Mimicking bacterial photosynthesis

Abstract

Photosynthesis in bacteria involves absorption of light by antenna chromophores and transfer of excitation to reaction centers, which convert the excitation energy to electrochemical potential energy in the form of transmembrane charge separation. A proton pump uses this stored energy to generate proton motive force across the membrane, which in turn is used to synthesize adenosine triphosphate (ATP). All of these steps can now be mimicked in the laboratory. Artificial antennas and reaction centers can be prepared from chromophores, electron donors and electron acceptors linked by covalent bonds. The artificial reaction centers can be inserted into the lipid bilayers of liposomes, where they act as constituents of transmembrane light-driven proton pumps. Finally, the proton gradient thus produced can be used to synthesize ATP via catalysis by FoFl-ATP synthase isolated from chloroplasts. The synthetic and natural systems can use light energy to produce ATP at comparable chemical potentials.

Injecting Electronic Excitation Energy into an Artificial Antenna System through an Ru2+ Complex

“…The overall occupation probability of Ox1 was chosen to be p = 0.006. This corresponds, according to Equation (2), to a mean concentration of 2.3 10 À3 mol L…”

“…2 + (PF 6 ) 2 (2): [Ru(bpy) 2 Cl 2 ] (110.7 mg, 0.21 mmol) and 1 (50.6 mg, 0.16 mmol) were dissolved in ethylene glycol (5 mL). The mixture was placed in a modified microwave oven and irradiated at 450 Watt for 2 min and, after a cooling down period, for another 2 minutes.…”

“…[1][2][3][4] Artificial photonic antenna materials that work well have been obtained by inserting fluorescent dye molecules into zeolite L crystals. [5] Zeolite L is an aluminosilicate with one-dimensional channels running along the c axis of the hexagonal crystals.…”

“…[6] Its stoichiometry with monovalent cations is (M) 9 [Al 9 -Si 27 O 72 ]·n H 2 O, where n equals 21 in fully hydrated materials and 16 at about 20 % relative humidity. The number of channels in a zeolite L crystal of diameter d c given in nm is equal to 0.265(d c ) 2 . As an example, a crystal with a diameter of 550 nm consists of about 80 000 parallel channels.…”

“…) and an s value of 2 (corresponds to oxazine 1) we obtain Equation (2). We refer to reference [5] for further details.…”