Permeability-controllable membranes. Part 8. Electrical redox sensitive permeation through a multibilayer-immobilized film containing a ferrocenyl group as a redox site

Abstract

Multibilayer-immobilized films containing a ferrocenyl group as a redox site at a hydrophobic alkyl chain (FeC₁₁C₁₈N⁺) or as a hydrophilic head group of bilayer-forming dialkylammonium amphiphiles (2C₁₆N⁺Fc) have been prepared by ion-complexation with poly(styrenesulphonate)(PSS^–). Redox reactions of ferrocene groups in multibilayer films (FcC₁₁C₁₈N⁺/PSS^– and 2C₁₆N⁺ Fc/PSS^–) have been shown to occur only in the fluid state of bilayer matrices above their phasetransition temperatures (T_c= 35 and 26°C, respectively), as confirmed by cyclic voltammetry. The permeability of water-soluble, non-ionic fluorescent probes through the multibilayer film cast on a platinium minigrid sheet is enhanced by a factor of 2–5 by the electrochemical oxidation of a ferrocenyl unit in the fluid multibilayer film above its T_c, compared with that of the reduced form. Permeability could be changed reversibly over at least 20 cycles by repeated redox reactions in the case of the 2C₁₆N⁺ Fc/PSS^– film containing an Fc unit near the hydrophilic moiety. In contrast, the change in permeability of the FcC₁₁C₁₈N⁺/PSS^– film with a redox site in the hydrophobic dialkyl chain became irreversible under continuous redox reactions.