Optimal Oxygen Concentration Research Articles

Two new species of microaerophilic sulfur spirilla, Spirillum winogradskii sp. nov. and Spirillum kriegii sp. nov.

New microaerophilic sulfur-oxidizing spirilla were isolated from hydrogen sulfide sludge of wastewater treatment plants. Strains D-427 and D-430 have spiral cells that are highly motile due to bipolar flagellum bundles covered with mucous sheaths. Under a phase-contrast microscope, these bundles are visible as single polar flagella. Spheroplasts are formed in the stationary growth phase. Both strains are obligate organotrophs able to oxidize a number of reduced sulfur compounds. The oxidation of sulfide and polysulfide leads to the formation of intracellular globules of elemental sulfur; thiosulfate oxidation results in tetrathionate accumulation in the medium. The cells are unable to utilize reduced sulfur compounds in the energy metabolism; their oxidation is caused by a chemical interaction with H2O2 and O2, synthesized in the electron transport chain. Both strains are obligate microaerophiles with an optimal oxygen concentration in the gas phase of 2 and 0.8% for strains D-427 and D-430, respectively. The strains utilize a limited number of organic acids as growth substrates, mainly tricarboxylic-acid-cycle intermediates. The DNA G+C content is 38.0 mol % (T(m)) for strain D-427 and 38.9 mol % for strain D-430. Phylogenetic analysis, based on the comparison of 16S rRNA gene sequences, revealed that the new isolates of sulfur spirilla are the most closely related to Spirillum volutans, the type species of the genus (97.4% similarity). They were assigned to the genus Spirillum within the class Beta-proteobacteria as two new species, S. winogradskii sp. nov. (D-427T = DSM 12756T) and S. kriegii sp. nov. (B-430T = BKM B-2372T). The emended description of the genus Spirillum is provided.

Optimal oxygen concentration for the detection of single indocarbocyanine molecules in a polymeric matrix

The problem of oxygen influence on the triplet quenching and photobleaching of a single dye molecule embedded in a polymer matrix was investigated. Indocarbocyanine in polymethylmetacrylate was used as a model system. A well-chosen amount of oxygen in the gaseous environment above the sample was shown to efficiently improve the conditions for the single molecule detection. Experiments on molecular ensembles suggest this amount to be close to 2% of oxygen in an otherwise inert atmosphere.

Cellular Reaction to Hypoxia: Sensing and Responding to an Adverse Environment

Multicellular organisms have developed sophisticated physiologic mechanisms by which they maintain their tissues at the optimal oxygen concentration. This level is important so that the benefits of free oxygen can be realized, while limiting the potential harms. Despite these efforts, there exist physiologic and pathophysiologic conditions where oxygen delivery drops below what is necessary for the tissue. Under these circumstances, the cell then goes through a series of coordinated responses in a time and oxygen concentration-dependent manner. The gene expression changes are designed to maintain cellular and tissue viability, and are comprised of transcriptional as well as post-transcriptional events. As we understand more about the hypoxic response, we realize how it can impact normal development, wound healing, and the malignant progression of a solid tumor.

Room air resuscitation—two decades of neonatal research

Experimental as well as clinical studies have demonstrated that room air is as efficient as pure oxygen for newborn resuscitation. Recent data even indicate that outcome is improved if pure oxygen is avoided. Thus, in a meta-analysis, neonatal mortality was significantly lower in those newly born infants resuscitated with 21% than with 100% oxygen. Short-term recovery is also improved in the room air group since time to first breath is shorter, heart rate at 90 s and 5 min Apgar score are higher. Animal data indicate that injury in a number of organs, including the brain, is aggravated by giving pure oxygen to newly born depressed infants even for a brief period. Although the optimal oxygen concentration probably is not known for newborn infants in need of resuscitation, pure oxygen should be avoided. These data should be reflected in new guidelines that are under way.

HgO-added YBa2Cu3O7−δ superconductors

The HgO-added YBa2Cu3O7−δ (YBCO) superconductor has been studied for its structural and superconducting properties. Polycrystalline YBCO samples were synthesized through solid-state reaction method by adding HgO in different concentrations without using oxygen annealing. All the samples showed a sharp superconducting transition temperature around 90 K. The X-ray diffraction patterns of all the samples revealed monophasic Y-123 nature. The structural studies were carried out by neutron scattering and Rietveld analysis. The neutron scattering revealed that Hg is not incorporated in the Y-123 system and has shown optimum oxygen concentration. The significant role played by the HgO is to provide oxygen ambient through its decomposition, thus changing the oxygen balance in favour of high Cu-valence state.

Effects of the plasma oxygen concentration on the formation of SiO xC y films by low temperature PECVD

Experiments were made to produce SiO x C y coatings by PECVD on polycarbonate substrates at a temperature below 80 °C, using a gaseous mixture of methyltrimethoxy-silane (MTMOS) [CH 3Si(OCH 3) 3] with O 2 and CH 4. Under those conditions, the effects of the oxygen concentration in the plasma on the film thermal shock and long-term stability, hardness and growth rate were studied using Fourier transform infrared absorption spectrocopy (FTIR) and optical emission spectroscopy (OES). It is concluded that for given deposition conditions there is an optimum oxygen concentration in the plasma compatible with films presenting a best compromise in terms of the indicated properties, which is determined essentially by a competition between the reaction rates at the substrate surface for Si–O–Si formation and Si–OH elimination by dehydration reactions, and the deposition rate of silanol groups formed in the plasma phase. The overall results suggest that this competition is sensitive to the plasma electron temperature.

In vivo fractional P(i) absorption and NaPi-II mRNA expression in rainbow trout are upregulated by dietary P restriction.

Mammalian type II sodium-phosphate cotransporter (NaPi-II) and inorganic phosphate uptake stimulator (PiUS) genes are upregulated by dietary phosphorus (P) restriction to increase intestinal and renal P transport, but little is known about NaPi-II and PiUS regulation in other vertebrates. We studied the 1). the tissue distribution and dietary regulation of NaPi-II, PiUS, and sodium-glucose cotransporter (SGLT1) mRNA and NaPi-II protein in juvenile rainbow trout (Oncorhynchus mykiss) and 2). effects of dietary P on intestinal Pi absorption in vivo. NaPi-II, PiUS, and SGLT1 mRNA were found in the proximal and distal intestine, pyloric ceca, and kidney. PiUS mRNA was also found in the heart, gill, blood, stomach, liver, skin, and muscle. Tissue distribution of NaPi-II protein correlated with that of NaPi-II mRNA except in gill ionocytes where NaPi-II antibodies recognized related epitopes. Chronic consumption of a low-P diet increased NaPi-II and PiUS but not SGLT1 mRNA abundance in the intestine and kidney. Unlike mammals, there was no detectable shift in tissue or cellular localization of NaPi-II protein in response to dietary P restriction. Regulation of NaPi and PiUS mRNA expression was observed only in fish grown under optimal aqueous oxygen concentrations. In vivo fractional absorption of Pi by the intestine decreased in fish fed high-P diets. Decreases in absorption were less pronounced in fish previously fed low-P diets, suggesting that diet history modulates acute regulation of P absorption. Regulation of dietary Pi absorption in vivo may involve a specific change in intestinal NaPi-II and PiUS gene expression.

Reduction of Nitric Oxide from Combustion Flue Gas by Bituminous Coal Char in the Presence of Oxygen

A detailed parametric study quantifying the effect of various operating parameters on the reduction of nitric oxide (NO) in the presence of oxygen by inexpensive carbons was carried out. The selectivity of the carbon−NO reaction over the parasitic carbon−oxygen reaction was measured by a global selectivity parameter, defined as milligrams of NO reduced per gram of carbon consumed. An increase in the reaction temperature, bed height, and inlet NO concentration leads to a higher selectivity factor. However, there exists an optimum particle size of carbon that maximizes this selectivity. Whereas, in the absence of oxygen, the rate of the carbon−NO reaction was insignificant, the presence of oxygen in the inlet creates active sites that convert NO to nitrogen. An optimum inlet oxygen concentration provided the highest degree of NO reduction. The operating conditions can be selected to achieve >90% NO reduction at a selectivity of 60−100 mg of NO reduced/g of carbon.

Synthesis, Structure, and Electrochemistry of Acetylide and Oxo Incorporated Mixed Fe/Mo and Fe/W Chalcogen-Bridged Clusters

Thermolysis of a benzene solution containing [Fe2Mo(CO)10(μ3-Se)2] (1) and [(η5-C5Me5)W(CO)3C⋮CPh] (2) under an optimum concentration of oxygen in the reaction medium yields the cluster [(η5-C5Me5)MoWFe2(O)(μ3-Se)(μ4-Se)(CO)8(CCPh)] (3), containing a monooxygenated metal center. Under an argon atmosphere, thermolysis of [Fe2Mo(CO)10(μ3-S)2] (4) with [(η5-C5Me5)W(CO)3C⋮CPh] (2) in benzene leads to an oxygen-free mixed metal cluster [(η5-C5Me5)MoWFe4(μ3-S)3(μ4-S)(CO)14(CCPh)] (9). Interestingly, on reacting a benzene solution of 4 with 2 and [(η5-C5Me5)Mo(CO)3C⋮CPh] (5) under an increased concentration of oxygen in the reaction medium gave way to clusters [(η5-C5Me5)WMo2(μ-O)2(μ-S)(μ3-CCPh){Fe2(CO)6(μ3-S)2}2] (6), [(η5-C5Me5)WMo(O)2(μ-O)(μ-CCPh){Fe2(CO)6(μ3-S)2}] (7), and [(η5-C5Me5)Mo3(μ-O)2(μ-S)(μ3-CCPh){Fe2(CO)6(μ3-S)2}2] (8) with higher oxygen content. The structures of the newly formed clusters 3, 6, 7, 8, and 9 were established crystallographically and the oxo-containing Mo and W clusters investigated electrochemically.

Influence of oxygen tension on apoptosis and hatching in bovine embryos cultured in vitro

Various oxygen tensions are employed for in vitro embryo production. Since it is known that oxygen tension can influence the efficiency of embryo production and embryo quality, the aim of our study was to define an optimal oxygen concentration for bovine embryo production in vitro in synthetic oviduct fluid (SOF). Embryo quality criteria were hatching ability and the degree of apoptosis as assessed by TUNEL staining and Bax gene expression. In Experiment 1, the effects of 2, 5 and 20% O2 tensions on embryo development were compared. The highest rate of eight-cell embryos (47%) at 72hpi was obtained under 20% O2. However, it seemed that 2 and 5% O2 were also suitable as assessed by embryo survival rates at 144hpi (29 and 30% at morula stage), 168hpi (21 and 19% at blastocyst stage) and 216hpi (14 and 17% at hatched blastocyst stage). In Experiment 2, comparisons were made between effects of 5, 20% and alternating O2 (20% O2 to 72hpi and then changed to 5% O2 up to 216hpi) on embryo development. Alternating the O2 tension significantly reduced the number of hatching blastocysts to 7%. Staining with TUNEL revealed that apoptosis occurred in all tested hatched blastocysts, but a significantly lower apoptotic cell ratio was found in embryos cultured under 5% O2 (P<0.05). Total cell number of embryos cultured under 5% and alternating oxygen was significantly higher than that of other groups (P<0.05). Bax gene expression was detected by means of RT–PCR in only 2 of 66 hatched blastocysts. It can be concluded that 5% oxygen is optimal for bovine embryo culture in cell free media. Moreover, it is very likely that the apoptosis detected by TUNEL staining in this study is Bax-independent.

Oxygen driven reconstruction dynamics of Ni(977) measured by time-lapse scanning tunneling microscopy

Time-lapse scanning tunneling microscopy (STM) has been used to observe the oxygen induced reconstruction behavior of Ni(977), a stepped metallic surface. Previous studies using helium atom diffraction resolved the macroscopic kinetics for the reversible step-doubling and -singling of this vicinal surface. Sequential STM imaging recorded at elevated temperature has now elucidated atomic-level mechanistic details for the merging of steps in the presence of small amounts of adsorbed oxygen, less than 2% of a monolayer. Point contact between neighboring steps decorated with chemisorbed oxygen facilitates rapid step coalescence by means of zippering. An optimal oxygen concentration of step edge saturation was found to enable the step merging to proceed most rapidly. Excess oxygen was found to hinder the coalescence of neighboring steps through the possible growth of overlayer structures on the terraces. At sufficiently high temperatures, the surface is driven back to single steps due to oxygen dissolution. The departure of oxygen from the surface through dissolution, as well as the associated presence of oxygen in the selvedge region, may both play a role in destabilizing the double steps. Local step density influences the coalescence behavior by defining the number of available step edge sites. The microscopic details made available by time-resolved STM imaging illuminate some of the mechanistic steps related to the initial stages of metallic oxidation, and the sensitivity of surface morphological transformations to local surface structure and adsorbate coverage.

Optimum oxygen concentration for the optoelectronic properties of IR sensitive VOx thin films

VO x films were fabricated on thermally grown SiO 2 layers by reactive r.f. sputtering at room temperature. The working pressure was 5 mTorr, adjusted by changing Ar and O 2 flow from 1:1 to 10:1. Post annealing was performed at the temperatures of 200°C, 300°C, 400°C, 450°C, and 500°C. Electrical resistivities of VO x films were measured at various temperatures from 25°C to 80°C and the temperature coefficient of resistance (TCR) was calculated for each film. The resistivity decreases with the increase of the annealing temperature and shows two steps of critical drops at 300°C and 450°C, respectively. This is attributed to the phase transitions of the as-deposited VO x as characterized by X-ray diffraction (XRD). Considering both the TCR and resistivities, it is concluded that the optimum oxygen concentration, x in the VO x films approaches to 2.25 (V 4 O 9 ).

Microaerophilic bacterial biomass measurements based on Adenosine Triphosphate and direct counting techniques in a semi-solid agar column

Microaerophilic-diazotrophic bacterial biomass was measured by Adenosine Triphosphate (ATP) extraction and direct counting/biovolume techniques. Microaerophilic bacterial growth in a semi-solid agar column is visible in the form of sharp, well-defined growth rings at different depths within the column according to oxygen requirements. The microaerophilic zone is found between 3 and 15 mm below the agar surface, where the dissolved oxygen concentration varies from 4 to 172 µM. Biomass measurements calculated using a conventional conversion factor C/ATP of 250 were around ten times lower than those calculated according to the direct counting/biovolume technique. In the present study, we propose a conversion factor of 356 µg C/mL ATP that gives biomass measurements nearer to those obtained by direct counting. The highest bacterial metabolic activity was found between 5 and 10 mm depth (0.15 ± 0.029 µg ATP mL–1), coinciding with optimum oxygen concentration levels for microaerophilic growth (6.5 to 114 µM).

Variations of the leakage current density and the dielectric constant of Pt/(Ba,Sr)TiO3/Pt capacitors by annealing under a N2 atmosphere

This article reports variations of the leakage current density of Pt/40 nm-(Ba,Sr)TiO3/Pt capacitors after annealing under a N2 atmosphere containing oxygen of about 0.01 ppm. Annealing a capacitor under a N2 atmosphere at 750 °C for 30 min results in an increase of the leakage current density at 1.5 V by more than six orders of magnitude compared to that of a capacitor annealed under the optimum oxygen concentration (about 5% in O2) at the same temperature. The dielectric constant was decreased after annealing under the N2 atmosphere. The composition of (Ba,Sr)TiO3 (BST) films, measured by Auger electron spectroscopy, did not show any difference between the two samples. The major reason for the huge increase in the leakage current density is due to the roughening of top Pt electrodes by the annealing under N2 atmosphere. Such roughening imposes a strong stress to the BST film surface and generates surface trap states. The stress-induced trap states reduce the interfacial potential barrier height for Schottky emission and result in increased leakage current densities. Capping of the top Pt electrode with a very thin BST layer (about 10 nm) before the annealing eliminates surface roughening, preserves a low leakage current level, and increases dielectric constants.

Effects of the O2 concentration on the removal efficiency of volatile organic compounds with dielectric barrier discharges in Ar and N2

This article presents experimental results on the effects of the O2 concentration on the removal efficiency of two exemplaric volatile organic compounds (VOCs): toluene (TOL) and trichloroethylene (TCE), with dielectric barrier discharges in dry Ar and N2. For both carrier gases, there is an optimal oxygen concentration of 0.3% for the removal efficiency, suggesting optimal utilization of oxygen radicals for VOC attack, rather than ozone production which has slow reaction rates with TOL and TCE. This is manifested by measurements of ozone concentrations in mixtures of Ar/O2/TCE as a function of the oxygen concentration, showing a minimum at maximal removal efficiencies. All results are discussed in terms of changes in the discharge behavior, radical formation, and chemical reaction pathways with changing O2 concentration in the carrier gas.

Responses of tomato seeds to osmoconditioning as related to temperature and oxygen

AbstractUntreated (control) tomato seeds germinated at temperatures ranging from 15 to 35°C. There was a positive linear relationship between the rate of germination (expressed as the reciprocal of time to obtain 50% germination) and temperature up to the thermal optimum. At higher temperatures, the negative relationship was also linear. The thermal optimum for seed germination was 27–28°C and the lower and maximal temperatures were around 9 and 40°C, respectively. Germination was strongly reduced in atmospheres containing less than 10% oxygen. After pretreatment at 15°C in a polyethylene glycol-8000 solution at –1.0 MPa, seeds germinated faster in a wider range of temperatures, and this stimulatory effect remained after drying back the seeds. Such a pretreatment did not change the optimal and maximal temperatures of germination, but decreased the lower temperature to about 6°C. The beneficial effect of osmoconditioning increased as the duration of the treatment increased and was maximal after 5–7 days. Osmotic pretreatment also reduced the sensitivity of seeds to oxygen deprivation; 50% of the seeds germinated within 7 days in 5% oxygen. The range of temperatures and the concentrations of oxygen which were effective in osmoconditioning were very similar to those which allowed the germination of untreated seeds. In particular, the optimal temperature (27–28°C) and oxygen concentrations (more than 10%) for osmoconditioning and germination were the same. These results confirm that the beneficial effect of osmotic pretreatment (priming) corresponds to the realization of germinationsensu stricto(phase II of the germination process).

Oxidative dehydrogenation of iso-butane to iso-butene I. Metal phosphate catalysts

Metal pyrophosphates catalyse the oxidative dehydrogenation of iso-butane to iso-butene at 450–550°C using a feed gas of 75 mol% iso-butane and 5% O 2. Ni 2P 2O 7 is the most selective catalyst with the iso-butene selectivity reaching to a maximum value of 82.2% at 550°C. Ag 4P 2O 7 and Zn 2P 2O 7 are also effective, but the iso-butene selectivities were slightly lower than that of Ni 2P 2O 7. Pyrophosphates of Mg, Cr, Co, Mn, and Sn catalyse the oxidative dehydrogenation, but the iso-butene selectivity was 43.8–65.7% at the temperature where the maximum iso-butene yield is observed. The optimum oxygen concentration for iso-butene formation was 5–15 mol%, but the increase in O 2 concentration did not increase the iso-butene selectivity. No adsorbed oxygen species was found by means of TPD. The lattice oxygen of the pyrophosphates began to react with H 2 at 200–400°C. Reactivity of the lattice oxygen of pyrophosphates can be estimated from the value of ΔH f 0 for the corresponding oxide. More than 2 desorption peaks were observed in the TPD spectra of NH 3 adsorbed on the pyrophosphates, and a linear correlation was found between the concentration of acid amount of the catalysts and the specific rate of iso-butene formation. This strongly suggests that the acidic sites play a key role in the iso-butene formation.

Influence of the deposition conditions of SnO2 thin films by reactive sputtering on the sensitivity to urban pollutants

Abstract Thin films of SnO 2 were deposited by r.f. magnetron sputtering from a SnO 2 target varying the oxygen concentration from 0 to 20% within the sputtering plasma. The samples were characterized by electrical conductivity measurements for different pollutant gas mixtures. The electrical measurements were performed in a temperature range between 100 and 350°C with NO 2 concentrations varying from 50 to 800 ppb and also with interference gases such as CO (10 ppm) and H 2 O (∼1–80%). The aim of the work was to determine the optimum concentration of oxygen introduced in the sputtering plasma to obtain the best response to these gases on using tin oxide as gas sensor. Techniques such as XPS and GAXRD were used to study the influence of the deposition parameters on the stoichiometry and morphology of the SnO 2 thin films. It was observed that thin films deposited at room temperature and with the sputtering plasma containing 8% of O 2 showed the best sensitivity values, and therefore, the optimum number of adsorption sites needed for a good gas adsorption. These sensors had a SnO 2 grain size of ∼5 nm, all of them were substoichiometric before the thermal treatment and the film growth was columnar. A selective response to NO 2 and CO/air mixtures can be achieved by suitable choice of the sensor operating temperature. The results obtained with a relative humidity (∼1–80%) on the sensitivity to low NO 2 concentrations need further investigation due to the large interference effect of water vapor shown at all operating temperatures.

Role of oxygen tension during cartilage formation by periosteum.

Tissue engineering makes regeneration of cartilage possible but requires optimization of culture conditions. The effects of oxygen tension on cartilage metabolism are controversial in the literature, and we could find no information detailing the optimal oxygen concentration for growing new cartilage (neochondrogenesis). Periosteal cells and tissues can be used to grow cartilage in vivo and in vitro. In this study, using a standard periosteal organ culture model, we found that cartilage formation by periosteal explants is affected by the ambient oxygen concentrations. A total of 480 periosteal explants from 30 2-month-old New Zealand White rabbits were cultured in agarose suspension at different oxygen concentrations (1-90%) for 6 weeks. Chondrogenesis, which was analyzed by histomorphometry and quantitative collagen typing, was maximal at 12-15% oxygen. There were no significant differences in chondrogenesis in the range of 12-45%. There was inhibition of cartilage and type-II collagen formation at very high (90%) and very low (1-5%) oxygen concentrations. However, contrary to what some have thought, chondrogenesis is maximal under aerobic conditions. If this is true for systems other than periosteal implants, it would have important implications for growing cartilage in vitro.

Effects of oxygen, nitrogen, and temperature on gasoline biodegradation in soil

Biodegradation was considered to be a feasible approach to remediate petroleum hydrocarbon-contaminated soil from a site at the University of Idaho. Before a full-scale treatment process was designed, the biodegradative capacity of the soil's indigenous microorganisms was tested. Gas chromatography was used to measure gasoline vapor components in the headspace above the contaminated soils held in closed containers. In a study of biodegradation kinetics, gasoline degradation rates under various conditions (different soil cores, temperatures, oxygen concentrations, and nutrient concentrations) were tested. It was found that gasoline hydrocarbons could be biodegraded at relatively high rates after appropriate nutrient additions. An unexpected observation was that the optimal concentration of oxygen for the gasoline-degrading microorganisms in these soils was only 10%.