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91.
Pérez-Picaso L Rios MY Hernández AN Martínez J 《Magnetic resonance in chemistry : MRC》2006,44(10):959-961
The rhizobacteria Burkholderia cepacia biosynthesized the new tetrapeptide Cyclo[N-(Lys-Phe)-Orn-Val] (1), a 2,5-diketopiperazine, and the known siderophore azurechelin (salicylic acid). The structure of 1 was established by means of IR, UV, 1H and 13C NMR, double dimension experiments and MS. 相似文献
92.
Sanz R Fernandez Y Castroviejo MP Pérez A Fañanas FJ 《The Journal of organic chemistry》2006,71(16):6291-6294
The treatment of 2-fluorophenyl 2-iodophenylamines, ether, and thioether, easily prepared from commercially available products, with 3.3 equiv of t-BuLi and further reaction with selected electrophiles gives rise to functionalized carbazole, dibenzofuran, and dibenzothiophene derivatives in a direct and regioselective manner. The process involves an anionic cyclization on a benzyne-tethered aryllithium intermediate. 相似文献
93.
Optimization of LC-MS/MS using triple quadrupole mass analyzer for the simultaneous analysis of carbosulfan and its main metabolites in oranges 总被引:2,自引:0,他引:2
This paper describes an analytical method involving a simple solvent extraction for the simultaneous liquid chromatography coupled to quadrupole tandem mass spectrometry (LC-MS/MS) determination of carbosulfan, its most toxic metabolite -carbofuran -, and its other main metabolites - 3-hydroxycarbofuran, 3-ketocarbofuran, 3-hydroxy-7-phenolcarbofuran, 3-keto-7-phenolcarbofuran, 7-phenolcarbofuran and dibutylamine - in oranges. Chromatography was performed on a Zorbax Bonus-RP (150 mm × 2.1 mm, 5 μm). The mobile phase was a ternary gradient water-methanol-acetonitrile with 1.0 mM ammonium acetate at flow rate of 0.2 ml min−1. The LC separation and MS/MS optimization were studied to select the most appropriate operating conditions. The method developed has also been validated. The limits of quantification (LOQs) were from 1 μg kg−1 for carbofuran to 10 μg kg−1 for 3-keto-7-phenolcarbofuran. Extracts spiked with carbosulfan and its metabolites, at LOQ level, yielded average recoveries in the range 60-94%, with relative standard deviations (R.S.D.s) less than 15%. Calibration curves for carbosulfan and its metabolites (range LOQ-1000LOQ) were linear, with coefficients of correlations better than 0.990. The method was successfully applied to establish the primary degradation products in oranges treated with carbosulfan. The LC-MS/MS method developed is simple, rapid, and suitable for the quantification and confirmation of carbosulfan and seven of its main metabolites in orange at levels lower than 10 μg kg−1. 相似文献
94.
It is known that the symmetric group S
n
, for n ≥ 5, and the alternating group A
n
, for large n, admit a Beauville structure. In this paper we prove that A
n
admits a Beauville (resp. strongly real Beauville) structure if and only if n ≥ 6 (resp n ≥ 7). We also show that S
n
admits a strongly real Beauville structure for n ≥ 5. 相似文献
95.
In this paper we introduce the Single Period Coverage Facility Location Problem. It is a multi-period discrete location problem
in which each customer is serviced in exactly one period of the planning horizon. The locational decisions are made independently
for each period, so that the facilities that are open need not be the same in different time periods. It is also assumed that
at each period there is a minimum number of customers that can be assigned to the facilities that are open. The decisions
to be made include not only the facilities to open at each time period and the time period in which each customer will be
served, but also the allocation of customers to open facilities in their service period. 相似文献
96.
Yolanda Fuertes 《Archiv der Mathematik》2010,95(1):15-18
Mestre has shown that if a hyperelliptic curve C of even genus is defined over a subfield
k ì \mathbbC{k \subset \mathbb{C}} then C can be hyperelliptically defined over the same field k. In this paper, for all genera g > 1, g o 1{g\equiv1} mod 4, hence odd, we construct an explicit hyperelliptic curve defined over
\mathbbQ{\mathbb{Q}} which can not be hyperelliptically defined over
\mathbbQ{\mathbb{Q}}. 相似文献
97.
Marta Llorca Marinella Farré Yolanda Picó Damià Barceló 《Analytical and bioanalytical chemistry》2010,398(3):1145-1159
The analytical suitabilities of three different liquid chromatography–tandem mass spectrometry (LC-MS/MS) systems, (1) triple quadrupole (QqQ), (2) conventional 3D ion trap (IT), and (3) quadrupole–linear IT (QqLIT), to determine trace levels of perfluorinated compounds (PFCs) in fish and shellfish were compared. Sample preparation was performed using alkaline extraction and solid-phase-extraction cleanup. This evaluation was focused on both quantitative (sensitivity, precision, and accuracy) and qualitative (identification capabilities) aspects. In the three instruments, the former facet was evaluated using selected reaction monitoring (SRM), which is the standard mode for quantitative LC-MS/MS analysis. Accuracy was similar in the three systems, with recoveries always over 70 %. Precision was better for the QqLIT and QqQ systems (7–15%) than for the IT system (10–17%). The QqLIT (working in SRM mode) and QqQ systems offered a linear dynamic range of at least 3 orders of magnitude, whereas that of the IT system was 2 orders of magnitude. The QqLIT system achieved at least 20-fold higher sensitivity than the QqQ system, and this was at least tenfold higher sensitivity than for the IT system. In the IT system, identification was based on sensitive full mass range acquisition and MS n fragmentation and in the QqLIT system, it was based on the use of an information-dependent-acquisition scan function, which allows the combination of an SRM or MS full scan acting as the survey scan and an enhanced product ion scan followed by MS3 as the dependent scan in the same analysis. Three instruments were applied to monitor the content in fish and shellfish (anchovies, swordfish, tuna, mussels, and oysters) obtained from Valencia and Barcelona markets (Spain). The eight target PFCs were detected at mean concentrations in the range from 10 ng ?kg-1 (perfluoro-7-methyloctanoic acid and perfluoro-1-decanesulfonate) to 4,200 ng ?kg-1 (perfluoropentanoic acid). Furthermore, perfluoroheptanoic and perfluoroundecanoic acids (not covered as target analytes) were identified in some samples. Figure
PFCs in the environment 相似文献
98.
99.
100.
Yolanda Vasquez Amanda E. Henkes J. Chris Bauer Raymond E. Schaak 《Journal of solid state chemistry》2008,181(7):1509-1523
The concept of nanocrystal conversion chemistry, which involves the use of pre-formed nanoparticles as templates for chemical transformation into derivative solids, has emerged as a powerful approach for designing the synthesis of complex nanocrystalline solids. The general strategy exploits established synthetic capabilities in simple nanocrystal systems and uses these nanocrystals as templates that help to define the composition, crystal structure, and morphology of product nanocrystals. This article highlights key examples of “conversion chemistry” approaches to the synthesis of nanocrystalline solids using a variety of techniques, including galvanic replacement, diffusion, oxidation, and ion exchange. The discussion is organized according to classes of solids, highlighting the diverse target systems that are accessible using similar chemical concepts: metals, oxides, chalcogenides, phosphides, alloys, intermetallic compounds, sulfides, and nitrides. 相似文献