A Strong Convergence Theorem for Equilibrium problems and Generalized Hybrid mappings

Mediterranean Journal of Mathematics - In this paper, we introduce a new modified Ishikawa iteration for finding a common element of the set of solutions of an equilibrium problem and the set of...     

Synthesis of Cu-mediated nano-sized salbutamol-imprinted polymer and its use for indirect recognition of ultra-trace levels of salbutamol

Cu²⁺-mediated salbutamol-imprinted polymer nanoparticles, synthesized by precipitation polymerization, were mixed with graphite powder and n-eicosane in order to fabricate a modified carbon paste electrode. This electrode was then applied for indirect differential pulse voltammetry determination of salbutamol. In the presence of Cu²⁺ ions, the formed Cu²⁺–salbutamol complex was adsorbed in to the pre-designed cavities of the MIP particles, situated on the electrode surface. Since the electrochemical signal of salbutamol was intrinsically small, the oxidation peak of the participant Cu²⁺, after reduction step, was recorded and used as an indication of salbutamol amount, adsorbed in the electrode. Different variables influencing the sensor performance were studied and the best conditions were chosen for the determination purpose. Correlation between the sensor response to salbutamol and its concentration was linear in the range of 1.0 × 10⁻⁹–5.5 × 10⁻⁸ M. Detection limit was calculated equal to 6.0 × 10⁻¹⁰ M (S/N). Five replicated determination of salbutamol (1 × 10⁻⁸ M) resulted in standard error of 3.28%, meaning a satisfactory precision of the determination method. The prepared sensor was applied for real sample analysis. In order to minimize the interference effect, the synthesized polymer was successfully used as a solid phase sorbent for salbutamol extraction, before analysis of real samples by the developed sensor.     

An Efficient,One‐Pot,Green Synthesis of Tetracyclic Imidazo[2,1‐b]Thiazoles via Electrochemically Induced Tandem Heteroannulation Reactions

A series of novel catechol‐fused tetracyclic compounds, with an imidazo[2,1‐b]thiazole central core, were successfully synthesized through the anodic oxidation of catechols in the presence of 2‐mercaptobenzimidazole in aqueous solution. The cyclic voltammetric results indicate that a one‐pot four‐step sequential reaction occurs between 2‐mercaptobenzimidazole and the electrochemically derived o‐benzoquinones affording fused polyheterocyclic compounds. The mechanism of this catalyst‐free, domino reaction is proved as an ECEC pathway using controlled‐potential coulometry. In addition, the electrosyntheses of fused compounds have been successfully performed in ambient conditions in an undivided cell using an environmentally friendly method with high atom economy. The structures of products were characterized by FT‐IR, ¹H NMR, ¹³C NMR, and HRMS spectrometric methods.     

Temperature effects on electrical double layer at solid-aqueous solution interface

Despite the significant influence of solution temperature on the structure of electrical double layer, the lack of theoretical model intercepts us to explain and predict the interesting experimental observations. In this work, we study the structure of electrical double layer as a function of thermochemical properties of the solution by proposing a phenomenological temperature dependent surface complexation model. We found that by introducing a buffer layer between the diffuse layer and stern layer, one can explain the sensitivity of zeta potential to temperature for different bulk ion concentrations. Calculation of the electrical conductance as function of thermochemical properties of solution reveals the electrical conductance not only is a function of bulk ion concentration and channel height but also the solution temperature. The present work model can provide deep understanding of micro- and nanofluidic devices functionality at different temperatures.     

Polypyrrole coated ZnO nanorods on platinum wire for solid-phase microextraction of amitraz and teflubenzuron pesticides prior to quantitation by GC-MS

The authors describe a new sorbent for amitraz and teflubenzuron pesticides. It consists of a platinum wire coated with polypyrrole-coated ZnO nanorods. The nanocomposite was prepared by a two-step process. In the first step, oriented ZnO nanorods were hydrothermally grown in situ on a platinum wire. Subsequently, oxidative vapor phase polymerization of pyrrole was performed on FeCl₃-impregnated ZnO nanorods to give a porous polypyrrole film. The organic/inorganic nanocomposite synthesized through hydrothermal deposition and chemical vapor deposition polymerization yields material with attractive properties. The coated wire was applied to solid-phase microextraction of amitraz (in the form of 2,4-dimethylaniline resulting from the hydrolysis of amitraz) and teflubenzuron. The effects of extraction temperature, extraction time, sample pH value and salt concentration were optimized. The analytes 2,4-dimethylaniline and teflubenzuron were then quantified by GC-MS. Under optimum conditions, the LODs range between 0.1 and 0.15 ng.mL^?1. Relative standard deviations at two concentration are <8.3% for intraday precision and <10.3% for inter-day precision. In all cases, the fiber to fiber reproducibility is <12.2%. For both analytes the linear dynamic ranges are 0.5–300 ng.mL^?1. The procedure was successfully applied to the analysis of spiked agricultural water samples.

Open image in new window

Graphical abstract A novel inorganic/organic hybrid nanocomposite was synthesized through in situ hydrothermal deposition of ZnO nanorods and ten placing a thin layer of polypyrrole on them by chemical vapor deposition polymerization. This nanocomposite was applied to fabricate a solid-phase microextraction fiber for the extraction of amitraz and teflubenzuron pesticides residue from agricultural samples prior to their quantitation by GC-MS.

     

An efficient conversion of catechols into 6H‐benzofuro[3,2‐c][1]‐benzopyran‐6‐one derivatives

Coupling of in‐situ generated o‐benzoquinones with 4‐hydroxycoumarin as a nucleophile has been studied in the presence of potassium ferricyanide as an oxidizing agent in aqueous solution. The results indicate that the quinones derived from catechols, participate in Michael addition reactions with 4‐hydroxycoumarin to form the 6H‐benzofuro[3,2‐c][1]benzopyran‐6‐one derivatives.     

Novel Catalytic Acetylation of Alcohols with Preyssler's Anion, [NaP5Wa30O110]14– 1

Sodium 30-tungstopentaphosphate, the so-called Preyssler's anion with a formula of [NaP₅W₃₀O₁₁₀]^14– (I) catalyzes the acetylation of alcohols (C _n H_{2n + 1}OH, n = 2, 3, 4, 5) with acetic acid. High yield is obtained with I as pure acid or supported on silica. Both homogeneous and heterogeneous catalysts are discussed and compared. H₁₄[NaP₅W₃₀O₁₁₀], abbreviated as H₁₄-P₅, under homogeneous conditions, as well as supported on silica (heterogeneous conditions) is found to be an excellent catalyst. Our data indicate that, when the ammonium salt of I is employed as the catalyst, the yield increases as the alcohol carbon-chain is increased. This behavior is found to be quite general. The catalysts can be easily recovered and recycled with retention of their initial structure and activity.     

N,N′‐Bis(arylmethylidene)arylmethanediamines: Suitable Precursors for the Synthesis of 1‐Pyrroline Derivatives

A simple and appropriate procedure for the synthesis of 4,5‐dihydro‐5‐hydroxy‐3H‐pyrrole‐3,3‐dicarbonitrile derivatives is reported. The advantages of this method are one‐pot conditions, high yield of products, short reaction times, and no need of metal catalyst. The structures are confirmed spectroscopically (IR, ¹H‐ and ¹³C‐NMR, and EI‐MS) and by elemental analyses. A plausible mechanism for this reaction is proposed (Scheme 2).     

Development of an ultrasound‐assisted emulsification microextraction method for the determination of chlorpyrifos and organochlorine pesticide residues in honey samples using gas chromatography with mass spectrometry

A simple, rapid, and efficient ultrasound‐assisted emulsification microextraction method followed by gas chromatography mass spectrometry in selected ion monitoring mode was developed for the determination of organochlorine pesticides in honey samples. The type and volume of organic extraction solvent, pH, effect of added salt content, and centrifuging time and speed were investigated. Under the optimum extraction conditions, 30 μL of 1, 2‐dibromoethane (extraction solvent) was immersed into an ultrasonic bath for 1 min at 40°C. The limits of detection and quantification for all target pesticides were 0.003–0.06 and 0.01–0.2 ng/g_, respectively. The extraction recovery was 91–100% and the enrichment factors were 168–192. The relative standard deviation for the method was <6% for intraday (n = 6) and <8% for interday precision (n = 4). The proposed method was successfully applied for the analysis of organochlorine pesticides in honey samples.