Engineered C–N Lyase: Enantioselective Synthesis of Chiral Synthons for Artificial Dipeptide Sweeteners

Aspartic acid derivatives with branched N‐alkyl or N‐arylalkyl substituents are valuable precursors to artificial dipeptide sweeteners such as neotame and advantame. The development of a biocatalyst to synthesize these compounds in a single asymmetric step is an as yet unmet challenge. Reported here is an enantioselective biocatalytic synthesis of various difficult N‐substituted aspartic acids, including N‐(3,3‐dimethylbutyl)‐l ‐aspartic acid and N‐[3‐(3‐hydroxy‐4‐methoxyphenyl)propyl]‐l ‐aspartic acid, precursors to neotame and advantame, respectively, using an engineered variant of ethylenediamine‐N,N′‐disuccinic acid (EDDS) lyase from Chelativorans sp. BNC1. This engineered C–N lyase (mutant D290M/Y320M) displayed a remarkable 1140‐fold increase in activity for the selective hydroamination of fumarate compared to that of the wild‐type enzyme. These results present new opportunities to develop practical multienzymatic processes for the more sustainable and step‐economic synthesis of an important class of food additives.     

AgONO‐Assisted Direct CH Arylation of Heteroarenes with Anilines

A novel copper‐catalyzed C?H arylation of heteroarenes with anilines by an in situ diazonium reaction is established by using silver nitrite (AgONO) as an unconventional nitrosating reagent under acid‐free conditions. It provides a complementary approach for the C?H arylation of electron‐rich heteroarenes with aromatic amines affording a variety of heterobiaryls in moderate to good yields.     

Development and investigation of the flexible hydrogen sensor based on ZnO-decorated Sb2O3 nanobelts

Hydrogen is regarded as the next-gen fuel for vehicles to avoid the emission of toxic gases, which needs a continuous monitoring of the concentration level. In the design of the H₂ sensor, especially of flexible type, a sensing layer will be blended, which affects the sensing performance of the device. Based on this concern, the present investigation is carried out to understand the effect of the bending angle toward the sensing performance of bare and ZnO (n-type)-decorated Sb₂O₃ (p-type) nanobelt–based sensors for hydrogen gas. The sensing element was prepared by the thermal chemical vapor deposition followed by the drop-casting method. Furthermore, the role of the zinc precursor (molar concentration—1 M–3 M) on the preparation of ZnO-decorated Sb₂O₃ nanobelts was studied. Various techniques were used to confirm the formation of ZnO-decorated nanobelts such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), and Fourier transform infrared spectroscopy (FTIR). From these analyses, 1 M concentration of the zinc precursor shows uniform distribution of nanoparticles over the surface of Sb₂O₃ nanobelts. However, agglomeration was observed when the concentration of the zinc precursor increases from 1 M to 3 M. Later, the prepared nanobelts were deposited on the OverHead Projector (OHP) sheet by the doctor blade method for sensing hydrogen gas at 100 °C at a concentration of 1000–3000 ppm. In addition to it, the effect of the substrate bending angle (0°, 45°, 60°, and 90°) was analyzed at a fixed concentration of H₂ gas (1000 ppm). From this study, it is clear that the highest sensing response was achieved for 1 M decorated nanobelts compared with bare as well as other concentrations because of uniform distribution of nanoparticles on the surface of nanobelts. Moreover, the prepared sample demonstrates better sensing performance with the bending of substrates, which suggests that the prepared sensor could be used for flexible electronic devices. The prepared nanobelts show a good H₂ gas–sensing response even with bending of the substrates. The work suggests that the prepared sensor is applicable for flexible electronic devices.     

Selective optical generation of coherent acoustic nanocavity modes

Femtosecond pump-probe experiments on a Ga0.85In0.15As nanocavity enclosed by two Ga(0.85)In(0.15)As/AlAs phonon Bragg mirrors reveal selective generation of terahertz confined acoustic modes and regular folded phonons. Selective generation of the confined modes alone is achievable for laser excitation at certain energies below the mirror absorption edges, corresponding to electronic transitions within the cavity layer only. Calculations based on the photoelastic effect explain the experimental results. Decay times of cavity and regular modes evidence longer decay times and anharmonic effects for the cavity mode.     

Influence of activation of Si29+ ion-implantation in GaAs on ohmic contact resistance and electrical performances of MESFETs

The active layers of Metal Semiconductor Field Effect Transistors (MESFETs) are obtained by Si²⁹⁺ ion implantation in GaAs. Implantation was done at 35 keV with a higher dose near the wafer surface for facilitating easier formation of ohmic contacts, and at 180 keV with a lower dose for obtaining the device channel. Post-implantation annealing was carried out in a rapid thermal processor for activating the implants. Very high activation levels of about 60% for the n⁺ GaAs layer, and 85% for the n-GaAs channel layer were achieved by annealing at 955 °C for 25 s. Activation was characterized using C–V profiling, secondary ion mass spectrometry and by electrical device data of fabricated MESFETs. We attempt an experimental correlation between the ohmic contact resistance (R _c) and activation of both the n⁺ and the channel layer. It was found that very high and simultaneous activation of the n⁺ and channel layers results in very low contact resistances. The conduction of source-drain current into the channel is easily facilitated due to reduction in the resistance of the transition region at the interface of n⁺-contact and n-channel layers.     

A membrane-less enzymatic fuel cell with layer-by-layer assembly of redox polymer and enzyme over graphite electrodes

Layer-by-layer (LBL) assembly of alternate osmium redox polymers and glucose oxidase, at anode, and laccase, at cathode, using graphite electrodes form a membrane-less glucose/O(2) enzymatic fuel cell providing a power density of 103 μW cm(-2) at pH 5.5.     

Spectrofluorometric studies on the binding interaction of bioactive imidazole with bovine serum albumin: a DFT based ESIPT process

Bioactive imidazole derivatives were synthesized and characterized by NMR spectra, mass and CHN analysis. An excited state intramolecular proton transfer (ESIPT) process in hydroxy imidazole has been studied using emission spectroscopy. In hydrocarbon solvent, the tautomer emission predominates over the normal emission and in alcoholic solvent like ethanol; a dramatic enhancement of normal emission is observed which was due to increased solvation. DFT calculation on energy, charge distribution of the rotamers in the ground and excited states of the imidazole derivative were performed and discussed. PES calculation indicates that the energy barrier for the interconversion of two rotamers is too high in the excited state than in the ground state. The interaction between bioactive imidazole derivative and bovine serum albumin (BSA) was investigated.     

Efect of Varying Dzyaloshinskii–Moriya Interaction on the Bistable Nano-Scale Soliton Switching

The efect of Dzyaloshinskii–Moriya(D-M) interaction on the bistable nano-scale soliton switching ofers the possiblity of developing a new innovative approach for data storage technology. The dynamics of Heisenberg ferromagnetic spin system is expressed in terms of generalized inhomogeneous higher order nonlinear Schro¨dinger(NLS) equation. The bistable soliton switching in the ferromagnetic medium is established by solving the associated coupled evolution equations for amplitude and velocity of the soliton using the fourth order Runge–Kutta method numerically.     

Breather-like director reorientations in a nematic liquid crystal with nonlocal nonlinearity

The nature of nonlinear molecular deformations in a homeotropically aligned nematic liquid crystal (NLC) is presented. We start from the basic dynamical equation for the director axis of a NLC with elastic deformations and adopt space curve mapping procedure to analyze the dynamics. The NLC is governed by an integro-differential perturbed nonlocal nonlinear Schrödinger equation and we solve the same using Jacobi elliptic function method aided with symbolic computation and construct an exact solitary wave solution. In order to better understand the effect of nonlocality on the director reorientations of nematic liquid crystal, we have constructed the component forms of director axis using Darboux vector transformation. This intriguing property as a result of the relation between the coherence of the breather-like solitary deformation and the nonlocality reveals a strong need for a deeper understanding in the theory of self-localization in NLC systems.