Critical Behavior of Binary Mixtures of Nitrobenzene?+?n-Undecane and Nitrobenzene?+?n-Dodecane

Turbidities and isobaric heat capacities per unit volume, in a wide temperature range, have been measured for critical binary solutions of {nitrobenzene?+?n-undecane} and {nitrobenzene?+?n-dodecane}. The critical exponents and the system-dependent critical amplitudes were deduced. The non-critical and the critical-fluctuation induced contributions to the background heat capacities were determined. We also obtained the coupling constant $ \bar{u} $ by analyzing the coexistence curve data with crossover theory. These parameters were used to test some universal amplitude ratios and together with the coexistence-curve data to test the complete scaling theory. It is shown that the contribution from heat capacity plays an important role in describing the asymmetric criticality of the coexistence curve.     

The [2?+?2?+?2] mechanisms of trimerization of three ethynes and monosilaethylenes

The mechanisms of [2?+?2?+?2] reactions of three ethynes and monosilaethylenes to form benzene and 1,3,5-trisilacyclohexane were studied by ab initio MO methods. The reaction mechanisms were analyzed by configuration interaction/localized molecular orbital/CASSCF calculations. Although the [2?+?2?+?2] reaction of ethyne is typically ??homologous?? concerted, that of monosilaethylene is polarized (ionic-cyclic) one-step reaction. In addition, the aromaticity along the intrinsic reaction coordinate pathway was studied using the index of deviation from aromaticity. Although the transition state of trimerization of ethyne does not have an aromatic nature for the ??- and ??-bonds formation system, the crossing point of the ??-bond formation and ??-bond breaking shows an aromatic nature.     

Thermodynamic and transport properties for binary and ternary mixtures of 2-methyltetrahydrofuran?+?chlorobenzene?+?cyclopentanone at T?=?298.15?K

Abstract  

Experimental densities ρ, viscosities η, and refractive indices n _D of the ternary mixtures consisting of 2-methyltetrahydrofuran + chlorobenzene + cyclopentanone and constituted binary mixtures were measured at T = 298.15 K for the liquid region and at ambient pressure for the whole composition range. Excess molar volumes V_\textm^\textEV_{\text{m}}^{\text{E}}, deviations in the viscosity Δη, and deviations in the refractive index Δn _D from the mole fraction average for the mixtures were derived from the experimental data. The excess partial molar volumes V_\textm,i^\textEV_{{\text{m}},i}^{\text{E}} were also calculated. The binary and ternary data of V_\textm^\textEV_{\text{m}}^{\text{E}}, Δη, and Δn _D were correlated as a function of the mole fraction by using the Redlich–Kister and the Cibulka equations, respectively. McAllister’s three-body interaction model is used for correlating the kinematic viscosity of binary mixtures with the mole fraction.     

Oxygen excess nonstoichiometry and thermodynamic quantities of La2NiO4?+?δ

The oxygen excess nonstoichiometry of La₂NiO_4 + δ is measured as a function of temperature and oxygen partial pressure (pO₂) by coulometric titration method. A positive deviation from the ideal dilution solution behavior is exhibited, and the partial molar thermodynamic quantities of La₂NiO_4 + δ are calculated from the Gibbs–Helmholtz equation for regular solution by introducing the activity coefficient of the charge carriers. The activity coefficient of holes is successfully calculated by using the Joyce–Dixon approximation of the Fermi–Dirac integral. The effective mass of holes ( m_\texth^* m_{\text{h}}^{{*}} ) is 1.27–1.29 times the rest mass (m _h), which indicate the action of band-like conduction and allow the effect of the small degree of polaron hopping to be ignored. The activity coefficient of holes calculated against the oxygen nonstoichiometry clearly illustrates the early positive deviation of the activity coefficient of holes from unit, leading to g_{\texth ^·} \gamma_{{{\text{h}}^{ \bullet }}}  ≈ 14 at δ ≈ 0.08, which is quite close to the literature value of g_{\texth ^·} \gamma_{{{\text{h}}^{ \bullet }}}  ≈ 10 at δ ≈ 0.08. All the evaluated thermodynamic quantities are in good agreement with the experimental literature values.     

Computational study on the reaction mechanism of the gas-phase atom-negative ion of S?+?NO2 ?: comparative study of mechanism with S?+?O3 reaction as isoelectronic and isostructure systems

The reaction mechanism of sulfur vapor (S) with nitrite ion (NO₂ ⁻) has been investigated theoretically on the triplet and singlet potential energy surfaces (PESs). All stationary points for the title reaction have been optimized at the B3LYP/6-311+G(3df) level. The energetic data have been obtained at the CCSD(T)//B3LYP level employing the 6-311+G(3df) basis set. Five stable collision complexes, ³IN1 (S–ONO⁻), ³IN2 (cyclic SONO⁻), ¹IN1 (cis S–ONO⁻), ¹IN2 (S–NO₂ ⁻), and ¹IN3 (trans S–ONO⁻), have been considered on the triplet and singlet PESs through barrier-less and exothermic processes. By starting from these complexes, a simple mechanism has been obtained on the triplet PES while a complex mechanism has been considered on the singlet PES. The calculated results show that there are no favorable paths for the reaction of S with NO₂ ⁻ on the singlet PES. Therefore, the S + NO₂ ⁻ reaction proceeds only on the triplet PES to produce ³SO + ³NO⁻ as main products. The results from the comparative study of S + NO₂ ⁻ reaction mechanism with S + O₃ (as isoelectronic and isostructure reactions) on the singlet PES show similarities in the overall trend of reaction mechanism and atom connectivity and differences in the stability of intermediates and the energy barriers of transition states.     

Electrically driven oxygen separation through gadolinia-doped ceria using PrBaCo2O5?+?x and NdBaCo2O5?+?x electrodes

Oxygen gas can be electrochemically separated from ambient air with very high purity and compressed by using a solid-electrolyte ion-transport membrane. An electrolyte with high ionic conductivity such as gadolinium-doped ceria (CGO) and mixed conducting electrodes are used to construct the electrochemical cell. To achieve high oxygen flux, the electrodes must exhibit very fast electrode kinetics. Here, we report the performances of mixed conducting PrBaCo₂O_5 + x and NdBaCo₂O_5 + x electrodes in oxygen separation in a planar CGO electrolyte-supported cell. The properties of the electrode materials were evaluated using potentiostatic and potentiodynamic measurements and alternating current impedance spectroscopy. The oxygen flux was also measured using gas chromatography to confirm the absence of gas leaks. The electrodes demonstrated very low polarization resistances as a result of very high cathodic and anodic reaction rates at temperatures of 600–800 °C. High oxygen gas flow rates were observed on applying potentials up to 1 V with an almost linear relationship between the applied potential and the molar flow rate of oxygen gas.     

O?+?C2H4 potential energy surface: lowest-lying singlet at the multireference level

Extensive density functional theory (DFT) calculations have been performed to develop a force field for the classical molecular dynamics (MD) simulations of various azobenzene derivatives. Besides azobenzene, we focused on a thiolated azobenzene’s molecular rod (4′-{[(1,1′-biphenyl)-4-yl]diazenyl}-(1,1′-biphenyl)-4-thiol) that has been previously demonstrated to photoisomerize from trans to cis with high yields on surfaces. The developed force field is an extension of OPLS All Atoms, and key bonding parameters are parameterized to reproduce the potential energy profiles calculated by DFT. For each of the parameterized molecule, we propose three sets of parameters: one best suited for the trans configuration, one for the cis configuration, and finally, a set able to describe both at a satisfactory degree. The quality of the derived parameters is evaluated by comparing with structural and vibrational experimental data. The developed force field opens the way to the classical MD simulations of self-assembled monolayers (SAMs) of azobenzene’s molecular rods, as well as to the quantum mechanics/molecular mechanics study of photoisomerization in SAMs.     

Photoinduced [4?+?2] cycloaddition reactions of benzo[b]thiophene-2,3-dione with alkenes

[4?+?2]-Photocycloadditions of benzo[b]thiophene-2,3-dione with electron-rich and electron-deficient alkenes have been described. Olefins preferentially add at both carbonyl groups to give the head-to-head [4?+?2] cycloadducts, i.e., dioxanes only. Comprehensive molecular orbital calculations at DFT-B3LYP level have been carried out to address the mechanism as well as regiochemical course of the reaction.     

Conformational Distribution of Bradykinin [bk?+?2?H]2+ Revealed by Cold Ion Spectroscopy Coupled with FAIMS

We employ cold ion spectroscopy (CIS) in conjunction with high-field asymmetric waveform ion mobility spectrometry (FAIMS) to study the peptide bradykinin in its doubly protonated charge state ([bk?+?2?H](2+)). Using FAIMS, we partially separate the electrosprayed [bk?+?2?H](2+) ions into two conformational families and selectively introduce one of them at a time into a cold ion trap mass spectrometer, where we probe them by UV photofragment spectroscopy. Although the two conformational families have distinct electronic spectra, some cross-conformer contamination can be observed under certain conditions. We demonstrate that this contamination comes from isomerization of ions energized during and/or after their separation and not from incomplete separation of the initially electrosprayed conformations in the FAIMS stage. By varying the injection voltage of the ions into our mass spectrometer, we can intentionally induce isomerization to produce what seems to be a gas phase equilibrium distribution of conformers. This distribution is different from the one produced initially by electrospray, indicating that some of the conformers are kinetically trapped and may be related to conformers that are more favored in solution.     

Solubility, Dissolution Enthalpy and Entropy of Isoimperatorin in Ethanol?+?Water Solvent Systems from 288.2 to 328.2?K

The solubility of isoimperatorin in pure solvents and solvent mixtures was measured by UV spectrophotometry from 288.2 to 328.2?K. The solubility of isoimperatorin in binary ethanol and water solvent systems increases with temperature and with decrease of the mole fraction of water in the solvent mixture. The solubility data were correlated with a modified Apelblat equation. The enthalpy and entropy of dissolution of isoimperatorin were evaluated using the van??t Hoff equation.     

Size scaling behaviour in protein domains belonging to the all-α, all-β, α / β, and α?+?β folding classes

We studied the size scaling behaviour in an ensemble of 8,614 non-redundant protein domains belonging to the all-α, all-β, α / β, and α + β folding classes. We find that the most compact structural domains can be characterized by an effective exponent ν _eff  = 0.39 ± 0.01, which is larger than the value for “collapsed-polymers,” i.e., ν = 1/3. We also show that the global ν _eff -exponent is an average of the scaling regimes for short and long compact chains, where the values change from ν _eff ≈ 0.37 to ν _eff ≈ 0.45 at chain length of ca. 269. A transition from short-chain to long-chain scaling behaviour is found in all major folding classes, over a window of chain lengths between 216 and 269 residues. In addition, variations in scaling exponent with respect to folding class indicates that the smallest domains in the (all-β) and (α / β) families appear to be more compact structures than the smallest (all-α)- and (α + β)-domains.     

Geometrical and Electronic Properties of Neutral and Anionic AlnBm (n?+?m?=?13) Clusters

Successively substituted Al₁₃ cluster by B atom both neutral and anionic Al _n B _m  (n + m = 13) clusters have been investigated by the density functional theory (DFT) at B3LYP/6-31G (d) level, the aim is to understand the evolution of the structural and electronic properties as a function of composition. The results clearly show Al₁₃ cluster as well as Al rich Al _n B _m clusters prefer the icosahedral geometries while increasing boron contents promote quasi-planar configurations. The geometrical structures of the optimized anionic Al _n B _m ⁻ clusters are very close to those of the neutral clusters with smaller structural modifications. Overall, the vertical ionization potential (VIP), the adiabatic electron affinity (AEA), and the energy gaps (E _g ) of Al _n B _m clusters decrease with increasing of substitution. The largest values of second-order energy differences ( \Updelta₂E), VIP\Updelta_{2}E), VIP, and E _g of Al₁₂B cluster indicate it possesses the most stability among all the investigated clusters, which accords to the experimental results. The simulated photoelectron spectroscopies (PES) of Al _n B _m ⁻ clusters have also been discussed in this article.     

Characterization of non-stoichiometric co-sputtered Ba0.6Sr0.4(Ti1???x Fe x )1?+?x O3???δ thin films for tunable passive microwave applications

The fabrication of novel iron-doped barium strontium titanate thin films by means of radio frequency (RF) magnetron co-sputtering is shown. Investigations of the elemental composition and the dopant distribution in the thin films obtained by X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, and time-of-flight secondary ion mass spectroscopy reveal a homogeneous dopant concentration throughout the thin film. The incorporation of the iron dopant and the temperature-dependent evolution of the crystal structure and morphology are analyzed by electron paramagnetic resonance spectroscopy, X-ray diffraction, Raman spectroscopy, atomic force microscopy, and scanning electron microscopy. In summary, these results emphasize the RF magnetron co-sputter process as a versatile way to fabricate doped thin films.     

Synthesis of Sb(VO3)3 and study of ternary system xNH4VO3?+?(1???x)(NH4)2HPO4?+?Sb2O3

Sb(VO₃)₃ has been synthesized by interaction between NH₄VO₃ and Sb₂O_3. The compound crystallizes in monoclinic system with lattice parameters: a = 17.150; b = 15.940; c = 14.600 Å and angle ?? = 90.50°. The scanning electronic microscopy shows thin flat plates measuring ~20 ??m along with detritus material. The synthesis was simulated by thermal analysis and the final product identified by X-ray diffraction. Thermal analyses of the ternary system xNH₄VO₃ + (1 ? x)(NH₄)₂HPO₄ + Sb₂O₃ lead to the formation of Sb(VO₃)₃ and SbPO₄ at 500 °C. At high temperature (900 °C), SbVO₄, SbOPO₄, VO and SbP₅O₁₄ are formed. The data of thermal analysis match with the composition of intermediate and final products. No solid solutions containing simultaneously PO ₄ ^?3 and VO ₄ ^?3 ions have been found.     

Excess Molar Volumes of Oligo(Oxyethylene Glycol) Monodecyl Ethers in n-Dodecane, and Apparent Dipole Moments of {(Oligo(Oxyethylene Glycol) Monodecyl Ethers?+?n-Heptane, n-Decane or n-Dodecane} at T?=?298.15?K

Excess molar volumes and relative permittivities at a frequency of 30?kHz of oligo(oxyethylene glycol) monodecyl ethers (C₁₀E _m ) for m?=?1?C8 in n-heptane, n-decane or n-dodecane solutions were determined for the mole fraction range 0?<?x?<?0.04 at the temperature of 298.15?K. By using Frohlich??s equation the apparent dipole moments, ??, of C₁₀E _m were calculated, and the limiting values, ?? ₀, were determined by extrapolating to infinite dilution. The values of ?? ₀ increase linearly with increasing number of oxyethylene units (m) of oligo(oxyethylene glycol) monodecyl ethers in the range m?=?2?C8, while ?? ₀ of C₁₀E₁ is less than its extrapolated value. By comparing the present results with our previous ones measured in n-heptane and decane, a solvent effect on ?? ₀ was found. The excess partial molar volumes of oligo(oxyethylene glycol) monodecyl ethers at infinite dilution increase with increasing m. Those results are discussed from the viewpoint of the interactions between oligo(oxyethylene glycol) monodecyl ethers and solvent molecules.