Field-ion microscopy of GaAs and GaP

Clean surfaces of GaAs and GaP were studied by field-ion microscope (FIM). Field-ion images with ordered surfaces were first obtained in pure hydrogen, neon-50% hydrogen and pure neon gases at 78 K, by using channeltron electron multiplier arrays (CEMA). The field-ion images of GaAs were quite similar to those of GaP with respect to the surface structure and the image contrast. They showed the anisotropies of the ion emission and the surface structure between the [111] and $\text{[}\text{1}\text{1}\text{1}\text{]}$ orientations. Ring steps expected from a spherical surface were observed on the (111) and {100} planes, but not on the $\text{[}\text{1}\text{1}\text{1}\text{]}$ and {110} planes. The regional brightness of the FIM patterns was discussed in terms of the Knor and Müller model and the atomic and electronic structures of the surface. The image field of these crystals was much lower than that of metals usually used in FIM. For example, the image field strength for the hydrogen and GaAs system was about 1.1 V/Å. The reduction of the field necessary to image was also discussed in terms of the field penetration effect.     

Enormously extended π-electronic conjugation system of dimeric octaethylporphyrin transmitted with anthracene

Based on the fact that anthracene (Anth) possesses much higher similarity in electron-releasing ability to porphyrin nucleus than the other polyacenes, the dimeric octaethylporphyrin (OEP) derivatives 4 and 5 (OEP–Anth–OEP) were synthesized and their structure–property relationships were examined, as compared with related OEP dimers 1–3. Among them, the derivative 4 showed enormously high electronic communication between two terminal OEP rings, potentially providing a suitable unit of the electronic structure for molecular design of the OEP devices operating with less energy and with higher sensitivity to outside stimuli.     

Nonlinear optical characteristics of carbon disulfide

The nonlinear refractive index γ of CS₂ is studied using laser pulses of various durations (from 110 fs to 75 ns). It is found that γ increases with increasing pulse duration within the picosecond region (from (3 ± 0.6) × 10^?15 cm² W^?1 at 110 fs to (3.5 ± 0.7) × 10^?14 cm² W^?1 at 75 ns) due to orientational nonlinearities. Variations in the sign of γ caused by the thermal effect at different pulse durations and repetition rates are analyzed. It is demonstrated that the fast electronic component, the component associated with molecular processes, causing positive nonlinear refraction, and the acoustic component, responsible for negative nonlinear refraction, manifest themselves simultaneously. The results of a study of the nonlinear absorption of carbon disulfide are presented. The two-and three-photon absorption coefficients of CS₂ are determined to be (5 ± 1.5) × 10^?11 cm W^?1 and (2.8 ± 0.8) × 10^?23 cm³ W^?2, respectively.     

Synthesis of Organosilyl-Functionalized Cage-Type Germanoxanes Containing Fluoride Ions

Eight corners of a double-four ring cage-type germanoxane, containing a fluoride ion, were successfully silylated by the combination of chlorosilanes and silazanes. Three different silyl groups, trimethylsilyl, dimethylsilyl, and dimethylvinylsilyl, were attached on the corners of germanoxane cage. The solubility and reactivity of the cage modified with dimethylvinylsilyl groups were significantly increased, allowing for further reaction. Hydrosilylation reaction between dimethylvinylsilylated cage geramanoxanes and dimethylsilylated cage siloxanes afforded porous solids. Functionalization of the corners of germanoxanes with silyl groups should provide valuable building blocks in various functional materials.     

Germanium lasers in the range from far-infra red to millimetre waves

Recent experimental and theoretical achievements are reviewed on three types of laser oscillation inp-type germanium; the intervalence band (IVB) laser oscillation due to transitions between the light-hole band and the heavy-hole band, the light-hole cyclotron resonance (LHCR) laser oscillation, and the heavy hole cyclotron resonance (HHCR) maser oscillation. Described for the IVB oscillation are fundamental characteristics (such as the wavelength range of oscillation and the cooperation with higherharmonic cyclotron resonances), the polarization characteristics of radiation and influence of uniaxial stress on the oscillation. The present status of the attempt at single line oscillation is also described. As for the LHCR oscillation, the formation of population inversion and the amplification are explained on the basis of quantum mechanical calculations of the valence bands in crossed electric and magnetic fields.     

Chain-terminus triggered chiral memory in an optically inactive 3(10)-helical peptide

A new optically inactive 3(10)-helical peptide with a side-chain cross-linking was found to exhibit chiral memory stored in the peptide backbone, whose chirality was induced by a noncovalent interaction of a chiral molecule at the N-terminal end of the peptide.     

Steroidal glycosides from the bulbs of Camassia leichtlinii and their cytotoxic activities.

Phytochemical analysis of the bulbs of Camassia leichtlinii (Liliaceae) resulted in the isolation of six new spirostanol saponins, a new furostanol saponin, a cholestane glucoside, and four known steroidal saponins. The structures of the new saponins were determined by detailed analysis of their spectral data, including two-dimensional NMR spectroscopy, and by the results of hydrolytic cleavage. Cytotoxic activities of the isolated compounds against human oral squamous cell carcinoma (HSC-2) cells and normal human gingival fibroblasts (HGF) are also reported.     

Alkylation‐, Heating‐, and Doping‐Induced Emission Enhancement of a Polyaromatic Tube in the Solid State

A polyaromatic tube with a subnanometer‐sized cavity was efficiently prepared on a gram‐scale through the stereo‐controlled cyclotrimerization of a diphenylanthracene derivative as a key step. The facile exterior alkylation of the polyaromatic framework leads to a moderately fluorescent tube (R=‐OC₁₀H₂₁; Φ_F=20 %) in the solid state. The emission intensity of the solid‐state alkyl‐substituted tube is remarkably enhanced upon heating (up to 1.6 times, Φ_F=31 %) as well as doping with fluorescent dyes (up to 4.2 times, Φ_F=83 %) through efficient energy transfer.     

Temperature dependent control of the solubility of gallium nitride in supercritical ammonia using mixed mineralizer

Using a mass-loss method, we investigated the solubility change of gallium nitride (GaN) in supercritical ammonia with mixed mineralizers [ammonium chloride (NH₄Cl)?+?ammonium bromide (NH₄Br) and NH₄Cl?+?ammonium iodide (NH₄I)]. The solubilities were measured over the temperature range 450–550 °C, at 100 MPa. The solubility increased with NH₄Cl mole fraction at 450 °C and 100 MPa. The temperature dependence of the solubility curve was then measured at an equal mole ratio of the two mineralizers. The slope of the solubility–temperature relationship in the mixed mineralizer was between those of the individual mineralizers. These results show that the temperature dependence of the solubility of GaN can be controlled by the mineralizer mixture ratio. The results of the van’t Hoff plot suggest that the solubility species were unchanged over the investigated temperature range. Our approach might pave the way to realizing large, high-quality GaN crystals for future gallium-nitride electronic devices, which are increasingly on demand in the information-based age.     

Application of an automated synthesis suite to parallel solution-phase peptide synthesis

An in-house developed automated synthesis suite was used to prepare a library of 72 tetrapeptide derivatives, the starting materials for pharmaceutically attractive pentapeptides, employing a convergent strategy. An initial set of 18 dipeptides were synthesized on a large-scale (100-1000 g) using automated synthesis workstations, and then 72 tetrapeptides were synthesized on a medium scale (5-10 g) using an automated system. Each di- or tetrapeptide was prepared in a single operating cycle using a modified methanesulfonic acid method, then a sub-library of 56 pentapeptides were synthesized in parallel, on a small-scale (100 mg-1 g) using a robotic workstation.