Revealing the Nano‐Level Molecular Packing in Chitosan–NiO Nanocomposite by Using Positron Annihilation Spectroscopy and Small‐Angle X‐ray Scattering

Chitosan–NiO nanocomposite (CNC) is shown to be a potential dielectric material with promising properties. CNCs containing NiO nanoparticles (0.2, 0.6, 1, 2, 5 wt %) are prepared through chemical methods. The inclusion of NiO nanoparticles in the chitosan matrix is confirmed by scanning electron microscopy (SEM) and X‐ray diffraction. The morphology of the NiO nanoparticles and the nanocomposites is investigated by transmission electron microscopy and SEM, respectively. Positron annihilation lifetime spectroscopy (PALS) and the coincidence Doppler broadening (CDB) technique are used to quantify the free volume and molecular packing in the nanocomposites. The triplet‐state positronium lifetime and the corresponding intensity show the changes in nanohole size, density, and size distribution as a function of NiO loading. Small‐angle X‐ray scattering indicates that the NiO aggregates are identical in all the CNCs. The momentum density distribution obtained from CDB measurements excludes the possibility of a contribution of vacant spaces (pores) available in NiO aggregates to the free volume of nanocomposites upon determination by using PALS. The results show systematic variation in free‐volume properties and nano‐level molecular packing as a function of NiO loading, which is presumed to play a vital role in determining the various properties of the nanocomposites.     

Computational Science and Engineering Online (CSE-Online): a cyber-infrastructure for scientific computing

With the expansion of the Internet and World Wide Web (or the Web), research environments have changed dramatically. As a result, the need to be able to efficiently and securely access information and resources from remote computer systems is becoming even more critical. This paper describes the development of an extendable integrated Web-accessible simulation environment for computational science and engineering called Computational Science and Engineering Online (CSE-Online; http://cse-online.net). CSE-Online is based on a unique client-server software architecture that can distribute the workload between the client and server computers in such a way as to minimize the communication between the client and server, thus making the environment less-sensitive to network instability. Furthermore, the new software architecture allows the user to access data and resources on one or more remote servers as well as on the computing grid while having the full capability of the Web-services collaborative environment. It can be accessed anytime and anywhere from a Web browser connected to the network by either a wired or wireless connection. It has different modes of operations to support different working environments and styles. CSE-Online is evolving into middleware that can provide a framework for accessing and managing remote data and resources including the computing grid for any domain, not necessarily just within computational science and engineering.     

Electrical conductivity of a metal powder struck by a spark

Equivalent resistance of a polydisperse powder layer struck by an electric spark is evaluated. Particles were computationally created and mixed using discrete element method; the mixing protocol homogenized particle size distribution within the sample. The conductivity was determined from the equivalent resistance network for the simulated powder bed. A plasma streamer attached to a particle on top of the sample. For each particle contact, an electrical breakdown was assumed; each individual contact resistance was calculated considering its geometry and plasma resistivity. Results of calculations compare well with the available experimental data.     

Synthesis of a tetrasaccharide related to the triterpenoid saponin isolated from Schima noronhae

A concise synthesis of a tetrasaccharide related to the cell-growth inhibitory triterpenoid saponin isolated from Schima noronhae is reported. A late stage 2,2,6,6-tetramethylpiperidinyloxy (TEMPO)-mediated oxidation of a primary hydroxyl group to carboxylic acid has been achieved under phase-transfer conditions. Stereoselective glycosylations were carried out using thioglycoside or glycosyl trichloroacetimidate activation using sulfuric acid immobilized on silica (H₂SO₄–silica) in conjunction with N-iodosuccinimide and alone, respectively.     

Ruthenium(II) complexes incorporating tridentate Schiff base ligands: synthesis,spectroscopic, redox,catalytic and biological properties

A series of new diamagnetic ruthenium(II) complexes of the type [RuCl(CO)(B)(L)] (where B = PPh₃, AsPh₃ or Py; L = monobasic tridentate Schiff base ligands derived from o‐aminophenol or o‐aminothiophenol with ethylacetoacetate or ethylbenzoylacetate) have been synthesized and these complexes were characterized by physico‐chemical and spectroscopic methods. Cyclic voltammograms of all the complexes show quasi‐reversible oxidation in the range 0.24–1.05 V and the quasi‐reversible reduction in the range ? 0.14 to ? 0.51 V. The observed redox potentials show little variation with respect to the replacement of triphenyl phosphine/arsine by pyridine. The complexes were tested as catalysts in the oxidation of primary and secondary alcohols using molecular oxygen at room temperature and also in C? C coupling reactions. Further, the antibacterial properties of the free ligands and their metal complexes were evaluated against certain bacteria such as Escherichia coli and Staphylococcus aureus. Copyright © 2010 John Wiley & Sons, Ltd.     

Purification of a Lectin from M. rubra Leaves Using Immobilized Metal Ion Affinity Chromatography and Its Characterization

Lectins represent a heterogeneous group of proteins/glycoproteins with unique carbohydrate specificity, with wide range of biomedical applications. The multi-step purification protocols generally used for purification of lectin result in a significant reduction in the final yield and activity. In the present study, Morus rubra lectin (MRL) was purified to homogeneity from the leaves using a single-step immobilized metal ion affinity chromatography (IMAC) procedure. The approximate molecular weight of purified MRL resolved as a single band on SDS-PAGE was 52?kDa. Final percentage yield of purified lectin by IMAC was calculated as 74.7?%. Purified MRL was specific to three sugars, galactose, d-galactosamine and N-acetyl-d-galactosamine, and rendered haemagglutination (HA) activity towards different human blood group RBCs. MRL showed stability over a wide range of temperature (up to 80?°C) and pH (4?C11). Chelation of the lectin with EDTA did not alter HA which indicates that metal ion is not required for activity. In the presence of Fe²⁺, Ca²⁺, Zn²⁺, Ni²⁺, Mn²⁺, Na⁺ and K⁺, HA activity was reduced to 50?%, whereas the presence of trivalent metal ions (Fe3⁺ and Al³⁺) and Cu²⁺ did not affect the activity. In the presence of Mg²⁺ and Hg²⁺, only 25?% of HA activity remained.     

Characterization and optimization of Ce0.6Zr0.4−x Mn x O2 (x ≤ 0.4)

In situ synthesis method is used to synthesize g-C₃N₄-P25 composite photocatalysts with different mass rations. The experiment result shows that P25 particles with diameter at range of 20–30 nm were embedded homogenously in the sheets of g-C₃N₄. Coupling g-C₃N₄ with P25 can not only improve the visible light absorption, but also improve the visible light photocatalytic activity of P25. The g-C₃N₄-P25 nanocomposite has the higher photocatalytic activity than g-C₃N₄ under visible light. The optimal g-C₃N₄ content with the highest photocatalytic activity is determined to be 84 %, which is almost 3.3 times higher than that of individual g-C₃N₄ under the visible light. The enhanced visible light photocatalytic activity could be ascribed to the formation of g-C₃N₄ and TiO₂ heteojunction, which results in an efficient separation and transfer of photo-induced charge carriers. The electron spin resonance results show that the ^·O₂ ^? radicals are main active species for g-C₃N₄ and the g-C₃N₄-P25 nanocomposites.     

Nanostructured lead-free ferroelectric Na0.5Bi0.5TiO3-BaTiO3 whiskers: synthesis mechanism and structure

Nanostructured lead-free ferroelectric Na(0.5)Bi(0.5)TiO(3)-BaTiO(3) (NBTBT) whiskers with a high aspect ratio were synthesized topochemically using Na(2)Ti(6)O(13) (NTO) as a host structure for the first time. High energy X-ray diffraction coupled with an atomic pair distribution function (PDF) and Raman scattering analyses were used to confirm the average structure of the lead-free NBTBT whiskers, which was found to be rhombohedral, i.e. a ferroelectric enabling type. High resolution transmission electron microscopic (HRTEM) analysis revealed local monoclinic-type structural distortions, indicating a modulated structure at the nanoscale in the morphotropic phase boundary (MPB) composition of the lead-free NBTBT whiskers. The structural rearrangement during the synthesis of the lead-free NBTBT whiskers was found to occur via translation of the edge shared octahedra of NTO into a corner sharing coordination. High temperature morphological changes that depict the disintegration of the isolated whiskers into their individual grains due to the higher grain boundary energy have been found to occur in close analogy with Rayleigh-type instability.     

Copper oxide-modified glassy carbon electrode prepared through copper hexacyanoferrate–G5-PAMAM dendrimer templates as electrocatalyst for carbohydrate and alcohol oxidation

We describe the modification of a glassy carbon electrode by electro-deposition of copper hexacyanoferrate (CuHCF) in the presence of an amine-terminated dendrimer (PAMAM) as a template. The electrode containing the CuHCF template was cycled in alkaline solution to generate a layer of cupric oxide (CuO). The mechanism of the formation of CuO and its electrocatalytic activity were investigated by cyclic voltammetry. Scanning electron microscopy reveals that the CuO prepared by this method has a meso-porous grid-like appearance. The formation of CuO was identified by XPS analysis of the modified electrode. The ability of the CuHCF film towards the electrocatalytic oxidation of carbohydrates and alcohols was detected using cyclic voltammetry. The over-potential required for carbohydrate and alcohol oxidation is lowered by ~400 mV compared to other chemically modified electrodes reported in the literature. Simple methodology has been adopted in this work for the preparation of the catalytically active electrode, and this work also explains the structure directing effect of dendrimer and its influence on the electrocatalytic oxidation of analytes.     

Ene-like addition of an oxoammonium cation to alkenes: highly selective route to allylic alkoxyamines

The oxoammonium cation of 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate (1) adds rapidly at room temperature in an ene-like fashion to trisubstituted alkenes to afford allylic alkoxyamines in high yield. [reaction: see text]