Abstract
Stable thin films were made by casting vesicle dispersions of didodecyldimethylammonium 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 these liquid crystal films than on bare edge-plane PG electrodes or electrodes modified with mediators with Hb in solution. The formal potential was pH dependent, suggesting that one electron and one proton are involved in the reduction of Fe(III) hemes. A second quasi-reversible redox couple involving reduction of HbFe(II) was also observed in Hb-DDAB films. Trichloroacetic acid was catalytically reduced by the films at potentials of this more negative reduction. UV-vis and reflectance absorbance infrared spectra indicated that hemoglobin was not grossly denatured in the DDAB films, although conformational differences from the native state in solution are possible. Differential scanning calorimetry suggested that the films contain lamellar liquid crystalline DDAB arranged in bilayers. Electronic absorbance linear dichroism showed that Hb is preferentially oriented in the films.
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