Synthesis,Characterization, and Antibacterial Activity of Novel (1H‐Benzo[d]imidazole‐2‐yl)‐6‐(diethylamino)‐3H‐one‐xanthene,Phenoxazine, and Oxazine

A series of novel (1H‐benzo[d]imidazole‐2‐yl)‐6‐(diethylamino)‐3H‐one‐xanthene, phenoxazine, and oxazine derivatives have been synthesized from 2‐(2′,4′‐dihydroxyphenyl) benzimidazole intermediate. Synthesized compounds 8a , 8b , 8c , 8d are fluorescent in solution, photophysical properties of compounds were studied and results revealed that compounds absorb and emit in UV–visible region with good fluorescence quantum yield. Synthesized compounds are thermally stable up to 300°C. The antibacterial activities of the synthesized compounds were studied by the well‐diffusion method. Escherichia coli (ATTC‐25922), Staphylococcus aureus (ATCC‐25923), Micrococcus (ATCC‐4698), and Bacillus subtilis (ATCC‐55422) were used to investigate the antibacterial activities.     

Nanoscale characterization of different stiction mechanisms in electrostatically driven MEMS devices based on adhesion and friction measurements

In this work, for the first time different stiction mechanisms in electrostatic micro-electromechanical systems (MEMS) switches were studied. In these devices stiction can be caused by two main mechanisms: dielectric charging and meniscus formation resulting from the adsorbed water film between the switch bridge and the dielectric layer. The effect of each mechanism and their interaction were investigated by measuring the adhesive and friction forces under different electrical stress conditions and relative humidity levels. An atomic force microscope (AFM) was used to perform force-distance and friction measurements on the nanoscale. A novel technique was proposed to measure the induced surface potential over the dielectric surface and was used to explain the obtained adhesive and friction results. The evolution of adhesive force with time was monitored in order to study the charging/discharging processes in the dielectric film. The assessment methodology is employed for application in RF-MEMS switches and could be extended to other electrostatic MEMS devices. The study provides an in-depth understanding of different stiction mechanisms, and explanation for the literature reported device level measurements for electrostatic capacitive MEMS switches.     

Role of surface roughness and lubricant film thickness in nanolubrication of sliding components in adaptive optics

Silver-coated copper particles with various silver loading were prepared by a direct liquid-to-particle conversion process in spray pyrolysis reactor system. The prepared particles were completely densified at 900°C within a residence time of 2.1 s and had core-shell structure, of which formation mechanism was proposed. The mean diameter of particles was 0.45 μm. Copper particles of 20 wt.% of silver loading were stable under air and 95% of copper remained as metallic copper even after 1 month of exposure to air. This enhanced air-stability contributed to the enhanced electrical property of conductive film obtained from the coated particles. The conductive film obtained from 15 wt.% of silver-coated copper particles had a sheet resistance of 1.2 mΩ square(-1). This low resistance resulted from the lack of oxide layer and low sintering temperature of silver layer.     

ac anddc electroluminescence in CaS:Cu,Sm phosphors

Theac anddc electroluminescence in CaS:Cu, Sm have been investigated. The luminescence spectra show three peaks in the visible region. The brightness-voltage dependence satisfies the relationB=B ₀ exp (−b/V ^1/2) with two modes of variation. The nature of this dependence indc andac at different frequencies is discussed. The electroluminescence brightness also depends on the temperature of the phosphors and shows a peak around 80.0;C. The electroluminescence efficiency increases with applied voltage up to 2200 V and this dependence on V is explained on the basis of a transport process of the Schottky emission type.     

Humidity effect on the interaction between carbon nanotubes and graphite

An atomic force microscope is used to study the effect of humidity on the interaction between carbon nanotubes anchored to atomic force microscopy tips and various samples. Commercial silicon tips were also used for comparison. Adhesion force and dissipative energy were measured between these tips and highly oriented pyrolytic graphite (HOPG) and PMMA in contact mode. The data provides a detailed understanding of carbon nanotube interactions as a function of humidity.     

Resolution and isolation of enantiomers of (±)‐isoxsuprine using thin silica gel layers impregnated with l‐glutamic acid,comparison of separation of its diastereomers prepared with chiral derivatizing reagents having l‐amino acids as chiral auxiliaries

Thin silica gel layers impregnated with optically pure l ‐glutamic acid were used for direct resolution of enantiomers of (±)‐isoxsuprine in their native form. Three chiral derivatizing reagents, based on DFDNB moiety, were synthesized having l ‐alanine, l ‐valine and S‐benzyl‐l ‐cysteine as chiral auxiliaries. These were used to prepare diastereomers under microwave irradiation and conventional heating. The diastereomers were separated by reversed‐phase high‐performance liquid chromatography on a C₁₈ column with detection at 340 nm using gradient elution with mobile phase containing aqueous trifluoroacetic acid and acetonitrile in different compositions and by thin‐layer chromatography (TLC) on reversed phase (RP) C₁₈ plates. Diastereomers prepared with enantiomerically pure (+)‐isoxsuprine were used as standards for the determination of the elution order of diastereomers of (±)‐isoxsuprine. The elution order in the experimental study of RP‐TLC and RP‐HPLC supported the developed optimized structures of diastereomers based on density functional theory. The limit of detection was 0.1–0.09 µg/mL in TLC while it was in the range of 22–23 pg/mL in HPLC and 11–13 ng/mL in RP‐TLC for each enantiomer. The conditions of derivatization and chromatographic separation were optimized. The method was validated for accuracy, precision, limit of detection and limit of quantification. Copyright © 2014 John Wiley & Sons, Ltd.