ENHANCED ELECTRON-TRANSFER FOR MYOGLOBIN IN SURFACTANT FILMS ON ELECTRODES

The Fe(III)/Fe(II) redox couple of the heme protein myoglobin (Mb) gave standard electron-transfer rate constants about 1000-fold larger in liquid crystal films of didodecyldimethyl ammonium bromide (DDAB) on pyrolytic graphite (PG) electrodes than in aqueous solutions. Electron-transfer rates of Mb were also enhanced in films of soluble cationic and anionic surfactants adsorbed on PG. Results suggest a role for strongly adsorbed surfactant at electrode-film interfaces, which may prevent adsorption of macromolecular impurities which can block electron transfer. Mb-DDAB films were prepared by spontaneous insertion of Mb from solution into water-insoluble cast films of DDAB. The resulting films 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 preferentially oriented myoglobin wit h the iron heme in a high spin state. Mb-DDAB films showed good charge-transport rates, which allowed Mb to be used as a redox catalyst. Reductions of the organohalide pollutants trichloroacetic acid and ethylene dibromide were catalyzed by Mb-DDAB films on PG electrodes at voltages 1.0-1.3 V less negative than direct reductions.