Application of a microfluidic reaction system for CdSe nanocrystal preparation: their growth kinetics and photoluminescence analysis

We used a microreactor for CdSe nanocrystal preparation and explored the effects of experimental conditions on the properties of the products. The particle growth kinetics and photoluminescence properties of the nanocrystals showed identical trends to previous reports, indicating the efficiency of the current method for analysis of rapid nanocrystal synthesis as well as industrial production of CdSe nanocrystals.     

Thermotropic liquid-crystalline peptide derivatives: oligo(glutamic acid)s forming hydrogen-bonded columns

We report on new thermotropic liquid-crystalline oligo(amino acid) derivatives forming columnar structures. These are based on branched oligo(glutamic acid)s and 2-(3,4-dialkyloxyphenyl)ethyl moieties. An oligo(glutamic acid) derivative, alpha,gamma-bis(L-glutamoyl) L-glutamic acid tetra[2-(3,4-dioctadecyloxyphenyl)ethyl]ester, shows a hexagonal columnar phase, whilst a glutamic acid derivative, alpha,gamma-bis[2-(3,4-dioctadecyloxyphenyl)ethyl] L-glutamate, does not show a mesophase. Hydrogen bonds formed by the oligo(glutamic acid) moieties should contribute to the induction of the columnar liquid-crystalline properties. In addition, we have examined the effects of the molecular chirality of the oligo(glutamic acid) parts and the functionalisation at the focal position of the taper shaped molecules on the liquid-crystalline properties of the compounds.     

Korngrößenänderung beim Carburieren von Wolfram und Sintern von Wolframcarbid

The change of grain size during each stage of the process was studied, mainly by optical and electron microscopy. The grain size has a marked effect on the properties of cemented carbide. In order to determine the process of formation of WC powder, the cross section and the surface of the carburized powder were examined microscopically. The mechanisms of carburization and grain growth were clarified. The microstructural relationship between the WC powder and the cemented carbide was also determined. The Co from the ball milled WC-Co mixed powder was extracted and the remaining WC powder was studied microscopically and by determining the grain size distribution. Methods of particle crushing and their effect on differences between various forms of WC powder were studied. Grain growth in sintering and the effect of grain size distribution were also studied. It was concluded that grain growth begins long before the appearance of the liquid phase. Finally it was pointed out that the inner structure of WC should be studied at the atomic level.     

Automated DNA fragment collection by capillary array gel electrophoresis in search of differentially expressed genes

An automatic DNA fragment collector using capillary array gel electrophoresis has been developed. A sheath flow technique is used for not only detection but also collection of DNA fragments. In a sheath flow cell, the DNA fragments separated by 16 capillaries flow independently into corresponding sampling capillaries. The fraction collector consists of 16 sampling trays and each sampling tray is set beneath each end of the sampling capillaries to collect the flow-through DNA fragments. Certain DNA fragments are automatically sorted by controlling the movement of the sampling trays according to the signals from the system. The collector experimentally separated two mixtures of polymerase chain reaction (PCR) products: one prepared by using eight different sizes (base lengths from 161 to 562) of DNAs; and the other prepared by a differential display (DD) method with cDNA fragments. Collected DNA fragments are amplified by PCR and measured by electrophoresis. DNA fragments with base length differences of one (base lengths 363 and 364) were successfully separated. A separated DNA fragment from the DD sample was also successfully sequenced. In addition, differentially expressed DNA fragments were automatically sorted by comparative analysis, in which two similar cDNA fragment groups, labeled by two different fluorophores, respectively, were analyzed in the same gel-filled capillary. These results show that the automatic DNA fragment collector is useful for gene hunting in research fields such as drug discovery and DNA diagnostics.     

Structural investigation of zeolite-templated, ordered microporous carbon by scanning tunneling microscopy and Raman spectroscopy

Scanning tunneling microscopy (STM) and Raman spectroscopy have been employed for a detailed structural characterization of an ordered microporous carbon synthesized in the nanochannels of zeolite Y by a templating approach. The carbon exhibited an exceptionally high adsorption capacity together with a long-range structural organization on the nanometer scale. As revealed by STM, this material exhibited both terrace-like and periodic (approximately 1.4 nm) stripe-like nanostructures. The vertical separation between contiguous terraces was measured to be also about 1.4 nm and was thus coincident with the structural periodicity deduced by X-ray diffraction. The terraces of the carbon material were shown to consist of arrays of approximately 1 nm wide carbon clusters. The carbon clusters displayed only a limited degree of local order within the terraces but not long-range periodicity. Likewise, STM indicated that the micropore structure of this carbon originated from the large number of voids that separate adjacent clusters, being morphologically very different from that commonly found in activated carbons. The range of void sizes measured by STM (0.8-2.3 nm) was in complete agreement with the pore size distribution determined from nitrogen adsorption measurements. The origin of the nanostructural features observed for this microporous carbon was discussed on the basis of the surface structure of the zeolite Y template. Finally, Raman spectroscopy provided evidence that the carbon clusters were made up of nanographenes with a curved topology.     

Determination of molybdenum(VI) in natural water and rock by ion-exchange absorptiometry combined with flow analysis

Ion-exchange absorptiometry combined with flow analysis has been applied to the determination of trace amounts of molybdenum(VI) in natural water and rock. By using a pretreatment column packed with Sephadex G-25 gel, molybdenum(VI) in a sample solution can be sorbed selectively on the gel at pH 3.5. The molybdenum(VI) in the column was desorbed with EDTA as the molybdenum(VI)-EDTA complex, and the solution was introduced into a Tiron solution stream. The yellow complex formed between molybdenum(VI) and Tiron in the flow system was then concentrated on a QAE-Sephadex A-25 anion exchanger packed in a flow-through silica micro-cell. The attenuation of incident light by the molybdenum(VI)-Tiron complex on the anion exchanger in the cell was continuously recorded with a spectrophotometer at 410 nm. The complex on the anion exchanger was easily desorbed with sodium nitrate, so the flow-through cell could be used repeatedly. The minimum amount that could be detected corresponded to 15 ng of molybdenum(VI). Molybdenum(VI) in three or four sample solutions could be determined within 1 h.     

Nanostructure of a "carpet"-like dense layer/polyelectrolyte brush layer in a block copolymer monolayer at the air-water interface

The "carpet"/brush double layer structure in the polyelectrolyte layer in the amphiphilic diblock copolymer monolayer at the air-water interface was quantitatively studied by in situ neutron reflectometry in addition to X-ray reflectivity measurements. As a result of the higher contrast between polyelectrolyte [poly(methacrylic acid)] and solvent (D(2)O) for the neutron, the brush structure could be estimated more accurately as a function of surface pressure, that is, brush density. The thickness of the carpet layer, which is thought to be formed to reduce the interfacial free energy between water and the hydrophobic layer, was almost constant at 10-20 A at any surface pressure studied. Growth was clearly observed in the whole brush length with increasing surface pressure, and it was estimated to be almost 60% of the full-stretch length of the ionic polymer chain. Furthermore, by the comparison of density profiles by neutron and X-ray reflectometry, an anomalous hydration was suggested.     

Quantum Chemical Calculations on the Structure and Adsorption Properties of NO and N2O on Ag+ and Cu+ Ion-Exchanged Zeolites

Ab initio cluster quantum chemical calculations at the Hartree–Fock (HF/Lanl2dz) and correlated second-order Moller–Plesset perturbation theory (MP2/Lanl2dz) levels were performed for NO and N₂O interactions with Ag⁺ and Cu⁺ ion-exchanged zeolites. The interaction energies were estimated in a conventional way and also corrected for basis set superposition errors. It was shown that the highly dispersed Ag⁺ counterions establish twofold coordination to the lattice oxygens on the zeolite surface, similar to the case of Cu⁺ ions. However, both NO and N₂O bind relatively strongly to the Cu active sites of Cu⁺ ion-exchanged zeolites than those of the Ag⁺ site of the Ag⁺ ion-exchanged zeolites. Based on the results of these calculations, the two different forms of adsorption for these molecules on the catalyst surface, the nature of their binding and characteristics of the adsorption properties have been discussed. Finally, some comparisons with the results obtained by a variety of density functional theory calculations on target systems have been presented.     

Nucleophilic vinylic substitutions of (Z)-(2-aroyloxyvinyl)phenyl-λ-iodanes with tetrabutylammonium halides: vinylic SN2 reactions and ligand coupling on iodine(III)

Treatment of (Z)-(β-benzoyloxyvinyl)phenyl-λ³-iodanes, readily prepared from ethynyl(phenyl)(tetrafluoroborato)-λ³-iodane via stereoselective Michael-type addition of benzoic acids in methanol in the presence of sodium benzoates, with tetrabutylammonium halides in THF at 65 °C results in a vinylic S_N2 reaction to give the inverted (E)-β-benzoyloxyvinyl halides in high yields.     

Novel fluorous prolinol as a pre-catalyst for catalytic asymmetric borane reduction of various ketones

Novel prolinol carrying two perfluorohexylethyl groups at the α-position was prepared from l-proline as a starting chiral substrate. Catalytic asymmetric reduction of various ketones, including mono-, di-, and trifluoromethylated acetophenones, using fluorous oxazaborolidines derived from fluorous prolinol afforded the corresponding alcohols in good to excellent yields and with high enantioselectivities (up to 93.2% ee). The fluorous prolinol was recovered without any fluorous solvents or silica gel by simply cooling the organic phase and filtration.