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Research chips away at photosynthesis mysteryA team of researchers has developed a new analytical technique that, for the first time, allows them to directly measure the energy transport pathways in photosynthesis. The new method, while adding to the basic understanding of photosynthesis – the process used by plants to convert sunlight into energy – also could become an important tool for developing more efficient sunlight-to-energy conversion devices, like solar cells. An article on the advance, “Two-Dimensional Spectroscopy of Electronic Couplings in Photosynthesis,” was published in the March 31 issue of Nature. Robert Blankenship, professor and chair of the ASU department of chemistry and biochemistry and one of the researchers involved in the project, said the work focused on a classic photosynthesis process, in which light is absorbed by an “antenna system,” and then the energy is transported to other parts of the photosynthetic protein. The research team was headed by Graham Fleming of the University of California-Berkeley and Lawrence Berkeley National Laboratory, and Minhaeng Cho, of Korea University in Seoul. Blankenship’s research group isolated and purified the photosynthetic protein complexes that were studied at Berkeley, and has studied them in detail using biochemical and genetic methods, as well as laser analysis. The team used a new two-dimensional spectroscopy technique to directly measure the electronic coupling between energy levels in the protein bacteriochlorophyll a. The technique revealed in unprecedented detail the fundamental cause of energy transport in this photosynthetic protein. The researchers used a sequence of three carefully timed laser pulses to map out how energy moves through different parts of the photosynthetic bacteriochlorophyll a protein, from the light harvesting antenna pigment to the reaction center where it is used to create useful chemicals. They found that excitation energy absorbed by the antenna pigments in the bacteriochlorophyll a protein, doesn’t simply cascade down the energy ladder to the reaction center. Rather, distinct energy transport pathways exist that depend on the different protein parts and their interactions with each other. While the work will shed light on some of the basic mechanisms in photosynthesis, a more exciting aspect lies beyond the analysis of the bacteriochlorophyll a protein, Blankenship said. The work “establishes a new type of electronic spectroscopy as a tool that can be used to study complex systems that have multiple light absorbing components in them,” Blankenship says. “Photosynthesis systems are sort of classic cases where this is found. They have multiple pigments and you can watch the transfer from one to the other.” “It is possible to apply this method to synthetic devices and other systems,” he adds. “We can potentially use this new technique to probe in a more detailed way anything that has light absorption in it and anything that is colored.” By Skip Derra. Derra, with Marketing & Strategic Communications,
can be reached at (480) 965-4823 or (skip.derra@asu.edu).
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