Toshiaki Shirakawa

Oxygen species adsorbed on ultraviolet-irradiated magnesium oxide

The adsorption of oxygen, under u.v. irradiation, on the surface of MgO outgassed at 1123 K has been studied at 77 K by temperature-programmed desorption and e.s.r. spectroscopy. During adsorption ozonide and superoxide ions were formed in equal amounts. The formation of these oxygen species is explained by the reaction of oxygen molecules with a short-lived exciton produced by the absorption of a photon at a surface O2– species in a very low coordination state. Thermal decomposition of the oxygen species adsorbed at 77 K has also been studied under a dynamic vacuum. It proceeds in four steps: (i) O–3 is transformed into O– and O2 between 77 and 300 K; (ii) O– is changed into O2–2 between 77 and 473 K; (iii) O–2 is also transformed into O2–2, with the evolution of O2 between 300 and 673 K; (iv) finally O2–2 is changed into O2– and O2 between 673 and 1123 K. This mechanism is also consistent with energy considerations. The formation and thermal decomposition of superoxide ions proceeds similarly both on surfaces subjected to u.v. irradiation and on surfaces containing thermally preadsorbed hydrogen.

Effect of surface charge on adsorption of bovine serum albumin as studied by ellipsometry 1. Adsorption on cationic monolayer

The adsorption of bovine serum albumin (BSA) onto a cationic monolayer (N,N-dimethyl-N,N-dialkylammonium chloride) spread at the air/water interface was studied by ellipsometry. Both thicknesses and refractive indices of the BSA layer adsorbed at the monolayer/solution interface are estimated from the observed change in phase difference and the ratio of reflection coefficients. The amount of adsorption of BSA resembles a Langmuir type isotherm. The adsorption changes with pH asymmetrically with respect to the pH of maximum adsorption, which was calculated to be 5.06 ± 0.47 mg/m2. The amount of maximum adsorption implies that the BSA molecule adsorbs to the surface in a mode intermediate between “side-on” and “end-on”.

Effect of surface charge on adsorption of bovine serum albumin 2. Interaction of protein molecules with an anionic monolayer, as studied by ellipsometry, radiotracer and surface tension measurements

The adsorption of bovine serum albumin (BSA) onto an anionic monolayer of sodium docosylsulfate (SDocS) spread at the air/water interface was studied by ellipsometry. The adsorption behavior of BSA was estimated from the observed changes in phase differences and in the ratio of reflection coefficients. The dynamic process of BSA adsorption was measured after the injection of BSA solution into the aqueous substrate of SDocS monolayer. The gentle stirring of the substrate solution for 10 min was found to be enough to make the solution homogeneous without damaging the monolayer. The adsorption characteristics of BSA onto a negatively charged surface was compared with that onto a positively charged surface previously reported.The amount of adsorption depended on time and showed a maximum with an initial rapid rise, followed by gradual decrease toward the ultimate equilibrium value. The amount and time of the maximum adsorption depended on the concentration of BSA added to the aqueous substrate.Separate radiotracer measurement, using35S-labeled SDocS monolayer, which is insoluble by itself, revealed that SDocS is solubilized into the bulk solution when BSA is added to the aqueous substrate.

Effects of composition and molecular packing on ionic properties of lipid monolayer having both cationic and anionic head groups

The effects of composition and molecular packing on the overall ionic property of mixed monolayer involving cationic, anionic and zwitterionic lipids were studied by measuring surface potential change when the concentration of sodium or calcium ions in the aqueous substrate was varied. Those lipids used were N,N-dimethyl-N-n-hexadecyl-n-octadecyl ammonium chloride (DDAC) as cationic lipid, stearic acid (StH) or sodium docosylsulfate (SDocS) as anionic lipid, and 1,2-dipalmitoyl-sn-glycero-3-phosphorylethanolamine (PE) and 1,2-distearoyl-sn-glycero-3-phosphorylcholine (PC) as ampholytic lipids. For the equimolar mixture of StH and DDAC, the reversal of apparent charge is observed when molecular packing exceeds 3.25 X 10(-10) M/cm2. The effect is rendered to the discreteness of cationic and anionic charges in the monolayer. It was also found that the addition of 30% of PC drastically changes the ionic property of PE closer to that of PC.

Analysis of the permeation of CO2 through glassy polymers

Abstract Dual-mode sorption and mobility parameters for the transport of CO 2 in glassy poly (ethylene terephthalate) were determined from the pressure dependence of the apparent diffusion coefficients, D a , below 1 atm at various temperatures. Experimental values of these diffusion coefficients were obtained from permeation time-lag measurements. Values of D a calculated by means of the above parameters are in excellent agreement with the experimental data. Moreover, the permeation time-lag curves calculated by the finite-difference technique in conjunction with the dualmode sorption parameters are consistent with the experimental time-lag curves. These results appear to support the validity of the dual-mode sorption model of gas transport in glassy polymers. However, equally good agreement between the calculated and experimental curves was obtained by using the apparent solubility and diffusion coefficient without the dual-mode sorption parameters. Similar results were obtained with poly(vinyl acetate)/CO 2 system at temperatures both above and below the glass transition temperature.

Hydration of the organized molecular assembly of ionic surfactants as studied by vapor pressure and x-ray diffraction

Equilibrium vapor pressure of water was measured for ionic surfactant-water binary systems as a function of water content over the temperature range 5–11°C. The measurement of x-ray powder diffraction has also been performed to characterize the microscopic structures of these two-component systems. Examined surfactants were the homologs of sodium alkyl sulfate and alkyltrimethylammonium bromide. It was found that dodecyl and decyl sulfate formed solid di-and trihydrate respectively, while octyl sulfate and the cationic surfactants formed lyotropic liquid crystal instead. The x-ray long spacing of the liquid crystals scarcely varied with water content.Enthalpy of vaporization was calculated for both solid hydrates and lyotropic liquid crystals.

Pressure Induced Change of The Nature of The Isotropic to Nematic Phase Transition for 4-(Trans-4-Butylcyclohexyl)Benzonitrile

Abstract Pressure-volume isotherms for 4-(trans-4-butylcylohexyl)benzonitrile were measured by means of piston-cylinder method. This substance has a monotropic nematic phase at atmospheric pressure. But over a pressure, the nature of isotropic to nematic phase transition changed from monotropic to enantiotropic phase transition. It is the first observation in P-V-T experiments that the monotropic isotropic-nematic transition changes enantiotropic under pressure.

Packing of Alkyl Group on Oxidized Silicon Wafer by Silylation, Studies by AFM and Ellipsometry

Oxidized surface of the silicon single crystal was silylized by octadecyltrichlorosilane (OTS) to give highly hydrophobic surface which shows contact angle larger than 110 ° against water. The optimal condition of OTS silylation was developed to plant alkyl chain as close as possible on oxidized silicon surface and to give well-qualified hydrophobic surface. The silylated surface was examined in water by AFM. The image shows that the methyl groups of octadecyl chains are arranged at the surface to have a cross sectional area of 0.43 ± 0.07 nm2. While, the thickness and the refractive indices of alkylated layers on silicon surface were estimated by Ellipsometric measurements, from which each octadecyl chain was found to occupy 0.6 ± 0.1 nm2, which is in good agreement with that estimated by AFM.

ISOTOPE EXCHANGE BY TRIBOCHEMICAL REACTION

Isotope exchange reaction H2 + D2 = 2HD occurs at room temperature tribochemically by vibration of SiC. This reaction, which is distinct from thermal reaction, has an induction period at initial stage and the rate of the reaction increases with increasing vibrating time.