Hiroaki Sugino

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.

Langmuir-Blodgett films of reaction centers of Rhodopseudomonas viridis: photoelectric characteristics

Abstract A stable monolayer of the isolated reaction centers (RCs) from a photosynthetic bacterium, Rhodopseudomonas viridis was prepared on a water subphase. The behavior of the monolayer was studied with reference to their surface pressure-area isotherms. The results show that a densely packed monolayer could be obtained by optimizing the initial spreading densities. Langmuir-Blodgett (LB) films which had a dense, close-packed structure could be produced with high initial density of material and high surface pressure. The absorption spectrum of this LB film was similar to that of solubilized RCs. Upon illumination with near infrared light, a sandwich device of LB films exhibited an initial current or voltage transient followed by a steady component. These results indicated that the function of photon/electron conversion of RCs was still retained in the LB films. The LB film fabrication described, giving a steady photocurrent, provides a possible method for the application of membrane proteins in biodevices.

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.

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.

Reconstitution and immobilization of photo-reaction units from photosynthetic bacterium Rhodopseudomonas viridis

Abstract Photo-reaction units (PRUs) were solubilized from chromatophores of the photosynthetic bacterium Rhodopseudomonas viridis under high salt concentration using Triton X-100 as a detergent. The absorption spectrum of isolated PRUs was similar to that of native chromatophores. Isolated PRUs were composed of reaction centers (RCs) and light-harvesting (LH) proteins. Purified PRUs were reconstituted into liposomes. The Q Y absorption bands derived from bacteriochlorophyll (BChl) b in LH subunits of PRUs were red-shifted from 1000 nm in the isolated PRUs solution to 1006 nm in the reconstituted liposomes, contrasting with the 1015 nm for native PRUs in chromatophores. To make a photo-electrochemical conversion layer for photocell or biosensor, we deposited PRU liposomes on a solid substrate by electrodeposition. The orientation angle between the molecular axis of PRUs and the disk normal was 2.4° for the deposited PRU liposomes, compared with 20.5° for purified chromatophores deposited. This demonstrates that the vertical alignment of protein molecules with the disk normal was superior for electrodeposited protein molecules immobilized using PRU liposomes compared with those using purified chromatophores.