Betulin, a natural triterpene possessing a wide range of biological activities, has been modified via Steglich esterification to produce a methacrylate derivative capable of participating in radical ...polymerization. The modification is intended to increase the solubility of betulin, which is almost insoluble in water, by incorporating into the composition of an amphiphilic copolymer. The resulting solubility of betulin in water increased from 8·10−5 mg/mL to more than 10 mg/mL per betulin. For this, well‐defined biocompatible thermoresponsive copolymers with high betulin content have been synthesized through the conventional and RAFT copolymerizations of betulin methacrylate (BeMA) with methoxy oligo(ethylene glycol) methacrylate (MOEGMA). BeMA was more reactive in the BeMA‐MOEGMA pair; the resulting copolymers were slightly enriched with BeMA units (r1 = 1.70, r2 = 0.93). The copolymers exhibited LCST‐type behavior. LCST was tuned by balancing the hydrophobic betulin and hydrophilic OEG fragments. The molecular weight characteristics of polymers and their behavior in aqueous and organic solutions have been studied. Copolymers obtained by conventional polymerization had lower cloud points than RAFT copolymers of the same composition. The copolymers are characterized by low critical micelle concentrations that decrease as the BeMA fraction in the copolymers increases. RAFT copolymers were shown to form unimolecular micelles resistant to dissociation, which is promising for their use in targeted drug delivery.
Display omitted
•The resistance of poly(ethylene glycol) methacrylates towards hydrolysis is independent of the ethoxylated chain length.•Nontrivial concentration dependences of the hydrolysis rate ...are associated with a change in acidity.•Pronounced self-acceleration of hydrolysis with increasing conversion is observed when using methacrylic acid as a catalyst.•The hydrolysis kinetics is described by a second order equation.
Hydrolysis of water-soluble industrially important mono- and poly(ethylene glycol) methacrylates catalyzed by sulfuric acid and organic monomeric acids (methacrylic and 2-acrylamido-2-methylpropanesulfonic acid) has been studied in aqueous solutions. Chemical stability of the methacrylates in dilute solutions was found to be independent of the length of ethoxylated fragments. Structurization of the studied solutions and the increase in concentration of hydrogen ions in concentrated solutions of the ethoxylated esters were shown to be the reason for the revealed unusual influence of the initial monomer concentration on the hydrolysis rate. The pronounced self-acceleration effect was observed for the methacrylic acid catalyzed reaction with increase in conversion.
Gaseous detector with a sub-keV electron equivalent threshold is a very perspective tool for the precision measurement of the neutrino magnetic moment and for observing coherent scattering of ...neutrinos on nuclei. The progress in the development of low noise electronics makes it possible to register the rare events at the threshold less than 100 eV. The construction of the gaseous detector is given and the typical pulses with amplitudes of a few eV observed on a bench scale installation are presented. The possible implications for future experiments are discussed.
A procedure for assessing processes that occur in a rock mass during the creation of underground workings and predicting the stress-strain state of the mass during continued excavation, which has ...been adopted for design substantiation of the final construction of the Rogunskaya HPP, is described. The proposed method of evaluating development of deformation in a rock mass enclosing a working and mathematical interpretation of separate stages of deformation development can also be adopted as a basis for other entities.
Introduction. In the current process of climate change, the phenomenon of unusual rainfall and flooding is causing widespread flooding and causing great loss of life and property. In addition, the ...most vulnerable structures are dams and reservoirs. A dam failure causes a disaster that can threaten human lives and entire socio-economic activities. There are many causes of dam failure, of which hydraulic fracturing is considered one of the most likely causes as it causes concentrated seepage leading to the risk of dam failure. Hydraulic fracturing is a process in which cracks form in soil or rock and then propagate under water pressure. Hydraulic fracturing is not a new topic, nor is it an old one, receiving a lot of attention from scientists, but it is still a controversial issue. Many opinions are given. This paper aims to summarize the mechanism of hydraulic fracturing based on previous studies and at the same time proposes some methods to prevent hydraulic fracturing in an earthen dam.Materials and methods. Literature analysis of sources related to the phenomenon of hydraulic fracturing.Results. Hydraulic fracturing is closely related to the phenomena of differential settlement of dam soils and building structures. In earth-fill dams, the phenomenon of differential settlement often occurs in the areas between the fill soil of the dam and the side masses of the dam site, fill soil and concrete structures such as culverts and spillways, foundation structural elements, the impermeable core of the dam and adjacent soil zones. Based on an analysis of the causes of hydraulic fracturing, a number of measures were proposed to reduce the risk of hydraulic fracturing.Conclusions. Hydraulic fracturing, that is, the formation of cracks and cavities in the soil mass, which contribute to the formation of concentrated seepage paths. The occurrence of hydraulic fracturing increases the likelihood of seepage instability in the dam, which affects the safety of the dam and can lead to serious damage. Implementing hydraulic fracturing prevention techniques is critical to ensuring safe dam operating conditions.
Photocatalytic fatigue of the polymer nanocomposites Orekhov, Andrey V.; Artem’ev, Yurii M.; Pavilaynen, Galina V.
Vestnik of Saint Petersburg University. Applied Mathematics. Computer Science. Control Processes,
2022, Letnik:
18, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We discuss the change in mechanical properties of polymeric nanocomposites with photoactive components caused by solar range lighting. Given degradation photoassisted processes are related with the ...semiconductor nature of component photoactive particles as photocatalysts. Semiconductor particles can be transferred into electron-exited states due to light quanta absorption. One possible way out from these states is through redox electrochemical reactions with neighbor molecules. The redox reactions can produce transformations of polymer structure and composition, decreasing its mechanical strength. The term “photoca-talytic fatigue” denotes a special case of the photo-degradation of polymers resulted only in a change in the strength value of the material. We review not numerous published data on investigations of changes in mechanical properties of polymeric nanocomposite, and mainly in the strength value, arisen from solar range light irradiation. We compare the degradation processes of polymeric nanocomposites containing photoactive components and of the high-cycle fatigue in metals. Likewise, we propose the use of equations of metal high-cycle fatigue curves as a possible approach to mathematical modeling of the processes of polymeric nanocomposites photodegradation. In this, the number of cycles is substitution with exposure time. Especially, the high-cycle fatigue curve equation for the samples with stress concentrations is considered. The experimental parameters of the “photocatalytic fatigue” equation for polymer nanocomposites containing photoactive components are calculated using the Monte Carlo method.
MUNIN (Multidimensional NMR Spectra Interpretation), a recently introduced approach exploiting the mathematical concept of three-way decomposition, is proposed for separation and quantitative ...relaxation measurements of strongly overlapped resonances in sets of heteronuclear two-dimensional spectra that result from typical relaxation experiments. The approach is general and may also be applied to sets of two-dimensional spectra with arbitrary modulation along the third dimension (e.g., J-coupling, diffusion). Here, the method is applied for the analysis of 15N rotating frame relaxation data.
We conducted the first genetic analysis of a wide a range of rural Russian populations in European Russia with a panel of DNA markers commonly used in Human DNA identification. We examined a total of ...647 samples from indigenous ethnic Russian populations in Arkhangelsk, Belgorod, Voronezh, Kursk, Rostov, Ryazan, and Orel regions. We employed a multiplex genotyping kit, COrDIS Plus, to genotype Short Tandem Repeat (STR) loci, which included markers officially recommended for DNA identification in the Russian Federation, the United States, and the European Union. In the course of our study, we created a database of allele frequencies, examined the distribution of alleles and genotypes in seven rural Russian populations, and analyzed the genetic relationships between these populations. We found that, although multidimensional analysis indicated a difference between the Northern Russian gene pool and the rest of the Russian European populations, a pairwise comparison using 19 STR markers among all populations did not reveal significant differences. This is in concordance with previous studies, which examined up to 12 STR markers in urban Russian populations. Therefore, the database of allele frequencies created in this study can be applied for forensic examinations and DNA identification among the ethnic Russian population over European Russia. We also noted a decrease in the levels of heterozygosity in the northern Russian population compared to southern and central Russian populations, which is consistent with trends identified previously using classical gene markers and analysis of mitochondrial DNA.
PDF
