Yoshimitsu Tachi (Lecturer)

1. Current Research and Principal Research Interests

  Our current research in the Biochemical Reactions (BCR) group involves synthetic organic and bioinorganic chemistry. In the bioinorganic area, our objective is to gain a fundamental structural, spectroscopic, and mechanistic understanding of copper protein active sites of biological and environmental importance via the synthesis, characterization, and analysis of the reactivity of model complexes. We are also interested in developing new models of key intermediates in the catalytic cycles of non-heme diiron enzymes. The current goal of our research is to synthesize and characterize a variety of metal complexes of different N-donor ligands, pyridine, amine, and so on.

Elucidation of Catalytic Mechanism of Cytochrome c Oxidase
   The main objective is to build a model compound of cytochrome c oxidase (CcO),  which contains a dinuclear metal site, a non-heme copper and a heme, as an efficient oxygen activation system. A hetero-bimetallic iron/copper complex supported by a hybrid heme/non-heme ligand system is reported the first example which contains a m-peroxo bridge between the two metal ions. To seek the O2 activation mechanism in CcO, reactivity of the hetero-dinuclear Fe/Cu centers, effect of the ligating axial imidazole, and the role of tyrosine crosslinked to imidazole in the enzymatic system have been investigated in detail in model systems. 

New Modeling of Metalloenzymes
   Recent efforts have also been directed to modeling of other multi-nuclear metalloenzymes as typical oxygenation and/or oxidation catalysts which utilize activated dioxygen and oxidize various organic molecules in good regio- and/or stereo-selectivity. Three types of ligands have been synthesized and characterization and reactivity studies of the corresponding di- and multi-nuclear copper and iron complexes are now in progress: (i) Unsymmetric bidentate ligands consisting of distinct tri- and tetradentate metal-binding moieties, (ii) Tri-nucleating ligands for modeling of multi-copper enzyme active sites, and (iii) Binaphthol-based bidentate ligands for asymmetric oxygenation reaction.

2. Selected Publications

1.“Fine-tuning of copper(I)-dioxygen reactivity by 2-(2-pyridyl)ethylamine bidentate ligands”, M. Taki, S. Teramae, S. Nagatomo, Y. Tachi, T. Kitagawa, S. Itoh, and S. Fukuzumi, J. Am. Chem. Soc., 124, 6367-6377 (2002). 

2. “Oxidative degradation of β-diketiminate ligand in copper(II) and zinc(II) complexes”, S. Yokota, Y. Tachi, and S. Itoh, Inorg. Chem. 41, 1342-1344 (2002). 

3. “Reactivity of Bis(μ-oxo)dicopper(III) Complex toward External Substrates”, M. Taki, Y. Tachi, S. Fukuzumi, and S. Itoh, J. Inorg. Biochem., 86, 449-449 (2001). 

4. “Modulation of Coordination Chemistry in Copper(I) Complexes Supported by Bis[2-(2-pyridyl)ethyl]amine-based Tridentate Ligands”, T. Osako, Y. Tachi, M. Taki, S. Fukuzumi, and S. Itoh, Inorg. Chem., 40, 6604-6609 (2001).

5. “Oxygen Activation on Cu-Fe Heterodimetallic Complexes as Models of Terminal Oxidases”, Y. Naruta, Y. Tachi, T. Chishiro, A. E. Wigger, and F. Tani, J. Inorg. Biochem., 86, 355-355 (2001).

6. “A new β-Diketiminate Ligand Carrying a Functional Group on the Carbon Framework. Synthesis and Characterization of a Linear Polymeric Copper(I) Complex”, S. Yokota, Y. Tachi, N. Nishiwaki, M. Ariga, and S. Itoh, Inorg. Chem., 40, 5316-5317 (2001). 

7. “A Cu(II)-Mediated C-H Oxygenation of Sterically Hindered Tripyridine Ligands to Form Triangular Cu(II) Complexes”, M. Kodera, Y. Tachi, T. Kita, H. Kobushi, Y. Sumi, K. Kano, M. Shiro, M. Koikawa, T. Tokii, M. Ohba, and H. Okawa, Inorg. Chem., 39, 226-234 (2000).

8. “Crystal Structure and Reversible O2-Bindig of a Room Temperature Stable μ-η22-Peroxodicopper(II) Complex of a Sterically Hindered Hexapyridine Dinucleating Ligand”, M. Kodera, K. Katayama, Y. Tachi, K. Kano, S. Hirota, S. Fujinami, and M. Suzuki, J. Am. Chem. Soc., 121, 11006-11007 (1999).

9. “A Superoxodicopper(II) Complex Oxidatively Generated by a Reaction of Di-μ-hydroxodicopper(II) Complex with Hydrogen Peroxide”, M. Kodera, Y. Tachi, S. Hirota, K. Katayama, H. Shimakoshi, K. Kano, K. Fujisawa, Y. Moro-oka, Y. Naruta, and T. Kitagawa, Chem. Lett., 5, 389-390 (1998). 

10. “Efficient Oxidation of Various Phenols Catalyzed by Di-μ-hydroxodicopper(II) Complexes of a Hexapyridine Dinuceating Ligand”, M. Kodera, H. Shimakoshi, Y. Tachi, K. Katayama, and K. Kano, Chem. Lett., 5, 441-442 (1998).