Hirofumi Kawazumi

Rapid Transformation from Spherical Nanoparticles, Nanorods, Cubes, or Bipyramids to Triangular Prisms of Silver with PVP, Citrate, and H2O2

Rapid sphere-to-prism (STP) transformation of silver was studied in aqueous AgNO(3)/NaBH(4)/polyvinylpyrrolidone (PVP)/trisodium citrate (Na(3)CA)/H(2)O(2) solutions by monitoring time-dependent surface plasmon resonance (SPR) bands in the UV-vis region, by examining transmission electron microscopic (TEM) images, and by analyzing emitted gases during fast reaction. Roles of PVP, Na(3)CA, and H(2)O(2) were studied without addition of a reagent, with different timing of each reagents addition, and with addition of H(2)O(2) to mixtures of spheres and prisms. Results show that prisms can be prepared without addition of PVP, although it is useful to synthesize smaller monodispersed prisms. A new important role of citrate found in this study, besides a known role as a protecting agent of {111} facets of plates, is an assistive agent for shape-selective oxidative etching of Ag nanoparticles by H(2)O(2). The covering of Ag nanoparticles with carboxylate groups is necessary to initiate rapid STP transformation by premixing citrate before H(2)O(2) addition. Based on our data, rapid prism formation starts from the consumption of spherical Ag particles because of shape-selective oxidative etching by H(2)O(2). Oxidative etching of spherical particles by H(2)O(2) is faster than that of prisms. Therefore, spherical particles are selectively etched and dissolved, leaving only seeds of prisms to grow into triangular prisms. When pentagonal Ag nanorods and a mixture of cubes and bipyramids were used as sources of prisms, rod-to-prism (RTP), cube-to-prism (CTP), and bipyramid-to-prism (BTP) transformations were observed in Ag nanocrystals/NaBH(4)/PVP/Na(3)CA/H(2)O(2) solutions. Shape-selective oxidative etching of rods was confirmed using flag-type Ag nanostructures consisting of a triangular plate and a side rod. These data provide useful information for the size-controlled synthesis of triangular Ag prisms, from various Ag nanostructures and using a chemical reduction method, having surface plasmon resonance (SPR) bands at a desired wavelength.

Plasmon-Enhanced Photocurrent Generation from Self-Assembled Monolayers of Phthalocyanine by Using Gold Nanoparticle Films

The effect of localized electric fields on the photocurrent responses of phthalocyanine that was self-assembled on a gold nanoparticle film was investigated by comparing the conventional and the total internal reflection (TIR) experimental systems. In the case of photocurrent measurements, self-assembled monolayers (SAMs) of a thiol derivative of palladium phthalocyanine (PdPc) were prepared on the surface of gold-nanoparticle film that was fixed on the surface of indium-tin-oxide (ITO) substrate via a polyion (PdPc/AuP/polyion/ITO) or on the ITO surface (PdPc/ITO). Photocurrent action spectra from the two samples were compared by using the conventional spectrometer, and were found that PdPc/AuP/polyion/ITO gave considerably larger photocurrent signals than PdPc/ITO under the identical concentration of PdPc. In the case of the TIR experiments for the PdPc/AuP/polyion/ITO and the PdPc/AuP/Glass systems, incident-angle profiles of photocurrent and emission signals were correlated with each other, and they were different from that of the PdPc/ITO system. Accordingly, it was demonstrated that the photocurrent signals were certainly enhanced by the localized electric fields of the gold-nanoparticle film.

Multidigestion in continuous flow tandem protease-immobilized microreactors for proteomic analysis

Proteolysis by sequence-specific proteases is the key step for positive sequencing in proteomic studies integrated with mass spectrometry (MS). The conventional method of in-solution digestion of protein is a time-consuming procedure and has limited sensitivity. In this study, we report a simple and rapid system for the analysis of protein sequence and protein posttranslational modification by multienzymatic reaction in a continuous flow using the enzyme (trypsin, chymotrypsin, or alkaline phosphatase)-immobilized microreactor. The feasibility and performance of the single microreactor and tandem microreactors that were connected by the different microreactors were determined by the digestion of nonphosphoprotein (cytochrome c) and phosphoproteins (β-casein and pepsin A). The single microreactor showed rapid digestion compared with that of in-solution digestions. Multiple digestion by the tandem microreactors showed higher sequence coverage compared with that by in-solution or the single microreactor. Moreover, the tandem microreactor that was made by using the combination of protease-immobilized microreactor and phosphatase-immobilized microreactor showed the capability for phosphorylation site analysis in phosphoproteins without the use of any enrichment strategies or radioisotope labeling techniques. This approach provides a strategy that can be applied to various types of linking microreactor-based multienzymatic reaction systems for proteomic analysis.

Diode laser-based indirect absorbance detector for capillary electrophoresis

A near-infrared detector has been developed for use in capillary electrophoresis (CE). The detector has a double beam arrangement with signal- to-reference ratioing and operates with a 670-nm diode laser as the light source. The laser beam can be modulated to allow a.c. signal recovery using lock-in amplification. Near-infrared laser dyes have been investigated as background absorbers, and the singly-charged cationic dye rhodamine 700 found to exhibit suitable characteristics for use in indirect absorbance detection in methanol-water mixtures. Separations of a series of tetraalkylammonium compounds have been performed on both a commercial CE apparatus with indirect UV detection and on a home-made instrument incorporating the diode laser detector. The limit of detection (2 × peak-to-peak noise) for the tetrabutylammonium ion with diode laser-based indirect absorbance is 2 · 10−5 M. Both positive and negative peaks are found for these positively- charged analytes displacing a positively charged background absorber. Transfer ratios for all peaks are quantitated and the results compared with theoretical treatments of displacement in indirect detection. For analytes with mobility less than the indirect absorbing ion, measurement of peak area leads directly to the quantity of analyte present in the sample solution.

Angular difference Doppler profiles of the excited hydrogen atom produced in eCH4 collisions and dissociation dynamics of methane

Abstract The Doppler profiles of the Balmer-β lines of H*(n = 4) produced in eCH4 collisions were measured at a resolution of 0.0065 nm. The angular difference Doppler profiles, the difference of two profiles taken at 90° and 45° (55°) with respect to the electron beam, were calculated. Component 1 (the peak of the translational energy distribution at 3 eV and the threshold energy at 21.6 eV) showed a clear anisotropy; the asymmetry parameter b is 0.24 and the anisotropy of atomic emission Jp is 0. The asymmetry parameter shows that the dissociation is slow with respect to the rotation, and/or that the dissociation proceeds toward different directions with respect to the transition dipole moment. These finding that non-spherical Rydberg states converging to either the A2A1 state or the (1t−22 state of CH+4 are intermediate states for the formation of component 1.

Synthesis of Ag–Au and Ag–Pd alloy triangular hollow nanoframes by galvanic replacement reactions without and with post-treatment using NaCl in an aqueous solution

Ag–Au and Ag–Pd alloy triangular hollow nanoframes were prepared using galvanic replacement (GR) reactions of Ag nanoprisms with HAuCl4 and Na2PdCl4 in an aqueous solution. Their growth mechanisms were studied by observing transmission electron microscopic (TEM) and TEM-energy dispersed X-ray spectroscopic (EDS), XRD, and ultraviolet (UV)-visible (Vis)-near infrared (NIR) extinction spectral data. Results show that Ag–Au alloy triangular frames start with formation of a truncated prism, followed by expansion of a hollow structure to the interior of the prism, reformation of the triangular shape, and finally formation of a triangular frame at ambient temperature within a few minutes. On the other hand, triangular Ag–Pd alloy plates are slowly formed by the addition of Na2PdCl4 and heating at 100 °C for 30–120 min. Results show that post-treatment using saturated NaCl solution is effective for the transformation of Ag–Pd alloy nanoplates to Ag–Pd nanoframes. The difference in the formation of nanoframes is explained by the difference in the dealloying rates between Ag–Au alloys by AuCl4− and Ag–Pd alloys by Pd2+. XRD data suggested that hexagonally closed packed (hcp) layers are involved as major components of the triangular Ag–Au and Ag–Pd alloy nanoframes.

Observation of fluidic behavior in a polymethylmethacrylate-fabricated microchannel by a simple spectroscopic analysisPresented at the International Symposium on Microchemistry and Microsystems (ISMM 2001), Kawasaki, Japan, September 16?18, 2001.

An easy-to-use and low cost microreactor made of polymethylmethacrylate was mechanically fabricated with a microchannel (200 microm x 200 microm). The laminar flow behavior was investigated by visualizing the flow of red and green aqueous solutions. Digitized color images from a CCD camera were analyzed by resolving the color in RGB mode. Numeric data from red and green color components in the images could reveal the fluidic behavior in the microchannel because the spatial spectroscopic information corresponds to the color solution flows. Effects of corner shapes in a turn, flow rate and surface roughness were observed on the mixing of the laminar flows. A right angle turn and unevenness of +/-10% of the inner wall surface almost mixed the two color laminar flows.

Translational energy distribution and asymmetry parameter of the excited hydrogen atom produced in e-C2H2 collisions: Dissociation dynamics of acetylene

Dissociative excitation of acetylene induced in e‐C2H2 collisions was investigated by measuring the Doppler profile and its angular dependence from H*(n=4) at a resolution of 0.0065 nm. The translational energy distribution and the angular difference Doppler profile were calculated. The Balmer line was unpolarized. There are three major dissociation processes for H*(n=4) from C2H2; their threshold energies and translational energy distributions are (1) 20.8, 0–2 eV, (2) ∼30, 3–5 eV, and (3) 35–40, 6–8 eV, respectively. Component 1 showed a clear anisotropy: the asymmetry parameter b is 0.5±0.1 and the anisotropy of atomic emission Jp is 0. Thus, component 1 should be produced by predissociation through Rydberg states converging to the (2σu)−1 state. The decrease of b from the theoretical maximum is due to arbitrary direction of the momentum transfer vector and a relatively long lifetime of the intermediate excited states. Components 2 and 3 are also anisotropic and b>0.

Electron energy-loss spectra of toluene and xylenes

Abstract The electron energy-loss spectra of toluene, o -xylene, m -xylene and p -xylene have been measured at electron energies of 50 eV and of 3 eV above the threshold; the scattering angles were 23, 45 and 68° at 3 eV. The spectra of the four molecules are similar. Three new bands have been observed at 3.7–3.8, 4.6 and 5.5 eV, and they are assigned as transitions from the ground state to the first three triplet states.

Distributions over the 4s, 4p and 4d sublevels and hydrogen atom emission cross sections following e-H2 collisions

Abstract The azimuthal quantum number (s, p, d) distributions of the excited hydrogen atom ( n = 4) produced in electron-impact dissociation of H 2 were measured by a time-resolved single-photon counting method. Relative emission intensities at 19–32 eV were approximately I (4s): I (4p): I (4d) = 31:14:53, and those at 50–100 eV were 21:15:62; the cascade effect was small. The absolute emission cross sections (in units of 10 −20 cm 2 ) of three sublevels (s, p, d) were calculated: σ(4s) = 3.8, σ(4p) = 2.7 and σ(4d) = 12.3 at 100 eV. This distribution is consistent with a model in which the dissociation proceeds axially in the Σ and Π symmetries and the azimuthal quantum number distribution within each symmetry is statistical.