Book of Abstracts - Ruhr-Universität Bochum

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ISBOMC `10 5.7 – 9.7. 2010 Ruhr-Universität Bochum
Construction of Organometalloenzymes
Yoshihito Watanabe a
a Nagoya University, Graduate School of Science, Department of Chemistry, Chikusa, 464-8602,
Nagoya, Japan. E-mail: yoshi@nucc.cc.nagoya-u.ac.jp
A variety of protein structures are employed in nature as frameworks for the deposition of metal
cofactors to provide metalloenzymes. Very recently, we have designed a myoglobin mutant as a
model for a substrate bound form of cytochrome P450 and site
specific aromatic hydroxylation was found to proceed by a
stochiometric amount of H 2 O 2 in a few seconds. 1 As an
extension of our efforts for the construction of
organometalloproteins, we have replaced the heme prosthetic
group with a series of M(salophen) complexes, Rh(Phebox) (Fig
1), and Cu complexes. 2 Instead of these small protein cavities,
we have also employed a protein having a large cavity, i.e., apo-
ferritin (apo-Fr). Ferritin is an iron storage protein and its apoform
has been employed as nano-reactors. We have also
prepared a zero-valent palladium cluster by chemical reduction
of palladium ions in the apo-ferritin cage and examined its catalytic hydrogenation activity. The
palladium clusters catalyzes size-selective olefin hydrogenation because substrates must penetrate into
the ferritin cavity through the size restricted channels. 3 Through the Pd•apo-Feritin study, we have
found that there are Pd ion binding sites in the apo-ferritin to capture as many as 300 Pd ions. Thus,
we have examined crystal structures of apo-ferritin containing various amounts of Pd ions. The crystal
structures of Pd•apo-Fr has been refined to 1.65Å resolution (Fig 2). 4 We have further found that
Pd II (allyl) ion utilizes
different binding sites
bearing different
coordination structures
(Fig 3). The Pd(allyl)•
apo-Fr composites show
catalytic activities for the
Suzuki coupling reaction
as shown below. 5
References
1) T. D. Pfister, et al., J. Biol. Chem. 280, 12858 (2005). 2) M. Koshiyama, et al., J. Am. Chem. Soc.
127, 6556 (2005). 3) M. Suzuki, et al., Angew. Chem. Int. Ed. 43, 2527 (2004). 4) T. Ueno, et al., J.
Am. Chem. Soc. 131, 2094 (2009). 5) T. Ueno, et al., J. Am. Chem. Soc. 130, 10512 (2008).
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Fig.1 Apo-Mb•Rh(Phebox) composite
structure.
Fig.2 The crystal structure of apo-Fr•Pd. Fig.3 The crystal structure of apo-Fr•Pd(allyl).