F-19 AND H-1-NMR INVESTIGATION OF CYCLODEXTRIN FLUOROCARBON ALKYL CARBOXYLATE SURFACTANT INCLUSION COMPLEXES/

A F-19 NMR chemical shift study of a homologous series of perfluorocar bon (fc) [CxF2x+1CO2Na, x = 3, 4, 6-9] surfactants (S) has been carrie d out in D2O and in binary solvent (D2O + cyclodextrin (CD)) systems a t 22 degrees C. Both beta-CD and modified cyclodextrins were used. Com plementary H-1 NMR chemical shift data for the cyclodextrins in binary solvent (D2O + S) systems were also obtained. Values of the complex-i nduced chemical shifts (CIS) for selected host or guest nuclei are obs erved to increase with increasing alkyl chain (C-x) length of the surf actant when the CD/S complex has a 1:1 stoichiometry. However, for com plexes having stoichiometries other than 1:1 CD/S, somewhat different trends in the CIS values were observed. Binding constants (K-i) have b een obtained from the analysis of F-19 and H-1 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, K-i in creases as C-x increases; however, differences in the binding affinity , stoichiometry, and inclusion geometry of the CD/S complexes mere obs erved to depend on the type of cyclodextrin. The latter can be underst ood in terms of the steric effects created by the introduction of alky l groups in the annulus region of the cyclodextrin.