Faculty Profiles - TAKEOKA, Yukikazu

Papers - TAKEOKA, Yukikazu

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Effect of supporting electrolyte concentration on the electrochemical reaction of redox-active surfactant micelles in aqueous solutions Reviewed

Y Takeoka, T Aoki, K Sanui, N Ogata, R Watanabe

JOURNAL OF ELECTROANALYTICAL CHEMISTRY Vol. 438 ( 1-2 ) page： 153 - 158 1997.11

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

The effect of NaCl concentration on the redox potential of alpha-ferrocenylundecyl-omega-hydroxy-polyoxyethylene (FPEG) micelles has been studied in aqueous solutions. With increasing NaCl concentration, the anodic half-wave potentials E-1/2 of cyclic voltammograms of the aqueous solutions shift to higher potential, and the peak currents of the cyclic voltammograms decrease. The results are discussed in terms of thermodynamics of the micelle formation. An equation which interprets the correlation between the E-1/2, the salt concentration, diffusion coefficient of the micelle D-M, and the aggregation number m, has been derived. The changes in D-M and m with NaCl concentration do not explain the change in the value of E-1/2. The decrease in the equilibrium constant for the micelle-disruption K-d with increasing NaCl concentration affects the redox-potential of the FPEG micellar solutions. (C) 1997 Elsevier Science S.A.

Web of Science

Cyclic voltammetric study of redox-active surfactant by hydrogel-modified electrode Reviewed

Y Takeoka, T Aoki, K Sanui, N Ogata, M Watanabe

POLYMER GELS AND NETWORKS Vol. 5 ( 4 ) page： 369 - 383 1997

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

The dissolved states of redox-active non-ionic surfactant (FPEG) in the swollen state of N-isopropyl acrylamide (NIPA) hydrogel have been studied by using a gel-modified electrode. The pronounced decrease in the peak current and the negative shift in the formal potential of CV at the gel-modified electrode, as compared with the normal GC electrode, was observed in the micelle-solution; this indicates that the diffusive FPEG molecules which form the micelle hardly penetrate into the NIPA gel. This result suggests that there exists all interaction between FPEG molecules and the NIFA gel in the vicinity of the surface of the NIPA gel in the micelle-solution. However, this also indicates that a small amount of FPEG molecules which can form micelles exist in the NIPA gel. (C) 1997 Elsevier Science Ltd.

Web of Science

Cyclic voltammetric study of redox-active surfactant by gel-modified electrode Reviewed

Yukikazu Takeoka, Takashi Aoki, Kohei Sanui, Naoya Ogata, Masayoshi Watanabe

Polymer Gels and Networks Vol. 5 page： 369-383 1997

Effect of supporting electrolyte concentration on the electrochemical reaction of redox-active surfactant micelles in aqueous solutions Reviewed

Yukikazu Takeoka, Takashi Aoki, Kohei Sanui, Naoya Ogata, Masayoshi Watanabe

J.Electroanal.Chem. Vol. 438 page： 153-158 1997

Electrochemical studies of a redox-active surfactant. Correlation between electrochemical responses and dissolved states Reviewed

Y Takeoka, T Aoki, K Sanui, N Ogata, M Watanabe

LANGMUIR Vol. 12 ( 2 ) page： 487 - 493 1996.1

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Electrochemical studies of a nonionic surfactant, alpha-(ferrocenylundecyl)-omega-hydroxy-oligo(ethylene oxide) (FPEG), have been conducted in 0.16 M NaCl aqueous solution at a glassy carbon electrode. The correlation between electrochemical responses and dissolved states has been examined in detail. Cyclic voltammograms (upsilon = 10 mV/s) of the FPEG solutions change with the concentration; below the critical micelle concentration (cmc), the voltammetric shape is of a typical surface-confined species, while above the cmc the diffusion-controlled waves are superimposed at the cathodic side of the surface waves, and far above the cmc the voltammetric shape is of a typical diffusion-controlled species. FPEG in the aqueous solutions adsorbs onto the glassy carbon electrode surface to form a monolayer because of its surface activity. The adsorption isotherm has been represented by the Frumkin isotherm, which includes the repulsive interaction between the adsorbed FPEG molecules. Above the cmc, FPEG forms micelles. Chronoamperometrically determined apparent diffusion coefficients of the micellar solutions decrease with increasing concentrations. This has been interpreted in terms of the change in the diffusion species by disruption of the micelles into monomers at the cmc in the concentration gradient in diffusion layers. Cyclic voltammetric peak potentials of the micellar solutions shift toward the anodic side with the concentration. This behavior has been explained as the electrochemical reaction coupled with a preceding disassembled reaction of the micelles.

Web of Science

Electrochemical Studies of a Redox-active Surfactants. Correlation between Electrochemical Responses and Dissolved States Reviewed

Yukikazu Takeoka, Takashi Aoki, Kohei Sanui, Naoya Ogata, Masayoshi Watanabe

Langmuir Vol. 12 page： 487-493 1996

RELATIONSHIPS BETWEEN VASCULAR BUNDLES OF PANICLE NECK INTERNODE AND CHARACTERS OF HEAD UNDER DIFFERENT PLANTING DENSITIES AND NITROGEN FERTILIZERS APPLIED IN ORYZA-SATIVA L

HJ CUI, RZ JIN, Y TAKEOKA

JAPANESE JOURNAL OF CROP SCIENCE Vol. 64 ( 2 ) page： 216 - 220 1995.6

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：CROP SCIENCE SOC JAPAN

Investigations were carried out on the characters of rachilets, grains and grain weight per panicle of the growing rice plant cv. Shimokita under different planting density and nitrogen fertilizer norm conditions during the maturity stage of growth. The large vascular bundle (LVB), and small vascular bundle (SVB) of the panicle neck internode (PNI) and partial different internode were examined under a microscope. Analysing the above dare with various statistical methods, the change in LVB number of PNI and its relationship with rachilets, grains or grain weight were determined. The average numbers of LVB and SVB were 9.0 and 16.5, and the variable range were 5-13 and 11-22, respectively. The frequency distribution of these attributes in the Ist internode and itscoefficient variation was significantly larger that the other internodes. The number of LVB and SVB in PNI appeared to positively correlated; the former with the primary rachilets having a correlation coefficient (CC) of 0.894** and the latter with the secondary rachilets a CC of 0.764**. The LVB and SVB of the PNI exhibited a significantly higher positive correlation with the total grains at a CC of 0.955** and 0.850**, respectively. The number of LVB and SVB of the PNI increased with increasing nitrogen fertilizer norm. The number of LVB and SVB of the PNI decreased with increasing planting densities.

DOI： 10.1626/jcs.64.216

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Scopus

ELECTROCHEMICAL CONTROL OF DRUG-RELEASE FROM REDOX-ACTIVE MICELLES Reviewed

Y TAKEOKA, T AOKI, K SANUI, N OGATA, M YOKOYAMA, T OKANO, Y SAKURAI, M WATANABE

JOURNAL OF CONTROLLED RELEASE Vol. 33 ( 1 ) page： 79 - 87 1995.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Electrochemical control of drug release was demonstrated by redox-active micelles of non-ionic surfactants having a ferrocenyl moiety (FPEG). The surfactants formed micelles at the concentrations above the critical micelle concentration (CMC = 0.1 mM) in normal saline solutions when they existed as the reduced form (FPEG), whereas the micelles were disassembled into monomers when they existed as the oxidized form (FPEG(+)). This change was reversible and electrochemically controlled. The electroactivity of FPEG determined by cyclic voltammetry was quite sensitive to the aggregation states. Perylene, which was used as a model of hydrophobic drugs, could be solubilized in a 2 mM FPEG normal saline solution, however, it was hardly solubilized in a 2 mM FPEG(+) solution that was made by oxidation of the former solution. Quick and discrete response for releasing perylene from the redox active micelles was achieved by using controlled potential bulk electrolysis method.

Web of Science

INTERACTION BETWEEN REDOX-ACTIVE NON IONIC SURFACTANT MICELLE AND POLY(ACRYLIC ACID) Reviewed

Y TAKEOKA, T AOKI, K SANUI, N OGATA, M WATANABE

KOBUNSHI RONBUNSHU Vol. 52 ( 10 ) page： 657 - 661 1995

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：SOC POLYMER SCIENCE JAPAN

A non-ionic redox active surfactant, alpha-ferrocenylundecyl-omega-hydroxy-oligo(ethylene oxide), exhibits high ability to form polymer complexes with poly(acrylic acid) at a micelle forming concentration, in spite of the low molecular weight of the oligo(ethylene oxide) site. The fraction of carboxyls associated with ether oxygens (theta) between them has a high value (ca. 0.8) which is independent of the concentration of poly(acrylic acid). The complex formation seemed to be caused by hydrogen bonding and hydrophobic interactions. The complex formation influenced on electrochemical reactions of the redox active surfactant.

Web of Science

Electrochemical control of drug release from redox-active micelles Reviewed

Yukikazu Takeoka, Takashi Aoki, Kohei Sanui, Naoya Ogata, Masayuki Yokoyama, Teruo Okano, Yasuhisa Sakurai, Masayoshi Watanabe

J. Controlled Release Vol. 33 page： 79-87 1995

Interaction between redox-active non-ionic surfactant micelle and poly(acrylic acid) Reviewed

Yukikazu Takeoka, Takashi Aoki, Kohei Sanui, Naoya Ogata, Masayoshi Watanabe

Kobunsi Ronbunshu Vol. 52 page： 642-647 1995

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Papers - TAKEOKA, Yukikazu