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1

Determination of oxidation products of 5-methylcytosine in plants by chemical derivatization coupled with liquid chromatography/tandem mass spectrometry analysis.  

PubMed

Cytosine methylation (5-methylcytosine, 5-mC) in DNA is an important epigenetic mark that has regulatory roles in various biological processes. In plants, active DNA demethylation can be achieved through direct cleavage by DNA glycosylases, followed by replacement of 5-mC with cytosine by base excision repair (BER) machinery. Recent studies in mammals have demonstrated 5-mC can be sequentially oxidized to 5-hydroxymethylcytosine (5-hmC), 5-formylcytosine (5-foC), and 5-carboxylcytosine (5-caC) by Ten-eleven translocation (TET) proteins. The consecutive oxidations of 5-mC constitute the active DNA demethylation pathway in mammals, which raised the possible presence of oxidation products of 5-mC (5-hmC, 5-foC, and 5-caC) in plant genomes. However, there is no definitive evidence supporting the presence of these modified bases in plant genomic DNA, especially for 5-foC and 5-caC. Here we developed a chemical derivatization strategy combined with liquid chromatography-electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method to determine 5-formyl-2'-deoxycytidine (5-fodC) and 5-carboxyl-2'-deoxycytidine (5-cadC). Derivatization of 5-fodC and 5-cadC by Girard's reagents (GirD, GirT, and GirP) significantly increased the detection sensitivities of 5-fodC and 5-cadC by 52-260-fold. Using this method, we demonstrated the widespread existence of 5-fodC and 5-cadC in genomic DNA of various plant tissues, indicating that active DNA demethylation in plants may go through an alternative pathway similar to mammals besides the pathway of direct DNA glycosylases cleavage combined with BER. Moreover, we found that environmental stresses of drought and salinity can change the contents of 5-fodC and 5-cadC in plant genomes, suggesting the functional roles of 5-fodC and 5-cadC in response to environmental stresses. PMID:24970241

Tang, Yang; Xiong, Jun; Jiang, Han-Peng; Zheng, Shu-Jian; Feng, Yu-Qi; Yuan, Bi-Feng

2014-08-01

2

Oxidation-induced conformational changes in calcineurin determined by covalent labeling and tandem mass spectrometry.  

PubMed

The Ca(2+)/calmodulin activated phosphatase, calcineurin, is inactivated by H2O2 or superoxide-induced oxidation, both in vivo and in vitro. However, the potential for global and/or local conformation changes occurring within calcineurin as a function of oxidative modification, that may play a role in the inactivation process, has not been examined. Here, the susceptibility of calcineurin methionine residues toward H2O2-induced oxidation were determined using a multienzyme digestion strategy coupled with capillary HPLC-electrospray ionization mass spectrometry and tandem mass spectrometry analysis. Then, regions within the protein complex that underwent significant conformational perturbation upon oxidative modification were identified by monitoring changes in the modification rates of accessible lysine residues between native and oxidized forms of calcineurin, using an amine-specific covalent labeling reagent, S,S'-dimethylthiobutanoylhydroxysuccinimide ester (DMBNHS), and tandem mass spectrometry. Importantly, methionine residues found to be highly susceptible toward oxidation, and the lysine residues exhibiting large increases in accessibility upon oxidation, were all located in calcineurin functional domains involved in Ca(2+)/CaM binding regulated calcineurin stimulation. These findings therefore provide initial support for the novel mechanistic hypothesis that oxidation-induced global and/or local conformational changes within calcineurin contribute to inactivation via (i) impairing the interaction between calcineurin A and calcineurin B, (ii) altering the low-affinity Ca(2+) binding site in calcineurin B, (iii) inhibiting calmodulin binding to calcineurin A, and/or (iv) by altering the affinity between the calcineurin A autoinhibitory domain and the catalytic center. PMID:25286016

Zhou, Xiao; Mester, Caitlin; Stemmer, Paul M; Reid, Gavin E

2014-11-01

3

Electrochromic devices embodying W oxide/Ni oxide tandem films  

SciTech Connect

Six-layer electrochromic devices of indium tin oxide (ITO)/NiO{sub x}H{sub y}/WO{sub 3}/ZrP-electrolyte/WO{sub 3}/ITO were made by reactive dc magnetron sputtering and lamination. The WO{sub 3} layer between the acidic ZrP-based electrolyte and the NiO{sub x}H{sub y} layer served as optically passive protective layer. The optical inactivity of the protective layer could be understood from arguments based on electron density of states. {copyright} 2001 American Institute of Physics.

Azens, A.; Vaivars, G.; Veszelei, M.; Kullman, L.; Granqvist, C. G.

2001-06-15

4

Perovskite catalysts for oxidative coupling  

DOEpatents

Perovskites of the structure A.sub.2 B.sub.2 C.sub.3 O.sub.10 are useful as catalysts for the oxidative coupling of lower alkane to heavier hydrocarbons. A is alkali metal; B is lanthanide or lanthanum, cerium, neodymium, samarium, praseodymium, gadolinium or dysprosium; and C is titanium.

Campbell, Kenneth D. (Charleston, WV)

1991-01-01

5

Measurement of oxidative stress parameters using liquid chromatography–tandem mass spectroscopy (LC–MS\\/MS)  

Microsoft Academic Search

There is increasingly intense scientific and clinical interest in oxidative stress and the many parameters used to quantify the degree of oxidative stress. However, there remain many analytical limitations to currently available assays for oxidative stress markers. Recent improvements in software, hardware, and instrumentation design have made liquid chromatography and tandem mass spectroscopy (LC–MS\\/MS) methods optimal choices for the determination

Witold M. Winnik; Kirk T. Kitchin

2008-01-01

6

MEASUREMENT OF OXIDATIVE STRESS PARAMETERS USING LIQUID CHROMATOGRAPHY - TANDEM MASS SPECTROSCOPY (LC-MS/MS)  

EPA Science Inventory

What is the study? An invited review article. Measurement of oxidative stress parameters using liquid chromatography-tandem mass spectroscopy (LC-MS/MS) Why was it done? Although oxidative stress is frequently cited as a cause of various adverse biological eff...

7

Detailed balance analysis of area de-coupled double tandem photovoltaic modules  

NASA Astrophysics Data System (ADS)

This paper describes how layers of area de-coupled top and bottom cells in photovoltaic tandem modules can increase the efficiency of two-terminal tandem devices. The point of the area de-coupling is to allow the number of top cells to differ from the number of bottom cells. Within each of the layers, the cells can be horizontally series-connected and the layers can then be current- or voltage-matched with each other in a tandem module. Using detailed balance modeling, it is shown that two-terminal tandem modules of this type can achieve the same theoretical efficiency as stacks of independently operated cells, often referred to as four-terminal cells. Optimal ratios of the number of bottom cells to the number of top cells are calculated. Finally, it is shown that modules with a bottom layer consisting of 60 cells with a band gap of 1.11 eV, resembling standard silicon modules, offer sufficient resolution to optimize the number of top cells and achieve high efficiency over a large range of top cell band gaps. This result extends the list of materials that can be used as top cells in two-terminal tandem modules with silicon bottom cells.

Strandberg, Rune

2015-01-01

8

Flight and Analytical Methods for Determining the Coupled Vibration Response of Tandem Helicopters  

NASA Technical Reports Server (NTRS)

Chapter one presents a discussion of flight-test and analysis methods for some selected helicopter vibration studies. The use of a mechanical shaker in flight to determine the structural response is reported. A method for the analytical determination of the natural coupled frequencies and mode shapes of vibrations in the vertical plane of tandem helicopters is presented in Chapter two. The coupled mode shapes and frequencies are then used to calculate the response of the helicopter to applied oscillating forces.

Yeates, John E , Jr; Brooks, George W; Houbolt, John C

1957-01-01

9

Lewis acid catalysis and Green oxidations: sequential tandem oxidation processes induced by Mn-hyperaccumulating plants.  

PubMed

Among the phytotechnologies used for the reclamation of degraded mining sites, phytoextraction aims to diminish the concentration of polluting elements in contaminated soils. However, the biomass resulting from the phytoextraction processes (highly enriched in polluting elements) is too often considered as a problematic waste. The manganese-enriched biomass derived from native Mn-hyperaccumulating plants of New Caledonia was presented here as a valuable source of metallic elements of high interest in chemical catalysis. The preparation of the catalyst Eco-Mn1 and reagent Eco-Mn2 derived from Grevillea exul exul and Grevillea exul rubiginosa was investigated. Their unusual polymetallic compositions allowed to explore new reactivity of low oxidative state of manganese-Mn(II) for Eco-Mn1 and Mn(IV) for Eco-Mn2. Eco-Mn1 was used as a Lewis acid to catalyze the acetalization/elimination of aldehydes into enol ethers with high yields; a new green and stereoselective synthesis of (-)-isopulegol via the carbonyl-ene cyclization of (+)-citronellal was also performed with Eco-Mn1. Eco-Mn2 was used as a mild oxidative reagent and controlled the oxidation of aliphatic alcohols into aldehydes with quantitative yields. Oxidative cleavage was interestingly noticed when Eco-Mn2 was used in the presence of a polyol. Eco-Mn2 allowed direct oxidative iodination of ketones without using iodine, which is strongly discouraged by new environmental legislations. Finally, the combination of the properties in the Eco-Mn catalysts and reagents gave them an unprecedented potential to perform sequential tandem oxidation processes through new green syntheses of p-cymene from (-)-isopulegol and (+)-citronellal; and a new green synthesis of functionalized pyridines by in situ oxidation of 1,4-dihydropyridines. PMID:25263417

Escande, Vincent; Renard, Brice-Loïc; Grison, Claude

2014-09-30

10

Quantification of Fatty Acid Oxidation Products Using On-line High Performance Liquid Chromatography Tandem Mass Spectrometry  

PubMed Central

Oxidized fatty acids formed via lipid peroxidation are implicated in pathological processes such as inflammation and atherosclerosis. A number of methods may be used to detect specific oxidized fatty acids containing a single or multiple combinations of epoxide, hydroxyl, ketone and hydroperoxide moieties on varying carbon chain lengths from C8 up to C30. Some of these methods are nonspecific and their use in biological systems is fraught with difficulty. Measures of specific-oxidized fatty acid derivatives help in identifying oxidation pathways in pathological processes. We used liquid chromatography coupled with electrospray ionization tandem mass spectrometry (LC-MS/MS) as efficient, selective and sensitive methods for identifying and analyzing multiple specific fatty acid peroxidation products in human plasma and other biological matrices. We then distilled the essential components of a number of these analyses to provide an efficient protocol by which fatty acid oxidation products and their parent compounds can be determined. In this protocol, addition of synthetic internal standard to the sample, followed by base hydrolysis at elevated temperature, and liquid-liquid phase sample extraction with lighter than water solvents facilitates isolation of the oxidized fatty acid species. These species can be identified and accurately quantified using stable isotope dilution and multiple reaction monitoring. Use of a coupled multiplexed gradient HPLC system on the front end enables high-throughput chromatography and more efficient use of mass spectrometer time. PMID:23499838

Levison, Bruce S.; Zhang, Renliang; Wang, Zeneng; Fu, Xiaoming; DiDonato, Joseph A.; Hazen, Stanley L.

2013-01-01

11

Synthesis of Substituted Pyrazoles via Tandem Cross-Coupling/Electrocyclization of Enol Triflates and Diazoacetates  

PubMed Central

The synthesis of 3,4,5-trisubstituted pyrazoles via a tandem catalytic cross-coupling/electrocyclization of enol triflates and diazoacetates is presented. The initial scope of this methodology is demonstrated on a range of differentially substituted acyclic and cyclic enol triflates as well as an elaborated set of diazoacetates to provide the corresponding pyrazoles with a high degree of structural complexity. PMID:21682322

Babinski, David J.; Aguilar, Hector R.; Still, Raymond; Frantz, Doug E.

2011-01-01

12

Quantification of Oxidative DNA Lesions in Tissues of Long-Evans Cinnamon Rats by Capillary High-performance Liquid Chromatography-Tandem Mass Spectrometry Coupled with Stable Isotope-dilution Method  

PubMed Central

The purpose of our study was to develop suitable methods to quantify oxidative DNA lesions in the setting of transition metal-related diseases. Transition metal-driven Fenton reactions constitute an important endogenous source of reactive oxygen species (ROS). In genetic diseases with accumulation of transition metal ions, excessive ROS production causes pathophysiological changes, including DNA damage. Wilson’s disease is an autosomal recessive disorder with copper toxicosis due to deficiency of ATP7B protein needed for excreting copper into bile. The Long-Evans Cinnamon (LEC) rat bears a deletion in Atp7b gene and serves as an excellent model for hepatic Wilson’s disease. We used a sensitive capillary LC-ESI-MS/MS/MS method in conjunction with stable-isotope dilution technique to quantify several types of oxidative DNA lesions in liver and brain of LEC rats. These lesions included 5-formyl-2?-deoxyuridine, 5-hydroxymethyl-2?-deoxyuridine, and the 5?R and 5?S diastereomers of 8,5?-cyclo-2?-deoxyguanosine and 8,5?-cyclo-2?-deoxyadenosine. Moreover, the levels of these DNA lesions in the liver and brain increased with age and correlated with age-dependent regulation of the expression of DNA repair genes in LEC rats. These results provide significant new knowledge for better understanding the implications of oxidative DNA lesions in transition metal-induced diseases, such as Wilson’s disease, as well as in ageing and ageing-related pathological conditions. PMID:21323344

Wang, Jin; Yuan, Bifeng; Guerrero, Candace; Bahde, Ralf; Gupta, Sanjeev; Wang, Yinsheng

2011-01-01

13

Indium tin oxide-free tandem polymer solar cells on opaque substrates with top illumination.  

PubMed

Top-illuminated, indium tin oxide (ITO)-free, tandem polymer solar cells are fabricated on opaque substrates in an inverted device configuration. In the tandem cell, a wide band gap subcell, consisting of poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) blended with [70]PCBM is combined with a small band gap subcell consisting of a mixture of poly[{2,5-bis(2-hexyldecyl)-2,3,5,6-tetrahydro-3,6-dioxopyrrolo[3,4-c]pyrrole-1,4-diyl}-alt-{[2,2'-(1,4-phenylene)bisthiophene]-5,5'-diyl}] (PDPPTPT) and [60]PCBM. Compared to the more common bottom-illuminated inverted tandem polymer solar cells on transparent ITO substrates, the front and back cells must be reversed when using opaque substrates and a transparent and conductive top contact must be employed to enable top illumination. A high conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer in combination with Ag lines surrounding the active area as current collection electrode is used for this purpose. The tandem polymer solar cell on an opaque glass/metal substrate yields a power conversion efficiency of 6.1% when the thicknesses of the photoactive layers are balanced for optimum performance. This is similar to the equivalent inverted tandem device fabricated on a transparent glass/ITO substrate. PMID:25051293

Gupta, Dhritiman; Wienk, Martijn M; Janssen, René A J

2014-08-27

14

Tandem catalytic oxidative deacetylation of acetoacetic esters and heteroaromatic cyclizations.  

PubMed

One pot syntheses of furan, thiophene, and pyrrole were accomplished by oxidative deacetylation using Mn(iii)/Co(ii) catalysts and the Paal-Knorr reaction from 1,5-dicarbonyl compounds, which are prepared from the conjugate addition of ethyl acetoacetate to ?,?-unsaturated carbonyl compounds. The oxidative deacetylation and reductive cyclization of ?-ketoesters derived from ethyl acetoacetate and o-nitrobenzyl bromides efficiently produced diversely substituted indoles. PMID:25573411

Ju, Yeming; Miao, Di; Yu, Ruiyang; Koo, Sangho

2015-02-18

15

Tandem strip mill's multi-parameter coupling dynamic modeling based on the thickness control  

NASA Astrophysics Data System (ADS)

The rolling process is determined by the interaction of a number of different movements, during which the relative movement occurs between the vibrating roll system and the rolled piece, and the roll system's vibration interacts with the strip's deformation and rigid movement. So many parameters being involved leads to a complex mechanism of this coupling effect. Through testing and analyzing the vibration signals of the mill in the rolling process, the rolling mill's coupled model is established with comprehensive consideration of the coupling interaction between the mill's vertical vibration, its torsional vibration and the working roll's horizontal vibration, and vibration characteristics of different forms of rolling mill's vibration are analyzed under the coupling effect. With comprehensive attention to the relationship between the roll system, the moving strip and the rolling parameters' dynamic properties, and also from the strip thickness control point of view, further research is done on the coupling mechanism between the roll system's movement and the moving strip's characteristics in the rolling process. As a result, the law of inertial coupling and the stiffness coupling effect caused by different forms of the roll system's vibration is determined and the existence of nonlinear characteristics caused by the elastic deformation of moving strip is also found. Furthermore, a multi-parameter coupling-dynamic model is established which takes the tandem strip mill as its research object by making a detailed kinematics analysis of the roll system and using the principle of virtual work. The coupling-dynamic model proposes the instruction to describe the roll system's movement, and analyzes its dynamic response and working stability, and provides a theoretical basis for the realization of the strip thickness' dynamic control.

Peng, Yan; Zhang, Yang; Sun, Jianliang; Zang, Yong

2015-02-01

16

Tandem strip mill's multi-parameter coupling dynamic modeling based on the thickness control  

NASA Astrophysics Data System (ADS)

The rolling process is determined by the interaction of a number of different movements, during which the relative movement occurs between the vibrating roll system and the rolled piece, and the roll system's vibration interacts with the strip's deformation and rigid movement. So many parameters being involved leads to a complex mechanism of this coupling effect. Through testing and analyzing the vibration signals of the mill in the rolling process, the rolling mill's coupled model is established with comprehensive consideration of the coupling interaction between the mill's vertical vibration, its torsional vibration and the working roll's horizontal vibration, and vibration characteristics of different forms of rolling mill's vibration are analyzed under the coupling effect. With comprehensive attention to the relationship between the roll system, the moving strip and the rolling parameters' dynamic properties, and also from the strip thickness control point of view, further research is done on the coupling mechanism between the roll system's movement and the moving strip's characteristics in the rolling process. As a result, the law of inertial coupling and the stiffness coupling effect caused by different forms of the roll system's vibration is determined and the existence of nonlinear characteristics caused by the elastic deformation of moving strip is also found. Furthermore, a multi-parameter coupling-dynamic model is established which takes the tandem strip mill as its research object by making a detailed kinematics analysis of the roll system and using the principle of virtual work. The coupling-dynamic model proposes the instruction to describe the roll system's movement, and analyzes its dynamic response and working stability, and provides a theoretical basis for the realization of the strip thickness' dynamic control.

Peng, Yan; Zhang, Yang; Sun, Jianliang; Zang, Yong

2015-03-01

17

Copper-catalyzed tandem phosphination-decarboxylation-oxidation of alkynyl acids with H-phosphine oxides: a facile synthesis of ?-ketophosphine oxides.  

PubMed

The general method for the tandem phosphination-decarboxylation-oxidation of alkynyl acids under aerobic conditions has been developed. In the presence of CuSO4·5H2O and TBHP, the reactions provide a novel access to ?-ketophosphine oxides in good to excellent yields. This transformation allows the direct formation of a P-C bond and the construction of a keto group in one reaction. PMID:25855268

Zhang, Pengbo; Zhang, Liangliang; Gao, Yuzhen; Xu, Jian; Fang, Hua; Tang, Guo; Zhao, Yufen

2015-04-23

18

CFD-CAA Coupled Calculations of a Tandem Cylinder Configuration to Assess Facility Installation Effects  

NASA Technical Reports Server (NTRS)

This paper presents a numerical assessment of acoustic installation effects in the tandem cylinder (TC) experiments conducted in the NASA Langley Quiet Flow Facility (QFF), an open-jet, anechoic wind tunnel. Calculations that couple the Computational Fluid Dynamics (CFD) and Computational Aeroacoustics (CAA) of the TC configuration within the QFF are conducted using the CFD simulation results previously obtained at NASA LaRC. The coupled simulations enable the assessment of installation effects associated with several specific features in the QFF facility that may have impacted the measured acoustic signature during the experiment. The CFD-CAA coupling is based on CFD data along a suitably chosen surface, and employs a technique that was recently improved to account for installed configurations involving acoustic backscatter into the CFD domain. First, a CFD-CAA calculation is conducted for an isolated TC configuration to assess the coupling approach, as well as to generate a reference solution for subsequent assessments of QFF installation effects. Direct comparisons between the CFD-CAA calculations associated with the various installed configurations allow the assessment of the effects of each component (nozzle, collector, etc.) or feature (confined vs. free jet flow, etc.) characterizing the NASA LaRC QFF facility.

Redonnet, Stephane; Lockard, David P.; Khorrami, Mehdi R.; Choudhari, Meelan M.

2011-01-01

19

Characterization of four Phyllanthus species using liquid chromatography coupled to tandem mass spectrometry.  

PubMed

This paper reports a comparison of four Phyllanthus species (P. amarus, P. stipulatus, P. niruri and P. tenellus), commonly known as stone breaker, by the characterization of the chemical profile of their aqueous extracts. Such characterization was carried out using liquid chromatography coupled to ion trap tandem mass spectrometry (LC-IT-MS(n)) under reversed-phase gradient elution mode. The results of MS/MS and MS(3) on-line experiments, using the electrospray ionization source in the positive and negative mode, are extensively discussed. Furthermore, quercetin-3-O-?-d-glucuronopyranoside was isolated in multimilligram scale from the aqueous extract of P. stipulatus and characterized by mass spectrometry and NMR. Although it is an unusual flavonol in natural products, LC-IT-MS(n) experiments showed it to be present also in P. amarus. PMID:23611623

Sprenger, Ricardo da Fontoura; Cass, Quezia Bezerra

2013-05-24

20

High-performance liquid chromatography coupled with tandem mass spectrometry applied for metabolic study of ginsenoside Rb 1 on rat  

Microsoft Academic Search

Liquid chromatography coupled with mass spectrometry and tandem mass spectrometry has been applied to investigate the in vivo metabolism of ginsenoside Rb1 in rat. Both positive electrospray ionization mass spectrometry and negative electrospray ionization mass spectrometry were used to identify the Rb1 and its metabolites in rat plasma, urine, and feces samples. Oxygenation and deglycosylation were found to be the

Tianxiu Qian; Zhi-Hong Jiang; Zongwei Cai

2006-01-01

21

Palladium-catalyzed C-h functionalization of acyldiazomethane and tandem cross-coupling reactions.  

PubMed

Palladium-catalyzed C-H functionalization of acyldiazomethanes with aryl iodides has been developed. This reaction is featured by the retention of the diazo functionality in the transformation, thus constituting a novel method for the introduction of diazo functionality to organic molecules. Consistent with the experimental results, the density functional theory (DFT) calculation indicates that the formation of Pd-carbene species in the catalytic cycle through dinitrogen extrusion from the palladium ethyl diazoacetate (Pd-EDA) complex is less favorable. The reaction instead proceeds through Ag2CO3 assisted deprotonation and subsequently reductive elimination to afford the products with diazo functionality remained. This C-H functionalization transformation can be further combined with the recently evolved palladium-catalyzed cross-coupling reaction of diazo compounds with aryl iodides to develop a tandem coupling process for the synthesis of ?,?-diaryl esters. DFT calculation supports the involvement of Pd-carbene as reactive intermediate in the catalytic cycle, which goes through facile carbene migratory insertion with a low energy barrier (3.8 kcal/mol). PMID:25794590

Ye, Fei; Qu, Shuanglin; Zhou, Lei; Peng, Cheng; Wang, Chengpeng; Cheng, Jiajia; Hossain, Mohammad Lokman; Liu, Yizhou; Zhang, Yan; Wang, Zhi-Xiang; Wang, Jianbo

2015-04-01

22

Benzene oxidation coupled to sulfate reduction  

USGS Publications Warehouse

Highly reduced sediments from San Diego Bay, Calif., that were incubated under strictly anaerobic conditions metabolized benzene within 55 days when they were exposed initially to I ??M benzene. The rate of benzene metabolism increased as benzene was added back to the benzene-adapted sediments. When a [14C]benzene tracer was included with the benzene added to benzene-adapted sediments, 92% of the added radioactivity was recovered as 14CO2. Molybdate, an inhibitor of sulfate reduction, inhibited benzene uptake and production of 14CO2 from [14C]benzene. Benzene metabolism stopped when the sediments became sulfate depleted, and benzene uptake resumed when sulfate was added again. The stoichiometry of benzene uptake and sulfate reduction was consistent with the hypothesis that sulfate was the principal electron acceptor for benzene oxidation. Isotope trapping experiments performed with [14C]benzene revealed that there was no production of such potential extracellular intermediates of benzene oxidation as phenol, benzoate, p-hydroxybenzoate, cyclohexane, catechol, and acetate. The results demonstrate that benzene can be oxidized in the absence of O2, with sulfate serving as the electron acceptor, and suggest that some sulfate reducers are capable of completely oxidizing benzene to carbon dioxide without the production of extracellular intermediates. Although anaerobic benzene oxidation coupled to chelated Fe(III) has been documented previously, the study reported here provides the first example of a natural sediment compound that can serve as an electron acceptor for anaerobic benzene oxidation.

Lovley, D.R.; Coates, J.D.; Woodward, J.C.; Phillips, E.J.P.

1995-01-01

23

Vanadium-catalyzed regioselective oxidative coupling of 2-hydroxycarbazoles.  

PubMed

The first regioselective oxidative coupling of 2-hydroxycarbazoles is described. With a vanadium catalyst and oxygen as the terminal oxidant, dimers with an ortho-ortho' coupling pattern were obtained with high selectivity. Further oxidation led to ortho'-ortho' coupling to generate a tetramer, which provided insight that the atropisomerization barriers of the unsymmetrical biaryl bonds are much lower than expected. PMID:25590578

Liu, Lei; Carroll, Patrick J; Kozlowski, Marisa C

2015-02-01

24

Operational experience for coupled operation of the Holifield tandem electrostatic accelerator and isochronous cyclotron  

SciTech Connect

Coupled operation of the 25 MV tandem accelerator and the Oak Ridge Isochronous Cyclotron of the Holifield Heavy Ion Research Facility began in January 1981. Since that time the use of the cyclotron in this mode has become routine. Thirty-six different ion species in the range from /sup 9/Be to /sup 150/Nd have been accelerated; 106 separate beam setups have been provided. Since the beginning of coupled operation, significant improvement of cyclotron systems, and setup and operating techniques, have been made. The graphite electrostatic deflector septum formerly used for high-current light ion beams has been replaced by a thin molybdenum septum. Extraction system positioning mechanisms have been refined and recalibrated and more precise and reliable position readouts have been provided. The computer-based control system has been improved. The frequency range of the rf system has been increased to eliminate an energy dead-band. Cyclotron setup calculations have been improved and standardized methods have been developed to consistently achieve well-centered orbits, correct beam extraction system positions, and electrostatic and magnetic strengths. A totally new beam bunching system has been installed. The improvements in the phase-lock system of the beam buncher have been especially effective. A large number of obsolete and unreliable power supplies have been replaced. Beam extraction efficiency has been increased from approx.50% to approx.70%. Accuracy of obtaining the desired energy without fine tuning is now approx.1% compared to 2 to 3% in early coupled operation. Beam setup time (tuning) has been reduced by approx.20%. Unscheduled maintenance has been reduced by a factor of two.

Martin, J.A.; Dowling, D.T.; Haynes, D.L.; Hudson, E.D.; Jones, C.M.; Juras, R.C.; Lane, S.S.; Ludemann, C.A.; Meigs, M.J.; Milner, W.T.

1986-10-01

25

Determination of the glucocorticoids prednisone, prednisolone, dexamethasone, and cortisol in human serum using liquid chromatography coupled to tandem mass spectrometry  

Microsoft Academic Search

Glucocorticoids are an important component of immunosuppressive therapy for solid organ transplantation. A method to quantitate prednisone, prednisolone, dexamethasone and cortisol in human serum has been developed. Analysis is performed utilizing reversed-phase liquid chromatography coupled to tandem mass spectrometry. The method was validated to a lower limit of quantitation of 5.4ng\\/ml for prednisone and cortisol, and 10.7ng\\/ml for dexamethasone and

Valerie A Frerichs; Kathleen M Tornatore

2004-01-01

26

Detection and identification of sulphonamide drugs in municipal waste water by liquid chromatography coupled with electrospray ionisation tandem mass spectrometry  

Microsoft Academic Search

High-performance liquid chromatography coupled with positive-ion electrospray ionisation tandem mass spectrometry was used for the determination and confirmation of 13 sulphonamide drugs in environmental water samples in the low ng\\/L-range. Enrichment with concentration factors of 130–670 was performed by solid phase extraction, achieving recoveries of 50 to 90%. After gradient elution HPLC, detection and quantification was performed using selected reaction

C. Hartig; T. Storm; M. Jekel

1999-01-01

27

Eukaryotic coupled translation of tandem cistrons: identification of the influenza B virus BM2 polypeptide.  

PubMed Central

Previous nucleotide sequence analysis of RNA segment 7 of influenza B virus indicated that, in addition to the reading frame encoding the 248 amino acid M1 protein, there is a second overlapping reading frame (BM2ORF) of 585 nucleotides that has the coding capacity for 195 amino acids. To search for a polypeptide product derived from BM2ORF, a genetically engineered beta-galactosidase-BM2ORF fusion protein was expressed in Escherichia coli and a polyclonal rabbit antiserum was raised to the purified fusion protein. This antiserum was used to identify a polypeptide, designated BM2 protein (Mr approximately equal to 12,000), that is synthesized in influenza B virus-infected cells. To understand the mechanism by which the BM2 protein is generated from influenza B virus RNA segment 7, a mutational analysis of the cloned DNA was performed and the altered DNAs were expressed in eukaryotic cells. The expression patterns of the M1 and BM2 proteins from the altered DNAs indicate that the BM2 protein initiation codon overlaps with the termination codon of the M1 protein in an overlapping translational stop-start pentanucleotide, TAATG, and that the expression of the BM2 protein requires 5'-adjacent termination of M1 synthesis. Our data suggest that a termination-reinitiation scheme is used in translation of a bicistronic mRNA derived from influenza B virus RNA segment 7, and this strategy has some analogy to prokaryotic coupled stop-start translation of tandem cistrons. Images Fig. 2. Fig. 3. Fig. 4. Fig. 5. Fig. 6. Fig. 7. Fig. 8. PMID:2114979

Horvath, C M; Williams, M A; Lamb, R A

1990-01-01

28

Oxidative coupling of methane by water as the oxidant on perovskite oxide catalysts  

Microsoft Academic Search

We found that methane was selectively oxidized by water to give C2 hydrocarbons and hydrogen on ATi1-xBxO3-d (A=Sr, Ba, B=Mg, Ca). The coupling activity and selectivity on SrTi0.4Mg0.6O3-d in the presence of steam was ~95%, which was much higher than that on pure SrTiO3. This suggests that the selective oxidative coupling of methane by water was catalyzed by the oxide

Xiaohong Li; Keiichi Tomishige; Kaoru Fujimoto

1996-01-01

29

Tandem oxidative dearomatization/intramolecular Diels-Alder reaction for construction of the tricyclic core of palhinine A.  

PubMed

A concise construction of the 6/6/5 tricyclic core of Lycopodium alkaloid palhinine A (1) has been accomplished. The developed synthetic strategy featured a tandem oxidative dearomatization/intramolecular Diels-Alder reaction to construct C/D rings and an intramolecular 5-exo-trig radical cyclization to install the B ring of palhinine A (1). The developed approach paves the way for the total synthesis of palhinine A (1). PMID:22497445

Zhao, Changgui; Zheng, Huaiji; Jing, Peng; Fang, Bowen; Xie, Xingang; She, Xuegong

2012-05-01

30

[Research progress in microbial methane oxidation coupled to denitrification].  

PubMed

Methane oxidation coupled to denitrification is an essential bond to connect carbon- and nitrogen cycling. To deeply research this process will improve our understanding on the biochemical cycling of global carbon and nitrogen. As an exogenous gaseous carbon source of denitrification, methane can both regulate the balance of atmospheric methane to effectively mitigate the greenhouse effect caused by methane, and reduce the cost of exogenous carbon source input in traditional wastewater denitrification treatment process. As a result, great attention has being paid to the mechanical study of the process. This paper mainly discussed the two types of methane oxidation coupled to denitrification, i. e., aerobic methane oxidation coupled to denitrification (AME-D) and anaerobic methane oxidation coupled to denitrification (ANME-D), with the focus on the microbiological coupling mechanisms and related affecting factors. The existing problems in the engineering application of methane oxidation coupled to denitrification were pointed out, and the application prospects were approached. PMID:24697087

Zhu, Jing; Yuan, Meng-Dong; Liu, Jing-Jing; Huang, Xiao-Xiao; Wu, Wei-Xiang

2013-12-01

31

Regiospecific synthesis of neuroprotective 1,4-benzoxazine derivatives through a tandem oxidation-Diels-Alder reaction.  

PubMed

The tandem oxidation-inverse electron demand Diels-Alder reaction of o-aminophenol derivatives and enamines has been accomplished at room temperature using a stoichiometric amount of manganese dioxide as the oxidant to furnish highly substituted 1,4-benzoxazine cycloadducts with complete regiochemical control. Because of its efficiency in introducing diverse elements in both cycloaddition partners, this one-pot process should allow the assembly of libraries of biologically relevant 1,4-benzoxazine derivatives. In this respect, the 3,3-diphenyl-substituted-1,4-benzoxazine derivative was found to be a potent neuroprotective agent in an animal model of excitotoxic lesions in newborn mice. PMID:25686764

Nguyen, Khac Minh Huy; Schwendimann, Leslie; Gressens, Pierre; Largeron, Martine

2015-03-11

32

Integrated autothermal reactor concepts for oxidative coupling and reforming of  

E-print Network

. . . . . . . . . . . . . . . 58 3 Development of a packed bed membrane reactor with a dual function OCM/SRM catalyst 63 Abstract#12;Integrated autothermal reactor concepts for oxidative coupling and reforming of methane #12-90-365-2985-3, DOI 10.3990/1.9789036529853 #12;INTEGRATED AUTOTHERMAL REACTOR CONCEPTS FOR OXIDATIVE COUPLING

Twente, Universiteit

33

Titanium oxidation by rf inductively coupled plasma  

NASA Astrophysics Data System (ADS)

The development of titanium dioxide (TiO2) films in the rutile and anatase phases is reported. The films have been obtained from an implantation/diffusion and sputtering process of commercially pure titanium targets, carried out in up to 500 W plasmas. The experimental outcome is of particular interest, in the case of anatase, for atmospheric pollution degradation by photocatalysis and, as to the rutile phase, for the production of biomaterials required by prosthesis and implants. The reactor employed consists in a cylindrical pyrex-like glass vessel inductively coupled to a 13.56 MHz RF source. The process takes place at a 5×10-2 mbar pressure with the target samples being biased from 0 to -3000 V DC. The anatase phase films were obtained from sputtering the titanium targets over glass and silicon electrically floated substrates placed 2 cm away from the target. The rutile phase was obtained by implantation/diffusion on targets at about 700 °C. The plasma was developed from a 4:1 argon/oxygen mixture for ~5 hour processing periods. The target temperature was controlled by means of the bias voltage and the plasma source power. The obtained anatase phases did not require annealing after the plasma oxidation process. The characterization of the film samples was conducted by means of x-ray diffraction, scanning electron microscopy, x-ray photoelectron spectroscopy and Raman spectroscopy.

Valencia-Alvarado, R.; de la Piedad-Beneitez, A.; López-Callejas, R.; Barocio, S. R.; Mercado-Cabrera, A.; Peña-Eguiluz, R.; Muñoz-Castro, A. E.; Rodríguez-Méndez, B. G.; de la Rosa-Vázquez, J. M.

2014-05-01

34

Magnetostructural and magnetodielectric coupling in spinel oxides  

NASA Astrophysics Data System (ADS)

Spinels oxides are of great interest functionally as multiferroic, battery, and magnetic materials as well as fundamentally because they exhibit novel spin, structural, and orbital ground states. Competing interactions are at the heart of novel functional behavior in spinels. Here, we explore the intricate landscape of spin, lattice, and orbital interactions in magnetic spinels by employing variable-temperature high-resolution synchrotron x-ray powder diffraction, total neutron scattering, magnetic susceptibility, dielectric, and heat capacity measurements. We show that the onset of long-range magnetic interactions often gives rise to lattice distortions. We present the complete crystallographic descriptions of the ground state structures of several spinels, thereby paving the way for accurate modeling and design of structure-property relationships in these materials. We also report the emergence of magnetodielectric coupling in the magnetostructural phases of some of the studied spinels. We begin by examining spin-lattice coupling in the Jahn-Teller active systems NiCr2O4 and CuCr2O4. Orbital ordering yields a cubic to tetragonal lattice distortion in these materials above their magnetic ordering temperatures, however, we find that magnetic ordering also drives structural distortions in these spinels through exchange striction. We provide the first orthorhombic structural descriptions of NiCr 2O4 and CuCr2O4. Our observation of strong spin-lattice coupling in NiCr2O4 and CuCr 2O4 inspired the study of magnetodielectric coupling in these spinels. Magnetocapacitance measurements of NiCr2O4 reveal multiferroic behavior and new magnetostructural distortions below the Neel temperature. This observation illustrates the sensitivity of dielectric measurements to magnetostructural transitions in spinel materials. Finally, in the examination of NiCr2O4 we show that magnetodielectric coupling is well described by Ginzburg-Landau theory. In addition to exchange striction, geometric frustration couples spin interactions to the lattice of the spinels MgCr2O4 and ZnCr2O4. Novel spin ground states that are important for memory and quantum computing applications are predicted to exist in these spinels. However, their structural and spin ground states are not well understood. We find that tetragonal and orthorhombic phases coexist in antiferromagnetic MgCr2O4 and ZnCr2O4. The structural deformations in these materials lift spin degeneracy by primarily distorting the pyrochlore Cr sublattice. In subsequent studies, we probe the effect of adding dilute spins on the non-magnetic cation sites of MgCr2O 4 and ZnCr2O4. Substitution of Co2+ cations in Zn1-xCoxCr2O4 completely suppress the spin-Jahn-Teller distortion of ZnCr2O4 while, Cu2+ substitutions in Mg1-xCuxCr 2O4 and Zn1-xCuxCr2O 4 induce Jahn-Teller distortions at temperatures above their magnetic ordering temperatures. The Jahn-Teller distortions of Mg1-xCu xCr2O4 and Zn1-xCuxCr 2O4 do not lift spin degeneracy, therefore magnetic ordering is still suppressed down to low temperatures. We show that only more than 20% magnetic A substituents can lift spin degeneracy in MgCr 2O4 and ZnCr2O4. We have also examined the magnetostructural phase transition of the spinel Mn3O4. We show that Mn3O4 undergoes a magnetostructural phase transition from tetragonal I4 1/amd symmetry to a phase coexistence regime consisting of tetragonal I41/amd and orthorhombic Fddd symmetries. Phase coexistence in Mn3O4 is mediated by strain due to a significant lattice mismatch between the low temperature orthorhombic phase and the high temperature tetragonal phase. We propose that strain could be used to control the structure and properties of Mn3O4. Our investigations of spin-driven lattice distortions in spinel oxides illustrate that structural phase coexistence is prevalent for spinels with Neel temperatures below 50 K.

Kemei, Moureen Chemurgor

35

Determination of oxidized phosphatidylcholines by hydrophilic interaction liquid chromatography coupled to fourier transform mass spectrometry.  

PubMed

A novel liquid chromatography-mass spectrometry (LC-MS) approach for analysis of oxidized phosphatidylcholines by an Orbitrap Fourier Transform mass spectrometer in positive electrospray ionization (ESI) coupled to hydrophilic interaction liquid chromatography (HILIC) was developed. This method depends on three selectivity criteria for separation and identification: retention time, exact mass at a resolution of 100,000 and collision induced dissociation (CID) fragment spectra in a linear ion trap. The process of chromatography development showed the best separation properties with a silica-based Kinetex column. This type of chromatography was able to separate all major lipid classes expected in mammalian samples, yielding increased sensitivity of oxidized phosphatidylcholines over reversed phase chromatography. Identification of molecular species was achieved by exact mass on intact molecular ions and CID tandem mass spectra containing characteristic fragments. Due to a lack of commercially available standards, method development was performed with copper induced oxidation products of palmitoyl-arachidonoyl-phosphatidylcholine, which resulted in a plethora of lipid species oxidized at the arachidonoyl moiety. Validation of the method was done with copper oxidized human low-density lipoprotein (LDL) prepared by ultracentrifugation. In these LDL samples we could identify 46 oxidized molecular phosphatidylcholine species out of 99 possible candidates. PMID:25874761

Sala, Pia; Pötz, Sandra; Brunner, Martina; Trötzmüller, Martin; Fauland, Alexander; Triebl, Alexander; Hartler, Jürgen; Lankmayr, Ernst; Köfeler, Harald C

2015-01-01

36

Determination of serum methylmalonic acid by alkylative extraction and liquid chromatography coupled to tandem mass spectrometry  

Microsoft Academic Search

Despite the new advances in bioanalytical techniques, the analysis of low-molecular-weight organic acids in complex matrices is still a challenge. Although new strategies applying liquid chromatography–tandem mass spectrometry (LC–MS\\/MS) seem to be promising, sample preparation methodologies hamper its application in most clinical laboratories. The quantitation of methylmalonic acid (MMA) in biological matrices is an emblematic example due to its low

Valdemir Melechco Carvalho; Fernando Kok

2008-01-01

37

Tandem mobile robot system  

DOEpatents

A robotic vehicle system for terrain navigation mobility provides a way to climb stairs, cross crevices, and navigate across difficult terrain by coupling two or more mobile robots with a coupling device and controlling the robots cooperatively in tandem.

Buttz, James H. (Albuquerque, NM); Shirey, David L. (Albuquerque, NM); Hayward, David R. (Albuquerque, NM)

2003-01-01

38

Asymmetric synthesis of the main core of kaurane family members triggered by an oxidative polycyclization-pinacol tandem process.  

PubMed

Polycyclization processes represent expeditious routes used in both nature and the laboratory to produce complex polycyclic molecules. A new stereoselective oxidative variant of such a polycyclization has been developed in which the cascade is triggered by a phenol dearomatization and is concluded by a pinacol transposition. This unprecedented avenue combines the synthetic power of a polycyclization and a transposition in tandem and enables the rapid formation of the tetracyclic main core of kaurane diterpenes containing several asymmetric and quaternary carbon centers in a single step from a simple phenol derivative. PMID:25191786

Desjardins, Samuel; Maertens, Gaëtan; Canesi, Sylvain

2014-09-19

39

IMPACT OF OXYGEN MEDIATED OXIDATIVE COUPLING ON ADSORPTION KINETICS  

EPA Science Inventory

The presence of molecular oxygen in the test environment promotes oxidative coupling (polymer formation) of phenolic compounds on the surface of granular activated carbon (GAC). Both adsorption equilibria and adsorption kinetics are affected by these chemical reactions. Lack of...

40

Magnetic coupling among spinel iron oxide microparticles by Mssbauer spectroscopy  

E-print Network

L-437 Magnetic coupling among spinel iron oxide microparticles by Mössbauer spectroscopy E. Tronc cristalline au sein d'agrégats est suggérée. Abstract 2014 Mössbauer spectra of hydrous spinel iron oxide particles with thermal fluctuations oftheir magnetization vector (M) among the easy directions

Boyer, Edmond

41

High ethylene to ethane processes for oxidative coupling  

DOEpatents

Oxidative coupling of lower alkane to higher hydrocarbon is conducted using catalyst comprising barium and/or strontium component and a metal oxide combustion promoter in the presence of vapor phase halogen component. High ethylene to ethane mole ratios in the product can be obtained over extended operating periods.

Chafin, Richard B. (Hurricane, WV); Warren, Barbara K. (Charleston, WV)

1991-01-01

42

Identification of the Related Substances in Ampicillin Capsule by Rapid Resolution Liquid Chromatography Coupled with Electrospray Ionization Tandem Mass Spectrometry  

PubMed Central

Rapid Resolution Liquid Chromatography coupled with Electrospray Ionization Tandem Mass Spectrometry (RRLC-ESI-MSn) was used to separate and identify related substances in ampicillin capsule. The fragmentation behaviors of related substances were used to identify their chemical structures. Finally, a total of 13 related substances in ampicillin capsule were identified, including four identified components for the first time and three groups of isomers on the basis of the exact mass, fragmentation behaviors, retention time, and chemical structures in the literature. This study avoided time-consuming and complex chemosynthesis of related substances of ampicillin and the results could be useful for the quality control of ampicillin capsule to guarantee its safety in clinic. In the meantime, it provided a good example for the rapid identification of chemical structures of related substances of drugs. PMID:25530907

Cheng, Xian Long; Liu, Yang; Liang, Miao; Dong, Honghuan; Lv, Beiran; Luo, Zhiqiang; Tang, Mingmin

2014-01-01

43

Microwave-assisted tandem organocatalytic peptide-coupling intramolecular aza-Michael reaction: ?,?-unsaturated N-acyl pyrazoles as Michael acceptors.  

PubMed

Conjugated N-acyl pyrazoles have been successfully employed in the organocatalytic enantioselective intramolecular aza-Michael reaction as ester surrogates. Bifunctional squaramides under microwave irradiation provided the best results in this transformation. Furthermore, this protocol has been combined with a peptide-coupling reaction in a tandem sequence. The final products were easily converted into the corresponding ethyl esters. PMID:25336358

Sánchez-Roselló, María; Mulet, Cristina; Guerola, Marta; del Pozo, Carlos; Fustero, Santos

2014-11-24

44

Quantification of anthelmintic drug residues in milk and muscle tissues by liquid chromatography coupled to Orbitrap and liquid chromatography coupled to tandem mass spectrometry.  

PubMed

A simple method for the determination of some anthelmintic drugs and phenylbutazone residues in milk and muscle was developed. Following a fast and easy extraction and evaporation procedure, the extract was injected into an ultra performance liquid chromatography system coupled to a single stage Orbitrap detector. The high mass resolution of 50,000 full width at half maximum and corresponding narrow mass windows permitted a very selective and sensitive detection of analytes without requiring fragmentation of the observed [M+H](+) or [M+Na](+) ions. This eliminated some difficulties which have plagued the analysis of compounds belonging to the group of avermectins. The analytical method was validated according to the EU commission decision for Orbitrap based, but also for more traditional tandem mass spectrometry based detection and quantification. Equal repeatability but significantly higher sensitivity for critical compounds (avermectins) was obtained for the Orbitrap based detection. A result of this study was the conclusion that analytes with poor fragmentation properties (e.g. sodium-cationized molecules) can be more easily quantified by single stage high resolution mass spectrometry than by tandem mass spectrometry. PMID:21726729

Kaufmann, A; Butcher, P; Maden, K; Walker, S; Widmer, M

2011-08-15

45

Nitric Oxide Enhances Charge-Coupled Device  

NASA Technical Reports Server (NTRS)

Simple treatment increases and stabilizes quantum efficiency of charge-coupled-device photodetector illuminated on back surface at wavelengths less than 4,500 Angstrom. Must be biased in strong accumulation mode. Physical principle of enhancement explained more fully in "Metal Film Increases CCD Output" (NPO-16815). Useful for imaging at wavelengths from ultraviolet to blue; for example, in astronomical observations.

Hecht, Michael H.; Poindexter, Edward H.

1990-01-01

46

Determination of serum methylmalonic acid by alkylative extraction and liquid chromatography coupled to tandem mass spectrometry.  

PubMed

Despite the new advances in bioanalytical techniques, the analysis of low-molecular-weight organic acids in complex matrices is still a challenge. Although new strategies applying liquid chromatography-tandem mass spectrometry (LC-MS/MS) seem to be promising, sample preparation methodologies hamper its application in most clinical laboratories. The quantitation of methylmalonic acid (MMA) in biological matrices is an emblematic example due to its low concentration, the need for derivatization to increase its molecular weight, and the presence of the physiologically more abundant isomer succinic acid. Here we present a new strategy for rapid and sensitive MMA quantitation by combining alkylative extraction and LC-MS/MS. Alkylative extraction conditions were optimized to allow endogenous detection of MMA using only 50 microL of serum with a short sample preparation procedure. The formation of a unique ion from the MMA dipentafluorobenzyl derivative in negative atmospheric pressure chemical ionization (APCI) allowed its detection with high sensitivity and with no interference from succinic acid, a more abundant physiologically present isomer. PMID:18616922

Carvalho, Valdemir Melechco; Kok, Fernando

2008-10-01

47

Simultaneous analysis of 28 urinary VOC metabolites using ultra high performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (UPLC-ESI/MSMS).  

PubMed

Volatile organic compounds (VOCs) are ubiquitous in the environment, originating from many different natural and anthropogenic sources, including tobacco smoke. Long-term exposure to certain VOCs may increase the risk for cancer, birth defects, and neurocognitive impairment. Therefore, VOC exposure is an area of significant public health concern. Urinary VOC metabolites are useful biomarkers for assessing VOC exposure because of non-invasiveness of sampling and longer physiological half-lives of urinary metabolites compared with VOCs in blood and breath. We developed a method using reversed-phase ultra high performance liquid chromatography (UPLC) coupled with electrospray ionization tandem mass spectrometry (ESI/MSMS) to simultaneously quantify 28 urinary VOC metabolites as biomarkers of exposure. We describe a method that monitors metabolites of acrolein, acrylamide, acrylonitrile, benzene, 1-bromopropane, 1,3-butadiene, carbon-disulfide, crotonaldehyde, cyanide, N,N-dimethylformamide, ethylbenzene, ethylene oxide, propylene oxide, styrene, tetrachloroethylene, toluene, trichloroethylene, vinyl chloride and xylene. The method is accurate (mean accuracy for spiked matrix ranged from 84 to 104%), sensitive (limit of detection ranged from 0.5 to 20 ng mL(-1)) and precise (the relative standard deviations ranged from 2.5 to 11%). We applied this method to urine samples collected from 1203 non-smokers and 347 smokers and demonstrated that smokers have significantly elevated levels of tobacco-related biomarkers compared to non-smokers. We found significant (p<0.0001) correlations between serum cotinine and most of the tobacco-related biomarkers measured. These findings confirm that this method can effectively quantify urinary VOC metabolites in a population exposed to volatile organics. PMID:23062436

Alwis, K Udeni; Blount, Benjamin C; Britt, April S; Patel, Dhrusti; Ashley, David L

2012-10-31

48

Fast quantification of endogenous carbohydrates in plasma using hydrophilic interaction liquid chromatography coupled with tandem mass spectrometry.  

PubMed

Endogenous carbohydrates in biosamples are frequently highlighted as the most differential metabolites in many metabolomics studies. A simple, fast, simultaneous quantitative method for 16 endogenous carbohydrates in plasma has been developed using hydrophilic interaction liquid chromatography coupled with tandem mass spectrometry. In order to quantify 16 endogenous carbohydrates in plasma, various conditions, including columns, chromatographic conditions, mass spectrometry conditions, and plasma preparation methods, were investigated. Different conditions in this quantified analysis were performed and optimized. The reproducibility, precision, recovery, matrix effect, and stability of the method were verified. The results indicated that a methanol/acetonitrile (50:50, v/v) mixture could effectively and reproducibly precipitate rat plasma proteins. Cold organic solvents coupled with vortex for 1 min and incubated at -20°C for 20 min were the most optimal conditions for protein precipitation and extraction. The results, according to the linearity, recovery, precision, matrix effect, and stability, showed that the method was satisfactory in the quantification of endogenous carbohydrates in rat plasma. The quantified analysis of endogenous carbohydrates in rat plasma performed excellently in terms of sensitivity, high throughput, and simple sample preparation, which met the requirement of quantification in specific expanded metabolomic studies after the global metabolic profiling research. PMID:25359182

Zhu, Bangjie; Liu, Feng; Li, Xituo; Wang, Yan; Gu, Xue; Dai, Jieyu; Wang, Guiming; Cheng, Yu; Yan, Chao

2015-01-01

49

Numerical model of tandem organic light-emitting diodes based on a transition metal oxide interconnector layer  

NASA Astrophysics Data System (ADS)

By utilizing a two-step process to express the charge generation and separation mechanism of the transition metal oxides (TMOs) interconnector layer, a numerical model was proposed for tandem organic light emitting diodes (OLEDs) with a TMOs thin film as the interconnector layer. This model is valid not only for an n-type TMOs interconnector layer, but also for a p-type TMOs interconnector layer. Based on this model, the influences of different carrier injection barriers at the interface of the electrode/organic layer on the charge generation ability of interconnector layers were studied. In addition, the distribution characteristics of carrier concentration, electric field intensity and potential in the device under different carrier injection barriers were studied. The results show that when keeping one carrier injection barrier as a constant while increasing another carrier injection barrier, carriers injected into the device were gradually decreased, the carrier generation ability of the interconnector layer was gradually reduced, the electric field intensity at the interface of the organic/electrode was gradually enhanced, and the electric field distribution became nearly linear: the voltage drops in two light units gradually became the same. Meanwhile, the carrier injection ability decreased as another carrier injection barrier increased. The simulation results agree with the experimental data. The obtained results can provide us with a deep understanding of the work mechanism of TMOs-based tandem OLEDs.

Feiping, Lu; Yingquan, Peng; Yongzhong, Xing

2014-04-01

50

Metal-free tandem oxidative aryl migration and C-C bond cleavage: synthesis of ?-ketoamides and esters from acrylic derivatives.  

PubMed

A novel tandem metal-free oxidative aryl migration/C-C bond-cleavage reaction, mediated by hypervalent iodine reagent, has been discovered. The presented transformation provided straightforward access to important ?-ketoamide and ?-ketoester derivatives from readily available acrylic derivatives via a concerted process of 1,2-aryl shift concomitant with C-C bond cleavage. PMID:25343425

Liu, Le; Du, Liang; Zhang-Negrerie, Daisy; Du, Yunfei; Zhao, Kang

2014-11-01

51

Quantification of Neurotransmitters in Mouse Brain Tissue by Using Liquid Chromatography Coupled Electrospray Tandem Mass Spectrometry  

PubMed Central

A simple and rapid liquid chromatography tandem mass spectrometry method has been developed for the determination of BH4, DA, 5-HT, NE, EP, Glu, and GABA in mouse brain using epsilon-acetamidocaproic acid and isotopically labeled neurotransmitters as internal standards. Proteins in the samples were precipitated by adding acetonitrile, and then the supernatants were separated by a Sepax Polar-Imidazole (2.1?mm × 100?mm, i.d., 3??m) column by adding a mixture of 10?mM ammonium formate in acetonitrile/water (75?:?25, v/v, 300??l/min) for BH4 and DA. To assay 5-HT, NE, EP, Glu, and GABA; a Luna 3?? C18 (3.0?mm × 150?mm, i.d., 3??m) column was used by adding a mixture of 1% formic acid in acetonitrile/water (20?:?80, v/v, 350??l/min). The total chromatographic run time was 5.5?min. The method was validated for the analysis of samples. The calibration curve was linear between 10 and 2000?ng/g for BH4 (r2 = 0.995) , 10 and 5000?ng/g for DA (r2 = 0.997) , 20 and 10000?ng/g for 5-HT (r2 = 0.994) , NE (r2 = 0.993) , and EP (r2 = 0.993) , and 0.2 and 200??g/g for Glu (r2 = 0.996) and GABA (r2 = 0.999) in the mouse brain tissues. As stated above, LC-MS/MS results were obtained and established to be a useful tool for the quantitative analysis of BH4, DA, 5-HT, NE, EP, Glu, and GABA in the experimental rodent brain. PMID:25258696

Kim, Tae-Hyun; Choi, Juhee

2014-01-01

52

Direct-Coupling O? Bond Forming Pathway in Cobalt Oxide Water Oxidation Catalysts  

E-print Network

We report a catalytic mechanism for water oxidation in a cobalt oxide cubane model compound, in which the crucial O–O bond formation step takes place by direct coupling between two CoIV(O) metal oxo groups. Our results are ...

Wang, Lee-Ping

53

Simultaneous determination of five constituents in Qinpijiegu capsule by high-performance liquid chromatography coupled with tandem mass spectrometry.  

PubMed

A rapid high-performance liquid chromatography coupled with tandem mass spectrometry method was developed for the simultaneous determination of five constituents in Qinpijiegu capsule (QJC), a classical Tibetan prescription. The separation of five compounds such as aesculin, aesculetin, fraxin, peimine and peiminine was performed on a Purospher STAR LP RP-C18 (250 × 4.6 mm, 5 ?m) column with linear gradient elution of acetonitrile-0.3‰ formic acid water in 13 min. Detection was carried out by multiple reaction monitoring mode using electrospray ionization in the positive and negative ion switching mode. The sample was prepared with ultrasound extraction with methanol, which could obtain higher extraction efficiency and shorter extraction time comparing to reflux extraction with alkalized chloroform-methanol. The proposed method was applied to analyze three batches of samples with acceptable linearity (r(2) > 0.9977), precision [relative standard deviation (RSD) < 7.40%], repeatability (RSD < 2.49%), stability [relative error (RE) < 9.15%] and recovery (RSD < 10.76%). This is the first development of a multicomponent quantitation method for the quality control of QJC. Furthermore, the new established method was proven to be highly sensitive and effective in evaluating the quality of QJC. PMID:24920654

Zhao, Minmin; Ding, Weijing; Wang, Shuang; Gao, Meng; Fu, Shan; Zhang, Juan; Li, Tao; Wu, Yin; Wang, Qiao

2015-02-01

54

Determination of perfluorooctane sulfonate and perfluorooctanoic acid in food packaging using liquid chromatography coupled with tandem mass spectrometry.  

PubMed

This research aimed to monitor the amounts of PFOS and PFOA in food packaging and study the migration of PFOS and PFOA from food packaging, using a saliva simulant and pressurized liquid extraction (PLE) technique. Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) was employed to determine residues of PFOS and PFOA by using a gradient reversed-phase method with ammonium acetate/acetonitrile buffer. A good linearity was established for PFOS and PFOA in a range of 0.05-10 ?gL(-1), with R2 ? 0.9998. Of the samples extracted by methanol, the highest concentration of PFOS was found in fast-food container samples, at a level of 92.48 ng dm(-2). For PFOA, the highest concentration in samples extracted by methanol was found in ice cream cup samples, at a level of 16.91 ng dm(-2). The amounts of PFOS and PFOA that migrated from food packaging samples through contact with saliva simulant were 4.80 and 4.55 ng dm(-2), respectively. Saliva simulant could leach PFOS and PFOA from the group of the thickest paper samples (?1 dm2 g(-1)) at levels of 7.01 and 6.41 ng dm(-2), respectively, indicating that paper with greater thickness and less area might release larger quantities of coated/added PFOS or PFOA. PMID:22265653

Poothong, Somrutai; Boontanon, Suwanna Kitpati; Boontanon, Narin

2012-02-29

55

Hydrophilic interaction liquid chromatography coupled with tandem mass spectrometry for acidic herbicides and metabolites analysis in fresh water.  

PubMed

Theoretical papers and environmental applications of hydrophilic interaction liquid chromatography (HILIC) have been published for a wide range of analytes, but to our knowledge, no study focused on acidic herbicides (e.g., triketones, phenoxy acids, sulfonylurea, and acidic metabolites of chloroacetanilides). Matrix effects are the main obstacle to natural sample analysis by liquid chromatography coupled with tandem mass spectrometry (MS) via an electrospray ionization (ESI) interface. Therefore, we paid particular attention on limiting interference by (i) adapting the emerging HILIC technique, which is generally considered more sensitive than conventional reversed phase liquid chromatography and (ii) optimizing the solid phase extraction (SPE) step using a design of experiment. A rapid and reliable off line SPE-HILIC-ESI-MS/MS method was thus developed for the quantification of acidic herbicides in fresh water, with limits of quantifications (LOQs) ranging from 5 to 22 ng L(-1). Then, the analysis of freshwater samples highlighted the robustness of the method, and the importance of the chloroacetanilides metabolites among the studied analytes. PMID:24859693

Fauvelle, Vincent; Mazzella, Nicolas; Morin, Soizic; Moreira, Sylvia; Delest, Brigitte; Budzinski, Hélène

2015-03-01

56

Strategies in protein sequencing and characterization: multi-enzyme digestion coupled with alternate CID/ETD tandem mass spectrometry.  

PubMed

A strategy based on a simultaneous multi-enzyme digestion coupled with electron transfer dissociation (ETD) and collision-induced dissociation (CID) was developed for protein sequencing and characterization, as a valid alternative platform in ion-trap based proteomics. The effect of different proteolytic procedures using chymotrypsin, trypsin, a combination of both, and Lys-C, was carefully evaluated in terms of number of identified peptides, protein coverage, and score distribution. A systematic comparison between CID and ETD is shown for the analysis of peptides originating from the in-solution digestion of standard caseins. The best results were achieved with a trypsin/chymotrypsin mix combined with CID and ETD operating in alternating mode. A post-database search validation of MS/MS dataset was performed, then, the matched peptides were cross checked by the evaluation of ion scores, rank, number of experimental product ions, and their relative abundances in the MS/MS spectrum. By integrated CID/ETD experiments, high quality-spectra have been obtained, thus allowing a confirmation of spectral information and an increase of accuracy in peptide sequence assignments. Overlapping peptides, produced throughout the proteins, reduce the ambiguity in mapping modifications between natural variants and animal species, and allow the characterization of post translational modifications. The advantages of using the enzymatic mix trypsin/chymotrypsin were confirmed by the nanoLC and CID/ETD tandem mass spectrometry of goat milk proteins, previously separated by two-dimensional gel electrophoresis. PMID:25479873

Nardiello, Donatella; Palermo, Carmen; Natale, Anna; Quinto, Maurizio; Centonze, Diego

2015-01-01

57

Quantification of endogenous brassinosteroids in sub-gram plant tissues by in-line matrix solid-phase dispersion-tandem solid phase extraction coupled with high performance liquid chromatography-tandem mass spectrometry.  

PubMed

A matrix solid-phase dispersion (MSPD)-tandem mixed mode anion exchange (MAX)-mixed mode cation exchange (MCX) solid phase extraction-high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS) method was developed for quantification of six endogenous brassinosteroids (BRs) (24-epibrassinolide, 24-epicastasterone, 6-deoxo-24-epicastasterone, dolichosterone, teasterone and typhasterol) in rice plant tissues. Non-polar interferences were removed effectively by C8 dispersant used in MSPD, while the following tandem MAX-MCX process facilitated the elimination of polar and ionizable compounds. The weak reversed-phase retention feature of MAX-MCX leaded to good compatibility of the elution solvents in the in-line coupled MSPD-MAX-MCX system. This system was optimized for extraction and purification of BRs in plant samples. The effects of the type of solid phase, the elution solvent, the extraction temperature and the clean-up material were studied. Before HPLC separation, BRs purified were derivatized by m-aminophenylboronic acid to enhance the sensitivity of MS/MS to BRs. Compared with traditional liquid-liquid extraction and solid phase extraction (LLE-SPE), the proposed MSPD-MAX-MCX method showed higher extraction efficiency, lower matrix effect, and advantages of easy manipulation and time-saving. The in-line MSPD-MAX-MCX coupled with HPLC-MS/MS method provided a linear response over two orders of magnitude of BRs concentration with correlation coefficients above 0.9982, limits of detection between 0.008 and 0.04ngmL(-1), relative standard deviations (RSDs) below 29.4%, and recoveries above 77.8%. The proposed method has been successfully applied to analysis of endogenous BRs in rice plant at booting stage and maturity stage. PMID:25092597

Wang, Lu; Duan, Chunfeng; Wu, Dapeng; Guan, Yafeng

2014-09-12

58

On-line electrochemistry/thermospray/tandem mass spectrometry as a new approach to the study of redox reactions: the oxidation of uric acid.  

PubMed

The electrochemical oxidation pathway of uric acid was determined by on-line electrochemistry/thermospray/tandem mass spectrometry. Intermediates and products formed as a result of electrooxidation were monitored as the electrode potential was varied. Several reaction intermediates have been identified and characterized by tandem mass spectrometry. The tandem mass spectrometric results provide convincing evidence that the primary intermediate produced during the electrooxidation of uric acid has a quinonoid diimine structure. The results indicate that once formed via electrooxidation, the primary intermediate can follow three distinct reaction pathways to produce the identified final products. The final electrochemical oxidation products observed in these studies were urea, CO2, alloxan, alloxan monohydrate, allantoin, 5-hydroxyhydantoin-5-carboxamide, and parabanic acid. The solution reactions that follow the initial electron transfer at the electrode are affected by the vaporizer tip temperature of the thermospray probe. In particular, it was found that at different tip temperatures either hydrolysis or ammonolysis reactions of the initial electrochemical oxidation products can occur. Most importantly, the results show that the on-line combination of electrochemistry with thermospray/tandem mass spectrometry provides otherwise difficult to obtain information about redox and associated chemical reactions of biological molecules such as the structure of reaction intermediates and products, as well as providing insight into reaction pathways. PMID:2774199

Volk, K J; Yost, R A; Brajter-Toth, A

1989-08-01

59

Mössbauer study of perovskite oxides for oxidative coupling of Ch4 and absorption of Co2  

NASA Astrophysics Data System (ADS)

Perovskite oxides, (Ba0.95 Ca0.05) (Co1- x Fe x ) O3-?, are prominent materials for oxidative coupling of methane and for CO2 absorption at high temperature, and these oxides before and after treatment in CH4 and CO2 atmosphere were analysed by Mössbauer spectroscopy. The perturbation of microstructure by substitution of Ba sites with Ca, and the electron transfer of mixed valences in Fe and Co ions with the formation of oxygen vacancies at high temperatures, are considered to contribute strongly to the selectivity of CH4 coupling and the rapid absorption of CO2 at high temperatures.

Nomura, K.; Homonnay, Z.; Vertes, A.; Chechersky, V.; Nath, A.; Ujihira, Y.; Hayakawa, T.; Takehira, K.

1997-05-01

60

Coupling of enzymatic and immunoassay steps to detect E. coli: a new, highly sensitive tandem technique for the analysis of low levels of bacteria  

Microsoft Academic Search

A tandem technique for the detection of very low levels E. coli within about 2h is demonstrated. The technique couples the widely employed microbial enzymatic detection methods with an immunoassay step. The bacterial marker enzyme, E. coli ?-D-galactosidase, was used in conjunction with synthetic enzyme substrates to produce products that could be measured with a highly sensitive enzyme-labelled immunosorbent assay

Ramadan A. Abuknesha; Fatima Darwish

2005-01-01

61

Evaluation of Multidimensional Chromatography Coupled with Tandem Mass Spectrometry (LC\\/LC?MS\\/MS) for Large-Scale Protein Analysis:  The Yeast Proteome  

Microsoft Academic Search

Highly complex protein mixtures can be directly analyzed after proteolysis by liquid chromatography coupled with tandem mass spectrometry (LC-MS\\/MS). In this paper, we have utilized the combination of strong cation exchange (SCX) and reversed-phase (RP) chromatography to achieve two-dimensional separation prior to MS\\/MS. One milligram of whole yeast protein was proteolyzed and separated by SCX chromatography (2.1 mm i.d.) with

Junmin Peng; Joshua E. Elias; Carson C. Thoreen; Larry J. Licklider; Steven P. Gygi

2003-01-01

62

Residue determination of glyphosate, glufosinate and aminomethylphosphonic acid in water and soil samples by liquid chromatography coupled to electrospray tandem mass spectrometry  

Microsoft Academic Search

This paper describes a method for the sensitive and selective determination of glyphosate, glufosinate and aminomethylphosphonic acid (AMPA) residues in water and soil samples. The method involves a derivatization step with 9-fluorenylmethylchloroformate (FMOC) in borate buffer and detection based on liquid chromatography coupled to electrospray tandem mass spectrometry (LC–ESI-MS\\/MS). In the case of water samples a volume of 10mL was

María Ibáñez; Óscar J. Pozo; Juan V. Sancho; Francisco J. López; Félix Hernández

2005-01-01

63

Determination of Niacin and Its Metabolites Using Supercritical Fluid Chromatography Coupled to Tandem Mass Spectrometry  

PubMed Central

Niacin, a water-soluble vitamin belonging to the vitamin B group, has been known to cause various problems in the human body when deficient. The vitamin is derived from the diet and afterwards, niacin and its metabolites are secreted in blood or urine. It can be analyzed using liquid chromatography (LC) coupled to mass spectrometry, but niacin and its metabolites are very polar compounds. Recently, supercritical fluid chromatography (SFC) is gaining attention for polar compound analysis. To our best knowledge, the report on the analysis of endogenous-very hydrophilic metabolites in biofluids by SFC has not been found. In this study, we investigated whether the separation of hydrophilic metabolites in biofluids is achievable by SFC. In addition, we also examined the applicability of SFC coupled to MS in extrapolating unknown metabolites by means of spectra information. As a result, an analysis method to quantify the target compounds using SFC/MS/MS was constructed for niacin and its metabolites. Additional putative metabolites from niacin were also identified using the MS fragmentation spectra in plasma and urine. Consequently, the method using SFC/MS/MS allowed for the analysis of polar compounds with low log?P ranging from ?3.7 to 0.29. This study is the first report of the separation of niacin and its seven metabolites in human urine and these results showed that SFC-MS/MS can be an alternative technique for hydrophilic metabolite analysis. PMID:25386386

Taguchi, Kaori; Fukusaki, Eiichiro; Bamba, Takeshi

2014-01-01

64

Tear proteomic analysis of Sjögren syndrome patients with dry eye syndrome by two-dimensional-nano-liquid chromatography coupled with tandem mass spectrometry  

PubMed Central

We examined the tear film proteome of patients with Sjögren's syndrome (SS) and dry eye syndrome (group A), patients with dry eye symptoms (group B) and normal volunteers (group C). Tear samples were pooled from 8 subjects from each group and were subjected to two-dimensional-nano-liquid chromatography coupled with tandem mass spectrometry (2D-nano-LC-MS/MS). The tear breakup time for group A was significantly reduced compared with group B and C (P < 0.001). Group A (Schirmer I test, 2.13 ± 2.38?mm/5?min) had markedly lower tear volume than group B (5.94 ± 4.75?mm/5?min) and C (14.44 ± 6.57?mm/5?min) (P < 0.001). Group A had significantly higher normalized tear protein content (1.8291 ± 0.2241??g/mm) than group B (1.0839 ± 0.1120??g/mm) (P = 0.001) and C (0.2028 ± 0.0177??g/mm) (P = 0.001). The 2D-nano-LC-MS/MS analysis identified a total of 435 proteins, including 182 (54.8%), 247 (74.4%) and 278 (83.7%) in group A, B, and C, respectively, with 56 (16.7%) proteins including defensin ?1, clusterin and lactotransferrin unique to group A. In conclusion, dry eye syndrome in SS patients is associated with an altered proteomic profile with dysregulated expression of proteins involved in a variety of important cellular process including inflammation, immunity, and oxidative stress. PMID:25159733

Li, Bing; Sheng, Minjie; Li, Jianhua; Yan, Guoquan; Lin, Anjuan; Li, Min; Wang, Weifang; Chen, Yihui

2014-01-01

65

Hydrogen sulfide oxidation is coupled to oxidative phosphorylation in mitochondria of Solemya reidi  

SciTech Connect

Solemya reidi, a gutless clam found in sulfide-rich habitats, contains within its gills bacterial symbionts thought to oxidize sulfur compounds and provide a reduced carbon food source to the clam. However, the initial step or steps in sulfide oxidation occur in the animal tissue, and mitochondria isolated from both gill and symbiont-free foot tissue of the clam coupled the oxidation of sulfide to oxidative phosphorylation (adenosine triphosphate (ATP) synthesis). The ability of Solemya reidi to exploit directly the energy in sulfide for ATP synthesis is unprecedented, and suggests that sulfide-habitat animals that lack bacterial symbionts may also use sulfide as an inorganic energy source.

Powell, M.A.; Somero, G.N.

1986-08-01

66

Enantiomeric analysis of drugs of abuse in wastewater by chiral liquid chromatography coupled with tandem mass spectrometry.  

PubMed

The manuscript concerns the development and validation of a method for enantiomeric analysis of structurally related amphetamines (amphetamine, methamphetamine, 4-methylenedioxymethamphetamine (MDMA), 3,4-methylenedioxyamphetamine (MDA) and 3,4-methylenedioxy-N-ethylamphetamine (MDEA)), ephedrines (ephedrine, pseudoephedrine and norephedrine) and venlafaxine in wastewater by means of chiral chromatography coupled with tandem mass spectrometry. Solid-phase extraction on Oasis HLB sorbent used for sample clean-up and concentration of analytes resulted in very good recoveries accounting for >70%. Signal suppression during MS analysis was negligible for most studied analytes. Resolution of enantiomers of chiral drugs was found to be higher than 1. Preliminary assay validation was undertaken. The mean correlation coefficients of the calibration curves, which were on average higher than 0.997 for all studied analytes, showed good linearity of the method in the studied range. Intra- and inter-day repeatabilities were on average less than 5%. The method quantification limits in wastewater were at low ppt levels and varied from 2.25 to 11.75ng/L. The method was successfully applied for the analysis of raw and treated wastewater samples collected from four wastewater treatment plants. A common occurrence of 1R,2S (-)-ephedrine, 1S,2S (+)-pseudoephedrine and venlafaxine in both raw and treated wastewater samples was observed. Amphetamine, methamphetamine, MDMA and MDEA were also detected in several wastewater samples. The study of enantiomeric fractions of these chiral drugs proved their variable non-racemic composition. The influence of wastewater treatment processes on the enantiomeric composition of chiral drugs was also noted and might indicate enantioselective processes occurring during treatment, although more comprehensive research has to be undertaken to support this hypothesis. PMID:20537654

Kasprzyk-Hordern, Barbara; Kondakal, Vishnu V R; Baker, David R

2010-07-01

67

Enhanced separation and characterization of deamidated peptides with RP-ERLIC-based multidimensional chromatography coupled with tandem mass spectrometry.  

PubMed

Deamidation of asparaginyl residues in proteins produces a mixture of asparaginyl, n-aspartyl, and isoaspartyl residues, which affects the proteins' structure, function, and stability. Thus, it is important to identify and quantify the products to evaluate the effects in biological systems. It is still a challenging task to distinguish between the n-Asp and isoAsp deamidation products in a proteome-wide analysis because of their similar physicochemical properties. The quantification of the isomeric deamidated peptides is also rather difficult because of their coelution/poor separation in reverse-phase liquid chromatography (RPLC). We here propose a RP-ERLIC-MS/MS approach for separating and quantifying on a proteome-wide scale the three products related to deamidation of the same peptide. The key to the method is the use of RPLC in the first dimensional separation and ERLIC (electrostatic repulsion-hydrophilic interaction chromatography) in the second, with direct online coupling to tandem MS. The coelution of the three deamidation-related peptides in RPLC is then an asset, as they are collected in the same fraction. They are then separated and identified in the second dimension with ERLIC, which separates peptides on the basis of both pI and GRAVY values. The coelution of the three products in RPLC and their efficient separation in ERLIC were validated using synthetic peptides, and the performance of ERLIC-MS/MS was tested using peptide mixtures from two proteins. Applying this sequence to rat liver tissue, we identified 302 unique N-deamidated peptides, of which 20 were identified via all three deamidation-related products and 70 of which were identified via two of them. PMID:22239700

Hao, Piliang; Qian, Jingru; Dutta, Bamaprasad; Cheow, Esther Sok Hwee; Sim, Kae Hwan; Meng, Wei; Adav, Sunil S; Alpert, Andrew; Sze, Siu Kwan

2012-03-01

68

Rapid and sensitive hormonal profiling of complex plant samples by liquid chromatography coupled to electrospray ionization tandem mass spectrometry  

PubMed Central

Background Plant hormones play a pivotal role in several physiological processes during a plant's life cycle, from germination to senescence, and the determination of endogenous concentrations of hormones is essential to elucidate the role of a particular hormone in any physiological process. Availability of a sensitive and rapid method to quantify multiple classes of hormones simultaneously will greatly facilitate the investigation of signaling networks in controlling specific developmental pathways and physiological responses. Due to the presence of hormones at very low concentrations in plant tissues (10-9 M to 10-6 M) and their different chemistries, the development of a high-throughput and comprehensive method for the determination of hormones is challenging. Results The present work reports a rapid, specific and sensitive method using ultrahigh-performance liquid chromatography coupled to electrospray ionization tandem spectrometry (UPLC/ESI-MS/MS) to analyze quantitatively the major hormones found in plant tissues within six minutes, including auxins, cytokinins, gibberellins, abscisic acid, 1-amino-cyclopropane-1-carboxyic acid (the ethylene precursor), jasmonic acid and salicylic acid. Sample preparation, extraction procedures and UPLC-MS/MS conditions were optimized for the determination of all plant hormones and are summarized in a schematic extraction diagram for the analysis of small amounts of plant material without time-consuming additional steps such as purification, sample drying or re-suspension. Conclusions This new method is applicable to the analysis of dynamic changes in endogenous concentrations of hormones to study plant developmental processes or plant responses to biotic and abiotic stresses in complex tissues. An example is shown in which a hormone profiling is obtained from leaves of plants exposed to salt stress in the aromatic plant, Rosmarinus officinalis. PMID:22098763

2011-01-01

69

Coupling permanganate oxidation with microbial dechlorination of tetrachloroethene.  

PubMed

For sites contaminated with chloroethene non-aqueous-phase liquids, designing a remediation system that couples in situ chemical oxidation (ISCO) with potassium permanganate (KMnO4) and microbial dechlorination may be complicated because of the potentially adverse effects of ISCO on anaerobic bioremediation processes. Therefore, one-dimensional column studies were conducted to understand the effect of permanganate oxidation on tetrachloroethene (PCE) dechlorination by the anaerobic mixed culture KB-1. Following the confirmation of PCE dechlorination, KMnO4 was applied to all columns at a range of concentrations and application velocities to simulate varied distances from oxidant injection. Immediately following oxidation, reductive dechlorination was inhibited; however, after passing several pore volumes of sterile growth medium through the columns after oxidation, a rebound of PCE dechlorination activity was observed in every inoculated column without the need to reinoculate. The volume of medium required for a rebound of dechlorination activity differed from 1.1 to 8.1 pore volumes (at a groundwater velocity of 4 cm/d), depending on the specific condition of oxidant application. PMID:17290967

Sahl, Jason W; Munakata-Marr, Junko; Crimi, Michelle L; Siegrist, Robert L

2007-01-01

70

OXIDATIVE COUPLING OF METHANE USING INORGANIC MEMBRANE REACTORS  

SciTech Connect

The objective of this research is to study the oxidative coupling of methane in catalytic inorganic membrane reactors. A specific target is to achieve conversion of methane to C{sub 2} hydrocarbons at very high selectivity and higher yields than in conventional non-porous, co-feed, fixed bed reactors by controlling the oxygen supply through the membrane. A membrane reactor has the advantage of precisely controlling the rate of delivery of oxygen to the catalyst. This facility permits balancing the rate of oxidation and reduction of the catalyst. In addition, membrane reactors minimize the concentration of gas phase oxygen thus reducing non selective gas phase reactions, which are believed to be a main route for the formation of CO{sub x} products. Such gas phase reactions are a cause of decreased selectivity in the oxidative coupling of methane in conventional flow reactors. Membrane reactors could also produce higher product yields by providing better distribution of the reactant gases over the catalyst than the conventional plug flow reactors. Membrane reactor technology also offers the potential for modifying the membranes both to improve catalytic properties as well as to regulate the rate of the permeation/diffusion of reactants through the membrane to minimize by-product generation. Other benefits also exist with membrane reactors, such as the mitigation of thermal hot-spots for highly exothermic reactions such as the oxidative coupling of methane. The application of catalytically active inorganic membranes has potential for drastically increasing the yield of reactions which are currently limited by either thermodynamic equilibria, product inhibition, or kinetic selectivity.

Dr. Y.H. Ma; Dr. W.R. Moser; Dr. A.G. Dixon; Dr. A.M. Ramachandra; Dr. Y. Lu; C. Binkerd

1998-04-01

71

Trace level liquid chromatography tandem mass spectrometry quantification of the mutagenic impurity 2-hydroxypyridine N-oxide as its dansyl derivative.  

PubMed

A derivatization LC-MS/MS method was developed and qualified for the trace level quantification of 2-hydroxypyridine N-oxide (HOPO). HOPO is a coupling reagent used in the syntheses of active pharmaceutical ingredients (APIs) to form amide bonds. HOPO was recently confirmed to generate a positive response in a GLP Ames bacterial-reverse-mutation test, classifying it as a mutagenic impurity and as such requiring its control in APIs to the threshold of toxicological concern (TTC). The derivatization reagent 5-dimethylamino-1-naphthalenesulfonyl chloride (dansyl chloride) was used in a basic solution to convert HOPO into the corresponding dansyl-derivative. The derivative was separated from different APIs and reagents by liquid chromatography. The detection of the HOPO dansyl-derivative was achieved by mass spectrometry in selected reaction monitoring (SRM) mode. The LC-MS/MS method had a reporting limit of 0.1ng/mL HOPO, which corresponds to 0.1ppm HOPO relative to an API at 1mg/mL, and a linearity range of 0.1-25ng/mL HOPO analyte. Recoveries of HOPO standards spiked into three different API matrices at 0.2, 1.2, and 20ppm levels were all within 90-100%. An SRM-based confirmatory methodology using the ratios of two fragment ions at three CID energies was developed to verify the identity of HOPO when present at ?0.6ppm. This identity confirmation can be employed to prevent potential false positive detection of mutagenic impurities at trace level. It can be broadly applicable for the confirmation of analytes when the analytes generate at least two major fragments in tandem mass spectrometry experiments. PMID:25683628

Ding, Wei; Huang, Yande; Miller, Scott A; Bolgar, Mark S

2015-03-20

72

Catalytic aerobic oxidation and tandem enantioselective cycloaddition in cascade multicomponent synthesis.  

PubMed

An efficient multicomponent cascade transformation for the highly diastereo- and enantioselective synthesis of complex natural product inspired polycyclic products from simple starting materials is described. The cascade is initiated by copper-catalyzed aerobic C?H oxidation of cyclopentadiene to cyclopentadienone followed by double catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides. The cascade synthesis efficiently yields structurally complex 5,5,5-tricyclic products with eight stereocenters with good yields and excellent diastereo- and enantiocontrol using one catalyst. PMID:25676025

Potowski, Marco; Merten, Christian; Antonchick, Andrey P; Waldmann, Herbert

2015-03-23

73

Noxa couples lysosomal membrane permeabilization and apoptosis during oxidative stress.  

PubMed

The exact roles of lysosomal membrane permeabilization (LMP) in oxidative stress-triggered apoptosis are not completely understood. Here, we first studied the temporal relation between LMP and mitochondrial outer membrane permeabilization (MOMP) during the initial stage of apoptosis caused by the oxidative stress inducer H2O2. Despite its essential role in mediating apoptosis, the expression of the BH3-only Bcl-2 protein Noxa was dispensable for LMP. In contrast, MOMP was dependent on Noxa expression and occurred downstream of LMP. When lysosomal membranes were stabilized by the iron-chelating agent desferrioxamine, H2O2-induced increase in DNA damage, Noxa expression, and subsequent apoptosis were abolished by the inhibition of LMP. Importantly, LMP-induced Noxa expression increase was mediated by p53 and seems to be a unique feature of apoptosis caused by oxidative stress. Finally, exogenous iron loading recapitulated the effects of H2O2 on the expression of BH3-only Bcl-2 proteins. Overall, these data reveal a Noxa-mediated signaling pathway that couples LMP with MOMP and ultimate apoptosis during oxidative stress. PMID:23770082

Eno, Colins O; Zhao, Guoping; Venkatanarayan, Avinashnarayan; Wang, Bing; Flores, Elsa R; Li, Chi

2013-12-01

74

Frequency-selective surface coupled metal-oxide-metal diodes  

NASA Astrophysics Data System (ADS)

Metal-Oxide-Metal diodes offer the possibility of directly rectifying infrared radiation. To be effective for sensing or energy harvesting they must be coupled to an antenna which produces intense fields at the diode. While antennas significantly increase the effective capture area of the MOM diode, it is still limited and maximizing the captured energy is still a challenging goal. In this work we investigate integrating MOM diodes with a slot antenna Frequency Selective Surface (FSS). This maximizes the electromagnetic capture area while minimizing the transmission line length which helps reduce losses because metal losses are much lower at DC than at infrared frequencies. Our design takes advantage of a single self-aligned patterning step using shadow evaporation. The structure is optimized at 10.6 µm to have less than 2% reflection (polarization sensitive) and simulations predict that 70% of the incident energy is dissipated into the oxide layer. Initial experimental results fabricated with e-beam lithography are presented and the diode coupled FSS is shown to produce a polarization sensitive unbiased DC short circuit current. This work is promising for both infrared sensing and imaging as well as direct conversion of thermal energy.

Kinzel, Edward C.; Brown, Robert L.; Ginn, James C.; Lail, Brian A.; Slovick, Brian A.; Boreman, Glenn D.

2013-06-01

75

Microfluidic chip based nano liquid chromatography coupled to tandem mass spectrometry for the determination of abused drugs and metabolites in human hair.  

PubMed

A microfluidic chip based nano-HPLC coupled to tandem mass spectrometry (nano-HPLC-Chip-MS/MS) has been developed for simultaneous measurement of abused drugs and metabolites: cocaine, benzoylecgonine, cocaethylene, norcocaine, morphine, codeine, 6-acetylmorphine, phencyclidine, amphetamine, methamphetamine, MDMA, MDA, MDEA, and methadone in the hair of drug abusers. The microfluidic chip was fabricated by laminating polyimide films and it integrated an enrichment column, an analytical column and a nanospray tip. Drugs were extracted from hairs by sonication, and the chromatographic separation was achieved in 15 min. The drug identification and quantification criteria were fulfilled by the triple quardropule tandem mass spectrometry. The linear regression analysis was calibrated by deuterated internal standards with all of the R(2) at least over 0.993. The limit of detection (LOD) and the limit of quantification (LOQ) were from 0.1 to 0.75 and 0.2 to 1.25 pg/mg, respectively. The validation parameters including selectivity, accuracy, precision, stability, and matrix effect were also evaluated here. In conclusion, the developed sample preparation method coupled with the nano-HPLC-Chip-MS/MS method was able to reveal the presence of drugs in hairs from the drug abusers, with the enhanced sensitivity, compared with the conventional HPLC-MS/MS. PMID:22281681

Zhu, Kevin Y; Leung, K Wing; Ting, Annie K L; Wong, Zack C F; Ng, Winki Y Y; Choi, Roy C Y; Dong, Tina T X; Wang, Tiejie; Lau, David T W; Tsim, Karl W K

2012-03-01

76

Oxidative coupling of methane with ac and dc corona discharges  

SciTech Connect

The oxidative coupling of methane (OCM) is being actively studied for the production of higher hydrocarbons from natural gas. The present study concentrated on the oxidative conversion of methane in an atmospheric pressure, nonthermal plasma formed by ac or dc corona discharges. Methyl radicals are formed by reaction with negatively-charged oxygen species created in the corona discharge. The selectivity to products ethane and ethylene is affected by electrode polarity, frequency, and oxygen partial pressure in the feed. Higher C{sub 2} yields were obtained with the ac corona. All the ac corona discharges are initiated at room temperature (i.e., no oven or other heat source is used), and the temperature increases to 300--500 C due to the exothermic reactions and the discharge itself. The largest C{sub 2} yield is 21% with 43.3% methane conversion and 48.3% C{sub 2} selectivity at a flowrate of 100 cm{sup 3}/min when the ac corona is at 30 Hz, 5 kV (rms) input power was used. The methane conversion may be improved to more than 50% by increasing the residence time, but the C{sub 2} selectivity decreases. A reaction mechanism including the oxidative dehydrogenation (OXD) of ethane to ethylene is presented to explain the observed phenomena. The results suggest that ac and/or dc gas discharge techniques have significant promise for improving the economics of OCM processes.

Liu, C.; Marafee, A.; Hill, B.; Xu, G.; Mallinson, R.; Lobban, L. [Univ. of Oklahoma, Norman, OK (United States). Inst. of Natural Gas Utilization] [Univ. of Oklahoma, Norman, OK (United States). Inst. of Natural Gas Utilization

1996-10-01

77

HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY COUPLED WITH TANDEM MASS SPECTROMETRY APPLIED FOR METABOLIC STUDY OF SPINOSIN BY RAT INTESTINAL FLORA  

Microsoft Academic Search

A rapid, sensitive and selective liquid chromatography–tandem mass spectrometric (HPLC-MS\\/MS) method was developed and validated for the determination of spinosin, a pharmacologically active constituent isolated from Zizyphi Spinosi Semen (ZSS). This method was used to examine the degradation kinetics of spinosin by rat intestinal flora and to elucidate the structure of its metabolite. The analysis was performed using an aqueous

Ting Zhang; Junbo Xie; Yanqing Zhang; Dawei Chen

2012-01-01

78

Quantitative determination of the diastereoisomers of hexabromocyclododecane in human plasma using liquid chromatography coupled with electrospray ionization tandem mass spectrometry  

Microsoft Academic Search

A sensitive, simple and feasible method has been developed and validated for the simultaneous determination of three diastereoisomers of hexabromocyclododecane (HBCD) in human plasma using liquid chromatography tandem mass spectrometry (LC–MS\\/MS). The simple pretreatment generally involved protein precipitation with methanol (MeOH). The separation was performed with a C18 reverse phase column. The mobile phases were 5mM ammonium acetate (NH4AC) in

Caiming Tang

79

Pesticide Residue Analysis in Waters by Solid?Phase Microextraction Coupled to Gas Chromatography?Tandem Mass Spectrometry  

Microsoft Academic Search

A new analytical method is proposed for determining 34 multi?class pesticides in drinking and natural (ground, surface and sea) waters. The method combines the advantages of solid?phase microextraction (SPME) and gas chromatography?tandem mass spectrometry (GC?MS?MS). Polydimethylsiloxane (PDMS) and polydimethylsiloxane\\/divinylbenzene (PDMS\\/DVB) stationary phases were evaluated and the optimization of the main extraction parameters was carried out in order to improve sensitivity

F. J. Arrebola; S. Cortes Aguado; A. Garrido Frenich; J. L. Martínez Vidal

2004-01-01

80

A direct temperature-resolved tandem mass spectrometry study of cholesterol oxidation products in light-aged egg tempera paints with examples from works of art  

NASA Astrophysics Data System (ADS)

Cholesterol (1) constitutes approximately 5% of the lipid fraction of eggs. The compound is therefore abundant in fresh egg tempera paints. The fate of cholesterol upon light ageing of egg tempera paint binding medium was investigated by direct temperature resolved mass spectrometry (DTMS) and tandem mass spectrometry (DTMSMS). Cholesterol oxidation products (COPs) such as 5,6-epoxycholestan-3-ol (2) and 3-hydroxycholest-5-en-7-one (3) were positively identified in light-aged egg binding medium. Given the fast rate of oxidation of cholesterol, the corresponding oxidation products are better markers for egg tempera than the cholesterol molecule itself. Cholesterol and COPs were discovered in paints on German baroque altar pieces from the 16th and 18th C and in a 20th C glaze on a Mark Rothko Seagram Mural painting at Tate by DTMS fingerprinting analysis of paint microsamples.

van den Brink, Oscar F.; Ferreira, Ester S. B.; van der Horst, Jerre; Boon, Jaap J.

2009-07-01

81

Structural elucidation of N-oxidized clemastine metabolites by liquid chromatography/tandem mass spectrometry and the use of Cunninghamella elegans to facilitate drug metabolite identification.  

PubMed

Cunninghamella elegans is a filamentous fungus that has been shown to biotransform drugs into the same metabolites as mammals. In this paper we describe the use of C. elegans to aid the identification of clemastine metabolites since high concentrations of the metabolites were produced and MS(n) experiments were facilitated. The combination of liquid chromatography and tandem mass spectrometry with two different ionization techniques and hydrogen/deuterium exchange were used for structural elucidation of the clemastine metabolites. Norclemastine, four isomers of hydroxylated clemastine, and two N-oxide metabolites were described for the first time in C. elegans incubations. The N-oxidations were confirmed by hydrogen/deuterium exchange and deoxygenation (-16 Da) upon atmospheric pressure chemical ionization mass spectrometry. By MS(n) fragmentation it was concluded that two of the hydroxylated metabolites were oxidized on the methylpyrridyl moiety, one on the aromatic ring with the chloro substituent, and one on the aromatic ring without the chlorine. PMID:20411584

Tevell Aberg, Annica; Löfgren, Helena; Bondesson, Ulf; Hedeland, Mikael

2010-05-30

82

Iodine-catalyzed oxidative coupling reactions utilizing c?h and x?h as nucleophiles.  

PubMed

In recent decades, iodine-catalyzed oxidative coupling reactions utilizing C?H and X?H as nucleophiles have received considerable attention because they represent more efficient, greener, more atom-economical, and milder bond-formation strategies over transition-metal-catalyzed oxidative coupling reactions. This Focus Review gives a brief summary of recent development on iodine-catalyzed oxidative coupling reactions utilizing C?H and X?H as nucleophiles. PMID:25683644

Liu, Dong; Lei, Aiwen

2015-04-01

83

Flow induced vibration of two rigidly coupled circular cylinders in tandem and side-by-side arrangements at a low Reynolds number of 150  

NASA Astrophysics Data System (ADS)

Flow induced vibration of two rigidly coupled identical circular cylinders in tandem and side-by-side arrangements at a low Reynolds number of 150 is studied numerically. The two cylinders vibrate in the cross-flow direction and have the same displacement. The Navier-Stokes equations are solved by the finite element method and the equation of motion of the cylinders is solved by the fourth-order Runge-Kutta algorithm. Simulations are conducted for a constant mass ratio of 2 and the gap ratios (defined as the ratio of the centre-to-centre distance between the two cylinders L to the cylinder diameter D) of 1.5, 2, 4, and 6. The reduced velocities range from 0.5 to 15 with an increment of 0.5 for the tandem arrangement and from 0.5 to 30 with an increment of 0.5 for the side-by-side arrangement. It is found that the gap between the two cylinders has significant effect on the response. For a tandem arrangement, the lock-in regime of the reduced velocity is narrower than that of a single cylinder for L/D = 1.5 and 2 and wider than later for L/D = 4 and 6. If the two cylinders are allowed to vibrate in the cross-flow direction, the vortex shedding from the upstream cylinder occurs at L/D as small as 2. The most interesting phenomenon found in the side-by-side arrangement is the combination of vortex-induced vibration (VIV) and galloping at L/D = 1.5 and 2. For L/D = 1.5 and 2, the response is dominated by VIV as Vr<15 and by galloping as Vr>15. At reduced velocities close to 15, the response is a combination of VIV and galloping.

Zhao, Ming

2013-12-01

84

Tandem tracking  

USGS Multimedia Gallery

Biologist Sabrina Davenport tandem tracks the Lower Missouri River during high water on June 2, 2011.  Two boats (note boat out window) tracking in tandem can detect fish effectively across a wider river and can turn to search behind wing dikes and sandbars where sturgeon can hide during h...

85

Calculation of the Lateral Stability of a Directly Coupled Tandem-Towed Fighter Airplane and Correlation with Experimental Data  

NASA Technical Reports Server (NTRS)

A theoretical method is presented for predicting the dynamic lateral stability characteristics of an airplane towed in tandem by a much larger airplane. Values of period and time to damp to one-half amplitude and rolling motions calculated by an analog computer have been correlated with results of two experimental investigations conducted in the Langley free-flight tunnel which were part of a U.S. Air Force program (Project FICON) to develop a satisfactory arrangement by which a bomber could tow a parasite fighter. In general, the theoretical results agree with the experimental results.

Shanks, Robert E.

1958-01-01

86

Determination of parabens in urine samples by microextraction using packed sorbent and ultra-performance liquid chromatography coupled to tandem mass spectrometry.  

PubMed

A simple, sensitive, and selective method using ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) was developed and validated for simultaneous determination of parabens [methyl paraben (MeP), ethyl paraben (EtP), propyl paraben (PrP), butyl paraben (BuP), and benzyl paraben (BzP)] in human urine samples. After microextraction by packed sorbent (MEPS) using a C18 phase, the parabens were separated on a Kinetex C18 column (100 mm × 2.1 mm × 1.7 ?m) within 4.6 min using isocratic elution. These compounds were detected on a triple quadrupole tandem mass spectrometer using the multiple reactions monitoring (MRM) mode via an electrospray ionization source operating in the negative ionization mode. Important factors that influence MEPS performance were evaluated, such as the sample pH, draw-eject sample volume, clean-up step, and desorption conditions. The proposed MEPS/UPLC-MS/MS method presented a linear range from 0.5 ng mL(-1) (limit of quantification - LOQ) to 50 ng mL(-1), and interassay precision with coefficients of variation lower than 15%, and relative standard error values of the accuracy ranged from -8.8% to 15%. The MEPS/UPLC-MS/MS method was applied successfully to determine parabens in urine samples from 30 postpartum volunteers, enabling assessment of human exposure to these compounds. PMID:25463195

Cristina Jardim, Valeria; de Paula Melo, Lidervan; Soares Domingues, Diego; Costa Queiroz, Maria Eugênia

2015-01-01

87

A novel strategy for target profiling analysis of bioactive phenylethanoid glycosides in Plantago medicinal plants using ultra-performance liquid chromatography coupled with tandem quadrupole mass spectrometry.  

PubMed

Phenylethanoid glycosides are a group of phenolic compounds with diverse biological activities such as hypotensive, diuretic, and hypoglycemic effects. In this study, a target profiling analysis approach using ultra-performance liquid chromatography coupled with tandem quadrupole mass spectrometry (MS) was established on the basis of parent ion scanning for m/z 161, the characteristic product ion for phenylethanoid glycosides. It was successfully employed to discriminate the chemical composition of phenylethanoid glycosides between Plantaginis Herba and Plantaginis Semen, two medicinal parts of Plantago plants, which are widely used as herbal medicine in China. Totally, 34 phenylethanoid glycosides were characterized and tentatively identified by their retention times, MS, and tandem quadrupole MS (MS/MS) data. Combined with chemometrics analysis of principal component analysis and orthogonal projection to latent structural discriminate analysis, eight of them, especially acteoside and plantamajoside, were picked out and contributed to the chemical distinction between Plantaginis Herba and Plantaginis Semen, which might be responsible for the differences in diuretic and hypotensive effects between the two medicinal parts. This new approach for target profiling provides not only a novel idea for specific analysis of active chemical constituents in the same type, but also a promising and reference method for quality evaluation of traditional Chinese medicines. PMID:22740256

Qi, Meng; Xiong, Aizhen; Geng, Fang; Yang, Li; Wang, Zhengtao

2012-06-01

88

Determination of tetracycline antibiotics in fatty food samples by selective pressurized liquid extraction coupled with high-performance liquid chromatography and tandem mass spectrometry.  

PubMed

For the determination of trace residues of tetracycline antibiotics in fatty food samples, selective pressurized liquid extraction coupled with high-performance liquid chromatography and tandem mass spectrometry was applied in this study. Copper(II) isonicotinate was first used as online cleanup adsorbent in the selective pressurized liquid extraction process. The adsorbent to sample ratio, extraction temperature, extraction time, and recycle times, etc. were optimized. The tetracyclines in food samples of pork, chicken meat, and clam meat were detected by liquid chromatography with tandem mass spectrometry. Tetracycline was found at levels of 0.32 and 0.53 ?g/g and oxytetracycline was found at 0.14 and 0.21 ?g/g in chicken meat and clam meat, respectively, while chlorotetracycline and deoxytetracycline were below the detection limit. The detection limit (S/N = 3) for these four tetracyclines were from 0.2 to 3.3 ng/g, the recoveries were from 75.8 to 110.5%, and relative standard deviations were from 5.5 to 13.6%. Copper(II) isonicotinate showed a higher purification capacity than other cleanup adsorbents for extraction of antibiotics in fatty food and the recovery showed predominance compared with a pressurized liquid extraction method without adsorbent. The study demonstrated that copper(II) isonicotinate would be a promising cleanup adsorbent in pressurized liquid extraction for the analysis of trace organic pollutants in complicated samples. PMID:25394992

Jiao, Zhe; Zhang, Suling; Chen, Hongwei

2015-01-01

89

Identification and quantitation of cocaine, benzoylecgonine, and cocaethylene in blood, serum, and plasma using ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS).  

PubMed

Cocaine is a widely abused stimulant. Numerous methods exist for the identification of the drug, or more commonly, one of its metabolites in urine. Urine testing is useful for most cases, but it is necessary to use other matrices in forensic situations and when subjects are anuric. We describe a novel method for the analysis of cocaine, benzoylecgonine, and cocaethylene in blood, serum, and plasma utilizing ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS). Sample preparation has been minimized to a simple deproteinization step in which each specimen is mixed with an acetonitrile-internal standard mixture. The method has excellent precision across the linear range of 25-2,000 ng/mL for each analyte. With a run-time of 4 min, this method provides a significant improvement over traditional GC/MS methods. PMID:20077068

Kriger, Scott; Gunn, Josh; Terrell, Andrea R

2010-01-01

90

Comparison of electrospray ionization and atmospheric chemical ionization coupled with the liquid chromatography-tandem mass spectrometry for the analysis of cholesteryl esters.  

PubMed

The approach of two different ionization techniques including electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was tested for the analysis of cholesteryl esters (CEs). The retention time (RT), signal intensity, protonated ion, and product ion of CEs were compared between ESI and APCI. RT of CEs from both ionizations decreased with increasing double bonds, while it increased with longer carbon chain length. The ESI process generated strong signal intensity of precursor ions corresponding to [M+Na](+) and [M+NH4](+) regardless of the number of carbon chains and double bonds in CEs. On the other hand, the APCI process produced a protonated ion of CEs [M+H](+) with a weak signal intensity, and it is selectively sensitive to detect precursor ions of CEs with unsaturated fatty acids. The ESI technique proved to be effective in ionizing more kinds of CEs than the APCI technique. PMID:25873970

Lee, Hae-Rim; Kochhar, Sunil; Shim, Soon-Mi

2015-01-01

91

Comparison of Electrospray Ionization and Atmospheric Chemical Ionization Coupled with the Liquid Chromatography-Tandem Mass Spectrometry for the Analysis of Cholesteryl Esters  

PubMed Central

The approach of two different ionization techniques including electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was tested for the analysis of cholesteryl esters (CEs). The retention time (RT), signal intensity, protonated ion, and product ion of CEs were compared between ESI and APCI. RT of CEs from both ionizations decreased with increasing double bonds, while it increased with longer carbon chain length. The ESI process generated strong signal intensity of precursor ions corresponding to [M+Na]+ and [M+NH4]+ regardless of the number of carbon chains and double bonds in CEs. On the other hand, the APCI process produced a protonated ion of CEs [M+H]+ with a weak signal intensity, and it is selectively sensitive to detect precursor ions of CEs with unsaturated fatty acids. The ESI technique proved to be effective in ionizing more kinds of CEs than the APCI technique.

Lee, Hae-Rim; Kochhar, Sunil; Shim, Soon-Mi

2015-01-01

92

Analysis of sphingomyelin in meat based on hydrophilic interaction liquid chromatography coupled to electrospray ionization-tandem mass spectrometry (HILIC-HPLC-ESI-MS/MS).  

PubMed

The amount of sphingomyelin in different kinds of meat was analyzed by hydrophilic interaction liquid chromatography (HILIC-HPLC) coupled with electrospray ionization-tandem mass spectrometry (ESI-MS/MS). Analysis comprised sphingomyelin species with the five different sphingoid bases dihydrosphingosine (d18:0), sphingosine (d18:1(Delta4)), 4,8-sphingadienine (d18:2(Delta4,8)), 4-hydroxysphinganine (phytosphingosine (t18:0)), and 4-hydroxy-8-sphingenine (t18:1), and fatty acids with 12-26 carbon atoms as well as their (poly)unsaturated (up to four double bonds) and monohydroxylated analogues. Most sphingolipids contained sphingosine (d18:1) as the predominant sphingoid base, while stearic acid and palmitic acid were found as prevalent fatty acids. Total amounts vary from 361-471 mg/kg, whereas the meat of the wild animals showed considerably lower amounts. PMID:20175585

Fischbeck, Anne; Krüger, Melanie; Blaas, Nina; Humpf, Hans-Ulrich

2009-10-28

93

Analysis of chloramphenicol residues in the macroalgae Ulva lactuca through ultra-high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS).  

PubMed

Antibiotic use is a well-described practice to promote animal health whether for prevention or treatment. Nonetheless, it can also cause a number of potentially harmful effects that dictate the need to implement regulation to assure a reduction of hazards to the consumers and the environment. Chloramphenicol (CAP) is a broad-spectrum antibacterial excluded from use in animal food production but despite this, reports of illegal use still persist. More recently, awareness has risen that the surrounding natural ecosystems can potentially be contaminated by pharmaceuticals and the extent of their effects in non-target organisms is already under the scope of researchers. To face the demanding new challenges a methodology for the determination of CAP in the green macroalgae Ulva lactuca by ultra-high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS) was developed, optimized and fully validated following the guidelines of the EC Decision 2002/657. PMID:25579630

Leston, Sara; Freitas, Andreia; Nunes, Margarida; Barbosa, Jorge; Pardal, Miguel Ângelo; Ramos, Fernando

2015-02-15

94

Multiresidue analytical method for the determination of antimicrobials, preservatives, benzotriazole UV stabilizers, flame retardants and plasticizers in fish using ultra high performance liquid chromatography coupled with tandem mass spectrometry  

Microsoft Academic Search

A multiresidue analytical method for the determination of emerging pollutants belonging to personal care products (PCPs) (antimicrobials, preservatives), benzotriazole UV stabilizers (BUVSs) and organophosphorus compounds (OPCs) in fish has been developed using high speed solvent extraction (HSSE) followed by silica gel clean up and ultra fast liquid chromatography coupled with tandem mass spectrometry (UFLC–MS\\/MS) analysis. Developed extraction and clean up

Joon-Woo Kim; Babu Rajendran Ramaswamy; Kwang-Hyeon Chang; Tomohiko Isobe; Shinsuke Tanabe

2011-01-01

95

Treatment of pharmaceutical effluent by ultrasound coupled with dual oxidant system  

Microsoft Academic Search

In this study, sonolysis (US), a dual oxidant system (DOX), and ultrasound coupled with a dual oxidant system (US\\/DOX) were employed to degrade real pharmaceutical effluent. In a DOX system, two effective oxidizing agents such as hydrogen peroxide and activated persulphate were used simultaneously. In this work, for the first time, an easily available waste material, iron swarf, was used

Senthilnathan Nachiappan; Karuppan Muthukumar

2012-01-01

96

Using FISH-SIMS to Study Marine Methane Oxidation Coupled to the Reduction of Metal Oxides, a Plausible Microbial Metabolism for Subsurface Mars  

NASA Astrophysics Data System (ADS)

In the shallow martian subsurface, microbial life could be supported by methane oxidation coupled to the reduction of sulfate or metal oxides. Here, we report results of efforts to characterize the organisms involved in manganese-dependent marine methane oxidation.

House, C. H.; Beal, E. J.; Orphan, V. J.

2010-04-01

97

Magnetoelectric Coupling Effects in Multiferroic Complex Oxide Composite Structures  

NASA Astrophysics Data System (ADS)

A central goal of electronics based on correlated materials or `Mottronics' is the ability to switch between distinct collective states with a control voltage. Small changes in structure and charge density near a transition can tip the balance between competing phases, leading to dramatic changes in electronic and magnetic properties. In this work, we demonstrate that an electric field induced two-step ferroelastic switching pathway in (011) oriented 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-PT) substrates can be used to tune the Verwey metal-insulator transition in epitaxial Fe3O4 films in a stable and reversible manner. We also observe robust non-volatile resistance switching in Fe3O4 up to room temperature, driven by ferroelastic strain. These results provides a framework for realizing non-volatile and reversible tuning of order parameters coupled to lattice-strain in epitaxial oxide heterostructures over a broad range of temperatures, with potential device applications.

Liu, Ming; Hoffman, Jason; Wang, Jing; Zhang, Jinxing; Nelson-Cheeseman, Brittany; Bhattacharya, Anand

2013-05-01

98

Catalytic oxidative coupling of methane over Li/MgO using N2 O as an oxidant  

E-print Network

at about 60 kPa. . . 94 LIST OF TABLES TABLE 1. Catalytic Performance for CH~ Oxidative Coupling Page 2. Promoted Metal Oxide Catalysts for Oxidative Coupling of Methane 3. The Effect of N~O Partial Pressure on the Catalytic Reaction over Li/MgO... of them, as listed by Lunsford(24), are shown in Table 2. Extensive studies have been reported on Li ? promoted MgO (Li/MgO), since early work of Lunsford and coworkers(33). In the original study, 7/ Li ? doped MgO was the catalyst at. 720 C. Using...

Yamamoto, Hiroshi

1992-01-01

99

Determination of irinotecan and its metabolite SN-38 in rabbit plasma and tumors using a validated method of tandem mass spectrometry coupled with liquid chromatography.  

PubMed

New tandem mass spectrometric method coupled with liquid chromatography (LC-MS/MS) has been developed to determine the total concentration of camptothecin derivatives (irinotecan and SN-38) regardless of inter-conversion phenomenon between carboxylate and lactone forms. At first, all sample solutions were acidified for 1h in order to completely convert CPT derivatives into their lactone forms and then CPT derivatives were extracted with organic solution containing diethyl ether and ethyl acetate (2:1, v/v) just after alkalization in the range pH 8.0-8.5 in acid-treated solutions. Analytes were separated on a reverse phase C18 column (150×2.1mm) and eluted isocratically with a mobile phase which consisted of acetonitrile-methanol-buffer (0.1% formic acid, 5mM ammonium formate) (3:4:3, v/v). CPT derivatives were monitored by tandem mass spectrometry in electrospay-positive ionization and multiple reaction mode programmed to the following transitions (m/z): '587.6?167.2' of CPT-11, '393.6?349.3' of SN-38 and '349.4? 305.2' of CPT. The method was validated to have the proper linearity (r(2)>0.99) over the range of 5-1000ng/ml of CPT-11 and 1-250ng/ml of SN-38 with good accuracy (89.8-114.3%) and precision (less than 10%). In all stability tests, concentration of CPT-11 and SN-38 had been left in the acceptable range of 88.8-110.7% when sample solutions were acidified before determination of CPT derivatives. Newly developed LC-MS/MS method was suitable for the determination of CPT derivatives of both rabbit plasma and tumor tissues in the pharmacokinetic study. PMID:24927278

Park, Dae J; Won, Jun H; Cho, A R; Yun, Hye J; Heo, Jeong H; Hwhang, Tae H; Lee, Dae H; Kim, Woo M

2014-07-01

100

Electro-mechanical coupling of semiconductor film grown on stainless steel by oxidation  

NASA Astrophysics Data System (ADS)

Electro-mechanical coupling phenomenon in oxidation film on stainless steel has been discovered by using current-sensing atomic force microscopy, along with the I-V curves measurements. The oxidation films exhibit either ohmic, n-type, or p-type semiconductor properties, according to the obtained I-V curves. This technique allows characterizing oxidation films with high spatial resolution. Semiconductor properties of oxidation films must be considered as additional stress corrosion cracking mechanisms.

Lin, M. C.; Wang, G.; Guo, L. Q.; Qiao, L. J.; Volinsky, Alex A.

2013-09-01

101

Sensitive detection of ?-agonists in pork tissue with novel molecularly imprinted polymer extraction followed liquid chromatography coupled tandem mass spectrometry detection.  

PubMed

A novel molecularly imprinted polymer micro-spheres (MIPMs) with phenylethanolamine A as the template and the p-vinylbenzoic acid as the functional monomer were synthesized for the selective absorption of clenbuterol and other ?-agonists including brombuterol, bromchlorbuterol, clorprenaline and ractopamine. The absorption performances of the MIPMs were studied and the experimental results demonstrated that the extraction capacities of five ?-agonists with MIPMs were about from 2.7 to 3.4 times as much as that with non-imprinted polymer micro-spheres. Based on the clean-up of five ?-agonists in pork tissues with MIPMs, a sensitive determination method for five ?-agonists coupled with ultra performance chromatography coupled tandem mass spectrometry detection has been developed. The limits of detection for five ?-agonists were <0.02?g/kg. The mean recoveries and repeatability of five ?-agonists in pork tissues varied from 70.0% to 116.0% and from 2.5% to 10.4%, respectively. The developed method was successfully applied to analysis of 22 real pork tissues samples. PMID:25872428

Wang, Peilong; Liu, Ximeng; Su, Xiaoou; Zhu, Ruohua

2015-10-01

102

Polyamines in biological samples: Rapid and robust quantification by solid-phase extraction online-coupled to liquid chromatography–tandem mass spectrometry  

PubMed Central

Polyamines are ubiquitous active biogenic amines which contribute to basic cellular functions. Hence, their quantification in samples of diverse biological origins is essential for understanding how they function, especially in disease-relevant conditions. We present here a robust, high-throughput solid-phase extraction online coupled to a liquid chromatography–tandem mass spectrometry (SPE–LC/MS/MS) approach for the simultaneous quantification of eight polyamines in various biological samples. The polyamines include 1,3-diaminopropane, putrescine, cadaverin, N-acetyl-putrescine, spermidine, spermine, N1-acetyl-spermine, and l-ornithine. The novelty of the work is the use of two SPE columns online coupled to LC/MS/MS, which minimizes the sample pretreatment to a single derivatization step. The analysis is complete within 4 min, making the method highly suitable for routine clinical analysis and high throughput screenings. The method was fully validated with serum samples. Dynamic ranges were 0.03 to 15 ?g/ml for ornithine and 1 to 500 ng/ml for other polyamines, which cover physiological concentrations in serum samples. Lower limits of quantification (LLoQ) were found to be between 0.1 and 5 ng/ml. As a proof of concept, we investigated gender differences in polyamine levels by analyzing the serum levels of 102 subjects. PMID:24485539

Magnes, Christoph; Fauland, Alexander; Gander, Edgar; Narath, Sophie; Ratzer, Maria; Eisenberg, Tobias; Madeo, Frank; Pieber, Thomas; Sinner, Frank

2014-01-01

103

Profiling of oxidized phospholipids in lipoproteins from patients with coronary artery disease by hollow fiber flow field-flow fractionation and nanoflow liquid chromatography-tandem mass spectrometry.  

PubMed

Oxidized phospholipids (Ox-PLs) are oxidatively modified PLs that are produced during the oxidation of lipoproteins; oxidation of low density lipoproteins especially is known to be associated with the development of coronary artery disease (CAD). In this study, different lipoprotein classes (high density, low density, and very low density lipoproteins) from pooled plasma of CAD patients and pooled plasma from healthy controls were size-sorted on a semipreparative scale by multiplexed hollow fiber flow field-flow fractionation (MxHF5), and Ox-PLs that were extracted from each lipoprotein fraction were quantified by nanoflow liquid chromatography-tandem mass spectrometry (nLC-ESI-MS/MS). The present study showed that oxidation of lipoproteins occurred throughout all classes of lipoproteins with more Ox-PLs identified from CAD patient lipoproteins: molecular structures of 283 unique PL species (including 123 Ox-PLs) from controls and 315 (including 169 Ox-PLs) from patients were identified by data-dependent collision-induced dissociation experiments. It was shown that oxidation of PLs occurred primarily with hydroxylation of PL; in particular, a saturated acyl chain such as 16:0, 18:0, or even 18:1 at the sn-1 location of the glycerol backbone along with sn-2 acyl chains with at least two double bonds were identified. The acyl chain combinations commonly found for hydroxylated Ox-PLs in the lipoproteins of CAD patients were 16:0/18:2, 16:0/20:4, 18:0/18:2, and 18:0/20:4. PMID:25494038

Lee, Ju Yong; Byeon, Seul Kee; Moon, Myeong Hee

2015-01-20

104

Methyl Radicals in Oxidative Coupling of Methane Directly Confirmed by Synchrotron VUV Photoionization Mass Spectroscopy  

PubMed Central

Gas-phase methyl radicals have been long proposed as the key intermediate in catalytic oxidative coupling of methane, but the direct experimental evidence still lacks. Here, employing synchrotron VUV photoionization mass spectroscopy, we have directly observed the formation of gas-phase methyl radicals during oxidative coupling of methane catalyzed by Li/MgO catalysts. The concentration of gas-phase methyl radicals correlates well with the yield of ethylene and ethane products. These results lead to an enhanced fundamental understanding of oxidative coupling of methane that will facilitate the exploration of new catalysts with improved performance. PMID:23567985

Luo, Liangfeng; Tang, Xiaofeng; Wang, Wendong; Wang, Yu; Sun, Shaobo; Qi, Fei; Huang, Weixin

2013-01-01

105

Methyl Radicals in Oxidative Coupling of Methane Directly Confirmed by Synchrotron VUV Photoionization Mass Spectroscopy  

NASA Astrophysics Data System (ADS)

Gas-phase methyl radicals have been long proposed as the key intermediate in catalytic oxidative coupling of methane, but the direct experimental evidence still lacks. Here, employing synchrotron VUV photoionization mass spectroscopy, we have directly observed the formation of gas-phase methyl radicals during oxidative coupling of methane catalyzed by Li/MgO catalysts. The concentration of gas-phase methyl radicals correlates well with the yield of ethylene and ethane products. These results lead to an enhanced fundamental understanding of oxidative coupling of methane that will facilitate the exploration of new catalysts with improved performance.

Luo, Liangfeng; Tang, Xiaofeng; Wang, Wendong; Wang, Yu; Sun, Shaobo; Qi, Fei; Huang, Weixin

2013-04-01

106

A quantitative assay for reductive metabolism of a pesticide in fish using electrochemistry coupled with liquid chromatography tandem mass spectrometry.  

PubMed

This is the first study to use electrochemistry to generate a nitro reduction metabolite as a standard for a liquid chromatography-mass spectrometry-based quantitative assay. This approach is further used to quantify 3-trifluoromethyl-4-nitrophenol (TFM) reductive metabolism. TFM is a widely used pesticide for the population control of sea lamprey (Petromyzon marinus), an invasive species of the Laurentian Great Lakes. Three animal models, sea lamprey, lake sturgeon (Acipenser fulvescens), and rainbow trout (Oncorhynchus mykiss), were selected to evaluate TFM reductive metabolism because they have been known to show differential susceptibilities to TFM toxicity. Amino-TFM (aTFM; 3-trifluoromethyl-4-aminophenol) was the only reductive metabolite identified through liquid chromatography-high-resolution mass spectrometry screening of liver extracts incubated with TFM and was targeted for electrochemical synthesis. After synthesis and purification, aTFM was used to develop a quantitative assay of the reductive metabolism of TFM through liquid chromatography and tandem mass spectrometry. The concentrations of aTFM were measured from TFM-treated cellular fractions, including cytosolic, nuclear, membrane, and mitochondrial protein extracts. Sea lamprey extracts produced the highest concentrations (500 ng/mL) of aTFM. In addition, sea lamprey and sturgeon cytosolic extracts showed concentrations of aTFM substantially higher than thoose of rainbow trout. However, other fractions of lake sturgeon extracts tend to show aTFM concentrations similar to those of rainbow trout but not with sea lamprey. These data suggest that the level of reductive metabolism of TFM may be associated with the sensitivities of the animals to this particular pesticide. PMID:25730707

Bussy, Ugo; Chung-Davidson, Yu-Wen; Li, Ke; Li, Weiming

2015-04-01

107

Nickel-mediated stereocontrolled synthesis of spiroketals via tandem cyclization-coupling of ?-bromo ketals and aryl iodides.  

PubMed

A ketal-tether approach for the stereoselective synthesis of [5,5] and [5,6]-spiroketals based on reductive coupling catalyzed by the readily available Ni complex is demonstrated. Either an intermolecular or an intramolecular stereospecific cascade has been achieved as well. PMID:24256807

Peng, Yu; Xu, Xiao-Bo; Xiao, Jian; Wang, Ya-Wen

2014-01-14

108

Determination of pesticide residues in samples of green minor crops by gas chromatography and ultra performance liquid chromatography coupled to tandem quadrupole mass spectrometry.  

PubMed

A method was developed for pesticide analysis in samples of high chlorophyll content belonging to the group of minor crops. A new type of sorbent, known as ChloroFiltr, was employed for dispersive-solid phase extraction cleanup (dispersive-SPE) to reduce the unwanted matrix background prior to concurrent analysis by gas chromatography and ultra-performance liquid chromatography coupled to tandem quadrupole mass spectrometry (GC-MS/MS and UPLC-MS/MS). Validation experiments were carried out on green, unripe plants of lupin, white mustard and sorghum. The overall recoveries at the three spiking levels of 0.01, 0.05 and 0.5 mg kg(-1) fell in the range between 68 and 120% (98% on average) and 72-104% (93% on average) with relative standard deviation (RSD) values between 2 and 19% (7% on average) and 3-16% (6% on average) by GC-MS/MS and UPLC-MS/MS technique, respectively. Because of strong enhancement or suppression matrix effects (absolute values >20%) which were exhibited by about 80% of the pesticide and matrix combinations, acceptably accurate quantification was achieved by using matrix-matched standards. Up to now, the proposed method has been successfully used to study the dissipation patterns of pesticides after application on lupin, white mustard, soya bean, sunflower and field bean in experimental plot trials conducted in Poland. PMID:25476298

Walorczyk, Stanis?aw; Dro?d?y?ski, Dariusz; Kierzek, Roman

2015-01-01

109

Simultaneous determination of the repertoire of classical neurotransmitters released from embryonal carcinoma stem cells using online microdialysis coupled with hydrophilic interaction chromatography-tandem mass spectrometry.  

PubMed

Dynamic, continuous, and simultaneous multi-analysis of transmitters is important for the delineation of the complex interactions between the neuronal and intercellular communications. But the analysis of the whole repertoire of classical transmitters of diverse structure is challenging due to their different physico-chemical properties and to their high polarity feature which leads to poor retention in traditional reversed-phase columns during LC-MS analysis. Here, an online microdialysis coupled with hydrophilic interaction chromatography-tandem mass spectrometry (online MD-HILIC-MS/MS) detection method was developed for the simultaneous measurement of the repertoire of classical transmitters (acetylcholine, serotonin, dopamine, norepinephrine, glutamate, GABA, and glycine). Stable isotope labeled internal standards and authentic matrix have been applied to guarantee reliable results. The method was successfully employed to reveal the characteristics of transmitter release from embryonal carcinoma stem cells. The method features simple procedure (no sample preparation), high recovery (? 73%), high accuracy (89.36%?RE?116.89%), good reproducibility (2.18%? RSD ?14.56%), and sensitive limits of detection (2 pg for acetylcholine, serotonin, and glutamate, 10 pg for dopamine, norepinephrine, GABA, and glycine). It can be flexibly applied to determine the contents of the classical transmitters in other biological matrix samples with minor changes. PMID:25300220

Tang, Ya-Bin; Sun, Fan; Teng, Lin; Li, Wen-Bin; An, Shi-Min; Zhang, Chun; Yang, Xin-Jie; Lv, Hao-Yu; Ding, Xu-Ping; Zhu, Liang; Chen, Hong-Zhuan

2014-11-01

110

Application of QuEChERS based method for the determination of pesticides in nutraceutical products (Camellia sinensis) by liquid chromatography coupled to triple quadrupole tandem mass spectrometry.  

PubMed

A QuEChERS (quick, easy, cheap, effective, rugged, and safe) based method has been evaluated and validated for the determination and quantification of approximately 100 LC-amenable pesticides in nutraceutical products obtained from green tea (Camellia sinensis). Extraction was performed with acidified acetonitrile (acetic acid 1% (v/v)), and additional clean-up steps were not necessary. Pesticides determination was achieved using ultra high performance liquid chromatography coupled to triple quadrupole tandem mass spectrometry (UHPLC-QqQ-MS/MS). Total running time was 11min. Pesticides were quantified using matrix-matched calibration. Recoveries ranged from 70% to 117% and relative standard deviation (RSD) was lower than 20% at concentration levels of 25, 50 and 100?g/kg for intra-day precision and equal or lower than 25% for inter-day precision. Limits of quantification (LOQ) were equal or lower than 25?g/kg. The validated method was applied to commercial nutraceutical products, detecting acetamiprid (56?g/kg) and carbendazim (13?g/kg) in two samples. PMID:25660875

Martínez-Domínguez, Gerardo; Nieto-García, Antonio José; Romero-González, Roberto; Frenich, Antonia Garrido

2015-06-15

111

Antioxidant activity guided separation of major polyphenols of marjoram (Origanum majorana L.) using flash chromatography and their identification by liquid chromatography coupled with electrospray ionization tandem mass spectrometry†.  

PubMed

Marjoram extracts have been separated into polar and nonpolar parts using liquid-liquid extraction. Both polar and nonpolar parts of the extracts were further fractionated by flash chromatography. The obtained fractions (90 polar and 45 nonpolar fractions) were investigated for their antioxidant activities by 2,2-diphenylpicrylhydrazyl and ferric ion reducing antioxidant power assays. A direct, positive, and linear relationship between antioxidant activity and total phenolic content of the fractions was observed. Based on antioxidant and total phenolic content data, the three fractions with the high antioxidant activities from polar and nonpolar part of the extract were analyzed for their constituent polyphenols by liquid chromatography coupled with electrospray ionization tandem mass spectrometry. Compounds were identified by matching the mass spectral data and retention time with those of authentic standards. Identification of the compounds for which there were no "in-house" standards available was carried out by accurate mass measurement of the precursor ions and product ions generated from collision-induced dissociation. Rosmarinic acid was found to be the strongest antioxidant polyphenol conferring the highest antioxidant activity to fractions 47 and 17 of polar and nonpolar part of the extract, respectively. The identification of the rosmarinic acid was further confirmed by (1) H NMR spectroscopy. PMID:25161079

Hossain, Mohammad B; Camphuis, Gabriel; Aguiló-Aguayo, Ingrid; Gangopadhyay, Nirupama; Rai, Dilip K

2014-11-01

112

In vivo study on the neurotransmitters and their metabolites change in depressive disorder rat plasma by ultra high performance liquid chromatography coupled to tandem mass spectrometry.  

PubMed

A sensitive and versatile, ultra-high performance, liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method coupled to pre-column derivatization for the simultaneous determination of 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), dopamine (DA), norepinephrine (NE), homovanillic acid (HVA), ?-aminobutyric acid (GABA) and glutamic acid (Glu) was developed and validated in rat plasma. The analytes were dansylated under strong alkaline conditions after protein precipitation extraction, which were analyzed on a BEH C18 column using a gradient elution. The lower limit of quantification (LLOQ) values for 5-HT, 5-HIAA, DA, NE, HVA, GABA and Glu were 1.00, 1.00, 0.991, 0.992, 1.02, 1000, and 5030pmol/mL, respectively. Good linearity was obtained (r>0.99) and the intra- and inter-day precisions of the method (relative standard deviation, RSD%) were lower than 12%. The method was novel, sensitive and specific which can provide an alternative method for the quantification of neurotransmitters and their metabolites in plasma samples. PMID:25746753

Zhao, Longshan; Zheng, Shuning; Su, Guangyue; Lu, Xiumei; Yang, Jingyu; Xiong, Zhili; Wu, Chunfu

2015-04-15

113

Identification of components in Zhi-Zi-Da-Huang decoction by HPLC coupled with electrospray ionization tandem mass spectrometry, photodiode array and fluorescence detectors.  

PubMed

High-performance liquid chromatography (HPLC) coupled with electrospray ionization (ESI) tandem mass spectrometry (MS) in positive and negative ion mode and photodiode array (PDA) and fluorescence detectors (FD) was applied to simultaneously characterise thirty active components in Zhi-Zi-Da-Huang decoction (ZZDHD). The analysis was preformed on a Lichrospher C(18) column (4.6 mm x 250 mm, 5 microm) using a binary eluent (0.1% aqueous acetic acid (A) and methanol (B), 1 ml/min) under gradient conditions. Based on the retention times (t(R)), UV spectral data, fluorescence characteristics, results of extracted ion current (EIC), information of molecular weight and mass fragmentation behaviours, 17 flavonoids, five anthraquinones, two coumarins and six iridoids were detected and identified. The ESI-MS/MS fragmentation behaviour of iridoids, flavonoids, anthraquinones, coumarins was also proposed. The fragmentation patterns proposed could be extended to the components mentioned above but in different herbs and prescriptions. The method was useful for the identification of unknown components in the herbal system and other complex samples, especially for which standards are unavailable. PMID:19356878

Wang, Hang; Feng, Fang

2009-07-12

114

Quantification of dapaconazole in human plasma using high-performance liquid chromatography coupled to tandem mass spectrometry: application to a phase I study.  

PubMed

A simple, selective and sensitive method based on high-performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) has been developed for the determination of dapaconazole in human plasma using tioconazole as internal standard. The drugs were extracted from plasma by liquid-liquid extraction with ether/hexane (80/20, v/v). The chromatography separation was performed on a Genesis(®) C18 reversed phase analytical column 4?m (100×2.1mm i.d.) with a mobile phase of methanol/acetonitrile/water (80/10/10, v/v/v)+ammonium acetate (0.5mM). Dapaconazole was quantified using a mass spectrometer with an electrospray source in the ESI positive mode (ES+) configured for multiple reaction monitoring (MRM) to monitor the transitions 415.1>159.2 and 387.0>131.0 for dapaconazole and tioconazole, respectively. The method had a chromatography run time of 3.8min and a linear calibration curve over the range 0.2-100ng/mL (r=0.9998). The lower limit of quantification (LLOQ) was 0.2ng/mL. The precision and accuracy values of the assay were within ±10%. The stability tests indicate no significant degradation under the conditions of the experiment. This method was used for a phase I study of topical administration of dapaconazole tosylate in healthy human male volunteers. PMID:24705538

de Moraes, Fernanda C; Bittencourt, Samara F; Perissutti, Elisa; Frencentese, Francesco; Arruda, André M M; Chen, Lu Shi; Babadópulos, Tainah; De Nucci, Gilberto

2014-05-01

115

Dispersive liquid-liquid microextraction coupled with programmed temperature vaporization-large volume injection-gas chromatography-tandem mass spectrometry for multiclass pesticides in water.  

PubMed

A simple solvent-less procedure for the determination of seventeen pesticides and related compounds in environmental water and wastewater using dispersive liquid-liquid microextraction (DLLME) coupled with gas chromatography-mass spectrometry in tandem (GC-MS/MS) with large-volume injection, having a programmed temperature vaporizer (PTV-LVI), is described. The parameters affecting the extraction efficiency of the target analytes from water samples were systematically investigated. A response surface Doehlert design was used. The best extraction conditions involved a rapid injection of a mixture of 1.9 mL of acetonitrile (as a dispersant) and 178 ?L of trichloroethane (as an extractant) into 10 mL of water placed in a conical bottom glass tube. After manually shaken for 3.0 min and centrifugation at 3600 rpm (5 min), 50 ?L of the sedimented phase was directly injected into the PTV-LVI-GC-MS/MS system. The limits of quantitation (LOQs) ranged from 0.5 to 18 ng L?¹ for all pesticides, except empentrin (132 ng L?¹). The relative standard deviations (RSDs) for the analytes ranged between 0.8 and 14.6% for both intraday and interday precision. Accuracy, expressed as the mean extraction recovery, was between 70 and 130%. Using the internal standard method and surrogate deuterated standards, the total concentration of pesticides was in the range from 2.7 to 440 ng L?¹ in seawater, river water and sewage water. PMID:22818774

Carro, A M; Fernández, S; Racamonde, I; García-Rodríguez, D; González, P; Lorenzo, R A

2012-08-31

116

[Analysis of aldicarb and its metabolites in ginger using ultra performance liquid chromatography-tandem mass spectrometry coupled with multiplug filtration clean up with multiwalled carbon nanotubes].  

PubMed

A simple and rapid pretreatment procedure was developed for the simultaneous determination of aldicarb and its metabolites, aldicarb sulfone and aldicarb sulfoxide in ginger. The samples were extracted with acetonitrile, and then cleaned up with multiplug filtration using multiwalled carbon nanotubes (MWCNTS). The eluate was dried with nitrogen gas at room temperature, and redissolved in an acetonitrile-water (5:95, v/v) mixture, then quantified by ultra performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS) operated in positive multiple reaction monitoring (MRM) mode. A linear relationship was achieved in the range of 0.5 -200 microg/L for the peak areas to the mass concentrations of the target compounds with the linear correlation coefficients (r2) higher than 0.99. The recoveries at three spiked levels of 2, 20 and 200 microg/kg were in the range from 71.4% to 89.8% with the relative standard deviations (RSDs, n = 6) from 0.7% to 13.2% under the selected conditions. The limits of quantification (LOQ, S/N = 10) of aldicarb, aldicarb sulfone, and aldicarb sulfoxide in ginger were 1.0, 2.0 and 1.0 microg/kg, respectively. The results demonstrate that the developed method is rapid, cost-effective, and can meet the requirements of the multiple pesticide residue analysis. The method is applicable to determine aldicarb and its metabolites in ginger. PMID:25269263

Ma, Lili; Jia, Li; Zhou, Xinran; Liu, Yan; Fan, Xiaojing; Pan, Canping

2014-06-01

117

Dissipation and residues determination of propamocarb in ginseng and soil by high-performance liquid chromatography coupled with tandem mass spectrometry.  

PubMed

Two-year field trials were performed at two experimental sites to investigate dissipation and terminal residues of propamocarb in ginseng root, stem, leaf, and soil by high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS). Mean recoveries ranged from 80.5 to 95.6% with relative standard deviations (RSDs) of 5.5-9.1% at fortified levels of 0.01, 0.02, 0.05 and 0.20 mg kg(-1). The half-lives of propamocarb were 5.00-11.36 days in root, 5.07-11.46 days in stem, 6.83-11.31 days in leaf and 6.44-8.43 days in soil. The terminal residues of propamocarb were below the maximum residue limits (MRLs) of EU (0.20 mg kg(-1)) and South Korea (0.50 mg kg(-1) in fresh ginseng and 1.0 mg kg(-1) in dried ginseng) over 28 days after last spraying at recommended dosage. The results provide a quantitative basis for establishing the MRL and give a suggestion of safe and reasonable use of propamocarb in ginseng. PMID:24791956

Wang, Chunwei; Wang, Yan; Gao, Jie; Xu, Yuncheng; Cui, Lili

2014-09-01

118

Carbamazepine in municipal wastewater and wastewater sludge: ultrafast quantification by laser diode thermal desorption-atmospheric pressure chemical ionization coupled with tandem mass spectrometry.  

PubMed

In this study, the distribution of the anti-epileptic drug carbamazepine (CBZ) in wastewater (WW) and aqueous and solid phases of wastewater sludge (WWS) was carried out. A rapid and reliable method enabling high-throughput sample analysis for quicker data generation, detection, and monitoring of CBZ in WW and WWS was developed and validated. The ultrafast method (15s per sample) is based on the laser diode thermal desorption-atmospheric pressure chemical ionization (LDTD-APCI) coupled to tandem mass spectrometry (MS/MS). The optimization of instrumental parameters and method application for environmental analysis are presented. The performance of the novel method was evaluated by estimation of extraction recovery, linearity, precision and detection limit. The method detection limits was 12 ng L(-1) in WW and 3.4 ng g(-1) in WWS. The intra- and inter-day precisions were 8% and 11% in WW and 6% and 9% in WWS, respectively. Furthermore, three extraction methods, ultrasonic extraction (USE), microwave-assisted extraction (MAE) and accelerated solvent extraction (ASE) with three different solvent condition such as methanol, acetone and acetonitrile:ethyle acetate (5:1, v/v) were compared on the basis of procedural blank and method recovery. Overall, ASE showed the best extraction efficiency with methanol as compared to USE and MAE. Furthermore, the quantification of CBZ in WW and WWS samples showed the presence of contaminant in all stages of the treatment plant. PMID:22967548

Mohapatra, D P; Brar, S K; Tyagi, R D; Picard, P; Surampalli, R Y

2012-09-15

119

A multi-residue method for determination of 70 organic micropollutants in surface waters by solid-phase extraction followed by gas chromatography coupled to tandem mass spectrometry.  

PubMed

A multi-residue method, based on gas chromatography coupled to tandem mass spectrometry (GC-MS/MS), has been developed for the determination of 70 organic micropollutants from various chemical classes (organochlorinated, organophosphorous, triazines, carbamate and urea, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, pharmaceuticals, phenols, etc.) in surface waters. A single-step SPE extraction using OASIS HLB cartridges was employed for the recovery of target micropollutants. The method has been validated according to monitoring performance criteria of the Water Framework Directive, taking into account the approved guidelines on quality assurance and quality control. The recoveries ranged from 60 to 110 %, the coefficient of variation from 0.84 to 27.4 %, and the uncertainty from 6 to 37 %. The LOD varied from 6.0 to 40 ng/L. The limits of quantification for the priority pollutants anthracene, alachlor, atrazine, benzo(a)pyrene, chlorfenvinphos, diuron, isoproturon, nonylphenol, simazine, and terbutryn fulfill the criterion of <30 % of the relevant environmental standards. The method was employed to investigate the water quality in the basin of a transboundary river, Strymonas, in NE Greece during three sampling campaigns conducted in the year 2013. Thirty-nine compounds were detected in the river water. Metolachlor, diuron, isoproturon, salicylic acid, chlorfenvinphos, 1,2-benzanthracene, pyrene, diflubenzuron, and carbaryl exhibited the highest detection frequencies. PMID:25109470

Terzopoulou, Evangelia; Voutsa, Dimitra; Kaklamanos, George

2015-01-01

120

Development of a scalable model for predicting arsenic transport coupled with oxidation and adsorption reactions  

E-print Network

, high concentrations of arsenic in groundwater pose considerable risk to human health (Smith et al understanding of the transport, adsorption and oxidation of arsenic in groundwater systems will help betterDevelopment of a scalable model for predicting arsenic transport coupled with oxidation

Clement, Prabhakar

121

Mesoporous amorphous rare earth silicates, new catalysts of methane oxidative coupling  

Microsoft Academic Search

253 The catalytic reaction of methane oxidative coupling (MOC) is a direct route to produce ethylene from natural gas. Rare earth oxides are efficient catalysts for this reaction [1?3]. This paper is the first report on the catalytic activity of mesoporous amorphous rare earth materials based on SiO 2 in the MOC reaction; lanthanum and cerium ions or their mixture

A. G. Dedov; A. S. Loktev; N. O. Tel’pukhovskaya; K. V. Parkhomenko; I. I. Moiseev

2008-01-01

122

MEASUREMENT OF NITRIC OXIDE PRODUCTION IN HUMANS USING 15N-ARGININE AND TANDEM LC/MS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Nitric oxide (NO) plays a critical role in several physiologic processes, including modulation of peripheral vascular resistance, gastrointestinal peristalsis, inflammation and neuronal function. NO is synthesized in tissues by three classes of nitric oxide synthases (NOS) and rapidly degraded to ni...

123

Quantitative determination of Astragaloside IV, a natural product with cardioprotective activity, in plasma, urine and other biological samples by HPLC coupled with tandem mass spectrometry.  

PubMed

Astragaloside IV is a novel cardioprotective agent extracted from the Chinese medical herb Astragalus membranaceus (Fisch) Bge. This agent is being developed for treatment for cardiovascular disease. Further development of Astragaloside IV will require detailed pharmacokinetic studies in preclinical animal models. Therefore, we established a sensitive and accurate high performance liquid chromatography (HPLC) coupled with tandem mass spectrometry (LC/MS/MS) quantitative detection method for measurement of Astragaloside IV levels in plasma, urine as well as other biological samples including bile fluid, feces and various tissues. Extraction of Astragaloside IV from plasma and other biological samples was performed by Waters OASIS(trade mark) solid phase extraction column by washing with water and eluting with methanol, respectively. An aliquot of extracted residues was injected into LC/MS/MS system with separation by a Cosmosil C18 5 microm, 150 mm x 2.0 mm) column. Acetonitrile:water containing 5 microM NaAc (40:60, v/v) was used as a mobile phase. The eluted compounds were detected by tandem mass spectrometry. The average extraction recoveries were greater than 89% for Astragaloside IV and digoxin from plasma, while extraction recovery of Astragaloside IV and digoxin from tissues, bile fluid, urine and fece ranged from 61 to 85%, respectively. Good linearity (R2>0.9999) was observed throughout the range of 10-5000 ng/ml in 0.5 ml rat plasma and 5-5000 ng/ml in 0.5 ml dog plasma. In addition, good linearity (R2>0.9999) was also observed in urine, bile fluid, feces samples and various tissue samples. The overall accuracy of this method was 93-110% for both rat plasma and dog plasma. Intra-assay and inter-assay variabilities were less than 15.03% in plasma. The lowest quantitation limit of Astragaloside IV was 10 ng/ml in 0.5 ml rat plasma and 5 ng/ml in 0.5 ml dog plasma, respectively. Practical utility of this new LC/MS/MS method was confirmed in pilot pharmacokinetic studies in both rats and dogs following intravenous administration. PMID:15990371

Zhang, Weidong; Zhang, Chuan; Liu, Runhui; Li, Huiliang; Zhang, Jintao; Mao, Chen; Chen, Chunlin

2005-08-01

124

Metal-free oxidative decarbonylative coupling of aromatic aldehydes with arenes: direct access to biaryls.  

PubMed

A metal-free oxidative decarbonylative coupling of aromatic aldehydes with electron-rich or electron-deficient arenes to produce biaryl compounds was developed. This novel coupling was proposed to proceed via a non-chain radical homolytic aromatic substitution (HAS) type mechanism, based on the substrate scope, ortho-regioselectivity, radical trapping experiments and DFT calculation studies. With the ready availability of aromatic aldehydes and arenes, metal-free conditions should make this coupling attractive for the biaryl synthesis. PMID:25731601

Tang, Ren-Jin; He, Qing; Yang, Luo

2015-04-01

125

Chemically Induced Oscillatory Exchange Coupling in Chromium Oxide Clusters  

SciTech Connect

Theoretical electronic structure studies of the ground state geometries, binding energies, and magnetic coupling of Cr{sub 2}O {sub n} (n=1{endash}6) clusters have been carried out within a density functional scheme. It is shown that the magnetic coupling of the Cr atoms oscillates from antiferromagnetic to ferromagnetic and back as O atoms are added. Detailed electronic structure analysis reveals that the oscillatory exchange coupling has a chemical origin and is induced by changes in the electronic states between Cr and O sites close to the Fermi energy. {copyright} {ital 1999} {ital The American Physical Society }

Reddy, B.V.; Khanna, S.N. [Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000 (United States)] [Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000 (United States)

1999-10-01

126

Total synthesis of the marine metabolite (±)-polysiphenol via highly regioselective intramolecular oxidative coupling.  

PubMed

(±)-Polysiphenol (1), an atropisomerically stable 4,5-dibrominated 9,10-dihydrophenanthrene from Polysiphonia ferulacea, was prepared by a biomimetically inspired highly regioselective intramolecular oxidative coupling of a dibrominated dihydrostilbene. The installation of the two bromine atoms prior to oxidative coupling prevents further oxidation to a planar aromatized phenanthrene. By this strategy, the synthesis of (±)-polysiphenol was achieved in four steps in 70% overall yield. Synthesis of the naturally occurring 5,5'-(ethane-1,2-diyl)bis(3-bromobenzene-1,2-diol) (2) (the likely biogenetic precursor of polysiphenol) and 5,5'-(ethane-1,2-diyl)bis(3,4,6-tribromobenzene-1,2-diol) (9) are also reported. The origins of the regioselectivity in the oxidative coupling are explored. PMID:21875052

Barrett, Tim N; Braddock, D Christopher; Monta, Anna; Webb, Michael R; White, Andrew J P

2011-09-23

127

Analysis of chlormequat and mepiquat by hydrophilic interaction chromatography coupled to tandem mass spectrometry in food samples.  

PubMed

In this work a LC-MS/MS method for the determination of two quaternary ammonium growth regulators (chlormequat and mepiquat) in food is reported. The separation was based on hydrophilic interaction liquid chromatography (HILIC) without the use of ion-pair reagents. A gradient elution of acetonitrile and formic acid/ammonium formate buffer from 60 to 40% acetonitrile was enough to achieve a resolution >1.5 in less than 4.0min. The HILIC system was coupled to a triple quadrupole mass spectrometer equipped with a heated electrospray probe (H-ESI) providing sub-pg LODs in SRM mode. A straightforward sample treatment (SPE C18 clean-up) was enough to provide MLODs at low ppb levels when analysing a range of food samples that covered different kinds of matrices such as fresh fruit, vegetables, fruit juices, baby food, bread, coffee and beer. Chlormequat was found in seven samples (0.8-126ng/g) but mepiquat was only detected in bread and coffee samples (0.9-166ng/g). PMID:19328494

Esparza, X; Moyano, E; Galceran, M T

2009-05-15

128

?-Ketoglutarate Dehydrogenase and Glutamate Dehydrogenase Work in Tandem To Modulate the Antioxidant ?-Ketoglutarate during Oxidative Stress in Pseudomonas fluorescens?  

PubMed Central

?-Ketoglutarate (KG) is a crucial metabolite in all living organisms, as it participates in a variety of biochemical processes. We have previously shown that this keto acid is an antioxidant and plays a key role in the detoxification of reactive oxygen species (ROS). In an effort to further confirm this intriguing phenomenon, Pseudomonas fluorescens was exposed to menadione-containing media, with various amino acids as the sources of nitrogen. Here, we demonstrate that KG dehydrogenase (KGDH) and NAD-dependent glutamate dehydrogenase (GDH) work in tandem to modulate KG homeostasis. While KGDH was sharply decreased in cells challenged with menadione, GDH was markedly increased in cultures containing arginine (Arg), glutamate (Glu), and proline (Pro). When ammonium (NH4) was utilized as the nitrogen source, both KGDH and GDH levels were diminished. These enzymatic profiles were reversed when control cells were incubated in menadione media. 13C nuclear magnetic resonance and high-performance liquid chromatography studies revealed how KG was utilized to eliminate ROS with the concomitant formation of succinate. The accumulation of KG in the menadione-treated cells was dependent on the redox status of the lipoic acid residue in KGDH. Indeed, the treatment of cellular extracts from the menadione-exposed cells with dithiothreitol, a reducing agent, partially restored the activity of KGDH. Taken together, these data reveal that KG is pivotal to the antioxidative defense strategy of P. fluorescens and also point to the ROS-sensing role for KGDH. PMID:19376872

Mailloux, Ryan J.; Singh, Ranji; Brewer, Guy; Auger, Christopher; Lemire, Joseph; Appanna, Vasu D.

2009-01-01

129

Ruthenium-Catalyzed Concurrent Tandem Reactions University of North Carolina  

E-print Network

Ruthenium-Catalyzed Concurrent Tandem Reactions Greg Boyce University of North Carolina February 8. Enyne Cascades I. Dienyne Metathesis II. Ring Rearrangement Metathesis III. Metathesis/Non-Metathesis I of Tandem Reactions ­ Sequential tandem reactions involve coupling transformations that operate

Johnson, Jeff S.

130

MEASUREMENT OF PYRETHROID RESIDUES IN ENVIRONMENTAL AND FOOD SAMPLES BY ENHANCED SOLVENT EXTRACTION/SUPERCRITICAL FLUID EXTRACTION COUPLED WITH GAS CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY  

EPA Science Inventory

The abstract summarizes pyrethorid methods development research. It provides a summary of sample preparation and analytical techniques such as supercritical fluid extraction, enhance solvent extraction, gas chromatography and tandem mass spectrometry....

131

Simultaneous determination of dextromethorphan, dextrorphan and doxylamine in human plasma by HPLC coupled to electrospray ionization tandem mass spectrometry: application to a pharmacokinetic study.  

PubMed

In the present study, a fast, sensitive and robust method to quantify dextromethorphan, dextrorphan and doxylamine in human plasma using deuterated internal standards (IS) is described. The analytes and the IS were extracted from plasma by a liquid-liquid extraction (LLE) using diethyl-ether/hexane (80/20, v/v). Extracted samples were analyzed by high performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS). Chromatographic separation was performed by pumping the mobile phase (acetonitrile/water/formic acid (90/9/1, v/v/v) during 4.0min at a flow-rate of 1.5 mL min?¹ into a Phenomenex Gemini® C18, 5 ?m analytical column (150 × 4.6 mm i.d.). The calibration curve was linear over the range from 0.2 to 200 ng mL?¹ for dextromethorphan and doxylamine and 0.05 to 10 ng mL?¹ for dextrorphan. The intra-batch precision and accuracy (%CV) of the method ranged from 2.5 to 9.5%, and 88.9 to 105.1%, respectively. Method inter-batch precision (%CV) and accuracy ranged from 6.7 to 10.3%, and 92.2 to 107.1%, respectively. The run-time was for 4 min. The analytical procedure herein described was used to assess the pharmacokinetics of dextromethorphan, dextrorphan and doxylamine in healthy volunteers after a single oral dose of a formulation containing 30 mg of dextromethorphan hydrobromide and 12.5mg of doxylamine succinate. The method has high sensitivity, specificity and allows high throughput analysis required for a pharmacokinetic study. PMID:22651995

Donato, J L; Koizumi, F; Pereira, A S; Mendes, G D; De Nucci, G

2012-06-15

132

Budesonide quantification by HPLC coupled to atmospheric pressure photoionization (APPI) tandem mass spectrometry. Application to a comparative systemic bioavailability of two budesonide formulations in healthy volunteers.  

PubMed

In the present study, a novel, fast, sensitive and robust method to quantify budesonide in human plasma using 3-keto-desogestrel as the internal standard (IS) is described. The analyte and the IS were extracted from human plasma by liquid-liquid extraction (LLE) using ether. Extracted samples were analyzed by high performance liquid chromatography coupled to Atmospheric pressure photoionization tandem mass spectrometry (HPLC-APPI-MS/MS). Chromatography was performed isocratically on a C18, 5 ?m analytical column. The temperature of the autosampler was kept at 6 °C and the run time was 4.00 min. A linear calibration curve over the range 7.5-1000 pg ml?¹ was obtained and the lowest concentration quantified was 7.5 pg ml?¹, demonstrating acceptable accuracy and precision. This analytical method was applied in a relative bioavailability study in order to compare a test budesonide 64 ?g/dose nasal spray formulation vs. a reference 64 ?g/dose nasal spray formulation (Budecort Aqua) in 48 volunteers of both sexes. The study was conducted in an open randomized two-period crossover design and with a one-week washout period. Plasma samples were obtained over a 14 h interval. Since the 90% CI for both C(max), AUC(last) and AUC(0-inf) were within the 80-125% interval proposed by the Food and Drug Administration and ANVISA, it was concluded that budesonide 64 ?g/dose nasal spray was bioequivalent to Budecort Acqua® 64 ?g/dose nasal spray, according to both the rate and extent of absorption. PMID:21233029

Borges, Ney Carter do Carmo; Astigarraga, Rafael Barrientos; Sverdloff, Carlos Eduardo; Borges, Bruno Carter; Paiva, Thaís Rodrigues; Galvinas, Paulo Rebelo; Moreno, Ronilson Agnaldo

2011-02-01

133

Determination of trichothecenes A (T-2 toxin, HT-2 toxin, and diacetoxyscirpenol) in the tissues of broilers using liquid chromatography coupled to tandem mass spectrometry.  

PubMed

A stable and sensitive method has been developed for use in food and livestock product safety for the detection of mycotoxins. This newly developed method allows for the determination of T-2 toxin, HT-2 toxin and diacetoxyscirpenol (DAS) in heart, liver, spleen, lung, kidney, Glandular stomach, muscular stomach, small intestine, muscle, bone and brain samples from broilers using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The samples were initially extracted with ethyl acetate before being filtered through a 0.22?m nylon syringe filter and subjected to chromatographic separation on a reversed-phase C18 (50×2.1mm, 3?m) column. A mobile phase composed of 0.1% acetic acid and 10mM ammonium acetate in methanol and water was used in an assay of the levels of T-2 toxin, HT-2 toxin and DAS. For the analysis of the target compounds, the mass spectrometer was operated under positive electrospray ionization conditions in the selected reaction monitoring mode. The limit of detection was in the range of 0.02-0.05ng/g, whereas the limit of quantification was in the range of 0.08-0.15ng/g. The extraction recoveries of spiked samples from the high, intermediate and low levels ranged from 58.5% to 110.5%, and the relative standard deviation (RSD (%)) values were less than 17.0%. The results of inter- and intra-day precision (RSD (%)) were within 14.7%. The results revealed that the present method could be successfully applied to the analysis of T-2 toxin, HT-2 toxin and DAS in the real samples. PMID:24231141

Yang, Lingchen; Zhao, Zhiyong; Wu, Aibo; Deng, Yifeng; Zhou, Zhenlei; Zhang, Jianpeng; Hou, Jiafa

2013-12-30

134

Determination of volatile organic compounds in water by headspace solid-phase microextraction gas chromatography coupled to tandem mass spectrometry with triple quadrupole analyzer.  

PubMed

In the present work, a rapid method with little sample handling has been developed for determination of 23 selected volatile organic compounds in environmental and wastewater samples. The method is based on headspace solid-phase microextraction (SPME) followed by gas chromatography coupled to tandem mass spectrometry (GC-MS/MS) determination using triple quadrupole analyzer (QqQ) in electron ionization mode. The best conditions for extraction were optimised with a factorial design taking into account the interaction between different parameters and not only individual effects of variables. In the optimized procedure, 4 mL of water sample were extracted using a 10 mL vial and adding 0.4 g NaCl (final NaCl content of 10%). An SPME extraction with carboxen/polydimethylsiloxane 75 ?m fiber for 30 min at 50°C (with 5 min of previous equilibration time) with magnetic stirring was applied. Chromatographic determination was carried out by GC-MS/MS working in Selected Reaction Monitoring (SRM) mode. For most analytes, two MS/MS transitions were acquired, although for a few compounds it was difficult to obtain characteristic abundant fragments. In those cases, a pseudo selected reaction monitoring (pseudo-SRM) with three ions was used instead. The intensity ratio between quantitation (Q) and confirmation (q) signals was used as a confirmatory parameter. The method was validated by means of recovery experiments (n=6) spiking mineral water samples at three concentration levels (0.1, 5 and 50 ?g L(-1)). Recoveries between 70% and 120% were generally obtained with relative standard deviations (RSDs) lower than 20%. The developed method was applied to surface water and wastewater from a wastewater treatment plant and from a municipal solid-waste treatment plant. Several compounds, like chloroform, benzene, trichloroethylene, toluene, tetrachloroethylene, dibromochloromethane, xylenes and bromoform were detected and confirmed in all the samples analyzed. PMID:21907025

Cervera, M I; Beltran, J; Lopez, F J; Hernandez, F

2011-10-17

135

Fully validated assay for the quantification of endogenous nucleoside mono- and triphosphates using online extraction coupled with liquid chromatography-tandem mass spectrometry.  

PubMed

An analytical method coupling online solid-phase extraction (SPE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed to quantify 16 endogenous nucleoside mono- and triphosphates in cellular samples. Separation was achieved on a porous graphitic carbon (PGC) column without ion-pairing agent in the mobile phase. Low levels of the ion-pairing agent diethylamine (DEA) added to the reconstitution solution were necessary to prevent peak tailing of nucleoside triphosphates. The mass spectrometer, a triple quadrupole with an electrospray ionisation source, was operated in positive mode. Two multiple reaction monitoring (MRM) segments were programmed, each an internal standard. Extraction and separation of nucleoside mono- and triphosphates were obtained within 20 min. The total duration of a single run was 37 min. Calibration curves, performed with labelled nucleotides added to the sample matrix, ranged from 0.29 to 18.8 pmol injected for deoxyribonucleotides and from 3.9 to 3,156 pmol for ribonucleotides. Accuracy did not deviate more than -14.6 and 10.2 % from nominal values for all compounds at all levels. CV results were all lower than 17.0 % for the LLOQ level and 14.6 % for the other levels. Quality control (QC) samples were also in agreement with acceptance criteria, except for the lower QC of GMP. Ion suppression, matrix effect, extraction recoveries and stability were assessed. After validation, the method was applied to the evaluation of the effects of gemcitabine and hydroxyurea on nucleotide pools in Messa cells. PMID:24633509

Machon, Christelle; Jordheim, Lars Petter; Puy, Jean-Yves; Lefebvre, Isabelle; Dumontet, Charles; Guitton, Jérôme

2014-05-01

136

Quantification of cyproheptadine in human plasma by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry in a bioequivalence study.  

PubMed

A rapid, sensitive and specific method to quantify cyproheptadine in human plasma using amitriptyline as the internal standard (IS) is described. The analyte and the IS were extracted from plasma by liquid-liquid extraction using a diethyl-ether/dichloromethane (70/30; v/v) solvent. After removing and drying the organic phase, the extracts were reconstituted with a fixed volume of acetonitrile/water (50/50 v/v)+0.1% of acetic acid. The extracts were analyzed by high performance liquid chromatography coupled to electrospray tandem mass spectrometry (LC-MS/MS). Chromatography was performed isocratically using an Alltech Prevail C18 5 µm analytical column, (150 mm?x?4.6 mm I.D.). The method had a chromatographic run time of 4 min and a linear calibration curve ranging from 0.05 to 10 ng/mL (r2?>?0.99). The limit of quantification was 0.05 ng/mL. This HPLC/MS/MS procedure was used to assess the bioequivalence of cyproheptadine in two cyproheptadine?+?cobamamide (4 mg?+?1 mg) tablet formulations (Cobactin® [cyproheptadine?+?cobamamide] test formulation supplied from Zambon Laboratórios Farmacêuticos Ltda. and Cobavital® from Solvay Farma (standard reference formulation)). A single 4 mg?+?1 mg [cyproheptadine?+?cobamamide] dose of each formulation was administered to healthy volunteers. The study was conducted using an open, randomized, two-period crossover design with a 1-week washout interval. Since the 90% CI for Cmax and AUCs ratios were all within the 80-125% bioequivalence limit proposed by the US Food and Drug Administration, it was concluded that the cyproheptadine test formulation (Cobactin®) is bioequivalent to the Cobavital® formulation for both the rate and the extent of absorption of cyproheptadine. PMID:21432861

Mendes, Gustavo Duarte; Arruda, André; Chen, Lu Shi; de Almeida Magalhães, José Cássio; Alkharfy, Khalid M; De Nucci, Gilberto

2012-01-01

137

Rapid screening of N-oxides of chemical warfare agents degradation products by ESI-tandem mass spectrometry.  

PubMed

Rapid detection and identification of chemical warfare agents and related precursors/degradation products in various environmental matrices is of paramount importance for verification of standards set by the chemical weapons convention (CWC). Nitrogen mustards, N,N-dialkylaminoethyl-2-chlorides, N,N-dialkylaminoethanols, N-alkyldiethanolamines, and triethanolamine, which are listed CWC scheduled chemicals, are prone to undergo N-oxidation in environmental matrices or during decontamination process. Thus, screening of the oxidized products of these compounds is also an important task in the verification process because the presence of these products reveals alleged use of nitrogen mustards or precursors of VX compounds. The N-oxides of aminoethanols and aminoethylchlorides easily produce [M + H](+) ions under electrospray ionization conditions, and their collision-induced dissociation spectra include a specific neutral loss of 48 u (OH + CH2OH) and 66 u (OH + CH2Cl), respectively. Based on this specific fragmentation, a rapid screening method was developed for screening of the N-oxides by applying neutral loss scan technique. The method was validated and the applicability of the method was demonstrated by analyzing positive and negative samples. The method was useful in the detection of N-oxides of aminoethanols and aminoethylchlorides in environmental matrices at trace levels (LOD, up to 500 ppb), even in the presence of complex masking agents, without the use of time-consuming sample preparation methods and chromatographic steps. This method is advantageous for the off-site verification program and also for participation in official proficiency tests conducted by the Organization for the Prohibition of Chemical Weapons (OPCW), the Netherlands. The structure of N-oxides can be confirmed by the MS/MS experiments on the detected peaks. A liquid chromatography-mass spectrometry (LC-MS) method was developed for the separation of isomeric N-oxides of aminoethanols and aminoethylchlorides using a C18 Hilic column. Critical isomeric compounds can be confirmed by LC-MS/MS experiments, after detecting the N-oxides from the neutral loss scanning method. PMID:24553657

Sridhar, L; Karthikraj, R; Lakshmi, V V S; Raju, N Prasada; Prabhakar, S

2014-08-01

138

Biquadratic coupling through nano-oxide layers in pinned layers of IrMn-based spin valves  

NASA Astrophysics Data System (ADS)

We have investigated the coupling between top and bottom pinned layers through various nano-oxide layers (NOLs) in IrMn-based spin valves. The NOLs were formed by using oxygen-plasma oxidation or natural oxidation on 1 nm metallic layers. By inserting naturally oxidized Co-NOLs in the pinned layer, strong ferromagnetic coupling through NOLs and high specularity at the NOL interface were achieved. In contrast, when the plasma-oxidized Co-NOLs were inserted, ferromagnetic coupling through NOLs disappeared, plausibly due to the formation of nonferromagnetic oxides, which led to a low magnetoresistance (MR). Insertion of naturally oxidized Ni80Fe20-NOLs showed the same results as that of naturally oxidized Co-NOLs. On the other hand, biquadratic coupling between top and bottom pinned-Co90Fe10 layers was observed by inserting plasma-oxidized Ni80Fe20-NOLs. The highest MR was obtained when the field was applied along the direction perpendicular to the field-annealing direction. Similar biquadratic coupling was also found with naturally oxidized or plasma-oxidized Fe-NOLs. We suggest that the biquadratic coupling between pinned Co90Fe10 layers through NOLs results from the coupling between Fe (or Co90Fe10) and Fe+3 oxides

Lai, Chih-Huang; Lu, K. H.

2003-05-01

139

Oxidative Folding: Coupling Conformational Folding and Disulfide Formation  

Microsoft Academic Search

\\u000a Determining how a string of amino acid residues folds into the ­biologically active protein conformation remains as one of\\u000a the most important and challenging tasks in biology. Protein folding is usually a fast reaction in which transient intermediates\\u000a in the folding pathway are short lived, highly dynamic, and very difficult to be trapped, isolated, and characterized. The\\u000a technique of oxidative

Salvador Ventura; Rowen J. Y. Chang

140

Tandem Mass Spectrometry in Physiology  

NSDL National Science Digital Library

Tandem mass spectrometry coupled to liquid chromatography (LC-MS/MS) allows identification of proteins in a complex mixture without need for protein purification ("shotgun" proteomics). Recent progress in LC-MS/MS-based quantification, phosphoproteomic analysis, and targeted LC-MS/MS using multiple reaction monitoring (MRM) has made LC-MS/MS a powerful tool for the study of cell physiology.

2007-12-01

141

Oxidative Coupling of Methane over Li/MgO: Catalyst and Nanocatalyst Performance  

NASA Astrophysics Data System (ADS)

The Li/MgO catalyst and nanocatalyst were prepared by the incipient wetness impregnation and sol-gel method, respectively. The catalytic performance of the Li/MgO catalyst and nanocatalyst on oxidative coupling of methane was compared. The catalysts prepared in two ways were characterized by X-ray powder diffraction, Brunauer-Emmett-Teller surface and transmission electron microscope. The catalyst was tested at temperature of 973-1073 K with constant total pressure of 101 kPa. Experimental results showed that Li/MgO nanocatalyst in the oxidative coupling of methane would result in higher conversion of methane, higher selectivity, and higher yield of main products (ethane and ethylene) compared to ordinary catalyst. The results show the improved influence of nanoscale Li/MgO catalyst performance on oxidative coupling of methane.

Farsi, Ali; Moradi, Ali; Ghader, Sattar; Shadravan, Vahid

2011-02-01

142

Steady-state and transient catalytic oxidation and coupling of methane  

SciTech Connect

This project addresses the conversion of methane from natural gas into ethane, ethylene and higher hydrocarbons. Our research explores the mechanistic and practical implications of carrying out the methane oxidative coupling reaction in reactor designs other than conventional packed-beds with co-fed reactants. These alternate reactor designs are needed to prevent the full oxidation of methane, which limits C{sub 2}, yields in methane oxidative coupling reactions. The research strategy focuses on preventing contact between the 0{sub 2} reactant required for favorable overall thermodynamics and the C{sub 2+} products of methane coupling. The behavior of various reactor designs are simulated using detailed kinetic transport models. These simulations have suggested that the best way to prevent high C0{sub 2} yields is to separate the oxygen and hydrocarbon streams altogether. As a result, the project has focused on the experimental demonstration of proton transport membrane reactors for the selective conversion of methane into higher hydrocarbons.

Iglesia, E.; Perry, D.L.; Heinemann, H.

1995-06-01

143

Feasibility of a tandem photocatalytic oxidation-adsorption system for removal of monoaromatic compounds at concentrations in the sub-ppm-range.  

PubMed

Unlike previous photocatalytic oxidation (PCO) studies incorporated with adsorption, this study investigates the feasibility of applying a tandem PCO-adsorption hybrid technique regarding low-level monoaromatic compound removal. The PCO efficiencies decreased as the hydraulic diameter (HD) increased. A PCO reactor of a medium HD size was selected for further experiments. Under conditions relevant to the use of the PCO system, the CO level measured during the PCO process was minimal in comparison to indoor CO levels. Trace level formations of formaldehyde and acetaldehyde were observed during the photocatalytic process, but these compounds were undetectable at the activated carbon unit outlet. The degradation efficiencies, obtained from the PCO unit, exhibited a dependence on both the inlet concentration (IC) and relative humidity (RH), whereas those from the PCO-adsorption hybrid system did not. Under specific conditions, the PCO unit presented a high degradation efficiency of close to, or exceeding 90%, in regards to ethyl benzene, o-xylene, and m,p-xylene. However, the benzene air concentrations, after being treated by the PCO unit, substantially exceeded the USEPA inhalation reference concentration guideline of 30microgm(-3) (corresponding to 0.01ppm). In contrast, the PCO-adsorption hybrid system presented a high removal efficiency of close to 100% regarding all compounds, regardless of the IC or RH range. Consequently, it is suggested that the PCO-adsorption hybrid system has a synergistic advantage of photocatalysis and adsorption in regards to the BTEX elimination process. PMID:19666187

Jo, Wan-Kuen; Yang, Chang-Hee

2009-09-01

144

Steady-state and transient catalytic oxidation and coupling of methane  

SciTech Connect

Four papers have been published on mechanisms and site requirements for oxidative coupling of methane to ethane and ethylene and on synthesis of thin catalytic films during fiscal 1993. These publications also describe a unique inhibiting effect of water on the rate of undesired full oxidation pathways during oxidative coupling. Five quarterly reports have been written and submitted during the covered period. These findings and recently reported models of surface and gas phase reactions of methane suggest the use of membrane reactors and of cyclic methane decomposition schemes in order to avoid deleterious full oxidation reactions and to increase C{sub 2} yields above 25%. In fiscal 1994, we will proceed with the testing of proton-conducting membranes that we have recently fabricated. We will also continue our emerging effort in cyclic decomposition of methane and scavenging of fragments on supported metal catalysts.

Heinemann, H.; Iglesia, E.; Perry, D.L.

1993-12-31

145

Mixed-metal MIL-100(Sc,M) (M=Al, Cr, Fe) for Lewis acid catalysis and tandem C-C bond formation and alcohol oxidation.  

PubMed

The trivalent metal cations Al(3+) , Cr(3+) , and Fe(3+) were each introduced, together with Sc(3+) , into MIL-100(Sc,M) solid solutions (M=Al, Cr, Fe) by direct synthesis. The substitution has been confirmed by powder X-ray diffraction (PXRD) and solid-state NMR, UV/Vis, and X-ray absorption (XAS) spectroscopy. Mixed Sc/Fe MIL-100 samples were prepared in which part of the Fe is present as ?-Fe2 O3 nanoparticles within the mesoporous cages of the MOF, as shown by XAS, TGA, and PXRD. The catalytic activity of the mixed-metal catalysts in Lewis acid catalysed Friedel-Crafts additions increases with the amount of Sc present, with the attenuating effect of the second metal decreasing in the order Al>Fe>Cr. Mixed-metal Sc,Fe materials give acceptable activity: 40?% Fe incorporation only results in a 20?% decrease in activity over the same reaction time and pure product can still be obtained and filtered off after extended reaction times. Supported ?-Fe2 O3 nanoparticles were also active Lewis acid species, although less active than Sc(3+) in trimer sites. The incorporation of Fe(3+) into MIL-100(Sc) imparts activity for oxidation catalysis and tandem catalytic processes (Lewis acid+oxidation) that make use of both catalytically active framework Sc(3+) and Fe(3+) . A procedure for using these mixed-metal heterogeneous catalysts has been developed for making ketones from (hetero)aromatics and a hemiacetal. PMID:25348903

Mitchell, Laura; Williamson, Patrick; Ehrlichová, Barbora; Anderson, Amanda E; Seymour, Valerie R; Ashbrook, Sharon E; Acerbi, Nadia; Daniels, Luke M; Walton, Richard I; Clarke, Matthew L; Wright, Paul A

2014-12-15

146

Measurement of tissue acyl-CoAs using flow-injection tandem mass spectrometry: acyl-CoA profiles in short-chain fatty acid oxidation defects  

PubMed Central

The primary accumulating metabolites in fatty acid oxidation defects are intramitochondrial acyl-CoAs. Typically, secondary metabolites such as acylcarnitines, acylglycines and dicarboxylic acids are measured to study these disorders. Methods have not been adapted for tissue acyl-CoA measurement in defects with primarily acyl-CoA accumulation. Our objective was to develop a method to measure fatty acyl-CoA species that are present in tissues of mice with fatty acid oxidation defects using flow-injection tandem mass spectrometry. Following the addition of internal standards of [13C2] acetyl-CoA, [13C8] octanoyl-CoA, and [C17] heptadecanoic CoA, acyl-CoA’s are extracted from tissue samples and are injected directly into the mass spectrometer. Data is acquired using a 506.9 neutral loss scan and multiple reaction-monitoring (MRM). This method can identify all long, medium and short-chain acyl-CoA species in wild type mouse liver including predicted 3-hydroxyacyl-CoA species. We validated the method using liver of the short-chain-acyl-CoA dehydrogenase (SCAD) knock-out mice. As expected, there is a significant increase in [C4] butyryl-CoA species in the SCAD ?/? mouse liver compared to wild type. We then tested the assay in liver from the short-chain 3-hydroxyacyl-CoA dehydrogenase (SCHAD) deficient mice to determine the profile of acyl-CoA accumulation in this less predictable model. There was more modest accumulation of medium chain species including 3-hydroxyacyl-CoA’s consistent with the known chain-length specificity of the SCHAD enzyme. PMID:23117082

Palladino, Andrew A.; Chen, Jie; Kallish, Staci; Stanley, Charles A.; Bennett, Michael J.

2013-01-01

147

Synthesis of ethylene via oxidative coupling of methane. I. Determination of active catalysts  

Microsoft Academic Search

Ethylene and ethane (Câ's) have been synthesized by catalytic oxidative coupling of methane at atmospheric pressure and temperatures of 500 to 1000°C. A great number of metal oxides, supported on an ..cap alpha..-alumina support, have been screened for activity and selectivity in the normal, concurrent feeding mode of reactants, as well as, in the sequential or feed programming mode. The

G. E. Keller; M. M. Bhasin

1982-01-01

148

Rh(III)-catalyzed traceless coupling of quinoline N-oxides with internal diarylalkynes.  

PubMed

Quinoline N-oxides were found to undergo Cp*Rh(III)-catalyzed coupling with internal diarylalkynes to provide 8-functionalized quinolines through a cascade process that involves remote C-H bond activation, alkyne insertion, and intramolecular oxygen atom transfer. In this reaction, the N-oxide plays a dual role, acting as a traceless directing group as well as a source of oxygen atom, as confirmed by an (18)O-labeling experiment. PMID:25263712

Sharma, Upendra; Park, Yoonsu; Chang, Sukbok

2014-10-17

149

Copper-mediated formally dehydrative biaryl coupling of azine N-oxides and oxazoles.  

PubMed

A copper-mediated formally dehydrative biaryl coupling of azine N-oxides and oxazoles has been developed. The C-C bond-forming process proceeds, accompanied by the removal of the oxygen atom from the azine core, to directly afford the azine-oxazole biaryl linkage. Moreover, this system requires no noble transition metals such as palladium and rhodium, which are common promotors in the related dehydrogenative couplings with the azine N-oxide. Thus, the present protocol can provide a unique and less expensive approach to the azine-containing biheteroaryls of substantial interest in pharmaceutical and medicinal chemistry. PMID:25611158

Odani, Riko; Hirano, Koji; Satoh, Tetsuya; Miura, Masahiro

2015-02-20

150

Oxidative Coupling of Enolates, Enol Silanes and Enamines: Methods and Natural Product Synthesis  

PubMed Central

The oxidative coupling of enolates, enol silanes, and enamines provides a direct method for the construction of useful 1,4-dicarbonyl synthons. Despite being first reported in 1935, with subsequent important advances beginning in the 1970’s, the development of this powerful reaction into a reliable methodology was somewhat limited. In recent years, there have been a number of reports from several research groups demonstrating advances in several neglected areas of oxidative coupling. This microreview summarizes these new advances in methodology and provides an overview of recent natural product syntheses that showcase the power of these transformations. PMID:23471479

Guo, Fenghai; Clift, Michael D.

2013-01-01

151

Coupled Mn(II) Oxidation Pathways by a Planktonic Roseobacter-like Bacterium  

NASA Astrophysics Data System (ADS)

Bacteria belonging to the Roseobacter clade of the alpha-Proteobacteria are numerically abundant in coastal waters, ecologically significant in the cycling of (in)organic sulfur, and occupy a wide range of environmental niches. Here we reveal that Roseobacter-like bacteria may play a previously unrecognized role in the oxidation and cycling of manganese (Mn) in coastal waters. A diverse array of Mn(II)-oxidizing Roseobacter-like species were isolated from Elkhorn Slough, a coastal estuary adjacent to Monterey Bay, California. One isolate (designated AzwK-3b), in particular, rapidly oxidizes Mn(II) to insoluble Mn(III, IV) oxides. Interestingly, AzwK-3b is 100% identical (at the 16S rRNA level) to a previously reported Pfiesteria-associated Roseobacter-like bacterium, which does not posses the ability to oxidize Mn(II). Manganese(II) oxidation rates by live cultures and cell-free filtrates are substantially higher when incubated in the presence of light. Rates of oxidation by washed cell extracts, however, are light independent, which are actually identical to rates by cell-free filtrates incubated in the dark. Thus, AwwK-3b induces two Mn(II) oxidation mechanisms when incubated in the presence of light as opposed to predominantly direct enzymatic oxidation in the dark. Within the light, production of photochemically-active metabolites is coupled with initial direct enzymatic Mn(II) oxidation, resulting in substantially accelerated Mn(II) oxidation rates. Thus, Roseobacter-like bacteria may not only greatly influence Mn(II) oxidation and cycling within coastal surface waters, but may also induce a novel photo-oxidation pathway providing an alternative means of Mn(II) oxidation within the photic zone.

Hansel, C. M.; Francis, C. A.

2005-12-01

152

Amine-functional magnetic polymer modified graphene oxide as magnetic solid-phase extraction materials combined with liquid chromatography-tandem mass spectrometry for chlorophenols analysis in environmental water.  

PubMed

A novel planar-structure amine-functional magnetic polymer modified graphene oxide nanocomposite (NH2-MP@GO) was synthesized. The properties were characterized by transmission electron microscopy (TEM) and Fourier-transform infrared spectrometry (FTIR). The obtained adsorption results showed that the NH2-MP@GO had great adsorptive ability toward five chlorophenols (CPs), including 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP) and pentachlorophenol (PCP). Based on these, an effective magnetic solid-phase extraction (MSPE) procedure coupled with high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the preconcentration and determination of the five CPs in environmental water samples was developed. Various experimental parameters that could affect the extraction efficiencies had been investigated in detail. Under the optimum conditions, the enrichment factors of the method for the target CPs were found to be 1000. The proposed method was successfully applied for the analysis of environmental water samples with recoveries ranging from 86.4 to 99.8% with correlation coefficients (R) higher than 0.9994. Good linearities were obtained ranging from 10 to 500ng/L for 2-CP, 5 to 500ng/L for 2,4-DCP, 2 to 500ng/L for 2,4,6-TeCP and 2,3,4,6-TeCP, and 1 to 500ng/L for PCP, respectively. The limits of quantitation for the five CPs were 0.6-9.2ng/L. It was confirmed that the planar-structure NH2-MP@GO was a kind of highly effective MSPE materials used for the trace CPs analyses. PMID:25160956

Pan, Sheng-Dong; Zhou, Li-Xin; Zhao, Yong-Gang; Chen, Xiao-Hong; Shen, Hao-Yu; Cai, Mei-Qiang; Jin, Mi-Cong

2014-10-01

153

Nanocrystal assembly for tandem catalysis  

DOEpatents

The present invention provides a nanocrystal tandem catalyst comprising at least two metal-metal oxide interfaces for the catalysis of sequential reactions. One embodiment utilizes a nanocrystal bilayer structure formed by assembling sub-10 nm platinum and cerium oxide nanocube monolayers on a silica substrate. The two distinct metal-metal oxide interfaces, CeO.sub.2--Pt and Pt--SiO.sub.2, can be used to catalyze two distinct sequential reactions. The CeO.sub.2--Pt interface catalyzed methanol decomposition to produce CO and H.sub.2, which were then subsequently used for ethylene hydroformylation catalyzed by the nearby Pt--SiO.sub.2 interface. Consequently, propanal was selectively produced on this nanocrystal bilayer tandem catalyst.

Yang, Peidong; Somorjai, Gabor; Yamada, Yusuke; Tsung, Chia-Kuang; Huang, Wenyu

2014-10-14

154

"Nanocrystal bilayer for tandem catalysis"  

SciTech Connect

Supported catalysts are widely used in industry and can be optimized by tuning the composition and interface of the metal nanoparticles and oxide supports. Rational design of metal-metal oxide interfaces in nanostructured catalysts is critical to achieve better reaction activities and selectivities. We introduce here a new class of nanocrystal tandem catalysts that have multiple metal-metal oxide interfaces for the catalysis of sequential reactions. We utilized a nanocrystal bilayer structure formed by assembling platinum and cerium oxide nanocube monolayers of less than 10 nm on a silica substrate. The two distinct metal-metal oxide interfaces, CeO2-Pt and Pt-SiO2, can be used to catalyse two distinct sequential reactions. The CeO2-Pt interface catalysed methanol decomposition to produce CO and H2, which were subsequently used for ethylene hydroformylation catalysed by the nearby Pt-SiO2 interface. Consequently, propanal was produced selectively from methanol and ethylene on the nanocrystal bilayer tandem catalyst. This new concept of nanocrystal tandem catalysis represents a powerful approach towards designing high-performance, multifunctional nanostructured catalysts

Yamada, Yusuke; Tsung, Chia Kuang; Huang, Wenyu; Huo, Ziyang; E.Habas, Susan E; Soejima, Tetsuro; Aliaga, Cesar E; Samorjai, Gabor A; Yang, Peidong

2011-01-24

155

Proton translocation coupled to trimethylamine N-oxide reduction in anaerobically grown Escherichia coli.  

PubMed Central

Proton translocation coupled to trimethylamine N-oxide reduction was studied in Escherichia coli grown anaerobically in the presence of trimethylamine N-oxide. Rapid acidification of the medium was observed when trimethylamine N-oxide was added to anaerobic cell suspensions of E. coli K-10. Acidification was sensitive to the proton conductor 3,5-di-tert-butyl-4-hydroxybenzylidenemalononitrile (SF6847). No pH change was shown in a strain deficient in trimethylamine N-oxide reductase activity. The apparent H+/trimethylamine N-oxide ratio in cells oxidizing endogenous substrates was 3 to 4 g-ions of H+ translocated per mol of trimethylamine N-oxide added. The addition of trimethylamine N-oxide and formate to ethylenediaminetetraacetic acid-treated cell suspension caused fluorescence quenching of 3,3'-dipropylthiacarbocyanine [diS-C3-(5)], indicating the generation of membrane potential. These results indicate that the reduction of trimethylamine N-oxide in E. coli is catalyzed by an anaerobic electron transfer system, resulting in formation of a proton motive force. Trimethylamine N-oxide reductase activity and proton extrusion were also examined in chlorate-resistant mutants. Reduction of trimethylamine N-oxide occurred in chlC, chlG, and chlE mutants, whereas chlA, chlB, and chlD mutants, which are deficient in the molybdenum cofactor, could not reduce it. Protons were extruded in chlC and chlG mutants, but not in chlA, chlB, and chlD mutants. Trimethylamine N-oxide reductase activity in a chlD mutant was restored to the wild-type level by the addition of 100 microM molybdate to the growth medium, indicating that the same molybdenum cofactor as used by nitrate reductase is required for the trimethylamine N-oxide reductase system. PMID:7031034

Takagi, M; Tsuchiya, T; Ishimoto, M

1981-01-01

156

Hydrogen and formate oxidation coupled to dissimilatory reduction of iron or manganese by Alteromonas putrefaciens  

USGS Publications Warehouse

The ability of Alteromonas putrefaciens to obtain energy for growth by coupling the oxidation of various electron donors to dissimilatory Fe(III) or Mn(IV) reduction was investigated. A. putrefaciens grew with hydrogen, formate, lactate, or pyruvate as the sole electron donor and Fe(III) as the sole electron acceptor. Lactate and pyruvate were oxidized to acetate, which was not metabolized further. With Fe(III) as the electron acceptor, A. putrefaciens had a high affinity for hydrogen and formate and metabolized hydrogen at partial pressures that were 25-fold lower than those of hydrogen that can be metabolized by pure cultures of sulfate reducers or methanogens. The electron donors for Fe(III) reduction also supported Mn(IV) reduction. The electron donors for Fe(III) and Mn(IV) reduction and the inability of A. putrefaciens to completely oxidize multicarbon substrates to carbon dioxide distinguish A. putrefaciens from GS-15, the only other organism that is known to obtain energy for growth by coupling the oxidation of organic compounds to the reduction of Fe(III) or Mn(IV). The ability of A. putrefaciens to reduce large quantities of Fe(III) and to grow in a defined medium distinguishes it from a Pseudomonas sp., which is the only other known hydrogen-oxidizing, Fe(III)-reducing microorganism. Furthermore, A. putrefaciens is the first organism that is known to grow with hydrogen as the electron donor and Mn(IV) as the electron acceptor and is the first organism that is known to couple the oxidation of formate to the reduction of Fe(III) or Mn(IV). Thus, A. putrefaciens provides a much needed microbial model for key reactions in the oxidation of sediment organic matter coupled to Fe(III) and Mn(IV) reduction.

Lovley, D.R.; Phillips, E.J.P.; Lonergan, D.J.

1989-01-01

157

Oxidation-induced biquadratic coupling in Co/Fe/MgO/Fe(001)  

NASA Astrophysics Data System (ADS)

We investigate the interlayer exchange coupling in Co/Fe/MgO/Fe(001) via molecular-beam epitaxy synthesis and magneto-optic Kerr effect measurements across wedged samples. By independently varying the oxygen contents of the MgO film and the Fe/MgO interface, the biquadratic coupling is found to be correlated with the interfacial oxidation. Furthermore, the temperature dependence indicates that the biquadratic coupling originates from indirect exchange interactions with magnetic impurities in the MgO spacer.

Chiang, Y. F.; Wong, Jared J. I.; Tan, X.; Li, Yan; Pi, K.; Wang, W. H.; Tom, H. W. K.; Kawakami, R. K.

2009-05-01

158

Residue determination of glyphosate, glufosinate and aminomethylphosphonic acid in water and soil samples by liquid chromatography coupled to electrospray tandem mass spectrometry.  

PubMed

This paper describes a method for the sensitive and selective determination of glyphosate, glufosinate and aminomethylphosphonic acid (AMPA) residues in water and soil samples. The method involves a derivatization step with 9-fluorenylmethylchloroformate (FMOC) in borate buffer and detection based on liquid chromatography coupled to electrospray tandem mass spectrometry (LC-ESI-MS/MS). In the case of water samples a volume of 10 mL was derivatized and then 4.3 mL of the derivatized mixture was directly injected in an on-line solid phase extraction (SPE)-LC-MS/MS system using an OASIS HLB cartridge column and a Discovery chromatographic column. Soil samples were firstly extracted with potassium hydroxide. After that, the aqueous extract was 10-fold diluted with water and 2 mL were derivatized. Then, 50 microL of the derivatized 10-fold diluted extract were injected into the LC-MS/MS system without pre-concentration into the SPE cartridge. The method has been validated in both ground and surface water by recovery studies with samples spiked at 50 and 500 ng/L, and also in soil samples, spiked at 0.05 and 0.5 mg/kg. In water samples, the mean recovery values ranged from 89 to 106% for glyphosate (RSD <9%), from 97 to 116% for AMPA (RSD < 10%), and from 72 to 88% in the case of glufosinate (RSD < 12%). Regarding soil samples, the mean recovery values ranged from 90 to 92% for glyphosate (RSD <7%), from 88 to 89% for AMPA (RSD <5%) and from 83 to 86% for glufosinate (RSD <6%). Limits of quantification for all the three compounds were 50 ng/L and 0.05 mg/kg in water and soil, respectively, with limits of detection as low as 5 ng/L, in water, and 5 microg/kg, in soil. The use of labelled glyphosate as internal standard allowed improving the recovery and precision for glyphosate and AMPA, while it was not efficient for glufosinate, that was quantified by external standards calibration. The method developed has been applied to the determination of these compounds in real water and soil samples from different areas. All the detections were confirmed by acquiring two transitions for each compound. PMID:16038204

Ibáñez, María; Pozo, Oscar J; Sancho, Juan V; López, Francisco J; Hernández, Félix

2005-07-22

159

Pathways of advanced oxidation of phenol by Fenton's reagent--identification of oxidative coupling intermediates by extractive acetylation.  

PubMed

Homogeneous Fenton reaction (H(2)O(2)/Fe(2+) system) using significantly substoichiometric concentrations of H(2)O(2) oxidant to oxidize phenol was characterized focusing on the formation of stable aromatic intermediates. Beyond the most abundant benzenediols, the pattern of aromatic intermediates was chiefly characterized by hydroxylated biphenyls and diphenyl ethers with different degrees of hydroxylation. Hydroxylated dibenzofurans (DBF), p,p'-dioxins, as well as highly condensed aromatic intermediates including polyols of polycyclic aromatic hydrocarbons (PAHs), could also be detected, but in lower concentrations. The formation of aromatic intermediates could be predicted on the basis of oxidative coupling reactions of resonance-stabilized radicals generated by the attack of the highly reactive hydroxyl radicals (OH*) on phenol. GC/MS identification of oxidative coupling intermediates was performed after derivatization of the solvent extracts. Derivatization reactions included silylation to give TMS (trimethylsilyl) ethers, as well as single-step extractive acetylation using acetic anhydride in alkaline aqueous solutions (pH 10.5) to give acetates. Solvent extraction of aqueous solutions, a prerequisite to generate TMS ethers, caused strong discrimination of polyols due to their low distribution coefficients in non-polar solvents. This discrimination could be overcome by extracting the in-situ formed acetates of the intermediates. Extractive acetylation allowed the detection of tri-, tetra-, and penta-hydroxylated aromatic intermediates generated by Fenton oxidation processes, which have been overlooked upto now. Thus, extractive acetylation to detect stable aromatic intermediates covering a wide range of hydroxylation degrees can foster the understanding, monitoring, and management of advanced oxidation processes, especially in the field of wastewater treatment. PMID:19539292

Poerschmann, Juergen; Trommler, Ulf

2009-07-17

160

Characterization of in vitro and in vivo metabolites of carnosic acid, a natural antioxidant, by high performance liquid chromatography coupled with tandem mass spectrometry.  

PubMed

Carnosic acid (CA) is a widely employed antioxidant and the main active component in rosemary and sage, but its metabolism remains largely unknown. The present study investigated the metabolism of CA in vitro and in vivo for the first time, using high performance liquid chromatography coupled with hybrid triple quadrupole-linear ion trap mass spectrometry (HPLC-Q-trap-MS). A couple of scan modes were adopted in mass spectrometer domain, including Q1 full scan, neutral loss scan-information dependent acquisition-enhanced product ion (NL-IDA-EPI) and precursor ion scan-information dependent acquisition-enhanced product ion (PI-IDA-EPI). In particular, a prediction was carried out on the basis of in vitro metabolism results, and gave birth to a multiple ion monitoring-information dependent acquisition-enhanced product ion (MIM-IDA-EPI) mode aiming to detect the trace metabolites in CA-treated biological samples. A total of ten metabolites (M4-13), along with three degradative products (M1-3), were identified for CA from in vitro metabolism models, including liver microsomes of human and rats (HLMs and RLMs), human intestinal microsomes (HIMs) and two species of Cunninghamella elegans. Twelve (U1-12) and six (F1-6) metabolites were detected from CA-treated urine and feces, respectively. In addition, five metabolites (SM2-6) in vivo were purified and definitely identified using NMR spectroscopy. The results of both in vitro and in vivo metabolism studies indicated poor metabolic stability for CA, and the glucuronidation and oxidation metabolisms extensively occurred for CA in vitro, while oxidation, glucuronidation and methylation were the main metabolic pathways observed in vivo. PMID:24291799

Song, Yuelin; Yan, Haixia; Chen, Jinfeng; Wang, Yitao; Jiang, Yong; Tu, Pengfei

2014-02-01

161

Novel solid-state polycondensation I. Oxidative-coupling polymerization of 2,6-dihydroxynaphthalene.  

PubMed

Grinding crystals of 2,6-dihydroxynaphthalene-benzylamine complex with FeCl3.6H2O powder in a mortar resulted in the 1,5-oxidative-coupling polymerization of 2,6-dihydroxynaphthalene at room temperature. PMID:12132488

Suzuki, Masato; Yatsugi, Yutaka

2002-01-21

162

Electric coupling between distant nitrate reduction and sulfide oxidation in marine sediment.  

PubMed

Filamentous bacteria of the Desulfobulbaceae family can conduct electrons over centimeter-long distances thereby coupling oxygen reduction at the surface of marine sediment to sulfide oxidation in deeper anoxic layers. The ability of these cable bacteria to use alternative electron acceptors is currently unknown. Here we show that these organisms can use also nitrate or nitrite as an electron acceptor thereby coupling the reduction of nitrate to distant oxidation of sulfide. Sulfidic marine sediment was incubated with overlying nitrate-amended anoxic seawater. Within 2 months, electric coupling of spatially segregated nitrate reduction and sulfide oxidation was evident from: (1) the formation of a 4-6-mm-deep zone separating sulfide oxidation from the associated nitrate reduction, and (2) the presence of pH signatures consistent with proton consumption by cathodic nitrate reduction, and proton production by anodic sulfide oxidation. Filamentous Desulfobulbaceae with the longitudinal structures characteristic of cable bacteria were detected in anoxic, nitrate-amended incubations but not in anoxic, nitrate-free controls. Nitrate reduction by cable bacteria using long-distance electron transport to get privileged access to distant electron donors is a hitherto unknown mechanism in nitrogen and sulfur transformations, and the quantitative importance for elements cycling remains to be addressed. PMID:24577351

Marzocchi, Ugo; Trojan, Daniela; Larsen, Steffen; Meyer, Rikke Louise; Revsbech, Niels Peter; Schramm, Andreas; Nielsen, Lars Peter; Risgaard-Petersen, Nils

2014-08-01

163

On the radiative coupling between mesospheric and thermospheric nitric oxide  

NASA Astrophysics Data System (ADS)

A photochemical model of nitric oxide from 40 to 250 km has been used to study the distribution of NO in the mesosphere and lower thermosphere. The model includes a parameterization of NO photolysis that can account for the opacity of a varying thermospheric NO layer. This model is used to test the suggestion that increases in thermospheric NO which increase this opacity 'shield' NO at lower altitudes by decreasing the photolytic destruction rate. The model was 'tuned' to reproduce two recent observations of thermospheric NO, the high latitude rocket experiment of Eparvier and Barth (1992) and the midlatitude ground-based microwave experiment of Clancy et al. (1992). In the first case, the model indicated that the large thermospheric NO layer could have caused significant shielding and up to a factor of 2 effect on the mesospheric NO is seen. On the other hand, for the midlatitude observation the NO optical pathlength was too small to be significant. A time dependent version of the model was used to study the response of mesospheric NO to auroral energy input during winter. Under conditions which combine rapid transport and NO self-shielding, the model suggests that NO density increases could propagate into the upper stratosphere.

Siskind, David E.

1994-11-01

164

Enzymatic Processing of Fumiquinazoline F: A Tandem Oxidative-Acylation Strategy for the Generation of Multicyclic Scaffolds in Fungal Indole Alkaloid Biosynthesis†  

PubMed Central

Aspergillus fumigatus Af293 is a known producer of quinazoline natural products including the antitumor fumiquinazolines, of which the simplest member is fumiquinazoline F (FQF) with a 6-6-6 tricyclic core derived from anthranilic acid, tryptophan, and alanine. FQF is the proposed biological precursor to fumiquinazoline A (FQA) where the pendant indole side chain has been modified via oxidative coupling of an additional molecule of alanine, yielding a fused 6-5-5 imidazoindolone. We recently identified fungal anthranilate-activating non-ribosomal peptide synthetase (NRPS) domains through bioinformatics approaches. One domain previously identified is part of the trimodular NRPS Af12080, which we predict is responsible for FQF formation. We now show that two adjacent A. fumigatus ORFs, a monomodular NRPS Af12050 and a flavoprotein Af12060, are necessary and sufficient to convert FQF to FQA. Af12060 oxidizes the 2',3'-double bond of the indole side chain of FQF, and the three-domain NRPS Af12050 activates L-Ala as the adenylate, installs it as the pantetheinyl thioester on its carrier protein domain and acylates the oxidized indole for subsequent intramolecular cyclization to create the 6-5-5 imidazolindolone of FQA. This work provides experimental validation of the fumiquinazoline biosynthetic cluster of A. fumigatus A293, and describes an oxidative annulation biosynthetic strategy likely shared among several classes of polycyclic fungal alkaloids. PMID:20804163

Ames, Brian D.; Liu, Xinyu; Walsh, Christopher T.

2010-01-01

165

Observation of T-2 and HT-2 glucosides from Fusarium sporotrichioides by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS)  

Technology Transfer Automated Retrieval System (TEKTRAN)

Cultures of Fusarium sporotrichioides were extracted and subjected to evaluation by high performance liquid chromatography – tandem mass spectrometry (LC-MS/MS). Along with the expected T-2 and HT-2 toxins, compounds 162 m/z higher than the toxins were observed. Fragmentation behavior of the larger ...

166

Oxygen reduction electrocatalyst based on strongly coupled cobalt oxide nanocrystals and carbon nanotubes.  

PubMed

Electrocatalyst for oxygen reduction reaction (ORR) is crucial for a variety of renewable energy applications and energy-intensive industries. The design and synthesis of highly active ORR catalysts with strong durability at low cost is extremely desirable but remains challenging. Here, we used a simple two-step method to synthesize cobalt oxide/carbon nanotube (CNT) strongly coupled hybrid as efficient ORR catalyst by directly growing nanocrystals on oxidized multiwalled CNTs. The mildly oxidized CNTs provided functional groups on the outer walls to nucleate and anchor nanocrystals, while retaining intact inner walls for highly conducting network. Cobalt oxide was in the form of CoO due to a gas-phase annealing step in NH(3). The resulting CoO/nitrogen-doped CNT (NCNT) hybrid showed high ORR current density that outperformed Co(3)O(4)/graphene hybrid and commercial Pt/C catalyst at medium overpotential, mainly through a 4e reduction pathway. The metal oxide/carbon nanotube hybrid was found to be advantageous over the graphene counterpart in terms of active sites and charge transport. Last, the CoO/NCNT hybrid showed high ORR activity and stability under a highly corrosive condition of 10 M NaOH at 80 °C, demonstrating the potential of strongly coupled inorganic/nanocarbon hybrid as a novel catalyst system in oxygen depolarized cathode for chlor-alkali electrolysis. PMID:22957510

Liang, Yongye; Wang, Hailiang; Diao, Peng; Chang, Wesley; Hong, Guosong; Li, Yanguang; Gong, Ming; Xie, Liming; Zhou, Jigang; Wang, Jian; Regier, Tom Z; Wei, Fei; Dai, Hongjie

2012-09-26

167

Simultaneous speciation of selenium and sulfur species in selenized odorless garlic (Allium sativum L. Shiro) and shallot (Allium ascalonicum) by HPLC-inductively coupled plasma-(octopole reaction system)-mass spectrometry and electrospray ionization-tandem mass spectrometry.  

PubMed

The simultaneous speciation of selenium and sulfur in selenized odorless garlic (Allium sativum L. Shiro) and a weakly odorous Allium plant, shallot (Allium ascalonicum), was performed by means of a hyphenated technique, a HPLC coupled with an inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) equipped with an octopole reaction system (ORS). The aqueous extracts of them contained the common seleno compound that was identified as gamma-glutamylmethylselenocysteine by an electrospray ionization-tandem mass spectrometry (ESI-MS/MS). Normal garlic contains alliin as the major sulfur-containing compound, which is the biological precursor of the garlic odorant, allicin. Alliin, however, was not detected in the extracts of the selenized odorless garlic. At least, four unidentified sulfur-containing compounds were detected in odorless garlic and shallot. Moreover, these Allium plants showed chemopreventive effects against human leukemia cells. PMID:16233877

Ogra, Yasumitsu; Ishiwata, Kazuya; Iwashita, Yuji; Suzuki, Kazuo T

2005-11-01

168

Ammonia oxidation coupled to CO2 fixation by archaea and bacteria in an agricultural soil.  

PubMed

Ammonia oxidation is an essential part of the global nitrogen cycling and was long thought to be driven only by bacteria. Recent findings expanded this pathway also to the archaea. However, most questions concerning the metabolism of ammonia-oxidizing archaea, such as ammonia oxidation and potential CO(2) fixation, remain open, especially for terrestrial environments. Here, we investigated the activity of ammonia-oxidizing archaea and bacteria in an agricultural soil by comparison of RNA- and DNA-stable isotope probing (SIP). RNA-SIP demonstrated a highly dynamic and diverse community involved in CO(2) fixation and carbon assimilation coupled to ammonia oxidation. DNA-SIP showed growth of the ammonia-oxidizing bacteria but not of archaea. Furthermore, the analysis of labeled RNA found transcripts of the archaeal acetyl-CoA/propionyl-CoA carboxylase (accA/pccB) to be expressed and labeled. These findings strongly suggest that ammonia-oxidizing archaeal groups in soil autotrophically fix CO(2) using the 3-hydroxypropionate-4-hydroxybutyrate cycle, one of the two pathways recently identified for CO(2) fixation in Crenarchaeota. Catalyzed reporter deposition (CARD)-FISH targeting the gene encoding subunit A of ammonia monooxygenase (amoA) mRNA and 16S rRNA of archaea also revealed ammonia-oxidizing archaea to be numerically relevant among the archaea in this soil. Our results demonstrate a diverse and dynamic contribution of ammonia-oxidizing archaea in soil to nitrification and CO(2) assimilation and that their importance to the overall archaeal community might be larger than previously thought. PMID:21368116

Pratscher, Jennifer; Dumont, Marc G; Conrad, Ralf

2011-03-01

169

Characterization of the Metal-Binding Site of Bovine Growth Hormone through Site-Specific Metal-Catalyzed Oxidation and High-Performance Liquid Chromatography–Tandem Mass Spectrometry  

Microsoft Academic Search

Metal-catalyzed oxidation was used to identify metal-binding His residues in bovine growth hormone (bGH), which has not been characterized well crystallographically due to a high propensity of bGH to aggregate. bGH was exposed to Cu2+ and ascorbate (ascorbate\\/Cu2+\\/O2). 2-Oxo-His formation was identified by HPLC–tandem mass spectrometry (MS\\/MS) analysis of a tryptic digest. Two 2-oxo-His-containing fragments were detected, T2(O) (MH2+2 =

Susan W. Hovorka; Todd D. Williams; Christian Schöneich

2002-01-01

170

Nanocellulose coupled flexible polypyrrole@graphene oxide composite paper electrodes with high volumetric capacitance  

NASA Astrophysics Data System (ADS)

A robust and compact freestanding conducting polymer-based electrode material based on nanocellulose coupled polypyrrole@graphene oxide paper is straightforwardly prepared via in situ polymerization for use in high-performance paper-based charge storage devices, exhibiting stable cycling over 16 000 cycles at 5 A g-1 as well as the largest specific volumetric capacitance (198 F cm-3) so far reported for flexible polymer-based electrodes.A robust and compact freestanding conducting polymer-based electrode material based on nanocellulose coupled polypyrrole@graphene oxide paper is straightforwardly prepared via in situ polymerization for use in high-performance paper-based charge storage devices, exhibiting stable cycling over 16 000 cycles at 5 A g-1 as well as the largest specific volumetric capacitance (198 F cm-3) so far reported for flexible polymer-based electrodes. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr07251k

Wang, Zhaohui; Tammela, Petter; Strømme, Maria; Nyholm, Leif

2015-02-01

171

Exploiting shape effects of La2O3 nanocatalysts for oxidative coupling of methane reaction  

NASA Astrophysics Data System (ADS)

High activity towards oxidative coupling of methane and high selectivity for C2 hydrocarbons could be achieved over La2O3 nanorods with a large surface area, strong surface basic sites, electron deficient surface oxygen species and defined surface structure compared with La2O3 nanoparticles at low temperature.High activity towards oxidative coupling of methane and high selectivity for C2 hydrocarbons could be achieved over La2O3 nanorods with a large surface area, strong surface basic sites, electron deficient surface oxygen species and defined surface structure compared with La2O3 nanoparticles at low temperature. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr03617k

Huang, Ping; Zhao, Yonghui; Zhang, Jun; Zhu, Yan; Sun, Yuhan

2013-10-01

172

TBAI-Catalyzed Oxidative Cross-Coupling of Phenols and 2-Aminoacetophenones.  

PubMed

An iodide-catalyzed oxidative cross-coupling between phenols and 2-aminoacetophenones has been developed. Using catalytic amounts of tetrabutylammoniumiodide (TBAI) as an iodine-containing catalyst and aqueous solutions of tert-butyl hydro-peroxide (TBHP) as the stoichiometric co-oxidant, a variety of ?-phenoxylated 2-aminoacetophenones could be obtained in yields of up to 92% after remarkably short reaction times (20 min). This is a very rare example for an iodide-catalyzed intermolecular cross-coupling utilizing phenols. However, this efficient methodology could be further extended toward an intramolecular variant which gives direct access to a range of dihydro-4H-benzo[e][1,3]oxazin-4-ones. PMID:25763470

Xu, Wei; Nachtsheim, Boris J

2015-03-20

173

Transient characteristics for proton gating in laterally coupled indium-zinc-oxide transistors.  

PubMed

The control and detection over processing, transport and delivery of chemical species is of great importance in sensors and biological systems. The transient characteristics of the migration of chemical species reflect the basic properties in the processings of chemical species. Here, we observed the field-configurable proton effects in a laterally coupled transistor gated by phosphorosilicate glass (PSG). The bias on the lateral gate would modulate the interplay between protons and electrons at the PSG/indium-zinc-oxide (IZO) channel interface. Due to the modulation of protons flux within the PSG films, the IZO channel current would be modified correspondingly. The characteristic time for the proton gating is estimated to be on the order of 20 ms. Such laterally coupled oxide based transistors with proton gating are promising for low-cost portable biosensors and neuromorphic system applications. PMID:25741771

Liu, Ning; Zhu, Li Qiang; Xiao, Hui; Wan, Chang Jin; Liu, Yang Hui; Chao, Jin Yu

2015-03-25

174

Nanocellulose coupled flexible polypyrrole@graphene oxide composite paper electrodes with high volumetric capacitance.  

PubMed

A robust and compact freestanding conducting polymer-based electrode material based on nanocellulose coupled polypyrrole@graphene oxide paper is straightforwardly prepared via in situ polymerization for use in high-performance paper-based charge storage devices, exhibiting stable cycling over 16,000 cycles at 5 A g(-1) as well as the largest specific volumetric capacitance (198 F cm(-3)) so far reported for flexible polymer-based electrodes. PMID:25630958

Wang, Zhaohui; Tammela, Petter; Strømme, Maria; Nyholm, Leif

2015-02-28

175

Intramolecular Anodic Olefin Coupling Reactions: Using Competition Studies to Probe the Mechanism of Oxidative Cyclization Reactions  

PubMed Central

A competition experiment was designed so that the relative rates of anodic cyclization reactions under various electrolysis conditions can be determined. Reactions with ketene dithioacetal and enol ether-based substrates that use lithium methoxide as a base were shown to proceed through radical cation intermediates that were trapped by a sulfonamide anion. Results for the oxidative coupling of a vinyl sulfide with a sulfonamide anion using the same conditions were consistent with the reaction proceeding through a nitrogen-radical. PMID:20302359

Xu, Hai-Chao; Moeller, Kevin D.

2014-01-01

176

Facile synthesis of dibranched conjugated dienes via palladium-catalyzed oxidative coupling of N-tosylhydrazones.  

PubMed

A facile and highly regioselective Pd-catalyzed oxidative coupling of N-tosylhydrazones providing efficient access to 2,3-disubstituted-1,3-butadienes has been developed. This process features readily available starting materials and mild reaction conditions. Further transformations of the obtained dibranched 1,3-dienes, through Diels-Alder reactions and indene synthesis, are also demonstrated, which reveal their great potential for synthetic utility. PMID:23991430

Jiang, Huanfeng; He, Li; Li, Xianwei; Chen, Huoji; Wu, Wanqing; Fu, Wei

2013-10-14

177

A Critical Assessment of Li\\/MgO-Based Catalysts for the Oxidative Coupling of Methane  

Microsoft Academic Search

Li\\/MgO is one of the most frequently investigated catalysts for the oxidative coupling of methane. Besides catalytic testing, it is also a suitable system to perform surface science experiments and quantum chemical calculations, which is not possible for many other active catalysts. However, the real structure of Li\\/MgO, the nature of the active center and the structure - activity relationship

Sebastian Arndt; Guillaume Laugel; Sergey Levchenko; Raimund Horn; Manfred Baerns; Matthias Scheffler; Robert Schlögl; Reinhard Schomäcker

2011-01-01

178

Intramolecular anodic olefin coupling reactions: using competition studies to probe the mechanism of oxidative cyclization reactions.  

PubMed

A competition experiment was designed so that the relative rates of anodic cyclization reactions under various electrolysis conditions can be determined. Reactions with ketene dithioacetal and enol ether-based substrates that use lithium methoxide as a base were shown to proceed through radical cation intermediates that were trapped by a sulfonamide anion. Results for the oxidative coupling of a vinyl sulfide with a sulfonamide anion using the same conditions were consistent with the reaction proceeding through a nitrogen-radical. PMID:20302359

Xu, Hai-Chao; Moeller, Kevin D

2010-04-16

179

Oxidative coupling of methane over lanthana catalysts. I. Identification and role of specific active sites  

SciTech Connect

The present work aims at coorelating the surface characteristics of a {open_quotes}working{close_quotes} catalyst under the conditions of the oxidative coupling of methane (OCM) with mechanistic aspects of the reaction deduced from transient experiments focused on the total oxidation pathway. Several lanthana samples with variable surface area and morphology are tested with a view to identifying the exact nature of OCM-specific active sites. The lanthana surface, characterized by XPS, TEM, XRD, FTIR, and in situ DRIFT spectroscopy, appears to be mostly decarbonated and dehydroxylated under reaction conditions. Low coordination sites localized on step edges are related to the total oxidation pathway, while basic sites associated with oxygen vacancies enable the oxygen activation leading to the initial methane activation. Structure sensitivity effects are explained within this proposal of differentiated sites on a typical OCM catalyst. 32 refs., 13 figs., 4 tabs.

Lacombe, S.; Geantet, C.; Mirodatos, C. [Institut de Recherches sur la Catalyse, Villeurbanne (France)] [Institut de Recherches sur la Catalyse, Villeurbanne (France)

1995-02-01

180

Sulfide Oxidation Coupled to Arsenate Reduction by a Diverse Microbial Community in a Soda Lake†  

PubMed Central

We characterized the arsenate-reducing, sulfide-oxidizing population of Mono Lake, California, by analyzing the distribution and diversity of rrnA, cbbL, and dissimilatory arsenate reductase (arrA) genes in environmental DNA, arsenate-plus sulfide-amended lake water, mixed cultures, and isolates. The arsenate-reducing community was diverse. An organism represented by an rrnA sequence previously retrieved from Mono Lake and affiliated with the Desulfobulbaceae (Deltaproteobacteria) appears to be an important member of the arsenate-reducing, sulfide-oxidizing community. Sulfide oxidation coupled with arsenate reduction appears to proceed via a two-electron transfer, resulting in the production of arsenite and an intermediate S compound that is subsequently disproportionated. A realgar-like As/S mineral was formed in some experiments. PMID:16517653

Hollibaugh, James T.; Budinoff, Charles; Hollibaugh, Ryan A.; Ransom, Briana; Bano, Nasreen

2006-01-01

181

A model for coupled sulfate reduction and methane oxidation in the sediments of Saanich Inlet  

NASA Astrophysics Data System (ADS)

A methane-sulfate coupled reaction diffusion model has been developed to describe the inverse relationship commonly observed between methane and sulfate concentrations in the pore waters of anoxic marine sediments. The sediment column was divided into two zones; an upper zone where diagenetic reaction rates are limited by the concentration of oxidizable organic matter and a lower zone in which reaction rates are limited by the concentration of oxidizing agent - sulfate. For each zone differential equations describing the distribution of methane and sulfate were derived. The boundary conditions used to solve these equations resulted in a set of four coupled equations. When fit to data from Saanich Inlet (B.C., Canada) and Skan Bay (Alaska) the model not only reproduces the observed methane and sulfate pore water concentration profiles but also accurately predicts the methane oxidation and sulfate reduction rates. Maximum methane oxidation rates occur at the transition boundary from the upper to the lower layer. In Saanich Inlet sediments from 23 to 40% of the downward sulfate flux is consumed in methane oxidation while in Skan Bay this value is only about 12%.

Devol, A. H.; Anderson, J. J.; Kuivila, K.; Murray, J. W.

1984-05-01

182

Application of dried blood spots combined with high-performance liquid chromatography coupled with electrospray ionisation tandem mass spectrometry for simultaneous quantification of vincristine and actinomycinD  

Microsoft Academic Search

A sensitive, specific and efficient high-performance liquid chromatography-tandem mass spectrometry assay for the simultaneous\\u000a determination of vincristine and actinomycin-D in human dried blood spots is presented. Dried blood spots were punched out\\u000a of a collection paper with a 0.25-in.-diameter punch. The analytes were extracted from the punched-out disc using sonication\\u000a during 15 min in a mixture of acetonitrile–methanol–water (1:1:1, v\\/v\\/v) containing

Carola W. N. Damen; Hilde Rosing; Jan H. M. Schellens; Jos H. Beijnen

2009-01-01

183

A high-performance liquid chromatography-tandem mass spectrometry method coupled with protein precipitation for determination of granisetron in human plasma and its application to a comparative pharmacokinetic study.  

PubMed

A rapid, simple and validated method based on liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) has been developed for the determination of granisetron in human plasma. Plasma samples were pre-purified by protein precipitation procedure. The chromatographic separation was achieved with Synergi Polar-RP (75?×?2 mm, 4 µm) column using a mixture of 5 mm pH4.0 ammonium formate and methanol (300:316, v/v) under isocratic conditions at a flow rate of 0.3 mL/min. The detection was performed on a triple quadrupole tandem mass spectrometer in multiple reaction monitoring mode using positive electrospray ionization. The analysis time was about 2.5 min. The method was fully validated over the concentration range 0.1-10 ng/mL. The lower limit of quantification was 0.1 ng/mL. Inter- and intra-batch precision was <6.1% and the accuracy was within 95.6-100.0%. The mean extraction recovery was 96.3%. Selectivity, matrix effect and stability were also validated. The method was applied to the comparative pharmacokinetic study of granisetron in Chinese healthy subjects. PMID:24811001

Zhou, Ying; Jiang, Ji; Hu, Pei; Wang, Hongyun

2014-12-01

184

Electric-induced oxide breakdown of a charge-coupled device under femtosecond laser irradiation.  

PubMed

A femtosecond laser provides an ideal source to investigate the laser-induced damage of a charge-coupled device (CCD) owing to its thermal-free and localized damage properties. For conventional damage mechanisms in the nanosecond laser regime, a leakage current and degradation of a point spread function or modulation transfer function of the CCD are caused by the thermal damages to the oxide and adjacent electrodes. However, the damage mechanisms are quite different for a femtosecond laser. In this paper, an area CCD was subjected to Ti: sapphire laser irradiation at 800 nm by 100 fs single pulses. Electric-induced oxide breakdown is considered to be the primary mechanism to cause a leakage current, and the injured oxide is between the gate and source in the metal-oxide semiconductor field-effect transistor (MOSFET) structure for one CCD pixel. Optical microscopy and scanning electron microscopy are used to investigate the damaged areas and the results show that the electrodes and the oxide underneath are not directly affected by the femtosecond laser, which helps to get rid of the conventional damage mechanisms. For the primary damage mechanism, direct damage by hot carriers, anode hole injection, and an enlarged electric field in the insulating layer are three possible ways to cause oxide breakdown. The leakage current is proved by the decrease of the resistance of electrodes to the substrate. The output saturated images and the dynamics of an area CCD indicate that the leakage current is from an electrode to a light sensing area (or gate to source for a MOSFET), which proves the oxide breakdown mechanism. PMID:24216654

Gao, Liuzheng; Zhu, Zhiwu; Shao, Zhengzheng; Cheng, Xiang'ai; Chang, Shengli

2013-11-01

185

Cu-Catalyzed Aerobic Oxidative Three-Component Coupling Route to N-Sulfonyl Amidines via an Ynamine Intermediate.  

PubMed

Cu-catalyzed aerobic oxidative three-component coupling of a terminal alkyne, secondary amine, and sulfonamide enables efficient synthesis of amidines. The use of Cu(OTf)2 (5 mol %) produces amidines selectively without Glaser-Hay alkyne homocoupling products. Preliminary studies suggest that the reaction pathway involves initial oxidative coupling of the terminal alkyne with the secondary amine, followed by hydroamidation of the ynamine intermediate with the sulfonamide. PMID:25594112

Kim, Jinho; Stahl, Shannon S

2015-02-20

186

Asymmetric tandem organic solar cells  

NASA Astrophysics Data System (ADS)

Organic photovoltaics (OPVs) is an area that has attracted much attention recently as a potential low cost, sustainable source of energy with a good potential for full-scale commercialisation. Understanding the factors that determine the efficiency of such cells is therefore a high priority, as well as developing ways to boost efficiency to commercially-useful levels. In addition to an intensive search for new materials, significant effort has been spent on ways to squeeze more performance out of existing materials, such as multijunction cells. This thesis investigates double junction tandem cells in the context of small molecule organic materials. . Two different organic electron donor materials, boron subphthalocyanine chloride (SubPc) and aluminium phthalocyanine chloride (ClAlPc) were used as donors in heterojunctions with C60 to create tandem cells for this thesis. These materials have been previously used for solar cells and the absorption spectra of the donor materials complement each other, making them good candidates for tandem cell architectures. The design of the recombination layer between the cells is considered first, with silver nanoparticles demonstrated to work well as recombination centres for charges from the front and back sub-cells, necessary to avoid a charge build-up at the interface. The growth conditions for the nanoparticles are optimised, with the tandem cells outperforming the single heterojunction architecture. Optical modelling is considered as a method to improve the understanding of thin film solar cells, where interference effects from the reflective aluminium electrode are important in determining the magnitude of absorption a cell can achieve. The use of such modelling is first demonstrated in hybrid solar cells based on a SubPc donor with a titanium oxide (TiOx) acceptor; this system is ideal for observing the effects of interference as only the SubPc layer has significant absorption. The modelling is then applied to tandem cells where it is used to predict the short-circuit current (Jsc) generation of the sub-cells, which is not accessible experimentally. Current-matching is then used to predict the Jsc of the complete tandem device. . As a support to the optical modelling, ellipsometry measurements of thin films of ClAlPc are presented. These films of known thickness are analysed to extract the complex refractive index for use in optical modelling calculations. A dependence of the complex refractive index on film thickness and substrate is also noted. Finally, the external quantum efficiency (EQE) technique is considered as applied to solar cells, and an additional method is proposed to characterise current balancing in asymmetric tandem cells under illumination. This technique is verified experimentally by two separate sets of data..

Howells, Thomas J.

187

A simulated countercurrent moving-bed chromatographic reactor for the oxidative coupling of methane: Experimental results  

SciTech Connect

The oxidative coupling reaction of methane (OCM) represents a potential commercial ethylene production route. However, the highest reported yields do not exceed 20%. The methane coupling reaction is accompanied by the undesired conversion of methane to carbon oxides. The relative amount of oxygen and methane along with other parameters, including temperature, determine the favored reaction pathway. High hydrocarbon to oxygen feed ratios give high ethane/ethylene selectivities but at the expense of the hydrocarbon conversion. When the methane to oxygen feed ratio is low, combustion is favored. The simulated countercurrent moving-bed chromatographic reactor (SCMCR) is applied to the OCM. A modified experimental configuration is designed and evaluated. A four-section apparatus, each containing a reaction and two separation columns, is used to quickly separate the reactants and products using the principles of simulated countercurrent flow. Simultaneous reaction and separation of the reactive products column is desired, but unattainable because of an incompatibility between OCM reaction and separation temperatures. Microreactor yields with a samarium oxide catalyst gives yields between 2% and 10%. Yields as high as 50% are observed with the same catalyst and run conditions in the SCMCR. These yields are significantly higher than previously reported values. The effects of temperature, feed switching time, and methane to oxygen feed ratio have been investigated. The reactor, while not fully optimized, does give promise as an alternative production method for ethylene.

Tonkovich, A.L.Y. [Pacific Northwest Lab., Richland, WA (United States); Carr, R.W. [Univ. of Minnesota, Minneapolis, MN (United States). Dept. of Chemical Engineering and Materials Sciences

1994-09-01

188

Base-promoted cross-dehydrogenative coupling of quinoline N-oxides with 1,3-azoles.  

PubMed

An efficient cross-dehydrogenative coupling of quinoline N-oxides and 1,3-azoles has been developed under external oxidant and metal free conditions. The desired products were isolated in good to excellent yields for 26 examples. This methodology provides a practical pathway to biheteroaryls and features high practicality, high efficiency, and environmental friendliness. PMID:25738406

Chen, Xiaopei; Cui, Xiuling; Yang, Fangfang; Wu, Yangjie

2015-03-20

189

Catalytic oxidation of CO by N2O conducted via the neutral oxide cluster couple VO2/VO3.  

PubMed

Neutral vanadium and cobalt oxide clusters are generated at the same time employing a V-Co mixed target. Experimental results indicate that the reaction VO2 + N2O ? VO3 + N2 occurs in a fast flow reactor. This interpretation is further supported for a gas mixture of CO and N2O in the flow cell: regeneration of VO2 is observed for this case via the reaction VO3 + CO ? VO2 + CO2. A full catalytic cycle for the reaction N2O + CO ? N2 + CO2 is thus complete at room temperature enabled by the VO2/VO3 cluster couple. DFT calculations demonstrate that the entire catalytic process is overall barrierless and reproduce the experimental results quite well. PMID:23685848

Wang, Zhe-Chen; Yin, Shi; Bernstein, Elliot R

2013-07-01

190

Rapid identification of synthetic colorants in food samples by using indium oxide nanoparticle-functionalized porous polymer monolith coupled with HPLC-MS/MS.  

PubMed

A synthetic protocol for the preparation of an indium oxide nanoparticle-functionalized poly(methacrylic acid-glycidyl methacrylate-ethylene dimethacrylate-ethanediamine) monolithic column is reported. Various techniques, including scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermal gravimetric analysis-derivative thermogravimetric analysis were employed to characterize the synthesized monolith. The modified monolithic column was coupled with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) for determining synthetic colorants in various food samples. Under optimized conditions, good linearity was obtained for all the targets with squared regression coefficients greater than 0.9982. The limits of detection (S/N = 3) for 12 synthetic colorants were in the range of 0.012-2.97 ?g kg(-1). The intra-day and inter-day relative standard deviations, ranging from 2.7% to 8.5%, were within the acceptable range. The developed method was successfully applied to the determination of synthetic colorants in food samples (candy, milk, jelly, jam, canned food, juice, and carbonated drink). Target recoveries at different spiked levels ranged from 73.5% to 112.1% with relative standard deviations of less than 10.3%. PMID:25313528

Qi, Ruifang; Zhou, Xiao; Li, Xiqian; Ma, Jiutong; Lu, Chunmei; Mu, Jun; Zhang, Xuguang; Jia, Qiong

2014-12-01

191

Micro-solid phase extraction coupled with high-performance liquid chromatography-tandem mass spectrometry for the determination of stimulants, hallucinogens, ketamine and phencyclidine in oral fluids.  

PubMed

A confirmatory method for the determination of illicit drugs based on micro-solid phase extraction with modified tips, made of a functionalized fiberglass with apolar chains of octadecylsilane into monolithic structure, has been developed in this study. Drugs belonging to different chemical classes, such as amphetamine, methamphetamine, methylenedioxyamphetamine, methylenedioxyethylamphetamine, methylenedioxymethylamphetamine, cocaine, benzoylecgonine, ketamine, mescaline, phencyclidine and psilocybine were analyzed. The quantitation was performed by liquid chromatography-tandem mass spectrometry and the analytes were detected in positive ionization by means of an electrospray source. The limits of quantification ranged between 0.3 ng mL(-1) for cocaine and 4.9 ng mL(-1) for psilocybine, with coefficients of determination (r(2)) >0.99 for all the analytes as recommended in the guidelines of Society of Forensic Toxicologists-American Association Forensic Sciences. PMID:20800724

Sergi, Manuel; Compagnone, Dario; Curini, Roberta; D'Ascenzo, Giuseppe; Del Carlo, Michele; Napoletano, Sabino; Risoluti, Roberta

2010-08-24

192

Quantitative determination of plant phenolics in Urtica dioica extracts by high-performance liquid chromatography coupled with tandem mass spectrometric detection.  

PubMed

A method for quantification of 45 plant phenolics (including benzoic acids, cinnamic acids, flavonoid aglycones, C- and O-glycosides, coumarins, and lignans) in plant extracts was developed, based on reversed phase HPLC separation of extract components, followed by tandem mass spectrometric detection. The phenolic profile of 80% MeOH extracts of the stinging nettle (Urtica dioica L.) herb, root, stem, leaf and inflorescence was obtained by using this method. Twenty-one of the investigated compounds were present at levels above the reliable quantification limit, with 5-O-caffeoylquinic acid, rutin and isoquercitrin as the most abundant. The inflorescence extracts were by far the richest in phenolics, with the investigated compounds amounting 2.5-5.1% by weight. As opposed to this, the root extracts were poor in phenolics, with only several acids and derivatives being present in significant amounts. The results obtained by the developed method represent the most detailed U. dioica chemical profile so far. PMID:24054211

Or?i?, Dejan; Franciškovi?, Marina; Bekvalac, Kristina; Svir?ev, Emilija; Beara, Ivana; Lesjak, Marija; Mimica-Duki?, Neda

2014-01-15

193

Catalytic partial oxidation coupled with membrane purification to improve resource and energy efficiency in syngas production.  

PubMed

Catalytic partial oxidation coupled with membrane purification is a new process scheme to improve resource and energy efficiency in a well-established and large scale-process like syngas production. Experimentation in a semi industrial-scale unit (20?Nm(3) ?h(-1) production) shows that a novel syngas production scheme based on a pre-reforming stage followed by a membrane for hydrogen separation, a catalytic partial oxidation step, and a further step of syngas purification by membrane allows the oxygen-to-carbon ratio to be decreased while maintaining levels of feed conversion. For a total feed conversion of 40?%, for example, the integrated novel architecture reduces oxygen consumption by over 50?%, with thus a corresponding improvement in resource efficiency and an improved energy efficiency and economics, these factors largely depending on the air separation stage used to produce pure oxygen. PMID:25571881

Iaquaniello, G; Salladini, A; Palo, E; Centi, G

2015-02-01

194

Simultaneous determination of clozapine and its N-desmethyl and N-oxide metabolites in plasma by liquid chromatography/electrospray tandem mass spectrometry and its application to plasma level monitoring in schizophrenic patients.  

PubMed

A liquid chromatography tandem mass spectrometry (LC-MS-MS) assay method for the simultaneous determination of clozapine and its N-desmethyl (norclozapine) and N-oxide metabolites in human plasma is described. The compounds were extracted from plasma by a single step liquid-liquid extraction procedure and analyzed using a high performance liquid chromatography electrospray tandem mass spectrometer system. The compounds were eluted isocratically on a C-18 column, ionized using positive ion atmospheric pressure electrospray ionization method by a TurboIonspray source and analyzed using multiple reaction monitoring mode. The ion transitions monitored were m/z 327 --> m/z 270 for clozapine, m/z 313 --> m/z 192 for norclozapine, m/z 343 --> m/z 256 for clozapine-N-oxide and m/z 421--> m/z 201 for internal standard. The standard curves of clozapine, norclozapine and clozapine-N-oxide were linear over the range of 1 ng/ml to 1000 ng/ml when 0.5 ml of plasma was used for the analysis (r(2) >0.998). Three pooled plasma samples collected from patients who were treated with clozapine were used as long-term quality control samples to check the validity of spiked standard curve samples made at various times. The intra- and inter-assay variations for the spiked standard curve and quality control samples were less than 14%. These variations for the long-term patient quality control samples were less than 11%. The LC-MS-MS assay for simultaneous determination of clozapine, norclozapine and clozapine-N-oxide reported here is highly specific, sensitive, accurate and rapid. This method is currently being used for the plasma level monitoring of clozapine and its N-desmethyl and N-oxide metabolites in patients treated with clozapine. The plasma levels of clozapine, norclozapine and clozapine-N-oxide varied widely within and among patients. The data revealed that the norclozapine and clozapine N-oxide metabolites were present at about 58%+/-14% and 17%+/-6% of clozapine concentrations in plasma, respectively. PMID:11470207

Aravagiri, M; Marder, S R

2001-09-01

195

Solventless oxidative coupling of amines to imines by using transition-metal-free metal-organic frameworks.  

PubMed

A highly efficient, simple, and versatile transition-metal-free metal-organic framework catalytic system is proposed for the oxidative coupling of amines to imines. The catalytic protocol features high activities and selectivities to target products; compatibility with a variety of substrates, including aliphatic amines and secondary amines; and the possibility to efficiently and selectively promote amine cross-coupling reactions. A high stability and recyclability of the catalyst is also observed under the investigated conditions. Insights into the reaction mechanism indicate the formation of a superoxide species able to efficiently promote oxidative couplings. PMID:24801486

Qiu, Xuan; Len, Christophe; Luque, Rafael; Li, Yingwei

2014-06-01

196

Tandem robot control system and method for controlling mobile robots in tandem  

SciTech Connect

A control system for controlling mobile robots provides a way to control mobile robots, connected in tandem with coupling devices, to navigate across difficult terrain or in closed spaces. The mobile robots can be controlled cooperatively as a coupled system in linked mode or controlled individually as separate robots.

Hayward, David R. (Albuquerque, NM); Buttz, James H. (Albuquerque, NM); Shirey, David L. (Albuquerque, NM)

2002-01-01

197

Identification and quantification of grapefruit juice furanocoumarin metabolites in urine: an approach based on ultraperformance liquid chromatography coupled to linear ion trap-Orbitrap mass spectrometry and solid-phase extraction coupled to ultraperformance liquid chromatography coupled to triple quadrupole-tandem mass spectrometry.  

PubMed

Grapefruit is a rich source of flavonoids but also contains furanocoumarins, which are known to strongly interact with a variety of medications. Thus, characterization of grapefruit furanocoumarin metabolites may help in a better understanding of grapefruit-drug interactions. In the present work, identification of the main metabolites of grapefruit juice furanocoumarins in urine was performed by ultraperformance liquid chromatography (UPLC) coupled to linear ion trap-Orbitrap mass spectrometry (LTQ-Orbitrap). Glucuronides of 6',7'-dihydroxybergamottin and a hydroxybergamottin-like metabolite were identified for the first time as grapefruit juice metabolites. Afterward, a fast and sensitive method based on solid-phase extraction (SPE) and UPLC coupled to triple quadrupole-tandem mass spectrometry (QqQ-MS/MS) was developed for determination of the identified metabolites in urine. The proposed method was applied to urine samples of five volunteers after intakes of moderate doses of grapefruit, lemon, and orange juices. Furanocoumarin metabolites were only detected in urines after consumption of grapefruit juice. PMID:24568314

Regueiro, Jorge; Vallverdú-Queralt, Anna; Negreira, Noelia; Simal-Gándara, Jesús; Lamuela-Raventós, Rosa M

2014-03-01

198

The Role of Ile87 of CYP158A2 in Oxidative Coupling Reaction  

PubMed Central

Both CYP158A1 and CYP158A2 are able to catalyze an oxidative C-C coupling reaction producing biflaviolin or triflaviolin in Streptomyces coelicolor A3(2). The substrate-bound crystal structures of CYP158A2 and CYP158A1 reveal that the side chain of Ile87 in CYP158A2 points to the active site contacting the distal flaviolin molecule, however, the bulkier side chain of Lys90 in CYP158A1 (corresponding to Ile87 in CYP158A2) is toward the distal surface of the protein. These results suggest that these residues could be important in determining product regiospecificity. In order to explore the role of the two residues in catalysis, the reciprocal mutants, Ile87Lys and Lys90Ile, of CYP158A2 and CYP158A1, respectively, were generated and characterized. The mutant Ile87Lys enzyme forms two isomers of biflaviolin instead of three isomers of biflaviolin in wild-type CYP158A2. CYP158A1 containing the substitution of lysine with isoleucine has the same catalytic activity compared with the wild-type CYP158A1. The crystal structure of Ile87Lys showed that the BC loop in the mutant is in a very different orientation compared with the BC loop in both CYP158A1/A2 structures. These results shed light on the mechanism of the oxidative coupling reaction catalyzed by cytochrome P450. PMID:22203090

Zhao, Bin; Bellamine, Aouatef; Lei, Li; Waterman, Michael R.

2012-01-01

199

Ubiquitous long-range antiferromagnetic coupling across the interface between superconducting and ferromagnetic oxides  

NASA Astrophysics Data System (ADS)

The so-called proximity effect is the manifestation, across an interface, of the systematic competition between magnetic order and superconductivity. This phenomenon has been well documented and understood for conventional superconductors coupled with metallic ferromagnets; however it is still less known for oxide materials, where much higher critical temperatures are offered by copper oxide-based superconductors. Here we show that, even in the absence of direct Cu–O–Mn covalent bonding, the interfacial CuO2 planes of superconducting La1.85Sr0.15CuO4 thin films develop weak ferromagnetism associated to the charge transfer of spin-polarised electrons from the La0.66Sr0.33MnO3 ferromagnet. Theoretical modelling confirms that this effect is general to all cuprate/manganite heterostructures and the presence of direct bonding only affects the strength of the coupling. The Dzyaloshinskii–Moriya interaction, also at the origin of the weak ferromagnetism of bulk cuprates, propagates the magnetisation from the interface CuO2 planes into the superconductor, eventually depressing its critical temperature.

de Luca, G. M.; Ghiringhelli, G.; Perroni, C. A.; Cataudella, V.; Chiarella, F.; Cantoni, C.; Lupini, A. R.; Brookes, N. B.; Huijben, M.; Koster, G.; Rijnders, G.; Salluzzo, M.

2014-11-01

200

The role of Ile87 of CYP158A2 in oxidative coupling reaction  

SciTech Connect

Both CYP158A1 and CYP158A2 are able to catalyze an oxidative C-C coupling reaction producing biflaviolin or triflaviolin in Streptomyces coelicolor A3(2). The substrate-bound crystal structures of CYP158A2 and CYP158A1 reveal that the side chain of Ile87 in CYP158A2 points to the active site contacting the distal flaviolin molecule, however, the bulkier side chain of Lys90 in CYP158A1 (corresponding to Ile87 in CYP158A2) is toward the distal surface of the protein. These results suggest that these residues could be important in determining product regiospecificity. In order to explore the role of the two residues in catalysis, the reciprocal mutants, Ile87Lys and Lys90Ile, of CYP158A2 and CYP158A1, respectively, were generated and characterized. The mutant Ile87Lys enzyme forms two isomers of biflaviolin instead of three isomers of biflaviolin in wild-type CYP158A2. CYP158A1 containing the substitution of lysine with isoleucine has the same catalytic activity compared with the wild-type CYP158A1. The crystal structure of Ile87Lys showed that the BC loop in the mutant is in a very different orientation compared with the BC loop in both CYP158A1/A2 structures. These results shed light on the mechanism of the oxidative coupling reaction catalyzed by cytochrome P450.

Zhao, Bin; Bellamine, Aouatef; Lei, Li; Waterman, Michael R. (Vanderbilt)

2012-05-15

201

Control of the neurovascular coupling by nitric oxide-dependent regulation of astrocytic Ca2+ signaling  

PubMed Central

Neuronal activity must be tightly coordinated with blood flow to keep proper brain function, which is achieved by a mechanism known as neurovascular coupling. Then, an increase in synaptic activity leads to a dilation of local parenchymal arterioles that matches the enhanced metabolic demand. Neurovascular coupling is orchestrated by astrocytes. These glial cells are located between neurons and the microvasculature, with the astrocytic endfeet ensheathing the vessels, which allows fine intercellular communication. The neurotransmitters released during neuronal activity reach astrocytic receptors and trigger a Ca2+ signaling that propagates to the endfeet, activating the release of vasoactive factors and arteriolar dilation. The astrocyte Ca2+ signaling is coordinated by gap junction channels and hemichannels formed by connexins (Cx43 and Cx30) and channels formed by pannexins (Panx-1). The neuronal activity-initiated Ca2+ waves are propagated among neighboring astrocytes directly via gap junctions or through ATP release via connexin hemichannels or pannexin channels. In addition, Ca2+ entry via connexin hemichannels or pannexin channels may participate in the regulation of the astrocyte signaling-mediated neurovascular coupling. Interestingly, nitric oxide (NO) can activate connexin hemichannel by S-nitrosylation and the Ca2+-dependent NO-synthesizing enzymes endothelial NO synthase (eNOS) and neuronal NOS (nNOS) are expressed in astrocytes. Therefore, the astrocytic Ca2+ signaling triggered in neurovascular coupling may activate NO production, which, in turn, may lead to Ca2+ influx through hemichannel activation. Furthermore, NO release from the hemichannels located at astrocytic endfeet may contribute to the vasodilation of parenchymal arterioles. In this review, we discuss the mechanisms involved in the regulation of the astrocytic Ca2+ signaling that mediates neurovascular coupling, with a special emphasis in the possible participation of NO in this process. PMID:25805969

Muñoz, Manuel F.; Puebla, Mariela; Figueroa, Xavier F.

2015-01-01

202

A comparative mechanistic study of Cu-catalyzed oxidative coupling reactions with N-phenyltetrahydroisoquinoline.  

PubMed

A comparative mechanistic study of Cu-catalyzed oxidative coupling reactions of N-phenyltetrahydroisoquinoline with different nucleophiles was conducted. Two previously reported combinations of catalyst and oxidant were studied, CuCl(2)·2H(2)O/O(2) and CuBr/tert-butyl hydroperoxide (TBHP). On the basis of a synthetic study with different nucleophiles, the electrophilicity of the intermediate iminium ion was estimated and differences between the two methods were revealed. The key intermediate in the aerobic method is shown to be an iminium ion, formed through oxidation by copper(II), which can react with any nucleophile of sufficient reactivity. The role of oxygen is the reoxidation of the reduced catalyst. In the CuBr/TBHP system, an ?-amino peroxide is proposed as a true intermediate within the catalytic cycle, formed from the amine and TBHP by a Cu-catalyzed radical reaction pathway and acting as a precursor to the iminium ion intermediate. PMID:22338603

Boess, Esther; Schmitz, Corinna; Klussmann, Martin

2012-03-21

203

Liquid chromatography coupled with tandem mass spectrometry to characterise trace levels of cyanobacteria and dinoflagellate toxins in suspended solids and sediments.  

PubMed

Microcystins, anatoxins and okadaic acid are toxins produced by freshwater cyanobacteria and marine dinoflagellates. These toxins have been the responsible for the illness and death of biota and humans. To determine their presence in water during blooms, sensitive analytical methods are needed. In this study, we have developed a new liquid chromatography tandem mass spectrometry (LC-MS/MS) method for fast multiresidue determination of five toxins in suspended material and sediment samples. For each target compound, two selected reaction monitoring (SRM) transitions were optimised. Chromatographic conditions were optimised considering that the compounds analysed had different chemical structure and chromatographic behaviour. Using a Luna C18 column and specific SRM transitions, five phytotoxins were resolved. Method detection limits (MDL) for anatoxin-a, microcystins RR, LR and YR and okadaic acid were 7.1, 3.3, 81.7, 102.8 and 28.8 ng g(-1) dry weight in sediment, respectively. The developed analytical method was successfully applied to analyse the presence of toxins in suspended solids and sediment from Ebro River (NE Spain) and Ebro delta-associated lagoons. Anatoxin-a was detected downstream of the Riba-Roja reservoir with levels ranging from 20 to 1120 ng g(-1) dry weight of suspended solids. Okadaic acid was only detected in three samples collected in the Alfacs Bay (Ebro delta, Spain) affected by Dinophysis blooms in 2012. PMID:25619981

Rivetti, Claudia; Gómez-Canela, Cristian; Lacorte, Silvia; Barata, Carlos

2015-02-01

204

Determination of eight artificial sweeteners and common Stevia rebaudiana glycosides in non-alcoholic and alcoholic beverages by reversed-phase liquid chromatography coupled with tandem mass spectrometry.  

PubMed

The method for the determination of acesulfame-K, saccharine, cyclamate, aspartame, sucralose, alitame, neohesperidin dihydrochalcone, neotame and five common steviol glycosides (rebaudioside A, rebaudioside C, steviol, steviolbioside and stevioside) in soft and alcoholic beverages was developed using high-performance liquid chromatography and tandem mass spectrometry with electrospray ionisation (HPLC-ESI-MS/MS). To the best of our knowledge, this is the first work that presents an HPLC-ESI-MS/MS method which allows for the simultaneous determination of all EU-authorised high-potency sweeteners (thaumatin being the only exception) in one analytical run. The minimalistic sample preparation procedure consisted of only two operations; dilution and centrifugation. Linearity, limits of detection and quantitation, repeatability, and trueness of the method were evaluated. The obtained recoveries at three tested concentration levels varied from 97.0 to 105.7%, with relative standard deviations lower than 4.1%. The proposed method was successfully applied for the determination of sweeteners in 24 samples of different soft and alcoholic drinks. PMID:25471292

Kubica, Pawe?; Namie?nik, Jacek; Wasik, Andrzej

2015-02-01

205

Rapid analysis of three ?-agonist residues in food of animal origin by automated on-line solid-phase extraction coupled to liquid chromatography and tandem mass spectrometry.  

PubMed

An automated online solid-phase extraction with liquid chromatography and tandem mass spectrometry method was developed and validated for the detection of clenbuterol, salbutamol, and ractopamine in food of animal origin. The samples from the food matrix were pretreated with an online solid-phase extraction cartridge by Oasis MCX for <5 min after acid hydrolysis for 30 min. The peak focusing mode was used to elute the target compounds directly onto a C18 column. Chromatographic separation was achieved under gradient conditions using a mobile phase composed of acetonitrile/0.1% formic acid in aqueous solution. Each analyte was detected in two multiple reaction monitoring transitions via an electrospray ionization source in a positive mode. The relative standard deviations ranged from 2.6 to 10.5%, and recovery was between 76.7 and 107.2% at all quality control levels. The limits of quantification of three ?-agonists were in the range of 0.024-0.29 ?g/kg in pork, sausage, and milk powder, respectively. This newly developed method offers high sensitivity and minimum sample pretreatment for the high-throughput analysis of ?-agonist residues. PMID:24916570

Mi, Jiebo; Li, Shujing; Xu, Hong; Liang, Wei; Sun, Tao

2014-09-01

206

Comprehensive determination of polycyclic aromatic hydrocarbons in Chinese herbal medicines by solid phase extraction and gas chromatography coupled to tandem mass spectrometry.  

PubMed

A simple and highly sensitive gas chromatography-tandem mass spectrometry (GC-MS/MS) method combined with solid-phase extraction cleanup was established for the comprehensive determination of 16 Environmental Protection Agency (EPA) polycyclic aromatic hydrocarbons?(PAHs) in various kinds of Chinese herbal medicines (CHMs). A solid-phase extraction (SPE) purification strategy, including three parallel procedures, was developed depending on sample type, and satisfactory purification performances were achieved for all selected CHMs. The limits of detection ranged from 0.12 to 1.08 ?g kg(-1) for the analyzed PAHs. The average recoveries were in the range of 65.9 % to 100.8 %, except for naphthalene (43.8 %-75.9 %), and the relative standard deviations were ?12.8 %. The proposed method was successfully applied to the analysis of PAHs in 24 CHMs including five roots, three stems, four flowers, two fruits, four seeds, three leaves, and three barks. In the samples analyzed, all 16 PAHs are present. Their sum ranges from 21.1 to 2236.3 ?g kg(-1). The entire procedure was shown to be effective and conveniently fast, and may serve as an alternative screening protocol for the determination of PAHs in CHMs. PMID:25636228

Cui, Zongyan; Ge, Na; Zhang, Ang; Liu, Yongming; Zhang, Jinjie; Cao, Yanzhong

2015-03-01

207

Multi-analyte high performance liquid chromatography coupled to high resolution tandem mass spectrometry method for control of pesticide residues, mycotoxins, and pyrrolizidine alkaloids.  

PubMed

A new reliable and highly sensitive method based on high performance liquid chromatographic (HPLC) separation and high resolution tandem mass spectrometric detection (HRMS/MS) has been developed and validated for determination of 323 pesticide residues, 55 mycotoxins, and 11 plant toxins represented by pyrrolizidine alkaloids. The method was validated for three matrices, leek, wheat, and tea differing in nature/amount of co-extracts that may cause various matrix effects. For target analytes isolation, optimized QuEChERS-based (quick, easy, cheap, effective, rugged, and safe) extraction procedure was employed. Spectral HRMS/MS library has been established providing an entire spectrum of fragment ions for each analyte, which allows unbiased identification and confirmation of target compounds. The limits of quantification (LOQs) of target analytes were below 10?gkg(-1) for 82%, 81%, and 61% for matrices leek, wheat, and tea, respectively. Recoveries were in the acceptable range (70-120%) according to SANCO/12571/2013 for most of target analytes, except for highly polar 'masked' mycotoxin deoxynivalenol-3-glucoside with recoveries 35%, 47%, and 42% for matrices leek, wheat, and tea, respectively. The linearities of calibration curves expressed as coefficients of determination were in the range of 0.9661-1.000, and repeatabilities expressed as relative standard deviations (RSDs) at LOQs lied in the range of 0.25-13.51%. The trueness of the method was verified using several certified reference materials (CRMs) and proficiency test samples. PMID:25732310

Dzuman, Zbynek; Zachariasova, Milena; Veprikova, Zdenka; Godula, Michal; Hajslova, Jana

2015-03-10

208

Simultaneous determination of ?-Hydroxybutyrate (GHB) and its analogues (GBL, 1.4-BD, GVL) in whole blood and urine by liquid chromatography coupled to tandem mass spectrometry.  

PubMed

A simple liquid chromatography-tandem mass spectrometry (LC-MS-MS) method has been developed and validated for simultaneous identification and quantification of ?-hydroxybutyrate (GHB), ?-butyrolactone (GBL), 1.4-butanediol (1.4-BD), and ?-valerolactone (GVL) in whole blood from forensic cases. The sample preparation of whole blood involved protein precipitation by acidic methanol. Urine samples were diluted and evaluated in relation to a control at the cutoff concentration. Hexadeutero GHB (GHB-d(6)) was used as the internal standard. Separation was achieved by reversed-phase chromatography, and detection was by MS-MS in MRM mode. The linear range for all compounds was from 1.0 to 100 mg/kg in whole blood with a limit of quantification of about 1 mg/kg. The method was validated with regards to selectivity, recovery, accuracy and precision, and stability. The method is currently applied to investigations on suspected drug-facilitated sexual assaults, driving under the influence of drugs, and general intoxication with these substances. PMID:21219697

Johansen, Sys Stybe; Windberg, Charlotte Norup

2011-01-01

209

Amino acid derived CuII compounds as catalysts for asymmetric oxidative coupling of 2-naphthol.  

PubMed

We report the synthesis and characterization of several novel aminopyridine - L-amino acid derived Cu(II)-complexes. The ligands are prepared by a one-pot reductive alkylation of the L-amino acid scaffold and the respective aminopyridine Cu(II)-complexes were obtained by reaction with CuCl2 or Cu(acetato)2. All compounds were characterized by spectroscopic techniques, as well as ESI-MS. Two of the Cu(II)-complexes were characterized by single-crystal X-ray diffraction, one of them, [Cu(II)(L)(CH3COO)] (HL = (S)-3-phenyl-2-(pyridin-2-ylmethylamino)propanoic acid), being the first ever reported aminopyridine-class Cu(II) complex bearing a tridentate N,N,O donor set and a monodentate acetato ligand. The complexes are tested as catalysts in the oxidative coupling of 2-naphthol in organic solvent-water mixtures using dioxygen as the terminal oxidant. The effect of variables such as ligand denticity and substituents, as well as solvent, temperature and oxidant intake, on the overall performance is studied. In general, moderate to low conversions of 2-naphthol to 1,1'-bi-2-naphthol (BINOL) are obtained. The catalysts also showed moderate to low enantioselectivity. Some aspects of the reaction mechanism were elucidated by spectroscopy, electrochemical and theoretical studies. It was found that basic additives are important for activity, but these also increase the formation of secondary oxidation products. The addition of peroxide scavengers such as KI resulted in an increase of conversion, the yield of BINOL and enantioselectivity. PMID:25434677

Adão, Pedro; Barroso, Sónia; Carvalho, M Fernanda N N; Teixeira, Carlos M; Kuznetsov, Maxim L; Pessoa, João Costa

2015-01-28

210

Weathering of the Rio Blanco quartz diorite, Luquillo Mountains, Puerto Rico: Coupling oxidation, dissolution, and fracturing  

USGS Publications Warehouse

In the mountainous Rio Icacos watershed in northeastern Puerto Rico, quartz diorite bedrock weathers spheroidally, producing a 0.2-2 m thick zone of partially weathered rock layers (???2.5 cm thickness each) called rindlets, which form concentric layers around corestones. Spheroidal fracturing has been modeled to occur when a weathering reaction with a positive ??V of reaction builds up elastic strain energy. The rates of spheroidal fracturing and saprolite formation are therefore controlled by the rate of the weathering reaction. Chemical, petrographic, and spectroscopic evidence demonstrates that biotite oxidation is the most likely fracture-inducing reaction. This reaction occurs with an expansion in d (0 0 1) from 10.0 to 10.5 A??, forming 'altered biotite'. Progressive biotite oxidation across the rindlet zone was inferred from thin sections and gradients in K and Fe(II). Using the gradient in Fe(II) and constraints based on cosmogenic age dates, we calculated a biotite oxidation reaction rate of 8.2 ?? 10-14 mol biotite m-2 s-1. Biotite oxidation was documented within the bedrock corestone by synchrotron X-ray microprobe fluorescence imaging and XANES. X-ray microprobe images of Fe(II) and Fe(III) at 2 ??m resolution revealed that oxidized zones within individual biotite crystals are the first evidence of alteration of the otherwise unaltered corestone. Fluids entering along fractures lead to the dissolution of plagioclase within the rindlet zone. Within 7 cm surrounding the rindlet-saprolite interface, hornblende dissolves to completion at a rate of 6.3 ?? 10-13 mol hornblende m-2 s-1: the fastest reported rate of hornblende weathering in the field. This rate is consistent with laboratory-derived hornblende dissolution rates. By revealing the coupling of these mineral weathering reactions to fracturing and porosity formation we are able to describe the process by which the quartz diorite bedrock disaggregates and forms saprolite. In the corestone, biotite oxidation induces spheroidal fracturing, facilitating the influx of fluids that react with other minerals, dissolving plagioclase and chlorite, creating additional porosity, and eventually dissolving hornblende and precipitating secondary minerals. The thickness of the resultant saprolite is maintained at steady state by a positive feedback between the denudation rate and the weathering advance rate driven by the concentration of pore water O2 at the bedrock-saprolite interface. ?? 2008 Elsevier Ltd. All rights reserved.

Buss, H.L.; Sak, P.B.; Webb, S.M.; Brantley, S.L.

2008-01-01

211

Weathering of the Rio Blanco Quartz Diorite, Luquillo Mountains, Puerto Rico: Coupling Oxidation, Dissolution, And Fracturing  

SciTech Connect

In the mountainous Rio Icacos watershed in northeastern Puerto Rico, quartz diorite bedrock weathers spheroidally, producing a 0.2-2 m thick zone of partially weathered rock layers ({approx}2.5 cm thickness each) called rindlets, which form concentric layers around corestones. Spheroidal fracturing has been modeled to occur when a weathering reaction with a positive {Delta}V of reaction builds up elastic strain energy. The rates of spheroidal fracturing and saprolite formation are therefore controlled by the rate of the weathering reaction. Chemical, petrographic, and spectroscopic evidence demonstrates that biotite oxidation is the most likely fracture-inducing reaction. This reaction occurs with an expansion in d (0 0 1) from 10.0 to 10.5 {angstrom}, forming 'altered biotite'. Progressive biotite oxidation across the rindlet zone was inferred from thin sections and gradients in K and Fe(II). Using the gradient in Fe(II) and constraints based on cosmogenic age dates, we calculated a biotite oxidation reaction rate of 8.2 x 10{sup -14} mol biotite m{sup -2} s{sup -1}. Biotite oxidation was documented within the bedrock corestone by synchrotron X-ray microprobe fluorescence imaging and XANES. X-ray microprobe images of Fe(II) and Fe(III) at 2 {micro}m resolution revealed that oxidized zones within individual biotite crystals are the first evidence of alteration of the otherwise unaltered corestone. Fluids entering along fractures lead to the dissolution of plagioclase within the rindlet zone. Within 7 cm surrounding the rindlet-saprolite interface, hornblende dissolves to completion at a rate of 6.3 x 10{sup -13} mol hornblende m{sup -2} s{sup -1}: the fastest reported rate of hornblende weathering in the field. This rate is consistent with laboratory-derived hornblende dissolution rates. By revealing the coupling of these mineral weathering reactions to fracturing and porosity formation we are able to describe the process by which the quartz diorite bedrock disaggregates and forms saprolite. In the corestone, biotite oxidation induces spheroidal fracturing, facilitating the influx of fluids that react with other minerals, dissolving plagioclase and chlorite, creating additional porosity, and eventually dissolving hornblende and precipitating secondary minerals. The thickness of the resultant saprolite is maintained at steady state by a positive feedback between the denudation rate and the weathering advance rate driven by the concentration of pore water O{sub 2} at the bedrock-saprolite interface.

Buss, H.L.; Sak, P.B.; Webb, S.M.; Brantley, S.L.

2009-05-12

212

Experimental study on the oxide trap coupling effect in metal oxide semiconductor field effect transistors with HfO2 gate dielectrics  

NASA Astrophysics Data System (ADS)

In this Letter, the coupling effect between multi-traps in HfO2 gate dielectrics is experimentally studied in scaled high-?/metal-gate metal oxide semiconductor field effect transistors (MOSFETs). Deviated from conventional understanding, mechanism that affects trap coupling is found, which is originated from local carrier density perturbation due to random dopant fluctuation (RDF) in the channel. The competition of conventional Coulomb repulsion effect and RDF induced local carrier density perturbation effect results in the nonmonotonic voltage dependence of trap coupling intensity.

Ren, Pengpeng; Wang, Runsheng; Jiang, Xiaobo; Qiu, Yingxin; Liu, Changze; Huang, Ru

2014-06-01

213

Determination of Phenolic Acids and Flavonoids in Taraxacum formosanum Kitam by Liquid Chromatography-Tandem Mass Spectrometry Coupled with a Post-Column Derivatization Technique  

PubMed Central

A liquid chromatography-tandem mass spectrometry method (LC-MS/MS) was developed for the determination of phenolic acids and flavonoids in a medicinal Chinese herb Taraxacum formosanum Kitam. Initially, both phenolic acids and flavonoids were extracted with 50% ethanol in a water-bath at 60 °C for 3 h and eventually separated into acidic fraction and neutral fraction by using a C18 cartridge. A total of 29 compounds were separated within 68 min by employing a Gemini C18 column and a gradient solvent system of 0.1% formic acid and acetonitrile at a flow rate of 1.0 mL/min. Based on the retention behavior as well as absorption and mass spectra, 19 phenolic acids and 10 flavonoids were identified and quantified in T. formosanum, with the former ranging from 14.1 ?g/g to 10,870.4 ?g/g, and the latter from 9.9 ?g/g to 325.8 ?g/g. For further identification of flavonoids, a post-column derivatization method involving shift reagents such as sodium acetate or aluminum chloride was used and the absorption spectral characteristics without or with shift reagents were compared. An internal standard syringic acid was used for quantitation of phenolic acids, whereas (±) naringenin was found suitable for quantitation of flavonoids. The developed LC-MS/MS method showed high reproducibility, as evident from the relative standard deviation (RSD) values for intra-day and inter-day variability being 1.0–6.8% and 2.0–7.7% for phenolic acids and 3.7–7.4% and 1.5–8.1% for flavonoids, respectively, and thus may be applied for simultaneous determination of phenolic acids and flavonoids in Chinese herb and nutraceuticals. PMID:22312251

Chen, Hung-Ju; Inbaraj, Baskaran Stephen; Chen, Bing-Huei

2012-01-01

214

Detection of 22 antiepileptic drugs by ultra-performance liquid chromatography coupled with tandem mass spectrometry applicable to routine therapeutic drug monitoring.  

PubMed

The purpose of this study was to develop an ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method of 22 antiepileptics for routine therapeutic monitoring. The antiepileptics used in the analyses were carbamazepine, carbamazepine-10,11-epoxide, clobazam, N-desmethylclobazam, clonazepam, diazepam, N-desmethyldiazepam, ethosuximide, felbamate, gabapentin, lamotrigine, levetiracetam, N-desmethylmesuximide, nitrazepam, phenobarbital, phenytoin, primidone, tiagabine, topiramate, valproic acid, vigabatrin and zonisamide. After protein precipitation of 50??L plasma with methanol, the supernatant was diluted with water or was evaporated to dryness and reconstituted with mobile phase in the case of benzodiazepines. Separation was achieved on an Acquity UPLC BEH C?? column with a gradient mobile phase of 10?mm ammonium acetate containing 0.1% formic acid and methanol at a flow rate of 0.4?mL/min. An Acquity TQD instrument in multiple reaction monitoring mode with ion mode switching was used for detection. All antiepileptics were detected and quantified within 10?min, with no endogenous interference. All the calibration curves showed good linearity in the therapeutic range (r² ?

Shibata, Mai; Hashi, Sachiyo; Nakanishi, Haruka; Masuda, Satohiro; Katsura, Toshiya; Yano, Ikuko

2012-12-01

215

Determination and occurrence of phenoxyacetic acid herbicides and their transformation products in groundwater using ultra high performance liquid chromatography coupled to tandem mass spectrometry.  

PubMed

A sensitive method was developed and validated for ten phenoxyacetic acid herbicides, six of their main transformation products (TPs) and two benzonitrile TPs in groundwater. The parent compounds mecoprop, mecoprop-p, 2,4-D, dicamba, MCPA, triclopyr, fluroxypr, bromoxynil, bentazone, and 2,3,6-trichlorobenzoic acid (TBA) are included and a selection of their main TPs: phenoxyacetic acid (PAC), 2,4,5-trichloro-phenol (TCP), 4-chloro-2-methylphenol (4C2MP), 2,4-dichlorophenol (DCP), 3,5,6-trichloro-2-pyridinol (T2P), and 3,5-dibromo-4-hydroxybenzoic acid (BrAC), as well as the dichlobenil TPs 2,6-dichlorobenzamide (BAM) and 3,5-dichlorobenzoic acid (DBA) which have never before been determined in Irish groundwater. Water samples were analysed using an efficient ultra-high performance liquid chromatography (UHPLC) method in an 11.9 min separation time prior to detection by tandem mass spectrometry (MS/MS). The limit of detection (LOD) of the method ranged between 0.00008 and 0.0047 µg·L(-1) for the 18 analytes. All compounds could be detected below the permitted limits of 0.1 µg·L(-1) allowed in the European Union (EU) drinking water legislation. The method was validated according to EU protocols laid out in SANCO/10232/2006 with recoveries ranging between 71% and 118% at the spiked concentration level of 0.06 µg·L(-1). The method was successfully applied to 42 groundwater samples collected across several locations in Ireland in March 2012 to reveal that the TPs PAC and 4C2MP were detected just as often as their parent active ingredients (a.i.) in groundwater. PMID:25514054

McManus, Sarah-Louise; Moloney, Mary; Richards, Karl G; Coxon, Catherine E; Danaher, Martin

2014-01-01

216

Rapid analysis of aflatoxin M1 in milk using dispersive liquid-liquid microextraction coupled with ultrahigh pressure liquid chromatography tandem mass spectrometry.  

PubMed

A simple, rapid, and sensitive method based on simultaneous protein precipitation and extraction of aflatoxin M1 (AFM1) followed by dispersive liquid-liquid microextraction (DLLME) and ultrahigh pressure liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) analysis was developed for the determination of AFM1 in milk samples. In order to precipitate the proteins and extract AFM1 from milk, a sample pretreatment using acetonitrile and NaCl as the extraction/denaturant solvent and salting-out agent, respectively, was optimised. Subsequently, the acetonitrile (upper) phase, containing AFM1, was used as the disperser solvent in DLLME, and extractant (chloroform) and water were added in turn to the extract to perform the DLLME process. The main parameters affecting the extraction efficiency of the whole analytical procedure, such as acetonitrile volume, amount of salt, type and volume of extractant and water volume, were carefully optimised by experimental design. Under optimum conditions, the developed method provides an enrichment factor of 33 and detection and quantification limits (0.6 and 2.0 ng kg(-1), respectively) below the maximum levels imposed by current regulations for AFM1 in milk and infant milk formulae. Recoveries (61.3-75.3%) and repeatability (RSD < 10, n = 3), tested in different types of milk at four AFM1 levels, met the performance criteria required by EC Regulation No. 401/2006. Moreover, the matrix effect on the signal intensity of the analyte was negligible. The proposed method provides a rapid extraction and an accurate determination of AFM1 in milk and formula milk using a simple and inexpensive sample preparation procedure. PMID:23942569

Campone, Luca; Piccinelli, Anna Lisa; Celano, Rita; Russo, Mariateresa; Rastrelli, Luca

2013-10-01

217

DETERMINATION OF URINARY F2-ISOPROSTANES AS AN OXIDAITVE BIOMARKER IN PATIENTS WITH DIABETES MELLITUS TYPE 2 BY LIQUID CHROMATOGRAPHY-ELECTROSPRAY TANDEM MASS SPECTROMETRY  

Microsoft Academic Search

A liquid chromatography tandem mass spectrometry (LC-MS\\/MS)-ion trap coupled with electrospray ionization was described for determination of trace biological molecular, urinary F2- Isoprostanes (F2-IsoPs), a sensitive biomarker of oxidative stress in vivo, in Thai patients with diabetic mellitus (DM) type 2 and compare with normal subjects. Spot urine samples were collected from 28 DM patients and 19 normal subjects and

Atinuch Nartnampong; Supatra Porasuphatana

2008-01-01

218

Glaser oxidative coupling on peptides: stabilization of ?-turn structure via a 1,3-butadiyne constraint.  

PubMed

The Glaser-Eglinton reaction between either two C or N propargylglycine (Pra or NPra) amino acids, in the presence of copper(II), led to cyclic hexa- and octapeptides constrained by a butadiyne bridge. The on-resin cyclization conditions were analyzed and optimized. The consequences of this type of constraint on the three dimensional structure of these hexapeptides and octapeptides were analyzed in details by NMR and molecular dynamics. We show that stabilized short cyclic peptides could be readily prepared via the Glaser oxidative coupling either with a chiral (Pra), or achiral (NPra) residue. The 1,3-butadiyne cyclization, along with disulfide bridged and lactam cyclized hexapeptides expands the range of constrained peptides that will allow exploring the breathing of amino acids around a ?-turn structure. PMID:25456082

Auberger, Nicolas; Pisa, Margherita Di; Larregola, Maud; Chassaing, Gérard; Peroni, Elisa; Lavielle, Solange; Papini, Anna-Maria; Lequin, Olivier; Mallet, Jean-Maurice

2014-12-15

219

Oxidative coupling of methane over lanthana catalysts: II. A mechanistic study using isotope transient kinetics  

SciTech Connect

The elementary steps dealing with the methane and oxygen activation in the reaction of oxidative coupling of methane (OCM) over lanthana catalysts have been investigated by means of state-of-the-art transient kinetic techniques. Methane and oxygen activation over lanthana catalysts are shown to combine reversible and irreversible steps, parallel for methane and consecutive for oxygen. In both processes, the surface residence time of activated species per active site is found to be below the time resolution of 1 ms, characteristic of the temporal analysis of products reactor. Evidence of a strong interaction between gaseous and lattice oxygen and of an inhibiting effect of carbon dioxide on both methane and oxygen activation is also provided. Specific sites pertaining to each of these routes are proposed, accounting for the various kinetic effects which are observed under the OCM conditions.

Lacombe, S.; Mirodatos, C. [Institut de Recherches sur la Catalyse, Villeurbanne (France)] [Institut de Recherches sur la Catalyse, Villeurbanne (France); Zanthoff, H. [Ruhr-Universitaet Bochum (Germany)] [Ruhr-Universitaet Bochum (Germany)

1995-08-01

220

Mechanistic study of silver-mediated furan formation by oxidative coupling.  

PubMed

Density functional calculations and experiments have been carried out to unravel the mechanism of a silver-mediated furan formation by oxidative coupling. Various possible reaction paths were considered and the most favorable channel has been identified on the basis of the calculated solvent-corrected Gibbs free-energy profiles. The mechanism represented by this route consists of a radical and a subsequent ionic route. The silver cation has a double role in the mechanism: it is the oxidant in the radical steps and the catalyst for the ionic steps, which is in accordance with the experimental observations. The two most important aspects of the optimal route are the formation of a silver-acetylide, reacting subsequently with the enolate radical, and the aromatic furan-ring formation in a single step at the latter, ionic segment of the reaction path. Our findings could explain several experimental observations, including the "key-promoter role" of silver, the preference for ionic cyclization, and the reduced reactivity of internal acetylides. PMID:25284602

Daru, János; Benda, Zsuzsanna; Póti, Ádám; Novák, Zoltán; Stirling, András

2014-11-17

221

Oxidative coupling of CH{sub 4} over molybdates: Catalyst performance and characterization  

SciTech Connect

The effect oxidative coupling of methane, a variety of molybdates were used as catalysts with sustained activity for more than 280 h. The reaction was studied by cofeeding methane and oxygen at atmospheric pressure, through continuous conventional flow reactors containing the catalyst. The effects of operating conditions were studied and the optimum reactor temperature to achieve high yields of ethane and ethylene was ca. 700-780 {degrees}C, depending on the reactor dimensions. The influence of reactor dimensions on the distribution of products is also reported. Molybdate catalysts are active and yet resistant to deactivation and sintering. Selectivities X(C{sub 2})% up to 20.0 and 7.0% were observed, respectively. The reactor feed had a CH{sub 4} to O{sub 2} ratio of ca. 1.1. The authors results present the effects of varying several operating conditions and the significant gas-phase products observed were H{sub 2}, C{sub 2}H{sub 4}, C{sub 2}H{sub 6}, C{sub 3}H{sub 6}, H{sub 2}O, and traces of HCHO and CH{sub 3}OH. C{sub 2}H{sub 2} formation was not observed. The main oxidation products were CO{sub 2} and CO. Structural characterization of the molybdates was carried out by elemental analysis, infrared spectroscopy (IR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). 46 refs., 8 figs., 2 tabs.

Kiwi, J.; Thampi, K.R.; Graetzel, M. [Institut de chimie physique, Lausanne (Switzerland)] [and others

1992-02-06

222

One-pot total synthesis of streptindole, arsindoline B and their congeners through tandem decarboxylative deaminative dual-coupling reaction of amino acids with indoles.  

PubMed

This paper described a decarboxylative deaminative dual-coupling reaction of amino acids with indoles to afford BIM scaffolds and its further application to the one-pot total synthesis of natural products. This method featured a stimulating example of activating amino acids in one pot as multi-carbon building blocks for transformation into final targets which are equipped with amino acid side chain backbones. PMID:25744588

Xiang, Jiachen; Wang, Jungang; Wang, Miao; Meng, Xianggao; Wu, Anxin

2015-04-14

223

Rapid Chemoselective Bioconjugation Through the Oxidative Coupling of Anilines and Aminophenols  

PubMed Central

A highly efficient protein bioconjugation method is described involving the addition of anilines to o-aminophenols in the presence of sodium periodate. The reaction takes place in aqueous buffer at pH 6.5 and can reach high levels of completion in 2–5 min. The product of the reaction has been characterized using X-ray crystallography, which revealed that an unprecedented oxidative ring contraction occurs after the coupling step. The compatibility of the reaction with protein substrates has been demonstrated through the attachment of small molecules, polymer chains, and peptides to p-aminophenylalanine residues introduced into viral capsids through amber stop codon suppression. The coupling of anilines to o-aminophenol groups derived from tyrosine residues is also described. The compatibility of this method with thiol modification chemistry is shown through the attachment of a near-IR fluorescent chromophore to cysteine residues inside the viral capsid shells, followed by the attachment of integrin-targeting RGD peptides to anilines on the exterior surface. PMID:21919497

Behrens, Christopher R.; Hooker, Jacob M.; Obermeyer, Allie C.; Romanini, Dante W.; Katz, Elan M.; Francis, Matthew B.

2012-01-01

224

Using ultrashort optical pulses to couple ferroelectric and ferromagnetic order in an oxide heterostructure.  

PubMed

A new approach to all-optical detection and control of the coupling between electric and magnetic order on ultrafast timescales is achieved using time-resolved second-harmonic generation (SHG) to study a ferroelectric (FE)/ferromagnet (FM) oxide heterostructure. We use femtosecond optical pulses to modify the spin alignment in a Ba(0.1)Sr(0.9)TiO3 (BSTO)/La(0.7)Ca(0.3)MnO3 (LCMO) heterostructure and selectively probe the ferroelectric response using SHG. In this heterostructure, the pump pulses photoexcite non-equilibrium quasiparticles in LCMO, which rapidly interact with phonons before undergoing spin-lattice relaxation on a timescale of tens of picoseconds. This reduces the spin-spin correlations in LCMO, applying stress on BSTO through magnetostriction. This then modifies the FE polarization through the piezoelectric effect, on a timescale much faster than laser-induced heat diffusion from LCMO to BSTO. We have thus demonstrated an ultrafast indirect magnetoelectric effect in a FE/FM heterostructure mediated through elastic coupling, with a timescale primarily governed by spin-lattice relaxation in the FM layer. PMID:25534775

Sheu, Y M; Trugman, S A; Yan, L; Jia, Q X; Taylor, A J; Prasankumar, R P

2014-01-01

225

Phase diagrams of voltage-gated oxide interfaces with strong Rashba coupling  

NASA Astrophysics Data System (ADS)

We propose a model for the two-dimensional electron gas formed at the interface of oxide heterostructures that includes a Rashba spin-orbit coupling proportional to an electric field oriented perpendicularly to the interface. Taking into account the electron density dependence of this electric field confining the electron gas at the interface, we report the occurrence of a phase separation instability (signaled by a negative compressibility) for realistic values of the spin-orbit coupling and of the electronic band-structure parameters at zero temperature. We extend the analysis to finite temperatures and in the presence of an in-plane magnetic field, thereby obtaining two phase diagrams that exhibit a phase separation dome. By varying the gating potential, the phase separation dome may shrink and vanish at zero temperature into a quantum critical point where the charge fluctuates dynamically. Similarly, the phase separation may be spoiled by a planar magnetic field even at zero temperature leading to a line of quantum critical points.

Bucheli, D.; Grilli, M.; Peronaci, F.; Seibold, G.; Caprara, S.

2014-05-01

226

Using ultrashort optical pulses to couple ferroelectric and ferromagnetic order in an oxide heterostructure  

NASA Astrophysics Data System (ADS)

A new approach to all-optical detection and control of the coupling between electric and magnetic order on ultrafast timescales is achieved using time-resolved second-harmonic generation (SHG) to study a ferroelectric (FE)/ferromagnet (FM) oxide heterostructure. We use femtosecond optical pulses to modify the spin alignment in a Ba0.1Sr0.9TiO3 (BSTO)/La0.7Ca0.3MnO3 (LCMO) heterostructure and selectively probe the ferroelectric response using SHG. In this heterostructure, the pump pulses photoexcite non-equilibrium quasiparticles in LCMO, which rapidly interact with phonons before undergoing spin–lattice relaxation on a timescale of tens of picoseconds. This reduces the spin–spin correlations in LCMO, applying stress on BSTO through magnetostriction. This then modifies the FE polarization through the piezoelectric effect, on a timescale much faster than laser-induced heat diffusion from LCMO to BSTO. We have thus demonstrated an ultrafast indirect magnetoelectric effect in a FE/FM heterostructure mediated through elastic coupling, with a timescale primarily governed by spin–lattice relaxation in the FM layer.

Sheu, Y. M.; Trugman, S. A.; Yan, L.; Jia, Q. X.; Taylor, A. J.; Prasankumar, R. P.

2014-12-01

227

Two pathways of carbon dioxide catalyzed oxidative coupling of phenol by peroxynitrite.  

PubMed

Carbon dioxide catalyzed oxidative coupling of phenol by peroxynitrite occurs by two pathways distinguished by the isomer ratio of 2,2'- to 4,4'-biphenols. As already established, at neutral pH and moderate phenol concentrations, both biphenols are formed in comparable yields by the coupling of two phenoxyl radicals. However, at high pH and phenol concentration, 2,2'-biphenol is the only identified coupled product, and its formation does not involve phenoxyl radicals. Instead, under these conditions, a previously unreported long-lived (t(1/2) approximately 10 s at pH 10 and 1 mM phenol) diamagnetic intermediate with an absorption maximum at 400 nm is observed. This intermediate is formed from phenolate concomitantly with the decay of peroxynitrite and disappears via reaction with phenol [k = (2.4 +/- 0.1) x 10 M(-)(1) s(-)(1) at pH 10.5] to form 2,2'-biphenol. We also find that para-benzoquinone, previously unreported, is formed in up to 5% yield relative to the initial peroxynitrite concentration. The appearance of an absorption band above 500 nm, which might be due to quinhydrone, indicates that hydroquinone is a likely para-benzoquinone precursor. The dependence of para-benzoquinone yields on pH and phenol concentration suggests that its formation is related to the nonradical pathway of 2,2'-biphenol formation. This novel nonradical pathway of 2,2'-biphenol formation might be relevant to the mechanisms of reaction of phenolic antioxidants with peroxynitrite. The existence of two distinct pathways of biphenol formation implies that, apart from a CO(3)(*)(-)/NO(2)(*) radical pair, another reactive intermediate is formed during the carbon dioxide catalyzed decay of peroxynitrite. PMID:16544942

Papina, Alina A; Koppenol, Willem H

2006-03-01

228

Intramolecular dearomative oxidative coupling of indoles: a unified strategy for the total synthesis of indoline alkaloids.  

PubMed

Indole alkaloids, one of the largest classes of alkaloids, serve as an important and rich source of pharmaceuticals and have inspired synthetic chemists to develop novel chemical transformations and synthetic strategies. Many biologically active natural products contain challenging indoline scaffolds, which feature a C3 all-carbon quaternary stereocenter that is often surrounded by a complicated polycyclic ring system. The creation of this quaternary stereocenter creates an inherent synthetic challenge because the substituents on the carbon center cause high steric repulsion. In addition, the presence of nitrogen atoms within the surrounding polycyclic rings can lead to synthetic difficulties. Oxidative coupling between two sp(3)-hybridized carbon anions provides a unique and powerful method for building C-C single bonds, especially for generating a C-C bond that joins one or two vicinal quaternary stereocenters. Although chemists have known of this transformation for a long time, they have only applied this reaction in total synthesis of complex natural products during the past decade. The progress of this class of reaction depends on the use of indole moieties as coupling partners. In this Account, we summarize our recent efforts to develop iodine-mediated intramolecular dearomative oxidative coupling (IDOC) reactions of indoles as part of a unified strategy for the total synthesis of three classes of indoline alkaloids. We categorized these IDOC reactions into three types based on their mode of connection to the indole moiety. In type I, the carboanion nucleophile was tethered to the indole at the C3 position. This reaction enabled the assembly of skeleton A, which features a spiro ring at the C3 position of the indole. We demonstrated the efficiency of this method by quickly assembling two classes of tetracyclic compounds and completing the total synthesis of (-)-communesins F, A, and B. For the type II IDOC reactions, the carboanion nucleophile residing at the C2 position of the indole formed a quaternary center at the C3 position of indole to produce skeleton B. We applied this IDOC reaction to synthesize two akuammiline alkaloids, vincorine and aspidophylline A. Type III IDOC reactions employed substrates with a preinstalled ring at the C2 and C3 positions of the indole. These transformations proceeded smoothly to afford polycyclic ring system C, which we used in the first enantioselective total synthesis of Kopsia alkaloid methyl N-decarbomethoxychanofruticosinate. These results further demonstrate how new chemical strategies and reactions facilitate both the first total syntheses of natural products and the discovery of more efficient synthetic routes. PMID:25667972

Zi, Weiwei; Zuo, Zhiwei; Ma, Dawei

2015-03-17

229

Chemical Profiling of Re-Du-Ning Injection by Ultra-Performance Liquid Chromatography Coupled with Electrospray Ionization Tandem Quadrupole Time-of-Flight Mass Spectrometry through the Screening of Diagnostic Ions in MSE Mode  

PubMed Central

The broad applications and mechanism explorations of traditional Chinese medicine prescriptions (TCMPs) require a clear understanding of TCMP chemical constituents. In the present study, we describe an efficient and universally applicable analytical approach based on ultra-performance liquid chromatography coupled to electrospray ionization tandem quadrupole time-of-flight mass spectrometry (UPLC-ESI-Q/TOF-MS) with the MSE (E denotes collision energy) data acquisition mode, which allowed the rapid separation and reliable determination of TCMP chemical constituents. By monitoring diagnostic ions in the high energy function of MSE, target peaks of analogous compounds in TCMPs could be rapidly screened and identified. “Re-Du-Ning” injection (RDN), a eutherapeutic traditional Chinese medicine injection (TCMI) that has been widely used to reduce fever caused by viral infections in clinical practice, was studied as an example. In total, 90 compounds, including five new iridoids and one new sesquiterpene, were identified or tentatively characterized by accurate mass measurements within 5 ppm error. This analysis was accompanied by MS fragmentation and reference standard comparison analyses. Furthermore, the herbal sources of these compounds were unambiguously confirmed by comparing the extracted ion chromatograms (EICs) of RDN and ingredient herbal extracts. Our work provides a certain foundation for further studies of RDN. Moreover, the analytical approach developed herein has proven to be generally applicable for profiling the chemical constituents in TCMPs and other complicated mixtures. PMID:25875968

Wang, Zhenzhong; Geng, Jianliang; Dai, Yi; Xiao, Wei; Yao, Xinsheng

2015-01-01

230

Rapid profiling and identification of triterpenoid saponins in crude extracts from Albizia julibrissin Durazz. by ultra high-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry.  

PubMed

Ultra high-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UHPLC/ESI-Q-TOF-MS/MS) was applied to separate and identify triterpenoid saponins in crude extract from the stem bark of Albizia julibrissin Durazz. The molecular weights were determined by comparing quasi-molecular ions [M+NH(4)](+) in positive mode and [M-H](-) and [M-2H](2-) ions in negative mode. The MS/MS spectra of the [M-H](-) ions for saponins provided a wealth of structural information related to aglycone skeletons, sugar types and linked sequence. On the basis of the fragmentation behavior of known saponins isolated before, saponins from this plant were identified, even though references were not available. As a result, a total of twenty-eight saponins in the crude extract were identified, which all had a common basic skeleton of the triterpene oleanolic acid and eight of them were new compounds. PMID:21530133

Han, Lifeng; Pan, Guixiang; Wang, Yuefei; Song, Xinbo; Gao, Xiumei; Ma, Baiping; Kang, Liping

2011-07-15

231

A new approach for the estimation of expanded uncertainty of results of an analytical method developed for determining antibiotics in seawater using solid-phase extraction disks and liquid chromatography coupled with tandem mass spectrometry technique.  

PubMed

Although the uncertainty estimate should be a necessary component of an analytical result, the presentation of measurements together with their uncertainties is still a serious problem, especially in the monitoring of the presence of pharmaceuticals in the environment. Here we discuss the estimation of expanded uncertainty in analytical procedures for determining residues of twelve pharmaceuticals in seawaters using solid-phase extraction (SPE) with H2O-Philic BAKERBOND speed disks and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). Matrix effects, extraction efficiency and absolute recovery of the developed analytical method were determined. A validation was performed to obtain the method's linearity, precision, accuracy, limits of detection (LODs) and quantification (LOQs). The expanded uncertainty of the data obtained was estimated according to the Guide to the Expression of Uncertainty in Measurement and ISO 17025:2005 standard. We applied our method to the analysis of drugs in seawaters samples from the coastal area of the southern Baltic Sea. As a result, a new approach (concerning the uncertainty estimation as well as the development of analytical method) to the analysis of pharmaceutical residues in environmental samples is presented. The information given here should facilitate the introduction of uncertainty estimation in chromatographic measurements on a much greater scale than is currently the case. PMID:23885670

Borecka, Marta; Bia?k-Bieli?ska, Anna; Siedlewicz, Grzegorz; Kornowska, Kinga; Kumirska, Jolanta; Stepnowski, Piotr; Pazdro, Ksenia

2013-08-23

232

On-line solid-phase extraction of large-volume injections coupled to liquid chromatography-tandem mass spectrometry for the quantitation and confirmation of 14 selected trace organic contaminants in drinking and surface water.  

PubMed

We describe the development and validation of an on-line solid-phase extraction of large-volume injections coupled to liquid chromatography-tandem mass spectrometry method for the simultaneous quantitation and confirmation of 14 selected trace organic contaminants in drinking and surface water. Selected compounds were: anti-infectives (clarithromycin, sulfamethoxazole and trimethoprim), an anticonvulsant (carbamazepine) and its transformation product 10,11-dihydrocarbamazepine, an antihypertensive (enalapril), antineoplastics (cyclophosphamide and methotrexate), herbicides (atrazine, cyanazine, and simazine) and two of their transformation products (deethylatrazine and deisopropylatrazine) and an antiseptic (triclocarban). The breakthrough volume determinations showed that out of all the investigated sorbents, the Strata-X on-line solid-phase extraction column showed the best performance. The method used a load volume of 10.0 mL and was validated using the corresponding matrices, yielding for most compounds, R(2)>0.99. Extraction recoveries ranged from 60 to 109%. The intra- and inter-day precision were <14 and <16%, respectively. The method detection limits ranged from 0.6 to 6 ng L(-1). Matrix effects were in general low. The performance of the on-line method was demonstrated with the analysis of real water samples. The application of alternative techniques of confirmation was also explored using accurate mass measurements on a time-of-flight mass spectrometer and the data-dependent reverse energy ramp scan on a triple quadrupole. PMID:19875124

Garcia-Ac, Araceli; Segura, Pedro A; Viglino, Liza; Fürtös, Alexandra; Gagnon, Christian; Prévost, Michèle; Sauvé, Sébastien

2009-11-27

233

Selectively Adsorptive Extraction of Phenylarsonic Acids in Chicken Tissue by Carboxymethyl ?-Cyclodextrin Immobilized Fe3O4 Magnetic Nanoparticles Followed Ultra Performance Liquid Chromatography Coupled Tandem Mass Spectrometry Detection  

PubMed Central

Carboxymethyl ?-cyclodextrin immobilized Fe3O4 magnetic nanoparticles (CM-?-CD-Fe3O4) were synthesized for the selectively adsorptive extraction of five phenylarsonic acids including p-amino phenylarsonic acid, p-nitro phenylarsonic acid, p-hydroxy phenylarsonic acid, p-acylamino phenylarsonic acid and p-hydroxy-3-nitro phenylarsonic acid in chicken tissue. Using ultra performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS), a highly sensitive analytical method was proposed for the determination of five phenylarsonic acids. It was shown that CM-?-CD-Fe3O4 could extract the five phenylarsonic acids in complex chicken tissue samples with high extraction efficiency. Under the optimal conditions, a high enrichment factor, ranging from 349 to 606 fold, was obtained. The limits of detection (LODs) (at a signal-to-noise ratio of 3) were in the range of 0.05–0.11 µg/kg for the five phenylarsonic acids. The proposed method was applied for the determination of five target phenylarsonic acids in chicken muscle and liver samples. Recoveries for the spiked samples with 0.2 µg/kg, 2.0 µg/kg and 20 µg/kg of each phenylarsonic acids were in the range of 77.2%–110.2%, with a relative standard deviation (RSD) of less than 12.5%. PMID:25215503

Jia, Jing; Zhang, Wei; Wang, Jing; Wang, Peilong; Zhu, Ruohua

2014-01-01

234

Palladium-catalyzed aerobic oxidative coupling of enantioenriched primary allylic amines with sulfonyl hydrazides leading to optically active allylic sulfones.  

PubMed

A range of highly enantioenriched primary allylic amines underwent palladium-catalyzed oxidative coupling with sulfonyl hydrazides open to air at room temperature to give structurally diverse allylic sulfones in moderate to excellent yields with excellent retention of ee. PMID:24584133

Wang, Ting-Ting; Wang, Fu-Xiang; Yang, Fu-Lai; Tian, Shi-Kai

2014-04-14

235

Regulating proton-coupled electron transfer for efficient water splitting by manganese oxides at neutral pH  

NASA Astrophysics Data System (ADS)

Manganese oxides have been extensively investigated as model systems for the oxygen-evolving complex of photosystem II. However, most bioinspired catalysts are inefficient at neutral pH and functional similarity to the oxygen-evolving complex has been rarely achieved with manganese. Here we report the regulation of proton-coupled electron transfer involved in water oxidation by manganese oxides. Pyridine and its derivatives, which have pKa values intermediate to the water ligand bound to manganese(II) and manganese(III), are used as proton-coupled electron transfer induction reagents. The induction of concerted proton-coupled electron transfer is demonstrated by the detection of deuterium kinetic isotope effects and compliance of the reactions with the libido rule. Although proton-coupled electron transfer regulation is essential for the facial redox change of manganese in photosystem II, most manganese oxides impair these regulatory mechanisms. Thus, the present findings may provide a new design rationale for functional analogues of the oxygen-evolving complex for efficient water splitting at neutral pH.

Yamaguchi, Akira; Inuzuka, Riko; Takashima, Toshihiro; Hayashi, Toru; Hashimoto, Kazuhito; Nakamura, Ryuhei

2014-06-01

236

Regulating proton-coupled electron transfer for efficient water splitting by manganese oxides at neutral pH  

PubMed Central

Manganese oxides have been extensively investigated as model systems for the oxygen-evolving complex of photosystem II. However, most bioinspired catalysts are inefficient at neutral pH and functional similarity to the oxygen-evolving complex has been rarely achieved with manganese. Here we report the regulation of proton-coupled electron transfer involved in water oxidation by manganese oxides. Pyridine and its derivatives, which have pKa values intermediate to the water ligand bound to manganese(II) and manganese(III), are used as proton-coupled electron transfer induction reagents. The induction of concerted proton-coupled electron transfer is demonstrated by the detection of deuterium kinetic isotope effects and compliance of the reactions with the libido rule. Although proton-coupled electron transfer regulation is essential for the facial redox change of manganese in photosystem II, most manganese oxides impair these regulatory mechanisms. Thus, the present findings may provide a new design rationale for functional analogues of the oxygen-evolving complex for efficient water splitting at neutral pH. PMID:24977746

Yamaguchi, Akira; Inuzuka, Riko; Takashima, Toshihiro; Hayashi, Toru; Hashimoto, Kazuhito; Nakamura, Ryuhei

2014-01-01

237

NON-ENZYMATIC REDUCTION OF QUINONE METHIDES DURING OXIDATIVE COUPLING OF MONOLIGNOLS: IMPLICATIONS FOR THE ORIGIN OF BENZYL STRUCTURES IN LIGNINS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Lignin is believed to be synthesized by oxidative coupling of 4-hydroxyphenylpropanoids. In native lignin there are some types of reduced structures that cannot be explained by oxidative coupling. In the present work we showed via biomimetic model experiments that nicotinamide adenine dinucleotide (...

238

Successive C-C Coupling of Dienes to Vicinally Dioxygenated Hydrocarbons: Ruthenium Catalyzed [4+2] Cycloaddition across the Diol, Hydroxycarbonyl or Dione Oxidation Levels  

PubMed Central

The ruthenium(0) catalyst generated from Ru3(CO)12 and tricyclohexylphosphine or BIPHEP promotes successive C-C coupling of dienes to vicinally dioxygenated hydrocarbons across the diol, hydroxyketone and dione oxidation levels to form products of [4+2] cycloaddition. A mechanism involving diene-carbonyl oxidative coupling followed by intramolecular carbonyl addition from the resulting allylruthenium intermediate is postulated. PMID:23448269

Geary, Laina M.; Glasspoole, Ben W.; Kim, Mary M.; Krische, Michael J.

2013-01-01

239

Chemical control of magnetism: oxidation-induced ferromagnetic spin coupling in the chromium dimer evidenced by photoelectron spectroscopy.  

PubMed

The photoelectron spectrum of the dichromium oxide cluster anion, Cr2O-, and the analysis by the density-functional theory revealed that the spins of the two Cr atoms in Cr2O- are ferromagnetically coupled, and that its total spin magnetic moment is as large as 9 mu(B). This ferromagnetic spin coupling is induced by oxidation; the mixing of Cr 3d with O 2p orbitals plays an important role in a spin coupling between the localized electrons at the two Cr sites bridged by the O atom. The present finding is in marked contrast to the pure chromium dimer, which is known to be antiferromagnetic due to the strong sextuple Cr-Cr bond. PMID:12689285

Tono, Kensuke; Terasaki, Akira; Ohta, Toshiaki; Kondow, Tamotsu

2003-04-01

240

Fast and simultaneous determination of eleven synthetic color additives in flour and meat products by liquid chromatography coupled with diode-array detector and tandem mass spectrometry.  

PubMed

In this study, an efficient, fast and sensitive method for the simultaneous determination of eleven synthetic color additives (Allura red, Amaranth, Azo rubine, Brilliant blue, Erythrosine, Indigotine, Ponceau 4R, New red, Sunset yellow, Quinoline yellow and Tartrazine) in flour and meat foodstuffs is developed and validated using HPLC coupled with DAD and MS/MS. The color additives were extracted with ammonia-methanol and was further purified with SPE procedure using Strata-AW column in order to reduce matrix interference. This HPLC-DAD method is intended for a comprehensive survey of color additives in foods. HPLC-MS/MS method was used as the further confirmation and identification. Validation data showed the good recoveries in the range of 75.2-113.8%, with relative standard deviations less than 15%. These methods are suitable for the routine monitoring analysis of eleven synthetic color additives due to its sensitivity, reasonable time and cost. PMID:25794727

Qi, Ping; Lin, Zi-Hao; Chen, Gui-Yun; Xiao, Jian; Liang, Zhi-An; Luo, Li-Ni; Zhou, Jun; Zhang, Xue-Wu

2015-08-15

241

Analysis of coupled Sr/Ca and 87Sr/ 86Sr variations in enamel using laser-ablation tandem quadrupole-multicollector ICPMS  

NASA Astrophysics Data System (ADS)

We present in this study results obtained with a laser-ablation coupled with both a quadrupole and a multi-collector ICPMS. The simultaneous in situ Sr/Ca and 87Sr/ 86Sr measurements along growth profiles in enamel allows the concomitant diet and migration patterns in mammals to be reconstructed. Aliquots of the powdered international standard NIST "SRM1400 Bone Ash" with certified Sr and Ca contents, was sintered at high pressure and temperature and was adopted as the reference material for external reproducibility and calibration of the results. A total of 145 coupled elemental and isotopic measurements of herbivores enamel from the Kruger National Park, South Africa, gives intra-tooth Sr/Ca and 87Sr/ 86Sr variations that are well larger than external reproducibility. Sr/Ca profiles systematically decrease from the dentine-enamel junction to the outer enamel whereas 87Sr/ 86Sr profiles exhibit variable patterns. Using a simple geometric model of hypsodont teeth growth, we demonstrate that a continuous recording of the 87Sr/ 86Sr variations can be reconstructed in the tooth length axis. This suggests that the mobility of a mammal can be reconstructed over a period of more than a year with a resolution of a ten of days, by sampling enamel along growth profiles. Our geometric model of hypsodont teeth growth predicts that an optimal distance between two successive profiles is equal to the enamel thickness. However, this model does not apply to the Sr/Ca signal which is likely to be altered during the enamel maturation stage due to differential maturation processes along enamel thickness. Here, the observed constant decreases of the Sr/Ca ratios in the ungulates of Kruger National Park suggests that they did not changed of diet, while some of them were migrating.

Balter, Vincent; Telouk, Philippe; Reynard, Bruno; Braga, José; Thackeray, Francis; Albarède, Francis

2008-08-01

242

Insights into proton-coupled electron transfer mechanisms of electrocatalytic H2 oxidation and production  

PubMed Central

The design of molecular electrocatalysts for H2 oxidation and production is important for the development of alternative renewable energy sources that are abundant, inexpensive, and environmentally benign. Recently, nickel-based molecular electrocatalysts with pendant amines that act as proton relays for the nickel center were shown to effectively catalyze H2 oxidation and production. We developed a quantum mechanical approach for studying proton-coupled electron transfer processes in these types of molecular electrocatalysts. This theoretical approach is applied to a nickel-based catalyst in which phosphorous atoms are directly bonded to the nickel center, and nitrogen atoms of the ligand rings act as proton relays. The catalytic step of interest involves electron transfer between the nickel complex and the electrode as well as intramolecular proton transfer between the nickel and nitrogen atoms. This process can occur sequentially, with either the electron or proton transferring first, or concertedly, with the electron and proton transferring simultaneously without a stable intermediate. The electrochemical rate constants are calculated as functions of overpotential for the concerted electron-proton transfer reaction and the two electron transfer reactions in the sequential mechanisms. Our calculations illustrate that the concerted electron-proton transfer standard rate constant will increase as the equilibrium distance between the nickel and nitrogen atoms decreases and as the pendant amines become more flexible to facilitate the contraction of this distance with a lower energy penalty. This approach identifies the favored mechanisms under various experimental conditions and provides insight into the impact of substituents on the nitrogen and phosphorous atoms. PMID:22529352

Horvath, Samantha; Fernandez, Laura E.; Soudackov, Alexander V.; Hammes-Schiffer, Sharon

2012-01-01

243

Biological oxidation of Fe(II) in reduced nontronite coupled with nitrate reduction by Pseudogulbenkiania sp. Strain 2002  

NASA Astrophysics Data System (ADS)

The importance of microbial nitrate-dependent Fe(II) oxidation to iron biogeochemistry is well recognized. Past research has focused on oxidation of aqueous Fe2+ and structural Fe(II) in oxides, carbonates, and phosphate, but the importance of structural Fe(II) in phyllosilicates in this reaction is only recently studied. However, the effect of clay mineralogy on the rate and the mechanism of the reaction, and subsequent mineralogical end products are still poorly known. The objective of this research was to study the coupled process of microbial oxidation of Fe(II) in clay mineral nontronite (NAu-2), and nitrate reduction by Pseudogulbenkiania species strain 2002, and to determine mineralogical changes associated with this process. Bio-oxidation experiments were conducted using Fe(II) in microbially reduced nontronite as electron donor and nitrate as electron acceptor in bicarbonate-buffered medium under both growth and nongrowth conditions to investigate cell growth on this process. The extents of Fe(II) oxidation and nitrate reduction were measured by wet chemical methods. X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and 57Fe-Mössbauer spectroscopy were used to observe mineralogical changes associated with Fe(III) reduction and Fe(II) oxidation in NAu-2. The bio-oxidation extent under growth and nongrowth conditions reached 67% and 57%, respectively. Over the same time period, nitrate was completely reduced under both conditions to nitrogen gas (N2), via an intermediate product nitrite. Abiotic oxidation by nitrite partly accelerated Fe(II) oxidation rate under the growth condition. The oxidized Fe(III) largely remained in the nontronite structure, but secondary minerals such as vivianite, ferrihydrite, and magnetite formed depending on specific experimental conditions. The results of this study highlight the importance of iron-bearing clay minerals in the global nitrogen cycle with potential applications in nitrate removal in natural environments.

Zhao, Linduo; Dong, Hailiang; Kukkadapu, Ravi; Agrawal, Abinash; Liu, Deng; Zhang, Jing; Edelmann, Richard E.

2013-10-01

244

A novel validated procedure for the determination of nicotine, eight nicotine metabolites and two minor tobacco alkaloids in human plasma or urine by solid-phase extraction coupled with liquid chromatography-electrospray ionization-tandem mass spectrometry  

PubMed Central

A novel validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) procedure was developed and fully validated for the simultaneous determination of nicotine-N-?-D-glucuronide, cotinine-N-oxide, trans-3-hydroxycotinine, norcotinine, trans-nicotine-1?-oxide, cotinine, nornicotine, nicotine, anatabine, anabasine and cotinine-N-?-D-glucuronide in human plasma or urine. Target analytes and corresponding deuterated internal standards were extracted by solid-phase extraction and analyzed by LC-MS/MS with electrospray ionization (ESI) using multiple reaction monitoring (MRM) data acquisition. Calibration curves were linear over the selected concentration ranges for each analyte, with calculated coefficients of determination (R2) of greater than 0.99. The total extraction recovery (%) was concentration dependent and ranged from 52–88 % in plasma and 51–118 % in urine. The limit of quantification for all analytes in plasma and urine were 1.0 ng/mL and 2.5 ng/mL respectively with the exception of cotinine-N-?-D-glucuronide which was 50 ng/mL. Intra-day and inter-day imprecision were ?14 % and ?17 % respectively. Matrix effect (%) was sufficiently minimized to ?19 % for both matrices using the described sample preparation and extraction methods. The target analytes were stable in both matrices for at least 3 freeze thaw cycles, 24 hours at room temperature, 24 hours in the refrigerator (4 °C) and 1 week in the freezer (?20 °C). Reconstituted plasma and urine extracts were stable for at least 72 hours storage in the liquid chromatography autosampler at 4 °C. The plasma procedure has been successfully applied in the quantitative determination of selected analytes in samples collected from nicotine-abstinent human participants as part of a pharmacokinetic study investigating biomarkers of nicotine use in plasma following controlled low dose (7 mg) transdermal nicotine delivery. Nicotine, cotinine, trans-3-hydroxycotinine and trans-nicotine-1?-oxide were detected in the particular sample presented herein. The urine procedure has been used to facilitate the monitoring of unauthorized tobacco use by clinical study participants at the time of physical examination (before enrolment) and on the pharmacokinetic study day. PMID:20097626

Miller, Eleanor I; Norris, Hye-Ryun K; Rollins, Douglas E; Tiffany, Stephen T; Wilkins, Diana G

2010-01-01

245

Nitric oxide: a modulator, but not a mediator, of neurovascular coupling in rat somatosensory cortex.  

PubMed

We investigated the role of nitric oxide (NO)/cGMP in the coupling of neuronal activation to regional cerebral blood flow (rCBF) in alpha-chloralose-anesthetized rats. Whisker deflection (60 s) increased rCBF by 18 +/- 3%. NO synthase (NOS) inhibition by N(omega)-nitro-L-arginine (L-NNA; topically) reduced the rCBF response to 9 +/- 4% and resting rCBF to 80 +/- 8%. NO donors [S-nitroso-N-acetylpenicillamine (SNAP; 50 microM), 3-morpholinosydnonimine (10 microM)] or 8-bromoguanosine 3', 5'-cyclic-monophosphate (8-BrcGMP; 100 microM)] restored resting rCBF and L-NNA-induced attenuation of the whisker response in the presence of L-NNA, whereas the NO-independent vasodilator papaverine (1 mM) had no effect on the whisker response. Basal cGMP levels were decreased to 35% by L-NNA and restored to 65% of control by subsequent SNAP superfusion. Inhibition of neuronal NOS by 7-nitroindazole (7-NI; 40 mg/kg ip) or soluble guanylyl cyclase by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 100 microM) significantly reduced resting rCBF to 86 +/- 8 and 92 +/- 10% and whisker rCBF response to 7 +/- 4 and 12 +/- 3%, respectively. ODQ reduced tissue cGMP to 54%. 8-BrcGMP restored the whisker response in the presence of 7-NI or ODQ. We conclude that NO, produced by neuronal NOS, is a modulator in the coupling of neuronal activation and rCBF in rat somatosensory cortex and that this effect is mainly mediated by cGMP. L-NNA-induced vasomotion was significantly reduced during increased neuronal activity and after restoration of basal NO levels, but not after restoration of cGMP. PMID:10444508

Lindauer, U; Megow, D; Matsuda, H; Dirnagl, U

1999-08-01

246

Identification of metabolites of honokiol in rat urine using 13C stable isotope labeling and liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry.  

PubMed

A general approach based on stable isotope labeling and UPLC/Q-TOF-MS analysis of in vivo novel metabolites of honokiol has been developed in our study. In this method, urine samples were collected after intravenous administration of mixture of regular and [(13)C6]-labeled honokiol at 1:1 ratio to healthy rats. The metabolites could be easily recognized by the determination of a chromatographically co-eluted pair of isotopomers (MS doublet peaks) with similar peak intensities and mass difference corresponding to that between isotope-labeled and non-isotope-labeled honokiol. A total of 51 metabolites were detected, 37 of which were tentatively identified based on mass accuracy (<5 ppm). Among them, 33 of honokiol metabolites were first reported with 5 metabolites belonging to phase I and other 32 metabolites belonging to phase II metabolites. Our results highlighted that the main phase I metabolic pathways of honokiol in rats were oxidation, and the phase II metabolic pathways were sulfation, glucuronidation, acetylation as well as amino acids conjugation. This was the first research focused on the biotransformation of honokiol in rats, and the identification of these metabolites might provide us essential information for further pharmacological and clinical studies of honokiol. PMID:23618226

Liu, Juan; Tang, Minghai; Lai, Huijun; Dong, Yinfeng; Xie, Caifeng; Ye, Haoyu; Ma, Liang; Qiu, Neng; Li, Yanfang; Cai, Lulu; Chen, Lijuan

2013-06-21

247

Reaction progress kinetic analysis of a copper-catalyzed aerobic oxidative coupling reaction with N-phenyl tetrahydroisoquinoline.  

PubMed

The results from a kinetic investigation of a Cu-catalyzed oxidative coupling reaction between N-phenyl tetrahydroisoquinoline and a silyl enol ether using elemental oxygen as oxidant are presented. By using reaction progress kinetic analysis as an evaluation method for the obtained data, we discovered information regarding the reaction order of the substrates and catalysts. Based on this information and some additional experiments, a refined model for the initial oxidative activation of the amine substrate and the activation of the nucleophile by the catalyst was developed. The mechanistic information also helped to understand why silyl nucleophiles have previously failed in a related Cu-catalyzed reaction using tert-butyl hydroperoxide as oxidant and how to overcome this limitation. PMID:25203932

Scott, Martin; Sud, Abhishek; Boess, Esther; Klussmann, Martin

2014-12-19

248

Palladium-catalyzed regioselective benzylation-annulation of pyridine N-oxides with toluene derivatives via multiple C-H bond activations: benzylation versus arylation.  

PubMed

A palladium-catalyzed cross-dehydrogenative coupling (CDC) reaction of pyridine N-oxides with toluenes has been developed that operates under mild conditions. 2-Benzylpyridines can be obtained directly by this method via a CDC reaction between unactivated toluenes and pyridine N-oxides. In addition, azafluorene N-oxides, of value for future medicinal chemistry applications, can be obtained successfully by this procedure via four tandem C-H bond activations. PMID:25607468

Kianmehr, Ebrahim; Faghih, Nasser; Khan, Khalid Mohammed

2015-02-01

249

Fabrication of an on-line enzyme micro-reactor coupled to liquid chromatography-tandem mass spectrometry for the digestion of recombinant human erythropoietin.  

PubMed

Our aim was to develop a fast and efficient on-line method using micro-reactors for the digestion and deglycosylation of recombinant human erythropoietin extracted from equine plasma. The trypsin digestion micro reactors were fabricated using fused silica capillaries with either a dextran-modified coating or a porous monolith that was able to immobilise the enzyme. These were both found to be reasonably robust and durable, with the trypsin immobilised on dextran-modified fused silica capillaries offering better reproducibility than the micro-reactor based upon covalent attachment of this enzyme to the polymer. It is also evident that the enzyme attached micro reactors produced some tryptic peptides in a greater yield than in-solution digestion. A peptide-N-glycosidase F reactor was also fabricated and, when coupled with the trypsin reactor, the deaminated peptides T5 DAM and T9 DAM from recombinant human erythropoietin could also be detected by LC-ESI-MS/MS analysis. These results were better than those achieved using off-line digestion plus deglycosylation reactions and the analysis required far less time and effort to complete. The use of this on-line approach improved the sensitivity, efficiency and speed of our confirmation methodology that is based upon detecting the unique peptide segments of recombinant human erythropoietin that has been affinity extracted from positive equine plasma samples. PMID:25640120

Foo, Hsiao Ching; Smith, Norman W; Stanley, Shawn M R

2015-04-01

250

Exchange-coupled bimagnetic cobalt/iron oxide branched nanocrystal heterostructures.  

PubMed

A colloidal seeded-growth strategy, relying on time-programmed delivery of selected stabilizing surfactants, has been developed to synthesize bimagnetic hybrid nanocrystals (HNCs) that consist of a single-crystal tetrapod-shaped skeleton of ferrimagnetic (FiM) iron oxide functionalized with multiple polycrystalline spherical domains of ferromagnetic (FM) Co. Due to the direct bonding interfaces formed between the two materials at the relevant junction regions, the HNCs exhibit FiM-FM exchange coupling, which transcribes into a rich scenario of significantly modified properties (not otherwise achievable with any of the single components or with their physical mixtures), including higher saturation magnetization and coercitivity values, exchange biasing, and enhanced thermal stability due to induced extra anisotropy. The availability of these new types of HNCs suggests that development of appropriate synthetic tools for arranging distinct material domains in predetermined spatial arrangements could lead to a more rational design of nanoheterostructures potentially exploitable as active elements in future generations of magnetic recording devices. PMID:19072127

Casavola, Marianna; Falqui, Andrea; García, Miguel Angel; García-Hernández, Mar; Giannini, Cinzia; Cingolani, Roberto; Cozzoli, P Davide

2009-01-01

251

Soil remediation using a coupled process: soil washing with surfactant followed by photo-Fenton oxidation.  

PubMed

In the present work the use of a coupled process, soil washing and photo-Fenton oxidation, was investigated for remediation of a soil contaminated with p,p'-DDT (DDT) and p,p'-DDE (DDE), and a soil artificially contaminated with diesel. In the soil washing experiments, Triton X-100 (TX-100) aqueous solutions were used at different concentrations to obtain wastewaters with different compositions. Removal efficiencies of 66% (DDT), 80% (DDE) and 100% (diesel) were achieved for three sequential washings using a TX-100 solution strength equivalent to 12 times the effective critical micelle concentration of the surfactant (12 CMC(eff)). The wastewater obtained was then treated using a solar photo-Fenton process. After 6h irradiation, 99, 95 and 100% degradation efficiencies were achieved for DDT, DDE and diesel, respectively. In all experiments, the concentration of dissolved organic carbon decreased by at least 95%, indicating that residual concentration of contaminants and/or TX-100 in the wastewater was very low. The co-extraction of metals was also evaluated. Among the metals analyzed (Pb, Cr, Ni, Cu, Cd, Mn and Co), only Cr and Mn were detected in the wastewater at concentrations above the maximum value permitted by current Brazilian legislation. The effective removal of contaminants from soil by the TX-100 washing process, together with the high degradation efficiency of the solar photo-Fenton process, suggests that this procedure could be a useful option for soil remediation. PMID:19853992

Villa, Ricardo D; Trovó, Alam G; Nogueira, Raquel F Pupo

2010-02-15

252

Pristine graphdiyne-hybridized photocatalysts using graphene oxide as a dual-functional coupling reagent.  

PubMed

Advanced functional hybrids based on carbon materials (CMs) represent one of the main achievements of scientific communities. To achieve the hybridization, pristine CMs have to be chemically modified, or surfactants, which are nonfunctional for the performances of the hybrids, have to be employed as a cross-linkage. The construction of pristine CM-based hybrids using dual-functional coupling reagents, which work not only as a glue for hybridization but also as a functional component for enhanced performance, is strongly desired. Here, we report that pristine graphdiyne (GD), a recently synthesized new carbon allotrope, can be facilely hybridized with Ag/AgBr using graphene oxide (GO) as a cross-linkage. We demonstrate that compared to Ag/AgBr, Ag/AgBr/GO, and Ag/AgBr/GD, our Ag/AgBr/GO/GD exhibits an enhanced photocatalytic performance toward the degradation of methyl orange (MO) pollutant under visible light irradiation. In our Ag/AgBr/GO/GD, GO serves not only as a glue for a successful hybridization, but also as a functional component for enhanced catalytic performance. Beyond GD, our work likely paves a new avenue for the fabrication of advanced functional hybrids based on pristine carbon allotropes, wherein desired functions or properties might be achieved by choosing desired CMs and desired hybridized components. PMID:25418916

Zhang, Xiao; Zhu, Mingshan; Chen, Penglei; Li, Yongjun; Liu, Huibiao; Li, Yuliang; Liu, Minghua

2015-01-14

253

Solid phase extraction coupled to liquid chromatography-tandem mass spectrometry analysis of sulfonamides, tetracyclines, analgesics and hormones in surface water and wastewater in Luxembourg.  

PubMed

In the early 1990s different studies highlighted the relationship between pharmaceuticals, human health and the environment. Among the emerging contaminants, antibiotics are obviously of high concern, because of their potential for inducing antibiotic resistance. In addition, natural and synthetic hormones are relevant because of their potential endocrine-disrupting effects on wildlife. This investigation focuses on the analysis of four classes of veterinary and human pharmaceuticals (sulfonamides, tetracyclines, analgesics and hormones) in surface water and wastewater in Luxembourg. The selected eleven pharmaceuticals include four sulfonamides (sulfathiazole, sulfamethoxazole, sulfadimethoxine and sulfamethazine), two tetracyclines (tetracycline and oxytetracycline), two analgesics (ibuprofen and diclofenac), and three hormones (2 naturals, estrone and beta-estradiol, and a synthetic one, 17-alpha-ethinyl estradiol). The most innovative parts of this study are the simultaneous extraction of the above-mentioned pharmaceuticals as well as tracking their behaviour during flood events in a small river catchment. The method includes pre-concentration by solid phase extraction using Oasis HLB (Hydrophilic Lipophilic Balance) which gave superior results compared to Chromabond C-18EC, Chromabond(R) EASY and Bond Elut PLEXA cartridges, also evaluated in this investigation. The analysis of the investigated pharmaceutical compounds is carried out by high performance liquid chromatography coupled to a triple quadrupole mass spectrometer. The limits of quantification were 1 ng L(-1), except for beta-estradiol (2 ng L(-1)) and 17-alpha-ethinyl estradiol (6 ng L(-1)). Recovery rates range from 70 to 94%, with relative standard deviations between 4 and 19%. Application of this method to river concentration and flood events revealed high concentrations of ibuprofen (10-4000 ng L(-1)), with highest levels during flood events, while concentrations of estrogens (1-240 ng L(-1)) and sulfonamides (1-20 ng L(-1)) were comparatively low. PMID:19477484

Pailler, J-Y; Krein, A; Pfister, L; Hoffmann, L; Guignard, C

2009-08-01

254

Mössbauer study of the methane oxidative coupling catalysts with K2NiF4 layer structure  

NASA Astrophysics Data System (ADS)

Six complex oxide catalysts with K2NiF4-type structure were prepared by solid state reaction for methane oxidative coupling (MOC). Mössbauer spectroscopy and other methods were used to identify the structure of the samples and the electronic configuration of iron atoms, and the results were correlated with the MOC reactivity. It is found that the partial substitution of iron in the lattice by Li, Zn or Mg results in the formation of high spin Fe(IV) and surface oxygen species O-, which are assumed to be responsible for the high activity and C2 selectivity for MOC.

Yan, Qijie; Shen, Jianyi; Wang, Ye; Fu, Xiancai

1992-04-01

255

On-line solid-phase extraction coupled to ultra-performance liquid chromatography with tandem mass spectrometry detection for the determination of benzotriazole UV stabilizers in coastal marine and wastewater samples.  

PubMed

Benzotriazoles are a group of UV absorbing compounds considered emerging contaminants that are used in different personal care products, and therefore, it is of high interest to develop sensitive and fast methods for investigating their presence in the environment. In this work, we present the development and application of a novel method based on on-line solid-phase extraction coupled to ultra-performance liquid chromatography with tandem mass spectrometry detection (SPE-UPLC-MS/MS) for the determination of seven benzotriazole UV stabilizers (BUVSs) in coastal marine and wastewater samples. This process is compared with a conventional off-line SPE procedure followed by UPLC-MS/MS. The parameters affecting the performance of the sample preparation and determination processes were evaluated. The results indicate that the on-line procedure provides for better sensitivity and reproducibility and is faster and easier than the off-line procedure. The detection limits and quantification limits achieved were in the range of 0.6-4.1 ng?L(-1) and 2.1-14 ng?L(-1) and relative standard deviation between 6.2 and 10%. The developed method was applied to coastal marine and wastewater samples from Gran Canaria Island (Spain). All of the BUVSs studied were detected in the samples from wastewater treatment plants and two were found in the seawater samples (UV P in the range of 2.8-4.4 ng?L(-1) and UV 360 between 3.6 and 5.2 ng?L(-1)). PMID:22411539

Montesdeoca-Esponda, Sarah; Sosa-Ferrera, Zoraida; Santana-Rodríguez, José Juan

2012-05-01

256

Quantitative determination of oseltamivir and oseltamivir carboxylate in human fluoride EDTA plasma including the ex vivo stability using high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry.  

PubMed

Oseltamivir, the ethyl ester prodrug of the neuramidase inhibitor oseltamivir carboxylate, is licensed for the treatment of patients with influenza virus infection. Here we describe the development and validation of an assay for the simultaneous quantification of oseltamivir and oseltamivir carboxylate in human fluoride EDTA plasma including the ex vivo stability using liquid chromatography coupled to tandem mass spectrometry. Sample pretreatment consisted of protein precipitation with 8% (v/v) trichloroacetic acid in water using only 50 ?L plasma. Chromatographic separation was performed on a reversed phase C18 column (150 mm × 2.0 mm ID, particle size 4 ?m) with a stepwise gradient using 0.1% formic acid and methanol at a flow rate of 250 ?L/min. A triple quadrupole mass spectrometer operating in the positive ionization mode was used for detection and drug quantification. The method was validated over a range of 3-300 ng/mL for oseltamivir and 10-10,000 ng/mL for oseltamivir carboxylate. Deuterated oseltamivir and oseltamivir carboxylate were used as internal standards. The intra-assay accuracies and precisions for oseltamivir were between -8.8 and 16.3% at the LLOQ level, whereas for all other concentration levels this was -8.6 and 14.5%. For oseltamivir carboxylate the intra-assay accuracies and precisions were between -10.9 and 10.7% at all levels. Furthermore, oseltamivir was stable in plasma and whole blood ex vivo in commercially available fluoride EDTA tubes for at least 24h at 2-8 °C. This method is now applied for the determination of both compounds in specific patient populations to evaluate current dosing guidelines. PMID:22418071

Kromdijk, W; Rosing, H; van den Broek, M P H; Beijnen, J H; Huitema, A D R

2012-04-01

257

Significant enhancement in the efficiency and selectivity of iron-catalyzed oxidative cross-coupling of phenols by fluoroalcohols.  

PubMed

Significant enhancement of both the rate and the chemoselectivity of iron-catalyzed oxidative coupling of phenols can be achieved in fluorinated solvents, such as 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP), 2,2,2-trifluoroethanol (TFE), and 1-phenyl-2,2,2-trifluoroethanol. The generality of this effect was examined for the cross-coupling of phenols with arenes and polycyclic aromatic hydrocarbons (PAHs) and of phenol with ?-dicarbonyl compounds. The new conditions were utilized in the synthesis of 2'''-dehydroxycalodenin?B in only four synthetic steps. PMID:25655277

Gaster, Eden; Vainer, Yulia; Regev, Almog; Narute, Sachin; Sudheendran, Kavitha; Werbeloff, Aviya; Shalit, Hadas; Pappo, Doron

2015-03-27

258

Monodisperse Sr-La2O3 hybrid nanofibers for oxidative coupling of methane to synthesize C2 hydrocarbons  

NASA Astrophysics Data System (ADS)

The synergistic effects from combinations of each component's functionality in hybrid Sr-La2O3 nanofibers brought about an improved catalytic behaviour for oxidative coupling of methane carried out at high temperatures, which cannot be achieved over the conventional Sr doped La2O3 spherical catalyst.The synergistic effects from combinations of each component's functionality in hybrid Sr-La2O3 nanofibers brought about an improved catalytic behaviour for oxidative coupling of methane carried out at high temperatures, which cannot be achieved over the conventional Sr doped La2O3 spherical catalyst. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr06660j

Song, Jianjun; Sun, Yongnan; Ba, Rongbin; Huang, Shuangshuang; Zhao, Yonghui; Zhang, Jun; Sun, Yuhan; Zhu, Yan

2015-01-01

259

Controlled surface modification of Ti-40Nb implant alloy by electrochemically assisted inductively coupled RF plasma oxidation.  

PubMed

Low temperature metal oxidation induced by plasma in the absence of liquid electrolytes can be useful for the surface preparation of orthopedic devices since residues from these may be harmful and need to be removed before implantation. In this study the oxidation of Ti-40Nb for biomedical application was achieved by employing an inductively coupled radio frequency oxygen plasma. The correlation between the growth mode of the surface oxide and the electric conductivity ratio of the plasma and the oxide phase were studied by varying the sample temperature, oxygen gas pressure and additional bias potential. The plasma treated samples were characterised by confocal laser microscopy, SEM, EBSD, XPS, TEM and ToF-SIMS. The surface energy was determined by contact angle measurements using the Owens-Wendt-Rabel-Kaelble method. Well adhering oxide layers consisting of TiO2 and Nb2O5 with thicknesses between 50 and 150 nm were obtained. Surface roughness values and microstructure indicate that the growth mode of the oxide can be well controlled by the sample temperature and oxygen gas pressure. At temperatures above 450°C a migration of Ti ions towards the surface controls the growth process. A bias potential higher than +50 V causes rough and defective surfaces with high surface energies. PMID:23891813

Göttlicher, Markus; Rohnke, Marcus; Helth, Arne; Leichtweiß, Thomas; Gemming, Thomas; Gebert, Annett; Eckert, Jürgen; Janek, Jürgen

2013-11-01

260

Recruitment of the adaptor protein Nck to PECAM-1 couples oxidative stress to canonical NF-?B signaling and inflammation.  

PubMed

Oxidative stress stimulates nuclear factor ?B (NF-?B) activation and NF-?B-dependent proinflammatory gene expression in endothelial cells during several pathological conditions, including ischemia/reperfusion injury. We found that the Nck family of adaptor proteins linked tyrosine kinase signaling to oxidative stress-induced activation of NF-?B through the classic I?B kinase-dependent pathway. Depletion of Nck prevented oxidative stress induced by exogenous hydrogen peroxide or hypoxia/reoxygenation injury from activating NF-?B in endothelial cells, increasing the abundance of the proinflammatory molecules ICAM-1 (intracellular adhesion molecule-1) and VCAM-1 (vascular cell adhesion molecule-1) and recruiting leukocytes. Nck depletion also attenuated endothelial cell expression of genes encoding proinflammatory factors but not those encoding antioxidants. Nck promoted oxidative stress-induced activation of NF-?B by coupling the tyrosine phosphorylation of PECAM-1 (platelet endothelial cell adhesion molecule-1) to the activation of p21-activated kinase, which mediates oxidative stress-induced NF-?B signaling. Consistent with this mechanism, treatment of mice subjected to ischemia/reperfusion injury in the cremaster muscle with a Nck inhibitory peptide blocked leukocyte adhesion and emigration and the accompanying vascular leak. Together, these data identify Nck as an important mediator of oxidative stress-induced inflammation and a potential therapeutic target for ischemia/reperfusion injury. PMID:25714462

Chen, Jie; Leskov, Igor L; Yurdagul, Arif; Thiel, Bonnie; Kevil, Christopher G; Stokes, Karen Y; Orr, A Wayne

2015-01-01

261

Biological Oxidation of Fe(II) in Reduced Nontronite Coupled with Nitrate Reduction by Pseudogulbenkiania sp. Strain 2002  

SciTech Connect

Nitrate contamination in soils, sediments, and water bodies is a significant issue. Although much is known about nitrate degradation in these environments, especially via microbial pathways, a complete understanding of all degradation processes, especially in clay mineral-rich soils, is still lacking. The objective of this study was to study the potential of removing nitrate contaminant using structural Fe(II) in clay mineral nontronite. Specifically, the coupled processes of microbial oxidation of Fe(II) in microbially reduced nontronite (NAu-2) and nitrate reduction by Pseudogulbenkiania species strain 2002 was investigated. Bio-oxidation experiments were conducted in bicarbonate-buffered medium under both growth and nongrowth conditions. The extents of Fe(II) oxidation and nitrate reduction were measured by wet chemical methods. X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and 57Fe-Mössbauer spectroscopy were used to observe mineralogical changes associated with Fe(III) reduction and Fe(II) oxidation in nontronite. The bio-oxidation extent under growth and nongrowth conditions reached 93% and 57%, respectively. Over the same time period, nitrate was completely reduced under both conditions to nitrogen gas (N2), via an intermediate product nitrite. Magnetite was a mineral product of nitrate-dependent Fe(II) oxidation, as evidenced by XRD data and TEM diffraction patterns. The results of this study highlight the importance of iron-bearing clay minerals in the global nitrogen cycle with potential applications in nitrate removal in soils.

Zhao, Linduo; Dong, Hailiang; Kukkadapu, Ravi K.; Agrawal, A.; Liu, Deng; Zhang, Jing; Edelmann, Richard E.

2013-10-15

262

Biosynthesis of Hexahydroxyperylenequinone Melanin via Oxidative Aryl Coupling by Cytochrome P-450 in Streptomyces griseus  

PubMed Central

Dihydroxyphenylalanine (DOPA) melanins formed from tyrosine by tyrosinases are found in microorganisms, plants, and animals. Most species in the soil-dwelling, gram-positive bacterial genus Streptomyces produce DOPA melanins and melanogenesis is one of the characteristics used for taxonomy. Here we report a novel melanin biosynthetic pathway involving a type III polyketide synthase (PKS), RppA, and a cytochrome P-450 enzyme, P-450mel, in Streptomyces griseus. In vitro reconstitution of the P-450mel catalyst with spinach ferredoxin-NADP+ reductase/ferredoxin revealed that it catalyzed oxidative biaryl coupling of 1,3,6,8-tetrahydroxynaphthalene (THN), which was formed from five molecules of malonyl-coenzyme A by the action of RppA to yield 1,4,6,7,9,12-hexahydroxyperylene-3,10-quinone (HPQ). HPQ readily autopolymerized to generate HPQ melanin. Disruption of either the chromosomal rppA or P-450mel gene resulted in abolishment of the HPQ melanin synthesis in S. griseus and a decrease in the resistance of spores to UV-light irradiation. These findings show that THN-derived melanins are not exclusive in eukaryotic fungal genera but an analogous pathway is conserved in prokaryotic streptomycete species as well. A vivid contrast in THN melanin biosynthesis between streptomycetes and fungi is that the THN synthesized by the action of a type III PKS is used directly for condensation in the former, while the THN synthesized by the action of type I PKSs is first reduced and the resultant 1,8-dihydroxynaphthalene is then condensed in the latter. PMID:16291687

Funa, Nobutaka; Funabashi, Masanori; Ohnishi, Yasuo; Horinouchi, Sueharu

2005-01-01

263

Tandem mirror fusion research  

SciTech Connect

The tandem mirror program has evolved considerably in the last decade. Of significance is the viable reactor concept embodied in the MARS design. An aggressive experimental program, culminating in the operation of MFTF-B in late 1986, will provide a firm basis for refining the MARS design as necessary for constructing a reactor prototype in the 1990s.

Baldwin, D.E.

1983-12-02

264

Evolution of the Total Synthesis of (-)-Okilactomycin Exploiting a Tandem Oxy-Cope Rearrangement/Oxidation, the Petasis-Ferrier Union/Rearrangement and Ring Closing Metathesis  

PubMed Central

An effective, asymmetric total synthesis of the antitumor antibiotic (-)-okilactomycin (1) and assignment of the absolute configuration, has been achieved exploiting a convergent strategy. Highlights of the synthesis include: a diastereoselective oxy-Cope rearrangement/oxidation sequence to install the C(1) and C(13) stereogenic centers; a Petasis-Ferrier union/rearrangement to construct the highly functionalized tetrahydropyranone inscribed within the thirteen membered macrocycle ring, employing for the first time a sterically demanding acetal; an intramolecular chemoselective acylation to access an embedded bicyclic lactone; and an efficient ring closing metathesis (RCM) reaction to generate the macrocyclic ring. PMID:19170499

Smith, Amos B.; Bosanac, Todd; Basu, Kallol

2009-01-01

265

Fast and simple screening for the simultaneous analysis of seven metabolites derived from five volatile organic compounds in human urine using on-line solid-phase extraction coupled with liquid chromatography-tandem mass spectrometry.  

PubMed

Recently, the International Agency for Research on cancer classified outdoor air pollution and particulate matter from outdoor air pollution as carcinogenic to humans (IARC Group 1), based on sufficient evidence of carcinogenicity in humans and experimental animals and strong mechanistic evidence. In particular, a wide variety of volatile organic compounds (VOCs) are volatized or released into the atmosphere and can become ubiquitous, as they originate from many different natural and anthropogenic sources, such as paints, pesticides, vehicle exhausts, cooking fumes, and tobacco smoke. Humans may be exposed to VOCs through inhalation, ingestion, or dermal contact, which may increase the risk of leukemia, birth defects, neurocognitive impairment, and cancer. Therefore, the focus of this study was the development of a simple, effective and rapid sample preparation method for the simultaneous determination of seven metabolites (6 mercaptic acids+t,t-muconic acid) derived from five VOCs (acrylamide, 1,3-butadiene, acrylonitrile, benzene, and xylene) in human urine by using automated on-line solid-phase extraction (SPE) coupled with liquid chromatography-electrospray tandem mass spectrometry (LC-MS/MS). An aliquot of each diluted urinary sample was directly injected into an autosampler through a trap column to reduce contamination, and then the retained target compounds were eluted by back-flush mode into an analytical column for separation. Negative electrospray ionization tandem mass spectrometry was utilized for quantification. The coefficients of correlation (r(2)) for the calibration curves were greater than 0.995. Reproducibility was assessed by the precision and accuracy of intra-day and inter-day precision, which showed results for coefficient of variation (CV) that were low 0.9 to 6.6% and 3.7 to 8.5%, respectively, and results for recovery that ranged from 90.8 to 108.9% and 92.1 to 107.7%, respectively. The limits of detection (LOD) and limits of quantification (LOQ) were determined to within 0.010 to 0.769 ng mL(-1) and 0.033 to 2.564 ng mL(-1) in this study. A stability study test included 3 freeze/thaw cycles during short-term storage at room temperature for 36 h and long-term storage at -20 °C for 1 month, and the CV (coefficient of variation) showed less than 8.4, 7.4 and 9.7%, respectively. To the best of our knowledge, this is the first study to provide simple, small injection volumes (40 µL) and a rapid LC-MS/MS method combined with an on-line SPE step for the simultaneous detection, identification, and quantification of seven metabolites derived from five VOCs in human urine for evaluation of the future risk of human exposure to volatile organic compounds. PMID:25476333

Chiang, Wen-Chieh; Chen, Chao-Yu; Lee, Ting-Chen; Lee, Hui-Ling; Lin, Yu-Wen

2015-01-01

266

Insights into the reaction mechanism of CO oxidative coupling to dimethyl oxalate over palladium: a combined DFT and IR study.  

PubMed

Oxidative coupling of toxic pollutant CO to form the platform raw chemical material dimethyl oxalate (DMO) has been industrialized however the catalytic mechanism has been unknown so far. The reaction mechanism of CO oxidative coupling to form DMO on a Pd(111) surface has been investigated using density functional theory (DFT) and in situ diffuse reflectance infrared (DRIR) spectroscopy. DFT calculations and in situ DRIRS measurements indicate that two co-adsorbed intermediates COOMe and OCCO, initiate the reaction. C-C coupling occurs earlier due to a low coupling barrier and small steric hindrance. The results also suggest that Pd(111) is selective towards DMO over DMC, and that CO pre-adsorption and CO in excess effectively enhance the yield of DMO. The microscopic elucidation of this important reaction suggests improvements in coal-to-EG (CTEG) production which can be applied in practice to effectively enhance the yield and reduce the cost. The results may help with further fine-tuning and designing of high-efficient noble metal catalysts. PMID:25759866

Li, Qiaohong; Zhou, Zhangfeng; Chen, Ruiping; Sun, Baozhen; Qiao, Luyang; Yao, Yuangen; Wu, Kechen

2015-04-14

267

Rapid liquid chromatography-tandem mass spectrometry analysis of 4-hydroxynonenal for the assessment of oxidative degradation and safety of vegetable oils.  

PubMed

A novel method for the UHPLC-MS/MS analysis of (E)-4-hydroxynonenal (4-HNE) is described. The method is based on derivatization of 4-HNE with pentafluorophenylhydrazine (1) or 4-trifluoromethylphenylhydrazine (2) in acetonitrile in the presence of trifluoroacetic acid as catalyst at room temperature and allows complete analysis of one sample of vegetable oil in only 21min, including sample preparation and chromatography. The method involving hydrazine 1, implemented in an ion trap instrument with analysis of the transition m/z 337?154 showed LOD=10.9nM, average accuracy of 101% and precision ranging 2.5-4.0% RSD intra-day (2.7-4.1% RSD inter-day), with 4-HNE standard solutions. Average recovery from lipid matrices was 96.3% from vaseline oil, 91.3% from sweet almond oil and 105.3% from olive oil. The method was tested on the assessment of safety and oxidative degradation of seven samples of dietary oil (soybean, mixed seeds, corn, peanut, sunflower, olive) and six cosmetic-grade oils (avocado, blackcurrant, apricot kernel, echium, sesame, wheat germ) and effectively detected increased 4-HNE levels in response to chemical (Fenton reaction), photochemical, or thermal stress and aging, aimed at mimicking typical oxidation associated with storage or industrial processing. The method is a convenient, cost-effective and reliable tool to assess quality and safety of vegetable oils. PMID:25818139

Gabbanini, Simone; Matera, Riccardo; Valvassori, Alice; Valgimigli, Luca

2015-04-15

268

Identification and quantification of adducts between oxidized rosmarinic acid and thiol compounds by UHPLC-LTQ-Orbitrap and MALDI-TOF/TOF tandem mass spectrometry.  

PubMed

LTQ Orbitrap MS/MS was used to identify the adducts between quinones derived from rosmarinic acid (RosA) and thiol compounds, including cysteine (Cys), glutathione (GSH), and peptides digested from myosin. Two adducts of quinone-RosA/Cys and quinone-RosA/2Cys, one quinone-RosA/GSH adduct, and three quinone-RosA/peptide adducts were identified by extracted ion and MS(2) fragment ion chromatograms. By using MALDI-TOF/TOF MS, the adduction reaction between RosA and myosin in myofibrillar protein isolates was determined, demonstrating that the accurate reaction site was at Cys949 of myosin. The effect of reaction conditions, including stirring time, temperature, and oxidative stress, on the formation of adducts was further investigated. The formation of quinone-RosA/Cys and quinone-RosA/GSH increased with stirring time. Both adducts increased with temperature, whereas the reactivity of the addition reaction of GSH was higher than that of Cys. With increasing oxidation stress, the formation of quinone-RosA/GSH adduct increased and that of quinone-RosA/Cys adduct decreased. PMID:25541907

Tang, Chang-bo; Zhang, Wan-gang; Dai, Chen; Li, Hui-xia; Xu, Xing-lian; Zhou, Guang-hong

2015-01-28

269

Solar-to-Chemical Energy Conversion with Photoelectrochemical Tandem Cells.  

PubMed

Efficiently and inexpensively converting solar energy into chemical fuels is an important goal towards a sustainable energy economy. An integrated tandem cell approach could reasonably convert over 20% of the sun's energy directly into chemical fuels like H2 via water splitting. Many different systems have been investigated using various combinations of photovoltaic cells and photoelectrodes, but in order to be economically competitive with the production of H2 from fossil fuels, a practical water splitting tandem cell must optimize cost, longevity and performance. In this short review, the practical aspects of solar fuel production are considered from the perspective of a semiconductor-based tandem cell and the latest advances with a very promising technology - metal oxide photoelectrochemical tandem cells - are presented. PMID:23574955

Sivula, Kevin

2013-01-01

270

Studies of nitrile oxide cycloadditions, and the phenolic oxidative coupling of vanillin aldoxime by Geobacillus sp. DDS012 from Italian rye grass silage.  

PubMed

During studies directed towards the discovery of nitrile hydrolysing enzymes from thermophiles, vanillin aldoxime was incubated with the thermophilic organism, Geobacillus sp. DDS012 isolated from Italian rye grass (Lolium multiflorum) silage. The predominant product was a dihydro-dimer, which could only be characterised by LC-MS. This was initially imagined to be the product of cycloaddition of vanillin aldoxime with the corresponding nitrile oxide, but preparation of the supposed adduct and model studies excluded this possibility. The rate constant for the second order dimerisation of 4-O-acetyl vanillin nitrile oxide was measured (1.21 x 10(-4) M(-1) s(-1), 0.413 M, 25 degrees C) and the (13)C-NMR signal for the nitrile oxide carbon was observed (delta(C) 34.4, br. t (1)J(13)C,(14)N circa 50 Hz). Treatment of vanillin aldoxime with potassium persulfate and iron sulfate gave material with the same LC-MS properties as the natural product, which is therefore identified as 5,5'-dehydro-di-(vanillin aldoxime) 1d formed by phenolic oxidative coupling. PMID:18264580

Kelly, David R; Baker, Simon C; King, David S; de Silva, Deepa S; Lord, Gwyn; Taylor, Jason P

2008-02-21

271

Real-time Measurement of Secondary Organic Aerosols From The Photo-oxidation of Toluene Using Atmospheric Pressure Chemical Ionisation Tandem Mass Spectrometry  

NASA Astrophysics Data System (ADS)

A system has been developed to study the chemical composition of secondary or- ganic aerosol (SOA) from the photo-oxidation of hydrocarbons using real-time atmo- spheric pressure chemical ionisation triple quadrupole mass spectrometry (APCI/MS- MS) analysis. To complement existing work with a smog chamber, a two-litre dynamic reaction cell has been built. This has a residence time of around two minutes (instead of several hours for smog chamber experiments), thus permitting on-line analysis. Sample gases are introduced into the air stream and irradiated by a 1000 W xenon arc lamp. Af- ter dilution, some of the mixture from the reaction cell is introduced in the MS ion source via a heated probe, with the particle number density being determined by a condensation nucleus counter on the remainder. The focus so far has been on SOA from the photo-oxidation of toluene by HO radicals in presence of NO, with the HO radicals being generated by the photolysis of Isopy- lNitrite (IPN). Prior to performing analyses on the SOA, target compounds (detected in the particulate phase in other studies) were selected and three ions designated to make a fingerprint for each compound. Finally, by using either a denuder, a granu- lar bed diffusion battery or a filter, both gas and particulate phases have been studied independently and compared. Preliminary results show that a number of target compounds, such as methylglyoxylic acid, benzaldehyde or cresol, have been detected in both gas and particulate phases. Most of these compounds appear to be present mainly in the gas phase. An exhaustive identification of organic compounds is a part of the on-going work.

Collin, F.; Arias, M. C.; Merritt, J. V.; Hastie, D. R.

272

The SUMO E3-ligase PIAS1 couples reactive oxygen species-dependent JNK activation to oxidative cell death  

PubMed Central

Human endometrial stromal cells (HESCs) exposed to reactive oxygen species (ROS) mount a hypersumoylation response in a c-Jun N-terminal kinase (JNK)-dependent manner. The mechanism that couples JNK signaling to the small ubiquitin-related modifier (SUMO) pathway and its functional consequences are not understood. We show that ROS-dependent JNK activation converges on the SUMO pathway via PIAS1 (protein inhibitor of activated STAT1). Unexpectedly, PIAS1 knockdown not only prevented ROS-dependent hypersumoylation but also enhanced JNK signaling in HESCs. Conversely, PIAS overexpression increased sumoylation of various substrates, including c-Jun, yet inhibited basal and ROS-dependent JNK activity independently of its SUMO ligase function. Expression profiling demonstrated that PIAS1 knockdown enhances and profoundly modifies the transcriptional response to oxidative stress signals. Using a cutoff of 2-fold change or more, a total of 250 ROS-sensitive genes were identified, 97 of which were not dependent on PIAS1. PIAS1 knockdown abolished the regulation of 43 genes but also sensitized 110 other genes to ROS. Importantly, PIAS1 silencing was obligatory for the induction of several cellular defense genes in response to oxidative stress. In agreement, PIAS1 knockdown attenuated ROS-dependent caspase-3/7 activation and subsequent apoptosis. Thus, PIAS1 determines the level of JNK activity in HESCs, couples ROS signaling to the SUMO pathway, and promotes oxidative cell death.—Leitao, B. B., Jones, M. C., Brosens, J. J. The SUMO E3-ligase PIAS1 couples reactive oxygen species-dependent JNK activation to oxidative cell death. PMID:21676946

Leitao, Beatriz B.; Jones, Marius C.; Brosens, Jan J.

2011-01-01

273

Scope and Mechanistic Study of the Coupling Reaction of ?, ?-Unsaturated Carbonyl Compounds with Alkenes: Uncovering Electronic Effects on Alkene Insertion vs Oxidative Coupling Pathways  

PubMed Central

The cationic ruthenium-hydride complex [(C6H6)(PCy3)(CO)RuH]+BF4? (1) was found to be a highly effective catalyst for the intermolecular conjugate addition of simple alkenes to ?,?-unsaturated carbonyl compounds to give (Z)-selective tetrasubstituted olefin products. The analogous coupling reaction of cinnamides with electron-deficient olefins led to the oxidative coupling of two olefinic C–H bonds in forming (E)-selective diene products. The intramolecular version of the coupling reaction efficiently produced indene and bicyclic fulvene derivatives. The empirical rate law for the coupling reaction of ethyl cinnamate with propene was determined as: rate = k[1]1[propene]0[cinnamate]?1. A negligible deuterium kinetic isotope effect (kH/kD = 1.1±0.1) was measured from both (E)-C6H5CH=C(CH3)CONHCH3 and (E)-C6H5CD=C(CH3)CONHCH3 with styrene. In contrast, a significant normal isotope effect (kH/kD = 1.7±0.1) was observed from the reaction of (E)-C6H5CH=C(CH3)CONHCH3 with styrene and styrene-d10. A pronounced carbon isotope effect was measured from the coupling reaction of (E)-C6H5CH=CHCO2Et with propene (13C(recovered)/13C(virgin) at C? = 1.019(6)), while a negligible carbon isotope effect (13C(recovered)/13C(virgin) at C? = 0.999(4)) was obtained from the reaction of (E)-C6H5CH=C(CH3)CONHCH3 with styrene. Hammett plots from the correlation of para-substituted p-X-C6H4CH=CHCO2Et (X = OCH3, CH3, H, F, Cl, CO2Me, CF3) with propene and from the treatment of (E)-C6H5CH=CHCO2Et with a series of para-substituted styrenes p-Y-C6H4CH=CH2 (Y = OCH3, CH3, H, F, Cl, CF3) gave the positive slopes for both cases (? = +1.1±0.1 and +1.5±0.1, respectively). Eyring analysis of the coupling reaction led to the thermodynamic parameters, ? H‡ = 20±2 kcal mol?1 and S‡ = ?42±5 e.u. Two separate mechanistic pathways for the coupling reaction have been proposed on the basis of these kinetic and spectroscopic studies. PMID:22368318

Kwon, Ki-Hyeok; Lee, Do W.; Yi, Chae S.

2011-01-01

274

Distant electric coupling between nitrate reduction and sulphide oxidation investigated by an improved nitrate microscale biosensor  

NASA Astrophysics Data System (ADS)

Bacteria are apparently able to transmit electrons to other bacteria (Summers et al. 2010) or to electrodes (Malvankar et al. 2011) by some kind of nanowires (Reguera et al. 2005, Gorbi et al. 2006). Lately it has been shown that such transfer may occur over distances of centimetres in sediments, thereby coupling sulphide oxidation in deeper layers with oxygen reduction near the surface (Nielsen 2011). The finding of these long-distance electrical connections originated from analysis of O2, H2S, and pH profiles measured with microsensors. Nitrate is thermodynamically almost as good an electron acceptor as O2, and we therefore set up an experiment to investigate whether long-distance electron transfer also happens with NO3-. Aquaria were filled with sulphidic marine sediment from Aarhus Bay that was previously used to show long-distance electron transfer to O2. The aquaria were equipped with a lid so that they could be completely filled without a gas phase. Anoxic seawater with 300 ?M NO3- was supplied at a constant rate resulting in a steady state concentration in the aquatic phase of 250 ?M NO3-. The reservoir with the nitrate-containing water was kept anoxic by bubbling it with a N2/CO2 mixture and was kept at an elevated temperature. The water was cooled on the way to the aquaria to keep the water in the aquaria undersaturated with gasses, so that bubble formation by denitrification in the sediment could be minimised. Profiles of NO3-, H2S, and pH were measured as a function of time (2 months) applying commercial sensors for H2S and pH and an improved microscale NO3- biosensor developed in our laboratory. The penetration of NO3- in the sediment was 4-5 mm after 2 months, whereas sulphide only could be detected below 8-9 mm depth. The electron acceptor and electron donor were thus separated by 4-5 mm, indicating long distance electron transfer. A pH maximum of about 8.6 pH units at the NO3- reduction zone similar to a pH maximum observed in the O2 reduction zone of electro-active sediments could be observed. This pH maximum was the strongest evidence for long-distance electron transfer in oxic sediments, but cannot be taken as proof in denitrifying sediments as conventional denitrification may also produce elevated pH. We are now searching for the NO3- reducing bacteria that may be active in long-distance electron transfer in our sediment. Gorby, Y. A., S. Yanina, et al. (2006). Electrically conductive bacterial nanowires produced by Shewanella oneidensis strain MR-1 and other microorganisms. Proceedings of the National Academy of Sciences of the United States of America 103(30): 11358-11363. Malvankar, N. S., M. Vargas, et al. (2011). Tunable metallic-like conductivity in microbial nanowire networks. Nature Nanotechnology 6(9): 573-579. Nielsen, L. P., N. Risgaard-Petersen, et al. (2010). Electric currents couple spatially separated biogeochemical processes in marine sediment. Nature 463(7284): 1071-1074. Reguera, G., K. D. McCarthy, et al. (2005). Extracellular electron transfer via microbial nanowires. Nature 435(7045): 1098-1101. Summers, Z. M., H. E. Fogarty, et al. (2010). Direct Exchange of Electrons Within Aggregates of an Evolved Syntrophic Coculture of Anaerobic Bacteria. Science 330(6009): 1413-1415.

Marzocchi, U.; Revsbech, N. P.; Nielsen, L. P.; Risgaard-Petersen, N.

2012-04-01

275

High-throughput hydrophilic interaction chromatography coupled to tandem mass spectrometry for the optimized quantification of the anti-Gram-negatives antibiotic colistin A/B and its pro-drug colistimethate.  

PubMed

Colistin is a last resort's antibacterial treatment in critically ill patients with multi-drug resistant Gram-negative infections. As appropriate colistin exposure is the key for maximizing efficacy while minimizing toxicity, individualized dosing optimization guided by therapeutic drug monitoring is a top clinical priority. Objective of the present work was to develop a rapid and robust HPLC-MS/MS assay for quantification of colistin plasma concentrations. This novel methodology validated according to international standards simultaneously quantifies the microbiologically active compounds colistin A and B, plus the pro-drug colistin methanesulfonate (colistimethate, CMS). 96-well micro-Elution SPE on Oasis Hydrophilic-Lipophilic-Balanced (HLB) followed by direct analysis by Hydrophilic Interaction Liquid Chromatography (HILIC) with Ethylene Bridged Hybrid--BEH--Amide phase column coupled to tandem mass spectrometry allows a high-throughput with no significant matrix effect. The technique is highly sensitive (limit of quantification 0.014 and 0.006 ?g/mL for colistin A and B), precise (intra-/inter-assay CV 0.6-8.4%) and accurate (intra-/inter-assay deviation from nominal concentrations -4.4 to +6.3%) over the clinically relevant analytical range 0.05-20 ?g/mL. Colistin A and B in plasma and whole blood samples are reliably quantified over 48 h at room temperature and at +4°C (<6% deviation from nominal values) and after three freeze-thaw cycles. Colistimethate acidic hydrolysis (1M H2SO4) to colistin A and B in plasma was completed in vitro after 15 min of sonication while the pro-drug hydrolyzed spontaneously in plasma ex vivo after 4 h at room temperature: this information is of utmost importance for interpretation of analytical results. Quantification is precise and accurate when using serum, citrated or EDTA plasma as biological matrix, while use of heparin plasma is not appropriate. This new analytical technique providing optimized quantification in real-life conditions of the microbiologically active compounds colistin A and B offers a highly efficient tool for routine therapeutic drug monitoring aimed at individualizing drug dosing against life-threatening infections. PMID:25441071

Mercier, Thomas; Tissot, Fréderic; Gardiol, Céline; Corti, Natascia; Wehrli, Stéphane; Guidi, Monia; Csajka, Chantal; Buclin, Thierry; Couet, William; Marchetti, Oscar; Decosterd, Laurent A

2014-11-21

276

Peroxidase-Catalyzed Oxidative Coupling of Phenols in the Presence of Geosorbents  

SciTech Connect

This study focuses on elucidation of the reaction behaviors of peroxidase-mediated phenol coupling in the presence of soil/sediment materials. Our goal is a mechanistic understanding of the influences of geosorbent materials on enzymatic coupling reactions in general and the development of methods for predicting such influences. Extensive experimental investigations of coupling reactions were performed under strategically selected conditions in systems containing model geosorbents having different properties and chemical characteristics. The geosorbents tested were found to influence peroxidase-mediated phenol coupling through one or both of two principal mechanisms; i.e., (1) mitigation of enzyme inactivation and/or (2) participation in cross-coupling reactions. Such influences were found to correlate with the chemical characteristics of the sorbent materials and to be simulated well by a modeling approach designed in this paper. The results of the study have important implications for potential engineering implementation and enhancement of enzymatic coupling reactions in soil/subsurface remediation practice.

Huang, Qingguo; Weber, Walter J., Jr.

2003-03-26

277

Destruction of commercial pesticides by cerium redox couple mediated electrochemical oxidation process in continuous feed mode  

Microsoft Academic Search

Mediated electrochemical oxidation was carried out for the destruction of commercial pesticide formulations using cerium(IV) in nitric acid as the mediator electrolyte solution in a bench scale set up. The mediator oxidant was regenerated in situ using an electrochemical cell. The real application of this sustainable process for toxic organic pollutant destruction lies in its ability for long term continuous

Subramanian Balaji; Sang Joon Chung; Jae-Yong Ryu; Il Shik Moon

2009-01-01

278

Tandem resonator reflectance modulator  

DOEpatents

A wide band optical modulator is grown on a substrate as tandem Fabry-Perot resonators including three mirrors spaced by two cavities. The absorption of one cavity is changed relative to the absorption of the other cavity by an applied electric field, to cause a change in total reflected light, as light reflecting from the outer mirrors is in phase and light reflecting from the inner mirror is out of phase with light from the outer mirrors. 8 figs.

Fritz, I.J.; Wendt, J.R.

1994-09-06

279

Tandem resonator reflectance modulator  

DOEpatents

A wide band optical modulator is grown on a substrate as tandem Fabry-Perot resonators including three mirrors spaced by two cavities. The absorption of one cavity is changed relative to the absorption of the other cavity by an applied electric field, to cause a change in total reflected light, as light reflecting from the outer mirrors is in phase and light reflecting from the inner mirror is out of phase with light from the outer mirrors.

Fritz, Ian J. (Albuquerque, NM); Wendt, Joel R. (Albuquerque, NM)

1994-01-01

280

Mössbauer effect study of tight spin coupling in oxidized chloro-5,10,15,20- tetra(mesityl)porphyrinatoiron(III)  

NASA Astrophysics Data System (ADS)

Mössbauer spectra of a polycrystalline form of oxidized chloro-5,10,15,20-tetra(mesityl)porphyrin- atoiron(III) [Fe(TMP)Cl], compound A, were recorded over a range of temperatures (4.2-195 K) and magnetic fields (0-6 T). These spectra of compound A exhibit magnetic features which are markedly different from those of the analogous protein complexes, horse radish peroxidase compound I (HRP-I) and compound ES of cytochrome c peroxidase, even though chemical evidence and optical spectroscopy indicate that compound A is similar to the others in comprising a Fe(IV) complex within a porphyrin cation radical. We interpret the data by employing a spin Hamiltonian model in which the central Fe(IV) complex, with S=1, is tightly coupled to a S=1/2 system of the oxidized porphyrin to yield a net S=3/2 system as suggested by the susceptibility measurements. The theoretical treatment yields information on the d-electron energies which is similar to that more directly available in the peroxidase spectra. The strength of the axial crystal field is found to increase progressively in the series HRP-I, ES, compound A, while the spin coupling in A is the strongest of the three by several orders of magnitude. The good fits to experimental data confirm the efficacy of the theoretical treatment which may be applicable to a variety of other coupled systems.

Boso, Brian; Lang, George; McMurry, Thomas J.; Groves, John T.

1983-08-01

281

Mechanistic studies on a Cu-catalyzed aerobic oxidative coupling reaction with N-phenyl tetrahydroisoquinoline: structure of intermediates and the role of methanol as a solvent.  

PubMed

The mechanism of an aerobic copper-catalyzed oxidative coupling reaction with N-phenyl tetrahydroisoquinoline was investigated. The oxidized species formed from the reaction of the amine with the copper catalyst were analyzed by NMR-spectroscopy. An iminium dichlorocuprate was found to be the reactive intermediate and could be structurally characterized by X-ray crystallography. The effect of methanol to effectively stabilize the iminium ion was investigated and shown to be beneficial in an oxidative allylation reaction. PMID:21561084

Boess, Esther; Sureshkumar, Devarajulu; Sud, Abhishek; Wirtz, Cornelia; Farès, Christophe; Klussmann, Martin

2011-06-01

282

Oxidative photoredox-catalytic activation of aliphatic nucleophiles for C(sp(3))-C(sp(2)) cross-coupling reactions.  

PubMed

In the light you will find the road (Led Zeppelin): Visible-light photoredox catalysis leads the way in overcoming the reactivity limitations of alkyl nucleophiles in cross-coupling reactions. Iridium-triggered oxidative photoredox activation of alkyltrifluoroborate or carboxylic acids affords alkyl radicals, which undergo nickel-catalyzed cross-coupling reactions. PMID:25324184

Jahn, Emanuela; Jahn, Ullrich

2014-12-01

283

The Efficacy of Oxidative Coupling for Promoting In-Situ Immobilization of Hydroxylated Aromatics in Contaminated Soil and Sediments Systems - Final Report  

SciTech Connect

The study clearly shows that the structure and composition of the organic matter of soils and sediments are essential considerations for the selection of materials for engineered applications of oxidative coupling processes. A rate model was developed to facilitate quantitative evaluation and mechanistic interpretation of these fairly complex coupling processes.

Weber Jr., W. J.

2000-10-01

284

Li-doped MgO as catalysts for oxidative coupling of methane: A positron annihilation study  

NASA Astrophysics Data System (ADS)

Magnesium oxides intentionally doped with lithium (with a maximum Li content of 40 tool%) for use as catalysts for oxidative coupling of methane were characterized by means of positron annihilation. The positron lifetime spectra, which could be reasonably well interpreted within the framework of the well-known trapping model, depend on the amount of Li doping of the MgO suggesting that positrons are trapped at dispersed small Li 2CO 3 precipitates. Very similar dependencies on lithium doping of the C 2 selectivity and the positron trapping rate ? imply an intimate relationship between the concentration of [Li] 0-centers (also referred to as [Li +O -] centers) and the selective activity of Li/MgO during catalytic reactions.

Dai, G. H.; Yan, Q. J.; Wang, Y.; Liu, Q. S.

1991-08-01

285

Critical Role for Tetrahydrobiopterin Recycling by Dihydrofolate Reductase in Regulation of Endothelial Nitric-oxide Synthase Coupling  

PubMed Central

Tetrahyrobiopterin (BH4) is a required cofactor for the synthesis of nitric oxide by endothelial nitric-oxide synthase (eNOS), and BH4 bioavailability within the endothelium is a critical factor in regulating the balance between NO and superoxide production by eNOS (eNOS coupling). BH4 levels are determined by the activity of GTP cyclohydrolase I (GTPCH), the rate-limiting enzyme in de novo BH4 biosynthesis. However, BH4 levels may also be influenced by oxidation, forming 7,8-dihydrobiopterin (BH2), which promotes eNOS uncoupling. Conversely, dihydrofolate reductase (DHFR) can regenerate BH4 from BH2, but the functional importance of DHFR in maintaining eNOS coupling remains unclear. We investigated the role of DHFR in regulating BH4 versus BH2 levels in endothelial cells and in cell lines expressing eNOS combined with tet-regulated GTPCH expression in order to compare the effects of low or high levels of de novo BH4 biosynthesis. Pharmacological inhibition of DHFR activity by methotrexate or genetic knockdown of DHFR protein by RNA interference reduced intracellular BH4 and increased BH2 levels resulting in enzymatic uncoupling of eNOS, as indicated by increased eNOS-dependent superoxide but reduced NO production. In contrast to the decreased BH4:BH2 ratio induced by DHFR knockdown, GTPCH knockdown greatly reduced total biopterin levels but with no change in BH4:BH2 ratio. In cells expressing eNOS with low biopterin levels, DHFR inhibition or knockdown further diminished the BH4:BH2 ratio and exacerbated eNOS uncoupling. Taken together, these data reveal a key role for DHFR in eNOS coupling by maintaining the BH4:BH2 ratio, particularly in conditions of low total biopterin availability. PMID:19666465

Crabtree, Mark J.; Tatham, Amy L.; Hale, Ashley B.; Alp, Nicholas J.; Channon, Keith M.

2009-01-01

286

Demonstrating Advanced Oxidation Coupled with Biodegradation for Removal of Carbamazepine (WERF Report INFR6SG09)  

EPA Science Inventory

Carbamazepine is an anthropogenic pharmaceutical found in wastewater effluents that is quite resistant to removal by conventional wastewater treatment processes. Hydroxyl radical-based advanced oxidation processes can transform carbamazepine into degradation products but cannot m...

287

Solar-powered electrochemical oxidation of organic compounds coupled with the cathodic production of molecular hydrogen.  

PubMed

A Bi-doped TiO2 anode, which is prepared from a mixed metal oxide coating deposited on Ti metal, is shown to be efficient for conventional water splitting. In this hybrid photovoltaic-electrochemical system, a photovoltaic (PV) cell is used to convert solar light to electricity, which is then used to oxidize a series of phenolic compounds at the semiconductor anode to carbon dioxide with the simultaneous production of molecular hydrogen from water/proton reduction at the stainless steel cathode. Degradation of phenol in the presence of a background NaCl electrolyte produces chlorinated phenols as reaction intermediates, which are subsequently oxidized completely to carbon dioxide and low-molecular weight carboxylic acids. The anodic current efficiency for the complete oxidation of phenolic compounds ranges from 3% to 17%, while the cathodic current efficiency and the energy efficiency for hydrogen gas generation range from 68% to 95% and 30% to 70%, respectively. PMID:18656909

Park, Hyunwoong; Vecitis, Chad D; Hoffmann, Michael R

2008-08-21

288

Carbon-coated magnetic palladium: applications in partial oxidation of alcohols and coupling reactions.  

EPA Science Inventory

Magnetic carbon supported Pd catalyst has been synthesized via in situ generation of nanoferrites and incorporation of carbon from renewable cellulose via calcination; catalyst can be used for oxidation of alcohols, amination reaction and arylation of aryl halides (cross coupli...

289

Stereoselective tandem cascade furan cycloadditions.  

PubMed

Oligofurans linked by a rigid tether undergo tandem cycloaddition reactions with high stereoselectivity. The reaction of bisfurans with dimethyl acetylenedicarboxylate (DMAD) involves tandem [4 + 2]/[4 + 2] cycloadditions in a pincer mode. The reaction of oligofurans with arynes involves stereoselective tandem [4 + 2]/[4 + 2] cycloaddition reactions in a domino mode. The corresponding aryne adducts have been transformed into extended perylene derivatives by deoxygenation and aromatization with HCl/EtOH. PMID:24228899

Criado, Alejandro; Vilas-Varela, Manuel; Cobas, Agustín; Pérez, Dolores; Peña, Diego; Guitián, Enrique

2013-12-20

290

Oxidative coupling of methylamine with an aminyl radical: direct amidation catalyzed by I2/TBHP with HCl.  

PubMed

Oxidative coupling of methylamines with an aminyl radical to construct amides was developed in the presence of an I2/TBHP catalyst under acidic conditions via the two cleavages of the sp(3) C-N bond of aryl-methylamines and the sp(2) C-N bond of N-substituted formamides respectively. This transition-metal-free protocol provides a novel synthetic tool for the construction of N-substituted amides and a series of arylamides can be easily obtained with good yields. PMID:24618846

Gao, Lingfeng; Tang, Haoming; Wang, Zhiyong

2014-04-21

291

?-Shaped Bis(areno)-1,4-dihydropyrrolo[3,2-b]pyrroles Generated by Oxidative Aromatic Coupling.  

PubMed

A synthesis of dihydropyrrolo[3,2-b]pyrroles fused with two peripheral arenes or heterocyclic units has been realized through the concise route. These nearly planar compounds were prepared starting from assembling the central core via condensation of 2-aryl or 2-heteroarylbenzaldehydes with aromatic amines and diacetyl, followed by double intramolecular oxidative aromatic coupling. This two-step procedure afforded the desired products in overall yields of 5-36%, and it tolerates structural diversity of starting materials. All the final dyes exhibit strong blue fluorescence in solution. PMID:25692662

Krzeszewski, Maciej; Gryko, Daniel T

2015-03-01

292

Carbon Isotopic Evidence for Coupled Sulfate Reduction-Methane Oxidation in Amazon Fan Sediments  

NASA Astrophysics Data System (ADS)

Carbon isotope ratios of dissolved inorganic carbon were measured on porewaters from Amazon Fan sediments collected on Ocean Drilling Program Leg 155. Values as low as -49.6‰ vs. PDB were recorded, with the lowest values coinciding with the base of the sulfate reduction zone at each site. The values indicate that on the order of 50-85% of sulfate reduction in Amazon Fan sediments takes place by methane oxidation. Estimated rates of methane oxidation range from 0.3-1.0x10 -5 moles/l/yr. The reasons for the high percentage of sulfate reduction taking place by methane oxidation are thought to be the large decrease in fan sedimentation rates in the early Holocene and the terrestrial source of organic matter in fan sediments.

Burns, Stephen J.

1998-03-01

293

Negative tandem mirror  

SciTech Connect

A tandem mirror configuration can be created by combining hot electron end cell plasmas with neutral beam pumping. A region of large negative potential formed in each end cell confines electrons in the central cell. The requirement of charge neutrality causes the central cell potential to become negative with respect to ground in order to confine ions as well as electrons. We discuss the method of producing and calculating the desired axial potential profile, and show the calculated axial potential profile and plasma parameters for a negative configuration of TMX-Upgrade.

Poulsen, P.; Allen, S.L.; Casper, T.A.; Grubb, D.P.; Jong, R.A.; Nexsen, W.E.; Porter, G.D.; Simonen, T.C.

1981-11-30

294

Monolithic tandem solar cell  

DOEpatents

A single-crystal, monolithic, tandem, photovoltaic solar cell is described which includes (a) an InP substrate having upper and lower surfaces, (b) a first photoactive subcell on the upper surface of the InP substrate, (c) a second photoactive subcell on the first subcell; and (d) an optically transparent prismatic cover layer over the second subcell. The first photoactive subcell is GaInAsP of defined composition. The second subcell is InP. The two subcells are lattice matched. 9 figs.

Wanlass, M.W.

1994-06-21

295

Probe diagnostics of argon-oxygen-tetramethyltin capacitively coupled plasmas for the deposition of tin oxide thin films  

SciTech Connect

Langmuir probe measurements in nondepositing and depositing rf capacitively coupled (CCP) plasmas are briefly reviewed and compared to the results obtained in our rf system used for the deposition of tin oxide (SnO{sub 2}) thin films from argon-oxygen-tetamethyltin [Sn(CH{sub 3}){sub 4}] plasmas. Typically in our experimental conditions for tin oxide deposition, values of kT{sub eff}= 1.2-1.5 eV and n{sub e}=3-5x10{sup 9} cm{sup -3} were measured. These values are consistent with those generally reported in other depositing discharges. The shape of the electron energy probability function (EEPF), obtained from the Druyvesteyn procedure, was discussed too. As a consequence of the two electron heating mechanisms in capacitively coupled discharges, that is, ohmic and stochastic heating, the electrons have a bi-Maxwellian EEPF at low pressure (in the range of 10-100 mTorr). Moreover, a deep 'hole' appears in the EEPF at the energy which could correspond to the resonant peak of the vibrational excitation cross section of some molecules which can be present in the discharge, such as N{sub 2}, CH{sub 4}, or CO.

Pulpytel, J.; Morscheidt, W.; Arefi-Khonsari, F. [Laboratoire de Genie des procedes Plasmas, Ecole Nationale Superieure de Chimie Paris, Universite Pierre et Marie Curie, Paris 6 (France)

2007-04-01

296

Convergence of G Protein-Coupled Receptor and Nitric Oxide Pathways Determines the Outcome to Cardiac Ischemic Injury  

PubMed Central

Heart failure caused by ischemic heart disease is a leading cause of death in the developed world. Treatment is currently centered on regimens involving G protein-coupled receptors (GPCRs) or nitric oxide (NO). These regimens are thought to target distinct molecular pathways. We showed that these pathways were interdependent and converged on the effector GRK2 (GPCR kinase 2) to regulate myocyte survival and function. Ischemic injury coupled to GPCR activation, including GPCR desensitization and myocyte loss, requires GRK2 activation, and we found that cardioprotection mediated by S-nitrosylation and inhibition of GRK2 depended on endothelial nitric oxide synthase (eNOS). Conversely, the cardioprotective effects of NO bioactivity were absent in a knock-in mouse with a form of GRK2 that cannot be S-nitrosylated. Because GRK2 and eNOS inhibit each other, the balance of the activities these enzymes in the myocardium determined the outcome to ischemic injury. Our findings suggest new insights into the mechanism of action of classic drugs used to treat heart failure and new therapeutic approaches to ischemic heart disease. PMID:24170934

Huang, Z. Maggie; Gao, Erhe; Fonseca, Fabio; Hayashi, Hiroki; Shang, Xiying; Hoffman, Nicholas E.; Chuprun, J. Kurt; Tian, Xufan; Tilley, Doug G.; Madesh, Muniswamy; Lefer, David J.; Stamler, Jonathan S.; Koch, Walter J.

2014-01-01

297

Lead-Calcium Hydroxyapatite: Cation Effects in the Oxidative Coupling of Methane  

NASA Astrophysics Data System (ADS)

The properties of calcium hydroxyapatite and a number of lead-calcium hydroxyapatites are examined, and their activities in the conversion of methane with nitrous oxide and oxygen as oxidants are compared. The introduction of a small quantity of lead considerably alters both the conversion of methane and the selectivities to the various products. The introduction of lead appears to assist in the stabilization of methyl radicals, while the formation of ensembles of surface lead atoms brings methyl radicals into sufficiently close proximity so as to induce bonding between the radicals and formation of ethane.

Matsumura, Yasuyuki; Sugiyama, Shigeru; Hayashi, Hiromu; Moffat, John B.

1995-01-01

298

Synfuels from fusion: producing hydrogen with the Tandem Mirror Reactor and thermochemical cycles  

SciTech Connect

This volume contains the following sections: (1) the Tandem Mirror fusion driver, (2) the Cauldron blanket module, (3) the flowing microsphere, (4) coupling the reactor to the process, (5) the thermochemical cycles, and (6) chemical reactors and process units. (MOW)

Werner, R.W.; Ribe, F.L.

1981-01-21

299

Alkyne hydroacylation: switching regioselectivity by tandem ruthenium catalysis.  

PubMed

By using tandem Ru-catalysis, internal alkynes can be coupled with aldehydes for the synthesis of ?,?-unsaturated ketones. The catalyst promotes alkyne transformations with high regioselectivity, with examples that include the differentiation of a methyl vs ethyl substituent on the alkyne. Mechanistic studies suggest that the regioselectivity results from a selective allene formation that is governed by allylic strain. PMID:25608143

Chen, Qing-An; Cruz, Faben A; Dong, Vy M

2015-03-11

300

Intracellular measurements of anti-HIV drugs indinavir, amprenavir, saquinavir, ritonavir, nelfinavir, lopinavir, atazanavir, efavirenz and nevirapine in peripheral blood mononuclear cells by liquid chromatography coupled to tandem mass spectrometry  

Microsoft Academic Search

A sensitive and accurate liquid chromatography–tandem mass spectrometric (LC–MS\\/MS) method for the intracellular determination of nine antiretroviral drugs in human peripheral blood mononuclear cells (PBMCs) is proposed. PBMCs are isolated by density gradient centrifugation using Vacutainer™ CPT tubes and cell count is performed with a Coulter® instrument. Single-step extraction of drugs from PBMCs pellets is performed with MeOH 50% (with

S. Colombo; A. Beguin; A. Telenti; J. Biollaz; T. Buclin; B. Rochat; L. A. Decosterd

2005-01-01

301

Expeditious Enyne Construction from Alkynes via Oxidative Pd(II) Catalyzed Heck-Type Coupling  

PubMed Central

The enyne, ubiquitous in natural products, can be a challenge to generate since these moieties require many synthetic transformations to assemble them. We developed a simpler protocol to construct enynes while we found that this oxidative reaction was tolerant in substrate scope. In addition, the utility of this reaction was demonstrated through the attempt in synthesizing antifungal agent Lamisi™. PMID:20161498

Hadi, Victor; Yoo, Kyung Soo; Jeong, Min; Jung, Kyung Woon

2009-01-01

302

Access to cinnamyl derivatives from arenes and allyl esters by a biomimetic aerobic oxidative dehydrogenative coupling.  

PubMed

An efficient biomimetic aerobic oxidative dehydrogenative alkenylation of arenes with allyl esters is presented. The reaction proceeds under an ambient pressure of oxygen with relatively low catalyst loading of palladium acetate, employing catalytic amounts of electron-transfer mediators (ETMs). This study represents a new environmentally friendly method for the synthesis of cinnamyl derivatives. PMID:24606049

Gigant, Nicolas; Bäckvall, Jan-E

2014-03-21

303

Plutonium-uranium mixed oxide characterization by coupling micro-X-ray diffraction and absorption investigations  

NASA Astrophysics Data System (ADS)

Plutonium-uranium mixed oxide (MOX) fuels are currently used in nuclear reactors. The potential differences of metal redox state and microstructural developments of the matrix before and after irradiation are commonly analysed by electron probe microanalysis. In this work the structure and next-neighbor atomic environments of Pu and U oxide features within unirradiated homogeneous MOX and irradiated (60 MW d kg -1) MOX samples was analysed by micro-X-ray fluorescence (?-XRF), micro-X-ray diffraction (?-XRD) and micro-X-ray absorption fine structure (?-XAFS) spectroscopy. The grain properties, chemical bonding, valences and stoichiometry of Pu and U are determined from the experimental data gained for the unirradiated as well as for irradiated fuel material examined in the center of the fuel as well as in its peripheral zone (rim). The formation of sub-grains is observed as well as their development from the center to the rim (polygonization). In the irradiated sample Pu remains tetravalent (>95%) and no (<5%) Pu(V) or Pu(VI) can be detected while the fuel could undergo slight oxidation in the rim zone. Any slight potential plutonium oxidation is buffered by the uranium dioxide matrix while locally fuel cladding interaction could also affect the redox of the fuel.

Degueldre, C.; Martin, M.; Kuri, G.; Grolimund, D.; Borca, C.

2011-09-01

304

Light induced carbon dioxide reduction by water at binuclear ZrOCo(II) unit coupled to Ir oxide nanocluster catalyst.  

PubMed

An all-inorganic polynuclear unit consisting of an oxo-bridged binuclear ZrOCo(II) group coupled to an iridium oxide nanocluster (IrO(x)) was assembled on an SBA-15 silica mesopore surface. A photodeposition method was developed that affords coupling of the IrO(x) water oxidation catalyst with the Co donor center. The approach consists of excitation of the ZrOCo(II) metal-to-metal charge-transfer (MMCT) chromophore with visible light in the presence of [Ir(acac)3] (acac: acetylacetonate) precursor followed by calcination under mild conditions, with each step monitored by optical and infrared spectroscopy. Illumination of the MMCT chromophore of the resulting ZrOCo(II)-IrO(x) units in the SBA-15 pores loaded with a mixture of (13)CO2 and H2O vapor resulted in the formation of (13)CO and O2 monitored by FT-IR and mass spectroscopy, respectively. Use of (18)O labeled water resulted in the formation of (18)O2 product. This is the first example of a closed photosynthetic cycle of carbon dioxide reduction by water using an all-inorganic polynuclear cluster featuring a molecularly defined light absorber. The observed activity implies successful competition of electron transfer between the IrO(x) catalyst cluster and the transient oxidized Co donor center with back electron transfer of the ZrOCo light absorber, and is further aided by the instant desorption of the CO and O2 product from the silica pores. PMID:25033315

Kim, Wooyul; Yuan, Guangbi; McClure, Beth Anne; Frei, Heinz

2014-08-01

305

Design of a visible light driven photo-electrochemical/electro-Fenton coupling oxidation system for wastewater treatment.  

PubMed

In this study, we report on a photo-electrochemical/electro-Fenton oxidation (PEC/EF) system by coupling visible light driven photo-electrochemical oxidation (PEC) and electro-Fenton oxidation (EF) in an undivided cell. Bi2WO6 nanoplates deposited on FTO glass (Bi2WO6/FTO) and Fe@Fe2O3 core-shell nanowires supported on activated carbon fiber (Fe@Fe2O3/ACF) were used as the anode and the cathode in the PEC/EF system, respectively. This novel PEC/EF system showed much higher activity than the single PEC and EF systems on degradation of rhodamine B in aqueous solution at natural pH. Moreover, the degradation and the instantaneous current efficiencies of the PEC/EF system were increased by 154% and 26% in comparison with the sum of those of single PEC and EF systems, respectively. These significant enhancements could be attributed to the synergetic effect from better separation of photo-generated carriers in the photo-anode and the transfer of photo-electrons to the oxygen diffusion cathode to generate more electro-generated H2O2 and hydroxyl radicals on the Fenton cathode. The better separation of photo-generated carriers contribute more to the overall degradation enhancement than the photo-electrons generated H2O2 and the subsequent Fenton reaction on the cathode during the PEC/EF process. PMID:23017238

Ding, Xing; Ai, Zhihui; Zhang, Lizhi

2012-11-15

306

Inductively coupled plasma etching of hafnium-indium-zinc oxide using chlorine based gas mixtures  

NASA Astrophysics Data System (ADS)

We report the etching characteristics of a stacked hafnium-indium-zinc oxide (HIZO) with a photoresist using the gas mixture of chlorine and argon (Cl2/Ar). The etching behaviors of HIZO have been investigated in terms of a source power, a bias power and a chamber pressure. As the concentration of Cl2 was increased compared to pure Ar, the etch rate of HIZO film was found slightly different from that of indium-zinc oxide (IZO) film. Moreover, to investigate the etching mechanism systematically, various inspections were carried out such as atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) depending on the portion of Cl2. Additionally, we compared the etching mechanism of HIZO film with IZO film to confirm the difference of chemical bonds caused by the influence of hafnium doping.

Choi, Yong-Hee; Jang, Ho-Kyun; Jin, Jun-Eon; Joo, Min-Kyu; Piao, Mingxing; Shin, Jong Mok; Kim, Jae-Sung; Na, Junhong; Kim, Gyu Tae

2014-04-01

307

Interactions and coupling between emissions of methane and nitrous oxide from animal husbandry  

Microsoft Academic Search

The gases methane (CH4) and nitrous oxide (N2O) contribute to global warming, while N2O also affects the ozone layer. Sources of greenhouse gas emissions in animal husbandry include animals, animal houses (indoor\\u000a storage of animal excreta), outdoor storage, manure and slurry treatment (e.g., composting, anaerobic treatment), land application\\u000a and chemical fertilisers. Although in many countries emphasis is put on reduction

G. J. Monteny; C. M. Groenestein; M. A. Hilhorst

2001-01-01

308

Activated carbon electrodes: Electrochemical oxidation coupled with desalination for wastewater treatment.  

PubMed

The wastewater usually contains low-concentration organic pollutants and some inorganic salts after biological treatment. In the present work, the possibility of simultaneous removal of them by combining electrochemical oxidation and electrosorption was investigated. Phenol and sodium chloride were chosen as representative of organic pollutants and inorganic salts and a pair of activated carbon plate electrodes were used as anode and cathode. Some important working conditions such as oxygen concentration, applied potential and temperature were evaluated to reach both efficient phenol removal and desalination. Under optimized 2.0V of applied potential, 38°C of temperature, and 500mLmin(-1) of oxygen flow, over 90% of phenol, 60% of TOC and 20% of salinity were removed during 300min of electrolysis time. Phenol was removed by both adsorption and electrochemical oxidation, which may proceed directly or indirectly by chlorine and hypochlorite oxidation. Chlorophenols were detected as degradation intermediates, but they were finally transformed to carboxylic acids. Desalination was possibly attributed to electrosorption of ions in the pores of activated carbon electrodes. The charging/regeneration cycling experiment showed good stability of the electrodes. This provides a new strategy for wastewater treatment and recycling. PMID:25585871

Duan, Feng; Li, Yuping; Cao, Hongbin; Wang, Yi; Crittenden, John C; Zhang, Yi

2015-04-01

309

Spin-flop coupling and exchange bias in embedded complex oxide micromagnets  

SciTech Connect

The magnetic domains of embedded micromagnets defined in epitaxial La0.7Sr0.3MnO3 (LSMO) thin films and LaFeO3/LSMO bilayers were investigated using soft x-ray magnetic microscopy. Square micromagnets with 2 x 2 m dimensions aligned with their edges parallel to the easy axes of LSMO provide an ideal experimental geometry for probing the influence of interface exchange coupling on the magnetic domain patterns. The observation of unique domain patterns not found in ferromagnetic metal microstructures, namely divergent antiferromagnetic vortex domains and Z -type domains, suggests the simultaneous presence of spin-flop coupling and local exchange bias in this system.

Takamura, Yayoi [ORNL] [ORNL; Folven, Eric [Norwegian University of Science and Technology] [Norwegian University of Science and Technology; Shu, Jonathan B.R. [University of California, Davis] [University of California, Davis; Lukes, Karl [University of California, Davis] [University of California, Davis; Binzhi, Li [University of California, Davis] [University of California, Davis; Scholl, Andreas [Lawrence Berkeley National Laboratory (LBNL)] [Lawrence Berkeley National Laboratory (LBNL); Young, Anthony [Lawrence Berkeley National Laboratory (LBNL)] [Lawrence Berkeley National Laboratory (LBNL); Retterer, Scott T [ORNL] [ORNL; Tybell, Thomas [Lawrence Berkeley National Laboratory (LBNL)] [Lawrence Berkeley National Laboratory (LBNL); Grepstad, Jostein [Norwegian University of Science and Technology] [Norwegian University of Science and Technology

2013-01-01

310

Enzyme catalysed tandem reactions.  

PubMed

To transfer to the laboratory, the excellent efficiency shown by enzymes in Nature, biocatalysis, had to mimic several synthetic strategies used by the living organisms. Biosynthetic pathways are examples of tandem catalysis and may be assimilated in the biocatalysis field for the use of isolated multi-enzyme systems in the homogeneous phase. The concurrent action of several enzymes that work sequentially presents extraordinary advantages from the synthetic point of view, since it permits a reversible process to become irreversible, to shift the equilibrium reaction in such a way that enantiopure compounds can be obtained from prochiral or racemic substrates, reduce or eliminate problems due to product inhibition or prevent the shortage of substrates by dilution or degradation in the bulk media, etc. In this review we want to illustrate the developments of recent studies involving in vitro multi-enzyme reactions for the synthesis of different classes of organic compounds. PMID:23490810

Oroz-Guinea, Isabel; García-Junceda, Eduardo

2013-04-01

311

Mössbauer spectrometric study of nonstoichiometric perovskite, A (Co0.8Fe0.2) O3-° (A=Ba, Sr, Ca), for oxidative coupling of methane  

NASA Astrophysics Data System (ADS)

Nonstoichiometric perovskites. A(Co0.8Fe0.2)O3-6, were prepared by a pyrolysis of mixed metal citrates, and the catalytic property and structure of these perovskites were investigated. The efficiency of an oxidative coupling of methane increases with the order of Ba. Sr, and Ca substituted in A site and decreases with the amounts of deficient oxygens. The mixed valence of B site ions in the disordering of deficient oxygen is considered to contribute mainly to the oxidative coupling of methane.

Nomura, Kiyoshi; Goda, Takeshi; Ujihira, Yusuke; Hayakawa, Takashi; Takehira, Katsuomi

1992-04-01

312

Coupled reductive and oxidative sulfur cycling in the phototrophic plate of a meromictic lake.  

PubMed

Mahoney Lake represents an extreme meromictic model system and is a valuable site for examining the organisms and processes that sustain photic zone euxinia (PZE). A single population of purple sulfur bacteria (PSB) living in a dense phototrophic plate in the chemocline is responsible for most of the primary production in Mahoney Lake. Here, we present metagenomic data from this phototrophic plate--including the genome of the major PSB, as obtained from both a highly enriched culture and from the metagenomic data--as well as evidence for multiple other taxa that contribute to the oxidative sulfur cycle and to sulfate reduction. The planktonic PSB is a member of the Chromatiaceae, here renamed Thiohalocapsa sp. strain ML1. It produces the carotenoid okenone, yet its closest relatives are benthic PSB isolates, a finding that may complicate the use of okenone (okenane) as a biomarker for ancient PZE. Favorable thermodynamics for non-phototrophic sulfide oxidation and sulfate reduction reactions also occur in the plate, and a suite of organisms capable of oxidizing and reducing sulfur is apparent in the metagenome. Fluctuating supplies of both reduced carbon and reduced sulfur to the chemocline may partly account for the diversity of both autotrophic and heterotrophic species. Collectively, the data demonstrate the physiological potential for maintaining complex sulfur and carbon cycles in an anoxic water column, driven by the input of exogenous organic matter. This is consistent with suggestions that high levels of oxygenic primary production maintain episodes of PZE in Earth's history and that such communities should support a diversity of sulfur cycle reactions. PMID:24976102

Hamilton, T L; Bovee, R J; Thiel, V; Sattin, S R; Mohr, W; Schaperdoth, I; Vogl, K; Gilhooly, W P; Lyons, T W; Tomsho, L P; Schuster, S C; Overmann, J; Bryant, D A; Pearson, A; Macalady, J L

2014-09-01

313

Hexagonal Ag nanoarrays induced enhancement of blue light emission from amorphous oxidized silicon nitride via localized surface plasmon coupling.  

PubMed

A significant enhancement of blue light emission from amorphous oxidized silicon nitride (a-SiNx:O) films is achieved by introduction of ordered and size-controllable arrays of Ag nanoparticles between the silicon substrate and a-SiNx:O films. Using hexagonal arrays of Ag nanoparticles fabricated by nanosphere lithography, the localized surface plasmons (LSPs) resonance can effectively increase the internal quantum efficiency from 3.9% to 13.3%. Theoretical calculation confirms that the electromagnetic field-intensity enhancement is through the dipole surface plasma coupling with the excitons of a-SiNx:O films, which demonstrates a-SiNx:O films with enhanced blue emission are promising for silicon-based light-emitting applications by patterned Ag arrays. PMID:25402058

Ma, Zhongyuan; Ni, Xiaodong; Zhang, Wenping; Jiang, Xiaofan; Yang, Huafeng; Yu, Jie; Wang, Wen; Xu, Ling; Xu, Jun; Chen, Kunji; Feng, Duan

2014-11-17

314

Doped Mott insulators in (111) bilayers of perovskite transition-metal oxides with a strong spin-orbit coupling.  

PubMed

The electronic properties of Mott insulators realized in (111) bilayers of perovskite transition-metal oxides are studied. The low-energy effective Hamiltonians for such Mott insulators are derived in the presence of a strong spin-orbit coupling. These models are characterized by the antiferromagnetic Heisenberg interaction and the anisotropic interaction whose form depends on the d orbital occupancy. From exact diagonalization analyses on finite clusters, the ground state phase diagrams are derived, including a Kitaev spin liquid phase in a narrow parameter regime for t(2g) systems. Slave-boson mean-field analyses indicate the possibility of novel superconducting states induced by carrier doping into the Mott-insulating parent systems, suggesting the present model systems as unique playgrounds for studying correlation-induced novel phenomena. Possible experimental realizations are also discussed. PMID:23432283

Okamoto, Satoshi

2013-02-01

315

Doped Mott Insulators in (111) Bilayers of Perovskite Transition-Metal Oxides with a Strong Spin-Orbit Coupling  

SciTech Connect

The electronic properties of Mott insulators realized in (111) bilayers of perovskite transition-metal oxides are studied. The low-energy effective Hamiltonians for such Mott insulators are derived in the presence of a strong spin-orbit coupling. These models are characterized by the antiferromagnetic Heisenberg interaction and the anisotropic interaction whose form depends on the $d$ orbital occupancy. From exact diagonalization analyses on finite clusters, the ground state phase diagrams are derived, including a Kitaev spin liquid phase in a narrow parameter regime for $t_{2g}$ systems. Slave-boson mean-field analyses indicate the possibility of novel superconducting states induced by carrier doping into the Mott-insulating parent systems, suggesting the present model systems as unique playgrounds for studying correlation-induced novel phenomena. Possible experimental realizations are also discussed.

Okamoto, Satoshi [ORNL

2013-01-01

316

Dye Sensitized Tandem Photovoltaic Cells  

SciTech Connect

This work provided a new way to look at photoelectrochemical cells and their performance. Although thought of as low efficiency, a the internal efficiency of a 9% global efficiency dye sensitized solar cell is approximately equal to an 18% efficient silicon cell when each is compared to their useful spectral range. Other work undertaken with this contract also reported the first growth oriented titania and perovskite columns on a transparent conducting oxide. Other work has shown than significant performance enhancement in the performance of dye sensitized solar cells can be obtained through the use of coupling inverse opal photonic crystals to the nanocrystalline dye sensitized solar cell. Lastly, a quick efficient method was developed to bond titanium foils to transparent conducting oxide substrates for anodization.

Barber, Greg D.

2009-12-21

317

Glutamate Utilization Couples Oxidative Stress Defense and the Tricarboxylic Acid Cycle in Francisella Phagosomal Escape  

PubMed Central

Intracellular bacterial pathogens have developed a variety of strategies to avoid degradation by the host innate immune defense mechanisms triggered upon phagocytocis. Upon infection of mammalian host cells, the intracellular pathogen Francisella replicates exclusively in the cytosolic compartment. Hence, its ability to escape rapidly from the phagosomal compartment is critical for its pathogenicity. Here, we show for the first time that a glutamate transporter of Francisella (here designated GadC) is critical for oxidative stress defense in the phagosome, thus impairing intra-macrophage multiplication and virulence in the mouse model. The gadC mutant failed to efficiently neutralize the production of reactive oxygen species. Remarkably, virulence of the gadC mutant was partially restored in mice defective in NADPH oxidase activity. The data presented highlight links between glutamate uptake, oxidative stress defense, the tricarboxylic acid cycle and phagosomal escape. This is the first report establishing the role of an amino acid transporter in the early stage of the Francisella intracellular lifecycle. PMID:24453979

Ramond, Elodie; Gesbert, Gael; Rigard, Mélanie; Dairou, Julien; Dupuis, Marion; Dubail, Iharilalao; Meibom, Karin; Henry, Thomas; Barel, Monique; Charbit, Alain

2014-01-01

318

Inorganic proton conducting electrolyte coupled oxide-based dendritic transistors for synaptic electronics  

NASA Astrophysics Data System (ADS)

Ionic/electronic hybrid devices with synaptic functions are considered to be the essential building blocks for neuromorphic systems and brain-inspired computing. Here, artificial synapses based on indium-zinc-oxide (IZO) transistors gated by nanogranular SiO2 proton-conducting electrolyte films are fabricated on glass substrates. Spike-timing dependent plasticity and paired-pulse facilitation are successfully mimicked in an individual bottom-gate transistor. Most importantly, dynamic logic and dendritic integration established by spatiotemporally correlated spikes are also mimicked in dendritic transistors with two in-plane gates as the presynaptic input terminals.Ionic/electronic hybrid devices with synaptic functions are considered to be the essential building blocks for neuromorphic systems and brain-inspired computing. Here, artificial synapses based on indium-zinc-oxide (IZO) transistors gated by nanogranular SiO2 proton-conducting electrolyte films are fabricated on glass substrates. Spike-timing dependent plasticity and paired-pulse facilitation are successfully mimicked in an individual bottom-gate transistor. Most importantly, dynamic logic and dendritic integration established by spatiotemporally correlated spikes are also mimicked in dendritic transistors with two in-plane gates as the presynaptic input terminals. Electronic supplementary information (ESI) available: The structures and transfer characteristics of the IZO junctionless transistor working in bottom-gate mode and in-plane gate mode. See DOI: 10.1039/c3nr05882d

Wan, Chang Jin; Zhu, Li Qiang; Zhou, Ju Mei; Shi, Yi; Wan, Qing

2014-04-01

319

Glutamate utilization couples oxidative stress defense and the tricarboxylic acid cycle in Francisella phagosomal escape.  

PubMed

Intracellular bacterial pathogens have developed a variety of strategies to avoid degradation by the host innate immune defense mechanisms triggered upon phagocytocis. Upon infection of mammalian host cells, the intracellular pathogen Francisella replicates exclusively in the cytosolic compartment. Hence, its ability to escape rapidly from the phagosomal compartment is critical for its pathogenicity. Here, we show for the first time that a glutamate transporter of Francisella (here designated GadC) is critical for oxidative stress defense in the phagosome, thus impairing intra-macrophage multiplication and virulence in the mouse model. The gadC mutant failed to efficiently neutralize the production of reactive oxygen species. Remarkably, virulence of the gadC mutant was partially restored in mice defective in NADPH oxidase activity. The data presented highlight links between glutamate uptake, oxidative stress defense, the tricarboxylic acid cycle and phagosomal escape. This is the first report establishing the role of an amino acid transporter in the early stage of the Francisella intracellular lifecycle. PMID:24453979

Ramond, Elodie; Gesbert, Gael; Rigard, Mélanie; Dairou, Julien; Dupuis, Marion; Dubail, Iharilalao; Meibom, Karin; Henry, Thomas; Barel, Monique; Charbit, Alain

2014-01-01

320

Production date determination of uranium-oxide materials by inductively coupled plasma mass spectrometry.  

PubMed

The paper describes analytical methods developed for the production date determination of uranium-based nuclear materials by the measurement of 230Th/234U isotope ratio. An improved sample preparation method for the destructive analysis involving extraction chromatographic separation with TEVA resin was applied prior to the measurement by isotope dilution inductively coupled plasma sector field mass spectrometry (ICP-SFMS). The results obtained were compared with the direct, quasi-non-destructive measurement using laser ablation ICP-SFMS technique for age determination. The advantages and limitations of both methods are discussed. PMID:17765059

Varga, Zsolt; Surányi, Gergely

2007-09-01

321

Molecular characterization of a microbial consortium involved in methane oxidation coupled to denitrification under micro-aerobic conditions  

PubMed Central

Methane can be used as an alternative carbon source in biological denitrification because it is nontoxic, widely available and relatively inexpensive. A microbial consortium involved in methane oxidation coupled to denitrification (MOD) was enriched with nitrite and nitrate as electron acceptors under micro-aerobic conditions. The 16S rRNA gene combined with pmoA phylogeny of methanotrophs and nirK phylogeny of denitrifiers were analysed to reveal the dominant microbial populations and functional microorganisms. Real-time quantitative polymerase chain reaction results showed high numbers of methanotrophs and denitrifiers in the enriched consortium. The 16S rRNA gene clone library revealed that Methylococcaceae and Methylophilaceae were the dominant populations in the MOD ecosystem. Phylogenetic analyses of pmoA gene clone libraries indicated that all methanotrophs belonged to Methylococcaceae, a type I methanotroph employing the ribulose monophosphate pathway for methane oxidation. Methylotrophic denitrifiers of the Methylophilaceae that can utilize organic intermediates (i.e. formaldehyde, citrate and acetate) released from the methanotrophs played a vital role in aerobic denitrification. This study is the first report to confirm micro-aerobic denitrification and to make phylogenetic and functional assignments for some members of the microbial assemblages involved in MOD. PMID:24245852

Liu, Jingjing; Sun, Faqian; Wang, Liang; Ju, Xi; Wu, Weixiang; Chen, Yingxu

2014-01-01

322

Development of high band gap materials for tandem solar cells and simulation studies on mechanical tandem solar cells  

NASA Astrophysics Data System (ADS)

Development of low cost, high efficiency tandem solar cells is essential for large scale adoption of solar energy especially in densely populated regions of the world. In this thesis four-terminal mechanical (stack like) tandem solar cells were evaluated using detailed simulation models and design criteria for selecting candidate materials were established. Since silicon solar cells are low cost and have a multi-giga watt global manufacturing and supply chain capacity already in place then only tandem stacks incorporating silicon as one of the layers in the device was investigated. Two candidate materials which have high band gaps that could be used as top cells in the mechanical tandem device were explored as part of the thesis. Dye-sensitized solar cells (DSSC) sensitized with N719 dye (one of the candidates for the top cell) were fabricated with the goal of enabling a flexible processing path to lower cost. Stainless steel (SS) mesh substrates were used to fabricate anodes for flexible DSSC in order to evaluate them as replacements for more expensive Transparent Conducting Oxides (TCO's). Loss mechanisms in DSSC's due to SS mesh oxidation were quantified and protective coatings to prevent oxidation of SS mesh were developed. The second material which was evaluated for use as the top cell was copper zinc tin sulfide (CZTS). CZTS was deposited through a solution deposition route. Detailed investigations were done on the deposited films to understand the chemistry, crystal structure and its opto-electronic properties. Deposited CZTS films were found to be highly crystalline in <112> direction. The films had a direct band gap of 1.5 eV with absorption coefficient greater than 104 cm -1 in agreement with published values. In the second part of the thesis detailed electrical and optical simulation models of the mechanical tandem solar cells were developed based on the most up-to-date materials physical constants available for each layer. The modeling was used to quantify the various theoretical and practical loss mechanisms in tandem devices. Two configurations were evaluated, first was silicon / germanium tandem cell and the second was gallium arsenide / silicon tandem cell. The simulation models were validated by their close match to the performance of experimental standalone solar cells devices reported in the literature. Finally the efficiency limits of the present generation of high band gap solar cells were discussed. Voltage and current loss of the high band gap solar cells were compared with present generation silicon solar cells and challenges in improving their efficiencies were described.

Vijayakumar, Vishnuvardhanan

323

FEM simulation of oxidation induced stresses with a coupled crack propagation in a TBC model system  

NASA Astrophysics Data System (ADS)

Plasma sprayed thermal barrier coating systems are used on top of highly stressed components, e.g. on gas turbine blades, to protect the underlying substrate from the high surrounding temperatures. A typical coating system consists of the bond-coat (BC), the thermal barrier coating (TBC), and the thermally grown oxide (TGO) between the BC and the TBC. This study examines the failure mechanisms which are caused by the diffusion of oxygen through the TBC and the resulting growth of the TGO. To study the behaviour of the complex failure mechanisms in thermal barrier coatings, a simplified model system is used to reduce the number of system parameters. The model system consists of a bond-coat material (fast creeping Fecralloy or slow creeping MA956) as the substrate with a Y2O3 partially stabilised plasma sprayed zircon oxide TBC on top and a TGO between the two layers. Alongside the experimental studies a FEM simulation was developed to calculate the stress distribution inside the simplified coating system [1]. The simulation permits the identification of compression and tension areas which are established by the growth of the oxide layer. Furthermore a 2-dimensional finite element model of crack propagation was developed in which the crack direction is calculated by using short trial cracks in different directions. The direction of the crack in the model system is defined as the crack direction with the maximum energy release rate [2,3]. The simulated stress distributions and the obtained crack path provide an insight into the possible failure mechanisms in the coating and allow to draw conclusions for optimising real thermal barrier coating systems. The simulated growth stresses of the TGO show that a slow creeping BC may reduce lifetime. This is caused by stress concentration and cracks under the TGO. A slow creeping BC on the other hand reduces the stresses in the TBC. The different failure mechanisms emphasise the existence of a lifetime optimum which depends on the creep properties of the used bond-coat material. Experimental results show a good agreement with the predicted failure mechanisms.

Seiler, P.; Bäker, M.; Rösier, J.

2010-06-01

324

Thickness-dependent crossover from charge- to strain-mediated magnetoelectric coupling in ferromagnetic/piezoelectric oxide heterostructures.  

PubMed

Magnetoelectric oxide heterostructures are proposed active layers for spintronic memory and logic devices, where information is conveyed through spin transport in the solid state. Incomplete theories of the coupling between local strain, charge, and magnetic order have limited their deployment into new information and communication technologies. In this study, we report direct, local measurements of strain- and charge-mediated magnetization changes in the La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 system using spatially resolved characterization techniques in both real and reciprocal space. Polarized neutron reflectometry reveals a graded magnetization that results from both local structural distortions and interfacial screening of bound surface charge from the adjacent ferroelectric. Density functional theory calculations support the experimental observation that strain locally suppresses the magnetization through a change in the Mn-eg orbital polarization. We suggest that this local coupling and magnetization suppression may be tuned by controlling the manganite and ferroelectric layer thicknesses, with direct implications for device applications. PMID:24313563

Spurgeon, Steven R; Sloppy, Jennifer D; Kepaptsoglou, Despoina Maria Demie; Balachandran, Prasanna V; Nejati, Siamak; Karthik, J; Damodaran, Anoop R; Johnson, Craig L; Ambaye, Hailemariam; Goyette, Richard; Lauter, Valeria; Ramasse, Quentin M; Idrobo, Juan Carlos; Lau, Kenneth K S; Lofland, Samuel E; Rondinelli, James M; Martin, Lane W; Taheri, Mitra L

2014-01-28

325

Electro-optic switching in iron oxide nanoparticle embedded paramagnetic chiral liquid crystal via magneto-electric coupling  

SciTech Connect

The variation in optical texture, electro-optic, and dielectric properties of iron oxide nanoparticles (NPs) embedded ferroelectric liquid crystal (FLC) with respect to change in temperature and electrical bias conditions are demonstrated in the current investigations. Improvement in spontaneous polarization and response time in nanocomposites has been attributed to magneto-electric (ME) coupling resulting from the strong interaction among the ferromagnetic nanoparticle's exchange field (due to unpaired e{sup ?}) and the field of liquid crystal molecular director. Electron paramagnetic resonance spectrum of FLC material gives a broad resonance signal with superimposed components indicating the presence of a source of spin. This paramagnetic behavior of host FLC material had been a major factor in strengthening the guest host interaction by giving an additional possibility of (a) spin-spin interaction and (b) interactions between magnetic-dipole and electric-dipole moments (ME effects) in the composite materials. Furthermore, the phenomenon of dielectric and static memory effect in these composites are also observed which yet again confirms the coupling of magnetic NP's field with FLC's director orientation. We therefore believe that such advanced soft materials holding the optical and electrical properties of conventional LCs with the magnetic and electronic properties of ferromagnetic nanoparticles are going to play a key role in the development of futuristic multifunctional optical devices.

Goel, Puja, E-mail: pujagoel@gmail.com [Division of Agricultural Chemicals, Indian Agricultural Research Institute, New Delhi 110012 (India); Arora, Manju; Biradar, Ashok M. [Materials Physics and Engineering Division, CSIR-National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi 110012 (India)

2014-03-28

326

Monomolecular layers and thin films of silane coupling agents by vapor-phase adsorption on oxidized aluminum  

SciTech Connect

Thin films of tetraethoxysilane [TEOS], (3-bromopropyl)trimethoxysilane [BPS], trimethoxyvinylsilane [VS], and 3-(trimethoxysilyl) propyl methacrylate [TPM] on oxidized aluminum surfaces have been investigated by reflection-absorption FTIR spectroscopy, ellipsometry, contact angle, and quartz crystal microbalance (QCM) measurements. Gravimetric measurements with the QCM can reveal quantitative aspects of adsorption and film formation, even for films as thin as monolayers. Adsorption of these silane coupling agents from solution typically produces multilayer films. Vapor-phase adsorption of TEOS and TPM at room temperature results in monomolecular layers. The coupling agents VS and BPS require additional heating after the vapor-phase adsorption to initiate the hydrolysis and condensation reactions necessary for the surface attachment, which produces one to three layers. For vapor adsorbed films a packing density of 4-7 molecules/nm{sup 2} was found. The data strongly suggest that the organic moieties in several of these films have a preferential orientation on the surface; they can be viewed as two-dimensional, oligomeric siloxane networks with oriented organic chains. Subsequent heating of TPM films results in structural rearrangements; heating of TEOS results in complete condensation to SiO{sub 2} films. 43 refs., 6 figs., 4 tabs.

Kurth, D.G.; Bein, T. [Purdue Univ., West Lafayette, IN (United States)

1992-08-06

327

Nitrogen-containing microporous conjugated polymers via carbazole-based oxidative coupling polymerization: preparation, porosity, and gas uptake.  

PubMed

Facile preparation of microporous conjugated polycarbazoles via carbazole-based oxidative coupling polymerization is reported. The process to form the polymer network has cost-effective advantages such as using a cheap catalyst, mild reaction conditions, and requiring a single monomer. Because no other functional groups such as halo groups, boric acid, and alkyne are required for coupling polymerization, properties derived from monomers are likely to be fully retained and structures of final polymers are easier to characterize. A series of microporous conjugated polycarbazoles (CPOP-2-7) with permanent porosity are synthesized using versatile carbazolyl-bearing 2D and 3D conjugated core structures with non-planar rigid conformation as building units. The Brunauer-Emmett-Teller specific surface area values for these porous materials vary between 510 and 1430 m(2) g(-1) . The dominant pore sizes of the polymers based on the different building blocks are located between 0.59 and 0.66 nm. Gas (H2 and CO2 ) adsorption isotherms show that CPOP-7 exhibits the best uptake capacity for hydrogen (1.51 wt% at 1.0 bar and 77 K) and carbon dioxide (13.2 wt% at 1.0 bar and 273 K) among the obtained polymers. Furthermore, its high CH4 /N2 and CO2 /N2 adsorption selectivity gives polymer CPOP-7 potential application in gas separation. PMID:23913850

Chen, Qi; Liu, De-Peng; Luo, Min; Feng, Li-Juan; Zhao, Yan-Chao; Han, Bao-Hang

2014-01-29

328

Biocompatible magnetofluorescent probes: luminescent silicon quantum dots coupled with superparamagnetic iron(III) oxide.  

PubMed

Luminescent silicon quantum dots (SiQDs) are gaining momentum in bioimaging applications, based on their unique combination of optical properties and biocompatibility. Here, we report the development of a multimodal probe that combines the optical properties of silicon quantum dots with the superparamagnetic properties of iron oxide nanoparticles to create biocompatible magnetofluorescent nanoprobes. Multiple nanoparticles of each type are coencapsulated within the hydrophobic core of biocompatible phospholipid-polyethyleneglycol (DSPE-PEG) micelles. The size distribution and composition of the magnetofluorescent nanoprobes were characterized by transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). Enhanced cellular uptake of these probes in the presence of a magnetic field was demonstrated in vitro. Their luminescence stability in a prostate cancer tumor model microenvironment was demonstrated in vivo. This paves the way for multimodal silicon quantum-dot-based nanoplatforms for a variety of imaging and delivery applications. PMID:20738120

Erogbogbo, Folarin; Yong, Ken-Tye; Hu, Rui; Law, Wing-Cheung; Ding, Hong; Chang, Ching-Wen; Prasad, Paras N; Swihart, Mark T

2010-09-28

329

Manifold, bus support and coupling arrangement for solid oxide fuel cells  

DOEpatents

Individual, tubular solid oxide fuel cells (SOFCs) are assembled into bundles called a module within a housing, with a plurality of modules arranged end-to-end in a linear, stacked configuration called a string. A common set of piping comprised of a suitable high temperature resistant material (1) provides fuel and air to each module housing, (2) serves as electrically conducting buses, and (3) provides structural support for a string of SOFC modules. Ceramic collars are used to connect fuel and air inlet piping to each of the electrodes in an SOFC module and provide (1) electrical insulation for the current carrying bus bars and gas manifolds, (2) damping for the fuel and air inlet piping, and (3) proper spacing between the fuel and air inlet piping to prevent contact between these tubes and possible damage to the SOFC. 11 figs.

Parry, G.W.

1988-04-21

330

Overview of the Applications of Tandem Mass Spectrometry (MS\\/MS) in Food Analysis of Nutritionally Harmful Compounds  

Microsoft Academic Search

Tandem mass spectrometry (MS\\/MS) has proved to be a useful and a time saving analytical tool, with many applications of direct detection of target molecules in food samples. When coupled with chromatographic techniques, it combines the separation capabilities of chromatography and the power of MS\\/MS as an identification and confirmation method. This article reviews the use of tandem mass spectrometry

Stamatia I. Kotretsou; Aglaia Koutsodimou

2006-01-01

331

Laboratory Studies of the Atmospheric Oxidation of Dimethyl Sulfide Using Laser Flash Photolysis Coupled with Tunable Diode Laser Absorption Spectroscopy.  

NASA Astrophysics Data System (ADS)

The oxidation of dimethyl sulfide (DMS) plays an important role in modifying or regulating global climate via the formation of H_2SO _4(g) and, subsequently, new cloud condensation nuclei. Laser flash photolysis coupled with tunable diode laser absorption spectroscopy was employed to study the kinetics and mechanisms of photochemical oxidation of DMS under laboratory conditions. Quantitative determinations of end products from elementary steps were emphasized to elucidate the detailed reaction mechanism. The yields of HX (X = OD, Cl or Br) from the reactions of X with DMS (and EMS in case of OD) in the absence of O_2 were quantitatively determined. Our results have clearly demonstrated that hydrogen abstraction is the dominant pathway in the oxidation of DMS and EMS initiated by OH. The HCl yield from the Cl + DMS reaction is strongly pressure dependent and approaches unity as P to 0. HBr yields from the Br + DMS reaction were found to be substantial. H_2CO formation was observed from the subsequent oxidation of the methylthiolmethyl radical in the presence of O_2 and in the absence or presence of NO. Under the appropriately established experimental conditions, the mechanism leading to the formation of H_2CO was evaluated. The rate coefficients for the CH_3SCH _2O_2 self reaction and the reaction of CH_3SCH _2O_2 with NO were determined. In addition, the H_2 CO yield from the CH_3SCH _2O_2 + NO reaction pathway was examined. The CH_3 yields from the reaction of DMS with Cl and OH were studied. These results show that radical addition to DMS followed by CH _3 elimination is an extremely minor channel for the radical + DMS reactions. The CO quantum yield from OCS photodissociation at 248 nm has been measured. Measurements at 297 K and total pressure from 4 to 100 Torr N_2 + N_2O show the CO yield to be greater than 0.95 and more likely unity. This result suggests that the contribution of OCS as the source of stratospheric sulfate aerosol is actually larger than previously thought.

Zhao, Zhizhong

1995-01-01

332

Access to biaryl sulfonamides by palladium-catalyzed intramolecular oxidative coupling and subsequent nucleophilic ring opening of heterobiaryl sultams with amines.  

PubMed

The installation of sulfonamide pharmacophores on heterobiaryls has successfully been executed by a previously unknown palladium-catalyzed intramolecular oxidative coupling in N-arylsulfonyl heterocycles followed by novel ring opening of heterobiaryl sultams with amine nucleophiles. The protocol has a wide scope of substrates warranting broad applications in the synthesis of heterobiaryls containing an o-sulfonyl or carboxyl functional group. PMID:25710285

Laha, Joydev K; Dayal, Neetu; Jethava, Krupal P; Prajapati, Dilip V

2015-03-01

333

An ab Initio Study on the Oxidative Coupling of Methane over a Lithium-Doped MgO Catalyst: Surface Defects and Mechanism  

E-print Network

on the catalytic cycle responsible for coupling of methane by molecular oxygen over a lithium-doped magnesium oxide convert methane to more useful higher carbon products that can easily be transported to the consuming, developing a less expensive catalytic conversion method is of great interest and technological significance

Truong, Thanh N.

334

Using Coupled Mesoscale Experiments and Simulations to Investigate High Burn-Up Oxide Fuel Thermal Conductivity  

NASA Astrophysics Data System (ADS)

Nuclear energy is a mature technology with a small carbon footprint. However, work is needed to make current reactor technology more accident tolerant and to allow reactor fuel to be burned in a reactor for longer periods of time. Optimizing the reactor fuel performance is essentially a materials science problem. The current understanding of fuel microstructure have been limited by the difficulty in studying the structure and chemistry of irradiated fuel samples at the mesoscale. Here, we take advantage of recent advances in experimental capabilities to characterize the microstructure in 3D of irradiated mixed oxide (MOX) fuel taken from two radial positions in the fuel pellet. We also reconstruct these microstructures using Idaho National Laboratory's MARMOT code and calculate the impact of microstructure heterogeneities on the effective thermal conductivity using mesoscale heat conduction simulations. The thermal conductivities of both samples are higher than the bulk MOX thermal conductivity because of the formation of metallic precipitates and because we do not currently consider phonon scattering due to defects smaller than the experimental resolution. We also used the results to investigate the accuracy of simple thermal conductivity approximations and equations to convert 2D thermal conductivities to 3D. It was found that these approximations struggle to predict the complex thermal transport interactions between metal precipitates and voids.

Teague, Melissa C.; Fromm, Bradley S.; Tonks, Michael R.; Field, David P.

2014-12-01

335

Manifold, bus support and coupling arrangement for solid oxide fuel cells  

DOEpatents

Individual, tubular solid oxide fuel cells (SOFCs) are assembled into bundles called a module within a housing, with a plurality of modules arranged end-to-end in a linear, stacked configuration called a string. A common set of piping comprised of a suitable high temperture resistant material (1) provides fuel and air to each module housing, (2) serves as electrically conducting buses, and (3) provides structural support for a string of SOFC modules. The piping thus forms a manfold for directing fuel and air to each module in a string and makes electrical contact with the module's anode and cathode to conduct the DC power generated by the SOFC. The piping also provides structureal support for each individual module and maintains each string of modules as a structurally integral unit for ensuring high strength in a large 3-dimensional array of SOFC modules. Ceramic collars are used to connect fuel and air inlet piping to each of the electrodes in an SOFC module and provide (1) electrical insulation for the current carrying bus bars and gas manifolds, (2) damping for the fuel and air inlet piping, and (3) proper spacing between the fuel and air inlet piping to prevent contact between these tubes and possible damage to the SOFC.

Parry, Gareth W. (East Windsor, CT)

1989-01-01

336

Carbohydrate oxidation coupled to Fe(III) reduction, a novel form of anaerobic metabolism  

USGS Publications Warehouse

An isolate, designated GC-29, that could incompletely oxidize glucose to acetate and carbon dioxide with Fe(III) serving as the electron acceptor was recovered from freshwater sediments of the Potomac River, Maryland. This metabolism yielded energy to support cell growth. Strain GC-29 is a facultatively anaerobic, Gram-negative motile rod which, in addition to glucose, also used sucrose, lactate, pyruvate, yeast extract, casamino acids or H2 as alternative electron donors for Fe(III) reduction. Stain GC-29 could reduce NO-3, Mn(IV), U(VI), fumarate, malate, S2O32-, and colloidal S0 as well as the humics analog, 2,6-anthraquinone disulfonate. Analysis of the almost complete 16S rRNA sequence indicated that strain GC-29 belongs in the Shewanella genus in the epsilon subdivision of the Proteobacteria. The name Shewanella saccharophilia is proposed. Shewanella saccharophilia differs from previously described fermentative microorganisms that metabolize glucose with the reduction of Fe(III) because it transfers significantly more electron equivalents to Fe(III); acetate and carbon dioxide are the only products of glucose metabolism; energy is conserved from Fe(III) reduction; and glucose is not metabolized in the absence of Fe(III). The metabolism of organisms like S. saccharophilia may account for the fact that glucose is metabolized primarily to acetate and carbon dioxide in a variety of sediments in which Fe(III) reduction is the terminal electron accepting process.

Coates, J.D.; Councell, T.; Ellis, D.J.; Lovley, D.R.

1998-01-01

337

CHARACTERIZATION OF DOXYLAMINE AND PYRILAMINE METABOLITES VIA THERMOSPRAY/MASS SPECTROMETRY AND TANDEM MASS SPECTROMETRY  

EPA Science Inventory

Analysis of doxylamine N-oxide and pyrilamine N-oxide as synthetic standards and biologically derived metabolites by thermospray mass spectrometry (TSP/MS) provided (M + H)+ ions for each metabolite. TSP/tandem mass spectrometry (TSP/MS/MS) of the (M + H)+ ions provided fragment ...

338

Atmospheric oxygen levels, anaerobic methane oxidation, and the coupling of the global COS cycles by sulfate reduction  

NASA Astrophysics Data System (ADS)

Changes in the partitioning between the reduced and oxidized reservoirs of carbon and sulfur are the dominant control on atmospheric oxygen levels, and the partitioning itself depends to a large degree on microbial redox processes remineralizing organic matter (OM). However, the controls of organic matter preservation in marine sediments are one of the most complex and controversial issues in contemporary biochemistry. Knowledge how the transition from one electron acceptor to another affects OM remineralization rates is scant even for the transition from aerobic to anaerobic respiration. Much less is known about the transition from anaerobic respiration to fermentation. Although the individual pathways of methane generation are known, our understanding of the complex interactions between different bacterial groups remains limited, resulting in considerable difficulties to resolve these questions in microcosm experiments. Here we show that a dramatic drop in seawater sulfate concentrations during the Early Cretaceous (Wortmann & Chernyavsky, Nature 2007) resulted in a global breakdown of microbial sulfate reduction in the marine subsurface biosphere. This event resulted in a positive excursion of the global ?13C-value, suggesting that organic matter remineralization rates dropped by more than 50%. This implies that the methanogenic microbial community was unable to increase their metabolic rates, despite the increased supply of organic matter. the reduced availability of sulfate for anaerobic methane oxidation did not increase the flux of isotopically light carbon into the ocean/atmosphere system. We therefore speculate that the capacity of marine methanogenic ecosystems to synthesize extracellular enzymes to hydrolyze organic matter is specific to the prevailing type of organic matter. This results in a positive coupling of the metabolic activity of both ecosystems, which in turn is a necessary prerequisite to decouple reduced carbon and sulfur burial, a key requirement to stabilize atmospheric oxygen levels.

Wortmann, U. G.; Chernyavsky, B. M.

2007-12-01

339

New Effective Material Couple--Oxide Ceramic and Carbon Nanotube-- Developed for Aerospace Microsystem and Micromachine Technologies  

NASA Technical Reports Server (NTRS)

The prime driving force for using microsystem and micromachine technologies in transport vehicles, such as spacecraft, aircraft, and automobiles, is to reduce the weight, power consumption, and volume of components and systems to lower costs and increase affordability and reliability. However, a number of specific issues need to be addressed with respect to using microsystems and micromachines in aerospace applications--such as the lack of understanding of material characteristics; methods for producing and testing the materials in small batches; the limited proven durability and lifetime of current microcomponents, packaging, and interconnections; a cultural change with respect to system designs; and the use of embedded software, which will require new product assurance guidelines. In regards to material characteristics, there are significant adhesion, friction, and wear issues in using microdevices. Because these issues are directly related to surface phenomena, they cannot be scaled down linearly and they become increasingly important as the devices become smaller. When microsystems have contacting surfaces in relative motion, the adhesion and friction affect performance, energy consumption, wear damage, maintenance, lifetime and catastrophic failure, and reliability. Ceramics, for the most part, do not have inherently good friction and wear properties. For example, coefficients of friction in excess of 0.7 have been reported for ceramics and ceramic composite materials. Under Alternate Fuels Foundation Technologies funding, two-phase oxide ceramics developed for superior high-temperature wear resistance in NASA's High Operating Temperature Propulsion Components (HOTPC) project and new two-layered carbon nanotube (CNT) coatings (CNT topcoat/iron bondcoat/quartz substrate) developed in NASA's Revolutionary Aeropropulsion Concepts (RAC) project have been chosen as a materials couple for aerospace applications, including micromachines, in the nanotechnology lubrication task because of their potential for superior friction and wearf properties in air and in an ultrahigh vacuum, spacelike environment. At the NASA Glenn Research Center, two-phase oxide ceramic eutectics, Al2O3/ZrO2(Y2O3), were directionally solidified using the laser-float-zone process, and carbon nanotubes were synthesized within a high-temperature tube furnace at 800 C. Physical vapor deposition was used to coat all quartz substrates with 5-nm-thick iron as catalyst and bondcoat, which formed iron islands resembling droplets and serving as catalyst particles on the quartz. A series of scanning electron micrographs showing multiwalled carbon nanotubes directionally grown as aligned "nanograss" on quartz is presented. Unidirectional sliding friction eperiments were conducted at Glenn with the two-layered CNT coatings in contact with the two-phase Al2O3/ZrO2(Y2O3) eutectics in air and in ultrachigh vacuum. The main criteria for judging the performance of the materials couple for solid lubrication and antistick applications in a space environment were the coefficient of friction and the wear resistance (reciprocal of wear rate), which had to be less than 0.2 and greater than 10(exp 5) N(raised dot)/cubic millimetes, respectively, in ultrahigh vacuum. In air, the coefficient of friction for the CNT coatings in contact with Al2O3/ZrO2 (Y2O3) eutectics was 0.04, one-fourth of that for quartz. In an ultrahigh vacuum, the coefficient of friction for CNT coatings in contact with Al2O3/ZrO2 (Y2O3) was one-third of that for quartz. The two-phase Al2O3/ZrO2 (Y2O3) eutectic coupled with the two-layered CNT coating met the coefficient of friction and wear resistance criteria both in air and in an ultrahigh vacuum, spacelike environment. This material's couple can dramatically improve the stiction (or adhesion), friction, and wear resistance of the contacting surfaces, which are major issues for microdevices and micromachines.

Miyoshi, Kazuhisa; VanderWal, Randall L.; Tomasek, Aaron J.; Sayir, Ali; Farmer, Serene C.

2004-01-01

340

Tandem Cylinder Noise Predictions  

NASA Technical Reports Server (NTRS)

In an effort to better understand landing-gear noise sources, we have been examining a simplified configuration that still maintains some of the salient features of landing-gear flow fields. In particular, tandem cylinders have been studied because they model a variety of component level interactions. The present effort is directed at the case of two identical cylinders spatially separated in the streamwise direction by 3.7 diameters. Experimental measurements from the Basic Aerodynamic Research Tunnel (BART) and Quiet Flow Facility (QFF) at NASA Langley Research Center (LaRC) have provided steady surface pressures, detailed off-surface measurements of the flow field using Particle Image Velocimetry (PIV), hot-wire measurements in the wake of the rear cylinder, unsteady surface pressure data, and the radiated noise. The experiments were conducted at a Reynolds number of 166 105 based on the cylinder diameter. A trip was used on the upstream cylinder to insure a fully turbulent shedding process and simulate the effects of a high Reynolds number flow. The parallel computational effort uses the three-dimensional Navier-Stokes solver CFL3D with a hybrid, zonal turbulence model that turns off the turbulence production term everywhere except in a narrow ring surrounding solid surfaces. The current calculations further explore the influence of the grid resolution and spanwise extent on the flow and associated radiated noise. Extensive comparisons with the experimental data are used to assess the ability of the computations to simulate the details of the flow. The results show that the pressure fluctuations on the upstream cylinder, caused by vortex shedding, are smaller than those generated on the downstream cylinder by wake interaction. Consequently, the downstream cylinder dominates the noise radiation, producing an overall directivity pattern that is similar to that of an isolated cylinder. Only calculations based on the full length of the model span were able to capture the complete decay in the spanwise correlation, thereby producing reasonable noise radiation levels.

Lockhard, David P.; Khorrami, Mehdi R.; CHoudhari, Meelan M.; Hutcheson, Florence V.; Brooks, Thomas F.; Stead, Daniel J.

2007-01-01

341

Pulsating Tandem Microbubble for Localized and Directional Single-Cell Membrane Poration  

NASA Astrophysics Data System (ADS)

The interaction of laser-generated tandem microbubble (maximum diameter of about 50?m) with single (rat mammary carcinoma) cells is investigated in a 25-?m liquid layer. Antiphase and coupled oscillation of the tandem microbubble leads to the formation of alternating, directional microjets (with max microstreaming velocity of 10m/s) and vortices (max vorticity of 350000s-1) in opposite directions. Localized and directional membrane poration (200 nm to 2?m in pore size) can be produced by the tandem microbubble in an orientation and proximity-dependent manner, which is absent from a single oscillating microbubble of comparable size and at the same stand-off distance.

Sankin, G. N.; Yuan, F.; Zhong, P.

2010-08-01

342

A novel use of oxidative coupling reactions for determination of some statins (cholesterol-lowering drugs) in pharmaceutical formulations  

NASA Astrophysics Data System (ADS)

New, accurate and reliable spectrophotometric methods for the assay of three statin drugs, atorvastatin calcium (AVS), fluvastatin sodium (FVS) and pravastatin sodium (PVS) in pure form and pharmaceutical formulations have been described. All methods involve the oxidative coupling reaction of AVS, FVS and PVS with 3-methyl-2-benzothiazolinone hydrazone hydrochloride monohydrate (MBTH) in the presence of Ce(IV) in an acidic medium to form colored products with ?max at 566, 615 and 664 nm, respectively. Beer's law was obeyed in the ranges of 2.0-20.0, 4.9-35.4 and 7.0-30.0 ?g mL -1 for AVS-MBTH, FVS-MBTH and PVS-MBTH, respectively. Molar absorptivities for the above three methods were found to be 3.24 × 10 4, 1.05 × 10 4 and 0.68 × 10 4 L mol -1 cm -1, respectively. Statistical treatment of the experimental results indicates that the methods are precise and accurate. The proposed methods have been applied to the determination of the components in commercial forms with no interference from the excipients. A comparative study between the suggested procedures and the official methods for these compounds in the commercial forms showed no significant difference between the two methods.

Ashour, Safwan; Bahbouh, Mahmoud; Khateeb, Mouhammed

2011-03-01

343

Enhancement of magnetoresistance with low interlayer coupling by insertion of a nano-oxide layer into a free magnetic layer  

NASA Astrophysics Data System (ADS)

We studied the interlayer coupling strength (Hin) and GMR ratio of a spin-valve with the top free layer, separated by a nano-oxide layer (NOL). With the total thickness of the top free layer being fixed at 60Å, the physical properties of the NOL spin-valve were studied with the thickness (tf) of the free layer under the inserted NOL and compared with those of the normal spin-valve with the same thickness as tf. It was found that the spin-valve with NOL has a higher GMR ratio than that of the normal spin-valve at the optimal condition (tf=40Å) after thermal annealing at T =250°C. The NOL spin-valve also shows a lower Hin than that of the optimal normal spin-valve with tf=40Å, which is comparable to that of the normal spin-valve with tf=60Å. This indicates that the enhancement of GMR, while keeping the Hin to be low, can be achieved by inserting a NOL into the top free layer.

Nam, Chunghee; Lee, Ki-Su; Cho, B. K.

2005-05-01

344

Electronically coupled hybrid structures by graphene oxide directed self-assembly of Cu2-xS nanocrystals.  

PubMed

Here, we describe an electronically coupled hybrid material consisting of graphene oxide (GO) flakes and inorganic Cu2-xS nanocrystals (NCs) formed via a self-assembly route. As a result of the amphiphilic nature of the water-dispersible GO flakes, the hydrophobic Cu2-xS NCs self-assemble in between the GO flakes, resulting in a large-interface hybrid structure with ordered close-packed NCs. We demonstrate that the optical properties of the hybrid GO/Cu2-xS structures are governed by the injection of electrons from the GO flakes to the valence band of the vacancy-doped plasmonic Cu2-xS NCs. This leads to a suppression of the plasmon band of the Cu2-xS NCs and to a softening of the Raman G-band of the GO flakes. Our results indicate that graphene derivatives can act not only as a self-assembly directing template, but also as a tool to affect the optical properties of self-assembled NCs in a chemical process, enhanced by the high interface area of the composite. PMID:25798550

Neyshtadt, Shany; Kriegel, Ilka; Rodríguez-Fernández, Jessica; Hug, Stephan; Lotsch, Bettina; Da Como, Enrico

2015-04-01

345

Complex orbital state stabilized by strong spin-orbit coupling in a metallic iridium oxide IrO2  

NASA Astrophysics Data System (ADS)

Resonant x-ray diffraction experiments were performed for the metallic iridium oxide IrO2. We observed anisotropic tensor of susceptibility (ATS) scattering, the spectrum of which shows a sharp contrast between the L3 and L2 edges. At the L3 edge, resonance excitations were clearly observed from the core 2p orbitals to both the 5d t2g and eg orbitals. In contrast, the resonance mode associated with 5d t2g orbitals was indiscernible at the L2 edge. This contrasting behavior indicates that Ir 5d t2g orbitals are fairly close to the Jeff=1/2 state due to the strong spin-orbit coupling in 5d transition-metal ions, as in the Mott insulator Sr2IrO4. Our results clearly demonstrate that ATS scattering is a useful probe for investigating complex orbital states in a metallic material, where novel phenomena such as the spin Hall effect are expected.

Hirata, Yasuyuki; Ohgushi, Kenya; Yamaura, Jun-ichi; Ohsumi, Hiroyuki; Takeshita, Soshi; Takata, Masaki; Arima, Taka-hisa

2013-04-01

346

Interplay between spin-orbit coupling and Hubbard interaction in SrIrO3 and related Pbnm perovskite oxides  

NASA Astrophysics Data System (ADS)

There has been a rapidly growing interest in the interplay between spin-orbit coupling (SOC) and the Hubbard interaction U in correlated materials. A current consensus is that the stronger the SOC, the smaller is the critical interaction Uc required for a spin-orbit Mott insulator, because the atomic SOC splits a band into different total angular momentum bands, narrowing the effective bandwidth. It was further claimed that at large enough SOC, the stronger the SOC, the weaker the Uc, because in general the effective SOC is enhanced with increasing electron-electron interaction strength. Contrary to this expectation, we find that, in orthorhombic perovskite oxides (Pbnm), the stronger the SOC, the bigger the Uc. This originates from a line of Dirac nodes in Jeff=1/2 bands near the Fermi level, inherited from a combination of the lattice structure and a large SOC. Due to this protected line of nodes, there are small hole and electron pockets in SrIrO3, and such a small density of states makes the Hubbard interaction less efficient in building a magnetic insulator. The full phase diagram in U vs SOC is obtained, where nonmagnetic semimetal, magnetic metal, and magnetic insulator are found. Magnetic ordering patterns beyond Uc are also presented. We further discuss implications of our finding in relation to other perovskites such as SrRhO3 and SrRuO3.

Zeb, M. Ahsan; Kee, Hae-Young

2012-08-01

347

Insulin acutely improves mitochondrial function of rat and human skeletal muscle by increasing coupling efficiency of oxidative phosphorylation.  

PubMed

Insulin is essential for the regulation of fuel metabolism and triggers the uptake of glucose by skeletal muscle. The imported glucose is either stored or broken down, as insulin stimulates glycogenesis and ATP synthesis. The mechanism by which ATP production is increased is incompletely understood at present and, generally, relatively little functional information is available on the effect of insulin on mitochondrial function. In this paper we have exploited extracellular flux technology to investigate insulin effects on the bioenergetics of rat (L6) and human skeletal muscle myoblasts and myotubes. We demonstrate that a 20-min insulin exposure significantly increases (i) the cell respiratory control ratio, (ii) the coupling efficiency of oxidative phosphorylation, and (iii) the glucose sensitivity of anaerobic glycolysis. The improvement of mitochondrial function is explained by an insulin-induced immediate decrease of mitochondrial proton leak. Palmitate exposure annuls the beneficial mitochondrial effects of insulin. Our data improve the mechanistic understanding of insulin-stimulated ATP synthesis, and reveal a hitherto undisclosed insulin sensitivity of cellular bioenergetics that suggests a novel way of detecting insulin responsiveness of cells. PMID:24212054

Nisr, Raid B; Affourtit, Charles

2014-02-01

348

Covalently coupled hybrid of graphitic carbon nitride with reduced graphene oxide as a superior performance lithium-ion battery anode  

NASA Astrophysics Data System (ADS)

An in situ chemical synthetic approach has been designed for the fabrication of a covalently coupled hybrid consisting of graphitic carbon nitride (g-C3N4) with reduced graphene oxide (rGO) with differing g-C3N4/rGO ratio. The epoxy groups of graphene oxide (GO) undergo a nucleophilic substitution reaction with dicyandiamide (C2H4N4) to form the C2H4N4-GO composite via a covalent C-N bond, and then both the in situ polymerization of C2H4N4 and the thermal reduction of GO can be achieved at higher temperatures, forming the covalently coupled g-C3N4-rGO. FT-IR, CP-MAS NMR and XPS analyses, clearly revealed a covalent interaction between the g-C3N4 and rGO sheets. The g-C3N4-rGO exhibits an unprecedented high, stable and reversible capacity of 1525 mA h g-1 at a current density of 100 mA g-1 after 50 cycles. Even at a large current density of 1000 mA g-1, a reversible capacity of 943 mA h g-1 can still be retained. The superior electrochemical performance of g-C3N4-rGO is attributed to the specific characteristics of the unique nanostructure of g-C3N4-rGO and the concerted effects of g-C3N4 and rGO, including covalent interactions between the two moieties, the good conductivity and high special surface area of the nanocomposite, as well as the template effect of the planar amino group of g-C3N4 for the dispersed decoration of Li+ ions.An in situ chemical synthetic approach has been designed for the fabrication of a covalently coupled hybrid consisting of graphitic carbon nitride (g-C3N4) with reduced graphene oxide (rGO) with differing g-C3N4/rGO ratio. The epoxy groups of graphene oxide (GO) undergo a nucleophilic substitution reaction with dicyandiamide (C2H4N4) to form the C2H4N4-GO composite via a covalent C-N bond, and then both the in situ polymerization of C2H4N4 and the thermal reduction of GO can be achieved at higher temperatures, forming the covalently coupled g-C3N4-rGO. FT-IR, CP-MAS NMR and XPS analyses, clearly revealed a covalent interaction between the g-C3N4 and rGO sheets. The g-C3N4-rGO exhibits an unprecedented high, stable and reversible capacity of 1525 mA h g-1 at a current density of 100 mA g-1 after 50 cycles. Even at a large current density of 1000 mA g-1, a reversible capacity of 943 mA h g-1 can still be retained. The superior electrochemical performance of g-C3N4-rGO is attributed to the specific characteristics of the unique nanostructure of g-C3N4-rGO and the concerted effects of g-C3N4 and rGO, including covalent interactions between the two moieties, the good conductivity and high special surface area of the nanocomposite, as well as the template effect of the planar amino group of g-C3N4 for the dispersed decoration of Li+ ions. Electronic supplementary information (ESI) available: N species content (at%) of g-C3N4-rGO-1 based on XPS analysis; the first cycle discharge capacity, charge capacity and coulombic efficiency for the g-C3N4, rGO, and g-C3N4-rGO-n (n = 0.25, 0.5, 1, 2, 3) electrodes; nitrogen adsorption/desorption isotherm of g-C3N4; cycle performance of the g-C3N4-rGO-n (n = 0.25, 0.5, 3) electrodes at a current rate of 100 mA g-1 between 3.0 and 0.01 V versus Li+/Li. See DOI: 10.1039/c4nr03145h

Fu, Yongsheng; Zhu, Junwu; Hu, Chong; Wu, Xiaodong; Wang, Xin

2014-10-01

349

Role of oxidative stress in defective renal dopamine D1 receptor-G protein coupling and function in old Fischer 344 rats.  

PubMed

Aging is associated with an increase in oxidative stress. Previously, we have reported that dopamine failed to inhibit proximal tubular Na-K-ATPase and to promote sodium excretion in old rats (Beheray S, Kansra V, Hussain T, and Lokhandwala MF. Kidney Int 58: 712-720, 2000). This was due to uncoupling of dopamine D1 receptors from G proteins resulting from hyperphosphorylation of D1 receptors. The present study was designed to test the role of oxidative stress in the age-related decline in renal dopamine D1 receptor function. We observed that old animals had increased malondialdehyde (MDA) levels, a biomarker of oxidative stress, and decreased D1 receptor number and protein in the proximal tubules (PT) compared with adult rats. In old rats, there was increased G protein-coupled receptor kinase-2 (GRK-2) abundance, increased basal serine phosphorylation of D1 receptors, and defective D1 receptor-G protein coupling in PT membranes. Interestingly, supplementation with an antioxidant, tempol (1 mmol/l in drinking water for 15 days), lowered MDA levels and normalized D1 receptor number and protein in old rats to the level seen in adult rats. Furthermore, tempol decreased GRK-2 abundance and D1 receptor serine phosphorylation and restored D1 receptor-G protein coupling in PT of old rats. The functional consequence of these changes was the restoration of the natriuretic response to D1 receptor activation in tempol-supplemented old rats. Therefore, in old rats, tempol reduces oxidative stress and prevents GRK-2 membranous abundance and hyperphosphorylation of D1 receptors, resulting in restoration of D1 receptor-G protein coupling and the natriuretic response to SKF-38393. Thus tempol, by lowering oxidative stress, normalizes the age-related decline in dopamine receptor function. PMID:16757732

Fardoun, Riham Zein; Asghar, Mohammad; Lokhandwala, Mustafa

2006-11-01

350

Assessing the kinetics of high temperature oxidation of Inconel 617 in a dedicated HTR impure helium facility coupling thermogravimetry and gas phase chromatography  

NASA Astrophysics Data System (ADS)

A new facility coupling thermogravimetric analysis (TGA) with gas phase chromatography (GPC) has been developed. This facility is dedicated for studying high temperature oxidation of Inconel 617 in impure helium environment containing H2O, H2 and CO at very low partial pressures (in the Pa range), which is representative of the high temperature reactor (HTR) concept developed within the Generation IV Forum. Simultaneous acquisition of mass gain and gas composition has allowed the influence of carbon monoxide and water vapour on the kinetics of oxidation to be studied. GPC measurements of gas consumption have allowed the plotting of individual mass gain curves for oxidation by H2O and CO. During isothermal exposure at 1123 K for 20 h, the oxidation was mainly due to water vapour with a minor contribution of carbon monoxide during the first hours. The contribution of water vapour to the oxidation kinetics was extracted. It was shown to obey a complete parabolic law and to be limited by an interfacial reaction during the first few hours of oxidation and to be controlled by a mixed interfacial and diffusion process, diffusion becoming the rate-determining step for long term oxidation. There was very good agreement between GPC measurements and the experimental TGA results.

Chapovaloff, J.; Rouillard, F.; Combrade, P.; Pijolat, M.; Wolski, K.

2013-10-01

351

Reduction of Matrix-Induced Oxide Interferences on Rare Earth Elements and Platinum Using a Desolvating Nebulizer System with Quadrupole Inductively Coupled Plasma Mass Spectrometry  

NASA Astrophysics Data System (ADS)

This paper will examine the use of a specialized low-flow desolvating nebulizer system for reduction of oxide mass spectral interferences that can occur in quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS). This nebulizer system uses an inert low-flow nebulizer (100 microliters/min) coupled to an inert, heated membrane desolvator for efficient water vapor removal before sample aerosol injection to the Q-ICP-MS instrument. Water vapor from conventional nebulizer / spray chamber systems used with Q-ICP-MS can cause numerous mass spectral interferences. One general example is metal oxides formed from the combination of oxygen (from injected water) with sample matrix components. Two specific examples of metal oxide interferences will be investigated with and without membrane desolvation: Ba and Ce oxides on several low-mass rare earth elements (Sm, Eu, and Gd) and Hf oxides on platinum. Rare earth elements are critically important components of modern electronics (ex. magnets, lasers, cell phones, computers) and platinum is a widely used catalyst. Figures of merit for both a conventional nebulizer/spray chamber and the desolvating nebulizer systems will include operating conditions, interference intensities and reduction factors, background equivalent concentrations (BECs), and instrument detection limits (IDLs).

Smith, F.

2013-12-01

352

Flow through cascades in tandem  

NASA Technical Reports Server (NTRS)

An exact treatment of the problem of finding the incompressible, inviscid two-dimensional flow around two cascades in tandem is presented. The analysis includes solutions of both the direct and the inverse problems. These problems are solved by conformally mapping the tandem cascade onto the region between two concentric circles in which region there are suitably placed flow singularities. Formulas for the velocity and the potential in the annular region are presented in a closed form by means of elliptic functions. The equations are presented in a form suitable for computation.

Spraglin, William E

1951-01-01

353

Fast and comprehensive multi-residue analysis of a broad range of human and veterinary pharmaceuticals and some of their metabolites in surface and treated waters by ultra-high-performance liquid chromatography coupled to quadrupole-linear ion trap tandem mass spectrometry.  

PubMed

The present work describes the development of an analytical method, based on automated off-line solid phase extraction (SPE) followed by ultra-high-performance liquid chromatography coupled to quadrupole linear ion trap tandem mass spectrometry (UPLC-QqLIT) for the determination of 81 pharmaceutical residues, covering various therapeutic groups, and some of their main metabolites, in surface and treated waters (influent and effluent wastewaters, river, reservoir, sea and drinking water). For unequivocal identification and confirmation, two selected reaction monitoring (SRM) transitions per compound are monitored. Quantification is performed by the internal standard approach, indispensable to correct matrix effects. Moreover, to obtain an extra tool for confirmation of positive findings, an information dependent acquisition (IDA) experiment was performed, with SRM as survey scan and an enhanced product ion (EPI) scan as dependent scan. Compound identification was carried out by library search, matching the EPI spectra achieved at one fixed collision energy with those present in a library. The main advantages of the method are automation and speed-up of sample preparation by the reduction of extraction volumes for some matrices, the fast separation of a big number of pharmaceuticals, its high sensitivity (limits of detection in the low ng/L range), selectivity, due to the use of tandem mass spectrometry, reliability since a significant number of isotopically labeled compounds are used as internal standards for quantification and finally, the analysis of tap, reservoir and sea waters, since information about occurrence of pharmaceuticals in these matrices is still sparse. As part of the validation procedure, the method developed was applied to the analysis of pharmaceutical residues in waste and surface waters from different sites in Catalonia (North East of Spain). PMID:22704668

Gros, Meritxell; Rodríguez-Mozaz, Sara; Barceló, Damià

2012-07-27

354

Simultaneous speciation of selenium and sulfur species in selenized odorless garlic ( Allium sativum L. Shiro) and shallot ( Allium ascalonicum) by HPLC–inductively coupled plasma-(octopole reaction system)-mass spectrometry and electrospray ionization-tandem mass spectrometry  

Microsoft Academic Search

The simultaneous speciation of selenium and sulfur in selenized odorless garlic (Allium sativum L. Shiro) and a weakly odorous Allium plant, shallot (Allium ascalonicum), was performed by means of a hyphenated technique, a HPLC coupled with an inductively coupled plasma-mass spectrometry (HPLC–ICP-MS) equipped with an octopole reaction system (ORS). The aqueous extracts of them contained the common seleno compound that

Yasumitsu Ogra; Kazuya Ishiwata; Yuji Iwashita; Kazuo T. Suzuki

2005-01-01

355

Fully-automated on-line solid phase extraction coupled to high-performance liquid chromatography-tandem mass spectrometric analysis at sub-ng/L levels of selected estrogens in surface water and wastewater.  

PubMed

A fully-automated on-line solid phase extraction liquid chromatographic/electrospray ionization tandem mass spectrometric method for the analysis of estrone (E1), 17-?-estradiol (?-E2), 17-?-ethinylestradiol (EE2), 17-?-estradiol (?-E2) and estriol (E3) in surface water and wastewater was developed. The method showed a very good linearity from 250 ng/L down to compound specific quantification limits, which were included between 0.25 and 2.00 ng/L. These limits were obtained with 2.5 mL aliquots of injected sample and the total analysis time per sample was slightly less than 10 min. Under these conditions, detection limits were 0.15 ng/L for E1, 0.31 ng/L for ?-E2, 0.52 ng/L for EE2, 0.59 ng/L for ?-E2 and 0.95 ng/L for E3. The method reliability was tested on different kinds of real samples spiked with the estrogens, obtaining recoveries approximately included between 71 and 95%. The application to samples collected in rivers, lakes and wastewater treatment plants evidenced the presence of the investigated compounds at sub-ng/L or low ng/L concentration levels. PMID:23433884

Ciofi, L; Fibbi, D; Chiuminatto, U; Coppini, E; Checchini, L; Del Bubba, M

2013-03-29

356

Ultrasound/microwave-assisted solid-liquid-solid dispersive extraction with high-performance liquid chromatography coupled to tandem mass spectrometry for the determination of neonicotinoid insecticides in Dendrobium officinale.  

PubMed

A one-step ultrasound/microwave-assisted solid-liquid-solid dispersive extraction procedure was used for the simultaneous determination of eight neonicotinoids (dinotefuran, nitenpyram, thiamethoxam, clothianidin, imidacloprid, acetamiprid, thiacloprid, imidaclothiz) in dried Dendrobium officinale by liquid chromatography combined with electrospray ionization triple quadrupole tandem mass spectrometry in multiple reaction monitoring mode. The samples were quickly extracted by acetonitrile and cleaned up by the mixed dispersing sorbents including primary secondary amine, C18 , and carbon-GCB. Parameters that could influence the ultrasound/microwave-assisted extraction efficiency such as microwave irradiation power, ultrasound irradiation power, temperature, and solvent were investigated. Recovery studies were performing well (70.4-113.7%) at three examined spiking levels (10, 50, and 100 ?g/kg). Meanwhile, the limits of quantification for the neonicotinoids ranged from 0.87 to 1.92 ?g/kg. The method showed good linearity in the concentration range of 1-100 ?g/L with correlation coefficients >0.99. This quick and useful analytical method could provide a basis for monitoring neonicotinoid insecticide residues in herbs. PMID:25348589

Zheng, Shuilian; Wu, Huizhen; Li, Zuguang; Wang, Jianmei; Zhang, Hu; Qian, Mingrong

2015-01-01

357

Direct analysis of 18 flavonol glycosides, aglycones and terpene trilactones in Ginkgo biloba tablets by matrix solid phase dispersion coupled with ultra-high performance liquid chromatography tandem triple quadrupole mass spectrometry.  

PubMed

Analysis and quality control of Ginkgo biloba have been comprehensively studied. However, little attention has been devoted to the simultaneous extraction and analysis of flavonols and terpene trilactones, especially for direct quantification of flavonol glycosides. This work described a rapid strategy for one-step extraction and quantification of the components. A matrix solid phase dispersion (MSPD) method was designed for the extraction of ginkgo ingredients and compared with the heat-reflux and ultrasonic extraction methods. An ultra-high performance liquid chromatography (UHPLC)-tandem-triple-quadrupole-mass spectrometry (QQQ-MS) method was developed for detection of the 18 components, including 10 original flavonol glycosides, 3 aglycones, and 5 lactones. Subsequently, the proposed strategy was used for the analysis of 12 G. biloba tablets. Results showed that MSPD produced comparable extraction efficiency but consumed less time and required lower solvent volumes compared with conventional methods. Without hydrolysis, the concentration detected was much closer to the original in the sample. The total flavonol glycoside contents in ginkgo tablets ranged from 3.59 to 125.21?gmg(-1), and the terpene trilactone varied from 3.45 to 57.8?gmg(-1) among different manufacturers. In conclusion, the proposed MSPD and UHPLC-QQQ-MS is rapid and sensitive in providing comprehensive profile of chemical constituents especially the genuine flavonol glycosides for improved quality control of ginkgo products. PMID:24876067

Liu, Xin-Guang; Yang, Hua; Cheng, Xiao-Lan; Liu, Lei; Qin, Yong; Wang, Qi; Qi, Lian-Wen; Li, Ping

2014-08-01

358

A fully automated method for simultaneous determination of aflatoxins and ochratoxin A in dried fruits by pressurized liquid extraction and online solid-phase extraction cleanup coupled to ultra-high-pressure liquid chromatography-tandem mass spectrometry.  

PubMed

According to current demands and future perspectives in food safety, this study reports a fast and fully automated analytical method for the simultaneous analysis of the mycotoxins with high toxicity and wide spread, aflatoxins (AFs) and ochratoxin A (OTA) in dried fruits, a high-risk foodstuff. The method is based on pressurized liquid extraction (PLE), with aqueous methanol (30 %) at 110 °C, of the slurried dried fruit and online solid-phase extraction (online SPE) cleanup of the PLE extracts with a C18 cartridge. The purified sample was directly analysed by ultra-high-pressure liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) for sensitive and selective determination of AFs and OTA. The proposed analytical procedure was validated for different dried fruits (vine fruit, fig and apricot), providing method detection and quantification limits much lower than the AFs and OTA maximum levels imposed by EU regulation in dried fruit for direct human consumption. Also, recoveries (83-103 %) and repeatability (RSD?

Campone, Luca; Piccinelli, Anna Lisa; Celano, Rita; Russo, Mariateresa; Valdés, Alberto; Ibáñez, Clara; Rastrelli, Luca

2015-04-01

359

Mixed-mode solid-phase extraction coupled with liquid chromatography tandem mass spectrometry to determine phenoxy acid, sulfonylurea, triazine and other selected herbicides at nanogram per litre levels in environmental waters.  

PubMed

The method presented uses a mixed-mode anion exchange SPE and liquid chromatography tandem mass spectrometry to analyze 5 sulfonylurea, 8 phenoxy acid, 12 triazine and 6 other herbicides in environmental waters. The mixed-mode SPE cartridge is able to retain a wide range of herbicides with acidic-neutral-basic characteristics, particularly the highly polar and acidic compounds clopyralid, dicamba and picloram. The neutral and basic herbicides can be effectively eluted with methanol, after which the acidic herbicides can be eluted using acidified methanol. The method has achieved an LOD of 0.7-3ng/L for the sulfonylureas, 4-12ng/L for the phenoxy acids and 0.4-30ng/L for the triazine and additional herbicides, with recoveries in the range 76-107%, 73-126%, and 65-104%, respectively. The precision of the method, calculated as relative standard deviation (RSD), was below 10% for both sulfonylurea and phenoxy acid herbicides, and less than 20% for the remaining herbicides. The developed method was used to determine the concentration of target herbicides in a range of environmental waters, and many of the target herbicides were detected at ng/L level. PMID:24373535

Zhang, Pei; Bui, Anhduyen; Rose, Gavin; Allinson, Graeme

2014-01-17

360

Chiral on-line solid phase extraction coupled to liquid chromatography-tandem mass spectrometry assay for quantification of (R) and (S) enantiomers of methadone and its main metabolite in plasma.  

PubMed

The authors aimed at developing a liquid chromatography tandem mass spectrometry (LC-MS/MS) method with online extraction to determine (R)- and (S)- methadone enantiomers and its main metabolite 2-ethylidine-1,5-dimethyl-3,3 diphenylpyrrolidine (EDDP) in plasma. The analysis combined straightforward sample preparation, consisting of protein precipitation with acetonitrile, and an online enrichment by a flush/back-flush cycle before the second dimension chromatography. Using D3-deuterated internal standards allows overcoming significant relative matrix effect. Our method was linear up to 2000 ng/mL. This simple sample preparation provides sensitive (the limit of quantitation is 25 ng/mL for (R,S)-methadone and EDDP and 12.5 ng/mL for (R)- and (S)- methadone), accurate and precise (the intra-day and inter-day imprecision and inaccuracy are lower than 15%) quantification of the plasma concentration of these drugs. We have developed a reliable LC-MS/MS method for both routine therapeutic drug monitoring and pharmacokinetics studies and for toxicology analysis in the setting of methadone treatment or intoxication. PMID:25618682

Bouquié, Régis; Hernando, Hélène; Deslandes, Guillaume; Ben Mostefa Daho, Amina; Renaud, Christian; Grall-Bronnec, Marie; Dailly, Eric; Jolliet, Pascale

2015-03-01

361

Determination of chlormequat and mepiquat in pear, tomato, and wheat flour using on-line solid-phase extraction (Prospekt) coupled with liquid chromatography-electrospray ionization tandem mass spectrometry.  

PubMed

A sensitive and selective method is presented for the simultaneous analysis of the pesticides chlormequat and mepiquat at trace levels in tomato, pear, and wheat flour. The method entails direct injection of the food extract onto an on-line solid-phase extraction (SPE) instrument (Prospekt) using a strong cation-exchange resin. Analyte separation and detection is done by liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS-MS). Surrogate standards (d9-chlormequat, d6-mepiquat) are employed to compensate for recovery losses and potential MS-MS signal suppression. The method achieves a limit of quantification for both cationic analytes at or below 5 microg/kg, and good intra- and inter-assay precision with mean variability values <7% over a concentration range up to 195 microg/kg. This study also addresses potential analyte carry-over in an SPE on-line system, as well as the robustness of the procedure and its applicability in routine quality control operations. PMID:12214689

Riediker, Sonja; Obrist, Heinrich; Varga, Natalia; Stadler, Richard H

2002-08-01

362

Multiresidue determination of fluoroquinolones in poultry muscle and kidney according to the regulation 2002/657/EC. A systematic comparison of two different approaches: Liquid chromatography coupled to high-resolution mass spectrometry or tandem mass spectrometry.  

PubMed

This work involved the optimization and validation of two methods according to the Commission Decision 2002/657/EC directives for determining fluoroquinolones residues in samples of poultry muscle and kidney: ciprofloxacin, danofloxacin, difloxacin, enrofloxacin, flumequine, marbofloxacin, nalidixic acid, norfloxacin, ofloxacin, oxolinic acid, pipemidic acid and sarafloxacin. The extraction procedure was based on a QuEChERS approach, whose optimization employed a Box-Behnken 3(3) factorial design. A liquid chromatography-tandem mass spectrometry method (LC-MS/MS) was developed for determining the twelve analytes using the multiple reaction monitoring mode (MRM). Accuracy, evaluated by recovery studies, varied from 88.8 to 112.2% for the selected levels with RSD values lower than 12.3%. The second validated method employed high resolution mass spectrometry (HRMS) performed in the single ion monitoring mode (SIM), determining nine among twelve analytes. The validation parameters were evaluated as satisfactory, with recoveries from 82.5 to 114.4% and RSD lower than 8.7%. Decision limits and detection capabilities for both methods were reported. The two methods were statistically compared using the Student's t test, at 95% confidence level, resulting in no significant difference. PMID:25577647

Rocha, Diego G; Santos, Flavio A; da Silva, Júlio César C; Augusti, Rodinei; Faria, Adriana F

2015-01-30

363

Mobility platform coupling device and method for coupling mobility platforms  

DOEpatents

A coupling device for connecting a first mobility platform to a second mobility platform in tandem. An example mobility platform is a robot. The coupling device has a loose link mode for normal steering conditions and a locking position, tight link mode for navigation across difficult terrain and across obstacles, for traversing chasms, and for navigating with a reduced footprint in tight steering conditions.

Shirey, David L. (Albuquerque, NM); Hayward, David R. (Albuquerque, NM); Buttz, James H. (Albuquerque, NM)

2002-01-01

364

Magnetic order and interfacial coupling in oxide thin films and heterostructures probed with soft x-ray dichroism  

SciTech Connect

The combination of novel magnetic properties induced by reduced dimensionality and strong magnetic interactions across interfaces leads to intriguing new properties in magnetic hetero- and nanostructures not observed in the constituent materials in bulk form. It is the careful optimization of the characteristics of the individual layers as well as the magnetic coupling across the interface that allows us to control the magnetic properties and tailor them for devices, e.g., in information storage and processing technology. Soft x-ray magnetic spectroscopies can make unique contributions to improving our understanding of complex magnetic nanostructures since these techniques provide elemental, valence- and site-symmetry specific information with high sensitivity and tunable probing depth. X-ray magnetic circular dichroism (XMCD) is sensitive to (unidirectional) ferromagnetic order, while x-ray magnetic linear dichroism (XMLD) can also detect (uniaxial) antiferromagnetic order. A crystalline electric field with cubic symmetry induces only a weak angular dependence in XMCD spectra [1] but can cause a very pronounced anisotropy in XMLD spectra [2]. Furthermore, non-magnetic sites with a distorted local cubic symmetry can give rise to an x-ray linear dichroism (XLD). In this presentation, we discuss how to distinguish between the individual contributions to soft x-ray dichroism spectra in order to extract the wealth of information about magnetic thin films, interfaces and hetero- and nanostructures contained in the data [3, 4, 5] We determined the magnetic structure of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} (LSMO)/La{sub 0.7}Sr{sub 0.3}FeO{sub 3} (LSFO) superlattices with 6 unit cell thick sublayers using soft x-ray magnetic dichroism [5]. Circular dichroism was employed to study the characteristics of the ferromagnetic LSMO layer indicating a reduced magnetic ordering temperature of 200 K compared to the bulk value of 360 K. Linear dichroism is used to analyze the antiferromagnetic order in the LSFO layers which persists up to the bulk Neel temperature near 400 K. Our experiments clearly show that when the magnetization of the LSMO layer is aligned with a magnetic field, a torque is created on the Fe moments in the LSFO layer through exchange coupling at the interface realigning the Fe moments as well. Through comparison with theoretical calculations we are able to show that independent of the LSMO magnetization direction in the sample surface plane, the Fe moments are always oriented perpendicular to the Mn moments. This perpendicular alignment is due to the frustrated exchange coupling at the interface and the weak anisotropy in the thin LSFO layer. Revisiting previous XMLD studies of the Co/NiO(001) interface taking the impact of the crystal electric field on the XMLD into account for the first time, we show that NiO(001) exhibits a crystallographic and magnetic domain structure near the surface that is identical to that of the bulk. Upon Co deposition perpendicular coupling of Co and Ni moments is observed [2, 3] that persists even in the presence of uncompensated interface moments. We also measured the asphericity and the energy splitting of the 4f states in EuO thin films [4] - a material with fascinating properties and of technological importance for spintronics applications - using XMLD. Our measurements, which are confirmed by multiplet calculations, show that there is significant 4f anisotropy. This suggests that pinning of the f states by the local environment becomes feasible and can be tuned by external conditions, chemical doping, and strain for use in device applications. Moreover, we will discuss the impact of epitaxial strain on the magnetic properties and XMLD spectra of complex oxide thin films.

Arenholz, Elke; van der Laan, G.

2009-02-01

365

Tandem motors reduce well costs  

Microsoft Academic Search

The new generation of tandem mud motors that recently appeared on the drilling scene is significantly affecting drilling efficiency worldwide. These motors provide drillers with increased horsepower at the bit, higher torque, and faster rates of penetration (ROP). With advanced engineering and more durable materials, motor life is being extended, thereby increasing the time between bit trips and reducing drilling

M. Hooper; C. Daigle; R. Crowe

1995-01-01

366

Tandemly repeated trinucleotides — comparative analysis  

Microsoft Academic Search

Characteristics of 64 possible tandem trinucleotide repeats (TSSR) from Homo sapiens (hs), Mus musculus (mm) and Rattus norvegicus (rn) genomes are presented. Comparative analysis of TSSR frequency depending on their repetitiveness and similarity of the TSSR length distributions is shown. Comparative analysis of TSSR sequence motifs and association between type of motif and its length (n) using ?-coefficient method (quantitatively

Monika Piwowar; Jan Meus; Piotr Piwowar; Justyna Stefaniak; Irena Roterman

2006-01-01

367

DNA Damage by Ionizing Radiation: Tandem Double Lesions by Charged Particles  

NASA Technical Reports Server (NTRS)

Oxidative damages by ionizing radiation are the source of radiation-induced carcinogenesis, damage to the central nervous system, lowering of the immune response, as well as other radiation-induced damages to human health. Monte Carlo track simulations and kinetic modeling of radiation damages to the DNA employ available molecular and cellular data to simulate the biological effect of high and low LET radiation io the DNA. While the simulations predict single and double strand breaks and base damages, so far all complex lesions are the result of stochastic coincidence from independent processes. Tandem double lesions have not yet been taken into account. Unlike the standard double lesions that are produced by two separate attacks by charged particles or radicals, tandem double lesions are produced by one single attack. The standard double lesions dominate at the high dosage regime. On the other hand, tandem double lesions do not depend on stochastic coincidences and become important at the low dosage regime of particular interest to NASA. Tandem double lesions by hydroxyl radical attack of guanine in isolated DNA have been reported at a dosage of radiation as low as 10 Gy. The formation of two tandem base lesions was found to be linear with the applied doses, a characteristic of tandem lesions. However, tandem double lesions from attack by a charged particle have not been reported.

Huo, Winifred M.; Chaban, Galina M.; Wang, Dunyou; Dateo, Christopher E.

2005-01-01

368

Palladium-catalyzed intramolecular oxidative coupling involving double C(sp(2))-H bonds for the synthesis of annulated biaryl sultams.  

PubMed

The palladium-catalyzed intramolecular oxidative coupling described herein involves a double C(sp(2))-H bond functionalization in sulfonanilides, providing a workable access to biaryl sultams annulated into a six-membered ring that are otherwise difficult to obtain by literature methods. The other synthetic applications of this protocol including the synthesis of biaryl sultams containing a seven-membered ring and analogous sultones are also presented. PMID:25121579

Laha, Joydev K; Jethava, Krupal P; Dayal, Neetu

2014-09-01

369

Iodine-Catalyzed Oxidative Cross-Coupling of Indoles and Azoles: Regioselective Synthesis of N-Linked 2-(Azol-1-yl)indole Derivatives.  

PubMed

A highly efficient iodine-catalyzed regioselective oxidative cross-coupling of an indole C-H bond and azole N-H bond is described. This metal-free reaction can be easily carried out at room temperature under mild and environmentally friendly conditions and provides a series of N-linked 2-(azol-1-yl)indole derivatives in moderate to excellence yields. PMID:25791508

Beukeaw, Danupat; Udomsasporn, Kwanchanok; Yotphan, Sirilata

2015-04-01

370

Graphene oxide nanoplatelets as excellent electrochemical active materials for VO 2+\\/ VO 2 + and V 2+\\/V 3+ redox couples for a vanadium redox flow battery  

Microsoft Academic Search

Graphene oxide nanoplatelets (GONPs) are presented as electrochemical active materials for VO2+\\/VO2+ and V2+\\/V3+ redox couples for a vanadium redox flow battery. The structures and electrochemical properties of GONPs treated at different temperatures were investigated by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and cyclic voltammetry. The results indicate that GONPs treated at

Pengxian Han; Haibo Wang; Zhihong Liu; Xiao Chen; Wen Ma; Jianhua Yao; Yuwei Zhu; Guanglei Cui

371

Copper-catalyzed oxidative C(sp(3))-H/N-H coupling of sulfoximines and amides with simple alkanes via a radical process.  

PubMed

A copper-catalyzed oxidative C(sp(3))-H/N-H coupling of sulfoximines with simple alkanes was developed. This protocol involved C(sp(3))-N bond formation via a radical pathway and tolerated a series of functional groups, such as chloro, methyl and aryl, on the phenyl rings. Apart from sulfoximines, amides, saccharin and aniline also worked well to give the corresponding N-alkylated products. PMID:25727724

Teng, Fan; Sun, Song; Jiang, Yan; Yu, Jin-Tao; Cheng, Jiang

2015-04-01

372

Oxidative coupling of methane over Li\\/Sn\\/MgO catalysts. Use of a fluidized bed reactor at low gas velocities  

Microsoft Academic Search

A fluidized bed reactor has been used to carry out methane oxidative coupling (MOC) over a Li\\/Sn\\/MgO catalyst. The influence of the operating conditions (CH4\\/O2 ratio, total flowrate, temperature, particle size) has been studied, with most of the experiments concentrated in the region of low fluidizing velocities. In this work, hydrocarbon yields around 20% have been obtained, which are among

A. Santos; M. Menéndez; J. Santamaría

1997-01-01

373

[Determination of the migration of bisphenol diglycidyl ethers from food contact materials by high performance chromatography-tandem mass spectrometry coupled with multi-walled carbon nanotubes solid phase extraction].  

PubMed

A comprehensive analytical method based on high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was developed for measuring 6 exogenous endocrine disruptors--bisphenol diglycidyl ethers, including bisphenol A diglycidyl ether (BADGE), bisphenol A glycidyl (2,3-dihydroxypropyl) ether (BADGE x H2O), bisphenol A glycidyl (3-chloro-2-hydroxypropyl) ether ( BADGE x HCl), bisphenol A (3-chloro-2-hydroxypropyl) (2,3-dihydroxypropyl) ether (BADGE x H2O x HCl), bisphenol F diglycidyl ether (BFDGE) and bisphenol F bis (3-chloro-2-hydroxypropyl) ether (BFDGE x 2HCl). The samples were extracted with methyl tert-butyl ether (MTBE) by ultrasonic wave assistant extraction. The extracts were cleaned up and concentrated on multi-walled carbon nanotubes (MWCNTs). The target compounds were analyzed by HPLC-MS/MS under positive ion mode using a COSMOSIL C18 column as analytical column. Under the optimal conditions, the calibration curves showed a good linearity in the concentration range of 1.0-100.0 microg/L for 6 target compounds. The correlation coefficients (r2) were higher than 0.999 1. Recoveries of 6 analytes at three spiked levels ranged from 78.6% to 89.9%, with relative standard deviations (RSDs) less than 10%. The detection limits of the method ranged from 0.5 to 1.5 microg/L. The method is sensitive and simple, and is suitable for the rapid determination of the migration of bisphenol diglycidyl ethers from food contact materials. PMID:21381429

Wu, Xinhua; Ding, Li; Li, Zhonghai; Zhang, Yanli; Liu, Xiaoxia; Wang, Libing

2010-11-01

374

Simultaneous determination of N7-alkylguanines in DNA by isotope-dilution LC-tandem MS coupled with automated solid-phase extraction and its application to a small fish model.  

PubMed

In the present study, we report the development of a sensitive and selective assay based on LC (liquid chromatography)-MS/MS (tandem MS) to simultaneously measure N7-MeG (N7-methylguanine) and N7-EtG (N7-ethylguanine) in DNA hydrolysates. With the use of isotope internal standards (15N5-N7-MeG and 15N5-N7-EtG) and on-line SPE (solid-phase extraction), the detection limit of this method was estimated as 0.42 fmol and 0.17 fmol for N7-MeG and N7-EtG respectively. The high sensitivity achieved here makes this method applicable to small experimental animals. This method was applied to measure N7-alkylguanines in liver DNA from mosquito fish (Gambusia affinis) that were exposed to NDMA (N-nitrosodimethylamine) and NDEA (N-nitrosodiethylamine) alone or their combination over a wide range of concentrations (1-100 mg/l). Results showed that the background level of N7-MeG in liver of control fish was 7.89+/-1.38 mmol/mol of guanine, while N7-EtG was detectable in most of the control fish with a range of 0.05-0.19 mmol/mol of guanine. N7-MeG and N7-EtG were significantly induced by NDMA and NDEA respectively, at a concentration as low as 1 mg/l and increased in a dose-dependent manner. Taken together, this LC-MS/MS assay provides the sensitivity and high throughput required to evaluate the extent of alkylated DNA lesions in small animal models of cancer induced by alkylating agents. PMID:17134374

Chao, Mu-Rong; Wang, Chien-Jen; Yen, Cheng-Chieh; Yang, Hsi-Hsien; Lu, Yao-Cheng; Chang, Louis W; Hu, Chiung-Wen

2007-03-15

375

Tandem motors increase well bore penetration rate  

SciTech Connect

Running a positive displacement downhole motor with tandem power sections and the proper bit significantly increases the rate of penetration and reduces stalling problems. The use of positive displacement mud motors (PDMs) with two power sections has improved penetration rates on a number of drilling applications in western Canada. The majority of all the tandem motor runs to date have been successful. Results of these tandem runs show that tandem motors should be considered in any situation where a single motor is run. This paper reviews the performance of tandem motors at several case sites. It describes the design, rate of penetration, bit selection, mud systems, and use in horizontal wells.

Matthews, S. [Halliburton Drilling Systems, Calgary, Alberta (Canada); McCosh, R. [CenAlta Well Services Inc., Calgary, Alberta (Canada)

1996-02-26

376

Sticky interconnect for solution-processed tandem solar cells.  

PubMed

Graphene oxide (GO) can be viewed as a two-dimensional, random diblock copolymer with distributed nanosize graphitic patches and highly oxidized domains, thus capable of guiding the assembly of other materials through both ?-? stacking and hydrogen bonding. Upon mixing GO and conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) in water, a dispersion with dramatically increased viscosity is obtained, which turns into sticky thin films upon casting. Surprisingly, the insulating GO makes PEDOT much more conductive by altering its chain conformation and morphology. The GO/PEDOT gel can function as a metal-free solder for creating mechanical and electrical connections in organic optoelectronic devices. As a proof-of-concept, polymer tandem solar cells have been fabricated by a direct adhesive lamination process enabled by the sticky GO/PEDOT film. The sticky interconnect can greatly simplify the fabrication of organic tandem architectures, which has been quite challenging via solution processing. Thus, it could facilitate the construction of high-efficiency tandem solar cells with different combinations of solution-processable materials. PMID:21615169

Tung, Vincent C; Kim, Jaemyung; Cote, Laura J; Huang, Jiaxing

2011-06-22

377

Unexpected weak magnetic exchange coupling between haem and non-haem iron in the catalytic site of nitric oxide reductase (NorBC) from Paracoccus denitrificans1.  

PubMed

Bacterial NOR (nitric oxide reductase) is a major source of the powerful greenhouse gas N2O. NorBC from Paracoccus denitrificans is a heterodimeric multi-haem transmembrane complex. The active site, in NorB, comprises high-spin haem b3 in close proximity with non-haem iron, FeB. In oxidized NorBC, the active site is EPR-silent owing to exchange coupling between FeIII haem b3 and FeBIII (both S=5/2). On the basis of resonance Raman studies [Moënne-Loccoz, Richter, Huang, Wasser, Ghiladi, Karlin and de Vries (2000) J. Am. Chem. Soc. 122, 9344-9345], it has been assumed that the coupling is mediated by an oxo-bridge and subsequent studies have been interpreted on the basis of this model. In the present study we report a VFVT (variable-field variable-temperature) MCD (magnetic circular dichroism) study that determines an isotropic value of J=-1.7 cm-1 for the coupling. This is two orders of magnitude smaller than that encountered for oxo-bridged diferric systems, thus ruling out this configuration. Instead, it is proposed that weak coupling is mediated by a conserved glutamate residue. PMID:23421449

Van Wonderen, Jessica H; Oganesyan, Vasily S; Watmough, Nicholas J; Richardson, David J; Thomson, Andrew J; Cheesman, Myles R

2013-05-01

378

Simultaneous quantification of atomoxetine as well as its primary oxidative and O-glucuronide metabolites in human plasma and urine using liquid chromatography tandem mass spectrometry (LC/MS/MS).  

PubMed

A sensitive and selective liquid chromatography tandem mass spectrometry (LC/MS/MS) method for the determination of atomoxetine and its metabolites (4-hydroxyatomoxetine, N-des-methylatomoxetine, and 4-hydroxyatomoxetine-O-glucuronide) has been developed for human plasma and urine. Using stable-labeled internal standards, the method proved to be accurate and precise for the analytes in all species, resulting in inter-batch accuracy (percent relative error, %RE) within 100+/-13% and inter-batch precision (relative standard deviation, %RSD) within 11%. Stability was demonstrated for the analytes in neat solutions and the reconstitution solvent, as well as plasma and urine (with or without the deconjugation reagent). The method was simple, robust (utilized for the analysis of several hundred clinical study samples), and amenable to high sample throughput. PMID:15967301

Mullen, John H; Shugert, Richard L; Ponsler, George D; Li, Qimin; Sundaram, Bhaskar; Coales, Heather L; Yakupkovic, Joseph E; Lelacheur, Richard M; Wheeler, William J; Belas, Frank J; Sauer, John-Michael

2005-07-15

379

Thermodynamics of technetium related to nuclear waste disposal: Solubilities of Tc(IV) oxides and the electrode potential of the Tc(VII)/Tc(IV)--oxide couple  

SciTech Connect

Solubilities of Tc(IV) oxides have been determined in a number of solutions in the pH range 1 to 10. Technetium oxide was prepared by precipitation upon purified sand with a 30% excess of hydrazine and by electrodeposition. The oxide-covered sand was transferred to a small column, and the solutions to be studied were continuously cycled through the column. The electrodeposited oxide was formed on a platinum mesh electrode, and after careful rinsing, the solution to be studied was added to the electrolytic cell. The concentrations of total technetium and Tc(IV) species in the solutions were periodically determined by separating the oxidized and reduced technetium species using a solvent extraction procedure and counting the beta activity of the /sup 99/Tc with a liquid scintillation counter. In basic solutions, the concentrations of Tc(IV) species in equilibrium with the oxide were in the range of 10/sup /minus/8/ to 10/sup /minus/9/ mol/L and tended to increase slightly with pH. In acid solutions the concentrations were much higher and were consistent with literature data on the hydrolytic species of Tc(IV). Solubilities appeared to reach a minimum in the intermediate pH range, and they were generally a factor of three or four lower for oxides electrodeposited in basic solutions compared to those for oxides electrodeposited from acid solution. The oxides were hydrated, and assuming a formula of TcO/sub 2//center dot/nH/sub 2/O, the value of n was found to be 1.63 +- 0.28. These data can be used to estimate Tc(IV) solubilities for cases where solubility limits transport of technetium in reducing environments of high-level waste repositories. 22 refs., 7 figs., 9 tabs.

Meyer, R E; Arnold, W D; Case, F I; O'Kelley, G D

1989-06-01

380

Reversed-phase chiral liquid chromatography on polysaccharide-based stationary phase coupled with tandem mass spectrometry for simultaneous determination of four stereoisomers of MK-0974 in human plasma.  

PubMed

MK-0974 (1a), N-[(3R,6S)-6-(2,3-difluorophenyl)-2-oxo-1-(2,2,2-trifuoroethyl)azepan-3-yl]-4-(2-oxo-2,3-dihydro-1H-imidazo-[4,5-B] pyridine-1-yl)piperidine-1-carboxamide, is a novel calcitonin gene-related peptide (CGRP) receptor antagonist with two chiral centers. Direct separation of its four stereoisomers (1a-d) was achieved using a cellulose chiral stationary phase, a Chiralcel OJ-RH column (150 mm x 4.6 mm), under reversed-phase condition, following the extraction of 0.2 mL plasma on Oasis muElution HLB 96-well solid-phase-extraction (SPE) plate. The tandem mass spectrometric detection was conducted in the positive-ion mode with a turbo-ion-spray (TIS) interface using multiple-reaction-monitoring on a Sciex API3000. Addition of ammonium trifluoroacetate to low-organic mobile phase improved detection sensitivity by more than 30-fold. The simultaneous quantification of the four stereoisomers in human plasma was validated over the ranges of 0.5-5000 nM for 1a and 0.5-500 nM for its three isomers (1b-d). Intraday validation, conducted with five lots of human control plasma, resulted in <12.4% (% coefficient of variation, CV) precision and 96.3-105.4% accuracy for all four stereoisomers. Further evaluation indicated that the assay was specific, the samples were stable after three freeze/thaw cycles, the recovery was reasonable (above 65%) and no matrix effect was observed for all four isomers. Investigation on the chiral integrity of 1a indicated that the diastereomer 1c, inversion at azepinone-3 carbon, was the only isomer observed in the post-dose clinical samples and accounted for 2.4-5.2% of MK-0974 exposure in the circulatory system. The possibility of inversion during blood collection, plasma storage and sample preparation was ruled out, while inversion was observed in the clinical formulation accounting for approximately 0.12% of 1a in a 100-mg capsule. PMID:18799366

Xu, Yang; Musson, Donald G

2008-10-01

381

Simultaneous and enantioselective determination of cis-epoxiconazole and indoxacarb residues in various teas, tea infusion and soil samples by chiral high performance liquid chromatography coupled with tandem quadrupole-time-of-flight mass spectrometry.  

PubMed

A novel and sensitive method for simultaneous enantiomeric analysis of two pesticides-cis-epoxiconazole and indoxacarb-in various teas, black tea infusion, and soil samples has been developed. The samples were initially subjected to acetonitrile extraction followed by cleanup using lab-made florisil/graphitized carbon black mixed solid phase extraction (SPE) column (for the different teas and soil samples) and a BondElut C18-SPE column (for the black tea infusion samples). Separation of the analytes was performed on a chiral stationary phase using high performance liquid chromatography (HPLC) under a reversed-phase isocratic elution mode followed by tandem quadrupole time-of-flight mass spectrometry (Q-TOF/MS) detection. The mobile phase components, mobile phase ratios, flow rates, column temperatures, and MS parameters were all optimized to reach high sensitivity and selectivity, good peak shape, and satisfactory resolution. The performance of the method was evaluated based on the sensitivity, linearity, accuracy, precision, and matrix effects. Under optimal conditions, for the various teas (green tea, black tea, and puer tea), fresh tea leaf, soil and black tea infusion samples spiked at low, medium, and high levels, the mean recoveries for the four enantiomers ranged from 61.0% to 129.7% with most relative standard deviations (RSDs) being 17.1% or below. Good linearity can be achieved with regression coefficients (R) of 0.9915 or above for all target enantiomers, and matrix-matched calibration concentration ranging from 5.0 to 1000?g/L. The limits of detection (LODs) for all four target enantiomers were 1.4?g/kg or below in the different teas and soil samples and 0.05?g/kg or below in the black tea infusion, whereas the limits of quantification (LOQs) for those did not exceed 5.0?g/kg and 0.2?g/L, respectively. The proposed method is convenient and reliable and has been applied to real tea samples screening. It has also been extended for studies on the degradation kinetics and environmental behaviors in the field trials, providing additional information for reliable risk assessment of these chiral pesticides. PMID:25108768

Zhang, Xinzhong; Luo, Fengjian; Lou, Zhengyun; Lu, Meiling; Chen, Zongmao

2014-09-12

382

Analysis of phytohormones in vermicompost using a novel combinative sample preparation strategy of ultrasound-assisted extraction and solid-phase extraction coupled with liquid chromatography-tandem mass spectrometry.  

PubMed

Vermicompost (VC), a widely used premium organic fertilizer, is the by-product of symbiotic interactions between earthworms and microorganisms living within them. It has been postulated that phytohormones are plausible "magic compounds" in VC that are responsible for making them such good fertilizers. Thus, a novel approach involving ultrasound-assisted extraction (UAE) and solid-phase extraction (SPE) was developed as a fast and efficient sample preparation method to screen for different classes of phytohormones in VC by liquid chromatography-tandem mass spectrometric (LC-MS/MS) analysis. Nine phytohormones from three different classes, including trans-zeatin (tZ), kinetin (K), N(6)-[2-isopentyl]adenine (iP), N(6)-benzyladenine (BA), N(6)-isopentenyladenosine (iPR), indole-3-acetic acid (IAA), 4-[3-indolyl]butyric acid (IBA), 1-naphthaleneacetic acid (NAA) and (+)-abscisic acid (ABA), were simultaneously screened. The extraction parameters influencing UAE ef?ciency were optimized to provide comparable recovery to the conventional mix-stirring (MSt) method. The optimized UAE method was subsequently applied on the analysis of phytohormones in VC, i.e. phytohormone extract was further pre-concentrated and puri?ed using C18 and MCX SPE cartridges prior to LC-MS/MS analysis. The following phytohormones, namely iP, iPR and IAA, were detected and quantified to be 0.49, 0.53, 79.78ngg(-1), respectively; tZ was found to be below the limit of quantitation. Recoveries of 10.2%, 9.1%, 18.9% and 0.3% for tZ, iP, iPR and IAA were obtained. This is one of the few reported works for the successful detection and quantitation of cytokinins and auxins in VC, that provided the key empirical evidence to explain the growth efficacy of applying VC in promoting plant growth. Additionally, this pioneering work could potentially be applicable for the analysis of other types of organic fertilizers such as composts and activated composted materials awaiting phytohormone analyzes for quality assessment and control. PMID:25882426

Zhang, Hong; Tan, Swee Ngin; Teo, Chee How; Yew, Yan Ru; Ge, Liya; Chen, Xin; Yong, Jean Wan Hong

2015-07-01

383

Liquid Chromatography with Post-Column Reagent Addition of Ammonia in Methanol Coupled to Negative Ion Electrospray Ionization Tandem Mass Spectrometry for Determination of Phenoxyacid Herbicides and their Degradation Products in Surface Water  

PubMed Central

A new liquid chromatography (LC)-negative ion electrospray ionization (ESI?)–tandem mass spectrometry (MS/MS) method with post-column addition of ammonia in methanol has been developed for the analysis of acid herbicides: 2,4-dichlorophenoxy acetic acid, 4-chloro-o-tolyloxyacetic acid, 2-(2-methyl-4-chlorophenoxy)butyric acid, mecoprop, dichlorprop, 4-(2,4-dichlorophenoxy) butyric acid, 2,4,5-trichlorophenoxy propionic acid, dicamba and bromoxynil, along with their degradation products: 4-chloro-2-methylphenol, 2,4-dichlorophenol, 2,4,5-trichlorophenol and 3,5-dibromo-4-hydroxybenzoic acid. The samples were extracted from the surface water matrix using solid-phase extraction (SPE) with a polymeric sorbent and analyzed with LC ESI? with selected reaction monitoring (SRM) using a three-point confirmation approach. Chromatography was performed on a Zorbax Eclipse XDB-C18 (50 × 4.6 mm i.d., 1.8 ?m) with a gradient elution using water-methanol with 2 mM ammonium acetate mobile phase at a flow rate of 0.15 mL/min. Ammonia in methanol (0.8 M) was added post-column at a flow rate of 0.05 mL/min to enhance ionization of the degradation products in the MS source. One SRM transition was used for quantitative analysis while the second SRM along with the ratio of SRM1/SRM2 within the relative standard deviation determined by standards for each individual pesticide and retention time match were used for confirmation. The standard deviation of ratio of SRM1/SRM2 obtained from standards run on the day of analysis for different phenoxyacid herbicides ranged from 3.9 to 18.5%. Limits of detection (LOD) were between 1 and 15 ng L?1 and method detection limits (MDL) with strict criteria requiring <25% deviation of peak area from best-fit line for both SRM1 and SRM2 ranged from 5 to 10 ng L?1 for acid ingredients (except dicamba at 30 ng L?1) and from 2 to 30 ng L?1 for degradation products. The SPE-LC-ESI? MS/MS method permitted low nanogram-per-liter determination of pesticides and degradation products for surface water samples. PMID:20212919

Raina, Renata; Etter, Michele L.

2010-01-01

384

The efficacy of oxidative coupling for promoting in-situ immobilization of hydroxylated aromatics in contaminated soil and sediment systems. 1998 annual progress report  

SciTech Connect

'Hydroxylated aromatic compounds (HAC''s) and their precursors are common contaminants of surface and subsurface systems at DOE facilities. The environmental fate and transport of such compounds, particularly in subsurface systems, is generally dominated by their sorption and desorption by soils and sediments. Certain secondary chemical reactions, most specifically abiotic and/or enzymatic oxidative coupling, may be significant in controlling the sorption and subsequent desorption of such hydroxylated aromatics by soils and sediments. The principal objectives of this study are to investigate: (1) the role of abiotic/enzymatic coupling reactions on the immobilization of HAC''s; (2) the effects of environmental factors on such immobilization; and (3) preliminary engineering approaches utilizing enhanced abiotic/enzymatic coupling reactions to immobilize hydroxylated aromatics in-situ. Information gathered from the study will be useful in quantifying the behavior of this class of organic compounds in various subsurface contamination scenarios relevant to DOE facilities, and in specifying strategies for the selection and design of remediation technologies. Over the first two years of this three-year project, the authors have developed a significantly improved understanding of the mechanisms of hydroxylated aromatic compound sorption and immobilization by natural soils and sediments. Immobilization in this context is attributed to oxidative coupling of the hydroxylated aromatics subsequent to their sorption to a soil or sediment, and is quantified in terms of the amount of a sorbed target compound retained by a sorbent after a series of sequential water and solvent extractions. The presence of oxygen, metal oxides, and organic matter, all of which can potentially catalyze/facilitate the abiotic oxidative coupling of HAC''s, were investigated during these first two years. Three different HAC''s: phenol, trichlorophenol and o-cresol were included in the experimental program. Inorganic soil matrices were represented by a glacial wash sand (Wurtsmith sand) having very low organic content. Because the chemical nature of soil organic matter may potentially affect the extent of coupling or immobilization, sorbents having different organic matter compositions are being investigated. Two of the three studied to date are near-surface soils, characterized by geologically younger organic material (Fox Forest soil and Fox Grassland soil). The third sorbent is an older and diagenetically altered soil (Lachine Shale). Sorbent preparation, characterization and experimental protocol development were completed in the first year of the study while the second year of the project has focused primarily on experiments with natural systems, as planned. Preliminary work with engineered systems has been initiated earlier than scheduled in order to integrate and relate all aspects of the study.'

Weber, W.J. [Univ. of Michigan, Ann Arbor, MI (US); Bhandari, A. [Kansas State Univ., Manhattan, KS (US)

1998-06-01

385

Fundamental studies of the mechanism of catalytic reactions with catalysts effective in the gasification of carbon solids and the oxidative coupling of methane. Quarterly report, October 1, 1994--December 31, 1994  

SciTech Connect

This report describes research on the oxidative coupling of methane and catalysts involved in coal gasification. Topics include methane pyrolysis and catalysts, and magnetic properties of the coal gasification catalyst Ca-Ni-K-O system.

Iglesia, E.; Perry, D.L.; Heinemann, H.

1994-12-01

386

Sulfur and oxygen isotope fractionation during sulfate reduction coupled to anaerobic oxidation of methane is dependent on methane concentration  

NASA Astrophysics Data System (ADS)

Isotope signatures of sulfur compounds are key tools for studying sulfur cycling in the modern environment and throughout earth's history. However, for meaningful interpretations, the isotope effects of the processes involved must be known. Sulfate reduction coupled to the anaerobic oxidation of methane (AOM-SR) plays a pivotal role in sedimentary sulfur cycling and is the main process responsible for the consumption of methane in marine sediments - thereby efficiently limiting the escape of this potent greenhouse gas from the seabed to the overlying water column and atmosphere. In contrast to classical dissimilatory sulfate reduction (DSR), where sulfur and oxygen isotope effects have been measured in culture studies and a wide range of isotope effects has been observed, the sulfur and oxygen isotope effects by AOM-SR are unknown. This gap in knowledge severely hampers the interpretation of sulfur cycling in methane-bearing sediments, especially because, unlike DSR which is carried out by a single organism, AOM-SR is presumably catalyzed by consortia of archaea and bacteria that both contribute to the reduction of sulfate to sulfide. We studied sulfur and oxygen isotope effects by AOM-SR at various aqueous methane concentrations from 1.4±0.6 mM up to 58.8±10.5 mM in continuous incubation at steady state. Changes in the concentration of methane induced strong changes in sulfur isotope enrichment (?S34) and oxygen isotope exchange between water and sulfate relative to sulfate reduction (?O), as well as sulfate reduction rates (SRR). Smallest ?S34 (21.9±1.9‰) and ?O (0.5±0.2) as well as highest SRR were observed for the highest methane concentration, whereas highest ?S34 (67.3±26.1‰) and ?O (2.5±1.5) and lowest SRR were reached at low methane concentration. Our results show that ?S34, ?O and SRR during AOM-SR are very sensitive to methane concentration and thus also correlate with energy yield. In sulfate-methane transition zones, AOM-SR is likely to induce very large sulfur isotope fractionation between sulfate and sulfide (i.e. >60‰) and will drive the oxygen isotope composition of sulfate towards the sulfate-water oxygen isotope equilibrium value. Sulfur isotope fractionation by AOM-SR at gas seeps, where methane fluxes are high, will be much smaller (i.e. 20 to 40‰).

Deusner, Christian; Holler, Thomas; Arnold, Gail L.; Bernasconi, Stefano M.; Formolo, Michael J.; Brunner, Benjamin

2014-08-01

387

Tandem motors reduce well costs  

SciTech Connect

The new generation of tandem mud motors that recently appeared on the drilling scene is significantly affecting drilling efficiency worldwide. These motors provide drillers with increased horsepower at the bit, higher torque, and faster rates of penetration (ROP). With advanced engineering and more durable materials, motor life is being extended, thereby increasing the time between bit trips and reducing drilling costs. This article reviews the performance, design, and operation of these motors.

Hooper, M.; Daigle, C. [Halliburton Energy Services, Houston, TX (United States); Crowe, R. [Halliburton Energy Services, Aberdeen (United Kingdom)

1995-10-01

388

Tandem compressors in gas storage  

Microsoft Academic Search

To demonstrate that a single gas-turbine compressor set can be an attractive economic alternative to multiunit reciprocating compressors for use in typical gas-storage injection and withdrawal cycles, Cooper Rolls Inc. and Union Gas Ltd., Canada, installed a unique tandem-driven centrifugal compressor rated at 19,690 kW at the Dawn compressor station in south Ontario. Preliminary operating data indicate that the actual

D. W. Wood; R. G. Reid

1979-01-01

389

Rotational stability of tandem mirrors  

Microsoft Academic Search

The general stability equation for low-m rotational-ballooning instabilities in axisymmetric mirror geometry is derived for an isotropic pressure plasma, including a boundary term which represents the stabilizing effect of an unspecified anchor. The corresponding variational principle, together with a particular quadrupole anchor model, is used to compute the low-..beta.. rotational-interchange marginal stability condition for a conventional tandem mirror. The stability

J. P. Freidberg; D. A. D'Ippolito

1983-01-01

390

Rotational stability of tandem mirrors  

Microsoft Academic Search

The general stability equation for low-m rotational-ballooning instabilities in axisymmetric mirror geometry is derived for an isotropic pressure plasma, including a boundary term which represents the stabilizing effect of an unspecified anchor. The corresponding variational principle, together with a particular quadrupole anchor model, is used to compute the low-? rotational-interchange marginal stability condition for a conventional tandem mirror. The stability

J. P. Freidberg; D. A. D’Ippolito

1983-01-01

391

All-catalytic, efficient, and asymmetric synthesis of alpha,omega-diheterofunctional reduced polypropionates via "one-pot" Zr-catalyzed asymmetric carboalumination-Pd-catalyzed cross-coupling tandem process.  

PubMed

A highly efficient method for the synthesis of stereochemically pure (>/=99% ee and >50/1 dr) alpha,omega-diheterofunctional reduced polypropionates has been developed. The essential features of the method are represented by the conversion of inexpensive styrene into 2-methyl-4-phenyl-1-pentanol (1) in 50% yield over two steps from styrene via Zr-catalyzed asymmetric carboalumination (ZACA) reaction in the presence of (NMI)2ZrCl2 and Pd-catalyzed vinylation of the in situ generated isoalkylalanes in the presence of Zn(OTf)2 and a catalytic amount of Pd(DPEphos)Cl2. This ZACA-Pd-catalyzed vinylation may be repeated as needed without purification. After the final ZACA reaction, oxidation with O2 provides alpha-hydroxy-omega-phenyl reduced polypropionates, which can be fully or partially purified by chromatography. After acetylation, Ru-catalyzed oxidative cleavage of the Ph ring, and reduction with BH3.THF, the second chromatographic purification provides stereoisomerically pure alpha,omega-diheterofunctional reduced polypropionates (e.g., 9 and 11) that can be further converted to key intermediates 6 and 7 for the synthesis of ionomycin (4) and borrelidin (5), respectively, by known reactions. PMID:15740104

Novak, Tibor; Tan, Ze; Liang, Bo; Negishi, Ei-Ichi

2005-03-01

392

Advances in tandem reactions with organozinc reagents.  

PubMed

The design and implementation of tandem reactions provides organic chemists with numerous challenges, in particular that of undesired cross-reactivity between substrates. Among organometallics, the use of organozinc reagents in tandem reactions provides several advantages as a result of their broad functional group tolerance and compatibility with transition metals. This review highlights prominent examples of recent advances in tandem reactions with organozinc reagents that illustrate their potential in organic synthesis. PMID:25708795

Kim, Ju Hyun; Ko, Young Ok; Bouffard, Jean; Lee, Sang-Gi

2015-04-10

393

Short Tandem Repeat DNA Internet Database  

National Institute of Standards and Technology Data Gateway

SRD 130 Short Tandem Repeat DNA Internet Database (Web, free access)   Short Tandem Repeat DNA Internet Database is intended to benefit research and application of short tandem repeat DNA markers for human identity testing. Facts and sequence information on each STR system, population data, commonly used multiplex STR systems, PCR primers and conditions, and a review of various technologies for analysis of STR alleles have been included.

394

Novel biomarkers of protein oxidation sites and degrees using horse cytochrome c as the target by mass spectrometry  

NASA Astrophysics Data System (ADS)

Biomarkers held both incredible application and significant challenge in probing the oxidation mechanisms of proteins under oxidative stress. Here, mass spectrometry (MS) coupled with liquid chromatography (LC) was applied to establish a new pipeline to probe the oxidation sites and degrees of horse cytochrome c (HCC) with its oxidative products serving as the biomarkers. Samples of native and UV/H 2O 2 oxidized HCCs were digested by trypsin and subjected to biomarker discovery using LC/MS and tandem mass spectrometry (MS/MS). Experiment results proved that the main oxidation sites were located at Cys 14, Cys 17, Met 65 and Met 80 residues in peptides C 14AQC(heme)HTVEK 22, C 14AQCHTVEK 22, E 60ETLMEYLENPKK 73, M 80IFAGIK 86 and M 80IFAGIKK 87. Quantitative analysis on the oxidized peptides showed the oxidation degrees of target sites had positive correlations with extended oxidation dose and controlled by residues types and their accessibility to solvent molecules. Being able to provide plentiful information for the oxidation sites and oxidation degrees, the identified oxidized products were feasibility biomarkers for HCC oxidation, compared with the conventional protein carbonyl assay.

Zong, Wansong; Liu, Rutao; Guo, Changying; Sun, Feng

2011-05-01

395

Recent Activities at Tokai Tandem Accelerator  

NASA Astrophysics Data System (ADS)

Recent activities at the JAEA-Tokai tandem accelerator facility are presented. The terminal voltage of the tandem accelerator reached 19.1 MV by replacing acceleration tubes. The multi-charged positive-ion injector was installed in the terminal of the tandem accelerator, supplying high-current noble-gas ions. A superconducting cavity for low-velocity ions was developed. Radioactive nuclear beams of 8,9Li and fission products, produced by the tandem accelerator and separated by the ISOL, were supplied with experiment. Recent results of nuclear physics experiments are reported.

Ishii, Tetsuro

2010-05-01

396

The characterization of tandem and corrugated wings  

NASA Astrophysics Data System (ADS)

Dragonfly wings have two distinct features: a tandem configuration and wing corrugation. Both features have been extensively studied with the aim to understand the superior flight performance of dragonflies. In this paper we review recent development of tandem and corrugated wing aerodynamics. With regards to the tandem configuration, this review will focus on wing/wing and wing/vortex interactions at different flapping modes and wing spacing. In addition, the aerodynamics of tandem wings under gusty conditions will be reviewed and compared with isolated wings to demonstrate the gust resistance characteristics of flapping wings. Regarding corrugated wings, we review their structural and aerodynamic characteristics.

Lian, Yongsheng; Broering, Timothy; Hord, Kyle; Prater, Russell

2014-02-01

397

Hybrid tandem photovoltaic devices with a transparent conductive interconnecting recombination layer  

SciTech Connect

Highlights: ? This work enhanced power conversion efficiency of the hybrid tandem solar cell from 1.0% to 2.6%. ? The interfacial series resistance of the tandem solar cell was eliminated by inserting ITO layer. ? This work shows the feasibility of the highly efficient hybrid tandem solar cells. -- Abstract: We demonstrate hybrid tandem photovoltaic devices with a transparent conductive interconnecting recombination layer. The series-connected hybrid tandem photovoltaic devices were developed by combining hydrogenated amorphous silicon (a-Si:H) and polymer-based organic photovoltaics (OPVs). In order to enhance the interfacial connection between the subcells, we employed highly transparent and conductive indium tin oxide (ITO) thin layer. By using the ITO interconnecting layer, the power conversion efficiency of the hybrid tandem solar cell was enhanced from 1.0% (V{sub OC} = 1.041 V, J{sub SC} = 2.97 mA/cm{sup 2}, FF = 32.3%) to 2.6% (V{sub OC} = 1.336 V, J{sub SC} = 4.65 mA/cm{sup 2}, FF = 41.98%) due to the eliminated interfacial series resistance.

Kim, Taehee; Choi, Jin Young; Jeon, Jun Hong; Kim, Youn-Su; Kim, Bong-Soo; Lee, Doh-Kwon; Kim, Honggon; Han, Seunghee [Solar Cell Research Center, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 136-791 (Korea, Republic of)] [Solar Cell Research Center, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 136-791 (Korea, Republic of); Kim, Kyungkon, E-mail: kimkk@ewha.ac.kr [Solar Cell Research Center, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 136-791 (Korea, Republic of) [Solar Cell Research Center, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 136-791 (Korea, Republic of); Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750 (Korea, Republic of)

2012-10-15

398

Comparative metabolites in plasma and urine of normal and type 2 diabetic rats after oral administration of the traditional Chinese scutellaria-coptis herb couple by ultra performance liquid chromatography-tandem mass spectrometry.  

PubMed

Scutellaria-coptis herb couple is widely used traditional Chinese medicine (TCM) in treating type 2 diabetes; however, the in vivo integrated metabolism of its main bioactive components in type 2 diabetic rats remains unknown. In this paper, ultra-performance liquid chromatography (UPLC) coupled to quadrupole time-of-flight (Q-TOF) and the MetaboLynx™ software combined with mass defect filtering (MDF) together provided unique high throughput capabilities for drug metabolism study with excellent MS mass accuracy and enhanced MS(E) data acquisition. This rapid automated analysis method was successfully applied for screening and identification of the absorbed and metabolized constituents after oral administration of scutellaria-coptis extract to rats. The results showed that a total of 14 metabolites of two parent compounds were detected and tentatively identified in vivo based on the characteristics of their protonated ions. Main parent components of scutellaria-coptis extract such as baicalin and berberine were absorbed into the blood circulation of the rats. Differences of metabolite classes were not observed between normal and type 2 diabetic rat plasma and urine samples. However, the concentrations of baicalin and methylated berberine in type 2 diabetic rat plasma were much higher than those in normal sample. While, the concentrations of these two compounds in type 2 diabetic rat urine were remarkably lower than those in normal sample. This helped maintain a high blood drug concentration which might be beneficial for the treatment of type 2 diabetes. Additionally, the developed method was simple and reliable, revealing that it could be used to rapid screen and propose the structures of active components responsible for pharmacological effects of scutellaria-coptis and to better clarify its action mechanism. This work suggests that the integrative metabolism approach makes a useful template for drug metabolism research of TCMs. PMID:24976485

Jiang, Shu; Xu, Jun; Qian, Da-Wei; Shang, Er-Xin; Liu, Pei; Su, Shu-Lan; Leng, Xue-Jiao; Guo, Jian-Ming; Duan, Jin-Ao; Du, Leyue; Zhao, Min

2014-08-15

399

47 CFR 69.111 - Tandem-switched transport and tandem charge.  

Code of Federal Regulations, 2013 CFR

...circuits used in the tandem to end office links (or a surrogate based on the proportion...circuits used in the tandem to end office links (or a surrogate based on the proportion...circuits used in the tandem to end office links (or a surrogate based on the...

2013-10-01

400

47 CFR 69.111 - Tandem-switched transport and tandem charge.  

Code of Federal Regulations, 2012 CFR

...circuits used in the tandem to end office links (or a surrogate based on the proportion...circuits used in the tandem to end office links (or a surrogate based on the proportion...circuits used in the tandem to end office links (or a surrogate based on the...

2012-10-01

401

47 CFR 69.111 - Tandem-switched transport and tandem charge.  

Code of Federal Regulations, 2014 CFR

...circuits used in the tandem to end office links (or a surrogate based on the proportion...circuits used in the tandem to end office links (or a surrogate based on the proportion...circuits used in the tandem to end office links (or a surrogate based on the...

2014-10-01

402

47 CFR 69.111 - Tandem-switched transport and tandem charge.  

Code of Federal Regulations, 2011 CFR

...circuits used in the tandem to end office links (or a surrogate based on the proportion...circuits used in the tandem to end office links (or a surrogate based on the proportion...circuits used in the tandem to end office links (or a surrogate based on the...

2011-10-01

403

An IETS study of a silane coupling agent; the interaction of 3-(trimethoxysilyl)propanethiol with aluminium oxide and silver surfaces  

NASA Astrophysics Data System (ADS)

The inelastic electron tunnelling spectrum of a silane coupling agent, 3-(trimethoxysilyl)propanethiol, is presented. Approximately monolayer quantities of this silane are present on the barrier oxide of an aluminium-aluminium oxide-metal tunnelling junction, in which the counter electrode is either lead or silver. It is deduced from the IETS spectra that the alkoxy groups of this silane condense with the surface hydroxyl groups. No interaction with the lead is observed but the silver layer clearly reacts with the thiol group of the silane molecule, since the thiol stretching vibration is absent in the spectra, and probably forms the corresponding silver thiolate. The influence of this reaction on the conformation of the bound silane is discussed.

Van Velzen, Peter N. T.

1984-05-01

404

Slurry sampling fluorination assisted electrothermal vaporization-inductively coupled plasma-atomic emission spectrometry for the direct determination of metal impurities in aluminium oxide ceramic powders.  

PubMed

A new analytical procedure for the direct determination of metal impurities (Cr, Cu, Fe and V) in aluminium oxide ceramic powders by slurry sampling fluorination assisted electrothermal vaporization-inductively coupled plasma-atomic emission spectrometry (ETV-ICP-AES) is reported. A polytetrafluoroethylene (PTFE) emulsion was used as a fluorinating reagent to promote the vaporization of impurity elements in aluminium oxide ceramic powders from the graphite tube. A vaporization stage with a long ramp time and a short hold time provided the possibility of temporal analyte-matrix separation. The experimental results indicated that a 10 microL 1% m/v slurry of aluminium oxide could be destroyed and vaporized completely with 600 micrograms PTFE under the selected conditions. Two aluminium oxide ceramic powder samples were used without any additional pretreatment. Analytical results obtained by using standard addition method with aqueous standard solution were checked by comparison of the results with pneumatic nebulization (PN)-ICP-AES based on the wet-chemical decomposition and analyte-matrix separation. The limits of detection (LODs) between 0.30 microgram g-1 (Fe) and 0.08 microgram g-1 (Cu) were achieved, and, the repeatability of measurements was mainly better than 10%. PMID:11270230

Peng, T; Chang, G; Wang, L; Jiang, Z; Hu, B

2001-03-01

405

Efficient Tandem Polymer Solar Cells Fabricated by All-Solution Processing  

Microsoft Academic Search

Tandem solar cells, in which two solar cells with different absorption characteristics are linked to use a wider range of the solar spectrum, were fabricated with each layer processed from solution with the use of bulk heterojunction materials comprising semiconducting polymers and fullerene derivatives. A transparent titanium oxide (TiOx) layer separates and connects the front cell and the back cell.

Jin Young Kim; Kwanghee Lee; Nelson E. Coates; Daniel Moses; Thuc-Quyen Nguyen; Mark Dante; Alan J. Heeger

2007-01-01

406

Emerging catalytic applications of transition metal oxide nanomaterials under microwave and conventional heating  

NASA Astrophysics Data System (ADS)

Heterogeneous transition metal oxide catalysts have advantages over homogeneous catalysts, such as easy separations and efficient recycling and minimization of metal traces in the products. Transition metal oxide nanomaterials with different properties such as shapes and particle size were synthesized by hydrothermal, solvothermal, solvent-free and by energy efficient microwave heating methods and characterized using X-Ray and microscopic techniques. The synthesized catalysts were tested for tandem reactions to form quinoxalines, oxidations of hydrocarbons to form alcohols, aldehydes and ketones, epoxidation, epoxide ring opening, and N-aryl coupling reactions. The kinetics and energy consumption associated with these reactions were compared for both microwave and conventionally heated reactions. Further, Synchrotron radiation-based time-resolved XRD experiments under a wide variety of temperature and pressure conditions were conducted to study the reactions under working conditions. EXAFS and XANES data collections were performed to determine inter-atomic distances and oxidation states of the catalysts.

Sithambaram, Shanthakumar

407

NiSO4-catalyzed C-H activation/C-S cross-coupling of 1,2,3-triazole N-oxides with thiols.  

PubMed

An efficient nickel-catalyzed protocol for C-S cross-coupling through the direct functionalization of 2-aryl-1,2,3-triazole N-oxide C-H bonds with aryl or alkyl thiols, or diphenyl disulfide has been developed. The targeted N(+)-O(-) bond cleavage can be observed during the reaction, and thus obviates the need to use an additional deoxygenation step. This new protocol for the preparation of thiolated 2-aryl-1,2,3-triazoles appears to offer good yields with high regioselectivity, mild conditions, and a wide substrate scope. PMID:25683342

Zhu, Jiayi; Chen, Yu; Lin, Feng; Wang, Baoshuang; Chen, Zhengwang; Liu, Liangxian

2015-03-11

408

Detection of some stable species during the oxidation of methane by coupling a jet-stirred reactor (JSR) to cw-CRDS  

NASA Astrophysics Data System (ADS)

We present the coupling of a jet-stirred reactor to detection by cw-CRDS in the near infrared and first results obtained during the oxidation of methane. The mixture is rapidly expanded from the jet-stirred reactor into a 80 cm-long cw-CRDS cell maintained at a the pressure around