Electrochemistry and electrocatalysis with myoglobin in biomembrane-like surfactant-polymer 2C12N+PA− composite films

Biomembrane-like polyionic complex, 2C12N+PA−, was prepared by reacting sodium polyacrylate (Na+PA−) with didodecyldimethylammonium bromide (2C12N+Br−). Stable thin films made from 2C12N+PA−, with incorporated myoglobin (Mb), on pyrolytic graphite (PG) electrodes were then characterized by electrochemistry and other techniques. Cyclic voltammetry of Mb-2C12N+PA− films showed a pair of well-defined quasi reversible peaks for MbFe(III)/Fe(II) couple at about −0.19 V versus SCE in pH 5.5 buffers. The electron transfer rate between Mb and PG electrodes was greatly facilitated in the microenvironment of 2C12N+PA− films. Square wave voltammetry data were used to estimate the apparent heterogeneous electron transfer rate constants by nonlinear regression analysis using a model featuring dispersion of formal potentials. Positions of Soret absorption bands suggested that Mb keeps its secondary structure similar to its native state in 2C12N+PA− films at the medium pH. The results of differential scanning calorimetry and X-ray diffraction suggest that synthesized 2C12N+PA− lipid films have an ordered multibilayer structure and the incorporated Mb does not disturb this structure. Oxygen was catalytically reduced by Mb-2C12N+PA− films with a significant decrease in the electrode potential. MbFe(I), a highly reduced form of Mb, was also produced in Mb-2C12N+PA− films at about –1.09 V, and could be used to catalytically reduce organohalide pollutants such as perchloroethylene (PCE) and trichloroethylene (TCE). The catalytic reduction peak currents had linear relationships with concentrations of PCE and TCE in a range of 10–100 μM. The potential applications of the film electrode as a sensor for detecting organohalides are discussed.