Change in band configuration of quantum wells from type-II to type-I by increasing Sb composition x

InGaAs/AlAsSb systems lattice matched to InP have two distinguishable features: a high conduction band offset and type-II band configuration. Although, the former results in a large intersubband transition (ISBT) at conduction band, the latter makes it difficult to use the effective interband transition (IBT). To overcome this latter problem, the effect of the Sb was investigated because Sb would act as a band modulator from type-II to type-I. In_0.57Ga_0.43As_1-xSb_x/AlAs_0.48Sb_0.52 single quantum well (SQW) samples with various Sb compositions x, were grown on GaAs substrates via AlAs_0.48Sb_0.52 buffer layer. Their photoluminescence (PL) properties were examined to identify their band configurations. When the excitation laser power was increased, the PL property of In_0.57Ga_0.43As SQW sample, showed a larger blue shift than that of ones. This indicates that the band configuration modulates from type-II to type-I when the antimonide composition is larger than 0.13. These findings indicate that new functional devices can be fabricated using a combination of IBT and ISBT.     

Ratiometric fluorescence detection of a tag fused protein using the dual-emission artificial molecular probe

We have successfully developed a ratiometric detection system for protein of interest using the complementary recognition pair of the tetra-aspartate peptide tag and the SNARF-appended Zn(ii)-DpaTyr probe.     

Formal total synthesis of (-)-emetine using catalytic asymmetric allylation of cyclic imines as a key step

[reaction: see text] Catalytic asymmetric allylation of 3,4-dihydro-6,7-dimethoxyisoquinoline was carried out using allyltrimethoxysilane in the presence of Cu(I) and tol-BINAP. The allyl adduct thus obtained was transformed to a chiral synthetic intermediate for (-)-emetine in good yield. The procedure was applied to the total synthesis of ent-emetine.     

Novel synthesis of the ortho ester derivative of 4,5-epoxymorphinan

[reaction: see text]. A method was found for the novel synthesis of ortho ester derivatives that are potentially useful as selective epsilon opioid receptor ligands. An unexpected 17-(cyclopropylmethyl)-4,5alpha-epoxy-6alpha-hydroxy-3,7,7-trimethoxy-8-oxa-6,14-endoethanomorphinan was produced when 17-(cyclopropylmethyl)-4,5alpha-epoxy-3-methoxy-6alpha,14-dihydroxy-6beta-(1,3-dithia-2-yl)-morphinan was treated in methanol with trimethyl orthoformate and CuO/CuCl2. This ortho ester derivative was then converted to an ester with acid. The structure of the ortho ester was determined by 2D NMR (HMBC) and mass spectra.     

Three-phase solvent systems for comprehensive separation of a wide variety of compounds by high-speed counter-current chromatography

Three-phase solvent systems were efficiently utilized for high-speed counter-current chromatography (HSCCC) to separate multiple components with a wide range of hydrophobicity. The compositions of three-phase systems were optimized according to their physical parameters such as volume ratio, viscosity and specific gravity of upper (UP), middle (MP) and lower (LP) phases. The three-phase systems composed of n-hexane-methyl acetate-acetonitrile-water (4:4:3:4, v/v/v/v) was selected for HSCCC separation of a mixture of 15 standard compounds with a wide range in hydrophobicity from beta-carotene to tryptophan. The separation was initiated by filling the column with a mixture of MP and LP both as a stationary phase followed by elution with UP to separate the hydrophobic compounds. Then the mobile phase was switched to MP to elute the moderately hydrophobic compounds, and finally the polar compounds still retained in the column were fractionated by eluting the column with LP. The system successfully resolved all 15 compounds in one-step operation in 70 min.     

Preparation of single-enantiomer 2-methyl-4-heptanol, a pheromone of Metamasius hemipterus, using (S)-2-methoxy-2-(1-naphthyl)propionic acid

To investigate the resolution of secondary alcohols using 2-methoxy-2-(1-naphthyl)propionic acid (MalphaNP acid), 2-methyl-4-heptanol, one of the aggregation pheromones of Metamasius hemipterus, was resolved using (S)-MalphaNP acid. As a chiral-resolving agent, MalphaNP acid is superior to 3,3,3-trifluoro-2-methoxy-2-phenylpropionic acid (MTPA) in terms of HPLC separation and NMR shielding. A better separation of diastereomeric MalphaNP esters was observed when n-hexane-THF was used as the eluent for silica gel HPLC. The solvolysis of the diastereomeric MalphaNP esters gave (R)-2-methyl-4-heptanol and its enantiomer; enantiopure (S)-MalphaNP acid was also recovered. In addition, the preferred conformation of the MalphaNP ester was confirmed using methyl (R)-3-hydroxyvalerate as an authentic compound.     

Water as a cofactor in the unidirectional light-driven proton transfer steps in bacteriorhodopsin

Recent evidence for involvement of internal water molecules in the mechanism of bacteriorhodopsin is reviewed. Water O-H stretching vibration bands in the Fourier transform IR difference spectra of the L, M and N intermediates of bacteriorhodopsin were analyzed by photoreactions at cryogenic temperatures. A broad vibrational band in L was shown to be due to formation of a structure of water molecules connecting the Schiff base to the Thr46-Asp96 region. This structure disappears in the M intermediate, suggesting that it is involved in transient stabilization of the L intermediate prior to proton transfer from the Schiff base to Asp85. The interaction of the Schiff base with a water molecule is restored in the N intermediate. We propose that water is a critical mobile component of bacteriorhodopsin, forming organized structures in the transient intermediates during the photocycle and, to a large extent, determining the chemical behavior of these transient states.     

Preparation and characterization of methacrylate-based semi-micro monoliths for high-throughput bioanalysis

Hexyl methacrylate (HMA)-based monolithic semi-micro columns were prepared by in situ polymerization within the confines of 1.02-mm-i.d. silicosteel tubing for reversed-phase and/or precipitation–redissolution liquid chromatography. Practically useful monolithic columns with adequate separation efficiency, high permeability, and good mechanical strength were successfully obtained using a polymerization mixture comprising 24% hexyl methacrylate (HMA), 6% ethylene dimethacrylate (EDMA), 44.5% 1-propanol, and 25.5% 1,4-butanediol. The column performance was evaluated through the separations of a series of alkylbenzenes. At a normal flow rate of 50 μL min⁻¹, the produced HMA-based monolithic columns typically exhibited 3,000 theoretical plates for a 20-cm-long column, and the pressure drop was generally less than 1 MPa per 20 cm. The monolithic columns were resistant to at least 15 MPa, and could be properly operated at 15–20 times higher flow rate than normal, reducing the separation time to 1/15–1/20. The HMA-based monolithic columns were applied to rapid and efficient separations of proteins such as ribonuclease A, cytochrome c, transferrin, and ovalbumin in the precipitation–redissolution mode. Using a CH₃CN gradient elution at a flow rate of 1,000 μL min⁻¹, four proteins were baseline separated within 20 s.     

Image quality of microns-thick specimens in the ultra-high voltage electron microscope

Image quality of MeV transmission electrons is an important factor for both observation and electron tomography of microns-thick specimens with the high voltage electron microscope (HVEM) and the ultra-HVEM. In this work, we have investigated image quality of a tilted thick specimen by experiment and analysis. In a 3 MV ultra-HVEM, we obtained transmission electron images in amplitude contrast of 100 nm gold particles on the top surface of a tilted 5 μm thick amorphous epoxy-resin film. From line profiles of the images, we then measured and evaluated image blurring, contrast, and the signal-to-noise ratio (SNR) under different effective thicknesses of the tilted specimen and accelerating voltages of electrons. The variation of imaging blurring was consistent with the analysis based on multiple elastic scattering. When the effective thickness almost tripled, image blurring increased from ～3 to ～20 nm at the accelerating voltage of 3 MV. For the increase of accelerating voltage from 1 to 3 MV in the condition of the 14.6 μm effective thickness, due to the reduction of multiple scattering effects, image blurring decreased from ～54 to ～20 nm, and image contrast and SNR were both obviously enhanced by a factor of ～3 to preferable values. The specimen thickness was shown to influence image quality more than the accelerating voltage. Moreover, improvement on image quality of thick specimens due to increasing the accelerating voltage would become less when it was further increased from 2 to 3 MV in this work.     

Topmost-surface-sensitive Si-2p photoelectron spectra of clean Si(1 0 0)-2 × 1 measured with photoelectron Auger coincidence spectroscopy

Topmost-surface-sensitive Si-2p photoelectron spectra of a clean Si(1 0 0)-2 × 1 surface have been measured using Si-2p photoelectron Si-L₂₃VV Auger coincidence spectroscopy (Si-2p–Si-L₂₃VV PEACS). The escape depth of the PEACS electrons is estimated to be ～1.2 Å. The results support the assignments of the Si up-atoms, the Si down-atoms, the Si 2nd-layer, and the Si bulk proposed in previous researches. The Si-2p component with a binding energy of ?0.23 eV relative to the bulk Si-2p_3/2 peak, is shown to originate mainly from the topmost surface. Site selectivity of PEACS is indicated to be achieved to some degree by carefully selecting the kinetic energy of the Auger electrons. Since PEACS can be applied to any surface, the present study opens a new approach to identify PES components.