Electronic structure and Raman spectroscopy study of dibarium magnesium orthoborate,Ba2Mg(BO3)2

The samples of dibarium magnesium orthoborate Ba₂Mg(BO₃)₂ were synthesized by solid-state reaction. The X-ray diffraction (XRD) patterns and Raman spectra of the samples were collected. Electronic structure and vibrational spectroscopy of Ba₂Mg(BO₃)₂ were systematically investigated by first principle calculation. A direct band gap of 4.4 eV was obtained from the calculated electronic structure results. The top valence band is constructed from O 2p states and the low conduction band mainly consists of Ba 5d states. Raman spectra for Ba₂Mg(BO₃)₂ polycrystalline were obtained at ambient temperature. The factor group analysis results show the total lattice modes are 5E_u + 4A_2u + 5E_g + 4A_1g + 1A_2g + 1A_1u, of which 5E_g + 4A_1g are Raman-active. Furthermore, we obtained the Raman active vibrational modes as well as their eigenfrequencies using first-principle calculation. With the assistance of the first-principle calculation and factor group analysis results, Raman bands of Ba₂Mg(BO₃)₂ were assigned as E_g (42 cm⁻¹), A_1g (85 cm⁻¹), E_g (156 cm⁻¹), E_g (237 cm⁻¹), A_1g (286 cm⁻¹), E_g (564 cm⁻¹), A_1g (761 cm⁻¹), A_1g (909 cm⁻¹), E_g (1165 cm⁻¹). The strongest band at 928 cm⁻¹ in the experimental spectrum is assigned to totally symmetric stretching mode of the BO₃ units.     

Measurement and correlation of (vapor + liquid) equilibria for the {2-propoxyethanol (C3E1) + n-hexane} and the {2-propoxyethanol (C3E1) + n-heptane} systems

2-Propoxyethanol (C₃E₁) is one of nonionic surfactants which are a particularly interesting class of substances due to both inter-molecular and intra-molecular association. Binary (vapor + liquid) equilibrium data were measured for {2-propoxyethanol (C₃E₁) + n-hexane} and {2-propoxyethanol (C₃E₁) + n-heptane} systems at temperatures ranging from (303.15 to 323.15) K. A static apparatus was used in this study. The experimental data were correlated well with a lattice fluid equation of state that combines the multi-fluid non-random lattice fluid model with Veytsman statistics for (intra + inter)-molecular association.     

Esterification of (RS)-Ibuprofen by native and commercial lipases in a two-phase system containing ionic liquids

Four commercially available lipases and two native lipases from Aspergillus niger AC-54 and Aspergillus terreus AC-430 were used for the resolution of (RS)-Ibuprofen in systems containing the ionic liquids [BMIM][PF₆] and [BMIM][BF₄]. The lipases showed higher conversion in a two-phase system using [BMIM][PF₆] and isooctane compared to that in pure isooctane. Although the best enzyme was a commercially available lipase from Candida rugosa (E = 8.5), another native lipase, produced in our laboratory, from A. niger gave better enantioselectivity (E = 4.6) than the other lipases tested (E = 1.9–3.3.). After thorough optimization of several reaction conditions (type and ratios of isooctane/ionic liquid, amount of enzyme, and reaction time), the E-value of A. niger lipase (15% w/v) could be duplicated (E = 9.2) in a solvent system composed of [BMIM][PF₆] and isooctane (1:1) after 96 h of reaction.     

Thermodynamics of the oxidation–reduction reaction {2 glutathionered(aq) + NADPox(aq)=glutathioneox(aq) + NADPred(aq)}

Microcalorimetry, spectrophotometry, and high-performance liquid chromatography (h.p.l.c.) have been used to conduct a thermodynamic investigation of the glutathione reductase catalyzed reaction {2 glutathione_red(aq) + NADP_ox(aq)=glutathione_ox(aq) + NADP_red(aq)}. The reaction involves the breaking of a disulfide bond and is of particular importance because of the role glutathione_red plays in the repair of enzymes. The measured values of the apparent equilibrium constant K^′ for this reaction ranged from 0.5 to 69 and were measured over a range of temperature (288.15 K to 303.15 K), pH (6.58 to 8.68), and ionic strength I_m (0.091 mol · kg⁻¹ to 0.90 mol · kg⁻¹). The results of the equilibrium and calorimetric measurements were analyzed in terms of a chemical equilibrium model that accounts for the multiplicity of ionic states of the reactants and products. These calculations led to values of thermodynamic quantities at T=298.15 K and I_m=0 for a chemical reference reaction that involves specific ionic forms. Thus, for the reaction {2 glutathione_red⁻(aq) + NADP_ox³⁻(aq)=glutathione_ox²⁻(aq) + NADP_red⁴⁻(aq) + H⁺(aq)}, the equilibrium constant K=(6.5±4.4)·10⁻¹¹, the standard molar enthalpy of reaction Δ_rH^o_m=(6.9±3.0) kJ · mol⁻¹, the standard molar Gibbs free energy change Δ_rG^o_m=(58.1±1.7) kJ · mol⁻¹, and the standard molar entropy change Δ_rS^o_m=−(172±12) J · K⁻¹ · mol⁻¹. Under approximately physiological conditions (T=311.15 K, pH=7.0, and I_m=0.25 mol · kg⁻¹ the apparent equilibrium constant K^′≈0.013. The results of the several studies of this reaction from the literature have also been examined and analyzed using the chemical equilibrium model. It was found that much of the literature is in agreement with the results of this study. Use of our results together with a value from the literature for the standard electromotive force E^o for the NADP redox reaction leads to E^o=0.166 V (T=298.15 K and I=0) for the glutathione redox reaction {glutathione_ox²⁻(aq) + 2 H⁺(aq) + 2 e⁻=2 glutathione_red⁻(aq)}. The thermodynamic results obtained in this study also permit the calculation of the standard apparent electromotive force E^′o for the biochemical redox reaction {glutathione_ox(aq) + 2 e⁻=2 glutathione_red(aq)} over a wide range of temperature, pH, and ionic strength. At T=298.15 K, I=0.25 mol · kg⁻¹, and pH=7.0, the calculated value of E^′o is −0.265 V.     

Excess properties and vapour pressure of (3-diethylaminopropylamine + n-alkanes)

The vapour pressures of liquid (3-diethylaminopropylamine (3-DEPA) + n-heptane) mixtures were measured by a static method between T = (303.15 and 343.15) K at 10 K intervals. The molar excess enthalpies H^E at T = 303.15 K were measured for the systems {3-DEPA + C_nH_2n+2 (n = 6, 7, 12)}. The molar excess Gibbs free energies G^E were obtained with Barker’s method and fitted to the Redlich–Kister equation. The Wilson equation was also used. Deviations between experimental and predicted G^E and H^E, by using group contribution UNIFAC (Gmehling version) model, were evaluated.     

Chloro/bromotrimethylsilane-Cu(NO3)2·3H2O: Safe and efficient reagent system for the decarboxylative ipso-nitration and dibromination of cinnamic acids

Further synthetic potential of halotrimethylsilane-nitrate salt mixture is revealed. A mixture of TMSX-Cu(NO₃)₂·3H₂O system is found to be an efficient reagent system for both the decarboxylative nitration (ipso-nitration) when X = Cl, and dibromination of cinnamic acids, with X = Br, under mild conditions. The reactions are safe and simple, affording the corresponding products (E)-β-nitrostyrenes, and anti-2,3-dibromo-3-phenylpropanoic acids in high yields with high selectivity in a relatively short time. Use of hazardous and toxic nitrating systems such as acetyl nitrate and brominating agents such as molecular bromine can be avoided.     

Kinetics of hematite chlorination with Cl2 and Cl2 + O2: Part I. Chlorination with Cl2

Preliminary tests of the chlorination of two iron oxides (wüstite and hematite) in various chlorinating gas mixtures were performed by thermogravimetric analysis (TGA) under non-isothermal conditions. Wüstite started to react with chlorine from about 200 °C generating ferric chloride and hematite as the final reaction products. The presence of a reducing and oxidizing agent in the chlorinating gas mixtures influenced the chlorination reactions of both iron oxides, during non-isothermal treatment, only at temperatures higher than 500 °C.The chlorination kinetics of hematite with Cl₂ have been studied in details between 600 and 1025 °C under isothermal chlorination. The values of the apparent activation energy (E_a) were about 180 and 75 kJ/mol in the temperature ranges of 600–875 and 875–1025 °C, respectively. The apparent reaction order with respect to Cl₂ was found to be 0.67 at 750 °C. Mathematical model fitting of the kinetics data was carried out to determine the most probable reaction mechanisms.     

Quasi-reversible two-electron reduction of oxygen at gold electrodes modified with a self-assembled submonolayer of cysteine

The electrochemical reduction of molecular oxygen (O₂) has been performed at gold electrodes modified with a submonolayer of a self-assembly (sub-SAM/Au) of a thiol compound (typically cysteine (CYST)) in O₂-saturated 0.5 M KOH. At bare gold electrode O₂ reduction reaction proceeds irreversibly, while this reaction is totally hindered at gold electrodes with a compact structure of CYST over its surface. The partial reductive desorption of the compact CYST monolayer was achieved by controlling the potential of the CYST/Au electrode, leading to the formation of a submonolayer coverage of the thiol compound over the Au electrode surface (sub-SAM/Au), at which the CYST molecules selectively block the Au(1 0 0) and Au(1 1 0) fractions (the so-called rough domains) of the polycrystalline Au while the Au(1 1 1) component (the so-called smooth domains) remains bare (i.e., uncovered with CYST). This sub-SAM/Au electrode extraordinarily exhibits a quasi-reversible two-electron reduction of molecular oxygen (O₂) in alkaline medium with a peak separation (ΔE_p) between the cathodic and anodic peak potentials (E_p^c,E_p^a) of about 60 mV. The ratio of the anodic current to the cathodic one is close to unity. The formal potential (E^o′) of this reaction is found to equal −150 mV vs. Ag/AgCl/KCl(sat.).     

Reactions of a hydrido(hydrosilylene)tungsten complex with oxiranes

Reactivity of a hydrido(hydrosilylene)tungsten complex, Cp¹(CO)₂(H)WSi(H)[C(SiMe₃)₃] (1), toward oxiranes was investigated. Treatment of 1 with racemic mono-substituted oxiranes with a substituent R (R = Ph, vinyl, ^tBu, or ⁿBu) at room temperature produced dihydrido(vinyloxysilyl)tungsten complexes, (E)- and/or (Z)-Cp¹(CO)₂(H)₂W{Si(H)(OCHCHR)[C(SiMe₃)₃]} [(E/Z)-2: R = Ph, (E)-3: R = vinyl, (E)-4: R = ^tBu, (E/Z)-5: R = ⁿBu] in high yields via regioselective ring-opening of oxiranes. When the substituent R on oxirane was relatively large, (E)-isomers (2, 3, and 4) were obtained predominantly (87–97%), while the substituent was a relatively small ⁿBu group, an approximately 1:1 mixture of (E)- and (Z)-isomers [(E/Z)-5] was obtained. Reaction of 1 with 2,2-dimethyloxirane afforded the corresponding complex, Cp¹(CO)₂(H)₂W{Si(H)(OCHCMe₂)[C(SiMe₃)₃]} (6), quantitatively. A reaction mechanism is also discussed.     

Kinetics and mechanism of the chromic oxidation of 3-O-methyl-d-glucopyranose

The oxidation of 3-O-methyl-d-glucopyranose (Glc3Me) by Cr^VI in acid medium yields Cr^III, formic acid and 2-O-methyl-d-arabinose as final products when a 50-times or higher excess of Glc3Me over Cr^VI is used. The redox reaction takes place through the combination of Cr^VI → Cr^IV → Cr^II and Cr^VI → Cr^IV → Cr^III pathways. Intermediacy of free radicals and Cr^II in the reaction was demonstrated by the observation of induced polymerization of acrylamide and detection of CrO₂²⁺ formed by reaction of Cr^II with O₂. Intermediate oxo-Cr^V–Glc3Me species were detected by EPR spectroscopy. In 0.3–0.5 mol/L HClO₄, intermediate Cr^V rapidly decompose to the reaction products, while, at pH 5.5–7.5, where the redox processes are very slow, five-coordinate Cr^V bis-chelates of the pyranose and furanose forms of Glc3Me remain more than 15 h in solution. The C1–C2 bond cleavage of Glc3Me upon reaction with Cr^VI distinguishes this derivative from glucose, which is oxidized to gluconic acid.     

Non-isothermal decomposition kinetics,thermal behavior and computational detonation properties on 4-amino-1,2,4-triazol-5-one (ATO)

The thermal behavior of 4-amino-1,2,4-triazol-5-one (ATO) was studied under non-isothermal condition by DSC method in a sealed cell of stainless steel. The melting enthalpy and melting entropy of ATO are 21.34 ± 0.49 kJ mol⁻¹ and 46.54 ± 0.30 J mol⁻¹ K⁻¹, respectively. The kinetic parameters were obtained from the analysis of DSC curves by Kissinger method, Ozawa method, the differential method and the integral method. The main exothermic decomposition reaction mechanism of ATO is classified as nucleation and growth, and the kinetic parameters of the reaction are E_a = 119.50 kJ mol⁻¹ and A = 10^9.03 s⁻¹. The gas products and condensed phase products of the thermal decomposition of ATO were studied on two simultaneous devices of the fast thermolysis reaction cell (gas reaction cell) in situ in conjunction with rapid scan transform infrared spectroscopy (RSFT-IR) and the solid reaction cell in situ. The heat of formation (HOF) for ATO was evaluated by G3 theory. The detonation velocity (D) and detonation pressure (P) were estimated by using the well-known Kamlet–Jacobs equation, based on the theoretical HOF and the determined crystal density.     

Effect of Co60 γ-irradiation on the optical properties of thin films from the system GeSe3–Sb2Se3–ZnSe

Optical transmittance in the range from 200 nm to 1100 nm is measured for fresh and γ-irradiated thermally evaporated chalcogenide films of GeSe₃, Sb₂Se₃, ZnSe, (GeSe₃)₈₀(Sb₂Se₃)₂₀ and (GeSe₃)₇₀(Sb₂Se₃)₁₀(ZnSe)₂₀. The effect of ZnSe incorporation with both GeSe₃, Sb₂Se₃ results in amorphous γ-radiation sensitive (GeSe₃)₇₀(Sb₂Se₃)₁₀(ZnSe)₂₀ composition as obtained from the estimated optical parameters. Optical energy gap, E_g, for (GeSe₃)₇₀(Sb₂Se₃)₁₀(ZnSe)₂₀ film shows a noticeable decrease from 1.81 eV at 0 kGy to 1.52 eV at 690 kGy and conversely the corresponding band tail width, E_e, increases from 0.123 eV at 0 kGy to 0.138 eV at 690 kGy. By contrast, the estimated values of E_g and E_e for (GeSe₃)₈₀(Sb₂Se₃)₂₀ compositions, show no change with different γ-irradiation doses in the same range. The obtained results could be explained in terms of the band edge shift into the energy gap due to either the formation of localized states at the edges or weakening in the composition cohesive energy as reformation of new weaker bonds appear.     

Volumetric study of (2-methoxyethanol + tetrahydrofuran + cyclohexane) at T=298.15 K

The excess molar volumes V_m^E at T=298.15 have been determined in the whole composition domain for (2-methoxyethanol + tetrahydrofuran + cyclohexane) and for the parent binary mixtures. Data on V_m^E are also reported for (2-ethoxyethanol + cyclohexane). All binaries showed positive V_m^E values, small for (methoxyethanol + tetrahydrofuran) and large for the other ones. The ternary V_m^E surface is always positive and exhibits a smooth trend with a maximum corresponding to the binary (2-methoxyethanol + cyclohexane). The capabilities of various models of either predicting or reproducing the ternary data have been compared. The behaviour of V_m^E and of the excess apparent molar volume of the components is discussed in both binary and ternary mixtures. The results suggest that hydrogen bonding decreases with alcohol dilution and increases with the tetrahydrofuran content in the ternary solutions.     

The pyrolysis characteristics of moso bamboo

In the research, thermogravimetry (TG), a combination of thermogravimetry and Fourier transform infrared spectrometer (TG–FTIR) and X-ray diffraction (XRD) were used to investigate pyrolysis characteristics of moso bamboo (Phyllostachys pubescens). The Flynn–Wall–Ozawa and Coats–Redfern (modified) methods were used to determine the apparent activation energy (E_a). The TG curve indicated that the pyrolysis process of moso bamboo included three steps and the main pyrolysis occurred in the second steps with temperature range from 450 K to 650 K and over 68.69% mass was degraded. TG–FTIR analysis showed that the main pyrolysis products included absorbed water (H₂O), methane gas (CH₄), carbon dioxide (CO₂), acids and aldehydes, ammonia gas (NH₃), etc. XRD analysis expressed that the index and width crystallinity of moso bamboo gradually increased from 273 K to 538 K and cellulose gradually degraded from amorphous region to crystalline region. The E_a values of moso bamboo increased with conversion rate increase from 10 to 70. The E_a values were, respectively 153.37–198.55 kJ/mol and 152.14–197.87 kJ/mol based on Flynn–Wall–Ozawa and Coats–Redfern (modified) methods. The information was very helpful and significant to design manufacturing process of bio-energy, made from moso bamboo, using gasification or pyrolysis methods.     

Excess thermodynamic properties of binary mixtures of N,N-dimethylacetamide with water or water-d2 at temperatures from 277.13 K to 318.15 K

Densities of binary mixtures of N,N-dimethylacetamide (DMA) with water (H₂O) or water-d₂ (D₂O) were measured at the temperatures from T=277.13 K to T=318.15 K by means of a vibrating-tube densimeter. The excess molar volumes V_m^E, calculated from the density data, are negative for the (H₂O + DMA) and (D₂O + DMA) mixtures over the entire range of composition and temperature. The V_m^E curves exhibit a minimum at x(DMA)≅0.4. At each temperature, this minimum is slightly deeper for the (D₂O + DMA) mixtures than for the corresponding (H₂O + DMA) mixtures. The difference between D₂O and H₂O systems becomes smaller when the temperature increases. The V_m^E results were correlated using a modified Redlich–Kister expansion. The partial molar volume of DMA plotted against x(DMA) goes through a sharp minimum in the water-rich region around x(DMA)≅0.08. This minimum is more pronounced the lower the temperature and is deeper in D₂O than in H₂O at each temperature. Again, the difference becomes smaller as the temperature increases. The excess expansion factor α^E plotted against x(DMA) exhibit a maximum in the water rich region of the mole fraction scale. At each temperature, this maximum is higher for the (D₂O + DMA) mixtures than for the corresponding (H₂O + DMA) mixtures, and the difference becomes smaller as the temperature increases. At its maximum, α^E can be even more than 25 per cent of total value of the cubic expansion coefficient α in the (H₂O + DMA) and (D₂O + DMA) mixtures.     

Bioelectrocatalytic formate oxidation and carbon dioxide reduction at high current density and low overpotential with tungsten-containing formate dehydrogenase and mediators

We show a great possibility of mediated enzymatic bioelectrocatalysis in the formate oxidation and the carbon dioxide (CO₂) reduction at high current densities and low overpotentials. Tungsten-containing formate dehydrogenase (FoDH1) from Methylobacterium extorquens AM1 was used as a catalyst and immobilized on a Ketjen Black-modified electrode. For the formate oxidation, a high limiting current density (j_lim) of ca. 24 mA cm^− 2 was realized with a half wave potential (E_1/2) of only 0.12 V more positive than the formal potential of the formate/CO₂ couple (E°′_CO2) at 30 °C in the presence of methyl viologen (MV^2 +) as a mediator, and j_lim reached ca. 145 mA cm^− 2 at 60 °C. Even when a viologen-functionalized polymer was co-immobilized with FoDH1 on the porous electrode, j_lim of ca. 30 mA cm^− 2 was attained at 60 °C with E_1/2 = E°′_CO2 + 0.13 V. On the other hand, the CO₂ reduction was also realized with j_lim ≈ 15 mA cm^− 2 and E_1/2 = E°′_CO2 − 0.04 V at pH 6.6 and 60 °C in the presence of MV^2 +.     

Hydroesterification of cyclohexene using the complex Pd(PPh3)2(TsO)2 as catalyst precursor: Effect of a hydrogen source (TsOH,H2O) on the TOF and a kinetic study (TsOH: p-toluenesulfonic acid)

The hydroesterification of cyclohexene is catalyzed by a preformed Pd(PPh₃)₂(TsO)₂ complex I in methanol as solvent. The effect of PPh₃, TsOH, and water on the TOF has been evaluated. The system I/PPh₃/TsOH=1/6/8, in the presence of 800 ppm of H₂O, at 373 K and under 2.0 MPa of CO leads to a TOF as high as 850 h⁻¹. The increase of TOF observed adding a hydride source such as TsOH and H₂O suggests that Pd-hydride species plays a key role in the first step of the catalytic cycle. The initial reaction rate increases linearly with the concentration of cyclohexene and of MeOH and passes through a maximum with increasing the pressure of CO. The rate equation r₀=k₁P_CO (1+k₂P_CO+k₃P_CO²)⁻¹ fits well the experimental data. The values of k₁, k₂, and k₃ have been evaluated at different temperatures. From the plot ln k versus 1/T, E₁=19.4 kcal/mol, E₂=20.6 kcal/mol and E₃=6.5 kcal/mol have been evaluated. On the basis of experimental evidences and of the kinetic study, a catalytic cycle mechanism has been proposed.     

Electron excitation coefficients of neutral and ionic levels of krypton in Townsend discharges

In this paper, we present experimental results for excitation coefficients of krypton atoms to several Kr and Kr⁺ excited levels for E/N (electric field to gas particle number density ratio usually in units of Townsend, 1 Td = 10^− 21 V m²) values from 7 × 10^− 20 V m² to above 1 × 10^− 17 V m². The data have been obtained in two different parallel plate self-sustained Townsend discharge drift tubes. The spatial distribution of the emission intensities were recorded and then normalized to give excitation coefficients at the anode, by using the electron flux at this point. The values of these coefficients are placed on an absolute scale by using a standard tungsten ribbon lamp calibrated against a primary blackbody radiation standard. The ionization rates at different E/N are obtained from the spatial emission profiles.The data for atomic krypton levels 2p₂, 2p₃, 2p₅, 2p₆, 2p₇, 2p₈, 3p₅ and 3p₆ (in Paschen notation) were converted to excitation coefficients by using quenching coefficients from the literature. The emission coefficients of eight 4s²4p⁴ (³P)5p levels of Kr⁺ have also been measured for E/N values from about 1 × 10^− 18 V m² up to nearly 8 × 10^− 18 V m².     

Liquid–liquid equilibrium calculation in binary water + nonionic surfactant CiEj systems with a new mass-action law model based on continuous thermodynamics

A systematic study of the LLE for a number of aqueous solutions of n-alkyl polyglycol ethers (C_iE_j) with tail length i from 4 to 12 and head length j from 1 to 6 is presented. For calculation a new thermodynamic model was developed basing on the mass-action law and continuous thermodynamics. Besides the micellization the self association of water is taken into account. The resulting polydisperse mixture of micelles and water associates is described by two continuous aggregation-size distribution functions depending on temperature and surfactant concentration. The Gibbs energy of the mixture is calculated by the Flory-Huggins theory with a temparature dependent parameter χ. The model is applied to 13 water + C_iE_j systems with LCST behavior and to the three systems water + C₄E₁, water + C₁₀E₄ and water + C₁₀E₅ with closed-loop miscibility gaps. For the former 13 systems four parameters were fitted to the experimental equilibrium data. For the systems with closed-loop miscibility gaps two additional parameters were necessary, due two the more extended temperature range. The agreement between calculated and experimental data is very good for nearly all systems of both types.