Published papers

Chemical oxygen demand (COD) was measured directly with a simple electrochemical method using a boron-doped diamond (BDD) electrode. By applying a highly positive potential (+2.5 V vs Ag/AgCl) to an aqueous electrolyte containing potassium hydrogen phthalate, glucose, and lactic acid or sodium dodecylbenzenesulfonate using a BDD electrode, an anodic current corresponding to the electrolytic decomposition of these organic compounds was observed. No such current was seen on glassy carbon or platinum electrodes due to a significant background current caused by the oxygen evolution reaction. The electric charge for the anodic current observed at the BDD electrode was found to be consistent with the theoretical charge required for the electrolytic decomposition of the organic compounds to CO2 and was used to calculate COD. This analysis was performed by a simple I-t measurement at constant potential using a BDD electrode, and no calibration was needed. This new simple indicator, "ECOD" (electrochemical oxygen demand), will be useful for continuous monitoring of industrial wastewater with low protein concentrations and on-site instant analysis of natural water with a BDD electrode-based portable ECOD meter. © 2014 American Chemical Society.

This chapter gives a brief review of recent developments on the applications of boron-doped diamond (BDD) electrodes. Specifically, electrochemical applications of BDD electrodes for water treatment, ozone generation, organic synthesis, and electrochemical analysis. Additionally several recent examples of recent developments for electrochemical analysis are introduced. © 2014 Elsevier Ltd. All rights reserved.

To introduce halogen-bond interactions between a cation and an anion, a novel FeIII complex from iodine-substituted ligands involving a paramagnetic nickel dithiolene anion was prepared and characterized. The compound exhibited the synergy between a spin-crossover transition and a spin-Peierls-like singlet formation. The halogen-bond interactions between the iodine and the sulfur atoms stabilized the paramagnetic state of π-spins and played a crucial role in the synergistic magnetic transition between d- and π-spins. In addition, the compound showed the light-induced excited spin state trapping effect. Something to get crossover: An FeIII complex with iodine-substituted ligands involving a paramagnetic nickel dithiolene anion shows a synergy between a spin-crossover transition and a spin-Peierls-like singlet formation. The halogen-bond interactions between the iodine and the sulfur atoms stabilized the paramagnetic state of π-spins and played a significant role in the synergistic magnetic transition between d- and π-spins. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electrochemical detection of Se (IV) and (VI) was investigated at gold-modified boron-doped diamond electrodes. Cyclic voltammetry in acid condition showed that the onset of current flows of Se (IV) and Se (VI) occurred at almost similar potentials. Furthermore, the currents at the peak potential of ∼0.9 V (vs. Ag/AgCl) showed high linearity against concentrations of both Se (IV) and Se (VI) with estimated limits of detection (S/N = 3) of 20 and 50 ppb, respectively. However, whereas oxidation peaks of Se (IV) and Se (VI) can be observed in acid and neutral pH, only oxidation peak of Se (IV) appeared in high pH. The possibility to differentiate a mixture of Se (IV) and Se (VI) by applying cyclic voltammogram (CV) at acidic and basic conditions was discussed, and it was promising, especially because, previously, it always stated that Se (VI) was not electrochemically active. © 2013 Springer Science+Business Media New York.

This study presents the in vivo electrochemical monitoring of pH using boron doped diamond (BDD) microelectrode and silver needles for potential application in medical diagnosis. Accurate calibration curve for pH determination were obtained through in vitro electrochemical measurements. The increase induced in stomach pH by treatment with pantoprazole was used to demonstrate that it is possible to monitor the pH in vivo using the simple and noninvasive system proposed herein. Using the results of the in vivo and in vitro experiments, a quantitative analysis of the increase in stomach pH is also presented. It is proposed that the catheter-free pH monitoring system presented in this study could be potentially employed in any biological environment.

As a prototype for a "highly sensitive electrochemical detection system for single drop analysis using boron-doped diamond (BDD) electrodes", a three-electrode system for the measurement of samples consisting of a single drop was fabricated. An Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) system, employing the Bosch process in order to realize high-aspect-ratio near vertical structures, was used to etch the BDD. A single drop (10 μL) was analyzed using the resulting fabricated 'BDD chip electrode' which exhibited the typical superior electrochemical properties of BDD electrodes. © 2013 The Royal Society of Chemistry.

We have prepared photomagnetic Langmuir-Blodgett films composed of an amphiphilic azobenzene and a magnetic polyoxometalate. The obtained film possesses a well-organized layered structure where polyoxometalate anions are sandwiched by azobenzene cations in a single-layered manner. Reversible photoisomerization of azobenzene was achieved even at low temperature, accompanying intensity changes in the d-d transition of polyoxometalate anions. The photomagnetic effect was observed reversibly upon alternate UV and visible light irradiation. Based on polarized spectroscopy, the observed photomagnetic effect is ascribed to the structure-distortion of polyoxometalate layers. © 2013 The Royal Society of Chemistry.

The mononuclear ferric compound Fe(H-5-Cl-thsa-Me)(5-Cl-thsa-Me) ·H2O (1) was synthesized and characterized using powder/single-crystal X-ray diffraction, Mössbauer spectroscopy, differential scanning calorimetry (DSC), and magnetic susceptibility measurements. This photo-responsive compound shows reversible, two-step spin-crossover behaviour. Moreover, dielectric anomalies were observed during the spin transitions, demonstrating the multifunctional properties of compound 1. © 2013 The Royal Society of Chemistry.

The maximum current flowed with zero resistance, referred to the critical current density, is desired to be sufficiently large in order to apply superconducting wire rods and electromagnets to various devices. Although the critical current density can be enhanced by introduction of non-superconducting impurities, the transition temperature would become diminished in such a case. Here, we report modulation of a critical current density in heavily boron-doped diamonds (BDDs) by changing the surface-termination without introducing any impurity. The surface of a BDD was changed between hydrogen- and oxygen-termination. As a result, the critical current density could be modulated in a reversible manner between the hydrogen- and oxygen-terminated diamonds with maintenance of the superconducting transition temperature. This is because the volume fractions of the superconducting phases were modulated by surface modification. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Diamonds for shiny teeth: A novel pinpoint ozone-water production unit for dental treatment using boron-doped diamond (BDD) microelectrodes is developed (see picture). The superiority of such BDD microelectrodes over simple and easy-to-handle units, in terms of the larger activities for ozone production and disinfection, is demonstrated. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The title compound, [Co(C14H18N2O 6)], is the first structurally characterized example of a β-ketoiminato CoII complex without axial ligands. It adopts a square-planar cis-[CoN2O2] coordination geometry, and lies on a mirror plane. The planar complexes are stacked along 21 screw axes parallel to b to form columns, the Co⋯Co distance in the column being 3.5213 (2) Å. © 2004 International Union of Crystallography Printed in Great Britain - all rights reserved.

Two new cyanide-bridged 3d-4f hetero-dinuclear complexes, namely Ln(DMF)4(H2O)3(μ-CN)Co(CN)5 · H2O (Ln=Nd (1) and Gd (2), DMF=N,N-dimethylformamide), were synthesized by the facile reaction of LnCl3.6H2O and K3Co(CN)6. Characterization includes microanalysis, IR spectrometric identifications, X-ray crystallographic analysis and magnetic properties. Both 1 and 2 crystallize in the centrosymmetric monoclinic space group P21/n (No. 14) with Z=4. The lanthanide(III) ions are eight-coordinate in a square-antiprism arrangement, while cobalt(III) ions are six-coordinate in an octahedral environment in each complex. A cyanide bridge links an LN(III) ion to a Co(III) ion. Molecules in the crystal cell of each compound are held together by van der Waals forces and a network of hydrogen bonding. Magnetic analysis shows that antiferromagnetic interactions are observed below 7 K for both 1 and 2, which are attributed to intermolecular interactions between the Ln(III) ions in the network through hydrogen bonds. This series of compounds may be of importance in photo-induced magnetism because of the cyanide bridge between 3d and 4f metals.

The electrochemical, photochemical and chemical control of the magnetic properties in molecular compounds is described. The preparation of various thin films of CrCr and FeFe Prussian blue on a conducting electrode allowed us to control the magnetic properties by varying the oxidation state of the component metals. The magnetic properties of CrCr Prussian blue show that the critical temperature and coercive field can be drastically modified by electrochemical treatment. That is, the compound, CrII 1.29CrIII 0.14 [CrIII(CN)6] has ferrimagnetic properties with Tc (critical temperature) = 240 K and Hc (coercive field) = 25 G, while the reduced form, KCrII 1.29CrIII 0.14 [CrII(CN)6], has Tc = 100 K and Hc = 220 G. Similarly, it was found that the critical temperature of FeFe Prussian blue shifts continuously from paramagnetic to magnetic with Tc = 12 K. These changes can be expressed as K4FeII 4[FeII (CN)6]3 (paramagnetic) ⇆ FeIII 4[FeII(CN)6]3 (ferromagnetic, Tc = 4.5 K) + 4 K+ + 4e- and FeIII 4[FeII(CN)6]3 (ferromagnetic, Tc = 4.2 K) + 3Cl- - 3e- ⇆ FeIII 4[FeIII(CN)6] 3(Cl)3 (Tc = 12 K). Furthermore, we have discovered that the FeCo Prussian blue and Co valence tautomeric compounds exhibit photo-reversible magnetization effects. The photoinduced magnetization in FeCo Prussian blue is expressed as Na0.4CoII-HS 0.3CoIII-LS [FeII(CN)6] (paramagnetic) ⇆ Na0.4CoII-HS 1.3[FeIII (CN)6] (ferrimagnetic, Tc = 26 K and Hc = 6000 G), where HS and LS denote high-spin and low-spin. An example of the photoinduced valence tautomeric behavior is expressed as [CoIII-LS(3,5-dbsq)(3,5-dbcat)(tmeda)] ⇆ [CoII-HS(3,5-dbsq)2(tmeda)], where tmeda, 3,5-dbsq and 3,5-dbcat represent N,N,N′,N′-tetramethylethylenediamine, 3,5-di-tert-butyl-1,2-semiquinonate and 3,5-di-tert-butyl-1,2-catecholate, respectively. Additionally, we succeeded in tuning the phase transition temperature by varying the ligand field of the Co ions in the FeCo Prussian blue. Brief comments are also included regarding the first examples of light-induced excited spin state trapping observed in an FeIII complex, i.e. [FeIII-LS(pap)2]ClO4·H2O ⇆ [FeIII-HS(pap)2]- ClO4·H2O (pap = N-2-pyridylmethylidene-2-hydroxy-phenylaminato) and a photoinduced structural change observed in a CuII complex, [CuII(dieten)2](BF4)2 [dieten = bis(N,N-diethylethylenediamine)].

Incorporation of photochromic compounds into magnetic systems is one of the new strategies being implemented to realize the control of magnetic properties by photoillumination. We have designed composite materials comprising iron oxide particles and photochromic spiropyran vesicles as cast films on substrates. Photofunctional magnetic vesicles of amphiphilic spiropyran (SP1822) containing iron oxide particles exhibit superparamagnetic properties at room temperature. Both photoisomerization and photoinduced aggregation of the photoresponsive magnetic vesicles were observed, even without any supporting media such as solvents or polymer matrixes. As a result of the assembly of the vesicles, magnetic dipolar interactions among adjacent iron oxide particles were induced by photoillumination at room temperature, even in the solid state.

In the title compound, [Cu(ClO4)2(C3H 10N2)2], the Cu atom is located at a center of symmetry. Despite asymmetric introduction of TV-methyl groups into the ethylenediamine moieties, a second-order Jahn-Teller effect produces a typical semi-coordination trans-[CuN4(O2)] environment with long axial Cu - O bonds of 2.569 (2) Å. The Cu - N bond distances are 2.004 (2) and 2.057 (2) Å. © 2003 International Union of Crystallography Printed in Great Britain - all rights reserved.

Photoinduced magnetization of the cyano-bridged 3d-4f heterobimetallic assembly Nd(DMF)4(H2O)3(μ-CN)Fe(CN)5·H2O (1) (DMF = N,N-dimethylformamide) is described in this paper. The χMT values are enhanced by about 45% after UV light illumination in the temperature range of 5-50 K. We propose that UV light illumination induces a structural distortion in 1. This small structural change is propagated by molecular interactions in the inorganic network. Furthermore, the cooperativity resulting from the molecular interaction functions to increase the activation energy of the relaxation processes, which makes observation of the photoexcited state possible. The flexible network structure through the hydrogen bonds in 1 plays an essential role for the photoinduced phenomenon. This finding may open up a new domain for developing the molecule-based magnetic materials. Copyright © 2003 American Chemical Society.

The initial rough, faceted surfaces of boron-doped conductive polycrystalline diamond electrodes were smoothed by Ar+ ion sputtering at very low energy (50 eV). A lower background current was measured at the modified electrodes with a mirror-like appearance than at the initial polycrystalline electrodes. The electrochemical responses to several redox systems also showed a morphological-dependence in some cases. Here, we discuss the electrochemical properties of the diamond electrodes with the smoothed surfaces from the point of view of a novel electrode material.

The first preparation of an Fe(II) spin-crossover complex including a 1,3-dithiole ligand is reported. Crystal analyses of both the low- and the high-temperature phases reveal that short S⋯S contacts play a key role in an abrupt spin transition.

A polymer matrix isolation technique was examined as a potentially novel strategy for realizing optically switchable materials. Not only was a ferricinium ion ([Cp2FeIII]+) produced, but also was produced an isomer of ferrocene (Cp2Fe) with high spin FeII in a poly(methyl methacrylate) (PMMA) matrix film containing CCl4 by the photoillumination of ferrocene at low temperature. The high spin state could be maintained for an extended period when the sample was kept below ≈ 130 K. This is the first observation of a photoinduced spin transition for ferrocene. The strategy that we used to achieve the spin transition using optical stimuli may open up many possibilities for the development of new magneto-optical devices.

Photofunctional magnetic vesicles of spiropyran (SP1822) that contain iron oxide particles, which exhibit super-paramagnetic properties at room temperature, were prepared. Photoinduced aggregation of the vesicles was observed by UV illumination. As a result, we were able to increase the magnetization value by photoillumination at room temperature.