Face selectivity of inclusion complexation of viologens with ?2-cyclodextrin and 6-O-(2-sulfonato-6-naphthyl)-?2-cyclodextrin

Article abstract of DOI:10.1021/jp020428f

Face selectivity in binding of methyloctyl viologen (C₁C₈V²⁺: 1) and adamantylmethyl viologen (AdaC₁V²⁺: 2) with ?2-CD and 6-O-(2-sulfonato-6-naphthyl)-?2-CD (?2-CD-NS: 4) has been investigated. Circu

Full text of DOI:10.1021/jp020428f

7186
J. Phys. Chem. B 2002, 106, 7186-7192
Face Selectivity of Inclusion Complexation of Viologens with â-Cyclodextrin and
6
-O-(2-Sulfonato-6-naphthyl)-â-cyclodextrin
Joon Woo Park,* Hee Eun Song, and Soo Yeon Lee
Department of Chemistry, Ewha Womans UniVersity, Seoul 120-750, Korea
ReceiVed: February 13, 2002; In Final Form: May 7, 2002
2
+
Face selectivity in binding of methyloctyl viologen (C
1
C
8
V : 1) and adamantylmethyl viologen
V : 2) with â-CD and 6-O-(2-sulfonato-6-naphthyl)-â-CD (â-CD-NS: 4) has been investigated.
Circular dichroic titration of 1 and 2 with â-CD gave the binding constants and the molar ellipticities [θ]254nm
2+
(AdaC
1
-
1
2
-1
-1
2
of the â-CD complexes as 890 M and -2000 deg cm dmole for 1, and as 7300 M and -3600 deg cm
-
1
2
-1
dmole for 2. The [θ] values of the complexes are much less negative than -8500 deg cm dmole of
â-CD-viologen compound 3 in which the viologen is covalently bonded to the primary face of â-CD.
Fluorescence quenching of the naphthyl group of 4 by 1 and 2 is much more efficient than that of 6-methoxy-
2-naphthalenesulfonate (MNSS), but residual fluorescence was observed even at high viologen concentration.
The binding constants of the viologens with 4 and the fractions of the residual fluorescence with respect to
-
1
-1
fully monomeric 4 were determined as 4700 M and 0.09 for 1 and 10 400 M and 0.15 for 2. Comparing
the steady-state fluorescence quenching and time-resolved fluorescence studies, it appeared that the bipyridinium
moiety of 2 is predominantly on the secondary side of â-CD of 4, whereas that of 1 favors the primary side,
mainly due to the direct charge transfer interaction between the naphthyl and bipyridinium groups: without
the interaction, it would prefer the secondary face 14 times more favorably to the primary face. The rate
constants of the photoinduced electron-transfer reactions between the bipyridinium group on the secondary
8
-1
8
-1
face and the naphthyl group are 1.9 × 10 s for the 1/4 complex and 7.9 × 10 s for the 2/4 complex.
Introduction
primary side of CDs.6,7 However, as the ICD of a chromophore
6
,7
gives the same sign on the both sides of CDs, the negative
ICD cannot be taken as an unequivocal evidence for the location
of the bipyridinium group with respect to CD cavities. Also,
the conclusion is in conflict with an expectation that the
bipyridinium group would prefer the wider secondary side by
ion-dipole interaction as the electrostatic potential outside the
Cyclodextrins (CDs) are torus-like cyclic oligosaccharides
with hydrophobic cavities capable of forming inclusion com-
plexes with a variety of organic molecules in aqueous solution.
Because of these characteristics, CDs have been widely used
as biomimetic microreactors, novel media for photophysical and
photochemical studies, and building blocks for supramolecular
structures and functional units as well as in various fields of
1
6
secondary rim is negative.
In this paper, we reexamined the face selectivity of the
inclusion complexation of alkyl viologen through the studies
1
,2
industries. Guest molecules can be included from both ends
of CD cavities. The face selective inclusion complexation with
CDs is believed to be important in molecular recognition and
chemical reactions mediated by CDs as the size of opening,
acidity of hydroxyl groups, and electrostatic potential of the
ends are different. There has been much effort to determine the
structures, and thus the face selectivity, of CD-inclusion
2+
on the complexation of methyloctyl viologen (C1C8V : 1) and
2
+
adamantylmethyl viologen (AdaC1V : 2) with native â-CD
and 6-O-(2-sulfonato-6-naphthyl)-â-CD (â-CD-NS: 4) by a
combination of a variety of spectroscopic techniques. From these
studies and comparison of ICD spectra of the viologen/â-CD
complexes with that of a â-CD-viologen compound 3, it was
3
-5
6-8
complexes: NMR
and circular dichroic
spectroscopic
methods have been widely utilized for this purpose. Molecular
9
10
modeling and the nonlinear free energy relationship model
have been also used to determine and/or predict the guest
orientation in the CD complexes. However, there is a paucity
of experimental evidence on the face selectivity of the com-
plexes. Long alkyl chains are a typical part of guest molecules
that are included into CD cavities.11-14 Inclusion complexation
of alkyl viologens, 1,1′-dialkyl-4,4′-bipyridinium salts, with CDs
has been a subject of numerous studies.6
,7,14,15
On the basis of
the negative induced circular dichroism (ICD) of diheptyl
viologen/CD complexes and rules for ICD derived from the
Kirwood-Tinoco equation, Kodaka suggested that the bipyri-
dinium moiety of the viologen is placed above the narrower
*
To whom correspondence should be addressed. Phone: +82-2-3277-
2
346. Fax: +82-2-3277-2384. E-mail: jwpark@mm.ewha.ac.kr.
1
0.1021/jp020428f CCC: $22.00 © 2002 American Chemical Society
Published on Web 06/28/2002

Inclusion Complexation of Viologens with â-CD
J. Phys. Chem. B, Vol. 106, No. 29, 2002 7187
shown that the bipyridinium moieties of 1 and 2 are preferen-
tially placed on the secondary side of â-CD in their complexes
with native â-CD. The rate constants of photoinduced electron-
transfer reactions in the viologen/4 complexes were also
obtained.
Experimental Section
Materials. Chemicals were obtained from Aldrich. â-CD and
,4′-bipyridine were recrystallized from water and vacuum-dried.
4
The chloride salts of methyloctyl viologen 1 and mono-6-(1-
methyl-4,4′-bipyridino)-â-CD 3 were prepared as reported in a
1
4
previous paper. The synthesis and characterization of 6-O-
17
(
2-sulfonato-6-naphthyl)-â-CD 4 were reported elsewhere. The
compound 2 was prepared as described below.
Synthesis of 1-Adamantyl-1′-methyl-4,4′-bipyridinium
Dichloride, 2. To a solution of 4,4′-bipyridine (6.0 g, 38 mmol)
in ethanol (15 mL) at 40 °C was added a solution of
dinitrochlorobenzene (3.8 g, 20 mmol) in 15 mL of ethanol
dropwise, and stirring was continued for 40 h at the same
temperature. After evaporating off the solvent, the residue was
washed with dry diethyl ether and recrystallized from ethanol
to obtain 2.3 g (6.4 mmol; 32% yield) of 1-(2,4-dinitrophenyl)-
Figure 1. Induced circular dichroism spectra of 2 in the presence of
-
4
â-CD. The concentration of 2 was 1.0 × 10 M. The concentrations
of â-CD are shown in the figure.
4
,4′-bipyridinium chloride, 5. The compound 5 (1.0 g, 2.8 mmol)
and 1-adamantanamine (0.63 g, 4.2 mmol) were dissolved in
0 mL of methanol and refluxed for 3 h under N2 atmosphere.
1
After evaporating off the methanol solvent, 40 mL of water
was added and then filtered. The filtrate was evaporated to
dryness, and the resulting solid was recrystallized in 2-propanol
to obtain 0.67 g (75% yield) of white crystalline 1-adamantyl-
4
,4′-bipyridinium chloride, 6. The compound 2 was obtained
Figure 2. Dependence of the apparent molar ellipticity of 2 (A) and
1
(B) on the concentration of â-CD.
by reacting 6 with large excess of CH3I in ethanol, followed
by counterion exchange through stirring the aqueous viologen
solution in the presence of AgCl, in nearly quantitative yield.
Results and Discussion
1
4
Binding of Viologens with â-CD and Circular Dichroic
Recrystallization from 2-propanol/ethanol (10:1 v/v) gave the
analytically pure 2.
2+
Properties of the â-CD Complexes. Both C1C8V (1) and
2
+
Data for 5: 1H NMR (D2O) δ 9.44 (d, 1H), 9.30 (d, 2H),
.99 (dd, 1H), 8.88 (dd, 2H), 8.74 (d, 2H), 8.34 (d, 1H), 8.07
AdaC1V (2) are achiral molecules and do not show circular
dichroism. However, in the presence of â-CD, they exhibited
virtually identical negative induced circular dichroism (ICD)
around 255 nm. This is due to the complexation of the viologens
with the chiral host. The ICD spectra grow as the concentration
of â-CD becomes higher (Figure 1). The dependences of
ellipticity at 254 nm on the concentration of â-CD are presented
8
(
dd, 2H).
Data for 6: 1H NMR (D2O) δ 9.25 (d, 2H), 8.79 (d, 2H),
8
.42 (d, 2H), 7.93 (d, 2H), 2.30 (s, 9H), 1.88 (t, 6H).
Data for 2: UV(H2O) λmax/nm (logꢀ), 264(4.31); mp 270 °C
dec); H NMR (D2O) δ 9.37 (d, 2H), 9.06 (d, 2H), 8.54 (d,
1
(
in Figure 2.
4
H), 4.52 (s, 3H), 2.41 (s, 9H), 1.86 (t, 6H); Anal. Calcd for
C21H26N2Cl2‚3H2O: C, 58.47; H, 7.47; N, 6.49; Found: C,
8.75; H, 7.84; N, 6.51.
Spectral Measurements. H NMR spectra were obtained on
If we assume 1:1 complexation between the viologen (V2+)
and â-CD (eq 1), the apparent molar ellipticity ([θ]) of a
spectrum taken at an initial viologen concentration [V]0 and
â-CD concentration [â-CD]0 is expressed as eq 2.
5
1
a Bruker 250 MHz spectrometer. Absorption spectra were
recorded with a GBC Cyntra 20 spectrophotometer. Difference
spectra for charge-transfer complexation were taken from mixing
tandem double cells. Steady-state fluorescence spectra were
obtained with a Hitachi F-3010 spectrofluorimeter. Fluorescence
lifetime measurements were performed using a time-correlated
single photon counting setup assembled at Pohang University.
Circular dichroism spectra were taken with a JASCO J-810
spectropolarimeter. The bandwidth was set at 2 nm and the
response time was 2 s. The â-CD-free solutions having the same
concentration of viologens were used as blanks. Spectra of 10
repetitive scans taken at the scan speed of 50 nm per min were
averaged and smoothed using JASCO software. All measure-
ments were carried out at 25 °C using an appropriate temperature
controller. Unless otherwise specified, ionic strength of solutions
was maintained as 0.10 M with NaCl.
2
+
2+
V
+ â-CD a V -â-CD;
2
+
2+
K ) [V -â-CD]/[V ][ â-CD] (1)
2
+
[θ] ) ([θ]complex{([V ] + [â - CD] + 1/K) -
0
0
2
+
2
2+
(
[V ] + [â - CD] + 1/K) - 4[V ] [â - CD] })/
x
0 0 0 0
2
+
2
[V ] (2)
0
where [θ]complex is the molar ellipticity of the complex at the
measured wavelength. The [θ] versus [â-CD] data fitted well
to eq 2, and the determined K and [θ]complex are given in Table
1. The binding constants of 1 (890 ( 60 M ) and 2 (7300 (
400 M ) with â-CD are close to the reported binding constants
of n-octylammonium (750 M ) and 1-adamantanammonium
(8430 M ) chlorides with â-CD, implying that the bindings
0
-
1
-1
-
1 13
-
1 4

7188 J. Phys. Chem. B, Vol. 106, No. 29, 2002
Park et al.
TABLE 1: Association Constants and the Characteristics of
the Complexes of Viologens with â-CD and â-CD-NS 4 in
0.1 M Aqueous NaCl Solutions at 25 °C
â-CD
â-CD-NS
[
θ]complex/
K/M-
1
deg cm dmole
2 -1a
KC/M-1b
4700 ( 200 0.09 ( 0.01
Icomplex/Imonc
viologen
+
1
2
: C1C8V2
890 ( 60
-2000 ( 100
2
+
: AdaC1V 7300 ( 400 -3600 ( 100 10400 ( 400 0.15 ( 0.05
a
λ ) 254 nm. The [θ] value of â-CD-V2+
C 3 which bears
1
covalently bonded viologen at the primary face of â-CD is -8540 deg
2
-1 b
.
Apparent binding constants with monomeric 4. c The
cm dmole
ratio of the fluorescence intensities of 1:1 complex and monomeric 4.
-
5
Figure 4. Quenching of the fluorescence of 1.0 × 10 M solutions
of MNSS (A) and 4 (B) by 2. The concentrations of 2 are shown in
the figures.
Figure 3. Circular dichroism spectra of 1/â-CD (A), 2/â-CD (B)
complexes, and 3 (C). The spectra of the complexes were calculated
from ICD spectra using measured complexation constants.
-
5
Figure 5. Dependence of the fluorescence intensity of 1.0 × 10
M
solutions of MNSS and 4 on the concentration of viologens: (A), MNSS
2+
2+
of the viologens are mainly driven by inclusion of the
hydrophobic groups into â-CD cavity.
+ C
1
C
1
V
1 1
; (B), MNSS + 2; (C), 4 + C C V ; (D), 4 + 1; (E), 4 +
2
.
We calculated the concentration of the viologen/â-CD
complexes using the determined binding constants and then
generated the ICD spectra of 1/â-CD and 2/â-CD complexes.
The spectra were compared with that of a â-CD-tethered
viologen 3 in Figure 3. Kodaka derived a general rule for circular
naphthalene to viologen.2
0-22
The fluorescence quenching of
â-CD-NS (4) and 2-methoxy-6-naphthalenesulfonate (MNSS)
by 2 is compared in Figure 4. The dependences of the
fluorescence intensity of 4 and MNSS on the concentrations of
the viologen quenchers are shown in Figure 5. Figures 4 and 5
show that the fluorescence quenching of 4 by 1 and 2 is much
more efficient than that of MNSS. In contrast to this, the
quenching by dimethyl viologen (C1C1V ), which has little
binding affinity to â-CD, was less efficient for both fluoro-
phores. These results indicate clearly that the efficient quenching
of the fluorescence of 4 by 1 and 2 is facilitated by the inclusion
complexation of the quenchers with the â-CD-tethered fluoro-
phore. Such inclusion-facilitated efficient quenching was dem-
onstrated with other â-CD-tethered fluorophores and quench-
6
,7,18
dichroism induced by a chiral macrocycle including CDs.
The rule predicts that the absolute value of ICD is larger when
a chromophore is placed on the narrower-rim side of the
macrocycle than on the wider-rim side. The rule also predicts
that the sign and magnitude of ICD depend on the angle (Φ)
between the axis of macrocycle and the direction of transition
moment of the chromophore: the sign changes at Φ ) 54.7°,
and the magnitude becomes greater as the deviation of Φ from
2
+
5
4.7° is larger. The major transition of a viologen is the A f
B3 transition near 260 nm which is directed along the long axis
21,23
ers.
Even at high concentrations of 1 and 2, the fluorescence
6
of the viologen. The negative circular dichroism of 3 near 260
of 4 was not completely quenched, and residual fluorescence
was observed (Figure 5). This is an indication that the complexes
between the quenchers and 4 are still fluorescent.
We have shown in a previous report that the fluorescent
host 4 forms a dimer with the dimerization constant (eq 3) of
nm suggests that the angle between CD axis and the long axis
of viologen in 3 is less than 54.7°. This differs from the
conclusion drawn from a NMR study that the long axis of
viologen in a â-CD-viologen compound directs approximately
perpendicular to the CD axis.19 The estimation of the orientation
of the viologen moiety with respect to â-CD in 3 is beyond the
scope of this work. However, the smaller ellipticity of the â-CD
complexes than that of 3 can be regarded as an evidence that
the bipyridinium groups in the viologen/â-CD complexes are
1
7
-1
9
700 M via mutual inclusion of the naphthyl groups into â-CD
cavities of counter molecules and the fluorescence intensity of
a naphthyl group in the dimer is 2.2 times greater than that in
the monomer.
placed on the secondary side of â-CD cavity rather than the
2
â-CD-NS a (â-CD-NS)2;
primary side claimed by Kodaka.6,7 Other conclusive evidences
2
for this were obtained from the binding studies of 1 and 2 with
K ) [(â-CD-NS) ]/[â-CD-NS] (3)
D 2
4
described below.
Binding of Viologens with â-CD-NS and Intracomplex
Quenching Studied by Fluorescence. Viologens quench the
naphthalene fluorescence via electron transfer from the excited
As â-CD cavities in the dimer of 4 are occupied by naphthyl
groups, the dimer cannot form inclusion complexes with the
viologen guests, but the monomer of 4 forms the complex with

Inclusion Complexation of Viologens with â-CD
J. Phys. Chem. B, Vol. 106, No. 29, 2002 7189
CHART 1: Possible Structures of the Complexes
between â-CD-NS 4 and a Viologen with a Hydrophobic
Group
-4
Figure 6. Fluorescence decay profiles of 3.0 × 10 M 4 in the absence
-
3
of viologen (A) and in the presence of 1.0 × 10 M 2 (B). The decay
profile of 4 in the presence of 1 was omitted for clarity.
decays of uncomplexed monomer and dimer of 4 were resolved
poorly. The shorter component can be attributed to the
complexes of the viologens with 4.
In the absence of static quenching, i.e., in case when the type
I complex is not formed, the ratio (τcomplex/τmon) of lifetimes of
the complex and the monomeric 4 is expected to be the same
as the ratio (γ) of fluorescence intensities of the respective
species. The quenching by 2 seems to belong to this case as
the ratio of lifetimes is 0.13 ((0.05), whereas γ was observed
as 0.15 ((0.02). On the other hand, in case of 1, the ratio of
lifetimes is 0.39 ((0.05), which is much greater than the γ value
of 0.09 ((0.01). This suggests that 1 forms the type I complex
as well as the type II complex.
a guest and the monomer-dimer equilibrium is shifted by the
complexation.
As shown in Chart 1, two types of 4/viologen complexes are
possible. One is that the bipyridinium moiety is placed on the
primary side of 4 (type I complex), and the other is that it is
placed on the secondary side (type II complex). The proximity
of naphthyl and bipyridinium groups in a type I complex would
result in a charge-transfer interaction (vide infra) and a static-
like quenching.22 The distance between naphthyl and bipyri-
dinium groups in the type II complex appears to be not short
enough to show the static quenching as evidenced by the residual
fluorescence.
As the type I complex of the 1/4 system is not fluorescent,
the ratio of fluorescence lifetimes of the type II complex and
monomeric 4, 0.39 ((0.05), is equal to the ratio (γII) of the
fluorescence intensities of the corresponding species. Thus KII/
When we consider the apparent complexation (eq 4) and
the weight-averaged fluorescence intensity of the complexes
(KI + KII) becomes equal to γII/γ, which is 0.23 ((0.06), from
(Icomplex), the KC and Icomplex are related to the microscopic
eq 6 after putting II ) 0 and dividing both sides by Imonomer.
This corresponds to KI/KII ratio of ca. 3.3. As KI + KII is
binding constants, KI and KII, defined in Chart 1 by eqs 5 and
6
:
-
1
determined as 4700 M (Table 1), KI and KII are estimated as
-
1
2
+
3600 and 1100 M , respectively.
â-CD-NS + V a complex;
K ) [complex]/[â-CD-NS][V ] (4)
The rate constant of the intracomplex electron-transfer
reaction (ket) in the type II complex is related to the fluorescence
lifetimes of monomeic 4 and the complex by eq 7:
2
+
C
K ) K + K
(5)
C
I
II
K I + K I
I I
II II
1
1
τmon
Icomplex
)
(6)
ket )
-
(7)
K + K
τcomplex
I
II
8
-1
where the subscripts I and II represent the type I and II
complexes, respectively.
From the lifetime data, ket’s were calculated as 1.9 × 10 s
8 -1
for 1/4 and 7.9 × 10 s for the 2/4 complexes. These values
are the through-space/solvent electron-transfer rate constants
from the excited naphthyl to bipyridinium groups in the
respective complexes. As ket varies exponentially with the
donor-acceptor distance, the result suggests that the bipyri-
dinium group of 1 in its type II complex with 4 locates farther
from the wider secondary rim of â-CD than that of 2 in the
corresponding complex.
An equation relating the observed fluorescence intensity of
a given solution of 4 to the concentration of the viologen
quencher 1 or 2 was derived as a function of KD, KC, and the
ratio (γ) of fluorescence intensities of the complex and mon-
omeric 4 and shown in the Appendix. The KC and γ values
obtained by the fitting of the experimental data (Figure 5) to
the equation are listed in Table 1.24
2
5
We also investigated the fluorescence decay profiles of 4 both
in the absence and in the presence of the viologens, 1 and 2. In
the absence of viologens, the decay curve fitted a biexponential
function with lifetimes of τ1 ) 8.5 ((1.0) ns and τ2 ) 14.5
Charge-Transfer Interaction between Naphthyl and Bi-
pyridinium Groups in the Complexes of 4 with Viologens.
The addition of the viologen 1 or 2 to a solution of 4 results in
a diffused absorption above 350 nm (Figure 7). This is due to
(
(2.0) ns, which correspond to those of monomer and dimer
the ground-state charge-transfer interaction between a naphthyl
17
20-22
of 4, respectively. However, the decay profiles in the presence
of 1 and 2 exhibit a shorter component of which lifetimes are
group and the bipyridinium moiety of viologens.
The shape
of the spectra was virtually identical for both viologens, but
the dependence of the absorbance on the concentration of the
viologen was quite different (see inset of Figure 7). The fitting
3
.3 ((0.2) ns for 1 and 1.1 ((0.2) ns for 2, together with a
long component having lifetime of ca. 9 ns (Figure 6): the

7190 J. Phys. Chem. B, Vol. 106, No. 29, 2002
Park et al.
Figure 7. Absorption spectra of 0.50 mM 4 at various concentrations
of 1 (the blank was 0.50 mM 4). The concentrations of 1 are 0.30,
0
.70, 1.54, 2.57, and 11.25 mM (from bottom to top). The inset shows
the dependence of the charge-transfer band absorption of 0.5 mM 4 at
62 nm on the concentration of 1 (A, D) and 2 (B, C). The data in C
3
+
3
and D were taken in the presence of 50 mM AdaNH .
Figure 8. 1H NMR spectra of the aromatic region: (A), 6.7 mM 2 +
6
4
.7 mM â-CD; (B), 6.7 mM 2 + 6.7 mM 4; (C), 8.8 mM 1 + 6.7 mM
2
+
of the charge-transfer absorption versus [V ] relationship to
the 1:1 complexation scheme was not successful, presumably
because of the complication from the monomer-dimer equi-
librium of 4. To simulate the interaction between a naphthyl
group of the monomeric 4 and viologens, we induced the
+
; (D), 6.7 mM AdaNH
3
+ 6.7 mM 4.
To confirm the different complexation behaviors of 1 and 2
with 4, we took NMR spectra of the complexes and compared
them with that of the AdaNH3 /4 complex (Figure 8). The
chemical shifts of the bipyridinium protons of 2 are little affected
by the binding with 4. Also the chemical shifts of naphthyl
protons of 4 are similar in 2/4 and AdaNH3 /4 complexes. In
contrast to this, the chemical shifts of the protons of both groups
move to upfield upon complexation between 1 and 4. Such
upfield shifts were observed in aromatic donor-viologen dyad
molecules and ascribed to the intramolcular charge-transfer
complexation causing ring current effect.
The fluorescence studies showed that the microscopic binding
+
+
monomer by the addition of 1-adamantanammonium (AdaNH3 )
to the solution of 4 and titrated the solution with viologens (see
2
6
inset of Figure 7). The titration data fitted well to a Benesi-
Hildebrand equation (eq 8) and the KCT values were found to
+
-
1
-1
be 26 ((1) M for 1 and 77 ((2) M for 2. We also
determined the charge-transfer complexation constant of 1 with
-
1
MNSS as 48 ((2) M :
2
7
2
+
∆
A /[V ] ) K ∆ꢀ [â-CD-NS] - K ∆A
CT
(8)
CT
CT
CT
CT
-
1
constants, KI and KII, between 1 and 4 are 3600 and 1100 M ,
respectively. The inclusion of the hydrophobic octyl chain into
the â-CD cavity of 4 and the intracomplex charge-transfer
interaction between the bipyridinium and naphthyl groups
contribute to the stability of the type I complex. If we assume
independent contribution of the two factors to the microscopic
binding constant for the formation of the type I complex, KI
can be represented as KI ) Koctyl,I‚KCT, where Koctyl,I is the
contribution from the inclusion of the octyl group and thus the
expected binding constant in the absence of the charge-transfer
interaction. As the charge-transfer complexation constant of 1
In contrast to the gradual increase of the charge-transfer
absorption in the titration of 4 with 1 or 2 in the presence of
+
AdaNH3 (curves C and D in Figure 7), the titration in the
+
absence of AdaNH3 showed a sharp rise of absorption
reflecting binding of the viologens with CD cavity of 4.
However, the trends of the two viologens are quite different. In
the titration with 2 (curve B), the initial absorption rise is small,
and the absorption increases gradually as the concentration of
2
becomes higher and the titration curve is nearly parallel to
+
that taken in the presence of AdaNH3 (curve C). We explain
this in terms of the formation of the type II complex between
-
1
with MNSS, 48 M , is approximated for the KCT value, the
-
1
2
and 4 giving the initial small absorption rise and the interaction
Koctyl,I is calculated as 75 M . This value is much smaller than
-
1
of the naphthyl group expelled by 2 with another 2, in similar
the KII value, 1100 M . Thus, we can soundly conclude that
the preference of the bipyridinium group of 1 for the primary
face of 4 is mainly due to the charge-transfer interaction, and
without the interaction, the group would prefer the secondary
face about 14 times to the primary face.
+
fashion with that expelled by AdaNH3 . The difference of
absorbance of curves B and C at high concentration of 2 is about
0
.01. This can be ascribed to the long-range charge-transfer
absorption between the naphthyl and bipyridinium groups
separated by â-CD cavity.22 Unlike 2, the titration with 1 shows
a large increase in charge-transfer absorption, and the absorption
The bipyridinium groups of the viologen guests 1 and 2 in
their complexes with native â-CD can also be placed on both
sides of â-CD as in the complexes with 4. The formation of a
complex between a viologen with a hydrophobic group and
native â-CD is mainly driven by the inclusion of the hydro-
phobic group into the â-CD cavity. The difference in the binding
constants of a viologen with native â-CD and 4 forming the
type II complexes would reflect the contribution of the
electrostatic effect to the stability of the complex with 4. The
small difference in the binding constants of 2 with â-CD and
4, compared to the complexes of 1, strongly suggests that the
bipyridinium moiety in the 2/â-CD complex is mainly placed
on the secondary face: the electrostatic free energy in the type
-
3
becomes almost leveled off at [1] > 4 × 10 M (curve A).
This can be taken as an evidence that the 1/4 exists predomi-
nantly as the type I complex in which the naphthyl and
bipyridinium groups can interact directly.
Structures of the Complexes between 4 and viologens and
the Face Selectivity of Binding. The studies on the charge-
transfer interaction in the preceding section indicate clearly that
the bipyridinium moiety of 2 in its complex with 4 is on the
secondary face of â-CD (type II complex), whereas that of 1 is
mainly on the primary face (type I complex). These are in good
agreement with the results of fluorescence study.

Inclusion Complexation of Viologens with â-CD
J. Phys. Chem. B, Vol. 106, No. 29, 2002 7191
II complex of 2 with 4 is estimated as -0.9 kJ mol-1 from the
ratio of binding constants of the complexes 2/â-CD and 2/4.
corresponding complex of 2, because the bipyridinium group
of 1 is farther apart from the secondary rim of â-CD cavity
than that of 2. We believe that the results of this work would
be very important in interpreting various CD-mediated chemical
reactions and designing CD-based supramolecules.
The microscopic binding constant (KI,CD) of 1 with native
â-CD from the primary side would be the same as Koctyl,I, 75
-1
M , the binding constant of 1 with 4 forming the type I
complex. Thus, the microscopic binding constant (KII,CD) of 1
with native â-CD from the secondary side is calculated as 810
Acknowledgment. This work was supported by Korea
Research Foundation Grant (KRF-2000-DP0204). The authors
thank Prof. A. R. Katrizky of the University of Florida for the
helpful suggestion on the synthesis of the 1-adamantyl derivative
of 4,4′-bipyridinium compound and Prof. T. H. Joo for lifetime
measurements through CRM/KOSEF cooperation.
-1
-1
M
from the apparent binding constant of 890 M . The KII,CD
-
1
value can also be estimated as 790 M from the KII value of
the type II complex between 1 and 4 by correcting the
electrostatic contribution. These results indicate that the binding
of 1 with native â-CD from the secondary side placing the
bipyridinium group on the secondary side is about 10 times more
favored than the binding from the primary side. This agrees well
with the tentative conclusion drawn from ICD studies. A theory
of ICD predicts that the magnitude of ICD becomes smaller as
the chromophore is farther apart from the rim of the cavity of
the chiral macrocyclic host.6 Based on this, the smaller ICD
of the 1/â-CD complex than 2/â-CD can be taken as an evidence
that the bipyridinium group in the former complex locates farther
from the secondary rim than that of the latter complex. This is
consistent with the difference in the intracomplex electron-
transfer rate in the type II complex of the viologens with 4.
Appendix
Analysis on the Binding of Viologen Guests with â-CD-
NS by Fluorescence Measurements. The fluorescence quench-
2+
ing of â-CD-NS (4) fluorescence by viologens (V ) with hydro-
phobic groups is mainly due to the inclusion complexation, and
the dynamic quenching is negligible at low concentrations of
,7
2+
V . The observed fluorescence intensity of a solution contain-
2
+
ing â-CD-NS and V is the sum of the contributions from
2+
â-CD-NS monomer and dimer, and the complex â-CD-NS/V :
Iobs) Imon[â-CD-NS] + 2 Idimer[(â-CD-NS) ] +
The result obtained in this work that the bipyridinium group
of 2 is exclusively placed on the secondary face in the complexes
with native â-CD as well as with 4 is reminiscent of a report
2
Icomplex[complex] (A-1)
+
that the ammonium group of the â-CD complex of AdaNH3
where I’s denote the fluorescence intensities per naphthyl group
expected when all of the â-CD-NS molecules are present as
the respective species. Using eqs 3 and 4 in the text, eq A-1
can be rewritten as eq A-2:
4
is on the secondary face of â-CD. A plausible explanation for
this is that the opening of the primary side of â-CD is not large
enough to accommodate the adamantyl group inside the
narrower rim of the â-CD cavity, while protruding the substi-
tuted hydrophilic groups through the rim. The origin of the face
selectivity in the complexation of 1 with â-CD is not certain at
this point. However, it is noted that a CNDO/2 calculation
showed that the electrostatic potential outside the primary face
of CDs is positive, whereas it is negative outside the secondary
face.16 The bipyridinium dication would favor the secondary
face by ion-dipole interaction. This is in line with a suggestion
2
Iobs) Imon[â-CD-NS] + 2K I
[â-CD-NS] +
D dimer
2+
K I
[â-CD-NS][V ] (A-2)
C complex
2
+
2+
2+
2+
From the mass balance of V , [V ] is given as [V ] ) [V ]0/
2
+
2+
(
1+ KC[â-CD-NS]) and is approximated as [V ] ) [V ]0
1 - KC[â-CD-NS]) as KC[â-CD-NS] , 1. From a mass balance
(
equation with respect to the total concentration (Ctot) of [â-CD-
NS] and the above relationship, the concentration of monomeric
â-CD-NS is expressed as eq A-3:
2
8
by Davies et al. that the electronic effect plays a decisive role
for guest orientation in CD complexes and that the electron
withdrawing group of a guest molecule locates in the primary
rim of CDs.
[â-CD-NS] )
2
+
2
2
2+
2+
(
1 + K [V ] ) + 4C (2K - K [V ] ) - (1 + K [V ] )
Conclusions
x
C
0
tot
D
C
0
C
0
2
2+
2
(2K - K [V ] )
D C 0
From the induced circular dichroic study on the complexation
of methyloctyl viologen 1 and adamantylmethyl viologen 2 with
â-CD and comparison of the ICD spectra with the circular
dichroic spectra of a â-CD-viologen compound 3 and fluores-
cence and NMR studies on the complexation of 1 and 2 with
(A-3)
2
+
2+
Putting [V ] ) [V ]0(1 - KC[â-CD-NS]) and then eq A-3
into eq A-2, we get an equation relating the fluorescence
intensity as a function of [V ]0 and Ctot. From the equation,
the fluorescence intensity in the absence of a viologen, I0, is
expressed as eq A-4, and the ratio of fluorescence intensities in
2
+
6
-O-(2-sulfonato-6-naphthyl)-â-CD 4, we obtained the fol-
lowing conclusions. (1) The bipyridinium group of 1 is placed
on the secondary side of the â-CD cavity 10 times more
favorably than the primary side in its complex with native â-CD.
2
+
the presence and in the absence of V is given as eq A-5:
(
2) In the complex of 1 with 4, the bipyridinium group is placed
(
Idimer - Imon)(1 - 1 + 8K C ) + 4I
K C
dimer D tot
on the primary side 3.3 times more favorably than the secondary
side because of the charge-transfer interaction between the
bipyridinium and 2-sulfonatonaphthyl groups: without the
interaction, the secondary side would be favored by 14 times.
x
D
tot
I0 )
(A-4)
4KD
I
2
)
I0
(4K {[â-CD-NS] + 2K â[â-CD-NS] +
D D
(4) The adamantyl group of 2 is placed on the secondary side
in the complexes with native â-CD as well as 4. (5) The
magnitude of the induced circular dichroism of the viologen 1
in the complexation with native â-CD is smaller than that of
the viologen 2, and the intracomplex electron-transfer rate
constant is slower in the complex of 1 with 4 than in the
2+
K γ[â-CD-NS][V ] (1 - K [â-CD-NS])})/
C
0
C
[(1 - â)( 1 + 8K C - 1) + 4âK C ] (A-5)
x
D
tot
D tot
where â and γ represent Idimer/Imon and Icomplex/Imon, respectively.

7192 J. Phys. Chem. B, Vol. 106, No. 29, 2002
Park et al.
Nonlinear least-squares fitting of the I/I0 data taken at various
(12) Park, J. W.; Song, H. J. J. Phys. Chem. 1989, 93, 6454.
(13) Park, J. W.; Park, K. H. J. Inclusion Phenom. Mol. Recognit. Chem.
994, 17, 277.
2
+
[V ]0 keeping constant Ctot (Figure 5) yields the parameters
1
in eq A-3: to reduce the fitting parameters, we used KD and â
values from a previous study,17 and KC and γ values were
determined from the fitting.
(14) Park, J. W.; Choi, N. H.; Kim, J. H. J. Phys. Chem. 1996, 100,
769.
(15) (a) Quintela, P. A.; Diaz, A.; Kaifer, A. E. Langmuir 1988, 4, 663.
(
b) Diaz, A.; Quintela, P. A.; Schuette, J. M.; Kaifer, A. E. J. Phys. Chem.
1
1
1
4
2
988, 92, 3537. (c) Lee, C.; Kim, C.; Park, J. W. J. Electroanal. Chem.
994, 374, 115. (d) Mirzoian, A.; Kaifer, A. E. Chem. Eur. J. 1997, 3,
052. (e) John, S. A.; Okajima, T.; Ohsaka, T. J. Electroanal. Chem. 1999,
66, 67. (f) Mu, T. W.; Liu, L.; Li, X. S.; Guo, Q. X. J. Phys. Org. Chem.
001, 14, 559.
References and Notes
(1) For compilations on recent researches on cyclodextrins, see: (a)
ComprehensiVe Supramolecular Chemistry; Szejtli, J., Osa, T., Eds.;
Pergamon Press: Oxford, 1996; Vol. 3. (b) Chem. ReV. 1998, 98, 1741-
(16) (a) Sakurai, M.; Kitagawa, M.; Hoshi, H.; Inoue, Y.; Chujo, R.
2
1
076.
Chem. Lett. 1988, 895. (b) Kitagawa, M.; Hoshi, H.; Sakurai, M.; Inoue,
Y.; Chujo, R. Bull. Chem. Soc. Jpn. 1988, 16, 4225.
(2) Wenz, G. Angew. Chem., Int. Ed. Engl. 1994, 33, 803.
3) (a) Schneider, H.-J.; Hacket, F.; R u¨ diger, V. Chem. ReV. 1998, 98,
(
(17) Park, J. W.; Song, H. E.; Lee, S. Y. J. Phys. Chem. B 2002, 106,
755 and references therein. (b) Bergeron, R. J.; Channing, M. A.; Gilbeily,
5177.
G. J.; Pillor, D. M. J. Am. Chem. Soc. 1977, 99, 5146. (c) Bergeron, R. J.;
Channing, M. A.; McGovern, K. A.; Roberts, W. P. Bioorg. Chem. 1979,
(
(
(
18) Kodaka, M. J. Phys. Chem. A 1998, 102, 8101.
19) Ikeda, H.; Du, Y.; Nakamura, A.; Toda, F. Chem. Lett. 1991, 1198.
20) (a) Yoon, K. B. Chem. ReV. 1993, 93, 321. (b) Le, T. P.; Rogers,
8, 263. (d) Yoshida, N.; Seiyama, A.; Fujimoto, M. J. Phys. Chem. 1990,
94, 4254. (e) Kano, K.; Kato, Y.; Kodera, M. J. Chem. Soc., Perkin Trans.
2 1996, 1211. (f) Fronza, G.; Mele, A.; Redenti, E.; Ventura, P. J. Org.
J. E.; Kelly, L. A. J. Phys. Chem. A 2000, 104, 6778.
(21) Park, J. W.; Park, S. H.; Lee, B. A.; Lee, S. Y. Chem. Lett. 1997,
Chem. 1996, 61, 909. (g) Kano, K.; Kamo, H.; Negi, S.; Kitae, T.; Takaoka,
R.; Yamaguchi, M.; Okubo, H.; Hirama, M. J. Chem. Soc., Perkin Trans.
1043.
(22) Park, J. W.; Lee, B. A.; Lee, S. Y. J. Phys. Chem. 1998, 102, 8209.
2
1999, 15. (h) Heda, S.; Ishikawa, S.; Neya, S.; Funasaki, N. J. Phys.
Chem. B 1999, 103, 2579. (i) Ishizu, T.; Kintsu, K.; Yamamoto, H. J. Phys.
Chem. B 1999, 103, 8992.
(23) (a) Kuroda, Y.; Ito, M.; Sera, T.; Ogoshi, H. J. Am. Chem. Soc.
1993, 115, 7003. (b) Acquavella, M. F.; Evans, M. E.; Farraher, S. W.;
Nevoret, C. J.; Abelt, C. J. J. Chem. Soc., Perkin Trans. 2 1995, 385. (c)
Hubbard, B. K.; Beilstein, L. A.; Heath, C. E.; Abelt, C. J. J. Chem. Soc.,
Perkin Trans. 2 1996, 10.
(4) Gelb, R. I.; Schwartz, L. M.; Laufer, D. A. J. Chem. Soc., Perkin
Trans. 2 1984, 15.
(5) (a) R u¨ diger, V.; Eliseev, A.; Simova, S.; Schneider, H.-J.; Blan-
damer, M. J.; Cullis, P. M.; Meyer, A. J. J. Chem. Soc., Perkin Trans. 2
(24) To avoid the complications from the dynamic quenching, the data
taken at [Viologen] e 1.0 mM were used for fitting.
(25) Yonemoto, E. H.; Saupe, G. B.; Schmehl, R. H.; Hubig, S. M.;
Riley, R. L.; Iverson, B. L.; Mallouk, T. E. J. Am. Chem. Soc. 1994, 116,
4786.
1
1
996, 2119. (b) McAlpine, S. R.; Garcia-Garibay, M. A. J. Org. Chem.
996, 61, 8307.
(
6) (a) Kodaka, M.; Fukaya, T. Bull. Chem. Soc. Jpn. 1986, 59, 2032.
(
(
2
(
b) Kodaka, M.; Fukaya, T. Bull. Chem. Soc. Jpn. 1989, 62, 1154.
+
(
7) Kodaka, M. J. Am. Chem. Soc. 1993, 115, 3702.
(26) The binding constant of AdaNH3 with the â-CD-NS monomer
4
-1
(8) (a) Kodaka, M.; Fukaya, T. Bull. Chem. Soc. Jpn. 1975, 48, 375.
was determined as 1.0 × 10 M from fluorescence titration of a â-CD-
NS solution with the guest. The fraction of â-CD-NS present as the â-CD-
b) Shimizu, H.; Katto, A.; Hatano, M. Bull. Chem. Soc. Jpn. 1979, 52,
678. (c) Krois, D.; Brinker, U. H. J. Am. Chem. Soc. 1998, 120, 11627.
d) Kodaka, M. J. Phys. Chem. A 1998, 102, 8101. (e) Zhang, X.; Nau, W.
+
NS/AdaNH3 complex is calculated to be 0.998 in the solution of 5.0 ×
-
4
-2
+
10 M â-CD-NS and 5.0 × 10 M AdaNH3 .
M. Angew. Chem., Int. Ed. 2000, 39, 544. (g) Bobek, M. M.; Krois, D.;
Brinker, U. H. Org. Lett. 2000, 2, 1999. (h) Mayer, B.; Zhang, X. Y.; Nau,
W. M.; Marconi, G. J. Am. Chem. Soc. 2001, 123, 5240.
(27) (a) Hwang, H. J.; Lee, S. K.; Lee, S.; Park, J. W. J. Chem. Soc.,
Perkin Trans. 2 1999, 1081. (b) Hwang, H. J.; Lee, S.; Park, J. W. Bull.
Korean Chem. Soc. 2000, 21, 245.
(
9) Lipkowitz, K. B. Chem. ReV. 1998, 98, 1829 and references therein.
(28) (a) Davies, D. M.; Savage, J. R. J. Chem. Res. (S) 1993, 94; J.
Chem. Res. (M), 1993, 660. (b) Davies, D. M.; Deary, M. E. J. Chem. Soc.,
Perkin Trans. 2 1995, 1287. (c) Davies, D. M.; Deary, M. E.; Wealleans,
D. I. J. Chem. Soc., Perkin Trans. 2 1998, 193.
(
(
10) Liu, L.; Guo, Q.-X. J. Phys. Chem. B 1999, 103, 3461.
11) Rekharsky, M. V.; Inoue, Y. Chem. ReV. 1998, 98, 1875 and
references therein.