Microwave assisted IMDAF# reaction: Microwave irradiation applied with success to cycloaddition reaction of N-propargyl-N-p-tolyl-N-2-furfurylamines

The new tertiary furfurylamine with triple bond as a dienophylic part i. e. N-(5-methyl-2-furfuryl)-N-prop-2-ynyl-p-toluidine (1) was prepared and the intramolecular Diels-Alder reaction of the amine (1) was performed under microwave irradiation conditions and by heating a benzene solution of the amine under nitrogen. Comparing the results of the usual thermal and the MAOS reaction, we confirmed our expectations that MAOS could promote the outcome of IMDA reaction of the suitably N-substituted tertiary 2-furfuryl-amines. In the present example, N-p-tolyl-5-methyl-5,7a-dihydro-5,7a-epoxyisoindoline was obtained in much better yield and of higher purity.The acronym for: Intramolecular Diels-Alder Reaction of Furan.The acronym for: Microwave-Assisted Organic Synthesis.     

Fe-containing nanoparticles used as effective catalysts of lignin reforming to syngas and hydrogen assisted by microwave irradiation

Active iron-containing nanosized components have been formed on the lignin surface. The metal was deposited on the lignin from an ethanol solution of Fe(acac)₃ and from a colloid solution of iron metal particles obtained beforehand by metal vapor synthesis. These active components are able to absorb microwave radiation and are suitable for microwave-assisted high-rate dehydrogenation and dry reforming of lignin without addition of a carbon adsorbent, as a supplementary radiation absorbing material, to the feedstock. The dependence of the solid lignin heating dynamics on the concentration of supported iron particles was investigated. The threshold Fe concentration equal to 0.5 wt.%, providing the highest rate of sample heating up to the reforming and plasma generation temperature was identified. The microstructure and magnetic properties of iron-containing nanoparticles supported on lignin were studied before and after the reforming. The Fe₃O₄ nanoparticles and also core-shell Fe₃O₄@γ-Fe-С nanostructures are formed during the reforming of lignin samples. The catalytic performance of iron-based nanoparticles toward the lignin conversion is manifested as increasing selectivity to hydrogen and syngas, which reaches 94% at the Fe concentration of 2 wt.%. It was found that with microwave irradiation under argon, hydrogen predominates in the gas. In the СО₂ atmosphere, dry reforming takes place to give syngas with the СО/Н₂ ratio of ~?0.9. In both cases, the degree of hydrogen recovery from lignin reaches 90–94%.

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Graphical abstract The microwave-supported deposition of iron on the lignin surface gives active well defined nanoparticles Fe₃O₄ and also core-shell Fe₃O₄@γ-Fe-С nanostructures. These nanocomponents provide for high-rate microwave-assisted dehydrogenation and dry reforming of lignin.

     

Efficient library synthesis of imidazoles using a multicomponent reaction and microwave irradiation

Optimization of Radziszewski's four-component reaction employing a microwave-assisted protocol, led to a small library of 48 imidazoles with a success rate of 65% (conversion > 45%). All three diversity points of the four-component reaction were varied. Aromatic and aliphatic inputs were successfully implemented and mono-, di-, tri- and tetrasubstituted imidazoles with various substitution patterns were synthesized. Furthermore, unsymmetrical diketones could successfully be used which improved the intrinsic diversity of the method significantly. If the unsymmetrical diketone 1,2-phenylpropanedione (R¹ and R²) was used two regioisomers were formed. Depending on the type of amine (R⁴) and aldehyde (R³) applied, regioselectivity was modest to good. Based on these results, a reaction mechanism is proposed.     

Response of Nb3Ge microbridges to microwave irradiation

We studied the response of Nb₃Ge constant thickness microbridges to microwave irradiation in the frequency range of 0.5 to 70 GHz. The observed current-voltage characteristics exhibit sharp constant-voltage steps up to 19.5 K. At sufficiently high temperatures and frequencies an oscillatory dependence of the critical currentI ₀ is observed which is not predicted by the vortex model but can be explained by pure Josephson behaviour. Series connected microbridges show phase-locking as long as their distance is less than the perpendicular penetration depth .Dedicated to Prof. Dr. H.E. Müser on the occasion of his 60th birthday     

Green chemistry: Efficient epoxides ring-opening with 1-butanol under microwave irradiation

Two activated carbons treated with mineral acids (HNO₃ and sulfonitric mixture) have been tested as acid catalysts in the epoxides (1,2-epoxyhexane and styrene oxide) ring-opening reaction with 1-butanol under microwave (MW) irradiation. The mayor obtained product is that resulting of the alcohol addition to the most substituted carbon in the epoxide ring. The most active catalyst is that treated with sulfonitric mixture. The use of a MW oven allows achieving to the complete conversion of styrene oxide in only 2 min.     

Synthesis of nanocrystalline ZnTiO3 perovskite thin films by sol-gel process assisted by microwave irradiation

Nanocrystalline ZnTiO₃ thin films have been grown on Si (1 0 0) at room temperature by using simple, cost effective sol-gel process assisted by microwave irradiation for thermal treatment. For comparison purpose the deposited films have subjected to two kinds of annealing treatments: first set by using conventional annealing and second set by irradiating the deposited films at different microwave powers for 10 min. In both treated films, formation of cubic phase ZnTiO₃ structure has been observed. It is evident that there is a dramatic structural modification when the deposited films are exposed to microwave. It is evident that there is a dramatic change in the morphological properties of the films irradiated in microwave compared to the conventional annealing temperature. Microwave exposed films have shown 19% of Zn, 19% of Ti and 62% of O in the films close to the stiochiometry of the ZnTiO₃, where as annealed films have shown 18% of Zn, 17.5% of Ti, and 64.5% of O in the films of ZnTiO₃. Plausible mechanism for the formation of cubic phase of ZnTiO₃ at low microwave powers has also been discussed. This new innovative microwave heating could open a door for the advanced technologies to cut down the process cost in post treatment of the materials.     

Quantum entanglement generation on magnons assisted with microwave cavities coupled to a superconducting qubit

We present protocols to generate quantum entanglement on nonlocal magnons in hybrid systems composed of yttrium iron garnet (YIG) spheres, microwave cavities and a superconducting (SC) qubit. In the schemes, the YIGs are coupled to respective microwave cavities in resonant way, and the SC qubit is placed at the center of the cavities, which interacts with the cavities simultaneously. By exchanging the virtual photon, the cavities can indirectly interact in the far-detuning regime. Detailed protocols are presented to establish entanglement for two, three and arbitrary N magnons with reasonable fidelities.     

Multiplex H_2 CARS thermometry in a microwave assisted diamond CVD plasma

Rapid temperature measurements in a low pressure, microwave assisted, diamond CVD plasma are reported. By using a “modeless” laser as the Stokes source for H CARS, accurate single-shot and averaged temperatures were obtained which agreed with values obtained from laser induced fluorescence measurements. The speed of data acquisition afforded by multiplex CARS allowed variations of temperature to be monitored with changing plasma conditions induced by variations of pressure, gas composition and microwave power. The application of the technique for “on-line” monitoring of plasma processes is briefly discussed. Received: 13 February 1996 / Accepted: 12 June 1996     

Mesoscopic superconductors under irradiation: microwave spectroscopy of Andreev states

We show that irradiation of a voltage-biased superconducting quantum point contact at frequencies of the order of the gap energy can remove the suppression of subgap dc transport through Andreev levels. Quantum interference among resonant scattering events involving photon absorption is furthermore shown to make microwave spectroscopy of the Andreev levels feasible. We also discuss how the same interference effect can be applied for detecting weak electromagnetic signals up to the gap frequency, and how it is affected by dephasing and relaxation.     

Synthesis of 1,5-benzothiazepine derivatives bearing 2-phenoxy-quinoline moiety via 1,3-diplolar cycloaddition reaction

A series of 1,5-benzothiazepine derivatives were synthesized by the reaction of 1,5-benzothiazepine containing 2-phenoxy-quinoline with benzohydroximinoyl chlorides and hydrazonoyl chlorides at room temperature. The structures of these novel compounds were confirmed by spectrum, elemental, and X-ray crystallographic analysis.     

Enhancement of pulsed laser ablation assisted with continuous wave laser irradiation

Continuous wave(CW) laser irradiation is employed to enhance the pulsed laser ablation of silicon and stainless steel(316 L)samples. Different surface temperatures generated by the CW laser irradiation are set as the initial working circumstance for the pulsed laser ablation. The diameter and depth of laser-ablated craters are measured to study threshold fluence, pulse incubation coefficient and ablation rate under different surface temperatures. Numerical simulation employing Heat Transfer in Solid and Deformed Geometry Interface modules in COMSOL is performed to estimate ablation rate theoretically based on Hertz-Knudsen equation. The realized crater-related data are analyzed to further obtain their dependences on surface temperature. The parametric and morphological studies indicate that the weakened plasma shielding effect and thermal diffusion in the ablated region induced by the CW laser irradiation lead to the enhanced pulsed laser ablation significantly.     

Rapid synthesis and size control of CuInS2 semi-conductor nanoparticles using microwave irradiation

The properties of CuInS₂ semi-conductor nanoparticles make them attractive materials for use in next-generation photovoltaics. We have prepared CuInS₂ nanoparticles from single source precursors via microwave irradiation. Microwave irradiation methods have allowed us to increase the efficiency of preparation of these materials by providing uniform heating and rapid reaction times. The synergistic effect of varying thiol capping ligand concentrations as well as reaction temperatures and times resulted in fine control of nanoparticle growth in the 3–5 nm size range. Investigation of the photophysical properties of the colloidal nanoparticles were performed using electronic absorption and luminescence emission spectroscopy. Qualitative nanoparticles sizes were determined from the photoluminescence (PLE) data and compared to HRTEM images.

Blue luminescence of nanocrystalline PbWO4 phosphor synthesized via a citrate complex route assisted by microwave irradiation

Nanocrystalline PbWO₄ phosphor powders, which have scheelite structure, were successfully synthesized at low temperatures via a modified citrate complex route assisted by microwave irradiation. Crystallization of the PbWO₄ precursor were detected at 400 °C, and entirely completed at 500 °C. Prepared PbWO₄ nanocrystallites showed primarily spherical and disperse morphology. The average crystallite sizes were between 18 and 29 nm, showing an ordinary tendency to increase with temperature. The nanocrytalline PbWO₄ phosphor powders exhibited spread-eagle shape of blue luminescence. Especially the PbWO₄ phosphor powders prepared at 600 °C showed the strongest luminescent intensity, which was due to the higher crystallinity and homogeneous particle morphology.     

Microwave scattering properties of sand particles: Application to the simulation of microwave radiances over sandstorms

The single-scattering properties of sand/dust particles assumed to be ellipsoids are computed from the discrete dipole approximation (DDA) method at microwave frequencies 6.9-89.0 GHz in comparison with the corresponding Lorenz-Mie solutions. It is found that the single-scattering properties of sand particles are strongly sensitive to the shapes of the particles. The bulk scattering properties of sandstorms composed of spherical or nonspherical particles are investigated by averaging the single-scattering properties of these particles over log-normal particle size distributions. Furthermore, a vector radiative transfer model is used to simulate microwave radiances. The microwave brightness temperatures in the vertical polarization model are essentially not sensitive to sand particle habit, whereas microwave brightness temperature polarization differences are influenced by particle habit. It is shown that microwave brightness temperatures and brightness temperature polarization differences may be useful for estimating the effective particle sizes and mass loading of sandstorms.     

Manipulation of localized charge states in n-MOSFETs with microwave irradiation

We demonstrate how the charge state of a trap at the Si/SiO₂ interface in a MOSFET can be controlled by microwave irradiation. The device is immersed in a static magnetic field at 300 mK and operates at small bias. Under such experimental conditions the electron spins are almost fully polarized. The electron occupancy of the trap is reversibily raised from one to two electrons by turning on a microwave field of less than 10 μW. Such contactless method controls the charge bound to defects close to the channel and it enables the fast initialization of the charge and spin state of the trapped electrons. This is particularly important in those spin resonance quantum computation schemes where a channel current senses the charge state, to improve the switching clock and to eliminate the related noise.     

Annealing of PrF3 nanoparticles by microwave irradiation

The influence of microwave irradiation on the recovery of nanocrystalline PrF₃ powders has been experimentally analyzed by nuclear magnetic resonance (NMR) at T = 1.5 K. It is established that the relaxation times of ¹⁴¹Pr and ¹⁹F nuclei rise significantly with an increase in the hydrothermal-treatment time, whereas the ¹⁴¹Pr NMR spectra narrow, which indicates a decrease in the number of defects in the lattices of nanosamples.     

Shot noise in a quantum dot coupled to carbon nanotube terminals applied with a microwave field

We have investigated the spectral density of shot noise for the system of a quantum dot (QD) coupled to two single-wall carbon nanotube terminals irradiated with a microwave field on the QD. The terminal features are involved in the shot noise through modifying the self-energy of QD. The contributions of carbon nanotube terminals to the shot noise exhibit obvious behaviors. The novel side peaks are associated with the photon absorption and emission procedure accompanying the suppression of shot noise. The shot noise in balanced absorption belongs to sub-Poissonian, and it is symmetric with respect to the gate voltage. The differential shot noise displays intimate relation with the nature of carbon nanotubes and the applied microwave field. It exhibits asymmetric behavior for the unbalanced absorption case versus gate voltage. The Fano factor of the system exhibits the deviation of shot noise from the Schottky formula, and the structures of terminals obviously contribute to it. The super-Poissonian and sub-Poissonian shot noise can be achieved in the unbalanced absorption in different regime of source-drain bias.     

Ultrasonic-assisted synthesis of chrysin derivatives linked with 1,2,3-triazoles by 1,3-dipolar cycloaddition reaction

The 1,3-dipolar cycloaddition reaction between 7-(3-azidopropoxy)-5-hydroxyflavone and phenylacetylene was carried out to investigate the synthesis of 7-(3-(4-phenyl-1,2,3-triazol-1-yl)propoxy)- 5-hydroxyflavone in presence of ultrasound (sono-synthesis) and absence of ultrasound (conventional method) under relatively optimized solvent and catalyst conditions. The reaction rate was notably accelerated with the help of ultrasound irradiation. An experiment was especially carried out for investigating the acceleration mechanism of ultrasound on the cycloaddition. A novel series of chrysin derivatives linked with 1,2,3-triazoles were obtained by the copper(I)-catalyzed 1,3-dipolar Huisgen cycloaddition reaction using t-BuOH/H(2)O (1:1 v/v) as reaction solvents and CuSO(4)·5H(2)O/sodium ascorbate as the catalyst at room temperature in the presence of ultrasound irradiation. Their structures are elucidated by NMR, ESI MS, IR and Elemental analysis.     

Oscillations of the magnetoresistance of a two-dimensional electron gas under microwave irradiation: Influence of the irradiation frequency

We present measurements of the magnetoresistance of a two-dimensional electron gas (2DEG) under continuous microwave as a function of the irradiation frequency. In a previous work by Simovič et al. [Phys. Rev. B 71 (2005) 233303], the magnetoresistance under microwave was shown to be modulated by oscillations of large amplitude that are periodic with magnetic field, their period and phase depending strongly on the electron density. Here we show that the phase and the amplitude of the microwave-induced oscillations also depend on the frequency of irradiation and the sign of the magnetic field.     

Microwave assisted combustion synthesis of CdFe2O4: Magnetic and electrical properties

CdFe₂O₄ particles were synthesized by the microwave assisted combustion method using two different fuels—glycine and urea. Microwave heating provides higher chemical yield within a minute. The synthesized particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), ac impedance spectroscopy, vibrating sample magnetometry (VSM) and electron spin resonance (ESR) methods. XRD analysis shows the cubic structure of CdFe₂O₄. The high and low frequency absorption bands of CdFe₂O₄ were found using FTIR analysis. Spherical morphology was revealed from the SEM images. ESR and VSM measurements reveal the antiferromagnetic behavior of CdFe₂O₄. The electrical conductivities of CdFe₂O₄ synthesized using glycine and urea are 6.5×10⁻⁷ S cm⁻¹ and 4.7×10⁻⁸ S cm⁻¹ respectively at 240 ^oC. At elevated temperatures an occurrence of increase in conductivity was observed, which indicates the semiconducting behavior of CdFe₂O₄. The dielectric spectral analysis reveals that dielectric constant of CdFe₂O₄ decreases with frequency and increases with temperature.