Enhanced host–guest complexation of short chain perfluoroalkyl substances with positively charged β-cyclodextrin derivatives

Abstract

Short chain perfluoroalkyl substances (PFAS), replacements for long chain legacy PFAS such as perfluorooctanoic acid (PFOA), have similar toxicity, negative health effects, and exceptional persistence as long chain PFAS. β-Cyclodextrin (β-CD) is a powerful host–guest complexing agent for a number of legacy PFAS, suggesting potential β-CD-based remediation processes. We report herein that the addition of charged functional groups at the perimeter of β-CD has a pronounced influence on the strength of the β-CD:PFAS complex. The presence of a positively charged amine functionality on the perimeter of β-CD significantly increases the complexation of legacy and short chain PFAS. We assigned the enhanced complexation to electrostatic attraction between the negatively charged PFAS head group and the positively charged β-CD derivative. In comparison to neutral β-CD, addition of a negative charge to β-CD decreases complexation to PFAS due to electrostatic repulsion between the negatively charged polar head group of PFAS and the negatively charged β-CD. 19F NMR titration experiments illustrate the complexation of short chain PFAS by positive charged β-CDs over neutral β-CD, with increases up to 20 times depending on the PFAS guest. The results give further understanding to the nature of the β-CD:PFAS host–guest complex and the various intermolecular forces that drive complexation. Positively charged β-CDs appear to be potential complexing agents for remediation of short chain PFAS.