Stereoselective Isomerization of Unsymmetrical Diallyl Ethers to Allyl (E)-Vinyl Ethers by a Cationic Iridium Catalyst

The stereoselective isomerization of unsymmetrical diallyl ethers to allyl (E)-vinyl ethers was carried out in the presence of a cationic iridium(I) catalyst. The catalyst prepared in situ by treating [Ir(cod)(PPh₂Me)₂]PF₆ with hydrogen was found to be an excellent catalyst to selectively isomerize the less substituted allyl group to an (E)-vinyl ether.     

Cationic copolymerization of 3,3-bis(chloromethyl) oxetane with vinyl compounds

Copolymerizations of 3,3-bis(chloromethyl)oxetane (BCMO) with some vinyl compounds were carried out with cationic catalysts in various solvents to determine what kind of vinyl compound is able to copolymerize with BCMO. p-Methylstyrene (pMS), 2-chloroethyl vinyl ether (CEVE), α-methylstyrene (αMS), and isobutene (IB) were used as comonomers. The rate of consumption of each monomer was measured by gas chromatrography. Plots of copolymer composition in the copolymerization of BCMO with pMS were characterized by S-shaped curves in several solvents. As poly-BCMO is insoluble and the vinyl polymers are soluble in benzene, the polymers obtained were separated into benzene-soluble and benzene-insoluble fractions, and the composition of each fraction was determined by elemental analysis. It was found that pMS, CEVE and IB formed a copolymer with BCMO, but αMS produced no copolymer with BCMO. Thus the formation of copolymer between a cyclic ether and some vinyl monomers was observed by a cationic mechanism. The cross-propagation mechanism is discussed on the basis of these results.     

Enzymatic synthesis of chondroitin and its derivatives catalyzed by hyaluronidase

The enzymatic polymerization to provide synthetic chondroitin and its derivatives is reported here, the first example of such in vitro synthesis to date. N-Acetylchondrosine (GlcAbeta(1-->3)GalNAc) oxazoline (1a) and its derivatives (1b-1f) were designed and synthesized as novel transition state analogue substrate monomers for catalysis by hyaluronidase. Hyaluronidase is a hydrolysis enzyme of chondroitin that also catalyzes the formation of repeated glycosidic bonds in in vitro synthesis, rather than in the catabolic direction. Monomers of 2-methyl (1a), 2-ethyl (1b), and 2-vinyl (1f) oxazoline derivatives were polymerized using this enzyme, via ring-opening polyaddition with total control of regioselectivity and stereochemistry. These reactions provided the corresponding synthetic chondroitin (natural type; N-acetyl, 2a) and the derivatives (unnatural type) with N-propionyl (2b) and N-acryloyl (2f) functional groups at the C2 position of all the galactosamine units, in good yields. Monomers of 2-n-propyl (1c) and 2-isopropyl (1d) oxazoline derivatives were polymerized to produce 2c and 2d in low yield. The 2-phenyl oxazoline derivative (1e) did not afford any enzyme-catalyzed products. M(n) values of 2a and 2b reached 4800 and 4000, respectively. The M(n) value of 2a corresponds to that of the naturally occurring chondroitin. Thus, hyaluronidase catalysis allows the in vitro production of not only natural type but also the formation of unnatural type chondroitins.     

X-ray absorption intensity at high-energy region

We theoretically discuss X-ray absorption intensity in high-energy region far from the deepest core threshold to explain the morphology-dependent mass attenuation coefficient of some carbon systems, carbon nanotubes (CNTs), highly oriented pyrolytic graphite (HOPG) and fullerenes (C₆₀). The present theoretical approach is based on the many-body X-ray absorption theory including the intrinsic losses (shake-up losses). In the high-energy region the absorption coefficient has correction term dependent on the solid state effects given in terms of the polarization part of the screened Coulomb interaction W_p. We also discuss the tail of the valence band X-ray absorption intensity. In the carbon systems C 2s contribution has some influence on the attenuation coefficient even in the high energy region at 20 keV.     

Structural transition of pentacene monolayer on Ga bilayer: From brick-wall structure to herringbone pattern of molecular dimers

Utilizing the substrate of Ga bilayer grown on Si(1 1 1)-√3 × √3-Ga, we have investigated the structural transition of pentacene monolayer induced by moderate annealing. Short-range ordering has been observed in the monolayer pentacene deposited at room temperature. Annealing the sample at ∼350 K produced ordered pentacene monolayer with the “brick-wall” adsorption pattern. The STM images with sub-molecular resolution revealed that the orbital symmetry of the HOMO is reduced from D_2h to C_2v, due to the substrate-molecule interaction, while the deeper HOMO-1 orbital remains intact. Further annealing at ∼400 K led to the formation of molecular dimers as well as the structural transition from “brick-wall” packing to “herringbone” pattern.     

Dynamical stability of the BRS supersymmetry and the Gribov problem

The stability of the Becchi-Rouet-Stora supersymmetry is studied on the basis of a simple non-gauge model invariant under BRS supersymmetry. The Nambu-Goldstone theorem is stated and the spontaneous breakdown of the BRS supersymmetry is illustrated by the above non-gauge model. This indicates that the dynamical stability of BRS supersymmetry in non-abelian gauge theories should also be carefully examined, if one takes the Faddeev-Popov lagrangian as a basis of the formal canonical treatment. We show that a better understanding of the Gribov problem is required to establish the stability of the BRS supersymmetry in non-abelian gauge theories to non-perturbative accuracy.     

Radiation-induced polymerization at high dose rate. V. Butadiene in bulk

Bulk butadiene was polymerized by a cationic mechanism in a wide dose rate range. The M?_n of the product was about 2300, independent of dose rate. The polymer had 83% residual unsaturation and the remaining double bond was 77% trans and 23% vinyl and had no cis unit. When the polymer yield exceeded 10% gel was formed, but the value of the residual unsaturation in the polymer remained unchanged. This indicated a mechanism that correlated propagation, cyclization, and crosslinking reactions with a cationic intermediate.     

Self-organization of surfactant-metal-ion complex nanofibers on graphite surfaces and their application to fibrously concentrated platinum nanoparticle formation

We report the fabrication of self-organized surfactant nanofibers containing platinum ions on a highly oriented pyrolytic graphite (HOPG) surface from mixed solutions of hexadecyltrimethylammonium hydroxide (C16TAOH) and hydrogen hexachloroplatinate (IV) (H2PtCl6). The fibrous surfactant self-assembly was stable in air, even after being soaked in water, in contrast to surfactant hemicylindrical micelles, which are stable only at graphite/solution interfaces. The results show that the graphite surface served as an essential template for the specific formation of fibrous surfactant self-assemblies. In addition, when surfactant nanofibers containing metal ions were treated with hydrazine, platinum nanoparticles concentrated in the nanofibers formed on the HOPG surface. We also prepared surfactant nanofibers containing gold ions on HOPG surfaces and formed gold nanoparticles in the nanofibers.     

Larch (Larix kaempferi) xylem parenchyma cells respond to subfreezing temperature by deep supercooling

In previous studies, xylem parenchyma cells (XPCs) in the boreal softwood species larch, which has thick and rigid walls similar to those of XPCs in boreal hardwood species, were shown to respond to subfreezing temperature by deep supercooling during summer but change their freezing behavior to extracellular freezing during winter. In this study, we re-examined freezing behavior of XPCs in larch by observation of deep etching of frozen samples as well as observation of re-warmed samples after freezing using a cryo-scanning electron microscope. The results showed that XPCs in larch adapts to subfreezing temperature by deep supercooling throughout all seasons. Such freezing behavior is the same as that of XPCs in boreal hardwood species.     

Evidence of subsurface oxygen vacancy ordering on reduced CeO2(111)

Surface and subsurface oxygen vacancies on the slightly reduced CeO(2)(111) surface have been studied by atomic resolution dynamic force microscopy at 80 K. Both types of defect are clearly identified by the comparison of the observed topographic features with the corresponding structures predicted from recent first-principles calculations. By combining two simultaneously acquired signals (the topography and the energy dissipated from the cantilever oscillation), we are able to unambiguously locate subsurface oxygen vacancies buried at the third surface atomic layer. We report evidence of local ordering of these subsurface defects that suggests the existence of a delicate balance between subtle interactions among adjacent subsurface oxygen vacancy structures.