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排序方式: 共有406条查询结果,搜索用时 12 毫秒
61.
Vera L.M. Silva Artur M.S. Silva Rosa M. Claramunt Concepción López Dionisia Sanz Lourdes Infantes Ángela Martínez López Felipe Reviriego Ibon Alkorta José Elguero 《Tetrahedron》2019,75(48):130690
Tetrakis(1H-pyrazol-1-yl)methanes are very rare compounds of which only two are known: the unsubstituted 1 obtained classically by Hückel in 1937 from carbon tetrachloride and prepared again several times and the 3,5-dimethyl substituted 2 obtained serendipitously by Pombeiro in 2009. We have now extended this group to include four new derivatives 8, 9, 11 and 12 bearing methyl groups. The X-ray crystal structure of the four compounds has been determined. They have been studied by NMR both in solution (1H, 13C, 15N) and in the solid state (13C and 15N). DFT calculations of the six compounds (geometries, energies and absolute shieldings) have been used to discuss the experimental observations. 相似文献
62.
Fluorescent sensor array in a microfluidic chip 总被引:1,自引:0,他引:1
Basabe-Desmonts L Benito-López F Gardeniers HJ Duwel R van den Berg A Reinhoudt DN Crego-Calama M 《Analytical and bioanalytical chemistry》2008,390(1):307-315
Miniaturization and automation are highly important issues for the development of high-throughput processes. The area of micro total analysis systems (muTAS) is growing rapidly and the design of new schemes which are suitable for miniaturized analytical devices is of great importance. In this paper we report the immobilization of self-assembled monolayers (SAMs) with metal ion sensing properties, on the walls of glass microchannels. The parallel combinatorial synthesis of sensing SAMs in individually addressable microchannels towards the generation of optical sensor arrays and sensing chips has been developed. [figure: see text] The advantages of microfluidic devices, surface chemistry, parallel synthesis, and combinatorial approaches have been merged to integrate a fluorescent chemical sensor array in a microfluidic chip. Specifically, five different fluorescent self-assembled monolayers have been created on the internal walls of glass microchannels confined in a microfluidic chip. 相似文献
63.
Rodríguez-Castrillón JA Moldovan M García Alonso JI Lucena JJ García-Tomé ML Hernández-Apaolaza L 《Analytical and bioanalytical chemistry》2008,390(2):579-590
Isotope pattern deconvolution is a mathematical technique for isolating distinct isotope signatures from mixtures of natural
abundance and enriched tracers. In iron metabolism studies measurement of all four isotopes of the element by high-resolution
multicollector or collision cell ICP–MS allows the determination of the tracer/tracee ratio with simultaneous internal mass
bias correction and lower uncertainties. This technique was applied here for the first time to study iron uptake by cucumber
plants using 57Fe-enriched iron chelates of the o,o and o,p isomers of ethylenediaminedi(o-hydroxyphenylacetic) acid (EDDHA) and ethylenediamine tetraacetic acid (EDTA). Samples of root, stem, leaves, and xylem sap,
after exposure of the cucumber plants to the mentioned 57Fe chelates, were collected, dried, and digested using nitric acid. The isotopic composition of iron in the samples was measured
by ICP–MS using a high-resolution multicollector instrument. Mass bias correction was computed using both a natural abundance
iron standard and by internal correction using isotope pattern deconvolution. It was observed that, for plants with low 57Fe enrichment, isotope pattern deconvolution provided lower tracer/tracee ratio uncertainties than the traditional method
applying external mass bias correction. The total amount of the element in the plants was determined by isotope dilution analysis,
using a collision cell quadrupole ICP–MS instrument, after addition of 57Fe or natural abundance Fe in a known amount which depended on the isotopic composition of the sample. 相似文献
64.
Jorge J. Betancor Claudio Jerez Sandra M. Molina Lourdes Rodríguez-Mesa 《Monatshefte für Mathematik》2008,153(2):89-103
In this paper we study the Hankel transformation and convolution on certain spaces
of entire functions and its dual
that is a space of hyperfunctions and contains the (even)-Schwartz space S
e
′. We prove that the Hankel transform is an automorphism of
. Also the Hankel convolutors of
are investigated.
Authors’ addresses: Jorge J. Betancor, Claudio Jerez and Lourdes Rodríguez-Mesa, Departamento de Análisis Matemático, Universidad
de la Laguna, Campus de Anchieta, Avda. Astrofísico Francisco Sánchez, s/n, 38271 La Laguna (Sta. Cruz de Tenerife), Espa?a;
Sandra M. Molina, Departamento de Matemáticas, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata,
Funes 3350 (7600), Mar del Plata, Argentina 相似文献
65.
Ion mobility spectrometry of volatile compounds from Iberian pig fat for fast feeding regime authentication 总被引:1,自引:0,他引:1
Alonso R Rodríguez-Estévez V Domínguez-Vidal A Ayora-Cañada MJ Arce L Valcárcel M 《Talanta》2008,76(3):591-596
Characteristic ion mobility spectra for volatile compounds present in fat were used to authenticate the feeding regime of Iberian pigs. Volatile compounds were obtained by heating the solid samples at 150 degrees C for 40 min. This produced a headspace that was introduced in the spectrometer ionization chamber by means of a highly purified nitrogen stream. The spectra thus, obtained for the fat samples were processed chemometrically in order to assess their usefulness for discriminating meat from free-range pigs fed on pasture and acorns and confined pigs fed with commercial feed including high-oleic acid products. Principal component analysis was used as both an exploratory tool and a variable reduction method, and linear discriminant analysis was employed to classify 65 subcutaneous fat samples according to pig feeding regime. Only 2.3% of the samples from pigs reared in confinement were misclassified. 95.5% of the free-range samples were correctly predicted. 相似文献
66.
An extraction method for the quantitative analysis of polybrominated diphenyl ethers (PBDEs) in aqueous samples has been evaluated. The analytical methodology includes the sample filtration through glass fiber filter and subsequent extraction of dissolved phase compounds by C18 solid-phase disk extraction. Dependence of extraction efficiency on factors such as pollutant concentrations, sample volume, and stability during storage has been investigated. Mean extraction efficiencies of 97% for total PBDEs (13 tri- to heptabrominated congeners at spiking levels in the range of 15-90pg) with a RSD between 9 and 20% were achieved. Higher recoveries were observed for the more volatile PBDEs (112%) in relation to more brominated congeners (88%). The developed methodology was successfully applied to the analysis of these compounds in atmospheric deposition and snow samples from remote sites in Europe with method detection and quantitation limits in the range of 2.1-10pgL(-1) for almost all congeners, which allow the determination of PBDEs in remote areas with levels in the range of low to medium pgL(-1) for SigmaPBDEs. 相似文献
67.
Possible molecular mechanisms of the gas-phase ion/molecule reaction of VO2+ in its lowest singlet and triplet states (1A1/3A' ') with propyne have been investigated theoretically by density functional theory (DFT) methods. The geometries, energetic values, and bonding features of all stationary and intersystem crossing points involved in the five different reaction pathways (paths 1-5), in both high-spin (triplet) and low-spin (singlet) surfaces, are reported and analyzed. The oxidation reaction starts by a hydrogen transfer from propyne molecule to the vanadyl complex, followed by oxygen migration to the hydrocarbon moiety. A hydride transfer process to the vanadium atom opens four different reaction courses, paths 1-4, while path 5 arises from a hydrogen transfer process to the hydroxyl group. Five crossing points between high- and low-spin states are found: one of them takes place before the first branching point, while the others occur along path 1. Four different exit channels are found: elimination of hydrogen molecule to yield propynaldehyde and VO+ (1Sigma/3Sigma); formation of propynaldehyde and the moiety V-(OH2)+; and two elimination processes of water molecule to yield cationic products, Prod-fc+ and Prod-dc+ where the vanadium atom adopts a four- and di-coordinate structure, respectively. 相似文献
68.
Quezada E Delogu G Viña D Santana L Picciau C Podda G Uriarte E 《Magnetic resonance in chemistry : MRC》2008,46(7):701-705
The synthesis of four pyranocoumarins starting from phloroglucinol and the complete (1)H and (13)C NMR assignment of seven pyranocoumarins has been performed using 1D and 2D NMR techniques including COSY, HMQC and HMBC experiments. 相似文献
69.
Veerendra Kalyan Jagannadh Bindu Prabhath Bhat Lourdes Albina Nirupa Julius Sai Siva Gorthi 《Analytical and bioanalytical chemistry》2016,408(7):1909-1916
In this article, we present a novel approach to throughput enhancement in miniaturized microfluidic microscopy systems. Using the presented approach, we demonstrate an inexpensive yet high-throughput analytical instrument. Using the high-throughput analytical instrument, we have been able to achieve about 125,880 cells per minute (more than one hundred and twenty five thousand cells per minute), even while employing cost-effective low frame rate cameras (120 fps). The throughput achieved here is a notable progression in the field of diagnostics as it enables rapid quantitative testing and analysis. We demonstrate the applicability of the instrument to point-of-care diagnostics, by performing blood cell counting. We report a comparative analysis between the counts (in cells per μl) obtained from our instrument, with that of a commercially available hematology analyzer. 相似文献
70.
Synthesis, photophysical properties, and laser behavior of 3-amino and 3-acetamido BODIPY dyes 总被引:1,自引:0,他引:1
Liras M Prieto JB Pintado-Sierra M Arbeloa FL García-Moreno I Costela A Infantes L Sastre R Amat-Guerri F 《Organic letters》2007,9(21):4183-4186
The asymmetrically substituted BODIPY dyes 9a and 9b have been synthesized through a key redox step involving the alpha-nitroso derivative of the starting pyrrol. Both dyes emit fluorescence with quantum yields of ca. 0.7, but only 8b behaves as a good laser dye, with an efficiency of 48% in ethanol solution. 相似文献