Doklady Chemistry最新文献

The parameters of the synthesis of catalysts by the solution combustion method using oxalic acid as a reducing agent were investigated. The activity of the catalysts was determined in the production of hydrogen and carbon nanofibers by the catalytic decomposition of methane. The efficiency of oxalic acid was demonstrated in the preparation of a nickel catalyst (90% Ni/10% Al₂O₃), which does not require the preliminary reduction with hydrogen. Regression analysis identified that the yields of carbon and hydrogen are most strongly affected by temperature among other synthesis parameters.

Glassy chalcogenides A^VB^VI obtained by solidification of high-temperature melts inherit the polymolecular nature of the melt. The influence of this circumstance on the optical properties of glasses is important for the fabrication of optical fibers and has not been adequately studied. Bulk samples of high-purity As_40 – xS_60 + x glasses (0 < x < 5) containing less than (1–2) × 10^–5 wt % metal and silicon impurities and not more than (0.5–1) × 10^–4 wt % carbon, oxygen, and hydrogen compounds were manufactured, and optical fibers were fabricated from these materials. The IR spectra of 12 cm-long bulk samples and optical fibers of up to 15 m length were recorded in the 1000–2000 cm^–1 spectral range. The spectra of the bulk samples and the optical fibers showed absorption bands with maxima at 1950, 1805, 1460, and 1320 cm^–1, due to the presence of super-stoichiometric amount of sulfur in the glass. The corresponding extinction coefficients were determined. The results of the study indicate that the stoichiometry of As₂S₃ can be considered as a factor significantly affecting the optical characteristics of glass.

The study is aimed at the development of a non-catalytic process for removal of nitrogen oxides from flue gases of thermal generating units. The results of experimental studies of a modified two-stage selective non-catalytic reduction of nitrogen oxides with injection of a reducing agent (urea) below the stoichiometric amount in each stage are described. The possibility of attaining a higher and more stable reducing efficiency compared with the conventional one-stage process and minimization of the formation of ammonia as a secondary pollutant is demonstrated.

New 1,5,3,7-diazadiphosphacyclooctanes with N,O-, N,N-, N,S-, and N,N,S-heterocyclic substituents at the nitrogen atoms have been synthesized. The influence of the nature of amines containing sp²-hybridized nitrogen atom in the ortho-position of the heterocyclic substituent on the result of Mannich condensation in phosphine–paraformaldehyde–primary amine system has been revealed. The stabilization of intermediate acyclic products—aminomethyl(hydroxymethyl)arylphosphines and bis(aminomethyl)arylphosphines—due to amino–imine tautomerism is responsible for the low yield of the target cyclic diphosphines based on the above amines.

Dipinodiazafluorenes are hybrid nopinane-annelated heterocycles whose molecules include a heterocyclic core of 4,5-diazafluorene fused with fragments of terpene hydrocarbon; they can selectively extract palladium (88−100%), gold (42−96%), and ruthenium (8−19%) by single extraction from acidic aqueous solutions (pH 1.2) containing complex mixtures of 3d elements and noble metals.

A one-pot synthesis of random multiblock copolymers of norbornene and cyclooctene was performed for the first time. It was shown that the first-generation Grubbs Ru–carbene complex enables the synthesis of these copolymers directly from monomers. The one-pot synthesis starts with the metathesis polymerization of norbornene, which has a markedly higher ring strain. Then cyclooctene polymerization takes place, being accompanied by interchain macromolecular cross-metathesis, to give the block copolymer structure. In comparison with the previously studied reaction of polynorbornene and polycyclooctene, the one-pot method affords copolymers with a higher molar weight at a lower catalyst consumption.

The review characterizes the role of the basic targets of antibacterial agents: efflux pumps, enzymes (DNA gyrases as a subclass of topoisomerases, homoserine transacetylase, various classes of sortases, aromatase, lipoteichoic synthase, polyketide synthase, pantothenate synthetase, acetyl-CoA carboxylase, sensory histidine kinase, kinase, cyclooxygenase, etc.), penicillin-binding protein, quorum sensing systems, and adhesins in significant biochemical processes of pathogen maintenance and virulence manifestation. It has been demonstrated that a chemical can exhibit the antimicrobial effect when it binds to protein molecules responsible for pathogenicity of a microorganism. The role of quinazolinone derivatives exhibiting high reactivity and stability in chemical processes and characterized by a wide spectrum of pharmacological activity, including antimicrobial activity with respect to various Gram-positive and Gram-negative bacteria, has been determined. It has been shown that structural changes induced by introducing various substituents contribute to a change in the degree of hydrophilicity and, as a result, determine a different degree of penetration of the drug through the cell membrane, the ability to form intermediate complex compounds stabilized by a system of hydrogen bonds, as well as by van der Waals and stacking interactions, with enzymatic targets, receptor regulatory proteins, and signaling systems of pathogen cells. The results of mathematical modeling of the mechanism of action of the compounds synthesized by the authors of the article are discussed. The possibility of creating a pharmaceutical with a pronounced antimicrobial activity by combining the quinazolinone core with various heterocyclic derivatives is assessed. The considered regularities are of practical importance for the researchers in the field of medicinal chemistry, organic synthesis, biotechnology, clinical pharmacology, and pharmaceutical chemistry and technology, whose efforts are aimed at designing a new drug.

In the course of synthesis of oligosaccharides related to fragments of the capsular polysaccharide of Haemophilus influenzae type e, reactions of 2-O-trifluoromethanesulfonate β-D-glucopyranoside derivatives with the azide anion were studied. The reactions gave products of both nucleophilic substitution and rearrangement accompanied by 6-membered pyranose ring contraction to a 5-membered ring through (O5–C2)-cyclization. The formation of these products was interpreted for the first time using quantum mechanical calculations.

3-Bromo- and 6-chloroquinolines or 2-bromo-1-methylbenzimidazole react with red phosphorus in the KOH/DMSO (Н₂О) system on heating (100–120°C, 3 h) to form in high yield the products of selective reduction (with retention of the aromatic heterocycle): quinoline or 1-methylbenzimidazole, respectively.

A simple and feasible approach to the synthesis of new amine derivatives of acridine based on the methodology of direct C–H functionalization has been developed. The inhibitory effect of the synthesized compounds toward cholinesterases and carboxylesterase as well as their antioxidant activity have been studied. A high anti-BChE activity has been shown for N-methylpiperazine derivative promising for further optimization to design on its basis new series of compounds efficient for the treatment of neurodegenerative diseases.