Russian Chemical Bulletin最新文献

A new one-step method for the synthesis of the PtCo/ZSM-5 catalysts for CO oxidation was proposed. Heteronuclear acetate complexes of the empirical composition PtCo_x(AcO)_y containing Pt^II and Pt^IV in ratios with Co of 1: 1 or 1: 2 were used as precursors. According to the data of scanning and transmission electron microscopy and XPS, the impregnation of the HZSM-5 zeolite (Si/Al = 28) with a solution of the complexes in glacial acetic acid followed by decomposition at 200 or 300 °C leads to the stabilization of highly dispersed partially reduced Pt^δ+ particles interacting with cobalt ions on the zeolite surface. Their joint action and a possibility of formation of new Pt—O_x—Co sites active in the preferential oxidation of CO ensure high efficiency and selectivity of the process in an H₂ excess. At the relatively low Pt content from 0.1 to 0.3 wt.%, the complete conversion of CO on these catalysts is achieved in the wide temperature range from 50 to 130 °C.

The review is devoted to chemical modifications and properties of aminopurines, particularly 2(6)-mono- and 2,6-diaminopurines, the introduction of a glycoside moiety into the aminopurine system, and applications of aminopurines.

A series of substituted N-phenoxyacetyltaurates was synthesized from the corresponding phenoxyacetates by the reaction with potassium taurate. The unusual solid-state structure was established for potassium salt of N-(4-chlorophenoxyacetyl)taurine. According to the X-ray diffraction data, it consists of three symmetry-independent layers. Apart from ionic interactions and hydrogen bonds, the layers are stabilized by weak C—H⋯Cl van der Waals interactions. N-Substituted potassium taurates effectively reduced the level of lipopolysaccharide-induced proinflammatory cytokines in Raw264,7 cells. N-(3-Methoxyphenoxyacetyl)taurine inhibited a broad spectrum of key inflammatory mediators. The evaluation of biosafety demonstrated the absence of cytotoxicity of the compounds under study.

The DFT CAM-B3LYP/6-311++G(d,p) method showed that two migration mechanisms are possible for the 4-methoxybenzyl group in the pentamethoxycarbonylcyclopentadiene ring, namely, 1,5-sigmatropic shifts with an energy barrier ΔE^≠_ZPE = 32.5 kcal mol⁻¹ in the gas phase and a dissociative pathway through the formation of a tight ion pair with a lower activation barrier ΔE^≠_ZPE = 24.2 kcal mol⁻¹ in methanol (PCM). In contrast, the 4-nitrobenzyl group migrates in this system only via 1,5-sigmatropic shifts both in the gas phase and in methanol with higher activation barriers ΔE^≠_ZPE = 33.6 and 33.3 kcal mol⁻¹, respectively, whereas migrations of the benzhydryl group in the pentamethoxycarbonylcyclopentadiene ring occur via the dissociation—recombination mechanism both in the gas phase and in methanol with fairly low activation barriers ΔE^≠_ZPE = 24.0 and 21.5 kcal mol⁻¹, respectively.

The review is concerned with specific features of the molecular and electronic structure as well as spectral characteristics of palladium carboxylate complexes Pd₄(μ-L)₄(μ-RCO₂)₄ (R is an organic or organoelement substituent; L = CO, SR′, OOR′, CNR′, NO) having a planar rectangular metal core. The results of density functional quantum chemical calculations (including energy and vibrational frequency calculations) are analyzed. It was demonstrated that the most favorable arrangement of ligands around the metal core depends primarily on the nature of the ligand L, whereas the properties of the substituents R and R′ have little effect. The results of theoretical studies are consistent with experimental data.

Quantum chemical calculations performed reproduce well the experimental data on the temperature dependence of the magnetic susceptibility of mononuclear complexes [Ln(PyrCOO)(acac)₂(H₂O)₂] (Ln = Dy, Er, Yb, Eu, Gd, Tb, Ho, Tm; PyrCOOH is pyrazine-2-carboxylic acid) in a DC magnetic field. The calculated signs of zero-field splitting energy, which are negative for all the complexes studied, make it possible to consider the complexes as single-molecule magnets.

The formation of binuclear complexes of bis(18-crown-6)stilbene with Ho^III ions in anhydrous MeCN was studied by spectrophotometry and NMR spectroscopy. The quantum yields of the reversible E—Z photoisomerization of the complex under study were measured. The changes in the molar magnetic susceptibility of the binuclear complex caused by E—Z photoisomerization in solution at room temperature were demonstrated by the Evans method. The distances between the paramagnetic Ho^III ions in the complexes of E and Z isomers of bis(18-crown-6)stilbene were evaluated by density functional theory calculations.

This review analyzes the experimental and theoretical works in the field of spin chemistry, which is the basis for describing physical processes that occur when influencing the strength and plasticity of solids using constant magnetic fields, magnetic resonance excited in structure defects, as well as hyperfine interaction of magnetic nuclei. The conditions for observing these analogs of spin-dependent chemical processes in crystals are determined, and the various methods for identifying magnetic field-stimulated elementary events are considered.

According to the NMR studies, N-(2-bromocyclohexyl)triflamide and N-(2-bromocyclohexyl)-N′-(triflyl)amidine exist as trans-isomers with equatorially oriented substituents. The quantum chemical calculations of all conformers of cis- and trans-isomers of these compounds and their fluorine-substituted analogs in the gas phase and in the solution confirm a higher stability of the experimentally proved eq-eq-conformers. No direct correlation between the H⋯X hydrogen bond length (X is halogen) and stability of the conformers (because of a lower ability of the NH group than OH to be the hydrogen bond donor) for the compounds under study and the presence of intramolecular interactions of the oxygen or fluorine atoms of the triflamide group with the hydrogen atoms of the cycle were proved by a comparison of the calculation results with those for 2-halocyclohexanols.

Halogenation of 3-nitro-6-phenyl- and 3-formyl-6-phenyl-2H-thiopyrans with bromine or iodine nitrate led to 5-halo-2H-thiopyrans. Chlorination of 3-nitro-6-phenyl-2H-thiopyrans and imides of 6-phenyl-2H-thiopyran-2,3-dicarboxylic acids resulted in (2R*,3S*,4R*)-configured 2,3,4-trichloro-3,4-dihydro-2H-thiopyrans. Bromination of 3-nitro-2H-thiopyrans was shown to proceed under conditions of both electrophilic and radical halogenation.