Synthetic Enzyme Shows Promise As Way To Make Hydrogen Cheaply

Amid growing concerns over pollution and energy shortages, an economy based on clean-burning hydrogen fuel could curb future energy crises and ease global warming. But scientists have been stymied in their attempts to develop a process for producing an inexpensive and abundant supply of this gas, even though it is the most common element in the universe. Current manufacturing methods -- such as electrolysis and the catalytic stripping of hydrogens from hydrocarbons, are both costly and inefficient.

"Fortunately, nature has already solved the problem by designing numerous microorganisms that efficiently make or use hydrogen in support of their metabolic activities," said Thomas Rauchfuss, a professor of chemistry and a researcher at the university's materials research laboratory. "If we can fully understand how this natural process works, perhaps we can duplicate it commercially."

About two years ago, the hydrogen-producing enzymes for several microorganisms were isolated, purified and crystallized. "Late last year and early this year, the chemical structures for two of these big biological catalysts were announced, and it was as though the curtains had been drawn back," Rauchfuss said. "We immediately went to our lab and began efforts to make a look-alike for the natural catalyst."

Rauchfuss and his fellow molecule makers -- visiting postdoctoral research associate Michael Schmidt and graduate research assistant Stephen Contakes -- have successfully synthesized much of the active site of one hydrogenase enzyme.

The researchers presented their results at the American Chemical Society national meeting in New Orleans, Aug. 22-26. A paper reporting their findings is scheduled to appear in the Journal of the American Chemical Society.

Like the original enzyme, the hydrogenase look-alike contains an integral metal-metal bond, connected to several ligands -- including iron sulfide, carbon monoxide and cyanide. "Nature really designed an amazing structure," Rauchfuss said. "Carbon monoxide and cyanide are poisons. This enzyme is not something you would normally associate with life."

Unlike the original enzyme, however, the new version does not yet fully function as a catalyst. "We can get it to spit out some hydrogen, but then it stops for some reason," Rauchfuss said. "We don't yet know how to make the system 'turnover' for continuous hydrogen production."

Because the synthetic replication process is still in the early stages of development, "there is considerable room for improvement," Rauchfuss said. "For example, the natural enzyme contains thousands of atoms, whereas our synthetic version contains only 25 atoms, so it is not surprising that our simple model is not perfect. But this is a very big step in the right direction."