Researchers long have seen hydrogen-based gases as a way to solve the emissions problem that our global dependence on fossil fuels has created. However, a major stumbling block is that the production of hydrogen for these fuels has never been efficient or cost-effective enough for mass production.

Chemistry professor Thomas Rauchfuss and collaborators are looking to biological processes to find an efficient source of hydrogen gas as an environmentally friendly fuel. (Image source: Fred Zwicky)

A team of researchers from the University of Illinois and the University of California, Davis have tried to solve this. Chemists on the team have discovered more about how synthetic enzymes can play a role in the simple production of hydrogen.

A team led by University of Illinois Chemistry Professor Thomas Rauchfuss has identified a biological enzyme, or hydrogenase, that can help synthesize hydrogen more efficiently than any current process. Specifically, they worked with one of the two varieties of these enzymes—iron-iron enzymes—because it can generate hydrogen gas faster than the other, nickel-iron enzymes.

Hydrogenases are basically nature’s machinery for making and burning hydrogen gas. “Hydrogenases are enzymes, which can be thought of as small machines embedded in a fluffy protein,” Rauchfuss told Design News. “The machine [equals the] active site.”

Moreover, these enzymes either “eat” H2 or secrete H2 depending on their circumstances (their environment), Rauchfuss explained.  “If the organism is stuck deep in the mud away from air, they ferment biomass, and release H2. Their only way to pull H2 from their substrates is using hydrogenases.”

On the other hand, organisms higher up toward the surface with eat the H2 by using hydrogenases to pull electrons out of H2 and use those electrons to convert some oxidant, he told us.

Finding the right recipe

Researchers set out to find the right chemical composition to synthesize a hydrogenase based on the iron-iron material balance to interact efficiently with hydrogen for potential fuel production. “Organisms have only one way of interacting with H2, and that way involves hydrogenase enzymes,” Rauchfuss said. “Otherwise H2 just does not interact with living creatures. It’s just inert. But hydrogenases do interact with H2 and then wire their interaction to other parts of the cell.”

Before embarking on the project, the chemists on the team already had a general understanding of the chemical composition of the active sites within the enzyme. Building upon this knowledge, they came up with a hypothesis that the sites were assembled using 10 parts: four carbon monoxide molecules, two cyanide ions, two iron ions, and two groups of a sulfur-containing amino acid called cysteine.

Eventually, researchers discovered that they had hypothesized wrong. It was instead more likely that the enzyme’s engine was composed of two identical groups containing five chemicals: two carbon monoxide molecules, one cyanide ion, one iron ion, and one cysteine group. The groups form one tightly bonded unit, and the two units combine to give the engine a total of 10 parts.

However, there was even another surprise in store for researchers after doing laboratory analysis of the lab-synthesized enzyme, Rauchfuss said. The team realized their formula for enzyme composition is incomplete. There are actually 11 bits required to make the active site engine rather than 10.

Researchers plan to continue their work by searching for that last piece of the puzzle. The team reported their findings in a paper the Proceedings of the National Academy of Science.

While it’s unclear what specific applications will come out of the work. The research could provide an assembly kit that will be instructive to other catalyst design projects. “The take-away from this study is that it is one thing to envision using the real enzyme to produce hydrogen gas, but it is far more powerful to understand its makeup well enough to able to reproduce it for use in the lab,” Rauchfuss said. 

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco and New York City. In her free time she enjoys surfing, traveling, music, yoga and cooking. She currently resides in a village on the southwest coast of Portugal.