Moscow University Chemistry Bulletin最新文献

Four amino phases representing 3-aminopropyl silica gel batches with different numbers of grafted functional groups are compared. To evaluate the chromatographic properties of the adsorbents, the Tanaka test for hydrophilic stationary phases is used and the retention of polar substances of various classes in the HILIC (hydrophilic) mode is studied. It is shown that even small changes in the nitrogen content between different batches of 3-aminopropyl silica gel have a significant effect on the retention of polar analytes. The hydrophilicity of a substrate is shown to have the greatest effect on its chromatographic behavior, and its evaluation using the Tanaka test is the basis for selecting a batch to separate specific classes of polar substances or for further modification to obtain new phases.

The acid–base properties of 1,2,3-benzotriazole (Bta) at 25°C and I = 0.1 mol/L KCl are studied in an aqueous solution by the pH-metric method. It is found that in the strongly acidic region of the solution, one of the two nitrogen atoms of the pyridine type of the Bta triazole rings undergoes protonation, and at high pH values, hydrogen abstraction occurs from the NH fragment of the molecule. The obtained values of the protonization constants of 1,2,3-benzotriazole log K₁ and log K₂ are 8.27 and 0.65, respectively. Using the potential of a silver electrode, the equilibria of silver(I) complex formation with 1,2,3-benzotriazole are studied. The data obtained indicate that Ag⁺ replaces the hydrogen ions of the ligand molecule and forms AgBta and ({text{AgBta}}_{2}^{ - }) complexes with the stability constants log β₁ = 8.50 (AgBta) and log β₂ = 12.65 (({text{AgBta}}_{2}^{ - })).

This article defines a group of intermolecular contacts for a monosystemic molecular structure described by one of the crystallographic symmetry groups (space, subperiodic, point) in n-dimensional Euclidean space with unoccupied special positions. The definition of a monoid of contacts for a polysystemic molecular structure is given. Crisp and fuzzy Cayley graphs of groups and monoids of contacts are constructed. Some examples of crystal structures are considered.

A design is proposed for a crucible electrothermal atomizer with a vertical arrangement of evaporation, condensation, and atomization zones in graphite cylindrical blocks with transverse heating. The heat treatment is carried out in such a cylindrical column: the evaporation of a solid sample evaporation and the condensation of vapors, and then the evaporation of the condensate into the atomization zone, in which vapors were filtered through the porous medium of the graphite filter into the analytical zone. The metrological characteristics of the determination of elements in solid organomineral samples are improved due to the separation of matrix components and the reduction of interference.

The dynamics of sedimentation of whole blood cells and erythrocyte mass during sequential dilution with dextran solutions in vitro has been studied. Nonmonotonic changes in the optical density of the border between erythrocytes deposited both in their own plasma and in model systems were revealed. Fluctuations in the average and instantaneous rates of the process recorded at the boundary of cell subsidence confirm the nonlinear and cooperative nature of erythrocyte sedimentation, which is associated with the formation and separation of phases between cellular, liquid and gaseous components of blood. The structural reorganization of this dynamic system can be modulated in various ways, for example, by adding dextran solutions used in clinical practice in the case of blood loss, for detoxification, treatment and prevention of thrombophlebitis and shock conditions. It has been shown that the macro- and microkinetics of the erythrocyte sedimentation process depends both on the degree of dilution of blood (or model systems) by dextrans and on their molecular weight. The results obtained are consistent with the phase hypothesis of the settling of blood cells as a biocolloid, and can also be used in clinical hemotransfusiology to select an individual dosage of infusion solutions.

New recombinant strains of Penicillium verruculosum with a high level of expression of homologous endo-β-1,4-glucanase II and heterologous phytase A of A. niger, as well as heterologous endo-1,4-β-xylanase E of P. canescens and phytase A of A. niger, are created. This allows us to obtain highly active feed enzyme preparations (EPs) capable of simultaneously significantly reducing the viscosity of nonstarch polysaccharides (NPSs), as well as increasing the bioavailability of phosphorus and minerals of grain-based feed and, thus, increasing the digestibility of nutrients of agricultural animal and poultry feed. Specific EP activities for specific substrates (xylan, β-glucan, and phytate) are studied and the qualitative and quantitative component composition of new EPs is determined. A recipient strain δnia D, into which heterologous endo-1,4-β-xylanase E of P. canescens is successfully cloned, is obtained based on a new enzyme preparation containing homologous endo-β-1,4-glucanase II and heterologous phytase A of A. niger. In this way, a promising producer of three target enzymes is obtained simultaneously.

The tacA gene encoding the TacA repressor protein is cloned by the method for “walking” in uncloned DNA from the genomic DNA of the fungus Penicillium verruculosum B1-221-151. Knockout of the tacA and niaD genes by the CRISPR/CAS9 method leads to the production of a new recipient strain P. verruculosum ΔniaDΔtacA, characterized by a higher rate of extracellular protein biosynthesis. Analysis of the cbhI gene transcription and expression in the original P. verruculosum B1-221-151 strain and in the P. verruculosum ΔniaDΔtacA strain shows a sharp increase in the level of the cbhI gene transcription as early as 2 h after the start of induction with cellobiose, cellotriose, gentiobiose, and a mixture of di- and trisaccharides compared with transcription of the cbhI gene in the original strain. The specific activity of cellobiohydrolase I, the main enzyme of the cellulolytic complex of the P. verruculosum fungus, tripled after 96 h of fermentation of the ΔtacA strain compared with the initial strain.

The effectiveness of drug penetration into the inner tissues of the eye under local application is significantly limited by the barrier effect of the cornea and by the washout of the drug with the lacrimal fluid. To increase the bioavailability of a drug, it is proposed to include the drug in the chitosan particles formed by two types of chitosan: 5 kDa chitosan and 72 kDa glycol-chitosan. Chitosan particles with the loaded angiotensin-converting enzyme inhibitor enalaprilat, capable to reduce intraocular pressure, are characterized by dynamic light scattering and scanning electron microscopy. Particles formed by 5 kDa chitosan have an average hydrodynamic diameter from 85 to 125 nm and a positive ζ potential of +21 ± 3 mV, while particles formed by 72 kDa glycol-chitosan have a size from 440 to 480 nm and are characterized by a ζ potential of +10 ± 2 mV. The percentage of enalaprilat inclusion in the chitosan particles is 25% and 40%, respectively. In vivo experiments showed that the inclusion of the drug int the chitosan particles can increase the retention time of enalaprilat in the lacrimal film of rabbits.

NAD⁺-dependent formate dehydrogenase (FDH, EC 1.2.1.2) from methylotrophic bacterium Pseudomonas sp.101 (PseFDH) has one of the highest thermal stability among all known enzymes of this group. The introduction of a number of amino acid substitutions into PseFDH made it possible to obtain a multipoint mutant PseFDH SM4S enzyme with even higher temperature and chemical stability. Previously, we showed that the introduction of additional single point replacements S131A, or S160A, or E170D into PseFDH SM4S led to further stabilization of the enzyme. In this work, based on the PseFDH SM4S S131A mutant, new mutant FDHs obtained, in which, compared to PseFDH SM4S, we added double S131A/E170D (M2), triple S131A/S160A/E170D (M3) and quadruple S131A/S160A/E170D/S145A (PseFDH SM4A M3) amino acids replacements. The new PseFDH mutants were overexpressed in E. coli cells, purified and characterized. The S131A/E170D and S131A/S160A/E170D changes provided further improving thermal stability. The introduction of the S145A substitution into PseFDH SM4A M3 leads to a significant decrease in (K_{{text{M}}}^{{{text{NA}}{{{text{D}}}^{ + }}}}) and (K_{{text{M}}}^{{{text{HCO}}{{{text{O}}}^{ - }}}}) while maintaining the catalytic constant at the same level. This mutant form can be successfully used in NADH regeneration systems, as well as for the detection of NAD⁺ and formate in biological systems.