中村 光伸

We describe a new strategy for multi-pyrene-modification of RNA sequences to form a unique structure of pyrene arrays on duplex RNA that exhibits remarkably strong excimer fluorescence.

We studied the RNA oligomers having pyrenylmethyl substituents at the 2′-O-sugar residues. It has been shown that the pyrene-modified RNAs can form duplexes with complementary RNA sequences without loss of thermal stability. Absorption, fluorescence, and circular dichroism spectra revealed that the multiply incorporated pyrenes are projected toward the outside of RNA duplexes and assembled in helical aromatic arrays along the minor grooves of the RNA duplexes. The helical pyrene arrays exhibited remarkably strong excimer fluorescence. In the present work, we carried out the fluorescence quenching of the excimer derived from the pyrene-arrays assembled on RNA duplexes in order to evaluate the mobility of the exciton along the pyrene array.

Electrochemical biosensors for the detection of specific DNA sequences have been described. The redox-modified DNA sequences were hybridized with the 3′-thiol-modified DNA sequences as capture DNA strand. The resulting duplexes were assembled on a gold electrode surface to make DNA chip. Upon addition of fully complementary DNA or mismatchcontaining DNA, the time-dependent changes in redox signal were monitored. Mismatched DNA gave less than 20% change when compared with fully matched DNA under the same conditions. The present assay format is thus applicable in discrimination of mutated DNA from fully matched DNA.

The helical pyrene arrangement on duplex RNA has been evident from the computer simulations that gave the circular dichroism (CD) bands being well consistent with the experimentally observed CD. The pyrenearrays exhibit the strong excimer fluorescence whose intensity is dependent on the nucleotide sequences and contexts of duplex RNA.

Disulfide functionalized hairpin-forming DNAs having an anthraquinone linker as a redox probe with variable number of A-T base pairs were synthesized. The electron transfer through the DNAs in selfassembled monolayers on gold surface was studied.

The self-assembled monolayers (SAMs) of RNA duplex containing pyrenylmethyl group(s) at the 2′-O-position(s) were prepared. Photo-irradiation of the pyrene-RNA SAMs in the presence of methyl viologen as an electron carrier efficiently generated cathodic photocurrent

Self-assembled monolayers (SAMs) of pyrene-modified DNA were prepared on gold electrode and their photoelectrochemical properties were investigated. The cathodic photocurrent was generated by photoirradiation of the SAM in the presence of methyl viologen as an electron carrier. The photocurrent efficiency increased with increasing the distance between the pyrene and the gold substrate.

The electrochemical method based on the strand exchange reaction (SER) for the detection of DNA single-base mismatch has been developed. Different electrochemical responses due to the slower SER rates for mismatch containing DNA than fully matched DNA were observed by using the redox-modified partial duplex DNA immobilized on gold electrode as an analytical probe.

A facile synthesis of new anthraquinone (AQ)-modified oligonucleotides was described. The AQ-oligomer-bound electrode was used for the electrochemical detection of a single base mismatch in DNA.

Multiple pyrene modified RNA duplex exhibits pyrene excimer fluorescence. The pyrene excimer fluorescence is significantly enhanced with an increase in the number of incorporated pyrenes. The pyrenes in the RNA helically aggregate with partial π-stacking along outside of double stranded helical backbone.

A new pyrene-excimer probe was developed for the detection of single-base mismatches in DNA.

Electromagnetic wave absorption consistent of unsaturated polyester resin and 20-60 mass% of white charcoal powder were developed and their electromagnetic wave absorption characteristics, electrical resisitivities and bulk densities were measured. The electrical resistivity was decreased the increasing amount of white charcoal powder, namely 1.5 x 107 ?cm and 2 x 102 ?cm in the specimens with 20% and 60% of white charcoal, respectively. The bulk density of the specimen changed from 1.15 to 1.00 with increasing amount of charcoal powder. The specimens with 50% and 60% of white charcoal powder absorbed remarkably the electromagnetic wave of GHz range.

Synthesis and magnetic properties of M-type hexagonal ferrites with chemical composition of AFe12O19 (A = Ba and Sr) were studied. Nitrates of barium, strontium and iron were used as starting materials. The precursor of M-type ferrites was prepared mainly by the polymerization of metal-citric complex with various amounts of ethylene glycol, and heating the gel at 300 oC. The precursor was ground, pressed by uniaxial compression in a die and heated at 750-950 oC in air. From these results, large coercive force of the samples in this study is probably caused by achievement of small grain size under the single domain size by polymerized complex method.

The structure of a wood ceramics was examined by Raman spectroscopy and X-ray diffractometry. A composite material was prepeared by heat treatment of a medium density fiberboard (MDF) impregnated with phenolic resin in vacuum at 600-1200.DEG.C.. The composite material heat-treated at 600-800.DEG.C. was amorphous in terms of Raman spectra. It showed a short-distance order in the direction of the c axis. The relationship was examined between the model of structural change and the electrical characteristic. The composite material was composed of rystallized graphite-like carbon, amorphous carbon and polyaromatic compounds. Disordered, two-dimensional electroconductive graphite layer was formed from benzene rings of non-electroconductive polycyclic aromatic compound. It had a considerable influenced on the electric resistance. There were two unidentified peaks in the Raman spectrum. The product may be applied for porous functional materials.

Electrochemical properties of redox-active DNA bound to gold surface were described.

The electromagnetic wave absorption characteristics of Bincho-charcoals and bamboo charcoals made by carbonizing Ubame-oak and Mousou-bamboo at the temperature of 550 to 1100 oC were measured by a network analyzer accompanied by electrical resistivity measurement, X-ray diffraction analysis and SEM observation. The electrical resistivities of Bincho-charcoal and bamboo charcoal decreased remarkably with increasing carbonization temperature in the same tendency, namely 4 x 102 ?cm at 600 oC and 8 ?cm at 650 oC, respectively. The permittivities of both charcoals increased with increasing carbonizing temperature. Large absorptions were observed in both charcoals carbonized at 600 and 650 oC. The frequencies of peak absorption of both charcoals shifted to higher frequency side with increasing carbonization temperature.

The clectromagnetic wave absorption characteristics of woodceramics/SiC composites made by sintering the compacted mixtures of phenolic resin powder, wood powder and SiC powder were examined by a network analyzer with and attachment for measuring S-parameter and discussed in connection with the bulk density, X-ray analysis, electrical resistivity and SEM microstructure. The woodceramics made by caronizing the compacted mixture of 30 wt% phenolic resin powder and 70 wt% wood powder showed the large sbsorption peak at the frequency of about 2 GHZ and the addition of SiC powder to the starting mixture shifted the absorption peak of the sintered composite to the higher frequency, namely 9 GHz for the specimen containing 47% SiC. The addition of SIC accelerated the graphitization of the matrix woodceramics, increased the permittivity and bulk density, and decreased the electrical resistivity.

The electromagnetic wave absorption characteristics of woodceramics boards carbonized at relatively low temperatures (600, 650, 700, 750, and 800 oC) were measured mainly by a network analyzer with an attachment for measuring S-parameter (complex reflection coefficient) and discussed in connection with the electrical resistivity, lattice parameter, bulk density and SEM microstructure changes. The electrical resistivity increased with increasing carbonization temperature. The woodceramics boards carbonized at 650-700 oC showed remarkable absorption (about 50 dB) at the frequency of about 7 GHz. The peak frequency and the amount of absorption decreased with increasing carbonization temperature. The boards carbonized at 750-800 oC showed the absorption of about 40 dB at the frequency of about 0.8 GHz. The board carbonized at 600 oC scarcely showed absorption chracteristics.

In order to improve the mechanical and electrical properties of woodceramics, which have been ordinarily made by carbonizing the MDFs (medium-density fiberboards) impregnated with phenolic resin, molten aluminum and brass were impregnated into the woodceramics borads with had been carbonized at 1073 K (800 oC). The apparent densities of non-impregnated, Al-impregnated and brass-impregnated woodceramics were 0.83, 1.8 and 3.8 Mg m-3, respectively. The volume percentages of impregnated aluminium and brass were 54% and 39%, respectively. The maximum bending stress values of non-impregnated, Al-impregnated and brass-impregnated woodceramics were 10 Mpa, 50 MPa, and 80 MPa, respectively. The electrical resistivity values of non-impregnated, Al-impregnated and brass-impregnated woodceramics were 2.1 x 10-3, 4.6 x 10-7, and 9.0 x 10-7 ?m, respectively.

A new powder method has been developed in order to improve the mechanical strength of woodceramics, which have been ordinarily made by sintering the MDFs (Medium Density Fiberboards) impregnated with phenolic resin. Wood powder, phenolic resin powder, wood ceramics powder, copper powder and copper fiber were mixed and compacted at the pressure of 98 MPa at room temperature and sintered at 1073 and 1293 K. The increase in copper content of the specimen increased the bending strength. The maximum bending strength (83 MPa) was obtained when the specimen containing 95 mass% of copper was sintered at 1073 K. In the case of sintering at 1293 K the maximum bending strength increased to 97 MPa. The addition of copper powder, ductility increased remarkably.