Electrochemical properties of myoglobin embedded in Langmuir–Blodgett and cast films of synthetic lipids

Abstract

Electrochemical parameters, formal potentials (E0′), electron-transfer rate constants (k0′), and diffusion coefficients (Dct) have been determined for myoglobin (Mb) embedded in the Langmuir–Blodgett (LB) and cast films of five synthetic lipids including two types of polymeric lipids bearing ammonium or poly(ethylene glycol) as a head group. The heterogeneous electron-transfer rate constants of MbFeIII/MbFeII in these films were ca. 102–103-fold larger than those for Mb in solution at an indium tin oxide electrode. Myoglobin-lipid LB films on basal-plane pyrolytic graphite (PG) electrodes gave 3–10-fold larger k0′ values compared with cast films of the same lipid. The Mb–lipid films showed gel to liquid-crystal phase transitions consistent with bilayer structures. The peak current of the square wave voltammograms for the cast Mb–lipid films showed breaks in the phase-transition temperature regions of the corresponding lipid films. Dependence of k0′ on lipid structure was not significant. A variety of synthetic lipids provided suitable microenvironments for the enhanced electron transfer of Mb. Immobilized Mb in the lipid films was stable for more than a month. The specific orientation of Mb in all Mb–lipid films was shown by linear dichroism. The orientation does not depend on the type of the lipids.