Физическая химия. Рубрика в журнале - Вестник Южно-Уральского государственного университета. Серия: Химия
Статья научная
Adsorption of malachite green dye over the adsorbents (Ad) derived from Sapindus seed hull (S) and Camelina (C) after treatment with sulphuric acid is studied. Batch adsorption study on both Ad is compared as a function of various parameters such as pH, time, initial concentration and temperature. The isotherm data is found to be best presented by Langmuir model for both adsorbents. Separation factor (RL) revealed a favorable adsorption. Further, the rate of adsorption followed pseudo-first order kinetics. The intraparticle diffusion model facilitates to understand mass transfer in adsorption of dye molecules. Thermodynamic analysis on both Ad revealed the spontaneity of the phenomena at higher temperature. The comparative study illustrated higher adsorption capacity of CAd in comparison to SAd.
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Calorimetric study of polyketone formed from carbon monoxide, ethylene and butene-1
Статья научная
The temperature dependence of the heat capacity for partially crystalline polyketone derived from carbon monoxide with ethylene and butene-1 (the butane units content is 14.6 mol %) was studied over the range 6-520 K by the methods of precision adiabatic vacuum calorimetry and differential scanning calorimetry. Thermodynamic characteristics of the glass transition and glassy state and melting characteristics were determined. The standard thermodynamic functions, namely, C0p, H0(T) - H0(0), S0(T) - S0(0) and G0(T) - G0(0), were calculated for the temperature range from T → 0 to 400 K, based on the experimental data. Thermal stability temperature for polyketone (520 K) has been specified by the thermogravimetry method.
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Capabilities of structure modeling for azaheterocycles and the comparison to FTIR spectroscopy data
Статья научная
The capabilities of algorithms Globa-AlteQ, MultiGen-AlteQ, MOPS-AlteQ for modeling the structures of both individual molecules and their complexes in liquids, solutions and crystals have been considered. The calculated and experimental IR spectra have been compared. It has been shown that the frequencies in the calculated and experimental spectra are consistent with the correlation coefficients of not less than 0.99, which indicates good possibilities of the methods in modeling both individual molecules and their complexes in liquids, solutions and crystals. Moreover, the proposed methods can be successfully used to further confirm the structure. This is especially important for liquids and solutions where direct structure determination by X-ray diffraction methods is impossible.
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Combined approach to UV-Vis study of 2-allyl and 2-ethylthioquinolines in various solutions
Статья научная
Combined approach to analysis of 2-allylthioquinoline and 2-ethylthioquinoline solutions has been performed on the basis of UV-Vis spectroscopy. Experimental and calculated electronic absorption spectra of these compounds in various solvents: acetone, benzene, carbon tetrachloride, dichloromethane, ethanol have been considered. The negative solvatochromic effect has been observed. The results of our calculations have revealed that the spectra of various conformers of 2-allylthioquinoline differ more essentially than the spectra of 2-ethylthioquinoline conformers. It has been shown that the location of λ max band doesn’t drastically depend on allyl or alkyl substitution at the sulfur atom.
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Comparative analysis of theoretical and experimental UV-spectra of 2- and 8-thioquinoline
Статья научная
The comparative analysis of the calculated electronic absorption spectra of various forms of 2- and 8-thioquinoline and the experimental UV spectra of their solutions in various solvents has been carried out. Two conformational isomers of SH-forms have been analyzed for each compound. Calculations of other tautomeric forms of these compounds, namely NH-forms of 2-thioquinoline (2-thioquinolone) and 8-thioquinoline (zwitter-ion), and S-forms (anions) and 1-H-2-thioquinolinium cation have been analyzed additionally. It is shown that the absorption bands in the spectrum of 8-thioquinoline solution correspond to the electronic transitions in the SH-tautomer. On the contrary, the absorption bands in a spectrum of 2-thioquinoline solution correspond to the electronic transitions in the NH-tautomer and S-anion. The spreading of absorption bands in the experimental spectra is associated with conformational and tautomeric equilibrium which is established in the solutions of the considered compounds.
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![Covalent doping of g-C3N4 with the benzo[c][1,2,5]-chalcogenadiazole acceptor blocks: photocatalysis and electronic structure](/file/thumb/147239539/covalent-doping-of-g-c3n4-with-the-benzo-c-125chalcogenadiazole-acceptor.png "Covalent doping of g-C3N4 with the benzo[c][1,2,5]-chalcogenadiazole acceptor blocks: photocatalysis and electronic structure")
Статья научная
The methodology of in situ thermal synthesis has been developed for the semiconductors based on graphitic carbon nitride (g-C3N4) doped by benzo[c][1,2,5]chalcogenadiazoles (chalcogen Ch = O, S, Se). Benzo[c][1,2,5]chalcogendiazoles were obtained by methods previously presented in the literature. The purity of the resulting organic structures was confirmed by 1H and 13C NMR, GC-MS, IR-spectroscopy, elemental analysis, and the melting point determination. The technique for obtaining g-C3N4 samples consists in sintering melamine and the required acceptor block mixture at 550 °C in a neutral atmosphere. For pure and doped g-C3N4 its structure formation fact was confirmed by PXRD, IR-spectroscopy and 13C NMR. Semiconductor and other properties of carbon nitride materials were studied by UV-spectroscopy, PL-spectroscopy, cyclic voltammetry technique, SEM conbined with EDS, as well as by plotting nitrogen sorption-desorption isotherms. A series of photocatalytic water-splitting experiments under the UV-light (λ = 365 nm) action in the presence of samples of pure and doped carbon nitride as a photocatalyst, hexachloroplatinic acid as a co-catalyst, and triethanolamine as a electron-sacrificial agent was carried out. The amount of hydrogen formed during the water-splitting experiment was determined for every hour using the GC-method. It was found that all three dopants positively affected photophysical and catalytic properties of the materials. Quantum chemical calculations confirmed that the benzo[c][1,2,5]chalcogenadiazoles served as acceptor blocks with accumulation of the most of the HOMO electron density.
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Decision tree for mechanism of antitumor drugs action prediction
Статья научная
Classification by the mechanism of action of antitumor drugs using quantitative descriptors has been carried out in this study. The dataset of drugs includes 115 compounds with known activity and mechanism of action. The structures have been taken from the National Cancer Institute database. The dataset includes: 30 structures with the mechanism of alkylation action, 23 compounds are topoisomerase I inhibitors, 16 structures are topoisomerase II inhibitors, 17 compounds are DNA/RNA antimetabolites (dihydrofolate reductase inhibitors), 16 molecules are DNA antimetabolites, and 13 compounds are antimitotic drugs. A decision tree has been constructed for determination of each class of the compounds using 3D descriptors that have been computed by MERA software. Analysis of the results has shown that each mechanism of drug action is characterized by a set of descriptors. Important quantum-chemical descriptors of structures with mechanism for alkylation action, DNA/RNA antimetabolites, and DNA antimetabolites have been determined. Quantum-chemical and geometric descriptors for structures of topoisomerase II inhibitors and geometric descriptors for structures of topoisomerase I inhibitors have been established. An important energy descriptor for antimitotic drugs has been determined. The typical descriptor values for active and inactive structures for each mechanism of action have been determined. The quality recognition of active structures for each mechanism of drugs action has been determined. The highest recognition quality value of active and inactive compounds is observed in the decision tree of topoisomerase II inhibitors. The minimal recognition quality value of active and inactive compounds is observed in the decision tree of DNA/RNA-antimetabolites. The suggested decision trees can be used for determination of the action mechanism of antitumor drugs.
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Features of the pnictogen bonds formed by neighboring nitro groups in crystals
Статья научная
Features of pnictogen O…N bonds were considered from the point of view of analyzing various geometric orientations of the neighboring nitro groups NO2…NO2 observed in molecular crystals. The “idealized” orientation for a pnictogen bond, where the nucleophilic fragment of the atom O of one nitro group was directed to the electrophilic site of the atom N of the other one, and the “stacking” orientation, which was characterized by the parallel stacking of nitro groups, differ in the features of the electron density and electrostatic potential distribution between O and N atoms. The applied electronic criterion, obtained with the use of quantum chemical calculations with periodic boundary conditions, confirmed that for the considered O…N interactions the necessary condition for their classification as pnictogen bonds was met.
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Formation (decomposition) enthalpy calculations for crystal lattices of alkaline-earth fluorides
Статья научная
A series of calculations of structural and thermochemical properties has been carried out for the alkaline-earth fluorides. The calculations have been carried out using the modified model of effective ionic radii and the model of enthalpy calculation for the crystal lattice. The results of the calculations are in accordance with the known experimental data within confidence intervals.
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Статья научная
Methodological features of the crystal structure modeling for compounds with three-center halogen bond formed by two electron donors S-I+-S in polyiodide crystals were considered within the framework of periodic calculations based on localized atomic orbitals. The analysis of applying the different basis sets, effective core potentials, density functional theory functionals, and Grimme dispersion corrections revealed their effect on the geometric, electronic and vibrational properties obtained in calculations. Distribution of S-I bond lengths in S-I+-S fragment was analyzed. The effect of hybrid functional was demonstrated in the significant elongation of S-I distance. The treatment of dispersion interactions via Grimme approach did not significantly influence obtained results. The calculated vibration modes in medium wavenumber region of characteristic cationic stretching vibrations were validated according to experimental Raman spectra and were found to be in good agreement for C-N, C-C and C=S stretching vibrations. Small-core effective potential was shown to be effective for representation of bond lengths in S-I+-S fragment and gave reasonable results for vibrational data for cationic stretching vibrations. Taking into account relativistic effect on the level of basis set led to fine reproducibility of S-I bond lengths although in polyiodides of complex structure it should be treated with caution due to possible incorrect representation of interanionic distances.
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Статья научная
A method for the kinetic photometric determination of oxalate ion in aqueous solutions, including extracts from foodstuffs, has been suggested. The initial rate method has been used: the straight parts of kinetic curves (approximately 5 min) are processed by the least square method to get the slope coefficients used as analytical signals. The procedure is based upon the oxalate ion action as an activator in the iron(II)-catalyzed reaction of iodide oxidation by potassium bromate. Unlike the previously used light absorbance in the UV region, the suggested procedure controls the rate of the iodine-starch complex formation at 590 nm. The greatest initial rate for the reaction is at pH 5.05 of the acetate buffer solution and the optimal concentration of soluble starch 0.30 mg/mL. The calibration graph is linear in the oxalate concentration range (0.1-10) mg/mL. In this interval precision error varies between 0.67 % and 4.71 %, accuracy error is within (0.22-9.30) %. The procedure has been applied to food analysis by the standard addition method. Aqueous extract has been obtained from 2.5 g of finely chopped sample of raw beet, stirred with 100 mL of water for 1 h, centrifuged, filtered, and quantitatively transferred to 250-mL volumetric flask. Determination of oxalate in 1-mL aliquot has required the same volume of colored beet extract for a reference solution, but otherwise the procedure stands valid. The oxalate content has been found to equal (379 ± 2) mg/g of the raw beet (P = 0,95; n = 4), with 0.6 % precision error and 3.0 % accuracy error.
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Methods for calculating and matching thermodynamic properties of silicate and borate compounds
Статья научная
New methods for processing the experimental and calculated thermodynamic data have been elaborated and the existing ones have been improved. The developed approaches provide a physically reasonable description of the first-order phase transitions, which makes it possible to compare and correct the values of their thermodynamic properties, as well as to calculate the thermodynamic parameters of unstudied compounds. Regression equations have been proposed for calculating the standard entropy and enthalpy of formation of lithium, sodium, and potassium silicates and borates. The resulting entropy and enthalpy values for 14 alkali metal silicates and 12 alkali metal borates can be used to optimize the technological processes for manufacturing glass, ceramics, and coatings.
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Статья научная
A series of porous composite SiO2-TiO2 and pure TiO2 spherical particles were prepared via the peroxo route and subsequently used as the support for catalyst. Aminopropyltrimethoxysilane (APTMS) was grafted to the surface of support in the strictly unhydrous media leading to bonding of free amino groups to the support surface covalently. Procedure of APTMS grafting is easy to perform and may be spread for grafting other different functional groups to the inorganic surfaces of the catalyst support. The support samples were calcined at various temperatures in order to optimize the preparation conditions and boost the density of surface amino groups. It has been found that the quantity of grafted APTMS varies insignificantly for the different support samples. Grafted amino groups would be applied as active catalytic sites in different reactions of organic chemistry such as acylation of amines and alcohols, polymerization of lactones with hydroxyl groups, isomerization of unsaturated compounds, aldol condensation, Diels-Alder, Michael, Knoevenagel reactions. The mechanisms of reaction activation by amino groups are the transfer of electron density to a reacting molecule and formation of an intermediate complex. While widely applied catalysts are liquid amines, it is desirable to transform these substances into the heterogeneous form for better regeneration and purification of reaction products from the initial reagents. Prepared catalysts exhibit high amino groups load equal to 1 mmol/g, taking into account the localization of amino groups on the surface of the catalyst.
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Novel photoanode based on hierarchically structured Ti-P double oxide
Статья научная
The study of trialkylborane as a component of the initiating system with oxygen was carried out using the example of graft polymerization of alkyl(meth)acrylate vinyl butyl ether copolymer units on pectin polysaccharide. The amine complex triethylborane-hexamethylenediamine was introduced into a boiling mixture of an aqueous solution of pectin in vinyl butyl ether, after which a solution of the active monomer, alkyl(meth)acrylate, containing methacrylic acid, was introduced by the compensation method to isolate triethylborane from the complex. As a result of synthesis from a mixture containing butyl acrylate, three immiscible parts were formed: organic, aqueous, and between them a “sponge” that did not dissolve in any of the phases. In the case of methyl methacrylate, only two parts were formed in the mixture: organic and aqueous. Water-soluble and organic polymers were dried under vacuum conditions to constant weight at T = 20-25 °C. Gravimetric analysis showed that the “sponge” was a mixture of water-soluble and organic polymers at 50:50 ratio. To do this, the dried polymers were dissolved alternately in water and vinyl butyl ether. Graft copolymers pectin-methyl methacrylate-vinyl butyl ether and pectin-butyl acrylate-vinyl butyl ether were isolated from the aqueous phase of the synthesized systems, in relation to the introduced acrylate. In comparison with the original pectin, the molecular weight of the water-soluble fraction increased significantly. Comparison of the IR spectrum of the graft copolymer pectin-methyl methacrylate-vinyl butyl ether with the IR spectra of pectin and the IR spectrum of pectin-methyl methacrylate indicated that all the bands characteristic of pectin, polymethyl methacrylate, and polyvinyl butyl ether were observed for the new polymer sample. Freeze-dried samples of pectin and pectin-methyl methacrylate-vinyl butyl ether graft copolymer were examined using scanning electron microscopy. A comparative analysis showed a change in the structure of pectin fibers as a result of its copolymerization with a copolymer of methyl methacrylate-vinyl butyl ether. The obtained data confirm the addition of synthetic polymers alkyl (meth) acrylate-vinyl butyl ether to the basis of the pectin macromolecule. New substances are polymer molecules containing natural and synthetic fragments with an ordered structure. Such compounds are promising as the basis for wound healing coatings.
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Photocatalytic properties of fluorinated tetraarylantimony carboxylates
Статья научная
Organic dyes are widely used in different kinds of manufacturing. As a result, they become common organic contaminants, and lead to water pollution. Therefore, the search of effective methods for such compound destruction is of interest. One of such methods is the photocatalytic destruction by antimony organic compounds. It has been found out that the incorporation of tetraarylantimony monocarboxylates (Ar4SbOC(O)R, Ar = Ph, R = C6F5 (1), CF2CF2CF3 (2), CF2Br (3); Ar = p-Tol, R = CF2CF3 (4), CF2CF2CF3 (5)) and further irradiation of solutions with UV radiation causes photocatalytic degradation of organic dyes methylene blue (MB) and methyl violet (MV) in their aqueous solutions. The change of concentration of organic dyes could be seen due to change in peak intensity at 554 nm and 665 nm in the UV spectra of MB and MV. Tetraphenylantimony carboxylates 1-3 showed higher photocatalytic activity than tetra(p-tolyl) antimony carboxylates 4, 5. Thus, MB decomposition was 90.5-98.8 %, MV: 97.7-100 % after 60 min irradiation of aqueous solutions containing compounds 1-3. While in the presence of 4, 5, decomposition of MB and MV was 55.1-53.2 % and 71.2-78.7 %, respectively. In both cases, methyl violet was susceptible to more total destruction than methylene blue. The experiments showed the probability of repeatable use of the photocatalysts. After full decay of the pigment, tetraarylantimony carboxylate precipitated by centrifugation, the precipitate was decanted and used for the next cycle. As a result of two photodegradation processes, the mass of tetraarylantimony carboxylates decreased on average by 50 % after washing and drying, but the carboxylates were still effective, which proved the possibility of the photocatalyst repeatable use and their stability.
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Статья научная
The influence of aluminum on the structure of alkali borosilicate glasses with various ratios of network former cations and modifier cations has been studied with the use of vibrational spectroscopy. It has been found that addition of modest amounts of aluminum to borosilicate glasses decreases the difference of sodium and potassium distribution between silicon- and boron-containing structural units of the glasses. This fact allows consideration of aluminum as an additive contributory to homogeneity of borosilicate glasses containing both sodium and potassium, as well as increase in thermal and chemical stability of matrix materials based on such glasses.
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Structure of lithium pyrosilicate melts according to data of high-temperature Raman spectroscopy
Статья научная
Decomposition of the high-frequency range of Raman spectra for 60Li 2O·40SiO 2 melts (Li60) into the Gaussian line shape was performed. The basic structural fragments of melts and their ratio were determined, and the peculiarities of their interaction with the change in temperature were identified.
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Статья научная
In the present work the influence of duration of thermal treatment on the properties and photocatalytic performance of carbon nitride materials is investigated. Preparation of photocatalytic material proceeded in the eutectic molten salts KCl/LiCl mixture. This way of thermal treatment results in crystalline material with ordered structure, improved in comparison to convenient preparation methods. Duration was altered in range from 2 to 10 hours. Materials were studied by the methods of X-ray diffraction patterns, scanning electron microscopy. It was found that most ordered materials with the maximal degree of crystallinity are formed after 2-6 hours of high-temperature treatment. Elongation of thermal treatment up to 8 and 10 hours leads to less ordered material with the enhanced share o amorphous phase. Carbon nitride materials were used as photocatalysts for the selective oxidation of benzyl alcohol to benzaldehyde and demonstrate high selectivities to target product. 2 hours of thermal treatment leads to formation of photocatalyst with the highest conversion (79.2 %) and selectivity (92.4 %) values. Less effective material is formed after 10 hours of treatment, where selecivity level retained, while conversion drops to 48.6 %. Morphology of materials has maximal effect on the photocatalytic properties - high crystallinity is the main feature of catalytically effective materials.
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Theoretical evaluation of phenyl-substituted aziridines, azirines and epoxides reactivity
Статья научная
The reactivity of three-membered heterocycles such as phenyl-substituted aziridines, azirines, epoxides was studied in comparison with styrenes, azomethines and carbonyl compounds which are most often used in organic synthesis in nucleophilic and electrophilic reactions. In accordance with electronic reactivity indices of nucleophilicity and electrophilicity calculated on the base of DFT approach, the substituted molecules of azirines, aziridines, and epoxides exhibit the similar reactivity to aldehydes and styrenes. In all cases, our predictions were checked against the experimental observations given in literature. All considered compounds mainly characterizes by the properties of medium-strength electrophiles. Aziridines, azirines, epoxides with two aryl groups show the best electrophilic properties. This observation can be used in predictions of reactivity for these classes of compounds. Among three-membered heterocycles, the best nucleophilic properties were observed for substituted epoxy cycles. We have found that the dual descriptor based on Fukui functions cannot be recommended for predictions the reactivity of aziridines and epoxides. The values of the dual descriptor on both carbon atoms in three-membered ring significantly differ, while the experimental data on nucleophilic addition indicate that the reaction proceeds at both carbon atoms. Nevertheless, for phenyl-substituted azirines, the descriptor based on Fukui functions shows its effectiveness quite well.
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Статья научная
A theoretical study of the crystal lattice of titanium dioxide (anatase), its spatial and thermodynamic characteristics, face growth characteristics and ways of formation of its macromolecular structures is performed. It is shown that the growth along c axis of the crystal is more favorable thermodynamically. The variants for controlling of the growth of various faces by introducing of the acidic and basic components, as well as by temperature changes are proposed.
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