How does β-cyclodextrin affect the aggregation of sodium perfluoroheptanoate in aqueous solution: a 19F NMR study

¹H and ¹⁹F NMR spectra were recorded for D₂O solutions of sodium perfluoroheptanoate with defined concentrations up to 200 mM, in the absence and presence of β-cyclodextrin (15 mM). Analysis of ¹H chemical shift data obtained by the method of continuous variations (Job’s method) confirms the formation of 1:1 inclusion complexes for the perfluoroheptanote anion in β-cyclodextrin and leads to an estimate for the apparent inclusion constant (≥10⁴ M⁻¹). In addition, analysis of ¹⁹F chemical shift data based on two simplifying assumptions (monodisperse perfluoroheptanoate solutions below the critical micellar concentration (CMC), and a single self-associated state after the CMC) enables to interpret all the experimental chemical shift data and allows to determine CMC values for the absence and presence of β-cyclodextrin (104 and 116 mM). It is shown that the self-association of perfluoroheptanoate and its inclusion in β-cyclodextrin lead to shielding and deshielding of the fluorine atoms, respectively.