Superprism effect in a metal-clad terahertz photonic crystal slab

We report an experimental demonstration of the superprism effect in a photonic crystal slab at terahertz frequencies. For a 10% frequency variation around 0.28 THz, the refraction angle at the output facet of a wedge-shaped photonic crystal varies by about 15 degrees. A comparison with the predictions of a band structure calculation demonstrates that a three-dimensional treatment, accurately modeling the finite slab thickness and the metallic boundary conditions, is required for even a qualitative agreement with the experimental observations.     

Nucleation of the β-hairpin structure in a linear hybrid peptide containing α-, β- and γ-amino acids

Synthesis and conformational studies of a short linear peptide containing a pyrrole amino acid (1, Paa) and a furan amino acid (2, Faa), namely Boc-hGly-Faa-d-Pro-Gly-Paa-hGly-Faa-OMe (3), were carried out in which it was established that peptide 3 adopted a well-defined β-hairpin structure in DMSO-d₆.     

Production of liquid fuels and chemicals from pyrolysis of Bangladeshi bicycle/rickshaw tire wastes

Tire wastes in the form of used bicycle/rickshaw tires available in Bangladesh were pyrolyzed in a fixed-bed fire-tube heating reactor under different pyrolysis conditions to determine the role of final temperature, sweeping gas flow rate and feed size on the product yields and liquid product composition. Final temperature range studied was between 375 and 575 °C and the highest liquid product yield was obtained at 475 °C. Liquid products obtained under the most suitable conditions were characterized by elemental analyses, FT-IR, ¹H NMR and GC–MS techniques. The results show that it is possible to obtain liquid products that are comparable to petroleum fuels and valuable chemical feedstock from bicycle/rickshaw tire wastes if the pyrolysis conditions are chosen accordingly.     

Can Li Atoms Anchored on Boron- and Nitrogen-Doped Graphene Catalyze Dinitrogen Molecules to Ammonia? A DFT Study

The most successful electrochemical conversion of ammonia from dinitrogen molecule reported to date is through a Li mediated mechanism. In the framework of the above fact and that Li anchored graphene is an experimentally feasible system, the present work is a computational experiment to identify the potential of Li anchored graphene as a catalyst for N₂ to NH₃ conversion as a function of (a) minimum number of Li atoms needed for anchoring on graphene sheets and (b) the role of chemical modification of graphene surfaces. The studies bring forth an understanding that Li anchored graphene sheets are potential catalysts for ammonia conversion with preferential adsorption of N₂ through end-on configuration on Li atoms anchored on doped and pristine graphene surfaces. This mode of adsorption being characteristic of Nitrogen Reduction Reaction (NRR) through enzymatic pathway, examination of the same followed by analysis of electronic properties demonstrates that tri-Li atoms (Tri Atom Catalysts, TACs) are more efficient as catalysts for NRR as compared to two Li atoms (Di Atom Catalysts, DACs). Either way, the rate determining step was found to be *NH₂→*NH₃ step (mixed pathway) with ΔG_max=1.02 eV and *NH₂−*NH₃→*NH₂ step (enzymatic pathway) with ΔG_max=1.11 eV for 1B doped TAC and DAC on graphene sheet, respectively. Consequently, this work identifies the viability of Li anchored graphene based 2-D sheets as hetero-atom catalyst for NRR.     

Plastic scintillators and related analytical procedures for radionuclide analysis

This article is a general overview of the potential capacities of plastic scintillators in radionuclide activity determination. Plastic scintillation (PS) behaves as liquid scintillation does, but with some differences related to the solid state of plastic scintillators. These differences are the base of some drawbacks and some advantages, related to the use of PS. This article describes how these capacities are affected by PS composition, sample preparation, scintillation mechanisms and quenching calibration procedures. It also describes the capabilities for alpha and beta emitter determination and discrimination through the use of PS microspheres and PS resins and their application to different types of samples and radionuclide determination.     

Nitrosative Stress Response in <Emphasis Type="Italic">Vibrio cholerae</Emphasis>: Role of <Emphasis Type="Italic">S</Emphasis>-Nitrosoglutathione Reductase

Vibrio cholerae, the causative agent of cholera, poses serious threats to humans worldwide. V. cholerae faces host inflammatory response and encounters nitrosative stress before establishing successful colonization. It is not clear how V. cholerae combats nitric oxide and reactive nitrogen species. In the present study, we used three clinical strains of V. cholerae and tested their nitrosative stress response pattern towards sodium nitroprusside (SNP) and S-Nitrosoglutathione (GSNO). Among them, V. cholerae, belonging to both O1 and O139 serotypes, showed moderate resistance to SNP and GSNO. However, a V. cholerae strain belonging to non O1 and non O139 showed sensitivity to SNP but resistance towards GSNO. Reduced glutathione and glutathione reductase play a significant role to combat nitrosative stress in V. cholerae. This is the first report where we show the presence of GSNO reductase activity in V. cholerae and that it plays an important role to detoxify S-Nitrosoglutathione. GSNO reductase activity of V. cholerae was regulated by posttranslational modification through S-nitrosylation under in vitro conditions which could be reversed by dithiothreitol (DTT). In addition, we show that biofilm formation remained unaffected under nitrosative stress in V. cholerae.     

Efficient synthesis of functionalized olefins by Wittig reaction using Amberlite resin as a mild base

A convenient procedure for the synthesis of olefins by the reaction of stabilized, semistabilized, and nonstabilized phosphorous ylides with various aldehydes or ketone using Amberlite resin as a mild base is described. Our developed method offers facile and racemization-free synthesis of α,β-unsaturated amino esters and chiral allylic amine. The developed methodology offers mild reaction conditions, high efficiency, and facile isolation of the final products, a practical alternative to known procedures.     

Transition-metal-free regioselective thiocyanation of phenols,anilines and heterocycles

An expedient direct and regioselective thiocyanation of phenols, anilines and heterocycles is described. Transformation is realized via the direct CH functionalization under transition metal free conditions at ambient temperature in excellent yields. Method proved to be monoselective and variety of functional groups tolerated the reaction conditions. The practicality of the protocol is demonstrated in gram scale synthesis of a precursor of PPAR δ agonist in excellent yield.     

Electromechanical Response of Nanostructured Polymer Systems with no Mechanical Pre‐Strain

A dielectric elastomer derived from a polystyrene‐block‐poly(ethylene‐co‐butylene)‐block‐polystyrene triblock copolymer swollen with a midblock‐selective solvent is reported to show promise as a nanostructured organic actuator requiring no pre‐strain. This might provide an attractive alternative to conventional acrylic, siloxane, and polyurethane elastomers since the electromechanical properties are composition‐tunable.

     

The Dowd–Beckwith Reaction: History,Strategies, and Synthetic Potential

Ring-expansion strategies are valuable synthetic tools that take benefit of existing ring structures and evade the unfavorable enthalpic-and entropic effects that arise with end-to-end cyclizations. One potentially important class of such reactions is the Dowd–Beckwith reaction, the ring-expansion of ketones via alkoxy radicals. The exciting advancement in this research area is starting to show its potential, as demonstrated by applying this methodology in strategy-level bond formation to synthesize complex natural products. This Review aims to provide the first comprehensive survey of the development of the Dowd–Beckwith reaction spanning three decades from the initial report to the present day, thus providing the readers with great detail about the contributions of this reaction to organic synthesis. We hope that this review will further disclose the salient features of the Dowd–Beckwith reaction for synthetic applications and encourage the development of new, more advanced applications.