Biological activities of phenolic compounds isolated from galls of Terminalia chebula Retz. (Combretaceae)

The aqueous extract of galls from Terminalia chebula Retz. (Combretaceae) was fractionated on Diaion and refractionated on octadecyl silica column. Six phenolic compounds were isolated and identified as gallic acid (1), punicalagin (2), isoterchebulin (3), 1,3,6-tri-O-galloyl-β-D-glucopyranose (4), chebulagic acid (5) and chebulinic acid (6). All of the compounds showed stronger 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and melanin inhibitory activities than ascorbic acid, butylated hydroxytoluene, α-tocopherol, arbutin and kojic acid, the reference compounds. Gallic acid (1) exhibited inhibitory activity against nitric oxide production in lipopolysaccharide-activated macrophages. However, all isolated compounds exhibited less activity than the reference compounds in mushroom tyrosinase inhibition and human tumour cytotoxicity assays. This study has demonstrated that the phenolic compounds isolated from galls of T. chebula might contribute significantly due to their antioxidant and whitening activities.     

Dehydrogenation of methanol to methyl formate over supported Ni, Pd and Pt catalysts. Anomalous catalytic functions of PdZn and PtZn alloys

Pd/ZnO and Pt/ZnO exhibited high catalytic performance for the dehydrogenation of methanol to methyl formate upon the formation of PdZn and PtZn alloys.     

Spectroscopic studies of 4-substituted pyridinium 2-pyridylcarbonylmethylide-rhodium(I) complexes and x-ray molecular structure of (1,5-cyclooctadiene) (4-methylpyridinium 2-pyridylcarbonylmethylide)rhodium(I) perchlorate

(1,5-Cyclooctadiene) (4-substituted pyridinium 2-pyridylcarbonylmethylide)- rhodium(I) perchlorates, [Rh(COD)(C₅H₄NC(O)C?H₊C₅H₄X-4)]ClO₄ [COD = 1,5-cyclooctadiene; X = CH₃C(O), CH₃OC(O), C₆H₅, CH₃, and H], have been prepared. They are shown to have the geometry with coordination by the pyridyl nitrogen and carbonyl oxygen atoms of the ylide ligands and to exhibit intramolecular rearrangement of coordinated COD in chloroform, methanol, and dimethyl sulphoxide based on IR and ¹H NMR spectroscopies. Although the ylides have exhibited fluorescence bands due to an intramolecular charge-transfer transition and phosphorescence bands due to a carbonyl ³(n?π^*) transition, the complexes have given emission bands due to the metal-to-ylide ligand charge-transfer transition. A.single crystal X-ray crystal structure has been determined for [Rh(COD)(C₅H₄NC(O)C?H₊C₅H₄CH₃-4)]ClO₄. The crystals are monoclinic, space group P2₁/n with cell dimensions a = 14.887(3), b = 20.274(4), c = 6.966(1) Å, β = 96.13(1)°, and Z = 4. The structure has been refined by a block-diagonal least-squares method to final R = 0.060 for 2997 independent reflections with |F_o| > 3σ(F). The ylide carbon-pyridinium nitrogen bond distance is 1.420(10) Å. The bonded distances from rhodium to the midpoints of the double bonds of COD are 1.982(11) and 2.014(12) Å.     

Interface models and processing technologies for surface passivation and interface control in III-V semiconductor nanoelectronics

Interface models and processing technologies are reviewed for successful establishment of surface passivation, interface control and MIS gate stack formation in III-V nanoelectronics. First, basic considerations on successful surface passivation and interface control are given, including review of interface models for the band alignment at interfaces, and effects of interface states in nanoscale devices. Then, a brief review is given on currently available surface passivation technologies for III-V materials, including the Si interface control layer (ICL)-based passivation scheme by the authors’ group. The Si-ICL technique has been successfully applied to surface passivation of nanowires and to formation of a HfO₂ high-k dielectric/GaAs interfaces with low values of the interface state density.     

Control of composition and crystallinity in hydroxyapatite films deposited by electron cyclotron resonance plasma sputtering

Hydroxyapatite (HAp) films were deposited by electron cyclotron resonance plasma sputtering under a simultaneous flow of H₂O vapor gas. Crystallization during sputter-deposition at elevated temperatures and solid-phase crystallization of amorphous films were compared in terms of film properties. When HAp films were deposited with Ar sputtering gas at temperatures above 460 °C, CaO byproducts precipitated with HAp crystallites. Using Xe instead of Ar resolved the compositional problem, yielding a single HAp phase. Preferentially c-axis-oriented HAp films were obtained at substrate temperatures between 460 and 500 °C and H₂O pressures higher than 1×10⁻² Pa. The absorption signal of the asymmetric stretching mode of the PO₄³⁻ unit (ν₃) in the Fourier-transform infrared absorption (FT-IR) spectra was the narrowest for films as-crystallized during deposition with Xe, but widest for solid-phase crystallized films. While the symmetric stretching mode of PO₄³⁻ (ν₁) is theoretically IR-inactive, this signal emerged in the FT-IR spectra of solid-phase crystallized films, but was absent for as-crystallized films, indicating superior crystallinity for the latter. The Raman scattering signal corresponding to ν₁ PO₄³⁻ sensitively reflected this crystallinity. The surface hardness of as-crystallized films evaluated by a pencil hardness test was higher than that of solid-phase crystallized films.     

Mechanisms of network rearrangement and compaction in a-SiNx:H films exposed to synchrotron radiation

The network of hydrogenated silicon nitride (a-SiN_x:H) films deposited by plasma-enhanced chemical vapor deposition is compacted when the film is irradiated by high-energy photons in the range from vacuum-ultraviolet to soft X-rays (hν>100 eV). In situ monitoring by spectroscopic ellipsometry of the change in the film’s optical response discriminated between the photon-stimulated structural change and the solely temperature-dependent change of the dielectric constant. To elucidate the compositional difference before and after irradiation, the dielectric function of a-SiN_x:H was modelled by a mixture of its component dielectric functions, i.e., of Si₃N₄, crystalline Si, and voids, under the Bruggeman effective medium approximation. Irradiation decreased the nominal volumes of void and c-Si components from their initial values by 44% and 49%, respectively. The resulting total 9.8% reduction in thickness can be explained by the compaction model. The photolytic origin of the reaction was demonstrated by the quick commencement and termination of the changes in optical evolution in response to the supply and cessation of irradiation, as well as by the insensitivity of the change in the refractive index to the temperature of irradiation. The microscopic process which is primarily responsible for the rearrangement of the network is cross-linking between the H-terminated –SiH_x and –NH_y species followed by the release of H₂. In contrast to this, the creation of dangling bonds is a minor process.     

3-O-(E)-p-coumaroyl tormentic acid from Eriobotrya japonica leaves induces caspase-dependent apoptotic cell death in human leukemia cell line

Eleven triterpene acids, 1-11, isolated from the leaves of Eriobotrya japonica, were evaluated for inhibition of DNA topoisomerase (Topo) I and cytotoxicity against human leukemia (HL60) and melanoma cell lines (CRL1579). Among the compounds tested, four compounds, δ-oleanolic acid (4), ursolic acid (5), 3-O-(E)-p-coumaroyl tormentic acid (8), and betulinic acid (10), exhibited potent Topo I inhibitory activity (IC(50) 20.3-36.5 μM) and cytotoxicity against HL60 (EC(50) 5.0-8.1 μM). Upon assessing the apoptosis-inducing activity in HL60 cells, compound 8 exhibited induction of apoptosis detected by the observation of DNA fragmentation and membrane phospholipid exposure in flow cytometry. Western blot analysis showed that compound 8 markedly reduced the levels of procaspases-3 and 9, while being increased the levels of cleaved caspases-3 and 9. On the other hand, compound 8 exerted almost no influence on the expression of caspase-8. In addition, compound 8 increased significantly Bax/Bcl-2 ratio and activated caspase-2. These results suggested that compound 8 induced apoptotic cell death in HL60 via mainly mitochondrial pathway by, at least in part, Topo I inhibition. Therefore, compound 8 may be promising lead compound for developing an effective drug for treatment of leukemia.     

Mechanism and control of current transport in GaN and AlGaN Schottky barriers for chemical sensor applications

Strong interests are recently emerging for development of integrated high-performance chemical sensor chips. In this paper, the present status of understanding and controlling the current transport in the GaN and AlGaN Schottky diodes is discussed from the viewpoint of chemical sensor applications. For this purpose, a series of works recently carried out by our group are reviewed in addition to a general discussion. First, current transport in GaN and AlGaN Schottky barriers is discussed, introducing the thin surface barrier (TSB) model to explain the anomalously large leakage currents. Following this, attempts to reduce the leakage currents are presented and discussed. Then, as an example of gas-phase sensors using Schottky barriers, a Pd/AlGaN/GaN Schottky diode hydrogen sensor developed recently by our group is presented with a discussion on the sensing mechanism and related current transport. On the other hand, in liquid-phase sensors, contact is made between liquid and semiconductor which is regarded as a kind of Schottky barrier by electrochemists. As one of such liquid-phase sensors, open-gate AlGaN/GaN heterostructure field effect transistor (HFET) pH sensor developed recently by our group is presented. Finally, a brief summary is given together with some remarks for future research.