Palladium-containing hypercrosslinked polystyrene as an easy to prepare catalyst for Suzuki reaction in water and organic solvents

A simple and rapid procedure for the incorporation of nanosized Pd particles into hypercrosslinked polystyrene matrix was developed. The prepared catalyst has shown high activity in the coupling of aryl bromides and chlorides with phenylboronic acid, with water being the preferred solvent. The catalyst can be recycled two times without loss of activity.     

Synthesis and properties of magnetite nanoparticles with peroxide-containing polymer shell and nanocomposites based on them

Magnetite nanoparticles (Fe₃O₄ NPs) with peroxide-containing polymer shell have been synthesized using the method of coprecipitation from the mixture solutions of Fe (II) and Fe (III) salts in the presence of peroxide-containing copolymer (PCC). Polymer shell presence has been proved by elemental and complex thermal analysis. Synthesized Fe₃O₄ NPs possess superparamagnetic properties. Their specific saturation magnetization decreases gradually from 65 to 54 A·m²·kg⁻¹ with increasing PCC concentration owing to the surface spin pinning effect caused by a polymer shell. The average sizes of Fe₃O₄ NPs estimated from the data of XRD analysis and magnetic measurements are in the range of 9–12 nm. The NP sizes determined by the DLS method lie in the range of 150–270 nm; this result is significantly larger than the sizes estimated by the two aforementioned methods evidencing a tendency for Fe₃O₄ NPs toward self-association. Cross-linked composite films based on polyvinyl alcohol have been obtained via radical curing initiated by the PCC shell of nanoparticles. The resulting composite films are magnetically sensitive films with rather high physico-mechanical properties (tensile strength reaches 48–67 MPa and relative elongation – 4%–21% depending on cross-linking degree), a priori non-toxic and biocompatible, which makes them promising materials for various applications.     

Bioprospecting Fluorescent Plant Growth Regulators from Arabidopsis to Vegetable Crops

The phytohormone auxin is involved in almost every process of a plant’s life, from germination to plant development. Nowadays, auxin research connects synthetic chemistry, plant biology and computational chemistry in order to develop innovative and safe compounds to be used in sustainable agricultural practice. In this framework, we developed new fluorescent compounds, ethanolammonium p-aminobenzoate (HEA-pABA) and p-nitrobenzoate (HEA-pNBA), and investigated their auxin-like behavior on two main commercial vegetables cultivated in Europe, cucumber (Cucumis sativus) and tomato (Solanum lycopersicum), in comparison to the model plant Arabidopsis (Arabidopsis thaliana). Moreover, the binding modes and affinities of two organic salts in relation to the natural auxin indole-3-acetic acid (IAA) into TIR1 auxin receptor were investigated by computational approaches (homology modeling and molecular docking). Both experimental and theoretical results highlight HEA-pABA as a fluorescent compound with auxin-like activity both in Arabidopsis and the commercial cucumber and tomato. Therefore, alkanolammonium benzoates have a great potential as promising sustainable plant growth stimulators to be efficiently used in vegetable crops.     

Ultra-rapid microwave sintering of pure and Y2O3-doped MgAl2O4

MgAl₂O₄ samples were microwave sintered to near-full density in rapid processes with heating rates on the order of 100°C/min and zero isothermal hold. The experiments were carried out using a gyrotron system for microwave processing of materials operating at a frequency of 24 GHz with a maximum power of 6 kW. In the regimes with a preset heating rate sustained by the automatically regulated microwave power, the maximum achieved density was about 95% of the theoretical value in pristine MgAl₂O₄ samples (maximum sintering temperature 1650°C) and about 97% in 1 wt.% Y₂O₃-doped samples (1700°C). In the regimes with a fixed microwave power (about 3.5 kW), translucent spinel samples with a relative density above 99% were obtained at 1700°C. The duration of the high-temperature stage of sintering was 1.5-10 minutes. The suggested mechanism responsible for the enhanced densification involves development of a thermal instability and formation of transient liquid phases at grain boundaries. The estimated specific absorbed power in the samples during the high-temperature stage of ultra-rapid microwave sintering was 27-80 W/cm³, similar to the values observed in dc field-assisted flash sintering experiments.     

Flat coil-based tunnel diode oscillator enabling to detect the real shape of the superconductive transition curve and capable of imaging the properties of HTSC films with high spatial resolution

Owing to a pick-up coil's flat design, relatively low MHz-range operation frequency, and six orders relative resolution a flat coil-based tunnel diode oscillator has advantages, compared to all other methods. They become crucial in studies with thin high-T_c superconductivity (HTSC) materials (with small signals), especially at the start of the Cooper pairs’ formation. Due to this the superconductivity precursor ‘paramagnetic’ effect was detected recently in YBaCuO films at N/S transition. It precedes Meissner ejection and specifies details of the shape of the transition curve. We discuss the influence of the currents on this effect, and the relationship between the quality of the material and the shape of the effect. A new imaging device has also been created based on this test method (using a focused He–Ne laser beam as a probing signal), capable of imaging the properties of HTSC films with 3 μm spatial resolution. The method is based on detection of the inductance and Q-factor value changes of a single-layer flat coil, placed at the face of the sample. This leads to frequency and/or amplitude changes of the stable oscillator. The test device enabled 2D-mapping of the grain structure of a bridge-shaped YBaCuO film. Basically, the method is capable of imaging 2D-current distribution in thin HTS with sub-μm spatial-resolution, using non-bolometric response. However, the achieved resolution 3 μm of a bolometric nature (in a given device with 3.5 mm-size coil) by no means is limited by the abilities of the method, but mainly, it depends on how narrowly it is possible to focus the probing beam, while the own resolution of a present flat coil-based technique is better than 0.1 μm, and can be improved essentially by reducing the coil size.     

Organometallic radical-adducts of fullerenes C60, C70, and single-walled carbon nanotubes derived from (cyclopentadienyl)molybdenumtricarbonyl dimer

Interaction of the metal-centered free radicals [CpMo(CO)3]* generated photochemically from the corresponding dimer [CpMo(CO)3]2 with fullerenes C60, C70, or single-walled carbon nanotubes in toluene results in the radical-adducts investigated by using TGA, ESR, Raman and X-ray Photo-electron spectroscopy. Comparison was made with the chromium analogues previously studied.     

Statistical Analysis of Dispersed Solid Products

The features of condensed phase dispersion using a previously developed theoretical-set model for material of randomly packed particles are analyzed. As a result of this a rule is obtained for the distribution of grinding products with respect to particle size in the form of the distribution function density and the corresponding distribution function. The result obtained corresponds entirely with experimental data.     

Potential of the High-Energy Hot Compaction in a Vacuum for Creating Materials with an Ultrafine Structure and High Strength

The typical form of specimens prepared by high-energy hot pressing in a vacuum using different deformation schemes and also the results of studying compaction, structure formation, and the physicomechanical properties of different materials in relation to billet heating temperature are presented. The structure and properties of specimens prepared by vacuum sintering are given for comparison. The efficiency of high-energy pressing of single-phase materials (nickel and molybdenum) and two-phase composites (dispersion-strengthened nickel Ni NiO and WC Co hard alloys) is demonstrated. The method makes it possible to prepare compact billets at quite low temperatures that provides retention of a fine-grained structure within them. As a result of this the materials have high mechanical properties that exceed those of specimens prepared by traditional methods.     

Hard Alloy WC – 24% Ni Obtained in the Solid Phase from Ultrafine WC, NiO, and C Powders. Part 1. Density and Structure of Specimens

We have studied the density and structure of specimens of the alloy WC – 24 mass% Ni, obtained by combining into one step the processes of synthesis of the metallic phase and compaction of the ultrafine mixture of WC – Ni powders by high-energy pressing and sintering. We have established that reduction of nickel monoxide by carbon occurs at temperatures of 650-750°C and does not affect the shrinkage process which in the case of sintering begins only at a temperature of 1050°C. High-energy pressing of briquettes sintered at the indicated temperature reduces their porosity from 30-25% down to 8-4%. Specimens of porosity <1% can be obtained by pressing at 1150°C or 1050°C in the case of triple pressing. Raising the temperature at which the briquettes are heated is accompanied by enlargement of the pores together with a decrease in the total porosity, but at temperatures of 1300°C (sintering) and 1250°C (pressing), the pore dimensions are sharply reduced. The high density of the specimens pressed at low temperature does not provide low electrical resistance, which suggests the presence of weakly connected boundaries. When the specimens are sintered and pressed in the solid phase, we observe the growth of tungsten carbide particles. It is most rapid at 1150-1250°C, while at 1050°C the particle growth process slows down. Reduction of the metal oxide when the powders are heated promotes formation of structure in the higher temperature range.     

Hierarchic Material Structure

The concept of hierarchic structure of materials is examined from the viewpoints of the physical basis of it as well as the general system significance. The physical basis is provided by Weisskopf's quantum ladder model for substance structure, whose general system representation is provided by the property of complete decomposition for composite systems. A block diagram is considered for the internal architecture of materials, and it is used to examine general questions of structure evolution and defect formation in response to external factors. The concept is also related to the structural engineering materials.