A Scrutiny on the Reductive Amination of Carbonyl Compounds Catalyzed by Homogeneous Rh(I) Diphosphane Complexes

The reductive amination of a series of aldehydes with secondary amines and H₂ in the presence of a homogeneous Rh-diphosphane catalyst was studied in order to establish a general mechanism of this reaction and to identify conditions for the improvement of the amine/alcohol ratio in the product. Several possible intermediates as constituents of changing equilibria like half-aminals, N,O-acetals and aminals were observed in the reaction mixture by means of ¹H NMR spectroscopy. In individual trials, these compounds could be successfully hydrogenated under the conditions applied for reductive amination (50 bar H₂ pressure, MeOH). Some evidence is accumulated that half-aminals and N,O-acetals might be key intermediates of the reductive amination. Moreover, it was found that the formation of the undesired product alcohol is likely based on the reduction of the starting carbonyl compound. However, due to numerous equilibria consisting of several intermediates, general conclusions are hard to be drawn. Proof will be given that, in several cases, the efficiency of the reductive amination of aliphatic aldehydes can be significantly improved by prehydrogenation of the cationic [Rh(dppb)(COD)]⁺ complex.     

Prediction of tensile modulus of nanocomposites based on polymeric blends

A simple model was proposed for predicting the Young’s modulus of nanocomposites based on polymeric blends. First, a simple model was derived for binary blends containing only two polymers. This model is more useful for those blends with high degree of continuity. Therefore, the morphology of the blend is divided into parallel and series regions and the percolation theory is used to calculate the volume fraction of these phases. In the next step, the addition of nanoclay, as a third component, is being considered. These nanoparticles may possibly find locations at the matrix, minor or interface. In the latter case, the model was expanded into a three-phase model including the matrix, dispersed and a third phase containing nanoclay which itself was split into series and parallel sections. A model related to the reinforcing effect of nanoclay was employed and combined with the above model to estimate the modulus of this ternary nanocomposite. The experimental data which is obtained from nanocomposite based on low-density polyethylene/thermoplastic starch/Cloisite 30B were compared with the model results and revealed a good agreement with each other. Also, the model predictions were compared with other experimental data from literature sources to verify the model accuracy. The comparison showed that the model predictions can predict the experimental data rationally. This model can be used to determine the structure of a nanocomposite without any other expensive tests.     

On the dispersion of CNTs in polyamide 6 matrix via solution methods: assessment through electrical, rheological, thermal and morphological analyses

In this study, polyamide 6 (PA 6)/multi-walled carbon nanotube (MWCNT) nanocomposites were prepared by different solution methods based on phase inversion, drop-casting and simple evaporation processes. Optical microscopy and field emission scanning electron microscopy techniques were used to investigate the dispersion states of the nanotubes in PA 6 matrix. The results indicated that the dispersion state of MWCNTs in the nanocomposites prepared by the phase inversion-based method was better than those in the nanocomposites prepared by the other two methods. Electrical, rheological, differential scanning calorimetry and thermo-gravimetric analysis measurements showed that the PA 6/MWCNTs nanocomposites prepared by the phase inversion-based method had higher electrical conductivity, storage modulus, crystallization temperature and thermal stability in comparison with those prepared by the other two methods, attributed to the better dispersion state of MWCNTs. These results confirmed achievement of a good dispersion state of MWCNTs within PA 6 matrix by the phase inversion-based efficient approach.     

Characterization and tests of planar Co3O4 model catalysts prepared by chemical vapor deposition

The chemical vapor deposition method was used to deposit thin films of cobalt oxide starting with cobalt (II) acetylacetonate and oxygen. The deposition process was investigated and the obtained films were identified as a cubic spinel-type polycrystalline Co₃O₄ with a crystallite size of 30–40 nm. The coating was carbon-free and the surface oxygen concentration was measured to be 66 at.% with AES analysis. Smooth and highly uniform thin films were deposited on planar stainless steel substrates and subjected to TPR and catalysis tests that show positive correlation. The apparent activation energy of Co₃O₄ reduction to CoO was measured to be (33±5) kJ/mol. The catalytic activity of Co₃O₄ was investigated toward the conversion of both propane and ethanol to carbon dioxide. Though the catalytic action was registered at the same temperature, the deactivation process was seen to be different. The catalytic conversion of ethanol induces a fast deactivation process, which was linked to its high ability to reduce Co₃O₄.     

Measurement of Micro Kinetics of Hydrogenation in Liquid Phase Using Raman Spectroscopy

Hydrogenation of liquid organic hydrogen carriers is usually carried out in liquid phase. To measure the kinetics of this hydrogenation, an experimental setup using in situ Raman spectroscopy for analysis of the reaction mixture is proposed. With this setup it is possible to perform hydrogenation reactions at temperatures of up to 573 K and pressures up to 25 MPa. For validation of the experimental setup the hydrogenation of 1‐octene was measured in liquid phase. The reaction progress can be monitored in detail by Raman spectroscopy. To determine kinetic parameters from the experimental data, two modeling approaches were applied: a classic kinetic model and a thermodynamic kinetic model. The results were compared to literature data.     

A computational and experimental investigation of the mechanical properties of single ZnTe nanowires

One-dimensional nanostructures such as ZnTe, CdTe, Bi(2)Te(3) and others have attracted much attention in recent years for their potential in thermoelectric devices among other applications. A better understanding of their mechanical properties is important for the design of devices. A combined experimental and computational approach has been used here to investigate the size effects on the Young's modulus of ZnTe nanowires (NWs). The mechanical properties of individual ZnTe nanowires in a wide diameter range (50-230 nm) were experimentally measured inside a high resolution transmission electron microscope using an atomic force microscope probe with the ability to record in situ continuous force-displacement curves. The in situ observations showed that ZnTe NWs are flexible nanostructures with the ability to withstand relatively high buckling forces without becoming fractured. The Young's modulus is found to be independent of nanowire diameter in the investigated range, in contrast to reported results for ZnO NWs and carbon nanotubes where the modulus increases with a decrease in diameter. Molecular dynamics simulations performed for nanowires with diameters less than 20 nm show limited size dependence for diameters smaller than 5 nm. The surface atoms present lower Young's modulus according to the simulations and the limited size dependency of the cylindrical ZnTe NWs is attributed to the short range covalent interactions.     

Synthesis and Characterization of Anti-fungus,Anti-corrosion and Self-cleaning Hybrid Nanocomposite Coatings Based on Sol–Gel Process

Anti-corrosion, anti-fungus, and self-cleaning properties of coatings containing ZnO–TiO₂, SiO₂–TiO₂ and SiO₂/TiO₂/ZnO nanoparticles synthesized based on sol–gel precursors using tetra methoxysilane, 3-glycidoxypropyl trimethoxysilane, tetra (n-butyl orthotitanate) and zinc acetate dihydrate were investigated by FESEM, EDAX and TEM analyses. Results indicated uniform dispersion of inorganic nanoparticles in the range of 20–40 nm in size. Anti-corrosion property of the hybrid coating was characterized by EIS measurements and parametrically analyzed in an equivalent circuit when the coating was exposed to salt solution. Results showed that, ZnO and TiO₂ nanoparticles enhance anti-corrosion property of the hybrid coatings. Anti-fungus and anti-bacterial properties of the coatings were determined by diameter of inhibition zone and inhabitation of bacterial growth, respectively. The coating containing ZnO and TiO₂ nanoparticles showed anti-fungus and anti-bacterial properties which were related to their photocatalytic properties. Degradation of methylene blue in aqueous solution was determined by UV–Visible tests which indicated self-cleaning property of the coatings containing ZnO and TiO₂ nanoparticles.     

Crystalline Intermediate Phases in the Sol–Gel-Based Synthesis of La2NiO4+δ

X-ray diffraction and transmission electron microscopy were applied to investigate a sol–gel synthetic process for the mixed oxygen ion and electron conductor La₂NiO_4+δ with a K₂NiF₄ structure type. The development of the La₂NiO_4+δ is elucidated considering the influence of calcination temperatures and dwell times. Following the thermal decomposition of nitrate and organic precursors in an intermediate step, the lanthanum nickel oxide is obtained after a short dwell time above 750°C. This occurs by the transformation of an ultrafinely dispersed powder consisting of lanthanum oxycarbonate, lanthanum oxide, and nickel oxide. The pure La₂NiO_4+δ phase was obtained by similar solid-state reactions between nanocrystalline powder particles at just 950°C.     

Discovery of Riociguat (BAY 63‐2521): A Potent,Oral Stimulator of Soluble Guanylate Cyclase for the Treatment of Pulmonary Hypertension

Direct stimulation of soluble guanylate cyclase (sGC) represents a promising therapeutic strategy for the treatment of a range of diseases, including the severely disabling pulmonary hypertension (PH). Optimization of the unfavorable DMPK profile of previous sGC stimulators provided riociguat, which is currently being investigated in phase III clinical trials for the oral treatment of PH.

     

Effects of cold working and heat treatment on microstructure and wear behaviour of Cu–Be alloy C17200

The effects of cold work process between aging and solution heat treatment on the microstructure, hardness and the tribologic behaviour of a copper–beryllium (Cu–Be) alloy C17200 were investigated. The wear behaviour of the alloys was studied using ‘pin on disc’ method under dry conditions. The results show that the formation of fine grained structure and γ phase particles enhances the mechanical properties of the alloy; nonetheless, they do not reduce the wear rate. This is attributed to the capability of the softer specimens to maintain oxygen rich compounds during the dry sliding test.