Details of a Researcher - Einaga, Yasuaki

Papers - Einaga, Yasuaki

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The one-dimensional chain structure of [Cu(en)₂Pt(CN) ₄] (en is ethylenediamine)

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section E: Structure Reports Online 62 ( 4 ) 2006.04

ISSN 1600-5368

The title compound, catena-poly[di-μ-cyano-1:2κ²C:N;-1: 2′κ²C:N-dicyano-1-κ²C- bis(ethylenediamine-2κ²N,N′)platinum(II)copper(II)], [CuPt(CN)₄(C₂H₈N₂)₂] _n, (I), consists of one-dimensional chains running along the [111] direction. Both Cu and Pt atoms are located on centres of symmetry in an alternating array of [Cu(en)₂]²⁺ (en is ethylenediamine) and [Pt(CN)₄]^2- units. The Pt-C coordination bond distances of 1.985 (4) and 1.995 (4) Å are longer than those of an analogous Ni^II complex. Moreover, due to Jahn-Teller distortion, the axial Cu-N bond distance of 2.562 (5) Å is longer than the equatorial ones of 2.014 (4) and 2.017 (4) Å. © 2006 International Union of Crystallography All rights reserved.

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Synthesis and crystal structures of the flexible Schiff base complex bis(N-1,2-diphenylethyl-salicydenaminato-κ²N,O)copper(II) (methanol)

Akitsu Takashiro, Einaga Yasuaki

Polyhedron 25 ( 5 ) 1089 - 1095 2006.03

ISSN 0277-5387

A new mononuclear copper(II) complex incorporating a bulky Schiff base ligand, bis(N-1,2-diphenylethyl-salicydenaminato-κ²N,O) copper(II) (green form) and its co-crystal containing methanol solvent molecules (brown form) have been synthesized and characterized by X-ray crystallography, XRD, IR and diffuse reflectance spectra in the solid state. This is a rare case in that both solvent free and containing crystals can be isolated and characterized. Both forms adopt a compressed tetrahedral trans-[CuN ₂O₂] coordination geometry with coordination bond angles of trans-N-Cu-N = 157.0(4)° and trans-O-Cu-O = 151.1(3)° for the brown form and trans-N-Cu-N = 141.3(3)° and trans-O-Cu-O = 139.9(2)° for the green form. The methanol solvent molecules force the complex of the brown form to adopt a more planar coordination environment in the solid state. Semi-empirical calculations (ZINDO) revealed the magnitude of the dipole moment of both molecules and that the energy of the green form is 5.7 kJ mol ^-1 higher than that of the brown form. In addition, absorption spectra in various organic solvents were measured and a relationship between absorption spectra and polarity of the solvents is discussed. © 2005 Elsevier Ltd. All rights reserved.

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Structures, magnetic properties, and XPS of cyanide-bridged Nd ^III/Sm^III/Gd^III-Cr^III complexes

Akitsu Takashiro, Einaga Yasuaki

Inorganica Chimica Acta 359 ( 5 ) 1421 - 1426 2006.03

ISSN 0020-1693

Synthesis, structural characterization, and spectroscopic and magnetic properties of three new cyano-bridged 3d-4f bimetallic complexes, Ln ^III(DMF)₄(H₂O)₃Cr^III (CN)₆·nH₂O (Ln = Nd, Sm, Gd), have been described. The Nd-Cr complex crystallizes in the monoclinic P2₁/n space group with the following unit cell parameters: a = 20.063(7) Å, b = 8.967(4) Å, c = 18.023(6) Å, b = 96.12(3)°, V = 3224(2) Å³, and Z = 4. The neodymium (III) ion, which adopts anti-prism eight-coordination environment, is linked to the [Cr^III(CN) ₆]^3- moiety through a bridging cyanide ligand with Nd-N = 2.550(4) Å and Nd-N-C = 164.4(4)°. The variable-temperature (0.5 T at 2-300 K) and variable-field (0-5 T at 2 and 5 K) magnetic measurements reveal that the weak interaction of Gd-Cr complexes differs from that of Nd-Cr and Sm-Cr ones mainly because of the lack of orbital angular momentum. The XPS and diffuse reflectance electronic spectra were also measured to discuss charge transfer transitions concerning π-backdonation from the viewpoint of magneto-optical functions. © 2005 Elsevier B.V. All rights reserved.

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Trans-Bis(4-aminopyridine-κN)bis(succinimidato-κN)copper(II) dihydrate

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section E: Structure Reports Online 62 ( 3 ) 2006.03

ISSN 1600-5368

The title compound, [Cu(C₄H₄NO₂) ₂(C₅H₆N₂)₂] ·2H₂O has its metal atom in a square-planar trans-[CuN ₄] coordination environment; the Cu^II atom lies on a center of symmetry. Both succinimidate and 4-aminopyridine ligands behave as monodentate ligands, which coordinate through deprotonated imidate and pyridine (not amino) N atoms, respectively. The 4-aminopyridine is the first ligand in such Cu^II complexes containing two different N atoms to take potentially different coordination modes. © 2006 International Union of Crystallography All rights reserved.

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Photomagnetic Langmuir-Blodgett films consisting of azobenzene and Prussian Blue

Yamamoto Takashi, Umemura Yasushi, Sato Osamu, Einaga Yasuaki

Science and Technology of Advanced Materials 7 ( 2 ) 134 - 138 2006.03

ISSN 1468-6996

A photomagnetic organized thin film consisting of an amphiphilic azobenzene, a smectite clay, and Prussian Blue has been prepared by utilizing the Langmuir-Blodgett (LB) method and an ion-exchange reaction. The magnetic LB films were revealed to possess an organized layered structure, and reversible photoisomerization of the azobenzene was observed even in the LB films. Upon photoillumination at 2 K, reversible changes in the magnetization were realized with the value of ca. 11%. This photoswitching in the magnetization is due to changes in the electrostatic field induced by photoisomerization of the azobenzene. A large photoinduced change in the magnetization would be owing to the highly ordered structure of the LB films. In order to verify the correlation between the film structure and photoswitching efficiency, the LB films have been fabricated in other condition. As results, it is confirmed that the packing state of the azobenzene plays an important and crucial role in accomplishment of the highly efficient photomagnetic switching. © 2006 Elsevier Ltd. All rights reserved.

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Electroanalysis of sulfonamides by flow injection system/high-performance liquid chromatography coupled with amperometric detection using boron-doped diamond electrode

Preechaworapun Anchana, Chuanuwatanakul Suchada, Einaga Yasuaki, Grudpan Kate, Motomizu Shoji, Chailapakul Orawon

Talanta 68 ( 5 ) 1726 - 1731 2006.02

ISSN 0039-9140

Sulfonamides (SAs) were electrochemically investigated using cyclic voltammetry at a boron-doped diamond (BDD) electrode. Comparison experiments were carried out using a glassy carbon electrode. The BDD electrode provided well-resolved oxidation, irreversible cyclic voltammograms and higher current signals when compared to the glassy carbon electrode. Results obtained from using the BDD electrode in a flow injection system coupled with amperometric detection were illustrated. The optimum potential from a hydrodynamic voltammogram was found to be 1100 mV versus Ag/AgCl, which was chosen for the HPLC-amperometric system. Excellent results of linear range and detection limit were obtained. This method was also used for determination of sulfonamides in egg samples. The standard solutions of 5, 10, and 15 ppm were spiked in a real sample, and percentage of recoveries was found to be between 90.0 and 107.7. © 2005 Elsevier B.V. All rights reserved.

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Construction of two-dimensional arrays gold nanoparticles monolayer onto boron-doped diamond electrode surfaces

Tian Ru Hai, Rao Tata Narasinga, Einaga Yasuaki, Zhi Jin Fang

Chemistry of Materials 18 ( 4 ) 939 - 945 2006.02

ISSN 0897-4756

A novel method has been developed to immobilize macroscopic two-dimensional arrays of Au nanoparticles (AuNPs) onto the surfaces of boron-doped diamond (BDD) electrodes. These AuNP-modified surfaces are prepared by self-assembly of differently sized colloidal Au particles onto the BDD surfaces. A dense and well-distributed AuNP monolayer onto the BDD surfaces was obtained by pretreating the BDD surface with allylamine by photochemical reaction. These modified surfaces have been characterized by XPS, SEM, and electrochemical cyclic voltammetry (CVs). SEM data indicated that the AuNPs are immobilized and well-dispersed, forming a uniform monolayer on the amine-terminated activated BDD surfaces in two dimensions. Cyclic voltammtric (CV) results indicate that the immobilized AuNPs monolayer onto BDD electrode shows excellent electrochemical properties, implying facile electrochemical communication between the AuNPs monolayer and BDD substrate through the amine linkers. © 2006 American Chemical Society.

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Use of nickel implanted boron-doped diamond thin film electrode coupled to HPLC system for the determination of tetracyclines

Treetepvijit Surudee, Preechaworapun Anchana, Praphairaksit Narong, Chuanuwatanakul Suchada, Einaga Yasuaki, Chailapakul Orawon

Talanta 68 ( 4 ) 1329 - 1335 2006.02

ISSN 0039-9140

The electrochemical analysis of tetracyclines was investigated using nickel-implanted boron-doped diamond thin film electrode (Ni-DIA) by cyclic voltammetry and high performance liquid chromatographic with amperometry. Cyclic voltammetry was used to study the electrochemical oxidation of tetracyclines. Comparison experiments were carried out utilizing as-deposited BDD and glassy carbon electrodes. Ni-DIA electrode provided well-resolved oxidative irreversible cyclic voltammograms and the highest current signals among the electrode studied. High performance liquid chromatography (HPLC) with amperometric detection was also studied. The chromatography was performed using a commercially available Inertsil C18 column, with the mobile phase being: 80% phosphate buffer (pH 2.5)-20% acetonitrile and detected at 1.55 V. The methods were validated over the concentration range 0.05-100 ppm with the overall average recoveries from 83.3 to 102.5% and R.S.D. of less than 10%. The proposed method was further applied to analyse shrimp samples. © 2005 Elsevier B.V. All rights reserved.

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Synthesis of ferrocene-modified phenylazomethine dendrimers possessing redox switching

Suzuki Mana, Nakajima Reina, Tsuruta Masanori, Higuchi Masayoshi, Einaga Yasuaki, Yamamoto Kimihisa

Macromolecules 39 ( 1 ) 64 - 69 2006.01

ISSN 0024-9297

The phenylazomethine dendrimer (DPA) with amino groups at the terminal (end-amine dendrimer) was synthesized by the convergent method without protection from 4,4′-diamino-3,3′,5, 5′-tetramethylbenzophenone (DTB) as the raw material. The amino groups enabled the periphery of the dendrimer (DPA) to be modified by functional molecules, and we succeeded in the synthesis of the end-ferrocene dendrimer (A), which was perfectly modified by the ferrocenes, in one step with high yields. The stepwise metal complexation from the core was also observed in A G2 and A G3. The equilibrium constant K of the terminal imine connected with ferrocnes was determined to be 10 times smaller than that of the N-diphenylmethylene imine (ca. 10⁵ [M^-1]); however, it was strong enough for metal assembling. We found that A G3 showed redox switching by the addition of metal ions. The potential jump of the modified ferrocenes from 0.32 to 0.42 V was observed, when the complexation of Fecl₃, which started from the first layer, reached the third-layer imines next to the ferrocenes. This behavior was reversible based on the encapsulation reversibility and releasing of iron ions. © 2006 American Chemical Society.

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Photo-control of magnetization by photochromic compounds

Einaga Yasuaki

Bulletin of the Chemical Society of Japan 79 ( 3 ) 361 - 372 2006

ISSN 0009-2673

The development of new magnetic materials in which magnetic properties are combined with optical properties has been extensively studied. So far, several photo-responsive molecular solids have been reported. However, the strategies that are necessary to achieve photoinduced switching in a solid state are yet to be clarified. Here, I have focused on composite materials as a novel strategy for realizing such photo-functional magnetic systems. These include the incorporation of organic photochromes into magnetic systems, e.g., photo-controllable magnetic vesicles and LB films containing Prussian blue or iron oxide nanoparticles and azobenzene. © 2006 The Chemical Society of Japan.

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Reversible photocontrol of molecular assemblies of metal complex containing azo-amphiphiles

Einaga Yasuaki, Mikami Rie, Akitsu Takashiro, Li Guangming

Thin Solid Films 493 ( 1-2 ) 230 - 236 2005.12

ISSN 0040-6090

Photo-controllable molecular systems, [M(en)₂][Pt(en) ₂Cl₂](1)₄ (M²⁺=Pt²⁺, Pd²⁺ and en=ethylenediamine), have been designed by the self-assembly of chloride-bridged platinum/palladium complexes and photochromic amphiphiles of the azobenzene derivative, 4-[4-(N-methyl-N-n-dodecylamino)phenylazo]benzene sulfonic acid (designated as compound 1). Reversible structural changes caused by cis-trans photoisomerization of azo groups in compound 1 were observed by alternating illumination of UV and visible light. Visible illumination resulted in the formation of the plate-like structures, whereas UV illumination resulted in fragmentation of the assembling structures. Reversible changes were observed in the electronic states of the chloride-bridged platinum/palladium complexes; the plate-like structures exhibited charge transfer absorption of chloride-bridged platinum complexes and delocalized Pt(II)/Pt(IV) states, while the fragments of the separated complexes exhibited no charge transfer bands. As a consequence, we have discovered that the reversible structural changes in this system could be controlled by photoillumination. © 2004 Elsevier B.V. All rights reserved.

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Syntheses, crystal structures and electronic properties of a series of copper(II) complexes with 3,5-halogen-substituted Schiff base ligands and their solutions

Akitsu Takashiro, Einaga Yasuaki

Polyhedron 24 ( 18 ) 2933 - 2943 2005.12

ISSN 0277-5387

We have systematically investigated the structural features, electronic properties, thermally-induced structural phase transitions and absorption spectra depending on the solvent for ten Cu(II) complexes with 3,5-halogen-substituted Schiff base ligands. Structural characterization of two new complexes, bis(N-R-1-phenylethyl- and N-R,S-2-butyl-5-bromosalicydenaminato- κ²N,O)copper(II), reveals that they afford a compressed tetrahedral trans-[CuN₂O₂] coordination geometry with trans-N-Cu-N = 159.4(2)° and trans-O-Cu-O = 151.7(3)° for the 1-phenylethyl complex and trans-N-Cu-N = 157.9(3)° and trans-O-Cu-O = 151.0(3)° for the 2-butyl one. All the complexes exhibit a structural phase transition by heating in the solid state regardless of their structures at room temperature. The absorption spectra of a series of ten complexes exhibit a slight shift of the d-d band at 16 000-20 000 cm^-1 and remarkable shift of the π-π* band at 24 000-28 000 cm^-1, which suggests that the dipole moment of the solvents presumably affects the conformation of the π-conjugated moieties of the ligands rather than the coordination environment. We have also attempted 'photochromic solute-induced solvatochromism' by a system of bis(N-R-1-phenylethyl-3,5- dichlorosalicydenaminato-κ²N,O)copper(II) and photochromic 4-hydroxyazobenzene in chloroform solution. We successfully observed a change of the d-d and π-π* bands of the complex in the absorption spectra caused by cis-trans photoisomerization of 4-hydroxyazobenzene. © 2005 Elsevier Ltd. All rights reserved.

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Observation of the anisotropic photoinduced magnetization effect in Co-Fe Prussian blue thin films fabricated by using clay Langmuir-Blodgett films as a template

Yamamoto Takashi, Umemura Yasushi, Sato Osamu, Einaga Yasuaki

Journal of the American Chemical Society 127 ( 46 ) 16065 - 16073 2005.11

ISSN 0002-7863

Thin films of cobalt-iron cyanide (Co-Fe Prussian blue) have been fabricated by means of the modified Langmuir-Blodgett (LB) method using a smectite clay mineral (montmorillonite). In this combined method, clay LB films play a template role in the formation of the Co-Fe Prussian blue thin layer. The films were revealed to possess a well-organized structure not only in perpendicular directions to the film surface but also in parallel directions to the film surface. The photoinduced electron transfer from the iron ion to the cobalt through the bridging cyanide in the films occurred at low temperature (8 K), similar to that in the bulk Co-Fe Prussian blue. The films clearly exhibited magnetic anisotropy with regards to the direction of the applied magnetic field. Moreover, the photoinduced magnetization effect in the films was also found to be anisotropic. © 2005 American Chemical Society.

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Pt-implanted boron-doped diamond electrodes and the application for electrochemical detection of hydrogen peroxide

Ivandini Tribidasari A., Sato Rika, Makide Yoshihiro, Fujishima Akira, Einaga Yasuaki

Diamond and Related Materials 14 ( 11-12 ) 2133 - 2138 2005.11

ISSN 0925-9635

Pt-modified diamond electrodes were fabricated for electroanalytical applications by implantation method at 750 keV Pt²⁺ with a dose of 5 × 10¹⁴ cm^{- 2}. The electrochemical behavior has been studied for oxidation of hydrogen peroxide by using cyclic voltammetry and flow injection analysis in phosphate buffer solution (pH 7). The electrode exhibited high catalytic activity and excellent electrochemical stability with a very low background current in comparison to Pt metal electrode. Very low limit of detection, 30 nM (S / N = 3), were examined with RSD of 2.91% (n = 20). These results indicate that metal-implanted method could be a promising method for controlling the electrochemical properties of diamond electrodes. © 2005 Elsevier B.V. All rights reserved.

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Synthesis, crystal structures and electronic properties of Schiff base nickel (II) complexes

Akitsu Takashiro, Einaga Yasuaki

Polyhedron 24 ( 14 ) 1869 - 1877 2005.10

ISSN 0277-5387

Two new mononuclear nickel (II) complexes incorporating Schiff base ligands, bis(N-R-1-phenylethyl- or N-2-propyl-3,5-dichlorosalicydenaminato) nickel (II), have been synthesized and characterized. The former chiral brown paramagnetic complex adopts a compressed tetrahedral [NiN₂O ₂] coordination geometry of Λ(R,R) absolute configuration with the coordination bond angles of N-Ni-N = 116.3(2)°and O-Ni-O = 141.4(2)°. On the other hand, the latter green diamagnetic complex adopts a square planar trans-[NiN₂O₂] coordination geometry. It is revealed that flexible distortion of the [NiN₂O₂] coordination environment and the overall dipole moment of the complexes are affected by both electronic withdrawing Cl-substituents and steric factors of the ligands. A structural phase transition occurs by heating in the solid state for both complexes. Negative solvatochromism relating to d-d and π-π* transitions can be observed, depending on the polarity of the solvents in which these complexes are dissolved. Furthermore, we have attempted to design a supramolecular solvatochromism system induced by a photochromic solute, that is a CHCl₃ solution of the chiral Ni(II) complex and polar 4-hydroxyazobenzene solute. After UV light irradiation, we have successfully observed slight spectral changes of the π-π* bands in absorption and CD spectra due to conformational change of the R-1-phenylethylamine moieties of the chiral ligands. © 2005 Elsevier Ltd. All rights reserved.

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The light-induced excited spin state trapping effect on Ni(dmit) ₂ salt with an Fe(III) spin-crossover cation

Takahashi Kazuyuki, Cui HengBo, Kobayashi Hayao, Einaga Yasuaki, Sato Osamu

Chemistry Letters 34 ( 9 ) 1240 - 1241 2005.09

ISSN 0366-7022

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Photoswitchable magnetic nanoparticles of Prussian blue with amphiphilic azobenzene

Taguchi Minori, Yamada Koji, Suzuki Koji, Sato Osamu, Einaga Yasuaki

Chemistry of Materials 17 ( 17 ) 4554 - 4559 2005.08

ISSN 0897-4756

A novel type of photocontrollable Prussian blue (PB) magnetic nanoparticle has been designed and prepared by using the reverse micelle technique. These magnetic nanoparticles possess a well-organized nanoscale structure. Reversible photoisomerization of azobenzene chromophores realized photoswitching of the magnetization. The photoisomerization of the composite materials was accompanied by a geometrically confined structural change within the reverse micelles, as reflected by changes in the dipole moment and the electrostatic field. As a result, the magnetization values could be switched reversibly by using alternating UV and visible light illumination. © 2005 American Chemical Society.

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Gold-nanoparticle-dispersed boron-doped diamond electrodes for electrochemical oxidation of oxalic acid

Ivandini Tribidasari A., Naono Yasutomo, Nakajima Atsushi, Einaga Yasuaki

Chemistry Letters 34 ( 8 ) 1086 - 1087 2005.08

ISSN 0366-7022

Electrochemical behavior of gold-nanoparticle-dispersed diamond electrodes have been studied for the oxidation of oxalic acid in phosphate buffer solution. Comparison is made with gold, as-deposited diamond and gold-implanted diamond. The electrodes combine the high catalytic activity of gold and the low background current of diamond electrodes. Moreover, the electrodes can overcome the problem of stability as it is found when using other electrodes. Copyright © 2005 The Chemical Society of Japan.

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Photoswitchable magnetic layer-by-layer films consisting of azobenzene derivatives and iron oxide nanoparticles

Suda Masayuki, Miyazaki Yasuo, Hagiwara Yuki, Sato Osamu, Shiratori Seimei, Einaga Yasuaki

Chemistry Letters 34 ( 7 ) 1028 - 1029 2005.07

ISSN 0366-7022

The photoswitchable magnetic thin films have been designed by alternate depositions of bipolar amphiphilic azobenzene and Fe₃O₄ nanoparticles by using the layer-by-layer adsorption technique. In these films, reversible photoisomerizations of the azobenzene chromophore affected the electrostatic interaction between the azobenzene chromophore and the surface of Fe₃O₄ nanoparticles. As a result, we have succeeded in controlling the magnetization of these films by photoillumination at room temperature. Copyright © 2005 The Chemical Society of Japan.

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Electroanalysis of tetracycline using nickel-implanted boron-doped diamond thin film electrode applied to flow injection system

Treetepvijit Surudee, Chuanuwatanakul Suchada, Einaga Yasuaki, Sato Rika, Chailapakul Orawon

Analytical Sciences 21 ( 5 ) 531 - 535 2005.05

ISSN 0910-6340

The electrochemical analysis of tetracycline was investigated using nickel-implanted boron-doped diamond thin film electrode by cyclic voltammetry and amperometry with a flow injection system. Cyclic voltammetry was used to study the electrochemical oxidation of tetracycline. Comparison experiments were carried out using as-deposited boron-doped diamond thin film electrode (BDD). Nickel-implanted boron-doped diamond thin film electrode (Ni-DIA) provided well-resolved oxidation irreversible cyclic voltammograms. The current signals were higher than those obtained using the as-deposited BDD electrode. Results using nickel-implanted boron-doped diamond thin film electrode in flow injection system coupled with amperometric detection are presented. The optimum potential for tetracycline was 1.55 V versus Ag/AgCl. The linear range of 1.0 to 100 μM and the detection limit of 10 nM were obtained. In addition, the application for drug formulation was also investigated. 2005 © The Japan Society for Analytical Chemistry.

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