A stimuli-responsive supramolecular assembly between inverted cucurbit[7]uril and hemicyanine dye

Article abstract of DOI:10.1039/c8nj03344g

The effect of inverted curcurbit[7]uril (iQ[7]) on the binding mode of 2-(4-(dimethylamino)styryl)-1-methylpyridinium (DASPMI) was determined in this study. A large fluorescence enhancement of DASPMI was realized by the formation of an inclusion complex with iQ[7]. A 1:1 inclusion complex was determined through UV absorption and fluorescence spectroscopies, ¹H nuclear magnetic resonance (NMR) spectroscopy, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), and isothermal titration calorimetry (ITC) at different pH values. In addition, we also devised a method for the controlled release of DASPMI from the iQ[7] macrocycle by adding α,α′-diamino-p-xylene.

Full text of DOI:10.1039/c8nj03344g

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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Stimuli-Responsive Supramolecular Assembly between Inverted
cucurbit[7]uril and Hemicyanine Dye
Zhong-Zheng Gao,a Jinglan Kan,b Zhu Tao,a Bing Bian,c Xin Xiao,*a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
The effect of inverted curcurbit[7]uril (iQ[7]) on the binding mode of 2-(4-(dimethylamino)styryl)-1-methylpyridinium
(DASPMI) was determined in this study. A large fluorescence enhancement of DASPMI was realized by the formation of an
inclusion complex with iQ[7]. A 1:1 inclusion complex was determined through UV absorption and fluorescence
spectroscopy, 1H nuclear magnetic resonance (NMR) spectroscopy, matrix-assisted laser desorption ionization time-of-
flight mass spectrometry (MALDI-TOF MS), and isothermal titration calorimetry (ITC) under different pH values.
Additionally, we also devised a method for the controlled release of DASPMI from the iQ[7] macrocycle by adding α,α'-
diamino-p-xylene.
www.rsc.org/
nanomaterials,26 and drug delivery.27,28 In 2005, inverted
cucurbit[n]urils (iQ[n]s, n=6, 7) were first discovered by Isaacs
and Kim.29 As a new type of cucurbit[n]uril, little research on
Introduction
the host-guest chemistry of iQ[n]s had been conducted.30-33 In
our previous work, our group determined that iQ[6] with p-
phenylenediamine interacts, as well as α,ω-alkyldiammonium
and symmetric viologens guests;34,35 we also discovered the
With the rapid development of novel fluorescent compounds,
the field of supramolecular chemistry has benefited from the
practical use of fluorescent dyes.1,2 Significant fluorescence
changes can appear after the complexation of a fluorescent
dye with a macrocycle.3-5 Assays have been devised that rely
on an indicator-displacement strategy, in which the analyte
competitively displaces a fluorescent guest, resulting in a
change in fluorescence intensity.6,7 Previously reported
examples describe the introduction of a third component into
a solution of a host/dye interaction system, and the third
component displaces the fluorescent dye from the system so
that the solution recovers to the initial fluorescence
condition.8-10
The interactions of macrocyclic hosts with fluorescent dyes
have been extensively investigated for the complexation
properties of the resulting fluorescent dyes, for example,
calix[n]arenes, cucurbit[n]urils, pillar[n]arenas, et. al.11-14 Of
note, cucurbit[n]urils (Q[n]s, n=5-8, 10, 13-15)15-20 as
additional new macrocyclic compounds in supramolecular
chemistry have shown numerous potential applications
ranging from molecular recognition,21-23 nanotechnology,24,25
interaction of iQ[7] with lanthanide cations36a
,
α,ω-
alkyldiammonium36b and dialkyl-4,4′-bipyridinium dicationic
guests.37,38
Styryl pyridinium dye and its derivative have often been
used as fluorescent probes for nucleotides and DNA analysis39-
41, metal ion detection42, and single cell micro-viscosity tests43.
The binding behaviour of styryl pyridinium dye and its
derivative with cucurbit[n]urils (n=6, 7) has been reported, and
the results showed that a large fluorescence enhancement of a
hemicyanine by supramolecular interaction with Q[6]
occurred.40 Q[7] included the dye through ion-dipole
interaction with
a
1:2 stoichiometry.41,44a Lately, the
interactions of styryl pyridinium derivative with twisted
cucurbit[14]uril was also investigated.44b Furthermore, Styryl
pyridinium dye was also examined for its ability to bind to
other macrocyclic receptors.45-48
To extend our general interest regarding the
supramolecular chemistry of iQ[n]s, herein, we report that we
used UV absorption and fluorescence spectroscopy, 1H NMR
spectroscopy, MALDI-TOF mass spectrometry, isothermal
titration calorimetry(ITC), and a computational method to
document that fluorescence enhancement occurs when 2-(4-
(dimethylamino)styryl)-1-methylpyridinium iodide (DASPMI)
interacts with iQ[7] (Fig. 1). DASPMI is more sensitive to acids,
and we found different binding models between DASPMI and
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The protonated form of DASPMI was determined firstly by
addition of deuterium chloride to observe the color of the
solution changing from yellow to colorless, and then checking
the pH of the solution using a pH test paper.
ITC measurements
Microcalorimetric experiments were performed using an
isothermal titration calorimeter Nano ITC (TA, USA) in aqueous
solution. The experiments of DASPMI with iQ[7] consisted of
25 consecutive injections (6 μL) of a DASPMI (1.0×10-3)
solution into the microcalorimetric reaction cell (1.3 mL)
charged with a solution of iQ[7] (1.0×10-4). The heat evolved
was recorded at 298.15 K. The heat of reaction was corrected
for the heat of dilution of the guest solution determined in
separate experiments. All solutions were degassed prior to
titration experiment by sonication. Computer simulations
(curve fitting) were performed using the Nano ITC analyze
software.
Fig. 1 Structures for iQ[7] and DASPMI and α,α'-diamino-p-xylene.
iQ[7] under different pH values. Additionally, the recognition-
mediated supramolecular complex was judiciously tuned by
introducing selected release-stimulants (α,α'-diamino-p-xylene,
Fig. 1) to demonstrate the controlled release of the
chromophoric dye (DASPMI) from the host-guest assembly.
MALDI-TOF mass spectrometer
MALDI-TOF mass spectra were taken on a Bruker BIFLEX III
ultra-high resolution Fourier transform ion cyclotron
Experimental Section
resonance (FT-ICR) mass spectrometer with
α-cyano-4-
Materials and methods
hydroxycinnamic acid as matrix. The MALDI-TOF experiments
were carried out by adding the DASPMI solution (1.0×10−3
mol·L, 100 μL) into an iQ[7] solution(1.0×10−4 mol·L-1, 1.0 mL).
The solution concentration was about 1.0 × 10−4 mol·L-1
(DASPMI−iQ[7] = 1:1).
Deionized water was used for all experiments. Starting
materials and solvents for syntheses were purchased
commercially and used as supplied without further purification.
iQ[7] was prepared and purified according to our previously
published
procedure.49
2-(4-(dimethylamino)styryl)-1-
Quantum chemistry calculations
methylpyridinium iodide (DASPMI) and α,α'-diamino-p- xylene
were received from Aldrich Chemical, USA and purified by
vacuum sublimation process.
All calculations were processed with the Gaussian 09 software
package. The initial geometries of all structures were
constructed with the aid of the Hyperchem Release 7.52
package. Becke’s three-parameter hybrid functional with the
correlation functional of Lee, Yang and Parr (B3LYP) was used
for full geometry optimization at the 6-311g(d,p) level of
theory for C, H, N, O.
Nuclear magnetic resonance measurements
1
All NMR spectra, including H NMR spectrum for the titration
experiments and 1H-1H COSY NMR spectrum, were recorded at
20°C on a VARIAN INOVA-400 spectrometer with SiMe4 as an
internal reference at 20°C. D2O was used as a field-frequency
lock and the observed chemical shifts are reported in parts per
million (ppm) relative to that for the internal standard (TMS at
0.0 ppm).
Results and Discussions
Binding behaviour in aqueous solution
UV-Vis absorption and fluorescence emission spectra
1H NMR spectroscopy
UV-Vis absorption spectra of the host-guest complexes were
performed in
The binding interaction of DASPMI and iQ[7] was also
investigated using 1H NMR. It has been reported that the 1H
NMR peaks of guest protons inside the low-polarizability cavity
of Q[n] shift upfield, and interactions with the carbonyl
oxygens of Q[n] result in downfield shifts due to the
deshielding of the protons.50,51 The 1H NMR spectroscopy
measurements indicate that DASPMI forms a host-guest
inclusion complex with the iQ[7] host. Titration 1H NMR
spectra obtained using a fixed amount of iQ[7] and various
equivalents of DASPMI are shown in Fig. 2. Compared with the
free guest DASPMI, the H1 proton signals of N-dimethyl for
DASPMI showed a gradual upfield shift of approximately 0.3
ppm, and the signal for the H2 proton showed an obvious
1 cm quartz cells on an Aglient 8453
spectrophotometer at room temperature. Fluorescence
spectra measurements were performed in 1 cm quartz cells on
a
Varian Cary Eclipse fluorescence spectrophotometer
equipped with a xenon discharge lamp at room temperature.
The host and guests were dissolved in distilled water. The
absorption spectra was obtained at a concentration of 2.0×10-5
mol·L-1 DASPMI and different iQ[7] concentrations for the
iQ[7]@DASPMI system at 25 °C. The fluorescence spectra was
obtained by excitation at 491 nm with 10 nm emission and
excitation bandwidths (600V) at a concentration of 2.0×10-5
mol·L-1 DASPMI and different iQ[7] concentrations for the
iQ[7]@DASPMI system.The pH was adjusted to pH = 7 with
sodium phosphate.
The second absorption spectrum was obtained at pH=2
and other conditions were the same. The fluorescence spectra
was obtained by excitation at 326 nm with 10 nm emission and
excitation bandwidths (750V) at a concentration of 2.0×10-5
mol·L-1 DASPMIH+ and different iQ[7] concentrations for the
iQ[7]@DASPMIH+ system.
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Fig. 2 1H NMR spectra (400 MHz, D2O) of iQ[7] in the (A) absence and
(B) presence of 0.18, (C) 0.30, (D) 0.45, (E) 0.68, (F) 0.85, and (G) 1.05
equiv. of DASPMI and (H) 1H NMR spectrum of DASPMI at 20 °C.
Fig. 3 (A) UV spectra and (B) fluorescence spectra of DASPMI (2.0×10-5
M) with increasing concentration (0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7,
0.8, 0.9, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0 equiv.) of
iQ[7]at pH=7(excitation wavelength at 491nm). The (C, D) shows the
concentrations and the corresponding ∆A and ∆F vs. NiQ[7]/NDASPMI
curve.
downfield shift of approximately 0.2 ppm in a 1:1 host-guest
ratio in D2O. Additionally, the proton signals for the benzene
ring H3, H4 showed an upfield shift approximately 0.66 and
0.70 ppm, respectively. The proton signals for the double
bonds H5, H6 also showed an upfield shift about 0.14 and 0.30
ppm, respectively. This occurred because of the shielding
effect of the electron-rich cavities of iQ[7], suggesting that the
deep inclusion of the N-dimethyl and benzene ring moiety of
the guest DASPMI occurs in the cavity of iQ[7] due to the
formation of complex iQ[7]@ DASPMI. In contrast, the proton
signals for pyridine ring H7, H9, H10 showed a downfield shift in
the range of 0.04-0.25 ppm, and the H8 proton signals showed
no significant shift, which indicated that the pyridine ring
interacts with the carbonyl groups of iQ[7]. These
experimental data indicated that the benzene ring, the N-
dimethyl, and the double bonds were included in the low-
polarizability cavity of iQ[7], and that the pyridine ring and the
N-methyl on the pyridine ring were predominantly located in a
deshielding environment, which generated a 1׃1 host-guest
inclusion complex in aqueous solution. Formation of the
inclusion complex between DASPMI and the host (iQ[7])
molecule was also confirmed by 1H-1H correlation
spectroscopy nuclear magnetic resonance(COSY NMR)
spectrum (Fig. S1).
Fig. 4 ITC profile of iQ[7] with DASPMI in aqueous solution at 298.15 K.
UV-Vis absorption and fluorescence spectra
The absorption intensity changes upon complexation of iQ[7]
with DASPMI was first examined. As shown in Fig. 3A, DASPMI
has an absorption maximum centered at 437 nm and a
fluorescence peak at 582 nm in aqueous solution. Upon
addition of iQ[7], the complexation of DASPMI was followed by
fluorescence response of DASPMI significantly increased upon the
addition of iQ[7] (Fig. 3B). The fluorescence intensity was enhanced
approximately 18 times when 3 equiv. of iQ[7] was added to the
system. In addition, the fluorescence emission exhibited a blue shift
from 582 nm to 574 nm. Their curve of ΔA and ΔF vs. NiQ[7]/NDASPMI
(based on the continuous variation method) clearly showed that
both the UV and fluorescence spectral data for DASPMI fit well to
the 1:1 stoichiometry of the host-guest inclusion complexes (Fig. 3C,
3D ) in aqueous solution.
a
decrease from 0.53 to 0.45 in absorption with a
bathochromic shift from 437 to 455 nm up to a 1:1 host-guest
ratio. With the addition of iQ[7], the absorption maximum
peak was observed to increase from 0.45 to 0.48 with a
bathochromic shift with the addition of 3 equiv. of iQ[7], which
indicated the formation of a host-guest complex. The
Isothermal titration calorimetry (ITC)
Isothermal titration calorimetry (ITC) is one of the most
effective techniques for investigating host-guest interactions
because it not only determines the thermodynamic
parameters (ΔSο, ΔHο, ΔGο), but it also provides the association
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constant (Ka). To further understand the nature of host-guest namely, the low-polarizability cavity of iQ[7], and the pyridine
complexations of iQ[7] with DASPMI, we carried out ITC ring, the N-methyl on the pyridine ring, and two methyl groups
experiments. The experimental data (Fig. 4, Table S1) showed of the N-methyl were predominantly located in a deshielded
that the association constant (Ka) of DASPMI with iQ[7] is environment. We speculated that the possible reason for this
(6.58±0.53)×105 M-1, which is higher than Ka value of Q[7] with is that the ionic dipole interaction between the positive
DASPMI41b. The high binding constant allows iQ[7] and DASPMI nitrogen of the pyridyl moiety of N-dimethyl and the portal
to form a stable inclusion complex in aqueous solution,
carbonyl oxygens of iQ[7] and the hydrophobic interaction of
The intermolecular complexation interactions between iQ[7] the cavity of iQ[7] could be the driving forces for the formation
and DASPMI was driven by both favourable enthalpy changes of such a 1:1 host-guest inclusion complex in an acid media at
and favourable entropy changes. Furthermore, the resolution pH2. Formation of an inclusion complex between DASPMIH+
of the binding molar ratio value is n = 0.981±0.017, which and host(iQ[7]) molecule was also confirmed by 1H-1H COSY
suggests that the interaction ratio of iQ[7] and DASPMI was NMR spectrum (Fig. S5†).
1:1.
UV-Vis absorption and fluorescence spectra
We also measured the absorption and fluorescence intensity
MALDI-TOF mass spectrum
MALDI-TOF mass spectrometry (MS) provided further evidence changes in acid media (pH=2) because the guest DASPMI was
for DASPMI inclusion complexes with iQ[7]. Observation of the more sensitive to acid. The absorption intensity changes of
double charged peak at m/z = 1402.04, corresponding to iQ[7]- DASPMIH+ were significantly different from those of DASPMIH.
DASPMI (calculated for[(C16H19IN2)@(C42H42N28O14)- I-]+, DASPMIH+ has an absorption maximum centered at 326 nm.
1402.30), confirmed the formation of the 1:1 inclusion The UV absorption intensity at 437 nm was very weak. Upon
complex in aqueous solution, which is in agreement with what addition of iQ[7], the complexation of DASPMIH+ was followed
we have observed in aqueous solution by 1H NMR by a decrease from 0.57 to 0.45 in absorption with a blue shift
spectroscopy and isothermal titration calorimetry (Fig. S3).
from 326 to 319 nm up to a 1:1.2 host-guest ratio, as shown in
Fig. 6A. The absorption maximum peak was observed to be
increased from 0.45 to 0.51 with a blue shift upon addition of
3 equiv. of iQ[7]. Fig. 6B shows the maximum fluorescence
Binding behaviour in hydrochloric acid media at pH=2
1H NMR spectroscopy
Fig. 5 1H NMR spectra (400 MHz, pD=2) of iQ[7] in the (A) absence and
presence of 0.25 (B), 0.54 (C), 0.72 (D), 0.88 (E) and 1.02 (F) equiv. of
DASPMIH+ and the (G) 1H NMR spectrum of DASPMIH+ at 20 °C.
Fig. 6 (A) UV spectra and (B) fluorescence spectra of DASPMIH+
(2.0×10-5) with increasing concentration (0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6,
0.7, 0.8, 0.9, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0 equiv.) of
iQ[7] at pH=2 (excitation wavelength at 326nm). The (C, D) shows the
concentrations and the corresponding ΔA and ΔF vs. NiQ[7]/NDASPMI
curve.
To determine the binding mode of the protonated form of
DASPMI (DASPMIH+), the 1H NMR and 1H-1H COSY NMR
spectra(Fig. S4†
) of DASPMIH+ were obtained by adding
deuterium HCl to the dye solution at pH2 while the solution
colour changed from yellow to colourless. The 1H NMR
spectrum was different from that of the former DASPMI. As
shown in Fig. 5, there was no significant chemical shift for the
the group of N-dimethyl (proton H1) at 1:1 host-guest ratio. All
the proton signals for benzene ring H3, H4 and the double
bonds H5, H6 showed an upfield shift. The pyridine ring proton
H7-H10 and the N-methylproton H2 moved downfield.
intensity of DASPMIH+ centered at 584 nm at pH2. The fluorescence
response of DASPMIH+ increased upon the addition of iQ[7], and
the fluorescence emission did not show obvious movement with
the addition of 1 equiv. of iQ[7], nor did the fluorescence intensity
significantly change. Their curve of ΔA and ΔF vs. NiQ[7]/NDASPMI
(based on the continuous variation method) clearly showed that
both the UV and fluorescence spectral data of DASPMIH+ fit well to
the 1:1 stoichiometry of the host–guest inclusion complexes (Fig.
6C, 6D).
According to the experimental data, we concluded that
when DASPMIH+ was mixed with iQ[7], it penetrated through
the cavity of iQ[7]. The benzene ring and the double bonds
were predominantly located in
a shielded environment,
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Isaacs’s group,28 and itis higher than that for voluminous
DASPMI. Fig. S7-S8 display the H NMR spectra, which shows
Quantum chemistry calculations
1
To better understand the host–guest complexation of iQ[7]
with DASPMI and DASPMIH+, molecular modeling was
the binding interaction of α,α'-diamino-p-xylene and iQ[7] in
D2O and at pD=2. Next, we used α,α'-diamino-p-xylene, a
stronger iQ[7] binder that forms an efficient inclusion complex
with iQ[7]. When α,α'-diamino-p-xylene was added, the
fluorescent complex would be replaced by the non-fluorescent
α,α'-diamino-p-xylene-iQ[7] complex and uncomplexed
DASPMI. The fluorescence curves of the 1:1 fluorescent
complex (2.0×10-5) with increasing concentrations of α,α'-
diamino-p-xylene are shown in Fig. 8. The experimental results
showed that when 4.0 equiv of α,α'-diamino-p-xylene was
added, the fluorescence intensity of iQ[7]-DASPMI decreased
until it was close to the fluorescence intensity of DASPMI itself.
The competitive effect between iQ[7] and DASPMI was also
employed
to
provide
information
regarding
the
supramolecular architectures by density functional theory
(DFT) calculations at the B3LYP/6-311g(d,p) level. Fig. 7 shows
the low energy conformations of the host–guest complexes,
which clearly revealed that DASPMI and DASPMIH+ form stable
1:1 inclusion complexes.The double bonds of the benzene ring
were located in the cavity of iQ[7], and the N-methyl on the
pyridine ring was located just outside the host’s portal, which
was in good agreement with the NMR results.
The competitive effect between DASPMI and α,α'-diamino-p-
xylene
The above experimental results show that the guest of DASPMI examined using 1H NMR. In the presence of α,α'-diamino-p-
was located in the hydrophobic cavity of iQ[7] to form an xylene, the DASPMI signals returned to the original state of the
inclusion complex with a ratio of 1:1 in aqueous solution at free guest, as seen in Fig. S9, accompanied by a color change
pH=2. Fig. S6 shows the H NMR spectra of DASPMIH+ in the of the solution under UV light at 365 nm (Fig. S10
†
),
1
presence of NaOD, demonstrating that upon adding NaOD to corroborating the complete rupture of the complex in aqueous
the DASPMIH+ system at pD=2, the signals of DASPMI in the solution. In acid media at pH2, we obtained the same
DASPMIH+ system returned to the original state of the free experimental results. (Fig. S11-S13
†). In addition, such a
DASPMI molecule. This indicates the effective dissociation of phenomenon of competition was clearly observed with the
the original DASPMIH+ with the re-formation of guest DASPMI naked eye, because the solution of DASPMI was brown, and
species.
Fig. 8 (A) Fluorescence spectra of iQ[7]-DASPMI (0.02 mmol) with
increasing concentration (0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8,
2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4.0 equiv) of α,α'-diamino-
p-xylene in aqueous solution and (A) and the fluorescence curves at
different states (B): (a) DASPMI (blue), (b) iQ[7]-DASPMI (1:1) (black),
(c) iQ[7]-DASPMI-α,α'-diamino-p-xylene (1:1:4) (red). The inset shows
the concentrations and the corresponding ΔF vs. Nα,α'-diamino-p-
xylene/Nsystem curve.
when 1.0 equiv. of iQ[7] was added, the solution turned from
brown to yellow. Then, 4.0 equiv of α,α'-diamino-p-xylene was
added to this solution, and the solution turned brown again
(
(
Fig. S10
†); this behaviour was observed in acid media (pH2)
Fig. S13†). This gives additional support for the mechanism
Fig.
7 The theoretically calculated structures of the inclusion
based on competition as proposed.
complexes (A, B) iQ[7]-DASPMI and (C, D) iQ[7]-DASPMIH+ viewed from
the (A, C) front and (B, D) side.
Conclusion
Our next aim was to devise a method for the controlled
release of DASPMI from the iQ[7] macrocycle. Usually, acid-
base neutralization52 or metal-ion decomplexation by
chelators53 have been demonstrated as resetting. Similarly,
host-guest complexes provide another possibility through the
addition of a competitive guest to release the molecule. In this
context, we have employed α,α'-diamino-p-xylene as the
stimuli, which was selected based on the binding affinity
toward iQ[7]. The association constant of α,α'-diamino-p-
xylene with iQ[7] (Ka = (9±1)×106 M-1) has been reported by
In conclusion, we demonstrated a convenient fluorescence
enhancement approach to construct photochemically sensitive
supramolecular assemblies of iQ[7] and a fluorogenic dye
(DASPMI). A 1:1 inclusion complex was determined through
UV absorption and fluorescence spectroscopy, 1H NMR
spectroscopy, MALDI-TOF mass spectrometry, and isothermal
titration calorimetry (ITC) under different pH values. Apart
from the prominent modulation in the molecular properties of
DASPMI, the complex’s response to selected stimuli, α,α'-
diamino-p-xylene, demonstrated the controlled exchange and
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release action desired with such noncovalently interaction
assemblies for activation of dye/drug for therapeuticuses. This
study lays a foundation for the design of fluorescence
enhancement by a supramolecular interaction mode.
Conflicts of interest
There are no conflicts of interest to declare.
Acknowledgements
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Graphical Abstract
Stimuli-Responsive Supramolecular Assembly between Inverted
cucurbit[7]uril and Hemicyanine Dye
Zhong-Zheng Gaoa, Jinglan Kanb, Zhu Taoa, Bing Bianc, Xin Xiaoa,*
The effect of inverted curcurbit[7]uril (iQ[7]) on the binding mode of 2-(4-(dimethyl
amino)styryl)-1-methylpyridinium (DASPMI) was determined in this study. A 1:1 inclusion
complex was determined through UV absorption and fluorescence spectroscopy, 1H nuclear
magnetic resonance (NMR) spectroscopy, matrix-assisted laser desorption ionization
time-of-flight mass spectrometry (MALDI-TOF MS), and isothermal titration calorimetry (ITC)
under different pH values. Additionally, we also devised a method for the controlled release of
DASPMI from the iQ[7] macrocycle by adding α,α'-diamino-p-xylene.