Published papers

In heterostructures with broken inversion symmetry, the electrons' motion is coupled to their spin through interface-driven spin-orbit coupling: the Rashba effect. The Rashba effect enables the interconversion between spin and charge currents, offering a variety of novel spintronic phenomena and functionalities. However, despite the significant progress in Rashba physics, controlling the spin-charge conversion in metallic heterostructures remains a major challenge. We show that molecular self-assembly provides a way to engineer the Rashba spin-charge converters. We demonstrate that magnetoresistance and voltage generation originating from the spin-charge conversion in metallic heterostructures can be manipulated by decorating the surface with selfassembled organic monolayers through the cooperative molecular field effect. We also demonstrate reversible phototuning of the spin-charge conversion through light-driven molecular transformations using a molecule that can photoisomerize between the trans and cis states. These findings, with the almost-infinite chemical tunability of organic monolayers, pave the way toward molecular engineering of spin-orbit devices.

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Boron-doped diamond (BDD) represents a powerful and innovative electrode material. In particular, in combination with fluorinated solvents such as 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), the system exhibits the largest known electrochemical window of approximately 5 V in protic media. Furthermore, the anodic treatment allows the direct formation of oxyl radicals, which are known to exhibit specific reactivity. The electrochemical dehydrogenative phenol-phenol cross-coupling is a versatile and useful transformation to non-symmetric biphenols. This electro-organic conversion can be divided into two regimes: initial oxidation at the anode and the electrolyte-controlled follow-up reaction. This work intends to provide an answer about the influence of BDD electrodes on oxidation reactions in electrosynthesis. Depending on the electro-organic transformation, the support material of BDD, its boron content, and its fabrication method have a significant influence on the electrosynthetic efficiency.

© 2019 American Chemical Society. A thermoresponsive smart window that can switch its transmittance to control heating from sunlight is attracting great attention. Such windows made from a hydrogel of a thermoresponsive polymer such as poly(N-isopropylacrylamide) (PNIPAm) or hydroxypropyl cellulose (HPC) have been successful and can switch their transmittance at room temperature. However, such hydrogels occasionally freeze in cold places, degrading their transmittance. Thus, a thermoresponsive hydrogel that can be used in various geographical regions is desired. Here, we produced a thermoresponsive smart window with freezing resistance made from HPC and glycerol. We could adjust its switching temperature by simply changing the amount of added glycerol, letting us easily change it to room temperature for practical use. These smart windows show high cyclic performance, freezing resistance, and heat shielding, demonstrating great potential.

This journal is © The Royal Society of Chemistry. We report the development of a micro total analysis system (μTAS) based on electrochemical measurements and dielectrophoretic sorting for screening of NAD(P)-dependent oxidoreductases. In this system, the activity of enzymes immobilized on microbeads, together with their encoding DNA, can be measured with a boron-doped diamond (BDD) electrode in each compartment (∼30 nL) of the microfluidic system. The 30 nL droplets containing microbead-displayed genes of enzymes with higher activity can then be recovered by dielectrophoretic sorting. Previously, we developed the NAD(P)H-measuring device containing the BDD electrode for high-throughput measurement of the activity of NAD(P)-dependent oxidoreductases. In this study, we fabricated an encapsulating device and a droplet-sorting device for nanoliter-size droplets, for the first time, and then combined these three devices to construct a μTAS for directed evolution of NAD(P)-dependent oxidoreductases. We confirmed that this system works by proof-of-principle experiments and successfully applied this system for screening of randomized libraries of NAD-dependent dehydrogenases.

Copyright © 2019 American Chemical Society. An important technique to realize novel electron- A nd/or proton-based functionalities is to use a proton-electron coupling mechanism. When either a proton or electron is excited, the other one is modulated, producing synergistic functions. However, although compounds with proton-coupled electron transfer have been synthesized, crystalline molecular compounds that exhibit proton-transfer-coupled spin-transition (PCST) behavior have not been reported. Here, we report the first example of a PCST Fe(II) complex, wherein the proton lies on the N of hydrazone and pyridine moieties in the ligand at high-spin and low-spin Fe(II), respectively. When the Fe(II) complex is irradiated with light, intramolecular proton transfer occurs from pyridine to hydrazone in conjunction with the photoinduced spin transition via the PCST mechanism. Because the light-induced excited high-spin state is trapped at low temperatures in the Fe(II) complex- A phenomenon known as the light-induced excited-spin-state trapping effect-the light-induced proton-transfer state, wherein the proton lies on the N of hydrazone, is also trapped as a metastable state. The proton transfer was accomplished within 50 ps at 190 K. The bistable nature of the proton position, where the position can be switched by light irradiation, is useful for modulating proton-based functionalities in molecular devices.

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim An oxidative cleavage reaction of the acyl−carbon bond in phenylacetone derivatives under cathodic reduction is reported. This particular transformation is driven by the cathodic reduction of dissolved molecular oxygen to superoxide anions. Various cathode materials were examined, and we discovered that boron-doped diamond (BDD) enables highly efficient molecular conversion, owing to BDD's outstanding electrochemical property for utilizing the small amounts of molecular oxygen effectively. The scope of the reaction is broad and can be applied to a variety of substrates, ranging from ketones to esters and amides. As an electric current is directly employed to generate the superoxide anion, the reaction is metal- and catalyst-free. Electro-organic synthesis using the carbon-based BDD electrode thus provides access to sustainable molecular transformations.

© 2020 the Owner Societies. In this work, we quantify the electrogenerated chemiluminescence arising from the reaction of electrogenerated tris(bipyridine)ruthenium(iii) with hydroxyl ions, in terms of emission intensity and reaction rate. Different electrode materials (glassy carbon and boron-doped diamond) and different supporting electrolytes (perchlorate, phosphate, and carbonate) were investigated with pH variation. Relative quantification of the electrogenerated chemiluminescence was achieved using the Ru(bpy)32+/tri-n-propylamine system, taken as a reference, with relative emission as low as 600 and 230 times that observed at the same coreactant concentration and the same pH, respectively. The kinetics was investigated by foot of the wave analysis of cyclic voltammetry to measure the turnover frequency of the reaction. This journal is

© 2020 Elsevier B.V. Preparation of stable iridium-modified boron-doped diamond electrodes through electrodeposition was studied. The electrode was prepared by wet chemical seeding and thermal annealing that performed before and after the electrodeposition process in order to get a homogeneous deposition. The modified electrode from each step was characterized using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Raman and X-Ray photoelectron spectroscopy (XPS) to understand the surface topography and its elemental composition. In addition, cyclic voltammetry for arsenic (III) was performed to examine the electrochemical behavior of the modified diamond. At an optimum condition in a phosphate buffer solution pH 3 and a scan rate of 50 mV/s, a linear calibration curve in the concentration range of 1–100 μM with a detection limit of 4.64 μM was achieved. Excellent stability and repeatability were also observed with relative standard deviations of 2.6% and <0.4%, respectively. Additionally, the electrode exhibited good linearity and sensitivity towards the measurement of arsenic (III) in both arsenic (III)-added tap water and lake water samples.

© 2020 American Chemical Society. A high degree of tunability and versatility of organic chemistry has paved the way toward molecular engineering of electronic and spintronic devices. Here, we report molecular spin doping of a Pt film, the key material in spin orbitronics. The molecular spin doping using a monolayer of a metal terpyridine complex allows to control the interaction between the conduction electrons and localized magnetic moments in the Pt film. The interaction was probed by measuring the weak antilocalization, which demonstrates enhanced magnetic impurity scattering induced by the molecular spin doping. By measuring the spin-orbit torque generated by Pt doped with molecular spins, we found that the spin Hall effect is robust against the magnetic impurity scattering, showing that the significant spin-orbit coupling dominates the charge-to-spin conversion in Pt. These results demonstrate that the molecular spin doping paves the way to explore spin-orbitronics phenomena.

Nanodiamonds (NDs) are a type of biocompatible nanomaterial with easily modified surfaces and are considered as promising candidates in biomedicine. In this work, the inhibition of tumor cell migration by carboxylated nanodiamonds (cNDs) was investigated. AFM-based single cell adhesion and F-actin staining experiments demonstrated that cNDs treatment could enhance cell adhesion and impair assembly of the cytoskeleton. The mechanism analysis of the regulatory protein expression level also proved that cNDs could inhibit the migration of Hela cells by preventing the epithelial-mesenchymal transition (EMT) process through the transforming growth factor β (TGF-β) signaling pathway. The in vivo pulmonary metastasis model also showed that cNDs effectively reduced the metastasis of murine B16 melanoma cells. In summary, cNDs have been demonstrated to inhibit cancer cell migration in vitro and decrease tumor metastasis in vivo. Therefore, cNDs might have potential utility for specific cancer treatment.

Nickel has been known as a good catalyst due to its high activity and stability, but the potential formation of NiOOH is quite high. In this work, zinc together with nickel was used to modify the surface of boron-doped diamond (BDD) to lower the formation potential of NiOOH. Electro-deposition (multi pulse amperometry) technique was applied at a potential of -1.6 V for 600 s. The prepared electrode (NiZn-BDD) characterized using SEM-EDX and XPS shows that both nickel and zinc were deposited homogenously on the surface of BDD with the ratio of 1:2 for nickel:zinc.

High concentrations of CO2 in the atmosphere may cause climate and environmental changes. Therefore, various research has been extensively performed to reduce CO2 by converting CO2 directly into hydrocarbons. In this research, CO2 electrochemical reduction was studied using boron-doped diamond (BDD) modified with copper nanoparticles to improve BDD electrodes' catalytic properties. The deposition was performed by chronoamperometry technique at a potential of -0.6 V (vs. Ag/AgCl) and characterized using SEM, EDS, XPS, and cyclic voltammetry (CV). CO2 electrochemical reduction on BDD and Cu-BDD was carried out at -1.5 V (vs. Ag/AgCl) for 60 minutes. The products were analyzed using HPLC and GC. The product was mainly formic acid with a concentration of 11.33 mg/L and 33% faradaic efficiency on a Cu-BDD electrode.

The electrochemical nitrate reduction by using boron-doped diamond (BDD) and copper modified boron-doped diamond (Cu-BDD) electrodes was investigated at various potentials. Nitrate reduction efficiency and the products distribution was strongly dependent on the applied potential for both electrodes. The highest nitrate reduction efficiency of 77% was obtained at -2.0 V (vs. Ag/AgCl) by using Cu-BDD. Compared with BDD electrode, nitrate reduction on Cu-BDD electrode occurred at more positive potential. Copper oxides formed on BDD surface efficiently promoted enhanced conductivity of electrode to promote electrons transfer during nitrate reduction process. Meanwhile, the catalytic ability of copper was also conductive to the nitrate transformation. Therefore, the developed Cu-BDD would be a promising approach for efficient nitrate removal from groundwater.

In this paper we report on a study of the electrochemical behavior of lamotrigine (LTG) using boron-doped diamond (BDD) electrodes. Cyclic voltammetry of LTG in a phosphate buffer solution exhibited an oxidation signal at ca. +1.4 V (vs. Ag/AgCl). A reduction signal at −0.5 to −1.0 V (vs. Ag/AgCl) was observed only after oxidation of LTG. The oxidation signal was due to polymerization of LTG adsorbed on the BDD electrode, while the reduction signal was a consequence of a process involving the reduction of the azo group in the LTG-oxidized product. Continuous measurements of LTG aiming at in vivo monitoring were successfully investigated and an optimized chronoamperometry technique, in which the BDD microelectrode was clamped to the LTG oxidation potential (+1.4 V) for 2 s, then to the LTG reduction potential (−0.6 V) for 2 s, was implemented. The limits of detection (S/N = 3) were estimated to be 29 nM and 130 nM for the oxidation and reduction of LTG, respectively. The use of this chronoamperometry technique enables a high temporal resolution of 4 s for LTG measurements. BDD microelectrodes, therefore, are the ideal electrodes for performing continuous in vivo measurements of LTG.

© 2019 Elsevier B.V. Dimethyl sulfoxide (DMSO) is an excellent organic solvent, and widely used in laboratories and industries. Therefore, plenty amount of wastewater containing DMSO have been discharged. As the DMSO is high resistant to biological process which is mostly used for wastewater treatments, other strong treatments are needed. Electrochemical oxidation using boron-doped diamond (BDD) anode is a promising method due to effective generation of free hydroxyl radicals which are quite strong oxidizing agents. In this work, a simulated wastewater containing DMSO was treated by the anodic oxidation using BDD electrodes. We found that BDD electrodes could oxidize and completely mineralize DMSO. Removal of total organic carbon was more than 99% after the electrolysis for 5 h using BDD electrodes. This is first observation for the electrochemical mineralization of persistent DMSO. Moreover, BDD electrodes enabled to mineralize DMSO without electrolytic corrosion at low current densities and high pH of the solution for the treatments.

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim An electrochemical pinacol coupling reaction of acetophenone using a boron-doped diamond (BDD) electrode has been reported. This transformation is driven by the one-electron reduction of acetophenone on the BDD cathode, followed by an intermolecular radical coupling. Owing to the BDD's outstanding electrochemical properties, the pinacol-type compound has been obtained in good conversion yield. The roles of a supporting electrolyte and solvent were addressed; (1) lithium ions contribute to increase in the reactivity of the radical intermediate. (2) Addition of water promotes the electron transfer process at the BDD surface. The reaction is relatively tolerant to para-substituted acetophenone derivatives. Since electric current is directly employed as reducing reagents to generate a radical intermediate, the reaction is metal-free, sustainable, and inherently safe.

© 2018 American Chemical Society. We report on the use of boron doped diamond electrodes for the electrochemiluminescence (ECL) of the coreactant peroxydisulfate and the luminophore ruthenium(II)-tris(2,2′-bipyridine). Compared to common electrode materials (i.e., Pt, Au, glassy carbon), boron doped diamond has a large overpotential for the evolution of hydrogen in aqueous electrolyte solutions. This intrinsic feature enables reductive-oxidation ECL with peroxydisulfate to be obtained without interference from hydrogen evolution and with high reproducible signals and stable emission. We investigated the effects of the peroxydisulfate concentration and the pH on the ECL emission to find the optimal conditions for enhancing the signal.

© 2019 The Royal Society of Chemistry. We have developed a new method for fabricating all-diamond microelectrodes. The process comprises three steps: masking the tip of an electrode by electroplating with chromium, depositing undoped diamond, which acts as an insulator on the sides of the electrode, and removing the chromium mask to expose the tip of the electrode. The active area of the electrode can be easily controlled in combination only with a conventional electroplating technique.

© 2019 Hexacyanoferrate redox couple is extensively used as a benchmark to evaluate electrode activity in aqueous electrochemistry. Interestingly, boron-doped diamond (BDD) electrode shows surface-dependent behaviors: fast electron transfer rate on hydrogen terminated surface and slow rate on oxygen terminated surface. On the other hand, origin of the surface-dependent response still remains unclear. In this study, we spectroscopically investigated the determinants of electrochemical activity of this system using in situ ATR-IR technique. Our experiment revealed that adsorbed intermediate species of this redox system exist on the hydrogen terminated BDD. On the oxygen terminated BDD, the bands of adsorbed species were weakened, indicating that the oxygen functional groups specifically inhibited the adsorption of the intermediate species.

Copyright © 2019 American Chemical Society. Carbon-based materials are regarded as an environmentally benign alternative to the conventional metal electrode used in electrochemistry from the viewpoint of sustainable chemistry. Among various carbon electrode materials, boron-doped diamond (BDD) exhibits superior electrochemical properties. However, it is still uncertain how surface chemical species of BDD influence the electrochemical performance, because of the difficulty in characterizing the surface species. Here, we have developed in situ spectroscopic measurement systems on BDD electrodes, i.e., in situ attenuated total reflection infrared spectroscopy (ATR-IR) and electrochemical X-ray photoelectron spectroscopy (EC-XPS). ATR-IR studies at a controlled electrode potential confirmed selective surface hydroxylation. EC-XPS studies confirmed deprotonation of C-OH groups at the BDD/electrolyte interface. These findings should be important not only for better understanding of BDD's fundamentals but also for a variety of applications.