Moscow University Chemistry Bulletin最新文献

The contact printing method is widely used to create microchips and develop highly sensitive biosensors. This method is based on techniques for immobilizing biomolecules. In this work, two effective methods for covalent immobilization of oligonucleotides based on reactions of disulfide bond formation and azide–alkyne cycloaddition are optimized for the contact printing method. With both immobilization strategies, oligonucleotides retain the ability to hybridize with complementary DNA, which provides a basis for their practical use in bioanalytical applications.

In the green bacterium Chloroflexus aurantiacus, photosynthesis begins with light absorption by unique light-harvesting complexes known as chlorosomes. These structures consist of ~10⁴ molecules of bacteriochlorophyll (BChl) c, which assemble into intricate spatial configurations. Upon absorption of blue light (~460 nm) by the B band of the chlorosome, ultrafast energy conversion occurs, resulting in the excitation of the red Q_y band (~740 nm). We study this process using differential (light – darkness) absorption spectroscopy with a high temporal resolution (20 fs). The characteristic conversion time is determined to be 35 fs. Energy conversion precedes the slower exciton relaxation processes in the Q_y band (100–300 fs) and the energy transfer from the chlorosome to the baseplate and subsequently to the reaction center (tens of picoseconds). The physicochemical principles underlying intramolecular energy conversion in chlorosomes and the significance of this process for photosynthesis are discussed.

The structures of small silver clusters (Ag_n, n = 1–3, n =13) and their complexes with 7-aminocholesterol (NCh) are calculated using density functional theory with B3LYP5 parameterization. The 7-aminocholesterol ligand has two active coordination centers: lone pairs on the N- and O-atoms. Trends in the geometric structure and interaction energy of the silver–7-aminocholesterol complexes are evaluated depending on the size of the metal cluster. It is found that coordination of the metal cluster to the nitrogen atom is preferable in all cases. The most stable complex is Ag₃–NCh (Ag₃–(N)–NCh), for which the dissociation energy reaches 15.6 kcal/mol.

A method of one-stage cationization and crosslinking of potato and corn starches using epichlorohydrin as a crosslinking agent is developed. Samples of crosslinked cationic potato and corn starches with controlled viscosity properties are synthesized, whose aqueous dispersions exhibit pseudoplastic properties at various temperatures and degrees of crosslinking. It is found that the obtained crosslinked cationic starches retain their granular structure, and the degree of crystallinity of the samples slightly decreases regardless of the temperature (20–45°C), reaction time (24–96 h), and dose of the crosslinking agent (0.05–5.0%). It is shown that the rate of flocculation of kaolin suspensions increases with the increasing dose of the flocculant for all types of cationic starches. Regardless of the dose, the maximum sedimentation rate of kaolin in model systems is observed when using crosslinked cationic potato starch. The results obtained can be used to develop a technology for producing biodegradable crosslinked cationic starches as effective flocculants for cleaning aqueous solutions as an alternative to synthetic polyacrylamide derivatives.

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.