Determination of mercury(II) by invertase enzyme inhibition coupled with batch injection analysis

The determination of mercury(II) ions at the trace level by inhibition of the invertase enzyme-catalysed hydrolysis of sucrose into glucose and fructose coupled to electrochemical batch injection analysis was investigated using two approaches. In the first, the glucose produced was detected by injection of 100 microliters samples into the batch injection cell containing a platinum electrode modified by immobilised glucose oxidase. In the second, the glucose and fructose present in injected samples were oxidised directly at a copper-modified glassy carbon electrode. The experimental parameters were optimised and the degree of enzyme inhibition by mercury(II) ions under both conditions was measured. Mercury concentrations in the ng ml-1 range were determined by these two techniques with low sample and reagent consumption. Comparison is made between the two methods and perspectives as a screening test for field application are indicated.     

Molecularly imprinted polymer based potentiometric sensor for the determination of hydroxyzine in tablets and biological fluids

Molecular imprinting is a useful technique for the preparation of functional materials with molecular recognition properties. In this work, a biomimetic potentiometric sensor, based on a non-covalent imprinted polymer, was fabricated for the recognition and determination of hydroxyzine in tablets and biological fluids. The molecularly imprinted polymer (MIP) was synthesized by precipitation polymerization, using hydroxyzine dihydrochloride as a template molecule, methacrylic acid (MAA) as a functional monomer and ethylene glycol dimethacrylat (EGDMA) as a cross-linking agent. The sensor showed a high selectivity and a sensitive response to the template in aqueous system. The MIP-modified electrode exhibited a Nernstian response (29.4 ± 1.0 mV decade⁻¹) in a wide concentration range of 1.0 × 10⁻⁶ to 1.0 × 10⁻¹ M with a lower detection limit of 7.0 × 10⁻⁷ M. The electrode demonstrated a response time of ∼15 s, a high performance and a satisfactory long-term stability (more than 5 months). The method has the requisite accuracy, sensitivity and precision to assay hydroxyzine in tablets and biological fluids.     

Stability evaluation of tramadol enantiomers using a chiral stability-indicating capillary electrophoresis method and its application to pharmaceutical analysis

In this study, a chiral stability-indicating CE assay was developed for the stability evaluation of tramadol (TR) enantiomers in commercial tablets using maltodextrin as chiral selector. To investigate the stability-indicating power of the analytical method as well as stability evaluation of TR enantiomers, active pharmaceutical ingredient and TR tablets were subjected to photolysis, heat, oxidation and hydrolysis to conduct stress testing. Best separation for the TR enantiomers was achieved on an uncoated fused-silica capillary at 20 °C using borate buffer (50 mM, pH 10.2) containing 10% m/v maltodextrin. All determinations were performed by a UV detector at 214 nm. A constant voltage of 20 kV was applied to obtain the separation. The range of quantitation for both enantiomers was 5-100 μg/mL (R>0.996). Intra- and inter-day RSD (n=6) were less than 10%. The percent relevant errors were obtained to be less than 4.0 for both enantiomers. The limits of quantitation and detection for both enantiomers were 5 and 1.5 μg/mL, respectively. Degradation products resulting from the stress studies were the same for both enantiomers and did not interfere with the detection of the enantiomers.     

One‐Pot Synthesis of Sulfonamides and Sulfonyl Azides from Thiols using Chloramine‐T

A convenient synthesis of sulfonamides and sulfonyl azides from thiols is described. In situ preparation of sulfonyl chlorides from thiols was accomplished by oxidation with chloramine‐T (=N‐chlorotosylamide=N‐chloro‐4‐methylbenzenesulfonamide), tetrabutylammonium chloride (Bu₄NCl), and H₂O. The sulfonyl chlorides were then further allowed to react with excess amine or NaN₃ in the same pot.     

The effects of rigid polystyrene particles on the glass transition characteristics and mechanical wave attenuation of styrene‐butadiene rubber: Particle size and acoustic mismatch

Glass transition characteristics and mechanical wave attenuation of the neat and filled styrene‐butadiene rubber (SBR) containing 10 wt % of rigid monosize polystyrene particles of various diameters from several hundred microns down to several tens of nanometers were investigated by dynamic mechanical thermal analysis, impedance tube, and ultrasonic spectroscopy. The results showed the matrix damping capacity and the breadth of glass transition increase by reducing the size of rigid particles due to the matrix‐particles interfacial area increase as the major governing parameter. Matrix glass transition broadening toward higher temperatures was attributed to the increased dynamic heterogeneity induced by fillers, whereas the damping capacity increase was assigned to contribution of interfacial friction loss mechanism. The proposed postulation was confirmed based on the calculated temperature distribution of the relaxing matrix volume fraction. Sound wave attenuation by the matrix and PS particles filled systems led to a broad absorption peak for the former and appearance of a secondary absorption peak at lower frequencies for the latter. Intensity of this secondary peak was highest for the system containing PS nanoparticles. Finally, ultrasonic attenuation enhanced by the PS particle size to wavelength ratio increase according to α_sca ～ (d/λ)^0.38 scaling law and declined by replacing the dense particles with larger hollow PS particles. Comparison of the normalized attenuation of the PS particle filled SBR in various mechanical wave attenuation regimes implied low sensitivity to particle size in vibration, mild differentiation in the sound, and finally severe differentiation in the ultrasound regimes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 82–88, 2010     

Magnetically Recoverable Catalysts: Catalysis in Synthesis of Polyhydroquinolines

Molecules that contain polyhydroquinoline structural scaffolds are N-containing heterocycles which are of great interest to organic chemists and biologists. Polyhydroquinoline structural scaffolds which are known as calcium channel blockers have emerged as one of the most important class of drugs used for the treatment of cardiovascular and Alzheimer's diseases. Besides, recovery and reusability of catalysts are important issues to be discussed in modern catalysis research especially in organic synthesis. The concept of magnetically recoverable catalysts has been rapidly developed in recent times. Magnetic separation is an efficient strategy for the rapid separation of catalysts from the reaction medium. Also, an alternative to time-, solvent-, and energy-consuming separation techniques. In this review, we focused on the fabrication, surface-modification and characterization of nanomagnetic materials and their application, as magnetically recoverable catalysts, in the synthesis of polyhydroquinoline structural scaffolds.     

Green synthesis of silver nanoparticles using Eucalyptus comadulensis leaves extract and its immobilization on magnetic nanocomposite (GO-Fe3O4/PAA/Ag) as a recoverable catalyst for degradation of organic dyes in water

The magnetically recyclable graphene oxide-Fe₃O₄/polyallylamine (PAA)/Ag nanocatalyst was prepared via a green route using Eucalyptus comadulensis leaves extract as both reducing and stabilizing agent. The catalytic activity of this nanocatalyst was investigated for the reduction reaction of methylene blue and methyl orange in the presence of NaBH₄ in aqueous medium at room temperature. The prepared nanocatalyst was characterized by different methods such as Fourier transformed infrared spectroscopy, X-ray diffraction, scanning electron microscopy–energy dispersive X–ray spectroscopy, thermogravimetric analysis, vibrating sample magnetometer, transmission electron microscopy, and UV–visible spectroscopy. The results show that graphene oxide/PAA/Ag nanocatalyst has good activity and recyclability, and can be reused several times without major loss of activity in the reduction process. The apparent rate constants of the methyl orange (MO) and methylene blue (MB) were calculated to be 0.077 s⁻¹ (3 mg of catalyst) and 0.15 s⁻¹ (2 mg of catalyst), respectively.     

Evaluation of a mathematical model using experimental data and artificial neural network for prediction of gas separation

In recent times, membranes have found wide applications in gas separation processes. As most of the industrial membrane separation units use hollow fiber modules, having a proper model for simulating this type of membrane module is very useful in achieving guidelines for design and characterization of membrane separation units. In this study, a model based on Coker, Freeman, and Fleming＇s study was used for estimating the required membrane area. This model could simulate a multicomponent gas mixture separation by solving the governing differential mass balance equations with numerical methods. Results of the model were validated using some binary and multicomponent experimental data from the literature. Also, the artificial neural network （ANN） technique was applied to predict membrane gas separation behavior and the results of the ANN simulation were compared with the simulation results of the model and the experimental data. Good consistency between these results shows that ANN method can be successfully used for prediction of the separation behavior after suitable training of the network     

Synthesis of 1H-isochromenes, 4H-chromenes,and ortho-aminocarbonitrile tetrahydronaphthalenes from the same reactants by using metal-free catalyst

A facile and rapid multicomponent synthesis of pharmaceutically diverse 1H-isochromenes, 4H-chromenes, and ortho-aminocarbonitrile tetrahydronaphthalenes has been developed from benzaldehyde, malononitrile, and cyclohexanone. Three different methods from the same reactants, solvent, temperature, and catalyst lead to three products with excellent yields. All the reactions were followed with the Michael addition and cyclization. In this study, morpholine was used as an active metal-free base catalyst that increases the yields of products and decreases the time of reactions.     

Synthesis and Characterization of Poly(ether-block-amide) Membranes

Poly(ether-block-amide) membranes were made via casting a solution on a nonsolvent (water) surface. In this research, effects of different parameters such as ratio of solvent mixture (n-butanol/isopropanol), temperature, composition of coagulation bath (water) and polymer concentration, on quality of the thin film membranes were studied. The mechanism of membrane formation involves solution spreading, solvent–nonsolvent exchange, and partial evaporation of the solvent steps. Solvent- nonsolvent exchange is the main step in membrane formation and determines membrane morphology. However, at higher temperature of polymeric solution greater portion of solvent evaporates. The results showed that type of demixing process (mutual affinity between solvent and nonsolvent) has important role in film formation. Also, addition of solvent to the nonsolvent bath is effective on membrane morphology. The film quality enhances with increasing isopropanol ratio in the solvent mixture. This behavior can be related to increasing of solution surface tension, reduction of interfacial tension between solution and nonsolvent and delayed solvent-nonsolvent demixing. Uniform films were made at a temperature rang of 60–80 °C and a polymer concentration of 4–7 wt%. Morphology of the membranes was investigated with scanning electron micrograph (SEM). Pervaporation of ethyl butyrate/water mixtures was studied using these membranes and high separation performance was achieved. For ethyl butyrate/water mixtures, It was observed that both permeation flux and separation factor increase with increasing ethyl butyrate content in the feed. Increasing temperature in limited range studied resulted in decreasing separation factor and increasing permeation flux.