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At least 343 records · Page 19Linked to original sources
PubMed2000

Characterization of a commercial gas chromatography-flame ionization detection system for the in situ determination of C5-C10 hydrocarbons in ambient air.

A commercial automated gas chromatograph with preconcentration on solid adsorbents (AirmoVoc HC1010) was coupled with a mass spectrometer in parallel with the flame ionization detection (FID) system and characterized for its suitability for quasi continuous measurements of atmospheric hydrocarbons (HCs) with a time resolution of 20 min. Of the 50 identified HCs in the range C5-C10, 15 elute in isolated peaks and 20 in groups of two or more HCs. The remaining 15 HCs suffer from coelution by oxygenated and halogenated compounds. Procedures to minimize and quantify the blanks and the memory from the adsorbents are described. Calibration was based on a custom-made diffusion source. The accuracy of this calibration (+/-10%, 2sigma) was verified by analysis of a certified 70-component standard (average deviation: -4.3+/-2%). During a field experiment in Summer 1998, the HC1010 system was compared with a custom-made GC system with cryogenic preconcentration and much better separation properties but lower time resolution. In ambient air, good agreement (2sigma deviation <14% or 10 ppt) was found for HCs and groups of HCs that are free from coelution with oxygenated compounds, whereas large discrepancies (in some cases more than a factor of three) were found for those HCs that coelute with oxygenated compounds, as identified by MS. Analysis of the mass spectra from those peaks via specific target ions showed much better agreement with the FID system of the reference GC within 25%.

Air Pollutants↗
PubMedDate not supplied

Chemical polymorphism of the essential oils from populations of Thymus caespititius grown on the islands Pico, Faial and Graciosa (Azores).

The compositions of the essential oils isolated from the aerial parts of 11 populations of Thymus caespititius collected during the flowering phase on Pico, Faial and Graciosa (Azores) were studied by GC and GC-MS. The monoterpene fraction was dominant in all the oils analysed (55-90%) and consisted mainly of oxygen-containing compounds (44-79%). Sesquiterpenes represented an important fraction of the oils from the populations grown on Graciosa (13-28%). In contrast, this fraction was rather small in the oils from the populations grown on Pico and Faial (6-11%). Despite this, oxygen-containing compounds (4-18%) were always dominant. Cluster analysis of all identified oil components grouped the oils into three main clusters that corresponded with their main components. The oils from the 11 populations studied showed a clear chemical polymorphism that, in some cases, was more evident among populations growing on the same island than among those from different islands.

Azores↗
PubMed1999

Oxygen release kinetics from solid phase oxygen in Arctic Alaska.

Child's Pad is a gravel construction surface that was contaminated with petroleum during oil-field service operations in Deadhorse, Alaska. As part of a remedial action plan, a buffer strip of uncontaminated sandy gravel was placed along sections of the pad boundary. A magnesium peroxide formulation manufactured by Regenesis, and sold as Oxygen Release Compound (ORC), was placed in the buffer strips. The ORC was intended to supply oxygen to aerobic microorganisms capable of degrading petroleum. Studies were conducted in the laboratory to determine initial oxygen release kinetics from ORC in contact with barrier soil. Studies quantified the biotic and abiotic catalytic mechanisms for converting hydrogen peroxide (a possible MgO2 intermediate) and ORC to oxygen and water, the effects of temperature on oxygen release from ORC, and the effect of field exposure on ORC viability. Barrier soil exhibited sufficient catalytic activity to convert hydrogen peroxide to oxygen faster than the expected biological demand. The oxygen evolution rate (OER) from ORC was lower at 7 degrees C than 21 degrees C by more than two times. The ORC recovered from Child's Pad after less than 1 year retained nearly all of the original available oxygen, although physical bridging was evident.

Alaska↗
PubMed2006

Dopamine/serotonin receptor ligands. Part 15: Oxygenation of the benz-indolo-azecine LE 300 leads to novel subnanomolar dopamine D1/D5 antagonists.

Relying on the high affinities of the benz-indolo-azecine LE 300 (1) and the hydroxylated dibenz-azecine LE 404 (2b) for the D1/D5 receptor subtypes, we synthesized methoxylated, hydroxylated and an indole-N methylated derivatives of 1 (Fig. 1). Hydroxylation of azecine derivatives is beneficial with regard to the affinities and selectivities for all the dopamine receptor subtypes. The 'serotonin-derived' 3-oxygenated target compounds but not the 11-oxygenated analogues were superior to the unsubstituted LE 300. 11-Methoxy-7,14-dimethyl-6,7,8,9,14,15-hexahydro-5H-indolo[3,2-f][3]benzazecine (3e) was found to be the most potent antagonist at D2/D3/D4 and D5 receptor subtypes (Ki for D5 = 0.23 nmol) of all known benz-indolo-azecines.

Dopamine Antagonists↗
PubMed2004

Direct oxidation of 2',7'-dichlorodihydrofluorescein by pyocyanin and other redox-active compounds independent of reactive oxygen species production.

Formation of dichlorofluorescein (DCF), the fluorescent oxidation product of 2',7'-dichlorodihydrofluorescein (DCFH2), in cells loaded with the latter compound is often used to detect ROS formation. We previously found that exposure of DCFH2-loaded A549 cells to the Pseudomonas aeruginosa secretory product pyocyanin results in DCF formation, consistent with ROS production. However, since pyocyanin directly accepts electrons from NAD(P)H, we hypothesized that pyocyanin might directly oxidize DCFH2 to DCF without an ROS intermediate. Incubation of DCFH2 with pyocyanin rapidly resulted in DCF formation, the rate of which was proportional to the [pyocyanin] and was not inhibited by SOD or catalase. Phenazine methosulfate, a pyocyanin analog, was more effective than pyocyanin in generating DCF. Mitoxantrone and ametantrone also produced DCF. However, menadione, paraquat, plumbagin, streptonigrin, doxorubicin, daunorubicin, and 5-iminodaunorubicin did not. Pyocyanin, phenazine methosulfate, mitoxantrone, and ametantrone also oxidized dihydrofluorescein and 5- (and 6-) -carboxy-2',7'-dichlorodihydrofluorescein, whereas dihydrorhodamine was oxidized only by pyocyanin or phenazine methosulfate. Under aerobic conditions, the interaction of DCFH2 with pyocyanin or phenazine methosulfate (but not mitoxantrone or ametantrone) produced superoxide, as detected by spin trapping. Direct oxidation of the fluorescent probes needs to be controlled for when employing these compounds to assess ROS formation by biological systems exposed to redox active compounds.

Fluoresceins↗
PubMed2001

Biofiltration of a mixture of volatile organic emissions.

Air biofiltration is now under active consideration for the removal of the volatile organic compounds (VOCs) from polluted airstreams. To optimize this emerging environmental technology and to understand compound removal mechanisms, a biofilter packed with peat was developed to treat a complex mixture of VOCs: oxygenated, aromatic, and chlorinated compounds. The removal efficiency of this process was high. The maximum elimination capacity (ECmax) obtained was approximately 120 g VOCs/m3 peat/hr. Referring to each of the mixture's components, the ECmax showed the limits in terms of biodegradability of VOCs, especially for the halogenated compounds and xylene. A stratification of biodegradation was observed in the reactor. The oxygenated compounds were metabolized before the aromatic and halogenated ones. Two assumptions are suggested. There was a competition between bacterial communities. Different communities colonized the peat-based biofilter, one specialized for the elimination of oxygenated compounds, the others more specialized for elimination of aromatic and halogenated compounds. There was also substrate competition. Bacterial communities were the same over the height of the column, but the more easily biodegradable compounds were used first for the microorganism metabolism when they were present in the gaseous effluent.

Air Pollutants↗
PubMed1994

Biodegradation of trace levels of a complex organic pollutant mixture.

Three bacterial isolates with the ability to grow on a model mixture of ground water contaminants were obtained from a sewage works for treatment of industrial effluents, and from heavily and intermediately contaminated ground. The mixture consisted of benzene, toluene, o-xylene, nitrobenzene, 1,4-dichlorobenzene, o-cresol, naphthalene, tetrachloromethane and trichloroethylene, at concentrations ranging from 150 to 600 micrograms/l (2.1 mg/l in total). A supplement of 50 mg/l phenol was added to support growth and batch cultures were adapted for 6 weeks. Preliminary assays to check for degradative ability and toxicological assessments of the compounds using oxygen uptake rates were undertaken. Each isolate exhibited a different extent of degradation for the compounds. In 18 h incubation, from an initial figure of 1,966 micrograms/l (not including the primary substrate) the highest remaining total organic carbon of 800 micrograms/l was for the isolate from activated sludge. The effect of the organic compounds upon oxygen uptake rate was less marked for the micro-organisms from heavily polluted ground. As far as bioremediation of groundwater is concerned, the combination of both chemical structure variety and extremely low concentrations of individual chemicals in the mixture under investigation, make the present report relevant to many environmental problems.

Bacteria↗
PubMed1999

Molecular Mechanics (MM3) Calculations on Oxygen-Containing Phosphorus (Coordination IV) Compounds.

An MM3 force field has been developed for small oxygen-containing phosphorus (coordination IV) compounds. Experimental electron and neutron diffraction, X-ray, and infrared spectral data were utilized in parametrization when available. Results from previous ab initio calculations at both the restricted Hartree-Fock (RHF) and second-order Møller-Plesset (MP2) levels of theory with the standard 6-31G basis set supplemented missing structural data, rotational profiles, and vibrational frequencies. Negative hyperconjugation (the anomeric effect) affects the structures and energies of the molecules under study which contain one or more sp(3)-hybridized oxygen atoms. Natural bond order (NBO) analysis was helpful in identifying the key orbital interactions involved in this effect.

Journal Article↗
PubMed2004

Diverse modes of reactivity of dialkyl azodicarboxylates with P(III) compounds: synthesis, structure, and reactivity of products other than the Morrison-Brunn-Huisgen intermediate in a Mitsunobu-type reaction.

The reactivity of diethyl azodicarboxylate (DEAD)/diisopropyl azodicarboxylate (DIAD) with P(III) compounds bearing oxygen or nitrogen substituents is explored. Compounds with structures quite different from that of Morrison-Brunn-Huisgen intermediate R'(3)P(+)N(CO(2)R)N(-)(CO(2)R) (1), observed in the Mitsunobu reaction, have been established by using X-ray crystallography and NMR spectroscopy. Thus reactions with X(6-t-Bu-4-Me-C(6)H(2)O)(2)P-NH-t-Bu [X = S (8), CH(2) (9)] or XP(mu-N-t-Bu)(2)P-NH-t-Bu [X = Cl (14) or NH-t-Bu (15)] and DEAD/DIAD lead to phosphinimine-carbamate-type of products X[6-t-Bu-4-Me-C(6)H(2)O](2)P[N-t-Bu][N(CO(2)R)NH(CO(2)R)] [X = S, R = Et (16); X = CH(2), R = Et (17); X = CH(2), R = i-Pr (18)] or XP(mu-N-t-Bu)(2)P(N-t-Bu)[N-(CO(2)-i-Pr)-N(H)(CO(2)-i-Pr) [X = Cl (19), NH-t-Bu (20)]. Treatment of 19 with 2,2,2-trifluoroethanol afforded the product [(CF(3)CH(2)O)P(mu-N-t-Bu)(2)P(+)(NH-t-Bu)[N(CO(2)-i-Pr)(HNCO(2)-i-Pr)]][Cl(-)] (21) whose structure is close to one of the intermediates proposed in the Mitsunobu reaction. The isocyanate CH(2)(6-t-Bu-4-Me-C(6)H(2)O)(2)P-NCO (10) underwent 1,3-(P,C) cycloaddition with DEAD/DIAD to lead to CH(2)(6-t-Bu-4-Me-C(6)H(2)O)(2)P[N(CO(2)R)N(CO(2)R)-C(O)-N] [R = Et (22), i-Pr (23)]. Reaction of 22-23 with 1,1'-bi-2-naphthol or catechol leads to novel tetracoordinate CH(2)(6-t-Bu-4-Me-C(6)H(2)O)(2)P(2,2'-OC(10)H(6)-C(10)H(6)-OH)[NC(O)-(CO(2)R)NH(CO(2)R)] [R = Et (24), i-Pr (25)] or pentacoordinate CH(2)(6-t-Bu-4-Me-C(6)H(2)O)(2)P(1,2-O(2)C(6)H(4))[NHC(O)-N(CO(2)R)NH(CO(2)R)] [R = Et (26), i-Pr (27)] compounds in which the original NCO residue is retained; this mode of reactivity is quite different from that observed for the MBH betaine 1. In 27, the nitrogen, rather than the oxygen, occupies an apical position of the trigonal bipyramidal phosphorus violating the commonly assumed preference rules for apicophilicity. It is shown that the previously reported azide derivative 3, obtained from the reaction of 11 with DIAD, undergoes a Curtius-type rearrangement to lead to the fused cyclodiphosphazane [(CH(2)(6-t-Bu-4-Me-C(6)H(2)O)(2))P(OC(O-i-Pr)NN(CO(2)-i-Pr)N)](2) (28); this compound is in equilibrium with its monomeric form in solution at >300 K. Finally, reaction of S(6-t-Bu-4-Me-C(6)H(2)O)(2)P(OPh) (13) with DIAD gave the hexacoordinate compound S[6-t-Bu-4-Me-C(6)H(2)O](2)P(OPh)[N(CO(2)-i-Pr)NC(O-i-Pr)O] (30) with an intramolecular S-->P bond. X-ray crystallographic evidence for compounds 16, 19, 21, 22, 25, 27, 28, and 30 has been provided.

Alkylation↗
PubMed1981

Serum lipoproteins modulate oxygenated sterol insertion into human red cell membranes.

The insertion of oxygenated sterol compounds into human red blood cell membranes as well as the consequent transformation of the red cells to an echinocyte shape and the expansion of the membranes are impeded by the presence of serum lipoproteins in the incubation medium. All density classes of human serum lipoproteins bind oxygenated sterol compounds, and lipoproteins can act as acceptors of oxygenated sterols previously inserted into red cells. Since oxygenated sterols have been reported to be atherogenic, the modulating and possibly protective effects of serum lipoproteins on oxygenated sterol-induced derangement of cell membrane structure and function may provide a useful model for further study.

Cholesterol↗
PubMed1989

Methylreductic acid and hydroxymethylreductic acid: oxygen radical-forming agents in heated starch.

Two compounds forming oxygen radicals were isolated from heated starch by monitoring the potency to form 8-hydroxydeoxyguanosine from deoxyguanosine during purification procedures. These compounds were identified as hydroxymethylreductic acid and methylreductic acid. The former compound was mutagenic to Salmonella strains TA100, TA102 and TA104 and the latter compound induced sister-chromatid exchanges in human NL3 cells. Hydroxymethylreductic acid was found to be a novel compound. Considerable amounts of these compounds were detected in various heat-processed foods.

Animals↗
PubMed1987

Antiarthritic gold compounds effectively quench electronically excited singlet oxygen.

Although certain gold [Au(I)] compounds have been used effectively in the treatment of rheumatoid arthritis for some years, the molecular basis for such therapeutic action has been unclear. One possible mechanism of the action of Au(I) compounds is that they protect unsaturated membrane lipids and proteins against oxidative degradation caused by activated phagocytes that are not properly regulated. In this study it has been shown that superoxide ion (O-2.), a product of activated phagocytes, can be oxidized to electronically excited singlet oxygen (O1(2)delta g), an agent that is capable of peroxidation of unsaturated fatty acid derivatives. It has also been shown that antiarthritic Au(I) compounds are effective deactivators of O1(2)delta g with quenching constants on the order of 10(7) M-1 sec-1.

Arthritis, Rheumatoid↗
PubMed2006

A method for controlling hydrogen sulfide in water by adding solid phase oxygen.

This work evaluates the addition of solid phase oxygen, a magnesium peroxide (MgO(2)) formulation manufactured by Regenesis (oxygen-releasing compounds, ORC), to inhibit the production of hydrogen sulfide (H(2)S) in an SRB-enriched environment. The initial rate of release of oxygen by the ORC was determined over a short period by adding sodium sulfite (Na(2)SO(3)), which was a novel approach developed for this study. The ability of ORCs to control H(2)S by releasing oxygen was evaluated in a bench-scale column containing cultured sulfate reducing bacteria (SRB). After a series of batch tests, 0.4% ORC was found to be able to inhibit the formation of H(2)S for more than 40 days. In comparison, the concentration of H(2)S dropped from 20 mg S/L to 0.05 mg S/L immediately after 0.1% hydrogen peroxide (H(2)O(2)) was added, but began to recover just four days later. Thus, H(2)O(2) does not seem to be able to inhibit the production of sulfide for an extended period of time. By providing long-term inhibition of the SRB population, ORC provides a good alternative means of controlling the production of H(2)S in water.

Hydrogen Peroxide↗
PubMed1985

Effects of three histaminergic compounds on function and oxygen consumption of isolated guinea-pig hearts.

First experiences in man indicate, that even in catecholamine-insensitive congestive cardiomyopathy a considerable improvement of myocardial function can be attained by the H2-receptor agonist impromidine. In an isolated, pressure-volume work performing guinea-pig heart preparation cardiac effects of three histaminergic compounds (Na,5-dimethylhistamine (HC1)2, 5-ethyl-Na-methyl-histamine (HC1)2, Na,Na-dimethyl-histamine (HC1)2) were examined. Influences on function and myocardial oxygen consumption were compared to those obtained by impromidine. Dose-response curves for the histamine derivatives were 1.7-2.5 orders of magnitude right of the impromidine curves. Maximal inotropic stimulation was greater for Na,5-dimethyl-histamine (HC1)2 than for impromidine. All compounds exhibited a high chronotropic effect and, at high concentrations, a net coronary dilating effect.

Animals↗
PubMed1981

Effects of oxygen and sulphydryl-containing compounds on irradiated transforming DNA. Part I. Actions of dithiothreitol.

The actions and interactions of oxygen and the sulphydryl-containing compound dithiothreitol (DTT) upon the radiation sensitivity of the biological activity of purified Bacillus subtilis transforming DNA have been examined. It has previously been shown that the sensitivity of transforming DNA irradiated in dilute solution is less when irradiation is performed in 100 per cent O2 than when in 100 per cent N2, i.e. O2 protects transforming DNA with a dose-modifying factor of about 0.7. DTT protects transforming DNA in a manner that is dependent on DTT concentration and on gassing conditions. In O2 the DTT protection can largely be attributed to the scavenging of .OH radicals by the DTT, but in anoxia DTT exerts a further protective effect which results in an increasing oxygen enhancement ratio (o.e.r.) with increasing DDT concentration to a maximum o.e.r. of about 14 at 2-5 mM DTT. This additional protective effect of DTT is attributable to hydrogen atom donation from DTT to DNA radicals, thus chemically repairing the DNA. Oxygen appears to block this chemical repair reaction.

Bacteria↗