Takahito Imai

Effect of pulsed DC current on neck growth between tungsten wires and tungsten plates during the initial stage of sintering by the spark plasma sintering method

The spark plasma sintering of tungsten wires to tungsten plates was investigated to assess the effect of the current. Neck growth between wires and plates was about 1.5 larger in the presence of current than when the current was absent. The neck growth was controlled by an evaporation–condensation mechanism. The mechanism, however, does not relate to the sintering of tungsten, but to the control of a surface oxide reduction, in agreement with previous investigations.

Biomimetic alignment of zinc oxide nanoparticles along a peptide nanofiber.

Zinc oxide (ZnO) has potential applications in solar cells, chemical sensors, and piezoelectronic and optoelectronic devices due to its attractive physical and chemical properties. Recently, a solution-phase method has been used to synthesize ZnO crystals with diverse (from simple to hierarchical) nanostructures that is simple, of low cost, and scalable. This method requires template molecules to control the morphology of the ZnO crystals. In this paper, we describe the design and synthesis of two short peptides (RU-003,Ac-AIEKAXEIA-NH(2); RU-027, EAHVMHKVAPRPGGGAIEKAXEIA-NH(2); X = l-2-naphthylalanine) and the characterization of their self-assembled nanostructures. We also report their potential for ZnO mineralization and the alignment of ZnO nanoparticles along peptide nanostructures at room temperature. Interestingly, nonapeptide RU-003 predominantly formed a straight fibrous structure and induced the nucleation of ZnO at its surface, leading to an alignment of ZnO nanoparticles along a peptide nanofiber. This novel method holds promise for the room-temperature fabrication of ZnO catalysts with increased specific surface area, ZnO-gated transistors, and ZnO-based nanomaterials for optical applications.

Ultrathin Gold Nanoribbons Synthesized within the Interior Cavity of a Self-Assembled Peptide Nanoarchitecture

There is increasing interest in gold nanocrystals due to their unique physical, chemical, and biocompatible properties. In order to develop a template-assisted method for the fabrication of gold nanocrystals, we demonstrate here the de novo design and synthesis of a β-sheet-forming nonapeptide (RU006: Ac-AIAKAXKIA-NH2, X = L-2-naphthylalanine) which undergoes self-assembly to form disk-like nanoarchitectures approximately 100 nm wide and 2.5 nm high. These self-assemblies tend to form a network of higher-order assemblies in ultrapure water. Using RU006 as a template molecule, we fabricated ultrathin gold nanoribbons 50-100 nm wide, 2.5 nm high, and micrometers long without external reductants. Furthermore, in order to determine the mechanism of ultrathin gold nanoribbon formation, we synthesized four different RU006 analogues. On the basis of the results obtained using RU006 and these analogues, we propose the following mechanism for the self-assembly of RU006. First, RU006 forms a network by the cooperative association of disk-like assemblies in the presence of AuCl4(-) ions that are encapsulated and concentrated within the interior cavity of the network architectures. This is followed by electron transfer from the naphthalene rings to Au(III), resulting in slow growth to form ultrathin gold nanoribbons along the template network architectures under ambient conditions. The resulting ribbons retain the dimensions of the cavity of the template architecture. Our approach will allow the construction of diverse template architectural morphologies and will find applications in the construction of a variety of metallic nanoarchitectures.

A New Method of Determining Short-Range Order Parameter in Relaxor Pb(Ni1/3Nb2/3)O3 by Magnetic Susceptibility Measurement.

We synthesized Pb(Ni1/3Nb2/3)O3 (PNN) and performed selected-area electron diffraction (SAD) in order to investigate the structure of the B-site array. In addition to the reflection from the basic cell, the SAD pattern of sintered PNN corresponds to the reciprocal plane normal to the [011] zone axis and showed diffuse scatterings at (½½½) positions. We also measured the magnetic susceptibility of PNN and discussed the short-range ordering around Ni2+ ions by analyzing the susceptibility based on a simple model.

Photosalient Phenomena that Mimic Impatiens Are Observed in Hollow Crystals of Diarylethene with a Perfluorocyclohexene Ring

A diarylethene with a perfluorocyclohexene ring formed hollow crystals by sublimation under normal pressure. Upon UV irradiation of the crystals, they showed remarkable photosalient phenomena and scattered into small pieces. The speed of the flying debris released from the crystal by UV irradiation exceeded several meters per second. To clearly show a photosalient effect resembling the scattering behavior of Impatiens on a smaller scale, small fluorescent beads (1-μm diameter) were inserted into the hollow crystal. Consequently, scattering of the beads was observed as UV irradiation caused deformation and bursting of the hollow structure. This phenomenon is unique to hollow crystals, and the ability to effectively induce remarkable photosalient phenomena is similar to the behavior of hollow-structured Impatiens in nature.

Phase transition of ferroelectric (LixNa1−x)NbO3 films with 0 ≤ x ≤ 0.13 by applying an electric field

We fabricated 001-oriented (LixNa1−x)NbO3 (LNN) films with 0 ≤ x ≤ 0.13 on (001)SrTiO3 substrates by pulsed laser deposition. From the structural and electrical studies, we found that the crystal structure of the LNN film changed by applying an electric field, and the newly formed metastable phases did not return to the original phase. The ferroelectric properties were drastically changed by the phase transition induced by applying electric field. The induced metastable phase returned to the initial phase by heating. Finally, we first determined the phase relation in the LNN film between applying electric field and chemical composition (Li content, x).

Roles of aromatic side chains and template effects of the hydrophobic cavity of a self-assembled peptide nanoarchitecture for anisotropic growth of gold nanocrystals

Gold nanocrystals are promising as catalysts and for use in sensing/imaging systems, photonic/plasmonic devices, electronics, drug delivery systems, and for photothermal therapy due to their unique physical, chemical, and biocompatible properties. The use of various organic templates allows control of the size, shape, structure, surface modification and topology of gold nanocrystals; in particular, currently the synthesis of gold nanorods requires a cytotoxic surfactant to control morphology. To control the shape of gold nanocrystals, we previously demonstrated the de novo design and synthesis of a β-sheet-forming nonapeptide (RU006: Ac-AIAKAXKIA-NH2, X=L-2-naphthylalanine, Nal) and the fabrication of gold nanocrystals by mixing RU006 and HAuCl4 in water. The reaction afforded ultrathin gold nanoribbons 50-100 nm wide, several nanometers high, and microns long. To understand the mechanism underlying gold nanoribbon formation by the RU006 system, we here report (i) the effects of replacement of the Nal aromatic side chain in the RU006 sequence with other aromatic moieties, (ii) the electrochemical properties of aromatic side chains in the de novo designed template peptides to estimate the redox potential and number of electrons participating in the gold crystallization process, and (iii) the stoichiometry of the RU006 system for gold nanoribbon synthesis. Interestingly, RU006 bearing a naphthalene moiety (oxidation peak potential of 1.50 V vs Ag/Ag(+)) and an analog [Ant(6)]-RU006 bearing a bulky anthracene moiety (oxidation peak potential of 1.05 V vs Ag/Ag(+)) allowed the growth of anisotropic (ribbon-like) and isotropic (round) gold nanocrystals, respectively. This trend in morphology of gold nanocrystals was attributed to spatially-arranged hydrophobic cavities sufficiently large to accommodate the gold precursor and to allow directed crystal growth driven by cross-linking reactions among the naphthalene rings. Support for this mechanism was obtained by decreasing the mole fraction of [Ant(6)]-RU006 against the total concentration of [Ant(6)]-RU006 and [Phe(6)]-RU006: absorption spectra similar to that for RU006 were obtained. Differences in the redox properties of the anthracene and naphthalene moieties scarcely affected morphology. We propose that construction of an appropriate hydrophobic cavity is important for templating gold nanocrystal architectures by peptide self-assembly. This mechanism would be applicable for developing simple, low toxicity, mild synthetic methods for constructing metallic nanomaterials for therapeutic use.

Ferroelectric properties of (Li,K,Na)NbO3 epitaxial films fabricated by pulsed laser deposition

(LixK0.1Na0.9−x)NbO3 (x = 0, 0.05, 0.1, and 0.2) epitaxial films were prepared by pulsed laser deposition on SrRuO3/(001)SrTiO3 substrates. Reciprocal space mapping indicated that the crystal systems of the films were antiferroelectric orthorhombic at x = 0, antiferroelectric orthorhombic and/or ferroelectric monoclinic depending on film thickness at x = 0.05, ferroelectric monoclinic at x = 0.1, and ferroelectric rhombohedral at x = 0.2. Polarization–electric field responses were ferroelectric for all the films. At x = 0.05, the remanent polarization was maximized to ~35 µC/cm2, which was more than four times larger than that at x = 0. This was probably due to a stabilized monoclinic phase under a high electric field.

α-Helical Peptide-Gold Nanoparticle Hybrids: Synthesis, Characterization, and Catalytic Activity

BACKGROUND Gold nanoparticles are promising nanomaterials for catalytic reactions, sensing/imaging systems, photonic/plasmonic devices, and electronics because of their unique physical and chemical properties. To date, significant catalytic activities of gold nanoparticles have been reported for reactions such as carbon monooxide oxidation and 4-nitrophenol reduction, and diverse gold nanoparticle morphologies such as nanospheres, wires, rods, and cubes have been achieved using a variety of capping/stabilizing organic molecules. However, there are few reports on the simultaneous assembly of peptides forming secondary structures and metallic nanoparticles into peptide-metallic particle hybrids under mild aqueous conditions and demonstration of their use as catalysts. Furthermore, the gold nanoribbon surfaces are covered with β-sheet structures, disrupting the access of substrates to the active sites, thereby possibly inhibiting their catalytic activity. OBJECTIVES The main objective of this study is design, synthesis, and characterization of peptidegold nanoparticle hybrids that are prepared by an α-helical conformation of a template and examination of the catalytic activities of the hybrids. METHODS We here report (i) the design, synthesis, and characterization of a new template peptide, RU025, that tends to form an α-helical conformation and self-assembles into network nanoarchitectures in aqueous solution through possibly hydrophobic and electrostatic interactions, (ii) the characterization of gold seed crystals synthesized by mixing RU025 and HAuCl4, (iii) the characterization of peptide-gold nanoparticle hybrids directed by crystal growth with NaBH4 and the dependence on the conditions used for nucleation, and (iv) the catalytic activities of the hybrids towards the reduction of 4-nitrophenol to 4-aminophenol in the presence of excess NaBH4. RESULTS We demonstrated the design, synthesis, and characterization of a new template peptide, RU025, that tends to form an α-helical conformation and self-assembles into network nanoarchitectures in aqueous solution. Gold seed crystals were synthesized by mixing RU025 and HAuCl4 in a 1:2 molar ratio, followed by further reduction of the gold seed crystals with NaBH4. This reaction afforded worm-like gold nanoparticles embedded in the peptide self-assemblies. The peptide-gold nanoparticle hybrids exhibited catalytic activities for the Langmuir-Hinshelwood type reduction of 4-nitrophenol to 4-aminophenol in the presence of excess NaBH4, with an activation energy of 33 kJ mol-1. CONCLUSION The size and morphology of gold nanoparticles can be tuned in the nanometer range by altering the peptide concentration relative to HAuCl4 and by changing the nucleation time. This method for constructing peptide-metallic nanoparticle hybrids, in which metallic nanoparticles are dispersed in the peptide self-assemblies, provides highly reactive catalysts.

Incorporation of an N-methyl amino acid into a template peptide alters anisotropy in the crystal growth of gold nanoparticles synthesized by the peptide template method

BACKGROUND Gold nanocrystals have unique physicochemical and biocompatible properties, and hold promise for use as catalysts and in the fields of electronics, photonic and/or plasmonic devices, sensing and/or imaging systems, targeted drug delivery, and photothermal therapies. A variety of organic templates have been used to control the size, shape, and structure of gold nanocrystals, and to modify their surfaces. For the control of the shape of gold nanocrystals, we previously designed and synthesized a β-sheet-forming nonapeptide (RU006: Ac- AIAKAXKIA-NH2, X = L-2-naphthylalanine, Nal). A mixture of RU006 and HAuCl4 in water produced ultrathin gold nanoribbons with 50-100 nm wide, several nanometers high, and microns long. OBJECTIVES The main objective of this study is the control of the nanoribbon crystal growth by designing and synthesizing RU006 analogs containing an N-methyl-L-alanine residue. METHODS We report (i) the design and synthesis of four RU006 analogs in which an L-alanine (Ala) at four positions in the RU006 sequence (N-methylated RU006 analogs) is replaced with an N-methyl alanine, (ii) conformational and morphological analyses of the self-assembled Nmethylated RU006 analogs, (iii) gold nanocrystal synthesis by the peptide templating method with N-methylated RU006 analogs, and (iv) the roles of peptide self-assembly in anisotropic gold crystal growth. RESULTS RU006 with an N-methyl moiety at the center position resulted in flattened/platelet gold nanocrystals. It was also found that decreasing the mole fraction of RU006 in mixtures with Nmethylated RU006 analogs afforded significantly different absorption spectra compared to that obtained using RU006 alone under gold nanocrystal synthesis conditions. CONCLUSION We found that morphology of gdd nanocrystals is significantly affected by electron transfer from the naphthalene rings to HAuCl4, accompanied by cross-linking reactions between spatially adjacent naphthalene rings within the hydrophobic cavity of a template assembly.