Barbosa Gabriel D, Tavares Frederico W, Striolo Alberto
School of Sustainable Chemical, Biological and Materials Engineering, The University of Oklahoma, Norman, Oklahoma 73019, United States.
Escola de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 21941-909, Brazil.
J Chem Theory Comput. 2024 Aug 14. doi: 10.1021/acs.jctc.4c00459.
Per- and polyfluoroalkyl substances (PFAS) constitute a class of synthetic compounds with exceptional interfacial properties. Their widespread use in many industrial applications and consumer products, combined with their remarkable chemical and thermal stability, has led to their ubiquitous presence in environmental matrices, including surface water and groundwater. To replace PFAS with fluorine-free surfactants, it is necessary first to develop a deep molecular-level understanding of the mechanisms responsible for the exceptional properties of PFAS. For instance, it has been shown that fluorine-free surfactants with highly branched or methylated chains can achieve low surface tensions at air-water interfaces and can provide highly hydrophobic surface coatings. Although molecular simulations combined with experiments are promising for uncovering these mechanisms, the reliability of simulation results depends strongly on the accuracy of the force fields implemented. At the moment, atomistic force fields are not available to describe PFAS in a variety of environments. Ab initio methods could help fill this knowledge gap, but they are computationally demanding. As an alternative, ab initio calculations could be used to develop accurate force fields for atomistic simulations. In this work, a new algorithm is proposed, which, built from accurate ab initio calculations, yields force fields for perfluorinated sulfonic and perfluoroalkyl acids. The accuracy of the new force field was benchmarked against solvation free energy and interfacial tension data. The new force fields were then used to probe the interfacial behavior of the PFAS surfactants. The interfacial properties observed in our simulations were compared with those manifested by two branched fluorine-free surfactants. The good agreement achieved with experiments and ab initio calculations suggests that the proposed protocol could be implemented to study other perfluorinated substances and help in the design of fluorine-free surfactants for targeted applications.
全氟和多氟烷基物质（PFAS）是一类具有特殊界面性质的合成化合物。它们在许多工业应用和消费品中广泛使用，再加上其卓越的化学和热稳定性，导致它们普遍存在于环境介质中，包括地表水和地下水。要用无氟表面活性剂替代PFAS，首先有必要深入从分子层面了解导致PFAS具有特殊性质的机制。例如，已表明具有高度支化或甲基化链的无氟表面活性剂在气-水界面可实现低表面张力，并能提供高度疏水的表面涂层。虽然分子模拟与实验相结合有望揭示这些机制，但模拟结果的可靠性在很大程度上取决于所采用力场的准确性。目前，尚无原子力场可用于描述多种环境中的PFAS。从头算方法有助于填补这一知识空白，但计算量很大。作为一种替代方法，可使用从头算计算来开发用于原子模拟的精确力场。在这项工作中，提出了一种新算法，该算法基于精确的从头算计算构建，可生成全氟磺酸和全氟烷基酸的力场。新力场的准确性以溶剂化自由能和界面张力数据为基准进行了验证。然后使用新力场来探究PFAS表面活性剂的界面行为。将我们模拟中观察到的界面性质与两种支化无氟表面活性剂表现出的性质进行了比较。与实验和从头算计算取得的良好一致性表明，所提出的方案可用于研究其他全氟化物，并有助于设计用于特定应用的无氟表面活性剂。
