A Ring‐Flippable Sugar as a Stimuli‐Responsive Component of Liposomes

For the development of a liposome that takes in and out a drug in response to stimuli, 2,4‐diaminoxylose (Xyl), which allows stimuli‐responsive conformational switches between ⁴C₁ and ¹C₄, was incorporated into a lipid structure: Xyl derivatives with C8 and C16 methylene chains at the 1,3‐positions (C8Xyl and C16Xyl) were synthesized. ¹H NMR spectroscopy indicates that the addition of Zn²⁺ and then H⁺ induces conformational switches from the chair (⁴C₁) to the reverse chair (¹C₄) and ¹C₄‐to‐⁴C₁, respectively, at Xyl; this leads to transformation of the lipids between linear and bent structures. Osmotic pressure and electron microscopy studies demonstrate that C8Xyl in water forms spherical solid aggregates (C8Xyl?Zn), which are converted into liposomes (C8Xyl+Zn) upon the addition of Zn²⁺, and C16Xyl forms liposomes regardless of the presence of Zn²⁺. The aggregates of C8Xyl±Zn incorporated a fluorophore and only C8Xyl+Zn released the content upon the addition of HCl. This study shows that Xyl could be a stimuli‐responsive component of a liposome.     

Self‐Discriminating Termination of Chiral Supramolecular Polymerization: Tuning the Length of Nanofibers

Directing the supramolecular polymerization towards a preferred type of organization is extremely important in the design of functional soft materials. Proposed herein is a simple methodology to tune the length and optical chirality of supramolecular polymers formed from a chiral bichromophoric binaphthalene by the control of enantiomeric excess (ee). The enantiopure compound gave thin fibers longer than a few microns, while the racemic mixture favored the formation of nanoparticles. The thermodynamic study unveils that the heterochiral assembly gets preference over the homochiral assembly. The stronger heterochiral binding over homochiral one terminated the elongation of fibrous assembly, thus leading to a control over the length of fibers in the nonracemic mixtures. The supramolecular polymerization driven by π–π interactions highlights the effect of the geometry of a twisted π‐core on this self‐sorting assembly.     

A Twist‐Assisted Biphenyl Photosensitizer Passable Through Glucose Channel

While the development of low‐molecular‐weight drugs is saturating, agents for photodynamic therapies (PDTs) may become alternative seeds in pharmaceutical industry. Among them, orally administrative, cancer‐selective, and side effect‐free photosensitizers (PSs) that can be activated by tissue‐penetrative near‐infrared (NIR) lights are strongly demanded. We discovered such a PS from scratch by focusing on a twist‐assisted spin‐orbit charge transfer intersystem crossing (ISC) mechanism in a biphenyl derivative, which was demonstrated by thorough photophysical studies. The unique ISC mechanism enables the PS to be small and slim so as to pass through glucose transporters and exert a PDT effect selectively on a cancer cell line. The smallness will allow for oral administration and fast clearance, which have been agenda of approved PSs with larger molecular weights. We also demonstrated that our PS was able to be activated with an NIR pulse laser through two‐photon excitation.     

Surface and morphological characterization of polysiloxane-block-polyimides

Two series of polysiloxane-block-polyimides were synthesized by the method of solution imidization of the polyamic acids prepared from the dianhydride/diamine combinations of 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA)/2,2-bis[4-(4-aminophenoxy) phenyl] propane (BAPP) (Series A) and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA)/bis[4-(3-aminophenoxy) phenyl] sulfone (BAPSM) (Series B) with three kinds of w-diamino-poly(dimethylsiloxane) with different number-average molecular weight added as a part of diamine. These polysiloxane-block-polyimides, having various compositions and chain lengths of the polysiloxane segments, were subjected to solution casting to prepare their films, and their surface and interface properties were analyzed by contact angle, XPS, AFM, and SEM. It was found that the surface tension and surface topography were greatly influenced by the composition and molecular weight of the polysiloxane segments because of their surface enrichment, which was affected by the environment and substrate with which the copolyimides had contacted. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2239–2251, 1997     

Resonant photorefractive effect in InGaAs/GaAs multiple quantum wells

Semi-insulating InGaAs/GaAs multiple quantum wells are fabricated by metal-organic vapor-phase epitaxy and proton implantation. Two-wave mixing gain and four-wave mixing diffraction efficiency are measured at wavelengths of 0.91-0.94microm in the Franz-Keldysh geometry. We observe a large photorefractive effect caused by the excitonic electro-optic effect. The maximum diffraction efficiency reaches ~1.5x10(-4) .     

Three novel bis(indole) alkaloids from a stony coral, Tubastraea sp.

Three novel bis(indole) alkaloids with an unprecedented skeleton have been isolated from a stony coral, Tubastraea sp. These indoles could biogenetically be derived from two molecules of aplysinopsin via a Diels-Alder reaction.     

Synthesis of amphiphilic particles in the presence of inert solvents and their application to lipase immobilization

To develop monodisperse amphiphilic polymer particles on which a large amount of lipase could be immobilized, we performed seed polymerizations of glycidyl methacrylate and allyl methacrylate in the presence of nonpolar inert and polar inert solvents. The amphiphilic porous polymer particles, which had both hydrophilic guanidino groups and hydrophobic stearoyl groups, were synthesized in the presence of n‐decane and had a large amount of macropores with diameters of 50–1000 nm. The amount of lipase immobilized on the amphiphilic particles synthesized in the presence of n‐decane was 3.85 times that of the lipase immobilized on the amphiphilic particles synthesized in the absence of a solvent. The immobilized lipase prepared with the amphiphilic particles synthesized in the presence of n‐decane exhibited a high transesterification activity in n‐hexane and could be used repeatedly without a considerable activity loss. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 874–884, 2002; DOI 10.1002/pola.10178     

Study on the Salting-out Effect using Silica Species by FAB-MS

The salting-out effect has been characterized on the basis of the relative peak intensity of silica species, observed by FAB-MS (fast atom-bombardment mass spectrometry) in solutions of sodium chloride, sodium nitrate, sodium sulfate, calcium chloride, lithium chloride and magnesium chloride. A critical change in the peak intensity ratios of the linear and cyclic tetramers of silica against the sodium ion (Na⁺) concentrations was observed at Na⁺ concentration between 0.1 and 1 mol⋅dm⁻³. The degrees of the changes of these peak intensity ratios increased in the order NaNO₃ < Na₂SO₄ < NaCl. In CaCl₂ solutions, these peak intensity ratios changed significantly at Ca²⁺ concentrations between 0.05 and 0.5 mol⋅dm⁻³. The salting-out effect observed is the total change in the concentration of silica brought about by complex factors, such as the changing solubility of silicate complexes, the increases in the concentrations of different kinds of soluble silicate complexes induced by changes in the hydrophobicity and hydrophilicity of the solution, and the contribution of hydrolysis.     

Sodium borosilicate glasses prepared by the sol-gel process

A sodium borosilicate gel of composition 80SiO₂·15B₂O₃·5Na₂O (wt%) was prepared from tetraethyl orthosilicate, trimethyl borate, sodium methylate, H₂O, and HCl as the catalyst. Variation of specific surface area and porosity as a function of heating temperature indicated that closed pores were opened at temperatures lower than 400°C and collapsed above 450°C. From TG and DTA curves, about 19% Si and B atoms are evaluated to have −OH bonds. X-ray diffraction patterns indicated crystallization of low-cristobalite out of the gel when it was heated at 700°C for 5 h, showing a difference from a melt-quenched glass of the same composition.     

Light scattering of polyaniline films responding to electrochemical switching

When a laser with 543, 668 or 790±50 nm was used to irradiate the reduced polyaniline film on an indium tin oxide electrode in hydrochloric acid, the light was scattered in all directions. The intensity of the scattered light decreased with increase in the detection angle up to the right angle. When the electrode potential was scanned between the insulating and the conducting domain, the intensity varied sigmoidally with hysteresis. The intensity increased with a decrease in the absorbance. The scattering of the light can be ascribed to multiple reflection, luminescence, or Rayleigh scattering. The spectra of the scattered light was identical with that of the incident light, suggesting the absence of luminescence. The intensity increased with an increase in thickness of the film, indicating a negligible contribution of multiple reflection. Since the volume of the oxidized film is larger than that of the reduced one, the film synthesized in the oxidized state is deformed by the electrode reduction. Then, the film density becomes locally inhomogeneous and this may give rise to the Rayleigh scattering. The potential-variation of the light scattering occurred at a more negative potential than that of the absorbance at 310 nm and of the current did.