Published papers

To develop a new spin-crossover functional material, a magnetic hybrid compound [Fe(qsal)2][Ni(mnt)2] was designed and synthesized (Hqsal = N-(8-quinolyl)salicylaldimine, mnt = maleonitriledithiolate). The temperature dependence of magnetic susceptibility suggested the coexistence of the high-spin (HS) Fe(III) cation and π-radical anion at room temperature and a magnetic transition below 100 K. The thermal variation of crystal structures revealed that strong π-stacking interaction between the π-ligand in the [Fe(qsal)2] cation and [Ni(mnt)2] anion induced the distortion of an Fe(III) coordination structure and the suppression of a dimerization of the [Ni(mnt)2] anion. Transfer integral calculations indicated that the magnetic transition below 100 K originated from a spin-singlet formation transformation in the [Ni(mnt)2] dimer. The magnetic relaxation of Mössbauer spectra and large thermal variation of a g-value in electron paramagnetic resonance spectra below the magnetic transition temperature implied the existence of a magnetic correlation between d-spin and π-spin.

Real-time recording of the kinetics of systemically administered drugs in in vivo microenvironments may accelerate the development of effective medical therapies. However, conventional methods require considerable analyte quantities, have low sampling rates and do not address how drug kinetics correlate with target function over time. Here, we describe the development and application of a drug-sensing system consisting of a glass microelectrode and a microsensor composed of boron-doped diamond with a tip of around 40 μm in diameter. We show that, in the Guinea pig cochlea, the system can measure - simultaneously and in real time - changes in the concentration of bumetanide (a diuretic that is ototoxic but applicable to epilepsy treatment) and the endocochlear potential underlying hearing. In the rat brain, we tracked the kinetics of the drug and the local field potentials representing neuronal activity. We also show that the actions of the antiepileptic drug lamotrigine and the anticancer reagent doxorubicin can be monitored in vivo. Our microsensing system offers the potential to detect pharmacological and physiological responses that might otherwise remain undetected.

The electrochemical oxidation behavior of hydroxide ions at the surface of boron-doped diamond (BDD) electrodes is presented. The hydroxide ion oxidation behavior was found to be affected by the surface conditions of the BDD electrode. Over the NaOH concentration range of 0.5-10 mM, a well-defined voltammetric wave attributed to hydroxide ion oxidation was observed at ∼1.25 V versus a Ag/AgCl reference electrode when using an anodically oxidized BDD (AO-BDD) electrode, while it was observed at around ∼1.15 V when a cathodically reduced BDD (CR-BDD) electrode was used. Although the hydroxide ion oxidation profiles were slightly different for the AO-BDD and CR-BDD electrodes, the peak currents was each found to have linear relationships with the NaOH concentration over the same range.

In this chapter, photo-modulation of superconducting and magnetic properties is described. First, the superconducting property of a boron-doped diamond is investigated, in which the critical current density varies dramatically between the hydrogen- and oxygen-terminated diamond. Second, the superconducting diamond is modified with an azobenzene molecular layer to modulate the superconductivity upon photoirradiation. In this composite superconductor, the critical current density is reversibly amplified by 55% upon photoisomerization of the azobenzene layer. Third, Prussian Blue, a coordination polymer, is integrated with the semiconducting titanium oxide nanosheets to modulate the magnetic property upon photoirradiation. In this magnetic heterostructure, photoinduced magnetic phase transition of Prussian Blue is present by injecting photoexcited electrons from titanium oxide nanosheets.

A previous dose-escalation study of sulfasalazine (SSZ), an inhibitor of cystine-glutamate exchange transporter xc (–), in the variant form of CD44 (CD44v)-positive cancer stem cells (CSCs) suggested that administration of SSZ induces the reduction of CD44v-positive cells and intracellular reduced glutathione (GSH) levels in patients with advanced gastric cancer (AGC). Here we report a study to evaluate SSZ in combination with cisplatin in patients with CD44v-expressing AGC refractory to cisplatin. SSZ was given by oral administration four times daily with 2 weeks on and 1 week off. Cisplatin at 60 mg/m2 was administered every 3 weeks. Of the 15 patients who underwent prescreening of CD44v expression, 8 patients were positive, and 7 patients were treated with the dose level of SSZ at 6 g/day. One patient experienced dose-limiting toxicity (DLT) as grade 3 anorexia. Although no other patients experienced DLT, 4 patients required dose interruption or reduction of SSZ; thus, we terminated further dose escalation. No patient achieved objective response, but 1 patient completed six cycles with stable disease for more than 4 months as well as reduction of intratumoral GSH level. The combination of SSZ plus cisplatin was manageable, although dose modification was frequently required during a short observational period.

Anodic stripping voltammetry (ASV) of nickel ions in phosphate buffer solution (PBS) have been investigated at boron-doped diamond (BDD) electrodes. The deposition potential at 0.1 V (vs. Ag/AgCl) for 300 s in 0.1 M PBS pH 3 was found as the optimum condition. The condition was applied for the determination of nickel contained in nickel hydroxide nanoparticles. A linear calibration curve can be achieved of Ni(OH)2-NPs in the concentration range of x to x mM with an estimated limit of detection (LOD) of 5.73 × 10-6 mol/L.

Electrolytic cells for electrochemical oxygen demand (ECOD) measurements based on total electrolytic decomposition at a boron-doped diamond (BDD) electrode were developed for rapid measurement of organic pollutants at low concentrations. Using improved electrolytic cells designed for efficient mass transfer, the ECOD for 10 μM potassium hydrogen phthalate (theoretical ECOD: 2.3 mg-O2 L-1) was determined in a relatively short electrolysis time. Thus, ECOD measurements using these cells would be useful for estimating organic water pollution in industrial waste and lake water.

The electrochemical reduction of CO2 was investigated in an aqueous ammonia solution using boron-doped diamond electrodes. Methanol was mainly produced by reduction at a potential of -1.3 V (vs. Ag/AgCl) with a faradaic efficiency as high as 24.3%. Also, even in an aqueous ammonium bicarbonate solution (pH 7.9) without CO2 bubbling, methanol was produced, while no methanol production was observed at higher (10.6) and lower pH (3.38). These observations suggest that the selectivity for methanol production in aqueous ammonia solutions is due to the electrochemical reduction of bicarbonate ions which are formed by the reaction between ammonia and CO2. Moreover, we present the important role of ammonia as an electrolyte for the selective production of methanol by electrochemical reduction of CO2.

The magnetic properties of layered double hydroxides (LDH) containing transition metal ions can still develop, compared with layered metal hydroxide salts which exhibit structure-dependent magnetism. In this article, we report the preparation of a hybrid magnet composed of Co-Ni LDH and n-alkylsulfonate anions (Co-Ni-CnSO3 LDH). As Co-Ni LDH is anion-exchangeable, we can systematically control the interlayer spacing by intercalating n-alkylsulfonates with different carbon numbers. The magnetic properties were examined with temperature- and field-dependent magnetization measurements. As a result, we have revealed that the coercive field depends on the basal spacing. It is suggested that increasing the basal spacing varies the competition between the in-plane superexchange interactions and long-range out-of-plane dipolar interactions. Moreover, a jump in the coercive field at around 20 Å of the basal spacing is assumed to be the modification of the magnetic ordering in Co-Ni-CnSO3 LDH.

Heterometallic Prussian blue analogues are known to exhibit thermally induced charge transfer, resulting in switching of optical and magnetic properties. However, charge-transfer phase transitions have not been reported for the simplest FeFe cyanide-bridged systems. A mixed-valence FeII/FeIII cyanide-bridged coordination polymer, ([Fe(Tp)(CN)3]2Fe(bpe)5H2O)n, which demonstrates a thermally induced charge-transfer phase transition, is described. As a result of the charge transfer during this phase transition, the high-spin state of the whole system does not change to a low-spin state. This result is in contrast to FeCo cyanide-bridged systems that exhibit charge-transfer-induced spin transitions.

The recovery of copper from wastewater is a key issue for environmental and economic aspects. The wastewater treatment containing copper ions has been carried out by various techniques. Among them, the electrodeposition is the "clean" method that is able to achieve the recovery of copper without requiring addition of chemicals and generating sludge or secondary wastes. However, the current efficiency would tend to decrease especially in a dilute solution, because hydrogen evolution and oxygen reduction reaction would occur as competition reaction. In this article, we study on the recovery of copper from dilute cupric sulfate solution as a model wastewater by an electrodeposition method using boron-doped diamond electrodes which have relatively higher hydrogen overpotential. Two types of boron-doped diamond electrodes were prepared with different boron doping level. The boron-doped diamond electrodes could achieve the recovery of copper with higher current efficiency because of inhibiting hydrogen evolution reaction, compared with glassy carbon electrode.

Dihydroquinazoline FeII complexes, namely [Fe(pq-R)2](X)2·xCH3OH·yCH3CN·zH2O (R = 2-py: X = ClO4 -, x = 1, y = 0, z = 2 (1), BF4 -, x = 0, y = 2, z = 1.75 (2), CF3SO3 -, x = 1, y = 1, z = 0 (3); and X = ClO4 -: R = 2-OCH3, x = 0, y = 0, z = 1 (4), R = 3-OCH3, x = 0, y = 0, z = 1 (5)), were prepared and the effects of the solvent, counteranion and ligand substituent on spin crossover properties were discussed. Comparison of X-ray diffraction data for these complexes revealed the sole presence of high-spin FeII at 298 K and the bond distances around the FeII center at low temperature fall much closer to those at high temperature, which is consistent with variable-temperature dc magnetic susceptibility data. However, the loss of solvent induced a significant change in the spin state of complexes 1 and 2. Moreover, fits to magnetic data of the desolvated samples provide crossover temperatures of T1/2 = 182.9(6), 157.0(8) and 138.3(5) K for 1-des (ClO4 -), 2-des (BF4 -) and 3-des (CF3SO3 -), respectively, indicative of the anion-dependent transition temperature. The cooperativity operating in the complexes is thought to be mainly from the intermolecular π⋯π interactions between dihydroquinazoline rings on the neighboring molecules. The ligand substituent effect was also investigated on FeII SCO properties. This work revealed the spin crossover properties of new types of dihydroquinazoline Fe(ii) complexes, including the transition temperature, the degree of completion and the cooperative nature of the transition, which can be optimally designed when developing new spin-crossover materials.

A heterostructure of diamagnetic magnesium-aluminium layered double hydroxides (Mg-Al LDHs) and photomagnetic cobalt-iron Prussian Blue analogue (Co-Fe PBA) was designed, synthesized and then designated as LDH-PB. The cyanide-bridged Co-Fe PBA was two-dimensionally intercalated into the Mg-Al LDH template by the stepwise anion exchange method. LDH-PB showed ferrimagnetic properties with in-plane antiferromagnetic exchange interactions, as well as small photo-induced magnetization by visible light illumination due to the low dimensional structures and the characteristic photo-induced electronic states of the mixed valence of FeIII(low spin, S = 1/2)-CN-CoII(high spin, S = 3/2)-NC-FeII (low spin, S = 0).

Cyclohexadienone derivatives possessing α-D-glucopyranosyl moiety were designed and synthesized using chemical oxidation or electrochemical oxidation with boron-doped diamond electrode in the final stage. In the chiral induction studies, catalytic hydrogenation provided high diastereoselectivity (dr ratio: > 9:1). Conformational analyses of the C-glucoside structures were performed by NOE experiments and force field calculations, and supported the observed regio-selectivity.

A novel co-reactant-free electrogenerated chemiluminescence (ECL) system is developed where Ru(bpy)3 2+ emission is obtained on boron-doped diamond (BDD) electrodes. The method exploits the unique ability of BDD to operate at very high oxidation potential in aqueous solutions and to promote the conversion of inert SO4 2- into the reactive co-reactant S2O8 2-. This novel procedure is rather straightforward, not requiring any particular electrode geometry, and since the co-reactant is only generated in situ, the interference with biological samples is minimized. The underlying mechanism is similar to that of the Ru(bpy)3 2+/S2O8 2- system; however, the intensity of the emitted signal increases linearly with [SO4 2-] up to ∼0.6 M, with possible implications for analytical uses of the proposed procedure.

Electrolytic corrosion of boron-doped diamond (BDD) electrodes after applying a high positive potential to decompose organic compounds in aqueous solution was studied. Scanning electron microscopy images, Raman spectra, and glow discharge optical emission spectroscopy revealed that relatively highly boron-doped domains were primarily corroded and relatively low boron-doped domains remained after electrolysis. The corrosion due to electrolysis was observed especially in aqueous solutions of acetic acid or propionic acid, while it was not observed in other organic compounds such as formic acid, glucose, and methanol. Electron spin resonance measurements after electrolysis in the acetic acid solution revealed the generation of methyl radicals on the BDD electrodes. Here, the possible mechanisms for the corrosion are discussed. Dangling bonds may be formed due to abstraction of OH groups from C-OH functional groups by methyl radicals generated on the surface of the BDD electrodes. As a result, the sp3 diamond structure would be converted to the sp2 carbon structure, which can be easily etched. Furthermore, to prevent electrolytic corrosion during electrolysis, both the current density and the pH condition in the aqueous solution were optimized. At low current densities or high pH, the BDD electrodes were stable without electrolytic corrosion even in the acetic acid aqueous solution.

The electrochemical detection of oxytocin using boron-doped diamond (BDD) electrodes was studied. Cyclic voltammetry of oxytocin in a phosphate buffer solution exhibits an oxidation peak at +0.7 V (vs. Ag/AgCl), which is attributable to oxidation of the phenolic group in the tyrosyl moiety. Furthermore, the linearity of the current peaks obtained in flow injection analysis (FIA) using BDD microelectrodes over the oxytocin concentration range from 0.1 to 10.0 μM with a detection limit of 50 nM (S/N = 3) was high (R2 = 0.995). Although the voltammograms of oxytocin and vasopressin observed with an as-deposited BDD electrode, as well as with a cathodically-reduced BDD electrode, were similar, a clear distinction was observed with anodically-oxidized BDD electrodes due to the attractive interaction between vasopressin and the oxidized BDD surface. By means of this distinction, selective measurements using chronoamperometry combined with flow injection analysis at an optimized potential were demonstrated, indicating the possibility of making selective in situ or in vivo measurements of oxytocin.

The electrochemical reduction behavior of hypochlorite ions (ClO−) and hypochlorous acid (HClO) at the surface of boron-doped diamond electrodes is presented. The ClO− reduction behavior is strongly affected by the dissolved oxygen through homogeneous oxygen recovery reaction between ClO− and H2O2 as ORR product. As for HClO reduction, one-electron mechanism which is a peculiar characteristic of boron-doped diamond electrodes, was observed.

The progression of influenza varies according to age and the presence of an underlying disease; appropriate treatment is therefore required to prevent severe disease. Anti-influenza therapy, such as with neuraminidase inhibitors, is effective, but diagnosis at an early phase of infection before viral propagation is critical. Here, we show that several dozen plaque-forming units (pfu) of influenza virus (IFV) can be detected using a boron-doped diamond (BDD) electrode terminated with a sialic acid-mimic peptide. The peptide was used instead of the sialyloligosaccharide receptor, which is the common receptor of influenza A and B viruses required during the early phase of infection, to capture IFV particles. The peptide, which was previously identified by phage-display technology, was immobilized by click chemistry on the BDD electrode, which has excellent electrochemical characteristics such as low background current and weak adsorption of biomolecules. Electrochemical impedance spectroscopy revealed that H1N1 and H3N2 IFVs were detectable in the range of 20-500 pfu by using the peptide-terminated BDD electrode. Our results demonstrate that the BDD device integrated with the receptor-mimic peptide has high sensitivity for detection of a low number of virus particles in the early phase of infection.