Kinetic resolution of racemic alcohols catalyzed by minimal artificial acylases derived from l-histidine

The artificial acylases, tert-butyldiphenylsilyl ether and tris(trimethylsilyl)silyl ether of N(π)-methyl-N(α)-(2,4,6-triisopropylbenzenesulfonyl)-l-histidinol, are simple and small molecules, which contain only one chiral carbon center that originates from natural l-histidine. Asymmetric acylation of racemic secondary alcohols with isobutyric anhydride induced by these artificial acylases gave optically active isobutyrates and optically active alcohols with an S(k_{fast-reacting enantiomer}/k_{slow-reacting enantiomer}) value of up to 132. One hydrogen bonding interaction between a sulfonamidyl group of the catalysts and a substrate should be essential for inducing the high level of kinetic resolution through catalytic asymmetric acylation. Furthermore, a reusable polystyrene-bound artificial acylase was developed to examine its practicality.     

Water uptake and infrared absorption in SrZr<Subscript>0.95</Subscript>M<Subscript>0.05</Subscript>O<Subscript>3-</Subscript><Subscript>a</Subscript> (<Emphasis Type="Italic">M</Emphasis>=Ga,Sc, Y and Nd)

Summary Proton concentration in SrZr_0.95M_0.05O_3-α (M=Ga, Sc, Y and Nd) was measured with a thermobalance at different temperatures (T=673-973 K) and water vapor pressures (P_H2O=0.9-12.8 kPa). At all the pressures and temperatures examined, the amount of proton concentration in these samples is in the order of Sc>Y>Ga>Nd. By an equilibrium evaluation, we estimated the maximum possible proton concentration about 2.0 mol% in these samples. Infrared (IR) absorption spectra are measured in these samples. The absorption bands can be fitted by four (M=Ga, Y, Nd) or three (M=Sc) Gaussian bands.     

Synthesis of novel chiral bis(2-oxazolinyl)xanthene (xabox) ligands and their evaluation in catalytic asymmetric 1,3-dipolar cycloaddition reactions of nitrones with 3-crotonoyl-2-oxazolidinone

Chiral 4,5-bis(2-oxazolinyl)-(2,7-di-tert-butyl-9,9-dimethyl)-9H-xanthenes (xabox) were synthesized and the chiral environments were evaluated in catalytic asymmetric 1,3-dipolar cycloaddition reactions of nitrones resulting in good to excellent enantioselectivities. 1,3-Dipolar cycloaddition reactions of nitrones with 3-crotonoyl-2-oxazolidinone in the presence of a bis(2-oxazolinyl)xanthene (4c; xabox-Bn) and Mn(II) or Mg(II) complex as a chiral Lewis acid catalyst proceeded smoothly to give the corresponding cycloadducts ranging from 96:4 to >99:1 of endo:exo ratio and ranging from 91% to 98% ee for the endo adduct.     

Heat capacity measurement and DSC study of hafnium hydrides

Heat capacities, electrical conductivities and phase transition temperature of hafnium hydrides, HfH_x (0.99≤x≤1.83), were studied using a direct heating pulse calorimeter and a differential scanning calorimeter from room temperature to above 500 K. The heat capacity of HfH_1.83 was larger than that of pure hafnium and showed no anomaly of heat capacity. In contrast, there were λ-type peaks for the heat capacity and DSC curves for HfH_x (1.1≤x≤1.6) near 385 and 356 K. The anomalies of heat capacity and electrical conductivity of HfH_x (1.1≤x≤1.6) were considered the result of phase transition and order-disorder phase transition for hydrogen in the hafnium hydride lattice for HfH_x (1.1≤x≤1.3).     

Quantification of frequency dependence of mechanical effects induced by ultrasound

The physical or mechanical effects induced by ultrasound were investigated through the viscosity change in degradation of polymers. The viscosity change was observed with polyethylene oxide in both aqueous and benzene solution; while polystyrene in only benzene solution. The frequency of ultrasound in these experiments varies from 20 kHz to 1 MHz, under a constant dissipated power. The viscosity ratio and the apparent degradation rate were obtained as a function of the irradiation frequency. From the analysis of these experiments, the mechanical effects are found to slow down above 100 kHz when the frequency increases. In case of the analysis of solution viscosity, since this method yields the same apparent results in both aqueous and benzene solutions, our study propose an alternative simple, cost effective method to quantify the mechanical effects in sonochemistry.     

Pressure-sensitive paint measurement on co-rotating disks in a hard disk drive

There is much demand for improvement in the performance of a hard disk drive (HDD) along with recent rapid developments of information technology. While high-speed disk rotation of a HDD is necessary to accommodate such needs, it causes disk flutter induced by pressure fluctuation on disks and degrades reliability of a HDD. In order to understand the mechanism of the fluttering phenomenon, it is important to know pressure field on the rotating disk. However, it is impossible to measure the pressure by ordinary methods such as pressure taps. Pressure-sensitive paint (PSP) is a pressure measurement technique based on the oxygen quenching of luminescence and enables us to measure the pressure non-invasively. In general, however, the temperature sensitivity of PSP makes it difficult to measure the precise pressure on the surface with temperature distribution. We measured the time-averaged pressure on the disk rotating at 10 000-20 000 rpm for the first time by adopting a temperature-insensitive PSP composed of pyrene sulfonic acid (PySO₃H) as a luminophore. It was found that the pressure forms a concentric circular distribution and decreases toward the center of the disk. Additionally, we elucidate how disk rotational speed and spacing between co-rotating disks influence on the pressure field.     

Evidence for Fermi level shift in GaInAs/GaAs quantum wells upon nitrogen incorporation

GaInAs/GaAs and GaInNAs/GaAs quantum well (QW) structures grown by metalorganic vapor phase epitaxy have been studied by contactless electroreflectance spectroscopy. In addition to the N-related redshift of QW transitions, an increase in the electric field in the GaAs cap layer has been observed after the incorporation of nitrogen atoms into the GaInAs QW. This observation is associated with the tendency of the Fermi level shift to a given energy in the GaInNAs QW region due to N-related defects.     

Equality conditions for lower bounds on the smallest singular value of a bidiagonal matrix

Several lower bounds have been proposed for the smallest singular value of a square matrix, such as Johnson’s bound, Brauer-type bound, Li’s bound and Ostrowski-type bound. In this paper, we focus on a bidiagonal matrix and investigate the equality conditions for these bounds. We show that the former three bounds give strict lower bounds if all the bidiagonal elements are non-zero. For the Ostrowski-type bound, we present an easily verifiable necessary and sufficient condition for the equality to hold.     

Study of the surface structure of Si(1 1 1)-6 × 1(3 × 1)-Ag using X-ray crystal truncation rod scattering

The structure of the Si(1 1 1)-6 × 1-Ag surface is investigated using crystal truncation rod (CTR) scattering along 00 rod. For the measurement, we developed a manipulator suitable for observing CTR scattering at large momentum transfer perpendicular to the surface. The heights of the silver and reconstructed silicon atoms from the substrate were determined. We also compared the obtained positions with those of the Si(1 1 1)-√3 × √3-Ag surface and found that the heights of those reconstructed atoms are almost the same.     

The determination of deuteron site in SrZr0.95Sc0.05O3−α by neutron powder diffraction

High-resolution, powder, neutron diffraction data have been collected on the protonic conductors SrZr_0.95Sc_0.05O_3−α with and without dissolved heavy water at a temperature of 10 K. Diffraction data have been analyzed by the Rietveld and maximum entropy methods (MEM). The crystal structure of these samples at 10 K is successfully refined assuming a perovskite-type structure with the space group Pnma. The deuterons are located outside the ZrO₆/ScO₆ octahedra near oxygen atoms.