Publications by authors named "Shojiro Kimura"

16 Publications

  • Page 1 of 1

A ground-state-dominated magnetic field effect on the luminescence of stable organic radicals.

Chem Sci 2021 Jan 5;12(6):2025-2029. Epub 2021 Jan 5.

Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science 5-1 Higashiyama, Myodaiji Okazaki Aichi 444-8787 Japan

Organic radicals are an emerging class of luminophores possessing multiplet spin states and potentially showing spin-luminescence correlated properties. We investigated the mechanism of recently reported magnetic field sensitivity in the emission of a photostable luminescent radical, (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (PyBTM) doped into host -PyBTM molecular crystals. The magnetic field (0-14 T), temperature (4.2-20 K), and the doping concentration (0.1, 4, 10, and 22 wt%) dependence on the time-resolved emission were examined by measuring emission decays of the monomer and excimer. Quantum mechanical simulations on the decay curves disclosed the role of the magnetic field; it dominantly affects the spin sublevel population of radical dimers in the ground states. This situation is distinctly different from that in conventional closed-shell luminophores, where the magnetic field modulates their excited-state spin multiplicity. Namely, the spin degree of freedom of ground-state open-shell molecules is a new key for achieving magnetic-field-controlled molecular photofunctions.
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http://dx.doi.org/10.1039/d0sc05965jDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8179284PMC
January 2021

Magneto-Electric Directional Anisotropy in Polar Soft Ferromagnets of Two-Dimensional Organic-Inorganic Hybrid Perovskites.

Angew Chem Int Ed Engl 2021 Jun 24;60(26):14350-14354. Epub 2021 May 24.

Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan.

Two-dimensional organic-inorganic hybrid perovskites (2D-OIHPs) are attracting interest due to their structural tunability and rich functional characteristics, such as ferroelectricity and ferromagnetism. Here, we report the chiral-polar ferromagnetic 2D-OIHP copper chlorides with discernable electric polarization in the inorganic layers. In these systems, the magneto-electric (ME) correlation has been clearly observed by measuring a magneto-electric directional anisotropy (MEA), in which an optical absorption coefficient changes with reversal of the light propagating direction. We have found that the MEA can be induced by a low magnetic field of about 50 mT, reflecting soft magnetic nature. The present results suggest a new paradigm for designing functional ME multiferroics, which effectively couples magnetic and electric properties.
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http://dx.doi.org/10.1002/anie.202103121DOI Listing
June 2021

Radical-Based Coordination Polymers as a Platform for Magnetoluminescence.

J Am Chem Soc 2021 Apr 7;143(15):5610-5615. Epub 2021 Apr 7.

Institute for Molecular Science, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan.

Spin-correlated electronic and magnetic properties of organic radicals have been developed, but luminescence properties, based on interplay with spins, have rarely been reported. The effect of magnetic fields on luminescence (i.e., magnetoluminescence) is a rare example of such properties, observed to date only in radicals dispersed in host matrices. We now report a novel method for achieving radical magnetoluminescence involving radical-based coordination polymers (CPs). The luminescence properties of the bis(3,5-dichloro-4-pyridyl)(2,4,6-trichlorophenyl)methyl (bisPyTM) and tris(3,5-dichloro-4-pyridyl)methyl (trisPyM) radicals and their 1D and 2D Zn CPs were investigated. Although solid-state emissions of bisPyTM and trisPyM were not affected significantly by external magnetic fields at 4.2 K, those of CPs were greatly modulated. Studies of the crystal structures, magnetic properties, and the temperature-dependence and time-resolved properties of the magnetoluminescence indicate that the reduction of radical-radical interactions in CPs would be a key method for achieving magnetoluminescence.
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http://dx.doi.org/10.1021/jacs.1c00661DOI Listing
April 2021

Dirac Fermion Kinetics in 3D Curved Graphene.

Adv Mater 2020 Dec 28;32(48):e2005838. Epub 2020 Oct 28.

Advanced Institute for Materials Research, Tohoku University, Sendai, 980-8577, Japan.

3D integration of graphene has attracted attention for realizing carbon-based electronic devices. While the 3D integration can amplify various excellent properties of graphene, the influence of 3D curved surfaces on the fundamental physical properties of graphene has not been clarified. The electronic properties of 3D nanoporous graphene with a curvature radius down to 25-50 nm are systematically investigated and the ambipolar electronic states of Dirac fermions are essentially preserved in the 3D graphene nanoarchitectures, while the 3D curvature can effectively suppress the slope of the linear density of states of Dirac fermion near the Fermi level are demonstrated. Importantly, the 3D curvature can be utilized to tune the back-scattering-suppressed electrical transport of Dirac fermions and enhance both electron localization and electron-electron interaction. As a result, nanoscale curvature provides a new degree of freedom to manipulate 3D graphene electrical properties, which may pave a new way to design new 3D graphene devices with preserved 2D electronic properties and novel functionalities.
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http://dx.doi.org/10.1002/adma.202005838DOI Listing
December 2020

Excimer emission and magnetoluminescence of radical-based zinc(II) complexes doped in host crystals.

Chem Commun (Camb) 2020 Sep;56(76):11195-11198

Institute for Molecular Science, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan.

A ZnII complex based on a luminescent organic radical was doped into host molecular crystals. The 5, 10, and 20 wt%-doped crystals showed excimer emissions and their luminescent behaviours were significantly modulated by an external magnetic field. These are the first examples showing excimer emissions and magnetic-field-sensitive luminescent properties for complexes based on luminescent radicals. The excimer species contributing to magnetoluminescence was determined by analyzing the emission spectra and their magnetic-field dependencies. These results suggest the general nature of magnetic field effects on the luminescence of radicals as well as the importance of the type of interaction between radicals.
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http://dx.doi.org/10.1039/d0cc04830eDOI Listing
September 2020

Electrical Switching of the Nonreciprocal Directional Microwave Response in a Triplon Bose-Einstein Condensate.

Phys Rev Lett 2020 May;124(21):217401

Department of Physics, Tokyo Institute of Technology, Tokyo 152-8551, Japan.

We present a microwave electron spin resonance study of the quantum spin dimer system TlCuCl_{3}, which shows the magnetic-field-induced ordering with both antiferromagnetic spin order and ferroelectricity by the Bose-Einstein condensation (BEC) of triplon quasiparticles. Our main achievement is an electrical switching of the nonreciprocal directional microwave response in the triplon BEC phase. High-speed directional control of microwave absorption by applying an electric field has been accomplished in this Letter. The strength of the observed nonreciprocal microwave response well agrees with the calculation based on Kubo theory with the parameters, evaluated from the static electric polarization in this material.
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http://dx.doi.org/10.1103/PhysRevLett.124.217401DOI Listing
May 2020

Magnetochiral Dichroism in a Collinear Antiferromagnet with No Magnetization.

Phys Rev Lett 2020 May;124(21):217402

Department of Advanced Materials Science, University of Tokyo, Kashiwa 277-8561, Japan.

We show the directional dichroism in a collinear antiferromagnet MnTiO_{3}. The dichroism between two distinctive antiferromagnetic states with opposite signs of staggered magnetic moments can be regarded as magnetochiral dichroism in the absence of external fields. Electric-field reversal of antiferromagnetic domain causes a change in the absorption intensity of unpolarized light around 2.15 eV. The difference in optical absorption between two antiferromagnetic states is reversed for the light propagating in the opposite direction. The absorption coefficient displays a hysteretic behavior for a cycle of sweeping the external electric or magnetic field.
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http://dx.doi.org/10.1103/PhysRevLett.124.217402DOI Listing
May 2020

Magnetic Tunnel Junctions with a Nearly Zero Moment Manganese Nanolayer with Perpendicular Magnetic Anisotropy.

ACS Appl Mater Interfaces 2018 Dec 6;10(50):43305-43310. Epub 2018 Dec 6.

National Institute of Advanced Industrial Science and Technology (AIST), Spintronics Research Center , Tsukuba 305-8568 , Japan.

A magnetic nanolayer with a perpendicular magnetic easy axis and negligible magnetization is demonstrated. Even though a manganese metal is antiferromagnetic in bulk form, a few manganese monolayers grown on a paramagnetic ordered alloy template and capped by an oxide layer exhibit a strong perpendicular magnetic anisotropy field exceeding 19 T as well as a negligible magnetization of 25 kA/m. The nanolayer shows tunnel magnetoresistance. Moreover, the perpendicular magnetic anisotropy for the nanolayer can be reduced by applying an electric voltage. These findings will provide new insight into a creation of new nanolayer magnets.
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http://dx.doi.org/10.1021/acsami.8b15606DOI Listing
December 2018

Magnetoluminescence in a Photostable, Brightly Luminescent Organic Radical in a Rigid Environment.

Angew Chem Int Ed Engl 2018 Sep 27;57(39):12711-12715. Epub 2018 Jun 27.

Department of Chemistry, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.

We investigated the emission properties of a photostable luminescent organic radical, (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (PyBTM), doped into host molecular crystals. The 0.05 wt %-doped crystals displayed luminescence attributed to a PyBTM monomer with a room-temperature emission quantum yield of 89 %, which is exceptionally high among organic radicals. The 10 wt %-doped crystals exhibited both PyBTM monomer and excimer-centered emission bands, and the intensity ratio of these two bands was modulated drastically by applying a magnetic field of up to 18 T at 4.2 K. This is the first observation of a magnetic field affecting the luminescence of organic radicals, and we also proposed a mechanism for this effect.
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http://dx.doi.org/10.1002/anie.201805466DOI Listing
September 2018

Magnetic Switching by the In Situ Electrochemical Control of Quasi-Spin-Peierls Singlet States in a Three-Dimensional Spin Lattice Incorporating TTF-TCNQ Salts.

Chemistry 2018 Mar 15;24(17):4294-4303. Epub 2018 Feb 15.

Department of Chemistry, Graduate School of Science, Tohoku University, 6-3 Aramaki-Aza-Aoba, Aoba-ku, Sendai, 980-8578, Japan.

Magnetic phase switching in a coordination polymer is reported, which is demonstrated by combining two processes: (A) the pre-organization of magnetic/redox-active molecules into a framework, and (B) a post-treatment through electrochemical tuning of the pre-organized molecules. A TTF -TCNQ salt (TTF=tetrathiafulvalene; TCNQ=7,7,8,8-tetracyano-p-quinodimethane) was incorporated into a three-dimensional framework with paddlewheel-type dimetal(II, II) units ([M ]; M=Ru with S=1, 1; and Rh with S=0, 2), where the [M ] and TCNQ units form the coordinating framework, and TTF is located in the pores of framework, forming an irregular π-stacking alternating column with the TCNQ in the framework. In 1, the spins of [Ru ] and TCNQ units make a magnetic correlation through the framework upon decreasing the temperature from 300 K, which is, however, suddenly suppressed below 137 K (=T (1)) by the formation of a spin singlet in the TTF -TCNQ columns, as seen in the spin-Peierls transition (T (2)=200 K). This material was incorporated as a cathode in a Li-ion battery (LIB); a long-range ferrimagnetic correlation was formed through the three-dimensional [{Ru } TCNQ] framework at T =78 K in the discharge process. The reversible magnetic phase switching between the non-volatile ferrimagnetic and paramagnetic states, resulting from the local spin tuning of quasi-spin-Peierls singlet, is demonstrated through the discharge/charge cycling of the LIB.
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http://dx.doi.org/10.1002/chem.201704815DOI Listing
March 2018

Electron spin resonance spectral analysis of irradiated royal jelly.

Food Chem 2014 Jan 9;143:479-83. Epub 2013 Aug 9.

Osaka University of Pharmaceutical Sciences, 4-20-1 Nasahara, Takatsuki, Osaka 569-1094, Japan. Electronic address:

The analysis of unpaired electron components in royal jelly was carried out using electron spin resonance (ESR) with the aim to develop a detection method for irradiated royal jelly. The ESR spectrum of royal jelly had natural signals derived from transition metals, including Fe(3+) and Cu(2+), and a signal line near g=2.00. After irradiation, a new splitting asymmetric spectrum with overall spectrum width ca. 10mT at g=2.004 was observed. The intensities of the signals at g=2.004 increased in proportion to the absorbed dose in samples under different storage conditions: fresh frozen royal jelly and dried royal jelly powder at room temperature. The signal intensity of the fresh frozen sample was stable after irradiation. One year after 10kGy irradiation of dried powder, the signal intensity was sevenfold greater than before irradiation, although the intensity continued to steadily decrease with time. This stable radiation-induced radical component was derived from the poorly soluble constituent of royal jelly.
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http://dx.doi.org/10.1016/j.foodchem.2013.07.139DOI Listing
January 2014

Possible mechanism of growth inhibition by Scutellaria baicalensis in an estrogen-responsive mouse tumor cell line.

Oncol Rep 2011 May 1;25(5):1431-8. Epub 2011 Mar 1.

Department of Pathology, Research Institute, Osaka Medical Center for Cancer and Cardiovascular Diseases, 1-3-3 Nakamichi, Higashinari 537-8511, Japan.

We have studied the effects of Saiboku-to, a traditional Chinese medicine having suppressive activities for leukotriene production and release, on the proliferation of the estrogen-responsive mouse Leydig tumor cell line B-1F. In our previous reports, it is shown that Saiboku-to promotes, but Scutellaria baicalensis, one of the components (herbs) of Saiboku-to, significantly inhibits the proliferation of B-1F cells in vitro and in vivo, and induces DNA fragmentation and morphological changes such as nuclear aggregation and fragmentation. In this study, we examined telomerase activity, cell cycle, polyunsaturated fatty acid metabolism and expression of nuclear factor κB (NF-κB) in order to determine the mechanism of growth inhibition in B-1F cells treated with Scutellaria baicalensis. Telomerase activity was decreased in a dose-dependent manner in treated B-1F cells. Cellular populations in the sub-G0/G1 and G2/M phases were increased, but those in M phase had no change. Although cyclin D1 mRNA was highly expressed in the presence of estradiol (E2), cyclin A and E mRNA levels did not significantly change. When B-1F cells were treated with Scutellaria baicalensis, expression of cyclin D1 was suppressed and that of p21 was inversely increased. Moreover, Scutellaria baicalensis influenced arachidonic and linoleic acid metabolism, and increased production of 13(S)-HODE. In the presence of E2 Scutellaria baicalensis decreased expression of NF-κB p65 to 0.71-fold in B-1F cells. These results show that Scutellaria baicalensis might induce cell cycle arrest at G1 phase and apoptosis via inhibition of telomerase activity, changes of enzymatic activities in polyunsaturated fatty acid metabolism and suppression of NF-κB.
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http://dx.doi.org/10.3892/or.2011.1196DOI Listing
May 2011

Construction of a novel topological frustrated system: a frustrated metal cluster in a helical space.

Chemistry 2010 Sep;16(36):11139-44

Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.

A novel topologically frustrated pentanuclear cluster helicate [{Cu(II)(μ-L)(3)}(2)Cu(II) (3)(μ(3)-OH)](3+) (L(-)=3,5-bis(2-pyridyl)pyrazolate) has been synthesized and characterized. This cluster has a helical arrangement of ligands around the central metal core. Dzyaloshinsky-Moriya interactions are essential components to observe a gradual magnetization and forbidden transitions of high-field/multi-frequency (HF/MF)-ESR. The origin of the magnetic anisotropy of this compound is influenced by its helical spin structure, and consequently, the Cu(5)-cluster helicate introduces a unique magnetic anisotropy. This observation is a direct evidence of the topological part of the new spin phase in a magnetic system.
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http://dx.doi.org/10.1002/chem.201000676DOI Listing
September 2010

Proliferation of estrogen-responsive mouse tumor cell line B-1F stimulated by Saiboku-to, but inhibited by Scutellaria baicalensis, a component of Saiboku-to.

Oncol Rep 2009 Aug;22(2):257-64

Department of Pathology, Research Institute, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka 537-8511, Japan.

We have demonstrated that the proliferation of estrogen-responsive mouse Leydig tumor cell line B-1F is induced via suppression of 5-lipoxygenase activity followed by decrease of leukotrienes (LTs). Additionally, it has been reported that LTD4 induces apoptosis in B-1F cells. In this study, we examined effects of Saiboku-to, a traditional Chinese medicine having suppressive activities for LT production and release, on the proliferation. Saiboku-to promoted, but Scutellaria baicalensis, one of components (herbs) of Saiboku-to, significantly inhibited the proliferation of B-1F cells in vitro and in vivo. The action of Scutellaria baicalensis in B-1F cells was studied in more detail. Although Scutellaria baicalensis consists of flavonoids, iridoids, volatile oils and others, it and its major constituents had no direct effect on estrogen binding sites in B-1F cells. B-1F cells treated with Scutellaria baicalensis showed morphological changes such as nuclear aggregation and fragmentation. DNA fragmentation was also observed, indicating that Scutellaria baicalensis induces apoptosis in B-1F cells and that it or its constituents might be a good resource for searching new drugs, especially anti-cancer drugs. Moreover, Saiboku-to promoted B-1F cell proliferation, but Scutellaria baicalensis inhibited it, showing complexity of action of traditional Chinese medicines.
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August 2009

Detection of organic free radicals in irradiated Foeniculi fructus by electron spin resonance spectroscopy.

J Nat Med 2009 Jan 1;63(1):28-31. Epub 2008 Aug 1.

Osaka University of Pharmaceutical Sciences, 4-20-1 Nasahara, Takatsuki, Osaka, 569-1094, Japan.

Foeniculi fructus were irradiated with an electron beam and organic free radicals were detected by electron spin resonance (ESR) spectroscopy for the purpose of identifying radio-disinfected and sterilized herbal drugs. An ESR single-line spectrum near g = 2.005 was observed in the sample before irradiation. After irradiation, the intensity of the signal near g = 2.005 increased. In addition, two subsignals derived from cellulose radicals were observed approximately 3 mT to either side of the main signal, at g = 2.023 and g = 1.987. The intensity of the subsignal at g = 2.023 was proportional to the absorbed dose of radiation. The decrease in intensity of the signals was considerable 2 weeks after irradiation, and continued to decrease steadily thereafter. Among the signals, the fading of the subsignal at g = 2.023 was relatively small. The intensity of the subsignal at g = 2.023 was detectable for over 1 year in the sample that had been irradiated to the level of disinfection and sterilization. Therefore, organic free radicals in irradiated Foeniculi fructus can be measured rapidly and with high sensitivity by ESR spectroscopy. The stable signal at g = 2.023 is a promising indicator of the detection of irradiated herbal drugs.
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http://dx.doi.org/10.1007/s11418-008-0284-6DOI Listing
January 2009

Radiofrequency ablation in the treatment of small hepatocellular carcinomas: comparison of the radiofrequency effect with and without chemoembolization.

AJR Am J Roentgenol 2003 Oct;181(4):997-1003

Department of Gastroenterology, Hiroshima Prefectural Hospital, 1-5-54 Ujina-Kanda, Minami-ku, Hiroshima 734-8530, Japan.

Objective: The purpose of this study was to determine whether a combination of transcatheter arterial chemoembolization using doxorubicin and radiofrequency ablation can increase tumor destruction compared with radiofrequency alone in the treatment for hepatocellular carcinoma. SUBJECTS AND METHODS. Twenty-one patients with 26 nodules smaller than 3 cm in diameter were treated with radiofrequency ablation. Of these, 10 nodules were treated with a combination of radiofrequency ablation and chemoembolization using doxorubicin. All nodules were evaluated for size of induced coagulation, local recurrence, and complication.

Results: The therapeutic areas averaged 27.6 x 22.3 mm using an electrode with a 2-cm tip and 37.2 x 29.1 mm using an electrode with a 3-cm tip. With respect to the results for 14 nodules treated using an electrode with a 3-cm tip with or without chemoembolization, the greatest dimension of the area coagulated by combined therapy was significantly larger (longest axis dimension, 39.9 +/- 4.4 mm; shortest axis dimension, 32.3 +/- 5.2 mm; n = 7 nodules) than areas without chemoembolization (longest axis dimension, 34.6 +/- 2.6 mm; shortest axis dimension, 26.0 +/- 3.3 mm; n = 7 nodules) (longest and shortest axis dimensions, p < 0.05). No recurrence occurred in the nodules smaller than 2 cm in diameter. Among the nodules larger than 2 cm in diameter, one local recurrence was observed in seven nodules treated by combined therapy, while two local recurrences were observed in seven nodules treated by radiofrequency alone. Minor complications developed in three patients, two with persistent high fever and one with biliary stenosis.

Conclusion: The combination of radiofrequency ablation and transcatheter arterial chemoembolization using doxorubicin markedly increased the extent of induced coagulation compared with radiofrequency alone, despite a small number of patients and the preliminary nature of this study.
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http://dx.doi.org/10.2214/ajr.181.4.1810997DOI Listing
October 2003
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