These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

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

PubMed

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

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

2014-08-01

2

Gold(I)-Catalyzed Diazo Coupling: Strategy towards Alkene Formation and Tandem Benzannulation.  

PubMed

A gold(I)-catalyzed cross-coupling of diazo compounds to afford tetrasubstituted alkenes has been developed by taking advantage of a trivial electronic difference between two diazo substrates. A N-heterocyclic-carbene-derived gold complex is the most effective catalyst for this transformation. Based on this new strategy, a gold(I)-initiated benzannulation has been achieved through a tandem reaction involving a diazo cross-coupling, 6??electrocyclization, and oxidative aromatization. PMID:25156018

Zhang, Daming; Xu, Guangyang; Ding, Dong; Zhu, Chenghao; Li, Jian; Sun, Jiangtao

2014-10-01

3

Quantification of oxidative DNA lesions in tissues of Long-Evans Cinnamon rats by capillary high-performance liquid chromatography-tandem mass spectrometry coupled with stable isotope-dilution method.  

PubMed

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

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

2011-03-15

4

Tandem reactions initiated by copper-catalyzed cross-coupling: a new strategy towards heterocycle synthesis.  

PubMed

Copper-catalyzed cross-coupling reactions which lead to the formation of C-N, C-O, C-S and C-C bonds have been recognized as one of the most useful strategies in synthetic organic chemistry. During past decades, important breakthroughs in the study of Cu-catalyzed coupling processes demonstrated that Cu-catalyzed reactions are broadly applicable to a variety of research fields related to organic synthesis. Representatively, employing these coupling transformations as key steps, a large number of tandem reactions have been developed for the construction of various heterocyclic compounds. These tactics share the advantages of high atom economics of tandem reactions as well as the broad tolerance of Cu-catalyst systems. Therefore, Cu-catalyzed C-X (X = N, O, S, C) coupling transformation-initiated tandem reactions were quickly recognized as a strategy with great potential for synthesizing heterocyclic compounds and gained worldwide attention. In this review, recent research progress in heterocycle syntheses using tandem reactions initiated by copper-catalyzed coupling transformations, including C-N, C-O, C-S as well as C-C coupling processes are summarized. PMID:21879127

Liu, Yunyun; Wan, Jie-Ping

2011-10-21

5

Facile tandem Suzuki coupling/transfer hydrogenation reaction with a bis-heteroscorpionate Pd-Ru complex.  

PubMed

Design and synthesis of the bis(pyrazol-1-yl)methane based bis-heteroscorpionate Pd-Ru complex results in efficient tandem Suzuki coupling/transfer hydrogenation reaction with a broad range of substrate reactivity. PMID:25297718

Dehury, Niranjan; Tripathy, Suman Kumar; Sahoo, Anupam; Maity, Niladri; Patra, Srikanta

2014-10-22

6

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

PubMed Central

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

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

2011-01-01

7

Stir bar sorptive extraction coupled to liquid chromatography-tandem mass spectrometry for the2 determination of pesticides in water samples: method validation and measurement uncertainty3  

E-print Network

1 Title :1 Stir bar sorptive extraction coupled to liquid chromatography-tandem mass spectrometry sorptive extraction followed by liquid desorption and high performance liquid12 chromatography with tandem chromatography-tandem mass spectrometry (LC-30 MSMS), pesticides, surface water, validation, measurement

Paris-Sud XI, Université de

8

Protein Complexes Characterization in Arabidopsis thaliana by Tandem Affinity Purification Coupled  

E-print Network

237 Chapter 18 Protein Complexes Characterization in Arabidopsis thaliana by Tandem Affinity affinity purification approach followed by mass spectrometry analysis to try to identify and characterize in vivo protein complexes. Key words Arabidopsis thaliana, Protein complexes, Tandem affinity purification

Hirt, Heribert

9

Tandem iodine-mediated oxidations of tetrahydro-?-carbolines: total synthesis of eudistomins Y1-Y7.  

PubMed

An efficient iodine-mediated oxidation of tetrahydro-?-carbolines is described to yield aromatic ?-carboline products with tandem C-H oxidation. The utility of the method was demonstrated in total syntheses of the alkaloids eudistomins Y1-Y7. PMID:23615808

Panarese, Joseph D; Waters, Stephen P

2013-06-01

10

Quantitative analysis of heterocyclic amines in urine by liquid chromatography coupled with tandem mass spectrometry.  

PubMed

A sensitive, reproducible, and rapid analytical method for the analysis of trace-level heterocyclic amines (HCAs) that are expected to have high levels of human exposure was developed. Liquid-liquid extraction (LLE) with dichloromethane (DCM) followed by solid-phase extraction (SPE) was carried out. Liquid extraction with DCM under basic conditions was efficient in extracting HCAs from urine samples. For further purification, mixed mode cationic exchange (MCX) cartridges were applied to eliminate the remaining interferences after liquid extraction. Separation and quantification were performed by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) in selected reaction monitoring (SRM) mode. The overall recoveries ranged between 71.0% and 113.6% with relative standard deviations (RSDs) of 5.1% to 14.7% for the entire procedure. The limits of detection (LODs) and limits of quantification (LOQs) of the proposed analytical method were in the ranges of 0.04 to 0.10 ng/ml and 0.15 to 0.36 ng/ml, respectively. This method was applied to the analysis of monitoring in urine samples for Korean school children, and the results demonstrated that the method can be used for the trace determination of HCAs in urine samples. PMID:24269709

Shin, Jeoung Hwa; Na, Yun-Cheol; Chung, Joo Hee; Gorinstein, Shela; Ahn, Yun Gyong

2014-02-15

11

COUPLING OF BIOTIC AND ABIOTIC ARSENITE OXIDATION IN SOIL  

E-print Network

COUPLING OF BIOTIC AND ABIOTIC ARSENITE OXIDATION IN SOIL by Laura Camille Jones A thesis submitted;COUPLING OF BIOTIC AND ABIOTIC ARSENITE OXIDATION IN SOIL by Laura Camille Jones Approved ............................................................................................. 6 2 ARSENITE OXIDATION KINETICS AT THE MICROBE- MANGANESE OXIDE INTERFACE

Sparks, Donald L.

12

Enantiomeric determination of amlodipine in human plasma by liquid chromatography coupled to tandem mass spectrometry.  

PubMed

A sensitive method for the separation and determination of amlodipine enantiomers in plasma has been developed based on solid-phase extraction (SPE) with disposable extraction cartridges (DECs) in combination with chiral liquid chromatography (LC). The SPE technique is used to isolate the drug from the biological matrix and to prepare a cleaner sample before injection and analysis by HPLC coupled to mass spectrometry. The DEC is filled with ethyl silica (50 mg) and is first conditioned with a 2.5% ammonia in methanol solution and then with ammonium acetate buffer. A 1.0-ml volume of plasma is then applied on the DEC. The washing step is first performed with ammonium acetate buffer and secondly with a mixture of water and methanol (65:35, v/v), while the final elution step is obtained by dispensing methanol containing 2.5% of ammonia. The eluate is then collected and evaporated to dryness before being dissolved in the LC mobile phase and injected into the LC system. The stereoselective analysis of amlodipine is achieved on a Chiral AGP column containing alpha(1)-acid glycoprotein as chiral selector by using a mobile phase consisting of a 10-mM acetate buffer (pH 4.5) and 1-propanol (99:1, v/v). The LC system is coupled to tandem mass spectrometry with an APCI interface in the positive-ion mode. The chromatographed analytes are detected in the selected reaction monitoring mode (SRM). The MS/MS ion transitions monitored are 409 to 238 for amlodipine, and 260 to 116 for S-(-)-propranolol used as internal standard (IS). The method was validated considering different parameters, such as linearity, precision and accuracy. The limit of quantitation was found to be 0.1 ng/ml for each amlodipine enantiomer. PMID:12543511

Streel, B; Lainé, C; Zimmer, C; Sibenaler, R; Ceccato, A

2002-12-31

13

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

14

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

Microsoft Academic Search

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

C. Hartig; T. Storm; M. Jekel

1999-01-01

15

Determination of anethole trithione in human plasma using high performance liquid chromatography coupled with tandem mass spectrometric detection  

Microsoft Academic Search

A rapid, sensitive and reliable high performance liquid chromatographic method coupled with tandem mass spectrometry via electrospray ionization (ESI) source (HPLC–MS\\/MS) has been developed and validated for the determination of anethole trithione (ATT) in human plasma. Diazepam was employed as the internal standard (IS). Sample extracts following liquid–liquid extraction were injected into the HPLC–MS\\/MS system. The analyte and IS were

Tianmin Li; Zunjian Zhang; Haoyan Jiao; Lu Zhang; Yuan Tian; Yun Chen; Xiaoyang Pang; Jie Zhuang

2007-01-01

16

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

17

Tandem metal-oxide affinity chromatography for enhanced depth of phosphoproteome analysis.  

PubMed

In eukaryotic cells many diverse cellular functions are regulated by reversible protein phosphorylation. In recent years, phosphoproteomics has become a powerful tool to study protein phosphorylation because it allows unbiased localization, and site-specific quantification, of in vivo phosphorylation of hundreds of proteins in a single experiment. A common strategy to identify phosphoproteins and their phosphorylation sites from complex biological samples is the enrichment of phosphopeptides from digested cellular lysates followed by mass spectrometry. However, despite the high sensitivity of modern mass spectrometers the large dynamic range of protein abundance and the transient nature of protein phosphorylation remained major pitfalls in MS-based phosphoproteomics. Tandem metal-oxide affinity chromatography (MOAC) represents a robust and highly selective approach for the identification and site-specific quantification of low abundant phosphoproteins that is based on the successive enrichment of phosphoproteins and -peptides. This strategy combines protein extraction under denaturing conditions, phosphoprotein enrichment using Al(OH)3-based MOAC, tryptic digestion of enriched phosphoproteins followed by TiO2-based MOAC of phosphopeptides. Thus, tandem MOAC effectively targets the phosphate moiety of phosphoproteins and phosphopeptides and, thus, allows probing of the phosphoproteome to unprecedented depth. PMID:24136551

Beckers, Gerold J M; Hoehenwarter, Wolfgang; Röhrig, Horst; Conrath, Uwe; Weckwerth, Wolfram

2014-01-01

18

Novel Mass Spectrometric Method for Phosphorylation Quantification Using Cerium Oxide Nanoparticles and Tandem Mass Tags  

PubMed Central

The stoichiometry of protein phosphorylation significantly impacts protein function. The development of quantitative techniques in mass spectrometry has generated the ability to systematically monitor the regulation levels of various proteins. This study reports an integrated methodology using cerium oxide nanoparticles and isobaric tandem mass tag (TMT) labeling to assess absolute stoichiometries of protein phosphorylation. This protocol was designed to directly measure the dephosphorylation levels for a known phosphorylation site therefore allowing for quantification of phosphosites. Both the accuracy and precision of the method were verified using standard peptides and protein tryptic digests. This novel method was then applied to quantify phosphorylations on eukaryotic initiation factor 3H (eIF3H), a protein integral to overall eukaryotic protein translation initiation. To date, this is the first report of assessment of protein phosphorylation quantification on eIF3. PMID:22304650

Jia, Weitao; Andaya, Armann; Leary, Julie A.

2012-01-01

19

Static Longitudinal Stability of a Tandem-Coupled Bomber-Fighter Airplane Configuration Proposed by All American Airways, Inc.  

NASA Technical Reports Server (NTRS)

At the request of the Air Materiel Command an investigation was made in the Langley free-flight tunnel to determine the static longitudinal stability and control characteristics of models coupled together in a tandem configuration proposed by All American Airways, Inc. Force tests were made using 1/20-scale models of B-29 end F-80 airplanes to determine the effects of coupling the fighter to the tail of the bomber. The results of the investigation showed that for the bomber alone the aerodynamic center was 0.21 mean aerodynamic chord behind the center of gravity (stable) but that for the tandem configuration the aerodynamic center was 0.09 mean aerodynamic chord forward of the center of gravity, of the combination (unstable). The elevator effectiveness of the bomber was reduced approximately 50 percent by addition of the fighter. Some recent flight tests made in the free-flight tunnel with models simulating the proposed configuration indicate that the reduction in stability may be minimized by incorporating a hinged coupling permitting freedom in pitch.

Hewes, Donald E.

1950-01-01

20

Integrated autothermal reactor concepts for oxidative coupling and reforming of  

E-print Network

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

Twente, Universiteit

21

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

22

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

23

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

24

[High-sensitivity analysis of purines in alcoholic beverages using hydrophilic interaction chromatography coupled with tandem mass spectrometry].  

PubMed

In this study, we established a high-sensitivity analytical method for purines in alcoholic beverages using hydrophilic interaction chromatography coupled with tandem mass spectrometry. The alcoholic beverages were hydrolyzed with perchloric acid (60%) and subjected to strong cation exchange solid-phase extraction (Bond Elut SCX). The four purine bases (hypoxanthine, adenine, xanthine, guanine) in the extracted solution were separated by hydrophilic interaction chromatography with TSKgel Amide-80 as a separation column, 10 mM ammonium formate (pH 2.0) as mobile phase A, and acetonitrile/100 mM ammonium formate (pH 2.0) (90/10) as mobile phase B. The detection of purine bases was performed by tandem mass spectrometry with ESI. The linearity of this analytical method was not less than 0.996, and the repeatability was not more than 8.4% for each purine base. The recovery was in the range of 60-105%, and the detection limit was not more than 0.005 mg/100 mL. This established method is expected to be useful for quality control and surveillance of purines in alcoholic beverages. PMID:24990557

Kakigi, Yasuhiro; Yoshioka, Toshiaki; Nagatomi, Yasushi; Uyama, Atsuo; Mochizuki, Naoki

2014-01-01

25

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

26

Multiclass determination of phytochemicals in vegetables and fruits by ultra high performance liquid chromatography coupled to tandem mass spectrometry.  

PubMed

In this study a simultaneous determination of several classes of phytochemicals (isoflavones, glucosinolates, flavones, flavonols and phenolic acids) in tomato, broccoli, carrot, eggplant and grape has been carried out by ultra high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). Solid-liquid extraction assisted by rotary agitator was utilised, using a mixture of methanol:water (80:20, v/v) as solvent. The analytical procedure was validated in all the matrices, obtaining recoveries ranging from 60% to 120% with repeatability values (expressed as relative standard deviations, RSDs) lower than 25%. Limits of quantification (LOQs) were always equal or lower than 50?g/kg, except for some glucosinolates (125?g/kg). Finally the method was applied to different matrices such as tomato, broccoli, carrot, grape and eggplant, observing that chlorogenic acid was detected in most of the samples at higher concentrations in relation to the other compounds. PMID:23790894

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

2013-11-15

27

Oxidant-Free Dehydrogenative Coupling Reactions via Hydrogen Evolution.  

PubMed

Oxidant-free dehydrogenative coupling reactions: Recently, coupling reactions have followed a novel strategy for the construction of C?C, C?N, C?P, and S?S bonds by dehydrogenation without using any extra oxidant, via H2 evolution. These breakthroughs inspire a new direction in the construction of chemical bonds, towards more sustainable, highly atom-economical, and environmentally benign synthetic methods. PMID:25139249

He, Ke-Han; Li, Yang

2014-10-01

28

Separation of selenium-containing proteins in human and mouse plasma using tandem high-performance liquid chromatography columns coupled with inductively coupled plasma-mass spectrometry.  

PubMed

An analytical method that uses two different high-performance liquid chromatography (HPLC) columns in tandem has been developed that separates three major selenium-containing proteins (albumin, glutathione peroxidase, and selenoprotein P) found in human blood plasma. The first column was a heparin affinity column and the second was a gel filtration column whose outlet was directly connected to an inductively coupled plasma-mass spectrometer. The method successfully separated plasma selenium into the three selenium-containing proteins and revealed the preferential retention of selenium in the form of selenoprotein P in a selenium-deficient human and in selenium-deficient mice. Our results also confirm the results of previous studies that showed a preference for supplemented selenium to be taken up as selenoprotein P in rats. Advantages of the tandem column method are that it allows rapid and convenient analyses of the distribution of plasma selenium, and that it is suitable for stable isotope tracer studies and metal interaction studies. PMID:9918658

Koyama, H; Omura, K; Ejima, A; Kasanuma, Y; Watanabe, C; Satoh, H

1999-02-01

29

Cu(I)-catalyzed tandem benzyldiazoester coupling with terminal alkyne-allene formation-Michael reaction: application to the syntheses of oxa and azacycles.  

PubMed

A simple and practical procedure for the synthesis of aza- and oxacycles, which possess an array of stereogenic functionalities, is described. This protocol relies on tandem Cu-catalyzed coupling of suitably functionalized terminal alkyne with diazoester followed by isomerization and subsequent aza or oxa-Michael reaction, thus generating the required scaffold with high diastereoselectivity. PMID:21969100

Kumaraswamy, Gullapalli; Jayaprakash, Neerasa; Balakishan, Guniganti

2011-10-26

30

Magnetic coupling among spinel iron oxide microparticles by Mssbauer spectroscopy  

E-print Network

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

Boyer, Edmond

31

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

32

Homo- and hetero-oxidative coupling of benzyl anions.  

PubMed

The regioselective benzylic metalation of substituted toluenes using BuLi/KO-t-Bu/TMP(H) (LiNK metalation conditions) with subsequent in situ oxidative C-C coupling has been developed for the facile generation of 1,2-diarylethanes. A range of oxidants can be used for the oxidative coupling step, with 1,2-dibromoethane proving optimal. Heterocouplings can be achieved starting from a mixture of two different toluenes with a bias toward cross coupling achievable by using a 2-fold excess of one toluene starting material. The utility of this approach is illustrated by the synthesis of several biologically active natural products. A distinct advantage is that the synthetic steps typically required to preactivate the coupling substrates are eliminated and no transition metal is required to facilitate the C-C bond formation. PMID:22329345

Blangetti, Marco; Fleming, Patricia; O'Shea, Donal F

2012-03-16

33

Tandem repeat coupled with endonuclease cleavage (TREC): a seamless modification tool for genome engineering in yeast.  

PubMed

The complete synthetic Mycoplasma genitalium genome ( approximately 583 kb) has been assembled and cloned as a circular plasmid in the yeast Saccharomyces cerevisiae. Attempts to engineer the cloned genome by standard genetic methods involving the URA3/5-fluoroorotic acid (5-FOA) counter-selection have shown a high background of 5-FOA resistant clones derived from spontaneous deletions of the bacterial genome maintained in yeast. Here, we report a method that can seamlessly modify the bacterial genome in yeast with high efficiency. This method requires two sequential homologous recombination events. First, the target region is replaced with a mutagenesis cassette that consists of a knock-out CORE (an18-bp I-SceI recognition site, the SCEI gene under the control of the GAL1 promoter, and the URA3 marker) and a DNA fragment homologous to the sequence upstream of the target site. The replacement generates tandem repeat sequences flanking the CORE. Second, galactose induces the expression of I-SceI, which generates a double-strand break (DSB) at the recognition site. This DSB promotes intra-molecular homologous recombination between the repeat sequences, and leads to an excision of the CORE. As a result, a seamless modification is generated. This method can be adapted for a variety of genomic modifications and may provide an important tool to modify and design natural or synthetic genomes propagated in yeast. PMID:20228123

Noskov, Vladimir N; Segall-Shapiro, Thomas H; Chuang, Ray-Yuan

2010-05-01

34

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

PubMed Central

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

Kim, Tae-Hyun; Choi, Juhee

2014-01-01

35

Validation of determination of plasma metabolites derived from thyme bioactive compounds by improved liquid chromatography coupled to tandem mass spectrometry.  

PubMed

In the present study, a selective and sensitive method, based on microelution solid-phase extraction (?SPE) plate and ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) was validated and applied to determine the plasma metabolites of the bioactive compounds of thyme. For validation process, standards of the more representative components of the phenolic and monoterpene fractions of thyme were spiked in plasma samples and then the quality parameters of the method were studied. Extraction recoveries (%R) of the studied compounds were higher than 75%, and the matrix effect (%ME) was lower than 18%. The LODs ranged from 1 to 65 ?g/L, except for the thymol sulfate metabolite, which was 240 ?g/L. This method was then applied for the analysis of rat plasma obtained at different times, from 0 to 6h, after an acute intake of thyme extract (5 g/kg body weight). Different thyme metabolites were identified and were mainly derived from rosmarinic acid (coumaric acid sulfate, caffeic acid sulfate, ferulic acid sulfate, hydroxyphenylpropionic acid sulfate, dihydroxyphenylpropionic acid sulfate and hydroxybenzoic acid) and thymol (thymol sulfate and thymol glucuronide). The most abundant thyme metabolites generated were hydroxyphenylpropionic acid sulfate and thymol sulfate, their respective concentrations in plasma being 446 and 8464 ?M 1h after the intake of the thyme extract. PMID:22939267

Rubió, Laura; Serra, Aida; Macià, Alba; Borràs, Xenia; Romero, Maria-Paz; Motilva, Maria-José

2012-09-15

36

[Simultaneous determination of five yellow dyes in foods by high performance liquid chromatography coupled with tandem mass spectrometry].  

PubMed

A method based on high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS) was developed for simultaneous determination of five yellow industrial dyes. The separations were performed with an Agilent ODS C18 column at a flow rate of 0.3 mL/min. The mobile phase was 5 mmol/L ammonium acetate (containing 0.1% formic acid)-acetonitrile (3:2, v/v). Under the optimized detection conditions, the linear ranges for Chrysoidine G and Basic Yellow 2 were 5.0-80.0 mg/L, and for Acid Orange I, Acid orange Il and Acid Yellow 36 were 10.0-160.0 microg/L. The limits of quantification for Chrysoidine G, Basic Yellow 2, Acid Orange I, Acid Orange II and Acid Yellow 36 were 20, 20, 40, 40 and 40 ng/g, respectively. The relative standard deviations of reproducibility of this method for retention time and peak area were no more than 0.50% and 2.14%, respectively. The method was applied to determine the recoveries of the above five dyes in chicken, bean products and yellow croaker were between 79.8%-95.2% with satisfactory results. PMID:21574405

Lin, Saijun; Tu, Haiyun; Sun, Lan; Xiao, Hailong; Pan, Xiangrong; Ma, Xiaoyan

2011-01-01

37

[Determination of 16 quinolone residues in animal tissues using high performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry].  

PubMed

A confirmative method was developed with high performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (HPLC-MS/MS) to simultaneously detect 16 quinolone residues in animal tissues, which included nalidixinic acid, oxolinic acid, flumequine, norfloxacin, enoxacin, ciprofloxacin, lomefloxacin, danofloxacin, enrofloxacin, ofloxacin, sarafloxacin, difloxacin, marbofloxacin, pefloxacin, sparfloxacin and orbifloxacin. In the method, the 16 residues were extracted with acidified acetonitrile, cleaned-up with hexane, and concentrated with a rotary evaporator. Then the reconstituted sample solution was analyzed using HPLC-MS/MS in positive mode, with a Inertsil C8-3 column as the analytical column. The method was validated at 10, 50 and 100 microg/kg. The validation results were as follows: the linear ranges were from 10 to 100 microg/kg; the overall recoveries were from 62.4% to 102% with the relative standard deviations of 1.4%-11.9%. The method is simple, rapid, and accurate, and its performance could meet the requirements of the domestic and international legislation. The method is applicable to simultaneously confirm multi-residues of quinolones in animal tissues such as chicken muscle, chicken liver and fish muscle. PMID:17970104

Yue, Zhenfeng; Lin, Xiuyun; Tang, Shaobing; Chen, Xiaoxia; Ji, Caini; Hua, Honghui; Liu, Yu

2007-07-01

38

[Determination of 215 pesticide residues in ginger using liquid chromatography coupled with electrospray ionization tandem mass spectrometry].  

PubMed

A multiresidue analytical method was developed for the determination of 215 pesticides in ginger using liquid chromatography coupled with electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). The pesticide residues were extracted from ginger by acetonitrile containing 1% (v/v) acetic acid, cleaned-up by a Sep-Pak Vac cartridge, eluted with acetonitrile-toluene (3:1, v/v). The eluate was concentrated to about 0.5 mL with a rotary evaporator, dried with nitrogen at room temperature. The sample was redissolved in an acetonitrile-water mixture (3:2, v/v), then analyzed using LC-MS/MS in multiple reaction monitoring (MRM) mode via positive electrospray ionization. The recovery test was conducted at spiked level of limit of quantification (LOQ). The validation results were as follows: the overall recoveries were from 68.1% to 132.6% of which 94.4% of the recoveries were from 70% to 120%, with the relative standard deviations of 0.4%-25.0%. The limits of detection (S/N = 3) and the limits of quantification (S/N = 10) were 0.01-70.45 microg/L and 0.04-234.84 microg/L, respectively. The results demonstrated that this method is simple and with acceptable sensitivity and accuracy to meet the requirements of the multiple pesticide residue analysis. This method is applicable to determine 215 pesticide residues in ginger. PMID:20873579

Cao, Jing; Pang, Guofang; Wang, Minglin; Fan, Chunlin

2010-06-01

39

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

40

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

PubMed Central

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

Taguchi, Kaori; Fukusaki, Eiichiro; Bamba, Takeshi

2014-01-01

41

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

PubMed

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

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

2014-09-12

42

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

Microsoft Academic Search

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

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

2011-01-01

43

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

44

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

Microsoft Academic Search

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

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

2005-01-01

45

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

E-print Network

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

Wang, Lee-Ping

46

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

PubMed Central

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

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

2014-01-01

47

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

48

Metal-Free Tandem Oxidative Aryl Migration and C-C Bond Cleavage: Synthesis of ?-Ketoamides and Esters from Acrylic Derivatives.  

PubMed

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

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

2014-11-01

49

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

50

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

51

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

52

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

53

Human G-protein-coupled inwardly rectifying potassium channel (GIRK1) gene (KCNJ3): Localization to chromosome 2 and identification of a simple tandem repeat polymorphism  

SciTech Connect

The gene encoding the human G-protein-coupled inwardly rectifying potassium channel designated GIRK1 (gene symbol, KCNJ3) was mapped to chromosome 2 by analyzing its segregation in a panel of human-hamster somatic cell hybrids. This assignment was confirmed by fluorescence in situ hybridization to metaphase chromosomes, and the gene was further localized to band 2q24.1. A highly informative simple tandem repeat DNA polymorphism of the form (CA)[sub n] was identified and used to localize KCNJ3 within the genetic map of the long arm of chromosome 2. 8 refs., 1 fig., 2 tabs.

Stoffel, M.; Powell, K.L.; Espinosa, R. III; Philipson, L.H.; Le Beau, M.M.; Bell, G.I. (Univ. of Chicago, IL (United States))

1994-05-01

54

Coupling of nitrous oxide and methane by global atmospheric chemistry.  

PubMed

Nitrous oxide (N(2)O) and methane (CH(4)) are chemically reactive greenhouse gases with well-documented atmospheric concentration increases that are attributable to anthropogenic activities. We quantified the link between N(2)O and CH(4) emissions through the coupled chemistries of the stratosphere and troposphere. Specifically, we simulated the coupled perturbations of increased N(2)O abundance, leading to stratospheric ozone (O(3)) depletion, altered solar ultraviolet radiation, altered stratosphere-to-troposphere O(3) flux, increased tropospheric hydroxyl radical concentration, and finally lower concentrations of CH(4). The ratio of CH(4) per N(2)O change, -36% by mole fraction, offsets a fraction of the greenhouse effect attributable to N(2)O emissions. These CH(4) decreases are tied to the 108-year chemical mode of N(2)O, which is nine times longer than the residence time of direct CH(4) emissions. PMID:21071666

Prather, Michael J; Hsu, Juno

2010-11-12

55

Noxa couples lysosomal membrane permeabilization and apoptosis during oxidative stress.  

PubMed

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

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

2013-12-01

56

The oxidative coupling of methane and the oxidative dehydrogenation of ethane over a niobium promoted lithium doped magnesium oxide catalyst  

Microsoft Academic Search

The promoting effect of niobium in a Li\\/MgO catalyst for the oxidative coupling of methane (OCM) and for the oxidative dehydrogenation of ethane (ODHE) has been studied in some detail. It has been found that a Li\\/Nb\\/MgO catalyst with 16 wt % niobium showed the highest activity for the C2 production in the OCM reaction; the activity at 600 °C

H. M. Swaan; X. Li; K. Seshan; Ommen van J. G; J. R. H. Ross

1993-01-01

57

Coupling of ICRF waves and axial transport of high-energy ions owing to spontaneously excited waves in the GAMMA 10 tandem mirror  

NASA Astrophysics Data System (ADS)

Plasmas with high ion temperature of several kiloelectronvolts and a strong temperature anisotropy of greater than 10 were produced by ion cyclotron range of frequency (ICRF) heating in the GAMMA 10 tandem mirror. In such high-performance plasmas with strong anisotropy, high-frequency fluctuations, so-called Alfvén-ion-cyclotron (AIC) waves, are excited spontaneously. These AIC waves have several discrete peaks in the frequency spectrum. Coupling of the ICRF heating waves and the excited AIC waves was clearly observed in the density fluctuations measured with a newly developed reflectometer. Parametric decay from the heating ICRF waves to the AIC waves and low-frequency waves was also indicated. Alfvén waves with difference frequencies between the discrete peaks of the AIC waves were detected in a signal that measured the number of axially transported high-energy ions (over 6 keV) at the machine end, indicating pitch-angle scattering caused by the low-frequency waves. Energy transport along the magnetic field line is an important consideration when ICRF power is injected in the perpendicular direction to a magnetic field line. The importance of the spontaneously excited AIC waves for axial confinement of a tandem mirror through wave-wave couplings was demonstrated.

Ikezoe, R.; Ichimura, M.; Hirata, M.; Iwai, T.; Yokoyama, T.; Ugajin, Y.; Sato, T.; Iimura, T.; Saito, Y.; Yoshikawa, M.; Kohagura, J.; Shima, Y.; Imai, T.

2013-07-01

58

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

PubMed

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

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

2012-03-01

59

Frequency-selective surface coupled metal-oxide-metal diodes  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

60

Coupling oxidative signals to protein phosphorylation via methionine oxidation in Arabidopsis.  

PubMed

The mechanisms involved in sensing oxidative signalling molecules, such as H2O2, in plant and animal cells are not completely understood. In the present study, we tested the postulate that oxidation of Met (methionine) to MetSO (Met sulfoxide) can couple oxidative signals to changes in protein phosphorylation. We demonstrate that when a Met residue functions as a hydrophobic recognition element within a phosphorylation motif, its oxidation can strongly inhibit peptide phosphorylation in vitro. This is shown to occur with recombinant soybean CDPKs (calcium-dependent protein kinases) and human AMPK (AMP-dependent protein kinase). To determine whether this effect may occur in vivo, we monitored the phosphorylation status of Arabidopsis leaf NR (nitrate reductase) on Ser534 using modification-specific antibodies. NR was a candidate protein for this mechanism because Met538, located at the P+4 position, serves as a hydrophobic recognition element for phosphorylation of Ser534 and its oxidation substantially inhibits phosphorylation of Ser534 in vitro. Two lines of evidence suggest that Met oxidation may inhibit phosphorylation of NR-Ser534 in vivo. First, phosphorylation of NR at the Ser534 site was sensitive to exogenous H2O2 and secondly, phosphorylation in normal darkened leaves was increased by overexpression of the cytosolic MetSO-repair enzyme PMSRA3 (peptide MetSO reductase A3). These results are consistent with the notion that oxidation of surface-exposed Met residues in kinase substrate proteins, such as NR, can inhibit the phosphorylation of nearby sites and thereby couple oxidative signals to changes in protein phosphorylation. PMID:19527223

Hardin, Shane C; Larue, Clayton T; Oh, Man-Ho; Jain, Vanita; Huber, Steven C

2009-09-01

61

Coupling oxidative signals to protein phosphorylation via methionine oxidation in Arabidopsis  

PubMed Central

The mechanisms involved in sensing oxidative signalling molecules, such as H2O2, in plant and animal cells are not completely understood. In the present study, we tested the postulate that oxidation of Met (methionine) to MetSO (Met sulfoxide) can couple oxidative signals to changes in protein phosphorylation. We demonstrate that when a Met residue functions as a hydrophobic recognition element within a phosphorylation motif, its oxidation can strongly inhibit peptide phosphorylation in vitro. This is shown to occur with recombinant soybean CDPKs (calcium-dependent protein kinases) and human AMPK (AMP-dependent protein kinase). To determine whether this effect may occur in vivo, we monitored the phosphorylation status of Arabidopsis leaf NR (nitrate reductase) on Ser534 using modification-specific antibodies. NR was a candidate protein for this mechanism because Met538, located at the P+4 position, serves as a hydrophobic recognition element for phosphorylation of Ser534 and its oxidation substantially inhibits phosphorylation of Ser534 in vitro. Two lines of evidence suggest that Met oxidation may inhibit phosphorylation of NR-Ser534 in vivo. First, phosphorylation of NR at the Ser534 site was sensitive to exogenous H2O2 and secondly, phosphorylation in normal darkened leaves was increased by overexpression of the cytosolic MetSO-repair enzyme PMSRA3 (peptide MetSO reductase A3). These results are consistent with the notion that oxidation of surface-exposed Met residues in kinase substrate proteins, such as NR, can inhibit the phosphorylation of nearby sites and thereby couple oxidative signals to changes in protein phosphorylation. PMID:19527223

Hardin, Shane C.; Larue, Clayton T.; Oh, Man-Ho; Jain, Vanita; Huber, Steven C.

2009-01-01

62

Direct amidation from alcohols and amines through a tandem oxidation process catalyzed by heterogeneous-polymer-incarcerated gold nanoparticles under aerobic conditions.  

PubMed

We describe herein a highly elegant and suitable synthesis of amide products from alcohols and amines through a tandem oxidation process that uses molecular oxygen as a terminal oxidant. Carbon-black-stabilized polymer-incarcerated gold (PICB-Au) or gold/cobalt (PICB-Au/Co) nanoparticles were employed as an efficient heterogeneous catalyst depending on alcohol reactivity and generated only water as the major co-product of the reaction. A wide scope of substrate applicability was shown with 42 examples. The catalysts could be recovered and reused without loss of activity by using a simple operation. PMID:24166844

Soulé, Jean-François; Miyamura, Hiroyuki; Kobayashi, Sh?

2013-11-01

63

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

64

Highly(?98%) Stereo- and Regioselective Trisubstituted Alkene Synthesis of Wide Applicability via 1-Halo-1-alkyne Hydroboration–Tandem Negishi-Suzuki Coupling or Organoborate Migratory Insertion Protocol  

PubMed Central

(Z)-1-Halo-1-alkenylboranes (7), preparable in 82–90% yields as ?98% isomerically pure compounds via hydroboration of 1-halo-1-alkynes, have been converted to a wide range of trisubstituted alkenes via three different routes in the tail-to-head (T-to-H) direction, i.e., (i) Palladium-catalyzed Negishi-Suzuki tandem alkenylation, (ii) treatment of 7 with organolithium or Grignard reagents to generate ?-bromo-1-alkenylboronate complexes (10) that can undergo migratory insertion of a carbon group (R2) to form (E)-alkenylboranes (11) with inversion of alkene configuration (?98% inversion), followed by fluoride-promoted Suzuki alkenylation, and (iii) Negishi coupling to generate (Z)-alkenylboranes (8) in ?98% retention of configuration, followed by treatment with organolithium or Grignard reagents to produce trisubstituted alkenes with reversed stereo configurations. The synthetic utility of the present methodology has been demonstrated in the highly selective synthesis of side chain (4) of scyphostatin in 28% yield over nine steps in the longest linear sequence from allyl alcohol. Thus, this new tandem protocol has been emerged as the most widely applicable and highly selective route to trisubstituted alkenes including those that are otherwise difficult to prepare. PMID:24072993

Xu, Shiqing; Lee, Ching-Tien; Rao, Honghua

2013-01-01

65

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

PubMed

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

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

2010-01-01

66

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

PubMed Central

The biotransformation products of zearalenone, a Fusarium mycotoxin, were elucidated using the model plant Arabidopsis thaliana. After treatment of plant seedlings with 50 ?M 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 ?- and ?-zearalenol, were detected in the samples. Time courses for the different zearalenone metabolites were recorded and they give a closer insight into the metabolism kinetics. A scheme proposing the zearalenone metabolism in A. thaliana is given. The aspect of food safety regarding the (potential) occurrence of masked mycotoxins in agricultural commodities is discussed. PMID:17071522

BERTHILLER, F.; WERNER, U.; SULYOK, M.; KRSKA, R.; HAUSER, M.-T.; SCHUHMACHER, R.

2010-01-01

67

Characterization of the chemical constituents in Da-Huang-Gan-Cao-Tang by liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry and liquid chromatography coupled with ion trap mass spectrometry.  

PubMed

In this work, the chemical constituents in Da-Huang-Gan-Cao-Tang, a traditional Chinese formula, were studied by liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry and liquid chromatography coupled with ion trap mass spectrometry for the first time. Among the 146 compounds detected in Da-Huang-Gan-Cao-Tang, 104 compounds were identified unambiguously or tentatively based on their accurate molecular weight and multistage MS data, including one potential novel compound and two reported in Glycyrrhiza genus for the first time. The possible fragmentation pathways were proposed and fragmentation rules of the major types of compounds were concluded. This study provided an example to facilitate the tedious identification of chemical composition in traditional Chinese medicine, and maybe a promising reference approach to research the analogous formulae. PMID:24771648

Wang, Shufang; Chen, Pinghong; Xu, Yimin; Li, Xiaodong; Fan, Xiaohui

2014-07-01

68

Simultaneous determination of irbesartan and hydrochlorothiazide in human plasma using HPLC coupled with tandem mass spectrometry: Application to bioequivalence studies.  

PubMed

A sensitive, specific and selective liquid chromatography/tandem mass spectrometric method has been developed and validated for the simultaneous determination of irbesartan and hydrochlorothiazide in human plasma. Plasma samples were prepared using protein precipitation with acetonitrile, the two analytes and the internal standard losartan were separated on a reverse phase C(18) column (50mmx4mm, 3microm) using water with 2.5% formic acid, methanol and acetonitrile (40:45:15, v/v/v (%)) as a mobile phase (flow rate of 0.70mL/min). Irbesartan and hydrochlorothiazide were ionized using ESI source in negative ion mode, prior to detection by multiple reaction monitoring (MRM) mode while monitoring at the following transitions: m/z 296-->269 and m/z 296-->205 for hydrochlorothiazide, 427-->175 for irbesartan. Linearity was demonstrated over the concentration range 0.06-6.00microg/mL for irbesartan and 1.00-112.00ng/mL for hydrochlorothiazide. The developed and validated method was successfully applied to a bioequivalence study of irbesartan (300mg) with hydrochlorothiazide (12.5mg) tablet in healthy volunteers (N=36). PMID:20004542

Tutunji, Lara F; Tutunji, Maha F; Alzoubi, Mamoun I; Khabbas, Manal H; Arida, Adi I

2010-03-11

69

Determination of norcantharidin in mouse tissues by liquid chromatography coupled to tandem mass spectrometry and its tissue distribution study.  

PubMed

The purpose of this study is to determine the concentrations of norcantharidin (CAS NO: 5442-12-6) in mouse tissues and investigate its tissue distribution after intragastric administration of disodium norcantharidate solution. A highly sensitive and specific liquid chromatography-tandem mass spectrometric (LC-MS/MS) method was developed and validated, using ribavirin (CAS NO: 36791-04-5) as the internal standard (IS). Norcantharidin and IS were extracted from 0.3 mL tissue homogenates using protein precipitation with acetone under acid condition. The analyte was separated on a C18 reverse phase column and analyzed by MS/MS in the multiple reaction monitoring (MRM) mode using ESI with positive ionization, m/z 169?123 for norcantharidin and m/z 267?135 for IS. The developed method was validated over a linear range of concentrations 0.01~5 ?g·mL - 1 in liver, lung, kidney, stomach, small intestine, uterus and testis, 0.005~0.5 ?g·mL - 1 in heart, spleen and brain, the correlation coefficients (r2) were between 0.9918 and 0.9976. The tissue distribution study result was as follows: The AUC0-t of norcantharidin in tissues was in the order as follows: small intestine, stomach, uterus, kidney, testis, liver, lung, spleen, heart, brain. PMID:22473525

Zhang, R; Wang, J; Yuan, G; Wei, C; Liu, X; Wang, B; Gao, H; Guo, R

2012-06-01

70

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

71

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

72

Oxidative tandem nitrosation/cyclization of N-aryl enamines with nitromethane toward 3-(trifluoromethyl)quinoxalines.  

PubMed

A novel one-pot strategy for the synthesis of 3-trifluoromethylquinoxalines from N-aryl enamines and nitromethane was developed. The tandem reaction is achieved through nitrosation of alkenes, tautomerization and cyclization, which can be applicable to a wide range of enamines with excellent functional group tolerance and afford quinoxalines in moderate to good yields. PMID:25308914

Yang, Zhi-Jun; Liu, Chuan-Zhuo; Hu, Bo-Lun; Deng, Chen-Liang; Zhang, Xing-Guo

2014-10-28

73

Reduction Potentials of Rieske Clusters: Importance of the Coupling between Oxidation State and Histidine Protonation State  

E-print Network

state. Implications for the mechanism of quinol oxidation at the QO site of the cytochrome bc1 and b6f- quinol oxidizing cytochrome bc1 or b6f complex to -150 mV for a Rieske-type ferredoxin (1). In RieskeReduction Potentials of Rieske Clusters: Importance of the Coupling between Oxidation State

Crofts, Antony R.

74

Membrane assisted solvent extraction coupled with liquid chromatography tandem mass spectrometry applied to the analysis of alkylphenols in water samples.  

PubMed

This work describes the development and validation of a novel, simple, sensitive and environmental friendly analytical method for the determination of alkylphenols in different types of water samples. The methodology was based on a membrane assisted solvent extraction of only 15 mL of water sample with 500 ?L of hexane in combination with liquid chromatography-electrospray ionization tandem mass spectrometry in negative mode (LC-ESI-MS/MS). Acquisition was performed in the multiple reaction monitoring (MRM) mode recording two transitions for the identification of the target compounds. Quantitation is based on the use of deuterated labelled standards as surrogate standards. The figures of merit were satisfactory in all cases: absolute recoveries were close to 50% for most investigated compounds and relative recoveries varied between 81 and 108%. Repeatability and intermediate precision were <20% for all compounds. Uncertainty assessment of measurement was estimated on the basis of an in-house validation according to EURACHEM/CITAC guide. Quantitation limits of the method (MQL) were lower than 0.04 ?g L(-1) in all cases, which allow the achievement of the limits established by the Directive 2008/105/EC for surface and seawater samples and by the new proposal COM (2011) 876 final. The feasibility of the proposed method was demonstrated analyzing seawater, surface water and drinking water samples from different areas of A Coruña (Northwest of Spain). The analyses evidenced the presence of nonylphenol in seawater (MQL-0.13 ?g L(-1)) and surface water samples (0.12-0.19 ?g L(-1)). The highest concentration was observed in drinking water (0.25 ?g L(-1)). PMID:23394746

Salgueiro-González, N; Turnes-Carou, I; Muniategui-Lorenzo, S; López-Mahía, P; Prada-Rodríguez, D

2013-03-15

75

Tandem amine propargylation-Sonogashira reactions: new three-component coupling leading to functionalized substituted propargylic amines  

Microsoft Academic Search

Three-component coupling reactions of propargyl halides, amines, and organic halides in the presence of palladium–copper catalysis produced efficiently highly functionalized propargylic amines in good to excellent yields at room temperature. Extension to the synthesis of 2-(dialkylaminomethyl)benzo[b]furan or indole derivatives is described.

Nathanaël Olivi; Philippe Spruyt; Jean-François Peyrat; Mouâd Alami; Jean-Daniel Brion

2004-01-01

76

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

NASA Astrophysics Data System (ADS)

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

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

2010-04-01

77

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

NASA Astrophysics Data System (ADS)

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 and other abiotic rates. Here we explore the reactivity of biogenic Mn oxides formed by a common marine bacterium ( Roseobacter sp. AzwK-3b), which has been previously shown to oxidize Mn(II) via the production of extracellular superoxide. Oxidation of Mn(II) by superoxide results in the formation of highly reactive colloidal birnessite with hexagonal symmetry. The colloidal oxides induce the rapid oxidation of Mn(II), with dramatically accelerated rates in the presence of organics, presumably due to mineral surface-catalyzed organic radical generation. Mn(II) oxidation by the colloids is further accelerated in presence of both organics and light, implicating reactive oxygen species in aiding abiotic oxidation. Indeed, the enhancement of Mn(II) oxidation is negated when the colloids are reacted with Mn(II) in the presence of superoxide dismutase, an enzyme that scavenges the reactive oxygen species (ROS) superoxide. The reactivity of the colloidal phase is short-lived due to the rapid evolution of the birnessite from hexagonal to pseudo-orthogonal symmetry. The secondary particulate triclinic birnessite phase exhibits a distinct lack of Mn(II) oxidation and subsequent Mn oxide formation. Thus, the evolution of initial reactive hexagonal birnessite to non-reactive triclinic birnessite imposes the need for continuous production of new colloidal hexagonal particles for Mn(II) oxidation to be sustained, illustrating an intimate dependency of enzymatic and mineral-based reactions in Mn(II) oxidation. Further, the coupled enzymatic and mineral-induced pathways are linked such that enzymatic formation of Mn oxide is requisite for the mineral-induced pathway to occur. Here, we show that Mn(II) oxidation involves a complex network of abiotic and biotic processes, including enzymatically produced superoxide, mineral catalysis, organic reactions with mineral surfaces, and likely photo-production of ROS. The complexity of coupled reactions involved in Mn(II) oxidation here highlights the need for further investigations of microbially-mediated Mn oxide formation, including identifying the role of Mn oxide surfaces, organics, reactive oxygen species, and light in Mn(II) oxidation and Mn oxide phase evolution.

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

2011-10-01

78

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

PubMed Central

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

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

2013-01-01

79

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

PubMed

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

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

2014-11-01

80

Identification of poliumoside metabolites in rat feces by high performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry.  

PubMed

Poliumoside is one of the major phenylethanoid glycosides (PhGs) isolated from Callicarpae Caulis et Folium (CCF) which is a traditional Chinese medicine used for hemostasis in clinic. In this study, high performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry (HPLC/Q-TOF-MS) was applied to investigate the metabolites of poliumoside in rat feces after oral administration. A total of 66 metabolites were confirmed or tentatively identified. Poliumoside could be partly transformed into its positional isomer isopoliumoside in vivo, and poliumoside was easily hydrolyzed and metabolized into degradation products. The parent compound and its degradation products could further undergo extensive phase I and phase II metabolism. The results indicated that hydrolysis, hydroxylation, acetylation, sulfation, hydration, reduction, dehydrogenation and dimethylation were the major metabolic pathways of poliumoside. The major metabolic soft spots of poliumoside and the fragmentation patterns of the metabolites were also proposed. This study provided valuable information regarding the metabolites of poliumoside in rats. PMID:25215644

Deng, Rui; Xu, Yunhui; Feng, Feng; Liu, Wenyuan

2014-10-15

81

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

82

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

PubMed

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

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

2014-06-01

83

Fluorocarbon-bonded magnetic mesoporous microspheres for the analysis of perfluorinated compounds in human serum by high-performance liquid chromatography coupled to tandem mass spectrometry.  

PubMed

We report herein an extraction method for the analysis of perfluorinated compounds in human serum based on magnetic core-mesoporous shell microspheres with decyl-perfluorinated interior pore-walls (Fe3O4@mSiO2-F17). Thanks to the unique properties of the Fe3O4@mSiO2-F17 microspheres, macromolecules like proteins could be easily excluded from the mesoporous channels due to size exclusion effect, and perfluorinated compounds (PFCs) in protein-rich biosamples such as serum could thus be directly extracted with the fluorocarbon modified on the channel wall without any other pretreatment procedure. The PFCs adsorbed Fe3O4@mSiO2-F17 microspheres could then be simply and rapidly isolated by using a magnet, followed by being identified and quantified by LC-MS/MS (high-performance liquid chromatography coupled to tandem mass spectrometry). Five perfluorinatedcarboxylic acids (C6, C8-C11) and perfluorooctane sulfonate (PFOS) were selected as model analytes. In order to achieve the best extraction efficiency, some important factors including the amount of Fe3O4@mSiO2-F17 microspheres added, adsorption time, type of elution solvent, eluting solvent volume and elution time were investigated. The ranges of the LOD were 0.02-0.05 ng mL(-1) for the six PFCs. The recovery of the optimized method varies from 83.13% to 92.42% for human serum samples. PMID:25172813

Liu, Xiaodan; Yu, Yingjia; Li, Yan; Zhang, Haiying; Ling, Jin; Sun, Xueni; Feng, Jianan; Duan, Gengli

2014-09-24

84

Qualitative and quantitative determination of nine main active constituents in Pulsatilla cernua by high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry.  

PubMed

A novel qualitative and quantitative method using high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS) was developed for simultaneous determination of the nine major active constituents in Pulsatilla cernua (Thunb.) Bercht. et Opiz., namely anemoside A3 (1), anemoside B4 (2), 23-hydroxybetulinic acid (3), cirenshenoside S (4), pulsatilloside B (5), pulsatilloside C (6), oleanolic acid (7), ajugasterone C (8) and ?-ecdysterone (9), respectively. A Sapphire C18 column (250 mm × 4.6 mm, 5 ?m) and gradient elution were used during the analysis. The identification and quantification of the analytes were achieved on a hybrid quadrupole linear ion trap mass spectrometer. Multiple-reaction monitoring (MRM) scanning was employed for quantification with switching electrospray ion source polarity between positive and negative modes in a single run. All calibration curves showed good linearity (r(2) > 0.9948) within the test ranges. The intra and interday variations for nine analytes were less than 3.95 and 3.78%, respectively. The developed method was successfully applied to determine the investigated compounds in 15 batches of natural and cultured samples of P. cernua. The results indicated that the method was simple, rapid, specific and reliable, which is helpful to comprehensive evaluation of quality of P. cernua. PMID:21268254

Xu, Huijun; Shi, Xiaowei; Ji, Xiang; Du, Yingfeng; Zhu, Hong; Zhang, Lantong

2011-02-01

85

Rapid determination of sixteen sulfonylurea herbicides in surface water by solid phase extraction cleanup and ultra-high-pressure liquid chromatography coupled with tandem mass spectrometry.  

PubMed

A sensitive and very fast analytical method has been developed for the simultaneous quantification of sixteen sulfonylurea herbicides in surface water. An ultra-high-pressure liquid chromatography coupled with tandem mass spectrometry method with solid phase extraction for sample cleanup has been developed for screening sixteen sulfonylurea herbicides (oxasulfuron, thifensulfuron-methyl, cinosulfuron, metsulfuron methyl, sulfometuron methyl, triasulfuron, rimsulfuron, ethametsulfuron methyl, sulfosulfuron, tribenuron methyl, bensulfuron methyl, iodosulfuron methyl, pyrazosulfuron ethyl, prosulfuron, chlorimuron ethyl, ethoxysulfuron) in water samples simultaneously within 12 min. Water samples were acidified, and the target herbicides were extracted by passing through ProElut C18 extraction cartridges. After drying by nitrogen flow, the cartridges were eluted with elution solvents, and the eluate was then evaporated to dryness, redissolved and analyzed. The mobile phase composed of 0.02% formic acid and acetonitrile using gradient elution. A triple quadrupole mass spectrometer equipped with an electrospray ionization source operated in the positive ion with selective reaction monitoring mode. Each of the analytes in all the samples was monitored using protonated molecule and its two characteristic fragment ions for confirmation. The limits of detection for all analytes were below 1.0 ng/mL, except for sulfosulfuron and prosulfuron, and limits of quantitation were between 1 and 8 ng/mL for this method. Three water types were used for the validation of the method. PMID:21983197

Yan, Cuimin; Zhang, Beibei; Liu, Wenyuan; Feng, Feng; Zhao, Yonggang; Du, Hui

2011-11-15

86

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

PubMed

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

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

2014-11-01

87

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

88

Characterization of eight terpenoids from tissue cultures of the Chinese herbal plant, Tripterygium wilfordii, by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry.  

PubMed

In this study, a reliable method for analysis and identification of eight terpenoids in tissue cultures of Tripterygium wilfordii has been established using high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (HPLC-ESI-MS). Our study indicated that sterile seedlings, callus cultures and cell-suspension cultures can rapidly increase the amount of biological materials. HPLC-ESI-MS was used to identify terpenoids from the extracts of these tissue cultures. Triptolide, triptophenolide, celastrol and wilforlide A were unambiguously determined by comparing the retention times, UV spectral data, and mass fragmentation behaviors with those of the reference compounds. Another four compounds were tentatively identified as triptonoterpenol, triptonoterpene, 22?-hydroxy-3-oxoolean-12-en-29-oic acid and wilforlide B, based on their UV and mass spectrometry spectra. The quantitative analysis showed that all three materials contain triptolide, triptophenolide, celastrol, wilforlide A, and the contents of the four compounds in the cell-suspension cultures were 53.1, 240, 129 and 964?µg/g, respectively, which were at least 2.0-fold higher than these in the sterile seedlings and callus cultures. Considering the known pharmacological activity of triptolide and celastrol, we recommend the cell-suspension cultures as biological materials for future studies, such as clinical and toxicological studies. The developed method was validated by the evaluation of its precision, linearity, detection limits and recovery, and it was successfully used to identify and quantify the terpenoids in the tissue cultures. PMID:25237706

Su, Ping; Cheng, Qiqing; Wang, Xiujuan; Cheng, Xiaoqing; Zhang, Meng; Tong, Yuru; Li, Fei; Gao, Wei; Huang, Luqi

2014-09-01

89

Copper(I)-Catalyzed Oxidative Coupling between 2-Aminobenzothiazole and Terminal Alkyne: Formation of Benzothiazine.  

PubMed

An unprecedented formation of benzothiazine during copper(I)-catalyzed oxidative coupling of 2-aminobenzothiazole and terminal alkyne in air has been observed. This unique transformation possibly occurs through the ring opening of 2-aminobenzothiazole and subsequent oxidative coupling with alkyne followed by intramolecular cyclization. A variety of substituted benzo[b][1,4]thiazine-4-carbonitriles are obtained by this protocol. PMID:25325187

Mitra, Shubhanjan; Chakraborty, Amrita; Mishra, Subhajit; Majee, Adinath; Hajra, Alakananda

2014-11-01

90

An economical and environmentally friendly oxidative biaryl coupling promoted by activated MnO2.  

PubMed

An activated manganese dioxide (MnO2)-BF3·OEt2 oxidation system was developed to efficiently mediate the intramolecular as well as intermolecular biaryl coupling. The oxidative coupling proceeds smoothly at ambient temperature to deliver the corresponding five- to eight-membered tricyclic products in good to excellent yields. The employment of the combination of MnO2 and BF3·OEt2 is attractive on the basis of economical and environmental issues. PMID:25144866

Yang, Jingjing; Sun, Shutao; Zeng, Ziyu; Zheng, Hongbo; Li, Wei; Lou, Hongxiang; Liu, Lei

2014-10-21

91

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

92

Determination of phosphoserine/threonine by nano ultra-performance liquid chromatography-tandem mass spectrometry coupled with microscale labeling.  

PubMed

Protein phosphorylation is an important regulatory post-translational modification in many biochemical processes. The phosphopeptide analysis strategies developed in this study were all at microscale. After using a standard microwave oven to assist protein digestion, phosphoserine and phosphothreonine were tagged with chemical analogues, such as 2-mercaptoethanol and 3-mercapto-1-propanol, to enable simultaneously relative quantitation and identification. This method enabled the use of thio alcohols for direct labeling of phosphorylated sites (not labeled at the mercapto, amino, hydroxyl, or carboxyl groups) of phosphopeptides. Various digestion parameters (e.g., microwave power, reaction time, NH4HCO3 concentration) and derivatization efficiency parameters (e.g., reaction time, labeling tag concentration) were studied and optimized. In both control and experimental samples, microwave-assisted digestion coupled with relative quantitation using analogue tags enabled calculation of phosphopeptide ratios in the same sequence. A non-labeling method was also established for quantifying phosphopeptides in human plasma by using the abundant protein albumin as an internal control for normalizing relative quantities of phosphopeptides. Nano ultra-performance liquid chromatography (nanoUPLC) was combined with LTQ Orbitrap to enable simultaneous protein relative quantitation and identification. These strategies proved to be effective for quantifying phosphopeptides in biological samples. PMID:23994561

Chen, Rong-Chun; Chuang, Lea-Yea; Tseng, Wei-Lung; Tyan, Yu-Chang; Lu, Chi-Yu

2013-12-15

93

Precipitation of enzyme-catalyzed phenol oxidative coupling products: Background ion and pH effects  

Microsoft Academic Search

The effects of solution pH and background ion types and concentrations on the precipitation of polymeric products generated in the catalytically facilitated oxidative coupling of phenol were investigated systematically. The coupling reactions mediated by horseradish peroxidase were carried out under a specific predetermined experimental condition. Acids, bases, and\\/or selected salts of ions having different valences were then added to the

Qingguo Huang; Jixin Tang; Walter J. Weber

2005-01-01

94

Oxidative cross-coupling of allenyl ketones and organoboronic acids: expeditious synthesis of highly substituted furans.  

PubMed

Allenyl ketones are employed as coupling partners in palladium-catalyzed oxidative cross-coupling reactions with organoboronic acids. This reaction constitutes an efficient methodology for the synthesis of highly substituted furan derivatives. Palladium-carbene migratory insertion is proposed as the key step in this transformation. PMID:24615951

Xia, Ying; Xia, Yamu; Ge, Rui; Liu, Zhen; Xiao, Qing; Zhang, Yan; Wang, Jianbo

2014-04-01

95

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

Microsoft Academic Search

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

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

2008-01-01

96

Mechanistic study on the oxidative coupling of amines to imines on K-10 montmorillonite  

Microsoft Academic Search

A mechanistic study of the K-10 montmorillonite-catalyzed microwave-assisted oxidative self-coupling of benzylamine and cross coupling of benzylamines with anilines and aliphatic amines is described. The coupling of benzylamines readily produced benzylidene benzylamines, while reactions of benzylamine with aliphatic amines and anilines resulted in benzylidene alkylamines and benzylidene anilines. The mechanism of the reaction has been investigated by varying reaction conditions,

Valentina Atanassova; Kristen Ganno; Aditya Kulkarni; Shainaz M. Landge; Steven Curtis; Michelle Foster; Béla Török

2011-01-01

97

Microwave-assisted oxidative coupling of amines to imines on solid acid catalysts  

Microsoft Academic Search

A K-10 montmorillonite catalyzed microwave-assisted oxidative coupling of amines is described. Substituted benzylamines readily undergo self-coupling reactions to produce benzylidene–benzylamines, while aliphatic amines and anilines cannot form self-coupled products. A mixture of a benzylamine and an aniline or aliphatic amine, respectively, effectively, and selectively produces mixed imines, such as benzylidene–anilines and benzylidene–alkylamines.

Shainaz M. Landge; Valentina Atanassova; Muralidhara Thimmaiah; Béla Török

2007-01-01

98

Coupled oxidation of aromatic hydrocarbons by horseradish peroxidase and hydrogen peroxide  

Microsoft Academic Search

The oxidation capability of horseradish peroxidase (HRP) and hydrogen peroxide (H2O2) coupled oxidation of aromatic hydrocarbons (o-xylene-d10 and naphthalene-d8) was investigated. Batch experiments were conducted using horseradish peroxidase prepared in potassium phosphate buffer in the presence of H2O2. The oxidation of aromatic hydrocarbon was tested as a function of HRP at a fixed concentration of H2O2, and as a function

Jiasong Fang; Michael J Barcelona

2003-01-01

99

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

100

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

PubMed

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

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

2012-06-15

101

Qualitative and quantitative analysis on chemical constituents from Curculigo orchioides using ultra high performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry.  

PubMed

A rapid ultra-high performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UHPLC-ESI-Q-TOF/MS) method was developed for qualitative and quantitative determination of constituents in the rhizome of Curculigo orchioides. Qualitative analysis was performed on a Waters ACQUITY UHPLC @ HSS T3 column (1.8?m 100×2.1mm) using gradient elution with mobile phase of 0.1% formic acid and acetonitrile. Quantitative analysis was performed on an Agilent ZORBAX Eclipse plus C18 column (1.7?m 100×2.1mm) using gradient elution with mobile phase of 0.1% acetic acid and acetonitrile for at least 20min. Quadrupole TOF/MS in either full scan mode or extracted ion mode was used for qualitative and quantitative analysis of the constituents. According to the mass spectrometric fragmentation mechanism and UHPLC-ESI-Q-TOF-MS data, chemical structures of 45 constituents in the rhizome of Curculigo orchioides, including 19 phenols and phenolic glycosides, 16 lignans and lignan glycosides, 8 triterpenoid saponins, one flavone and one sesquiterpene, were identified tentatively on-line without the time-consuming process of isolation. In addition, 8 phenolic glycosides including 5-hydroxymethylfurfural (HMF), 2-hydroxy-5-(2-hydroxyethyl) phenyl-?-d-glucopyranoside (HPG), anacardoside (ACD), orcinol glucoside (OGD), orcinol-1-O-?-d-apiofuranosyl-(1?6)-?-d-glucopyranoside (OAG), 2,6-dimethoxybenzoic acid (DBA), curculigoside (CUR) and curculigine A (CCL) were quantitated in 11 collected samples and 10 commercial samples from different providers. The results show that UHPLC-ESI-Q-TOF-MS is a viable method for analysis and quality evaluation of the constituents from the rhizome of Curculigo orchioides. PMID:25305598

He, Yongjing; Dong, Xin; Jia, Xiaoxuan; Li, Mei; Yuan, Tingting; Xu, Hongtao; Qin, Luping; Han, Ting; Zhang, Qiaoyan

2015-01-01

102

Screening of drugs in equine plasma using automated on-line solid-phase extraction coupled with liquid chromatography-tandem mass spectrometry.  

PubMed

A rapid liquid chromatography-tandem mass spectrometry (LC-MS-MS) method was developed for the simultaneous screening of 19 drugs of different classes in equine plasma using automated on-line solid-phase extraction (SPE) coupled with a triple quadrupole mass spectrometer. Plasma samples were first protein precipitated using acetonitrile. After centrifugation, the supernatant was directly injected into the on-line SPE system and analysed by a triple quadrupole LC-MS-MS in positive electrospray ionisation (+ESI) mode with selected reaction monitoring (SRM) scan function. On-line extraction and chromatographic separation of the targeted drugs were performed using respectively a polymeric extraction column (2 cm L x 2.1mm ID, 25 microm particle size) and a reversed-phase C18 LC column (3 cm L x 2.1mm ID, 3 microm particle size) with gradient elution to provide fast analysis time. The overall instrument turnaround time was 9.5 min, inclusive of post-run and equilibration time. Plasma samples fortified with 19 targeted drugs including narcotic analgesics, local anaesthetics, antipsychotics, bronchodilators, mucolytics, corticosteroids, sedative and tranquillisers at sub-parts per billion (ppb) to low parts per trillion (ppt) levels could be consistently detected. No significant matrix interference was observed at the expected retention times of the targeted ion transitions. Over 70% of the drugs studied gave detection limits at or below 100 pg/mL, with some detection limits reaching down to 19 pg/mL. The method had been validated for extraction recovery, precision and sensitivity, and a blockage study had also been carried out. This method is used regularly in the authors' laboratory to screen for the presence of targeted drugs in pre-race plasma samples from racehorses. PMID:20122690

Kwok, W H; Leung, David K K; Leung, Gary N W; Wan, Terence S M; Wong, Colton H F; Wong, Jenny K Y

2010-05-01

103

Analysis of heterocyclic amines in hair by on-line in-tube solid-phase microextraction coupled with liquid chromatography-tandem mass spectrometry.  

PubMed

Mutagenic and carcinogenic heterocyclic amines (HCAs) are formed during heating of various proteinaceous foods, but human exposure to HCAs has not yet been elucidated in detail. To assess long-term exposure to HCAs, we developed a simple and sensitive method for measuring HCAs in hair by automated on-line in-tube solid-phase microextraction (SPME) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Using a Zorbax Eclipse XDB-C8 column, 16 HCAs were analyzed within 15 min. The optimum in-tube SPME conditions were 20 draw/eject cycles of 40 ?L sample at a flow rate of 200 ?L min(-1) using a Supel-Q PLOT capillary column as an extraction device. The extracted HCAs were easily desorbed from the column by passage of the mobile phase, with no carryover observed. This in-tube SPME LC-MS/MS method showed good linearity for HCAs in the range of 10-2000 pg mL(-1), with correlation coefficients above 0.9989 (n=18), using stable isotope-labeled HCA internal standards. The detection limits (S/N=3) of 14 HCAs except for MeA?C and Glu-P-1 were 0.10-0.79 pg mL(-1). This method was successfully utilized to analyze 14 HCAs in hair samples without any interference peaks, with quantitative limits (S/N=10) of about 0.17-1.32 pg mg(-1) hair. Using this method, we evaluated the exposure to HCAs in cigarette smoke and the suitability of using hair HCAs as exposure biomarkers. PMID:23790292

Kataoka, Hiroyuki; Inoue, Tsutomu; Saito, Keita; Kato, Hisato; Masuda, Kazufumi

2013-07-01

104

Achieving greater selectivity for the analysis of o-, m-, p-methylhippuric acids in workers' urine by ultra performance liquid chromatography coupled with tandem mass spectrometry.  

PubMed

A selective method analyzing separately o-, m- and p-methylhippuric acid isomers in workers' urine samples has been developed using ultra performance liquid chromatography coupled with tandem mass spectrometry. Chromatographic separation has been optimized to resolve the three isomers at baseline. Combined with this optimal separation, the mass spectrometer allowed rapid switching from MRM scan to full scan and product ion scan within the chromatographic peak. This feature allowed the retention of analyte chemical structure information for the three methylhippuric acid isomers in parallel with the simultaneous acquisition of quantitative data. Such an approach is unequaled for the reliability of the data generated and it can be applied to each isomer separately. The method was adjusted to a dynamic range between 0.2mM and 8.12mM for o-methylhippuric acid and p-methylhippuric acid, and between 0.41mM and 16.23mM for m-methylhippuric acid in order to cover the biological exposure index. A negligible matrix effect was observed with the conditions used. Also, intra-day and inter-day precisions were both <6% for all the concentration levels tested and the accuracy was evaluated at 97±4%. The inclusion of simultaneous full scan acquisitions did not prevent the robustness of the quantitative data. The method applied to the determination of inter-laboratory proficient test samples led to results in the tolerated range. Moreover, urine samples from workers were robustly quantified and the MHA levels were all below the biological exposure index reference value. PMID:23770736

Gagné, Sébastien

2013-07-15

105

Determination of caffeine, myosmine, and nicotine in chocolate by headspace solid-phase microextraction coupled with gas chromatography-tandem mass spectrometry.  

PubMed

The occurrence of the bioactive components caffeine (xanthine alkaloid), myosmine and nicotine (pyridine alkaloids) in different edibles and plants is well known, but the content of myosmine and nicotine is still ambiguous in milk/dark chocolate. Therefore, a sensitive method for determination of these components was established, a simple separation of the dissolved analytes from the matrix, followed by headspace solid-phase microextraction coupled with gas chromatography-tandem mass spectrometry (HS-SPME-GC-MS/MS). This is the first approach for simultaneous determination of caffeine, myosmine, and nicotine with a convenient SPME technique. Calibration curves were linear for the xanthine alkaloid (250 to 3000 mg/kg) and the pyridine alkaloids (0.000125 to 0.003000 mg/kg). Residuals of the calibration curves were lower than 15%, hence the limits of detection were set as the lowest points of the calibration curves. The limits of detection calculated from linearity data were for caffeine 216 mg/kg, for myosmine 0.000110 mg/kg, and for nicotine 0.000120 mg/kg. Thirty samples of 5 chocolate brands with varying cocoa contents (30% to 99%) were analyzed in triplicate. Caffeine and nicotine were detected in all samples of chocolate, whereas myosmine was not present in any sample. The caffeine content ranged from 420 to 2780 mg/kg (relative standard deviation 0.1 to 11.5%) and nicotine from 0.000230 to 0.001590 mg/kg (RSD 2.0 to 22.1%). PMID:24446916

Müller, Christoph; Vetter, Florian; Richter, Elmar; Bracher, Franz

2014-02-01

106

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

2014-08-25

107

Proton translocation coupled to quinol oxidation in ox heart mitochondria  

PubMed Central

The suitability of ubiquinol1 and duroquinol as pulse reductants for initiating respirationdriven proton translocation by aerobic ox heart mitochondria was investigated. At 25°C the Vmax. for oxidation was close to 280nmol of quinol oxidized/min per mg of protein, and the Km values were 8?m for ubiquinol1 and 28?m for duroquinol. Pulses of ubiquinol1 and duroquinol were rapidly and completely oxidized by aerobic mitochondria with a simultaneous acidification of the suspending medium as detected with a glass electrode. The ?H+/2e? ratios (Mitchell, 1966) calculated from the observed extent of acidification and the amount of quinol added were 3.62 for ubiquinol1 and 2.98 for duroquinol. These values are underestimates of the true value owing to proton back-flow across the membrane. An analogue computer model was used to correct the observed extent of respirationdriven acidification for proton back-flow. The corrected ?H+/2e? values were 4.01 for ubiquinol and 3.86 for duroquinol oxidation. Attempts to measure the rate of proton translocation with a pH-measuring system with a response time of 0.4s were not entirely satisfactory, owing to the relative slowness of the electrode response. Nevertheless the maximal rate of proton generation during ubiquinol1 oxidation was about 1200ng-ions of H+/min per mg of mitochondrial protein. It is concluded, contrarily to Chance & Mela (1967), that mitochondria exhibit a proton-translocating ubiquinol oxidase activity with a ?H+/2e? ratio of 4.0. PMID:4780696

Lawford, Hugh G.; Garland, Peter B.

1973-01-01

108

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

109

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

110

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

111

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

112

Degradation of organic dyes via bismuth silver oxide initiated direct oxidation coupled with sodium bismuthate based visible light photocatalysis.  

PubMed

Organic dye degradation was achieved via direct oxidation by bismuth silver oxide coupled with visible light photocatalysis by sodium bismuthate. Crystal violet dye decomposition by each reagent proceeded via two distinct pathways, each involving different active oxygen species. A comparison of each treatment method alone and in combination demonstrated that using the combined methods in sequence achieved a higher degree of degradation, and especially mineralization, than that obtained using either method alone. In the combined process direct oxidation acts as a pretreatment to rapidly bleach the dye solution which substantially facilitates subsequent visible light photocatalytic processes. The integrated sequential direct oxidation and visible light photocatalysis are complementary manifesting a > 100% increase in TOC removal, compared to either isolated method. The combined process is proposed as a novel and effective technology based on one primary material, sodium bismuthate, for treating wastewaters contaminated by high concentrations of organic dyes. PMID:22616904

Yu, Kai; Yang, Shaogui; Liu, Cun; Chen, Hongzhe; Li, Hui; Sun, Cheng; Boyd, Stephen A

2012-07-01

113

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

PubMed Central

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

Guo, Fenghai; Clift, Michael D.

2013-01-01

114

Rapid quantification of HIV protease inhibitors in human plasma by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry.  

PubMed

HIV protease inhibitors are important antiretroviral drugs which have substantially reduced the morbidity and mortality associated with HIV-1 infection. Recent data have shown relationships between plasma concentrations of the protease inhibitors and clinical response, which makes therapeutic drug monitoring valuable. We have developed and validated an assay, using liquid chromatography coupled with electrospray tandem mass spectrometry (LC/MS/MS), for the routine quantification of the six licensed protease inhibitors (amprenavir, indinavir, lopinavir, nelfinavir, ritonavir and saquinavir) and the pharmacologically active nelfinavir metabolite M8 in plasma. The sample pretreatment consisted of protein precipitation with a mixture of methanol and acetronitrile using only 100 microl of plasma. Chromatographic separation was performed on an Inertsil ODS3 column (50 x 2.0 mm i.d., particle size 5 microm), with a quick stepwise gradient using an acetate buffer (pH 5) and methanol, at a flow rate of 0.5 ml min(-1). The analytical run time was 5.5 min. The use of a 96-well plate autosampler allowed batch sizes up to 150 patient samples. The triple-quadrupole mass spectrometer was operated in the positive ion mode and multiple reaction monitoring was used for drug quantification. The method was validated over the concentration ranges 0.01-10 microg ml(-1) for indinavir and saquinavir, 0.1-10 microg ml(-1) for amprenavir, 0.05-10 microg ml(-1) for nelfinavir and ritonavir, 0.1-20 microg ml(-1) for lopinavir and 0.01-5 microg ml(-1) for M8. Saquinavir-d(5) and indinavir-d(6) were used as internal standards. The coefficients of variation were always <10% for both intra-day and inter-day precisions for each compound. Mean accuracies were also between the designated limits (+/-15%). The validated concentration ranges proved to be adequate in daily practice. This robust and fast LC/MS/MS assay is now successfully applied for routine therapeutic drug monitoring and pharmacokinetic studies in our hospital. PMID:12577282

Crommentuyn, K M L; Rosing, H; Nan-Offeringa, L G A H; Hillebrand, M J X; Huitema, A D R; Beijnen, J H

2003-02-01

115

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

116

Coupling characteristics of thin-film metal-oxide-metal diodes at 10.6 microns  

NASA Technical Reports Server (NTRS)

Direct detection experiments have demonstrated the coherent coupling of 10.6 micrometer radiation into photolithographically fabricated metal-oxide-metal tunnel junctions. A CO2 laser beam mechanically chopped at 1 KHz was focused at a variable angle of incidence with a power density of about 10 W/sq cm at the diodes. Diodes in which the junction resistance was much greater than the lead resistance displayed angular characteristics dominated by coherent antenna coupling.

Wang, S. Y.; Gustafson, T. K.; Izawa, T.

1975-01-01

117

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

Microsoft Academic Search

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

G. E. Keller; M. M. Bhasin

1982-01-01

118

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

119

Reduced Coupling of Oxidative Phosphorylation In Vivo Precedes Electron Transport Chain Defects Due to Mild Oxidative Stress in Mice  

PubMed Central

Oxidative stress and mitochondrial function are at the core of many degenerative conditions. However, the interaction between oxidative stress and in vivo mitochondrial function is unclear. We used both pharmacological (2 week paraquat (PQ) treatment of wild type mice) and transgenic (mice lacking Cu, Zn-superoxide dismutase (SOD1?/?)) models to test the effect of oxidative stress on in vivo mitochondrial function in skeletal muscle. Magnetic resonance and optical spectroscopy were used to measure mitochondrial ATP and oxygen fluxes and cell energetic state. In both models of oxidative stress, coupling of oxidative phosphorylation was significantly lower (lower P/O) at rest in vivo in skeletal muscle and was dose-dependent in the PQ model. Despite this reduction in efficiency, in vivo mitochondrial phosphorylation capacity (ATPmax) was maintained in both models, and ex vivo mitochondrial respiration in permeabilized muscle fibers was unchanged following PQ treatment. In association with the reduced P/O, PQ treatment led to a dose-dependent reduction in PCr/ATP ratio and increased phosphorylation of AMPK. These results indicate that oxidative stress uncouples oxidative phosphorylation in vivo and results in energetic stress in the absence of defects in the mitochondrial electron transport chain. PMID:22132085

Siegel, Michael P.; Kruse, Shane E.; Knowels, Gary; Salmon, Adam; Beyer, Richard; Xie, Hui; Van Remmen, Holly; Smith, Steven R.; Marcinek, David J.

2011-01-01

120

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

121

A coupled map lattice model for spontaneous pore formation in anodic oxidation  

E-print Network

We construct a coupled map lattice model for the 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

2010-03-05

122

Domain coupling and resistance in perpendicularly magnetized metal-oxide bilayers  

Microsoft Academic Search

Two of the interesting problems in magnetic heterostructures are the exchange coupling in multilayers and the stabilization of domains with magnetization perpendicular to the film plane. In this work, these two phenomena are combined and the stabilization of a perpendicular domain structure in an ultra thin (<10nm) metallic layer, grown on a magnetic oxide (Yttrium Iron Garnet, YIG) layer with

Yoonsoo Chun

2007-01-01

123

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

PubMed

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

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

2014-08-01

124

Palladium-catalyzed synthesis of 2-aminobenzoxazinones by aerobic oxidative coupling of anthranilic acids and isocyanides.  

PubMed

Isocyanides have emerged as valuable C1 building blocks in palladium catalysis. Their potential has, however, mainly been exploited for the synthesis of amidines and amidine-containing heterocycles. To illustrate the broader applicability of isocyanides, we have recently developed a novel oxidative coupling of diamines and isocyanides furnishing valuable guanidine-containing heterocycles. We here report the extension of this protocol to the coupling of anthranilic acids and isocyanides leading to medicinally relevant 2-aminobenzoxazinones. This is a particularly challenging substrate class for this reaction due to the possibility of undesired decarboxylative pathways and the susceptibility of the products to nucleophilic attack. Therefore, this work underlines the generality and broad potential of the oxidative coupling of bisnucleophiles and isocyanides, facilitating the further implementation of this chemistry in library design. PMID:24063265

Vlaar, Tjøstil; Orru, Romano V A; Maes, Bert U W; Ruijter, Eelco

2013-10-18

125

I2-catalyzed oxidative cross-coupling of methyl ketones and benzamidines hydrochloride: a facile access to ?-ketoimides.  

PubMed

An iodine-catalyzed oxidative cross-coupling of C-H/N-H has been demonstrated. This simple and efficient approach constructed ?-ketoimides in good to excellent yields from methyl ketones and benzamidines hydrochloride under metal-free and peroxide-free conditions. This synthetic strategy was achieved via an in situ iodination-based oxidative coupling pathway. PMID:24831723

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

2014-06-01

126

"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

127

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

128

Development of an assay method for the detection and quantification of protease and non-nucleoside reverse transcriptase inhibitors in plasma and in peripherical blood mononuclear cells by liquid chromatography coupled with ultraviolet or tandem mass spectrometry detection.  

PubMed

We present a simple chromatographic method to detect and quantify protease inhibitors (PI), metabolites and non-nucleoside reverse transcriptase inhibitors (NNRTIs) in human plasma of HIV-1 infected patients and in peripheral blood mononuclear cells (PBMCs) using either liquid chromatography coupled with ultraviolet (LC-UV) or liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). A solid-liquid extraction was carried out on 500 microl of plasma as pre-treatment. Calibration curve ranges were from 50 (100) to 5000 ng/ml (indinavir). PBMC pellets from 7 ml of blood were lysed with methanol/tris with a calibration curve ranging from 0.25 to 250 ng/pellet. Simple modifications in the mobile phase composition (slight increase of ammonium acetate concentration and addition of methanol for LC-UV) easily linked the two analytical systems. PMID:15797520

Pèlerin, Hélène; Compain, Séverine; Duval, Xavier; Gimenez, François; Bénech, Henri; Mabondzo, Aloïse

2005-05-01

129

The oxidative coupling of methane by lanthanum oxide catalysts: The influence of phase morphology on catalytic properties  

SciTech Connect

The major goal of this research is to make progress towards isolating and identifying the most active and selective phase(s) in the catalytic oxidative coupling of methane to C{sub 2} hydrocarbons by one of the most active and selective REO'' catalysts, La{sub 2}O{sub 3}.'' As discussed in the foregoing literature review, the catalyst preparation methods and the reaction conditions employed can result in the catalyst consisting of several coexisting rare earth compounds. Furthermore, it is conceivable, if not likely, that either the pure REO phase or one of these coexisting compounds is much more catalytically active towards the desired reaction than all others. It is therefore proposed that by employing strict catalyst preparation methods and multi-technique characterization, pure oxide, hydroxide, carbonate, hydroxycarbonate and oxycarbonate phases of lanthanum may be prepared and subsequently tested for catalytic performance such that the extent to which each of these phases are involved in the catalytic oxidative coupling of methane may be determined. 157 refs., 60 figs., 6 tabs.

Taylor, R.P.

1990-02-01

130

Bimolecular Coupling Reactions through Oxidatively Generated Aromatic Cations: Scope and Stereocontrol  

PubMed Central

Chromenes, isochromenes, and benzoxathioles react with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone to form stable aromatic cations that react with a range of nucleophiles. These oxidative fragment coupling reactions provide rapid access to structurally diverse heterocycles. Conducting the reactions in the presence of a chiral Brønsted acid results in the formation of an asymmetric ion pair that can provide enantiomerically enriched products in a rare example of a stereoselective process resulting from the generation of a chiral electrophile through oxidative carbon–hydrogen bond cleavage. PMID:23913987

Cui, Yubo; Villafane, Louis A.; Clausen, Dane J.

2013-01-01

131

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

132

Towards a zero-waste oxidative coupling of nonactivated aromatics by supported gold nanoparticles.  

PubMed

We show that gold nanoparticles are able to perform the direct oxidative coupling of nonactivated aromatics with O2 as the only co-reagent. In this reaction, the aromatic acts both as reactant and solvent. Biphenyl, for example, can be obtained from benzene with high selectivity and a turnover number (TON) of 230 per pass. Similarly, several substituted biaryls can be prepared. Pd performs only one TON and even when a second catalytic functionality is introduced, together with strong acidic conditions, TON is always lower than 100. Other catalysts require iodine for performing the reaction, leading to 2 kg of waste for 1 kg of biphenyl formed, whereas no waste is created by the oxidative coupling with gold nanoparticles. PMID:24889545

Serna, Pedro; Corma, Avelino

2014-08-01

133

Role of steam on the reaction performance of methane oxidative coupling over basic catalysts  

Microsoft Academic Search

The effect of steam on the oxidative coupling of methane over some basic catalysts was investigated. It has been found that the presence of steam in the reactant stream enhanced the methane conversion, C2 selectivity as well as the C2 yield. Another effect of the steam was the enhancement of the ethylene to ethane ratio. When the H2OCH4 ratio (mol)

Xu Zhusheng; Zhang Tao; Zang Lianfa; Wang Tao; Wu Jinrong; Chen Laiyuan; Lin Liwu

1996-01-01

134

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

PubMed Central

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

Xu, Hai-Chao; Moeller, Kevin D.

2014-01-01

135

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

PubMed

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

Xu, Hai-Chao; Moeller, Kevin D

2010-04-16

136

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

Microsoft Academic Search

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 mum2 and the pixel size is 7.5×

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

2011-01-01

137

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

138

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

PubMed

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

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

2013-10-14

139

Measurements of kinetic isotope effects and hydrogen\\/deuterium distributions over methane oxidative coupling catalysts  

Microsoft Academic Search

The kinetic isotope effect for CHâ compared to that for CDâ has been measured for the oxidative coupling reaction of methane over Li\\/MgO, SrCOâ, and SmâOâ catalysts in a flow reactor. Each catalyst gave results consistent with C-H bond breaking being the slow step. For temperatures between 680-780 C over Li\\/MgO, k{sub H}\\/k{sub D} decreased slightly with temperature. The isotope

P. F. Nelson; C. A. Lukey; N. W. Cant

1989-01-01

140

Tandem one-pot palladium-catalyzed coupling of hydrazones, haloindoles, and amines: synthesis of amino-N-vinylindoles and their effect on human colon carcinoma cells.  

PubMed

The synthesis of amino-substituted N-vinylazoles was achieved by a new palladium-assisted tandem catalytic reaction involving N-tosylhydrazones, halo-substituted azoles, and amines. Accordingly, two Csp(2)-N bonds were formed through two mechanistically distinct reactions using a single Pd(II)/Pd(0) catalyst system in a one-pot fashion. This work paves the way for the design of biological relevant compounds in an amino-substituted N-vinylindole series. Among several polyoxygenated derivatives evaluated, compounds 5e and 5u were found to exhibit good antiproliferative activity. PMID:25029590

Roche, Maxime; Bignon, Jérôme; Brion, Jean-Daniel; Hamze, Abdallah; Alami, Mouad

2014-08-15

141

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

PubMed

A rapid, simple and validated method based on liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) has been developed for the determination of granisetron in human plasma. Plasma samples were pre-purified by protein precipitation procedure. The chromatographic separation was achieved with Synergi Polar-RP (75?×?2 mm, 4 µm) column using a mixture of 5 mm pH4.0 ammonium formate and methanol (300:316, v/v) under isocratic conditions at a flow rate of 0.3 mL/min. The detection was performed on a triple quadrupole tandem mass spectrometer in multiple reaction monitoring mode using positive electrospray ionization. The analysis time was about 2.5 min. The method was fully validated over the concentration range 0.1-10 ng/mL. The lower limit of quantification was 0.1 ng/mL. Inter- and intra-batch precision was <6.1% and the accuracy was within 95.6-100.0%. The mean extraction recovery was 96.3%. Selectivity, matrix effect and stability were also validated. The method was applied to the comparative pharmacokinetic study of granisetron in Chinese healthy subjects. Copyright © 2014 John Wiley & Sons, Ltd. PMID:24811001

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

2014-12-01

142

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

SciTech Connect

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

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

1995-02-01

143

Determination of L-hydroxyproline using hydrophilic interaction chromatography coupled to tandem mass spectrometry with lyophilized concentrated extraction in milk and dairy products.  

PubMed

In this study, a screening and confirmation method for the determination of l-hydroxyproline (Hyp) as a target compound in milk and dairy products using high-performance liquid chromatography with tandem mass spectrometry was developed. The samples were lyophilized after acidic hydrolysis, followed by cleanup with graphitized carbon black to remove pigments. Hyp was separated by a hydrophilic interaction chromatographic column and analyzed by high-performance liquid chromatography with tandem mass spectrometry working with multiple reaction monitoring mode using an electrospray ionization interface in a positive-ion mode. Average recoveries in spiked milk and dairy products ranged from 68.0 to 101.1% with relative standard deviations between 2.0 and 11.7% (n = 7). A reagent-matched standard calibration curve was used for quantification of Hyp, with linear correlation coefficient (R(2)) > 0.99 in the concentration range of 0.1-100 ?g/mL. The LOQs were from 0.25 to 5 mg/kg, which were usually sufficient to verify the Hyp in samples. The confirmation concentration of Hyp ranged from 10 to 50 mg/kg. PMID:24777951

Zhu, Ai-ling; Peng, Tao; Chen, Dong-dong; Wang, Ping; Wang, Guo-min; Wang, Jin-hua; Jiang, Hai-yang; Fan, Chun-lin; Chen, Ying

2014-07-01

144

?-Oxidation and Glyoxylate Cycle Coupled to NADH: Cytochrome c and Ferricyanide Reductases in Glyoxysomes 1  

PubMed Central

Glyoxysomes isolated from castor bean (Ricinus communis L., var Hale) endosperm had NADH:ferricyanide reductase and NADH:cytochrome c reductase activities averaging 720 and 140 nanomole electrons/per minute per milligram glyoxysomal protein, respectively. These redox activities were greater than could be attributed to contamination of the glyoxysomal fractions in which 1.4% of the protein was mitochondrial and 5% endoplasmic reticulum. The NADH:ferricyanide reductase activity in the glyoxysomes was greater than the palmitoyl-coenzyme A (CoA) oxidation activity which generated NADH at a rate of 340 nanomole electrons per minute per milligram glyoxysomal protein. Palmitoyl-CoA oxidation could be coupled to ferricyanide or cytochrome c reduction. Complete oxidation of palmitoyl-CoA, yielding 14 nanomole electrons/per nanomole palmitoyl-CoA, was demonstrated with the acceptors, NAL, cytochrome c, and ferricyanide. Malate was also oxidized by glyoxysomes, if acetyl-CoA, ferricyanide, or cytochrome c was present. Glyoxysomal NADH:ferricyanide reductase activity has the capacity to support the combined rates of NADH generation by ?-oxidation and the glyoxylate cycle. PMID:16665778

Donaldson, Robert P.; Fang, Tung K.

1987-01-01

145

I2-catalyzed oxidative C(sp(3))-H/S-H coupling: utilizing alkanes and mercaptans as the nucleophiles.  

PubMed

By using alkanes and mercaptans as the nucleophiles with di-tert-butyl peroxide (DTBP) as the oxidant, I2-catalyzed oxidative C(sp(3))-H/S-H coupling was achieved. This protocol provides a novel process to construct C(sp(3))-S bonds from commercially available hydrocarbons and mercaptans. PMID:25297879

Yuan, Jiwen; Ma, Xu; Yi, Hong; Liu, Chao; Lei, Aiwen

2014-10-23

146

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

PubMed

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

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

2014-10-27

147

Transformation of trace organic compounds in drinking water by enzymatic oxidative coupling  

SciTech Connect

Enzymatic methods have shown promise for removing aromatic compounds from (high-strength) industrial wastewater. The removal of these compounds was studied at low levels that might be encountered in surface waters which receive some industrial discharge. The results indicate that enzymatic oxidative coupling using horseradish peroxidase and hydrogen perioxide may be useful in eliminating some aromatics that are not well-removed in biological or physical water treatment, but the nature of the byproducts must be determined to assure that the products are not more undesirable than the initial compounds. 21 references, 4 figures, 2 tables.

Maloney, S.W.; Manem, J.; Mallevialle, J.; Fiessinger, F.

1986-03-01

148

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

149

Observation of T-2 Toxin and HT-2 Toxin Glucosides from Fusarium sporotrichioides by Liquid Chromatography Coupled to Tandem Mass Spectrometry (LC-MS/MS)  

PubMed Central

The trichothecenes produced by solid and liquid cultures of Fusarium sporotrichioides were evaluated with high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). Along with the expected T-2 toxin HT-2 toxin and neosolaniol, two additional compounds were detected, which had ions 162 m/z higher than those in the mass spectra of T-2 toxin or HT-2 toxin. Fragmentation behavior of these two compounds was similar to that of T-2 toxin and HT-2 toxin. Based on LC-MS/MS behavior, it is proposed that the two compounds are T-2 toxin 3-O-glucoside and HT-2 toxin 3-O-glucoside. Production of the two glucosides was measured in kernels from wheat and oat inoculated with F. sporotrichiodes, as well as in cultures grown in liquid media and on cracked corn or rice. Production of glucosides in wheat and oats suggest that they may also be present in naturally contaminated cereals. PMID:22295176

Busman, Mark; Poling, Stephen M.; Maragos, Chris M.

2011-01-01

150

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

PubMed

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

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

2014-09-01

151

Development and Validation of Amisulpride in Human Plasma by HPLC Coupled with Tandem Mass Spectrometry and its Application to a Pharmacokinetic Study  

PubMed Central

In this study, authors developed a simple, sensitive and specific liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for quantification of Amisulpride in human plasma using Amisulpride-d5 as an internal standard (IS). Chromatographic separation was performed on Zorbax Bonus-RP C18, 4.6 × 75 mm, 3.5 ?m column with an isocratic mobile phase composed of 0.2% formic acid:methanol (35:65 v/v), at a flow-rate of 0.5 mL/min. Amisulpride, Amisulpride-d5 was detected at m/z 370.1?242.1 and 375.1?242.1. The drug and the IS were extracted by a liquid-liquid extraction method. The method was validated over a linear concentration range of 2.0–2500.0 ng/mL for Amisulpride with a correlation coefficient of (r2) ? 0.9982. This method demonstrated intra- and inter-day precision within 0.9 to 1.7 and 1.5 to 2.8 % and intra- and inter-day accuracy within 98.3 to 101.5 and 96.0 to 101.0 % for Amisulpride. Amisulpride was found to be stable at 3 freeze–thaw cycles, bench top and auto sampler stability studies. The developed method was successfully applied to a pharmacokinetic study. PMID:21886905

Mogili, Ramakotaiah; Kanala, Kanchanamala; Challa, Balasekhara Reddy; Chandu, Babu Rao; Bannoth, Chandrasekhar Kottapalli

2011-01-01

152

Simultaneous determination of fifteen constituents of jitai tablet using ultra high-performance liquid chromatography coupled with triple quadrupole electrospray tandem mass spectrometry.  

PubMed

An ultra-high-performance liquid chromatography-electrospray ionization tandem mass spectrometry (UHPLC-ESI-MS/MS) method was developed for simultaneous determination of fifteen constituents in Jitai tablet (JTT), a complex Traditional Chinese Medicine prescription (TCMP) used in treating opiate addiction. Benefitting from a small particle size (1.8 µm) C18 column, accelerated analysis with satisfactory resolution, sensitivity and selectivity were achieved in a single run within 7 min with linear gradient elution of acetonitrile-0.1% (v/v) formic acid in water. The analytical signal was obtained by multiple reaction monitoring transitions via electrospray ionization source operating in both positive and negative ionization mode. The approach was validated for linearity, sensitivity, precision, repeatability, stability and recovery. All analytes showed good linearity over a wide concentration range (r > 0.99). The method limits ranged from 0.03 ng/mL to 19.35 ng/mL which are sensitive enough for quality control studies. The developed method was successfully applied to the simultaneous determination of fifteen constituents in JTT. In conclusion, our experimental results demonstrate that UHPLC-ESI-MS/MS is a useful approach for the overall quality assessment of complex TCMPs. PMID:24476603

Wang, Shuping; Fu, Peng; Liu, Lei; Wang, Lingling; Peng, Chengcheng; Zhang, Weidong; Liu, Runhui

2014-01-01

153

Dynamic modeling and experimental validation for the electrical coupling in a 5-cell solid oxide fuel cell stack in the perspective of thermal coupling  

Microsoft Academic Search

The electrical coupling in a 5-cell solid oxide fuel cell (SOFC) stack is investigated in this research. The electrical characteristics tests of a single cell and the stack were performed in an electrical furnace. It was found that the single cell with the highest temperature does not give the highest output voltage in the stack test, which is different from

Hongliang Cao; Xi Li; Zhonghua Deng; Jianhua Jiang; Jie Yang; Jian Li; Yi Qin

2011-01-01

154

Determination of cyromazine and melamine in chicken eggs using quick, easy, cheap, effective, rugged and safe (QuEChERS) extraction coupled with liquid chromatography-tandem mass spectrometry.  

PubMed

A rapid and sensitive method has been developed for the simultaneous detection of cyromazine and melamine in chicken eggs using the quick, easy, cheap, effective, rugged and safe (QuEChERS) method coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS). The optimal extraction solvent for the liquid-liquid extraction was 5 mL of acetonitrile with a 0.1 M hydrochloric acid aqueous solution (99.5:0.5, v/v). The extract was cleaned with 0.5 g of anhydrous magnesium sulfate and 10 mg of graphitized carbon black. The analysis of cyromazine and melamine was accomplished by combining the use of an anion exchange LC column with tandem mass spectrometry in the positive electrospray ionization mode with selected reaction monitoring mode (SRM). The detection limits were 1.6 ng g(-1) for cyromazine and 8 ng g(-1) for melamine, and the quantitation limits were 5.5 ng g(-1) for cyromazine and 25 ng g(-1) for melamine. The recoveries of cyromazine and melamine in the spiked egg samples were 83.2% and 104.6%, respectively, with an relative standard deviation (RSD) of less than 18.1%. The intra-day and inter-day precisions, represented by the RSD, ranged from 1.5% to 8.8% and 6.8% to 14.3%, respectively. The proposed method was tested by analyzing chicken eggs from the markets and from the veterinary medicine laboratory. The concentrations of cyromazine and melamine detected in these samples were in the range of 20-94 ng g(-1). The results demonstrated that the QuEChERS method combined with LC-MS/MS is a simple, rapid and inexpensive method for the analysis of cyromazine and melamine in eggs. PMID:23101655

Wang, Pei-Cheng; Lee, Ren-Jye; Chen, Chung-Yu; Chou, Chi-Chung; Lee, Maw-Rong

2012-11-01

155

Identification and quantification of free radical scavengers in the flower buds of Lonicera species by online HPLC-DPPH assay coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry.  

PubMed

Flos Lonicerae, derived from the flower buds of several medicinal Lonicera species, is a commonly used herbal medicine with multiple pharmacological activities, one of the major ones being antioxidant activity. In this study, free radical scavengers in the flower buds of six Lonicera species were screened, identified and quantified by online HPLC-DPPH (1,1-diphenyl-2-picrylhydrazyl) assay coupled with LC quadrupole time-of-flight tandem mass spectrometry (Q-TOF MS/MS). The antioxidants were firstly screened from the complex plant matrix by the online HPLC-DPPH assay. Then the active compounds were identified by LC Q-TOF MS/MS, and the possible fragmentation pathways were proposed. The reactivity of antioxidants available was investigated using an internal standard method by online LC assay. The contents of 12 antioxidants were also determined or estimated by HPLC coupled with diode array detector. The total antioxidant capability determined by the online method was used as the marker to evaluate the quality of Flos Lonicerae. The results were important to clarify the material basis and therapeutic mechanism of Flos Lonicerae. PMID:21882208

Li, Yan-Jing; Chen, Jun; Li, Ying; Li, Ping

2012-04-01

156

The Role of Ile87 of CYP158A2 in Oxidative Coupling Reaction  

PubMed Central

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

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

2012-01-01

157

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

158

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

PubMed Central

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

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

2012-01-01

159

Enantioselective determination of 3-n-butylphthalide (NBP) in human plasma by liquid chromatography on a teicoplanin-based chiral column coupled with tandem mass spectrometry.  

PubMed

A novel and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated to determine the exposure of 3-n-butylphthalide (NBP) enantiomers in human plasma. The NBP enantiomers were extracted from human plasma using methyl tert-butyl ether. The baseline separation of R-(+)-NBP and S-(-)-NBP was achieved within 11.0min using a teicoplanin-based Astec Chirobiotic T column (250mm×4.6mm i.d., 5?m) under isocratic conditions at a flow rate of 0.6mL/min. The selection of the chiral stationary phase and the effect of the mobile phase composition on the resolution of the enantiomers were discussed. The selectivity, linearity, precision, accuracy, matrix effect, recovery, and stability were evaluated under optimized conditions. The LC-MS/MS method using 200?L of human plasma was linear over the concentration range of 5.00-400ng/mL for each enantiomer. The lower limit of quantification (LLOQ) for both enantiomers was 5.00ng/mL. The intra- and inter-assay precision values of the replicated quality control samples were within 8.0% for each enantiomer. The mean accuracy values for the quality control samples were within ±6.1% of the nominal values for R-(+)-NBP and S-(-)-NBP. No chiral inversion was observed during sample storage, preparation, and analysis. The method proved suitable for enantioselective pharmacokinetic studies of NBP after an oral administration of a therapeutic dose of racemic NBP. PMID:24103433

Diao, Xingxing; Ma, Zhiyu; Lei, Peng; Zhong, Dafang; Zhang, Yifan; Chen, Xiaoyan

2013-11-15

160

Simultaneous determination of phoxim and its photo-transformation metabolite residues in eggs using liquid chromatography coupled with electrospray ionization tandem mass spectrometry.  

PubMed

The principal objective of this study was to develop an appropriate, sensitive, and selective method for the simultaneous quantitative determination of phoxim and its photo-transformation product, O,O-diethyl alpha-cyanobenzylideneamino-thiophosphonate (DCTP) in both chicken and quail eggs. Eggs (1 g) were blended with anhydrous magnesium sulfate (1 g) for sample pretreatment and extracted with acetonitrile. The extracts were then further purified with SPE silica gel tubes deactivated with trimethylamine. Residues were analyzed via a reversed phase-liquid chromatography-tandem mass spectrometry (RP-LC-MS/MS) in positive-ion electrospray ionization (ESI) mode. Tebufenozide was utilized as an internal standard for the quantification of phoxim and its metabolite residues. The identification and quantification of analytes were based on ion transitions monitored by multiple reaction monitoring (MRM). LC-MS/MS analysis was performed from 0.02 to 1 mg kg(-1) and correlation coefficients (r(2)) ranging from 0.998 to 0.999 were obtained for both analytes in blank egg extracts. The relative standard deviations (RSDs) of intra- and inter-day variations ranged from 2.1% to 6.7% and from 2.8% to 6.4% for phoxim and DCTP in chicken and quail eggs. At all levels of fortification (0.02, 0.05, and 0.125 mg kg(-1)), the recoveries fell within a range of 81.3% to 93.6% for phoxim and 83.3% to 90.1% for DCTP. The matrix effect was <2%, due to the partial dilution of the sample. Decision limits (CCalpha) and detection capabilities (CCbeta) were in the range of 0.0005-0.0044 and 0.0054-0.0224 mg kg(-1), respectively. The method was evaluated further by analyzing real samples purchased from markets. All chicken and quail egg samples were free from residues of the target compounds. PMID:20638501

Lee, Jung Han; Park, Semin; Jeong, Won Young; Park, Hyung Jin; Kim, Hae Gyeong; Lee, Soo-Jung; Shim, Jae-Han; Kim, Soo Taek; Abd El-Aty, A M; Im, Moo Hyeog; Choi, Ok Ja; Shin, Sung Chul

2010-07-26

161

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

162

Synthesis of polycyclic isoindoline derivatives via tandem Pd-catalyzed coupling, propargyl-allenyl isomerization, [4 + 2] cycloaddition and aromatization reaction.  

PubMed

We report in this paper an interesting sequential reaction involving sequential Sonogashira coupling, propargyl-allenyl isomerization, [4 + 2] cycloaddition and aromatization reaction, which provides a facile method for the synthesis of a variety of polycyclic isoindoline derivatives from easily accessible starting materials. PMID:23051023

Zhu, Shugao; Cao, Jian; Wu, Luling; Huang, Xian

2012-11-16

163

Coupled Mercury-Cell Sorption, Reduction, and Oxidation on Methylmercury Production by Geobacter sulfurreducens PCA.  

PubMed

G. sulfurreducens PCA cells have been shown to reduce, sorb, and methylate Hg(II) species, but it is unclear whether this organism can oxidize and methylate dissolved elemental Hg(0) as shown for Desulfovibrio desulfuricans ND132. Using Hg(II) and Hg(0) separately as Hg sources in washed cell assays in phosphate buffered saline (pH 7.4), we report how cell-mediated Hg reduction and oxidation compete or synergize with sorption, thus affecting the production of toxic methylmercury by PCA cells. Methylation is found to be positively correlated to Hg sorption (r = 0.73) but negatively correlated to Hg reduction (r = -0.62). These reactions depend on the Hg and cell concentrations or the ratio of Hg to cellular thiols (-SH). Oxidation and methylation of Hg(0) are favored at relatively low Hg to cell-SH molar ratios (e.g., <1). Increasing Hg to cell ratios from 0.25 × 10(-19) to 25 × 10(-19) moles-Hg/cell (equivalent to Hg/cell-SH of 0.71 to 71) shifts the major reaction from oxidation to reduction. In the absence of five outer membrane c-type cytochromes, mutant ?omcBESTZ also shows decreases in Hg reduction and increases in methylation. However, the presence of competing thiol-binding ions such as Zn(2+) leads to increased Hg reduction and decreased methylation. These results suggest that the coupled cell-Hg sorption and redox transformations are important in controlling the rates of Hg uptake and methylation by G. sulfurreducens PCA in anoxic environments. PMID:25268220

Lin, Hui; Morrell-Falvey, Jennifer L; Rao, Balaji; Liang, Liyuan; Gu, Baohua

2014-10-21

164

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

165

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

166

Proteomic analysis of age dependent nitration of rat cardiac proteins by solution isoelectric focusing coupled to nano-HPLC tandem mass spectrometry  

PubMed Central

Protein nitration occurs as a result of oxidative stress induced by reactive oxygen (ROS) and reactive nitrogen species (RNS). Therefore, protein nitration serves as a hallmark for protein oxidation in vivo. We have previously reported on age dependent protein nitration in cardiac tissue of Fisher 344 BN-F1 rats analyzed by two-dimensional gel electrophoresis; however, only one specific nitration site was identified (Kanski et al., 2005a). In the present report, we used solution phase isoelectric focusing (IEF) followed by nanoHPLC-ESI-MS/MS that allowed us to obtain good MS/MS data to identify specific sites of protein nitration in cardiac tissue. As expected, more nitrated proteins were detected in cardiac tissue of old rats, including myosin heavy chain, neurofibromin, tropomyosin and nebulin-related anchoring protein. The post-translational modification of these cytoskeletal proteins may provide some rationale for the age-dependent functional decline of the heart. PMID:17481840

Hong, Sung Jung; Gokulrangan, Giridharan; Schoneich, Christian

2011-01-01

167

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

SciTech Connect

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

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

1995-08-01

168

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

169

Nitrate reduction coupled with pyrite oxidation in the surface sediments of a sulfide-rich ecosystem  

NASA Astrophysics Data System (ADS)

studies of denitrification have focused on organic carbon as an electron donor, but reduced sulfur can also support denitrification. Few studies have reported nitrate (NO3-) reduction coupled with pyrite oxidation and its stoichiometry in surface sediments, especially without experimental pyrite addition. In this study, we evaluated NO3- reduction coupled with sulfur oxidation by long-term incubation of surface sediments from a sulfide-rich ecosystem in Akita Prefecture, Japan. The surface sediments were sampled from a mud pool and a riverbed. Fresh sediments and water were incubated under anoxic conditions (and one oxic condition) at 20°C. NO3- addition increased the SO42- concentration and decreased the NO3- concentration. SO42- production (?SO42-) was strongly and linearly correlated with NO3- consumption (?NO3-) during the incubation period (R2 = 0.983, P < 0.01, and n = 8), and the slope of the regression (?NO3-/?SO42-) and the stoichiometry indicated sulfur-driven NO3- reduction by indigenous autotrophic denitrifying bacteria. Framboidal pyrite and marcasite (both FeS2) were present in the sediments and functioned as the electron donors for autotrophic denitrification. Both ?NO3- and ?SO42- were higher in the riverbed sediment than in the mud pool sediment, likely because of the higher amount of easily oxidizable S (pyrite) in the riverbed sediment. Consistently low ammonium (NH4+) concentrations indicated that NO3- reduction by dissimilatory NO3- reduction to NH4+ was small but could not be disregarded. Our results demonstrate that sulfide-rich ecosystems with easily oxidizable metal-bound sulfides such as FeS2 near the ground surface may act as denitrification hot spots.

Hayakawa, Atsushi; Hatakeyama, Mizuho; Asano, Ryoki; Ishikawa, Yuichi; Hidaka, Shin

2013-06-01

170

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. PMID:23545123

Zhu, Yingguang; Shi, Yian

2013-01-01

171

Development of a multi-mycotoxin analysis in beer-based drinks by a modified QuEChERS method and ultra-high-performance liquid chromatography coupled with tandem mass spectrometry.  

PubMed

An analytical method was developed for the identification and quantification of 15 mycotoxins (patulin, nivalenol, deoxynivalenol, aflatoxin B(1), B(2), G(1), G(2), M(1), T-2 toxin, HT-2 toxin, zearalenone, fumonisin B(1), B(2), B(3), and ochratoxin A) in beer-based drinks (beer, low-malt beer, new genre, and nonalcoholic) by a modified QuEChERS method and an ultra-high-performance liquid chromatography coupled with tandem mass spectrometry (UHPLC/MS/MS). Mycotoxins were extracted from samples using acetonitrile with sodium chloride, anhydrous magnesium sulfate, and sodium citrate, and were then purified with a solid phase extraction (SPE) cartridge including C18. The UHPLC conditions were also examined to establish its optimal conditions for separation. Fifteen mycotoxins were separated in a total of 6.5 min, and were quantified in the optimal mobile phase conditions. Determinations performed using this method produced high correlation coefficients of 15 mycotoxins (R>0.99) and recovery rates ranging from 70.3 to 110.7% with good repeatability (relative standard deviation RSD<14.6%). Further, 24 commercial beer-based drinks in Japan were analyzed using this method, and nivalenol, deoxynivalenol, and fumonisins were detected in several samples, but always under the limit of quantification (<5 ng/mL). These results suggest that the health risk to consumers from beer-based drinks in Japan is relatively low. PMID:21666361

Tamura, Masayoshi; Uyama, Atsuo; Mochizuki, Naoki

2011-01-01

172

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

173

Simultaneous determination of berberine, palmatine and jatrorrhizine by liquid chromatography-tandem mass spectrometry in rat plasma and its application in a pharmacokinetic study after oral administration of coptis-evodia herb couple.  

PubMed

A rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed to simultaneously determine berberine, palmatine and jatrorrhizine in rat plasma. After mixing with the internal standard (IS) tetrahydropalmatine, plasma samples were pretreated by protein precipitation with acetonitrile-methanol (1:2, v/v). Chromatographic separation was carried out on a C18 column using a mixture of water (containing 0.1% formic acid) and acetonitrile (30:70, v/v) as mobile phase. The detection was performed by selected reaction monitoring (SRM) mode via electrospray ionization (ESI) source operating in the positive ionization mode. The method was linear over the concentration range of 1.0-250.0 ng/mL for all components. The intra- and inter-day precision values were less than 14.6% and the deviations were within +/-4.0%. The fully validated LC-MS/MS method has been successfully applied to the pharmacokinetic study of berberine, palmatine and jatrorrhizine in rat plasma after oral administration of coptis-evodia herb couple. Three peaks were observed in both individual and mean plasma-concentration curves of berberine, palmatine and jatrorrhizine, which may be attributed to distribution re-absorption and enterohepatic circulation. PMID:18258496

Deng, Yating; Liao, Qiongfeng; Li, Suhua; Bi, Kaishun; Pan, Biyan; Xie, Zhiyong

2008-03-01

174

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 0.01 ng/mL, which were much lower than normally concerned concentrations for these typical anabolic androgenic steroids (AAS) (0.1 ng/mL). The linearity range was from the LOQ to 100 ng/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

175

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

PubMed Central

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

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

2014-01-01

176

[Determination of three perfluoro sulfonated chemicals in bivalve shells using high performance liquid chromatography-tandem mass spectrometry with the pretreatment of mixed inorganic acid digestion coupled with solid-phase extraction].  

PubMed

For the analysis of perfluorobutane sulfonate (PFBS), perfluorohexane sulfonate (PFHxS) and perfluorooctane sulfonate (PFOS) in shells, an extraction method of mixed inorganic acid digestion coupled with solid phase extraction (SPE) was established. The target compounds were determined by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The shell powder was at first digested with the mixture of nitric acid and hydrochloric acid, then the digestion solution was adjusted to pH 6 with sodium hydroxide, and cleaned up with Oasis WAX SPE cartridge. The perfluoro sulfonated chemicals were quantified with HPLC-MS/MS using electrospray ionization in negative ion mode with internal standard method. The limits of detection (LODs) were of 0.28 ng/g for PFBS, 0.42 ng/g for PFHxS and 0.43 ng/g for PFOS, and matrix recoveries of the perfluoro sulfonated chemicals were 94.88%-96.24%. The analytical results for the shells of two bivalves from Bohai Bay showed this pretreatment method is suitable for the determination of perfluoro sulfonated acids (PFSAs) in shells. Concentrations of PFSAs in the shells ranged from < LOD-0.70 ng/g, which were an order of magnitude lower than those in the soft tissues of these bivalves. PMID:20812629

Yang, Jin; Wang, Lei; Chen, Chen; Zhang, Jiao; Sun, Hongwen

2010-05-01

177

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

178

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

179

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

PubMed

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

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

2014-11-17

180

Domain coupling and resistance in perpendicularly magnetized metal-oxide bilayers  

NASA Astrophysics Data System (ADS)

Two of the interesting problems in magnetic heterostructures are the exchange coupling in multilayers and the stabilization of domains with magnetization perpendicular to the film plane. In this work, these two phenomena are combined and the stabilization of a perpendicular domain structure in an ultra thin (<10nm) metallic layer, grown on a magnetic oxide (Yttrium Iron Garnet, YIG) layer with perpendicular anisotropy, by interlayer exchange coupling was studied. Further, this bilayer was used to study the physics of interlayer coupling and the associated magnetoresistance including the contribution of domain walls to spin-dependent scattering. YIG thin films, deposited on a gadolinium gallium garnet (GGG) substrate using magnetron sputtering, were post-annealed to crystallize the film. The crystallization of the YIG film was optimized by X-ray diffraction, its perpendicular magnetization confirmed by two different magnetometry measurements, and the characteristic stripe domains imaged by magnetic force microscopy (MFM). Next, Fe films of various thicknesses were deposited on the YIG film. Under optimal growth conditions, and up to a critical thickness, the domain structure of Fe was found to be exchange coupled to that of YIG and showed the characteristic stripe domains structure. However, MFM imaging of such FM/YIG bilayers is not conclusive because of the possible effects of the stray magnetic fields from the substrate (YIG). To independently resolve the domain structure of the FM and YIG layers, clement specific X-ray photoemission electron microscopy (XPEEM) with magnetic circular dichroism (MCD) contrast, was performed at the Advanced Light Source. The XPEEM images revealed that the Co (FM) layer was coupled perpendicularly to the YIG layer up to a Co thickness of 5nm, but as the Co layer thickness was increased, domains of both the Co layer and the surface of the YIG film started to show an in-plane domain structure. Preliminary micromagnetic simulations showed that the volume exchange stiffness term at the interface plays a dominant role, when compared with the bilinear and biquadratic coupling contributions, in determining the interlayer coupling. Finally, the magnetoresistance (MR) of such FM/YIG bilayers, by lithographically patterning the FM layer on a YIG underlayer, was measured to both study the changes in the domain structure as a function of applied field and the contribution of the domain wall to the resistance. Since the YIG layer is insulating, such transport measurement would be dominated by the FM (Co) layer. MR measurement in longitudinal (field parallel to current direction) and transverse (field perpendicular to current direction) geometries revealed anisotropic MR (AMR) characteristics. However, the anomaly in the data when measured in the perpendicular mode (field perpendicular to the sample surface) was shown to be due to the Hall effect and domain coupling between FM and YIG layer. Detailed analysis of the perpendicular measurement showed sensitivity to the initial domain structure of the Co/YIG bilayer and this was interpreted in terms of the domain wall resistance contribution to the total MR.

Chun, Yoonsoo

181

Tandem photovoltaic cell using a thin-film polymer electrolyte  

SciTech Connect

A tandem photovoltaic cell has been fabricated using a thin-film plastic electrolyte to connect in optical and electrical series an n-type CdS thin-film and a p-type CdTe single crystal. The electrolyte was a thin film of poly(ethylene oxide) with a polysulfide redox couple. An open circuit voltage of 625 mV and a short-circuit current of 35 mA/cm/sup 2/ were obtained under illumination of 100 mW/cm/sup 2/ with a xenon lamp. The cell output in the present configuration is limited by the series resistance and insufficient band bending in the semiconductor electrodes due to unfavorable resistance matching of the components.

Skotheim, T.

1981-05-01

182

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

PubMed

A sensitive and accurate liquid chromatography-tandem mass spectrometric (LC-MS/MS) method for the intracellular determination of nine antiretroviral drugs in human peripheral blood mononuclear cells (PBMCs) is proposed. PBMCs are isolated by density gradient centrifugation using Vacutainer CPT tubes and cell count is performed with a Coulter instrument. Single-step extraction of drugs from PBMCs pellets is performed with MeOH 50% (with clozapine added as internal standard, I.S.) and the supernatant is injected onto a 2.1 mm x 30 mm SymmetryShield 3.5 microm-RP18 column equipped with a 2.1 x 10 mm guard column. Chromatographic separations are performed using a gradient program with a mixture of 2 mM ammonium acetate containing 0.1% formic acid and acetonitrile with 0.1% formic acid. Analytes quantification is performed by electro-spray ionisation-triple quadrupole mass spectrometry using the selected reaction monitoring (SRM) detection mode. The positive mode is used for the HIV protease inhibitors (PIs) indinavir, amprenavir, saquinavir, ritonavir, nelfinavir, lopinavir, atazanavir and the non-nucleoside reverse transcriptase inhibitors (NNRTIs) nevirapine, and the negative mode is applied for efavirenz. The calibration curves are prepared using blank PBMCs spiked with antiretroviral drugs at concentrations ranging from 0.5 to 100 ng/ml of cell extracts and fitted to a quadratic regression model weighted by 1/(concentration)(2). The lower limit of quantification is less than 0.5 ng/ml. The mean extraction recovery for all PIs/NNRTIs is always above 88%. The method is precise, with mean inter-day CV% within 0.6-10.2%, and accurate (range of inter-day deviation from nominal values -7.2 to +8.3%). This analytical method can be conveniently used in clinical research for the assessment of intracellular levels of all PIs/NNRTIs commercially available at present using a simple one-step cell extraction of PBMCs followed by liquid chromatography coupled with tandem triple quadripole mass detection. PMID:15833290

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

2005-05-25

183

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

NASA Astrophysics Data System (ADS)

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

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

2008-08-01

184

Metabolism of sanguinarine in human and in rat: characterization of oxidative metabolites produced by human CYP1A1 and CYP1A2 and rat liver microsomes using liquid chromatography-tandem mass spectrometry.  

PubMed

The quaternary benzo[c]phenanthridine alkaloid, sanguinarine (SA), has been detected in the mustard oil contaminated with Argemone mexicana, which produced severe human intoxications during epidemic dropsy in India. Today, SA metabolism in human and in rat has not yet been fully elucidated. The goal of this study is to investigate the oxidative metabolites of SA formed during incubations with rat liver microsomes (RLM) and recombinant human cytochrome P450 (CYP) and to tentatively identify the CYP isoforms involved in SA detoxification. Metabolites were analyzed by liquid chromatography combined with electrospray ionization-tandem mass spectrometry. Up to six metabolites were formed by RLM and their modified structure has been proposed using their mass spectra and mass shifts from SA (m/z 332). The main metabolite M2 (m/z 320) resulted from ring-cleavage of SA followed by demethylation, whereas M4 (m/z 348) is oxidized by CYP in the presence of NADPH. The diol-sanguinarine metabolite M6 (m/z 366) formed by RLM might derive from a putative epoxy-sanguinarine metabolite M5 (m/z 348). M4 and M6 could be detected in rat urine as their respective glucuronides. 5,6-Dihydrosanguinarine is the prominent derivative formed from SA in cells expressing no CYP. Oxidative biotransformation of SA was investigated using eight human CYPs: only CYP1A1 and CYP1A2 displayed activity. PMID:19804952

Deroussent, Alain; Ré, Micheline; Hoellinger, Henri; Cresteil, Thierry

2010-07-01

185

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

186

Pd-catalyzed oxidative coupling of arene C-H bonds with benzylic ethers as acyl equivalents.  

PubMed

A palladium-catalyzed oxidative coupling of arene C-H bonds with benzylic ethers via C-H bond activation is described. The reaction proceeds efficiently with a broad range of substrates bearing conventional directing groups with excellent functional group compatibility. This protocol potentially provides opportunities to use dibenzyl ethers as new acyl equivalents for catalytic acylation reactions. PMID:24320114

Han, Sangil; Sharma, Satyasheel; Park, Jihye; Kim, Mirim; Shin, Youngmi; Mishra, Neeraj Kumar; Bae, Jong Jin; Kwak, Jong Hwan; Jung, Young Hoon; Kim, In Su

2014-01-01

187

Simultaneous quantification of 17 constituents from Yuanhu Zhitong tablet using rapid resolution liquid chromatography coupled with a triple quadrupole electrospray tandem mass spectrometry.  

PubMed

A rapid resolution liquid chromatography coupled with a triple quadrupole mass spectrometry (RRLC-QQQ) was employed to identify and quantify the major bioactive constituents in Yuanhu Zhitong tablet (YZT), a traditional Chinese medicine. Seventeen constituents were simultaneously determined and quantified by reference standards in 9 min, namely scopoletin, protopine, ?-allocryptopine, tetrahydropalmatine, coptisine, tetrahydroberberine, corydaline, berberine, byakangelicin, byakangelicol, xanthotoxin, bergapten, pimpinellin, oxypeucedanin, imperatorin, osthole and isoimperatorin. All of them were performed on an Agilent XDB C(18) column (4.6 mm × 50 mm, 1.8 ?m) with linear gradient elution of acetonitrile-0.3% formic acid water (pH 2.7). The proposed method was applied to analyze 15 batches of samples with acceptable linearity (r(2), 0.9938-0.9999), precisions (RSD, 1.01-4.92%), repeatability (RSD, 1.33-4.91%), stability (RSD, 1.46-4.86%), recovery (RSD, 1.11-4.81%) of the seventeen compounds. Furthermore, the Hierarchical Cluster Analysis was applied to classify 15 samples based on characteristics of the 17 compound markers. As a result, the analytical method possessing high sensitivity and speed is suitable for the quality control of YZT. PMID:21733652

Zhang, Yingchun; Xu, Haiyu; Chen, Xiaomeng; Chen, Chang; Wang, Haijun; Meng, Fanyun; Yang, Hongjun; Huang, Luqi

2011-11-01

188

Matrix effect during the membrane-assisted solvent extraction coupled to liquid chromatography tandem mass spectrometry for the determination of a variety of endocrine disrupting compounds in wastewater.  

PubMed

Membrane-assisted solvent extraction (MASE) coupled to liquid chromatography-triple quadrupole mass spectrometry (LC-MS/MS) was studied for the determination of a variety of emerging and priority compounds in wastewater. Among the target analytes studied certain hormones (estrone (E1), 17?-estradiol (E2), androsterone (ADT), 17?-ethynyl estradiol (EE2), diethylstilbestrol (DES), equilin (EQ), testosterone (TT), mestranol (MeEE2), 19-norethisterone (NT), progesterone (PG) and equilenin (EQN)), alkylphenols (APs) (4-tert-octylphenol (4tOP), nonylphenol technical mixture (NPs) and 4n-octylphenol (4nOP)) and BPA were included. The work was primarily focused in the LC-MS/MS detection step, both in terms of variable optimization and with respect to the matrix effect study. Both, electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) were assessed both in the negative and positive mode, including the optimization of MS/MS operating conditions. The best results were obtained, in most of the cases, for ESI using 0.05% ammonium hydroxide as buffer solution in the mobile phase, composed with methanol and water. Under optimum detection conditions, matrix effect during the detection step was thoroughly studied. Dilution, correction with deuterated analogues and clean-up of the extracts were evaluated for matrix effect correction. Clean-up with Florisil together with correction with deuterated analogues provided the most satisfactory results, with apparent recoveries in the 57-136% range and method detection limits in the low ngL(-1) level for most of the analytes. For further validation of the method, two separated extraction procedures, the above mentioned MASE, and conventional solid phase extraction (SPE) were compared during the analysis of real samples and comparable results were successfully obtained for E1, E2, EE2, DES, NT, TT, EQ, PG, BPA, ADT, 4nOP, 4tOP, NPs and EQN. PMID:25001332

Iparraguirre, A; Navarro, P; Rodil, R; Prieto, A; Olivares, M; Etxebarria, N; Zuloaga, O

2014-08-22

189

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

PubMed

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

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

2009-08-01

190

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

PubMed Central

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

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

2013-01-01

191

Anaerobic oxidation of ethene coupled to sulfate reduction in microcosms and enrichment cultures.  

PubMed

Ethene is considered recalcitrant under anaerobic conditions, but biological reduction to ethane and oxidation to CO2 have been reported; however, little is known about these processes or the organisms carrying them out. In this report we describe sulfate dependent ethene consumption in microcosms prepared with sediments from a freshwater canal. A first dose of 0.6 mmol/L ethene was consumed within 77 days, and a second dose was largely consumed twelve days later. Material from this microcosm was transferred into growth medium with ethene as the only electron donor (except for trace amounts of vitamins) and sulfate as the electron acceptor. Four doses of ethene were consumed at increasing rates, and the cultures have been transferred at least eight times in this medium. Conversion of [(14)C]ethene primarily to (14)CO2 was demonstrated in fifth and sixth generation cultures, as well as production of sulfide in other cultures, confirming the ethene/sulfate couple. Ovoid cells 1-2 ?m in diameter were found in cultures containing ethene and sulfate, and quantitative PCR showed large increases in bacterial 16S rRNA gene copy number. Over half of a 16S rRNA gene clone library from a sixth-generation culture was a phylotype with a sequence ca. 90% identical with a clade of Deltaproteobacteria that includes Desulfovirga adipica and several Syntrophobacter spp. These studies have solidified the concept that deficits in mass balances for chloroethene fate in sulfate reducing zones of contaminated groundwater sites may be due to ethene oxidation, and suggest a unique phylotype is involved in this process. PMID:24033278

Fullerton, Heather; Crawford, Michael; Bakenne, Ademola; Freedman, David L; Zinder, Stephen H

2013-11-01

192

Studies on the preparation of bioactive lignans by oxidative coupling reaction. V. Oxidative coupling reaction of methyl (E)-3-(2-hydroxyphenyl)propenoate derivatives and lipid peroxidation inhibitory effects of the produced lignans.  

PubMed

The oxidative coupling reactions of 2-hydroxycinnamates were investigated as a continuation of our previous studies on 4-hydroxy derivatives. The reaction of 2-hydroxycinnamate 1 and 2-hydroxy-4-methoxycinnamate 3 with silver oxide afforded polymerized lignin-like products, while that of 2-hydroxy-bis(methoxymethoxy)cinnamates 5 and 6, after acetylation, gave the enol acetates, 8 and 14, of oxotetrahydrobenzoxanthene derivatives, respectively. These two products were also obtained by the oxidation of 5 and 6 with potassium hexacyanoferrate(III). In the reactions of 5 and 6 with iron(III) chloride, the major products were the partially demethoxymethoxylated compounds 9 and 15, respectively. Thus, the course of the reactions in the oxidation of 2-hydroxycinnamates is quite different from that in the case of 4-hydroxy derivatives. The product 8 and the corresponding oxotetrahydrobenzoxanthene derivative were found to show moderate inhibitory effects upon lipid peroxidation. PMID:7641311

Maeda, S; Masuda, H; Tokoroyama, T

1995-06-01

193

Characterization of aromatic glycosides in the extracts of Trollius species by ultra high-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry.  

PubMed

Ultra high-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UHPLC/ESI-Q-TOF MS/MS) was used to investigate the MS fragmentation behaviors of flavone C-glycosides present in the extracts of five Trollius species. In this study, the primary MS fragmentation pathways and key diagnostic fragment ions of flavone C-glycosides were systematically investigated and summarized to distinguish different types of derivatives and to trace other analogs in Trollius species. This method was useful, rapid, efficient and sensitive and allowed the simultaneous identification of different types of flavone C-glycosides present in other medicinal plants. The features of the MS fragmentation of these compounds indicated that the product ions were primarily the result of cleavage in the saccharide moiety, followed by hydrogen rearrangement and dehydration. In this study, thirty-six components including thirty-two flavone C-glycosides, two flavone O-glycosides and two phenylethanoid glycosides, were identified in the extracts of five Trollius species. Eleven of the flavone C-glycosides were identified by comparison with reference standards, and twenty-one flavone C-glycosides were tentatively identified based on their retention times, exact mass information and fragment ions. Two potentially new flavone C-glycosides (2?-O-vanilloylorientin and 2?-O-feruloylvitexin) were successfully characterized based on the summarized fragmentation pathways, and six known flavone C-glycosides (2?-O-glucosylvitexin, 2?-O-acetylorientin, 2?-O-acetylvitexin, 3?-O-acetylorientin, 3?-O-acetylvitexin and 6?-O-acetylvitexin) were identified in these plant species for the first time. In conclusion, the fragmentation pathways proposed in this paper were helpful for the identification of different types of flavone C-glycosides when no reference standards were available. PMID:23312385

Wu, Li-Zhen; Zhang, Xiao-Po; Xu, Xu-Dong; Zheng, Qing-Xia; Yang, Jun-Shan; Ding, Wan-Long

2013-03-01

194

Simultaneous determination of chlorpyrifos and 3,5,6-trichloro-2-pyridinol in duck muscle by modified QuEChERS coupled to gas chromatography tandem mass spectrometry (GC-MS/MS).  

PubMed

A rapid, specific, and sensitive method based on modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) coupled to gas chromatography tandem mass spectrometry (GC-MS/MS) was developed and validated for simultaneous determination of chlorpyrifos (CP) and its metabolite 3,5,6-trichloro-2-pyridinol (TCP) in duck muscle. The residues of CP and TCP were extracted by acidified acetonitrile. The fat layer of the extract was removed under -20 °C, then the organic layer was evaporated. The analytes were derivatized by N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide (MTBSTFA) and cleaned up by a mixture of 150 mg MgSO4, 25 mg graphitized carbon black (GCB), and 50 mg N-propylethylenediamine (PSA) to remove interference. The final extract was analyzed by GC-MS/MS. Recovery values at the spiking concentrations ranged from 86.2 to 92.3 % for CP and from 74.8 to 81.8 % for TCP, with relative standard deviations (RSDs) lower than 9.5 and 12.3, respectively. The correlation coefficients of CP (from 2 to 2,000 ?g/kg) and TCP (from 1 to 1,000 ?g/kg) were equal to or higher than 0.998. The limits of detection (LODs) were 0.3 and 0.15 ?g/kg, and the limits of quantification (LOQs) were 1.0 and 0.5 ?g/kg for CP and TCP in duck muscle, respectively. The average intra- and inter-day accuracy ranged from 84.6 to 91.2 % for CP and 75.6 to 82.3 % for TCP, and the intra- and inter-day precisions were from 5.8 to 8.2 % for CP and 6.5 to 11.9 % for TCP. Furthermore, the CP and TCP residues in duck muscle samples were detected for dietary risk assessment using the validated method. PMID:24691719

Li, Rui; He, Liang; Zhou, Ting; Ji, Xiaofeng; Qian, Mingrong; Zhou, Yu; Wang, Qiang

2014-05-01

195

Residue analysis of four diacylhydrazine insecticides in fruits and vegetables by Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) method using ultra-performance liquid chromatography coupled to tandem mass spectrometry.  

PubMed

The new analytical method using Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) procedure for simultaneous determination of diacylhydrazine insecticide residues in fruits and vegetables was developed using ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). The four insecticides (tebufenozide, methoxfenozide, chromafenozide, and halofenozide) were extracted from six fruit and vegetable matrices using acetonitrile and subsequently cleaned up using primary secondary amine (PSA) or octadecylsilane (C18) as sorbent prior to UPLC-MS/MS analysis. The determination of the target compounds was achieved in less than 3.0 min using an electrospray ionization source in positive mode (ESI+) for tebufenozide, methoxfenozide, and halofenozide and in negative mode (ESI-) for chromafenozide. The limits of detection were below 0.6 ?g kg(-1), while the limit of quantification did not exceed 2 ?g kg(-1) in different matrices. The QuEChERS procedure by using two sorbents (PSA and C18) and the matrix-matched standards gave satisfactory recoveries and relative standard deviation (RSD) values in different matrices at four spiked levels (0.01, 0.05, 0.1, and 1 mg kg(-1)). The overall average recoveries for this method in apple, grape, cucumber, tomato, cabbage, and spinach at four levels ranged from 74.2% to 112.5% with RSDs in the range of 1.4-13.8% (n = 5) for all analytes. This study provides a theoretical basis for China to draw up maximum residue limits and analytical method for diacylhydrazine insecticide in vegetables and fruits. PMID:21660414

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

2011-08-01

196

Surface properties of indium tin oxide treated by Cl2 inductively coupled plasma  

NASA Astrophysics Data System (ADS)

The effects of Cl2 inductively coupled plasma (ICP) treatment on the time dependence of work function (WF) and surface properties of indium tin oxide (ITO) were investigated. Kelvin probe (KP) measurements show that the WF after Cl2 ICP treatment is close to 5.9 eV. The WF decrease curve of Cl2 plasma treated ITO is fitted with double exponential functions with an adjusted R-square of 0.99. The mechanism under the decrease process is discussed by X-ray photoelectron spectroscopy (XPS). The ITO WF decrease after Cl2 ICP treatment performs much better than that after O2 ICP treatment and the chlorinated ITO keeps a WF increment of 0.3 eV compared with that without plasma treatment after 100 days. Other properties of chlorinated ITO surface such as morphology and transmittance change slightly. The results are significant for the understanding of degradation of Cl2 plasma treated ITO and the fabrication of organic semiconductor devices.

He, Kongduo; Yang, Xilu; Yan, Hang; Gong, Junyi; Zhong, Shaofeng; Ou, Qiongrong; Liang, Rongqing

2014-10-01

197

New insights into the first oxidative phenol coupling reaction during vancomycin biosynthesis.  

PubMed

OxyB catalyzes the first oxidative phenol coupling reaction in vancomycin biosynthesis. OxyB is a P450 hemoprotein whose activity is strictly dependent upon the presence of molecular oxygen. Here, it was shown that label from (18)O(2) is not incorporated into the monocyclic product during catalysis by OxyB. In addition, it was shown that OxyB can convert a model hexapeptide substrate containing (R)-Tyr6, instead of (S)-Tyr6, covalently linked as a C-terminal thioester to a peptidyl carrier protein (PCP-7S) derived from the vancomycin non-ribosomal peptide synthetase (NRPS), into the corresponding epimeric monocyclic product. The binding of this epimeric hexapeptide-PCP conjugate to the Fe(III) form of OxyB, as monitored by UV-vis spectroscopy, revealed a K(d)=35+/-5 microM. Thus, the enzyme reveals a surprising lack of stereospecificity in the binding and transformation of these epimeric substrates. PMID:18068978

Geib, Nina; Woithe, Katharina; Zerbe, Katja; Li, Dong Bo; Robinson, John A

2008-05-15

198

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

199

Computer simulation of spatial coupling in chemical oscillations of CO oxidation on two Pd(110) single crystals  

NASA Astrophysics Data System (ADS)

Gas-phase coupling between two Pd(110) single crystals in a UHV CO oxidation reaction in a continuous stirred tank reactor (CSTR) has been simulated by solving gas-phase mass balance equations with kinetic rate equations. This work was motivated by the experimental results which show that the frequency of partial pressure change in carbon monoxide is the same as the frequency of the work function change in the oscillation region and that the coupling between the two crystals occurred entirely via CO partial pressure. The computer simulation described here gives qualitative agreement with the experimental results. The change in the oscillatory region originating from the coupling of chemical oscillators which are slightly different to each other is successfully demonstrated by this model. The coupling of two oscillators having a simple periodic oscillation to produce mixed-mode oscillation was also successfully simulated.

Park, I. J.; Woo, S. I.

1993-09-01

200

Sexual intercourse with leukocytospermic men may be a possible booster of oxidative stress in female partners of infertile couples.  

PubMed

Human semen has undoubtedly significant influence on the organism of the female counterpart. At the same time there are no studies in English literature investigating the influence of sexual intercourse on oxidative stress level in women's organism. Seventeen infertile couples where male partners were with (n = 5) or without (n = 12) leukocytospermia were enrolled in the study. Systemic oxidative stress levels were measured, whereby twice in female partners - before and 8-12 h after sexual intercourse. The men with leukocytospermia were characterized by oxidative stress that was substantially transferred to their partners during sexual intercourse as revealed by increase in 8-isoprostanes level (median 32.7 vs. 70.4 ng/mmol creatinine, p = 0.006). Sexual intercourse with male partner having leukocytospermia increases the oxidative stress level in the women's organism that may interfere with fertilization. PMID:23316004

Mändar, R; Kullisaar, T; Borovkova, N; Punab, M

2013-05-01

201

Rate enhancement of photocatalytic cyanide oxidation by the application of an anodic bias/coupled semiconductor configuration  

SciTech Connect

In this study, photocatalytic cyanide degradation was investigated utilizing ultraviolet light (UV), an increase in titanium (IV) oxide (TiO{sub 2}) photocatalyst surface area, platinization of the photocatalyst, appropriate adjustment of pH, and the immobilization of TiO{sub 2}/ tin (IV) oxide (SnO{sub 2}) coupled semi-conductor film on an optically transparent electrode. The cyanide concentration was monitored using an ion selective electrode. The focus of this study was to explore the possibility of a viable process for the effective and complete photodegradation of cyanide ion. The long-term goal is the application of this process to industry. Cyanide detoxification has been successfully achieved in recent years. Research has shown that photocatalytic oxidation can completely degrade cyanide to nitrate via nitrite. However, the rate at which this oxidation occurs is not yet suitable for application in industry. Therefore, the need for an effective treatment is most urgent.

Munroe, N.D.H.; Tilleux, R. [Florida International Univ., Miami, FL (United States)

1996-12-31

202

Cofactor-apoprotein hydrogen bonding in oxidized and fully reduced flavodoxin monitored by trans-hydrogen-bond scalar couplings.  

PubMed

Hydrogen bonding plays a key role in the tight binding of the FMN cofactor and the regulation of its redox properties in flavodoxins. Hydrogen bonding interactions can be directly observed in solution by multidimensional heteronuclear NMR spectroscopy through the scalar couplings between donor and acceptor nuclei. Here we report on the detection of intermolecular trans-hydrogen-bond couplings ((h)J) between the flavin ring system and the backbone of Desulfovibrio vulgaris flavodoxin in the oxidized and the two-electron reduced states. For this purpose, experiments are adapted from pulse sequences previously applied to determining (h)J coupling constants in nucleic acid-base pairs and proteins. The resulting (h2)J(N,N), (h4)J(N,N), (h3)J(C,N), and (h1)J(H,N) couplings involve the (15)N(1), (13)C(2), and (15)N(3) nuclei of the pyrimidine moiety of FMN, whereas no such interactions are detectable for (13)C(4) and (15)N(5). Several long-range (15)N-(15)N, (13)C-(15)N, and (1)H-(15)N J-coupling constants within the flavin are obtained as "by-products". The magnitudes of both (h)J and regular J couplings are found to be dependent on the redox state. In general, good correlations between (h)J coupling constants and donor-group (1)H chemical shifts and also crystallographic donor-acceptor distances are observed. PMID:15515086

Löhr, Frank; Yalloway, Gary N; Mayhew, Stephen G; Rüterjans, Heinz

2004-11-01

203

Double quantum dot with tunable coupling in an enhancement-mode silicon metal-oxide semiconductor device with lateral geometry  

NASA Astrophysics Data System (ADS)

We present transport measurements of a tunable silicon metal-oxide semiconductor double quantum dot device with lateral geometry. The experimentally extracted gate-to-dot capacitances show that the device is largely symmetric under the gate voltages applied. Intriguingly, these gate voltages themselves are not symmetric. A comparison with numerical simulations indicates that the applied gate voltages serve to offset an intrinsic asymmetry in the physical device. We also show a transition from a large single dot to two well isolated coupled dots, where the central gate of the device is used to controllably tune the interdot coupling.

Tracy, L. A.; Nordberg, E. P.; Young, R. W.; Borrás Pinilla, C.; Stalford, H. L.; Ten Eyck, G. A.; Eng, K.; Childs, K. D.; Wendt, J. R.; Grubbs, R. K.; Stevens, J.; Lilly, M. P.; Eriksson, M. A.; Carroll, M. S.

2010-11-01

204

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

205

A novel use of oxidative coupling reactions for determination of some statins (cholesterol-lowering drugs) in pharmaceutical formulations  

Microsoft Academic Search

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

Safwan Ashour; Mahmoud Bahbouh; Mouhammed Khateeb

2011-01-01

206

Co-catalytic oxidative coupling of primary amines to imines using an organic nanotube-gold nanohybrid.  

PubMed

A novel nanohybrid structure was synthesized by assembling gold nanoparticles on polymerized polydiacetylene nanotubes. Combination of the nanohybrid with gallacetophenone afforded an efficient cooperative co-catalytic system for the oxidative coupling of primary amines into imines. The system is highly efficient and sustainable as it operates in high yields using minimal amounts of the metal and the quinone, under ambient atmosphere, at room temperature, in water, and is easily recycled. PMID:25347761

Jawale, Dhanaji V; Gravel, Edmond; Villemin, Elise; Shah, Nimesh; Geertsen, Valérie; Namboothiri, Irishi N N; Doris, Eric

2014-11-01

207

Direct oxidative coupling of N-acetyl indoles and phenols for the synthesis of benzofuroindolines related to phalarine.  

PubMed

Inspired by the biogenetic synthesis of benzofuroindoline-containing natural products, we designed an oxidative coupling between phenol and N-acetyl indoles. This straightforward and direct radical process, mediated by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and FeCl3 allowed the regioselective synthesis of benzofuro[3,2-b]indolines, whose structure is found in the natural product phalarine. PMID:25208884

Tomakinian, Terry; Guillot, Régis; Kouklovsky, Cyrille; Vincent, Guillaume

2014-10-27

208

Oxidative cross-dehydrogenative coupling between N-aryl tetrahydroisoquinolins and 5H-oxazol-4-ones through two methodologies: copper catalysis or a metal-free strategy.  

PubMed

A direct oxidative cross-dehydrogenative coupling (CDC) of N-aryl tetrahydroisoquinolins with 5H-oxazol-4-ones catalyzed by CuBr using air as the only oxidant has been developed, which could also proceed smoothly under a metal-free oxidative system with PhI(OAc)2 as the oxidant. A series of alkylated tetrahydroisoquinolin derivatives were obtained in good yields and excellent diastereoselectivities. PMID:25364789

Liu, Xihong; Zhang, Jinlong; Ma, Shixiong; Ma, Yunxia; Wang, Rui

2014-12-25

209

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

SciTech Connect

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

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

2013-10-15

210

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

211

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

PubMed Central

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

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

2011-01-01

212

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

213

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

214

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

215

Metal-Free Intermolecular Oxidative C-N Bond Formation via Tandem C-H and N-H Bond Functionalization  

PubMed Central

The development of a novel intermolecular oxidative amination reaction, a synthetic transformation that involves the simultaneous functionalization of both an N-H and C-H bond, is described. The process, which is mediated by an I(III) oxidant and contains no metal catalysts, provides a rapid and green method for synthesizing protected anilines from simple arenes and phthalimide. Mechanistic investigations indicate that the reaction proceeds via nucleophilic attack of the phthalimide on an aromatic radical cation, as opposed to the electrophilic aromatic amination that has been reported for other I(III) amination reactions. The application of this new reaction to the synthesis of a variety of substituted aniline derivatives is demonstrated. PMID:22010982

Kantak, Abhishek A.; Potavathri, Shathaverdhan; Barham, Rose A.; Romano, Kaitlyn M.

2011-01-01

216

Metal-free intermolecular oxidative C-N bond formation via tandem C-H and N-H bond functionalization.  

PubMed

The development of a novel intermolecular oxidative amination reaction, a synthetic transformation that involves the simultaneous functionalization of both a N-H and C-H bond, is described. The process, which is mediated by an I(III) oxidant and contains no metal catalysts, provides a rapid and green method for synthesizing protected anilines from simple arenes and phthalimide. Mechanistic investigations indicate that the reaction proceeds via nucleophilic attack of the phthalimide on an aromatic radical cation, as opposed to the electrophilic aromatic amination that has been reported for other I(III) amination reactions. The application of this new reaction to the synthesis of a variety of substituted aniline derivatives is demonstrated. PMID:22010982

Kantak, Abhishek A; Potavathri, Shathaverdhan; Barham, Rose A; Romano, Kaitlyn M; DeBoef, Brenton

2011-12-14

217

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

PubMed Central

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

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

2011-01-01

218

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

PubMed

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

Sivula, Kevin

2013-01-01

219

Studies on the preparation of bioactive lignans by oxidative coupling reaction. II. Oxidative coupling reaction of methyl(E)-3-(4,5-dihydroxy-2-methoxyphenyl)propenoate and lipid peroxidation inhibitory effects of the produced lignans.  

PubMed

The oxidative coupling reaction of methyl (E)-3-4(4,5-dihydroxy-2-methoxyphenyl)propenoate (10), obtainable from esculetin, has been studied using silver oxide and potassium hexacyanoferrate(III). The products were separated, after acetylation, by silica gel column chromatography. 1-Aryl-1,2-dihydronaphthalene derivative 12 was obtained as a major product, accompanied by the benzo[kl]xanthene derivative 13. In the oxidation with silver oxide, a benzodioxane compound 14a was produced additionally in a minor amount. Thus, the course of the reaction differed notably from those of ferulic or caffeic acid derivatives. The compounds 11, 12, 13 and 14a were tested for their inhibitory effects on lipid peroxidation in rat brain homogenate and rat liver microsomes. They showed activities more effective than that of idebenone in rat brain homogenate, and were found to be more potent than benzofuran lignans 4 and 5, and much more potent than (+/-)-alpha-tocopherol in rat liver microsomes. PMID:7697765

Maeda, S; Masuda; Tokoroyama, T

1994-12-01

220

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

SciTech Connect

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

Weber Jr., W. J.

2000-10-01

221

Oxidative Photoredox-Catalytic Activation of Aliphatic Nucleophiles for C(sp(3) )-C(sp(2) ) Cross-Coupling Reactions.  

PubMed

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

Jahn, Emanuela; Jahn, Ullrich

2014-12-01

222

Diverse reactions of PhI(OTf)2 with common 2-electron ligands: complex formation, oxidation, and oxidative coupling.  

PubMed

The crystal structures of bis-pyridine stabilized iodine dications [PhI(pyr)(2)](2+) are reported as triflate salts, representing the first ligand supported iodine dications to be structurally characterized. The pyridine complexes are susceptible to ligand exchange in reaction with stronger N-based donors such as 4-dimethylaminopyridine. Attempts to extend this reactivity to N-heterocyclic carbene and phosphine ligands, as has been accomplished in the earlier p-block groups, resulted in redox chemistry, with oxidation of the ligands rather than coordination. PMID:23148595

Pell, Thomas P; Couchman, Shannon A; Ibrahim, Sara; Wilson, David J D; Smith, Brian J; Barnard, Peter J; Dutton, Jason L

2012-12-01

223

Double quantum dot with tunable coupling in an enhancement-mode silicon metal-oxide semiconductor device with lateral geometry  

NASA Astrophysics Data System (ADS)

We present transport measurements of a tunable silicon metal- oxide-semiconductor double quantum dot device with lateral geometry. Experimentally extracted gate-to-dot capacitances show that the device is largely symmetric under the gate voltages applied. Intriguingly, these gate voltages themselves are not symmetric. Comparison with numerical simulations indicates that the applied gate voltages serve to offset an intrinsic asymmetry in the physical device. We also show a transition from a large single dot to two well isolated coupled dots, where the central gate of the device is used to controllably tune the interdot coupling. This work was supported by the LDRD program at Sandia National Laboratories, a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary Lockheed-Martin Company, for the U. S. DOE NNSA under Contract No. DE-AC04-94AL85000

Tracy, L. A.; Young, R. W.; Ten Eyck, G. A.; Eng, K.; Childs, K. D.; Wendt, J. R.; Grubbs, R. K.; Stevens, J.; Lilly, M. P.; Carroll, M. S.; Nordberg, E. P.; Borras Pinilla, C.; Stalford, H. L.; Eriksson, M. A.

2011-03-01

224

Synthesis of tylocrebrine and related phenanthroindolizidines by VOF3-mediated oxidative aryl-alkene coupling.  

PubMed

A highly convergent strategy to prepare phenanthroindolizidines is reported involving three consecutive C-C coupling reactions. This sequence features a novel VOF(3)-mediated aryl-alkene coupling in the final step, which enables regioselective preparation of C5-substituted phenanthroindolizidines for the first time. This strategy has been applied to the synthesis of eight natural and unnatural members in this class to investigate the scope of this chemistry and to explore structure-activity relationships. PMID:21142214

Niphakis, Micah J; Georg, Gunda I

2011-01-21

225

Oxide Etch Behavior in an Inductively Coupled C4F8 Discharge Characterized by Diode Laser Spectroscopy.  

NASA Astrophysics Data System (ADS)

This study reports on oxide and photoresist etch characteristics in an inductively coupled GEC Reference Cell as a function of reactor source power, bias power and pressure using C4F8. Diode laser absorption spectroscopy (DLAS) has shown that C4F8 is largely dissociated to form C2F4, CF2 and CF in the discharge. Over an oxide surface, CF2 and CF are consumed in the oxide etch process, but only when the bias power is sufficient to keep the oxide surface clean through energetic ion bombardment. For C4F8, this transition occurs at 60 eV (75 W bias power) in the GEC Cell. At higher bias powers (125 W) where oxide etching is fast ( 600 nm/min.), CF2 appears to be the key radical for the etch process since 50 percent (2.7-3.0 mTorr in a 15 mTorr C4F8 discharge) is consumed. These values were obtained by comparing the CF2 concentrations over non-reactive wafer surfaces versus blanket oxide wafer surfaces undergoing etching. CF is shown to display a similar trend, but its concentration is an order of magnitude less than CF2, and consequently cannot account on a mass basis for the amount of reactants necessary to balance the amount of etch products. Over a PR surface, neither CF2 nor CF concentrations vary as a function of PR etch rate. Consequently, they do not appear to be involved in the PR etch mechanism. However, PR etching is also critically dependent on bias power. PR films etch presumably due to energetic ion bombardment that degrades the PR film, making it liable to attack by fluorine.

Anderson, Harold; Barela, Marcus; Courtin, Geoff; Waters, Karla

2001-10-01

226

High-temperature catalytic oxidative conversion of propane to propylene and ethylene involving coupling of exothermic and endothermic reactions  

Microsoft Academic Search

Coupling of the exothermic catalytic oxidative conversion and endothermic thermal cracking (noncatalytic) reactions of propane to propylene and ethylene over the SrO\\/LaâOâ\\/SA5205 catalyst in the presence of steam and limited oxygen was investigated at different process conditions (temperature, 700--850 C; CâHâ\\/Oâ ratio in feed, 2.0--8.0; HâO\\/CâHâ ratio, 0.5--2.5; space velocity, 2,000--15,000 cm³\\/g h). In the presence of steam and limited

Vasant R. Choudhary; Vilas H. Rane; Amarjeet M. Rajput

2000-01-01

227

Nitrogen isotope fractionation during archaeal ammonia oxidation: Coupled estimates from isotopic measurements of ammonium and nitrite  

NASA Astrophysics Data System (ADS)

Ammonia-oxidizing archaea (AOA) are ubiquitous in marine and terrestrial environments and knowledge about the nitrogen (N) isotope effect associated with their ammonia oxidation activity will allow a better understanding of natural abundance isotope ratios, and therefore N transformation processes, in the environment. Here we examine the kinetic isotope effect for ammonia oxidation in a pure soil AOA culture (Ca. Nitrososphaera viennensis) and a marine AOA enrichment culture. We estimated the isotope effect from both isotopic signatures of ammonium and nitrite over the course of ammonia oxidation. Estimates of the isotope effect based on the change in the isotopic signature of ammonium give valuable insight, because these estimates are not subject to the same concerns (e.g., accumulation of an intermediate) as estimates based on isotopic measurements of nitrite. Our results show that both the pure soil AOA culture and a marine AOA enrichment culture have similar but substantial isotope effect during ammonia consumption (31-34 per mill; based on ammonium) and nitrite production (43-45 per mill; based on nitrite). The 15N fractionation factors of both cultures tested fell in the upper range of the reported isotope effects for archaeal and bacterial ammonia oxidation (10-41 per mill) or were even higher than those. The isotope fractionation for nitrite production was significantly larger than for ammonium consumption, indicating that (1) some intermediate (e.g., hydroxylamine) of ammonia oxidation accumulates, allowing for a second 15N fractionation step to be expressed, (2) a fraction of ammonia oxidized is lost via gaseous N forms (e.g., NO or N2O), which is 15N-enriched or (3) a fraction of ammonium is assimilated into AOA biomass, biomass becoming 15N-enriched. The significance of these mechanisms will be explored in more detail for the soil AOA culture, based on isotope modeling and isotopic measurements of biomass and N2O.

Mooshammer, Maria; Stieglmeier, Michaela; Bayer, Barbara; Jochum, Lara; Melcher, Michael; Wanek, Wolfgang

2014-05-01

228

Simultaneous determination of berberine, palmatine and jatrorrhizine by liquid chromatography–tandem mass spectrometry in rat plasma and its application in a pharmacokinetic study after oral administration of coptis–evodia herb couple  

Microsoft Academic Search

A rapid and sensitive liquid chromatography–tandem mass spectrometry (LC–MS\\/MS) method was developed to simultaneously determine berberine, palmatine and jatrorrhizine in rat plasma. After mixing with the internal standard (IS) tetrahydropalmatine, plasma samples were pretreated by protein precipitation with acetonitrile–methanol (1:2, v\\/v). Chromatographic separation was carried out on a C18 column using a mixture of water (containing 0.1% formic acid) and

Yating Deng; Qiongfeng Liao; Suhua Li; Kaishun Bi; Biyan Pan; Zhiyong Xie

2008-01-01

229

Effects of reducing agents and oxidants on excitation-contraction coupling in skeletal muscle fibres of rat and toad.  

PubMed Central

1. The mechanically skinned fibre technique was used to examine the role of oxidation-reduction in the control of Ca2+ release and contraction in rat and toad skeletal muscle fibres under physiological conditions of myoplasmic [Mg2+] and [ATP] and sarcoplasmic reticulum (SR) Ca2+ load. 2. None of the reducing agents, dithiothreitol (DTT, 10 mM), glutathione (GSH, 10 mM) or cysteine (1 and 5 mM), had any detectable effect on the peak force, duration or the total number of depolarization-induced responses that could be elicited in skinned fibres from either toad or rat muscle, except for a slight alteration in one case (GSH on the duration of the response in rat fibres) caused by an effect of the agent of the Ca2+ sensitivity of the contractile apparatus. 3. Application of the reactive disulphide, 2,2'-dithiodipyridine (DTDP, 100 microM), a potent oxidizing agent, never induced any measurable force response or noticeable depletion of SR Ca2+ in any fibre under the conditions used. When all Ca2+ uptake was prevented, DTDP treatment of rat fibres was found to cause a 2- to 3-fold increase in the low rate of Ca2+ "leak' from the SR. DTDP treatment also increased the responsiveness of toad muscle fibres to 1 or 2 mM caffeine. These effects could be largely reversed by treatment with DTT. These results indicate that oxidation of the Ca2+ release channel does not cause substantial channel opening under physiological conditions. 4. Depolarization-induced force responses in both rat and toad fibres were rapidly abolished in the presence of DTDP (10 or 100 microM), in a manner favoured by inactivation of the voltage sensors. The relatively impermeant oxidant, 5,5'-dithionitrobenzoic acid (DTNB, 100 microM), had an effect very similar to DTDP if applied intracellularly, but unlike DTDP, had little or no effect if applied extracellularly (at 5 mM) before skinning. Depolarization-induced responses could be restored by treatment with DTT (10 mM). Intracellular application of the sulfhydryl-alkylating agent, N-ethylmaleimide (NEM, 100 microM), had effects very similar to DTDP and DTNB. 5. These results are not consistent with the proposal that excitation-contraction coupling in skeletal muscle primarily involves the oxidative linkage of the voltage sensors to the Ca2+ release channels, but do show that oxidation of an intracellularly accessible site can interfere with the coupling, in a process made more sensitive by voltage sensor inactivation. PMID:8930846

Posterino, G S; Lamb, G D

1996-01-01

230

Studies on the preparation of bioactive lignans by oxidative coupling reaction. IV. Oxidative coupling reaction of methyl (E)-3-(3,4-dihydroxy-2-methoxyphenyl)propenoate and lipid peroxidation inhibitory effects of the produced lignans.  

PubMed

The oxidative coupling reaction of the hydroxycinnamate 11 derived from daphnetin has been investigated. The reaction with silver oxide afforded, after acetylation, a dihydrobenzofuran derivative 17 and a benzodioxane derivative 16a as major products accompanied with a small amount of a bis(benzylidene)succinate 18 and a dihydronaphthalene 19, while the oxidation with iron(III) chloride gave the dihydronaphthalene derivative 20 corresponding to 19. The reaction with potassium hexacyanoferrate(III) and Na2CO3 produced, after acetylation, 16a and 19 in lower yields. The propensity for product formation in the reaction of 11 is discussed in relation to data for the reactions of hydroxycinnamate derivatives studied so far. The obtained compounds were tested for inhibitory effects on lipid peroxidation in rat brain homogenate and rat liver microsomes. In the rat brain homogenate the five compounds showed inhibitory activity more potent than that of idebenone. Compounds 17 and 20 were then tested in rat liver microsomes, and found to be more potent than schizotenuin A and much more potent than (+/-)-alpha-tocopherol. PMID:7895311

Maeda, S; Masuda, H; Tokoroyama, T

1995-01-01

231

Electrochemically driven intramolecular oxidative aromatic coupling as a pathway toward ?-extended porphyrins.  

PubMed

A Ni(II) complex of a ?-extended porphyrin bearing three mesityl substituents and one electron-rich naphthalene moiety has been prepared via electrochemical oxidation. It was proven that the whole oxidative process starts from electrochemical generation of a radical-cation on the porphyrin core. Electrochemistry and spectroelectrochemistry of both a naphthalenyl-substituted porphyrin and a porphyrin with a fused naphthalenyl group on the ?-ring system provide clear distinction between metal- and ring-centered processes. The redox reactivity of the naphthalenyl-substituted metalloporphyrin in nonaqueous media is presented while outlining the most important structural factors which influence the reversible half-wave potentials for oxidation and reduction of this complex and the following chemical reactions which lead to an extended ?-system. PMID:23895324

Chen, Ping; Fang, Yuanyuan; Kadish, Karl M; Lewtak, Jan P; Koszelewski, Dominik; Janiga, Anita; Gryko, Daniel T

2013-08-19

232

Role of nitric oxide in the coupling of myocardial oxygen consumption and coronary vascular dynamics during pregnancy in the dog.  

PubMed

We examined the ability of cardiac endothelial nitric oxide synthase (eNOS) to couple myocardial oxygen consumption (MVo(2)) and oxygen delivery during pregnancy. Awake dogs were studied using echocardiography before and at 40 days, 50 days, and 60 days (60D) of pregnancy and at approximately 14 days postpartum. Left ventricular eNOS, phosphorylated eNOS, and copper, zinc-superoxide dismutase (CuZnSOD or SOD-1) were determined by immunoblotting. MVO(2) of left ventricular tissue samples was measured in vitro in response to increasing doses of bradykinin, enalapril maleate, and amlodipine. We examined the changes in passive diameter and flow-dependant arteriolar dilation of coronary arterioles. Echocardiography indicated increases in cardiac output ( approximately 60%) during pregnancy. Myocardial eNOS (21 +/- 4%), phosphorylated eNOS (19 +/- 3%), and SOD-1 (61 +/- 2.7%) protein levels were significantly increased at 60D. Bradykinin, enalapril maleate, and amlodipine (10(-4) mol/l) decreased MVO(2) in a nitric oxide-dependant manner (by 24 +/- 1.3% in controls and 34 +/- 2.2% at 60D; by 21 +/- 1.1% in controls and 29 +/- 1.1 at 60D; and by 22 +/- 2.5% in controls and 26 +/- 1.0% at 60D, respectively). Arterioles from pregnant dogs showed increased flow-dependant dilation in response to increased shear stress and larger passive diameter. Nitrite production was stimulated by bradykinin and carbachol in microvessels in vitro; pregnancy enhanced nitrite release. Myocardial eNOS, phosphorylated eNOS, and SOD-1 protein expression are increased during pregnancy, and this increase is associated with enhanced nitric oxide-dependant control of MVO(2). Thus increases in eNOS and SOD-1 promote the coupling of oxygen delivery and efficiency in the heart during pregnancy. PMID:17644579

Williams, Jeffrey G; Rincon-Skinner, Tibisay; Sun, Dong; Wang, Zipping; Zhang, Suhua; Zhang, Xiaoping; Hintze, Thomas H

2007-10-01

233

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

PubMed

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

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

2014-08-01

234

Monolithic tandem solar cell  

DOEpatents

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

Wanlass, Mark W. (Golden, CO)

1994-01-01

235

Monolithic tandem solar cell  

DOEpatents

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

Wanlass, M.W.

1994-06-21

236

Negative tandem mirror  

SciTech Connect

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

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

1981-11-30

237

Tandem metal relay catalysis: from cyclopropene to polysubstituted furan.  

PubMed

Transmetalation is a key step in traditional coupling reactions. Herein we discuss the most recent progress in the metal-metal relay catalysis based on a transmetalation strategy. An efficient synthetic strategy for the formation of polysubstituted furan derivatives from cyclopropenes based on the tandem metal relay catalysis (TMRC reaction) is summarized. PMID:24962613

Song, Chuanling; Wang, Jianwu; Xu, Zhenghu

2014-08-21

238

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

239

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

240

Spin-flop coupling and exchange bias in embedded complex oxide micromagnets.  

PubMed

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. PMID:25166703

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

241

Inductively coupled plasma etching of hafnium-indium-zinc oxide using chlorine based gas mixtures  

NASA Astrophysics Data System (ADS)

We report the etching characteristics of a stacked hafnium-indium-zinc oxide (HIZO) with a photoresist using the gas mixture of chlorine and argon (Cl2/Ar). The etching behaviors of HIZO have been investigated in terms of a source power, a bias power and a chamber pressure. As the concentration of Cl2 was increased compared to pure Ar, the etch rate of HIZO film was found slightly different from that of indium-zinc oxide (IZO) film. Moreover, to investigate the etching mechanism systematically, various inspections were carried out such as atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) depending on the portion of Cl2. Additionally, we compared the etching mechanism of HIZO film with IZO film to confirm the difference of chemical bonds caused by the influence of hafnium doping.

Choi, Yong-Hee; Jang, Ho-Kyun; Jin, Jun-Eon; Joo, Min-Kyu; Piao, Mingxing; Shin, Jong Mok; Kim, Jae-Sung; Na, Junhong; Kim, Gyu Tae

2014-04-01

242

Nitric Oxide Formation in a Premixed Flame With High-Level Plasma Energy Coupling  

Microsoft Academic Search

This paper presents quantitative planar laser-induced fluorescence (PLIF) imaging of nitric oxide (NO) in a transient-arc direct-current plasmatron igniter using premixed air\\/fuel mixtures. Quantitative measurements of NO are reported as a function of gas flow rate (20-50 standard cubic feet per hour), plasma power (100-900 mA, 150-750 W), and equivalence ratio (0.7-1.3). Images were corrected for temperature effects by using

Xing Rao; Igor B. Matveev; Tonghun Lee

2009-01-01

243

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

244

Kinetics and Mechanisms of Oxidative Cleavage of HIV RRE RNA by Rev-Coupled Transition Metal Chelates.  

PubMed

Catalytic metallodrugs were used to oxidatively cleave HIV-1 Rev Response Element RNA (RRE RNA), and the mechanisms of RNA cleavage were studied using a combination of matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS), fluorescence spectroscopy, and gel electrophoresis. The metallodrugs, which contained combinations of the transition metals Fe(2+), Co(2+), Ni(2+), and Cu(2+) and the Rev-coupled chelators DOTA, DTPA, EDTA, NTA, tripeptide GGH, and tetrapeptide KGHK, bind to and cleave HIV RRE RNA through heretofore unknown oxidative mechanisms. The broad spectrum of metal catalysts and co-reagents provided a means for systematic variation of oxidative reactivity without significant perturbation of binding between catalyst and RNA. Detailed MS analyses were used to monitor formation of RNA fragments containing terminal 2',3'-cyclic phosphate (2',3'-cPO4), 3'-phosphate (3'-PO4), 3'-phosphoglycolate (3'-PG), 5'- hydroxyl (5'-OH), 5'- phosphate (5'-PO4) and other nascent overhangs at sites of cleavage. The distinct overhangs corresponded to distinct mechanisms of oxidative hydrogen-abstraction (H abstraction), hydrolysis, and/or endonucleolysis, allowing a dissection of the contributions of various mechanisms of oxidative cleavage. Rapid co-reactant- and catalyst-dependent formation of fragments containing terminal 3'-PG, 3'-PO4 and 5'-PO4 overhangs appeared to be initiated primarily by H abstraction events. The standard thiobarbituric acid (TBA) assay was employed herein in a novel usage to monitor the formation of base 2-hydroxypropenal products produced by 4'-H abstraction in RNA. Formation of an adduct with TBA was monitored by fluorescence, and its quantification correlated with the formation of 3'-PG monitored by MALDI-TOF MS, confirming oxidative 4'-H abstraction as a major mechanism of rapid catalyst-mediated cleavage of RRE RNA. Rapid formation of 3'-PO4 overhangs was most likely a result of 5'-H abstraction. Apparent rates of formation of 3'-PG (a unique product of 4'-H abstraction) at differing nucleotide positions within the RNA were used to triangulate probable 3D positions of metal centers and establish the distance-dependence of 4'-H abstraction for certain catalytic metallodrugs. PMID:23626900

Joyner, Jeff C; Keuper, Kevin D; Cowan, J A

2013-04-01

245

Loss measurement of oxidized porous silicon optical waveguides by nondestructive end-fire coupling  

NASA Astrophysics Data System (ADS)

The oxidised porous silicon channel waveguides were fabricated by controlling the illumination intensities and anodisation time during anodisation process is reported in this paper. By the technique combined the optimisation end-fire coupling and cut-back methods, the relatively exact results of measured propagation loss, endface' s scattering loss and the mode mismatching loss of oxidised porous silicon channel waveguides were 12.5.2dB/cm, 4.6dB and 3.1dB respectively.

Jia, Zhenhong

2002-08-01

246

Coupled reductive and oxidative sulfur cycling in the phototrophic plate of a meromictic lake.  

PubMed

Mahoney Lake represents an extreme meromictic model system and is a valuable site for examining the organisms and processes that sustain photic zone euxinia (PZE). A single population of purple sulfur bacteria (PSB) living in a dense phototrophic plate in the chemocline is responsible for most of the primary production in Mahoney Lake. Here, we present metagenomic data from this phototrophic plate--including the genome of the major PSB, as obtained from both a highly enriched culture and from the metagenomic data--as well as evidence for multiple other taxa that contribute to the oxidative sulfur cycle and to sulfate reduction. The planktonic PSB is a member of the Chromatiaceae, here renamed Thiohalocapsa sp. strain ML1. It produces the carotenoid okenone, yet its closest relatives are benthic PSB isolates, a finding that may complicate the use of okenone (okenane) as a biomarker for ancient PZE. Favorable thermodynamics for non-phototrophic sulfide oxidation and sulfate reduction reactions also occur in the plate, and a suite of organisms capable of oxidizing and reducing sulfur is apparent in the metagenome. Fluctuating supplies of both reduced carbon and reduced sulfur to the chemocline may partly account for the diversity of both autotrophic and heterotrophic species. Collectively, the data demonstrate the physiological potential for maintaining complex sulfur and carbon cycles in an anoxic water column, driven by the input of exogenous organic matter. This is consistent with suggestions that high levels of oxygenic primary production maintain episodes of PZE in Earth's history and that such communities should support a diversity of sulfur cycle reactions. PMID:24976102

Hamilton, T L; Bovee, R J; Thiel, V; Sattin, S R; Mohr, W; Schaperdoth, I; Vogl, K; Gilhooly, W P; Lyons, T W; Tomsho, L P; Schuster, S C; Overmann, J; Bryant, D A; Pearson, A; Macalady, J L

2014-09-01

247

Ultra high performance liquid chromatography with photodiode array detector and quadrupole time-of-flight tandem mass spectrometry coupled with discriminant analysis to evaluate Angelicae pubescentis radix from different regions.  

PubMed

A rapid and effective method was developed for the qualitative and quantitative analysis of the major chemical constituents in Angelicae pubescentis radix by ultra high performance liquid chromatography with photodiode array detection and quadrupole time-of-flight tandem mass spectrometry. The chromatographic separation was achieved on an ACQUITY UHPLC BEH C18 column (2.1 × 100 mm, 1.7 ?m). Nine phenolic acids, 30 coumarins, bisabolangelone, and adenosine were identified by quadrupole time-of-flight tandem mass spectrometry. All calibration curves exhibited good linearity (r > 0.9996) within the linear ranges. The relative standard deviation calculated for intraday and interday precision, stability, and accuracy were <5%. The mean recovery ranged from 95.8 to 106%. The overall limits of detection and quantification were 0.025-0.160 and 0.100-0.560 ?g/mL, respectively. Discriminant analysis was investigated as a method for evaluating the quality of the samples with 100% correction in their classification. The results demonstrated that the developed method could successfully be used to differentiate samples from different regions and could be a helpful tool for detection and confirmation of the quality of traditional Chinese medicines. PMID:25044521

Ge, Ai-Hua; Ma, Wen-Fang; Wang, Chun-Peng; Li, Jin; He, Jun; Liu, Er-Wei; Adelakum, Tiwalade Adegoke; Zhang, Bo-Li; Gao, Xiumei; Chang, Yan-Xu

2014-09-01

248

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

249

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

SciTech Connect

The electronic properties of Mott insulators realized in (111) bilayers of perovskite transition-metal oxides are studied. The low-energy effective Hamiltonians for such Mott insulators are derived in the presence of a strong spin-orbit coupling. These models are characterized by the antiferromagnetic Heisenberg interaction and the anisotropic interaction whose form depends on the $d$ orbital occupancy. From exact diagonalization analyses on finite clusters, the ground state phase diagrams are derived, including a Kitaev spin liquid phase in a narrow parameter regime for $t_{2g}$ systems. Slave-boson mean-field analyses indicate the possibility of novel superconducting states induced by carrier doping into the Mott-insulating parent systems, suggesting the present model systems as unique playgrounds for studying correlation-induced novel phenomena. Possible experimental realizations are also discussed.

Okamoto, Satoshi [ORNL

2013-01-01

250

Guanylyl cyclase is an ATP sensor coupling nitric oxide signaling to cell metabolism  

PubMed Central

Defending cellular integrity against disturbances in intracellular concentrations of ATP ([ATP]i) is predicated on coordinating the selection of substrates and their flux through metabolic pathways (metabolic signaling), ATP transfer from sites of production to utilization (energetic signaling), and the regulation of processes consuming energy (cell signaling). Whereas NO and its receptor, soluble guanylyl cyclase (sGC), are emerging as key mediators coordinating ATP supply and demand, mechanisms coupling this pathway with metabolic and energetic signaling remain undefined. Here, we demonstrate that sGC is a nucleotide sensor whose responsiveness to NO is regulated by [ATP]i. Indeed, ATP inhibits purified sGC with a Ki predicting >60% inhibition of NO signaling in cells maintaining physiological [nucleotide]i. ATP inhibits sGC by interacting with a regulatory site that prefers ATP > GTP. Moreover, alterations in [ATP]i, by permeabilization and nucleotide clamping or inhibition of mitochondrial ATP synthase, regulate NO signaling by sGC. Thus, [ATP]i serves as a “gain control” for NO signaling by sGC. At homeostatic [ATP]i, NO activation of sGC is repressed, whereas insults that reduce [ATP]i, derepress sGC and amplify responses to NO. Hence, sGC forms a key synapse integrating metabolic, energetic, and cell signaling, wherein ATP is the transmitter, allosteric inhibition the coupling mechanism, and regulated accumulation of cGMP the response. PMID:14684830

Ruiz-Stewart, I.; Tiyyagura, S. R.; Lin, J. E.; Kazerounian, S.; Pitari, G. M.; Schulz, S.; Martin, E.; Murad, F.; Waldman, S. A.

2004-01-01

251

Comment on 'Mechanism for the increase of indium-tin-oxide work function by O{sub 2} inductively coupled plasma treatment' [J. Appl. Phys. 95, 586 (2004)  

SciTech Connect

A high work function on indium tin oxide (ITO) surfaces with O{sub 2} inductively coupled plasma (ICP) treatment was obtained in the paper: 'Mechanism for the increase of indium tin oxide work function by O{sub 2} inductively coupled plasma treatment' [Lee et al., J. Appl. Phys. 95, 586 (2004)]. They attributed this to the higher work function of the larger upward band bending and the larger electron affinity of the ITO near the surface by the ICP treatment. In this Comment, we indicate the mistake in their analysis of the observed result by synchrotron radiation photoemission spectroscopy.

Lin, Yow-Jon [Institute of Photonics, National Changhua University of Education, Changhua 500, Taiwan (China)

2007-02-01

252

Covalently coupled hybrid of graphitic carbon nitride with reduced graphene oxide as a superior performance lithium-ion battery anode.  

PubMed

An in situ chemical synthetic approach has been designed for the fabrication of a covalently coupled hybrid consisting of graphitic carbon nitride (g-C3N4) with reduced graphene oxide (rGO) with differing g-C3N4/rGO ratio. The epoxy groups of graphene oxide (GO) undergo a nucleophilic substitution reaction with dicyandiamide (C2H4N4) to form the C2H4N4-GO composite via a covalent C-N bond, and then both the in situ polymerization of C2H4N4 and the thermal reduction of GO can be achieved at higher temperatures, forming the covalently coupled g-C3N4-rGO. FT-IR, CP-MAS NMR and XPS analyses, clearly revealed a covalent interaction between the g-C3N4 and rGO sheets. The g-C3N4-rGO exhibits an unprecedented high, stable and reversible capacity of 1525 mA h g(-1) at a current density of 100 mA g(-1) after 50 cycles. Even at a large current density of 1000 mA g(-1), a reversible capacity of 943 mA h g(-1) can still be retained. The superior electrochemical performance of g-C3N4-rGO is attributed to the specific characteristics of the unique nanostructure of g-C3N4-rGO and the concerted effects of g-C3N4 and rGO, including covalent interactions between the two moieties, the good conductivity and high special surface area of the nanocomposite, as well as the template effect of the planar amino group of g-C3N4 for the dispersed decoration of Li(+) ions. PMID:25180888

Fu, Yongsheng; Zhu, Junwu; Hu, Chong; Wu, Xiaodong; Wang, Xin

2014-10-01

253

Korean red ginseng inhibits arginase and contributes to endotheliumdependent vasorelaxation through endothelial nitric oxide synthase coupling.  

PubMed

Korean red ginseng water extract (KG-WE) has known beneficial effects on the cardiovascular system via inducting nitric oxide (NO) production in endothelium. Endothelial arginase inhibits the activity of endothelial nitric oxide synthase (eNOS) by substrate depletion, thereby reducing NO bioavailability and contributing to vascular diseases including hypertension, aging, and atherosclerosis. In the present study, we demonstrate that KG-WE inhibits arginase activity and negatively regulates NO production and reactive oxygen species generation in endothelium. This is associated with increased dimerization of eNOS without affecting the protein expression levels of either arginase or eNOS. In a vascular tension assay, when aortas isolated from wild type mice were incubated with KG-WE, NO-dependent enhanced vasorelaxation was observed. Furthermore, KG-WE administered via by drinking water to atherogenic model mice being fed high cholesterol diet improved impaired vascular function. Taken together, these results suggest that KG-WE may exert vasoprotective effects through augmentation of NO signaling by inhibiting arginase. Therefore, KG-WE may be useful in the treatment of vascular diseases derived from endothelial dysfunction, such as atherosclerosis. PMID:23717158

Shin, Woosung; Yoon, Jeongyeon; Oh, Goo Taeg; Ryoo, Sungwoo

2013-03-01

254

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

255

Deposition of nano-sized metal-oxide using inductively coupled plasma chemical vapor deposition (ICP-CVD) technique for gas sensors applications  

Microsoft Academic Search

We propose a unique single-source sol-gel ICP-CVD (inductively-coupled plasma chemical vapor deposition) system to synthesize nano-scale metal-oxide materials as sensing layers on silicon for fabrication into gas sensors. We intend to compare our results with the existing techniques such as sol-gel, RF sputtering. Our ICP-CVD system has an inductive couple matching at 13.56 MHz and the capability of sustaining up

A. Srivastava; O. K. Tan; L. K. Ang; M. S. Tse; Y. C. Lee

2002-01-01

256

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

257

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

258

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

259

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

260

Blends of stearyl poly(ethylene oxide) coupling-polymer in chitosan as coating materials for polyurethane intravascular catheters.  

PubMed

To optimize the surface biocompatibility of the intravascular catheter, an amphiphilic coupling-polymer of stearyl poly (ethylene oxide) -co- 4,4'-methylene diphenyl diisocyanate-co- stearyl poly (ethylene oxide), for short MSPEO, was specially designed as the surface modifying additive (SMA). The blend of MSPEO in chitosan was coated on the outer wall of the catheters by the dip-coating method. The surface analysis was carried out by ATR-FTIR and contact angle measurements. The surface enrichment of MSPEO was confirmed. On the water interface, the larger the molecular weight of PEO was, the higher the surface enrichment. While on air interface, the case was the contrary. Three kinds of static test of clotting time, plasma recalcification time (PRT), prothrombin time (PT), and thrombin time (TT), as well as the static platelet adhesion experiment were carried out. The results indicated that the coated surface could resist the clotting effectively. In order to test the blood-compatibility of the coated catheters under a shear of blood flow, the dynamic experiment was performed through a closed-loop tubular system with the shear rate of 1500 s(-1). The results of blood regular testing at six different times (0, 5,10, 20, 30, and 60 min) indicated that the biocompatibility of the coating was nearly ideal. Finally, the SMA-MSPEO was proved to be non-chronic-toxic by animal experiments with rats and suitable as a coating material for clinical use. PMID:11410895

Wang, D A; Ji, J; Sun, Y H; Yu, G H; Feng, L X

2001-01-01

261

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

262

Alkyl groups as synthetic vehicles in gold-mediated oxidative coupling reactions.  

PubMed

The use of surface-bound alkyl and phenyl groups as synthetic vehicles in coupling reactions on oxygen-activated Au(111) is demonstrated by the formation of ethers via alkyl and phenyl iodides. Ethers are formed by successive additions of surface-bound alkyl groups to adsorbed atomic oxygen to form first the alkoxy and then the ether. The addition of the ethyl group to adsorbed oxygen on Au(111) is the rate-limiting step leading to diethyl ether formation. Alkyl groups also add to adsorbed alkoxy groups formed from alcohols. An unusual feature of the alkyl iodide reactions on Au is that oxygen is not required for the activation step; hence, opening new potential reactive pathways on metallic Au. PMID:23340817

Xu, Bingjun; Madix, Robert J; Friend, Cynthia M

2013-03-01

263

A Critical Test of the “Tunneling and Coupled Motion” Concept in Enzymatic Alcohol Oxidation  

PubMed Central

The physical mechanism of C-H bond activation by enzymes is the subject of intense study and we have tested the predictions of two competing models for C-H activation in the context of alcohol dehydrogenase. The kinetic isotope effects (KIEs) in this enzyme have previously suggested a model of quantum mechanical tunneling and coupled motion of primary (1°) and secondary (2°) hydrogens. Here we measure the 2° H/T KIEs with both and H and D at the 1° position and find that the 2° KIE is significantly deflated with D-transfer, consistent with the predictions of recent Marcus-like models of H-transfer. The results suggest that the fast dynamics of H-tunneling result in a 1° isotope effect on the structure of the tunneling ready state: the trajectory of D-transfer goes through a shorter donor-acceptor distance than that of H-transfer. PMID:24020836

Roston, Daniel; Kohen, Amnon

2013-01-01

264

Great enhancement of photocatalytic activity of nitrogen-doped titania by coupling with tungsten oxide.  

PubMed

The TiO2-N-x%WO3 composite photocatalysts were prepared by introducing WO3 into nitrogen-doped TiO2. The composite catalysts present much higher photocatalytic activity than TiO2 and nitrogen-doped TiO2 under both ultraviolet and visible light irradiation. Diffuse reflectance UV-vis spectra, XPS analysis, and IR spectra show that the coordinated nitrogen species (or N-metal-O linkages) may contribute to the visible light photocatalytic activity. WO3 coupling increases the active nitrogen species and thus enhances the visible light activity of the composite photocatalysts. The superior activity of TiO2-N-x%WO3 composite photocatalysts upon UV light irradiation can be rationalized in terms of efficient charge separation and high adsorption affinity of WO3. PMID:16854147

Gao, Bifen; Ma, Ying; Cao, Yaan; Yang, Wensheng; Yao, Jiannian

2006-07-27

265

Manifold, bus support and coupling arrangement for solid oxide fuel cells  

DOEpatents

Individual, tubular solid oxide fuel cells (SOFCs) are assembled into bundles called a module within a housing, with a plurality of modules arranged end-to-end in a linear, stacked configuration called a string. A common set of piping comprised of a suitable high temperature resistant material (1) provides fuel and air to each module housing, (2) serves as electrically conducting buses, and (3) provides structural support for a string of SOFC modules. Ceramic collars are used to connect fuel and air inlet piping to each of the electrodes in an SOFC module and provide (1) electrical insulation for the current carrying bus bars and gas manifolds, (2) damping for the fuel and air inlet piping, and (3) proper spacing between the fuel and air inlet piping to prevent contact between these tubes and possible damage to the SOFC. 11 figs.

Parry, G.W.

1988-04-21

266

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

267

Manifold, bus support and coupling arrangement for solid oxide fuel cells  

DOEpatents

Individual, tubular solid oxide fuel cells (SOFCs) are assembled into bundles called a module within a housing, with a plurality of modules arranged end-to-end in a linear, stacked configuration called a string. A common set of piping comprised of a suitable high temperture resistant material (1) provides fuel and air to each module housing, (2) serves as electrically conducting buses, and (3) provides structural support for a string of SOFC modules. The piping thus forms a manfold for directing fuel and air to each module in a string and makes electrical contact with the module's anode and cathode to conduct the DC power generated by the SOFC. The piping also provides structureal support for each individual module and maintains each string of modules as a structurally integral unit for ensuring high strength in a large 3-dimensional array of SOFC modules. Ceramic collars are used to connect fuel and air inlet piping to each of the electrodes in an SOFC module and provide (1) electrical insulation for the current carrying bus bars and gas manifolds, (2) damping for the fuel and air inlet piping, and (3) proper spacing between the fuel and air inlet piping to prevent contact between these tubes and possible damage to the SOFC.

Parry, Gareth W. (East Windsor, CT)

1989-01-01

268

Control of ion species in inductively coupled oxidation plasma by inert gas mixing  

SciTech Connect

We have controlled and investigated the ion density ratio ([O{sup +}]/[O{sub 2}{sup +}]) in oxidation plasma by He and Xe mixing. The ion density ratio increases from 0.26 to 0.97 by He mixing, and decreases to 0.015 by Xe mixing. The ratio is a strong function of the electron density and electron temperature. When the other conditions are fixed, the ion density ratio is proportional to the electron density in all the cases: the He/O{sub 2} and Xe/O{sub 2} mixtures as well as pure O{sub 2} plasma. This may be due to the increase in the dissociation rate and the process of ionization from O to O{sup +}. The rate of increase in the ion density ratio with the electron density is different in the two cases: In the He/O{sub 2} mixture, the rate of increase is slightly higher than that in the pure O{sub 2} plasma. However, the rate is very low in the Xe/O{sub 2} mixture. In the Xe/O{sub 2} mixture, the ion density ratio is actually a strong function of the electron temperature rather than the electron density.

Bai, K. H.; Chang, H. Y. [Memory Division, Semiconductor Business, Samsung Electronics, San no. 16 Banwol - Ri, Taean-Eup, Hwasung-City, Gyeonggi-Do, 445-701 (Korea, Republic of); Department of Physics, Korea Advanced Institute of Science and Technology, Taejon 305-701 (Korea, Republic of)

2006-12-01

269

Using Coupled Mesoscale Experiments and Simulations to Investigate High Burn-Up Oxide Fuel Thermal Conductivity  

NASA Astrophysics Data System (ADS)

Nuclear energy is a mature technology with a small carbon footprint. However, work is needed to make current reactor technology more accident tolerant and to allow reactor fuel to be burned in a reactor for longer periods of time. Optimizing the reactor fuel performance is essentially a materials science problem. The current understanding of fuel microstructure have been limited by the difficulty in studying the structure and chemistry of irradiated fuel samples at the mesoscale. Here, we take advantage of recent advances in experimental capabilities to characterize the microstructure in 3D of irradiated mixed oxide (MOX) fuel taken from two radial positions in the fuel pellet. We also reconstruct these microstructures using Idaho National Laboratory's MARMOT code and calculate the impact of microstructure heterogeneities on the effective thermal conductivity using mesoscale heat conduction simulations. The thermal conductivities of both samples are higher than the bulk MOX thermal conductivity because of the formation of metallic precipitates and because we do not currently consider phonon scattering due to defects smaller than the experimental resolution. We also used the results to investigate the accuracy of simple thermal conductivity approximations and equations to convert 2D thermal conductivities to 3D. It was found that these approximations struggle to predict the complex thermal transport interactions between metal precipitates and voids.

Teague, Melissa C.; Fromm, Bradley S.; Tonks, Michael R.; Field, David P.

2014-10-01

270

Peroxidase-mediated oxidative coupling of 1-naphthol: characterization of polymerization products.  

PubMed

The oxidative polymerization of 1-naphthol was investigated in the presence of horseradish peroxidase (HRP). Naphthol polymerization products (NPP) were characterized for their relative polarity using octanol--water partitioning experiments and reverse-phase high pressure liquid chromatography, for structure using size exclusion chromatography and liquid chromatography-mass spectrometry (LC/MS), and for ecotoxicity using inhibition of bacterial bioluminescence. Peroxidase addition resulted in the production of soluble and insoluble NPP. Soluble NPP was predominantly more polar than the parent naphthol and comprised of trimers and tetramers. Insoluble NPP oligomers included dimers, trimers and tetramers. The net aqueous-phase toxicity was significantly reduced due to polymer formation and subsequent precipitation. A reaction model deduced from the LC/MS fragmentation patterns of trimeric naphthol was proposed for NPP formation. Results from this study suggest that HRP-mediated treatment of naphthol contaminated soils can achieve risk reduction through (i) the formation of large hydrophobic oligomers that are immobilized on the soil matrix; and (ii) reduction in aqueous-phase toxicity due to polymer precipitation. PMID:15949834

Xu, Fangxiang; Koch, David E; Kong, In Chul; Hunter, Robert P; Bhandari, Alok

2005-06-01

271

Cu-catalysed oxidative C-H/C-H coupling polymerisation of benzodiimidazoles: an efficient approach to regioregular polybenzodiimidazoles for blue-emitting materials.  

PubMed

The Cu-catalysed oxidative C-H/C-H coupling reaction of azoles has been used for the first time to develop polymerisation, which provides an efficient method for the preparation of polybenzodiimidazoles. These polymers exhibit high molecular weights, regioregularity, blue-emitting performance and thermal stability. PMID:25248306

Huang, Quan; Qin, Xurong; Li, Bijin; Lan, Jingbo; Guo, Qiang; You, Jingsong

2014-10-14

272

An ab Initio Study on the Oxidative Coupling of Methane over a Lithium-Doped MgO Catalyst: Surface Defects and Mechanism  

E-print Network

An ab Initio Study on the Oxidative Coupling of Methane over a Lithium-Doped MgO Catalyst: Surface catalyst. To elucidate the mechanism by which methyl radicals are produced and the active sites transportation of this fuel economically unreasonable.1 One means to exploit the remote gas sources is to first

Truong, Thanh N.

273

Transition metal oxides with the perovskite structure show a wide variety of physical properties. This is correlated with the strong coupling between the electrons and the  

E-print Network

Summary Transition metal oxides with the perovskite structure show a wide variety of physical properties. This is correlated with the strong coupling between the electrons and the crystal lattice physical limit. Therefore, further increase of the circuit density requires the consideration of other

Hille, Sander

274

Direct oxidative coupling of enamides and 1,3-dicarbonyl compounds: a facile and versatile approach to dihydrofurans, furans, pyrroles, and dicarbonyl enamides.  

PubMed

An efficient manganese(III)-mediated oxidative coupling reaction between ?-aryl enamides and 1,3-dicarbonyl compounds has been developed. A series of dihydrofurans and dicarbonyl enamides were synthesized in moderate to good yields. Moreover, these dihydrofurans could be readily transformed into the corresponding furans and pyrroles via the Paal-Knorr reaction. PMID:25369562

Li, Pan; Zhao, Jingjing; Xia, Chungu; Li, Fuwei

2014-11-21

275

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

276

Overview of the Applications of Tandem Mass Spectrometry (MS\\/MS) in Food Analysis of Nutritionally Harmful Compounds  

Microsoft Academic Search

Tandem mass spectrometry (MS\\/MS) has proved to be a useful and a time saving analytical tool, with many applications of direct detection of target molecules in food samples. When coupled with chromatographic techniques, it combines the separation capabilities of chromatography and the power of MS\\/MS as an identification and confirmation method. This article reviews the use of tandem mass spectrometry

Stamatia I. Kotretsou; Aglaia Koutsodimou

2006-01-01

277

Design and Growth of III-V on Si Microwire Array Tandem Solar Cells Christopher T. Chen1  

E-print Network

Design and Growth of III-V on Si Microwire Array Tandem Solar Cells Christopher T. Chen1 , Daniel B Abstract -- Tandem Ga1-xInxP/Si microwire array solar cells are a route towards a high efficiency, low cost, flexible, wafer- free solar technology. Coupled full-field optical and device physics simulations of a Ga0

Atwater, Harry

278

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

279

[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

280

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

281

Parallel extraction columns and parallel analytical columns coupled with liquid chromatography/tandem mass spectrometry for on-line simultaneous quantification of a drug candidate and its six metabolites in dog plasma.  

PubMed

A method with parallel extraction columns and parallel analytical columns (PEC-PAC) for on-line high-flow liquid chromatography/tandem mass spectrometry (LC/MS/MS) was developed and validated for simultaneous quantification of a drug candidate and its six metabolites in dog plasma. Two on-line extraction columns were used in parallel for sample extraction and two analytical columns were used in parallel for separation and analysis. The plasma samples, after addition of an internal standard solution, were directly injected onto the PEC-PAC system for purification and analysis. This method allowed the use of one of the extraction columns for analyte purification while the other was being equilibrated. Similarly, one of the analytical columns was employed to separate the analytes while the other was undergoing equilibration. Therefore, the time needed for re-conditioning both extraction and analytical columns was not added to the total analysis time, which resulted in a shorter run time and higher throughput. Moreover, the on-line column extraction LC/MS/MS method made it possible to extract and analyze all seven analytes simultaneously with good precision and accuracy despite their chemical class diversity that included primary, secondary and tertiary amines, an alcohol, an aldehyde and a carboxylic acid. The method was validated with the standard curve ranging from 5.00 to 5000 ng/mL. The intra- and inter-day precision was no more than 8% CV and the assay accuracy was between 95 and 107%. PMID:11746878

Xia, Y Q; Hop, C E; Liu, D Q; Vincent, S H; Chiu, S H

2001-01-01

282

Tandem Cylinder Noise Predictions  

NASA Technical Reports Server (NTRS)

In an effort to better understand landing-gear noise sources, we have been examining a simplified configuration that still maintains some of the salient features of landing-gear flow fields. In particular, tandem cylinders have been studied because they model a variety of component level interactions. The present effort is directed at the case of two identical cylinders spatially separated in the streamwise direction by 3.7 diameters. Experimental measurements from the Basic Aerodynamic Research Tunnel (BART) and Quiet Flow Facility (QFF) at NASA Langley Research Center (LaRC) have provided steady surface pressures, detailed off-surface measurements of the flow field using Particle Image Velocimetry (PIV), hot-wire measurements in the wake of the rear cylinder, unsteady surface pressure data, and the radiated noise. The experiments were conducted at a Reynolds number of 166 105 based on the cylinder diameter. A trip was used on the upstream cylinder to insure a fully turbulent shedding process and simulate the effects of a high Reynolds number flow. The parallel computational effort uses the three-dimensional Navier-Stokes solver CFL3D with a hybrid, zonal turbulence model that turns off the turbulence production term everywhere except in a narrow ring surrounding solid surfaces. The current calculations further explore the influence of the grid resolution and spanwise extent on the flow and associated radiated noise. Extensive comparisons with the experimental data are used to assess the ability of the computations to simulate the details of the flow. The results show that the pressure fluctuations on the upstream cylinder, caused by vortex shedding, are smaller than those generated on the downstream cylinder by wake interaction. Consequently, the downstream cylinder dominates the noise radiation, producing an overall directivity pattern that is similar to that of an isolated cylinder. Only calculations based on the full length of the model span were able to capture the complete decay in the spanwise correlation, thereby producing reasonable noise radiation levels.

Lockhard, David P.; Khorrami, Mehdi R.; CHoudhari, Meelan M.; Hutcheson, Florence V.; Brooks, Thomas F.; Stead, Daniel J.

2007-01-01

283

Enhanced Work Function of Al-Doped Zinc-Oxide Thin Films by Oxygen Inductively Coupled Plasma Treatment  

NASA Astrophysics Data System (ADS)

Al-doped zinc-oxide (AZO) thin films treated by oxygen and chlorine inductively coupled plasma (ICP) were compared. Kelvin probe (KP) and X-ray photoelectron spectroscopy (XPS) were employed to characterize the effect of treatment. The results of KP measurement show that the surface work function of AZO thin films can increase up to 5.92 eV after oxygen ICP (O-ICP)'s treatment, which means that the work function was increased by at least 1.1 eV. However, after the treatment of chlorine ICP (Cl-ICP), the work function increased to 5.44 eV, and the increment was 0.6 eV. And 10 days later, the work function increment was still 0.4 eV after O-ICP's treatment, while the work function after Cl-ICP's treatment came back to the original value only after 48 hours. The XPS results suggested that the O-ICP treatment was more effective than Cl-ICP for enhancing the work function of AZO films, which is well consistent with KP results.

Li, Zebin; Wu, Zhonghang; Ju, Jiaqi; He, Kongduo; Chen, Zhenliu; Yang, Xilu; Yan, Hang; Ou, Qiongrong; Liang, Rongqing

2014-01-01

284

Aerobic methane oxidation coupled to denitrification in a membrane biofilm reactor: treatment performance and the effect of oxygen ventilation.  

PubMed

Aerobic methane-oxidation coupled to denitrification (AME-D) process was successfully achieved in a membrane biofilm reactor (MBfR). PVDF membrane was employed to supply the methane and oxygen for biofilm, which was coexistence of methanotrophs and denitrifier. With a feeding NO3(-)-N of 30 mg/L, up to 97% nitrate could be removed stably. The oxygen ventilation modes impacted the denitrification performance remarkably, resulting in different nitrate removal efficiencies and biofilm microorganism distribution. The biofilm sludge showed a high resistance to the DO inhibition, mainly due to the co-existing methanotroph being capable of utilizing oxygen perferentially within biofilm, and create an anoxic micro-environment. The denitrification of both nitrate and nitrite by biofilm sludge conformed to the Monod equation, and the maximum specific nitrate utilization rate (k) ranged from 1.55 to 1.78 NO3(-)-N/g VSS-d. The research findings should be significant to understand the considerable potential of MBfR as a bioprocess for denitrification. PMID:23582221

Sun, Fei-yun; Dong, Wen-yi; Shao, Ming-fei; Lv, Xiao-mei; Li, Ji; Peng, Liang-yu; Wang, Hong-jie

2013-10-01

285

Infinitely high selective inductively coupled plasma etching of an indium tin oxide binary mask structure for extreme ultraviolet lithography  

SciTech Connect

Currently, extreme ultraviolet lithography (EUVL) is being investigated for next generation lithography. Among the core EUVL technologies, mask fabrication is of considerable importance due to the use of new reflective optics with a completely different configuration than those of conventional photolithography. This study investigated the etching properties of indium tin oxide (ITO) binary mask materials for EUVL, such as ITO (absorber layer), Ru (capping/etch-stop layer), and a Mo-Si multilayer (reflective layer), by varying the Cl{sub 2}/Ar gas flow ratio, dc self-bias voltage (V{sub dc}), and etch time in inductively coupled plasmas. The ITO absorber layer needs to be etched with no loss in the Ru layer on the Mo-Si multilayer for fabrication of the EUVL ITO binary mask structure proposed here. The ITO layer could be etched with an infinitely high etch selectivity over the Ru etch-stop layer in Cl{sub 2}/Ar plasma even with a very high overetch time.

Park, Y. R.; Ahn, J. H.; Kim, J. S.; Kwon, B. S.; Lee, N.-E.; Kang, H. Y.; Hwangbo, C. K.; Ahn, Jinho; Seo, Hwan Seok [School of Advanced Materials Science and Engineering, Center for Human Interface Nanotechnology, and Center for Advanced Plasma Surface Technology, Sungkyunkwan University, 300 Chunchun-dong, Suwon, Kyunggi-do 440-746 (Korea, Republic of); Department of Physics, Inha University, Yonghyen-dong, Nam-gu, Incheon 402-751 (Korea, Republic of); Department of Materials Science and Engineering, Hanyang University, Seoul 133-792 (Korea, Republic of); Photomask Team, Memory Division, Semiconductor Business, Samsung Electronics Co., Ltd., Banwol-dong, Hwaseong, Kyunggi-do 445-701 (Korea, Republic of)

2010-07-15

286

Experimental evidence for the formation of doubly charged oxide and hydroxide ions in inductively coupled plasma mass spectrometry.  

PubMed

The formation of doubly charged polyatomic ions in inductively coupled plasma mass spectrometers was investigated using commercially available instruments. The species observed were ThO2+ and ThOH2+, which were found in similar amounts with the different instruments used in this study, when operated under routine analytical conditions. The signal ratios for ThO2+ were between 1.8 x 10(-4) and 4.2 x 10(-4) relative to the singly charged elemental ion and between 1.4 x 10(-2) and 2.2 x 10(-2) relative to the doubly charged elemental ion. The formation of ThOH2+, was between 1.1 x 10(-4) and 2.8 x 10(-4) relative to the singly charged elemental ion and between 0.72 x 10(-2) and 1.3 x 10(-2) relative to the doubly charged elemental ion. A mechanism is proposed for the formation of the doubly charged oxide and hydroxide ions that is based on the condensation of the doubly charged elemental ion with water or oxygen molecules in the interface region of the mass spectrometer. PMID:11496975

Hattendorf, B; Günther, D

2001-07-01

287

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. PMID:23665858

Wu, Han-Chun; Mryasov, Oleg N.; Abid, Mohamed; Radican, Kevin; Shvets, Igor V.

2013-01-01

288

Covalently coupled hybrid of graphitic carbon nitride with reduced graphene oxide as a superior performance lithium-ion battery anode  

NASA Astrophysics Data System (ADS)

An in situ chemical synthetic approach has been designed for the fabrication of a covalently coupled hybrid consisting of graphitic carbon nitride (g-C3N4) with reduced graphene oxide (rGO) with differing g-C3N4/rGO ratio. The epoxy groups of graphene oxide (GO) undergo a nucleophilic substitution reaction with dicyandiamide (C2H4N4) to form the C2H4N4-GO composite via a covalent C-N bond, and then both the in situ polymerization of C2H4N4 and the thermal reduction of GO can be achieved at higher temperatures, forming the covalently coupled g-C3N4-rGO. FT-IR, CP-MAS NMR and XPS analyses, clearly revealed a covalent interaction between the g-C3N4 and rGO sheets. The g-C3N4-rGO exhibits an unprecedented high, stable and reversible capacity of 1525 mA h g-1 at a current density of 100 mA g-1 after 50 cycles. Even at a large current density of 1000 mA g-1, a reversible capacity of 943 mA h g-1 can still be retained. The superior electrochemical performance of g-C3N4-rGO is attributed to the specific characteristics of the unique nanostructure of g-C3N4-rGO and the concerted effects of g-C3N4 and rGO, including covalent interactions between the two moieties, the good conductivity and high special surface area of the nanocomposite, as well as the template effect of the planar amino group of g-C3N4 for the dispersed decoration of Li+ ions.An in situ chemical synthetic approach has been designed for the fabrication of a covalently coupled hybrid consisting of graphitic carbon nitride (g-C3N4) with reduced graphene oxide (rGO) with differing g-C3N4/rGO ratio. The epoxy groups of graphene oxide (GO) undergo a nucleophilic substitution reaction with dicyandiamide (C2H4N4) to form the C2H4N4-GO composite via a covalent C-N bond, and then both the in situ polymerization of C2H4N4 and the thermal reduction of GO can be achieved at higher temperatures, forming the covalently coupled g-C3N4-rGO. FT-IR, CP-MAS NMR and XPS analyses, clearly revealed a covalent interaction between the g-C3N4 and rGO sheets. The g-C3N4-rGO exhibits an unprecedented high, stable and reversible capacity of 1525 mA h g-1 at a current density of 100 mA g-1 after 50 cycles. Even at a large current density of 1000 mA g-1, a reversible capacity of 943 mA h g-1 can still be retained. The superior electrochemical performance of g-C3N4-rGO is attributed to the specific characteristics of the unique nanostructure of g-C3N4-rGO and the concerted effects of g-C3N4 and rGO, including covalent interactions between the two moieties, the good conductivity and high special surface area of the nanocomposite, as well as the template effect of the planar amino group of g-C3N4 for the dispersed decoration of Li+ ions. Electronic supplementary information (ESI) available: N species content (at%) of g-C3N4-rGO-1 based on XPS analysis; the first cycle discharge capacity, charge capacity and coulombic efficiency for the g-C3N4, rGO, and g-C3N4-rGO-n (n = 0.25, 0.5, 1, 2, 3) electrodes; nitrogen adsorption/desorption isotherm of g-C3N4; cycle performance of the g-C3N4-rGO-n (n = 0.25, 0.5, 3) electrodes at a current rate of 100 mA g-1 between 3.0 and 0.01 V versus Li+/Li. See DOI: 10.1039/c4nr03145h

Fu, Yongsheng; Zhu, Junwu; Hu, Chong; Wu, Xiaodong; Wang, Xin

2014-10-01

289

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

290

Interplay between spin-orbit coupling and Hubbard interaction in SrIrO3 and related Pbnm perovskite oxides  

NASA Astrophysics Data System (ADS)

There has been a rapidly growing interest in the interplay between spin-orbit coupling (SOC) and the Hubbard interaction U in correlated materials. A current consensus is that the stronger the SOC, the smaller is the critical interaction Uc required for a spin-orbit Mott insulator, because the atomic SOC splits a band into different total angular momentum bands, narrowing the effective bandwidth. It was further claimed that at large enough SOC, the stronger the SOC, the weaker the Uc, because in general the effective SOC is enhanced with increasing electron-electron interaction strength. Contrary to this expectation, we find that, in orthorhombic perovskite oxides (Pbnm), the stronger the SOC, the bigger the Uc. This originates from a line of Dirac nodes in Jeff=1/2 bands near the Fermi level, inherited from a combination of the lattice structure and a large SOC. Due to this protected line of nodes, there are small hole and electron pockets in SrIrO3, and such a small density of states makes the Hubbard interaction less efficient in building a magnetic insulator. The full phase diagram in U vs SOC is obtained, where nonmagnetic semimetal, magnetic metal, and magnetic insulator are found. Magnetic ordering patterns beyond Uc are also presented. We further discuss implications of our finding in relation to other perovskites such as SrRhO3 and SrRuO3.

Zeb, M. Ahsan; Kee, Hae-Young

2012-08-01

291

Insulin acutely improves mitochondrial function of rat and human skeletal muscle by increasing coupling efficiency of oxidative phosphorylation.  

PubMed

Insulin is essential for the regulation of fuel metabolism and triggers the uptake of glucose by skeletal muscle. The imported glucose is either stored or broken down, as insulin stimulates glycogenesis and ATP synthesis. The mechanism by which ATP production is increased is incompletely understood at present and, generally, relatively little functional information is available on the effect of insulin on mitochondrial function. In this paper we have exploited extracellular flux technology to investigate insulin effects on the bioenergetics of rat (L6) and human skeletal muscle myoblasts and myotubes. We demonstrate that a 20-min insulin exposure significantly increases (i) the cell respiratory control ratio, (ii) the coupling efficiency of oxidative phosphorylation, and (iii) the glucose sensitivity of anaerobic glycolysis. The improvement of mitochondrial function is explained by an insulin-induced immediate decrease of mitochondrial proton leak. Palmitate exposure annuls the beneficial mitochondrial effects of insulin. Our data improve the mechanistic understanding of insulin-stimulated ATP synthesis, and reveal a hitherto undisclosed insulin sensitivity of cellular bioenergetics that suggests a novel way of detecting insulin responsiveness of cells. PMID:24212054

Nisr, Raid B; Affourtit, Charles

2014-02-01

292

Oxidative coupling of tyrosine and ferulic acid residues: Intra- and extra-protoplasmic occurrence, predominance of trimers and larger products, and possible role in inter-polymeric cross-linking  

Microsoft Academic Search

I discuss the range of oxidative phenolic coupling products formed from the tyrosine residues of cell wall glycoproteins and from the feruloyl residues of wall polysaccharides possibly by the action of peroxidases and\\/or laccases. In the cases of both tyrosine- and ferulate-coupling, the coupling products are not confined to dimers but include trimers and probably higher oligomers, which are sometimes

Stephen C. Fry

2004-01-01

293

R&D issues in scale-up and manufacturing of amorphous silicon tandem modules  

SciTech Connect

R & D on amorphous silicon based tandem junction devices has improved the throughtput, the material utilization, and the performance of devices on commercial tin oxide coated glass. The tandem junction technology has been scaled-up to produce 8.6&hthinsp;Ft{sup 2} monolithically integrated modules in manufacturing at the TF1 plant. Optimization of performance and stability of these modules is ongoing. {copyright} {ital 1999 American Institute of Physics.}

Arya, R.R.; Carlson, D.E.; Chen, L.F.; Ganguly, G.; He, M.; Lin, G.; Middya, R.; Wood, G.; Newton, J.; Bennett, M.; Jackson, F.; Willing, F. [Solarex, a Business Unit of Amoco/Enron Solar, 826 Newtown-Yardley Road, Newtown, Pennsylvania 18940 (United States)

1999-03-01

294

Facile synthesis of halogenated spiroketals via a tandem iodocyclization.  

PubMed

A strategy for the synthesis of spiroketal compounds through a tandem iodocyclization of 1-(2-ethynylphenyl)-4-hydroxybut-2-yn-1-one derivatives is presented. This reaction could proceed under very mild conditions in a short time and avoid the use of expensive and toxic metal catalysts. Moreover, the resulting halides can be further exploited by subsequent palladium-catalyzed coupling reactions, which act as the important intermediates for building other valuable compounds. PMID:24697268

Wang, Jia; Zhu, Hai-Tao; Li, Ying-Xiu; Wang, Li-Jing; Qiu, Yi-Feng; Qiu, Zi-Hang; Zhong, Mei-jin; Liu, Xue-Yuan; Liang, Yong-Min

2014-04-18

295

Automatic Quality Assessment of Peptide Tandem Mass Spectra  

Microsoft Academic Search

Motivation: A powerful proteomics methodology couples high-performance liquid chromatography (HPLC) with tandem mass spectrometry and database-search software, such as SEQUEST. Such a set-up, however, produces a large num- ber of spectra, many of which are of too poor quality to be useful. Hence a filter that eliminates poor spectra before the database search can significantly improve throughput and robustness. Moreover,

Marshall W. Bern; David Goldberg; W. Hayes Mcdonald; John R. Yates III

2004-01-01

296

Carbon nanomaterials as charge collectors in dye sensitized solar cells and tandems  

NASA Astrophysics Data System (ADS)

This research has set out to understand the physical and electrochemical properties of carbon nanomaterials as charge collector, catalyst and energy transfer induced redox couple modifier in dye sensitized solar cells, which may one day be a major source of electric power generation. This research focuses on (1) characterizing the use of carbon nanotubes, both single walled and multi walled, as catalyst and charge carrier collector (2) improving the performance of the carbon nanotubes with modification by graphene, and various doping (3) testing 2-d carbon nanomaterials, such as graphene and few layer graphene nanoribbons, characterizing an interesting new side effect of photobleaching the iodide/triiodide redox couple, and (4) using the flexibility of dry spun carbon nanotubes sheets and carbon nanotubes sheets for tandem structures and novel fiber architecture. A major motivation in using carbon nanostructures in dye sensitized solar cells is that the standard dye solar cell uses platinum coated on a transparent conductive oxide as the counter electrode. Platinum, a rare and costly metal, is subject to scarcity issues. With proper application, the single walled carbon nanotubes mats could be used for as a substitute that would give efficiencies equivalent to the reference dye solar cells with platinum, and the dry spun multi-walled carbon nanotubes were capable of achieving performance equivalent to platinum with mild doping and nanomaterials additives. The novel architectural design work performed here used these multi-walled carbon nanotubes taken in the form of dry spun sheets. The sheet, possessing a structure of its own, obviates the need for solution processing to create films, which allows it to be used for architectures that demand a freestanding sheet of carbon nanotubes or drawn into a fiber of bundled carbon nanotubes. These freestanding carbon nanotubes were used specifically for the tandem devices and the proposed fiber-based dye solar cells.

Velten, Josef Aaron

297

Reduction of Matrix-Induced Oxide Interferences on Rare Earth Elements and Platinum Using a Desolvating Nebulizer System with Quadrupole Inductively Coupled Plasma Mass Spectrometry  

NASA Astrophysics Data System (ADS)

This paper will examine the use of a specialized low-flow desolvating nebulizer system for reduction of oxide mass spectral interferences that can occur in quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS). This nebulizer system uses an inert low-flow nebulizer (100 microliters/min) coupled to an inert, heated membrane desolvator for efficient water vapor removal before sample aerosol injection to the Q-ICP-MS instrument. Water vapor from conventional nebulizer / spray chamber systems used with Q-ICP-MS can cause numerous mass spectral interferences. One general example is metal oxides formed from the combination of oxygen (from injected water) with sample matrix components. Two specific examples of metal oxide interferences will be investigated with and without membrane desolvation: Ba and Ce oxides on several low-mass rare earth elements (Sm, Eu, and Gd) and Hf oxides on platinum. Rare earth elements are critically important components of modern electronics (ex. magnets, lasers, cell phones, computers) and platinum is a widely used catalyst. Figures of merit for both a conventional nebulizer/spray chamber and the desolvating nebulizer systems will include operating conditions, interference intensities and reduction factors, background equivalent concentrations (BECs), and instrument detection limits (IDLs).

Smith, F.

2013-12-01

298

Assessing the kinetics of high temperature oxidation of Inconel 617 in a dedicated HTR impure helium facility coupling thermogravimetry and gas phase chromatography  

NASA Astrophysics Data System (ADS)

A new facility coupling thermogravimetric analysis (TGA) with gas phase chromatography (GPC) has been developed. This facility is dedicated for studying high temperature oxidation of Inconel 617 in impure helium environment containing H2O, H2 and CO at very low partial pressures (in the Pa range), which is representative of the high temperature reactor (HTR) concept developed within the Generation IV Forum. Simultaneous acquisition of mass gain and gas composition has allowed the influence of carbon monoxide and water vapour on the kinetics of oxidation to be studied. GPC measurements of gas consumption have allowed the plotting of individual mass gain curves for oxidation by H2O and CO. During isothermal exposure at 1123 K for 20 h, the oxidation was mainly due to water vapour with a minor contribution of carbon monoxide during the first hours. The contribution of water vapour to the oxidation kinetics was extracted. It was shown to obey a complete parabolic law and to be limited by an interfacial reaction during the first few hours of oxidation and to be controlled by a mixed interfacial and diffusion process, diffusion becoming the rate-determining step for long term oxidation. There was very good agreement between GPC measurements and the experimental TGA results.

Chapovaloff, J.; Rouillard, F.; Combrade, P.; Pijolat, M.; Wolski, K.

2013-10-01

299

Simultaneous determination of oxathiapiprolin and two metabolites in fruits, vegetables and cereal using a modified quick, easy, cheap, effective, rugged, and safe method and liquid chromatography coupled to tandem mass spectrometry.  

PubMed

An effective and rapid analytical method for the simultaneous determination of a new fungicide oxathiapiprolin and its metabolites (IN-E8S72 and IN-WR791) residues in fruits (grape, watermelon, watermelon peel), vegetables (cucumber, tomato, potato) and cereal (wheat) was developed by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) using the modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction concept. Three target compounds were extracted from all matrices with 1% (V/V) formic acid aqueous solution and acetonitrile then cleaned by dispersive solid phase extraction (dSPE) with octadecylsilane (C18) and graphitized carbon black (GCB). The determination of the target compounds was achieved within a 5.1min run time by using an UPLC HSS T3 column connected to an electrospray ionization source (ESI, positive ion mode) for oxathiapiprolin and the negative mode for the two metabolites. The method showed excellent linearity (R(2)>0.9904) for target compounds. The limit of detection (LOD) for the three compounds ranged from 0.5?gkg(-1) to 7.5?gkg(-1) and the limits of quantitation (LOQ) were 1?gkg(-1) and 10?gkg(-1) for oxathiapiprolin and the metabolites, respectively. The mean recoveries from seven matrices ranged from 81.5 to 110.7%, with intra-day relative standard deviations (RSDr) in the range of 0.8-12.0% for all three test compounds. The inter-day RSDR were less than 14.5% for all of the recovery tests. The method was successfully applied for simultaneous analysis of oxathiapiprolin and its metabolites in actual trial samples, indicating its effectiveness in investigating oxathiapiprolin and its metabolites in the food. PMID:24440097

Wu, Xiaohu; Xu, Jun; Dong, Fengshou; Liu, Xingang; Li, Yuanbo; Zheng, Yongquan

2014-02-14

300

Evaluation of laser diode thermal desorption (LDTD) coupled with tandem mass spectrometry (MS/MS) for support of in vitro drug discovery assays: increasing scope, robustness and throughput of the LDTD technique for use with chemically diverse compound libraries.  

PubMed

Within the drug discovery environment, the key process in optimising the chemistry of a structural series toward a potential drug candidate is the design, make and test cycle, in which the primary screens consist of a number of in vitro assays, including metabolic stability, cytochrome P450 inhibition, and time-dependent inhibition assays. These assays are often carried out using multiple drug compounds with chemically diverse structural features, often in a 96 well-plate format for maximum time-efficiency, and are supported using rapid liquid chromatographic (LC) sample introduction with a tandem mass spectrometry (MS/MS) selected reaction monitoring (SRM) endpoint, taking around 6.5 h per plate. To provide a faster time-to-decision at this critical point, there exists a requirement for higher sample throughput and a robust, well-characterized analytical alternative. This paper presents a detailed evaluation of laser diode thermal desorption (LDTD), a relatively new ambient sample ionization technique, for compound screening assays. By systematic modification of typical LDTD instrumentation and workflow, and providing deeper understanding around overcoming a number of key issues, this work establishes LDTD as a practical, rapid alternative to conventional LC-MS/MS in drug discovery, without need for extensive sample preparation or expensive, scope-limiting internal standards. Analysis of both the five and three cytochrome P450 competitive inhibition assay samples by LDTD gave improved sample throughput (0.75 h per plate) and provided comparable data quality as the IC?? values obtained were within 3 fold of those calculated from the LC-MS/MS data. Additionally when applied generically to a chemically diverse library of over 250 proprietary compounds from the AstraZeneca design, make and test cycle, LDTD demonstrated a success rate of 98%. PMID:22071442

Beattie, Iain; Smith, Aaron; Weston, Daniel J; White, Peter; Szwandt, Simon; Sealey, Laura

2012-02-01

301

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 11.0 ng/mL (plasma) and 0.1 ng/3 × 10(6) cells (PBMCs). The calibrated ranges were linear for vorinostat in plasma 11.0-1100 (11,000) ng/mL (metabolites) and PBMCs 0.1-10.0 ng/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

302

Status of tandem-mirror confinement  

NASA Astrophysics Data System (ADS)

Recent end-stopping experiments in TMX-Upgrade show strong plugging of the central cell by lower-density plugs, requiring both electron-cyclotron heating (ECRH) and 470 neutral-beam injection, consistent with the thermal-barrier concept. These experiments have low density (n 10 to the 12th power/cu cm) due to inefficient ECRH power coupling. Hot-ion and hot-electron buildup are consistent with Fokker-Planck calculations. No ion-cyclotron activity is observed in the plugs; occasional electron-cyclotron activity is observed. With plugging, axial lifetimes (tau/sub parallel/ 40 ms) are larger than radial (tau/sub perpendicular/ = 5 to 10 ms) due to observed non-ambipolar ion transport. Recent tandem-mirror theoretical activities are also surveyed.

Baldwin, D. E.

1983-08-01

303

CHARACTERIZATION OF DOXYLAMINE AND PYRILAMINE METABOLITES VIA THERMOSPRAY/MASS SPECTROMETRY AND TANDEM MASS SPECTROMETRY  

EPA Science Inventory

Analysis of doxylamine N-oxide and pyrilamine N-oxide as synthetic standards and biologically derived metabolites by thermospray mass spectrometry (TSP/MS) provided (M + H)+ ions for each metabolite. TSP/tandem mass spectrometry (TSP/MS/MS) of the (M + H)+ ions provided fragment ...

304

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

305

Metal-free Mizoroki-Heck type reaction: a radical oxidative coupling reaction of 2-chloro-dithiane with substituted olefins.  

PubMed

An efficient metal-free Mizoroki-Heck type reaction of di- and tri-substituted alkenes with 2-chloro-dithiane has been developed under ambient pressure of air or using a relatively low loading of BF3·Et2O. This study represents a new environmentally friendly method for the syntheses of dithianyl-substituted alkene derivatives via a radical oxidative coupling process. PMID:25268652

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

2014-11-21

306

Facile preparation of Pd nanoparticles supported on single-layer graphene oxide and application for the Suzuki-Miyaura cross-coupling reaction.  

PubMed

Pd nanoparticles supported on single layer graphene oxide (Pd-slGO) were prepared by gentle heating of palladium(ii) acetate (Pd(OAc)2) and GO in ethanol that served as a mild reductant of the Pd precursor. Pd-slGO showed a high catalytic performance (TON and TOF = 237?000) in the Suzuki-Miyaura cross-coupling reaction. PMID:24838740

Yamamoto, Shun-ichi; Kinoshita, Hiroshi; Hashimoto, Hideki; Nishina, Yuta

2014-06-21

307

Flow injection-spectrophotometeric determination of some catecholamine drugs in pharmaceutical preparations via oxidative coupling reaction with p-toluidine and sodium periodate  

Microsoft Academic Search

A new spectrophotometric flow injection method has been established for the determination of some catecholamine drugs (methyl dopa I, dopamine.HCl II and adrenaline III). The method is based on the oxidative coupling reaction of catecholamine with p-toluidine and sodium periodate to form an orange water-soluble dye product that has a maximum absorption at 480nm. Linearity was observed in the range

Loay K. Abdulrahman; Anas M. Al-Abachi; Mayada H. Al-Qaissy

2005-01-01

308

Modeling the high-temperature catalytic partial oxidation of methane over platinum gauze: Detailed gas-phase and surface chemistries coupled with 3D flow field simulations  

Microsoft Academic Search

The high-temperature catalytic partial oxidation (CPO) of methane over a platinum gauze reactor was modeled by three-dimensional numerical simulations of the flow field coupled with heat transport as well as detailed gas-phase and surface reaction mechanisms. Model results agree well with data of CPO experiments over Pt-gauzes in the literature, confirming the presence of strong mass and heat-transport limitations. The

Raúl Quiceno; Javier Pérez-Ramírez; Jürgen Warnatz; Olaf Deutschmann

2006-01-01

309

Oxidative coupling of alkenes with amides using peroxides: selective amide C(sp3)-H versus C(sp2)-H functionalization.  

PubMed

A new oxidative coupling of unactivated terminal alkenes with amides using peroxides is described, in which mono- and difunctionalization of alkenes are selectively achieved. In this reaction with amides, the chemoselectivity toward the functionalization of the C(sp(3))-H bonds adjacent to the nitrogen atom or the functionalization of the carbonyl C(sp(2))-H bonds across alkenes relies on the reaction conditions. PMID:25212419

Yang, Xu-Heng; Wei, Wen-Ting; Li, Hai-Bing; Song, Ren-Jie; Li, Jin-Heng

2014-11-01

310

Oxidative coupling of methane over Li\\/Sn\\/MgO catalysts. Use of a fluidized bed reactor at low gas velocities  

Microsoft Academic Search

A fluidized bed reactor has been used to carry out methane oxidative coupling (MOC) over a Li\\/Sn\\/MgO catalyst. The influence of the operating conditions (CH4\\/O2 ratio, total flowrate, temperature, particle size) has been studied, with most of the experiments concentrated in the region of low fluidizing velocities. In this work, hydrocarbon yields around 20% have been obtained, which are among

A. Santos; M. Menéndez; J. Santamaría

1997-01-01

311

Quantitative analysis of the novel anticancer drug ABT-518, a matrix metalloproteinase inhibitor, plus the screening of six metabolites in human plasma using high-performance liquid chromatography coupled with electrospray tandem mass spectrometry.  

PubMed

A liquid chromatographic/tandem mass spectrometric (LC/MS/MS) assay for the quantitative analysis of the novel anticancer drug ABT-518 and the screening of six potential metabolites in human plasma has been developed and validated to support a phase I study with the drug. ABT-518 is an inhibitor of matrix metalloproteinases, which are associated with tumor growth and development of metastasis. Plasma samples were prepared for analysis using a simple solid-phase extraction method on phenyl cartridges. LC separation was performed on a Zorbax extend C18 column (150 x 2.1 mm i.d., 5 microm particle size) using a mobile phase of methanol-aqueous 10 mM ammonium hydroxide (80:20, v/v) pumped at a flow-rate of 0.2 ml min(-1). An API2000 triple-quadrupole mass spectrometer was used for specific and sensitive detection. The best chromatographic speed (total run time 8 min) and peak shapes were obtained by employing an alkaline mobile phase (pH in aqueous phase approximately 10). Furthermore, an alkaline eluent was favored in order to obtain a better overall sensitivity for the protonated analytes. The dynamic range was from 10 to 1000 ng ml(-1) from 500 microl of plasma for ABT-518 and the metabolites were detected at levels of the same order of magnitude. Inter-assay accuracies for ABT-518 at five concentration levels were between -9.24 and 6.93% and inter-assay precisions were always <10.7%. Analyte stability was not critical during either storage or processing. This method was successfully applied in a phase I clinical study of ABT-518. The active drug, ABT-518, and all of the metabolites included in the assay could be identified in plasma from dosed patients. We believe that the method described in this paper using an alkaline mobile phase in combination with a basic stable analytical column may also be generally useful for the bioanalysis of other basic drugs. PMID:15039935

Stokvis, E; Rosing, H; Crul, M; Rieser, M J; Heck, A J R; Schellens, J H M; Beijnen, J H

2004-03-01

312

Improved tandem mirror fusion reactor  

Microsoft Academic Search

It is shown that the introduction of barrier potentials between the plugs and solenoid of a tandem mirror substantially reduce ion energy and density required in end plugs. Several means for creating barriers and some of the important physics issues are discussed.

D. E. Baldwin; B. G. Logan

1979-01-01

313

The nano-bio interface mapped by oxidative footprinting of the adsorption sites of myoglobin.  

PubMed

Oxidative footprinting has been used to study the structure of macromolecular assemblies such as protein-protein and protein-ligand complexes. We propose a novel development of this technique to probe the protein corona that forms at the surface of nanoparticles in any biological medium. Indeed, very few techniques allow studying this interface at the molecular and residue level. Based on hydroxyl radical-mediated oxidation of proteins and analysis by nanoscale liquid chromatography coupled to tandem mass spectrometry (nanoLC-MS/MS), two sites of adsorption of myoglobin on silica nanoparticles are identified. This method gives new insights in the understanding of protein adsorption on nanomaterials. PMID:25245420

Devineau, Stéphanie; Mathé, Christelle; Legros, Véronique; Gonnet, Florence; Daniel, Régis; Renault, Jean Philippe; Pin, Serge

2014-12-01

314

Multi-residue monitoring for the simultaneous determination of five nitrofurans (furazolidone, furaltadone, nitrofurazone, nitrofurantoine, nifursol) in poultry muscle tissue through the detection of their five major metabolites (AOZ, AMOZ, SEM, AHD, DNSAH) by liquid chromatography coupled to electrospray tandem mass spectrometry--in-house validation in line with Commission Decision 657/2002/EC.  

PubMed

Following the ban of four nitrofurans in the mid-90s (furazolidone, furaltadone, nitrofurantoine, nitrofurazone), the nifursol, a veterinary drug from the nitrofuran class of antibacterials which has been used prophylactically as feed additive for treating turkeys against histomoniasis (blackhead disease) was also declared in Annex IV of the European Union Directive no. 90/2377/EC in 2002 according to the Regulation no. 1756/2002/EC. As for the four other nitrofurans, nifursol disappears from tissues within a few days after treatment of food-producing animals. But toxic metabolites are still present for longer periods (several weeks or even months). The major metabolite that can readily be monitored in the tissues following nifursol abuse is the 3,5-dinitro-salicylic acid hydrazine (DNSAH). This article displays some improvements and the revalidation of the analytical method by liquid chromatography coupled to electrospray tandem mass spectrometry (LC-esiMS/MS) already in use in our laboratory for monitoring nitrofuran metabolites but also including the nifursol metabolite at the confirmatory minimum required performance level (MRPL) of 1 microg kg(-1). The validation is applied both to artificially and to naturally incurred turkey muscle. PMID:17386733

Verdon, Eric; Couedor, Pierrick; Sanders, Pascal

2007-03-14

315

Oxygen-coupled redox regulation of the skeletal muscle ryanodine receptor/Ca2+ release channel (RyR1): sites and nature of oxidative modification.  

PubMed

In mammalian skeletal muscle, Ca(2+) release from the sarcoplasmic reticulum (SR) through the ryanodine receptor/Ca(2+)-release channel RyR1 can be enhanced by S-oxidation or S-nitrosylation of separate Cys residues, which are allosterically linked. S-Oxidation of RyR1 is coupled to muscle oxygen tension (pO2) through O2-dependent production of hydrogen peroxide by SR-resident NADPH oxidase 4. In isolated SR (SR vesicles), an average of six to eight Cys thiols/RyR1 monomer are reversibly oxidized at high (21% O2) versus low pO2 (1% O2), but their identity among the 100 Cys residues/RyR1 monomer is unknown. Here we use isotope-coded affinity tag labeling and mass spectrometry (yielding 93% coverage of RyR1 Cys residues) to identify 13 Cys residues subject to pO2-coupled S-oxidation in SR vesicles. Eight additional Cys residues are oxidized at high versus low pO2 only when NADPH levels are supplemented to enhance NADPH oxidase 4 activity. pO2-sensitive Cys residues were largely non-overlapping with those identified previously as hyperreactive by administration of exogenous reagents (three of 21) or as S-nitrosylated. Cys residues subject to pO2-coupled oxidation are distributed widely within the cytoplasmic domain of RyR1 in multiple functional domains implicated in RyR1 activity-regulating interactions with the L-type Ca(2+) channel (dihydropyridine receptor) and FK506-binding protein 12 as well as in "hot spot" regions containing sites of mutation implicated in malignant hyperthermia and central core disease. pO2-coupled disulfide formation was identified, whereas neither S-glutathionylated nor sulfenamide-modified Cys residues were observed. Thus, physiological redox regulation of RyR1 by endogenously generated hydrogen peroxide is exerted through dynamic disulfide formation involving multiple Cys residues. PMID:23798702

Sun, Qi-An; Wang, Benlian; Miyagi, Masaru; Hess, Douglas T; Stamler, Jonathan S

2013-08-01

316

Static and dynamic aspects of coupling between creep behavior and oxidation on MC2 single crystal superalloy at 1150 °C  

Microsoft Academic Search

Creep tests were performed on thin wall specimens made of MC2 single crystal superalloy at 1150 °C and under controlled atmosphere. The results highlight the deleterious oxidation effect on creep properties. The assumption that oxidation leads to a non-load-bearing affected zone is insufficient to explain the difference in creep rate that was noticed between tests performed under synthetic air and

Sébastien Dryepondt; Daniel Monceau; Fabrice Crabos; Eric Andrieu

2005-01-01

317

Tandem hemodialysis and plasma exchange.  

PubMed

The combination of hemodialysis and plasma exchange as one tandem procedure was first described in 1999 by Siami et al. (ASAIO J 45:229-233), but larger pediatric case series were not described until 2012. Even in adults, there are only limited case series. If performed in sequence, up to 8 h of treatment time may be required. With the use of the tandem procedure in stable patients, the same procedures can be completed during the same time as a routine hemodialysis, which is more convenient for patients and may reduce healthcare costs. Little is known about the utilization of the combination of hemodialysis and plasma exchange in children. The purpose of this review is to summarize the adult and scarce pediatric experience. The results of a survey carried out by the authors using the Internet listserver "PedNeph" to obtain an overview of the current practice patterns of pediatric nephrologists are also presented. PMID:24022368

Filler, Guido; Clark, William F; Huang, Shih-Han S

2014-11-01

318

Single solid phase extraction method for the simultaneous analysis of polar and non-polar pesticides in urine samples by gas chromatography and ultra high pressure liquid chromatography coupled to tandem mass spectrometry.  

PubMed

A new multiresidue method has been developed and validated for the simultaneous extraction of more than two hundred pesticides, including non-polar and polar pesticides (carbamates, organochlorine, organophosphorous, pyrethroids, herbicides and insecticides) in urine at trace levels by gas and ultra high pressure liquid chromatography coupled to ion trap and triple quadrupole mass spectrometry, respectively (GC-IT-MS/MS, UHPLC-QqQ-MS/MS). Non-polar and polar pesticides were simultaneously extracted from urine samples by a simple and fast solid phase extraction (SPE) procedure using C(18) cartridges as sorbent, and dichloromethane as elution solvent. Recovery was in the range of 60-120%. Precision values expressed as relative standard deviation (RSD) were lower than 25%. Identification and confirmation of the compounds were performed by the use of retention time windows, comparison of spectra (GC-amenable compounds) or the estimation of the ion ratio (LC-amenable compounds). For GC-amenable pesticides, limits of detection (LODs) ranged from 0.001 to 0.436 ?g L(-1) and limits of quantification (LOQs) from 0.003 to 1.452 ?g L(-1). For LC-amenable pesticides, LODs ranged from 0.003 to 1.048 ?g L(-1) and LOQs ranged from 0.011 to 3.494 ?g L(-1). Finally, the optimized method was applied to the analysis of fourteen real samples of infants from agricultural population. Some pesticides such as methoxyfenozide, tebufenozide, piperonyl butoxide and propoxur were found at concentrations ranged from 1.61 to 24.4 ?g L(-1), whereas methiocarb sulfoxide was detected at trace levels in two samples. PMID:21645688

Cazorla-Reyes, Rocío; Fernández-Moreno, José Luis; Romero-González, Roberto; Frenich, Antonia Garrido; Vidal, José Luis Martínez

2011-07-15

319

An IETS study of a silane coupling agent; the interaction of 3-(trimethoxysilyl)propanethiol with aluminium oxide and silver surfaces  

NASA Astrophysics Data System (ADS)

The inelastic electron tunnelling spectrum of a silane coupling agent, 3-(trimethoxysilyl)propanethiol, is presented. Approximately monolayer quantities of this silane are present on the barrier oxide of an aluminium-aluminium oxide-metal tunnelling junction, in which the counter electrode is either lead or silver. It is deduced from the IETS spectra that the alkoxy groups of this silane condense with the surface hydroxyl groups. No interaction with the lead is observed but the silver layer clearly reacts with the thiol group of the silane molecule, since the thiol stretching vibration is absent in the spectra, and probably forms the corresponding silver thiolate. The influence of this reaction on the conformation of the bound silane is discussed.

Van Velzen, Peter N. T.

1984-05-01

320

On the effect of the Fe(2+)/Fe(3+) redox couple on oxidation of carbon in hot H3PO4  

NASA Technical Reports Server (NTRS)

Oxidation studies of graphite:glassy carbon composites have been carried out at 1 and 4.7 atm. pressures in conc. H3PO4 in the presence and absence of iron ions. The concentration of the acid was varied over 85-100 wt pct, and of the iron ions over 30-300 ppm; the temperature varied over 190-210 C. Unlike the effect of Fe, which has been observed to increase the corrosion of carbon in sulphuric acid, the corrosion in phosphoric acid was observed to be slightly decreased or not at all affected. This result arises because of the catalytic reduction of the oxidized surface groups of carbon by Fe(2+) ions. The catalytic reduction is possible because under the experimental conditions the redox potential of the Fe(2+)/Fe(3+) couple is lower than the open-circuit voltage of carbon.

Dhar, H. P.; Christner, L. G.; Kush, A. K.

1986-01-01

321

Enhanced catalytic performance of MnxOy-Na2WO4/SiO2 for the oxidative coupling of methane using an ordered mesoporous silica support.  

PubMed

The oxidative coupling of methane is a highly promising reaction for its direct conversion. Silica supported MnxOy-Na2WO4 is a suitable catalyst for this reaction. In this study, a variety of different SiO2 materials have been tested as supports. Surprisingly, the application of ordered mesoporous silicas, here exemplarily shown for SBA-15 as support materials, greatly enhances the catalytic performance. The CH4 conversion increased two fold and also the C2 selectivity is strongly increased. PMID:25302934

Yildiz, M; Aksu, Y; Simon, U; Kailasam, K; Goerke, O; Rosowski, F; Schomäcker, R; Thomas, A; Arndt, S

2014-10-23

322

The characterization of tandem and corrugated wings  

NASA Astrophysics Data System (ADS)

Dragonfly wings have two distinct features: a tandem configuration and wing corrugation. Both features have been extensively studied with the aim to understand the superior flight performance of dragonflies. In this paper we review recent development of tandem and corrugated wing aerodynamics. With regards to the tandem configuration, this review will focus on wing/wing and wing/vortex interactions at different flapping modes and wing spacing. In addition, the aerodynamics of tandem wings under gusty conditions will be reviewed and compared with isolated wings to demonstrate the gust resistance characteristics of flapping wings. Regarding corrugated wings, we review their structural and aerodynamic characteristics.

Lian, Yongsheng; Broering, Timothy; Hord, Kyle; Prater, Russell

2014-02-01

323

The IAE Peking HI-13 tandem accelerator  

NASA Astrophysics Data System (ADS)

A new tandem accelerator laboratory is under construction at the Institute of Atomic Energy in Peking. This institute was built in 1958 and equipped with a reactor, cyclotron, electrostatic accelerator and some other facilities to meet the increasing interest in nuclear study and its application in China. The project of this tandem laboratory was approved in 1978. A 13 MV tandem accelerator will be provided by the High Voltage Engineering Corporation of Burlington, Massachusetts, USA, and a Q3D magnetic spectrometer by AB Scanditronix, Sweden. Some auxiliary systems, experimental equipment and the tank of the tandem are being designed and manufactured in China.

Ju-xian, Yu

1981-05-01

324

Simultaneous trace determination of acidic non-steroidal anti-inflammatory drugs in purified water, tap water, juice, soda and energy drink by hollow fiber-based liquid-phase microextraction and ultra-high pressure liquid chromatography coupled to tandem mass spectrometry.  

PubMed

In this study, a two-phase hollow fiber liquid-phase microextraction (HF-LPME) coupling with ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method was developed for determination of four non-steroidal anti-inflammatory (NSAIDs)-salicylic acid, ibuprofen, naproxen and diclofenac in real water samples. The influencing parameters of HF-LPME sample preparation method, such as organic solvents (acceptor phase), pH of sample solution (donor phase), extraction time, stirring speed, extraction temperature and ionic strength were systematically optimized. Through the developed determination method, high enrichment factors (195-346) were achieved for the four drugs. The instrumental calibration curves of salicylic acid, naproxen, diclofenac, and ibuprofen show good linear relations (R>0.998) in the concentration range of 1-500, 5-2500, 10-5000 and 5-2500 ?g L(-1), respectively. The average recoveries of the four drugs in the low, medium and high spiked concentration levels (20-200, 50-500 and 100-1000 ?g L(-1)) were between 98-115% with relative standard deviation (RSD) values were less than 12% (n=6). Limits of detection (LOD) of salicylic acid, naproxen, diclofenac, and ibuprofen in water were 0.5, 0.5, 1.0, and 1.25 ?g L(-1), respectively. The determination method has been applied for the real samples (purified water, tap water, juice, soda and energy drinks), and the results show that salicylic acid was detected in tap water and soda, the concentrations were 2.85 ?g L(-1) and 61.22 ?g L(-1) separately, the RSD values were less than 9% (n=6). Salicylic acid and diclofenac were detected in energy drink, the concentrations were 44.62 ?g L(-1) and 8.31 ?g L(-1), the RSD values were less than 11% (n=6). PMID:23618157

Zhang, Haojie; Du, Zhenxia; Ji, Yu; Mei, Mei

2013-05-15

325

Fast and simultaneous determination of darunavir and eleven other antiretroviral drugs for therapeutic drug monitoring: method development and validation for the determination of all currently approved HIV protease inhibitors and non-nucleoside reverse transcriptase inhibitors in human plasma by liquid chromatography coupled with electrospray ionization tandem mass spectrometry.  

PubMed

For the quantification of all currently approved non-nucleoside reverse transcriptase inhibitors and protease inhibitors, including the new protease inhibitor darunavir and the active nelfinavir metabolite M8, an assay was developed, using liquid chromatography coupled with tandem mass spectrometry. The sample pretreatment consisted of a protein precipitation with a mixture of methanol and acetonitrile using only 100 microL plasma. Chromatographic separation was performed on a reversed-phase C18 column (150 x 2.0 mm, particle size 5 microm) with a quick stepwise gradient using an acetate buffer (pH 5) and methanol, at a flow rate of 0.25 mL/min. The analytical run time was only 10 min. The triple quadrupole mass spectrometer was operated in the positive ion mode and multiple reaction monitoring was used for drug quantification. The method was validated over a range of 0.1 to 20 microg/mL for amprenavir, atazanavir, efavirenz, indinavir, lopinavir, nelfinavir, the active nelfinavir metabolite M8, nevirapine and ritonavir, a range of 0.05 to 10 microg/mL for saquinavir and darunavir and a range of 0.5 to 100 microg/mL for tipranavir, based on observed concentration ranges in patients treated with these drugs. D5-squinavir, D6-indinavir, 13C6-efavirenz and dibenzepine were used as internal standards. The method was proven to be specific, accurate, precise and robust. Accuracies ranged from 88.5% to 102.2% and all precisions were less than 9.5%. Furthermore, the assay demonstrates a high sensitivity for all analytes and the stepwise gradient allows addition of new analytes into the same method. The method is now successfully applied for routine therapeutic drug monitoring and pharmacokinetic studies in HIV-infected patients. PMID:17610214

ter Heine, Rob; Alderden-Los, Carolien G; Rosing, Hilde; Hillebrand, Michel J X; van Gorp, Eric C M; Huitema, Alwin D R; Beijnen, Jos H

2007-01-01

326

Tandem mirror technology demonstration facility  

SciTech Connect

This report describes a facility for generating engineering data on the nuclear technologies needed to build an engineering test reactor (ETR). The facility, based on a tandem mirror operating in the Kelley mode, could be used to produce a high neutron flux (1.4 MW/M/sup 2/) on an 8-m/sup 2/ test area for testing fusion blankets. Runs of more than 100 h, with an average availability of 30%, would produce a fluence of 5 mW/yr/m/sup 2/ and give the necessary experience for successful operation of an ETR.

Not Available

1983-10-01

327

Synthesis of substituted azafluorenones from dihalogeno diaryl ketones by palladium-catalyzed auto-tandem processes.  

PubMed

Substituted azafluorenones were synthesized from different dihalogeno diaryl ketones under palladium catalysis by combining either Suzuki or Heck coupling with direct cyclizing arylation. Conditions were identified to allow both auto-tandem processes to proceed successfully from 3-(bromobenzoyl)- or 3-benzoyl-4-bromo-2-chloropyridines, as well as 4-benzoyl-2,3- and 4-benzoyl-2,5-dichloropyridines. PMID:25233952

Marquise, Nada; Dorcet, Vincent; Chevallier, Floris; Mongin, Florence

2014-11-01

328

Synthesis of ?-iodoketals from methyl ketones via sustainable and orthogonal tandem catalysis.  

PubMed

A highly efficient method for the direct synthesis of ?-iodoketals from methyl ketones has been developed via sustainable integration of orthogonal tandem catalytic reactions: copper(II) oxide catalyzed iodination reaction and the subsequent excess or regenerated iodine catalyzed regioselective ketalization reaction. PMID:23313964

Yang, Yan; Gao, Meng; Shu, Wen-Ming; Wu, Liu-Ming; Zhang, Dong-Xue; Wu, An-Xin

2013-02-21

329

Efficient Tandem Polymer Solar Cells Fabricated by All-Solution Processing  

Microsoft Academic Search

Tandem solar cells, in which two solar cells with different absorption characteristics are linked to use a wider range of the solar spectrum, were fabricated with each layer processed from solution with the use of bulk heterojunction materials comprising semiconducting polymers and fullerene derivatives. A transparent titanium oxide (TiOx) layer separates and connects the front cell and the back cell.

Jin Young Kim; Kwanghee Lee; Nelson E. Coates; Daniel Moses; Thuc-Quyen Nguyen; Mark Dante; Alan J. Heeger

2007-01-01

330

Magnetic phase coupled to an electric memory state in d0 oxide ZrO2 films  

Microsoft Academic Search

It is quite interesting to develop a multifunctional device using a single material with a simple structure. One of the possible candidates could be multiferroics, which are both ferroelectric and magnetic. By taking advantage of the strong spin-charge coupling, the electric field can control the magnetic polarization and the magnetic field can control the electric polarization. However, these multiferroics are

Y. Jo; I. R. Hwang; B. H. Park; K. J. Lee; S. I. Lee; M. H. Jung

2009-01-01

331

Atmospheric oxygen levels, anaerobic methane oxidation, and the coupling of the global COS cycles by sulfate reduction  

Microsoft Academic Search

Changes in the partitioning between the reduced and oxidized reservoirs of carbon and sulfur are the dominant control on atmospheric oxygen levels, and the partitioning itself depends to a large degree on microbial redox processes remineralizing organic matter (OM). However, the controls of organic matter preservation in marine sediments are one of the most complex and controversial issues in contemporary

U. G. Wortmann; B. M. Chernyavsky

2007-01-01

332

THE EFICACY OF OXIDATIVE COUPLING FOR PROMOTING IN-SITU IMMOBILIZATION OF HYDROXYLATED AROMATICS IN CONTAMINATED SOIL AND SEDIMENTS SYSTEMS  

EPA Science Inventory

An urgent science need for DOE is to obtain a better understanding of processes controlling the fate and transport of contaminants in subsurface environments in order to improve conceptual modeling capabilities and current remediation technologies. Our research on the oxidative c...

333

Magnetism of iron oxide based core-shell nanoparticles from interface mixing with enhanced spin-orbit coupling  

NASA Astrophysics Data System (ADS)

We show that the magnetism of core-shell nanoparticles (made of maghemite, ?-Fe2O3, cores and transition-metal and metal-oxide shells) is altered substantially by the interface, which is a doped iron-oxide layer formed naturally during the seed-mediated synthesis process, a route used typically to produce core-shell nanoparticles. Characteristics fundamental to useful applications, such as the anisotropy and superparamagnetic blocking temperature, were altered substantially with Cu, CoO, MnO, and NiO shells. To ascertain the origin of this behavior, the prototype ?-Fe2O3/CoO core-shell nanoparticles are described in detail. We show that the magnetism originates essentially from an interfacial doped iron-oxide layer formed via migration of shell ions, e.g., Co2+, into octahedral site vacancies in the surface layers of the ?-Fe2O3 core. For this system, an overall Fe morb/mspin=0.15±0.03 is measured (morb˜0 for the Fe-oxides) and an enhanced Co morb/mspin=0.65±0.03 elucidates the origin of the unexpectedly high overall anisotropy of the nanoparticle. This interfacial layer is responsible for the overall (e.g., bulk) magnetism and provides a perspective on how the magnetism of core-shell nanoparticles manifests from the selected core and shell materials.

Skoropata, E.; Desautels, R. D.; Chi, C.-C.; Ouyang, H.; Freeland, J. W.; van Lierop, J.

2014-01-01

334

A Coupled Model for Oxidative Dissolution of Spent Fuel and Transport of Radionuclides from an Initially Defective Canister  

Microsoft Academic Search

An earlier model for oxidative dissolution of spent fuel was developed by including the release behavior of actinides from the fuel surface and the barrier effect of Zircaloy claddings. The aim here is to explore the possibility and consequences of precipitation in the water film around the fuel pellets due to solubility and transport limitations of nuclides. The model has

Liu Longcheng; Ivars Neretnieks

2001-01-01

335

The development of copper-catalyzed aerobic oxidative coupling of H-tetrazoles with boronic acids and an insight into the reaction mechanism.  

PubMed

The development of a highly efficient and practical protocol for the direct C-N coupling of H-tetrazole and boronic acid was presented. A careful and patient optimization of a variety of reaction parameters revealed that this conventionally challenge reaction could indeed proceed efficiently in a very simple system, that is, just by stirring the tetrazoles and boronic acids under oxygen in the presence of different Cu(I) or Cu(II) salts with only 5?mol?% loading in DMSO at 100?°C. Most significantly, the reaction could proceed very smoothly in a regiospecific manner to afford the 2,5-disubstituted tetrazoles in high to excellent yields. A mechanistic study revealed that both tetrazole and DMSO are crucial for the generation of catalytically active copper species in the reaction process in addition to their role as reactant and solvent, respectively. It is demonstrated that in the reaction cycle, the Cu(I) catalyst could be oxidized to Cu(II) by oxygen to form a [CuT2D] complex (T = tetrazole anion; D = DMSO) through an oxidative copper amination reaction. The Cu(II) complex thus formed was confirmed to be the real catalytically active copper species. Namely, the Cu(II) complex disproportionates to aryl Cu(III) and Cu(I) in the presence of boronic acid. Facile elimination of the Cu(III) species delivers the C-N-coupled product. The results presented herein not only provide a reliable and efficient protocol for the synthesis of 2,5-disubstituted tetrazoles, but most importantly, the mechanistic results would have broad implications for the de novo design and development of new methods for Cu-catalyzed coupling reactions. PMID:24449340

Liu, Chao-You; Li, Yu; Ding, Jin-Ying; Dong, De-Wen; Han, Fu-She

2014-02-17

336

UPGRADE OF THE BUCHAREST FN TANDEM ACCELERATOR  

Microsoft Academic Search

The Bucharest FN Tandem Accelerator was put in operation in 1973 and upgraded a first time in 1983 to 9 MV. In the period 2006-2009 a second program of the tandem upgrade was performed aiming to transform this accelerator in a modern and versatile facility for atomic and nuclear physics studies as well as for different applications using accelerated ion

S. Dobrescu; I. Branzan; C. V. Craciun; G. Dumitru; C. Florea; D. Ghita; G. Ion; G. Mihon; D. Moisa; D. V. Mosu; G. Naghel; C. Paun; S. Papureanu; T. Sava

337

A coupled transport and solid mechanics formulation with improved reaction kinetics parameters for modeling oxidation and decomposition in a uranium hydride bed.  

SciTech Connect

Modeling of reacting flows in porous media has become particularly important with the increased interest in hydrogen solid-storage beds. An advanced type of storage bed has been proposed that utilizes oxidation of uranium hydride to heat and decompose the hydride, releasing the hydrogen. To reduce the cost and time required to develop these systems experimentally, a valid computational model is required that simulates the reaction of uranium hydride and oxygen gas in a hydrogen storage bed using multiphysics finite element modeling. This SAND report discusses the advancements made in FY12 (since our last SAND report SAND2011-6939) to the model developed as a part of an ASC-P&EM project to address the shortcomings of the previous model. The model considers chemical reactions, heat transport, and mass transport within a hydride bed. Previously, the time-varying permeability and porosity were considered uniform. This led to discrepancies between the simulated results and experimental measurements. In this work, the effects of non-uniform changes in permeability and porosity due to phase and thermal expansion are accounted for. These expansions result in mechanical stresses that lead to bed deformation. To describe this, a simplified solid mechanics model for the local variation of permeability and porosity as a function of the local bed deformation is developed. By using this solid mechanics model, the agreement between our reacting bed model and the experimental data is improved. Additionally, more accurate uranium hydride oxidation kinetics parameters are obtained by fitting the experimental results from a pure uranium hydride oxidation measurement to the ones obtained from the coupled transport-solid mechanics model. Finally, the coupled transport-solid mechanics model governing equations and boundary conditions are summarized and recommendations are made for further development of ARIA and other Sandia codes in order for them to sufficiently implement the model.

Salloum, Maher N.; Shugard, Andrew D.; Kanouff, Michael P.; Gharagozloo, Patricia E.

2013-03-01

338

Enhancing light out-coupling of organic light-emitting devices using indium tin oxide-free low-index transparent electrodes  

NASA Astrophysics Data System (ADS)

With its increasing and sufficient conductivity, the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been capable of replacing the widely used but less cost-effective indium tin oxides (ITOs) as alternative transparent electrodes for organic light-emitting devices (OLEDs). Intriguingly, PEDOT:PSS also possesses an optical refractive index significantly lower than those of ITO and typical organic layers in OLEDs and well matching those of typical OLED substrates. Optical simulation reveals that by replacing ITO with such a low-index transparent electrode, the guided modes trapped within the organic/ITO layers in conventional OLEDs can be substantially suppressed, leading to more light coupled into the substrate than the conventional ITO device. By applying light out-coupling structures onto outer surfaces of substrates to effectively extract radiation into substrates, OLEDs using such low-index transparent electrodes achieve enhanced optical out-coupling and external quantum efficiencies in comparison with conventional OLEDs using ITO.

Huang, Yi-Hsiang; Lu, Chun-Yang; Tsai, Shang-Ta; Tsai, Yu-Tang; Chen, Chien-Yu; Tsai, Wei-Lung; Lin, Chun-Yu; Chang, Hong-Wei; Lee, Wei-Kai; Jiao, Min; Wu, Chung-Chih

2014-05-01

339

Subsurface Uranium Fate and Transport: Integrated Experiments and Modeling of Coupled Biogeochemical Mechanisms of Nanocrystalline Uraninite Oxidation by Fe(III)-(hydr)oxides - Project Final Report  

SciTech Connect

Subsurface bacteria including sulfate reducing bacteria (SRB) reduce soluble U(VI) to insoluble U(IV) with subsequent precipitation of UO2. We have shown that SRB reduce U(VI) to nanometer-sized UO2 particles (1-5 nm) which are both intra- and extracellular, with UO2 inside the cell likely physically shielded from subsequent oxidation processes. We evaluated the UO2 nanoparticles produced by Desulfovibrio desulfuricans G20 under growth and non-growth conditions in the presence of lactate or pyruvate and sulfate, thiosulfate, or fumarate, using ultrafiltration and HR-TEM. Results showed that a significant mass fraction of bioreduced U (35-60%) existed as a mobile phase when the initial concentration of U(VI) was 160 µM. Further experiments with different initial U(VI) concentrations (25 - 900 ?M) in MTM with PIPES or bicarbonate buffers indicated that aggregation of uraninite depended on the initial concentrations of U(VI) and type of buffer. It is known that under some conditions SRB-mediated UO2 nanocrystals can be reoxidized (and thus remobilized) by Fe(III)-(hydr)oxides, common constituents of soils and sediments. To elucidate the mechanism of UO2 reoxidation by Fe(III) (hydr)oxides, we studied the impact of Fe and U chelating compounds (citrate, NTA, and EDTA) on reoxidation rates. Experiments were conducted in anaerobic batch systems in PIPES buffer. Results showed EDTA significantly accelerated UO2 reoxidation with an initial rate of 9.5?M day-1 for ferrihydrite. In all cases, bicarbonate increased the rate and extent of UO2 reoxidation with ferrihydrite. The highest rate of UO2 reoxidation occurred when the chelator promoted UO2 and Fe(III) (hydr)oxide dissolution as demonstrated with EDTA. When UO2 dissolution did not occur, UO2 reoxidation likely proceeded through an aqueous Fe(III) intermediate as observed for both NTA and citrate. To complement to these laboratory studies, we collected U-bearing samples from a surface seep at the Rifle field site and have measured elevated U concentrations in oxic iron-rich sediments. To translate experimental results into numerical analysis of U fate and transport, a reaction network was developed based on Sani et al. (2004) to simulate U(VI) bioreduction with concomitant UO2 reoxidation in the presence of hematite or ferrihydrite. The reduction phase considers SRB reduction (using lactate) with the reductive dissolution of Fe(III) solids, which is set to be microbially mediated as well as abiotically driven by sulfide. Model results show the oxidation of HS– by Fe(III) directly competes with UO2 reoxidation as Fe(III) oxidizes HS– preferentially over UO2. The majority of Fe reduction is predicted to be abiotic, with ferrihydrite becoming fully consumed by reaction with sulfide. Predicted total dissolved carbonate concentrations from the degradation of lactate are elevated (log(pCO2) ~ –1) and, in the hematite system, yield close to two orders-of-magnitude higher U(VI) concentrations than under initial carbonate concentrations of 3 mM. Modeling of U(VI) bioreduction with concomitant reoxidation of UO2 in the presence of ferrihydrite was also extended to a two-dimensional field-scale groundwater flow and biogeochemically reactive transport model for the South Oyster site in eastern Virginia. This model was developed to simulate the field-scale immobilization and subsequent reoxidation of U by a biologically mediated reaction network.

Peyton, Brent M. [Montana State University; Timothy, Ginn R. [University of California Davis; Sani, Rajesh K. [South Dakota School of Mines and Technology

2013-08-14

340

Activation of cGMP/Protein Kinase G Pathway in Postconditioned Myocardium Depends on Reduced Oxidative Stress and Preserved Endothelial Nitric Oxide Synthase Coupling  

PubMed Central

Background The cGMP/protein kinase G (PKG) pathway is involved in the cardioprotective effects of postconditioning (PoCo). Although PKG signaling in PoCo has been proposed to depend on the activation of the phosphatidylinositol 3?kinase (PI3K)/Akt cascade, recent data bring into question a causal role of reperfusion injury signaling kinase (RISK) in PoCo protection. We hypothesized that PoCo increases PKG activity by reducing oxidative stress–induced endothelial nitric oxide synthase (NOS) uncoupling at the onset of reperfusion. Methods and Results Isolated rat hearts were submitted to 40 minutes of ischemia and reperfusion with and without a PoCo protocol. PoCo reduced infarct size by 48% and cGMP depletion. Blockade of cGMP synthesis (1H?[1,2,4]oxadiazolo[4,3?a]quinoxalin?1?one) and inhibition of PKG (KT5823) or NOS (l?NAME) abolished protection, but inhibition of PI3K/Akt cascade (LY294002) did not (n=5 to 7 per group). Phosphorylation of the RISK pathway was higher in PoCo hearts. However, this difference is due to increased cell death in control hearts because in hearts reperfused with the contractile inhibitor blebbistatin, a drug effective in preventing cell death at the onset of reperfusion, RISK phosphorylation increased during reperfusion without differences between control and PoCo groups. In these hearts, PoCo reduced the production of superoxide (O2?) and protein nitrotyrosylation and increased nitrate/nitrite levels in parallel with a significant decrease in the oxidation of tetrahydrobiopterin (BH4) and in the monomeric form of endothelial NOS. Conclusions These results demonstrate that PoCo activates the cGMP/PKG pathway via a mechanism independent of the PI3K/Akt cascade and dependent on the reduction of O2? production at the onset of reperfusion, resulting in attenuated oxidation of BH4 and reduced NOS uncoupling. PMID:23525447

Inserte, Javier; Hernando, Victor; Vilardosa, Ursula; Abad, Elena; Poncelas-Nozal, Marcos; Garcia-Dorado, David

2013-01-01

341

Formation Of Carbon Oxides In CH4/O2 Plasmas Produced By Inductively Coupled RF Discharges At Low Pressure  

NASA Astrophysics Data System (ADS)

The formation of CO and CO2 has been studied in inductively coupled rf (13.56 MHz) discharges with varied mixtures of CH4 and O2 as feed gases at a total pressure of 10 Pa, flow rates of <10 sccm, and input powers of <500 W. The primary diagnostic tool has been TDLAS (tunable diode laser absorption spectroscopy) to measure absolute concentrations of molecular species as well as their kinetic and rovibrational temperatures. Of particular interest is the sudden transition between different modes of power coupling (capacitive and inductive mode, resp.) and the related changes of the plasma composition. We have found that the power threshold for this transition exhibits a clear hysteresis and depends on the oxygen content. Comparing the ratio of the CO- and CO2-concentrations in capacitive mode with corresponding data from a parallel-plate discharge, clear differences have been observed. The findings can partly be explained on the basis of plasma-chemical reaction chains using tabulated cross-sections in combination with estimations of the electron energy distribution function. Some observations (as, e.g. the presence of CO in inductively coupled plasmas that are fed by pure oxygen) cannot be understood from volume reactions only but point to an important role of surface processes, which depend on the materials of the discharge chamber and on its history and cleaning method.

Möller, Ivonne; Soltwisch, Henning

2003-06-01

342

Oxidative coupling and ring opening of furan on Ag(110): Formation of maleic anhydride, benzene, and bifuran  

Microsoft Academic Search

TPRS, EELS, and isotope experiments show that furan reacts with active oxygen on Ag(110) to form CO[sub 2], H[sub 2]O, and small amounts of the partially oxidized products maleic anhydride, bifuran, and benzene that evolve between 520 and 560 K. The first step in furan combustion is C-H bond activation by O[sub (a)], followed by O[sub (a)] attack at the

William W. Crew; Robert J. Madix

1993-01-01

343

Isoproterenol Induces Vascular Oxidative Stress and Endothelial Dysfunction via a Gi?-Coupled ?2-Adrenoceptor Signaling Pathway  

PubMed Central

Objective Sustained ?-adrenergic stimulation is a hallmark of sympathetic hyperactivity in cardiovascular diseases. It is associated with oxidative stress and altered vasoconstrictor tone. This study investigated the ?-adrenoceptor subtype and the signaling pathways implicated in the vascular effects of ?-adrenoceptor overactivation. Methods and Results Mice lacking the ?1- or ?2-adrenoceptor subtype (?1KO, ?2KO) and wild-type (WT) were treated with isoproterenol (ISO, 15 ?g.g?1.day?1, 7 days). ISO significantly enhanced the maximal vasoconstrictor response (Emax) of the aorta to phenylephrine in WT (+34%) and ?1KO mice (+35%) but not in ?2KO mice. The nitric oxide synthase (NOS) inhibitor L-NAME abolished the differences in phenylephrine response between the groups, suggesting that ISO impaired basal NO availability in the aorta of WT and ?1KO mice. Superoxide dismutase (SOD), pertussis toxin (PTx) or PD 98,059 (p-ERK 1/2 inhibitor) incubation reversed the hypercontractility of aortic rings from ISO-treated WT mice; aortic contraction of ISO-treated ?2KO mice was not altered. Immunoblotting revealed increased aortic expression of Gi?-3 protein (+50%) and phosphorylated ERK1/2 (+90%) and decreased eNOS dimer/monomer ratio in ISO-treated WT mice. ISO enhanced the fluorescence response to dihydroethidium (+100%) in aortas from WT mice, indicating oxidative stress that was normalized by SOD, PTx and L-NAME. The ISO effects were abolished in ?2KO mice. Conclusions The ?2-adrenoceptor/Gi? signaling pathway is implicated in the enhanced vasoconstrictor response and eNOS uncoupling-mediated oxidative stress due to ISO treatment. Thus, long-term ?2-AR activation might results in endothelial dysfunction. PMID:24622771

Davel, Ana P.; Brum, Patricia C.; Rossoni, Luciana V.

2014-01-01

344

Oxidative chemistry of the natural antioxidant hydroxytyrosol: hydrogen peroxide-dependent hydroxylation and hydroxyquinone\\/ o-quinone coupling pathways  

Microsoft Academic Search

Oxidation of the natural antioxidant hydroxytyrosol (1) with peroxidase\\/H2O2 in phosphate buffer at pH 7.4 led to the formation of two main ethyl acetate-extractable products. These could be isolated by preparative TLC after reduction and acetylation, and were identified as the tetraacetyl derivative of 2-(2,4,5-trihydroxyphenyl)ethanol (3) and the heptaacetyl derivative of the pentahydroxybiphenyl 4 by 2D NMR and MS analysis.

Maria De Lucia; Lucia Panzella; Alessandro Pezzella; Alessandra Napolitano; Marco d'Ischia

2006-01-01

345

Novel biomarkers of protein oxidation sites and degrees using horse cytochrome c as the target by mass spectrometry  

NASA Astrophysics Data System (ADS)

Biomarkers held both incredible application and significant challenge in probing the oxidation mechanisms of proteins under oxidative stress. Here, mass spectrometry (MS) coupled with liquid chromatography (LC) was applied to establish a new pipeline to probe the oxidation sites and degrees of horse cytochrome c (HCC) with its oxidative products serving as the biomarkers. Samples of native and UV/H 2O 2 oxidized HCCs were digested by trypsin and subjected to biomarker discovery using LC/MS and tandem mass spectrometry (MS/MS). Experiment results proved that the main oxidation sites were located at Cys 14, Cys 17, Met 65 and Met 80 residues in peptides C 14AQC(heme)HTVEK 22, C 14AQCHTVEK 22, E 60ETLMEYLENPKK 73, M 80IFAGIK 86 and M 80IFAGIKK 87. Quantitative analysis on the oxidized peptides showed the oxidation degrees of target sites had positive correlations with extended oxidation dose and controlled by residues types and their accessibility to solvent molecules. Being able to provide plentiful information for the oxidation sites and oxidation degrees, the identified oxidized products were feasibility biomarkers for HCC oxidation, compared with the conventional protein carbonyl assay.

Zong, Wansong; Liu, Rutao; Guo, Changying; Sun, Feng

2011-05-01

346

Identification of acteoside and its major metabolites in rat urine by ultra-performance liquid chromatography combined with electrospray ionization quadrupole time-of-flight tandem mass spectrometry.  

PubMed

In this study, metabolites in the urine samples of rats orally administered with acteoside, a phenylethanoid glycoside compound, were detected and identified using ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UPLC/ESI-QTOF-MS) combined with an automated MS(E) technique. Up to 35 metabolites (19 metabolites of the parent drug and 16 metabolites of the degradation products) were observed, including processes of oxidization, glucuronidation, sulfation, and methyl conjugation. According to the metabolic pathways, acteoside mainly functioned as a prodrug and underwent hydrolysis before being absorbed into the blood. The degradation products, especially caffeic acid and hydroxytyrosol, were involved in further metabolism which was responsible for the low oral bioavailability but obvious pharmacological activities of acteoside. In summary, this work provided valuable information on acteoside metabolism through the rapid and reliable UPLC/ESI-QTOF-MS technique, which could be widely used for the investigation of natural product metabolites. PMID:24141042

Qi, Meng; Xiong, Aizhen; Li, Pengfei; Yang, Qiming; Yang, Li; Wang, Zhengtao

2013-12-01

347

Time-delay-and-integration charge-coupled devices using tin oxide gate technology. [for Landsat MSS  

NASA Technical Reports Server (NTRS)

Doped tin oxide gates are used in a time-delay-and-integration (TDI) CCD scheme in an effort to develop a stable transparent gate technology. Design characteristics of the system are discussed, including 2 sections of 10 by 9 integration stages, four-phase buried channel construction, and 10 input parallel-in/serial-out output shift register at a video rate of 1.25 MHz. A quantum efficiency of 65% with smooth spectral response is attained by front surface imaging. The suitability of the system for the Landsat program is discussed in terms of TDI-CCD operating parameters.

Thompson, L. L.; Mccann, D. H.; Tracy, R. A.; Kub, F. J.; White, M. H.

1978-01-01

348

A peroxynitrite complex of copper: formation from a copper-nitrosyl complex, transformation to nitrite and exogenous phenol oxidative coupling or nitration  

PubMed Central

Reaction of nitrogen monoxide with a copper(I) complex possessing a tridentate alkylamine ligand gives a Cu(I)–(·NO) adduct, which when exposed to dioxygen generates a peroxynitrite (O=NOO?)–Cu(II) species. This undergoes thermal transformation to produce a copper(II) nitrito (NO2?) complex and 0.5 mol equiv O2. In the presence of a substituted phenol, the peroxynitrite complex effects oxidative coupling, whereas addition of chloride ion to dissociate the peroxynitrite moiety instead leads to phenol ortho nitration. Discussions include the structures (including electronic description) of the copper–nitrosyl and copper–peroxynitrite complexes and the formation of the latter, based on density functional theory calculations and accompanying spectroscopic data. PMID:19662443

Park, Ga Young; Deepalatha, Subramanian; Puiu, Simona C.; Lee, Dong-Heon; Mondal, Biplab; Sarjeant, Amy A. Narducci; del Rio, Diego; Pau, Monita Y. M.; Solomon, Edward I.; Karlin, Kenneth D.

2010-01-01

349

The use of a gas chromatograph coupled to a metal oxide sensor for rapid assessment of stool samples from irritable bowel syndrome and inflammatory bowel disease patients.  

PubMed

There is much clinical interest in the development of a low-cost and reliable test for diagnosing inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS), two very distinct diseases that can present with similar symptoms. The assessment of stool samples for the diagnosis of gastro-intestinal diseases is in principle an ideal non-invasive testing method. This paper presents an approach to stool analysis using headspace gas chromatography and a single metal oxide sensor coupled to artificial neural network software. Currently, the system is able to distinguish samples from patients with IBS from patients with IBD with a sensitivity and specificity of 76% and 88% respectively, with an overall mean predictive accuracy of 76%. PMID:24674940

Shepherd, S F; McGuire, N D; de Lacy Costello, B P J; Ewen, R J; Jayasena, D H; Vaughan, K; Ahmed, I; Probert, C S; Ratcliffe, N M

2014-06-01

350

Cross-coupling reaction between arylboronic acids and carboranyl iodides catalyzed by graphene oxide (GO)-supported Pd(0) recyclable nanoparticles for the synthesis of carboranylaryl ketones.  

PubMed

Well-dispersed palladium(0) nanoparticles with small and narrow size distributions were synthesized conveniently on a graphene oxide (GO) surface. The GO-supported nano-Pd(0) was found to be a highly efficient and recyclable catalyst for the carbonylative cross-coupling reaction between arylboronic acids and aryl and carboranyl iodides, respectively. Benzophenone and a series of carboranylaryl ketones, 1-R-2-[C(=O)Ar]-1,2-C2B10H10 (R = H, Me, Ph; Ar = C6H5, C6H4-4-OMe and C6H4-4-F), were synthesized and fully characterized. The catalyst was recyclable at least three times with sustained activity. PMID:24212191

Biying, Algin Oh; Vangala, Venu R; Chen, Chia Sze; Stubs, Ludger Paul; Hosmane, Narayan S; Yinghuai, Zhu

2014-04-01

351

Delivery of tobramycin coupled to iron oxide nanoparticles across the biofilm of mucoidal Pseudonomas aeruginosa and investigation of its efficacy  

NASA Astrophysics Data System (ADS)

Pseudomonas aeruginosa bacterium is a deadly pathogen, leading to respiratory failure in cystic fibrosis and nosocomial pneumonia, and responsible for high mortality rates in these diseases. P. aeruginosa has inherent as well as acquired resistance to many drug classes. In this paper, we investigate the effectiveness of two classes; aminoglycoside (tobramycin) and fluoroquinolone (ciprofloxacin) administered alone, as well as conjugated to iron oxide (magnetite) nanoparticles. P. aeruginosa possesses the ability to quickly alter its genetics to impart resistance to the presence of new, unrecognized treatments. As a response to this impending public health threat, we have synthesized and characterized magnetite nanoparticles capped with biodegradable short-chain carboxylic acid derivatives conjugated to common antibiotic drugs. The functionalized nanoparticles may carry the drug past the mucus and biofilm layers to target the bacterial colonies via magnetic gradient-guided transport. Additionally, the magnetic ferrofluid may be used under application of an oscillating magnetic field to raise the local temperature, causing biofilm disruption, slowed growth, and mechanical disruption. These abilities of the ferrofluid would also treat multi-drug resistant strains, which appear to be increasing in many nosocomial as well as acquired opportunistic infections. In this in vitro model, we show that the iron oxide alone can also inhibit bacterial growth and biofilm formation.

Armijo, Leisha M.; Kopciuch, Michael; Olszá½¹wka, Zuzia; Wawrzyniec, Stephen J.; Rivera, Antonio C.; Plumley, John B.; Cook, Nathaniel C.; Brandt, Yekaterina I.; Huber, Dale L.; Smolyakov, Gennady A.; Adolphi, Natalie L.; Smyth, Hugh D. C.; Osi?ski, Marek

2014-03-01

352

Pulsating Tandem Microbubble for Localized and Directional Single Cell Membrane Poration  

PubMed Central

The interaction of laser-generated tandem microbubble (maximum diameter about 50 ?m) with single (rat mammary carcinoma) cells is investigated in a 25-?m liquid layer. Anti-phase and coupled oscillation of the tandem microbubble leads to the formation of alternating, directional microjets (with max. microstreaming velocity of 10 m/s) and vortices (max. vorticity of 350,000 s?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 absence from a single oscillating microbubble of comparable size and at the same stand-off distance. PMID:20868077

Sankin, G.N.; Yuan, F.; Zhong, P.

2013-01-01

353

[Cloning, expression and screening tandem repeats of the Z domain of Staphylococcus aureus protein A].  

PubMed

To screen an efficient recombinant Staphylococcus aureus protein A (SpA) for preparing matrix for affinity purification of immunoglobulin G (IgG), a genetic engineering approach was used to obtain monomer, two, three, four and five tandem repeats genes of the Z domain of SpA, then the genes were cloned into expression vector pET-22b and subsequently expressed in Escherichia coli BL21 (DE3). After induction with lactose, the target proteins were purified by Ni2+ affinity chromatography. The proteins with two, three, four and five tandem repeats of the Z domain were then coupled to CNBr-activated Sepharose 4B as an affinity chromatography matrix for affinity purification of human IgG. Furthermore, the differences in protein yield and IgG-binding capacity at different recombinant proteins were analyzed. The target proteins with monomer and tandem repeats of the Z domain had an effective expression in the genetic engineering bacteria. IgG could be specifically absorbed from human plasma by affinity chromatography. The protein yield and amount of IgG absorption of per mole protein could be improved by increasing the tandem repeats number of the Z domain. Compared with other tandem repeats, four tandem repeats of the Z domain exhibited more protein yield (160 mg/10 g wet cells) and higher level of IgG absorption (34.4 mg human IgG/mL gel). Therefore, four tandem repeats of the Z domain is more suitable for preparing matrix for affinity purification of IgG. PMID:23593874

Wan, Yi; Zi, Jing; Zhang, Kun; Zhang, Zhimin; Zhang, Yuejuan; Wang, Yan; Wang, Jun

2012-12-01

354

Novel oxidative coupling reactions of cisapride or metaclopramide with phenoxazines and their applications in the determination of nitrite at trace level in environmental samples.  

PubMed

Phenoxazine (PNZ), 2-chlorophenoxazine (CPN) and 2-trifluoromethylphenoxazine (TPN) were used as new class of spectrophotometric reagents for the determination of nanoamounts of nitrite in presence of cisapride (CSP) and metaclopramide (MCP) as new electrophilic coupling reagents. The methods were based on the oxidation of CSP or MCP by nitrite in hydrochloric acid medium and coupling with PNZ, CPN or TPN to yield red color derivatives which were stable for about 3h and having an absorbance maximum in the range 520-530 nm. Beer's law is obeyed for nitrite in the concentration range 0.08-0.80 and 0.13-1.60 microg ml(-1) for phenoxazine-cisapride and phenoxazine-metaclopramide, respectively. The optimum reaction conditions and other important analytical parameters were established to enhance the sensitivity of these methods. Interference due to various non-target ions was also investigated. The methods were applied to the analysis of nitrite in environmental samples. The performance of proposed methods were evaluated by Student's t-test and variance ratio F-test indicated the significance of proposed methods over the reference spectrophotometric method (Association of Official Analytical Communities (AOAC) method for the determination of nitrite in water samples). PMID:17306617

Al-Okab, Riyad Ahmed; Syed, Akheel Ahmed

2007-11-01

355

Aligning Electronic and Protonic Energy Levels of Proton-Coupled Electron Transfer in Water Oxidation on Aqueous TiO2.  

PubMed

The high overpotential in water oxidation on anodes is a limiting factor for the large-scale application of photoelectrochemical cells. To overcome this limitation, it is essential to understand the four proton-coupled electron transfer (PCET) steps in the reaction mechanism and their implications to the overpotential. Herein, a simple scheme to compute the energies of the PCET steps in water oxidation on the aqueous TiO2 surface using a hybrid density functional is described. An energy level diagram for fully decoupled electron- and proton-transfer reactions in which both electronic and protonic levels are placed on the same potential scale is also described. The level diagram helps to visualize the electronic and protonic components of the overpotential, and points out what are needed to improve. For TiO2 , it is found that its catalytic activity is due to aligning the protonic energy levels in the PCET steps, while improving the activity requires also aligning the electronic levels. PMID:25056713

Cheng, Jun; Liu, Xiandong; Kattirtzi, John A; VandeVondele, Joost; Sprik, Michiel

2014-11-01

356

Development of a stable isotope approach for the inductively coupled plasma-mass spectrometry determination of oxidized metallothionein in biological materials.  

PubMed

The use of isotope dilution analysis (IDA) with inductively coupled plasma-mass spectrometry (ICP-MS) for the determination of oxidized metallothionein (MT) by a Cd-saturation method is investigated. The method developed here is a modification of an earlier methodology which used a radioactive Cd isotope ((109)Cd). While retaining the many advantages of this previous approach, the procedure presented here uses stable isotope ratio measurements ((114)Cd/(111)Cd) for the determination of MT. Experimental parameters governing the instrumental precision and accuracy for isotope ratio measurements of Cd by ICP-MS were characterized. Systematic errors, including mass bias, detector dead time, and spectroscopic interferences, could be easily corrected. The isotope dilution ICP-MS method was validated by the determination of very low levels of cadmium in biological certified reference materials (NIST SRM 2670 freeze-dried urine, IAEA H-8 horse kidney, and BCR TP-25 lichens). Finally, the IDA procedure was evaluated for the determination of oxidized MT by a Cd-saturation method previously developed using radioactive (109)Cd. The final procedure was applied to the quantification of MT in Long-Evans Cinnamon rat liver cytosol samples and the results were compared with data obtained for the same samples using the reference (109)Cd methodology. A good agreement between the analytical values obtained by both methods was observed. PMID:10873273

Valles Mota, J P; Linde Arias, A R; Fernández de la Campa, M R; García Alonso, J I; Sanz-Medel, A

2000-07-01

357

Striction-Coupled Magnetoresistance in Perovskite-type Manganese Oxides (Nd,Sm)_1/2Sr_1/2MnO_3  

NASA Astrophysics Data System (ADS)

Magnetoresistance (MR) of more than three orders of magnitude, which is strongly coupled to lattice striction, has been observed under a relatively low magnetic field (e.g., 0.4 T at 115 K) for a single crystal of perovskite-type manganese oxide with finely controlled ionic radii of the A-sites, (Nd,Sm)_1/2Sr_1/2MnO_3. The colossal MR phenomena are viewed as a first-order insulator-to-metal phase transition induced by a magnetic field, which accompanies a metamagnetic (antiferromagnetic-to-ferromagnetic) transition as well as a lattice-structural change. Clear hystereses as well as switching-like changes of magnetization, striction, and resistivity are observed in increasing and decreasing magnetic field at temperatures (113-160K) near above the Curie temperature. In this temperature region, the ferromagnetic double exchange interaction seems to be suppressed by localization of carriers and/or antiferromagnetic interaction. We speculate that this antiferromagnetic interaction is relevant to a charge-ordering instability, the real space ordering of doped holes, observed in many of the similar manganese oxides. This work was supported by New Energy and Industrial Technology Development Organization (NEDO) of Japan.

Kuwahara, H.; Tomioka, Y.; Moritomo, Y.; Asamitsu, A.; Tokura, Y.

1996-03-01

358

FORUM: Bioinspired Heme, Heme/non-heme Diiron, Heme/copper and Inorganic NOx Chemistry: ?NO(g) Oxidation, Peroxynitrite-Metal Chemistry and ?NO(g) Reductive Coupling  

PubMed Central

The focus of this Forum review highlights work from our own laboratories and those of others in the area of biochemical and biologically inspired inorganic chemistry dealing with nitric oxide (nitrogen monoxide, ·NO(g)) and its biological roles and reactions. The latter focus is on (i) oxidation of ·NO(g) to nitrate by nitric oxide dioxygenases (NOD’s), and (ii) reductive coupling of two molecules of ·NO(g) to give N2O(g). In the former case, NOD’s are described and the highlighting of possible peroxynitrite-heme intermediates and consequences of this are given by discussion of recent works with myoglobin and a synthetic heme model system for NOD action. Summaries of recent copper complex chemistries with ·NO(g) and O2(g) leading to peroxynitrite species are given. The coverage of biological reductive coupling of ·NO(g) deals with bacterial nitric oxide reductases (NOR’s) with heme/non-heme diiron active sites, and on heme/Cu oxidases such as cytochrome c oxidase which can mediate the same chemistry. Recent designed protein and synthetic model compound (heme/non-heme diiron or heme/copper) as functional mimics are discussed in some detail. We also highlight examples from the chemical literature, not necessarily involving biologically relevant metal ions, which describe the oxidation of ·NO(g) to nitrate (or nitrite) and possible peroxynitrite intermediates, or reductive coupling of ·NO(g) to give nitrous oxide. PMID:20666386

Schopfer, Mark P.; Wang, Jun; Karlin, Kenneth D.

2010-01-01

359

Recyclable heterogeneous copper oxide on alumina catalyzed coupling of phenols and alcohols with aryl halides under ligand-free conditions.  

PubMed

An efficient alumina-supported CuO-catalyzed O-arylation of phenols and aliphatic alcohols with various aryl as well as heteroaryl halides under ligand-free conditions are reported. This protocol provides a variety of diaryl ether and bis-diaryl ether motifs by reacting different aryl/aliphatic halides with differently substituted phenols and saturated alcohols in the presence of a catalytic amount of CuO on alumina and KOH as a base at moderate temperature under nitrogen atmosphere. The described methodology is simple, straightforward and efficient to afford the cross-coupled products in high yields under ligand-free conditions. The explored catalyst is inexpensive, air-stable and recyclable up to three cycles. PMID:21695321

Swapna, Kokkirala; Murthy, Sabbavarapu Narayana; Jyothi, Mocharla Tarani; Nageswar, Yadavalli Venkata Durga

2011-09-01

360

Oxidative coupling and ring opening of furan on Ag(110): Formation of maleic anhydride, benzene, and bifuran  

SciTech Connect

TPRS, EELS, and isotope experiments show that furan reacts with active oxygen on Ag(110) to form CO[sub 2], H[sub 2]O, and small amounts of the partially oxidized products maleic anhydride, bifuran, and benzene that evolve between 520 and 560 K. The first step in furan combustion is C-H bond activation by O[sub (a)], followed by O[sub (a)] attack at the [alpha]-carbon at 308 K. [sup 18]O[sub (a)] experiments prove that maleic anhydride is formed via intermediates where the furan ring has been cleaved. This contrasts with mechanisms proposed for maleic anhydride production from furan over VPO catalysts. 36 refs., 12 figs., 2 tabs.

Crew, W.W.; Madix, R.J. (Stanford Univ., CA (United States))

1993-01-27

361

Oxidative coupling of methane over SrO deposited on different commercial supports precoated with La{sub 2}O{sub 3}  

SciTech Connect

The influence of catalyst carrier or support (with different chemical compositions and surface properties), catalyst deposition method (viz., impregnation and coating), precursor for strontium oxide (SrO; Sr-nitrate, acetate, hydroxide, and carbonate), and loading of SrO and lanthanum oxide (La{sub 2}O{sub 3}; 0--25 wt%) on the surface properties and performance of catalyst in oxidative coupling of methane (OCM; at 850 C, gas hourly space velocity = 1.02 {times} 10{sup 5} cm{sup 3}/g{center_dot}h and CH{sub 4}/O{sub 2} = 4 or 16) was thoroughly investigated. The basicity, acidity, and O{sub 2} chemisorption of the catalysts were studied by the temperature programmed desorption (TPD) of CO{sub 2}, NH{sub 3}, and O{sub 2}, respectively, from 50 to 950 C. The total and strong basic sites, acidity, and OCM activity of the supported catalyst were strongly influenced by the support used and also by the La{sub 2}O{sub 3} loading on the support. The catalyst with a sintered low surface area porous silica-Alumina support and high (20 wt%) La{sub 2}O{sub 3} and SrO loadings showed the best performance in the OCM process. The OCM activity was influenced by SrO loading, but to a smaller extent, and also by the method of SrO deposition. The OCM activity of the supported catalysts could be related to their strong basic sites (measured in terms of the CO{sub 2} desorbed between 500 and 950 C).

Choudhary, V.R.; Mulla, S.A.R.; Uphade, B.S. [National Chemistry Lab., Pune (India). Chemical Engineering Div.] [National Chemistry Lab., Pune (India). Chemical Engineering Div.

1998-06-01

362

Coupling of solar-assisted advanced oxidative and biological treatment for degradation of agro-residue-based soda bleaching effluent.  

PubMed

This study evaluates the effect of integrated solar-assisted advanced oxidation process (AOP) and biological treatment on the extent of degradation of effluents from chlorination (C) and first alkaline extraction (E(1)) stages of soda pulp bleaching in agro-residue-based pulp and paper mill. Biodegradation of the effluents was attempted in suspended mode using activated sludge from the functional pulp and paper industry effluent treatment plant acclimatized to effluents in question. The photocatalytic treatment was employed using zinc oxide (ZnO) in slurry mode for decontamination of effluents in a batch manner and the degradation was evaluated in terms of reduction in chemical oxygen demand. The biological treatment (24 h) of C and E(1) effluent resulted in 30 and 57 % of degradation, respectively. Solar-induced AOP of C and E(1) effluents resulted in 53 and 43 % degradation under optimized conditions (2.5 g L(-1) ZnO at pH 8.0) after 6 h of exposure. For C effluent, a short duration of solar/ZnO (1 h) prior to biological treatment reduced the time required at biological step from 24 to 12 h for almost same extent (92 %) of degradation. However, sequential biological treatment (24 h) followed by solar/ZnO (2 h) resulted in 85.5 % degradation. In contrast, in the case of E(1) effluent, sequential biological (24 h)-solar/ZnO (2 h) system effectively degrades effluent to 95.4 % as compared to 84.8 % degradation achieved in solar/ZnO (2 h)-biological treatment (24 h) system. In the present study, the sequencing of photocatalysis with the biological treatment is observably efficient and technically viable process for the complete mineralization of the effluents. PMID:22645007

Dhir, Amit; Prakash, Nagaraja Tejo; Sud, Dhiraj

2012-11-01

363

Oak Ridge 25-MV tandem accelerator  

SciTech Connect

A brief description is presented of the scope and status of the heavy ion accelerator facility, and status of the project is discussed. Initial operation of the 25 MV tandem accelerator from National Electrostatics Corporation is covered. (GHT)

Jones, C.M.

1981-01-01

364

On decision making in tandem networks  

E-print Network

We study the convergence of Bayesian learning in a tandem social network. Each agent receives a noisy signal about the underlying state of the world, and observes her predecessor's action before choosing her own. We ...

Dia, Manal

2009-01-01

365

Graphene oxide-silica composite coating hollow fiber solid phase microextraction online coupled with inductively coupled plasma mass spectrometry for the determination of trace heavy metals in environmental water samples.  

PubMed

In this work, a novel graphene oxide-silica (GO-silica) composite coating was prepared for hollow fiber solid phase microextraction (HF-SPME) of trace Mn, Co, Ni, Cu, Cd and Pb followed by on-line inductively coupled plasma mass spectrometry (ICP-MS) detection. The structure of the prepared graphene oxide and GO-silica composite was studied and elucidated by atomic force microscopy (AFM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The GO-silica composite coated hollow fiber was characterized by scanning electron microscope (SEM), and the results show that the GO-silica composite coating possessed a homogeneous and wrinkled structure. Various experimental parameters affecting the extraction of the target metal ions by GO-silica composite coated HF-SPME have been investigated carefully. Under the optimum conditions, the limits of detection (LODs, 3?) for Mn, Co, Ni, Cu, Cd and Pb were 7.5, 0.39, 20, 23, 6.7 and 28 ng L(-1) and the relative standard deviations (RSDs, c(Mn, Co, Cd)=0.05 ?g L(-1), c(Ni, Cu, Pb)=0.2 ?g L(-1), n=7) were 7.2, 7.0, 5.6, 7.3, 7.8 and 4.6%, respectively. The accuracy of the proposed method was validated by the analysis of Certified Reference Material of GSBZ 50009-88 environmental water and the determined values were in a good agreement with the certified values. The proposed method has been successfully applied for the determination of trace metals in real environmental water samples with recoveries ranging from 85 to 119%. PMID:24725857

Su, Shaowei; Chen, Beibei; He, Man; Hu, Bin

2014-06-01

366

Nanocrystal bilayer for tandem catalysis Yusuke Yamada1, Chia-Kuang Tsung1,2, Wenyu Huang1,2, Ziyang Huo1, Susan E. Habas1,2,  

E-print Network

of activity, selectiv- ity and durability. The application of shape- and size-controlled metal oxide nano the composition and interface of the metal nanoparticles and oxide supports. Rational design of metal­metal oxide. We introduce here a new class of nanocrystal tandem catalysts that have multiple metal­metal oxide

Yang, Peidong

367

Total microcystins analysis in water using laser diode thermal desorption-atmospheric pressure chemical ionization-tandem mass spectrometry.  

PubMed

A new approach for the analysis of the cyanobacterial microcystins (MCs) in environmental water matrices has been developed. It offers a cost efficient alternative method for the fast quantification of total MCs using mass spectrometry. This approach permits the quantification of total MCs concentrations without requiring any derivatization or the use of a suite of MCs standards. The oxidation product 2-methyl-3-methoxy-4-phenylbutyric acid (MMPB) was formed through a Lemieux oxidation and represented the total concentration of free and bound MCs in water samples. MMPB was analyzed using laser diode thermal desorption-atmospheric pressure chemical ionization coupled to tandem mass spectrometry (LDTD-APCI-MS/MS). LDTD is a robust and reliable sample introduction method with ultra-fast analysis time (<15 s sample(-1)). Several oxidation and LDTD parameters were optimized to improve recoveries and signal intensity. MCs oxidation recovery yield was 103%, showing a complete reaction. Internal calibration with standard addition was achieved with the use of 4-phenylbutyric acid (4-PB) as internal standard and showed good linearity (R(2)>0.999). Limits of detection and quantification were 0.2 and 0.9 ?g L(-1), respectively. These values are comparable with the WHO (World Health Organization) guideline of 1 ?g L(-1) for total microcystin-LR congener in drinking water. Accuracy and interday/intraday variation coefficients were below 15%. Matrix effect was determined with a recovery of 91%, showing no significant signal suppression. This work demonstrates the use of the LDTD-APCI-MS/MS interface for the screening, detection and quantification of total MCs in complex environmental matrices. PMID:24745740

Roy-Lachapelle, Audrey; Fayad, Paul B; Sinotte, Marc; Deblois, Christian; Sauvé, Sébastien

2014-04-11

368

Base excision repair of oxidative DNA damage coupled with removal of a CAG repeat hairpin attenuates trinucleotide repeat expansion  

PubMed Central

Trinucleotide repeat (TNR) expansion is responsible for numerous human neurodegenerative diseases. However, the underlying mechanisms remain unclear. Recent studies have shown that DNA base excision repair (BER) can mediate TNR expansion and deletion by removing base lesions in different locations of a TNR tract, indicating that BER can promote or prevent TNR expansion in a damage location–dependent manner. In this study, we provide the first evidence that the repair of a DNA base lesion located in the loop region of a CAG repeat hairpin can remove the hairpin, attenuating repeat expansion. We found that an 8-oxoguanine located in the loop region of CAG hairpins of varying sizes was removed by OGG1 leaving an abasic site that was subsequently 5?-incised by AP endonuclease 1, introducing a single-strand breakage in the hairpin loop. This converted the hairpin into a double-flap intermediate with a 5?- and 3?-flap that was cleaved by flap endonuclease 1 and a 3?-5? endonuclease Mus81/Eme1, resulting in complete or partial removal of the CAG hairpin. This further resulted in prevention and attenuation of repeat expansion. Our results demonstrate that TNR expansion can be prevented via BER in hairpin loops that is coupled with the removal of TNR hairpins. PMID:24423876

Xu, Meng; Lai, Yanhao; Torner, Justin; Zhang, Yanbin; Zhang, Zunzhen; Liu, Yuan

2014-01-01

369

Estradiol coupling to human monocyte nitric oxide release is dependent on intracellular calcium transients: evidence for an estrogen surface receptor.  

PubMed

We tested the hypothesis that estrogen acutely stimulates constitutive NO synthase (cNOS) activity in human peripheral monocytes by acting on an estrogen surface receptor. NO release was measured in real time with an amperometric probe. 17beta-estradiol exposure to monocytes stimulated NO release within seconds in a concentration-dependent manner, whereas 17alpha-estradiol had no effect. 17beta-estradiol conjugated to BSA (E2-BSA) also stimulated NO release, suggesting mediation by a membrane surface receptor. Tamoxifen, an estrogen receptor inhibitor, antagonized the action of both 17beta-estradiol and E2-BSA, whereas ICI 182,780, a selective inhibitor of the nuclear estrogen receptor, had no effect. We further showed, using a dual emission microfluorometry in a calcium-free medium, that the 17beta-estradiol-stimulated release of monocyte NO was dependent on the initial stimulation of intracellular calcium transients in a tamoxifen-sensitive process. Leeching out the intracellular calcium stores abolished the effect of 17beta-estradiol on NO release. RT-PCR analysis of RNA obtained from the cells revealed a strong estrogen receptor-alpha amplification signal and a weak beta signal. Taken together, a physiological dose of estrogen acutely stimulates NO release from human monocytes via the activation of an estrogen surface receptor that is coupled to increases in intracellular calcium. PMID:10490972

Stefano, G B; Prevot, V; Beauvillain, J C; Fimiani, C; Welters, I; Cadet, P; Breton, C; Pestel, J; Salzet, M; Bilfinger, T V

1999-10-01

370

Coupling digestion in a pilot-scale UASB reactor and electrochemical oxidation over BDD anode to treat diluted cheese whey.  

PubMed

The efficiency of the anaerobic treatment of cheese whey (CW) at mesophilic conditions was investigated. In addition, the applicability of electrochemical oxidation as an advanced post-treatment for the complete removal of chemical oxygen demand (COD) from the anaerobically treated cheese whey was evaluated. The diluted cheese whey, having a pH of 6.5 and a total COD of 6 g/L, was first treated in a 600-L, pilot-scale up-flow anaerobic sludge blanket (UASB) reactor. The UASB process, which was operated for 87 days at mesophilic conditions (32?±?2 °C) at a hydraulic retention time (HRT) of 3 days, led to a COD removal efficiency between 66 and 97 %, while the particulate matter of the wastewater was effectively removed by entrapment in the sludge blanket of the reactor. When the anaerobic reactor effluent was post-treated over a boron-doped diamond (BDD) anode at 9 and 18 A and in the presence of NaCl as the supporting electrolyte, complete removal of COD was attained after 3-4 h of reaction. During electrochemical experiments, three groups of organochlorinated compounds, namely trihalomethanes (THMs), haloacetonitriles (HANs), and haloketons (HKs), as well as 1,2-dichloroethane (DCA) and chloropicrin were identified as by-products of the process; these, alongside free chlorine, are thought to increase the matrix ecotoxicity to Artemia salina. PMID:24793070

Katsoni, Alphathanasia; Mantzavinos, Dionissios; Diamadopoulos, Evan

2014-11-01

371

Formation of polymeric pigments in the presence of bacteria and comparison with chemical oxidative coupling—II. Catabolism of tyrosine and hydroxyphenylacetic acid by Alcaligenes eutrophus CH34 and mutants  

Microsoft Academic Search

The formation of polymeric pigments using bacteria was investigated to produce new polymers. Polymeric pigments are formed from mutant strains of Alcaligenes eutrophus which are not able to open the aromatic ring (tyu?) but transform tyrosine into p-hydroxyphenylacetic acid. This compound is then hydroxylated into homogentisic acid which undergoes oxidative coupling into polymeric pigments. Another carbon source is required to

C. David; A. Daro; E. Szalai; T. Atarhouch; M. Mergeay

1996-01-01

372

Analysis of protein solvent accessible surfaces by photochemical oxidation and mass spectrometry.  

PubMed

Protein surfaces are important in most biological processes, including protein-protein interactions, enzymatic catalysis, and protein-ligand binding. We report a method in which hydroxyl radicals generated by a rapid-UV irradiation of a 15% hydrogen peroxide solution were utilized to oxidize specific amino acid side chains of two model proteins (lysozyme, beta-lactoglobulin A), according to the residues' chemical reactivities and the solvent accessibility of the reactive carbons and sulfurs in the residue. Oxidized peptides generated by tryptic digestion were identified by electrospray-Fourier transform mass spectrometry. The specific sites of the stable modification were then identified by reverse-phase liquid chromatography coupled to quadropole ion trap tandem mass spectrometry. The solvent accessibility of the residue was shown to directly affect the rate of oxidation by this method (with the exception of methionine), supporting its use as a rapid measure of the solvent accessibility of specific residues, and in some cases, individual atoms. PMID:14750862

Sharp, Joshua S; Becker, Jeffrey M; Hettich, Robert L

2004-02-01

373

Thermodynamic Modeling of a Solid Oxide Fuel Cell to Couple with an Existing Gas Turbine Engine Model  

NASA Technical Reports Server (NTRS)

The Controls and Dynamics Technology Branch at NASA Glenn Research Center are interested in combining a solid oxide fuel cell (SOFC) to operate in conjunction with a gas turbine engine. A detailed engine model currently exists in the Matlab/Simulink environment. The idea is to incorporate a SOFC model within the turbine engine simulation and observe the hybrid system's performance. The fuel cell will be heated to its appropriate operating condition by the engine s combustor. Once the fuel cell is operating at its steady-state temperature, the gas burner will back down slowly until the engine is fully operating on the hot gases exhausted from the SOFC. The SOFC code is based on a steady-state model developed by The U.S. Department of Energy (DOE). In its current form, the DOE SOFC model exists in Microsoft Excel and uses Visual Basics to create an I-V (current-voltage) profile. For the project's application, the main issue with this model is that the gas path flow and fuel flow temperatures are used as input parameters instead of outputs. The objective is to create a SOFC model based on the DOE model that inputs the fuel cells flow rates and outputs temperature of the flow streams; therefore, creating a temperature profile as a function of fuel flow rate. This will be done by applying the First Law of Thermodynamics for a flow system to the fuel cell. Validation of this model will be done in two procedures. First, for a given flow rate the exit stream temperature will be calculated and compared to DOE SOFC temperature as a point comparison. Next, an I-V curve and temperature curve will be generated where the I-V curve will be compared with the DOE SOFC I-V curve. Matching I-V curves will suggest validation of the temperature curve because voltage is a function of temperature. Once the temperature profile is created and validated, the model will then be placed into the turbine engine simulation for system analysis.

Brinson, Thomas E.; Kopasakis, George

2004-01-01

374

Tandem repeats derived from centromeric retrotransposons  

PubMed Central

Background Tandem repeats are ubiquitous and abundant in higher eukaryotic genomes and constitute, along with transposable elements, much of DNA underlying centromeres and other heterochromatic domains. In maize, centromeric satellite repeat (CentC) and centromeric retrotransposons (CR), a class of Ty3/gypsy retrotransposons, are enriched at centromeres. Some satellite repeats have homology to retrotransposons and several mechanisms have been proposed to explain the expansion, contraction as well as homogenization of tandem repeats. However, the origin and evolution of tandem repeat loci remain largely unknown. Results CRM1TR and CRM4TR are novel tandem repeats that we show to be entirely derived from CR elements belonging to two different subfamilies, CRM1 and CRM4. Although these tandem repeats clearly originated in at least two separate events, they are derived from similar regions of their respective parent element, namely the long terminal repeat (LTR) and untranslated region (UTR). The 5? ends of the monomer repeat units of CRM1TR and CRM4TR map to different locations within their respective LTRs, while their 3? ends map to the same relative position within a conserved region of their UTRs. Based on the insertion times of heterologous retrotransposons that have inserted into these tandem repeats, amplification of the repeats is estimated to have begun at least ~4 (CRM1TR) and ~1 (CRM4TR) million years ago. Distinct CRM1TR sequence variants occupy the two CRM1TR loci, indicating that there is little or no movement of repeats between loci, even though they are separated by only ~1.4 Mb. Conclusions The discovery of two novel retrotransposon derived tandem repeats supports the conclusions from earlier studies that retrotransposons can give rise to tandem repeats in eukaryotic genomes. Analysis of monomers from two different CRM1TR loci shows that gene conversion is the major cause of sequence variation. We propose that successive intrastrand deletions generated the initial repeat structure, and gene conversions increased the size of each tandem repeat locus. PMID:23452340

2013-01-01

375

Cisapride a green analytical reagent for rapid and sensitive determination of bromate in drinking water, bread and flour additives by oxidative coupling spectrophotometric methods.  

PubMed

Green analytical methods using Cisapride (CPE) as green analytical reagent was investigated in this work. Rapid, simple, and sensitive spectrophotometric methods for the determination of bromate in water sample, bread and flour additives were developed. The proposed methods based on the oxidative coupling between phenoxazine and Cisapride in the presence of bromate to form red colored product with max at 520 nm. Phenoxazine and Cisapride and its reaction products were found to be environmentally friendly under the optimum experimental condition. The method obeys beers law in concentration range 0.11-4.00 g ml(-1) and molar absorptivity 1.41 × 10(4) L mol(-1)cm(-1). All variables have been optimized and the presented reaction sequences were applied to the analysis of bromate in water, bread and flour additive samples. The performance of these method was evaluated in terms of Student's t-test and variance ratio F-test to find out the significance of proposed methods over the reference method. The combination of pharmaceutical drugs reagents with low concentration create some unique green chemical analyses. PMID:23261631

Al Okab, Riyad Ahmed

2013-02-15

376

Cisapride a green analytical reagent for rapid and sensitive determination of bromate in drinking water, bread and flour additives by oxidative coupling spectrophotometric methods  

NASA Astrophysics Data System (ADS)

Green analytical methods using Cisapride (CPE) as green analytical reagent was investigated in this work. Rapid, simple, and sensitive spectrophotometric methods for the determination of bromate in water sample, bread and flour additives were developed. The proposed methods based on the oxidative coupling between phenoxazine and Cisapride in the presence of bromate to form red colored product with max at 520 nm. Phenoxazine and Cisapride and its reaction products were found to be environmentally friendly under the optimum experimental condition. The method obeys beers law in concentration range 0.11-4.00 g ml-1 and molar absorptivity 1.41 × 104 L mol-1 cm-1. All variables have been optimized and the presented reaction sequences were applied to the analysis of bromate in water, bread and flour additive samples. The performance of these method was evaluated in terms of Student's t-test and variance ratio F-test to find out the significance of proposed methods over the reference method. The combination of pharmaceutical drugs reagents with low concentration create some unique green chemical analyses.

Al Okab, Riyad Ahmed

2013-02-01

377

Monitoring of phosphorus oxide ion for analytical speciation of phosphite and phosphate in transgenic plants by high-performance liquid chromatography-inductively coupled plasma mass spectrometry.  

PubMed

Large amounts of phosphate fertilizers utilized in agriculture and their relatively poor efficiency are of high ecological and economic concern. Therefore, transgenic plants capable of metabolizing phosphite are being engineered. In support of this biotechnological task, analytical speciation of phosphorus in biological tissues is required. In this study, plant extracts were analyzed by liquid chromatography-inductively coupled plasma mass spectrometry at m/z of elemental phosphorus and phosphorus oxide ions. Using polymeric-based anion exchange column and millimolar concentration of nitric acid in potassium phthalate mobile phase (pH 2.5), phosphite and phosphate ions were baseline resolved with retention times 6.95 ± 0.03 and 7.90 ± 0.03 min and with a total chromatographic run time 10 min. The detection limits were 1.58 and 1.74 ?g P L(-1) at m/z 47, as compared to 2.18 and 2.04 ?g P L(-1) at m/z 31, respectively. The results obtained in real world samples for the two detection modes were in good agreement, yet signal acquisition at m/z 47 enabled better precision without collision/reaction cell (RSD below 2%) as compared to RSD around 4% obtained at m/z 31 using He-pressurized cell (3.5 mL min(-1)). PMID:23782169

Torres Elguera, Julio Cesar; Yañez Barrientos, Eunice; Wrobel, Katarzyna; Wrobel, Kazimierz

2013-07-10

378

Quantitative control of poly(ethylene oxide) surface antifouling and biodetection through azimuthally enhanced grating coupled-surface plasmon resonance sensing  

NASA Astrophysics Data System (ADS)

Grating Coupled-Surface Plasmon reflectivity measurements carried out under azimuth and polarization control (GC-SPR ? ? 0°) were used to optimize the process of gold surface dressing with poly(ethylene oxide) (PEO) derivatives of different molecular weight, with the final goal to maximize the discrimination between specific and non-specific binding events occurring at the surface. The kinetics of surface deposition of thiol-ending PEOs (0.3, 2 and 5 kDa), introduced as antifouling layers, was monitored. Non-specific binding events upon immersion of the surfaces into buffers containing either 0.1% bovine serum albumin or 1% Goat Serum, were evaluated as a function of polymer size and density. A biorecognition event between avidin and biotin was then monitored in both buffers at selected low and high polymer surface densities and the contribution of analyte and fouling elements to the signal was precisely quantified. The 0.3 kDa PEO film was unable to protect the surface from non-specific interactions at any tested density. On the other hand, the 2 and 5 kDa polymers at their highest surface densities guaranteed full protection from non-specific interactions from both buffers. These densities were reached upon a long deposition time (24-30 h). The results pave the way toward the application of this platform for the detection of low concentration and small dimension analytes, for which both non-fouling and high instrumental sensitivity are fundamental requirements.

Sonato, Agnese; Silvestri, Davide; Ruffato, Gianluca; Zacco, Gabriele; Romanato, Filippo; Morpurgo, Margherita

2013-12-01

379

Pd-Ni alloy nanoparticle doped mesoporous SiO? film: the sacrificial role of Ni to resist Pd-oxidation in the C-C coupling reaction.  

PubMed

A Pd-Ni alloy nanoparticle (NP) doped mesoporous SiO2 film was synthesized using a one pot inorganic-organic sol-gel process in the presence of structure director P123. Pure Pd and Ni NP containing films were also synthesized as controls. Overall a composition of 10 mol% metal (in the case of Pd-Ni, 5 mol% of each metal) and 90 equivalent mol% SiO2 was maintained in the heat-treated films. Grazing incidence X-ray diffraction and transmission electron microscopy studies of the final heat-treated Pd-Ni doped films revealed the (111) oriented growth of the Pd-Ni alloy NPs, with an average size of 5.3 nm, residing inside the mesopores of the SiO2 film. We performed the C-C coupling reaction employing the film-catalysts and the progress of the reaction was monitored using a fluorimeter. Overall, only the Pd-Ni alloy NP doped film showed good catalytic activity with excellent recyclability. It has been determined that the higher oxidising ability of metallic Ni restricted the oxidation of Pd in the Pd-Ni alloy catalyst under the reaction conditions, leading to the maintained reusability in consecutive cycles. PMID:25061004

Saha, Jony; Bhowmik, Koushik; Das, Indranee; De, Goutam

2014-09-21

380

Solid-phase extraction of Cu, Co and Pb on oxidized single-walled carbon nanotubes and their determination by inductively coupled plasma mass spectrometry.  

PubMed

A novel method using a microcolumn packed with single-walled carbon nanotubes (SWNTs) as a new adsorption material was developed for the preconcentration of trace Cu, Co and Pb in biological and environmental samples prior to their determination by inductively coupled plasma mass spectrometry (ICP-MS). SWNTs oxidized with concentrated nitric acid have been proved to possess an exceptional adsorption capability for the analytes due to their surface functionalization. The adsorption behaviors of the analytes on SWNTs under dynamic conditions were studied systematically. The main factors influencing the preconcentration and determination of the analytes (pH, sample flow rate and volume, eluent concentration and interfering ions) have been examined in detail. Under the optimum conditions, the detection limits for Cu, Co and Pb were 39, 1.2 and 5.4 pg mL(-1), respectively; the relative standard deviations (RSDs) were found to be less than 6.0% (n=9, c=1.0 ng mL(-1)). This method was validated using a certified reference material of mussel, and has been successfully applied for the determination of trace Cu, Co and Pb in real water sample with the recoveries of 96.0-109%. PMID:19473762

Chen, Shizhong; Liu, Cheng; Yang, Ming; Lu, Dengbo; Zhu, Li; Wang, Zhan

2009-10-15

381

Oligochitosan stimulated phagocytic activity of macrophages from blunt snout bream (Megalobrama amblycephala) associated with respiratory burst coupled with nitric oxide production.  

PubMed

The immunostimulating effects of oligochitosan have been proven in several fish, however, the mechanisms underlying the stimulation are not characterized. In the present study, the effects of oligochitosan were investigated using macrophages isolated from blunt snout bream (Megalobrama amblycephala). The results showed that the phagocytic activity of the macrophages was enhanced by the addition of oligochitosan in vitro and in vivo. The two of the most important antimicrobial pathways of macrophages, NADPH oxidase and iNOS pathways were included for further studies. The amounts of superoxide anion and the mRNAs of the five subunits of NADPH oxidase genes were significantly enhanced in the oligochitosan-treated macrophages and macrophages isolated from fish fed with feed containing oligochitosan. In addition, the NO production, iNOS activity and iNOS gene expression were all significantly increased in the presence of oligochitosan. Furthermore, the mRNA levels of the TNF-? and IL-1? were also significantly increased in the macrophages derived from fish fed with oligochitosan. In conclusion, the stimulation effects of oligochitosan on the phagocytic activity of the fish macrophages were associated with respiratory burst coupled with nitric oxide production. PMID:24968077

Liu, Lichun; Zhou, Yang; Zhao, Xiaoheng; Wang, Hong; Wang, Li; Yuan, Gailing; Asim, Muhammad; Wang, Weimin; Zeng, Lingbing; Liu, Xiaoling; Lin, Li

2014-11-01

382

Development and evaluation of a liquid chromatography tandem mass spectrometry method for simultaneous determination of salivary melatonin, cortisol and testosterone  

Microsoft Academic Search

Circadian disruption can have several possible health consequences, but is not well studied. In order to measure circadian disruption, in relation to shift or night work, we developed a simple and sensitive method for the simultaneous determination of melatonin, cortisol and testosterone in human saliva. We used liquid–liquid extraction (LLE) followed by liquid chromatography coupled to electrospray tandem mass spectrometry

Marie Aarrebo Jensen; Åse Marie Hansen; Peter Abrahamsson; Asger W. Nørgaard

2011-01-01

383

Development of a negative hydrogen ion source for tandem proton accelerator using transformer couled plasma sources  

Microsoft Academic Search

A negative hydrogen ion source based on the transformer coupled plasma (TCP) source has been developed for 1.75 MeV tandem proton accelerator to detect underground explosives and mines. The TCP-based ion source has been designed and constructed for H- beam currents of 10 mA at the extraction voltage of 30 kV. High-density hydrogen plasmas of 1012 cm-3 are generated by

I. S. Hong; Y. S. Hwang; Y. S. Cho

2002-01-01

384

Development of a negative hydrogen ion source for tandem proton accelerator using transformer couled plasma sources  

Microsoft Academic Search

A negative hydrogen ion source based on the transformer coupled plasma (TCP) source has been developed for 1.75 MeV tandem proton accelerator to detect underground explosives and mines. The TCP-based ion source has been designed and constructed for H? beam currents of 10 mA at the extraction voltage of 30 kV. High-density hydrogen plasmas of 1012 cm?3 are generated by

I. S. Hong; Y. S. Hwang; Y. S. Cho

2002-01-01

385

Recent advances of liquid chromatography–(tandem) mass spectrometry in clinical and forensic toxicology  

Microsoft Academic Search

Liquid chromatography (LC) coupled to mass spectrometry (MS) or tandem mass spectrometry (MS\\/MS) has become increasingly important in clinical and forensic toxicology as well as doping control and is now a robust and reliable technique for routine analysis in these fields. In recent years, methods for LC–MS(\\/MS)-based systematic toxicological analysis using triple quadrupole or ion trap instruments have been considerably

Frank T. Peters

2011-01-01

386

Global Analysis of the Membrane Subproteome of Pseudomonas aeruginosa using Liquid Chromatography-Tandem Mass Spectrometry  

Microsoft Academic Search

Pseudomonas aeruginosa is one of the most significant opportunistic bacterial pathogens in humans causing infections and premature death in patients with cystic fibrosis, AIDS, severe burns, organ transplants or cancer. Liquid chromatography coupled online with tandem mass spectrometry (LC-MS\\/MS) was used for the large-scale proteomic analysis of the P. aeruginosa membrane subproteome. Concomitantly, an affinity labeling technique, using iodoacetyl-PEO biotin

Josip Blonder; Michael B. Goshe; Wenzhong Xiao; David G. Camp; Mark A. Wingerd; Ronald W. Davis; Richard D. Smith

2004-01-01

387

Determination of organic acids in fruits and vegetables by liquid chromatography with tandem-mass spectrometry  

Microsoft Academic Search

A method using liquid chromatography coupled to tandem-mass spectrometry (LC–MS\\/MS) with triple quadrupole in selective reaction monitoring mode was developed to determine organic acids (glutamic, tartaric, quinic, malonic, malic, shikimic, ?-ketoglutaric, pyruvic, citric, succinic and fumaric acids) in fruits (melon, grape, peach, orange, lemon) and vegetables (green and red pepper, tomato, lettuce and lamb’s lettuce). The negative ion mode of

Pilar Flores; Pilar Hellín; José Fenoll

388

Start | View At a Glance | Author Index 219-5 Coupled Biotic and Abiotic Arsenite Oxidation Kinetics with Heterotrophic Soil Bacteria and a Poorly Crystalline  

E-print Network

Kinetics with Heterotrophic Soil Bacteria and a Poorly Crystalline Manganese Oxide. See more from(V) and that soil bacteria can also oxidize As(III). It is thought that heterotrophic As(III) oxidation is a detoxification mechanism for bacteria. Here, the apparent rate and rate constants of As(III) oxidation by four

Sparks, Donald L.

389

Development, Validation and Application of Tandem Mass Spectrometry for Screening of Inborn Metabolic Disorders in Kuwaiti Infants  

Microsoft Academic Search

Objective: The aim of this work was to develop a specific and validated tandem mass spectrometric (MS\\/MS) method for screening of amino acidopathies, organic acidurias, urea cycle disorders and fatty acid oxidation defects in Kuwaiti newborns and sick infants. Materials and Methods: A total of 1,520 blood samples were tested for inborn metabolic disorders in Kuwaiti newborns and sick infants.

Mohammed Abdel-Hamid; Klara Tisocki; Laila Sharaf; Dina Ramadan

2007-01-01

390

Synfuels from fusion: using the tandem mirror reactor and a thermochemical cycle to produce hydrogen  

SciTech Connect

This study is concerned with the following area: (1) the tandem mirror reactor and its physics; (2) energy balance; (3) the lithium oxide canister blanket system; (4) high-temperature blanket; (5) energy transport system-reactor to process; (6) thermochemical hydrogen processes; (7) interfacing the GA cycle; (8) matching power and temperature demands; (9) preliminary cost estimates; (10) synfuels beyond hydrogen; and (11) thermodynamics of the H/sub 2/SO/sub 4/-H/sub 2/O system. (MOW)

Werner, R.W. (ed.)

1982-11-01

391

Tandem transformation of glycerol to esters.  

PubMed

Tandem transformation of glycerol via microbial fermentation and enzymatic esterification is presented. The reaction can be performed with purified waste glycerol from biodiesel production in a continuous mode, combining continuous fermentation with membrane-supported enzymatic esterification. Continuous anaerobic fermentation was optimized resulting in the productivity of 2.4 g L?¹ h?¹ of 1,3-propanediol. Biphasic esterification of 1,3-propanediol was optimized to achieve ester yield of up to 75%. A hollow fibre membrane contactor with immobilized Rhizomucor miehei lipase was demonstrated for the continuous tandem fermentation-esterification process. PMID:22796408

Sotenko, Maria V; Rebroš, Martin; Sans, Victor S; Loponov, Konstantin N; Davidson, Matthew G; Stephens, Gill; Lapkin, Alexei A

2012-12-31

392

Alpha particle confinement in tandem mirrors  

SciTech Connect

Mechanisms leading to loss of alpha particles from non-axisymmetric tandem mirrors are considered. Stochastic diffusion due to bounce-drift resonances, which can cause rapid radial losses of high-energy alpha particles, can be suppressed by imposing a 20% rise in axisymmetric fields before the quadrupole transition sections. Alpha particles should then be well-confined until thermal energies when they enter the resonant plateau require. A fast code for computation of drift behavior in reactors is described. Sample calculations are presented for resonant particles in a proposed coil set for the Tandem Mirror Next Step.

Devoto, R.S.; Ohnishi, M.; Kerns, J.; Woo, J.T.

1980-10-10

393

Tandem mirror thermal barrier experimental program plan  

SciTech Connect

This report describes an experimental plan for the development of the Tandem Mirror Thermal Barrier. Included is: (1) a description of thermal barrier related physics experiments; (2) thermal barrier related experiments in the existing TMX and Phaedrus experiments; (3) a thermal barrier TMX upgrade; and (4) initiation of investigations of axisymmetric magnetic geometry. Experimental studies of the first two items are presently underway. Results are expected from the TMX upgrade by the close of 1981 and from axisymmetric tandem mirror experiments at the end of 1983. Plans for Phaedrus upgrades are developing for the same period.

Coensgen, F.H.; Drake, R.P.; Simonen, T.C.

1980-01-02

394

Coupling mediated by photorefractive phase grating between visible radiation and surface plasmon polaritons in iron-doped LiNbO3 crystal slabs coated with indium–tin oxide  

NASA Astrophysics Data System (ADS)

Photorefractive (PR) phase gratings were used in coupling energy between visible light and surface plasmon polaritons in indium–tin oxide (ITO)-coated iron-doped lithium niobate (Fe:LN) crystal slabs via electrostatic modification at the ITO/LN interface based on a strong photovoltaic effect. The energy coupling is considered to be responsible for several interesting observations: (1) dynamic reflectivity change from 3.25 to 37.0% of the very first reflection at the entrance slab interface, (2) total light reflectivity as high as 89%, and (3) two-dimensional diffraction patterns without external feedback needed.

Wang, Hao; Zhao, Hua; Xu, Chao; Li, Liang; Hu, Guangwei; Zhang, Jingwen

2014-10-01

395

Tandem mass spectrometry in the clinical chemistry laboratory  

Microsoft Academic Search

Tandem mass spectrometry is becoming an increasingly important analytical technology in the clinical laboratory environment. Applications in toxicology and therapeutic drug monitoring have opened the door for tandem mass spectrometry and now we are seeing a vast array of new applications being developed. It has been the combination of tandem mass spectrometry with sample introduction techniques employing atomospheric pressure ionization

Kent C. Dooley

2003-01-01

396

Tandem repeats finder: a program to analyze DNA sequences  

Microsoft Academic Search

A tandem repeat in DNA is two or more contiguous, approximate copies of a pattern of nucleotides. Tandem repeats have been shown to cause human disease, may play a variety of regulatory and evolutionary roles and are important laboratory and analytic tools. Extensive knowledge about pattern size, copy number, mutational history, etc. for tandem repeats has been limited by the

Gary Benson

1999-01-01

397

Metal-oxide interfaces: Where the action is  

NASA Astrophysics Data System (ADS)

Heterogeneous catalyst systems comprising metals supported on oxides are widespread. Evidence now suggests that it is the interfacial regions that are most catalytically active, and this has been exploited to create a tandem nanocatalyst system.

Stair, Peter C.

2011-05-01

398

Technology for large tandem mirror experiments  

SciTech Connect

Construction of a large tandem mirror (MFTF-B) will soon begin at Lawrence Livermore National Laboratory (LLNL). Designed to reach break-even plasma conditions, the facility will significantly advance the physics and technology of magnetic-mirror-based fusion reactors. This paper describes the objectives and the design of the facility.

Thomassen, K.I.

1980-09-04

399

Tandem oligonucleotide synthesis using linker phosphoramidites  

PubMed Central

Multiple oligonucleotides of the same or different sequence, linked end-to-end in tandem can be synthesized in a single automated synthesis. A linker phosphoramidite [R. T. Pon and S. Yu (2004) Nucleic Acids Res., 32, 623–631] is added to the 5?-terminal OH end of a support-bound oligonucleotide to introduce a cleavable linkage (succinic acid plus sulfonyldiethanol) and the 3?-terminal base of the new sequence. Conventional phosphoramidites are then used for the rest of the sequence. After synthesis, treatment with ammonium hydroxide releases the oligonucleotides from the support and cleaves the linkages between each sequence. Mixtures of one oligonucleotide with both 5?- and 3?-terminal OH ends and other oligonucleotides with 5?-phosphorylated and 3?-OH ends are produced, which are deprotected and worked up as a single product. Tandem synthesis can be used to make pairs of PCR primers, sets of cooperative oligonucleotides or multiple copies of the same sequence. When tandem synthesis is used to make two self-complementary sequences, double-stranded structures spontaneously form after deprotection. Tandem synthesis of oligonucleotide chains containing up to six consecutive 20mer (120 bases total), various trinucleotide codons and primer pairs for PCR, or self-complementary strands for in situ formation of double-stranded DNA fragments has been demonstrated. PMID:15814811

Pon, Richard T.; Yu, Shuyuan

2005-01-01

400

Solvent free permanganate oxidations  

Microsoft Academic Search

The oxidations of organic compounds by permanganate under solvent free conditions have been studied. Thiols and primary aromatic amines undergo oxidative coupling reactions to give disulfides and diazenes, respectively, sulfides are oxidized to sulfones, primary and secondary alcohols are converted to aldehydes and ketones, 1,4-diols and cyclic ethers give lactones and arenes are oxidized to the corresponding ?-ketones. The experimental

Ahmad Shaabani; Donald G. Lee

2001-01-01

401

Inverted Three-Junction Tandem Thermophotovoltaic Modules  

NASA Technical Reports Server (NTRS)

An InGaAs-based three-junction (3J) tandem thermophotovoltaic (TPV) cell has been investigated to utilize more of the blackbody spectrum (from a 1,100 C general purpose heat source GPHS) efficiently. The tandem consists of three vertically stacked subcells, a 0.74-eV InGaAs cell, a 0.6- eV InGaAs cell, and a 0.55-eV InGaAs cell, as well as two interconnecting tunnel junctions. A greater than 20% TPV system efficiency was achieved by another group with a 1,040 C blackbody using a single-bandgap 0.6- eV InGaAs cell MIM (monolithic interconnected module) (30 lateral junctions) that delivered about 12 V/30 or 0.4 V/junction. It is expected that a three-bandgap tandem MIM will eventually have about 3 this voltage (1.15 V) and about half the current. A 4 A/cm2 would be generated by a single-bandgap 0.6-V InGaAs MIM, as opposed to the 2 A/cm2 available from the same spectrum when split among the three series-connected junctions in the tandem stack. This would then be about a 50% increase (3xVoc, 0.5xIsc) in output power if the proposed tandem replaced the single- bandgap MIM. The advantage of the innovation, if successful, would be a 50% increase in power conversion efficiency from radioisotope heat sources using existing thermophotovoltaics. Up to 50% more power would be generated for radioisotope GPHS deep space missions. This type of InGaAs multijunction stack could be used with terrestrial concentrator solar cells to increase efficiency from 41 to 45% or more.

Wojtczuk, Steven

2012-01-01

402

An On-Target Performic Acid Oxidation Method Suitable for Disulfide Bond Elucidation Using Capillary Electrophoresis - Mass Spectrometry  

E-print Network

- modified oxytocin after 10 minutes of on-target performic oxidation performed at -20?C........................................................................................... 45 Figure 8. (a) Negative ion tandem mass spectrum for fully oxidized... oxytocin [M ? H + O6]- (CoxYIQNCoxPLG-NH2). Positive ion tandem mass spectra for the carbamidomethyl (CAM) modified oxytocin ion signals (b) [M + H + CAM]+ and (c) [M + H + 2CAM]+. .............................................................. 47...

Williams, Brad J.

2011-08-08

403

Efficient tandem synthesis of methyl esters and imines by using versatile hydrotalcite-supported gold nanoparticles.  

PubMed

Efficient basic hydrotalcite (HT)-supported gold nanoparticle (AuNP) catalysts have been developed for the aerobic oxidative tandem synthesis of methyl esters and imines from primary alcohols catalyzed under mild and soluble-base-free conditions. The catalytic performance can be fine-tuned for these cascade reactions by simple adjustment of the Mg/Al atomic ratio of the HT support. The one-pot synthesis of methyl esters benefits from high basicity (Mg/Al = 5), whereas moderate basicity greatly improves imine selectivity (Mg/Al = 2). These catalysts outperform previously reported AuNP catalysts by far. Kinetic studies show a cooperative enhancement between AuNP and the surface basic sites, which not only benefits the oxidation of the starting alcohol but also the subsequent steps of the tandem reactions. To the best of our knowledge, this is the first time that straightforward control of the composition of the support has been shown to yield optimum AuNP catalysts for different tandem reactions. PMID:22893610

Liu, Peng; Li, Can; Hensen, Emiel J M

2012-09-17

404

A High-throughput Approach for Subcellular IDENTIFICATION OF RAT LIVER PROTEINS USING SUBCELLULAR FRACTIONATION COUPLED WITH  

E-print Network

SUBCELLULAR FRACTIONATION COUPLED WITH TWO-DIMENSIONAL LIQUID CHROMATOGRAPHY TANDEM MASS SPECTROMETRY with two-dimensional liquid chromatography tandem mass spectrometry anal- ysis. A total of 564 rat proteins- teins with electron transfer activity or oxygen binding activity. Such characteristics were more

Tian, Weidong

405

Geobacter metallireducens gen. nov. sp. nov., a microorganism capable of coupling the complete oxidation of organic compounds to the reduction of iron and other metals  

Microsoft Academic Search

The gram-negative metal-reducing microorganism, previously known as strain GS-15, was further characterized. This strict anaerobe oxidizes several short-chain fatty acids, alcohols, and monoaromatic compounds with Fe(III) as the sole electron acceptor. Furthermore, acetate is also oxidized with the reduction of Mn (IV), U (VI), and nitrate. In whole cell suspensions, the c-type cytochrome(s) of this organism was oxidized by physiological

D. R. Lovley; S. J. Giovannoni; D. C. White; J. E. Champine; E. J. P. Phillips; Y. A. Gorby; S. Goodwin

1993-01-01

406

Tandem Reactions for Streamlining Synthesis  

PubMed Central

CONSPECTUS In 1980 Sharpless and Katsuki introduced the asymmetric epoxidation of prochiral allylic alcohols (the Sharpless-Katsuki Asymmetric Epoxidation), which enabled the rapid synthesis of highly enantioenriched epoxy alcohols. This reaction was a milestone in the development of asymmetric catalysis because it was the first highly enantioselective oxidation reaction. Furthermore, it provided access to enantioenriched allylic alcohols that are now standard starting materials in natural product synthesis. In 1981 Sharpless and coworkers made another seminal contribution by describing the kinetic resolution (KR) of racemic allylic alcohols. This work demonstrated that small-molecule catalysts could compete with enzymatic catalysts in KRs. For these pioneering works, Sharpless was awarded the 2001 Nobel Prize with Knowles and Noyori. Despite these achievements, the Sharpless KR is not an efficient method to prepare epoxy alcohols with high enantiomeric excess (ee). First, the racemic allylic alcohol must be prepared and purified. KR of the racemic allylic alcohol must be stopped at low conversion, because the ee of the product epoxy alcohol decreases as the KR progresses. Thus, better methods to prepare epoxy alcohols containing stereogenic carbinol carbons are needed. This Account summarizes our efforts to develop one-pot methods for the synthesis of various epoxy alcohols and allylic epoxy alcohols with high enantio-, diastereo-, and chemoselectivity. Our laboratory developed titanium-based catalysts for use in the synthesis of epoxy alcohols with tertiary carbinols. The catalysts are involved in the first step, which is an asymmetric alkyl or allyl addition to enones. The resulting intermediates are then subjected to a titanium-directed diastereoselective epoxidation to provide tertiary epoxy alcohols. Similarly, the synthesis of acyclic epoxy alcohols begins with asymmetric additions to enals and subsequent epoxidation. The methods described here enable the synthesis of skeletally diverse epoxy alcohols. PMID:18710197

HUSSAIN, MAHMUD M.; WALSH, PATRICK J.

2009-01-01

407

Tandem microwave waste remediation and decontamination system  

DOEpatents

The invention discloses a tandem microwave system consisting of a primary chamber in which microwave energy is used for the controlled combustion of materials. A second chamber is used to further treat the off-gases from the primary chamber by passage through a susceptor matrix subjected to additional microwave energy. The direct microwave radiation and elevated temperatures provide for significant reductions in the qualitative and quantitative emissions of the treated off gases. The tandem microwave system can be utilized for disinfecting wastes, sterilizing materials, and/or modifying the form of wastes to solidify organic or inorganic materials. The simple design allows on-site treatment of waste by small volume waste generators.

Wicks, George G. (North Aiken, SC); Clark, David E. (Gainesville, FL); Schulz, Rebecca L. (Gainesville, FL)

1999-01-01

408

LLNL multi-user tandem laboratory  

NASA Astrophysics Data System (ADS)

The Physics Department at Lawrence Livermore National Laboratory (LLNL) is building a new tandem Van de Graaff laboratory for nuclear physics and applied physics and technology programs. The laboratory has been funded by a coalition of users including several LLNL divisions, Sandia National Laboratories Livermore, and the University of California. The tandem is the former University of Washington injector FN. The accelerator is upgraded with a Pelletron charging system, Dowlish spiral inclined field beam tubes and SF 6 insulation. The laboratory incorporates several novel design concepts. Initial operation will be in June, 1987 with full operation in October, 1987. Design features, radiological controls, computer assisted operation, and experimental facilities of the laboratory are discussed.

Proctor, I. D.; Davis, J. C.; Eaton, M. R.; Garibaldi, J. L.; Moore, T. L.; Schumacher, B. J.; Southon, J. R.; Zimmerman, T. A.

1988-05-01

409

Mechanically stacked concentrator tandem solar cells  

NASA Technical Reports Server (NTRS)

Four-terminal mechanically stacked solar cells were developed for advanced space arrays with line-focus reflective concentrators. The top cells are based on AlGaAs/GaAs multilayer heterostructures prepared by low temperature liquid phase epitaxy. The bottom cells are based on heteroepitaxial InP/InGaAs liquid phase epitaxy or on homo-junction GaSb, Zn-diffused structures. The sum of the highest reached efficiencies of the top and bottom cells is 29.4 percent. The best four-terminal tandems have an efficiency of 27 to 28 percent. Solar cells were irradiated with 1 MeV electrons and their performances were determined as a function of fluence up to 10(exp 16) cm(exp-2). It was shown that the radiation resistance of developed tandem cells is similar to the most radiative stable AlGaAs/GaAs cells with a thin p-GaAs photoactive layer.

Andreev, V. M.; Rumyantsev, V. D.; Karlina, L. B.; Kazantsev, A. B.; Khvostikov, V. P.; Shvarts, M. Z.; Sorokina, S. V.

1995-01-01

410

Development of 1 MV tandem proton accelerator  

Microsoft Academic Search

A 1MV Tandem Proton Accelerator is being developed for the industrial applications such as high-energy implantation and explosive detection. The proton accelerator consists of a 10 mA negative hydrogen ion source, two Einzel lenses, accelerating tubes, a gas stripper, a 1MV 30 mA Cockroft-Walton high voltage power supply, vacuum pumping system, and a high pressure insulating gas system. The large

Y. S. Cho; W. S. Song; B. H. Choi

2001-01-01

411

Current and lattice matched tandem solar cell  

DOEpatents

A multijunction (cascade) tandem photovoltaic solar cell device is fabricated of a Ga.sub.x In.sub.1-x P (0.505.ltoreq.X.ltoreq.0.515) top cell semiconductor lattice matched to a GaAs bottom cell semiconductor at a low-resistance heterojunction, preferably a p+/n+ heterojunction between the cells. The top and bottom cells are both lattice matched and current matched for high efficiency solar radiation conversion to electrical energy.

Olson, Jerry M. (Lakewood, CO)

1987-01-01

412

DDES and IDDES of tandem cylinders.  

SciTech Connect

The paper presents an overview of the authors contribution to the BANC-I Workshop on the flow past tandem cylinders (Category 2). It includes an outline of the simulation approaches, numerics, and grid used, the major results of the simulations, their comparison with available experimental data, and some preliminary conclusions. The effect of varying the spanwise period in the simulations is strong for some quantities, and not others.

Balakrishnan, R.; Garbaruk, A.; Shur, M.; Strelets, M.; Spalart, P.; New Technologies and Services - Russia; St.-Peterburg State Polytechnic Univ.; Boeing Commercial Airplanes

2010-09-09

413

Short Tandem Repeat DNA Internet Database  

NSDL National Science Digital Library

This website contains comprehensive information relating to forensic DNA analysis. It has material from an introductory to an advanced level on forensic DNA technology. The material provides general information on DNA markers that are of interest to human identification. The site contains both introductory and in-depth discussions of short tandem repeats (STRs) and other DNA markers currently used by the forensic community. Powerpoint and PDF presentations on STR training material are available and can be readily downloaded.

2011-04-08