Organometallic amphiphiles: Oxidized ferrocene as headgroup for redox-switched bilayer and monolayer membranes

A family of 15 ferrocene derivatives has been prepared, most of which are reported for the first time. This includes FcCH(2)O-3-cholestanyl, 1; FCCH2O(CH2)(13)CH3, 2; FcCH(2)O(CH2)(15)CH3, 3; FcCH(2)O(CH2)(17)CH3, 4; FcCH(2)N[(CH2)(17)CH3](2), 5; FcCH(2)O(CH2)(8)OCH(2)Fc, 6; FcCH(2)O(CH2)(12)OCH(2)Fc, 7; FcCH(2)O(CH2)(16)OCH(2)Fc, 8; Fc-(CH2)(22)Fc, 9; FcCH(2)-3,17-beta-estradioxy-CH(2)Fc, 10; Fc-1,1'-[COO(CH2)(16)CH3], 11; FcCONH(CH2)(17)CH3, 12; Fc-1,1'-{CON[(CH2)(17)CH3](2)}(2), 13; Fc-1,1'-(COO-3-dihydrocholesteryl), 14; and Fc-1,1'-(COO-3-cholesteryl), 15. Redox potentials for 1-15 have been determined and are in the range 400-450 mV for 2-6 (vs SSCE) and 509 mV for 1, 972 mV for 7, 806 mV for 8, 711 mV for 9, 941 mV for 10, and 945 mV for 11 (vs Ag/AgCl). Upon oxidation with Ce(IV), aqueous suspensions of compounds 1-5 and 7-10 formed stable vesicles after sonication. The charged monomers that formed vesicles afforded aggregates in the 2000-3000 Angstrom range that were characterized by laser light scattering and negative stain electron microscopy. In the absence of an oxidizing agent, vesicles failed to form from any of the 15 monomers even after prolonged sonication. Addition of 500 mu M aqueous Na2S2O4 solution collapsed the vesicles formed from 1-5 and 7-10, and the original amphiphile monomers were detected afterward by thin layer chromatography. It was concluded from cyclic voltammetry that both ferrocene residues in 8 were oxidized. Vesicles formed from 7-10 represent the first examples of a redox-switched bolaamphiphile.