Computational protocol for predicting 19F NMR chemical shifts for PFAS and connection to PFAS structure
Computational protocol for predicting 19F NMR chemical shifts for PFAS and connection to PFAS structure
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DOI：
10.1002/jcc.26939
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发表时间：
2022-06
影响因子：
3
通讯作者：
Maleigh Mifkovic;Jessica Pauling;Shubham Vyas
中科院分区：
文献类型：
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作者：
Maleigh Mifkovic;Jessica Pauling;Shubham Vyas
全氟烷基和多氟烷基物质（PFAS）是一种强大的“永久”化学品，由于无法使用传统技术降解，它们已成为全球环境污染物。除了PFAS的持久性外，PFAS结构和功能的多样性给识别和修复带来了独特的挑战。由于许多PFAS缺乏标准，它们的识别变得更加复杂。本研究旨在开发一种利用密度泛函理论（DFT）计算和建立PFAS精确的19F NMR化学位移的协议，这有助于PFAS的识别。通过比较计算数据和实验测量值来评估溶剂化和基集的影响。结果表明，在该方法中加入色散校正后，计算的核磁共振参数精度在实验值的4 ppm以内。增加第二个扩散函数和额外的极化并没有提高精度，可能是因为氟的电负性不允许氟原子的电子密度被极化。包含各种隐式溶剂化（DMSO，氯仿和水）在准确性上产生了可以忽略不计的差异，并且总体上比气相计算更不准确。然后将最准确的方法应用于更环保的PFAS，并评估螺旋性质对核磁共振特征的影响。这项工作的意义是能够改进使用19F核磁共振鉴定结构多样的PFAS。
Per‐ and polyfluoroalkyl substances (PFAS) are robust “forever” chemicals that have become global environmental contaminants due to their inability to degrade using traditional techniques. In addition to the persistent nature of PFAS, the structural and functional diversity in PFAS creates a unique challenge in identification and remediation. Their identification is further complicated by the absence of standards for many PFAS. This work is aimed at developing a protocol for computing and establishing accurate 19F NMR chemical shifts for PFAS using density functional theory (DFT), which can aid in the identification of PFAS. The impact of solvation and basis sets was evaluated by comparing the computed data with the experimental measurements. Results showed the addition of dispersion corrections in the methodology improve the accuracy of calculated NMR parameters within 4 ppm of the experimental values. Adding a second diffuse function and additional polarization did not improve the accuracy, likely because of the electronegativity of fluorine which does not allow the electron density of fluorine atoms to be polarized. The inclusion of various implicit solvation (DMSO, chloroform, and water) yielded negligible differences in accuracy, and were overall less accurate than the gas phase calculations. The most accurate methodology was then applied to more environmentally relevant PFAS, and the impact of helical nature on the NMR signatures was evaluated. The implication of this work is to be able to improve the identification of structurally diverse PFAS using the 19F NMR.