A Multiwall Carbon Nanotube-chitosan Modified Electrode for Selective Detection of Dopamine in the Presence of Ascorbic Acid

A novel multiwall carbon nanotube-chitosan modified electrode has been prepared. The modified electrode resolves the overlapping voltammetric response of dopamine and ascorbic acid into two well-defined peak by 212 mV. The mechanism of discrimination of dopamine from ascorbic acid is discussed. Dopamine can be determined selectively with the carbon nanotube-chitosan modified electrode. The electrode shows good sensitivity, selectivity and stability.     

Selective Detection of Dopamine in the Presence of Uric Acid Using NiO Nanoparticles Decorated on Graphene Nanosheets Modified Screen‐printed Electrodes

A convenient, low cost, and sensitive electrochemical method, based on a disposable graphene nanosheets (GR) and NiO nanoparticles modified carbon screen printed electrode (NiO/GR/SPE), is described for the simultaneous determination of dopamine (DA) and uric acid (UA). The modified electrode exhibited good electrocatalytic properties toward the oxidation of DA and UA. A peak potential difference of 150 mV between DA and UA was large enough to determine DA and UA individually and simultaneously. The anodic peak currents of DA were found to be linear in the concentration range of 1.0–500.0 μM with the detection limit of 3.14×10^?7 M.     

改进的微波辅助无溶剂法提取薄荷和陈皮中的挥发油组分

An improved solvent free microwave extraction, in which a kind of microwave absorption medium （carbonyl iron powder） was used, was applied to the extraction of essential oil from dried menthol mint and orange peel without addition of any solvent and pretreatment. It took much less time of extraction （30 min） than microwave-assisted hydrodistillation （90 min） and conventional hydrodistillation （180 min）. The kinds of chemical compositions in essential oil extracted by different methods were almost the same and such improved solvent free microwave extraction can be a feasible way in extraction of essential oil from dried plant materials.     

α-环糊精包结碳纳米管涂层电极同时测定多巴胺和肾上腺素

本文发现α-环糊精包结碳纳米管涂层电极对多巴胺（DA）和肾上腺素（EP）具有显著的增敏和电分离作用，还原峰电位差达390 mV。研究表明α-环糊精包结碳纳米管涂层薄膜表现出了非常令人感兴趣的电催化特性。因抗坏血酸（AA）在α-环糊精包结碳纳米管涂层电极上的氧化是不可逆的，因此利用还原峰进行测定，消除了AA对DA和EP的干扰。由于成本低和制作简便，该电极可用于生物系统电化学研究的生物传感器。     

Challenge Approach of an Inexpensive Electrochemical Sensor for Rapid Selective Determination of two Non‐classical β‐Lactams in Presence of Different Degradants and Interference Substances

An inexpensive stability−indicating anodic voltammetric method for rapid determination of two non‐classical β ‐lactam antibiotics; Meropenem (MP) and Ertapenem (EP) has been developed and validated. The method was based on the enhancement of voltammetric response at a disposable graphite pencil electrode (GPE). Differential pulse voltammetric (DPV) method was developed for quantification of both drugs in B−R buffer solution (pH 2.0) at GPE. The GPE displayed very good voltammetric behavior with significant enhancement of the peak current compared to glassy carbon electrode (GCE). Stress stability studies were performed using 0.5 M of either HCl or NaOH and H₂O₂. Mass and infrared spectroscopy were used for identification of degradants and their pathways were illustrated. Under optimal conditions, the peak currents showed a linear dependence with drug concentrations. The achieved limits of detection (LOD) were 1.23, 2.07 and 1.50 μM for MP and two waves of EP, respectively. The developed voltammetric method was successfully applied for direct determination of MP and EP in drug substances, pharmaceutical vials and in presence of either their corresponding hydrolytic, oxidative‐degradants or interfering substances with no potential interferences. The differential pulse voltammograms were highly advantageous and applicable in QC laboratories for rapid, selective micro‐determination of MP and EP.     

Development of High Performance Heterogeneous Catalysts for Selective Cleavage of C−O and C−C Bonds of Biomass‐Derived Oxygenates

The environmental impact of CO₂ emissions via the use of fossil resources as chemical feedstock and fuels has stimulated research to utilize renewable biomass feedstock. The biogenic compounds such as polyols are highly oxygenated and their valorization requires the new methods to control the oxygen to carbon ratio of the chemicals. The catalytic cleavage of C?O bonds and C?C bonds is promising methods, but the conventional catalyst systems encounter the difficulty to obtain the high yields of the desired products. This review describes our recent development of the high performance heterogeneous catalysts for the valorization of the biogenic chemicals such as glycerol, furfural, and levulinic acid via selective cleavage of C?O bonds and C?C bonds in the liquid‐phase. Selective C?O bond cleavage by hydrogenolysis enables production of various diols useful as engineering plastics, antifreeze, and cosmetics in high yields. The success of the selective C?C bond scission of levulinic acid can be applied to a wide range of the biogenic oxygenates such as carboxylic acids, esters, lactones, and primary alcohols, in which the selective C?C bond scission at adjacent to the oxygen functional groups are achieved. Furthermore, valorization of glycerol by selective acetylation and acetalization, and of levulinic acid by hydrogenation is described. Our catalysts show excellent performance compared to the reported catalysts in the aforementioned valorization.     

Alumina Polished Glassy Carbon Electrode as a Simple Electrode for Lower Potential Electrochemical Detection of Dopamine in its Sub‐micromolar Level

The electrochemical behaviour of dopamine (DA) at a cleaned and alumina polished glassy carbon electrode (GCE) was studied using cyclic voltammetry (CV). The CV studies revealed that alumina polished GCE (AGCE) shows an enhanced oxidation peak current response with 217 mV negative potential shift towards DA than that of cleaned GCE. The differential pulse voltammetry result shows that the AGCE detects the DA in the linear concentration ranges from 0.15 to 25.25 µmol L^?1. The limit of detection was calculated as 0.046 µmol L^?1 with a sensitivity of 3.74 µA µmol L^?1 cm^?2 for the determination of DA. The fabricated AGCE shows a satisfactory selectivity, practicality along with appreciable repeatability and reproducibility.     

Real‐time Selective Detection of Hydrogen Peroxide Based on a Tantalum Deposited Pencil Lead Electrode for Evaluation of Enzyme Activities

In this study, we have carried out electrodeposition of tantalum (Ta) nanostructures on pencil lead electrode in non‐aqueous media at room temperature by applying a constant potential. The deposited Ta on pencil lead was examined for the catalytic effect regarding hydrogen peroxide (H₂O₂) reduction with voltammetry and amperometry. Ta/pencil lead electrode exhibited amperometric sensitivity of 0.317 μA mM⁻¹ cm⁻² and fast response time of 0.75 s, where selective detection of H₂O₂ was fulfilled without interruption from common electroactive biomaterials such as O₂, uric acid, ascorbic acid, dopamine, acetamidophenol, and glucose. For practical applications, the dynamic concentration changes of H₂O₂ during catalase and glucose oxidase‐involved reactions, either eliminating or producing H₂O₂, were successfully traced in real time with as‐prepared electrode. From the kinetics study for catalase and glucose oxidase, we evaluated Michaelis constants (K _m^app) as 7.8 mM for catalase and 37 mM for glucose oxidase, respectively.     

Incorporation of 5‐Hydroxyindazole into the Self‐Polymerization of Dopamine for Novel Polymer Synthesis

Investigation into the mussel‐inspired polymerization of dopamine has led to the realization that other compounds possessing potential quinone structures could undergo similar self‐polymerizations in mild buffered aqueous conditions. To this end, 5‐hydroxyindazole was added to a dopamine polymerization matrix in varying amounts, to study its incorporation into a polydopamine coating of silica particles. Solid‐state ¹³C NMR spectroscopy confirmed the presence of the indazole in the polymer shell when coated onto silica gel. SEM and DLS analysis also confirmed that the presence of the indazole in the reaction matrix yielded monodisperse polymer‐coated particles, which retained their polymer shell upon HF etching, except when high levels of the indazole were used. Characterization data and examination of incorporation mechanism suggests that the 5‐hydroxyindazole performs the function of a chain‐terminating agent. Cytotoxicity studies of the polymer particles containing 5‐hydroxyindazole showed dramatically lower toxicity levels compared to polydopamine alone.

     

Effect of Ionic Liquid Structure on the Electrochemical Response of Dopamine at Room Temperature Ionic Liquid‐modified Carbon Paste Electrodes (IL–CPE)

In this work 12 different ionic liquids (ILs) have been used added as co‐binders in the preparation of modified carbon paste electrodes (IL–CPEs) used for the voltammetric analysis of dopamine in Britton‐Robinson buffer. The ionic liquids studied were selected based on three main criteria: (1) increasing chain length of alkyl substituents (studying 1‐ethylimidazolium and ethyl, propyl, butyl, hexyl and decylmethylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids); (2) nature of the counter ion (dicyanamide, bis(trifluoromethylsulfonyl)imide and hexafluorophosphate) in 1‐butyl‐3‐methylimidazolium ionic liquids; and (3) cation ring structures (1‐butyl‐3‐methylimidazolium, 1‐butyl‐1‐methylpiperidinium, 1‐butyl‐1‐methylpyrrolidinium and 1‐butyl‐3‐methylpyridinium) in bis(trifluoromethylsulfonyl)imide or hexafluorophosphate (1‐butyl‐3‐methylimidazolium or 1‐butyl‐3‐methylpyridinium as cations) ionic liquids. The use of IL as co‐binders in IL–CPE results in a general enhancement of both the sensitivity and the reversibility of dopamine oxidation. In square wave voltammetry experiments, the peak current increased up to a 400 % when 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide was used as co‐binder, as compared to the response found with the unmodified CPE. Experimental data provide evidence that electrostatic and steric effects are the most important ones vis‐à‐vis these electrocatalytic effects on the anodic oxidation of dopamine on IL–CPE. The relative hydrophilicity of dicyanamide anions reduced the electrocatalytic effects of the corresponding ionic liquids, while the use of 1‐ethyl‐3‐methylimidazolium hexafluorophosphate or 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (two relatively small and highly hydrophobic ionic liquids) as co‐binders in IL–CPE resulted in the highest electrocatalytic activity among all of the IL–CPE studied.     

New Acyclic 12‐Hydroxygeranylgeraniol‐Derived Diterpenoids from the Seeds of Carpesium triste

Five new acyclic 12‐hydroxygeranylgeraniol‐derived diterpenoids, i.e., 1 – 5 , were isolated from the seeds of Carpesium triste. The structures including the absolute configurations of the new compounds were elucidated by spectroscopic methods. All the compounds, except for 2 , were evaluated for their in vitro cytotoxic activity against cultured SMMC‐7721 (human hepatoma), HL‐60 (human promyelocytic leukemia), and L02 (human hepatocyte) cells.     

Versatile Electrochemical Platform for the Determination of Phenol‐like Compounds Based on Laccases from Different Origins

Simple and fast methods for the monitoring of phenol‐like compounds are relevant in diverse fields ranging from waste management to neurosciences. Laccases are copper‐containing enzymes, which, depending on their origin, are able to oxidize different phenol compounds at different pH conditions. Through adequate laccase immobilization, disposable screen printed electrodes can be used as interphase to build amperometric phenol sensors. In this work three different laccases were studied for the determination of phenol‐like compounds, two of them are isoenzymes from Trametes trogii and the third one from Rhus vernicifera . Their immobilization on screen printed electrodes is presented for the construction of amperometric sensors. The electrode substrate is composed by graphite screen printed electrodes modified with carbon nanotubes and silica microspheres where, depending on the application, one of the three laccases is adsorbed. As each laccase shows an optimum working pH, they were conveniently selected to determine dopamine at physiological pH and catechol at acid pH. Determinations in the micromolar range were possible in both cases. Chronoamperometry shows to be an effective technique for their determinations, simpler than other electrochemical methods already presented in the literature.     

Highly Sensitive and Selective Determination of Dopamine in the Presence of Ascorbic Acid Using Gold Nanoparticles‐Decorated MoS2 Nanosheets Modified Electrode

Herein, a novel nanocomposite has been synthesized by molybdenum disulfide (MoS₂) nanosheets and gold nanoparticles (AuNPs) via a microwave‐assisted hydrothermal method, which possesses the specific features of both MoS₂ and AuNPs. The AuNPs@MoS₂ nanocomposite modified electrode exhibits excellent electrocatalytic activity toward dopamine (DA). Its oxidation peak current shows a linear dependence over the DA concentration in the range from 0.1 to 200 µM, with a detection limit of 80 nM (S/N=3). More importantly, the AuNPs@MoS₂‐based sensor can detect DA in the presence of a large excess of ascorbic acid. The AuNPs@MoS₂‐based sensor shows good sensitivity, reproducibility and selectivity, suggesting that the AuNPs@MoS₂ nanocomposite is a promising candidate in electrochemical sensing and other electrocatalytic applications.     

Water‐Soluble Methyl Orange Fibrils as Versatile Templates for the Fabrication of Conducting Polymer Microtubules

One‐dimensional methyl orange fibrils can be easily prepared. They are stable in acidic aqueous solutions and soluble in neutral water. When used to synthesize conducting polymer microtubules, the fibrils act as “hard templates” formally but as “soft templates” effectively. Microtubular structures of polypyrrole, polyaniline, and poly(3,4‐ethylenedioxythiophene) have been achieved successfully via such water‐soluble versatile templates.

     

Highly Sensitive and Selective Adsorptive Stripping Voltammetric Method Employing a Lead Film Screen‐printed Electrode for Determination of Cobalt as its Nioximate Complex

A carbon screen‐printed electrode modified in‐situ with lead film (PbF‐SPCE) was applied for the adsorptive stripping voltammetric determination of Co(II) in the form of a complex with 1,2‐cyclohexanedione dioxime. Lead film was electrochemically deposited in situ on SPCE from a 0.2 M ammonia buffer solution (pH 8.7) containing 5 ? 10^?5 M Pb(NO₃)₂ and 5 ? 10^?5 M nioxime. Due to the very low LOD (0.003 µgL^?1, i.e., 0.05 nmol L^?1 Co(II); t_acc=120s), the developed procedure could be rated among the most sensitive methods employing SPEs. The Ni(II) signal was significantly lower than the Co(II) one and the separation of Ni(II) and Co(II) peaks was even better at the PbF‐SPCE than at the hanging mercury drop electrode.     

A Modular Flow Design for the meta‐Selective C−H Arylation of Anilines

Described herein is an effective and practical modular flow design for the meta ‐selective C−H arylation of anilines. The design consists of four continuous‐flow modules (i.e., diaryliodonium salt synthesis, meta ‐selective C−H arylation, inline copper extraction, and aniline deprotection) which can be operated either individually or consecutively to provide direct access to meta ‐arylated anilines. With a total residence time of 1 hour, the desired product could be obtained in high yield and excellent purity without the need for column chromatography, and the residual copper content meets the standards for parenterally administered pharmaceutical substances.     

Nonlinear Estimation of the Equilibrium Potential for a Solid‐State Lead Ion‐Selective Electrode

Nonlinear regression was applied to three empirical equations to model the response of a solid‐state lead ion‐selective electrode (ISE). One particular equation, previously reported to describe the response of a fluoride ISE, was found to also describe the response of a solid‐state lead ISE. Nonlinear regression was applied to the early portion of the response curve for the lead ISE and used to estimate the equilibrium potential for a range of test solutions.     

CdSe Quantum Dots and N719‐Dye Decorated Hierarchical TiO2 Nanorods for the Construction of Efficient Co‐Sensitized Solar Cells

Three‐dimensional hierarchical TiO₂ nanorods (HTNs) decorated with the N719 dye and 3‐mercaptopropionic or oleic acid capped CdSe quantum dots (QDs) in photoanodes for the construction of TiO₂ nanorod‐based efficient co‐sensitized solar cells are reported. These HTN co‐sensitized solar cells showed a maximum power‐conversion efficiency of 3.93 %, and a higher open‐circuit voltage and fill factor for the photoanode with 3‐mercaptopropionic acid capped CdSe QDs due to the strong electronic interactions between CdSe QDs, N719 dye and HTNs, and the superior light‐harvesting features of the HTNs. An electrochemical impedance analysis indicated that the superior charge‐collection efficiency and electron diffusion length of the CdSe QD‐coated HTNs improved the photovoltaic performance of these HTN co‐sensitized solar cells.     

Use of a Commercially Available Wood‐Free Resin Pencil as Convenient Electrode for the ‘Voltammetry of Microparticles’ Technique

A wood‐free resin pencil comprised of a lead made of graphite particles dispersed in a polymeric matrix is proposed as a convenient low‐cost electrode for the ‘Voltammetry of Microparticles’ technique instead of paraffin impregnated graphite rods. The pencil electrode was successfully applied for the characterization of insulating (Prussian blue, zeolites) and conductive (silver selenide, pyrite) microparticles in various media. The voltammetric responses were comparable to, sometimes even better than, those obtained with applying other electrochemical techniques.     

Modification of the Electrode Surface by Ag Nanoparticles Decorated Nano Diamond‐graphite for Voltammetric Determination of Ceftizoxime

A modified glassy carbon electrode with a film of nano diamond? graphite nano mixture decorated with Ag nanoparticles (AgNPs? NDG/GCE) was constructed and used for sensitive voltammetric determination of ceftizoxime (CFX). Morphology of AgNPs? NDG/GCE has been examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Experimental variables such as deposited amount of the modifier suspension, pH of the supporting electrolyte and accumulation potential and time were optimized by monitoring of CV and LSV responses of CFX. The results illustrate that AgNPs? NDG/GCE exhibits an excellent electrocatalytic effect in the electro‐oxidation of CFX that leads to a considerable improvement in the corresponding anodic peak current. This also allows the development of a highly sensitive voltammetric sensor for the determination of CFX in pharmaceutical and clinical samples. Under the optimum conditions, the modified electrode showed a linear response to the concentration of CFX in the range of 0.02–7 µM with detection limit of 6 nM. The prepared modified electrode has some remarkable electrochemical properties such as simple preparation, high sensitivity, excellent repeatability and reproducibility and long‐term stability.