Setsuko Yajima

EMF response of neutral-carrier based ion-sensitive field effect transistors with membranes free of ionic sites

Response characteristics of field effect transistors covered by membranes containing neutral carriers and an organic liquid but neither a polymer nor ionic sites were determined. The commercially available 2-nitrophenyl octyl ether and dioctyl sebacate, both frequently used plasticizers for poly(vinyl chloride) ISE membranes, had impurity concentrations large enough to lead to small emf responses. Upon removal of these impurities by HPLC, no emf responses were detectable any more, which seems to be due to a negligibly small permselective uptake of primary ions into the membrane and not the high impedance of the membrane bulk. The use of membranes of the more polar nitrobenzene and 2-fluoro-2′-nitrodiphenyl ether resulted in small but transient emf responses. The absence of ionic sites led however to the failure of permselectivity and resulted in co-extraction even of the highly hydrophilic chloride ions. Liquid membranes containing neutral carriers but no ionic sites are thus not only unsuitable for ISEs due to their high impedance, but also because it is very likely that either the failure of permselectivity occurs or the concentration of primary ions permselectivity entering the membrane is too small to determine the phase boundary potential.

Decisive Factors in the Photoisomerization Behavior of Crowned Spirobenzopyrans: Metal Ion Interaction with Crown Ether and Phenolate Anion Moieties

The influence of metal ion interaction with crowned spirobenzopyrans on the photoisomerization behavior was investigated through the use of various solvents, crowned spirobenzopyrans, and metal ions. Studies on the photoisomerization behavior of crowned spirobenzopyrans in various solvents revealed that solvation of the phenolate anion moiety in the merocyanine form induced photoisomerization back to the spiropyran form, giving rise to negative photochromism. Metal ion interaction with the phenolate anion moiety similarly caused photoisomerization back to the spiropyran form, while that with the crown ether moiety just produced a polar environment and its influence on photoisomerization behavior was dependent on the affinity of the metal ion captured by the crown ether moiety for the phenolate anion. Therefore, photochromic switching of crowned spirobenzopyrans between positive and negative to control the metal ion interaction with the phenolate anion moiety through the crown ether moiety is possible. This finding suggests a molecular design method for crowned spirobenzopyrans showing desired ion-responsive photochromism.

Ion-sensor property and blood compatibility of neutral-carrier-type poly(vinyl chloride) membranes coated by phosphorylcholine polymers

Abstract Ion-selective membranes (ion-selective electrodes) were coated by biocompatible polymers, which are copolymers of methacryloyloxyethyl phosphorylcholine and an alkyl methacrylate, in order to develop blood compatible ion-selective electrodes. The sensor properties and biocompatibility of the ion-sensors were investigated using two types of alkyl methacrylates with different molecular weights. When the concentration of polymer solution for coating was relatively low, the ISEs showed good sensor properties, which lasted for at least 6 months. When the concentration of polymer solution for coating was relatively high, the coated ion-sensing membranes also showed good biocompatibility, which lasted for about a month.

Anion-sensitive field-effect transistors based on sol–gel-derived membranes incorporating quaternary ammonium salts

Quaternary alkylammonium chlorides were encapsulated or bonded covalently to sol–gel-derived membranes made of mixtures of two alkoxysilanes so as to obtain sensing membranes for anion-sensitive field-effect transistors. Both types of anion sensors responded to chloride-ion activity changes with high sensitivity. The anion-sensing membranes modified chemically by an alkoxysilyl derivative of quaternary ammonium salt are superior to those simply encapsulating an ammonium salt in their durability and protein-adsorption properties. The anion sensors are applicable to chloride-ion assay in serum samples.

Drastic selectivity reversal on crown-ether based ion-sensing membranes made of ordered mesoporous silica and conventional sol–gel derived one

A crown-ether based ion sensor, in which ordered mesoporous silica was used as a membrane material, was fabricated for the first time, and drastic selectivity reversal was attained in comparison with conventional sol-gel derived membrane based on the same crown ether.

Liquid crystal effect on neutral-carrier-type ion-sensing membranes

Liquid crystallinity of membrane solvent and neutral carriers for potentiometric ion sensors affects the orientation of neutral carrier molecules in the ion-sensing membranes, thus bringing about significant changes in the ion selectivity for the membrane electrodes.

Cation complexation, isomerization, and photoresponsive ionic conduction of a crown ether derivative carrying two spirobenzopyran units

Cation complexation and subsequent isomerization of a diaza-18-crown-6 derivative possessing two spirobenzopyran units, crowned bis(spirobenzopyran), were investigated in solution and compared with those of its corresponding derivative incorporating only one spirobenzopyran unit. Complexation of multivalent metal ions, especially Ca2+ and La3+, by crowned bis(spirobenzopyran) enhanced the isomerization of the spirobenzopyran moiety to the corresponding merocyanine form due to the effective intramolecular interaction between a crown-complexed cation and two phenolate anions in the cation complexes of the merocyanine form. Significant photoinduced switching of ionic conductivity was realized in composite films containing crowned bis(spirobenzopyran) and a calcium salt.

Supported sol–gel-derived membranes for neutral carrier-type ion-selective electrodes

For neutral carrier-type ion-selective electrodes, several sol–gel-derived membranes were designed which encapsulate valinomycin and bis(crown ether) derivatives as the neutral carriers. Relatively large size ion-sensing membranes based on sol–gel-derived glass were successfully fabricated by using membrane filters and sintered glass filters as the membrane supports. Potassium and sodium ion-selective electrodes, at the tip of which sol–gel-derived membranes containing a neutral carrier and a poly(tetrafluoroethylene) membrane filter were incorporated, exhibit high electrode performance in their sensitivity, selectivity, and response time. The supported sol–gel-derived membranes were also modified chemically by alkoxysilylated bis(crown ether) derivatives and were tested for their usefulness as sensing membranes of ion-selective electrodes.

METAL-ION STABILIZATION OF PHOTOINDUCED OPEN COLORED ISOMER IN CROWNED SPIROBENZOTHIAPYRAN

A spirobenzothiapyran derivative bearing a monoaza-12-crown-4 moiety affords significant thermal stability enhancement in the UV light induced colored merocyanine form of its photochromic moiety by metal-ion complexation of its crown ether moiety, although the complexation hardly induces the isomerization without photoirradiation.

Surface modification of PEN and PET substrates by plasma treatment and layer-by-layer assembly of polyelectrolyte multilayer thin films and their application in electroless deposition

The surfaces of the polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) substrates were modified by plasma treatment and then layer-by-layer (LbL) assembly of polyelectrolyte multilayer thin films from two oppositely charged polyelectrolytes. Negatively or positively charged palladium complex ions bound to oppositely charged multilayer surfaces and were reduced to form palladium nanoparticles and then a nickel film was electrolessly deposited on the substrate surfaces. The multilayers on PEN and PET substrate surfaces are suitable for supporting palladium nanoparticle catalysts and their properties can be controlled by the conditions of LbL assembly.