Formation and Evolution of Carbonaceous Asteroid Ryugu: Direct Evidence from Returned Samples

T. Nakamura, K. Ninomiya, I. Chiu, et al.
Science, 2022 in press. DOI: 10.1126/science.abn8671

Samples of the carbonaceous asteroid Ryugu were brought to Earth by the Hayabusa2 spacecraft. We analyzed seventeen Ryugu samples measuring 1-8 mm. CO2-bearing water inclusions are present within a pyrrhotite crystal, indicating that Ryugu’s parent asteroid formed in the outer Solar System. The samples contain low abundances of materials that formed at high temperatures, such as chondrules and Ca, Al-rich inclusions. The samples are rich in phyllosilicates and carbonates, which formed by aqueous alteration reactions at low temperature, high pH, and water/rock ratios < 1 (by mass). Less altered fragments contain olivine, pyroxene, amorphous silicates, calcite, and phosphide. Numerical simulations, based on the mineralogical and physical properties of the samples, indicate Ryugu’s parent body formed ~ 2 million years after the beginning of Solar System formation.


  • 大阪大学ホームページResOU
  • JAXAプレスリリース
  • KEKプレスリリース

  • Extended X-ray Absorption Fine Structure Spectroscopy Measurements and ab initio Molecular Dynamics Simulations Reveal the Hydration Structure of the Radium(II) Ion

    Akiko Yamaguchi,* Kojiro Nagata, Keita Kobayashi, Kazuya Tanaka, Tohru Kobayashi, Hajime Tanida, Kojiro Shimojo, Tetsuhiro Sekiguchi, Yui Kaneta, Shohei Matsuda, Keiichi Yokoyama, Tsuyoshi Yaita, Takashi Yoshimura, Masahiko Okumura, Yoshio Takahashi
    iScience, 2022, 25, 104763. DOI: 10.1016/j.isci.2022.104763

    Radium is refocused from the viewpoint of an environmental pollutant and cancer therapy using alpha particles, where it mainly exists as a hydrated ion. We investigated the radium hydration structure and the dynamics of water molecules by extended X-ray absorption fine structure (EXAFS) spectroscopy and ab initio molecular dynamics (AIMD) simulation. The EXAFS experiment showed that the coordination number and average distance between radium ion and the oxygen atoms in the first hydration shell are 9.2 ± 1.9 and 2.87 ± 0.06 Å , respectively. They are consistent with those obtained from the AIMD simulations, 8.4 and 2.88 Å . The AIMD simulations also revealed that the water molecules in the first hydration shell of radium are less structured and more mobile than those of barium, which is an analogous element of radium. Our results indicate that radium can be more labile than barium in terms of interactions with water.


  • 大阪大学ホームページResOU
  • JAEAプレスリリース

  • Comparison of the Therapeutic Effects of [211At]NaAt and [131I]NaI in an NIS-Expressing Thyroid Cancer Mouse Model

    Tadashi Watabe, Yuwei Liu, Kazuko Kaneda-Nakashima, Tatsuhiko Sato, Yoshifumi Shirakami, Kazuhiro Ooe, Atsushi Toyoshima, Eku Shimosegawa, Yang Wang, Hiromitsu Haba, Takashi Nakano, Atsushi Shinohara, Jun Hatazawa
    Int. J. Mol. Sci., 2022, 23, 9434. DOI: 10.3390/ijms23169434

    Astatine (211At) is an alpha-emitter with a better treatment efficacy against differentiated thyroid cancer compared with iodine (131I), a conventional beta-emitter. However, its therapeutic comparison has not been fully evaluated. In this study, we compared the therapeutic effect between [211At]NaAt and [131I]NaI. In vitro analysis of a double-stranded DNA break (DSB) and colony formation assay were performed using K1-NIS cells. The therapeutic effect was compared using K1-NIS xenograft mice administered with [211At]NaAt (0.4 MBq (n = 7), 0.8 MBq (n = 9), and 1.2 MBq (n = 4)), and [131I]NaI (1 MBq (n = 4), 3 MBq (n = 4), and 8 MBq (n = 4)). The [211At]NaAt induced higher numbers of DSBs and had a more reduced colony formation than [131I]NaI. In K1-NIS mice, dose-dependent therapeutic effects were observed in both [211At]NaAt and [131I]NaI. In [211At]NaAt, a stronger tumour-growth suppression was observed, while tumour regrowth was not observed until 18, 25, and 46 days after injection of 0.4, 0.8, and 1.2 MBq of [211At]NaAt, respectively. While in [131I]NaI, this was observed within 12 days after injection (1, 3, and 8 MBq). The superior therapeutic effect of [211At]NaAt suggests the promising clinical applicability of targeted alpha therapy using [211At]NaAt in patients with differentiated thyroid cancer refractory to standard [131I]NaI treatment.


    Tuning the Ground- and Excited-State Redox Potentials of Octahedral Hexanuclear Rhenium(III) Complexes by the Combination of Terminal Halide and N-Heteroaromatic Ligands

    Takashi Yoshimura,* Hayato Nishizawa, Kojiro Nagata, Akitaka Ito, Eri Sakuda, Shoji Ishizaka, Noboru Kitamura, Atsushi Shinohara
    ACS Omega, 2022, 7, 26965 − 26982. DOI: 10.1021/acsomega.2c03834

    The present study reports that the ground- and excited-state Re6(23e)/ReRe6(24e) redox potentials of an octahedral hexanuclear rhenium(III) complex can be controlled by systematically changing in the number and type of the N-heteroaromatic ligand (L) and the number of chloride ions at the six terminal positions. Photoirradiation of [Re63-S)8Cl6]4– with an excess amount of L afforded a mono-L-substituted hexanuclear rhenium(III) complex, [Re63-S)8Cl5(L)]3– (L = 4-dimethylaminopyridine (dmap), 3,5-lutidine (lut), 4-methylpyridine (mpy), pyridine (py), 4,4ʹ-bipyridine (bpy), 4-cyanopyridine (cpy), and pyrazine (pz)). The bis- and tris-lut-substituted complexes, trans- and cis-[Re63-S)8Cl4(lut)2]2– and mer-[Re63-S)8Cl3(lut)3], were synthesized by the reaction of [Re63-S)8Cl6]3– with an excess amount of lut in refluxed N,N-dimethylformamide. The mono-L-substituted complexes showed one-electron redox processes assignable to E1/2[Re6(23e)/Re6(24e)] = 0.49–0.59 V vs. Ag/AgCl. The ground-state oxidation potentials were linearly correlated with the pKa of the N-heteroaromatic ligand [pKa(L)], the 1H NMR chemical shift of the ortho proton on the coordinating ligand, and the Hammett constant (σ) of the pyridyl-ligand substituent. The series of [Re63-S)8X6–n(L)n]n–4 complexes (n = 0, X = Cl, Br, I, or NCS; n = 1–3, X = Cl) showed a linear correlation with the sum of the Lever electrochemical parameters at the six terminal ligands (ΣEL). The cyclic voltammograms of the mono-L-substituted complexes (L = bpy, cpy, and pz) showed one-electron redox waves assignable to E1/2(L0/L) = –1.28 to –1.48 V vs. Ag/AgCl. Two types of photoluminescences were observed for the complexes, originating from the cluster core-centered excited triplet state (3CC) for L = dmap, lut, mpy, and py, and from the metal-to-ligand charge-transfer excited triplet state (3MLCT) for L = bpy, cpy, and pz. The complexes with the 3CC character exhibited emission features and photophysical properties similar to those of ordinal hexanuclear rhenium complexes. The emission maximum wavelength of the complexes with 3MLCT shifted to the longer-wavelength in the order L = 4-phenylpyridine (ppy), bpy, cpy, and pz, which agreed with the difference between E1/2[Re6(23e)/Re6(24e)] and E1/2(L0/L). The calculated oxidation potential of the excited hexanuclear rhenium complex with the 3CC character was linearly correlated with pKa(L), σ, and ΣEL. The ground- and excited-state oxidation potentials were finely tuned by the combination of halide and L ligands at the terminal positions.


    Eight-Year Variations in Atmospheric Radiocesium in Fukushima City

    Akira Watanabe, Mizuo Kajino, Kazuhiko Ninomiya, Yoshitaka Nagahashi, Atsushi Shinohara
    Atmos. Chem. Phys., 2022, 22, 675 − 692. DOI: 10.5194/acp-22-675-2022

    After the Fukushima nuclear accident, atmospheric 134Cs and 137Cs measurements were taken in Fukushima city for 8 years, from March 2011 to March 2019. The airborne surface concentrations and deposition of radiocesium (radio-Cs) were high in winter and low in summer; these trends are the opposite of those observed in a contaminated forest area. The effective half-lives of 137Cs in the concentrations and deposition before 2015 (0.754 and 1.30 years, respectively) were significantly shorter than those after 2015 (2.07 and 4.69 years, respectively), which was likely because the dissolved radio-Cs was discharged from the local terrestrial ecosystems more rapidly than the particulate radio-Cs. In fact, the dissolved fractions of precipitation were larger than the particulate fractions before 2015, but the particulate fractions were larger after 2016. X-ray fluorescence analysis suggested that biotite may have played a key role in the environmental behavior of particulate forms of radio-Cs after 2014. However, the causal relationship between the seasonal variations in particle size distributions and the possible sources of particles is not yet fully understood. The current study also proposes an evaluation method of the consistency of a numerical model for radio-Cs resuspension and suggests that improvements to the model are necessary.


    Negative Muon Spin Rotation and Relaxation Study on Battery Anode Material, Spinel Li4Ti5O12

    Izumi Umegaki, Kazuki Ohishi, Takehito Nakano, Shoichiro Nishimura, Soshi Takeshita, Akihiro Koda, Kazuhiko Ninomiya, M. Kenya Kubo, Jun Sugiyama
    J. Phys. Chem. C, 2022, 126, 10506-10514. DOI: 10.1021/acs.jpcc.2c02055

    To study an intrinsic self-diffusion coefficient of Li+ (DLiJ) in a battery anode material, spinel Li4Ti5O12, negative and positive muon spin rotation and relaxation (μ±SR) spectra were measured using a powder sample in a temperature range of 100–400 K. The implanted μ+ in this study locates at an interstitial site near the O2– ion to form an O–H like bond, whereas the implanted μ is mainly captured by an oxygen nucleus, resulting in muonic oxygen formation. The μ+ at an interstitial site is known to diffuse at high temperatures. Nevertheless, the muonic oxygen is immobile until the spinel decomposition temperature. The field fluctuation rate determined with μSR (ν) increased with increasing temperature above 200 K with a 0.08(5) eV thermal activation energy. The ν(T) curve agreed well with the ν+(T) curve obtained with μ+SR. Thus, the origin of a fluctuation in the internal nuclear magnetic field was unambiguously confirmed as Li+ diffusion, i.e., the possibility of μ+ diffusion is clearly excluded. From the obtained ν±, DLiJ was estimated to be 8(2) × 10–12 cm2/s at 300 K with Ea = 0.08 eV, under the assumption that the Li+ ions at the regular tetrahedral site jump to the vacant octahedral site with a random walk process.


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  • Non-destructive 3D Imaging Method Using Muonic X-rays and a CdTe Double-Sided Strip Detector

    I-Huan Chiu, Shin’ichiro Takeda, Meito Kajino, Atsushi Shinohara, Miho Katsuragawa, Shunsaku Nagasawa, Ryota Tomaru, Goro Yabu, Tadayuki Takahashi, Shin Watanabe, Soshi Takeshita, Yasuhiro Miyake, Kazuhiko Ninomiya
    Sci. Rep., 2022, 12, 5261. DOI: 10.1038/s41598-022-09137-5

    Elemental analysis based on muonic X-rays resulting from muon irradiation provides information about bulk material composition without causing damage, which is essential in the case of precious or otherwise unreachable samples, such as in archeology and planetary science. We developed a three-dimensional (3D) elemental analysis technique by combining the elemental analysis method based on negative muons with an imaging cadmium telluride double-sided strip detector (CdTe-DSD) designed for the hard X-ray and soft \gamma-ray observation. A muon irradiation experiment using spherical plastic samples was conducted at the Japan Proton Accelerator Research Complex (J-PARC); a set of projection images was taken by the CdTe-DSD, equipped with a pinhole collimator, for different sample rotation angles. The projection images measured by the CdTe-DSD were utilized to obtain a 3D volumetric phantom by using the maximum likelihood expectation maximization algorithm. The reconstructed phantom successfully revealed the 3D distribution of carbon in the bulk samples and the stopping depth of the muons. This result demonstrated the feasibility of the proposed non-destructive 3D elemental analysis method for bulk material analysis based on muonic X-rays.


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  • Synthesis, Structures, and Equilibrium Reactions of La(III) and Ba(II) Complexes with Pyridine Phosphonate Pendant Arms on a Diaza-18-crown-6 Ether

    Kazuaki Baba, Kojiro Nagata, Tatsuo Yajima, and Takashi Yoshimura*
    Bull. Chem. Soc. Jpn., 2022, 95, 466-475. DOI: 10.1246/bcsj.20210414

    Structures of La(III) and Ba(II) complexes and their stabilities were investigated to develop a stable chelating ligand for Ac(III) and Ra(II) which are of interest in nuclear medicine using alpha particles. The La(III) and Ba(II) complexes (1 and 2) with a diaza-18-crown-6 ether bearing pyridine phosphonic acid ethyl ester pendant arms (L1) and the complexes (3 and 4) with a diaza-18-crown-6 ether bearing pyridine phosphonate pendant arms ((H2L2)2−) were synthesized and characterized. The structures of the new complexes were determined by single-crystal X-ray analysis. The La(III) complexes, 1 and 3, exhibited 11-coordinate structures, whereas the Ba(II) complexes, 2 and 4 exhibited 11- and 10-coordinate geometries, respectively. Potentiometric titrations were performed to determine the acid–base equilibrium and the complex formation reactions of the La(III) and Ba(II) complexes. In addition, the speciation of the complexes and the pH dependencies of the fractions in the aqueous solutions were performed. For the La(III) complexes, the species with the ligand bearing pyridine phosphonate pendant arms were observed to be more stable than those with the ligand bearing pyridine phosphonate ester pendant arms. The Ba(II) complexes showed the opposite trend. The species with the pyridine phosphonate ester ligand were observed to be more stable than the species with the pyridine phosphonate type ligand.


    Multi-Modal 3D Imaging of Radionuclides Using Multiple Hybrid Compton Cameras

    Akihisa Omata, Miho Masubuchi, Nanase Koshikawa, Jun Kataoka, Hiroki Kato, Atsushi Toyoshima, Takahiro Teramoto, Kazuhiro Ooe, Yuwei Liu, Keiko Matsunaga, Takashi Kamiya, Tadashi Watabe, Eku Shimosegawa, and Jun Hatazawa
    Sci. Rep., 2022, 12, 2546. DOI: 10.1038/s41598-022-06401-6

    For radiological diagnosis and radionuclide therapy, X-ray and gamma-ray imaging technologies are essential. Single-photon emission tomography (SPECT) and positron emission tomography (PET) play essential roles in radiological diagnosis, such as the early detection of tumors. Radionuclide therapy is also rapidly developing with the use of these modalities. Nevertheless, a limited number of radioactive tracers are imaged owing to the limitations of the imaging devices. In a previous study, we developed a hybrid Compton camera that conducts simultaneous Compton and pinhole imaging within a single system. In this study, we developed a system that simultaneously realizes three modalities: Compton, pinhole, and PET imaging in 3D space using multiple hybrid Compton cameras. We achieved the simultaneous imaging of Cs-137 (Compton mode targeting 662 keV), Na-22 (PET mode targeting 511 keV), and Am-241 (pinhole mode targeting 60 keV) within the same field of view. In addition, the imaging of Ga-67 and In-111, which are used in various diagnostic scenarios, was conducted. We also verified that the 3D distribution of the At-211 tracer inside a mouse could be imaged using the pinhole mode.


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