Convergent synthesis of the E'FGH' ring fragment of ciguatoxin 1B via an acetylene cobalt complex strategy

[reaction: see text] A convergent synthesis of the E'FGH' ring fragment of ciguatoxin has been accomplished through (i) coupling between the E' ring-acetylide and the H' ring-aldehyde, (ii) stereoselective F ring cyclization via an acetylene cobalt complex, (iii) conversion to a carbonyl function, and (iv) reductive hydroxy-ketone cyclization to construct the G ring.     

Biological control of cellulose

The enhancement of bacterial cellulose (BC) productivity using sucrose as a carbon source has been obtained by the co-cultivation of two different types of acetic acid bacteria. BC yields for the given mix ratio of bacteria were larger than that of control. The contents of water-soluble polymer (WSP) in the BC composites (BCCs) are a range of 5–30 wt-%. This will be due to the formation of glucose and fructose through the hydrolysis of sucrose by sucrase secreted from Acetobacter sp. In addition, this preparation method would be applied to synthesize a new type of BC having both high biodegradability and other functions.     

Thermoelectricity Generation and Electron–Magnon Scattering in a Natural Chalcopyrite Mineral from a Deep‐Sea Hydrothermal Vent

Current high‐performance thermoelectric materials require elaborate doping and synthesis procedures, particularly in regard to the artificial structure, and the underlying thermoelectric mechanisms are still poorly understood. Here, we report that a natural chalcopyrite mineral, Cu_1+xFe_1?xS₂, obtained from a deep‐sea hydrothermal vent can directly generate thermoelectricity. The resistivity displayed an excellent semiconducting character, and a large thermoelectric power and high power factor were found in the low x region. Notably, electron–magnon scattering and a large effective mass was detected in this region, thus suggesting that the strong coupling of doped carriers and antiferromagnetic spins resulted in the natural enhancement of thermoelectric properties during mineralization reactions. The present findings demonstrate the feasibility of thermoelectric energy generation and electron/hole carrier modulation with natural materials that are abundant in the Earth’s crust.     

Titanium and Zirconium Complexes with Non‐Salicylaldimine‐Type Imine–Phenoxy Chelate Ligands: Syntheses,Structures, and Ethylene‐Polymerization Behavior

New Ti and Zr complexes that bear imine–phenoxy chelate ligands, [{2,4‐di‐tBu‐6‐(RCH=N)‐C₆H₄O}₂MCl₂] ( 1 : M=Ti, R=Ph; 2 : M=Ti, R=C₆F₅; 3 : M=Zr, R=Ph; 4 : M=Zr, R=C₆F₅), were synthesized and investigated as precatalysts for ethylene polymerization. ¹H NMR spectroscopy suggests that these complexes exist as mixtures of structural isomers. X‐ray crystallographic analysis of the adduct 1 ?HCl reveals that it exists as a zwitterionic complex in which H and Cl are situated in close proximity to one of the imine nitrogen atoms and the central metal, respectively. The X‐ray molecular structure also indicates that one imine phenoxy group with the syn C?N configuration functions as a bidentate ligand, whereas the other, of the anti C?N form, acts as a monodentate phenoxy ligand. Although Zr complexes 3 and 4 with methylaluminoxane (MAO) or [Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ displayed moderate activity, the Ti congeners 1 and 2 , in association with an appropriate activator, catalyzed ethylene polymerization with high efficiency. Upon activation with MAO at 25 °C, 2 displayed a very high activity of 19900 (kg PE) (mol Ti)^?1 h^?1, which is comparable to that for [Cp₂TiCl₂] and [Cp₂ZrCl₂], although increasing the polymerization temperature did result in a marked decrease in activity. Complex 2 contains a C₆F₅ group on the imine nitrogen atom and mediated nonliving‐type polymerization, unlike the corresponding salicylaldimine‐type complex. Conversely, with [Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ activation, 1 exhibited enhanced activity as the temperature was increased (25–75 °C) and maintained very high activity for 60 min at 75 °C (18740 (kg PE) (mol Ti)^?1 h^?1). ¹H NMR spectroscopic studies of the reaction suggest that this thermally robust catalyst system generates an amine–phenoxy complex as the catalytically active species. The combinations 1 /[Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ and 2 /MAO also worked as high‐activity catalysts for the copolymerization of ethylene and propylene.     

Incident angle and energy dependences of low‐energy Ar+ ion sputtering of GaAs/AlAs multilayered system

Dependences of the depth resolution in Auger electron spectroscopy sputter‐depth profiling of a GaAs/AlAs superlattice reference material on the incident angle and energy of primary Ar⁺ ions were investigated. The results revealed that the depth resolution is improved for the lower primary energy as a square root of the primary energy of ions at both the incident angles of 50° and 70° , except for 100 eV at 50° , where the significant deterioration of the depth resolution is induced by the preferential sputtering of As in AlAs, and the difference in the etching rate between GaAs and AlAs. The deterioration of the depth resolution, i.e. the difference in the etching rate and the preferential sputtering, observed for 100 eV at 50° was suppressed by changing the incident angle of ions from 50° to 70° , resulting in the high‐depth resolution of ～1.3 nm. The present results revealed that the glancing incidence of primary ions is effective to not only reducing the atomic mixing but also suppressing the difference in the etching rates between GaAs and AlAs and the preferential sputtering in the GaAs/AlAs multilayered system. The results also suggest that careful attention is required for the optimization of conditions of sputter‐depth profiling using GaAs/AlAs superlattice materials under low‐energy ion irradiation. Copyright © 2009 John Wiley & Sons, Ltd.     

Direct fabrication of freely movable microplate inside photosensitive glass by femtosecond laser for lab-on-chip application

We demonstrate the fabrication of complicated three-dimensional (3D) microstructures embedded in a photosensitive glass by a high-order multiphoton process using a femtosecond (fs) laser. Direct writing of the fs laser followed by a post baking process and preferential etching in a dilute hydrofluoric (HF) acid solution results in a microplate that can freely move in hollow structures embedded in the glass. The fabricated structure functions as a microvalve that can control the flow direction of fluids in the microreactor. PACS 42.62.-b; 81.05.Kf; 82.50.Pt     

Processing of vacuum microelectronic devices by focused ion and electron beams

Localized physical and chemical reactions induced by focused ion and electron beams, i.e. dual beams, have been used to fabricate field emitters (FEs) and their arrays, field-emitter arrays (FEAs), without masking and annealing processes. Issues arising from beam processing such as beam-induced damage and contamination were eliminated to provide FEAs with low leakage current. Quick prototyping and repairing processes of FEs and FEAs using dual-beam processing have been demonstrated. Nb- or Au-gated Pt FEAs have been fabricated using dual beams. The fabricated FEAs showed a turn-on voltage of 40 V for field emission with a typical emission current of about 1 μA/tip. Received: 21 August 2002 / Accepted: 21 August 2002 / Published online: 12 February 2003 RID="*" ID="*"Corresponding author. Fax: +81-6/6850-6662, E-mail: takai@rcem.osaka-u.ac.jp