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Molecular Recognition of Terephthalic Acid by Supramolecular Self-Assembly of an Acridine-Pendant CyclenЦZnII Complex.

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Molecular Recognition of Terephthalic Acid
by Supramolecular Self-Assembly of an
Acridine-Pendant Cyclen -Zn" Complex**
Eiichi Kimura,* Takuya Ikeda, Mitsuhiko Shionoya,
and Motoo Shiro
Selective molecular recognition of anionic substrates is of current interest. One classic example of a receptor is the cationic
macrocyclic polyammonium compound that binds with phthalate
(0isomer) to form complex 1 more strongly than with isophthalate (rn isomer) or terephthalate ( p isomer) due to more favorable electrostatic and hydrogen bonding interactions."' More
recently, cryptate 2 was reported; here the substrate terephthalate dianion. which fits in the cavity, is bound by multiple hydrogen bonding, electrostatic, and hydrophobic interactions within
a macrobicyclic polyammonium cryptand.[']
The isolated complex 6 comprises two Zn" complexes 4 and
one terephthalate dianion. It was characterized by 'H NMR (in
[DJDMSO) and IR spectroscopy ( i j = 1599 cm-' (COO-),
1360 (COO-)) and elemental analysis.r51
We initially suspected this 2: 1 complex of having pronounced
intramolecular n (guest)-n (host) stacking interactions. However,
the X-ray crystal structure analysis of 6 . B F i .ClO, .3H,0r6]
(Fig. I ) , showed more complex interactions. The zinc(r1) ion
Another supramolecular approach to the selective molecular
recognition of anions could involve the formation of aggregates
by self-assembly of two or more molecular subunits through
noncovalent interactions. If the binding partners are sufficiently
complementary, the subunits might spontaneously build up an
ordered aggregate.
In the context of our work on zinc@) complexes of cyclen (3)
and its acridine-pendant derivative 4, which were initially designed for selective recognition of thymine and its derivatives,I3I
we have found that 4 has a fairly strong affinity for the benzoate
anion.[41It yields a 1 : 1 complex 5 with a stability constant of log
K = 2.25 f0.05 in aqueous solution ( K = [5]/([4][anion]) [M- '1,
ionic strength I = 0.10 (NaNO,), 25 "C). Complex 4 (10mM)
interacts with terephthalic acid ( 5 m ~ )in an aqueous solution containing ClO, ( 2 5 m ~ )at pH 8.4 [ 2 5 m ~TAPS
buffer (TAPS = N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid)] to form a crystalline precipitate of 6 immediately
in high yield (90% based on terephthalic acid).
Prof. Dr. E. Kimura, T. Ikeda, Dr. M. Shionoya
Department of Medicinal Chemistry, School of Medicine
Hiroshima University, Kasumi 1-2-3, Minami-ku, Hiroshima 734 (Japan)
Telefax: Int. code + (82) 257-5324
Dr. M. Shiro
Rigaku Corporation, Matsubdracho 3-9-12. Akishima, Tokyo 196 (Japan)
This work was supported by the Ministry of Education, Science and Culture in
Japan. Grant-in-Aid (Scientific Research (A), No. 04403024 (E. K.) and Scientific Research (C) No.06807172 (M. S.)), the Kato Memorial Bioscience Foundation. the Tokyo Biochemical Research Foundation (M.S.). and The Japan
Science Society (Sasagawa Scientific Research Grant (T. I.)). N M R instruments and a computer graphic system CAChe (Tetronix Co.) in the Medical
Molecules Exploring Center of Hiroshima University were used. cyclen =
Angew. Chem. h i . Ed. Engl. 1995, 34. N o . 6
Fig. 1. An ORTEP plot (30 % probability ellipsoids) of 6 BF; . ClO; - 3H,O. The
perchlotate anion, the tetrafluoroborate anion, and the three water molecules are
omitted for clarity. Selected bond lengths [A] and angles [ 1: Z n l - 0 1 * 1.946(7).
Zn2-03*, 1.906(7), Z n l - N l 2.283(7), Znl-N42.096(6). Z n l L N 7 2.184(8), Z n l N10 2.099(8), Zn2-N21 2.296(6), Zn2-N24 2.105(6), ZnZ-N27 2.184(8), Zn2N30 2.093(8); Ol*-Znl-N1 119.8(3), Ol*-Znl-N4 110.3(3). Ol*-Znl-N7 101.3(3).
01*-Znl-N10 117.4(3), 03*-Zn2-N21 116.7(3), 03*-Zn2-N24 113.4(3), 03*-Zn2N27 104.7(3). 03*-Zn2-N30 113.9(3).
resides in a distorted square-pyramidal environment, coordinated by four nitrogen atoms of the cyclen subunit and an oxygen
atom of the terephthalate carboxylate anion (01 * -Zn 1
1.946(7), 0 3* -Zn 2 1.906(7) A). In the crystal structure, the
intercomplex array is more interesting (Fig. 2). The counterions
(CIO, and BF,) lie in middle between two zinc(1r) complexes,
VCH Verlagsgesellschufi mhH, 0-69451 Wrinheim, 1995
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and contribute greatly to the
neutralization of the repulsive
cationic charges. Two of the three
water molecules lie in the vicinity
of each zinc(I1) ion and the third
in that of a counterion. It is assumed that all molecules in a
unit cell, that is two zinc(1r) complexes, one terephthalate dianion, one ClO, ion and one BF,,
and three water molecules, participate in the stabilization of
this complex. Furthermore, the
intermolecular interactions between the two acridine groups
(at the closest interplane contact
of 3.78A) and between an
acridine group and the ethylene
unit of a cyclen ring (closest contact 3.40 A) form a well-organized chainlike aggregate 7
(Scheme 1 ) . The pronounced
stability of this supramolecular
compound may be responsible
for its extremely low solubility in
Fig. 2. Arrangement of the comwater. Attempts to determine
plex 6.BF,.C10;.3HzO In the
the stability constant of this 2: 1
crystal along the crystallographic
complex by potentiometric pH
a axis.
titration were unsuccessful, since
the 2: 1 complex precipitated immediately upon addition of the
It became apparent that the tendency of 6 to self-assemble
into the supramolecule 7, which is insoluble in water, may permit terephthalate to be separated efficiently from its isomers
phthalate and isophthalate. The 2: 3 complexes of phthalate and
isophthalate with 4 were prepared as described for terephthalate.
Both complexes remained in aqueous solution and scarcely precipitated out. We then tested the separation in the following way:
0.4 mL of an aqueous solution of 4.2NO; (20mM)[81was added
to 0.4mL of a solution containing the o, m, p isomers (each
10 mM) at pH 8.4 (25mM TAPS buffer, 25mM NaClO,, 25 "C);
immediate precipitation occurred. After 6 hours, the mixture was
centrifuged and 0.54 mL of the upper solution layer was withdrawn and treated with D,O (0.06 mL, 0.3 'YO sodium [2,2,3,3D4]3-(trimethylsilyl)propionate). The 'H NMR spectrum of this
solution showed that thep isomer had almost completely disappeared, while most of the o (>95 %) and m (>90 %) isomers
remained. According to the 'H NMR spectrum in [DJDMSO of
the collected precipitates, the major component (80 %) was the
p isomer 6 ; a minor component (8 'YO) comprising the 2: 1 complex of 4 and isophthalate (m isomer) (the resulting composite;
p : m : o= 10: 1 :O). The best separation of terephthalate from the
m and o isomers with 4 ( p : m : o=15:1:0) was achieved when
5 'YO CH,CN was added to the above test solution.
We conclude that 4 selectively separates terephthalate as insoluble crystals from a mixture of terephthalate and its isomers
phthalate and isophthalate, not because its 2: 1 complex 6 has a
particularly high stability constant, but because it is additionally
stabilized by self-assembly into an ordered aggregate 7. Metal
complexes with aromatic pendants should also be useful for the
molecular recognition of other anionic molecules in aqueous
Received: September 20, 1995 [Z73341E]
German version: Angew. Chem. 1995, 107, 711
Keywords: complexes with nitrogen ligands . molecular recognition . supramolecular chemistry . zinc compounds
[I] a) E. Kimura, Pure Appl. Chem. 1993, 65, 355-359; b) .IInclusion Phenomena
1989, 7, 183-191: c) Pure Appl. Chem. 1989, 61, 823-828; d) E. Kimura, A.
Sakonaka, J. Am. Chem. SOC.1982, 104,4984-4985; e) E. Kimura, A. Sakonaka, T. Yatsunami, M. Kodama, ibid. 1981, 103,3041 -3045; d) E. Kimura, A.
Watanahe, M. Kodama, ibid. 1983,105,2063-2066; e) E. Kimura, M. Kodama,
T. Yatsunami, ibid. 1982, 103, 3041 -3045.
[2] a) J.-M. Lehn, R. MCric, J.-P. Vigneron, I. Bkouche-Waksman, C. Pascard, J.
Chem. SOC.Chem. Commun. 1991, 62-64; b) J.-M. Lehn, Angew. Chem. 1988,
100,91-116; Angew. Chem. Inf. Ed. Engl. 1988, 27.89-112.
[3] a) M. Shionoya, E. Kimura, M. Shiro,J Am. Chem. Soc. 1993, 115, 6730-6737;
b) M. Shionoya. T. Ikeda, E. Kimura, M. Shiro, ibid. 1995, 116, 3848-3859; c)
M. Shionoya, M. Sugiyama, E. Kimura, .lChem. Soc. Chem. Commun. 1995,
1747- 1748.
[4] Anion affinity for 3, see E. Kimura, T. Shiota, T. Koike. M. Shiro, M. Kodama,
J. Am. Chem. SOC.1990, 112, 5805-5811.
[5] Synthesis of6.BF; CIO; ' 3 H,O: A solutionof4.2CI0, (32.3 mg. 0.050 mmol)
in hot CH,CN (3 mL) was added to a solution of diammonium terephthalate
salts (5.0 mg, 0.025 mmol) in H,O (3 mL). After cooling. NaBF, (0.5 mL. 1M)
was added to the mixture, which was dried a desiccator in the presence of KOH
under reduced pressure. Orange prisms, suitable for X-ray analysis, were obtained (2Xmg, 88%). 1R (KBr): ? 1599 (COO-), 1451, 1360 (COO-), 1098,
1084,974,765,714,627 cm-'. 'HNMR (400 Hz, [DJDMSO. 2 0 m ~
at 30°C.
TMS): S = 2.40-2.46 (4H, m, NCH,), 2.65-2.90 (m, 24H: NCH,), 3.05-3.15
(m. 4H; NCH,), 4.1-4.2 (hr, 2H; cyclen-NH). 4.5-4.6 (br, 4H; cyclen-NH).
5.1 1 (hrs, 4H; ArCH,). 7.59 (t. J = 7.56 Hz. 4H; ArH), 7.80 (pseudo-t, J =7.80/
6.84Hz4H;ArH),X.i0(~,4H;terephthalate),X.l6(dd, J = 8.78,0.98 Hz,4H;
~ 30 ' C ,
ArH), 8.50 (d, J = 8.78 Hz, 4H; ArH). I3C NMR ([DJDMSO, 2 0 m at
TMS): d = 42.78, 43.55, 44.69, 45.32, 49.77, 125.08, 126.41, 126.43, 129.14,
129.84, 129.89, 137.38, 137.66, 148.12, 171.21. Anal. cdkd for
C 49.48; H 5.43; N 11.10. Found: C
49.43; H 5.49: N 11.03.
[6] Crystal data of 6.BF: .CIO;.3H,O: yellow prismatic crystal (0.2 x 0.15 x
0.05 mm'); the lattice parameters and intensity data were measured on a Rigaku
AFC7R diffractometer with graphite-monochromated Cu,, radiation and a
12 kW rotating anode generator. The structure was solved by direct methods
and expanded Fourier techniques. Some non-hydrogen atoms were refined anisotropically, while the rest were refined isotropically. Hydrogen atoms were
included but not refined. Empirical formula C,,H,8N,,0,,BF,CIZn,, monoclinic, space group P2, (no. 4), a = 9.406(2), b = 29.651(2). c =10.766(2) 8,
5,' = 111.7641', V = 2788.6(4) A', Z = 2, pralcd
= 1.503 gcm3. 20,,, = 120.2", radiation Cu,.(l. =1.54178 A), p = 21.99 cm-'. graphite monochromated, temperature 20.0 "C, scan type w-20, refinement full-matrix least-squares. The final
cycle of the refinement was based on 3572 observed reflections to give R = 0.047
and R , = 0.070. All calculations were performed using the teXsan 171program.
Further details of the crystal structure investigation can be obtained from the
Director of the Cambridge Crystallographic Data centre, 12 Union Road, GBCambridge CB2 1EZ (UK), on quoting the full journal citation.
[7] teXsan: Crystal Structure Analysis Package, Molcular Structure Corporation
(1985, 1992).
[8] The compound was prepared by a modified procedure [3b], using Zn(NO,),.6H,O instead of Zn(C10,),~6H,O.
Scheme I . Schematic representation of the chainlike aggregate I formed from 6
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Angew. Chem. tnt. Ed. Engl. 1995,34, N o . 6
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acid, terephthalic, acridines, complex, self, molecular, assembly, supramolecular, cyclenцznii, recognition, pendant
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