Light-driven proton transport across liposomal membranes enabled by Janus metal-organic layers

Summary 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 proton gradient generation via directional proton transport. Here, we report a light-driven proton pump based on two-dimensional, porphyrin-based Janus metal-organic layers (Janus-MOLs). The Janus-MOL, functionalized with carboxyquinone on one side and Acitretin on the other via a microemulsion-based method, was attached to liposome surface. 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 CFoF1-ATP synthase in a similar fashion as photosynthetic bacteria.