Shinya Oku

Structural changes in protein molecules adsorbed on ultrafine silica particles

The structural changes in horse cytochrome c, bovine ribonuclease A (RNase A), sperm whale myoglobin, ovalbumin, human hemoglobin, and bovine serum albumin (BSA) during adsorption on ultrafine silica particles have been studied. Since the intensity of light scattered by the ultrafine silica particles (average diameter 15 nm) is negligible, the structure of adsorbed protein molecules on the surface is directly estimated by measuring the circular dichroism (CD) spectra of the suspension of particles on which protein molecules were adsorbed. While the CD spectra of soft proteins such as hemoglobin and BSA were changed extensively by adsorption on ultrafine silica particles, those of rigid proteins such as cytochrome c and RNAse A were changed little. Changes in the CD spectrum of BSA during adsorption increased with decreasing pH. Thus, the magnitude of the structural changes is affected by both the flexibility of the protein molecules and the affinities of the particles for proteins. The BSA molecules desorbed from the ultrafine silica particles by addition of morpholine showed CD spectra similar to those of native BSA and hence were refolded. Thus, the conformational changes in BSA molecules produced by adsorption were highly reversible. The adsorption amounts of all these proteins on ultrafine silica particles were maximum at around their isoelectric points regardless of structural adaptability.

Conformational changes in protein molecules upon adsorption on ultrafine particles

Abstract Conformational changes in hemoglobin (a “soft” protein) and catalase (a relatively “soft” protein) upon adsorption on ultrafine silica particles (average diameter 15 nm) have been studied by circular dichroism (CD). Because the light scattering intensity of the ultrafine silica particles is very low, the secondary structure of protein molecules on solid surfaces can be estimated from the CD spectra of the suspension of the ultrafine silica particles on which proteins are adsorbed. The extent of the changes in the secondary structure of both the protein molecules was found to increase with decreasing pH and adsorbed amount. Hemoglobin showed the changes in the secondary structure up to high pH and high adsorbed amount. Therefore, soft proteins are susceptible to conformational changes upon adsorption on solid surfaces. These CD spectrum data give us some quantitative information about the conformational changes in protein molecules upon adsorption on solid surfaces.

Enhancement of Transport Characteristics in Poly(3-hexylthiophene) Films Deposited with Floating Film Transfer Method

A new solution-processed technique of floating film transfer method (FTM) is proposed for depositing organic thin film semiconductor. Organic field-effect transistors (OFETs) have been fabricated to evaluate the transport characteristics in poly(3-hexylthiophene) (P3HT) films deposited with FTM and spin-coating methodology. An enhancement of hole mobility was found in the FTM film by one order of magnitude as compared to that in spin-coated films. Absorption spectra as well as X-ray diffraction profiles represent well-grown lamella structures of P3HT with FTM transverse to the substrate, representing the advantage of this method suitable for the carrier transport.

Long-term air-stable n-channel organic thin-film transistors using 2,5-difluoro-1,4-phenylene-bis{2-[4-(trifluoromethyl)phenyl]acrylonitrile}.

A long-term air-stable n-type organic semiconductor, 2,5-difluoro-1,4-phenylene-bis{2-[4-(trifluoromethyl)phenyl]acrylonitrile}, was synthesized by a high-yield simple procedure of Knoevenagel condensation with aldehyde and acetonitrile derivatives. A fabricated organic thin-film transistor (OTFT) using this compound exhibited good n-channel OTFT properties with a high electron mobility of 0.17 cm(2) V(-1) s(-1) and an on/off current ratio of 10(6) under both vacuum and ambient air operation. After storage in ambient air for 1 year, a stored n-channel OTFT still shows good n-channel OTFT performance with little degradation in ambient air operation.

Ambipolar Transport in Bilayer Organic Field-Effect Transistor Based on Poly(3-hexylthiophene) and Fullerene Derivatives

Ambipolar characteristics in an organic field-effect transistor (FET) with a bilayer structure consisting of poly(3-hexylthiophene) (P3HT) and a fullerene derivative (PCBM) are reported. P3HT was deposited by a floating film transfer method (FTM) with toluene solution on spin-coated PCBM. The FTM-deposited film was found to show relatively high hole mobility even when cast using toluene solution. Even after coating P3HT on PCBM by FTM, a relatively high n-type transport was obtained. This indicates that FTM employed in this study is a mild way to coat an organic thin film on an organic semiconductor layer in terms of minimizing the effect of carrier transport in the underlayer. The transport characteristics have been discussed in comparison with those of ambipolar FETs prepared by other methods previously reported.

A Steady Operation of n-Type Organic Thin-Film Transistors with Cyano-Substituted Distyrylbenzene Derivative

A novel n-type organic semiconductor, cyano-substituted distyrylbenzene derivative, 1,4-bis2-[4-(trifluoromethyl)phenyl]acrylonitorilebenzene, was synthesized by Knoevenagel condensation with aldehyde and acetonitrile derivatives. Fabricated thin-film transistors (TFTs) exhibited high electron field-effect mobility of 10-2–10-1 cm2 V-1 s-1, on/off current ratio of 6×105. Hysteresis-free n-type transport characteristics observed in this device promises a steady operation of organic logic circuit. Almost same TFT characteristic was observed even after 1 month storage in ambient condition. The findings indicate that the material has a good resistance to atmospheric oxidants.