Structural,Mechanistic, Spectroscopic,and Preparative Studies on the Lewis Base Catalyzed,Enantioselective Sulfenofunctionalization of Alkenes

The full details of mechanistic investigation on enantioselective sulfenofunctionalization of alkenes under Lewis base catalysis are described. Solution spectroscopic identification of the catalytically active sulfenylating agent has been accomplished along with the spectroscopic identification of putative thiiranium ion intermediates generated in the enantiodetermining step. The structural insights gleaned from these studies informed the design of new catalyst architectures to improve enantioselectivity. In addition, structural modification of the sulfenylating agents had a significant and salutary effect on the enantioselectivity of sulfenofunctionalization which was demonstrated to be general for trans disubstituted alkenes. Whereas electronic modulation had little effect on the rate and selectivity, steric bulk on arylsulfenylphthalimides was very beneficial.     

First-principles study of the structure,mechanical properties,and phase stability of crystalline zirconia under high pressure

We presented a detailed study on the structure, mechanical properties, and phase stability for three zirconia crystals under hydrostatic pressure of 0–100 GPa by using density functional theory within the generalized gradient approximation. It is found that m-ZrO₂ presents three phase transitions with increasing pressure, while t-ZrO₂ and c-ZrO₂ do not. As the pressure increases, the band gap of m-ZrO₂ presents three abrupt changes. The band gap of t-ZrO₂ firstly decreases and then increases slowly. The band gap of c-ZrO₂ increases monotonically. An analysis of elastic constants shows that the three oxides are anisotropic under compression with increasing pressure. As the pressure increases, their fracture strength and plastic strength are improved and they are all ductile. The calculated formation enthalpies suggest that the elements (Zr + O₂) are able to form m-ZrO₂, t-ZrO₂, or c-ZrO₂ in the whole pressure range, indicating that zirconium and its alloys are easy to be oxidized.     

Nature of the Active Centers of In-, Zr-, and Zn-Aluminosilicates of the ZSM-5 Zeolite Structural Type

In-, Zr-, and Zn- containing elementoaluminosilicates of ZSM-5 zeolite structural type are synthesized by means of hydrothermal crystallization from alkaline alumina–silica gels. Based on the data of structural morphological studies on the samples, it is established that introducting metals into the zeolite structure leads to the formation of particles different in morphology and elemental composition. Studies of the electronic state of active centers in elementoaluminosilicates (E-AS) show that Zn²⁺ and In³⁺ cations are associated with oxygen ions in zeolite channels with bonding energies inherent in their oxides. The high value of Zn 3d bonding energy explains the stability of zinc ions in the Zn-AS structure with no formation of clusters under heating the sample by an electron microscope beam. The isomorphic substitution of Al³⁺ ions in the zeolite crystal lattice by Zr⁴⁺ and In³⁺ ions, despite the relatively low Zr 3d and In 3d bonding energies, also results in the stability of Zr-AS and In-AS systems. It is found that the aggregation of Zr and In into oxide clusters is observed only under strong heating with the electron beam after the destruction of the zeolite channel structure.     

Metal carbonyl clusters as precursors of heterogeneous catalysts: Hydrogenation and disproportionation of monoenes, dienes, and arenes in the presence of H2Ru4(CO)13, H2FeRu3(CO)13, and HRuCo3(CO)12 supported and activated on chromosorb. Characterization of the metal particles derived from H2Ru4(CO)13 by means of IR spectroscopy and TEM microscopy

The tetrahedral hydridic clusters H₂Ru₄(CO)₁₃ (1), H₂FeRu₃(CO)₁₃ (2), and HRuCo₃(CO)₁₂ (3) were supported on Chromosorb P and activated under dihydrogen flow. The resulting metal particles are active in the hydrogenation of pentenes, cyclic monoenenes and dienes, benzene, and toluene; these catalysts are effective under mild conditions and with a low metal loading. Experiments under dinitrogen showed that complex hydrogenation-dehydrogenation processes occur, as already observed for the same clusters during the homogeneous hydrogenation of cyclohexadienes. After the gas-chromatographic catalytic runs with cluster 1 as precursor, TEM microscopy showed the presence of very small supported metal particles (mean size 7.5 nm). The decomposition of cluster 1 to metal particles upon thermal treatment on Aerosil under vacuum or under dihydrogen was followed by means of IR spectroscopy; this catalyst hydrogenates benzene at room temperature with 100% conversion in a very short time (calculated activity was about 3200 TOFs).     

High-throughput first-principle calculations of the structural,mechanical, and electronic properties of cubic XTiO3 (X = Ca,Sr, Ba,Pb) ceramics under high pressure

High-throughput first-principle calculations are implemented to study the structural, mechanical, and electronic properties of cubic XTiO₃ (X = Ca, Sr, Ba, Pb) ceramics under high pressure. The effects of applied pressure on physical parameters, such as elastic constants, bulk modulus, Young's modulus, shear modulus, ductile-brittle transition, elastic anisotropy, Poisson's ratio, and band gap, are investigated. Results indicate that high pressure improves the resistance to bulk, elastic, and shear deformation for XTiO₃ ceramics. Pugh's ratios B/G reveal that CaTiO₃ and PbTiO₃ ceramics are ductile, but SrTiO₃ and BaTiO₃ ceramics are brittle under the ground state. The brittle-to-ductile transition pressures are 24.26 GPa for SrTiO₃ and 43.23 GPa for BaTiO₃. Under high pressure, the strong anisotropy promotes the cross-slip process of screw dislocations, and then enhances the plasticity of XTiO₃ ceramics. Meanwhile, XTiO₃ (X = Ca, Sr, Ba) is intrinsically an indirect-gap ceramic, but PbTiO₃ is a direct-gap ceramic. High pressure increases the band gap of XTiO₃ (X = Ca, Sr, Ba) ceramic, but decreases that of PbTiO₃ ceramic. This work is helpful for designing and applying XTiO₃ ceramics under high pressure.     

Specific features of the structure,reactivity, thermolysis,and magnetism of cymantrenecarboxylate complexes of lanthanides

The properties of the cymantrenecarboxylate (containing (CO)₃ Mn(η⁵-C₅H₄CO₂ ^- group) complexes of lanthanides obtained and studied by the authors in the years 2009–2015 are reviewed. The complexes represent a new type of heterometallic 3d–4f compounds. Both binuclear and polymer complexes of various types are synthesized. The variation of the synthesis conditions and the use of additional ligands make it possible to successively change the Mn: Ln ratio in a molecule of the compounds and to obtain the ratio equal to 3: 1, 2: 1, and 1: 1. The polymeric heteroleptic derivatives, acetate and acetyacetonate cymantrenecarboxylates, are synthesized. Using the photolabile cymantrene fragment as a source of Mn²⁺ ions, polynuclear Mn–Ln heterometallic cymantrenecarboxylates are obtained under the oxidative photolysis conditions. The influence of binuclear neodymium cymantrenecarboxylate on the polymerization of dienes is studied. The structures of the complexes, their physicochemical properties, and possibilities of practical application are considered.     

Bifunctional Onium and Potassium Iodides as Nucleophilic Catalysts for the Solvent-Free Syntheses of Carbonates,Thiocarbonates, and Oxazolidinones from Epoxides

The catalytic potential of organo-onium iodides as nucleophilic catalysts is aptly demonstrated in the synthesis of cyclic carbonates from epoxides and carbon dioxide (CO₂), as a representative CO₂ utilization reaction. Although organo-onium iodide nucleophilic catalysts are metal-free environmentally benign catalysts, harsh reaction conditions are generally required to efficiently promote the coupling reactions of epoxides and CO₂. To solve this problem and accomplish efficient CO₂ utilization reactions under mild conditions, bifunctional onium iodide nucleophilic catalysts bearing a hydrogen bond donor moiety were developed by our research group. Based on the successful bifunctional design of the onium iodide catalysts, nucleophilic catalysis using a potassium iodide (KI)-tetraethylene glycol complex was also investigated in coupling reactions of epoxides and CO₂ under mild reaction conditions. These effective bifunctional onium and potassium iodide nucleophilic catalysts were applied to the solvent-free syntheses of 2-oxazolidinones and cyclic thiocarbonates from epoxides.     

Interplay of thermochemistry and structural chemistry, the journal (volume 15, 2004) and the discipline

As practiced disciplines, structural chemistry, and thermochemistry need not necessarily be related. Yet such relationships, ranging from minor to very close, can help our overall understanding and detailed analyses of the species and methods under consideration. In the current study, these relations are made more evident from among the contents of the journal “Structural Chemistry” (Vol. 15) for the year 2004. The year’s articles have been reviewed, giving to most of those appearing therein a thermochemical commentary, “spin” or “slant.” A special emphasis is made on raising questions or noting possible future research topics that arise when looking at the relations noted earlier.     

On the selectivity of the biomimetic oxidation of the saturated hydrocarbon 1,3-dimethyladamantane in a Gif-type system containing a Fe2+ salt, picolinic acid, and pyridine

The effects of the composition of a heterogeneous catalytic system based on Fe₂SO₄ · 7H₂O, picolinic acid (pyridine-2-carboxylic acid), and pyridine and system preparation procedures on the selectivity of oxidation of 1,3-dimethyladamantane (1,3-DMA) with an aqueous 30% hydrogen peroxide solution in an aqueous acetonitrile solvent at room temperature and ambient pressure were studied. The yields of 1,3-DMA oxidation products were increased from fractions of a percent in initial experiments to the tens of percent under new catalytic conditions of final experiments. It was found that three different mechanisms can occur in the test system under various conditions; conceivably, these are radical, ion-molecule, and radical-cation mechanisms. In the first case, a statistical mixture of the products of 1,3-DMA oxidation at tertiary and secondary C-H bonds was formed. In the second and third cases, oxidation occurred only at secondary and tertiary C-H bonds, respectively. Unlike the first two cases, the selectivity of 1,3-DMA oxidation to a tertiary alcohol under conditions of the Gif-type test system corresponds to the selectivity of biological oxidation and, to the best of our knowledge, is the first example of this kind.     

Screening of laccase, manganese peroxidase, and versatile peroxidase activities of the genus Pleurotus in media with some raw plant materials as carbon sources

Species of the genus Pleurotus are among the most efficient natural species in lignin degradation belonging to the subclass of ligninolytic organisms that produce laccase (Lac), Mn-dependent peroxidase (MnP), versatile peroxidase (VP), and the H₂O₂-generating enzyme aryl-alcohol oxidase, but not lignin peroxidases. Production of Lac and oxidation of 2,6-dimethoxyphenol (DMP) in the presence and absence of Mn²⁺ were detected both in submerged fermentation (SF) of dry ground mandarine peels and in solid-state fermentation (SSF) of grapevine sawdust in all investigated Pleurotus species and strains. Evidence of cultivation methods having a distinct influence on the level of enzyme activities has been demonstrated. Most of the species and strains had higher Lac activity under SSF conditions than under SF conditions. DMP oxidation in the presence and absence of Mn²⁺ was detected in all investigated species and strains, but was lower under SF conditions than under SSF conditions for most of them. However, relative activities of DMP oxidation in the absence of Mn²⁺, as percentages of activity agasint DMP in the presence of Mn²⁺, were higher under conditions of SF than in SSF cultures in most of the investigated species and strains. The obtained results showed that strains of different origins have different efficiently ligninolytic systems and that conditions of SSF are more favorable for ligninolytic activity than those in SF owing to their similarity to natural conditions on wood substrates.     

Reactions of 2-allylthiobenzimidazole, -oxazole, -thiazole, and the isomeric thiones with dichlorocarbene

The reactions of 2-allylthiobenzimidazole, -oxazole, and-thiazole, and the thiones formed from them on heating, with dichlorocarbene have been investigated under phase transfer catalysis conditions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 243–248, February, 2000.     

Estimation of parameters characterizing the adsorption of sodium,potassium, and rubidium cryptates at the mercury electrode/solution interface

The adsorption of complexes formed by sodium, potassium, and rubidium cations with macrobicyclic ligand (kryptofix 222 with C₁₈H₃₆N₂O₆ composition) is studied as a function of the ligand concentration on a stationary mercury drop in 0.1 M solutions of corresponding sulfates and chlorides by using the differential capacitance technique. Based on the model of two parallel capacitors supplemented by the Frumkin isotherm, the adsorption parameters of studied cryptates are estimated by using the regression analysis technique. Differential capacitance curves calculated with the parameters found are compared with experimental data. The comparison of the found adsorption parameters makes it possible to reveal the effects of the nature of included cations and specifically adsorbed supporting-electrolyte anions on the adsorption behavior of cryptates under study.__________Translated from Elektrokhimiya, Vol. 41, No. 4, 2005, pp. 475–481.Original Russian Text Copyright © 2005 by Stenina, Sviridova.     

Effect of Different Saline,Alkaline Salts,Fertilizers and Surfactants on the Movement of Some Carbamoyl Group Containing Pesticides in Soils

Abstract

The influence of organic matter, calcium carbonate, flyash, saline and alkaline salts, inorganic fertilizers, surfactants and exchangeable ions on the mobility of five carbamoyl group containing pesticides has been studied using soil thin-layer chromatography. The variations in the R_f, R_B and R_M values of aldicarb, bavistin, carbofuran, dimecron and oxamyl under different treatments are reported and explained on the basis of adsorption and leachability.     

Quantum-chemical interpretation of the mass spectra of pyrrole,furan, and thiophene

A simple quantum-chemical interpretation of the mass-spectrometric fragmentation of organic molecules in which the probability of the cleavage of the bonds under the influence of electron impact is related to their self-consistent -electron orders and the possible rearrangement processes are described on the basis of the long-range bond orders is proposed. This approach was tested in the case of pyrrole, furan, and thiophene.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 620–624, May, 1987.     

Half-metallicity,magnetism, mechanical,thermal, and phonon properties of FeCrTe and FeCrSe half-Heusler alloys under pressure

The half-metallicity of Heusler alloys is quite sensitive to high pressure and disorder. To understand this phenomenon better, we systematically studied the half-metallic nature, magnetism, phonon, and thermomechanical properties of FeCrTe and FeCrSe Heusler alloys under high pressure using ab initio calculations based on density functional theory. The ground-state lattice constants for FeCrTe and FeCrSe alloys are 5.93 and 5.57 Å, respectively, consistent with available theoretical results. Formation energy, cohesive energy, elastic constants, and phonon dispersion confirmed that both compounds are thermodynamically and mechanically stable. The FeCrTe and FeCrSe alloys showed a half-metallic character with a band gap of 0.68 and 0.58 eV at 0 GPa pressure, respectively, and magnetic moments of 2.01 μ_B for both alloys, using generalized gradient approximation (GGA) approximation. FeCrTe alloy changes from metallic to half-metallic above 30 GPa pressure using GGA + U. The elastic properties were scrutinized, and it was found that, at 0 GPa pressure, FeCrTe is ductile, and FeCrSe is brittle. Under pressure, FeCrSe becomes brittle above 10 GPa pressure. Average sound velocity V_m, Debye temperature Ɵ_D, and heat capacity C_V were predicted under pressure. These outcomes will improve the integration of Fe-based half-Heusler alloys in spintronic devices.     

Nanocomposites of silver with arabinogalactan sulfate: Preparation,structure, and antimicrobial activity

Silver-containing nanocomposites based on sulfated arabinogalactan have been prepared under mild conditions. The products contain 2–12 nm silver nanoparticles stabilized by the polymer. The composites are readily water-soluble and reveal antimicrobial activity against a wide range of bacteria and fungi.

     

Analytical expressions for the electrical potential near planar, cylindrical, and spherical surfaces for symmetric electrolytes

The conjecture of Tuinier (J. Colloid Interface Sci. 258 (2003) 45) for the electrical potentials near a cylindrical surface and near a spherical surface under the conditions of symmetric electrolyte and large scaled radius are derived by solving the corresponding Poisson-Boltzmann equation. The surface charge density-surface potential relations for these surfaces are also derived under the conditions of constant surface potential. We show that the level of surface charge density for planar, cylindrical, and spherical surfaces follows the order spherical surface > cylindrical surface > planar surface.     

Thermal stability, crystallization, structure and morphology of syndiotactic 1,2-polybutadiene/organoclay nanocomposite

Syndiotactic 1,2-polybutadiene/organoclay nanocomposites were prepared and characterized by thermogravimetry analysis (TGA), X-ray diffraction (XRD), polarized optical microscopy (POM), and differential scanning calorimetry (DSC), respectively. The XRD shows that exfoliated nanocomposites are formed dominantly at lower clay concentrations (less than 2%), at higher clay contents intercalated nanocomposites dominate. At the same time, the XRD indicates that the crystal structures of sPB formed in the sPB/organoclay nanocomposites do not vary, only the relative intensity of the peaks corresponding to (0 1 0) and (2 0 0)/(1 1 0) crystal planes, respectively, varies. The DSC and POM indicate that organoclay layers can improve cooling crystallization temperature, crystallization rate and reducing the spherulite sizes of sPB. TGA shows that under argon flow the nanocomposites exhibit slight decrease of thermal stability, while under oxygen flow the resistance of oxidation and thermal stability of sPB/organoclay nanocomposites were significantly improved relative to pristine sPB. The primary and secondary crystallization for pristine sPB and sPB/organoclay (2%) nanocomposites were analyzed and compared based on different approaches. The nanocomposites exhibit smaller Avrami exponent and larger crystallization rate constant, with respect to pristine sPB. Primary crystallization under isothermal conditions displays both athermal nucleation and three-dimensional spherulite growth and under nonisothermal processes the mechanism of primary crystallization becomes very complex. Secondary crystallization shows a lower-dimensional crystal growth geometry for both isothermal and nonisothermal conditions. The activation energy of crystallization of sPB and sPB/organoclay nanocomposites under isothermal and nonisothermal conditions were also calculated based on different approaches.     

Measurement of the reactive and available solid-supported carboxylic,N-hydroxysuccinylated carboxylic,and aldehydo groups

We describe new colorimetric methods for the determination of the reactive and available solid-supported carboxylic,N-hydroxysuc cinylated carboxylic, and aldehydo groups under conditions usually applied for the coupling of biomolecules. The methods involve the reaction of the solid-supported functional groups with tyramine or cysteine, and the subsequent titration of the ligand coupled onto the solid supports using the commercially available bicinchoninic acid/copper protein assay reagent (BCA). The titration is based on the ability of these ligands to reduce Cu²⁺ to Cu⁺, which forms a chelate complex with bicinchoninic acid absorbing at 562 nm. The quantita tion is finally carried out through standard curves obtained using tyramine or cysteine solutions of known concentrations. The values obtained by the assays developed for several solid supports carrying carboxylic, NHS-ester, and aldehydo groups were well correlated with those obtained by other literature methods or provided by the manu facturers. All of the proposed methods are simple, more sensitive than other relevant literature methods, and require only commericially available reagents.     

Synthesis of mono-, di-, tri-, and tetraethyl-o-carboranes by electrophilic alkylation ofo-carborane with ethyl bromide in the presence of AICl3 and their transformations

Optimal conditions for the preparation of 9-ethyl-, 9,12-diethyl, 8,9,12-triethyl-, and 8,9,10,12-tetraethyl-o-carboranes under the action of EtBr on o-carborane in the presence of AICl₃ were determined. The behavior of these o-carborane derivatives towards electrophilic and nucleophilic reagents was studied. The presence of four ethyl groups in positions 8, 9, 10, and 12 of the carborane polyhedron increases the electron density on the boron atoms in positions 4, 5, 7, and II to the point where they are able to enter into reactions of electrophilic substitution, and in positions 3 and 6 to the point that they become resistant to the action of nucleophilic reagents. Reactions of 1,2-dilithium-8,9,10,12-tetraethyl-o-carborane with various electrophilic reagents were studied.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp 2755–2763, November, 1996.