Effect of phase transition on the electrochemical behavior of ferredoxin embedded in an artificial lipid membrane film

The effect of the phase transition of a bilayer membrane on the electrochemical behavior of ferredoxin embedded in a cast film of artificial lipid, 2C₁₈N⁺Br⁻, was investigated. The redox potential of ferredoxin embedded in the lipid film showed a linear, positive shift from −510 (± 2) to −466 (± 3) mV (vs. Ag|AgCl|saturated KCl) with increasing temperature from 25 to 53 °C. The diffusion coefficient (D) and heterogeneous electron transfer rate constant (k°^′) were evaluated at various temperatures by means of analyzing cyclic voltammograms. The overall shape of the simulated voltammograms fitted well with the experimentally observed voltammograms at various potential sweep rates, when the estimated D and k°^′ values were used for the simulation. The results of the temperature dependence of the estimated D and k°^′ values indicated that D and k°^′ were enhanced near the phase transition temperature (T_c), 46 °C, of the lipid film. The D and k°^′ values at temperatures above the T_c were approximately two-orders and one-order of magnitude larger than those estimated at temperatures under the T_c, respectively. The estimated D and k°^′ values were 2.1–5.8 × 10⁻¹⁰ cm² s⁻¹ and 1.2–1.6 × 10⁻⁴ cm s⁻¹ at 25 °C, and 3.5–3.7 × 10⁻⁸ cm² s⁻¹ and 1.1–1.2 × 10⁻³ cm s⁻¹ at 50 °C, respectively. The electrochemical behavior of ferredoxin in the lipid film changed drastically near the T_c.