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

doi:10.1016/j.isci.2022.104763

Extended X-ray absorption fine structure spectroscopy measurements and ab initio molecular dynamics simulations reveal the hydration structure of the radium(II) ion

iScience. 2022 Jul 19;25(8):104763. doi: 10.1016/j.isci.2022.104763. eCollection 2022 Aug 19.

Authors

Akiko Yamaguchi^{1

2

3

4}, Kojiro Nagata⁵, Keita Kobayashi¹, Kazuya Tanaka², Tohru Kobayashi⁴, Hajime Tanida⁴, Kojiro Shimojo⁴, Tetsuhiro Sekiguchi⁴, Yui Kaneta⁴, Shohei Matsuda⁴, Keiichi Yokoyama⁴, Tsuyoshi Yaita⁴, Takashi Yoshimura⁵, Masahiko Okumura¹, Yoshio Takahashi³

Affiliations

¹ Center for Computational Science and e-Systems, Japan Atomic Energy Agency, 148-4 Kashiwanoha Campus, 178-4 Wakashiba, Kashiwa, Chiba 277-0871, Japan.
² Advanced Science Research Center, Japan Atomic Energy Agency, 2-4 Shirakata, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan.
³ Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan.
⁴ Materials Sciences Research Center, Japan Atomic Energy Agency, 2-4 Shirataka, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan.
⁵ Radioisotope Research Center, Institute for Radiation Sciences, Osaka University, 2-4 Yamadaoka, Suita, Osaka 565-0871, Japan.

Abstract

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.

Keywords: Molecular dynamics; Nuclear spectroscopy; Nuclear structure.