bluuebunny/crossref_metadata_2025 huggingface dataset:
Asymmetric Strecker Route toward the Synthesis of Biologically Active α,α-Disubstituted α-Amino Acids
Authors: Ohfune Yasufumi , Shinada Tetsuro
Published: June 2003

A series of optically active α,α-disubstituted α-amino acids have been synthesized starting with an achiral or a racemic α-hydroxy or α-diazo ketone. In the present synthesis, the key transformation is an asymmetric version of the Strecker synthesis. An α-acyloxy ketone having a chiral amino acid as the acyloxy group afforded cyclic α-amino nitrile in a highly stereoselective manner; in this reaction the amino group and the chirality were diastereoselectively transplanted into the internal ketone group via an imine-enamine equilibrium of the cyclic ketimine intermediate. Oxidation of the amino group followed by removal of the resulting imino group and hydrolysis of the nitrile group afforded α-hydroxymethyl α-amino acid. The use of l-amino acid as the acyloxy group gave R enantiomer, and its S enantiomer was obtained when d-amino acid was employed. Some problematic processes that remained in the Strecker synthesis, i.e., preparation of the starting α-acyloxy ketone and oxidative conversion of α-amino nitrile into α-imino nitrile, are much improved as regards efficiency by the development of a Cu-catalyzed insertion of α-diazo ketone into N-protected α-amino acid, and as regards yields by the use of ozone as the oxidant. With these methods, various types of α,α-disubstituted α-amino acids have been synthesized including cyclic analogs, which can be viewed as a conformational variant of serine. Their incorporations into Leu-enkephalin have revealed that these amino acids play an important role not only to constrain the peptide conformation but also for high affinity bindings to the opioid receptors. Applications to the synthesis of biologically active natural products have been exemplified by the syntheses of the Corey intermediate of lactacystin and of marine natural products, manzacidin A and C.
Anisotropic Ring Current Effect of p-Nitrophenolate Ion Inclusion on the 1H NMR Signals of the Pyridinio Derivatives of α-Cyclodextrin
Authors: Ohtsuki Hideki , Ahmed Jalaluddin , Nagata Takuya , Yamamoto Tatsuyuki , Matsui Yoshihisa
Published: June 2003

The p-nitrophenolate ion (pNP−) was strongly bound to the mono- and dipyridinio derivatives of α-cyclodextrin (α-CD) in an aqueous 0.1 mol dm−3 Na2CO3 solution, and shifted the 1H NMR signals due to the α-CD C5-H’s to different directions, depending on the position of α-d-glucopyranose (anisotropic ring-current effect). In contrast, the iodide ion and p-hydroxybenzoate ion showed no such effect upon complexation. Furthermore, the C5-H’s of a dipyridinio derivative of β-CD was not subject to such an anisotropic ring-current effect of pNP−. These results indicate that the molecular rotation of pNP− is significantly retarded within the cavities of the pyridinio derivatives of α-CD by electrostatic and van der Waals interactions. Thus, electrostatic interactions are available for controlling the molecular motion or orientation of an ionic guest compound in a CD cavity and for the design of an enzyme-mimic modified CD.
Oxidative Reaction of Thiosulfate with Hydrogen Peroxide by Freezing
Authors: Sato Keiichi , Furuya Satoshi , Takenaka Norimichi , Bandow Hiroshi , Maeda Yasuaki , Furukawa Yoshinori
Published: June 2003

In order to investigate the characteristics of the oxidative reactions of low-valence sulfur compounds with H2O2 in the freezing process, a Na2S2O3 aqueous solution was mixed with a H2O2 aqueous solution, followed by freezing at −15 °C. After the designated time had passed, the concentrations of sulfur compounds were measured. The oxidation of thiosulfates was accelerated due to the freeze-concentration effect. The maximum reaction rate of the freezing reaction (−15 °C) was about 20-times faster than that in an aqueous solution (25 °C). In the aqueous-phase reaction, thiosulfates were transformed to tetrathionates as intermediates, or directly to sulfates, and all sulfur compounds were finally oxidized to sulfates. On the other hand, the tetrathionates and sulfates transformed by the freezing reaction were preserved in ice for a long time. The maximum amounts of the tetrathionates formed by freezing were about twice those in the aqueous-phase reaction. Once tetrathionates were formed by the freezing reaction, most of the formed tetrathionates coexisting with high concentrations of H2O2 were not transformed to sulfate, regardless of whether or not the sample was re-frozen. This observation is probably attributable to the difference in the pH value when tetrathionates are formed.
Kinetic Study of Tungsten Atoms (a 7S3 and a 5DJ) in the Presence of C2H4 and NH3 at Room Temperature
Authors: Ishikawa Yo-ichi , Matsumoto Yoshitaka
Published: June 2003

The gas-phase reactivity of W (a 7S3 and a 5DJ) with C2H4 and NH3 at room temperature was investigated using a time-resolved laser induced fluorescence (LIF) spectroscopy. Tungsten atoms were produced by a 266-nm multiphoton decomposition (MPD) of W(CO)6. The reactant pressure dependence of the pseudo-first-order depletion rates of W (a 7S3) could allow an estimation of the pseudo-second-order depletion rate constant of W (a 7S3), (4.5 ± 0.5) × 10−10 cm3 molecule−1 s−1 for C2H4 and (0.73 ± 0.10) × 10−10 for NH3 at 6.0-Torr total pressure with an Ar buffer. A simulation of the transient curves based on a modification of the observed apparent decay rate constants, involving nearby a 5DJ states in the presence of C2H4 and NH3, allowed us to separately estimate the contribution of the chemical quenching (W (a 7S3) + R → product(s)) and the physical quenching (W (a 7S3) + R → W (a 5D1) + R) processes. In the case of C2H4, chemical quenching appeared to dominate over the physical quenching, while the physical quenching was the main depletion process in the case of NH3. The large reactivity of the W (a 7S3) state not only for C2H4, but also for NH3, is discussed in terms of the relativistic effects.
Synthesis, Structure and Proton-Coupled Electron Transfer of μ-Oxo-μ-chloro and μ-Oxo-μ-alkoxo Dimeric Molybdenum(III) Ethylenediamine Complexes
Authors: Kiyoda Shunji , Akashi Haruo , Ichimura Akio , Shibahara Takashi
Published: June 2003

An oxo- and chloro-bridged dinuclear molybdenum(III) ethylenediamine complex, [Mo2(μ-O)(μ-Cl)(en)4]3+, was synthesized by the reaction of [MoCl3(thf)3] with ethylenediamine in DMF. μ-Oxo-μ-alkoxo-bridged dimolybdenum(III) ethylenediamine complexes [Mo2(μ-O)(μ-OMe)(en)4]3+, [Mo2(μ-O)(μ-OEt)(en)4]3+, and [Mo2(μ-O)(μ-OPr)(en)4]3+ were obtained by reactions of the mononuclear complex with ethylenediamine in methanol, ethanol, and propanol, respectively, where each solution contained LiBr. Bridged dimeric structures of these complexes were determined by X-ray crystallography. In an acidic aqueous solution, these oxo-bridged complexes underwent protonation on the bridging oxygen atoms and changes to the corresponding hydroxo-bridged complexes. Cyclic voltammetric measurements (pH 1.0–10.0) of complexes [Mo2(μ-O)(μ-Cl)(en)4]3+, [Mo2(μ-O)(μ-OMe)(en)4]3+, and [Mo2(μ-O)(μ-OEt)(en)4]3+ clearly showed that, accompanied by the oxidation of the complex, the coordinated amine is deprotonated, and the complex becomes a corresponding amido-coordinated complex.
In Situ Very-High-Energy Diffraction Studies of Thermal Decomposition of Transition Metal Trifluorides
Authors: Rau Julietta V , Rossi Albertini Valerio , Chilingarov Norbert S , Di Michiel Marco , Colonna Stefano , Ioffe Ilya N , Sidorov Lev N
Published: June 2003

The thermal decomposition of transition metal trifluorides MF3 (M = Mn, Fe, Co) was studied by collecting sequences of very-high-energy (89 keV) synchrotron radiation diffraction patterns. The real-time evolution of the crystal lattices was followed as a function of temperature and it was observed that the transition from MF3 to MF2 is generally accompanied by the formation of intermediate short-living phases –M2F5. One of them –Co2F5– is a phase which had never been observed before.
Reaction of Amino Acids in a Supercritical Water-Flow Reactor Simulating Submarine Hydrothermal Systems
Authors: Islam Md Nazrul , Kaneko Takeo , Kobayashi Kensei
Published: June 2003

A novel supercritical water flow-reactor was constructed in order to simulate submarine hydrothermal systems. The temperature of fluid inside the reaction tube could be monitored with thermocouples, which was proved to be different from the temperature outside the reaction tube. Oligomers of glycine up to tetraglycine were formed when a 100 mM glycine solution was heated at 200–350 °C for 2 minutes. None of glycine peptides were produced at 400 °C. It was suggested, however, that the formation of glycine condensates at higher temperature, including supercritical conditions of water. The stability of some amino acids under hydrothermal conditions was examined. ω-Amino acids and glutamic acid, which can form intramolecular condensates, showed higher stability than other α-amino acids at higher temperature, including supercritical conditions.
A Unique Two-Dimensional Terephthalate-Bridged Structure with Alternate Tetra- and Penta-Coordinate Cobalt(II) Sites. Synthesis, Crystal Structure and Magnetic Properties of [{Co3(tp)2(OH)2(phen)2}n]
Authors: Zhang Li-Juan , Zhao Xiao-Li , Cheng Peng , Xu Ji-Qing , Tang Xu , Cui Xiao-Bing , Xu Wei , Wang Tie-Gang
Published: June 2003

A two-dimensional (2D) cobalt coordination polymer [{Co3(tp)2(OH)2(phen)2}n] (1), bridged by the terephthalate (tp) ligand, was synthesized under hydrothermal conditions, and its structure was determined by single-crystal X-ray diffraction. Complex 1 crystallized in the triclinic space group P1- with a = 8.2620(11) Å, b = 10.4409(12) Å, c = 11.0840(10) Å, α = 111.332(8)°, β = 91.394(10)°, γ = 91.638(10)°, Z = 2, V = 889.65(18) Å3. A structure refinement showed that complex 1 is the first example of a two-dimensional (2D) framework with both carboxylate bridges and μ-hydroxo bridges, in which cobalt atoms adopt square-pyramidal and square-planar geometries. Complex 1 exhibited a interesting magnetic behavior: the shape of the μeff curve indicates a ferrimagnetic-like behavior between 300–41.0 K, immediately followed by a strong decay of the magnetic moment. Moreover, complex 1 was characterized by IR spectroscopy, inductively coupled plasma (ICP), elemental and thermogravimetric (TGA) analyses.
Tetranuclear Ru Complex Linked via Redox-Active Azobis(bipyridine) Ligands as a Redox-Responsive Photoswitch
Authors: Otsuki Joe , Li Dong-Mei , Sato Katsuhiko , Nakagome Asako , Takido Toshio , Yoshikawa Isao , Akasaka Tetsuo , Araki Koji
Published: June 2003

A tetranuclear Ru complex linked by 4,4″-azobis(2,2′-bipyridine) (azobpy), [Ru{(azobpy)Ru(bpy)2}3][PF6]8 (bpy = 2,2′-bipyridine) has been prepared and fully characterized. Cyclic and differential pulse voltammetries show that two kinds of oxidation occur, the one at the less positive potential being assigned to the oxidation of the three peripheral Ru ions, while the other to that of the central Ru ion. On a cathodic scan, a pair of three-electron (one electron on each azobpy) reductions of azobpy ligands appear at less negative potentials than terminal bpy ligands. A low-energy metal-to-ligand charge transfer (MLCT) absorption band involving the π*-orbitals of azobpy ligands is observed in addition to the usual MLCT band involving terminal bpy ligands. These results indicate the presence of a low-lying π* level of azobpy. A selective reduction of azobpy ligands renders the non-luminescent complex into a moderately luminescent species. This light switch is reversible, implying the utility of this branched structure in energy delivering molecular systems.
UV-Vis Absorption and CD Spectroelectrochemical Studies on S-Bridged Polycobalt(III) Complexes with 2-Aminoethanethiolate or l-Cysteinate
Authors: Miyashita Yoshitaro , Yoshida Hirokazu , Sato Tomohiro , Yamada Yasunori , Fujisawa Kiyoshi , Okamoto Ken-ichi
Published: June 2003

The UV-vis spectroelectrochemical properties of S-bridged tricobalt(III) complexes [CoIII{CoIII(aet or l-cys)3}2]3+ or 3− and dicobalt(III) complexes [CoIII{CoIII(aet or l-cys)3}(dien)]3+ or 0 (aet = 2-aminoethanethiolate, l-cys = l-cysteinate, dien = diethylenetriamine) were investigated using a thin-layer quartz cell with a platinum mesh working electrode. The absorption spectroelectrochemical measurements for the tricobalt(III) complexes indicated that a two-electron reduction proceeds through pseudo two-steps, CoIIICoIIICoIII → CoIIICoIICoIII → CoIIICoIICoII for the aet complex, while through pseudo one-step for the l-cys complex. The CD spectroelectrochemical measurements demonstrated that the optically active isomer (ΔΔ form) of the aet tricobalt(III) complex loses chirality during the one-electron reduction, whereas the ΔLLLΔLLL isomer of the l-cys tricobalt(III) complex is reduced with an inversion of configuration, to form the ΛLLLΛLLL isomer. The ΛLLLΛLLL isomer is reduced with a retention of configuration. The aet and l-cys dicobalt(III) complexes were converted to the corresponding tricobalt(III) complexes by electrochemical reduction, accompanied by the release of the Co(II) ion and dien ligand. It was also elucidated that this conversion occurred with a retention of configuration.
Selective Formation and Characterization of Oxorhenium(V) Complexes with 2-Methylquinolin-8-ylamido (Hamq). Interconversion between [ReOX2(Hamq)(PPh3)] and [ReOX2(Hamq)(OPPh3)] (X = Cl, Br)
Authors: Ohashi Tetuya , Miyashita Yoshitaro , Yamada Yasunori , Fujisawa Kiyoshi , Okamoto Ken-ichi
Published: June 2003

The reactions of Re(V) precursors [ReOX3(PPh3)2] (X = Cl, Br) with 8-amino-2-methylquinoline (H2amq) gave [ReOX2(Hamq)(PPh3)] (X = Cl, 1; Br, 2) as major products and [ReOX2(Hamq)(OPPh3)] (X = Cl, 3; Br, 4) as minor products. 3 and 4 were also obtained from the reaction of 1 and 2 with an excess of free OPPh3 ligand. The crystal structures of 1, 3, and 4 were determined by X-ray analyses. These complex molecules have a distorted octahedral geometry. The Re=O bond in 1 occupies the trans position to the amido N atom of the partially deprotonated H2amq ligand. Its distance (1.724(4) Å) is long due to the trans influence of the amido N atom. The Re=O bonds in 3 and 4 occupy the trans position to the O atom of the OPPh3 ligand, indicating a geometrical conversion during the ligand substitution reaction. Some intramolecular and/or intermolecular stacking interactions are also observed in the crystalline state. All complexes were characterized in the solid state by IR, far-IR, diffuse reflectance, and 31P{1H} CP-MAS NMR spectra. From UV-vis absorption and 31P{1H} NMR spectra, it was indicated that the PPh3 and OPPh3 ligands in 1–4 are released in solution.
Study of Intermolecular Interaction for the Spin-Crossover Iron(II) Compounds
Authors: Hayami Shinya , Kawajiri Ryo , Juhász Gergely , Kawahara Takayoshi , Hashiguchi Koichiro , Sato Osamu , Inoue Katsuya , Maeda Yonezo
Published: June 2003

The thermal spin transitions of iron(II) spin-crossover compounds [Fe(PM-iPA)2(NCS)2] (1) and [Fe(PM-iPA)2(NCSe)2] (2) (PM-iPA = N-(2′-pyridylmethyl)-isopropylamine) have occurred at T1/2 = 267 K and 376 K without thermal hysteresis. No light-induced excited spin state trapping (LIESST) effect was observed for compounds 1 and 2 even at 5 K. The iron(II) spin-crossover compounds [Fe(PM-L)2(NCX)2] (PM-A = N-(2′-pyridylmethyl)-aniline, PM-BiA = N-(2′-pyridylmethyl)-4-aminobiphenyl, PM-TeA = N-(2′-pyridylmethyl)-4-aminoterphenyl, PM-PEA = N-(2′-pyridylmethyl)-4-(phenylethynyl)aniline, and PM-AzA = N-(2′-pyridylmethyl)-4-(phenylazo)aniline; X = S and Se) with ligands having π-systems have exhibited the LIESST effect, and the critical LIESST temperature, Tc(LIESST), has been observed. The compounds 1 and 2 are crystallized at Pnna and C2/c at 298 K, respectively, and the space groups of the compounds remained unchanged until 100 K, although the compounds show the spin transition. The molecular packing structure and thermodynamic parameters of the spin transitions calculated from the magnetic susceptibility curves suggest that compounds 1 and 2 have no strong intermolecular interactions between the complexes, while the compounds with π-system ligands form π–π intra- and intermolecular interactions between the ligands. Our conclusion is that the intermolecular interactions play an important role in trapping a light-induced metastatble state.
A New Class of S-Bridged CoIIIMCoIII (M = NiII, PdII) Trinuclear Complexes with Mixed Aliphatic and Aromatic Thiolate Ligands: Synthesis, Characterization, and Stereochemistry
Authors: Hirotsu Masakazu , Endo Ryota , Yoshimura Takashi , Konno Takumi
Published: June 2003

Treatments of a mixture of CoCl2·6H2O, HL (Hpyt = 2-pyridinethiol, Hpymt = 2-pyrimidinethiol), and triethylamine with [Ni(aet)2] (aet = 2-aminoethanethiolate) in methanol led to the isolation of novel S-bridged CoIIINiIICoIII trinuclear complexes, [Ni{Co(aet)2(pyt)}2]2+ ([1]2+) and [Ni{Co(aet)2(pymt)}2]2+ ([2]2+), in which a NiII ion is coordinated by four aet S atoms from two tris(thiolato)-type [Co(aet)2(pyt or pymt)] units. The NiII ion in both [1]2+ and [2]2+ was replaced by a PdII ion through the reaction with Na2[PdCl4] in water, giving the corresponding CoIIIPdIICoIII trinuclear complexes, [Pd{Co(aet)2(pyt)}2]2+ ([3]2+) and [Pd{Co(aet)2(pymt)}2]2+ ([4]2+). The related CoIIIPdIICoIII trinuclear complexes composed of one [Co(aet)2(pyt or pymt)] and one [Co(aet)2(en)]+ units, [Pd{Co(aet)2(pyt)}{Co(aet)2(en)}]3+ ([5]3+) and [Pd{Co(aet)2(pymt)}{Co(aet)2(en)}]3+ ([6]3+), were also prepared by the reactions of a 1:1 mixture of [Ni{Co(aet)2(pyt or pymt)}2]2+ and [Ni{Co(aet)2(en)}2]4+ with Na2[PdCl4] in water, followed by the column chromatographic separation. The electronic absorption, CD, and NMR spectroscopies indicated that these CoIIIMCoIII trinuclear complexes produce only the racemic (ΔΔ⁄ΛΛ) isomer, in which each [Co(aet)2(pyt or pymt)] unit adopts a mer(S) configuration with two aet N atoms at the apical positions. For [1]2+, [2]2+, [3]2+, and [4]2+, another geometrical isomerism of syn–anti, which arises from the arrangement of the two terminal pyt or pymt S atoms, was identified.
Optical Properties of an Azobenzene Based Octupolar Near-IR Dye
Authors: Sengupta Saumitra , Sadhukhan Subir Kumar
Published: June 2003

Based on an azobenzene derived octupolar scaffold, a trigonally symmetric near-IR dye 4 (λmax 995 nm) has been prepared from common starting materials. The dye showed a pH dependent as well as a solvent dependent absorption behavior.
Photoinduced Electron Transfer Reactions of 3H-Pyrazole Derivatives. Formation of Solvent Adduct by Specific Sensitizer
Authors: Karatsu Takashi , Shiochi Nobuo , Aono Takumi , Miyagawa Nobukazu , Kitamura Akihide
Published: June 2003

3H-pyrazoles were photolyzed in the presence of 2,4,6-triphenylpyrylium tetrafluoroborate (TPP+) or 9,10-dicyanoanthracene (DCA) as a sensitizer. The obtained products were different depending on the sensitizers employed. The cyclopropene derivatives were produced in the cases of the DCA and TPP+ sensitizations and a solvent adduct was obtained for the TPP+ sensitization reaction. The difference in products is explained by the rates of the back electron transfer from the electron accepted sensitizers to the radical cation intermediates. In the DCA sensitization, the absorption band of the diazoalkene was observed but in the TPP+ sensitization it was not observed. From these results, it is apparent that the back electron transfer rates of the DCA sensitization reactions are faster than those of the TPP+ sensitization reactions.
Metallation Reactions on 2,2′-Bis(diphenylphosphinoyl)-1,1′-binaphthyl [BINAP(O)2]
Authors: Widhalm Michael , Mereiter Kurt
Published: June 2003

The behavior of BINAP(O)2 upon treatment with lithium or magnesium amides under various conditions has been studied. With 2,2,6,6-tetramethylpiperidinomagnesium bromide, the ortho positions of opposed phenyl rings were selectively metallated, forming stable intermediates, while the use of lithium amides caused rearrangements with displacement of one diphenylphosphinoyl group and the formation of strained P-heterocycles (2, 5, 6) with unusual architectures. Monophosphine oxides 2 and 3a have been reduced to phosphines 13 and 14 in good yield, while substituted BINAP(O)2 derivatives failed to give the desired diphosphines. The stereochemistry of six phosphine oxides (2, 3a, 5, 8, 9, 11a) and one phosphine (13) has been elucidated by crystal structure determinations.
Preparation and Magnetic Properties of Radical Anion Salts Derived from Styrylpyryliums and the Corresponding Photo-Dimers
Authors: Nakatsuji Shin′ichi , Ogawa Yuya , Akutsu Hiroki , Yamada Jun-ichi
Published: June 2003

The preparation and magnetic properties of organic radical anion salts derived from styrylpyrylium derivatives 1a and 2a are described and compared to those of the corresponding photo-dimers. The magnetic properties of the radical anions for TCNQ salt 1b and TCNQF4 salt 1c are rather different, showing antiferromagnetic interactions based on the 1-D Heisenberg model in the former, and ferromagnetic interactions in the latter. This difference is considered to be a result of the fairly large difference in their crystal structures. A considerable change in the magnetic properties was found between the radical anion salts of monomers and the corresponding photo-dimers, in which magnetic susceptibilities are largely diminished.
Palladium-Catalyzed Carbonylation of Homoallylic Amine Derivatives in the Presence of a Copper Co-catalyst
Authors: Mizutani Takanori , Ukaji Yutaka , Inomata Katsuhiko
Published: June 2003

γ-Lactams were synthesized from N-tosylhomoallylamines by a carbonylation reaction catalyzed by palladium and copper salts under the normal pressure of CO and O2 at room temperature. Monocarbonylation proceeded by the use of [PdCl2(CH3CN)2] and CuCl2 to afford 3-methyl-2-pyrrolidones, while the use of PdCl2 and CuCl switched the reaction from monocarbonylation to dicarbonylation to produce alkyl 2-oxopyrrolidine-3-acetate in good yields, respectively.
Convenient Synthesis of 4-Hydroxy-1,2-dihydroquinoline-3-carboxylate Derivatives and 4-Oxo-1,2,3,4-tetrahydroquinoline-3-carboxylates
Authors: Kobayashi Kazuhiro , Nakahashi Ryoji , Mano Masaaki , Morikawa Osamu , Konishi Hisatoshi
Published: June 2003

A magnesium amide-induced sequential conjugate addition/Claisen-type condensation between methyl 2-(methylamino)benzoate and α,β-unsaturated carboxylates has been found to provide convenient access to 4-hydroxy-1,2-dihydroquinoline-3-carboxylate derivatives and 4-oxo-1,2,3,4-tetrahydroquinoline-3-carboxylates.
Preparation and Structural Characterization of Bis[tris(trimethylsilyl)germyl]zinc, [(Me3Si)3Ge]2Zn
Authors: Nanjo Masato , Oda Takashi , Mochida Kunio
Published: June 2003

Bis[tris(trimethylsilyl)germyl]zinc, [(Me3Si)3Ge]2Zn, was prepared by the reaction of [tris(trimethylsilyl)germyl]lithium, (Me3Si)3GeLi(thf), with zinc chloride, ZnCl2, and by the reaction of tris(trimethylsilyl)germane, (Me3Si)3GeH, with diethylzinc, Et2Zn. The molecular structure of [(Me3Si)3Ge]2Zn was determined by spectroscopic and X-ray diffraction methods. In [(Me3Si)3Ge]2Zn, the two tris(trimethylsilyl)germyl ligands, (Me3Si)3Ge, are bonded in a linear fashion to the zinc atom and are staggered with respect to each other. The reactions of bis(germyl)zinc with substrates were also examined.
Sequential Interpenetrating Polymer Networks Synthesized from Polyester Based Polyurethane and Poly(butyl methacrylate)
Authors: Athawale Vilas D , Pillay Priti S
Published: June 2003

In this article we review the synthesis and morphology as well as the physical and mechanical properties of full- and semi-interpenetrating polymer networks (IPNs) obtained from polyester based polyurethane (PU) and poly(butyl methacrylate) (PBMA). The polyurethane was subsequently interpenetrated with butyl methacrylate monomer and ethylene glycol dimethacrylate as a crosslinker by radical polymerization using benzoyl peroxide as an initiator. Both full and semi IPNs (PU/PBMA IPNs) were obtained as soft films when cast in a glass mold. All PU/PBMA IPNs were characterized with respect to the swelling (%), apparent densities, thermal stability, morphology and mechanical properties. The morphology of the IPNs was studied by scanning electron microscopy. The effects of variations of the blend ratios on the above-mentioned properties were examined. Increasing the polyurethane component in the composite system notably increased the mechanical properties of all the IPNs. Full-IPNs exhibited higher apparent densities, mechanical properties and thermal stability than the corresponding semi-IPNs.
Preparation and Characterization of Nanostructured Electrodes by Electrophoretically Co-deposition of Pd and Pt Nanoparticles
Authors: Lai Long-Biao , Chen Dong-Hwang , Huang Ting-Chia
Published: June 2003

A novel Pd-doped Pt/Ti nanostructured electrode was prepared by the electrophoretic co-deposition of Pt and Pd nanoparticles on a Ti support in a reverse micellar solution of water/Aerosol OT/isooctane, followed by a heat treatment in air at 400 °C. The total catalyst loading (Pt and Pd) was fixed at 0.015 mmol/cm2, referred to the geometric area. The crystal structure, surface morphology, and elemental distribution of the resultant electrode were characterized by XRD, SEM, and SEM-WDS, respectively. The surface composition and electrocatalytic activity of the electrode were investigated by cyclic voltammetry in a solution of 0.5 M H2SO4 and a mixed solution of 0.1 M CH3OH and 1.0 M NaOH, respectively. The composition on the electrode surface could be controlled by adjusting the composition of the electrodeposition solution. Also, with increasing the Pd content on the electrode surface, the electrocatalytic activity of the Pd-doped Pt/Ti nanostructured electrodes for the oxidation of CH3OH first increased, and then decreased after reaching a maximum at a surface composition of 20 atom % Pd. When the Pd content on the electrode surface was larger than 60%, the electrocatalytic activity of the Pd-doped Pt/Ti nanostructured electrode was lower than that of the Pt/Ti electrode because most active sites were occupied by the relatively inactive Pd. This result revealed that the activity enhancement or diminution resulted from the doping of Pd in Pt at an atomic level might be achieved via the interaction between Pt and Pd nanoparticles. In addition, at a surface composition of 20 atom % Pd, the current density at 25 °C was 55 mA/cm2, revealing that the resultant electrode had a rather high current density and specific activity.
Vapochromism of Ionic Dyes in Thin Films of Sugar Gels
Authors: Matsushima Ryoka , Nishimura Naoko , Goto Kuniaki , Kohno Yoshiumi
Published: June 2003

Solid thin films of sugar gels containing ionic dyes, such as flavylium and thionine salts, exhibit extensive and vapor-specific color changes upon exposure to volatile organic compounds, such as methanol, ethanol, acetone, benzene, ether, and pyridine. Some of them show good vapochromic reversibility after repeated exposures, although extensive degradation occurs with pyridine vapor. Vapochromism has been explained in terms of solvation and stabilization of the dye molecules by permeated vapors, resulting in a shift of dye aggregation–deaggregation equilibria.
New Approach to Lowering of the Overvoltage for Oxygen Evolution on RuO2 and Related Metal-Oxide Electrodes by Ion Implantation
Authors: Tsujiko Akira , Kajiyama Kenji , Kanaya Masatoshi , Murakoshi Kei , Nakato Yoshihiro
Published: June 2003

The ion implantation method is applied to the improvement of the oxygen-evolution activity for metal oxide electrodes. The implantation of metal ions such as Co+, Zn+, and Ru+ into nanocrystalline RuO2 and RuxTi1−xO2 (x = 1/2 and 2/3) film electrodes caused negative shifts of current density (j) vs potential (U) curves for oxygen evolution by about 20–100 mV, indicating the lowering of the overvoltage for oxygen evolution. Detailed experiments have shown that the lowering of the overvoltage is neither due to a change in the chemical composition of the electrode surface nor due to an increase in the effective area of the electrode surface, but rather is due to production of certain crystal defects (such as atomic gaps) that can act as active sites for oxygen evolution. The result is of much interest, suggesting that the control of surface defect structures is a promising approach for the improvement of the oxygen evolution activity.
Electrolyte-promoted Easy Separation of Suspended TiO2 Particles with a Solids Retaining Type Centrifuge in Combination with Photoreactor to Degrade Dibutyl Phthalate
Authors: Hasegawa Kiyoshi , Ito Tomonori , Nakamura Wakako , Nagai Machi , Kagaya Shigehiro
Published: June 2003

Adjustment of a TiO2 suspension containing electrolytes to the isoelectric point (IEP) enabled easy separation of fine particles of TiO2 by a solids-retaining type centrifuge, which was combined with a batch photoreactor. Optimum separation conditions and reusability of the recovered TiO2 for the degradation of dibutyl phthalate (DBP) were examined. For synthesized waste water samples (5 μM DBP in tap and well water), suspended TiO2 was easily separated without addition of electrolytes after degradation of DBP.
Fabrication of Hollow Silica Microspheres through the Self-assembly Behavior of Polymers in W/O Emulsion
Authors: Park Jae-Hyung , Bae Seong-Youl , Oh Seong-Geun
Published: June 2003

The major focus of this study is on understanding the mechanism of formation of the hollow silica microspheres through the self-assembly behavior of polymers (PEG and PVP) in W/O emulsion and studying their particle morphology, particle size, and pore structure depending on the experimental conditions.
Growth of Pure β-Si3N4 Nanorods from the Synergic Nitrogen Sources
Authors: Xu Fen , Zhang Xu , Xi Wang , Hong Jie , Xie Yi
Published: June 2003

Pure β-Si3N4 nanorods with of 30–60 nm and length of 180–300 nm were synthesized from a mild benzene-thermal route at 450 °C, starting from SiCl4 and the synergic nitrogen sources of NaNH2 and NH4Cl. The obtained sample was characterized by XRD, TEM and XPS. The one-dimensional growth mechanism is assumed to be a vapor-liquid-solid (VLS) process.
Synthesis of 5-(Alkylphenylphosphoryl)-5-methyl-3,4-dihydro-2H-pyrroline N-Oxide as a New Spin Trapping Reagent
Authors: Shioji Kosei , Tsukimoto Shigeyuki , Tanaka Hidehiko , Okuma Kentaro
Published: June 2003

Novel DMPO analogues attached to a phenyl group at the phosphorus atom were synthesized and examined for their ability in the spin trapping of oxygen-centered radicals. The lipophilicities of these analogues were higher than those of DMPO.
Double Nucleophilic Addition of Ketene Silyl (Thio)acetals and Trimethylsilyl Cyanide to α,β-Unsaturated Aldimines Promoted by Aluminum Chloride
Authors: Shimizu Makoto , Kamiya Makiko , Hachiya Iwao
Published: June 2003

In the presence of AlCl3, a mixture of ketene silyl (thio)acetal and trimethylsilyl cyanide underwent 1,4- and subsequent 1,2-addition, respectively, with α,β-unsaturated imines to give ethyl(S-alkyl) 5-amino-6-cyanopentanoates in good yields.
Novel Cerium(III)–(R)-BNP Complex as a Storable Chiral Lewis Acid Catalyst for the Enantioselective Hetero-Diels–Alder Reaction
Authors: Hayano Tetsuji , Sakaguchi Toshiaki , Furuno Hiroshi , Ohba Masaaki , Okawa Hisashi , Inanaga Junji
Published: June 2003

A novel Ce(III)–(R)-BNP complex was conveniently prepared from CAN and (R)-BNP–Na, then successfully used as a homogeneous catalyst for the asymmetric hetero-Diels–Alder reaction affording, after acidic work-up, 6-substituted 5,6-dihydro-4H-pyran-4-one derivatives with high enantioselectivities (up to 94% ee). A mechanistically interesting positive nonlinear effect was also observed.
Selective Oxidation of Nitric Oxide against Nitrite by Oxo-iron(IV) Porphyrin at an ITO Electrode
Authors: Lei Jianping , Trofimova Natalia S , Ikeda Osamu
Published: June 2003

Electrochemical and spectroelectrochemical experiments at an ITO electrode clarified that O=FeIV(4-TMPyP) was formed via 1e− + 1H+ oxidation process of FeIII(4-TMPyP) in pH 7.4 PBS and the electrogenerated O=FeIV(4-TMPyP) selectively reacted with NO to give NO2− as the final product through an electrocatalytic cycle.
A Novel Ring Expansion of the Holey Ketolactam Derivative of C60
Authors: Iwamatsu Sho-ichi , Ono Fumiaki , Murata Shizuaki
Published: June 2003

The migrative addition reaction of phenylhydrazine to the ketolactam derivative of C60 occurred with a regioselective cage scission to give a 15-membered ring-opened fullerene bearing a methylene carbon and an acenaphthenequinone monophenylhydrazone unit along the orifice.
The Reaction of Metallothionein-3 with DTNB
Authors: Zheng Qi , Cai Bin , Chen Dong , Yu Wen-Hao , Wang Yun-Hua , Huang Zhong-Xian
Published: June 2003

MT3 reacts with DTNB by a biphasic process, which roots from the difference in reactions between two domains with DTNB. The β-domain reacts with DTNB faster, implying that the CPCP motif distorts the peptide and leads to the Cd3S9 cluster more accessible to solvent. This reaction is a SN2 process according to the activation entropy.
An Experimental Attempt to Identify a Moving Molecular Moiety in a Solvent Matrix
Authors: Goto Yoshitaka , Sugita Keijiro , Takahashi Toru , Ohga Yasushi , Asano Tsutomu
Published: June 2003

It was experimentally demonstrated that microscopic friction between a reactant molecule and the surrounding solvent during a unimolecular structural change increased with increasing bulkiness of substituents and it is suggested that this dependence can be used to identify a moving molecular moiety in the reactant inside of a solvation shell.
Enzymatic Synthesis and Antioxidant Property of Poly(allylamine)–Catechin Conjugate
Authors: Chung Joo Eun , Kurisawa Motoichi , Tachibana Yoichi , Uyama Hiroshi , Kobayashi Shiro
Published: June 2003

A polymeric conjugate containing a catechin group has been synthesized by laccase-catalyzed oxidation of catechin in the presence of poly(allylamine). The resulting conjugate showed a good antioxidant property against LDL peroxidation induced by a free radical.
A structural, phylogenetic, and functional study of 15.5-kD/Snu13 protein binding on U3 small nucleolar RNA
Authors: MARMIER-GOURRIER NATHALIE , CLÉRY ANTOINE , SENTY-SÉGAULT VÉRONIQUE , CHARPENTIER BRUNO , SCHLOTTER FLORENCE , LECLERC FABRICE , FOURNIER RÉGIS , BRANLANT CHRISTIANE
Published: June 2003

The 15.5-kD protein and its yeast homolog Snu13p bind U4 snRNA, U3 snoRNA, and the C/D box snoRNAs. In U4 snRNA, they associate with a helix-bulge-helix (K-turn) structure. U3 snoRNA contains two conserved pairs of boxes, C′/D and B/C, which were both expected to bind the 15.5-kD/Snu13 protein. Only binding to the B/C motif was experimentally demonstrated. Here, by chemical probing of in vitro reconstituted RNA/protein complexes, we demonstrate the independent binding of the 15.5-kD/Snu13 protein to each of the two motifs. Due to a highly reduced stem I (1 bp), the K-turn structure is not formed in the naked B/C motif. However, gel-shift experiments revealed a higher affinity of Snu13p for the B/C motif, compared to the C′/D motif. A phylogenetic analysis of U3 snoRNA, coupled with an analysis of Snu13p affinity for variant yeast C′/D and B/C motifs, and a study of the functionality of a truncated yeast U3 snoRNA carrying base substitutions in the C′/D and B/C motifs, revealed that conservation of the identities of residues 2 and 3 in the B/C K-turn is more important for Snu13p binding and U3 snoRNA function, than conservation of the identities of corresponding residues in the C′/D K-turn. This suggests that binding of Snu13p to K-turns with a very short helix I imposes sequence constraints in the bulge. Altogether, the data demonstrate the strong importance of the binding of the 15.5-kD/Snu13 protein to the C′/D and B/C motifs for both U3 snoRNP assembly and activity.
Biochemical analysis and scanning force microscopy reveal productive and nonproductive ADAR2 binding to RNA substrates
Authors: KLAUE YVONNE , KÄLLMAN ANNIKA M. , BONIN MICHAEL , NELLEN WOLFGANG , ÖHMAN MARIE
Published: June 2003

Scanning force microscopy (SFM) can be used to image biomolecules at high resolution. Here we demonstrate that single-molecule analysis by SFM complements biochemical data on RNA protein binding and can provide information that cannot be obtained by the usual biochemical methods. We have used this method to study the interaction between the RNA editing enzyme ADAR2 and RNA transcripts containing selective and nonselective editing sites. The natural selectively edited R/G site from glutamate receptor subunit B (GluR-B) was inserted into an RNA backbone molecule consisting of a completely double-stranded (ds) central part and incompletely paired ends derived from potato spindle tuber viroid (PSTVd). This molecule was efficiently edited at the R/G site, but promiscuous editing occurred at nonselective sites in the completely double-stranded region. The construct was also used to analyze binding of ADAR2 to wild-type and modified R/G editing sites in relation to binding at other nonselectively edited sites. Editing analysis together with SFM allow us to differentiate between binding and enzymatic activity. ADAR2 has been reported to have a general affinity to dsRNA. However, we show that there is a prominent bias for stable binding at sites selectively edited over other edited sites. On the other hand, promiscuous editing at nonselective sites apparently results from transient binding of the enzyme to the substrate. Furthermore, we find distinct sites with nonproductive binding of the enzyme.
The dynamic nature of the four-way junction of the hepatitis C virus IRES
Authors: MELCHER SONYA E. , WILSON TIMOTHY J. , LILLEY DAVID M.J.
Published: June 2003

Translation is initiated within the RNA of the hepatitis C virus at the internal ribosome entry site (IRES). The IRES is a 341-nucleotide element that contains a four-way helical junction (IIIabc) as a functionally important element of the secondary structure. The junction has three additional, nonpaired nucleotides at the point of strand exchange on one diagonal. We have studied the global conformation and folding of this junction in solution, using comparative gel electrophoresis and steady-state and time-resolved fluorescence resonance energy transfer. In the absence of divalent metal ions, the junction adopts an extended-square structure, in contrast to perfect four-way RNA junctions, which retain coaxial helical stacking under all conditions. The IIIabc junction is induced to fold on addition of Mg2+, by pairwise coaxial stacking of arms, into the conformer in which the unpaired bases are located on the exchanging strands. Fluorescence lifetime measurements indicate that in the presence of Mg2+ ions, the IIIabc junction exists in a dynamic equilibrium comprising approximately equal populations of antiparallel and parallel species. These dynamic properties may be important in mediating interactions between the IRES and the ribosome and initiation factors.
A snoRNA that guides the two most conserved pseudouridine modifications within rRNA confers a growth advantage in yeast
Authors: BADIS GWENAEL , FROMONT-RACINE MICHELINE , JACQUIER ALAIN
Published: June 2003

Ribosomal RNAs contain a number of modified nucleotides. The most abundant nucleotide modifications found within rRNAs fall into two types: 2′-O-ribose methylations and pseudouridylations. In eukaryotes, small nucleolar guide RNAs, the snoRNAs that are the RNA components of the snoRNPs, specify the position of these modifications. The 2′-O-ribose methylations and pseudouridylations are guided by the box C/D and box H/ACA snoRNAs, respectively. The role of these modifications in rRNA remains poorly understood as no clear phenotype has yet been assigned to the absence of specific 2′-O-ribose methylations or pseudouridylations. Only very recently, a slight translation defect and perturbation of polysome profiles was reported in yeast for the absence of the Ψ at position 2919 within the LSU rRNA. Here we report the identification and characterization in yeast of a novel intronic H/ACA snoRNA that we called snR191 and that guides pseudouridylation at positions 2258 and 2260 in the LSU rRNA. Most interestingly, these two modified bases are the most conserved pseudouridines from bacteria to human in rRNA. The corresponding human snoRNA is hU19. We show here that, in yeast, the presence of this snoRNA, and hence, most likely, of the conserved pseudouridines it specifies, is not essential for viability but provides a growth advantage to the cell.
An siRNA ribonucleoprotein is found associated with polyribosomes in Trypanosoma brucei
Authors: DJIKENG APPOLINAIRE , SHI HUAFANG , TSCHUDI CHRISTIAN , SHEN SHUIYUAN , ULLU ELISABETTA
Published: June 2003

Genetic interference by double-stranded RNA (dsRNA) or RNA interference (RNAi) triggers the sequence-specific degradation of cellular transcripts. The mediators of mRNA degradation are small interfering RNAs (siRNAs). Here, we report that in Trypanosoma brucei, 10%–20% of siRNAs cosediment with polyribosomes. Preventing the assembly of ribosomes on mRNAs results in a concomitant decrease of siRNAs sedimenting as high-molecular-weight complexes. We further provide evidence that siRNAs are associated with translating ribosomes and that this association is mediated by a 70-kD ribonucleoprotein complex.
Aminoacylation of an unusual tRNACys from an extreme halophile
Authors: EVILIA CARYN , MING XIAOTIAN , DASSARMA SHILADITYA , HOU YA-MING
Published: June 2003

The extreme halophile Halobacterium species NRC-1 overcomes external near-saturating salt concentrations by accumulating intracellular salts comparable to those of the medium. This raises the fundamental question of how halophiles can maintain the specificity of protein–nucleic acid interactions that are particularly sensitive to high salts in mesophiles. Here we address the specificity of the essential aminoacylation reaction of the halophile, by focusing on molecular recognition of tRNACys by the cognate cysteinyl-tRNA synthetase. Despite the high salt environments of the aminoacylation reaction, and despite an unusual structure of the tRNA with an exceptionally large dihydrouridine loop, we show that aminoacylation of the tRNA proceeds with a catalytic efficiency similar to that of its mesophilic counterparts. This is manifested by an essentially identical Km for tRNA to those of the mesophiles, and by recognition of the same nucleotide determinants that are conserved in evolution. Interestingly, aminoacylation of the halophile tRNACys is more closely related to that of bacteria than eukarya by placing a strong emphasis on features of the tRNA tertiary core. This suggests an adaptation to the highly negatively charged tRNA sugar-phosphate backbone groups that are the key elements of the tertiary core.
Inhibition of the protein kinase PKR by the internal ribosome entry site of hepatitis C virus genomic RNA
Authors: VYAS JASHMIN , ELIA ANDROULLA , CLEMENS MICHAEL J.
Published: June 2003

Translation of the hepatitis C genome is mediated by internal ribosome entry on the structurally complex 5′ untranslated region of the large viral RNA. Initiation of protein synthesis by this mechanism is independent of the cap-binding factor eIF4E, but activity of the initiator Met-tRNAf-binding factor eIF2 is still required. HCV protein synthesis is thus potentially sensitive to the inhibition of eIF2 activity that can result from the phosphorylation of the latter by the interferon-inducible, double-stranded RNA-activated protein kinase PKR. Two virally encoded proteins, NS5A and E2, have been shown to reduce this inhibitory effect of PKR by impairing the activation of the kinase. Here we present evidence for a third viral strategy for PKR inhibition. A region of the viral RNA comprising part of the internal ribosome entry site (IRES) is able to bind to PKR in competition with double-stranded RNA and can prevent autophosphorylation and activation of the kinase in vitro. The HCV IRES itself has no PKR-activating ability. Consistent with these findings, cotransfection experiments employing a bicistronic reporter construct and wild-type PKR indicate that expression of the protein kinase is less inhibitory towards HCV IRES-driven protein synthesis than towards cap-dependent protein synthesis. These data suggest a dual function for the viral IRES, with both a structural role in promoting initiation complex formation and a regulatory role in preventing inhibition of initiation by PKR.
In vitro selection for sense codon suppression
Authors: FRANKEL ADAM , ROBERTS RICHARD W.
Published: June 2003

The universal genetic code links the 20 naturally occurring amino acids to the 61 sense codons. Previously, the UAG amber stop codon (a nonsense codon) has been used as a blank in the code to insert natural and unnatural amino acids via nonsense suppression. We have developed a selection methodology to investigate whether the unnatural amino acid biocytin could be incorporated into an mRNA display library at sense codons. In these experiments we probed a single randomized NNN codon with a library of 16 orthogonal, biocytin-acylated tRNAs. In vitro selection for efficient incorporation of the unnatural amino acid resulted in templates containing the GUA codon at the randomized position. This sense suppression occurs via Watson-Crick pairing with similar efficiency to UAG-mediated nonsense suppression. These experiments suggest that sense codon suppression is a viable means to expand the chemical and functional diversity of the genetic code.
DnaK-facilitated ribosome assembly inEscherichia colirevisited
Authors: ALIX JEAN-HERVÉ , NIERHAUS KNUD H.
Published: June 2003

Assembly helpers exist for the formation of ribosomal subunits. Such a function has been suggested for the DnaK system of chaperones (DnaK, DnaJ, GrpE). Here we show that 50S and 30S ribosomal subunits from anEscherichia coli dnaK-null mutant (containing a disrupteddnaKgene) grown at 30°C are physically and functionally identical to wild-type ribosomes. Furthermore, ribosomal components derived from mutant 30S and 50S subunits are fully competent for in vitro reconstitution of active ribosomal subunits. On the other hand, the DnaK chaperone system cannot circumvent the necessary heat-dependent activation step for the in vitro reconstitution of fully active 30S ribosomal subunits. It is therefore questionable whether the requirement for DnaK observed during in vivo ribosome assembly above 37°C implicates a direct or indirect role for DnaK in this process.
RNA-binding activity of translation initiation factor eIF4G1 from Saccharomyces cerevisiae
Authors: BERSET CATHERINE , ZURBRIGGEN ANDREAS , DJAFARZADEH SIAMAK , ALTMANN MICHAEL , TRACHSEL HANS
Published: June 2003

We identified and mapped RNA-binding sites of yeast Saccharomyces cerevisiae translation initiation factor eIF4G1 and examined their importance for eIF4G1 function in vitro and in vivo. Yeast eIF4G1 binds to single-stranded RNA with three different sites, the regions of amino acids 1–82 (N terminus), 492–539 (middle), and 883–952 (C terminus). The middle and C-terminal RNA-binding sites represent RS (arginine and serine)-rich domains; the N-terminal site is asparagine-, glutamine- and glycine-rich. The three RNA-binding sites have similar affinity for single-stranded RNA, whereas the affinity for single-stranded RNA full-length eIF4G1 is about 100-fold higher (approximate Kd of 5 × 10−8 M). Replacement of the arginine residues in the middle RS site by alanine residues abolishes its RNA-binding activity. Deletion of individual RNA-binding sites shows that eIF4G1 molecules lacking one binding site are still active in supporting growth of yeast cells and translation in vitro, whereas eIF4G1 molecules lacking two or all three RNA-binding sites are strongly impaired or inactive. These data suggest that RNA-binding activity is required for eIF4G1 function.