Synthesis of polyisocyanide derived from phenylalanine and its temperature‐dependent helical conformation

Screw‐sense‐selective polymerization of the chiral isocyanide monomers derived from phenylalanine with NiCl₂ as a catalyst in methanol to yield helical‐conjugated polyisocyanide was investigated with respect to the thermal stability of its helical conformation. Poly(1‐tert‐butoxycarbonyl‐2‐phenylethyl isocyanide) (poly 1c ) took a stable helical conformer independent of the polymerization temperature. In poly(1‐ethoxycarbonyl‐2‐phenylethyl isocyanide) (poly 2c ), which had slightly smaller side groups, the helical conformation was thermally destabilized. The specific rotation and circular dichroism of poly 2c prepared at temperatures greater than 40 °C were considerably depressed in comparison with the values for poly 2c prepared at or below room temperature. Additionally, poly 2c prepared at low temperatures exhibited reversible temperature‐dependent specific rotation and circular dichroism, whereas poly 1c showed few changes. It is suggested that polyisocyanide derived from phenylalanine takes various helical conformers (i.e., from tightly to loosely coiled helices), the thermal stability of which depends on the size of the side group. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 399–408, 2002     

Localized chemical stimulation to micropatterned cells using multiple laminar fluid flows

Micropatterns of the electrically conjugating cardiomyocytes were prepared on a single cell level by microcontact printing (microCP), and the localized chemical stimulations were applied to the cellular pattern using multiple laminar flows. The locally delivered 1-octanol inactivated part of the myocyte patterns, while the other areas retained the activity showing spontaneous and synchronous pulsatility. Since both the cells and flows were well defined as micropatterns and each integrated on a chip, the obtained results simply demonstrate the cellular responses in a single-cell network.     

Preparation of Au/TiO2 nanocomposites and their catalytic activity for DPPH radical scavenging reaction

Au/TiO2 nanocomposites have been prepared by UV photolysis or chemical reduction of a Au(III) complex formed on a spherical or a rodlike TiO2 support, and their catalytic activity for 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging reaction was investigated. The chemical reduction with dimethylamine borane (DMAB) provided smaller gold nanoparticles than those synthesized by UV photolysis. Type of the TiO2 also affected the size of gold particles; smaller gold particles were deposited on the spherical TiO2 support than on rodlike one. For the radical scavenging reaction, the Au/TiO2 nanocomposites prepared by chemical reduction exhibited a higher catalytic activity than those photochemically prepared, and rodlike TiO2 provided a higher activity than spherical one. The effects of preparation methods and type of TiO2 supports on the catalytic activity are discussed.     

Association behavior of fluorine-containing and non-fluorine-containing methacrylate-based amphiphilic diblock copolymer in aqueous media

Fluorine-containing amphiphilic block copolymers, poly(sodium methacrylate)-block-poly(nonafluorohexyl methacrylate) (NaMAm-b-NFHMAn) (m:n = 61:12, 72:33, 64:57), and the corresponding non-fluorine-containing amphiphilic block copolymer, poly(sodium methacrylate)-block-poly(hexyl methacrylate) (NaMAm-b-HMAn) (m:n = 64:10, 69:37, 67:50), were synthesized. Both polyNaMA-b-polyNFHMA and polyNaMA-b-polyHMA formed micelles above critical micelle concentrations, (cmc's), around 3 x 10(-5) to 1 x 10(-4) mol/L, while neither polymer decreased surface tension of aqueous solutions. The size and shape of the micelles were examined by dynamic light scattering, small-angle neutron scattering, and small-angle X-ray scattering. PolyNaMA-b-polyHMA appeared to form only spherical micelles, while polyNaMA-b-polyNFHMA with a long NFHMA segment formed both spherical and rodlike micelles. The micelles of fluorine-containing block copolymers were obviously larger than those of non-fluorine-containing block copolymers with the same chain length and the same hydrophilic/hydrophobic chain ratio. The fluorine-containing block copolymer selectively solubilized fluorinated dye into the water phase when a mixture of decafluorobiphenyl and 2,6-dimethylnaphthalene was added to the micelle solution.     

Synthesis and evaluation of 1-arylsulfonyl-3-piperazinone derivatives as factor Xa inhibitors IV. A series of new derivatives containing a spiro[5H-oxazolo[3,2-a]pyrazine-2(3H),4'-piperidin]-5-one skeleton

In the course of development of factor Xa (FXa) inhibitor in an investigation involving the synthesis of 1-arylsulfonyl-3-piperazinone derivatives, we found new compounds containing a unique spiro skeleton. Among such compounds, (-)-7-[(6-chloro-2-naphthalenyl)sulfonyl]tetrahydro-8a-(methoxymethyl)-1'-(4-pyridinyl)-spiro[5H-oxazolo[3,2-a]pyrazine-2(3H),4'-piperidin]-5-one (28, M55529) had activity more favorable than those of previously reported compounds. The inhibitory activity of M55529 for FXa is IC(50)=2 nM, with high selectivity for FXa over thrombin and trypsin.     

Distannane mediated reaction of N-acyliminium ion pools with alkyl halides. A chain mechanism involving radical addition followed by electron transfer

Hexabutyldistannane was found to be an effective mediator allowing the reaction of N-acyliminium ion pools with alkyl halides. A chain mechanism involving the addition of an alkyl radical generated from an alkyl halide to an N-acyliminium ion followed by the one-electron reduction of the resulting radical-cation by distannane was proposed.     

Neutron in-beam Mössbauer spectroscopy of iron disulfide at 298 and 78 K

Emission Mössbauer spectra of ⁵⁷Fe arising from the ⁵⁶Fe(n, γ)⁵⁷Fe reaction in two crystal forms of iron disulfide were measured at room temperature and liquid nitrogen temperature. Both forms exhibited two doublets assignable to the parent material and the new species produced by the nuclear reaction. At low temperature three doublets explained the spectra obtained. Production of thermally unstable species after the neutron capture reaction was suggested.     

Spectroscopic and excited-state properties of tri-9-anthrylborane II: Electroabsorption and electrofluorescence spectra

Electroabsorption and electrofluorescence spectroscopies were conducted for tri-9-anthrylborane (TAB) doped in poly(methyl methacrylate) films (1.0 mol %) to reveal the spectroscopic and excited-state properties of the compound. TAB showed three distinct absorption bands: bands I [(19 - 25) x 10(3) cm(-1)], II [(25-31) x 10(3) cm(-1)], and III (>31 x 10(3) cm(-1)). The electroabsorption spectrum demonstrated that the electronic transitions in bands I and III accompanied electric dipole moment changes (Deltamu), while the change in the molecular polarizability contributed mainly to electroabsorption band II. Because of the similarities of the electroabsorption spectrum of band II with that of anthracene itself, band II was assigned to the electronic transition to the locally excited (LE) state of the anthryl group. On the other hand, bands I and III were best described by the electronic transitions to the excited charge-transfer (CT) states. The study demonstrated furthermore that the Deltamu value of TAB accompanied by the lowest-energy electronic transition was as large as 7.8 D, which agreed very well with that determined by the solvent dependences of the absorption and fluorescence maximum energies of TAB (approximately 8.0 D, ref 1): Deltamu = 7.8-8.0 D. The results proved explicitly that the excited state of TAB was localized primarily on the p orbital of the boron atom. Despite the dipole moment change (Deltamu = 7.8-8.0 D) for the lowest-energy electronic transition (band I), the electrofluorescence of TAB accompanied the change in the molecular polarizability. The spectroscopic and excited-state properties of TAB including the curious behavior of the electrofluorescence spectrum as mentioned above were discussed on the basis of theoretical considerations.