Factors Controlling Stereoselectivity in the Koenigs-Knorr Type D-Mannopyranosylation

Abstract

The factors controlling stereoselectivity in the formation of cyclohexyl α- and β-D-mannopyranosides with D-mannosyl chloride, cyclohexanol and silver triflate (AgOTf), were examined. For the syntheses of β-D-mannopyranosides, dichloromethane (CH₂Cl₂) as solvent could be used only at low temperature, while the use of tetrahydrofuran (THF) as solvent proved to be effective at room temperature. Diallyl ether (All₂O) was effectively used in CH₂Cl₂ as an olefinic additive. Stereoselectivities in these reactions were changed by use of THF as an oxonium ion source and All₂O as an inhibitor to prevent complex formation of the silver ion with the allyloxy group of the glycosyl donor.     

Systematic Experiment on Star Anomaly in pd Break up at E/A = 9.5 MeV

We measured pd breakup cross section at E _d = 19 MeV (E/A = 9.5 MeV) at Star configuration at 120° ≤ inclination angle α ≤ 180°, i.e. apart from Space Star configuration (α = 90°), and found that pd Star cross section at 120° ≤ α ≤ 180° agree with pd calculation, contrary to Köln data. By our systematic experiments on Star configurations so far and recent reliable pd calculations, existence of Space Star anomaly has been established in pd breakup at E/A = 9.5 and 13 MeV. Also it has been confirmed that no anomaly exist at Star configurations apart from Space Star.     

Dynamic structural changes at LiMn2O4/electrolyte interface during lithium battery reaction

Gaining a thorough understanding of the reactions on the electrode surfaces of lithium batteries is critical for designing new electrode materials suitable for high-power, long-life operation. A technique for directly observing surface structural changes has been developed that employs an epitaxial LiMn(2)O(4) thin-film model electrode and surface X-ray diffraction (SXRD). Epitaxial LiMn(2)O(4) thin films with restricted lattice planes (111) and (110) are grown on SrTiO(3) substrates by pulsed laser deposition. In situ SXRD studies have revealed dynamic structural changes that reduce the atomic symmetry at the electrode surface during the initial electrochemical reaction. The surface structural changes commence with the formation of an electric double layer, which is followed by surface reconstruction when a voltage is applied in the first charge process. Transmission electron microscopy images after 10 cycles confirm the formation of a solid electrolyte interface (SEI) layer on both the (111) and (110) surfaces and Mn dissolution from the (110) surface. The (111) surface is more stable than the (110) surface. The electrode stability of LiMn(2)O(4) depends on the reaction rate of SEI formation and the stability of the reconstructed surface structure.     

Surface carboxylation of porous regenerated cellulose beads by 4-acetamide-TEMPO/NaClO/NaClO2 system

A commercial regenerated bead cellulose was suspended in water at pH 4.8, and oxidized with NaClO₂ used as a primary oxidant and catalytic amounts of NaClO and 4-acetamide-2,2,6,6-tetramethylpiperidinyl-1-oxyl radical. Carboxylate groups were formed up to 1.87 mmol/g in the beads by the oxidation of C6 primary hydroxyls to carboxylates without significant weight losses or morphological changes. The spherical shapes, highly porous surface structures consisting of nano-sized fibrils, and the cellulose II crystal structure of the original beads were mostly maintained by the oxidation, indicating that the carboxylate groups formed are predominantly present on the fibril surfaces. Cation-exchange behavior of the TEMPO-oxidized cellulose beads was compared with carboxymethylated cellulose beads, showing that the former was characteristic and superior to the latter in terms of adsorption of metal ions and cationic polymers. Especially, the TEMPO-oxidized cellulose beads had high adsorption behavior of lead ion and high-molecular-weight cationic polymers.     

Bis(bipyridine)ruthenium(II) complexes with an aliphatic sulfinato donor: synthesis, characterization, and properties

Treatment of a thiolato-bridged Ru(II)Ag(I)Ru(II) trinuclear complex, [Ag{Ru(aet)(bpy)(2)}(2)](3+) (aet = 2-aminoethanthiolate; bpy = 2,2'-bipyridine), with NaI in aqueous ethanol under an aerobic condition afforded a mononuclear ruthenium(II) complex having an S-bonded sulfinato group, [1](+) ([Ru(aesi-N, S)(bpy)(2)](+) (aesi = 2-aminoethanesulfinate)). Similar treatment of optically active isomers of an analogous Ru(II)Ag(I)Ru(II) trinuclear complex, Δ(D)Δ(D)- and Λ(D)Λ(D)-[Ag{Ru(d-Hpen-O,S)(bpy)(2)}(2)](3+) (d-pen = d-penicillaminate), with NaI also produced mononuclear ruthenium(II) isomers with an S-bonded sulfinato group, Δ(D)- and Λ(D)-[2](+) ([Ru(d-Hpsi-O,S)(bpy)(2)](+) (d-psi = d-penicillaminesulfinate)), respectively, retaining the bidentate-O,S coordination mode of a d-Hpen ligand and the absolute configuration (Δ or Λ) about a Ru(II) center. On refluxing in water, the Δ(D) isomer of [2](+) underwent a linkage isomerization to form Δ(D)-[3] (+) ([Ru(d-Hpsi-N,S)(bpy)(2)](+)), in which a d-Hpsi ligand coordinates to a Ru(II) center in a bidentate-N,S mode. Complexes [1](+), Δ(D)- and Λ(D)-[2](+), and Δ(D)-[3](+) were fully characterized by electronic absorption, CD, NMR, and IR spectroscopies, together with single-crystal X-ray crystallography. The electrochemical properties of these complexes, which are highly dependent on the coordination mode of sulfinate ligands, are also described.     

Total synthesis of peumusolide A, NES non-antagonistic inhibitor for nuclear export of MEK

The first total synthesis of peumusolide A (1) has been achieved by combination of regio- and stereo-selective aluminum-mediated hydroiodination to 2-yn-1-ol and enantioselective reduction of 4-en-1-yn-3-one with the chiral oxazaborolidine as the key reactions. This total synthesis has unequivocally established our proposed absolute structure of 1.     

Compensation effect of Mg-doped a- and c-plane GaN films grown by metalorganic vapor phase epitaxy

The electrical and optical properties of Mg-doped a- and c-plane GaN films grown by metalorganic vapor phase epitaxy were systematically investigated. The photoluminescence spectra of Mg-doped a- and c-plane GaN films exhibit strong emissions related to deep donors when Mg doping concentrations are above 1×10²⁰ cm⁻³ and 5×10¹⁹ cm⁻³, respectively. The electrical properties also indicate the existence of compensating donors because the hole concentration decreases at such high Mg doping concentrations. In addition, we estimated the N_D/N_A compensation ratio of a- and c-plane GaN by variable-temperature Hall effect measurement. The obtained results indicate that the compensation effect of the Mg-doped a-plane GaN films is lower than that of the Mg-doped c-plane GaN films.     

Formation of Tsai-type 1/1 approximants in In-Pd-RE (RE: rare earth metal) alloys

The formation of the 1/1 crystal approximant phase (1/1 phase) to the icosahedral phase (i phase) in In-Pd-RE (RE: rare earth metal) systems has been investigated. A new series of 1/1 phases were found in In₅₃Pd₃₃RE₁₄ (RE; Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Tm) alloys. For Y, Sm, Gd, Tb, Dy, and Ho, the 1/1 phases were found in annealed alloys, indicating that they are thermodynamically stable. The atomic structure of the 1/1 phases was directly observed by high-angle annular dark-field imaging performed via scanning transmission electron microscopy, revealing that the 1/1 phases consisted of a periodic arrangement of Tsai-type icosahedral clusters. Further, the atomic size effect on i phase formation, as well as formation conditions previously reported for other Tsai-type i and 1/1 phases were examined. It was found that the ratio of the atomic radius of base metals such as In and Pd affects i phase formation. Moreover, the appropriate range of the radius ratio for i phase formation was narrower than that for 1/1 phase formation.