Cooperative self-assembly and molecular binding behavior of cyclodextrin-crown ether conjugates mediated by alkali metal ions

Article abstract of DOI:10.1039/b406656a

In order to quantitatively investigate their molecular binding ability, a series of cyclodextrin-crown ether conjugates containing β-cyclodextrin (β-CyD) and crown ether units, i.e. N-(benzoaza-15-crown-5) acylaminomethylene tethered 6-diethylenetriamino-6-deoxy-β-CyD (1), N-(benzoaza-15-crown-5)acylaminomethylene tethered 6-triethylenetetraamino-6- deoxy-β-CyD (2) and 4′,5′-dimethylene-benzo-15-crown-5 tethered 6-diethylenetriamino-6-deoxy-β-CyD (3), have been prepared as ditopic molecular receptors. Their inclusion complexation behavior with four representative fluorescent dyes, i.e. ammonium 8-anilino-l-naphthalenesulfonate (ANS), sodium 6-toluidino-2-naphthalenesulfonate (TNS), acridine red (AR) and rhodamine B (RhB), has been comprehensively investigated in aqueous NaH ₂PO₄/Na₂HPO₄ or KH ₂PO₄/K₂HPO₄ buffer solution (pH 7.20) by means of circular dichroism, fluorescence, and 2D NMR spectra. The results indicate that the self-assembly of crown ether modified β-CyD mediated by potassium ion exhibits a dimeric structure, which significantly enhances the original binding ability and molecular selectivity of parent β-CyD and its derivatives towards guest molecules through the cooperative binding of two hydrophobic CyD cavities with one guest. This cooperative binding mode of K⁺/CyD-crown ether systems are further confirmed by Job's experiments and 2D NMR investigations. Attributed to the positive contributions from the metal-ligated crown ether cap and K⁺-mediated dimerization of CyDs, the binding constant (Ks) values of CyD-crown ether conjugates 1-3 toward ANS are 10-83 times higher than that of β-CyD. The increased binding ability and molecular selectivity of CyD-crown ether conjugates are discussed from the viewpoints of size/shape-Fit and multiple recognition mechanism.

Full text of DOI:10.1039/b406656a

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A R T I C L E
Cooperative self-assembly and molecular binding behavior of
cyclodextrin–crown ether conjugates mediated by alkali metal ions
Yu Liu,* Zhong-Yu Duan, Yong Chen, Jian-Rong Han and Lv Cui
Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry, Nankai University,
Tianjin, 300071, P. R. China. E-mail: yuliu@public.tpt.tj.cn; Fax: +86-22-23503625
Received 4th May 2004, Accepted 22nd June 2004
First published as an Advance Article on the web 27th July 2004
In order to quantitatively investigate their molecular binding ability, a series of cyclodextrin–crown ether conjugates
containing -cyclodextrin (-CyD) and crown ether units, i.e. N-(benzoaza-15-crown-5)acylaminomethylene tethered
6-diethylenetriamino-6-deoxy--CyD (1), N-(benzoaza-15-crown-5)acylaminomethylene tethered 6-triethylenetetraamino-
6-deoxy--CyD (2) and 4′,5′-dimethylene-benzo-15-crown-5 tethered 6-diethylenetriamino-6-deoxy--CyD (3), have been
prepared as ditopic molecular receptors. Their inclusion complexation behavior with four representative fluorescent dyes,
i.e. ammonium 8-anilino-1-naphthalenesulfonate (ANS), sodium 6-toluidino-2-naphthalenesulfonate (TNS), acridine red
(AR) and rhodamine B (RhB), has been comprehensively investigated in aqueous NaH2PO4/Na2HPO4 or KH2PO4/K2HPO4
buffer solution (pH 7.20) by means of circular dichroism, fluorescence, and 2D NMR spectra. The results indicate that the
self-assembly of crown ether modified -CyD mediated by potassium ion exhibits a dimeric structure, which significantly
enhances the original binding ability and molecular selectivity of parent -CyD and its derivatives towards guest molecules
through the cooperative binding of two hydrophobic CyD cavities with one guest. This cooperative binding mode of
K+/CyD–crown ether systems are further confirmed by Job’s experiments and 2D NMR investigations. Attributed to the
positive contributions from the metal-ligated crown ether cap and K+-mediated dimerization of CyDs, the binding constant
(Ks) values of CyD–crown ether conjugates 1–3 toward ANS are 10–83 times higher than that of -CyD. The increased
binding ability and molecular selectivity of CyD–crown ether conjugates are discussed from the viewpoints of size/shape-
fit and multiple recognition mechanism.
of which possesses two different recognition sites, i.e. CyD and
Introduction
crown ether, and a flexible oligo(ethylenediamine) linker in a single
It is well known that crown ethers and cyclodextrins (CyDs)
molecule.Thereasonforchoosingoligo(ethylenediamine)fragments
can be taken as molecular receptors to selectively bind ionic and
as linker groups is that these flexible groups can appropriately adjust
molecular guests respectively forming host–guest complexes or
the distance and/or location of the crown ether unit relative to the
supramolecular species. Therefore, in the past few decades, a lot of
CyD cavity to fit the size/shape of the guest molecule, therefore
effort has been contributed to the design and synthesis of functional
enabling us to improve the binding ability of CyD–crown ether
crown ethers and CyD derivatives in order to enhance their original
conjugates through cooperative multiple recognition. The inclusion
ionic/molecular binding affinities and selectivities.1 Recently, many
complexation behavior of hosts 1–3 with some structure-related
approaches to appropriately introduce another recognition site, such
fluorescent dyes (Chart 2), i.e. ammonium 8-anilino-1-naphthalene-
as a CyD, calixarene or crown ether, to the parent CyD rim have
sulfonate (ANS), sodium 6-toluidino-2-naphthalenesulfonate (TNS),
been widely reported.2–8 For example, it was reported that crown
ether capped -CyDs can mimic the receptor sites of enzymes,5c and
thus successfully be used as artificial enzyme-mimetic systems to
accelerate the hydrolysis of p-nitrophenyl ester in the presence of
transition metal cations9 or as stationary-phase selector for chroma-
tography showing excellent enantioselectivity.10 Moreover, Suzuki
et al. reported the strong binding of tryptophan by crown ether-teth-
ered CyDs owing to the superiority of the CyD secondary-hydroxyl
side modification.7b In addition, Lincoln and coworkers reported
the inclusion complexation of Brilliant Yellow tetraanion with
diazacoronand linked -CyD dimer and their sodium analogues.11
These studies significantly advanced our understanding of the factors
governing host–guest inclusion complexation from the viewpoints of
multiple recognition and induced-fit mechanism between CyD-based
synthetic receptors and model substrates. Recently, we reported a
preliminary investigation into the molecular recognition behavior
of benzo-15-crown-5 tethered -CyDs, which were found able to
remarkably enhance the original binding ability of parent -CyD to-
wardscyclohexanecarboxylates12 andfluorescentdyes13 bythecoop-
erative binding of one guest molecule by two closely located binding
sites (crown ether and CyD). In the present work, we select three
novel benzoaza-15-crown-5 modified -CyDs, i.e. N-(benzoaza-
15-crown-5)-acylaminomethylene tethered 6-diethylenetriamino-6-
deoxy--CyD (1), N-(benzoaza-15-crown-5)-acylaminomethylene
tethered 6-triethylenetetraamino-6-deoxy--CyD (2) and 4′,5′-
dimethylene-benzo-15-crown-5 tethered 6-diethylenetriamino-6-
deoxy--CyD (3) (Chart 1) as ditopic molecular receptors, each
Chart 1 Host structures.
Chart 2 Guest structures.
T h i s j o u r n a l i s
©
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 2 3 5 9 – 2 3 6 4
2 3 5 9

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Scheme 1 Synthesis route.
acridine red (AR) and rhodamine B (RhB) is investigated in aqueous
NaH2PO4/Na2HPO4 or KH2PO4/K2HPO4 buffer solution (pH 7.20) at
25 °C. It is well documented that benzo-15-crown-5 can coordinate
with the Na+ or K+ cation by 1:1 or 2:1 stoichiometry respectively.14
Therefore, we hypothesize that, in the present case, the potassium
cation will mediate the dimerization of CyD–crown ether conjugates
1–3 through 2:1 sandwich complexation of crown ether units with
K+, and thus affect the binding ability and selectivity of CyD–crown
ether conjugates towards guest molecules. It is our special interest to
examine the molecular recognition mechanism concerning the un-
common CyD–crown ether self-assemblies mediated by alkali metal
ions, which will serve our further understanding of this important,
but less investigated, area in the field of supramolecular chemistry.
Results and discussion
As shown in Scheme 1, the cyclodextrin–crown ether conjugates
1
and 2 were synthesized in relatively low yields from
oligo(ethylenediamine) modified -CyDs.
Fig. 1 Circular dichroism spectra of 1–3 (1.0 × 10−4 mol dm−3) in
NaH2PO4/Na2HPO4 buffer solutions (pH 7.20).
Circular dichroism spectra
indicate that the coordination stoichiometry is 1:1 for CyD–crown
ether/Na+ complexes and 2:1 for CyD–crown ether/K+ complexes,
respectively. Fig. 2 shows a representative conductivity titration
curve for the 2:1 coordination of host 1 with KCl. Through
an approximative calculation based on the relatively high
concentration of Na+ or K+ ion ([Na+] = [K+] = 0.344 M) in the
phosphate buffer solution and the low host concentration employed
in all of the spectral experiments ([host] = 0–230 M) as well as the
reported association constant between benzo-15-crown-5 and Na+
or K+ in aqueous solution,20 we deduce that most of the benzo-crown
ether units in hosts 1–3 are coordinated with Na+ or K+ ion forming
CyD–crown ether/Na+ (K+) complexes.
Circular dichroism (CD) spectrometry has become a convenient
and widely employed method for the elucidation of the absolute
conformation of chiral organic compounds in the past three
decades.15,16 Moreover, achiral organic compounds can also show
an induced circular dichroism (ICD) signal in the corresponding
transition band in cases where there is a chiral microenvironment.
CyDs, which possess inherent chiral cavities, may provide such a
microenvironment for the included achiral chromophore. Therefore,
if a chromophoric group is closely attached to the CyD rim, the
corresponding ICD signal should be observed due to the interaction
between the appended chromophore and the chiral CyD cavity. This
phenomenon may be consequently used to elucidate the location
and orientation of the appended moiety. In this context, in order to
obtain information about the original conformation of CyD–crown
ether conjugates, we measured the CD spectra of hosts 1–3 in dilute
buffer solution. The results show that hosts 1–3 display fairly weak
ICD signals ( ≤ 0.5 dm3 mol−1cm−1) for the transitions of aromatic
chromophores in either NaH2PO4/Na2HPO4 or KH2PO4/K2HPO4
buffer solution (Fig. 1). According to the empirical rules that inter-
pret the ICD observed for a chromophore inside or outside of the
CyD cavity proposed by Kajtar,17 Harata,18 and Kodaka19 et al., we
can deduce that the aromatic rings in 1–3 are located distantly from
the CyD cavity. This conformation will provide a free CyD cavity for
the penetration of the guest molecule upon inclusion complexation.
Binding mode
The complexes of CyD–crown ether conjugates 1–3 with Na+ or
K+ cation were prepared in situ in aqueous solution. Conductivity
measurements of CyD–crown ether/NaCl (or KCl) systems
Fig. 2 Conductivity of KCl (5 × 10−4 M) in the aqueous solution of
host 1 at 25 °C.
2 3 6 0
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 2 3 5 9 – 2 3 6 4

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Furthermore, Job’s experiments by fluorescence spectrometric
methods were also performed to explore the stoichiometry for
the inclusion complexation of metal-ligated CyD–crown ether
conjugates with representative guests. Fig. 3 illustrates the Job’s
plots for the 1/AR system in NaH2PO4/Na2HPO4 or KH2PO4/
K2HPO4 buffer solution. In the measurement concentration
range, the plot for the 1/AR system in NaH2PO4/Na2HPO4 buffer
(Fig. 3a) shows a maximum at a molar fraction of 0.5, indicating
1:1 inclusion complexation between CyD–crown ether host and
guest molecule. On the other hand, the plot for the 1/AR system
in KH2PO4/K2HPO4 buffer (Fig. 3b) displays a maximum at 0.67,
which corresponds to 2:1 1/AR stoichiometry. This result indicates
that two CyD–crown ether components actively participate in
the binding of one guest molecule. Similar results are obtained
in the case of the inclusion complexation of other metal-ligated
CyD–crown ether conjugates with guest molecules. Therefore,
we can deduce that the CyD–crown ether conjugates 1–3 may
adopt different binding modes in NaH2PO4/Na2HPO4 and KH2PO4/
K2HPO4 buffer solution. In a NaH2PO4/Na2HPO4 buffer solution,
the CyD–crown ether conjugate adopts a conventional 1:1 bind-
ing mode upon inclusion complexation with the guest molecule,
where the Na+ ligated crown ether unit acts as a positively charged
cap near the narrow rim of CyD cavity and provides additional
binding interactions towards the accommodated guest through the
electrostatic attraction or repulsion between the metal-ligated crown
ether cap and charged guest molecule (Fig. 4a). However, these
CyD–crown ether conjugates prefer a sandwich binding mode upon
complexation with the guest molecule in a KH2PO4/K2HPO4 buffer
(Fig. 4b). In this mode, the guest molecule is cooperatively bound
by two CyD cavities, and K+ acts as not only a recognition site for
the charged guest but also a metal bridge to link the two adjacent
CyD units forming the self-assembled dimer.
Fig. 4 Binding mode of guest molecule with CyD–crown ether
conjugate in (a) NaH2PO4/Na2HPO4 and (b) KH2PO4/K2HPO4 buffers.
between TNS protons and the interior protons (H-3, H-5) of the CyD
cavity. Through the ascription of these correlations, we can find that
the cross-peaks A correspond to the correlations between the methyl
protons of TNS and the interior protons of CyD, and the cross-peaks
B correspond to the correlations between the protons in the phenyl
moiety (Ha, Hb) of TNS and the interior protons of CyD, while cross-
peaks C correspond to the correlations between the naphthalene pro-
tons (Hg, Hh) of TNS and the interior protons of CyD. Moreover, it
can be observed from the cross-peaksA, B and C that the correspond-
ing TNS protons (Ha, Hb, Hg, Hh) all show stronger correlations
with the H-5 protons of CyD than with the H-3 protons. Since the
H-3 protons are located near the wide side of the CyD cavity, while
the H-5 protons are near the narrow side, we can deduce that the
toluene and naphthalene units of TNS are respectively included in
two CyD cavities from the narrow side as illustrated in Fig. 4. One
possible explanation for these phenomena is that the CyD–crown
ether conjugate forms a dimeric self-assembly through the mediation
of a coordinated potassium center, which subsequently adopts a co-
operative binding mode upon inclusion complexation with TNS. On
the other hand, Fig. 5b merely exhibits one set of cross-peaks (peaks
D) assigned to the correlations between the Hg, Hh protons of TNS
and the interior protons of CyD, while the correlations with the H-3
protons are stronger than those with the H-5 protons. This means that
only the naphthalene unit of TNS penetrates into the CyD cavity from
the wide side but the toluene unit locates outside, which is consistent
with the hypothesized structure in Fig. 4. On the other hand, a kinetic
investigation by the time-dependent UV spectra of guest dyes in the
presence of host 1 (or 2) using a reported method21 indicates that the
rate of dyes entering the CyD cavities are much faster than those of
dyes leaving the CyD cavities. This means that the resulting com-
plexes of hosts 1–2 with guest dyes are stable in aqueous solution.
The different binding modes of Na+ or K+-coordinated
CyD–crown ether conjugates are further validated by 2D ROESY
experiments. Fig. 5 shows 2D ROESYspectroscopy for the inclusion
complexation of host 1 with TNS in both NaH2PO4/Na2HPO4 and
KH2PO4/K2HPO4 buffers. Fig. 5a shows the clear correlations
Binding ability and molecular selectivity
After validating the host–guest binding mode, we performed fluore-
scencetitrationexperimentstoquantitativelyinvestigatethemolecular
binding ability and selectivity of hosts 1–3 with guest molecules.
Fig. 6 illustrates the typical fluorescence changes ofAR upon gradual
addition of host 1 in an NaH2PO4/Na2HPO4 buffer solution.As can be
seen from Fig. 6, with the addition of host 1, the fluorescence inten-
sity ofAR gradually increases, accompanied by slight hypsochromic
shifts (3 nm, 559→556 nm from trace a to trace m) of the emission
peaks, which may be ascribed to the increased microenvironmental
hydrophobicity around the accommodated AR upon inclusion
complexation. The stability constant (Ks) of the inclusion complex
formed can be calculated from the gradual changes in fluorescence
intensity of guest (If) upon stepwise addition of host using a curve
fitting method.22 In the repeated measurements, the Ks values are
reproducible within an error of ±5%. The complex stability constants
(Ks) obtained by curve fitting are listed in Table 1, along with the free
energy change (−G°) of complex formation.
Fig. 3 Job’s plots for 1/AR system in (a) NaH2PO4/Na2HPO4 and
(b) KH2PO4/K2HPO4 buffers. ([1] + [AR] = 1.0 × 10−5 mol dm−3).
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 2 3 5 9 – 2 3 6 4
2 3 6 1

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Table 1 Complex stability constants (Ks) and Gibbs free energy changes
(−G°) for the inclusion complexation of organic dyes with CyD–crown
ether conjugates 1–3 in different buffer solutions (pH 7.20)
Host
Guest
Ks
102
logKs
−G°(kJ mol−1)
Ref.
a
a
a
a
b
b
b
b
b
b
b
b
b
b
b
b
c
c
c
c
c
c
c
c
c
c
c
c
-CyD
ANS
TNS
AR
RhB
ANS
TNS
AR
RhB
ANS
TNS
AR
RhB
ANS
TNS
AR
RhB
ANS
TNS
AR
RhB
ANS
TNS
AR
RhB
ANS
TNS
AR
2.01
3.57
3.42
3.71
3.51
4.67
3.27
3.84
3.23
3.86
3.12
3.98
3.22
3.82
3.50
3.94
3.53
4.03
3.20
4.26
3.01
4.34
3.83
4.11
3.93
4.42
3.44
4.63
11.5
20.4
19.5
21.2
3700
2630
5100
3260
46500
1880
6880
1720
7200
1330
9460
1680
6560
3200
8680
3430
10620
1570
18100
1015
22100
6740
13000
8500
26600
2730
42900
1–Na+
2–Na+
3–Na+
1–K+
20.05
26.64
18.69
21.90
18.47
22.02
17.83
22.69
18.41
21.79
20.01
22.48
20.18
22.98
18.24
24.30
17.16
24.80
21.85
23.48
22.43
25.26
19.61
26.44
2–K+
3–K+
RhB
a Reference 23. b In NaH2PO4/Na2HPO4 buffer solution. c In KH2PO4/
K2HPO4 buffer solution.
Fig. 6 Fluorescence spectral changes of AR (1.2 M) and nonlinear
least-squares analysis (inset) of the differential intensity (If) used to
calculate the complex stability constant (Ks) upon addition of 1 (0–90 M
from a to m) in NaH2PO4/Na2HPO4 buffer solution (pH 7.20).
Fig. 5 2D ROESY spectra of a mixture of host 1 with TNS in (a) KH2-
PO4/K2HPO4 and (b) NaH2PO4/Na2HPO4 buffers.
1–Na+: AR < ANS < RhB < TNS
2–Na+: AR < ANS < TNS < RhB
By comparing the enhancement effects for each guest, we can
see that the metal-ligated CyD–crown ether conjugates which gives
the highest enhancement for each guest dye (with the observed en-
hancement factors shown in the parentheses) are 3–K+ (× 83) for
ANS, 1–Na+ (× 12.6) for TNS, 3–K+ (× 8.4) for RhB, and 2–K+
(× 2.6) for AR, respectively. From a comparison of these enhance-
ment factors, we may conclude that the negatively charged guest
ANS and TNS are able to more fully exploit the cooperative bind-
ing of CyD–crown ether conjugates. This should be reasonable,
since the certain electrostatic attraction between the metal-ligated
crown ether cap and anionic guest provides a positive contribu-
tion to host–guest inclusion complexation and thus leads to high
binding affinities. On the other hand, as can be readily recognized
from Table 1, the Ks values for the inclusion complexation of
CyD–crown ether hosts with guest molecules increases in the fol-
lowing order:
3–Na+: ANS < AR < TNS < RhB
1–K+: AR < ANS < TNS < RhB
2–K+: ANS < AR < RhB < TNS
3–K+: AR < ANS < TNS < RhB
We can see that the relatively large guest molecules, such as
TNS and RhB, are better bound by CyD–crown ether conjugates
than the small guests. This may be attributed to the size-fit relation-
ship between these guests and the CyD–crown ether conjugates
possessing flexible long linkers, which consequently gives strong
van der Waals and hydrophobic interactions between host and
guest. Another interesting observation is that the T-shaped RhB
is better bound by K+-ligated CyD–crown ether conjugates than
by Na+-ligated ones. The stronger binding ability of CyD–crown
ether conjugates in KH2PO4/K2HPO4 buffer solution may arise
from the K+-mediated dimeric self-assembly of CyD–crown ether
conjugates. In our previous work, we have demonstrated that the
2 3 6 2
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 2 3 5 9 – 2 3 6 4

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linker group of bis(CyD)s can supply a well-organized pseudo
cavity which in turn provides additional binding interaction with
the benzoate branch of RhB by forming a sandwich inclusion
complex, and thus showing high binding affinity toward RhB.24
In the present case, K+-mediated CyD–crown ether conjugates can
also be regarded as a type of “bis(CyD)s” (Fig. 4b). Upon inclu-
sion complexation with guest molecules, these “bis(CyD)s” can
afford suitable pseudo cavities through the adjustment and orienta-
tion of the flexible linker group, in which the branch fragment of
T-shaped guests, such as RhB, can be appropriately accommodated.
This consequently leads to the strong binding ability of K+-ligated
CyD–crown ether conjugates for RhB and their high molecular
selectivity for the RhB/AR pair. Typically, native -CyD only gives
moderate binding ability for RhB (Ks = 5100 M−1) and relatively
low molecular selectivity (KsRhB/KsAR = 1.9) for the RhB/AR pair.
However, benefiting from the cooperative binding of two CyD
cavities, the 3–K+ assembly system displays significantly enhanced
binding ability for RhB and molecular selectivity for the RhB/AR
pair; that is 8.4 and 8.2 times higher than the corresponding values
of native -CyD, respectively.
In summary, we succeeded in preparing a series of CyD–
crown ether conjugates as ditopic molecular receptors. Further
investigations demonstrated that the high binding ability and
molecular selectivity of CyD–crown ether conjugates come not only
from the electrostatic interactions between the metal-ligated crown
ether cap and the charged guest molecules, but also the K+-mediated
self-assembly of CyD–crown ether conjugates. Significantly, this
concept opens an efficient channel to the design of new multi-site
hetero receptors involving crown ethers and/or CyDs. Based on the
uncommon self-assembly behavior of CyD–crown ether conjugates
mediated by alkali metal ions, further studies are currently in pro-
gress concerning the cooperative, multisite/multimode recognition
of sophisticated systems.
Synthesis of N-(benzoaza-15-crown-5)-acylaminomethylene
tethered 6-diethylenetriamino-6-deoxy--CyD (1)
As shown in Scheme 1, mono[6-diethylenetriamino-6-deoxy]--
CyD (1.8 g) and N-(chloracetyl)benzoaza-15-crown-5 (0.688 g)
were dissolved in DMF (30 mL), and triethylamine (15 ml) was
slowly added over one hour. The reaction mixture was stirred
at room temperature overnight and then heated to 75 °C under
nitrogen atmosphere for 12 hours. The solvent was removed
under reduced pressure on a rotary evaporator. The residue was
dissolved in a small amount of hot water, and subsequently the
resultant solution was poured into acetone with vigorous stirring
to produce a yellow precipitate. After collection by filtration,
the crude product was purified by column chromatography on
Sephadex G-25 with distilled, deionized water as eluent to give a
pure sample (0.50 g, yield 18%). Mp 240 °C (dec.); 1H NMR (D2O,
300 MHz, TMS, ppm):  2.0–3.0 (m, 11H), 3.0–4.0 (m, 58 H), 4.1
(m, 2H), 4.9 (m, 7 H), 6.9 (m, 4 H). IR (KBr):  3325, 2927, 1650,
1502, 1455, 1361, 1257, 1155, 1079, 1032, 944, 847, 755, 705,
579 cm−1. Anal. Calcd. for C62H102O39N4·12H2O: C, 42.71; H, 7.28;
N, 3.21. Found: C, 42.75; H, 7.14; N, 3.31%. UV/vis (H2O) max/nm
(/dm3 mol−1 cm−1): 273 (2620).
Synthesis of N-(benzoaza-15-crown-5)-acylaminomethylene
tethered 6-triethylenetetraamino-6-deoxy--CyD (2)
Mono[6-triethylenetetraamino-6-deoxy]--CyD (2.0 g) and N-
(chloracetyl) benzoaza-15-crown-5 (0.688 g) were dissolved in
DMF (30 mL), and triethylamine (15 mL) was slowly added over
one hour. The reaction mixture was stirred at room temperature
under nitrogen atmosphere for one day and then at 80 °C for two
days. The solvent was removed under reduced pressure on a rotary
evaporator. The residue was dissolved in a small amount of water
(15 mL), and subsequently the resultant solution was poured into 2:1
(v/v) acetone–ethanol (500 mL) with vigorous stirring to produce a
yellow precipitate. The above procedure was repeated twice. After
collection by filtration, the crude product was purified by column
chromatographyonSephadexG-25withthedistilled,deionizedwater
as eluent to give a pure sample (0.24 g, yield 10%). Mp 226 °C (dec.);
1H NMR (D2O, 300 MHz, TMS, ppm):  2.0–2.8 (m, 16H), 3.2–4.0
(m, 58H), 4.2 (m, 2H), 4.9 (m, 7H), 6.8 (m, 4H). IR (KBr):  3327,
2928, 1652, 1502, 1455, 1362, 1257, 1203, 1154, 1079, 1032, 941,
847, 754, 705, 580, 407 cm−1.Anal. Calcd for C64H107O39N5·8H2O: C,
44.83; H, 7.23; N, 4.08. Found: C, 44.70; H, 7.17; N, 4.12%. UV/vis
(H2O) max/nm (/dm3 mol−1 cm−1): 273 (2150).
Experimental
Materials
All chemicals were reagent grade and used without further
purification unless noted otherwise. N,N-Dimethylformamide
(DMF)wasdriedovercalciumhydridefortwodaysandthendistilled
under reduced pressure prior to use. Mono[6-diethylenetriamino-6-
deoxy]--CyD and mono[6-triethylenetetraamino-6-deoxy]--CyD
were prepared according to the literature procedures,25 and N-
(chloracetyl)benzoaza-15-crown-5 was synthesized by the reaction
of 11,12-benzo-1,7,10,13-tetraoxa-4-aza-cyclopentadec-11-ene
(benzoaza-15-crown-5) with chloracetyl chloride in anhydrous
acetonitrile.26 4′,5′-Dimethylene-benzo-15-crown-5 tethered 6-
diethylenetriamino-6-deoxy--CyD (3) was synthesized according
to our previous report.12
Acknowledgements
This work was supported by NNSFC (90306009 and 20272028), and
Special Fund for Doctoral Program from the Ministry of Education
of China (No. 20010055001), which are gratefully acknowledged.
Apparatus and measurements
References
Elemental analyses were performed on a Perkin-Elmer-2400C
instrument. NMR spectra were recorded on aVarian MercuryVX300
instrument. Circular dichroism (CD) and UV-vis spectra were re-
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J-715S spectropolarimeter and a Shimadzu UV-2401PC spectropho-
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solution (pH 7.20, 0.2 M) was similarly prepared by dissolving di-
potassium hydrogen phosphate trihydrate (32.86 g) and potassium
dihydrogen phosphate (7.6 g) in 1000 mL of deionized water.
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