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 by: Mary Zhu (Photo : Mary Zhu/ Arizona State University )

Arizona State University scientists have captured images of photosynthesis in action. The snapshots reveal how water is split into protons, electrons and oxygen.

The water-splitting process in Photosystem II (PSII) is one of the major reasons for evolution of complex life on earth. Higher lifeforms depend on this process for their energy needs.

"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, professor of chemistry and biochemistry at ASU.

Scientists worldwide are trying to find efficient and inexpensive ways of oxidizing water to oxygen gas, hydrogen ions and electrons. ASU Regents' Professor Devens Gust, the center's director said that photosynthetic organisms have already found the system and use just calcium and manganese atoms to split water.

Understanding the process could help other scientists develop systems that can produce fuel using sunlight, researchers said.

Oxygen, during photosynthesis, is produced at a metal site that has four atoms of manganese and one of calcium that are held together in a metal cluster. The cluster is connected to protein PSII, which acts as a catalyst during the water-splitting process. Four flashes of light are needed to free one molecule of oxygen from two molecules of water. Note that the water molecules are attached to the metal cluster.

According to Fromme, using X-ray crystallography to obtain images of this process is problematic due to two reasons. Firstly, X-rays could damage the process, leading to incomplete information and secondly, the images obtained would be static.

"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 in a news release. "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.'"

Researchers could get damage-free snapshots of the process in action. The team's ultimate goal is to make a movie of the entire process.

Photosystem II nanocrystals were used in the study. Researchers found that protein and the metal cluster undergo structural changes during the water-splitting event. The cluster elongates, enabling water molecules to move in.

The study is published in the journal Nature.

Other scientists are trying to find simpler ways of splitting water in the laboratory. Recently, ASU researchers tried to copy a design from nature to develop artificial leaf.