Combustion synthesis and luminescence properties of Dy-doped MgO nanocrystals

MgO nanocrystals doped with Dy³⁺ have been synthesized by a combustion method. The synthesized sample is characterized by X-ray diffraction, transmission electron micrograph, Fourier transform infrared, and photoluminescence spectroscopy. The as-prepared MgO nanocrystals appear to be single cubic crystalline phase and the diameter is in the range of 20–25 nm. The hypersensitive transition (⁴F_9/2→⁶H_13/2 of Dy³⁺) emission is prominent in the emission spectra resulting from the low-symmetry local site at which Dy³⁺ ions locate. In addition, the dependence of the luminescence intensity on Dy³⁺ concentration is also discussed.     

Optogenetic Control of Voltage‐Gated Calcium Channels

Voltage‐gated Ca²⁺ (Ca_V) channels mediate Ca²⁺ entry into excitable cells to regulate a myriad of cellular events following membrane depolarization. We report the engineering of RGK GTPases, a class of genetically encoded Ca_V channel modulators, to enable photo‐tunable modulation of Ca_V channel activity in excitable mammalian cells. This optogenetic tool (designated optoRGK) tailored for Ca_V channels could find broad applications in interrogating a wide range of Ca_V‐mediated physiological processes.     

Synergic nitrogen source route to inorganic fullerene-like boron nitride with vessel, hollow sphere, onion, and peanut nanostructures

In this paper we describe the large-scale synthesis of inorganic fullerene-like (IF-like) hexagonal boron nitride with vessel, hollow sphere, peanut, and onion structures by reacting BBr(3) with the synergic nitrogen sources NaNH(2) and NH(4)Cl at 400-450 degrees C for 6-12 h. The composition of products could be confirmed to be pure boron nitride with hexagonal structures by the XRD patterns and FT-IR, XPS, and EDXA spectra. The representative HRTEM images clearly reveal the layerlike features of the products. Here, the peanut-like structure of the IF-like BN is reported for the first time, and added to the list as one kind of new morphology of BN nanomaterials. The similarity in the structure between h-BN and graphite is responsible for the formation of IF-like BN with nanostructures of vessels, hollow spheres, peanuts, and onions.     

Correlations between gas permeation and free-volume hole properties of polyurethane membranes

A series of polyurethane films based on hard segments consisting of toluene diisocyanate and 1,4-butanediol and different soft segments consisting of hydroxyl terminated polybutadiene, hydroxyl terminated polybutadiene/styrene and hydroxyl terminated polybutadiene/acrylonitrile were synthesized by solution polymerization separately. Positron annihilation lifetimes were measured at room temperature for all samples studied. We found that both the free volume size and fractional free-volume decreased with the increase of hard segment content. On the other hand, direct relationship between the gas permeability and the free-volume has been established based on the free-volume parameters and gas diffusivity measured. Experimental results revealed that the free-volume plays an important role in determining the gas permeability.     

The effects of flow angle and shear rate within the spinneret on the separation performance of poly(ethersulfone) (PES) ultrafiltration hollow fiber membranes

The effects of dope flow rate and flow angle within a spinneret during spinning hollow fiber membranes on the morphology, water permeability and separation performance of poly(ethersulfone) ultrafiltration hollow fiber membranes were investigated. For this purpose, two spinnerets with different flow angles were designed and used. The dope solution, containing polyethersulphone (PES)/N-methyl-2-pyrrolidone (NMP)/diethylene glycol (DG) with a weight ratio of 23/41/36, which was very close to its cloud point (binodal line), was used in order to speed up the coagulation of nascent fibers so that the relaxation effect on molecular orientation was reduced. The wet-spinning process was purposely chosen to fabricate the hollow fibers without extra drawing. Therefore, the effects of gravity and elongation stress on fiber formation could be significantly reduced and the orientation induced by shear stress within the spinneret could be frozen into the wet-spun fibers. Experimental results suggest that higher dope flow rates (shear rates) in the spinneret produce UF hollow fiber membranes with smaller pore sizes and denser skin layers due to the enhanced molecular orientation. Hence, the pore size and the water permeability decrease, but the solute separation increases. Hollow fibers spun from a conical spinneret have smaller mean pore sizes with larger geometric standard deviations, thus exhibiting lower water flux and greater solute separation than hollow fibers spun from a traditional straight spinneret. In addition, SEM studies indicate macrovoids response differently for the 90° straight and 60° conical spinnerets when increasing the dope flow rate. Macrovoids can be significantly suppressed and almost disappear in the 90° spinneret at high dope flow rates. This phenomenon cannot be observed for the 60° conic spinneret.     

Preparation of the Solid Electrolytes Li4+xAlxSi1‐xO4‐yLi3PO4 and Their Ionic Conductivity

The ion conductors Li_4+xAl_xSi_1‐xO₄‐yLi₃PO₄ (x = 0 to 0.5, y = 0 to 0.6) were prepared by the Sol‐Gel method. The powder and sintered samples were characterized by DTA‐TG, XRD, SEM, and AC impedance techniques. The conductivity and sinterability increased when y increased from 0 to 0.4 in the Li_4+xAl_xSi_1‐xO₄‐yLi₃PO₄. The particle size of the powder samples is about 0.13 μm. The maximum conductivity at 20 °C is 3.128 × 10^?5s cm^?1 for Li_4.4Al_0.4Si_0.6O₄‐0.4 Li₃PO₄.     

Effects of adsorbates on supported platinum and iridium clusters: Characterization in reactive atmospheres and during alkene hydrogenation catalysis by X-ray absorption spectroscopy

MgO-, SiO2-, and gamma-Al2O3-supported platinum clusters and particles (with average diameters ranging from 11 to 45 A) and zeolite-supported Ir4 clusters (approximately 6 A in diameter) were characterized by extended X-ray absorption fine structure spectroscopy in the presence of H2, O2, ethene, propene, and ethane, as well as under conditions of alkene hydrogenation catalysis. The results indicate that under various atmospheres, the presence of adsorbates affects the smaller platinum clusters (11 A) on gamma-Al2O3 more substantially than the larger platinum particles (i.e., those greater than approximately 21 A in average diameter) on MgO or SiO2. When Pt/gamma-Al2O3 was exposed to H2, the platinum morphology did not change, although the Pt-Pt bond distance increased. In contrast, when the same sample was exposed to O2, complete oxidative fragmentation took place. This processes was reversed following subsequent treatment with H2. Exposure to alkenes changed both the morphology and electron density (as indicated by X-ray absorption near-edge spectra) of the gamma-Al2O3-supported platinum clusters. Under conditions of alkene hydrogenation catalysis at room temperature, the electronic properties and the structure of the platinum clusters were found to depend on the reactant composition and the nature of molecules involved in the reaction process. The effects of the reactant gases on the smaller iridium clusters (Ir4) were substantially less pronounced, apparently as a consequence of the extremely small number of atoms in each iridium cluster.     

Theoretical Investigation on Radical—Coupling Reactivity of Indolinonic Aminoxyls

Indolinonic aminoxyls can effectively scavenge various radicals by directly coupling with them or by initatin superoxide dismutase.To better understand the radical-coupling reactions,DFT method B3LYP/6-31G(d,p) was employed to calculate variations of free energy for the coupling reactions and other physico-chemical parameters.The radical-coupling activity difference between aminoxyls was elucidated to a large extent in terms of elctronic properties of substituents.     

An Efficient Method for the Enamination of 1,3‐Dicarbonyl Compounds with Ceric Ammonium Nitrate (CAN)

An efficient method for the enamination of 1,3‐dicarbonyl compounds by employing ceric ammonium nitrate (CAN) as the catalyst has been described. A variety of β‐amino‐α,β‐unsaturated ketones and esters have been synthesized in excellent yield within a short reaction time under solvent‐free conditions.     

Improved Electrochemical Synthesis of Nitro-substituted 1-Aryl-2-pyrrolidinecarbonitriles

Anodic cyanation is expected to provide a promising method for synthesis of nitriles by reason of its positional reactivity and simple operation1. Within our ongoing interest in cyano group incorporation into small heterocyclic ring systems2, 3, the elect…