Neutron diffraction evidence of microscopic charge inhomogeneities in the CuO2 plane of superconducting La2-xSrxCuO4 (0<or=x<or=0. 30)

High-resolution atomic pair distribution functions have been obtained using neutron powder diffraction data from La2-xSrxCuO4 over the range of doping 0相似文献   

Absence of residual quasiparticle conductivity in the underdoped cuprate YBa2Cu4O8

We report measurements of the in-plane thermal conductivity kappa of the stoichiometric underdoped cuprate YBa2Cu4O8 (Y124) below 1 K. kappa(T) is shown to follow a simple phononic T3 dependence at the lowest temperature T for both current directions, with a negligible linear quasiparticle contribution. This observation is in marked contrast with behavior reported in optimally doped cuprates, and implies that extended zero-energy (or low-energy) quasiparticles are absent in Y124.     

XPS and LEED study of Pd and Au growth on alumina/Cu-Al surface

Metal-insulator-metal system was prepared using the single-crystalline Cu-9at.% Al(1 1 1) support. Oxidation of the substrate under well-controlled conditions at elevated temperature leads to the formation of well-ordered aluminium oxide layer. The Pd-Au topmost layer was prepared by a step-by-step deposition of both metals afterwards on the oxide layer at room temperature. Low energy electron diffraction (LEED) measurement did not confirm epitaxial growth of the metal overlayer and gave only a rise of diffuse background after each deposition step. The growth of Pd-Au overlayer exhibited Stranski-Krastanov mode influenced by intermetallic interaction between those metals. No binding energy shifts were visible for the core-level photoelectron peaks of the substrate and the oxide using X-ray photoelectron spectroscopy (XPS). In contrast, the binding energy shifts of Pd 3d and Au 4f photoelectron levels in both directions were observed during all depositions. Bimetallic interactions between the metals as well as size effects are further discussed.     

Study for noise reduction in synchrotron radiation based scanning tunneling microscopy by developing insulator-coat tip

To solve difficulties of instability and inaccuracy in synchrotron radiation based scanning tunneling microscopy, a method to reduce noise was investigated. New insulator-coat tips were developed to shut out electrons coming from a wide area that damage the spatial resolution. By changing the exposed conductive area at the end of the insulator-coat tips, the effect of noise reduction was estimated. The tip with an exposure area of 50 nm in diameter was found to reduce noise effectively. Also a key discriminating condition was found to obtain the local signal, which is based on the modulation of the X-ray-induced tip current caused by excitation of the specific element.     

Zirconium-catalyzed chemoselective methylalumination of ethers, amines, and sulfides bearing two terminal alkenyl groups

Chemoselectivity in the methylalumination reaction of unsymmetrical ethers, amines, and sulfides bearing two different terminal alkenyl groups, a 13-tetradecenyl group and an allyl, 4-pentenyl or 6-heptenyl group was examined. The methylalumination of the allyl derivatives proceeded with complete chemoselectivity to afford only the 13-tetradecenyl-monomethylated products. In the methylalumination reactions of the 4-pentenyl and the 6-heptenyl derivatives, in addition to the 13-tetradecenyl-monomethylated products, and dimethylated products were also obtained. However, as in the case of the allyl derivatives, monomethylation to the shorter 4-pentenyl or 6-heptenyl group was not observed, except in the case of 6-heptenyl 13-tetradecenyl amine. The unique selectivity was rationalized upon how readily the intramolecular ligand exchange reaction between intermediate zirconocenium-alkene and zirconocenium-heteroatom complexes could occur.     

Synthesis and isomerization of conjugated oligomers containing azoimidazole unit

The Suzuki (for O1 – O3 ) and Stille (for O4 ) coupling polymerization of 2‐(phenylazo)imidazole bearing the benzyl protecting group at the 1‐position gave conjugated oligomers. The transformation from the neutral imidazole in the conjugated oligomer O2 , consisted of the alternating 2,5‐didecyl‐1,4‐phenylene unit, to the cationic imidazolium salt O2S was performed. Depending on the chemical structure of coupling partners, the absorption maximum of conjugated oligomers showed red shift or blue shift from that of the model compound M with the benzene ring at the 4,5‐positions. The absorption maximum wavelength of the cationic conjugated oligomer O2S showed a blue shift from that of the neutral conjugated oligomer O2 . The trans‐to‐cis photoisomerization of the azoimidazole unit in conjugated oligomers was observed by irradiating the light at 436 nm, and the conversion degree to the cis structure had a rough correlation with the maximum absorption wavelength of materials. The trans‐to‐cis photoisomerization in the film state was sluggish. On the other hand, the cis‐to‐trans thermal isomerization of the azoimidazole unit was confirmed and the absorbance returned to the initial state before the photoisomerization. The trans‐to‐cis photoisomerization of the cationic conjugated oligomer O2S required large energy, and the prolonged light irradiation might decompose the azoimidazole unit. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Catalytic asymmetric alkylation of α-cyanocarboxylates and acetoacetates using a phase-transfer catalyst

The catalytic asymmetric alkylation of α-cyanocarboxylates and acetoacetates with an alkyl halide was performed under phase-transfer conditions to afford compounds which have a chiral quaternary carbon with up to 97% and 94% ee, respectively. As applications of this method, chiral 2-oxindole derivatives and a β-lactam derivative were synthesized.     

Determination of overt carnitine palmitoyltransferase by reversed-phase high-performance liquid chromatography

A method for the determination of carnitine palmitoyltransferase I (CPT I; EC 2.3.1.19) in isolated rat liver mitochondria by reversed-phase high-performance liquid chromatography is described. Enzyme activity is assayed by direct determination of coenzyme A (CoA) released from palmitoyl-CoA within 60 min by a linear gradient system. CPT 1 in rat liver mitochondria can be assayed from only 30 micrograms of mitochondrial protein per millilitre of assay mixture. The changes in the kinetic parameters of CPT I, including Ki for malonyl-CoA, resulting from the fasting-feeding cycle are also discussed.     

Chelation of cadmium ions by phytochelatin synthase: role of the cysteine-rich C-terminal.

The interactions between Cd(2+) and the C-terminal region of phytochelatin (PC) synthase using recombinant wild-type and mutant PC synthase were studied. We show that site-directed mutagenesis of Cys residues at C(358)C(359)XXXC(363)XXC(366) motif decreases the number of Cd(2+) and other heavy metal ions interacting with the enzyme, and that the motif binds the metals discriminatingly. The optimum binding ratio of PC synthase to Cd(2+) was also determined. The findings indicate that Cys exists as a free SH residue and that it is involved in the regulation of PC enzyme activity by transferring the metals into closer proximity with the catalytic domain. These results are important in understanding heavy metal detoxification mechanisms in higher plants, a step towards phytoremediated-applications.