Electronic structure of high-valent transition metal corrolazine complexes. The young and innocent?

This is a first quantum chemical study of corrolazine complexes. DFT calculations suggest that despite their extremely contracted central cavities, compared with porphyrins, a variety of corrolazine complexes may be expected to exist as stable compounds. The calculations also indicate that corrolazine complexes may be regarded as strongly electron-deficient analogues of corrole complexes. Thus, the calculated valence ionization potentials of P(V) and Cu(III) corrolazine derivatives are dramatically higher than those of analogous corrole derivatives. In addition, DFT calculations on Fe(IV) and Mn(IV) corrole and corrolazine derivatives suggest that compared with the often noninnocent corrole ligands, corrolazines are electronically more innocent and stabilize "purer" high-valent states of transition metal ions.     

The gel-like structure of polymer in thin films: an explanation of the thickness dependent glass transition?

The understanding of the origin of the thickness (h) dependent glass transition temperature, T_g(h), reported over the last decade for supported and freely standing thin polymer films, is still unclear. Indeed, the spin-coating process, the interfacial adsorption as well as the freezing-in of non-equilibrated chain conformations and orientations caused by fast solvent evaporation could result in partially disentangled chains which can be depicted as a gel-like structure. The effect of PMMA stereoregularity on the chain conformation and orientation and its persistence length in thin films is discussed. Moreover, striking evolutions of T_g(h) by changing the nature of the solvent support the assumption of a specific organisation of the chains in thin films which can hold over thickness far above Rg.     

The possibility of semiconductor–metal transition in a spherical quantum dot

We observe an abrupt change in diamagnetic susceptibility at critical donor concentration for an $\text{ Al }_\mathrm{x}\text{ Ga }_\mathrm{1-x}\text{ As/GaAs }$ Al x Ga 1 ? x As/GaAs quantum dot system in the effective mass approximation indicating a possible semiconductor metal transition. The effect of confining potential and the laser intensity on the abrupt change in diamagnetic susceptibility has also been studied. The effect of nonparabolicity of the conduction band has been included in our calculations. Results are presented and discussed.     

Electronic and geometric structure of the protonated forms of nickel β-diketonates

The effect of protonation on the electronic and spatial structure of nickel malonodialdehynate Ni(Mal)₂ and acetylacetonate Ni(Acac)₂ were studied by quantum chemical density functional theory (DFT) method. The metal ring geometry, the energies and the composition of molecular orbitals (MO), the effective charges on atoms, and the total overlap populations were determined, and the possible proton location sites were identified. The variation of the MO energy depending on the electron density distribution on the protonated and non-protonated ligands was considered. Proton addition to one of the oxygen atoms was shown to be most likely.     

The sol–gel transition of mullite spinning solution in relation to the formation of ceramic fibers

Continuous mullite ceramic fibers were fabricated by a sol–gel dry spinning technique. The sol was prepared from an aqueous solution of aluminum nitrate (AN), aluminum isopropoxide (AIP) and tetraethylorthosilicate (TEOS). The sol–gel transition was investigated by measuring the volume, the solid content, the viscosity and the rheological properties of the solution. Shear viscosity η of the mullite sol varied dynamically with concentrating time and temperature. Combine size analysis of sol particles and TEM analysis on this basis, the growth character of sol particles agglomeration and its structural evolution were discussed. By adjusting the temperature, the gelling degree could stabilize at a certain value and the sol–gel transition could be transferred to the spinning line. Continuous fibers were spun from such sols immediately before gelling in a laboratory dry spinning apparatus. The spinneret contained thirty circular holes, each having a diameter of 0.2 mm. The temperature inside the spinning channel was 100–120 °C, the winding speed was 100–300 m/min. Sintering of the precursor fibers at 1,100 °C yields crack-free mullite ceramic fibers.     

Three-quantum transition probabilities in the ν3 manifold of SF6 and the assignment of the observed 3ν3 transition in the i.r. spectrum

A theoretical expression has been derived for the intensity of a three-vibrational-quantum electric-dipole transition and has been used to calculate the intensities of the transitions from the ground state to the two F_1u components of 3ν₃ of SF₆. The calculated intensity of 1.02 × 10⁻² km/mol is in reasonable agreement with the observed intensity of 4.8 × 10⁻² km/mol.     

The effect of Sb content on glass-forming ability,the thermal stability,and crystallization of Ge–Se chalcogenide glass

The glass formation and devitrification of intermediate alloys in the Sb–Ge–Se system were studied by differential scanning calorimetry. A comparison of various simple quantitative methods to assess the level of stability of the glassy materials in the bove mentioned system is presented. All of these methods are based on characteristic temperatures, such as the glass transition temperature, T _g, the onset temperature of crystallization, T _in , the temperature corresponding to the maximum crystallization rate, T _p, or the melting temperature, T _m . In this case, k _gl may be more suitable for estimating the glass thermal stability in above composition range than ΩT. In this work the parameter K _r (T) is added to the stability criteria. The thermal stability of some ternary compounds of the Sb–Ge–Se type has been evaluated experimentally and correlated with the activation energies of crystallization by this kinetic criterion and compared with those evaluated by other criteria. All the results of criteria and kinetic parameter K _r (T) confirm that the thermal stability decrease with increasing Sb content in the glassy system. The crystallization results are analyzed and both the activation energy of crystallization process and the crystallization mechanism are characterized. Finally, identification of the crystalline phases was made by recording the X-ray diffraction pattern of the transformed material. This pattern shows the existence of microcrystallites of two phases, the first is germanium Selenide GeSe₂ and the second is Sb₂Se₃ in amorphous matrix for annealed of Sb_2.5Ge_22.5Se₇₅ and Sb₁₀Ge₁₅Se₇₅ glass.     

The role of dipole—dipole interactions in the formation of the structure of amorphous Teflon AF2400 and complexation of acetone with perfluorodioxolane rings

FTIR spectroscopy investigation have shown that the contact of acetone with the film of Teflon AF2400 led to changes in the intensities of some absoption bands of the polymer and to the splitting of the stretching vibration band ν_C=O of acetone. The theoretical vibration spectrum of a model of AF2400 repeat unit was obtained. It is in good agreement with the experimental spectrum of the film of this polymer. The bands, whose intensities change during the contact of the AF2400 film with acetone, belong to the stretching and deformation vibrations of the C-F bond of the dioxolane ring as a whole. Structural, energy, and electron characteristics of a complex of acetone with the perfluorodioxolane ring were calculated by the B3LYP/6-31G(d) method. The dipole-dipole character of interaction of acetone with the repeat unit of AF2400 with the involvement of the whole dioxolane ring was demonstrated. The polarizabilies of the C=O bonds in acetone and the C-F bonds in the dioxolane ring of the polymer are substantially changed, which is in good agreement with the experimental IR spectrum of the AF2400 film that had been in the contact with acetone. The results of quantum chemical and molecular dynamics calculations testify the orthogonal-block structure of the chains in AF2400, which explains great stiffness and a large free volume of this polymer.     

The influence of cobalt incorporation and cobalt precursor selection on the structure and bioactivity of sol–gel-derived bioactive glass

Cobalt (Co) is a potential therapeutic ion used to enhance angiogenesis through a stabilizing effect on hypoxia-inducible factor 1 alpha (HIF-1α), and its incorporation into the structure of bioactive glass is a promising strategy to enable sustained local delivery of Co to a wound site or bone defect. Here Co-releasing bioactive glasses were obtained through the sol–gel method, comparing cobalt nitrate and cobalt chloride as precursors. The effect of using different Co precursors on the sol–gel synthesis and in the obtained bioactive glass structure, chemical composition, morphology, dissolution behaviour, hydroxycarbonate apatite (HCA) layer formation was investigated. When the chloride salt was used as Co precursor, evidence of crystalline cobalt (II, III) oxide (Co₃O₄) phase formation was found, along with the presence of Co³⁺ species as evaluated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), whereas an amorphous glass containing mainly Co²⁺ species was obtained when the nitrate salt was the Co source. The presence of a crystalline phase decreased the surface area and pore volume of the final glass, consequently reducing the Co-release rate. Evidence of HCA layer formation after immersion in simulated body fluid (SBF) was still found when different precursors were used, although the rate of formation was reduced by the presence of Co. Therefore, this study showed that Co incorporation and the proper selection of the precursor could affect the final material structure, and properties, and should be considered when designing new bioactive glass compositions for tissue engineering applications.

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The calculation of Cs and Rb conductivities in the region of liquid–plasma transition

The conductivity and thermal conductivity of Cs and Rb are calculated in the liquid phase and in the region between the plasma (gas) and the liquid states. The last area is located at the temperatures higher than the critical one, near the critical point. The Ziman formalism originated from the liquid metal theory was used for the calculations. The results of present calculations were compared with available experiments and calculations of other researchers. It was found that the liquid state formalism can be applied to expanded liquid Cs and Rb at densities higher than the critical one, but another type of models is necessary at lower densities.     

The rotation and the phase transition in solid C60

The interaction between C60's in solid C60 has been calculated by (exp-6-1) potential, and the cause and the controlled factor of the high rapid rotations of C60 's were discussed. In order to describe the disordered degree of C60 rotation, an equivalent M is introduced. The phase transitions at the ~260 K and at the ~90 K are studied from the viewpoint of C60 rotation. The potential barriers of the ordered rotation below the ~260 K and the disordered rotation above the ~260 K have been given, and the effect of the external pressure on the temperature of phase transition has also been given.     

The role of intra- and intermolecular hydrogen bonds in the formation of β-cyclodextrin head-to-head and head-to-tail dimers. The results of ab initio and semiempirical quantum-chemical calculations

The conformation of a free -cyclodextrin molecule optimized by the MNDO/PM3 quantum-chemical calculations has C₇ symmetry. The right orientation of the interglucose hydrogen bonds in -cyclodextrin, in which the 2-OH groups act as the proton donors and the O atoms of the nearby 3"-OH groups function as the proton acceptors, is advantageous for thermodynamic reasons. The ring of seven H bonds thus formed stabilizes the symmetrical form of -cyclodextrin. The -cyclodextrin head-to-head dimer has D ₇ symmetry and consists of molecules whose 2-OH groups partcipate as proton donors in the formation of fourteen complementary intermolecular hydrogen bonds. The energy of H bonds in the -cyclodextrin monomer and dimer was estimated to be 1.0--1.4 kcal mol^–1. Of the two possible -cyclodextrin dimers, the head-to-tail dimer is more thermodynamically stable. The thermodynamic preference of the right orientation of the inter-glucose H bonds in -cyclodextrin was confirmed by the MP2/6-31G(d,p)//6-31G(d,p) ab initio calculations for maltose (-glucodioside). The maltose molecule with inter-glucose H bonds of the type 2-OHO(3")-H is more stable than the structure with the H-(2)OH-O(3") orientation of H bonds with a difference of 2.7 kcal mol^–1. According to the MNDO/PM3 method, the maltose structure with the right H bond orientation is more stable by 3.1 kcal mol^–1.     

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.     

The polarographic determination of indium in zinc-base alloys : The determination of indium in zinc and in “lead-free” zinc alloys

The use of a potassium iodide base electrolyte for the separation of the polarographic steps due to indium and cadmium is discussed and theoretical data relating to the interference of the step due to lead with that due to indium are presented. An experimental study is given together with details of the attempted removal of lead interference. A method is presented for the polarographic determination of indium in zinc alloys, applicable when the lead concentration is small compared with that of indium.     

Studies of the atomization mechanism in a graphite furnace—I. The contents of the gaseous impurities in the furnace and their variations

Using theoretical calculations of the partial pressures of gaseous impurities in the atmosphere in a GFA as a basis, the authors arrived at conclusions which are at variance with those of L'vov and frech and their co-workers. Accordingly, the partial pressure of free oxygen (p_o) in a GFA originates predominantly from the thermal decomposition of the oxides of the analyte and impurities in the matrix during atomization when the temperature is higher than 1000°C; then, p_o depends on the nature of the sample. The total amount of oxygen in a GFA depends on the initial amount of it in the argon gas and the amount released from the sample when the temperature is lower than 1000°C.The variation of the partial pressure of CO is for the first time characterized as follows: the content of CO, which is mainly dependent on the sample and the total amounts of gaseous impurities in the argon purge gas, does not vary markedly with the temperature and other factors during the whole process of atomization. The gaseous impurities exist mainly in the form of CO.     

Enthalpies of formation of SmCo alloys in the composition range 10–22 at. % Sm

Several intermetallic compounds exist in the composition range 10–22 at.% Sm(Sm₂Co₁₇, SmCo₅, Sm₂Co₇) but their preparation as single-phase specimens is very difficult. In order to determine the enthalpies of formation of these compounds, measurements were carried out on four alloys containing respectively 12.9 at.% Sm, 16.4 at.% Sm, 17 at.% Sm and 19.8 at.% Sm, annealed in the temperature range 950–1100 °C. The compositions of the phases present in each specimen were deduced from the characterization of the measured alloys by scanning electron microscopy, electron microanalysis and X-ray diffraction.The heats of formation were deduced from solution calorimetry in molten tin. The variation of the experimental results as a function of the samarium content enabled the enthalpy of formation of SmCo₅ ( − 40.8 kJ mol⁻¹) to be determined. The same ΔH_f value as determined for the phase quenched from 950 °C was measured for SmCo₅ kept at room temperature after very slow cooling. This result did not confirm the eutectoid decomposition previously reported for SmCo₅.The extrapolation of the measured values for the higher and lower samarium contents leads to the evaluation of the enthalpies of formation of Sm₂Co₁₇ (−152 kJ mol⁻¹) and Sm₂Co₇ (−99kJ mol⁻¹).     

Electronic structure and property studies of the first crowned [60] fulleropyrrolidine

The computations of the electronic structures and properties of a novel crowned [60] fulleropyrrolidine (CFP) were performed by means of AM1 methods. It has been indicated that CFP has four isomers in which the dihedral angle between phenyl group and pyrrolidine ring is around ±90°. The study of electronic structures showed that the energy levels of frontier orbitals are determined mainly by C_(60). C_(60) acted as an electronic acceptor, whereas crown ether acted as an electronic donor, which implies that there exists intramolecular charge transfer effect in this molecule. The study of nonlinear optical properties implied that the hyperpolarizability of CFP can match that of p-nitroaniline. In the meantime, the hyperpolarizability properties of CFP could be influenced by the orientation of crown ether moiety.