Products Cited in Publications Worldwide Modulation of Host-Guest Complexation of Pfas with Ph Ionizable Β-Cyclodextrin Derivatives

Modulation of Host-Guest Complexation of Pfas with Ph Ionizable Β-Cyclodextrin Derivatives

O'Shea, KE; Restrepo-Osorio, Rodrigo

DOI:

Abstract

Poly- and perfluoroalkyl substances (PFAS) are pollutants of serious concern due to their adverse health effects, widespread use, and resistance to degradation. β-cyclodextrins (β-CDs) form strong β-CD:PFAS complexes with a wide variety of PFAS. We report herein the incorporation of ionizable functional groups on the primary rim of β-CD, to control the complexation of PFAS as a function of solution pH. The binding constants (KCD:PFAS) of short-chain and long-chain PFAS by amino-β-CDs and thiol-β-CDs decrease by 56 to 98 % with a change in solution pH from neutral to alkaline conditions. The observed reduction in binding constants (KCD:PFAS) with increased pH is assigned to the increased electrostatic repulsion between negatively charged functional group amended to the β-CD (host) and negatively charged PFAS polar head group (guest) under alkaline conditions. The inclusion of two pH-dependent ionizable functional groups to the host was achieved by employing 6-(3-hydroxybenzylamino)-6-deoxy-β- cyclodextrin [(3-OH)BnNHβ-CD]. The phenol functionality is converted from a neutral to an anionic species while the benzyl-amino group is cationic under neutral pH and converted to neutral charge under alkaline conditions, thus the β-CD host can be converted from a positive charge to a negative charge by varying solution pH. The (3-OH)BnNHβ-CD exhibits strong pH-modulated binding with long-chain perfluorocarboxylic acids (PFCAs), evidenced in an 88 % decrease in the association constant with PFOA under alkaline conditions. The association constant for (3-OH)BnNHβ-CD with hexafluoropropylene oxide dimer acid (HFPO-DA), a branched perfluoroether carboxylic acid (PFECA), however, decreases by nearly 50 % under alkaline conditions compared to an 81 % and 98 % decrease observed for mono-thiol and mono-amino β-CDs, respectively. A 95 % decrease in binding in PFOA is observed for mono-thiol-β-CD, while heptakis-(6-mercapto-6-deoxy)-β-cyclodextrin, with seven ionizable thiol groups leads to a modest 23 % decrease for complexation of PFOA with change from neutral to alkaline pH. Steric effects due to chain branching within PFAS in combination with size and number of substituents on the β-CD reduce the impact of pH effects on binding. This study demonstrates derivatization of β-CD with pH ionizable functional groups can be used to control the β-CD binding of PFAS as a possible strategy for the removal and recovery of PFAS from contaminated water streams.

Keywords

Host-guest complexation ; PFAS ; cyclodextrin ; remediation: pH

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