Variation of the electronic properties of zigzag boron nitride nanotubes by Al-doping: a DFT study

Boron nitride nanotubes (BNNTs) are semiconductors with a wide band gap. In comparison with carbon nanotubes (CNTs), BNNTs have higher chemical stability, excellent mechanical properties and higher thermal conductivity. In this paper, we study the effect of diameters and substituting B and N atoms of various zigzag BNNTs with Al, on structural and electronic properties of BNNTs in solid state using the density functional theory method. The results of calculations of density of states and band structure (band) showed that the band gap between the valence and conduction level increases as a result of the enhancement of tube diameter of BNNTs. Finally, the results showed that the electronic properties of the pristine BNNTs can be improved by doping Al atom in the zigzag configuration of tubes.     

Benzoylferrocene-modified carbon nanotubes paste electrode as a voltammetric sensor for determination of hydrochlorothiazide in pharmaceutical and biological samples

The electrooxidation of hydrochlorothiazide (HCT) at the surface of a benzoylferrocene modified multi-walled carbon nanotube paste electrode was studied using electrochemical approaches. Under the optimized conditions (pH 7.0), the square wave voltammetric peak current of HCT increased linearly with HCT concentration in the ranges of 6.0?×?10^?7 to 3.0?×?10^?4 M. The detection limit was 9.0?×?10^?8 M HCT. The diffusion coefficient (D?=?1.75?×?10^?5 cm²/s) and electron transfer coefficient (α?=?0.45) for HCT oxidation were also determined. The proposed sensor was successfully applied for the determination of HCT in human urine and tablet samples.     

Electrocatalytic oxidation and highly selective voltammetric determination of L-cysteine at the surface of a 1-[4-(ferrocenyl ethynyl)phenyl]-1-ethanone modified carbon paste electrode.

A carbon paste electrode (CPE) chemically modified with 1-[4-(ferrocenyl ethynyl)phenyl]-1-ethanone (4-FEPEMCPE) was employed to study the electrocatalytic oxidation of L-cysteine using cyclic voltammetry, differential pulse voltammetry and double potential step chronoamperometry as diagnostic techniques. The diffusion coefficient (D = 7.863 x 10(-6) cm2 s(-1)) of L-cysteine was also estimated using chronoamperometry. The electron-transfer coefficient, alpha (= 0.40), for L-cysteine at the surface of 4-FEPEMCPE was determined using cyclic voltammetry technique. It was found that under an optimum pH (= 7.00), the oxidation of L-cysteine at the surface of such an electrode occurred at a potential of about 350 mV less positive than that of an unmodified CPE. The catalytic oxidation peak currents represented a linear dependence on the L-cysteine concentration. Linear analytical curves were obtained in the ranges of 9.0 x 10(-5) - 4.9 x 10(-3) M and 2.0 x 10(-5) - 2.8 x 10(-3) M of L-cysteine with correlation coefficients of 0.9981 and 0.9982 in cyclic voltammetry and differential pulse voltammetry, respectively. The detection limits (2 sigma) were determined to be 9.9 x 10(-6) M and 5 x 10(-6) M with cyclic voltammetry and differential pulse voltammetry, respectively. The influences of twenty other amino acids, such as glutamine, L-glutamic acid, L-glysine, L-histidine, L-isoleucine, L-leucine, L-arginine hydrochloride, L-aspargine, L-aspartic acid, S-carboxy methyl-L-cysteine, L-methionine, L-phenyl alanine, L-proline, L-serine, L-threonine, L-cystine, cysteamine and gluthathione, on the current response of the sensor were examined. The obtained results did not show any influence on the analytical signal of L-cysteine by these amino acids (except for cysteamine). The method was also used for the selective determination of L-cysteine in patient-blood plasma and some pharmaceutical preparations by using standard addition method.     

Adsorption behaviour of some metal complexes with ferron on Zeo-Karb-226: An atomic absorption spectrophotometric (AAS) study

Summary The adsorption behaviour of ten metal complexes Cr(III), Cr(VI), Mn(II), Fe(II), Fe(III), Co(II), Ni(II), Cu(II), Cd(II) and Pb(II) with ferron on Zeo-Karb-226 in the H⁺ form was investigated at eight different pH-values in order to develop a preconcentration technique for trace amounts of these elements in aqueous solution. The concentrations of the remaining unadsorbed metal ions were determined by atomic absorption spectrophotometry. Under the present experimental conditions, Cr(III) and Pb(II) can be quantitatively determined within the pH range 4–8, while for Cd(II), the optimum pH-range is 7–11. But at pH 11, more than 95% of Cu(II) and Co(II) can be extracted from aqueous solution. The suitability of the technique has been evaluated by analyzing cadmium in simulated water samples. The results indicate that as low as 5 g 1^–1 of CD can be recovered with more than 96% efficiency from 11 of simulated water solution.

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Adsorptionsverhalten einiger Metallkomplexe mit Ferron an Zeokarb-226: eine AAS-Untersuchung

Zusammenfassung Das Adsorptionsverhalten der Komplexe von Cr(III), Cr(VI), Mn(II), Fe(II), Fe(III), Co(II), Ni(II), Cu(II), Cd(II) und Pb(II) mit Ferron an Zeokarb-226 in der H⁺-Form wurde bei acht verschiedenen pH-Werten untersucht, um eine Anreicherungsmethode für Spuren dieser Elemente zu entwickeln. Die Konzentrationen der verbliebenen nicht adsorbierten Metallionen wurden mit Hilfe der AAS bestimmt. Cr(III) und Pb(II) können im pH-Bereich 4–8 quantitativ erfaßt werden, während der optimale Bereich für Cd(II) bei pH 7–11 liegt. Bei pH 11 werden jedoch mehr als 95% Cu(II) und Co(II) aus der wäßrigen Lösung extrahiert. Der Nutzen des Verfahrens wurde durch Bestimmung von Cd(II) in simulierten Wasserproben erwiesen. Noch 5 g/l Cd können zu mehr als 96% aus 11 Wasserprobe wiedergefunden werden.

     

Rapid and Efficient Synthesis of Imidazolines and Bisimidazolines Under Microwave and Ultrasonic Irradiation

Small assemblies of 2-imidazolines and bisimidazolines from appropriate nitriles and ethylenediamine with catalytic amounts of P₂S₅ employing a microwave assisted protocol were prepared. Sonication of this system also led to successful synthesis of 2-imidazolines and bisimidazolines. Another advantage of these systems is the ability to carry out large scale reactions.     

Adjustability as a requirement of ideal clocks

A coordinate frame is considered as an arrangement of clocks that meet certain criteria of synchronization. Einstein's ideal clock is compared with the behavior required for clocks to maintain synchrony in the group of coordinate frames that leaves Maxwell's equations invariant. The required clock rates differ from the rate of Einstein's clock. An ideal adjustable clock is defined as an Einstein clock augmented by variable “gearing” that can offset its rate. Ongoing adjustment of these clocks enables them to meet all synchronization criteria in the group of coordinate frames. The need for adjustment is due to the well known invariance of Maxwell's equations under a group of coordinate transformations larger than the Lorentz group, and has nothing to do with imperfections in clocks. It is shown that the adjustments needed by ideal adjustable clocks to maintain synchrony can be measurably separated from additional adjustments that may be needed to compensate for random imperfections. The necessity for adjustment brings with it the necessity for ongoing measurement of the light signals whose exchange defines synchronization. Implications are discussed, both for the interpretation of Maxwell's equations and for the role of measuring instruments.     

Hydrolysis of acetylcholinesterase inhibitors--organophosphorus acid anhydrolase enzyme immobilization on photoluminescent porous silicon platforms

We report on the immobilization of an OPAA enzyme on luminescent porous silicon devices, and on the utilization of this new platform to hydrolyze p-nitrophenyl-soman.     

A Recursive Construction for New Symmetric Designs

We introduce a recursive construction of regular Handamard matrices with row sum 2h for h=±3ⁿ. Whenever q=(2h – 1)² is a prime power, we construct, for every positive integer m, a symmetric designs with parameters (4h²(q^m+1 – 1)/(q – 1), (2h² – h)q^m, (h² – h)q^m).     

New alkaloids from Phoebe grandis (Nees) Merr

The alkaloidal extract of the leaves of Phoebe grandis (nees) merr. have provided two new minor alkaloids; phoebegrandine D (1), a proaporphine-tryptamine dimer, and phoebegrandine E (2), an indoloquinolizidine. This is the first report on the occurrence of an indoloquinolizidine in the Phoebe species. The crude extract also exhibited antiplasmodial activity (IC50<8 microg mL-1). The structures of the novel compounds were elucidated by spectroscopic methods, notably 2D NMR and HRMS.