ハイドレートの水分子カゴ状構造、カゴの分子が同じでも複数の形をとることを発見～環境にやさしいエネルギー・環境材料設計に向けた水分子の結晶構造制御に新しい視点～

2025-10-23 産業技術総合研究所

チアン分子が異なるハイドレート構造を誘起するイメージ図
結晶構造可視化ソフトVESTA（https://jp-minerals.org/vesta/en/）を使用して作成

＜関連情報＞

• https://www.aist.go.jp/aist_j/press_release/pr2025/pr20251023/pr20251023.html
• https://onlinelibrary.wiley.com/doi/10.1002/sstr.202500470

水骨格の構造的柔軟性：単一の大きなゲスト誘導構造Hおよび構造IIハイドレート構造 Structural Flexibility of Water Frameworks: A Single Large Guest-Inducing Structure-H and Structure-II Hydrate Structures

Yusuke Jin, Hiroshi Fujihisa, Masato Kida, Satoshi Takeya, Jiro Nagao
Small Structures  Published: 17 October 2025
DOI:https://doi.org/10.1002/sstr.202500470

Abstract

A unique clathrate hydrate system in which a single guest molecule, thiane, induces the formation of both structure-II (sII) and structure-H (sH) hydrates under different thermodynamic conditions is reported. According to the experimental phase equilibrium data, the sII hydrate is thermodynamically more stable than the sH hydrate at lower temperatures. However, only the sH hydrate forms first from CH₄–water–thiane mixtures, revealing a discrepancy between thermodynamic stability and actual crystallization behavior. Raman spectroscopy, supported by density functional theory and energy calculations using the COMPASS III force field, confirms that thiane adopts the chair conformation in both sII and sH hydrate structures. Among the CH₄, CO₂, and CH₄/CO₂ systems, only CH₄ forms an sH hydrate with thiane, indicating that the crystallization pathway is likely small guest dominant and governed by the nucleation process. Collectively, these findings highlight the thiane hydrate system as a valuable model for investigating structural adaptability and host–guest interactions across different clathrate frameworks.