Vol 66, No 7 (2017)

The problems of choosing metal-modifier for the surface of graphite electrodes used in voltammetric methods for analysis of a series of elements in solutions are reviewed. The presence of the modifier enhances the sensitivity of determination of elements using the graphite electrode, eliminates the impeding influence of some side processes, and makes it possible to determine elements having no electrooxidation peaks in the voltammograms in the working region of potentials of the graphite electrode.

The quantum chemical study of the mechanism was performed for tricarbonyl η⁶-complexes of coronene I-M and kekulene II-M (M = Cr, Mo, W) by the density functional method. The activation barriers of η⁶,η⁶-interring haptotropic rearrangements (IHR), being the migration of the metaltricarbonyl group M(CO)₃ from one six-membered aromatic ring to another, were determined. The processes of η⁶,η⁶-IHR in the metal tricarbonyl complexes with relatively high polycyclic aromatic hydrocarbons (PAH) I and II occur with close energy barriers (ΔG^≠ ≈ 20—25 kcal mol^–1), which are lower than the barriers (ΔG^≠ ~ 30 kcal mol^–1) of similar transformations measured or calculated earlier for the chromium tricarbonyl complexes of naphthalene and its derivatives and other PAH. For the molybdenum tricarbonyl complexes the activation barriers of η⁶,η⁶-IHR decrease additionally by ~ 5 kcal mol^–1 compared to those for the chromium tricarbonyl complexes, whereas for the tungsten tricarbonyl complexes they increase again and become approximately equal to the activation barriers of similar chromium tricarbonyl complexes. All stationary states on the potential energy surface determining the mechanism of η⁶,η⁶-IHR are characterized by a decrease in hapticity compared to the initial and final complexes.

Electron absorption and Fourier-transform IR spectroscopy was used to determine that the reaction of 1-methylimidazole (1-MeIm) with a nitrosyl complex of meso-tetra-p-tolylporphyrinate cobalt (Co(TTP)(NO)) at 210—240 K led to the formation of the six-coordinate complex (1-MeIm)Co(TTP)(NO), which was stable at low temperatures both in the solid state and in a solution of toluene. Based on the temperature dependence of the equilibrium constants, the thermodynamic parameters of complexation were calculated, which indicated a weak binding of the 1-methylimidazole ligand with the Co-porphyrin nitrosyl complex.

Two new iodobismuthates with the composition LnBiI₆•13H₂O (Ln = La, Nd) were synthesized and their crystal structures were determined. The compound LaBiI₆•13H₂O crystalizes in the orthorhombic space group Pna2₁, a = 24.206(5), b = 8.405(1), c = 26.360(5) Å; the compound NdBiI₆•13H₂O crystalizes in the monoclinic space group P2₁/n, a = 14.553(3), b = 13.386(3), c = 27.541(6) Å, β = 92.80(3)°. In both crystal structures, the cations Ln(H₂O)₉³⁺ and the anions BiI₆^3– alternate, forming a NaCl-type structure, and the structures themselves differ in the arrangement of water of crystallization that leads to the formation of dissimilar systems of hydrogen bonds. Both compounds undergo decomposition when heated, which is accompanied first by a partial liberation of water molecule, followed by pyrohydrolysis to form oxoiodides LnOI as final solid products. According to optical measurements, the band gap of the obtained compounds was equal to 1.78 (La) and 1.71 (Nd) eV.

Catalytic hydrogenation of benzene, biphenyl, and ortho-, metha-, and para-isomers of terphenyl over a 3 wt.% Pt/C at 180 °C and 70 atm was studied. The directions of hydrogenation of each substrate were revealed. Relationships between structures of the substrate and hydrogen consumption rates were found. It was shown that hydrogenation rate decreases on going from benzene to terphenyl and with increasing degree of the substrate hydrogenation. Hydrogenation rate of terphenyl isomers decreases in the following order: p-terphenyl > > m-terphenyl > o-terphenyl.

The electrochemical properties of a series of sterically hindered o-benzoquinones in aprotic solvents were examined. The reaction of O₂ and KO₂ with o-benzoquinones and electrogenerated o-semiquinone radical anions was studied. The formation of o-semiquinone radical anions in the reactions of KO₂ with the studied o-quinones was detected using UV-visible and ESR spectroscopy. The influence of the test compounds on lipid peroxidation was considered at the molecular and tissue levels in vitro. In the most cases, o-quinones exhibit antioxidant activity, which varies depending on the type of lipid substrate.

A method for the synthesis of promising nitric oxide donors in living organisms, 1,1´-[methylenebis(oxy)]bis[3-alkyl-3-(2-haloethyl)triaz-1-ene 2-oxides] was elaborated. The method involved replacement of hydroxy groups of the corresponding 1,1´-[methylenebis(oxy)]bis[3-alkyl-3-(2-hydroxyethyl)triaz-1-ene 2-oxides] by halogen atoms and, in some cases, the exchange of one halogen atom for another.

A method for the synthesis of imidazo[4,5-e]benzo[1,2-c;3,4-c´]difuroxanes, potential nitric oxide donors, has been developed. The synthesized compounds were characterized by IR and NMR spectroscopy, high resolution mass spectrometry, and elemental analysis.

We have developed preparative methods for the synthesis of substituted fulvenes including inden-2-ylphosphonic acid fragments, as well as aromatic and heterocyclic substituents, based on bis(trimethylsilyl)inden-2-ylphosphonate and substituted azomethines in the presence of sodium hydride as an efficient initiator of the reaction. Subsequent treatment of the phosphonates with methanolic solution of sodium methoxide furnished water-soluble disodium salts of the corresponding phosphonic acids.

Dicationic ionic liquids with bis(trifluoromethylsulfonyl)imide anions and dimethylimidazolic moieties linked by the polymeric siloxane chain in the cation structure have been synthesized. Thermal stability of the compounds synthesised was studied by TGA; glass transition temperatures, viscosities and volatility in vacuo were measured. Applicability of these ionic liquids as heat carriers under high dynamic vacuum conditions is shown.

Polymerization under ultrahigh pressure without involvement of initiators was used to synthesize amorphous copolymers of perfluoro-2,2-dimethyl-1,3-dioxole and perfluoro(propyl vinyl ether). The copolymers have molecular masses within 2•10⁴—7•10⁴ au, possess high optical transparency in the telecom ranges of wavelength at 0.85, 1.3, and 1.5 μm and very low refractive index n = 1.293—1.314 at the wavelength λ = 632.8 nm. They can form films and are promising as claddings for optical fibers and waveguides. Amorphous films with the thickness of 1—4 μm were prepared by spin-coating from solutions of the perfluorinated copolymers in perfluorodecalin.

Kinetic characteristics of the reaction between natural thiols, viz., glutathione, cysteine, and homocysteine, and peroxyl radicals formed upon decomposition of the azo initiator AAPH (2,2´-azobis(2-methylpropionamidine) dihydrochloride) in aqueous solutions at 37 °С were determined by the competing reaction method. The kinetics of radicals formation in the reaction between natural thiols and H₂O₂ was studied by the inhibitor method. The polymethine dye, pyridinium 3,3´-di-γ-sulfopropyl-9-methylthiacarbocyanine, was used as the radical scavenger. Cysteine was found to exhibit the highest activity in the reactions with peroxyl radicals and in the free radical generation upon the reaction with H₂O₂. The data obtained can be useful for understanding the physiological role of thiols in oxidative processes.

New 5-anilino-1,2,4-thiadiazole derivatives with different substituents at position 3 were synthesized and their influence on the key binding sites of NMDA receptors, inhibitory activity against acetylcholinesterase, butyrylcholinesterase, and carboxylesterase, as well as antioxidant properties were studied. The compounds with a 2-aminopropyl fragment were found to be efficient blockers of allosteric modulator [³H]ifenprodil binding site of the NR2B-containing NMDA receptors and moderate butyrylcholinesterase inhibitors. Some compounds were found to be able to simultaneously block the [³H]ifenprodil and intrachannel [³H]MК-801 binding sites of NMDA receptors. Compounds containing a 2-aminopropenyl fragment did not exhibit activity against NMDA receptors and butyrylcholinesterase, but showed high radical-scavenging activity.

Circular dichroism spectra of the optically active (R)- and (S)-enantiomers of N,N-(dimethylamino)ethylferrocene (Ugi´s amine) were studied for a free form and for their diastereomeric salts with с l(+)-tartaric acid.

A number of tris(2-hydroxyethyl)ammonium arylchalcogenylacetates ArYCH₂CO₂^–• •HN⁺(CH₂CH₂OH)₃ (1—4) (Ar = aryl; Y = O, S, SO₂) were synthesized. Their structure was established by IR and ¹H, ¹³C, ¹⁵N NMR spectroscopy. The influence of compounds 1—4 on the growth and development of yeast fungi Saccharomyces cerevisiae was studied. Compounds 1—4 were found to be efficient, safe, and available synthetic stimulants of these processes. The use of compounds 1—4 in low concentrations (from 10^–8 to 10^–4 wt.%, depending on the time of cultivation, concentration, and the anion type) reduced the lag-phases of development and increased the generation rate of yeast cells by 2—5 times. The amount of yeast cells increased by 2—3 times, while the content of protein in the biomass increased by 13—15%. The fermentation of sugar- and starch-containing raw material with yeast Saccharomyces cerevisiae increased the yield of ethyl alcohol (biofuel) by 5—9%.