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1

Green oxidations: Titanium dioxide induced tandem oxidation coupling reactions  

PubMed Central

Summary The application of titanium dioxide as an oxidant in tandem oxidation type processes is described. Under microwave irradiation, quinoxalines have been synthesized in good yields from the corresponding ?-hydroxyketones.

Jeena, Vineet

2009-01-01

2

Tandem Cycloisomerization/Suzuki Coupling of Arylethynyl MIDA Boronates  

PubMed Central

A tandem gold-catalyzed cycloisomerization/Suzuki cross coupling sequence involving arylethynyl-N-methyliminodiacetic acid boronates is described. Combining the mildness of homogeneous gold catalysis with the versatility of N-methyliminodiacetic acid (MIDA) boronates, this tandem two-step method enables the rapid assembly of various aryl-substituted heterocycles without having to isolate or purify any heterocyclic MIDA boronate intermediates. Another major advantage of this method is that a wide range of heterocycles bearing different aryl groups may be made from a single MIDA boronate alkyne precursor.

Chan, Julian M. W.; Amarante, Giovanni W.; Toste, F. Dean

2011-01-01

3

Differential length measurement using low coherence coupled tandem interferometry  

NASA Astrophysics Data System (ADS)

This paper presents the use of low coherence coupled tandem interferometry to measure the differential length of two independent Fabry-Perot (F-P) type microcavities. The two discrete F-P type microcavities are formed between the cleaved end of a fibre and a reflective surface, which could for example, be a pressure sensing membrane or any other component of a transducing element. The technique is an all-optical fibre based sensing configuration in which the sensing cavities are at widely separated locations in an environment where strong temperature gradients may exist. The sensing system is based on two sequential cavities arranged in tandem. The lengths of the cavities are probed by a temperature stabilised fibre based Michelson interferometer operating with a broadband light source. One arm of the probing Michelson interferometer is scanned using a piezo fibre stretcher resulting in an optical path length difference (OPD) between the two arms. The optical interconnecting leads from the probing Michelson interferometer to the two F-P locations are not an active part of the sensor configuration and therefore this configuration is largely insensitive to temperature and strain effects on these interconnecting leads. It is only the probing Michelson interferometer which has to be temperature stabilised. This arrangement allows the F-P measurement cavities to be separated by distances in the range of tens of meters.

Smith, Martin D.; MacPherson, William N.; Maier, Robert R. J.

2013-05-01

4

Characterization of bisphenol A metabolites produced by Portulaca oleracea cv. by liquid chromatography coupled with tandem mass spectrometry.  

PubMed

The garden plant portulaca (Portulaca oleracea cv.) efficiently removes bisphenol A (BPA), an endocrine-disrupting chemical, from a hydroponic solution, but the molecular mechanisms underlying BPA metabolism by portulaca remain unclear. In this study, BPA metabolites converted by portulaca were analyzed by liquid chromatography coupled with tandem mass spectrometry. We observed the hydroxylation of BPA and the oxidization of it to quinone. Polyphenol oxidases are likely to contribute to BPA degradation by portulaca. PMID:22738977

Watanabe, Ippei; Harada, Kazuo; Matsui, Takeshi; Miyasaka, Hitoshi; Okuhata, Hiroshi; Tanaka, Satoshi; Nakayama, Hideki; Kato, Ko; Bamba, Takeshi; Hirata, Kazumasa

2012-01-01

5

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

6

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, K.D.

1991-06-25

7

Copper-mediated tandem oxidative C(sp2)-H/C(sp)-H alkynylation and annulation of arenes with terminal alkynes.  

PubMed

The copper-mediated tandem oxidative C(sp(2))-H/C(sp)-H cross-coupling and intramolecular annulation of arenes with terminal alkynes has been developed, which offers a highly efficient approach to the 3-methyleneisoindolin-1-one scaffold. In this oxidative coupling process, Cu(OAc)2 acts as both the promoter and the terminal oxidant. This protocol features a wide substrate scope; high functional group tolerance; exclusive chemo-, regio-, and stereoselectivity; and simple, easily available, and inexpensive reaction system. The transformation has demonstrated for the first time that Cu(OAc)2 can be renewable after undergoing an oxidative reaction. PMID:24855896

Dong, Jiaxing; Wang, Fei; You, Jingsong

2014-06-01

8

Desymmetrization of diols by a tandem oxidation/Wittig olefination reaction.  

PubMed

Diols are desymmetrized by a tandem oxidation/Wittig olefination to give alpha,beta-unsaturated hydroxy esters without the requirement for protecting group strategies; the alpha,beta-unsaturated hydroxy esters are transformed into dienyl diesters using a second oxidation/Wittig olefination sequence using PCC. PMID:16718329

Phillips, David J; Pillinger, Kathryn S; Li, Wei; Taylor, Angela E; Graham, Andrew E

2006-06-01

9

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.

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

2013-01-01

10

"One-pot" access to dihydrofurans via tandem oxidative difunctionalization and ring contraction of aminopyrans.  

PubMed

An operationally simple and efficient protocol for the construction of dihydrofuran derivatives has been accomplished via a sequential addition of N-chlorosuccinimide and a base to 2-amino-4H-pyran derivatives in alcohol medium. The one-pot protocol proceeding via tandem oxidative difunctionalization and ring contraction provides an entirely new strategy for the construction of the dihydrofuran skeleton. PMID:24846686

Mandha, Santhosh Reddy; Alla, Manjula; Nanubolu, Jagadeesh Babu

2014-06-01

11

Tandem organic light-emitting diode with a molybdenum tri-oxide thin film interconnector layer  

NASA Astrophysics Data System (ADS)

A 10-nm-thick molybdenum tri-oxide (MoO3) thin film was used as the interconnector layer in tandem organic light-emitting devices (OLEDs). The tandem OLEDs with two identical emissive units consisting of N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)-benzidine (NPB)/tris(8-hydroxyquinoline) aluminum (Alq3) exhibited current efficiency-current density characteristics superior to the conventional single-unit devices. At 20 mA/cm2, the current efficiency of the tandem OLEDs using the interconnector layers of MoO3 thin film was about 4.0 cd/A, which is about twice that of the corresponding conventional single-unit device (1.8 cd/A). The tandem OLED showed a higher power efficiency than the conventional single-unit device for luminance over 1200 cd/m2. The experimental results demonstrated that a MoO3 thin film with a proper thickness can be used as an effective interconnector layer in tandem OLEDs. Such an interconnector layer can be easily fabricated by simple thermal evaporation, greatly simplifying the device processing and fabrication processes required by previously reported interconnector layers. A possible explanation was proposed for the carrier generation of the MoO3 interconnector layer.

Lu, Fei-Ping; Wang, Qian; Zhou, Xiang

2013-03-01

12

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

13

Detection of new radiation-induced DNA lesions by liquid chromatography coupled to tandem mass spectrometry.  

PubMed

High-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS) has been used to search for the formation of as yet unidentified radiation-induced DNA lesions. For that purpose, the characteristic fragmentation of most of 2'-deoxyribonucleosides that corresponds to the loss of the 2-deoxyribose moiety (loss of 116 mass units) has been utilized to specifically detect modified nucleosides. Aerated aqueous solutions of DNA were exposed to ionizing radiation, and subsequently DNA was digested to nucleosides with a cocktail of endo- and exonucleases. HPLC/ESI-MS/MS analysis of the resulting 2'-deoxyribonucleoside mixture allowed us to detect four novel DNA modifications. In a subsequent step, the sensitivity of the tandem mass spectrometer was used to search for the formation of the newly detected lesions in the DNA of gamma-irradiated cells. Thus, one of the four newly detected lesions was found to be significantly generated in cellular DNA upon exposure to ionizing radiation. In addition, the latter lesion was also shown to be present in untreated cells, indicating that the modified nucleoside could be formed endogenously. PMID:15384140

Regulus, Peggy; Spessotto, Sébastien; Gateau, Mathilde; Cadet, Jean; Favier, Alain; Ravanat, Jean-Luc

2004-01-01

14

Tandem oxidative processes catalyzed by polymer-incarcerated multimetallic nanoclusters with molecular oxygen.  

PubMed

Heterogeneous catalysis and one-pot tandem reactions are key for efficient and practical organic syntheses and for green and sustainable chemistry. Heterogeneous catalysts can be recovered and reused. These catalysts can be applied to efficient systems, such as continuous-flow systems. Tandem reactions often proceed via highly reactive but unstable intermediates. Tandem reactions do not require workup or much purification of the intermediate. This Account summarizes recent developments that we have made in the field of multifunctional heterogeneous metal nanocluster catalysts for use in tandem reactions based on aerobic oxidation reactions as key processes. We constructed our heterogeneous metal nanoclusters via two important procedures--microencapsulation and cross-linking--using polystyrene-based copolymers with cross-linking moieties. These frameworks can efficiently stabilize small metal nanoclusters to maintain high catalytic activity without aggregation and leaching of nanoclusters. Aggregation and leaching are prevented by weak but multiple interactions between metal nanocluster surfaces and benzene rings in the copolymer as well as by the physical envelopment of cross-linked polymer backbones. Small nanoclusters, including multimetallic alloy clusters (nanoalloys), can be "imprisoned" into these cross-linked polymer composites. The term we use for these processes is polymer incarceration. Direct oxidative esterifications were achieved with polymer-incarcerated (PI) Au nanocluster catalysts. Amides were synthesized from alcohols and amines under aerobic oxidative conditions with PI bimetallic nanocluster catalysts composed of Au and Fe-group metals that formed separated nanoclusters rather than alloys. Oxidative lactam formation from amino alcohols was also achieved. On the other hand, imines could be prepared selectively from alcohols and amines with PI Au-Pd bimetallic nanoclusters. We also achieved the integration of the aerobic oxidation of allylic alcohols and the following Michael reaction catalyzed by trimetallic PI catalysts containing Au-Pd alloy nanoclusters and tetraalkoxyborates as cross-linkers. All of these heterogeneous catalysts could be recovered by simple operations and reused without significant loss of activity or any leaching of metals. We have demonstrated that the polymer incarceration method enables the simultaneous immobilization of several metals, with which we can achieve one-pot tandem oxidative processes using molecular oxygen as an oxidant within the multifunctional heterogeneous catalysts. Suitable choices of metals and bimetallic structures are crucial for the reactivity and the selection of reaction pathways. PMID:24661043

Miyamura, Hiroyuki; Kobayashi, Sh?

2014-04-15

15

Oxidative coupling of methane on silver catalysts  

Microsoft Academic Search

Bulk silver catalysts were found to be active for the oxidative coupling of methane to ethane and ethylene if operated under oxygen-limited conditions at atmospheric pressure and at temperatures above 1020 K. The addition of small amounts of sodium phosphate as promoter increases markedly the C2 selectivity (to values above 90%) and yield (>10%) by efficient suppression of reaction steps

X. Bao; M. Muhler; R. Schlögl; G. Ertl

1995-01-01

16

Determination of F2-isoprostanes in urine by online solid phase extraction coupled to liquid chromatography with tandem mass spectrometry.  

PubMed

F(2)-isoprostanes are a unique class of prostaglandin-like compounds formed in vivo, which have been established as biomarkers of oxidative stress. Accurate analysis has been challenging due to lack of specificity for the isoforms of isoprostanes and lengthy sample preparation procedures to enable trace quantitative analysis. A quantitative analytical method was developed for the determination of F(2)-isoprostanes in rat and hamster urine by online solid phase extraction (SPE) coupled with liquid chromatography and tandem mass spectrometry (LC-MS/MS). The online SPE LC-MS/MS procedure has significant advantages over alternative methods with respect to specificity, sensitivity, simplicity, and speed. The assay enables the detection of iPF(2alpha)-III, iPF(2alpha)-IV, and iPF(2alpha)-VI over a linear dynamic range of 0.1-50 ng/mL in rat urine samples. This range covers the basal levels of these F(2)-isoprostanes. The limit of quantitation (LOQ) for the standard isoprostanes was about 0.3 ng/mL. The average recoveries ranged from 73 to 115% depending upon the individual F(2)-isoprostane isomers in rat urine. Additionally, the method was used to determine increases of endogenous urine iPF(2alpha)-VI and iPF(2alpha)-III in hamsters challenged with either low-fat or high-fat diets. PMID:20476785

Langhorst, Marsha L; Hastings, Michael J; Yokoyama, Wallace H; Hung, Shao-Ching; Cellar, Nicholas; Kuppannan, Krishna; Young, Scott A

2010-06-01

17

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

18

Determination of Fusarium mycotoxins by liquid chromatography/tandem mass spectrometry coupled with immunoaffinity extraction.  

PubMed

A method for the simultaneous quantitative determination of deoxynivalenol (DON), T-2 toxin (T-2), HT-2 toxin (HT-2) and zearalenone (ZEN) in wheat and biscuit by liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) coupled with immunoaffinity extraction is described. A clean-up was carried out using a DZT MS-PREP immunoaffinity column (IAC), and the effect of the sample dilution rate and sample loading was investigated. Furthermore, the effects of ion suppression of a multifunctional column (MFC) and the IAC in the clean-up were compared. The results with the DZT MS-PREP IAC showed that it is possible to make the sample dilution rate low, and indicated a higher solvent-tolerance than usual with an IAC. Sample loading was optimized at 0.25 g. Ion suppression was lowered by purification of the toxins using the DZT MS-PREP IAC. Recoveries of each mycotoxin from wheat and biscuit samples spiked at two levels ranged from 78 to 109%. The limits of detection in wheat and biscuit was in the range of 0.03-0.33 ng x g(-1). From these studies, it is suggested that use of an IAC is effective in the clean-up of each mycotoxin, and, when combined with LC/ESI-MS/MS, it is good for the determination of mycotoxins in foodstuffs due to its rapidity and high sensitivity. PMID:20658684

Tanaka, Hiroki; Takino, Masahiko; Sugita-Konishi, Yoshiko; Tanaka, Toshitsugu; Leeman, David; Toriba, Akira; Hayakawa, Kazuichi

2010-08-30

19

Determination of fungicides in wine by mixed-mode solid phase extraction and liquid chromatography coupled to tandem mass spectrometry  

Microsoft Academic Search

A novel procedure for the determination of nine selected fungicides (metalaxyl-M, azoxystrobin, myclobutanil, flusilazole, penconazole, tebuconazole, propiconazole, diniconazole and difenoconazole) in wine samples is presented. Sample enrichment and purification is simultaneously performed using mixed-mode, anion exchange and reversed-phase, OASIS MAX solid-phase extraction (SPE) cartridges. Analytes were determined by liquid chromatography coupled to tandem mass spectrometry using atmospheric pressure electrospray ionization

I. Carpinteiro; M. Ramil; I. Rodríguez; R. Cela

20

Magnoelastic coupling in magnetic oxide nanoparticles  

NASA Astrophysics Data System (ADS)

Phonons are exquisitely sensitive to finite length scale effects in a wide variety of materials. To investigate confinement in combination with strong magnetoelastic interactions, we measured the infrared vibrational properties of MnO and CoFe2O4 nanoparticles and their parent compounds. For MnO, a charge and bonding analysis reveals that Born effective charge, local effective charge, total polarizability, and the force constant are overall lower in the nanoparticles compared to the bulk. We find that the spin-lattice coupling drops from ˜7 cm-1 in the single crystal to <1 cm-1 in the nanoparticles. For CoFe2O4, the spectroscopic response is sensitive to the size-induced crossover to the superparamagnetic state, which occurs between 7 and 10 nm, and a spin-phonon coupling analysis supports the core-shell model. Moreover, it provides an estimate of the thickness of the magnetically disordered shell, increasing from 0.4 nm in the 14 nm particles to 0.8 nm in the 5 nm particles, demonstrating that the associated local lattice distortions take place on the length scale of the unit cell. These findings are important for understanding finite length scale effects in magnetic oxides and other more complex functional oxides.

Sun, Qi; Baker, Sheila; Birkel, Christina; Seshadri, Ram; Tremel, Wolfgang; Christianson, Andrew; Musfeldt, Janice

2012-02-01

21

Methane oxidative coupling using membrane reactors  

NASA Astrophysics Data System (ADS)

The application of membrane reactors has great potential to increase the desired product yield of reactions which are limited by thermodynamic equilibria, product inhibition, or kinetic selectivity due to undesired parallel and/or series reactions. In the present research program, oxidative coupling of methane (OCM) is studied by using catalytic inorganic membrane reactors in order to achieve higher selectivity and yield towards Csb2 hydrocarbons (mainly ethylene and ethane). The use of membrane reactor configurations enables the control of the oxygen supply to the methane coupling reaction system and thus suppresses the further oxidation of the Csb2 hydrocarbons. Methane oxidative coupling catalysts, different perovskites and other oxygen conducting materials were synthesized by co-precipitation, sol-gel, and cavitation methods and characterized by XRD, SEM, EDX, DSC, as well as by permeation measurements. In addition to materials research, various membrane synthesis techniques, such as pore filling of porous membranes, stabilization of gamma alumina membranes, and preparation and modification of dense oxygen conducting membranes, were investigated. Both porous and dense membrane reactors were used in this study. A thermally treated porous Vycor membrane tube has sufficient resistance to the permeate gas flow and therefore provides a uniform supply of oxygen to the OCM catalyst side of the membrane reactor. The oxygen flow rate can be easily regulated by adjusting the pressure on the oxygen-feed side. Experimental study of OCM in the porous Vycor membrane reactor showed that, under the same operating conditions, higher Csb2 selectivity could be achieved in a membrane reactor than in a conventional co-feed quartz tube reactor. For the same conversion level, higher Csb2 yield was achieved in a Vycor membrane reactor. Oxygen-conducting dense membranes have the unique property of allowing selective permeation of oxygen, and a cheap oxygen source such as air can be used as the oxidant for OCM, thus eliminating the contamination of the product by nitrogen. Although the dense membrane reactor gave slightly lower Csb2 yield than the conventional co-feed, packed bed quartz tube reactor, it outperformed the co-feed reactor with the catalyst packed inside the dense membrane tube. To further elucidate the effect of reactor configuration, operation conditions and kinetic parameters on the performance of membrane reactors, a cross-flow reactor model including staged-feed of one of the reactants and product removal along the reactor length was developed. The performances of the cross-flow reactors with different feed policies were analyzed in terms of residence time, reaction order, and rate constant, and the feed distribution or overall feed ratio was optimized so that the yield of the desired product at the outlet of the reactor was maximized. Based on the general model, methane oxidative coupling in cross-flow reactors was analyzed by using the OCM kinetics, and the effects of contact time, temperature, total pressure, dilution gas, and gas permeability on the reactor performance were investigated.

Lu, Yaping

22

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

SciTech Connect

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 of many oxidative stress markers. In particular, LC-MS/MS often provides the advantages of higher specificity, higher sensitivity, and the capacity to determine multiple analytes (e.g. 4-11 oxidative stress markers per LC run) when compared to other available methods, such as gas chromatography-MS, immunoassays, spectrophotometric or flourometric assays. LC-MS/MS methods are also compatible with cleanup and sample preparation methods including prior solid phase extraction or automated two dimensional LC/LC chromatography followed by MS/MS. LC-MS/MS provides three analytical filtering functions: (1) the LC column provides initial separation as each analyte elutes from the column. (2) The first MS dimension isolates ions of a particular mass-to-charge (m/z) ratio. (3) The selected precursor ion is fragmented into product ions that provide structural information about the precursor ion. Quantitation is achieved based on the abundances of the product ions. The sensitivity limits for LC-MS/MS usually lie within the range of fg-pg of analyte per LC on-column injection. In this article, the present capabilities of LC-MS/MS are briefly presented and some specific examples of the strengths of these LC-MS/MS assays are discussed. The selected examples include methods for isoprostanes, oxidized proteins and amino acids, and DNA biomarkers of oxidative stress.

Winnik, Witold M. [Environmental Carcinogenesis Division, Mail Drop B143-06, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711 (United States)], E-mail: winnik.witold@epa.gov; Kitchin, Kirk T. [Environmental Carcinogenesis Division, Mail Drop B143-06, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711 (United States)

2008-11-15

23

Tandem sequence of phenol oxidation and intramolecular addition as a method in building heterocycles.  

PubMed

A tandem phenol oxidation-Michael addition furnishing oxo- and -aza-heterocycles has been developed. Dirhodium caprolactamate [Rh(2)(cap)(4)] catalyzed oxidation by T-HYDRO of phenols with alcohols, ketones, amides, carboxylic acids, and N-Boc protected amines tethered to their 4-position afforded 4-(tert-butylperoxy)cyclohexa-2,5-dienones that undergo Brønsted acid catalyzed intramolecular Michael addition in one-pot to produce oxo- and -aza-heterocycles in moderate to good yields. The scope of the developed methodology includes dipeptides Boc-Tyr-Gly-OEt and Boc-Tyr-Phe-Me and provides a pathway for understanding the possible transformations arising from oxidative stress of tyrosine residues. A novel method of selective cleavage of O-O bond in hindered internal peroxide using TiCl(4) has been discovered in efforts directed to the construction of cleroindicin F, whose synthesis was completed in 50% yield over just 3 steps from tyrosol using the developed methodology. PMID:23110614

Ratnikov, Maxim O; Farkas, Linda E; Doyle, Michael P

2012-11-16

24

Method development for identification of ketobemidone metabolites in microdialysate samples by coupled-column capillary liquid chromatography-tandem mass spectrometry.  

PubMed

Methodologies for identification of ketobemidone metabolites in microdialysate samples utilizing coupled-column capillary liquid chromatography-electrospray quadrupole time-of-flight tandem mass spectrometry are presented. Two different methods were developed to efficiently analyze the metabolites norketobemidone, ketobemidone N-oxide and hydroxyketobemidone, respectively. Both methods include on-line desalting and trapping of the analytes on micro-solid-phase extraction columns with different retention mechanisms. Norketobemidone and ketobemidone N-oxide were trapped on a C18 column and then eluted by back-flush followed by isocratic separation on a fluorinated reversed-phase type silica gel column (Fluofix). Retention equations are proposed for the chromatographic observations made on the Fluofix column. Hydroxyketobemidone was trapped on a phenylboronic acid column by complex formation at basic pH and then eluted at acidic pH directly into to the mass spectrometer. Oxidation of hydroxyketobemidone to its corresponding quinone was also observed. The methods were successfully used to analyze synthetic ketobemidone metabolites in dilute low-volume microdialysis samples. PMID:18343391

Sundström, Ingela; Andrén, Per E; Westerlund, Douglas

2008-05-01

25

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

26

Materials considerations for the coupling of thermochemical hydrogen cycles to tandem mirror reactors  

Microsoft Academic Search

Candidate materials are discussed and initial choices made for the critical elements in a liquid Li-Na Cauldron Tandem Mirror blanket and the General Atomic Sulfur-Iodine Cycle for thermochemical hydrogen production. V and Ti alloys provide low neutron activation, good radiation damage resistance, and good chemical compatibility for the Cauldron design. Aluminide coated In-800H and siliconized SiC are materials choices for

O. H. Krikorian

1980-01-01

27

Materials considerations for the coupling of thermochemical hydrogen cycles to tandem mirror reactors  

SciTech Connect

Candidate materials are discussed and initial choices made for the critical elements in a liquid Li-Na Cauldron Tandem Mirror blanket and the General Atomic Sulfur-Iodine Cycle for thermochemical hydrogen production. V and Ti alloys provide low neutron activation, good radiation damage resistance, and good chemical compatibility for the Cauldron design. Aluminide coated In-800H and siliconized SiC are materials choices for heat exchanger components in the thermochemical cycle interface.

Krikorian, O.H.

1980-05-23

28

Materials considerations for the coupling of thermochemical hydrogen cycles to tandem mirror reactors  

SciTech Connect

Candidate materials are discussed and initial choices made for the critical elements in a liquid Li-Na Cauldron Tandem Mirror blanket and the General Atomic Sulfur-Iodine Cycle for thermochemical hydrogen production. V and Ti alloys provide low neutron activation, good radiation damage resistance, and good chemical compatibility for the Cauldron design. Aluminide coated In-800H and siliconized SiC are materials choices for heat exchanger components in the thermochemical cycle interface.

Krikorian, O.H.

1980-10-10

29

The oxidative coupling of methane over potassium-modified antimony oxide  

Microsoft Academic Search

The current interest in the direct conversion of methane higher homologs reflects the commercial importance of nay such technology. Direct conversion has not yet proven successful mainly because the direct coupling of methane is a thermodynamically prohibited process at temperatures and pressures of interest. If an oxidizing agent is present, however, either partial oxidation to methanol or oxidative coupling can

M. Y. Lo; S. Agarwal; G. Marcelin

1987-01-01

30

Measurement of trimethylamine-N-oxide by stable isotope dilution liquid chromatography tandem mass spectrometry.  

PubMed

Trimethylamine-N-oxide (TMAO) levels in blood predict future risk for major adverse cardiac events including myocardial infarction, stroke, and death. Thus, the rapid determination of circulating TMAO concentration is of clinical interest. Here we report a method to measure TMAO in biological matrices by stable isotope dilution liquid chromatography tandem mass spectrometry (LC/MS/MS) with lower and upper limits of quantification of 0.05 and >200?M, respectively. Spike and recovery studies demonstrate an accuracy at low (0.5?M), mid (5?M), and high (100?M) levels of 98.2, 97.3, and 101.6%, respectively. Additional assay performance metrics include intraday and interday coefficients of variance of <6.4 and <9.9%, respectively, across the range of TMAO levels. Stability studies reveal that TMAO in plasma is stable both during storage at -80°C for 5years and to multiple freeze thaw cycles. Fasting plasma normal range studies among apparently healthy subjects (n=349) show a range of 0.73-126?M, median (interquartile range) levels of 3.45 (2.25-5.79)?M, and increasing values with age. The LC/MS/MS-based assay reported should be of value for further studies evaluating TMAO as a risk marker and for examining the effect of dietary, pharmacologic, and environmental factors on TMAO levels. PMID:24704102

Wang, Zeneng; Levison, Bruce S; Hazen, Jennie E; Donahue, Lillian; Li, Xin-Min; Hazen, Stanley L

2014-06-15

31

Online Monitoring Oxidative Products and Metabolites of Nicotine by Free Radicals Generation with Fenton Reaction in Tandem Mass Spectrometry  

PubMed Central

In general, over 70% absorbed nicotine is metabolized to cotinine and trans-3?-hydroxycotinine by cytochrome oxidase P450, and nicotine is also a major addictive and the psychoactive component in cigarettes. As a xenobiotic metabolism, hydrophobic compounds are usually converted into more hydrophilic products through enzyme systems such as cytochrome oxidase P450, sulfotransferases, and UDP-glucuronosyltransferases to deliver drug metabolites out of the cell during the drug metabolic process. In this study, an electrodeless electrochemical oxidation (EEO) reaction via Fenton reaction by producing free radical to react with nicotine to immediately monitor the oxidative products and metabolic derivatives of nicotine by tandem mass spectrometer (MS) is done. Fenton reaction generates free radicals via ferrous ion (Fe2+) and hydrogen peroxide (H2O2) to oxidize DNA and to degrade proteins in cells. In the EEO method, the oxidative products of nicotine including cotinine, cotinine-N-oxide, trans-3?-hydroxycotinine, nornicotine, norcotinine, 4-oxo-4-(3-pyridyl)-butanoic acid, 4-hydroxy-4-(3-pyridyl)-butanoic acid, and nicotine-N?-oxide were detected by tandem mass spectrometer to simulate the changes of nicotine and its derivatives in a time-dependent manner.

Liang, Shih-Shin; Shiue, Yow-Ling; Kuo, Chao-Jen; Liao, Wei-Ting; Tsai, Eing-Mei

2013-01-01

32

Online monitoring oxidative products and metabolites of nicotine by free radicals generation with Fenton reaction in tandem mass spectrometry.  

PubMed

In general, over 70% absorbed nicotine is metabolized to cotinine and trans-3'-hydroxycotinine by cytochrome oxidase P450, and nicotine is also a major addictive and the psychoactive component in cigarettes. As a xenobiotic metabolism, hydrophobic compounds are usually converted into more hydrophilic products through enzyme systems such as cytochrome oxidase P450, sulfotransferases, and UDP-glucuronosyltransferases to deliver drug metabolites out of the cell during the drug metabolic process. In this study, an electrodeless electrochemical oxidation (EEO) reaction via Fenton reaction by producing free radical to react with nicotine to immediately monitor the oxidative products and metabolic derivatives of nicotine by tandem mass spectrometer (MS) is done. Fenton reaction generates free radicals via ferrous ion (Fe(2+)) and hydrogen peroxide (H2O2) to oxidize DNA and to degrade proteins in cells. In the EEO method, the oxidative products of nicotine including cotinine, cotinine-N-oxide, trans-3'-hydroxycotinine, nornicotine, norcotinine, 4-oxo-4-(3-pyridyl)-butanoic acid, 4-hydroxy-4-(3-pyridyl)-butanoic acid, and nicotine-N'-oxide were detected by tandem mass spectrometer to simulate the changes of nicotine and its derivatives in a time-dependent manner. PMID:23983622

Liang, Shih-Shin; Shiue, Yow-Ling; Kuo, Chao-Jen; Guo, Su-Er; Liao, Wei-Ting; Tsai, Eing-Mei

2013-01-01

33

The performance and structure of rare earth oxides modified by strontium fluoride for methane oxidative coupling  

Microsoft Academic Search

Strontium fluoride promoted rare earth (La, Nd, Sm, Eu, Gd, Dy, and Y) oxides were more selective than the corresponding unpromoted rare earth oxides for the methane oxidative coupling to ethane and ethene. The XRD results indicated that the partial anionic or cationic exchanges and interaction between the oxide and fluoride phases took place in most of the catalysts studied

Ruiqiang Long; Yaping Huang; Weizheng Weng; Huilin Wan; Khirui Tsai

1996-01-01

34

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

35

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...

36

Formation of oligomeric alkenylperoxides during the oxidation of unsaturated fatty acids: an electrospray ionization tandem mass spectrometry study.  

PubMed

This study reports the identification of oligomeric alkenylperoxides by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS(2)), during the oxidation of oleic, linoleic and linolenic acids with Fenton's (Fe(2+)/H(2)O(2)) and Fe(2+)/O(2) systems. The reactions were followed by ferrous oxidation-xylenol orange method together with GC-MS and GC-FID, allowing to observe that both oxidation systems are different in terms of hydroperoxide evolution, probably due to the presence of different intermediate reactive species: perferryl ion and OH(·) radical responsible for the decomposition of lipid hydroperoxides and formation of new compounds. The analysis of ESI-MS in the negative mode, obtained after oxidation of each fatty acid, confirmed the presence of the monomeric oxidation products together with other compounds at high mass region above m/z 550. These new ions were attributed to oligomeric structures, identified by the fragmentation pathways observed in the tandem mass spectra. PMID:22359325

Villaverde, Juan José; Santos, Sónia A O; Maciel, Elisabete; Simões, Mário M Q; Pascoal Neto, Carlos; Domingues, M Rosário M; Silvestre, Armando J D

2012-02-01

37

Gold-Catalyzed Oxidative Coupling Reactions with Aryltrimethylsilanes  

PubMed Central

During continuing studies with a novel oxidative gold oxyarylation reaction, arylsilanes were found to be competent coupling partners, providing further evidence for an intramolecular electrophilic aromatic substitution mechanism. While providing complementary yields to the previously described boronic acid methods, the use of trimethylsilanes reduces the observation of homocoupling byproducts and allows for facile intramolecular coupling reactions.

Brenzovich, William E.; Brazeau, Jean-Francois; Toste, F. Dean

2010-01-01

38

High ethylene to ethane processes for oxidative coupling  

DOEpatents

Oxidative coupling of lower alkane to higher hydrocarbon is conducted using a 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, R.B.; Warren, B.K.

1991-12-17

39

Oxidative coupling of methane with ac and dc corona discharges  

Microsoft Academic Search

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

Changjun Liu; Abdulathim Marafee; Bobby Hill; Genhui Xu; Richard Mallinson; Lance Lobban

1996-01-01

40

Preparation on oligostilbenes of isorhapontigenin by oxidative coupling reaction.  

PubMed

Four new compounds 1-4 were obtained from an oxidative coupling reaction of (E)-isorhapontigenin using FeCl(3) as oxidant. Their structures and stereochemistry were determined on the basis of spectroscopic evidence [UV, IR, MS, (1)H-, (13)C-NMR, NOE and 2D NMR], and their possible formation mechanisms were also discussed, respectively. PMID:14758010

Yao, Chun-Suo; Zhou, Li-Xin; Lin, Mao

2004-02-01

41

Simultaneous quantification of tetrahydrobiopterin, dihydrobiopterin, and biopterin by liquid chromatography coupled electrospray tandem mass spectrometry.  

PubMed

A simple and rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based method was developed for the quantification of tetrahydrobiopterin (BH4), dihydrobiopterin (BH2), and biopterin (B) in human umbilical vein endothelial cells (HUVECs). Freshly prepared cell samples were treated with a mixture consisting of 0.2M trichloroacetic acid (TCA) and a cocktail of various antioxidants in order to precipitate proteins and other cellular components and to stabilize red/ox conditions in the lysates. Chromatography of the cell lysates was performed on a Poroshell 120 SB-C18 column (2.7?m, 150×2.1mm) using a stepwise gradient elution made from two mobile phases. Quantification was performed on a triple quadrupole mass spectrometer employing electrospray ionization with the operating conditions as multiple reaction monitoring (MRM) at positive ion mode. Total chromatographic run time was 23min. The method was validated for analysis in HUVECs, and the limits of quantification were 1nM for BH4 and BH2 and 2.5nM for B. Standard curves were linear in the concentration ranges of 1 to 100nM for BH4 and BH2 and 2.5 to 100nM for B. The current study reports a novel method for the simultaneous and direct quantification of BH4, BH2, and B in a single injection. PMID:22940649

Fismen, Lise; Eide, Torunn; Djurhuus, Rune; Svardal, Asbjørn M

2012-11-15

42

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

43

Underivatized polyamine analysis in plant samples by ion pair LC coupled with electrospray tandem mass spectrometry.  

PubMed

Polyamines are key regulators of cell development and many plant responses to environmental challenges, however, their functions still remain unclear in complex interactions with other hormones and in biotic or abiotic stress. This lack of knowledge derives from the difficulties on measuring natural polyamines in plants. Here, we present a fast multiresidue method for putrescine (Put), 1,3-diaminopropane (DAP), l-ornithine, spermidine (Spd) and spermine (Spn) measurements in plant samples. Polyamine determination is based on a perchloric acid extraction followed by a simple filtration procedure without previous derivatization. Polyamines are resolved by HPLC in a C18 common column and quantified by electrospray ionization tandem mass spectrometry. (13)C(4)-putrescine and 1,7-diaminoheptane standards were added prior to sample extraction to achieve an accurate quantification in a single run. Chromatography of polyamines presents poor retention when reverse phase C18 common columns are used, because they are very polar compounds and contain several positive charges. To circumvent this problem ionic pairing technique has been used successfully with heptafluorobutyric acid (HFBA) at 1mM in the aqueous phase and 25mM in the sample. Improvement of the signal depleted by HFBA has been achieved by adding 1% of propionic acid to the aqueous and organic eluents. All together, gives a method accurate enough to determine polyamines in plants. To demonstrate the usefulness of the method it has been validated in Arabidopsis thaliana samples and polyamines have been determined in several genotypes that over express (35S::ADC2 line 3.6) or are disrupted (adc2) in the Arginine Decarboxylase2 (ADC2) gene. PMID:19303315

Sánchez-López, Jose; Camañes, Gemma; Flors, Víctor; Vicent, Cristian; Pastor, Victoria; Vicedo, Begonya; Cerezo, Miguel; García-Agustín, Pilar

2009-07-01

44

Analysis of perfluoroalkyl substances in cord blood by turbulent flow chromatography coupled to tandem mass spectrometry.  

PubMed

A fast on-line analytical method based on turbulent flow chromatography (TFC) in combination with tandem mass spectrometry has been applied for the first time for the analysis of eighteen perfluoroalkyl substances (PFASs), in cord blood. A simple and rapid sample pre-treatment was optimised consisting on protein precipitation of 100 ?L of sample with acetonitrile (1:1) followed by centrifugation during 10 min. The method was adapted to be sensitive enough and robust with minimum sample injection volume requirements (20 ?L). The optimised methodology presented method limits of detection (MLOD) between 0.031 and 0.76 ?g/L, detection capabilities (CC?) in the range between 0.005 and 0.99 ?g/L and decision limits (CC?) ranging from 0.006 to 1.16 ?g/L. The recoveries in blank blood were calculated by spiking experiments with a mixture of 18 PFASs and established between 70 and 126% for most of compounds. Isotopic dilution was carried out for quantification of selected analytes. In-house validation of this new approach was carried out according to the requirements in the 2002/657/EC Decision. Finally the good applicability of this new approach was proved by the analysis of 60 cord blood samples from two different Mediterranean cities, Barcelona (Spain) and Heraklion (Greece). Ions perfluorohexanesulfonate (PFHxS) and perfluorooctanesulfonate (PFOS) were found at highest concentration and the more frequently compounds were PFHxS, PFOS and perfluorooctanoic acid (PFOA). The newly developed method proved to be suitable for large-scale epidemiologic studies, and to the data on PFASs exposure during pregnancy. PMID:22789815

Llorca, Marta; Pérez, Francisca; Farré, Marinella; Agramunt, Sílvia; Kogevinas, Manolis; Barceló, Damià

2012-09-01

45

Solar hydrogen production by tandem cell system composed of metal oxide semiconductor film photoelectrode and dye-sensitized solar cell  

NASA Astrophysics Data System (ADS)

Photocatalytic and photoelectrochemical approaches to solar hydrogen production in our group were introduced. In photocatalytic water splitting system using NiOx/ TiO2 powder photocatalyst with concentrated Na2CO3 aqueous solution, solar energy conversion efficiency to H2 and O2 production (STH efficiency) was 0.016%. In addition, STH efficiency of visible light responding photocatalyst, NiOx/ promoted In0.9Ni0.1TaO4, was estimated at 0.03%. In photoelectrochemical system using an oxide semiconductor film phptoelectrode, STH efficiencies of meosporous TiO2 (Anatase) , mesoporous visible light responding S-doped TiO2 (Anatase) and WO3 film were 0.32-0.44% at applied potential of 0.35 V vs NHE, 0.14% at 0.55 V and 0.44% at 0.9 V, respectively. Finally, solar hydrogen production by tandem cell system composed of an oxide semiconductor photoelectrode, a Pt wire counter electrode and a dye-sensitized solar cell (DSC) was investigated. As photoelectrodes, meosporous TiO2 (Anatase), mesoporous S-doped TiO2 (Anatase), WO3, BiVO4 and Fe2O3 film were tested. STH efficiency of tandem cell system composed of a WO3 film photoelectrode, and a two-series-connected DSC (Voc = 1.4 V) was 2.5-2.8%. In conclusion, it is speculated that more than 5% STH efficiency will be obtained by tandem cell system composed of an oxide semiconductor photoelectrode and a two-series-connected DSC in near future. This suggests a cost-effective and practical application of this system for solar hydrogen production.

Arakawa, H.; Shiraishi, C.; Tatemoto, M.; Kishida, H.; Usui, D.; Suma, A.; Takamisawa, A.; Yamaguchi, T.

2007-10-01

46

Screening and characterization of natural antioxidants in four Glycyrrhiza species by liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry.  

PubMed

Licorice, derived from the dried roots and rhizomes of several species of genus Glycyrrhiza L. (Leguminosae family), has been traditionally used in herbal medicine for over 4000 years. In recent years, the interest in antioxidative constituents in licorice has greatly increased. In this work, a new method based on 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) spiking test combined with HPLC coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (Q-TOF MS/MS) analysis was developed to screen and identify the antioxidants in licorice. The results of the method validation indicated that the developed method was reliable and repeatable. Compared with DPPH on-line method, the HPLC-Q-TOF MS/MS method combined with DPPH spiking test offered much higher sensitivity and resolution. Using this method, 35 radical scavengers were screened from four Glycyrrhiza species (G. inflata, G. glabra, G. pallidiflora and G. uralensis), and 21 of them were unambiguously or tentatively identified by HPLC-Q-TOF MS/MS. Among the 21 identified flavonoids, 10 compounds had been reported to possess antioxidative activities in the previous studies, and the radical scavenging activities of the other 11 compounds were reported for the first time. The effects of six purified flavonoids on DPPH radical and lipid peroxidation were evaluated for validation of the developed method. The results indicated that HPLC-Q-TOF MS/MS coupled with DPPH treatment is an efficient and powerful method to discover the potential antioxidative compounds from the complex natural product mixtures. In this study, the identified components with free radical scavenging activity, would help to explain the therapeutic benefit of licorice in the treatment of human disease associated with oxidative stress. PMID:21968349

Li, Yan-Jing; Chen, Jun; Li, Ying; Li, Qin; Zheng, Yun-Feng; Fu, Yu; Li, Ping

2011-11-11

47

Oxidative coupling of methane I. Alkaline earth compound catalysts  

Microsoft Academic Search

The catalytic performance of oxides, sulfates, phosphates, carbonates, fluorides, and aluminates of Be, Mg, Ca, Sr, and Ba was studied for the oxidative coupling of methane to C{sub n} hydrocarbons (n ⥠2). To compare the various catalytic compounds, normalized reaction conditions were applied: T = 740°C, P{sub CHâ}{sup °} = 660 mbar, P{sub Oâ}{sup °} = 80 mbar, P{sub

J. A. S. P. Carreiro; M. Baerns

1989-01-01

48

Oxidative coupling of methane II. Composite catalysts of basic materials  

Microsoft Academic Search

Composite catalysts consisting of Li, Na, and K carbonates, hydroxides, oxides, and sulfates supported on CaO and in some instances on α-AlâOâ, MgO, and CaSOâ have been tested for the oxidative coupling of methane to C{sub n} hydrocarbons (n ⥠2). Normalized reaction conditions were generally T = 740°C, P°{sub CHâ} = 0.67 bar, P°{sub Oâ} = 0.074 bar, and

J. A. S. P. Carreiro; M. Baerns

1989-01-01

49

Simultaneous analysis of eight nucleoside triphosphates in cell lines by liquid chromatography coupled with tandem mass spectrometry.  

PubMed

In this study, we developed a new method for the simultaneous determination of eight endogenous ribonucleoside triphosphates and deoxyribonucleoside triphosphates based on a combination of a selective sample preparation and an ion-pair liquid chromatography-electrospray tandem mass spectrometry. The sample preparation was based on a protein precipitation coupled with a solid phase extraction using a weak-anion-exchange cartridge. The analytical separation of the nucleotides was achieved on a porous graphitic carbon stationary phase with a binary elution gradient program employing ion-pairing reagents (diethylamine and hexylamine) and organic eluent (methanol). The triple quadrupole mass spectrometer operated in both negative and positive multiple reaction monitoring modes. The calibration assay used the stable isotope labelled analogs of each compounds as standard. Standard calibrations were from 0.25 to 10pmol injected according to deoxyribonucleotides and from 12.5 to 3000pmol injected according to ribonucleotides. The within-run precision of the assay was less than 14.5% and the between-run precision was less than 12.4% for each analytes. Assay accuracy was in the range of 92.3-107.6%. This method allows the determination of NTP and dNTP pools from lysats of several cell lines or peripheral blood mononuclear cell from patient. Assays were performed with different preparation of cells to confirm the quality and the relevance of the described method. PMID:19805008

Cohen, Sabine; Megherbi, Mehdi; Jordheim, Lars Petter; Lefebvre, Isabelle; Perigaud, Christian; Dumontet, Charles; Guitton, Jérôme

2009-11-15

50

Enantioselective determination of acylamino acid fungicides in vegetables and fruits by chiral liquid chromatography coupled with tandem mass spectrometry.  

PubMed

An efficient and sensitive enantioselective method for simultaneous determination of three acylamino acid fungicides in vegetables and fruits was presented by high-performance liquid chromatography (HPLC) coupled with tandem mass spectrometry. The three fungicides (benalaxyl, furalaxyl, and metalaxyl) residues in samples were extracted with acetonitrile containing 1% acetic acid and an aliquot was cleaned up with Si-(CH(2))(3)-NH-(CH(2))(2)-NH(2) and C(18) sorbent. Complete enantioseparation of three acylamino acid fungicides enantiomers was obtained under reversed-phase conditions on a cellulose tris (4-chloro-3-methylphenylcarbamate) column at 25°C using acetonitrile-0.1% formic acid solution (45:55, v/v) as a mobile phase. The elution orders of the eluted enantiomers were determined by a circular dichroism (CD) detector. The linearity, matrix effect, recovery, and precision were evaluated. Good linearity was obtained over the concentration range of 0.5-250 ?g/L for each enantiomer in the standard solution and sample matrix calibration curves. There was no significant matrix effect for three fungicides determination based on the method. The inter-day mean recoveries, intra-day repeatability, and inter-day reproducibility varied from 81.3 to 95.7%, 2.2 to 9.4%, and 2.3 to 9.6%, respectively. The method provided high selectivity and sensitivity, and limits of quantification for enantiomers of three fungicides in vegetables and fruits were both 1 ?g/kg. PMID:22753298

Zhang, Hu; Wang, Xinquan; Jin, Lixia; Qian, Mingrong; Wang, Xiangyun; Xu, Hao; Qi, Peipei; Wang, Qiang; Wang, Minghua

2012-08-01

51

Quantitative determination of capecitabine and its six metabolites in human plasma using liquid chromatography coupled to electrospray tandem mass spectrometry.  

PubMed

Capecitabine is the oral prodrug of the anticancer drug 5-fluorouracil (5-FU). The purpose of this study was to quantify capecitabine and its metabolites including 5'-deoxy-5-fluorocytidine (5'-dFCR), 5'-deoxy-5-fluorouridine (5'-dFUR), 5-FU, dihydro-5-fluorouracil (FUH(2)), ?-fluoro-ureidopropionic acid (FUPA) and fluoro-?-alanine (FBAL) in human plasma using liquid chromatography coupled to electrospray tandem mass spectrometry. To this end two individual assays were developed: one for the simultaneous quantification of capecitabine, 5'-dFCR and 5'-dFUR using reversed phase chromatography and gradient elution, and one assay for 5-FU, FUH(2), FUPA and FBAL using hydrophilic interaction chromatography and isocratic elution. Both assays were fully validated according to current FDA guidelines. Total run time for the capecitabine assay was 9.0min, and of the 5-FU assay 5.0min. Analyte extraction was performed by protein precipitation. Stable labeled isotopes for each of the analytes were used as internal standards. The linear ranges of the analytes were 50-6000ng/mL for the capecitabine assay and 50-5000ng/mL for the 5-FU assay. Validation results demonstrate that capecitabine and its metabolites can be rapidly, accurately, precisely and robustly quantified in human plasma with the presented methods. Both assays are currently in extensive use in support of pharmacokinetic studies in patients treated with capecitabine or 5-FU. PMID:23270936

Deenen, Maarten J; Rosing, Hilde; Hillebrand, Michel J; Schellens, Jan H M; Beijnen, Jos H

2013-01-15

52

Nonradioactive assay for detecting isoprenyl diphosphate synthase activity in crude plant extracts using liquid chromatography coupled with tandem mass spectrometry.  

PubMed

Terpenoids form the largest class of plant metabolites involved in primary and secondary metabolism. Isoprenyl diphosphate synthases (IDSs) catalyze the condensation of the C(5) terpenoid building blocks, isopentenyl diphosphate and dimethylallyl diphosphate, to form geranyl diphosphate (C(10)), farnesyl diphosphate (C(15)), and geranylgeranyl diphosphate (C(20)). These branch point reactions control the flow of metabolites that act as precursors to each of the major terpene classes-monoterpenes, sequiterpenes, and diterpenes, respectively. Thus accurate and easily performed assays of IDS enzyme activity are critical to increase our knowledge about the regulation of terpene biosynthesis. Here we describe a new and sensitive nonradioactive method for carrying out IDS assays using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) to detect the short-chain prenyl diphosphate products directly without dephosphorylation. Furthermore, we were able to separate cisoid and transoid isomers of both C(10) enzyme products (geranyl diphosphate and neryl diphosphate) and three C(15) products [(E,E)-, (Z,E)-, and (Z,Z)-farnesyl diphosphate]. By applying the method to crude protein extracts from various organs of Arabidopsis thaliana, Nicotiana attenuata, Populus trichocarpa, and Picea abies, we could determine their IDS activity in a reproducible fashion. PMID:22266300

Nagel, Raimund; Gershenzon, Jonathan; Schmidt, Axel

2012-03-01

53

Determination of baicalin in rat cerebrospinal fluid and blood using microdialysis coupled with ultra-performance liquid chromatography-tandem mass spectrometry  

Microsoft Academic Search

An in vivo microdialysis sampling method coupled with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS\\/MS) was employed for continuous simultaneous monitoring of unbound baicalin in rat blood and brain. Microdialysis probes were inserted into the jugular vein and brain cerebrospinal fluid (CSF) of Sprague-Dawley rats then, following administration of baicalin at doses of 24mg\\/kg via the candal vein, samples were collected

Huifeng Huang; Yu Zhang; Rui Yang; Xing Tang

2008-01-01

54

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

55

Application of hollow fibre liquid phase microextraction for the multiresidue determination of pesticides in alcoholic beverages by ultra-high pressure liquid chromatography coupled to tandem mass spectrometry  

Microsoft Academic Search

An alternative method has been developed to determine more than 50 pesticides in alcoholic beverages using hollow fibre liquid phase microextraction (HF-LPME) followed by ultra-high pressure liquid chromatography coupled to tandem mass spectrometry (UHPLC–MS\\/MS), without any further clean-up step. Pesticides were extracted from the sample to the organic solvent immobilized in the fibre and they were desorbed in methanol prior

P. Plaza Bolaños; R. Romero-González; A. Garrido Frenich; J. L. Martínez Vidal

2008-01-01

56

Investigation of photochemical behavior of pesticides in a photolysis reactor coupled on-line with a liquid chromatography–electrospray ionization tandem mass spectrometry system  

Microsoft Academic Search

The photochemical behavior of pesticides in a photolysis reactor coupled on-line with a liquid chromatography–electrospray ionization mass spectrometer (LC–h?-MS) was investigated. This paper describes the application of LC–h?-MS, in combination with tandem mass spectrometry (MS–MS), to identification of phototransformation products and to the establishment of possible photolytic pathways of pesticides. In addition, the applicability of LC–h?-MS as an alternative to

Dietrich A. Volmer

1998-01-01

57

Cu2O-catalyzed tandem ring-opening/coupling cyclization process for the synthesis of 2,3-dihydro-1,4-benzodioxins.  

PubMed

2,3-Dihydro-1,4-benzodioxins can be prepared in a tandem one-pot procedure by reaction of o-iodophenols with epoxides catalyzed by Cu2O/1,10-phenanthroline/Cs2CO3 system. The reaction is suggested to occur via a novel ring-opening/coupling mechanism, giving moderate to good yields. Moreover, both aryl and aliphatic epoxides are tolerated under these conditions. PMID:18665603

Bao, Weiliang; Liu, Yunyun; Lv, Xin; Qian, Weixing

2008-09-01

58

Liquid chromatography coupled to tandem mass spectrometry (LCMS\\/MS) determination of phase II metabolites of the mycotoxin zearalenone in the model plant Arabidopsis thaliana  

Microsoft Academic Search

The biotransformation products of zearalenone, a Fusarium mycotoxin, were elucidated using the model plant Arabidopsis thaliana. After treatment of plant seedlings with 50?µM zearalenone, both the liquid media and the plant extracts were analysed by liquid chromatography coupled to tandem mass spectrometry (LC-MS\\/MS). An array of 17 different metabolites, most prominently glucosides, malonylglucosides, di-hexose- and hexose–pentose disaccharides of zearalenone, and

F. Berthiller; U. Werner; M. Sulyok; R. Krska; M.-T. Hauser; R. Schuhmacher

2006-01-01

59

Conversion of methane to benzene via oxidative coupling and dehydroaromatization  

Microsoft Academic Search

The combination of methane oxidative coupling and dehydroaromatization processes by catalysts arranged in a double-layer bed leads to an increase in the benzene productivity under inert atmosphere. This effect is ascribed to an increase in the ethylene production, which plays a role of intermediary.

J. S. Espindola; N. R. Marcilio; O. W. Perez-Lopez

2007-01-01

60

Identification of ginkgolic acid (15:1) metabolites in rats following oral administration by high-performance liquid chromatography coupled to tandem mass spectrometry.  

PubMed

1. In this article, metabolites of ginkgolic acid (GA) (15:1) in rats plasma, bile, urine and faeces after oral administration have been investigated for the first time by high-performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) with the aid of on-line hydrogen/deuterium (H/D) exchange technique and ?-glucuronidase hydrolysis experiments. 2. After oral administration of GA (15:1, M0) to rats at a dose of 10 mg/kg, it was found that metabolites M1-M5 together with parent compound (M0) existed in rat plasma; parent compound (M0) and metabolites M2-M5 were observed in rat bile, and parent compound (M0) with metabolites M1 and M2 were discovered in rat faeces, and there was no parent compound and metabolite detectable in rat urine. 3. Two oxidative metabolites of GA (15:1, M0) were identified as 2-hydroxy-6-(pentadec-8-enyl-10-hydroxy) benzoic acid (M1) and 2-hydroxy-6-(pentadec-8-enyl-11-hydroxy-13-carbonyl) benzoic acid (M2), respectively. Metabolites M3, M4 and M5 were identified as the mono-glucuronic acid conjugates of parent compound (M0), M1 and M2, respectively. 4. The results indicated that M1 and M2 with parent compound (M0) were mainly eliminated in faeces and three glucuronide metabolites (M3, M4 and M5) excreted in bile as the predominant forms after oral administration of GA (15:1) to rats. PMID:23205533

Xia, Hongjun; Liu, Zhenhua; Hu, Haihong; Zhou, Hui; Zeng, Su

2013-05-01

61

Oxidation of aromatic contaminants coupled to microbial iron reduction  

USGS Publications Warehouse

THE contamination of sub-surface water supplies with aromatic compounds is a significant environmental concern1,2. As these contaminated sub-surface environments are generally anaerobic, the microbial oxidation of aromatic compounds coupled to nitrate reduction, sulphate reduction and methane production has been studied intensively1-7. In addition, geochemical evidence suggests that Fe(III) can be an important electron acceptor for the oxidation of aromatic compounds in anaerobic groundwater. Until now, only abiological mechanisms for the oxidation of aromatic compounds with Fe(III) have been reported8-12. Here we show that in aquatic sediments, microbial activity is necessary for the oxidation of model aromatic compounds coupled to Fe(III) reduction. Furthermore, a pure culture of the Fe(III)-reducing bacterium GS-15 can obtain energy for growth by oxidizing benzoate, toluene, phenol or p-cresol with Fe(III) as the sole electron acceptor. These results extend the known physiological capabilities of Fe(III)-reducing organisms and provide the first example of an organism of any type which can oxidize an aromatic hydrocarbon anaerobically. ?? 1989 Nature Publishing Group.

Lovley, D. R.; Baedecker, M. J.; Lonergan, D. J.; Cozzarelli, I. M.; Phillips, E. J. P.; Siegel, D. I.

1989-01-01

62

A novel solution for hydroxylated PAHs removal by oxidative coupling reaction using Mn oxide  

Microsoft Academic Search

In this study, removals of 1-naphthol by oxidative-coupling reaction using birnessite, one of the natural Mn oxides present in soil, was investigated in various experimental conditions (reaction time, Mn oxide loadings, pH). The removal efficiency of 1-naphthol by birnessite was high in all the experimental conditions, and UV-visible and mass spectrometric analyses on the supernatant after reaction confirmed that the

Ki-Hoon Kang; Dong-Min Lim; Hyun-Sang Shin

2008-01-01

63

General approach on chemistry and stress coupling effects during oxidation  

NASA Astrophysics Data System (ADS)

In this paper, the mechanism of growth strain is discussed based on the irreversible evolving equations by considering the coupling effects of stress and chemical reaction during isothermal oxidation, and a simple model relating the growth strain and the oxide thickness is developed. If the effect of the stress on the chemical reaction is not taken into account, the model reduces to the Clarke assumption. The expression of Dox is exhibited, and its value can be determined by experiments. The stress evolving equations are derived, where the viscoplastic strain of the oxide and metal and the growth strain of the oxide are considered. Numerical results are given and compared with results from experiments and the existing model. There is good agreement between the proposed model and the experimental data.

Suo, Yaohong; Shen, Shengping

2013-10-01

64

Determination of higenamine in human plasma and urine using liquid chromatography coupled to positive electrospray ionization tandem mass spectrometry.  

PubMed

Higenamine is an active ingredient of Aconite root in Chinese herbal medicine and might be used as a new agent for a pharmaceutical stress test and was approved to undergo clinical pharmacokinetic study. Therefore, there exists a need to establish a sensitive and rapid method for the determination of higenamine in human plasma and urine. This paper described a sensitive and rapid method based on liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) for the determination of higenamine in human plasma and urine. Solid-phase extraction (SPE) was used to isolate the compounds from biological matrices followed by injection of the extracts onto an Atlantis dC18 column with isocratic elution. The mobile phase was 0.05% formic acid in water-methanol (40:60, v/v). The mass spectrometry was carried out using positive electrospray ionization (ESI) and data acquisition was carried out in the multiple reaction monitoring (MRM) mode. The method was fully validated over the concentration range of 0.100-50.0 ng/mL and 1.00-500 ng/mL in plasma and urine, respectively. The lower limits of quantification (LLOQs) were 0.100 and 1.00 ng/mL in plasma and urine, respectively. Inter- and intra-batch precision was less than 15% and the accuracy was within 85-115% for both plasma and urine. Extraction recovery was 82.1% and 56.6% in plasma and urine, respectively. Selectivity, matrix effects and stability were also validated in human plasma and urine. The method was applied to the pharmacokinetic study of higenamine hydrochloride in Chinese healthy subjects. PMID:21393074

Feng, Sheng; Hu, Pei; Jiang, Ji

2011-04-01

65

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

66

Multiresidue determination of veterinary drugs in aquaculture fish samples by ultra high performance liquid chromatography coupled to tandem mass spectrometry.  

PubMed

A simple, selective and fast multiresidue method was developed for the determination of 32 veterinary drug residues belonging to several families, in gilthead sea bream (Sparus aurata) by ultra high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). The extraction was based on modified QuEChERS (quick, easy, cheap, effective, rugged and safe) procedure, using as extraction solution a mixture of acetonitrile and methanol (75:25, v/v), and it reduces sample handling, increasing sample throughput in relation to current methodologies. The developed method was validated and mean recovery ranged from 69% to 125% (at 10, 25, 50 and 100 ?g/kg). Intra and interday precision, estimated as the same levels and expressed as relative standard deviation, RSD, were lower than 20% and 30%, respectively. Limits of detection (LODs) and quantification (LOQs) were lower than 7.5 and 25 ?g/kg, respectively, except for danofloxacin, oxytetracycline and tetracycline (LOD and LOQ of 15.0 and 50 ?g/kg, respectively). Decision limit (CC(?)) and detection capability (CC(?)) were also calculated and ranged from 16.7 ?g/kg (levamisole) to 605.0 (flumequine) ?g/kg and from 23.5 ?g/kg (levamisole) to 611.5 ?g/kg (flumequine), respectively. The expanded uncertainty, U, was also evaluated ant it was below 25% at 100 ?g/kg level, except for tetracycline (28%). Finally, the method was applied to ten samples obtained from local supermarkets in Almería (Spain) and traces of some compounds were detected. PMID:22465276

Lopes, Renata Pereira; Reyes, Rocío Cazorla; Romero-González, Roberto; Vidal, José Luis Martínez; Frenich, Antonia Garrido

2012-05-01

67

A new high-throughput analysis for drug metabolism profiling using liquid chromatography coupled with tandem mass spectrometry.  

PubMed

We developed 3 liquid chromatography (LC) methods coupled to tandem mass spectrometry for comprehensive high-throughput profiling of drug metabolism, employing different columns with gradient systems of aqueous 10 mmol/L ammonium acetate and acetonitrile. The methods were established using testosterone (TST), imipramine (IMP), acetaminophen (APAP) and salbutamol (SBM), which have markedly different values of partition coefficient, P. Method I, using an octadecylized silica (ODS) column (ACQUITY UPLC BEH C18) with a steep gradient, was suitable for analyzing TST and its metabolites, and IMP and its metabolites. These substrates could not be analyzed by Method II, using another ODS column (Atlantis dC18), or Method III, using an Atlantis HILIC silica column. APAP and its metabolites could be analyzed simultaneously by Method II, but not Method I or III. SBM and its metabolites could be detected simultaneously only by Method III. The developed analytical methods were further evaluated with a panel of 18 additional drugs. Based on the retention times and peak shapes, we propose general criteria, in terms of calculated LogP (cLogP) value, for method selection. Broadly speaking, drugs with high cLogP, those with intermediate cLogP and those with low cLogP were best analyzed by Methods I, II and III, respectively, although drugs with borderline values of cLogP could be evaluated by both the relevant methods. The injection cycle for each method was within 10 min, including up to 3 min conditioning time. These methods are expected be useful in high-throughput screening assays to examine biotransformations of candidate drugs. PMID:23471703

Kusumoto, K; Nagao, T; Ogihara, T

2013-04-01

68

Determination of fungicides in wine by mixed-mode solid phase extraction and liquid chromatography coupled to tandem mass spectrometry.  

PubMed

A novel procedure for the determination of nine selected fungicides (metalaxyl-M, azoxystrobin, myclobutanil, flusilazole, penconazole, tebuconazole, propiconazole, diniconazole and difenoconazole) in wine samples is presented. Sample enrichment and purification is simultaneously performed using mixed-mode, anion exchange and reversed-phase, OASIS MAX solid-phase extraction (SPE) cartridges. Analytes were determined by liquid chromatography coupled to tandem mass spectrometry using atmospheric pressure electrospray ionization (LC-ESI-MS/MS). Parameters affecting the chromatographic determination and the extraction-purification processes were thoroughly investigated. Under optimized conditions, 10 mL of wine were firstly diluted 1:1 with ultrapure water and then passed through the mixed-mode SPE cartridge at a flow of ca. 5 mLmin(-1). After a washing step with 5 mL of an aqueous NH(4)OH solution (5%, w:v), analytes were recovered with just 1 mL of methanol and injected in the LC-MS/MS system without any additional purification. The selective extraction process avoided significant changes in the ionization efficiency for red and white wine extracts in comparison with pure standards in methanol. Performance of the method was good in terms of precision (RSDs<11%) and accuracy (absolute recoveries>72%, determined against pure standards in methanol) reporting method LOQs in the range of 0.01-0.79 ngmL(-1) for target compounds, which are far below the EU maxima residue levels (MRLs) for fungicides in vinification grapes and wine. Several commercial wines from different geographic areas in Spain were analyzed. In most samples, metalaxyl-M and azoxystrobin were found at concentrations up to several ngmL(-1). PMID:20971470

Carpinteiro, I; Ramil, M; Rodríguez, I; Cela, R

2010-11-26

69

Ethyl-glucuronide and ethyl-sulfate in placental and fetal tissues by liquid chromatography coupled with tandem mass spectrometry.  

PubMed

The aim of this study was to develop a method for the determination of ethyl-glucuronide (EtG) and ethyl-sulfate (EtS), two direct ethanol metabolites, in early placental and fetal human tissues, as potential biomarkers of transplacental ethanol transfer from the mother to the fetus. Placental and fetal tissue samples were obtained from women undergoing voluntary termination of pregnancy at 12 weeks of gestation. Samples were deproteinized and directly injected into a liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) system. Limits of detection of 13.0 and 23.0 pmol/g and lower limits of quantification of 22.0 and 40.0 pmol/g were reached for EtG and EtS, respectively. Inter- and intraday imprecision and accuracy were always lower than 15%. The method was applied to 70 samples (35 placentas and 35 fetal tissues). Of 35 samples, 4 samples collected from 4 women tested positive for EtG and EtS, always showing higher concentrations for EtG. The placenta/fetal tissue ratio for EtG was 2.9 ± 0.9, whereas EtS showed a ratio of 1.7 ± 0.7. Preliminary results suggest that these metabolites are present in both tissues. Further studies should now corroborate the hypothesis, not yet confirmed, that transplacental transfer of ethanol takes place not only for the parent compound but also for EtG and EtS. PMID:21787742

Morini, Luca; Falcón, Maria; Pichini, Simona; Garcia-Algar, Oscar; Danesino, Paolo; Groppi, Angelo; Luna, Aurelio

2011-11-01

70

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

71

C(60)-Bodipy dyad triplet photosensitizers as organic photocatalysts for photocatalytic tandem oxidation/[3+2] cycloaddition reactions to prepare pyrrolo[2,1-a]isoquinoline.  

PubMed

C(60)-Bodipy hybrids exhibiting strong absorption of visible light and long-lived triplet excited states were used as photocatalysts for tandem oxidation/[3+2] cycloaddition of tetrahydroisoquinoline with N-phenylmaleimide to produce pyrrolo[2,1-a]isoquinolines. The reaction is substantially accelerated, compared to that catalyzed by Ru(bpy)(3)Cl(2). PMID:23535970

Huang, Ling; Zhao, Jianzhang

2013-05-01

72

PTSA-catalyzed Mannich-type-cyclization-oxidation tandem reactions: one-pot synthesis of 1,3,5-substituted pyrazoles from aldehydes, hydrazines and alkynes.  

PubMed

A convenient one-pot Mannich-type-cyclization-oxidation tandem process has been developed for the synthesis of 1,3,5-trisubstituted pyrazoles derivatives from aldehydes, hydrazines and alkynes using p-toluenesulfonic acid monohydrate (PTSA) as a multifunctional catalyst. This method provides a flexible and rapid route to 1,3,5-trisubstituted pyrazoles. PMID:22592555

Liu, Pei; Pan, Ying-Ming; Xu, Yan-Li; Wang, Heng-Shan

2012-06-28

73

Sensitive determination of polychlorinated biphenyls in environmental water samples by headspace solid-phase microextraction with bamboo charcoal@iron oxide black fibers prior to gas chromatography with tandem mass spectrometry.  

PubMed

We have investigated the feasibility of bamboo charcoal@iron oxide black for the headspace solid-phase microextraction of polychlorinated biphenyls in environmental water samples. Bamboo charcoal@iron oxide black was prepared and used as a solid-phase microextraction coating material, and gas chromatography with tandem mass spectrometry was used for detection. Several important factors affecting the extraction efficiency were systematically investigated and optimized. Under the optimum conditions, the experimental data exhibited wide linear range over the range 0.2-1000 ng/L and low limits of detection in the range of 4.7-22.2 pg/L. The novel coating was successfully used for the enrichment and determination of polychlorinated biphenyls in real environmental water samples. All these results indicated that bamboo charcoal@iron oxide black-based headspace solid-phase microextraction coupled to gas chromatography with tandem mass spectrometry was an excellent alternative for the sensitive analysis of polychlorinated biphenyls at ultratrace levels in the environment. PMID:24723552

Liu, Yan-Long; Chen, Xiang-Feng; Wang, Xia; Zhou, Jia-Bin; Zhao, Ru-Song

2014-06-01

74

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

75

Modeling of the catalytic oxidative coupling of methane  

Microsoft Academic Search

Catalytic reaction equations describing processes typical of oxidative coupling catalysts were incorporated into a gas-phase, chemical kinetics model. Modeling is used to predict limits in Câ yield, describe product trends as a function of gas-phase and generalized catalyst behavior and use these results as a guide to catalyst design. The catalytic reaction set included methane activation, hydrocarbon activation and\\/or product

L. M. Hair; W. J. Pitz; M. W. Droege; C. K. Westbrook

1992-01-01

76

Oxidative coupling of methane in a modified ?-alumina membrane reactor  

Microsoft Academic Search

Methane oxidative coupling experiments were conducted in a porous ?-alumina membrane reactor using Mn–W–Na\\/SiO2 catalyst, and its performance was compared with a packed reactor operated at similar conditions. The ?-alumina membrane tube was thermally stabilized by treating the membrane tube with La(NO3)3 aqueous solution and calcining at 900°C. Non-uniform oxygen permeation was achieved by partially coating the outer surface with

Yaping Lu; Anthony G Dixon; William R Moser; Yi Hua Ma

2000-01-01

77

Dissipation and residues of clethodim and its oxidation metabolites in a rape-field ecosystem using QuEChERS and liquid chromatography/tandem mass spectrometry.  

PubMed

A rapid, sensitive and selective method using Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) procedure for simultaneous determination of clethodim and its oxidation metabolites (clethodim sulfoxide and clethodim sulphone) in soil, rape plant and rape seed was developed using high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS). The limits of detection (LODs) of the proposed method ranged from 0.002mg/kg to 0.01mg/kg, and average recoveries were 78.7-104.2%. The trial results showed that clethodim dissipated so rapidly that few clethodim residues were detectable. Clethodim sulfoxide dissipated quickly in rape plant and soil with half-lives of 4.3 and 4.0days, respectively. Clethodim sulphone showed a tendency of rapid increase initially followed by a decrease in rape plant but could not be detected in soil. The terminal residues of clethodim in rape seedsat harvest time were below the maximum residue limit (MRL, 0.5mg/kg). PMID:24054227

You, Xiangwei; Liang, Lin; Liu, Fengmao

2014-01-15

78

The active phase in sodium-doped calcium oxide catalysts for oxidative coupling of methane  

SciTech Connect

The reactivity of pure and sodium-promoted calcium catalysts toward the oxidative coupling of methane at 640{degree}C has been investigated. While the pure calcium oxide was essentially a combustion catalyst, sodium-promoted calcium oxide exhibited significant C{sub 2} productivity. Study of the deactivation of both pure and promoted catalysts demonstrated that the presence of calcium oxide was necessary for both catalysts to be active. This observation, combined with the effects of sodium doping on C{sub 2} selectivity, suggests that the active phase on Na/CaO catalysts toward C{sub 2} formation consists of sodium species associated with calcium oxide. This active phase was destroyed when calcium oxide was converted into calcium carbonate under reaction conditions.

Peng, X.D.; Stair, P.C. (Northwestern Univ., Evanston, IL (USA))

1991-03-01

79

Quantitative determination of chloramphenicol in milk powders by isotope dilution liquid chromatography coupled to tandem mass spectrometry.  

PubMed

A method is described for the determination of residues of the illegal antibiotic chloramphenicol (CAP) in milk powders. The analyte is quantified by liquid chromatography coupled to electrospray ionisation tandem mass spectrometry (LC-ESI-MS-MS) operating in negative ion multiple reaction monitoring mode (MRM) after a liquid-liquid extraction followed by a clean-up step on solid phase extraction (SPE) cartridge. Because of the presence of two chlorine atoms in the CAP molecule, four specific transition reactions of CAP were monitored by MS-MS in selecting m/z 321 --> 257, 321 --> 152 (35Cl2) and m/z 323 --> 257, 323 --> 152 (37Cl35Cl). Two calibration curves were constructed by plotting the area ratio of m/z 321 --> 152 versus 326 --> 157 and m/z 321 --> 257 versus 326 --> 262 against their corresponding amount ratio. Indeed, even if m/z 321 --> 152 was found to give a higher MS-MS response (calibration curve used by default), an interfering chemical substance was sometimes observed for some milk extracts and not for the transition m/z 321 --> 257. The quantitation method was validated according to the European Union (EU) criteria for the analysis of veterinary drug residues at 0.1, 0.2 and 0.5 microg/kg concentration levels using d5-CAP as internal standard. The decision limit (CCalpha) and detection capability (CCbeta) of CAP in milk were calculated for m/z 321 --> 152 at 0.02 microg/kg and 0.03 microg/kg, respectively, and for m/z 321 --> 257 at 0.02 microg/kg and 0.04 microg/kg, respectively. At the lowest fortification level (i.e. 0.1 microg/kg), repeatability and within-laboratory reproducibility were calculated for m/z 321 --> 257 both at 0.02 microg/kg and for m/z 321 --> 152 at 0.03 and 0.05 microg/kg, respectively. Moreover, the measurement of uncertainty of the analytical method was calculated at the same spiking levels and falls within the precision values of the within-laboratory reproducibility. This method can be applied to several types of milk powders (e.g. full cream, skim) and can serve as a monitoring tool to avoid that unacceptable levels of residues of CAP enter the food chain. PMID:15553164

Guy, Philippe A; Royer, Delphine; Mottier, Pascal; Gremaud, Eric; Perisset, Adrienne; Stadler, Richard H

2004-10-29

80

The effect of alkali promoters in oxidative coupling of methane with Mn-oxide catalysts  

Microsoft Academic Search

The catalytic oxidalive coupling of metnane to ethylene and ethane with manganese oxide catalysts promoted with alkali metal\\u000a and alkali metallic-chloride has been studied at atmospheric pressure in a fixed bed flow reactor.\\u000a \\u000a The main studies of reaction were carried out over maganese oxide catalysts promoted with sodium chloride and the structure\\u000a and surface morphology of these catalysts was characterized

Sang-Chai Kim; Chang-Shin Sunwoo; Eui-Yeon Yu

1990-01-01

81

Selective oxidative coupling of methane to ethane and ethylene over supported lead oxide catalysts  

Microsoft Academic Search

Catalytic performances of lead oxide supported on MgO which has been discovered to exhibit excellent characteristics for the oxidative coupling of methane to Câ hydrocarbons have been studied. A 20 wt % PbO\\/MgO catalyst gave 13% methane conversion, 98% oxygen conversion, and 71% Câ selectivity at 800°C, a time factor of 1.0 g . h\\/mol, a feed gas composition for

Kenji Asami; Shigeru Hashimoto; Tsutomu Shikada; Kaoru Fujimoto; Hiroo Tominaga

1987-01-01

82

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

83

Electronic, magnetic, and structural coupling across oxide interfaces  

NASA Astrophysics Data System (ADS)

Many complex oxide materials exhibit a strong interplay between spin, charge, and lattice effects. This coupling leads to a variety of novel electronic and magnetic properties, including charge ordered and magnetic states, ``colossal'' magnetoresistance (CMR), and a range of electron transport behavior. The possibility of integrating these different kinds behavior with other types of functionalities has motivated the development of new, artificially structured complex oxide-based materials systems, such as composite multiferroic heterostructures. In certain cases, the atomic-scale interface of these structures can dominate the observed behavior, with new physical properties emerging. For example, in epitaxial ferromagnetic/ferroelectric heterostructures, it is possible to achieve large magnetoelectric coupling that is controlled directly by the charge degrees of freedom. We have studied this coupling using a variety of techniques, including magnetization, magneto-optic Kerr effect magnetometry, and x-ray absorption spectroscopy. In addition, structural distortions that arise exclusively at the interface can influence simultaneously the interfacial electronic transport and magnetic properties. Using high resolution synchrotron scattering, we have determined the interplay between new interfacial structural motifs and the resulting electronic and magnetic function at the interface.

Ahn, Charles

2012-02-01

84

Regio- and stereoselective intermolecular oxidative phenol coupling in Streptomyces.  

PubMed

Intermolecular oxidative phenol coupling is the main process in nature for the formation of atroposelective biaryl compounds. Although well defined in plants and fungi, this type of dimerization reaction in bacteria is poorly understood. Therefore, the biosynthesis of julichromes, spectomycins, and setomimycin was investigated. The monomeric subunits of these biarylic pre-anthraquinones are derived from a common polyketidic precursor, yet the coupling reaction proceeds in a regioselective manner, with the position of attachment of the two subunits depending on the specific streptomycete strain. By using genome analysis and deletion experiments, the biosynthetic gene clusters were identified. Furthermore, it was established that cytochrome P450 enzymes are fundamentally involved during dimerization of the polyketide monomers. PMID:24746278

Präg, Andreas; Grüning, Björn A; Häckh, Matthias; Lüdeke, Steffen; Wilde, Marcel; Luzhetskyy, Andriy; Richter, Michael; Luzhetska, Marta; Günther, Stefan; Müller, Michael

2014-04-30

85

Quantitative Analysis of amino acid oxidation markers by tandem mass spectrometry  

PubMed Central

Oxidative stress plays a central role in the pathogenesis of diverse chronic inflammatory disorders including diabetic complications, cardiovascular disease, aging, neurodegenerative disease, autoimmune disorders and pulmonary fibrosis. Protein misfolding can lead to chronic endoplasmic reticulum (ER) stress which can exacerbate oxidative stress. This can trigger apoptotic cascades resulting in chronic inflammatory disorders. Despite intense interest in origins and magnitude of oxidative stress, ability to quantify oxidants has been limited because they are short-lived. We have developed quantitative mass spectrometry (MS) based analytical strategies to analyze stable end-products of protein oxidation. These molecules provide quantitative and mechanistic assessment of degree of oxidative stress in cell cultures, tissues and biofluids of animal models of disease and human samples. Our studies support the hypothesis that unique reactive intermediates generated in localized microenvironments of vulnerable tissues promote end-organ damage. The ability to quantify these changes and assess response to therapies will be pivotal in understanding disease mechanisms and monitoring efficacy of therapy.

Vivekanandan-Giri, Anuradha; Byun, Jaeman; Pennathur, Subramaniam

2011-01-01

86

-3000 V dc bias Ti oxidation by inductively coupled plasma  

NASA Astrophysics Data System (ADS)

Broadening the outer oxidized layer of titanium by means of plasmas commands considerable interest in the biomedical research area due to its potential in human biocompatibility enhancement. Some early results of titanium substrate superficial oxidation experiments which have been conducted in a cylindrical vessel inductively coupled to a 13.56 MHz RF generator with a 500 W output are presented. The oxidation process was carried out in a 20 % oxygen and 80 % argon mixture at work pressures in the 5×10-3-1 mbar range, while the samples were dc biased down to -3000 V. The substrate temperature appears to be directly dependent on this voltage, reaching 685 °C at the maximum bias when a diffusive oxidation process gives rise to the TiO2 and ?-TiO rutile phases. These were characterized by means of x-ray diffraction and scanning electron microscopy revealing atomic percentage concentrations of oxygen, with respect to those of titanium, between 68 and 13 at.%. The optimum modified layer depth reached 5 ?m at a 5×10-2 mbar work pressure.

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

2008-12-01

87

Liquid chromatography coupled to tandem mass spectrometry for the residue determination of ethylenethiourea (ETU) and propylenethiourea (PTU) in water.  

PubMed

Ethylenethiourea (ETU) and propylenethiourea (PTU) are the main degradation products of dithiocarbamates fungicides, which are widely used in agriculture from several years ago. Their determination in water at low concentrations (e.g. sub-ppb levels) is highly problematic due to their polar character and low molecular size. In the present study, two analytical methodologies have been developed and compared for the selective and sensitive determination of ETU and PTU in various types of waters. Both approaches are based on liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) with electrospray ionization, using triple quadrupole analyzer. Whereas the first methodology used an on-line solid-phase extraction (SPE) step in order to reach the adequate sensitivity, the second one avoided sample treatment and was based on direct injection into an ultra high performance liquid chromatography (UHPLC-MS/MS) system, making use of a new-generation instrument in order to reach sub-ppb analyte levels in water. Strong matrix effects (typically leading to signal enhancement) were observed for most of the evaluated waters, especially when applying the on-line SPE method, surely due to the higher amount of sample injected into the system. The use of the own analyte (ETU-d?)) as isotope-labelled internal standard (ILIS) allowed to compensate these effects and to achieve an accurate ETU quantification at low concentrations. Moreover, three simultaneous transitions, operating in selected reaction monitoring mode, were acquired for both ETU and ETU-d?. This fact together with the evaluation of their relative intensity ratios assured the reliable identification of the analyte in the water samples. The two optimized methodologies were validated by analysis of six different samples (two drinking water, two groundwater and two surface water), spiked at two levels (0.1 and 1.0 ?g/L), and analyzed each in quintuplicate. Satisfactory accuracy and precision, with recoveries ranging from 73 to 104% and RSDs lower than 20%, were obtained for ETU. Limits of detection for ETU were found to be 0.058 ?g/L and 0.027 ?g/L with direct injection and with the on-line methodology, respectively. No satisfactory recoveries were obtained, in general, for PTU despite using its own deuterium-labelled molecule for matrix effects correction. Notable differences in the chemical behaviour between PTU and PTU-d? were observed, which lead to significant variation in their chromatographic retention time and ionization efficiency. Thus, no satisfactory correction of matrix effects could be reached illustrating that the use of deuterated ILIS can be problematic in some particular cases. Despite the poor correction, a semi-quantitative analysis would be feasible for PTU at sub-ppb levels in water. To the best of our knowledge, this is the first article reporting the use of LC-MS/MS for the trace level determination of these problematic analytes in water. PMID:22578799

Ripollés, Cristina; Sancho, Juan V; López, Francisco J; Hernández, Félix

2012-06-22

88

Rapid quantification of nebivolol in human plasma by liquid chromatography coupled with electrospray ionization tandem mass spectrometry  

Microsoft Academic Search

A simple, sensitive and rapid liquid chromatographic\\/electrospray ionization tandem mass spectrometric method was developed and validated for the quantitation of nebivolol in human plasma. The method involved a simple single-step liquid–liquid extraction with diethyl ether\\/dichloromethane (70\\/30). The analyte was chromatographed on Waters symmetry® C18 reversed-phase chromatographic column by isocratic elution with water:acetonitrile:formic acid (30:70:0.03, v\\/v) and analyzed by mass spectrometry

N. V. S. Ramakrishna; K. N. Vishwottam; M. Koteshwara; S. Manoj; M. Santosh; D. P. Varma

2005-01-01

89

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

90

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

91

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

92

Rapid residue analysis of four triazolopyrimidine herbicides in soil, water, and wheat by ultra-performance liquid chromatography coupled to tandem mass spectrometry.  

PubMed

A sensitive and effective method for simultaneous determination of triazolopyrimidine sulfonamide herbicide residues in soil, water, and wheat was developed using ultra-performance liquid chromatography coupled with tandem mass spectrometry. The four herbicides (pyroxsulam, flumetsulam, metosulam, and diclosulam) were cleaned up with an off-line C18 SPE cartridge and detected by tandem mass spectrometry using an electrospray ionization source in positive mode (ESI+). The determination of the target compounds was achieved in <2.0 min. The limits of detection were below 1 ?g kg(-1), while the limits of quantification did not exceed 3 ?g kg(-1) in different matrices. Quantitation was determined from calibration curves of standards containing 0.05-100 ?g L(-1) with r(2)?>?0.997. Recovery studies were conducted at three spiked levels (0.2, 1, and 5 ?g kg(-1) for water; 5, 10, and 100 ?g kg(-1) for soil and wheat). The overall average recoveries for this method in water, soil, wheat plants, and seeds at three levels ranged from 75.4% to 106.0%, with relative standard deviations in the range of 2.1-12.5% (n = 5) for all analytes. PMID:21221546

Liu, Xingang; Xu, Jun; Li, Yuanbo; Dong, Fengshou; Li, Jing; Song, Wenchen; Zheng, Yongquan

2011-03-01

93

Coupled catalytic oscillators: CO oxidation over polycrystalline Pt  

SciTech Connect

The authors have observed unusual oscillation in the rate of CO oxidation over a polycrystalline Pt wire loop. In contrast to simple oscillations between states of low and high reactivity, the unusual oscillations occurred between low, intermediate, and high values of the reaction rate. Experiments were performed at atmospheric pressure in a gas flow reactor over a range of gas temperatures and CO partial pressures. The reaction rate was measured using a thermocouple spotwelded to the loop. For a given CO partial pressure, oscillations occurred over a range of gas temperatures. Oscillations were simple at high gas temperatures and became complex as the temperature was lowered. When the authors monitored two thermocouples on opposite sides of the loop, they found that oscillations on the two sides occurred in phase, but differed in details of shape and amplitude. When they cut the loop and separated the halves, the complex oscillations at lower gas temperatures disappeared, and oscillations on the half-loops occurred with different frequencies. Results obtained by varying the separation showed that coupling between the half-loops occurred primarily through the gas phase. When the loop was spotwelded back together, oscillations became resynchronized, and complex waveforms reappeared at lower gas temperatures. To their knowledge, this is the first experimental demonstration that coupling chemical oscillators can increase the parameter space over which oscillatory instabilities occur. 47 refs.

Tsia, P.K.; Maple, M.B.; Herz, R.K. (Univ. of California, La Jolla (USA))

1988-10-01

94

Analysis of UV ink photoinitiators in packaged food by fast liquid chromatography at sub-ambient temperature coupled to tandem mass spectrometry.  

PubMed

A fast method of liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) was developed for the analysis of eleven UV ink photoinitiators in packaged food. Chromatographic separation was achieved in a pentafluorophenylpropyl (PFPP) column at 5°C and acetonitrile:25 mM formic acid-ammonium formate (pH 2.7) in gradient elution. To reduce sample treatment, a QuEChERS (quick, easy, cheap, effective, rugged and safe) method for the extraction and clean-up of UV photoinitiators in packaged foods was evaluated. Triple quadrupole working in H-SRM on Q1 mode was used for both quantitation and confirmation purposes and the most intense and selective transitions were chosen. Quality parameters of the developed QuEChERS LC-MS/MS method were established and applied for the analysis of photoinitiators in food packaged at ng kg(-1) levels. PMID:21183186

Gallart-Ayala, Héctor; Núñez, Oscar; Moyano, Encarnación; Galceran, Maria Teresa

2011-01-21

95

A tandem mass spectrometric study of the N-oxides, quinoline N-oxide, carbadox, and olaquindox, carried out at high mass accuracy using electrospray ionization  

NASA Astrophysics Data System (ADS)

A mass spectrometric study of three N-oxides, quinoline N-oxide, and the synthetic antibiotics carbadox and olaquindox, was carried out with a hybrid quadrupole/time-of-flight (TOF) mass spectrometer coupled with electrospray (ES) and atmospheric pressure chemical ionization (APCI) sources. The full scan mass spectra of the N-oxides obtained with ES are similar to those obtained with APCI, and the characteristic fragment ions corresponding to [M+H-O]+[radical sign] were observed in the full scan mass spectrum of each N-oxide examined. The protonated molecule of each N-oxide was subjected to collision-induced dissociation (CID) and accurate mass measurements were made of each fragment ion so as to determine its elemental composition. Fragment ions generated at enhanced cone voltages upstream of the first mass-resolving element were subjected to CID so as to identify the direct product ion-precursor ion relationship. Plausible structures have been proposed for most of the fragment ions observed. Elimination of OH[radical sign] radicals generated from the N-->O functional group is a characteristic fragmentation pathway of the N-oxides. The expulsion of radicals and small stable molecules is accompanied by formation and subsequent contraction of heterocyclic rings.

Miao, Xiu-Sheng; March, Raymond E.; Metcalfe, Chris D.

2003-12-01

96

Autosomal short tandem repeat analysis of ancient DNA by coupled use of mini- and conventional STR kits.  

PubMed

Multiplex autosomal short tandem repeat (STR) genotyping enables researchers to obtain genetic information from ancient human samples. In this study, we tested newly developed AmpF?STR(®) MiniFiler™ kit for autosomal STR analysis of ancient DNA (aDNA), using human femurs (n = 8) collected from medieval Korean tombs. After extracting aDNA from the bones, autosomal STR analyses were repeated for each sample using the AmpF?STR(®) MiniFiler™ and Identifiler™ kits. Whereas only 21.87% of larger-sized loci profiles could be obtained with the Identifiler™ kit, 75% of the same loci profiles were determined by MiniFiler™ kit analysis. This very successful amplification of large-sized STR markers from highly degraded aDNA suggests that the MiniFiler™ kit could be a useful complement to conventional STR kit analysis of ancient samples. PMID:22268568

Oh, Chang Seok; Lee, Sang Jun; Park, Jun Bum; Lee, Soong Deok; Seo, Seung Bum; Kim, Hye Yeon; Kim, Jaehyup; Kim, Yi-Suk; Shin, Dong Hoon

2012-05-01

97

Rh(III)-catalyzed oxidative coupling of N-aryl-2-aminopyridine with alkynes and alkenes.  

PubMed

[RhCp*Cl(2)](2) (1-2 mol %) can catalyze the oxidative coupling of N-aryl-2-aminopyridines with alkynes and arylates to give N-(2-pyridyl)indoles and N-(2-pyridyl)quinolones, respectively, using Cu(OAc)(2) as an oxidant. Coupling with styrenes gave mono- and/or disubstituted olefination products. PMID:21038875

Chen, Jinlei; Song, Guoyong; Pan, Cheng-Ling; Li, Xingwei

2010-12-01

98

Nanocrystal bilayer for tandem catalysis  

Microsoft Academic Search

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

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

2011-01-01

99

Analysis of chloramphenicol in honeys of different geographical origin by liquid chromatography coupled to electrospray ionization tandem mass spectrometry.  

PubMed

A sensitive liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed to detect trace amounts of the antibiotic chloramphenicol (CAP) in honey. The methodology entailed a solid-phase extraction of aqueous honey solutions followed by liquid-liquid partitioning, filtration and direct injection onto the LC-MS/MS system. Honey extracts were spiked with an isotopically labelled internal standard (d(5)-CAP) to compensate for analyte loss and potential ion suppression during the MS stage. Detection of the analyte was achieved by negative ionization electrospray in the selected reaction monitoring (SAM) mode. For confirmation, four characteristic mass transitions were monitored each for the analyte and the surrogate standard. The method was validated according to the latest European Union criteria for the analyses of veterinary drug residues in food. At all three fortification levels studied (0.1, 0.2, 0.5 microg kg(-1)) the method was accurate to within 15%. The repeatability and within-laboratory reproducibilities were <12 and 18%, respectively. The decision limit (CC alpha) and detection capability (CC beta) were both <0.1 microg kg(-1). The procedure provides a sensitive and reliable method for the determination of residues of chloramphenicol in honey. Numerous raw honeys of various geographical origins were analysed, showing extensive contamination particularly those of Chinese origin. PMID:12775475

Verzegnassi, L; Royer, D; Mottier, P; Stadler, R H

2003-04-01

100

Automated analysis of perfluorinated compounds in human hair and urine samples by turbulent flow chromatography coupled to tandem mass spectrometry.  

PubMed

Perfluorinated compounds (PFCs) are ubiquitous contaminants of humans and animals worldwide. PFCs are bioaccumulated because of their affinity for proteins. It has been shown they could have a variety of toxicological effects and cause damage to human health, emphasizing the need for sensitive and robust analytical methods to assess their bioaccumulation in humans. In this paper we report the development and validation of an analytical method for analysis of PFCs in the non-invasive human matrices hair and urine. The method is based on rapid and simple sample pre-treatment followed by online turbulent flow liquid chromatography and tandem mass spectrometry (TFC-LC-MS-MS) for analysis of 21 PFCs. The method was validated for both matrices. Percentage recovery was between 60 and 105 for most compounds in both matrices. Limits of quantification ranged from 0.1 to 9 ng mL(-1) in urine and from 0.04 to 13.4 in hair. The good performance of the method was proved by investigating the presence of selected PFCs in 24 hair and 30 urine samples from different donors living in Barcelona (NE Spain). The results were indicative of bioaccumulation of these compounds in both types of sample. PFOS and PFOA were most frequently detected in hair and PFBA in urine. PMID:22227745

Perez, Francisca; Llorca, Marta; Farré, Marinella; Barceló, Damià

2012-03-01

101

Stability of the proteasome inhibitor bortezomib in cell based assays determined by ultra-high performance liquid chromatography coupled to tandem mass spectrometry.  

PubMed

Bortezomib represents the first clinically approved proteasome inhibitor for multiple myeloma. Research conducted on its intracellular kinetics in target cells and on possibly related mechanisms of resistance is sparse so far. We therefore developed and validated a highly sensitive ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC/MS/MS) method for bortezomib quantification within cultured myeloma cells and media. Fast gradient UPLC based on a BEH C18 column (1.7?m particle size) with aqueous formic acid and acetonitrile as mobile phase. Selective extraction procedures using protein precipitation extraction (PPE) and liquid-liquid extraction (LLE) were established and compared. Extracted bortezomib was quantified by positive electrospray tandem mass spectrometry using deuterated D8-bortezomib as internal standard. The calibrated ranges were 0.5-2500pg per sample. For LLE, overall accuracies varied between 99.2% and 112% (medium) and 89.9% and 111% (cells), while overall precision ranged from 1.13% to 13.0% (medium) and 2.80% to 12.7% (cells), respectively. Recovery rates (cells/medium) were >77%/>65% for LLE and >89%/63% for PPE. Matrix effects were generally lower for LLE compared to PPE. Regardless of the extraction method, retrievable amounts of bortezomib were considerably reduced after 24h of incubation (0.2, 1, 5, and 25nM). Revealing greater dependence on the extent of acidification, retrieval of bortezomib can be increased distinctly in acidified solution or acidified culture medium. Thus, particular attention needs to be paid to the occurring bortezomib degradation in neutral culture medium since correct quantification of intracellular bortezomib can only be achieved in relation to the corresponding extracellular concentration. PMID:24780258

Clemens, Jannick; Longo, Magdalena; Seckinger, Anja; Hose, Dirk; Haefeli, Walter Emil; Weiss, Johanna; Burhenne, Jürgen

2014-06-01

102

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

103

On-line column coupled isotachophoresis-capillary zone electrophoresis hyphenated with tandem mass spectrometry in drug analysis: Varenicline and its metabolite in human urine.  

PubMed

A new highly advanced analytical approach, based on two-dimensional column coupled CE (ITP-CZE) hyphenated with tandem mass spectrometry (MS/MS, here triple quadrupole, QqQ) was developed, evaluated and applied in biomedical field in the present work. Capillary isotachophoresis (ITP) coupled on-line with capillary zone electrophoresis (CZE) used in hydrodynamically closed separation system was favorable for increasing the sample load capacity, increasing the analyte concentration, and removing the deteriorative highly conductive major matrix constituents. These factors considerably reduced the concentration limits of detection (cLOD) and external sample preparation (comparing to single column CZE), and, by that, provided favorable conditions for the mass spectrometry (enhanced signal to noise ratio, reproducibility of measurements, working life of MS). Here, the CZE-ESI combination provided more effective interfacing than ITP-ESI resulting in both a higher obtainable intensity of MS detection signal of the analyte as well as reproducibility of measurements of the analyte's peak area. The optimized ITP-CZE-ESI-QqQ method was successfully evaluated as for its performance parameters (LOD, LOQ, linearity, precision, recovery/accuracy) and applied for the direct identification and ultratrace (pgmL(-1)) determination of varenicline and, in addition, identification of its targeted metabolite, 2-hydroxy-varenicline, in unpretreated/diluted human urine. This application example demonstrated the real analytical potential of this new analytical approach and, at the same time, served as currently the most effective routine clinical method for varenicline. PMID:24793857

Pieš?anský, Juraj; Maráková, Katarína; Veizerová, Lucia; Galba, Jaroslav; Mikuš, Peter

2014-05-15

104

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.

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

2014-01-01

105

Biomimetic oxidative coupling of benzylamines and 2-aminophenols: synthesis of benzoxazoles.  

PubMed

Aerobic oxidation: in a biomimetic approach, a mixture of redox catalysts forms couples that effect the aerobic oxidation of a mixture of benzylamine and 2-aminophenol derivatives to give the corresponding benzoxazoles. This biomimetic oxidation proceeds smoothly under mild conditions and the protocol can also be used for preparing benzimidazoles and benzothiazoles. PMID:22968931

Endo, Yoshinori; Bäckvall, Jan-E

2012-10-22

106

Direct detection of tetrahydrobiopterin (BH4) and dopamine in rat brain using liquid chromatography coupled electrospray tandem mass spectrometry.  

PubMed

A simple and rapid liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed for the quantification of tetrahydrobiopterin (BH4) and dopamine in rat brain using epsilon-acetamidocaproic acid (AACA) as an internal standard. Proteins in the samples were precipitated with acetonitrile and then the supernatants were separated by a Sepax Polar-Imidazole (2.1 × 100 mm, i.d., 3 ?m) column using a mixture of 10mM ammonium formate in acetonitrile/water (75:25, v/v) as the mobile phase at a flow rate of 300 ?l/min. Quantification was performed on a triple quadrupole mass spectrometer employing electrospray ionization with the operating conditions as multiple reaction monitoring (MRM) and positive ion mode from m/z 242.1 ? 166.0 for BH4, m/z 154.1 ? 90.0 for dopamine and m/z 174.1 ? 114.0 for AACA (IS). The total chromatographic run time was for 5.5 min. The method was validated for the analysis of samples: the limit of detection was 10 ng/g. The calibration curve was linear between 10-2000 ng/g for BH4 (r(2)=0.995) and 10-5000 ng/g for dopamine (r(2)=0.997) in the rat brain. Thus, good correlated LC-ESI/MS/MS results were obtained and found to be a powerful tool for the quantitative analysis of BH4 and dopamine in the rat brain. PMID:22382017

Kim, Hak Rim; Kim, Tae-Hyun; Hong, Sung-Hyun; Kim, Hyung-Gun

2012-03-23

107

Determination of alkyl alkylphosphonic acids by liquid chromatography coupled with electrospray ionization tandem mass spectrometry using a dicationic reagent.  

PubMed

A new analytical method based on liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) is proposed and validated for the identification and quantification of alkyl alkylphosphonic acids (AAPAs) in aqueous matrices. Retrospective detection and identification of degradation products of chemical warfare agents is important as an indicator of possible use of chemical warfare agents or of environmental contamination. A commercially available solution of 1,9-nonanediyl-bis-(3-methylimidazolium)bisfluoride (NBMI) allowed detection of AAPAs by positive mode electrospray ionization mass spectrometry by forming an adduct with AAPAs. MS/MS experiments using an ion trap analyzer were carried out for unambiguous identification of AAPAs. Different parameters were optimized in order to obtain both an adequate chromatographic separation and a high sensitivity using experimental design methodology. Quantification was done with matrix-matched calibration standards of AAPAs. The method was validated in terms of linearity (r(2) >0.982), intra- and inter-day precisions (RSD below 15%), and robustness. The method is sensitive enough for the determination of AAPAs in aqueous matrices, with limits of detection in the 1-5 ng mL(-1) range and limits of quantification in the 5-20 ng mL(-1) range. Finally, the method was successfully applied to determine these AAPAs in aqueous samples provided by the Organization for the Prohibition of Chemical Weapons during 26(th) and 29(th) official proficiency tests. The added advantage of this method is identification of low mass range analyte at high mass range, which obviates the background noise at low mass range. PMID:23059880

Tak, Vijay; Purhoit, Ajay; Pardasani, Deepak; Garg, Prabhat; Jain, Rajeev; Dubey, D K

2012-11-30

108

Rapid quantification of miglustat in human plasma and cerebrospinal fluid by liquid chromatography coupled with tandem mass spectrometry.  

PubMed

Miglustat (OGT 918) is an iminosugar recently introduced in therapeutic as potential alternative therapy in disorders found in several diseases such as Tay-Sachs, Gaucher or Niemann-Pick diseases. A highly sensitive liquid-chromatography-electrospray tandem mass spectrometry (LC-MS/MS) assay was developed for the quantification of miglustat in human plasma and cerebrospinal fluid (CSF). The sample preparation consists in a simple protein precipitation with a mixture of acetonitrile/methanol (75/25) which yields 100% recovery. The isocratic separation utilizes an Atlantis Hilic (3 microm, 150 mm x 2.1 mm) column, with a mobile phase of acetonitrile/water/ammonium acetate buffer (75/10/15, v/v/v) delivered at 230 microl/min. Selected reaction monitoring (SRM) mode was used with the transitions m/z 220-->158 for the miglustat and m/z 208-->m/z 146 for the miglitol (internal standard). Good linearity was observed in a range from 125 to 2500 ng/ml and from 50 to 1000 ng/ml, for plasma and CSF, respectively. The within-run precision of the assay was less than 6%, and the between-run run precision was less than 6.5%, for six replicates at each of three concentrations and evaluated on three separated days for both plasma and CSF mediums. Assay accuracy was in the range of 98-106.5%. Stability of miglustat was reported under a variety of storage conditions. The miglustat concentrations in two children are presented to demonstrate the clinical interest of this new method. PMID:19095507

Guitton, Jérôme; Coste, Sylvie; Guffon-Fouilhoux, Nathalie; Cohen, Sabine; Manchon, Monique; Guillaumont, Marc

2009-01-15

109

Identification of 20(S)-protopanaxatriol metabolites in rats by ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry and nuclear magnetic resonance spectroscopy.  

PubMed

20(S)-Protopanaxatriol (PPT), one of the aglycones of ginsenosides, has been shown to exert cardioprotective effects against myocardial ischemic injury. However, studies on PPT metabolism have rarely been reported. This study is the first to investigate the in vivo metabolism of PPT following oral administration by ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UPLC-Q/TOF-MS) and nuclear magnetic resonance (NMR) spectroscopy. The structures of the metabolites were identified based on the characteristics of their MS data, MS(2) data, and chromatographic retention times. A total of 22 metabolites, including 17 phase I and 5 phase II metabolites, were found and tentatively identified by comparing their mass spectrometry profiles with those of PPT. Two new monooxygenation metabolites, (20S,24S)-epoxy-dammarane-3,6,12,25-tetraol and (20S,24R)-epoxy-dammarane-3,6,12,25-tetraol, were chemicallly synthesized and unambiguously characterized according to the NMR spectroscopic data. The metabolic pathways of PPT were proposed accordingly for the first time. Results revealed that oxidation of (1) double bonds at ?((24,25)) to form 24,25-epoxides, followed by rearrangement to yield 20,24-oxide forms; and (2) vinyl-methyl at C-26/27 to form corresponding carboxylic acid were the predominant metabolic pathways. Phase II metabolic pathways were proven for the first time to consist of glucuronidation and cysteine conjugation. This study provides valuable and new information on the metabolism of PPT, which is indispensable for understanding the safety and efficacy of PPT, as well as its corresponding ginsenosides. PMID:24184656

He, Chunyong; Zhou, Dandan; Li, Jia; Han, Han; Ji, Guang; Yang, Li; Wang, Zhengtao

2014-01-01

110

Reaction kinetics and transformation products of 1-naphthol by Mn oxide-mediated oxidative-coupling reaction  

Microsoft Academic Search

In this study, the transformation of 1-naphthol via oxidative-coupling reaction was investigated using Mn oxides. 1-Naphthol was transformed completely by birnessite, which is one of the natural Mn oxides present in soil. The surface area-normalized specific rate constant, ksurf, for 1-naphthol was determined to be 9.66×10?4L\\/m2min using observed pseudo-first-order rate constants with respect to birnessite loading. The transformation of 1-naphthol

Hyun-Sang Shin; Dong-Min Lim; Doo-Hee Lee; Ki-Hoon Kang

2009-01-01

111

Controlling Spatial Coupling in Catalytic CO Oxidation on Platinum  

Microsoft Academic Search

Reaction-rate oscillations are known to occur in oxidation reactions on a variety of metal catalysts. The most extensively studied system of this type is the oxidation of carbon monoxide on platinum. Most studies have focused on temporal behavior. Recently, we constructed an experiment in which we can study both the spatial and temporal behavior of CO oxidation on Pt thin-film

C. D. Lund; S. Y. Yamamoto; C. M. Surko; M. B. Maple

1997-01-01

112

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

113

Methyl radicals in oxidative coupling of methane directly confirmed by synchrotron VUV photoionization mass spectroscopy.  

PubMed

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

114

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.

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

2013-01-01

115

Phosphine Oxides as Stabilizing Ligands for the Palladium-Catalyzed Cross-Coupling of Potassium Aryldimethylsilanolates  

PubMed Central

The palladium-catalyzed cross-coupling reaction of potassium (4-methoxyphenyl)dimethylsilanolate (K+1?) with aryl bromides has been demonstrated using triphenylphosphine oxide as a stabilizing ligand. Unsymmetrical biaryls can be prepared from a variety of aryl bromides in good yield with short reaction times. Qualitative kinetics studies compared effects of different phosphine oxides on the rate of cross-coupling and established the beneficial effect of these ligands in the reaction of electron-rich arylsilanolates. The improved yield and reproducibility of the cross-coupling of several bromides was demonstrated by direct comparison of reactions performed with and without triphenylphosphine oxide under non-rigorous exclusion of oxygen.

Denmark, Scott E.; Smith, Russell C.; Tymonko, Steven A.

2012-01-01

116

Qualitative and quantitative analysis of traditional Chinese medicine Niu Huang Jie Du Pill using ultra performance liquid chromatography coupled with tunable UV detector and rapid resolution liquid chromatography coupled with time-of-flight tandem mass spectrometry.  

PubMed

An ultra performance liquid chromatography coupled with tunable UV detector (UPLC-TUV) and rapid resolution liquid chromatography coupled with time-of-flight tandem mass spectrometry (RRLC-Q-TOF) method was developed for the quality assessment of Niu Huang Jie Du Pill (NHJDP), a commonly used traditional Chinese medicine (TCM). Ten compounds were simultaneously identified by electrospray ion mass spectrometry (ESI/MS) and comparison with reference standards and literature data. All of them were quantified by UPLC method. Baseline separation was achieved on an ODS-140HTP C(18) column (2.3mum, 100mmx2.1mm I.D.) with linear gradient elution of acetonitrile-0.1% formic acid. This developed method provides good linearity (r(2)>0.9996), repeatability (RSD<3.63%), intra- and inter-day precisions (RSD<0.86%) with accuracies (97.88-101.56%) and recovery (98.88-101.92%) of 10 major constituents, namely baicalin, baicalein, wogonoside, wogonin, glycyrrhizic acid, liquiritin, rhein, emodin, chrysophanol and physcion. In addition, the principal component analysis (PCA) coupled with the UPLC fingerprint was applied to classify the NHJDP samples according to their manufacture corporation. This proposed method with high sensitivity and selectivity was successfully utilized to analyze 10 major bioactive compounds in 30 batches of NHJDPs, and the results demonstrate that this analytical method is simple and suitable for the original discrimination and quality control of this TCM. PMID:19783115

Liang, Xu; Zhang, Lin; Zhang, Xi; Dai, Weixing; Li, Haiyun; Hu, Liwei; Liu, Hui; Su, Juan; Zhang, Weidong

2010-02-01

117

Application of hollow fibre liquid phase microextraction for the multiresidue determination of pesticides in alcoholic beverages by ultra-high pressure liquid chromatography coupled to tandem mass spectrometry.  

PubMed

An alternative method has been developed to determine more than 50 pesticides in alcoholic beverages using hollow fibre liquid phase microextraction (HF-LPME) followed by ultra-high pressure liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS), without any further clean-up step. Pesticides were extracted from the sample to the organic solvent immobilized in the fibre and they were desorbed in methanol prior to chromatographic analysis. Experimental parameters related to microextraction such as type of organic solvent, extraction time and agitation rate have been optimized. The extraction method has been validated for several types of alcoholic beverages such as wine and beer, and no matrix effect was observed. The technique requires minimal sample handling and solvent consumption. Using optimum conditions, low detection limits (0.01-5.61microgL(-1)) and good linearity (R(2)>0.95) were obtained. Repeatability and interday precision ranged from 3.0 to 16.8% and from 5.9 to 21.2%, respectively. Finally the optimized method was applied to real samples and carbaryl, triadimenol, spyroxamine, epoxiconazole, triflumizol and fenazaquin were detected in some of the analyzed samples. The obtained results indicated that the new method can be successfully applied for extraction and determination of pesticides in alcoholic beverages, increasing sample throughput. PMID:18762301

Bolaños, P Plaza; Romero-González, R; Frenich, A Garrido; Vidal, J L Martínez

2008-10-24

118

Depletion study of enrofloxacin and its metabolite ciprofloxacin in edible tissues and feathers of white leghorn hens by liquid chromatography coupled with tandem mass spectrometry.  

PubMed

To ensure delivery of safe foods to consumers, withdrawal times for drugs must be respected according to the maximum residual limits established by regulatory agencies. Because of availability and price, feather meal is currently incorporated into animal feed as a protein source for farm species. Few data are available on residual drugs in feathers from treated animals. A depletion study was performed with laying hens treated intramuscularly with 5% enrofloxacin (Enromic) at 10 mg/kg body weight over 3 days. Thirty-three birds were treated and slaughtered at different times between 6 and 216 h after treatment; and samples of muscle plus skin, liver, kidney, and feathers were collected. High-performance liquid chromatography coupled with a tandem mass spectrometry method was validated before sample analysis to determine the decision limit, detection capability, recovery, and precision. Liver was the edible tissue with the slowest drug depletion. A withdrawal time of 6 days was calculated based on European Union maximum residual limits (100 microg/kg). A withdrawal time of 9 days was calculated based on Japan maximum residual limits (10 microg/kg). Enrofloxacin plus ciprofloxacin concentrations in feathers remained high through all sampling periods. Thus, feathers from treated animals should not be fed to food-producing animals. PMID:17803156

San Martín, B; Cornejo, J; Iragüen, D; Hidalgo, H; Anadón, A

2007-08-01

119

Determination of Sudan dyes in chili pepper powder by online solid-phase extraction with a butyl methacrylate monolithic column coupled to liquid chromatography with tandem mass spectrometry.  

PubMed

A poly(butyl methacrylate-co-ethylene dimethacrylate) monolithic column was fabricated and used as a novel sorbent for online solid-phase extraction coupled to liquid chromatography with tandem mass spectrometry for the simultaneous determination of Sudan I-IV in chili pepper powder. The prepared columns were characterized by scanning electron microscopy, nitrogen adsorption-desorption, and pressure drop measurements. Online solid-phase extraction was performed on the synthesized monolithic column using 10 mM ammonium acetate solution as the loading solution with the aid of an online cleanup chromatography system. The desorption of Sudan I-IV was achieved with acetonitrile as the eluting solution at the flow rate of 0.5 mL/min. The extracted analytes were subsequently eluted into a C18 analytical column for chromatographic separation using a mixture of 10% acetonitrile/90% formic acid (0.5%) solution as the mobile phase. Under the optimized conditions, the developed method had linear range of 1.0-50 ?g/kg, a detection limit of 0.3 ?g/kg, and a quantification limit of 1.0 ?g/kg for each analyte. The intraday and interday recoveries of Sudan I-IV in chili pepper powder samples ranged from 94.8 to 100.9% and 94.9 to 99.4%, respectively. The intraday and interday precision were between 3.37-7.01% and 5.01-7.68%, respectively. PMID:24723310

Liu, Yao; Wang, Man-Man; Ai, Lian-Feng; Zhang, Chang-Kun; Li, Xin; Wang, Xue-Sheng

2014-07-01

120

Quality evaluation of Hypericum japonicum by using high-performance liquid chromatography coupled with photodiode array detector and electrospray ionization tandem mass spectrometry.  

PubMed

A high-performance liquid chromatography coupled with photodiode array detection and electrospray ionization tandem mass spectrometry (HPLC-PAD-ESI-MS(n)) method was developed to evaluate the quality of Hypericum japonicum through establishing chromatographic fingerprint and simultaneous determination of seven phenolic compounds. The analysis was achieved on an Ultimate XB-C(18) analytical column (250 mm x 4.6 mm i.d., 5 microm) using an aqueous solution of acetic acid (pH 3.8) and methanol as the mobile phase. Ten samples of H. japonicum from various habitats were investigated and the correlation coefficients of similarity were determined from the HPLC fingerprints. By using an online ESI-MS(n), 20 common peaks in chromatographic fingerprints were identified as phenols, including flavones and their glycosides, flavonones and their glucosides, flavanols, xanthones, phloroglucinols, phenyl propanoids and chromones. Based on the above study, seven phenols which are considered to be major constituents in H. japonicum, including 3,4-dihydroxybenzoic acid (1), taxfolin-7-O-alpha-L-rhamnoside (7), 7-dihydroxy-2-(1-methylpropyl)chromone-8-beta-D-glucoside (8), isoquercitrin (14), quercitrin (16), quercetin-7-O-alpha-L-rhamnoside (18) and quercetin (19) were quantified by the validated HPLC-PAD method. This developed method by combination of chromatographic fingerprint and quantification analysis could be applied to control the quality of H. japonicum. PMID:19358152

Gao, Wei-Na; Luo, Jian-Guang; Kong, Ling-Yi

2009-09-01

121

[Determination of N-carbamyl-L-glutamic acid in feedstuff by high performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry].  

PubMed

A method was developed for the determination of N-carbamyl-L-glutamic acid (NCG) in feedstuff by high performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS). The feedstuff samples were extracted with methanol, cleaned-up by a ProElut mixed-mode of strong anion exchange inverse column (PXA). Then the samples were separated with HPLC and detected with MS/MS in multiple reaction monitoring (MRM) mode via positive electrospray ionization (ESI+). The fragment ions of m/z 148.0 and m/z 84.0 were used for qualitative analysis, and m/z 130.0 was selected for quantitative analysis. The limit of detection for NCG was 24 microg/kg (S/N > 3), and the limit of quantification was 80 microg/kg (S/N > 10). The standard calibration curve was linear over the range of 20-1,000 microg/L, and the correlation coefficient was 0. 999 9. The recoveries of NCG in feedstuff were 104.0%, 103.5%, 95.3%, at the three spiked levels of 80, 200, 500 mg/kg with the relative standard deviations (RSDs) of 7.5%, 6.3% and 5.8%. The results showed that the method is simple, fast, highly sensitive, specific and with good purification effect. It can be applied to the analysis and determination of NCG in feedstuff. PMID:24822455

Tang, Shengyun; Wang, Yuanxing; Wen, Pingwei; Xin, Zhen

2014-02-01

122

Multi-residue enantiomeric analysis of pharmaceuticals and their active metabolites in the Guadalquivir River basin (South Spain) by chiral liquid chromatography coupled with tandem mass spectrometry.  

PubMed

This paper describes the development and application of a multi-residue chiral liquid chromatography coupled with tandem mass spectrometry method for simultaneous enantiomeric profiling of 18 chiral pharmaceuticals and their active metabolites (belonging to several therapeutic classes including analgesics, psychiatric drugs, antibiotics, cardiovascular drugs and ?-agonists) in surface water and wastewater. To the authors' knowledge, this is the first time an enantiomeric method including such a high number of pharmaceuticals and their metabolites has been reported. Some of the pharmaceuticals have never been studied before in environmental matrices. Among them are timolol, betaxolol, carazolol and clenbuterol. A monitoring programme of the Guadalquivir River basin (South Spain), including 24 sampling sites and five wastewater treatment plants along the basin, revealed that enantiomeric composition of studied pharmaceuticals is dependent on compound and sampling site. Several compounds such as ibuprofen, atenolol, sotalol and metoprolol were frequently found as racemic mixtures. On the other hand, fluoxetine, propranolol and albuterol were found to be enriched with one enantiomer. Such an outcome might be of significant environmental relevance as two enantiomers of the same chiral compound might reveal different ecotoxicity. For example, propranolol was enriched with S(-)-enantiomer, which is known to be more toxic to Pimephales promelas than R(+)-propranolol. Fluoxetine was found to be enriched with S(+)-enantiomer, which is more toxic to P. promelas than R(-)-fluoxetine. PMID:23579471

López-Serna, Rebeca; Kasprzyk-Hordern, Barbara; Petrovi?, Mira; Barceló, Damià

2013-07-01

123

Simultaneous determination of four biogenic and three volatile amines in anchovy by ultra-high-performance liquid chromatography coupled to tandem mass spectrometry.  

PubMed

A new method has been developed and validated for the simultaneous determination of four biogenic (putrescine, cadaverine, histamine, and tyramine) and three volatile amines (trimethylamine, triethylamine, and tripropylamine) in anchovy. Separation and determination of the selected compounds were carried out by ultra-high-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS), using an electrospray ionization source (ESI) in positive ion mode. Chromatographic separation was carried out using an aqueous solution of formic acid (0.1%) and methanol as mobile phase in gradient mode. The method was validated, and mean recoveries were evaluated at three concentration levels (75, 150, and 250 ?g/kg), ranging from 70 to 110% at the three levels assayed. Intra- and interday precision, expressed as relative standard deviation (RSD), were lower than 15% and 20%, respectively. Limits of quantitation (LOQs) were 25 ?g/kg for all cases, except for that of TMA, which was set at 60 ?g/kg. The developed procedure was applied to determine the target compounds in anchovy samples stored during 7 days at 4 °C, observing the increasing in the concentration of these compounds at longer storage time. PMID:22559197

Romero-González, Roberto; Alarcón-Flores, María Isabel; Martínez Vidal, José Luis; Garrido Frenich, Antonia

2012-05-30

124

[Rapid analysis of eight lipophilic pesticide residues in vegetables by dispersive liquid-liquid microextraction coupled with gas chromatography-tandem mass spectrometry].  

PubMed

A novel method for rapid determination of eight lipophilic pesticides in vegetables was developed using dispersive liquid-liquid micro-extraction (DLLME) coupled with gas chromatography-tandem mass spectrometry (GC-MS/MS). The analyte in the vegetable was extracted with water-acetone (5 : 1, v/v) solution. Then, the extract was transferred into a centrifugal tube with 25 mg primary secondary amine (PSA), 50 mg C18 and 25 mg graphitized carbon black powder. The important parameters that affected the extraction efficiency were studied, such as the extraction and dispersed solvents, and the extraction time. The results showed that a good extraction efficiency was obtained, with acetone used as the dispersed solvent and 50.0 microL chlorobenzene used as the extraction solvent. Under the optimum conditions, the enrichment factors ranged from 526 to 878. The linearity ranges of the eight targeted compounds were 0.005 - 10 mg/kg, and the limits of detection (signal/noise = 3) were 0.001 - 0.02 mg/kg, with the correlation coefficients varying from 0.992 1 to 0.998 9. The recoveries of the pesticides ranged from 60.1% to 82.5% with the relative standard deviations between 1.2% and 9.6%. The method has been used to analyze the eight lipophilic pesticide residues in vegetable samples with satisfactory results. PMID:23256389

Zhou, Min; Li, Wei; Du, Xiaoting; Xia, Zhongxing; Chen, Meichun

2012-08-01

125

[Determination of deoxynivalenol in grain and its products by solid-phase extraction coupled with high performance liquid chromatography-tandem mass spectrometry].  

PubMed

A method was established for the determination of deoxynivalenol (vomitoxin) in grain and its products based on solid-phase extraction coupled with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The sample was firstly extracted by acetonitrile-water (84:16, v/v). The extract was then cleaned-up by an HLB solid phase extraction cartridge. The separation was carried out on a Phenomenex Kinetex C18 column (100 mm x4. 6 mm, 2.6 microm) with a gradient elution using 0.3% per hundred ammonia solution-acetonitrile as mobile phases. The analysis of deoxynivalenol was performed under electrospray negative ionization mode. The limit of detection (LOD, S/N= 3) and the limit of quantification (LOQ, S/N = 10) were 20 microg/kg and 50 microg/kg, respectively. A good linearity (r > 0.99) was achieved for the target compound over the range of 20-1000 pg/L. The recoveries at the three spiked levels (50, 100, 500 microg/kg) in the blank matrices such as flour, barley, soybean, rice, cornmeal, cassava and wheat, were varied from 75.6% to 111.0% with the relative standard deviations no more than 13. 0%. The method is accurate, efficient, sensitive and practical. The cost of pretreatment is obviously reduced by replacing immunoaffinity columns and Mycosep columns with HLB columns which have the same purification effect. PMID:23451526

Huang, Juan; Chen, Guosong; Zhang, Xiaoyan; Shen, Chongyu; Lü, Chen; Wu, Bin; Liu, Yan; Chen, Huilan; Ding, Tao

2012-11-01

126

Simultaneous determination of seven ginsenosides in Du Shen Tang decoction by rapid resolution liquid chromatography (RRLC) coupled with tandem mass spectrometry.  

PubMed

A rapid quantification of seven ginsenosides in Du Shen Tang decoction, the decoction of the root of Panax ginseng was investigated by rapid resolution liquid chromatography coupled with tandem mass spectrometry (RRLC-MS/MS). All analytes including seven major constituents, namely ginsenoside-Re, Rg1, Rb1, Rc, Rb2, Rd and Rf were analysed simultaneously in short time and provide good linearity (r>0.9976), repeatability (RSD<5.67%), intra- and inter-day precisions (RSD<5.06%) with accuracies (94.65-105.31%) and recovery (93.76-106.82%) by using optimised methods. In addition, the content of seven ginsenosides in the decoction prepared by the root of 2-year-old, 4-year-old and 6-year-old Panax ginseng was also analysed. The results showed the concentration of ginsenosides detected in Du Shen Tang decoction was affected by the difference in collected times of the root of Panax ginseng. The established method could be used as a rapid and reliable approach for assessment of the quantity of Du Shen Tang decoction. PMID:23993583

Guo, Na; Ablajan, Keyume; Fan, Bin; Yan, Han; Yu, Youhua; Dou, Deqiang

2013-12-15

127

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

128

Anastrozole quantification in human plasma by high-performance liquid chromatography coupled to photospray tandem mass spectrometry applied to pharmacokinetic studies.  

PubMed

A rapid, sensitive and specific method for quantifying the aromatase inhibitor (anastrozole) in human plasma using dexchlorpheniramine as the internal standard (I.S.) is described herein. The analyte and the I.S. were extracted from 200 microl of human plasma by liquid-liquid extraction using a mixture of diethyl ether:dichloromethane (70:30, v/v) solution. Extracts were removed and dried in the organic phase then reconstituted with 200 microl of acetonitrile:water (50:50; v/v). The extracts were analyzed by high performance liquid chromatography coupled with photospray tandem mass spectrometry (HPLC-MS-MS). Chromatography was performed isocratically on a Genesis, C18 4 microm analytical column (100 mm x 2.1mm i.d.). The method had a chromatographic run time of 2.5 min and a linear calibration curve ranging from 0.05-10 ng ml(-1). The limit of quantification (LOQ) was 0.05 ng ml(-1). This HPLC-MS-MS procedure was used to assess pharmacokinetic studies. PMID:17240203

Mendes, Gustavo D; Hamamoto, Daniele; Ilha, Jaime; Pereira, Alberto dos Santos; De Nucci, Gilberto

2007-05-01

129

Bioactivity-based liquid chromatography-coupled electrospray ionization tandem ion trap/time of flight mass spectrometry for ??AR agonist identification in alkaloidal extract of Alstonia scholaris.  

PubMed

Although chromatographic fingerprinting combined with chemometrics, is a rational method for the quality control of traditional Chinese medicine (TCM), chemometrics cannot fully explore the relationship between chemical information and the efficacy of the potential activity. In the present work, a cell-based ?? adrenergic receptor (??AR) agonist functional evaluation model coupled with high-performance liquid chromatography was developed to screen the potential ??AR agonist components in the alkaloidal extract of Alstonia scholaris leaves. Using a liquid chromatography with ion trap time-of-flight mass spectrometry (LCMS-IT-TOF) system, the potential bioactive compounds in the prescription were identified and deduced based on the mass spectrometric fragmentation patterns, tandem mass spectrometry (MS/MS) data, and relevant literature. Several new ??AR agonists of indole alkaloids were successfully found, and their activities were confirmed through an in vivo relaxant test on guinea pig tracheal muscles. The developed method is rapid and reliable compared with conventional fingerprinting and showed high sensitivity and resolution for the identification of ??AR agonists in TCM prescriptions. This strategy clearly demonstrates that bioactivity-integrated fingerprinting is a powerful tool not only in screening and identifying potential lead compounds and in determining the therapeutic material basis of Chinese herbal prescriptions, but also in supplying suitable chemical markers for their quality control. PMID:22269170

Hou, Yuanyuan; Cao, Xuelin; Dong, Linyi; Wang, Liqiang; Cheng, Binfeng; Shi, Qian; Luo, Xiaodong; Bai, Gang

2012-03-01

130

Analytical method for the determination of halogenated norbornene flame retardants in environmental and biota matrices by gas chromatography coupled to tandem mass spectrometry.  

PubMed

A new methodology for the analysis of Dechlorane Plus and related compounds (DPMA, Dec 602, Dec 603 and Dec 604) by gas chromatography coupled to negative chemical ionization tandem mass spectrometry (GC-NCI-MS-MS) was developed for three different matrices, including environmental (sediment and sludge) and biota (fish) samples. Analytical parameters such as linearity, repeatability and reproducibility, recoveries, limits of detection and limits of quantification were evaluated, showing satisfactory values for the developed methodology. Moreover, a comparison with the analysis by GC-NCI-MS was carried out. Method limits of detection (MDLs), ranging between 0.12 and 1.26 pg/g dw, 1.16-2.90 pg/g dw and 2.30-21.1 pg/g lw for sediment, sludge and fish respectively, were much better than those obtained by GC-MS, with improvement factor up to 320. The applicability of the developed methodology was demonstrated by the analysis of real samples collected in a non-producing area, the Ebro river basin (Spain). DP values were up to 1.61 ng/g dw, 18.8 ng/g dw and 2.24 ng/g lw for sediment, sludge and fish samples, respectively. PMID:22695692

Barón, Enrique; Eljarrat, Ethel; Barceló, Damià

2012-07-27

131

Determination of six chemotherapeutic agents in municipal wastewater using online solid-phase extraction coupled to liquid chromatography-tandem mass spectrometry.  

PubMed

Due to the increased consumption of chemotherapeutic agents, their high toxicity, carcinogenicity, their occurrence in the aquatic environment must be properly evaluated. An analytical method based on online solid-phase extraction coupled to liquid chromatography-tandem mass spectrometry was developed and validated. A 1mL injection volume was used to quantify six of the most widely used cytotoxic drugs (cyclophosphamide, gemcitabine, ifosfamide, methotrexate, irinotecan and epirubicin) in municipal wastewater. The method was validated using standard additions. The validation results in wastewater influent had coefficients of determination (R(2)) between 0.983 and 0.998 and intra-day precision ranging from 7 to 13% (expressed as relative standard deviation %RSD), and from 9 to 23% for inter-day precision. Limits of detection ranged from 4 to 20ngL(-1) while recovery values were greater than 70% except for gemcitabine, which is the most hydrophilic compound in the selected group and had a recovery of 47%. Matrix effects were interpreted by signal suppression and ranged from 55 to 118% with cyclophosphamide having the highest value. Two of the target anticancer drugs (cyclophosphamide and methotrexate) were detected and quantified in wastewater (effluent and influent) and ranged from 13 to 60ngL(-1). The proposed method thus allows proper monitoring of potential environmental releases of chemotherapy agents. PMID:24388503

Rabii, Farida W; Segura, Pedro A; Fayad, Paul B; Sauvé, Sébastien

2014-07-15

132

A Method for Multiple Mycotoxin Analysis in Wines by Solid Phase Extraction and Multifunctional Cartridge Purification, and Ultra-High-Performance Liquid Chromatography Coupled to Tandem Mass Spectrometry  

PubMed Central

An analytical method using two solid phase extractions and ultra-high-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS) was developed for the identification and quantification of 14 mycotoxins (patulin, deoxynivalenol, aflatoxins B1, B2, G1, G2, M1, T-2 toxin, HT-2 toxin, zearalenone, fumonisins B1, B2, B3, and ochratoxin A) in domestic and imported wines. Mycotoxins were purified with an Oasis HLB cartridge, followed by a MultiSepTM #229 Ochra. As a result, sufficient removal of the pigments and highly polar matrices from the red wines was achieved. UHPLC conditions were optimized, and 14 mycotoxins were separated in a total of 13 min. Determinations performed using this method produced high correlation coefficients for the 14 mycotoxins (R > 0.990) and recovery rates ranging from 76 to 105% with good repeatability (relative standard deviation RSD < 12%). Twenty-seven samples of domestic and imported wines were analyzed using this method. Although ochratoxin A (OTA) and fumonisins (FMs) were detected in several samples, the FM levels were less than limits of quantification (LOQs) (1 ?g/L), and even the largest of the OTA levels was below the EU regulatory level (2 ?g/L). These results suggest that the health risk posed to consumers from the wines available in Japan is relatively low.

Tamura, Masayoshi; Takahashi, Ayumi; Uyama, Atsuo; Mochizuki, Naoki

2012-01-01

133

A sensitive method for determination of allergenic fragrance terpene hydroperoxides using liquid chromatography coupled with tandem mass spectrometry.  

PubMed

Different compositions of monoterpenes are utilized for their pleasant scent in cosmetics and perfumes. However, the most commonly used fragrance terpenes easily oxidize upon contact with air, forming strongly skin-sensitizing hydroperoxides. Due to their thermolability and low UV absorbance, detection methods for hydroperoxides are scarce. For the first time, a simple and sensitive method using LC/ESI-MS/MS was developed to quantitatively determine hydroperoxides from the common fragrance compounds linalool, linalyl acetate, and limonene. The method was applied to autoxidized petitgrain oil and sweet orange oil. A separation was accomplished using a C3 column. The method LOD for the investigated hydroperoxides in the essential oils was below 0.3 ?g/mL, corresponding to 0.3 ppm. For prevention purposes and according to EU regulations, concentrations in cosmetics exceeding 100 ppm in "rinse-off" and 10 ppm in "stay-on" products of linalool and limonene must be labeled. However, the products may still contain allergens, such as hydroperoxides, formed by oxidative degradation of their parent terpenes. The sensitivity and selectivity of the presented LC/MS/MS method enables detection of hydroperoxides from the fragrance terpenes linalool, linalyl acetate, and limonene. However, for routine measurements, the method requires further validation. PMID:23404959

Rudbäck, Johanna; Islam, Nurul; Nilsson, Ulrika; Karlberg, Ann-Therese

2013-04-01

134

Highly enantioselective oxidative couplings of 2-naphthols catalyzed by chiral bimetallic oxovanadium complexes with either oxygen or air as oxidant.  

PubMed

The chiral bimetallic oxovanadium complexes have been designed for the enantioselective oxidative coupling of 2-naphthols bearing various substituents at C6 and/or C7. The chirality transferring from the amino acid to the axis of the biphenyl in oxovanadium complexes 2 was found to occur with the use of UV and CD spectra and DFT calculation. The homo-coupling reaction with oxygen as the oxidant was promoted by 5 mol % of an oxovanadium complex derived from L-isoleucine and achiral biphenol to afford binaphthols in nearly quantitative yields with high enantioselectivities of up to 98% ee. An oxovanadium complex derived from L-isoleucine and H8-binaphthol is highly efficient at catalyzing the air-oxidized coupling of 2-naphthols with excellent enantioselectivities of up to 97% ee. 51V NMR study shows that the oxovanadium complexes have two vanadium(V) species. Kinetic studies, the cross-coupling reaction, and HRMS spectral studies on the reaction have been carried out and illustrate that two vanadium(V) species are both involved in catalysis and that the coupling reaction undergoes a radical-radical mechanism in an intramolecular manner. Quantum mechanical calculations rationalize the importance of the cooperative effects of the axial chirality matching S-amino acids on the stereocontrol of the oxidative coupling reaction. The application of the transformation in the preparation of chiral ligands and conjugated polymers confirms the importance of the current process in organic synthesis. PMID:17956093

Guo, Qi-Xiang; Wu, Zhi-Jun; Luo, Zhi-Bin; Liu, Quan-Zhong; Ye, Jian-Liang; Luo, Shi-Wei; Cun, Lin-Feng; Gong, Liu-Zhu

2007-11-14

135

A serially coupled stationary phase method for the determination of urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine by liquid chromatography ion trap tandem mass spectrometry.  

PubMed

Oxidative attack to DNA is of particular interest since DNA modifications can lead to heritable mutations. The most studied product of DNA oxidation is 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG). While 8-oxodG determination in blood and tissue cells is prone to artifacts, its measurement in urine employing liquid chromatography tandem mass spectrometry (LC-MS/MS) has gained more and more interest for increased reliability. LC-MS/MS can be affected by matrix effects and this is particularly true when ion trap is used as MS analyzer, due to ion accumulation in the trap and related space charge effect. In the present work, we have developed a LC-MS/MS method where the combination of cation exchange and reverse phase solid phases resulted in LC separation optimization. This together with the employment of an isotopically labeled internal standard, allowed the usage of ion trap LC-MS/MS, typically not employed for quantitative measurement in biological samples, for the measurement of 8-oxodG in urine samples from control populations. Four different urine matrices were employed for method validation. Limit of quantitation was set at least at 0.5 ng/ml. While analyzing urine samples from healthy volunteers, 8-oxodG levels reported as ng/ml were statistically different comparing males with females (p<0.05, Mann Whitney test); while comparing results normalized for creatinine no statistical significant difference was found. Mean urinary 8-oxodG level found in healthy volunteers was 1.16±0.46 nmol/mmol creatinine. The present method by enhancing at best the chromatographic performances allows the usage of ion trap LC-MS/MS for the measurement of 8-oxodG in urine samples from control populations. PMID:24251117

Rota, Cristina; Cristoni, Simone; Trenti, Tommaso; Cariani, Elisabetta

2013-01-01

136

Screening for anthocyanins using high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry with precursor-ion analysis, product-ion analysis, common-neutral-loss analysis, and selected reaction monitoring  

Microsoft Academic Search

A systematic method for anthocyanin identification using tandems mass spectrometry (MS\\/MS) coupled to high-performance liquid chromatography (HPLC) with photo-diode array detection (PDA) was developed. Scan for the precursor ions of commonly found anthocyanidins (cyanidin, delphinidin, malvidin, pelargonidin, petunidin, and peonidin) using LC\\/MS\\/MS on a triple quadrupole instrument allows for the specific determination of each category of anthocyanins. Further characterization of

Qingguo Tian; M. Monica Giusti; Gary D. Stoner; Steven J. Schwartz

2005-01-01

137

Identification of a novel selenium metabolite, Se-methyl- N-acetylselenohexosamine, in rat urine by high-performance liquid chromatography–inductively coupled plasma mass spectrometry and –electrospray ionization tandem mass spectrometry  

Microsoft Academic Search

The major urinary metabolite of selenium (Se) in rats was identified by HPLC–inductively coupled argon plasma mass spectrometry (ICP–MS) and –electrospray tandem mass spectrometry (ESI–MS\\/MS). As the urine sample was rich in matrices such as sodium chloride and urea, it was partially purified to meet the requirements for ESI–MS. The group of signals corresponding to the Se isotope ratio was

Yasumitsu Ogra; Kazuya Ishiwata; Hiromitsu Takayama; Norio Aimi; Kazuo T Suzuki

2002-01-01

138

Determination of ochratoxin A and T-2 toxin in alcoholic beverages by hollow fiber liquid phase microextraction and ultra high-pressure liquid chromatography coupled to tandem mass spectrometry  

Microsoft Academic Search

A new method for the determination of ochratoxin A and T-2 toxin in alcoholic beverages (wine and beer) by hollow fiber liquid microextraction was optimized. The extraction step was followed by ultra high-pressure liquid chromatography coupled to tandem mass spectrometry (UHPLC–MS\\/MS). The extraction procedure was based on the extraction of mycotoxins from the sample to the organic solvent (1-octanol) immobilized

R. Romero-González; A. Garrido Frenich; J. L. Martínez Vidal; M. M. Aguilera-Luiz

2010-01-01

139

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

140

Demonstration of side coupling to cladding modes through zinc oxide nanorods grown on multimode optical fiber.  

PubMed

A novel concept is introduced that utilizes the scattering properties of zinc oxide nanorods to control light guidance and leakage inside optical fibers coated with nanorods. The effect of the hydrothermal growth conditions of the nanorods on light scattering and coupling to optical fiber are experimentally investigated. At optimum conditions, 5% of the incident light is side coupled to the cladding modes. This coupling scheme could be used in different applications such as distributed sensors and light combing. Implementation of the nanorods on fiber provides low cost and controllable nonlithography-based solutions for free space to fiber coupling. Higher coupling efficiencies can be achieved with further optimization. PMID:24104829

Fallah, H; Chaudhari, M; Bora, T; Harun, S W; Mohammed, W S; Dutta, J

2013-09-15

141

Cr(III) oxidation coupled with Mn(II) bacterial oxidation in the environment  

Microsoft Academic Search

Purpose  Cr(III) oxidation to Cr(VI) significantly increases Cr mobility and toxicity and thus its environmental risks. Manganese (Mn)\\u000a oxides may serve as the potential oxidants of Cr(III) in environment. Natural Mn oxides in the environment are believed to\\u000a be derived from bacterial oxidation. The objective of this study was to examine the Cr(III) oxidation capacity of biogenic\\u000a Mn oxide and the

Ji-Zheng He; You-Ting Meng; Yuan-Ming Zheng; Li-Mei Zhang

2010-01-01

142

Selective oxidative homo- and cross-coupling of phenols with aerobic catalysts.  

PubMed

Simple catalysts that use atom-economical oxygen as the terminal oxidant to accomplish selective ortho-ortho, ortho-para, or para-para homo-couplings of phenols are described. In addition, chromium salen catalysts have been discovered as uniquely effective in the cross-coupling of different phenols with high chemo- and regioselectivity. PMID:24797179

Lee, Young Eun; Cao, Trung; Torruellas, Carilyn; Kozlowski, Marisa C

2014-05-14

143

Mixed-mode liquid chromatography coupled to tandem mass spectrometry for the analysis of aminoglycosides in meat.  

PubMed

A novel LC-MS/MS method has been developed for the determination of 13 aminoglycoside antibiotics in meat products. Among the chromatographic columns tested, the mixed-mode Obelisc R provided the best performance. Electrospray has been used for the coupling of the LC and the effect of temperature on the ionization has been evaluated. The mass spectra of AGs have been studied in order to select the most adequate precursor and product ions for quantitation and confirmation in SRM mode, showing that the single charged [M+H](+) provided better precisions than the double charged [M+2H](2+). Accurate mass measurements have been performed in order to confirm the molecular composition of the product ions, allowing the establishment of a new mechanism for some product ions of STR and DHSTR. A sample treatment based on an extraction and a SPE clean-up has been applied to a wide variety of meat products such as frankfurters; sausages; and minced meat of pork, veal, and chicken. Method limits of quantitation in the low microgram per kilogram level (1-50 ?g kg(-1)), precisions %RSD below 15 % and accuracies expressed as relative errors below 23 % have been obtained, making the proposed method suitable for routine analysis. PMID:24881895

Alechaga, Elida; Moyano, Encarnación; Galceran, M Teresa

2014-08-01

144

Demonstrating Advanced Oxidation Coupled With Biodegradation For Removal of Carbamazepine  

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...

145

Oxidative coupling of methane. II. Formation of active sites by lead and tin oxides on MgO  

Microsoft Academic Search

The oxidative coupling of methane has been studied over Sn-Mg-O catalysts with varying amounts of Sn. The addition of small amounts of tin oxide to MgO increased both the rate of methane conversion and the Câ selectivity. A maximum Câ selectivity of 40% was obtained over 0.4 at.% Sn-Mg-O at 780° at a methane conversion of 20%. The maximum in

S. K. Agarwal; R. A. Migone; G. Marcelin

1990-01-01

146

Palladium-catalyzed oxidative carbonylative coupling of arylboronic acids with terminal alkynes to alkynones.  

PubMed

We describe here an interesting palladium-catalyzed oxidative carbonylation of arylboronic acids with terminal alkynes. By the appropriate combination of a palladium salt, a ligand, and an oxidant, the desired alkynones were isolated in moderate to good yields. Notably, all the reactions were performed at room temperature, and moisture and air can be tolerated by this procedure. More importantly, this is the first example of oxidative carbonylative coupling of arylboronic acids with alkynes which filled the missing link in carbonylative coupling reactions. PMID:24968345

Natte, Kishore; Chen, Jianbin; Neumann, Helfried; Beller, Matthias; Wu, Xiao-Feng

2014-08-14

147

Plasma-Chemical Synthesis of Oxide Powders Using Transformer-Coupled Discharge  

NASA Astrophysics Data System (ADS)

An experimental investigation of transformer-coupled discharge in an Ar-O2 mixture with the addition of SiCl4, TiCl4 and ZrCl4 has been carried out under the atmospheric pressure of plasma-forming gases. Discharge power and discharge heat losses have been determined, and the dispersion and phase composition of reaction products (oxide powders) has been analyzed with SEM and X-ray diffraction analysis. Investigations reveal the formation of ultrafine oxide powders in the case of vaporized chloride (SiCl4 and TiCl4) injecting into the transformer coupled discharge. In the case of fine powder (ZrCl4) injection, full oxidation was not observed and reaction products consisted of a mixture of ZrO2 and ZrOCl2. A conclusion has been made regarding the perspectives of using transformer-coupled discharge to produce ultrafine oxide powders.

M. Ulanov, I.; V. Isupov, M.; Yu Litvinsev, A.; A. Mischenko, P.

2013-04-01

148

The effects of transition metal oxides on the methane oxidative coupling activity of doped MgO catalysts  

SciTech Connect

Magnesium oxide samples doped with different loadings of zinc and manganese oxides with and without lithium carbonate being present in the preparation were evaluated for their catalytic activity towards the oxidative coupling of methane to higher hydrocarbons. When Li{sub 2}CO{sub 3} is excluded, the exhaustive reactions of methane to form carbon oxides are favored. With a doped Li{sub 2}CO{sub 3} is excluded, the exhaustive reactions of methane to form carbon oxides are favored. With a doped Li{sub 2}CO{sub 3}/MgO catalyst, a methane conversion of > 25% and a selectivity to C{sub 2} hydrocarbons of near 60% was retained but not enhanced in the presence of different loadings of Zn oxide at 805 C. Low loading of Mn oxide on Li{sub 2}CO{sub 3}/MgO resulted in a methane conversion of > 35% and a selectivity to C{sub 2} hydrocarbons of near 50%. At high Mn oxide loadings the methane conversion decreases and the C{sub 2} selectivity is less than 30% due to more exhaustive oxidation. The activity of the doped catalyst is related to the physico-chemical properties, especially surface morphology, and metal oxide reducibility on the basis of SEM, XRD and electron microprobe analysis.

Larkins, F.P.; Nordin, M.R. (Univ. of Tasmania, Hobart (Australia))

1991-07-01

149

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

150

Determination of eight nitrosamines in water at the ng L(-1) levels by liquid chromatography coupled to atmospheric pressure chemical ionization tandem mass spectrometry.  

PubMed

In this work, we have developed a sensitive method for detection and quantification of eight N-nitrosamines, N-nitrosodimethylamine (NDMA), N-nitrosomorpholine (NMor), N-nitrosomethylethylamine (NMEA), N-nitrosopirrolidine (NPyr), N-nitrosodiethylamine (NDEA), N-nitrosopiperidine (NPip), N-nitroso-n-dipropylamine (NDPA) and N-nitrosodi-n-butylamine (NDBA) in drinking water. The method is based on liquid chromatography coupled to tandem mass spectrometry, using atmospheric pressure chemical ionization (APCI) in positive mode with a triple quadrupole analyzer (QqQ). The simultaneous acquisition of two MS/MS transitions in selected reaction monitoring mode (SRM) for each compound, together with the evaluation of their relative intensity, allowed the simultaneous quantification and reliable identification in water at ppt levels. Empirical formula of the product ions selected was confirmed by UHPLC-(Q)TOF MS accurate mass measurements from reference standards. Prior to LC-MS/MS QqQ analysis, a preconcentration step by off-line SPE using coconut charcoal EPA 521 cartridges (by passing 500 mL of water sample) was necessary to improve the sensitivity and to meet regulation requirements. For accurate quantification, two isotope labelled nitrosamines (NDMA-d(6) and NDPA-d(14)) were added as surrogate internal standards to the samples. The optimized method was validated at two concentration levels (10 and 100 ng L(-1)) in drinking water samples, obtaining satisfactory recoveries (between 90 and 120%) and precision (RSD<20%). Limits of detection were found to be in the range of 1-8 ng L(-1). The described methodology has been applied to different types of water samples: chlorinated from drinking water and wastewater treatment plants (DWTP and WWTP, respectively), wastewaters subjected to ozonation and tap waters. PMID:21819861

Ripollés, Cristina; Pitarch, Elena; Sancho, Juan V; López, Francisco J; Hernández, Félix

2011-09-19

151

Detection of seven pesticides in cucumbers using hollow fibre-based liquid-phase microextraction and ultra-high pressure liquid chromatography coupled to tandem mass spectrometry.  

PubMed

A liquid-phase microextraction (LPME) methodology based on the use of porous polyvinylidene fluoride (PVDF) hollow fibres was developed for extracting seven pesticides from cucumbers. The seven pesticides include propoxur, carbofuran, atrazine, cyanatryn, metolachlor, prometryn and tebuconazole. The PVDF hollow fibre provides higher extraction efficiency due to its higher porosity and better solvent compatibility. A new desorption methodology was developed since some pesticides were absorbed by the wall pore of the PVDF. Ultra-high pressure liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS) was used for pesticide analysis. In order to obtain high recoveries and enrichment factors of the analytes, several parameters such as method of sealing, acceptor phase (organic solvents), stirring speed, extraction time, salting out effect, desorption mode and time were optimized. A fast, simple method for closing fibre ends was practiced by using mechanical crimping. Pesticides were extracted from the sample to the organic solvent and then desorbed in a mixture of methanol:water (1:1 v/v) prior to chromatographic analysis. Limits of detection (LOD) for the multi-reaction-monitoring (MRM) mode of the method varies from 0.01 to 0.31 ?g/kg with optimized sample preparation. Calibration curves are linear with R² ? 0.991. Enrichment factor of the hollow fibre LPME ranges from 100 to 147. Matrix effect has been considered and is in the range of 76-122%. The relative recoveries from cucumber samples are between 63% and 119% with the relative standard deviation (RSD, n=6) lower than 20%. PMID:22682952

Wang, Jianfeng; Du, Zhenxia; Yu, Wenlian; Qu, Shuping

2012-07-20

152

Pharmacokinetic study of free mangiferin in rats by microdialysis coupled with microbore high-performance liquid chromatography and tandem mass spectrometry.  

PubMed

Mangiferin (2-beta-D-glucopyranosyl-1,3,6,7-tetrahydroxyxanthen-9-one) has been isolated from the herbal root of Anemarrhena asphodeloides Bung showing antioxidative, antiviral, and anticancer effect. An in vivo microdialysis sampling method coupled to microbore high-performance liquid chromatography (HPLC) was employed for continuous monitoring of free mangiferin in rat blood. Microdialysis probes were inserted into the jugular vein/right atrium and brain striatum of Sprague-Dawley rats, and mangiferin at doses of 10, 30 or 100 mg/kg were then administered via the femoral vein. Dialysates were collected every 10 min and injected directly into a microbore HPLC system. Mangiferin was separated by a reversed-phase C18 microbore column (150 x 1 mm) from dialysate within 10 min. The mobile phase consisted of acetonitrile-0.05% phosphoric acid-tetrahydrofuran (10:75:15, v/v/v) with a flow-rate of 0.05 ml/min. The wavelength of the UV detector was set at 257 nm. The limit of quantification for mangiferin was 0.05 microg/ml and in vivo recovery of mangiferin at concentrations of 1, 5 and 10 microg/ml was in range of 37.7-39.8%. The results indicate that the pharmacokinetics of mangiferin at doses of 10-30 mg/kg reveals a linear relation, while doses of 30-100 mg/kg show a nonlinear pharmacokinetic phenomenon. Mangiferin was undetectable in brain dialysate. The proposed method provides a technique for rapid and sensitive analysis of free mangiferin in rat blood and further application in pharmacokinetic study. Furthermore, the metabolites of mangiferin in the rat bile were confirmed by LC electrospray ionization (ESI) tandem mass spectrometry (MS-MS). PMID:12613830

Lai, Ling; Lin, Lie-Chwen; Lin, Jer-Huei; Tsai, Tung-Hu

2003-02-14

153

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

154

Chemical synthesis of dioxygen-18 labelled omega-/beta-oxidized cysteinyl leukotrienes: analysis by gas chromatography-mass spectrometry and gas chromatography-tandem mass spectrometry.  

PubMed

Cysteinyl leukotrienes (LT) C4, LTD4 and LTE4 are potent mediators of anaphylaxis and inflammation. LTE4 is extensively metabolized in man mainly by omega-oxidation followed by subsequent beta-oxidation to more polar and biologically inactive metabolites. This paper describes a method for the synthesis of [1,20-18O2]-carboxy-LTE4, [1,18-18O2]-carboxy-dinor-LTE4, and [1,16-18O2]-carboxy-14,15-dihydro-tetranor-LTE4 starting from the unlabelled dimethyl esters of 20-carboxy-LTA4, 18-carboxy-dinor-LTA4 and 16-carboxy-14,15-dihydro-tetranor-LTA4, respectively, by separate chemical conjugation with cysteine hydrochloride in H2-18O-methanol followed by alkaline hydrolysis with Li18OH. The isotopic purity of the isolated reaction products was 94% at 18O for all three preparations while only 0.3% remained unlabelled as confirmed by negative-ion chemical-ionization gas chromatography-mass spectrometry (GC-NICI-MS) after their catalytical reduction/desulphurization and derivatization. The 18O2-labelled compounds are demonstrated to be suitable internal standards for quantification by GC-NICI-MS and GC-NICI-tandem MS. We found by GC-NICI-tandem MS that the excretion rate of 20-carboxy-LTE4 is comparable to that of LTE4 (both in nmol/mol creatinine, mean +/- S.E.) in healthy children (26.7 +/- 4.7 vs. 32.0 +/- 6.0, n = 9) and adults (13.9 +/- 1.1 vs. 27.2 +/- 5.4, n = 3). PMID:7663693

Tsikas, D; Fauler, J; Frölich, J C

1995-05-19

155

Quantitation of sorafenib and its active metabolite sorafenib N-oxide in human plasma by liquid chromatography-tandem mass spectrometry  

PubMed Central

A simple and rapid method with high performance liquid chromatography/tandem mass spectrometry is described for the quantitation of the kinase inhibitor sorafenib and its active metabolite sorafenib N-oxide in human plasma. A protein precipitation extraction procedure was applied to 50 µL of plasma. Chromatographic separation of the two analytes, and the internal standard [2H3 13C]-sorafenib, was achieved on a C18 analytical column and isocratic flow at 0.3 mL/min for 4 min. Mean within-run and between-run precision for all analytes were <6.9 % and accuracy was <5.3%. Calibration curves were linear over the concentration range of 50 to 10,000 ng/mL for sorafenib and 10 to 2,500 ng/mL for sorafenib N-oxide. This method allows a specific, sensitive, and reliable determination of the kinase inhibitor sorafenib and its active metabolite sorafenib N-oxide in human plasma in a single analytical run.

Li, Lie; Zhao, Ming; Navid, Fariba; Pratz, Keith; Smith, B. Doug; Rudek, Michelle A.; Baker, Sharyn D.

2010-01-01

156

Coupled catalytic oscillators: CO oxidation over polycrystalline Pt  

Microsoft Academic Search

The authors have observed unusual oscillation in the rate of CO oxidation over a polycrystalline Pt wire loop. In contrast to simple oscillations between states of low and high reactivity, the unusual oscillations occurred between low, intermediate, and high values of the reaction rate. Experiments were performed at atmospheric pressure in a gas flow reactor over a range of gas

P. K. Tsia; M. B. Maple; R. K. Herz

1988-01-01

157

Palladium-catalyzed oxidative CH/CH cross-coupling of pyridine N-oxides with five-membered heterocycles.  

PubMed

Using Ag2CO3 as an additive, we developed the Pd-catalyzed intermolecular C-H/C-H cross-coupling of pyridine N-oxides with five-membered heterocycles such as 1-benzyl-1,2,3-triazoles, thiophens and furans. This protocol provides an efficient and regioselective approach for the synthesis of unsymmetrical biheteroaryl molecules. PMID:24999920

Liu, Wei; Yu, Xin; Li, Yahui; Kuang, Chunxiang

2014-07-22

158

Electrochemical production of hydrogen coupled with the oxidation of arsenite.  

PubMed

The production of hydrogen accompanied by the simultaneous oxidation of arsenite (As(III)) was achieved using an electrochemical system that employed a BiOx-TiO2 semiconductor anode and a stainless steel (SS) cathode in the presence of sodium chloride (NaCl) electrolyte. The production of H2 was enhanced by the addition of As(III) during the course of water electrolysis. The synergistic effect of As(III) on H2 production can be explained in terms of (1) the scavenging of reactive chlorine species (RCS), which inhibit the production of H2 by competing with water molecules (or protons) for the electrons on the cathode, by As(III) and (2) the generation of protons, which are more favorably reduced on the cathode than water molecules, through the oxidation of As(III). The addition of 1.0 mM As(III) to the electrolyte at a constant cell voltage (E cell) of 3.0 V enhanced the production of H2 by 12% even though the cell current (I cell) was reduced by 5%. The net effect results in an increase in the energy efficiency (EE) for H2 production (?EE) by 17.5%. Furthermore, the value ?EE, which depended on As(III) concentration, also depended on the applied E cell. For example, the ?EE increased with increasing As(III) concentration in the micromolar range but decreased as a function of E cell. This is attributed to the fact that the reactions between RCS and As(III) are influenced by both RCS concentration depending on E cell and As(III) concentration in the solution. On the other hand, the ?EE decreased with increasing As(III) concentration in the millimolar range due to the adsorption of As(V) generated from the oxidation of As(III) on the semiconductor anode. In comparison to the electrochemical oxidation of certain organic compounds (e.g., phenol, 4-chlorophenol, 2-chlorophenol, salicylic acid, catechol, maleic acid, oxalate, and urea), the ?EE obtained during As(III) oxidation (17.5%) was higher than that observed during the oxidation of the above organic compounds (?EE = 3.0-15.3%) with the exception of phenol at 22.1%. The synergistic effect of As(III) on H2 production shows that an energetic byproduct can be produced during the remediation of a significant inorganic pollutant. PMID:24386985

Kim, Jungwon; Kwon, Daejung; Kim, Kitae; Hoffmann, Michael R

2014-02-01

159

In situ coupled oxidation cycle catalyzed by highly active and reusable Pt-catalysts: dehydrogenative oxidation reactions in the presence of a catalytic amount of o-chloranil using molecular oxygen as the terminal oxidant.  

PubMed

An in situ coupled oxidation cycle that allows catalytic oxidation of a substrate with catalytic amounts of o-chloranil and novel reusable polymer-immobilized platinum nanocluster catalysts using molecular oxygen as the terminal oxidant was developed. PMID:20871889

Miyamura, Hiroyuki; Maehata, Kanako; Kobayashi, Shu

2010-11-14

160

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

161

Synthesis of the carbon framework of scholarisine A by intramolecular oxidative coupling.  

PubMed

Scholarisine A, isolated from the leaves of Alstonia scholaris, is a monoterpene indole alkaloid with an unprecedented cage-like structure. In this paper, preparation of the distinctive cage-like core skeleton of scholarisine A is described. The key feature of this synthetic strategy is an intramolecular oxidative coupling reaction at the late stage to construct a 10-oxa-tricyclo[5.3.1.0(3,?8)]undecan-9-one structure fused with indolenine. Intramolecular oxidative coupling by using N-iodosuccinimide gave the carbon framework of scholarisine A in moderate yield, which is the first example of intramolecular oxidative-coupling reaction between non-activated enolate and indole. This study lays the foundation for continued investigations towards the total synthesis of scholarisine A. PMID:23400955

Watanabe, Tsugunori; Kato, Nobuki; Umezawa, Naoki; Higuchi, Tsunehiko

2013-03-25

162

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

163

Cr(III) Oxidation Coupled With Microbially-Mediated Mn(II) Oxidation  

SciTech Connect

Cr(VI) can be reduced to less toxic and mobile Cr(III) species through abiotic and biological processes. Reductive immobilization of Cr(VI) has been widely explored as a cost effective technology for site remediation; Mn oxides are regarded as primary oxidants for Cr(III) oxidation in the environment; and Generation of Mn oxides from Mn(II) in natural environments is believed to be biologically catalyzed.

Youxian Wu; Baolin Deng

2006-04-05

164

Iron-catalyzed radical oxidative coupling reaction of aryl olefins with 1,3-dithiane.  

PubMed

An alternative method to an iron-catalyzed radical oxidative cross-coupling reaction followed by 2-chloro-1,3-dithiane and aryl olefins for the synthesis of ?-chloro substituent 1,3-dithiane products is presented. The described method has the advantage of mildness of the reaction conditions and tolerates a variety of functional groups. Preliminary mechanistic studies have confirmed the first example of a coupling of 1,3-dithiane with unactivated alkenes that proceeds via an iron-catalyzed oxidative radical intermediate along the reaction pathway. PMID:24749868

Du, Wenbin; Tian, Lixia; Lai, Junshan; Huo, Xing; Xie, Xingang; She, Xuegong; Tang, Shouchu

2014-05-01

165

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.

Guo, Fenghai; Clift, Michael D.

2013-01-01

166

Oxidative coupling of arylboronic acids with arenes via Rh-catalyzed direct C-H arylation.  

PubMed

Oxidative coupling of three different arenes and a thiophene derivative with various arylboronic acids was achieved with a [RhCl(C2H4)2]2/P[p-(CF3)C6H4]3 catalyst system. Commercially available 2,2,6,6-tetramethylpiperidine-N-oxyl radical (TEMPO) was used as a stoichiometric oxidant. A 2-pyridyl group and an imine functional group served as ortho-directing groups to mediate the direct C-H arylation by a Rh complex. Moderate to excellent yields were obtained for the coupling reactions. PMID:18072783

Vogler, Thomas; Studer, Armido

2008-01-01

167

Oxidative Phosphorylation coupled with Aerobic and Anaerobic Respiration in a Bacterial Cell-free System  

Microsoft Academic Search

IT has been presumed that in anaerobic respiration, such as nitrate1 or sulphate2 respiration, formation of some high-energy phosphate is coupled with the process in a similar way to oxidative phosphorylation in aerobic respiration. We have reported3 that, in the whole cell system of Pseudomonas denitrificans, radioactive inorganic phosphate (32Pi) is incorporated into labile organic phosphates coupled with the denitrification

Tomoko Ohnishi; Takeshi Mori

1962-01-01

168

Kinetic studies of the oxidative coupling of methane over a NaOH\\/CaO catalyst  

Microsoft Academic Search

The effects of the partial pressures of oxygen and methane as well as temperature on the rates of C[sub 2] hydrocarbon formation, carbon oxide formation, and total methane conversion in the oxidative coupling of methane over a NaOH\\/CaO catalyst were studied at differential operating conditions in a microcatalytic fixed-bed reactor. Temperature and partial pressures of the reactants were varied within

L. Lehmann; M. Baerns

1992-01-01

169

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

170

Spin Structure in an Interfacially Coupled Epitaxial Ferromagnetic Oxide Heterostructure  

NASA Astrophysics Data System (ADS)

We report the spin structure of an exchange-biased ferromagnetic oxide heterostructure, La0.67Sr0.33MnO3/SrRuO3, through magnetization and polarized neutron reflectometry measurements. We reveal that the magnetization reversal process of the La0.67Sr0.33MnO3 biased layer critically depends on the frozen-in spin structure of the SrRuO3 biasing layer during the cooling process. Furthermore, we observe unexpected double-shifted hysteresis loops of the biased layer that originates from the formation of lateral 180° magnetic domains within the biasing layer, a new mechanism not found in conventional exchange-bias systems.

Ke, X.; Belenky, L. J.; Lauter, V.; Ambaye, H.; Bark, C. W.; Eom, C. B.; Rzchowski, M. S.

2013-06-01

171

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

172

Comparative characterization of basicity and acidity of metal oxide catalysts for the oxidative coupling of methane by different methods  

Microsoft Academic Search

A comprehensive study of the surface basicity and acidity of alkaline earth metal oxides, La2O3\\/CaO, CeO2\\/CaO and ZnO-doped NaOH (11 mol-%)\\/CaO which had earlier been tested as catalysts for the oxidative coupling of methane was performed. For determining the acid-base properties two probe reactions, i.e., the decomposition of 2-propanol to acetone and propene and the retroaldolisation of diacetone alcohol, further

Petra Käßner; Manfred Baerns

1996-01-01

173

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  

Microsoft Academic Search

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+NH4]+ in positive mode and [M?H]? and [M?2H]2? ions in negative mode. The MS\\/MS spectra of the [M?H]?

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

2011-01-01

174

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

175

Coupled-map-lattice model for spontaneous pore formation in anodic oxidation  

NASA Astrophysics Data System (ADS)

We construct a coupled map lattice model for spontaneous pore formation in anodic oxidation in two dimensions and perform numerical simulations, after we explain steady flat solutions, their linear stability, and a single pore solution for a model of Parkhutik and Shershulsky.

Sakaguchi, Hidetsugu; Zhao, Jie

2010-03-01

176

Coupled-map-lattice model for spontaneous pore formation in anodic oxidation  

Microsoft Academic Search

We construct a coupled map lattice model for spontaneous pore formation in anodic oxidation in two dimensions and perform numerical simulations, after we explain steady flat solutions, their linear stability, and a single pore solution for a model of Parkhutik and Shershulsky.

Hidetsugu Sakaguchi; Jie Zhao

2010-01-01

177

Coupled-map-lattice model for spontaneous pore formation in anodic oxidation.  

PubMed

We construct a coupled map lattice model for spontaneous pore formation in anodic oxidation in two dimensions and perform numerical simulations, after we explain steady flat solutions, their linear stability, and a single pore solution for a model of Parkhutik and Shershulsky. PMID:20365743

Sakaguchi, Hidetsugu; Zhao, Jie

2010-03-01

178

Ferric hydrogensulfate catalyzed aerobic oxidative coupling of 2-naphthols in water or under solvent free conditions  

Microsoft Academic Search

The symmetric oxidative coupling reactions of 2-naphthol derivatives with both ferric hydrogensulfate in water and silica ferric hydrogensulfate in solvent free conditions were carried out. The advantages of this green procedure are: inexpensive catalyst or co-catalyst, reusability of catalyst, organic solvent-free procedures and simple workup.

Hossein Eshghi; Mehdi Bakavoli; Hassanali Moradi

2009-01-01

179

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

PubMed

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. PMID:24088951

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

2013-11-21

180

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; Louise Meyer, Rikke; Peter Revsbech, Niels; Schramm, Andreas; Peter Nielsen, Lars; Risgaard-Petersen, Nils

2014-08-01

181

Simultaneous solid phase extraction coupled with liquid chromatography tandem mass spectrometry and gas chromatography tandem mass spectrometry for the highly sensitive determination of 15 endocrine disrupting chemicals in seafood.  

PubMed

This study aimed to develop a sensitive and reliable multi-residue method for the determination of trace amounts of endocrine disrupting chemicals including five phthalate esters (PAEs), five monoalky phthalate esters (MPEs), four alkylphenols (APs) and bisphenol A (BPA) in seafood. Ultrasonic liquid extraction was selected for extraction based on acetonitrile, instead of frequently-used n-hexane, due to its lower background of PAEs. Application of solid phase extraction (SPE) with primary secondary amine (PSA, 1g/6mL) cartridge achieved the relatively low matrix effects for MPEs and BPA in seafood. To our knowledge, it is the first study reporting about simultaneous extraction and purification of PAEs, MPEs, APs and BPA in biota samples. To obtain the maximum sensitivity, both liquid chromatography tandem mass spectrometry (LC-MS/MS) and gas chromatography tandem mass spectrometry (GC-MS/MS) were applied for analysis. This method was validated and tested on fish, mollusk and prawn. Sufficient linearity was verified by Mandel's fitting test for the matrix-matched calibrations used in this study for MPEs, APs and BPA, between 0.5ng/g and 200ng/g or 400ng/g. And correlation coefficients of all calibrations suppressed 0.99 for all analytes. Good recoveries were obtained, ranging from 60% to 127% for most compounds. The sensitivity was good with method detection limits (MDLs) of 0.015-2.2ng/g wet weight (ww) for all compounds. Most MDLs are much lower than those in previous reports. The sensitive method was then applied on real fish, mollusk and prawn samples from the Yangtze River Delta sea area (China), and all the target compounds were detected with the maximum concentrations of PAEs, MPEs, APs and BPA up to 219.3ng/g ww, 51.4ng/g ww, 62.0ng/g ww and 8.6ng/g ww, respectively. PMID:25023229

Gu, Yun-Yun; Yu, Xue-Jun; Peng, Jin-Feng; Chen, Shu-Bing; Zhong, Ying-Ying; Yin, Da-Qiang; Hu, Xia-Lin

2014-08-15

182

Tandem Mass Spectrometry-based Detection of C4?-Oxidized Abasic Sites at Specific Positions in DNA Fragments  

PubMed Central

Oxidative damage to DNA has been linked to aging, cancer, and other biological processes. Reactive oxygen species and various antitumor agents including bleomycin and ionizing radiation have been shown to cause oxidative DNA sugar damage. Detection of DNA lesions is important for understanding the toxicological or therapeutic consequences associated with such agents. C4?-oxidized abasic sites (C4-AP) are produced by the antitumor drug bleomycin and ionizing radiation. The currently available methods for detection of C4-AP cannot provide both structural and sequence information. We have developed an LC- ESI-MS based approach for specific detection and mapping of C4-AP from a mixture of lesions. We show using Fe-bleomycin-damaged DNA, that C4-AP can be detected at cytosine and thymine sites by direct mass spectrometric (MS) analysis. Our results reveal that collision-induced dissociation of C4-AP-containing oligonucleotides results in preferential fragmentation at C4-AP sites with the formation of the unique a* ions (18 a.m.u more than the a-B ions) that allow mapping of the C4-AP sites. Various chemical modification strategies (e.g. reduction with NaBH4 and NaBD4 and derivatization with methoxyamine and hydrazine, followed by liquid-chromatography (LC)-MS analysis) were also used for unambiguous detection of C4-AP sites. Finally, we show that the methods described here can detect the presence of C4-AP at specific sites in a complex sample such as hydroxyl radical-damaged DNA. The LC-MS approach was also used for the simultaneous detection of the other C4?-oxidation end product, 3?-phosphoglycolate (3PG) at a specific site in hydroxyl radical-damaged DNA. Thus, LCMS provides a rapid and direct approach for the detection and mapping of oxidative DNA lesions.

Chowdhury, Goutam; Guengerich, F. Peter

2013-01-01

183

Chromium(III) Oxidation Coupled with Microbially Mediated Mn(II) Oxidation  

Microsoft Academic Search

Reductive immobilization of Cr(VI) has been widely explored as a cost-effective approach for Cr-contaminated site remediation. In soils containing manganese oxides, however, the immobilized form of chromium, i.e., Cr(III), could potentially be reoxidized. In this study, batch experiments were conducted to assess whether there were any microbial processes that could accelerate Cr(III) oxidation in aerobic, manganese-containing systems. The results showed

Youxian Wu; Baolin Deng; Huifang Xu; Hiromi Kornishi

2005-01-01

184

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

185

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.

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

2013-01-01

186

Nanocrystal bilayer for tandem catalysis  

NASA Astrophysics Data System (ADS)

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; Habas, Susan E.; Soejima, Tetsuro; Aliaga, Cesar E.; Somorjai, Gabor A.; Yang, Peidong

2011-05-01

187

"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

188

Reusable solid-phase microextraction coating for direct immersion whole-blood analysis and extracted blood spot sampling coupled with liquid chromatography-tandem mass spectrometry and direct analysis in real time-tandem mass spectrometry.  

PubMed

Three different biocompatible polymers were tested and evaluated in order to improve the whole-blood biocompatibility of previously developed C18-polyacrylonitrile (C18-PAN) thin-film solid-phase microextraction (SPME) coating. Among all methods of modification, UV-dried thin PAN-over C18-PAN provided the best results. This coating presented reusable properties and reproducible extraction efficiency for at least 30 direct extractions of diazepam from whole blood [relative standard deviation (RSD) = 12% using external calibration and 4% using isotope dilution calibration]. The amount of absolute recovery for direct immersion analysis and based on the free concentration of diazepam in blood matrix was about 4.8% (desorption efficiency = 98%). The limit of quantitation (LOQ) for the developed solid-phase microextraction liquid chromatography-tandem mass spectrometry (SPME-LC-MS/MS) method for direct whole-blood analysis was 0.5 ng/mL. The optimized modification of the coating was then used for an extracted blood spot (EBS) sampling approach, a new sampling method which is introduced to address the limitations of dried blood spot sampling. EBS was evaluated using LC-MS/MS and direct analysis in real time (DART)-MS/MS, where, for a 5 ?L blood spot, LOQs of 0.2 and 1 ?g/mL, respectively, were achieved for extraction of diazepam. PMID:22928515

Mirnaghi, Fatemeh S; Pawliszyn, Janusz

2012-10-01

189

The relationship between catalyst morphology and performance in the oxidative coupling of methane  

SciTech Connect

A detailed study of the oxidative coupling of methane over magnesium oxide and lithium-doped MgO catalysts is presented. The morphology of a number of different catalysts has been examined by detailed transmission electron microscopy and the results have been correlated with catalyst performance, in particular selectivity to C[sub 2] hydrocarbons. Three samples of magnesium oxide have been prepared by different methods. Magnesium oxides prepared from the hydroxide, (ex OH), and from burning magnesium ribbon in air show similar morphology, exposing largely (100) planes; they also show very similar catalytic selectivity and specific activity. Steps and corner sites are present in much greater density on the ex OH samples than on the ribbon residue, and, since catalyst performance is unchanged, it is clear that these sites play no significant part in the catalysis over these materials. The active site is therefore located on the planar (100) surfaces. The most selective magnesium oxide catalyst was prepared by thermal decomposition of magnesium hydroxycarbonate and exposed a greater proportion of higher index mean crystal planes, e.g., (111), than the less selective forms of magnesium oxide. The morphology/performance relationship has also been examined for lithium-doped magnesium oxide catalysts. The emergence of a dislocation at the surface of the crystallite provides a locus for [Li[sup +]O[sup [minus

Hargreaves, J.S.J.; Hutchings, G.J.; Joyner, R.W.; Kiely, C.J. (Univ. of Liverpool (United Kingdom))

1992-06-01

190

Photo-oxidative tuning of individual and coupled GaAs photonic crystal cavities  

NASA Astrophysics Data System (ADS)

We demonstrate a new photo-induced oxidation technique for tuning GaAs photonic crystal cavities using a $390~\\mathrm{nm}$ pulsed laser with an average power of $10~\\mathrm{\\mu W}$. The laser oxidizes a small $\\left(\\sim 500~\\mathrm{nm}\\right)$ diameter spot, reducing the local index of refraction and blueshifting the cavity. The tuning progress can be actively monitored in real time. We also demonstrate tuning an individual cavity within a pair of proximity-coupled cavities, showing that this method can be used to correct undesired frequency shifts caused by fabrication imperfections in cavity arrays.

Piggott, Alexander Y.; Lagoudakis, Konstantinos G.; Sarmiento, Tomas; Bajcsy, Michal; Shambat, Gary; Vu?kovi?, Jelena

2014-06-01

191

Photo-oxidative tuning of individual and coupled GaAs photonic crystal cavities.  

PubMed

We demonstrate a photo-induced oxidation technique for tuning GaAs photonic crystal cavities using a low-power 390 nm pulsed laser. The laser oxidizes a small (< 1 ?m) diameter spot, reducing the local index of refraction and blueshifting the cavity. The tuning progress can be actively monitored in real time. We also demonstrate tuning an individual cavity within a pair of proximity-coupled cavities, showing that this method can be used to tune individual cavities in a cavity network, with applications in quantum simulations and quantum computing. PMID:24977595

Piggott, Alexander Y; Lagoudakis, Konstantinos G; Sarmiento, Tomas; Bajcsy, Michal; Shambat, Gary; Vu?kovi?, Jelena

2014-06-16

192

Immobilization of Laccase for Oxidative Coupling of Trans-Resveratrol and Its Derivatives  

PubMed Central

Trametes villosa Laccase (TVL) was immobilized through physical adsorption on SBA-15 mesoporous silica and the immobilized TVL was used in the oxidative coupling of trans-resveratrol. Higher loading and activity of the immobilized enzyme on SBA-15 were obtained when compared with the free enzyme. The effects of reaction conditions, such as buffer type, pH, temperature and substrate concentration were investigated, and the optimum conditions were screened and resulted in enzyme activity of up to 10.3 ?mol/g·h. Furthermore, the oxidative couplings of the derivatives of trans-resveratrol were also catalyzed by immobilized TVL. The immobilized TVL was recyclable and could maintain 78% of its initial activity after reusing it four times.

Zhang, Hong; Xun, Erna; Wang, Jiaxin; Chen, Ge; Cheng, Tiexin; Wang, Zhi; Ji, Tengfei; Wang, Lei

2012-01-01

193

An in situ XRD investigation of singly and doubly promoted manganese oxide methane coupling catalysts  

Microsoft Academic Search

In situ X-ray diffraction (XRD) and concurrent measurements of catalytic performance have been used to characterize the solid phases present during various stages in the history of working methane coupling catalytic systems. Three such systems were studied: unpromoted, K-promoted, and KCl-promoted manganese oxide. In each case the effect of pulses of CHClâ on the activity, selectivity, and catalyst structure was

G. D. Moggridge; T. Rayment; R. M. Lambert

1992-01-01

194

The hybrid plasma–catalytic process for non-oxidative methane coupling to ethylene and ethane  

Microsoft Academic Search

Non-oxidative methane coupling in hybrid plasma–catalytic reactors was studied. The hybrid system which combined the gliding discharge (GD) and mobile (spouted) bed of catalyst particles revealed high efficiency in the methane conversion. Two catalysts from Pt and Pd supported by alumina ceramics were prepared and tested. The methane conversion was investigated in two GD reactors supplied by 1-phase or 3-phase

M. M?otek; J. Sentek; K. Krawczyk; K. Schmidt-Sza?owski

2009-01-01

195

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

196

Combined Single-pass Conversion of Methane Via Oxidative Coupling and Dehydro-aromatization  

Microsoft Academic Search

A single-pass process with the combination of oxidative coupling (OCM) and dehydro-aromatization (MDA) for the direct conversion of methane is carried out. With the assistance of the OCM reaction over the SrO–La2O3\\/CaO catalyst loaded on top of the catalyst bed, the duration of the dehydro-aromatization reaction catalyzed by a 6Mo\\/HMCM-49 catalyst shows a significant improvement, and. the initial deactivation rate

Yonggang Li; Tonghao Wu; Wenjie Shen; Xinhe Bao; Yide Xu

2005-01-01

197

Influence of some donor–acceptor couples on surface conductivity of aluminum doped zinc oxide  

Microsoft Academic Search

Zinc oxide is a wide-band semiconductor, which exhibits n-type conductivity that can be stabilised by using dopants pertaining to the third group b like Al3+. The conductivity of thick layers of doped material was tested in the presence of donor–acceptor couples, namely oxygen, water, CO and NO2 and their influence was related to the charge transfer reactions, which take place

M. Mezzanotte; R. Palombari

2005-01-01

198

Studies on the Coupling Product between Oxidation Products Derived from Pentachlorophenol and Cyclodextrins  

Microsoft Academic Search

The coupling products (CPs), which were formed via the peroxosulfate catalyzed oxidation of pentachlorophenol (PCP) with iron(III)-tetrakis(sulfonatophenyl)porphyrin (Fe(III)-TPPS) in the presence of hydroxypropyl-? -cyclodextrin (HP-? -CD) or HP-? -CD, were separated by ultrafiltration from the reaction mixture. When the percentages of chlorine species in the reaction mixture were calculated from the concentrations of organic chlorine in the reaction mixture and

MASAMI FUKUSHIMA; KENJI TATSUMI

2006-01-01

199

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

PubMed Central

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 CO2 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 CO2 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 CO2 using the 3-hydroxypropionate–4-hydroxybutyrate cycle, one of the two pathways recently identified for CO2 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 CO2 assimilation and that their importance to the overall archaeal community might be larger than previously thought.

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

2011-01-01

200

Tandem Mirror Reactor Systems Code (Version I)  

SciTech Connect

A computer code was developed to model a Tandem Mirror Reactor. Ths is the first Tandem Mirror Reactor model to couple, in detail, the highly linked physics, magnetics, and neutronic analysis into a single code. This report describes the code architecture, provides a summary description of the modules comprising the code, and includes an example execution of the Tandem Mirror Reactor Systems Code. Results from this code for two sensitivity studies are also included. These studies are: (1) to determine the impact of center cell plasma radius, length, and ion temperature on reactor cost and performance at constant fusion power; and (2) to determine the impact of reactor power level on cost.

Reid, R.L.; Finn, P.A.; Gohar, M.Y.; Barrett, R.J.; Gorker, G.E.; Spampinaton, P.T.; Bulmer, R.H.; Dorn, D.W.; Perkins, L.J.; Ghose, S.

1985-09-01

201

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.

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

2006-01-01

202

Comprehensive analysis of ß-lactam antibiotics including penicillins, cephalosporins, and carbapenems in poultry muscle using liquid chromatography coupled to tandem mass spectrometry.  

PubMed

A comprehensive method for the quantitative residue analysis of trace levels of 22 ß-lactam antibiotics, including penicillins, cephalosporins, and carbapenems, in poultry muscle by liquid chromatography in combination with tandem mass spectrometric detection is reported. The samples analyzed for ß-lactam residues are hydrolyzed using piperidine in order to improve compound stability and to include the total residue content of the cephalosporin ceftifour. The reaction procedure was optimized using a full experimental design. Following detailed isotope labeling, tandem mass spectrometry studies and exact mass measurements using high-resolution mass spectrometry reaction schemes could be proposed for all ß-lactams studied. The main reaction occurring is the hydrolysis of the ß-lactam ring under formation of the piperidine substituted amide. For some ß-lactams, multiple isobaric hydrolysis reaction products are obtained, in accordance with expectations, but this did not hamper quantitative analysis. The final method was fully validated as a quantitative confirmatory residue analysis method according to Commission Decision 2002/657/EC and showed satisfactory quantitative performance for all compounds with trueness between 80 and 110% and within-laboratory reproducibility below 22% at target level, except for biapenem. For biapenem, the method proved to be suitable for qualitative analysis only. PMID:23430185

Berendsen, Bjorn J A; Gerritsen, Henk W; Wegh, Robin S; Lameris, Steven; van Sebille, Ralph; Stolker, Alida A M; Nielen, Michel W F

2013-09-01

203

Determination of dexmedetomidine in human plasma using high performance liquid chromatography coupled with tandem mass spectrometric detection: application to a pharmacokinetic study.  

PubMed

A rapid, sensitive and selective high performance liquid chromatography-electrospray ionization-tandem mass spectrometry method (HPLC-ESI-MS/MS) was developed and validated for the determination and pharmacokinetic investigation of dexmedetomidine (DMED) in human plasma. Dexmedetomidine and the internal standard (ondansetron) were extracted in a single step with diethyl-ether from 1.0 mL of alkalinized plasma. The mobile phase was a mixture of acetonitrile and 0.5% formic acid solution (30:70, v/v) at a flow rate of 0.2 mL min(-1). The detection was performed on a triple quadrupole tandem mass spectrometer in the selected reaction monitoring (SRM) mode using the respective [M+H]+ ions m/z 201.0-->95.1 for DMED and m/z 294.1-->170.1 for the IS. The assay exhibited a linear dynamic range of 5-5000 pg mL(-1) with the correlation coefficient above 0.9995. The lower limit of quantification (LLOQ) was 5 pg mL(-1) with a relative standard deviation of less than 15%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. The validated HPLC-MS/MS method has been successfully applied to study the pharmacokinetics of three level doses of DMED in Chinese healthy volunteers. PMID:19577876

Li, Wenjing; Zhang, Zunjian; Wu, Lili; Tian, Yuan; Feng, Shudan; Chen, Yun

2009-12-01

204

Anaerobic oxidation of methane coupled to nitrate reduction in a novel archaeal lineage.  

PubMed

Anaerobic oxidation of methane (AOM) is critical for controlling the flux of methane from anoxic environments. AOM coupled to iron, manganese and sulphate reduction have been demonstrated in consortia containing anaerobic methanotrophic (ANME) archaea. More recently it has been shown that the bacterium Candidatus 'Methylomirabilis oxyfera' can couple AOM to nitrite reduction through an intra-aerobic methane oxidation pathway. Bioreactors capable of AOM coupled to denitrification have resulted in the enrichment of 'M. oxyfera' and a novel ANME lineage, ANME-2d. However, as 'M. oxyfera' can independently couple AOM to denitrification, the role of ANME-2d in the process is unresolved. Here, a bioreactor fed with nitrate, ammonium and methane was dominated by a single ANME-2d population performing nitrate-driven AOM. Metagenomic, single-cell genomic and metatranscriptomic analyses combined with bioreactor performance and (13)C- and (15)N-labelling experiments show that ANME-2d is capable of independent AOM through reverse methanogenesis using nitrate as the terminal electron acceptor. Comparative analyses reveal that the genes for nitrate reduction were transferred laterally from a bacterial donor, suggesting selection for this novel process within ANME-2d. Nitrite produced by ANME-2d is reduced to dinitrogen gas through a syntrophic relationship with an anaerobic ammonium-oxidizing bacterium, effectively outcompeting 'M. oxyfera' in the system. We propose the name Candidatus 'Methanoperedens nitroreducens' for the ANME-2d population and the family Candidatus 'Methanoperedenaceae' for the ANME-2d lineage. We predict that 'M. nitroreducens' and other members of the 'Methanoperedenaceae' have an important role in linking the global carbon and nitrogen cycles in anoxic environments. PMID:23892779

Haroon, Mohamed F; Hu, Shihu; Shi, Ying; Imelfort, Michael; Keller, Jurg; Hugenholtz, Philip; Yuan, Zhiguo; Tyson, Gene W

2013-08-29

205

Modeling of the simulated countercurrent moving-bed chromatographic reactor used for the oxidative coupling of methane.  

National Technical Information Service (NTIS)

The oxidative coupling reaction of methane (OCM) is a potential industrial reaction for the efficient production of ethylene. Replacement of current technologies requires significant product yield improvements. An experimental novel reactor design, the mo...

A. L. Y. Tonkovich R. W. Carr

1994-01-01

206

Chemoselectivity in oxidative coupling of bifunctional nucleophiles with dinucleoside H-phosphonate and dinucleoside H-phosphonothioate diesters.  

PubMed

Chemoselectivity and stereospecificity of iodine mediated oxidative couplings using separate diastereomers of dinucleoside H-phosphonate and H-phosphonothioate with various N- and O-binucleophiles were investigated. PMID:14565444

Nilsson, Johan; Kraszewski, Adam; Stawinski, Jacek

2003-01-01

207

Regiocontrolled aerobic oxidative coupling of indoles and benzene using Pd catalysts with 4,5-diazafluorene ligands  

PubMed Central

Palladium-catalyzed aerobic oxidative cross-couplings of indoles and benzene have been achieved by using 4,5-diazafluorene derivatives as ancillary ligands. Proper choice of the neutral and anionic ligands enables control over the reaction regioselectivity.

Campbell, Alison N.; Meyer, Eric B.

2011-01-01

208

Spin orbit coupling, electron correlations and exotic magnetism in 5d complex Ir oxides  

NASA Astrophysics Data System (ADS)

In 5d Iridium oxides, a large spin-orbit coupling of ˜ 0.5 eV, inherent to heavy 5d elements, is not small as compared with the width of d bands and often modifies the landscape of the electronic structure substantially. This is distinct from those of 3d transition metal oxides and gives rise to a variety of novel electronic phases. Layered Ir^4+ perovskite Sr2IrO4 is recently revealed to be a novel Jeff=1/2 Mott insulator [1,2], where even a moderate Coulomb U can open up a correlation gap because of the large spin-orbit coupling. In the three dimensional analogue of Sr2IrO4, SrIrO3, the large spin-orbit coupling manifests itself in a contrasted way, where the interplay of strong spin-orbit coupling and lattice distortions brings the system almost to a band insulator. SrIrO3 is in fact a very low carrier density semimetal with unusual transport and magnetic properties. If Jeff=1/2 Ir^4+ is placed on a honeycomb lattice or a geometrically frustrated lattice such as pyrochlore lattice, even more exotic states might be anticipated, including a correlated topological insulator [3] and a Kiteav magnet [4]. Our attempt to explore such spin-orbit coupling induced states will be reported.[4pt] Work done in collaboration with T. Takayama, B.J.Kim, S.Fujiyama, K.Ohashi, J.Matsuno, H.Osumi and T.Arima. [4pt] [1] B.J.Kim et al., Phys Rev Lett 101, 076402 (2008). [0pt] [2] B. J. Kim, H. Ohsumi, T. Komesu, S. Sakai, T. Morita, H. Takagi, and T. Arima, Science 323, 1329 (2009). [0pt] [3] Shitade et al., Phys. Rev. Lett. 102, 256403 (2009). [0pt] [4] J. Chaloupka, G.Jackeli, and G.Khaliullin, Phys. Rev. Lett. 105, 027204 (2010)

Takagi, Hidenori

2012-02-01

209

Interchain coupled chain dynamics of poly(ethylene oxide) in blends with poly(methyl methacrylate): Coupling model analysis  

NASA Astrophysics Data System (ADS)

Quasielastic neutron scattering and molecular dynamics simulation data from poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) blends found that for short times the self-dynamics of PEO chain follows the Rouse model, but at longer times past tc = 1-2 ns it becomes slower and departs from the Rouse model in dependences on time, momentum transfer, and temperature. To explain the anomalies, others had proposed the random Rouse model (RRM) in which each monomer has different mobility taken from a broad log-normal distribution. Despite the success of the RRM, Diddens et al. [Eur. Phys. Lett. 95, 56003 (2011)] extracted the distribution of friction coefficients from the MD simulations of a PEO/PMMA blend and found that the distribution is much narrower than expected from the RRM. We propose a simpler alternative explanation of the data by utilizing alone the observed crossover of PEO chain dynamics at tc. The present problem is just a special case of a general property of relaxation in interacting systems, which is the crossover from independent relaxation to coupled many-body relaxation at some tc determined by the interaction potential and intermolecular coupling/constraints. The generality is brought out vividly by pointing out that the crossover also had been observed by neutron scattering from entangled chains relaxation in monodisperse homopolymers, and from the segmental ?-relaxation of PEO in blends with PMMA. The properties of all the relaxation processes in connection with the crossover are similar, despite the length scales of the relaxation in these systems are widely different.

Ngai, K. L.; Wang, Li-Min

2011-11-01

210

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

211

Design and analysis of a coupled solid oxide fuel cell and metal hydride bed system  

NASA Astrophysics Data System (ADS)

Solid oxide fuel cells have exhibited excellent performance at high temperature for a few years. However, the fuel supply and the practical fuel cell application need to be improved especially for transportation or stand-alone facility usage. Two modified hydrogen storage models (two vessel and three vessel hydrogen storage system) are presented in this study. The gravimetric density and volumetric density are calculated in order to meet the DOE requirements. Furthermore, the time dependence model of hydrogen releasing in metal hydride bed (MHB) is built up. And the simulations are carried on in isothermal and adiabatic conditions. The simulation results indicate: the isothermal model can provide sufficient hydrogen flow until the MHB is emptied; the adiabatic model can only last short period because of the fast temperature decreasing in MHB. The steady state and time dependence model of coupled solid oxide fuel cells (SOFC) and MHB system are also investigated. The steady state model focuses on the heat recycle process for coupled system. The calculation shows the heat generated in system can provide enough energy for inner recycle. On the other hand, the time de-pendence model mainly concerns the time delay in such a coupled system. The simu-lation shows the time delay mainly comes from hydrogen feed.

Song, Ke

212

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

213

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

214

A Facile Cu(I)-Catalyzed Oxidative Coupling of Anilines to Azo Compounds and Hydrazines with Diaziridinone under Mild Conditions  

PubMed Central

A mild and highly efficient Cu(I)-catalyzed oxidative coupling of anilines is described. Various primary and secondary anilines can be efficiently coupled under mild conditions to the corresponding azo compounds and hydrazines in high yields. This method provides a direct and practical access to these compounds, and is also amenable to gram scale with no special precautions to exclude air or moisture.

Zhu, Yingguang; Shi, Yian

2013-01-01

215

Heterogeneously catalyzed selective aerobic oxidative cross-coupling of terminal alkynes and amides with simple copper(II) hydroxide.  

PubMed

Simple copper(II) hydroxide Cu(OH)(2) could act as an efficient heterogeneous catalyst for selective oxidative cross-coupling of a broad range of terminal alkynes and amides using air as a sole oxidant, giving the corresponding ynamides in moderate to high yields (56-93% yields). PMID:22497008

Jin, Xiongjie; Yamaguchi, Kazuya; Mizuno, Noritaka

2012-05-21

216

Synthesis of indazoles and azaindazoles by intramolecular aerobic oxidative C-N coupling under transition-metal-free conditions.  

PubMed

A transition-metal-free oxidative C-N coupling method has been developed for the synthesis of 1H-azaindazoles and 1H-indazoles from easily accessible hydrazones. The procedure uses TEMPO, a basic additive, and dioxygen gas as the terminal oxidant. This reaction demonstrates better reactivity, functional group tolerance, and broader scope than comparable metal catalyzed reactions. PMID:24590598

Hu, Jiantao; Xu, Huacheng; Nie, Pengju; Xie, Xiaobo; Nie, Zongxiu; Rao, Yu

2014-04-01

217

Ag/Au mixed sites promote oxidative coupling of methanol on the alloy surface.  

PubMed

Nanoporous gold, a dilute alloy of Ag in Au, activates molecular oxygen and promotes the oxygen-assisted catalytic coupling of methanol. Because this trace amount of Ag inherent to nanoporous gold has been proposed as the source of oxygen activation, a thin film Ag/Au alloy surface was studied as a model system for probing the origin of this reactivity. Thin alloy layers of Agx Au1-x , with 0.15?x?0.40, were examined for dioxygen activation and methanol self-coupling. These alloy surfaces recombine atomic oxygen at different temperatures depending on the alloy composition. Total conversion of methanol to selective oxidation products, that is, formaldehyde and methyl formate, was achieved at low initial oxygen coverage and at low temperature. Reaction channels for methyl formate formation occurred on both Au and Au/Ag mixed sites with a ratio, as was predicted from the local 2-dimensional composition. PMID:24633724

Xu, Bingjun; Siler, Cassandra G F; Madix, Robert J; Friend, Cynthia M

2014-04-14

218

An organocatalytic oxidative coupling strategy for the direct synthesis of arylated quaternary stereogenic centers.  

PubMed

A broadly applicable oxidative coupling strategy of 3-substituted catechols and carbon-centered pro-nucleophiles for the construction of arylated quaternary stereogenic centers has been developed. Pivoting on a base-catalyzed addition of a carbon-centered acid to an in situ generated o-benzoquinone, the method is general and atom-economical and provides remarkably efficient access to one of the most challenging structural motifs. Furthermore, use of chiral bifunctional organocatalysts allows the process to be rendered asymmetric (up to 81% ee). PMID:17924643

Bogle, Katherine M; Hirst, David J; Dixon, Darren J

2007-11-01

219

Oxidative coupling of methane in a mixed-conducting perovskite membrane reactor  

Microsoft Academic Search

Ionic-electronic mixed-conducting perovskite-type oxide La0.6Sr0.4Co0.8Fe0.2O3 was applied as a dense membrane for oxygen supply in a reactor for methane coupling. The oxygen permeation properties were studied in the pO2-range of 10?3?1 bar at 1073–1273 K, using helium as a sweeping gas at the permeate side of the membrane. The oxygen semi-permeability has a value close to 1 mmol m?2 s?1

J. E. ten Elshof; H. J. M. Bouwmeester; H. Verweij

1995-01-01

220

High-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry for the determination of flocoumafen and brodifacoum in whole blood.  

PubMed

A high-performance liquid chromatographic-tandem mass spectrometric (HPLC-MS-MS) assay was developed and validated to determine quantitatively flocoumafen and brodifacoum in whole blood using warfarin as an internal standard (IS). Liquid-liquid extraction, using ethyl acetate, was used to isolate flocoumafen, brodifacoum and the IS from the biological matrix. Detection was performed on a mass spectrometer by negative electrospray ionization (ESI) in multiple reaction monitoring (MRM) mode. The calibration curves were linear (r(2) > 0.998) in the concentration range of 0.1-100.0 ng ml(-1) with a lower limit of quantification of 0.05 ng ml(-1) for flocoumafen, and 0.1 ng ml(-1) for brodifacoum in whole blood. Intra-day and inter-day relative standard deviations (RSDs) were less than 8.0% and 10.8%, respectively. Recoveries of flocoumafen and brodifacoum ranged from 78.0% to 83.7%. This assay can be used to determine trace flocoumafen and brodifacoum in whole blood to investigate suspected poisoning of human and animals. PMID:17177169

Jin, Mi-Cong; OuYang, Xiao-Kun; Chen, Xiao-hong

2007-01-01

221

Quantitative and selective assay of 5-methylindirubine, an inhibitor of cyclin-dependent kinases, in murine plasma using coupled liquid chromatography and electrospray tandem mass spectrometry.  

PubMed

A sensitive and rapid LC-MS/MS assay for the quantitative determination of 5-methylindirubine (5-MI) in murine plasma is described. A 50-microL-murine plasma aliquot was spiked with an internal standard, indirubine-3-monoxime (IMO), and extracted with 1.25 mL diethyl ether. Dried extracts were reconstituted in methanol-water (8:2, v/v) and 10 microL-volumes were injected onto the HPLC system. Separation was achieved on a Gemini C18 column (150 mm x 2.1 mm ID, particle size 5 microm) using an alkaline eluent (10 mM ammonium hydroxide-methanol (5:95, v/v)). Detection was performed by negative ion electrospray followed by tandem mass spectrometry. The assay quantifies 5-MI in a range from 1 to 500 ng/mL using 50 microL of murine EDTA plasma samples. Validation results demonstrate that 5-MI concentrations can be accurately and precisely quantified in murine plasma. This assay is used to support pre-clinical pharmacologic studies with 5-MI. PMID:17631060

Vainchtein, Liia D; Rosing, Hilde; Maier, Armin; Fiebig, Heinz-Herbert; Schellens, Jan H M; Beijnen, Jos H

2007-09-01

222

A validated assay for the simultaneous quantification of six tyrosine kinase inhibitors and two active metabolites in human serum using liquid chromatography coupled with tandem mass spectrometry.  

PubMed

A sensitive, sophisticated and practical bioanalytical assay for the simultaneous determination of six tyrosine kinase inhibitors (imatinib, sunitinib, nilotinib, dasatinib, pazopanib, regorafenib) and two active metabolites (N-desmethyl imatinib and N-desethyl sunitinib) was developed and validated. For the quantitative assay, a mixture of three stable isotopes as internal standards was added to human serum, standards and controls. Thereafter, samples were pre-treated using protein precipitation with methanol. The supernatant was diluted with water and injected into an ultra pressure liquid chromatographic system with an Acquity TQ tandem mass spectrometry detector. The compounds were separated on an Acquity BEH C18 analytical column (100mm×2.1mm ID, 1.7?m particle size) and eluted with a linear gradient system. The ions were detected in the multiple reaction monitoring mode. The lower limit of quantification and the linearity of all compounds generously met with the concentrations that are to be expected in clinical practice. The developed bioanalytical assay can be used for guiding TKI therapy in daily clinical practice as well as for investigator-initiated research. PMID:24013127

van Erp, Nielka P; de Wit, Djoeke; Guchelaar, Henk-Jan; Gelderblom, Hans; Hessing, Trees J; Hartigh, Jan den

2013-10-15

223

[Determination of seven pesticide residues in bamboo shoots by high performance liquid chromatography-tandem mass spectrometry coupled with solid-phase extraction].  

PubMed

A simple and efficient method based on solid-phase extraction (SPE) and high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was developed for the determination of butylene fipronil, chlorpyrifos, chlorantraniliprole, fipronil, imidacloprid, indoxacarb and phoxim residues in bamboo shoots. The sample was extracted with acetonitrile and purified by a primary secondary amine (PSA) solid-phase extraction cartridge. The detection of targets was performed by HPLC-MS/MS with multiple reaction monitoring (MRM) mode. All the seven pesticides were completely separated in 15 min with an excellent linear relationship. The limits of detection and the limits of quantification for the seven pesticides were 0.02-0.5 microg/kg and 0.08-1.5 microg/kg, respectively. The recoveries of the seven pesticides spiked in a bamboo shoot sample at the levels of 4, 8, 32 microg/kg were in the range from 76.0% to 102.6% (the RSD < or = 11.0%, n = 3). The method was successfully applied to the real bamboo shoot samples. The method has high accuracy and sensitivity, and is simple and quick. It can meet the requirement of the simultaneous determination of the seven pesticides in bamboo shoots. PMID:23697174

Ding, Ming; Zhong, Donglian; Tang, Fubin; Fang, Wei

2013-02-01

224

Quantification of 2-acetyl-1-pyrroline in rice by stable isotope dilution assay through headspace solid-phase microextraction coupled to gas chromatography-tandem mass spectrometry.  

PubMed

A new and convenient synthesis of 2-acetyl-1-pyrroline (2AP), a potent flavor compound in rice, and its ring-deuterated analog, 2-acetyl-1-d(2)-pyrroline (2AP-d(2)), was reported. A stable isotope dilution assay (SIDA), involving headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-positive chemical ionization-ion trap-tandem mass spectrometry (GC-PCI-IT-MS-MS), was developed for 2AP quantification. A divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber was used for HS-SPME procedure and parameters affecting analytes recovery, such as extraction time and temperature, pH and salt, were studied. The repeatability of the method (n=10) expressed as relative standard deviation (RSD) was 11.6%. A good linearity was observed from 5.9 to 779 ng of 2AP (r(2)=0.9989). Limits of detection (LOD) and quantification (LOQ) for 2AP were 0.1 and 0.4 ng g(-1) of rice, respectively. The recovery of spiked 2AP from rice matrix was almost complete. The developed method was applied to the quantification of 2AP in aerial parts and grains of scented and non-scented rice cultivars. PMID:20800726

Maraval, Isabelle; Sen, Kemal; Agrebi, Abdelhamid; Menut, Chantal; Morere, Alain; Boulanger, Renaud; Gay, Frédéric; Mestres, Christian; Gunata, Ziya

2010-08-24

225

Stir bar sorptive extraction coupled to liquid chromatography-tandem mass spectrometry for the determination of pesticides in water samples: method validation and measurement uncertainty.  

PubMed

Stir bar sorptive extraction followed by liquid desorption and high performance liquid chromatography with tandem mass spectrometry (SBSE-LD-LC-MSMS) has been developed for the determination of 15 pesticides or selected metabolites from different families (herbicides, insecticides, fungicides) in surface water samples. The optimization of parameters that could influence SBSE-LD efficiency was carried out by means of experimental design. Optimized conditions were established as follows concerning extraction time, stirring speed, aqueous medium characteristics (ionic strength and polarity) and back desorption solvent and time, respectively: 3 h (800 rpm), addition of 10% of sodium chloride, no addition of methanol as organic modifier, and 15 min ultrasonic desorption in equivolume mixtures of acetonitrile-methanol. A specific and thorough cleanup procedure was developed and applied to each stir bar to avoid possible carry-over between consecutive extractions with the same stir bar. Pesticide quantification in water was achieved thanks to matrix matched calibration. Mean recoveries ranged from 93 to 101% (RSD <17%, n=30). Validated limits of quantification in matrix were between 0.02 and 1 µg L(-1), depending on the compound. A specific experimental design was conducted to evaluate the measurement uncertainty, which was comprised between 13 and 51%, whatever the pesticide and the concentration level. The applicability of the SBSE-LD-LCMSMS method was evaluated by analyzing surface water samples and by comparing with conventional solid phase extraction-LC-MSMS procedure. PMID:24148364

Margoum, Christelle; Guillemain, Céline; Yang, Xi; Coquery, Marina

2013-11-15

226

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

227

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

228

Nitric oxide synthase regulation of cardiac excitation-contraction coupling in health and disease.  

PubMed

Significant advances in our understanding of the ability of nitric oxide synthases (NOS) to modulate cardiac function have provided key insights into the role NOS play in the regulation of excitation-contraction (EC) coupling in health and disease. Through both cGMP-dependent and cGMP-independent (e.g. S-nitrosylation) mechanisms, NOS have the ability to alter intracellular Ca(2+) handling and the myofilament response to Ca(2+), thereby impacting the systolic and diastolic performance of the myocardium. Findings from experiments using nitric oxide (NO) donors and NOS inhibition or gene deletion clearly implicate dysfunctional NOS as a critical contributor to many cardiovascular disease states. However, studies to date have only partially addressed NOS isoform-specific effects and, more importantly, how subcellular localization of NOS influences ion channels involved in myocardial EC coupling and excitability. In this review, we focus on the contribution of each NOS isoform to cardiac dysfunction and on the role of uncoupled NOS activity in common cardiac disease states, including heart failure, diabetic cardiomyopathy, ischemia/reperfusion injury and atrial fibrillation. We also review evidence that clearly indicates the importance of NO in cardioprotection. This article is part of a Special Issue entitled "Redox Signalling in the Cardiovascular System". PMID:24631761

Simon, Jillian N; Duglan, Drew; Casadei, Barbara; Carnicer, Ricardo

2014-08-01

229

Microwaves and their coupling to advanced oxidation processes: enhanced performance in pollutants degradation.  

PubMed

This review assesses microwaves (MW) coupled to advanced oxidation processes (AOPs) for pollutants degradation, as well as the basic theory and mechanisms of MW dielectric heating. We addressed the following couplings: MW/H2O2, MW/UV/H2O2, MW/Fenton, MW/US, and MW/UV/TiO2, as well as few studies that tested alternative oxidants and catalysts. Microwave Discharge Electrodeless Lamps (MDELs) are being extensively used with great advantages over ballasts. In their degradation studies, researchers generally employed domestic ovens with minor adaptations. Non-thermal effects and synergies between UV and MW radiation play an important role in the processes. Published papers so far report degradation enhancements between 30 and 1,300%. Unfortunately, how microwaves enhance pollutants is still obscure and real wastewaters scarcely studied. Based on the results surveyed in the literature, MW/AOPs are promising alternatives for treating/remediating environmental pollutants, whenever one considers high degradation yields, short reaction times, and small costs. PMID:23573926

Nascimento, Ulisses M; Azevedo, Eduardo B

2013-01-01

230

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

DOEpatents

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

231

Efficient and Stereoselective Synthesis of Yellow Scale Pheromone via Alkyne Haloboration, Zr-Catalyzed Asymmetric Carboalumination of Alkenes (ZACA Reaction), and Pd-Catalyzed Tandem Negishi Coupling  

PubMed Central

A Pd-catalyzed reaction of allylzincs with the 1-octyne bromoboration product gives the desired allyl-alkenyl coupling products in good yields except with H2C=CHCH2ZnBr. This reaction is suitable for converting an alkyne bromoboration product 3 into 4 with no isomerization or ?-elimination. The Pd-catalyzed isoalkyl-alkenyl coupling of 4 with the isoalkylzinc reagent derived from 2 provides yellow scale pheromone (1) of ?98% isomeric purity in 34% in six steps from TBDPS-protected homoallyl alcohol.

Xu, Zhaoqing; Negishi*, Ei-ichi

2008-01-01

232

An inorganic geochemical argument for coupled anaerobic oxidation of methane and iron reduction in marine sediments.  

PubMed

Here, we present results from sediments collected in the Argentine Basin, a non-steady state depositional marine system characterized by abundant oxidized iron within methane-rich layers due to sediment reworking followed by rapid deposition. Our comprehensive inorganic data set shows that iron reduction in these sulfate and sulfide-depleted sediments is best explained by a microbially mediated process-implicating anaerobic oxidation of methane coupled to iron reduction (Fe-AOM) as the most likely major mechanism. Although important in many modern marine environments, iron-driven AOM may not consume similar amounts of methane compared with sulfate-dependent AOM. Nevertheless, it may have broad impact on the deep biosphere and dominate both iron and methane cycling in sulfate-lean marine settings. Fe-AOM might have been particularly relevant in the Archean ocean, >2.5 billion years ago, known for its production and accumulation of iron oxides (in iron formations) in a biosphere likely replete with methane but low in sulfate. Methane at that time was a critical greenhouse gas capable of sustaining a habitable climate under relatively low solar luminosity, and relationships to iron cycling may have impacted if not dominated methane loss from the biosphere. PMID:24460948

Riedinger, N; Formolo, M J; Lyons, T W; Henkel, S; Beck, A; Kasten, S

2014-03-01

233

Measurement of phospholipids by hydrophilic interaction liquid chromatography coupled to tandem mass spectrometry: the determination of choline containing compounds in foods.  

PubMed

A hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC LC-MS/MS) method using multiple scan modes was developed to separate and quantify 11 compounds and lipid classes including acetylcholine (AcCho), betaine (Bet), choline (Cho), glycerophosphocholine (GPC), lysophosphatidylcholine (LPC), lysophosphatidylethanolamine (LPE), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphocholine (PCho) and sphingomyelin (SM). This includes all of the major choline-containing compounds found in foods. The method offers advantages over other LC methods since HILIC chromatography is readily compatible with electrospray ionization and results in higher sensitivity and improved peak shapes. The LC-MS/MS method allows quantification of all choline-containing compounds in a single run. Tests of method suitability indicated linear ranges of approximately 0.25-25 ?g/ml for PI and PE, 0.5-50 ?g/ml for PC, 0.05-5 ?g/ml for SM and LPC, 0.5-25 ?g/ml for LPE, 0.02-5 ?g/ml for Cho, and 0.08-8 ?g/ml for Bet, respectively. Accuracies of 83-105% with precisions of 1.6-13.2% RSD were achieved for standards over a wide range of concentrations, demonstrating that this method will be suitable for food analysis. 8 polar lipid classes were found in a lipid extract of egg yolk and different species of the same class were differentiated based on their molecular weights and fragment ion information. PC and PE were found to be the most abundant lipid classes consisting of 71% and 18% of the total phospholipids in egg yolk. PMID:21737084

Zhao, Yuan-Yuan; Xiong, Yeping; Curtis, Jonathan M

2011-08-12

234

Pharmacokinetic-pharmacodynamic study of subcutaneous injection of depot nandrolone decanoate using dried blood spots sampling coupled with ultrapressure liquid chromatography tandem mass spectrometry assays.  

PubMed

Context: Testosterone (T) and nandrolone (N) esters require deep im injections by medical personnel but these often deposit injectate into sc fat so that more convenient sc self-administration may be feasible. Objective: To investigate the feasibility and pharmacology of sc injection of N decanoate in healthy men using dried blood spot (DBS) for frequent blood sampling without clinic visits. Setting and Design: Healthy male volunteers received 100 mg N decanoate by a single sc injection. Finger-prick capillary blood was spotted onto filter paper before injection daily at home for 21 d and stored at room temperature. Venous whole blood was also spotted onto filter paper before and weekly for 3 wk after injection. DBS were extracted for assay of N and T by liquid chromatography tandem mass spectrometry in a single batch with serum concentrations estimated with adjustment for capillary blood sample volume and hematocrit to define peak (N) or nadir (T) time and concentration from individual daily measurements. Results: Daily serum N peaked 2.50 ± 0.25 (SEM) ng/mL at a median (range) of 6 (4-13) days causing a reduction in serum T from 3.50 ± 0.57 ng/mL at baseline to a nadir of 0.38 ± 0.13 (SEM) ng/mL (89 ± 3% suppression) at a median (range) of 8 (5-16) days. Simultaneously sampled capillary, venous whole blood, and serum gave almost identical results for serum T and N. Finger-pricks and sc injections were well tolerated. Conclusions: This study demonstrates that A) DBS sampling with liquid chromatography mass spectrometry steroid analysis achieves frequent time sampling in the community without requiring clinic visits, venesection, or frozen serum storage, and B) androgen esters in an oil vehicle can be delivered effectively by sc injection, thus avoiding the need for medically supervised deep-im injections. PMID:24684468

Singh, Gurmeet K S; Turner, Leo; Desai, Reena; Jimenez, Mark; Handelsman, David J

2014-07-01

235

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.

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

2012-01-01

236

Liquid chromatography coupled to tandem mass spectrometry and high resolution mass spectrometry as analytical tools to characterize multi-class cytostatic compounds.  

PubMed

Cytostatic compounds used in the treatment of cancer have emerged as a new generation of water contaminants due to the continuous amounts administered to patients and to the fact that a variable proportion is excreted unchanged. In this study, we have evaluated the performance of liquid-chromatography-tandem mass spectrometry (LC-MS/MS) and high resolution mass spectrometry using an Orbitrap analyzer (LC-HRMS) for the multiresidue determination of multi-class cytostatic compounds. In a first step, ionization conditions were tested in positive electrospray mode and optimum fragmentation patterns were determined. For LC-MS/MS, two selected reaction monitoring (SRM) transitions were optimized and for LC-HRMS, the molecular ion with 5 ppm error and two product ions were defined. Following, the chromatographic conditions were optimized considering that compounds analyzed have a very different chemical structure and chromatographic behavior. The best performance was obtained with a Luna C18 column, which permitted the separation of the 26 compounds in 15 min. Finally, the performance of LC-MS/MS and LC-HRMS was compared in terms of linearity, sensitivity, intra and inter-day precision and overall robustness. While LC-MS/MS provided good identification capabilities due to selective SRM transitions, LC-Orbitrap proved to be 100 times more sensitive. This study provides a comprehensive overview on the MS conditions to determine the outmost used cytostatic compounds and provides a spectral library to be used for the identification of these compounds in water or biological matrices. PMID:23313302

Gómez-Canela, Cristian; Cortés-Francisco, Nuria; Ventura, Francesc; Caixach, Josep; Lacorte, Silvia

2013-02-01

237

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

238

Pharmacokinetic study of free mangiferin in rats by microdialysis coupled with microbore high-performance liquid chromatography and tandem mass spectrometry  

Microsoft Academic Search

Mangiferin (2-?-d-glucopyranosyl-1,3,6,7-tetrahydroxyxanthen-9-one) has been isolated from the herbal root of Anemarrhena asphodeloides Bung showing antioxidative, antiviral, and anticancer effect. An in vivo microdialysis sampling method coupled to microbore high-performance liquid chromatography (HPLC) was employed for continuous monitoring of free mangiferin in rat blood. Microdialysis probes were inserted into the jugular vein\\/right atrium and brain striatum of Sprague–Dawley rats, and mangiferin

Ling Lai; Lie-Chwen Lin; Jer-Huei Lin; Tung-Hu Tsai

2003-01-01

239

Screening and characterization of natural antioxidants in four Glycyrrhiza species by liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry  

Microsoft Academic Search

Licorice, derived from the dried roots and rhizomes of several species of genus Glycyrrhiza L. (Leguminosae family), has been traditionally used in herbal medicine for over 4000years. In recent years, the interest in antioxidative constituents in licorice has greatly increased. In this work, a new method based on 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) spiking test combined with HPLC coupled with electrospray ionization

Yan-Jing Li; Jun Chen; Ying Li; Qin Li; Yun-Feng Zheng; Yu Fu; Ping Li

2011-01-01

240

Long-range oxidative damage in duplex DNA: the effect of bulged G in a G-C tract and tandem G/A mispairs  

PubMed Central

Two series of duplex DNA oligomers were prepared having an anthraquinone derivative (AQ) covalently linked at a 5?-terminus. Irradiation of the AQ at 350 nm leads to injection of an electron hole (radical cation) into the DNA. The radical cation migrates through the DNA causing reaction primarily at Gn sequences. In one series, GA tandem mispairs are inserted between GG steps to assess the effect of the mispair on the transport of the radical cation, reaction (damage) caused by the radical cation at the mispair, and repair of the resulting damage by formamidopyrimidine DNA glycosylase (Fpg). In the second series, a bulged guanine in a G3C2 sequence is interposed between the GG steps. These experiments reveal that neither G/A tandem mispairs nor bulged guanines are significant barriers to long-range charge migration in DNA. The radical cation does not cause reaction at guanines in the G/A tandem mispair. Reaction does occur at the bulged guanine, but it is repaired by Fpg.

Boone, Edna; Schuster, Gary B.

2002-01-01

241

Oxidative coupling of methane on oxygen-semipermeable yttria-doped bismuth oxide ceramics in a reducing atmosphere  

SciTech Connect

Oxidative coupling of methane (OCM) on oxygen-semipermeable {delta}-phase 25 mol % Y{sub 2}O{sub 3}/Bi{sub 2}O{sub 3} (BY25) in a reducing (methane) atmosphere was studied by measuring transient catalytic properties and weight change of the ceramics when exposed to a methane stream at high temperatures (>800 C). Compared to the results obtained in a fixed-bed reactor operated in the cofeed mode, BY25 ceramics in a pellet form exhibit extremely high C{sub 2} selectivity (94%) and appreciable reactivity (C{sub 2} formation rate of 0.7 {micro}mol/g{center_dot}s) for OCM in a highly reducing methane atmosphere. Experimental results are also reported to show the effects of temperature, flow rate, methane exposure time, helium purge time, and helium to methane ratio on catalytic properties of BY25 pellets in a methane atmosphere. The results indicate that BY25 ceramic membrane materials possess desired catalytic properties for OCM membrane reactor applications.

Zeng, Y.; Lin, Y.S. [Univ. of Cincinnati, OH (United States). Dept. of Chemical Engineering] [Univ. of Cincinnati, OH (United States). Dept. of Chemical Engineering

1997-02-01

242

Planar Multielectrode Array Coupled Complementary Metal Oxide Semiconductor Image Sensor for In vitro Electrophysiology  

NASA Astrophysics Data System (ADS)

A multielectrode array coupled complementary metal oxide semiconductor (CMOS) image sensor (MARC sensor) was developed for an in vitro electrophysiology experiment. The sensor chip was fabricated by a standard CMOS process, and has a 64 microelectrode array and a 180× 180 photodiode pixel array. The size of an on-chip microelectrode is 60× 60 ?m2 and the pixel size is 7.5× 7.5 ?m2. In addition, Pt black was fabricated on microelectrodes to obtain stimulation electrodes. The imaging function was demonstrated by the anatomical observation of a mouse hippocampal slice, and the electrical recording function was also demonstrated by monitoring the extracellular field potentials of the brain slice using on-chip microelectrodes. The MARC sensor is compatible with existing in vitro multichannel recording systems. This is the first report supporting our concept that microelectrode arrays and large-sized optical systems can be integrated onto single large-scale integration (LSI) architecture.

Nakajima, Arata; Noda, Toshihiko; Sasagawa, Kiyotaka; Tokuda, Takashi; Ishikawa, Yasuyuki; Shiosaka, Sadao; Ohta, Jun

2011-04-01

243

Nitric oxide signaling in the brain: translation of dynamics into respiration control and neurovascular coupling.  

PubMed

The understanding of the unorthodox actions of neuronal-derived nitric oxide ((•)NO) in the brain has been constrained by uncertainties regarding its quantitative profile of change in time and space. As a diffusible intercellular messenger, conveying information associated with its concentration dynamics, both the synthesis via glutamate stimulus and inactivation pathways determine the profile of (•)NO concentration change. In vivo studies, encompassing the real-time measurement of (•)NO concentration dynamics have allowed us to gain quantitative insights into the mechanisms inherent to (•)NO-mediated signaling pathways. It has been of particular interest to study the diffusion properties and half-life, the interplay between (•)NO and O(2) and the ensuing functional consequences for regulation of O(2) consumption, the role of vasculature in shaping (•)NO signals in vivo, and the mechanisms that are responsible for (•)NO to achieve the coupling between glutamatergic neuronal activation and local microcirculation. PMID:22758631

Laranjinha, João; Santos, Ricardo M; Lourenço, Cátia F; Ledo, Ana; Barbosa, Rui M

2012-07-01

244

Palladium-catalyzed oxidative C-N bond coupling involving a solvent-controlled regioselective bromination process.  

PubMed

Stereoselective palladium-catalyzed oxidative C-N bond coupling reactions between aromatic amines and alkenes involving a solvent-controlled regioselective bromination process under 1 atm of oxygen atmosphere are disclosed, providing easy access to two different brominated enamines. The addition of hydrogen peroxide (30% aq) as a co-oxidant in the system is crucial for the dehydrogenative aminohalogenation under molecular oxygen (1 atm), and in such a case, the C-N bond coupling/electrophilic bromination reaction cascade is proposed. Furthermore, the different reaction media leads to a switched regioselectivity of the process. PMID:25010511

Ji, Xiaochen; Huang, Huawen; Xiong, Wenfang; Huang, Kunbo; Wu, Wanqing; Jiang, Huanfeng

2014-08-01

245

Copper-catalyzed oxidative coupling of formamides with salicylaldehydes: synthesis of carbamates in the presence of a sensitive aldehyde group.  

PubMed

A diverse library of novel carbamates was synthesized utilizing copper-catalyzed oxidative C-O coupling of formamides and salicylaldehydes. Sensitive aldehyde groups remained intact in the presence of an oxidant and a transition-metal salt. Salicylaldehydes bearing electron-donating, electron-withdrawing, and halogen groups as well as 1-hydroxy-2-naphthaldehydes provided the desired carbamates in good to excellent yields. PMID:24588581

Barve, Balaji D; Wu, Yang-Chang; El-Shazly, Mohamed; Chuang, Da-Wei; Cheng, Yuan-Bin; Wang, Jeh-Jeng; Chang, Fang-Rong

2014-04-01

246

Coupled biotic-abiotic Mn(II) oxidation pathway mediates the formation and structural evolution of biogenic Mn oxides  

Microsoft Academic Search

Manganese (Mn) oxides are among the strongest oxidants and sorbents in the environment, impacting the transport and speciation of metals, cycling of carbon, and flow of electrons within soils and sediments. The oxidation of Mn(II) to Mn(III\\/IV) oxides has been primarily attributed to biological processes, due in part to the faster rates of bacterial Mn(II) oxidation compared to observed mineral-induced

D. R. Learman; S. D. Wankel; S. M. Webb; N. Martinez; A. S. Madden; C. M. Hansel

2011-01-01

247

Coupled biotic–abiotic Mn(II) oxidation pathway mediates the formation and structural evolution of biogenic Mn oxides  

Microsoft Academic Search

Manganese (Mn) oxides are among the strongest oxidants and sorbents in the environment, impacting the transport and speciation of metals, cycling of carbon, and flow of electrons within soils and sediments. The oxidation of Mn(II) to Mn(III\\/IV) oxides has been primarily attributed to biological processes, due in part to the faster rates of bacterial Mn(II) oxidation compared to observed mineral-induced

D. R. Learman; S. D. Wankel; S. M. Webb; N. Martinez; A. S. Madden; C. M. Hansel

2011-01-01

248

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.

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

2012-01-01

249

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

250

Simple coupling chemistry linking carboxyl-containing organic molecules to silicon oxide surfaces under acidic conditions.  

PubMed

The coupling chemistry of carboxymethylated amylose with organo-silanized silicon oxide surfaces at pH 7.4 and 2.0 was investigated using atomic force microscopy (AFM) based single-molecule force spectroscopy. At close to neutral pH, carbodiimide activation of a carboxylic acid affords formation of an amide bond with an amino surface linker. At pH 2.0, no activation with carbodiimide was required to anchor carboxymethylated amylose between an AFM tip and a glass substrate. At the same time, the mean bond rupture force f(r) dropped from 1.65 ± 0.37 nN at pH 7.4 to 1.39 ± 0.30 nN at pH 2.0 without carbodiimide, indicating that a different link to the surface can be formed at low pH. The coupling mechanism at pH 2.0 was elucidated by a series of experiments, in which the surface was functionalized with four different organosilanes, each containing characteristic functional groups. The results are rationalized with an acid-catalyzed ester condensation between a carboxyl group and a free, unreacted silanol group in the surface anchor or on the surface. PMID:20822126

Schmidt, Sebastian W; Christ, Timo; Glockner, Christian; Beyer, Martin K; Clausen-Schaumann, Hauke

2010-10-01

251

Automated online dual-column extraction coupled with teicoplanin stationary phase for simultaneous determination of (R)- and (S)-propranolol in rat plasma using liquid chromatography-tandem mass spectrometry.  

PubMed

An automated online sample extraction method for rat plasma was developed and validated for the quantification of (R)- and (S)-propranolol following the intravenous administration of either the racemate or the individual enantiomers at 5 mg/kg. A dual-column extraction system coupled to a chiral stationary phase (CSP) was used in conjunction with liquid chromatography-tandem mass spectrometry. In this method, two Oasis HLB extraction columns (50x1.0 mm) in parallel were used for online plasma sample purification and teicoplanin CSP (Chirobiotic T) was used for the enantiomeric separation. This method allowed the use of one of the extraction columns for purification while the other was being equilibrated. Hence, the time required for re-conditioning the extraction columns did not contribute to the total analysis time per sample, which resulted in a relatively shorter run time and higher throughput. The lower limit of detection was 0.5 ng/ml and the lower limit of quantification was 2 ng/ml for each enantiomer using 25 microl of rat plasma. The method was validated with a linear calibration curve between 2 and 2000 ng/ml for (R)- and (S)-propranolol, respectively. The intra- and inter-day precision (C.V.) was no more than 7.6% and the accuracy of the assay was between 92 and 103%. The teicoplanin CSP proved to be rugged with excellent reproducibility of chromatographic parameters. PMID:12705972

Xia, Yuan-Qing; Bakhtiar, Ray; Franklin, Ronald B

2003-05-25

252

Ionic Liquid-Based One-Step Micellar Extraction of Multiclass Polar Compounds from Hawthorn Fruits by Ultrahigh-Performance Liquid Chromatography Coupled with Quadrupole Time-of-Flight Tandem Mass Spectrometry.  

PubMed

An ionic liquid (IL)-based one-step micellar extraction procedure was developed for the extraction of multiclass polar analytes (protocatechuic acid, chlorogenic acid, epicatechin, hyperoside, isoquercitrin, quercetin) from hawthorn fruits and their determination using ultrahigh-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry (UHPLC-Q-TOF/MS). Compared to conventional organic solvent extractions, this newly proposed method was much easier, more sensitive, environmentally friendly, and effective as well. Several important parameters influencing the micellar extraction efficiency are discussed, such as selection of ILs, surfactant concentration, and extraction time. Under the optimal conditions, good linearity was achieved for each analyte with correlation coefficients (r(2)) ranging from 0.9934 to 0.9999, and the recovery values ranged from 89.3 to 106% with relative standard deviations lower than 5.5%. Results suggest that the IL-based one-step micellar extraction could be an alternative and promising means in future food analysis. PMID:24845828

Hu, Shuai-Shuai; Yi, Ling; Li, Xing-Ying; Cao, Jun; Ye, Li-Hong; Cao, Wan; Da, Jian-Hua; Dai, Han-Bin; Liu, Xiao-Juan

2014-06-11

253

Report on three aliphatic dimethylarsinoyl compounds as common minor constituents in marine samples. An investigation using high-performance liquid chromatography/inductively coupled plasma mass spectrometry and electrospray ionisation tandem mass spectrometry.  

PubMed

Three water-soluble aliphatic arsenicals, dimethylarsinoyl acetate (DMAA), dimethylarsinoyl ethanol (DMAE), and dimethylarsinoyl propionate (DMAP), were identified in marine biological samples. Sample extracts in methanol/water (1 + 1) were analysed by cation-exchange high-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC/ICPMS). Eluate fractions from the HPLC/ICPMS analyses containing the compounds in question were collected and subjected to analysis by electrospray ionisation tandem mass spectrometry (ESI-MS/MS), which provided supportive evidence for the structures of the three compounds. The concentrations of the three arsenicals were determined in 37 marine organisms comprising algae, crustaceans, bivalves, fish and mammals by HPLC/ICPMS. The three arsenicals DMAA, DMAE and DMAP, which occurred at microg kg(-1) concentrations, were detected in 25, 23 and 17 of the 37 samples analysed, respectively. The limits of detection were 2-3 microg kg(-1) dry mass. The data illustrate that the three compounds are common minor constituents in marine samples. This is the first report on DMAE and DMAP as naturally occurring species in marine samples. The presence of DMAA and DMAE supports a proposed biosynthesis of arsenobetaine (AB) from dimethylarsinoylribosides. Alternative proposals, which explain the presence of the compounds in marine samples, are addressed briefly in the paper. PMID:15593252

Sloth, Jens J; Larsen, Erik H; Julshamn, Kåre

2005-01-01

254

Automated and sensitive determination of four anabolic androgenic steroids in urine by online turbulent flow solid-phase extraction coupled with liquid chromatography-tandem mass spectrometry: A novel approach for clinical monitoring and doping control.  

PubMed

A novel method for automated and sensitive analysis of testosterone, androstenedione, methyltestosterone and methenolone in urine samples by online turbulent flow solid-phase extraction coupled with high performance liquid chromatography-tandem mass spectrometry was developed. The optimization and validation of the method were discussed in detail. The Turboflow C18-P SPE column showed the best extraction efficiency for all the analytes. Nanogram per liter (ng/L) level of AAS could be determined directly and the limits of quantification (LOQs) were 0.01ng/mL, which were much lower than normally concerned concentrations for these typical anabolic androgenic steroids (AAS) (0.1ng/mL). The linearity range was from the LOQ to 100ng/mL for each compound, with the coefficients of determination (r(2)) ranging from 0.9990 to 0.9999. The intraday and interday relative standard deviations (RSDs) ranged from 1.1% to 14.5% (n=5). The proposed method was successfully applied to the analysis of urine samples collected from 24 male athletes and 15 patients of prostate cancer. The proposed method provides an alternative practical way to rapidly determine AAS in urine samples, especially for clinical monitoring and doping control. PMID:24840468

Guo, Feng; Shao, Jing; Liu, Qian; Shi, Jian-Bo; Jiang, Gui-Bin

2014-07-01

255

Identification of metabolites in WZS-miniature pig urine after oral administration of Danshen decoction by HPLC coupled with diode array detection with electrospray ionization tandem ion trap and time-of-flight mass spectrometry.  

PubMed

Danshen (DS) is a widely used traditional Chinese medicine for treating cardiovascular and cerebrovascular diseases. A simple, rapid and sensitive method was developed for identification of the in vivo metabolites in urine of WZS-miniature pigs after oral administration of DS decoction by HPLC coupled with diode array detection with electrospray ionization tandem ion trap and time-of-flight mass spectrometry. This method has been successfully applied to simultaneous identification of 50 compounds (including 11 new ones) in pig urine. In addition, one new compound, (3-hydroxyphenyl) crylic acid glycine methyl ester (C1), along with eight known ones were first isolated by column chromatography and identified by spectroscopic means, including 1D/2DNMR and mass spectrometry, as reference substances. Ten phenolic compounds (protocatechuic aldehyde, protocatechuic acid, caffeic acid, danshensu, ferulic acid, isoferulic acid, rosmarinic acid and salvianolic acid A/B/D) were found to be the main absorbed original constituents of DS decoction, which underwent the metabolic reactions of glucuronidation, sulfation, methylation, hydrogenation and glycine conjugation in vivo. In conclusion, the developed method is applicable to the analysis and identification of constituents in biological matrices after administration of DS decoction. PMID:23212729

Zhao, Xin; Yang, Dong-Hui; Zhou, Qi-Le; Xu, Feng; Zhang, Lei; Liang, Jing; Liu, Guang-Xue; Cai, Shao-Qing; Yang, Xiu-Wei

2013-06-01

256

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

257

NADH oxidation and NAD+ reduction catalysed by tightly coupled inside-out vesicles from Paracoccus denitrificans.  

PubMed

Tightly coupled inside-out vesicles were prepared from Paracoccus denitrificans cells (SPP, sub-Paracoccus particles) and characterized kinetically. The rate of NADH oxidation, catalysed by SPP, increases 6-8 times on addition of gramicidin. The vesicles are capable of catalysing Delta micro H+-dependent reverse electron transfer from quinol to NAD+. The kinetic parameters of the NADH-oxidase and the reverse electron transfer carried out by membrane-bound P. denitrificans complex I were estimated and compared with those of the mitochondrial enzyme. The data demonstrate that catalytic properties of the dinucleotide-binding site of the bacterial and mitochondrial complex I are almost identical, pointing out similar organization of the site in mammals and P. denitrificans. Inhibition of the bacterial complex I by a specific inhibitor of Q reduction, rotenone, is very different from that of the mitochondrial enzyme. The inhibitor is capable of suppressing the NADH oxidation reaction only at micromolar concentrations, while the activity of mitochondrial enzyme is suppressed by nanomolar concentrations of rotenone. In contrast to the mitochondrial enzyme, rotenone, even at concentrations as high as 10 micro m, does not inhibit the reverse, Delta micro H+-dependent NAD+-reductase reaction on SPP. PMID:12180978

Kotlyar, Alexander B; Borovok, Natalia

2002-08-01

258

Tandem hydrofoil system  

Microsoft Academic Search

A tandem hydrofoil system enables an improvement in the lift-drag ratio of a high-speed ship. The conditions for favorable application of this type of foil structure are determined. The data on hydrofoil boats using a tandem system are presented. The problem of the stability of the vertical plane motion of a hydrofoil with bow and stern foils is considered. The

Konstantin I. Matveev; Ivan Ivanovich Matveev

2001-01-01

259

Solar water oxidation using nickel-borate coupled BiVO4 photoelectrodes.  

PubMed

A naturally abundant nickel-borate (Ni-Bi) complex is demonstrated to successfully catalyze the photoelectrochemical (PEC) water oxidation of BiVO4 electrodes at 1.23 VRHE with nearly 100% faradaic efficiency for oxygen evolution. Ni-Bi is electrodeposited (ED) and photodeposited (PD) for varying times on BiVO4 electrodes in the 0.1 M borate electrolyte with 1 mM Ni(2+) at pH 9.2. Surprisingly, optimally deposited Ni-Bi films (ED-10 s and PD-30 min) display the same layer thickness of ca. 40 nm. Both Ni-Bi films enhance the photocurrent generation of BiVO4 at 1.23 VRHE by a factor of 3-4 under AM 1.5-light irradiation (100 mW cm(-2)) along with ca. 250% increase in the incident and absorbed photon-to-current efficiencies. Impedance analysis further reveals that the charge transfer resistance at BiVO4 is markedly decreased by Ni-Bi deposits. The primary role of Ni-Bi has been suggested to be a hole-conductor making photogenerated electrons more mobile and catalyzing a four-hole transfer to water through cyclic changes between the lower and higher Ni oxidation states. However, thick Ni-Bi films (>~40 nm) significantly reduce the PEC performance of BiVO4 due to the kinetic bottleneck and charge recombination. Under identical PEC conditions (0.1 M, pH 9.2), the borate electrolyte (good proton acceptor) is found to be better than nitrate (poor proton acceptor), indicative of a proton-coupled electron transfer pathway in PEC water oxidation. PMID:23529529

Choi, Sung Kyu; Choi, Wonyong; Park, Hyunwoong

2013-05-01

260

Cytogenetic, Y chromosome microdeletion, sperm chromatin and oxidative stress analysis in male partners of couples experiencing recurrent spontaneous abortions  

Microsoft Academic Search

Purpose  Etiology in majority of couples experiencing recurrent spontaneous abortions (RSA) is still unknown. The aim of the study\\u000a was to find the role of cytogenetic abnormalities, Y chromosome microdeletion, oxidative stress (OS) and sperm DNA fragmentation\\u000a in male partners of couples experiencing RSA.\\u000a \\u000a \\u000a \\u000a \\u000a Methods  Forty-eight couples with history of RSA and 20 fertile controls were included in the study. The study

S. Venkatesh; J. Thilagavathi; K. Kumar; D. Deka; P. Talwar; Rima Dada

261

Peroxidase-catalyzed oxidative coupling of phenols in the presence of geosorbents: rates of non-extractable product formation.  

PubMed

Oxidative coupling processes in subsurface systems comprise a form of natural contaminant attenuation in which hydroxylated aromatic compounds (HACs) are incorporated into soil/sediment organic matter matrices. Here we describe the oxidative coupling of phenol catalyzed by horseradish peroxidase (HRP) in systems containing two geosorbents having organic matter of different composition; specifically Chelsea soil, a near-surface geologically young soil having a predominantly humic-type soil/sediment organic matter (SOM) matrix, and Lachine shale, a diagenetically older natural material having a predominantly kerogen-type SOM matrix. It was found that each of these two different types of natural geosorbents increased the formation of non-extractable coupling products (NEPs) over that which occurred in solids-free systems. The extent of coupling was higher in the systems containing humic-type Chelsea SOM than in those containing kerogen-type Lachine SOM. It was observed that HRP inactivation by free radical attack was significantly reduced in the presence of each geosorbent. A rate model was developed to facilitate quantitative evaluation and mechanistic interpretation of such coupling processes. Experimental rate measurements revealed thatthe greater extent of reaction observed in the presence of Chelsea soil than in the presence of Lachine shale can be attributed to two factors: (i) more effective protection of HRP from inactivation by the Chelsea SOM and (ii) the greater reactivity of Chelsea SOM with respect to cross-coupling. Interrelationships among enzyme protection, cross-coupling reactivity, and SOM chemistry are discussed. PMID:11878372

Huang, Qingguo; Selig, Hildegarde; Weber, Walter J

2002-02-15

262

An ultra-low Pd loading nanocatalyst with high activity and stability for CO oxidative coupling to dimethyl oxalate.  

PubMed

A Pd/?-Al2O3 nanocatalyst with ultra-low Pd loading exhibits high activity and stability for CO oxidative coupling to dimethyl oxalate, which was prepared by a Cu(2+)-assisted in situ reduction method at room temperature. The small size and high dispersion of Pd nanoparticles facilitated by Cu(2+) ions are responsible for the excellent catalytic activity. PMID:23552772

Peng, Si-Yan; Xu, Zhong-Ning; Chen, Qing-Song; Chen, Yu-Min; Sun, Jing; Wang, Zhi-Qiao; Wang, Ming-Sheng; Guo, Guo-Cong

2013-06-28

263

Synthesis of Diazo-Bridged BODIPY Dimer and Tetramer by Oxidative Coupling of ?-Amino-Substituted BODIPYs.  

PubMed

A diazo-bridged BODIPY dimer and tetramer were prepared by the oxidative coupling reaction of ?-amino-substituted BODIPYs. The structure of the dimer was elucidated by X-ray diffraction analysis, showing its coplanar orientation of two BODIPY units. Effective extension of ?-conjugation was confirmed by optical and electrochemical investigations. PMID:24811272

Yokoi, Hiroki; Hiroto, Satoru; Shinokubo, Hiroshi

2014-06-01

264

Supercritical fluid extraction and temperature-programmed desorption of phenol and its oxidative coupling products from activated carbon  

Microsoft Academic Search

Activated carbon remains one of the most economical adsorbents for the removal of contaminants from water. In particular, activated carbon is known to have an extremely high affinity for phenol and its derivatives. This has been shown to be the result of a catalytic process wherein activated carbon catalyzes the oxidative coupling reactions of phenol in aqueous solution when molecular

Raashina Humayun; Gurkan Karakas; Philip R. Dahlstrom; Umit S. Ozkan; David L. Tomasko

1998-01-01

265

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.

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

2014-01-01

266

Direct aqueous supercritical fluid extraction coupled on-line with liquid chromatography-tandem mass spectrometry for the analysis of polyether ionophore antibiotics in water.  

PubMed

A direct aqueous SFE system designed to extract water samples contained in vials has been coupled on-line with a reverse phase LC-MS-MS system using a single 10-port valve. An SFE trap system using C(1) stationary phase connected to a C(18) analytical HPLC column enabled the SFE-LC-MS-MS analysis of three polyether ionophore antibiotics in water using a step gradient. A quantitative SFE-LC-MS-MS method has been developed whereby the progress of SFE can be monitored directly on-line such that ionophore recovery profile data from a single water sample can be obtained. Using a continuous direct aqueous SFE period of 75 min, the SFE-LC-MS-MS recoveries of the ionophores were: monensin 76.2% with RSD 4.1%, lasalocid 84.6% with RSD 3.8% and narasin 91.2% with RSD 3.2%. With positive ion electrospray ionization, the SFE-LC-MS-MS system using a 4 mL water sample provided multiple reaction monitoring (MRM) limits of detection for monensin and lasalocid each equivalent to 90 ng/L whereas 30 ng/L for narasin. A two-way valve controlling carbon dioxide distribution to the SFE vessel has provided a means for the initial investigation of the recovery of ionophore sodium salts from water using static SFE. PMID:20381053

Ramsey, Edward D; Rees, Anthony T; Wei, Guo; Liu, Jing Y; Wu, Xiu H

2010-05-14

267

Multiresidue pesticide analysis of tuber and root commodities by QuEchERS extraction and ultra-performance liquid chromatography coupled to tandem mass spectrometry.  

PubMed

A simple, rapid, and reliable multiresidue method to determine 84 pesticides in potato and carrot samples by ultra-performance liquid chromatography coupled to MS/MS has been developed and fully validated for routine analysis according to ISO/IEC 17025:2005. The method makes use of a buffered Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) sample preparation procedure based on a single extraction with acidified acetonitrile, followed by partitioning with salts. Chromatographic conditions were optimized in order to achieve a rapid separation in the multiple reaction monitoring mode. Performance characteristics of the method, including an estimation of measurement uncertainty using validation data, are reported for both matrixes. Calibration curves were linear from 0.010 to 0.150 mg/kg for most compounds. The LOD and LOQ were 0.006 and 0.010 mg/kg, respectively, except for fluorocloridone, fluquinconazol, and hexitiazox, which were 0.030 and 0.050 mg/kg, respectively. Recoveries obtained were in the range 70-116%, with intraday precision values < or = 20% RSD and interday precision values < or = 25% RSD at two different concentration levels. The overall uncertainty of the method was estimated at two concentrations as being lower than 34% in all cases. The method has been applied to the analysis of 70 vegetable samples, and imidacloprid and linuron were the pesticides most frequently found in potato and carrot commodities, respectively. PMID:23175961

Garrido Frenich, Antonia; Martín Fernández, María del Mar; Díaz Moreno, Laura; Martínez Vidal, Jose Lúis; López-Gutiérrez, Noelia

2012-01-01

268

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

269

A novel mechanism of bisphenol A removal during electro-enzymatic oxidative process: chain reactions from self-polymerization to cross-coupling oxidation.  

PubMed

The catalyzed removal of bisphenol A (BPA) by a horseradish peroxidase (HRP) cathode in the presence of humic acid (HA) was investigated. At an optimal condition, the removal of BPA achieved 100% within 2min reaction. In the electro-enzymatic process, products were analyzed by high performance liquid chromatography with diode array detector (HPLC-DAD) and high performance size exclusion chromatography (HPSEC). HPLC-DAD results showed that BPA was oxidized into self-polymers and then self-polymers as important intermediate products decreased and disappeared. HPSEC results showed the order of molecular weight (MW): HA+BPA cross-coupling products>HA self-coupling products>initial HA. According to above results, a novel mechanism of BPA transformation in the presence of HA was proposed in electro-enzymatic process. In summary, under oxidation of in situ hydrogen peroxide on HRP electrode, the BPA first are polymerized into self-polymers, and then, the polymers may be incorporated into HA matrix and finally larger MW of BPAn-HA might be formed. The presence of HA can provide chain reactions from BPA self-polymerization to cross-coupling oxidation. Therefore, in the presence of HA, the electro-enzymatic oxidation is an effective way to improve BPA removal. PMID:23732003

Li, Haitao; Zhao, He; Liu, Chenming; Li, Yuping; Cao, Hongbin; Zhang, Yi

2013-08-01

270

Concerning the dependence of the selectivity of the formation of ethane and ethylene on the degree of methane conversion during its oxidative coupling  

SciTech Connect

The dependence of the maximum selectivity and the limiting yield of C{sub 2} hydrocarbons on the degree of methane conversion during its gas-phase oxidative coupling were calculated by means of kinetic simulation. The correlation between the results of the calculations and the rersults obtained in the experimental studies dealing with catalytic oxidative coupling of methane is discussed.

Vedeneev, V.I.; Arutyunov, V.S.; Basevich, V.Ya.

1995-03-01

271

Active H+ transport in the turtle urinary bladder. Coupling of transport to glucose oxidation  

PubMed Central

The turtle urinary bladder acidifies the contents of its lumen by actively transporting protons. H+ secretion by the isolated bladder was measured simultaneously with the rate of 14CO2 evolution from [14C]glucose. The application of an adverse pH gradient resulted in a decline in the rate of H+ secretion (JH) and in the rate of glucose oxidation (JCO2). The changes in JH and JCO2 were linear functions of the pH difference across the membrane. Hence, JH and JCO2 were linearly related to each other. The slope, deltaJH/deltaJCO2 was found to be similar in half-bladders from the same animal but was seen to vary widely in a population of turtles. To investigate the effect of pH gradients on deltaJH/deltaJCO2, two experiments were performed in each of 14 hemibladders. In one, JH and JCO2 were altered by changing the luminal pH. In the other, they were altered by changing the ambient pCO2 while the luminal pH was kept constant. The average slope, deltaJH/deltaJCO2, in the presence of pH gradients was 14.45 eq-mol-1. In the absence of gradients in the same hemibladders it was 14.72, delta = 0.27 +/- 1.46. The results show that H+ transport is organized in such a way that leaks to protons in parallel to the pump are negligible. Analysis of the transport system by use of the Essig-Caplan linear irreversible thermodynamic formalism shows that the system is tightly coupled. The degree of coupling, q, given by that analysis was measured and found to be at or very near the maximum theoretical value.

1976-01-01

272

Qualitative analysis and enantiospecific determination of angular-type pyranocoumarins in Peucedani Radix using achiral and chiral liquid chromatography coupled with tandem mass spectrometry.  

PubMed

Angular-type pyranocoumarins (APs), the derivatives of khellactone, are widely documented as the main active constituents in Peucedani Radix (Chinese name: Qian-hu). Owing to the natural occurrence of chiral centers, enantiomers of APs are extensively distributed in the original plant, and enantioselective performances have been definitely demonstrated for these enantiomers. In current study, the chemical characterization of the major and minor APs in Peucedani Radix was performed using ultra high performance liquid chromatography coupled with diode array detector and hybrid ion trap-orbitrap mass spectrometry. On the other hand, a heart-cut two-dimensional achiral-chiral liquid chromatography combining triple quadropole-linear ion trap mass spectrometry system (2D LC-MS/MS) was developed for simultaneous enantiospecific quantification of eighteen coumarins, including seven pairs of enantiomers. Eleven APs (1-11) were recruited to propose UV absorption characteristics and electrospray ionization fragmentation patterns of APs. A total of 42 components were categorized into APs based on their UV spectral properties and identified according to the proposed mass fragmentation pathways, while two linear-type furanocoumarins (12-13) were unambiguously assigned by further purification. A Capcell core RP-C18 column was employed in the primary LC dimension to achieve efficient racemic separation for the main chemical constituents (1-9 and 12-13) in Peucedani Radix, while a Chiralpak AD-RH column was utilized in the secondary dimension to contribute enantioselective separation for seven enantiomerically enriched components (1, 3 and 5-9). Collectively, the results provided the chemical evidences for revealing the material basis of the therapeutic effects of Peucedani Radix, and the developed 2D LC-MS/MS system in the present study is expected to be an ideal tool for the quality control of Peucedani Radix as well as a reliable technique for complex matrices containing both achiral and chiral components. PMID:24630501

Song, Y L; Jing, W H; Du, G; Yang, F Q; Yan, R; Wang, Y T

2014-04-18

273

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

PubMed

The design of molecular electrocatalysts for H(2) 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 H(2) 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

2012-09-25

274

Nitric oxide contracts longitudinal smooth muscle of opossum oesophagus via excitation-contraction coupling  

PubMed Central

The effects of sodium nitroprusside (SNP) and diethylenetriamine/nitric oxide adduct (DETA/NO), putative nitric oxide (NO) donors, on opossum oesophageal longitudinal smooth muscle were investigated using isometric tension and intracellular micro-electrode recordings.SNP produced concentration-dependent contractions of oesophageal longitudinal smooth muscle with an EC50 of 239.6 ± 78.2 ?m (mean ±s.e.m., n = 10). Maximal contraction induced by SNP (1 mm) was about 75.5 ± 8.5 % (n = 10) of the 60 mm KCl-induced contraction. The SNP-induced contraction was resistant to tetrodotoxin (TTX; 1 ?m), but abolished by nifedipine (1 ?m), as well as by niflumic acid (300 ?m) and 9-anthroic acid (9-AC; 1 mm), Ca2+-activated Cl? channel blockers.DETA/NO at concentrations of 100 and 500 ?m induced 83.1 ± 24.4 and 104.1 ± 34.9 % of the 60 mm KCl-induced contraction (n = 4), respectively, which was abolished by nifedipine (1 ?m), niflumic acid (300 ?m) and 9-AC (1 mm).Pre-application of 1H-[1,2,4]oxidiazolo[4,3,-?]quinoxalin-1-one (ODQ) (10 ?m), a guanylate cyclase inhibitor, significantly inhibited the SNP-induced contraction, whereas 8-bromo-cGMP (1 mm), a membrane-permeable analogue of cGMP, mimicked the SNP-induced contraction.Intracellular recordings revealed that SNP (300 ?m) depolarized resting membrane potentials (RMPs) and increased the frequency of spontaneous spike-like action potentials. However, these electrical alterations were eliminated by pretreatment with niflumic acid (300 ?m).These results suggest that NO produces an excitation-contraction coupling in opossum oesophageal longitudinal smooth muscle via a cGMP-dependent signalling pathway. This contraction depends on extracellular Ca2+ entry through activation of L-type Ca2+ channels.

Zhang, Yong; Paterson, William G

2001-01-01

275

Interplay of spin-orbit coupling, correlations, and crystal anisotropy in 5d oxides  

NASA Astrophysics Data System (ADS)

We investigate the correlated d-level electronic structure of 5d Ir and Os oxide compounds by fully ab initio quantum-chemical many-body calculations on finite embedded clusters. The wave-function quantum-chemical methods provide a promising alternative to density-functional-based approaches to the electronic structure of solids. The computed d-d excitations in square-lattice, honeycomb, pyrochlore, and chain-like iridates compare well with recent RIXS (resonant inelastic x-ray scattering) data. We also perform a detailed analysis of the relativistic spin-orbit wave functions and compute observables such as the ground-state expectation value of the spin-orbit operator. The latter is in principle accessible from x-ray absorption and provides information on the role of t2g--,eg couplings in the ground-state wave function and on the strength of non-cubic fields that lift the degeneracy of the t2g levels. As concerns the departure from cubic symmetry, interesting effects are found in A2Ir2O7 pyrochlores, where the highly anisotropic, hexagonal configuration of the adjacent A-site ions breaks cubic symmetry even in the absence of O-ligand trigonal distortions and moreover competes with the latter. Our findings open new perspectives in pyrochlore oxides. In 227 iridates, the outcome of this competition is decisive for the actual realization of any type of non-trivial topological ground state. In 227 spin systems with S /2, e.g., Cd2Os2O7, this interplay decides the sign of the single-ion anisotropy and the degree of magnetic frustration.

Hozoi, Liviu

2013-03-01

276

Quantitative analysis of PD 0332991 in mouse plasma using automated micro-sample processing and microbore liquid chromatography coupled with tandem mass spectrometry.  

PubMed

In the oncology therapeutic area, the mouse is the primary animal model used for efficacy studies. Often with mouse pharmacokinetic (PK) and pharmacokinetic/pharmacodynamic (PK/PD) studies, less than 20 ?L of total plasma sample volume is available for bioanalysis due to the small size of the animal and the need to split samples for other measurements such as biomarker analyses. The need to conduct automated "small volume" sample processing for quantitative bioanalysis has therefore increased. An automated fit for purpose protein precipitation (PPT) method using a Hamilton MicroLab Star (Reno, NV, USA) to support mouse PK and PK/PD studies for an oncology drug candidate PD 0332991, (a specific inhibitor of cyclin-dependent kinase 4 (CDK-4) currently in development) for processing "small volumes" was developed. The automated PPT method was achieved by extracting and processing 10 ?L out of a minimum sample volume of 15 ?L plasma utilizing the Hamilton MicroLab Star. A 96-conical shallow well plate by Agilent Technologies, Inc (Wilmington, DE, USA) was the labware of choice used in the automated Hamilton "small volume" method platform. Analyses of a 10 ?L plasma aliquot from 15 ?L of plasma study samples were conducted by both automated and manual PPT method. All plasma samples were quantitated using a Sciex API 4000 triple quadrupole mass spectrometer coupled with an Eksigent Express HT Ultra HPLC system. The chromatography was achieved using an Agilent microbore C(18) Extend, 1.0 × 50 mm, 3.5 ?m column at a flow rate of 0.150 mL/min with a total run time of 1.8 min. Accuracy and precision of standard and QC concentration levels were within 90-107% and <14%, respectively. Calibration curves were linear over the dynamic range of 1.0-1000 ng/mL. PK studies for PD 0332991 were conducted in female C3H mice following intravenous administration at 1mg/kg and oral administration at 2mg/kg. PK values such as area under curve (AUC), volume of distribution (Vd), clearance (Cl), half life (T(1/2)) and bioavailability (F%) demonstrated less than 11% difference between the automated Hamilton and manual PPT methods. The results demonstrate that the automated Hamilton PPT method can accurately and precisely aliquot 10 ?L of plasma from 15 ?L or larger volume plasma samples. The fit for purpose Hamilton PPT method is suitable for routine analyses of plasma samples from micro-sampling PK and PK/PD samples to support discovery studies. PMID:21889427

Smith, Danielle; Tella, Max; Rahavendran, Sadayappan V; Shen, Zhongzhou

2011-10-01

277

Analysis of the benzene oxide-DNA adduct 7-phenylguanine by liquid chromatography-nanoelectrospray ionization-high resolution tandem mass spectrometry-parallel reaction monitoring: Application to DNA from exposed mice and humans.  

PubMed

Benzene oxide, the initial metabolite of the human carcinogen benzene, reacts with DNA producing 7-phenylguanine (7-PhG) and other products. We developed a highly sensitive liquid chromatography-nanoelectrospray ionization-high resolution tandem mass spectrometry-parallel reaction monitoring method for the analysis of 7-PhG in DNA. Accuracy and precision of the method were established and the detection limit was about 8amol of 7-PhG injected on the column and less than 1 adduct per 10(9) nucleotides in DNA. 7-PhG was detected in calf thymus DNA reacted with 1?M to 10mM benzene oxide. The method was applied for the analysis of DNA isolated from bone marrow, lung, and liver of B6C3F1 mice treated by gavage with 50mg/kg benzene in corn oil 5 times weekly for 4weeks. 7-PhG was not detected in any of these DNA samples. The method was applied to DNA from mouse hepatocytes exposed to 100?M benzene oxide and human TK-6 lymphoblasts exposed to 100?M, 1, and 10mM benzene oxide. 7-PhG was only detected in TK-6 cell DNA from the 10mM exposure. The method was also applied to leukocyte DNA from 10 smokers and 10 nonsmokers. 7-PhG was detected in only one DNA sample, from a nonsmoker. The results of this study do not support the hypothesis that the benzene oxide-DNA adduct 7-PhG is involved in carcinogenesis by benzene. PMID:24632417

Zarth, Adam T; Cheng, Guang; Zhang, Zhaobin; Wang, Mingyao; Villalta, Peter W; Balbo, Silvia; Hecht, Stephen S

2014-05-25

278

A dual-cathode electro-Fenton oxidation coupled with anodic oxidation system used for 4-nitrophenol degradation  

Microsoft Academic Search

The degradation of 4-nitrophenol was investigated using a novel electrochemical oxidation system, in which the anodic oxidation at Ti\\/SnO2–Sb2O5–IrO2 electrode and the electro-Fenton oxidation with two cathodes were involved. In this system, gas diffusion electrode (GDE) was used to generate H2O2 by O2 reduction and graphite electrode was employed for the reduction of Fe3+ regenerating Fe2+. When the potential values

Y. Y. Chu; Y. Qian; W. J. Wang; X. L. Deng

279

Direct determination of glyphosate and its major metabolite, aminomethylphosphonic acid, in fruits and vegetables by mixed-mode hydrophilic interaction/weak anion-exchange liquid chromatography coupled with electrospray tandem mass spectrometry.  

PubMed

A novel method was developed for the direct, sensitive, and rapid determination of glyphosate and its major metabolite, aminomethylphosphonic acid (AMPA), in fruit and vegetable samples by mixed-mode hydrophilic interaction/weak anion-exchange liquid chromatography (HILIC/WAX) coupled with electrospray tandem mass spectrometry (ESI-MS/MS). Homogenized samples were extracted with water, without derivatization or further clean-up, and the extracts were injected directly onto the Asahipak NH2P-50 4E column (250 mm × 4.6 mm i.d., 5 ?m). The best results were obtained when the column was operated under mixed-mode HILIC/WAX elution conditions. An initial 10-min washing step with acetonitrile/water (10:90, v/v) in HILIC mode was used to remove potentially interfering compounds, and then the analytes were eluted in WAX mode with acetonitrile and water containing 0.1 molL(-1) ammonium hydroxide under gradient elution for the ESI analysis in negative ion mode. Limits of quantification of glyphosate and AMPA were 5 ?gkg(-1) and 50 ?gkg(-1), respectively, with limits of detection as low as 1.2 ?gkg(-1) for glyphosate and 15 ?gkg(-1) for AMPA. The linearity was satisfactory, with correlation coefficients (r)>0.9966. Recovery studies were carried out on spiked matrices (6 vegetables, 3 fruits) with glyphosate at four concentrations and AMPA at three concentrations. The mean recoveries for glyphosate and AMPA were 75.3-110% and 76.1-110%, respectively, with relative standard deviations in the range of 1.1-13.8%. The intra-day precision (n=7) for glyphosate and AMPA in vegetable and fruit samples spiked at an intermediate level between 5.9% and 7.5%, and the inter-day precision over 11 days (n=11) was between 7.0% and 13%. PMID:23261284

Chen, Ming-Xue; Cao, Zhao-Yun; Jiang, Yan; Zhu, Zhi-Wei

2013-01-11

280

Determination of melamine in animal feed based on liquid chromatography tandem mass spectrometry analysis and dynamic microwave-assisted extraction coupled on-line with strong cation-exchange resin clean-up.  

PubMed

In this work, a new method was developed for the determination of melamine (MEL) in animal feed. The method was based on the on-line coupling of dynamic microwave-assisted extraction (DMAE) to strong cation-exchange (SCX) resin clean-up. The MEL was first extracted by 90% acidified methanol aqueous solution (v/v, pH = 3) under the action of microwave energy, and then the extract was cooled and passed through the SCX resin. Thus, the protonated MEL was retained on the resin through ion exchange interaction and the sample matrixes were washed out. Some obvious benefits were achieved, such as acceleration of analytical process, together with reduction in manual handling, risk of contamination, loss of analyte, and sample consumption. Finally, the analyte was separated by a liquid chromatograph with a SCX analytical column, and then identified and quantitatived by a tandem mass spectrometry with positive ionization mode and multiple-reaction monitoring. The DMAE parameters were optimized by the Box-Behnken design. The linearity of quantification obtained by analyzing matrix-matched standards is in the range of 50-5,000 ng g(-1). The limit of detection and limit of quantification obtained are 12.3 and 41.0 ng g(-1), respectively. The mean intra- and inter-day precisions expressed as relative standard deviations with three fortified levels (50, 250, and 500 ng g(-1)) are 5.1% and 7.3%, respectively, and the recoveries of MEL are in the range of 76.1-93.5%. The proposed method was successfully applied to determine MEL in different animal feeds obtained from the local market. MEL was detectable with the contents of 279, 136, and 742 ng g(-1) in three samples. PMID:19756536

Chen, Ligang; Zeng, Qinglei; Du, Xiaobo; Sun, Xin; Zhang, Xiaopan; Xu, Yang; Yu, Aimin; Zhang, Hanqi; Ding, Lan

2009-11-01

281

Metabolites profile of Xian-Ling-Gu-Bao capsule, a traditional Chinese medicine prescription, in rats by ultra performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry analysis.  

PubMed

Xian-Ling-Gu-Bao capsule (XLGB), a well-known traditional Chinese medicine prescription (TCMP), is widely used for the treatment of osteoporosis. However, due to lack of metabolism research, the effective material of XLGB is still unknown. It entails a huge obstacle for the clinical-safe medication administration and quality control of XLGB. To explore the metabolic fate of multiple components of XLGB, herein, we proposed a "representative structure based homologous xenobiotics identification" (RSBHXI) strategy based on ultra performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry (UPLC/Q-TOF-MS) and mass defect filter (MDF) technique. A total of 147 XLGB-related xenobiotics were identified or tentatively characterized in rat biofluids after oral administration of XLGB, including 134 (57 prototype components and 77 metabolites) in plasma, 93 (37 prototype components and 56 metabolites) in urine and 118 (46 prototype components and 72 metabolites) in bile. Our results indicated that prenylated flavonol glycosides from Herba epimedii, prenylated flavonoids from Fructus psoraleae, saponins from Radix dipsaci and Rhizoma anemarrahenae, as well as tanshinones from Radix Salviae Miltiorrhizae were major absorbed chemical components of XLGB. Hydrolysis, glucuronidation and sulfation were major metabolic reactions of XLGB. As more xenobiotics were detected in bile than those in urine, it demonstrated that multiple components of XLGB underwent comprehensive hepatobiliary excretion. The present study expands our knowledge about the metabolism of XLGB which will be conducive to revealing its in vivo pharmacological material basis. In addition, the application of RSBHXI strategy provides a new approach for metabolite identification of TCMPs and other complex mixture. PMID:24731969

Geng, Jian-liang; Dai, Yi; Yao, Zhi-hong; Qin, Zi-fei; Wang, Xin-luan; Qin, Ling; Yao, Xin-sheng

2014-08-01

282

Quantification of endogenous brassinosteroids in plant by on-line two-dimensional microscale solid phase extraction-on column derivatization coupled with high performance liquid chromatography-tandem mass spectrometry.  

PubMed

An on-line two-dimensional microscale solid phase extraction (2D?SPE)-on column derivatization (OCD)-high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS) method was developed for quantification of brassinosteroids (BRs) in plant tissues. Five BRs with widest distribution in plant species and high bioactivity (24-epibrassinolide, 24-epicastasterone, 6-deoxo-24-epicastasterone, teasterone and typhastero) were selected as target analytes. 2D?SPE column packed sequentially with phenyl boronic acid silica sorbent (the first dimension) and C18 silica sorbent (the second dimension) was used to selectively extract and enrich BRs by 110-146 times. OCD was carried out on the second dimension of 2D?SPE column with m-aminophenylboronic acid (m-APBA) as a derivatization reagent, enhancing the sensitivity of MS/MS to BRs by 13-8437 times. It was also found that pre-trap of derivatization reagent on the C18 section of 2D?SPE column could increase reaction efficiency by 3-10 times. The whole process time of the on-line system was less than 30min. The detection limits of the method for five BRs were between 1.4 and 6.6pg with RSDs less than 10%. Endogeneous BRs in tomato leaves were analyzed by using this method. Owing to the high selectivity of this on-line 2D?SPE system, BRs in plant extracts could be quantified using matrix-free standard calibration method with relative recoveries in the range of 80-124%. PMID:23702098

Wu, Qian; Wu, Dapeng; Shen, Zheng; Duan, Chunfeng; Guan, Yafeng

2013-07-01

283

Enantioselective synthesis of 2-substitued-tetrahydroisoquinolin-1-yl glycine derivatives via oxidative cross-dehydrogenative coupling of tertiary amines and chiral nickel(II) glycinate.  

PubMed

The asymmetric synthesis of 2-substituted-tetrahydroisoquinolin-1-yl glycines was achieved by an oxidative cross-dehydrogenative coupling (CDC) reaction. This method for activation of the ?-C-H bonds of amines with chiral nickel(II) glycinate using o-chloranil as the sole oxidant afforded highly diastereoselective coupling adducts. The decomposition of coupling adducts readily afforded 2-substituted-tetrahydroisoquinolin-1-yl glycine derivatives. PMID:24111642

Zhou, Shengbin; Wang, Jiang; Lin, Daizong; Zhao, Fei; Liu, Hong

2013-11-15

284

The mechanism for proton-coupled electron transfer from tyrosine in a model complex and comparisons with Y(Z) oxidation in photosystem II.  

PubMed Central

In the water-oxidizing reactions of photosystem II (PSII), a tyrosine residue plays a key part as an intermediate electron-transfer reactant between the primary donor chlorophylls (the pigment P(680)) and the water-oxidizing Mn cluster. The tyrosine is deprotonated upon oxidation, and the coupling between the proton reaction and electron transfer is of great mechanistic importance for the understanding of the water-oxidation mechanism. Within a programme on artificial photosynthesis, we have made and studied the proton-coupled tyrosine oxidation in a model system and been able to draw mechanistic conclusions that we use to interpret the analogous reactions in PSII.

Sjodin, Martin; Styring, Stenbjorn; Akermark, Bjorn; Sun, Licheng; Hammarstrom, Leif

2002-01-01

285

Interactions of soil-derived dissolved organic matter with phenol in peroxidase-catalyzed oxidative coupling reactions.  

PubMed

The influence of dissolved soil organic matter (DSOM) derived from three geosorbents of different chemical composition and diagenetic history on the horseradish peroxidase (HRP) catalyzed oxidative coupling reactions of phenol was investigated. Phenol conversion and precipitate-product formation were measured, respectively, by HPLC and radiolabeled species analysis. Fourier transform infrared (FTIR) spectroscopy and capillary electrophoresis (CE) were used to characterize the products of enzymatic coupling, and the acute toxicities of the soluble products were determined by Microtox assay. Phenol conversion and precipitate formation were both significantly influenced by cross-coupling of phenol with dissolved organic matter, particularly in the cases of the more reactive and soluble DSOMs derived from two diagenetically "young" humic-type geosorbents. FTIR and CE characterizations indicate that enzymatic cross-coupling in these two cases leads to incorporation of phenol in DSOM macromolecules, yielding nontoxic soluble products. Conversely, cross-coupling appears to proceed in parallel with self-coupling in the presence of the relatively inert and more hydrophobic DSOM derived from a diagenetically "old" kerogen-type shale material. The products formed in this system have lower solubility and precipitate more readily, although their soluble forms tend to be more toxic than those formed by dominant cross-coupling reactions in the humic-type DSOM solutions. Several of the findings reported may be critically important with respect to feasibility evaluations and the engineering design of associated remediation schemes. PMID:14740756

Huang, Qingguo; Weber, Walter J

2004-01-01

286

Quantification of ethylenediamine-N,N'-bis(hydroxysulfophenylacetic) acid regioisomers and structural characterisation of its related polycondensation products by porous graphitic carbon high-performance liquid chromatography coupled to electrospray tandem mass spectrometry.  

PubMed

Among the commercial ethylenediamine-N,N'-bis(2-hydroxy)phenylacetic acid/iron(III) derivatives, ethylenediamine-N,N'-bis(2-hydroxy-5-sulphophenylacetic) acid/iron(III) (EDDHSA/Fe) represents one of the promising chelates for the treatment of chlorotic plants. Industrial synthesis of EDDHSA/Fe leads to relevant amounts of o,o-EDDHSA condensation products (o,o-EDDHSAcps) and other secondary products that might have important relevance from the agronomic point of view. However, their chemical structures have remained unknown to date. Analysis of iron complexes by ion-pair reversed-phase chromatography, coupled with electrospray tandem mass spectrometry revealed the presence of the meso-o,o-EDDHSA/Fe, rac-o,o-EDDHSA/Fe, o,p-EDDHSA/Fe regioisomers, the hydroxyl derivative of o,o-EDDHSA/Fe, and the three main EDDHSA condensation products chelating the iron(III) (EDDHSAcps/nFe). However, the chromatographic peaks of EDDHSAcps/Fe are not well resolved due to the large numbers of stereoisomers and the poor efficiency of the ion-pair reversed-phase separation method. An alternative chromatographic method is based on porous graphitic carbon (PGC) separation after pre-column decomplexation of the chelates with trifluoracetic acid, which was developed to allow detection of EDDHSA stereo/regioisomers, EDDHSAcps, and low-molecular-weight by-products. This extensive PGC-HPLC-ESI-MS/MS investigation provides quantitative determination of meso-o,o-EDDHSA, rac-o,o-EDDHSA and o,p-EDDHSA, in addition to characterisation of EDDHSAcps and the low-molecular-weight by-products. PGC separation coupled to a triple quadrupole ESI-MS detector allowed characterisation of free ligands using collision-induced dissociation experiments in positive and negative ionisation mode, providing comparative evaluation of EDDHSAcps in three commercial samples. For detection, the PGC-HPLC-ESI-MS/MS is the best method according to the limit of quantification and limit of detection (picomolar and sub-picomolar detection, respectively) for determination of meso-EDDHSA and rac-o,o-EDDHSA. Synthesis, purification and quantification of o,o-EDDHSA and o,p-EDDHSA by (1)H-nuclear magnetic resonance are also reported. PMID:24028933

Biasone, Alessandro; Cianci, Giusto; Di Tommaso, Donata; Piaggesi, Alberto; D'Alessandro, Nicola

2013-10-18

287

Controls on N2 production via iron reduction coupled to anaerobic ammonium oxidation  

NASA Astrophysics Data System (ADS)

Iron (Fe) reduction coupled to anaerobic ammonium (NH4+) oxidation is a novel nitrogen (N) cycling pathway that can lead to ecosystem N loss via production of dinitrogen (N2), nitrate (NO3-), or nitrite (NO2-). This pathway, termed Feammox, can short circuit the N cycle via direct N2 production or lead to N2O and N2 production via denitrification of Feammox-generated NO2- and NO3-. Theoretically, Feammox becomes less thermodynamically favorable as pH increases, with pH 6.5 as the threshold for favorability of Feammox to NO2- or NO3-. Availability of iron oxides may also limit Feammox rates because high labile C availability drives high Fe reduction rates under anaerobic soil conditions. In contrast, NH4+ availability may not be a strong control on Feammox rates if gross mineralization and/or dissimilatory NO3- reduction to NH4+ continue to produce NH4+ under anaerobic conditions. We performed laboratory experiments using surface soils (0-10 cm depth) from the Luquillo Experimental Forest, Puerto Rico to investigate the controls on Feammox rates. Soil slurries were pre-incubated in an oxygen (O2)-free glove box for 6 days to deplete background O2, NO2-, and NO3-. We measured the 30N2 mole fraction of produced N2 at 24 hours after the addition of either 15NH4+ alone or 15NH4+ in stoichiometric equivalency with an amorphous Fe(III) gel (HFO) to the soil slurries (n = 8). Feammox rates were conservatively estimated from 30N2 alone because 30N2 production could result only from Feammox of 15NH4+ whereas 29N2 production could result from a variety of pathways. In soils at pH 4.27 ± 0.02, we measured rates of Feammox ranging from 0.32 ± 0.13 ?g N g-1 d-1 (± SE), following 15NH4+ addition alone, to 1.20 ± 0.28 ?g N g-1 d-1 with the addition of both 15NH4+ and Fe(III). In soils at pH 6.12 ± 0.03, Feammox rates ranged from 0.03 ± 0.01 ?g N g-1 d-1, following 15NH4+ addition alone, to 0.02 ± 0.01 ?g N g-1 d-1 with the addition of both 15NH4+ and Fe(III). Our data suggest that the threshold for thermodynamic favorability of Feammox may be lower than calculated (~6.2) and that the Fe oxide limitation of Feammox rates is less important at high pH. Feammox is most likely to occur in highly weathered soils rich in poorly crystalline Fe that experience fluctuating redox conditions so that Fe oxides are replenished and relatively low pH conditions are restored during oxic periods.

Yang, W. H.; Weber, K.; Silver, W. L.

2011-12-01

288

Interfacial refractive index sensing using visible-excited intrinsic zinc oxide photoluminescence coupled to whispering gallery modes  

NASA Astrophysics Data System (ADS)

Whispering gallery modes (WGMs) excited by the intrinsic photoluminescence (PL) in zinc oxide microspherical resonators are investigated in this work. The microspheres were synthesized via a one-pot hydrothermal technique. A polymer was applied after the synthesis to fill remaining pores in the oxide particle. Defect-related ZnO PL was excited in the visible, coupling to WGMs. The observed WGMs red-shift with increasing refractive index of the surrounding medium with a sensitivity of 90-100 nm/refractive index unit. The spherical microresonators may be used to investigate binding to and structure at the particle/solution interface.

Moirangthem, Rakesh Singh; Erbe, Andreas

2013-07-01

289

Liquid-phase polymer-based retention and coupled electrocatalytic oxidation to remove Arsenic in the presence of competitive species  

Microsoft Academic Search

The goal was to remove arsenate species in the presence of competitive anions by coupling of liquid-phase polymer-based retention,\\u000a LPR, a procedure based on the selective As(V) adsorption properties of cationic water-soluble polymers, with an electro-catalytic\\u000a oxidation process (EO) of As(III) into its more easily removable As(V). The electro-catalytic oxidation of As(III) to As(V)\\u000a was performed with an organic supporting

María del Carmen Aguirre; Bernabé L. Rivas; Carlos Peña; Luis Basaez

290

Oxidative coupling of methane over Li +-added Y 2O 3 catalyst prepared from Y(OH) 3  

Microsoft Academic Search

Oxidative coupling of methane was carried out over various metal oxide catalysts (MgO, Y2O3, La2O3, Sm2O3 and Ho2O3) modified with Li+ and the catalytic performance of the catalysts was examined. Li+-added Y2O3 catalyst, which was prepared by impregnation of Y2O3 with an aqueous solution of Li2CO3, was the most effective for the formation of ethene and ethane among all the

Sakae Takenaka; Tomohiro Kaburagi; Ichiro Yamanaka; Kiyoshi Otsuka

2001-01-01

291

Thermal decomposition of Ca(Oh) 2 from acetylene manufacturing: a route to supports for methane oxidative coupling catalysts  

Microsoft Academic Search

Oxidative coupling of methane (OCM) is one of the most widely studied catalytic reactions nowadays, due mainly to the large amounts of natural gas whose use to produce heavier hydrocarbons and alcohols would increase its profitability [1-5]. The reaction is generally performed using basic catalysts, supported on MgO or CaO, doped with alkaline or rare-earth cations [6-10]. In this letter,

M. J. Hologado; V. Rives; S. San Román

1992-01-01

292

An investigation of the oxygen pathways in the oxidative coupling of methane over MgO-based catalysts  

SciTech Connect

The catalytic effects of MgO, Li/MgO, and Sn/Li/MgO in the oxidative coupling of methane to ethane and ethane have been studied between 923 to 1073 K. In order to probe the role of surface oxygen in the reaction, pulses of oxygen were followed by pulses of either methane, ethane, ethene, or carbon monoxide. 56 refs., 8 figs., 3 tabs.

Mallens, E.P.J.; Hoebink, J.H.B.J.; Marin, G.B. [Schuit Inst. of Catalysis, Eindhoven (Netherlands)] [Schuit Inst. of Catalysis, Eindhoven (Netherlands)

1996-05-01

293

Copper (II) Schiff base catalysed aerobic oxidative coupling of 2-naphthols: an efficient and simple synthesis of binaphthols  

Microsoft Academic Search

Copper (II) Schiff base complexes of 2-(1-phenylethyl imino) methylphenol (3), methyl-N-(2-hydroxyphenyl)-l-serine (4) and methyl-N-(2-hydroxyphenyl)-l-tyrosine (5) were found to be an efficient catalyst for the aerobic oxidative coupling of 2-naphthols to binaphthols. Among the various copper (II) Schiff base complexes, the complex 3 was found to be the most reactive for this transformation.

Vishal B. Sharma; Suman L. Jain; Bir Sain

2004-01-01

294

Catalytic properties of mesoporous amorphous silicates of rare-earth elements in the methane oxidative coupling reaction  

Microsoft Academic Search

The influence of the composition of new materials—mesoporous amorphous lanthanide silicates—on the features of their porous\\u000a structure and the effectiveness of the oxidative coupling of methane (single-stage production of ethylene, ethane, and their\\u000a homologues from methane) is revealed. The synergistic effect in this reaction of La and Ce ions introduced into the silicate\\u000a matrix at the sol-gel synthesis stage, which

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

2010-01-01

295

Effects of superbasic catalysts prepared by promoting MgO with bialkali metal compounds on the oxidative coupling of methane  

Microsoft Academic Search

The improvement in methane conversion, C[sub 2] selectivity, and stability with time-on-stream for the oxidative coupling of methane (OCM) has been studied by employing superbasic catalysts prepared by promoting MgO with various binary alkali metal compounds. The performance of the resulting catalysts is found to strongly depend on the nature of the alkali metal compounds forming the pair, the promoter

E. Ruckenstein; A. Z. Khan

1993-01-01

296

An Investigation of the Oxygen Pathways in the Oxidative Coupling of Methane over MgO-Based Catalysts  

Microsoft Academic Search

The oxidative coupling of methane to ethane and ethene has been investigated by admitting pulses of pure methane, pure oxygen, and mixtures of methane and oxygen to MgO, Li\\/MgO, and Sn\\/Li\\/MgO at temperatures ranging from 923 to 1073 K in a Temporal Analysis of Products (TAP) set-up. Moreover, pulses of oxygen followed by pulses of either methane, ethane, ethene, or

E. P. J. Mallens; J. H. B. J. Hoebink; GBMM Marin

1996-01-01

297

Tapered aluminum-doped vertical zinc oxide nanorod arrays as light coupling layer for solar energy applications  

Microsoft Academic Search

Tapered aluminum-doped vertical zinc oxide nanorod arrays have been prepared by using simple electrodeposition at 75°C from an aqueous solution of zinc nitrate and aluminum nitrate. Two substrates were used, i.e., copper indium gallium (di)selenide solar cells and a solar thermal absorber. The resulting nanorod arrays were of high optical quality, indicting their applicability as a light coupling layer via

Jie Chen; Hong Ye; Lorenz Aé; Yang Tang; David Kieven; Thorsten Rissom; Julia Neuendorf; Martha Ch. Lux-Steiner

2011-01-01

298

Coupled reductive and oxidative degradation of 4-chloro-2-nitrophenol by a co-immobilized mixed culture system  

Microsoft Academic Search

The restriction of oxygen transfer in Ca-alginate beads used for the immobilization of microbial cells was applied to a coupled reductive and oxidative microbial degradation of the xenobiotic 4-chloro-2-nitrophenol (CNP). The conversion of CNP by Enterobacter cloacae under anaerobic conditions led to the formation of 4-chloro-2-aminophenol (CAP, 81%) and 4-chloro-2-acetaminophenol (CAAP, 16%) after 50 h incubation. CAP, the main reduction

Jiirgen Beunink; Hans-Jiirgen Rehm

1990-01-01

299

Determination of moxifloxacin and its oxidation products with kinetic evaluation under potassium permanganate treatment in acidic solution by ultra-performance liquid chromatography/tandem mass spectrometry.  

PubMed

A simple, sensitive, and reproducible ultra-performance LC method for the determination of moxifloxacin (MOXI) oxidation stability under permanganate treatment in acidic conditions (pH 3.0-6.0) was developed. Besides the MOXI peak [retention time (RT) = 2.58], four additional products (RT = 0.86, 0.91, 1.42, and 1.89) were observed in all conditions tested. The oxidation process followed second-order reaction kinetics and depended upon solution acidity. The highest reaction rate constant was observed at pH 3.0, and this value decreased as the pH was increased to 6.0. The oxidation products were characterized, and their fragmentation pathways, derived from MS/MS data, were proposed. Two of these products were identified as hydroxyl derivatives of MOXI and two others as their oxidation product analogs with molecular ions of 418.4 and 416.4 m/z, respectively. PMID:24645506

Hubicka, Urszula; Zmudzki, Pawe?; Zajdel, Pawe?; Krzek, Jan

2013-01-01

300

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.

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

2011-01-01

301

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

The cationic ruthenium-hydride complex [(C(6)H(6))(PCy(3))(CO)RuH](+)BF(4) (-) (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 (k(H)/k(D) = 1.1±0.1) was measured from both (E)-C(6)H(5)CH=C(CH(3))CONHCH(3) and (E)-C(6)H(5)CD=C(CH(3))CONHCH(3) with styrene. In contrast, a significant normal isotope effect (k(H)/k(D) = 1.7±0.1) was observed from the reaction of (E)-C(6)H(5)CH=C(CH(3))CONHCH(3) with styrene and styrene-d(10). A pronounced carbon isotope effect was measured from the coupling reaction of (E)-C(6)H(5)CH=CHCO(2)Et with propene ((13)C(recovered)/(13)C(virgin) at C(?) = 1.019(6)), while a negligible carbon isotope effect ((13)C(recovered)/(13)C(virgin) at C(?) = 0.999(4)) was obtained from the reaction of (E)-C(6)H(5)CH=C(CH(3))CONHCH(3) with styrene. Hammett plots from the correlation of para-substituted p-X-C(6)H(4)CH=CHCO(2)Et (X = OCH(3), CH(3), H, F, Cl, CO(2)Me, CF(3)) with propene and from the treatment of (E)-C(6)H(5)CH=CHCO(2)Et with a series of para-substituted styrenes p-Y-C(6)H(4)CH=CH(2) (Y = OCH(3), CH(3), H, F, Cl, CF(3)) 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

2012-01-01

302

Rational construction of strongly coupled metal-metal oxide-graphene nanostructure with excellent electrocatalytic activity and durability.  

PubMed

The interaction within heterogeneous nanostructures can provide a great opportunity to radically enhance their electrocatalytic properties and increase their activity and durability. Here a rational, simple, and integrated strategy is reported to construct uniform and strongly coupled metal-metal oxide-graphene nanostructure as an electrocatalyst with high performance. We first simply synthesized the interacted SnO2-prGO (protected and reduced graphene oxide) hybrid with SnO2 nanoparticles (?4 nm) selectively anchored on the oxygenated defects of rGO using an in situ redox and hydrolysis reaction. After the deposition of Pt, uniform Pt NPs are found to contact intimately and exclusively with the SnO2 phase in the SnO2-prGO hybrid. This constructed nanostructure (Pt-SnO2-prGO) exhibits significantly improved electrocatalytic activity (2.19-fold) and durability (2.08-fold) toward methanol oxidation over that of the state-of-the-art Pt/C catalyst. The detailed explanation of the strong coupling between SnO2 and graphene as well as between Pt and SnO2 is discussed, revealing that such a process can be used to immobilize various metal catalysts on metal-oxide-decorated catalysts for realizing advanced catalytic systems with enhanced performance. PMID:24919010

Huang, Haoliang; Liu, Yingju; Gao, Qiongzhi; Ruan, Weishuo; Lin, Xiaomin; Li, Xin

2014-07-01

303

Comparative characterization of four laccases from Trametes versicolor concerning phenolic C-C coupling and oxidation of PAHs.  

PubMed

The laccase genes lccalpha, lccbeta, lccgamma and lccdelta encoding four isoenzymes from Trametes versicolor have been cloned and expressed in Pichia pastoris. Biochemical characterization allowed classification of these laccases into two distinct groups: Lccalpha and Lccbeta possessed higher thermal stability, but lower catalytic activity towards 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) compared to Lccgamma and Lccdelta. Activities of the laccases were quite different as well. Laccase Lccdelta showed highest phenolic C-C coupling activity with sinapic acid, but lowest oxidizing activity towards polycyclic aromatic hydrocarbons (PAHs). Highest activity towards PAHs was observed with Lccbeta. After 72h, more than 80% of fluorene, anthracene, acenaphthene and acenaphthylene were oxidized by Lccbeta in the presence of ABTS. Investigation of the structural basis of the different activities of the laccases demonstrated the impact of positions 164 and 265 in the substrate binding site on oxidation of PAHs. PMID:18367094

Koschorreck, Katja; Richter, Sven M; Swierczek, André; Beifuss, Uwe; Schmid, Rolf D; Urlacher, Vlada B

2008-06-01

304

Silylesterification of oxidized multi-wall carbon nanotubes by catalyzed dehydrogenative cross-coupling between carboxylic and hydrosilane functions  

NASA Astrophysics Data System (ADS)

Surface modification of oxidized carbon nanotubes (O-CNTs) with silicon based anchoring groups (R-SiR3) is a relatively uncommon approach of the CNTs functionalization. Hydrosilane derivatives constitute an attractive subclass of compounds for silanization reactions on the CNTs surface. In this work, we report on the ZnCl2 catalytically controlled reaction (hydrosilane dehydrogenative cross-coupling, DHCC) of fluorinated hydrosilane probes with the carboxylic functions present on the surface of oxidized multi-wall carbon nanotubes. Carbon nanotubes functionalized with essentially alcohol groups are also used to compare the selectivity of zinc chloride toward carboxylic groups. To assess the efficiency of functionalization, X-ray Photoelectron Spectroscopy is used to determine the qualitative and quantitative composition of the different samples. Solubility tests on the oxidized and silanized MWNTs are also carried out in the framework of the Hansen Solubility Parameters (HSP) theory to apprehend at another scale the effect of DHCC.

Seffer, J.-F.; Detriche, S.; Nagy, J. B.; Delhalle, J.; Mekhalif, Z.

2014-06-01

305

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

306

Status of BINP proton tandem accelerator  

NASA Astrophysics Data System (ADS)

The status of a unique 2.0 MeV, 10 mA proton tandem accelerator with vacuum insulation is presented. The accelerator is intended to be used in facilities generating resonant gamma rays for explosives detection and epithermal neutrons for boron neutron-capture therapy of brain tumors. A magnetically coupled DC voltage multiplier derived from an industrial ELV-type electron accelerator is used as a high voltage source for the accelerator. A dc high current negative ion source has been developed for injection into the tandem. In the tandem accelerator there is set of nested potential electrodes with openings which form a channel for accelerating the negative hydrogen ion beam and subsequently accelerating the proton beam after stripping in the gas target. The electrodes are connected to a high voltage feedthrough insulator to which required potentials are applied from the high voltage power supply by means of a resistor voltage divider. In the paper the first experimental results obtained with the vacuum insulated tandem accelerator are also given.

Burdakov, A.; Davydenko, V.; Dolgushin, V.; Dranichnikov, A.; Ivanov, A.; Farrell, J. P.; Khilchenko, A.; Kobets, V.; Konstantinov, S.; Krivenko, A.; Kudryavtsev, A.; Tiunov, M.; Savkin, V.; Shirokov, V.; Sorokin, I.

2007-08-01

307

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.

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

2011-01-01

308

Isotope effect due to {15N}/{14N} substitution on 14N? 14N coupling constants in nitrous oxide  

NASA Astrophysics Data System (ADS)

14N and 17O NMR spectra of a solution of nitrous oxide, NNO in acetonitrile were measured on a Bruker AM 300 spectrometer. The 14N NMR spectrum reveals two narrow lines at about -147 and -231 ppm relative to external nitromethane assigned to the central and terminal nitrogen atoms, respectively. Both lines exhibit mutual spin-spin splittings equal to 4.233 (±0.006) Hz. The 17O NMR spectrum also reveals a rather narrow line with a chemical shift of 110 ppm relative to external water with a clearly seen 1:1:1 triplet structure due to a 1J( 14N? 17O) coupling constants of 35.8 (±0.3) Hz. Accurate experimental values were obtained using the QUADR program. Comparison of the 1J( 14N? 14N) coupling constant measured in the present study with 1J( 15N? 15N) coupling constant equal to -9.16 (±0.3) Hz (or -4.65 (±0.2) Hz on the basis of 14N? 14N coupling constants) obtained previously by Bhattacharrya and Dailey reveals a strong, double primary isotope effect of about 10%. This can be considered as one of the largest isotope effects on coupling constants ever measured.

Strelenko, Yu. A.; Sergeyev, N. M.

1996-04-01

309

The importance of heterogeneous and homogeneous reactions in oxidative coupling of methane over chloride promoted oxide catalysts  

Microsoft Academic Search

The formation of ethene from ethane and methane in a silica reactor has been studied both in the presence and in the absence of chloride-containing catalysts. Some homogeneous conversion of ethane to ethene occurs in the gas phase through direct dehydrogenation, oxidative dehydrogenation, and, when HCl is present, chlorine radical induced reactions. Methyl chloride is detected in the gas phase

R. Burch; E. M. Crabb; G. D. Squire; S. C. Tsang

1989-01-01

310

Robust detection of tyrosine phosphatase activity by coupling chymotrypsin-assisted selective peptide cleavage and a graphene oxide-based fluorescent platform.  

PubMed

A versatile graphene oxide (GO)-based fluorescent assay is developed for the detection of protein tyrosine phosphatase activity by coupling with a chymotrypsin-assisted selective peptide cleavage reaction. PMID:24923797

Wang, Fangfang; Liu, Chenghui; Fan, Yunlong; Wang, Yucong; Li, Zhengping

2014-07-01

311

Determination of lanthanides in rock samples by inductively coupled plasma mass spectrometry using thorium as oxide and hydroxide correction standard  

NASA Astrophysics Data System (ADS)

Determination of lanthanides by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) using modified mathematical correction method has been studied. Normally, the ICP-MS analysis of middle and heavier lanthanides becomes difficult by severe spectroscopic overlap of M +, MO + or MOH + ions from lighter lanthanides and Ba. A correction method based on a single element oxide yield measurement, is a simple approach to correct for the above spectroscopic overlaps. But the uncertainty in the oxide and hydroxide yields measurement of lanthanides and barium over a long period of time can lead to inaccurate results even under fixed plasma conditions. To correct this, thorium was adopted as an oxide and hydroxide correction standard. Using a ratio of lanthanide oxide yield to thorium oxide yield, the lanthanide correction factors (LCF) were established and incorporated in the mathematical correction scheme. The same factors were also established for hydroxide correction. The proposed modified correction scheme was applied to the determination of lanthanides by ICP-MS from the USGS Standard Rock samples AGV-1 and G-2. The results are in good agreement with the reported values. The method also proved to be useful in isotopic ratio measurement of lanthanides having severe isobaric overlaps.

Raut, Narendra M.; Huang, Li-Shing; Aggarwal, Suresh K.; Lin, King-Chuen

2003-05-01

312

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

313

Oxidative coupling of the pyrogallol B-ring with a galloyl group during enzymatic oxidation of epigallocatechin 3-O-gallate.  

PubMed

In order to clarify the mechanism for formation of catechin oligomers during the fermentation stage of black tea manufacture, epigallocatechin-3-O-gallate, the most abundant tea flavanol in fresh tea leaves, was enzymatically oxidized and the resulting unstable quinone metabolites were converted to phenazine derivatives by treatment with o-phenylenediamine. In addition to formation of monomeric and dimeric derivatives, four trimeric derivatives were isolated whose structures were determined by application of spectroscopic methods. The derivatives differed from each other in the location of the phenazine moieties and in the atropisomerism of the biphenyl bond. The results suggested that oxidative coupling of the galloyl group with the B-ring proceeds by a quinone dimerization mechanism similar to that for production of theasinensins. PMID:17320123

Li, Yan; Tanaka, Takashi; Kouno, Isao

2007-04-01

314

Advanced oxidation processes coupled with electrocoagulation for the exhaustive abatement of Cr-EDTA  

Microsoft Academic Search

Using Cr-EDTA as a model system, a two-step method has been investigated for the abatement of persistent chromium complexes in water. The treatment consists of an oxidative decomposition of the organic ligands by means of ozonization or electrochemical oxidation at a boron doped diamond (BDD) electrode, followed by removal of the metal via electrochemical coagulation. In the designed synthetic waste,

Christian Durante; Marco Cuscov; Abdirisak Ahmed Isse; Giancarlo Sandonà; Armando Gennaro

2011-01-01

315

Alterations in the diabetic myocardial proteome coupled with increased myocardial oxidative stress underlies diabetic cardiomyopathy  

Microsoft Academic Search

Diabetic cardiomyopathy has been documented as an underlying etiology of heart failure (HF) among diabetics. Although oxidative stress has been proposed to contribute to diabetic cardiomyopathy, much of the evidence lacks specificity. Furthermore, whether alterations occur at the cardiac proteome level in diabetic cardiac complications with attendant oxidative stress remains unknown. Therefore, we sought to identify cardiac protein changes in

Milton Hamblin; David B. Friedman; Salisha Hill; Richard M. Caprioli; Holly M. Smith; Michael F. Hill

2007-01-01

316

Simulation of a catalytic membrane reactor for oxidative coupling of methane  

Microsoft Academic Search

There is considerable interest in direct and indirect conversion of methane to more valuable products such as basic feedstock and liquid fuel. However, total oxidation of methane leading to useless carbon dioxide and water is thermodynamically favored over the formation of ethane and ethylene, and in addition the desired Câ products tend to undergo further oxidation. Considerable efforts screening a

S. Cheng; X. Shuai

1995-01-01

317

Photocatalytic one-electron oxidation of biphenyl derivatives strongly coupled with the TiO2 surface.  

PubMed

One-electron oxidation of various biphenyl derivatives such as biphenyl (BP), 4-hydroxybiphenyl (HBP), 4,4'-biphenol (DHBP), 4-methoxy-4'-hydroxybiphenyl (MHBP), 4-cyano-4'-hydroxybiphenyl (CNHBP), 4-biphenylmethanol (BPM), and 4-biphenylethanol (BPE) adsorbed on the surface of TiO2 powder slurried in acetonitrile has been investigated by time-resolved diffuse reflectance spectroscopy. From the Langmuir adsorption isotherms for BP and HBP, it is suggested that the OH group plays an important role in adsorbing on the surface ofTiO2. The spectroscopic characteristics of charge transfer complexes of substrates and the TiO2 surface have been studied by steady-state diffuse reflectance spectroscopy. The high efficiency of a one-electron oxidation reaction was observed for hydroxyl-substituted BPs (HBP, DHBP, MHBP, CNHBP), compared with BPM and BPE, indicating that the strength of the electronic coupling element (H(DA)) between the electron acceptor and donor is a key factor in the one-electron oxidation of a substrate adsorbed on the TiO2 powder. The effects of the distance between the electron donor and the acceptor on the electronic coupling element are also discussed. PMID:15835148

Tachikawa, Takashi; Tojo, Sachiko; Fujitsuka, Mamoru; Majima, Tetsuro

2004-03-30

318

Influence of carbon dioxide on the catalytic oxidative coupling of methane over A-La2O3 and II-La2O2CO3.  

National Technical Information Service (NTIS)

Previous work correlated oxycarbonate and ability of La oxide-based materials to promote the oxidative coupling of methane (OCM). Since A-La(sub 2)O(sub 3) and II-La(sub 2)O(sub 2)CO(sub 3) may be prepared from each other by loss and gain of CO(sub 2) at ...

R. P. Taylor

1992-01-01

319

An asymmetric cladding gain-coupled DFB laser with oxide defined metal surface grating by MOCVD  

Microsoft Academic Search

Fabrication processes which utilize only a single epitaxial growth step are very attractive in the GaAs-AlGaAs system. We report a ridge waveguide gain-coupled DFB laser which utilizes only a single growth step for the laser structure and incorporates a silicon dioxide defined titanium (Ti) surface grating for the gain-coupling mechanism. The asymmetric cladding lasers in this study were grown by

M. L. Osowski; J. S. Hughes; R. M. Lammert; J. J. Coleman

1997-01-01

320

Ultrathin limit of exchange bias coupling at oxide multiferroic/ferromagnetic interfaces.  

PubMed

Exchange bias coupling at the multiferroic- ferromagnetic interface in BiFeO? /La?.? Sr?.? MnO? heterostructures exhibits a critical thickness for ultrathin BiFeO? layers of 5 unit cells (2 nm). Linear dichroism measurements demonstrate the dependence on the BiFeO? layer thickness with a strong reduction for ultrathin layers, indicating diminished antiferromagnetic ordering that prevents interfacial exchange bias coupling. PMID:23847010

Huijben, M; Yu, P; Martin, L W; Molegraaf, H J A; Chu, Y-H; Holcomb, M B; Balke, N; Rijnders, G; Ramesh, R

2013-09-14

321

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

322

Metal free oxidative coupling of aryl formamides with alcohols for the synthesis of carbamates.  

PubMed

A direct transformation of N-aryl formamides to the corresponding carbamates via the formation of isocyanate intermediates is achieved in good yields using hypervalent iodine as an oxidant. PMID:24569949

Reddy, N Veera; Prasad, K Rajendra; Reddy, P Sudhir; Kantam, M Lakshmi; Reddy, K Rajender

2014-04-14

323

Use of a prior-oxidation procedure for the determination of iodine by inductively coupled plasma-atomic emission spectrometry  

SciTech Connect

A simple prior-oxidation procedure is described for the determination of low concentrations of iodine by inductively coupled plasma-atomic emission spectrometry (ICP-AES) in the ultraviolet and vacuum ultraviolet (VUV) regions of the spectrum. For measuring spectral lines in the VUV region, the monochromator and the enclosed external optical path between the ICP source and the entrance slit of the monochromator have both been purged with nitrogen to minimize oxygen absorption below 190 nm. Iodine atomic emission lines at 206.16 and 183.04 nm have been selected as the analytical lines. The ICP-AES intensity is enhanced by a factor of up to 50 by prior oxidation of the iodide to elemental iodine using several oxidizing additives, presumably because of increased sample-transport efficiency between the nebulizer and the plasma. The best attainable detection limits (3-sigma criterion) for iodine at 183.04 and 206.16 nm were 2.00 and 13.9 ng/mL, respectively, in the presence of 3.5-M perchloric acid or 0.2-M hydrogen peroxide, while the corresponding detection limits were 0.088 and 0.56 ..mu..g/mL in the absence of an oxidizing additive. The typical analytical working graphs obtained under the optimized operating conditions were rectilinear over approximately five orders of magnitude in concentration.

Nakahara, T.; Wasa, T.

1987-09-01

324

Evolution of the total synthesis of (-)-okilactomycin exploiting a tandem oxy-cope rearrangement/oxidation, a Petasis-Ferrier union/rearrangement, and ring-closing metathesis.  

PubMed

An effective, asymmetric total synthesis of the antitumor antibiotic (-)-okilactomycin (1), as well as 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 13-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

2009-02-18

325

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.

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

2009-01-01

326

Probabilistic approaches to alignment with tandem repeats  

PubMed Central

Background Short tandem repeats are ubiquitous in genomic sequences and due to their complex evolutionary history pose a challenge for sequence alignment tools. Results To better account for the presence of tandem repeats in pairwise sequence alignments, we propose a simple tractable pair hidden Markov model that explicitly models their presence. Using the framework of gain functions, we design several optimization criteria for decoding this model and describe resulting decoding algorithms, ranging from the traditional Viterbi and posterior decoding to block-based decoding algorithms tailored to our model. We compare the accuracy of individual decoding algorithms on simulated and real data and find that our approach is superior to the classical three-state pair HMM. Conclusions Our study illustrates versatility of pair hidden Markov models coupled with appropriate decoding criteria as a modeling tool for capturing complex sequence features.

2014-01-01

327

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

328

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

329

Tandem photovoltaic cells formed in single fullerene films by impurity doping  

NASA Astrophysics Data System (ADS)

Tandem photovoltaic cells were formed in single fullerene films by doping with molybdenum oxide and cesium carbonate. A heavily doped n+p+-homojunction acted as an ohmic interlayer between the two pn-homojunction cells. The observed photovoltaic properties of the tandem cell were shown to be consistent with the energy band diagram mapped using a Kelvin probe.

Ishiyama, Norihiro; Kubo, Masayuki; Kaji, Toshihiko; Hiramoto, Masahiro

2012-12-01

330

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.

331

Electro-oxidative polymerization and spectroscopic characterization of novel amide polymers using diphenylamine coupling  

SciTech Connect

The authors have electropolymerized 1,1{prime}-bis[[p-phenylamino(phenyl)]amido-]ferrocene from CH{sub 3}CN, tetrahydrofuran (THF), and CH{sub 2}Cl{sub 2} to form an alternating main chain polymer of diphenylbenzidine and ferrocene. As a comparison, the authors have electropolymerized 1,4 bis[[p-phenylamino(phenyl)]amido-]benzene which lacks the electrochemical response of the ferrocene group. In nonaqueous solvents, the diphenylbenzidine group shows two reversible le{sup {minus}} oxidations. The second le{sup {minus}} oxidation of the diphenylbenzidine overlaps with the le{sup {minus}} oxidation of the ferrocene group at 0.88 V vs. Ag/AgCl in CH{sub 2}Cl{sub 2}. The electrochemistry of the polymer film in aqueous acid shows two le{sup {minus}} waves consistent with oxidation of the diphenylbenzidine group to the cation and then the dication. The spectroelectrochemistry of both polymer films show broad, low-energy, near-IR bands in aprotic solvents such as CH{sub 2}Cl{sub 2}, THF, and CH{sub 3}CN and aqueous solutions with pH < 3. The authors assign these bands to intermolecular {pi} stacking of the protonated diphenylbenzidinium cations. The electrochemistry of both materials is chemically reversible and forms the basis for electrochromic and redox applications.

Wang, L.; Wang, Q.Q.; Cammarata, V. [Auburn Univ., AL (United States). Dept. of Chemistry

1998-08-01

332

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

333

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

334

Determination of the ubiquinol-10 and ubiquinone-10 (coenzyme Q10) in human serum by liquid chromatography tandem mass spectrometry to evaluate the oxidative stress.  

PubMed

A method for the rapid and simultaneous determination of ubiquinone-10 (coenzyme Q10, CoQ(10)) and the reduced form ubiquinol-10 (CoQ(10)H(2)) in human serum by LC-MS-MS with electrospray ionization (ESI) in the positive mode is here proposed. High selective identification and sensitive quantitation of both analytes have been carried out by monitoring the transition from the corresponding precursor ion to the product ion. Prior to the chromatographic analysis, serum samples (100 microl) were subject to a conventional pre-treatment based on protein precipitation, liquid-liquid extraction, evaporation to dryness and reconstitution with 95:5 methanol/hexane (v/v). The overall method has enabled to achieve low detection limits--5.49 and 15.8 ng/ml for CoQ(10) and CoQ(10)H(2), respectively--which were estimated with serum. The accuracy and potential matrix effects have been studied with spiked serum resulting recoveries between 92.82 and 106.97%. The proposed method has been applied to serum samples from healthy middle-age women, in which the CoQ(10)H(2)/CoQ(10) ratio has been used as marker of oxidative stress. PMID:17996879

Ruiz-Jiménez, J; Priego-Capote, F; Mata-Granados, J M; Quesada, J M; Luque de Castro, M D

2007-12-21

335

Separation and identification of underivatized plasma acylcarnitine isomers using liquid chromatography-tandem mass spectrometry for the differential diagnosis of organic acidemias and fatty acid oxidation defects.  

PubMed

A simple HPLC-MS/MS method has been established to separate and identify underivatized acylcarnitine isomers. Human plasma samples were deproteinized and concentrated. Acylcarnitines were separated on a reverse phase column and detected with triple quadrupole linear ion trap mass spectrometry. Deuterium-labeled internal standards were used for quantitation. To identify acylcarnitines without pure standards, information-dependent acquisition linking to enhanced product ion scan mode was used. 112 acylcarnitines, including stereoisomers, were found in samples of patients. Dicarboxylic acylcarnitines, such as methylmalonylcarnitine and glutarylcarnitine, were detected with high sensitivity. Three stereoisomers of (R,S)2-methyl-3-hydroxy butyrylcarnitine were detected in samples of patients with ?-ketothiolase deficiency. Validation results revealed excellent precision and accuracy of the method. In general the within- and between-run coefficients of variation (CV%) were less than 15%, and recoveries were in the range of 92.7-117.5%. In addition, the reference intervals of acylcarnitines for children aged 3-day to13-year old were established. Using the new method and reference intervals, we have correctly diagnosed 49 patients with fatty acid oxidation defects or organic acidemias in 176 high-risk patients. PMID:24169039

Peng, Minzhi; Fang, Xiefan; Huang, Yonglan; Cai, Yanna; Liang, Cuili; Lin, Ruizhu; Liu, Li

2013-12-01

336

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

337

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

338

Spin-Flop Coupling and Exchange Bias in Embedded Complex Oxide Micromagnets  

NASA Astrophysics Data System (ADS)

The magnetic domains of embedded micromagnets with 2?m×2?m dimensions defined in epitaxial La0.7Sr0.3MnO3 (LSMO) thin films and LaFeO3/LSMO bilayers were investigated using soft x-ray magnetic microscopy. Square micromagnets 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 reported for 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; Folven, Erik; Shu, Jonathan B. R.; Lukes, Karl R.; Li, Binzhi; Scholl, Andreas; Young, Anthony T.; Retterer, Scott T.; Tybell, Thomas; Grepstad, Jostein K.

2013-09-01

339

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

340

Coupling Fenton and biological oxidation for the removal of nitrochlorinated herbicides from water.  

PubMed

The combination of Fenton and biological oxidation for the removal of the nitrochlorinated herbicides alachlor, atrazine and diuron in aqueous solution has been studied. The H2O2 dose was varied from 20 to 100% of the stoichiometric amount related to the initial chemical oxygen demand (COD). The effluents from Fenton oxidation were analyzed for ecotoxicity, biodegradability, total organic carbon (TOC), COD and intermediate byproducts. The chemical step resulted in a significant improvement of the biodegradability in spite of its negligible or even slightly negative effect on the ecotoxicity. Working at 60% of the stoichiometric H2O2 dose allowed obtaining highly biodegradable effluents in the cases of alachlor and atrazine. That dose was even lower (40% of the stoichiometric) for diuron. The subsequent biological treatment was carried out in a sequencing batch reactor (SBR) and the combined Fenton-biological treatment allowed up to around 80% of COD reduction. PMID:24333521

Sanchis, S; Polo, A M; Tobajas, M; Rodriguez, J J; Mohedano, A F

2014-02-01

341

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

342

Oxidation of water by a nonhaem diiron(IV) complex via proton-coupled electron transfer.  

PubMed

A high-potential nonhaem (?-oxo)diiron(IV) complex was found to oxidize water to a hydroxyl radical via PCET, instead of forming an O-O bond. The rate-determining step requires a second water molecule, proposed to act as a base to promote proton transfer. This work shows that additional factors besides a high redox potential are required to effect O-O bond formation. PMID:24108275

Wang, Dong; Que, Lawrence

2013-11-25

343

Lactate Oxidation Coupled to Iron or Electrode Reduction by Geobacter sulfurreducens PCA?  

PubMed Central

Geobacter sulfurreducens PCA completely oxidized lactate and reduced iron or an electrode, producing pyruvate and acetate intermediates. Compared to the current produced by Shewanella oneidensis MR-1, G. sulfurreducens PCA produced 10-times-higher current levels in lactate-fed microbial electrolysis cells. The kinetic and comparative analyses reported here suggest a prominent role of G. sulfurreducens strains in metal- and electrode-reducing communities supplied with lactate.

Call, Douglas F.; Logan, Bruce E.

2011-01-01

344

Lactate oxidation coupled to iron or electrode reduction by Geobacter sulfurreducens PCA.  

PubMed

Geobacter sulfurreducens PCA completely oxidized lactate and reduced iron or an electrode, producing pyruvate and acetate intermediates. Compared to the current produced by Shewanella oneidensis MR-1, G. sulfurreducens PCA produced 10-times-higher current levels in lactate-fed microbial electrolysis cells. The kinetic and comparative analyses reported here suggest a prominent role of G. sulfurreducens strains in metal- and electrode-reducing communities supplied with lactate. PMID:22003020

Call, Douglas F; Logan, Bruce E

2011-12-01

345

Electromechanical coupling in anodic niobium oxide: Electric field-induced strain, internal stress, and dielectric response  

NASA Astrophysics Data System (ADS)

Seemingly, contradictory results have been reported so far for electrostriction in anodic oxides. Furthermore, no definitive agreement could be obtained with theory. In this paper, in situ techniques are combined to elucidate electrostriction in anodic niobium oxide. The dependence of strain, internal stress, and dielectric constant on the electric field is measured by, respectively, spectroscopic ellipsometry, curvature, and impedance measurements. The through-thickness strain is tensile and proportional to the square of the electric field. The in-plane internal stress is compressive and proportional to the square of the electric field at low field values. The internal stress is predicted relatively well by the Maxwell stress because of the weak dependence of the dielectric constant on the volume change of the oxide. The dielectric constant decreases with the electric field, the dependence being quadratic. While the evolution of the strain and stress with the electric field can be ascribed to the dependence of the dielectric constant on strain, the dependence of the dielectric constant on the electric field contains an explicit strain and electric field dependence. A mechanism for the latter is proposed.

Van Overmeere, Q.; Blaffart, F.; La Mantia, F.; Di Quarto, F.; Proost, J.

2012-06-01

346

Surface plasmon resonance of gold and silver nanoparticle monolayers: effect of coupling and surface oxides  

NASA Astrophysics Data System (ADS)

Material properties are described by some physical parameters such as temperature or pressure. Optical properties of materials are very important for applications where is light as electromagnetic wave dominant. Behavior of the light in interaction with materials depends on refractive indices. These indices are same for various sizes of materials, but in nanoscale dimensions, they depend on some phenomena. Herein, we present the study of the silver (Ag) nanoparticle (NP) monolayer film and its dielectric properties. The aim of the study is to explain phenomenon why it is necessary to use effective material properties for Ag NPs, where these properties are size-dependent. The plasmonic properties of NP have been investigated by the finite domain time difference (FDTD) simulation methods. Although the good agreement of plasmonic resonances was found for gold (Au) NP film, a significant mismatch in the resonance energy for Ag NP film was observed. The deviation was assigned to the presence of silver oxide (Ag2O) in Ag NPs as a surface layer. This real structure of Ag NPs can be replaced by structure with suitable effective material properties. Results depict importance of the effective material properties in Ag NP film for reason of the presence of silver oxide. The Ag NPs with surface oxide exhibits linear tendency in the deviation of the effective dielectric function, which agrees with the experimental observations.

Kuzma, Anton; Chovan, Jozef; Uherek, František; Weis, Martin

2013-10-01

347

Chromatin tandem affinity purification sequencing  

PubMed Central

Chromatin immunoprecipitation coupled with ultra-high-throughput sequencing (ChIP-seq) is a widely used method for mapping the interactions of proteins with DNA. However, the requirements for ChIP-grade antibodies impede wider application of this method, and variations in results can be high owing to differences in affinity and cross-reactivity of antibodies. Therefore, we developed chromatin tandem affinity purification (ChTAP) as an effective alternative to ChIP. Through the use of affinity tags and reagents that are identical for all proteins investigated, ChTAP enables one to directly compare the binding between different transcription factors and to directly assess the background in control experiments. Thus, ChTAP -seq can be used to rapidly map the genome-wide binding of multiple DNA -binding proteins in a wide range of cell types. ChTAP can be completed in 3–4 d, starting from cross-linking of chromatin to purification of ChIP DNA.

Soleimani, Vahab D; Palidwor, Gareth A; Ramachandran, Parameswaran; Perkins, Theodore J; Rudnicki, Michael A

2014-01-01

348

Tandems as injectors for synchrotrons  

SciTech Connect

This is a review on the use of Tandem electrostatic accelerators for injection and filling of synchrotrons to accelerate intense beams of heavy-ions to relativistic energies. The paper emphasizes the need of operating the Tandems in pulsed mode for this application. It has been experimentally demonstrated that at the present this type of accelerators still provides the most reliable and best performance.

Ruggiero, A.G.

1992-08-01

349

Tandems as injectors for synchrotrons  

SciTech Connect

This is a review on the use of Tandem electrostatic accelerators for injection and filling of synchrotrons to accelerate intense beams of heavy-ions to relativistic energies. The paper emphasizes the need of operating the Tandems in pulsed mode for this application. It has been experimentally demonstrated that at the present this type of accelerators still provides the most reliable and best performance.

Ruggiero, A.G.

1992-01-01

350

Noncollinear magnetism and spin-orbit coupling in 5d pyrochlore oxide Cd2Os2O7.  

PubMed

We investigate the electronic and magnetic properties of the pyrochlore oxide Cd2Os2O7 using the density-functional theory plus on-site repulsion (U) method, and depict the ground-state phase diagram with respect to U. We conclude that the all-in-all-out noncollinear magnetic order is stable in a wide range of U. We also show that the easy-axis anisotropy arising from the spin-orbit coupling plays a significant role in stabilizing the all-in-all-out magnetic order. A pseudogap was observed near the transition between the antiferromagnetic metallic and insulating phases. Finally, we discuss possible origins of the peculiar low-temperature (T) properties observed in experiments. PMID:23004316

Shinaoka, Hiroshi; Miyake, Takashi; Ishibashi, Shoji

2012-06-15

351

Surface modification of organic polymers with bioactive titanium oxide without the aid of a silane-coupling agent.  

PubMed

Polyethylene (PE), polyethylene terephthalate (PET), ethylene-vinyl alcohol copolymer (EVOH), and poly(epsilon-caprolactam) (Nylon 6) were successfully modified with a thin crystalline titanium oxide layer on their surfaces by a simple dipping into a titanium alkoxide solution and a subsequent soak in hot HCl solution, without the aid of a silane-coupling agent. The surface modified polymers formed a bone-like apatite layer in a simulated body fluid (SBF) within a period of 2 days. PE, PET, and Nylon 6 formed an apatite layer faster and had a higher adhesive strength to the apatite. Three-dimensional fabrics with open spaces in various sizes containing such surface modified polymer fibers are expected to be useful as bone substitutes, since they may be able to form apatite on their constituent fibers in the living body, and thus, integrate with living bone. PMID:17277978

Balas, F; Kokubo, T; Kawashita, M; Nakamura, T

2007-06-01

352

Doped Mott Insulators in (111) Bilayers of Perovskite Transition-Metal Oxides with a Strong Spin-Orbit Coupling  

NASA Astrophysics Data System (ADS)

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 t2g 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

2013-02-01

353

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

354

Determination of urinary 8-hydroxydeoxyguanosine by automated coupled-column high performance liquid chromatography: a powerful technique for assaying in vivo oxidative DNA damage in cancer patients  

Microsoft Academic Search

An automated analytical method has been developed for determination of the oxidative DNA adduct, 8-hydroxydeoxyguanosine (8OHdG) in human urine, based on coupled-column high performance liquid chromatography with electrochemical detection. Urine is concentrated on Bondelut CH by means of an automated sample processor, and the enriched sample injected on to a polymeric reversed phase column coupled in line with an electrochemical

C. Tagesson; M. Källberg; C. Klintenberg; H. Starkhammar

1995-01-01

355

Analysis of superconductor oxides YBa 2Cu 3O 8?x by inductively coupled plasma atomic emission spectrometry and complexometric titration  

Microsoft Academic Search

The elemental composition of superconductor oxides YBa2Cu3O8?x were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) and complexometric titration. Samples were dissolved in dilute HCl. A sequential PU 7000 Philips inductively coupled plasma atomic emission spectrometer was used for the measurements. A comparison of the different atom and ion emission lines of yttrium, barium and copper was carried out.

Lilli Paama; Paavo Peramäki; Lauri H. J. Lajunen

1996-01-01

356

Oxidatively generated base damage to cellular DNA by hydroxyl radical and one-electron oxidants: Similarities and differences.  

PubMed

Hydroxyl radical (OH) and one-electron oxidants that may be endogenously formed through oxidative metabolism, phagocytosis, inflammation and pathological conditions constitute the main sources of oxidatively generated damage to cellular DNA. It is worth mentioning that exposure of cells to exogenous physical agents (UV light, high intensity UV laser, ionizing radiation) and chemicals may also induce oxidatively generated damage to DNA. Emphasis is placed in this short review article on the mechanistic aspects of OH and one-electron oxidant-mediated formation of single and more complex damage (tandem lesions, intra- and interstrand cross-links, DNA-protein cross-links) in cellular DNA arising from one radical hit. This concerns DNA modifications that have been accurately measured using suitable analytical methods such as high performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry. Evidence is provided that OH and one-electron oxidants after generating neutral radicals and base radical cations respectively may partly induce common degradation pathways. In addition, selective oxidative reactions giving rise to specific degradation products of OH and one-electron oxidation reactions that can be used as representative biomarkers of these oxidants have been identified. PMID:24820329

Cadet, Jean; Wagner, J Richard

2014-09-01

357

Investigation of oxide growth and stability on n-GaAs and n-InP by coupling transient photocurrent and surface analysis  

Microsoft Academic Search

Investigation of oxide chemistry and reactivity of III–V semiconductors has been undergone with an electrochemical approach coupled with surface analysis. Growth and stability of anodic oxides obtained on n-GaAs and n-InP was investigated with potensiostatic mode under illumination at pH 9. For the two compounds, the transient photocurrent, the recovery of the photocurrent and XPS analysis were performed in the

I. Gérard; N Simon; A Etcheberry

2001-01-01

358

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, January 1, 1993--March 31, 1993  

SciTech Connect

Work continued on the development of catalysts for the steam gasification of chars and for the oxidative coupling of methane. Testing of the catalysts Ni-Ca-K-oxides and Co-Ca-K-oxides are described for gasification research; results of the testing of a Co-Mg-oxide catalysts for methane conversion are also described.

Heinemann, H.; Somorjai, G.A.; Perry, D.L.

1993-03-01

359

Bodipy derivatives as organic triplet photosensitizers for aerobic photoorganocatalytic oxidative coupling of amines and photooxidation of dihydroxylnaphthalenes.  

PubMed

We used iodo-Bodipy derivatives that show strong absorption of visible light and long-lived triplet excited states as organic catalysts for photoredox catalytic organic reactions. Conventionally most of the photocatalysts are based on the off-the-shelf compounds, usually showing weak absorption in the visible region and short triplet excited state lifetimes. Herein, the organic catalysts are used for two photocatalyzed reactions mediated by singlet oxygen ((1)O2), that is, the aerobic oxidative coupling of amines and the photooxidation of dihydroxylnaphthalenes, which is coupled to the subsequent addition of amines to the naphthoquinones, via C-H functionalization of 1,4-naphthoquinone, to produce N-aryl-2-amino-1,4-naphthoquinones (one-pot reaction), which are anticancer and antibiotic reagents. The photoreactions were substantially accelerated with these new iodo-Bodipy organic photocatalysts compared to that catalyzed with the conventional Ru(II)/Ir(III) complexes, which show weak absorption in the visible region and short-lived triplet excited states. Our results will inspire the design and application of new organic triplet photosensitizers that show strong absorption of visible light and long-lived triplet excited state and the application of these catalysts in photoredox catalytic organic reactions. PMID:23668289

Huang, Ling; Zhao, Jianzhang; Guo, Song; Zhang, Caishun; Ma, Jie

2013-06-01

360

Electro-optic switching in iron oxide nanoparticle embedded paramagnetic chiral liquid crystal via magneto-electric coupling  

NASA Astrophysics Data System (ADS)

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-) 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; Arora, Manju; Biradar, Ashok M.

2014-03-01

361

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

362

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

363

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

364

I2-promoted selective oxidative cross-coupling/annulation of 2-naphthols with methyl ketones: a strategy to build naphtho[2,1-b]furan-1(2H)-ones with a quaternary center.  

PubMed

A highly efficient and selective molecular iodine-promoted oxidative cross-coupling/annulation between 2-naphthols and methyl ketones has been realized. The reaction successfully constructed a new quaternary carbon center within 3(2H)-furanones. Our synthetic strategy provided an in situ iodination-based oxidative coupling pathway. Based on the experimental results, a self-sequenced iodination/Kornblum oxidation/Friedel-Crafts/oxidation/cyclization mechanism was proposed. PMID:24588728

Gao, Qinghe; Wu, Xia; Liu, Shan; Wu, Anxin

2014-03-21

365

Computational study on mechanism of Rh(III)-catalyzed oxidative Heck coupling of phenol carbamates with alkenes.  

PubMed

A systematic theoretical study on the Rh-catalyzed oxidative Heck-coupling of phenol carbamates with alkenes is carried out. Two possible mechanisms (i.e. arene activation-first and alkene activation-first mechanisms) are examined. As to the C-H activation step, four mechanisms including oxidative addition, electrophilic substitution, concerted metallation-deprotonation (CMD), and ?-bond metathesis are evaluated. The calculation results indicate that the arene activation-first mechanism is more favorable for the overall catalytic cycle. This mechanism involves three steps: arene C-H activation at the position ortho to the carbamate directing group affording a six-membered rhodiacycle intermediate, insertion of the alkene double bond into the Rh(III)-aryl bond, and a final ?-H elimination step to release the product and re-generate the catalyst. The rate determining step of the overall catalytic cycle is the arene C-H activation step, which is found to proceed through the acetate-assisted CMD mechanism. PMID:23385440

Zhang, Qi; Yu, Hai-Zhu; Li, Yi-Tong; Liu, Lei; Huang, Yong; Fu, Yao

2013-03-28

366

Radical O-O coupling reaction in diferrate-mediated water oxidation studied using multireference wave function theory.  

PubMed

The O-O (oxygen-oxygen) bond formation is widely recognized as a key step of the catalytic reaction of dioxygen evolution from water. Recently, the water oxidation catalyzed by potassium ferrate (K2FeO4) was investigated on the basis of experimental kinetic isotope effect analysis assisted by density functional calculations, revealing the intramolecular oxo-coupling mechanism within a di-iron(vi) intermediate, or diferrate [Sarma et al., J. Am. Chem. Soc., 2012, 134, 15371]. Here, we report a detailed examination of this diferrate-mediated O-O bond formation using scalable multireference electronic structure theory. High-dimensional correlated many-electron wave functions beyond the one-electron picture were computed using the ab initio density matrix renormalization group (DMRG) method along the O-O bond formation pathway. The necessity of using large active space arises from the description of complex electronic interactions and varying redox states both associated with two-center antiferromagnetic multivalent iron-oxo coupling. Dynamic correlation effects on top of the active space DMRG wave functions were additively accounted for by complete active space second-order perturbation (CASPT2) and multireference configuration interaction (MRCI) based methods, which were recently introduced by our group. These multireference methods were capable of handling the double shell effects in the extended active space treatment. The calculations with an active space of 36 electrons in 32 orbitals, which is far over conventional limitation, provide a quantitatively reliable prediction of potential energy profiles and confirmed the viability of the direct oxo coupling. The bonding nature of Fe-O and dual bonding character of O-O are discussed using natural orbitals. PMID:24686771

Kurashige, Yuki; Saitow, Masaaki; Chalupský, Jakub; Yanai, Takeshi

2014-06-28

367

Oxidative C(sp(3))-H bond cleavage, C-C and C[double bond, length as m-dash]C coupling at a boron center with O2 as the oxidant mediated by platinum(ii).  

PubMed

Dimethyl- and diphenylplatinum(ii) fragments Pt(II)R2 (R = Me, Ph) enable facile and efficient oxidative C(sp(3))-H bond cleavage and stepwise C-C and C[double bond, length as m-dash]C coupling at the boron atom of a coordinated 1,5-cyclooctanediyldi(2-pyridyl)borato ligand with O2 as the sole oxidant. PMID:24287586

Pal, S; Zavalij, P Y; Vedernikov, A N

2014-05-25

368

Acidity/basicity of rare-earth oxides and their catalytic activity in oxidative coupling of methane to C sub 2 -hydrocarbons  

SciTech Connect

Rare-earth metal oxides (viz. La{sub 2}O{sub 3}, CeO{sub 2}, Sm{sub 2}O{sub 3}, Eu{sub 2}O{sub 3}, and Yb{sub 2}O{sub 3}) have been compared for their acid and base strength distribution (measured by stepwise thermal desorption of CO{sub 2} from 323 to 1,173 K and TPD of NH{sub 3} from 323 to 1,223 K, respectively) and their catalytic activity/selectivity in oxidative coupling of methane to C{sub 2}-hydrocarbons at 973-1,123 K (space velocity = 108,000 cm{sup 3}/g{sup {minus}h} and CH{sub 4}O{sub 2} = 4 and 8). The catalyst activity and selectivity showed dependence on both the surface acidity and basicity. However, the relationship of the catalytic activity/selectivity with the surface acidity/basicity is not straightforward; it is quite complex. Stronger acid sites are found to be harmful for the selectivity. There is a possibility of an involvement of an acid-base pair (M{sub LC}{sup n+} O{sub LC}{sub 2{minus}}, where subscript LC denotes low coordination) on the surface in the abstraction of the H-atom from adsorbed methane molecule by its polarization followed by heterolytic C-H bond rupture to form CH{sub 3}{sup {minus}} (which interacts with M{sub LC}{sup n+}) and (OH){sub LC}{sup {minus}} and a transfer of electron from the carbanion to O{sub 2}, resulting methyl radical and O{sub 2}{sup {minus}}. Regeneration of basic sites and the possibility of formation of O{sup {minus}} species on the catalyst surface are discussed.

Choudhary, V.R.; Rane, V.H. (National Chemical Lab., Pune (India))

1991-08-01

369

New developments in the analysis of fragrances and earthy-musty compounds in water by solid-phase microextraction (metal alloy fibre) coupled with gas chromatography-(tandem) mass spectrometry.  

PubMed

Fragrances are widespread aquatic contaminants due to their presence in many personal care products used daily in developed countries. Levels of galaxolide and tonalide are commonly found in surface waters, urban wastewaters and river sediments. On the other hand, earthy-musty compounds confer bad odour to drinking water at levels that challenge the analytical capabilities. The combined determination of earthy-musty compounds and fragrances in water would be a breakthrough to make the traditional organoleptic evaluation of the water quality stricter and safer for the analyst. Two approaches were attempted to improve the analytical capabilities: analyte pre-concentration with a newly developed PDMS-DVB solid-phase microextraction fibre on metal alloy core and sensitive detection by tandem mass spectrometry (MS/MS). The optimization of SPME parameters was carried out using a central composite design and desirability functions. The final optimum extraction conditions were: headspace extraction at 70°C during 40 min adding 200 g L(-1) of NaCl. The detection limits in tandem MS (0.02-20 ng L(-1)) were marginally lower compared to full scan except for geosmin and trichloroanisol which go down to 0.1 and 0.02 ng L(-1), respectively. The analysis of different water matrices revealed that fragrances and earthy-musty compounds were absent from ground- and drinking waters. Surface waters of river Leça contained levels of galaxolide around 250 ng L(-1) in the 4 terminal sampling stations, which are downstream of WWTPs and polluted tributaries. Geosmine was ubiquitously distributed in natural waters similarly in rivers Leça and Douro at concentrations <7 ng L(-1). PMID:21530789

Machado, S; Gonçalves, C; Cunha, E; Guimarães, A; Alpendurada, M F

2011-05-30

370

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

371

Fueling of tandem mirror reactors  

SciTech Connect

This paper summarizes the fueling requirements for experimental and demonstration tandem mirror reactors (TMRs), reviews the status of conventional pellet injectors, and identifies some candidate accelerators that may be needed for fueling tandem mirror reactors. Characteristics and limitations of three types of accelerators are described; neutral beam injectors, electromagnetic rail guns, and laser beam drivers. Based on these characteristics and limitations, a computer module was developed for the Tandem Mirror Reactor Systems Code (TMRSC) to select the pellet injector/accelerator combination which most nearly satisfies the fueling requirements for a given machine design.

Gorker, G.E.; Logan, B.G.

1985-01-01

372

Comparison of tandem-in-space and tandem-in-time mass spectrometry in gas chromatography determination of pesticides: Application to simple and complex food samples  

Microsoft Academic Search

Gas chromatography coupled to tandem mass spectrometry (GC–MS\\/MS) is one of the most powerful techniques in pesticide residue analysis. MS\\/MS can be conceived in two ways: tandem in space (e.g. triple quadrupole, QqQ) or in time (e.g. ion trap, IT). QqQ and IT are commonly interfaced to GC; however, there has not been any direct comparison between them in pesticide

A. Garrido Frenich; P. Plaza-Bolaños; J. L. Martínez Vidal

2008-01-01

373

165?Activation of the G-protein Coupled Receptor 43 Attenuates High Glucose-induced Vascular Oxidative Stress.  

PubMed

Vascular oxidative stress has been found to be a prominent feature underlying the vascular abnormalities of patients with insulin-resistance and type-2 diabetes. Short chain fatty acids (SCFA) i.e. acetate (NaA), propionate and butyrate are by-products of resistant starch fermentation by anaerobic bacteria in the intestine. SCFA have been shown to be anti-inflammatory against vascular oxidative stress, but the molecular mechanism of SCFA action remains unknown. GPCR43 belongs to a family of orphan G-protein coupled receptor (GPCR) and is a newly discovered receptor of SCFA. In this study we investigated the relationship between high glucose-induced oxidative stress and the levels of expression of GPCR43 in cultured human pulmonary microvascular endothelial cells (HPMEC) and human saphenous vein segments (HSV) in the presence or absence of NaA (5 mM), a reported agonist of GPCR43. Compared to the control endothelial cells or HSV cultured in the normal glucose (5 mM) medium, high glucose (24 h) significantly increased reactive oxygen species (ROS) production by both HPMEC (48.5 ± 12.6%; p < 0.05) and HSV as measured by lucigenin (5 mM)-chemiluminescence and DHE fluorescence. Increased ROS production was accompanied by significant increases in NADPH oxidase 2 (Nox2) and p53. GPCR43 was detected in HPMEC as shown by immunofluorescence flow cytometry, and the endothelium and media of HSV as shown by confocal microscopy and immuno-histo-chemistry. NaA itself (used in normal glucose medium) increased the levels of GPCR43 expression without significant effect on vascular ROS production and Nox2 expression. However, when used together with high glucose, NaA attenuated significantly the high glucose-induced ROS production by both HPMEC and HSV and inhibited endothelial apoptosis. In conclusion, GPCR43 plays an important role in maintaining vascular redox-homeostasis under high glucose challenge. GPCR43 agonists such as acetate may have the therapeutic potential for treating oxidative stress-related vascular complications in patients with insulin-resistance and type-2 diabetes. PMID:24922965

Ghazaly, Maziah; Lee, Christopher; Li, Jian-Mei

2014-06-01

374

The efficacy of oxidative coupling for promoting in-situ immobilization of hydroxylated aromatics in contaminated soil and sediment systems. 1998 annual progress report  

Microsoft Academic Search

'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

W. J. Weber; A. Bhandari

1998-01-01

375

An experimental study on the oxidative coupling of methane in a direct current corona discharge reactor over Sr\\/LaâOâ catalyst  

Microsoft Academic Search

The homogeneous and catalytic oxidative coupling of methane (OCM) for converting methane directly into higher hydrocarbons has been the subject of a large body of research. The present study on conversion of methane in dc corona discharge packed bed reactors may significantly improve the process economics. Experimental investigations have been conducted in which all the reactive gases pass through a

Abdulathim Marafee; Changjun Liu; Genhui Xu; Richard Mallinson; Lance Lobban

1997-01-01

376

Preliminary Study on the Determination of Boron and Cadmium Impurities in Uranium Oxide and Uranium Metals by Inductively Coupled Plasma-Atomic Emission Spectroscopy.  

National Technical Information Service (NTIS)

Boron and cadmium impurities in U metal and U sub 3 O sub 8 may be determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) after their separation from the U matrix by multiple extractions with tri-n-octyl phosphine oxide (TOPO). Us...

B. R. Bear, M. C. Edelson, B. Gopalan, V. A. Fassel

1983-01-01

377

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

378

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

379

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

380

Nuclear angiotensin-(1-7) receptor is functionally coupled to the formation of nitric oxide  

PubMed Central

The kidney is an important target for the actions of the renin-angiotensin system (RAS) and this tissue contains a complete local RAS that expresses the bioactive peptides angiotensin II (ANG II) and Ang-(1–7). We find both angiotensin type 1 (AT1R) and type 2 (AT2R) receptors expressed on renal nuclei that stimulate reactive oxygen species and nitric oxide (NO), respectively. Since Ang-(1–7) also exhibits actions within the kidney and the Ang-(1–7)/Mas receptor protein contains a nuclear localization sequence, we determined the expression of Ang-(1–7) receptors in nuclei isolated from the kidneys of young adult sheep. Binding studies with 125I-[Sar1Thr8]-ANG II revealed sites sensitive to the Ang-(1–7) antagonist [d-Ala7]-Ang-(1–7) (DALA, A779), as well as to AT2 and AT1 antagonists. Incubation of Ang-(1–7) [10?15 to 10?9 M] with isolated cortical nuclei elicited a dose-dependent increase in the fluorescence of the NO indicator [4-amino-5-methylamino-2?,7?]-difluorofluorescein diacetate. The NO response to Ang-(1–7) was abolished by the NO inhibitor N-nitro-l-arginine methyl ester and DALA, but not the AT1 antagonist losartan or the AT2 blocker PD123319. Immunofluorescent studies utilizing the Ang-(1–7)/Mas receptor antibody revealed immunolabeling of the proximal tubules but not staining within the glomerulus in cortical sections of the sheep kidney. In the nuclear fraction of isolated proximal tubules, immunoblots revealed the precursor angiotensinogen and renin, as well as functional activity for ACE, ACE2, and neprilysin. We conclude that renal nuclei express Ang-(1–7)/Mas receptors that are functionally linked to NO formation. The marked sensitivity of the intracellular NO response to Ang-(1–7) implicates a functional role of the Ang-(1–7) axis within the nucleus. Moreover, evidence for the precursor and enzymatic components of the RAS within the nuclear compartment of the proximal tubules provides a potential pathway for the intracellular generation of Ang-(1–7).

Gwathmey, TanYa M.; Westwood, Brian M.; Pirro, Nancy T.; Tang, Lijun; Rose, James C.; Diz, Debra I.

2010-01-01

381

Developmental competence of bovine early embryos depends on the coupled response between oxidative and endoplasmic reticulum stress.  

PubMed

The stress produced by the coupling of reactive oxygen species (ROS) and endoplasmic reticulum (ER) has been explored extensively, but little is known regarding their roles in the early development of mammalian embryos. Here, we demonstrated that the early development of in vitro-produced (IVP) bovine embryos was governed by the cooperative action between ROS and ER stress. Compared with the tension produced by 5% O2, 20% O2 significantly decreased the blastocyst formation rate and cell survival, which was accompanied by increases in ROS and in levels of sXBP-1 transcript, which is an ER stress indicator. In addition, treatment with glutathione (GSH), a ROS scavenger, decreased ROS levels, which resulted in increased blastocyst formation and cell survival rates. Importantly, levels of sXBP-1 and ER stress-associated transcripts were reduced by GSH treatment in developing bovine embryos. Consistent with this observation, tauroursodeoxycholate (TUDCA), an ER stress inhibitor, improved blastocyst developmental rate, trophectoderm proportion, and cell survival. Moreover, ROS and sXBP-1 transcript levels were markedly decreased by supplementation with TUDCA, suggesting a possible mechanism governing the mutual regulation between ROS and ER stress. Interestingly, knockdown of XBP-1 transcripts resulted in both elevation of ROS and decrease of antioxidant transcripts, which ultimately reduced in vitro developmental competence of bovine embryos. Based on these results, in vitro developmental competence of IVP bovine embryos was highly dependent on the coupled response between oxidative and ER stresses. These results increase our understanding of the mechanism(s) governing early embryonic development and may improve strategies for the generation of IVP embryos with high developmental competence. PMID:24695629

Yoon, Seung-Bin; Choi, Seon-A; Sim, Bo-Woong; Kim, Ji-Su; Mun, Seong-Eun; Jeong, Pil-Soo; Yang, Hae-Jun; Lee, Youngjeon; Park, Young-Ho; Song, Bong-Seok; Kim, Young-Hyun; Jeong, Kang-Jin; Huh, Jae-Won; Lee, Sang-Rae; Kim, Sun-Uk; Chang, Kyu-Tae

2014-05-01

382

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

383

Exergy & Economic Analysis of Catalytic Coal Gasifiers Coupled with Solid Oxide Fuel Cells  

SciTech Connect

The National Energy Technology Laboratory (NETL) has undertaken a review of coal gasification technologies that integrate with solid oxide fuel cells (SOFC) to achieve system efficiencies near 60% while capturing and sequestering >90% of the carbon dioxide. One way to achieve an overall system efficiency of greater than 60% is in a power plant in which a catalytic coal gasifier produces a syngas with a methane composition of roughly 25% on a dry volume basis and this is sent to a SOFC, with CO{sub 2} capture occurring either before or after the SOFC. Integration of a catalytic gasifier with a SOFC, as opposed to a conventional entrained flow gasifier, is improved due to (a) decreased exergy destruction inside a catalytic, steam-coal gasifier producing a high-methane content syngas, and (b) decreased exergy destruction in the SOFC due to the ability to operate at lower air stoichiometric flow ratios. For example, thermal management of the SOFC is greatly improved due to the steam-methane reforming in the anode of the fuel cell. This paper has two main goals. First, we converted the levelized cost of electricity (LCOE) estimates of various research groups into an average internal rate of return on investment (IRR) in order to make comparisons between their results, and to underscore the increased rate of return on investment for advanced integrated gasification fuel cell systems with carbon capture & sequestration (IGFC-CCS) compared with conventional integrated gasification combined cycle (IGCC-CCS) systems and pulverized coal combustion (PCC-CCS) systems. Using capital, labor, and fuel costs from previous researchers and using an average price of baseload electricity generation of $61.50 / MW-hr, we calculated inflation-adjusted IRR values of up to 13%/yr for catalytic gasification with pressurized fuel cell and carbon dioxide capture and storage (CCS), whereas we calculate an IRR of ?4%/yr and ?2%/yr for new, conventional IGCC-CCS and PCC-CCS, respectively. If the carbon dioxide is used for enhanced oil recovery rather than for saline aquifer storage, then the IRR values improve to 16%/yr, 10%/yr, and 8%/yr, respectively. For comparison, the IRR of a new conventional IGCC or PCC power plant without CO{sub 2} capture are estimated to be 11%/yr and 15.0%/yr, respectively. Second, we conducted an exergy analysis of two different configurations in which syngas from a catalytic gasifier fuels a SOFC. In the first case, the CO{sub 2} is captured before the SOFC, and the anode tail gas is sent back to the catalytic gasifier. In the second case, the anode tail gas is oxy-combusted using oxygen ion ceramic membranes and then CO{sub 2} is captured for sequestration. In both cases, we find that the system efficiency is greater than 60%. These values compare well with previous system analysis. In future work, we plan to calculate the IRR of these two cases and compare with previous economic analyses conducted at NETL.

Siefert, Nicholas; Litster, Shawn

2012-01-01

384

Tandem Terminal Ion Source  

SciTech Connect

OAK-B135 Tandem Terminal Ion Source. The terminal ion source (TIS) was used in several experiments during this reporting period, all for the {sup 7}Be({gamma}){sup 8}B experiment. Most of the runs used {sup 1}H{sup +} at terminal voltages from 0.3 MV to 1.5 MV. One of the runs used {sup 2}H{sup +} at terminal voltage of 1.4 MV. The other run used {sup 4}He{sup +} at a terminal voltage of 1.37 MV. The list of experiments run with the TIS to date is given in table 1 below. The tank was opened four times for unscheduled source repairs. On one occasion the tank was opened to replace the einzel lens power supply which had failed. The 10 kV unit was replaced with a 15 kV unit. The second time the tank was opened to repair the extractor supply which was damaged by a tank spark. On the next occasion the tank was opened to replace a source canal which had sputtered away. Finally, the tank was opened to replace the discharge bottle which had been coated with aluminum sputtered from the exit canal.

None

2000-10-23

385

0.1 V 13 GHz Transformer-Based Quadrature Voltage-Controlled Oscillator with a Capacitor Coupling Technique in 90 nm Complementary Metal Oxide Semiconductor  

NASA Astrophysics Data System (ADS)

A low power-supply voltage and high-frequency quadrature voltage-controlled oscillator (QVCO) using a combination of capacitor coupling and transformer feedback techniques is presented. The capacitor coupling technique can boost the transconductance of the LC-VCO core and coupling transconductance of QVCO at high frequency. Also, this technique can improve the quality factor of the QVCO at high frequency with low power-supply voltage, compared with the conventional QVCO. In addition, the capacitor coupling QVCO with transformer feedback can improve the quality factor of QVCO. Using this topology, the QVCO is able to operate at over 10 GHz with lower power-supply voltage. Implemented in the 90 nm complementary metal oxide semiconductor (CMOS) process, the proposed QVCO measures 1-MHz-offset phase noise of -94 dBc/Hz at 13 GHz while consuming 0.68 mW from a 0.1 V power-supply.

Kamimura, Tatsuya; Lee, Sang-yeop; Tanoi, Satoru; Ito, Hiroyuki; Ishihara, Noboru; Masu, Kazuya

2012-04-01

386

Oxidative and stepwise grafting of dopamine inner-sphere redox couple onto electrode material: electron transfer activation of dopamine.  

PubMed

The immobilization of dopamine, a neurotransmitter, onto macroelectrode and microelectrode surfaces has been performed following two strategies. The first consists of a one-step grafting based on electrochemical oxidation of an amino group in acidic media. The second is a stepwise process starting with electrochemical grafting of diazonium, leading to the attachment of aryl layer bearing an acidic headgroup, followed by chemical coupling leading to immobilized dopamine molecules onto the electrode surface. Electrochemical, infrared (IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) analyses evidence that both methods are suitable for the immobilization of dopamine onto millimetric and micronic electrodes. The electrochemical responses of modified electrodes demonstrate that the electroactivity of the attached dopamine layer appears unaffected by the nature of the spacer, alkyl or aryl layers, suggesting that the communication, through tunneling, between the attached dopamine and the electrode is possible. More interestingly, the dopamine-modified electrode exhibits electron transfer activation toward dopamine in solution. As a result, not only does the dopamine modified electrode yield a fast electron transfer with lower ?E(p) (30 mV) than the majority of pretreatment procedures but also the ?E(p) is as small as that observed for more complex surface treatments. PMID:24171668

Ghilane, Jalal; Hauquier, Fanny; Lacroix, Jean-Christophe

2013-12-01

387

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

388

Model and experimental investigations of aluminum oxide slurry transportation and vaporization behavior for nebulization inductively coupled plasma optical emission spectrometry.  

PubMed

We analyzed aluminum oxide (Al2O3) by slurry introduction inductively coupled plasma (ICP) optical emission spectrometry through modeling and experimentation. We also studied the relationship between the ICP nebulizer gas flow, the spray chamber geometry, and the particle size of Al2O3 in an attempt to minimize the need for correction factors by ensuring an efficient aerosol mass transport. A cut-off point for the particle size was implemented at approximately 7-10 ?m for the sample introduction system. Based on modeling using a customized computer model and some experimental evidences, the maximum particle size for complete vaporization is approximately 7 ?m. For a gas flow of 0.8 Lmin(-1), particles with a diameter of up to 8 ?m can be evaporated with an efficiency of 68% and particles as large as 5 ?m can be evaporated completely within the nebulization gas flow region. The Al2O3 sintering block was ground using a self-made alumina mortar combined with a mixer mill device for particle reduction. The sample slurry was prepared by directly dispersing powdered Al2O3 in an aqueous solution with an addition of 0.5 wt% poly (acrylate amine) (NH4PAA) as the dispersant. The accuracy of the results was compared with the data obtained through high-pressure digestion with acid and with the value of a certified reference material, NIST SRM 699 alumina. PMID:23598231

Wang, Zheng; Zhang, Junye; Zou, Huijun; Dong, Min; Qiu, Deren; Yang, Pengyuan

2013-03-30

389

Magnetization States of All-Oxide Spin Valves Controlled by Charge-orbital Ordering of Coupled Ferromagnets  

PubMed Central

Charge-orbital ordering is commonly present in complex transition metal oxides and offers interesting opportunities for novel electronic devices. In this work, we demonstrate for the first time that the magnetization states of the spin valve can be directly manipulated by charge-orbital ordering. We investigate the interlayer exchange coupling (IEC) between two epitaxial magnetite layers separated by a nonmagnetic epitaxial MgO dielectric. We find that the state of the charge-orbital ordering in magnetite defines the strength, and even the sign of the IEC. First-principles calculations further show that the charge-orbital ordering modifies the spin polarized electronic states at the Fe3O4/MgO interfaces and results in a sufficiently large phase shift of wave function which are responsible for the observed IEC sign change across Verwey temperature. Our findings may open new interesting avenues for the electric field control of the magnetization states of spin valves via charge-orbital ordering driven IEC sign change.

Wu, Han-Chun; Mryasov, Oleg N.; Abid, Mohamed; Radican, Kevin; Shvets, Igor V.

2013-01-01

390

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

391

[A high throughput coupled with high performance liquid chromatography-tandem mass spectrometry method for determination of aflatoxin B1, B2, G1, G2 in 10 traditional Chinese medicines].  

PubMed

As the dilution procedure was applied, a simple, rapid and cost-effective high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for determination of aflatoxin B1, B2, G1, and G2 was successfully by performed in a total 83 samples of 10 traditional Chinese medicines (TCMs), which were collected from 5 different hospital pharmacies and 5 different medical stores in Guangzhou city. Matrix effects of these 10 TCMs were ranged from 80.23% to 115.5% in low, intermediate and high concentration levels, indicating that the negative effect was overcome in this study. Meanwhile, the analysis method was proved to be stable and reliable during the whole analysis using Semen Armeniacae Amarum spiked 3 concentration levels of standard solution as quality control samples and the RSD < 6.6% was obtained. The contamination levels of 83 investigated samples were 13.89% and 17.02% in hospital pharmacies and medical stores, respectively. The result was presented to provide relevant reference and supplement to those researchers in TCMs analysis and screening. PMID:24761645

Zheng, Run-Sheng; Xu, Hui; Peng, Yuan-Xia; Wang, Wen-Li; Zhan, Ruo-Ting; Chen, Wei-Wen

2014-01-01

392

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

393

Simultaneous determination of aflatoxin B(1) and ochratoxin A in licorice roots and fritillary bulbs by solid-phase extraction coupled with high-performance liquid chromatography-tandem mass spectrometry.  

PubMed

An effective method was developed for screening licorice roots and fritillary bulbs for contamination by aflatoxin B(1) and ochratoxin A using high-performance liquid chromatography connected to tandem mass spectrometry (HPLC-MS/MS). The samples were pre-concentrated and purified using solid-phase extraction, which provided satisfactory results. The separation was performed on a Waters Xbridge(TM) C18 column with a linear gradient of acetonitrile - water containing 5mM ammonium acetate. The MS spectrum was acquired in positive mode with both single quadrupole (Q1) and multiple reaction monitoring (MRM). The optimised method offered a good linear correlation (r(2)>0.9967), excellent precision (RSD<2.83%) and acceptable recovery (from 92.78 to 105.37%). The limits of detection (LOD) and the limits of quantification (LOQ) were less than 0.024 ?g/kg and 0.095 ?g/kg, respectively. The validated method was successfully applied to the rapid screening for AFB(1) and OTA in licorice roots and fritillary bulbs. PMID:23411213

Wang, Lizhi; Wang, Zhen; Gao, Weiwei; Chen, Juan; Yang, Meihua; Kuang, Ying; Huang, Linfang; Chen, Shilin

2013-06-01

394

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

395

Orthogonal separation and identification of long-chain peptides from scorpion Buthus martensi Karsch venom by using two-dimensional mixed-mode reversed phase-reversed phase chromatography coupled to tandem mass spectrometry.  

PubMed

Peptide components of scorpion venom have been employed as useful pharmacological tools in the study of ion channel function. The isolation of individual components is necessary for determination of their biological significance. Here, we have described a novel reversed phase (RP)/ion exchange stationary phase, Click oligo ethylene glycol (Click OEG), and the chromatographic efficiency of its mixed-mode sorbent in peptide separation experiments. The Click OEG presents a mixed-mode RP/weak anion-exchange type stationary phase at pH 3.5 and mixed-mode RP/weak cation-exchange type stationary phase at pH 6.0, and it was suitable for separation of long-chain peptides in scorpion venom. Subsequently, a two dimensional mixed-mode RP-RP system based Click OEG and C18 with different pH values in two dimensions was developed for orthogonal separation of scorpion venom. Furthermore, two fractions were analyzed in depth, and 11 long-chain peptides were purified and sequences were identified by using tandem mass spectrometry incorporating the tryptic approach. Among these, we isolated six novel peptides including one peptide with a new sequence and five transcript-level peptides, and speculated on their possible bioactivities. PMID:23373063

Xu, Junyan; Zhang, Xiuli; Guo, Zhimou; Yan, Jingyu; Yu, Long; Li, Xiuling; Xue, Xingya; Liang, Xinmiao

2013-03-21

396

TiAlN/TiAlON/Si3N4 tandem absorber for high temperature solar selective applications  

NASA Astrophysics Data System (ADS)

A tandem absorber of TiAlN/TiAlON/Si3N4 is prepared using a magnetron sputtering process. The graded composition of the individual component layers of the tandem absorber produces a film with a refractive index increasing from the surface to the substrate, which exhibits a high absorptance (0.95) and a low emittance (0.07). The tandem absorber is stable in air up to 600 °C for 2 h, indicating its importance for high temperature solar selective applications. The thermal stability of the tandem absorber is attributed to high oxidation resistance and microstructural stability of the component materials at higher temperatures.

Barshilia, Harish C.; Selvakumar, N.; Rajam, K. S.; Sridhara Rao, D. V.; Muraleedharan, K.; Biswas, A.

2006-11-01

397

5-Nitroisocoumarins from tandem Castro–Stephens coupling—6- endo-dig cyclisation of 2-iodo-3-nitrobenzoic acid and arylethynes and ring-closure of methyl 2-alkynyl-3-nitrobenzoates with electrophiles  

Microsoft Academic Search

Reaction of 2-iodo-3-nitrobenzoic acid with arylalkynyl copper(I) reagent gave 3-aryl-5-nitroisocoumarins. Castro–Stephens coupling was followed by in situ Cu-catalysed ring-closure. 1H NMR and X-ray crystallography showed the cyclisations to be 6-endo, contrasting with reports of 5-exo cyclisation of analogous 2-iodobenzoate esters with alkynes. Sonogashira couplings of methyl 2-iodo-3-nitrobenzoate with phenylacetylene and with trimethylsilylacetylene gave the corresponding 2-alkynyl-3-nitrobenzoate esters. With HgSO4, the

Esther C. Y. Woon; Archana Dhami; Mary F. Mahon; Michael D. Threadgill

2006-01-01

398

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

399

Low-level quantitation of oxycodone and its oxidative metabolites, noroxycodone, and oxymorphone, in rat plasma by high-performance liquid chromatography–electrospray ionization–tandem mass spectrometry  

Microsoft Academic Search

A method was developed for quantification of oxycodone, noroxycodone, and oxymorphone in small volumes (50?l) of rat plasma by high-performance liquid chromatography–electrospray ionization–tandem mass spectrometry using turbo ion-spray. Deuterated (d3) opioid analogues acted as internal standards. Sample preparation involved protein precipitation with acetonitrile, centrifugal evaporation, and reconstitution in mobile phase; analyte separation was performed on a C18 (5?m, 2.1mm×50mm) column

Stephen R. Edwards; Maree T. Smith

2007-01-01

400

Weak coupling BCS-like superconductivity in the pnictide oxide Ba1-xNaxTi2Sb2O (x=0 and 0.15)  

NASA Astrophysics Data System (ADS)

We report the results of low-temperature heat capacity measurements of the pnictide oxide superconductor BaTi2Sb2O doped with sodium. The temperature- and field-dependent heat capacity data are well described by a single-gap BCS theory. The estimated values for the normal-state Sommerfeld constant, the heat capacity jump at Tc, and the electron-phonon coupling constant are in favor of a conventional weak coupling superconductivity mediated by electron-phonon interaction. The results are discussed with regard to and compared with recent first-principles calculations.

Gooch, Melissa; Doan, Phuong; Tang, Zhongjia; Lorenz, Bernd; Guloy, Arnold M.; Chu, Paul C. W.

2013-08-01

401

Intramolecular metal-free oxidative aryl-aryl coupling: an unusual hypervalent-iodine-mediated rearrangement of 2-substituted N-phenylbenzamides.  

PubMed

Hypervalent-iodine-mediated oxidative coupling of the two aryl groups in either 2-acylamino-N-phenyl-benzamides or 2-hydroxy-N-phenylbenzamides, with concomitant insertion of the ortho-substituted N or O atom into the tether, has been described for the first time. This unusual metal-free rearrangement reaction involves an oxidative C(sp(2) )?C(sp(2) ) aryl-aryl bond formation, cleavage of a C(sp(2) )?C(O) bond, and a lactamization/lactonization. Furthermore, unsymmetrical diaryl compounds can be easily obtained by removing the tether within the cyclized product. PMID:24764255

Shang, Siyun; Zhang-Negrerie, Daisy; Du, Yunfei; Zhao, Kang

2014-06-10

402

Quantification of vorinostat and its main metabolites in plasma and intracellular vorinostat in PBMCs by liquid chromatography coupled to tandem mass spectrometry and its relation to histone deacetylase activity in human blood.  

PubMed

Vorinostat (suberoylanilide hydroxamic acid) is the first approved histone deacetylase (HDAC) inhibitor for the treatment of cutaneous T-cell lymphoma after progressive disease following two systemic therapies. Intracellular access of vorinostat is essential to exert its epigenetic effects. Therefore, we studied the relationship between vorinostat extracellular (plasma) and intracellular (peripheral blood mononuclear cells, PBMCs) concentration and assessed its concentration-effect relationship by HDAC activity testing. Assays were developed and validated for the low nanomolar quantification of vorinostat and two inactive metabolites in human plasma and PBMCs. For the vorinostat extraction from plasma and PBMCs solid-phase extraction and liquid-liquid extraction methods were applied. Extraction recoveries ranged from 88.6% to 114.4% for all analytes and extraction methods. Extracts were chromatographed on a Phenomenex Luna column isocratically (plasma) or by gradient (PBMCs) consisting of acidic ammonium acetate, acetonitrile, and methanol. The analytes were quantified using deuterated internal standards and positive electrospray tandem mass spectrometry (multiple reaction monitoring) with lower limits of quantification of 11.0ng/mL (plasma) and 0.1ng/3×10(6) cells (PBMCs). The calibrated ranges were linear for vorinostat in plasma 11.0-1100 (11,000) ng/mL (metabolites) and PBMCs 0.1-10.0ng/3×10(6) cells with correlation coefficients >0.99, an overall accuracy varying between -6.7% and +3.8% in plasma, -8.1% and -1.5% in PBMCs, and an overall precision ranging from 3.2% to 6.1% in plasma and 0.8% to 4.0% in PBMCs (SD batch-to-batch). The application to blood samples from healthy volunteers incubated with vorinostat revealed accumulation of vorinostat in PBMCs, effective intracellular HDAC inhibition at therapeutic vorinostat concentrations and a direct vorinostat concentration dependency to HDAC inhibition. PMID:24636840

Liu, Lu; Detering, Jan-Christoph; Milde, Till; Haefeli, Walter Emil; Witt, Olaf; Burhenne, Jürgen

2014-08-01

403

Simple assay for monitoring seven quinolone antibacterials in eggs: extraction with hot water and liquid chromatography coupled to tandem mass spectrometry. Laboratory validation in line with the European Union Commission Decision 657/2002/EC.  

PubMed

A simple and rapid method able to determine residues of seven quinolone antibacterials in whole eggs is presented here. This method is based on the matrix solid-phase dispersion technique with hot water as extractant followed by liquid chromatography-tandem mass spectrometry. After depositing 1.5 g of an egg sample containing the analytes and the analyte surrogate (norfloxacin) on sand (crystobalite), this material was packed into an extraction cell. Quinolones were extracted by flowing 6 mL of water acidified with 50 mmol/L formic acid through the cell heated at 100 degrees C. After pH adjustment and filtration of the extract, 100 microL of it was injected into the LC column. MS data acquisition was performed in the multiple reaction monitoring mode, selecting two precursor ion to product ion transitions for each target compound. Hot water appeared an efficient extracting medium, since absolute recoveries of the analyte in egg at the level of 20 ng/g were 89-103%. Estimated limits of quantification (S/N=10) were 0.2-0.6 ng/g. Based on the EU Commission Decision 2002/657/EC, the method was validated in terms of ruggedness, specificity, linearity, within-laboratory reproducibility, decision limit (CCalpha and detection capability (CCbeta). Depending on the particular analyte, CCalphas ranged between 0.41 and 2.6 ng/g, while CCbetas were 0.64-3.7 ng/g. The method was linear in the 3-30 ng/g range, with typical R(2) values higher than 0.97. The within-laboratory reproducibility (n=21) at 6 ng/g level was in the 9.0-12% range. After validation, a depletion study of enrofloxacin and one of its metabolites, i.e. ciprofloxacin, in eggs was conducted. PMID:19095237

Bogialli, Sara; D'Ascenzo, Giuseppe; Di Corcia, Antonio; Laganà, Aldo; Tramontana, Giovanna

2009-01-30

404

A novel and rapid method for determination of natamycin in wines based on ultrahigh-performance liquid chromatography coupled to tandem mass spectrometry: validation according to the 2002/657/EC European decision.  

PubMed

A novel, simple, and rapid reversed-phase liquid chromatography-tandem mass spectrometric methodology was developed for the analysis of natamycin in wine samples. Natamycin was protonated to form singly charged ions in an electrospray positive ion mode. Data acquisition under MS/MS was achieved by applying multiple reaction monitoring (MRM) of three fragment ion transitions (666.3 ? 648.2, 666.3 ? 503.3, and 666.3 ? 485.2) to provide a high degree of sensitivity and specificity. Chromatographic separation was performed on a rapid resolution column using a mobile phase consisting of an acetonitrile/water mixture with a total run time of 5.0 min. After only filtration as pretreatment, the sample was injected into the chromatographic system. The proposed method was validated in terms of selectivity, trueness, precision, decision limit (CC?), and detection capability (CC?) according to 2002/657/EC Commission decision. The values for trueness, reported as bias (%), agreed with those established by the aforementioned document. Repeatability (intraday variability) values were 12.37% at a concentration of 1.0 ?g L(-1) and 8.99-4.19% at concentrations between 2.5 and 10 ?g L(-1). The overall within-laboratory (interday variability) reproducibility was 15.47% at a concentration of 1.0 ?g L(-1), which was significantly lower than the indicative value reported in the EU decision. The results indicated that the proposed approach is a sensitive, fast, reproducible, and robust methodology suitable for the analysis of natamycin levels in wine samples. PMID:22052154

Repizo, Leonardo Mariño; Martinez, Luis Dante; Olsina, Roberto A; Cerutti, Soledad; Raba, Julio

2012-01-01

405

Quantitative determination of the novel anticancer drug E7070 (indisulam) and its metabolite (1,4-benzenedisulphonamide) in human plasma, urine and faeces by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry.  

PubMed

E7070 (indisulam) is a novel anticancer drug currently undergoing clinical investigation. We present a sensitive and specific method for the quantitative determination of E7070 and its metabolite M1 (1,4-benzenedisulphonamide) in human plasma, urine and faeces. The analytes and their tetra-deuterated analogues, which were used as internal standards, were isolated from the biological matrix by solid-phase extraction with OASIS cartridges (0.5 mL plasma or 1 mL urine) and by liquid-liquid extraction with ethyl acetate at pH 5 (1 mL faecal homogenate). The analytes were separated on a C8 reversed-phase chromatographic column and analyzed using electrospray ionization and tandem mass spectrometric detection in the negative ion mode. The validated concentration ranges in plasma were 0.1-20 microg/mL for E7070 and 0.01-2 microg/mL for M1. In urine and faecal homogenate, a concentration range from 0.05-10 microg/mL or microg/g, respectively, was validated for both analytes. Validation of the plasma assay was performed according to the most recent FDA guidelines. The assay fulfilled all generally accepted requirements for linearity (r > 0.99, residuals between -8 and 10%), accuracy (-13.5 to 1.4%) and precision (all less than 11%) in the tested matrices. We investigated recovery, stability (working solutions at -20 degrees C and at room temperature, biological matrices at -20 degrees C, room temperature and after 3 freeze/thaw cycles; final extracts at room temperature) and robustness. All these parameters were found acceptable. This method is suited for mass balance studies or therapeutic drug monitoring, as demonstrated by a case example showing plasma concentrations and cumulative excretion of E7070 and M1 in urine and faeces. Furthermore, we show the presence of E7070 metabolites in patient urine. PMID:15517526

Beumer, Jan Hendrik; Rosing, Hilde; Hillebrand, Michel J X; Nan-Offeringa, Lianda G A H; Foley, Karen; Yule, S Murray; Heck, Albert J R; Schellens, Jan H M; Beijnen, Jos H

2004-01-01

406

[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

407

Separation and quantification of four isomers of indole-3-acetyl-myo-inositol in plant tissues using high-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry.  

PubMed

Indole-3-acetyl-myo-inositol (IAInos) is one of the most important auxin conjugates for storage and transportation of auxin. The information of its composition, distribution, and metabolism is particularly desired for elucidating the related signal transduction pathways of the plant hormones. However, separation and quantification of the four individual IAInos isomers in plant tissues have not been reported so far. In this work, we first synthesized and isolated four IAInos isomers using semi-preparative high-performance liquid chromatography (HPLC). The IAInos isomer structures were characterized using liquid chromatography-electrospray ionization quadrupole time-of-flight tandem mass spectrometry (LC-QTOF/MS) and nuclear magnetic resonance spectroscopy (NMR). Using these pure compounds as internal or external standards, an efficient LC-MS method was developed for simultaneous detection of indole-3-acetic acid, methyl indole-3-acetic acid ester, and the four IAInos isomers in plant tissue samples. The linear working range and lower limit of detection for the four IAInos isomers are 10-2,000 ng mL(-1) and 5.0 ng mL(-1), respectively. The stabilities and interconversion pathways of IAInos isomers were studied using our synthetic isomers. It was found that two IAInos isomers existed in Zea mays kernels, while all of the four IAInos isomers were present in the roots of Arabidopsis thaliana. The content of IAInos in A. thaliana roots was much lower than in the Z. mays kernels. The methodology in this article provides useful techniques and methods for systematic study on the phytophysiology and phytochemistry of IAA conjugates and other related plant hormones. PMID:24633567

Wu, Tongbo; Liang, Yuan; Zhu, Xiaocui; Zhao, Meiping; Liu, Huwei

2014-05-01

408

Hinge-thiol coupling of monoclonal antibody to silanized iron oxide particles and evaluation of magnetic cell depletion.  

PubMed

Iron oxide particles of average size 0.5-1.5 microns, covered by a silane coat carrying amino groups (Bio-Mag, Advanced Magnetics, Boston), were derivatized by reaction with N-[(gamma-maleimidobutyryl)oxy]-succinimide (GMBS), N-hydroxysuccinimidyl iodoacetate (NHIA), 2-iminothiolane (2-It), or N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP). The derivatized particles were suitable for the reaction with sulfhydryl groups and subsequently coated with monoclonal antibodies (MoAbs) of different classes and isotypes (IgM, IgG1, IgG2a, IgG2b, IgG3) as well as polyclonal rabbit anti-mouse IgG (RAM). The antibodies were reduced by dithiothreitol (DTT) and covalently conjugated to the BioMag derivatives via liberated sulfhydryls of the hinge region. The observed conjugation ratios, expressed as protein/iron (micrograms/mg), could be reproducibly varied for optimization. These ratios were dependent on the type and amount of antibody offered for coupling to the derivatized particles, decreasing as follows: polyclonal = IgM greater than IgG2b greater than IgG2a = IgG3 greater IgG1. The conjugation ratios were also dependent on the type and amount of the spacer used to derivatize the BioMag particles, decreasing as follows: GMBS greater than NHIA greater than 2-It greater than SPDP. The magnetically responsive magnetite-antibody conjugates ("magneto-beads"), carrying MoAb BMA 081 (anti-CD8; IgG2a), MoAb BB10 (anti-CD10/CALLA; IgG2b), MoAb VIL-A1 (anti-CD10; IgM), and polyclonal RAM, coupled similarly via 3.6 mumol of GMBS spacer per mg of Fe, were further investigated with respect to a depletion effect on specific cell subsets. The rates of cell depletion were found to be strongly dependent on the individual characteristics of the antibody used.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:2151562

Hermentin, P; Doenges, R; Franssen, U; Bieva, C; Vander Brugghen, F J; Stryckmans, P; Friesen, H J; Optaczy, B; Schneider, S; Ax, W

1990-01-01

409

Decomposition of 1,4-dioxane by photo-Fenton oxidation coupled with activated sludge in a polyester manufacturing process.  

PubMed

The cyclic ether 1,4-dioxane is a synthetic industrial chemical that is used as a solvent in producing paints and lacquers. The EPA and the International Agency for Research on Cancer(IARC) classified 1,4-dioxane as a GROUP B2(probable human) carcinogen. 1,4-dioxane is also produced as a by-product during the manufacture of polyester. In this research, a polyester manufacturing company (i.e. K Co.) in Gumi, Korea was investigated regarding the release of high concentrations of 1,4-dioxane (about 600 mg/L) and whether treatment prior to release should occur to meet with the level of the regulation standard (e.g., 5 mg/L in 2010). A 10 ton/day pilot-scale treatment system using photo-Fenton oxidation was able to remove approximately 90% of 1,4-dioxane under the conditions that concentrations of 2800 ppm H(2)O(2) and 1,400 ppm FeSO(4) were maintained along with 10 UV-C lamps (240 microW/cm(2)) installed and operated continuously during aeration. However, the effluent concentration of 1,4-dioxane was still high at about 60 mg/L where TOC concentration in the effluent had been moreover increased due to decomposed products such as aldehydes and organic acids. Thus, further investigation is needed to see whether the bench scale (reactor volume, 8.9 L) of activated sludge could facilitate the decomposition of 1,4-dioxane and their by-products (i.e., TOC). As a result, 1,4-dioxane in the effluent has been decreased as low as 0.5 mg/L. The optimal conditions for the activated sludge process that were obtained are as follows: DO, 3-3.5 mg/L; HRT, 24 h; SRT 15 d; MLSS, 3,000 mg/L. Consequently, photo-Fenton oxidation coupled with activated sludge can make it possible to efficiently decompose 1,4-dioxane to keep up with that of the regulation standard. PMID:19273900

So, M H; Han, J S; Han, T H; Seo, J W; Kim, C G

2009-01-01

410

Dimeric 1,3-propanediaminetetraacetato lanthanides as the precursors of catalysts for the oxidative coupling of methane.  

PubMed

From neutral solutions, dimeric 1,3-propanediaminetetraacetato lanthanides (NH4)2[Ln2(1,3-pdta)2(H2O)4]·8H2O [Ln = La, 1; Ce, 2] and K2[Ln2(1,3-pdta)2(H2O)4]·11H2O [Ln = La, 3; Ce, 4] (1,3-H4pdta = 1,3-propanediaminetetraacetic acid, C11H18N2O8) were isolated in high yields. The reaction of excess strontium nitrate with 1 resulted in the formation of a two dimensional coordination polymer [La2(1,3-pdta)2(H2O)4]n·[Sr2(H2O)6]n·[La2(1,3-pdta)2(H2O)2]n·18nH2O (5) at 70 °C. Complexes 1-4 show a similar central molecular structure. The lanthanide ions are coordinated by two nitrogen atoms, four carboxy oxygen atoms from one 1,3-pdta ligand, two from the neighboring 1,3-pdta ligand forming a four-membered ring and two water molecules. Complex 5 has two kinds of dimeric lanthanum unit and extends into a 2D coordination polymer through strontium ions and bridged oxygen atoms, and forms a fourteen membered ring linked by oxygen atoms from carboxy groups of pdta. Complexes 1-4 are soluble in water. The (13)C{(1)H} NMR experiments for complex 1 were tested in solution. Thermal products from 1 and 5 show good catalytic activities towards the oxidative coupling reaction of methane (OCM). The conversion of methane and selectivity to C2 reached 29.7% and 51.7% at 750 °C for the product of 5. From TGA, XRD and SEM analyses, the thermal products from 1 and 5 are rod- and poly-shaped, which are assigned as lanthanum oxocarbonate and a mixture of La2O3, SrCO3 and La2O2CO3 for 1 and 5, respectively. The precurs