When mixed with imidazolium ion-based room-temperature ionic liquid, pristine single-walled carbon nanotubes formed gels after being ground. The heavily entangled nanotube bundles were found to untangle within the gel to form much finer bundles. Phase transition and rheological properties suggest that the gels are formed by physical cross-linking of the nanotube bundles, mediated by local molecular ordering of the ionic liquids rather than by entanglement of the nanotubes. The gels were thermally stable and did not shrivel, even under reduced pressure resulting from the nonvolatility of the ionic liquids, but they would readily undergo a gel-to-solid transition on absorbent materials. The use of a polymerizable ionic liquid as the gelling medium allows for the fabrication of a highly electroconductive polymer/nanotube composite material, which showed a substantial enhancement in dynamic hardness.
An amphiphilic hexa-peri-hexabenzocoronene self-assembles to form a pi-electronic, discrete nanotubular object. The object is characterized by an aspect ratio greater than 1000 and has a uniform, 14-nanometer-wide, open-ended hollow space, which is an order of magnitude larger than those of carbon nanotubes. The wall is 3 nanometers thick and consists of helical arrays of the pi-stacked graphene molecule, whose exterior and interior surfaces are covered by hydrophilic triethylene glycol chains. The graphitic nanotube is redox active, and a single piece of the nanotube across 180-nanometer-gap electrodes shows, upon oxidation, an electrical resistance of 2.5 megohms at 285 kelvin [corrected]. This family of molecularly engineered graphite with a one-dimensional tubular shape and a chemically accessible surface constitutes an important step toward molecular electronics.
Printable electrical devices [1,2] are attractive for the development of microelectromechanical systems (MEMS) including sensors, switches, and micromachines. In particular, printable actuators that can infinitely operate in air at low voltages would give a breakthrough in the design of miniaturized mechanical devices. Conjugated polymers can be regarded as potential materials for the fabrication of such soft actuators. [3][4][5][6][7] Although a few examples of conjugated polymer actuators that can work in air have been reported, [8] their complicated configurations require multistage processing that involve, for example, sputter deposition of metallic layer electrodes and electrochemical deposition of polymer layers. Herein we report the first dry actuator that can be fabricated simply through layer-by-layer casting with "bucky gel", a
Self-assembly of a Gemini-shaped, chiral amphiphilic hexa-perihexabenzocoronene having two chiral oxyalkylene side chains, along with two lipophilic side chains, yields graphitic nanotubes with one-handed helical chirality. The nanotubes are characterized by an extremely high aspect ratio of >1,000 and have a uniform diameter of 20 nm and a wall thickness of 3 nm. The nanotubes with right-and left-handed helical senses were obtained from the (S)-and (R)-enantiomers of the amphiphile, respectively, due to an efficient translation of point chirality into supramolecular helical chirality. The (S)-and (R)-enantiomers coassemble at varying mole ratios to give nanotubes, whose circular dichroism profiles are almost unchanged over a wide range of the enantiomeric excess of the amphiphile (100 -20%). The high level of chirality amplification thus observed indicates a long-range cooperativity in the selfassembling process. In sharp contrast, a hexabenzocoronene amphiphile with chiral lipophilic side chains did not form nanotubular assemblies. The present work demonstrates the majority rule in noncovalent systems and also may provide a synthetic strategy toward realization of molecular solenoids. chirality ͉ self-assembly H elicity is one of the most essential structural elements for certain biomolecules such as peptides and DNA. The prominent functions of these biological components have motivated chemists to design artificial helical architectures (1-8), which can be used for a variety of applications such as chiral separation (9, 10) and sensing (11-15), asymmetric synthesis (16), liquid crystals (17-19), nonlinear optics (20, 21), and so forth. Recently, a hot issue of chirality has emerged in relation to the helicity of the hexagonal carbon lattice in carbon nanotubes, because it determines the conductive properties of carbon nanotubes (22-24). Conductive polymers with helical architectures (25) also have attracted attention in view of the concept of molecular solenoids (26,27), although this concept has yet been a dream of scientists, because there are no molecular objects that fulfill certain requisites for conductivity and helicity. Here, we report an example of conductive tubular objects consisting of one-handed helical arrays of a -stacked chiral molecular graphene. Self-assembly of hexa-peri-hexabenzocoronene (HBC) derivatives to form discotic liquid crystals and nanofibers has been studied extensively by Müllen and coworkers (28,29). We recently found that an amphiphilic HBC derivative (1) (Fig. 1) self-assembles in polar organic solvents such as tetrahydrofuran (THF) to give graphitic nanotubes, whose wall consists of a bilayer tape formed from bilaterally coupled columns of -stacked HBC units (30). In the course of this work, we have noticed that the self-assembly of 1, although achiral, gives a mixture of coiled and tubular assemblies under certain conditions, suggesting that the tubular objects also bear a helical structural element. This observation prompted us to design chiral HBC amphiphiles 2 and 3 (Fi...
Helices have long attracted the attention of chemists, both for their inherent chiral structure and their potential for applications such as the separation of chiral compounds or the construction of molecular machines. As a result of steric forces, polymeric o-phenylenes adopt a tight helical conformation in which the densely packed phenylene units create a highly condensed π-cloud. Here, we show an oligomeric o-phenylene that undergoes a redox-responsive dynamic motion. In solution, the helices undergo a rapid inversion. During crystallization, however, a chiral symmetry-breaking phenomenon is observed in which each crystal contains only one enantiomeric form. Crystals of both handedness are obtained, but in a non-racemic mixture. Furthermore, in solution, the dynamic motion of the helical oligomer is dramatically suppressed by one-electron oxidation. X-ray crystallography of both the neutral and oxidized forms indicated that a hole, generated upon oxidation, is shared by the repeating o-phenylene units. This enables conformational locking of the helix, and represents a long-lasting chiroptical memory.
SignificanceMultiple effectors of bacterial pathogens target immune kinases such as BAK1 and BIK1, but it is unclear whether this strategy is employed by fungal pathogens. We reveal here that a fungal effector named NIS1 is broadly conserved in filamentous fungi in the Ascomycota and Basidiomycota, thus being regarded as a core effector, and has the ability to suppress PAMP-triggered immunity. Importantly, NIS1 targets BAK1 and BIK1, interfering with their essential functions for immune activation upon pathogen recognition. Multifaceted analyses including the knockout of NIS1 revealed that it plays a critical role in fungal infection. These findings demonstrate that to infect host plants, filamentous fungi deploy a core effector that attacks conserved immune kinases critical for the ancestral defense system.
Populations of the gecko lizard Gekko hokouensis (Gekkonidae, Squamata) on Okinawajima Island and a few other islands of the Ryukyu Archipelago, Japan, have the morphologically differentiated sex chromosomes, the acrocentric Z chromosome and the subtelocentric W chromosome, although the continental representative of this species reportedly shows no sex chromosome heteromorphism. To investigate the origin of sex chromosomes and the process of sex chromosomal differentiation in this species, we molecularly cloned the homologues of six chicken Z-linked genes and mapped them to the metaphase chromosomes of the Okinawajima sample. They were all localized to the Z and W chromosomes in the order ACO1/IREBP-RPS6-DMRT1-CHD1-GHR-ATP5A1, indicating that the origin of ZW chromosomes in G. hokouensis is the same as that in the class Aves, but is different from that in the suborder Ophidia. These results suggest that in reptiles the origin of sex chromosomes varies even within such a small clade as the order Squamata, employing a variety of genetic sex determination. ACO1/IREBP, RPS6, and DMRT1 were located on the Z long arm and the W short arm in the same order, suggesting that multiple rearrangements have occurred in this region of the W chromosome, where genetic differentiation between the Z and W chromosomes has been probably caused by the cessation of meiotic recombination.
Free-radical polymerization of an imidazolium ion-based ionic liquid bearing a methacrylate group, gelling with single-walled carbon nanotubes (SWNTs), allows fabrication of a mechanically reinforced, electroconductive soft material (bucky plastic). A film sample of this material displays an excellent conductivity of 1 S cm(-1) and a 120-fold enhancement of the Young's modulus at a 7 wt % content of SWNTs. The conductivity is temperature-dependent in the range 5-300 K, suggesting that the conductive process involves carrier hopping. Scanning electron and atomic force micrographs of a bucky plastic film display the presence of crosslinked networks consisting of finely dispersed SWNTs. Such nanotube networks, developed in the polymer matrix, likely suppress slipping of entrapped polymer molecules via a strong interfacial interaction and also facilitate intertubular carrier transport. Although a bucky plastic derived from a vinylimidazolium ion-based ionic liquid monomer shows a comparable conductivity to that of the methacrylate version, the film is brittle irrespective of the presence or absence of SWNTs.
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