The structure and properties of cold-rolled strips with a thickness of 3 mm from an experimental aluminum alloy 1580 with a lower scandium content of 0.03% (wt.) relative to the grade of the aluminum ...alloy and a 5083 similar alloy without scandium were studied. Ingots obtained at the laboratory installation of semicontinuous casting of the foundry department of the Siberian Federal University (Siberian Federal University, Russia, Krasnoyarsk) were used. The preparation of ingots for rolling included milling up to sizes of 40 × 100 × 145 mm and annealing according to a two-stage mode: at a temperature of 350 °C for 3 h (first stage) and at a temperature of 425 °C for 4 h (second stage). Hot rolling was carried out in the laboratory of the Department of Metal Forming at the Siberian Federal University at a temperature of 450 °C on a two-roll hot rolling mill with a roll diameter of 330 mm and a barrel length of 520 mm to a thickness of 5 mm, which corresponded to a total reduction of 88% with a single reduction of 2–5%. For cold rolling, a two-roll sheet rolling mill with a roll diameter of 200 mm and a barrel length of 400 mm grade LS 400 AUTO was used. Rolling was carried out to a thickness of 3 mm with a single reduction of 2–5%, and then the strip was annealed. The results of determining the mechanical properties by tension by the universal LFM400 machine showed that with an increase in the annealing temperature in the range from 250 to 350 °C for 3 h, ultimate tensile strength of the cold-rolled strips of aluminum alloy 1580 decreases from 385 to 365 MPa. For aluminum alloy 5083, a decrease in this strength characteristic is also observed from 345 to 320 MPa. A decreasing tendency with increasing annealing temperature was also observed for the conditional yield strength
R
p
, and over the entire range of annealing temperatures, the values of
R
p
for strips of alloy 1580 were higher than for alloy 5083 by 35–40 MPa, which amounted to 14–17% The values of the plastic properties, for which the value of the elongation to failure was analyzed, were close throughout the range of annealing temperatures for both alloys. The results of the analysis of micro- and fine structure allowed to conclude that an increase in the strength properties of cold-rolled and annealed sheets from the experimental alloy 1580, compared with alloy 5083, is a consequence of the addition of scandium in the experimental alloy 1580, which leads to an increase in the temperature of recrystallization of the alloy, preserving it contains a subgrain structure and dispersion hardening caused by precipitation of Al
3
(Sc, Zr) phase particles during the decomposition of a solid solution.
The results of experimental investigation of mechanical properties of sheet metal from an experimental aluminum alloys Al-Mg system alloyed with scandium have been represented. It was established ...that the deformed and annealed semi-finished products of these alloys have higher strength properties. Testing of welded samples made from these semi-finished products showed high corrosion resistance and strength of welded joints.
This article analyzes the processability and properties of sheet products made of a large grade 1580 alloy ingot with a lower scandium content in the range of its specifications. The processability ...of the ingot upon hot and cold rolling are estimated and the influence of percent reduction and annealing modes on properties of cold-rolled semifinished products from the alloy under consideration are analyzed. The experiments are performed with a commercial large ingot with a cross section of 500 × 2100 mm made of 1580 alloy with scandium content of 0.067 wt %. The experimental procedure is comprised of several steps of rolling and thermal treatment of sheet semifinished products at various stages of the developed mode of metal deformation and tests of mechanical properties of the respective samples using an LFM 400 kN universal testing machine. In order to perform experiments, a template with the sizes of 60 × 500 × 900 mm is cut out of the ingot and then billets for rolling are produced with sizes of 50 × 180 × 300 mm, which are exposed to homogenized two-stage annealing predeveloped for this alloy. As a consequence of the hot rolling of annealed billets at 450°C and the cumulative percent reduction of ε
∑
= 84–90%, sheet semifinished products are obtained with a thickness of 5–8 mm. Then, after their annealing at
t
= 320°C for 6 h, by means of cold rolling, thin semifinished sheets with a thickness from 2 to 6 mm are produced. Their mechanical properties in deformed and annealed states are analyzed, demonstrating that, upon cold rolling to ε
∑
= 38%, the strength properties of 1580 alloy increase to σ
0.2
= 380 MPa; then, the growth intensity decelerates and, at ε
∑
= 60%, this variable is 400 MPa. The influence of annealing at
t
= 250–350°C on the mechanical properties of sheet semifinished products is also analyzed. It is detected that it decreases the strength properties and increases plasticity; the maximum offset yield stress corresponds to the annealing temperature of 250–275° at sufficiently high plasticity. It is established that, in terms of the strength properties, the sheet semifinished products made of 1580 alloy with lower scandium content are superior to those made of similar AW-5083 (United States) alloy without the addition of scandium by 10–15%, and the plasticity properties are 40–60% higher.
The optimal conditions for the preconcentration of
90
Sr from natural water samples with carbonate-containing zirconium hydroxide of T-3K grade were determined. A method was developed for the ...determination of
90
Sr in natural waters with strontium concentration with T-3K sorbent of a low detection limit: 0.03 Bq/L from 1 L water samples, 0.02 Bq/L from 2 L sample. The method was tested during monitoring of
90
Sr in natural reservoirs in the Sverdlovsk oblast and Chelyabinsk oblast and in water samples from monitoring and observation wells in a long-term RW storage facility locations. It was shown that the developed method can be used without constant monitoring of the yield of strontium in the concentrate for natural waters with a calcium concentration of ≤76 mg/L and a total hardness of ≤5.2 mM, but in view of the established elution yield of 91 ± 1 and 81 ± 2% from 1 and 2 L water samples, respectively, which simplifies and speeds up the analysis. With higher hardness of natural waters, the strontium elution yield as a function of calcium concentration or water hardness reported in the article can be used to determine the yield of strontium in the concentrate.
Aim.
To evaluate strength of magnesium ion complexes with levofloxacin and moxifloxacin.
Materials and methods
. Complexation of levofloxacin, moxifloxacin, and reference ligands ...(ethylenediaminetetraacetate (EDTA), sodium citrate, and glycine) with magnesium ions in the range from 0.0 to 1.0 mmol / l was studied. The technique developed by the authors (patent RU 2680519 C1) was used to measure the rate of a model formation reaction of a magnesium phosphate coarse dispersion. Complexing activity of ligands was expressed in relation to EDTA activity and compared with the theoretical ion exchange equilibrium constants. The half maximal effective concentration (C50) calculated by the Michaelis − Menten equation was used to evaluate the dependence of the complexing activity on the dose.
Results.
A correlation between the activity of EDTA, citrate ions, and glycine and the theoretical equilibrium constants (R = −0.87, p < 0.001) was found. In the range from 0.0 to 0.4 mmol / l, both levofloxacin and moxifloxacin showed a lesser complexing effect than EDTA (p < 0.001), and in the range from 0.6 to 1.0 mmol / l, their complexing effect was comparable (p > 0.050). The activity of fluoroquinolones did not differ at any concentration (p > 0.050), but moxifloxacin C50 (0.13 mmol / l; 95% confidence interval (CI) 0.11–0.15) was significantly lower than that of levofloxacin (0.22 mmol / l; 95% CI 0.19–0.26), (p < 0.001). Within the 0.4–1.0 mmol / l concentration range, the activity of levofloxacin was higher than that of citrate ions and glycine (p < 0.001). Complexing activity of moxifloxacin was higher than that of citrate ions within the range of 0.2–1.0 mmol / l, and in the range of 0.4–1.0 mmol / l, it was higher than that of glycine (p < 0.001).
Conclusion.
The proposed method showed that the complexing activity of fluoroquinolones was close to that of EDTA and exceeded the activity of citrate ions and glycine. The complexation of fluoroquinolones may be associated with their ability to induce side effects associated with magnesium deficiency.
Aim.
To study the effect of proton pump inhibitors (PPIs) on the development of hypomagnesemia in patients with paroxysmal atrial fibrillation (AF) on the background of autonomic sinus node ...dysfunction (ASND).
Material and methods.
A prospective cohort study included 32 patients with an established diagnosis of ASND and often recurrent paroxysmal AF. The main group consisted of 17 patients who took pantoprazole at a dose of 20 mg 2 times a day as treatment of diagnosed duodenal erosions within 6 weeks from the time of the initial visit to an arrhythmologist. The remaining 15 patients did not take PPIs and were included in the control group. The determination of magnesium in whole blood, plasma and formed elements was carried out twice in all patients – at the initial visit and after 6 weeks. In addition, in the experiment, complex-forming activity of solutions of various PPIs (esomeprazole, pantoprazole, rabeprazole and omeprazole) with respect to magnesium ions was studied. The author’s method was used, based on turbidimitric determination of the light transmission during the heterogeneous reaction of the formation of magnesium phosphates in the presence of the analyzed drug or without it.
Results.
There were no significant differences in the magnesium content in the blood of patients of the main and control groups before taking PPIs. After taking of pantoprazole by the patients of the main group there were significant differences between main and control groups in magnesium in whole blood (0.48 0.44-0.51 mmol/l vs 0.55 0.5-0.61 mmol/l, p=0.01) and its values in formed elements (0.52 0.45-0.67 mmol/l vs 0.75 0.65-1.2 mmol/l, p=0.009). Analysis of magnesium content in patients of the main group before and after taking of pantoprazole also showed a significant decrease in intracellular concentrations of the element (0.6 0.51-1.0 mmol/l vs 0.52 0.45-0.67 mmol/l, p=0.002), as well as decrease in its total content in whole blood (0.51 0.45-0.59 mmol/l vs 0.48 0.44-0.51 mmol/l, p=0.04). To substantiate the observed effects it was experimentally proved the possibility of formation of strong complex compounds between the ions of magnesium and PPIs: the highest activity was demonstrated by rabeprazole and pantoprazole (coefficients of complex formation per unit of total organic carbon – 1.5 and 0.72, respectively) and the lowest – omeprazole and esomeprazole (0.04 and 0.09, respectively).
Conclusion.
A decrease of magnesium content in whole blood and formed elements in patients with paroxysmal AF on the background of ADSN was mediated by a six-week intake of pantoprazole in a dose of 20 mg 2 times a day for the treatment of concomitant erosion of the duodenum. When choosing PPIs for arrhythmological patients with concomitant gastro-duodenal pathology, it is advisable to be guided by the complexing activity of drugs with respect to magnesium ions: the most pronounced metal-ligand interaction with magnesium was shown by rabeprazole and pantoprazole, and the least – omeprazole and esomeprazole.
The purpose
of research is to determine directions for optimizing the educational process with the introduction of new methodological approaches. For this purpose, the paper set the tasks to analyze ...the current methodological aspects of the component of the pedagogical process of teaching chemistry to first-year students of the medical and preventive faculty of the Ural State Medical University (USMU, Yekaterinburg); asess the impact of new methodological approaches in teaching on the performance of students. The discipline “Chemistry” is studied in the first semester, classroom hours for the discipline include lectures (32 hours), practical exercises and laboratory work (34 hours), which are conducted at the department of general chemistry of USMU.
Materials and methods.
The methodology for teaching chemistry to first-year students of the medical and preventive faculty of USMU (Ekaterinburg) is analyzed. The largest faculty was selected for the study. Over the course of 10 years, during the period of Federal State Educational Standard-3, the number of students at this faculty increased from two streams in the 2012-2013 academic year (300 people) up to four streams in the 2022-2023 academic year (700 people). Attestation in the discipline takes place in the form of a written test with an assessment (exam). Statistical processing of data on exam results and rating scores in the semester was carried out in the Microsoft Excel 2019 program. The obtained indexes are presented as arithmetic mean values and standard error of the mean (M±m).
Results.
Pearson's r-correlation coefficients were calculated to assess the linear relationship of variables: the percentage of correct answers in the exam ticket, the final student rating in the semester, the exam rating, the certification grade. To test the hypothesis about the effectiveness of the chosen teaching methodology, Pearson's test of agreement (χ2 ) was calculated for the sample size of students (n ≥ 100). The pedagogical process carried out in teaching chemistry to first-year students of the medical and preventive faculty is a complex system that includes target, content, activity, performance, resource components. The activity component of the organization of the pedagogical process was modified as follows: a new form of the examination card was developed, as close as possible to the form of control materials for the unified state exam in chemistry, the structure of the practical lesson was rationalized, and a new laboratory workshop was created and tested. The results of the exam in chemistry were analyzed using Pearson's goodness-of-fit test at a significance level of p<0, 05 in two groups of questions: 1 - on topics covered by a laboratory workshop and 2 - on topics not provided with laboratory work. The rating indexes of students when performing tasks related to the first group of questions are significantly higher than in the second group. ><0,05 in two groups of questions:
1
- on topics covered by a laboratory workshop and
2
- on topics not provided with laboratory work. The rating indexes of students when performing tasks related to the first group of questions are significantly higher than in the second group.
Conclusion.
When using an optimized laboratory practice in chemistry, the most rational form of the lesson is chosen, in which laboratory experiments are included. Comprehensive planning of such classes is carried out differently. The didactic tasks of the lesson are subordinated to highlighting what is essential in the content of the educational material. The presence of an optimized workshop significantly contributes to the choice of the most effective methods and forms of training for a given lesson, leading to an increase in student performance. It is shown that the updated form of the laboratory workshop in chemistry, along with the rationalization of the structure of the lesson and the form of the exam make it possible to achieve maximum learning outcomes with a limited time interval for classroom work. The new form of the examination card, along with the modernized practicum, contributed to the high marks in the exam. It is shown that a properly organized form of passing the exam allows you to adjust the progress of each student and set an objective assessment in chemistry.
As a part of the study, a comparative analysis of different generations three representative’s lipophilic properties of cephalosporin antibiotics, namely cefazolin, cefotaxime and cefepime, was ...carried out. Lipophilicity is a very important physicochemical property of medicinal substances, since it determines their ability to pass through protective barriers, distribute, accumulate in tissues and body fluids, be broken down and excreted, which, in turn, affects the manifestation of antibacterial activity and the cytotoxic effect of antibiotics. During the experiment, a series of drugs aqueous solutions were prepared, then the antibiotics were extracted with highly purified olive oil, after which the aqueous phase was taken and the osmolality value for it was determined. Based on the calibration dependences of the osmolality value on the concentration of the antibiotic in the aqueous phase after extraction, the logarithms of the distribution coefficients in the «oil/water» system were calculated, which is a numerical indicator of the lipophilicity of substances. Using the capabilities of the online platform «Molinspiration Cheminformatics Software», the theoretical values of the studied drugs distribution coefficients logarithms were also determined, and the theoretical values correlated with the experimental ones. Based on the data obtained, it was revealed that the studied antibiotics have low lipophilicity, which decreases in the order: cefotaxime > cefazolin > cefepime. The work also assessed the relationship between solution pH and lipophilic properties. Pearson's r-coefficients between pH and antibiotic concentrations in oil after extraction of cefotaxime and cefazolin show a weak inverse relationship between the studied parameters. For cefepime solutions, a similar linear correlation coefficient demonstrates a direct high relationship between the pH of the solution and the lipophilicity of the antibiotic. The results of the study can be taken into account during antibiotic therapy with appropriate cephalosporins, as well as when creating a new generation of antibiotics. For citation: Kataeva N.N., Naronova N.A., Golitsyna K.O., Belokonova N.A., Shulepova K.E. Evaluation of cephalosporin’s lipophilic properties. ChemChemTech Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.. 2024. V. 67. N 7. P. 55-62. DOI: 10.6060/ivkkt.20246707.7018.
Results of researches of process of hot rolling of ingots from the experimental aluminum alloy which is economically alloyed by scandium are given. The computer model of process of hot rolling with ...the use of which the straining, temperature and speed processing modes conditions is calculated and also power parameters of processing is calculated in applied to industrial conditions. It is shown that the use in the model of a certain shape of the ingot faces (Petrov's lock) and indirect rolling action in the edging stand is made it possible to reduce the likelihood of the formation and further development of micro cracks on the edges of rolled metal. The adequacy of results of modeling was confirmed by carrying out pilot-industrial tests when rolling large-size ingots from the experimental alloy and obtaining batches of hot-rolled plates and sheets of various sizes. The tensile test was used to study deformed samples after rolling and samples obtained on five regimes of heat treatment with varying heating temperatures of 300, 350 and 380 oС and holding time in the furnace for 1 and 3 hours. The results of the studies on samples of hot-rolled sheets 10 mm thick showed that, compared with the initial state, the strength characteristics of the metal after heat treatment are reduced by an average of 12-20%, and plastic characteristics increase by 50-65%. In this case, the heat treatment regimes 1 - 3 give a good ratio of the ductility and plastic properties of the metal.
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