Published papers

Novel polymorph of the ferric spin crossover complex, β-[Fe(qsal) 2]I 3 [qsalH = N-(8-quinolyl)salicylaldimine], has been prepared and characterized by magnetic susceptibilities and Mössbauer spectra. β polymorph exhibited a cooperative complete spin transition with a thermal hysteresis of 25 K and a tendency to be quenched in the high-spin (HS) state, which is contrastive to a gradual incomplete spin conversion in α polymorph. © 2011 Springer Science+Business Media B.V.

The influence of the boron doping level in boron doped diamond electrodes (BDD) on the electro-generation of active intermediates (hydroxyl radicals and hydrogen peroxide) involved in the oxidation of organic compounds has been studied. It is shown that the boron doping level of diamond electrodes has no influence on the amount of hydroxyl radicals produced at the electrode surface in contrast with hydrogen peroxide, whose formation is favored by low boron doping levels. The influence of the boron doping level on the degradation of formic acid is also investigated. It is shown that lowly doped diamond films have a slight advantage; proving that hydrogen peroxide does not participate in the process. Moreover, the experimental results were compared with a theoretical model, which considers that the oxidation reaction is fast and controlled by mass transfer. All BDD electrodes showed a good agreement with the model independently of the boron doping level. However, the accuracy of the model tend to decrease with increasing boron content, which is probably due to the participation of active couples, which are known to be present at the surface of diamond films with high boron doping levels. © 2011 The Electrochemical Society.

Water-dispersible biotin-modified biofunctional ferromagnetic L1o FePt nanoparticles (NPs) have been synthesized by using a silica nanoreactor strategy. The coercivity field of the NPs was 16 kOe at room temperature, with a particle size of around 5.19 nm. Biotin-coated L1o FePt NPs were biocompatible in an aqueous environment and show site-specific interactions with avidin compounds that could potentially yield a new magnetic material for biological applications, such as for biomolecular recognition.© 2011 The Chemical Society of Japan.

The electrochemical detection of Cd2 has been performed by anodic stripping voltammetry on boron doped diamond (BDD) electrodes. A new technique is proposed, which involves adding a known amount of copper to the sample to deposit an amalgam of Cd-Cu on the surface of the BDD electrode. This amalgam is then stripped during voltammetry measurements, allowing the generation of highly accurate calibration curves for Cd detection (r2 0.99) with a lower detection limit of 10 ppb. The conditions that are used for the anodic stripping voltammetry measurements have been optimized to avoid the deposition of cadmium and the appearance of the stripping peak related to copper. Real samples could contain a certain amount of copper, so the influence of small variations of Cu2 concentration has been investigated and it was found that such variations have no influence on the accuracy of the calibration curve for Cd detection. The influence of other metals that could be dissolved in the sample has also been studied, and it was shown that lead and selenium have a negative influence on the technique. However, this negative interference can be eliminated by increasing the concentration of copper that is introduced in the sample. Furthermore, other species such as boron or chromium have no influence on the anodic stripping voltammetry measurements, so accurate calibration curves for Cd determination could be constructed in the presence of Pb, Se, B and Cr. © 2011 The Electrochemical Society.

The boron doped diamond (BDD) electrode is presented as an appropriate candidate for next generation glass-free, highly stable and accurate pH sensors. The method used in this study is based on the potential change related to the hydrogen evolution reaction following a current step, which is pH dependent. Alkali cations in the solution have no influence on the accuracy of the pH calibration curve, which provides an advantage with respect to the conventional pH glass electrode. The unwanted influence of electrochemically active compounds in solution can be avoided by adjusting the current density applied during chronopotentiometric measurements. The accuracy of the pH measurements is due to the excellent stability as well as the wide potential window and low background current of BDD electrodes. This faculty was not observed when using conventional electrode materials. The efficacy of this new type of pH sensor has been tested using tap water as a typical real sample. © 2011 The Owner Societies.

Reward-induced burst firing of dopaminergic neurons has mainly been studied in the primate midbrain. Voltammetry allows high-speed detection of dopamine release in the projection area. Although voltammetry has revealed presynaptic modulation of dopamine release in the striatum, to date, reward-induced release in awakened brains has been recorded only in rodents. To make such recordings, it is possible to use conventional carbon fibres in monkey brains but the use of these fibres is limited by their physical fragility. In this study, constant-potential amperometry was applied to novel diamond microelectrodes for high-speed detection of dopamine. In primate brains during Pavlovian cue-reward trials, a sharp response to a reward cue was detected in the caudate of Japanese monkeys. Overall, this method allows measurements of monoamine release in specific target areas of large brains, the findings from which will expand the knowledge of reward responses obtained by unit recordings. © 2011 Elsevier Ireland Ltd and the Japan Neuroscience Society.

We report the temperature dependent (100-300 K) conductivity of Berlin green and Prussian blue powders. The method of electronic conduction in vacuum dried Berlin green is identified as hopping of localized electrons and vacuum dried Prussian blue is reaffirmed as an insulator. The assignment of the conduction mechanism is based upon fits to the experimental data, and the different conductivities of the two samples can be understood in terms of both molecular and simple crystalline energy levels of the solids. © 2011 American Physical Society.

Fouling of electrode surfaces by electrode reaction products or by biological spectator species is known to inactivate electrochemical sensors and thus limit their use in biological conditions. Here we present an investigation on the stability of boron doped diamond (BDD) electrodes with different levels of doping. Three different doping levels were used (0.1, 1 and 5% in the carbon phase). The highly doped (5%) BDD is of particular interest as it is here used for the first time for biological applications. Three different redox reactions were examined based on their electrode reaction characteristics: ruthenium(iii) hexaammine (outer sphere), ferrocyanide (suface dependent), dopamine (adsorption mediated). The effect of albumin at blood concentration was studied. All results were compared with glassy carbon. There were no significant differences for the outer sphere electrochemistry, but all the BDDs showed improved resistance to fouling for the ferrocyanide oxidation. The electrocatalytic activity of BBD towards dopamine oxidation increased with increased boron content. However, this appears to be due to a larger number of defect sites which also increases the vulnerability to fouling by albumin and by electrode reaction products and the 5% BDD had similar properties to glassy carbon in this regard. These results suggest that it is possible to optimise the BDD performance for specific applications and that the large potential window for BDD may be due, at least in part, to its relatively poor electrocatalytic activity. © the Owner Societies.

The magnetic properties of different-sized Pt nanoparticles coated by alkanethiol molecules with different carbon chain lengths (1-octadecanethiol, 1-dodecanthiol, and 1-octanethiol) were systematically studied by means of magnetic measurement, x-ray magnetic circular dichroism (XMCD), x-ray absorption near-edge structure (XANES), and electron spin resonance (ESR). Furthermore, azobenzene-derivatized thiol coating of Pt nanoparticles was performed to detect the effect on magnetic characteristics of the geometrical transformation between cis and trans states induced by photoisomerization. All samples showed the ferromagnetism inherent in Pt. In all of the prepared particles Curie temperatures above 300 K were observed. The largest magnetization at 5 K was observed for the longest chain length of alkanethiol and the smallest particle size. The coercive force at 5 K increased as the chain length increased and the particle size decreased. The geometrical transformation of coated molecules barely affected the magnetization and coercive force. The increase in coercive force was accompanied by the enhanced contribution of the orbital magnetic moment. The origins of ferromagnetism and magnetic anisotropy in Pt nanoparticles are discussed in terms of the contribution from the coating molecules and downsizing effects. The appearance of ferromagnetism is mainly interpreted based on two mechanisms, i.e., the electronic band magnetism based on the Stoner criterion for ferromagnetism and the orbital ferromagnetism due to electrons captured in the atomiclike orbital on the particle surface. The chain-length and particle-size-dependent magnetic anisotropy is explained in terms of the change in angular momentum depending on the adsorption condition, especially the coverage ratio, of alkanethiol on the particle surface. This is consistent with the existence of orbital ferromagnetism in the Pt nanoparticle. © 2011 American Physical Society.

Electrochemical selective detection of not only As(III) but also As(V) has been investigated by anodic stripping voltammetry. Here, instead of using modified working electrodes, simple as-deposited boron-doped diamond (BDD) electrodes were used with the addition of gold ions in the sample solution as a catalyst for the electrochemical reaction. A potential-step technique was performed to minimize the hydrogen evolution effect that occurs at the highly negative potential such as -1.5 V (vs. Ag/AgCl) for the reduction of As(V). The present method realized very high sensitivity with an experimental detection limit of 12ppb and excellent stability for the detection of both As(III) and As(V) as well as mixed solutions of these forms. © 2010 The Chemical Society of Japan.

A one-dimensional iron(ii) spin-crossover compound [Fe(3py-im) 2(NCS)2]·7H2O (1) (3py-im = 2,4,5-tris(4-pyridly)-imidazole) has been solvothermally synthesized and structurally characterized. Compound 1 crystallizes in the monoclinic space group P2/c with a = 11.9078(2), b = 9.9474(1), c = 17.7290(3) and β = 102.361(2)° at 105 K. Studies on the variable-temperature magnetic susceptibilities and Mössbauer spectra suggest that compound 1 undergoes incomplete spin transition behaviour. Pressure effects on the transition behaviour have also been investigated, the thermal-induced spin transition becomes more gradual and the critical temperature shifts towards slightly higher temperature range when external pressure increases. However, the spin transition can not be completed by applying external pressure even as high as 0.79 GPa. © The Royal Society of Chemistry 2010.

We show experimentally that room-temperature ferromagnetism can be induced in ZnO/ZnS core/shell nanoparticles without any magnetic components. This ferromagnetism could be attributed to p-p coupling interactions between S 3p and O 2p electrons arising from the redistribution of charges between Zn and O or S atoms. Our present findings possibly open up a new way for introducing magnetism in semiconductor-based "spintronics" devices. © 2010 The Chemical Society of Japan.

Three novel N,N′-bis(2-hydroxy-3-methoxybenzylidene)-1,3- diaminopropane dimeric lanthanide complexes, namely, [{H2L}Sm(NO 3)3]2·H2O (1), [{H 2L}Gd(NO3)3]4·CH 3OH (2), [{H2L}Lu(NO3)3] 4·H2O (3) (H2L = N,N′-bis(2- hydroxy-3-methoxybenzylidene)-1,3-diaminopropane) and three new N,N′-bis(2-hydroxy-3-methoxybenzylidene)-1,3-diaminopropane 3d-Gd heterodinuclear complexes, namely, [{LCo}(CH3COO)(CH 3COOH)Gd(NO3)2] (4), [{LNi(MeOH) 2}Gd(NO3)3]·2MeOH (5) and [{(L)Zn(HNO3)}Gd(NO3)3]·NO 3·H3O·MeOH (6) have been synthesized and isolated. X-ray crystallographical analysis reveals that complexes 1-3 are isomorphic with unique dimeric topology. Complexes 4-6 are of discrete 3d-4f dinuclear cores. Magnetic properties of complexes 2 and 4-6 are systematically investigated. Complexes 4 and 5 are ferromagnetic, while 2 and 6 are antiferromagnetic. © 2010 Elsevier B.V. All rights reserved.

We have reported not only the above examples but also several additional examples of sensitive detection by BDD electrodes, such as uric acid [25], NADH [26], acids [27], toxic gases [28], etc. In fact, some of the examples are now in progress for the development of practical electrochemical sensor applications. Furthermore, in order to add other functions and improve the electrochemical properties, BDD electrodes with surfaces chemically modified by functional organic molecules are also actively being developed [29, 30]. Thus, it appears likely that, in the near future, electrochemical sensors using BDD can be applied for environmental analysis and medical analysis. © Springer Science+Business Media B.V. 2010.

In this report, we determined protein tyrosine kinase (PTKs) activity in human epidermoid carcinoma cells (A431) by employing a novel electrochemical method using boron-doped diamond (BDD) electrodes that enables the electrochemical oxidation of tyrosine (Tyr), phosphorylated Tyr (Tyr-P) and sulfated Tyr (Tyr-S) in water-based solutions. Cyclic voltammetry for Tyr, Tyr-P and Tyr-S showed well-defined oxidation peaks at 0.8. V for Tyr, 1.4. V for Tyr-P and 1.7. V for Tyr-S, respectively. Very little work has been reported previously on the detection of Tyr-P and Tyr-S, probably due to their high oxidation potentials. We utilized electrochemical methods for the detection of kinase activity in connection with poly(Glu-Tyr) modified magnetic beads. Linear-sweep voltammograms for the electrochemical detection of PTKs activity were carried out using BDD electrodes consisting of peptide-modified magnetic beads. Without phosphorylation of the peptide-modified magnetic beads using PTKs, we observed clear oxidation peaks for Tyr oxidation and no significant electrochemical responses for Tyr-P oxidation at 1.4. V for the background. On the other hand, with phosphorylation of the beads using PTKs, the peak oxidation current at 1.4. V clearly increased, while the peak oxidation current for Tyr oxidation decreased. This indicates that PTKs activity could be successfully detected by using electrochemical methods employing BDD electrodes. This method was utilized for the in vitro kinase activity detection of human cell lysate, and the electrochemical measurements were compatible with the Enzyme-Linked ImmunoSorbent Assay based method. Our results indicate that the electrochemical method can be applied to real samples such as cell lysate. © 2010 Elsevier B.V.

The physical and electrochemical properties of boron-doped polycrystalline diamond electrodes, prepared with various B/C ratio, i.e., 0.1%, 0.5% (BDD-A), 1% (BDD-B), and 5% (BDD-C), were investigated. Electrochemical measurements of the heavily boron-doped films (BDD-C) showed giant electric double-layer capacitance and activity which is significantly larger than BDD-A and BDD-B as well as glassy carbon electrodes. However, interestingly, actual boron concentration of BDD-C was observed to be almost the same as that of BDD-B by secondary ion mass spectroscopy (SIMS) and glow discharge optical emission spectroscopy (GDOES) analysis. It is suggested that the large capacitance is due to a few sp2-bonded carbon impurities, which was observed only in BDD-C, although the amount of the sp2-bonded nondiamond species are very small. In the present work, the reason for the interesting electrochemical properties of heavily boron-doped diamond electrodes is discussed. Furthermore, dimensional stability of the electrodes was also confirmed by conducting harsh anodic treatment. © 2010 Elsevier B.V. All rights reserved.

We describe a simple bench top method for fabricating boron-doped diamond (BDD) microband electrodes and copper-modified BDD microband electrodes. The method described here is inexpensive, robust, renewable, simple, and the BDD microband electrodes and the copper-modified BDD microband electrodes are very easy to fabricate. An advantage of the method is not only its simplicity but also the renewability. That is, even if the surface of the electrode is deactivated after an electrochemical reaction, it can be renewed by simply cutting off the end. As one of the example of application, we report on the selective detection of glucose in solution containing interference species such as Ascorbic acid (AA) and Uric acid (UA) by preparing Cu-modified BDD microband electrodes. Even in solutions containing 2 or 3 times the amount of interfering species compared to the glucose concentration, the Cu-modified BDD microband electrodes showed good selectivity and high durability. © 2010 Elsevier B.V. All rights reserved.

Amperometric gas sensor of arsine was developed using gold-modified diamond electrodes as the working electrodes. The detection method was conducted in high concentration of H2SO4. The reaction was declared based on two oxidation steps, involving oxidation of As3- to As 0 at mild potential in strong acid, followed by electrochemical oxidation of As0 to As3+ at gold-based electrodes. Linear calibration curve was observed in the concentration range of 5-50 ppb (r 2 = 0.985) with detection limit of ∼4.43 ppb (S/N = 3). Current decreasing of measurement was found ∼5.5% for 5 measurements. However, better stability was observed after the 5th measurement, indicated that the sensor could be applied for long time measurement. Investigation to several possible interference gasses, i.e. SO2, H2S, NO, NO 2, CO, O3 and H2 indicated no significant interference of the gas to arsine measurements. © 2010 Elsevier B.V. All rights reserved.