Characterization of a Silk‐Resinified Compact Fabricated Using a Pulse‐Energizing Sintering Device

Pulse electric current sintering is used to prepare a compact from resinificated hydrous silk powder. Compacts with no remnant silk powders are formed with 20 wt% added water, 20–40 MPa molding pressure, and >353 K molding temperature. The latter two are much lower than those used for conventional hot pressing. No dependence on molding pressure and temperature are found in XRD or FT‐IR analysis, except for a compact molded at 473 K, for which silk fibroin decomposition is confirmed by DSC, EGA‐MS, and molecular weight measurements. The compact's three‐point bending strength depends on the molding temperature, except for the temperature at which silk fibroin decomposes. The maximum three‐point bending strength resembles that of general‐purpose epoxy resin and is much higher than that of PLA.

     

Star-shaped poly(lactic acid) with carboxylic acid terminal groups via poly-condensation

A series of star-shaped poly(lactic acid)s with carboxylic acid terminal groups have been synthesized by direct poly-condensation of lactic acid in the presence of a poly-carboxylic acid core molecule with triphenylphosphonium trifluoromethanesulfonate (TPP-T) catalyst.These star-polymers had thermal properties not very much different from those of star-shaped poly(lactic acid) with hydroxyl terminal groups and linear poly(lactic acid), irrespective of the structure of the core molecule and number of polymer arms. Solubility and degradability of these star-polymers were, however, greatly enhanced compared to those of star-polymers with hydroxyl terminal groups and increased depending on the number of polymer arms. From the star-shaped polymers, a variety of ammonium salts and the corresponding carboxyamides were successfully prepared.     

Structures and mechanical properties of electrospun cellulose nanofibers/poly(ε-caprolactone) composites

Poly(ε-caprolactone) (PCL) is one of the ecofriendly biodegradable polymers with excellent moldability but with rather low mechanical properties especially for the industrial and biomedical use. In this research, to overcome the problem, the two types of cellulose nanofibers, the cellulose acetate nanofibers (CA-NF) and the cellulose nanofibers (C-NF), were composited into PCL for the enhancement of the mechanical properties of PCL. CA-NF were prepared by electrospinning and converted into C-NF afterward by deacetylation. It was found that the Young's modulus of the CA-NF/PCL composite at the fiber concentration of 35 wt% significantly increased by ~3 times as compared with that of neat PCL, whereas C-NF/PCL of the same fiber concentration also increased by ~4.5 times. It was also found that the Young's moduli of CA-NF/PCL nearly reached the theoretical values calculated by the equation suggested by Tsai, but that the Young's moduli of C-NF/PCL could not reach the theoretical values. It indicates that CA-NF possessed better compatibility with PCL than C-NF, agreeing well with the fracture-surface analyses of the two composites by the scanning electron microscopy.     

Well‐defined,environment‐friendly synthesis of polypeptides based on phosgene‐free transformation of amino acids into urethane derivatives and their applications

In this study, both naturally occurring and artificial amino acids were successfully transformed into the corresponding urethane derivatives using diphenyl carbonate. The urethanes thus prepared could be efficiently cyclized into amino acid N‐carboxyanhydrides (NCAs) without the requirement of phosgene. In addition, the presence of primary amines converted the urethane derivatives into NCAs and initiated the ring‐opening polymerization of the in situ formed NCAs, allowing for the well‐defined synthesis of polypeptides. These polypeptides contained initiating ends functionalized by an amine‐derived residue and propagating ends bearing the reactive amino group. By precise control of the structures of the polypeptides, various polypeptide conjugates such as block copolymers and graft copolymers were successfully synthesized as designed, and their applications in antifouling coatings against proteins, drug delivery systems and biosensors were demonstrated. © 2019 Society of Chemical Industry     

Effect of organic groups on hydrogen adsorption properties of periodic mesoporous organosilicas

We investigate the hydrogen adsorption properties of periodic mesoporous organosilicas (PMOs) and focus, in particular, on how these properties are affected by diverse organic groups embedded in the walls. PMOs with π electrons on the pore surface adsorb more hydrogen molecules per unit area and have a higher isosteric heat of hydrogen adsorption (Q_st). The number of adsorbed hydrogen molecules per unit area correlates well with the density of organic groups on the pore surface. We attribute the high Q_st to the high polarizability of organic groups with π electrons, which enhances the dispersion force. The molecular order of organic groups affects the adsorption-site affinity to hydrogen molecules as well as the location of adsorption sites. For phenylene-bridged PMOs with crystal-like pore walls, Q_st decreases rapidly with increasing hydrogen loading, which indicates two types of adsorption sites with different affinities to hydrogen molecules: one is an exposed CH bond and the other is a siloxane bond. However, Q_st for phenylene-bridged PMOs with amorphous pore walls exhibits a moderate slope, which might be caused by the random order of organic groups; this results in several types of adsorption sites with various affinities.     

Force measurement enabling precise analysis by dynamic force spectroscopy

Dynamic force spectroscopy (DFS) makes it possible to investigate specific interactions between two molecules such as ligand-receptor pairs at the single-molecule level. In the DFS method based on the Bell-Evans model, the unbinding force applied to a molecular bond is increased at a constant rate, and the force required to rupture the molecular bond is measured. By analyzing the relationship between the modal rupture force and the logarithm of the loading rate, microscopic potential barrier landscapes and the lifetimes of bonds can be obtained. However, the results obtained, for example, in the case of streptavidin/biotin complexes, have differed among previous studies and some results have been inconsistent with theoretical predictions. In this study, using an atomic force microscopy technique that enables the precise analysis of molecular interactions on the basis of DFS, we investigated the effect of the sampling rate on DFS analysis. The shape of rupture force histograms, for example, was significantly deformed at a sampling rate of 1 kHz in comparison with that of histograms obtained at 100 kHz, indicating the fundamental importance of ensuring suitable experimental conditions for further advances in the DFS method.     

采用MAMMOS技术的高密度光记录

MAMMOS(Magnetic Amplifying Magneto－ Optical System:磁畴扩大磁光系统 )是实现高密度磁光盘的有效方法。不仅能得到不依赖于磁畴长度的较大的读出信号振幅,而且还能实现超出光学系统衍射极限的分辨率。过去,为实现磁畴的复印与扩大,要对记录膜面施加垂直方向的外部磁场。而现在得知,同时施加垂直磁场和水平方向的磁场,可大幅度地提高微小磁畴的读出特性。确认采用施加水平磁场的方法,在λ =635 nm, NA=0.55的条件下, 0.15μ m的连续磁畴也能获得 BER=2× 10－ 4的读出效果。     

Effect of Talc Size on Surface Roughness and Glossiness of Polypropylene Injection Molding Application to Automotive Plastics

Talc-containing polypropylene (PP) resin is extensively employed in automobiles. Herein, considering the microstructure transfer process in injection molding, the effect of the talc's dispersibility and particle size on this process and its impact on the gloss level of the product were investigated. Results show that a fine unevenness of about several micrometers was self-formed by the shrinkage of PP in nontransferred areas due to the blending of talc. Additionally, the amount of self-formed unevenness tended with an increase in the average particle size of talc. Furthermore, due to PP shrinkage and different densities of talc, it was observed that a fine tiger-stripe pattern was self-formed using special molds with modified microstructure. This self-formed fine unevenness changes the gloss level owing to the diffused light reflection effect. This study proposes controlling this change by controlling the average particle size of talc and structure of the mold. POLYM. ENG. SCI., 60:132–139, 2020. © 2019 Society of Plastics Engineers     

Bacterially Secretable Single-Chain Tandem Macrocyclic Peptides for High Affinity and Inhibitory Activity

The inhibition of protein-protein interactions (PPIs) is an effective approach for therapy. Owing to their large binding surface areas to target proteins, macrocyclic peptides are suitable molecules for PPI inhibition. In this study, we developed single-chain tandem macrocyclic peptides (STaMPtides) that inhibits the vascular endothelial growth factor (VEGF) receptor 2 (VEGFR2). They were artificially designed to comprise two different VEGFR2-binding macrocyclic peptides linked in tandem by peptide linkers and secreted by Corynebacterium glutamicum. Most potent VEGFR2-inhibitory STaMPtides with length-optimized linkers exhibited >1000 times stronger inhibitory activity than their parental monomeric peptides, possibly due to the avidity effect of heterodimerization. Our approach of using STaMPtides for PPI inhibition may be used to inhibit other extracellular factors, such as growth factors and cytokines.     

Roles of inherent metallic species in secondary reactions of tar and char during rapid pyrolysis of brown coals in a drop-tube reactor

Two pairs of raw and acid-washed coal samples were prepared from Yallourn and Loy Yang brown coals, and subjected to rapid pyrolysis in a drop-tube reactor at 1073-1173 K in a stream of N₂ or H₂O/N₂ mixture. Examinations were made on the roles of the inherent metallic species in the secondary reactions of nascent tar and char that were formed by the intraparticle primary reactions. The experimental results revealed that the inherent metallic species were essential for vary rapid steam reforming/gasification of the nascent tar/char and simultaneous suppression of soot formation. In the absence of the metallic species, the soot formation from the tar accounted as much as 15-19 and 6-13% of the carbon in coal in N₂ and H₂O/N₂, respectively. The metallic species reduced the yield of soot to 6-8% in N₂ by enhancing the reforming of tar by H₂O generated from the pyrolysis of coal. In the H₂O/N₂ stream, instead of soot formation, a net gasification conversion up to 17% within 4.3 s was observed in the presence of the metallic species as a result of catalytic gasification of the nascent char. Moreover, the metallic species catalyzed the steam reforming of the nascent tar, giving its conversion up to 99%. Over the range of the conditions employed, a one-to-one stoichiometry was established between the steam consumption and the yield of carbon oxides formed by the steam reforming/gasification and water-gas-shift reaction.