Hydrolysis of phosphodiester with hydroxo- or carboxylate-bridged dinuclear Ni(II) and Cu(II) complexes

Article abstract of DOI:10.1039/b008994j

A hydroxo- or carboxylate-bridged dinuclear Ni(II) complexes with N,N,N′,N′-tetrakis((6-methyl-2-pyridyl)methyl)- 1,3-diaminopropan-2-ol has been synthesized as models for Ni(II)-substituted phosphotriesterase, which are more active catalysts for hydrolys

Full text of DOI:10.1039/b008994j

Hydrolysis of phosphodiester with hydroxo- or carboxylate-bridged dinuclear
Ni(II) and Cu(II) complexes
Kazuya Yamaguchi,*a Fumio Akagi,a Shuhei Fujinami,b Masatatsu Suzuki,b Mitsuhiko Shionoya,c and
Shinnichiro Suzukia
a Department of Chemistry, Graduate School of Science, Osaka University, 1-16 Machikaneyama, Toyonaka, Osaka
560-0043, Japan. E-mail: kazu@ch.wani.osaka-u.ac.jp
b Department of Chemistry, Faculty of Science, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan
c
Department of Chemistry, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo
113-0033, Japan
Received (in Cambridge, UK) 8th November 2000, Accepted 15th January 2001
First published as an Advance Article on the web 8th February 2001
A hydroxo- or carboxylate-bridged dinuclear Ni(II) com-
plexes with N,N,NA,NA-tetrakis{(6-methyl-2-pyridyl)me-
thyl}-1,3-diaminopropan-2-ol has been synthesized as mod-
els for Ni(II)-substituted phosphotriesterase, which are more
active catalysts for hydrolysis of phosphodiester than the
corresponding dinuclear Cu(II) and Zn(II) complexes.
absorption band of released 4-nitrophenolate in 20% MeCN
aqueous solution at 35.0 ± 0.1 °C. Buffer solutions (20 mM
HEPES, pH 6.5–8.0; TAPS, pH 8.5–9.0; CAPS, pH 9.5–10.7)9
were used, and the ionic strength adjusted to 0.10 with NaNO3.
The observed first-order rate constant, kobs/s21 for the hydroly-
sis reaction was calculated from the dependency of n on the
initial concentration (2.0–8.0 mM) of BNP. The second-order
rate constants, kBNP/M21 s21 for BNP hydrolysis are given by
fitting of the kinetic eqn (1).
It has recently been shown that a number of phosphate esterases
are activated by two metal ions.1 For example, phospho-
triesterases which hydrolyze organophosphate triesters, known
to be potent insecticides and neurotoxins, require several metal
ions [Zn(II), Cd(II), Ni(II), Co(II) and Mn(II)] for their activities.2
Pseudomonas diminuta phosphotriesterase has two Zn(II) atoms
per subunit. The binuclear metal site was confirmed by the 2.1
Å resolution X-ray crystal structure of the enzyme. 3 The
n = kobs[BNP] = kBNP[complex][BNP]
(1)
The kBNP values for the Ni(II) and Cu(II) complexes (1, 2, 3,
and 4) were determined to be (3.4 ± 0.2) 3 1022, (3.5 ± 0.1) 3
1022, (1.8 ± 0.1) 3 1024 and (1.8 ± 0.1) 3 1024 M21 s21 at pH
10.1 and 35.0 °C, respectively. The results demonstrate that the
nucleophilic reactions catalyzed by the Ni(II) complexes are ca.
200 times faster than those by the Cu(II) complexes. Koike and
Kimura reported that mononuclear Zn(II) complexes [Zn([12]a-
neN3)(OH) and Zn([12]aneN4)(OH)]10 catalyze the hydrolysis
structure of the active site is very similar to urease, a Ni(II
)
enzyme catalyzing the hydrolysis of urea, characterized by a
bridging carbamylated Lys, two His ligands for each metal ion,
and a bridging solvent ligand.4 Interestingly, Ni(II)-substituted
phosphotriesterase has a higher specific activity than the native
Zn(II) enzyme, while the Cu(II)-substituted enzyme has a similar
activity to the native one.2 Although there have been numerous
reports of esterase model systems using well defined metal
of BNP, with kBNP of 2 3 1025 and 13 3 1025 M21 s21
,
respectively, at 35.0 °C.5d The second-order rate constant for
BNP hydrolysis with the Zn2(Me4-tpdp) complex is 6.7 3 1024
complexes [Zn(II), Cu(II), Co(III) and Ln(III)], 5 only a few Ni(II
)
M21 21 under almost the same conditions.11 It is interesting
s
model complexes have been studied in relation to the structure
and reactivity in the hydrolysis of phosphodiesters. 6 In order to
understand the mechanistic roles of the metal ions in phosphate
ester hydrolysis, we have examined hydrolysis catalyzed by
that the Ni(II) complexes are more effective than the Cu(II) and
Zn(II) complexes for phosphate ester hydrolysis. It should be
noted that the hydrolysis activity of a mononuclear Ni(II
)
complex (Ni(Me2-bpa)(H2O)(ClO4)2, 5)12 is lower than those of
dinuclear 1 and 2; kBNP for the mononuclear Ni(II) complex (6.4
hydroxo- or carboxylate-bridged dinuclear Ni(II) and Cu(II
)
complexes. We have found that the hydrolysis activities of the
dinuclear Ni(II) complexes are significantly greater than those
of the Cu(II) and Zn(II) complexes.
3 1023 M21 21
s at pH 10.1) is 5–6 times smaller than those for
the dinuclear Ni(II) complexes 1 and 2. The result suggests that
the dinuclear Ni(II) complexes are the cooperative hybrid
catalysts.5d
[Ni2(Me4-tpdp)(MeCO2)(H2O)2](ClO4)2 1 was prepared by
the reaction of [Ni2(Me4-tpdp)(OH)](ClO4)2 2 with equimolar
MeCO2H in acetone at room temp. and was recrystallized from
MeCN–H2O as light green crystals.7 The X-ray crystal
structure8 of 1 reveals that the two hexacoordinate Ni(II) ions
bridged by alkoxide and acetate anions are 3.62 Å apart. The
geometries of both the Ni(II) sites are octahedral, with oxygen
atoms of water molecules at the sixth coordination site.
[Cu2(Me4-tpdp)(CH3CO2)](ClO4)2 3 was prepared by the
reaction of [Cu2(Me4-tpdp)(OH)(H2O)](ClO4) 4 with equimo-
lar MeCO2H in acetone at room temperature and was recrystal-
lized from methanol–diethyl ether as dark green crystals. The
X-ray crystal structure8 of 3 reveals that the two pentacoordi-
nate Cu(II) ions bridged by alkoxide and acetate anions are 3.54
Å apart. The geometries of both the Cu(II) centers are distorted
square pyramidal.
The DPP-bridged dinickel complexes,13 [Ni2(Me4-
tpdp)(DPP)](ClO4)2 5, and the BNP-bridged dicopper complex,
[Cu2(Me4-tpdp)(BNP)](ClO4)2 6, were obtained by the reaction
of 2 with equimolar DPP, and 4 with equimolar BNP in acetone
solution, respectively. For X-ray crystal structure analysis, 5
was recrystallized from dry methanol while 6 was recrystallized
from dry acetonitrile–diethyl ether. As shown in Fig. 1, the X-
ray crystal structures of 5 and 6 reveal that the metal ions are
bridged by alkoxide and phosphate diester.8 The geometries of
both the Cu sites in 6 are distorted square pyramidal, while the
geometries of both the Ni sites in 5 are octahedral, with oxygen
atoms of methanol at the sixth coordination site. The crystal
structures of 1, 3, 5, 6 and [Zn2(M4-tpdp)(BNP)]2+ indicate that
the Ni(II) centers are hexacoordinate, whereas the Cu(II) and
11
Zn(II
)
centers are pentacoordinate; the hexacoordinate Ni(II)
As a model reaction of phosphotriesterase, we examined the
hydrolysis of bis(4-nitrophenyl)phosphate (BNP) with the
dinuclear metal complexes 1–4. The hydrolysis rates (n)
catalyzed by the complexes (2.0 mM) were measured by the
initial slope method following an increase in the 395 nm
sites would be more favorable for the formation of an active
intermediate complex bound BNP than the pentacoordinate
Cu(II) and Zn(II) sites. The substrate could coordinate to Ni(II
)
ions under conditions that the nucleophile remains bound, and
might react with the nucleophile, whereas the substrate
DOI: 10.1039/b008994j
Chem. Commun., 2001, 375–376
This journal is © The Royal Society of Chemistry 2001
375

Scheme 1 Suggested mechanism of BNP hydrolysis with hydroxo- or
carboxylate-bridged dinuclear complexes (M
C6H4NO2).
= Ni or Cu; R =
Scheme 1. The hexacoordinate dinuclear Ni(II) complexes are
more active catalysts for phosphate diester hydrolysis than the
corresponding pentacoordinate dinuclear Cu(II) and Zn(II
)
complexes. The coordination number of the metal ions in an
intermediate complex would be important for phosphodiester
hydrolysis.
This work was supported by Grant-in-Aids for Scientific
Research on Priority Area No.12640538 from the Ministry of
Education, Science, Sports and Culture of Japan, to whom we
express our thanks.
Fig. 1 Perspective views of [Ni2(Me4-tpdp)(DPP)(MeOH)2]2+ (a) and
[Cu2(Me4-tpdp)(BNP)] 2+ (b). Hydrogen atoms are omitted for clarity.
Notes and references
1 D. E. Wilcox, Chem. Rev., 1992, 96, 2435.
2 G. A. Omburo, J. M. Kuo, L. S. Mullins and F. M. Raushel, J. Biol.
Chem., 1992, 267, 13278.
3 J. L. Vanhooke, M. M. Benning, F. M. Raushel and H. M. Holden,
Biochemistry, 1996, 35, 6020.
4 E. Jabri, M. B. Carr, R. P. Hausinger and P. A. Karplus, Science, 1995,
268, 998.
5 For example: (a) E. L. Hegg and J. N. Burstyn, Coord. Chem. Rev.,
1998, 173, 133; (b) J. R. Morrow and W. C. Trogler, Inorg. Chem.,
1988, 27, 3387; (c) N. H. Williams, B. Takasaki, M. Wall and J. Chin,
Acc. Chem. Res., 1999, 32, 485; (d) T. Koike and E. Kimura, J. Am.
Chem. Soc., 1991, 113, 8935; (e) D. H. Vance and A. W. Czarnik, J. Am.
Chem. Soc., 1993, 115, 12 165.
6 M. A. De Rosch and W. C. Trogler, Inorg. Chem., 1990, 29, 2409; J. R.
Morrow, L. A. Buttrey and K. Berback, Inorg. Chem., 1992, 31, 16.
7 Me4-tpdp: N,N,NA,NA-tetrakis{(6-methyl-2-pyridyl)methyl}-1,3-diami-
nopropan-2-ol (Y. Hayashi, T. Kayatani, H. Sugimoto, M. Suzuki, K.
Inomata, A. Uehara, Y. Mizutani, T. Kitagawa and Y. Maeda, J. Am.
Chem. Soc., 1995, 117, 11 220).
coordinated to Cu(II) or Zn(II) ions could react only with
exogenous nucleophile.
k
BNP Values for 1 and 2 are plotted against pH in Fig. 2. The
inflection point at pH 8.0 for 2 almost coincides with the pKa
value of 7.9 for the coordinated water of 2. Therefore, the OH2
ligand in 2 must be a good nucleophile for phosphodiester. On
the other hand, the inflection point for 1 is shifted to a higher
pH. These findings might be caused by ligand exchange of
acetate with the substrate. The pH dependence of the UV–VIS
spectrum of 1 was measured at 25.0 ± 0.1 °C. The UV–VIS
spectrum of 1 was similar to that of 2 at high pH, with isosbestic
points being observed (data not shown). The equilibrium
constant for acetate binding was calculated as 25 ± 2 from the
absorbance change at 488 nm in the pH range 7.5–11.0 and
suggests that the acetate ligand in 1 readily dissociates and
exchanges with hydroxide at high pH. This is consistent with
the fact that the reactivity of 1 is similar to that of 2 at high pH
while acetate ion in 1 would be a competitive inhibitor of the
hydrolysis of BNP at low pH. Complex 2 behaves as a catalyst
as revealed by the yield of product ( > 200% relative to
complex) when the reaction of 8.0 mM BNP with 2.0 mM
complex was carried out for 12 h at pH 10.1 and 35.0 °C.
However, BNP hydrolysis with 2 inhibited (by 30%) upon the
addition of an equimolar amount of 4-nitrophenyl phosphate
(NPP), the hydrolysis product of BNP, at pH 10.1 and 35.0 °C
NPP is also a competitive inhibitor with the substrate.
8 Crystal data: for 1: C33H46O14N6Cl2Ni2, M = 936.06, monoclinic,
P21/n (no. 14), a = 17.336(1), b = 13.045(1), c = 18.060(1) Å, b =
100.938(5)°, V = 4010.0(5) Å3, Z = 4, m(Mo-Ka) = 11.45 cm21, 6698
reflections measured, 5724 unique reflections collected [I > 3s(I)], T =
153 K, Rint
=
0.0264,
R
=
0.060, Rw
=
0.096. For 3:
C37H50O12N6Cl2Cu2, M = 968.83, monoclinic, P21/c (no.14), a =
17.577(3), b = 17.387(2), c = 14.257(2) Å, b = 100.63(1)°, V =
4282(1) Å3, Z
= 4, m(Mo-Ka) =
11.84 cm21, 7300 reflections
measured, 6088 unique reflections collected [I > 3s(I)], T = 153 K, Rint
= 0.0305, R = 0.053, Rw = 0.079. For 5: C46H59Cl2N6O16Ni2P, M =
1171.28, monoclinic, P21/n, a = 13.5091(4), b = 20.927(1), c =
18.0299(9) Å, b = 96.4758(5)°, V = 5064.6(4) Å3, Z = 4, m(Mo-Ka)
= 0.956 cm21, 11459 reflections measured, 8547 unique reflections
collected [I > 3s(I)], T = 138.2 K, Rint = 0.02299, R = 0.052, and Rw
In conclusion, the mechanism of BNP hydrolysis with the
dinuclear Ni(II) and Cu(II) complexes can be summarized by
=
0.078. For 6: C48H59.5Cl2Cu2N8.5O19.5P, M = 1296.52, or-
thorhombic, Pnma, a = 22.941(4), b = 36.360(4), c = 14.160(2) Å, V
= 11812(2) Å3, Z = 8, m(Mo-Ka) = 9.15 cm21, 7732 reflections
measured, 5142 unique reflections collected [I > 2.60s(I)], T = 288.2
K,
R
=
0.081, Rw
=
0.114. CCDC 153180–153183. See
http://www.rsc.org/suppdata/cc/b0/b008994j/ for crystallographic data
in .cif or other electronic format.
9 HEPES: N-2-hydroxyethylpiperazine-NA-2-ethanesulfonic acid; TAPS:
N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid; CAPS: cy-
clohexylaminopropanesulfonic acid.
10 [12]aneN3: 1,5,9-triazacyclododecane; [12]aneN4: 1,4,7,10-tetraazacy-
clododecane.
11 M. Suzuki et al., unpublished data.
Fig. 2 Dependence of kBNP on pH for the hydrolysis with complex 1 (2) and
complex 2 (5) in 20% MeCN aqueous solution at 35.0 °C.
12 Me2-bpa: bis{(6-methyl-2-pyridyl)methyl}amine.
13 DPP: diphenylphosphate.
376
Chem. Commun., 2001, 375–376