Date: 16:00-18:00, Friday, November 28, 2025
講演者：藤田 了
Speaker: Satoru Fujita
タイトル: ICP質量分析計内で起こるメタンを原料とした炭素カテネーションの検証
Title : Verification of Carbon Catenation from Methane using ICP-MS
要旨:
誘導結合プラズマ質量分析法(ICP-MS)において、コリジョンリアクションセル(CRC)は一般的に測定対象以外のイオンによる干渉スペクトルの除去を目的として用いられる。これに対し、平田研究室ではCRCから有機試料を導入し、第一四重極フィルター(Q1)で選択された一次イオンと衝突させることでICP-MSで有機化合物を測定する手法を開発した(Hirata et al., 2024)。
本研究では初期太陽系を構成する主要物質の一つであるメタンに一次イオンとしてアルゴンイオンを衝突させ、炭素のカテネーションがどのように起こるか検証を行った。その結果、メタンの濃度を変えることで異なる質量範囲でピークが検出された。また、検出されたピークに周期性があるかどうかを確認するためにケンドリック質量解析法(Kendrick et al., 1963)を用いてプロットを行った。
Speaker: Mika YOSHIOKA
Title: Enantiomer–Racemate Separation in Alanine Aqueous Solutions Triggered by Formation of High-Pressure Ice
To explain the origin of amino-acid homochirality, it is essential to identify mechanisms capable of amplifying a small initial excess of the L-enantiomers. While evaporation-driven crystallization is known to enrich excess enantiomers (Breslow and Levine, 2006), it is unclear whether this kind of process occurs under high-pressure conditions, such as inside icy planetary bodies. In this study, I focused on the differences between enantiomeric crystals and racemic crystals and examined how they behave under high-pressure conditions.
Compressibility measurements using a diamond anvil cell showed that L-alanine crystals are more compressible than DL-alanine. In addition, solubility measurements up to 0.8 GPa revealed contrasting pressure responses: L-alanine becomes about 20% more soluble, whereas the DL-alanine solubility remains constant. Thermodynamic considerations indicate that the pressure-induced difference in solubility between L-alanine and DL-alanine arises from the pressure-dependent volume difference.
Moreover, to investigate the precipitation behavior of alanine from an aqueous solution at pressures where liquid water coexists with high-pressure ice, four types of alanine aqueous solutions with different L:D ratios were compressed up to about 2.5 GPa. Upon compression, ice VI first appeared and subsequently transformed into ice VII. Alanine crystals precipitated, triggered by the formation of ice VI. The crystallization behavior of alanine was found to depend strongly on the enantiomeric composition of the solution. In the L:D = 10:0 and 9:1 systems, only L-alanine crystallized, while in the L:D = 7:3 and 5:5 systems, only DL-alanine crystallized.
To determine which phase precipitates when high-pressure ice begins to form, I modeled the concentration increase caused by the removal of liquid water. As high-pressure ice precipitates, the decrease in liquid water increases the concentration of alanine. Using measured solubilities at the pressure where ice VI first appears, precipitation conditions for L- and DL-alanine can be estimated. This model predicts that L-alanine crystallizes first in 10:0 and 9:1 solutions, whereas DL-alanine crystallizes first in 7:3 and 5:5 solutions—consistent with high-pressure experiments.
These results suggest a mechanism for enantiomer-racemate separation accompanied by the precipitation of high-pressure ice. Such selective crystallization during high-pressure ice formation provides a plausible pathway for amplifying small initial L-excesses in icy planetary environments.