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排序方式: 共有665条查询结果,搜索用时 15 毫秒
401.
Gerardo Cebrián-Torrejón Landry Kablan Maria Elena Ferreira David Rodríguez de la Cruz Antonio Doménech-Carbó Ninfa Vera de Bilbao 《Natural product research》2015,29(21):2054-2058
This article is focused on the seasonal variation in the contents of 5-methoxycanthin-6-one from the leaves of Zanthoxylum chiloperone (Rutaceae). Based on the pharmacological interest presented by 5-methoxycanthin-6-one, its seasonal variation in Z. chiloperone leaves was analysed in order to determine the best time for harvesting, optimising the 5-methoxycanthin-6-one content. The seasonal dynamics of canthinone alkaloids can be the key to improve the isolation from natural sustainable sources, such as leaves. Complementarily, this study describes the phytochemistry of leaf from this Ruraceae species. 相似文献
402.
Omar Y. Chabán Rosa M. Domínguez Armando Herize María Tosta Angela Cuenca Gabriel Chuchani 《Journal of Physical Organic Chemistry》2007,20(5):307-312
The gas phase thermal decarbonylation of α,β‐unsaturated aldehydes E‐2‐butenal and E‐3‐phenyl‐2‐methylpropenal was studied in a static system over the temperature range 380.5–490.0 °C and pressure range 55.5–150 Torr. The reactions are homogeneous and unimolecular and obey a first‐order rate law. The rate coefficient is represented by the following Arrhenius equations: The elimination products of 2‐butenal are propene and CO gas, while 3‐phenyl‐2‐methylpropenal produces α‐methylstyrene, cis‐trans‐β‐methylstyrene, indan, and CO gas. Kinetic and thermodynamic parameters suggest these elimination reactions to proceed through a three‐membered cyclic transition state type of mechanisms. However, a two steps mechanisms for the formation of a carbene type of intermediate through a four‐membered cyclic transition structure can not be overlooked. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
403.
Tellitu I Serna S Herrero MT Moreno I Domínguez E SanMartin R 《The Journal of organic chemistry》2007,72(4):1526-1529
The hypervalent iodine reagent PIFA promotes the intramolecular electrophilic cyclization of easily accessible alkynylamides and alkynyl carboxylic acids, leading to the formation of pyrrolidinone and lactone skeletons, respectively, in a very efficient way. A synthetic study and a mechanistic proposal for these transformations are presented. 相似文献
404.
Carbon screen-printed electrodes (CSPE) modified with silver nanoparticles present an interesting alternative in the determination of lamotrigine (LTG) using differential pulse adsorptive stripping voltammetry.Metallic silver nanoparticle deposits have been obtained by electrochemical deposition. Scanning electron microscopy measurements show that the electrochemically synthesized silver nanoparticles are deposited in aggregated form.The detection limit for this analytical procedure was 3.72 × 10−7 M. In terms of reproducibility, the precision of the above mentioned method in %R.S.D. values was calculated at 2.58%.The method was applied satisfactorily to the determination of LTG in pharmaceutical preparations. 相似文献
405.
Carlos M. Martínez‐Viturro Domingo Domínguez 《Journal of heterocyclic chemistry》2007,44(5):1035-1043
406.
Juan C. Rodríguez‐Domínguez Alexander Balbuzano‐Deus Miguel A. López‐López Juan C. Rodríguez‐Domínguez Gilbert Kirsch 《Journal of heterocyclic chemistry》2007,44(1):273-275
407.
Domínguez-Lledó FC Galindo-Riaño MD Díaz-López IC García-Vargas M Granado-Castro MD 《Analytical and bioanalytical chemistry》2007,389(2):653-659
In this work, a bulk liquid membrane method has been applied for Ni enrichment and separation from natural waters. The carrier-mediated
transport was accomplished by pyridine-2-acetaldehyde benzoylhydrazone dissolved in toluene as a complexing agent. The preconcentration
was achieved through pH control of source and receiving solutions via a counterflow of protons. The main variables were optimized
by using a modified simplex technique. High transport efficiencies (101.2 ± 1.8–99.7 ± 4.2%) were provided by the carrier
for nickel ions in a receiving phase of 0.31 mol L−1 nitric acid after 9–13 h depending on sample salinity. The precision of the method was 2.05% (without a saline matrix) and
4.04% (with 40 g L−1 NaCl) at the 95% confidence level and the detection limit of the blank was 0.015 μg L−1 Ni for detection by atomic absorption spectroscopy. The applicability of the method was tested on certified reference and
real water samples with successful results, even for saline samples. The relative errors were −0.60% for certified reference
materials and ranged from −0.39 to 2.90% and from 0.3 to 11.05% for real samples, obtained by comparison of inductively coupled
plasma mass spectrometry and adsorptive cathodic stripping voltammetry measurements, respectively. 相似文献
408.
409.
Sensitive determination of herbicides in food samples by nonaqueous CE using pressurized liquid extraction 总被引:2,自引:0,他引:2
Carabias-Martínez R Rodríguez-Gonzalo E Miranda-Cruz E Domínguez-Alvarez J Hernández-Méndez J 《Electrophoresis》2007,28(20):3606-3616
We have developed a method involving extraction with mixtures of solvents under pressure (pressurized liquid extraction (PLE)) for the determination of triazine herbicides in a series of samples from the food industry. The organic extracts obtained were subjected to a clean-up step with SPE, using Oasis MCX sorbents, after which they were analyzed by NACE. Potato was chosen as a representative matrix of horticultural products since it has a high water content. Spiked potato samples were used to optimize extraction conditions. In order to compare the results obtained with NACE, different studies were also conducted using HPLC. The detection limits in NACE were similar to those found with HPLC and were of the order of 10-15 microg/kg, depending on the analyte. Satisfactory results were obtained on applying the method proposed for the potato matrix (PLE with separation by electrophoresis) to other food matrices such as other tubercles, fruits, vegetables and cereals. 相似文献
410.
Oliveira E Amara I Bellido D Odena MA Domínguez E Pagès M Goday A 《Journal of mass spectrometry : JMS》2007,42(11):1485-1495
Protein identification in systems containing very highly abundant proteins is not always efficient and usually requires previous enrichment or fractionation steps in order to uncover minor proteins. In plant seeds, identification of late embryogenesis abundant (LEA) proteins is often masked by the presence of the large family of storage proteins. LEA-proteins are predicted to play a role in plant stress tolerance. They are highly hydrophilic proteins, generally heat-stable, and correlate with dehydration in seeds or vegetative tissues. In the present work, we analyze the protein composition of heat-stable Arabidopsis thaliana seed extracts after treatment with trichloroacetic acid (TCA). The composition of the proteins that precipitate and those that remain in solution in 3% TCA was analyzed by two different approaches: 1D SDS-PAGE coupled to LC-ESI-MSMS analysis and a gel-free protocol associated with LC-MALDI-MSMS. Our results indicate that treating total heat-soluble extracts with 3% TCA is an effective procedure to remove storage proteins by selective precipitation and this fractionation step provides a soluble fraction highly enriched in Lea-type proteins. The analysis and determination of protein identities in this acid-soluble fraction by MS technology is a suitable system for large-scale identification of Lea-proteins present in seeds. 相似文献