CONVERSION OF LIGHT ENERGY TO PROTON POTENTIAL IN LIPOSOMES BY ARTIFICIAL PHOTOSYNTHETIC REACTION CENTERS

During photosynthesis, photoinduced electron transport across membrane s is carried out by pigment molecules organized into reaction centres by membrane-spanning proteins, The resulting transmembrane electrochem ical potential is then coupled to the movement of protons across the m embrane(1). Photoinduced electron transport followed by thermal electr on transfer, leading to charge separation over distances of 8 nm, has been demonstrated in artificial mimics of the photosynthetic reaction centre comprising covalently linked electron donors and acceptors(2-10 ). Here we report the assembly of an artificial mimic of the photosynt hetic apparatus which transports protons across a lipid bilayer when i lluminated Our model reaction centre is a molecular 'triad', consistin g of an electron donor and acceptor linked to a photosensitive porphyr in group, This triad is incorporated into the bilayer of a liposome. W hen excited, it establishes a reduction potential near the outer surfa ce of the bilayer and an oxidation potential near its inner surface, I n response to this redox potential gradient, a freely diffusing quinon e molecule alternates between its oxidized and reduced forms to ferry protons across the bilayer with an overall quantum yield of 0.004, cre ating a pH gradient between the inside and outside of the liposome.