Diffuse mode bifurcation of soil causing convection-like shear investigated by group-theoretic image analysis

Diffuse mode bifurcation of soil under plane-strain compression test is shown, by means of an image analysis based on group-theoretic bifurcation theory, to trigger convection-like shear and to precede shear band formation. First digital photos of Toyoura sand specimens are processed by PIV (particle image velocimetry) to gather digitized images of deformation. Next bifurcation from a uniform state is detected by expanding these images into the double Fourier series and finding a predominant harmonic diffuse bifurcation mode based on that theory. This harmonic bifurcation mode, which is the mixture of a few harmonic functions, expresses complex convection-like shear. Last bifurcation from a non-uniform state is detected by decomposing each image into a few images with different symmetries to extract non-harmonic diffuse bifurcation modes. Diffuse modes of bifurcation, which hitherto were hidden behind predominant uniform compressive deformation, have thus been made transparent by virtue of the group-theoretic image analysis proposed. A possible course of deformation suggested herein is the evolution of diffuse mode bifurcation with a convection-like bifurcation mode breaking uniformity and symmetry, followed by the formation of shear bands through localization.     

Synthetic Utilization of α-Phosphonovinyl Anions

The α-phosphonovinyl anions, generated in situ from treatment of β-hetero-substituted vinyl-phosphonates 1a-c with LDA (or LTMP), were trapped with various electrophiles such as chlorotriorganosilanes, chlorotrimethylgermane, chlorotriorganotins, dimethyl disulfide, and halogen to afford the corresponding β-hetero-substituted α-functionalized vinylphosphonates 2–14 in good to excellent yields. The Friedel-Crafts reaction of α-(silyl) or α-(germyl)phosphonoketene dithioacetals 2, 9 or 4 with acid chlorides gave α-acylated phosphonoketene dithioacetals 15–19 in 53–91 % yields. The palladium-catalyzed cross-coupling reaction of β-ethoxy-α-(tributylstannyl)vinylphosphonate 13 with a variety of organic halides (R = acyl, allyl, aryl etc.) provided β-ethoxy-α-substituted vinylphosphonates 20–25 in good to moderate yields. The palladium-mediated cross-coupling reaction of α-(iodo)-vinyl-phosphonates 7, 14 with terminal acetylenes afforded α-alkynylated vinylphosphonates 26–29 in 69–83 % yields.     

Two‐dimensional replica‐exchange method for predicting protein–ligand binding structures

We have developed a two‐dimensional replica‐exchange method for the prediction of protein–ligand binding structures. The first dimension is the umbrella sampling along the reaction coordinate, which is the distance between a protein binding pocket and a ligand. The second dimension is the solute tempering, in which the interaction between a ligand and a protein and water is weakened. The second dimension is introduced to make a ligand follow the umbrella potential more easily and enhance the binding events, which should improve the sampling efficiency. As test cases, we applied our method to two protein‐ligand complex systems (MDM2 and HSP 90‐alpha). Starting from the configuration in which the protein and the ligand are far away from each other in each system, our method predicted the ligand binding structures in excellent agreement with the experimental data from Protein Data Bank much faster with the improved sampling efficiency than the replica‐exchange umbrella sampling method that we have previously developed. © 2013 Wiley Periodicals, Inc.     

Preparation of co‐polymethyl(alkoxy)siloxanes by acid‐catalyzed controlled hydrolytic copolycondensation of methyl(trialkoxy)silane and tetraalkoxysilane

Polymethyl(alkoxy)siloxane copolymers, poly(MTES‐co‐TEOS), and poly(MTMS‐co‐TMOS), are prepared by acid‐catalyzed controlled hydrolytic co‐polycondensation of methyl(trialkoxy)silane MeSi(OR)₃ (R = Et (MTES) and Me (MTMS)) and tetra‐alkoxysilane Si(OR)₄ (R = Et (TEOS) and Me (TMOS)), respectively. The products are purified by fractional precipitation to provide polymethyl(alkoxy)siloxane copolymers with molecular weight 1000–10,000 (poly(MTES‐co‐TEOS)) or 1700–100,000 (poly(MTMS‐co‐TMOS)) that are stable to self‐condensation. These polymers are soluble in common organic solvents except for hexane, and form flexible and transparent free‐standing films with a tensile strength of 4.0–10.0 MPa. The structure of the polymethyl(alkoxy)siloxane copolymers is thought to be a random or a block co‐polymer. They are found to provide coating films with an adhesive strength up to 10, a refractive index of 1.36–1.40, and a dielectric constant of 3.5–3.6. The products also show better weathering stability than polyethoxysiloxane due to the hydrolytic polycondensation of TEOS. Field emission‐scanning electron micrography analysis reveals that coating films are composed of a micro‐phase separated structure. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4732–4741     

Structure and crystallization of sub-elementary fibrils of bacterial cellulose isolated by using a fluorescent brightening agent

The structure and crystallization of carefully isolated sub-elementary fibrils (SEFs) of bacterial cellulose have been investigated using TEM, WAXD, and high-resolution solid-state ¹³C NMR. The addition of a suitable amount of fluorescent brightener (FB) to the incubation medium of Acetobacter xylinum effectively suppressed the aggregation of the SEFs into the microfibrils, as previously reported. However, this study confirmed for the first time that serious structural change in the SEFs occurs during the removal of excess FB by washing with buffer solutions having pH values higher than 6 or with the alkaline aqueous solution that was frequently used in previous studies. In contrast, the isolation of unmodified SEFs was successfully performed by utilizing a washing protocol employing pH 7 citrate–phosphate buffer solution containing 1% sodium dodecyl sulfate. High-resolution solid-state ¹³C NMR and WAXD measurements revealed that the SEFs thus isolated are in the noncrystalline state in which the pyranose rings of the almost parallel cellulose chains appear to be stacked on each other. The respective CH₂OH groups of the SEFs adopt the gt conformation instead of the tg conformation found in cellulose I _α and I _β crystals, and undergo significantly enhanced molecular motion in the absence of intermolecular hydrogen bonding associated with these groups. The main chains are also subject to rapid motional fluctuations while maintaining the parallel orientation of the respective chains, indicating that the SEFs have a liquid crystal-like structure with high molecular mobility. Moreover, the SEFs crystallize into cellulose I _β when the FB molecules that may adhere to the surface of the SEFs are removed by extraction with boiling 70 v/v% ethanol and 0.1N NaOH aqueous solution. On the basis of these results, the crystallization of the SEFs into the I _α and I _β forms is discussed, including the possible formation of the crystalline-noncrystalline periodic structure in native cellulose.