Synthesis and characterization of novel optically active and photoactive aromatic polyesters containing 1,8-naphthalimidyl pendant group by step-growth polymerization

Novel optically active polyesters (PE)s by step-growth polymerization of a chiral diacid containing naphthalimidyl and flexible chiral groups with different diols via direct polyesterification reaction with tosyl chloride/pyridine/dimethylformamide system as condensing agent were prepared. The resulting PEs were characterized using FT-IR, ¹H NMR, UV–vis spectroscopy, fluorimetry, and elemental analysis. Fluorescence properties of the PE3h as a representative one were examined in several polar aprotic solvents which reveal that this polymer has photoactive properties. Furthermore, thermal properties of these polymers were investigated using thermogravimetric and differential thermogravimetric analyses. The glass-transition temperatures of PE3b and PE3f were recorded between 264 and 220 °C by differential scanning calorimetry, and the 10% weight loss temperatures were ranging from 350 °C under nitrogen. The obtained macromolecules are readily soluble in many organic solvents.     

Electromechanical Properties of Acceptor‐Doped Lead‐Free Piezoelectric Ceramics

We have studied the processing and electromechanical properties of Mn and Fe‐doped 0.88[Bi_0.5Na_0.5TiO₃]–0.08[Bi_0.5K_0.5TiO₃]–0.04[Bi_0.5Li_0.5TiO₃] piezoelectric ceramics prepared by the mixed oxide route. Different amounts of Mn (0.01, 0.014, 0.015, 0.016, 0.017, 0.02, 0.022) or Fe (0.0125, 0.015, 0.0175) were doped to this lead‐free piezoelectric composition. Ceramics were sintered at different temperatures (1075°C–1150°C) to achieve the highest density and mechanical quality factor. Mn or Fe doping resulted in a considerable enhancement of Q_m in both planar and thickness resonance modes. In 1.5 mol% Mn‐doped ceramics sintered at 1100°C, a planar Q_m of about 970 and tanδ of 0.88% were obtained. In Fe‐doped ceramics, a planar Q_m as high as 900 was achieved. Acceptor dopants also resulted in decreasing the coupling coefficients, the piezoelectric charge coefficient, and the dielectric constant.     

Synthesis of novel optically active poly(ester imide)s by direct polycondensation reaction promoted by tosyl chloride in pyridine in the presence of N,N‐dimethyformamide

4,4′‐Hexafluoroisopropylidene‐2,2‐bis(phthalic acid anhydride) (1) was treated with L ‐methionine (2) in acetic acid and the resulting 4,4′‐(hexafluoroisopropylidene)‐N,N′‐bis(phthaloyl‐L ‐methionine) diacid (4) was obtained in high yields. The direct polycondensation reaction of this diacid with several aromatic diols, such as bisphenol A (5a), phenolphthalein (5b), 1,4‐dihydroxybenzene (5c), 4,4′‐dihydroxydiphenyl sulfide (5 d), 4,6‐dihydroxypyrimidine (5e), 4,4′‐dihydroxydiphenyl sulfone (5f), and 2,4′‐dihydroxyacetophenone (5g), was carried out in a system of tosyl chloride (TsCl), pyridine (Py), and N,N‐dimethylformamide (DMF). The reactions with TsCl were significantly promoted by controlling alcoholysis with diols, in the presence of catalytic amounts of DMF, to give a series of optically active poly(ester imide)s, (PEI)s, with good yield and moderate inherent viscosity ranging from 0.43 to 0.67 dL/g. The polycondensation reactions were significantly affected by the amounts of DMF, molar concentration of monomers, TsCl and Py, aging time, temperature, and reaction time. All of the aforementioned polymers were fully characterized by ¹H NMR, FTIR, elemental analysis, and specific rotation. Some structural characterization and physical properties of these optically active PEIs are reported. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 455–460, 2006     

Facile and green synthesis of ZnO nanostructures in a room-temperature ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Pure hexagonal phase of ZnO nanoparticles have been successfully synthesized via microwave assisted decomposition of zinc acetate precursor in a green solvent, the ionic liquid, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide in a very short time scale. The ZnO nanoparticles were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction.     

Preparation of nanospinels NiMnxFe2−xO4 using sol–gel method and their applications on removal of azo dye from aqueous solutions

In this paper, nanospinels NiMn_xFe_2−xO₄ (x = 0.05, 0.1, 0.3, 0.5, 0.7, and 1) were prepared by sol–gel method in the presence of nitrate–metal–ethylene glycol (EG) polymerized complex. The nanospinels were characterized using thermogravimetry analysis (TGA), X-ray powder diffraction (XRD), Fourier infrared spectroscopy (FTIR), and transmission electron microscope (TEM). The adsorption of an azo dye, reactive blue 5 (RB5), from water was determined using the prepared nanospinels. The effect of operational parameters such as the initial dye concentration, the concentration of nanospinels, temperature, and pH on the degradation of dye was investigated. The adsorption process follows second-order kinetics and Arrhenius behavior. Two common models, the Langmuir and Freundlich isotherms were used to investigate the interaction of dye and nanospinels. The isotherm evaluations revealed that the Freundlich model provides better fit to the experimental data than that of the Langmuir model. The photocatalytic degradation of RB5 at pH 1 under UV irradiation was examined. The results showed that the degradation of RB5 dye follows merely an adsorption process.     

"Off-On" Electrochemical Hairpin-DNA-Based Genosensor for Cancer Diagnostics

A simple and robust "off-on" signaling genosensor platform with improved selectivity for single-nucleotide polymorphism (SNP) detection based on the electronic DNA hairpin molecular beacons has been developed. The DNA beacons were immobilized onto gold electrodes in their folded states through the alkanethiol linker at the 3'-end, while the 5'-end was labeled with a methylene blue (MB) redox probe. A typical "on-off" change of the electrochemical signal was observed upon hybridization of the 27-33 nucleotide (nt) long hairpin DNA to the target DNA, in agreement with all the hitherto published data. Truncation of the DNA hairpin beacons down to 20 nts provided improved genosensor selectivity for SNP and allowed switching of the electrochemical genosensor response from the on-off to the off-on mode. Switching was consistent with the variation in the mechanism of the electron transfer reaction between the electrode and the MB redox label, for the folded beacon being characteristic of the electrochemistry of adsorbed species, while for the "open" duplex structure being formally controlled by the diffusion of the redox label within the adsorbate layer. The relative current intensities of both processes were governed by the length of the formed DNA duplex, potential scan rate, and apparent diffusion coefficient of the redox species. The off-on genosensor design used for detection of a cancer biomarker TP53 gene sequence favored discrimination between the healthy and SNP-containing DNA sequences, which was particularly pronounced at short hybridization times.     

Enhancing multivariate pattern analysis for magnetoencephalography through relevant sensor selection

While the popularity of multivariate pattern classification is growing rapidly in magnetoencephalography (MEG) data analysis, the analysis pipelines used by the neuroscience community are still missing some fundamental machine-learning techniques and principles that would increase their effectiveness. Here, we show that MEG decoding accuracy improves significantly with the addition of feature selection methods to the analysis pipeline. We compare one unsupervised and two supervised feature reduction methods in the current study. Our results show that supervised feature selection methods like statistical dependency and mutual information improve decoding performance and attain higher session-to-session reliability compared to unsupervised dimensionality reduction methods like principal component analysis. Furthermore, we demonstrate that the selected sensors in the data related to a visual task at each time point are consistent with the pattern reflecting the sweep of information in the ventral visual pathway.     

Enhancement of electrocatalytic O<Subscript>2</Subscript> reduction on carbon nanotube-supported Pt alloys nanoparticles in gas diffusion electrodes

The use of Pt binary and ternary alloys prepared by alloying of Pt with transition metals, as catalysts for fabricating of gas diffusion electrodes (GDEs) is reported. Electrocatalytic properties of oxygen reduction reaction (ORR) were evaluated by cyclic voltammetry, electrochemical impedance spectroscopy, polarization experiments and chronoamperometry. The morphology of the GDEs and elemental compositions of the Pt alloys were characterized by X-ray diffraction (XRD) analysis and inductively coupled plasma atomic emission spectroscopy (ICP-AES) system. The results indicate that the introduction of Pd and Cd as transition metals in Pt alloys provides fast ORR kinetics. The performance of GDEs with Pt–Pd alloy surfaces for ORR was also studied as a function of overall composition and surface atomic distribution of Pt alloys. The results also show that alloying of Pt with transition metals and various amounts of Pt and Pd in the binary catalysts has a large effect on the performance of GDEs for ORR.