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Marcetta Y Darensbourg
Ph. D., University of Illinois Awards:
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Current Activities The evolutionarily perfected catalytic sites in most hydrogenase enzymes are comprised of two base metals, bridged by sulfurs and buried deeply in the proteins, that function in hydrogen production from protons and electrons, or, according to the reverse reaction, to use H2 as a fuel source. We strive to understand how such molecular constructions of nickel and iron, or two iron atoms, ligated by carbon monoxide and cyanide so as to be surprisingly familiar to organometallic chemists, are able to efficiently compete with platinum in fuel cell assemblies. It is our hypothesis that the [FeFe]H2ase enzyme has the diiron organometallic trapped in an "entatic" high energy state which is rotated relative to analogous compounds on the chemist's benchtop. Such a rotated state is stabilized in non-symmetric compounds outfitted with electron-donating ligands. Computational studies further suggest the need for steric hindrance at the bridgehead of the S to S linker. Synthetic efforts are focused on such [FeIFeI] compounds which are evaluated as electrocatalysts for H2 production. At the FeIIFeI/II redox level, H2 uptake and activation is assayed by isotopic exchange in D2O/H2 mixtures. The ultimate goal is the synthesis of base metal, hydrogen-processing catalysts ultimately for replacement of platinum in fuel cell electrodes.   We also pursue the new paradigm for enzyme active site construction that has been discovered in the Acetyl CoA Synthase (ACS) enzyme active site and develop square planar NiN2S2 and other MN2S2 complexes as a new class of ligands that support organometallic chemistry. We posit that the binuclear makeup of these active sites may be interpreted in terms of metal-dithiolates as ligands to a second, catalytically active metal. This is the basis of design of ACS biomimetics and studies of fundamental ligand properties such as electronic, steric, and hemi-lability effects. We have shown that the Merrifield synthesis of the small peptides can also produce resin-bound NiN2S2 which bind other metals at sulfur in imitation of the ACS enzyme. Our ultimate goal is to take advantage of the ligating properties of the evolutionarily perfected NiN2S2 ligands for the production of resin supported, site-isolated organometallic catalysts. Our research is augmented by interface with Professor Michael Hall, a computational chemist who has interest in computing reaction mechanisms for enzymes, many times anchoring those calculations in spectroscopic properties of the small molecule analogues which we make. We also collaborate with Professor Manuel Soriaga, an electrochemist with interest in fuel cell development. Students in the MYD group become knowledgeable in inorganic and organometallic synthesis, bioorganometallic chemical processes, x-ray crystallography, electrochemical analysis and various spectroscopies. Selected Publications De Novo Design in Inorganic Chemistry: Di-Iron(I) Complexes as Accurate Structural Models of the Reduced Form of Iron-Iron Hydrogenase, Jesse W. Tye. Marcetta Y. Darensbourg, and Michael B. Hall, Inorg. Chem. 2006, 45, 1552-1559. A Nickel Tripeptide as a Metallodithiolate Ligand Anchor for Resin-Bound Organometallics, Kayla N. Green, Stephen P. Jeffery, and Marcetta Y. Darensbourg, J. Am. Chem. Soc. 2006, 128, 6493-6498. Iron Nitrosyl Complexes as Models for Biological Nitric Oxide Transfer Reagents, Chao-Yi Chiang, Marcetta Y. Darensbourg, Journal of Biological Inorganic Chemistry, 2006, 11, 359-370. Making a natural fuel cell, Marcetta York Darensbourg, Nature, 2005, 433, 589-591. Dual Electron Uptake at Iron and Ligand in an Asymmetric [FeFe] Hydrogenase Model Compound, Jesse W. Tye, Jonghyuk Lee, Hsiao-Wan Wang, Rosario Mejia-Rodriguez, Joseph H. Reibenspies, Michael B. Hall, Marcetta Y. Darensbourg Inorg. Chem. 2005, 44, 5550-5552. Characterization of Steric and Electronic Properties of NiN2S2 Complexes as S-donor Metallodithiolate Ligands, Marilyn V. Rampersad, Stephen P. Jeffery, Melissa L. Golden, Jonghyuk Lee, Joseph H. Reibenspies, Donald J. Darensbourg, Marcetta Y. Darensbourg, J. Am. Chem. Soc. 2005, 127, 17323-17334. |
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