Magnetically reusable nanocatalysts in biginelli synthesis of dihydropyrimidinones (DHPMs)

Abstract

Molecules containing dihydropyrimidinone (DHPMs) structures are very important in pharmaceutical and medicinal chemistry due to their excellent biological activities application in synthesis of natural products. Biginelli condensation reaction between an aldehyde, urea/thiourea and a carbonyl compound is the most popular strategy for the synthesis of dihydropyrimidinones. Magnetic recoverable nanocatalysts can be readily separated from reaction medium by using an external magnet, without the need for filtration, centrifugation or other tedious workup processes. In recent times, the catalytic potential of magnetically recoverable nanocatalysts was evaluated in a variety of Biginelli reactions. In this review, we focus on the application of magnetically recoverable gold nanocatalysts in Biginelli synthesis of dihydropyrimidinone derivatives.     

Preparation of selective micro glucose sensor without permselective membrane by electrochemical deposition of ruthenium and glucose oxidase

A carbon fiber microelectrode, surface of which ruthenium and glucose oxidase (GOx) were electrochemically codeposited, has been investigated. The Ru deposition onto the microelectrode increased current response to H₂O₂ oxidation, while decreased oxidation currents due to interfering substances, such as ascorbic acid, uric acid, p-acetamidophenol, l-cysteine and dopamine. The codeposition of Ru and GOx gave further suppression of the interfering signals with keeping the current response to H₂O₂. When amperometric glucose sensing was conducted by using the GOx and Ru modified microelectrode, an increase in GOx concentration in the deposition bath enlarged oxidation current of H₂O₂ generated from glucose oxidation by GOx. The presence of ascorbic acid in analyte gave no error in detection of glucose and errors caused by uric acid was +3% at the most for measuring 5 mM glucose, which is the normal physiological level in blood.     

Membranes for gas separation based on poly(1-trimethylsilyl-1-propyne)–silica nanocomposites

Nanocomposite membranes based on poly(1-trimethylsilyl-1-propyne) (PTMSP) and silica were synthesized by sol–gel copolymerization of tetraethoxysilane (TEOS) with different organoalkoxysilanes in tetrahydrofuran solutions of PTMSP. The influence of the synthesis parameters (type and concentration of organoalkoxysilanes, temperature and time) on the silica conversion and the gas permeation performance of PTMSP–silica nanocomposite membranes was investigated and discussed in this paper. The nanocomposite membranes were characterized by single and mixed gas permeation, thermogravimetric analysis and scanning electron microscopy. The butane permeability and the butane/methane selectivity increased simultaneously when high silica conversion was obtained and the size of particle was in the range 20–40 nm. For the sake of comparison, nanocomposite membranes based on PTMSP were also prepared by dispersing silica particles with different functional groups into the PTMSP casting solution. The addition of fillers to the polymer matrix can be performed up to a higher content of silica (30% silica-filled PTMSP in contrast to 6 wt.% for the in situ-generated silica). In this case, the simultaneous increase in butane permeability and butane/methane selectivity was significantly higher when compared to the nanocomposite membranes prepared by sol–gel process. The addition of fillers with 50% of surface modification with hydrophobic groups (Si–C₈H₁₇ and Si–C₁₆H₃₃) seems not to lead to a significant increase of the butane/methane selectivity and butane permeability when compared to the silica with hydrophilic surface groups, probably because of the unfavorable polymer/filler interaction, leading to an agglomeration of the long n-alkyl groups at the surface of the polymer. An increase of butane permeability up to six-fold of unfilled polymer was obtained.     

Silica-coated magnetic nanoparticles functionalized cobalt complex: a recyclable and efficient catalyst for the C−C bond formation

In this study, the Co-based catalyst was prepared by cobalt immobilization on the surface of functionalized silica-coated magnetic NPs (Fe₃O₄@SiO₂-CT-Co) as a magnetically core–shell nanocatalyst and characterized by FT-IR, TGA, XRD, VSM, SEM, TEM, EDX, EDX mapping, and ICP techniques and appraised in the Suzuki–Miyaura cross-coupling reaction under mild reaction conditions. The results displayed the superparamagnetic behavior of the Fe₃O₄ NPs core encapsulated by SiO₂ shell, and the size of the particles was estimated about 30 nm. Compared with the previously reported catalysts, the engineered Fe₃O₄@SiO₂-CT-Co catalyst provided perfect catalytic performance for the Suzuki–Miyaura cross-coupling reaction in water as a green solvent and it was much cheaper in the comparison with the traditional Pd-based catalysts. Importantly, the durability of magnetic nanocatalyst was studied and observed that it is stable under the reaction conditions and could be easily reused for at least six successive cycles without any significant decrease in its catalytic activity.

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Design and characterization of [(Et)3 N-H]FeCl4 as a nanomagnetic ionic liquid catalyst for the synthesis of xanthene derivatives under solvent-free conditions

The triethylamine-based nanomagnetic ionic liquid, [(Et)₃ N-H]FeCl₄, was synthesized, and its structural and chemical characteristics were detected. The thermogravimetric analysis indicated its high thermal stability with a decomposition temperature higher than 300 °C. Additionally, [(Et)₃ N-H]FeCl₄ was used to efficiently catalyze the synthesis of xanthene derivatives under solvent-free conditions at 120 °C. [(Et)₃ N-H]FeCl₄ was recycled and reused at least five times.

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Nanoparticle dispersion and coagulation in a turbulent round jet

Nanoparticle dispersion and coagulation behaviors in a turbulent round jet were studied in this article. An experimental system was designed to generate a uniformly distributed air–nanoparticle two-phase flow in a turbulent round jet. The particle size distribution (PSD) was measured by a scanning mobility particle sizer (SMPS) in the near field of the jet. The particle diameters were nearly constant in the potential core due to the high carrying velocity and laminar characteristic of the flow but grew larger in the region of high turbulence intensities because the vortex structures in the mixing layer promoted coagulation. Furthermore, the migration property of small-sized nanoparticles forced them to be preserved in the potential core also leading to the diameter increase. The comparison of the particle concentration distributions at different sections indicated that the shear layer is the major region for the mixing of particle-laden stream and ambient air. The particle diameters in the axial direction experienced three stages including a slightly changed stage, an increasing stage and a constant stage. The diameter increase should be attributed to turbulence coagulation.     

A robust-adaptive fuzzy coverage control for robotic swarms

In this paper, a decentralized adaptive control scheme for multi-robot coverage is proposed. This control method is designed based on centroidal Voronoi configuration integrated with robust adaptive fuzzy control techniques. We consider simple single integrator mobile robots used for covering dynamical environments, where an adaptive fuzzy logic system is used to approximate the unknown parts of control law. A robust coverage criterion is used to attenuate the adaptive fuzzy approximation error and measurement noises to a prescribed level. Therefore, the robots motion is forced to obey solutions of a coverage optimization problem. The advantages of the proposed controller can be listed as robustness to external disturbances, computation uncertainties, and measurement noises, while applicability on dynamical environments. A Lyapunov-function based proof is given of robust stability, i.e. convergence to the optimal positions with bounded error. Finally, simulation results are demonstrated for a swarm coverage problem simultaneous with tracking mobile intruders.     

Two-Fluid Dark Energy Models in Bianchi Type-III Universe with Variable Deceleration Parameter

Some new exact solutions of Einstein’s field equations have come forth within the scope of a spatially homogeneous and anisotropic Bianchi type-III space-time filled with barotropic fluid and dark energy by considering a variable deceleration parameter. We consider the case when the dark energy is minimally coupled to the perfect fluid as well as direct interaction with it. Under the suitable condition, the anisotropic models approach to isotropic scenario. We also find that during the evolution of the universe, the equation of state (EoS) for dark energy ω ^(de), in both cases, tends to ?1 (cosmological constant, ω ^(de)=?1), by displaying various patterns as time increases, which is consistent with recent observations. The cosmic jerk parameter in our derived models are in good agreement with the recent data of astrophysical observations under appropriate condition. It is observed that the universe starts from an asymptotic Einstein static era and reaches to the ΛCDM model. So from recently developed Statefinder parameters, the behaviour of different stages of the universe has been studied. The physical and geometric properties of cosmological models are also discussed.     

Novel polyester/SiO2 nanocomposite membranes: Synthesis,properties and morphological studies

In this paper, a new type of soluble polyester/silica (PE/SiO₂) hybrid was prepared by the ultrasonic irradiation process. The coupling agent γ-glycidyloxypropyltrimethoxysilane (GOTMS) was chosen to enhance the compatibility between the polyester (PE) and silica (SiO₂). Furthermore, the effects of the coupling agent on the morphologies and properties of the PE/SiO₂ hybrids were investigated using UV-vis and FT-IR spectroscopies and FE-SEM. The densities and solubilities of the PE/SiO₂ hybrids were also measured. The results show that the size of the silica particle was markedly reduced by the introduction of the coupling agent, which made the PE/SiO₂ hybrid films become transparent. Furthermore, thermal stability, residual solvent in the membrane film and structural ruination of membranes were analyzed by thermal gravimetric analysis (TGA). The effects of SiO₂ nanoparticles on the glass transition temperature (T_g) of the prepared nanocomposites were studied by differential scanning calorimetry (DSC). Moreover, their mechanical properties were also characterized. It can be observed that the Young's moduli (E) of the hybrid films increase linearly with the silica content. The results obtained from gas permeation experiments with a constant pressure setup showed that adding SiO₂ nanoparticles to the polymeric membrane structure increased the permeability of the membranes.