Comparison of the Surface Activity and Bulk Aggregation of Ferrocenyl Surfactants with Cationic and Anionic Headgroups

We report the synthesis and aqueous solution properties of a novel redox-active surfactant, Fc(CH 2 ) 11 SO 3 - Na +, where Fc is ferrocene. Electrochemical oxidation of Fc to the ferrocenium cation (Fc + ) reversibly transforms the anionic surfactant (Fc(CH 2 ) 11 SO 3 - ) into a zwitterionic species (Fc + (CH 2 ) 11 SO 3 - ). When dissolved at concentrations between 0.15 and 0.4 mM in aqueous solutions containing 10 mM Li 2 SO 4, oxidation is accompanied by the reversible transformation of a solution of monomeric species of Fc(CH 2 ) 11 SO 3 - into vesicle-like ( D h = 70 ± 8 nm, R g / R h = 1.0 ± 0.3) surfactant assemblies of Fc + (CH 2 ) 11 SO 3 - . In contrast, at concentrations above 0.4 mM, oxidation reversibly transforms a solution of globular ( D h = 6 ± 2 nm) micelles into vesicle-like assemblies of Fc + (CH 2 ) 11 SO 3 - . These various oxidation-induced changes in aggregation are reflected in the interfacial properties of this surfactant system, which are substantially different from those of ferrocenyl surfactants with cationic headgroups (Fc(CH 2 ) 11 N + (CH 3 ) 3 ).