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| 1.
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Nagatani, Hirohisa ; Fujisawa, Masataka ; Imura, Hisanori ; 永谷, 広久 ; 井村, 久則
概要:
金沢大学理工研究域物質化学系<br />Molecular association between biocompatible dendritic polymers, dendrigraft poly-l-lysines (DGLs), a
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nd an anionic fluorescent probe, 8-anilino-1-naphthalenesulfonate (ANS-), was studied at the polarized water|1,2-dichloroethane (DCE) interface. The fluorescence intensity of ANS measured in aqueous solution was enhanced by the coexistence of DGLs over a wide pH range (2 < pH < 10), where ANS and DGL exist as a monoanionic form and a polycation, respectively. The voltammetric responses indicated that the positively charged DGLs were adsorbed at the water|DCE interface, whereas ANS- was transferred across the interface accompanied by the adsorption process. The interfacial behavior of the DGL-ANS associates was analyzed by potential-modulated fluorescence (PMF) spectroscopy. The PMF results demonstrated that the ion association between DGLs and ANS at the water|DCE interface is strongly affected by the applied potential and the dendritic generation of DGL. By applying appropriate potentials, the ANS anion was dissociated from its ion associate with DGLs at the interface and transferred into the organic phase, whereas DGLs remained in the aqueous phase. The Gibbs free energy of ion association (ΔGD···ANS) was estimated for the second-fourth generation DGLs (DGL-G2-G4) and the G4 polyamidoamine (PAMAM) dendrimer as a control. The highest stability of the DGL-G4-ANS associate manifested itself through ΔGD···ANS: DGL-G4-ANS (>G4 PAMAM dendrimer-ANS) > DGL-G3-ANS > DGL-G2-ANS. The results elucidated the efficient anion-binding ability of higher generation DGLs and its potential dependence at the liquid|liquid interface. © 2018 American Chemical Society.<br />Embargo Periods 12 Months
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| 2.
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Yamamoto, Sho ; Nagatani, Hirohisa ; Imura, Hisanori ; 永谷, 広久 ; 井村, 久則
概要:
金沢大学理工研究域物質化学系<br />The adsorption and self-aggregation of anionic porphyrins were studied at the polarized water|1,2-di
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chloroethane (DCE) interface by polarization-modulation total internal reflection fluorescence (PM-TIRF) spectroscopy. 5,10,15,20-Tetrakis(4-sulfonatophenyl)porphyrin diacid (H4TPPS2-) and protoporphyrin IX (H2PP2-) exhibited high surface activities at the interface. The selective excitation of interfacial species in PM-TIRF measurements elucidated the potential-induced aggregation mechanism of the porphyrins. The J-aggregates of H4TPPS2- were reversibly formed only at the water|DCE interface by applying appropriate potentials even when the porphyrins exist as monomers in the aqueous and organic solutions. In the H2PP2- system, the slow aggregation process was found in the negative potential region. The spectral characteristics and the signal phase of PM-TIRF indicated that the H2PP2- monomers were adsorbed with relatively standing orientation and that the long axis of the J-aggregates was nearly in plane of the interface. H2PP2- was also investigated at the biomimetic phospholipid-adsorbed water|DCE interface. The competitive adsorption of neutral glycerophospholipids effectively inhibited the potential-dependent adsorption and interfacial aggregation processes of H2PP2-. The results demonstrated that the aggregation state of the charged species can reversibly be controlled at liquid|liquid interfaces as a function of externally applied potential. © 2017 American Chemical Society.<br />Embargo Period 12 months
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| 3.
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Morita, Kotaro ; Shibata, Kenichi ; Nagatani, Hirohisa ; Hirayama, Naoki ; Imura, Hisanori
概要:
Covalent grafting of chromotropic acid (CA) moiety to a glassy carbon electrode was performed by electrochemical reducti
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on of the corresponding diazonium cation generated in situ. Grafted electrodes were subjected to the electrochemical detection of multivalent cations using Fe(CN)6 3-/4- as an electrochemical probe molecule. In the absence of metal cations, redox reaction of the anionic probe was depressed by electrostatic repulsion between the probe and negatively charged CA moieties on the electrode surface. Binding of tetravalent cations such as Zr(IV) and Hf(IV) and trivalent cations such as Al(III) and lanthanide(III) to the CA moiety on the electrode surface resulted in an increase in the current intensity of the probe due to a decrease in electrostatic repulsion. Highly selective detection of the tetravalent cations was achieved in the micromolar concentration range at pH 1.0. © The Japan Society for Analytical Chemistry.
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| 4.
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Nagatani, Hirohisa ; Harada, Makoto ; Tanida, Hajime ; Sakae, Hiroki ; Imura, Hisanori
概要:
Total-reflection X-ray absorption fine structure (TR-XAFS) technique was applied for the first time to an interface betw
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een two immiscible electrolyte solutions under potentiostatic control. The hydration structure of bromide ions was investigated at polarized 2-octanone/water interfaces. TR-XAFS spectra at Br K-edge measured in the presence of hexyltrimethylammonium bromide (C 6TAB) were slightly modified depending on the Galvani potential difference (Δowφ). The extended X-ray absorption fine structure analysis exposed hydration structure changes of bromide ions at the polarized interface. The coordination structure of bromide ions at the interface could be analyzed as compared with bromide ions dissolved in aqueous solution and Br --exchanged resin having quaternary ammonium groups. The results indicated that bromide ions were associated with C6TA+ at the polarized interface. The relative contribution of ion association form of bromide ions with quaternary ammonium groups was enhanced at a potential close to the ion transfer of C6TA+, where the interfacial concentration of C6TA+ is increased as a function of Δowφ. © 2014 AIP Publishing LLC.
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| 5.
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Okamura, Hiroyuki ; Takagi, Hitomi ; Isomura, Taku ; Morita, Kotaro ; Nagatani, Hirohisa ; Imura, Hisanori
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Selective synergism for the extraction of lanthanoids(III) (Ln) with β-diketones such as 2-thenoyltrifluoroacetone, 2-na
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phthoyltrifluoroacetone, and benzoylacetone has been investigated in the presence of trioctylphosphine oxide as a hydrophobic neutral ligand in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide as an ionic liquid. The extractability of heavier Ln was remarkably enhanced, resulting in a significant improvement in the separation of Ln. It was found that the present synergism is ascribed to the formation of cationic ternary complexes, followed by ion exchange into the ionic liquid.
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| 6.
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Sakae, Hiroki ; Nagatani, Hirohisa ; Morita, Kotaro ; Imura, Hisanori
概要:
Molecular encapsulation of anionic porphyrins in NH2-terminated polyamidoamine (PAMAM) dendrimers and the interfacial be
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havior of the dendrimer-porphyrin associates were studied at the polarized water|1,2-dichloroethane (DCE) interface. Formation of the ion associates was significantly dependent on the pH condition and on generation of dendrimers. 5,10,15,20-Tetrakis(4-sulfonatophenyl)porphyrin (ZnTPPS4-) associated with the positively charged fourth-generation (G4) PAMAM dendrimer was highly stabilized in acidic aqueous solution without protolytic demetalation in a wide range of pH values (pH > 2). In contrast to the zinc(II) complex, the free base porphyrin (H2TPPS4-) was readily protonated under acidic conditions even in the presence of the dendrimers. In addition, the J-aggregates of diprotonated species, (H4TPPS2-) n, were preferably formed on the dendrimer. The interfacial mechanism of the dendrimer-porphyrin associates was analyzed in detail by potential-modulated fluorescence (PMF) spectroscopy. PMF results indicated that the dendrimers incorporating porphyrin molecules were transferred across the positively polarized water|DCE interface via adsorption step, whereas the transfer responses of the porphyrin ions released from the dendrimers were observed at negatively polarized conditions. A negative shift of the transfer potential of porphyrin ions compared to the intrinsic transfer potential was apparently observed for each ion association system. The ion association stability between the dendrimer and the porphyrin molecules could be estimated from a negative shift of the transfer potential. ZnTPPS4- exhibited relatively strong interaction with the higher generation dendrimer, whereas H2TPPS4- was less effectively associated with the dendrimers. © 2014 American Chemical Society.
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| 7.
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Nagatani, Hirohisa ; Saka, Hiroki ; Torikai, Taishi ; Sagara, Takamasa ; Imura, Hisanori
概要:
The heterogeneous photoinduced electron-transfer reaction of the ion associates between NH<inf>2</inf>-terminated polyam
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idoamine (PAMAM) dendrimers and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato zinc(II) (ZnTPPS4-) was studied at the polarized water|1,2-dichloroethane (DCE) interface. The positive photocurrent arising from the photoreduction of ZnTPPS4- by a lipophilic quencher, decamethylferrocene, in the interfacial region was significantly enhanced by the ion association with the PAMAM dendrimers. The photocurrent response of the dendrimer-ZnTPPS4- associates was dependent on the pH condition and on the generation of dendrimer. A few cationic additives such as polyallylamine and n-octyltrimethyammonium were also examined as alternatives to the PAMAM dendrimer, but the magnitude of the photocurrent enhancement was rather small. The high photoreactivity of the dendrimer-ZnTPPS4- associates was interpreted mainly as a result of the high interfacial concentration of photoreactive porphyrin units associated stably with the dendrimer which was preferably adsorbed at the polarized water|DCE interface. The photochemical data observed in the second and fourth generation PAMAM dendrimer systems demonstrated that the higher generation dendrimer which can incorporate a porphyrin molecule more completely in the interior is less efficient for the photocurrent enhancement at the interface. These results indicated that the photoreactivity of ionic reactant at a polarized liquid|liquid interface can readily be modified via ion association with the charged dendrimer. © 2015 American Chemical Society.
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| 8.
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Yamamoto, Sho ; Nagatani, Hirohisa ; Morita, Kotaro ; Imura, Hisanori
概要:
Potential-dependent adsorption behavior of meso-substituted water-soluble porphyrins at the polarized water|1,2-dichloro
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ethane (DCE) interface was studied by polarization-modulation total internal reflection fluorescence (PM-TIRF) spectroscopy. In the PM-TIRF experiments, the fluorescence signal from the interfacial region was analyzed as a function of the periodic modulation of linear-polarizations (p and s) of the incident excitation beam. The potential-dependence of PM-TIRF responses for meso-substituted porphyrins, 5,10,15,20-tetrakis(N-methylpyridyl)porphyrin (H2TMPyP4+) and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H2TPPS4-), indicated that both free base porphyrins were adsorbed with relatively lying orientations at the polarized water|DCE interface. The average orientation angles (θ) were estimated as θ = 61 ± 1°for H2TMPyP4+ and θ = 65 ± 1°for H2TPPS4- with respect to the interface normal. The wavelength-dependence of polarization-modulated fluorescence signals (PM-TIRF spectrum), which corresponds to "pure" emission spectrum of interfacial species, clearly indicated that H2TMPyP4+ and H2TPPS4- are adsorbed with a modification of the solvation at the interface. These results demonstrated a high ability of the PM-TIRF spectroscopy for the direct characterization of fluorescent species adsorbed at polarized liquid|liquid interfaces. © 2016 American Chemical Society.<br />Embargo Period 12 months / This article has Supplementary data
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| 9.
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Sakae, Hiroki ; Fujisawa, Masataka ; Nagatani, Hirohisa ; Imura , Hisanori
概要:
The ion transfer and adsorption mechanism of flavin derivatives, riboflavin (RF) and flavin mononucleotide (FMN), at the
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polarized water|1,2-dichloroethane (DCE) interface were studied in the presence of the fourth generation (G4) amino-terminated polyamidoamine (PAMAM) dendrimer or hyperbranched bis-MPA polyester-64-hydroxyl (HBP). The flavin derivatives associated with the positively charged G4 PAMAM dendrimer both in the aqueous solution and at the water|DCE interface. Spectroelectrochemical analysis through potential-modulated fluorescence spectroscopy demonstrated that the dendrimer-bound flavin derivatives were transferred across the water|DCE interface in the positive potential region, while the interfacial adsorption of flavin derivatives in the negative potential region was effectively inhibited by the competitive adsorption of the neutral G4 HBP molecules. © 2016 Elsevier B.V.<br />Embargo Period 12 months / This article has Supplementary material of the different file.
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| 10.
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Sakae, Hiroki ; Nagatani, Hirohisa ; Imura, Hisanori
概要:
The transfer and adsorption reactions of ionizable drug molecules, i.e. dipyridamole (DIP), propranolol (PRO) and warfar
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in (WAR), at the water|1,2-dichloroehtane (DCE) interface were studied in the presence of the carboxylate- terminated generation 3.5 (G3.5) or amino-terminated generation 4 (G4) polyamidoamine (PAMAM) dendrimers. The ionic partition diagram of the ionizable drugs was determined through the voltammetric analysis of ion transfer responses. In the DIP system, the additional voltammetric responses associated with the interfacial adsorption were observed in the positive potential region. Although the spectroscopic features of the drug species in the aqueous solution were hardly affected by the addition of the dendrimers, the ion transfer currents in the DIP and PRO systems were decreased in the presence of the G3.5 PAMAM dendrimer indicating the intermolecular association between the cationic drugs and negatively charged dendrimers in the interfacial region. The interfacial mechanism of the fluorescent DIP species was investigated in detail by potential-modulated fluorescence (PMF) spectroscopy. The PMF results demonstrated that the monoprotonated form, HDIP+, was transferred across the water|DCE interface accompanied by the adsorption process. The interfacial mechanism of the DIP species was significantly modified by the dendrimer, depending on the pH condition. Under acidic conditions, the positively charged G3.5 PAMAM dendrimer adsorbed at the interface effectively prevented the coadsorption of HDIP+. At higher pHs, DIP (or HDIP+) interacted with the hydrophobic interior moiety (or negatively charged periphery) of the dendrimers. © 2016 Elsevier Ltd. All rights reserved.<br />Embargo Period 24 months / This article has Supplementary data.
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