Oxidation of methylbenzenes by heteropoly compounds in solution

Conclusions heteropoly compounds in acetic acid solution oxidize methylbenzenes to form mixtures of aromatic alcohols, aldehydes, di- and polyarylmethanes. The reaction may be carried out catalytically in the presence of oxygen. Results were obtained indicating the formation of an intermediate radical-cation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheska, No. 5, pp. 1010–1017, May, 1984.     

Observation of photon-assisted noise in a diffusive normal metal-superconductor junction

We report measurements of nonequilibrium noise in a diffusive normal metal-superconductor (N-S) junction in the presence of both dc bias and high-frequency ac excitation. We find that the shot noise of a diffusive N-S junction is doubled compared to a normal diffusive conductor. Under ac excitation of frequency nu the shot noise develops features at bias voltages |V| = hnu/(2e), which bear all the hallmarks of a photon-assisted process. Observation of these features provides clear evidence that the effective charge of the current carriers is 2e, due to Andreev reflection.     

Complete Scale of Isomorphisms for Elliptic Pseudodifferential Boundary-Value Problems

The aim of the paper is to establish a complete scale of isomorphismsfor elliptic pseudodifferential boundary value problems generatedby the operators of the Boutet de Monvel algebra. The resultis an extension of the corresponding known results on ellipticdifferential boundary value problems. Because for any ellipticpseudodifferential boundary value problem there exists a parametrixbelonging to the Boutet de Monvel algebra, the proof presentedis much shorter than the known proof for differential problems.Systems that are elliptic in the sense of Douglis and Nirenbergare also considered.     

Domain structure in a nematic layer under oscillatory Couette flow

The formation of a spatially modulated structure (domains) in a homeotropically aligned layer of a nematic liquid crystal (NLC) under an oscillatory Couette flow are described theoretically by using the hydrodynamic equations for an NLC which are linearized with respect to perturbations. The shear frequencies at which the phenomenon is determined by the inertial properties of the medium are considered. It is shown that the domain size is equal to the thickness h of an NLC layer and that the dependence of the threshold value of the shear amplitude u _th on the frequency ω and the layer thickness h is described by the expression u _th = const/(ωh²). The calculated results are compared with the experimental data.     

Exploring the Subtle Effect of Aliphatic Ring Size on Minor Actinide-Extraction Properties and Metal Ion Speciation in Bis-1,2,4-Triazine Ligands

The synthesis and evaluation of three novel bis-1,2,4-triazine ligands containing five-membered aliphatic rings are reported. Compared to the more hydrophobic ligands 1 – 3 containing six-membered aliphatic rings, the distribution ratios for relevant f-block metal ions were approximately one order of magnitude lower in each case. Ligand 10 showed an efficient, selective and rapid separation of Am^III and Cm^III from nitric acid. The speciation of the ligands with trivalent f-block metal ions was probed using NMR titrations and competition experiments, time-resolved laser fluorescence spectroscopy and X-ray crystallography. While the tetradentate ligands 8 and 10 formed Ln^III complexes of the same stoichiometry as their more hydrophobic analogues 2 and 3 , significant differences in speciation were observed between the two classes of ligand, with a lower percentage of the extracted 1:2 complexes being formed for ligands 8 and 10 . The structures of the solid state 1:1 and 1:2 complexes formed by 8 and 10 with Y^III, Lu^III and Pr^III are very similar to those formed by 2 and 3 with Ln^III. Ligand 10 forms Cm^III and Eu^III 1:2 complexes that are thermodynamically less stable than those formed by ligand 3 , suggesting that less hydrophobic ligands form less stable An^III complexes. Thus, it has been shown for the first time how tuning the cyclic aliphatic part of these ligands leads to subtle changes in their metal ion speciation, complex stability and metal extraction affinity.     

Electron transport in CaMnO3 − δ at elevated temperatures: a mobility analysis

The drift mobility of electron charge carriers in oxygen non-stoichiometric manganite CaMnO_3???δ was calculated by combining the total electrical conductivity and oxygen non-stoichiometry data at 700–950 °С and oxygen partial pressure varying between 10^?6 and 1 atm. The carrier concentration changes with pressure and temperature were obtained with the help of the earlier-developed defect model involving reactions of oxygen exchange and thermal excitation of manganese sites. The activation energy for mobility is found to increase with oxygen non-stoichiometry. High-temperature electron transport properties of the manganite CaMnO_3???δ can be explained in terms of activated jumps of n-type small polarons in adiabatic regime. The relatively small mobility of charge carriers is explained by strong localization of polarons on manganese sites.     

Thermodynamics of oxygen in CaMnO3 − δ

The experimental data for equilibrium oxygen content were used in order to extract increments of partial molar thermodynamic functions of oxygen with changes of oxygen stoichiometry in calcium manganite CaMnO_3???δ . It is shown that along with the oxygen exchange reaction, thermal excitation of Mn⁴⁺ cations plays an important role in equilibration of charged manganese species that appear in response to the loss of oxygen at heating. The interrelation of partial molar enthalpy and entropy of oxygen with electron and ion defect formation parameters is obtained in approximation of the point defect model. The nearly linear changes of oxygen partial molar enthalpy are shown to directly reflect thermally driven changes in concentration of Mn³⁺ cations.     

Reaction reversibility in α-pinene thermal isomerization: improving the kinetic model

Revision of the experimental data on α-pinene thermal isomerization attained in supercritical ethanol allowed us to expand the reaction scheme, which includes now six main products and eleven reversible reactions. The equilibrium constants of every reaction (K _{T, j} and K _Φ, j) were calculated to allow for reversibility of reactions. The thermochemical data of the pure compounds required to calculate constants K _{T, j} and K _{Φ, j} (standard enthalpy and entropy of formation Δ_f H° (298.15 K), Δ_f S° (298.15 K), heat capacity C _p (T), critical parameters T _cr and p _cr, boiling point T _b, and the acentric factor ω) were preliminary estimated using the empirical Joback and Benson methods. A kinetic model based on the new expanded scheme of reversible reactions was successfully identified and its kinetic parameters k _j (600 K) and E _j were determined. Detailed examination of the new kinetic model allowed us to refine the generally accepted mechanism of α-pinene thermal isomerization and to distinguish additional features of the multistep process.     

ChemInform Abstract: First‐Principles Calculations of the Elastic and Electronic Properties of the Cubic Perovskites SrMO3 (M: Ti,V, Zr and Nb) in Comparison with SrSnO3.

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