Kenichi Ozawa

A comparative study of plasma membrane Mg2+-ATPase activities in normal, regenerating and malignant cells

Plasma membranes have been prepared from rat normal liver cells, regenerating liver cells and Yoshida ascites hepatoma 66 cells after intact cells were first bound to polylysine-coated polyacrylamide beads, and the membrane-associated Mg2+ -ATPase activity was assayed directly on beads with membrane attached. With plasma membranes from normal liver cells, Km for ATP and V were found to be higher than those in regenerating liver cells and hepatoma cells. Vanadate caused a different sensitivity of the activity, without an effect in normal liver cells and with an inhibition in regenerating liver cells and hepatoma cells. The activity in normal and regenerating liver cells decreased with increasing temperature above 24-30 degrees C, while the activity in hepatoma cells continued to increase linearly to 37 degrees C. Unlike the enzyme in normal and regenerating liver cells, the hepatoma enzyme was shown to have a higher phase transition temperature and lower activation energies. In all three kinds of cells the activity was increased by the dephosphorylation of plasma membranes and unaffected by the phosphorylation. By means of histochemical Mg2+ -ATPase staining applied on polyacrylamide gels, at least three major bands which show the enzymic activity were visible in normal and regenerating liver and a single band was detected in hepatoma cells.

Electron–Hole Recombination Time at TiO2 Single-Crystal Surfaces: Influence of Surface Band Bending

Photocatalytic activity is determined by the transport property of photoexcited carriers from the interior to the surface of photocatalysts. Because the carrier dynamics is influenced by a space charge layer (SCL) in the subsurface region, an understanding of the effect of the potential barrier of the SCL on the carrier behavior is essential. Here we have investigated the relaxation time of the photoexcited carriers on single-crystal anatase and rutile TiO2 surfaces by time-resolved photoelectron spectroscopy and found that carrier recombination, taking a nanosecond time scale at room temperature, is strongly influenced by the barrier height of the SCL. Under the flat-band condition, which is realized in nanometer-sized photocatalysts, the carriers have a longer lifetime on the anatase surface than the rutile one, naturally explaining the higher photocatalytic activity for anatase than rutile.

Performance of PF BL-13A, a vacuum ultraviolet and soft X-ray undulator beamline for studying organic thin films adsorbed on surfaces

We report on the present status of a vacuum ultraviolet and soft X-ray undulator beamline, BL-13A, located at the Photon Factory. BL-13A is mainly dedicated to the study of organic thin films adsorbed on well-defined surfaces, using angle-resolved photoelectron spectroscopy (ARPES), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS). The photon-energy resolution (E/ΔE) is estimated to be about 10000 at a photon energy of 64 eV with an exit-slit width of 30 μm. The photon intensity is estimated to be 2.9 × 1012 to 5.6 × 108 photons/s for photon energies of 30-1600 eV with an exit-slit width of 100 μm at the ring current of 450 mA. An ultrahigh vacuum (UHV) chamber equipped with an electron-energy analyzer (Gamma Data/Scienta, SES 200) is used as the main end station for ARPES, XPS, and XAS measurements. A sample can be transferred from a UHV chamber for sample preparation or from a UHV chamber for the evaporation of organic materials. The sample-holder acceptors are equipped with a heating and cooling system. The overall electron-energy resolution is estimated to be about 12 meV at a photon energy of 30 eV.

Photoelectron Spectroscopy Study of the Oxidation of ZrC (100)

Ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) are used to study the oxidation of a ZrC(100) surface. When the surface is exposed to O2 at room temperature, carbon atoms in the surface region are found to be depleted and the substrate zirconium atoms are oxidized. The Zr oxide is proposed to be a ZrO-like state at low coverage (<3 L) and to become a ZrOx (1<x<2) state with further O2 exposure. When the 100-L-O2-exposed surface is heated at elevated temperatures, the work function is substantially decreased. By heating at 1000°C, the work function reaches a minimum value which is lower than that of the clean surface by 0.6 eV. The oxidation state which gives the minimum work function is deduced to be an ordered ZrO-like state whose periodicity is similar to that of ZrC(100) based on XPS and low-energy electron diffraction (LEED) measurements.

Photoelectron spectroscopy study of the oxidation of TiC(100)

The oxidation process of a TiC(100) surface has been investigated by photoelectron spectroscopy (PES) and low-energy electron diffraction (LEED). It is found that, when the surface is exposed to O2 at room temperature, the C atoms in the substrate are depleted and the substrates Ti atoms are oxidized to form a disordered TiOx (1.5<x<2.0) layer at 100–4000 L. When the surface covered with the TiOx layer is heated, the work function decreases with increasing heating temperature. The work function reaches its minimum value, which is lower than that of the clean surface by ~1.0 eV, upon heating at 900–1000°C. With heating to ~1000°C, the TiOx oxide layer is reduced to a TiO-like state. The structure of the TiO-like layer is discussed on the basis of LEED and angle-resolved PES results, and it is proposed that the oxide layer is a well-ordered TiO(100) layer which is epitaxially grown on the TiC(100) surface.

The interaction of water with oxygen-modified ZrC(100) surfaces

Abstract The adsorption of water on oxidized ZrC(100) surfaces at room temperature has been investigated using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). It is found that the reactivity of the ZrC(100) is much enhanced when the surface is covered with an ordered suboxide (ZrO) like layer; the ZrC(100) surface is inert towards H 2 O adsorption, while H 2 O is found to adsorb dissociatively on the ZrC(100) surface covered with the ordered ZrO-like layer forming hydroxyl (OH) species and atomic O species.

Electron-hole recombination on ZnO(0001) single-crystal surface studied by time- resolved soft X-ray photoelectron spectroscopy

Time-resolved soft X-ray photoelectron spectroscopy (PES) experiments were performed with time scales from picoseconds to nanoseconds to trace relaxation of surface photovoltage on the ZnO(0001) single crystal surface in real time. The band diagram of the surface has been obtained numerically using PES data, showing a depletion layer which extends to 1 μm. Temporal evolution of the photovoltage effect is well explained by a recombination process of a thermionic model, giving the photoexcited carrier lifetime of about 1 ps at the surface under the flat band condition. This lifetime agrees with a temporal range reported by the previous time-resolved optical experiments.

Adsorption of methanol on ZrC(100) and (111) surfaces

Ultraviolet photoelectron spectroscopy (UPS) has been used to study methanol adsorption on ZrC(100) and (111) surfaces. It is found that methanol adsorbs molecularly on the ZrC(100) surface at room temperature. On the other hand, UPS study shows that methanol is dissociated on the ZrC(111) surface; methoxy species and completely dissociated atomic species (C, H and O atoms) are coexistent on the ZrC(111) surface, and complete dissociation is dominant in the initial stage of adsorption.

Phonon-Dressed Two-Dimensional Carriers on the ZnO Surface

Two-dimensional (2D) metallic states formed on the

PHOTOELECTRON SPECTROSCOPY STUDY OF AMMONIA ADSORPTION ON

\mathrm{ZnO}(10\overline{1}0)