Unidirectional Transmembrane Photoinduced Electron Transfer with Artificial Metallopeptides

The ability to drive unidirectional photoinduced electron transfer through an insulating lipid membrane is one of the most striking features of the thylakoid membrane, and recreating this property artificially is considered as one of the holy grails of artificial photosynthesis. Here, we report two artificial metallopeptides, WALP23-Re ₂ and WALP23-Ru ₂ , that were embedded in the membrane of dissymmetric liposomes containing an electron donor in the inner compartment and an electron acceptor in the bulk aqueous phase. Upon light irradiation under air, unidirectional electron transfer was observed from one side of the membrane to the other one with both metallopeptides. However, the mechanism of photoinduced electron transfer strongly depended on the metal center: the neutral WALP23-Re ₂ peptide achieved genuine electron transfer through the membrane, but with the tetracationic WALP23-Ru ₂ peptide the transmembrane electron transfer appeared to be the result of light-induced leakage of the electron donor molecules through the lipid bilayer, followed by electron transfer on the same side of the membrane by peptides assembled parallel to the membrane. These results highlight both the unique potential of the neutral metallopeptide WALP23-Re₂ to drive transmembrane photoinduced electron transfer in artificial photosynthetic systems, as well as the importance of membrane-leakage studies to validate the working mechanism of such supramolecular systems.