(609b) Computational Design of Macrocyclic Sorbents for Effective Removal of Chlorinated Volatile Organic Compounds (CVOCs) and 1,4-Dioxane from Groundwater.

Chlorinated volatile organic compounds (CVOCs) and 1,4-dioxane are common contaminants found in Superfund sites and are considered high-priority substances by the CDC’s Substance Priority List due to their potential for toxic human exposure. The contamination of water resources by these substances due to industrial activity has received substantial attention in the recent years. While cost-effective bioremediation solutions are in high demand, a significant challenge is that mixtures of CVOCs and 1,4-dioxane are unfeasible for bioremediation due to a) requirement of aerobic conditions for 1,4-dioxane metabolism but anaerobic conditions for most CVOC metabolisms b) inhibition of 1,4-dioxane biodegradation in presence of CVOCs. Commercial adsorbents such as granular activated carbon (GAC) and AMBERSORB are unable to effectively separate mixtures of these contaminants, resulting in need for new adsorbent materials. Macrocycle-based sorbents offer a promising solution for selectively separating CVOCs and 1,4-dioxane through unique host-guest chemistries that leverage their internal hydrophobicity. Among these, pillararenes are attractive candidates as adsorbents due to their reported ability to selectively adsorb 1,4-dioxane and higher adsorption capacity than GAC and AMBERSORB. The conformational flexibility of pillararenes resulting from rotation of phenyl units is an influential factor on internal structure dynamics, relative conformer abundance, and energetics for adsorption. In this work, we have considered pillararenes of different aperture size and functionalization to investigate conformation energetics as well as uptake of CVOCs and 1,4-dioxane. We used density functional theory to study various motifs in adsorbate binding. In addition, we employed nudged elastic band calculations to investigate the viability of adsorption pathways for the target adsorbates. Our simulation results suggest that addition of functional groups on macrocycles can result in variations in energetics of pillararene conformers, leading to qualitatively different dominant conformers between various functionalized pillararenes. Additionally, our models predict differences in binding energies for adsorption of target adsorbates on different pillararenes. This provides the basis for postulating equilibrium selectivities of these adsorbents for various target adsorbates. Furthermore, our results reveal no significant energetic barriers related to adsorption of target adsorbates in cavities of various pillararenes. Overall, this study enhances our understanding of the relevant physics related to adsorption in pillararenes and lays the groundwork for extending our modeling to other macrocyclic adsorbents.