Disk- and rod-shaped molecules are incompatible in coassembly, as the former tend to stack one-dimensionally whereas the latter tend to align in parallel. Because this type of incompatibility can be ...more pronounced in condensed phases, different-shaped molecules generally exclude one another. We report that supramolecular polymerization of a disk-shaped chiral monomer in nematic liquid crystals comprising rod-shaped molecules results in order-increasing mesophase transition into a single mesophase with a core-shell columnar geometry. This liquid crystalline material responds quickly to an applied electric field, resulting in unidirectional columnar ordering. Moreover, it can be modularly customized to be optoelectrically responsive simply by using a photoisomerizable rod-shaped module. The modular strategy allows for cooperative integration of different functions into elaborate dynamic architectures.
Time-resolved direct observations of proteins in action provide essential mechanistic insights into biological processes. Here, we present mechanisms of action of protein disulfide isomerase ...(PDI)-the most versatile disulfide-introducing enzyme in the endoplasmic reticulum-during the catalysis of oxidative protein folding. Single-molecule analysis by high-speed atomic force microscopy revealed that oxidized PDI is in rapid equilibrium between open and closed conformations, whereas reduced PDI is maintained in the closed state. In the presence of unfolded substrates, oxidized PDI, but not reduced PDI, assembles to form a face-to-face dimer, creating a central hydrophobic cavity with multiple redox-active sites, where substrates are likely accommodated to undergo accelerated oxidative folding. Such PDI dimers are diverse in shape and have different lifetimes depending on substrates. To effectively guide proper oxidative protein folding, PDI regulates conformational dynamics and oligomeric states in accordance with its own redox state and the configurations or folding states of substrates.
Peristaltic crawling, which is the moving mechanism of earthworm‐like limbless creatures in narrow spaces, is a challenging target to mimic by using soft materials. Here we report an unprecedented ...hydrogel actuator that enables not only a peristaltic crawling motion but also reversing its direction. Our cylindrically processed hydrogel contains gold nanoparticles for photothermal conversion, a thermoresponsive polymer network for switching the electrical permittivity of the gel interior, and cofacially oriented 2D electrolytes (titanate nanosheets; TiNSs) to synchronously change their anisotropic electrostatic repulsion. When a hydrogel, which was designed to include cofacially oriented TiNSs along the cylindrical gel axis, is pointwisely photoirradiated with a visible‐light laser, it spatiotemporally expands immediately (<0.5 s) and largely (80 % of its original length) in an isovolumetric manner. When the irradiation spot is moved along the cylindrical gel axis, the hydrogel undergoes peristaltic crawling due to quick and sequential elongation/contraction events and moves oppositely toward the laser scanning direction. Thus, when the scanning direction is switched, the crawling direction is reversed. When gold nanorods are used in place of gold nanoparticles, the hydrogel becomes responsive to a near‐infrared light, which can deeply penetrate into bio tissues.
Soft robot: An unprecedented photoresponsive hydrogel actuator enables earthworm‐like peristaltic crawling and reverses its direction by scanning with a laser spotlight. This anomalous optical control was made possible by a rapid, large, repeatable, spatiotemporal, and anisotropic photothermal deformation of a hydrogel that contains gold nanoparticles in titanate nanosheets.
Abstract
Although various biomimetic soft materials that display structural hierarchies and stimuli responsiveness have been developed from organic materials, the creation of their counterparts ...consisting entirely of inorganic materials presents an attractive challenge, as the properties of such materials generally differ from those of living organisms. Here, we have developed a hydrogel consisting of inorganic nanosheets (14 wt%) and water (86 wt%) that undergoes thermally induced reversible and abrupt changes in its internal structure and mechanical elasticity (23-fold). At room temperature, the nanosheets in water electrostatically repel one another and self-assemble into a long-periodic lamellar architecture with mutually restricted mobility, forming a physical hydrogel. Upon heating above 55 °C, the electrostatic repulsion is overcome by competing van der Waals attraction, and the nanosheets rearrange into an interconnected 3D network of another hydrogel. By doping the gel with a photothermal-conversion agent, the gel-to-gel transition becomes operable spatiotemporally on photoirradiation.
Antheraea yamamai silk contains long poly(alanine) sequences that contribute to β-sheet crystals, which are responsible for the high tensile strength of silk fibers. We determined the crystal ...structure, physical properties, and morphology of A. yamamai cocoon silk fibers. The crystal lattice of A. yamamai silk fiber consists of antiparallel β-pleated sheets with an orthogonal unit cell (a = 10.72 Å, b = 9.73 Å, c fiber axis = 6.80 ± 0.05 Å). Wide-angle X-ray scattering and birefringence measurements revealed that stretching deformation does not affect the crystal structure but contributes to alignment of silk molecules along the fiber axis in the partial amorphous phase. Crystallinity and amino acid sequence analyses suggested that the poly(alanine) region can be partially crystallized. The long poly(alanine) sequences therefore do not contribute to the mechanical, thermal, or structural properties of A. yamamai silk. Our results may aid the design and development of A. yamamai silk-based materials.
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•The crystal structure of Antheraea yamamai silk were investigated.•The mechanical and thermal properties of A. yamamai silk were characterized.•The poly(alanine) sequence was partially crystalized in the beta-sheet crystals.
Covalent organic synthesis commonly uses the strategy of selective bond cleavage and formation. It a similar approach can be applied stepwisely to noncovalent synthesis, more exotic or challenging ...nanostructures might become achievable. Here, we report that ferrocene-based tetratopic pyridyl ligands, which can dynamically change their geometry by means of thermal rotation of their cyclopentadienyl rings in solution, assemble with AgBF4 into discrete metal-organic nanotubes with large and uniform diameters. The nanotubes can be cut into metal-organic nanorings through selective attenuation of the inter-nanoring interaction via ferrocene oxidation. The resultant nanorings can be transferred onto inorganic substrates electrostatically or allowed to reassemble to form the original nanotube by the reductive neutralization of their oxidized ferrocene units.
Fluids that contain ordered nanostructures with periodic distances in the visible-wavelength range, anomalously exhibit structural colours that can be rapidly modulated by external stimuli. Indeed, ...some fish can dynamically change colour by modulating the periodic distance of crystalline guanine sheets cofacially oriented in their fluid cytoplasm. Here we report that a dilute aqueous colloidal dispersion of negatively charged titanate nanosheets exhibits structural colours. In this 'photonic water', the nanosheets spontaneously adopt a cofacial geometry with an ultralong periodic distance of up to 675 nm due to a strong electrostatic repulsion. Consequently, the photonic water can even reflect near-infrared light up to 1,750 nm. The structural colour becomes more vivid in a magnetic flux that induces monodomain structural ordering of the colloidal dispersion. The reflective colour of the photonic water can be modulated over the entire visible region in response to appropriate physical or chemical stimuli.
Semiconducting colloidal quantum dots and their assemblies exhibit superior optical properties owing to the quantum confinement effect. Thus, they are attracting tremendous interest from fundamental ...research to commercial applications. However, the electrical conducting properties remain detrimental predominantly due to the orientational disorder of quantum dots in the assembly. Here we report high conductivity and the consequent metallic behaviour of semiconducting colloidal quantum dots of lead sulphide. Precise facet orientation control to forming highly-ordered quasi-2-dimensional epitaxially-connected quantum dot superlattices is vital for high conductivity. The intrinsically high mobility over 10 cm
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and temperature-independent behaviour proved the high potential of semiconductor quantum dots for electrical conducting properties. Furthermore, the continuously tunable subband filling will enable quantum dot superlattices to be a future platform for emerging physical properties investigations, such as strongly correlated and topological states, as demonstrated in the moiré superlattices of twisted bilayer graphene.
A mixture of ferrocene-based tetratopic pyridyl ligands FcL1 and FcL2 undergoes self-sorting upon competitive coordination with AgBF4, affording homomeric nanotubes FcNT1 and FcNT2 as a mixture. No ...mutual interference for the nanotubular growth occurred between FcNT1 and FcNT2 even when one of these ligands was used in large excess with respect to the other. 2D X-ray diffraction analysis of unidirectionally oriented nanotube samples, prepared by using the capillary technique, revealed that although FcL1 as reported previously stacks helically in the resulting nanotube FcNT1 FcL2 prefers to stack with no discernible helical twist in FcNT2. Such a difference in their stacking geometries is most likely a major reason for why mixed-ligand metal–organic nanotubes are not constructed upon competitive coordination of FcL1 and FcL2 with AgBF4.
Paramylon, which is a β-(1,3)-D-glucan photosynthesized by Euglena, was chemically modified by esterification. Various paramylon triesters with different alkyl chain lengths (carbon numbers 2–12) ...were successfully prepared. All of the paramylon triesters have higher thermal degradation temperatures than that of neat paramylon. Moreover, it was found that the paramylon triesters with C2–C6 alkyl chains are crystalline polymers with melting temperatures from 281 °C to 114 °C, and those with C8–C12 alkyl chains are amorphous polymers, confirmed by both DSC and X-ray diffraction analysis. Paramylon triesters with C3–C12 alkyl chains could shape self-sustaining films by both solvent-casting and melt-quench methods with high optical transmittance and sufficient tensile strength or elongation at break. Thermal and mechanical properties of paramylon triesters can be controlled freely from hard to soft by substituted acyl length. In the cases of the crystalline paramylon triesters, highly oriented and crystallized films could be fabricated by the thermally stretched method, and their tensile strengths have been obviously improved. Well-oriented X-ray fiber diagrams of the stretched and crystallized films suggest that all of the paramylon triesters have rare 5-fold helix conformation of molecular chains in crystal.
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