Ruthenium carbenes as catalysts in stereoselective ene–yne metathesis/Diels–Alder and ene–yne metathesis/Diels–Alder/cross coupling multicomponent reactions

An ene–yne cross metathesis of silyl substituted alkynes and alkenes followed by a Diels–Alder reaction of the metathesis product 2-silyl-1,3-dienes has been developed. The dienes thus prepared in situ were shown to participate in highly diastereoselective Diels–Alder reactions. In one case the silicon substituted Diels–Alder cycloadduct was subsequently used without isolation and purification in a Hiyama cross coupling reaction. The cross coupling reactions enable these silicon dienes to be used as synthons for a variety of other dienes.     

Kinetic investigation of propane oxidation on diluted Mo1–V0.3–Te0.23–Nb0.125–Ox mixed-oxide catalysts

Reaction kinetics and proposed mechanism for the oxidation of propane over diluted Mo₁–V_0.3–Te_0.23–Nb_0.125–O _x are described. The kinetic study allowed determination of the orders of propane disappearance, propene formation, CO _x formation, and acids formation. The results show that selective oxidation of propane to propylene over this catalyst follows the Langmuir-Hinshelwood mechanism. Deep oxidation of propane to carbon dioxide is first order with respect to hydrocarbon, and partial order (0.21) with respect to oxygen. The selective oxidation of propane to acrylic acid is half order with respect to hydrocarbon and partial order (0.11) with respect to oxygen, while water does not participate directly in propane transformation. The result also shows that the overall reaction consists of three parallel process channels. One main sequence of consecutive reactions leads to the desired product.     

Thermal decomposition of RDX/AP by TG–DSC–MS–FTIR

The method of TG–DSC–MS–FTIR simultaneous analysis has been used to study the thermal decomposition mechanism of the RDX/AP (1/2) mixture. TG–DSC showed that there were two mass loss processes for thermal decomposition of RDX/AP. The first one was mainly ascribed to the thermal decomposition of RDX. Addition of AP to RDX causes decomposition to take place abruptly, after melting, resulting in a very sharp and strong peak at lower temperature. The apparent activation energies, calculated by model-free Friedman method, of this process were negative. The second mass loss process of RDX/AP was confirmed to be the thermal decomposition of AP, catalyzed by RDX. This process can be divided into three stages, which were an nth-order autocatalytic and two one-dimensional diffusion stages, respectively. There was a competition among the formation reactions of N₂O, HNCO, and HCl for the first stage and between NO₂ and N₂O for the later two stages. The production of N₂O dominated in the second stage, while NO₂ did in the third stage.     

Online NMR spectroscopic study of species distribution in MEA–H2O–CO2 and DEA–H2O–CO2

Quantitative online NMR spectroscopy was used for studying the species distribution in solutions of carbon dioxide in aqueous monoethanolamine (MEA) and diethanolamine (DEA). The mass fraction of the amine in the unloaded solution was 0.2 and 0.3 g/g, respectively, the carbon dioxide loading was up to 1.1 ??molCO₂/molamine$1.1\text{\hspace{0.17em}??}\text{mo}{\text{l}}_{\text{C}{\text{O}}_2}/\text{mo}{\text{l}}_{\text{amine}}$, temperatures were between 293 and 353 K. A special apparatus was designed that allows preparing the mixtures gravimetrically and applying pressures up to 25 bar to keep the carbon dioxide in solution. It was coupled to a 400 MHz NMR spectrometer by heated capillaries. By using both ¹H and ¹³C NMR spectroscopy quantitative information on the concentrations of the following species were obtained: amine, carbamate, bicarbonate, and carbon dioxide. Due to the fast proton transfer between molecular and protonated amine, only the sum of their concentrations can be determined. Furthermore, a byproduct, 2-oxazolidone, was observed and quantified. The experimental data were used for developing a thermodynamic model of the studied electrolyte solutions based on the extended Pitzer G^E-model. In the model development, also vapor–liquid equilibrium data from the literature were included. The model gives reliable results both for the species distribution and the vapor–liquid equilibrium of the studied mixtures.     

Hypervalence and the delocalizing versus localizing propensities of H 3– , Li 3– , CH 5– and SiH 5–

Lithium and silicon have the capability to form hypervalent structures, such as Li₃^– and SiH₅^–, which is contrasted by the absence of this capability in hydrogen and carbon, as exemplified by H₃^– and CH₅^– which, although isoelectronic to the former two species, have a distortive, bond-localizing propensity. This well-known fact is nicely confirmed in our DFT study at BP86/TZ2P. We furthermore show that the hypervalence of Li and Si neither originates from the availability of low-energy 2p and 3d AOs, respectively, nor from differences in the bonding pattern of the valence molecular orbitals; there is, in all cases, a 3-center-4-electron bond in the axial X–A–X unit. Instead, we find that the discriminating factor is the smaller effective size of C compared to the larger Si atom, and the resulting lack of space around the former. Interestingly, a similar steric mechanism is responsible for the difference in bonding capabilities between H and the effectively larger Li atom. This is so, despite the fact that the substituents in the corresponding symmetric and linear dicoordinate H₃^– and Li₃^– are on opposite sides of the central atom. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Effect of electron radiation on electrical parameters of Zn/n-Si/Au–Sb and Zn/ZnO/n-Si/Au–Sb diodes

In this study, RF-magnetron sputtered ZnO thin film as an interlayer was used to improve radiation tolerance of the Schottky diodes. The structural and optical measurements showed that the ZnO thin films have hexagonal crystal structure with preferential c-axis orientation, 20.39 nm grain sizes and 3.15 eV bandgap. The electrical parameters such as ideality factor, barrier height and series resistance of Zn/n-Si/Au–Sb and Zn/ZnO/n-Si/Au–Sb diodes were calculated before and after electron radiation at 25, 50 and 75 gray doses. Deviation values of the parameters showed that the ZnO as an interlayer caused to improved radiation tolerance of the diodes.

     

Recent developments in polymer–block–polypeptide and protein–polymer bioconjugate hybrid materials

In the last few years, polymer bioconjugates have been shown to be useful in many emerging areas of materials science. Consequently, the synthesis of polymer bioconjugates has suddenly become a central topic in polymer chemistry. The versatility and robust nature of modern synthetic methods such as controlled radical polymerisation (CLRP),¹ ring-opening polymerisation (ROP), and ‘click’ chemistry make them excellent tools for the preparation of tailor-made polymer bioconjugates. CLRP in combination with other techniques has been shown to be a mature technology for building tailor-made block copolymers and protein–polymer conjugates with a wide range of applications, especially in biomedical domains. This review describes the recent advances and progress in the rapidly expanding field of bioconjugation, outlining the work performed up to 2012.     

Theoretical Study of Chemical Binding of Noble Gas Atom and Transition Metal Complexes: Ng–NiCO, Ng–NiN2, Ng–CoCO (Ng = He–Xe)

Summary. Ab initio multireference and coupled cluster methods (MR-SDCI(+Q), CASPT2, CCSD(T)) and density functional theory methods (B3LYP, MPWPW91) have been applied to examine geometrical structures and vibrational frequencies of noble gas (Ng) – transition metal compounds, Ng–NiCO, Ng–NiN₂, and Ng–CoCO (Ng = He, Ne, Ar, Kr, Xe). It is shown that the respective compounds can have a larger binding energy than a typical van der Waals interaction energy. The binding mechanism is explained by a partial electron transfer from a noble gas atom to the low-lying 4s and 3d vacant orbitals of the transition metal atom. Theoretical calculations show that the binding of noble gas atom results in a large shift of the bending frequency: 361.1cm^–1 (NiCO) to 403.5cm^–1 (Ar–NiCO); 308.5cm^–1 (NiN₂) to 354.8cm^–1 (Ar–NiN₂); 373.0cm^–1 (CoCO) to 422.6cm^–1 (Ar–CoCO). The corresponding experimental frequencies determined in solid argon are 409.1cm^–1 (NiCO), 357.0cm^–1 (NiN₂), and 424.9cm^–1 (CoCO), which are much closer to the corresponding frequency of Ar–NiCO, Ar–NiN₂, and Ar–CoCO, respectively.     

Theoretical Study of Chemical Binding of Noble Gas Atom and Transition Metal Complexes: Ng–NiCO, Ng–NiN2, Ng–CoCO (Ng = He–Xe)

Ab initio multireference and coupled cluster methods (MR-SDCI(+Q), CASPT2, CCSD(T)) and density functional theory methods (B3LYP, MPWPW91) have been applied to examine geometrical structures and vibrational frequencies of noble gas (Ng) – transition metal compounds, Ng–NiCO, Ng–NiN₂, and Ng–CoCO (Ng = He, Ne, Ar, Kr, Xe). It is shown that the respective compounds can have a larger binding energy than a typical van der Waals interaction energy. The binding mechanism is explained by a partial electron transfer from a noble gas atom to the low-lying 4s and 3d vacant orbitals of the transition metal atom. Theoretical calculations show that the binding of noble gas atom results in a large shift of the bending frequency: 361.1cm^–1 (NiCO) to 403.5cm^–1 (Ar–NiCO); 308.5cm^–1 (NiN₂) to 354.8cm^–1 (Ar–NiN₂); 373.0cm^–1 (CoCO) to 422.6cm^–1 (Ar–CoCO). The corresponding experimental frequencies determined in solid argon are 409.1cm^–1 (NiCO), 357.0cm^–1 (NiN₂), and 424.9cm^–1 (CoCO), which are much closer to the corresponding frequency of Ar–NiCO, Ar–NiN₂, and Ar–CoCO, respectively.     

Low temperature carbon monoxide catalytic oxidation at the Pd/Ce–Zr–Al–Ox catalyst

The homogeneous chemical composition ceria–zirconia–alumina (Ce–Zr–Al–O_x) nano-alloy were successfully synthesized by surfactant-assisted parallel flow co-precipitation method and applied as supports for low temperature CO oxidation. The experiment conditions were studied in detailed. At 0.92 wt% Pd loading, 30,000 ppm CO could be completely oxidized to CO₂ at 30 °C at a WHSV of 4,380 ml g^?1 h^?1 over the Pd/Ce–Zr–Al–O_x (n_Ce:n_Zr = 3:1) catalyst. Pd/Ce–Zr–Al–O_x catalysts were systematical studied by mean of BET, XRD and TEM analysis. XRD characterization showed that zirconium element entered into cubic structure of ceria and leaded to structure distortion. Addition of aluminum increased specific surface area of ceria–zirconia solid solution substantially. The average pore diameter of Ce–Zr–Al–O_x support palladium catalysts were the key impact factor for CO oxidation. When the Pd/Ce–Zr–Al–O_x catalysts had highly dispersed palladium nanoparticles, large average pore diameter, suitable surface area and pore volume, the activity of CO oxidation was the best.     

The Structure of Oxide Ga–Sb–Ni–P–W–O/SiO2 Catalyst and Its Catalytic Properties in Propane Ammoxidation

The structure of the multicomponent catalyst Ga₁Ni₁P₂W_0.5Sb₆O _x /SiO₂ and its catalytic properties in propane ammoxidation are studied. The catalyst is nanostructured and consists of noncoherently spliced blocks of a multiply promoted phase with a structure of gallium antimonate, which covers SiO₂ particles with a thin layer. In the multiply promoted compound with a structure of gallium antimonate, Ni²⁺ ions partially substitute for Ga³⁺ and W⁶⁺ ions partially substitute for Sb⁵⁺. This leads to an increase in the crystalline lattice parameters a and c. Phosphate ions are stabilized in the region of block interfaces. The catalyst is characterized by high efficiency in propane ammoxidation.     

ESI–IT–MSn and DFT calculation for electron affinities of bimetallic oxovanadium complexes

Abstract  

The MS ⁿ spectra of three bimetallic oxovanadium complexes were obtained using an ion trap. The fragmentation pathways were elucidated. Common features and major differences between ESI–QTOF–MS/MS and ESI–IT–MS ⁿ spectra were compared. Electron affinities of several radical molecular anions were calculated by DFT and these could be used as an indicator of the ions’ stability.     

Effect of synthesis method on oxygen adsorption/desorption properties of La–Sr–Co–Fe–O perovskite-type oxide

There has been a growing interest in utilizing La–Sr–Co–Fe–O perovskite-type oxide for efficient high temperature oxygen adsorption applications and oxygen removal process. In this paper, we focus our attention on the analysis of the determinants of the synthesis methods of La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ (LSCF) powders for the oxygen adsorption/desorption applications. To this aim, LSCF powders were successfully synthesized by different synthesis routes using polymerized complex and citrate methods. The effects of synthesis methods on the structure, particle size, specific surface area, oxygen adsorption/desorption kinetics, and oxygen uptake capacities of LSCF perovskite-type oxides were investigated. The oxygen adsorption/desorption capacities and kinetics of the LSCF oxides increase with increasing (1) the temperature from 700 to 900 °C and (2) the surface area observed at a given temperature. Collectively, the experimental observations suggest that particle sizes may play an important role in oxygen uptake capacities and adsorption/desorption kinetics.     

Solid–liquid–gas equilibrium of the naphthalene–biphenyl–CO2 system: Measurement and modeling

The first and last melting points (FLMP) method was employed to measure the melting temperature–composition (T–w$T–w$) data at solid–liquid–gas (SLG) equilibrium for the naphthalene–biphenyl–CO₂ system. Results show that the system's phase diagram is simple eutectic under all investigated pressures (0.1, 3.0, 6.0 and 8.0 MPa), and the system's eutectic composition is almost constant. The (T–w$T–w$) data measured with a high-pressure differential scanning calorimetry are in good agreement with these from FLMP. The semi-predictive model using solubility data (SMS) and the calculation model combining with G^E models (CMG) for binary systems were extended to this ternary system. For the SMS model, the Peng–Robinson equation of state (PR-EoS) with the van der Waals one-fluid mixing rule was used to correlate the solubility data of the two solutes in CO₂ to obtain the two interaction parameters k₁₂ and k₁₃ and calculate the fugacity coefficients of the solutes in the liquid and vapor phases; the UNIFAC method was also applied to the activity coefficient of the solutes in the liquid phase. For the CMG model, the PR-EoS combining respectively the MHV1, LCVM, and modified LCVM (mLCVM) mixing rules was applied to the fugacity coefficients of the solutes. Results show that the CMG model with MHV1 gives the best prediction of the system's SLG equilibrium, while the SMS model and the CMG model with mLCVM provide comparable and acceptable results.     

Synthesis of bicyclic lactones via I2-mediated intramolecular tandem C–C/C–O bond formation

The iodine/DMAP-mediated intramolecular tandem C–C/C–O bond forming reaction of malonate bearing alkene moiety proceeded to give bicyclic lactones with good diastereoselectivity in good yield. The mechanistic investigation was also discussed on the basis of various control experimental results.     

Synthesis and structural characterization of copper–molybdenum–sulfur and copper–tungsten–sulfur cluster complexes (n-Bu4N)[OMS3Cu3Br2L2] with heterocyclic thiones as ligands

Reaction of (NH₄)₂[WOS₃] or (NH₄)₂[MoO₂S₂], n-Bu₄NBr, CuCl and Imt in acetone solvent afforded air- and moisture-stable clusters (n-Bu₄N)[MOS₃Cu₃(Imt)₂Br₂] (M = W or Mo, Imt = imidazolidine-2-thione). These compounds have been characterized by IR, UV–Vis, ¹H and ¹³C NMR spectra and single-crystal X-ray diffraction. They are crystallographically isostructural, with Imt and [MOS₃]²⁻ acting as monodentate and bidentate S-donor ligands, respectively. In the anions, the three Cu atoms have different coordination environments, one being distorted tetrahedral with Imt and Br as terminal ligands, the other two being approximately trigonal planar with Imt as a terminal ligand for one and Br as a terminal ligand for the other. W and Mo have approximately tetrahedral coordination geometry, with a terminal O and three triply-bridging S atoms. The NH groups of the Imt ligands serve as donors in intramolecular N–H?Br and in intermolecular N–H?Br and N–H?O hydrogen bonds, linking the anions to form layers with the cations in cavities.     

Solid–liquid phase equilibria in the system K2SO4–MgSO4–H2O at 318 K

The polythermal solubility diagram of the system K₂SO₄–MgSO₄–H₂O presents the formation of three double salts, picromerite, leonite, langbeinite appearing in this order with increasing temperature. In the temperature range between 314.15 K and 320.65 K, picromerite and leonite ought to coexist. The search in the literature revealed a lack of isothermal phase equilibrium data within this temperature range. Therefore, the solubility in the system K₂SO₄–MgSO₄–H₂O was determined in the whole concentration range at 318 K. The solid phases, epsomite, leonite, picromerite and arcanite occur with increasing potassium sulfate concentration. A two-salt point of leonite and picromerite is established at 0.618 molal K₂SO₄ and 3.030 molal MgSO₄ at the temperature of investigation.     

TG/DSC studies of modified 1–vinyl-2-pyrrolidone–divinylbenzene copolymers

In this paper, the synthesis and characterization of porous copolymers of 1-vinyl-2-pyrrolidone with divinylbenzene are presented. They were obtained by suspension polymerization as pure polymers or composite materials with different inorganic fillers. The influence of the type of filler on the textural and thermal properties was investigated in detail. It was found that the value of the porous surface area and the degree of double bonds’ conversion of composites are much lower than in the case of pure copolymers. Thermal properties of the obtained materials were investigated by the means of thermogravimetry and differential scanning calorimetry.     

固相萃取–HPLC–ICP/MS法测定水中的烷基汞

建立了固相萃取、高效液相色谱与电感耦合等离子体质谱联用技术测定水中烷基汞的方法。对固相萃取、高效液相色谱和电感耦合等离子体质谱的实验条件进行了优化。在优化条件下,甲基汞和乙基汞的检出限分别为0.5,0.7 ng/L。对地表水、工业废水和生活污水3种水样分别加标10.0,50.0 ng/L进行测定,测定结果的相对标准偏差为3.3%~9.6%(n=6),加标回收率在81.0%~103.0%之间。该方法灵敏度高,实用性强。     

NOx-Sorbing Metal Oxides, MnOx–CeO2. Oxidative NO Adsorption and NOx–H2 Reaction

(n)MnO_x–(1–n)CeO₂ binary oxides have been studied for the sorptive NO removal and subsequent reduction of NO_x sorbed to N₂ at low temperatures (150 °C). The solid solution with a fluorite-type structure was found to be effective for oxidative NO adsorption, which yielded nitrate (NO^– ₃) and/or nitrite (NO^– ₂) species on the surface depending on temperature, O₂ concentration in the gas feed, and composition of the binary oxide (n). A surface reaction model was derived on the basis of XPS, TPD, and DRIFTS analyses. Redox of Mn accompanied by simultaneous oxygen equilibration between the surface and the gas phase promoted the oxidative NO adsorption. The reactivity of the adsorbed NO_x toward H₂ was examined for MnO_x–CeO₂ impregnated with Pd, which is known as a nonselective catalyst toward NO–H₂ reaction in the presence of excess oxygen. The Pd/MnO_x–CeO₂ catalyst after saturated by the NO uptake could be regenerated by micropulse injections of H₂ at 150 °C. Evidence was presented to show that the role of Pd is to generate reactive hydrogen atoms, which spillover onto the MnO_x–CeO₂ surface and reduce nitrite/nitrate adsorbing thereon. Because of the lower reducibility of nitrate and the competitive H₂–O₂ combustion, H₂–NO reaction was suppressed to a certain extent in the presence of O₂. Nevertheless, Pd/MnO_x–CeO₂ attained 65% NO-conversion in a steady stream of 0.08% NO, 2% H₂, and 6% O₂ in He at as low as 150 °C, compared to ca. 30% conversion for Pd/–Al₂O₃ at the same temperature. The combination of NO_x-sorbing materials and H₂-activation catalysts is expected to pave the way to development of novel NO_x-sorbing catalysts for selective deNO_x at very low temperatures.