We have developed novel methods of near-field microspectroscopy by combining near-field optical microscopy with linear and non-linear optical techniques. The developed near-field microscope achieves high spatial resolution and high time resolution, and is applied to studies of local excitations and wave functions of single noble metal nanoparticles. We demonstrate that the plasmon wave functions and the optical fields in the vicinity of nanoparticles are visualized by the near-field methods. Based on these results, we clearly show that localized electromagnetic field enhancement in the vicinity of nanoparticles is one of the most important factors in surface-enhanced spectroscopies. We also extended the methods to ultrafast optical measurements, and show space-resolved ultrafast transient response of single gold nanorods. The characteristic spatio-temporal features observed in the nanorods are revealed to be arising from the changes of the plasmon-mode wave functions upon elevation of photo-induced electronic temperature of the nanorod.
We studied local excitations and wave functions of single noble metal nanoparticles by using newly developed methods of near-field microspectroscopy. We demonstrate that plasmon wave functions and optical fields in the neighbor of nanoparticles are visualized by the near-field methods.
Stimuli-responsive polymers and their application to biomaterials have been widely studied. On the other hand, as a novel biomimetic polymer, we have been studying a polymer with an autonomous self-oscillating function by utilizing oscillating chemical reactions. So far, we have succeeded in developing a novel self-oscillating polymer and gels by utilizing the Belousov–Zhabotinsky (BZ) reaction. The self-oscillating polymer is composed of poly(N-isopropylacrylamide) (PNIPAAm), in which Ru(bpy)32+ is incorporated as a catalyst for the BZ reaction. Under the coexistence of the reactants (malonic acid, sodium bromate, and nitric acid), the polymer undergoes spontaneous cyclic soluble–insoluble changes or swelling–deswelling changes (in the case of gel) without any on–off switching of external stimuli. In this paper, our recent studies on the self-oscillating polymer and the design of functional material systems using the polymer are summarized.
As a novel biomimetic polymer, we have been studying a polymer with an autonomous self-oscillating function by utilizing oscillating chemical reactions. In this paper, our recent studies on the self-oscillating polymer and the design of functional material systems are summarized.
ω-Hydroxy ketones and diketones, which are important starting materials for the synthesis of cycloalkanones and heterocyclic compounds, were prepared by the one-step reaction of methyl ketones with α,ω-diols under the influence of an iridium complex and a base. The selectivity of ω-hydroxy ketones and diketones could be controlled by varying the starting ratio of methyl ketones to α,ω-diols. For example, reaction using acetophenone (5 equiv) with respect to 1,6-hexanediol (1 equiv) in the presence of [IrCl(cod)]2, PPh3, and KOH without solvent gave 1,10-diphenyl-1,10-decanedione in almost quantitative yield, while reaction using acetophenone (1 equiv) to 1,6-hexanediol (4 equiv) led to 8-hydroxy-1-phenyl-1-octanone in 92% yield. This methodology was successfully extended to the reaction of arylacetonitriles with α,ω-diols leading to diaryldinitriles.
ω-Hydroxy ketones and diketones, which are important starting materials for the synthesis of cycloalkanones and heterocyclic compounds, were prepared by one-step reaction of methyl ketones with α,ω-diols under the influence of an iridium complex and a base.
A Monte Carlo (MC) simulation in the isobaric–multithermal (MUTH) ensemble has been carried out for a bulk Lennard–Jones fluid system that consists of 108 particles to investigate the validity of the algorithm. After we obtain the best estimate of the MUTH (isobaric–multithermal) weight factor, the probability distributions, the expectation values of some physical quantities, and the radial distribution functions are calculated for the temperature range between T*=0.417 and 1.00 under the pressure of P*=2.42×10−3 from the MUTH MC production run by adopting reweighting techniques. The thermodynamic quantities exhibit the characteristics of first-order phase transitions at T*=0.726, which correspond to the transition from face-centered-cubic (f.c.c.) solid to liquid by judging from the radial distribution functions and the snapshots. The obtained contour representation of the probability distribution at T*=0.726 and P*=2.42×10−3 shows two distinct configurational spaces. The changes in thermodynamic quantities at the phase-transition temperature of Lennard–Jones argon (at 87 K under 1 atm) were also compared with those of real argon.
Of the three components of the liquid junction potential between electrolyte solutions in different solvents, the component due to the interaction between different solvents (component (c)) was studied using mixed solvent/pure solvent junctions. According to our model of component (c), the component at a mixed solvent/pure solvent junction should vary linearly with the volume fraction of the mixed solvent. We previously confirmed this experimentally. However, there are exceptional cases in which nonlinear (curved) relationships are observed. In the present work, I found that most of the curved relationships are obtained for mixtures between an amphiprotic solvent (water, formamide, or N-methylformamide) and an aprotic solvent of very low acceptor number (N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, acetone, or hexamethylphosphoric triamide). In contrast, for an aprotic solvent of moderate acceptor number (nitromethane, dimethyl sulfoxide, acetonitrile, or propylene carbonate), linear or near-linear relationships are observed. The observed curved relationships were concluded to be due to that the structure-forming amphiprotic solvent is more likely to and the aprotic solvent less likely to settle at the interphasial region than in the bulk, because the dipolar molecules of the aprotic solvent of very low acceptor number have a vague positive charge-center.
Spectrophotometric study was applied to the interaction of SbF3 with para-, meta-, and ortho-substituted meso-tetraarylporphyrins (H2t(Xp)p; X: H, OCH3, CH3, and Cl) in CHCl3. The 1:1 formation constants of the resulting complexes were calculated at several temperatures by the computer fitting of absorbances of solutions versus mole ratio data with appropriate equations. Thermodynamic parameters (ΔG0, ΔH0, and ΔS0) have been determined and the influence of electron donation and steric effect of the substituted aryl groups in the free base porphyrins on the stability of the complexes is discussed.
Mononuclear [Cu(HL)] (1) and trinuclear [Cu3(L)2] (3) complexes were synthesized, where H3L (1,1,1-tris[(salicylideneamino)methyl]ethane) is a tripodal ligand obtained by condensation of 1,1,1-tris(aminomethyl)ethane and salicylaldehyde in a 1:3 mole ratio. Another mononuclear complex [Cu(HL′)] (2), where one of the three arms was disconnected probably due to thermal hydrolysis, was also obtained. The crystal structures, electronic spectra, and electrochemical and magnetic properties of the complexes were studied. In 1, one of the arms of H3L is not coordinated to the metal atom, and the ligand serves as a tetradentate N2O2 ligand, the complex assuming a slightly distorted square-planar structure. In the trinuclear complex, an imine nitrogen atom and a phenolate oxygen atom of one arm of each terminal unit coordinate to the central CuII ion to form a linear trinuclear complex. The coordination geometry about each Cu is square planar. All of the complexes involve π–π stacking interactions between the molecules in the crystal structures, which are responsible for weak magnetic interactions. An electrochemical study of 3 in DMSO showed that the central CuII is more easily reduced to CuI than the terminal Cu ions. The mononuclear complexes, 1 and 2, show a quasi-reversible CuII/I couple almost at the same position as that of the terminal Cu ions of 3.
In-site gold electro-deposition and electro-dissolution have been examined using polycrystalline gold-coated quartz crystal electrode in a room-temperature ionic liquid of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4). In EMIBF4 media containing 1-ethyl-3-methylimidazolium chloride, the species of AuI (probably [AuICl2]−) resulting from the electrochemical oxidation of the Au surface was very stable and a reversible voltammetric response of the AuI/Au0 couple was observed at 0.25 V vs. Ag wire quasi-reference electrode (Ag(QRE)). In situ electrochemical quartz crystal microbalance (EQCM) technique combined with cyclic voltammetry, double potential-step chronoamperometry and double potential-step chronocoulometry has been successfully applied to investigate the cathodic deposition of AuI ion to Au metal and the anodic dissolution of Au from the Au electrode surface. It was found that the frequency change of quartz crystal electrode during the electrolysis can be interpreted in terms of rigid mass changes based on the Sauerbrey equation. The EQCM analysis of the electro-dissolution and electro-deposition of Au in the potential range of −0.60 to 0.50 V vs. Ag(QRE) gave the molecular mass equivalent of Au (197 g mol−1) corresponding to a one-electron reduction and oxidation of the AuI/Au0 redox couple.
The hydrophobic value <H> and hydrophobic moment value <μ> of helical peptides correlate with membrane–peptide interactions such as ion channel forming or membrane perturbation. In this paper, two cationic amphiphilic peptides, ALSAALKAALSWASLAAKLAASLA-amide (Ap) and KK-ALSAALKAALSWASLAAKLAASLA-KK-amide (KAp), consisting of 24 and 28 amino acid residues, respectively, were synthesized to acquire antimicrobial activities and to reduce the high hemolytic activity of cationic helical peptide, LARLLARLLARLLRALLRALLRAL-amide (46), reported previously. Both peptides were designed to possess higher hydrophobic values and lower hydrophobic moment values than those of 46. Circular dichroism (CD) measurements of the peptides showed that the peptides had lower α-helical content than that of 46 in aqueous solutions as well as the membrane mimetic environments. 46 did not show any antibacterial activity whereas KAp and Ap had antibacterial activities against Gram-positive and -negative bacteria. In contrast, the hemolytic activities of Ap and KAp decreased to less than that of 46. Electrophysiological experiments were carried out to compare ion channel formation. Both peptides showed ion conductance patterns distinguishable from the patterns of 46 and pore forming with flexible structures was suggested. In addition, the flanking cationic residues of KAp tended to increase the channel opening durations.
The stereochemistry of nucleophilic addition of amines to (E)-1-tosyl-1,3-butadiene was investigated. The Z/E ratios of the resulting allylic sulfones varied with amines, solvents, temperature, and concentration. When diethylamine was reacted in low concentration at high temperature, the corresponding sterically unfavorable (Z)-4-amino-2-butenyl sulfone was preferentially obtained. The stereochemistry of nucleophilic addition of amines to ethyl (E)-2,4-pentadienoate, which possesses an ester group as a conjugated electron-withdrawing group instead of a p-toluenesulfonyl (Ts) group, was also found to realize similar high Z selectivity. The predominant formation of Z isomers in both cases was rationalized by a “syn effect,” which might be mainly due to n⁄σ→π* interaction and/or 6π-electron homoaromaticity.
Dicyclohexane-annelated anthracene was synthesized by a new efficient method, which employed the Diels–Alder reaction between in situ-generated 2,3-dehydronaphthalene and dicyclohexane-fused furan. The molecule adopted antiparallel face-to-face slipped π-stacking in its crystal structure, which induced an excimer-like emission in the solid state.
The intercalation compound of a layered titanate with 2-aminoethanethiol was synthesized to prepare and support Au nanoparticles with morphology replicated by two-dimensional nanospace. The morphology of the formed Au nanoparticles was revealed to be plate, and the thickness and diameter of the platy particles varied with the added amount of Au source; less than 0.7 nm and ca. 6.8 nm, less than 0.9 nm and ca. 6.5 nm, and less than 0.9–1.0 nm and ca. 5.7 nm at molar Au/SH ratios of 0.5, 1.5, and 2.0 respectively. Platy Au nanoparticle-supported layered titanate (Au/SH ratio of 0.5) was thermally stable up to 180 °C in air and 160 °C in helium, respectively.
Highly dispersed metal oxide nanoparticle sols are of great interest in science and engineering because of their broad potential applications in optics, electronics, sensors, catalysis, biomedicines, and even in cosmetics. Here, we report the size-controlled synthesis of cerium oxide nanoparticle sols by a reflux method with poly(vinylpyrrolidone) as a coating agent to afford stable monodispersions of spherical particles with size of 50–120 nm. The size of nanoparticles can be easily controlled by appropriate adjustment of the molecular weight of the added polymer. Colloidal crystals of cerium oxide are also obtained by evaporation of the cerium oxide sol. As cerium oxide has a larger refractive index than silica and polymers typically used for the preparation of colloidal crystals, the present sols are expected to be useful for the fabrication of high-performance photonic crystals.
The ion exchange of dodecylammonium ion was examined for two potassium lithium titanates; the titanates were K0.80Ti1.71Li0.29O3.97 prepared by a solid-state reaction at 800 °C and K0.66Ti1.73Li0.27O3.93 prepared by a solid-state reaction at 1020 °C followed by reaction with aqueous H2SO4 and subsequent annealing. A single phase intercalation compound formed successfully for K0.66Ti1.73Li0.27O3.93 (the amount of the adsorbed dodecylammonium was 2.1 mmol g−1) by reaction with an aqueous solution of dodecylammonium chloride. On the other hand, the parent titanate remained for K0.80Ti1.71Li0.29O3.97 (1.4 mmol g−1).
Transmission gratings of holographic polymer dispersed liquid crystals (HPDLCs) have been designed and fabricated based on partial fluorination of the polymer matrix using three types of fluorinated monomers carrying different numbers of fluorine atoms and structures, viz. 2-(perfluoroalkyl)ethyl methacrylate (PFEMA), 2,2,2-trifluoroethyl methacrylate (TFEMA), and 2,2,2-trifluoroethyl acrylate (TFEA). Addition of fluorinated monomer gave long saturation time, increased off state diffraction efficiency, small anchoring strength and driving voltage. Anchoring strength and driving voltage of methacrylate monomers (PFEMA and TFEMA) were lower than that of TFEA, implying that the fluorine segments of these monomers are preferentially exposed to the interfaces. HPDLC film having low driving voltage and response time of below 10 ms has been fabricated with 20 wt % PFEMA at 40 wt % LC.
Upon ionic complexation of tris(2-aminoethyl)amine and di- or trialkoxybenzoic acids with normal and branched chains, hexagonal columnar mesophases were generated. The two parameters, the length and the cross-sectional area of the alkyl chains, were investigated to unveil the volume effect of the alkyl chains on the formation and stabilization of the columnar mesophases. The thermal stabilities of the columnar phases were strongly depended on the molar ratio of the acids to the amine. The highest clearing temperature (the most stable mesophase) was obtained at a ratio specific to the alkyl chain volume, not necessarily stoichiometric. We estimated the packing fraction (Vcomp⁄Vcell) on the basis of the volume of the ionic complexes at these particular ratios (Vcomp) and that of the unit cell of the Colhex phases (Vcell). The most suitable packing fractions for the Colhex phases of the present ammonium carboxylates were estimated to be in a range of 0.63–0.66.