Thermophoto-emf of hot carriers in <Emphasis Type="Italic">γ</Emphasis>-irradiated single crystals of Cadmium Mercury Tellurides

The effect of γ-irradiation on thermophoto-emf of hot carriers in n-Cd_0.94Hg_0.06Тe and р-Cd_0.82Hg_0.18Тe single crystals has been studied. The dependence of the pattern of |U_tp| curves on E in the test Cd_xHg_1—хTe crystals is explained by the change in the degree of spatial heterogeneity of these crystals resulted from the accumulation of point radiation defects at relatively low D_γ and their spatial ordering caused by the introduction of a large number of point radiation defects at higher exposures. The proposed mechanism for the effect of γ-irradiation on the thermophoto-emf of hot carriers explains satisfactorily the dependence of |U_tp| kinetics on radiation dose, sample composition, temperature, and field strength.     

Extraction-pyrolytic synthesis and luminescent properties of europium and terbium polytantalates

The promise of synthesis of europium and terbium polytantalates MTa _x O _y , where М = Eu, Tb; x = 7, y = 19; x = 5, y = 14; x = 3, y = 9 by low-temperature extraction-pyrolytic method has been shown. Luminescent properties of the prepared polytantalates have been assessed from excitation and luminescence spectra at 300 K. The dependence of luminescent characteristics of the studied rare earth metal polytantalates on the temperature and time of precursor pyrolysis has been established.     

Effect of γ-irradiation on conductivity of cadmium-mercury-tellurium single crystals in weak and strong electric fields

The effect of γ-radiation on electrical conductivity of Cd _x Hg_{1 ? x} Te (0.25 ≤ x ≤ 0.95) single crystals in weak and strong electric fields has been investigated. It has been shown that at relatively low fields in which charge carriers are still warm, the dependence (Δσ/σ₀) ～ E ² is observed because of the dominance of scattering on acoustic lattice vibrations with the increasing electric field strength; with a further increase in the field strength, the carriers become hot and the dependence of σ upon E becomes linear. The effect of irradiation by Γ-rays on the dependence of σ upon E in these samples is explained by a significant concentration of the intrinsic impurity centers in the crystals and their redistribution with the increasing radiation dose.     

Circular dichroism of photoemission of Fe<Subscript>1/4</Subscript>TiTe<Subscript>2</Subscript>

High-resolution ARPES has been employed for examination of angular distribution of valence band photoelectrons emitted by a Fe_1/4TiTe₂ single crystal near the point Γ of the Brillouin zone in the most symmetrical directions ΓK (A-H) and ΓM (A-L) under excitation with synchrotron radiation (21.5 eV, He I) at 50 K. It has been found out that excitation with circular polarized synchrotron radiation results in essential circular dichroism in angular dependence of valence band photoemission of Fe_1/4TiTe₂. Analysis of entire experimental data has revealed that the dichroic effect is also related to the chiral geometry of the experiment. The decrease in symmetry induces dichroism, thus allowing determination of electron states at intercalant atoms.     

Crystal structure of a cobalt oxide LuBaCo<Subscript>4</Subscript>O<Subscript>7</Subscript>

Crystals of LuBaCo₄O_7+δ (114Lu) have been obtained by spontaneous crystallization of slowly cooled nonstoichiometric melt of the system Lu-Ba-Co-O. The crystals have been characterized by EDX microprobe and synchrotron radiation powder diffraction. Structure refinement has been carried out (automated diffractometer Bruker X8 APEX with a CCD detector, MoK _α, graphite monochromator, ?_max = 32.54°). Parameters of the hexagonal unit cell: space group P6₃ mc, a = 6.2601(1) Å c = 10.2017(3) Å V = 346.23(1) Å₃, Z = 2, d _calc = 6.331 g/cm₃. Framework structure of the wurtzite type has been refined anisotropically to R-factor 0.0174. Charge balance in the compound and geometrical matching of structural fragments are discussed.     

Effect of donor and acceptor properties of solvents on the kinetics of photoreduction of sterically hindered <Emphasis Type="Italic">о</Emphasis>-benzoquinones

Effect of the solvent nature on the kinetics of photoreduction of 3,6-di-tert-butyl-1,2-benzoquinone and its six derivatives in the presence of N,N-dimethylaniline and 4-(N,N-dimethylamino)benzaldehyde has been investigated. It has been found that for the о-quinone—amine pair, for which the free energy change of electron transfer is ΔG_e > +0.11 eV, the rate constant of о-quinone photoreduction k_H decreases proportionally to the increase in the acceptor number of the solvent. For the о-quinone—amine pair with ΔG_e < +0.11 eV, the k_H value decreases proportionally to the increase in the donor number of the solvent. It has been established that the enhancement of the electron-acceptor properties of the solvent leads to the emergence of kinetic isotope effect for the reactant pairs of 3,6-di-tert-butyl-1,2-benzoquinone and 4,5-dimethoxy-3,6-di-tert-butyl-1,2-benzoquinone with N,N-di-methylaniline (ΔG_e = +0.11 and +0.22 eV, respectively).     

Synthesis,Spectroscopic and Computational Studies of CT Complexes of Amino Acids with Iodine as σ Acceptor

Understanding the charge transfer process between bioactive molecules and inorganic or organic molecules is significant as this interaction can be used to interpret bioactive molecule–receptor interactions. A comprehensive spectrophotometric study has been performed to explore the complexation chemistry of the amino acids, tyrosine, lysine and arginine, with iodine as σ acceptor. The molecular structure, spectroscopic characteristics and the interactive modes have been deduced from UV–Vis and IR spectra. The binding ratio of complexation has been determined to be 1:1 for iodine with the amino acids. The association constant (K), extinction coefficient (ε _max), ionization potential (IP), energy of the charge transfer complex (E _CT), resonance energy (R _N ), dissociation energy (W) and standard Gibbs energy (ΔG°) have been computed. An in silico study has been carried out using GAMESS computations to understand the structural features. Highest occupied molecular orbital and lowest unoccupied molecular orbital calculations helped us in characterizing the chemical reactivity and kinetic stability of the molecules. A good consistency between experimental and computational results has been found.     

Diffusion and phase behavior of a hydroxypropylcellulose-poly(ethylene glycol) system

The solubility and interdiffusion between hydroxypropylcellulose samples of various molecular masses (M _w = 8 × 10⁴, 14 × 10⁴, 37 × 10⁴, 85 × 10⁴, and 115 × 10⁴) and poly(ethylene glycol) (M _w = 400 and 1500) in the range 18–210°C have been studied by optical interferometry and polarization microscopy methods. Oligomeric poly(ethylene glycols) have been considered as solvents for hydroxypropylcellulose. Phase diagrams have been constructed, and Flory-Huggins thermodynamic interaction parameters have been calculated. For the hydroxypropylcellulose-poly(ethylene glycol) 400 system, an LC and crystalline equilibria have been realized. An increase in the M _w of hydroxypropylcellulose to 1500 leads to the appearance of a wide region of amorphous phase segregation with a UCST, whereas the liquidus line is conserved at high concentrations of hydroxypropylcellulose. Such a superposition of two kinds of phase equilibrium that is achieved only with a change in M _w of the oligomeric solvent has been observed for the first time. For all the systems under examination, the kinetics of diffusion mixing has been estimated and the activation energies of the process have been calculated. The concentration dependences of diffusion coefficients demonstrate jumps in the mesomorphic-transition region.     

Characterization and crystal structure of a new layered cadmium diphosphate: KCdHP<Subscript>2</Subscript>O<Subscript>7</Subscript>∙2H<Subscript>2</Subscript>O

A new potassium cadmium hydrogen diphosphate dihydrate, KCdHP₂O₇?2H₂O (1), has been synthesized by slow evaporation at room temperature and characterized by FT-IR, Raman, TG-DTA, and single crystal X-ray diffraction. Compound (1) crystallizes in the orthorhombic Pcmn space group with the unit cell parameters a = 6.5814(8) Å, b = 7.9428(9) Å, c = 15.961(6) Å, V = 834.4(3) Å3 and Z = 4. Its structure consists of polyhedral layers parallel to the ab plane where each CdO₆ octahedron (m position) shares four edges with three different diphosphate groups. In the Cd octahedron, two oxygen atoms residing in (m) special positions belong to coordinated water molecules. These layers are joint by K⁺ cations (4c Wyckoff position) and hydrogen bonds, leading thus to a two-dimensional framework. The structural model is supported by the bond-valence-sum validation tool as calculated valences are close to the formal oxidation numbers.     

Thermal polymerization of styrene: New data on the conversion dependence of the initiation rate

With the aid of new acceptors of free radicals usable at high temperatures (T > 100°C), the rate of initiation w _i has been measured experimentally for the thermal polymerization of styrene at 122.5°C in a wide range of conversions C = 0–80%. It has been shown that the value of w _i tends to increase in the course of polymerization transformation in agreement with the w _i = f(C) relationship calculated from the kinetic data on the thermal polymerization of styrene in the absence of counters of free radicals. Hypothetical reasons for this non-trivial tendency have been formulated. The experimental dependence w _i = f(C) has been measured for the first time and has been invoked to refine currently available mathematical models for the thermal polymerization of styrene that assume that w _i remains invariable in the course of polymerization transformation.     

Coordination Polyhedra MC<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (M Is <Emphasis Type="Italic">s</Emphasis>-Metal Atom) in Crystal Structures

The crystallochemistry of compounds containing s-metal atoms in the carbon environment has been analyzed using the method of Voronoi–Dirichlet intersecting sectors and polyhedra. The chemical nature of the s metal has been found to affect the characteristics of the Voronoi–Dirichlet polyhedra. It is shown that the volume of Voronoi–Dirichlet polyhedron is practically independent of the coordination number of the s-metal atom.     

Effect of solvent nature on the photoreduction kinetics of substituted benzoquinones

Effect of the solvent nature on the kinetics of photoreduction of substituted benzoquinones in the presence of hydrogen donors has been studied. It has been found that the effective photoreduction rate constant (k_H) for quinones decreases with an increase in solvent polarity. For the 3,6-di-tert-butylbenzoquinone–1,2-N,N-dimethylaniline pair, the dependence of ln k_H on the difference of the reciprocals of optical and static solvent permitivities (1/ε _∞–1/ε₀) is stepwise with a break point corresponding to CH₂Cl₂. A similar relationship lnk_H = f(1/ε _∞–1/ε₀) is observed for the p-chloranil–mesitylene pair. In the study of the photoreduction kinetics for a series of seven o-benzoquinones in the presence of p-derivatives of N,N-dimethylaniline in CH₂Cl₂, it has been found that the dependence of k_H on the free energy of electron transfer (ΔG_e) has a maximum for the 3,6-di-tert-butylquinone-1,2–N,N-dimethylaniline pair at ΔG_e = 0.11 eV.     

Dynamic structure of organic compounds in solution according to NMR data and quantum mechanical calculations: I. Soman

Dynamic structure of Soman diastereoisomers has been studied with the goal of obtaining accurate information to simulate molecular mechanisms of its action on living systems. The potential energy surface for internal rotation about the single P–O and O–C bonds has been constructed in terms of the Møller–Plesset second-order perturbation theory using 6-311G(d,p) basis set. The relative contributions of different conformers have been estimated by solving the vibrational problem according to the large-amplitude vibration model. The conformational dependences of the ⁴J_CF and ³J_CP coupling constants for the S,S and S,R diastereoisomers of Soman have been calculated at the FPT DFT B3LYP/6-311++G(2df,2p) level of theory. The calculated vibrationally averaged coupling constants have been compared with the available experimental data to determine the structure of the most toxic Soman stereoisomer.     

Thermodynamic Properties of Polyphenylquinoxaline in the Temperature Range of <Emphasis Type="Italic">T</Emphasis> → 0 to 570 K

The thermodynamic properties of amorphous polyphenylquinoxaline in the temperature range of 6 to 570 K are studied via precision adiabatic vacuum calorimetry and differential scanning calorimetry. The thermodynamic characteristics of glass transition are determined. Standard thermodynamic functions C^°_p, H°(T) ? H°(0), S°(Т) ? S°(0), and G°(T) ? H°(0) in the range of T → 0 to 570 K and the standard entropy of formation at T = 298.15 K are calculated. The low-temperature (T ≤ 50 K) heat capacity is analyzed using a multifractal model for the processing of heat capacity, fractal dimension D values are determined, and conclusions on the topological structure of the compound are drawn.     

Phase-equilibrium and cellulose-coagulation kinetics for cellulose solutions in <Emphasis Type="Italic">N</Emphasis>-methylmorpholine-<Emphasis Type="Italic">N</Emphasis>-oxide

The dissolution of cellulose in N-methylmorpholine-N-oxide monohydrate and the dissolution of N-methylmorpholine-N-oxide monohydrate in water have been studied via optical interferometry. A part of the phase diagram for the cellulose/N-methylmorpholine-N-oxide system has been constructed. The phase diagram is characterized by crystalline equilibrium, hysteresis of the melting temperatures of the solvents, and a region of anisotropy. Optical interferometry has been used for the first time to study the kinetics of cellulose coagulation during the interaction of cellulose solutions in N-methylmorpholine-N-oxide with water and water solutions of N-methylmorpholine-N-oxide. Information on the values of interdiffusion coefficients and the morphologies of the resulting cellulose films has been obtained. The possibility to use optical interferometry to analyze the interaction of a solution with the coagulating agent in the case of cellulose fiber and film formation has been demonstrated. The influences of temperature, the nature of the coagulating agent, and the cellulose content on the kinetics of the process and morphologies of the formed films have been shown. The use of N-methylmorpholine-N-oxide as a part of the coagulation system decreases the rate of interdiffusion of solutions, thereby resulting in a more uniform and dense morphology of cellulose films. Increased temperature causes diffusion acceleration, thereby leading to the formation of an anisotropic morphology of the cellulose films.     

Power consumption for an agitated vessel equipped with pitched blade turbine and short baffles

Power characteristics for an agitated vessel equipped with planar short baffles of length L and pitched blade turbine of pitch β are presented in the paper. The studies were carried out in the vessel of inner diameter D = 0.6 m, where the baffles were located in the distance p from the vessel bottom (p + L = H). Torque was measured using strain gauge method within the turbulent regime of the flow of Newtonian liquid in the agitated vessel. The effects of the pitch β and geometrical parameter p/H on the power number Ne were determined mathematically. The results showed that, for the assumed value of the angle β, the function Ne = f (L/H) decreases with the decrease in the baffle length L (i.e. with the increase in the parameter p). Moreover, for the assumed value of the baffle length L, the function Ne = f (β) increases with the increase in the angle β of the inclination of the impeller blade.     

4,7,13,16,21,24-Hexaoxa-1,10-diazoniabicyclo[8.8.8]hexacosane hydrogen phosphate octahydrate: Synthesis and crystal structure

A crystalline hydrated salt of the 2.2.2-cryptand and phosphoric acid, [H₂(Crypt-222)](HPO₄) · 8H₂O (I), is synthesized. Its crystal structure is studied using X-ray diffraction analysis (space group P2₁/n, a = 9.244 Å, b = 25.750 Å, c = 13.218 Å, β = 95.87°, Z = 4; direct method, full-matrix least-squares method in the anisotropic approximation to R = 0.055 for 4622 reflections, CAD4 automated diffractometer, λMoK _α radiation). The structure contains the 2.2.2-cryptand dication with the rare exo-exo, conformation with two H atoms at two N atoms directed outside from the cavity. A P atom of the HPO ₄ ^2? anion has a considerably distorted tetrahedral coordination. The crystal of compound I contains a branched infinite three-dimensional system of intermolecular (interionic) hydrogen bonds.     

<Emphasis Type="Italic">N</Emphasis>-aryl-<Emphasis Type="Italic">o</Emphasis>-iminobenzoquinones as novel regulators of radical polymerization

The effect of a number of quinoid compounds on methyl methacrylate polymerization initiated by azo-bis(isobutyronitrile) has been studied. It has been revealed that N-aryl-o-iminobenzoquinones, in contrast to o-benzoquinones, can provide radical polymerization of methyl methacrylate in controllable mode. The efficiency of the compounds as chain growth regulators has been found to depend on their composition and reaction conditions. It has been established that 4,6-di-tert-butyl-N-(2,6-diethylphenyl)-o-iminobenzoquinone and 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-iminobenzoquinone under radical initiation conditions provide the synthesis of poly(methyl methacrylate) with wide-range molecular weight, retaining polydispersity indices about ~1.4–1.8 up to deep conversions.     

The first principle computational study for the competitive mechanisms of oxidative aromatization of 2-substituted imidazolines using KMnO<Subscript>4</Subscript>/SiO<Subscript>2</Subscript>

The efficiently oxidized various types of 2-substituted imidazolines to the corresponding imidazoles using potassium permanganate supported on silica gel (KMnO₄/SiO₂) under mild conditions and at room temperature have been reported before. In this study, the competitive concerted, catalytic stepwise (E ₁ cb′ _Cat .) and E ₁ cb′ mechanisms of the oxidative aromatization process of 2-imidazolines to the corresponding imidazoles using KMnO₄/SiO₂ have been theoretically investigated by DFT-B3LYP/6-31G** method. The achieved data from this computational study confirmed that the reaction occurs by stepwise E ₁ cb′ mechanism on the basis of the anomeric effect.