PubMed Health⌕ Search

Biomedical subjects

Kaname Yoshida

Publications and source records attributed to Kaname Yoshida.

13 recordsLinked to original sources
PubMed2006

A photoelectrochemical device with a nanostructured SnO2 electrode modified with composite clusters of porphyrin-modified silica nanoparticle and fullerene.

A silica nanoparticle has been successfully employed as a nanoscaffold to self-organize porphyrin and C60 molecules on a nanostructured SnO2 electrode. The quenching of the porphyrin excited singlet state on the silica nanoparticle is suppressed significantly, showing that silica nanoparticles are promising scaffolds for organizing photoactive molecules three-dimensionally in nanometer scale. Marked enhancement of the photocurrent generation was achieved in the present system compared with the reference system, where a gold core was employed as a scaffold of porphyrins instead of a silica nanoparticle. The rather small incident photon-to-current efficiency relative to a similar photoelectrochemical device using a silica microparticle may result from poor electron and hole mobility in the composite film due to poor connection between the composite clusters of a porphyrin-modified silica nanoparticle and C60 in micrometer scale.

Journal Article↗
PubMed2006

Structure and photoelectrochemical properties of phthalocyanine and perylene diimide composite clusters deposited electrophoretically on nanostructured SnO2 electrodes.

Clusters of phthalocyanine and phthalocyanine-perylene diimide have been prepared and electrophoretically deposited on nanostructured SnO2 electrodes. The structure and photoelectrochemical properties of the clusters have been investigated by using UV-visible absorption, dynamic light scattering (DLS), atomic force microscopy (AFM), transmission electron microscopy (TEM), and photoelectrochemical and photodynamical measurements. Enhancement of the photocurrent generation efficiency in the composite system has been achieved relative to that in the phthalocyanine reference system without the perylene diimide. Such information will be valuable for the design of molecular photoelectrochemical devices that exhibit efficient photocurrent generation.

Journal Article↗
PubMed2005

Host-guest interactions in the supramolecular incorporation of fullerenes into tailored holes on porphyrin-modified gold nanoparticles in molecular photovoltaics.

Novel gold nanoparticles modified with a mixed self-assembled monolayer of porphyrin alkanethiol and short-chain alkanethiol were prepared (first step) to examine the size and shape effects of surface holes (host) on porphyrin-modified gold nanoparticles. The porphyrin-modified gold nanoparticles with a size of about 10 nm incorporated C60 molecules (guest) into the large, bucket-shaped holes, leading to the formation of a supramolecular complex of porphyrin-C60 composites (second step). Large composite clusters with a size of 200-400 nm were grown from the supramolecular complex of porphyrin-C60 composites in mixed solvents (third step) and deposited electrophoretically onto nanostructured SnO2 electrodes (fourth step). Differences in the porphyrin:C60 ratio were found to affect the structures and photoelectrochemical properties of the composite clusters in mixed solvents as well as on the SnO2 electrodes. The photoelectrochemical performance of a photoelectrochemical device consisting of SnO2 electrodes modified with the porphyrin-C60 composites was enhanced relative to a reference system with small, wedged-shaped surface holes on the gold nanoparticle. Time-resolved transient absorption spectroscopy with fluorescence lifetime measurements suggest the occurrence of ultrafast electron transfer from the porphyrin excited singlet states to C60 or the formation of a partial charge-transfer state in the composite clusters of supramolecular complexes formed between porphyrin and C60 leading to efficient photocurrent generation in the system. Elucidation of the relationship between host-guest interactions and photoelectrochemical function in the present system will provide valuable information on the design of molecular devices and machines including molecular photovoltaics.

Journal Article↗
PubMed2005

Effects of fullerene substituents on structure and photoelectrochemical properties of fullerene nanoclusters electrophoretically deposited on nanostructured SnO2 electrodes.

Two kinds of fullerene derivatives have been designed to examine the effect of the fullerene substituents on the structure and photoelectrochemical properties of fullerene clusters electrophoretically deposited on nanostructured SnO(2) electrodes. The cluster sizes increase and the incident photon-to-current efficiencies decrease with introduction of large substituents into C(60). The trend for photocurrent generation efficiency as well as surface morphology on the electrode can be explained by the steric bulkiness around the C(60) molecules. A C(60) molecule with two alkoxy chains is suggested to give a bilayer vesicle structure, irrespective of the hydrophobic nature of both the C(60) and alkoxy chain moieties. Such information will be valuable for the design of photoactive molecules, which are fabricated onto electrode surfaces to exhibit high energy conversion efficiency.

Journal Article↗
PubMed2005

Aggregated structure analysis of polymer-protected platinum/ruthenium colloidal dispersions using EXAFS, HRTEM, and electron diffraction measurements.

Polymer-protected platinum/ruthenium colloidal dispersions were prepared by refluxing mixed solutions of hexachloroplatinic(IV) acid and ruthenium(III) chloride in a mixture of ethanol/water (1/1 v/v) in the presence of poly(N-vinyl-2-pyrrolidone). The electronic spectra and transmission electron micrographs suggested that the colloidal dispersions are almost composed of the mixture of the small monometallic Pt and Ru clusters over all the ratio of Pt/Ru compositions. Extended X-ray absorption fine structure analyses and high resolution electron microprobe analyses indicated that no Pt/Ru alloy clusters exist in the dispersions, and the aggregation occurs between small monometallic Pt clusters (diameter ca. 15 A) and partially oxidized Ru microclusters (diameter less than 10 A). Electron diffraction measurements also suggested that the diffraction pattern of aggregated Pt/Ru cluster particles prepared by the simultaneous reduction of Pt and Ru ions is the same as that of the physical mixture of the small monometallic Pt and Ru clusters separately prepared. Therefore, it can be concluded that the aggregated Pt/Ru cluster particles, with 10 to 60 A in diameter, are built up by small monometallic Pt clusters and partially oxidized Ru microclusters, and that Pt/Ru alloy clusters are not formed.

Journal Article↗
PubMed2004

Confined organization of Au nanocrystals in glycolipid nanotube hollow cylinders.

Mild fabrication of anisotropic metal-lipid nanotube (LNT) nanocomposites, in which Au nanoparticles of 3-10 nm wide are organized in a glycolipid nanotube hollow cylinder, has been achieved by filling the internal channel of the LNT with HAuCl(4) aqueous solution by capillary force and subsequent photochemical reduction of [AuCl(4)](-).

Freeze Drying↗
PubMed2003

Creation of double silica nanotubes by using crown-appended cholesterol nanotubes.

New crown-appended cholesterol-based organogelators 1-3, which have one or two cholesterol skeletons as a chiral aggregate-forming site, two amino groups as an acidic proton binding site, and one crown moiety as a cation binding site, were synthesized, and the gelation ability was evaluated in organic solvents. These gelators could gelatinize several organic solvents under 1.0 wt %, indicating that 1-3 act as a versatile gelator of various organic solvents. We observed CD spectra of the acetic acid or propionic acid gels of 1-3 to characterize the aggregation mode in the organogel system. In the CD spectrum of the acetic acid gel 1, the positive sign for the first Cotton effect indicates that the dipole moments of azobenzene chromophores tend to orient into the clockwise direction. On the other hand, propionic acid gels 2 and 3, bearing only one cholesterol, moiety exhibit a negative sign for the first Cotton effect, strongly suggesting that the dipole moments of the azobenzene chromophores orient into the anticlockwise direction. The TEM images of the 1+acetic acid gel resulted in the helical ribbon and tubular structures. Sol-gel polycondensation of tetraethoxysilane (TEOS) was carried out with 1-3 as templates in the gel phase. The silica obtained from the 1+acetic acid gel showed the helical ribbon with 200-1700 nm width and the tubular structure of the silica with constant about 560 nm outer diameter. As far as can be recognized, all the helicity possesses a right-handed helical motif. Since the exciton coupling band of the organogel also shows P (right-handed) helicity, we consider that a microscopic helicity is reflected by a macroscopic helicity. On the other hand, the tubular structure of the silica obtained from the organogels 2 and 3 is somewhat different from that prepared from the organogel 1. The careful examination of SEM and TEM pictures revealed that the tube wall of the silica features a roll-paper-like multilayer structure. Thus, this paper demonstrates successful and rare examples for precise transcription of gel superstructures into inorganic silica materials.

Cholesterol↗
PubMed2003

Inhomogeneous substitution of polyhalogenated copper-phthalocyanine studied by high-resolution imaging and electron crystallography.

The present study was aimed at distinguishing halogen atoms substituted in a molecule of copper-phthalocyanine (CuPc) by high-resolution transmission electron microscopy (HRTEM). The subject was carried out on octabromooctachloro-CuPc and obtained HRTEM images suggested inhomogeneous distribution of bromine and chlorine atoms at 1-, 2-, 3- and 4-substitution positions of CuPc in image contrast. As a result of electron crystallography, the occupancy of bromine atoms at the 1-position (and equally at the 4-position) was found to be 52%, which is slightly higher than for random substitution. This small deviation causes apparent inhomogeneous image contrast of halogen substitution observed in the high-resolution images, as concluded from computer simulation of images. Such potential to detect inhomogeneity in substitution by TEM should be important for the chemical understanding of substitution reactions at the atomic level.

Journal Article↗
PubMed2002

Morphological control of helical solid bilayers in high-axial-ratio nanostructures through binary self-assembly.

Mixed molecular species of cardanyl glucoside derived from renewable resources provide nanotubes upon self-assembly in water, while the saturated homologue generated a twisted fibrous morphology. The cardanyl glucoside mixture was fractionated into four individual components in order to study their contribution to the nanotube formation. The rational control of self-assembled helical morphologies was achieved by binary self-assembling of the saturated and monoene derivatives. This method can generate a diversity of self-assembled high-axial-ratio nanostructures (HARNs), ranging from twisted ribbons and helical ribbons to nanotubes.

Calorimetry, Differential Scanning↗
PubMed2002

Self-assembling structures of long-chain phenyl glucoside influenced by the introduction of double bonds.

Four long-chain phenyl glucoside amphiphiles possessing a saturated or unsaturated long alkyl chain group as the self-assembling unit of a highly organized molecular architecture were synthesized. Their self-assembling properties were investigated by EF-TEM, SEM, CD, FT-IR, and XRD. Compound 2 possessing one double bond in the lipophilic portion showed twisted helical fibers, which formed a bilayered structure with a 3.59 nm period, while compound 3 showed the helical ribbons and left-handed nanotubular structures with 150-200 nm inner diameters and ca. 20 nm of wall. Very interestingly, compound 4 possessing three double bonds showed a nanotubular structure with ca. 70 nm of inner diameter through a helical ribbon, which formed a loose bilayered structure with 4.62 nm. These results indicate that self-assembling properties strongly depend on the number of cis double bonds.

Circular Dichroism↗