Reaction of 3,4-disubstituted 1,2,5-oxadiazole 2-oxides with dipolarophiles : Substituent and solvent effect on the reaction courses

A variety of symmetrically or unsymmetrically 3,4-disubstituttd furoxans such as dicyano, dialkyl, diacyl, bis(phenylsulfonyl), N.N'-dialkyldicarbamoyl, 3(or 4)-methyl-4(or -3)-phenyl(or nitro, ethoxy, phenoxy, phenylthio, pyrrolidinyl, phenylsulfonyl), 3(or 4)-ethyl-4(or -3)phcnyl, and 3(or 4)-ethoxy-4(or -3)-phenylsulfonylruroxan reacted with dipolarophiles in toluene or xylene at the refluxing temperature to give nitrone-type 1,3-dipolar cycloadducts, 5-substituted 1-aza-2,8-dioxabicyclo-[3.3.0]octanes and/or 3-substituted 2-isoxazoline 2-oxides. On the other hand, some of the furoxans gave 2-isoxazolines via nitrile oxide 1,3-dipolar cycloaddition in a toluene (or xylene)-DMF solvent at the refluxing temperature.     

Crystal Structure, Electric and Magnetic Properties of Layered Cobaltite β-NaxCoO2

The layered oxide thermoelectric material β-Na_0.67CoO₂ has been studied by powder neutron diffraction, electric and magnetic measurements. This compound includes an edge-sharing CoO₆ slab and a highly vacant Na⁺ sheet in a unit cell (space group symmetry C2/m, a=4.9023(4) Å, b=2.8280(2) Å, c=5.7198(6) Å and β=105.964(6)° at 300 K). The evaluated formal valence of cobalt ion, +3.33(1), is ascribed to the coexistence of Co³⁺ and Co⁴⁺ in the ratio 2:1. Polycrystalline β-Na_0.67CoO₂, a p-type thermoelectric material, exhibits metallic behavior of the electric resistivity below 300 K. The Curie-Weiss-type magnetic susceptibility indicates antiferromagnetic interactions between magnetic cobalt ions in the edge-sharing CoO₆ slab.     

1H-NMR Relaxation of Water Molecules in the Aqueous Microcrystalline Cellulose Suspension Systems and Their Viscosity

An intensive study for aqueous microcrystalline cellulose (MCC) suspensions was carried out in view of the relationship between a viscosity and a 1H spin-spin relaxation time (T2) of water. An investigation was carried out for four suspension systems with the different particle size distributions. The proton mole ratio () of bound water against MCC particles and T2 of bound water (T2,b) were evaluated from the T2 values obtained by Carr-Purcell- Meiboom-Gill (C.P.M.G) method and those by solid echo method, respectively. As a result of these analyses, the T2,b value for the aqueous MCC suspension was evaluated as 5 × 10–3 s and it was found that the system having a larger tended to show a higher viscosity. By relating the above results to the observation of the suspensions by an optical microscope, it was concluded that a network formed by MCC particles plays an important role in generating a high viscosity of MCC suspension, and that an averaged mobility of water molecules is sensitively affected by the network structure.     

Preparation and biological activity of 2-[4-(thiazol-2-yl)phenyl]propionic acid derivatives inhibiting cyclooxygenase.

A series of 2-[4-(thiazol-2-yl)phenyl]propionic acids substituted at various positions were prepared by the reaction of diethyl 2-methyl-2-(4-thiocarbamoylphenyl)malonates with alpha-bromoaldehyde diethyl acetals or alpha-haloketones followed by hydrolysis of esters. The inhibition of prostaglandin H synthetase (cyclooxygenase) was assayed by use of an enzyme preparation from guinea pig polymorphonuclear leukocytes. Examination of the structure-activity relationship of these compounds indicated that the substitution pattern with halogens at position 3 (R1) of the benzene ring and a methyl group in position 4 (R2) and/or 5 (R3) of the thiazole ring were favorable for inhibitory activity. The compounds bearing bulky alkyl or polar functional groups at the R2 position were weak inhibitors. The potent inhibitors of cyclooxygenase were tested for their ability to reduce carrageenin-induced inflammation of rat paws. These derivatives had strong anti-inflammatory activity based on their strong inhibition of cyclooxygenase, with some exceptions, including those with a thiomethyl group at R1.     

Synthesis and characterization of novel aromatic polyamides from 3,4-bis(4-aminophenyl)-2,5-diphenylfuran and aromatic diacid chlorides

A new highly phenylated heterocyclic diamine, 3,4-bis(4-aminophenyl)-2,5-diphenylfuran, was synthesized in three steps from 4–-nitrodeoxybenzoin. The low temperature solution polycondensation of the diamine with various aromatic diacid chlorides afforded tetraphenylfuran-containing aromatic polyamides with inherent viscosities of 0.2–0.8 dL/g. Copolyterephthalamides were obtained from the diamine and 4,4′-oxydianiline. The polyamides were generally soluble in a wide range of solvents that included N,N-dimethylacetamide, N-methyl-2-pyrrolidone, pyridine, and m-cresol. Glass transition temperatures of the polyamides and copolyamides ranged from 302–342°C, and 10% weight loss was observed above 480°C in nitrogen.     

NMR Spectroscopic Observation of a Metal‐Free Acetylide Anion

A metal‐free acetylide was observed by using NMR spectroscopy. Metal‐free acetylides are closely related to reactive intermediates (carbanions) in solution; therefore, they have been regarded as unobservable species. However, we generated this highly reactive and unstable species through the deprotonation of phenylacetylene by using the strong nonmetallic phosphazene base tBu‐P4. In the presence of tBu‐P4, the J coupling between the ethynyl carbon and hydrogen nuclei (¹J_C,H) of phenylacetylene disappeared; this indicates the deprotonation of the alkyne terminal. Furthermore, a large low‐field shift (approximately 90 ppm) of the alkyne carbon resonance was observed. We concluded that we have observed a metal‐free carbanion with a formal charge on an sp‐hybridized carbon atom for the first time.     

Interaction between dyes and polyelectrolytes. XIII. Effect of dye aggregation on the excitation energy transfer between bound dyes

Effect of polyanions on the aggregation of methylene blue (MB) was investigated spectrophotometrically. The following polyanions were used: potassium poly(vinyl sulfate), potassium poly(styrenesulfonate), sodium poly(methacrylate), and sodium poly(acrylate). The state of aggregation was largely dependent on the kind of polyanion and polyanion-MB ratio. MB-photo-sensitized isomerization of cis-p-(phenylazo)phenyltrimethylammonium iodide(cis-PTA) to the transisomer was used advantageously to investigate the effect of dye aggregation on the triplet excitation energy transfer between cationic dyes bound to polyanions. Although the efficiency of the excitation energy transfer between MB and cis-PTA was enhanced by the addition of polyanions, the formation of highly aggregated MB reduced the efficiency of the excitation energy transfer. Correlation with the dye aggregation induced by polyanions and the efficiency of excitation energy transfer between dyes was discussed.     

Effect of various halide salts on the incompatibility of cyanocobalamin and ascorbic acid in aqueous solution

Combination of cyanocobalamin (VB12) and ascorbic acid (VC) has been widely seen in pharmaceutical products and dietary supplements. However, VB12 has been reported that its behavior in stability in aqueous solution is quite different when VC is mixed. In the present study, we examined the stabilities of these vitamins in acetate buffer (pH 4.8) using high performance liquid chromatography. Degradation of VB12 was not observed in the absence of VC in the buffer. However, when VC was mixed in the VB12 solution, VB12 concentrations decreased in accordance with VC degradation. VB12 and VC degradations were inhibited by adding sodium halides to acetate buffer at pH 4.8. These stabilization effects were also observed in the range from pH 3.5 to 5.3 and by adding potassium, magnesium, and calcium halides. Furthermore, our data demonstrated that increases in the halide anion concentrations and atomic number (Cl-相似文献   

Conformations and steric and stacking interactions of trisubstituted ureas and thioureas with alkyl and phenyl groups

The monomeric ν(N—H) vibrations of various trisubstituted ureas of the R₂UPh type and -thioureas of the R₂TUPh type have been studied. The trans—out isomerism in the former and the trans—out—cis isomerism in the latter are discussed from the point of view of steric effect. The monomeric ν(N—H) vibrations of RPhUPh and RPhTUPh are also examined. The single band appearing in the spectrum of both ureas is characteristic of the cis form; this suggests the existence of phenyl—phenyl interaction (the stacking interaction proposed by Galabov et al. [10]). Behavior of ν(N—H) vibrations at several concentrations is shown to be clearly different in the three forms (trans, out and cis). The presence of the cis form is confirmed by solvent effect experiments.