Hiroki Sone

Isolation, structure, and synthesis of dolastatin D, a cytotoxic cyclic depsipeptide from the sea gare Dolabella auricularia

Abstract Dolastatin D ( 1 ), a cytotoxic cyclic depsipeptide possessing the novel β-amino acid (2 R ,3 R )-3-amino-2-methylbutanoic acid [(2 R ,3 R ]- 3 ] as a component, has been isolated from the Japanese sea hare Dolabella auricularia . The absolute stereostructure of 1 was elucidated on the basis of spectroscopic analysis and chemical degradation and was further confirmed by synthesis.

Hydride vapor-phase epitaxy growth of high-quality GaN bulk single crystal by epitaxial lateral overgrowth

Selective area growth (SAG) of GaN using the HVPE method was carried out to obtain a high-quality GaN bulk single crystal. Selectivity of the GaN growth was excellent and the GaN layer had no cracks. The FWHM (195 arcsec) of the X-ray rocking curve for (0004) diffraction was narrower than that (348 arcsec) of the sample grown by the conventional method. Overgrowth of the GaN on the SiO 2 mask was enhanced in the direction. Cathode luminescence intensity of this overgrowth region was much stronger than that of the window region. It was found that a reduction in stress is achieved by narrowing the window area, and the epitaxial lateral overgrowth on the mask is effective in obtaining high-quality GaN layer.

ISOLATION AND STEREOSTRUCTURE OF DOLASTATIN I, A CYTOTOXIC CYCLIC HEXAPEPTIDE FROM THE JAPANESE SEA HARE DOLABELLA AURICULARIA

Abstract Dolastatin I ( 1 ), a cyclic hexapeptide containing three kinds of five-membered heterocycles (oxazole, thiazole, and oxazoline), has been isolated from the Japanese sea hare Dolabella auricularia . The gross structure of 1 was elucidated by spectroscopic analysis. The absolute stereostructure of 1 was determined by chiral HPLC analysis of the amino acid components obtained by acid hydrolysis of 1 . Dolastatin I ( 1 ) exhibited cytotoxicity against HeLa S 3 cells with an IC 50 value of 12 μg/mL.

Micro-Raman and cathodoluminescence studies of epitaxial laterally overgrown GaN with tungsten masks: A method to map the free-carrier concentration of thick GaN samples

Cathodoluminescence (CL) and micro-Raman spectroscopy were applied to study microscopically the optical and structural properties of two epitaxial-laterally overgrown GaN structures with tungsten masks in 〈11_00〉 and 〈112_0〉 direction, respectively. A free-carrier concentration higher than 1019 cm−3 was observed right above the masks, leading to a gradient in free-carrier concentration over the whole layer thickness. We used the normalized longitudinal-optical-phonon intensity and the broad band around 650 cm−1 as a measure for the free-electron concentration, which is a promising method to determine the free-carrier concentration justified by the good correlation with CL results.

Selective Area Growth of GaN Using Tungsten Mask by Metalorganic Vapor Phase Epitaxy

We studied selective area growth (SAG) of GaN using a tungsten (W) mask with an atmospheric metalorganic vapor phase epitaxy (MOVPE) system. No GaN polycrystals were observed on the W mask regions, and the selectivity of GaN growth on window regions proved to be excellent. The GaN stripes developed into different shapes depending on the direction of stripe mask patterns. If the stripe was along , a triangular shape with {1101} facets was formed. If the stripe was along , a trapezoidal shape with a smooth (0001) surface on top and rough surfaces on both sides was obtained. The lateral overgrowth of GaN on the W mask occurred in both cases. The growth mechanisms and the facet formation were similar to those found in SAG using a SiO2 mask.

Isolation, structure, and synthesis of dolastatin C, a new depsipeptide from the sea hare Dolabella auricularia

Abstract Dolastain C ( 1 ), a new depsipeptide exhibiting weak cytotoxicity, has been isolated from the Japanese sea hare Dolabella auricularia . The structure of 1 was elucidated by spectroscopic analysis and chemical degradation. The synthesis of 1 was carried out to confirm the structure unambiguously.

Crystal Orientation Fluctuation of Epitaxial-Lateral-Overgrown GaN with W Mask and SiO2 Mask Observed by Transmission Electron Diffraction and X-Ray Rocking Curves

Fluctuation of the crystal orientation of epitaxial-lateral-overgrown (ELO) GaN with a tungsten (W) mask is compared to that with a SiO2 mask by means of selected-area transmission electron diffraction (TED) and X-ray rocking curves (XRCs). XRCs of (0004) reflection exhibited three peaks for ELO-GaN on a SiO2 mask, and were confirmed to originate from domains of different c-axis orientation by TED. On the other hand, fluctuation of the c-axis was not observed for ELO-GaN with a W mask. These results indicate that the crystalline quality of ELO-GaN with a W mask is better than that with a SiO2 mask.

Selective Area Growth (SAG) and Epitaxial Lateral Overgrowth (Elo) of GaN Using Tungsten Mask

Selective area growth (SAG) and epitaxial lateral overgrowth (ELO) of GaN using tungsten (W) mask by metalorganic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE) have been studied. The selectivity of the GaN growth on the W mask as well as the SiO 2 mask is excellent for both MOVPE and HVPE. The ELO-GaN layers are successfully obtained by HVPE on the stripe patterns along the crystal axis with the W mask as well as the SiO 2 mask. There are no voids between the SiO 2 mask and the overgrown GaN layer, while there are triangular voids between the W mask and the overgrown layer. The surface of the ELO-GaN layer is quite uniform for both mask materials. In the case of MOVPE, the structures of ELO layers on the W mask are the same as those on the SiO 2 mask for the and stripe patterns. No voids are observed between the W or SiO 2 mask and the overgrown GaN layer by using MOVPE.