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Tiny Bio-Engines Use Carbon Dioxide as Fuel

Hemoglobin photosynthesis model

Hemoglobin model. In red and yellow, solar antennae. Between the protein scaffolds (blue corkscrews) is the molecule (in orange and blue) responsible for processing CO2. Courtesy: Matthew Hartings.

Imagine tapping on your iPod and fighting climate change, at least, a little bit.

A chemistry lab on AU’s campus is developing technology that could eventually lead to fuel cells that use solar power to consume carbon dioxide, a compound humans have assured our atmosphere holds in overabundance.

The key is photosynthesis.

You’ll remember from grade school that green plants the world over use energy from sunlight to turn carbon dioxide and water into sugar. Chemistry professor Matthew Hartings and his students are working to mimic photosynthesis in other biological proteins, specifically, DNA coded for the hemoglobin of the Ascaris suum nematode — a parasitic roundworm that attacks pigs.

This particular protein is best equipped for the task on multiple counts. Hemoglobin is evolution’s winner in the gas-binding race, and Hartings explains that within hemoglobin “there’s a really nice pocket for a gas molecule to come in and set up.” It’s a hospitable protein, and so work is focused on directing action within hemoglobin to adapt to processing carbon dioxide.

The result is a hybrid of protein and metal, a biological machine. “Proteins give us life, but the metals make the life interesting,” says Hartings.

The heme that typically binds with oxygen or carbon monoxide and that gives hemoglobin many of its characteristics (like its red color) is replaced with other molecules, for instance, nickel cyclam, which Hartings calls “one of the best carbon dioxide catalysts out there.”

To spur reaction with nickel cyclam, the team will attach light-sensitive solar antennae (ruthenium complexes) to the surface of the protein. The antennae can transfer electrons — energy — into the hemoglobin to drive chemical reactions that consume CO2 and release formic acid. Energy is stored in the formic acid’s chemical bonds, and this is what can be converted into electrical energy.

Together, this simple biological system and carefully placed metals react to provide energy that, one day, could be used in fuel cells.

“I could tell you I’d like to have global warming solved in the next two years.” But Hartings scoffs. If ever applied in the products we use every day, he thinks, the impact of this research would be quite small. He believes real battles against climate change will need to occur on an industrial level. Yet Hartings does recognize the potential for some benefit, both in carbon consumption and scientific discovery.

Mimicking photosynthesis from inside a protein is a technical challenge, to say the least, and is an area of untapped research. “I’m trying to make a small protein do the same thing plants do, with a huge amount of biological machinery,” explained Hartings.

For Hartings this work isn’t all about direct application — though there may be opportunities for that. “We go into our labs, and we try to learn new things, and we’re surprised. And surprises happen when you do science, and the really historically important scientists were the ones who recognized the discoveries they made and what they could be used for.”

For now, Hartings and his student lab staff are testing best methods for replacing hemes and perfecting electron transfer.

They are also taking a step toward reversing the paradigms for how we fuel our lives.