mM within 90minutes. Due to the dissolution of copper plate by the cyanide ions, the concentration of copper ions increased rapidly at first and then decreased with the efficient destruction of cyanide ions. Combined with the SEM-EDX and XPS analysis of the anode surface, it was concluded that the generation of copper oxides occurred at the anode surface, which exhibited catalytic activities for cyanide removal. Meantime, ESR results confirmed the generation of hydroxyl radicals in solution. Hydroxyl radicals generated in the reaction between copper cyanides complexs and H2O2 were responsible for the cyanide removal. Once the cyanide removal was completed, part of the copper ions was reduced and deposited onto the cathode and part of the copper ions was deposited onto the anode. Therefore, the next recycle for cyanide removal by copper oxides catalytic oxidation at the anode and the Fenton-like oxidation in the solution began. Cyanate was identified as the only product in this system.

One-pot synthesis of CdS@Nb2O5 core–shell nanostructures with enhanced photocatalytic activity

CdS@NbxOy core–shell nanostructures were used as heterogeneous catalysts for oxidizing organic compounds in aqueous media under ultraviolet light. The core/shell nanocrystals contained two nanostructured semiconductor that enhanced the catalytic properties of the material under UV–Vis irradiation. The developed core/shell nanocrystals displayed significant catalytic activity during the oxidation of organic substrates and may be suitable for degrading organic pollutants in water. The ESI–MS spectrum obtained for methylene blue after exposure to the nanostructured semiconductor nanoparticles revealed a hydroxylation caused by hydroxyl radicals in solution, forming a species at m/z=301.

Multiscale QM/MM molecular dynamics study on the first steps of guanine damage by free hydroxyl radicals in solution.

Understanding the damage of DNA bases from hydrogen abstraction by free OH radicals is of particular importance to understanding the indirect effect of ionizing radiation. Previous studies address the problem with truncated DNA bases as ab initio quantum simulations required to study such electronic-spin-dependent processes are computationally expensive. Here, for the first time, we employ a multiscale and hybrid quantum mechanical-molecular mechanical simulation to study the interaction of OH radicals with a guanine-deoxyribose-phosphate DNA molecular unit in the presence of water, where all of the water molecules and the deoxyribose-phosphate fragment are treated with the simplistic classical molecular mechanical scheme. Our result illustrates that the presence of water strongly alters the hydrogen-abstraction reaction as the hydrogen bonding of OH radicals with water restricts the relative orientation of the OH radicals with respect to the DNA base (here, guanine). This results in an angular anisotropy in the chemical pathway and a lower efficiency in the hydrogen-abstraction mechanisms than previously anticipated for identical systems in vacuum. The method can easily be extended to single- and double-stranded DNA without any appreciable computational cost as these molecular units can be treated in the classical subsystem, as has been demonstrated here.

A DFT study on reaction of eupatilin with hydroxyl radical in solution

AbstractAntioxidants scavenge reactive oxygen species and, therefore, are vitally important in the living cells. The antioxidant properties of eupatilin have recently been reported. In this article, the reactions of eupatilin with the hydroxyl radical (OH•) in solution are studied using density functional theory calculations and the polarizable continuum model. Three mechanisms are considered including: sequential electron proton transfer (SEPT), sequential proton loss electron transfer (SPLET), and hydrogen abstraction (HA). Three solvents with different polarities, that is, benzene, methanol, and water, are used to investigate the effect of the environment on the mechanisms. The relative Gibbs free energies and enthalpies corresponding to different mechanisms are calculated. Our results show that SEPT is thermodynamically favored in aqueous solution. Once the eupatilin anion is produced, the second step in SPLET mechanism is thermodynamically favored in methanol and water. The HA mechanism is thermodynamically favored in gas, benzene, methanol, and water. This mechanism is more energetically favorable to occur in a more polar solvent. The natural bond orbital charges and spin densities as well as the singly occupied molecular orbital are then analyzed. It is concluded that the HA process is governed by proton coupled electron transfer mechanism. The attack of the radical takes place preferentially at position 7 of eupatilin. © 2012 Wiley Periodicals, Inc.

Nanophase iron-enhanced chemical reactivity of ground lunar soil

The plan to resume robotic and manned missions to the Moon in the next decade has led to a renewed interest in the properties of lunar soils, ranging from geological to chemical to toxicological. As an approximation of the effects of crushing and weathering on the Moon, previous work (W. T. Wallace et al. (2009) Meteor. Planet. Sci. 44: 961–970) demonstrated that freshly ground lunar soil is extremely active, as measured by the production of hydroxyl radicals in solution. The present study was performed in order to understand the origin of this reactivity. We have ground 8 lunar soils of varying maturity and source (highland or mare) and measured the hydroxyl-radical production and decay of the reactivity. It was determined that there is a direct correlation between the reactivity and the amount of nanophase metallic iron particles (as a function of soil maturity) in the samples; thus, the highland soils, with their lower total FeO contents, and less nanophase iron, are less reactive than ground mare soils. However, there was no obvious correlation between maturity and source (highland or mare), with respect to the amount of time required for deactivation to a non-reactive state. These results provide the first chemical reactivity values as an important property of lunar soils, necessary data for returning humans to the Moon.

Dps proteins prevent Fenton-mediated oxidative damage by trapping hydroxyl radicals within the protein shell

Dps (DNA-binding proteins from starved cells) proteins belong to a widespread bacterial family of proteins expressed under nutritional and oxidative stress conditions. In particular, Dps proteins protect DNA against Fenton-mediated oxidative stress, as they catalyze iron oxidation by hydrogen peroxide at highly conserved ferroxidase centers and thus reduce significantly hydroxyl radical production. This work investigates the possible generation of intraprotein radicals during the ferroxidation reaction by Escherichia coli and Listeria innocua Dps, two representative members of the family. Stopped-flow analyses show that the conserved tryptophan and tyrosine residues located near the metal binding/oxidation center are in a radical form after iron oxidation by hydrogen peroxide. DNA protection assays indicate that the presence of both residues is necessary to limit release of hydroxyl radicals in solution and the consequent oxidative damage to DNA. In general terms, the demonstration that conserved protein residues act as a trap that dissipates free electrons generated during the oxidative process brings out a novel role for the Dps protein cage.

X-ray Footprinting at Beamline X28C: A National Resource for Studying Macromolecular Structure and Dynamics

X-ray footprinting employs intense X-rays produced by synchrotron radiation to generate hydroxyl radicals in solution on microseconds-milliseconds timescales. These hydroxyls radicals undergo stable reaction with solvent accessible sites of macromolecule and produce covalent modifications, which are appropriate to probing macromolecule dynamics under physiological condition. For nucleic acids, one analyzes the pattern of fragments after X-ray exposure by gel electrophoresis; the protected sections that are not cleaved yield a 'footprint'. For proteins, the exposed samples are digested with proteases and analyzed by liquid chromatography- and tandem-mass spectrometry to determine the extent and sites of modification. The data provide detailed structural information to map tertiary contacts of macromolecular interactions, which can subsequently be used as constraints for molecular modeling to generate high-resolution structures. This method is unique in providing 'local' structural information in solution for gaining insight into dynamic processes involving, large RNA-protein and protein-protein assemblies on biologically relevant timescales. The method also can uniquely probe the 'local' structure of large complexes poised at equilibrium for functional states of interest, and has been extended to in vivo studies. Beamline X28C is located at the National Synchrotron Light Source of Brookhaven National Laboratory. An expanding set of user groups utilize this national resourcemore » funded by the National Institute of Biomedical Imaging and Bioengineering of the National Institutes of Health. The facility is operated by the Center for Synchrotron Biosciences and the Center for Proteomics and Bioinformatics of Case Western Reserve University. The facility supports both onsite and offsite user access. Beam time is allocated online through peer reviewed user proposal system. Examples of recent research projects are provided.« less