Spinach may help convert sunlight into clean alternative fuel

Popeye's favourite snack spinach, which gave the cartoon character super strength, also has the ability to convert sunlight into a clean, efficient alternative fuel.

Purdue University physicists are part of an international group using spinach to study the proteins involved in photosynthesis, the process by which plants convert the sun's energy into carbohydrates used to power cellular processes.

"The proteins we study are part of the most efficient system ever built, capable of converting the energy from the sun into chemical energy with an unrivalled 60 per cent efficiency," said Yulia Pushkar, a Purdue assistant professor of physics involved in the research.

"Understanding this system is indispensable for alternative energy research aiming to create artificial photosynthesis," Pushkar said.

During photosynthesis plants use solar energy to convert carbon dioxide and water into hydrogen-storing carbohydrates and oxygen.

Artificial photosynthesis could allow for the conversion of solar energy into renewable, environmentally friendly hydrogen-based fuels.

In Pushkar's laboratory, students extract a protein complex called Photosystem II from spinach they buy at the supermarket.

It is a complicated process performed over two days in a specially built room that keeps the spinach samples cold and shielded from light.

Once the proteins have been carefully extracted, the team excites them with a laser and records changes in the electron configuration of their molecules.

"These proteins require light to work, so the laser acts as the sun in this experiment," Pushkar said.

"Once the proteins start working, we use advanced techniques like electron paramagnetic resonance and X-ray spectroscopy to observe how the electronic structure of the molecules change over time as they perform their functions," she said.

Photosystem II is involved in the photosynthetic mechanism that splits water molecules into oxygen, protons and electrons.

During this process a portion of the protein complex, called the oxygen-evolving complex, cycles through five states in which four electrons are extracted from it, Pushkar said.