Transmembrane Electron Transfer as Catalyzed by Poly(ethylenimine)-Linked Manganese Porphyrins

Poly(ethylenimine)-linked manganese porphyrins associate with phospholipid bilayers in a manner that allows the porphyrin to penetrate the membrane to a depth limited by the hydrocarbon spacer linking it to the extremely hydrophilic polymer. Control of the length of this spacer group and the sidedness of the incorporation of these complexes in liposome membranes permit systematic variation of the minimum distances separating two such derivatives incorporated from opposite sides of the membrane bilayer. Examination of transmembrane electron transport as catalyzed by these porphyrin complexes reveals that significant rates of electron transfer are observed only when the edge-to-edge distance separating two porphyrins is approximately 4 A or less. Comparison to theory and relevance to biological electron transfer are discussed.