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-η2:η2-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).
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