How Can Scientists Replicate Photosynthesis in the

Life on Earth is powered by the sun's energy. The chloroplasts found in plants and some other organisms can efficiently capture and convert solar energy to sugars through a process known as photosynthesis. Now, scientists have developed an artificial photosystem that may one day allow for solar-powered food or fuel production in the lab.

Dr. Darius Kuciauskas

HYPOTHESIS: Synthetic Compounds Can

Imitate a Photosynthetic System

In nature, a photosystem contains pigments and proteins embedded in a linear sequence in the membrane of a chloroplast. This arrangment allows for effective capture and orderly transfer of electrons from one photosystem to another and eventually to a final electron acceptor for powering synthesis of sugar.

Dr. Darius Kuciauskas (koo-si-AHS-kuhs) of Virginia Commonwealth University and his colleagues thought they could produce an artificial photosystem that carried out the initial steps of photosynthesis. Kuciauskas and his team predicted that when they shined light on four pigment molecules with energy-conducting chemical bonds, the pigment molecules would capture and channel light energy through the "wirelike" bonds. The electrons traveling through the bonds would then pass to, and electrically charge, an acceptor molecule that was placed at the center of the pigment complex.

Kuciauskas and his colleagues use laser systems such as this one to study light absorption in molecules that might one day be used in an artificial photosystem.

METHODS: Design and Build a

Pigment-Protein Light-Harvesting Complex

Kuciauskas and his team set out to create the photosystem. The team started with purple pigment molecules called porphyrins. These molecules absorb light energy and are related to naturally occurring chlorophyll. The scientists joined four of the porphyrins to each other. To the center-most porphyrin, they attached a ball-shaped cluster of 60 carbon atoms called C60, or fullerene.

RESULTS: The Artificial Photosystem Captured and Transferred Electrons

The four porphyrin pigments captured light energy, and the bonds passed electrons to the C60 acceptor molecule. The acceptor held the charge for only one microsecond—about one millionth of a second.

CONCLUSION: Artificial Photosystems Are Possible

The Kuciauskas team concluded that their complex does act as an artificial photosystem, at least for a fleeting instant. Kuciauskas and his colleagues have continued their work, aiming to modify the complex further so it can hold its energy longer. Ultimately, they hope their photosystem can power chemical reactions for making important organic molecules that serve as food or fuel.

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