FILMS OF HEMOGLOBIN AND DIDODECYLDIMETHYLAMMONIUM BROMIDE WITH ENHANCED ELECTRON-TRANSFER RATES

Stable thin films were made by casting vesicle dispersions of didodecy ldimethylammonium bromide (DDAB) containing the protein hemoglobin (Hb ) onto edge-plane pyrolytic graphite (PG) electrodes. The heme Fe(III) /Fe(II) couple of Hb had an electron transfer rate much greater in the se liquid crystal films than on bare edge-plane PG electrodes or elect rodes modified with mediators with Hb in solution. The formal potentia l was pH dependent, suggesting that one electron and one proton are in volved in the reduction of Fe(III) hemes. A second quasi-reversible re dox couple involving reduction of HbFe(II) was also observed in Hb-DDA B films. Trichloroacetic acid was catalytically reduced by the films a t potentials of this more negative reduction. UV-vis and reflectance a bsorbance infrared spectra indicated that hemoglobin was not grossly d enatured in the DDAB films, although conformational differences from t he native state in solution are possible. Differential scanning calori metry suggested that the films contain lamellar liquid crystalline DDA B arranged in bilayers. Electronic absorbance linear dichroism showed that Hb is preferentially oriented in the films.