Yoshiko Takenaka

Focal conics in a smectic-A liquid crystal in microwrinkle grooves

Focal conic domains (FCDs) in smectic-A (SmA) liquid crystals (LCs) are a broad class of curvature defects in a layered system. Here, we report a regular array of FCDs in octylcyanobiphenyl in a SmA phase confined within sinusoidal microgrooves of microwrinkles with a specific periodicity. A semi-hybrid alignment is imposed by the air–LC interface (homeotropic) and the LC–curved-microwrinkle interface (unidirectional planar). The FCDs are periodically packed along the groove direction when the wrinkle wavelength is larger than a critical value of approximately 4 μm. The periodicity of the FCDs monotonically increases with increasing the wrinkle wavelength. From our optical observation, we propose an internal layer structure of the FCDs composed of a set of Dupin cyclides with the eccentricity of the basic ellipse being approximately 0.75.

Autonomous Oscillation of Polymer Chains Induced by the Belousov–Zhabotinsky Reaction

We investigated the self-oscillating behaviors of two types of polymer chains induced by the Belousov–Zhabotinsky (BZ) reaction. One consisted of N-isopropylacrylamide (NIPAAm) and the Ru catalyst of the BZ reaction, and the other consisted of NIPAAm, the Ru catalyst, and acrylamide-2-methylpropanesulfonic acid (AMPS) with a negatively charged domain as a solubility control site. A comparison of the two types of self-oscillation systems showed that the anionic AMPS portion of the polymer chain significantly affected the self-oscillating behavior under strongly acidic condition. The periods of self-oscillation for the two types of self-oscillating polymer chains were investigated by changing the initial concentrations of the three BZ substrates and the temperature. As a result, it was demonstrated that the period of self-oscillation could be controlled by the concentration of the BZ substrates and the temperature. Furthermore, the activation energies of the two types of the self-oscillating polymer chains gave similar values as normal BZ reactions, i.e., not including the self-oscillating polymer system with a Ru moiety. In addition, it was clarified the activation energy was hardly affected by the initial concentration of the three BZ substrates.

Global genetic response in a cancer cell: self-organized coherent expression dynamics.

Understanding the basic mechanism of the spatio-temporal self-control of genome-wide gene expression engaged with the complex epigenetic molecular assembly is one of major challenges in current biological science. In this study, the genome-wide dynamical profile of gene expression was analyzed for MCF-7 breast cancer cells induced by two distinct ErbB receptor ligands: epidermal growth factor (EGF) and heregulin (HRG), which drive cell proliferation and differentiation, respectively. We focused our attention to elucidate how global genetic responses emerge and to decipher what is an underlying principle for dynamic self-control of genome-wide gene expression. The whole mRNA expression was classified into about a hundred groups according to the root mean square fluctuation (rmsf). These expression groups showed characteristic time-dependent correlations, indicating the existence of collective behaviors on the ensemble of genes with respect to mRNA expression and also to temporal changes in expression. All-or-none responses were observed for HRG and EGF (biphasic statistics) at around 10–20 min. The emergence of time-dependent collective behaviors of expression occurred through bifurcation of a coherent expression state (CES). In the ensemble of mRNA expression, the self-organized CESs reveals distinct characteristic expression domains for biphasic statistics, which exhibits notably the presence of criticality in the expression profile as a route for genomic transition. In time-dependent changes in the expression domains, the dynamics of CES reveals that the temporal development of the characteristic domains is characterized as autonomous bistable switch, which exhibits dynamic criticality (the temporal development of criticality) in the genome-wide coherent expression dynamics. It is expected that elucidation of the biophysical origin for such critical behavior sheds light on the underlying mechanism of the control of whole genome.

Effects of surfactant concentration on formation of high-aspect-ratio gold nanorods.

The effects of surfactant concentration in a growth solution on the elongation of gold nanorods were examined. Gold nanorods were synthesized in solutions with different concentrations of hexadecyltrimethylammonium bromide (HTAB): 100, 200, 300, 400, 500, and 600 mM. The nanorods grown in a solution with higher surfactant concentrations were longer (aspect ratio ~30) than those grown in that with lower concentrations (aspect ratio <10). The self-assembled surfactant structures in the solutions were analyzed using viscosity measurement and small-angle X-ray scattering. These results showed a decrease in the inter-micellar distance with increasing surfactant concentration. Taking the chemical equilibrium for the complex formation between Au ions and HTAB micelles into account, we found that the free Au ion concentration decreases accompanied with the increase in the surfactant concentration. This decrease in the free Au ion concentration suppresses undesirable secondary nucleation of gold crystals in a growth solution, resulting in gold nanorod elongation.

Near-infrared-light-responsive liquid-crystalline composite gels with photo-healing ability

ABSTRACT We developed photo-healable composite gels consisting of liquid crystal, microparticles, and gold nanorods. Upon irradiation with near-infrared light, the temperature of the composite gels rapidly increased above a gel-sol transition temperature by the photothermal effect of gold nanorods. Then, we successfully performed photoinduced gel-sol transition of composite gels based on the phase transition of liquid crystals induced by the photothermal effect. In addition, we achieved photo-healing of surface cracks made on the composite gels by means of the photothermal gel-sol transition.

Aspect-ratio-controlled Au Nanorods: Preparation and Dispersion toward Applications

The synthesis of aspect-ratio-controlled gold nanorods is introduced. Gold nanorods are usually synthesized in a liquid-state surfactant solution. In this paper, we present that their synthesis in a gel-state surfactant solution is useful to control their diameter and length in wide range. The diameter is controlled from ~10 to 80 nm. According to the previous study, it is reported that a decrease in the curvature of the surfactant bilayer neighboring the gold surface affects the increase in the nanorod diameter. In this paper, we synthesize the nanorods with different kinds of surfactants and confirm that the mechanism is appropriate. We also introduce a method to control the long-axis length of gold nanorods in a gel-state surfactant solution from several tens of nm to 1 μm. The dispersion method of high-aspect-ratio gold nanorods is also presented.