Investigation of kinetic and mechanism of triphenylphosphine addition to para‐naphthoquinone

This work reports the results of a kinetic and mechanistic investigations of the addition reaction of triphenylphosphine to para‐naphtoquinone in 1,2‐dichloromethane as solvent. The order of reaction with respect to the reactants was determined using initial rate method, and the rate constant was obtained on the basis of pseudo‐first‐order method. Variable time method using Uv–Vis spectrophotometry (at 400 nm) was utilized for monitoring this addition reaction, for which the following Arrhenius equation was obtained: The resulting activation parameters E_a, ΔH^#, ΔG^#, and ΔS^# at 300 K were 13.63, 14.42, 18.75 kcal mol^?1, and ?14.54 cal mol^?1K^?1, respectively. The results suggest that the reaction is first order with respect to both triphenylphosphine and para‐naphthoquinone. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 427–433, 2005     

A constrained error-based MPC for path following of quadrotor with stability analysis

This paper proposes a linear constrained model predictive control (MPC) to solve the path following problem for quadrotor unmanned aerial vehicles. In the controller, an augmented model is employed to completely eliminate the tracking error due to external disturbances imposed on the quadrotor. The proposed controller is capable of improving the trade-off between feasibility and performance of the system. By approximating the control input sequence in MPC with Laguerre function, the computational burden significantly decreases and the closed-loop performance improves. In addition, a prescribed stability procedure is applied to guarantee the asymptotic stability of the quadrotor error dynamics. Besides, the proposed method improves the numerical ill-conditioning problem in solving MPC, by modifying the position of the closed-loop system poles to lie inside the unit circle. In the simulation results, two scenarios for the quadrotor tracking problem are considered. The results demonstrate the capability and the effectiveness of the proposed control strategy in disturbance rejection, fast trajectory tracking and the quadrotor stability, while a desired performance is achieved.     

Simulation of a Single-Mode Tunnel-Junction-Based Long-Wavelength VCSEL

We investigate the physics of an internal device for a high-performance, vertical-cavity surface-emitting laser operating at 1.305 μm. Experimental results are analyzed using as the simulation software a photonic-integrated-circuit simulator in 3D (PICS3D), which is a state-of-the-art 3D simulator for surface- and edge-emitting laser diodes, semiconductor optical amplifiers, and other similar active waveguide devices. The 2D/3D semiconductor equations are coupled to the optical modes in both lateral and longitudinal directions. Optical properties such as the quantum well/wire/dot optical gain and spontaneous emission rates are computed self-consistently. Careful adjustments of material parameters led to an excellent agreement between simulation and measurements. Simulation results show that the maximum output power is limited by electron leakage from quantum wells.     

A one-pot stereoselective synthesis of novel polyfunctionalized imidazolidines

A facile, one-pot stereoselective synthesis of novel trans-4,5-dihydroxy-2-aryl-1,3-bis(heteroaryl)imidazolidines is achieved by a cyclocondensation reaction of 2 equiv of heteroarylamines with benzaldehyde derivatives, in the presence of guanidinium chloride as a polyfunctional organocatalyst, with aqueous glyoxal to afford the title products. This general protocol provides a wide range of new polyfunctionalized imidazolidines in good to high yields.     

Influence of NO2 attachment on the nuclear magnetic shielding tensors of N and B nuclei in C30B15N15 heterofullerene: a DFT study

Adsorption of nitrogen dioxide in three different configurations on the exterior surface of C₃₀B₁₅N₁₅ is studied using density functional theory calculations. To this end, we optimized the structures of raw C₃₀B₁₅N₁₅ and nine NO₂–C₃₀B₁₅N₁₅ complexes at the B3LYP/6-31G^* level of theory and then calculated chemical shielding (CS) tensors at the GIAO-B3LYP/6-311G^** level for the optimized structures. The calculated chemical shielding isotropy (CSI), chemical shielding anisotropy (CSA), and orientation of CS tensors (Euler angles) reveal that the adsorption configurations (nitro, trans-nitrite, and cis-nitrite) have different effects on the electronic structure of C₃₀B₁₅N₁₅. Natural atomic charges based on natural population analysis (NPA) were used to justify the changes in CSI values after gas sorption.     

Silica Gel Catalyzed Stereoselective Conversion of Dialkyl 2-(3-acetyl-4-hydroxy-1-naphthyl)-3-(triphenylphosphoranylidene) butanedioates to Dialkyl 2-(3-acetyl-4-hydroxy-1-naphthyl)-2-butenedioates in Solvent-Free Conditions

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, by 1-hydroxy-2-acetonaphthone leads to vinyltriphenylphosphonium salts, which undergo aromatic electrophilic substitution reaction with conjugate base to produce dialkyl 2-(3-acetyl-4-hydroxy-1-naphthyl)-3-(triphenylphosphoranylidene) butanedioates. Silica gel was found to catalyze conversion of dialkyl 2-(3-acetyl-4-hydroxy-1-naphthyl)-3-(triphenylphosphoranylidene) butanedioates to dialkyl 2-(3-acetyl-4-hydroxy-1-naphthyl)-2-butenedioates in solvent-free conditions at 90°;C in fairly good yields.     

Ultrasound‐assisted emulsification microextraction combined with injection‐port derivatization for the determination of some chlorophenoxyacetic acids in water samples

An efficient method based on ultrasound‐assisted emulsification microextraction followed by injection‐port derivatization GC analysis was developed to determine 2,4‐dichlorophenoxyacetic acid (2,4‐D) and 4‐chloro‐2‐methylphenoxyacetic acid (MCPA) in natural water samples. In this procedure, 12.5 μL of 1‐undecanol was injected slowly into a 12 mL home‐designed centrifuge glass vial containing an aqueous sample of the analytes located inside an ultrasonic water bath. The resulting emulsion was centrifuged, and 1 μL of the separated organic solvent together with 1 μL of the derivatization reagent were injected into a GC equipped with a flame ionization detector. Several factors that influence the derivatization and extraction were optimized. Under the optimal conditions, the LODs were 0.33 and 1.7 μg/L for MCPA and 2,4‐D, respectively. Preconcentration factors of 670 and 836 were obtained for MCPA and 2,4‐D, respectively. The precision of the proposed method was evaluated in terms of repeatability, which was <5.7% (n = 5). The applicability of the proposed method was evaluated by extraction and determination of chlorophenoxyacetic acids from some natural waters, which indicated that the matrices of natural waters have no significant effect on the extraction and derivatization efficiency of this method.     

Application of Solid-Phase Extraction Coupled with Dispersive Liquid–Liquid Microextraction for the Determination of Benzaldehyde in Injectable Formulation Solutions

Solid-phase extraction followed by dispersive liquid–liquid microextraction (SPE-DLLME) technique has been developed as a new analytical approach for extracting, cleaning up and preconcentrating benzaldehyde, a toxic oxidation product of the widely used preservative and co-solvent benzyl alcohol, in injectable formulation solutions. SPE of benzaldehyde from samples was carried out using C₁₈ sorbent. After the elution of benzaldehyde from the sorbent by using acetonitrile, DLLME technique was performed on the obtained solution. Benzaldehyde was preconcentrated by using DLLME technique. Thus, 1.5 mL acetonitrile extract (disperser solvent) and 55.0 µL 1,2-dichloroethane (extraction solvent) were added to 5 mL ultra pure water and a DLLME technique was applied. Several variables that govern the proposed technique were studied and optimized. Under optimum conditions, the method detection limit (LOD) of benzaldehyde calculated as three times the signal-to-noise ratio (S/N) was 0.08 µg L^?1. The relative standard deviation (RSD) for four replicates was 5.8 %. The calibration graph was linear within the concentration range of 0.5–500 µg L^?1 for benzaldehyde. The proposed method has been successfully applied to the analysis of the benzaldehyde in injectable formulation solutions (diclofenac, vitamin B-complex and voltaren) and the relative recoveries were between 88 and 92 % and show that matrix has a negligible effect on the performance of the proposed method.