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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Characteristic Vertical Profiles of Cloud Water Composition in Marine Stratocumulus Clouds and Relationships With Precipitation

This study uses airborne cloud water composition measurements to characterize the vertical structure of air-equivalent mass concentrations of water-soluble species in marine stratocumulus clouds off the California coast. In this work, a total of 385 cloud water samples were collected in the months of July and August between 2011 and 2016 and analyzed for water-soluble ionic and elemental composition. Three characteristic profiles emerge: (i) a reduction of concentration with in-cloud altitude for particulate species directly emitted from sources below cloud without in-cloud sources (e.g., Cl - , Na + ); (ii) an increase of concentration with in-cloud altitude (e.g., NO 2 - , formate); and (iii) species exhibiting a peak in concentration in the middle of cloud (e.g., non-sea salt SO 4 2- , NO 3 - , organic acids). Vertical profiles of rainout parameters such as loss frequency, lifetime, and change in concentration with respect to time show that the scavenging efficiency throughout the cloud depth depends strongly on the thickness of the cloud. Thin clouds exhibit a greater scavenging loss frequency at cloud top, while thick clouds have a greater scavenging loss frequency at cloud base. The implications of these results for treatment of wet scavenging in models are discussed.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Modeling and sensitivity analysis of mass transfer in active multilayer polymeric film for food applications

The barrier performance of multilayer polymeric films for food applications has been significantly improved by incorporating oxygen scavenging materials. The scavenging activity depends on parameters such as diffusion coefficient, solubility, concentration of scavenger loaded and the number of available reactive sites. These parameters influence the barrier performance of the film in different ways. Virtualization of the process is useful to characterize, design and optimize the barrier performance based on physical configuration of the films. Also, the knowledge of values of parameters is important to predict the performances. Inverse modeling and sensitivity analysis are sole way to find reasonable values of poorly defined, unmeasured parameters and to analyze the most influencing parameters. Thus, the objective of this work was to develop a model to predict barrier properties of multilayer film incorporated with reactive layers and to analyze and characterize their performances. Polymeric film based on three layers of Polyethylene terephthalate (PET), with a core reactive layer, at different thickness configurations was considered in the model. A one dimensional diffusion equation with reaction was solved numerically to predict the concentration of oxygen diffused into the polymer taking into account the reactive ability of the core layer. The model was solved using commercial software for different film layer configurations and sensitivity analysis based on inverse modeling was carried out to understand the effect of physical parameters. The results have shown that the use of sensitivity analysis can provide physical understanding of the parameters which highly affect the gas permeation into the film. Solubility and the number of available reactive sites were the factors mainly influencing the barrier performance of three layered polymeric film. Multilayer films slightly modified the steady transport properties in comparison to net PET, giving a small reduction in the permeability and oxygen transfer rate values. Scavenging capacity of the multilayer film increased linearly with the increase of the reactive layer thickness and the oxygen absorption reaction at short times decreased proportionally with the thickness of the external PET layer.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Impacts of ENSO events on cloud radiative effects in preindustrial conditions: Changes in cloud fraction and their dependence on interactive aerosol emissions and concentrations

The impacts of the El Niño–Southern Oscillation (ENSO) events on shortwave and longwave cloud radiative effects (CRE SW and CRE LW ) and the underlying changes in cloud fraction as well as aerosol emissions, wet scavenging and transport are quantified using three 150-year simulations in preindustrial conditions by the CESM model. Compared to recent observations from Clouds and the Earth’s Radiant Energy System (CERES), the model simulation successfully reproduced larger variations of CRE SW over the tropical western and central Pacific, Indonesian regions, and the eastern Pacific Ocean, as well as large variations of CRE LW located mainly within the tropics. The ENSO cycle is found to dominate interannual variations of cloud radiative effects, especially over the tropics. Relative to those during La Niña events, simulated cooling (warming) effects from CRE SW (CRE LW ) during El Niño events are stronger over the tropical western and central Pacific Ocean, with the largest difference exceeding 40 Wm –2 (30 Wm –2 ), with weaker effects of 10–30 Wm –2 over Indonesian regions and the subtropical Pacific Ocean. Here, sensitivity tests show that variations of cloud radiative effects are mainly driven by ENSO-related changes in cloud fraction. The variations in medium and high cloud fractions each account for about 20–50% of the interannual variations of CRE SW over the tropics and almost all of the variations of CRE LW between 60°S and 60°N. The variation of low cloud fraction contributes most interannual variations of CRESW over the mid-latitude oceans. Variations in natural aerosol concentrations considering emissions, wet scavenging and transport explained 10–30% of the interannual variations of both CRE SW and CRE LW over the tropical Pacific, Indonesian regions and the tropical Indian Ocean. Changes in wet scavenging of natural aerosol modulate the variations of cloud radiative effects. Because of increased (decreased) precipitation over the tropical western Pacific Ocean in El Niño (La Niña) events, increased (decreased) wet scavenging of natural aerosols dampens more than 4–6% of variations of cloud radiative effects averaged over the tropics. In contrast, increased surface winds cause feedbacks that increase sea spray emissions that enhance the variations by 3–4% averaged over the tropics.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Molecular Hydrogen Yields from the Alpha Self-Radiolysis of Nitric Acid Solutions Containing Plutonium or Americium

The yield of molecular hydrogen, as a function of nitric acid concentration, from the a-radiolysis of aerated nitric acid and sulfuric acid mixtures containing plutonium or americium has been investigated. Comparison of experimental measurements with predictions of a Monte Carlo radiation track chemistry model shows that, in addition to scavenging of the hydrated electron, its precursor, and the hydrogen atom, the quenching of excited state water is important in controlling the yield of hydrogen. In addition, increases in solution acidity cause a significant change in the track reactions that can be explained as resulting from scavenging of e aq - by H aq + to form H • . While plutonium has been shown to be an effective scavenger of precursors of molecular hydrogen below 0.1 mol dm-3 nitrate, previously reported effects of plutonium on G(H 2 ) a between 1 and 10 mol dm -3 nitric acid were not reproduced. Modelling results suggest that plutonium is unlikely to effectively compete with nitrate ions in scavenging the precursors of molecular hydrogen at higher nitric acid concentrations and this was confirmed by comparing hydrogen yields from plutonium solutions with those from americium. Finally, comparison between the radionuclide, ion accelerator experiments and model predictions leads to the conclusion that the high dose rate of accelerator studies does not significantly affect the measured hydrogen yield. These reactions provide insight into the important processes for liquors common in the reprocessing of spent nuclear fuel and the storage of highly radioactive liquid waste prior to vitrification.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2011

Can radiation damage to protein crystals be reduced using small-molecule compounds?

Free-radical scavengers that are known to be effective protectors of proteins in solution are found to increase global radiation damage to protein crystals. Protective mechanisms may become deleterious in the protein-dense environment of a crystal. Recent studies have defined a data-collection protocol and a metric that provide a robust measure of global radiation damage to protein crystals. Using this protocol and metric, 19 small-molecule compounds (introduced either by cocrystallization or soaking) were evaluated for their ability to protect lysozyme crystals from radiation damage. The compounds were selected based upon their ability to interact with radiolytic products (e.g. hydrated electrons, hydrogen, hydroxyl and perhydroxyl radicals) and/or their efficacy in protecting biological molecules from radiation damage in dilute aqueous solutions. At room temperature, 12 compounds had no effect and six had a sensitizing effect on global damage. Only one compound, sodium nitrate, appeared to extend crystal lifetimes, but not in all proteins and only by a factor of two or less. No compound provided protection at T = 100 K. Scavengers are ineffective in protecting protein crystals from global damage because a large fraction of primary X-ray-induced excitations are generated in and/or directly attack the protein and because the ratio of scavenger molecules to protein molecules is too small to provide appreciable competitive protection. The same reactivity that makes some scavengers effective radioprotectors in protein solutions may explain their sensitizing effect in the protein-dense environment of a crystal. A more productive focus for future efforts may be to identify and eliminate sensitizing compounds from crystallization solutions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Assessing the Role of Iron Sulfides in the Long Term Sequestration of Uranium by Sulfate-Reducing Bacteria

This overarching aim of this project was to identify the role of biogenic and synthetic iron-sulfide minerals in the long-term sequestration of reduced U(IV) formed under sulfate-reducing conditions when subjected to re-oxidizing conditions. The work reported herein was achieved through the collaborative research effort conducted at Arizona State University (ASU) and the University of Michigan (UM). Research at ASU, focused on the biogenesis aspects, examined the biogeochemical bases for iron-sulfide production by Desulfovibrio vulgaris, a Gram-negative bacterium that is one of the most-studied strains of sulfate-reducing bacteria. A series of experimental studies were performed to investigate comprehensively important metabolic and environmental factors that affect the rates of sulfate reduction and iron-sulfide precipitation, the mineralogical characteristics of the iron sulfides, and how uranium is reduced or co-reduced by D. vulagaris. FeS production studies revealed that controlling the pH affected the growth of D. vulgaris and strongly influenced the formation and growth of FeS solids. In particular, lower pH produced larger-sized mackinawite (Fe 1+x S). Greater accumulation of free sulfide, from more sulfate reduction by D. vulgaris, also led to larger-sized mackinawite and stimulated mackinawite transformation to greigite (Fe 3 S 4 ) when the free sulfide concentration was 29.3 mM. On the other hand, using solid Fe(III) (hydr)oxides as the iron source led to less productivity of FeS due to their slow and incomplete dissolution and scavenging of sulfide. Furthermore, sufficient free Fe 2+ , particularly during Fe(III) (hydr)oxide reductions, led to the additional formation of vivianite [Fe 3 (PO 4 ) 2 •8(H 2 O)]. The U(VI) reduction studies revealed that D. vulgaris reduced U(VI) fastest when accumulating sulfide from concomitant sulfate reduction, since direct enzymatic and sulfide-based reductions of U(VI) occurred in parallel. The UO 2 produced in presence of ferrous iron was poorly crystalline. At UM, laboratory-scale reactor studies were performed to assess the potential for the predominant abiotic reductants formed under sulfate reducing conditions (SRCs) to: (1) reduce U(VI) in contaminated groundwater sediments), and (2) inhibit the re-oxidation of U(IV) species, and in particular, uraninite (UO 2 (s)). Under SRCs, mackinawite and aqueous sulfide are the key reductants expected to form. To assess their potential for abiotic reduction of U(VI) species, a series of experiments were performed in which either FeS or S(-II) was added to solutions of U(VI), with the rates of conversion to U(IV) solids monitored as a function of pH, and carbonate and calcium concentration. In the presence of FeS and absence of oxygen or carbonate, U(IV) was completely reduced uraninite. S(-II) was also found to be an effective reductant of aqueous phase U(VI) species and produced uraninite, with the kinetics and extent of reduction depending on geochemical conditions. U(VI) reduction to uraninite was faster under higher S(-II) concentrations but was slowed by an increase in the dissolved Ca or carbonate concentration. Rapid reduction of U(VI) occurred at circumneutral pH but virtually no reduction occurred at pH 10.7. In general, dissolved Ca and carbonate slowed abiotic U(VI) reduction by forming stable Ca-U(VI)-carbonate soluble complexes that are resistant to reaction with aqueous sulfide. To investigate the stability of U(IV) against re-oxidation in the presence of iron sulfides by oxidants in simulated groundwater environments, and to develop a mechanistic understanding the controlling redox processes, continuously-mixed batch reactor (CMBR) and flow-through reactor (CMFR) studies were performed at UM. In these studies a series of experiments were conducted under various oxic groundwater conditions to examine the effectiveness of FeS as an oxygen scavenger to retard UO 2 dissolution. The results indicate that FeS is an effective oxygen scavenger, and can lower the rate of oxidative dissolution of UO 2 by over an order of magnitude compared to the absence of FeS, depending on pH, FeS content, and DO concentrations. Column reactor studies were performed at UM to assess the impact of mackinawite on uraninite oxidation under hydrodynamic flow conditions more representative of packed porous media at contaminated groundwater sites. In these studies, Rifle sediments were packed in the two columns which were subjected to different bioreduction steps and then run in parallel. The first column was bioreduced under SRCs (i.e., with sulfate in the influent) to generate mackinawite, mixed with uraninite, gamma-sterilized to inhibit subsequent microbiological activity, and then subjected to groundwater influent containing first nitrite and then oxygen. The second column was bioreduced (but in absence of sulfate in the influent) so that no iron sulfides would form, and then subjected to identical steps and influent as the first column. When nitrite was introduced in the influent of both columns, no significant release of U(VI) relative to the anoxic flow prior to nitrite addition occurred. However, when oxygen was introduced, the column which had undergone sulfate reduction (and had produced mackinawite as later verified by XAS) significantly lowered the peak U(VI) effluent concentrations, and in general, slowed U(VI) release considerably compared to the column with no FeS. Overall, these studies demonstrated that the presence of mackinawite can be a significant scavenger of oxygen and inhibit the oxidation of uraninite by oxygen, whereas nitrite had little impact on uraninite oxidation either in the presence or absence of FeS.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Aerosol responses to precipitation along North American air trajectories arriving at Bermuda

North American pollution outflow is ubiquitous over the western North Atlantic Ocean, especially in winter, making this location a suitable natural laboratory for investigating the impact of precipitation on aerosol particles along air mass trajectories. We take advantage of observational data collected at Bermuda to seasonally assess the sensitivity of aerosol mass concentrations and volume size distributions to accumulated precipitation along trajectories (APT). The mass concentration of particulate matter with aerodynamic diameter less than 2.5 µm normalized by the enhancement of carbon monoxide above background (PM 2.5 /ΔCO) at Bermuda was used to estimate the degree of aerosol loss during transport to Bermuda. Results for December–February (DJF) show that most trajectories come from North America and have the highest APTs, resulting in a significant reduction (by 53 %) in PM 2.5 /ΔCO under high-APT conditions (> 13.5 mm) relative to low-APT conditions (< 0.9 mm). Moreover, PM 2.5 /ΔCO was most sensitive to increases in APT up to 5 mm (–0.044 µg m –3 ppbv –1 mm –1 ) and less sensitive to increases in APT over 5 mm. While anthropogenic PM 2.5 constituents (e.g., black carbon, sulfate, organic carbon) decrease with high APT, sea salt, in contrast, was comparable between high- and low-APT conditions owing to enhanced local wind and sea salt emissions in high-APT conditions. The greater sensitivity of the fine-mode volume concentrations (versus coarse mode) to wet scavenging is evident from AErosol RObotic NETwork (AERONET) volume size distribution data. A combination of GEOS-Chem model simulations of the 210 Pb submicron aerosol tracer and its gaseous precursor 222 Rn reveals that (i) surface aerosol particles at Bermuda are most impacted by wet scavenging in winter and spring (due to large-scale precipitation) with a maximum in March, whereas convective scavenging plays a substantial role in summer; and (ii) North American 222 Rn tracer emissions contribute most to surface 210 Pb concentrations at Bermuda in winter (~75 %–80 %), indicating that air masses arriving at Bermuda experience large-scale precipitation scavenging while traveling from North America. A case study flight from the ACTIVATE field campaign on 22 February 2020 reveals a significant reduction in aerosol number and volume concentrations during air mass transport off the US East Coast associated with increased cloud fraction and precipitation. These results highlight the sensitivity of remote marine boundary layer aerosol characteristics to precipitation along trajectories, especially when the air mass source is continental outflow from polluted regions like the US East Coast.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

The Use of Graphene and Its Derivatives for Liquid-Phase Transmission Electron Microscopy of Radiation-Sensitive Specimens

We present that one of the key challenges facing liquid-phase transmission electron microscopy (TEM) of biological specimens has been the damaging effects of electron beam irradiation. The strongly ionizing electron beam is known to induce radiolysis of surrounding water molecules, leading to the formation of reactive radical species. In this study, we employ DNA-assembled Au nanoparticle superlattices (DNA-AuNP superlattices) as a model system to demonstrate that graphene and its derivatives can be used to mitigate electron beam-induced damage. We can image DNA-AuNP superlattices in their native saline environment when the liquid cell window material is graphene, but not when it is silicon nitride. In the latter case, initial dissociation of assembled AuNPs was followed by their random aggregation and etching. Using graphene-coated silicon nitride windows, we were able to replicate the observation of stable DNA-AuNP superlattices achieved with graphene liquid cells. We then carried out a correlative Raman spectroscopy and TEM study to compare the effect of electron beam irradiation on graphene with and without the presence of water and found that graphene reacts with the products of water radiolysis. We attribute the protective effect of graphene to its ability to efficiently scavenge reactive radical species, especially the hydroxyl radicals which are known to cause DNA strand breaks. We confirmed this by showing that stable DNA-AuNP assemblies can be imaged in silicon nitride liquid cells when graphene oxide and graphene quantum dots, which have also recently been reported as efficient radical scavengers, are added directly to the solution. Lastly, we anticipate that our study will open up more opportunities for studying biological specimens using liquid-phase TEM with the use of graphene and its derivatives as biocompatible radical scavengers to alleviate the effects of radiation damage.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Three-dimensional piezoelectric vibration energy harvester using spiral-shaped beam with triple operating frequencies

This work has demonstrated a novel piezoelectric energy harvester without a complex structure and appended component that is capable of scavenging vibration energy from arbitrary directions with multiple resonant frequencies. In this harvester, a spiral-shaped elastic thin beam instead of a traditional thin cantilever beam was adopted to absorb external vibration with arbitrary direction in three-dimensional (3D) spaces owing to its ability to bend flexibly and stretch along arbitrary direction. Furthermore, multiple modes in the elastic thin beam contribute to a possibility to widen the working bandwidth with multiple resonant frequencies. The experimental results show that the harvester was capable of scavenging the vibration energy in 3D arbitrary directions; they also exhibited triple power peaks at about 16 Hz, 21 Hz, and 28 Hz with the powers of 330 μW, 313 μW, and 6 μW, respectively. In addition, human walking and water wave energies were successfully converted into electricity, proving that our harvester was practical to scavenge the time-variant or multi-directional vibration energies in our daily life.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2010

Radioactive iodine separations and waste forms development.

Reprocessing nuclear fuel releases gaseous radio-iodine containing compounds which must be captured and stored for prolonged periods. Ag-loaded mordenites are the leading candidate for scavenging both organic and inorganic radioiodine containing compounds directly from reprocessing off gases. Alternately, the principal off-gas contaminant, I2, and I-containing acids HI, HIO3, etc. may be scavenged using caustic soda solutions, which are then treated with bismuth to put the iodine into an insoluble form. Our program is focused on using state-of-the-art materials science technologies to develop materials with high loadings of iodine, plus high long-term mechanical and thermal stability. In particular, we present results from research into two materials areas: (1) zeolite-based separations and glass encapsulation, and (2) in-situ precipitation of Bi-I-O waste forms. Ag-loaded mordenite is either commercially available or can be prepared via a simple Ag+ ion exchange process. Research using an Ag+-loaded Mordenite zeolite (MOR, LZM-5 supplied by UOP Corp.) has revealed that I2 is scavenged in one of three forms, as micron-sized AgI particles, as molecular (AgI)x clusters in the zeolite pores and as elemental I2 vapor. It was found that only a portion of the sorbed iodine is retained after heating at 95o C for three months. Furthermore, we show that even when the Ag-MOR is saturated with I2 vapor only roughly half of the silver reacted to form stable AgI compounds. However, the Iodine can be further retained if the AgI-MOR is then encapsulated into a low temperature glass binder. Follow-on studies are now focused on the sorption and waste form development of Iodine from more complex streams including organo-iodine compounds (CH3I). Bismuth-Iodate layered phases have been prepared from caustic waste stream simulant solutions. They serve as a low cost alternative to ceramics waste forms. Novel compounds have been synthesized and solubility studies have been completed using competing groundwater anions (HCO3-, Cl- and SO42-). Distinct variations in solubility were found that related to the structures of the materials.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Circadian rhythmicity of amyloid‐beta‐related molecules is disrupted in the choroid plexus of a female Alzheimer's disease mouse model

Abstract The choroid plexus (CP) is part of the blood‐cerebrospinal fluid barrier (BCSFB) and was recently described as an important component of the circadian clock system. It is the principal source of cerebrospinal fluid (CSF) and responsible for the synthesis and secretion of various neuroprotective peptides including those involved in amyloid‐β (Aβ) transport/degradation, contributing to Aβ homeostasis. Inadequate Aβ metabolic clearance and transport across the BCSFB have been associated with circadian dysfunctions in Alzheimer's disease (AD) patients. To investigate whether AD pathology influences Aβ scavengers circadian expression, we collected CP at different time points from an AD mouse model (APP/PS1) (female and male animals, aged 6‐ and 12‐months‐old) and analyzed their mRNA expression by Real‐time RT‐PCR. Only angiotensin‐converting enzyme (Ace) expression in 6‐month‐old female wild‐type mice and transthyretin (Ttr) expression in 12‐month‐old female wild‐type mice presented significant rhythmicity. The circadian rhythmicity of Ace and Ttr, prompt us to analyze the involvement of circadian rhythm in Aβ uptake. A human CP papilloma (HIBCPP) cell line was incubated with Aβ‐488 and uptake was evaluated at different time points using flow cytometry. Aβ uptake displayed circadian rhythmicity. Our results suggest that AD might affect Aβ scavengers rhythmicity and that Aβ clearance is a rhythmic process possibly regulated by the rhythmic expression of Aβ scavengers.

Furtado, André↗
DOE OSTI2025

A review on bacteria-derived antioxidant metabolites: their production, purification, characterization, potential applications, and limitations

Abstract Antioxidants are organic molecules that scavenge reactive oxygen species (ROS) and reactive nitrogen species (RNS), thereby maintaining cellular redox balance in living organisms. The human body synthesizes endogenous antioxidants, whereas humans obtain exogenous antioxidants from other organisms such as plants, animals, fungi, and bacteria. This review primarily focuses on the antioxidant potential of natural metabolites and extracts from five major bacterial phyla, including the well-studiedActinobacteriaandCyanobacteria, as well as less-studiedBacteroides,Firmicutes, andProteobacteria.The literature survey revealed that the metabolites and the extracts with antioxidant activity can be obtained from bacterial cells and their culture supernatants. The metabolites with antioxidant activity include pigments, phycobiliproteins, polysaccharides, mycosporins-like amino acids, peptides, phenolic compounds, and alkaloids. Both metabolites and extracts demonstrate in vitro antioxidant capacity through radical-scavenging, metal-reducing, and metal-chelating activity assays. In in vivo models, they can scavenge ROS and RNS directly and/or indirectly eliminate them by enhancing the activities of antioxidant enzymes, such as catalase, superoxide dismutase, and glutathione peroxidase. Due to their antioxidant activities, they may find applications in the cosmetic industry as anti-aging agents for the skin and in medicine as drugs or supplements for combating oxidative stress-related disorders, such as neurodegenerative diseases and diabetes. The literature survey also elucidated that some metabolites and extracts with antioxidant activity also exhibited strong antimicrobial properties. Therefore, we consider that they may have future applications in the treatment of infectious diseases, the preparation of pathogen-free healthy foods, and the extension of food shelf life.

Pharmacology & Pharmacy↗
DOE OSTI2012

PrP{sup C} displays an essential protective role from oxidative stress in an astrocyte cell line derived from PrP{sup C} knockout mice

Highlights: Black-Right-Pointing-Pointer PrP{sup C} in solution acts as a radical scavenger. Black-Right-Pointing-Pointer PrP{sup C} reduces hydrogen peroxide toxicity in astrocytes. Black-Right-Pointing-Pointer Increase in ROS disrupted the cell cycle in the PrP{sup C}-knockout astrocytes. Black-Right-Pointing-Pointer PrP{sup C} prevents the cell death independently of an SOD-like activity. -- Abstract: The PrP{sup C} protein, which is especially present in the cellular membrane of nervous system cells, has been extensively studied for its controversial antioxidant activity. In this study, we elucidated the free radical scavenger activity of purified murine PrP{sup C} in solution and its participation as a cell protector in astrocytes that were subjected to treatment with an oxidant. In vitro and using an EPR spin-trapping technique, we observed that PrP{sup C} decreased the oxidation of the DMPO trap in a Fenton reaction system (Cu{sup 2+}/ascorbate/H{sub 2}O{sub 2}), which was demonstrated by approximately 70% less DMPO/OH{sup {center_dot}}. In cultured PrP{sup C}-knockout astrocytes from mice, the absence of PrP{sup C} caused an increase in intracellular ROS (reactive oxygen species) generation during the first 3 h of H{sub 2}O{sub 2} treatment. This rapid increase in ROS disrupted the cell cycle in the PrP{sup C}-knockout astrocytes, which increased the population of cells in the sub-G1 phase when compared with cultured wild-type astrocytes. We conclude that PrP{sup C} in solution acts as a radical scavenger, and in astrocytes, it is essential for protection from oxidative stress caused by an external chemical agent, which is a likely condition in human neurodegenerative CNS disorders and pathological conditions such as ischemia.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Hydroxysafflor yellow A attenuates high glucose-induced pancreatic β-cells oxidative damage via inhibiting JNK/c-jun signaling pathway

Highlights: • High glucose-induced oxidative stress can lead to pancreatic β-cells damage. • HSYA can reduce pancreatic β-cells apoptosis by attenuating oxidative damage. • HSYA can scavenge oxidative stress and inhibit apoptosis through JNK/c-Jun signaling pathway. Pancreatic β-cells apoptosis and dysfunction induced by glucose toxicity were attributed to the formation of excess oxidative damage. Some studies have found that hydroxysafflor yellow A has strong effects to scavenge oxidative stress and inhibit apoptosis. In order to explore the influence of HSYA on oxidative stress induced by high glucose and the potential mechanisms, we set up a high glucose damage model and induced oxidative stress in INS-1 rat insulinoma cells. N-acetylcysteine was added as a group of oxidative stress scavenger. After 72 h of cultivation, the related indexes of oxidative stress (reactive oxygen species, catalase, glutathione peroxidase, lipid peroxidation, and superoxide dismutase), apoptosis (caspase3, parp) and the function of glucose stimulated insulin secretion were determined. In addition, the signaling pathway proteins of C-Jun NH2 -terminal kinases (JNK), phosphorylated JNK, C-jun, phosphorylated C-jun were evaluated. Fluorescence microscopy, qRT-PCR, western blotting were the main methods used in the experiment. Our results showed that hydroxysafflor yellow A reduced pancreatic β-cells apoptosis by attenuating oxidative damage, and JNK/c-Jun signaling pathway was involved. It indicated a significant mechanism for the positive impacts of HSYA on oxidative stress induced by high glucose, and provide important basis for using HSYA in diabetic prevention and therapy.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

Oxidative Dissolution of UO2 in a Simulated Groundwater Containing Synthetic Nanocrystalline Mackinawite

The long-term success of in situ reductive immobilization of uranium (U) depends on the stability of U(IV) precipitates (e.g., uraninite) under oxic conditions. Field and laboratory studies have implicated iron sulfide minerals as redox buffers or oxidant scavengers that may slow oxidation of reduced U(VI) solid phases by oxygen and Fe(III). Yet, the inhibition mechanism(s) and reaction rates of uraninite (UO2) oxidative dissolution by oxic species such as oxygen in FeS-bearing systems remain largely unresolved. To address this knowledge gap, abiotic batch experiments were conducted with synthetic UO2 in the presence and absence of synthetic mackinawite (FeS) under simulated groundwater conditions of pH = 7, PO2 = 0.02 atm, and PCO2 = 0.05 atm (equivalent to total dissolved carbonate of 0.01 M). The kinetic profiles of dissolved uranium indicate that FeS inhibited UO2 dissolution for 51 hr by effectively scavenging oxygen and keeping dissolved oxygen (DO) low. During this time period, oxidation of structural Fe(II) and S(-II) of FeS were found to control the DO levels, leading to the formation of iron oxyhydroxides and elemental sulfur, respectively, as verified by X-ray diffraction (XRD), Mössbauer and X-ray absorption spectroscopy (XAS). After FeS was depleted due to oxidation, DO levels increased and UO2 oxidative dissolution occurred at an initial rate of rm = 1.2 ± 0.4 ×10-8 mol•g-1•s-1, higher than rm = 5.4 ± 0.3 ×10-9 mol•g-1•s-1 in the control experiment where FeS was absent. Soluble U(VI) products were adsorbed by iron oxyhydroxides (i.e. nanogoethite and ferrihydrite) formed from FeS oxidation, which facilitated the detachment of U(VI) surface complexes and more rapid dissolution of UO2. XAS analysis confirmed the adsorption of U(VI) species, and also showed that U(VI) was not significantly incorporated into iron oxyhydroxide structure. This work reveals that both the oxygen scavenging by FeS and the adsorption of U(VI) to FeS oxidation products may be important in U reductive immobilization systems subject to redox cycling events.

Containing↗
DOE OSTI2014

Zinc oxide nanoparticles induce migration and adhesion of monocytes to endothelial cells and accelerate foam cell formation

Metal oxide nanoparticles are widely used in industry, cosmetics, and biomedicine. However, the effects of exposure to these nanoparticles on the cardiovascular system remain unknown. The present study investigated the effects of nanosized TiO{sub 2} and ZnO particles on the migration and adhesion of monocytes, which are essential processes in atherosclerogenesis, using an in vitro set-up of human umbilical vein endothelial cells (HUVECs) and human monocytic leukemia cells (THP-1). We also examined the effects of exposure to nanosized metal oxide particles on macrophage cholesterol uptake and foam cell formation. The 16-hour exposure to ZnO particles increased the level of monocyte chemotactic protein-1 (MCP-1) and induced the migration of THP-1 monocyte mediated by increased MCP-1. Exposure to ZnO particles also induced adhesion of THP-1 cells to HUVECs. Moreover, exposure to ZnO particles, but not TiO{sub 2} particles, upregulated the expression of membrane scavenger receptors of modified LDL and increased cholesterol uptake in THP-1 monocytes/macrophages. In the present study, we found that exposure to ZnO particles increased macrophage cholesterol uptake, which was mediated by an upregulation of membrane scavenger receptors of modified LDL. These results suggest that nanosized ZnO particles could potentially enhance atherosclerogenesis and accelerate foam cell formation. - Highlights: • Effects of metal oxide nanoparticles on foam cell formation were investigated. • Exposure to ZnO nanoparticles induced migration and adhesion of monocytes. • Exposure to ZnO nanoparticles increased macrophage cholesterol uptake. • Expression of membrane scavenger receptors of modified LDL was also increased. • These effects were not observed after exposure to TiO{sub 2} nanoparticles.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2011

Interfacial Electron Transfer Dynamics for [Ru(bpy) 2 ((4,4'-PO 3 H 2 ) 2 bpy)] 2+ Sensitized TiO 2 in a Dye-Sensitized Photoelectrosynthesis Cell: Factors Influencing Efficiency and Dynamics

Nanosecond laser flash photolysis and photocurrent measurements have been used to investigate use of [(Ru(bpy)2(4,4'-(PO3H2)2bpy)]2+ attached to TiO2 nanoparticle films, TiO2-RuII, in a dye-sensitized photoelectrosynthesis cell (DSPEC) configuration for H2 production. In these experiments, laser flash excitation of TiO2-RuII and rapid injection lead to TiO2(e-)-RuIII with subsequent TiO2(e-)-RuIII → TiO2-RuII back electron transfer monitored on the nsec time scale with and without added triethanolamine (TEOA) and deprotonated ethylenediaminetetraacetic tetra-anion (EDTA4-) as irreversible electron transfer donors. With added TEOA or EDTA4-, a competition exists between back electron transfer and scavenger oxidation with the latter leading to H2 production in the photoelectrosynthesis cell. Reduction of TiO2(e-)-RuIII by both TEOA and EDTA4- occurs with kD ~ 106 M-1 s-1. EDTA4- is a more efficient scavenger by a factor of ~3 because of a more favorable partition equilibrium between the film and the external solution. Its increased scavenger efficiency appears in incident photon-to-current conversion efficiency (IPCE) measurements, in electron collection efficiencies (ηcoll), and in photocurrent measurements with H2 production. Evaluation of electron collection efficiencies by transient current measurements gave ηcoll ~ 24% for TEOA and ~ 70% for EDTA4-. The dynamics of back electron transfer are minimized, and collection efficiencies, photocurrents, and hydrogen production are maximized by application of a positive applied bias consistent with the results of I-V measurements. A pH dependent plateau is reached at ~0 V at pH = 4.5 (EDTA4-) and at ~ -0.4 V at pH 6.7 (TEOA). The difference is qualitatively consistent with the influence of pH on electron population in trap states below the conduction band and the role they play in back electron transfer. The excitation dependence of IPCE measurements matches the spectrum of TiO2-RuII with IPCE values ~3 times higher for EDTA4- than for TEOA as noted above. Absorbed photon-to-current efficiency (APCE) values are light-intensity dependent because of the effect of multiple injection events and the influence of increasing trap site electron densities on back electron transfer. The key to efficient H2 production is minimizing back electron transfer. Application of a sufficiently positive potential relative to ECB for TiO2 accelerates loss of electrons from the film in competition with back electron transfer allowing for H2 production with efficiencies approaching 14.7% under steady-state irradiation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

How fishing intensity affects the spatial and trophic ecology of two gull species breeding in sympatry

Abstract Fisheries produce large quantities of discards, an important resource for scavenging seabirds. However, a policy reform banning discards, which is soon to be implemented within the EU, will impose a food shortage upon scavengers, and it is still largely unknown how scavengers will behave. We studied the diet (hard remains), trophic (stable isotope analysis), and foraging (individual tracking) ecology of two gull species breeding in sympatry: Audouin’s gull Larus audouinii (AG) and yellow-legged gull Larus michahellis (YLG), in South Portugal, under normal fishery activity (NFA; work days) and low fishery activity (LFA; weekends), over two consecutive years. We established a pattern of dietary, spatial, and temporal segregation between the two gull species. Under LFA, yellow-legged gulls reduced their time spent at-sea, thus foraging more in alternative habitats (e.g. refuse dumps) and widening their isotopic niche (i.e. generalist behaviour). Contrastingly, Audouin’s gull had a narrower trophic niche (i.e. specialist behaviour), foraging exclusively at-sea, reducing the amount of demersal fish and increasing the amount of pelagic fish in their diet. Under NFA, both species foraged mostly at-sea, feeding almost exclusively on fish, with increased consumption of demersal species (i.e. fishery discards). In general, yellow-legged gull had a broader trophic niche (i.e. generalist behaviour) when compared with the narrower isotopic niche of Audouin’s gull (i.e. specialist behaviour). Overall, both gull species relied heavily on fishery discards. However, there was visible dietary, spatial, and temporal segregation between the two species, associated with their dietary and habitat preferences that could be attributed to the availability of anthropogenic resources, such as fishery discards.

Matos, Diana M.↗