| Budget Amount *help |
¥15,800,000 (Direct Cost: ¥15,800,000)
Fiscal Year 2005: ¥8,000,000 (Direct Cost: ¥8,000,000)
Fiscal Year 2004: ¥7,800,000 (Direct Cost: ¥7,800,000)
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| Research Abstract |
Hydrogenase is essential to hydrogen metabolism and represents highly active catalyst for the production and utilization of H_2, hence their active sites are targets for synthetic chemistry. During this research project, we have made substantial progresses in reproduction of the structure and the functions of hydrogenase.
1) Aiming to model the active sites, we have synthesized a tetranuclear Fe-Ni-Ni-Fe complex [(CO)_3Fe(μ-S^tBu)_3NiBr]_2(1)from FeBr_2(CO)_4, NaS^tBu, and NiBr_2(EtOH)_4. The key for successful preparation of the tetranuclear complex is to conduct all procedures at -40℃. Thermal instability of the compound arises from the weak interaction between Fe(II) and CO ligands. Indeed, complex 1 appeared to be relatively stable under CO atmosphere.
2) The tetranuclear complex 1 can be regarded as a dimeric form of dinuclear Fe-Ni complexes weakly bridged by bromides. Simple replacement reactions of bromide with thiolates took place, and a series of dinuclear Fe-Ni complexes were obtained. The dinuclear complexes possess facially arranged three CO lgands on iron, one terminal and two bridging thiolate ligands, and another two sulfur-donors terminally bound to nickel. These Fe-Ni complexes comprise important features of the active site of [NiFe] hydrogenases, and they offer a possibility for reaction chemistry regarding the enzymatic function.
3) The CO-inhibited form of [NiFe] hydrogenase is suggested to bind a CO molecule at the nickel site, whereas CO complexes of Ni(II) and Ni(III) are uncommon. One of the artificial dinuclear Fe-Ni models appeared to react with CO to afford a dinuclear complex with a Ni(II)-bound CO. The reaction was found to be reversible, as demonstrated for the native active site. In order to provide suitable complexes for reaction models, one of the thiolate ligands between Fe and Ni was replaced with chloride.
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