Chemists at the University of California, Davis, and Stanford University are revealing how bacteria make free hydrogen and perhaps opening ways for science to imitate them. Producing hydrogen easily and cheaply by chemical water splitting is a dream goal for clean, sustainable energy and bacteria have been doing exactly that for billions of years.
David Britt, professor of chemistry at UC Davis and co-author on the paper sets up the story with, “It’s pretty interesting that bacteria can do this. We want to know how nature builds these catalysts – from a chemist’s perspective, these are really strange things.”
The bacterial catalysts are based on precisely organized clusters of iron and sulfur atoms, with side groups of cyanide and carbon monoxide. Those molecules are highly toxic unless properly controlled, Britt noted.
The cyanide and carbon monoxide groups were known to come from the amino acid tyrosine, Britt said. Jon Kuchenreuther, a postdoctoral researcher in Britt’s laboratory, used a technique called electron paramagnetic resonance to study the structure of the intermediate steps.
They found a series of chemical reactions involving a type of highly reactive enzyme called a radical SAM enzyme. The tyrosine is attached to a cluster of four iron atoms and four sulfur atoms, then cut loose leaving the cyanide and carbon monoxide groups behind.
Britt explains, “People think of radicals as dangerous, but this enzyme directs the radical chemistry, along with the production of normally poisonous CO and CN, along safe and productive pathways.”
Kuchenreuther, Britt and colleagues also used another technique, Fourier Transform Infrared to study how the iron-cyanide-carbon monoxide complex is formed. That work will be published separately.
“Together, these results show how to make this interesting two-cluster enzyme,” Britt said. “This is unique, new chemistry.”
Britt’s laboratory houses the California Electron Paramagnetic Resonance center, the largest center of its kind on the west coast.
The other authors on the paper are: at UC Davis, postdoctoral researchers William Myers and Troy Stich, project scientist Simon George and graduate student Yaser NejatyJahromy; and at Stanford University, James Swartz, professor of chemical engineering and bioengineering.
This team’s work is at the very leading edge of research technology. The search for hydrogen releases with simple chemical reactions is an enticing prospect. The notion of an endlessly recycling store of fuel from some kind of hydrogen-based system would end the need to discover naturally formed supplies.
The team’s work is however in the discovery phase. How or if it can get to lab replication, on to engineering and scaling to commercial rates are questions months or years out. Still, the crack, the peek is exciting – somehow humanity is going to break out and find the practical inexhaustible energy supply systems that make economic sense.
That is sure to be followed by fuel production technologies to build out another economic phase of growth and prosperity.