Photosynthesis photographed for the first time
Researchers at ASU capture a 'molecular movie' of water splitting into oxygen, protons and electrons.
Thu, Jul 10, 2014 at 12:25 PM
Every school kid learns about photosynthesis, but a new study shows the life-giving process in action for the first time.
As published this week in the journal Nature, an international team of researchers has photographed photosynthesis in action using the world's fastest X-ray laser, which captures events that take place in one-quadrillionth of a second. Using this ultrafast laser, the researchers were able to document the previously unseen moments when photosynthesis converts water into oxygen, protons and electrons. "This study is the first step towards our ultimate goal of unraveling the secrets of water splitting and obtaining molecular movies of biomolecules," said the paper's senior author, Arizona State University professor Petra Fromme.
The photosynthetic process visualized in the new study involves the moment when water molecules and light combine in a cluster of metal including four manganese atoms and one calcium atom. The cluster is bound to a protein in the plant called PSII (Photosystem II), which catalyzes the process. Four flashes of light allow two water molecules to become one oxygen molecule, four hydrogen ions and four hydrogen electrons.
The researchers have been studying photosynthesis to mimic it in artificial systems. ASU's Center for Bio-Inspired Solar Fuel, which supported the study, is trying to develop what it calls an "artificial leaf" that could generate electricity. ASU Regents' professor Devens Gust said in a news release that one of the major challenges in creating the artificial leaf is "discovering an efficient, inexpensive catalyst for oxidizing water to oxygen gas, hydrogen ions and electrons. Photosynthetic organisms already know how to do this, and we need to know the details of how photosynthesis carries out the process using abundant manganese and calcium."
The current research will allow chemists to move forward in creating artificial photosynthetic catalysts, which can convert create fuels using sunlight. "The research ... gives us, for the very first time, a look at how the catalyst changes its structure while it is working," Gust said in a news release.
The next stage of the research, as Fromme hinted, is to go beyond the snapshot to create "molecular movies" of the entire process by which plants make the oxygen the rest of the world depends upon. This, in turn, will further the research into fuels that can be generated by photosynthetic-like processes. ASU graduate student Shibom Basu, one of the lead authors of the new paper, called this "the most exciting aspect of the work."
The research was funded by a broad coalition of organizations, including the Department of Energy and the National Institutes of Health.
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Inset photo from Mary Zhu shows the Oxygen-Evolving Complex (OEC) of PS II cycles through five states.