JOURNAL OF PINEAL RESEARCH, Issue 1 2001
Akihiko Wakatsuki
Our objective was to investigate the effects of melatonin on the free radical-induced oxidative damage to mitochondria in fetal rat brain. Female Wistar rats on day 19 of pregnancy were used. Melatonin (10 mg/kg) or vehicle (control) was injected intraperitoneally 60 min prior to laparotomy for removal of the fetuses. The mitochondrial fraction was isolated from the fetal rat brain of each group. Superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities were measured. As indicators of mitochondrial respiratory activity, we determined the respiratory control index (RCI) and the adenosine 5-diphosphate/oxygen (ADP/O) ratio in the presence and absence of 2.5 ,M hypoxanthine and 0.02 units/mL xanthine oxidase. Mitochondrial lipid peroxidation was determined by measuring the concentration of thiobarbituric acid reactive substances in fetal brain mitochondria in the presence or absence of 2.5 ,M hypoxanthine, 0.02 units/mL xanthine oxidase, and 50 ,M FeSO4. The free radical-induced rates of inhibition of mitochondrial RCI and the ADP/O ratio were both significantly lower in the fetal rat brains treated with melatonin compared with those of the controls (RCI, 44.25±15.02% vs. 25.18±5.86%, P<0.01; ADP/O ratio, 50.74±23.05% vs. 13.90±7.80%, P<0.001). The mitochondrial lipid peroxidation induced by free radicals was significantly reduced in the melatonin-treated group compared with the controls (484.2±147.2% vs. 337.6±61.0%, P<0.01). Pretreatment with melatonin significantly increased the activity of GSH-Px (20.35±5.27 to 28.93±11.01 mU/min mg,1 protein, P<0.05) in fetal rat brain mitochondria, but the activity of SOD did not change significantly. Results indicate that the administration of melatonin to the pregnant rat may prevent the free radical-induced oxidative mitochondrial damage to fetal rat brain by a direct antioxidant effect and the activation of GSH-Px. [source]

EFFECT OF HEADSPACE OXYGEN AND FILMS OF DIFFERENT OXYGEN TRANSMISSION RATE ON TOXIN PRODUCTION BY CLOSTRIDIUM BOTULINUM TYPE E IN RAINBOW TROUT FILLETS STORED UNDER MODIFIED ATMOSPHERES

JOURNAL OF FOOD SAFETY, Issue 3 2000
ISABELLE DUFRESNE
ABSTRACT Studies were conducted to determine the effect of various levels of headspace oxygen (0,100%, balance CO2) or film oxygen transmission rate (OTR) on the time to toxicity in modified atmosphere packaged (MAP) fresh trout fillets challenged with C. botulinum type E (102 spore/g) and stored under moderate temperature abuse conditions (12C). In all cases, trout were toxic within 5 days, irrespective of the initial levels of oxygen in the package headspace. However, spoilage preceded toxigenesis. Packaging of trout fillets in low gas barrier films, with OTRs ranging from 4,000 to 10,000 cc/m2/day at 24C and 0% relative humidity, also had no effect on time to toxicity in all MAP trout fillets. All fillets were toxic within 4,5 days and spoilage again preceded toxigenesis. This study has shown that the addition of headspace O2, either directly to a package or indirectly by using a low gas barrier film, had no influence on the time to toxigenesis or spoilage. Additional barriers, other than headspace O2 or film transmission rate, need to be considered to ensure the safety of MAP trout fillets, particularty at moderate temperature abuse conditions. [source]

SUPPLEMENTARY OXYGEN AND WOUND HEALING IN VASCULAR SURGERY: TOO SIMPLE TO BE TRUE?

ANZ JOURNAL OF SURGERY, Issue 6 2007
FRACS, John P. Harris AM
No abstract is available for this article. [source]

CT31 HYPERBARIC OXYGEN IN POST-CARDIAC SURGERY STROKE PATIENTS , THE CHRISTCHURCH EXPERIENCE

ANZ JOURNAL OF SURGERY, Issue 2007
A. J. Gibson
Introduction Post-operative strokes occur in a small percentage of adult cardiac surgical patients and have devastating consequences for these patients. There is evidence to suggest that Cerebral Arterial Gas Embolism (CAGE) is an important aetiological factor in most of these cases. Hyperbaric Oxygen therapy (HBOT) is the administration of 100% oxygen at greater than atmospheric pressure. It is accepted as the definitive treatment for CAGE related to SCUBA diving accidents. The similarities between this and the pathophysiology of post cardiac-surgical strokes due to iatrogenic CAGE suggest that beneficial effects from HBOT may accrue to these patients. Purpose The purpose of this study is to review the experience of treating post cardiac-surgical stroke patients in our local hyperbaric oxygen facility, including their presentation, delay before treatment and outcomes. The current evidence base is reviewed. Method A retrospective case series analysis was conducted. Results Over a 10 year period, patients with post cardiac-surgical strokes and who presented within the first 48 hours were referred for HBOT, of whom 12 were treated. The neurological outcomes were excellent in all but one case who died. A review of the literature provides a rational basis for the potential benefits of HBOT in this scenario, but at present there is only limited clinical data to support its use. Conclusion The postulated mechanisms for the development of post cardiac-surgical strokes provide a sound theoretical basis for the suggestion that the use of HBOT is associated with improved outcomes. However there is no prospective data to support such a claim. Such a trial would be problematic and until more evidence is available, HBOT should be considered on a case by case basis. [source]

OXYGEN AND CARBON ISOTOPE ANALYSIS OF HUMAN TOOTH ENAMEL FROM THE NEW KINGDOM SITE OF TOMBOS IN NUBIA

ARCHAEOMETRY, Issue 5 2010
M. R. BUZON
This study examines the feasibility of using oxygen isotope analysis of tooth carbonate to identify immigrants from the New Kingdom site of Tombos in Nubia (n = 30). In comparison with published data, the results (,18Oca,VSMOW = 31.4,) imply a substantial presence of immigrants. However, further analysis of these data strongly suggests the need to consider hydrological and cultural factors such as the contribution of aquifer waters to the Nile, use of groundwater sources, and differences in handling and storage of water. The carbon isotope analysis, in conjunction with published 87Sr/86Sr data, provides additional support for the presence of immigrants at Tombos. [source]

SICKLE CELL DISEASE: ROLE OF REACTIVE OXYGEN AND NITROGEN METABOLITES

CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 9 2007
Katherine C Wood
SUMMARY 1Sickle cell disease (SCD) is an inherited disorder of haemoglobin synthesis that is associated with significant morbidity and mortality due to sequelae of episodic vaso-occlusive events: pain crises and multiorgan damage. The microvascular responses to the initiation, progression and resolution of vaso-occlusive events are consistent with an inflammatory phenotype as suggested by activation of multiple cell types, an oxidatively stressed environment and endothelial cell dysfunction. 2Decreased anti-oxidant defences in SCD patients and mice are accompanied by activation of enzymatic (NADPH oxidase, xanthine oxidase) and non-enzymatic (sickle haemoglobin auto-oxidation) sources of reactive oxygen species. The resultant oxidative stress leads to dysfunction/activation of arteriolar and venular endothelial cells, resulting in impaired vasomotor function and blood cell,endothelial cell adhesion. 3Changes in substrate and cofactor availability for endothelial cell nitric oxide synthase may underlie reactive oxygen- and nitrogen-induced events that contribute to SCD-induced vasculopathy. 4The emerging role of reactive oxygen and nitrogen species in the pathogenesis of SCD provides a platform for the development of novel agents to treat this painful and lethal disease. [source]

Particle in Cell Simulation of Low Temperature Laboratory Plasmas

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 8-9 2007
K. Matyash
Abstract Several applications of PIC simulations for understanding basic physics phenomena in low-temperature plasmas are presented: capacitive radiofrequency discharges in Oxygen, dusty plasmas and negative ion sources for heating of fusion plasmas. The analysis of these systems based on their microscopic properties as accessible with PIC gives improved insight into their complex behavior. These studies are results of joint efforts over about one decade of research groups from Greifswald University, Germany; Bari University, Italy; Keio University, Japan and Innsbruck University, Austria. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Experimental Study and Modelling of Formation and Decay of Active Species in an Oxygen Discharge

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 1 2005
A.-M. Diamy
Abstract A microwave (2.45 GHz) oxygen discharge (3 hPa, 150 W, 50 mL.min,1) is studied by optical emission spectroscopy of O(5P) (line 777.4 nm) and of the atmospheric system of O2(head-line 759.4 nm). Calibration of the spectral response of the optical setup is used to determine the concentrations of O(5P) and O2(b). The concentration of the O(5P) atoms is in the range 108,109 cm,3 and the concentration of the O2(b) molecules is in the range 1014 , 2 × 1014 cm,3 along the discharge tube. An attempt is made to simulate the experimental results by using coupling the Boltzmann equation, homogeneous energy transfer V-V and V-T, heterogeneous reactions on the walls (energy transfer and recombination of atoms) and a kinetic scheme (electronic transfer and chemical reactions). The Boltzmann equation includes momentum transfer, inelastic and superelastic processes and e-e collisions. V-V and V-T transfer equations are obtained from the SSH theory and the kinetic scheme includes 65 reactions with 17 species [electrons e, ions O, and O2,, fundamental electronic neutral species O(3P), O2, O2(X,v), O3 and excited neutral species O2(a), O2(b), O2(A), O(1D), O(1S), O(5P), O(4d 5Do), O(5s 5So), O(3d 5Do) and O(4s 5So)]. A fair agreement between experimental results and modelling is obtained with the following set of fitting values: , heterogeneous deactivation coefficient for O2(b) , = 2.6 × 10,2; , rate constant of reaction [O(1D) + O(3P) , 2 O(3P)] k34 = 1.4 × 10,11 cm3.s,1; , electron concentration in the range 1010 , 1011 cm,3. Modelling shows that the recombination coefficient for oxygen atoms on the silica wall (range 1.4 × 10,3 , 0.2 × 10,3) is of the same order as the values obtained in a previous paper and that the ratio ([O] / 2 [O2]initial) is about 33,50%. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Oxygen sensing in foetal and adult red blood cells

ACTA PHYSIOLOGICA, Issue 3 2007
Michael Berenbrink
No abstract is available for this article. [source]

Occlusive Dressing versus Oxygen Mist Therapy Following CO2 Laser Resurfacing

DERMATOLOGIC SURGERY, Issue 6 2000
Teri Onouye BA
Background. Oxygen is an essential element for collagen synthesis and reepithelialization. The use of topical oxygen after CO2 laser resurfacing has not been studied. Objective. To compare the rate and quality of healing in wounds treated with an oxygen mist to those treated with occlusive dressing following CO2 laser resurfacing. Methods. Three patients underwent CO2 laser resurfacing to each half of the face 3 weeks apart. Postoperatively, half of the face was treated with an oxygen mist protocol for 5 days, while the other half was treated with occlusive dressing for 4 days. Results. At postoperative day 5, significantly less crusting was observed on the half of the face treated with the oxygen mist protocol (p < 0.05). Conclusion. The oxygen mist postoperative protocol may offer patients similar overall healing rates and significantly less crusting compared to occlusive dressing. [source]

Green Synthesis of Silver Nanoparticles Using Ionic Liquid and Application for the Detection of Dissolved Oxygen

ELECTROANALYSIS, Issue 6 2010
Tsung-Hsuan Tsai
Abstract The electrochemical synthesis of silver nanoparticles (nano-Ag) has been successfully carried out on glassy carbon electrode (GCE) and indium tin oxide electrode (ITO) using 1-butyl-3-methylimidazolium tetrafluoroborate (BMT) as green electrolytes. Further the electrodeposited nano-Ag modified ITO electrode has been examined using atomic force microscopy (AFM), and X-ray diffraction studies (XRD). The electrodeposited Ag nanoparticles on ITO were found in the size range of 5 to 35,nm. The nano-Ag film modified GCE was further coated with nafion (Nf) and BMT (1,:,1 ratio) mixture and found to be stable in BMT and in pH,7 phosphate buffer solution (PBS). The nano-Ag/BMT-Nf film modified GCE successfully applied for the oxygen reduction reaction in neutral pH (pH,7.0 PBS). The proposed film modified GCE successfully reduces the over potential and show well defined reduction peaks for the detection of dissolved oxygen using cyclic voltammetry (CV) and rotating disc voltammetry (RDE). The film also applied for the detection of dissolved oxygen using electrochemical impedance spectroscopic studies (EIS). [source]

Electroreduction of Oxygen and Electrooxidation of Methanol at Carbon and Single Wall Carbon Nanotube Supported Platinum Electrodes

ELECTROANALYSIS, Issue 10 2008
Ahmad, Nozad Golikand
Abstract The present research aimed at investigating the electrocatalytic properties and the electrochemical deposition of Pt nanoparticles on carbon powder, carbon nanotube and preparation of carbon and single wall carbon nanotube supported platinum electrodes. The Pt nanoparticles were synthesized by electroreduction of hexachloroplatinic acid in aqueous solution at ,200,mV. Electrocatalytic properties of the modified electrodes for oxygen reduction were investigated by cyclic voltammetry in O2 saturated solution containing 0.1,M HClO4. Methanol electrooxidation at the modified surfaces in 0.5,M HCLO4 was studied by cyclic voltammetry. The corresponding results showed that the Pt/SWCNT/GC electrode exhibits more improved catalytical activity than the Pt/C/GC electrode. [source]

Exploration of Stable Sonoelectrocatalysis for the Electrochemical Reduction of Oxygen

ELECTROANALYSIS, Issue 12 2005
Biljana S, ljuki
Abstract A series of modified electrodes were prepared both via solvent evaporation and electrochemical cycling of azobenzene and derivatives and various quinones and assessed for their suitability as oxygen reduction electrocatalysts and sonoelectrocatalysts. Glassy carbon electrodes were modified via solvent evaporation with 1,2-dihydroxyanthraquinone and 1,2-diazonium-9,10-anthraquinone while edge plane and basal plane pyrolytic graphite electrodes were modified by the same procedure with 9,10-phenanthraquinone. The stability of the attached moiety was accessed in each case under ultrasound. For comparison the same electrode substrates were modified with 9,10-phenanthraquinone by electrochemical cycling and also exposed to ultrasound. The observed results suggest the use of the glassy carbon electrodes modified with azobenzene and derivatives via solvent evaporation as the optimal carbon based sonoelectrocatalysts for oxygen reduction in term of stability under insonation and high catalytic rate. [source]

Electropolymerized Pyrrole-Substituted Manganese Phthalocyanine Films for the Electroassisted Biomimetic Catalytic Reduction of Molecular Oxygen

ELECTROANALYSIS, Issue 2 2005
Nazaré, Pereira Rodrigues
Abstract We report for the first time on the electroassisted biomimetic activation of molecular oxygen by a newly prepared electropolymerized polypyrrole-manganese phthalocyanine film. The prepared films and their intervention in the electroassisted catalytic reduction of molecular oxygen were analyzed by cyclic voltammetry and UV-visible spectrophotometry on optically transparent electrodes. The obtained results demonstrate the probable existence of the key-steps responsible for the suggested formation of the highly reactive manganese oxo intermediate. [source]

Oxygen and Temperature Control during the Cultivation of Microorganisms using Substrate Feeding

ENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 3 2007
J. Vanags
Aerobic fermentation via substrate feeding controlled by O2 and temperature supplements the tools for the experimental and possibly industrial use. This substrate-feeding algorithm was realized with the help of the flexible Bioprocess controller BIO-2. [source]

Gas-Phase Chemistry of Vanadium Oxide Cluster Cations VmOn+ (m = 1,4; n = 1,10) with Water and Molecular Oxygen

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 31 2008
Sandra Feyel
Abstract Bare vanadium oxide cluster cations VmOn+ (m = 1,4; n =1,10) generated by electrospray ionization are investigated with respect to their reactivity toward water and molecular oxygen by using mass spectrometric techniques. Besides ion hydration, the ion/molecule reactions of VmOn+ with oxygen-labeled water (H218O) also lead to 16O/18O exchange reactions of the vanadium oxide clusters cations. Although the probability of degenerate 16O/18O exchange between VmOn+ and water is fairly high for the cluster cations with a medium valence state of vanadium, oxygen-atom exchange reactions between VmOn+ and 18O2 can only be accomplished by VO+, V3O6+, and V4O8+. Particularly interesting is the fact that not only oxygen atoms from vanadyl units are exchanged in the cluster cations, but bridging oxygen atoms are also most likely involved in the processes. Other reaction channels for the interaction of VmOn+ cluster cations with molecular oxygen are reported as well, such as oxidative degradation of the low-valent cluster cations upon collision with O2 and formation of association complexes for the high-valent cluster cations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

An Efficient Molybdenum(VI)-Catalyzed Direct Substitution of Allylic Alcohols with Nitrogen, Oxygen, and Carbon Nucleophiles

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 5 2009
Hongwei Yang
Abstract Direct nucleophilic substitution of allylic alcohols with various nitrogen, oxygen, and carbon nucleophiles catalyzed by MoO2(acac)2 was realized. The corresponding products were obtained in moderate-to-excellent yields. Studies of the reaction mechanism showed that a carbenium intermediate was formed in the transition state. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Diastereoselective Reactions of the Tiglic Acid Functionality Mediated by Oxazolidine Chiral Auxiliaries: A Mechanistic Comparison of DMD andm -CPBA Epoxidations versus Singlet Oxygen and PTAD Ene Reactions

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2005
Aurelia Pastor
Abstract 2,2-Dimethyloxazolidines have been utilized as chiral auxiliaries for the diastereoselective functionalization of the optically active tiglic acid derivatives (S)- 1 by means of epoxidation with DMD or m -CPBA and ene reactions with 1O2 or PTAD. In the DMD and m -CPBA epoxidations, high diastereoselectivities but opposite senses of diastereomer selection were observed. In contrast, the stereochemistry of the 1O2 and PTAD ene reactions depended on the size of the attacking enophile: whereas essentially perfect diastereoselectivity was obtained with PTAD, much lower stereoselection was observed with 1O2. The stereochemical results for the DMD and m -CPBA epoxidations and the PTAD ene reaction are explained in terms of the energy differences for the corresponding diastereomeric transition states, dictated by steric and electronic effects. The PTAD ene reaction for these tiglic acids (S)- 1 provides, after removal of the chiral auxiliaries, an attractive synthetic route for optically active ,-amino acid derivatives.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Oxygen sensing in hypoxic pulmonary vasoconstriction: using new tools to answer an age-old question

EXPERIMENTAL PHYSIOLOGY, Issue 1 2008
Gregory B. Waypa
Hypoxic pulmonary vasoconstriction (HPV) becomes activated in response to alveolar hypoxia and, although the characteristics of HPV have been well described, the underlying mechanism of O2 sensing which initiates the HPV response has not been fully established. Mitochondria have long been considered as a putative site of oxygen sensing because they consume O2 and therefore represent the intracellular site with the lowest oxygen tension. However, two opposing theories have emerged regarding mitochondria-dependent O2 sensing during hypoxia. One model suggests that there is a decrease in mitochondrial reactive oxygen species (ROS) levels during the transition from normoxia to hypoxia, resulting in the shift in cytosolic redox to a more reduced state. An alternative model proposes that hypoxia paradoxically increases mitochondrial ROS signalling in pulmonary arterial smooth muscle. Experimental resolution of the question of whether the mitochondrial ROS levels increase or decrease during hypoxia has been problematic owing to the technical limitations of the tools used to assess oxidant stress as well as the pharmacological agents used to inhibit the mitochondrial electron transport chain. However, recent developments in genetic techniques and redox-sensitive probes may allow us eventually to reach a consensus concerning the O2 sensing mechanism underlying HPV. [source]

Electrochemical Reduction of Oxygen on Carbon Supported Pt and Pt/Ru Fuel Cell Electrodes in Alkaline Solutions

FUEL CELLS, Issue 4 2003
E.H. Yu
Abstract A study of O2 reduction in 1 M NaOH solution at gas diffusion electrodes made from carbon supported Pt and Pt/Ru catalysts is reported. Two Tafel regions were observed for both the Pt and Pt/Ru electrodes. Although the same mechanism was suggested for oxygen reduction on both Pt and Pt/Ru catalysts, the O2 reduction activity was lower on Ru. Electrochemical Impedance Spectroscopy (EIS) analysis was carried out at different potentials and showed the significant contribution of diffusion on the reaction process and kinetics. The effect of methanol on O2 reduction was investigated in solutions containing various concentrations of methanol. The electrode performance deteriorated with increasing methanol concentration because of a mixed cathode potential. The methanol tolerance, i. e., the methanol concentration which polarises the O2 reduction reaction for O2 reduction, at the Pt/C electrode with a Pt loading of 1.2 mg cm,2 is 0.2 M methanol in 1 M NaOH. [source]

[FeFe]-hydrogenase-like gene is involved in the regulation of sensitivity to oxygen in yeast and nematode

GENES TO CELLS, Issue 4 2009
Michihiko Fujii
Oxygen is essential for the life of aerobic organisms, but reactive oxygen species (ROS) derived from oxygen can be a threat for it. Many genes are involved in generation of ROS, but not much attention has been focused on the reactions from which ROS are generated. We therefore screened for mutants that showed an increased sensitivity to oxidative stress in the nematode Caenorhabditis elegans, and isolated a novel mutant, oxy-4(qa5001). This mutant showed an increased sensitivity to a high concentration of oxygen, and decreased longevity at 20 °C but not at 26 °C. The genetic analysis has revealed that oxy-4 had a causative mutation in an [FeFe]-hydrogenase-like gene (Y54H5A.4). In the yeast Saccharomyces cerevisiae, a deletion of NAR1, a possible homologue of oxy-4, also caused a similar increased sensitivity to oxygen. [FeFe]-hydrogenases are enzymes that catalyze both the formation and the splitting of molecular hydrogen, and function in anaerobic respiration in anaerobes. In contrast, [FeFe]-hydrogenase-like genes identified in aerobic eukaryotes do not generate hydrogen, and its functional roles are less understood. Our results suggested that [FeFe]-hydrogenase-like genes were involved in the regulation of sensitivity to oxygen in S. cerevisiae and C. elegans. [source]

An In Situ Device to Measure Oxygen in the Vadose Zone and in Ground Water: Laboratory Testing and Field Evaluation

GROUND WATER MONITORING & REMEDIATION, Issue 2 2008
Bradley M Patterson
Oxygen probes developed to measure in situ oxygen concentrations in gaseous and aqueous environments were evaluated in laboratory tests and during long-term field evaluation trials at contaminated sites. The oxygen probes were shown to have a linear calibration and to be accurate compared to conventional dissolved oxygen electrodes and gas chromatography, both of which require labor-intensive sample collection and processing. The probes, once calibrated, required no maintenance or recalibration for up to a period of 7 years in low-oxygen environments, demonstrating long-term stability. Times to achieve 90% of the stabilized concentration (t90) after a step change in aqueous oxygen concentration were 100,120 min in laboratory experiments and up to 180 min in field experiments, which is adequate for monitoring subsurface changes. Field application data demonstrated that the oxygen probes could monitor oxygen concentrations in hydrocarbon-contaminated ground water to a depth of 20 m below the water table or in pyritic vadose zones over extended periods. During bioremediation field trials, oxygen monitoring enabled estimation of oxygen utilization rates by microorganisms and hydrocarbon biodegradation rates. Also, probes were able to monitor the development of ground water desaturation during air sparging trials, enabling the automated assessment of the distribution of injected air. [source]

Insertion of Molecular Oxygen in Transition-Metal Hydride Bonds, Oxygen-Bond Activation, and Unimolecular Dissociation of Metal Hydroperoxide Intermediates.

HELVETICA CHIMICA ACTA, Issue 3 2008
Short Communication
Abstract Thermal activation of molecular oxygen is observed for the late-transition-metal cationic complexes [M(H)(OH)]+ with M=Fe, Co, and Ni. Most of the reactions proceed via insertion in a metalhydride bond followed by the dissociation of the resulting metal hydroperoxide intermediate(s) upon losses of O, OH, and H2O. As indicated by labeling studies, the processes for the Ni complex are very specific such that the O-atoms of the neutrals expelled originate almost exclusively from the substrate O2. In comparison to the [M(H)(OH)]+ cations, the ionmolecule reactions of the metal hydride systems [MH]+ (M=Fe, Co, Ni, Pd, and Pt) with dioxygen are rather inefficient, if they occur at all. However, for the solvated complexes [M(H)(H2O)]+ (M=Fe, Co, Ni), the reaction with O2 involving OO bond activation show higher reactivity depending on the transition metal: 60% for the Ni, 16% for the Co, and only 4% for the Fe complex relative to the [Ni(H)(OH)]+/O2 couple. [source]

Quenching of Singlet Oxygen by Tertiary Aliphatic Amines.

HELVETICA CHIMICA ACTA, Issue 10 2006
Products, Structural Effects on Rates
Abstract A kinetic and product study of the reaction of a series of , -methyl-substituted N -methylpiperidines with thermally generated 1O2 in MeCN was carried out. It was found that as the number of , -methyl groups (Me in , -position relative to the N-atom) increases, the rate of 1O2 quenching (physical plus chemical) slightly decreases. This finding shows that, with respect to the reaction rate, steric effects are much more important than electronic effects as the latter should have produced the opposite result. The opposite outcome was instead found for the chemical quenching that leads to the N -demethylation products and N -formyl derivatives. The same trend was observed for the ratio between N -demethylation and formation of the N -formyl derivatives (NH/NCHO ratio). All these results are consistent with the mechanism reported in Scheme,1 where an exciplex is first formed that by a H-atom transfer process produces an , -amino-substituted C-radical. The latter forms the product of N -demethylation by one electron oxidation, or affords the N -formyl derivative by radical coupling (Scheme,1). Similar results were obtained with N,N -dimethylcyclohexanamine. However, this ,acyclic' amine exhibited behaviors quite distinct from those of the N -methylpiperidines series, with respect to reaction rate, extent of chemical quenching, and NH/NCHO ratio. [source]

Effect of the Media on the Quantum Yield of Singlet Oxygen (O2(1,g)) Production by 9H -Fluoren-9-one: Solvents and Solvent Mixtures

HELVETICA CHIMICA ACTA, Issue 2 2003
Claudia
We have investigated the effect of a series of 18 solvents and mixtures of solvents on the production of singlet molecular oxygen (O2(1,g), denoted as 1O2) by 9H -fluoren-9-one (FLU). The normalized empirical parameter E derived from ET(30) has been chosen as a measure of solvent polarity using Reichardt's betaine dyes. Quantum yields of 1O2 production (,,) decrease with increasing solvent polarity and protic character as a consequence of the decrease of the quantum yield of intersystem crossing (,ISC). Values of ,, of unity have been found in alkanes. In nonprotic solvents of increasing polarity, ,ISC and, therefore, ,, decrease due to solvent-induced changes in the energy levels of singlet and triplet excited states of FLU. This compound is a poor 1O2 sensitizer in protic solvents, because hydrogen bonding considerably increases the rate of internal conversion from the singlet excited state, thus diminishing ,, to values much lower than those in nonprotic solvents of similar polarity. In mixtures of cyclohexane and alcohols, preferential solvation of FLU by the protic solvent leads to a fast decrease of ,, upon addition of increasing amounts of the latter. [source]

Direct Spectroscopic Evidence for a Photodoping Mechanism in Polythiophene and Poly(bithiophene- alt -thienothiophene) Organic Semiconductor Thin Films Involving Oxygen and Sorbed Moisture

ADVANCED MATERIALS, Issue 46 2009
Jing-Mei Zhuo
Direct infrared spectroscopic evidence has been obtained for photodoping of high mobility regioregular poly(3-alkylthiophene) and poly[2,5-bis(3-alkyllthiophen-2-yl) thieno (3,2-b)thiophene] with the attendant formation of hydroxide counter-ions. This reveals the central role of dissolved water, explains the key features of degradation of the electrical characteristics of organic semiconductors in the ambient (see figure), and points to possible strategies to further improve their stability. [source]

Multicolor Fluorescent and Permeation-Selective Microbeads Enable Simultaneous Sensing of pH, Oxygen, and Temperature

ADVANCED MATERIALS, Issue 21 2009
Matthias I. J. Stich
Multicolor fluorescent microbeads made from various polymers and incorporated into a binder polymer to produce a material whose three signals (measuring pH, temperature, and presence of O2) can be unambiguously assigned after either spectral or time-resolved separation. This renders the material well suited for continuous sensing of these parameters in blood or other bioliquids. [source]

Composite Material for Simultaneous and Contactless Luminescent Sensing and Imaging of Oxygen and Carbon Dioxide,

ADVANCED MATERIALS, Issue 12 2006
M. Borisov
"Seeing" oxygen and carbon dioxide: A sensor material is described that enables simultaneous imaging and monitoring of carbon dioxide and oxygen (see figure). It relies on the measurement of the phase shift of the luminescence decay time of a material composed of microbead-contained indicators (with well-separated excitation and emission wavelengths) and polymers with excellent permeation selectivities as well as favorable optical and adhesive properties. [source]

Effect of packaging materials and dissolved oxygen on the survival of probiotic bacteria in yoghurt

INTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 6 2004
Akshat Talwalkar
Summary The effects of packaging materials on the dissolved oxygen and the survival of the probiotic bacteria in yoghurt were studied. Oxygen adapted and non-oxygen adapted strains of Lactobacillus acidophilus and Bifidobacterium spp. were incorporated in yoghurts, which were packaged in oxygen permeable high-impact polystyrene (HIPS), oxygen-barrier material (NupakTM) and NupakTM with an oxygen scavenging film (Zero2TM). During storage the dissolved oxygen increased steadily in HIPS packaged yoghurt whereas it remained low in yoghurts packaged in NupakTM and Zero2TM. In all yoghurts, no significant decreases were observed in the viability of either oxygen adapted or non-oxygen adapted cells of L. acidophilus and Bifidobacterium spp. Thus, although the dissolved oxygen in yoghurt can be influenced by the type of packaging material, it may not affect the survival of probiotic bacteria in yoghurts. [source]

Palladium on Carbon-Catalyzed Synthesis of Benzil Derivatives from 1,2-Diarylalkynes with DMSO and Molecular Oxygen as Dual Oxidants

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010
Shigeki Mori
Abstract A palladium on carbon (Pd/C)-catalyzed synthetic method for the preparation of benzil derivatives from 1,2-diarylalkynes has been established using dimethyl sulfoxide (DMSO) and molecular oxygen as dual oxidants. Regardless of the electrical nature of the functional groups on the aromatic rings, 1,2-diarylalkynes were oxidized to the corresponding benzil derivatives in high to excellent yields. Furthermore, the oxidation could efficiently be catalyzed by both the dry and wet types of Pd/C under atmospheric conditions. [source]