Methylthiouracil‐modified Carbon Paste Electrode as a New Voltammetric Sensor Based on a 1,4‐Michael Addition Reaction for Detection of Dopamine

A sensitive dopamine sensor was constructed based on the modified carbon paste electrode with methylthiouracil as a nucleophile in the 1,4‐Michael addition reaction. An ECE mechanism was suggested for dopamine oxidation at the modified electrode. Design of experiments was used in the optimization of variables. Under the optimum conditions, calibration graph was linear in the range of 0.20–15.0 µM with a detection limit of 73 nM. The relative standard deviations (n=5) for 0.50 µM of dopamine was 3.83 %. The selectivity of the sensor was also studied. The developed sensor was applied for analysis of pharmaceutical and biological samples.     

Functionalization of Multi Carbon Nanotubes with 1,2‐Naphthoquinone‐4‐sulfonic Acid Sodium: A Novel Sulphydryl Compounds Sensor Based on Functionalized Carbon Nanotube Film Using Michael Addition

The functionalized multi‐wall carbon nanotube with 1,2‐naphthoquinone‐4‐sulfonic acid sodium (Nq‐MWNT) was fabricated by a simple and low‐cost method. Techniques of scanning electron microscope (SEM) with energy dispersive X‐ray (EDX) analysis, fourier transform infrared spectroscopy (FT‐IR), ultraviolet visible spectroscopy (UV‐vis) and cyclic voltammetry (CV) were used to characterize the property of the Nq‐MWNT. The results showed that the MWNT with high functionalization of Nq can be obtained using this simple method. The Nq‐MWNT modified carbon paste electrode (Nq‐MWNT/CPE) was fabricated by drop‐casting technique. The resulted modified electrode was tested successfully to detection D‐penicillamine (D‐PA) and captopril (CAP) in an aqueous solution. It is found that D‐PA and CAP participate in Michael addition reaction with Nq on MWNT to form the corresponding thioquinone derivative. The reoxidation of adducts at a potential of less positive than D‐PA and CAP at the surface of the bare CPE leads to an increase in the oxidative current, which is proportional to the concentration of D‐PA and CAP. The catalytic response showed a wide linear range (3‐200 μM and 1‐130 μM for D‐PA and CAP, respectively) as well as its experimental limit of detection can be achieved 0.8 μM, and 0.4 μM for D‐PA and CAP, respectively. The modified electrode for D‐PA and CAP determination is of the property of simple preparation, good stability and high sensitivity. Furthermore, the fabricated electrode was used to determine the content of D‐PA and CAP in the tablet, suggesting the good accuracy of the method.     

Electrocatalytic Oxidation and Voltammetric Determination of Hydrazine on the Tetrabromo‐p‐Benzoquinone Modified Carbon Paste Electrode

The electrochemical properties of hydrazine studied at the surface of a carbon paste electrode spiked with p‐bromanil (tetrabromo‐p‐benzoquinone) using cyclic voltammetry (CV), double potential‐step chronoamperometry and differential pulse voltammetry (DPV) in aqueous media. The results show this quinone derivative modified carbon paste electrode, can catalyze the hydrazine oxidation in an aqueous buffered solution. It has been found that under the optimum conditions (pH 10.00), the oxidation of hydrazine at the surface of this carbon paste modified electrode occurs at a potential of about 550 mV less positive than that of a bar carbon paste electrode. The electrocatalytic oxidation peak current of hydrazine showed a linear dependent on the hydrazine concentrations and linear analytical curves were obtained in the ranges of 6.00×10^?5 M–8.00×10^?3 M and 7.00×10^?6 M–8.00×10^?4 M of hydrazine concentration with CV and differential pulse voltammetry (DPV) methods, respectively. The detection limits (3σ) were determined as 3.6×10^?5 M and 5.2×10^?6 M by CV and DPV methods. This method was also used for the determination of hydrazine in the real sample (waste water of the Mazandaran wood and paper factory) by standard addition method.     

Highly Sensitive Voltammetric Speciation and Determination of Inorganic Arsenic in Water and Alloy Samples Using Ammonium 2‐Amino‐1‐Cyclopentene‐1‐Dithiocarboxylate

A simple, fast, reproducible (2.5% RSD at 3.0 μg/L), and sensitive method is described for quantifying As(III) (0.3 μg/L detection limit, 0.5–440 μg/L dynamic range). Anodic stripping voltammetry (ASV) is performed after accumulating arsenic at a mercury film electrode at ?0.350 V vs. Ag/AgCl (saturated KCl) for 20 s in 0.2 M HCl containing 8 μM ammonium 2‐amino‐1‐cyclopentene‐1‐dithiocarboxylate (AACD), without oxygen removal. This is the first report of using AACD in ASV and in electrochemical quantification of As(III). Total arsenic is determined after sodium‐sulfite‐reduction of As(V) to As(III). Interferences are minimal. Method validation involved water and metal alloy samples.     

KF-蒙脱土催化下丙二腈与α,β-不饱和酮的迈克尔加成反应

本论文研究了KF-蒙脱土催化下丙二腈与α,β-不饱和酮的迈克尔加成反应,研究发现在不同的反应温度下可以得到加成和环化两种不同的产物。该方法和现有的方法相比具有产率高、反应条件温和、操作简单、试剂易得等优点。     

A Novel and Efficient Catalyst to One‐Pot Synthesis of 2‐Amino‐4H‐Chromenes by Methanesulfonic Acid

Methanesulfonic acid efficiently catalyzes the one‐pot, three component reaction of an aromatic aldehyde, malonitrile and α or β‐naphthol to yield 2‐amino‐4H‐chromenes in very good yields.     

Acetylferrocene Modified Carbon Paste Electrode; A Sensor for Electrocatalytic Determination of Hydrazine

The electrocatalytic oxidation of hydrazine at a carbon paste electrode spiked with acetylferrocene as a mediator was studied by cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. In contrast to other ferrocenic compounds, acetylferrocene exhibits a chemical irreversible behavior, but it can act as an effective mediator for electrocatalytic oxidation of hydrazine, too. The heterogeneous electron transfer rate constant between acetylferrocene and the electrode substrate (carbon paste) and the diffusion coefficient of spiked acetylferrocene in silicon oil were estimated to be about 3.45×10^?4 cm s^?1 and 4.45×10^?9 cm² s^?1, respectively. It has been found that under the optimum conditions (pH 7.5) the oxidation of hydrazine occurs at a potential of about 228 mV less positive than that of an unmodified carbon paste electrode. The catalytic oxidation peak current of hydrazine was linearly dependent on its concentration and the obtained linear range was 3.09×10^?5 M–1.03×10^?3 M. The detection limit (2σ) has been determined as 2.7×10^?5 M by cyclic voltammetry. Also, the peak current was increased linearly with the concentration of hydrazine in the range of 1×10^?5 M–1×10^?3 M by differential pulse voltammetry with a detection limit of 1×10^?5 M. This catalytic oxidation of hydrazine has been applied as a selective, simple, and precise new method for the determination of hydrazine in water samples.     

Voltammetric Determination of Metronidazole Using a Sensor Based on Electropolymerization of α‐Cyclodextrin over a Carbon Paste Electrode

An electrochemical sensor for metronidazole (MTZ) was built via the surface modification of a carbon paste electrode (CPE) by a film obtained through electropolymerization of α‐cyclodextrin (CPE_α‐CD). The CPE_α‐CD was characterized by cyclic voltammetry (CV) and atomic force microscopy (AFM), by both techniques was demonstrated that the polymer film is coating the electrode surface. The electroreduction behaviour of MTZ in HClO₄ media as a supporting electrolyte was studied by differential‐pulse voltammetric (DPV) technique. The DPV electrochemical process was observed to be diffusion controlled and irreversible. Under optimal conditions, the peak current was proportional to MTZ concentration in the range of 0.5 to 103.0 μM with a detection limit of 0.28±0.02 μM. The method was successfully applied to quantify of MTZ in pharmaceutical formulations. In addition, this proposed MTZ sensor exhibited good reproducibility, long‐term stability and fast current response.     

Electrocatalytic Oxidation of 2‐Thiouracil and 2‐Thiobarbituric Acid at a Carbon‐Paste Electrode Modified with Cobalt Phthalocyanine

Voltammetric behavior of two mercaptopyrimidine derivatives (2‐thiouracil and 2‐thiobarbituric acid) has been studied by cyclic voltammetry at a cobalt phthalocyanine (CoPc)‐modified carbon‐paste electrode. The results of voltammetric determinations showed that the CoPc in the matrix of modified electrode acts as catalyst for electrooxidation of these thiols (RSH), lowering the overpotential of the reaction and significantly increasing the sensitivity for detection of thiols in neutral conditions. The results of voltammetric and polarization measurements in solutions with various pHs were used for prediction of the mechanism of electrocatalytic oxidation at the surface of modified electrode. These results showed that at the modified electrode, electrochemical oxidation of thiolate anion (RS^?) is the rate‐determining step. It was found that the modified electrode exhibits good selectivity for catalytic oxidation of mercaptopyrimidines over other biologically important mercaptans such as cysteine, glutathione and thioglycolic acid. The results demonstrate that the peak current for thiol oxidation has a linear variation with the concentration in the range of 1×10^?2–1×10^?5 M. This system can be used for sensitive and selective voltammetric detection of mercaptopyrimidine derivatives.     

A Simple and Efficient Electrochemical Sensor for Electrocatalytic Reduction of Nitrite Based on Poly(4‐aminoacetanilide) Film Using Carbon Paste Electrode

In this study, the electrochemical reduction of nitrite was investigated on poly(4‐aminoacetanilide) (PPAA) forming by cyclic voltammetry at the surface of carbon paste electrode. The electrochemical properties of the modified electrode have been studied by cyclic voltammetry and double potential step chronoamperometry. Results showed that in the optimum condition (pH = 0.00) the reduction of nitrite occurred at a potential about 667 mV more positive than that unmodified carbon paste electrode. This amount of electrocatalytic ability is high compared with other electrocatalysts. Using a chronoamperometric method, the catalytic rate constant (k) was calculated 8.4 × 10⁴ cm³ mol^‐1 s^‐1. Also, the electrocatalytic reduction peak currents was found to be linear with the nitrite concentration in the ranges of 5 × 10^‐4 M to 2.5 × 10^‐2 M and 2 × 10^‐5 M to 7 × 10^‐3 M with detection limits (2σ) were determined as 4.5 × 10^‐4 M and 1 × 10^‐5 M by cyclic voltammetry (CV) and hydrodynamic amperometry methods respectively. Recovery experiments exhibit the satisfactory results.     

Synthesis of 2‐Aryl‐1‐arylmethyl‐1H‐1,3‐benzimidazole Derivatives Using Silica‐bonded Propyl‐S‐sulfonic Acid as Recyclable Solid Acid Catalyst

A highly selective synthesis of 2‐aryl‐1‐arylmethyl‐1H‐1,3‐benzimidazoles from the reaction of o‐phenylenediamine and aromatic aldehydes in the presence of silica‐bonded propyl‐S‐sulfonic acid (SBSSA) at 80°C in water in good to excellent yields was developed.     

One‐Pot Syntheses of 2‐(2‐Sulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetic Acid Derivatives via Reactions of 3‐(2‐Isothiocyanatophenyl)prop‐2‐enoic Acid Derivatives with Thiols or Sodium Sulfide

Two efficient methods for the preparation of 2‐(2‐sulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetic acid derivatives 3 under mild conditions have been developed. The first method is based on the reaction of 3‐(2‐isothiocyanatophenyl)prop‐2‐enoates 1a – 1c with thiols in the presence of Et₃N in THF at room temperature, leading to the corresponding dithiocarbamate intermediates 2 , which underwent spontaneous cyclization at the same temperature by an attack of the S‐atom at the prop‐2‐enoyl moiety in a 1,4‐addition manner (Michael addition) to give 2‐(2‐sulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetates in one pot. The second method involves treatment of 3‐(2‐isothiocyanatophenyl)prop‐2‐enoic acid derivatives 1b – 1d with Na₂S leading to the formation of 2‐(2‐sodiosulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetic acid intermediates 5 by a similar addition/cyclization sequence, which are then allowed to react with alkyl or aryl halides to afford derivatives 3 . 2‐(2‐Thioxo‐4H‐3,1‐benzothiazin‐4‐yl)acetic acid derivatives 6 can be obtained by omitting the addition of halides.     

The Environmentally Friendly Energetic Salt (ATZ)(TNPG) Based on 4‐Amino‐1, 2, 4‐triazole (ATZ) and Trinitrophloroglucinol (TNPG)

The environmentally friendly energetic salt (ATZ)(TNPG) (ATZ = 4‐amino‐1, 2, 4‐triazole, TNPG = trinitrophloroglucinol) was synthesized and characterized by elemental analysis and FT‐IR spectroscopy. The crystal structure was determined by X‐ray single crystal diffraction. It crystallizes in monoclinic space group P2₁/c and its crystal density is 1.832 g · cm^–3. Thermal decomposition mechanisms were investigated through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). In addition, the experimental data showed that the energy of combustion was approximately equal to the energies of combustion of RDX (1, 3, 5‐trinitro‐1, 3, 5‐triazacyclohexane) and HMX (1, 3, 5, 7‐tetranitro‐1, 3, 5, 7‐tetraazocane). The non‐isothermal kinetics parameters were also studied by applying Kissinger's, Ozawa's, and Starink's methods. Determination of the sensitivities revealed higher sensitivities of (ATZ)(TNPG) as compared to (ATZ)(PA) (PA = picrate).     

Silica‐bonded S‐sulfonic Acid as a Recyclable Catalyst for Synthesis of 2,3‐Dihydroquinazolin‐4(1H)‐ones

2,3‐Dihydroquinazolin‐4(1H)‐one derivatives were synthesized via a one‐pot, three component reaction of isatoic anhydride and an aromatic aldehyde with ammonium acetate or primary amine catalyzed by silica‐bonded S‐sulfonic acid in ethanol at 80°C. The reaction work‐up is simple and the catalyst is easily separated from the products by filtration. The heterogeneous catalyst was recycled for ten runs upon the condensation reaction of isatoic anhydride and 4‐chlorobenzaldehyde with ammonium acetate without losing its catalytic activity.     

Michael-Addition Reaction of Malononitrile with α,β-Unsaturated Cycloketones Catalyzed by KF／Al2O3

A series of KF/Al2O3 catalyzed Michael-addition reactions between malononitrile and α,β-unsaturated cycloketones in DMF solution were studied. At room temperature, 2-cyano-3-aryl-3-(1,2,3,4-tetrahydronaphthalen-1-one-2-yl) propionitrile derivatives were synthesized by the reaction between 2-arylmethylidene-1,2,3,4-tetra-hydronaphthalen-1-one and malononitrile. However, if the temperature was increased to 80℃, 2-amino-3-cyano-4-aryl-4H-benzo[h]chromene derivatives were obtained in high yields. When the α,β-unsaturated ketones were replaced by 2,6-biarylmethylidenecyclohexanone or 2,5-biarylmethylidenecyclopentanone, another series of 2-amino-3-cyano-4H-pyran derivatives was isolated successfully. The structures of the products were confirmed by X-ray diffraction analysis.     

过无溶剂、无催化的aza-Michael加成反应合成b氨基酸衍生物

本文报道一种安全,环境有好,经济实用的合成b氨基酸衍生物的新方法。利用α,β不饱和化合物和脂肪族胺,通过无溶剂、无催化的aza-Michael加成反应,高产率的合成b氨基酸衍生物。     

Simultaneous Voltammetric Determination of Uric Acid and Ascorbic Acid Using a Carbon‐Paste Electrode Modified with Multi‐Walled Carbon Nanotubes/Nafion and Cobalt(II)nitrosalophen

A composition of multiwalled carbon nanotube (MWCNT), Nafion and cobalt(II)‐5‐nitrosalophen (CoNSal) is applied for the modification of carbon‐paste electrode (CPE). The pretreated MWCNT is well dispersed in the alcoholic solution of Nafion under the ultrasonic agitation, and the resulted suspension is used as modifier (with 10% w/w) in the matrix of the paste electrode. The prepared electrode further modified by addition of 3 wt% of CoNSal. The resulted modified electrode is used as a sensitive voltammetric sensor for simultaneous determination of uric acid (UA) and ascorbic acid (AA). The electrode showed efficient electrocatalytic activity in lowering the anodic overpotentials and enhancement of the anodic currents. This electrode is able to completely resolve the voltammetric response of UA and AA. The effects of potential sweep rate and pH of the buffer solution on the response of the electrode, toward UA and AA, and the peak resolution is thoroughly investigated by cyclic and differential pulse voltammetry (CV and DPV). The best peak resolution for these compounds using the modified electrode is obtained in solutions with pH 4. The ΔE_p for UA and AA in these methods is about 315 mV, which is considerably better than previous reports for these compounds. A linear dynamic range of 1×10^?7 to 1×10^?4 M with a detection limit of 6×10^?8 M is resulted for UA in buffered solutions with pH 4.0. The voltammetric response characteristics for AA are obtained as, the linear range of 5×10^?7 to 1×10^?4 M with the detection limit of 1×10^?7 M. The voltammetric detection system was very stable and the reproducibility of the electrode response, based on the six measurements during one month, was less than 3.5% for the slope of the calibration curves of UA and AA. The prepared modified electrode is successfully applied for the determination of AA and UA in mixture samples and reasonable accuracies are resulted.