Asymmetric Synthesis of Spiroketals with Aminothiourea Catalysts

Chiral spiroketal skeletons are found as core structures in a range of bioactive compounds. These natural compounds and their analogues have attracted much attention in the field of drug discovery. However, methods for their enantioselective construction are limited, and easily available optically active spiroketals are rare. We demonstrate a novel catalytic asymmetric synthesis of spiroketal compounds that proceeds through an intramolecular hemiacetalization/oxy‐Michael addition cascade mediated by a bifunctional aminothiourea catalyst. This results in spiroketal structures through the relay formation of contiguous oxacycles, in which multipoint recognition by the catalyst through hydrogen bonding imparts high enantioselectivity. This method offers facile access to spiroketal frameworks bearing an alkyl group at the 2‐position, which are prevalent in insect pheromones. Optically active (2S,5S)‐chalcogran, a pheromone of the six‐spined spruce bark beetle, and an azide derivative could be readily synthesized from the bicyclic reaction product.     

Spectrophotometric determination of titanium with o-carboxyphenylfluorone in cationic micellar media, and its equilibrium and kinetic studies

Spectrophotometric determination of titanium(IV) was accomplished with o-carboxyphenylfluorone (OCPF) in the presence of hexadecyltrimethyl ammonium chloride (HTAC) under strongly acidic media. In the determination of titanium(IV), Beer's law was obeyed in the range of 24-340 ng mL⁻¹ with an effective molar absorption coefficient (at 530 nm) and relative standard deviation of 2.24 × 10⁵ dm³ mol⁻¹ cm⁻¹ and 0.64% (n = 8), respectively. The severe interference of iron ions was easily eliminated by the addition of ethylenediaminetetraacetic acid (EDTA); the effects of other foreign substances were low. Equilibrium and kinetic studies under analytical conditions were investigated to quantitatively evaluate the reaction mechanism. The obtained orange complex is considered to be Ti(OCPF)₄. Its stability log K_f and rate constant K_obs are 16.88 and 1.65 × 10⁻² s⁻¹, respectively. It is suggested that the color of the complex is related to the species of OCPF in the solution.     

Electronic structures of Laves phase compounds

The electronic structures of Laves phase compounds AB₂ (A = Y, Zr, Nb; B = Cr, Mn, Co, Ni) were investigated systematically by the LMTO method within the framework of the LSD approximation. Comparing the calculated total energy for hypothetical para-, ferro-, and antiferromagnetic state with the C14 and the C15 structure, the theoretical predictions are in good agreement with the experiments concerning the stability of the crystal structure and the magnetism. The magnetic stability critically depends upon the change of the lattice spacing, which leads to the colorful behaviors of the magnetism in Fe Laves phase compounds and the anomalous volume change in the antiferromagnetic state of YMn₂.     

Development of copolymer of CR-39 with high sensitivity to low let particles

Several types of copolymers of CR-39 were prepared to find its usefulness as a nuclear track detector of high sensitivity. Track responses of these copolymers were investigated by irradiating energetic ions from proton through Ar. The copolymer of CR-39 monomer with N-isopropylacrylamide (NIPAAm) shows higher sensitivity than that of pure CR-39 for low LET particles such as protons. Preliminary results are reported for the track responses of copolymers (CR-39/NIPAAm) with various contents of NIPAAm as well as the etching properties.     

A practical method for monitoring <Superscript>129</Superscript>I concentration in airborne release

Summary To establish a practical method for monitoring ¹²⁹I concentration in airborne release from the Tokai reprocessing plant, the ¹²⁹I collecting performance of sampling media used was tested by in situ experiments. The results indicated that the combined use of an activated charcoal-impregnated filter paper and an activated charcoal cartridge gives a collection efficiency of more than 90% for a one-week sampling of real airborne effluent, at sampling flow rates of 40.6-75.0 l^. min^-1. The sampling and measurement conditions suitable for a routine-base monitoring are demonstrated.     

Behaviors of sodium glycochenodeoxycholate and sodium glycoursodeoxycholate in binary mixed micelles of bile salt and nonionic surfactant

The behavior of sodium glycochenodeoxycholate (NaGCDC) and sodium glycoursodeoxycholate (NaGUDC) in binary mixed micelles consisting of bile salt and octaoxyethylene glycol mono n-decyl ether (C₁₀E₈) has been studied on the basis of micellar compositions, polarities of the interior of intramicelles, mean aggregation numbers and ¹H NMR measurements. Micellar compositions for both NaGCDC---C₁₀E₈ and NaGUDC---C₁₀E₈ systems showed a tendency to change from C₁₀E₈-rich micelles to bile-salt-rich micelles with an increase on the mole fraction of bile salts from the results of both theoretical calculations using the critical micelle concentration and the micellar polarity. The microenvironment of intramicelles for the NaGCDC---C₁₀E₈ system was found to be more hydrophobic than that for the NaGUDC---C₁₀E₈ system. Mean aggregation numbers of mixed micelles for both systems decreased abruptly with an increase in the mole fraction of bile salts in the range of low mole fraction, but those for NaGCDC were larger than those for NaGUDC. Furthermore, from the results of ¹H NMR measurements, the motions of the methyl group protons in the 18 position of the molecular structure of NaGCDC were slightly restricted with an increase in the mole fraction of NaGCDC. In contrast, the methyl group protons in the 18 and 19 positions of the molecular structure of NaGUDC became freer with an increase in the mole fraction of NaGUDC.     

Effect of hyperfine interaction on the luminiscence of Pb2+ and Bi3+ centers in alkaline-earth chalcogenides

Emission spectra of MgS, CaO, CaS, CaSe and SrS phosphors activated with a Pb²⁺ or a Bi³⁺ ion are measured at 4.2 K. By the analysis of the phonon structure of the ³A_1u → ¹A₁g emission band, it is found that the hyperfine interaction provokes the zero-phonon line on the emission band for the alkaline-earth chalcogenide phosphors activated with a Pb²⁺ or a Bi³⁺ ion.     

Behavior of semiconductive tin oxide electrodes in molten lithium chloride+potassium chloride eutectic

In molten LiCl+KCl eutectic at 450°C, current and differential capacity were measured with the potentiodynamic method at Sb-doped polycrystalline tin oxide films prepared on Pyrex glass substrates. SnO₂ electrodes usable in high temperature melts were constructed with special care to keep a definite working area. The melt-stable and semiconductive oxide shows a stable polarizable potential region with a span of about 1 V from chlorine evolution to cathodic decomposition of the oxide. Small residual current in the polarizable region indicates a possibility to use the oxide as an indicator electrode in the melt. The interfacial capacity is assigned to the space charge capacity of the electrode side and its potential dependence is explained using the Mott-Schottky equation. A linear Mott-Schottky plot was obtained after several potential scans and the flat band potential was estimated as ?1.29 V vs. 1 M Pt-(II)/Pt. The oxide surface in contact with the melt is subject to change during scanning in order to establish a stable melt-oxide interface where the specific adsorption of Cl^? ions plays an important role for the stabilization.