The interpretation of ion mobility coupled to mass spectrometry (IM-MS) data to predict unknown structures is challenging and depends on accurate theoretical estimates of the molecular ion collision cross section (CCS) against a buffer gas in a low or atmospheric pressure drift chamber. The sensitivity and reliability of computational prediction of CCS values depend on accurately modeling the molecular state over accessible conformations. In this work, we developed an efficient CCS computational workflow using a machine learning model in conjunction with standard DFT methods and CCS calculations. Furthermore, we have performed Traveling Wave IM-MS (TWIMS) experiments to validate the extant experimental values and assess uncertainties in experimentally measured CCS values. The developed workflow yielded accurate structural predictions and provides unique insights into the likely preferred conformation analyzed using IM-MS experiments. The complete workflow makes the computation of CCS values tractable for a large number of conformationally flexible metabolites with complex molecular structures.

In recent years, there have been increasing initiatives undertaken worldwide to employ alternative per- and polyfluoroalkyl substances (PFAS) molecules in order to minimize the environmental and health effects associated with legacy PFAS molecules. Hexafluoropropylene oxide dimer acid (HFPO-DA), commonly known as GenX, is one of the important replacements currently used for PFOA. However, growing investigations suggest that GenX is identified in natural settings, including soils and groundwater, thus emphasizing the need to understand their sorption behavior in these environments. This study provides molecular-level insights into the impact of three different common soil constituents, namely, clay minerals, that vary in mineralogical composition and surface charge distribution in dictating the adsorption and transport characteristics of GenX on a fundamental molecular level for the first time using molecular dynamics simulations. The surface complexation of GenX varies significantly between the three clay minerals, and the factors that dictate the complexation are completely different. Depending upon the clay minerals, both surface-adsorbed and solution-phase GenX are observed. Importantly, the interfacial structure, nearest neighbor coordination, and dynamic behavior of GenX and their correlation with legacy PFAS in minerals systems are presented.