A. Bencini, A. Bianchi, E. Garc ´ı a-Espa n˜ a et al.
FULL PAPER
[
[
[
3]
4]
measured by an initial-slope method monitoring the increase in the
H. A ¨ı t-Haddou, J. Sunoaka, S. L. Wiskur, J. F. Folmer-And-
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4014Ϫ4016.
4
03-nm absorption of the released 4-nitrophenolate ion at 298.1
[24]
Ϯ 0.1 K by using the procedure reported previously.
The ionic
B. Altava, M. I. Burguete, S. V. Luis, J. F. Miravet, E. Garc ´ı a-
Espa n˜ a, V. Marcelino, C. Soriano, Tetrahedron 1997, 53,
4
strength was adjusted to 0.15 with NaClO . The reaction solu-
tion was maintained at 298.1 Ϯ 0.1 K. MOPS (pH ϭ 7.0Ϫ7.8),
TAPS (pH ϭ 7.8Ϫ8.9), CHES (pH ϭ 8.9Ϫ9.7) and CAPSO (pH ϭ
4751Ϫ4761.
5] [5a]
P. Molenveld, J. F. J. Engbersen, D. N. Reinhoudt, Eur. J.
9
4
.1Ϫ10.2) buffers were used (50 m). In a typical experiment, after
[5b]
Org. Chem. 1999, 3269Ϫ3275.
P. Molenveld, J. F. J.
-nitrophenyl
acetate
and
[Zn
the
L2](ClO
dizinc
·4H
complexes
and
Engbersen, Chem. Soc. Rev. 2000, 29, 75Ϫ86.
[
[
Zn
Zn
2
L1](ClO
L3](ClO
4
)
)
4
·2H
·2H
2
O,
2
4
)
4
2
O
[6]
[7]
J. Blasko, T. C. Bruice, Acc. Chem. Res. 1999, 32, 475Ϫ484 and
references therein.
E. L. Hegg, J. N. Burstyn, Coord. Chem. Rev. 1998, 173,
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1999, 182, 243 and references therein.
2
4
4
2
3
O (0.1Ϫ1.0 m) in 10% CH CN solutions at
II
appropriate pH (the reference experiment does not contain the Zn
complex) were mixed, the UV absorption decay was recorded im-
mediately and was monitored generally until 2% decay of 4-nitro-
phenyl acetate. For all three ligands, two species — [Zn
and [Zn
[
8] [8a]
3
ϩ
M. Yashiro, A. Ishikubo, M. Komiyama, J. Chem. Soc.,
2
LOH]
Chem. Commun. 1995, 1793Ϫ1794. [ M. Yashiro, A. Ishi-
8b]
2ϩ
2 2
L(OH) ]
— promote NA hydrolysis; in the case of L1,
[
8c]
2
ϩ
kubo, M. Komiyama, Chem. Commun. 1997, 83Ϫ84.
S.
measurements in the pH range 7.5Ϫ8.2, where the [Zn
2
2
L1(OH) ]
Matsuda, M. Yashiro, A. Kuzuya, A. Ishikubo, M. Komiyama,
complex is absent from the solution, allowed us to determine se-
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cond-order kNA1 rate constants for promoted hydrolysis by the
[9]
P. Rossi, F. Felluga, P. Tecilla, F. Formaggio, M. Crisma, C.
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monohydroxo species [Zn
2
L1OH]3 and to extrapolate the kNA2
ϩ
values for this species in the pH range 8.7Ϫ10.0, where both species
are present in solution. Measurements in the pH range 8.7Ϫ10.0
allowed us to determine kOBS values. The second-order rate con-
[10]
2ϩ
stants kNA2 for the dihydroxo complex [Zn
2
L1(OH)
2
]
are calcu-
lated by subtracting from the kOBS value at a given pH the kNA1
value at the same pH. An analogous procedure was used for the
L2 and L3 complexes. Errors in kNA values were generally 5%. The
hydrolysis rate of BNP to give mono(p-nitrophenyl)phosphate
[
[
[
[
11]
12]
13]
14]
117, 5462Ϫ5469.
S. Kondo, K. Shinbo, T. Yamaguchi, K. Yoshida, Y. Yano, J.
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(
MNP) and p-nitrophenolate (the hydrolysis products were ident-
1
31
ified by means of H and P NMR spectroscopy) in the presence
of the dizinc complexes with L1ϪL3 was measured by an initial-
slope method monitoring the increase in the 403 nm absorption of
the p-nitrophenolate at 308.1 Ϯ 0.1 K using a similar procedure to
that reported for NA. The ionic strength was adjusted to 0.1 with
Chem. 2001, 165, 291Ϫ294.
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2437Ϫ2442.
[15]
[16]
D. E. Fenton, H. Okawa, Chem. Ber./Recueil 1997, 130,
33Ϫ442.
4
NMe
MOPS (pH ϭ 6.5Ϫ7.8), TAPS (pH ϭ 7.8Ϫ8.9), CHES (pH ϭ
.9Ϫ10.1) and CAPS (pH ϭ 10.1Ϫ11.4) buffers were used (50 m).
Freshly prepared stock solutions of the zinc complexes and of BNP
1Ϫ10 m) where used in the measurements. In a typical experi-
4 3
NO . The reaction solution was maintained at 308.1 Ϯ 0.1 K.
S.-A. Li, D.-X. Yang, D.-F. Li, J. Huang, W.-X. Tang, New J.
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[
[
[
[
[
[
17]
18]
19]
20]
21]
8
(
ment, immediately after BNP and the zinc complexes were mixed
in aqueous solutions at the appropriate pH value (the reference
II
experiment does not contain the Zn complex), the UV absorption
spectrum was recorded and monitored generally until 2% decay of
BNP (for each second-order rate constant determination at least
five experiments were monitored until 20Ϫ30%). For all systems,
S. R. Korupoju, N. Mangayarkarasi, P. S. Zacharias, J. Mi-
zuthani, H. Nishihara, Inorg. Chem. 2002, 41, 4099Ϫ4101.
2ϩ
only the dihydroxo complexes [Zn
2
L(OH)
2
]
(L ϭ L1ϪL3) pro-
22] [22a]
B. M. Trost, V. S. C. Yeh, Angew. Chem. Int. Ed. 2002, 41,
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tration (0.1Ϫ1.0 m) at a given pH value gave a straight line, and
[22b]
861Ϫ863.
H. I. Park, L.-J. Ming, Angew. Chem. Int. Ed.
1
999, 38, 2914Ϫ2916.
then we determined the slope/[zinc complex] ratio as the second-
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s
]. Errors in kBNPP values were
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23c]
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Acknowledgments
Financial support by the DGCYT Generalitat Valenciana Project
CTIDIB/2002/244 (Spain) Project no. BQU2003-09215-CO3-01,
and Italian Ministero dell’Istruzione, dell’Universit a` e della Ricerca
2
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(COFIN 2002) is gratefully acknowledged.
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