ENHANCED ELECTRON-TRANSFER FOR MYOGLOBIN IN SURFACTANT FILMS ON ELECTRODES

The Fe(III)/Fe(II) redox couple of the heme protein myoglobin (Mb) gav e standard electron-transfer rate constants about 1000-fold larger in liquid crystal films of didodecyldimethyl ammonium bromide (DDAB) on p yrolytic graphite (PG) electrodes than in aqueous solutions. Electron- transfer rates of Mb were also enhanced in films of soluble cationic a nd anionic surfactants adsorbed on PG. Results suggest a role for stro ngly adsorbed surfactant at electrode-film interfaces, which may preve nt adsorption of macromolecular impurities which can block electron tr ansfer. Mb-DDAB films were prepared by spontaneous insertion of Mb fro m solution into water-insoluble cast films of DDAB. The resulting film s were stable for a month in pH 5.5-7.5 buffers containing 50 mM NaBr. Spectroscopic, thermal, and electrochemical characterizations suggest that the films consist of lamellar liquid crystal DDAB containing pre ferentially oriented myoglobin wit h the iron heme in a high spin stat e. Mb-DDAB films showed good charge-transport rates, which allowed Mb to be used as a redox catalyst. Reductions of the organohalide polluta nts trichloroacetic acid and ethylene dibromide were catalyzed by Mb-D DAB films on PG electrodes at voltages 1.0-1.3 V less negative than di rect reductions.