Synthesis of polyamides from active 1-benzotriazolyl diesters and diamines under mild conditions

The effect of the solvent on the inherent viscosity of polyamides was investigated in the polycondensation of new active 1-benzotriazolyl diesters, such as 1,1′-(adipolydioxy)bisbenzotriazole and 1,1′-(isophthaloyldioxy)bisbenzotriazole, with diamines. The preferred polymerization media were polar aprotic solvents, including N-methyl-2-pyrrolidone and hexamethylphosphoramide. The solution polycondensation at room temperature afforded a series of polyamides having inherent viscosities as high as 1.8 from both aliphatic and aromatic diamines. The 1-benzotriazolyl diesters were more reactive than di(2,4-dinitrophenyl) isophthalate toward diamines. Prior to polymer synthesis, the aminolysis of some active monoesters was carried out as a model compound study.     

Crystal engineering for topochemical polymerization of muconic esters using halogen-halogen and CH/pi interactions as weak intermolecular interactions

We now report the molecular and crystal structure design of muconic ester derivatives on the basis of crystal engineering using halogen-halogen contacts and CH/pi interactions. The solid-state photoreaction pathway of the dibenzyl (Z,Z)-muconates as the 1,3-diene dicarboxylic acid monomers depends on the structure of the ester groups. The substitution of a halogen atom for the aromatic hydrogen of a benzyl group induces topochemical polymerization to produce stereoregular polymers in a crystalline form, whereas the unsubstituted benzyl derivative isomerizes to yield the corresponding E,E isomer under similar conditions. The topochemical polymerization process is directly confirmed by the fact that the single-crystal structures before and after the polymerization are very similar to each other. From the crystal structure analysis for a series of substituted benzyl (Z,Z)- and (E,E)-muconates, it has been revealed that the planar diene moieties are closely packed to form a columnar structure in the crystals. The stacking of the polymerizable monomers is characterized by a stacking distance of 4.9-5.2 A along the columns. This structure is supported by a halogen-halogen interaction between the chlorine or bromine atoms introduced at the p position of the benzyl groups in addition to an aromatic stacking due to the CH/pi interaction between the benzylic methylene hydrogens and aromatic rings. The design of a monomer packing corresponds to the type and position of the introduced halogen atom and also the polymorphs. To make a stacking distance of 5 A using both halogen-halogen and CH/pi interactions as supramolecular synthons is important for the molecular design of muconic ester derivatives appropriate for topochemical polymerization.     

Biological and environmental reference materials from the National Institute for Environmental Studies (Japan)

Biological reference materials for elemental speciation were prepared at the National Institute for Environmental Studies. A new human hair reference material, prepared by cryogenic grinding using a ceramic disc mill, is in the process of certification for methyl-Hg and trace elements. Hijiki seaweed reference material was prepared for As speciation studies, primarily for use in the analysis of As(V). Scallop tissue reference material will be certified for arsenobetaine.     

Exchange of injected hydrogen isotopes between diffusing and trapped states in Al

Abstract

Exchange of hydrogen isotopes between diffusing and trapped populations was found with successive injections of 25 keV D₂ ⁺ and 100 or 140 keV H₂ ⁺ into Al surface by simultaneously detecting elastically recoilled hydrogen and deuterium using 2 MeV He⁺.

When backward diffusion of injected hydrogen toward surface was supposed to be impeded or by-passed by structural changes in the subsurface layer due to ion bombardment, effective replacement cross-section of about 1.4 × 10^?18 cm² was observed. Otherwise, namely when the hydrogen backward diffusion is supposed to be rather free, the effective cross section of about 7.8 × 10^?18 was observed.

Due to the difference in energy of the first and second injections, this phenomenon is different from that so called “isotopic exchange”, which occurs through collisional process.     

Fiber Structure,Tensile Behavior and Antibacterial Activity of Polylactide/Poly(butylene terephthalate) Bicomponent Fibers Produced by High-Speed Melt-Spinning

Abstract

Various types of bicomponent fibers composed of polylactide (PLA) and poly(butylene terephthalate) (PBT) with different molecular weights, arranging the polymers separately in the skin or core, were produced by high-speed melt-spinning. The bicomponent spinning, arranging the PLA with high molecular weight (melt flow rate =1.9?g/10?min, L-lactide content = 98.7%) in the skin and the PBT with low molecular weight (IV = 0.835–0.865 dL/g) in the core, resulted in orientation-induced crystallization in the PLA component at the spinning speed of 2?km/min. This crystallization effect was ascribed to a chain-extending treatment applied to the original PLA (MFR = 4.0?g/10?min) to increase its molecular weight. By the treatment the PLA could crystallize when spun even at 1?km/min in its single-component spinning. On the other hand, the bicomponent spinning system interfered with the orientation-induced crystallization of PBT in the core. As a result, the critical spinning speed needed to generate the orientation-induced crystallization in the core PBT was elevated to 4?km/min. The inferior tensile behavior of the bicomponent fibers, as compared to the single-component PLA or PBT fibers, suggested poor compatibility between PLA and PBT. Transesterification reactions rarely occurred at the interface of the two polymers. The bicomponent fibers prepared from high molecular weight PLA and low molecular weight PBT, however, showed sufficient antibacterial activity and physical properties to be suitable for designing medical clothing materials.     

Computational quantum magnetism: Role of noncollinear magnetism

We are witnessing today a golden age of innovation with novel magnetic materials and with discoveries important for both basic science and device applications. Computation and simulation have played a key role in the dramatic advances of the past and those we are witnessing today. A goal-driving computational science—simulations of every-increasing complexity of more and more realistic models has been brought into greater focus with greater computing power to run sophisticated and powerful software codes like our highly precise full-potential linearized augmented plane wave (FLAPW) method. Indeed, significant progress has been achieved from advanced first-principles FLAPW calculations for the predictions of surface/interface magnetism. One recently resolved challenging issue is the role of noncollinear magnetism (NCM) that arises not only through the SOC, but also from the breaking of symmetry at surfaces and interfaces. For this, we will further review some specific advances we are witnessing today, including complex magnetic phenomena from noncollinear magnetism with no shape approximation for the magnetization (perpendicular MCA in transition-metal overlayers and superlattices; unidirectional anisotropy and exchange bias in FM and AFM bilayers; constricted domain walls important in quantum spin interfaces; and curling magnetic nano-scale dots as new candidates for non-volatile memory applications) and most recently providing new predictions and understanding of magnetism in novel materials such as magnetic semiconductors and multi-ferroic systems.     

A new hydrophobic linker effective for the in situ synthesis of DNA-CPG conjugates as tools for SNP analysis

DNA chips consisting of DNA oligonucleotide probes immobilized on the surface of solid supports are very powerful tools for rapid analysis of multiple samples. In this Letter we describe a new method for the efficient synthesis of DNA probes without their serious elimination by use of a new hydrophobic 16-hyroxydecanoic linker and a new non-aqueous reagent of MeNH₂/THF for the deprotection of the base and phosphate protecting groups on CPG resins. The elimination of DNA probes in this new method could be suppressed more than 20-fold compared with the previous method using a hexaethylene glycol linker and concd NH₄OH. Moreover, we carried out SNPs detection by use of our DNA-CPG conjugate to show the utility of our new linker and deprotection conditions.