Showing papers on "Oxygen published in 2003"
TL;DR: A mediator-less microbial fuel cell was optimized in terms of various operating conditions and showed linear relationship with the fuel added at low concentration, and the electronic charge was well correlated with substrate concentration from up to 400 mg l(-1) of COD(cr).
963 citations
TL;DR: The observation that As( III) is oxidized in parallel to the oxidation of Fe(II) by O2 and by H2O2 and that the As(III) oxidation is not inhibited by *OH-radical scavengers at neutral pH is significant for the understanding of arsenic redox reactions in the environment and in arsenic removal processes as well as for theUnderstanding of Fenton reactions in general.
Abstract: The oxidation kinetics of As(III) with natural and technical oxidants is still not well understood, despite its importance in understanding the behavior of arsenic in the environment and in arsenic removal procedures. We have studied the oxidation of 6.6 μM As(III) by dissolved oxygen and hydrogen peroxide in the presence of Fe(II,III) at pH 3.5−7.5, on a time scale of hours. As(III) was not measurably oxidized by O2, 20−100 μM H2O2, dissolved Fe(III), or iron(III) (hydr)oxides as single oxidants, respectively. In contrast, As(III) was partially or completely oxidized in parallel to the oxidation of 20−90 μM Fe(II) by oxygen and by 20 μM H2O2 in aerated solutions. Addition of 2-propanol as an •OH-radical scavenger quenched the As(III) oxidation at low pH but had little effect at neutral pH. High bicarbonate concentrations (100 mM) lead to increased oxidation of As(III). On the basis of these results, a reaction scheme is proposed in which H2O2 and Fe(II) form •OH radicals at low pH but a different oxidant...
736 citations
TL;DR: In this article, the authors focus on the chemical reactions occurring during low-temperature oxidation of coal and develop a kinetic model to predict the self-heating and gas emission in coal seams.
531 citations
TL;DR: Advances have been made in elucidating possible oxygen-sensing systems and regulatory components that are involved in these responses, which lead to the induction of a plant-specific and energy-conserving pathway of sucrose degradation, which decreases oxygen consumption and improves plant performance.
522 citations
TL;DR: In this article, the authors reviewed previous studies on iron and steel oxidation in oxygen or air at high temperatures and found that the scale structures are similar to those formed on iron, but for longer-time oxidation, because of the less adherent nature, the scale structure developed are typically much more complex.
Abstract: This paper reviews previous studies on iron and steel oxidation in oxygen or air at high temperatures. Oxidation of iron at temperatures above 700°C follows the parabolic law with the development of a three-layered hematite/magnetite/wustite scale structure. However, at temperatures below 700°C, inconsistent results have been reported, and the scale structures are less regular, significantly affected by sample-preparation methods. Oxidation of carbon steel is generally slower than iron oxidation. For very short-time oxidation, the scale structures are similar to those formed on iron, but for longer-time oxidation, because of the less adherent nature, the scale structures developed are typically much more complex. Continuous-cooling conditions, after very short-time oxidation, favor the retention of an adherent scale, suggesting that the method proposed by Kofstad for deriving the rate constant using continuous cooling or heating-oxidation data is more appropriate for steel oxidation. Oxygen availability has certain effects on iron and steel oxidation. Under continuous cooling conditions, the final scale structure is found to be a function of the starting temperature for cooling and the cooling rate. Different scale structures develop across the width of a hot-rolled strip because of the varied oxygen availability and cooling rates at different locations.
488 citations
TL;DR: The structures of naphthalene dioxygenase are determined that show a molecular oxygen species bound to the mononuclear iron in a side-on fashion and provide the basis for a reaction mechanism and for the high stereospecificity of the reaction catalyzed by naphthaene diodesase.
Abstract: Binding of oxygen to iron is exploited in several biological and chemical processes. Although computational and spectroscopic results have suggested side-on binding, only end-on binding of oxygen to iron has been observed in crystal structures. We have determined structures of naphthalene dioxygenase that show a molecular oxygen species bound to the mononuclear iron in a side-on fashion. In a complex with substrate and dioxygen, the dioxygen molecule is lined up for an attack on the double bond of the aromatic substrate. The structures reported here provide the basis for a reaction mechanism and for the high stereospecificity of the reaction catalyzed by naphthalene dioxygenase.
473 citations
TL;DR: The heart and those striated muscles that contract for long periods, having available almost limitless oxygen, operate in sustained steady states of low sarcoplasmic oxygen pressure that resist change in response to changing muscle work or oxygen supply.
Abstract: The heart and those striated muscles that contract for long periods, having available almost limitless oxygen, operate in sustained steady states of low sarcoplasmic oxygen pressure that resist change in response to changing muscle work or oxygen supply. Most of the oxygen pressure drop from the erythrocyte to the mitochondrion occurs across the capillary wall. Within the sarcoplasm, myoglobin, a mobile carrier of oxygen, is developed in response to mitochondrial demand and augments the flow of oxygen to the mitochondria. Myoglobin-facilitated oxygen diffusion, perhaps by virtue of reduction of dimensionality of diffusion from three dimensions towards two dimensions in the narrow spaces available between mitochondria, is rapid relative to other parameters of cell respiration. Consequently, intracellular gradients of oxygen pressure are shallow, and sarcoplasmic oxygen pressure is nearly the same everywhere. Sarcoplasmic oxygen pressure, buffered near 0.33 kPa (2.5 torr; equivalent to approximately 4 micro mol l(-1) oxygen) by equilibrium with myoglobin, falls close to the operational K(m) of cytochrome oxidase for oxygen, and any small increment in sarcoplasmic oxygen pressure will be countered by increased oxygen utilization. The concentration of nitric oxide within the myocyte results from a balance of endogenous synthesis and removal by oxymyoglobin-catalyzed dioxygenation to the innocuous nitrate. Oxymyoglobin, by controlling sarcoplasmic nitric oxide concentration, helps assure the steady state in which inflow of oxygen into the myocyte equals the rate of oxygen consumption.
470 citations
TL;DR: In this paper, the Stokes-Einstein relation was used to measure the oxygen transport properties of several organic electrolytes through measurements of oxygen solubility and electrolyte viscosity.
Abstract: The oxygen transport properties of several organic electrolytes were characterized through measurements of oxygen solubility and electrolyte viscosity. Oxygen diffusion coefficients were calculated from electrolyte viscosities using the Stokes-Einstein relation. Oxygen solubility, electrolyte viscosity, and oxygen partial pressure were all directly correlated to discharge capacity and rate capability. Substantial improvement in cell performance was achieved through electrolyte optimization and increased oxygen partial pressure. The concentration of oxygen in the electrode under discharge was calculated using a semi-infinite medium model with simultaneous diffusion and reaction. The model was used to explain the dependence of cell performance on oxygen transport in organic electrolyte. © 2003 The Electrochemical Society. All rights reserved.
463 citations
Patent•
20 Feb 2003TL;DR: In this article, the authors present methods and systems for supplying supplemental oxygen to patients for use in sub-acute care which maintains healthy blood oxygen content in the patients by controlled dosing of oxygen with a measured response to the patient's actual oxygen content.
Abstract: Methods and systems for supplying supplemental oxygen to patients for use in sub-acute care which maintains healthy blood oxygen content in the patients by controlled dosing of oxygen with a measured response to the patient's actual blood oxygen content are disclosed. The dosing can be provided by simple ON/OFF control over the delivery of oxygen or the amount of oxygen delivered to the patient with each inhalation can be varied in response to the patient's need as determined by a more sophisticated control scheme, such as a PID loop control algorithm, that utilizes the difference between the patient's actual blood oxygen content and a target blood oxygen content and/or trends in the blood oxygen content. The systems and methods are particularly directed at patients receiving supplemental oxygen in a sub-acute care environment.
443 citations
TL;DR: The properties of various oxygen permeable polymers for matrix of optical oxygen sensor and various dye probes for oxygen sensing are described in this article, where the properties of polycyclic aromatic hydrocarbons and metalloporphyrins are compared.
Abstract: Oxygen detection techniques are used in various fields, such as chemical or clinical analysis and environmental monitoring. Recently, a variety of devices and sensors based on photo-luminescent or photoexcited state quenching of organic dyes have been developed to measure oxygen partial pressure on the solid surface. Many optical oxygen sensors are composed of organic dyes, such as polycyclic aromatic hydrocarbons (pyrene, pyrene derivative etc.), transition metal complexes (Ru2+, Os2+, Ir3+ etc.), metalloporphyrins (Pt2+, Pd2+, Zn2+ etc.) and fullerene (C60 and C70) immobilized in oxygen permeable polymer films. In this review, the properties of various oxygen permeable polymers for matrix of optical oxygen sensor and various dye probes for oxygen sensing are described.
428 citations
TL;DR: Time-resolved, high-resolution scanning tunneling microscopy unraveled an adsorbate-mediated diffusion mechanism of oxygen vacancies on rutile TiO2(110), leading to an anisotropic oxygen vacancy diffusion pathway perpendicular to the bridging oxygen rows.
Abstract: Defects such as oxygen vacancies play a crucial role in the surface properties of transition metal oxides. By means of time-resolved, high-resolution scanning tunneling microscopy, we unraveled an adsorbate-mediated diffusion mechanism of oxygen vacancies on rutile TiO2(110). Adsorbed oxygen molecules mediate vacancy diffusion through the loss of an oxygen atom to a vacancy and the sequential capture of an oxygen atom from a neighboring bridging oxygen row, leading to an anisotropic oxygen vacancy diffusion pathway perpendicular to the bridging oxygen rows.
TL;DR: In this article, superfine Fe 2 O 3 nanoparticles were evaluated both as a catalyst and as an oxidant for carbon monoxide oxidation, and it was found that the nanoparticles are much more effective as carbon dioxide catalysts than the non-nano oxide powder.
Abstract: NANOCAT ® Superfine Fe 2 O 3 nanoparticles were evaluated both as a catalyst and as an oxidant for carbon monoxide oxidation. It was found that the nanoparticles are much more effective as carbon monoxide catalysts than the non-nano oxide powder. For the Fe 2 O 3 nanoparticles, the reaction order is first-order with respect to the partial pressure of carbon monoxide, and zero-order with respect to the partial pressure of oxygen. The apparent activation energy was 14.5 kcal mol −1 and the normalized reaction rate was 19 s −1 m −2 at 300 °C. In the absence of oxygen, Fe 2 O 3 nanoparticles oxidize carbon monoxide directly as an oxidant. The resulting reduced forms of Fe 2 O 3 also catalyze a disproportionation reaction for a considerable amount of carbon monoxide. The significant amount of carbon monoxide it can remove through the catalytic oxidation, direct oxidation, and the disproportionation reaction make it a very promising material in certain special applications, such as removing the carbon monoxide from a burning cigarette, where the potential toxicity of other, more conventional catalysts would be undesirable. The higher activity of Fe 2 O 3 nanoparticles over non-nano Fe 2 O 3 powders was attributed to a small particle size (3 nm), the presence of an hydroxylated phase of iron oxide (FeOOH), as revealed by both high resolution transmission electron microscopy (HRTEM) and a comparable study of FeOOH (goethite) powder.
TL;DR: In this paper, the possibility of using oxides of Cu, Co, Mn, and Ni as oxygen carriers was investigated, and particles were prepared by deposition of the metal oxides on γ-Al2O3 particles by so-called dry impregnation.
Abstract: Chemical-looping combustion (CLC) is a combustion technology with inherent separation of the greenhouse gas CO2. The technique involves the use of a metal oxide as an oxygen carrier, which transfers oxygen from the combustion air to the fuel. Two reactors are used in the process: (i) a fuel reactor where the metal oxide is reduced by reaction with the fuel, and (ii) an air reactor where the reduced metal oxide from the fuel reactor is oxidized with air. The possibility of using oxides of Cu, Co, Mn, and Ni as oxygen carriers was investigated. Particles were prepared by deposition of the metal oxides on γ-Al2O3 particles by so-called dry impregnation. The reactivity of the oxygen carrier particles was evaluated in a thermogravimetric analyzer (TGA), where the alternating atmosphere which an oxygen carrier encounters in a CLC system was simulated by exposing the sample to alternating reducing (10% CH4, 5% CO2, 10% H2O) and oxidizing (10% O2) conditions at temperatures between 750 and 950 °C. The particles ...
TL;DR: Two functions for free oxygen radical cation channel activation are proposed: initialization/amplification of stress signals and control of cell elongation in root growth, suggesting conserved mechanisms and functions.
Abstract: Free oxygen radicals are an irrefutable component of life, underlying important biochemical and physiological phenomena in animals. Here it is shown that free oxygen radicals activate plasma membrane Ca2+- and K+-permeable conductances in Arabidopsis root cell protoplasts, mediating Ca2+ influx and K+ efflux, respectively. Free oxygen radicals generate increases in cytosolic Ca2+ mediated by a novel population of nonselective cation channels that differ in selectivity and pharmacology from those involved in toxic Na+ influx. Analysis of the free oxygen radical-activated K+ conductance showed its similarity to the Arabidopsis root K+ outward rectifier. Significantly larger channel activation was found in cells responsible for perceiving environmental signals and undergoing elongation. Quenching root free oxygen radicals inhibited root elongation, confirming the role of radical-activated Ca2+ influx in cell growth. Net free oxygen radical-stimulated Ca2+ influx and K+ efflux were observed in root cells of monocots, dicots, C3 and C4 plants, suggesting conserved mechanisms and functions. In conclusion, two functions for free oxygen radical cation channel activation are proposed: initialization/amplification of stress signals and control of cell elongation in root growth.
Journal Article•
TL;DR: In this article, the reduction potentials of wine polyphenols and oxygen, as well as that of the Fe3+/Fe2+ couple, have been calculated for wine conditions and form the basis for discussing how these redox systems are likely to interact.
Abstract: The chemical, biochemical, and enological literature has been broadly surveyed to identify the reaction mechanisms of oxygen and of its intermediate reduction products that should apply to wine. The reduction potentials of redox couples derived from wine polyphenols and oxygen, as well as that of the Fe3+/Fe2+ couple, have been calculated for wine conditions and form the basis for discussing how these redox systems are likely to interact. Values obtained for wine quinone/catechol couples agree well with those reported for wine-model conditions. Catechol derivatives are oxidized sequentially to semiquinones and quinones, while oxygen is reduced in turn to hydroperoxyl radicals and hydrogen peroxide. The whole process is mediated by redox cycling of the Fe3+/Fe2+ couple, which is made possible by the lowering of its reduction potential by coordination of Fe3+ to hydroxy acids. Hydrogen peroxide is then further reduced by Fe2+ in the Fenton reaction to produce hydroxyl radicals, which oxidize saturated hydroxy compounds. Intermediate radicals may react with oxygen, providing an additional pathway for its reduction. Thus, both ferric and ferrous ions, which are present in wine, perform an important catalytic function. The antioxidant activity of bisulfite is largely restricted to its reaction with hydrogen peroxide. Direct reaction of sulfur dioxide with oxygen, which is a radical chain process, is prevented by the radical scavenging activity of polyphenols.
TL;DR: Based on the experimental determination of the reaction orders of OH−, O2 and the intermediate Mn3+ ion, this paper proposed a chemical oxidation mechanism for the catalytic oxygen reduction, in which oxygen reduction proceeds through chemical oxidation of the discharge product of MnO2 rather than through a direct two-electron reduction.
TL;DR: Evidence suggests that the RBC acts as deliverer of oxygen and 'sensor' of local oxygen gradients, and NO over-production mediates systemic hypotension and microvascular reactivity, and is seemingly protective of microv vascular blood flow during sepsis.
Abstract: The microcirculation is a complex and integrated system that supplies and distributes oxygen throughout the tissues. The red blood cell (RBC) facilitates convective oxygen transport via co-operative binding with hemoglobin. In the microcirculation oxygen diffuses from the RBC into neighboring tissues, where it is consumed by mitochondria. Evidence suggests that the RBC acts as deliverer of oxygen and 'sensor' of local oxygen gradients. Within vascular beds RBCs are distributed actively by arteriolar tone and passively by rheologic factors, including vessel geometry and RBC deformability. Microvascular oxygen transport is determined by microvascular geometry, hemodynamics, and RBC hemoglobin oxygen saturation. Sepsis causes abnormal microvascular oxygen transport as significant numbers of capillaries stop flowing and the microcirculation fails to compensate for decreased functional capillary density. The resulting maldistribution of RBC flow results in a mismatch of oxygen delivery with oxygen demand that affects both critical oxygen delivery and oxygen extraction ratio. Nitric oxide (NO) maintains microvascular homeostasis by regulating arteriolar tone, RBC deformability, leukocyte and platelet adhesion to endothelial cells, and blood volume. NO also regulates mitochondrial respiration. During sepsis, NO over-production mediates systemic hypotension and microvascular reactivity, and is seemingly protective of microvascular blood flow.
TL;DR: This perfusion bioreactor system serves as an in vitro model of zonation that could be further extended to study the role of gradients in ischemia-reperfusion injury, toxicity, and bioartificial liver design.
Abstract: We have developed a perfusion bioreactor system that allows the formation of steady state oxygen gradients in cell culture. In this study, gradients were formed in cultures of rat hepatocytes to study the role of oxygen in modulating cellular functions. A model of oxygen transport in our flat-plate reactor was developed to estimate oxygen distribution at the cell surface. Experimental measurements of outlet oxygen concentration from various flow conditions were used to validate model predictions. We showed that cell viability was maintained over a 24-h period when operating with a physiologic oxygen gradient at the cell surface from 76 to 5 mmHg O(2) at the outlet. Oxygen gradients have been implicated in the maintenance of regional compartmentalized metabolic and detoxification functions in the liver, termed zonation. In this system, physiologic oxygen gradients in reactor cultures contributed to a heterogeneous distribution of phosphoenolpyruvate carboxykinase (predominantly localized upstream) and cytochrome p450 2B (predominantly localized downstream) that correlates with the distribution of these enzymes in vivo. The oxygen gradient chamber provides a means of probing the oxygen effects in vitro over a continuous range of O(2) tensions. In addition, this system serves as an in vitro model of zonation that could be further extended to study the role of gradients in ischemia-reperfusion injury, toxicity, and bioartificial liver design.
TL;DR: In this article, the effect of varying physical and chemical properties of activated carbons on adsorption of elemental mercury (Hg0) was studied by treating two activated carbonons to modify their surface functional groups and pore structures.
TL;DR: In this article, computer modeling techniques have been used to examine the mechanistic features of oxygen ion transport in the La8Sr2Si6O26 and La9.33Si6 O26 apatiteoxides at the atomic level.
Abstract: Computer modelling techniques have been used to examine the mechanistic features of oxygen ion transport in the La8Sr2Si6O26 and La9.33Si6O26 apatite-oxides at the atomic level. The potential model reproduces the observed complex structures of both phases, which are comprised of [SiO4] tetrahedral units and La/O channels. Defect simulations have examined the lowest energy interstitial and vacancy sites. The results suggest that oxygen ion migration in La8Sr2Si6O26 is via a vacancy mechanism with a direct linear path between O5 sites. Interstitial oxygen migration is predicted for La9.33Si6O26via a non-linear (sinusoidal-like) pathway through the La3/O5 channel. The simulations demonstrate the importance of local relaxation of [SiO4] tetrahedra to assist in the facile conduction of oxygen interstitial ions. In general, the modelling study confirms that the high ionic conductivity in silicate-based apatites (with oxygen excess or cation vacancies) is mediated by oxygen interstitial migration.
TL;DR: In this paper, the inhibitory effect of molecular oxygen in photo-initiated polymerization of acrylate resins has been completely eliminated by operating in a carbon dioxide atmosphere, and the high speed polymerization was followed in situ by real-time infrared spectroscopy, thus allowing conversion versus time curves to be recorded for curing reactions occurring within a fraction of a second.
TL;DR: In this paper, the reaction mechanism in atomic layer deposition (ALD) of ruthenium from biscyclopentadienyl ruthensium (RuCp 2 ) and oxygen were studied in situ with a quadruple mass spectrometer (QMS) and a quartz crystal microbalance (QCM).
Abstract: Reaction mechanisms in atomic layer deposition (ALD) of ruthenium from bis(cyclopentadienyl)ruthenium (RuCp 2 ) and oxygen were studied in situ with a quadruple mass spectrometer (QMS) and a quartz crystal microbalance (QCM). In addition, QMS was used to study ALD of platinum from (methylcyclopentadienyl)trimethylplatinum (MeCpPtMe 3 ) and oxygen. The QMS studies showed that the reaction by-products H 2 O and CO 2 were released during both the oxygen and the metal precursor pulses. Adsorbed oxygen layer on the metal surface thus oxidizes part of the ligands during the metal precursor pulse. The remaining ligand species become oxidized and a new layer of adsorbed oxygen forms on the surface during the following oxygen pulse. The QCM analysis of the ruthenium process showed a mass decrease during the RuCp 2 pulse and a mass increase during the oxygen pulse, which further supports the proposed mechanism.
TL;DR: In this article, the effect of AQ surface concentration on the kinetics of oxygen reduction has been investigated and the rate constant of the chemical reaction between semiquinone radical anion of AQ and molecular oxygen has been determined.
TL;DR: Low metabolic rates at cold Antarctic temperatures keep absolute rates of mitochondrial ROS production low and control oxidative stress at habitat temperatures, but progressive mitochondrial uncoupling and formation of hazardous ROS contribute to bias mitochondrial functioning under temperature stress in vitro.
Abstract: Formation of reactive oxygen species (ROS) in mitochondrial isolates from gill tissues of the Antarctic polar bivalve Laternula elliptica was measured fluorimetrically under in vitro conditions. When compared to the rates measured at habitat temperature (1 degrees C), significantly elevated ROS formation was found under temperature stress of 7 degrees C and higher. ROS formation correlated significantly with oxygen consumption in individual mitochondrial preparations over the entire range of experimental temperatures (1-12 degrees C). ROS generation per mg of mitochondrial protein was significantly higher in state 3 at maximal respiration and coupling to energy conservation, than in state 4+, where ATPase-activity is inhibited by oligomycin and only proton leakage is driving the residual oxygen consumption. The percent conversion of oxygen to the membrane permeant hydrogen peroxide amounted to 3.7% (state 3) and 6.5% (state 4+) at habitat temperature (1 degrees C), and to 7% (state 3) and 7.6% (state 4+) under experimental warming to 7 degrees C. This is high compared to 1-3% oxygen to ROS conversion in mammalian mitochondrial isolates and speaks for a comparatively low control of toxic oxygen formation in mitochondria of the polar bivalve. However, low metabolic rates at cold Antarctic temperatures keep absolute rates of mitochondrial ROS production low and control oxidative stress at habitat temperatures. Mitochondrial coupling started to fall beyond 3 degrees C, closely to pejus temperature (4 degrees C) of the bivalve. Accordingly, the proportion of state 4 respiration increased from below 30% at 1 degrees C to over 50% of total oxygen consumption at 7 degrees C, entailing reduced ADP/O ratios under experimental warming. Progressive mitochondrial uncoupling and formation of hazardous ROS contribute to bias mitochondrial functioning under temperature stress in vitro. Deduced from a pejus temperature, heat stress commences already at 5 degrees C, and is linked to progressive loss of phosphorylation efficiency, increased mitochondrial oxygen demand and elevated oxidative stress above pejus temperatures.
TL;DR: In this article, the adsorption of thermally cracked atomic oxygen on the Pt(1) surface has been investigated using X-ray photoelectron spectroscopy (XPS), co-axial impact collision ion scattering spectrum (CAICISS), and low energy electron diffraction (LEED).
TL;DR: In this paper, the role of the adsorbed oxygen has been studied by examining the variations of the electrical conductivity of the catalysts during the processes of oxygen adsorption-desorption.
Abstract: The catalytic combustion of some volatile organic compounds (VOCs) has been investigated over LaMnO3 and LaCoO3 perovskite-type oxides. Redox titration has shown that cobalt is present in LaCoO3 exclusively in the 3+ oxidation state whereas LaMnO3 contains considerable amount of Mn4+ (35%) in addition to Mn3+. VOCs reactivity towards total oxidation follows the trend: acetone > isopropanol > benzene. The oxidation of isopropanol occurs through the formation of acetone in the homogeneous reaction. The increase of the oxygen partial pressure is beneficial for total oxidation of acetone. The adsorptive properties of the catalysts towards the VOCs and H2 have been examined by means of temperature programmed desorption. The LaMnO3 surface is the most reactive to the adsorption of VOCs and H2. The role of the adsorbed oxygen has been studied by examining the variations of the electrical conductivity of the catalysts during the processes of oxygen adsorption–desorption.
TL;DR: Oxygen concentration is low inside the transport phloem in planta and that this results in adaptive changes inphloem metabolism and function, indicating a partial inhibition of respiration.
Abstract: We have investigated the consequences of endogenous limitations in oxygen delivery for phloem transport in Ricinus communis. In situ oxygen profiles were measured directly across stems of plants growing in air (21% [v/v] oxygen), using a microsensor with a tip diameter of approximately 30 μm. Oxygen levels decreased from 21% (v/v) at the surface to 7% (v/v) in the vascular region and increased again to 15% (v/v) toward the hollow center of the stem. Phloem sap exuding from small incisions in the bark of the stem was hypoxic, and the ATP to ADP ratio (4.1) and energy charge (0.78) were also low. When 5-cm stem segments of intact plants were exposed to zero external oxygen for 90 min, oxygen levels within the phloem decreased to approximately 2% (v/v), and ATP to ADP ratio and adenylate energy charge dropped further to 1.92 and 0.68, respectively. This was accompanied by a marked decrease in the phloem sucrose (Suc) concentration and Suc transport rate, which is likely to be explained by the inhibition of retrieval processes in the phloem. Germinating seedlings were used to analyze the effect of a stepwise decrease in oxygen tension on phloem transport and energy metabolism in more detail. Within the endosperm embedding the cotyledons—next to the phloem loading sites—oxygen decreased from approximately 14% (v/v) in 6-d-old seedlings down to approximately 6% (v/v) in 10-d-old seedlings. This was paralleled by a similar decrease of oxygen inside the hypocotyl. When the endosperm was removed and cotyledons incubated in a 100 mm Suc solution with 21%, 6%, 3%, or 0.5% (v/v) oxygen for 3 h before phloem sap was analyzed, decreasing oxygen tensions led to a progressive decrease in phloem energy state, indicating a partial inhibition of respiration. The estimated ratio of NADH to NAD+ in the phloem exudate remained low (approximately 0.0014) when oxygen was decreased to 6% and 3% (v/v) but increased markedly (to approximately 0.008) at 0.5% (v/v) oxygen, paralleled by an increase in lactate and ethanol. Suc concentration and translocation decreased when oxygen was decreased to 3% and 0.5% (v/v). Falling oxygen led to a progressive increase in amino acids, especially of alanine, γ-aminobutyrat, methionine, and isoleucine, a progressive decrease in the C to N ratio, and an increase in the succinate to malate ratio in the phloem. These results show that oxygen concentration is low inside the transport phloem in planta and that this results in adaptive changes in phloem metabolism and function.
TL;DR: In this article, the measurements of the solubility of carbon dioxide and oxygen in a commonly used room temperature ionic liquid, butyl methyl imidazolium tetrafluoroborate ([bmim][BF4]), are reported as a function of temperature between 303 K and 343 K and at pressures close to atmospheric.
Abstract: The measurements of the solubility of carbon dioxide and oxygen in a commonly used room temperature ionic liquid, butyl methyl imidazolium tetrafluoroborate ([bmim][BF4]), are reported as a function of temperature between 303 K and 343 K and at pressures close to atmospheric. A new experimental apparatus, based on a saturation method, is presented. The solubility is expressed in terms of molarities, mole fractions, and Henry's law coefficients. From their variation with temperature, the partial molar thermodynamic functions of solvation such as the standard Gibbs energy, the enthalpy, and the entropy are calculated. The precision of the experimental data, considered as the average absolute deviation of the Henry's law coefficients from appropriate smoothing equations, is 4% for oxygen and 3% for carbon dioxide.
TL;DR: In this article, an oxidative (oxygen and air) RF-plasma treatment of HDPE was found as an effective tool for improving wettability, as well as for increasing its surface micro-hardness.