Self-inclusion behavior and circular dichroism of aliphatic chain-linked β-cyclodextrin-viologen compounds and their reduced forms depending on the side of modification

Article abstract of DOI:10.1021/jo0515834

The self-inclusion behavior and induced circular dichroism (ICD) characteristics of two β-cyclodextrin (β-CD) derivatives, in which a 1-methyl-4,4′-bipyridinium (viologen) group is connected by an octamethylene chain to either the primary (2²⁺) or secondary (3 ²⁺) side of β-CD, and of their reduced forms, are investigated. ¹H NMR studies showed that 2²⁺ forms an intramolecular self-inclusion complex with K_in = 3.1 ± 0.4, whereas 3 ²⁺ forms a head-to-head type of dimer with K_D = 65 ± 10 M^-1 at 25 °C. 2²⁺ and 3²⁺ form [2]pseudorotaxanes with α-CD, with the secondary side of the α-CD facing the viologen moiety. The ICD characteristics of mono-6-[4-(1-methyl-4- pyridinio)-1-pyridinio]-β-CD (1²⁺), 2²⁺, 3 ²⁺, and methyloctyl viologen-β-CD complexes were obtained for the oxidized and reduced states of the viologen units. The results indicated dimer formation for 1°, and intramolecular complexation for 2^.+ and 2° in which the reduced viologen units are outside the β-CD cavity. The results also indicated intramolecular complexation for 3^.+ and 3°, but with reduced viologen units inside the cavity. This work provides unequivocal evidence of the preference of the secondary side of cyclodextrins for viologen groups, regardless of their oxidation states, and the dependence of ICD of the viologen chromophores on their location with respect to the CD cavity.

Full text of DOI:10.1021/jo0515834

Self-Inclusion Behavior and Circular Dichroism of Aliphatic
Chain-Linked â-Cyclodextrin-Viologen Compounds and Their
Reduced Forms Depending on the Side of Modification
,†
†,§
†
‡
Joon Woo Park,* Soo Yeon Lee, Hyun Jung Song, and Kwanghee Koh Park
Department of Chemistry, Ewha Womans University, Seoul 120-750, Korea, and Department of
Chemistry, Chungnam National University, Daejeon 305-764, Korea
jwpark@ewha.ac.kr
Received July 29, 2005
The self-inclusion behavior and induced circular dichroism (ICD) characteristics of two â-cyclodextrin
(
â-CD) derivatives, in which a 1-methyl-4,4′-bipyridinium (viologen) group is connected by an
2+
2+
octamethylene chain to either the primary (2 ) or secondary (3 ) side of â-CD, and of their reduced
1
2+
forms, are investigated. H NMR studies showed that 2 forms an intramolecular self-inclusion
2+
complex with Kin ) 3.1 ( 0.4, whereas 3 forms a head-to-head type of dimer with K
D
) 65 ( 10
at 25 °C. 2 and 3 form [2]pseudorotaxanes with R-CD, with the secondary side of the R-CD
facing the viologen moiety. The ICD characteristics of mono-6-[4-(1-methyl-4-pyridinio)-1-pyridinio]-
-
1
2+
2+
M
2+
2+
2+
â-CD (1 ), 2 , 3 , and methyloctyl viologen-â-CD complexes were obtained for the oxidized and
reduced states of the viologen units. The results indicated dimer formation for 1°, and intramolecular
complexation for 2 and 2° in which the reduced viologen units are outside the â-CD cavity. The
results also indicated intramolecular complexation for 3 and 3°, but with reduced viologen units
inside the cavity. This work provides unequivocal evidence of the preference of the secondary side
of cyclodextrins for viologen groups, regardless of their oxidation states, and the dependence of
ICD of the viologen chromophores on their location with respect to the CD cavity.
•
+
•
+
Introduction
CD derivatives with a suitable pendant group can form
3
-8
self-included complexes intramolecularly
or inter-
molecularly.9
-13
It was shown that CD derivatives with
Cyclodextrins (CDs) are important hosts in supramo-
lecular chemistry, and have been widely used in various
fields of basic research and industries.1 CDs can be
modified at either the narrower primary hydroxyl side
the same pendant group but on different sides sometimes
7
exhibit quite contrasting self-inclusion, guest-binding
2
or the wider secondary hydroxyl side of the cavities. The
(
2) (a) Khan, A. R.; Forgo, P.; Stine, K. J.; D’Souza, V. T. Chem.
Rev. 1998, 98, 1977. (b) Tian, S. P.; Zhu, H. H.; Forgo, P.; D’Souza, V.
T. J. Org. Chem. 2000, 65, 2624. (c) Engeldinger, E.; Armspach, D.;
Matt, D. Chem. Rev. 2003, 103, 4147.
(3) (a) Ueno, A.; Ikeda, A.; Ikeda, H.; Ikeda, T.; Toda, F. J. Org.
Chem. 1999, 64, 382. (b) Liu, Y.; Li, B.; Wada, T.; Inoue, Y. Supramol.
Chem. 1999, 10, 173. (c) Liu, Y.; You, C. C.; Wada, T.; Inoue, Y. J.
Org. Chem. 1999, 64, 3630.
(4) (a) Liu, Y.; You, C. C.; Kunieda, M.; Nakamura, A.; Wada, T.;
Inoue, Y. Supramol. Chem. 2000, 12, 299. (b) Xie, H. Z.; Wu, S. K.
Supramol. Chem. 2001, 13, 545. (c) Tanabe, T.; Usui, S.; Nakamura,
A.; Ueno, A. J. Inclusion Phenom. Macrocyclic Chem. 2000, 36, 79. (d)
Li, D. B.; Ng, S.-C.; Novak, I. Tetrahedron Lett. 2002, 43, 1871.
*
To whom correspondence should be addressed. Fax: +82-2-3277-
2
384.
†
Ewha Womans University.
Present address: Biomedical Research Institute, Korea Institute
§
of Science and Technology, Seoul 136-791, Korea.
‡
Chungnam National University.
(1) For a compilation of recent research on cyclodextrins, see the
following: (a) Szejtli, J., Osa, T., Eds. Comprehensive Supramolecular
Chemistry; Elsevier: Oxford, U.K., 1996; Vol. 3. (b) D’Souza, V. T.;
Lipkowitz, K. B. Chem. Rev. 1998, 98, 1741.
1
0.1021/jo0515834 CCC: $30.25 © 2005 American Chemical Society
Published on Web 10/06/2005
J. Org. Chem. 2005, 70, 9505-9513
9505

Park et al.
behaviors,7,8,14 or enzyme-like activity.14 It has also been
well-recognized that the orientation of guest molecules
in CD complexes, and thus the selectivity for the side of
the CD cavity in the inclusion of guest molecules, is
important to the physicochemical properties of CD com-
plexes and in designing CD-based supramolecular struc-
and inclusion complexation of viologens with CDs has
been a subject of numerous studies.1
5,17,19-23
â-CD deriva-
tives with covalently linked viologen units exhibit many
interesting inclusion behaviors, depending on the oxida-
tion states of the viologen unit.9
,10,24-28
For the â-CD-
viologen compounds in which the bipyridinium group is
15-17
tures.
A potentially powerful method for determining
2+
directly attached to the primary side of â-CD (1 and
the structures of CD complexes is induced circular
dichroism (ICD), which theoretically relates the sign and
magnitude of the ICD spectrum of a chromophore to the
the analogues having various N-alkyl groups), facile
dimerization of the â-CD-viologens was observed upon
9
10
one-electron or two-electron reduction of the viologen
moiety. In contrast to this, the â-CD-viologens in which
the viologen unit is linked to the secondary face of the
location and orientation of the chromophore with respect
to the CD cavity.1
6-21
However, there is a paucity of
reports showing an ICD spectral change of the same
chromophore, depending on its location in CD com-
2+
â-CD via polymethylene chains (3 and the analogue
with a tetramethylene linkage instead of an octameth-
ylene chain) exhibit little tendency to dimerize upon one-
1
6,17
plexes.
Viologens (N,N′-disubstituted 4,4′-bipyridinium salts)
have been widely used as electron acceptors or mediators
in many photochemical and electrochemical reactions,
26
electron reduction of their viologen moiety, but the two-
2+
electron reduction product of 3 exhibits a much higher
stability against reaction with water than does the two-
2
+
electron reduction product of 1 or dimethyl viologen
2
+ 26,27
(
5) (a) Nielson, M. B.; Nielson, S. B.; Becker, J. Chem. Commun.
998, 475. (b) Dodziuk, H.; Chmurski, K.; Jurczak, J.; Kozminski, W.;
Lukin, O.; Sitkowski, J.; Stefaniak, J. J. Mol. Struct. 2000, 519, 33.
c) Anibarro, M.; Gessler, K.; Uson, I.; Sheldrick, G. M.; Harata, K.;
Uekama, K.; Hirayama, F.; Abe, Y.; Saenger, W. J. Am. Chem. Soc.
001, 123, 11854.
6) (a) Matsumura, S.; Sakamoto, S.; Ueno, A.; Mihara, H. Chem.s
(MV ).
Facile photoinduced electron-transfer reac-
1
2+
2+
tions from excited guest photosensitizers to 1 or 3 via
inclusion complexation were also reported.2
4,28
(
2
(
Eur. J. 2000, 6, 1781. (b) Impellizzeri, G.; Pappelardo, G.; D’Alessandro,
F.; Rizzarelli, E.; Saviano, M.; Iacovino, R.; Benedetti, E.; Pedone, C.
Eur. J. Org. Chem. 2000, 1065. (c) Berthault, P.; Birlirakis, N.
Tetrahedron: Asymmetry 2000, 11, 2463.
(
7) (a) Park, K. K.; Kim, Y. S.; Lee, S. Y.; Song, H. E.; Park, J. W.
J. Chem. Soc., Perkin Trans. 2 2001, 2114. (b) Liu, Y.; You, C.-C.;
Zhang, H.-Y.; Zhao. Y.-L. Eur. J. Org. Chem. 2003, 1415.
(
8) (a) Murakami, T.; Harata, K.; Morimoto, S. Chem. Lett. 1988,
5
53. (b) Suzuki, I.; Obata, K.; Anzai, J.; Ikeda, H.; Ueno, A. J. Chem.
Soc., Perkin Trans. 2 2000, 1705.
(
9) Park, J. W.; Choi, N. H.; Kim, J. H. J. Phys. Chem. 1996, 100,
7
69.
In this work, we studied self-inclusion behavior and
(
10) Mirzoian, A.; Kaifer, A. E. Chem. Commun. 1999, 1603.
11) Park, J. W.; Song, H. E.; Lee, S. Y. J. Phys. Chem. B 2002,
2
+
(
circular dichroism characteristics of â-CD-viologens 2
1
06, 5177.
2+
and 3 and their one- and two-electron-reduced com-
pounds by H NMR and circular dichroism spectroscopic
(12) (a) Park, J. W.; Song, H. E.; Lee, S. Y. J. Org. Chem. 2003, 68,
1
7
071. (b) Gao, X.-M.; Tong, L.-H.; Zhang, Y.-L.; Hao, A.-Y.; Inoue, Y.
Tetrahedron Lett. 1999, 40, 969. (c) Gao, X.-M.; Zhang, Y.-L.; Tong,
L.-H.; Ye, Y.-H.; Ma, X.-Y.; Liu, W.-S.; Inoue, Y. J. Inclusion Phenom.
Macrocyclic Chem. 2001, 39, 77. (d) de Jong, M. R.; Berthault, P.; van
Hoek, A.; Visser, A. J. W. G.; Huskens, J.; Reinhoudt, D. N. Supramol.
Chem. 2002, 14, 143. (e) Lecourt, I.; Mallet, T. M.; Sinay, P. Tetraheron
Lett. 2002, 43, 5533. (f) Petter, R. C.; Salek, J. S.; Sikorski, C. T.;
Kumaravel, G.; Lin, F. T. J. Am. Chem. Soc. 1990, 112, 3860. (g)
Hoshino, T.; Miyauchi, M.; Kawaguchi, Y.; Yamaguchi, H.; Harada,
A. J. Am. Chem. Soc. 2000, 122, 9876. (h) B u¨ gler, J.; Sommerdijk, N.
A. J. M.; Visser, A. J. W. G.; van Hoek, A.; Nolte, R. J. M.; Engbersen,
J. F. J.; Reinhoudt, D. N. J. Am. Chem. Soc. 1999, 121, 28. (i) Liu, Y.;
Zhang, H.-Y.; Diao, C.-H. Org. Lett. 2003, 5, 251.
2+
2+
methods. The compounds 2
and 3
were chosen
because they have similar linkage lengths between the
â-CD skeleton and bipyridinium groups, but the side of
attachment is different. The major points to be addressed
are as follows: (1) difference in the self-inclusion behavior
of 22 and 3 , and their reduced forms; (2) generalization
+
2+
of the previously observed face selectivity of the oxidized
form of viologens in their intermolecular complexation
15,17
with CDs
to the reduced forms of viologen as well as
(
13) (a) Fujimoto, T.; Sakata, Y.; Kaneda, T. Chem. Commun. 2000,
143. (b) Fujimoto, T.; Sakata, Y.; Kaneda, T. Chem. Lett. 2000, 764.
c) Fujimoto, T.; Nakamura, A.; Inoue, Y.; Sakata, Y.; Kaneda, T.
Tetrahedron Lett. 2001, 42, 7987.
14) (a) Breslow, R.; Czarnik, A. W.; Lauer, M.; Leppkes, R.; Winkler,
to intramolecular complexation; (3) ICD characteristics
of the oxidized and reduced viologen chromophores
located in the different positions with respect to the CD
cavity.
2
(
(
J.; Zimmerman, S. J. Am. Chem. Soc. 1986, 108, 1969. (b) D’Souza, V.
T.; Bender, M. L. Acc. Chem. Res. 1987, 20, 146. (c) Breslow, R.; Dong,
S. D. Chem. Rev. 1998, 98, 1997.
(
15) Park, J. W.; Song, H. E.; Lee, S. Y. J. Phys. Chem. B 2002,
06, 7186 and references therein.
16) (a) Bobek, M. M.; Krois, D.; Brinker, U. Org. Lett. 2000, 2, 1999.
(22) (a) Matsue, T.; Kato, T.; Akiba, U.; Osa, T. Chem. Lett. 1985,
1825. (b) Mirzoian, A.; Kaifer, A. E. Chem.sEur. J. 1997, 3, 1052.
(23) (a) Diaz, A.; Quintela, P. A.; Schuette, J. M.; Kaifer, A. E. J.
Phys. Chem. 1988, 92, 3537. (b) Lee, C.; Kim, C.; Park, J. W. J.
Electroanal. Chem. 1994, 374, 115. (c) Lee, C.; Moon, M. S.; Park, J.
W. J. Electroanal. Chem. 1996, 407, 161.
1
(
(
b) Allenmark, S. Chirality 2003, 15, 409. (c) Zhang, X.; Nau, W. M.
Angew. Chem., Int. Ed. 2000, 39, 544. (d) Bakirci, H.; Zhang, X.; Nau,
W. M. J. Org. Chem. 2005, 70, 39.
(
17) Park, J. W.; Song, H. J. Org. Lett. 2004, 6, 4869.
(24) Du, Y.-q.; Nakamura, A.; Toda, F. Bull. Chem. Soc. Jpn. 1990,
63, 3351.
(
18) (a) Harata, K.; Uedaira, H. Bull. Chem. Soc. Jpn. 1975, 48, 375.
(
b) Shimizu, H.; Kaito, A.; Hatano, M. Bull. Chem. Soc. Jpn. 1979, 52,
(25) Du, Y.-q.; Harada, T.; Nakamura, A.; Ueno, A.; Toda, F. Chem.
Lett. 1990, 2235.
2
678. (c) Shimizu, H.; Kaito, A.; Hatano, M. Bull. Chem. Soc. Jpn. 1981,
5
4, 513.
(
(26) Park, K. K.; Han, S. Y.; Park, Y.-H.; Park, J. W. Tetrahedron
Lett. 1997, 38, 4231.
19) (a) Kodaka, M.; Fukaya, T. Bull. Chem. Soc. Jpn. 1986, 59,
2
(
032. (b) Kodaka, M.; Fukaya, T. Bull. Chem. Soc. Jpn. 1989, 62, 1154.
(27) Park, J. W.; Kim, J. H.; Hwang, B. K.; Park, K. K. Chem. Lett.
1994, 2075.
c) Kodaka, M. J. Phys. Chem. 1991, 95, 2110.
(
(
20) Kodaka, M. J. Am. Chem. Soc. 1993, 115, 3702.
21) Kodaka, M. J. Phys. Chem. A 1998, 102, 8101.
(28) Park, J. W.; Park, S. H.; Lee, B. A.; Lee, S. Y. Chem. Lett. 1997,
1043.
9506 J. Org. Chem., Vol. 70, No. 23, 2005

Self-Inclusion Complexation of â-CD-Viologens
spectrum on concentration, the self-inclusion complex-
ation of 22 should be intramolecular.
+
The assignments of the NMR signals to the nonin-
cluded species and the self-inclusion complex are easily
made from the effect of AdaCl on the spectra. The
resonance signals that decrease upon the addition of
AdaCl are assigned to those from the complexed species,
whereas signals increased by the presence of AdaCl are
assigned to those from the nonincluded species. No
appreciable difference was observed between chemical
shifts of the bipyridinium and aliphatic-linkage protons
+
of the nonincluded species and those of its Ada complex.
Microscopically, the intramolecular self-included complex
of 22 (sic-2 ) is in equilibrium with the nonincluded
+
2+
2+
2+
open form (ni-2 ), and only the ni-2 is in direct
equilibrium with Ada, as expressed in eqs 1 and 2,
however Ada binding shifts the self-inclusion complex-
+
ation equilibrium of eq 1 to the left.
2
+
2+
2+
2+
ni-2 / sic-2 ; K ) [sic-2 ]/[ni-2 ]
(1)
in
2
+
+
+
2+
ni-2 + Ada / Ada -2 ; K
)
ADA
2+
+
+
2+
[Ada -2 ]/([Ada ][ni-2 ]) (2)
1
V2+ (22+):
FIGURE 1. H NMR (D
2
O) spectra of â-CD-6-N-C
8
-
3
2+
-3
2+
-3
(
A) 4.0 × 10 M 2 , (B) 0.8 × 10 M 2 , (C) 0.8 × 10
M
From the integration ratios of the resonance signals
of the spectra taken in the absence of AdaCl, the
2+
-3
-3
2+
-3
2
+ 1.0 × 10 M AdaCl, (D) 0.8 × 10 M 2 + 3.6 × 10
+
M AdaCl. Peaks from the Ada ion are marked as ‘x’. Primed
2
+
intramolecular complexation constant (Kin) of 2 was
determined to be 3.1 ( 0.4: the average values of the
integration ratios of a to a′, b to b′, and θ to θ′ protons
were used for the calculation. From the NMR integration
data, the apparent intramolecular complexation con-
stants (Kin,app) of 2 in the presence of AdaCl were found
to be 0.66 ( 0.06 when the initial concentration of AdaCl
(
′) peaks are those from the included complex.
Results and Discussion
The synthesis of the dichloride salt of 32+ has been
described in a previous paper.26 The compound 2 ‚2Cl
2+
-
2+
is synthesized and fully characterized in this work. First,
1
2+
2+
+
-3
+
we present H NMR spectra of 2 and 3 , and discuss
the self-inclusion behavior of the â-CD-viologen com-
([Ada ]
o
) is 1.0 × 10 M, and 0.17 ( 0.01 at [Ada ]
o
)
-
3
+
3.6 × 10 M. This gave the binding constant of Ada
2
+
2+
-1 30
pounds. Next, we show the ICD characteristics of 1 -
with ni-2 (KADA) as 6500 ( 700 M . The KADA value
2
+
2+
3
and their reduced forms, and relate them to the
of 2 is smaller than the reported binding constant of
+
-1 29
structures of the self-included complexes and ICD rules
Ada with native â-CD, 8900 ( 1000 M , presumably
+
2+
of CD complexes derived theoretically.
due to electrostatic interaction in the Ada -2 complex.
The bipyridinium dication is too hydrophilic to be
included inside the â-CD cavity.21 The aliphatic spacer
between the â-CD skeleton and the bipyridinium unit of
1
H NMR Study of Mono-6-deoxy-6-N-[4-(1-methyl-
4
-pyridinio)-1-pyridiniooctyl]amino-â-CD (â-CD-6-
N-C
spectra of 2 in the absence and presence of 1-adaman-
tylammonium chloride (AdaCl). The spectra taken in the
absence of AdaCl (spectra A and B) show more than four
resonance signals in the bipyridinium proton resonance
region. This suggests the presence of more than one
2
+
2+
1
8
V
: 2 ). Figure 1 shows the partial H NMR
2
+
2+
2+
2
as well as 3 is long enough to traverse the CD
cavity. This was shown as cross-peaks between â-CD
protons and aliphatic-linkage protons in a two-dimen-
sional ROESY spectrum (see Supporting Information).
Thus it would be safe to conclude that the bipyridinium
1
2+
chemical species with a slow exchange rate on the H
group of 2 is outside the secondary side of the â-CD
1
NMR time scale. No significant variation of the H NMR
cavity in the intramolecular self-inclusion complex.
2+
1
spectra of 2 with its concentration was found, indicating
H NMR Study of Mono-2-O-[4-(1-methyl-4-pyri-
2+
2+
2+
little tendency of intermolecular association of 2 . The
8
dinio)-1-pyridinio]octyl-â-CD (â-CD-2-O-C V : 3 ).
1
2+
Figure 2 shows the 1H NMR spectra of 3 . At high
2+
presence of AdaCl changes the H NMR spectrum of 2
in the resonance region of bipyridinium protons as well
as in the aliphatic linkage proton regions. As the Ada+
ion has a large binding affinity for the â-CD cavity and
replaces the self-included appended groups from the
concentration, the spectra also show more than four
2+
peaks in the bipyridinium region as in the case of 2 .
2+
2+
However, in contrast to 2 , the spectrum of 3 exhibits
2
+
a large concentration dependence. The spectrum of 3
2
9
cavity, these results indicate the self-inclusion com-
taken at 0.85 mM (spectrum C) is almost identical to that
2
+
2+
plexation of 2 and disruption of the complexation by
of 2 in the presence of a high concentration of AdaCl
+
Ada ion. As intermolecular self-inclusion is ruled out
1
(30) As ni-22+ and the Ada
+
-22+ complex cannot be differentiated
because of the lack of dependence of the H NMR
2+
from the NMR spectra, Kin,app is expressed as Kin,app ) [sic-2 ]/{[ni-
2
+
+
2+
2
] + [Ada -2 ]} and is related to Kin and the concentration of
+ + +
(
29) (a) Gelb, R. I.; Schwartz, L. M.; Laufer, D. A. J. Chem. Soc.,
uncomplexed Ada ([Ada ]) by Kin,app ) Kin/(1 + KADA[Ada ]). Combina-
tion of the mass balance for 2 and the definition of equilibrium
+ + 2+
2+
Perkin Trans. 2 1984, 15. (b) Gelb, R. I.; Schwartz, L. M. J. Inclusion
Phenom. Mol. Recognit. Chem. 1989, 7, 538.
o o
constants gives [Ada ] ) [Ada ] - [2 ] (Kin - Kin,app)/{Kin(1 + Kin,app)}.
J. Org. Chem, Vol. 70, No. 23, 2005 9507

Park et al.
NMR signals of the included species. Thus we can
conclude that 32 mostly forms the HH dimer. Such HH
dimers are stabilized by mutual inclusion of the pendant
+
9
-13
groups into the CD cavities of counter molecules.
The
2+
dimerization equilibrium of 3 is expressed in eq 3,
where (3 ) represents the HH dimer. The ratios of
2
monomer to dimer of 3 were calculated from the
average value of NMR integration ratios of a to a′, b to
2+
2+
2
+
b′, and η to η′ protons for each concentration of 3 . The
) of 32 was obtained from the
+
dimerization constant (K
concentration dependence of the ratio, and was found to
D
-
1
be 65 ( 10 M .
2
+
2+
2+
2+ 2
2
ni-3 / (3 ) ; K ) [(3 ) ]/[ni-3 ]
(3)
2
D
2
General Aspects of Induced Circular Dichroism
of CD Complexes and CD Derivatives. Induced
circular dichroism (ICD) has been widely used for studies
of inclusion complexation of guest molecules with CDs
and structures of the CD complexes or CD deriva-
tives.6
,7,12,15-21
The structural features are usually de-
duced from ICD spectra using the rules derived for ICD
of chiral supramolecular systems, which were initially
1
V2+ (32+):
FIGURE 2. H NMR (D
2
O) spectra of â-CD-2-O-C
8
18,19
derived for CD complexes
and then generalized for
-
3
2+
-3
2+
-3
(
A) 14 × 10 M 3 , (B) 3.4 × 10 M 3 , (C) 0.85 × 10
M
complexes of chiral macrocycles.2 The rules predict the
following: (1) the sign of ICD is positive for a transition
polarized parallel to the axis of macrocyclic host, and
negative for that polarized perpendicular to the axis; (2)
the sign of ICD is reversed when a chromophore moves
from the inside of the host cavity to the outside, and the
direction of the transition moment is not changed; (3) the
absolute value of ICD is greater when a chromophore
exists on the outside of the narrower rim than when it
exists on the outside of the wider rim; (4) the ICD value
of a transition polarized perpendicularly to the axis of a
macrocycle is -1/2 of that of a parallelly polarized one,
and the sign of the ICD changes at 54.7 °C. The rules
were also found to be useful for conformational analysis
0,21
2+
-3
2+
-3
3
, (D) 0.85 × 10 M 3 + 4.9 × 10 M AdaCl. Notations of
protons and marks are the same as those in Figure 1.
(
Figure 1D), and the spectrum changes little with the
presence of AdaCl (Figure 2D). These results clearly
suggest that 32+ forms the intermolecular self-inclusion
complex. The peaks that increase in intensity by lowering
the concentration of 32 are assigned to those from the
+
2+
nonincluded form (ni-3 ), and those that decrease in
intensity by lowering the concentration are from the
intermolecularly self-included complex of 3 .
For intermolecular association of 3 , dimerization is
the first step. Both head-to-tail (HT) and head-to-head
HH) arrangements of the â-CD moiety are possible in
2+
2+
(
of CD derivatives with covalently bonded chromo-
the dimer. In the HT dimer, the aliphatic linkage of a
molecule traverses the CD cavity of its counter molecule,
placing its own bipyridinium group in proximity to the
bipyridinium group of the counter molecule. A stronger
association beyond dimerization is not feasible, as the
protruding group would interfere with the inclusion of
the nonincluded pendant group of the dimer into the CD
cavity of another molecule to form a trimer. The bipyri-
dinium moiety of the nonincluded pendant in the HT
dimer would be far from the CD cavity, and is expected
to show a resonance similar to that of the ni-3 . Thus,
if the intermolecularly self-included complex is mostly
the HT dimer, the peak intensities of protons of the
included pendant group cannot be larger than those of
the corresponding protons of the nonincluded pendant
group. Spectrum A in Figure 2 clearly indicates that this
phores.6
,7,15,21
The major transition of viologens is a π-π*
32
transition that is polarized along the long axis of the
viologen.1
5,19,20
Circular Dichroism of Oxidized Forms of â-CD-
Viologens. Figure 3 shows ICD spectra of â-CD-
2+
2+
viologens 1 -3 in aqueous solution. In all cases,
negative Cotton effects are observed around 255 nm,
corresponding to the absorption band of the viologen
moiety. This indicates that the bipyridinium chro-
mophores are present outside the â-CD cavity, and that
the angle between the axes of CD and viologen is less
than 54.7°. No appreciable concentration dependence of
2+
2
+
the apparent molar ellipticities [θ]app was found for 1
2+
2+
and 2 , whereas the magnitude of [θ]app of 3 became
greater as the concentration was increased. The [θ]app
versus concentration profiles of 2 , 3 , and the one-
electron reduction product of 3 , 3 , are shown in Figure
2+
2+
2
+
is not the case for 3 , and suggests that the major
dimeric species of 3 is not the HT type. In case of the
HH dimer of 3 , the pendant groups of both molecules
are included, placing the bipyridinium groups on the
primary side of the counter molecules and showing the
2+
•+
2+
31
4
.
2
+
2+
To confirm the intramolecular self-inclusion of 2 and
obtain ICD characteristics of the sic-22 and ni-2
+
2+
2
+
species, we recorded the ICD spectra of 2 in the
presence of various concentrations of AdaCl (Figure 5).
As the concentration of AdaCl becomes greater, the
(
31) At high concentrations of 32+, weak peaks are observed at 9.23
and 8.76 ppm. Absence of the peaks at low concentration and the
2
+
similarity of the position of these peaks to those of the sic-2 suggest
that these might be from the HT dimer existing as a minor species.
(32) Braterman, P. S.; Song, J.-I. J. Org. Chem. 1991, 56, 4678.
9508 J. Org. Chem., Vol. 70, No. 23, 2005

Self-Inclusion Complexation of â-CD-Viologens
+
(
K
ADA,app) of Ada with the â-CD-viologen by eq 4.
+
[
θ]app ) ([θ] + [θ] K
[Ada ])/
o
c
ADA,app
+
(
1 + KADA,app[Ada ]) (4)
2
+
o
where [θ] is the apparent molar ellipticity of 2 in the
2
-1
absence of AdaCl, -2200 ( 100 deg cm dmol ; [θ]
c
is
complex. The
ADA,app is related to Kin and KADA, defined in eqs 1 and
+
2+
the molar ellipticity of the Ada -2
K
2
2+
+
, by eq 5; [2 ] denotes the concentration of Ada -
2+
2+
2+
unbound 2 , which is [sic-2 ] + [ni-2 ].
+
2+
+
2+
KADA,app ) [Ada -2 ]/([Ada ][2 ]) )
KADA/(1 + K ) (5)
in
-4
FIGURE 3. Circular dichroism spectra of 1.0 × 10 M â-CD-
The nonlinear least-squares fitting of the ICD titration
data of 2 with AdaCl shown in Figure 5 gave a KADA,app
2
+
2+
viologens 1 -3
.
2+
-
1
value of 1600 ( 200 M and a [θ] value of -300 ( 100
c
deg cm2 dmol . Using the Kin value of 3.1 ( 0.4
obtained from NMR measurements, the KADA value for
-1 33
2
+
-1
2
is estimated to be 6600 ( 1500 M . This agrees with
-
1
the value of 6500 ( 700 M obtained from NMR data.
value of 22 can be given as the sum of the
o
+
The [θ]
contributions from sic-2 ([θ]sic) and ni-2 ([θ]ni) by eq
; fsic denotes the fraction of the self-included complex
and is calculated to be 0.75 ( 0.03 from Kin ) 3.1 ( 0.4.
2
+
2+
6
[
θ] ) [θ] fsic + (1 - f )[θ] (6)
o
sic
sic
ni
Because the relative orientation and position of the
bipyridinium group with respect to the â-CD unit would
be similar in ni-22 and the Ada -2 complex, the ICD
+
+
2+
characteristics of both species might also be similar.
2
-1
Using [θ]
c
) -300 ( 100 deg cm dmol for [θ]ni, the
FIGURE 4. Concentration dependences of apparent molar
2+
[
θ]sic value of 2 is calculated to be -2800 ( 300 deg
2
+
2+
ellipticity of 2 (b) and 3 (O) at 255 nm. Inset shows the
2
-1
cm dmol from eq 6, using the observed value of [θ] )
o
•
+
concentration dependence of molar ellipticity of 3 at 398 nm
in the absence (∆) and presence (2) of 1.0 × 10 M AdaCl.
2
-1
-
3
-2200 ( 100 cm dmol and fsic ) 0.75 ( 0.03. The [θ]sic
value is similar to that for the â-CD complex of methyl-
2+
2
-1 15
octyl viologen (C
1 8
C V ), -2000 ( 100 deg cm dmol .
However, it is much smaller than the molar ellipticity of
2+
2
-1
1
, -8500 ( 200 deg cm dmol , in which the bipyri-
dinium moiety is present above the primary face of the
â-CD. As the bipyridinium moiety of 22 in the self-
included complex should be above the secondary face of
â-CD, the present result supports the conclusion that the
+
2
+
1 8
bipyridinium unit of the C C V -â-CD complex is
15
mostly above the secondary side of CDs, rather than
1
9,20
above the primary side as claimed by Kodata.
2+
The concentration dependence of the ICD of 3 (Figure
4
3
) agrees well with the finding from the NMR study that
2+
forms an intermolecular self-inclusion complex. The
+
[
(
θ]app of 32 is the sum of contributions from monomeric
M) and dimeric (D) species, and is given in eq 7.
FIGURE 5. Dependence of the circular dichroic spectrum of
[θ]app ) [θ] f + [θ] (1 - f ); f )
D D M D D
-4
2+
1
.0 × 10 M 2 on the concentration of AdaCl. Concentrations
2
+
1/2
2+
-3 -3 -3
{(8K [3 ] + 1) - 1}/4K [3 ] (7)
D o D o
of AdaCl are 0.00, 0.20 × 10 , 0.50 × 10 , 1.0 × 10 , 2.0 ×
-3
-3
10
, and 5.0 × 10 M (from bottom to top).
D M
where f and
is the fraction of 32 in dimeric form; [θ]
+
magnitude of the ICD band of 22+ becomes smaller. This
suggests that the ICD band of 22 is mainly due to self-
inclusion complexation. As [θ]app is the weight average
of the contributions from the existing species, the [θ]app
+
(33) For the fitting, we first assumed [Ada+]
calculated the trial parameters, KADA,app and [θ] . [Ada ]’s were then
- [θ]app)/([θ] - [θ] )} for
+
o
) [Ada ], and
+
c
+
+
2+
corrected by [Ada ] ) [Ada ]
o
- [2
]
o
{([θ]
o
o
c
each piece of data, and we again calculated the parameters. This
process was repeated until we obtained consistent fitted parameters.
+
is related to [Ada ] and the apparent binding constant
J. Org. Chem, Vol. 70, No. 23, 2005 9509

Park et al.
ellipticity of the 3 -R-CD [2]pseudorotaxane is very
2+
2
+
close to that of the self-included complex of 2 . This
might be due to combination of two factors. One is that
the parent â-CD moiety is too far from the bipyridinium
chromophore in the [2]pseudorotaxane to contribute to
the ICD signals significantly. This is well supported by
the small ellipticity of the nonincluded forms and the
+
Ada complex (vide supra). The other is that the bipyri-
2+
dinium group in the 3 -R-CD [2]pseudorotaxane is
adjacent to the secondary face of the R-CD, and R-CD and
â-CD would induce similar circular dichroism in the
viologen chromophore. To check the latter, we performed
-
4
2+
an ICD titration of 1.00 × 10 M C
1
C
C V
8
8
V
with R-CD
with R-CD
2+
and found the binding constant of C
1
and the molar ellipticity of the complex to be 3300 ( 300
-
1
2
-1
M
and -1920 ( 40 deg cm dmol , respectively. The
FIGURE 6. Effect of R-CD on the circular dichroism spectrum
corresponding values for the â-CD complex were reported
-
4
2+
of 1.0 × 10 M 3 . Concentrations of R-CD are 0.00, 2.0 ×
-
1
2
-1 15
as 890 ( 60 M and -2000 ( 100 deg cm dmol
.
-
3
-3
-3
-3
-3
10
, 5.0 × 10 , 10 × 10 , 20 × 10 , and 50 × 10 M (from
-4 2+
This indicates that R-CD and â-CD complexes of the
viologen show essentially the same ICD, though the
stability of the R-CD complex is greater.
top to bottom). Inset shows the spectra of 1.0 × 10 M 2 in
-3
the absence (solid line) and presence (dashed line) of 50 × 10
M R-CD.
2
+
The effect of R-CD on the ICD spectrum of 2 is much
2
+
2+
[
θ]
D
are the molar ellipticities (per viologen unit) of the
less pronounced than that of 3 . The spectrum of 2
monomeric and dimeric forms, respectively. The nonlin-
continues to grow even above 20 mM R-CD, whereas it
2+
2+
ear least-squares fitting of the [θ]app versus [3 ]
o
profile
virtually levels off in the case of 3 . The sluggish
-
1
2+
to eq 7 gave K
D
) 80 ( 30 M , [θ]
cm dmol , and [θ] ) -40 ( 30 deg cm dmol
there is a relatively large uncertainty in the fitted K
value, it is in fair agreement with that obtained from the
D
) -4600 ( 700 deg
dependence of [θ] of 2 on the concentration of R-CD
2
-1
2
-1
M
.
Though
reflects the smaller apparent binding constant of R-CD
with 22 due to the intramolecular self-inclusion of the
+
D
pendant group. The [θ]
value of 22 was -2900 deg cm
+
2
c
-
1
-1
NMR results, 65 ( 10 M .
dmol in the presence of 50 mM R-CD, which is similar
It is noted that the monomeric form of 32 shows a
+
2+
2+
to that of sic-2 . This strongly implies that sic-2 and
2+
negligibly small ellipticity. This can be taken as evidence
that the 3 monomer has little tendency toward in-
tramolecular self-inclusion complexation, as suggested
2 -R-CD [2]pseudorotaxane have very similar ICD
2
+
characteristics, and that the secondary face of the ring
2
+
R-CD is oriented toward the viologen unit in the 2 -R-
CD [2]pseudororaxane as it is in the 3 -R-CD [2]-
1
2+
from the H NMR results. Also, the small ICD ellipticity
2+
2+
values of ni-2 and ni-3 suggest that the bipyridinium
chromophores of these species are too far from the â-CD
skeleton to feel the chiral environment significantly. The
bipyridinium moieties of (3 )
of the â-CD, and exhibit much larger ellipticity values
than that of sic-2 , in which the bipyridinium moiety is
placed above the secondary face. This is also in good
agreement with the theoretical prediction
pseudorotaxane.
2+
The equilibria of the self-inclusion complexation of 2
and 32 and their [2]pseudorotaxane formation with
R-CD, together with the molar ellipticitity data, are
summarized in Scheme 1.
+
2+
2
are above the primary face
2
+
Circular Dichroism of One-Electron-Reduced
â-CD-Viologens. Irradiation of a deaerated aqueous
19,20
2+
that the CD
solution of viologen in the presence of Ru(bpy)
3
and
complex having a chromophore above the primary face
exhibits a much larger ellipticity than that having the
chromophore above the secondary face of the CD cavity.
EDTA at pH 10 reduces the viologen dication to the
viologen radical cation, which is stable in the absence of
33
9
-5
oxygen. The photosensitized reduction of 3.2 × 10
M
2
+
2+
2+
2+
•+
•+
Formation of [2]Pseudorotaxanes of 2 and 3
â-CD-viologens 1 -3 to radical cations 1 -3 was
achieved, and UV-vis and ICD spectra were taken at
various irradiation times. In all cases, no significant
dependence of the shape and the molar ellipticities of the
ICD spectra on the concentration of the viologen radical
with r-CD. The â-CD-viologens 22+ and 3 can form
2]pseudorotaxanes with R-CD, in which the R-CD ring
is stationed on the octamethylene linkages. To further
2+
[
2+
confirm the different self-inclusion behaviors of 2 and
2
+
•+
3
and examine the orientation of R-CD in the [2]-
cations (see inset of Figure 4 for 3 ) was observed; the
pseudorotaxanes, we studied the complexation behaviors
concentrations of the viologen radical cations were cal-
2
+
2+
-1
of 2 and 3 with R-CD. Figure 6 shows the circular
dichroism titration results. The ICD signals of â-CD-
viologens become more intense as the concentration of
R-CD increases. This reflects inclusion of the aliphatic
spacers of the â-CD-viologens into the R-CD cavity,
forming [2]pseudorotaxanes.
culated from absorption data using ꢀ602 ) 13 700 M
-
1 9
•+
•+
cm . Figure 7 shows the ICD spectra of 1 -3 .
It is known that the viologen radical cations form a
dimer by stacking interaction, for which the absorption
spectrum is distinctly different from that of the
monomer.9
,23b,c
The shape of the ICD spectra of the radical
The titration data of 32 were fitted to eq 4 after
+
cations 1 -3 in Figure 7 is virtually the same as that
of the absorption spectrum of the monomeric form. This
can be explained by the relatively small dimerization
•+
•+
+
substituting [R-CD] for [Ada ], and gave the apparent
binding constant of R-CD with 32 and the [θ]
+
value of
c
-1
•+
•+
the [2]pseudorotaxane as 160 ( 30 M and -2800 ( 200
constants: the dimerization constants of 1 and 3 via
the stacking interaction were reported as 500 and 750
2
-1
deg cm dmol , respectively. Interestingly, the molar
9510 J. Org. Chem., Vol. 70, No. 23, 2005

Self-Inclusion Complexation of â-CD-Viologens
SCHEME 1. Self-Inclusion Complexation, [2]Pseudorotaxane Formation with r-CD, and Molar
2
+
2+ a
Ellipticities, [θ], of 2 and 3
a
θ]’s are taken at 255 nm and given in deg cm2 dmol-1 units. 12+, for which [θ] is -8500 deg cm2 dmol-1, does not form either a
[
self-inclusion complex or [2]pseudorotaxane with R-CD.
along the long axis of viologen. Thus it appears that the
•
+
•+
V
2
unit of 3 is inside the â-CD cavity, whereas that of
•
+
•+
•+
is outside the cavity. For 1 , the inclusion of the V
group into its â-CD cavity is not feasible sterically, and
thus the V group should be outside of the primary face
•
+
of the â-CD cavity. The large negative Cotton effect of
•
+
•+
•+
1
suggests that the long axis of V of 1 is almost
parallel to the â-CD axis.
•
+
1 8
We also took the ICD spectrum of the C C V -â-CD
complex, which was obtained from the photosensitized
reduction of C
â-CD. The spectral shape and molar ellipticity of the
2+
-2
1
C
8
V
in the presence of 1.0 × 10
M
•
+
C C V -â-CD complex were almost indistinguishable
1 8
•
+
•+
from those of 2 . This suggests that the V moiety in
•
+
the â-CD-C
1
C
8
V
complex is also located above the
secondary rim of â-CD. The order of magnitude of the
•
+
•+
•+
FIGURE 7. Circular dichroism spectra of 3.0 × 10 M 1e--
-
5
ICD ellipticities is 3 > 1 . 2 . This agrees with the
prediction from theoretical calculations that the order of
magnitude of the ICD ellipticities for a given transition
is (inside CD cavity) > (above the primary face) > (above
the secondary face).1
•
+
•+
reduced â-CD-viologens 1 -3 . Inset shows the spectrum
•
+
-3
of 3 in the presence of 50 × 10 M R-CD.
-
1
9,26
M , respectively,
which predicts that the fraction of
9,20
monomeric forms would be greater than 0.97 under the
present experimental conditions. The presence of AdaCl
resulted in a decrease in the intensity of the ICD bands
We also investigated the effect of R-CD on the ICD
•
+
•+
spectrum of 3 . The positive ICD signal of 3 was
decreased by the presence of R-CD, and became negative
•
+
•+
•+
of 2 and 3 (see inset of Figure 4 for 3 ), and no
•+
+
-3
and similar to that of 2 at a high concentration of R-CD
appreciable ICD band was seen at [Ada ]
o
> 15 × 10
(
[
see the inset of Figure 7). This reflects the formation of
M, although the absorption spectra indicated the forma-
tion of viologen radical cations. This and the lack of
•
+
2]pseudorotaxane between R-CD and 3 , and indicates
•
+
dependence of the ICD characteristics of 2•+ and 3 on
•+
that the V moiety is outside the CD cavity in the [2]-
•
+
•
+
pseudorotaxane. In contrast to 3 , the addition of R-CD
their concentrations suggest that the ICD bands of 2
and 3 are mainly due to intramolecular self-inclusion
of the pendant groups into the â-CD cavity.
Figure 7 shows that the sign of the ICD bands of 1
and 2 is opposite to that of 3 . One possible explanation
for this is that the V moieties of 1 -3 are outside
the â-CD cavity, but there is a parallel/perpendicular
•+
•
+
to the 2 solution gave no appreciable change in the ICD
spectrum. This implies that the self-inclusion complex-
•
+
•
+
ation of 2 is nearly quantitative, and that the position
•
+
•+
•+
•+
of V in the 2 -R-CD [2]pseudorotaxane complex is
•
+
•
+
•+
•+
almost the same as in the self-inclusion complex of 2 ;
i.e., the V moiety is adjacent to the secondary face of
R-CD in the [2]pseudorotaxane.
•
+
•
+
•+
orientation difference between the V units of 1 and
•+
•+
2
and that of 3 , with respect to the â-CD axis.
Circular Dichroism of Two-Electron-Reduced
â-CD-Viologens. Two-electron reductions of viologen
However, CPK modelings indicated that the aliphatic
linkages are not long enough to allow the perpendicular
2+
2+
units of â-CD-viologens 1 -3 to 1°-3° were achieved
•+
26
orientation of the V moiety in the intramolecularly self-
by continuous electrolysis, and ICD spectra of 1°-3°
•
+
•+
included complexes of 2 and 3 . Thus the opposite sign
were recorded in situ. The spectra are shown in Figure
8. In all cases, no appreciable ICD signal was observed
above 450 nm, indicating that the reduction products are
of the ICD bands can be taken as an indication of the
inside/outside difference in the location of the V units
•
+
-
with respect to the â-CD cavity. It was reported that,
free from the contamination of 1e -reduced species.
2
+
•+
unlike the V group, the V moiety has an appreciable
The spectrum of 2° shows a negative band, whereas
that of 3° exhibits a positive one. This is analogous to
binding affinity for the â-CD cavity, with binding con-
-
1 22
-
stants of 30-100 M . As the transitions responsible
the observation made with 1e -reduced forms of the
•+
for the ICD bands of V are also π-π*, they are polarized
corresponding compounds (Figure 7), and indicates that
J. Org. Chem, Vol. 70, No. 23, 2005 9511

Park et al.
SCHEME 2. Self-Inclusion Behaviors and Molar
2+
2+a
Ellipticities of Reduced Forms of 1 -3
-
FIGURE 8. Circular dichroism spectra of 2e -reduced â-CD-
viologens 1°-3°.
the V° moiety of 2° is present mostly outside of the â-CD
cavity, whereas that of 3° is inside the cavity. The
compound 1° shows a split-type ICD, but the shape of
the spectrum is slightly different from a typical exciton-
split band; the magnitude of ellipticity of the positive
band is smaller than that of the negative band, and the
spectrum has a shoulder in the crossover region.
a
•+
[
θ]’s are taken at 398 nm for V and 380 nm for V°, and are
2
-1
in deg cm dmol units.
The presence of the monomeric form of 1° could account
for the higher reactivity of 1° than of 3°. The higher
reactivity of 2° than of 1° and 3° can be attributed to the
presence of the V° unit of 2° outside the â-CD cavity, and
thus its exposure to the bulk aqueous phase.
The shape of the ICD spectrum of 1° can be interpreted
in terms of the monomer-dimer equilibrium of the
compounds. Mirzoian and Kaifer suggested that 1° forms
a cyclic dimer by mutual inclusion of the V° unit into the
â-CD cavity of the counter molecule.10 The dimerization
Conclusions
3
4
-1
constant was estimated to be in the range 10 -10 M ,
which gives the fraction of monomeric 1° in the 0.16-
Two â-CD-viologens in which 1-methyl-4,4′-bipyri-
dinium units are linked to the primary and the secondary
side of the â-CD via an octamethylene linkage show quite
contrasting self-inclusion behavior and induced circular
dichroism (ICD). The compound having the pendant
0
.4 range under the experimental condition [1°]total ≈ 1.5
-3
×
10 M. The dimer is expected to show a typical exciton-
split curve as reported for the similar-type dimer of 6-O-
2-sulfonato-6-naphthyl)-â-CD.11 The monomeric 1° would
(
2
+
group on the primary side (2 ) forms an intramolecular
self-inclusion complex having the viologen moiety outside
the secondary face of the â-CD cavity, with Kin ≈ 3.1,
give a negative ICD band similar to that of 2°, but with
higher molar ellipticity. The sum of contributions from
both the dimeric and monomeric 1° appears to result in
the observed unusual ICD pattern of 1°. The scheme for
self-inclusion complexation of 1°-3° and the molar el-
lipticity data of the complexes are summarized in Scheme
2
+
whereas that modified at the secondary side (3 ) forms
the head-to-head-type dimer in which the viologen moi-
eties are placed outside the primary face of the â-CD
-
1
cavity, with K
forms of the â-CD-viologens form intramolecular self-
inclusion complexes. The reduced viologen units of 2
and 2° are outside the â-CD cavity, whereas those of 3
and 3° are inside the cavity. The â-CD-viologens, in both
oxidized and reduced states of the viologen moiety, form
2]pseudorotaxanes with R-CD in which the secondary
D
≈ 65 M . One- or two-electron-reduced
2
.
Finally, we discuss briefly the reactivity of the two-
•
+
+
electron-reduced â-CD-viologens. It is known that the
two-electron-reduced viologen (V°) reacts with water and
is transformed into redox inert species, which does not
•
absorb light above 300 nm.2
6,27,34
Previously, we reported
[
that the pseudo-first-order rate constants for the reac-
face of the ring R-CD is oriented toward the viologen unit.
This work shows that the viologen unit, regardless of its
oxidation state, prefers to reside above the secondary face
rather than above the primary face of CDs; the reduced
viologen units prefer the inside of the CD cavity more
than the outside of the primary face but less than the
outside of the secondary face. The ICD characteristics of
tions of 1° and 3° are about 1/5 and 1/100, respectively,
26
of that of neutral dimethyl viologen (MV°). The differ-
ence in the reactivity among 1°-3° was also revealed in
the present work. Though we used the same concentra-
2+
2+
tion of 1 -3 and the same electrolysis time, we always
observed that the average concentration of V° during
circular dichroism measurements is on the order of 2° <
2+
2+
â-CD-viologens 2 and 3 , mono-6-deoxy-6-[4-(1-meth-
1
° < 3°. This implies that the order of reactivity of the
2+
yl-4-pyridinio)-1-pyridinio]-â-CD (1 ), and methyloctyl
viologen neutrals is 2° > 1° > 3°. The high stability of 3°
against the reaction with water can be attributed to the
extensive encapsulation of its neutral viologen moiety
inside the â-CD cavity via self-inclusion complexation.
2+
1 8
viologen (C C V )-â-CD complex in both oxidized and
reduced states of the viologen unit are obtained. The
dependence of the ICD of viologen chromophores on their
locations with respect to the CD cavity, which was
predicted theoretically, is demonstrated unequivocally.
This work also confirms the dimerization of 1° from ICD,
(
34) Kim, J. Y.; Lee, C.; Park, J. W. J. Electroanal. Chem. 2001,
5
04, 104.
9512 J. Org. Chem., Vol. 70, No. 23, 2005

Self-Inclusion Complexation of â-CD-Viologens
and explains the order of reactivity of the viologen
neutrals with water, 2° > 1° > 3°, on the basis of the
structures of self-included complexes. We believe that the
results provided here would be very useful in the
structural elucidation and design of the CD-based su-
pramolecular structures. Also, the change in the self-
inclusion behaviors of 32 upon the reduction of the
viologen unit could be utilized to modulate the as-
sembling behaviors of the â-CD-viologens by light and
electrical stimuli.
product. The product was washed with hot ethanol (20 mL)
and then purified by cation-exchange chromatography on a
CM-25 column using a linear gradient of aqueous NaCl
solution (0.0-0.5 M). The fractions showing UV absorption and
optical rotation were combined, desalted by ultrafiltration
through MW cutoff 500 cellulose membrane, and finally freeze-
dried to obtain 0.11 g (23% yield based on 4) of analytically
+
2+
-
1
pure 2 ‚2Cl : mp 222 °C dec; H NMR (D O, δ
2
HDO
) 4.800) δ
1.25-1.85 (m, 10H), 2.1-2.3 (br s, 2H), 2.7-4.1 (m, 44H), 4.54
(
s, 3H), 4.91 (br s, 2H), 5.1-5.3 (m, 7H), 8.53-8.67 (br s, 2.5H),
8
9
.69-8.77 (br s, 1.5H), 9.09 (d, 2H), 9.12-9.18 (br s, 0.5H),
.23 (br d, 1.5H); MALDI TOF MS 1415.76, calcd for
2
+
[
C
61
H
97
N
3
O
34
]
97 3 2
1415.59. Anal. Calcd for C61H N O34Cl ‚
Experimental Section
9H
2
O: C, 44,42; H, 7.03; N, 2.55. Found: C, 44.24; H, 6.95; N,
2
.43.
Materials and Concentration Calculations. Dichloride
Photochemical Reduction of Viologens to Viologen
salts of mono-6-deoxy-6-[4-(1-methyl-4-pyridinio)-1-pyridinio]-
Radical Cations. The reduction of viologen dication to
2
+
9
2+ 9
â-CD (1 ), methyloctyl viologen (C
1
C
8
V
), and mono-2-O-
viologen radical cation was carried out by irradiating the
2+
26
-5
-5
[
4-(1-methyl-4-pyridinio)-1-pyridinio]octyl-â-CD (3
)
were
deaerated 3.2 × 10 M viologen solution containing 5 × 10
2
+
described in previous reports. All spectral measurements were
carried out at 25 °C. The ionic strength of the solutions was
fixed at 0.1 M with NaCl. The concentrations of viologens and
viologen radical cations were assayed from UV-vis absorption
M Ru(bpy)
as a photosensitizer and 0.1 M EDTA as a
3
sacrificial electron donor in 0.1 M aqueous NaCl at pH 10 with
9
a tungsten lamp. The reduction was monitored by the
characteristic UV-vis absorption of the viologen radical
-
1
-1
-1
-1
9
data using ꢀ262 ) 21 000 M cm and ꢀ602 ) 13 700 M cm
,
cation.
9
respectively. The concentrations of CDs were calculated from
Electrochemical Reduction of Viologen to Viologen
Neutrals and Circular Dichroism Spectra of Viologen
Neutrals. A spectroelectrochemical cell was assembled with
a demountable 100 µm path length rectangular cuvette and
optical rotation data using reported specific rotations.35
Mono-6-deoxy-6-N-[4-(1-methyl-4-pyridinio)-1-pyridin-
2
+
-
iooctyl]amino-â-CD Dichloride (2 ‚2Cl ). Mono-6-deoxy-
2
6
6
-amino-â-CD (â-CD-6-NH
toluenesulfonyl)-â-CD via a â-CD-6-azide intermediate. To
a solution of â-CD-6-NH (4.12 g, 3.64 mmol) in dry DMF (40
2
) was prepared from mono-6-O-(p-
an ITO coated glass cover as described. The cell was filled
3
6
-3
with 6.7 × 10 M viologen solution in 0.10 M KCl at pH 8.9,
2
adjusted with 0.01 M borate buffer, and mounted in the cell
compartment of a spectropolarimeter. The CD spectra of
viologen neutral were recorded in situ while applying -1.2 V
versus Ag wire potentiostatically. The high-tension voltage
(HV) data from the spectropolarimeter were converted to
absorbance data, and the concentration of viologen neutral was
mL) under a nitrogen atmosphere at 25 °C was added 1,8-
diiodooctane (1.47 g, 4.00 mmol) dropwise, and the solution
was stirred for 8 h at the same temperature. After evaporation
of the solvent under reduced pressure, acetone (250 mL) was
added to obtain 4.53 g of precipitate. The crude product was
purified by reverse-phase column chromatography on C18
-
1
calculated from the absorbance data using ꢀ394 ) 41 500 M
-
1 27
silica column using a linear gradient of aqueous CH
3
CN (0-
cm
.
The calibration of HV data was made with viologen
3
0 v/v %) to afford 3.0 g (60% yield) of mono-6-deoxy-6-(8-
radical cation solutions.
iodooctyl)amino-â-CD 4. To the solution of 4 (0.43 g, 0.31 mmol)
in dry DMF (5 mL) was added a solution of 1-methyl-4,4′-
bipyridinium iodide (0.93 g, 3.1 mmol) in dry DMF (5 mL),
and the reaction mixture was heated at 50 °C for a day under
a nitrogen atmosphere. After evaporation of the solvent,
acetone (100 mL) was added to obtain the yellow crude
Acknowledgment. This work was supported by
CRM/KOSEF of Korea University.
Supporting Information Available: General procedure
1
for spectral measurements, H NMR and two-dimensional
2
+
2+
ROESY spectra of 2 and 3 . This material is available free
of charge via the Internet at http://pubs.acs.org.
(
35) Szejtli, J. Chem. Rev. 1998, 98, 1743.
(
36) Ashton, P. R.; Koniger, R. J. Org. Chem. 1996, 61, 903.
JO0515834
J. Org. Chem, Vol. 70, No. 23, 2005 9513