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At least 127 records · Page 7Linked to original sources
PubMed2006

Comprehensive two-dimensional gas chromatography in the analysis of volatile samples of natural origin: a multidisciplinary approach to evaluate the influence of second dimension column coated with mixed stationary phases on system orthogonality.

The study evaluates the influence of selectivity tuning of the stationary phase of the second dimension on the orthogonality of a comprehensive two-dimensional gas chromatography (GC x GC) system. Two different sets of columns, providing independent and semi-independent separation mechanisms were used. The first consisted of a first dimension separating analytes on a volatility basis (i.e. a non-polar polydimethylsiloxane (OV1) column) combined with a second dimension separating by polarity, using columns coated with 100% polyethylene glycol (CW20M), CW20M/OV1 mixtures in ratios of 25-75%, and polydimethylsiloxane, 7% phenyl, 7% cyanopropyl (OV1701). The second set consisted of a first dimension separating analytes on a polarity basis (100% CW20M column) combined with a second dimension separating by volatility, consisting of columns coated with 100% OV1, OV1/CW20M mixtures in ratios of 25-75%, and 100% OV1701. Medium-complexity mixtures of natural origin (i.e. peppermint essential oil and a standard mixture of suspected allergens) consisting of components in a relatively limited range of molecular weights (MW) and volatilities, but belonging to different classes of compounds in a wide range of polarity (mono- and sesquiterpenoids, hydrocarbons and oxygenated compounds) were analysed with the above sets of columns. Different approaches were used to evaluate peak spreading on the GC x GC separation plane and degree of orthogonality of the column sets, namely: (1) a Factor Analysis (FA) approach, estimating the correlation coefficients and spreading angles of the sample components in the two-dimensional chromatographic plane; (2) an Informational Theory (IT) approach, based on determining a group of parameters including: informational entropy, % synentropy and similarity (H); and (3) an approach based on estimating the amount of separation space used, i.e. a practical parameter that directly refers to the experimental separation plane of the GC x GC chromatogram. Results showed that peak spreading in the chromatographic plane, when CW20M and OV1 are combined in different ratios, can be predicted from retention mechanisms, and that the degree of orthogonality measured with different approaches, is consistent with the divergent nature, in terms of polarity of the stationary phases combined in the GC x GC system.

Allergens↗
PubMed1984

The arachidonic acid cascade. The prostaglandins, thromboxanes and leukotrienes.

Certain polyunsaturated fatty acids, such as arachidonic acid, are metabolized by oxygenation into a large family of biologically active substances, the prostanoids. These include the prostaglandins, thromboxanes, prostacyclins, leukotrienes and also a number of related compounds. Oxygenation can take place at many different positions of arachidonic acid. A cyclo-oxygenase introduces oxygen at C-11 and converts the resulting peroxy compound into a 9, 11-endoperoxide structure. The cyclic peroxides thus formed, PGG2 and PGH2, are highly potent compounds and are the immediate precursors of the prostaglandins, thromboxanes and prostacyclin. Other enzymes, the lipoxygenases, may instead introduce oxygen at C-5, C-8, C-9, C-12 or C-15: further conversions from, for example, the initially formed 5- or 15-hydroperoxy acids may lead to the leukotrienes. The prostanoids display strong and varied biological activities, and have effects on numerous processes in the body. In some pathological conditions the prostanoids play important roles. For example, certain products of the arachidonic acid cascade are considered to be mediators of the inflammatory response: they are formed during the process, contribute to the symptoms of erythema, vascular leakage, fever, pain and chemotaxis, and inhibition of their biosynthesis can be achieved at different levels by the anti-inflammatory drugs.

Animals↗
PubMed1994

Postpartum erythrophagocytosis, iron storage and iron secretion in the endometrium of the tree shrew (Tupaia) during pregnancy.

Tree shrews (Tupaia belangeri) develop a bidiscoid endotheliochorial placenta. In addition, histiotrophe secreted by uterine glands is absorbed by the paraplacental trophoblast. Histiotrophe which is rich in iron is necessary for erythropoiesis in the young embryo. This report is part of a study of the accumulation and metabolism of iron in the endometrium of precisely dated pregnant Tupaia belangeri by application of electron spectroscopy and histochemistry. In the endometrium of tree shrews which had been pregnant at least once, iron-laden granules were present in macrophages and secreting cells of uterine glands. Iron accumulated in the endometrium shortly after parturition, when macrophages phagocytosed erythrocytes at small haematomas 0.2-0.5 mm in diameter. These haematomas arose during parturition after bleeding into the uterine stroma when the placental discs were detached. At 24 h after parturition the following structural consequences of the erythrolysosomal breakdown of phagocytosed erythrocytes could be observed: free cytosolic siderin granules, membrane-bound siderosomes, telolysosomes (some of which contained myelin figures or lipid droplets) and mixed telolysosomes (containing membranous stacks and siderin granules). During the lysosomal degradation of phagocytosed erythrocytes, iron was transferred from haemoglobin into a different macromolecular compound. Electron energy loss spectra detected from inside siderosomes indicated an iron-oxygen compound, and high-power bright field electron micrographs of siderosomes demonstrated the ultrastructural pattern characteristic of ferritin. At about d 12 of a new pregnancy, macrophages containing siderosomes closely approached the bases of secreting cells of endometrial glands. This strongly suggests that iron is transferred from the macrophages to the glandular cells. Within the glandular cells, iron-rich histiotrophe was synthesised and released into the glandular lumen. Within the uterine cavity this histiotrophe was absorbed by the omphalopleure. We suggest that among eutherians, postpartum erythrophagocytosis, the transfer of iron from macrophages to uterine glands, and the paraplacental uptake of iron, represent an ancestral mechanism of iron supply to the embryo.

Animals↗
PubMed2000

Interpretation of mass spectra from organic compounds in aerosol time-of-flight mass spectrometry

Organic compounds containing a variety of functional groups have been analyzed using aerosol time-of-flight mass spectrometry. Both positive and negative laser desorption/ionization mass spectra have been acquired for compounds of relevance to ambient air particulate matter, including polycyclic aromatic hydrocarbons, heterocyclic analogues, aromatic oxygenated compounds such as phenols and acids, aliphatic dicarboxylic acids, and reduced nitrogen species such as amines. In many cases, positive ion mass spectra are similar to those found in libraries for 70-eV electron impact mass spectrometry. However, formation of even-electron molecular ions due to adduct formation also plays a major role in ion formation. Negative ion mass spectra suggest that organic compounds largely disintegrate into carbon cluster fragments (C(n)- and C(n)H-). However, information about the heteroatoms present in organic molecules, especially nitrogen and oxygen, is carried dominantly by negative ion spectra, emphasizing the importance of simultaneous analysis of positive and negative ions in atmospheric samples.

Journal Article↗
PubMed2005

Volatile constituents of redblush grapefruit (Citrus paradisi) and pummelo (Citrus grandis) peel essential oils from Kenya.

The volatile constituents of cold-pressed peel essential oils of redblush grapefruit (Citrus paradisi Macfadyen forma Redblush) and pummelo (Citrus grandis Osbeck) from the same locality in Kenya were determined by GC and GC-MS. A total of 67 and 52 compounds, amounting to 97.9 and 98.8% of the two oils, respectively, were identified. Monoterpene hydrocarbons constituted 93.3 and 97.5% in the oils, respectively, with limonene (91.1 and 94.8%), alpha-terpinene (1.3 and 1.8%), and alpha-pinene (0.5%) as the main compounds. Sesquiterpene hydrocarbons constituted 0.4% in each oil. The notable compounds were beta-caryophyllene, alpha-cubebene, and (E,E)-alpha-farnesene. Oxygenated compounds constituted 4.2 and 2.0% of the redblush grapefruit and pummelo oils, respectively, out of which carbonyl compounds (2.0 and 1.3%), alcohols (1.4 and 0.3%), and esters (0.7 and 0.4%) were the major groups. Heptyl acetate, octanal, decanal, citronellal, and (Z)-carvone were the main constituents (0.1-0.5%). Perillene, (E)-carveol, and perillyl acetate occurred in the redblush grapefruit but were absent from the pummelo oil. Nootkatone, alpha- and beta-sinensal, methyl-N-methylanthranilate, and (Z,E)-farnesol were prominent in both oils.

Citrus↗
PubMed1998

Evaluation of sink effects on VOCs from a latex paint.

The sink strength of two common indoor materials, a carpet and a gypsum board, was evaluated by environmental chamber tests with four volatile organic compounds (VOCs): propylene glycol, ethylene glycol, 2-(2-butoxyethoxy)ethanol (BEE), and Texanol. These oxygenated compounds represent the major VOCs emitted from a latex paint. Each chamber test included two phases. Phase 1 was the dosing/sorption period during which sink materials (pieces of carpet and gypsum board samples) were exposed to the four VOCs. The sink strength of each material tested was characterized by the amount of the VOCs adsorbed or absorbed. Phase 2 was the purging/desorption period during which the chambers with the dosed sink materials were flushed with purified air. The reemission rates of the adsorbed VOCs from the sinks were reflected by the amount of the VOCs being flushed. Phase 1 results indicated that the sink strength for the four target compounds is more than 1 order of magnitude higher than that for other VOCs previously tested by the U.S. Environmental Protection Agency (EPA). The high sink strength reflected the unusually high sorption capacity of common indoor materials for the four VOCs. Phase 2 results showed that reemission was an extremely slow process. If all the VOCs adsorbed were reemittable, it would take more than a year to completely flush out the VOCs from the sink materials tested. The long reemission process can result in chronic and low-level exposure to the VOCs after painting interior walls and surfaces.

Air Pollution, Indoor↗
PubMed2003

Overall mass transfer coefficient for pollutant emissions from small water pools under simulated indoor environmental conditions.

Small chamber tests were conducted to experimentally determine the overall mass transfer coefficient for pollutant emissions from still aqueous solutions under simulated indoor (residential or occupational) environmental conditions. The tests covered six organic compounds with a Henry's constant range from 3.33 x 10(-7) to 3.67 x 10(-3) (atm m(3)/mol). The estimated overall liquid phase mass transfer coefficients for still solutions varied from 1.8 x 10(-6) to 5.7 x 10(-3) m/h; the estimated liquid phase mass transfer coefficients were 9.7 x 10(-3) m/h for the reference compound (oxygen) and 5.00 x 10(-3) to 6.04 x 10-(3) m/h for the test compounds. An empirical model is proposed to estimate the overall mass transfer coefficient, which can be used to predict pollutant emissions from still aqueous solutions (e.g. pools and puddles) in indoor environments.

Air Pollution, Indoor↗
PubMed1981

Phagocytosing human neutrophils inactivate their own granular enzymes.

During phagocytosis, neutrophils generate reactive oxygen metabolites and release lysosomal enzymes into the extracellular medium. We have investigated the possibility that these enzyme are inactivated by the oxygen compounds. Phagocytosing neutrophils from 12 patients with chronic granulomatous disease, which do not generate these oxygen metabolites, released two to three times more activity of lysozyme and beta-glucuronidase than did normal neutrophils. This difference proved to be due to a decrease of approximately 20% of the total activity of these enzymes in normal neutrophils, but not in neutrophils of patients with chronic granulomatous disease. This inactivation of enzymes took place during phagocytosis of opsonized zymosan particles as well as during stimulation of normal cells with phorbol myristate acetate. The inactivation was not due to formation of inhibitors. The lysosomal enzymes were not activated when the neutrophils were stimulated under anaerobic conditions. Addition of catalase, superoxide dismutase, or albumin gave no protection against the oxidative damage; reduced glutathione gave partial protection. The oxidative inactivation was more pronounced in the presence of azide. Measurement of the activity and the amount of protein of acid alpha-glucosidase in the cells showed that the specific activity of this enzyme decreased by approximately 50% during 30 min of phagocytosis. This indicates that the inactivation of the lysosomal enzymes takes place in the phagolysosomes, before the enzymes have leaked into the extracellular medium.

Extracellular Space↗
PubMed2002

Caged O(2). Reaction of cytochrome bo(3) oxidase with photochemically released dioxygen from a cobalt peroxo complex.

We developed the synthesis of the caged oxygen donor (micro-peroxo)(micro-hydroxo)bis[bis(bipyridyl)cobalt(III)] complex (HPBC) as nitrate salt, which has, compared with the perchlorate-form described previously [MacArthur, R., Sucheta, A., Chong, F.F. & Einarsdottir, O. (1995) Proc. Natl Acad. Sci. USA, 92, 8105-8109], greatly enhanced solubility. Now, the quantum efficiency of the photolytical release of dioxygen was determined to be 0.4 per photon at a laser wavelength of 308 nm, which was used to observe biological reactions. The X-ray structure of HPBC has been solved, and the molecular interactions of photochemically generated oxygen with cytochrome oxidase were investigated with optical and FT-IR spectroscopy: it acts as acceptor of electrons transferred from prereduced cytochrome bo(3), the heme-copper oxidase from Escherichia coli. FT-IR spectra revealed typical absorbance difference changes in the carbonyl region of cytochrome bo(3), supported by bandshifts due to solvent isotope exchange and by assignment using site-directed mutants. IR difference spectra of the photooxidation reaction using the caged oxygen compound, and of the photoreduction reaction using the caged electron donor FMN, have inverted shapes. The spectroscopic signals of carboxyl groups are thus equivalent in both reactions: the use of chemically produced oxygen allows the observation of the ongoing molecular changes of cytochrome bo(3) oxidase under quasi-physiological conditions.

Cobalt↗
PubMed2005

Measurement of volatile organic compounds in the urban atmosphere of Harris County, Texas, USA.

Volatile organic compounds (VOCs) are a major component of urban air pollution. It is well documented that exposure to certain types of VOCs can cause adverse health effects such as cancer, immune and neurological damage, and reproductive and endocrine disorders. Urban air samples were collected at five locations in Harris County, Texas to determine the measurement of VOCs in the ambient air of residential areas in close proximity to industrial facilities that emit toxic air pollutants into the air. Three locations used in this study were located along the Houston Ship Channel (HSC), in the heart of one of the largest petrochemical complexes in the nation. Two other sampling locations were located many miles away from the ship channel and any industrial facilities that are required to report toxic air emissions. Air samples were collected daily over an 8-h period from December 2002 to March 2003. The samples were collected in 6-L stainless steel Silonite-coated canisters and analyzed using a modified version of EPA Method TO-15. A total of 53 compounds was quantitated using a gas chromatograph mass spectrometer system coupled to a cryogenic preconcentrator. Eighteen alkanes and oxygenated compounds were identified, along with 7 alkenes and 5 aromatic compounds. Several alkanes such as butane, isobutane, 2-methyl butane, and pentane were detected at all five sites. The total VOC concentrations determined were highest at two of the industrial sites and lowest at the site farthest away from the ship channel and any industrial facilities. This study concluded that the atmosphere near Harris County's industrial complex had higher concentrations of VOCs than the atmosphere in areas farther away from the HSC. The atmosphere of areas downwind from emission sources were found to be directly affected by toxic air emissions from industrial process but not at the levels seen in areas closer to the HSC.

Air↗
PubMed2003

Oxidation of C-H bonds by [(bpy)2(py)RuIVO]2+ occurs by hydrogen atom abstraction.

Anaerobic oxidations of 9,10-dihydroanthracene (DHA), xanthene, and fluorene by [(bpy)(2)(py)Ru(IV)O](2+) in acetonitrile solution give mixtures of products including oxygenated and non-oxygenated compounds. The products include those formed by organic radical dimerization, such as 9,9'-bixanthene, as well as by oxygen-atom transfer (e.g., xanthone). The kinetics of these reactions have been measured. The kinetic isotope effect for oxidation of DHA vs DHA-d(4) gives k(H)/k(D) > or = 35 +/- 1. The data indicate a mechanism of initial hydrogen-atom abstraction forming radicals that dimerize, disproportionate and are trapped by the oxidant. This mechanism also appears to apply to the oxidations of toluene, ethylbenzene, cumene, indene, and cyclohexene. The rate constants for H-atom abstraction from these substrates correlate well with the strength of the C-H bond that is cleaved. Rate constants for abstraction from DHA and toluene also correlate with those for oxygen radicals and other oxidants. The rate constant for H-atom transfer from toluene to [(bpy)(2)(py)Ru(IV)O](2+) appears to be close to that predicted by the Marcus cross relation, using a tentative rate constant for hydrogen atom self-exchange between [(bpy)(2)(py)Ru(III)OH](2+) and [(bpy)(2)(py)Ru(IV)O](2+).

Anthracenes↗
PubMed1985

Transcription of the Escherichia coli fumarate reductase genes (frdABCD) and their coordinate regulation by oxygen, nitrate, and fumarate.

The fumarate reductase enzyme complex allows Escherichia coli to grow anaerobically with fumarate as a terminal electron acceptor for oxidative phosphorylation when the preferred compounds oxygen and nitrate are not available. We used the pKO promoter test vectors to identify a single promoter for the frdABCD genes which encode fumarate reductase. Expression of galactokinase from the frd promoter-galK operon fusion plasmid was repressed by oxygen and by nitrate and was induced by fumarate, indicating that frd gene expression is regulated at the transcriptional level by these terminal electron acceptors. S1 nuclease analysis, using a single-stranded DNA probe from the frd promoter region and mRNA isolated from a fumarate reductase-induced culture, revealed that the frd mRNA transcript initiates with an adenine residue 93 bases prior to the start of frdA translation. No promoters internal to the frd genes were revealed with the plasmid promoter screening system. S1 nuclease analysis revealed that the frd mRNA terminates in a uridine-rich region centered at 46 bases after the last codon of frdD. A stem and loop structure previously described as the growth rate-dependent attenuator for the linked ampC gene precedes the frd mRNA terminus. This result confirms the proposal that the stem and loop structure serves the dual role of a frd terminator anaerobically and an ampC attenuator aerobically. The four frd genes encoding the subunits of the fumarate reductase complex thus comprise an operon which is regulated at the transcriptional level in response to the cellular availability of the alternate electron acceptors oxygen, nitrate, and fumarate.

Base Sequence↗
PubMed1997

2-Methyl-thiazolidine-2,4-dicarboxylic acid as prodrug of L-cysteine. Protection against paracetamol hepatotoxicity in mice.

Toxic doses of paracetamol (acetaminophen) destroy the cellular defense system in hepatic tissue. The degree of the destruction can be assessed be measuring the metabolism of sulfhydryl compounds, oxygen radicals and the release of certain enzymes. Administration of 2-methyl-thiazolidine-2,4-dicarboxylic acid (CP; 1.2 mmol/kg) to mice 12 h prior to a toxic dose of paracetamol (600 mg/kg) suppressed the increase of aminotransferase activities in blood serum and the levels of reactive oxygen species in liver tissue. A protective effect of CP was also observed with respect to depletion of non-protein sulfhydryl compounds, cysteine and glycogen. The findings demonstrate that the cysteine prodrug CP is effective in preventing liver damage of a hepatotoxic dose of paracetamol in vivo. A further advantage of the new compound is the long duration of the effect of more than 12 h.

Acetaminophen↗
PubMed1984

[Action of oxygen on cells in total anabiosis].

It is demonstrated that under the action of gaseous oxygen, biological objects being investigated under complete anabiosis lose their viability, i.e. the original nature of the viable structure of the cell becomes disrupted. The phenomenon is caused by the fact that the conditions of complete anabiosis arrest the action of enzymatic systems which either prevent the formation of toxic oxygen compounds, or dissociate these compounds.

Animals↗
PubMed1994

Efficacy of selected disinfectants against mycobacteria and cryptosporidia.

We have tested the in-vitro efficacy of various disinfectants against clinical isolates of Mycobacterium tuberculosis, Mycobacterium avium-intracellulare, and against the protozoon Cryptosporidium parvum. The disinfectants were tested both with and without an organic load. 'Sactimed sinald' (a quaternary ammonium compound), 'Steris 20' (a peracetic acid compound) and 'Pentapon DC1' (a beta-ene compound) were all equally as effective as 'Cidex' (glutaraldehyde) against all the mycobacteria tested, as well as C. parvum. 'Virkon' (a per-oxygen compound) and 'Phoraid' (an iodine compound) were less effective than glutaraldehyde. 'Pentapon DHY' (a beta-ene compound) was ineffective against any of the organisms tested. We have also assessed a method of determining disinfectant efficacy using [35S]-methionine labelling of proteins, which appears promising, although it requires further evaluation.

Animals↗
PubMed1999

Reactive nitrogen and oxygen species ameliorate experimental cryptosporidiosis in the neonatal BALB/c mouse model.

Four-day-old BALB/c mice were infected by the oral administration of 50,000 Cryptosporidium parvum oocysts, and the resulting infection was scored histologically and by counting colonic oocysts. Infection occurred in the ileum and proximal colon (but not duodenum and jejunum), peaked on days 14 to 18, and was cleared between days 24 and 30. Nitric oxide (NO) appeared to play a protective role in this model as evidenced by the facts that plasma nitrite and nitrate levels increased during the period of peak parasitosis; immunohistochemically detected inducible nitric oxide synthase (iNOS) was increased in the ileum and colon enterocytes of infected animals; the NOS inhibitor L-N-iminoethyl lysine or N-nitro-L-arginine methyl ester (L-NAME) decreased the elevated plasma nitrite and nitrate levels while exacerbating the infection and increasing oocyst shedding; administration of a NO donor, S-nitroso-N-penicillamine, reduced oocyst and infection scores; and neonatal iNOS knockout mice exhibited a slightly longer infection than control animals. The oral administration of oocysts to L-NAME-treated BALB/c mice, but not control animals, between 24 and 40 days old resulted in the fecal excretion of oocysts 1 week later. Administration of the antioxidant ascorbic acid also exacerbated the C. parvum infection, suggesting a protective role for reactive nitrogen and/or reactive oxygen compounds, while administration of the superoxide scavenger superoxide dismutase exacerbated the infection. Taken together these data suggest that both reactive nitrogen and reactive oxygen species play protective roles in experimental cryptosporidiosis.

Animals↗
PubMed1995

Microbial conversion of milbemycins: oxidation of milbemycin A4 and related compounds at the C-25 ethyl group by Circinella umbellata and Absidia cylindrospora.

Microbial oxidation of milbemycin A4 at the C-25 ethyl group was performed. Milbemycin A4 was converted to 31- and 32-hydroxy derivatives by Circinella umbellata SANK 44272 along with 24- and 30-hydroxy derivatives. Related compounds, 5-ketomilbemycin A4 5-oxime and 13 beta-fluoromilbemycin A4 were similarly converted to the hydroxylated compounds by this microorganism. Absidia cylindrospora SANK 31472 converted milbemycin A4 to the corresponding 32-oic acid, 24-hydroxy derivative and a few oxygenated compounds including at the C-25 ethyl group.

Anthelmintics↗