Selective vinyl cationic polymerization of monomers with two cationically polymerizable groups. I. p-isopropenylphenyl glycidyl ether: An epoxy-functionalized α-methylstyrene

p-Isopropenylphenyl glycidyl ether (IPGE), a monomer of dual cationic functionality (isopropenyl and epoxy), was polymerized by a variety of initiators, and optimum conditions were established for its selective vinyl cationic polymerization. The hydrogen iodide/iodine (HI/I₂) initiating system or iodine polymerized selectively the isopropenyl group in CH₂Cl₂ at a low temperature (?78°C), to produce soluble poly(IPGE) with epoxy pendants. Under these conditions, the number-average molecular weight of the polymers was inversely proportional to the initial initiator concentration, indicating the formation of long-lived propagating species. Soluble poly(IPGE) was also obtained at ?15 and ?40°C by HI/I₂ or iodine. However, at these higher temperatures, transfer and/or termination reactions took place to give olefin-terminated polymers, in which some of the pendant epoxy groups were consumed. BF₃OEt₂ (a metal halide) and CF₃SO₃H (a strong protonic acid) polymerized both epoxy and isopropenyl groups of IPGE and yielded crosslinked insoluble polymers.     

Regio- and stereoselective 12-O-demethylation of schizandrin into gomisin T, an important intermediate to gomisin A, by Mortierella sp. (TM-I1104)

A strain TM-I1104 identified as Mortierella sp. was discovered from soil as the most efficient fungus, which converted schizandrin into gomisin T in 91% regioselectivity by microbial 12-O-demethylation. Under optimum conditions, the yield of gomisin T reached around 80%. The faculty of 12-O-demethylation was specific on (+)-schizandrin (natural form) and the optical purity of gomisin T converted from (±)-schizandrin was 96% ee.     

Unisized two-dimensional platinum clusters on silicon(111)-7x7 surface observed with scanning tunneling microscope

Uni-sized platinum clusters (size range of 5-40) on a silicon(111)-7 x 7 surface were prepared by depositing size-selected platinum cluster ions on the silicon surface at the collision energy of 1.5 eV per atom at room temperature. The surface thus prepared was observed by means of a scanning tunneling microscope (STM) at the temperature of 77 K under an ambient pressure less than 5 x 10(-9) Pa. The STM images observed at different cluster sizes revealed that (1) the clusters are flattened and stuck to the surface with a chemical-bond akin to platinum silicide, (2) every platinum atom occupies preferentially the most reactive sites distributed within a diameter of approximately 2 nm on the silicon surface at a cluster size up to 20, and above this size, the diameter of the cluster increases with the size, and (3) the sticking probability of an incoming cluster ion on the surface increases with the cluster size and reaches nearly unity at a size larger than 20.     

Asymmetric reduction of alkyl phenyl ketones with a chiral hydride reagent prepared from lithium aluminum hydride and (S)-4-anilino-3-methylamino-1-butanol

The asymetric reduction of alkyl phenyl ketones with a chiral hydride reagent derived from lithium aluminum hydride and (S)-4-anilino-3-methylamino-1-butanol, which is prepared from (S)-aspartic acid, gives (S)-alkylphenylcarbinols in high chemical and optical yields.     

Characterization of homoionic Fe-type montmorillonite: Potential chemical species of iron contaminant

Fe²⁺-montmorillonite with Fe²⁺ ions occupying cation exchange sites is an ideal transformation product in bentonite buffer material. In our previous study on preparation and characterization of Fe²⁺-montmorillonite, the montmorillonite sample that adsorbed Fe²⁺ ions on almost all of the cation exchange sites was prepared using a FeCl₂ solution under an inert gas condition [N. Kozai, Y. Adachi, S. Kawamura, K. Inada, T. Kozaki, S. Sato, H. Ohashi, T. Ohnuki, T. Banba, J. Nucl. Sci. Technol. 38 (2001) 1141]. In view of the unstable nature of iron(II) chemical species, this study attempted to determine the potential contaminant iron chemical species in the sample. Nondestructive elemental analysis revealed that a small amount of chloride ions remained dispersed throughout the clay particles. The chloride ion retention may be due to the adsorption of FeCl⁺ ion pairs in the initial FeCl₂ solution and the subsequent containment of the Cl⁻ ions that are dissociated from the FeCl⁺ ion pairs during excess salt removal treatment. Two explanations are advanced for the second process: the slow release of the remaining Cl⁻ ions from the collapsed interlayer of the montmorillonite, and the transformation of a minor fraction of the remaining FeCl⁺ ion pairs to iron(III) hydroxide chloride complexes having low solubility.     

Palladium-catalyzed asymmetric synthesis of axially chiral allenylsilanes and their application to SE2' chirality transfer reactions

Stepwise application of the Pd-catalyzed S(N)2' reaction and the desilylative S(E)2' reaction to the ambivalent 2-bromo-1-silyl-1,3-dienes provides a novel route to the highly enantioselective construction of tertiary and quaternary propargylic stereogenic centers via axially chiral allenylsilanes.     

Electronic structures of size-selected single-layered platinum clusters on silicon(111)-7x7 surface at a single cluster level by tunneling spectroscopy

Tunneling spectra of size-selected single-layered platinum clusters (size range of 5-40) deposited on a silicon(111)-7x7 surface were measured individually at a temperature of 77 K by means of a scanning tunneling microscope (STM), and the local electronic densities of states of individual clusters were derived from their tunneling spectra measured by placing an STM tip on the clusters. In a bias-voltage (V(s)) range from -3 to 3 V, each tunneling spectrum exhibits several peaks assignable to electronic states associated with 5d states of a constituent platinum atom and an energy gap of 0.1-0.6 eV in the vicinity of V(s)=0. Even when platinum cluster ions having the same size were deposited on the silicon(111)-7x7 surface, the tunneling spectra and the energy gaps of the deposited clusters are not all the same but can be classified in shape into several different groups; this finding is consistent with the observation of the geometrical structures of platinum clusters on the silicon(111)-7x7 surface. The mean energy gap of approximately 0.4 eV drops to approximately 0.25 eV at the size of 20 and then decreases gradually as the size increases, consistent with our previous finding that the cluster diameter remains unchanged, but the number density of Pt atoms increases below the size of 20 while the diameter increases, but the density does not change above it. It is concluded that the mean energy gap tends to decrease gradually with the mean cluster diameter. The dependence of the mean energy gap on the mean Pt-Pt distance shows that the mean energy gap decreases sharply when the mean Pt-Pt distance exceeds that of a platinum metal (0.28 nm).     

Phenolic constituents from the rhizomes of Dryopteris crassirhizoma

A new phenolic glycoside, dryopteroside (1), was isolated from the rhizomes of Dryopteris crassirhizoma (Dryopteridaceae), together with five known compounds, 4beta-carboxymethyl-(-)-epicatechin (2), isobiflorin (3), biflorin (4), 1-beta-D-glucopyranosyloxy-3-methoxy-5-hydroxybenzene (5) and (+)-catechin-6-C-beta-D-glucopyranoside (6). The new compound was elucidated to be 1-butanoyl-3-C-beta-D-glucopyranosyl-5-methyl-phloroglucinyl-6-O-beta-D-glucopyranoside (1) by chemical and various spectroscopic analyses. The known compounds 2-6 were first reported from the genus Dryopteris.     

Synthesis, isolation, and structural characterization of the C4h isomer of metal(1,2-naphthalocyanine) and its one-dimensional conductor of the axially substituted species

The C4h isomer of the 1,2-Nc (1,2-naphthalocyaninato) ligand has been efficiently isolated as a hydrated magnesium complex by the fractional crystallization from the benzene/acetone solution after treating the crude mixture of the four isomers (C4h, C(s), C2v, D2h) with benzene. The C4h symmetry has been confirmed by X-ray structure analysis. The central metal ion has been demetalated and subsequently converted to the Li2 complex followed by conversion to the cobalt(II) complex. Electrochemical oxidation of the Co(III)(1,2-Nc)(CN)2 anion prepared from the cobalt(II) complex with TPP (tetraphenylphosphonium) has yielded a partially oxidized salt, TPP[Co(III)(1,2-Nc-C4h(CN)2]2. The crystal comprises slipped stacked Co(III)(1,2-Nc-C4h)(CN)2 one-dimensional chains and one-dimensional arrays of TPPs. The conductivity at room temperature is 0.1 S cm(-1), and the temperature dependence is semiconducting with a small activation energy of about 0.05 eV. The positive temperature-independent value of about 60 microV deg(-1) observed in the thermoelectric power measurements suggests that the salt is in the correlated hopping regime.