Unidirectional transmembrane photoelectron transfer with artificial metallopeptides

Unidirectional transmembrane electron transfer is an essential process in natural photosynthesis, where it plays a key role in separating reaction products and slowing charge recombination.1 Making artificial molecules that functionally mimic photosynthetic proteins and achieve transmembrane electron transfer is already a chemical endeavour.2–7 Distinguishing genuine transmembrane electron transfer through an impermeable lipid membrane, from light-induced leakage of electron donors through the membrane followed by photoelectron transfer on one side of the bilayer, is even more difficult.8–10Here, we report two artificial metallopeptides, WALP23-Ru2 and WALP23-Re2, that drive photoelectron transfer from an electron donor located inside a liposome, to an acceptor located outside. A sensitive membrane leakage assay was used to demonstrate that WALP23-Re2 indeed achieved genuine photoelectron transfer through the membrane, with negligible contribution from leakage. By contrast, photoelectron transfer with WALP23-Ru2 was clearly the result of leakage of the electron donor through the membrane, followed by photoinduced electron transfer on one side of the membrane. These results demonstrate the unique potential of neutral metallopeptides such as WALP23-Re2 to drive transmembrane electron transfer in artificial photosynthetic systems, while highlighting the importance of leakage studies for the understanding of how such systems really work.