Journal of the American Chemical Society
Communication
number of hydrogen bonds. The differences among Zn-L1, Zn-
L2, and Zn-L3 were significantly smaller than that found in Mg-
Ln, but the rates were the same order of magnitude. The results
suggest that the coordinated water molecule is activated by the
metal ion, depending on the strength of the M−O (carboxylate)
bond.
enzymes, but the zinc ion can deactivate the enzymes because of
an induced change in the coordination geometry or conforma-
tional change of the protein.2,15 The present work indicates that
the reactivity of our magnesium complexes are presumably
regulated by the hydrogen bonds. This suggests the indispen-
sable role of Mg2+ ions in the activation of the enzymes that is
coupled with the mode of the hydrogen bond, which must be
precisely regulated by the conformational change of protein. It is
needless to say that the electrostatically heterogeneous environ-
ment in the enzymes is necessary to realize the excellent
reactivity.18,19
A proposed mechanism is shown in Figure 3. The acidity of the
coordinated water molecule is increased due to the presence of
ASSOCIATED CONTENT
* Supporting Information
X-ray crystallographic data for Mg-L1, Mg-L2, Zn-L1, and Zn-
■
S
1
L2 in CIF format and details (Table S1, Figure S1); H NMR
spectra of the complexes (Figure S2) and for the hydrolysis
(Figure S3); and experimental details. This material is available
AUTHOR INFORMATION
Corresponding Author
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This work was supported by JSPS KAKENHI (Grant No.
26410072).
■
Figure 3. Proposed mechanism for the hydrolysis of TNPP by M-L2. R1
and NH represent aromatic and the adjacent NH groups in L2. R2
denotes 4-nitrophenyl group. The intermediate is an outer-sphere (left)
or inner-sphere (right) complex. In this figure, the arrows showing the
attack of OH− (paths A, B) via outer-sphere mechanism are omitted.
REFERENCES
■
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another complex via the coordinated water molecule (outer-
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