Hideki Toyotama

EXCIMER EMISSION OF ANTHRACENE, PERYLENE, CORONENE AND PYRENE MICROCRYSTALS DISPERSED IN WATER

Abstract Microcrystals of aromatic hydrocarbons such as perylene, pyrene, coronene and anthracene were prepared as an aqueous suspended solution by a stratificational sublimation with water onto a substrate cooled by liquid nitrogen. Aqueous solutions of microcrystals showed anomalous fluorescence spectra different from those of bulk crystals; coronene exhibited monomer and broad excimer emissions, while pyrene showed a red-shifted excimer band, and anthracene or perylene showed both excimer and monomer bands. The relative intensities of two bands were varied systematically with the size of the microcrystals. The dual emissions are explained by assuming two emission centers, one is in the mid and another is on the periphery of microcrystals. The diffusion lengths of exciton were estimated for anthracene and perylene microcrystals from the intensity ratio of two emission bands.

Control of protein orientation in molecular photoelectric devices using Langmuir—Blodgett films of photosynthetic reaction centers from Rhodopseudomonas viridis

A photoelectric device was prepared using Langmuir—Blodgett (LB) films of photosynthetic reaction centers (RCs). Monolayers of RCs from Rhodopseudomonas viridis were deposited on transparent electrodes. The orientation of the RCs on the electrode surface was controlled using various substrates with different surface wettabilities. The degree of alignment was evaluated by measuring the polarities of light-induced electric responses. The orientation was also measured by means of an enzyme-linked immunosorbent assay that uses antibodies to distinguish opposite sites of the RCs. Photocells comprised of RC-LB films showed a steady-state photocurrent. The direction of the current flow was regulated by altering the orientation of the RCs.

Optical Properties of Perylene Microcrystals

Abstract The optical properties of perylene microcrystals in wide range of crystal size from 50 ran to 1 μm were measured. The interesting behavior of exciton in microcrystals with less than 200nm was found. For example, with decreasing the crystal size, self-trapped exciton states in microcrystals shifted to the high energy side. Therefore, the strong luminescence from free-exciton was observed, and life time of self-trapped exciton became shorter .

Oriented immobilization of bacterial photosynthetic membrane.

SummaryWe have examined a method for oriented immobilization of photosynthetic membrane fragments on a solid surface by specific avidin-biotin interaction. Photosynthetic membrane fragments from the purple non-sulphur photosynthetic bacterium Rhodopseudomonas viridis, of which the H-subunit of the photosynthetic reaction centre was biotinylated, was immobilized on an avidin-adsorbed plate. Orientation of the immobilized membrane on the plastic plate was checked by an antisera binding assay that could react to the respective sides of the membrane: the H-subunit side was selectively adsorbed on the plate. Light-induced potential and current responses could be measured when the membrane immobilized on the SnO2-coated glass plate was dried and sandwiched with a counter electrode of Hg. The electrical response in the immobilized membrane was much improved in comparison with the control (membranes were simply adsorbed on the plate), supporting the idea that the membranes have an orientation on solid surfaces.

A novel ISFET-type biosensor based on P450 monooxygenases.

We made a biosensor based on ion-sensitive field effect transistor (ISFET) using P450 monooxygenase. ISFETs are electrical devices and have been used as pH sensors. We used genetically engineered P450 monooxygenase for our research because of its high enzymatic activity. The fusion enzyme between rat CYP1A1P450 monooxygenase and yeast NADPH-cytochrome P450 oxidoreductase was expressed in yeast Saccharomyces cerevisiae strain AH22. Yeast microsomal membranes were immobilized in an agarose layer on the ISFET. o-Deethylation of 7-ethoxycoumarin to 7-hydroxycoumarin was catalyzed by the enzyme in the presence of nicotinamide adenine dinucleotide phosphate reduced form (NADPH). Formation of 7-hydroxycoumarin from 7-ethoxycoumarin was also measured by fluorescence. The difference of the voltage between the ISFET device and control device without enzymes showed a voltage increase along with the enzymatic reaction of P450 monooxygenases, and this voltage increase in the device was inhibited by addition of MnCl(2), an inhibitor of P450 monooxygenase. There was a positive correlation between the voltage increase in the ISFET device and the fluorescence intensity. This is the first electrochemical biosensing using P450 monooxygenases immobilized on the ISFET, and is applicable to the sensing of chlorophenol compounds.

ZnO Thin Films Prepared by Ion-Assisted Deposition Methods

Transparent conducting ZnO films were prepared by an ion-assisted deposition method. The glass substrate was irradiated with Ar ions during deposition of amorphous films and the c-axis-oriented ZnO film with the lowest resistivity is obtained when the growing film is irradiated with Ar plasma. Optical emission lines due to Ar, Zn2, Zn and O of neutral species were detected. In particular, the ratio of emission line intensity O(777 nm)/Zn(635 nm) is closely related with film properties. The control of plasma conditions by the check of the emission line intensity provides a method of obtaining a high-quality transparent conducting ZnO film.

Thermal stability of dried photosynthetic membrane film for photoelectrodes

Abstract Thermal stability was examined on a photoelectrode made from dried film of a photosynthetic membrane (chromatophore) isolated from a photosynthetic bacterium Rhodopseudomonas viridis . Below 60°C, neither the optical absorbance of the film nor its photoelectric response were affected when heated for 1 h. When the temperature was raised over 120 °C, both the absorbance and the response were lost. The temperature of half-denaturation of the chromatophore was 90 °C. X-ray diffraction of the film showed that heating did not cause the complete denaturation of the proteins of chromatophores. Heating did not destroy the secondary structure ( α -helix) of the proteins but the bundles of α -helices were distorted.

Light-induced electrical responses of dried chromatophore film: effect of the addition of cytochrome c

Chromatophores, photosynthetic membranes of photosynthetic bacteria, were isolated and cast on a transparent electrode to form films. The absorption spectrum of the film was similar to that of the native chromatophore. This indicated that the chromophore-protein structures were maintained through drying. Electrical transients of the film on the light pulsed excitation were examined. The amplitude and decay of the electrical transient of the film were altered by the addition of horse heart cytochrome c to the chromatophore of Rhodobacter sphaeroides R-26, which lacks the reaction centre-bound cytochrome c. The addition of cytochrome c into the film resulted in an increase in the light-induced current and a decrease in current decay.

Effects of counterions on the orientation control of photosynthetic reaction center proteins in an applied bias-voltage Langmuir–Blodgett method

Abstract Molecular orientation of photosynthetic reaction center protein (RC) was controlled during film deposition in Langmuir–Blodgett (LB) film preparation by the polarity of an applied bias voltage. The orientation of RCs was examined by measuring a displacement current. The effects of counterions in the subphase (including both bivalent cations and polyions) were studied to clarify the mechanism involved in orientation control by an applied bias voltage. Results confirmed that the orientation of an RC at the water surface was governed by the electrostatic repulsion between the electric double layer near the substrate and the dipole of the RC.

Displacement current measurements of the dynamic charge transfer of photosynthetic reaction centers in monolayer LB films

Abstract The photosynthetic reaction center (RC) from the photosynthetic bacterium Rhodopsuedomonas viridis is a unique protein in which lightinduced charge separation occurs. The charge-transfer process of the RCs was analyzed by a displacement current method in which two electrodes sandwiching the LB film without contact. A displacement current was detected for even a monolayer RC-LB film when it was irradiated with light. The action spectrum of the displacement current was in agreement with the absorption spectrum of solublized RCs, indicating that the current originates from the charge separation within the RCs. Furthermore, displacement currents for two types of LB films, in whichthe orientations of the RCs were opposite, yielded polarities that were opposite to each other. Thus, this method can be used to evaluate the unidirectional electron transfer in monolayers of RCs.