Electron transfer catalyzed by phospholipid-linked manganese mesoporphyrin derivatives in lipid bilayers modified electrodes

Electron transfer of manganese mesoporphyrin (MnMP) derivatives in phospholipid (dipalmitoylphosphatidyl-chorine; DPPC) membrane electrodes has been studied by electrochemical CV and impedance measurements. In the MnMP-embedded phospholipid membrane electrode, the electron transfer takes place via Mn(III)/Mn(II) redox in the MnMP. The electron transfer is influenced by the temperature of the lipid membrane, where in the gel form of the phospholipid at temperatures lower than 40 degrees C, the electron transfer cannot be observed, probably because the movement of MnMP in the phospholipid is strongly hindered. The electron transfer can take place at temperatures higher than the transition from the gel form to the fluid of the phospholipid membrane at around 42 degrees C. The electron transfer of the MnMP + DPPC membrane electrode, in which MnMP is not linked with the phospholipid, is relatively fast at the transient temperature, The overall rate of the electron transfer is controlled by a diffusion in the DPPC membrane involving electron hopping between Mn(II)/Mn(III) redox in MnMP and the physical diffusion of MnMP. The electron transfer of the MnMP covalently linked with the phospholipid by spacer methylene groups (PE-C-n-MnMP; n = 0, 5, and 11) becomes relatively slow and is greatly influenced by the spacer length. The order of the electron transfer rate is PE-C-5-MnMP > PE-C-0-MnMPPE-C-11-MnMP, in which for PE-C-11-MnMP the slower process of diffusion is involved. (C) 1997 Elsevier Science S.A.