Vol 91, No 6 (2017)
- Year: 2017
- Articles: 32
- URL: https://journals.rcsi.science/0036-0244/issue/view/10332
Chemical Thermodynamics and Thermochemistry
Estimating the parameters of the microheterogeneous structure of metal melts according to viscometric experimental data in terms of the absolute reaction rate theory
Abstract
The temperature dependences of the viscosity of microheterogeneous metal melts are analyzed in terms of the Frenkel–Eyring theory. Using viscometric experimental data, the sizes of dispersed particles in metal melts whose components undergo eutectic and monotectic interactions are numerically estimated.
Emergence of convective flows during diffusional mass transfer in ternary gas systems: The effect of component concentrations
Abstract
Specific features of diffusional mass transfer in ternary gas mixtures and their relation to the concentration of the densest component in a mixture are studied experimentally under isothermic conditions. At certain compositions of the gas mixture, unique diffusion regimes develop in the system that are characterized by a considerable rate of mass transfer and are attributed to the presence of concentration convection. We show that transitions from the diffusional and convective regimes can be predicted using the stability theory extended to isothermal mixing in ternary gas systems. Theoretical predictions are compared to experimental data.
Thermodynamic properties of liquid copper–lanthanum alloys
Abstract
Mixing enthalpies of alloys in the Cu–La system are measured using isoperibolic calorimetry method over the ranges 0 < xLa < 0.185 at 1400–1430 K and 0.659 < xLa < 1 at 1370 K. They have moderate exothermic values over the whole concentration range and agree with literature data. Activities of the components, enthalpies and entropies of formation of intermetallics in this system, and its phase diagram are optimized using an ideal associated solution (IAS) model, and agree with most literature data. The updated thermodynamic properties can be used in further investigation of multicomponent systems based on the binary Cu–La.
Effect of metal-free porphyrins on the thermal–oxidative breakdown of biocompatible polymers
Abstract
The inhibitory effect of metal-free porphyrins on the thermal–oxidative breakdown of several biocompatible polymers is observed for the first time. Differential thermal analysis shows that the thermal stability of poly(ethylene oxide) and triblock copolymers of ethylene oxide and propylene oxide increases by 80–100 K, compared to the initial breakdown temperatures of these polymers in the presence of metal-free porphyrins (up to 3 wt %).
Oxidation of ethanol on NaX zeolite modified with transition metals
Abstract
NaLaX, NaX + Co, and NaPdX catalysts are synthesized by modification of NaX zeolite with transition metals (La, Co, Pd). The activity of the prepared materials in catalytic ethanol oxidation is studied in the temperature range of 423–723 K. It is shown that NaPdX and NaX + Co accelerate the reactions of partial and complete oxidation of ethanol as the temperature rises. NaLaX accelerates both intramolecular and intermolecular dehydration of alcohol. It is shown that the NaPdX (1.0% Pd) sample has the highest activity in the complete oxidation of alcohol with the formation of CO2.
Reactivity and mechanism of the action of C60 fullerene used as an inhibitor for the radical chain oxidation of 1,4-dioxane
Abstract
The kinetics and mechanism of the antioxidative action of С60 fullerene are studied via highly sensitive manometry and kinetic spectrophotometry, based on the example of a model reaction of the initiated oxidation of 1,4-dioxane. The adequacy of the proposed mechanism according to the experimental data is analyzed by means of mathematical modeling. The mechanism behind the inhibiting process is found to be a multi-center radical reaction. The rate constants of the elementary stages are determined.
Experimental investigation of a unidirectional network of four chemical oscillators pulse-coupled through an inhibitor
Abstract
Dynamical synchronous modes in a network of four nearly identical chemical oscillators unidirectionally coupled via inhibitory pulse coupling with time delay τ (when a spike in one oscillator inhibits the next oscillator in the circle after time delay τ), are obtained experimentally. The Belousov–Zhabotinsky reaction is used as a chemical oscillator. The existence of four main modes is confirmed experimentally: in-phase (IP) oscillations; an anti-phase (AP) mode, in which any two neighboring oscillators have a phase shift equal to half of global period T; a walk mode (W), in which oscillators produce consecutive spikes in the direction of the connection with a phase shift between neighboring oscillators equal to T/4; and a walk-reverse mode (WR), when the oscillators produce consecutive spikes (with phase shift T/4), but in the direction opposite the connections (the mode opposite to the W mode). In addition to the main modes, OS modes in which at least one of the four oscillators is suppressed, and “2+1+1” modes in which two neighboring oscillators produce spikes simultaneously and the phases of the third and the fourth oscillators are shifted by T/3 and 2T/3, respectively, are found. It is shown that the modes found experimentally correspond to those found in simulations.
Physical Chemistry of Solutions
Thermodynamics of reactions of complex formation for Ce3+ and Er3+ ions with glycine in an aqueous solution
Abstract
Enthalpies of complex formation for glycine (HL±) with Ce3+ and Er3+ ions at 298.15 K and the value of the ionic strength of 0.5 (KNO3) are determined by calorimetric means using two independent procedures. Thermodynamic characteristics of the reactions of formation for complexes of glycine with Ce3+ and Er3+ ions at various [metal]: [ligand] molar ratios are calculated.
Theoretical study of solvent effect on the ligand field parameter in [M(CO)6]n complexes (M = V–, Cr, Mn+, Fe2+)
Abstract
In this work, the structure, ionization energies, electron affinity, frontier orbitals analysis, and octahedral field splitting parameter of [M(CO)6]n (M = V–, Cr, Mn+, Fe2+) complexes in the gas phase were computed at MPW1PW91/qzvp level of theory. Also, the effect of solvent on structural parameters, frontier orbital energies and octahedral field splitting parameter of complexes was studied using polarizable continuum model (PCM). The results indicate that the polarity of solvents and substitution significantly affect the structures and properties of the studied complexes.
Effects of composition and temperature on viscosity, ultrasound velocity, and refractive index of propiophenone–benzyl acetate binary mixtures at 303.15–323.15 K
Abstract
Liquid density, viscosity, ultrasonic velocity and refractive index values have been reported for the binary system of propiophenone and benzyl acetate at temperatures 303.15–313.15 K for the whole compositions. Equations have been developed for the effect of temperature and concentration on viscosity, ultrasonic velocity and refractive index. The nature of molecular interaction has been concluded from the excess properties as well as from the newly developed equations.
Thermodynamic studies of iron chelation with doxycycline in acidic medium
Abstract
Doxycycline (DOX) is a broad-spectrum tetracycline antibiotic synthetically derived from oxytetracycline. The complex formation of this drug with iron(III) was studied using spectrophotometry. The thermodynamic parameters of the systems were calculated using the changes in the absorption spectra which occur due to hydrogen bond or complex formation. Thermodynamic parameters of the formation of iron(III) complex with doxycycline (ΔH, ΔG, ΔS, and stability constants) were determined spectrophotometrically at a wavelength corresponding to absorption maximum (374.5 nm) at three different temperatures (22, 35, and 45°C). The obtained data show that the complex has metal to ligand molar ratio of 1: 2 at pH 2–3. The stability constants were calculated to be 13.99 × 106, 7.06 × 105, and 1.29 × 106 by mole ratio method at 22, 35, and 45°C, respectively.
Thermodynamics of sulfamethoxazole dissolution in organic solvents at 293.15–323.15 K
Abstract
The solubilities of the sulfonamide—sulfamethoxazole in methanol, ethanol, 1-propanol, 2-propanol, and chloroform have been determined at 293.15–323.15 K by a static equilibrium method. The experimental results can be approximated with Apelblat equation. The positive enthalpy ΔsolH and entropy ΔsolS for each system revealed that sulfamethoxazole dissolution in each solvent is an entropy-driven process.
Structure of Matter and Quantum Chemistry
Molecular dynamics models and thermodynamic characteristics of hydrogen bonds in 1,2-ethanediol
Abstract
A correlation between the lifetimes of hydrogen bonds and the thermodynamic characteristics of their formation and breaking, and the experimental relaxation times of dielectric spectra and the energy characteristics of relaxation processes, is observed via molecular dynamics (MD) simulation of the rearranging of the network structure of 1,2-ethanediol. The MD torsional frequency of the transition of gauche conformer tGg′ at 224.1 cm−1 and the experimental frequency of the band maximum of torsional vibrations at 230 cm−1 in the infrared spectrum correlate with the oscillation frequency of molecules at 240 cm−1 inside clusters in the Dissado–Hill (DH) model. The MD and DH models indicate a predominantly parallel alignment of the electric dipole moments of conformers tGg′ in the three-dimensional network of hydrogen bonds of the liquid 1,2-ethanediol phase.
Activation diffusion of oxygen under conditions of the metal-semiconductor phase transition in vanadium dioxide
Abstract
Density functional theory is used to calculate the energies of formation of oxygen vacancies and migration of oxygen in the monoclinic and rutile phases of vanadium dioxide. The results are compared to estimates of the parameters of activation diffusion of oxygen using data from the electron-beam modification of thin film structures of vanadium dioxide and their subsequent reduction in the temperature range of 20–100°C. It is shown that diffusion in both phases of vanadium dioxide has a preferential direction of oxygen migration along axis а in the monoclinic phase and axis с in the rutile phase. The difference between the rate of oxygen vacancy generation upon electron-beam exposure above and below the temperature of metal–semiconductor phase transition is explained by the jump (~150%) in the activation energy of oxygen diffusion upon the structural transition of rutile–monoclinic phase. The mobility of oxygen (oxygen vacancies) correspondingly changes by more than an order of magnitude.
Theoretical studies on magnetic properties of a binuclear paddle wheel Cu(II) complex {Cu2(μ2-O2CCH3)4}(OCNH2CH3)2
Abstract
The magnetic properties of a binuclear copper(II) complex {Cu2(μ2-O2CCH3)4}(OCNH2CH3)2 have been investigated on the basis of density functional theory with the broken symmetry (BS) approach. The magnetic coupling constant J values for the investigated complex have been calculated by different methods (HF, m06, PBE, B3LYP, B3PW91, B3P86, BLYP, BPW91, BP86) and basis sets (TZVP, TZV, 6-31G, 6-31++G) for the metal centers, and SVP basis set for the other atoms. The best calculated J value is‒142.6 cm−1, which is in the excellent agreement with the experimental value (J = −101 ± 2 cm−1). By investigating the spin density distribution from the magnetic centers to the atoms of ligands and the singly occupied molecular orbitals (SOMOs) of the Cu(II) ions at the low spin group states, we found that there is a spin delocalization between the Cu(II) ions and acetate ligands.
Physical Chemistry of Nanoclusters and Nanomaterials
Enthalpy of mixing of porous nanocluster polyoxometalates of keplerate-type Mo72Fe30 with polyvinyl alcohol and polyethylene glycol
Abstract
The interaction between porous spherical nanocluster polyoxometalate and water-soluble nonionic polymers (polyvinyl alcohol and polyethylene glycol) in the compositions of film is studied via calorimetry. The concentration dependences of the enthalpies of these processes are obtained using calculations based on the thermodynamic cycle.
Synthesis of nanoscale nickel(II) and cobalt(II) sulfides
Abstract
Ranges of stability and regions of the stoichiometric stability of sulfide phases of nickel(II) and cobalt(II) are determined in water–salt solutions. Regions of the homogeneity of NiS and CoS monosulfides are considered. The composition of a microemulsion used as a nanoreactor for synthesizing sulfides is determined, and its phase diagram is plotted. The results from estimating the size of the obtained nanocrystals are presented.
Features of the reduction of graphene from graphene oxide
Abstract
Features of the reduction of graphene from graphene oxide in media containing hydrazine hydrate, ethylene glycol, and hydrogen are studied. X-ray energy dispersive spectroscopy, Raman spectroscopy, and scanning electron microscopy data indicate that this process proceeds through the high-temperature annealing of graphene oxide in a hydrogen environment.
Formation of micro- and nanosized particles of the Fe–Al–Co system in water solutions and its magnetic properties
Abstract
Samples of the Fe–Al–Co system are obtained electrochemically in a water solution. The kinetic dependences that describe the processes that occur in microparticles of aluminum in water solutions are established. The phase composition of the synthesized samples is determined via X-ray diffraction and Mössbauer spectroscopy. It is shown that the main contribution to the fine magnetic structure of Fe–Al–Co is made by the magnetically ordered structure with a hyperfine field around 348 kOe formed by a mechanical mixture of FeCo and Al.
Effect of the thermoelastic properties of components on the melting point of filamentary nanoparticles of Cu, Ag, and Au in the matrix of anodic Al2O3
Abstract
The strain energy in nanocomposites based on porous anodic aluminum oxide and filamentary nanoparticles of Cu, Ag, and Au is simulated numerically. The results allow us to estimate the contribution from mechanical stresses produced upon heating, due to differences between the thermal coefficients of the linear expansion of elements of heterogeneity upon a change in the melting point of spatially confined metallic filamentary nanoparticles. The dependence of the energy of deformation on the structural parameter associated with the concentrations of Cu, Ag, and Au fibers in the considered nanocomposite systems is studied. It is found that at temperatures close to 1000°C, the contribution from mechanical stresses to the change in melting point, quantitatively expressed by the studied energy characteristic, is negligible in comparison to the contribution from the surface.
Size, zeta potential, and semiconductor properties of hybrid CdS–ZnS nanoparticles in a stable aqueous colloidal solution
Abstract
A stable aqueous colloidal solution of core–shell CdS–ZnS nanoparticles is obtained via the chemical condensation of carboxyl-containing diamine complexone (disodium salt of ethylenediaminetetraacetic acid). CdS nanoparticles coated with ZnS exhibit 20 times greater luminescence and more stability, compared to CdS nanoparticles without ZnS on their surface.
Physical Chemistry of Surface Phenomena
Sorption of humic substances on a weakly basic anion-exchange resin: Relationship with the adsorbate structure
Abstract
Adsorption of a broad range of humic substances (HS) of different origins and fractional compositions on a macroporous weakly basic anion-exchange resin is studied. It is found that the nature of the HS has a substantial effect on both the efficiency of sorption and the mechanism of interaction with the adsorbent. The dependence of the determined thermodynamic parameters of sorption on the HS origin, composition, and structure is shown for a broad range of HS. It is concluded that the results can be used to predict the sorption properties of weakly basic anion-exchange resins with respect to HS of known origin and structural group composition.
Sorption prehistory: A way of studying the properties of impurities in multicomponent polymer systems
Abstract
In industrial synthesis of stereoregular polymers, substances such as multicomponent catalysts are known to contaminate a final product, thus becoming impurities to be removed from a polymer. Here, we show that liquid sorbates, when added to impurities inside a polymer, can be used as probes in studying the polymer’s prehistory of sorption and mass transfer. The main features of this process are described and discussed.
Effect of temperature on the adsorption of phosphatidylcholine by silicon-containing materials with various degrees of order
Abstract
Features of the adsorption of phosphatidylcholine (PCh) by inorganic silicon-containing materials with various degrees of order (MCM-41, MMC-1, and silica gel) from solutions in hexane under equilibrium conditions in the temperature range of 283–323 K are considered. It is found that the adsorption of the phospholipid within the Ce = (0.6–4.0) × 10–4 mmol/dm3 range of concentrations on the investigated materials is characterized by monomolecular absorption. Differential thermodynamic characteristics (ΔG, ΔH, and ΔS) of the sorption of PCh by silicon-containing materials with various degrees of order in the temperature range of 283–323 K are considered. An increase in the affinity of silicon-containing materials toward the phospholipid upon an increase in the temperature of the sorption process is observed.
Physical Chemistry of Separation Processes: Chromatography
Method for performing a single act of the reversible separation of ideal solution components
Abstract
A method for performing a single act of separation of the components contained in a liquid solution of optical isomers in a reversible process is proposed. Mechanisms that allow the reversible separation of mixture components at least in theory are discussed.
Photochemistry and Magnetochemistry
Preparation, characterization of Fe, Ce Co-doped flower-like TiO2 photocatalysts and their properties in photocatalytic oxidation of arsenite
Abstract
Preoxidation process is usually needed in the treatment of arsenic containing water because arsenite (i.e., As(III)) is less easily to be removed by adsorption. Nano-scale titanium dioxide (TiO2) is an efficient photocatalyst for arsenite oxidation. In this study, a series of photocatalysts of un-doped, single-doped and co-doped flower-like TiO2 were successfully prepared by template method using Fe(NO3)3 · 9H2O, ammonium ceric nitrate and tetrabutyl titanate (Ti(OC4H9)4) as precursors and glucan as template. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and N2 adsorption-desorption measurement were employed to characterize the morphology, crystal structure and surface structure of the samples. The photoabsorbance of the obtained catalysts was measured by UV–Vis absorption spectroscopy, and the photocatalytic activities of the prepared samples under UV light were estimated by measuring the oxidation rate of As(III) in an aqueous solution. The characterizations indicated that the prepared photocatalysts had flowerlike structures, consisted of anatase phase and possessed high surface area of ca. 160 m2/g. It was shown that the Fe, Ce co-doped flower-like TiO2 could be used as an effective catalyst in photocatalytic oxidation reactions. The synergistic effect of Fe and Ce co-doping played an important role in improving the photocatalytic activity. In addition, the possibility of cyclic usage of the co-doped flower-like TiO2 was also confirmed, the photocatalytic activity of flower-like TiO2 remained 88% of that of the fresh sample after being used four times.
Luminescence properties YVO4 powders doped with dysprosium and alkaline-earth metals
Abstract
YVO4:Dy and YVO4:Dy,M (M = Mg, Ca, Sr, Ba) powders were prepared by sintering at 900°C. According to XRD patterns, all samples are well crystallized, single-phase YVO4. SEM showed that the morphology of the samples did not show apparent changes. Under 275 nm excitation, the strongest emission line is observed at 576.6 nm, corresponding to the transition from 4F9/2–6H13/2 level of Dy3+ ion. The yellow/blue (Y/B) intensity ratio 4F9/2–6H13/2 to 4F9/2–6H15/2 values of Dy3+ for the phosphors doped with different divalent alkaline-earth metal ions is changes slightly. For the YVO4:Dy3+ particles, this value is maximal, which indicates that the color of the with YVO4:Dy3+ samples is the most pure.
Short Communications
Thermodynamic parameters analysis of ethidium bromide and mitoxantrone binding with DNA by adsorption isotherms
Abstract
Analysis of the adsorption isotherms by virtue of experimentally obtained data of anti-tumorous compound mitoxantrone and ethidium bromide binding with DNA has been carried out. The obtained data showed that throughout the comparatively simple linear isotherm, the more precise values of the binding constant K and number of nucleotides n, per binding site were received. Based on the values of K, those for the enthalpy changes at complex-formation of these ligands with DNA were obtained.
Phase diagrams of diphenyl ether–n-tetradecane and diphenyl–n-tetradecane systems
Abstract
Phase equilibria in diphenyl ether–n-tetradecane and diphenyl–n-tetradecane systems are investigated calorimetrically. The phase diagrams of these systems are calculated using the Schröder–Le Châtelier equation. Based on the calculated data, an experimental study of phase equilibria by means of differential scanning calorimetry is planned. The melting points, fusion enthalpies of the eutectics, and their compositions are determined. The liquidus curves of the systems are built using the experimental data.
Synthesis of phosphorus-doped soft carbon as anode materials for lithium and sodium ion batteries
Abstract
Phosphorus-doped soft carbon was synthesized by a facile phosphoric acid-assisted route. It is found that the phosphorus-doped soft carbon used as lithium ion battery anode exhibits a high reversible capacity of 333.6 mA h g–1 with the first cycle coulombic efficiency of 87.0% at the current density of 30 mA g–1. When used as sodium ion battery anode, it also shows great storage performance, with a reversible capacity of 121.3 mA h g–1 with an initial coulombic efficiency of 65.0% at the current density of 10 mA g–1. Besides, good rate capability and stable cycling performance are also observed for both lithium and sodium ion batteries, indicating potential of their application in large-scale storage devices.
Methods and Techniques of Physicochemical Studies
Analysis of the oxidative modification of proteins by means of fluorescence and elastic scattering
Abstract
The fluorescence of pure tryptophan and tryptophan residues in albumin is studied at an excitation wavelength of 288 nm. The range of wavelength registration is 280–380 nm. A broad fluorescence band at 350–355 nm and an elastic scattering line at 288 nm are observed in the spectrum measured at 90° relative to the primary beam. The fluorescence of pure tryptophan and tryptophan in albumin is greatly reduced under the impact of the plasma radiation of a spark discharge, while the elastic scattering peak remains unchanged within the limits of error. A comparison of the elastic scattering and fluorescence indicates that tryptophan loses its inherent property to fluoresce under an external influence. The structure of the other tryptophan levels remains unchanged.