The FeFe-hydrogenases are of great interest because they can catalyze both the
forward and reversed dihydrogen uptake/evolution reactions. Under optimal
conditions a single molecule of FeFe-hydrogenase can produce approximately 9000
molecules of hydrogen per second. This translates into a theoretical capacity
for refueling the hydrogen tank of the Space Shuttle within 30 minutes. Thus,
hydrogenases are considered as desirable biological targets for hydrogen-based
energy production and utilization technologies.
Organisms that possess FeFe-hydrogenases are widely distributed among different
microorganisms, including hyperthermophiles and algae. But understanding the
chemistry driving the efficient hydrogen conversion has been difficult, due to
in part because the molecules themselves are so large and complex. Now,
researchers at Montana State University and collaborators have solved part of
the puzzle by looking at a synthetic biomimetic molecule that structurally
models the active site of these metalloenzymes.
Using sulfur K-edge x-ray absorption spectroscopy data from SSRL's beam line
6-2, the researchers probed the nature and the strength of the chemical
interaction between the 4Fe- and the 2Fe-containing subclusters of the active
site H-cluster. By comparing the spectra of each subcluster and the biomimetic
H-cluster framework, the team found evidence for considerable electron
delocalization between the subclusters, suggesting that the H-cluster is an
electronically inseparable [6Fe-6S] cluster. Computer modeling on the separate
and combined subclusters also show this delocalization by the presence of
molecular orbitals that span the entire 6Fe-framework. Thus, the catalytic
activity is determined by both subclusters together, not just the [2Fe-2S]
subcluster that has been the focus of much past research.
To learn more about this research see the full scientific highlight at:
http://www-ssrl.slac.stanford.edu/research/highlights_archive/FeFe.html
Schwab, D. E.; Tard, C.; Brecht, E.; Peters, J. W.; Pickett, C. J.; Szilagyi,
R. K. Chem. Commun. 2006, 3696-3698.
