Sol-Gel Processing of Transparent PLZT((Pb,La)(Zr,Ti)O3) Fibers

PLZT((Pb,La)(Zr,Ti)O₃) ceramic fibers were prepared by the sol-gel method from a solution of lead acetate trihydrate, lanthanum isopropoxide, zirconium n-propoxide and titanium isopropoxide containing 2-methoxyethanol as the solvent. The as-drawn gel fibers were pretreated in an autoclave and preheated in flowing H₂O vapor prior to the heat-treatment for crystallization. The effects of autoclaving and preheating in flowing H₂O vapor on the structure and composition of the resultant fibers were investigated. Optically transparent single phase perovskite PLZT fibers of 5–15 m in thickness and 5 cm in length were successfully prepared when the autoclave-treatment and the preheating in flowing H₂O vapor were conducted prior to crystallization. These treatments are thought to promote hydrolysis of the organic groups and polycondensation reaction in the gel fibers, leading to the successful formation of dense, crack-free transparent PLZT fibers.     

Structure and biosynthetic implication of (S)-NHAB, a novel shunt product, from a disruptant of the actVI-ORFA gene for actinorhodin biosynthesis in Streptomyces coelicolor A3(2)

A novel shunt product was isolated from a disruptant of the actVI-ORFA gene involved in the biosynthesis of actinorhodin (ACT) in Streptomyces coelicolor A3(2). Its structure was elucidated as 1,4-naphthoquinone-8-hydroxy-3-[3(S)-acetoxy-butyric acid], (S)-NHAB, based on NMR, MS, and CD spectroscopic data as well as a single crystal X-ray crystallographic analysis. The formation of (S)-NHAB involves a retro-Claisen type C-C bond cleavage of an ACT biosynthetic intermediate. Feeding experiments with [1-¹³C] and [2-¹³C] acetates indicated its biosynthetic origin as a single octaketide chain. The relevant gene product, Act-ORFA, which is a functionally unknown protein, is proposed to play a regulatory role related to the multi-enzymatic steps to ACT production, based on the metabolic profile of its disruptant and the wide distribution of actVI-ORFA homologues in the gene clusters for Streptomyces aromatic polyketides.     

Catalytic transformation of methane over in-loaded ZSM-5 zeolite in the presence of ethene

Methane is shown to react with ethene over In-loaded ZSM-5 to higher hydrocarbons such as propene and toluene at around 673 K. Such methane conversion is not catalyzed by proton-exchanged ZSM-5 (H-ZSM-5) under the same conditions, only C2H4 being converted to higher hydrocarbons. By using 13C-labeled methane (13CH4) as a reactant, the reaction paths for the formation of propene, benzene and toluene were examined. 13C-labeled propene (13CC2H6) is formed by the reaction of 13CH4 with C2H4. The lack of 13C-labeled benzene revealed that propene is not transformed to benzene, which instead originates entirely from C2H4. The 13C atom is inserted both into the methyl group and benzene ring in the toluene formed. This indicates that toluene is formed by two reaction paths; the reaction of 13CC2H6 with butenes formed by the dimerization of C2H4 and the reaction of benzene with 13CH4. The existence of the latter path was proved by the direct reaction of 13CH4 with benzene. The reaction of methane with benzene was also carried out in a continuous flow system over In-loaded ZSM-5. The reaction afforded 7.6% and 0.9% yields of toluene and xylenes, respectively, at 623 K.     

Some aspects of plasma copolymerization of acetylene with N2 and/or water

Plasma polymerizations of mixture of acetylene-N₂, acetylene-H₂O, were investigated by using an electrodeless glow discharge from a 13.5-MHz radiofrequency source. Properties of plasma polymers were examined as functions of mole ratios of N₂ and/or H₂O to acetylene. The concentration of trapped free radicals and the internal stress in a plasma polymer decreased as the mole ratio of N₂ or H₂O increased. Water showed the most pronounced effects in those properties at the mole ratio of 0.3. Gas permeabilities increased by the copolymerization of N₂ and/or H₂O. Surface energies were also investigated by analysis of contact angles of liquids. Copolymerization of N₂ caused a remarkable increase in polar contribution of surface energy. Some fundamental aspects of flow-rate pressure relationship of mixed gases are presented.     

Synthesis of open-ended MoS2 nanotubes and the application as the catalyst of methanation

We report the synthesis of open-ended MoS2 nanotubes and their application as the catalyst for methanation of carbon monoxide with hydrogen. Because the catalysis of the methanation reaction occurs at relatively low temperatures, such nanotubes may provide new solutions toward harnessing the environmental load caused by CO emission.     

1,4‐Addition polymerization of 1,4‐bis(4‐benzylpyridinium)butadiyne triflate in a dipolar aprotic solvent

1,4‐Bis(4‐benzylpyridinium)butadiyne triflate was aggregated in dimethylformamide and spontaneously converted into the 1,4‐addition type of polydiacetylene. The polymerization took place in a dipolar aprotic solvent with a large dielectric constant that could enhance the aggregation of the ionic diacetylene salt through the electrostatic interaction. The molecular weight of the diacetylene was leveled off after 30 h at 80 °C to reach 1.5 × 10⁴ (number‐average molecular weight) that consisted of the 1,4‐addition type of polydiacetylene similar to polydiacetylenes obtained in the conventional solid‐state polymerization. Electron spin resonance spectra revealed that diradicals were generated at the earlier state aggregation to give rise to a solution polymerization. The UV spectra also suggested the presence of the activated aggregation associated with the polymerization as well as the eximer emission spectra. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3534–3541, 2002     

Interconversion behavior of the C-H bond in the CH4+ radical cation: ab initio molecular dynamics study

Thermal motion of CH4+ is investigated by performing an ab initio molecular dynamics method with the second-order M?ller-Plesset (MP2)/6-311G** force field. In the trajectories obtained at 400 K, we have observed rapid interconversion behavior of the geometrical parameters of CH4+ with the frequency of 0.6/ps, where the C-H pair forming the small angle around 55 degrees is switched to another pair on subpicosecond time scale. The switching patterns are found to be classified into the following two types. Type 1: one C-H of the small angled C-H pair is switched to one C-H of the other C-H pair. Type 2: the small angled C-H pair is switched to the other C-H pair, which has been newly observed in the present ab initio MD calculation. The four C-H bonds of CH4+ are characterized by the long and short C-H bonds in a time region of the trajectories, and also for the time-evolution of C-H bonds such interconversion behavior is observed. The switching patterns of the geometrical parameters are compared with those in the interconversion scheme between six equivalent C2v symmetry structures of CH4+ [Paddon-Row, M. N. et al., J Am Chem Soc 1985, 107, 7696]. We have also investigated the electronic energy fluctuation due to thermal motion of CH4+. The standard deviation of total electronic energy at 400 K is evaluated to be 1.2 kcal/mol.     

Retention,enantioselectivity and enantiomeric elution order of propranolol and its ester derivatives on an alpha1-acid glycoprotein-bonded column

Summary The retention, enantionselectivity and enantiomeric elution order of racemic propranolol (PP) and its ester derivatives (O-acetyl,-propionyl,-butyrul and-valeryl PP) on an ₁-acid glycoprotein (AGP)-bonded column have been investigated by changing eluent composition (eluent pH, buffer concentration, type and content of organic modifier). The retention of these cationic solutes, PP and its ester derivatives, was influenced by eluent pH, ionic strength and organic modifier content. The enantioselectivity was dependent on eluent pH and type of organic modifier. Reversal of the enantiomeric elution order of ester derivatives of PP (O-propionyl-butyryl) and-valeryl PP) occurred around eluent pH 6–7. These results suggst that chiral recognition or binding properties may be altered by the change in eluent composition, espeically eluent pH and type of organic modifier.     

Dioxo-molybdenum(VI) and mono-oxo-molybdenum(IV) complexes supported by new aliphatic dithiolene ligands: new models with weakened Mo=O bond characters for the arsenite oxidase active site

The cis-dioxo-molybdenum(VI) complexes, [MoO2(L(H))2]2- (1b), [MoO2(L(S))(2)]2- (2b), and [MoO2(L(O))2]2- (3b) (L(H) = cyclohexene-1,2-dithiolate, L(S) = 2,3-dihydro-2H-thiopyran-4,5-dithiolate, and L(O) = 2,3-dihydro-2H-pyran-4,5-dithiolate), with new aliphatic dithiolene ligands were prepared and investigated by infrared (IR) and UV-vis spectroscopic and electrochemical methods. The mono-oxo-molybdenum(IV) complexes, [MoO(L(H))2]2- (1a), [MoO(L(S))2]2- (2a), and [MoO(L(O))2]2- (3a), were further characterized by X-ray crystal structural determinations. The IR and resonance Raman spectroscopic studies suggested that these cis-dioxo molybdenum(VI) complexes (1b-3b) had weaker Mo=O bonds than the common Mo(VI)O2 complexes. Complexes 1b-3b also exhibited strong absorption bands in the visible regions assigned as charge-transfer bands from the dithiolene ligands to the cis-MoO2 cores. Because the oxygen atoms of the cis-Mo(VI)O2 cores are relatively nucleophilic, these complexes were unstable in protic solvents and protonation might occur to produce Mo(VI)O(OH), as observed with the oxidized state of arsenite oxidase.     

Liquid chromatographic determination of penicillins by postcolumn degradation with sodium hypochlorite using an hollow-fibre membrane reactor

A sensitive, high-performance liquid chromatographic method involving postcolumn degradation with sodium hypochlorite and using a hollow-fibre membrane as a reactor is described for the determination of penicillins. Penicillins were separated on a C18 column followed by postcolumn reaction with sodium hypochlorite and sodium hydroxide using aminated and sulphonated hollow-fibre membrane reactors immersed in each solution, and detected at 270-280 nm based on the UV absorbances of the degradation products. At penicillin concentrations of 2 micrograms/ml, the precisions (relative standard deviation) were 2.28-4.78%. The detection limits of the proposed method were 2.5-25 ng for each penicillin at a signal-to-noise ratio of 3. Ampicillin and its metabolites [(5R,6R)-ampicilloic acid, the (5S,6R)-epimer and (2R)-pierazine-2',5'-dione] in human serum and urine were simultaneously determined by this method.