Doklady Physical Chemistry最新文献

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.

A novel approach to the preparation of a hard-elastic polymeric material based on ultra-high-molecular-weight polyethylene using the strategy of crazing of polymers was proposed. This approach comprises the process of deformation of the pristine films of ultra-high-molecular-weight polyethylene via the environmental intercrystallite crazing mechanism and the subsequent low-temperature spontaneous strain recovery upon stress relaxation. As a result, the material acquires new properties typical of hard-elastic materials: restoration of the porous structure with pore sizes in the nanometer range (less than 10 nm) after the secondary deformation in air up to ~20 vol %, high reversibility of deformation (50–85%), and the effect of opening and closing of pores under cyclic loading. The mechanism of this phenomenon was proposed, and the fields of practical applications of this kind of mechanosensitive material were indicated.

A novel approach to the development of nanocomposite materials based on high-density polyethylene and an inorganic flame retardant, magnesium hydroxide, via the fundamental strategy of environmental crazing of polymers has been advanced. Efficient methods for incorporation of magnesium nitrate as a precursor into mesoporous polymeric matrices have been proposed, and optimal conditions providing high-conversion in situ hydrolysis of magnesium salt to magnesium hydroxide within the confined space of mesopores of polymeric matrixes have been found. As a result of in situ hydrolysis, spherical or needle-shaped magnesium hydroxide nanoparticles are found to be uniformly distributed within the volume of the high-density polyethylene matrix. The obtained nanocomposite polymeric materials with a low content of magnesium hydroxide nanoparticles (up to 30 wt %) are characterized by reduced flammability and mechanical characteristics comparable to those of the initial polymer.

Bubbles are widely used in modern technologies from the synthesis of nanomaterials (ultrasonic sonochemistry and pulsed laser ablation in liquids) to solar geoengineering (global warming inhibition) and biomedicine (drug delivery across the blood–brain barrier). IMET RAS is developing conceptually new diffusion-bubbling membranes with combined mass transport and theoretically infinite selectivity, in which bubbles act as oxygen carriers. This review covers the latest experimental and theoretical results of studying the mass transport, nucleation, and dynamics of oxygen bubbles in innovative bubble-diffusion membranes with a core–shell structure. Directions for further research are indicated. A high potential of diffusion-bubbling membranes for efficient oxygen separation from air is noted.

Disjoining pressures in thin liquid films around nanosized wettable spherical particles and in thin vapor layers around non-wettable particles were calculated as functions of the lyophility degree, film thickness, and particle size on the basis of the expression for the grand thermodynamic potential as a molecular density functional. A characteristic feature of this approach is the full consideration of hard-sphere molecular correlations using the fundamental measure theory in the density functional theory (DFT) and calculation of the complete dependence of the grand thermodynamic potential of the system on the stable droplet or bubble size. Although the newly calculated dependences of the disjoining pressure are in a qualitative agreement with those found using a simpler gradient version of the molecular density functional, the results of the two methods considerably differ quantitatively. It was confirmed that the disjoining pressure in a liquid film around a nanosized lyophilic particle increases with increasing particle size and lyophilicity.

Hydrogenation of furfural in the presence of heterogeneous catalysts has recently attracted increased interest as a method for the synthesis of oxygen-containing compounds of various classes based on renewable raw materials. The composition of the catalyst and the conditions of its preparation essentially determine which of the routes of reductive conversions during the hydrogenation of furfural will be predominant. The present review summarizes and examines methods for controlling the physicochemical and functional properties of Pd-, Ni-, Co-, and Cu-containing catalytic compositions, as the most common and practically significant in the hydrogenation of furfural. The influence of the nature of the support, the composition of the active metal precursor, and the conditions for the formation of metal nanoparticles on the activity and selectivity of supported catalysts in the reductive conversions of furfural under aqueous-phase hydrogenation conditions has been demonstrated by numerous examples. Promising directions of research on the development of methods for the synthesis of efficient catalysts with controlled functional properties in the hydrogenation of furfural are considered. The bibliography includes 127 references.

A method for the controlled filling of pores in metal–organic frameworks (MOFs) with ionic liquids (ILs) has been proposed, which can be applied for selective gas sorption in MOFs. Using an example of MOF ZIF-8 and IL [BMIm]⁺[BF₄]⁻, composites with different IL content have been prepared with monitoring by electron paramagnetic resonance (EPR) of nitroxide spin probes. The effect of IL on the sorption of nitrogen(II) oxide into these composites has been studied using inversion gas chromatography.

The paper describes the pyrolytic transformation of hydrolysis lignin in 1,4-dioxane at a temperature of 250°C and a pressure of 13.0 MPa and the subsequent Ru/C-catalyzed hydrogenation of the products at a temperature of 250°C and a pressure of 10.0 MPa in an autoclave. It has been found that the thermal pyrolysis of hydrolysis lignin with 1,4-dioxane and the catalytic hydrogenation of pyrolysis products are accompanied by C−O and C−C bond cleavage and formation of a products mixture consisting of soluble oligomer and monomer phenol derivatives, products of their hydrogenolysis and hydrogenation, and also mixtures of C₁−C₅ gas hydrocarbons and C₂−C₅ alcohols, and ethers formed mainly during the destruction of the solvent (1,4-dioxane) under the reaction conditions.

The effect of cucurbit[7,8]urils on the absorption and luminescent properties of bis-thiacarbocyanine (bis-TCC) based on 3,3'-dimethylthiacarbocyanine (TCC) perchlorate in water was studied. The existence of two forms of bis-TCC that absorb in the long-wavelength and short-wavelength ranges was established. The properties of the form absorbing in the long-wavelength region are similar to those of the TCC monomer (monomer form), whereas the form absorbing in the short-wavelength region exhibits the properties of the non-fluorescent TCC dimer (dimer form). The effect of cucurbit[7,8]urils was manifested as shifts of the absorption and fluorescence maxima, increase in the fluorescence intensity of both the monomer and the dimer forms, and the presence of thermally activated delayed fluorescence of the dimer form in deoxygenated solutions at room temperature. The results derived from spectral and luminescent measurements indicate the ability of bis-TCC to form complexes with cucurbit[7,8]urils.

The energies of enol and keto forms for 36 3-hydroxymaleimide derivatives have been calculated by the DFT and DLPNO methods. The results clearly show that, with only a few exceptions, the enol form is energetically more favorable by 16–60 kJ mol^–1, and the energy difference depends on the substituent in the 4-position. Global electrophilic index has been calculated for all the compounds, which demonstrates that the keto form is generally more electrophilic, and electrophilicity depends on the substituent in the 4-position. Two possible structures of hydroxymaleimide anion have been evaluated; the deprotonation of the oxygen atom turns out to be the most energetically favorable.