Theoretical and Experimental Chemistry最新文献

Nanosized biocompatible UV (X-ray) luminescent carboxymethylated chitosan, cross-linked and activated with terbium cations, has been obtained and characterized by IR and NMR spectroscopies, UV and X-ray luminescence, and TEM. The material can be used for the development of new bioimaging systems, targeted drug delivery, and release under X-ray irradiation.

The current state of research on heterogeneous photocatalytic systems for selective oxidative transformations of organic compounds of various classes with a singlet oxygen is analyzed. The main physicochemical characteristics of ¹O₂, as well as the mechanisms of its generation and detection, are presented. The processes of selective photocatalytic oxidation of saturated and unsaturated organic compounds, alcohols, aldehydes, organic acids, sulfides, and amines in systems involving solid-state photoactive materials of various nature, in particular organic photosensitizers on porous supports, inorganic semiconductors, covalent organic frameworks, coordination polymers, etc. are considered. Possible directions for further research in this field are outlined.

Polymer microfibres (polymer mats) based on polycaprolactone and filled with metallic silver nanoparticles were obtained by electrospinning. Ascorbic acid was used as a reducing agent for Ag⁺ ions, either individually or in combination with the naturally occurring macrocyclic compound β-cyclodextrin (β-CD), which also stabilizes for Ag⁰ nanoparticles. The presence of Ag⁰ nanoparticles in the fibres was confirmed by UV spectroscopy, X-ray phase analysis method, and transmission electron microscopy. It has been shown that the use of β-CD during the reduction of Ag⁺ ions allows smaller silver crystallites to be obtained, while also resulting in decreased thermal stability of the material. This material can be used for the development of biocompatible composites with an antibacterial activity for a medical applications.

Zinc oxide nanoparticles (NPs) with an average crystallite size of 22 nm and a bandgap energy of 3.26 eV have been obtained using neem (Azadirachta indica) leaf extract as a natural green stabilizing agent. Significant reduction of 2,2-diphenyl-1-picrylhydrazyl (DPPH) quantity by ZnO NPs in dark has been found in the result of DPPH scavenging studies. This effect is explained by reductive action of the compounds from neem extract, immobilized on ZnO NPs, and it is an indicator of their antioxidant activity. It is shown that ZnO NPs demonstrate strong antimicrobial activity against Staphylococcus aureus, Escherichia coli and Candida albicans.

The influence of the preparation method (impregnation of γ-Al₂O₃ vs. sol–gel method) on the physicochemical and catalytic properties of Ni-Mo-Al oxide systems in the CO₂-mediated oxidative dehydrogenation of n-butane into C₄ alkenes/dienes has been analyzed. It is shown that the catalyst obtained by a sol–gel method is characterized by a prevalence of the crystalline Al₂(MoO₄)₃ phase in the composition and a lower acidity/basicity ratio. These features ensure higher selectivity and specific productivity toward the target buta-1,3-diene.

The effect of the polarity and volume fraction of organic solvents (n-heptane, isopropylacetate, ethylacetate, dichloromethane, and 1,2-dichloroethane) on the catalytic benzoylation of alanine, serine, and glutamic acid in a water–organic solvent two-phase system in the presence of pyridine N-oxide derivatives has been studied. It is found that the reaction occurs in a kinetic region, the effective rate constants increase with increasing solvent polarity. The possibility of replacing chlorine-containing solvents with ethyl acetate and isopropyl acetate was demonstrated, resulting in only a minor decrease in reaction rate (~10%) without a significant reduction in product yield.

Floating perlite-TiO₂ and perlite-TiO₂/Ag composites have been obtained and their photocatalytic performance in the photodegradation of polycyclic aromatic hydrocarbons (PAHs), namely anthracene, pyrene, fluoranthene, and benz[a]anthracene, has been investigated. The phase composition and morphology of the samples have been characterized by X-ray diffraction analysis, TEM, and SEM methods. It is shown that the floating perlite-based composites exhibit high photocatalytic activity, providing more than 85% degradation of the studied PAHs under UV irradiation within 180 min.

The equilibrium geometry and electronic structure of oligomers modeling the polymer poly[2,6-(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-alt-4,7-(2,1,3-benzothiadiazole)] (PSBTBT) with several monomeric units ranging from 1 to 10 have been calculated using density functional theory (B3LYP/6-31G**). The computational results indicate that, for the investigation of materials used in organic solar cells (including determination of frontier molecular orbital energies, exciton dissociation energies, etc.), large polymer systems can be substituted by studying their lower oligomer analogues.

A Cu₂O layer was formed on a SnO₂ substrate by electrochemical deposition from an alkaline citrate electrolyte. This layer was then treated with hydroiodic acid solution to form a film consisting of γ-CuI crystals with size of 70-90 nm. It is shown that CuI in the film behaves a p-type semiconductor, which photosensitive in the 300-420 nm range and exhibits a maximum photocurrent at potential E = –0.33 V vs. silver chloride electrode. The developed method for forming CuI films can be used to determine concentration of copper ions in the initial electrolyte

The results of a study on the stability of the activity and selectivity of Ga- and Zn-containing catalysts based on BEA zeolite in the oxidative dehydrogenation of propane with CO₂ have been analyzed. According to X-ray diffraction, nitrogen adsorption/desorption, and Raman spectroscopy data, the observed changes in catalytic activity and selectivity over 10 h of operation are attributed to surface carbonization involving Brønsted acid sites. The catalytic activity is restored after regeneration in a temperature-programmed oxidation mode (20% O₂ + 80% He, 650°C).