Sweet Sunbeams and Creative Catalysts

Photo courtesy of Greg Stewart/SLAC National Accelerator Laboratory

This artist's rendering shows a Photosystem II crystal hit by a femtosecond X-ray pulse. The resulting X-ray diffraction pattern (bottom) is used to map the overall protein structure. The X-ray emission spectrum (top) is simultaneously collected and used to probe the intactness and oxidation state of the crystal's key manganese complex (Mn4Ca).

After snowy days and freezing nights, practically everyone is looking forward to warmer weather. So (presumably) are plants. After all, they've had to ride out the season too, without the luxury of slipping inside for a piping hot cup of cocoa or a tot of something even stronger.

In a sense, plants also survive frozen winters on sugary snacks. They spend long summer days making sugars through the process of photosynthesis – using a spot of sunlight to combine water with carbon dioxide in order to make glucose.

Seems like a simple recipe, but it's a pretty complicated process. It's also a pretty important one, especially since the oxygen that results – almost a waste product to plants – keeps people alive. As a consequence, researchers have long wanted to see that photosynthetic reaction in action.

They recently got their shot – literally – thanks to the world's most powerful X-ray laser and efforts supported by researchers at the Office of Science's SLAC National Accelerator Laboratory and Lawrence Berkeley National Laboratory (Berkeley Lab). SLAC's Linac Coherent Light Source (LCLS) produces extremely bright, extremely fast pulses of X-rays. They are so fast – about 3-4 trillion times faster than the blink of an eye (figuring that an average eye-blink happens in about 300-400 milliseconds) that they can be used to capture the action of atoms and molecules.

So scientists focused the LCLS on Photosystem II, the protein ‘machinery' in plants (as well as algae and some microbes) that produces oxygen during photosynthesis. Specifically, they focused on the catalyst which accelerates that reaction in fairly dramatic fashion. That gave them images of what the catalyst looked like. To further increase their understanding, researchers simultaneously used a technique called spectroscopy.

Together, in work which was recently published in Science, those techniques gave researchers their best look yet at photosynthesis in action. But it begs the question: Why bother? After all, don't researchers follow the ‘touch' football rules that if it's still breathing, and it isn't bleeding (too much), then there's nothing to worry about and play goes on?

Enlarge Photo

Photo courtesy of Brad Plummer

From left, SLAC scientists Sebastien Boutet, Mark Messerschmidt and Garth Williams participated in an experiment at SLAC's Linac Coherent Light Source that explored crystallized samples of Photosystem II.

Researchers (presumably) do. But in addition to the whole breathing thing, the research also represents an important step toward the ultimate goal of potentially someday producing fuels directly from sunlight through artificial photosynthesis.

Scientists are interested in photosynthesis because of its catalyst, the simple cluster of calcium and manganese atoms that drive the oxygen-producing reaction in Photosystem II. Knowing exactly what that catalyst looks like and how it works may help scientists and engineers shape others, which drive reactions toward new and desired products. There are plenty of possibilities – catalysts are already essential to the production of everything from fuels to pharmaceuticals and fertilizers to foods, and represent a $12 billion-per-year market in the United States.

That's the Office of Science at work; scientific actions on fast reactions that may help keep all of us warm and growing.

The Department's Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information please visit http://science.energy.gov/about. For more information about SLAC National Accelerator Laboratory, please go to http://www.slac.stanford.edu/, and for more information about Berkeley Lab, please go to: http://www.lbl.gov/.

Charles Rousseaux is a Senior Writer in the Office of Science.