Hisanao Usami

Optical properties of diatom silica frustule with special reference to blue light

Using fresh water diatom, identified as Melosira variance which is growing faster than other algae in the ponds, we characterized the ultrastructure of its silica frustule by electron microscopic observations. On hypothesizing that the ultrastructure has some meanings in photosynthesis, behaviors of a single frustule toward light irradiation were analyzed using an optical fiber. We found that the frustule absorbed light mainly in the blue wavelength region. The theoretical analyses of optical properties supported experimental results and suggested a strong interaction between blue light and inner silica materials. It is speculated that the interaction served for partial extinction of excessive irradiation of blue light and for enhancing photosynthesis of the diatom.

Clay-inclusion photocyclodimerization : intercalation and migration of stilbazolium ions

Photocyclodimerization and the emissive properties of 4-[2-(p-substituted phenyl)ethenyl]pyridinium ions (stilbazolium ions)(1) intercalated between clay interlayer have been studied in order to clarify the intercalation and mobility of the ions. A statistical product ratio of homo- and cross-bred cyclodimers was observed in the irradiation of an equimolar co-intercalated mixture of 4-[2-(p-tolyl)ethenyl](1b) and 4-[2-(p-cyanophenyl)ethenyl]-pyridinium chlorides (1c). In contrast, when 1b and 1c were intercalated separately, the homodimers were formed predominantly, and the cross : homo ratios increased with increasing adsorption. This indicates that the molecular diffusion of stilbazolium ions between clay particles is much slower, as was also shown by a quenching study of the excimer fluorescence of 1b by 1c.

Adhesion between high strength and high modulus polyethylene fibers by use of polyethylene gel as an adhesive

The use of polyethylene gels to adhere high strength and high modulus polyethylene fibers together has been investigated. It was found that the joint strength obtained using high density polyethylene (HDPE) gel in decalin or tetralin depended on the heating temperature and time of the gel. When heated at 100°C for 30 min, the gel showed such a high joint strength that polyethylene fibers were torn, and this should be enough for practical uses. The results of the present study demonstrate that utilization of the polyethylene gel as an adhesive is an extremely effective method when polyethylene fibers are used in composite materials.

Nanotubes of Biomimetic Supramolecules Constructed by Synthetic Metal Chlorophyll Derivatives.

Various supramolecular nanotubes have recently been built up by lipids, peptides, and other organic molecules. Major light-harvesting (LH) antenna systems in a filamentous anoxygenic phototroph, Chloroflexus (Cfl.) aurantiacus, are called chlorosomes and contain photofunctional single-wall supramolecular nanotubes with approximately 5 nm in their diameter. Chlorosomal supramolecular nanotubes of Cfl. aurantiacus are constructed by a large amount of bacteriochlorophyll(BChl)-c molecules. Such a pigment self-assembles in a chlorosome without any assistance from the peptides, which is in sharp contrast to the other natural photosynthetic LH antennas. To mimic chlorosomal supramolecular nanotubes, synthetic models were prepared by the modification of naturally occurring chlorophyll(Chl)-a molecule. Metal complexes (magnesium, zinc, and cadmium) of the Chl derivative were synthesized as models of natural chlorosomal BChls. These metal Chl derivatives self-assembled in hydrophobic environments, and their supramolecules were analyzed by spectroscopic and microscopic techniques. Cryo-transmission electron microscopic images showed that the zinc and cadmium Chl derivatives could form single-wall supramolecular nanotubes and their outer and inner diameters were approximately 5 and 3 nm, respectively. Atomic force microscopic images suggested that the magnesium Chl derivative formed similar nanotubes to those of the corresponding zinc and cadmium complexes. Three chlorosomal single-wall supramolecular nanotubes of the metal Chl derivatives were prepared in the solid state and would be useful as photofunctional materials.

Structures and physiological functions of silica bodies in the epidermis of rice plants

We characterized silica structures in the epidermis of rice plant leaves and investigated their physiological functions from optical and mechanical viewpoints. By treating the distribution of silica bodies as a triangular lattice in the xy plane, and performing a theoretical optical analysis on this lattice, we discovered that a reduction in the photonic density of states may inhibit leaves of rice plant from being heated markedly higher than 20 °C. Ladderlike structures in the epidermis were mechanically investigated. These structures are conjectured to inhibit flat leaves from undergoing twisting torsions, which may assist the leaf to absorb sunlight more effectively for photosynthesis.

Spatially controlled photocycloaddition of a clay-intercalated stilbazolium cation

A stilbazolium cation included in clay interlayers undergoes an efficient and regioselective photocycloaddition to afford a syn head-to-tail dimer with suppression of the cis–trans isomerization.

Nanocomposite of silk fibroin nanofiber and montmorillonite: Fabrication and morphology

The purpose of our research is creating a new nanocomposite material. Generally silk fibroin (SF) is regarded as a promising base material for biomedical uses. The incorporation of montmorillonite (MMT) into SF fibers would improve physical properties of the SF fibers. We investigated a new method of combining electospun SF with MMT. Specifically, electrospun silk nanofibers were treated with methanol and dipped in a MMT suspension. We could obtain a nanosheet composite of silk nanofibers and MMT. Their ultrastructures were successfully visualized by high resolution transmission electron microscopy. This compound was comprised of individual silk nanofibers surrounded by thin layers of MMT, each with a thickness of about 1.2 nm. This structure was confirmed by elemental analysis. We also performed IR, NMR and X-ray diffraction analyses in conjunction with morphological data. Conclusively we obtained a new composite of silk nanofiber and MMT, which has never been reported. Using this unique nanocomposite biological tests of its application for a scaffold for tissue engineering are under way.

Sensitized photoisomerization of cis-stilbazoliumions intercalated in saponite clay layers

Sensitized photoisomerization of the cis-stilbazolium ion 1 by ruthenium tris-2,2′-bipyridine [Ru(bpy)32+] was studied in saponite clay layers. The reaction yield was 100 times higher than the reaction yield in a homogeneous solution. The Stern–Volmer constant of the luminescence of Ru(bpy)32+ by 1 was 3.4×105 d mol-1, which made the quenching rate constant faster than the diffusion limiting rate. The fast quenching rate implies a static quenching by 1 in the vicinity of Ru(bpy)32+. The reaction efficiency showed a maximum when 70 mol% of 1 was intercalated on the basis of the cation exchange capacity (CEC), where the ruthenium complex and 1 are suitably arranged in the saponite layer for effective photoelectron transfer and subsequent electron relay.

Microstructure Investigation on Micropore Formation in Microporous Silica Materials Prepared via a Catalytic Sol–Gel Process by Small Angle X–Ray Scattering

The so-called sol-gel technique has been shown to be a template-free, efficient way to create functional porous silica materials having uniform micropores. This appears to be closely linked with a postulation that the formation of weakly branched polymer-like aggregates in a precursor solution is a key to the uniform micropore generation. However, how such a polymer-like structure can precisely be controlled, and further, how the generated low-fractal dimension solution structure is imprinted on the solid silica materials still remain elusive. Here we present fabrication of microporous silica from tetramethyl orthosilicate (TMOS) using a recently developed catalytic sol-gel process based on a nonionic hydroxyacetone (HA) catalyst. Small angle X-ray scattering (SAXS), nitrogen adsorption porosimetry, and transmission electron microscope (TEM) allowed us to observe the whole structural evolution, ranging from polymer-like aggregates in the precursor solution to agglomeration with heat treatment and microporous morphology of silica powders after drying and hydrolysis. Using the HA catalyst with short chain monohydric alcohols (methanol or ethanol) in the precursor solution, polymer-like aggregates having microscopic correlation length (or mesh-size) < 2 nm and low fractal dimensions ∼2, which is identical to that of an ideal coil polymer, can selectively be synthesized, yielding the uniform micropores with diameters <2 nm in the solid materials. In contrast, the absence of HA or substitution of 1-propanol led to considerably different scattering behavior reflecting the particle-like aggregate formation in the precursor solution, which resulted in the formation of mesopores (diameter >2 nm) in the solid product due to apertures between the particle-like aggregates. The data demonstrate that the extremely fine porous silica architecture comes essentially from a gaussian polymer-like nature of the silica aggregates in the precursor having the microscopic mesh-size and their successful imprint on the solid product. The result offers a general but significantly efficient route to creating precisely designed fine porous silica materials under mild condition that serve as low refractive index and efficient thermal insulation materials in their practical applications.

Micellar effect on the photosensitized debromination of 2,3-dibromo-3-phenylpropionic acid. Control of forward and back electron transfers

The zinc tetraphenylporphyrin (ZnTPP)- and zinc tetrasodiumtetra(p-sulphonatophenyl)porphyrin (ZnTPPS)-sensitized photodebromination of 2,3-dibromo-3-phenylpropionic acid (1) in the presence of a sacrificial reductant yielding cinnamic acid has been studied in cationic cetyltrimethylammonium bromide (CTAB) micellar solution. The photosensitized electron transfer and the resultant debromination are significantly affected by the solubilizing sites of sensitizer and dibromide (1) in the micelle. The debromination proceeds most efficiently when the anionic sensitizer and (1) are adsorbed on the cationic micellar surface. The overall efficiency is controlled mostly by the back electron transfer rather than the forward one, which is competitive with the subsequent debromination steps. The cationic micellar surface is effective for the electron-transfer debromination when both or either of the sensitizers is anionically charged.