Thermodynamic and Structural Insights into Endocrine Disruptor Adsorption

Endocrine disrupting chemicals (EDCs) pose a significant threat to human health and to the environmentat very low concentrations due to their ability to mimic natural hormones. Adsorption-based removal of EDCs from water is an increasingly attractive decontamination strategy, yet the structural and chemical factors governing the binding of these molecules to common adsorbents remain poorly understood. In this work, we employ well-tempered metadynamics simulations to compute the free energies of adsorption for 12 EDCs on the surface of a single-walled carbon nanotube (SW-CNT). We find that binding free energies correlate broadly with the number of electrons, reflecting the importance of dispersion interactions, but that this relationship has several notable exceptions. Conformational flexibility is identified as an additional critical factor: molecules bearing two aromatic groups connected via a heteroatom (oxygen or nitrogen) can adopt coplanar configurations that maximize π-stacking interactions with the CNT surface, leading to substantially stronger binding. Conversely, sterically rigid molecules, regardless of the presence of aromatic groups or increased number of electrons, bind weakly to the CNT surface. These findings demonstrate that both the chemical composition and conformational flexibility of an EDC must be considered when evaluating the suitability of CNT-based adsorbents for water decontamination applications, as well as showing the importance of extensive computational studies as complementary to experiment.