A new, one-pot, multi-component synthesis of imines of 3-amino-2-arylimidazo[1,2-a]pyridines, 3-amino-2-arylimidazo[1,2-a]pyrazines, and 3-amino-2-arylimidazo[1,2-a]pyrimidines

An efficient, one-pot, multi-component synthesis of 3-amino-2-arylimidazo[1,2-a]pyridines, 3-amino-2-arylimidazo[1,2-a]pyrazines, and 3-amino-2-arylimidazo[1,2-a]pyrimidines is described. Heating a mixture of a 2-aminopyridine, 2-aminopyrazine or 2-aminopyrimidine, a benzaldehyde, and imidazoline-2,4,5-trione under solvent-free conditions afforded imine derivatives of the title compounds in excellent yields. Single-crystal X-ray analysis conclusively confirms the structure of these bridgehead bicyclic 5-6 heterocycles.     

RKM for solving Bratu‐type differential equations of fractional order

The purpose of the present paper is to propose an efficient numerical method for solving the differential equations of Bratu‐type with fractional order in reproducing kernel Hilbert space. The exact solution is calculated in the form of a convergent series with easily computable components. Finally, some examples are given to illustrate the efficiency and applicability of the method. Copyright © 2015 John Wiley & Sons, Ltd.     

A new reliable algorithm based on the sinc function for the time fractional diffusion equation

This paper deals with the numerical solution of time fractional diffusion equation. In this work, we consider the fractional derivative in the sense of Riemann-Liouville. At first, the time fractional derivative is discretized by integrating both sides of the equation with respect to the time variable and we arrive at a semi–discrete scheme. The stability and convergence of time discretized scheme are proven by using the energy method. Also we show that the convergence order of this scheme is O(τ2?α). Then we use the sinc collocation method to approximate the solution of semi–discrete scheme and show that the problem is reduced to a Sylvester matrix equation. Besides by performing some theorems, the exponential convergence rate of sinc method is illustrated. The numerical experiments are presented to show the excellent behavior and high accuracy of the proposed hybrid method in comparison with some other well known methods.     

Tailoring Copper Nanocrystals towards C2 Products in Electrochemical CO2 Reduction

Favoring the CO₂ reduction reaction (CO2RR) over the hydrogen evolution reaction and controlling the selectivity towards multicarbon products are currently major scientific challenges in sustainable energy research. It is known that the morphology of the catalyst can modulate catalytic activity and selectivity, yet this remains a relatively underexplored area in electrochemical CO₂ reduction. Here, we exploit the material tunability afforded by colloidal chemistry to establish unambiguous structure/property relations between Cu nanocrystals and their behavior as electrocatalysts for CO₂ reduction. Our study reveals a non‐monotonic size‐dependence of the selectivity in cube‐shaped copper nanocrystals. Among 24 nm, 44 nm and 63 nm cubes tested, the cubes with 44 nm edge length exhibited the highest selectivity towards CO2RR (80 %) and faradaic efficiency for ethylene (41 %). Statistical analysis of the surface atom density suggests the key role played by edge sites in CO2RR.     

Electrosynthesis of symmetric and highly conjugated benzofuran via a unique ECECCC electrochemical mechanism: evidence for predominance of electrochemical oxidation versus intramolecular cyclization

Electrochemical oxidation of hydroquinone, catechol, and some of their monosubstituted derivatives has been studied in the presence of 3-hydroxy-1H-phenalen-1-one (2) as a nucleophile in water/acetonitrile (80/20) solutions using cyclic voltammetry and controlled-potential coulometry methods. The results revealed that quinones derived from oxidation of hydroquinones and catechols participate in Michael addition reactions with 2. The formed adducts convert to the corresponding benzofuran derivatives via different mechanisms. In this work, we derived a variety of products with good yields using controlled potential electrochemical oxidation at a graphite electrode in an undivided cell.     

Decarboxylative A3‐coupling reactions: An overview

The propargylamine motif is not only prevalent in a wide variety of pharmaceuticals and other biologically active compounds but also utilized as a versatile building block in organic synthesis. Among the various methods for the synthesis of propargylamine derivatives, A³‐coupling represents one of the most general and attractive routes, since it offers the possibility for the construction of complex molecules from simple starting materials (amines, aldehydes, and alkynes) in one‐step with high atom economy. However, the use of volatile alkynes is the main disadvantage of this reaction. Recently, alkynyl carboxylic acids were successfully used as easily accessible and high stable surrogates for alkynes (via in situ decarboxylation) in A³‐coupling reactions. This Focus‐Review aims to give an overview of the decarboxylative A³‐coupling reactions by hoping that it will be beneficial to elicit further research in this appealing research arena. A special emphasis is placed on mechanistic aspect of reactions which may allow possible new insights into catalyst improvement.     

Analytical Solutions to Gas Flow Problems in Low Permeability Porous Media

In most of conventional porous media the flow of gas is basically controlled by the permeability and the contribution of gas flow due to gas diffusion is ignored. The diffusion effect may have significant impact on gas flow behavior, especially in low permeability porous media. In this study, a dual mechanism based on Darcy flow as well as diffusion is presented for the gas flow in homogeneous porous media. Then, a novel form of pseudo pressure function was defined. This study presents a set of novel analytical solutions developed for analyzing steady-state and transient gas flow through porous media including effective diffusion. The analytical solutions are obtained using the real gas pseudo pressure function that incorporates the effective diffusion. Furthermore, the conventional assumption was used for linearizing the gas flow equation. As application examples, the new analytical solutions have been used to design new laboratory and field testing method to determine the porous media parameters. The proposed laboratory analysis method is also used to analyze data from steady-state flow tests of three core plugs. Then, permeability (k) and effective diffusion coefficient (D _e) was determined; however, the new method allows one to analyze data from both transient and steady-state tests in various flow geometries.     

Hammett constants and NMR shifts of α-acyloxy carboxamide derivatives

Geometrical structures, Hammett constants, ¹H and ¹³C chemical shift values, molecular electrostatic potential maps, and several thermodynamic parameters of α-acyloxy carboxamide derivatives (4a–o) were calculated using HF and DFT/B3LYP methods with 6-31G(d) basis set. The optimized structures were compared with analogous compound. The ¹H and ¹³C NMR shielding tensors were computed with the Gauge-Independent Atomic Orbital (GIAO) method. Comparison of the experimental ¹H and ¹³C NMR chemical shifts of 4a–o molecules with the theoretical data indicates good agreement.     

An ab initio study on the nature of σ-hole interactions in pnicogen-bonded complexes with carbene as an electron donor

ABSTRACT

A theoretical study of the complexes formed between ZH₂X (Z = P, As, Sb, Bi; X = F, Cl, Br, CN, NC, OH, NH₂) and an N-heterocyclic carbene (imidazol-2-ylidene) is carried out by means of ab initio calculations. According to molecular electrostatic potential analysis, it is inferred that the divalent C atom of the carbene can act as a Lewis base with the pnicogen atom Z of ZH₂X. The pnicogen bond distances (Z–C) are in the range of 2.050–2.911 for these complexes. While the Z?X bonds are longer than the corresponding Z?C bonds in the X = Cl and Br complexes, most of the Z?X bonds are short enough to suggest that they should be considered as covalent bonds which have lost some degree of covalency. For a given Z, the ZH₂Br forms the strongest complex, followed by ZH₂Cl and ZH₂F. On the other hand, the binding energy in the halogenated ZH₂X complexes follows the reverse ranking expected based on the values of the σ-hole of the isolated ZH₂X monomers. The nature of the pnicogen bond interaction in these complexes is analysed by quantum theory of atoms in molecules (QTAIM) and natural bond orbital methods. According to QTAIM analysis, a partially covalent character can be attributed to the pnicogen bonds studied here.     

Effect of cationization on adsorption of silver nanoparticles on cotton surfaces and its antibacterial activity

Cotton was cationized by exhaustion method using 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CHPTAC) as a cation-generating agent. Adsorption of silver nanoparticles on normal and cationized cotton was studied by exhaustion method at temperatures of 80°C and 100°C. Two exhaustion baths were used, containing nanosilver colloidal solutions stabilized by two different stabilizers and various concentrations of silver nanoparticles. Fourier-transform infrared (FT-IR) spectra of normal and cationized samples confirmed the existence of quaternary ammonium groups on cationized cellulose fibers. X-ray diffraction (XRD) patterns showed that crystallinity of the modified cellulose fibers was decreased. Scanning electron microscope (SEM) images revealed that the surface of the modified cotton was rougher than that of normal cotton. In addition, SEM images showed the presence of silver nanoparticles on the surface of treated fabric samples. The amount of silver particles adsorbed on the fabric samples was determined using inductively coupled plasma-optical emission spectrometer. Antibacterial tests were performed against Escherichia coli bacteria as an indication of antibacterial effect of samples. Cationized cotton samples adsorbed more silver nanoparticles and then had greater ability to inhibit bacteria.