研究者詳細 - 山本　崇史

論文 - 山本　崇史

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Selective C-N Bond Cleavage in Unstrained Pyrrolidines Enabled by Lewis Acid and Photoredox Catalysis

Aida, K; Hirao, M; Saitoh, T; Yamamoto, T; Einaga, Y; Ota, E; Yamaguchi, J

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 146 （ 44 ） 30698 - 30707 2024年10月

ISSN 0002-7863

Cleavage of inert C-N bonds in unstrained azacycles such as pyrrolidine remains a formidable challenge in synthetic chemistry. To address this, we introduce an effective strategy for the reductive cleavage of the C-N bond in N-benzoyl pyrrolidine, leveraging a combination of Lewis acid and photoredox catalysis. This method involves single-electron transfer to the amide, followed by site-selective cleavage at the C2-N bond. Cyclic voltammetry and NMR studies demonstrated that the Lewis acid is crucial for promoting the single-electron transfer from the photoredox catalyst to the amide carbonyl group. This protocol is widely applicable to various pyrrolidine-containing molecules and enables inert C-N bond cleavage including C-C bond formation via intermolecular radical addition. Furthermore, the current protocol successfully converts pyrrolidines to aziridines, γ-lactones, and tetrahydrofurans, showcasing its potential of the inert C-N bond cleavage for expanding synthetic strategies.

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Tailoring Unstrained Pyrrolidines via Reductive C–N Bond Cleavage with Lewis Acid and Photoredox Catalysis

Marina Hirao, Kazuhiro Aida, Tsuyoshi Saitoh, Takashi Yamamoto, Yasuaki Einaga, Eisuke Ota, Junichiro Yamaguchi

（American Chemical Society (ACS)） 2024年07月

Skeletal remodeling of unstrained azacycles such as pyrrolidine remains a formidable challenge in synthetic chemistry. To achieve such remodeling, continuous development of the cleavage of inert C–N bonds is essential. In this study, we introduce an effective strategy for the reductive cleavage of C–N bond in N-benzoyl pyrrolidine, leveraging a combination of Lewis acid and photoredox catalysis. This method involves single-electron transfer to the amide, followed by site-selective cleavage at C2–N bond. Cyclic voltammetry and NMR studies demonstrated that the Lewis acid is crucial for promoting the single-electron transfer from the photoredox catalyst to the amide carbonyl group. This protocol is widely applicable to various pyrrolidine-containing molecules and enables inert C–N bond cleavage including C–C bond formation via intermolecular radical addition. Furthermore, the current protocol successfully converts pyrrolidines to aziridines, lactones, and tetrahydrofurans, demonstrating the potential to expand synthetic strategies in skeletal remodeling.

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Cu, Fe, N-doped Carbon Nanotubes Prepared through Silica Coating for Selective Oxygen Reduction to Water in Acidic Media

Kato M., Abe D., Xie S., Sato S., Fujibayashi N., Matsumoto K., Onoda A., Hayashi T., Mitsui T., Fujiwara K., Yamamoto T., Einaga Y., Tadgell C.A., Kato Y., Asakura K., Yagi I.

Chemcatchem （Wiley） 16 （ 15 ） 2024年05月

ISSN 1867-3880

We report Cu, Fe, N-doped carbon nanotubes, (Cu,Fe)−N−CNT, as electrocatalysts for the oxygen reduction reaction (ORR) in acidic media. (Cu,Fe)−N−CNT was prepared using a silica coating method in pyrolysis to minimize the formation of carbon-coated metal oxide or carbide nanoparticles, which are known to be inactive for the H<inf>2</inf>O<inf>2</inf> reduction. (Cu,Fe)−N−CNT shows a turnover frequency of 0.66 e− site−1 s−1 at +0.8 V vs. RHE and H<inf>2</inf>O<inf>2</inf> yields of <1 % for the ORR with a utilization factor of active sites of 82 %. Kinetic analysis reveals that 4e− transfer rates for (Cu,Fe)−N−CNT are higher than those of a monometallic counterpart of Fe−N−CNT. In situ X-ray absorption spectroscopy enables us to determine redox potentials: E°’(FeIII/FeII)=0.65 V vs. RHE and E°’(CuII/CuI)=0.45 V for (Cu,Fe)−N−CNT, and E°’(FeIII/FeII)=0.65 V for Fe−N−CNT. These results indicate that bimetallic doping into carbon nanotubes gives the effect on kinetic parameters but not on thermodynamic ones. In other words, there is no direct electronic interactions between the Cu and Fe active sites for (Cu,Fe)-N-CNT because such interactions should modulate their redox potentials.

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Designing Molecularly Imprinted Polymer-Modified Boron-Doped Diamond Electrodes for Highly Selective Electrochemical Drug Sensors

Ishii, K; Ogata, G; Yamamoto, T; Sun, SY; Shiigi, H; Einaga, Y

ACS SENSORS （ACS Publications） 9 （ 3 ） 1611 - 1619 2024年03月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 2379-3694

Drug detection in biological solutions is essential in studying the pharmacokinetics of the body. Electrochemical detection is an accurate and rapid method, but measuring multiple drugs that react at similar potentials is challenging. Herein, we developed an electrochemical sensor using a boron-doped diamond (BDD) electrode modified with a molecularly imprinted polymer (MIP) to provide specificity in drug sensing. The MIP is a polymer material designed to recognize and capture template molecules, enabling the selective detection of target molecules. In this study, we selected the anticancer drug doxorubicin (DOX) as the template molecule. In the electrochemical measurements using an unmodified BDD, the DOX reduction was observed at approximately −0.5 V (vs Ag/AgCl). Other drugs, i.e., mitomycin C or clonazepam (CZP), also underwent a reduction reaction at a similar potential to that of DOX, when using the unmodified BDD, which rendered the accurate quantification of DOX in a mixture challenging. Similar measurements conducted in PBS using the MIP-BDD only resulted in a DOX reduction current, with no reduction reaction observed in the presence of mitomycin C and CZP. These results suggest that the MIP, whose template molecule is DOX, inhibits the reduction of other drugs on the electrode surface. Selective DOX measurement using the MIP-BDD was also possible in human plasma, and the respective limits of detection of DOX in PBS and human plasma were 32.10 and 16.61 nM. The MIP-BDD was durable for use in six repeated measurements, and MIP-BDD may be applicable as an electrochemical sensor for application in therapeutic drug monitoring.

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Electrochemical Diagnosis of Urinary Tract Infection Using Boron-Doped Diamond Electrodes

Zhang, ZP; Ogata, G; Asai, K; Yamamoto, T; Einaga, Y

ACS SENSORS （ACS Publications） 8 （ 11 ） 4245 - 4252 2023年11月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 2379-3694

Efficient detection of sodium nitrite in human urine could be used to diagnose urinary tract infections rapidly. Here, we demonstrate a fast and novel method for the selective detection of sodium nitrite in different human urine samples using electrolysis with a bare boron-doped diamond electrode. The measurement is performed without adding any other species, such as enzymes, and uses a simple electrochemical approach with an oxidation step followed by reduction. In the present study, we pay attention to the reduction potential range for the measurement, which is substantially different from many previous literature reports that focus on the oxidation reaction. The determination of added sodium nitrite based on cyclic voltammetry or differential pulse voltammetry is employed for two pooled urine samples and three individual urine matrices. From this, the linear response ranges for sodium nitrite detection are 0.5-10 mg/L (7.2-140 μmol/L) and 10-400 mg/L (140-5800 μmol/L). The results from these urine samples convert well to the calibration curve, with a limit of detection established as 0.82 mg/L (R2 = 0.9914), which is clinically relevant.

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Selective Electro-Oxidation of Cumene Utilizing a Flow Reactor Equipped with Diamond Electrodes

Shogo Nihongi, Riyako Matsuoka, Tsuyoshi Saitoh, Yasuaki Einaga, Takashi Yamamoto

Current Research in Green and Sustainable Chemistry （ELSEVIER） 7 100378 2023年10月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り

Although oxidation of benzylic C(sp3)−H bonds is an important process for synthesizing biologically active compounds, the reactions generically require hazardous reagents, catalysts, and harsh conditions. Since electro-organic synthesis utilizes electricity itself as a reagent, reactions can proceed well even under ambient conditions. Herein, we report a selective oxidation of cumene in an electrochemical flow reactor. Cumyl alcohol was selectively obtained under optimum amount of charge and current density. The selective oxidation of cumene to cumyl alcohol was achieved because overoxidation of cumyl alcohol into acetophenone was suppressed by the electrochemical flow reactor.

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Observation of peripheral airways using ultra-thin fiberscope.

Kinoshita T, Terai H, Ikemura S, Takada N, Fukui T, Irie H, Miyazawa R, Funatsu Y, Okamura T, Koh H, Yamamoto T, Shigematsu R, Ohgino K, Oka K

Respirology (Carlton, Vic.) 28 （ 9 ） 881 - 884 2023年09月

ISSN 1323-7799

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Spin Manipulation in a Metal-Organic Layer through Mechanical Exfoliation for Highly Selective CO2 Photoreduction

Wu, DY; Yin, HQ; Wang, ZS; Zhou, MR; Yu, CF; Wu, J; Miao, HX; Yamamoto, T; Zhaxi, W; Huang, ZT; Liu, LY; Huang, W; Zhong, WH; Einaga, Y; Jiang, J; Zhang, ZM

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 62 （ 18 ） e202301925 2023年04月

ISSN 14337851

Spin manipulation of transition-metal catalysts has great potential in mimicking enzyme electronic structures to improve activity and/or selectivity. However, it remains a great challenge to manipulate room-temperature spin state of catalytic centers. Herein, we report a mechanical exfoliation strategy to in situ induce partial spin crossover from high-spin (s=5/2) to low-spin (s=1/2) of the ferric center. Due to spin transition of catalytic center, mixed-spin catalyst exhibits a high CO yield of 19.7 mmol g−1 with selectivity of 91.6 %, much superior to that of high-spin bulk counterpart (50 % selectivity). Density functional theory calculations reveal that low-spin 3d-orbital electronic configuration performs a key function in promoting CO<inf>2</inf> adsorption and reducing activation barrier. Hence, the spin manipulation highlights a new insight into designing highly efficient biomimetic catalysts via optimizing spin state.

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Spin Manipulation in a Metal-Organic Layer through Mechanical Exfoliation for Highly Selective CO₂ Photoreduction

Dayu Wu, Hua-Qing Yin, Zeshi Wang, Mingren Zhou, Chengfeng Yu, Jing Wu, Huixian Miao, Takashi Yamamoto, Wenjiang Zhaxi, Zetao Huang, Luying Liu, Wei Huang, Wenhui Zhong, Yasuaki Einaga, Jun Jiang, Zhi-Ming Zhang

Angewandte Chemie International Edition （Wiley-VCH GmbH） 62 （ 18 ） e202301925 2023年04月

研究論文（学術雑誌）, 共著, 責任著者, 査読有り

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Amine-Functionalized Diamond Electrode for Boosting CO₂ Reduction to CO

Tatsuhiko Mikami, Takashi Yamamoto, Mai Tomisaki, Yasuaki Einaga

ACS Sustainable Chemistry & Engineering （American Chemical Society） 10 （ 45 ） 14685 - 14692 2022年11月

研究論文（学術雑誌）, 共著, 責任著者, 査読有り

Carbon capture, utilization, and storage (CCUS) have been attracting much attention as an initiative to achieve carbon neutrality. In the capture and storage strategy, amines are widely used for highly efficient separation and capturing of CO₂ since amines react with CO₂ to form carbamates. In the utilization strategy, CO₂ electroreduction is a promising method to convert CO₂ into value-added compounds because reaction conditions are relatively mild and easily controlled. In this work, toward combining CO₂ capture and storage technologies and CO₂ electroreduction, we focused on amine modification of the electrode surface, in which boron-doped diamond (BDD) was chosen as a sustainable electrode material. CO₂ electroreduction using the amine-modified BDD was performed, and an applied potential dependence of the product selectivity was examined. In situ attenuated total reflectance-infrared measurements showed that the peak intensity of the stretching vibration of the carbonyl group at around 1640 cm^-1 decreased as applied potentials became more negative. The effect of amine modification of the BDD surface lies in the formation of a C-N bond during CO₂ electroreduction, resulting in the enhancement of the selectivity of CO production up to 8 times compared to the unmodified BDD.

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Electro-conversion of cumene into acetophenone using boron-doped diamond electrodes

Mana Kitano, Tsuyoshi Saitoh, Shigeru Nishiyama, Yasuaki Einaga, Takashi Yamamoto

Beilstein Journal of Organic Chemistry （Beilstein-Institut） 18 1154 - 1158 2022年09月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り, ISSN 1860-5397

A straightforward electro-conversion of cumene into acetophenone has been reported using boron-doped diamond (BDD) electrodes.This particular conversion is driven by the addition reaction of a cathodically generated hydroperoxide anion to an anodically generated cumyl cation, where the BDD’s wide potential window enables the direct anodic oxidation of cumene into the cumyl cation. Since electricity is directly employed as the oxidizing and reducing reagents, the present protocol is easy to use, suitable for scale-up, and inherently safe.

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Anodic Oxidation of Phenols: A Key Step for the Synthesis of Natural Products

Takashi Yamamoto, Tsuyoshi Saitoh, Yasuaki Einaga, Shigeru Nishiyama

2021年09月

研究論文（学術雑誌）, 共著, 筆頭著者, 責任著者, 査読有り

Fabrication and electrochemical properties of boron-doped SiC

Kazuki Uchiyama, Takashi Yamamoto, Yasuaki Einaga

Carbon （Carbon） 174 240 - 247 2021年04月

責任著者, 査読有り, ISSN 0008-6223

Silicon carbide (SiC) has excellent properties such as chemical and physical stability, biocompatibility, and high thermal conductivity. However, electrical conductivity of SiC is not high enough for electrochemical applications, which has been a major challenge. Here, in order to improve the conductivity, we prepared boron-doped SiC (SiC:B) and evaluated the electrochemical properties. SiC and SiC:B were fabricated by a microwave plasma chemical vapor deposition method. Structural characterization revealed that the main phase of SiC:B is 3C–SiC where the concentration of doped boron could be controlled by tuning the growth conditions. Electrochemical properties were evaluated by cyclic voltammetry measurements, indicating that the reactivity and sensitivity of the SiC:B electrode was comparable of that of the glassy carbon electrode.

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Weak Antilocalization and Spin Hall Effect in Pt Films Doped with Molecular Spin

Wataru Iwamoto, Takashi Yamamoto, Kaname Tsuchii, Yuya Tazaki, Akio Asami, Hiroki Hayashi, Yasuaki Einaga, Kazuya Ando

ACS Applied Electronic Materials （American Chemical Society (ACS)） 2 （ 7 ） 2098 - 2103 2020年07月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 2637-6113

© 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.

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Surface Rashba-Edelstein Spin-Orbit Torque Revealed by Molecular Self-Assembly

S. Haku, A. Ishikawa, A. Musha, H. Nakayama, T. Yamamoto, K. Ando

Physical Review Applied （Physical Review Applied） 13 （ 4 ） 044069 2020年04月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 2331-7019

© 2020 American Physical Society. © 2020 American Physical Society. We report the observation of a spin-orbit torque (SOT) originating from the surface Rashba-Edelstein effect. We find that the SOT in a prototypical spin-orbitronic system, a Pt/Co bilayer, can be manipulated by molecular self-assembly on the Pt surface. This provides evidence that the Rashba spin-orbit coupling at the Pt surface generates a sizable SOT, which is hidden by the strong bulk and interface spin-orbit coupling. We show that the molecular tuning of the surface Rashba-Edelstein SOT is consistent with density-functional-theory calculations. These results illustrate the crucial role of the surface spin-orbit coupling in the SOT generation, which alters the landscape of metallic spin-orbitronic devices.

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Avian Influenza Virus Detection by Optimized Peptide Termination on a Boron-Doped Diamond Electrode

Teruhiko Matsubara, Michiko Ujie, Takashi Yamamoto, Yasuaki Einaga, Tomo Daidoji, Takaaki Nakaya, Toshinori Sato

ACS Sensors （American Chemical Society (ACS)） 5 （ 2 ） 431 - 439 2020年02月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 2379-3694

Copyright © 2020 American Chemical Society. The development of a simple detection method with high sensitivity is essential for the diagnosis and surveillance of infectious diseases. Previously, we constructed a sensitive biosensor for the detection of pathological human influenza viruses using a boron-doped diamond electrode terminated with a sialyloligosaccharide receptor-mimic peptide that could bind to hemagglutinins involved in viral infection. Circulation of influenza induced by the avian virus in humans has become a major public health concern, and methods for the detection of avian viruses are urgently needed. Here, peptide density and dendrimer generation terminated on the electrode altered the efficiency of viral binding to the electrode surface, thus significantly enhancing charge-transfer resistance measured by electrochemical impedance spectroscopy. The peptide-terminated electrodes exhibited an excellent detection limit of less than one plaque-forming unit of seasonal H1N1 and H3N2 viruses. Furthermore, the improved electrode was detectable for avian viruses isolated from H5N3, H7N1, and H9N2, showing the potential for the detection of all subtypes of influenza A virus, including new subtypes. The peptide-based electrochemical architecture provided a promising approach to biosensors for ultrasensitive detection of pathogenic microorganisms.

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Enhancement of coercivity of self-assembled stacking of ferrimagnetic and antiferromagnetic nanocubes

Keisuke Sawano, Keishi Tsukiyama, Makoto Shimizu, Mihiro Takasaki, Yuya Oaki, Takashi Yamamoto, Yasuaki Einaga, Christian Jenewein, Helmut Cölfen, Hideo Kaiju, Tetsuya Sato, Hiroaki Imai

Nanoscale （Royal Society of Chemistry (RSC)） 12 （ 14 ） 7792 - 7796 2020年

研究論文（学術雑誌）, 共著, 査読有り, ISSN 2040-3364

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An electrochemical aptamer-based sensor prepared by utilizing the strong interaction between a DNA aptamer and diamond.

Asai K, Yamamoto T, Nagashima S, Ogata G, Hibino H, Einaga Y

The Analyst （Analyst） 145 （ 2 ） 544 - 549 2019年11月

共著, 査読有り, ISSN 0003-2654

© 2020 The Royal Society of Chemistry. Stable and continuous biosensing of electroactive species in vivo has been achieved by using boron-doped diamond (BDD) electrodes owing to their outstanding electrochemical properties. However, the present problem in biosensing using BDD electrodes is how to specifically measure/detect the target molecules, including electrochemically inactive species. A possible solution is to fabricate an electrochemical aptamer-based (E-AB) sensor using a BDD electrode. In a preliminary investigation, we found that DNA aptamers strongly adsorb on the BDD surface and the aptamer-adsorbed BDD apparently worked as an E-AB sensor. The present study reports the performance of the aptamer-adsorbed BDD electrode as an E-AB sensor. Doxorubicin (DOX), a widely used chemotherapeutic, was chosen as a target molecule. The sensor could be prepared by just dipping BDD in an aptamer solution for only 30 min, and the electrochemical signals were dependent on the DOX concentration. The adsorption of DNA was strong enough for continuous measurements and even a sonication treatment. Such behaviors were not observed when using gold and glassy carbon electrodes. In a kinetic measurement, distortion by a sluggish response was observed for both association and dissociation phases, indicating that the interaction between DOX and the aptamer involves several kinetic processes. By fitting to a Langmuir isotherm, a limit of detection of 49 nM and a maximum detectable concentration of 2.3 μM were obtained. Although the sensitivity was lower than those of the well-established E-AB sensors of gold, the values are within a drug's therapeutic range. Overall, the present work demonstrates that a DNA aptamer and a BDD electrode is an effective combination for an E-AB sensor with stable sensitivity, and a wide variety of DNA aptamers can be applied without any special treatment.

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Observation of Proton Transfer Coupled Spin Transition and Trapping of Photoinduced Metastable Proton Transfer State in an Fe(II) Complex.

Nakanishi T, Hori Y, Sato H, Wu SQ, Okazawa A, Kojima N, Yamamoto T, Einaga Y, Hayami S, Horie Y, Okajima H, Sakamoto A, Shiota Y, Yoshizawa K, Sato O

Journal of the American Chemical Society （Journal of the American Chemical Society） 141 （ 36 ） 14384 - 14393 2019年08月

共著, 査読有り, ISSN 0002-7863

An important technique to realize novel electron- and/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.

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Influence of the Nature of Boron-Doped Diamond Anodes on the Dehydrogenative Phenol-Phenol Cross-Coupling

Gleede B., Yamamoto T., Nakahara K., Botz A., Graßl T., Neuber R., Matthée T., Einaga Y., Schuhmann W., Waldvogel S.

ChemElectroChem （ChemElectroChem） 6 （ 10 ） 2771 - 2776 2019年05月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 2196-0216

© 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.

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論文 - 山本　崇史