July 10, 2014
Researchers Develop Novel Method To Observe Mysterious Photosynthesis Process
Brett Smith for redOrbit.com - Your Universe Online
In the pursuit of a renewable energy source, scientists have been trying to understand the exact mechanism behind photosynthesis, and now a large team of scientists has successfully captured the detailed “snapshots” of the process using a powerful laser, according to a report in Nature Communications.
“An effective method of solar-based water-splitting is essential for artificial photosynthesis to succeed but developing such a method has proven elusive,” said study author Vittal Yachandra, a chemist with the Lawrence Berkeley National Laboratory.
"The water splitting process is known to be divided into four steps," noted study author Henry Chapman, a professor at the University of Hamburg and a member of the Hamburg Center for Ultrafast Imaging CUI. "But no-one has actually seen these four steps."
The researchers investigated a process known as photosynthesis II, which involves a manganese-calcium complex that catalyzes the cycle that yields molecular oxygen when energized by solar photons. To observe the process, the team grew miniscule nano-crystals of the photosystem II complex using bacteria that employ photosynthesis.
These crystals were then lit up with a powerful laser to spark the water splitting process. The scientists used double light flashes to induce the changeover from phase S1 to stage S3, as this transition was anticipated to show the most important dynamics. The scientists watched how the molecular structure of the photosystem II complex changed during the entire process.
"We were surprised by the large conformational changes we could witness," said team member Petra Fromme, a bio-physical chemist from Arizona State University. "Actually, the changes are so large that there is an overall structure change, which even changes the dimensions of the unit cell, the smallest building block in a crystal."
The division of water during photosynthesis is a catalytic process, which means photosystem II enables the reaction without being spent. Catalysis plays a major role in many areas of chemistry.
"The technique we employed has a huge potential not only for photosynthesis, but for catalysis in general," Fromme said. "If you would be able to observe all steps of a catalytic reaction, you would be able to optimize it."
"Our study also proves that molecular movies of biochemical processes are possible with a X-ray Free-Electron Laser," Chapman said.
The research team triggered the reaction numerous times as they monitored it with precisely delayed X-ray flashes. The process produced a series of still frames that can be combined into a molecular movie.
"Such a movie can reveal the ultrafast dynamics of chemical reactions," Chapman added. "But we still need to get to higher resolution first."
The researchers said they are getting “tantalizingly close” to being able to engineer photosynthesis.
"This is a major step toward the goal of making a movie of the molecular machine responsible for photosynthesis, the process by which plants make the oxygen we breathe, from sunlight and water," explained team member John Spence, an ASU professor of physics and scientific leader of the National Science Foundation funded BioXFEL Science and Technology Center.