Electro-optical Kerr effect of azo-dye-doped liquid crystals using nulled intensity method

ABSTRACT

The electro-optical Kerr effect and pre-transition behavior have been investigated for different concentration of dimethyl-aminoazobenzene dye-doped nematic liquid crystal by using the nulled intensity method. Measurement results have showed that the molecular reorientation of liquid crystals induced by photoisomerization of azo dyes come about to increase an amount of Kerr constant at low percentages of dye concentration. Additionally, the results of pre-transition temperature which were obtained by extrapolating the invers Kerr constant as a function of temperature have been found to be in good agreement with predictions of the Landau-De Gennes model.     

Application of a sensitive nanocomposite-based electrochemical sensor for voltammetric determination of dicyclomine hydrochloride in real samples

In the present study a glassy carbon electrode, modified with nanocomposite of gold nanoparticles/multiwalled carbon nanotubes (GNPs/MWCNTs/GCE), was used for determination of dicyclomine hydrochloride (DcCl). The results showed that synergetic effects of GNPs and MWCNTs highly improved electrochemical response and sensitivity of the sensor. The electrochemical oxidation of DcCl was investigated by cyclic voltammetry and differential pulse voltammetry. Also, scanning electron microscopy and energy dispersive x-ray spectroscopy were used to evaluate microstructure of electrochemical sensor. The effect of various experimental parameters including pH and scan rate on the voltammetric response of DcCl were investigated. Under the optimal conditions linear response was observed in range of 1.0–1.2 × 10² µmol L^?1 for DcCl. The lower detection limit was found to be 0.40 µmol L^?1 for DcCl. The investigated method showed good stability, reproducibility and repeatability. The proposed sensor was successfully applied to the determination of DcCl in real samples.     

Catalytic effects of some Keggin-type heteropoly acids and polyoxometalates on selective nitration of phenols

Catalytic amounts of heteropoly acids and polyoxometalates promoted mononitration of phenolic compounds using iron(III) nitrate nonahydrate and bismuth(III) nitrate pentahydrate in dichloromethane at room temperature. Tungstophosphoric acid cesium salt, Cs_2.5H_0.5PW₁₂O₄₀, in a heterogeneous phase, exhibited significant rate enhancement of reactions as well as ortho selectivity without over-nitration and oxidation byproducts.     

Prediction of rizatriptan trace level in biological samples: An application of the adaptive-network-based fuzzy inference system (ANFIS) in assisting drug dose monitoring

Introduction: Solvent bar microextraction technique is a sample preparation method prior to analysis for complicated matrices such as urine, blood, stem cell culture, and wastewater. This method, when coupled with adaptive-network-based fuzzy inference system, can detect and predict the concentration of trace elements and drugs at ultra-trace levels in complicated matrices.

Material and method: Rizatriptan was used as a model drug for validation of this method. Therefore, six parameters (pH of donor and acceptor phase, stirring rate, time, temperature, and salt addition) affecting the preconcentration and determination of this drug were investigated. In this method, pH gradient was applied to transfer the drug into the solvent bar. MATLAB version 2010 was used for data analysis. Construction of an input-output mapping was done based on the results obtained from the experiments. For the simulation, the ANFIS architecture was employed to model nonlinear functions, identify nonlinear components in a control system, and predict a chaotic time series, all yielding remarkable results. Based on the best model chosen, the drug was preconcentrated and analyzed under the optimum condition.

Results and discussion: The figures of merit were as follows: preconcentration factor: 127; limit of detection: 15?ng?mL^?1; limit of quantification: 50?ng?mL^?1; R²:0.999; RSD: 3.0%(interday) and 4.6% interaday. As a result, this method can be employed for preconcentration and microextraction of several elements, drugs, antibodies at trace levels in complicated matrices. After modeling, the optimum condition could be predicted without performing unnecessary and expensive experiments.

Conclusion: Certain biomarkers can also be preconcentrated and detected using the proposed method. It offers high sample clean up, therefore it can be used for clean validation. Prediction of the course of treatment may be possible with the proposed method, therefore it is highly practical, easy and cost-effective.     

Heteropolyacid immobilized on polymer/magnetic zeolite nanocomposite as a new and recyclable catalyst for the selective oxidation of alcohols

A new magnetic oxidation catalyst was prepared using immobilization of tungstophosphoric acid on poly(N-vinylimidazole) entrapped magnetic nanozeolite and characterized by FTIR, TGA, XRD, SEM, TEM, EDX, VSM, and ICP-OES. The resulting heterogeneous catalyst displays high catalytic performance for selective oxidation of alcohols compared to the other catalysts. The catalyst could be reused eight times without any loss of catalytic activity.     

MCM-41 mesoporous silica: a highly efficient and recoverable catalyst for rapid synthesis of α-aminonitriles and imines

In this work, pure MCM-41 mesoporous silica with active mesoporous sites has been successfully applied, as a highly efficient and recoverable catalyst, for the rapid and convenient synthesis of α-aminonitriles and imines. Various imines, as the intermediate of the Strecker reaction, were simply prepared from condensation of a wide range of aldehydes and amines in the presence of low loading of MCM-41 mesoporous silica under solvent-free conditions at room temperature in high to quantitative yields. Furthermore, the corresponding α-aminonitrile derivatives were prepared through the three-component Strecker reaction using trimethylsilylcyanide catalyzed by MCM-41 as a bifunctional heterogeneous mesoporous solid catalyst.     

Ionic Liquid Promoted One-Pot Three-Component Reaction: Synthesis of Annulated Imidazo[1,2-<Emphasis Type="Italic">a</Emphasis>]azines Using Trimethylsilylcyanide

Summary. Imidazo[1,2-a]azine derivatives are synthesized by a one-pot three-component reaction of an 2-aminoazine, an aldehyde, and trimethylsilylcyanide in the presence of 1-n-butyl-3-methylimidazolium bromide as a recoverable ionic liquid, in moderate to excellent yields with relatively short reaction times.     

An Efficient Solid Acid Promoted Synthesis of Quinoxaline Derivatives at Room Temperature

Quinoxaline derivatives have been synthesized in a very short time with excellent yields by the condensation of 1,2-diamines with aliphatic or aromatic 1,2-dicarbonyl compounds or benzilmonoxime in the presence of silica sulfuric acid as a very inexpensive solid acid catalyst at room temperature. The recovery and reuse of the catalyst are also satisfactory.     

Spectrophotometric Determination of Selected Antibiotics Using Prussian Blue Reaction

A simple, sensitive and accurate spectrophotometric method has been described for the determination of ampicillin(I), amoxicillin trihydrate(II) and cefazolin sodium(III). The procedure is based on the formation of Prussian Blue (PB) complex. The reaction between the acidic hydrolysis products of antibiotics (T = 60 °C) with mixture of Fe³⁺ and hexacyanoferrate(III) ions was evaluated for the spectrophotometric determination of the mentioned drugs. The maximum absorbance of the colored complex occurs at λ = 700 nm and the molar absorptivity is 3.0 × 10⁴ 1 mol^?1cm^?1. The effect of various parameters such as concentration of K₃Fe(CN)₆ and Fe³⁺, nature and amount of acids used, temperature and time of heating were investigated. Under optimum conditions the linear range of calibration graph was 2.0–12.0, 5.0–13.5 and 3.0–12.0 μg mL^?1 for ampicillin, amoxicillin and cefazolin, respectively. The relative standard deviation for the determination of 10 μg mL^?1 of antibiotics was about 0.5–1.5%. The proposed method was successfully applied to the determination of selected antibiotics from pharmaceutical preparations. The validity of the method was tested by the official methods and by the recovery studies of standard addition to pharmaceuticals.