A comparative study on inclusion complexation of substituted anilinonaphthalene sulfonic acids with 1,6,20,25-tetraaza[6.1.6.1]-paracyclophane and β-cyclodextrin

Article abstract of DOI:10.1007/s10847-018-0790-4

The inclusion complexations of paracyclophane (CP44) and β-cyclodextrin (β-CD) with several anilinonaphthalene sulfonic acids (ANSs) have been characterized via the enhancement of fluorescence spectra upon inclusion. β-CD and CP44 formed 1:1 inclusion complexes with ANSs, and the high stability of inclusion complexes of the latter was demonstrated. The thermodynamic parameters observed from the temperature dependence of the inclusion constants (van’t Hoff analysis) showed that CP44 inclusion complexations with ANSs are enthalpy-driven. Furthermore, the structure of the inclusion complexes was discussed based on ¹H- and 2D ROESY-NMR measurements. It was found that CP44 encapsulates the naphthalene moiety of ANSs. On the other hand, differences in the structures of the β-CD inclusion complexes were observed for the 4-OH-substituted ANS. The molecular recognition for the inclusion of β-CD was found to be sensitive compared with that of CP44. In addition, the local polarity inside the CP44 and β-CD cavities was evaluated using ANSs as the fluorescence probe. Based on these results, we have suggested that the local polarity of ANSs in the hydrophobic cavities of CP44 and β-CD plays an important role in quantum yield enhancement upon inclusion.

Full text of DOI:10.1007/s10847-018-0790-4

Journal of Inclusion Phenomena and Macrocyclic Chemistry
https://doi.org/10.1007/s10847-018-0790-4
ORIGINAL ARTICLE
A comparative study on inclusion complexation of substituted
anilinonaphthalene sulfonic acids with 1,6,20,25-tetraaza[6.1.6.1]-
paracyclophane and β-cyclodextrin
Yoshimi Sueishi1 · Ayari Itoh1 · Naoya Inazumi2 · Yoshihiro Osawa3 · Tadashi Hanaya1
Received: 27 November 2017 / Accepted: 15 February 2018
© Springer Science+Business Media B.V., part of Springer Nature 2018
Abstract
The inclusion complexations of paracyclophane (CP44) and β-cyclodextrin (β-CD) with several anilinonaphthalene sulfonic
acids (ANSs) have been characterized via the enhancement of fluorescence spectra upon inclusion. β-CD and CP44 formed
1:1 inclusion complexes with ANSs, and the high stability of inclusion complexes of the latter was demonstrated. The ther-
modynamic parameters observed from the temperature dependence of the inclusion constants (van’t Hoff analysis) showed
that CP44 inclusion complexations with ANSs are enthalpy-driven. Furthermore, the structure of the inclusion complexes
was discussed based on 1H- and 2D ROESY-NMR measurements. It was found that CP44 encapsulates the naphthalene
moiety of ANSs. On the other hand, differences in the structures of the β-CD inclusion complexes were observed for the
4-OH-substituted ANS. The molecular recognition for the inclusion of β-CD was found to be sensitive compared with that
of CP44. In addition, the local polarity inside the CP44 and β-CD cavities was evaluated using ANSs as the fluorescence
probe. Based on these results, we have suggested that the local polarity of ANSs in the hydrophobic cavities of CP44 and
β-CD plays an important role in quantum yield enhancement upon inclusion.
Keywords Cyclophane · Cyclodextrin · Inclusion complexation · Anilinonaphthalene sulfonic acid · Quantum yield of
inclusion complex
Introduction
has attracted much attention because they enable the design
of hydrophobic cavities of definite shapes and sizes [4–8].
The development of artificial carriers is of great importance
for drug delivery systems and newly functionalized cyclo-
phanes have been designed for this purpose [9]. However,
to date, studies on the inclusion complexation of organic
molecules with cyclophanes are not well established.
Anilinonaphthalene sulfonic acid (ANS) is sensitive
to the polarity of its local environment and constitutes a
very useful fluorescence probe [10]. ANS shows high fluo-
rescence in nonpolar solvents, but it is strongly quenched
in polar solvents such as water [10]. Therefore, ANS is
employed as a polarity probe in a variety of proteins and
host–guest inclusion complexes [11, 12]. In addition, the
measurement of the quantum yield of inclusion complexes
is informative for the characterization of photochemical pro-
cesses and inclusion behavior.
Cyclodextrins (CDs) are attractive hosts for inclusion chem-
istry due to their hydrophobic cavities [1]. They can form
inclusion complexes with many organic molecules and are
widely used in the pharmaceutical and food industries [2, 3].
Recently, the inclusion behavior of paracyclophanes (CPs)
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10847-018-0790-4) contains
supplementary material, which is available to authorized users.
* Yoshimi Sueishi
ysueishi@okayama-u.ac.jp
1
Department of Chemistry, Faculty of Science,
Okayama University, 3-1-1 Tsushima-naka, Kita-ku,
Okayama 700-8530, Japan
2
3
In this study, using four different anilinonaphthalene sul-
fonic acids as guest molecules, we have examined the inclu-
sion complexation of 1,6,20,25-tetraaza[6.1.6.1]paracyclo-
phane (CP44) and β-CD, and the enhancement of quantum
Technical Support Division, Graduate School of Science,
Osaka University, Toyonaka, Osaka 560-0043, Japan
Otsuka Electronics Co. Ltd., 1-10 Sasagaoka,
Minakuchi-cho, Kouka-shi, Shiga 528-0061, Japan
Vol.:(0123456789)
1 3

Journal of Inclusion Phenomena and Macrocyclic Chemistry
yield (Φ values) has been determined upon inclusion. The
results observed for CP44 were compared with those of
β-CD having a similar cavity size [13]. Furthermore, the
structure of inclusion complexes of CP44 and β-CD has been
established through 1H- and 2D ROESY-NMR experiments.
A characteristic inclusion complexation of 4-OH-substituted
ANS by β-CD was found by comparing with those by CP44.
The difference in the inclusion complex structures (molecu-
lar recognition for inclusion) and the dominant factor for the
quantum yields enhanced by inclusion were also discussed.
Experimental
Materials
The four different types of anilinonaphthalene sulfonic
acids and host molecules (CP44 and β-CD) used in this
study are shown in Fig. 1. CP44 and β-CD were purchased
from Tokyo Chemical Industry Co. (Tokyo, Japan) and
Wako Pure Chemicals (Osaka, Japan), respectively, and
were used without any further purification. It is useful to
compare the inclusion behavior of CP44 having charges in
macrocycle with that of hydrophobic β-CD having similar
ring size. 6-Anilinonaphthalene-2-sulfonic acid (2,6-ANS),
6-anilino-4-hydroxynaphthalene-2-sulfonic acid (2,4,6-
AHNS), and 7-anilino-4-hydroxynaphthalene-2-sulfonic
acid (2,4,7-AHNS) were obtained from Funakoshi (Tokyo,
Japan), Tokyo Chemical Industry Co. (Tokyo, Japan), and
Wako Pure Chemicals, respectively. 7-Anilinonaphthalene-
2-sulfonic acid (2,7-ANS) was prepared according to the
method reported by Bucherer and Stohmann [14], and
recrystallized from basic water. Identification was made by
1H NMR measurements. Water and 1,4-dioxane were puri-
fied by distillation and were used as solvents.
Fig. 1 Structures of paracyclophane (CP44), β-cyclodextrin (β-CD),
and ANS derivatives
sulfuric acid (0.050 M) as a standard: λ (excitation wave-
length)=347.5 nm and Φ=0.51 0.02 [15].
CD and CP44 inclusion complexes 1H-NMR spectra were
recorded in D2O and DCl–D2O acidic solutions respectively
with a Varian Mercury 300 spectrometer (300 MHz) at room
temperature. Chemical shifts are given as δ values relative
to HOD (δ 4.79) as an internal standard. 2D ROESY-NMR
measurements were carried out with a Varian VNS 600
NMR spectrometer (600 MHz) at 303 K. The mixing time
for ROESY measurements was 200 ms.
Fluorescence and NMR measurements of inclusion
complexes
Fluorescence spectra of ANS complexes with β-CD in water
were measured with a Shimadzu RF-5300PC spectropho-
tometer: [ANS]=2 µM (M=mol dm−3) and an excitation
wavelength of 320–350 nm. Temperature-controlled water
( 0.1 K) was used to control the reaction temperature. For
the inclusion with CP44, an aqueous HCl solution (hydro-
gen ion exponent (pH) 1) was used as a solvent to solubi-
lize CP44. No change in the absorption spectrum of ANS
under these conditions was previously confirmed. Φ val-
ues were determined using Otsuka Electronics Quantum
Efficiency Analysis System (QE 1000) equipped with a
half-moon unit (Osaka, Japan) at 298 0.5 K. The quan-
tum yield was calibrated by quinine bisulfate solution in
Results and discussion
The estimation of inclusion constants of β‑CD
and CP44
The typical fluorescence spectra of 2,7-ANS upon consecu-
tive addition of CP44 are shown in Fig. S1 in supplementary
1 3

Journal of Inclusion Phenomena and Macrocyclic Chemistry
data. A large enhancement in the fluorescence intensity in
the vicinity of 460 nm caused by 2,7-ANS inclusion com-
plexes was observed upon addition of CP44 to a solution of
2,7-ANS. To confirm the stoichiometry of the ANS-CP44
complex, fluorescence measurements were conducted by
varying the mole fraction of 2,7-ANS and CP44, i.e. con-
tinuous variation method (Job’s method) [16]. Job’s plots
for the changes in the fluorescence intensity of ANS showed
that the CP44 inclusion complex of 2,7-ANS was formed
with 1:1 stoichiometry (see Fig. S1 in supplementary data).
Similar results were obtained for the complexation of vari-
ous ANS derivatives with β-CD and CP44. The equilib-
rium for the 1:1 inclusion complexations of ANSs can be
expressed as:
the inclusion process. From the linear fit of the van’t Hoff
plots, the enthalpy and entropy changes were determined
for the inclusion complexations of ANSs with CP44 and
β-CD. Results for the thermodynamic parameters are listed
in Table 1. The enthalpy–entropy compensation effect has
been reported for many chemical reactions [18]. In Fig. 2,
the ΔH values for the inclusion complexation of ANSs with
CP44 and β-CD were plotted against the ΔS values. The
linear relationship obtained suggests that a single mecha-
nism is operating in the inclusion processes [19]. The par-
allel straight lines between CP44 and β-CD are due to a
free energy change caused by the CP44 host rather than to
a change in the mechanism. Figure 2 shows that the upper-
right and lower-left quadrants correspond to the entropy-
driven and enthalpy-driven complexations, respectively. The
ΔH–ΔS plots in Fig. 2 suggest that both CP44 and β-CD
bind to ANSs with favorable enthalpy. The major contribu-
tion to the favorable enthalpy of complexation comes from
the van der Waals interactions associated with the inclusion
of the non-polar part of ANS into the hydrophobic cavity of
ANS + Host ⇄ ANS − H
[ANS−H]
K =
(1)
[ANS][Host]
where ANS−H denotes the inclusion complex. Under the
condition of [Host] >> [ANS], fluorescence spectral data
were analyzed according to the Benesi–Hildebrand equation
(Eq. 2) [17]:
[Host]0
1
1
=
[Host]0 +
(2)
(F − F0)
F
∞ − F0
K[F∞ − F0]
where [Host]0 denotes initial concentrations of host mol-
ecules and F is the fluorescence intensity. A good linear rela-
tionship between [Host]0/(F−F0) and [Host]0 was obtained
(see Fig. S1b in supplementary data). The association con-
stants (K) for the 1:1 inclusion complex formation of β-CD
and CP44 can be determined from the slope and intercept
according to Eq. 2. The K values obtained for the inclusion
complexation of β-CD and CP44 at various temperatures are
listed in Table 1. K values for the inclusion with CP44 were
found to be larger compared with those with β-CD, suggest-
ing that CP44 forms more stable inclusion complexes.
The inclusion behavior can be better understood using
the enthalpy and entropy changes (ΔH and ΔS) obtained for
Fig. 2 Relationship between ΔH and ΔS for the inclusion complexa-
tion with ANS derivatives in an aqueous solution. Open circle: CP44
and filled circle: β-CD
Table 1 The inclusion constants and thermodynamic parameters for inclusion complexations with CP44 and β-CD
Guest
Host
10−3 K/M−1
ΔH/kJ mol−1 ΔS/kJ mol−1 K−1 (T298ΔS)
288 K 293 K
298 K
34
2.4 0.1 1.7 0.1
28 20
4.2 0.2 3.1 0.1
303 K
24
1.8 0.1
12
2.0 0.1
40
308 K
318 K
2,6-ANS
2,6-ANS
2,4,6-AHNS CP44
2,4,6-AHNS β-CD
2,7-ANS
2,7-ANS
2,4,7-AHNS CP44
2,4,7-AHNS β-CD
CP44 76
β-CD
7
46
1
1
1
−54
−25
−62
−52
−32
−33
−32
−41
3
1
3
2
2
1
3
3
−0.095 0.005 (−28)
−0.022 0.005 (−6.5)
−0.13 0.01 (−37)
1.3 0.1
9.0 0.3
1.5 0.1
1
1
1
−0.11 0.01 (−33)
CP44
β-CD
56
1
54
1
1
30
1
23
1
−0.018 0.008 (−5.2)
−0.053 0.003 (−16)
−0.017 0.001 (−5.0)
−0.062 0.006 (−19)
1.2 0.1 0.99 0.01 0.80 0.02 0.58 0.01
50 52 47 23
5.9 0.1 4.6 0.1
72
2
1
1
1
1
9.7 0.2 9.5 0.2
1 3

Journal of Inclusion Phenomena and Macrocyclic Chemistry
Table 2 Cross peaks observed in ROESY-NMR spectra of inclusion complexes of ANS derivatives with β-CD in D2O
Guest
Guest protonsa
Host protonsb
C(3)H
C(5)H
C(6)H
2,7-ANS
C(1)–H
C(4)–H
C(5)–H
C(8)–H
C(6,10)–H
C(1)–H
C(8)–H
C(4,5)–H
C(9)–H
C(1)–H
C(8)–H
C(9)–H
C(1)–H
C(5)–H
C(9)–H
−
−
−
−
+
+
−
−
+
−
−
++
−
−
+
++
+
+
++
++
++
++
++
−
+
+
−
++
++
−
+
−
−
−
−
−
+
−
+
+
−
−
−
−
−
2,6-ANS
2,4,6-AHNS
2,4,7-AHNS
(a)
2,6-ANS
2,7-ANS
2,4,7-AHNS
2,4,6-AHNS
(b)
β-CD
CP44 and β-CD. Furthermore, in the inclusion with CP44,
the additional electrostatic interaction of the positive charges
in CP44 ring with a negative charge of the sulfonate group
in ANS is operative.
upon association and the relaxation of water molecules from
the cavity. In water, the association process with β-CD is
characterized by small and negative entropies, and compen-
satory enthalpy–entropy relationships exist for inclusion pro-
cesses dominated by hydration phenomena [20, 21]. Nega-
tive enthalpies and entropies for β-CD and CP44 inclusions
characterize inclusion systems where van der Waals interac-
tions are dominant due to the tight fit of guest molecule to
the host cavity, which is in agreement with the suggestions
reported by Castronuovo et al. [20].
Based on thermal parameters for the β-CD complexa-
tion, the inclusion processes were discussed in detail by
Castronuovo et al. [20, 21]. Upon inclusion of β-CD, water
molecules are released from the hydrophobic hydration
shells to a bulk. The entropic term for inclusion processes
is determined by the loss of degrees of freedom occurring
1 3

Journal of Inclusion Phenomena and Macrocyclic Chemistry
Table 3 Cross peaks observed
in ROESY-NMR spectra of
inclusion complexes of ANS
derivatives with CP44 in DCl–
D2O solution
Guest
Guest protons
Host protonsa
C(1)H
C(2)H
C(3)H
C(4)H
C(5)H
2,7-ANS
C(4)–H
C(8)–H
C(9)–H
C(3)–H
C(4)–H
C(5)–H
C(2,7)–H
C(8)–H
C(5)–H
C(6)–H
C(8)–H
C(3,9)–H
C(3)–H
C(7)–H
C(9)–H
−
−
+
++
+
+
+
−
−
−
−
−
−
−
−
−
−
−
−
−
−
+
−
−
−
−
+
−
−
+
−
+
+
−
−
−
−
−
++
++
++
+
+
++
+
++
++
−
++
−
−
−
−
−
−
+
++
++
−
++
+
−
−
+
+
+
+
2,6-ANS
2,4,7-AHNS
−
−
−
+
−
−
−
−
2,4,6-AHNS
(a)
or C(5)–H of β-CD (Table 2), indicating that the naphthalene
moiety of ANS was encapsulated inside the β-CD cavity. In
CP44 inclusion, the C(3,4,5)–H protons of CP44 strongly
interacted with C(4,8)–H protons of 2,7-ANS (Table 3).
Cross peaks corresponding to protons in CP44 with the
C(10,11)–H protons of anilino-group in 2,7-ANS were not
detected. These show that the naphthalene moiety of 2,7-
ANS is deeply encapsulated in the CP44 cavity. Based on
these NMR results, the plausible structures of the inclusion
complexes of ANS derivatives with CP44 and β-CD are
depicted in Fig. 3. The results can be summarized as follows.
(1) Given the interaction between the protons of the naphtha-
lene moiety in ANSs and the ring protons of CP44 (Table 3),
the naphthalene moiety is deeply encapsulated into the CP44
cavity. (2) In the inclusion of 2,6-ANS, 2,7-ANS, and 2,4,7-
AHNSs by β-CD, the cross peaks arising from the C(5)–H
proton of β-CD and the C(1,4,5,8)–H protons of ANSs were
observed, indicating that the naphthalene moiety of ANS is
included in the β-CD cavity. (3) In 2,4,6-AHNS/β-CD, the
C(3)–H proton of β-CD strongly interacts with the C(9)–H
proton in ANS, and the cross peak between the C(6)–H pro-
ton of β-CD and the C(1)–H proton in ANS is observed. This
suggests that the 2,4,6-AHNS guest is deeply included from
the anilino-phenyl group side in the β-CD cavity (reversed
Structures of inclusion complexes with CP44
and β‑CD
NMR measurements are informative to elucidate the struc-
tures of inclusion complexes with CP44 and β-CD. The
induced chemical shifts of the guest protons indicate inclu-
sion of the proton moiety into the CP44 and CD cavities. The
1H-NMR spectra of 2,7-ANS in the presence of β-CD and
CP44 were shown in Fig. S2 in supplementary data. Larger
induced shifts of ANS protons due to aromatic ring cur-
rent effect were observed upon inclusion by CP44 compared
with those by β-CD. For example, the C(8)–H proton of 2,7-
ANS shifts upfield from 7.62 to 6.45 ppm upon inclusion by
CP44. The large induced chemical shifts are in agreement
with those reported for the inclusion of 2,7-dihydroxynaph-
thalene with paracyclophane [4].
2D ROESY-NMR experiments are useful to determine the
position of the guest molecules inside CP44 and β-CD cavi-
ties. The relative intensities of the cross peaks for the inclu-
sion complexes with β-CD and CP44 are listed in Tables 2
and 3, respectively [2D ROESY-NMR spectra were shown
in supplementary data (Figs. S3–S6)]. In the inclusion of
2,7-ANS with β-CD, the cross peaks of C(1,4,5,6,8)–H pro-
tons in 2,7-ANS were observed with the inner C(3)–H and/
1 3

Journal of Inclusion Phenomena and Macrocyclic Chemistry
Fig. 4 The relationship (closed circles) of the emission energy (EF)
of 2,7-ANS in 1,4-dioxane-water mixtures against ET(30) values. The
local polarities were evaluated from the EF values of 2,7-ANS inclu-
sion complexes with CP44 (open circle) and β-CD (open rectangle)
Table 4 The local polarity and Φcomplex values of ANS inclusion
complexes with β-CD and CP44 in an aqueous solution at 298 K
Guest
Host
ET(30)/kJ mol−1
Φcomplex
2,6-ANS
2,6-ANS
2,6-ANS
2,4,6-AHNS
2,4,6-AHNS
2,4,6-AHNS
2,7-ANS
2,7-ANS
2,7-ANS
–
–
~0
β-CD
CP44
–
β-CD
CP44
–
β-CD
CP44
–
β-CD
CP44
236.3
240.2
–
251.4
251.4
–
241.8
228.5
–
233.4
243.9
0.22 0.02
0.17 0.01
0.031 0.001
0.16 0.01
0.17 0.01
0.047 0.001
0.16 0.01
0.24 0.01
0.041 0.001
0.12 0.01
0.10 0.01
2,4,7-AHNS
2,4,7-AHNS
2,4,7-AHNS
1,4-dioxane-water mixture. The emission energy of 2,7-
ANS decreases with increasing ET(30) values for the solvent
mixture. Using the fluorescent probe 2,7-ANS, the micro-
environmental polarity inside the β-CD and CP44 cavities
was shown in Fig. 4. The local polarities of 2,7-ANS in
the β-CD and CP44 cavity were estimated to be 241.8 and
228.5 kJ mol−1, respectively. The local polarities of ANSs
and AHNSs in β-CD and CP44 cavities are listed in Table 4.
In the inclusion by β-CD, 2,4,6-AHNS incorporated from
the phenyl group side shows high polarity, which is compa-
rable to that by CP44. In the inclusion by CP44, 2,6-ANS
and 2,4,7-AHNS are located in polar environment, compared
with those by β-CD.
Fig. 3 Structures of inclusion complexes of ANS derivatives with
CP44 and β-CD based on 2D ROESY-NMR measurements
orientation for other ANSs), which is responsible for the
interaction by the hydrophilic OH group. These observa-
tions suggest that CP44 molecular recognitions are insensi-
tive compared with those of β-CD.
Enhancement of fluorescence quantum yields
ANS is used as a polarity probe in various heterogene-
ous systems like proteins. Figure 4 shows the plots of
the fluorescence emission energy of 2,7-ANS against the
empirical solvent polarity parameter [ET(30) value] in a
The quantum yields (Φ values) of inclusion complexes
were determined using an Otsuka fluorescence spectrometer
and are given by the following equation.
1 3

Journal of Inclusion Phenomena and Macrocyclic Chemistry
5. Odashima, K., Koga, K.: Design and syntheses of paracyclo-
phanes having charged side chains that are soluble in neutral
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FPComplex
APComplex
FP − FPGuest
AP − APGuest
ΦComplex
=
=
(3)
where FP and AP denote fluorescence photon number
and excitation photon number of inclusion complex, free
guest, and apparent solutions, respectively. FP and AP
values of apparent and guest solutions were measured and
the concentration of free guest ANS estimated using the
above mentioned inclusion constant K (Table 1). The thus-
obtained Φcomplex values are listed in Table 4. The inclusion
by CP44 and β-CD produces high enhancement in Φ values,
compared with Φ values in aqueous solution. In inclusions
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different. However, the Φ values for β-CD inclusion of 2,4,6-
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in polar solvent, ANS charge-transfer emission occurs and
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[22]. This is in agreement with the above observations.
In summary, we have determined the inclusion constants
of ANS derivatives with CP44 and β-CD. It was found
that CP44 forms more stable 1:1 inclusion complexes with
ANSs compared with those formed with β-CD. Based on
the ROESY-NMR spectra of the inclusion complexes, the
characteristic disposition of the guest molecules inside the
CP44 and β-CD cavities could be confirmed. In the case of
inclusion by CP44, the difference in inclusion modes for
HO-induced AHNSs was not observed, and thus molecular
recognition of CP44 occurs at a minor extent than that by
β-CD. Finally, Φ values for the inclusion complexes of
ANSs with CP44 and β-CD were determined. Based on
these values, we have suggested that the local polarity of
ANS plays an important role for the difference observed in
quantum yields.
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