Influence of Magnetite Nanoparticles Shape and Spontaneous Surface Oxidation on the Electron Transport Mechanism

The spontaneous oxidation of a magnetite surface and shape design are major aspects of synthesizing various nanostructures with unique magnetic and electrical properties, catalytic activity, and biocompatibility. In this article, the roles of different organic modifiers on the shape and formation of an oxidized layer composed of maghemite were discussed and described in the context of magnetic and electrical properties. It was confirmed that Fe3O4 nanoparticles synthesized in the presence of triphenylphosphine could be characterized by cuboidal shape, a relatively low average particle size (9.6 ± 2.0 nm), and high saturation magnetization equal to 55.2 emu/g. Furthermore, it has been confirmed that low-frequency conductivity and dielectric properties are related to surface disordering and oxidation. The electric energy storage possibility increased for nanoparticles with a disordered and oxidized surface, whereas the dielectric losses in these particles were strongly related to their size. The cuboidal magnetite nanoparticles synthesized in the presence of triphenylphosphine had an ultrahigh electrical conductivity (1.02 × 10−4 S/cm at 10 Hz) in comparison to the spherical ones. At higher temperatures, the maghemite content altered the behavior of electrons. The electrical conductivity can be described by correlated barrier hopping or overlapping large polaron tunneling. Interestingly, the activation energies of electrons transport by the surface were similar for all the analyzed nanoparticles in low- and high-temperature ranges.

Subcritical Water Extraction of Natural Products

Subcritical water refers to high-temperature and high-pressure water. A unique and useful characteristic of subcritical water is that its polarity can be dramatically decreased with increasing temperature. Therefore, subcritical water can behave similar to methanol or ethanol. This makes subcritical water a green extraction fluid used for a variety of organic species. This review focuses on the subcritical water extraction (SBWE) of natural products. The extracted materials include medicinal and seasoning herbs, vegetables, fruits, food by-products, algae, shrubs, tea leaves, grains, and seeds. A wide range of natural products such as alkaloids, carbohydrates, essential oil, flavonoids, glycosides, lignans, organic acids, polyphenolics, quinones, steroids, and terpenes have been extracted using subcritical water. Various SBWE systems and their advantages and drawbacks have also been discussed in this review. In addition, we have reviewed co-solvents including ethanol, methanol, salts, and ionic liquids used to assist SBWE. Other extraction techniques such as microwave and sonication combined with SBWE are also covered in this review. It is very clear that temperature has the most significant effect on SBWE efficiency, and thus, it can be optimized. The optimal temperature ranges from 130 to 240 °C for extracting the natural products mentioned above. This review can help readers learn more about the SBWE technology, especially for readers with an interest in the field of green extraction of natural products. The major advantage of SBWE of natural products is that water is nontoxic, and therefore, it is more suitable for the extraction of herbs, vegetables, and fruits. Another advantage is that no liquid waste disposal is required after SBWE. Compared with organic solvents, subcritical water not only has advantages in ecology, economy, and safety, but also its density, ion product, and dielectric constant can be adjusted by temperature. These tunable properties allow subcritical water to carry out class selective extractions such as extracting polar compounds at lower temperatures and less polar ingredients at higher temperatures. SBWE can mimic the traditional herbal decoction for preparing herbal medication and with higher extraction efficiency. Since SBWE employs high-temperature and high-pressure, great caution is needed for safe operation. Another challenge for application of SBWE is potential organic degradation under high temperature conditions. We highly recommend conducting analyte stability checks when carrying out SBWE. For analytes with poor SBWE efficiency, a small number of organic modifiers such as ethanol, surfactants, or ionic liquids may be added.

Development of heat-free self-compacting concretes of accelerated hardening for factory technologies

The article discusses the results of the development of multicomponent compositions of self-compacting concrete of accelerated hardening on the basis of the local raw material base of the city of Almaty. The achievement of the required indicators is ensured by the introduction of mineral fillers and a complex of mineral and organic modifiers into the concrete mixtures.

Short alkyl chain length ionic liquid as organic modifier in polypropylene/clay nanocomposite: a thermal comparative study

The most common polymeric nanocomposites are constituted of organically-modified clays. Generally, these organic modifiers are based on quaternary ammonium salts. These systems have as disadvantage the low thermal resistance of its modifiers under processing. Ionic liquids (IL) with different molecular structures can be used as organic modifier in lamellar clays-based polymeric nanocomposites, being promising not only to increase interactions between the nanoclay and the matrix, but also to increase the thermal resistance. In this study, polypropylene-based/montmorillonite nanocomposites were compared from two different organic modifiers. The use of short alkyl chain length imidazolium-based IL as montmorillonite modifier was investigated in terms of the thermal stability when compared to the usual quaternary ammonium salt surfactant. Integral procedure decomposition temperature was employed to determine the effect of these two different organoclay modifiers in PP-nanocomposites. The activation energy for these samples was calculated using Flynn–Wall–Ozawa (FWO) method. It was also used the multiple linear regression analysis to calculate the activation energy in order to evaluate the accuracy of this method when applied to nanocomposites. Article Highlights Short length alkyl group in ionic liquid was able to improve the thermal stability of PP-based nanocomposite. IPDT methodology is more realistic to evaluate the thermal stability of ionic liquid-based nanocomposite. MLR methodology was efficient to assess the entropic contribution associated to polymer-clay interactions, inter-lamellae spaces and interface morphology.

APPLICATION OF THE CHROMATOGRAPHIC PARAMETERS IN THE ASSESSMENT OF AMIDE DERIVATIVES’ BIOLOGICAL POTENTIAL

In silico approach is increasingly used in modern design to establish the qualitative / quantitative dependence between structure, physico-chemical properties and biological activity of the new molecule. The selection and application of appropriate molecular descriptors are important step in this process. Given the presence of the amide group in numerous pharmacologically and biologically active molecules, in the pharmaceutical and chemical industries its formation represents an eternal challenge and a significant transformation in the design of the synthetic plan. Evaluation of the biological potential of selected amide derivatives included theoretical and experimental determination of their lipophilicity, analysis of their bioavailability, study of their pharmacokinetic predictors and ecotoxicity parameters. The parameters (RM0, m and C0) obtained by applying reversed-phase thin layer chromatography (RP TLC18 F254s) in the presence of two organic modifiers, as assumed measures of lipophilicity of the examined amide derivatives were correlated with the studied parameters of biological activity by the linear regression method. The quality of the obtained mathematical models was confirmed by the values of statistical validation parameters.