´
86
E. Balogh-Hergovich et al. / Journal of Molecular Catalysis A: Chemical 206 (2003) 83–87
6
5
4
3
2
1
0
10
20
30
t / min
70
Fig. 2. Time course for the oxygenation of [CuII(fla)(idpa)]ClO4 (3) in the presence of sodium acetate. Conditions: 50 cm3 DMF, T = 100 ◦C,
[O2] = 7.7 × 10−3 mol dm−3, (᭹) 0.026 mmol 3, (᭛) 0.025 mmol 3 + 0.093 mmol NaOAc, (᭜) 0.026 mmol 3 + 0.272 mmol NaOAc, (×)
0.025 mmol 3 + 0.523 mmol NaOAc (experiments 1, 3, 4, and 5; Table 1).
copper(II) ion can be regarded as a distorted trigonal
bipyramidal with a τ value of 0.61 [13]. The two ni-
trogen atoms of the N3-ligand and one oxygen atom
of the flavonolate ligand occupy basal positions. The
remaining N-atom of the N3-ligand and the other
oxygen atom of the flavonolate ligand lie in apical
positions. The flavonolate ligand in 3 is bidentate,
however on addition of the carboxylate ions to the
complex they coordinate to the copper(II) in a mon-
odentate fashion just displacing one of the oxygen
atoms of the flavonolate ligand. According to that 3 is
converted to 5, where the flavonolate ligand becomes
monodentate. This may be the reason for the en-
hanced reactivity towards dioxygen. So 5 is converted
to 6 by incorporating both O-atoms of dioxygen into
the substrate with the concomitant release of carbon
monoxide, just in agreement with the enzyme reac-
tion. Seemingly, carboxylate coordination, as found
in the structure of quercetin 2,3-dioxygenase from
A. japonicus, is necessary for the enzyme reaction
in order to elicit reasonable reaction rates. On the
bases of these experiments we believe to have the
first evidence that carboxylate coordination plays an
important role in the enzyme reaction, and these re-
actions may be regarded as the first best mimicking
models for the enzyme. Further work is in progress to
work out structural and functional models of quercetin
2,3-dioxygenase in light of the recent knowledge of
its structure.
Acknowledgements
We thank the Hungarian National Research Fund
OTKA # T 03400 for financial support of this work.
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