Counterion Anchoring Effect on the Structure of the Solid-State Inclusion Complexes of β-Cyclodextrin and Sodium Perfluorooctanoate

Abstract

Characterization of the structure and dynamics for the solid inclusion complexes (ICs) between β-cyclodextrin (β-CD; host) and sodium perfluorooctanoate (SPFO; guest) was carried out using 1H/19F/13C NMR spectroscopy. The 1:1 and 2:1 β-CD/SPFO solid complexes were prepared by a modified dissolution method. Evidence for the formation of β-CD/SPFO ICs was provided by 13C DP (direct polarization) and CP (cross-polarization) solid-state NMR spectroscopy with magic angle spinning (MAS) at 20 kHz. The complexation-induced shifts (CIS) of 1H/19F/13C nuclei between solution and the solid state for β-CD/SPFO complexes and the closely related complexes of β-CD/PFOA (perfluorooctanoic acid) were compared. The counterion effect for SPFO and PFOA was observed according to their variable structure and binding as inclusion compounds with β-CD. The effect of sodium versus hydronium counterions on the structure and dynamics of inclusion complexes for these systems was supported by DSC, TGA, FT-IR, and powder X-ray diffrac...