Transmembrane electron transfer as catalyzed by phospholipid-linked manganese porphyrins

Phospholipid-linked porphyrins separated by spacer methylene groups (C-n), PE-C-n-MTTP and PE-C-n-MPFPP (n = 0, 5, 11; M = H-2, Mn) (Chart 1) were synthesized. The phospholipid-linked porphyrin complexes easily associated with phospholipid bilayers in a manner that allows the porphyrin portion to penetrate the membrane. Ground state transmembrane electron transfer catalyzed by the manganese complex of the phospholipid-linked porphyrins in egg PC and DPPC liposomes revealed that the porphyrin causes a significant accelerated electron transfer especially when n = 11 and that the electron transfer rate was controlled not only by the separated spacer methylene groups between the porphyrin and the phospholipid but also by the phase transition temperature of the lipid bilayers. Comparison of PE-C-n-MnTTP- and PE-C-n-MnPFPP-catalyzed electron transfer is made. Furthermore, the electron transfer was enhanced with an increase of imidazole concentration, implying that imidazole plays an important role in the electron transfer.