Electrochemical quercetin sensor based on a nanocomposite consisting of magnetized reduced graphene oxide, silver nanoparticles and a molecularly imprinted polymer on a screen-printed electrode.

An electrochemical quercetin (QR) sensor is described that is based on the use of magnetic reduced graphene oxide (MrGO) incorporated into a molecularly imprinted polymer (MIP) on the surface of a screen-printed electrode (SPE). The MrGO consists of reduced graphene oxide (rGO), magnetite (Fe3O4) and silver nanoparticles (Ag). The analyte (QR) is electrostatically adsorbed on the surface of the MrGO. Finally, the MIP was deposited via in-situ polymerization. The composite was characterized by X-ray diffraction, Fourier transform infrared spectroscopy and Vibrating sample magnetometry. The morphologies and electrochemical properties of different electrodes were characterized by Field emission scanning electron microscopy, Electrochemical impedance spectroscopy and differential pulse voltammetry. Under optimal conditions, the modified electrode has a linear response in the 20 nM to 250 µM QR concentration range. The limit of detection is 13 nM (at an S/N ratio of 3). The electrode is selective, stable, regenerable and reliable. It was applied to the determination of QR in spiked pharmaceutical samples and gave satisfactory results. Graphical abstract Schematic presentation of a method for sensing quercetin. It is based on the use of screen printed electrode modified with magnetized reduced graphene oxide and a molecularly imprinted polymer.

ansa-Rare-earth-metal catalysts for rapid and stereoselective polymerization of renewable methylene methylbutyrolactones.

Two ansa-half-sandwich rare-earth-metal (REM) dialkyl complexes supported by an ethylene-bridged fluorenyl (Flu)-N-heterocyclic carbene (NHC) ligand, [M{C(2)H(4)(η(5)-Flu-κ(1)-NHC)}(CH(2)SiMe(3))(2)] (M=Y, 1; Lu, 2), and a chiral ansa-sandwich samarocene incorporating a C(2) ligand, [Sm(η(5)-C(12)H(8))(2)(thf)(2)] (3), have been investigated for the coordination-addition polymerization of renewable methylene butyrolactones, α-methylene-γ-butyrolactone (MBL) and γ-methyl-α-methylene-γ-butyrolactone ((γ)MMBL). Both ansa-half-sandwich complexes 1 and 2 exhibit exceptional activity for the polymerization of (γ)MMBL at room temperature in dimethylformamide (DMF); with a 0.25 mol% catalyst loading, quantitative monomer conversion can be achieved under 1 min, giving a high turn-over frequency (TOF) of 24,000 h(-1). This TOF value represents a rate enhancement, by a factor of 8, 22, or 2400, over the polymerizations by unbridged samarocene [Sm(Cp*)(2)(thf)(2)] (Cp*=η(5) -pentamethylcyclopentadienyl), by bridged ansa-samarocene 3 with C(2) ligation, or by the corresponding REM trialkyls without the ansa-Flu-NHC ligation, respectively. Complexes 1 and 2 are also highly active for the polymerization of ß-methyl-α-methylene-γ-butyrolactone ((ß)MMBL), realizing the first example of the metal-mediated coordination polymerization of this monomer and its copolymerization with (γ)MMBL. More remarkably, the resulting P(ß)MMBL homopolymer is highly stereoregular (91% mm) and exhibits a high T(g) of 290 °C. In sharp contrast, catalysts 1 and 2 have poor activity and efficiency in the polymerization of the parent MBL or the acyclic analog methyl methacrylate. Polymerization and kinetic studies using the most active catalyst (1) of the series have uncovered characteristics of its (γ)MMBL polymerization and yielded a unimolecular propagation mechanism. A surprising chain-initiation pathway for the polymerization in DMF by 1 has been revealed, and catalytic polymerization in the presence of an organoacid has also been examined.

The effect of in-package cold plasma on the formation of polycyclic aromatic hydrocarbons in charcoal-grilled beef steak with different oils or fats.

In-package cold plasma (ICP) pretreatment is an emerging non-thermal food processing methods. In the current study, ICP on the formation of polycyclic aromatic hydrocarbons (PAHs) in grilled beef steaks with different oils and fats was evaluated, the influence of prolonged storage periods (1 d, 2 d) of raw meat after ICP pretreatment on the PAH inhibitory effect was investigated. The results showed that sunflower seed oil had an inhibitory effect on PAH formation; the groups with ICP pretreatment showed a significant decrease in PAH content (p < 0.05) according to the UHPLC results, inhibitory rates were dependent on the original contents in each group without ICP pretreatment, ranging from 35% to 96%. The optimal condition was grilling immediately after ICP pretreatment, and the results indicated that the nonpolar radical scavenging activity (RSA) of ungrilled meat was negatively correlated with PAH8 contents according the DPPH assay, while ICP pretreatment enhanced the RSAoil of raw meat.

Synergistic effects of layer-by-layer films for highly selective and sensitive electrochemical detection of trans-resveratrol.

Trans-resveratrol (TRA) possesses a variety of pharmacological activities, making important to explore simple, inexpensive, and reliable analytical methods for identification and quantification of it. We report on the synergistic effects originated from layer-by-layer films of graphene (Gr)-gold nanoparticles (Au) and molecularly imprinted polymers (MIPs) modified glassy carbon electrode (GCE) for electrochemical detection of TRA. To construct the TRA electrochemical sensor (GCE|Gr-Au/MIPs), the films of Gr-Au, MIPs were step by step formed onto GCE via in-situ and controllable electrodeposition and polymerization processes. The compositions, morphologies, and electrochemical properties of obtained films were investigated by various methods. Under the optimized experimental conditions, the electrochemical sensor showed superior performance toward selective and sensitive determination of TRA with K3[Fe(CN)6] as electrochemical signal probe. The electrochemical sensor was applied to determine TRA in real samples with good accuracy and recovery, verifying the broad and practical application prospects for foods and medicines analysis.

Palladium catalyst immobilized on functionalized microporous organic polymers for C-C coupling reactions.

Two microporous organic polymer immobilized palladium (MOP-Pd) catalysts were prepared from benzene and 1,10-phenanthroline by Scholl coupling reaction and Friedel-Crafts reaction, respectively. The structure and composition of the catalyst were characterized by FT-IR, TGA, N2 sorption, SEM, TEM, ICP-AES and XPS. MOP-Pd catalysts were found to possess high specific surface areas, large pore volume and low skeletal bone density. Moreover, the immobilized catalyst also had advantages, such as readily available raw materials, chemical and thermal stability, and low synthetic cost. The Pd catalyst is an effective heterogeneous catalyst for carbon-carbon (C-C) coupling reactions, such as the Heck reaction and Suzuki-Miyaura reaction, affording good to high yields. In these reactions, the catalyst was easily recovered and reused five times without significant activity loss.