O2 Environment Research Articles

First principles studies of CO2 and O2 chemisorption on La2O3 surfaces.

Periodic density functional theory calculations were performed to study the surface structures and stabilities of the La2O3 catalyst in CO2 and O2 environments, relevant to the conditions of the oxidative coupling of methane (OCM) reaction. Thermodynamic stabilities of the clean surfaces were predicted to follow the order of (001) ≥ (011) ≫ (110) > (111) > (101) > (100), with their direct band gaps at the Γ point following the similar order of (001) > (011) > (110) > (111) > (100) > (101). Hubbard U corrections to the La 4f and 5d orbitals do not qualitatively change the predictions of surface energies and band gaps. For the most stable (001) surface, CO2 chemisorption to form carbonate species is exothermic by -0.60 eV with a negligible energy barrier of 0.07 eV, whereas O2 chemisorption to form peroxide species is endothermic by 0.64 eV with a considerable energy barrier of 1.29 eV. For the slightly less stable (011) surface, both CO2 and O2 chemisorption can occur at different surface sites, and the same applies to the other studied surfaces. Dissociation temperatures of surface carbonate species range from 300 to 1000 K at pCO2 of 1 bar, which follow the order of (101) ≈ (110) > (111) ≈ (100) ≈ (011) ≫ (001), showing their strong sensitivity to the surface structure. Dissociation temperatures of surface peroxide species are mostly lower than the room temperature except for those of the (011) and (111) surfaces, although the significant kinetic barriers predicted should prevent their facile dissociation. Insights into the temperature-programmed desorption experiments and the methane reactivity of La2O3 in the OCM reaction were also given based on the results of our calculations.

Corrosion Protection of Transport Vehicles by Nanocoating of Decahydrobenzo[8]annulene-5,10-dihyrazone in Corrosive Environments and Weather Change

Transport industries use epoxy-coating for corrosion protection of stainless steel but this coating cannot provide protection in long duration in H2O, O2 (moist), CO2 and SO2 environment and weather change. Pollutants can create acidic medium for epoxy-coated stainless steel. These corrosive agents penetrate epoxy-coating by osmosis or diffusion process produce and produce chemical and corrosion reactions with base metal. These reactions enhance internal and external corrosion and accelerate internal disbonding in epoxy-coating and disintegrate base metal. This coating does not protect themselves and base metal. These pollutants and weather change elevate galvanic, pitting, stress, crevice, intergranular, blistering and embrittlemint corrosion whereas epoxy polymer exhibits swelling and dissolving corrosion. Pollutants and weather change can alter their physical, chemical and mechanical properties and tarnish their facial appearance. They can also change morphology epoxy-coated stainless steel. Corrosion mitigation of epoxy-coated stainless steel in ambient of H2O, O2(moist), CO2 and SO2 and weather change used Nano coating and filler technology. For this work decahydrobenzo[8]annulene-5,10-dihydrazone and SiC used as Nano coating and filler materials. Nano coating and filling work were completed by nozzle spray The corrosion rate of epoxy-coated stainless steel coupons was determined at 278, 283, 288, 293 and 2980K temperatures and times mentioned at these temperatures was 24, 48, 72, 96 and 120 h in different weather without coating and with Nano coating of decahydrobenzo[8]annulene-5,10-dihydrazone and SiC filler by help of weight loss experiment. Corrosion potential and corrosion current were determined by potentiostat. Coating efficiency and surface coverage area were calculated by gravimetric methods. The surface composite barrier formation was studied by activation energy, heat of adsorption, free energy, entropy and enthalpy.

Is Steam an Oxidant or a Reductant for Nickel/Doped-Ceria Cermets?

Nickel/doped‐ceria composites are promising electrocatalysts for solid‐oxide fuel and electrolysis cells. Very often steam is present in the feedstock of the cells, frequently mixed with other gases, such as hydrogen or CO2. An increase in the steam concentration in the feed mixture is considered accountable for the electrode oxidation and the deactivation of the device. However, direct experimental evidence of the steam interaction with nickel/doped‐ceria composites, with adequate surface specificity, are lacking. Herein we explore in situ the surface state of nickel/gadolinium‐doped ceria (NiGDC) under O2, H2, and H2O environments by using near‐ambient‐pressure X‐ray photoelectron and absorption spectroscopies. Changes in the surface oxidation state and composition of NiGDC in response to the ambient gas are observed. It is revealed that, in the mbar pressure regime and at intermediate temperature conditions (500–700 °C), steam acts as an oxidant for nickel but has a dual oxidant/reductant function for doped ceria.

Near-infrared uncaging or photosensitizing dictated by oxygen tension.

Existing strategies that use tissue-penetrant near-infrared light for the targeted treatment of cancer typically rely on the local generation of reactive oxygen species. This approach can be impeded by hypoxia, which frequently occurs in tumour microenvironments. Here we demonstrate that axially unsymmetrical silicon phthalocyanines uncage small molecules preferentially in a low-oxygen environment, while efficiently generating reactive oxygen species in normoxic conditions. Mechanistic studies of the uncaging reaction implicate a photoredox pathway involving photoinduced electron transfer to generate a key radical anion intermediate. Cellular studies demonstrate that the biological mechanism of action is O2-dependent, with reactive oxygen species-mediated phototoxicity in normoxic conditions and small molecule uncaging in hypoxia. These studies provide a near-infrared light-targeted treatment strategy with the potential to address the complex tumour landscape through two distinct mechanisms that vary in response to the local O2 environment.

Temperature and reaction atmosphere effects on the properties of corn stover biochar

Biochar properties can vary widely depending on feedstock and processing conditions, which can make meaningful comparisons between biochars difficult. Clear trends can be observed in slow pyrolysis biochar properties over a 300–800°C range of highest treatment temperatures (HTT). These trends, however, are much less consistent for biochars made under slightly oxidizing conditions, such as in gasification and internally‐heated kiln carbonization processes. In this study, slow pyrolysis biochars were produced from corn stover under either pure nitrogen or nitrogen + 5% oxygen atmospheres over a 200–800°C HTT range. For the biochars made at 300 and 400°C, the presence of oxygen in the reaction environment resulted in biochars with properties similar to those of biochars produced at higher HTTs in pure nitrogen. Addition of oxygen has only minor effects on biochar bulk oxygen content or abundance of surface oxygenated functionalities. Thermogravimetric analysis with mass spectroscopy (TGA‐MS) indicated that the apparent increase in HTT for chars made in the O2 environment at 300 and 400°C resulted in the removal of methyl and higher alkyl functionalities in the biomass feedstock. Advanced solid state 13C nuclear magnetic resonance spectroscopy (NMR) methods to quantify carbon functional group abundance and aromaticity supported this observation. Overall, addition of oxygen to the pyrolysis atmosphere will increase pyrolysis process severity but will not create oxygenated groups on biochar surfaces as biochar aging does. © 2016 American Institute of Chemical Engineers Environ Prog, 36: 696–707, 2017

Formation and Evolution of Oxide/Oxyhydroxide Corrosion Products on Low-Alloy Steel During Exposure to Near-Neutral pH Solutions Containing Oxygen and Nitrate

The evolution of corrosion product and the transient behavior of corrosion during the first 24 h of low-alloy steel exposure to near-neutral pH solutions containing O2 and are investigated in this work through periodic electrochemical polarization, spectroscopy, and characterization techniques. The formation of porous FeOOH products occurs a few hours following immersion, with morphologies distinctly dependent on O2 concentration. O2 diffusion is less in the FeOOH tubercle formations formed in 20 ppm O2 conditions, whereas the presence of Fe2O3 is exclusive to corrosion products of 6 ppm O2 environments. Charge transfer on the compounds involved governs corrosion protectiveness trends of the overall multi-layered product and reaction kinetics at sub-tubercle surface sites. Atypical 0.005 M and 0.015 M presence in the environment minimizes the cathodic potential range of O2 reduction and intensifies the corrosion of the low-alloy steel specimen. The chronology of corrosion product evolution is corroborated...

The effects of hypoxia on the stemness properties of human dental pulp stem cells (DPSCs).

Recent studies have demonstrated that culture under hypoxia has beneficial effects on mesenchymal stem cells (MSCs). However, there are limitations to achieving a stable condition in conventional hypoxic CO2 incubators. DPSCs are a unique type of MSCs which are promising in many regenerative therapies. In this study, we investigated the ideal hypoxic culture environment for DPSCs using a new system that can provide controlled O2 environment. The effects of hypoxia (3%, 5%) on the stemness properties of DPSCs. Their morphology, proliferation rate, expression of stem cell markers, migration ability, mRNA expression of angiogenic/neurotrophic factors and immunomodulatory genes were evaluated and compared. Additionally, the effect of the discrete secretome on proliferation, migration, and neurogenic induction was assessed. Hypoxic DPSCs were found to be smaller in size and exhibited larger nuclei. 5% O2 significantly increased the proliferation rate, migration ability, expression of stem cell markers (CXCR4 and G-CSFR), and expression of SOX2, VEGF, NGF, and BDNF genes of DPSCs. Moreover, secretome collected from 5%O2 cultures displayed higher stimulatory effects on proliferation and migration of NIH3T3 cells and on neuronal differentiation of SH-SY5Y cells. These results demonstrate that 5%O2 may be ideal for enhancing DPSCs growth, stem cell properties, and secretome trophic effect.

Regulation of HBEGF by Micro-RNA for Survival of Developing Human Trophoblast Cells.

IntroductionThe growth factor HBEGF is upregulated post-transcriptionally in the low O2 environment of the human placenta during the first 10 weeks of pregnancy. We have examined the possible roles of HBEGF turnover and micro-RNA (miRNA) in its regulation by O2 in human first trimester trophoblast.MethodsHTR-8/SVneo trophoblast cells were cultured at 2% or 20% O2. The cells were transfected with a dual luciferase reporter construct (psiCHECK-2) containing no insert (control), the HBEGF 3’ untranslated region (3’UTR), or sub-regions of the 3’UTR, as well as with siRNA for DGCR8. RNA was extracted from trophoblast cells cultured at 2% O2 for 0–4 h for next-generation sequencing. HBEGF was quantified by ELISA. HBEGF, DGCR8, and β–actin were examined by western blotting.ResultsProtein turnover studies, using 10 μg/ml cyclohexamide, 1 μg/ml lactocystin, or 100 μg/ml MG132, demonstrated faster HBEGF degradation at 20% O2 than 2% O2, mediated by the proteasome. However, proteasome inhibition failed to initiate HBEGF accumulation at 20% O2. Reporter assays, comparing to empty vector, demonstrated that the intact HBEGF 3’ UTR inhibited expression (0.26), while fragments containing only its flanking regions increased reporter activity (3.15; 3.43). No differential expression of miRNAs was found in trophoblast cells cultured at 2% and 20% O2. Nevertheless, HBEGF upregulation at 2% O2 was blocked when the miRNA-processing protein DGCR8 was silenced, suggesting a role for miRNA.ConclusionOur findings suggest involvement of flanking regions of the 3’UTR in activating HBEGF protein synthesis in response to 2% O2, possibly through a miRNA-mediated mechanism.

Development of a ReaxFF Reactive Force Field for the Pt-Ni Alloy Catalyst.

We developed the ReaxFF force field for Pt/Ni/C/H/O interactions, specifically targeted for heterogeneous catalysis application of the Pt-Ni alloy. The force field is trained using the DFT data for equations of state of Pt3Ni, PtNi3 and PtNi alloys, the surface energy of the PtxNi1-x(111) (x = 0.67-0.83), and binding energies of various atomic and molecular species (O, H, C, CH, CH2, CH3, CO, OH, and H2O) on these surfaces. The ReaxFF force field shows a Pt surface segregation at x ≥ 0.67 for the (111) surface and x ≥ 0.62 for the (100) surface in vacuum. In addition, from the investigation of the preferential alloy component of the adsorbates, it is expected that H and CH3 on the alloy surface to induce a segregation of Pt whereas the oxidation intermediates and products such as C, O, OH, H2O, CO, CH, and CH2 are found to induce Ni segregation. The relative order of binding strengths among adsorbates is a function of alloy composition and the force field is trained to describe the trend observed in DFT calculations, namely, H2 < H2O < CH3 ≈ O2 ≈ CO < OH < CH2 < C ≈ CH on Pt8Ni4, H2 < H2O < CO ≈ O2 < CH3 < OH < CH2 < CH < C on Pt9Ni3, and H2 < H2O < O2 < CO < CH3 < OH < CH2 < C ≈ CH on Pt10Ni2. Using this force field, we performed the grand-canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations for a Pt3Ni slab and a truncated cuboctahedral nanoparticle terminated by (111) and (100) faces, to examine the surface segregation trend under different gas environments. It is found that Pt segregates to the alloy surface when the surface is exposed to vacuum and/or H2 environment while Ni segregates under the O2 environment. These results suggest that the Pt/Ni alloy force field can be successfully used for the preparation of Pt-Ni nanobimetallic catalysts structure using GCMC and run MD simulations to investigate its role and the catalytic chemistry in catalytic oxidation, dehydrogenation and coupling reactions. The current Pt/Ni force field still is found to have difficulties in describing the observed segregation trend in Ni-rich alloy compositions (x < 0.6), suggesting the need for additional force field training and evaluation for its application to describe the characteristics and chemistry of Ni-rich alloys.

Metabolic responses to chronic hypoxic incubation in embryonic American alligators (Alligator mississippiensis)

Chronic hypoxic incubation is a common tool used to study developmental changes in reduced O2 conditions, and it has been useful for identifying phenotypically plastic periods during ontogeny in laboratory settings. Reptilian embryos can be subjected to natural hypoxia due to nesting strategy, and recent studies have been important in establishing the phenotypic responses of several species to low developmental oxygen. In particular, the cardiovascular responses of American alligators (Alligator mississippiensis) to low developmental oxygen have been detailed, including a substantial cardiac enlargement that may support a higher mass specific metabolic rate. However, embryo mass-specific metabolic demands of hypoxic incubated alligator embryos have not been measured. In this study, alligator eggs were incubated in 10% O2 (H) or 21% O2 (N) environments for the entire course of embryonic development. Acute metabolic measures in 21% and 10% O2 were taken for both H and N groups. We hypothesized that acute 10% O2 exposure has no impact on metabolic rate of embryonic alligators, and that metabolic rate is unaffected by chronic hypoxic incubation when studied in embryos measured at 21% O2. Our findings suggest phenotypic changes resulting from hypoxic incubation early in incubation, in particular relative cardiac enlargement, enable embryonic alligators to sustain metabolic rate during acute hypoxic exposure.

Thermal and Chemical Stability of n-Hexadecanethiol Monolayers on Au(111) in O2 Environments

Understanding the mechanisms of degradation of self-assembled monolayers (SAM) is required for their use in molecular devices and in general in long term applications. In this context, we investigated the thermal and chemical stability of n-hexadecanethiolate (C16T) monolayers on Au(111) exposed to O2. The degradation of the monolayers was followed by electrochemical (EC) techniques, surface enhancement Raman spectroscopy (SERS) and high resolution photoemission spectra (HR-XPS). The C16T monolayers were heated both under N2 and O2 flux up to 480K for different times. The degradation of the SAM in the presence of O2 is characterized by the appearance of oxidized sulfur species and sulfur atoms on the surface. The formation time in the dipping solution also affects the thermal stability of the monolayer. Molecular dynamics (MD) simulations and density functional theory (DFT) calculations were performed to elucidate the possible degradation mechanisms. MD shows that O2 molecules easily penetrate the monolayer reaching the Au surface. The DFT calculations identified two oxidation mechanisms which involve the S atom and the alpha carbon of the alkylthiolate. Both mechanisms are very exothermic. The oxidation of the sulfur atom produces a sulfinate which does not alter the monolayer structure. On the contrary, the oxidation of the alpha carbon induces the breakage of the SC bond, the adsorption of atomic S and the desorption of the alkyl chain as an aldehyde.

Observation of Titania and Titanate Phase Changes in Oxidation-Controlled ZnO/TiN and HfO2/TiN Thin Films: An X-ray Absorption Spectroscopy Study

We investigated the local electronic structures of oxidation-controlled TiN thin films for preparation of photocatalytic titania using soft X-ray absorption spectroscopy. It is shown that the TiN layers on top of oxides, such as HfO2 or ZnO, are easily oxidized by heat during postdeposition annealing (PDA) so as to form nitrogen-incorporated titania (N-TiO2). The local structures of the oxidized films evolved significantly depending on the bottom oxide and the PDA conditions; when TiN was deposited on HfO2, which is less reactive than ZnO, PDA at 700 °C stabilized a mixture of rutile and anatase phases under almost any gas (N2 or O2) environments. On the other hand, when TiN was deposited on ZnO, which is reactive enough to oxidize the TiN layers substantially, the PDA resulted in a rich phase diagram according to the gas environment: under N2 environment, an anatase local structure is dominant, whereas under O2 environment, a rutile or yet another local structure with a high symmetry, for example, perovs...

Highly spatially resolved structural and optical investigation of Bi nanoparticles in Y-Er disilicate thin films

Er-containing silicon compatible materials have been widely used as infrared emitters for microphotonics application. In this field, the additional introduction of a proper sensitizer permits to increase the Er excitation cross sections, thus increasing its optical efficiency. This work aims to investigate the influence of a post-transition metal, bismuth, on the optical properties of erbium-yttrium disilicate thin films synthesized by magnetron co-sputtering. After thermal treatments at 1000 °C in O2 or N2 environment, the presence of small precipitates, about 6 nm in diameter, was evidenced by transmission electron microscopy analyses. The spatially resolved chemical nature of the nanoparticles was discerned in the Si and O rich environments by means of scanning transmission electron microscopy–energy dispersive X-ray and scanning transmission electron microscopy–electron energy loss spectroscopy analyses performed with nanometric resolution. In particular, metallic Bi nanoparticles were stabilized in the N2 environment, being strongly detrimental for the Er emission. A different scenario was instead observed in O2, where the formation of Bi silicate nanoparticles was demonstrated with the support of photoluminescence excitation spectroscopy. In particular, a broad band peaked at 255 nm, correlated to the excitation band of Bi silicate nanoparticles, was identified in Er excitation spectrum. Thus Bi silicate clusters act as sensitizer for Er ions, permitting to improve Er emission up to 250 times with respect to the resonant condition. Moreover, the Er decay time increases in the presence of the Bi silicate nanoparticles that act as cages for Er ions. These last results permit to further increase Er optical efficiency in the infrared range, suggesting (Bi + Er)-Y disilicate as a good candidate for applications in microphotonics.

The target heating influence on the reactive magnetron sputtering process

A physicochemical model for the reactive magnetron sputtering of a “hot” target is described in this paper. The system consisting of eight algebraic equations was solved for a tantalum target sputtered in an O2 environment. It was established that the hysteresis effect disappears with the increase of the ion current density.

Rapid thermal annealing induced modification in structural and electronic structure properties of Ti0.95Co0.05O2⿿δ thin films

Thin film of Ti0.95Co0.05O2-δ was deposited on Si (100) using PLD method and annealed in O2 and N2 environment. Raman spectra confirm that all the films have rutile structure. Surface morphology indicates that the surface roughness and grain size increase with annealing. The electronic structure studied by NEXAFS spectroscopy at O K, Ti L3,2 and Co L3,2-edges revealed that peak intensities decrease significantly for the film annealed N2 environment. The ligand-field splitting estimated from the energy difference between the t2g and eg features in O K-edge spectra were 2.71eV for as-deposited and O2 annealed film, whereas reduced more than double (⿼1.32eV) for the film annealed in N2. Atomic multiplet calculations and experimentally observed NEXAFS spectra at Co L3,2-edge and Ti L3,2-edge confirm that Co present in 2+ and Ti in +4 valence state, whereas the multiplet structures of O2 annealed film looks similar to Co metal.

Anti-Müllerian hormone promotes pre-antral follicle growth, but inhibits antral follicle maturation and dominant follicle selection in primates.

What are the direct effects and physiological role of anti-Müllerian hormone (AMH) during primate follicular development and function at specific stages of folliculogenesis? AMH actions in the primate ovary may be stage-dependent, directly promoting pre-antral follicle growth while inhibiting antral follicle maturation and dominant follicle selection. AMH is expressed in the adult ovary, particularly in developing follicles. Studies in mice suggest that AMH suppresses pre-antral follicle growth in vitro, and inhibits primordial follicle recruitment and FSH-stimulated antral follicle steroidogenesis. For in vitro study, secondary follicles were isolated from ovaries of 12 rhesus macaques and cultured for 5 weeks. For in vivo study, intraovarian infusion was conducted on five monkeys for the entire follicular phase during two spontaneous menstrual cycles. For in vitro study, individual follicles were cultured in a 5% O2 environment, in alpha minimum essential medium supplemented with recombinant human FSH. Follicles were randomly assigned to treatments of recombinant human AMH protein or neutralizing anti-human AMH antibody (AMH-Ab). Follicle survival, growth, steroid production, steroidogenic enzyme expression, and oocyte maturation were assessed. For in vivo study, ovaries were infused with control vehicle or AMH-Ab during the follicular phase of the menstrual cycle. Cycle length, serum steroid levels, and antral follicle growth were evaluated. AMH exposure during culture weeks 0-3 (pre-antral stage) promoted, while AMH-Ab delayed, antrum formation of growing follicles compared with controls. AMH treatment during culture weeks 3-5 (antral stage) decreased (P < 0.05) estradiol (E2) production, as well as the mRNA expression of cytochrome P450 family 19 subfamily A polypeptide 1, by antral follicles relative to controls, whereas AMH-Ab increased (P < 0.05) follicular mRNA levels of the enzyme. Intraovarian infusion of AMH-Ab during the follicular phase of the menstrual cycle increased (P < 0.05) the average levels of serum E2 compared with those of the control cycles. Three of the five AMH-Ab-treated ovaries displayed multiple (n = 2-9) medium-to-large (2-8 mm) antral follicles at the mid-cycle E2 peak, whereas only one large (4-7 mm) antral follicle was observed in all monkeys during their control cycles. The average levels of serum progesterone were higher (P < 0.05) during the luteal phase of cycles following the AMH-Ab infusion relative to the vehicle infusion. The in vitro study of AMH actions on cultured individual macaque follicles was limited to the interval from the secondary to small antral stage. A sequential study design was used for in vivo experiments, which may limit the power of the study. The current study provides novel information on direct actions and role of AMH during primate follicular development, and selection of a dominant follicle by the late follicular phase of the menstrual cycle. We hypothesize that AMH acts positively on follicular growth during the pre-antral stage in primates, but negatively impacts antral follicle maturation, which is different from what is reported in the mouse model. NIH NICHD R01HD082208, NIH ORWH/NICHD K12HD043488 (BIRCWH), NIH OD P51OD011092 (ONPRC), Collins Medical Trust. There are no conflicts of interest. Not applicable.

Failure Mechanism Associated with the Thermally Grown Silica Scale in Environmental Barrier Coated C/SiC Composites

The barium strontium aluminosilicate and Y2Si2O7‐BSAS‐coated C/SiC composites were corroded in 50%H2O–50%O2 environments at 1250°C, respectively. It was found that the coated composites suddenly lost their strength as the corrosion time was up to 250 and 750 h, respectively. During the water vapor corrosion, a continuous silica scale was formed between the SiC bond coat and environmental barrier coatings, leading to the growth stress. The thickness of silica scale grew with the prolonged corrosion time, accompanied with the accumulation of growth stress in the silica scale. When the growth stress was greater than the bond strength between silica scale and SiC bond coat, the cracks would form and propagate along their interface, resulting in the spallation of EBCs, followed by the failure of the composites.

Thermal degradation kinetics of sawdust under intermediate heating rates

In this work, thermal degradation behavior of sawdust under N2 and O2 environments were investigated to derive the kinetics parameters. Thermogravimetric analysis was carried out at various intermediate heating rates (140–200°C/min). Kinetic parameters were calculated using Kissinger–Akahira–Sunose and Flynn–Wall–Ozawa models. It was found that the activation energy of both pyrolysis and oxycombustion were different from previous studies. Higher heating rate affected not only the temperature at maximum weight loss, but also the apparent activation energy in any conversions of biomass due to pyrolysis and oxycombustion. Activation energy of sawdust pyrolysis appeared to peak around 40–50% conversions while oxycombustion did around 15–25%. The activation energy was found to be in the range between 35–110kJ/mol and 35–129kJ/mol for pyrolysis and oxycombustion, respectively.

Catechol degradation on hematite/silica-gas interface as affected by gas composition and the formation of environmentally persistent free radicals.

Environmentally persistent free radicals (EPFRs) formed on a solid particle surface have received increasing attention because of their toxic effects. However, organic chemical fate regulated by EPFRs has rarely been investigated, and this information may provide the missing link in understanding their environmental behavior. Previous studies have suggested that the reduction of transition metals is involved in EPFRs formation. We thus hypothesize that an oxidative environment may inhibit EPFRs formation in particle-gas interface, which will consequently release free radicals and accelerate organic chemical degradation. Our result indicates that a 1% hematite coating on a silica surface inhibited catechol degradation in N2, especially at low catechol loadings on solid particles (SCT). However, under an O2 environment, catechol degradation decreased when SCT was <1 μg/mg but increased when SCT was >1 μg/mg. Stable organic free radicals were observed in the N2 system with g factors in the 2.0035–2.0050 range, suggesting the dominance of oxygen-centered free radicals. The introduction of O2 into the catechol degradation system substantially decreased the free radical signals and decreased the Fe(II) content. These results were observed in both dark and light irradiation systems, indicating the ubiquitous presence of EPFRs in regulating the fate of organic chemicals.

Discovery and dissection of metabolic oscillations in the microaerobic nitric oxide response network of Escherichia coli

The virulence of many pathogens depends upon their ability to cope with immune-generated nitric oxide (NO·). In Escherichia coli, the major NO· detoxification systems are Hmp, an NO· dioxygenase (NOD), and NorV, an NO· reductase (NOR). It is well established that Hmp is the dominant system under aerobic conditions, whereas NorV dominates anaerobic conditions; however, the quantitative contributions of these systems under the physiologically relevant microaerobic regime remain ill defined. Here, we investigated NO· detoxification in environments ranging from 0 to 50 μM O2, and discovered a regime in which E. coli NO· defenses were severely compromised, as well as conditions that exhibited oscillations in the concentration of NO·. Using an integrated computational and experimental approach, E. coli NO· detoxification was found to be extremely impaired at low O2 due to a combination of its inhibitory effects on NorV, Hmp, and translational activities, whereas oscillations were found to result from a kinetic competition for O2 between Hmp and respiratory cytochromes. Because at least 777 different bacterial species contain the genetic requirements of this stress response oscillator, we hypothesize that such oscillatory behavior could be a widespread phenomenon. In support of this hypothesis,Pseudomonas aeruginosa, whose respiratory and NO· response networks differ considerably from those of E. coli, was found to exhibit analogous oscillations in low O2 environments. This work provides insight into how bacterial NO· defenses function under the low O2 conditions that are likely to be encountered within host environments.