Electroanalytical Studies and Simultaneous Determination of Amlodipine Besylate and Atorvastatine Calcium in Binary Mixtures Using First Derivative of the Ratio‐Voltammetric Methods

The electrochemical behavior of atorvastatin and amlodipine at a glassy carbon electrode has been studied using different voltammetric techniques. First derivative of the ratio voltammetric methods for determination of amlodipine and atorvastatin in tablets in the presence of the other compound has been described. This technique depends on the measuring of first derivative of the ratio voltammograms of each concentration as a function of the increased concentrations. DP and SW voltammetric methods depend on first derivative of the ratio‐voltammetry by measurements of the selected potentials for amlodipine and atorvastatin. The linear response was within the range of 4×10^?6–1×10^?4 M for amlodipine and 2×10^?6–1×10^?4 M for atorvastatin. The proposed methods have been extensively validated.     

The influence of the support functions on the quality of enhanced multivariance product representation

This paper presents recently developed Enhanced Multivariance Product Representation (EMPR) method for multivariate functions. EMPR disintegrates a multivariate function to components which are respectively constant, univariate, bivariate and so on in ascending multivariance. Although the EMPR method has the same philosophy with the High Dimensional Model Representation (HDMR) method, it has been proposed to get better quality than HDMR’s with the help of the support functions. For this purpose, we investigate the EMPR truncation qualities with respect to the selection of the support functions. The obtained results and a number of numerical implementations to show the efficiency of the method are also given in this paper.     

Phosphorus–nitrogen compounds: Part 19. Syntheses,structural and electrochemical investigations,biological activities,and DNA interactions of new spirocyclic monoferrocenylcyclotriphosphazenes

The reactions of hexachlorocyclotriphosphazatriene, N₃P₃Cl₆, with N-alkyl-N-ferrocenylmethylethylene diamines, FcCH₂NH(CH₂)₂NHR₁ [R₁ = Me (1) and Et (2)], and sodium [3-(N-ferrocenylmethylamino)-1-propanoxide] (3) produce spirocyclic monoferrocenyl tetrachlorophosphazenes (1a–3a). The tetrapyrrolidinophosphazenes (1b–3b) are prepared from the reactions of corresponding phosphazenes (1a–3a) with excess pyrrolidine. The reaction of 1a with excess morpholine affords geminal-morpholino phosphazene (1c), whilst the reactions of 2a and 3a give diethylaminotrimorpholino (2c) and fully substituted morpholino products (3c), respectively. The structural investigations of the compounds are examined by Fourier transform IR, MS, ¹H, ¹³C, ³¹P NMR, DEPT, HETCOR, and HMBC techniques. The crystal structures of 3b and 3c are determined using X-ray crystallography. Cyclic voltammetric and chronoamperometric data show that compounds 1a–3a, 1b–3b, and 1c–3c exhibit electrochemically reversible one-electron oxidation of Fc redox centers which are hardly affected by the substituents on the phosphazene ring. The compounds 1b, 2b, 3b, and 3c are screened for antibacterial activities against Gram-positive and Gram-negative bacteria and for antifungal activities against yeast strains. In addition, the antituberculosis activities (in vitro) of these compounds are evaluated against INH-susceptible reference strain M. tuberculosis H37Rv, and six multi-drug resistant clinical M. tuberculosis isolates. Compound 2b is found to be the most active against the susceptible the reference strain. In addition, 1b, 2b, and 3c are active against all the multidrug-resistant clinical isolates at the highest concentrations. Gel electrophoresis data indicate that the compounds promote the formation of strand breaks in plasmid DNA. Almost all the concentrations lost of supercoiled DNA suggests that the compound 3b is very efficient plasmid-modifier. The compounds inhibit BamHI cleavage of pUC18 DNA while restricting HindIII.     

Exact solutions of some systems of fractional differential‐difference equations

In this paper, the ‐expansion method is proposed to establish hyperbolic and trigonometric function solutions for fractional differential‐difference equations with the modified Riemann–Liouville derivative. The fractional complex transform is proposed to convert a fractional partial differential‐difference equation into its differential‐difference equation of integer order. We obtain the hyperbolic and periodic function solutions of the nonlinear time‐fractional Toda lattice equations and relativistic Toda lattice system. The proposed method is more effective and powerful for obtaining exact solutions for nonlinear fractional differential–difference equations and systems. Copyright © 2014 John Wiley & Sons, Ltd.     

Potassium–Tertiary Butoxide–Assisted Addition of Thioglicolic Acid to Chalcone Derivatives Under Solvent-Free Conditions

A series of chalcone derivatives containing thioglicolic acid (4a–j) was prepared by addition of thioglicolic acid to the chalcones (3a–j) in the presence of KOt-Bu under solvent-free conditions. The mechanistic pathway of the reaction can be explained by the Michael-type addition of thioglicolic acid to chalcone derivatives (3a–j).     

Sensitive voltammetric assay of etoposide using modified glassy carbon electrode with a dispersion of multi-walled carbon nanotube

A sensitive electroanalytical method for the determination of anticancer drug etoposide (ETP) using adsorptive stripping differential pulse voltammetry (AdSDPV) at a multi-walled carbon nanotube-modified glassy carbon electrode (MWCNT-modified GCE) is presented. The surface morphology of modified electrode was characterized by scanning electron microscopy. The effects of accumulation time and potential, pH, scan rate, and amount of MWCNT suspension were investigated. The calibration curve was linear in the concentration range of 2.0?×?10^?8–2.0?×?10^?6 M with the detection limit of 5.4?×?10^?9 M. The reproducibility of the peak current was found at 1.55 % (n?=?5) RSD value in pH 6.0 Britton–Robinson buffer for the MWCNT-modified GCE. The method was then successfully utilized for the determination of ETP in pharmaceutical dosage form, and a recovery of 99.55 % was obtained. The possible oxidation mechanism of ETP was also discussed. The proposed electroanalytical method using MWCNT-modified GCE is the most sensitive method for the determination of ETP with lowest limit of detection in the previously published electrochemical methods.     

A novel piecewise multivariate function approximation method via universal matrix representation

Multivariance in science and engineering causes problematic situations even for continous and discrete cases. One way to overcome this situation is to decrease the multivariance level of the problem by using a divide—and—conquer based method. In this sense, Enhanced Multivariance Product Representation (EMPR) plays a part in the considered scenario and acts successfully. This method brings up a finite expansion to represent a multivariate function in terms of less-variate functions with the assistance of univariate support functions. This work aims to propose a new EMPR based algorithm which has two new features that improves the determination process of each expansion component through Fluctuation Free Integration method, which is an efficient method in evaluating multiple integrals through a universal matrix representation, and increases the approximation quality through inserting a piecewise structure into the standard EMPR algorithm. This new method is called Fluctuation Free Integration based piecewise EMPR. Some numerical implementations are also given to examine the performance of this proposed method.     

Kinetic and mechanistic features of carbon dioxide reforming of methane over Co–Ce/ZrO2 catalysts

Carbon dioxide reforming of methane (CDRM) is an effective route to utilize CO₂ and CH₄, the most abundant, thermodynamically stable and hazardous greenhouse gases. To overcome the economical impediments to favor CDRM's industrial applicability, its mechanistic features need to be revealed both for developing efficient catalysts and optimizing operational conditions. In this context, this work aims to obtain power-law type CDRM kinetic expressions over 5%Co–2%Ce/ZrO₂ and 10%Co–2%Ce/ZrO₂ catalysts and compare and analyze mechanistic routes to elucidate the effect of the Co:Ce ratio on kinetics. The empirical power-law type rate expressions were estimated with the reaction orders of 1.63 and 1.12 for CH₄ and 0.29 and –0.12 for CO₂ for 5%Co–2%Ce/ZrO₂ and 10%Co–2%Ce/ZrO₂ catalysts, respectively. Limited CH₄ activation and, thus, carbon formation due to low Co loading lead to accumulation of surface oxygen on ZrO₂ as redox ability of Ce becomes suppressed. This causes higher CO₂ activation barrier. The presence of H₂ in the feed slows down mechanistic steps involving CH_x. The reactions including CH₄ activation, most probably reversible direct CH₄ dissociation, are found to be rate determining.     

Characterization and ethylene adsorption of natural and modified clinoptilolites

The ethylene adsorption of Turkey clinoptilolite-rich tuff from Gordes and Bigadic region of western of Anatolia and their exchanged forms (K⁺, Na⁺ and Ca²⁺) were investigated. The clinoptilolite samples were characterized using XRD, TG-DTA and nitrogen adsorption methods. Adsorption isotherms for ethylene on natural and modified forms of both adsorbents at 277 K and 293 K were obtained at pressures up to 38 kPa. Uptake of ethylene increased as Na-CLN < Ca-CLN < K-CLN < Natural CLN for Gordes zeolite at 277 K, 293 K and for Bigadic zeolite at 277 K. For Bigadic zeolites at 293 K, uptake of ethylene increased in the order Ca-CLN < Na-CLN < K-CLN < Natural CLN. It was found that ethylene adsorption capacity of Bigadic clinoptilolite samples was much greater than Gordes clinoptilolite samples except K⁺ modified forms at both temperatures. These results show that both natural clinoptilolites have a considerable potential for the removal of ethylene.     

Bivariate nonparametric estimation of the Pickands dependence function using Bernstein copula with kernel regression approach

In this study, a new nonparametric approach using Bernstein copula approximation is proposed to estimate Pickands dependence function. New data points obtained with Bernstein copula approximation serve to estimate the unknown Pickands dependence function. Kernel regression method is then used to derive an intrinsic estimator satisfying the convexity. Some extreme-value copula models are used to measure the performance of the estimator by a comprehensive simulation study. Also, a real-data example is illustrated. The proposed Pickands estimator provides a flexible way to have a better fit and has a better performance than the conventional estimators.