Effect of multi-ethers and conventional alkoxysilanes as external donors on the 4th generation Ziegler-Natta catalysts for propylene polymerization

The multi-ether compounds with different numbers of methoxy groups containing 1,3-dimethoxy-2,2-bis(methoxymethyl)propane and 1-methoxy-2,2-bis(methoxymethyl)butane were synthesized using the Williamson reaction from pentaerythritol and 1,1,1-tris(hydroxymethyl)propane, respectively, in the presence of sodium hydride and methyl iodide in tetrahydrofuran and they were characterized by ¹H NMR, ¹³C NMR, and FTIR spectroscopy. These compounds were employed as external donors in the polymerization of propylene using the industrial Ziegler-Natta catalyst. A commercial spherical MgCl₂-supported Ziegler-Natta catalyst containing diisobutyl phthalate as the internal donor was used for the polymerization of propylene. The role of ether compounds and industrial alkoxysilanes on the properties of polypropylene were studied using the xylene solubility method, melt flow index, gel permeation chromatography, scanning electron microscopy, and differential scanning calorimetry. The addition of the electron donors has led to improvements in the activity and selectivity of the Ziegler-Natta catalyst system.     

Synthesis and MRSA PK inhibitory activity of thiazole containing deoxytopsentin analogues

The public health care crisis caused by the emergence of drug resistant bacterial strains, e.g., methicillin resistant Staphylococcus aureus (MRSA) has underlined the urgent need to accelerate the discovery of new chemical entities active against antibiotic resistant bacteria. We report here the synthesis of a series thiazole containing deoxytopsentin analogues, which show moderate activity against a target MRSA pyruvate kinase enzyme: an evolutionary conserved hub protein critical for bacterial survival. A Hantzsch thiazole coupling between α-oxo-1H-indole-3-thioacetamides and 2-bromo-1-(1H-indol-3-yl)-ethanones provided facile access to the thiazole containing deoxytopsentin compounds.     

New penta-ether as the internal donor in the MgCl2-supported Ziegler-Natta catalysts for propylene polymerization

The penta-ether compound was synthesized by the reaction of di(trimethylolpropane) with sodium hydride as the strong base and methyl iodide as the alkyl halide. This compound was characterized by NMR, FTIR, and GC techniques. The MgCl₂-supported titanium catalysts were incorporated with varying amounts of penta-ether compound as the internal donor and also the catalysts without the internal donor were synthesized. The synthesized catalysts and the conventional Ziegler- Natta catalyst were characterized. The titanium contents were determined by spectrophotometry, magnesium by complexometric titration and chloride by argentometric titration. The effects of the new internal donor on propylene polymerization with the prepared MgCl₂-supported Ziegler-Natta catalysts were investigated and then these results were compared to the results obtained using the conventional diisobutyl phthalate-besed-Ziegler-Natta catalyst. The highest crystallinity degree, melting temperature, and isotacticity of polypropylene were obtained using the catalyst with a penta-ether/Mg molar ratio equal to 0.21.     

QTAIM and stress tensor interpretation of the (H2O)5 potential energy surface

Using the quantum theory of atoms in molecules a near complete combined directed spanning quantum topology phase diagram (QTPD) was constructed from the nine (H₂O)₅ reaction‐pathways and five unique Poincaré–Hopf solutions that were found after an extensive search of the MP2 potential energy surface. Two new energy minima that were predicted from earlier work are found and include the first (H₂O)₅ conformer with a 3‐D_QT quantum topology. The stress tensor Poincaré–Hopf relation indicated a preference for 2‐D_QT (H₂O)₅ topologies as well as the presence of coupling between shared‐shell O? H BCPs to the hydrogen‐bond BCPs that share an H NCP. The complexity of the near complete combined QTPD was explained in terms of the O…O bonding interactions that were found in six of the nine (H₂O)₅ reaction‐pathways and for all points of the combined QTPD. The stabilizing role of the O…O bonding interactions from the values of the total local energy density was explored. © 2016 Wiley Periodicals, Inc.     

Covalent attachment of organic monolayers to silicon carbide surfaces

This work presents the first alkyl monolayers covalently bound on HF-treated silicon carbide surfaces (SiC) through thermal reaction with 1-alkenes. Treatment of SiC with diluted aqueous HF solutions removes the native oxide layer (SiO2) and provides a reactive hydroxyl-covered surface. Very hydrophobic methyl-terminated surfaces (water contact angle theta = 107 degrees ) are obtained on flat SiC, whereas attachment of omega-functionalized 1-alkenes also yields well-defined functionalized surfaces. Infrared reflection absorption spectroscopy, ellipsometry, and X-ray photoelectron spectroscopy measurements are used to characterize the monolayers and show their covalent attachment. The resulting surfaces are shown to be extremely stable under harsh acidic conditions (e.g., no change in theta after 4 h in 2 M HCl at 90 degrees C), while their stability in alkaline conditions (pH = 11, 60 degrees C) also supersedes that of analogous monolayers such as those on Au, Si, and SiO2. These results are very promising for applications involving functionalized silicon carbide.     

Recent developments on application of nanometal-oxide based gas sensor arrays

It is shown that the sensor arrays can acquire more information on a given sample than an individual sensor. The main classes of gas-sensing materials include metal-oxide semiconductors. Gas sensors based on chemiresistive semiconducting metal-oxides have many potential benefits including, their very low cost, fast response, recovery time, simple electronic interface, ease of use, and ability to detect a large analytes. Recent advances in gas sensor arrays have shown the capability to incorporate nanomaterial based cross-reactive array. In this way it is possible to increase the surface/volume ratio of the sensing layer. Therefore the surface scattering is better influenced by adsorbed species and change in sensor conductivity is higher. Also the sensitivity of semiconductor oxide materials can be improved by using of nanoparticles. Gas sensor arrays based on nanotechnology can rapidly, sensitively, and selectively detect target molecules.     

Surface processes in MEMS technology

This review focuses on the problem of adhesion in microelectromechanical systems and on the application of the principles and techniques of surface science to understand and manipulate, at the atomic level, the interfacial forces which are responsible for strong adhesion in microdevices. Various approaches developed for reducing both release and in-use adhesion are discussed. They include surface roughening and chemical passivation. Results of ultrahigh vacuum studies on well-characterized surfaces are compared to experiments on test structures, such as cantilever beam arrays, which are specifically designed to study the surface properties of real micromechanical devices under normal operating conditions.     

A Comparison of Differently Synthesized Gold‐coated Magnetic Nanoparticles as ‘Dispersible Electrodes’

Gold‐coated magnetic nanoparticles (Au@MNPs) have attracted significant interest in electrochemistry in recent years. This is especially the case with their application as dispersible electrodes where modified Au@MNPs are dispersed into a solution, selectively bind to the analyte of interest and are then brought to an electrode via application of a magnetic field for measurement. This paper characterizes four types of Au@MNPs with different sizes, shapes, and method of synthesis as dispersible electrodes. The Au@MNPs were characterized by transmission electron microscopy and X‐ray photoelectron spectroscopy and scanning electron microscopy. In addition, the electrochemical behaviour of Au@MNPs was investigated using cyclic voltammetry. The four sorts of Au@MNPs were evaluated with regards to the three main features required in the dispersible electrodes approach, well‐defined morphology, well‐defined electrochemistry and fast response to a magnetic field. The Cubic‐Au@MNPs, which presents the simplest synthetic route, showed the best electrochemical stability and performance, responding quickly to a magnet and had a well defined shape.     

A High Performance Route for the Synthesis of Dihydropyrrolo[1,2‐f]phenanthridine Scaffolds by using a One‐pot Four‐component Reaction

Synthesis of a series pyridine containing dihydropyrrolo core fused phenanthridines by a one‐pot four‐component reaction in an efficient route is reported. This report contains the reaction of pyridinecarbaldehydes, malononitrile, and phenanthridine in the presence of alkyl isocyanides.     

Effect of fiber geometry on macroscale friction of ordered low-density polyethylene nanofiber arrays

Ordered low-density polyethylene (LDPE) nanofiber arrays are fabricated from silicon nanowire (SiNW) templates synthesized by a simple wet-chemical process based on metal-assisted electroless etching combined with colloidal lithography. The geometrical effect of nanofibrillar structures on their macroscale friction is investigated over a wide range of diameters and lengths under the same fiber density. The optimum geometry for contacting a smooth glass surface is presented with discussions on the compromise between fiber tip-contact area and fiber compliance. A friction design map is developed, which shows that the theoretical optimum design condition agrees well with the LDPE nanofiber geometries exhibiting high measured friction.