A La(OTf)3 catalyzed synthesis of tetrasubstituted pyrroles under microwave irradiation has been developed affording various α-aryl tetrasubstituted pyrroles in acceptable to good yields (36–82% yield) through condensation/alkyne azacyclization/isomerization sequence. Functionalized α-aryl pentasubstituted pyrroles could be prepared from tetrasubstituted pyrroles through easy transformations. 相似文献
Herein we discovered that a Nile Red-based probe with a cinnamoyl unit was highly selective and sensitive to N2H4. Hydrazinolysis by N2H4 would release a hydroxyl substituted Nile Red and result in remarkable fluorescence quench. Importantly, Cys/Hcy would not interrupt the N2H4 recognition. This is because, for this probe, the combination of the π-π conjugate system can stabilize the ethylene union, which results in the nucleophilic addition of the thiol group of Cys/Hcy becomes non-effective. 相似文献
A Pd(II)-catalyzed cascade Heck/intramolecular C(sp2)–H amidation reaction is described for the synthesis of 4-aryl-2-quinolinone derivatives. Substituted cinnamamide containing 2-(pyridin-2-yl)ethanamine unit reacts with aryl iodide to form intermediate by Heck reaction. Then, the intermediate takes place intramolecular amidation via C(sp2)–H activated process promoted by orientation group. 相似文献
In this study, we investigated the enzymatic synthesis of a semi-synthetic cephalosporin, cefadroclor, from 7-aminodesacetoxymethyl-3-chlorocephalosporanic acid (7-ACCA) and p-OH-phenylglycine methyl ester (D-HPGM) using immobilized penicillin G acylase (IPA) in organic co-solvents. Ethylene glycol (EG) was employed as a component of the reaction mixture to improve the yield of cefadroclor. EG was found to increase the yield of cefadroclor by 15–45%. An investigation of altered reaction parameters including type and concentration of organic solvents, pH of reaction media, reaction temperature, molar ratio of substrates, enzyme loading, and IPA recycling was carried out in the buffer mixture. The best result was a 76.5% conversion of 7-ACCA, which was obtained from the reaction containing 20% EG (v/v), D-HPGM to 7-ACCA molar ratio of 4:1 and pH 6.2, catalyzed by 16 IU mL?1 IPA at 20 °C for 10 h. Under the optimum conditions, no significant loss of IPA activity was found after seven repeated reaction cycles. In addition, cefadroclor exhibited strong inhibitory activity against yeast, Bacillus subtilis NX-2, and Escherichia coli and weaker activity against Staphylococcus aureus and Pseudomonas aeruginosa. Cefadroclor is a potential antibiotic with activity against common pathogenic microorganisms. 相似文献
Well-dispersed Au/Bi nanoparticles with average size below 10 nm were prepared by using NaBH4 to reduce HAuCl4 with glucose as dispersant. The obtained Au/Bi NPs were well characterized by UV-Vis spectra, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and electrochemical measurements. The electrochemical study found that Bi adlayers on the surface of Au nanoparticles owns two kinds of surface structures, including a low coverage (2 × 2)-Bi adlayer and a close-packed (p × √3)-2 Bi adlayer due to the strong interaction between the two Bi layers and the below Au atoms, which is same with that bulk on Au surface. 相似文献
A novel method based on the coupling of membrane-supported headspace single-drop microextraction with gas chromatography?mass spectrometry (GC–MS) is developed for the determination of chlorobenzenes in water samples. For the determination of five chlorobenzenes, a 15 μL toluene microdrop was placed inside the plastic membrane and exposed for 10 min for headspace extraction while stirring at 1000 rpm. The microdrop was then picked up by a microsyringe and directly injected into the injector block of the GC–MS instrument. Under the optimized operation conditions, the calculated calibration curves gave a high level of linearity for all targets with correlation coefficients range from 0.9945 to 0.9987. The limits of detection range from 0.01 to 0.05 μg/L and the RSDs for most of chlorobenzenes were below 7%. The method is simple, sensitive, and stable for single drop microextraction. Its applicability is demonstrated by the determination of chlorobenzenes in tap water samples. 相似文献
A modified polyacrylamide gel route was used to prepare SrFe12O19 magnetic nanoparticles; ethylenediaminetetraacetic acid (EDTA) was used as a carboxyl chelating agent. The phase purity, morphology and magnetic properties of as-prepared samples were analyzed via X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometery (VSM). XRD analysis indicates that high-purity SrFe12O19 magnetic nanoparticles can be synthesized at 700°C in air. The characteristic peaks of as-prepared sample at 210, 283, 321, 340, 381, 411, 432, 475, 532, 618, 686, and 726 cm–1 were observed in Raman spectra. SEM and TEM show that the synthesized SrFe12O19 magnetic nanoparticles are uniform with the mean particle size of ~60 nm. VSM measurement shows that the maximum magnetic energy product (BH)max of sample prepared using EDTA as a chelating agent is higher than that of sample prepared using citric acid as a chelating agent.
Coherent exciton-phonon coupling in CdSe/ZnS nanocrystals have been investigated by temperature-dependent two-dimensional electronic spectroscopy (2DES) measurements. Benefiting from the ability of 2DES to dissect assembles in nanocrystal films, we have clearly identified experimental evidences of coherent coupling between exciton and phonon in CdSe/ZnS nanocrystals. In time domain, 2DES signals of excitonic transitions beat at a frequency resonant to a longitudinal optical phonon mode; in energy domain, phonon side bands are distinct at both Stokes and anti-Stokes sides. When temperature increases, phonon-induced exciton dephasing is observed with dramatic broadening of homogeneous linewidth. The results suggest exciton-phonon coupling is essential in elucidating the quantum dynamics of excitonic transitions in semiconductor nanocrystals. 相似文献