Cationic,Methylene‐Bridged,Intramolecular Donor‐Acceptor Systems Based on Zirconium and Hafnium and Phosphino‐methanides

A new access to cationic zirconium and hafnium compounds [L₂MCH₂PR₂][MeB(C₆F₅)₃] (L = Cp, Ind; R = iso‐Pr, tert‐Bu; M = Zr, Hf) exhibiting an intramolecular donor‐acceptor system was established by treating the precursors L₂M(Me)CH₂PR₂ with B(C₆F₅)₃ (BCF). Precursors 1 – 6 [L₂M(Me)CH₂PR₂ with L = Cp, Ind; R = iso‐Pr, tert‐Bu; M = Zr, Hf] were fully characterized. The crystal structures of these compounds revealed large M–CH₂–P bond angles with values of about 134° indicating the absence of interactions between the Lewis‐acid and Lewis‐base. The cationic compounds [L₂MCH₂PR₂][MeB(C₆F₅)₃] ( 7 – 12 ) were obtained by treatment of 1 – 6 with BCF. They were characterized by NMR spectroscopy, mass spectrometry, and elemental analyses; in H/D‐scrambling experiments with H₂/D₂ mixtures 7 – 12 disclosed their reactivity towards cleavage of hydrogen.     

Highly Ordered Mesoporous Cobalt-Copper Composite Oxides for Preferential CO Oxidation

Highly ordered mesoporous cobalt-copper composite oxides were prepared by the nanocasting method with various Co and Cu ratios. The catalysts obtained were characterized by X-ray diffraction, N₂ adsorption–desorption, H₂-temperature programmed reduction, CO-temperature programmed desorption and X-ray photoelectron spectroscopy. All of the catalysts had uniform mesopores and high surface areas. The distinct catalytic properties of these well-characterized mesoporous materials were demonstrated for preferential CO oxidation. It is found that the mesoporous cobalt-copper composite oxides, exhibited the higher catalytic activity for CO conversion and selectivity compared with the mesoporous Co₃O₄ and mesoporous CuO. Among these catalysts the mesoporous cobalt-copper catalyst with Co:Cu molar ratio of 70:30, shows the best catalytic activity and the broadest operating temperature “window” for the high CO conversion in the range of 125–200^oC. The higher catalytic activity was attributed to the higher CO adsorption and oxygen vacancies.     

Effects of mechanical stretching on average orientation of cellulose and pectin in onion epidermis cell wall: A polarized FT-IR study

The organization of polysaccharides in plant cell walls is important for the mechanics of plant cells. Spectral analysis of cell walls by polarized IR can reveal polysaccharide organization, but may be complicated by dipoles not aligned with the backbone. For instance, analysis of uniaxially-aligned cellulose Iβ film revealed that the dipole transition vector of the 1160 cm^?1 band involving stretch vibrations of glycosidic C1–O–C4 linkages is approximately at 30° with respect to the backbone of the cellulose chain, because of coupling with C5–O–C1 bonds in the six-membered rings. In the case of homogalacturonan, the dipole transition vector of the ester carbonyl group vibration (ν_C=O, 1745 cm^?1) is expected to be nearly normal to the homogalacturonan backbone. Using this information and the dichroism equation, the change in net orientation of cell wall polymers upon mechanical stretch was determined by polarized IR analysis. Never-dried abaxial outer epidermal cell walls of the second scale of onion bulb were mechanically stretched along longitudinal or transverse directions with respect to the long axis of the cells and then dried while under mechanical stretch. The average orientations of both 1160 and 1745 cm^?1 vibration transition dipoles were rotated by ~5° and ~4°, respectively, along the stretch direction from their initial random distributions upon longitudinal strain by 14%; and by ~4° and ~3°, respectively, upon transverse strain by 12%. These results imply that both cellulose microfibrils and pectins in the cell wall are passively realigned along the stretch direction by external mechanical force. The analytical methodology developed here will be useful to study how cell wall polymers might reorganize during cell wall growth and development.     

Effect of addition of 1-butyl-3-methylimidazolium thiocyanate on conductivity of Na-containing polymer electrolyte

Research in the environmentally friendly energy field has grown rapidly due to severe problems such as global warming and climate change. Sodium-ion technology is one of the most promising alternatives to lithium-ion batteries. Use of ionic liquids containing thiocyanate anion has been considered because of their low cost, low viscosity, and nonhazardous nature. In this work, polyethylene oxide (PEO)–sodium perchlorate (NaClO₄) samples containing different amounts of 1-butyl-3-methylimidazolium thiocyanate ionic liquid were prepared by a solution casting method. Addition of the ionic liquid to the PEO–NaClO₄ electrolyte further increased the ionic conductivity. The electrolyte containing 30 wt% ionic liquid exhibited the maximum ionic conductivity of ~5.0 × 10^?4 S/cm at room temperature. Fourier-transform infrared (FT-IR) spectroscopy revealed the interaction between the polymer chain and salt ion complexes for various sodium salt contents. Differential scanning calorimetry (DSC) demonstrated that the crystallinity was reduced by addition of 1-butyl-3-methylimidazolium thiocyanate ionic liquid.     

Synthesis of TiO<Subscript>2</Subscript> nanotubes using different alkaline media and their applications in photocatalysis and DSSCs

TiO₂ nanotubes (TNTs) were successfully synthesized from different alkaline media (i.e., NaOH and KOH) by using a microwave hydrothermal process. The effects of different alkaline media on the formation of TiO₂ nanotubes and their physicochemical properties were investigated. The phases of different TiO₂ nanostructures were studied by using X-ray diffraction patterns. Morphologies of the nanostructures were observed with a transmission electron microscope. The optical properties of the nanostructures were evaluated through the absorption behavior using UV–Vis diffuse reflectance spectroscopy. The photocatalytic activities of the TiO₂ nanostructures were evaluated by the degradation of methylene blue aqueous dye solution under the simulated solar light irradiation. Similarly, the photovoltaic efficiencies of the prepared samples were investigated by making photo-anode layers in the Dye Sensitized Solar Cells (DSSCs). The results revealed that in comparison to the single layered TiO₂ nanostructures in the DSSC, creation of a double layer structure significantly enhanced the efficiency of DSSC.     

Synthesis of 5-aroylamino-3H-1,3,4-thiadiazole-2-thiones and their tautomerism

5-Aroylamino-3H-1,3,4-thiadiazole-2-thiones 2 have been synthesized by acylation of 5-amino-3H-1,3,4-thiadiazole-2-thione 1 . 5-Aroylamino-3H-1,3,4-thiadiazole-2-thiones can exist in two tautomeric forms — a thiol form and a thione form. On the basis of the ¹³C nmr spectra and additional experimental information, it has been established that the thione form is the stable form in which these compounds exist.     

Polyarylate–polystyrene block copolymer from macro-azoinitiator: Synthesis and its thermal properties

A macro-azoinitiator containing polyarylate segment and azo group was prepared by the solution polycondensation of azobiscyanopentanoyl chloride and hydroxy-terminated polyarylates having viscosity-average molecular weights of 6200, 8100, and 12 400. These macro-azoinitiators were used in the radical polymerization of styrene to synthesize polyarylate-polystyrene block copolymers. Thermal properties measured by the differential scanning calorimetry indicated the phase separated morphology of the block copolymers except at low molecular weight of the block constituents. © 1993 John Wiley & Sons, Inc.     

Thermogravimetric study of polyacrylamide with evolved gas analysis

Dried samples of polyacrylamide in an He atmosphere have been subjected to thermogravimetric analysis in the 30–600°C range, and the evolved gases were monitored by FTIR. Water, ammonia, and small quantities of carbon dioxide are released in the first stages of decomposition (220–340°C), where the polymer chains remain intact and the reaction occurs on the pendant amide groups. In the second stage of decomposition (340–440°C), the majority of the weight loss occurs, and main chain breakdown occurs, releasing carbon dioxide, water, nitrile compounds, and imides. Trapping of the gases in this stage and analysis by GC–FTIR and GC–MS reveals the presence of more than 20 decomposition products, and confirms that a large proportion of these can be assigned to glutarimide and its substituted analogs. Imidization and dehydration reactions on the amide groups, as well as free radical breakdown of the main chains, with inter- and intramolecular hydrogen transfer, can account for many of the products of the decomposition. © 1993 John Wiley & Sons, Inc.