A hemicyanine and cucurbit[n]uril inclusion complex: competitive guest binding of cucurbit[7]uril and cucurbit[8]uril

Article abstract of DOI:10.1080/10610278.2019.1624748

The interaction between the hemicyanine indole derivative H and the cucubit[n]urils Q[7] and Q[8] has been studied using ¹H NMR and UV spectroscopy as well as by fluorescence experiments. Competitive studies on the inclusion of H by Q[7] and Q[

Full text of DOI:10.1080/10610278.2019.1624748

Supramolecular Chemistry
ISSN: 1061-0278 (Print) 1029-0478 (Online) Journal homepage: https://www.tandfonline.com/loi/gsch20
A hemicyanine and cucurbit[n]uril inclusion
complex: competitive guest binding of
cucurbit[7]uril and cucurbit[8]uril
Weitao Xu, Jinglan Kan, Carl Redshaw, Bing Bian, Ying Fan, Zhu Tao & Xin
Xiao
To cite this article: Weitao Xu, Jinglan Kan, Carl Redshaw, Bing Bian, Ying Fan, Zhu
Tao & Xin Xiao (2019): A hemicyanine and cucurbit[n]uril inclusion complex: competitive
guest binding of cucurbit[7]uril and cucurbit[8]uril, Supramolecular Chemistry, DOI:
10.1080/10610278.2019.1624748
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SUPRAMOLECULAR CHEMISTRY
https://doi.org/10.1080/10610278.2019.1624748
ARTICLE
A hemicyanine and cucurbit[n]uril inclusion complex: competitive guest binding
of cucurbit[7]uril and cucurbit[8]uril
Weitao Xua, Jinglan Kanb, Carl Redshawc, Bing Biand, Ying Fana, Zhu Taoa and Xin Xiaoa
b
aKey Laboratory of Macrocyclic and Supramolecular Chemistry of Guizhou Province, Guizhou University, Guiyang, China; College of
Chemistry, Chemical Engineering and Materials Science, Collaborative Innovation Center of Functionalized Probes for Chemical Imaging in
Universities of Shandong, Key Laboratory of Molecular and Nano Probes, Ministry of Education, Shandong Normal University, Jinan, China;
d
cDepartment of Chemistry & Biochemistry, University of Hull, Hull, UK; College of Chemistry and Environmental Engineering, Shandong
University of Science and Technology, Qingdao, China
ABSTRACT
ARTICLE HISTORY
Received 21 March 2019
Accepted 22 May 2019
The interaction between the hemicyanine indole derivative H and the cucubit[n]urils Q[7] and Q
[8] has been studied using 1H NMR and UV spectroscopy as well as by fluorescence experi-
ments. Competitive studies on the inclusion of H by Q[7] and Q[8] have also been conducted,
and reveal that on changing the size of the Q[n] cavity, the binding behaviour can be very
different.
KEYWORDS
Hemicyanine; cucubit[n]urils;
competitive binding; host-
guest
The interaction between the hemicyanine shown and the cucubit[n]uril (n=7, 8) has been studied.
Changes in the size of the Q[n] cavity result in differing binding behaviour. The affinity for
different parts of the guest changes depending on the amount of Q[8] present, whereas for
variation in the amounts of Q[7] no changes were observed.
1. Introduction
inclusion studies using cucubit[n]urils, Q[n]s, and small
molecules (8–13), we and others (14–17) have noted
that the inclusion complex is often more stable than
its parent parts. Furthermore, encapsulation of dyes by
Q[n]s can lead to fluorescent enhancement (18). With
this in mind, we have investigated herein the inclusion
complex formed between the Q[n]s, where n = 7 or 8,
and the hemicyanine H – see Scheme 1. As part of this
work, we have also conducted competition studies on
the use of Q[7] and Q[8] towards H.
Cyanines have long been recognised as useful dye
materials, and have found widespread use in the
healthcare industry for example in immunoassays (1–
7). They have also been employed in the production of
CDs and DVDs, however there are issues with chemical
stability which render the discs unreadable over time.
Although there have been some advances in stability
via the use of stabilizes/additives to afford so-called
‘metal-stabilized cyanine’ or ‘super cyanine’, there is
still room for improvement given the sensitivity of
these systems to UV-rays. During our host-guest
The interaction of Q[7] with the two cyanine dyes
pseudoisocyanine (A) and pinacyanol (B) (see Scheme
CONTACT Xin Xiao
Guiyang 550025, China Carl Redshaw
gyhxxiaoxin@163.com
Key Laboratory of Macrocyclic and Supramolecular Chemistry of Guizhou Province, Guizhou University,
c.redshaw@hull.ac.uk Department of Chemistry & Biochemistry, University of Hull, Hull HU6 7RX, UK
Supplemental data for this article can be accessed here.
© 2019 Informa UK Limited, trading as Taylor & Francis Group

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W. XU ET AL.
Scheme 1. The cucubit[n]urils Q[7] and Q[8] and the guest H.
Scheme 2. Guests A and B used by Kaifer et al (19)., Guests C – G used by Nau and Mohanty (20).
2) has previously been studied in the presence of the
polystyrenesulfonate as J- and H-aggregate promoter
(19). The host-guest chemistry of the same cucubituril
was also examined with the cyanine-type dyes C to
G (see Scheme 3), and fluorescent lifetimes were
found to be extended (20). We also note that some
dyes of this type have been used in a number of
applications where DNA damage has been induced
(21–24).
2. Experimental section
2.1. Materials and apparatus
The hosts Q[7] and Q[8] were prepared according to the
literature methods (25–27). 2,3,3-Trimethylindolenine
was obtained from Aldrich and was used without
further purification. All other reagents were of analytical
grade and were used as received. Double-distilled water
was used for all experiments.
Scheme 3. Synthesis of H.

SUPRAMOLECULAR CHEMISTRY
3
Preparation of H/Q[7]: The required amounts of Q[7]
and H were respectively weighed according to the ratio
of NQ[7]:NH = 1:1, and then dissolved in distilled water
and stirred for 30 min. The solvent was then evaporated
to afford the 1:1 inclusion compound H/Q[7]. The same
procedure was employed for the H/Q[8] system.
Synthesis of H
fluorescence spectra were obtained by excitation at
540 nm with 10 nm emissions and excitation band-
widths. The aqueous solution of H was prepared with
a concentration of 1.00 × 10−4 mol/L. An aqueous solu-
tion of Q[7]/Q[8] was prepared with a concentration of
1.00 × 10−4 mol/L for absorption spectra determination.
The UV-vis absorption experiments were performed as
follows: 1 mL of a 1.00 × 10−4 mol/L stock solution of
H and various amounts of an aqueous 1.0 × 10−4 mol/L
Q[7] solution were transferred into a 10 mL volumetric
flask, and then the volumetric flask was filled to the
final volume with distilled water. Samples of these solu-
tions were combined to give solutions with an H:Q[7]/Q
[8] ratio of 0, 0.2, 0.4, 0.6. . . . and 3.0. The formation
constants of the H@Q[7]/Q[8] complexes (K) (1:1) were
calculated according to curve fitting method. The Jobs
plot method was used to determine the inclusion ratio
of the substance, NQ[7]:N(Q[7] + H) = 0, 0.1, 0.2, 0.3, . . ., 1.0.
Synthesis of 1
2,3,3-Trimethylindolenine (796.15 mg, 5 mmol) and
iodomethane (4258.80 mg, 30 mmol) were dissolved in
acetonitrile (40 mL). The solution was stirred under an
inert nitrogen atmosphere at reflux for 12 h. On cooling,
the resulting solution was filtered and the brown pre-
cipitate was washed with diethyl ether and then dried
in vacuum to afford 1 (1280.00 mg, 85%).1H NMR
(DMSOd6, 400 MHz) δ 7.90 (d, J = 5.9, 2.9 Hz, 1H), 7.82
(t, 1H), 7.64–7.60 (m, 2H), 3.96 (s, 3H), 2.75 (s, 3H), 1.52
(s, 6H), (Figure S1).
Synthesis of H
The dye H was synthesized according to the
reported procedure (28).
2.4. MALDI-TOF mass spectrometry
1 (301.17 mg, 1.0 mmol) and 4-dimethylaminoben-
zaldehyde (179.028 mg, 1.2 mmol) were dissolved in
ethyl alcohol (40 mL). The solution was stirred at reflux
under an inert nitrogen atmosphere for 12 h. On cool-
ing, the resulting solution was filtered and the kerme-
sinus-like precipitate was washed with diethyl ether and
MALDI-TOF mass spectrometry was recorded on
a Bruker BIFLEX III ultra-high resolution Fourier trans-
form ion cyclotron resonance (FT-ICR) mass spectro-
meter with ɑ-cyano-4-hydroxycinnamic acid as matrix.
3. Result and discussion
then dried in vacuum to give
H (376.14 mg,
87%).1H NMR (D2O, 400 MHz,) δ 8.04 (d, J = 15.7 Hz,
1H), 7.66 (d, J = 9.0 Hz, 2H), 7.46 (d, J = 7.2 Hz, 1H),
7.39–7.28 (m, 3H), 6.91 (d, J = 15.6 Hz, 1H), 6.70 (d, J =
9.0 Hz, 2H), 3.69 (s, 3H), 2.95 (s, 6H), 1.57 (s, 6H), (Figure
S2). And MALDI-TOF MS spectra are shown in Figure S3.
Usually, the above types of dyes are known to aggregate in
solution. Thus, in order to research the aggregation of dye
H, we examined the absorption and emission spectra of H in
solution as a function of concentration. As shown in Figure
S4 and S5, the UV-vis absorption spectra of H progressively
increased in intensity when the concentration of dye H was
gradually increased. Meanwhile, the emission spectra of
H progressively increased on gradually increasing the con-
centration of dye H when the concentration was lower than
1.2 × 10−5 mol/L. However, the fluorescence intensity gra-
dually decreases when the concentration exceeded
1.2 × 10−5 mol/L. This suggests that dye H will aggregate
when the concentration is more than 1.2 × 10−5 mol/L.
2.2. 1H NMR spectroscopy
To study the host-guest complexation of Q[7]/Q[8] and H,
1
all the H NMR spectra, including those for the titration
experiments, were recorded at 298.15 K on a JEOL JNM-
ECZ400S 400 MHz NMR spectrometer (JEOL) in D2O. D2
O was used as a field-frequency lock, and the observed
chemical shifts are reported in parts per million (ppm).
The concentration of Q[7]/Q[8] employed in the NMR
experiments was 5.0 × 10−4 mol/L.
3.1 Inclusion complex of H and Q[7]
The binding interactions between the guest H and Q[7]
1
can be conveniently monitored using H NMR spectro-
2.3. UV-Vis absorption and fluorescence emission
spectra
scopic data recorded in neutral D2O solution. Figure 1
(and table S1) shows the changes observed in the
1H NMR spectrum of H as progressively larger amounts
of Q[7] are added to the solution. Clear up-field shifts of
the signals of the protons g to k were observed as Q[7]
was added, whilst the protons at the end of the mole-
cule bearing the quaternary nitrogen experienced little
UV-vis absorption spectra of the host-guest complexes
were recorded using an Agilent 8453 spectrophot-
ometer at room temperature. Fluorescence emission
spectra were recorded on a VARIAN Cary Eclipse spec-
trofluorometer (Varian, Inc., Palo Alto, CA, USA). The

4
W. XU ET AL.
Figure 1. Interaction of H and Q[7] (20 °C): 1H NMR spectra (400 MHz, D2O) of H (ca. 0.5 mM) in the absence (a), 0.33 equiv.(b), 0.55
equiv. Q[7] (c), 0.80 equiv.(d), 1.05 equiv. Q[7] (e), 1.43 equiv.(f), 2.07 equiv.(g) and neat of Q[7] (h).
change. This indicates that the 4-NMe2-phenyl motif
and the ethylene linker were accommodated within
the cavity of Q[7] and the quaternary ammonium part
was out the portal (see cartoon, top right Figure 1). The
addition of a second equivalent of Q[7] had little effect
on the 1:1 inclusion complex.
indicating the formation of a inclusion complex in aqueous
solution. The K value is the same order of magnitude for the
Q[7] and the guest dye A (see Scheme 2) (19), and one order
of magnitude lower than that observed for Q[7] and dye
B (19). Furthermore, a Job’s plot (figure S6) based on the
continuous variation method clearly showed that the UV
spectra of H fitted well with a 1:1 stoichiometry for the host
−guest inclusion complex.
To further understand the binding of the guest H to Q[7],
we also employed UV-vis spectroscopy (Figure 2). The UV-
vis spectra were obtained using aqueous solutions contain-
ing a fixed concentration of guest H (1.0 × 10−5 mol·L−1) and
variable concentrations of Q[7]. The dye H has an absorp-
tion maximum centered at 559 nm. On gradually increasing
the Q[7] concentration in the H solution, the absorption
band of the guest exhibits a progressively higher absor-
bance due to the formation of the host-guest complex Q[7]
@H. Similar experiments were performed using fluores-
cence spectroscopy, and as shown in Figure 2(c), the fluor-
escence emission of H occurs at 600 nm with an excitation
wavelength at 540 nm in aqueous solution. On gradual
addition of Q[7] to a solution of the guest H, the emission
spectra of H progressively decreased in intensity as the
3.2 Inclusion complex of H and Q[8]
A similar investigation of the interaction of H and Q[8] by
1H NMR spectroscopy (see Figure 3 and Table S2), again
revealed chemical shift changes consistent with encapsula-
tion of the 4-NMe2-phenyl motif and the ethylene linker,
whilst the quaternary ammonium part was out the portal
(see cartoon right side Figure 3). Interestingly, on addition
of a second equivalent of Q[8], the data is consistent with
a situation where only the quaternary ammonium part is
included, while the 4-NMe2-phenyl motif lies outside the
portal, but is adjacent the second Q[8] molecule (see car-
toon bottom right Figure 3); the COSY of H and 1.96 equiv.
of Q[8] has also been studied (figure S7).
n(Q[7])/n(H) ratio increased. The UV and fluorescence data
for the molar ratio of the host Q[7] to the guest H can be
fitted to a 1:1 binding model. Moreover, the association
constant (K) is calculated according to the curve fitting
Upon addition of Q[8], the complexation of H afforded
a decrease from 0.68 to 0.59 in the absorption (see Figure 4
(a,b)) until a 1:1 host-guest ratio was achieved. On further
method, and was found to be (6.43
0.06)×104 M−1,

SUPRAMOLECULAR CHEMISTRY
5
Figure 2. (Colour online) (a) Electronic absorption and (c) fluorescence spectra of H (1 × 10−5 mol L−1) upon addition of increasing
amounts (0, 0.2, 0.4······2.6, 2.8, 3.0 equiv.) of Q[7], the concentrations and absorbance vs. NQ[7]/NH plots (b), and the concentrations
and emission vs. NQ[7]/NH plots (d).
Figure 3. Interaction of H and Q[8] (20 °C): 1H NMR spectra (400 MHz, D2O) of H (ca. 0.5 mM) in the absence (a), 0.30 equiv.(b), 0.61
equiv.(c), 0.84 equiv.(d), 1.02 equiv.(e), 1.18 equiv.(f), 1.30 equiv.(g), 1.44 equiv.(h), 1.54 equiv.(i), 1.65 equiv.(j), 1.72 equiv.(k), 1.93
equiv.(l) and neat (m) of Q[8].

6
W. XU ET AL.
Figure 4. (Colour online) (a) Electronic absorption and (c) fluorescence spectra of H (1 × 10−5 mol L−1) upon addition of increasing
amounts (0, 0.1, 0.2······1, 1.2, 1.4······3.0 equiv.) of Q[8], the concentrations and absorbance vs. NQ[8]/NH plots (b), and the
concentrations and emission vs. NQ[8]/NH plots (d).
addition of Q[8], the UV absorption band of the guest
exhibited progressively higher absorbance until the n(Q[8])
/n:(H) and was 2:1. These observations were consistent with
the initial formation of a 1:1 host-guest complex, and then
the subsequent formation of a 2:1 host-guest inclusion
complexes as the Q[8] concentration was increased. Also,
we calculated the association constant for the Q[8]@H
complex [K = (1.07 0.04) × 105] (1:1 Q[8]-guest complex),
which is greater than that observed for H with Q[7], indicat-
ing that the Q[8]@H complex is more stable than the Q[7]
@H complex. Further support for this comes from the fluor-
escence spectroscopic results, which are shown in Figure 4
(c,d). When increasing amounts of host Q[8] were added to
H, a decrease in the emission intensity at the maximum
emission wavelength (596 nm) was observed until a 1:1
host-guest ratio was achieved. On further addition of Q[8],
the same phenomena were observed to those observed in
the UV spectra. These results are consistent with the
observed 1H NMR spectra (Figure 3). The MALDI-TOF mass
spectrometry experiments provided further evidence for
the formation of a 1:1 stoichiometry for the host–guest
inclusion complexes of Q[7]/Q[8] and guest H. In their
MALDI-TOF MS spectra (Figure 5), major signals were
observed at m/z = 1468.839 and m/z = 1634.516, which
Figure 5. MALDI-TOF mass spectrometry of Q[7]@H (a) and Q[8]@H (b).

SUPRAMOLECULAR CHEMISTRY
7
correspond to [Q[7]@H-I−]+ (calculated 1468.416) and [Q[8]
@H-I−]+ (calculated 1634.556).
of the portal (see cartoon), whilst the Q[7] no longer
includes any of H.
For comparison, the addition of Q[7] to a solution of
the Q[8]@H inclusion complex was also studied. As
shown in figure S8 and S9, on gradually increasing the
Q[7] concentration in the Q[8]@H solution, there is no
effect on the Q[8]@H inclusion complex, which differs
from the behaviour observed when Q[8] is added to
a solution of the Q[7]@H complex. This is due to the
association constant for guest H with Q[8] being greater
than that of H with Q[7], and that the Q[8]@H complex
is more stable than the Q[7]@H complex.
To further investigate the competition between
H with Q[7] and Q[8], we examined the bonding beha-
viour of the host–guest inclusion complexes via spec-
troscopic methods (absorption and fluorescence
spectroscopy). As shown in Figure 7, when the host-
guest ratio n(Q[7])/n(H) was fixed at 1:1, and Q[8] was
then added to this solution, the UV absorption and
fluorescence spectra underwent marked changes. This
is consistent with the differing binding behaviour of Q
[8] towards H compared to that of Q[7].
3.3 Competition experiments of H with Q[7] and Q
[8]
We have also carried out competition studies on this
system to ascertain whether there is a preference for
1
inclusion by Q[7] or Q[8]. The H NMR spectra shown
in Figure 6 (and table S3) represent the system where
Q[7] is first added, and we have discussed the results
above. Once the molar ratio of Q[7] and H was about
1.0 (Figure 6(b)), subsequently Q[8] (0.87 equiv. of Q
[8], Figure 6(c); 1.80 equiv. of Q[8] Figure 6(d)) was
added. A slight down-field shift of the signals of the
protons of the 4-NMe2-phenyl motif and an obvious
up-field shift of the signals of the protons of the
ethylene linker and the quaternary ammonium part
was observed as Q[8] was added compared to the
situation when the molar ratio of Q[7] and H at
about 1.0. The specific shifts are as follows: the reso-
nances of protons Hh, He, Hg, Hf and Ha of
H exhibited an up-field shift of 0.02 ppm (from 7.87
ppm to 7.04 ppm), 0.47 ppm (from 7.51 ppm to 5.91
ppm), 0.45 ppm (from 6.94 ppm to 6.49 ppm), 0.87
ppm (from 3.96 ppm to 3.09 ppm), and 0.83 ppm
(from 1.80 ppm to 0.97 ppm), and the resonances of
protons Hd-Hc became two groups of peaks (at 7.16,
7.04 ppm) when Q[8] was added. This indicates that
the quaternary ammonium part and the ethylene lin-
ker were accommodated within the cavity of the Q[8]
and that the 4-NMe2-phenyl motif was external, ie out
4. Conclusions
In conclusion, we have investigated the host guest chem-
istry between the hemicyanine indole derivative H and
the cucubit[n]urils Q[7] and Q[8]. Results indicate that
there is a preference for inclusion of the 4-NMe2-phenyl
motif and the ethylene linker. However, if the studies are
conducted in the presence of a second equivalent of Q
[n], then, when n = 8, the situation is reversed and there is
a preference for inclusion of the quaternary ammonium
Figure 6. Interaction of H, Q[7] and Q[8] (20 °C): 1H NMR spectra (400 MHz, D2O) of H (ca. 0.5 mM) (a), in the presence of 1.02 equiv.
of Q[7] (b), in the presence of 0.87 equiv. of Q[8] (c), and in the presence of 1.80 equiv. of Q[8] (d).

8
W. XU ET AL.
Figure 7. (Colour online) (a) Electronic absorption and (b) fluorescence spectrometry of H/Q[7] (1:1, 1 × 10−5 mol L−1) upon addition
of increasing amounts (0, 0.2, 0.4······3.0 equiv.) of Q[8]; (c) the concentrations and absorbance vs. NQ[8]/NH/Q[7] plots; (d) the
concentrations and fluorescence emission vs. NQ[8]/NH/Q[7] plots.
motif. This contrasts with the behaviour observed for Q[7]
(see Figure 1), where use of excess Q[7] has no effect on
the 1:1 inclusion complex.
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