Simple Synthesis of Conformationally Fixed Glycosamine Analogues by Beckmann Rearrangement at the Carbohydrate Ring

Conformationally fixed carbohydrate analogues are promising small‐molecule inhibitors for hydrolases like O‐GlcNAcase (OGA); however, their synthesis usually requires many steps. Herein we describe cycloadditions of dichloroketene to various glycals and subsequent Beckmann rearrangements, which offer an easy and stereoselective entry to glycosamine derivatives in good yields. The reactions are applicable for hexoses, pentoses, and disaccharides, and transformations to the corresponding imidates proceed smoothly. First biological tests reveal that such imidates indeed inhibit human OGA.     

Synthesis of cellulose–metal nanoparticle composites: development and comparison of different protocols

Deposition of nanoparticles on the surface of a variety of materials is a subject of great interest due to their potential applications in electronic devices, sensing, catalysis and bio-medical sciences. In this context, we have explored and compared various methodologies to generate gold and silver nanoparticles on the surface of cellulose fibers. It was found that boiling of the cellulose fibers in alkaline solution of gold and silver salts led to the formation and immobilization of gold and silver nanoparticles. However, in case of lecithin treated and thiol-modified cellulose fibers, high temperature was not essentially required for the formation and deposition of nanoparticles on cellulose substrate. In both these cases, fairly uniform metal nanoparticles were obtained in good yields (~43 wt% gold loading in case of thiol modified cellulose fibers) at room temperature. Borohydride-reduction method resulted in relatively lower loading (~22 wt%) with a wide size distribution of gold and silver nanoparticles on cellulose fibers. All these nanoparticle–cellulose composites were thoroughly characterized using scanning electron microscopy, energy dispersive X-ray, Fourier transform infrared spectroscopy, UV–visible spectroscopy, and elemental analyzer. Thiol modified cellulose–gold nanoparticle composites served as active catalysts in the reduction of 4-nitrophenol into 4-aminophenol.     

Entropy generation in radiative motion of tangent hyperbolic nanofluid in presence of activation energy and nonlinear mixed convection

In this communication, an optimization of entropy generation is performed through thermodynamics second law. Tangent hyperbolic nanomaterial model is used which describes the important slip mechanism namely Brownian and thermophoresis diffusions. MHD fluid is considered. The novel binary chemical reaction model is implemented to characterize the impact of activation energy. Nonlinear mixed convection, dissipation and Joule heating are considered. Appropriate similarity transformations are implemented to get the required coupled ODEs system. The obtained system is tackled for series solutions by homotopy method. Graphs are constructed to analyze the impact of different flow parameters on entropy number, nanoparticle volume concentration, temperature and velocity fields. Total entropy generation rate is calculated via various flow variables. It is noticed from obtained results that entropy number depend up thermal irreversibility, viscous dissipation and Joule heating irreversibility and concentration irreversibility. Decreasing behavior of concentration is witnessed for higher estimations of chemical reaction variable. Entropy number is more for higher Hartmann number, Weissenberg number and chemical reaction variable while contrast behavior is noted for Bejan number.     

Optical Emission Spectroscopy of Abnormal Glow Region in Nitrogen Plasma

Optical emission spectroscopy of the active species in N₂ plasma is carried out to investigate their concentration as a function of discharge parameters such as filling pressure (2.0–7.0 mbar), source power (100–200 W) and gas flow rate (50–300 mg/min). The primary motivation of this work is to obtain reliable information about the concentration of the active species of N₂ plasma, which play an important role in plasma surface nitriding processes. Emission intensity from the selected electronic excited states of molecular and atomic species is evaluated as a function of discharge parameters to investigate their concentration. The emission intensity ratio I(N₂⁺)/I(N₂) and I(N⁺)/I(N) of the electronic transitions is also evaluated as a function of discharge parameters to investigate the relative dependence of their concentrations. It is observed that the concentration of the active species of N₂ plasma is strongly affected by the filling pressure and source power whereas flow rate has no significant effect. An increased occurrence of N₂⁺ molecular ions in comparison with N₂ molecules, and N⁺ ions in comparison with N atoms is observed with source power whereas decreased occurrence of N₂⁺ molecular ions in comparison with N₂ molecules, and N⁺ ions in comparison with N atoms is observed with the rise in filling pressure.     

Deposition of Diamond-like Carbon Films using Graphite Sputtering in Neon Dense Plasma

This paper reports the deposition of diamond-like carbon (DLC) films on Si <100>, using a low energy (1.45 kJ) dense plasma focus assisted sputtering of graphite insert at the tip of the tapered anode. The substrates are placed in front of the anode at different axial and angular positions and are exposed to multiple focus shots. The information regarding the DLC structure is acquired by using Raman spectroscopy. The spectra are characterized by two broad bands known as “G-band” and “D-band”. The results point towards the formation of DLC films with both sp³ (diamond like) and sp² (graphite like) domains. In X-ray diffraction (XRD) pattern, no additional peak is observed except a peak at 2θ = 69° which corresponds to the silicon (Si) substrate. The intensity of Si peak is reduced after treatment indicating the deposition of amorphous carbon. Scanning electron microscopy (SEM) results demonstrate that the smoothness of the film increases with increasing the substrate angular positions with respect to the anode axis. Energy dispersive X-ray (EDX) analysis reveals that the films deposited at lower axial and angular positions are thicker which is complemented by the cross-sectional views of the films.     

Light emission from sputtered aluminum atoms and ions produced by ion bombardment

Photon emission originating from sputtering of a polycrystalline aluminum surface under 1–10 keV ion (H⁺, He⁺, Ar⁺, Kr⁺ and Xe⁺) bombardment has been studied. Measured photon emission yields from the 3d ²D_3/2 resonance transition of sputtered excited Al atoms and calculated nuclear stopping powers are compared. The results demonstrate that elastic collisions play a major role in photon emission. Moreover, measurements of photon intensity as a function of the distance from the target surface show that decays of sputtered excited ions Al⁺ and Al²⁺ are faster than decays of excited Al atoms, and less affected by cascade repopulation and de-excitation of fast ions.     

The design and characteristics of direct current glow discharge atomic emission source operated with plain and hollow cathodes

A compact direct current glow discharge atomic emission source has been designed and constructed for analytical applications. This atomic emission source works very efficiently at a low-input electrical power. The design has some features that make it distinct from that of the conventional Grimm glow discharge source. The peculiar cathode design offered greater flexibility on size and shape of the sample. As a result the source can be easily adopted to operate in Plain or Hollow Cathode configuration. I-V and spectroscopic characteristics of the source were compared while operating it with plain and hollow copper cathodes. It was observed that with hollow cathode, the source can be operated at a less input power and generates greater Cu I and Cu II line intensities. Also, the intensity of Cu II line rise faster than Cu I line with argon pressure for both cathodes. But the influence of pressure on Cu II lines was more significant when the source is operated with hollow cathode.     

An Overview of the Genetics of Plant Response to Salt Stress: Present Status and the Way Forward

Salinity is one of the major threats faced by the modern agriculture today. It causes multidimensional effects on plants. These effects depend upon the plant growth stage, intensity, and duration of the stress. All these lead to stunted growth and reduced yield, ultimately inducing economic loss to the farming community in particular and to the country in general. The soil conditions of agricultural land are deteriorating at an alarming rate. Plants assess the stress conditions, transmit the specific stress signals, and then initiate the response against that stress. A more complete understanding of plant response mechanisms and their practical incorporation in crop improvement is an essential step towards achieving the goal of sustainable agricultural development. Literature survey shows that investigations of plant stresses response mechanism are the focus area of research for plant scientists. Although these efforts lead to reveal different plant response mechanisms against salt stress, yet many questions still need to be answered to get a clear picture of plant strategy to cope with salt stress. Moreover, these studies have indicated the presence of a complicated network of different integrated pathways. In order to work in a progressive way, a review of current knowledge is critical. Therefore, this review aims to provide an overview of our understanding of plant response to salt stress and to indicate some important yet unexplored dynamics to improve our knowledge that could ultimately lead towards crop improvement.     

Spectroscopic and crystallographic characterization of "alternative resting" and "resting oxidized" enzyme forms of bilirubin oxidase: implications for activity and electrochemical behavior of multicopper oxidases

While there is broad agreement on the catalytic mechanism of multicopper oxidases (MCOs), the geometric and electronic structures of the resting trinuclear Cu cluster have been variable, and their relevance to catalysis has been debated. Here, we present a spectroscopic characterization, complemented by crystallographic data, of two resting forms occurring in the same enzyme and define their interconversion. The resting oxidized form shows similar features to the resting form in Rhus vernicifera and Trametes versicolor laccase, characterized by "normal" type 2 Cu electron paramagnetic resonance (EPR) features, 330 nm absorption shoulder, and a short type 3 (T3) Cu-Cu distance, while the alternative resting form shows unusually small A(||) and high g(||) EPR features, lack of 330 nm absorption intensity, and a long T3 Cu-Cu distance. These different forms are evaluated with respect to activation for catalysis, and it is shown that the alternative resting form can only be activated by low-potential reduction, in contrast to the resting oxidized form which is activated via type 1 Cu at high potential. This difference in activity is correlated to differences in redox states of the two forms and highlights the requirement for efficient sequential reduction of resting MCOs for their involvement in catalysis.     

Vibrational analysis of mononitro substituted benzamides, benzaldehydes and toluenes. Part II. Transferability of valence force constants

A zero-order normal coordinate analysis of both the in-plane and out-of-plane vibrations was made for p-, m- and o-methylbenzaldehydes; 3,5-dichloro-p-anisamide; 3,5-dibromo-p-anisamide; 4-chloro-3-nitrotoluene; 2-bromo-4-nitrotoluene and 2-bromo-5-nitrotoluene by transferring the force constants obtained before hand. The observed and calculated frequencies agreed reasonably well demonstrating the transferability of the force field. On the basis of calculated potential energy distributions and eigen vectors, several assignments suggested by earlier workers have been revised.