Electromembrane extraction combined with cyclodextrin-modified capillary electrophoresis for the quantification of trimipramine enantiomers

A sensitive, simple and reproducible method was developed for preconcentration and determination of trimipramine (TPM) enantiomers in biological samples using electromembrane extraction combined with cyclodextrin‐modified capillary electrophoresis (CE). During the extraction, TPM enantiomers migrated from a 5 mL sample solution through a thin layer of 2‐nitrophenyl octyl ether NPOE immobilized in the pores of a hollow fiber, and into a 20 μL acidic aqueous acceptor phase presented inside the lumen of the fiber. A Box–Behnken design and the response surface methodology (RSM) were used for the optimization of different variables on extraction efficiency. Optimized extraction conditions were: NPOE as supported liquid membrane, inter‐electrode distance of 5 mm, stirring rate of 1000 rpm, 51 V potential difference, 34 min as the extraction time, acceptor phase pH 1.0 and donor phase pH 4.5. Then, the extract was analyzed using optimized cyclodextrin (CD)‐modified CE method for the separation of TPM enantiomers. Best results were achieved using 100 mM phosphate running buffer (pH 2.0) containing 10 mM α‐CD as the chiral selector, applied voltage of 18 kV and 20°C. The range of quantitation for both enantiomers was 20–500 ng/mL. The method was very reproducible so that intra‐ and interday RSDs (n=6) were <6%. The limits of quantitation and detection for both enantiomers were 20 and 7 ng/mL, respectively. Finally, this method was successfully applied to determine the concentration of TPM enantiomers in plasma and urine samples without any pre‐treatment.     

Study of parametric oscillation of an electrostatically actuated microbeam using variational iteration method

This paper deals with the study of parametric oscillation of an electrostatically actuated microbeam using variational iteration method. The paper considers a micro-beam suspended between two conductive micro-plates, subjected to a same actuation voltage. The nonlinear governing differential equation of motion about static equilibrium position using calculus of variation theory and Taylor series expansion has been linearized and implementing a Galerkin based reduced order model a Mathieu type equation has been obtained. By improving variational iteration method combining with method of strained parameters transition curves, separating stable from unstable regions have been obtained. The results of variational iteration method, perturbation and direct numerical integration methods for some cases selected from different regions (stable and unstable regions) have been compared.     

Structural changes in self-assembled monolayers initiated by ultraviolet light

Self-assembled monolayers of 2-anthracenethiol and 2-naphthalenethiol on gold (111) were irradiated with low-power UV light. Scanning tunneling microscope images recorded in situ show unusual structural changes. In the case of 2-anthracenethiol, structures measuring 4-7 nm wide and 30-40 nm in length are formed. Images taken 10 min after irradiation ceased to show further surface reorganization. With 2-naphthalenethiol SAMs, smaller structures form upon irradiation, which subsequently revert to resemble the original structure after time.     

Optimal control of the obstacle problem: optimality conditions

^** E-mail: k.aithadi{at}ucam.ac.ma In this paper, we investigate optimal control problem governedby variational inequality of the obstacle type. Existence ofsolution for the problem is proved and we also show how to obtainoptimality conditions for a penalized problem issued from theoriginal one.     

Bisleucocurine A, a novel bisindole alkaloid from Leuconotis griffithii

A novel bisindole alkaloid, bisleucocurine A (1), consisting of two strychnan skeletons with an N-1-C-17′ and a C-12-C-2′ bridges, was isolated from the leaves of Leuconotis griffithii and the structure was elucidated on the basis of spectroscopic data. Bisleucocurine A (1) showed cytotoxicity against various human cancer cell lines.     

New voltammetric strategy for simultaneous determination of norepinephrine, acetaminophen, and folic acid using a 5-amino-3′,4′-dimethoxy-biphenyl-2-ol/carbon nanotube paste electrode

A carbon paste electrode modified with 5-amino-3??,4??-dimethoxy-biphenyl-2-ol and carbon nanotubes was used for the sensitive voltammetric determination of norepinephrine (NE). The electrochemical response characteristics of the modified electrode toward NE, acetaminophen (AC), and folic acid (FA) were investigated by cyclic and square wave voltammetry (SWV). The results show an efficient catalytic activity of the electrode for the electrooxidation of NE, which leads to lowering its overpotential more than 160?mV. The modified electrode exhibits an efficient electron-mediating behavior together with well-separated oxidation peaks for NE, AC, and FA. Under the optimum pH of 7.0 in 0.1?M phosphate buffer solution, the SWV anodic peak current showed a linear relation vs. NE concentration in the range of 15.0 to 1,000.0???M with a detection limit of 8.0???M.     

Effect of Si substitution on electronic structure and magnetic properties of Heusler compounds Co2TiAl1−xSix

The electronic structures of Co-based Heusler compounds CoTiAl_1−xSi_x (x=0, 0.25, 0.5, 0.75 and 1) are calculated by first-principles using the full potential linearized augmented plane wave (FP-LAPW) method within GGA and LSDA+U scheme. Particular emphasis was put on the role of the main group elements. In recent years, the GGA calculations of Co₂TiAl (x=0) and Co₂TiSi (x=1) indicated that they are half-metallic, but the electronic structure of this compound with x=0.25, 0.5 and 0.75 has not been reported yet, neither theoretically nor experimentally. The calculated results reveal that these are half-metallic and exhibit an energy gap in the minority spin state and also show 100% spin polarization. The substitution of Al by Si leads to an increase in the number of valence electrons, with increasing x. Our calculated results clearly show that with the Si doping, the lattice parameter linearly decreases; bulk modulus increases, and the total magnetic moment increases. The calculated energy gap in the minority spin state, using GGA scheme, was smaller than that obtained by using LSDA+U scheme. The outcomes of this research also show that the Co-3d DOS and therefore, the magnetic properties of compounds are dependent on electron concentration of the main group elements and it will affect the degree of p-d orbital occupation.     

Dynamical thermal effects in InGaAsP microtubes at telecom wavelengths

We report on the observation of a dynamical thermal effect in InGaAsP microtubes at telecom wavelengths. The microtubes are fabricated by releasing a strained semiconductor bilayer and are picked up by abruptly tapered optical fibers for subsequent coupling with adiabatically tapered optical fibers. As a result of absorption by InAs quantum dots embedded in the tube structure, these microtubes show dynamical thermal effects at wavelengths around 1525 nm and 1578 nm, while they are passive at longer wavelengths near 1634 nm. The photon absorption induced thermal effect is visualized by generating a pair of microbottles. The dynamical thermal effect can be avoided or exploited for passive or active applications by utilizing appropriate resonance wavelengths.