Diazacoronand linked beta-cyclodextrin dimer complexes of Brilliant Yellow tetraanion and their sodium(I) analogues.

Article abstract of DOI:10.1039/b209759c

Complexation of the Brilliant Yellow tetraanion, 3(4-), by two new diazacoronand linked beta-cyclodextrin (beta CD) dimers 4,13-bis(2-(6A-deoxy-beta-cyclodextrin-6A-yl)aminooctylamidomethyl- and 4,13-bis(8-(6A-deoxy-beta-cyclodextrin-6A-yl)aminooctylamidomethyl)-4,13- diaza-1,7,10-trioxacyclopentadecane, 1 and 2, respectively, has been studied in aqueous solution. UV-visible spectrophotometric studies at 298.2 K, pH 10.0 and I = 0.10 mol dm-3 (NEt4ClO4) yielded complexation constants for the complexes 1 x 3(4-) and 2 x 3(4-), K1 = (1.08 +/- 0.01) x 10(5) and (6.21 +/- 0.08) x 10(3) dm3 mol-1, respectively. Similar studies at 298.2 K, pH 10.0 and I = 0.10 mol dm-3 (NaClO4) yielded K3 = (4.63 +/- 0.09) x 10(5) and (3.38 +/- 0.05) x 10(4) dm3 mol-1 for the complexation of 3(4-) by Na+ x 1 and Na+ x 2 to give Na+ x 1 x 3(4-) and Na+ x 2 x 3(4-), respectively. Potentiometric studies of the complexation of Na+ by 1 and 2 by the diazacoronand component of the linkers to give Na+ x 1 and Na+ x 2 yielded K2 = (2.00 +/- 0.05) x 10(3) and (1.8 +/- 0.05) x 10(3) dm3 mol-1, respectively, at 298.2 K and I = 0.10 mol dm-3(NEt4ClO4). For complexation of Na+ by 1 x 3(4-) and 2 x 3(4-) to give Na+ x 1 x 3(4-) and Na+ x 2 x 3(4-) K2K3/K1 = K4 = 8.6 x 10(2) and 9.8 x 10(3) dm3 mol-1, respectively. The pKaS of 1H4(4+) are 7.63 +/- 0.01, 6.84 +/- 0.02, 5.51 +/- 0.04 and 4.98 +/- 0.03, and those of 2H4(4+) are 8.67 +/- 0.02, 8.11 +/- 0.02, 6.06 +/- 0.02 and 5.14 +/- 0.05. The larger magnitude of K1 for 1 by comparison with K1 for 2 is attributed to the octamethylene linkers of 2 competing with 3(4-) for occupancy of the annuli of the beta CD entities while the competitive ability of the dimethylene linkers of 1 is less. A similar argument applies to the relative magnitudes of K3 for Na+ x 1 and Na+ x 2. Increased electrostatic attraction probably accounts for K3 > K1 for Na+ x 1 x 3(4-) and 1 x 3(4-) and for Na+ x 2 x 3(4-) and 2 x 3(4-). The lesser magnitudes of K2 and K4 for Na+ x 1 and Na+ x 1 x 3(4-) compared with those for Na+ x 2 and Na+ x 2 x 3(4-) are attributed to the octamethylene linkers of 2 producing a more hydrophobic environment for the diazacoronand than that produced by the dimethylene linkers of 1. 1H NMR spectroscopic studies and the syntheses of 1 and 2 are described.

Full text of DOI:10.1039/b209759c

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Diazacoronand linked ꢀ-cyclodextrin† dimer complexes of Brilliant
Yellow tetraanion and their sodium(I) analogues‡
Lee C. West,a Oska Wyness,a Bruce L. May,a Philip Clements,a Stephen F. Lincoln*a and
Christopher J. Eastonb
a Department of Chemistry, The University of Adelaide, Adelaide SA 5005, Australia
b Research School of Chemistry, The Australian National University, Canberra, ACT 0200,
Australia
Received 4th October 2002, Accepted 9th January 2003
First published as an Advance Article on the web 12th February 2003
Complexation of the Brilliant Yellow tetraanion, 34Ϫ, by two new diazacoronand linked β-cyclodextrin (βCD) dimers
4,13-bis(2-(6A-deoxy-β-cyclodextrin-6A-yl)aminoethylamidomethyl- and 4,13-bis(8-(6A-deoxy-β-cyclodextrin-6A-
yl)aminooctylamidomethyl)-4,13-diaza-1,7,10-trioxacyclopentadecane, 1 and 2, respectively, has been studied in
aqueous solution. UV-visible spectrophotometric studies at 298.2 K, pH 10.0 and I = 0.10 mol dmϪ3 (NEt4ClO4)
yielded complexation constants for the complexes 1ؒ34Ϫ and 2ؒ34Ϫ, K1 = (1.08 0.01) × 105 and (6.21 0.08) × 103
dm3 molϪ1, respectively. Similar studies at 298.2 K, pH 10.0 and I = 0.10 mol dmϪ3 (NaClO4) yielded K3 = (4.63
0.09) × 105 and (3.38 0.05) × 104 dm3 molϪ1 for the complexation of 34Ϫ by Naϩؒ1 and Naϩؒ2 to give Naϩؒ1ؒ34Ϫ
and Naϩؒ2ؒ34Ϫ, respectively. Potentiometric studies of the complexation of Naϩ by 1 and 2 by the diazacoronand
component of the linkers to give Naϩؒ1 and Naϩؒ2 yielded K2 = (2.00 0.05) × 102 and (1.8 0.05) × 103 dm3 molϪ1
,
respectively, at 298.2 K and I = 0.10 mol dmϪ3 (NEt4ClO4). For complexation of Naϩ by 1ؒ34Ϫ and 2ؒ34Ϫ to give Naϩؒ
1ؒ34Ϫ and Naϩؒ2ؒ34Ϫ K2K3/K1 = K4 = 8.6 × 102 and 9.8 × 103 dm3 molϪ1, respectively. The pKas of 1H44ϩ are 7.63
0.01, 6.84 0.02, 5.51 0.04 and 4.98 0.03, and those of 2H44ϩ are 8.67 0.02, 8.11 0.02, 6.06 0.02 and 5.14
0.05. The larger magnitude of K1 for 1 by comparison with K1 for 2 is attributed to the octamethylene linkers of 2
competing with 34Ϫ for occupancy of the annuli of the βCD entities while the competitive ability of the dimethylene
linkers of 1 is less. A similar argument applies to the relative magnitudes of K3 for Naϩؒ1 and Naϩؒ2. Increased
electrostatic attraction probably accounts for K3 > K1 for Naϩؒ1ؒ34Ϫ and 1ؒ34Ϫ and for Naϩؒ2ؒ34Ϫ and 2ؒ34Ϫ. The lesser
magnitudes of K2 and K4 for Naϩؒ1 and Naϩؒ1ؒ34Ϫ compared with those for Naϩؒ2 and Naϩؒ2ؒ34Ϫ are attributed to
the octamethylene linkers of 2 producing a more hydrophobic environment for the diazacoronand than that produced
by the dimethylene linkers of 1. 1H NMR spectroscopic studies and the syntheses of 1 and 2 are described.
and as catalysts.7 This study has a different emphasis in seeking
to characterise all of the equilibria leading to the formation
of the linked CD dimer complexes and the interactions within
them.
Introduction
β-Cyclodextrin (βCD, Fig. 1) is the basis of a wide range of
hosts constructed to complex a plethora of guests.1,2 Apart
from their intrinsic interest, such complexes have the potential
to be components of molecular devices.3,4 We are interested in
Results and discussion
building a variety of such complexes to gain a better under-
standing of the interactions controlling their stability. To this
end, we have synthesised two new diazacoronand linked β-
cyclodextrindimers,4,13-bis(2-(6A-deoxy-β-cyclodextrin-6A-yl)-
aminoethylamidomethyl)- and 4,13-bis(8-(6A-deoxy-β-cyclo-
dextrin-6A-yl)aminooctylamidomethyl)-4,13-diaza-1,7,10-tri-
oxacyclodecapentane, 1 and 2, where the linker contains a metal
ion binding diazacoronand (Fig. 1). Linked cyclodextrin dimers
and their metal complexes are capable of binding suitably
dimensioned guests in water and it is known that the length of
the linker between the two βCD entities can influence the
stabilities of the complexes formed.5 Accordingly, we have
chosen substantially different linker lengths in 1 and 2 to assess
their effect on complexation. The Brilliant Yellow tetraanion,
34Ϫ, was chosen as the guest because its charge minimises the
possibility of aggregation that characterises some extended
aromatic systems,6 it is likely to be electrostatically attracted by
a metal ion bound by the diazacoronand unit and because
its extended aromatic structure maximises the likelihood of
complexation. In other studies CD dimers joined by metal
ion binding linkers have been used as guest-selective hosts
Spectrophotometric complexation studies of Brilliant Yellow
tetraanion
The complexation of 34Ϫ by βCD, 1 and 2 was studied spectro-
photometrically at [34Ϫ total = 1.0 × 10Ϫ5 mol dmϪ3 and [βCD, 1
]
or 2]total varied in the range 1.0 × 10Ϫ6 Ϫ1.0 × 10Ϫ2 mol dmϪ3 in
0.05 mol dmϪ3 borate buffer prepared from boric acid and
either NEt4OH or NaOH at I = 0.10 mol dmϪ3 adjusted with
NEt4ClO4 and NaClO4, respectively. In the latter case all of 1
and 2 are completely complexed by Naϩ in Naϩؒ1 and Naϩؒ2 as
discussed below. The UV-visible absorption maximum of 34Ϫ
showed a small shift to shorter wavelengths in 1ؒ34Ϫ (523 nm)
Naϩؒ1ؒ34Ϫ (498 nm) and Naϩؒ2ؒ34Ϫ (507 nm) and no shift in 2ؒ
34Ϫ (462 nm), where the wavelengths in brackets are isosbestic
points consistent with 34Ϫ existing in the free state and in one
dominant complex (Figs. 2 and 3). Accordingly, the spectral
variations of 34Ϫ with changing concentrations of 1, 2, Naϩؒ1
and Naϩؒ2 were analysed by fitting the algorithm for the
formation of a 1 : 1 complex to the experimental data at 1 nm
intervals simultaneously over wavelength ranges where sig-
nificant changes in absorbance occurred as described in the
Experimental section and the derived complexation constants
appear in Table 1 together with those for Naϩؒ1 and Naϩؒ2
derived potentiometrically as described below. The algorithms
for 1 : 1 and 2 : 1, 1 : 2, and 2 : 1 complexation were also fitted to
† β-Cyclodextrin = cyclomaltoheptaose
‡ Electronic supplementary information (ESI) available: Molar
absorbance and 2D NMR ROESY spectra of 1 and 2, and their
complexes with 34Ϫ. See http://www.rsc.org/suppdata/ob/b2/b209759c/.
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 3
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 8 8 7 – 8 9 4
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Table 1 Complexation equilibria and constants in aqueous solution at pH 10.0 (0.05 mol dmϪ3 borate buffer), I = 0.10 mol dmϪ3 (NEt4ClO4 or
NaClO4) and 298.2 K.
Equilibrium
Complexation constantK/dm3molϪ1 a
(1.08 0.01) × 105 b
(6.21 0.08) × 103 b
(2.00 0.05) × 102 b
(1.80 0.05) × 103 b
(4.63 0.09) × 105 c
(3.38 0.05) × 104 c
8.6 × 102 d
9.8 × 103 d
(2.2 0.05) × 103 c
a Errors represent one standard deviation. b NEt4ClO4 supporting electrolyte. c NaClO4 supporting electrolyte. d K4 = K2K3/K1.
Fig. 2 Variation of the UV-visible spectrum of 1.00 × 10Ϫ5 dm3 molϪ1
34Ϫ at 298.2 K in 0.05 mol dmϪ3 aqueous B(OH)3/NEt4OH buffer at
pH 10.0 and I = 0.10 mol dmϪ3 (NEt4ClO4) in the presence of 1, A,
(523 nm) and 2, B, (462 nm) where in each case the concentration
was varied in the range 1.00 × 10Ϫ6 to 1.00 × 10Ϫ3 mol dmϪ3 and the
quantities in brackets refer to isosbestic points. The absorbance changes
with increasing concentration in the direction shown by the arrows.
Fig. 1 Structures of βCD and 1 and 2.
the spectral variations but in each case the best fit was obtained
with the 1 : 1 model as assessed from the magnitude of the least
squares error of the fit. Two typical absorbance changes at
single wavelengths are shown for the formation of Naϩؒ1ؒ34Ϫ
and Naϩؒ2ؒ34Ϫ in Fig. 4 and 1ؒ34Ϫ and 2ؒ34Ϫ in Fig. S1. The
equilibria between the complexes formed by 1 and 2 are shown
schematically in Fig. 5. The spectral changes shown by 34Ϫ on
complexation are modest probably because the sulfonate
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 8 8 7 – 8 9 4
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Fig. 4 A and B; variations of the molar absorbance of 1.00 × 10Ϫ5 dm3
Fig. 3 Variation of the UV-visible spectrum of 1.00 × 10Ϫ5 dm3 molϪ1
34Ϫ at 298.2 K in 0.05 mol dmϪ3aqueous B(OH)3/NaOH buffer at
pH 10.0 and I = 0.10 mol dmϪ3 (NaClO4) in the presence of Naϩؒ1, A,
(498 nm) and Naϩؒ2, B, (507 nm) where in each case the concentration
was varied in the range 1.00 × 10Ϫ6 to 1.00 × 10Ϫ3 mol dmϪ3 and the
quantities in brackets refer to isosbestic points. The absorbance changes
with increasing concentration in the direction shown by the arrows.
molϪ1 34Ϫ at 530 nm at 298.2 K in 0.05 mol dmϪ3 aqueous B(OH)3/
NaOH buffer at pH 10.0 and I = 0.10 mol dmϪ3 (NaClO4) with
increasing concentrations of [Naϩؒ1]total and [Naϩؒ2]total, respectively.
The curves represent the best fit of the algorithm for the formation
of Naϩؒ1ؒ34Ϫ and Naϩؒ2ؒ34Ϫ, respectively, to molar absorbance data at
1 nm intervals over the range 380–550 nm.
Potentiometric pKa and metal ion complexation studies
The pKa values and metal ion complexation constants were
groups which are strongly hydrated in the free dye remain so in
the complexed state such that the overall environmental change
experienced by 34Ϫ is also modest.
determined by potentiometric methods as described in the
4ϩ
Experimental section. For 1H4 at 298.2 K and I = 0.10 mol
dmϪ3 (NEt4ClO4) the pKa values = 7.63 0.01, 6.84 0.02,
5.51 0.04 and 4.98 0.03 and those of 2H44ϩ are 8.67 0.02,
8.11 0.02, 6.06 0.02 and 5.14 0.05. The octamethylene
linker stabilises the protonated states of 2 by comparison with
those of 1 possibly because they produce a more hydrophobic
environment at the amine nitrogens by comparison with that
induced by the dimethylene linkers of 1.
The greater stability of 1ؒ34Ϫ (K1 = 1.08 × 105 dm3 molϪ1) by
comparison with that of 2ؒ34Ϫ (K1 = 6.21 × 103 dm3 molϪ1) is
attributed to the self-complexation of the octamethylene linkers
of 2 competing with 34Ϫ for occupancy of the βCD annuli for
which 1H NMR evidence is presented below. As a consequence,
2 is only three times as effective in complexing 34Ϫ as is βCD in
βCDؒ34Ϫ (K1 = 2.20 × 103 dm3 molϪ1).6 This self-complexation
also affects the relative stabilities of Naϩؒ1ؒ34Ϫ and Naϩؒ2ؒ34Ϫ
(K3 = 4.63 × 105 and 3.38 × 104 dm3 molϪ1, respectively)
although the electrostatic attraction between the complexed
Naϩ of Naϩؒ1 and Naϩؒ2 and 34Ϫ does strengthen the com-
plexation of 34Ϫ in Naϩؒ1ؒ34Ϫ and Naϩؒ2ؒ34Ϫ several fold by
comparison with that in 1ؒ34Ϫ and 2ؒ34Ϫ. This is also reflected
in the alternative path to Naϩؒ1ؒ34Ϫ and Naϩؒ2ؒ34Ϫ (for which
K4 = 8.6 × 102 and 9.9 × 103 dm3 molϪ1, respectively) in which
Naϩ is bound more strongly than in Naϩؒ1 and Naϩؒ2 (K2 =
2.0 × 102 and 1.8 × 103 dm3 molϪ1, respectively). This is attri-
buted to the electrostatic attraction between complexed 34Ϫ
in 1ؒ34Ϫ and 2ؒ34Ϫ and Naϩ in the formation of Naϩؒ1ؒ34Ϫ and
The complexation constants for five metal ions appear in
Table 2, from which it is seen that 1H22ϩ, 1Hϩ, 1, 2H22ϩ, 2Hϩ
and 2 each complex metal ions. Of the alkali metal ions, only
Naϩ formed detectable complexes while each of the alkaline
earth ions formed complexes of stability varying in the general
sequence Mg2ϩ Ӷ Ca2ϩ > Sr2ϩ > Ba2ϩ. These variations reflect
§ In view of this it may be asked whether the derivation of K4 in Table 1
and Fig. 5 from data obtained in different supporting electrolytes is
valid. A measure of the effect of the separate presences of Naϩ and
ϩ
NEt4 as the electrolyte cation is gained for the ratios K3/K1 = 4.3 and
5.4 for 1 and 2, respectively, which reflect the specific effect of Naϩ
complexation and general electrolyte effects. For the 4,13-(6A-deoxy-β-
cyclodextrin-6A-yl)amidomethyl)-4,13-diaza-1,7,10-trioxacyclopenta-
decane analogue of 1 and 2 no Naϩ binding was detected by potentio-
metric methods consistent with K2 ≤ 100 dm3 molϪ1. For this system
K3/K1 = 2.05 which is attributed to either weak Naϩ complexation
alone or in combination with a general electrolyte effect or to a general
electrolyte effect alone. On this basis it appears that K3/K1 = 4.3 and
5.4 for 1 and 2 includes a modest specific effect of Naϩ binding in
the formation of Naϩؒ1ؒ34Ϫ and Naϩؒ2ؒ34Ϫ and that the derived K4 does
incorporate a significant electrostatic interaction between Naϩ bound
Naϩؒ2ؒ34Ϫ
.
The spectrum of 34Ϫ observed in 0.05 mol dmϪ3 borate buffer
prepared from boric acid and NEt4OH at I = 0.10 mol dmϪ3
adjusted with NEt4ClO4 differs from that observed in borate
buffer prepared from boric and NaOH at I = 0.10 mol dmϪ3
adjusted with NaClO4 at pH 10.0 (Fig. 6). The latter spectrum
is shifted to shorter wavelengths (a change also seen on
protonation of 34Ϫ) which probably reflects a stronger ion
association of 34Ϫ with Naϩ than with the much larger Et4Nϩ.§
by the diazacoronand of the linker and complexed 34Ϫ
.
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Fig. 5 Pathways for the complexation of 34Ϫ by 1 and 2.
plexes varying with the effective ionic radii, rM,8 of the metal
ions. This results in five-coordinate (or six-coordinate if it
assumed that six-coordination is retained through binding
a water ligand) Naϩ (rM = 100 pm and 102 pm, respectively)
and Ca2ϩ (rM = 100 pm, six-coordinate radius; no value for five-
coordination is available) forming the most stable complexes
2ϩ
in their groups. The formation of metal complexes by 1H2
2ϩ
and 2H2 and the increase in complex stability as deproto-
nation occurs is consistent with the secondary amines of the
βCD substituents being the protonation sites and electrostatic
2ϩ
repulsion between either 1H22ϩ, 1Hϩ, 2H2 or 2Hϩ and the
metal ion destabilising the complexes. The ten-fold lower
stability of Naϩؒ1 by comparison with that of Naϩؒ2 is attrib-
uted to the more hydrophobic environment in the vicinity of the
diazacoronand of 2 produced by the octamethylene linkers
decreasing the ability of water to compete for complexation of
Naϩ by comparison with the diazacoronand of 1 because of the
less hydrophobic environment that it experiences in the latter
case. (Under the conditions of this study no alkali or alkaline
earth ion complexes were detected for 4,13-diaza-1,7,10-trioxa-
cyclopentadecane, the precursor to 1 and 2, consistent with K2 ≤
100 dm3 molϪ1 and the hydrophobic character of 1 and 2
Fig. 6 UV-visible absorbance spectra of 34Ϫ (1.00 × 10Ϫ5 dm3 molϪ1) at
pH 10.0 in A, 0.05 mol dmϪ3 B(OH)3/NEt4OH buffer at I = 0.10 mol
dmϪ3 adjusted with NEt4ClO4 and B, 0.05 mol dmϪ3 B(OH)3/NaOH
buffer at I = 0.10 mol dmϪ3 adjusted with NaClO4 at pH 10.0.
the combined effects of metal ion hydration energies, metal ion
to diazacoronand bond energies and strain energies in the com-
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 8 8 7 – 8 9 4
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Table 2 Complexation constants (K) for metal complexes of 1 and 2
and their mono- and diprotonated forms at 298.2 K and I = 0.10 mol
dmϪ3 (NEt4ClO4)a
b
Complex and log(K/dm3molϪ1
)
Mmϩ
Mmϩؒ1H2
Mmϩؒ1Hϩ
Mmϩؒ1
2ϩ
c
c
Naϩ
Ca2ϩ
Sr2ϩ
Ba2ϩ
2.30 0.05
5.35 0.03
5.05 0.02
4.47 0.01
3.47 0.07
3.57 0.04
3.04 0.04
4.59 0.02
4.37 0.05
3.81 0.01
2ϩ
Mmϩ
Mmϩؒ2H2
Mmϩؒ2Hϩ
Mmϩؒ2
Naϩ
Mg2ϩ
Ca2ϩ
Sr2ϩ
2.89 0.04
≈2
4.49 0.04
4.06 0.05
4.10 0.04
2.99 0.05
2.53 0.03
4.89 0.04
4.45 0.04
4.54 0.03
3.26 0.05
2.95 0.03
5.15 0.03
5.07 0.04
4.82 0.03
Ba2ϩ
a For the alkali metal ions only Naϩ complexes were detected. No
complexation of Mg2ϩ by 1 or its protonated forms was detected.
b Errors represent one standard deviation. c No complex detected.
enhancing complexation. It is also possible that the two amide
oxygens of 1 and 2 may interact with metal ions bound by the
diazacoronand and increase complex stability. The amide
oxygens of 1,7-bis(methylcarbamoylmethyl)-4,10,13-trioxa-1,7-
diazacyclopentadecane9 and 1,10-bis(O-methylglycylglycyl)-
4,7,13,16-tetraoxa-1,10-diaza-cyclooctadecane10 have been
shown to bind Naϩ by both amide oxygens in addition to
binding by the nitrogen and oxygen donor atoms of the di-
azacoronand ring in methanol and the solid state, respectively.)
The difference in stability is much less for the more stable
alkaline earth M2ϩؒ1 and M2ϩؒ2 complexes possibly because the
divalent alkaline earths are more strongly hydrated. As a result
dehydration energetics may be more significant compared with
hydrophobic effects than is the case for the Naϩ complexes.
However, the alkaline earth complexes of 1Hϩ are less stable
than those of 2Hϩ and those of 1H22ϩ are much less stable than
those of 2H22ϩ. This is consistent with the closer proximity of
the protonated secondary amines of the βCD substituents
Fig. 7 The 2D 1H ROESY NMR (600 MHz) spectrum of a D2O
solution 0.014 mol dmϪ3 in 2 buffered at pD 10.0 by 0.1 mol dmϪ3 ND3/
ND4Cl buffer at 298.2 K. The rectangles enclose cross-peaks arising
from ROE interactions between the H2–H7 protons of the
octamethylene linkers and the βCD H3, H5 and H6 protons.
molϪ1.12) Cross peaks arising from ROE interactions between
the protons of 34Ϫ and the βCD H3, H5 and H6 of Naϩؒ2
are observed in the presence of 0.10 mol dmϪ3 NaClO4 at
pD ≈ 11 consistent with complexation in Naϩؒ2 also (Fig. S2).
On addition of two equivalents of sodium adamantane-1-
carboxylate, these cross peaks are also replaced by those arising
from ROE interactions between the adamantane-1-carboxylate
protons and the βCD H3, H5 and H6. No evidence for self-
complexation in either 1 or Naϩؒ1 was found probably because
the dimethylene linkers are too short.
2ϩ
in 1Hϩ and 1H2 generating a greater electrostatic repulsion
towards alkaline earth ion complexation. At pH 10.0, solutions
of the alkaline earth ions, 34Ϫ and either 1 or 2 formed precipi-
tates which may be salts of 34Ϫ. Thus, Naϩؒ1 and Naϩؒ2 were
the only metal binding species which could be studied in the
1
The H ROESY NMR (600 Mz) spectra of equimolar solu-
tions of either 1 or 2 and 34Ϫ in 0.1 mol dmϪ3 ND3/ND4Cl
buffer at pD 10.0 in D2O are characterised by strong-cross
peaks arising from ROE interactions between the protons of
34Ϫ and the βCD H3, H5 and H6 of 2 consistent with the com-
complexation of 34Ϫ
.
1H NMR spectroscopic studies
plexation of 34Ϫ in the βCD annuli of 1 and 2 in 1ؒ34Ϫ and 2ؒ34Ϫ
,
The 1H ROESY NMR (600 Mz) spectrum of 2 in D2O is shown
in Fig. 7 from which it is seen that cross-peaks arise from ROE
interactions between the H2-H7 protons of the octamethylene
linkers and the H3, H5 and H6 protons inside the βCD annuli
consistent with self-complexation of the octamethylene linkers
in the βCD annuli. (Self-complexation in linked CD dimers has
been reported previously as has the self-complexation of substi-
tuents of monomeric CDs.11) Addition of tetraethylammonium
adamantane-1-carboxylate results in the appearance of new
cross-peaks arising from ROE interactions of its protons and
the βCD H3, H5 and H6 protons consistent with complexation
of adamantane-1-carboxylate by 2. The intensities of these
cross peaks grow and those arising from H2-H7 of the octa-
methylene linkers of 2 diminish as adamantane-1-carboxylate
concentration is increased until a 2 : 1 mole ratio of adaman-
tane-1-carboxylate to 2 is reached and the cross-peaks arising
from the octamethylene linkers disappear consistent with ada-
mantane-1-carboxylate competing more strongly for occupancy
of the βCD annuli. (The complexation constant for the for-
mation of βCDؒadamantane-1-carboxylate = 1.8 × 104 dm3
respectively (Figs. S3 and S4‡). This is also the case for equi-
molar solutions of either 1 or 2 and 34Ϫ in 10Ϫ3 mol dmϪ3
NaOD and 0.10 mol dmϪ3 in NaClO4 (pD ≈ 11) consistent with
the formation of Naϩؒ1ؒ34Ϫ and Naϩؒ2ؒ34Ϫ complexes (Fig. S5‡
and Fig. 8), respectively. It is seen from Fig. 8 that there are no
cross-peaks arising from ROE interactions between H2–H7 of
the octamethylene linkers and βCD H3, H5 and H6 consistent
with the self-complexation process being weaker than the com-
plexation of 34Ϫ in Naϩؒ2ؒ34Ϫ. A similar situation applies in the
spectrum of 2ؒ34Ϫ (Fig. S4‡).
Conclusion
The linked βCD dimers, 1 and 2 and their Naϩؒ1 and Naϩؒ2
complexes bind 34Ϫ moderately to form 1ؒ34Ϫ, Naϩؒ1ؒ34Ϫ, 2ؒ34Ϫ
and Naϩؒ2ؒ34Ϫ, respectively, where the latter two complexes are
less stable as a consequence of the self-complexation of the
octamethylene linkers of 2 competing with 34Ϫ for occupancy of
the βCD annuli. The moderately greater stabilities of Naϩؒ1ؒ34Ϫ
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beam spectrophotometer. Wavelength ranges where the greatest
absorbance change occurred were selected for analysis. These
ranges were 470–520 nm for 1/34Ϫ, 480–550 for 2/34Ϫ, 380–550
nm for Naϩ/1/34Ϫ and for 380–550 nm Naϩ/2/34Ϫ
.
Complex stoichiometry and complexation constants were
determined through non-linear least squares fitting of algo-
rithms for the formation of 1 : 1, 1 : 1 and 2 : 1, 1 : 2, and 2 : 1
complexes to the absorbance variation of 34Ϫ with concen-
tration of 1 and 2 at 1 nm intervals by using Method 5 of Pitha
and Jones,13 through an in-house least squares regression
routine DATAFIT14 using the MATLAB formalism.15 Taking
the 1/34Ϫ system as an example, the observed absorbance, A, is
related to the molar absorbances of the species in solution, ε,
and their concentrations through:
A = ε1[1] ϩ ε3[34Ϫ] ϩ ε1ؒ3[1ؒ34Ϫ
]
where ε1 = 0 and species concentrations are related through the
complexation constant K2 = [1ؒ34Ϫ]/([1][34Ϫ]).
1H (300 MHz) and 13C (75.5 MHz) NMR spectra were run on
1
a Varian Gemini 300 spectrometer, and H (600 MHz) NMR
spectra were run on an Inova 600 spectrometer. Solutions of
34Ϫ alone or in the presence of either 1 or 2 were prepared to
give concentrations of 0.013–0.015 mol dmϪ3 in each constitu-
ent in either 0.10 mol dmϪ3 ND3/ND4Cl buffer at pD 10.0 or
10Ϫ3 mol dmϪ3 NaOD and 0.1 mol dmϪ3 in NaClO4 (pD ≈ 11)
in D2O. Chemical shifts were referenced against external tri-
methylsilylpropiosulfonic acid. ESI mass spectrometric studies
were made in positive ion mode with a Finnigan MAT ion trap
LC–Q mass spectrometer fitted with an electrospray ionisation
source. Accurate mass spectrometry was carried out at the
University of Tasmania, Hobart. Samples were dissolved in
water for injection. Elemental analyses were performed by the
Microanalytical Service of the Chemistry Department,
University of Otago, Dunedin, New Zealand. Both 1 and 2
decomposed upon heating which precluded the determination
of melting points. All reagents used were obtained from Aldrich
and were not further purified before use, unless otherwise
stated. βCD (Nihon Shokuhuin Kako Co.) was dried by heating
at 100 ЊC under vacuum for 18 h. All solvents used in syntheses
were redistilled and dried by standard methods.
Potentiometric titrations were carried out using a Metrohm
Dosimat E665 titrimeter, an Orion SA 720 potentiometer and
an Orion 8172 Ross Sureflow combination pH electrode that
was filled with 0.10 mol dmϪ3 either NEt4ClO4 or NaClO4.
Titration solutions were saturated with nitrogen by passing
a fine stream of bubbles (previously passed through aqueous
0.10 mol dmϪ3 NaOH followed by 0.10 mol dmϪ3 NaClO4)
through them for at least 15 min before the commencement of
the titration. During the titrations a similar stream of nitrogen
bubbles was passed through the titration solution which was
Fig. 8 The 2D 1H ROESY NMR (600 MHz) spectrum of a D2O
solution 0.014 mol dmϪ3 in 2 and 34Ϫ in 10Ϫ3 mol dmϪ3 NaOD and 0.1
mol dmϪ3 in NaClO4 (pD ≈ 11) at 298.2 K. The rectangles enclose the
cross-peaks arising from ROE interactions between the protons of 34Ϫ
and the βCD H3, H5 and H6 protons.
and Naϩؒ2ؒ34Ϫ by comparison with those of 1ؒ34Ϫ and 2ؒ34Ϫ
,
respectively, are attributed to the electrostatic attraction of
complexed Naϩ for 34Ϫ. Similarly, the moderately greater
stabilities of Naϩؒ1ؒ34Ϫ and Naϩؒ2ؒ34Ϫ by comparison with
those of Naϩؒ1 and Naϩؒ2, respectively, are attributed to the
electrostatic attraction of complexed 34Ϫ for Naϩ. Thus, the
hydrophobic driving force underlying the complexation of
34Ϫ in the βCD annuli of 1 and 2 has superimposed upon it
self-complexation processes and electrostatic attraction forces
which combine to determine the stabilities of the eight com-
plexes formed.
Experimental
General
Aqueous solutions were prepared with water purified with a
Waters Milli-Q system to give a specific resistance of >15 MΩ
cm which was then boiled for 30 min to remove CO2 and
allowed to cool in a container fitted with a soda lime guard
tube. Metal perchlorates (Fluka) were twice recrystallised from
water, and the anhydrous salts were was obtained by drying
to constant weight over P2O5 under vacuum prior to use.
(CAUTION. Anhydrous perchlorate salts are potentially explo-
sive and should be handled with care.) The disodium salt of
Brilliant Yellow (Aldrich 70%) was twice recrystallised from
methanol. The tetrahydrated di-tetraethylammonium salt of
Brilliant Yellow was prepared as previously described.6 UV-vis-
ible spectra of 34Ϫ alone or in the presence of either 1 or 2 in
0.05 mol dmϪ3 borate buffer (total buffer concentration at
pH 10.0 prepared from boric acid and either NEt4OH or NaOH
at I = 0.10 mol dmϪ3 adjusted with NEt4ClO4 and NaClO4,
magnetically stirred and held at 298.2
0.1 K in a water-
jacketed 20 cm3 titration vessel which was closed to the atmos-
phere except for a small vent for nitrogen. Either standardised
0.10 mol dmϪ3 NEt4OH or NaOH was titrated against solutions
that were 1.0 × 10Ϫ3 mol dmϪ3 in the species of interest, 5.0 ×
10Ϫ3 mol dmϪ3 in HClO4 and 9.5 × 10Ϫ2 mol dmϪ3 in either
NEt4ClO4 or NaClO4 (I = 0.10 mol dmϪ3). Values of E0 and
pKw were determined by titration of a solution that was 1.00 ×
10Ϫ4 mol dmϪ3 in HClO4 and 9.0 × 10Ϫ4 mol dmϪ3 in NaClO4
against 0.100 mol dmϪ3 NaOH. Values of pKa were determined
using the program SUPERQUAD.16 At least three runs were
performed for each system and at least two of these runs were
averaged; the criterion for selection for this averaging being that
χ2 for each run was < 12.6 at the 95% confidence level.
respectively) were run at 298.2
0.1 K in matched quartz
Syntheses
cuvettes of 1 cm path length against a reference containing
the same buffer and supporting electrolyte. Absorbance data
were collected at 1 nm intervals with a Cary 300 Bio double
6A-O-(4-methylbenzenesulfonyl)-β-cyclodextrin,17 4,13-bis(car-
boxymethyl)-4,13-diaza-1,7,10-trioxacyclopentadecane18 and
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 8 8 7 – 8 9 4
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6A-(2-aminoethyl)amino-6A-deoxy-β-cyclodextrin19 were pre-
pared by literature methods and good elemental analyses and
1H and 13C NMR spectroscopic data were obtained. Other
reagents (Aldrich) were used as received.
4,13-Bis(8-(6A-deoxy-ꢀ-cyclodextrin-6A-yl)aminooctylamido-
methyl)-4,13-diaza-1,7,10-trioxacyclopentadecane, 2. A mixture
of 4,13-bis(carboxymethyl)-4,13-diaza-1,7,10-trioxacyclopenta-
decane (0.101 g, 0.23 × 10Ϫ3 mol), 4-nitrophenol (0.064 g,
0.46 × 10Ϫ3 mol) and dicyclohexylcarbodiimide (0.098 g, 0.48 ×
10Ϫ3 mol) in dichloromethane (4 cm3) was stirred at room tem-
perature for 2 h. The reaction mixture was filtered through
Celite and the filtrate was evaporated under reduced pressure to
give the crude bis(4-nitrophenyl)ester as a yellow oil (IR 1763
cmϪ1). The residue was dissolved in N,N-dimethylformamide
(5 cm3) and 6A-(8-aminooctyl)amino)-6A-deoxy-β-cyclodextrin
(0.590 g, 0.46 × 10Ϫ3 mol) was added. The resultant yellow
solution was stirred at room temperature for 18 h and then
diluted with ether (50 cm3). The precipitated crude linked βCD
dimer was collected by vacuum filtration and dissolved in water
(15 cm3) and dilute HCl (1 cm3). The colourless solution was
washed with dichloromethane (5 × 15 cm3) and then concen-
trated to 10 cm3 under reduced pressure. The residue was
diluted with ethanol (100 cm3) and the resultant precipitate was
collected by vacuum filtration. The collected solid was dissolved
in water (10 cm3) and loaded onto a column of BioRex 70
6A-(8-Aminooctyl)amino)-6A-deoxy-ꢀ-cyclodextrin. A solution
of 6A-O-(4-methylbenzenesulfonyl)-β-cyclodextrin (2.028 g,
1.57 × 10Ϫ3 mol) and 1,8-diaminooctane (0.68 g, 4.72 × 10Ϫ3
mol) in 1-methylpyrrolidin-2-one (5 cm3) was stirred at 70 ЊC
for 18 h. The cooled reaction mixture was diluted with ethanol
(100 cm3) and the resultant precipitate was collected by vacuum
filtration and washed with ethanol (50 cm3) and ether (50 cm3).
The solid was dissolved in water (10 cm3) and loaded onto
a column of BioRex 70 cation exchange resin (Hϩ form, 4.5 ×
4.5 cm). The column was washed with water (200 cm3) and the
product was eluted with 1 mol dmϪ3 ammonia solution.
Fractions containing the product were combined and evapor-
ated under reduced pressure. The residue was dissolved in water
and the solution was filtered (0.02 µm) and freeze-dried to
give 6A-(8-aminooctyl)amino-6A-deoxy-β-cyclodextrin as
a
white powder (1.117 g, 56%). δH (300 MHz, D2O, pD ≈ 11) 4.88
(br s, 7H, H1), 3.5–3.9 (m, 26H, H3, H5, H6B–G), 3.3–3.5 (m,
13H, H2, H4), 3.12 (t, J = 9.0 Hz, 1H, H4A), 2.87 (br d, J = 12.0
Hz, 1H, H6A), 2.6 (m, 3H, H6AЈ, octamethylene H1), 2.4
(m, 2H, octamethylene H8), 1.0–1.5 (m, 12H, octamethylene
H2–7); δC (75.4 MHz, D2O, pD ≈ 11) 109.0, 108.8, 108.5, 107.7
(C1), 90.3 (C4A), 87.6, 87.4, 87.3, 86.5 (C4), 80.3, 80.0, 79.9,
79.6, 79.0, 78.5, 78.2, 78.1 (C2, C3, C5), 74.3 (C5A), 66.3 (C6),
53.9 (octamethylene C8), 52.3 (C6A), 46.9 (octamethylene
C1), 38.2, 34.0, 33.2, 32.2, 31.9 (octamethylene C2–7). ESI-ms
m/z 1262 (MϩHϩ). Elemental analysis for 6ؒ2H2O (C50H92-
N2O36) C, 46.29, H, 7.14, N, 2.16. Found: C, 46.31, H, 6.92, N,
2.22.
ϩ
cation exchange resin (NH4 form, 4.5 × 4.5 cm) which was
eluted sequentially with water (100 cm3) and 0.05 mol dmϪ3
ammonium hydrogen carbonate, taking 20 cm3 fractions.
Fractions containing the product were combined and evapor-
ated under reduced pressure. The residue was dried over P2O5
at room temperature under vacuum to give the product as a
white powder (0.242 g, 37%). δH (600 MHz, D2O, pD ≈ 11) 4.88
(m, 14H, H1), 2.9–3.9 (m, 102H, CD–H, diazacoronand–H),
2.2–2.8 (m, 14H, H6AЈ, octamethylene H1, diazacoronand
CH2-N), 1.0–1.6 (m, 24H, octamethylene H); δc (75.4 MHz,
D O, pD ≈ 11) 176.3, 176.2, 176.1, 175.4 (C᎐O), 105.7, 105.3,
᎐
2
103.8 (C1), 87.4 (C4A), 84.6, 84.5, 84.3, 84.1, 82.9 (C4), 77.5,
76.7, 75.9, 75.5, 74.8, 74.6 (C2,C3,C5), 71.5, 70.1, 69.9, 69.3
(C5A, diazacoronand–C), 63.1, 62.7, 60.6, 57.3, 51.7, 46.4, 42.2
(C6, diazacoronand C–N, octamethylene C1, octamethylene
C8), 31.9, 31.7, 31.5, 31.1, 30.4, 29.9, 29.7, 29.2, 29.1, 28.7, 28.4,
27.8 (octamethylene C2–7). ESI-ms m/z 2822 (M ϩ Hϩ), 1412
(M ϩ 2Hϩ), 942 (M ϩ 3Hϩ). Elemental analysis for 2ؒ13H2O
(C114H224N6O86) C, 44.82; H, 7.39; N, 2.75. Found C, 44.75;
H, 6.98; N, 2.82.
4,13-Bis(2-(6A-deoxy-ꢀ-cyclodextrin-6A-yl)aminoethylamido-
methyl)-4,13-diaza-1,7,10-trioxacyclopentadecane, 1. A mixture
of 4,13-bis(carboxymethyl)-4,13-diaza-1,7,10-trioxacyclopenta-
decane (0.107 g, 0.244 × 10Ϫ3 mol), 4-nitrophenol (0.070 g,
0.504 × 10Ϫ3 mol) and dicyclohexylcarbodiimide (0.108 g,
0.524 × 10Ϫ3 mol) in dichloromethane (5 cm3) was stirred at
room temperature for 2 h. The reaction mixture was filtered
through Celite and the filtrate was evaporated under reduced
pressure to give the crude bis(4-nitrophenyl)ester as a yellow oil
(I.R. 1763 cmϪ1). The oil was dissolved in N,N-dimethyl-
formamide (5 cm3) and 6A-(2-aminoethyl)amino-6A-deoxy-β-
cyclodextrin (0.578 g, 0.491 × 10Ϫ3 mol) was added. The result-
ant yellow solution was stirred at room temperature for 18 h
and then diluted with ether (50 cm3). The precipitated product
was collected by vacuum filtration and dissolved in water
(20 cm3). The solution was passed down a column of AG 4X4
anion exchange resin (free base form, 4.5 × 4.5 cm) which was
eluted with water (100 cm3). The eluent was concentrated under
reduced pressure to 10 cm3 and loaded onto a column of Bio-
Rex 70 cation exchange resin (NH4ϩ form, 4.5 × 4.5 cm) which
was eluted sequentially with water (100 cm3) and 0.05 mol dmϪ3
ammonium hydrogen carbonate, taking 20 cm3 fractions.
Fractions containing the product were combined and evapor-
ated under reduced pressure. The residue was dried over P2O5 at
room temperature under vacuum to give the product as a white
powder (0.346 g, 53%). δH (300 MHz, D2O, pD ≈ 11) 4.9 (bs,
14H, H1), 3.0–4.0 (m, 102H, βCD–H, diazacoronand-H),
2.6–2.8 (m, 14H, H6AЈ, dimethylene H1, NCH2). δC (75.4 MHz,
D2O, pD ≈ 11) 176.5, 173.6 (CO), 105.3 (C1), 86.9 (C4A), 84.2
(C4), 76.3, 75.5, 74.5, 72.9, 71.4, 70.1, 69.8 (C2, C3, C5,
diazacoronand C–O), 63.0 (C6), 60.8, 57.3, 56.9, 51.8, 50.0,
41.0, 39.2 (C6A, dimethylene C, diazacoronand C–N). ESI-ms
Acknowledgements
The award of University of Adelaide Postgraduate Research
Awards to L. C. W. and O. W. and project support from the
Australian Research Council is gratefully acknowledged.
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