Dispersive liquid–liquid microextraction followed by high-performance liquid chromatography for the determination of three carbamate pesticides in water samples

A simple, rapid and efficient method, dispersive liquid–liquid microextraction (DLLME) in conjunction with high-performance liquid chromatography (HPLC), has been developed for the determination of three carbamate pesticides (methomyl, carbofuran and carbaryl) in water samples. In this extraction process, a mixture of 35 µL chlorobenzene (extraction solvent) and 1.0 mL acetonitrile (disperser solvent) was rapidly injected into the 5.0 mL aqueous sample containing the analytes. After centrifuging (5 min at 4000 rpm), the fine droplets of chlorobenzene were sedimented in the bottom of the conical test tube. Sedimented phase (20 µL) was injected into the HPLC for analysis. Some important parameters, such as kind and volume of extraction and disperser solvent, extraction time and salt addition were investigated and optimised. Under the optimum extraction condition, the enrichment factors and extraction recoveries ranged from 148% to 189% and 74.2% to 94.4%, respectively. The methods yielded a linear range in the concentration from 1 to 1000 µg L^?1 for carbofuran and carbaryl, 5 to 1000 µg L^?1 for methomyl, and the limits of detection were 0.5, 0.9 and 0.1 µg L^?1, respectively. The relative standard deviations (RSD) for the extraction of 500 µg L^?1 carbamate pesticides were in the range of 1.8–4.6% (n = 6). This method could be successfully applied for the determination of carbamate pesticides in tap water, river water and rain water.     

A quantum mechanics/molecular mechanics study on the hydrolysis mechanism of New Delhi metallo-β-lactamase-1

New Delhi metallo-β-lactamase-1 (NDM-1) has emerged as a major global threat to human health for its rapid rate of dissemination and ability to make pathogenic microbes resistant to almost all known β-lactam antibiotics. In addition, effective NDM-1 inhibitors have not been identified to date. In spite of the plethora of structural and kinetic data available, the accurate molecular characteristics of and details on the enzymatic reaction of NDM-1 hydrolyzing β-lactam antibiotics remain incompletely understood. In this study, a combined computational approach including molecular docking, molecular dynamics simulations and quantum mechanics/molecular mechanics calculations was performed to characterize the catalytic mechanism of meropenem catalyzed by NDM-1. The quantum mechanics/molecular mechanics results indicate that the ionized D124 is beneficial to the cleavage of the C–N bond within the β-lactam ring. Meanwhile, it is energetically favorable to form an intermediate if no water molecule coordinates to Zn2. Moreover, according to the molecular dynamics results, the conserved residue K211 plays a pivotal role in substrate binding and catalysis, which is quite consistent with previous mutagenesis data. Our study provides detailed insights into the catalytic mechanism of NDM-1 hydrolyzing meropenem β-lactam antibiotics and offers clues for the discovery of new antibiotics against NDM-1 positive strains in clinical studies.     

The ring-opening of chiral oxazoline involving pyrrolidone

Chiral N-[1-benzyl-2-hydroxyethyl]-3-[2-oxo-pyrrole]propionamide (C₁₆H₂₂N₂O₃) was obtained unexpectedly from the reaction of oxazoline involving pyrrolidone with copper acetate monohydrate, and the structure was characterized by NMR, IR, elemental analysis, and X-ray analysis.     

The catalytic activity of Zn(II) and Mn(II) organometallic complexes

Zn(II) and Mn(II) organometallic complexes I and II were first used to catalyze the cyanosilylation reaction, and good catalytic results (24–99 %) were achieved. The catalytic activity of the complexes was determined by ¹H NMR.     

Synthesis and characterization of biphenyl liquid crystal based on natural molecules and 2(5H)-furanone moiety

Using 4′-hexyloxybiphenyl-4-ol and N-(5-alkoxy-3-bromo-2(5H)-furanonyl) amino acids as reactants, a series of novel biphenyl liquid crystal compounds containing natural molecule moieties, such as menthol, borneol, and amino acids, were synthesized via esterification. The structures of all novel compounds were confirmed by FTIR, ¹H NMR, ¹³C NMR, MS, and elemental analysis, and the liquid crystal properties of target compounds were characterized with DSC, XRD, and POM. The introduction of hexyloxy made the biphenyl esters have a potential to appear in mesomorphic phase and have a higher Tm, and bornyl moiety was more beneficial for the liquid crystal performance than a menthyl unit. Most compounds were mesomorphic phase liquid crystal molecules, and POM and XRD showed that they existed in smectic phase. These researches provide a theoretical basis for the synthesis of biphenyl ester liquid crystal materials via the utilization of 2(5H)-furanone derivates and natural molecules.     

Polarization-controlled leakage current and photovoltaic effect in highly preferentially oriented BiFeO3 film

Highly preferentially oriented polycrystalline BiFeO₃ thin film was grown on FTO/glass substrate by a sol–gel method annealed at 500 °C. XRD result showed that the film adopts highly (100) preferential orientation. SEM results indicate that the film is composed of large grains of 40–200 nm and the thickness is about 320 nm. Room temperature saturated polarization and large Pr ~55 μC/cm² were obtained. Leakage current was substantially reduced by the controlling of ferroelectric polarization. Polarization-modulated conduction mechanism was studied. Moreover, substantial photovoltaic effect was observed.     

Transparent conducting Sn:ZnO films deposited from nanoparticles

Homogeneous transparent conducting Sn:ZnO films on fused silica substrates were prepared by dip-coating from nanoparticle dispersions, while the nanocrystalline Sn:ZnO particles with different dopant concentrations were synthesized by microwave-assisted non-aqueous sol–gel process using Sn(IV) tert-butoxide and Zn(II) acetate as precursors and benzyl alcohol as solvent. The dopant concentration had a great impact on the electrical properties of the films. A minimum resistivity of 20.3 Ω cm was obtained for a porous Sn:ZnO film with initial Sn concentration of 7.5 mol% after annealing in air and post-annealing in N₂ at 600 °C. The resistivity of this porous film could further be reduced to 2.6 and 0.6 Ω cm after densified in Sn:ZnO and Al:ZnO reaction solution, respectively. The average optical transmittance of a 400-nm-thick Sn:ZnO film densified with Sn:ZnO after the two annealing steps was 91%.     

A new intraparticle mass transfer rate model for cyclic adsorption and desorption in a slab, cylinder or sphere

A new intraparticle mass transfer rate model for cyclic adsorption and desorption in a slab, cylinder or sphere is proposed on the basis of the asymptotic behaviors of the adsorption rate for short and long cycle periods. Through comparison with the exact solution and the linear driving force (LDF) model, the new model is shown to provide a very good approximation for the instantaneous amount adsorbed as well as the adsorption rate for dimensionless half-cycle period τ _c =0.001～1 and is much better than the LDF model.     

Synthesis and Properties of Oval‐Shaped Iron Oxide/Ethylene Glycol Mesostructured Nanosheets

We have demonstrated a new and facile bottom‐up protocol for the effective synthesis of oval‐shaped iron oxide/ethylene glycol (FeO_x/EG) mesostructured nanosheets. Deprotonated ethylene glycol molecules are intercalated into iron oxide layers to form an interlayer distance of 10.6 Å. These materials display some peculiar magnetic properties, such as the low Morin temperature T_M and ferromagnetism below this T_M value. CdSe/ZnS nanoparticles can be loaded onto these mesostructured nanosheets to produce nanocomposites that combine both magnetic and fluorescence functions. In addition, iron oxide/propanediol (or butanediol) mesostructured materials with increased interlayer distances can also be synthesized. The developed synthetic strategy may be extended toward the creation of other ultrathin mesostructured nanosheets.