Published papers

The electroreduction reaction of methyl cinnamate on a boron-doped diamond (BDD) electrode was investigated. The hydrodimer, dimethyl 3,4-diphenylhexanedioate (racemate/meso = 74:26), was obtained in 85% yield as the major product, along with small amounts of cyclic methyl 5-oxo-2,3-diphenylcyclopentane-1-carboxylate. Two new neolignan-type products were synthesized from the hydrodimer.

A key issue in molecular electronics is the control of electronic states by optical stimuli, which enables fast and high-density data storage and temporal-spatial control over molecular processes. In this article, we report preparation of a photoswitchable superconductor using a heavily boron-doped diamond (BDD) with a photochromic azobenzene (AZ) molecular layer. BDDs electrode properties allow for electrochemical immobilization, followed by copper(I)-catalyzed alkyne-azide cycloaddition (a click reaction). Superconducting properties were examined with magnetic and electrical transport measurements, such as field-dependent isothermal magnetization, temperature-dependent resistance, and the low-temperature voltage-current response. These measurements revealed reversible amplification of the critical current density by 55% upon photoisomerization. This effect is explained as the reversible photoisomerization of AZ inducing an inhomogeneous electron distribution along the BDD surface that renormalizes the surface pinning contribution to the critical current.

The electrochemical properties of an n-type phosphorus doped diamond (PDD) electrode were investigated and compared with a p-type boron doped diamond (BDD) electrode. The Mott-Schottky plots in 0.1 M HClO4 are reported and related to the energy band diagram of electrochemically pretreated BDD and PDD. These results revealed that the band position of anodically pretreated PDD corresponded to the one of anodically pretreated BDD. Moreover, it was found the flat-band potential of the anodically pretreated PDD decreased by ca. 1 V after cathodically pretreatment. The cyclic voltammetries for Ru(NH3)6 3+/2+ showed that electrochemical behaviors of PDD and BDD were entirely different in possible direction for charge transfer across the electrode-electrolyte inaterface. In addition, less n-type diode-like behavior was observed at the cathodically pretreated PDD than the anodically pretreated PDD. These results point out the importance of the surface chemistry controlled by electrochemical pretreatments.

A key issue in molecular electronics is the control of electronic states and properties by optical stimuli, which enables fast and high-density data storage. In this article, we report preparation of a photoswitchable room-temperature ferromagnetic material using FePt nanoparticles protected with a photochromic spiropyran ligand. Magnetic properties were examined with a field-dependent isothermal magnetization, and a photomagnetic effect was measured at room temperature. These measurements revealed room-temperature ferromagnetism and reversible switching of magnetization by 60% upon photochromic reaction of the spiropyran ligand. This gigantic photomagnetic effect is explained as spiropyran's large change in the dipole moment during photochromic reaction that tunes the magnitude of electron transfer at the interface.

The electrochemical reduction of carbon dioxide in aqueous solutions using boron-doped diamond (BDD) electrodes was investigated at ambient pressure and temperature. We discuss the effects of the alkali-metal (AM) cations, K+, Na+, Rb+ and Cs+, on the faradaic efficiency (FE) for the formation of formic acid. An FE of 71% was achieved in the case of a 0.075 M Rb+ solution neutralized to pH 6.2 by the addition of HCl. In the case of a Cs+ solution neutralized to pH 6.2, the highest FE was obtained with the more dilute concentration of 0.02 M. Of the four different solutions examined, the lowest FE was observed for the Na+ solution. Moreover, we found that the productivity for the production of formic acid is higher at higher current densities.

A novel neutral heteroleptic FeIII complex from two kinds of π-extended tridentate ligands was designed and prepared. The π-ligands formed a three-dimensional purely π-stacking interaction network. The present complex proved to be the first neutral spin-crossover (SCO) FeIII complex with a N3O3 coordination sphere exhibiting an abrupt SCO transition with a thermal hysteresis of 10 K and the light-induced excited spin-state trapping effect.

Boron-doped diamond (BDD) electrodes are recognized as being superior to other electrode materials due to their outstanding chemical and dimensional stability, their exceptionally low background current, the extremely wide potential window for water electrolysis that they have, and their excellent biocompatibility. However, whereas these properties have been utilized in the rapid development of electroanalytical applications, very few studies have been done in relation to their applications in electrocatalysis or electrosynthesis. In this report, following on from reports of the electrosynthesis of various products through anodic and cathodic reactions using BDD electrodes, the potential use of these electrodes in electrosynthesis is discussed.

The enormous demand for medical diagnostics has encouraged the fabrication of high- performance sensing platforms for the detection of glucose. Nonenzymatic glucose sensors are coming ever closer to being used in practical applications. Bimetallic catalysts have been shown to be superior to single metal catalysts in that they have greater activity and selectivity. Here, we demonstrate the preparation, characterization, and electrocatalytic characteristics of a new bimetallic Pt/Au nanocatalyst. This nanocatalyst can easily be synthesized by electrodeposition by sequentially depositing Au and Pt on the surface of a boron-doped diamond (BDD) electrode. We characterized the nanocatalyst by scanning electron microscopy (SEM), X-ray diffraction (XRD), and voltammetry. The morphology and composition of the nanocatalyst can be easily controlled by adjusting the electrodeposition process and the molar ratio between the Pt and Au precursors. The electrocatalytic characteristics of a Pt/Au/BDD electrode for the nonenzymatic oxidation of glucose were systematically investigated by cyclic voltammetry. The electrode exhibits higher catalytic activity for glucose oxidation than Pt/BDD and Au/BDD electrodes. The best catalytic activity and stability was obtained with a Pt:Au molar ratio of 50:50. Moreover, the presence of Au can significantly enhance the long-term stability and poisoning tolerance during the electro-oxidation of glucose. Measurements of glucose using the Pt/Au/BDD electrode were linear in the range from 0.01 to 7.5 mM, with a detection limit of 0.0077 mM glucose. The proposed electrode performs selective electrochemical analysis of glucose in the presence of common interfering species (e.g., acetaminophen, uric and ascorbic acids), avoiding the generation of overlapping signals from such species.

Characterization and crystal structure determination of 3d-4f cyano-bridged bimetallic assemblies, Ln(DMF)4(H2O)3Co(CN)6 · H2O (DMF = N,N′-dimethylformamide, Ln = Tb, Dy, Ho and Er) have been newly carried out. We have observed their isostructural features and gradual decreasing cell constants and corresponding changes of local bond distances and angles around the cyano-bridges in accord with the ionic radii changes due to lanthanoid contraction. In order to elucidate the reasons that only Nd-Fe and Nd-Co complexes can exhibit photo-induced magnetic functions, we have also investigated the electronic properties for several analogous 3d-4f complexes, Ln(DMF)4(H2O)3M(CN)6 · H2O (Ln = Ce, Nd, Sm, Gd, Tb, Dy, Ho and Er; M = Co and Fe), by means of X-ray photoelectron spectroscopy (XPS). We found that the characteristic bent features of Nd-N-C bond angles and the slight shift of binding energies of Ln 4d3/2 peaks in the 3d-4f systems being closed to mixed-valence states might be the reasons for the novel functions. © 2006 Elsevier Ltd. All rights reserved.

The first photocontrollable magnetic nanoparticles containing CdS and Prussian blue (PB) have been created using reverse micelles as nanoreactors. Photoinduced electron transfer from CdS to PB in the reverse micelle changed the magnetic properties of the composite nanoparticles from ferromagnetic to paramagnetic. The magnetization in the ferromagnetic region below 4 K was substantially decreased after UV light illumination and could be restored almost to its original level by thermal treatment at room temperature. This novel strategy of designing composite nanoparticles containing photoconductive semiconductors and magnetic materials to create photoswitchable magnetic materials may open many possibilities in the development of magneto-optical devices. © 2006 American Chemical Society.

We have attempted to control the helical pitch of a chiral nematic liquid crystal by the use of a photoresponsive chiral metal complex. For this purpose, a novel Ru(III) complex [Ru(acac)2(L)] was synthesized, where acac and L denote acetylacetonato and 1,3-bis-{4-[6-(4-phenylazo-phenoxy)-hexyloxy]- phenyl}-propane-1,3 -dionato, respectively. The complex underwent cis-trans photoisomerization in methanol when under UV (λmax = 360 nm) or visible (λmax = 450 nm) light illumination, respectively. When the complex was doped into a room-temperature nematic liquid crystal (ZLI-1132), it induced a chiral nematic phase. Under illumination with UV or visible light, the helical pitch of the chiral nematic phase could be changed reversibly by up to 50%. Corresponding to this change, the helical twisting power (HTP) of the complex varied between 34.0 and 22.0 μm-1, or between -43.9 and -26.6 μm-1 at 35.0 °C, where the positive and negative signs corresponded to the A- and Δ-enantiomers, respectively. This has been the first attempt at combining the ΔΛ chirality of an octahedral metal complex with the cis-trans isomerization of an azobenzene group in the development of a photoresponsive dopant. © 2006 American Chemical Society.

The synergy between the electrical conductivity within the stacks of Ni(dmit)2 in the newly electrocrystallized [Fe(qsal) 2][Ni(dmit)2]3· CH3CN· H2O and the spin conversion of Fe(qsal)2 is evidenced. In addition, the presence of a light-induced excited spin state trapping effect suggests that this complex is a prototypal photoswitchable spin-crossover molecular conductor. © 2006 American Chemical Society.

Electrochemical oxidation of oxalic acid has been investigated at bare, highly boron-doped diamond electrodes. Cyclic voltammetry and flow injection analysis with amperometric detection were used to study the electrochemical reaction. Hydrogen-terminated diamonds exhibited well-defined peaks of oxalic acid oxidation in a wide pH range. A good linear response was observed for a concentration range from 50 nM to 10 μM, with an estimated detection limit of ∼0.5 nM (S/N = 3). In contrast, oxygen-terminated diamonds showed no response for oxalic acid oxidation inside the potential window, indicating that surface termination contributed highly to the control of the oxidation reaction. An investigation with glassy carbon electrodes was conducted to confirm the surface termination effect on oxalic acid oxidation. Although a hydrogen-terminated glassy carbon electrode showed an enhancement of signal-to-background ratio in comparison with untreated glassy carbon, less stability of the current responses was observed than that at hydrogen-terminated diamond. © 2006 American Chemical Society.

The title compound, poly[[tetracyano-octa-μ-cyano-hexakis-(N- ethylethylenediamine)tricopper(II)dicobaltate(III)] tetrahydrate], [Cu(C 4H12N2)2]3[Co(CN) 6]2·4H2O or {[Cu3Co 2-(CN)12(C4H12N2) 6]·4H2O}n, was crystallized from an aqueous reaction mixture containing Cu(ClO4)2, N-ethylethylenediamine and K3[Co(CN)6] in a self-assembling process. The polymeric chains are extended through -Co III-CN-CuII-linkages involving four or two cyanide ligands of the centrosymmetric [Co(CN)6]3- complex ions, forming a two-dimensional ladder structure. The CuII atoms, one of which also lies on an inversion centre, have a distorted octahedral coordination geometry, the degree of tetragonal Jahn-Teller distortion being T = 0.785 and 0.810 (T is the ratio of mean inplane Cu - N bond lengths to axial Cu - N bond lengths). This local Jahn-Teller distortion results from the anisotropic features of this two-dimensional cyano-bridged structure. © 2006 International Union of Crystallography All rights reserved.

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 NiII 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.

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.

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.

Synthesis, structural characterization, and spectroscopic and magnetic properties of three new cyano-bridged 3d-4f bimetallic complexes, Ln III(DMF)4(H2O)3CrIII (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 [CrIII(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.

The title compound, [Cu(C4H4NO2) 2(C5H6N2)2] ·2H2O has its metal atom in a square-planar trans-[CuN 4] coordination environment; the CuII 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 CuII complexes containing two different N atoms to take potentially different coordination modes. © 2006 International Union of Crystallography All rights reserved.

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.