Composition dependence of crystallized lamellar morphology formed in crystalline-crystalline diblock copolymers

We have investigated the crystallized morphology formed at each temperature T_c (20 °C ≤ T_c ≤ 45 °C) in double crystalline poly(?-caprolactone)-block-polyethylene (PCL-b-PE) copolymers as a function of composition (or volume fraction of PE blocks ?_PE) by employing small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) techniques. When PCL-b-PE with ?_PE ≤ 0.58 was quenched from a microphase-separated melt into T_c, the crystallization of PE blocks occurred first to yield an alternating structure consisting of thin PE crystals and amorphous PE + PCL layers (PE lamellar morphology) followed by the crystallization of PCL blocks, where we can expect a competition between the stability of the PE lamellar morphology (depending on ?_PE) and PCL crystallization (on T_c). Two different morphologies were formed in the system judging from a long period. That is, the PCL block crystallized within the existing PE lamellar morphology at lower T_c (<30 °C) to yield a double crystallized alternating structure while it crystallized by deforming or partially destroying the PE lamellar morphology at higher T_c (>35 °C) to result in a significant increase of the long period. However, the temperature at which the morphology changed was almost independent of ?_PE. For PCL-b-PE with ?_PE ≥ 0.73, on the other hand, the morphology after the crystallization of PE blocks was preserved at every T_c investigated.     

Evolution of the fermi surface in metastable βL-(BEDT-TTF)2I3

We have been studying the variation of thermodynamic and transport properties as β-(BEDT-TTF)₂I₃ evolves from the ambient-pressure-cooled, structurally metastable low T_c (β_L) phase to the high T_c(β_H) phase. Annealing at ambient pressure for about a hundred hours near 100 K removes the β_L-associated incommensurate superstructure that forms below T₁₇₅ (≈ 175 K at ambient pressure). We find from measurements of the temperature dependent Hall coefficient and heat capacity that long term annealing also suppresses the lower temperature T₂₀ transition (≈ 20 K) that occurs in the β_L phase, leading to bulk β_H phase superconductivity. The results are consistent with the opening of the Fermi surface (FS) at T₂₀ in non-annealed samples but are not consistent with a 50% reduction in FS area for non-annealed β_L phase samples (compared to the area of the Fermi Surface in the β_H phase) or significant localization at T₁₇₅. Finally, we compare these results to our measurements of the temperature dependent Hall coefficient and T_c under pressure.     

Helix‐Grafted Pleckstrin Homology Domains Suppress HIV‐1 Infection of CD4‐Positive Cells

The size, functional group diversity and three‐dimensional structure of proteins often allow these biomolecules to bind disease‐relevant structures that challenge or evade small‐molecule discovery. Additionally, folded proteins are often much more stable in biologically relevant environments compared to their peptide counterparts. We recently showed that helix‐grafted display—extensive resurfacing and elongation of an existing solvent‐exposed helix in a pleckstrin homology (PH) domain—led to a new protein that binds a surrogate of HIV‐1 gp41, a validated target for inhibition of HIV‐1 entry. Expanding on this work, we prepared a number of human‐derived helix‐grafted‐display PH domains of varied helix length and measured properties relevant to therapeutic and basic research applications. In particular, we showed that some of these new reagents expressed well as recombinant proteins in Escherichia coli, were relatively stable in human serum, bound a mimic of pre‐fusogenic HIV‐1 gp41 in vitro and in complex biological environments, and significantly lowered the incidence of HIV‐1 infection of CD4‐positive cells.     

High-angle triple-axis specimen holder for three-dimensional diffraction contrast imaging in transmission electron microscopy

Electron tomography requires a wide angular range of specimen-tilt for a reliable three-dimensional (3D) reconstruction. Although specimen holders are commercially available for tomography, they have several limitations, including tilting capability in only one or two axes at most, e.g. tilt-rotate. For amorphous specimens, the image contrast depends on mass and thickness only and the single-tilt holder is adequate for most tomographic image acquisitions. On the other hand, for crystalline materials where image contrast is strongly dependent on diffraction conditions, current commercially available tomography holders are inadequate, because they lack tilt capability in all three orthogonal axes needed to maintain a constant diffraction condition over the whole tilt range. We have developed a high-angle triple-axis (HATA) tomography specimen holder capable of high-angle tilting for the primary horizontal axis with tilting capability in the other (orthogonal) horizontal and vertical axes. This allows the user to trim the specimen tilt to obtain the desired diffraction condition over the whole tilt range of the tomography series. To demonstrate its capabilities, we have used this triple-axis tomography holder with a dual-axis tilt series (the specimen was rotated by 90° ex-situ between series) to obtain tomographic reconstructions of dislocation arrangements in plastically deformed austenitic steel foils.     

Electron density measurement of cesium seeded negative ion source by surface wave probe

Electron density measurements of a large-scaled negative ion source were carried out with a surface wave probe. By comparison of the electron densities determined with the surface wave probe and a Langmuir probe, it was confirmed that the surface wave probe is highly available for diagnostic of the electron density in H(-) ion sources. In addition, it was found that the ratio of the electron density to the H(-) ion density dramatically decreases with increase of a bias voltage and the H(-) ions become dominant negative particles at the bias voltage of more than 6 V.     

Alginate polyelectrolyte ionotropic gels

The heterogeneous equilibrium for exchange of UO ₂ ²⁺ counter-ions in uranyl alginate exchange resin by H⁺ ions has been investigated using titrimetric and spectrophotometric techniques. The thermodynamic equilibrium constant was found to be 15.51±0.33 at 25 °C. The electrical conductivity of uranyl alginate in the form of circular discs has been examined as a function of temperature. The Arrhenius plot of log versus 1/T showed a complicated behaviour where three regions of conduction were separated by two distinct transition zones. This behaviour was interpreted by the transfer of electrons from alginate to the cross-linked uranyl ion with formation of free radicals and uranium ions of lower oxidation states in a sequence, followed by dimerization of these radicals in the final stages. The X-ray diffraction pattern indicated that the uranyl alginate complex is amorphous in nature. Infrared absorption spectra indicated the presence of UO ₂ ²⁺ chelated to the alginate macromolecular chains, and displayed _a CO ₂ ^– and _s CO ₂ ^– in the ranges of 1591 and 1410 cm^–1 respectively. Two geometrical structures for chelation of UO ₂ ²⁺ with the functional groups of alginate macromolecules have been suggested.