¹⁹F NMR Characterization of the Encapsulation of Emerging Perfluoroethercarboxylic Acids by Cyclodextrins

Abstract

Legacy perfluoroalkyl substances (PFASs) are known environmental pollutants with serious adverse health effects. Perfluoroethercarboxylic acids (PFECAs), emerging PFASs now being substituted for legacy PFASs, have recently been detected in the environment. Cyclodextrins (CDs) have been proposed as agents for the remediation of problematic pollutants, including legacy PFASs. The current study uses F NMR spectroscopy to measure the complexation of mono-, di-, and triether PFECAs by CDs for eventual environmental applications. Eight PFECAs were characterized byF and C NMR. The change in chemical shift of individual fluorines upon complexation of CDs at various stoichiometric ratios was used to determine the host-guest association constants. All studied PFECAs were most strongly encapsulated by β-CD, with association constants from 10-10 M depending on chain length and number of ether functionalities. F-H heteronuclear Overhauser effect spectroscopy (HOESY) NMR experiments were performed for the β-CD complexes of two branched monoethers, PFPrOPrA ("GenX") and PFDMMOBA, to elucidate the structural details of the complexes, determine the specific orientation, and position of β-CD along the PFAS chain, and assess the roles of hydrogen-bonding and PFECA branching on the host-guest interactions. The results give new understanding into the fundamental nature of the host-guest complex between cyclodextrins and perfluorinated surfactants.

Reduction of a Tetrafluoroterephthalonitrile‐β‐Cyclodextrin Polymer to Remove Anionic Micropollutants and Perfluorinated Alkyl Substances from Water

“…Under these conditions, 8 of 10 PFASs were removed to at least 95 %, with the short, four carbon perfluorobutanoic acid (PFBA) and branched 2,3,3,3,‐tetrafluoro 2‐(heptafluoropropoxy)proponate (GenX) removed to at least 80 %. These two PFASs bind to β‐CD with lower affinity, such that their removal may rely more heavily (or even exclusively) on interactions with amine/ammonium groups in polymer 2 (Figure b). Benchmarking 2 against GAC (20–40 Mesh, 425–850 μm) for the removal of 10 anionic PFAS shows that 2 exhibits superior performance when compared to GAC in experiments conducted under environmentally relevant conditions after 30 min and 8 h of contact time (Figure S4).…”

Supramolecular Amphiphiles Based on Pillar[5]arene and Meroterpenoids: Synthesis, Self-Association and Interaction with Floxuridine

“…It should be noted that in the case of the 3a/5/ FUDR system in a 1:1:1 ratio (1 × 10 −3 M), a shift of the fluorine signal by Δδ ~1.30 ppm is observed ( Figure 8 ) compared to free FUDR. Based on this, we can conclude that the shift of the fluorine signal in 3a/5/ FUDR to the downfield region of the spectrum indicates the inclusion of the FUDR molecule in the structure of the supramolecular associate, as well as the de-shielding of the fluorine atom caused by the presence of fluorine inside the associate 3a/5 [ 33 ]. An increase of the concentration of FUDR in the 3a/5/ FUDR system (1 × 10 −3 –1 × 10 −2 M) leads to the return of the 19 F signal to its original value.…”

Nitrile Reduction Reverses the Micropollutant Uptake Selectivity of a Tetrafluoroterephthalonitrile-β-Cyclodextrin Polymer

“…Broad-spectrum PFAS removal was also evaluated across a range of PFAS chain lengths and anionic head groups (carboxylic and (heptafluoropropoxy)proponate (GenX) removed to at least 80%. These two PFASs bind to β-CD with lower affinity, 33 such that their removal may rely more heavily (or even exclusively) on interactions with amine/ammonium groups in polymer 2 (Fig 4b). (Fig S4).…”