STUDY |
Light-triggered electron transfer drives the transport of calcium ions across a lipid bilayer in a system designed by authors. Authors added a lipophilic Ca2+-binding molecule to the artificial photosynthetic membrane in which they have previously demonstrated a light-driven proton pump. Their new molecular shuttle is a hydroquinone (shown) that chelates Ca2+, carrying the ion from the aqueous solution outside the phospholipid bilayer into the membrane's interior. An artificial photosynthetic reaction center--consisting of a carotenoid (C) linked to a porphyrin (P) and a naphthoquinone (Q)--spans the membrane. When irradiated, photoinduced electron transfer converts the triad to the charge-separated state C+-P-Q-. The carotenoid radical cation then oxidizes the shuttle molecule to its quinone form, which releases Ca2+ into the aqueous interior of the liposome. The ion transport results in the creation of both a Ca2+ concentration gradient and a membrane potential, the researchers find.
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