Primary Source Of Oxygen Research Articles

Iodine-Promoted Controlled and Selective Oxidation of (Aryl)(Heteroaryl)Methanes.

The development of direct and controlled oxidation of C(sp3)-H bonds is of great importance. Herein, an iodine-catalyzed controlled oxidation of (aryl)(heteroaryl)methanes to (aryl)(heteroaryl)methanols is disclosed under metal-free reaction conditions. A catalytic system comprised of iodine/silyl chloride with HI as an additive in the presence of dimethyl sulfoxide selectively oxidizes the C(sp3)-H bonds without being overoxidized to corresponding ketones. Therapeutically important aryl heteroaryl methanol derivatives were obtained in good yields. The preliminary mechanistic investigation proves that the primary source of oxygen is DMSO.

Choroidal assessment in diabetic maculopathy

Background and aim Diabetic maculopathy is a leading cause of visual loss in diabetic patients. The choroid is the outer retina's primary source of oxygen and nourishment and the only blood supply to the avascular fovea. Angiopathy of the choroid seems to have a role in the pathophysiology and progression of diabetic maculopathy. It has been theorized that unexplained visual acuity loss in diabetic patients might be linked to diabetic choroidopathy. The aim of this study was to evaluate choroidal changes in eyes with diabetic maculopathy using optical coherence tomography. Patients and methods In all, 20 eyes of 10 normal individuals and 94 eyes of 50 diabetic patients suffering from diabetic maculopathy were recruited in this study. The diabetic patients were categorized according to the type of maculopathy as demonstrated by fluorescein angiography into four subgroups: the focal edema group, the diffuse edema group, the ischemic maculopathy group, and the mixed maculopathy group. Choroidal thickness was measured subfoveally, 1 mm away from the fovea nasally, temporally, superiorly, and inferiorly using optical coherence tomography. Results There was a significant difference among the different groups in all the measured regions (P=0.001). The more severe the maculopathy, the thinner the choroid in all the measured regions. Conclusion The results of this study suggest a negative relationship between macular choroidal thickness and severity of diabetic maculopathy.

Mechanistic Understanding Leads to Increased Ionization Efficiency and Selectivity in Dielectric Barrier Discharge Ionization Mass Spectrometry: A Case Study with Perfluorinated Compounds.

Perfluorinated compounds have unique properties and many practical applications, but are difficult to ionize efficiently with soft ionization methods. An active capillary plasma ionization source based on dielectric barrier discharge ionization (DBDI) coupled with mass spectrometry was used to study the ionization pathway of perfluorinated compounds (PFCs), with the aim of both increasing the ionization efficiency and influencing the selectivity for generating product ions in negative ion mode. Cyclic and linear perfluorinated alkanes were found to mainly form [M - F]- and [M - F + O]- ions, respectively; the [M]-• ion was only obtained at low discharge voltage. Additionally, fluorine attachment [M + F]- was observed mostly for perfluorinated alkenes. An isotope labeling experiment with 18O2 showed that the primary source of oxygen in the substitution reaction is molecular oxygen, reacting with the analyte in the form of O-• ions. The abundance of [M - F + O]- ions can thus be enhanced by increasing the plasma voltage to produce a higher O-• ion density. The loss of the fluorine (without substitution by oxygen) was mainly observed at high frequency, a fact which can be exploited for tuning the ionization toward specific product ions. Overall, the mechanistic understanding of the ionization of PFCs allowed to increase the selectivity of the product ions, resulting in increased ionization efficiency.

Mechanism of aromatic hydroxylation of lidocaine at a Pt electrode under acidic conditions

Aromatic hydroxylation reactions, which are mainly catalyzed by cytochrome P450 (CYP) enzymes in vivo, are some of the most important reactions of Phase I metabolism, because insertion of a hydroxyl group into a lipophilic drug compound increases its hydrophilicity and prepares it for subsequent Phase II metabolic conjugation reactions as a prerequisite to excretion. Aromatic hydroxylation metabolites of pharmaceuticals may be obtained through various synthetic and enzymatic methods Electrochemical oxidation is an alternative with advantages in terms of mild reaction conditions and less hazardous chemicals. In the present study, we report that aromatic hydroxylation metabolites of lidocaine can be readily obtained electrochemically under aqueous acidic conditions at platinum electrodes. Our results show that the dominant N-dealkylation reaction can be suppressed by decreasing the solution pH below 0.5 resulting in selective 3-hydroxylidocaine, which is an in vivo metabolite of lidocaine. Experiments in 18O labelled water indicated that water is the primary source of oxygen, while dissolved molecular oxygen contributes to a minor extent to the hydroxylation reaction.

Implementation and 8-year follow-up of an uninterrupted oxygen supply system in a hospital in The Gambia.

SUMMARYSETTING: A 42-bed hospital operated by the Medical Research Council (MRC) Unit in The Gambia.OBJECTIVE: To devise, test and evaluate a cost-efficient uninterrupted oxygen system in the MRC Hospital.DESIGN: Oxygen cylinders were replaced with oxygen concentrators as the primary source of oxygen. An uninterruptable power supply (UPS) ensured continuity of power. Hospital staff were trained on the use of the new system. Eight years post-installation, an analysis of concentrator maintenance needs and costs was conducted and user feedback obtained to assess the success of the system.RESULTS: The new system saved at least 51% of oxygen supply costs compared to cylinders, with savings likely to have been far greater due to cylinder leakages. Users indicated that the system is easier to use and more reliable, although technical support and staff training are still needed.CONCLUSION: Oxygen concentrators offer long-term cost savings and an improved user experience compared to cylinders; however, some technical support and maintenance are needed to upkeep the system. A UPS dedicated to oxygen concentrators is an appropriate solution for settings where power interruptions are frequent but short in duration. This approach can be a model for health systems in settings with similar infrastructure.

Growth of nanotubes on zirconium in glycerol/fluoride electrolytes

The study examines anodic films formed on bulk and sputtered zirconium in ammonium fluoride/glycerol electrolyte with up to 5 vol.% added water, using film cross-sections prepared by focused ion beam and ultramicrotomy. The findings indicate porous films consisting of zirconium fluoride surrounding zirconia-based nanotubes. The fluoride arises due to faster migration of F − ions relative to O 2− ions; its dissolution exposes the nanotubes. Ion beam analyses revealed the highest amount of fluorine for films formed in electrolyte with no water addition. 18O tracer indicated that water was the primary source of oxygen in the films, which grew at an efficiency of ∼80%.

Aqueous geochemistry and oxygen isotope compositions of acid mine drainage from the Río Tinto, SW Spain, highlight inconsistencies in current models

The Río Tinto river in SW Spain is a classic example of acid mine drainage and the focus of an increasing amount of research including environmental geochemistry, extremophile microbiology and Mars-analogue studies. Its 5000-year mining legacy has resulted in a wide range of point inputs including spoil heaps and tunnels draining underground workings. The variety of inputs and importance of the river as a research site make it an ideal location for investigating sulphide oxidation mechanisms at the field scale. Mass balance calculations showed that pyrite oxidation accounts for over 93% of the dissolved sulphate derived from sulphide oxidation in the Río Tinto point inputs. Oxygen isotopes in water and sulphate were analysed from a variety of drainage sources and displayed δ 18O (SO4–H2O) values from 3.9 to 13.6‰, indicating that different oxidation pathways occurred at different sites within the catchment. The most commonly used approach to interpreting field oxygen isotope data applies water and oxygen fractionation factors derived from laboratory experiments. We demonstrate that this approach cannot explain high δ 18O (SO4–H2O) values in a manner that is consistent with recent models of pyrite and sulphoxyanion oxidation. In the Río Tinto, high δ 18O (SO4–H2O) values (11.2–13.6‰) occur in concentrated (Fe = 172–829 mM), low pH (0.88–1.4), ferrous iron (68–91% of total Fe) waters and are most simply explained by a mechanism involving a dissolved sulphite intermediate, sulphite–water oxygen equilibrium exchange and finally sulphite oxidation to sulphate with O 2. In contrast, drainage from large waste blocks of acid volcanic tuff with pyritiferous veins also had low pH (1.7), but had a low δ 18O (SO4–H2O) value of 4.0‰ and high concentrations of ferric iron (Fe(III) = 185 mM, total Fe = 186 mM), suggesting a pathway where ferric iron is the primary oxidant, water is the primary source of oxygen in the sulphate and where sulphate is released directly from the pyrite surface. However, problems remain with the sulphite–water oxygen exchange model and recommendations are therefore made for future experiments to refine our understanding of oxygen isotopes in pyrite oxidation.

Spectroscopic and Structural Characterization of Chlorine Loading Effects on Mo/Si:Ti Catalysts in Oxidative Dehydrogenation of Ethane

The structural changes induced in a silica-titania mixed-oxide support (1:1 molar ratio) by chlorine addition at different loading levels, their relation to the structural characteristics of supported MoOx species over the support, and their correlation with ethane oxidative dehydrogenation (ODH) activity have been examined. The molybdenum and chlorine precursors are incorporated into the Si/Ti support network as it forms during gelation by using a "one-pot" modified sol-gel/coprecipitation technique. In situ X-ray diffraction during calcination shows the Si/Ti 1:1 mixed-oxide support is in a state of nanodispersed anatase titania over amorphous silica. With the addition of molybdenum and chlorine modifier, this anatase feature becomes more pronounced, indicating a decreased dispersion of titania. The effective titania surface area on the chlorine-doped Si:Ti support obtained from 2-propanol temperature-programmed reaction supports this observation. Raman spectra of dehydrated samples point to an enhanced interaction of MoOx species with silica at the expense of titania. X-ray photoelectron spectroscopic results show that, without forming a molybdenum chloride, the presence of chlorine significantly alters the relative surface concentration of Si vs Ti, the electronic structure of the surface MoOx species, and the oxygen environment around supported MoOx species in the Si/Ti network. Secondary ion mass spectrometry detected the existence of SiCl fragments from the mass spectra, which provides molecular insight into the location of chlorine in Mo/Si:Ti catalysts. The observed increase in ethane ODH selectivity with chlorine modification may be ascribed to the MoOx species sharing more complex ligands with silica and titania with the indirect participation of chlorine. Steady-state isotopic transient kinetic analysis (SSITKA) is used to to examine the oxygen insertion and exchange mechanisms. The catalysts show very little oxygen exchange with the gas phase in the absence of a reaction medium. During the steady-state ODH reaction, lattice oxygen appears to be the primary source of oxygen in the formation of water and CO2.

Origin of Oxygen in Sulfate during Pyrite Oxidation with Water and Dissolved Oxygen: An In Situ Horizontal Attenuated Total Reflectance Infrared Spectroscopy Isotope Study

FeS2 (pyrite) is known to react with water and dissolved molecular oxygen to form sulfate and iron oxyhydroxides. This process plays a large role in the environmentally damaging phenomenon known as acid mine drainage. An outstanding scientific issue has been whether the oxygen in the sulfate and oxyhydroxide product was derived from water and/or dissolved oxygen. By monitoring the reaction in situ with horizontal attenuated total reflectance infrared spectroscopy, it was found that when using 18O isotopically substituted water, the majority of the infrared absorbance due to sulfate product red-shifted approximately 70 cm(-1) relative to the absorbance of sulfate using H(2)16O as a reactant. Bands corresponding to the iron oxyhydroxide product did not shift. These results indicate water as the primary source of oxygen in the sulfate product, while the oxygen atoms in the iron oxyhydroxide product are obtained from dissolved molecular oxygen.

A Comparative Study of Ti/Low-k HSQ (Hydrogen Silsesquioxane) and Ti/TEOS (Tetraethylorthosilicate) Structures at Elevated Temperatures

AbstractFor the benefit of reducing capacitance in multilevel interconnect technology, low-k dielectric HSQ (hydrogen silsesquioxane) has been used as a gapfill material in Al-metallization- based non-etchback embedded scheme. The vias are consequently fabricated through the HSQ layer followed by W plug deposition. In order to reduce the extent of via poisoning and achieve good W/Al contact, thin Ti/TiN stack films are typically deposited before via plug deposition. In this case, HSQ makes direct contact with the Ti layer. The reliability of the Ti/HSQ structures at elevated temperatures has been systematically studied in this work by using a variety of techniques. These results are also compared with those from Ti/TEOS (Tetraethylorthosilicate) structure, where TEOS is a conventional intra-metal dielectric. When the temperature is below 550 °C, a significant number of oxygen atoms are observed to diffuse into the titanium layer. The primary source of oxygen is believed to come from the HSQ film. When the temperature is above 550 °C, HSQ starts to react with Ti. At 700 °C, a TiO/Ti5Si3/HSQ stack structure forms. The Ti/HSQ system exhibits a higher reactivity than that of the Ti/TEOS system.

Kinetics of the oxygen evolution step in plants determined from flash-induced chlorophyll t a fluorescence

Photosystem II (PS II) of plants and cyanobacteria, which catalyzes the light-induced splitting of water and the release of oxygen, is the primary source of oxygen in the earth atmosphere. When activated by short light flashes, oxygen release in PS II occurs periodically with maxima after the third and the seventh flashes. Many other processes, including chlorophyll (Chl) t a fluorescence, are also modulated with period of four, reflecting their sensitivity to the activity of Photosystem II. A new approach has been developed for the analysis of the flash-induced fluorescence of Chl t a in plants, which is based on the use of the generalized Stern–Volmer equation for multiple quenchers. When applied to spinach thylakoids, this analysis reveals the presence of a new quencher of fluorescence whose amplitude is characterized by a periodicity of four with maxima after the third and the seventh flashes, in phase with oxygen release. The quencher appears with a delay of ≈ 0.5 ms followed by a rise time of 1.2–2 ms at pH 7, also in agreement with the expected time for oxygen evolution. It is concluded that the quencher is a product of the reaction leading to the oxygen evolution in PS II. The same quenching activity, maximal after the third flash, could be seen in dark adapted leaves, and provides the first fully time-resolved measurement of the kinetics of the oxygen evolution step in the leaf. Thus, the non-invasive probe of Chl t a fluorescence provides a new and sensitive method for measuring the kinetics of oxygen evolution with potential for use in plants and cyanobacteria t in vivo.

SUPERNOVAE, SUPERNEBULAE, AND NUCLEOSYNTHESIS.

ABSTRACT Supernova atmosphere calculations continue to show that variants of previously calculated carbon-deflagration models provide a good representation of the maximum light spectra of classical type Ia supernovae including the ultraviolet deficit. Careful consideration of the conditions leading to central thermonuclear runaway of degenerate carbon shows that runaway can, however, lead to detonation and direct conflict with observations. As witnessed by the spectra of type Ib supernovae, massive stars are expected to be the primary source of oxygen. Estimates of the absolute production of oxygen in massive stars suggest that if all stars more massive than ≡12 Msun; explode as supernovae, oxygen would be overproduced in the solar neighborhood, an effect exacerbated by the recent increase in the reaction rate for 12C(α, γ)16O.

Oxygen Acquisition of the Reedfish, Erpetoichthys Calabaricus

ABSTRACT In normoxic water at 25 °C, the reedfish (Erpetoichthys calabacicus) can breathe in both air and water, although water is the primary source of oxygen. This pattern of oxygen partitioning is altered by a number of factors. Increases in metabolic costs (e.g. locomotor activity) and decreases in aquatic oxygen concentration are met by increases in aerial oxygen uptake. Reedfish acclimated to 33 °C have increased lung breathing compared with fish acclimated to 25°C. Also, activity stimulates lung breathing more at 33 °C than at 25 °C. Unexpectedly, weight-specific oxygen uptake rates of reedfish at these two temperatures were not significantly different. In-creased lung-breathing compensates for changes in locomotor activity, dissolved oxygen and temperature, allowing reedfish to meet their overall oxygen requirements. Exposure of reedfish to six different combinations of oxygen and carbon dioxide indicated that lung ventilation frequencies were more labile than gill ventilation frequencies. The maximum change in lung ventilation rates was 849% above controls whereas the largest change in gill ventilation frequency was 27%. Exposure of reedfish to hyperoxia significantly de-pressed both gill and lung ventilation. Hypercapnic gases stimulated gill ventilation at both low (0·5%) and high (5%) concentrations; however, lung ventilation was only stimulated at the higher carbon dioxide concentration. The observed depression of gill ventilation frequencies in reedfish exposed to combinations of hypercapnic and hypoxic gases indicates that the inhibitory effect of low oxygen on gill ventilation dominates the stimulatory effect of hypercapnia. Overall, these data suggest that oxygen exerts a stronger influence in the control of respiration than carbon dioxide in this air-and water-breathing fish. Reedfish survived out of water for 6 and 8 h at 25 °C without obvious ill effects. Oxygen consumption rates of these fish were significantly less than those of similar sized reedfish measured in water at either 25 or 33°C. The respiratory physiology of the reedfish frees it from aquatic oxygen constraints and allows it to tolerate at least short-term terrestrial exposures.