Yoshio Nakahara

Morphological Changes in Vesicles and Release of an Encapsulated Compound Triggered by a Photoresponsive Malachite Green Leuconitrile Derivative

Photoinduced morphological changes in phosphatidylcholine vesicles are triggered by a Malachite Green leuconitrile derivative dissolved in the lipidic membrane, and are observed at Malachite Green derivative/lipid ratios <5 mol %. This Malachite Green derivative is a photoresponsive compound that undergoes ionization to afford a positive charge on the molecule by UV irradiation. The Malachite Green derivative exhibits amphiphilicity when ionized photochemically, whereas it behaves as a lipophilic compound under dark conditions. Cryo-transmission electron microscopy was used to determine vesicle morphology. The effects of the Malachite Green derivative on vesicles were studied by dynamic light scattering and fluorescence resonance energy transfer. Irradiation of vesicles containing the Malachite Green derivative induces nonspherical vesicle morphology, fusion of vesicles, and membrane solubilization, depending on conditions. Furthermore, irradiation of the Malachite Green derivative induces the release of a vesicle-encapsulated compound.

Potassium-ion-selective sensing based on selective reflection of cholesteric liquid crystal membranes

It is well-known that cholesteric liquid crystals have an optical property, selective reflection, due to changes in the pitch of their helical structure. This unique property of cholesteric liquid crystals can be used to attain a visual sensing system showing color changes as the detection signal. In this paper, we report a visual sensing membrane comprising cholesteric liquid crystals, in which a 15-crown-5 derivative was incorporated as ion recognizing sites, for K+ in aqueous solution. The resulting CLC membrane showed a shift of the reflection peak sensitive to K+ in water. We have also designed polymer-dispersed liquid crystal membranes that showed ion-selective reflection peak shifts with improved response time.

Fabrication and enzymatic degradation of fibronectin-based ultrathin films.

Novel fibronectin (FN)-based ultrathin films were prepared by layer-by-layer (LbL) assembly. Among the various combinations of extracellular matrix (ECM) proteins and glycosaminoglycans (GAGs) such as FN, gelatin (G), α-elastin (E) and heparin (Hep), FN/Hep, FN/G and FN/E nanofilms were successfully fabricated in phosphate buffer solutions (pH 7.4). The film thickness of the nanofilms, in which each component can interact with each other by FN-specific interactions, was larger than that of other LbL films (E/Hep, G/E and G/Hep) prepared by electrostatic interactions. The FN/G film was rapidly decomposed by treatment with elastase, thus demonstrating, the enzymatic biodegradability of the nanofilm. We prepared the FN/heparinoid multilayers composed of FN and dextran sulfate (Dex), and its thickness was much larger than that of the FN/α-poly(L-lysine hydrochloride) (PLL) film prepared by LbL assembly using common electrostatic interactions. Furthermore, the FN/G and FN/Dex nanofilms prepared by FN-specific interaction were more stable in Eagles MEM with 10% fetal bovine serum (FBS) than the electrostatic assembling films, FN/PLL and PLL/Dex. FN-based multilayers composed of FN and ECM components can be useful as artificial ECM films for tissue engineering and other biomedical applications.

Photoinduced micelle-to-vesicle transition and encapsulation of glucose by photoresponsive Malachite Green leuconitrile derivative

UV irradiation on a Malachite Green leuconitrile derivative afforded a cationic surfactant in aqueous solutions of sodium bis(2-ethylhexyl) sulfosuccinate. The result involved a micelle-to-vesicle transition and encapsulation which have been investigated by trapping experiment. Transmission electron microscopy was applied for direct observation of vesicle formation. The micellar solution was studied under dark conditions with pyrene emission spectra.

Investigation of polysilsesquioxane as a gate dielectric material for organic field-effect transistors

We fabricated pentacene field-effect transistors using polysilsesquioxane (PSQ) as a gate dielectric material that can be cured at sufficiently low temperatures for low cost plastic substrates. The surface roughness of the PSQ films were reduced by the introduction of 3-methacryloxypropyl groups, and their surface energy was controlled to match with that of the pentacene layers by the introduction of phenyl groups. Consequently, the carrier mobility was improved by two orders of magnitude and reached 0.38 cm2 V−1 s−1.

Self-assembling phenomena of benzo-18-crown-6/crowned-spirobenzopyran copolymers in aqueous solution and controlled release of entrapped organic dyes using external stimuli

A novel amphiphilic vinyl copolymer incorporating benzo-18-crown-6 (BC) and crowned spirobenzopyran (cSP) in the side chain [poly(BC-co-cSP)] was synthesized by free radical copolymerization. The spectroscopic measurements made it clear that poly(BC-co-cSP) forms a micelle in water and that its cSP moiety can bind a metal ion in the micelle. Photochromism based on the spirobenzopyran moiety was successfully observed even under conditions of micelle formation. These results indicate that two external stimuli, metal ions and light, can cause significant changes in the assembly state and physical properties of poly(BC-co-cSP). Release behaviors of encapsulated organic dyes from polymeric micelles consisting of poly(BC-co-cSP) were investigated in Tris–HCl buffer solution (pH 7.4) before and after addition of external stimuli. As a result, it was shown that the performances were largely affected by metal-ion addition and photoirradiation. Thus, controlled release of organic dyes from polymeric micelles was realized using a combination of UV-light and visible-light irradiation in water containing BaCl2.

Ultra-High-Sensitive Extraction-Photometric Determination of Sodium Ion Using Flow Injection Analysis with a Chromogenic Calix[4]arene Derivative and a Laser Interferometric Photothermal Detector

A novel flow injection analysis (FIA) system for ultra-high-sensitive determination of Na(+), which involves laser interferometric photothermal equipment as the detector, was designed using a proton-dissociable chromogenic calix[4]arene derivative with a dinitrophenol moiety as the extraction-photometric reagent. The chromogenic calix[4]arene derivative showed an excellent extractability toward Na(+), which reflected the cation-complexing property of the tetraethyl ester derivative of calix[4]arene. As the calibration graph of the Na(+) concentration could be successfully obtained at the nanomolar level by this method, the proposed FIA system was found to be promising for highly sensitive determination of Na(+) in very dilute samples such as supply water and cooling water in power plants.

Fluorescent silica nanoparticles modified chemically with terbium complexes as potential bioimaging probes: their fluorescence and colloidal properties in water

It generally requires a complicated reaction protocol for the synthesis of silylated fluorescent lanthanide complexes. In this study, a silylated terbium complex was prepared by a very simple procedure through formation of a Schiff base between a terbium complex bearing a formyl group and 3-aminopropyltriethoxysilane. Using the silylated terbium complex, highly fluorescent silica nanoparticles modified chemically with terbium complexes (Tb-SNPs) were efficiently synthesized by a reverse micelle method with Triton X-100 as a surfactant in cyclohexane. The fluorescence properties of Tb-SNPs were remarkably improved by photostability, pH dependence and fluorescence lifetime, compared to free terbium complexes. Also, Tb-SNPs hardly aggregated under aqueous conditions with different salt concentrations and pHs. From these results, it was found that Tb-SNPs are applicable under physiological aqueous conditions. Furthermore, as an application model, Tb-SNPs were used as the fluorescent label for the imaging of African green monkey kidney cells.

Single-molecule force spectroscopic study on chiral recognition of cysteine derivatives immobilized on a gold substrate by using AFM tips chemically modified with optically active crown ethers

The chiral recognition of cysteine derivatives immobilized on a gold substrate using atomic force microscopy (AFM) tips chemically modified with optically active crown ethers was quantitatively investigated with single-molecule force spectroscopy (SMFS). Interestingly, the chiral recognition ability of the optically active crown ether-modified tip was entirely opposite to that of its optical isomer-modified tip. The difference of rupture forces for the chiral recognition was determined to be about 40 pN under our experimental conditions.

Effect of photoirradiation on chromatographic separation of alkali metal ions using crowned-spirobenzopyran-immobilized silica

We successfully developed a novel photocontrollable chromatographic system for separation of alkali metal ions. Based on the finding that the metal-ion complexation of spirobenzopyran derivatives bearing a crown ether moiety, which we call crowned spirobenzopyran, can be drastically changed by photoirradiation, crowned spirobenzopyrans were immobilized covalently onto silica gels for stationary phases of ion chromatography. Under dark or UV-light irradiation conditions, a marked separation between Li+ and K+ was attained by silica gels modified chemically with crowned spirobenzopyran bearing an 18-crown-6 ring. On the other hand, no significant separation between the two metal ions was found under visible-light irradiation conditions. This result originates from the fact that the K+-complexing ability of crowned-spirobenzopyran-immobilized silica is switched by photoisomerization of the spirobenzopyran moiety from its merocyanine form to spiropyran form. Furthermore, computer simulations of separation of alkali metal ions by crowned spirobenzopyrans in the silica phase were conducted using molecular dynamics calculations.