19F and 1H NMR Investigation of Cyclodextrin/Fluorocarbon Alkyl Carboxylate Surfactant Inclusion Complexes

A 19F NMR chemical shift study of a homologous series of perfluorocarbon (fc) [CxF2x+1CO2Na, x = 3, 4, 6−9] surfactants (S) has been carried out in D2O and in binary solvent (D2O + cyclodextrin (CD)) systems at 22 °C. Both β-CD and modified cyclodextrins were used. Complementary 1H NMR chemical shift data for the cyclodextrins in binary solvent (D2O + S) systems were also obtained. Values of the complex-induced chemical shifts (CIS) for selected host or guest nuclei are observed to increase with increasing alkyl chain (Cx) length of the surfactant when the CD/S complex has a 1:1 stoichiometry. However, for complexes having stoichiometries other than 1:1 CD/S, somewhat different trends in the CIS values were observed. Binding constants (Ki) have been obtained from the analysis of 19F and 1H CIS values of the CD/S systems using equilibrium models in which 1:1, 1:1 plus 2:1, 1:1 plus 1:2 complexes, and uncomplexed species are present. In general, Ki increases as Cx increases; however, differences in the bind...