Understanding How Nature Works with Hydrogen: Modeling the Hydrogenases and Related Enzymes

A project supported by the U. S. National Institutes of Health
(RO1 GM61153-01)

Principal Investigator: Thomas B. Rauchfuss

International Collaborators:
Frédéric Gloaguen, Université Bretagne Occidentale
Luca De Gioia, University of Milano-Biocca

Coworkers:
Bryan E. Barton, B.S. Millikin University
Maria Caroll, B.S. Drew University
Amanda Mack, B.S. University of Rochester
Matthew T. Olsen, B.S. University of Virginia
Ross Putman, Undergraduate University of Illinois, UC
C. Matt Whaley, B.S. University of North Carolina - Wilmington

Recent Alumni:
Jinzhu Chen, Dalian Postdoctorate, Brookhaven National Labs
Aaron K. Justice, Research Scientist, British Petroleum
Ajay Kayal, Lawyer, Budd-Larner, P.C., Princeton
Josh Lawrence, Assistant Professor at Centenary College
Hongxiang Li, Scientist in the Organic Solids Laboratory, Chinese Acad. Sciences
Rachel C. Linck, Scientist, Chemir Analytical Services
Mike A. Reynolds, Research Scientist at Shell, Houston
Michael Schmidt, Research Scientist, Degussa, Augsburg, Germany
Jarl Ivar van der Vlugt, VENI Fellow at the T.U. Eindhoven
Jane L. Stanley, Patent Examiner, U.S. Patent Office
Phil I. Volkers, Senior Editor, Sapling Systems

X-ray Crystallography:
Scott R. Wilson, University of Illinois, UC

 

Hydrogenases are utilized by microorganisms to process H₂.  Hydrogenases catalyze the oxidation of H₂ to H⁺ and reducing equivalents as well as the reverse, the reduction of H⁺ to H₂. These processes, which are important in the cellular energy management, broadly affect many redox transformations of environmental significance (e.g. sulfate reduction). Some pathogenic organisms rely on hydrogen-linked metabolic pathways, including the eubacterium Helicobacter pylori, which is responsible for gastric ulcers and cancers that affect many millions of people.

The goal of our research is to understand how these enzymes work.  We pursue this question mainly by studying biomimetic models, i.e. metal complexes that look and behave like the active sites.  This area mainly relies on techniques of organometallic chemistry.  Students with interests in organometallics are well suited to contribute to this area, especially those students who also like to read beyond organometallics, e.g. biophysics, "green energy", organic synthesis, and spectroscopic and electrochemical methodologies.

A mechanistic understanding of the hydrogenases is likely to provide the foundations for new technologies for conversions of the ultimate clean fuel, H₂. Another attraction is that the catalysts are not based on platinum group metals.

[FeFe]-Hydrogenases

[FeFe]-Hydrogenases are evolutionarily more modern and in fact easier to model. Rapid progress on these sites is being made by us as well as by groups across the globe. The site consists of a diiron dithiolate with cyanide and CO as ligands as well as an appended 4Fe-4S cluster. A vacant or at least labile site is apparent on one Fe center. Substrate turn-over is localized on this site. Substrate activation is complemented by an amine-containing cofactor, which hovers over the catalytic site.
Program highlights:

• In 1999, our group crystallized models of the type [Fe₂(SR)₂(CO)₄(CN)₂]^2-.
  ("First Generation Analogues of the Binuclear Site in the Fe-Only Hydrogenases: Fe₂(SR)2(CO)₄(CN)22-", Schmidt, M.; Contakes, S. M.; Rauchfuss, T. B., J. Am. Chem. Soc. 1999, 121, 9736-7.)
• In 2001, we discovered that diiron dithiolates catalyze the reduction of protons to H₂.
  ("Biomimetic Proton Reduction Catalyzed by an Iron Carbonyl Thiolate", Gloaguen, F.; Lawrence, J. D.; Rauchfuss, T. B., J. Am. Chem. Soc. 2001, 123, 9476-7.)
• In 2001, we described the synthesis of diiron complexes containing the implied cofactor, the azadithiolate (SCH₂NHCH₂S), which was previously unknown.
  ("Diiron Azadithiolates: Synthesis, Structure, and Stereoelectronics", Lawrence, J. D.; Li, H.; Rauchfuss, T. B.; Bénard, M.; Rohmer M.-M., Angew. Chem. Int. Ed. 2001, 40, 1768-71.)
• In 2005, we prepared a diiron dithiolato complex containing a terminal hydride ligand.
  (“Characterization of the First Terminal Diferrous Hydride: Converging on the Mechanism of the Fe-only Hydrogenases” van der Vlugt, J. I.; Rauchfuss, T. B.; Whaley, C. M.; Wilson, S. R.  J. Am. Chem. Soc., 2005, 125, 16012-3.)
• In 2008, we showed that the adt cofactor is required to deprotonate diiron hydrides, an essential step in the oxidation of H₂.
  ("Aza- and Oxadithiolates Are Probable Proton Relays in Functional Models for the [FeFe]-Hydrogenases" Barton, B. E.; Olsen, M. T.; T. B. Rauchfuss  J. Am Chem. Soc. 2008, 130, 16834-16835.)

[NiFe]-Hydrogenases

[NiFe]-Hydrogenases are more pervasive. Modeling efforts in other labs have been ongoing for decades. The active site contains Fe(CO)(CN)₂ and Ni(Scys)₂ centers linked by a pair of cysteinyl thiolates. The ensemble provides a redox-active receptor for protons.



Program highlights:

• The first example of a nickel-iron dithiolato hydride was prepared by our group. We also showed that this species is an excellent catalyst for the reduction of H⁺ to H₂.
  ("Nickel-Iron-Dithiolato-Hydrides Relevant to the [NiFe]-Hydrogenase Active Site" Barton, B. E.; Whaley, C. M.; Rauchfuss, T. B. Gray, D. L.  J. Am. Chem. Soc. 2009, in press).  We have prepared several substituted derivatives of initial model.