A bimodal structure of solution-grown isotactic polypropylene with orthogonally crossed lamellae

Isotactic polypropylene (iPP) was crystallized from solution on a uniaxially-oriented iPP film. Small-angle x-ray scattering patterns obtained from the sample showed two perpendicularly crossed lameliae 9.3 nm thick that overgrew flat-on and edge-on on the substrate. In the through wide-angel x-ray diffraction pattern (taken with incident x-rays normal to the iPP film surface), strong hkO reflections were arranged in an hkO net pattern indicating that the a-axis of the monoclinic α unit cell was oriented parallel to the chain direction of the substrate. From this, it was concluded that the flat-on lamellae grew with the a-axis parallel to the chain axis of the substrate and with the b-axis parallel to its surface. In the edge wide-angle x-ray diffraction pattern (X-rays incident on the edge of the film), arced, strong 110 and 220 reflections from overgrown crystals were observed on the equator of the fiber pattern of the substrate. This indicated that the edge-on lamellae epitaxially grew with the c-axis aligned parallel to the chain axis of the substrate. The homoepitaxy explains the correlated growth mode between the orthogonally crossed lamellae: they grew epitaxially, the a-axis of one lamella coinciding with the c-axis of the other and the {010} planes in contact. © 1993 John Wiley & Sons, Inc.     

Surface phase behavior of di-n-tetradecyl hydrogen phosphate in Langmuir monolayers at the air-water interface

Surface phase behavior of di-n-tetradecyl hydrogen phosphate, DTP, has been studied by measuring pi-A isotherms with a film balance and observing monolayer morphology with a Brewster angle microscopy (BAM) at different temperatures. A generalized phase diagram, which shows a triple point for gas (G), liquid-expanded (LE) and liquid-condensed (LC) phases at about 32 degrees C, is constructed for the amphiphile. Below the triple point, a first-order G-LC phase transition has been shown to occur, whereas a first-order G-LE phase transition followed by another first-order LE-LC transition has been found to take place at a temperature above the triple point. The amphiphile shows the fingering LC domains with uniform brightness indicating the presence of untilted molecules. The domain shapes are independent of the change in temperature and compression rate. The existence of similar fingering domains over a wide range of temperature is rather uncommon in the monolayer systems and is considered to be due to the restricted movement of the molecules incorporating into the LC phase. Because the two-alkyl chains are directly attached to two covalent bonds of the phosphate head group, the rearrangement of the molecules, which is an essential condition for the circular domain formation, needs the movement of the whole molecules including the hydration sphere. The difficulty related to such a movement of the molecules causes fingering domains, which are independent of external variables.     

Photolysis of organopolysilanes. Reactions of trimethylsilylphenylsilylene with carbonyl compounds

Photolysis of tris(trimethylsilyl)phenylsilane (I) in the presence of acetone, diethyl ketone and cyclohexanone resulted in formation of the respective 2,2,2-trimethylphenyldisilanyl enol ethers in moderate yields. UV-irradiation of I in the presence of methyl acrylate, followed by treatment of the reaction mixture with isopropyl alcohol, afforded methyl 3-(1′-isopropoxy-1′-phenyltrimethyldisilanyl)propionate, in addition to an adduct arising from addition of a silicon-carbon double-bonded intermediate to the carbon-carbon double bond.     

Total synthesis of (+)-tubelactomicin A. 1. Stereoselective synthesis of the lower-half segment by an intramolecular Diels-Alder approach

[reaction: see text]. Starting from diethyl (R)-malate, synthesis of the lower-half segment of (+)-tubelactomicin A, a 16-membered macrolide antibiotic, has been achieved. The synthesis involved the highly endo- and pi-facial selective intramolecular Diels-Alder reaction achieved using a trisubstituted methacrolein derivative tethering a 10-carbon dienyne unit at the beta-carbon, which in turn was prepared from a known allylated malic acid derivative.     

Coordination-network-based ionic plastic crystal for anhydrous proton conductivity

An ionic coordination network consisting of protonated imidazole and anionic one-dimensional chains of Zn(2+) phosphate was synthesized. The compound possesses highly mobile ions in the crystal lattice and behaves as an ionic plastic crystal. The dynamic behavior provides a proton conductivity of 2.6 × 10(-4) S cm(-1) at 130 °C without humidity.     

Oxidative dehydrogenation of ethane to ethylene over NiO loaded on high surface area MgO

The oxidative dehydrogenation of ethane over NiO-loaded MgO with high surface area was carried out using a fixed-bed flow reactor at 600 °C under atmospheric pressure.

At 600 °C, the oxidative dehydrogenation of ethane (C₂H₆/O₂ = 1) without dilution with an inert gas resulted in C₂H₆ conversion of 68.8% and a high C₂H₄ selectivity of 52.8%, which corresponds to a C₂H₄ yield of 36.3%. In addition, the catalytic activity did not decrease for at least 10 h. X-ray photoelectron spectra of the catalysts after the reaction exhibited that the initial valence state of Ni²⁺ (NiO) was maintained during the oxidative dehydrogenation of ethane. However, when NiO-loaded MgO was reduced with H₂ prior to the reaction, C₂H₄ selectivity decreased to nearly zero and high CO and H₂ selectivities were observed with the C₂H₆ conversion of 50 %, indicating that partial oxidation of C₂H₆ proceeded. Therefore, it seems important to keep Ni species as an oxide phase on the support, and for this purpose, use of the high surface area of MgO is essential.     

Particle-size effect of nanoscale platinum catalysts in oxygen reduction reaction: an electrochemical and 195Pt EC-NMR study

Oxygen reduction reaction (ORR) measurements and (195)Pt electrochemical nuclear magnetic resonance (EC-NMR) spectroscopy were combined to study a series of carbon-supported platinum nanoparticle electrocatalysts (Pt/CB) with average diameters in the range of roughly 1-5 nm. ORR rate constants and H(2)O(2) yields evaluated from hydrodynamic voltammograms did not show any particle size dependency. The apparent activation energy of 37 kJ mol(-1), obtained for the ORR rate constant, was identical to that obtained for bulk platinum electrodes. Pt/CB catalysts on Nafion produced only 0.7-1% of H(2)O(2), confirming that the direct four-electron reduction of O(2) to H(2)O is the predominant reaction. NMR spectral features showed characteristic size dependence, and the line shapes were reproduced by using the layer-deconvolution model. Namely, the variations in the NMR spectra with particle size can be explained as due to the combined effect of the layer-by-layer variation of the s-type and d-type local density of states. However, the surface peak position of (195)Pt NMR spectra and the spin-lattice relaxation time of surface platinum atoms showed practically no change with the particle size variation. We conclude that there is a negligible difference in the surface electronic properties of these Pt/CB catalysts due to size variations and therefore, the ORR activities are not affected by the differences in the particle size.     

A hexapeptide motif that electrostatically binds to the surface of titanium

A hexapeptide motif, RKLPDA, that recognizes the surface of titanium was identified from a peptide phage selection. Mutational analyses showed electrostatic interaction was a major factor in the binding, paving a new way to modify the surface of Ti with active biomolecules.