Masatoshi Takeda

Recombinant Tol2 transposase with activity in Xenopus embryos

The Tol2 transposon system is a useful gene transduction technique, but the injection of mRNA is not sufficiently effective in Xenopus embryos to express Tol2 transposase (Tol2TP). To overcome this, we bacterially synthesized recombinant Tol2TP (rTol2TP) protein and showed that rTol2TP efficiently excised the Tol2 element from an injected donor plasmid in Xenopus embryos. Furthermore, injected embryos exhibited uniform and ubiquitous expression of an EGFP reporter gene placed within the Tol2 element. Importantly, size‐exclusion chromatography suggests that rTol2TP forms a tetramer, which differs from the reported hexamer formed by Hermes transposase, although both belong to the same hAT family. The use of rTol2TP may facilitate efficient gene transduction in Xenopus, and the biochemical characterization of Tol2TP.

Photoconductivity of icosahedral Al70.5Pd21Re8.5 : Semiconductorlike behavior of quasicrystals

Using the modulated photocurrent method to measure physical properties in the high-structural-quality single-phase icosahedral quasicrystalline alloy Al 70.5 Pd 21 Re 8.5 , we observed photocurrent similar to that in semiconductors in quasicrystals. The observed results were in agreement with those obtained by applying our recently developed photoconductivity model used for boron-rich semiconductors in which band-to-band photoexcitation and photoexcitation from a band to localized states followed by thermal excitation to the conduction band are both considered. Our results confirm the existence of a pseudogap at the Fermi energy E F and the tendency of carriers to localize near E F .

Absorption Edge Spectra of Boron-Rich Amorphous Films Constructed with Icosahedral Cluster

Optical absorption edge spectra of amorphous B, B 4 C and B 13 P 2 films, prepared by electron-beam deposition, were measured with a spectrophotometer in the wave length range of about 300∼700 nm. These were fitted by \(\alpha \hbar \omega =\)A\((\hbar \omega -E_{\rm opt})^{\rm n}\), where α , \(\hbar \omega\) , A and the constant E opt are the absorption coefficient, the photon energy, a constant and the optical gap energy, respectively. The exponent n was found to be 3 for the amorphous boron-rich films, though n was 2 for the usual amorphous semiconductors. From a comparison of the temperature dependence with that of crystalline β-rhombohedral boron (β- B ), the usual selection rule of indirect forbidden type transition did not hold in the amorphous solids of these boron-rich systems. Therefore the origin of n=3 was concluded to be the linear distribution of the densities of states. The value of the exponent n and the relatively small value of A were related to the complicated atomic and electronic str...

Time of flight experiments on amorphous and crystalline boron

Abstract Hole transport in amorphous and crystalline boron has been studied by the time of flight method. From the temperature dependence of the drift mobility in crystalline boron, the activation energy of the hole has been estimated to be 240 meV. It is considered that this energy corresponds to the depth of the hole trap in icosahedral B12 clusters. Dispersive (non-Gaussian) transient transport has been observed for amorphous boron films prepared by evaporation with substrate temperature less than 350°C. The estimated activation energies of the drift mobilities of the films were about 85 meV. In amorphous films prepared with substrate temperatures above 400°C, no dispersive transport was observed.

Possibility of semiconducting quasicrystal in boron-rich solids

Analyzing the crystalline structure of α- and β-rhombohedral boron as approximants of a quasicrystal, atomic structures of two unit cells (prolate and oblate rhombohedra) of an icosahedral quasicrystal are constructed. Based on the molecular orbital calculation, as the cohesive energy for the α-boron type quasicrystal has a value between those for α- and β-boron, such a structure can be realized. A neutral B12H12 icosahedral cluster is distorted to a cubic or rhombohedral one by the Jahn-Teller effect. The distortions of B12 cluster in the K2B12H12 and β-rhombohedral boron have the same signs as the lowest energy distortions in the calculation. Among the α-rhombohedral-type structures, the distortion of B12 is correlated with the rhombohedral axis angle, and the angle is the closest to the icosahedral angle for B6O and the distortion is the smallest for B-C. A search for semiconducting quasicrystal has been experimentally done in the B-C system. A meta-stable phase has been found on the way to crystallization of the B95C5 amorphous phase.

MOLECULAR ORBITAL CALCULATIONS FOR ICOSAHEDRAL BORON-RICH SOLIDS

Icosahedral boron-rich solids are unique semiconducting materials whose crystalline structures are composed of icosahedral clusters (B 12 ). Molecular orbital calculation was performed for the B 12 whose 12 outer bonds were terminated by 12 hydrogen atoms, i.e. B 12 H 12 . The results account for the Jahn-Teller effect in the B 12 which is closely related to electronic structures and some properties in boron-rich solids. The dipole matrix element was also calculated using the molecular orbitals. Anisotropy in optical absorption observed in some boron-rich solids can be explained with it. Some of them are considered to be candidates for semiconducting quasicrystals which have icosahedral symmetry. Using molecular orbital calculations, cohesive energies of crystals and quasicrystals have been estimated. They suggests that realization of the quasicrystalline structure is possible.