Enhanced redox stability and optical contrast of electrochromic copolymers from selenophene and 3-methylthiophene

Journal of Solid State Electrochemistry - A series of poly(selenophene-co-3-methylthiophene) films were synthesized by electrochemical copolymerization of selenophene and 3-methylthiophene under...     

Highly Sensitive Silver Nanorod Arrays for Rapid Surface Enhanced Raman Scattering Detection of Acetamiprid Pesticides

The determination of pesticide residue on agricultural products is increasingly important.Exposure to pesticides can cause severe acute reactions in humans, including aplastic anemia and leukemia.In this work, we developed a rapid and sensitive method to detect acetamiprid pesticide residue based on surface-enhanced Raman scattering.Silver nanorod (AgNR) arrays were fabricated by oblique angle deposition technology and were used as SERS substrates.Prior to detection, the AgNR arrays were cleaned with nitric acid solution or a mixture of methanol and acetone.Compared to the unwashed AgNR arrays, the AgNR arrays washed with methanol and acetone shows a signal enhancement 1000 times greater than the unwashed AgNR array due to the effective removal of the impurities on its surface.The limit of detection of acetamiprid was determined to be 0.05 mg/L.In addition, the molecular structure of acetamiprid was simulated and the corresponding vibration modes of the characteristic bands of acetamiprid were calculated by density function theory.To demonstrate its practical application, the AgNRs array substrates were applied successfully to the rapid identification of acetamiprid residue on a cucumber's surface.These results confirmed possibility of utilizing the AgNRs SERS substrates as a new method for highly sensitive pesticide residue detection.     

Insights into the N‐Heterocyclic Carbene (NHC)‐Catalyzed Intramolecular Cyclization of Aldimines: General Mechanism and Role of Catalyst

One of the most challenging questions in the Lewis base organocatalyst field is how to predict the most electrophilic carbon for the complexation of N‐heterocyclic carbene (NHC) and reactant. This study provides a valuable case for this issue. Multiple mechanisms (A, B, C, D, and E) for the intramolecular cyclization of aldimine catalyzed by NHC were investigated by using density functional theory (DFT). The computed results reveal that the NHC energetically prefers attacking the iminyl carbon (AIC mode, which is associated with mechanisms A and C) rather than attacking the olefin carbon (AOC mode, which is associated with mechanisms B and D) or attacking the carbonyl carbon (ACC mode, which is associated with mechanism E) of aldimine. The calculated results based on the different reaction models indicate that mechanism A (AIC mode), which is associated with the formation of the aza‐Breslow intermediate, is the most favorable pathway. For mechanism A, there are five steps: (1) nucleophilic addition of NHC to the iminyl carbon of aldimine; (2) [1,2]‐proton transfer to form an aza‐Breslow intermediate; (3) intramolecular cyclization; (4) the other [1,2]‐proton transfer; and (5) regeneration of NHC. The analyses of reactivity indexes have been applied to explain the chemoselectivity, and the general principles regarding the possible mechanisms would be useful for the rational design of NHC‐catalyzed chemoselective reactions.     

A highly stable black phosphorene nanocomposite for voltammetric detection of clenbuterol

A nanocomposite was prepared from graphene-like two-dimensional black phosphorene (BP, an allotrope of phosphorus) and nafion (Nf) treated with isopropanol (IP). A glassy carbon electrode (GCE) modified with this nanocomposite was found to be a viable sensor for voltammetric determination of clenbuterol (CLB). Unlike previously reported pure BP, the BP nanocomposite was stable towards water and oxygen. Its morphology, structure, electrochemically active surface area and electrochemical stability were investigated. The BP-Nf (IP) modified GCE displayed good electrochemical stability and electrocatalytic capacity with a low working potential of 0.94 V (vs. SCE), excellent peak current response for CLB in a linear concentration range of 0.06–24 μM with a detection limit of 3.7 nM (3σ/m) and a sensitivity of 0.14 μA·μM^?1·cm^?2 under optimal conditions. A sensing mechanism for the electro-oxidation of CLB was suggested and verified by density functional theory calculations under imitation of aqueous solution conditions. The sensor was successfully applied to the determination of CLB in bovine meat and bovine serum samples.

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Graphical abstract Highly-stable black phosphorene (BP) nanocomposite based on Nafion (Nf) was used to modify a glassy carbon electrode (GCE). It is shonw to be a viable electrochemical platform for sensitive voltammetric determination of trace clenbuterol (CLB) in bovine beef and bovine serum.

     

Grayanane diterpenoids with diverse bioactivities from the roots of Pieris formosa

During our continuing study on the roots of Pieris formosa, twelve new grayanane diterpenoids (1–12), together with eight known compounds (13–20), were obtained. Their structures with absolute configurations were characterized by a series of spectroscopic methods and X-ray diffraction. Compounds 1, 2, 4–5, 7–8, 14, and 19 exhibited significant analgesic activity in an acetic acid-induced writhing test. In particular, 7 and 14 were found to be 5 times more potent than morphine in the acetic acid-induced writhing test model. Compounds 1, 4, 9, 13, and 18 showed antifeedant activity against Plutella xylostella at 0.5 mg/mL. Compound 4 exhibited a 38.3% inhibitory effect against the KCNQ2 potassium channel at a concentration of 10 μM.     

Diterpenoids from the fruits of Rhododendron molle, potent analgesics for acute pain

Rhododendron molle G. Don is one of the most potent traditional Chinese medicines for pain relief. Prior investigations have shown that Rhododendrons are rich sources of terpenoids. In our continuing efforts to identify structurally unique and biologically interesting diterpenoids, the fruits of R. molle were collected from Guangxi Province. A chemical study was carried out on the EtOH extract, which led to the isolation of 18 diterpenoids including 12 new compounds. The isolation and structural elucidation of new compounds 1–12, as well as the evaluation of the antinociceptive activities of these compounds were reported.     

L-核糖的合成

介绍了近几年L-广核糖合成方法的改进与突破，重点讨论了L-广核糖的化学合成方法在反应条件、收率等方面的改善，还介绍了L-广核糖的微生物合成法的进展。     

Simultaneous Quantification of Puerarin and Daidzein in Rat Plasma by High-Performance Liquid Chromatography with Post-Column Modification and Fluorescence Detection

A sensitive HPLC method based on post-column modification and fluorescence detection has been developed for determination of puerarin and daidzein in rat plasma. Chromatographic separation was performed on a C₈ column with a linear gradient prepared from 0.5% aqueous acetic acid and 0.5% acetic acid in acetonitrile, delivered at a flow rate of 0.8 mL min⁻¹. Naringin was used as the internal standard. It was necessary to use acetic acid in the mobile phase to achieve good separation, but this led to fluorescence signal suppression, because puerarin and daidzein have native fluorescence at pH 8.0–9.0. To enhance the sensitivity, post-column modification with alkaline buffer was adopted. After this modification, detection sensitivity for puerarin and daizein increased more than 500-fold and 600-fold, respectively, compared with direct fluorescence detection. Signal-to-noise ratios for detection for puerarin were more than 150 times better than for UV detection after use of the same method of sample preparation. This sensitive analytical method was successfully used to determine pharmacokinetic data for puerarin and daidzein in rat plasma after oral administration of a single dose of Puerariae radix extract containing puerarin (approx. 8.4 mg) and daizein (approx. 5.9 mg) to male SD rats.     

Development of an HPLC–UV–ELSD Method for Quantification of Multiple Components of a Chinese Medicine Made from Radix salvia miltiorrhiza and Panax notoginseng

‘Fufang Danshen tablet’ (FDT), made from Radix salvia miltiorrhiza and Panax notoginseng, is a widely used botanical drug derived from traditional Chinese medicine. Quantification of the active components of Radix salvia miltiorrhiza and Panax notoginseng is very important for regulation of FDT products. In this study HPLC hyphenated with ultraviolet (UV) detection and evaporative light-scattering detection (ELSD) was used for simultaneous determination of nine active components (three salvianolic acids, three tanshinones, and three saponins) of FDT products. Separation was performed on a 250 mm × 4.6 mm i.d., 5.0 μm particle-size, C₁₈ column with linear gradient elution. UV detection at 280 and 254 nm was used for detection of the three salvianolic acids and the three tanshinones, respectively. ELSD was used for detection of the three saponins, which were difficult to analyze by use of UV detection. The linearity of the calibration plots was excellent over the concentration ranges investigated (values of R ² were >0.99 for all the analytes) and recovery measured at three concentrations was between 92.2 and 107.7%. The validated method was successfully used for simultaneous determination of these components in FDT products.