However, the LCLS X-ray laser comes in such brief pulses measured in quadrillionths of a second that they could probe the crystals at room temperature in a chemically active state, before any damage set in, and generate data on two of the four steps in oxygen generation.
"We decided to use two X-ray techniques at once at the LCLS: crystallography to look at the overall atomic structure of Photosystem II, and spectroscopy to document the position and flow of electrons in the catalyst," said Vittal Yachandra, a Berkeley Lab chemist and co-leader of the project. "The electrons are important because they are involved in making and breaking bonds and other processes at the heart of chemical reactions."
Another co-leader, SLAC physicist Uwe Bergmann, said, "This result is a critical step in the ultimate goal to watch the full cycle of the splitting of water into oxygen during photosynthesis." The use of both techniques also verified that the molecular structure of the samples is not damaged during measurement with the LCLS, he said. "It's the first time that we have resolved the structure of Photosystem II under conditions in which we know for sure that the machinery that does the water splitting is fully intact."
In future LCLS experiments, the researchers hope to study all the steps carried out by Photosystem II in higher resolution, revealing the full transformation of water molecules into oxygen molecules considered a key to unlocking the system's potential use in making alternative fuels.
"Getting a few of the critical snapshots of this transition would be the final goal," said Jan Kern, a chemist who holds a joint position at
|Contact: Andy Freeberg|
DOE/SLAC National Accelerator Laboratory