Site-Selective Supramolecular Complexation Activates Catalytic Ethane Oxidation by a Nitrido-Bridged Iron Porphyrinoid Dimer

Development of supramolecular methods to further activate a highly reactive intermediate is a fascinating strategy to create novel potent catalysts for activation of inert chemicals. Herein, a supramolecular approach to enhance the oxidizing ability of a high-valent oxo species of a nitrido-bridged iron porphyrinoid dimer that is a known potent molecular catalyst for light alkane oxidation is reported. For this purpose, a nitrido-bridged dinuclear iron complex of porphyrin-phthalocyanine heterodimer 3 ⁵⁺, which is connected through a fourfold rotaxane, was prepared. Heterodimer 3 ⁵⁺ catalyzed ethane oxidation in the presence of H₂O₂ at a relatively low temperature. The site-selective complexation of 3 ⁵⁺ with an additional anionic porphyrin (TPPS⁴⁻) through π–π stacking and electrostatic interactions afforded a stable 1:1 complex. It was demonstrated that the supramolecular post-synthetic modification of 3 ⁵⁺ enhances its catalytic activity efficiently. Moreover, supramolecular conjugates achieved higher catalytic ethane oxidation activity than nitrido-bridged iron phthalocyanine dimer, which is the most potent iron-oxo-based molecular catalyst for light-alkane oxidation reported so far. Electrochemical measurements proved that the electronic perturbation from TPPS⁴⁻ to 3 ⁵⁺ enhanced the catalytic activity.     

Fracture mechanism of liquid‐crystalline epoxy resin systems with different phase structures

A liquid‐crystalline epoxy resin was cured at two different temperatures. The phases of the cured systems clearly showed isotropic and nematic polydomain structures, which depended on the curing temperature. The fracture toughness of the systems was measured, and the fracture mechanism was investigated with polarized IR measurements. The nematic polydomain structure system showed considerably higher fracture toughness than the isotropic structure. Moreover, both systems exhibited a reorientation of the network chains near the fracture surface during the fracture process, and the region of the network reorientation in the nematic polydomain structure system was larger than that in the isotropic structure system. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4044–4052, 2004     

Optical Glucose Monitoring Based on Femtosecond Two-Color Pulse Interferometry

We demonstrate the potential of femtosecond two-color pulse interferometry for in vitro optical glucose monitoring, by dispersion of the group refractive index in a glucose solution sample with respect to a red-color light and a blue-color light. By comparison with femtosecond one-color pulse interferometry, the basic performance of the present system with regard to sensitivity, quantitativeness, and tolerance to surrounding disturbances, is evaluated. The resulting accuracy and precision of glucose determination are 77 and 118mg/dl for 10-mm-sample-thickness, respectively. This near-common-path configuration of the two-color pulse light provides good stability to fluctuations of sample temperature, which is important in clinical applications. Considering the performance of femtosecond two-color pulse interferometry as an optical glucose sensor, a suitable measurement site for in vivo optical glucose monitoring is discussed.     

Effect of plasma treatment on interface property of BCN/GaN structure

Interface properties of BCN/GaN metal-insulator-semiconductor (MIS) structures are investigated by X-ray photoelectron spectroscopy (XPS) and capacitance versus voltage (C-V) characteristics measurements. The BCN/GaN samples are fabricated by in situ process consisting of plasma treatment and deposition of BCN film in the plasma-assisted chemical vapor deposition (PACVD) apparatus. XPS measurement shows that the oxide formation at the BCN/GaN interface is suppressed by nitrogen (N₂) and hydrogen (H₂) plasma treatment. The interface state density is estimated from C-V characteristics measured at 1 MHz using Terman method. The minimum interface state density appears from 0.2 to 0.7 eV below the conduction band edge of GaN. The minimum value of the interface state density is estimated to be 3.0 × 10¹⁰ eV⁻¹ cm⁻² for the BCN/GaN structure with mixed N₂ and H₂ plasma treatment for 25 min. Even after annealing at 430 °C for 10 min, the interface state density as low as 6.0 × 10¹⁰ eV⁻¹ cm⁻² is maintained.     

A SAXS study of the nanometer scale hybrid structure of Si---Ti---C---O amorphous fibers

A small-angle X-ray scattering (SAXS) study was performed to reveal the nanometer scale hybrid structure of Si---Ti---C---O fibers prepared by the pyrolysis of polytitanocarbosilane. The SAXS profile for Si---Ti---C---O fibers is attributed to two different types of scattering entities: an anisotropic contribution from long filaments with diameters hundreds to thousands of Ångströms and an isotropic contribution from β-SiC fine clusters of about a nanometer in diameter. A drastic degradation in the tensile strength of the fibers is correlated to the characteristic variations in their long-and medium-range structure.     

Synthesis and orientation study of a magnetically aligned liquid‐crystalline chitin/poly(acrylic acid) composite

A high magnetic field of 5 T was used to fabricate a magnetically aligned, optically anisotropic, liquid‐crystalline chitin/poly(acrylic acid) composite. The aligned mesophase was fixed by photoinitiated free‐radical polymerization. From an examination of polarized optical micrographs and an X‐ray diffraction study, a high degree of orientation of 0.70 was observed for the composite with a higher liquid‐crystalline chitin concentration (10.70 wt %); the orientation was reduced with a decreased chitin concentration at a given acrylic acid concentration. The X‐ray data for the developed composite showed a uniplanar orientation for the chitin crystallites, with its molecular long axes perpendicular to the direction of the magnetic field. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 711–714, 2003     

Magnetoresistance of Fe3O4/Au/Fe3O4 and Fe3O4/Au/Fe spin-valve structures

A detailed study of the in-plane magnetotransport properties of spin valves with one and two Fe₃O₄ electrodes is presented. Fe₃O₄/Au/Fe₃O₄ spin valves exhibit a clear anisotropic magnetoresistance in small magnetic fields but no giant magnetoresistance (GMR). The absence of GMR in these structures is due to simultaneous magnetization reversal in the two Fe₃O₄ layers. By contrast, a negative GMR effect is measured on Fe₃O₄/Au/Fe spin valves. The negative GMR is attributed to an electron spin scattering asymmetry at the Fe₃O₄/Au interface or an induced spin scattering asymmetry in the Au interfacial layers.