Light-Driven Proton Transport Across Liposomal Membranes Enabled by Janus Metal-Organic Layers

Abstract

Photo-generation of a proton gradient over a lipid bilayer is of interest due to its essential role in photosynthetic bacteria. Membrane asymmetry is key to the generation of a proton gradient via directional proton transport. Here we report a light-driven proton pump based on two-dimensional, porphyrin-based Janus metal-organic layers (Janus-MOLs) embedded in liposomes. We developed a microemulsion-based method to functionalize the Janus-MOLs with carboxyquinone on one side and Acitretin on the other side. By attaching the Janus-MOLs to liposome surfaces, we obtained a mimic to photosynthetic bacteria. Upon photoexcitation, the porphyrins initiate electron and hole transfers to carboxyquinone and Acitretin, respectively, which undergo redox reactions with freely diffusing quinone (Q) / hydrosemiquinone (HQ·) in the lipid bilayer to produce a concentration gradient of quinone-based species. Owing to different pKa values of HQ+ and HQ ·, these redox reactions trigger proton transport across the membrane to create a pH gradient, which drives ATP production by CF0F1-ATP synthase in a similar fashion as photosynthetic bacteria.