An efficient one-pot synthesis of tetra-substituted pyrroles

The three-component reaction of primary amines, dialkyl acetylenedicarboxylates and β-nitrostyrene derivatives in the presence of Iron(III) chloride afforded 1,2,3,4-tetra-substituted pyrroles in high yields. These reactions could precede via domino Michael addition/cyclization process.     

Catalytic application of sulfonic acid‐functionalized titana‐coated magnetic nanoparticles for the preparation of 1,8‐dioxodecahydroacridines and 2,4,6‐triarylpyridines via anomeric‐based oxidation

We have developed green, efficient and powerful protocols for the preparation of 2,4,6‐triarylpyridines and 1,8‐dioxodecahydroacridines in the presence of Fe₃O₄@TiO₂@O₂PO₂(CH₂)₂NHSO₃H as a sulfonic acid‐functionalized titana‐coated magnetic nanoparticle catalyst under mild and solvent‐free reaction conditions. These protocols furnished the desired products in short reaction times with good to high yields (20–40 min and 80–86% in the case of 2,4,6‐triarylpyridines; 15–90 min and 80–93% in the case of 1,8‐dioxodecahydroacridines). The final step of the mechanistic route in the synthesis of 2,4,6‐triarylpyridines proceeds via an anomeric‐based oxidation. Also, the nanomagnetic core–shell catalyst can be recycled and reused in both cases of the scrutinized one‐pot multicomponent reactions with high turnover number and turnover frequency.     

ON THE STABILITY OF A FUNCTIONALLY GRADED RECTANGULAR MICRO-PLATE SUBJECTED TO HYDROSTATIC AND NONLINEAR ELECTROSTATIC PRESSURES

This article studies the stability of a functionally graded clamped-clamped micro-plate subjected to hydrostatic and electrostatic pressures. Equilibrium positions of the micro-plate are determined and shown in the state control space. To study the stability of the equilibrium positions, the motion trajectories are given for different initial conditions in the phase plane. Effects of the electrostatic and hydrostatic pressure changes on the deflection and stability of the micro-plate for some sample value of k are studied and values of the applied voltage and hydrostatic pressure leading system to unstable conditions by undergoing a saddle node and homoclinic bifurcations are determined.     

Planar graphs: Random walks and bipartiteness testing

We initiates the study of property testing in arbitrary planar graphs. We prove that bipartiteness can be tested in constant time, improving on the previous bound of for graphs on n vertices. The constant‐time testability was only known for planar graphs with bounded degree. Our algorithm is based on random walks. Since planar graphs have good separators, that is, bad expansion, our analysis diverges from standard techniques that involve the fast convergence of random walks on expanders. We reduce the problem to the task of detecting an odd‐parity cycle in a multigraph induced by constant‐length cycles. We iteratively reduce the length of cycles while preserving the detection probability, until the multigraph collapses to a collection of easily discoverable self‐loops. Our approach extends to arbitrary minor‐free graphs. We also believe that our techniques will find applications to testing other properties in arbitrary minor‐free graphs.     

Exploring and modeling the ion mobility spectrometry of perindopril: Example of protonation-dissociation reactions in large molecules

The current research is constructed for considering the chemical ionization and dissociation of perindopril in the positive mode of corona discharge ion mobility spectrometry. Four product ion peaks are observed in the ion mobility spectrum of perindopril erbumine at the cell temperature of 473 K. These peaks are assigned through the obtained intensity variation analysis in the ion mobility spectra over the elapsed time accompanied by the calculations backed by the validated density functional theory (DFT). In this regard, the most stable ionic species associated with each peak and the corresponding reliable generation pathways are found by the well-confirmed meta hybrid density functional method, M06-2X. The peaks are assigned to the protonated perindopril and its dissociation products, including counter ion and the related fragment ions. However, the structures of the neutral perindopril in the gas phase are thoroughly assessed to find a more stable one. The predicted chemical ionization products by the theory are in excellent agreement with our presented experiment here. Theoretical evaluations demonstrated that the production of a fragment by dissociation process occurs when perindopril gets a proton from the ionization region. Also, without protons, there is no dissociation process. Therefore, our mechanism investigated here is the proton transfer one. All possible sites of perindopril are considered theoretically for protonation along with their possible reactions. In addition to the computed PES, the assigned ions for obtained spectra are confirmed by the computed equilibrium constants and rate constants. Our theoretical results show that the peak of the main fragment is for M-CH₃CH₂OH produced by a reaction pathway involving no barrier. This study opens new perspectives in interpreting large molecules spectra for future studies.     

On the Thermal Degradation of a Novel Epoxy-Based Nanocomposite Cured With Tryptophan as an Environment-Friendly Curing Agent

The thermal degradation kinetics of diglycidyl ether of bisphenol-A (DGEBA) cured with tryptophan (Trp) in the presence of silica nanoparticles (SiNP) was investigated by thermogravimetry analysis. The activation energies of the solid-state decomposition process were evaluated using the advanced isoconversional method. The dependence of conversion (degradation) on the temperature and activation energy was determined allowing the calculation of master plots. The experimental master plots agreed with the first-order (F1) kinetic function for both neat epoxy and nanocomposite in the conversion range of 0.45–0.85. Using the kinetic model and the calculated kinetic parameters, the times at half conversion (α = 0.5) were computed for different degradation temperatures. The kinetic analysis showed that the degradation rate of the epoxy nanocomposite was lower than that of the neat epoxy for conversions between 0.45 and 0.85. Therefore, we concluded that adding SiNP to DGEBA/Trp can improve the thermal stability in the conversion range of 0.45–0.85.     

Novel nanocomposite membranes based on polybenzimidazole and Fe<Subscript>2</Subscript>TiO<Subscript>5</Subscript> nanoparticles for proton exchange membrane fuel cells

In this work, Fe₂TiO₅ nanoparticles were used for improving the proton conductivity, and water and acid uptake of polybenzimidazole (PBI)-based proton exchange membranes. The nanocomposite membranes have been prepared using different amounts of Fe₂TiO₅ nanoparticles and dispersed into a PBI membrane with the solution-casting method. The prepared membranes were then physico-chemically and electrochemically characterized for use as electrolytes in high-temperature PEMFCs. The PBI/Fe₂TiO₅ membranes (PFT) showed a higher acid uptake and proton conductivity compared with the pure PBI membranes. The highest acid uptake (156 %) and proton conductivity (78 mS/cm at 180 °C) were observed for the PBI nanocomposite membranes containing 4 wt% of Fe₂TiO₅ nanoparticles (PFT₄). The PFT₄ composite membrane showed 380 mW/cm² power density and 760 mA/cm² current density in 0.5 V at 180 °C at dry condition. The above results indicated that the PFT₄ nanocomposite membranes could be utilized as proton exchange membranes for high-temperature fuel cells.