A convenient synthesis method of 5-oxopyrazolo[4,3-b]pyridine-6-carboxylic acids and their nitriles

Chemistry of Heterocyclic Compounds - N-Boc-protected 5-formyl-1H-pyrazol-4-amines react with malonic acid in pyridine in the presence of pyrrolidine at 45–50°С or with malonic...     

Photoluminescence Spectroscopy of an Aqueous Solution of Uranyl Cloride upon Laser and LED Excitation

The excitation of an aqueous solution of uranyl chloride by a 410-nm semiconductor LED and 266- and 448-nm lasers is found to induce intense photoluminescence: several bands in the blue-green spectral range (494 to 565 nm). Upon excitation of uranyl chloride aqueous solution by a 468-nm LED, the photoluminescence spectrum is a relatively narrow strong band peaking at 508 nm, which was interpreted as the transition from spontaneous photoluminescence to superluminescence. A lasing scheme (similar to that for dye lasers) has been proposed.     

Temperature hysteresis phenomena in heterogeneous catalysis

Temperature hysteresis is observed only in exothermic heterogeneous catalytic reactions (viz., oxidation and methanation of CO or propene hydrogenation) and is absent in the case of endothermic reactions (dehydrogenation of isobutane) or reactions with heat close to zero (viz., 2-butene isomerization). Temperature hysteresis in hydrogenation reactions was discovered for the first time. The concept of local overheating of catalyst active sites caused by poor removal of the reaction heat is proposed to provide a noncontradictory interpretation of the appearance of hysteresis loops. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1379–1385, August, 2000.     

Add a Pinch of Tetrel: The Transformation of a Centrosymmetric Metal into a Nonsymmorphic and Chiral Semiconductor

Centrosymmetric skutterudite RhP₃ was converted to a nonsymmorphic and chiral compound RhSi_0.3P_2.7 (space group P2₁2₁2₁) by means of partial replacement of Si for P. The structure, determined by a combination of X-ray crystallography and solid state ³¹P NMR, exhibits branched polyanionic P/Si chains that are unique among metal phosphides. A driving force to stabilize the locally noncentrosymmetric cis-RhSi₂P₄ and fac-RhSi₃P₃ fragments is π-electron back-donation between the Rh t_2g-type orbitals and the unoccupied antibonding Si/P orbitals, which is more effective for Si than for P. In situ studies and total energy calculations revealed the metastable nature of RhSi_0.3P_2.7. Electronic structure calculations predicted centrosymmetric cubic RhP₃ to be metallic which was confirmed by transport properties measurements. In contrast, the electronic structure for chiral orthorhombic RhSi_0.3P_2.7 contained a bandgap, and this compound was shown to be a narrow gap semiconductor.     

On frequency and temperature dependence of limiting efficiency in direct utilization of quasi-monochromatic radiation

The solution to the problem on limiting (thermodynamically permissible) efficiency η_m of direct conversion of energy of quasi-monochromatic radiation into work known from the literature leads to physically unacceptable results (η_m<0) in the range of small frequencies ν and temperatures T _ν of converted radiation. It is shown that the noted feature is a consequence of the approximate character of the mentioned solution obtained without taking into account background heat radiation: the exact solution obtained for η_m is valid for all ν and T _ν ≥ 0 and turns into the solution known earlier for $\overset{\lower0.5em\hbox{$\overset{\lower0.5em\hbox{ Fiziki, Vol. 70, No. 3, 2000, pp. 34–36.     

Pressure-tuning of magnetism and linkage isomerism in iron(II) hexacyanochromate

A pressure-induced linkage isomerization of the cyanide anion has been observed in single crystals of a chromium(III)-iron(II) Prussian blue analogue of formula K0.4Fe4[Cr(CN)6]2.8 square1.2.16H2O (1). Upon application of pressure in the 0-1200 MPa range, the cyanide ligand rotates and becomes C-bonded to the iron(II) cations, leading to a stabilization of their diamagnetic low-spin states. The result is a decrease of magnetization and magnetic ordering temperatures from TC = 19 K at ambient pressure to 13 K at 1200 MPa. The initial magnetic properties can be restored on pressure release. The reversible movement of cyanide in the solid state can be exploited as a switch of the magnetic interaction at the molecular level.     

Development of Functional Composite Cu(II)-Polyoxometalate/PLA with Antimicrobial Properties

Novel composite self-disinfecting films of polylactic acid (PLA) filled with nanosized particles of double sodium–copper(II) paratungstate B Na₂Cu₃(CuOH)₂[W₁₂O₄₀(OH)₂]·32H₂O (POM) were developed. The solvent casting (POM/PLA film) and solvent-free melt extrusion methods (Extr. POM/PLA film) were applied for film preparation. The copper (II) ion release to water from both types of the films after 10 days at different temperatures demonstrated that the PLA matrix acts as a diffusion barrier, and the resulting concentration of released copper in water at room temperature remained low, at 0.79% for POM/PLA film and 0.51% for Extr. POM/PLA film. The POM-containing films reveals a significant inhibitory effect against E. coli ATCC 25922 in the agar diffusion test. The numbers of CFUs in washes of the films after incubation for 24 h were found to be 3.6 log CFU mL^–1 (POM/PLA film) and 4.1 log CFU mL^–1 (Extr. POM/PLA film). The films combine the antibacterial properties of POM and a bio-based polymer matrix, which makes them a prospective coating material for applications in hospital indoor environments. Excellent thermal stability of POM gives a technological advantage for industrial manufacturing to allow the processing of novel composite material in the solvent free (molten) state.     

Low temperature phase transition in ZnSe doped with nickel

Neutron diffraction and ultrasonic experiments as well as measurements of heat conductivity in ZnSe and Zn_1−xNi_xSe (x=0.0025) semiconductors have been carried out. As a result, a structural transition induced by Ni impurity has been found at      

Numerical calculation of the dielectric relaxation time distribution function in polar liquids

A numerical method for calculation of the relaxation time distribution function based on the discrete Fourier transform of the dispersion part of the complex dielectric permittivity is developed. The time relaxation distribution function is found for water; its dispersion of relaxation times is narrow. This is explained by the presence of distorted hydrogen bonds (the Pople model).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 37–40, March, 1982.