Birefringent side-hole fiber for use in strain sensor

Novel birefringent single-mode fibers are fabricated with a vacant hole on either side of the central elliptical core, referred to as side-hole fiber, and their intrinsic and tension-induced modal birefringences are measured to know their characteristic properties for the purpose of making a strain sensor. Five sampled side-hole fibers are prepared for measurements. The sensitivity of the strain sensor is primarily determined by two parameters, tension-induced and intrinsic modal birefringences. Tension-induced modal birefringence is controllable by optimal arrangement of the size and location of the side-holes in the cross-section of the fiber. A sensitivity diagram for designating and fabricating side-hole fibers is presented.     

Thiourea-catalyzed Morita-Baylis-Hillman reaction

Here, we describe our studies on the thiourea-catalyzed Morita-Baylis-Hillman (MBH) reaction. Chemoselective activation of carbonyl compounds via hydrogen bonding to thiourea as a catalyst is the key to drastic rate acceleration of this reaction. The application of chiral bis-thiourea-type organocatalysts, which can form a chiral double hydrogen-bonding network, is effective for enantioselective MBH reaction. A cooperative system of bis-thiourea compounds, synthesized from 1,2-diaminocyclohexane, and a Lewis base effectively promotes the MBH reaction at lower temperature, affording the MBH adducts in 33-95% yield with 44-90% ee. A plausible transition state model of the enantioselective MBH reaction is presented.     

High-Pressure Synthesis of Fully Occupied Tetragonal and Cubic Tungsten Bronze Oxides

A high-pressure reaction yielded the fully occupied tetragonal tungsten bronze K₃W₅O₁₅ (K_0.6WO₃). The terminal phase shows an unusual transport property featuring slightly negative temperature-dependence in resistivity (dρ/dT<0) and a large Wilson ratio of R_W=3.2. Such anomalous metallic behavior possibly arises from the low-dimensional electronic structure with a van Hove singularity at the Fermi level and/or from enhanced magnetic fluctuations by geometrical frustration of the tungsten sublattice. The asymmetric nature of the tetragonal tungsten bronze K_xWO₃-K_0.6−yBa_yWO₃ phase diagram implies that superconductivity for x≤0.45 originates from the lattice instability because of potassium deficiency. A cubic perovskite KWO₃ phase was also identified as a line phase—in marked contrast to Na_xWO₃ and Li_xWO₃ with varying quantities of x (<1). This study presents a versatile method by which the solubility limit of tungsten bronze oxides can be extended.     

Shape‐Selective Alkylation of Naphthalene over Zeolites: Steric Interaction of Reagents with Zeolites

Steric interaction of reagents with zeolites was studied in isopropylation, sec‐butylation, and tert‐butylation of naphthalene (NP) over several large‐pore zeolites to elucidate the mechanism of selective catalysis. Selectivities for dialkylnaphthalene (DAN) isomers were influenced by the type of zeolite and bulkiness of alkylating agent. Selective formation of β,β‐ and 2,6‐diisopropylnaphthalene (DIPN) occurred only over H‐mordenite (MOR) in the isopropylation of NP using propene; bulky transition states of α,α‐ and α,β‐DIPN are excluded because of steric restriction by the channels, resulting in selective formation of β,β‐ and 2,6‐DIPN. However, low selectivities for β,β‐ and 2,6‐DIPN were observed over the zeolites, SSZ‐24 (AFI), SSZ‐55 (ATS), and SSZ‐42 (IFR) with 12‐membered‐ring (12‐MR) pore entrances of one‐dimensional channels, CIT‐5 (CFI), UTD‐1 (DON), and SSZ‐53 (SFH) with 14‐membered‐ring (14‐MR) pore entrances of one‐dimensional channels, and Y‐zeolite (FAU), zeolite β (BEA), and CIT‐1 (CON) with 12‐MR pore entrances of three‐dimensional channels, because their channels are too large for the exclusion of bulky isomers. Catalysis over these zeolites occurs under kinetic and/or thermodynamic control, resulting in predominant formation of α,α‐ and α,β‐DIPN at lower temperatures and an increase of the stable isomer β,β‐DIPN at higher temperatures. The selectivities for β,β‐ and 2,6‐DAN were enhanced with the increase in bulkiness of alkylating agents: 1‐butene for sec‐butylation and 2‐methylpropene for tert‐butylation. In particular, β,β‐di‐tert‐butylnaphthalene (DTBN) was selectively formed in the tert‐butylation. The selectivities for β,β‐ and 2,6‐DAN were enhanced even in large channels: the transition states of the least bulky isomers only fit the channels because other bulky isomers are excluded by steric restriction of the channels. However, tert‐butylation over FAU, BEA, and CON had selectivities for 2,6‐DTBN of around 50–60%, although selectivities for β,β‐DTBN were almost 100% selectivity; these zeolites can hardly recognize the differences between 2,6‐ and 2,7‐DTBN. The results indicate that the fitting of the least bulky isomers to zeolite channels, leading to the exclusion of other bulky isomers, is essential for highly shape‐selective catalysis.     

AMPHIPHILIC COPOLYMERS AS MEDIA FOR LIGHT-INDUCED ELECTRON TRANSFER-II. ELECTROSTATIC EFFECT ON THE BACK ELECTRON TRANSFER

Abstract— Photosensitized reduction of zwitterionic viologen (SPV) and methyl viologen (MV²⁺) was investigated using an amphiliphilic copolymer having phenanthryl and sulfonate groups (APh) as photosensitizer in aqueous solutions. In the presence of triethanolamine the accumulation of SPV * (photoproduct) was found to be faster than that of MV⁺. This attributed to the electrostatic repulsion between SPV. and anionic segments of APh. Such difference between SPV and MV²⁺ was minimized in the case of the related monomer model. Retardation of the back reaction for the APh-SPV system was also demonstrated by laser photolysis, k _b= 8.7 × 10⁷ M ^-1 s^-1 for the polymer system as compared to k _b= 2.8 × 10⁹ M ^-1 s^-1 for the monomer model system. Strong salt-effects on the yield of the photoreduction and the rate of back reaction confirm the strong electrostatic interaction between the photoproducts and polyanions. This remarkable electrostatic effect of the polyanions was simulated by electrochemical redox reactions by using a graphite electrode coated with APh.     

Stereo- and regio-selective formation of 2-oxazolone telomers as potential synthetic intermediates for aminosugars

3-Acetyl-2-oxazolone readily undergoes free-radical homopolymerization as well as telomerization with polyhalomethanes, in which low telomer formation is highly stereo- and regio-selective.