Reversible formation and destruction of micelles of amphiphilic compounds in aqueous media. competition with pseudorotaxane formation

Article abstract of DOI:10.1246/bcsj.20090298

N-Alkyl-4,4′-bipyridiniums [4,4′-bpy-N-(CH₂) _nOAr]⁺(Cl^-) (n = 6 and 10, Ar = C ₆H₃-3,5-t-Bu₂, C₆H ₃-3,5-(OMe)₂, and C₆H₂-2,4,6-Me ₃), having the cationic bipyridinium group and a long hydrophobic alkyl chain, were prepared from the reaction of 4,4′-bipyridine with the corresponding alkyl chlorides. The amphiphilic compounds in water form micelles which encapsulate added pyrene in the hydrophobic core. Addition of α-cyclodextrin to the micellar solution converts a part of the aggregated amphiphilic molecules to their pseudorotaxane with α-cyclodextrin. Formation of the pseudorotaxanes is favored at lower temperature, as is observed by temperature dependent change of the absorption spectra.

Full text of DOI:10.1246/bcsj.20090298

378
Bull. Chem. Soc. Jpn. Vol. 83, No. 4, 378–384 (2010)
© 2010 The Chemical Society of Japan
Reversible Formation and Destruction of Micelles
of Amphiphilic Compounds in Aqueous Media.
Competition with Pseudorotaxane Formation
Yuji Suzaki, Toshiaki Taira, and Kohtaro Osakada*
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503
Received November 18, 2009; E-mail: kosakada@res.titech.ac.jp
¹
N-Alkyl-4,4¤-bipyridiniums [4,4¤-bpy-N-(CH2)nOAr]+(Cl ) (n = 6 and 10, Ar = C6H3-3,5-t-Bu2, C6H3-3,5-(OMe)2,
and C6H2-2,4,6-Me3), having the cationic bipyridinium group and a long hydrophobic alkyl chain, were prepared from the
reaction of 4,4¤-bipyridine with the corresponding alkyl chlorides. The amphiphilic compounds in water form micelles
which encapsulate added pyrene in the hydrophobic core. Addition of ¡-cyclodextrin to the micellar solution converts a
part of the aggregated amphiphilic molecules to their pseudorotaxane with ¡-cyclodextrin. Formation of the pseudo-
rotaxanes is favored at lower temperature, as is observed by temperature dependent change of the absorption spectra.
Amphiphilic compounds possessing both hydrophilic and
hydrophobic parts in the molecule, such as CTAB (cetyltri-
methylammonium bromide), SDS (sodium dodecyl sulfate), and
Triton X-100 (octylphenoxypolyethoxyethanol), form micelles
or other self-assembled aggregates, such as vesicles and bilayer
sheets, in water.1,2 The micelle particles composed of the
amphiphiles often contain added pigment or dye molecules in
their hydrophobic cavity. Such encapsulation of the micellar
solution is widely used to estimate critical micelle concen-
tration (CMC) of the amphiphiles in water.3 Spectroscopic
measurement of the micellar solution of various amphiphiles in
the presence of pyrene provide a good means to determine their
CMCs as well as to obtain information of the environment
around the pyrene.4 Addition of cyclodextrins (CDs), cyclic-
oligoglucoses composed of six to eight 1,4-linked D-gluco-
pyranose units,5 to the micellar solution has been reported to
change properties of the solution, such as surface activity,6
surface intensity,7 and conductivity8 as well as the spectro-
scopic and physicochemical results.9 They were attributed to
the formation of their pseudorotaxanes in which cyclodextrins
were threaded by the long alkyl chain of the amphiphile.10-12
In these mixtures of cyclodextrin and amphiphile in water,
formation of the micelle and of the pseudorotaxane competes
with each other as shown in Scheme 1.8b,8c,13-15
n
Amphiphile
Micelle
+
Amphiphile
Pseudorotaxane
CD
Scheme 1. Competitive formation of micelles and pseudo-
rotaxanes.
bly systems between pseudorotaxane formation and micellar
aggregation may lead to switching of the solution properties,
although reports on this subject are rare.6
In this paper, we report the reversible formation of micelles
and of pseudorotaxanes in an aqueous mixture of ¡-CD
and amphiphilic molecule by temperature alternation. It was
achieved by use of N-alkyl-4,4¤-bipyridiniums. A part of this
work has been reported in a preliminarily form.18
Results and Discussion
Studies on the mixture of ¢-cyclodextrin and SDS revealed
that formation of the pseudorotaxane with ¢-CD is much more
favored than that of the micelle because of more significant
interaction between ¢-CD and SDS than that among the
amphiphilic molecules in the micellar system.16 Recent kinetic
study of the ¢-CD-SDS system by EPR spectroscopy also
showed the complex formation of ¢-CD and SDS which occurs
with a higher association constant than that of micellization
of SDS in water.17 In these systems, high stability of the
pseudorotaxane prevents formation of micelles or the change of
the ratio of the pseudorotaxanes to the micelles in aqueous
media. On-off regulation of competing supramolecular assem-
Chart 1 lists N-alkyl-4,4¤-bipyridiniums used in this study.
Reaction of 4,4¤-bipyridine with Cl(CH2)nOAr (n = 6 and 10;
Ar = C6H3-3,5-t-Bu2, C6H3-3,5-(OMe)2, and C6H2-2,4,6-Me3)
¹
in DMF produces, [4,4¤-bpy-N-(CH2)nOAr]+(Cl ) (1a: n = 10,
Ar = C6H3-3,5-t-Bu2; 1b: n = 10, Ar = C6H3-3,5-(OMe)2; 1c:
n = 10, Ar = C6H2-2,4,6-Me3; and 1d: n = 6, Ar = C6H3-3,5-
(OMe)2). Compounds 1a-1c show amphiphilic nature; they are
soluble both in water and in common organic solvents, such as
dmso, acetone, CH2Cl2, and CHCl3. Compound 1d, however, is
soluble in water, sparingly soluble in dmso, and insoluble in
other organic solvents, due to the shorter polymethylene chain
than that of the other compounds.
Published on the web March 26, 2010; doi:10.1246/bcsj.20090298

Y. Suzaki et al.
Bull. Chem. Soc. Jpn. Vol. 83, No. 4 (2010)
379
Cl-
5
4
3
2
1
0
a
b
c
d
+
N
N
(CH2)n OAr
(A)
(B)
1a: n = 10, Ar = C6H3-3,5-t-Bu2
1b: n = 10, Ar = C6H3-3,5-(OMe)2
1c: n = 10, Ar = C6H2-2,4,6-Me3
1d: n = 6, Ar = C6H3-3,5-(OMe)2
Chart 1. Structure of N-alkyl-4,4¤-bipyridinium compounds,
1a-1d.
HDO
Me
NCH2CH2
(A)
C6H2
Methylene
NCH2
d a
c
b
0
0.2 0.4 0.6 0.8 1.0
OCH2
[1c]0/([1c]0 + [α-CD]0)
(B)
α-CD
α-CD
d, d'
a' c' b'
Figure 2. Job’s plots for 1c and ¡-CD (A) at 25 °C and (B)
at 60 °C based on 1H NMR peak area ratio of bipyridinium
protons (b and b¤). [1c]0 + [¡-CD]0 = 10 mM. The curve
calculated by assuming formation of a 1:1 pseudorotaxane
a
c
b
(C)
¹1
with association constants of 5000 and of 1000 M is
d' a' c' b'
shown in (A) and (B), respectively.
8
6
4
2
0
Table 1. Association Constants K for [2]Pseudorotaxane
Formation Reaction of ¡-CD with 1a-1d in D2Oa)
δ
Figure 1. 1H NMR spectra (D2O, 300 MHz, 25 °C) of (A)
1c ([1c] = 10 mM), (B) 1c and ¡-CD ([1c] = 10 mM,
[¡-CD] = 10 mM), and (C) 1c and ¡-CD ([1c] = 10 mM,
[¡-CD] = 30 mM).
¹1
¹1
[2]Pseudorotaxane
K/M at 25 °C
K/M at 60 °C
1a(¡-CD)
1b(¡-CD)
1c(¡-CD)
1d(¡-CD)
CTAB(¡-CD)
102b)
25000
5000
400
1110c)
29b)
12000
1000
N.D.
®
Reaction of ¡-CD with 1a-1d leads to formation of their
pseudorotaxanes as shown in eq 1.
a) Unless noted association constants K were estimated from
Job’s plot obtained from 1H NMR spectroscopy. b) Association
constants K were estimated from single point 1H NMR
measurement. c) Ref. 21.
Cl-
a
b
c
d
+
N
N
(CH2)n OAr
+
1a, 1b, 1c, 1d
α-CD
the signals of free 1c (¤ 7.62 (b), 8.17 (c), 8.51 (a), 8.81 (d)) in
the aromatic hydrogen region (Figure 1B). The former signals
(a¤, b¤, c¤, d¤) are assigned to the bipyridinium moiety of an
inclusion complex, 1c(¡-CD). Further addition of ¡-CD to
the mixture causes disappearance of the signals of free 1c
(Figure 1C). Signals of the C6H2 hydrogens in Figure 1C were
observed as two peaks with different intensity (¤ 6.82, 6.91),
indicating the presence of two isomers of 1c(¡-CD) with
different orientations of ¡-CD. The ratio of the isomers was
determined to be 82:18 by comparison of the integrations of the
1H NMR peak area. Job’s plots obtained from the peak area
ratio between b and b¤ show maximum at a molar fraction of
0.5 both at 25 and 60 °C (Figure 2), which confirms exclusive
formation of 1:1 complex, [2]pseudorotaxane. The correspond-
a' b' c' d'
K
+
ð1Þ
N
N
(CH2)n OAr
Cl-
1a(α-CD): n = 10, Ar = C6H3-3,5-t-Bu2
1b(α-CD): n = 10, Ar = C6H3-3,5-(OMe)2
1c(α-CD): n = 10, Ar = C6H2-2,4,6-Me3
1d(α-CD): n = 6, Ar = C6H3-3,5-(OMe)2
Inclusion complexes of ¡-CD with 1a in D2O/dmso-d6 (=3/1)
and [3]pseudorotaxane of two ¡-CDs and 1b were reported in
our previous reports.19,20 The MALDI-TOF MS spectrum
obtained from the mixtures of ¡-CD and 1c (and 1d) showed
peaks assigned to 1:1 complexes, 1c(¡-CD) (m/z = 1401.7)
and 1d(¡-CD) (m/z = 1363.7), respectively. Figure 1 com-
¹1
ing association constants K were determined to be 5000 M
¹1
(25 °C) and 1000 M (60 °C), respectively. Table 1 summa-
rizes association constants of ¡-CD and 1a-1d. Large depend-
ence of [2]pseudorotaxane formation on the structures of the
1
pares the H NMR spectra of 1c and of mixtures of ¡-CD and
¹1
1c. An equimolar mixture ([¡-CD] = [1c] = 10 mM) shows a
set of the signals at ¤ 7.75 (b¤), 8.24 (c¤), 8.59 (a¤), 8.82 (d¤) and
axle molecule (K = 102-25000 M at 25 °C) was observed.
The thermodynamic parameters of the [2]pseudorotaxane

380
Bull. Chem. Soc. Jpn. Vol. 83, No. 4 (2010)
Competitive Assembly of Amphiphiles
1.0
(A)
(A)
1.0
0.8
0.6
0.8
0.6
0.4
0.2
CMC
0.4
0.2
0
1.5
0
(B)
300
350
400
λ/ nm
(B)
1.0
0.5
2.0
CMC2
CMC1
1.5
1.0
0.5
0
0
1.0
(C)
0.8
0.6
0.4
0.2
300
350
λ/ nm
400
CMC
Figure 3. Absorption spectra of (A) pyrene (10 ¯M) and
[1a] ([1a] = 5 © 10
pyrene (10 ¯M) and [1b] ([1b] = 1.25 © 10 to 2.5 ©
10¹3 g mL¹1) in water at 25 °C.
to 2.5 © 10¹3 g mL¹1) and (B)
¹6
¹6
0
formation are determined to be ¦Ho = ¹8.8 kcal mol¹1, ¦So =
¹1
-6
-5
-4
-3
-2
¹14 cal mol¹1 K¹1, and ¦Go = ¹4.7 kcal mol for 1c(¡-CD)
¹1
and to be ¦Ho = ¹7.3 kcal mol¹1, ¦So = ¹13 cal mol¹1 K
,
log([compound]/g mL-1)
and ¦Go = ¹3.4 kcal mol for 1d(¡-CD), respectively, by
temperature dependence of association constant obtained by
1H NMR spectroscopy of the mixture of amphiphiles and ¡-CD
in D2O. The large negative values of ¦Ho and ¦Go suggest that
hydrophobic interaction between the cavity of ¡-CD and the
polymethylene chain of 1c contribute to enthalpy-controlled
thermodynamic stability of the [2]pseudorotaxane.5
¹1
Figure 4. Plots of the absorbance at 338 nm of the aqueous
mixture of pyrene ([pyrene] = 10 ¯M) and 1a-1c at 25 °C
on concentrations of (A) [1a], (B) [1b], and (C) [1c].
on plots of the absorbance vs. concentration of 1a (Figure 4).
DLS measurement shows the hydrodynamic radius of a micelle
in an aqueous solution of 1a ([1a] = 18.6 mM) as 61 nm at
25 °C. CMCs of 1b-1d were determined similarly (Figure 4
and Table 2). The mixture of pyrene and 1b shows change in
slope at [1b] = 0.65 mM (CMC1) and 2.1 mM (CMC2), which
is attributed to stepwise aggregation of 1b. The CMC value of
1c is similar to that of CTAB (0.92 mM) while those of 1a and
1b (CMC2) are smaller. DLS measurement of solution of 1b
([1b] = 5 mM at 25 °C) indicates a large particle with hydro-
dynamic radius of 2.6 © 103 nm where formation of suspended
solution due to further aggregation of 1b was observed at
high concentration. The hydrodynamic radius of micelle of 1b
does not depend significantly on temperature (hydrodynamic
The critical micelle concentrations (CMCs) of 1a-1c in
water were obtained by dye solubilization, while dynamic light
scattering (DLS) measurement was also conducted to determine
particle size of the formed aggregates. Figure 3 shows
absorption spectra of a mixture of pyrene ([pyrene] = 10 ¯M)
and 1a with different concentrations ([1a] = 5 © 10¹6 to 2.5 ©
10¹3 g mL¹1). The absorbance at 338 nm significantly increases
¹1
at concentrations of [1a] above 5 © 10¹4 g mL due to the
formation of micelles which encapsulate pyrene in the hydro-
phobic core. CMC values of 1a become larger at higher
temperatures or by addition of ¡-CD. The CMC of 1a was
determined to be 0.26 mM at 25 °C (0.50 mM at 60 °C) based

Y. Suzaki et al.
Bull. Chem. Soc. Jpn. Vol. 83, No. 4 (2010)
381
Table 2. CMC and Averaged Particle Sizes of 1a-1d in
Water
(A)
(B)
(C)
1.2
Temperature CMCa)
Averaged particle
sizeb)/nm
(i)
Compound
/°C
/mM
0.8
(iii)
(iv)
1a
25
25
50
60
25
25
25
0.26
61
N.D.
N.D.
N.D.
N.D.
0.19c)
0.34c)
0.50
0.30
0.56
0.65 (CMC1)
2.1 (CMC2)
1.0
0.92e)
0.4
(ii)
1a + ¡-CDd)
1a + ¡-CDe)
1b
N.D.
2.6 © 103 f)
0
1c
CTAB
25
25
110g)
2.6h)
300
350
λ/ nm
400
a) Determined by dye solubilization method using pyrene.
b) Determined by DLS. c) DPH (1,6-diphenylhexatriene) was
used as dye. d) [¡-CD]/[1a] = 0.4. e) [¡-CD]/[1a] = 10.
f) Suspension. g) At 19 °C. h) Ref. 21.
1.5
(i)
1.0
0.5
radius = 1.5 © 103 to 2.6 © 103 nm at 25-75 °C). The hydro-
dynamic radius of micelle of 1c ([1c] = 20 mM at 19 °C) was
determined to be 110 nm. So, the amphiphiles in this study
form micelles with much larger particle size than those of
CTAB.
(iii)
(ii), (iv)
Addition of ¡-CD to the solution of pyrene and 1a
([¡-CD] = 47.5 mM, [pyrene] = 10 ¯M, [1a] = 9.5 mM) at
25 °C causes significant decrease in the absorption at 338 nm
(Figures 5A-(i) and 5A-(ii)) due to degradation of micelles
of 1a and formation of the [2]pseudorotaxane 1a(¡-CD).
Heating the solution to 60 °C caused partial recovery of the
absorbance, suggesting reformation of micelle particles of 1a.
Re-cooling the solution to 25 °C decreases the absorbance
again (Figures 5A-(iii) and 5A-(iv)). Repetition of the temper-
ature change between 25 and 60 °C results in swinging of the
spectra between (ii) (or (iv)) and (iii), as shown in Figure 6.
Addition of ¡-CD to the aqueous solution of pyrene and
amphiphiles, 1b-1d and CTAB, causes similar decrease of the
absorbance at 338 nm, while change of the spectra by temper-
ature alternation between 25 and 60 °C lacked reversibility in
these solutions (Figures 5B and 5C).
The aqueous solution of the mixture of 1a and pyrene
([1a] = 2 mM, [pyrene] = 5 ¯M) shows weak emission at - =
375 (I1), 386 (I3) nm due to ³-³* transition of pyrene with the
I3/I1 ratio of 1.01 (-ex = 335 nm) (Figure 7A). Addition of ¡-
CD (10 mM) to the solution causes significant increase in the
intensity of the emission (Figure 7B). The intensity of emission
and I3/I1 ratio from the mixture of ¡-CD, 1a, and pyrene
(I3/I1 = 0.67) are similar to those from solution containing
pyrene (5 ¯M) (I3/I1 = 0.66). This change of emission can
be ascribed as follows. Pyrene is solubilized in water via
encapsulation into the cavity of micelle of 1a where the
photoexcited pyrene is quenched by bipyridinium unit of 1a.
Addition of ¡-CD to the micellar solution of 1a forms
individual pseudorotaxane species, 1a(¡-CD), via degradation
of the micelle structure. The small I3/I1 values (<0.70) in
Figures 7B and 7C indicate that these emissions are from the
pyrene molecule dissolved in water.4 Similar aqueous solutions
of the mixture of pyrene and 1b (and 1c) show emission with
0
300
350
λ/ nm
400
2.0
1.5
1.0
0.5
0
(i)
(ii)
(iv)
(iii)
300
350
λ/ nm
400
Figure 5. (A) Absorption spectra of ¡-CD, pyrene, and [1a]
([pyrene] = 10 ¯M, [1a] = 9.5 mM, [¡-CD] = 47.5 mM),
(B) absorption spectra of ¡-CD, pyrene, and [1b]
([pyrene] = 10 ¯M, [1b] = 5.0 mM, [¡-CD] = 30 mM),
(C) absorption spectra of ¡-CD, pyrene, and [1c]
([pyrene] = 10 mM, [1c] = 5.0 mM, [¡-CD] = 30 mM).
The spectra were recorded in the following order: (i)
before addition of ¡-CD at 25 °C, (ii) after addition of ¡-
CD at 25 °C, (iii) after heating to 60 °C, (iv) after cooling
to 25 °C.
the I3/I1 ratio of 0.72 and 0.85, respectively, indicating their
micelle also encapsulate pyrene in the cavity.
Scheme 2 summarizes a plausible mechanism for the
spectroscopic changes of a solution containing pyrene, ¡-CD,

382
Bull. Chem. Soc. Jpn. Vol. 83, No. 4 (2010)
Competitive Assembly of Amphiphiles
0.8
150
100
50
I1
(C)
0.6
0.4
0.2
(B)
(A)
I3
0
350
400
450
500
0
1
2
3
4
5
λ/ nm
Number of cycles
Figure 6. Switching cycles of absorbance of mixture of
1a, ¡-CD, and pyrene at 338 nm between 25 and 60 °C
([pyrene] = 10 ¯M, [1a] = 9.5 mM, [¡-CD] = 47.5 mM).
The normal distribution within 2 standard deviations of the
mean (® + 2·) was included.
Figure 7. Emission spectra of (A) 1a and pyrene
([pyrene] = 5 ¯M, [1a] = 2 mM), (B) 1a, ¡-CD, and
pyrene ([pyrene] = 5 ¯M, [1a] = 2 mM, [¡-CD] = 10
mM), and (C) pyrene ([pyrene] = 5 ¯M) in water.
Cl-
+
n
N
N
N
(CH2)10OAr
+ m pyrene
(A)
(B)
A
Cl-
Cl-
+
+
N
N
N
(CH2)10OAr
(CH2)10 OAr
+
B
α-CD
Scheme 2. Plausible mechanism for competing supramolecular assembly of amphiphiles.
and 1a at different temperatures. The amphiphilic molecules
aggregate via encapsulation of pyrene to form micelle A in
water (Scheme 2A). Although almost all of the molecule in
aqueous media are involved in the micelle, addition of ¡-CD
causes degradation of micellar aggregate and forms pseudo-
rotaxane with ¡-CD, B, leading to separation of pyrene from
the solution as a solid and consequent decrease of the
absorbance (Scheme 2B). Pseudorotaxane of 1a, upon heating,
tends to cause dethreading to separate ¡-CD from free
amphiphile which forms micelle A again, leading to encapsu-
lation of pyrene even in the presence of ¡-CD. Assemblies of
1a to form micelles and to form pseudorotaxane with ¡-CD
compete with each other in the presence of ¡-CD due to
comparable stabilities of the two kinds of supramolecular
aggregation. The association constants for formation of the
pseudorotaxane 1a(¡-CD) (K = 102 M at 25 °C, 29 M at
60 °C) are much smaller than those for the pseudorotaxane of
1b-1d. The mixture of 1a and ¡-CD in Figure 5A ([1a] =
9.5 mM, [¡-CD] = 47.5 mM) is estimated to contain 1a(¡-CD)
in 80% at 25 °C and 55% at 60 °C, respectively. Micelle
formation of 1a is also affected by temperature alternation
(CMC of 1a = 0.26 mM at 25 °C, 0.50 mM at 60 °C). As a
result, the ratio of concentration of 1a in the micelles and
1a(¡-CD) varies significantly by temperature alternation.
Reaction of ¡-CD with 1b (or 1c, CTAB) forms their
pseudorotaxanes dominantly in solution at both 25 and 60 °C
under the conditions shown in Figures 5B and 5C. Yields
of the pseudorotaxanes, 1b(¡-CD) and 1c(¡-CD), in these
solutions are estimated to be higher than 96% even at 60 °C
¹1
from their large association constants (K = 5000, 25000 M
¹1
at 25 °C, K = 1000, 12000 M at 60 °C). Negligible changes
in the absorption spectra of these mixtures by temperature
alternation are ascribed to high stability of the pseudorotaxanes.
Conclusion
The competitive supramolecular assembly in water was
investigated to reveal the micelle formation of amphiphilic N-
alkyl-4,4¤-bipyridiniums and pseudorotaxane formation of it
with ¡-CD. The association constants of [2]pseudorotaxane
¹1
¹1
¹
formation of ¡-CD and [4,4¤-bpy-N-(CH2)nOAr]+(Cl ) (n = 6
and 10; Ar = C6H3-3,5-t-Bu2, C6H3-3,5-(OMe)2, and C6H2-
2,4,6-Me3) vary in the range, K = 102-25000 M¹1, at 25 °C
depending on the amphiphiles. Molecules having proper length
of methylene chain, n = 10, show amphiphilic properties and

Y. Suzaki et al.
Bull. Chem. Soc. Jpn. Vol. 83, No. 4 (2010)
383
(10 mL) was stirred for 1 h at room temperature, followed by
addition of 1,6-dichlorohexane (7.6 mL, 52 mmol). The mixture
was stirred for another 23 h at 110 °C, before being quenched with
1 M HCl(aq) (100 mL). The water layer was extracted with CH2Cl2
(100 mL) and the organic extract was washed with water, dried
over MgSO4, filtered and concentrated under reduced pressure to
yield a crude product, which was purified by SiO2 column chroma-
tography (2 times, hexane/CH2Cl2 = 3/1 (Rf = 0.23), hexane/
AcOEt = 20/1 (Rf = 0.34)) and washing with hexane (15 mL)
to yield Cl(CH2)6O{C6H3-3,5-(OMe)2} as a white powder (1.1 g,
4.0 mmol, 15%). 1H NMR (300 MHz, CDCl3, r.t.): ¤ 1.43-1.56
(CH2, 4H), 1.73-1.86 (CH2, 4H), 3.55 (t, ClCH2, 2H, J = 7 Hz),
3.77 (s, CH3, 6H), 3.92 (t, OCH2, 2H, J = 7 Hz), 6.08 (s, C6H3,
3H); 13C{1H} NMR (75.5 MHz, CDCl3, r.t.): ¤ 25.4 (CH2), 26.6
(CH2), 29.0 (CH2), 32.4 (CH2), 45.0 (ClCH2), 55.3 (CH3), 67.7
(OCH2), 92.7 (C6H3), 93.2 (C6H3), 160.9 (C6H3), 161.4 (C6H3);
Found: C, 61.47; H, 7.55; Cl, 13.09%. Calcd for C14H21ClO3: C,
61.65; H, 7.76; Cl, 13.00%.
form stable micelles in water. Aqueous mixtures of ¡-CD and
the amphiphiles produce solutions which exhibit competitive
formation of micelle and pseudorotaxane. The amphiphilic
¹
molecule, [4,4¤-bpy-N-(CH2)10O(C6H3-3,5-t-Bu2)]+(Cl ) (1a),
forms pseudorotaxane 1a(¡-CD) with a relatively small
association constant, in which significant change of the ratio
of pseudorotaxane and micelles is induced reversibly by
temperature alternation. This supramolecular transformation
system may provide new means for artificial molecular
materials that respond to an external stimulus.
Experimental
¹
General. [4,4¤-bpy-N-(CH2)nOAr]+(Cl ) (1a; n = 10, Ar =
C6H3-3,5-t-Bu2 and 1b; n = 10, C6H3-3,5-(OMe)2) were pre-
pared according to a literature method.18,19 The other chemicals
were commercially available and used without further purifica-
tion. 1H and 13C{1H} NMR spectra were recorded on Varian
MERCURY300 and JEOL EX-400 spectrometers. 3-(Trimethyl-
silyl)-1-propanesulfonic acid sodium salt (DSS) was used as an
external standard in the 13C{1H} NMR measurements in D2O.
Matrix-assisted laser desorption ionization time of flight mass
spectra (MALDI-TOF MS) were obtained from a Shimadzu
AXIMA-CFR Plus spectrometer (matrix, 2-hydroxy-5-methoxy-
benzoic acid (super DHB)). The absorption spectra were recorded
using a JASCO V-530 UV-vis spectrometer. A 10 ¯L aliquot of a
2.0 M solution of pyrene in dmso was transferred to 2.0 mL of each
sample. Before measuring, the samples were stored at adequate
temperature using a JASCO EHC-477 peltiere-type thermostated
cell holder. The emission spectra were recorded using a JASCO
FP-6300 Spectrofluorometer. Elemental analysis was carried out
with a LECO CHNS-932 CHNS or Yanaco MT-5 CHN autore-
corder at the Center for Advanced Materials Analysis, Technical
Department, Tokyo Institute of Technology. The hydrodynamic
size of the micelles in aqueous solution was measured using an
Otsuka Electronics Co., Ltd. DLS-7000 spectrophotometer equip-
ped with a 10 mW He-Ne laser operating at 632.8 nm. Measure-
ment was performed at an angle of 90°, and the data obtained were
fitted using the CONTIN algorithm.
¹
[4,4¤-bpy-N-(CH2)10O(C6H2-2,4,6-Me3)]+(Cl ) (1c). A solu-
tion of Cl(CH2)10O(C6H2-2,4,6-Me3) (1.43 g, 4.6 mmol) and 4,4¤-
bipyridine (1.44 g, 9.2 mmol) in DMF (10 mL) was stirred at
100 °C for 28 h. The evaporation of the solvent yielded a brown
solid, which was purified by washing with Et2O, recrystallization
from CH2Cl2/Et2O (20 mL/200 mL) at room temperature, and
washing with Et2O to yield [4,4¤-bpy-N-(CH2)10O(C6H2-2,4,6-
¹
Me3)]+(Cl ) (1c) as a white solid (945 mg, 2.0 mmol, 44%).
1H NMR (300 MHz, CDCl3, r.t.): ¤ 1.17-1.49 (CH2, 12H), 1.70
(m, OCH2CH2, 2H), 1.75 (br, NCH2CH2, 2H), 2.17 (s, Me, 9H),
3.66 (t, OCH2, 2H, J = 7 Hz), 4.94 (t, NCH2, 2H, J = 7 Hz), 6.76
(s, C6H2, 2H), 7.75 (d, C10H8N2, 2H, J = 5 Hz), 8.43 (d, C10H8N2,
2H, J = 6 Hz), 8.77 (d, C10H8N2, 2H, J = 5 Hz), 9.55 (d, C10H8N2,
2H, J = 6 Hz); 13C{1H} NMR (75.5 MHz, CDCl3, r.t.): ¤ 16.1
(C6H2-4-CH3), 20.5 (C6H2-2,6-(CH3)), 26.0 (CH2, 2C), 28.9
(CH2), 29.2 (CH2), 29.3 (CH2, 2C), 30.3 (CH2), 31.8 (CH2), 61.3
(NCH2), 72.2 (OCH2), 121.6 (C10H8N2), 125.8 (C10H8N2), 129.2
(C6H2), 130.4 (C6H2), 132.7 (C6H2), 141.0 (C10H8N2), 145.7
(C10H8N2), 151.1 (C10H8N2), 153.2 (C10H8N2), 153.6 (C6H2);
Found: C, 69.48; H, 8.48; N, 5.61%. Calcd for C29H39ClN2O¢
2H2O: C, 69.23; H, 8.61; N, 5.57%.
¹
Cl(CH2)10O(C6H2-2,4,6-Me3). A solution of 2,4,6-trimethyl-
phenol (4.0 g, 29 mmol) and NaOH (1.6 g, 40 mmol) in DMF
(20 mL) was stirred for 2 h at room temperature, followed by
addition of 1,10-dichlorodecane (12.4 mL, 59 mmol). The mixture
was stirred for another 26 h at 100 °C, before being quenched with
1 M HCl(aq) (50 mL). The water layer was extracted with Et2O
(30 mL, 4 times) and the combined organic extract was washed
with water (20 mL, 2 times), dried over MgSO4, filtered and con-
centrated under reduced pressure to yield a crude product, which
was purified by SiO2 column chromatography (hexane/CH2Cl2 =
5/1, Rf = 0.34) to yield Cl(CH2)10O(C6H2-2,4,6-Me3) as a white
[4,4¤-bpy-N-(CH2)6O{C6H3-3,5-(OMe)2}]+(Cl ) (1d).
A
solution of Cl(CH2)6O{C6H3-3,5-(OMe)2} (800 mg, 2.9 mmol)
and 4,4¤-bipyridine (906 mg, 5.8 mmol) in DMF (8 mL) was stirred
at 110 °C for 25 h. The evaporation of the solvent yielded a brown
solid, which was purified by washing with Et2O, reprecipitation
from EtOH/Et2O (50 mL/500 mL) at room temperature to yield
¹
[4,4¤-bpy-N-(CH2)6O{C6H3-3,5-(OMe)2}]+(Cl ) (1d) as a gray
solid (635 mg, 1.5 mmol, 52%). 1H NMR (300 MHz, dmso-d6, r.t.):
¤ 1.28-1.52 (CH2, 4H), 1.68 (br, OCH2CH2, 2H), 1.98 (br, NCH2-
CH2, 2H), 3.67 (s, Me, 6H), 3.89 (t, OCH2, 2H, J = 6 Hz), 4.67 (t,
NCH2, 2H, J = 7 Hz), 6.04 (s, C6H3, 3H), 8.05 (d, C10H8N2, 2H,
J = 5 Hz), 8.65 (d, C10H8N2, 2H, J = 6 Hz), 8.86 (d, C10H8N2, 2H,
J = 5 Hz), 9.31 (d, C10H8N2, 2H, J = 6 Hz); 13C{1H} NMR (100
MHz, dmso-d6, r.t.): ¤ 25.0 (CH2), 25.2 (CH2), 28.4 (CH2), 30.7
(CH2), 55.1 (CH3), 60.2 (NCH2), 67.2 (OCH2), 92.6 (C6H3), 93.1
(C6H3), 121.9 (C10H8N2), 125.3 (C10H8N2), 140.8 (C10H8N2),
145.2 (C10H8N2), 150.8 (C10H8N2), 152.0 (C10H8N2), 160.3
(C6H3), 161.0 (C6H3); Found: C, 65.51; H, 6.82; N, 6.27%. Calcd
for C24H29ClN2O3¢0.5H2O: C, 65.82; H, 6.90; N, 6.40%.
1
powder (3.52 g, 11 mmol, 38%). H NMR (300 MHz, CDCl3, r.t.):
¤ 1.36-1.60 (CH2, 12H), 1.75-1.88 (ClCH2CH2, NCH2CH2, 4H),
2.28 (s, Me, 9H), 3.56 (t, ClCH2, 2H, J = 7 Hz), 3.76 (t, OCH2,
2H, J = 7 Hz), 6.85 (s, C6H2, 2H); 13C{1H} NMR (75.5 MHz,
CDCl3, r.t.): ¤ 16.1 (C6H2-4-CH3), 20.6 (C6H2-2,6-(CH3)2), 26.1
(CH2), 26.8 (CH2), 28.8 (CH2), 29.4 (CH2), 29.5 (CH2, 2C), 30.4
(CH2), 32.6 (CH2), 45.1 (ClCH2), 72.3 (OCH2), 129.3 (C6H2),
130.5 (C6H2), 132.7 (C6H2), 153.7 (C6H2); Found: C, 73.37; H,
9.75; Cl, 11.42%. Calcd for C19H31ClO: C, 73.40; H, 10.05; Cl,
11.40%.
¹
[(¡-CD){4,4¤-bpy-N-(CH2)10O(C6H2-2,4,6-Me3)}]+(Cl ) (1c-
(¡-CD)). 1H NMR data were obtained from a mixture of 1c
1
Cl(CH2)6O{C6H3-3,5-(OMe)2}. A solution of 3,5-dimethoxy-
phenol (4.0 g, 26 mmol) and NaOH (1.6 g, 40 mmol) in DMF
([1c] = 10 mM) and ¡-CD ([¡-CD] = 30 mM) in D2O. H NMR
(300 MHz, D2O, r.t.): ¤ 1.05-2.04 (CH2, 16H), 2.06 (s, Me), 2.18

384
Bull. Chem. Soc. Jpn. Vol. 83, No. 4 (2010)
Competitive Assembly of Amphiphiles
Zou, F. Tao, M. Jiang, Langmuir 2007, 23, 12791.
(s, Me), 3.35-3.79 (CH-¡-CD, OCH2, 38H), 4.50-4.54 (NCH2,
2H), 4.82-4.88 (CH-¡-CD, 6H), 6.82 (s, C6H2), 6.91 (s, C6H2),
7.75 (d, C10H8N2, 2H, J = 6 Hz), 8.24 (d, C10H8N2, 2H, J = 5 Hz),
8.59 (d, C10H8N2, 2H, J = 5 Hz), 8.82 (d, C10H8N2, 2H, J = 7 Hz);
MS (MALDI-TOF) found m/z 1401.7 [M ¹ Cl]+, calcd for
C65H99N2O31 m/z 1403.6.
7
2661.
8
T. Okubo, H. Kitano, N. Ise, J. Phys. Chem. 1976, 80,
a) T. Okubo, Y. Maeda, H. Kitano, J. Phys. Chem. 1989, 93,
3721. b) A. Diaz, P. A. Quintela, J. M. Schuette, A. E. Kaifer, J.
Phys. Chem. 1988, 92, 3537. c) P. Sehgal, M. Sharma, R. Wimmer,
K. L. Larsen, D. E. Otzen, Colloid Polym. Sci. 2006, 284, 916.
[(¡-CD){4,4¤-bpy-N-(CH2)6O(C6H3-3,5-(OMe)2)}]+(Cl ) (1d-
¹
(¡-CD)). 1H NMR data were obtained from a mixture of 1d
9
a) E. Junquera, E. Aicart, G. Tardajos, J. Phys. Chem. 1992,
1
([1d] = 10 mM) and ¡-CD ([¡-CD] = 50 mM) in D2O. H NMR
96, 4533. b) G. González-Gaitano, A. Compostizo, L. Sánchez-
Martín, G. Tardajos, Langmuir 1997, 13, 2235. c) G. González-
Gaitano, A. Crespo, A. Compostizo, G. Tardajos, J. Phys. Chem. B
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N. Muratore, I. V. Terekhova, Langmuir 2003, 19, 7188. f) A.
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Gaitano, G. Tardajos, J. Phys. Chem. B 2007, 111, 1368. g) A.
Guerrero-Martínez, D. Domínguez-Gutiérrez, M. A. Palafox, G.
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Montoro, M. H. Viñas, M. A. Palafox, A. Guerrero-Martínez, J.
Phys. Chem. B 2008, 112, 15691.
10 a) S. A. Nepogodiev, J. F. Stoddart, Chem. Rev. 1998, 98,
1959. b) G. Wenz, B.-H. Han, A. Müller, Chem. Rev. 2006, 106,
782. c) A. Harada, A. Hashidzume, H. Yamaguchi, Y. Takashima,
Chem. Rev. 2009, 109, 5974.
11 a) G. Schill, Catenanes, Rotaxanes, and Knots, Academic
Press, New York, 1971. b) Molecular Catenanes, Rotaxanes and
Knots, ed. by J.-P. Sauvage, C. Dietrich-Buchecker, Wiley-VCH,
Weinheim, 1999.
(300 MHz, D2O, r.t.): ¤ 1.19-1.69 (CH2, 4H), 1.87 (m, OCH2CH2,
2H), 2.06 (m, NCH2CH2, 2H), 3.39-3.84 (CH-¡-CD, OCH2, 38H),
4.53-4.65 (NCH2, 2H), 4.88-4.92 (CH-¡-CD, 6H), 5.65 (s, C6H3),
6.16 (s, C6H3), 7.83 (d, C10H8N2, 2H, J = 6 Hz), 8.30 (d, C10H8N2,
2H, J = 7 Hz), 8.67 (d, C10H8N2, 2H, J = 6 Hz), 8.89 (d, C10H8N2,
2H, J = 7 Hz); MS (MALDI-TOF) found m/z 1363.7 [M ¹ Cl]+,
calcd for C60H89N2O33 m/z 1363.6.
Determination of Equilibrium Constants for Formation of
1c(¡-CD). A D2O solution of 1c ([1c] = 6 mM) and ¡-CD ([¡-
CD] = 4 mM) was charged to an NMR tube. Fixing temperature of
the solution and comparison of the peaks at ¤ 7.62 (b) and 7.75 (b¤)
showed the equilibrium constant. K = 2511 (25 °C), 1734 (35 °C),
¹1
1173 (45 °C), 779 (55 °C), 566 (65 °C), 326 (75 °C), and 206 M
(85 °C).
Determination of Equilibrium Constants for Formation of
1d(¡-CD). A D2O solution of 1d ([1d] = 10 mM) and ¡-CD
([¡-CD] = 10 mM) was charged to an NMR tube. Fixing temper-
ature of the solution and comparison of the peaks at ¤ 7.81 (b) and
7.93 (b¤) showed the equilibrium constant. K = 615 (5 °C), 429
(15 °C), 289 (25 °C), 188 (35 °C), 125 (45 °C), and 83 M¹1 (55 °C).
12 Y. Suzaki, T. Taira, K. Osakada, M. Horie, Dalton Trans.
2008, 4823.
13 a) R. Palepu, V. C. Reinsborough, Can. J. Chem. 1988, 66,
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Zhu, X. Guo, Colloid Polym. Sci. 2003, 281, 876. e) N. Funasaki,
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14 Y. Wang, H. Xu, X. Zhang, Adv. Mater. 2009, 21, 2849.
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7027.
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We are grateful to Prof. Takakazu Yamamoto of our institute
for dynamic light scattering (DLS) and Dr. Masato Koizumi of
the Center for Advanced Materials Analysis, Technical Depart-
ment, Tokyo Institute of Technology for MALDI-TOF MS
measurements. This work was supported by a Grant-in-Aid for
Scientific Research for Young Scientists from the Ministry
of Education, Culture, Sports, Science and Technology, Japan
(No. 19750044) and by Global COE Program “Education and
Research Center for Emergence of New Molecular Chemistry.”
T.T acknowledges scholarship from Japan Society for the
Promotion of Science.
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