We study a model of a light-induced proton pump in artificial reaction centers. The model containsa molecular triad with four electron states (i.e., one donor state, two photosensitive group states, andone acceptor state) as well as a molecular shuttle having one electron and one proton-binding sites.The shuttle diffuses between the sides of the membrane and translocates protons energeticallyuphill: from the negative side to the positive side of the membrane, harnessing for this purpose theenergy of the electron-charge separation produced by light. Using the methods of quantum transporttheory we calculate the range of light intensity and transmembrane potentials that maximize both thelight-induced proton current and the energy transduction efficiency. We also study the effect oftemperature on proton pumping. The light-induced proton pump in our model gives a quantum yieldof proton translocation of about 55%. Thus, our results explain previous experiments on theseartificial photosynthetic reaction centers.
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