The Oxygen-Evolving Complex (OEC) of PS II cycles through five states, S0 to S4, where four electrons are sequentially extracted from the OEC in four light–driven, charge-separation events. The black ellipses show snapshots of the metal cluster observed in this study.
(Photo : Arizona State University/ Mary Zhu)
Scientists have managed to take the first pictures of photosynthesis in action as it splits water into electrons, oxygen, and protons.
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Photosynthesis is one of the fundamental processes of life on Earth, without it, our planet wouldn't have its oxygen-rich atmosphere, according to
"This study is the first step towards our ultimate goal of unraveling the secrets of water splitting and obtaining molecular movies of biomolecules," said Petra Fromme, the senior author of the new study, in a news release, issued by Arizona State University.
The "invention" of the water splitting process in Photosynthesis II (PSII) about 2.5 billion years ago that eventually led to the atmosphere composition seen today.
The development of an "artificial leaf" is one of the main goals of the ASU Center for Bio-Inspired Solar Fuel Production.
The center was the main supporter of this study.
"A crucial problem facing our Center for Bio-Inspired Fuel Production (Bisfuel) at ASU and similar research groups around the world is discovering an efficient, inexpensive catalyst for oxidizing water to oxygen gas, hydrogen ions and electrons," said ASU Regents' Professor Devens Gust, the center's director, according to the release. "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 research by Fromme and coworkers gives us, for the very first time, a look at how the catalyst changes its structure while it is working," Gust added. "Once the mechanism of photosynthetic water oxidation is understood, chemists can begin to design artificial photosynthetic catalysts that will allow them to produce useful fuels using sunlight."
In photosynthesis, oxygen is produced at a "special" metal site, which contains four manganese atoms and one calcium atom, connected together as a metal cluster.
This cluster is bound to PSII that catalyzes the light-driven process of water splitting. It requires four light flashes to extract one molecule of oxygen from two water molecules bound to the metal cluster, according to the release.
Fromme believes that there are two main drawbacks to obtaining structural and dynamical information on this process by traditional X-ray crystallography.
First, the pictures one can obtain with standard structural determination methods are static. Second, the quality of the structural information is affected by X ray damage.
"The trick is to use the world's most powerful X-ray laser, named LCLS, located at the Department of Energy's SLAC National Accelerator Laboratory," said Fromme. "Extremely fast femtosecond (10 -15 second) laser pulses record snapshots of the PSII crystals before they explode in the X-ray beam, a principle called 'diffraction before destruction.'"
The ultimate goal that researchers want to obtain is to record molecular movies of water splitting.
The study was published on July 9 in the journal Nature.