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Query: CAS:7782-44-7 (oxygen)
 369,292 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

17O-NMR measurements of labeled Pro-Leu-Gly-NH2 were carried out at different pH levels and in mixed solvents of water/acetonitrile. Complementary studies of the amide protons were carried out in acetonitrile-d3. Only the prolyl C = 17O group was sensitive to the pH level. Protonation of the amine group resulted in an upfield chemical shift of 18 ppm. The chemical shifts of each of the three oxygen sites was sensitive to the ratio water:acetonitrile. Solvent composition dependence of the chemical shift and linewidth suggests that the prolyl C = 17O is involved in intramolecular hydrogen bond formation when Pro-Leu-Gly-NH2 is dissolved in acetonitrile, while in water there is no intramolecular H bond.
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PMID:Hydrogen bonds in the tripeptide Pro-Leu-Gly-NH2. 17O and 1H studies. 614 61

A multiresidue method for carbamate insecticides was adapted for the determination of coumaphos and its oxygen analog in eggs and milk. Eggs were extracted with acetonitrile and milk was extracted with acetone. Co-extractives were removed using liquid partitioning and charcoal column procedures described in the carbamate method. Coumaphos and its oxygen analog were determined by using a high performance liquid chromatograph equipped with a fluorescence detector. Recovery studies were performed for the 2 compounds at levels of 0.01 and 0.10 ppm in eggs and 0.01 and 0.02 ppm in milk. Overall average recovery was 100% (range 95-109%). In a trial of the method by another laboratory, the recovery of coumaphos and its oxygen analog from milk averaged 87 and 96%, respectively. Data are presented on the capillary gas chromatographic/mass spectrometric confirmation of coumaphos residues.
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PMID:Determination of coumaphos and its oxygen analog in eggs and milk by using a multiresidue method with liquid chromatographic quantitation and capillary gas chromatographic/mass spectrometric confirmation. 668 14

To permit kinetic studies of the reactivity of unsaturated fatty acids towards oxygen radicals, it is essential to remove traces of hydroperoxides and other conjugated lipid impurities commonly present in commercial samples. Removal of these impurities has been satisfactorily achieved for oleic and linoleic acids by anaerobic low temperature recrystallization from acetonitrile. The UV spectra of commercial and purified samples are compared.
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PMID:Purification of oleic acid and linoleic acid. 685 55

Anodic oxidation of N-nitrosamines derived from various secondary amines has been investigated by cyclic voltammetry and controlled-potential electrolysis at a glassy carbon electrode in acetonitrile. The nitrosamines give one, two, or three irreversible anodic peaks, depending upon the structure of the parent secondary amines. Electrolysis of simple dialkylnitrosamines gave the corresponding nitramines with coulometric n-values between 1 and 1.5, together with beta-ketonitrosamines in which the carbonyl group is on the same side as the nitroso-oxygen atom. With N-nitrosopiperidine (derived from a cyclic amine), N-nitropiperidine was formed in the same way, but the beta-oxidized nitrosamine was not detected in the solution from electrolysis. Added water (ca. 1%) in acetonitrile had essentially no effect on the electrochemistry of simple dialkylnitrosamines, whereas the first anodic peak of N-nitrosopiperidine was increased and the formation of N-nitropiperidine was inhibited in the macroscale electrolysis. In deoxygenated acetonitrile, the first anodic peaks of all the nitrosamines examined were enhanced and the other anodic peaks became obscure. Macroscale electroysis gave neither the nitramines nor the beta-ketonitrosamines and the coulometric n-value increased. It is suggested that unidentified oxidation processes produce electroactive species whose further oxidation results in various degradation products.
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PMID:A novel oxidative degradation of N-nitrosamine via electron transfer. 714 37

Pseudomonas marginalis, capable of utilizing acetonitrile as the sole source of carbon and nitrogen, was isolated from an industrial waste site. P. marginalis metabolized acetonitrile into ammonia and acetate. The minimal inhibitory concentration values of different nitriles and amides for P. marginalis were in the range 5-300 mM. The bacterium was able to transform high-molecular-mass nitrile compounds and their respective amides into ammonia. The data from substrate-dependent kinetics showed that the Km and Vmax values of P. marginalis for acetonitrile were 33 mM and 67 nmol oxygen consumed min-1 (ml cell suspension)-1 respectively. The study with [14C]acetonitrile indicated that nearly 66% of the carbon was released as 14CO2 and 12% was associated with the biomass. The enzyme system involved in the hydrolysis of acetonitrile was shown to be intracellular and inducible. The specific activities of the enzymes nitrile aminohydrolase and amidase were determined in the cell-free extracts of P. marginalis. Both the enzymes could hydrolyze a wide range of nitriles and amides. The present study suggests that the biodegradation of organic nitriles and the bioproduction of organic acids may be achieved with the cells of P. marginalis.
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PMID:Pseudomonas marginalis: its degradative capability on organic nitriles and amides. 754 12

Concentration of water-saturated commercial samples of diethyl ether by a stream of nitrogen yielded an aqueous residue mutagenic in S. typhimurium strains TA100 and TA102, but not TA1535. Reverse phase high-performance liquid chromatography resolved the mixture into 4 UV absorbing peaks, each of which was positive for peroxide and mutagenic in strain TA100 and TA102. One of these was identified as H2O2 based on HPLC retention time and sensitivity to decomposition by catalase, and another as 1-ethoxyethylhydroperoxide, based on its 1H-NMR spectrum. The mutagenic peroxides appeared to be stable in water between pH 3 and 6, but unstable above pH 7; they were less stable in methanol, acetonitrile, and least stable in chloroform, in which they partially decomposed after 24 h at 20 degrees C. Generalization of the results suggests that adverse effects observed in vitro and in vivo with chemicals containing ether linkages that actually have been caused by contaminant peroxides and reactive oxygen compounds.
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PMID:Mutagenic peroxides in diethyl ether. 768 82

Characteristic chemiluminescence emission of singlet (1 delta g) molecular oxygen at 1268 nm is reported from a Haber-Weiss reaction. The reaction consists of mixing aqueous hydrogen peroxide with a solution of potassium superoxide, solubilized by 18-crown-6 ether in carbon tetrachloride or in dry acetonitrile at room temperature. Since the discovery of the enzyme superoxide dismutase by J.M. McCord and I. Fridovich [(1968) J. Biol. Chem. 243, 5733-5760], the identity of the reactive oxidant in superoxide-generating systems in biology has remained a chemical mystery. The results presented here suggest strongly that the reactive species is singlet oxygen generated via the Haber-Weiss reaction and not, as usually assumed, the hydroxyl radical, .OH, generated by the same reaction.
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PMID:Singlet molecular oxygen in the Haber-Weiss reaction. 780 42

Fluoride is known to inhibit the photodynamic activity of aluminium phthalocyanine in a variety of biological systems. In order to gain insight into this phenomenon, the effect of fluoride on the photophysical properties of free and albumin-bound chloroaluminum phthalocyanine sulfonate (AlPcSn) were studied. The association constant of NaF with AlPcSn in aqueous solution was measured as 500 +/- 20 M-1. This binding affects the photophysical properties of the dye: the absorption bands in the visible range are blue-shifted by 6-8 nm, and this effect is mirrored in the fluorescence emission spectrum. Human serum albumin significantly quenched the dye fluorescence independent of the presence of fluoride ion. The transient absorption spectrum of the excited dye triplet is unchanged by NaF, but the quantum yield for its generation is increased by 50%, with no decrease in its lifetime. Formation of fluoroaluminum phthalocyanine complexes was also observed in tetrabutylammonium fluoride-assisted solutions in wet acetonitrile. The fluoro-AlPcSn complex is a better photosensitizer for generation of singlet oxygen than the original dye-hydroxyl ion complex, as confirmed using the imidazole-N,N-dimethyl-4-nitrosoaniline method. On the other hand, the fluoro-AlPcSn complex exhibits an intense inhibitory effect on photohemolysis of red blood cells (RBC) even after the cells are washed to remove free dye and fluoride prior to irradiation, indicating that once the dye is attached to the cellular site, the fluoride ligand is no longer prone to displacement (by hydroxyl ion, for example). Nonetheless, it is clear from the spectroscopic data that the new fluoro complex is an efficient sensitizer for photooxidation.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The photochemical properties of fluoroaluminum phthalocyanine. 797 71

Conformational features of nicardipine in acetonitrile, in the absence and presence of Ca2+, were investigated by one-dimensional NMR and difference absorption spectroscopy techniques. The data show that in acetonitrile solution the antiperiplanar form of nicardipine is dominant. The addition of Ca2+ to the drug solution caused marked changes in the difference absorbance spectra in the 200-400 nm region and in many of its 1H and 13C NMR resonances. The changes were most significant up to a ratio of 0.5 Ca2+:drug. Analysis of the binding data showed the predominant species to be a 2:1 drug:Ca2+ "sandwich" complex with an estimated dissociation constant of 100 microM at 25 degrees C. One-dimensional nuclear Overhauser effect (NOE) experiments revealed through-space connectivities in the drug before and after Ca2+ binding. These changes in conjunction with the changes in 1H and 13C chemical shifts suggest a structure in which the 4-aryl ring substitute of the pyridine moiety moves closer to the C3-side chain in the presence of Ca2+. This attraction is achieved via the chelation of the Ca2+ ion by the oxygen atoms in the m-NO2 of the aryl group and the COOCH2 group in the side chain of the dihydropyridine ring, and gives rise to a stable synperiplanar conformation. A preference for this conformation was also observed in the Ca2+ complex of nifedipine in acetonitrile as inferred from the rather limited NOE data obtained. Our study provides a detailed solution structure for nicardipine and also leads to a suggestion of a role for Ca2+ in the action of this and possibly other dihydropyridines.
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PMID:Interaction of calcium channel antagonists with calcium: structural studies on nicardipine and its Ca2+ complex. 799 51

Curcumin, bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione, is a natural yellow-orange dye derived from the rhizome of Curcuma longa, an East Indian plant. In order to understand the photobiology of curcumin better we have studied the spectral and photochemical properties of both curcumin and 4-(4-hydroxy-3-methoxy-phenyl)-3-buten-2-one (hC, half curcumin) in different solvents. In toluene, the absorption spectrum of curcumin contains some structure, which disappears in more polar solvents, e.g. ethanol, acetonitrile. Curcumin fluorescence is a broad band in acetonitrile (lambda max = 524 nm), ethanol (lambda max = 549 nm) or micellar solution (lambda max = 557 nm) but has some structure in toluene (lambda max = 460, 488 nm). The fluorescence quantum yield of curcumin is low in sodium dodecyl sulfate (SDS) solution (phi = 0.011) but higher in acetonitrile (phi = 0.104). Curcumin produced singlet oxygen upon irradiation (lambda > 400 nm) in toluene or acetonitrile (phi = 0.11 for 50 microM curcumin); in acetonitrile curcumin also quenched 1O2 (kq = 7 x 10(6) M-1 s-1). Singlet oxygen production was about 10 times lower in alcohols and was hardly detectable when curcumin was solubilized in a D2O micellar solution of Triton X-100. In SDS micelles containing curcumin no singlet oxygen phosphorescence could be observed. Curcumin photogenerates superoxide in toluene and ethanol, which was detected using the electron paramagnetic resonance/spin-trapping technique with 5,5-dimethyl-pyrroline-N-oxide as a trapping agent. Unidentified carbon-centered radicals were also detected.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Spectral and photochemical properties of curcumin. 801 8


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