Asako Narita

Design of Ionic Liquids for Electrochemical Applications

Zwitterionic liquids composed of a tethered cation and anion were synthesized and their thermal properties and ionic conductivity were investigated as novel ionic liquids especially for electrochemical applications. We prepared nine zwitterions in this study. In addition, this paper includes 36 kinds of zwitterions already reported in order to discuss the relationship between the zwitterion structure and their properties. Most zwitterions melt above 100°C; their melting points are generally higher than that of simple ionic liquids. When an equimolar amount of lithium salt (LiTFSI, LiBETI, LiCF3SO3, LiBF4, or LiClO4) was added to the zwitterion, the mixture showed only a glass transition temperature Tg. The Tg values of the zwitterionic liquid/salt mixture showed the lowest value of –37°C when mixed with LiTFSI. This mixture also showed the highest ionic conductivity of 8.9 × 10–4 S cm–1 at 100°C. There is a good relationship between Tg and the ionic conductivity of the zwitterionic liquid/lithium salt mixtures.

Preparation for highly sensitive MRI contrast agents using core/shell type nanoparticles consisting of multiple SPIO cores with thin silica coating.

We describe here the facile and robust preparation methods for the multiple-SPIO-containing silica-coated core/shell type nanoparticles which can serve as a highly sensitive MRI contrast agent. The imidazolium-tethered core/shell type particles were synthesized, and the centrifugal selection for the multiple-SPIO-containing particles and the etching process to fabricate thin silica layers were carried out to improve the proton relaxivity of water tissue. We found that the synthetic particles can provide approximately 7-fold clearer contrasts than that of the particles before treatments. In addition, the particles can show good dispersibility at least for 1 week in aqueous media.

Structural factors to improve physico-chemical properties of zwitterions as ion conductive matrices

Thermal properties and ion conductive characteristics of equimolar mixtures of zwitterion and lithium salts (Z/L mixtures) have been investigated. Through a systematic study of their structure–property relationship, we describe a zwitterion structure that produces high ionic conductivity when the zwitterion is mixed with lithium salt. We found that a pure zwitterion containing imide anion melted at 87 °C and the melting point of pure zwitterions was lowered in proportion to the alkyl spacer chain length between the anion and cation sites. In Z/L mixtures, ionic liquid-like domain formed between the cation sites of zwitterions and the anions of lithium salts regardless of the anion structure of the zwitterions. However, the anion structure affected the transference number of the lithium cation in the Z/L mixtures. To improve the thermal stability and the ionic conductivity of Z/L mixtures, suitable alkyl chain length between the cation and anion sites was determined to be 5 to 7 CH2 units.

Lithium ion conduction in an organoborate zwitterion–LiTFSI mixture

An organoborate zwitterion-lithium salt mixture, prepared via selective borate formation of N-ethylimidazolium salt, exhibited ionic conductivity of 3.0 x 10(-5) S cm(-1) at 50 degrees C and a lithium transference number of 0.69.

Preparation and fluorescence properties of fluorophore-labeled avidin-biotin system immobilized on Fe3O4 nanoparticles through functional indolequinone linker

We prepared and characterized a new class of fluorophore-labeled magnetic nanoparticles (MNPs) possessing a hypoxia-responsive unit to construct a hypoxia-selective emission system. The indolequinone derivative as a hypoxia-response unit bearing biotin was synthesized and immobilized on Fe(3)O(4) MNP. Subsequent complexation of this functionalized MNP with fluorescein-labeled avidin formed fluorophore-labeled nanoparticles (AF-QB@MNP). The fluorescence intensity of AF-QB@MNP was suppressed because of the adjacent quenching function of the indolequinone moiety and MNP. Upon hypoxic treatment by NADPH:cytochrome P450 reductase, AF-QB@MNP was activated to liberate a fluorescence unit, leading to the significant enhancement of fluorescence emission, while a smaller enhancement in fluorescence emission occurred upon aerobic treatment. The AF-QB@MNP has a indispensable properties as a fluorescent probe for imaging of disease relevant hypoxic microenvironments.

Catch and release with DNA by imidazolium-presenting iron oxide nanoparticles via anion exchange

We present the catch and release technique with DNA using imidazolium-presenting nanoparticles via anion exchange. The imidazolium-tethered superparamagnetic iron oxide (SPIO) was prepared and the binding behavior to DNA was investigated. Accordingly, when the imidazolium cation forms an ion pair with the hydrophilic anion such as chloride, DNA can be absorbed onto the modified SPIO. In contrast, by anion exchange to hydrophobic anion such as TFSA−, the binding affinity greatly decreased, resulting in the release of DNA. Moreover, the release efficiency can be improved by introducing a silica layer at the surface of SPIOs. Finally, the catch and release with DNA was accomplished under mild conditions.

Tumor cell-specific prodrugs using arsonic acid-presenting iron oxide nanoparticles with high sensitivity

We report the tumor cell-selective prodrugs based on the arsonic acid-presenting iron oxide nanoparticles. We synthesized the well-dispersed nanoparticles having arsonoacetic acid which is composed of the low toxic As(V) form. From the analyses of the reaction products, it is suggested that the reduction by dithiothreitol with arsonoacetic acid and the modified nanoparticles could generate the highly-toxic As(III) species. In the MTT assays, it was found that the cell viabilities of HeLaS3 and especially HepG2 were reduced in the presence of the modified nanoparticles. In contrast, a slight effect on viability was observed with primary mouse hepatocytes. The viabilities showed good agreements with the amounts of intracellular reduced glutathione concentrations. Furthermore, the valid concentrations of the modified nanoparticles for tumor-specific cytotoxicity were similar level in MRI measurements. These results indicate that arsonic acid-presenting nanoparticles should be a good platform for developing highly-sensitive tumor-specific prodrugs.

Arsonic acid-presenting superparamagnetic iron oxide for pH-responsive aggregation under slightly acidic conditions

We report the synthesis and characterization of the arsonic acid-presenting superparamagnetic iron oxide (SPIO). We used arsonoacetic acid as the ligand for SPIOs in aqueous media. The surface modification of the SPIOs was accomplished via the ligand exchange from undecanoic acid to the carboxyl moiety of arsonoacetic acid. Consequently, the well-dispersed arsonic acid-presenting SPIOs in water were obtained. We found that the dispersion state of the arsonic acid-presenting SPIOs can be sharply regulated by pH changes in the biological significant region. The well dispersion state of the arsonic acid-presenting SPIOs can be maintained at the neutral pH region. In contrast, the arsonic acid-presenting SPIOs can sensitively form the aggregation below pH 6.1. Moreover, these dispersion states can be controlled reversibly by the pH alteration in the narrow region.

Regulation of dispersion/aggregation of phosphonium-presenting iron oxide nanoparticles by anion exchange

We describe synthesis of three kinds of phosphonium-presenting superparamagnetic iron oxides (SPIOs) with different anchoring motifs and their stimuli responsiveness to anion exchange. The series of the modified SPIOs with or without direct bonding to phosphonium bromides were prepared. With these modified SPIOs, an influence of the anion exchange on the dispersion states was investigated. Accordingly, the direct anchoring of phosphonium cation to the surface could contribute to improving sensitivity of the aggregation formation when the hydrophobicity of the surface was enhanced. Finally, it was found that the modified SPIOs with directlyconnected phosphonium cation immediately formed the assembly in the presence of citrate anion.