Gold Electrode Modified with Self‐Assembled Monolayer of Cysteamine‐Functionalized MWCNT and Its Application in Simultaneous Determination of Dopamine and Uric Acid

The voltammetric behavior of dopamine (DA) and uric acid (UA) on a gold electrode modified with self‐assembled monolayer (SAM) of cysteamine (CA) conjugated with functionalized multiwalled carbon nanotubes (MWCNTs) was investigated. The film modifier of functionalized SAM was characterized by means of scanning electron microscopy (SEM) and also, electrochemical impedance spectroscopy (EIS) using para‐hydroquinone (PHQ) as a redox probe. For the binary mixture of DA and UA, the voltammetric signals of these two compounds can be well separated from each other, allowing simultaneous determination of DA and UA. The effect of various experimental parameters on the voltammetric responses of DA and UA was investigated. The detection limit in differential pulse voltammetric determinations was obtained as 0.02 µM and 0.1 µM for DA and UA, respectively. The prepared modified electrode indicated a stable behavior and the presence of surface COOH groups of the functionalized MWCNT avoided the passivation of the electrode surface during the electrode processes. The proposed method was successfully applied for the determination of DA and UA in urine samples with satisfactory results. The response of the gold electrode modified with MWCNT‐functionalized SAM method toward DA, UA, and ascorbic acid (AA) oxidation was compared with the response of the modified electrode prepared by the direct casting of MWCNT.     

Synthesis,Characterization and Fluorescence Studies of Novel Tetrachloroperylene-Azo Hybrid Dyes

Novel rylene-azo hybrid dyes have been synthesized by condensation of azo-dyes with tetrachloroperylene dianhydride, possessing stupendous thermal, chemical and photochemical stability. Phenolic azo dyes are used for the nucleophilic replacement of chlorine substituents at 1,6,7,12-positions of perylene 3,4,9,10-dianhydride system. The absorption maxima (?_max) of these dyes have been determined in diverse solvents such as water, ethanol, methanol, ethyl acetate and N, N-dimethylformamide. Fluorescence spectra are taken in water and highest fluorescence was exhibited by dyes containing carboxylic groups. The ?_max and fluorescence of these dyes is greatly affected by polarity of solvents. The structures of newly synthesized rylene-azo hybrid dyes have been confirmed by UV, FTIR and ¹HNMR spectroscopy.     

Some results on stem covers of crossed modules

In this article, we prove the existence of stem covers for crossed modules, which generalizes the works of Schur (1904) [20] and Jones (1973) [11] in group theory. We also, using projective presentations, determine the structure of all stem covers of crossed modules whose second homologies are finite and, using this result, we give several results concerning them, which extend the classical ones for stem covers of groups.     

A fuzzy algorithm for continuous capacitated location allocation model with risk consideration

This paper presents a continuous capacitated location-allocation model with fixed cost as a risk management model. In the presented model, the fixed cost consists of production and installation costs. The model considers risk as percent of unsatisfied demands. The fixed cost is assigned to a zone with a predetermined radius from its center. Because of uncertain environment, demand in each zone is investigated as a fuzzy number. The model is solved by a fuzzy algorithm based on α-cut method. After solving the model based on different α-values, the zones with the largest possibilities are determined for locating new facilities and the best locations are calculated based on the obtained possibilities. Then, the model is solved based on different α-values to determine best allocation values. Also, this paper proposes a Cross Entropy (CE) algorithm considering multivariate normal and multinomial density functions for solving large scale instances and is compared with GAMS. Finally, a numerical example is expressed to illustrate the proposed model.     

Superparamagnetic iron oxide as an efficient catalyst for the one-pot, solvent-free synthesis of α-aminonitriles

Superparamagnetic Fe₃O₄ is shown to act as a very efficient catalyst for the one-pot, three-component synthesis of α-aminonitriles from aldehydes, amines, and TMSCN. The catalyst is easily recovered by the use of an external magnet and reused in several reactions without any noticeable loss of activity. The products are obtained rapidly at room temperature in good purity upon separation of the catalyst and evaporation of the volatiles of the reaction mixture.     

Solvatochromic behavior on the absorption and fluorescence spectra of Rose Bengal dye in various solvents

The absorption and fluorescence spectra of Rose Bengal dye were studied in various solvents. It was found that solvent effects on the absorption wavelength are consistent with the solvatochromic model of Kamlet, Abboud and Taft. The solvent polarizability value pi* was found to have a linear relationship with the absorption wavelength of the dye in various solvents. Additionally, the normalized transition energy value (E(T)(N)) showed some scattering when plotted versus Deltanu(af). Density functional calculations were used to assign the absorption in the region 540-570 nm to a pi-pi* transition between the HOMO and LUMO of the anion. Experimental ground state and excited state dipole moments were calculated by using the solvatochromatic shifts of absorption and fluorescence spectra as a function of the dielectric constant (epsilon) and refractive index (n). The dipole moment for Rose Bengal was found to be 1.72 Debye in the ground state, whereas this value was 2.33 Debye in the excited state.     

Electrochemical study of Azathioprine at thin carbon nanoparticle composite film electrode

Thin carbon nanoparticle/Nafion film (CNP/N), as a novel electrode material, is formed on the surface of the glassy carbon electrode in a simple solvent evaporation process. The electrochemical behavior of Azathioprine (Aza) at the CNP/N-modified electrode is investigated in detail by the means of cyclic voltammetry. During the electrochemical reduction of Aza, an irreversible cathodic peak is appeared. Cyclic voltammetric studies indicated that the reduction process has an irreversible and adsorption-like behavior. The observed reduction peak is attributed to a four-electron process referring to the reduction of nitro group to the corresponding hydroxylamine. The prepared electrode showed an excellent catalytic activity toward the electro-reduction of Aza leading to a significant improvement in sensitivity as compared to the bare glassy carbon electrode where the electrochemical activity for this compound is very weak.     

The effect of AlBr<Subscript>3</Subscript> additive on the thermal degradation of PMMA A study using TG-DTA-DTG,IR and PY-GC-MS techniques

The thermal behavior of poly(methyl methacrylate) (PMMA) was studied in the presence of AlBr₃ using TG-DTA-DTG, IR and Py-GC-MS techniques. Degradation products were identified. It was found that PMMA started degrading at a lower temperature due to the generation of free radicals (Br^•), being the product of decomposition of AlBr₃. Despite early destabilization of the system, stabilization zone was also highlighted. Flammability test was conducted to check the affectivity of AlBr₃. Degradation mechanism has been proposed. Pyrolysis of the system (PMMA–AlBr₃) was also monitored by heating it at different temperatures.     

Spectrophotometric method for quantitative determination of montelukast in bulk,pharmaceutical formulations and human serum

A simple ultraviolet spectrophotometric method for the estimation of montelukast in methanol has been devised and been compared with the existing pharmacopoeial RP-HPLC method for estimation of the drug. The limit of detection of montelukast at 283 nm was 75.2 ng/mL. The calibration was linear in the range of 3–45 μg/mL. Analytical parameters such as stability, selectivity, accuracy and precision have been established for the method in MONAKA® tablets and in human serum and evaluated statistically to assess the application of the method. The method was validated under the ICH and USP guidelines and found to comprise the advantages for simplicity, stability, sensitivity, reproducibility and accuracy for using as an alternate to the existing non-spectrophotometric methods for the routine analysis of the drug in pharmaceutical formulations and in pharmaceutical investigations involving montelukast.     

First principles calculations of electronic structure and magnetic properties of Cr-based magnetic semiconductors Al1−xCrxX (X=N, P, As, Sb)

First principles calculations based on the density functional theory (DFT) within the local spin density approximation are performed to investigate the electronic structure and magnetic properties of Cr-based zinc blende diluted magnetic semiconductors Al_1−xCr_xX (X=N, P, As, Sb) for 0≤x≤0.50.The behaviour of magnetic moment of Al_1−xCr_xX at each Cr site as well as the change in the band gap value due to spin down electrons has been studied by increasing the concentration of Cr atom and through changing X from N to Sb. Furthermore, the role of p-d hybridization is analyzed in the electronic band structure and exchange splitting of d-dominated bands. The interaction strength is stronger in Al_1−xCr_xN and becomes weaker in Al_1−xCr_xSb. The band gap due to the spin down electrons decreases with the increased concentration of Cr in Al_1−xCr_xX, and as one moves down along the isoelectronic series in the group V from N to Sb. Our calculations also verify the half-metallic ferromagnetic character in Cr doped AlX.