Thermal and ionic‐conductive behaviors of liquid crystalline polymers with alkali metal salt

In order to investigate the relationship between ionic conductivity and liquid crystallinity, we prepared the main‐chain type polyester having 1,4‐bisstyrylbenzene units and ethyleneoxide chain in the repeating unit. The main‐chain type polyester with lithium salt at the ratio of 0.04 per polymer repeating unit exhibited a smectic phase. However, the polyester with lithium salt (0.11) showed a nematic phase. The ionic conductivity of the polyester with lithium salt increased with increasing lithium salt concentration. The trans‐type polyester exhibited a liquid crystalline phase, while the cis‐type polyester did not show any mesophase. We found that the ionic conductivity of the trans‐type polyester with lithium salt (0.11) was larger than that of the cis‐type polyester with lithium salt (0.11). However, a liquid crystalline phase was found in the side‐chain type polyether with alkoxy chain length of below 12. A smectic phase was induced for the non‐mesomorphic polyethers with lithium salt. The layer spacing of the smectic A phase for the non‐mesomorphic polyether with lithium salt decreased from 55 to 41 Å with increasing temperature. The ionic conductivity of the polyether with lithium salt increased with decreasing the layer spacing. Copyright © 2001 John Wiley & Sons, Ltd.     

Preparation of non-contact ordered array of polystyrene colloidal particles by using a metallic thin film of fused hemispheres

A thin metallic bilayer consists of fused hollow hemispheres of 930 nm in diameter is fabricated by sputter deposition of Ti and Fe at 50 and 5 nm of thickness, respectively, onto an array of spherical polystyrene colloidal particles. The fused metal hemispheres are utilized to assemble polystyrene colloidal particles of smaller diameters (800 nm) into non-contact two-dimensional periodic array by trapping them in the metallic wells.     

Fixation of a cholesteric helical structure by the photopolymerization of a cholesteryl derived monomer

A cholesteryl derived monomer was synthesized according to a conventional synthetic route; it exhibits a cholesteric phase above 129°C, and shows a red colour due to selective reflection in the cholesteric phase. Photopolymerization of the monomer was carried out at 135°C in the cholesteric phase. The helical structure of the cholesteric phase of the monomer was frozen by photopolymerization. A peak based on the selective reflection of the cholesteric phase was detected at 615 nm in the transmittance UV-Vis spectrum. Mixtures of the monomer with a binaphthyl derivative were prepared to control the selective reflection wavelength; they all also exhibited a cholesteric phase. The selective reflection wavelength of the mixture was dependent upon the ratio of the binaphthyl derivative in the mixture. This wavelength became shorter with increasing ratio of the binaphthyl derivative. The polymer films obtained by photopolymerization displayed almost the same selective reflection wavelength as the corresponding mixtures before photopolymerization. The selective reflection wavelength of the polymer films did not change up to about 250°C.     

Measurement of turbulence decorrelation during transport barrier evolution in a high-temperature fusion plasma

A low power polychromatic beam of microwaves is used to diagnose the behavior of turbulent fluctuations in the core of the JT-60U tokamak during the evolution of the internal transport barrier. A continuous reduction in the size of turbulent structures is observed concomitant with the reduction of the density scale length during the evolution of the internal transport barrier. The density correlation length decreases to the order of the ion gyroradius, in contrast with the much longer scale lengths observed earlier in the discharge, while the density fluctuation level remain similar to the level before transport barrier formation.     

Two Distinct Structures of Membrane-Associated Homodimers of GTP- and GDP-Bound KRAS4B Revealed by Paramagnetic Relaxation Enhancement

KRAS homo-dimerization has been implicated in the activation of RAF kinases, however, the mechanism and structural basis remain elusive. We developed a system to study KRAS dimerization on nanodiscs using paramagnetic relaxation enhancement (PRE) NMR spectroscopy, and determined distinct structures of membrane-anchored KRAS dimers in the active GTP- and inactive GDP-loaded states. Both dimerize through an α4–α5 interface, but the relative orientation of the protomers and their contacts differ substantially. Dimerization of KRAS-GTP, stabilized by electrostatic interactions between R135 and E168, favors an orientation on the membrane that promotes accessibility of the effector-binding site. Remarkably, “cross”-dimerization between GTP- and GDP-bound KRAS molecules is unfavorable. These models provide a platform to elucidate the structural basis of RAF activation by RAS and to develop inhibitors that can disrupt the KRAS dimerization. The methodology is applicable to many other farnesylated small GTPases.     

Top-quark-mass enhancement in a seesaw-type quark mass matrix

We investigate the implications of a seesawtype mass matrix, i.e.,M _f?m _LM _F ^?1 m _R, for quarks and leptonsf under the assumption that the matricesm _L andm _R are common to all flavors (up-/down- and quark-/lepton-sectors) and the matricesM _F characterizing the heavy fermion sectors have the form [(unit matrix)+b _f (a democratic matrix)] whereb _f is a flavor parameter. We find that by adjusting the complex parameterb _f, the model can provide thatm _t?m _b while at the same time keepingm _u??m _d without assuming any parameter with hierarchically different values betweenM _U andM _D. The model with three adjustable parameters under the ??maximal?? top-quark-mass enhancement can give reasonable values of five quark-mass ratios and four KM matrix parameters.     

Development and applications of fluorogenic probes for mercury(II) based on vinyl ether oxymercuration

Mercury is a major threat to the environment and to human health. It is highly desirable to develop a user-friendly kit for on-site mercury detection. Such a method must be able to detect mercury below the threshold levels for drinking water, 1-2 ppb. We developed a fluorescence method based on the oxymercuration of vinyl ethers to detect mercury in dental and environmental samples. Chloride ions interfered with the oxymercuration reaction, but the addition of AgNO(3) solved this problem. Fine electronic and structural tuning led to the development of a more responsive probe that was less sensitive to chloride ion interference. This second-generation probe could detect 1 ppb mercury ions in water.     

Two Distinct Structures of Membrane‐Associated Homodimers of GTP‐ and GDP‐Bound KRAS4B Revealed by Paramagnetic Relaxation Enhancement

KRAS homo‐dimerization has been implicated in the activation of RAF kinases, however, the mechanism and structural basis remain elusive. We developed a system to study KRAS dimerization on nanodiscs using paramagnetic relaxation enhancement (PRE) NMR spectroscopy, and determined distinct structures of membrane‐anchored KRAS dimers in the active GTP‐ and inactive GDP‐loaded states. Both dimerize through an α4–α5 interface, but the relative orientation of the protomers and their contacts differ substantially. Dimerization of KRAS‐GTP, stabilized by electrostatic interactions between R135 and E168, favors an orientation on the membrane that promotes accessibility of the effector‐binding site. Remarkably, “cross”‐dimerization between GTP‐ and GDP‐bound KRAS molecules is unfavorable. These models provide a platform to elucidate the structural basis of RAF activation by RAS and to develop inhibitors that can disrupt the KRAS dimerization. The methodology is applicable to many other farnesylated small GTPases.