A tris(Zn(II)-1,4,7,10-tetraazacyclododecane) complex as a new receptor for phosphate dianions in aqueous solution

Article abstract of DOI:10.1021/ja9640408

A new tris(Zn(II)-cyclen) (Zn₃L³), which has three Zn(II)-macrocyclic tetraamine (cyclen) complexes connected through a 1,3,5-trimethylbenzene spacer, has been synthesized as a novel receptor for organic phosphate dianions in aqueous solution (cyclen = 1,4,7,10-tetraazacyclododecane and L³ = 1,3,5-tris(1,4,7,10-tetraazacyclododecan-1-ylmethyl)benzene). The design of Zn₃L³ was based on X-ray crystal structure analysis of the 1:3 complex of 4-nitrophenyl phosphate (NPP^2-) with Zn(II)-cyclen (ZnL¹) complex. The potentiometric pH titration of Zn₃L^3.3H₂O revealed the deprotonation constants of the three Zn(II)-bound H₂O molecules to be 6.1 (pK₁), 7.3 (pK₂), and 8.6 (pK₃) at 25 °C with I = 0.1 (NaNO₃). These three stepwise deprotonations and ¹H NMR spectra changes at various pD values in D₂O suggest that strong intramolecular hydrogen bonds link each adjacent Zn(II)-OH₂ (or Zn(II)-OH^-) at neutral pH in aqueous solution. At higher pH (> 9), the hydrogen bond network disrupts. The ³¹P NMR titration of Zn₃L^3.3H₂O with phenyl phosphate dianion (PP^2-) in D₂O confirmed the formation of a 1:1 complex (Zn₃L³-PP^2-). By potentiometric pH titrations, the 1:1 complex affinity constants, log K(aff) (K(aff) = [phosphate complex]/[Zn(II) complex] [phosphate] (M^-1)), were determined to be 5.8 with NPP^2-, 6.6 with PP^2-, 7.0 with α-D-glucose-1-phosphate, and 7.9 with phenyl phosphonate in aqueous solution. The tris(Zn(II)-cyclen) complex is found to be a much better host toward phosphates than the parent Zn(II)-cyclen (ZnL¹) (log K(aff) = 3.3 for ZnL¹-NPP^2-) or a bis(Zn(II)-cyclen) linked with a m-xylene spacer (Zn₂L²) (log K(aff) = 4.0 for Zn₂L²-NPP^2-).

Full text of DOI:10.1021/ja9640408

3068
J. Am. Chem. Soc. 1997, 119, 3068-3076
II
A Tris(Zn -1,4,7,10-tetraazacyclododecane) Complex as a New
Receptor for Phosphate Dianions in Aqueous Solution
,†
†
†
‡
Eiichi Kimura,* Shin Aoki, Tohru Koike, and Motoo Shiro
Contribution from the Department of Medicinal Chemistry, School of Medicine, Hiroshima
UniVersity, Kasumi 1-2-3, Minami-ku, Hiroshima, 734, Japan, and Rigaku Corporation X-ray
Research Laboratory, Matsubaracho 3-9-12, Akishima, Tokyo, 196, Japan
X
ReceiVed NoVember 22, 1996
II
3
II
Abstract: A new tris(Zn -cyclen) (Zn3L ), which has three Zn -macrocyclic tetraamine (cyclen) complexes
connected through a 1,3,5-trimethylbenzene spacer, has been synthesized as a novel receptor for organic phosphate
dianions in aqueous solution (cyclen ) 1,4,7,10-tetraazacyclododecane and L ) 1,3,5-tris(1,4,7,10-tetraaza-
cyclododecan-1-ylmethyl)benzene). The design of Zn3L was based on X-ray crystal structure analysis of the 1:3
3
3
2
-
II
1
complex of 4-nitrophenyl phosphate (NPP ) with Zn -cyclen (ZnL ) complex. The potentiometric pH titration of
3
II
Zn3L ‚3H2O revealed the deprotonation constants of the three Zn -bound H2O molecules to be 6.1 (pK1), 7.3 (pK2),
1
and 8.6 (pK3) at 25 °C with I ) 0.1 (NaNO3). These three stepwise deprotonations and H NMR spectra changes
II
at various pD values in D2O suggest that strong intramolecular hydrogen bonds link each adjacent Zn -OH2 (or
II
-
31
Zn -OH ) at neutral pH in aqueous solution. At higher pH (>9), the hydrogen bond network disrupts. The
P
3
2-
NMR titration of Zn3L ‚3H2O with phenyl phosphate dianion (PP ) in D2O confirmed the formation of a 1:1 complex
3
2-
(
Zn3L -PP ). By potentiometric pH titrations, the 1:1 complex affinity constants, log Kaff (Kaff ) [phosphate
II
-1
2-
2-
complex]/[Zn complex][phosphate] (M )), were determined to be 5.8 with NPP , 6.6 with PP , 7.0 with R-D-
II
glucose-1-phosphate, and 7.9 with phenyl phosphonate in aqueous solution. The tris(Zn -cyclen) complex is found
II
1
1
2-
to be a much better host toward phosphates than the parent Zn -cyclen (ZnL ) (log Kaff ) 3.3 for ZnL -NPP )
II
2
2
2-
or a bis(Zn -cyclen) linked with a m-xylene spacer (Zn2L ) (log Kaff ) 4.0 for Zn2L -NPP ).
8
,9
3-
Introduction
(iii) polyguanidinium cations (e.g., log Kaff ) 2.4 for 3-PO4
8
10
complex ), or (iv) sapphyrins (e.g., 4 with double-strand
DNA). The attractive forces are essentially coulombic forces
and strong hydrogen bonding between polycations of pro-
tonated (at neutral pH) amines and phosphate oxyanions.
Chemical design of efficient and selective host molecules for
various biologically important types of phosphate anion guests
has been attracting great interest. The majority of recently
synthesized hosts are organic molecules equipped with acidic
hydrogens at complementary positions to hydrogen bond with
their guest phosphate oxyanions. The 1:1 affinity constants (Kaff
(3) (a) Kimura, E.; Kodama, M.; Yatsunami, T. J. Am. Chem. Soc. 1982,
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T.; Fujioka, H.; Kodama, M. J. Org. Chem. 1990, 55, 42-46.
-
1
)
[phosphate complex]/[host][phosphate] (M )) are sometimes
as high as 10 -10 M in nonaqueous solutions such as CHCl3,
2
6
-1
CH3CN, and DMSO.1 These hydrogen bonds, however, cannot
(
4) (a) Dietrich, B.; Hosseini, W.; Lehn, J.-M.; Sessions, R. B. J. Am.
compete against the hydration of phosphate guests in water,
resulting in the dissociation of the host-guest complexes. To
date there have been only a limited number of phosphate
Chem. Soc. 1981, 103, 1282-1283. (b) Hosseini, M. W.; Lehn, J.-M. J.
Am. Chem. Soc. 1982, 104, 3525-3527. (c) Hosseini, M. W.; Lehn, J.-M.;
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3896-3904.
receptors that work in the hostile environment of an aqueous
system.2
-14
Representative examples are (i) multiprotonated
3
-6
or polycationic compounds such as polyamines (e.g., log Kaff
4-
3a
(5) Marecek, J. F.; Fischer, P. A.; Burrows, C. J. Tetrahedron Lett. 1988,
)
6.4 for 1-ATP complex ), (ii) polyquarternery ammonium
2
9, 6231-6234.
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7
2-
cations (e.g., log Kaff ) 2.1 for 2-HPO4 complex), and
(
4
†
Hiroshima University.
Rigaku Corporation.
Abstract published in AdVance ACS Abstracts, March 15, 1997.
L.; Wang, B.; Deffo, T.; Takusagawa, F.; Mertes, M. P.; Mertes, K. B.;
Paoletti, P. Bioorg. Chem. 1992, 20, 8-29. (c) Andr e´ s, A.; Arag o´ , J.;
Bencini, A.; Bianchi, A.; Domenech, A.; Fusi, V.; Garc ´ı a-Espa n˜ a, E.;
Paoletti, P.; Ram ´ı rez, J. A. Inorg. Chem. 1993, 32, 3418-3424. (d) Aquilar,
J. A.; Garc ´ı a-Espa n˜ a, E.; Guerrero, J. A.; Lui, S. V.; Llinares, J. M.; Miravet,
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2237-2239.
‡
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S0002-7863(96)04040-1 CCC: $14.00 © 1997 American Chemical Society

A New Zinc Receptor for Phosphate Dianions
J. Am. Chem. Soc., Vol. 119, No. 13, 1997 3069
These 1:1 complexes are stable at neutral pH with appreciably
high affinity constants.
II
Recently, Zn -macrocyclic polyamine complexes have
1
5
emerged as a novel family of host molecules. They were
originally conceived from the fact that phosphates act as
2
0
ligand to zinc(II) ions in carboxypeptidase A, alkaline phos-
2
1,22
23
2
-
phatase,
and phospholipase C.
It must be noted that
phosphate anions and hydroxyl anions compete for Zn , and
hence, the solution pH critically affects the affinity of phosphate
for Zn . This would be particularly true when these anions
interact with more than two zinc(II) ions, since these anions
are potentially bidentate donors.
Trinuclear zinc(II) complexes are found at active sites in zinc
enzymes such as phospholipase C from Bacillus cereus
(PLCBc) (8 in Scheme 1) and P1 nuclease. An X-ray crystal
structure of the complex 9 of PLCBc with a competitive inhibitor
(a phospholipid analog) revealed that the phosphate binds to
all three zinc(II) ions by replacing two of zinc-bound water
substrates (e.g., phosphomonoesters ) or inhibitors (e.g.,
II
HPO42 ) by reversibly coordinating to Zn in zinc enzymes.
-
II
16
The zinc(II) complexes of [12]aneN3 ([12]aneN3 ) 1,5,9-
II 21
triazacyclododecane)17 and cyclen (cyclen ) L ) 1,4,7,10-
1
1
18
tetraazacyclododecane, ZnL ) 5), which were discovered to
be good models for zinc enzymes such as carbonic anhydrase
and alkaline phosphatase, reversibly bind phosphate dianions
1
6
such as HPO42 , phenyl phosphate (PP ), and 4-nitrophenyl
-
2-
23
24
2-
phosphate (NPP ) to yield stable 1:1 complexes with affinity
constants of log Kaff ) 3.3 for 5-NPP2 complex. However,
-
18
1
+
metal-free cyclen (similarly dicationic species (L ‚2H ) at
neutral pH) had little interaction with these phosphate dianions.
2
3c,d
II
molecules in the native PLCBc.
The recent X-ray crystal structure analysis of (Zn -alcohol-
pendant-cyclen)3-PO43 complex 6 showed that three phosphate
-
II
Scheme 1
oxygens could coordinate to each Zn as the apical donors to
form a C3-symmetric complex.18 Moreover, a bis(Zn -cyclen)
II
2
complex linked with a m-xylene spacer (7, Zn2L ) was found
2
-
19
to bind with two oxyanions of NPP with log Kaff ) 4.0. In
-
all of these interactions, the P-O moiety becomes a mono-
dentate donor. A phosphate anion also acts as a monodentate
(11) (a) Claude, S.; Lehn, J.-M.; Schmidt, F.; Vigneron, J.-P. J. Chem.
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(
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Inorg. Chem. 1995, 34, 1823-1829.
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(
Since three coordination sites for water molecules (H2O and/
or OH ) are present in the active site of PLCBc, the interaction
with a phospholipid anion is seen to vary with pH, resulting in
3
-
(
(
6
217. (b) Kimura, E. Prog. Inorg. Chem. 1994, 41, 443-491. (c) Kimura,
(20) Mangani, S.; Ferraroni, M.; Orioli, P. Inorg. Chem. 1994, 33, 3421-
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L.; Falchuk, K. H. Physiol. ReV. 1993, 73, 79-118. (d) Coleman, J. E.
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Chem. ReV. 1996, 96, 2375-2433.
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M.; Foster, B. A.; Wyckoff, H. W. J. Mol. Biol. 1985, 186, 417-433. (b)
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543-549. (c) Hansen, S.; Hough, E.; Svensson, L. A.; Wong, Y.-L.; Martin,
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1
990, 112, 5805-5811. (b) Koike, T.; Kimura, E. J. Am. Chem. Soc. 1991,
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13, 8935-8941. (c) Koike, T.; Kimura, E.; Nakamura, I.; Hashimoto, Y.;
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18) Koike, T.; Kajitani, S.; Nakamura, I.; Kimura, E.; Shiro, M. J. Am.
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2, 775-787.
(
4

3070 J. Am. Chem. Soc., Vol. 119, No. 13, 1997
Kimura et al.
pH-dependent enzyme activity. However, no systematic study
on the cooperative phosphate recognition by three zinc(II) ions
had been conducted in model systems. In this paper, we
describe the synthesis of the novel trinuclear zinc(II) complex,
II
3
tris(Zn -cyclen) (10, Zn3L ), having a 1,3,5-trimethylbenzene
3
spacer (L ) 1,3,5-tris(1,4,7,10-tetraazacyclododecan-1-ylm-
ethyl)benzene), and interesting new properties toward phos-
phates, which are dependent on pH in aqueous solution.
Figure 1. An ORTEP drawing (30% probability ellipsoides) of the
:3 complex 11 of NPP2 with Zn -cyclen. All hydrogen atoms,
-
II
1
perchlorate anions, and water molecules are omitted for clarity. Selected
bond lengths (Å): Zn(1)-O(48) 1.917(4), Zn(2)-O(49) 1.936(4),
Zn(3)-O(50) 1.917(4), P(47)-O(46) 1.611(5), P(47)-O(48) 1.496(4),
P(47)-O(49) 1.487(4), P(47)-O(50) 1.503(4). Selected bond angles
(deg): C(37)-O(46)-P(47) 124.2(4), O(46)-P(47)-O(48) 105.5(2),
O(48)-P(47)-O(49) 112.8(2), O(49)-P(47)-O(50) 112.6(3), O(50)-
P(47)-O(46) 101.2(2), P(47)-O(48)-Zn(1) 130.8(2), P(47)-O(49)-
Zn(2) 128.9(2), P(47)-O(50)-Zn(3) 127.6(2).
the first example of a 1:3 complex of dianionic phosphate with
zinc(II) complexes. Three phosphorus-oxygen lengths (P-
Results and Discussion
2-
O(48), P-O(49), and P-O(50)) in NPP are almost equivalent
(ca. 1.5 Å), indicating that the dianionic charge of the NPP2
is equally distributed over the three oxygen atoms of the
phosphate, so that the phosphate dianion makes a C3-symmetric
guest having a 3-fold axis through the P-OAr bond. The
examples of a similar C -symmetric structure of µ -carbonato-
-
Isolation and X-ray Crystal Structure of a 1:3 Complex
2-
II
of 4-Nitrophenyl Phosphate (NPP ) with Three (Zn -
cyclen) Complexes (11). Prior to developing a new phosphate
receptor, we have characterized crystals precipitated from the
2-
II
mixture of 4-nitrophenyl phosphate (NPP ) and Zn -cyclen
3
3
1
28
(
ZnL ). Colorless prisms were obtained by slow concentration
bridged trinuclear zinc(II) complexes have been also reported.
1
under reduced pressure. The H NMR data and elemental
analysis (C, H, N) suggested that the complex was composed
3
Synthesis of Tris(cyclen) (L ) and Its Trizinc(II) Complex
(
10). The X-ray crystal structure of the trimeric complex 11
2-
1
of one NPP and three ZnL units. The X-ray crystal structure
analysis has revealed the structure of the trimeric complex 11
as shown in Figure 1, where each zinc(II) ions is bound to each
phosphate oxygen (O48, O49, and O50).25
18
and our previous complex 6 led us to design a trinuclear
zinc(II) complex for phosphate anions. Thus, we chose tris-
3
3
(
cyclen) (L ) and its trizinc(II) complex 10 (Zn3L ) bearing a
1
,3,5-trimethylbenzene spacer.
The Boc (tert-butyloxycarbonyl) group has been found to be
effective protecting group for the synthesis of some derivatives
2
9
of cyclic polyamines. Hence, we used 1,4,7-tris(tert-butyl-
oxycarbonyl)cyclen (13, 3Boc-cyclen) as shown in Scheme 2.
The reaction of 1,3,5-tris(bromomethyl)benzene (12)30 with 3.5
equiv of 13 in the presence of anhydrous Na2CO3 in CH3CN
slowly proceeded at 80 °C to give 9Boc-tris(cyclen) (14), which
was purified by column chromatography after treating a mixture
of 14 and the unreacted 13 with benzyl chloroformate (ZCl) to
convert 13 to the less polar compound 15. The recovered 15
can be converted to 13 by a conventional method (H2, Pd/C) in
80-90%.
II
The three bond lengths between Zn and oxygen atom of
NPP2 in 11 are almost equivalent (1.92-1.94 Å) and are almost
the same as those (ca. 1.92 Å) of the previous trimeric complex
Each Zn is in a distorted tetragonal-pyramidal environment
constituted by four nitrogen atoms (N1, N4, N7, and N10) of
-
(27) The Lippard group has isolated 1:1 complex of diphenyl phosphate
and dinuclear zinc complex. Tanase, T.; Yun, J. W.; Lippard, S. J. Inorg.
Chem. 1995, 34, 4220-4229.
18
II
6.
(28) (a) Murthy, N. N.; Karlin, K. D. J. Chem. Soc., Chem. Commun.
1993, 1236-1238. (b) Chen, X.-M.; Deng, Q.-Y.; Wang, G. Polyhedron
2-
cyclen and the phosphate oxygen (O48) of NPP .
1
994, 13, 3085-3089. (c) Bazzicalupi, C.; Bencini, A.; Bencini, A.; Bianchi,
The 1:2 complexes of NPP2 with zinc(II) complexes, in
-
A.; Corana, F.; Fusi, V.; Giorgi, C.; Paoli, P.; Paoletti, P.; Valtancoli, B.;
Zanchini, C. Inorg. Chem. 1996, 35, 5540-5548.
-
-
which two zinc(II) ions are linked by a O -P-O bridge, have
been isolated by several groups.2
6,27
To our knowledge, 11 is
(29) (a) Granier, C.; Guilard, R. Tetrahedron 1995, 51, 1197-1208. (b)
Boitrel, B.; Andrioletti, B.; Lachkar, M.; Guilard, R. Tetrahedron Lett. 1995,
36, 4995-4998. (c) Groth, A. M.; Lindoy, L. F.; Meehan, G. V. J. Chem.
Soc., Perkin Trans. 1 1996, 1553-1558.
(
25) For the crystal information files (CIFs) for the X-ray crystal structure
analysis of 10‚(NO3 )6‚3H2O and 11‚(ClO4 )4‚2H2O, see the Supporting
-
-
Information.
(
(30) (a) Mitchell, M. S.; Walker, D.-L.; Whelan, J.; Bosnich, B. Inorg.
Chem. 1987, 26, 396-400. (b) Meno, T.; Sako, K.; Suenaga, M.; Mouri,
M.; Shinmyozu, T.; Inazu, T.; Takemura, H. Can. J. Chem. 1990, 68, 440-
445.
26) (a) Hikichi, S.; Tanaka, M.; Moro-oka, Y.; Kitajima, N. J. Chem.
Soc., Chem. Commun. 1992, 814-815. (b) Adams, H.; Bailey, N. A.;
Fenton, D. E.; He, Q.-Y. J. Chem. Soc., Dalton Trans. 1995, 697-699.

A New Zinc Receptor for Phosphate Dianions
J. Am. Chem. Soc., Vol. 119, No. 13, 1997 3071
Scheme 2
Figure 2. An ORTEP drawing (30% probability ellipsoides) of 10.
All hydrogen atoms, four external nitrate anions, and water molecules
except a zinc(II)-bound water are omitted for clarity. Selected bond
lengths (Å): Zn(1)-O(2a) 2.04(2), Zn(2)-O(6a) 2.00(1), Zn(3)-O(1w)
1
2
2
2
.947(9), Zn(1)-N(1) 2.259(8), Zn(1)-N(4) 2.123(10), Zn(1)-N(7)
.14(1), Zn(1)-N(10) 2.14(1), Zn(2)-N(13) 2.277(9), Zn(2)-N(16)
.10(1), Zn(2)-N(19) 2.172(10), Zn(2)-N(22) 2.144(10), Zn(3)-N(25)
.202(8), Zn(3)-N(28) 2.120(9), Zn(3)-N(31) 2.177(10), Zn(3)-N(34)
3
The L ‚9HBr was obtained by the deprotection of 14 with
aqueous HBr in EtOH and was converted to the free form by
passing it through an anionic ion exchange resin column. The
free ligand L was allowed to react with Zn(NO3)2‚6H2O in
EtOH/water to afford 10‚6(NO3 )‚3H2O‚0.5EtOH as colorless
2.13(1). Selected bond angles (deg): Zn(1)-N(1)-C(37) 110.6(6),
Zn(2)-N(13)-C(38) 108.8(8), Zn(3)-N(25)-C(39) 110.1(5), N(1)-
Zn(1)-O(2a) 106.1(6), N(4)-Zn(1)-O(2a) 125.8(6), N(7)-Zn(1)-
O(2a) 112.9(6), N(10)-Zn(1)-O(2a) 101.0(6).
3
-
needles after recrystallization from EtOH/water.
-
X-ray Crystal Structure of 10‚6(NO3 )‚3H2O. The crystals
molecules, pK1, pK2, and pK3, were calculated to be 6.08 (
0.03, 7.25 ( 0.03, and 8.63 ( 0.03, respectively.
-
of 10‚6(NO3 )‚3H2O were subjected to X-ray crystal structure
analysis. An ORTEP drawing of 10‚6(NO3 )‚3H2O is shown
in Figure 2 with 30% probability thermal ellipsoids. Each
Zn -cyclen unit has a distorted tetragonal-pyramidal structure,
-
+
2
5
10a a 10b + H
10b a 10c + H
K ) [10b]aH
+
/[10a]
(1)
(2)
(3)
1
II
+
and zinc-nitrogen bond lengths are 2.10-2.28 Å, not unusual
K ) [10c]a /[10b]
2
H+
II
17,18,31
distances for Zn -cyclen complexes.
The apical coor-
+
dination sites of two among three zinc(II) ions are occupied by
two nitrate anions. An interesting feature is that the three Zn -
1
0c a 10d + H
K ) [10d]aH /[10c]
+
3
II
cyclen moieties are orientated to face the same side of the
molecule giving a pseudo-C3-symmetrical molecule with three
apical ligands of each three zinc(II) cations (one water molecule
and two nitrate anions) located on the same face.
a
For comparison, the relevant pK values of zinc(II)-bound
II
II
water in Zn -cyclen‚H O (5a), Zn -N-benzylcyclen‚H O (16,
2
2
4
18
II
ZnL ‚H2O), bis(Zn -cyclen) linked with p-xylene spacer (17,
Zn2L ‚2H2O), and bis(Zn -cyclen) linked with m-xylene
spacer (7, Zn2L ‚2H2O) should be noted. Two reference
complexes, 5 and 16, have higher pKa values of 7.9 (for 5a a
b + H ) and 7.6, respectively.
5
31
II
2
19
Determination of pKa Values of Zinc(II)-Bound Waters
of 10. The pKa values of three zinc(II)-bound waters of 10 were
determined by potentiometric pH titration against 0.10 M NaOH
aqueous solution with I ) 0.10 (NaNO3) at 25 °C. Figure 3a
+
17,18
II
5
The p-bis(Zn -cyclen)
3
shows a typical titration curve of isolated 10 (Zn3L ‚3H2O),
-
showing dissociation of three protons at 0 < eq(OH ) <
-
3
eq(OH ) is the number of equivalents of base added). Any
further deprotonation or precipitation of Zn(OH)2 was not
observed over pH 11. The crystal structure analysis of 10
showed that two zinc(II) ions have nitrate anions at apical
coordination site. Since it has been previously confirmed that
nitrate anion has only negligible interaction with zinc(II) ion in
3
2
aqueous solution, we presume that the nitrate anions in 10
are replaced by water molecules, which reside on three zinc(II)
ions of 10 in aqueous solution, and that the three dissociable
protons can be assigned to the zinc(II)-bound water molecules.
31
1
7 has two close values of 7.2 and 7.9. On the other hand,
II
the m-bis(Zn -cyclen) 7 has two more separate values: one is
+
+ 19
6
.7 (for 7a a 7b + H ) and the other is 8.5 (7b a 7c + H ).
The reason of the lower pK1 value and the higher pK2 value
33
II
By calculation using the program “BEST” and assuming eqs
with respect to pK of monomeric Zn -cyclen may be explained
a
+
+
3
II
1
1
)
-3 (where aH is the activity of H and 10a ) Zn3L ‚3H2O,
by strong intramolecular hydrogen bonding between the Zn -
3
-
3
-
-
II
0b ) Zn3L ‚(OH )‚2H2O, 10c ) Zn3L ‚2(OH )‚H2O, and 10d
OH and Zn -OH . In fact, 7b was isolated as a stable
2
3
-
-
Zn3L ‚3(OH )), the deprotonation constants of each water
crystalline 3(ClO4 ) salt. Very recently, a similar type of
II
-
II
L-Zn -OH2‚‚‚HO -Zn -L complex (L ) a tris(pyrazoyl)-
borate homologue) was isolated for X-ray crystal study and
discussed in relevance to the hydrogen bond network at the
active center of carbonic anhydrase. These discussions should
also be applicable for tris(Zn -cyclen) 10 (Vide infra).
(
31) Koike, T.; Takashige, M.; Kimura, E.; Fujioka, H.; Shiro, M. Chem.
Eur. J. 1996, 2, 617-623.
32) The pKa value of zinc(II)-bound water in 5 with I ) 0.1 (NaNO3)
at 25 °C has been found to be the same as that with I ) 0.1 (NaClO4) at
(
34
II
II
2
5 °C, indicating that nitrate anion has negligible interaction with Zn -
cyclen.
(
33) Martell, A. E.; Motekaitis, R. J. Determination and Use of Stability
(34) Ruf, M.; Weis, K.; Vahrenkamp, H. J. Am. Chem. Soc. 1996, 118,
9288-9294.
Constants, 2nd ed.; VCH: New York, 1992.

3072 J. Am. Chem. Soc., Vol. 119, No. 13, 1997
Kimura et al.
Scheme 3
Figure 3. Typical titration curves of 1 mM 10 (a) in the absence and
(
b) in the presence of 1 mM phenyl phosphate disodium salt in water
-
at 25 °C with I ) 0.10 (NaNO
equivalents of base added.
3
), where eq(OH ) is the number of
by two other peaks at pD 8.6. When more base was added, the
Ha peak showed an upfield shift back to δ 7.34 with sharpening
at pD 11.0.
An explanation of this behavior is presented graphically in
Scheme 3. It is assumed that 7a predominantly takes an “open-
form” (as in 7b′) at low pD (<5), since both of the zinc(II)-
bound waters are not deprotonated and have negligible inter-
action toward each other. Upon deprotonation of one of the
zinc(II)-bound waters, 7b favors a “closed-form” in which
intramolecular hydrogen bonding between the zinc(II)-bound
II
water and the zinc(II)-bound hydroxide bridges the two Zn -
36,37
cyclen moieties.
The downfield shift of Ha peak is probably
induced by the shielding effect of zinc(II) ions fixed close to
Ha. The second deprotonation generates 7c, which takes an
“
open-form” as in 7a. A repulsive interaction between the two
hydroxide anions may assist the “opening” of the structure.
Above pD 11, the two zinc(II)-bound waters in 7 are considered
to be completely deprotonated.
1
The pH-dependent H NMR experiment of 10 in D2O at 35
°
(
C has been carried out at pD 4.9, 6.1, 7.4, 8.5, 9.3, and 11.4
see Figure 5, respectively). The second (6.1), third (7.4), and
fourth (8.5) pD values were adjusted to match the three pKa
3
38
values of zinc(II)-bound waters in 10 (Zn3L ‚3H2O) at 35 °C.
1
II
Figure 4. Aromatic regions of H NMR spectra of m-bis(Zn -cyclen)
The aromatic protons (all three are equivalent) at pD 4.9 (Figure
5a) exhibit a somewhat broad shape at δ 7.42. As pD is
increased to 6.1, 7.4, and 8.5, this peak moved downfield with
broadening (broadest at pD 8.5 and δ 7.48). Further pD
increases caused an upfield shift to δ 7.38 at pD 9.3 and δ 7.37
at pD 11.4 with peak sharpening.
7
(5 mM) at different pD values at 35 °C. For the assignment of each
peak, see text.
1
II
H NMR Behaviors of Zn -N-benzylcyclen (16), m-Bis-
II
II
(
Zn -cyclen) (7), and Tris(Zn -cyclen) (10) in Aqueous
Solution at Various pD Values. It was expected that the pH-
By analogous consideration for the pH-dependent structural
change of 7 presented in Scheme 3, we propose two main
II
dependent conformational change of m-bis(Zn -cyclen) (7) and
II
tris(Zn -cyclen) (10), which we assumed in the previous
1
(36) An equivalent structure which has two zinc(II) ions bridged by an
section, should cause pH(pD)-dependent changes on H NMR
-
OH anion is not excluded. Very recently, Gutneh et al. has reported that
spectra in D2O solution. Hence, the 1H NMR spectra of
monomeric 16, dimeric 7, and trimeric 10 (all at 5 mM) at
various pD values in D2O were taken at 35 °C.
the dinuclear zinc(II) complex having a m-xylyl connectivity similar to that
-
of 7 has Zn- OH-Zn bridge structure in the solid state: Gultneh, Y.;
Allwar; Ahvazi, B.; Blaise, D.; Butcher, R. J.; Jasinski, J.; Jasinski, J. Inorg.
Chim. Acta 1996, 241, 31-38.
The chemical shifts of the aromatic ring protons of mono-
meric 16 did not change with pD ()5.9, 7.7, and 11.0),
indicating that little conformational change was induced by
(
37) Several crystal structures of “Zn2(µ-OH)2” structures have been
reported. (a) Chaudhuri, P.; Stockheim, C.; Wieghardt, K.; Deck, W.;
Gregorzik, R.; Vahrenkamp, H.; Nuber, B.; Weiss, J. Inorg. Chem. 1992,
3
6
1, 1451-1457. (b) Alsfasser, R.; Vahrenkamp, H. Chem. Ber. 1993, 126,
deprotonation of the zinc(II)-bound water. In comparison, the
95-701.
1
H NMR spectra of the dimeric complex 735 dramatically
(38) The pKa values of zinc(II)-bound waters of 10 at 35 °C with I )
changed as shown in Figure 4, illustrating the aromatic protons
0.10 (NaNO3) were determined to be 6.00 ( 0.03 (pK1), 7.20 ( 0.03 (pK2),
and 8.47 ( 0.03 (pK3), respectively, by potentiometric pH titration.
(
8
Ha, Hb, and Hc of 7, see Scheme 3) at pD (a) 5.0, (b) 6.6, (c)
.6, and (d) 11.0. While Hb and Hc did show little change, the
broad peak of Ha exhibited a downfield shift from δ 7.37 at pD
.0 to δ 7.59 at pD 6.6 with broadening and became overlapped
t
t
(
39) The trimeric structure of [{η2-H2B(3-Bu pz)2}Zn(µ-OH)]3 (3-Bu pz
t
denotes 3-C3N2Bu H2), which possesses approximately C3 symmetry with
each OH- group bridging to zinc(II) ions, has been isolated and characterized
5
[Gorrell, I. B.; Looney, A.; Parkin, G.; Rheingold, A. L. J. Am. Chem. Soc.
II
1
990, 112, 4068-4069]. We also reported the trimeric structure of (Zn -
-
-
(
35) In this study, 7 was synthesized via N-alkylation of 13 with R,R′-
[12]aneN3-OH )3‚3(ClO4 )‚HClO4, which was precipitated from pH 8
dibromo-m-xylene.
solution (ref 17a).

A New Zinc Receptor for Phosphate Dianions
J. Am. Chem. Soc., Vol. 119, No. 13, 1997 3073
Figure 7. Change in the 31P NMR chemical shift of PP2- (5 mM)
with increasing concentration of 10 in D O (pD 7.1 ( 0.1).
2
II
II
-
Zn -OH2 and Zn -OH , fixing 10 into a “closed-form” for
3
-
3
L ‚[Zn(OH2)]2‚[Zn(OH )] (10b) and for L ‚[Zn(OH2)]‚
Zn(OH )]2 (10c). The structure of 10c may be equivalent to
L ‚[Zn(OH2)]‚[Zn-OH-Zn)] (10e), in which two zinc(II) ions
are bridged by a hydroxide anion. (iii) Above pH 9 (pK3 )
.6), the hydrogen-bonding network starts to collapse due to
-
[
Figure 5. The pD-dependent change of aromatic protons in 10 (5 mM)
in D O at 35 °C.
2
3
8
II
-
repulsive intramolecular interactions among all the Zn -OH ,
changing to an “open-form”.
We may consider the existence of “half-closed-form” which
II
has two Zn -cyclen moieties on the upside of the molecule
and the other sitting horizontally as shown in 10f. However,
the pK1 value of 6.1 for the first equilibrium (10a a 10b +
+
H ) is significantly lower than the corresponding pK1 (6.7) for
+
7
(7a a 7b + H ). We therefore presume that the first
deprotonation is promoted by the presence of the other two
zinc(II)-bound waters. The CPK model studies of 10 suggest
that three zinc(II)-bound water molecules could come close to
each other, enough to allow direct hydrogen bonding between
II
-
II
-
II
three Zn - OH (or OH2) and/or Zn - OH-Zn bridging. This
II
cooperative assembly of three Zn -cyclen units was anticipated
to offer a suitable recognition site for C3-symmetrical guests
such as phosphate anions.
Affinity Constants of 1:1 Complex of 10 with Organic
Phosphate and Phosphonate Dianions in Aqueous Solutions.
To investigate complex formation between 10 and phosphates,
3
1
we conducted a P NMR titration experiment of 5 mM phenyl
2
-
2-
+
-
phosphate dianion (PP ) (pK4 ) 5.9 ) -log[PP ]aH /[HPP ],
-
Figure 6. Schematic model of conformational change of 10 dependent
on pH in aqueous solution. Round circles in all structures denote cyclen
rings in 10.
where HPP is phenyl hydrogen phosphate, see eq 4) with
varying concentrations (0-10 mM) of 10 in D2O at pD 7.1 (
0.1 and 35 °C (Figure 7). Under these conditions, the
-
2-
+
2-
-
conformations of 10 as shown in Figure 6. (i) At low pH (ca.
HPP a PP + H
K ) [PP ]a /[HPP ] (4)
4
H+
5
), 10a is a major species and its conformation is not fixed by
phosphorus chemical shift of PP2 moved from δ ca. 0 to δ
-1.3 during the addition of 1 equiv of 10. No further change
in chemical shift at higher concentration of 10 strongly suggests
1:1 complexation.
-
intramolecular interaction between zinc(II)-bound waters. The
X-ray crystal structure of 10 (Figure 2) obtained from pH 5
solution may suggest that an “open-form” predominates over a
“
closed-form”. (ii) As pH is raised to 6-8 (pK1 ) 6.1 and
pK2 ) 7.3), deprotonation of the zinc(II)-bound waters starts
to form an intramolecular hydrogen-bonding network between
For comparison, we obtained the 31P NMR of PP2- in D2O
3
(pD 8.5 ( 0.1) in the presence of zinc(II)-free ligand L , which

3074 J. Am. Chem. Soc., Vol. 119, No. 13, 1997
Kimura et al.
Figure 9. Distribution diagram for the species 18 (18a and/or 18b
2-
and/or 18c), 19 (19a and/or 19b), 10c, 10d, and PP for a 5 mM 10/5
mM PP2 mixture as a function of pH at 25 °C with I ) 0.1 (NaNO
-
).
3
The two other species which exist in less than 5% (10a and 10b) are
omitted for clarity.
Table 1. Phosphate (Phosphonate) Affinity Constants (log Kaff) of
II
II
2-
2-
m-Bis(Zn -cyclen) 7 and Tris(Zn -cyclen) 10 for NPP , PP
,
2
3
1, and 22 at 25 °C and I ) 0.10 (NaNO )
log Kaffa
phosphate
phosphonate)
(
(pK b
4
)
7
10
2
-
4.0c
4.6
NPP
PP
(5.2)
(5.8)
(6.1)
(7.0)
5.8
6.6
7.0
7.9
2
-
2
2
1
2
a
2
2-
2
2-
] (M-1) for 7 or
K
aff ) [Zn
2
L -RPO
3
complex]/[Zn L ][RPO
2 3
3
2-
3
2-
-1
b
[
(
0
Zn
[RPO
.10 (NaNO
3
L -RPO
3
complex]/[Zn
/[RPO
). From ref 19 with I ) 0.10 (NaClO ).
3
L ][RPO
3
] (M ) for 10. pK
4
) -log
2-
+
-
3
]a
H
3
H ]) obtained by pH titration at 25 °C with I )
c
3
4
Figure 8. Proposed structural change of the 1:1 complex of 10 and
2-
PP at various pH. Round circles denote cyclen rings in 10.
at pH 8.4. The deprotonation constant pK5 value of 7.4 for
zinc(II)-bound water in 18 is considerably higher than the pK1
() 6.1) of 10a in the absence of phosphate. This is due to the
competing phosphate interaction with this zinc(II) site. In the
light of the extremely high affinity constant of 1:1 complexation
+
3
+
was considered to exist as the tris(cyclen‚2H ) (L ‚6H ) at this
3
+
pH. It was found that L ‚6H induced only a negligible change
in the chemical shifts of phosphorus. This fact confirmed that
L ‚6H has little interaction with phosphate anions and that the
three zinc(II) ions in 10 are necessary for effective recognition
of phosphates.
3
+
2
-
of 10 with PP in comparison to that of 1:1 complexation of
II
2-
m-bis(Zn -cyclen) (7) with PP (log Kaff ) 4.6), we conclude
that 10 acts as a tripodal host. It has been shown that the
complex of PLCBc with an inorganic phosphate has an 18b type
of structure, namely, two of the three zinc(II) ions are bridged
by one oxygen of phosphate and the other zinc(II) binds to the
We then conducted a potentiometric pH titration for 10 (1
2
-
mM) and PP (1 mM) in water (I ) 0.1 (NaNO3)) with 0.1 M
NaOH at 25 °C to determine the 1:1 affinity constant (see Figure
3b). The phosphate complexes considered (18-20) are shown
2
3a,b
second oxygen of phosphate.
Hence, the species 18a and/
in Figure 8. The 1:1 complexation constant log Kaff and the
deprotonation constants pK5 and pK6, defined by eqs 5-7,
or 18b are more favorable structures of 18 and dramatically
stabilize the phosphate complex. It is also implied in Figure 9
that the second deprotonation of zinc(II)-bound water in 19b
occurs with a pKa of 9.3 to afford 20 which dissociates to
respectively, were determined to be 6.6, 7.4, and 9.3 by using
the program BEST.33
II
2
-
2-
phosphate and 10d. In conclusion, tris(Zn -cyclen) efficiently
1
1
1
0 + PP a 18
Kaff ) [18]/[10][PP ]
(5)
(6)
(7)
2-
recognizes PP in slightly acidic solution and the complex
dissociates at higher pH.
+
8 a 19 + H
K ) [19]aH
+
/[18]
/[19]
5
The 1:1 complexation constants with other phosphates such
2
-
as 4-nitrophenyl phosphate (NPP ), R-D-glucose-1-phosphate
21, and phenyl phosphonate 22 were similarly determined under
the same conditions as above and summarized in Table 1. For
+
9 a 20 + H
K ) [20]aH
+
6
2
-
Figure 9 shows the distribution diagram of five species (10c,
0d, 18 (18a and/or 18b and/or 18c), 19 (19a and/or 19b), and
complexation with NPP , the trimeric effect of 10 is about
II
1
300 times greater as compared to that of monomeric Zn -cyclen
2-
2-
II
PP ) for a 5 mM 10/5 mM PP mixture (the same concentra-
(5) and 60 times greater as compared to that of m-bis(Zn -
1
2-
tion as in the H NMR experiment described above) as a
cyclen) (7). For complexation with PP , 10 has 100 times
function of pH at 25 °C with I ) 0.10 (NaNO3). The population
greater affinity constants than 7. The affinity sequence of 10
2
-
2-
of 10-PP (1:1) complex 18 is over 90% below pH 6.4 (see
also Figure 8). As pH is raised, the population of 18 decreases
and the population of monohydroxide form 19 increases. The
concentration of the monohydroxide form reaches a maximum
is 22 (log Kaff ) 7.9) > 21 (log Kaff ) 7.0) > PP (log Kaff )
2-
6.6) > NPP (log Kaff ) 5.8). This sequence seems to parallel
order of basicity of these phosphates described by pK4 defined
2
-
2-
in eq 4: 22 (7.0) > 21 (6.1) > PP (5.8) > NPP (5.2).

A New Zinc Receptor for Phosphate Dianions
J. Am. Chem. Soc., Vol. 119, No. 13, 1997 3075
Hydroxyl groups of 21 may have negligible effects on the
complexation. It was unfortunate that we failed to isolate the
pKa values of zinc(II)-bound water of 10 in aqueous solution
have been determined by potentiometric pH titration, and the
formation of strong intramolecular hydrogen bonds yields a
“closed-form” of 10 at neutral pH, as suggested by three
stepwise deprotonation of the zinc(II)-bound waters and unique
1
:1 complexes as crystals of sufficient quality for X-ray crystal
structure study. However, in the light of the actual P-O
II
bonding to three Zn -cyclen complexes in Figure 1 and the
1
size of the 1,3,5-trimethylbenzene spacing unit between the three
H NMR behavior of 10 dependent on pH (pD). By potentio-
II
Zn -cyclen units, we consider 18a and/or 18b to be feasible
metric pH titrations, we found 10 to be an effective receptor
for C3-symmetric organic phosphates (and a phosphonate) in
slightly acidic pH solutions with high 1:1 affinity constants (log
Kaff), resulting from the cooperative recognition of three zinc(II)
ions. The cooperative recognition with trinuclear zinc(II)
complex may apply to other multidentate anions in aqueous
solution. The study of tris(zinc(II)-macrocyclic polyamine)
complexes may also be useful in understanding phosphate
substrate interactions with three zinc(II) center phosphatases
(e.g., phospholipase C).
for the 1:1 complex.
Since the trizinc(II) center of PLCBc (8) strongly interacts
with phospholipids (phosphodiesters), we also checked if the
interaction of 10 with phosphodiester monoanion could occur.
The pH titration of 10 in the presence of di-n-butyl phosphate
monoanion 23 (pKa is below 4), however, gave almost the same
curve as the titration curve in the absence of 23 (see Figure 3a)
within experimental error. This implies little interaction between
II
40
tris(Zn -cyclen) and phosphodiester monoanion. We con-
clude that 10 is a receptor selective for dianionic phosphates
and phosphonates.
Experimental Section
General Information. All reagents and solvents used were
purchased at the highest commercial quality and used without further
purification. All aqueous solutions were prepared using deionized and
distilled water. IR spectra were recorded on a Shimadzu FTIR-4200
1
spectrometer. H NMR spectra were recorded on a JEOL Alpha (400
MHz) spectrometer. Tetramethylsilane in CDCl
propionic-2,2,3,3-d acid sodium salt in D O were used as internal
references for H and 13C NMR measurements. The pD values in D
were corrected for a deuterium isotope effect using pD ) [pH-meter
3
and 3-(trimethylsilyl)-
4
2
1
2
O
reading] + 0.40.1
7c 31
P NMR spectra were recorded on a JEOL Lambda
O solution of 80% phosphoric acid was
(
202 MHz) spectrometer. A D
2
31
used as an external reference for P NMR. Elemental analysis was
performed on a Perkin Elmer CHN Analyzer 2400. Thin-layer (TLC)
and silica gel column chromatographies were performed using Merck
Art. 5554 (silica gel) TLC plates and Fuji Silysia Chemical FL-100D
(silica gel), respectively.
We initially suspected that the zinc(II)-bound hydroxide in
the complex 19a and 19b in Figure 8 might be well positioned
to attack the phosphorus atom of phosphate to cleave the P-OR
Crystallization of the 1:3 Complex of 4-Nitrophenyl Phosphate
(NPP2 ) and Three Zinc(II)-1,4,7,10-tetraazacyclododecane (Zn -
cyclen) (11). 4-Nitrophenyl phosphate disodium salt hexahydrate (25
mg, 67 µmol) was added to a solution of 1,4,7,10-tetraazacyclo-
dodecane-zinc(II) diperchlorate complex monohydrate (182 mg, 0.40
mmol) in water (3 mL) at room temperature. This mixture was
concentrated slowly under reduced pressure to provide a 1:3 complex
-
II
ester bond.41 However, acceleration of NPP2- cleavage hardly
II
-
4
of 4-nitrophenyl phosphate with Zn -cyclen 11‚(ClO
4
)
2
‚2H O (55
-
mg, 61%) as colorless prisms. For 11‚(ClO
300, 3177, 2955, 2919, 1611, 1591, 1518, 1485, 1445, 1375, 1578,
256, 1134, 1092 cm ; H NMR (CDCl
.89-2.96 (24H, m, CH ), 7.35 (4H, d, J ) 9.3 Hz, ArH), 8.27 (4H,
d, J ) 9.3 Hz, ArH). Anal. Calcd for C H N O PCl Zn ‚2H O:
4
)
4
2
‚2H O: IR (KBr pellet)
3
1
2
-1 1
3
2
) δ 2.75-2.82 (24H, m, CH ),
2
occurred at pH 7.0, 8.0, or 9.0 at 37 °C. The failure of
30
64 13 22
4
3
2
-
intramolecular OH attack at the zinc(II)-bound phosphate may
C, 26.42; H, 5.03; N, 13.35. Found: C, 26.00; H, 5.07; N, 13.33.
1,4,7-Tris(tert-butyloxycarbonyl)-1,4,7,10-tetraazacyclo-
dodecane (3Boc-cyclen) (13). A solution of di-tert-butyl dicarbonate
(7.9 g, 36 mmol) in CHCl (100 mL, passed through Al O ) was added
be attributable to the inert nature of complex 19c (equivalent
-
to 19a and 19b). We recently showed that the µ-OH -bridged
II
bis(Zn -cyclen) species 24 is kinetically inactive as a nucleo-
3
2
3
phile toward 4-nitrophenyl acetate.19,42
slowly (in 3 h) to a solution of cyclen (2.2 g, 13 mmol) and
triethylamine (5.5 mL, 39 mmol) in CHCl (120 mL) at room
temperature (slow addition of a (Boc) O solution is necessary for good
3
2
Conclusions
chemical yields). The reaction mixture was stirred for 24 h at room
temperature, and the organic solvent was removed under reduced
pressure. The remaining residue was purified by silica gel column
chromatography (hexanes/AcOEt) to provide 13 as a colorless amor-
phous solid (4.4 g, 72%). For 13: IR (KBr pellet) 3522, 2976, 2818,
2
-
The 1:3 complex (11) consisting of one molecule of NPP
II
and three Zn -cyclen complexes was isolated, and its X-ray
crystal structure analysis was carried out. On the basis of the
structure of 11, a new tris(Zn -cyclen) (10) was synthesized
II
-
1
1
1
(
691, 1464, 1418, 1366, 1272, 1250, 1171, 1100 cm
CDCl ) δ 1.45 (18H, brs, C(CH ), 1.47 (9H, brs, C(CH
.90 (4H, m, CH ), 3.17-3.43 (8H, m, CH ), 3.54-3.72 (4H, m, CH
) δ 28.51, 28.70, 45.01, 46.01, 48.85, 49.12, 49.49,
49.90, 50.52, 51.00, 79.22, 79.35, 79.51, 155.43, 155.62, 155.85.
;
H NMR
), 2.80-
);
via 3Boc-cyclen (13) as a potential host for C3-symmetrical
phosphate guests. The crystal structure of 10 (obtained at pH
3
3
)
3
3 3
)
2
2
2
2
5) was determined by X-ray crystal structure analysis. The three
13
C NMR (CDCl
3
II
(
40) Earlier, we showed that the Zn -macrocyclic triamine ([12]aneN3)
17b
complex has more interaction with anionic phosphates than 5. Hence,
we are now synthesizing homologues of 10 with [12]aneN3 as trizinc(II)
enzyme models.
1,3,5-Tris[4,7,10-tris(tert-butyloxycarbonyl)-1,4,7,10-tetraaza-
cyclododecan-1-ylmethyl]benzene (9Boc-tris(cyclen), 14) and 1-(Ben-
zyloxycarbonyl)-4,7,10-tris(tert-butyloxycarbonyl)-1,4,7,10-tetraaza-
cyclododecane (15). A solution of 1,3,5-tris(bromomethyl)benzene
(
41) Kimura, E.; Kodama, Y.; Koike, T.; Shiro, M. J. Am. Chem. Soc.
995, 117, 8304-8311.
42) Kimura, E.; Hashimoto, H.; Koike, T. J. Am. Chem. Soc. 1996, 118,
0963-10970.
1
(
12)30 (0.82 g, 2.3 mmol) and 3Boc-cyclen (13) (3.5 g, 7.4 mmol) in
(
1
3
CH CN (100 mL) was stirred at 80 °C under Ar in the presence of

3076 J. Am. Chem. Soc., Vol. 119, No. 13, 1997
Kimura et al.
anhydrous Na CO (1.57 g, 14.8 mmol). After 3 days of stirring,
insoluble inorganic salts were filtered off and the filtrate was
concentrated under reduced pressure. The resulting crude product was
2
3
Crystallographic Study of 11‚4(ClO
4
-)‚2H
2
O. A colorless pris-
-
matic crystal of 11‚4(ClO
4
2 68 13 4 3 r
)‚2H O (C30H N O24PCl Zn , M )
1363.87) having approximate dimensions of 0.35 × 0.20 × 0.15 mm
was sealed in a glass capillary and used for data collection. All
measurements were made on a Rigaku RAXIS IV imaging plate area
detector with graphite monochromated Mo KR radiation. Indexing was
performed from three 2.0° oscillation images which were exposed for
4.0 min. The data were collected at a temperature of 25 ( 1 °C to a
maximum 2θ value of 48.7°. A total of 454.0° oscillation images were
collected, each being exposed for 30.0 min. The crystal-to-detector
distance was 110.0 mm. The detector swing angle was 0.0°. Readout
was performed in the 100 µm pixel mode. The structure was solved
by direct methods (SIR 92) and expanded by means of Fourier
techniques (DIRDIF 94). All calculations were performed with the
3
dissolved in CHCl (50 mL), to which N,N-diisopropylethylamine (0.40
mL, 2.3 mmol) and benzyl chloroformate (0.33 mL, 2.31 mmol) were
added at 0 °C. After being stirred overnight at room temperature, the
reaction mixture was concentrated under reduced pressure. The
resulting crude product was purified by silica gel chromatography to
afford 15 (0.54 g, 12% yield based on used 13) and 9Boc-tris(cyclen)
(14, 3.0 g, 85% based on used 12) as colorless amorphous solids. For
1
1
5: IR (KBr pellet) 3520, 2977, 2810, 1692, 1480, 1416, 1366, 1269,
-
1 1
171 cm ; H NMR (CDCl
3
) δ 1.46 (18H, brs, C(CH
), 5.12 (2H, s, ArCH
3
.38 (5H, m, ArH); C NMR (CDCl ) δ 28.33, 28.37, 28.45, 50.40,
3
)
3
), 1.47 (9H,
brs, C(CH
3
)
3
), 3.25-3.50 (16H, m, CH
2
2
), 7.30-
1
3
7
6
1
1
7.20, 78.10, 126.95, 127.61, 128.08, 128.26, 128.48, 128.54, 136.41,
teXsan crystal structure analysis package developed by Molecular
Structure Corporation (1992, 1994). Crystal data for 11‚4(ClO
H O: monoclinic, space group P2 /a (No. 14), a ) 18.481(8) Å, b )
2 1
57.55. For 14: IR (KBr pellet) 2977, 2810, 1692, 1480, 1416, 1366,
-
4
)‚
-
1 1
316, 1269, 1171 cm ; H NMR (CDCl
), 3.17-3.70 (16H, m, CH ), 5.12 (2H, s, ArCH
) δ 28.51, 28.69, 47.35, 47.63, 49.79,
3
) δ 1.42, 1.46, 1.47 (27H, 3
2
1
2
7
brs, C(CH
)
3 3
2
2
), 7.307.38
3
3.901(3) Å, c ) 22.556(6) Å, â ) 111.80(3)°, V ) 5380.7 Å , Z )
1
3
(5H, m, ArH); C NMR (CDCl
3
3
, Dcalcd ) 1.683 g/cm , 2θmax ) 48.7°, total number of reflections )
5
3.47, 54.89, 79.37, 79.49, 131.70, 135.45, 155.36, 155.37, 155.39,
700. Three of the four perchlorate ions were disordered at the two
1
55.69.
locations indicated by the corresponding unprimed and primed numbers
of the oxygen atoms, respectively. The non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were included but not refined.
The final cycle of full-matrix least-squares refinement was based on
568 observed reflections (I > 3.00σ(I)) and 767 variable parameters
and converged (largest parameter shift was 0.03 times its esd) with
1
,3,5-Tris(1,4,7,10-tetraazacyclododecan-1-ylmethy)benzene Non-
3
ahydrobromide Dihydrate, L ‚9(HBr)‚2H
2
O. To a solution of
9
Boc-tris(cyclen) (14, 3.29 g, 2.1 mmol) in EtOH (100 mL) at 0 °C
was added slowly 47% aqueous HBr (12.5 mL, 0.73 mol). After being
stirred overnight at room temperature, the reaction mixture was
concentrated under reduced pressure below 40 °C. The resulting crude
6
unweighted and weighted agreement factors of R ()∑||F
o
| - |F
c
||/
powder was crystallized from EtOH/24% aqueous HBr to afford
2
2 0.5
∑
|F
o
|) ) 0.061 and R
w
) ((∑w(|F
o
| - |F
c
|) /∑wF
o
) ) ) 0.096.
3
L ‚9(HBr)‚2H
2
O as fine crystals (2.6 g, 88%): mp 266 °C (dec); IR
-
Crystallographic study of 10‚6(NO
3
2
)‚3H O. A colorless prismatic
(
(
(
KBr pellet) 3500, 2955, 2714, 1584, 1440, 1359, 1073 cm-1; 1H NMR
O) δ 2.92-3.08 (24H, m, CH ), 3.08-3.42 (24H, m, CH ), 3.40
6H, s, ArCH ), 7.33 (3H, s, ArH); C NMR (D O) δ 42.13, 42.46,
4.87, 47.64, 56.15, 132.34, 135.35. Anal. Calcd for C33
HBr‚2H O: C, 28.41; H, 5.71; N, 12.05. Found: C, 28.50; H, 5.85;
-
crystal of 10‚6(NO
3
2 72 18 3 r
)‚3H O (C33H N O21Zn , M ) 1253.18) having
D
2
2
2
approximate dimensions of 0.35 × 0.15 × 0.10 mm was mounted on
a glass fiber. All measurements were made on a Rigaku RAXIS IV
imaging plate area detector with graphite monochromated Mo KR
radiation. Indexing was performed from three 1.0° oscillation images
which were exposed for 4.0 min. The data were collected at a
temperature of 25 ( 1 °C to a maximum 2θ value of 52.8°. A total of
1
3
2
2
4
9
66 12
H N ‚
2
N, 11.82.
1
,3,5-Tris((1,4,7,10-tetraazacyclododecan-1-yl)methyl)benzene Tri-
-
zinc(II) Complex, 10‚6(NO
L was obtained by passing L ‚9(HBr)‚2H
an anionic exchange resin (Amberlite IRA-400, OH form) and
concentrating under reduced pressure. The resulting free L3 was
dissolved in 20 mL of 66% (v/v) aqueous EtOH, and a solution of
zinc(II) nitrate hexahydrate (0.69 g, 2.28 mmol) was added at 60 °C.
After being stirred overnight at 60 °C, the reaction mixture was
3
3
)‚3H O‚0.5EtOH. The acid-free ligand
2
4
4.5° oscillation images were collected, each being exposed for 30.0
3
2
O (1.0 g, 0.72 mmol) through
min. The crystal-to-detector distance was 125.0 mm. The detector
swing angle was 0.0°. Readout was performed in the 100 µm pixel
mode. The structure was solved by direct methods (SHELXS 86) and
expanded by Fourier techniques (DIRDIF 94). All calculations were
performed with the teXsan crystal structure analysis package developed
-
by Molecular Structure Corporation (1992, 1994). Crystal data for
concentrated under reduced pressure. The resulting colorless powder
-
-
10‚6(NO
3
)‚3H O: monoclinic, space group P1 (No. 1), a ) 15.668(6)
2
was crystallized from EtOH/water to afford 10‚6(NO
3
)‚3H O‚0.5EtOH
2
Å, b ) 15.914(3) Å, c ) 15.614(2) Å, R ) 91.730(10)°, â ) 111.80(3)°,
(
3
0.62 g, 67%) as colorless needles: mp >280 °C; IR (KBr pellet) 3491,
3
3
-
1
1
γ ) 116.85(2)°, V ) 3001.2 Å , Z ) 2, Dcalcd ) 1.387 g/cm , 2θmax
)
2
197, 1607, 1385, 1094 cm ; H NMR (D O) δ 2.63-3.12 (36H, m),
5
2.8°, total number of reflections ) 10 717. The non-hydrogen atoms
3
.18-3.33 (6H, m), 3.82-3.90 (3H, m), 4.05-4.20 (12H, m), 7.38
1
3
were refined anisotropically. Hydrogen atoms were included but not
refined. The final cycle of full-matrix least-squares refinement was
based on 7488 observed reflections (I > 3.00σ(I)) and 1367 variable
parameters and converged (largest parameter shift was 0.00 times its
(
3H, s, ArH); C NMR (D
2
O) δ 40.94, 41.05, 43.45, 43.56, 48.23,
18.13, 132.88. Anal. Calcd for C33 ‚3H O‚0.5EtOH: C,
2.00; H, 5.92; N, 19.76. Found: C, 32.16; H, 5.85; N, 19.75. The
1
3
H
66
N
18
O
18Zn
3
2
colorless prisms suitable for X-ray structure analysis were obtained by
recrystallization from EtOH/water.
esd) with unweighted and weighted agreement factors of R ()∑||F
o
|
2
2 0.5
-
|F ||/∑|F
c
o
|) ) 0.051 and R
w
) ((∑w(|F
o
c
| - |F |) /∑wF
o
) ) ) 0.071.
Potentiometric pH Titrations. The preparation of the test solutions
and the calibration method of the electrode system (Orion Research
Expandable Ion Analyzer EA920 and Orion Research Ross Combination
Acknowledgment. E.K. is thankful to the Grant-in-Aid for
1
8
pH Electrode 8102BN) were described earlier. All test solutions (50
Priority Project “Biometallics” (No. 08249103) from the
Ministry of Education, Science and Culture in Japan. NMR
instruments (a JEOL Alpha (400 MHz) spectrometer) in the
Research Center for Molecular Medicine (RCMM) in Hiroshima
University were used.
mL) were kept under an argon (>99.999% purity) atmosphere. The
potentiometric pH titrations were carried out with I ) 0.10 (NaNO )
3
at 25.0 ( 0.1 °C (or 35.0 ( 0.1 °C), and at least three independent
II
titrations were performed. Deprotonation constants of Zn -bound water
-
+
K′
n
2
()[HO -bound species][H ]/[H O-bound species], phosphate com-
plex affinity constants Kaff () [phosphate complex]/[host][phosphate],
where host is 7 or 10) were determined by means of the the program
BEST. All σ fit values defined in the program are smaller than 0.005.
Supporting Information Available: Tables crystallographic
parameters, atomic coordinates, equivalent isotropic temperature
factors, anisotropic temperature factors, bond distances, and
33
+
-
+
The K
5 °C are 10
respectively. The corresponding mixed constants, K
species]aH+/[H
W
()aH+
a
OH-), K′
, 10
W
-13.79
()[H ][OH ]), and f
H
values used at 25 and
-
14.00
, and 0.825, and 10-13.68, 10
-13.48
-
3
, and 0.823,
bond angles in CIF format for 10‚6(NO )‚3H O and
3
2
-
()[HO -bound
-
n
1
1‚4(ClO4 )‚2H2O (40 pages). See any current masthead page
+
+ +
2
O-bound species]), are derived using [H ] ) a
The species distribution values (%) against pH ()-log[H ] + 0.084)
were obtained using the program SPE.
H
/f
H
.
for ordering and Internet access instructions.
+
3
3
JA9640408