Thiamine hydrochloride as a promoter for the efficient and green synthesis of 12-aryl-8,9,10,12 tetrahydrobenzoxanthene-11-one derivatives in aqueous micellar medium

An environmentally benign, three-component, one-pot integrated chemical process has been developed for the synthesis of 12-aryl-8,9,10,12-tetrahydrobenzoxanthene-11-one by nucleophilic addition reaction between aldehyde and β-naphthol followed by Michael addition of dimedone, catalyzed by thiamine hydrochloride in aqueous micellar medium with excellent yield. Simple reaction conditions, no requirement of chromatographic separation, short reaction time, ease of isolation, use of inexpensive, easily recoverable and reusable catalyst makes this protocol very interesting from an economic and environmental perspective.     

Ni‐Catalyzed [4+3+2] Cycloaddition of Ethyl Cyclopropylideneacetate and Dienynes: Scope and Mechanistic Insights

A detailed study of the Ni‐catalyzed [4+3+2] cycloaddition reaction between ethyl cyclopropylideneacetate and dienynes has been conducted, resulting in the development of a new method for the synthesis of compounds containing nine‐membered rings. We studied the reactivity of various dienynes, together with their substituent and conformational effects. The mechanism of the reaction was probed by examining the stoichiometric reactions of the Ni complexes and dienynes.     

Mild method for the synthesis of 1H-indazoles through oxime-phosphonium ion intermediate

The synthesis of 1H-indazoles from o-aminobenzoximes is achieved via N–N bond formation using triphenylphosphine, I₂, and imidazole. Selective formation of oxime-phosphonium ion intermediate in the presence of the amino group is the driving force for this reaction. The nucleophilicity of the arylamino group and electrophilicity toward the N–O bond of oxime also control the reaction. The reaction proceeds at a faster rate with good to excellent yield under this mild reaction condition and is amenable to scale-up.     

An organocatalytic synthesis of N-sulfonyl imines using chloramine-T in aqueous medium

N-Sulfonyl imines have been synthesized in good to excellent yields from aldehydes and chloramine-T using proline as an organocatalyst in aqueous medium at ambient temperature. The protocol is applicable to a wide range of aldehydes, especially enals exhibit remarkable efficiency in the reaction. The reaction presumably occurs via iminium activation and opens new avenues for the synthesis of N-sulfonyl imines under environmentally benign and mild conditions.     

Ionic liquid 1-ethyl-3-methylimidazolium acetate: an attractive solvent for native chemical ligation of peptides

The ionic liquid 1-ethyl-3-methylimidazolium acetate ([C₂mim][OAc]) was successfully used as alternative solvent for native chemical ligation of peptide fragments to produce model peptide LYRAXCRANK (X = G, A, L, N, Q, K, and F). The commonly used buffer system including thiol additives such as thiophenol and benzyl mercaptan can be replaced by the nontoxic ionic liquid [C₂mim][OAc]. In addition to improving the solubility of the peptides in [C₂mim][OAc], yields and rates of the ligation reactions were found to be efficiently enhanced.     

Boric acid in aqueous micellar medium: an effective and recyclable catalytic system for the synthesis of aryl-7,8-dihydro[1,2,4]triazolo[4,3-a]pyrimidine-6-carbonitriles

A simple, green, and efficient protocol is reported for the preparation of aryl-7,8-dihydro[1,2,4]triazolo[4,3-a]-pyrimidine-6-carbonitriles through one-pot multi component reaction using substituted aromatic aldehydes, malononitrile, and 3-amino[1,2,4]triazole. The reaction is catalyzed by boric acid in aqueous micellar condition. Present protocol incorporates environmentally non-hazardous reaction condition, easy work-up, and use of recyclable catalytic system with associated benefits like excellent yield (84–96%) and shorter reaction time (20 min). Proposed methodology offers rapid access to substituted aryl-7,8-dihydro[1,2,4]triazolo[4,3-a]pyrimidine-6-carbonitriles with high atom-economy and catalytic efficiency.     

A hybrid nanofluid analysis near a parabolic stretched surface

Two dimensional incompressible steady viscous nano-fluid flow with the impacts of heat generation and porous medium is examined numerically. For this objective Ti₆Al₄v are taken as nano-particles dispersed in different base fluids such as methanol, engine oil and water. Basically in this study we will compare three different nano-fluids to assess their flow behaviour and thermal performance. The flow model is developed under certain assumptions. The two dimensional non-linear PDEs are converted into non-linear ODEs with suitable transformation. The numerical procedure is adopted to find the results by using Bvp4c technique in MATLAB. Moreover, graphs are generated for various parameters against the temperature and velocity profiles. The fluid behaviour for different parameter is examined on velocity and temperature profile. It is depicted that for high values of volume fraction and curvature parameter nano-particles leads to high velocity and temperature profile. Moreover, velocity profile decreases for permeability parameter, while temperature profile enhances for heat generation parameter. The influence of Nusselt number and skin friction also assessed. The model of entropy generation is also presented.     

Hydromagnetic parametric resonance instability of two superposed conducting fluids in porous medium

Rayleigh–Taylor instability of a heavy fluid supported by a lighter one through porous medium, in the presence of a uniform, horizontal and oscillating magnetic field is studied. The fluids are taken as viscous (obeying Darcy's law), uniform, incompressible, and infinitely conducting. The amplitude of the oscillating part of the field is taken to be small compared with its steady part. The dispersion relation is obtained in the form of a third-order differential equation, with time as the independent variable and with periodic coefficients, for the vertical displacement of the surface of separation of the two fluids from its equilibrium position. The oscillatory magnetic field of frequency ω$\omega$ and steady part _H0$H_0$ has a stabilizing influence on a mode of disturbance which is unstable in a steady magnetic field of strength _H0$H_0$. It is found that the oscillatory magnetic field and porosity of the porous medium have stabilizing effects, while the medium permeability has a destabilizing influence on the considered system. For a constant value of any of these physical parameters, the system has been found to be unstable (for small wavenumbers) as well as stable afterwards after a definite wavenumber value. The marginal stability case of parametric resonance holds when _M1=_M2=0$M_1=M_2=0$ (and hence m=0$m=0$), in which the characteristic exponents, and the corresponding solutions for u$u$ break down, is also investigated in detail. It is found, to order ?$?$, that the effect of an oscillating magnetic field has no stabilizing influence on a disturbance which is marginally stable in the steady magnetic field; while to order ?²${?}^2$, and when the magnetic field oscillates, a resonance between this mode of disturbances and the oscillating field leads to instability when _ρ2>_ρ1${\rho }_2>{\rho }_1$. It is found also, in this resonant case, that all the constant or varied physical parameters, mentioned above, have destabilizing influences on the considered system. Finally, the other two resonance points appear in non-porous media (i.e., when m=±iω$m=\pm \mathrm{i}\omega$ and m=±2iω$m=\pm 2\mathrm{i}\omega$), are disappeared here due to the presence of the porous medium.     

On the Nano/Micro-Mechanics of Metallic Glass

Metallic glass (MG) is amorphous and has some outstanding properties such as ultrahigh strength, superior elasticity, and excellent thermo-plasticity. However, as MG is relatively new to the metal family, the relationship between its physical properties and amorphous structure is still unclear. This article aims to provide an insightful discussion through a comprehensive review about the investigations in the past few decades on the scientific mechanisms of this class of material. The discussion of the paper will include the following key aspects: (1) the formation mechanism of an amorphous structure through glass transition, (2) the structural characterization and models, (3) the micromechanics of plastic event and shear band, and (4) the correlation between the amorphous structure and its mechanical properties.     

A Non‐Enzymatic Carbohydrate Sensor Based on Multiwalled Carbon Nanotubes Modified with Adsorbed Active Gold Particles

The voltammetric behavior of a glassy carbon electrode modified with multiwalled carbon nanotubes (MWCNTs) and Au particles was studied in alkaline medium towards the electrooxidation of some carbohydrates used as model compounds. The influence of carbohydrate concentration and scan rate on peak potentials, peak currents, etc., observed at the modified electrode was evaluated and critically discussed. The Au particles dispersed into multiwalled carbon nanotubes structures showed favorable electrocatalytic and analytical properties towards the electrooxidation of xylose and glucose molecules. Atomic force microscopy performed on the resulting modified electrode showed a well‐efficient 3D distribution of Au active particles having sharp‐edged and elongated grains along bundles of the MWCNTs. The three‐dimensional MWCNT‐Au composite structure of the catalyst act as a promoter to enhance the diffusive character of recorded currents and probably also increases the rate of the heterogeneous electron transfer of the electrooxidation process considered.