The Chameleon-like Nature of Zwitterionic Micelles: The Intrinsic Relationship of Anion and Cation Binding in Sulfobetaine Micelles

The rate of specific hydrogen ion-catalyzed hydrolysis of 2-(p-heptoxyphenyl)-1,3-dioxolane and acid-base equilibrium of 4-carboxy-1-n-dodecylpyridinium in zwitterionic micelles of SB3-14, C14H29NMe2+(CH2)(3)SO3- are controlled by NaClO4, which induces anionic character and uptake of H3O+ in the Micelles. Other salts, e.g., NaF, NaCl, NaBr, NaNO3, NaI, NaBF4, have similar, but smaller, effects on the uptake of H3O+. Salt effects upon zeta potentials of SB3-14 inicelles, estimated by capillary electrophoresis, are anion specific, and the anion order is similar to that of the rates of acid hydrolysis and of acid-base equilibria. Fluorescence quenching shows that the micellar aggregation number is not very sensitive to added salts, consistent with electrophoretic evidence. These specific anion effects follow the Hofmeister series and are related to anion hydration free energies.