MnIIILx/t-BuOOH-induced activation of dioxygen for the oxygenation of cyclohexene

Several manganese (III) complexes (Mn^IIIL_x) in combination with tert-butyl hydroperoxide (t-BuOOH) activate dioxygen (O₂) to oxygenate cyclohexene (c-C₆H₁₀) to its ketone, alcohol, and epoxide. The product profiles depend on the ligand and solvent matrix. With picolinate (PA), bipyridine (bpy), or triphenylphosphine oxide (OPPh₃) as the ligand in py/HOAc (2:1 molar ratio) dominant product is the ketone [c-C₆H₈(O)] whereas Schiff–base complexes produce c-C₆H₈(O), c-C₆H₉(OH) and the epoxide in almost equal yields. However, in MeCN c-C₆H₈(O) is the dominant product for all of the complexes.     

Sucrose dependence on the human serum albumin-dehydroepiandrosterone binding: Thermodynamic and fractal approach

In this paper, the effect of sucrose concentration (x) on the dehydroepiandrosterone (DHEA)-human serum albumin (HSA) binding was investigated by a biochromatographic approach. A mathematical development based on fractal geometry is proposed to provide a more realistic picture of the DHEA-HSA binding. The fractal dimension D of the cavity surface and the thermodynamic data of the binding mechanism were calculated at different sucrose concentrations in the bulk solvent. Results showed that under a critical sucrose concentration value x_c (domain I), the enhancement of the DHEA-HSA binding intensity was principally due to the increase of hydrophobic interaction between DHEA and HSA cavity. Above x_c (domain II), the salting-out agent levelled the HSA cavity surface irregularity and, consequently, the DHEA affinity for the HSA decreased. Moreover, for the domain II, the HSA-DHEA binding and the thermodynamic data are discussed using fractal concept of surface fluctuations.     

Stoichiometry and physical properties of ternary molybdenum chalcogenides MxMo6X8 (X = S,Se; M = Li,Sn, Pb)

Chemical and electrochemical insertion of Li at room temperature, as well as insertion of lead and tin at moderate temperatures (500°C), into the binary phase Mo₆X₈ forms ternary molybdenum chalcogenides M_xMo₆X₈ (X = S, Se). Crystallographic parameters, superconducting properties, and magnetic susceptibility are reported. The stoichiometry x for lead and tin is shown not to exceed x = 1, while for Li, x can reach approximately 4.0. For the lead and tin sulfide series, the hexagonal lattice parameters and superconducting critical temperatures (T_c) are invariant to changes in the nominal composition of 0.8 < x < 1.2, while both an increase in T_c and a small decrease in c_h is observed for the selenides; a narrow homogeneity range exists near x = 1 below 500°C for both these sulfides and selenides, the single-phase region being somewhat larger in the selenides. In contrast, several single-phase regions and large unit cell changes are observed in Li_xMo₆X₈ (0 < x < 3.2). Magnetic susceptibility measurements of the lithiated compounds at x ～ 3.2 reveals a structural phase transition at 140 and 185 K for the sulfide and selenide, respectively; but neither superconducts down to 1.5 K. At lower lithium concentration near x ～ 1.0, the T_c of the sulfide is raised from that of Mo₆S₈ (1.8 K) to 5.2 K but the T_c of Mo₆Se₈ (6.5 K) is depressed to 3.9 K.     

Synthesis of homologously pure bacteriochlorophyll-e and f analogues from BChls-c/d via transformation of the 7-methyl to formyl group and self-aggregation of synthetic zinc methyl bacteriopheophorbides-c/d/e/f in non-polar organic solvent

Homologously pure methyl bacteriopheophorbides-e and f (BPhes-e/f_M) were prepared from modification of naturally occurring bacteriochlorophylls-c and d (BChls-c/d), respectively, by transformation of the methyl to formyl group at the 7-position. The absolute configuration of the 1-hydroxyethyl group at the 3-position of (Zn-)BPhes-e/f_M was determined from comparison with structurally known BChl-c/d epimers. Visible spectra of synthetic (Zn-)BPhe-c/d/e/f_M showed that the 7¹-oxidation and the 8²/12¹/20-methylation affected Soret, Q_x and Q_y bands of both the monomeric (in a polar organic solvent) and oligomeric species (in a non-polar solvent).     

Phase transitions in a Cs2−xK1+xBiCl6 solid solution

A solid solution with a Cs_2?xK_1+xBiCl₆ (0 ≤ x ≤ 1) formulation and an elpasolite-related structure was prepared. At room temperature the symmetry is cubic (Fm3m) for x = 0 and triclinic $\text{(P}\text{I}\text{)}$ for x ≠ 0. For 0 ≤ x ≤ 1, various techniques enabled us to detect a phase transition of the ferroelastic-paraelastic type at t_c (°C) temperature. The t_c and ΔH_tc values are correlated to the size of the alkali ions.     

The magnetic properties of the manganese-gallium-aluminum-germanium system

The properties of solid solutions of composition MnGa_1?xAl_xGe formed from ferromagnetic MnGaGe (T_c = 185°C) and MnAlGe (T_c = 245°C) have been examined. In the range, 0 < x < 0.1, the Curie temperature and saturation magnetization are not a monotonic function of x as might be expected for a solid solution of two ferromagnets. Instead, for x = 0.025, the Curie temperature is actually ～77°C lower than that of MnGaGe. Despite the similarity in the structure and lattice constants of MnGaGe and MnAlGe, aluminum rich compositions, e.g., x = 0.95 show no solid solution. Attempts to prepare other ferromagnetic ternary Mn (IIIA) (IVA) compounds have not been successful.     

The sedimentation behaviour of semi-dilute solutions of poly(methyl methacrylate)

Sedimentation coefficients S of poly(methyl methacrylate) for a broad range of molecular weights M and concentrations 1 · 10⁻⁴ >; c >; 2 · 10⁻¹ (c in g ml⁻¹) in the good solvent acetone at 20°C and the theta solvent acetonitrile at 35°C are reported. The results in the dilute regime are discussed in connection with those reported on poly(methyl methacrylate) and the many data available for polystyrene. Both sets of experimental results are compared with the scaling theory. The predictions of the theory are mostly fulfilled as limiting slopes for lower concentrations and high molecular weights and require in good solvents experiments with very high M >; 3 · 10⁷.     

Perovskite tungsten bronze-type crystals of LixWO3 grown by chemical vapour transport and their characterisation

Crystals of Li_xWO₃ with nominal compositions, x=0.1, 0.25, 0.3, 0.35, 0.4 and 0.45 were grown by chemical vapour transport method using HgCl₂ as transporting agent. A complete transport was achieved with a temperature gradient T₁/T₂=800/700 °C revealing bluish-black crystals of sizes up to a few 10th of a millimeter. X-ray powder diffraction and infrared (IR) absorption spectra show Perovskite tungsten bronze of cubic symmetry (PTB_c) for x=0.45 and 0.4, mixed phase of PTB_c and Perovskite tungsten bronze of tetragonal symmetry (PTB_t) for x=0.35, 0.3 and 0.25 and of PTB_t and Perovskite tungsten bronze of orthorhombic symmetry (PTB_o) for x=0.1. The structure of PTB_t is explained by the off centring of the W-ions along c and tilting of the WO₆ octahedra around c. Crystal slices of mixed phase (i.e. PTB_c and PTB_t) reveal bright and dark areas on a sub-millimeter scale which are separated by sharp interfaces. Laser ablation inductively coupled plasma optical emission (LA ICP OES) analysis on small spot sizes show the separation into Li contents of x=0.18 (bright areas) and x=0.38 (dark areas) as threshold compositions of PTB_t and PTB_c, respectively. Polarized reflectivity using a microscope technique in the bright area of the crystals indicates strong anisotropic absorption effects with maximum between 1000 and 6000 cm⁻¹, which are related to optical excitations of polarons. Crystals of composition x=0.4 and 0.45 appear optically homogeneous and show an effective “free carrier-type plasma frequency” (w_p) of about 12,900 and 13,700 cm⁻¹, respectively.     

Studies of the system TaS2−xSex

Single crystal and powder samples of the system TaS_2?xSe_x have been prepared and studied. The range of solubility was found to extend from x = 0 to x = 2.0. X-Ray analysis has shown that mixed anion samples exhibit a series of hexagonal layered polymorphs similar to those found in TaS₂ and TaSe₂, with the a and c lattice parameters increasing monotonically from TaS₂ to TaSe₂. Electrical transport properties were measured on single crystals and found to be similar to the end compositions. Organic molecules such as pyridine and collidine were found to intercalate TaS_2?xSe_x for x ≦ 1.4, and superconducting transition temperatures were measured for both intercalated and unintercalated samples. The highest T_c obtained was 4.1 K in the 4H(c) phase of the sample TaS_1.6Se_0.4.     

Limits of the dilute regime for the solution viscosity of PMMA in good and in poor solvents

The concentration (c′) marking the first deviation from linearity in the Huggins plot of specific viscosity η_sp/c vs c) has been determined for PMMA in chloroform, benzene (good solvents), acetonitrile, chlorobutane (poor solvents) and acetonitrile/chlorobutane mixtures (cosolvent). The dependence of c′ on polymer chain length and on solvent quality is given. The results are analysed in terms of the influence on c′ of incipient coil overlap, peripheral entanglements and other interactions, such as polymer association.     

The effect of inert additives on the explosive mechanochemical synthesis of some metal chalcogenides

The effect of different inert additives on the mechanochemical synthesis of SnS was studied. A transition from explosive to nonexplosive mechanochemical reaction was observed. It was shown that this change takes place only when a critical volume x_c is occupied by inert material. The critical volume for a transition from an explosive to nonexplosive mechanochemical synthesis were determined for the chalcogenides of Zn, Cd, and Sn. The x_c values obtained are discussed. On the basis of the new data concerning the critical dimensions r_c of the exploding mechanical aggregates and the percolation phenomena, a mechanism for the transition from an explosive to nonexplosive mechanochemical synthesis is suggested.     

Study on the solid solution of YMn1−xFexO3: Structural, magnetic and dielectric properties

The solid solution of YMn_1−xFe_xO₃ (x=0.0, 0.1, 0.2, 0.3, 0.5, 1.0) was synthesized from the citrate precursor route. The hexagonal crystal structure related to YMnO₃ was stable for x?0.3. Rietveld refinement was carried out on the composition for x=0.3 and was refined to a major hexagonal phase (∼97%) with 3% of orthorhombic Y(Fe/Mn)O₃ phase. The a-axis lattice constant increases and the c-axis lattice constant decreases with x for x?0.2. The increase in the c-axis lattice constant at x=0.3 could be due to the doping of significant amount of d⁵ ion (high spin Fe³⁺ ion) in a trigonal bipyramidal crystal field. The detailed structural, magnetic and dielectric properties are discussed.     

Where are the Sn atoms in LaSb2Snx, 0.1?x?∼0.75?

The composition range and (composite modulated) structure of compounds within the wide range non-stoichiometric LaSb₂Sn_x, 0.1?x?0.75, solid solution is carefully investigated via a combined electron diffraction, XRD and electron probe microanalysis study. Evidence for metastability of the LaSb₂Sn_x phase at the low x composition end of the solid solution is presented. Direct evidence is found for a reasonably (although by no means perfectly) well ordered Sn sub-structure which is, in general, mutually incommensurable with respect to a very well ordered underlying LaSb₂ sub-structure along both a and c directions. The overall (3+2)-d superspace group symmetry is given along with a discussion of the consequences as regards the arrangement of the Sn atoms. The Sn sub-structure c-axis cell dimension shows very little variation with composition x providing direct experimental evidence of the importance of Sn-Sn metallic bonding (along one-dimensional [001] Sn strings) for the stability of the phase.     

Infrared and Mössbauer spectroscopic study of the metal-insulator transition in some oxides of perovskite structure

The IR spectra of some LaNi_1−xB_xO₃ (B = Cr, Fe, and Co) compounds having perovskite structure have been studied in the range 1000−300 cm⁻¹. An investigation of the changes in the metal-oxygen stretching frequency as x → x_c from the insulating side has been carried out. An important feature is that as x → x_c the vibrational features in the infrared spectra disappear when the resistivity is ∼10⁻¹ Ω cm which is of two orders of magnitude more than the value of ϱ₀ at which the temperature coefficient of resistance changes sign. Mössbauer studies on Fe-containing samples with various conductivities show that the isomer shift decreases as conductivity increases which is indicative of larger FeO overlap.     

Etude structurale des composés MxTiSe2 (M = Fe,Co, Ni)

New compounds M_xTiSe₂ have been prepared with M = Fe (x ? 0.66), M = Co or Ni (x ? 0.50). The metal M is located in vacant octahedral sites of the TiSe₂ host lattice (hexagonal unit cell a′, c′). An ordering of vacancies occurs if x ? 0.20. With M = Co or Ni (x = 0.50) and with M = Fe (0.25 ? x ? 0.66) isotypic compounds of Ti₃Se₄ can be obtained (M₃ □ X₄ type; monoclinic unit cell a ≈ a′ √3, b ≈ a′, c ≈ 2c′). The compounds Fe_0.38TiSe₂ and Co_0.38TiSe₂ (hexagonal unit cell a ≈ a′ √3, c ≈ 2c′) are of the M₂ □ X₃ type, variety 2c′. The Fe_0.25TiSe₂ and Co_0.25TiSe₂ monoclinic unit cells (a ≈ 2a′ √3, b ≈ 2a′, c ≈ 2c′) allow us to assume, for these two compounds, a structure of the M₅ □ ₃X₈ type, variety 2c′, identical to the Ti₅Se₈ one. The compound Ni_0.25TiSe₂ has an hexagonal unit cell (a ≈ 2a′, c ≈ 3c′); it belongs to a so-called 3c′ variety of the M₅ □ ₃X₈ type.     

Effect of cation size and size-disorder on the magnetic and electron transport properties of La0.7−xLnxSr0.3MnO3 (Ln=Gd and Dy)

Magnetic and electron transport properties of La_0.7−xLn_xSr_0.3MnO₃ with Ln=Gd and Dy have been investigated over a wide range of compositions to explore the effects of the radius of the A-site cation, 〈r_A〉, and the size-disorder as measured by σ². These manganates exhibit ferromagnetism and insulator–metal transitions up to a critical value of x (x_c), with the T_c (T_IM) values decreasing with 〈r_A〉. When x⩾x_c, however, the manganates cease to be ferromagnetic and instead they show an abrupt decrease in magnetization and increase in resistivity, suggesting the likely occurrence of electronic phase separation.     

Zur Definition von Selektivität,Spezifität und Empfindlichkeit von Analysenverfahren

The three metric, functional concepts named in the title can be defined without arbitrariness and their values may be calculated for any multicomponent-analytical procedure from the relation of the measurable physical quantities x _ito the contents c _kwhich are to be determined. This relation is mathematically a “mapping” (achieved by systems of functions). The system of “analytical functions” (x _i→ c _k) is the inverse of the system of “calibration functions” (c _k→ x _i) which alone can be directly gained by experiments. The ‘calibration matrix” (γik) whose elements γ_ik are the “partial sensitivities” \(\tfrac{{\partial x_i }}{{\partial c_k }}\) represents the system in first approximation but only locally, i.e. for the respective constitution of the sample. The “sensitivity” of the analytical procedure as a whole, is numerically given by the determinant of this matrix; the “selectivity” is derived from the condition that the inversion of the calibration system to the analytical system (of functions) shall be possible by an iteration process. “Specificity” is defined in analogy to selectivity. In the appendix it is explained why selectivity is the strongest means to reduce the expenditure for the complete calibration of multicomponent analyses to a realistic and tolerable degree.     

Thermodynamics of the amalgam cells {M-Amalgam|MCl or MCl2 (m)|AgCl|Ag} (M=Rb,Cs, Sr,Ba) and primary medium effects in (acetonitrile + water)

The potential difference E of the amalgam cell {M_xHg_1 − x|MCl or MCl₂ (m)| AgCl |Ag} (M=Rb, Cs, Sr, Ba) has been measured as a function of the mole fraction x_M of M metal in amalgams and of the molality m of MCl (or MCl₂) in (acetonitrile [A] + water [W]) solvent mixtures containing up to acetonitrile mass fraction w_A=0.50, at T=298.15 K. The respective molal-scale standard potential differences E^∘_m have been determined together with the relevant activity coefficients γ_± functions of the MCl (or MCl₂) molality. The E^∘_m dependence on the mole fraction x_A of acetonitrile in the solvent mixture within the range explored turns out to be linear for all the four metals M in the amalgams considered. Of course, also the difference ([E^∘_m]_W−[E^∘_m]_A), which is a measure of the primary medium effect upon transferring MCl (or MCl₂) from pure water [W] to the acetonitrile [A] mixture, is linear in x_A.In this context, following Feakins and French's scheme, which implies volume fraction statistics, analysis of the relevant mol · dm⁻³ scale primary medium effects, i.e., ([E^∘_c]_W−[E^∘_c]_A), upon MCl (or MCl₂), as a linear function of the logarithm of water volume fraction, would lead to primary hydration numbers of 4.2 for RbCl, 4.0 for CsCl, 10.7 for SrCl₂, and 10.3 for BaCl₂, respectively, in acceptable agreement with literature data by Bockris based on different methods.     

Structural and physical properties evolution in the 6H BaRu1−xMnxO3 synthesized under high pressure

The 6H BaRu_1−xMn_xO₃ with the hexagonal BaTiO₃ structure was synthesized using high-pressure sintering method. It is found that the lattice parameter deviates from Vegard's law at x=0.3 for the solid solutions due to the charge transfer effects at B-site. The substitution of Mn for Ru cations gives rise to the short-range magnetic ordering, due to the disordered arrangement of Ru and Mn cations. The compounds are weak ferromagnetic in the x range 0.05-0.40, with the maximal Curie temperature T_c 175.2 K at x=0.10. They are of spin-glass-like magnetism at lower temperature at x?0.1. With Mn doping, the 6H BaRuO₃ transforms to a semiconductor from the primal metal at x=0.30. The resistance as a function of temperature below about 70 K follows the two-dimensional variable-range hopping conduction mechanism in BaRu_0.50Mn_0.50O₃.