Hydrogen bond catalyzed chemoselective N-tert-butoxycarbonylation of amines

A novel, chemoselective mono-N-Boc protection of various structurally diverse amines with di-tert-butoxypyrocarbonate (Boc)₂O is described that relies on selective carbonyl activation by hydrogen bond formation. This mild, acid- and metal-free process requires only catalytic amounts of thiourea as hydrogen bond donor.     

All-optical half adder based on photonic crystals for BPSK signals

Optical and Quantum Electronics - This paper aims at first deriving the general forms of the electromagnetic vector and scalar potentials inside a cylindrical wave-guide by placing a 3D-charged...     

Encapsulation of Pd(II) into superparamagnetic nanoparticles grafted with EDTA and their catalytic activity towards reduction of nitroarenes and Suzuki–Miyaura coupling

A robust, safe and magnetically recoverable palladium catalyst was synthesized by anchoring Pd(II) onto ethylenediaminetetraacetic acid‐coated Fe₃O₄ (Fe₃O₄@EDTA) magnetic nanoparticles. The Fe₃O₄ magnetic nanoparticle‐supported Pd(II)–EDTA complex catalyst thus obtained was characterized using scanning and transmission electron microscopies, thermogravimetric analysis, vibrating sample magnetometry, X‐ray diffraction, and inductively coupled plasma atomic emission and Fourier transform infrared spectroscopies. Fe₃O₄@EDTA–Pd(II) was screened for the Suzuki reaction and reduction of nitro compounds in water. The Pd content of the catalyst was measured to be 0.28 mmol Pd g^?1. In addition, the Fe₃O₄@EDTA–Pd catalyst can be easily separated and recovered with an external permanent magnet. The anchored solid catalyst can be recycled efficiently and reused five times with only a very slight loss of catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.     

NiFe2O4@SiO2@Cu3(BTC)2 nanocomposite as a magnetic metal–organic framework

A new magnetic metal–organic framework (MOF), namely, NiFe₂O₄@SiO₂@Cu₃(BTC)₂, was synthesized via an in situ method using Fe(NO₃)₃, Ni(NO₃)₂, CuN₂O₆, TEOS, (3-aminopropyl)triethoxysilane, and benzene-1,3,5-tricarboxylic acid. Three different samples were fabricated according to a formula; xNiFe₂O₄@(100 − x)SiO₂@Cu₃(BTC)₂, where x = 10, 30, and 50. The integration of the intrinsic characteristic of Cu₃(BTC)₂ as an MOF with strong magnetic properties of NiFe₂O₄ could lead to an exquisite material with specific behaviors. X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), diffuse reflectance spectroscopy (DRS), photoluminescence (PL), vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), and simulated thermal analyzer (STA) were utilized to characterize the mentioned samples. Results approved that the synthesized compounds were composed of SiO₂ and Cu-MOF and NiFe₂O₄ crystalline phases with rod-like morphology. The similarity between the morphology of the synthesized samples and Cu-MOF approved that an appropriate fabrication method has been selected. This fact led to observe mesoporous composites with 38–90 m² g⁻¹ specific surface area. PL spectroscopy confirmed the near bandgap emission, ligand-to-metal charge transfer, and metal-to-ligand charge transfer. Although all the samples had magnetic hysteresis, the highest magnetization was seen in the 50NiFe₂O₄@SiO₂@Cu₃(BTC)₂ sample. This composite compound with a magnetization value of 2 emu g⁻¹ at 8000 Oe and a specific surface area of 90 m² g⁻¹ could be classified as a magnetic MOF (MMOF). STA results suggested that 400°C is the highest operating temperature for this compound.     

Magnetic Nanoparticles Supported Ionic Liquids Improve Firefly Luciferase Properties

Ionic liquids as neoteric solvents, microwave irradiation, and alternative energy source are becoming as a solvent for many enzymatic reactions. We recently showed that the incubation of firefly luciferase from Photinus pyralis with various ionic liquids increased the activity and stability of luciferase. Magnetic nanoparticles supported ionic liquids have been obtained by covalent bonding of ionic liquids-silane on magnetic silica nanoparticles. In the present study, the effects of [γ-Fe₂O₃@SiO₂][BMImCl] and [γ-Fe₂O₃@SiO₂][BMImI] were investigated on the structural properties and function of luciferase using circular dichroism, fluorescence spectroscopy, and bioluminescence assay. Enzyme activity and structural stability increased in the presence of magnetic nanoparticles supported ionic liquids. Furthermore, the effect of ingredients which were used was not considerable on K _m value of luciferase for adenosine-5′-triphosphate and also K _m value for luciferin.     

Field-emission enhancement of molybdenum oxide nanowires with nanoprotrusions

The field-emission properties of molybdenum oxide nanowires grown on a silicon substrate and its emission performance in various vacuum gaps are reported in this article. A new kind of molybdenum oxides named nanowires with nanoscale protrusions on their surfaces were grown by thermal vapor deposition with a length of ~1 μm and an average diameter of ~50 nm. The morphology, structure, composition and chemical states of the prepared nanostructures were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). According to XRD, XPS, and TEM analyses, the synthesized samples were composed of MoO₂ nanowires formed over a thin layer of crystalline Mo₄O₁₁. TEM observation revealed that these nanowires have some nanoscale protrusion on their surface. These nanoprotrusions resulted in enhancement of field-emission properties of nanowires comprising nanoprotrusions. The turn-on emission field and the enhancement factor of this type of nanostructures were measured 0.2 V/μm and 42991 at the vacuum gap of 300 μm, respectively. These excellent emission properties are attributed to the special structure of the nanowires that have potential for utilizing in vacuum nanoelectronic and microelectronic applications.     

All optical switching in azo-polymer planar waveguide

In this paper all optical switching in planar methyl red doped poly (methyl methacrylate) (MR/PMMA) waveguide and the effects of different parameters on this process are presented. Switching was achieved by a 488 nm Ar ion laser (pump beam) on a 633 nm He-Ne laser (probe beam) when passed through the waveguide. The effect of temperature and pump intensity, polarization and chopping frequency on switching is investigated. The switching process is attributed to trans-cis-trans photoisomerization of azo dyes in the polymer host. By studying the absorption spectrum of the sample, it is shown that both pump and probe laser beams are effective on the switching process.