Doklady Physical Chemistry最新文献

The effect of alkalinization of fulvic acid (FA) solutions on an increase in their optical density has been studied. To explain this phenomenon, FA particles existing in solutions at different pH have been studied by scanning electron microscopy (SEM) and scanning tunneling microscopy (STM). It has been found that an increase in pH results in a noticeable decrease in the size of the supramolecular assemblies of FA molecules from ~200 to ~100 nm. An STM study of FA samples demonstrates that FAs exist in solutions as supramolecular assemblies of several hundred nanometers in size formed by 10–20 nm FA particle molecules. The observed phenomenon has been explained using the existing ideas about the supramolecular fractal cluster organization of humic substances. The explanation states that the upper layer of F-clusters degrades to give FA particle molecules, while the cluster size is seen to decrease. The FA particle molecules cannot be detected by SEM due to their small size, but they are readily visualized by STM.

High-entropy carbides are a new class of inorganic compounds promising for a wide range of applications. A new concept was proposed for the synthesis of powders of high-entropy carbides by self-propagating high-temperature synthesis (SHS) in the gasless thermal explosion mode from previously mechanically synthesized and structured reaction mixtures. For the first time, high-entropy carbides TaTiNbVWC₅ and TaNbVMoWC₅ were produced by this method, and their crystal structure was determined and compared with those of similar compounds synthesized by sintering.

The isothermal concentration tetrahedron of the Li–Mn–Eu–O system was constructed for the first time by topological modeling based on fragmentary experimental data. The tetrahedron describes possible solid-state transformations in the system, which occur at a constant temperature with pressure varying. Thirty-two equilibria involving four crystalline phases were identified.

The reaction of a biphasic catalysis with microgels bearing catalytic groups adsorbed at liquid interface was simulated for the first time using dissipative particle dynamics. It was shown that the rate of the catalytic process increases with the degree of deformation of the polymer network, which depends on the fraction of the crosslinker and the solubility of the polymer in both phases. It was found that the highest reaction rate was observed when the microgel was soluble in both phases due to an increase in its porosity (in comparison with amphiphilic microgels) and in the water–microgel–oil contact area with a simultaneous decrease in the time for the reagents to reach the catalytic groups due to the flattening of the microgel. The results obtained can be useful for increasing the efficiency of a wide range of catalytic reactions of the type considered through the use of network-like macromolecules.

Large molecules of dyes or other substances can act as nano-adsorbents in aqueous surfactant solutions and, being coated with surfactant molecules, they resemble surfactant micelles with a solubilizate. These micelle-like particles were called protomicelles (or, more precisely, adsorption protomicelles, as in this paper). Their formation does not require a critical micelle concentration (CMC) and begins immediately when a surfactant is added to a solution. In this spectrophotometric study of Nile red (NR) in aqueous solutions of nonanoic acid (NOA), the first case where protomicelles were more important than micelles was demonstrated. It was shown that NR solubilization in both premicellar and micellar solutions proceeds through protomicelles rather than through NOA micelles. In the theoretical part of the paper, on the basis of the chemical potential of the nano-adsorbent, it was proved that the addition of a surfactant to a solution always increases the solubility of the nano-adsorbent. The dependence of adsorption on the curvature of the nano-adsorbent surface was considered, and it was shown that the adsorption equations for flat surfaces are applicable to curved surfaces with high accuracy.

Immobilized rhodium and iridium complexes have been prepared and characterized by X-ray photoelectron spectroscopy. For the first time, hyperpolarized ¹³C-ethylene was detected directly in the gas phase during acetylene hydrogenation with parahydrogen over immobilized iridium complexes. The line shape of polarized ¹³С‑ethylene unambiguously indicates that the hydrogen addition to the triple bond of acetylene over immobilized iridium complexes proceeds stereoselectively via syn-addition. It has been shown that the selective acetylene hydrogenation with parahydrogen over immobilized iridium complexes is an efficient chemical method for enriching the nuclear spin isomers of ethylene.

The kinetics of butyl lactate production by the interaction of ammonium lactate with n-butanol in the presence of water in the temperature range of 130–170°C in a closed system was studied for the first time as one of the stages of a new integrated technology for the production of lactic acid and polylactide. Also for the first time, a reaction scheme and kinetic model of ammonium lactate esterification with n-butanol were proposed, taking into account the side formation of lactamide and the acid catalysis of esterification by lactic acid. The developed kinetic model can be used for mathematical modeling of a reactor for the synthesis of butyl lactate.

Quantum chemical calculations utilizing DFT at 6-311++G(d,p) basis set in gaseous and aqueous phases for protonated and non-protonated species were conducted. To evaluate corrosion inhibition efficiency, four compounds, namely 4-methyl-5-hydroxymethylimidazole (MHI), benzimidazole (BI), 2‑amino BI (ABI), 2-hydroxymethyl-BI (HMB), imidazole (I), 2-methyl BI (MBI), 5-methyl-imidazole (MI), and 4-(1H-imidazol-1-yl) phenol (PHEN) were compared. Several considered chemical parameters were calculated such as HOMO, LUMO, ({{Delta }}{{E}_{g}}), dipole moment, ionization energy, electron affinity, hardness ((eta )), softness ((sigma )), electrophilicity, nucleophilicity, electron transfer (({{Delta }}N)), and back-donation energy (ΔE_b-d). Using a molecular dynamic modeling method, the adsorption behaviors of the researched chemicals on the Fe (1 1 0) surface were examined. The corrosion inhibition efficiency ranking followed the order PHEN > MBI > ABI > MHBI > BI > MHI > MI > I. It should be observed that the study’s findings are in strong accord with previously published findings on experimental inhibition efficiency.

A computer 3D-model was presented for the isobaric phase diagram of the ZrO₂–SiO₂–Al₂O₃ system with the formation of the ZrSiO₄ and Al₆Si₂O₁₃ compounds. Its geometric structure was derived through the sequential construction of a scheme of phase reactions, including all polymorphic transitions in the subsolidus and the rearrangement of the interaction of binary compounds, as well as zirconium and aluminum oxides; its transformation into a scheme of uni- and invariant states in the tabular and graphical (3D) forms; and the construction of a prototype and its transformation into a spatial model of the phase diagram of the real ZrO₂–SiO₂–Al₂O₃ system. Features of the iso- and polythermal sections of the phase diagram of the considered system, which were calculated using the thermodynamic NUCLEA database, were discussed in comparison with the sections of the obtained 3D-model.

It has been shown for acetylacetone as an example that the intramolecular hydrogen bond significantly affects the radiolytic transformations of organic compounds by suppressing the proton transfer from the primary radical cation to the molecule and also by promoting cleavage of the C–OH bond in the enol form. Due to these effects, the major heavy product of radiolysis at 295 K is 4-oxopent-2-en-2-yl acetate. Under boiling conditions (413 K), hydrogen bonds are cleaved, resulting in the predominant formation of 4-hydroxy-2-pentanone, which is not detected at 295 K.