POTENTIOMETRIC STUDY ON STABILITY OF SURFACTANT PLUS BETA-CYCLODEXTRIN COMPLEXES

The complexation constants K of beta-cyclodextrin with 13 ammonium surfactants were determined by a potentiometric method using electrodes selective to amphiphilic ions. Especially for C12, C14, and C16 tails, a model that provides for the formation of a second complex (beta-CD)2M+, with a K1/K2 ratio of about 600, provides a good fit with the experimental curves. Results show a poor influence of the polar group, for example in the case of the dodecyl chain. On the other hand, the pK1 values and the hydrophobic tail length are linked by a linear relation up to n = 12 carbon atoms; beyond, pK1 ends to be proportionally smaller and pK2 more important.