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991.
A convenient and efficient method for the preparation of unsymmetrical and symmetrical diacetylenic ketones bearing a carboxylate group. 相似文献
992.
E. Manuela Garrido Josél Costa Lima Cristina M. Delerue-matos Ana Maria Oliveira Brett 《International journal of environmental analytical chemistry》2013,93(1-2):149-157
Abstract Cyclic, differential pulse and square wave voltammetry were applied to develop an electroanalytical procedure for the determination of a group of herbicides used to treat rice crops: molinate, bensul-ruron-methyl, mefenacet and thiobencarb. The oxidation mechanism causes adsorption problems and consequent poisoning of the electrode surface by the products of the electrochemical reaction. Parameters such as pH, frequency and electrochemical electrode surface treatment were optimized. The analytical methodology developed using square wave voltammetry was applied to the determination of molinate and bensulfuron-methyl in simple or mixed commercial products. 相似文献
993.
Hsiu‐Fu Hsu Corresponding author Shih‐Jay Chien Hsiu‐Hui Chen Chien‐Hsing Chen Li‐Ya Huang Chung‐Hao Kuo 《Liquid crystals》2013,40(6):683-689
Liquid crystalline α,α′‐bis(4‐alkoxyphenylethynyl)oligothiophenes (bi‐ and ter‐thiophene) have been synthesized and their mesogenic behaviour and optical properties investigated. They all exhibited a nematic mesophase, and compounds with long alkoxy chains also showed lamellar phases. Increasing the number of thiophene units increased both the transition temperatures and the mesophase ranges. As for their optical properties, incorporating more thiophene units results in red‐shifted absorption and emission spectra, slightly enhanced quantum efficiency, and a larger Stoke's shift. Most importantly, in terms of the absorption and emission maxima, the incorporation of one 4‐alkoxyphenylethynyl moiety was found to be equivalent to adding one thiophene ring. 相似文献
994.
Sébastien Gagné 《Biomedical chromatography : BMC》2013,27(5):664-668
A novel method for the biological monitoring of benzene‐exposed workers has been developed through ultra‐performance liquid chromatography coupled to tandem mass spectrometry. The method uses trans,trans‐muconic acid in urine as the benzene‐exposure biomarker. The method was developed using a triple quadrupole mass spectrometer with enough sensitivity to facilitate diluting and injecting the urine samples directly, rather than performing a solid‐phase extraction procedure as is common in the available protocols. Moreover, compared with a conventional high‐pressure liquid chromatography system, the separation power provided by the ultra‐performance liquid chromatography system allows a 10‐fold reduction in run time. The method was adjusted to a dynamic range of between 198.9 and 4916.7 µg/L to cover the biological exposure index of trans,trans‐muconic acid in urine. Also, the method demonstrated intra‐day and inter‐day precision at 98%, and accuracy within an acceptable range of 101 ± 8%. The method has been used to quantify various types of urine samples, such as workers' urine and inter‐laboratory proficiency tests. Depending on the sample, the quantified levels ranged from less than the limit of quantitation to 3836.7 µg/L. No levels exceeding the calibration range were detected in the urine of workers, and the reported concentrations in urine for the proficiency tests were, as expected, based on known values. Moreover, the new method using sample dilution and faster chromatographic run was more effective, facilitating fast communication of results, as needed, to decision‐makers. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
995.
Steven A. Barker Jimo Borjigin Izabela Lomnicka Rick Strassman 《Biomedical chromatography : BMC》2013,27(12):1690-1700
We report a qualitative liquid chromatography–tandem mass spectrometry (LC/MS/MS) method for the simultaneous analysis of the three known N,N‐dimethyltryptamine endogenous hallucinogens, their precursors and metabolites, as well as melatonin and its metabolic precursors. The method was characterized using artificial cerebrospinal fluid (aCSF) as the matrix and was subsequently applied to the analysis of rat brain pineal gland‐aCSF microdialysate. The method describes the simultaneous analysis of 23 chemically diverse compounds plus a deuterated internal standard by direct injection, requiring no dilution or extraction of the samples. The results demonstrate that this is a simple, sensitive, specific and direct approach to the qualitative analysis of these compounds in this matrix. The protocol also employs stringent MS confirmatory criteria for the detection and confirmation of the compounds examined, including exact mass measurements. The excellent limits of detection and broad scope make it a valuable research tool for examining the endogenous hallucinogen pathways in the central nervous system. We report here, for the first time, the presence of N,N‐dimethyltryptamine in pineal gland microdialysate obtained from the rat. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
996.
The geometrical anisotropy in the shape of swallow-tailed ST liquid crystalline molecules results in an extremely strong tendency of an antiparallel order in the short range. Dielectric measurements on a binary system of a ST and a double ST compound show that even at a mole fraction of 0.5 this effect can be observed. The strong deviations from the statistical distribution of the directions of the molecular long axis is caused by the asymmetric repulsive forces and the dipole-dipole interaction. 相似文献
997.
Abstract The chemical modified β-cyclodextrin(CD), which bears a fluorophore group — N,N-dimethylamino-chalcone (DMAC), was synthesized. The self-inclusion behavior of this compound in aqueous solution and in alcohol/water mixed solvents was investigated in detail, and compared with the inclusion system of non-modified CD with free DMAC molecule. The results showed that a deep self-inclusion complex was formed for this compound in aqueous solution and had the ability to recognize different organic molecules by two fully different modes: “in-out” and “co-inclusion” mechanisms. The inclusion behavior of these systems in various ratio of alcohol/water mixture as solvents was investigated. The results indicated that the self-inclusion complex has a higher stability in alcohol/water mixed solvents than that in the case of non-modified CD. The chalcone group appended at β-CD enabled the host as a sensitive probe to study the inclusion behavior of CD. 相似文献
998.
999.
《Journal of heterocyclic chemistry》2017,54(2):1578-1589
Starting from pyrimidine‐2‐thiones, a set of new fused triazoles, thiazoles, and thiazines has been obtained. The mechanistic pathway and structures of all the novel products were ascertained on the foundation of spectral information and elemental analyses. The analgesic and anti‐inflammatory activities of all the prepared compounds were predestined. The outcomes disclosed that all of the examined samples revealed potent activity. Moreover, the relation between the structure and the activity has been researched. 相似文献
1000.
Luiz Carlos Domingos Batista Thiago Izidoro Silva Santos José E. Lima Santos Djalma Ribeiro da Silva Carlos A. Martínez-Huitle 《Electroanalysis》2021,33(1):57-65
MOF-235 is presented as an orange powder, with crystals of the octahedral formation. It was already used as adsorbent to remove different compounds from water; however, no attempts have been published about the exploration of the MOF-235 application as electrochemical sensor for organic compounds yet. MOF-235 was synthetized and after that, it was characterized by SEM, XRD and FTIR. Graphite electrodes (GEs) were modified with different MOF-235 ratio (5 %, 7 %, 10 %, 12 % and 14 %) and these modified GEs were characterized by cyclic voltammetry (CV) measurements in order to determine the effect of MOF-235 concentration on the current response. Results indicated that, a significant improvement on the current response was attained at MOF-235(10 %)/GE respect to unmodified GE. This behavior is related to the pore structure and multiple active sites on the MOF surface. The performance of the MOF-235(10 %)/GE as electrochemical sensor for detecting catechol was assessed by differential pulse voltammetry (DPV). Catechol detection response of MOF-based sensor provided a detection limit of about 12.79 μmol L−1 with a correlation coefficient (R2) of about 0.9928 ranging from 12 to 514 μmol L−1. Finally, MOF-235(10 %)/GE was used to determine catechol in real water matrixes. 相似文献