Diagram of the PbF<Subscript>2</Subscript>–SnF<Subscript>2</Subscript> system

A phase diagram of the PbF₂–SnF₂ system has been studied by differential thermal analysis and X-ray powder diffraction. The system forms Pb_1–хSn_хF₂ (х ≤ 0.33) solid solution and three compounds. Pb₂SnF₆ decomposes in solid state by a peritectoid reaction at 350°С; Pb₃Sn₂F₁₀ and PbSnF₄ melt by peritectic reactions at 565 and 380°С, respectively. The eutectic coordinates are 180°С, 90 mol % SnF₂.     

Interaction between hydrofluorosilicic acid and 1,10-phenanthroline: Hydrolytic stability of chelate complexes of silicon tetrafluoride with bidentate N-donors

Hexafluorosilicate (LH₂)SiF₆ and the cis-[SiF₄(L)] chelate complex characterized by ¹⁹F NMR are products of reaction between hydrofluorosilicic acid and 1,10-phenanthroline (L). XRD findings show that the structure of (LH₂)SiF₆ is stabilized by NH···F hydrogen bonds (N···F 2.618(4), 2.676(4) Å) and CH···F contacts. The relative resistance of the cis-[SiF₄(L)] complex to hydrolysis is associated with the chelate effect.     

Structure and energy of formation of β- and γ-cyclodextrin complexes with amino acid enantiomers

The interaction between cyclodextrins (CyD), β-CyD, and γ-CyD, and the L- and D-optical isomers of several amino acids (Ala, Leu, His, Phe) are calculated using DFT. It is found that the L-forms of the investigated amino acids bond more strongly to CyD, due to the different numbers of hydrogen bonds that form. The structures of the resulting complexes are analyzed.     

Times of metastable droplet relaxation to equilibrium states

Times of metastable droplet relaxation to their equilibrium state are calculated at saturated vapor pressures, depending on the droplet size. It is shown that for small droplets with radius R = 6 molecular diameters (or ~2 nm) the relaxation times are ~1 ns (which is comparable to the characteristic flight times of rarefied gas molecules). For large droplets with radius R ~ 800 molecular diameters, the relaxation times are as long as 10 μs. At a fixed droplet radius (6 ≤ R ≤ 800), the range of variation in relaxation time from the melting point to the critical temperature does not exceed one order of magnitude: the lower the temperature, the slower the relaxation process.     

The morphology and crystalline region distribution of polyacrylonitrile nanofibers prepared by electrospinning

The effects of electrospinning parameters in a wider range on the morphology and diameters of polyacrylonitrile (PAN) fibers are studied in detail. The fibers’ diameter increases from 288 to 3469 nm swiftly with the increasing PAN concentration. With the increasing voltage or prolonging gap distance, the diameter increases primarily and decreases later. The combined effects of surface tension, splitting and stretching, electric force, viscosity, and solvent volatilization are the main reasons. Ultrasonic etching method, Atomic force microscope (AFM), Scanning electron microscope (SEM) and X-ray diffraction (XRD) technology have been utilized to verify the nature structure of electrospun PAN fibers. Combining all the results, it is deduced that there are many grooves arranging nearly perpendicular to the fiber axis on the surface of electrospun PAN fibers. The thickness of relative ordered region is 40 to 190 nm and the thickness of amorphous region is 20 to 35 nm.     

Determination of aliphatic acids in natural waters using distillation and solid-phase extraction

A procedure is developed and conditions are optimized for the pretreatment of natural water using distillation with no prefiltration of acidified water in combination with preconcentration by solid-phase extraction (SPE) on a Strata-X polymeric adsorbent followed by derivatization for the determination of trace concentrations of C3–C18 aliphatic carboxylic acids by gas chromatography with mass spectrometric detection. It is shown that, at the distillation stage, 90% of free carboxylic acids of the homologous series are transferred to the distillate, which greatly facilitates the procedure of the analysis of natural water containing impurity particles and humic substances and ensures the achievement of the limit of detection for the analytes about 0.05 μg/L. It is found that, at the SPE stage, the adsorbents based on copolymers of styrene, divinylbenzene, and N-vinylpyrrolidone in plastic cartridges may serve as sources of additional pollution with benzoic, palmitic, and stearic acids in the eluates under investigation.     

Synthesis and properties of water-soluble silica nanoparticles

Methods for synthesis and optimum conditions of the formation of stable water-soluble silica nanoparticles are presented. The silica nanoparticles were synthesized by the hydrolytic polycondensation of tetraethoxysilane using two methods: under alkaline conditions (Stöber´s method) or in an acetic acid medium followed by the modification by grafting triethylene oxide moieties on the particle surface. The structure of the modified silica nanoparticles was confirmed by the data of IR and NMR spectroscopy. Polydispersity was evaluated by gel permeation chromatography and dynamic light scattering. The formation and stability of Langmuir monolayers of the silica nanoparticles modified by triethylene oxide moieties were studied.     

Polysaccharides as Effective Sorbents for Lead and Cadmium

Sorption of lead and cadmium cations from solutions of their salts on amorphous cellulose, potato starch, apple pectin, and chicory root inulin was studied. Sample preparation was performed in conditions (pH and stirring time and intensity) similar to those in the stomach and intestines of a typical person. The sorption properties of the studied polysaccharides with respect to both the individual heavy metals and their mixtures is variable. The sorption properties series are cellulose ≈ pectin < starch< inulin for Pb²⁺ and cellulose < pectin < starch ≈ inulin for Cd²⁺.     

Synthesis and optical properties of new coumarin derivatives based on 2-(2-chlorobenzylidene)malononitrile

A procedure has been developed for the conversion of the CS gas [2-(2-chlorobenzylidene)-malononitrile] to new 3-cyanocoumarin derivatives, 4-(2-chlorophenyl)-2-oxo-2H-chromene-3-carbonitriles. Study of the optical properties of the synthesized compounds has revealed strong fluorescence in the violet and blue regions.     

Composition and reactivity of aminolysis products of phenyl glycidyl ether with benzylamine

Composition of aminolysis products of phenyl glycidyl ether with benzylamine in various conditions was studied. The ratio of 1-(benzylamino)-3-phenoxypropan-2-ol and 1,1'-(benzylazanediyl)bis(3-phenoxypropan-2-ol) does not considerably depend on the nature of the solvent and is basically determined by ratio of initial reagents. 2,6-Bis(phenoxymethyl)morpholine was obtained by dehydration of aminodiol in conditions of Mitsunobu reaction with subsequent reductive debenzylation.