Shimoaka Takafumi, Ootsuki Masashi, Yamaguchi Yuta, Shioya Nobutaka, Hasegawa Takeshi
Division of Materials and Environment, Graduate School of Science and Technology, Gunma University, 1-5-1, Tenjin-cho, Kiryu, Gunma, 376-8515, Japan.
Division of Environmental Chemistry, Institute for Chemical Research (ICR), Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan.
Anal Sci. 2025 Aug;41(8):1355-1364. doi: 10.1007/s44211-025-00797-7. Epub 2025 Jun 5.
Recently, unique surface properties of poly- and perfluoroalkyl substances (PFAS) have been revealed to be derived from a two-dimensional (2D) packing of perfluoroalkyl (R) groups with perpendicularly standing orientation, i.e., the end-on orientation, which is revealed by the stratified dipole arrays (SDA) model. This indicates that analysis of the 2D aggregation of R groups is crucial for understanding the PFAS-specific properties, and analysis of the primary structure alone is insufficient. In the present study, we employ an analytical method of backscattering Raman spectrometry to explore the 2D aggregation of R groups in terms of molecular orientation. Measurements of solid particles of perfluoro-n-alkane with theoretical consideration of the Raman activity on backscattering optical arrangement make us find useful marker bands derived from the R groups. Analysis of the band enables us to determine the end-on orientation of the R chain about the surface of bulk PFAS: when the R chains are end-on oriented, the bands assigned to a specific symmetry species selectively disappear, whereas the other Raman-active bands remain. In short, the disappearance of the marker bands makes us determine the end-on orientation very easily. In addition, we demonstrate that the marker band can be used to visualize in-plane distribution of the end-on orientation by utilizing mapping measurements.
最近，聚氟烷基和全氟烷基物质（PFAS）独特的表面性质被揭示源于全氟烷基（R）基团以垂直站立取向，即端对端取向的二维（2D）堆积，这是由分层偶极子阵列（SDA）模型揭示的。这表明对R基团二维聚集的分析对于理解PFAS的特定性质至关重要，仅分析一级结构是不够的。在本研究中，我们采用背散射拉曼光谱分析法，从分子取向方面探索R基团的二维聚集。对全氟正构烷烃固体颗粒的测量以及对背散射光学装置上拉曼活性的理论考虑，使我们找到了源自R基团的有用标记带。对该谱带的分析使我们能够确定R链在块状PFAS表面的端对端取向：当R链呈端对端取向时，分配给特定对称物种的谱带会选择性消失，而其他拉曼活性谱带则保留。简而言之，标记带的消失使我们能够非常容易地确定端对端取向。此外，我们证明通过利用映射测量，标记带可用于可视化端对端取向的面内分布。
