二进小波神经网络用于示波计时电位测定

提出了二进小波神经网络的结构及算法，并用于单组分和多组分示波计时电位信号的浓度计算。在二进小波神经网络中选用了Morlet母小波和修理的误差反传前向神经网络。探讨了二进小波神经网络中的中小波基个数，初始学习速率因子和动量因子等参数对网络预测结果的影响。结果表明：二进小波神经网络对双组分和单组分示波计时电位信号中去极剂浓度的预测均有很好效果。     

An efficient strategy based on liquid‐liquid extraction and pH‐zone‐refining counter‐current chromatography for selective enrichment,separation, and purification of alkaloids and organic Acids from natural products

This study presents an efficient strategy based on liquid‐liquid extraction and pH‐zone‐refining counter‐current chromatography for selective enrichment, separation, and purification of alkaloids and organic acids from natural products. First, an acid or base modified two‐phase solvent system with maximum or minimum partition coefficient was developed for the liquid‐liquid extraction of the crude extract. As a result, alkaloids or organic acids could be selectively enriched in the upper or lower phase. Then pH‐zone‐refining counter‐current chromatography was employed to separate and purify the selectively enriched alkaloids or organic acids efficiently. The selective enrichment and separation of five bufadienolide from toad venom of Bufo marinus was used as an example to show the advantage of this strategy. As a result, 759 mg of selectively enriched bufadienolide was obtained from 2 g of crude extract and the total content of five targets was increased from 14.64 to 83%. A total of 31 mg of marinobufagin‐3‐adipoyl‐l ‐arginine, 42 mg of telocinobufagin‐3‐pimeloyl‐l ‐arginine, 51 mg of telocinobufagin‐3‐suberoyl‐l ‐arginine, 132 mg of marinobufagin‐3‐suberoyl‐l ‐arginine, and 57 mg of bufalin‐3‐suberoyl‐l ‐arginine were all simultaneously separated from 500 mg of selectively enriched sample, with the purity of 92.4, 97.5, 90.3, 92.1, and 92.8%, respectively.     

Tunable Electrochemical C−N versus N−N Bond Formation of Nitrogen‐Centered Radicals Enabled by Dehydrogenative Dearomatization: Biological Applications

Herein, an environmentally friendly electrochemical approach is reported that takes advantage of the captodative effect and delocalization effect to generate nitrogen‐centered radicals (NCRs). By changing the reaction parameters of the electrode material and feedstock solubility, dearomatization enabled a selective dehydrogenative C?N versus N?N bond formation reaction. Hence, pyrido[1,2‐a]benzimidazole and tetraarylhydrazine frameworks were prepared through a sustainable transition‐metal‐ and exogenous oxidant‐free strategy with broad generality. Bioactivity assays demonstrated that pyrido[1,2‐a]benzimidazoles displayed antimicrobial activity and cytotoxicity against human cancer cells. Compound 21 exhibited good photochemical properties with a large Stokes shift (approximately 130 nm) and was successfully applied to subcellular imaging. A preliminary mechanism investigation and density functional theory (DFT) calculations revealed the possible reaction pathway.     

Synergistic Relay Reactions To Achieve Redox‐Neutral α‐Alkylations of Olefinic Alcohols with Ruthenium(II) Catalysis

Herein, we report a ruthenium‐catalyzed redox‐neutral α‐alkylation of unsaturated alcohols based on a synergistic relay process involving olefin isomerization (chain walking) and umpolung hydrazone addition, which takes advantage of the interaction between the two rather inefficient individual reaction steps to enable an efficient overall process. This transformation shows the compatibility of hydrazone‐type “carbanions” and active protons in a one‐pot reaction, and at the same time achieves the first Grignard‐type nucleophilic addition using olefinic alcohols as latent carbonyl groups, providing a higher yield of the corresponding secondary alcohol than the classical hydrazone addition to aldehydes does. A broad scope of unsaturated alcohols and hydrazones, including some complex structures, can be successfully employed in this reaction, which shows the versatility of this approach and its suitability as an alternative, efficient means for the generation of secondary and tertiary alcohols.     

A novel H2O2 sensor based on the enzymatically induced deposition of polyaniline at a horseradish peroxide/aligned single-wall carbon nanotubes modified Au electrode

A novel H(2)O(2) sensor based on enzymatically induced deposition of electroactive polyaniline (PANI) at a horseradish peroxide (HRP)/aligned single-wall carbon nanotubes (SWCNTs) modified Au electrode is fabricated, and its electrochemical behaviors are investigated. Electrochemical impedance spectroscopy of the sensor confirmed the formation of PANI on SWCNTs through the HRP catalytic reaction. Cyclic voltammograms of PANI/HRP/SWCNTs modified Au electrodes showed a pair of well-defined redox peaks of PANI with reduction peak potentials of 0.211 and oxidation peak potentials of 0.293 V in 0.1 M HOAc-NaOAc (pH 4.3) solution. The oxidation peak current response of PANI is linearly related to H(2)O(2) concentration from 2.5 μM to 50.0 μM with a correlation coefficient of 0.9923 and a sensitivity of 200 μA mM(-1). The detection limit is determined to be 0.9 μM with a signal-to-noise ratio of 3. Thus, the synergistic performance of the enzyme, the highly efficient polymerization of PANI, and the templated deposition of SWCNTs provided an extensive platform for the design of novel electrochemical biosensors.     

Self‐Assembly of Aggregation‐Induced‐Emission Molecules

The last decade has witnessed rapid developments in aggregation‐induced emission (AIE). In contrast to traditional aggregation, which causes luminescence quenching (ACQ), AIE is a reverse phenomenon that allows robust luminescence to be retained in aggregated and solid states. This makes it possible to fabricate various highly efficient luminescent materials, which opens new paradigms in a number of fields, such as imaging, sensing, medical therapy, light harvesting, light‐emitting devices, and organic electronic devices. Of the various important features of AIE molecules, their self‐assembly behavior is very attractive because the formation of a well‐defined emissive nanostructure may lead to advanced applications in diverse fields. However, due to the nonplanar topology of AIEgens, it is not easy for them to self‐assemble into well‐defined structures. To date, some strategies have been proposed to achieve the self‐assembly of AIEgens. Herein, we summarize the most recent approaches for the self‐assembly of AIE molecules. These approaches can be sorted into two classes: 1) covalent molecular design and 2) noncovalent supramolecular interactions. We hope this will inspire more excellent work in the field of AIE.     

Nonenzymatic hydrogen peroxide sensor based on a polyaniline-single walled carbon nanotubes composite in a room temperature ionic liquid

A film consisting of polyaniline and single-walled carbon nanotubes was electro-polymerized on a platinum electrode in a room temperature ionic liquid. This resulted in a selective and non-enzymatic electrode for sensing hydrogen peroxide (HP). The morphology of the sensor film was characterized by scanning electron microscopy, cyclic voltammetry, and chronoamperometry. The composite film synthesized in an ionic liquid provided an electrode with enhanced selectivity and excellent stability. The electrode exhibited good electrocatalytic properties in terms of detection of HP, with a linear range from 5 µM to 1 mM, a detection limit of 1.2 µM, and a response time of around 4 s.     

A Non‐Enzymatic Glucose Sensor Based on Ni/MnO2 Nanocomposite Modified Glassy Carbon Electrode

A novel flower like 3D nickel/manganese dioxide (Ni/MnO₂) nanocomposite was synthesized by a kind of simple electrochemical method and the formation mechanism of flower like structure was also researched. In addition, morphology and composition of the nanocomposite were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), and X‐ray photoelectron spectroscopy (XPS). Then the Ni/MnO₂ nanocomposites were applied to fabricate electrochemical non‐enzymatic glucose sensor. The electrochemical investigation for the sensor indicated that it possessed an excellent electrocatalytic property for glucose, and could applied to the quantification of glucose with a linear range from 2.5×10^?7 to 3.5×10^?3 M, a sensitivity of 1.04 mA mM^?1 cm^?2, and a detection limit of 1×10^?7 M (S/N=3). The proposed sensor also presented attractive features such as interference‐free, and long‐term stability. The present study provided a general platform for the one‐step synthesis of nanomaterials with novel structure and can be extended to other optical, electronic and magnetic nanocompounds.     

Fullerene-based anodic stripping voltammetry for simultaneous determination of Hg(II), Cu(II), Pb(II) and Cd(II) in foodstuff

Various carbon nanomaterials for use in anodic stripping voltammetric analysis of Hg(II), Cu(II), Pb(II) and Cd(II) are screened. Graphene, carbon nanotubes, carbon nanofibers and fullerene (C₆₀), dispersed in chitosan (Chit) aqueous solution, are used to modify a glassy carbon electrode (GCE). The fullerene-chitosan modified GCE (C₆₀-Chit/GCE) displays superior performance in terms of simultaneous determination of the above ions. The electrodes and materials are characterized by electrochemical impedance spectroscopy, cyclic voltammetry, scanning electron microscopy, Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The excellent performance of C₆₀-Chit/GCE is attributed to the good electrical conductivity, large surface area, strong adsorption affinity and unique crystalline structure of C₆₀. Using differential pulse anodic stripping voltammetry, the assay has the following features for Hg(II), Cu(II), Pb(II) and Cd(II), respectively: (a) Peak voltages of +0.14, ?0.11, ?0.58 and???0.82 V (vs SCE); (b) linear ranges extending from 0.01–6.0 μM, 0.05–6.0 μM, 0.005–6.0 μM and 0.5–9.0 μM; and (c), detection limits (3σ method) of 3 nM (0.6 ppb), 14 nM (0.9 ppb), 1 nM (0.2 ppb) and 21 nM (2.4 ppb). Moreover, the modified GCE is well reproducible and suitable for long-term usage. The method was successfully applied to the simultaneous determination of these ions in spiked foodstuff.

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Graphical abstract Compared with graphene, carbon nanotubes and carbon nanofibers, an electrode modified with fullerene in chitosan electrode displays superior performance for the simultaneous anodic stripping voltammetric detection of Hg(II), Cu(II), Pb(II) and Cd(II).

     

新的四氢叶酸辅酶模型及与亲核试剂反应生成物的核磁共振研究

对新合成的四氢叶酸辅酶模型碘化１，２二甲基３对甲氧苯磺酰基咪唑啉及与亲核试剂反应后生成的产物进行了１ＨＮＭＲ谱的研究，通过化学位移及偶合常数研究探讨其规律性。