Published papers

Three Salen-like gadolinium complexes, namely, mononuclear (4f) complex [{H2L}Gd(NO3)3] (1), heterodinuclear (3d-4f) complex [{LCu}Gd(NO3)3]·0.25H2O (2) and dimeric heterotrinuclear (3d-4f-3d′) complex [{LCu}Gd(H2O)3{Fe(CN)6}]2·6H2O (3) [H2L = N,N′-ethylene-bis(3-methoxysalicylideneimine)] have been synthesized by stepwise reactions. X-ray diffraction analysis reveals that 1 is of a discrete structure in which H2L coordinates to gadolinium ion through O2O2 moiety. Then, addition of Cu(Ac)2·H2O to the mononuclear lanthanide complex yields expected heterodinuclear (3d-4f) complexes [{LCu}Gd(NO3)3]. 3 features a unique 1D ladder-like topology structure through the intermolecular double links of Cu-N bonds. The measurement of variable-temperature magnetic susceptibility reveals that complex 1 exhibits antiferromagnetic interaction while 2 and 3 exhibit ferromagnetic interaction between spin carriers. The correlations between the structure and magnetism are described and discussed. © 2010.

Dendritic polyphenylazomethines (DPA) could encapsulate ferroceniums by complexation of the electron-donating skeleton of the DPA imines. Upon addition of ferroceniums to a series of dendritic polyphenylazomethines (DPAGX, where X is the generation number, X = 1-4), the UV-vis spectra showed changes in a manner similar to that observed for the complexation of metal ions with DPAGX. Stepwise shifts in the isosbestic point were consistently observed with the number of imine groups in the first and second layers of the generation-4 dendrimer (DPAG4). DPAG2 and DPAG3 were also found to trap 6 equiv of ferroceniums. To investigate the complexation, UV-vis spectroscopy, 57Fe MoÌssbauer spectroscopy, electrospray ionization-mass spectroscopy (ESI-MS), cyclic voltammetry (CV), and fluorescence spectroscopy were performed. We confirmed that neutral ferrocenes cannot complex with the imine group while ferroceniums can. Utilizing the redox property of ferrocenes, we were able to electrochemically control the encapsulation and release of ferrocenes into the DPA in a manner similar to redox-responsive proteins such as ferritin. In addition to ferrocenes, oligoferrocenes could also be trapped in the DPA. The biferrocene cation(1+) was particularly suitable for electrochemical switching due to its stable mixed valence condition. The terferrocene dication(2+) encapsulated into DPAG4 could be fabricated into a thin film, which exhibited the near-infrared absorption of an intervalence charge-transfer (IV-CT) band, pointing the way toward the use of such systems in material science. © 2010 American Chemical Society.

Two lanthanide-containing 2D coordination polymers, [Ln(H 2salen)1.5(NO3)3]n [H2salen = N,N′- ethylenebis(salicylideneimine); Ln = Gd (1), Dy (2)], have been prepared by self-assembly method. The molecular magnetism and luminescence of the metal complexes had been studied. Complex 1 exhibits antiferromagnetic interaction between spin carriers. Complex 2 emits the H 2salen ligand luminescence. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA.

This paper describes the deposition of zinc(II) with anodic stripping voltammetry on the boron-doped diamond electrode. We illustrate the dependency of several parameters on the magnitude of the oxidation peak and try to optimize the method. The supporting electrolyte was found to influence the oxidation peak magnitude. Compared with acetic acid, the most frequently used supporting electrolyte, ammonia buffer solution leads to a four times higher signal. We assume that the formation of zinc complexes, primarily tetraaminezinc(II), are responsible for the better response. Further factors studied and assessed include buffer pH, buffer concentration, deposition potential, deposition time and scan rate. With the improved conditions, a final detection limit of 5 ppb was accomplished. © 2010 Elsevier Ltd. All rights reserved.

Three one-dimensional (1D) heterospin trimetallic chain-like polymers [{LCu(H2O)}Ln(MeOH)(H2O)2{(μ-CN)2Fe(CN)4}]·2H2O (1, Ln = La; 2, Ln = Nd; 3, Ln = Gd) were prepared by substitution of the nitrato ligands in [LCuLn] complexes with [Fe(CN)6]3- ions (H2L = N,N′-bis(3-methoxysalicylidene)propane-1,2-diamine). Single-crystal X-ray diffraction analysis revealed that the methyl on the salen-type ligand impeded the connection between cyanide groups and Cu(II) ions efficiently. Consequently, three novel one-dimensional (1D) trimetallic chain-like polymers were obtained with the linker [Fe(CN)6]3- ions interacting only with the lanthanide ions. The magnetic investigation for 3 indicated a ferrimagnetic chain may form. © 2009 Elsevier B.V. All rights reserved.

"Chemical Equation Presented" Flicking the switch: Photoirradiation has a dramatic effect on the superconducting properties of a passivated ultrathln Nb film functlonallzed with a photochromic self-assembled azobenzene (AZ) monolayer (see picture). These effects can be attributed to photoisomerization-induced changes in the amount of charge transfer between the substrate and the photochromic monolayer. The changes are accompanied by alternation of the surface dipoles. © 2010 Wiley-VCH Verlag GmbH &. Co. KGaA.

An array of TCNQ (TCNQ = 7,7,8,8-tetracyano-p-quinodimethane) lanthanide complexes, namely, [Ln2(TCNQ)4(H2O) 10(EtOH)2][2TCNQ]·xH2O [Ln = La (1, x = 5), Pr (2, x = 3)], [Ln2(TCNQ)4(H2O) 10][2TCNQ]·yH2O [Ln = Gd (3, y = 6), Dy (4, y = 5)] and [Ln(TCNQ)2(H2O)6][TCNQ]·H 2O·MeOH [Ln = Er (5), Lu (6)], have been synthesized by salt-elimination reactions. X-ray crystallographic analysis indicates that 1-6 are discrete ion complexes. Cations of 1-4 adopt a dimer structure, while cations of 5 and 6 display a monomer structure. The magnetic study proposes that an antiferromagnetic interaction between TCNQ radicals exists in 1-6. The depopulation of the Stark levels for 2 and 5 leads to a continuous decrease in χmT when the samples are cooled from 300 K to 2 K. The desolvated 3, namely, 3a exhibits a unique magnetic conversion from the magnetic disordering to the magnetic ordering at 4 K. 4 shows a ferromagnetic coupling between paramagnetic centers. © 2009 The Royal Society of Chemistry.

We have demonstrated that it is possible to reversibly photo-control the room temperature magnetism in a diluted magnetic semiconductor based on zinc oxide nanoparticles coated with azobenzene-derivatized thiols (Azo-ZnO NPs). These photochromic ligands provide a photo-function and at the same time act as a trigger for the generation of ferromagnetism at ZnO-S interface. UV irradiation increases the saturated magnetization of the Azo-ZnO NPs due to trans- to cis-isomerization in azobenzene-derivatized ligands, and following irradiation with visible light the magnetization is decreased due to inverse isomerization. X-ray photoelectron spectroscopy reveal that the photo-induced magnetization changes are strongly related to photo-induced changes in the chemical state of zinc atom in the ZnO. These photo-magnetic effects can be attributed to photo-induced changes in surface states of the ZnO due to photo isomerization in azobenzene ligands, which is accompanied by alterations in the lowest unoccupied molecular orbital level of the ligand, since magnetic properties of ZnO depend on carrier concentration, which correlated with surface states of the ZnO. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

(Graph Presented) Ultrathin fims composed of titania nanosheets and Prussian Blue were prepared by using the modified Langmuir-Blodgett technique. The ultrathin films could be deposited in a layer-by-layer manner with lamellar structure. Upon band gap excitation of titania nanosheets, the generated electrons were injected into ferromagnetic Prussian Blue, resulting in reduction to paramagnetic Prussian White. It was revealed that the reaction could proceed only in the presence of hole-scavenging interlayer water molecules. © 2009 American Chemical Society.

Treatments of p-ferrocenylbenzoate [p-NaOOCH4C6Fc, Fc=(η5-C5H5)Fe(η5-C 5H4)] with Ln(NO3)3·nH2O afford seven p-ferrocenylbenzoate lanthanide complexes {[Ln(OOCH4C6Fc)2(μ2-OOCH 4C6Fc)2(H2O)2] (H3O)}n [Ln=Ce (1), Pr (2), Sm (3), Eu (4), Gd (5), Tb (6) and Dy (7)]. X-ray crystallographic analysis reveals that the isomorphous complexes {[Ce(OOCH4C6Fc)2(μ2-OOCH 4C6Fc)2(H2O)2 ](H3O)}n (1) and {[Pr(OOCH4C6Fc)2(μ2-OOCH 4C6Fc)2(H2O)2] (H3O)}n (2) form a unique 1D double-bridged infinite chain structure bridged by μ2-OOCH4C6Fc groups. Each Ln(III) ion adopts a dodecahedron coordination environment with eight coordinated oxygen atoms from two terminal monodentate coordinated FcC6H4COO- units, two terminal monodentate coordinated H2O molecules and four μ2--OOCH4C6Fc units. The luminescent spectra reveal that only 4 and 6 exhibit characteristic emissions of lanthanide ions, Eu(III) and Tb(III) ions, respectively. The variable-temperature magnetic properties of 5 and 7 suggest that a ferromagnetic coupling between spin carriers may exist in 5. © 2009.

Magnetic properties of Ni thin films which were modified through the redox reaction in alkaline solution were investigated by means of magneto-optical Faraday effect. The magnetization process of Ni film on which Ni(II) compounds electrochemically forms was different from that of fresh Ni films. This indicates that the magnetic anisotropy is modified through the redox reaction Ni(0)/Ni(II) which may induce the change in the volume of metallic nickel region and/or the magnetic coupling between the metallic Ni and some compound including Ni(II) formed on the film surface.

The catalytic, electrocatalytic, or photocatalytic conversion of CO 2 into useful chemicals in high yield for industrial applications has so far proven difficult. Herein, we present our work on the electrochemical reduction of CO2 in seawater using a boron-doped diamond (BDD) electrode under ambient conditions to produce formaldehyde. This method overcomes the usual limitation of the low yield of higher-order products, and also reduces the generation of H2. In comparison with other electrode materials, BDD electrodes have a wide potential window and high electrochemical stability, and, moreover, exhibit very high Faradaic efficiency (74 %) for the production of formaldehyde, using either methanol, aqueous NaCl, or seawater as the electrolyte. The high Faradaic efficiency is attributed to the sp 3-bonded carbon of the BDD. Our results have wide ranging implications for the efficient and cost-effective conversion of CO2. Boron is a diamond's best friend: A boron-doped diamond (BDD) electrode exhibited very high Faradaic efficiency (74 %) for the production of formaldehyde using either methanol, aqueous NaCl, or seawater as the electrolyte at room temperature and ambient pressure. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The resistance of cathodically and anodically treated boron-doped diamond electrodes to dopamine fouling was investigated. It was found, using cyclic voltammetry and electrochemical impedance spectroscopy, that the cathodic preparation offers an increased resistance to fouling, in addition to an enhanced electrochemical response. © 2014 Elsevier B.V.

Electrochemical detection of hydrogen peroxide (H2O2) at a platinum-deposited boron doped diamond was studied for an application in melamine strip test. Deposition of Pt particles at a boron-doped diamond surface was performed using cyclic voltammetry method. The method was also used for electrochemical measurements. The oxidation-reduction peak currents of H 2O2 at + 0.6 V and - 0.1 V (vs. Ag/AgCl), respectively were found to be linear in the concentration range of 0.05-20 mM (R2 = 0.99). Linearity was also observed to be dependent on horseradish peroxidase (HRP) concentration in the constant concentration of H2O2. The method was then applied in immunochromatographic strip test for melamine detection to determine the activity of HRP labeled at melamine antibody. Taking an assumption that the activity of HRP was equivalent to melamine concentration, linearity of the current responses to the concentrations of standard melamine solutions in the range of 5-100 μg/ml could be achieved. Limit of detection of 0.51 μg/ml was estimated. The obtained results demonstrated that the designed biosensor for detection of H2O2 could be applied for the quantitative and selective detection of melamine. © 2014 Elsevier B.V.

The effects of sp2-bonded carbon impurities on the electrochemical properties of boron-doped diamond were investigated in moderately ([B] < 1020cm-3) and heavily ([B] > 1021cm-3) boron doping levels. Significant influences of sp2-bonded carbon impurities, which show glassy carbon-like electrochemical properties after anodic oxidation, were observed in heavily boron-doped diamond. This indicated that the significant effects of enhanced adsorption properties were possibly caused by surface relaxation of the strains induced by heavy boron doping and sp2-bonded carbon impurities. On the other hand, their durability was still similar to diamond electrodes rather than glassy-carbon electrodes because of the low fraction of sp2-bonded carbon impurities. Such "active" diamond electrodes are much less suitable for wastewater treatment than ordinary diamond electrodes due to a different oxygenevolution mechanism. On the other hand, "active" BDD electrodes have a much higher efficiency for electrochemical ozone production than other BDD electrodes. The electrode properties of BDD can be designed by controlling the boron doping level and introducing the sp2-bonded carbon impurities. The guidelines proposed in this study can be used effectively to design electrodes according to their individual application, such as for use as electrochemical sensors, in wastewater treatment or electrochemical ozone production.

An electrochemical method was developed for biodiesel, i.e., fatty acid methyl ester (FAME), production. A twocompartment cell completed with a cation-exchange separating membrane was utilized to minimize recombination between protons and hydroxide or methoxide ions, which leads to the low product yield. In addition to the product yield increase, the method was found to reduce the requirement of organic salt to be only in the cathode chamber. Electrolysis at low voltage (4.6 V) resulting high product yield (ca. 94% in 2 h) at Pt as well as a boron-doped diamond (BDD) electrode as the cathode, suggested the system was free from the dependence on electrode types.

Boron-doped diamond electrodes have attracted increasing interest from researchers due to their outstanding properties for electroanalysis and other electrochemical applications. Material quality and availability have come a long way since the initial reports on the basic electrochemical properties back in the late 1980s and early 1990s. In this review, we highlight how diamond electrochemistry has diversified and matured in recent years in terms of the understanding of structure-property relationships and the development of new applications of materials in electroanalytical chemistry. © Materials Research Society 2014.

Although oxidoreductases are widely used in many applications, such as biosensors and biofuel cells, improvements in the function of existing oxidoreductases or the discovery of novel oxidoreductases with greater activities is desired. To increase the activity of oxidoreductases by directed evolution, a powerful screening technique for oxidoreductases is required. In this study, we demonstrate the utility of boron-doped diamond (BDD) microelectrodes for quantitative and potentially high-throughput measurement of the activity of NAD(P)-dependent oxidoreductases. We first confirmed that BDD microelectrodes can quantify the activity of low concentrations (10-100 pM) of glucose-6-phosphate dehydrogenase and alcohol dehydrogenase with a measuring time of 1 ms per sample. In addition, we found that poisoning of BDD microelectrodes can be repressed by optimizing the pH and by adding l-arginine to the enzyme solution as an antiaggregation agent. Finally, we fabricated a microfluidic device containing a BDD electrode for the first time and observed the elevation of the oxidation current of NADH with increasing flow rate. These results imply that the combination of a BDD microelectrode and microfluidics can be used for high-throughput screening of an oxidoreductase library containing a large number (>106) of samples, each with a small (nanoliter) sample volume.

We developed a double-quantum mechanical/molecular mechanical (d-QM/MM) method for investigation of full outer-sphere electron transfer (ET) processes between a donor and an acceptor (DA) in condensed matter. In the d-QM/MM method, which employs the novel concept of multiple QM regions, one can easily specify the number of electrons, spin states and appropriate exchange-correlation treatment in each QM region, which is especially important in the cases of ET involving transition metal sites. We investigated Fe2+/3+ self-exchange and Fe3+ + Ru2+ → Fe2+ + Ru3+ in aqueous solution as model reactions, and demonstrated that the d-QM/MM method gives reasonable accuracy for the redox potential, reorganization free energy and electronic coupling. In particular, the DA distance dependencies of those quantities are clearly shown at the density functional theory hybrid functional level. The present d-QM/MM method allows us to explore the intermediate DA distance region, important for long-range ET phenomena observed in electrochemistry (on the solid-liquid interfaces) and biochemistry, which cannot be dealt by the half-reaction scheme with the conventional QM/MM. © 2014 The Owner Societies.

We investigated water interfaces of boron-doped diamond (BDD) terminated by hydrogen, oxygen, and hydroxyl groups by using density functional theory (DFT)-based molecular dynamics to elucidate the electrochemical behaviors of the as-grown and oxidized BDD electrodes. The reversible outer-sphere electron transfer on the as-grown electrode and the irreversibility on the oxidized electrode, observed in the experiment, are well explained by the BDD band position and subsurface band bending, which depend on the termination and interfacial dipoles. The reductive character of the H-terminated BDD is found, while the interface covered by the carbonyl oxygen is clearly oxidative. The redox character of the hydroxyl termination depends on the lateral hydrogen bonding network among the termination groups and is rather oxidative at the water interface. We also examined the preference of the boron position in the diamond and the stability of boron pairs and clusters. It is suggested that the wide distribution of the single boron dopants is crucial to the BDD conductivity, against the tendency of clustering. These results give novel atomistic aspects of the termination and the boron doping effects on the BDD electrodes, which is useful for further exploration of the efficient electrochemical applications of BDD.