Moscow University Chemistry Bulletin最新文献

FT-infrared and Raman spectra of 2-(2'-pyridyl)imidazole (2PI) in the solid state, as well as FTIR solutions spectra in carbon tetrachloride and dichloromethane, are investigated. Quantum-chemical calculations of the 2PI molecule and some of its clusters are fulfilled within several theory levels. Based on the joint analysis of the experimental and simulated data, the spectra are interpreted, taking into consideration the possibility of the formation of intermolecular hydrogen bonds.

The content of phenolic compounds and essential oil of four samples of Mentha longifolia L. of various origins is determined. As a result of the GC-MS analysis of the essential oil, significant intraspecific variability in the component composition is revealed. Mentha longifolia L. accumulates predominantly oxygenated monoterpenes formed according to the scheme limonene–piperitеnone–piperitone or pulegone, and their derivatives, in most cases without synthesizing in large quantities those following in the chain of biosynthesis, menthone and menthol, which are characteristic of peppermint.

This study focuses on producing alumina using a modified citrate method. The process involves thermally activating a chelate through biphasic drops between hydrated aluminum nitrate and citric acid. Thermal analysis via DSC/TGA followed by FTIR revealed absorption bands at varying temperatures until the formation of white crystallized alumina powder at 1000°C. XRD analysis indicated that the resulting sample has a refined hexagonal structure with the space group R-3c. SEM/EDAX analysis displayed a morphology resembling overlapping hives with a major chemical composition of Al and O. The dip-coating method applied a semi-colloidal Al-citric acid sol onto E335 steel substrate at a stable processing temperature of 700°C, confirmed by XRD analysis showing the formation of new crystals like AlFeO₃ and Al₁₁Fe₇. This structural configuration influenced dislocation density and microstrain inversely with grain size. SEM and EDS analysis confirmed the adhesion of alumina to the substrate through intermetallic phases.

This review presents the history of research on the luciferin–luciferase system of fireflies Luciola mingrelica at the Division of Chemical Enzymology, Department of Chemistry, Moscow State University, which began in the mid-1970s at the initiative of the first head of the Department, Professor I.V. Berezin. Based on the study of the kinetics of enzymatic oxidation of luciferin, a kinetic scheme of the reaction was proposed, according to which in an aqueous solution the luciferase reaction is a nonstationary enzymatic process and the turnover of the enzyme is very small due to the slow dissociation of the enzyme–product complex. Analysis of the bioluminescence and fluorescence spectra of the reaction product oxyluciferin and its analogs led to the conclusion that keto–enol tautomers of the phenolate forms of oxyluciferin (ketone, enol and enolate ion) are the most likely emitters in the luciferin–luciferase system of fireflies. Native luciferase preparations have been shown to contain phospholipids, whose removal leads to a decrease in the activity and stability of the enzyme. At the beginning of the 1990s, L. mingrelica luciferase was cloned. The enzyme in the primary sequence turned out to be close to other luciferases of the genus Luciola, cloned in Japan (more than 80% homology), but differed from the previously studied luciferase from American P. pyralis fireflies (67% homology). Using methods of random and site-specific mutagenesis, a library of mutant forms of L. mingrelica luciferase with altered bioluminescence spectra (green and red luciferases) was created. Thermostable mutants of luciferase were obtained by the method of directed evolution, and in particular, a highly active and thermostable mutant (4TS), on the basis of which an ATP-reagent was developed, which is still widely used in bioluminescent analysis by many researchers in Russia. Genetic engineering, computer modeling and site-specific mutagenesis methods have been used to clarify the role of the dynamic structure of the enzyme in the complex, three-stage oxidation of the luciferin. It has been shown that the emitter (electronically excited oxyluciferin) is an intramolecular label in the enzyme’s active site. The superposition of two or three emitter forms fixed in the bioluminescence spectra indicates the coexistence of various conformational forms of luciferase in the reaction medium, which are in dynamic equilibrium.

A method for the determination of nitrate in soil with digital image colorimetry is proposed. This approach is based on photometric methods for the determination of nitrates after extraction with potassium chloride from soil samples. The original method for determining nitrate as an azo dye (a product of the azo coupling reaction of 1-naphthylamine and sulfanilamide) is modified to achieve higher sensitivity and accuracy of colorimetric determination. This approach provides the metrological characteristics of the digital image colorimetric method that are similar to spectrophotometric ones. The adequacy of the proposed method is confirmed by analyzing standard samples and soil samples collected in the Moscow oblast.

The interaction mechanism of plant antioxidants is studied with IR and NMR spectroscopies (rutin interacts with a 2-hydroxypropyl-β-cyclodextrin as an example). Rutin is characterized by the aromatic skeleton’s incorporation into the cyclodextrin torus and stabilization brought about by the interaction between the cyclodextrin’s –OH groups and the carbohydrate moiety.

This article dealt with the saturated solubility values of deferiprone (which is an iron chelator agent) in aqueous mixtures of 1-propanol using experimental measurements as well as mathematical correlations. The solubility of deferiprone demonstrated a positive correlation with temperature and 1-propanol content. Four mathematical models were employed to correlate the solid-liquid equilibrium data, and the fitting results demonstrated that the computed solubility results from the employed computational cosolvency models were in good agreement with the experimental data. It was anticipated that these experimental solubilities, density values, and correlation results can be employed for pharmaceutical development such as purification, drug manufacturing, crystallization, and extraction on an industrial scale as well as in theoretical research.

The development of new heat-resistant cobalt alloys for the aerospace industry allows exceeding the temperature capabilities of nickel superalloys. Cobalt alloys, however, are less resistant to high-temperature oxidation, and alloying cobalt alloys with aluminum or chromium can lead to the formation of brittle topologically dense phases. As a solution to this problem, surface alloying with the chromium of cobalt alloys, carried out by the interaction of their preoxidized surface with chromium from the gas phase, is proposed.

This review focuses on the main methods for obtaining functionally substituted phthalocyanine complexes, as well as the precursor phthalonitriles containing various hydrophilic and hydrophobic groups. It presents a comparison of the optical and photochemical properties of phthalocyanines, including pathways for generating reactive oxygen species. The potential applications of phthalocyanines are outlined, including photocatalysis, fluorescent diagnostics, and photodynamic therapy for cancer and antibacterial treatments.

The use of drug delivery systems requires an understanding of the release kinetic patterns of an encapsulated drug or a model compound. In this work, the zero-order release of the pH-sensitive nitroxide radical 5,5-dimethyl-4-dimethylamino-2-ethyl-2-(4-pyridyl)-2,5-dihydroimidazole-1-oxyl (DPI) from poly-D,L-lactide (PDLLA) films into aqueous buffer solution was studied with continuous-wave electron paramagnetic resonance spectroscopy (EPR). The EPR method allowed for quantifying the DPI release kinetics from PDLLA films and analyzing rotational mobility and the concentration of the spin probe inside the films during their swelling and degradation. The EPR data were globally analyzed within the previously proposed phenomenological diffusion model based on the processes of pores formation and overgrowth in polyester films. The interaction between the doubly protonated DPI cation, formed in acid media inside the polymer pores, and the counterions of (oligo)lactic acid is proposed. Such interaction leads to the formation of bulk DPI-containing paramagnetic aggregates which make the release kinetics diffusion-controlled. This is in contrast to the pore-formation control observed for the standard spin probe 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxide (TEMPOL). Therefore, the release rate depends on the thickness of the film and the size and the charge of the dopant. Keywords: poly-D,L-lactide films; spin probes; electron paramagnetic resonance; mechanism of drug release; mathematical model of the release kinetics; zero-order release.