Interaction of a hemicyanine dye and its derivative with DNA and cucurbit[7]uril

Article abstract of DOI:10.1039/c4nj00068d

The host-guest interaction of trans-4-[4-(dimethylamino)styryl]-1- methylpyridinium iodide (DSMI) with cucurbit[7]uril (CB[7]) was investigated through fluorescence, absorption, ¹H NMR and mass spectrometry. DSMI can be included by CB[7] with 1:2 stoichiometry to form the DSMI/CB[7] complex, exhibiting a larger binding affinity than that of DNA. To make a comparison with DSMI, another pyridium vinyl group was introduced into the aniline ring of DSMI to get a hemicyanine derivative D2, and a ternary complex among D2, CB[7] and DNA was formed. All these provide new insights to investigate the interaction of organic dyes, CB[7] and DNA.

Full text of DOI:10.1039/c4nj00068d

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Interaction of a hemicyanine dye and its derivative
with DNA and cucurbit[7]uril†
Cite this: New J. Chem., 2014,
38, 3600
Shiguo Sun,* Ye Yuan, Zhiyong Li, Si Zhang, Hongyan Zhang and Xiaojun Peng
The host–guest interaction of trans-4-[4-(dimethylamino)styryl]-1-methylpyridinium iodide (DSMI) with
1
cucurbit[7]uril (CB[7]) was investigated through fluorescence, absorption, H NMR and mass spectrometry.
Received (in Montpellier, France)
15th January 2014,
Accepted 20th May 2014
DSMI can be included by CB[7] with 1 : 2 stoichiometry to form the DSMI/CB[7] complex, exhibiting a
larger binding affinity than that of DNA. To make a comparison with DSMI, another pyridium vinyl group
was introduced into the aniline ring of DSMI to get a hemicyanine derivative D2, and a ternary complex
among D2, CB[7] and DNA was formed. All these provide new insights to investigate the interaction of
organic dyes, CB[7] and DNA.
DOI: 10.1039/c4nj00068d
www.rsc.org/njc
Introduction
Recently, cucurbit[n]urils (CB[n]),1,2 pumpkin-shaped macrocylic
compounds comprised of n glycoluril units linked by pairs of
methylene bridges with rigid cavities, have shown numerous
applications ranging from molecular recognition,3–5 dye encap-
sulation,6,7 and drug delivery8,9 to self-assembly molecular
devices.10,11 The negative charge density on the carbonyl groups
and the inner surface of the hydrophobic cavity promote CB[n]s
to include small guest molecules12 and binding with metal
cations13 and cationic organic molecules via ion–dipole inter-
action.14 The effects, such as fluorescence enhancement, fluor-
escent lifetime extension and photostability improving, caused by
the interaction of CB[n]s and fluorescent dyes have been exten-
sively studied.6 However, the cooperation or competitive inter-
action between CB[n] and DNA has been rarely reported.15–18
These investigations will be helpful for improving the sensitivity
Scheme 1 Synthetic route for the D2.
of the fluorescent sensor,15–17 demonstrating the role of CB[n] in (DSMI, Scheme 1), a common cationic hemicyanine dye always
the fluorescent sensing process. Therefore, it is meaningful to used as a fluorescent probe for DNA analysis, has been investi-
pay attention to the interaction of organic dyes, CB[n]s and DNA. gated. As a homologue of CB[6], the bigger cavity of CB[7] can
Hemicyanine was often used as a fluorescent probe for DNA make it easy to self-assemble with DSMI, providing a further
analysis,19 cell microviscosity20 and metal ion detection.21 The approach to study the interaction of the dye with CB[n]s and
interactions between some hemicyanine dye derivatives or DNA, and its good solubility in water is more suitable for
styryl dyes with similar structure and CB[7] have been investi- biological applications. In continuation of our related research,11
gated,22–26 and the results demonstrated that CB[7] could bind the interaction between DSMI and CB[7] was investigated
to the dyes through ion–dipole interaction. In our previous through fluorescence, absorption, 1H NMR and mass spectro-
work,11 the chemically tunable interaction between CB[6] and metry, then the competitive binding interaction of DSMI with
trans-4-[4-(dimethylamino)styryl]-1-methylpyridinium iodide CB[7] and DNA was studied and the results demonstrated that
CB[7] had a larger binding affinity with DSMI than DNA. To
State Key Laboratory of Fine Chemicals, Dalian University of Technology, E 224,
make a comparison with DSMI, another pyridium vinyl group
was introduced into the aniline ring of DSMI to get a hemi-
cyanine derivative D2 (Fig. 1), in the case of D2, one pyridium
West Campus, Dalian, 116024, P. R. China. E-mail: shiguo@dlut.edu.cn;
Fax: +86 411 84986304
† Electronic supplementary information (ESI) available: NMR and mass spectra
vinyl of D2 can be included into the cavity of CB[7] and the other
of D2, MS and the fitting plot for DSMI/CB[7] and D2/CB[7] complexes. See DOI:
10.1039/c4nj00068d
can be intercalated into DNA to form a ternary complex.
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little modification.28 Phosphoryl chloride (50.0 g) was added to
DMF (81.2 g) in drops. Then Me2NPh (12.1 g) was added in
drops into the solution, and the reaction lasted for 10 h at
80 1C. The reactant was poured into the mixture of 600 g of ice
and 150 mL of 38% NaOH solution, and kept at 0 1C to give a
large amount of precipitate. The precipitate was filtered and
purified by column chromatography on silica gel (eluting with
petroleum ether: ethyl acetate 5 : 1) to give 4.5 g (25% of yield)
1
of (1). H NMR (400 MHz, CDCl3, d in ppm) 10.04 (s, 1H), 9.86
(s, 1H), 7.92 (d, J = 8.8, 1H), 7.03 (d, J = 8.8, 1H).
Compound D2 (2,4-bis[(E)-N-methyl-4-pyridinyl ethenyl]1-
dimethylamino benzene diiodide). The mixture of 4-dimethyl-
amino-benzol-1,3-dicarbaldehyde (1.77 g, 10.0 mmol), 1,4-
dimethylpyridinium iodide (4.7 g, 20.0 mmol) and piperdine
(1 mL) in 50 mL ethanol was refluxed for 4 h, the reactant was
cooled, and the precipitate was collected. Recrystallization was
carried out twice to give the dark purple product, 2.2 g of D2 with
yield of 37%. Anal. Calcd (found): C, 47.15 (47.03); H, 4.45 (4.40);
N, 6.87 (6.81). 1H NMR (400 MHz, D2O, d in ppm) 8.55 (d, J = 6.6,
2H), 8.50 (d, J = 6.6, 2H), 8.03 (d, J = 6.6, 2H), 7.98 (d, J = 6.6, 2H),
7.93 (s, 1H), 7.84 (d, J = 16.2, 1H), 7.72 (d, J = 16.2, 1H), 7.68 (d, J =
8.4, 1H), 7.31 (d, J = 16.2, 1H), 7.25 (d, J = 18.0, 1H), 7.21 (d, J =
8.8, 1H), 4.26 (s, 3H), 4.22 (s, 3H), 2.82 (s, 6H). 13C NMR
(100 MHz, D2O, d in ppm) 155.5, 154.0, 153.9, 144.8, 144.6,
140.5, 138.3, 131.1, 128.9, 128.0, 124.4, 124.0, 123.6, 121.6, 119.1,
47.5, 47.4, 44.6. HRMS m/z found: 357.2205 C24H27N3 (M+):
requires M, 357.2204. The corresponding spectra can be found
in Fig. S1–S3 (ESI†).
Fig. 1 The structures of DSMI, D2 and CB[7].
Experimental section
Materials and methods
The water used in the test was distilled water. Other solvents
and reagents were of analytical grade and used without further
purification. DSMI was synthesized as described in our pre-
vious study11 and CB[7] was synthesized according to the
literature.27 Calf thymus DNA (ct-DNA) was obtained from
Sigma Chemical Co. (USA).
NMR data were recorded in D2O on a VARIAN INOVA-400
spectrometer. Mass spectrometric data were obtained on a
Q-Tof mass spectrometer (Micromass, Manchester, England).
Absorption spectra were measured on a Perkin-Elmer Lambda
35 UV-Vis spectrophotometer. Fluorescence measurements Results and discussion
were performed on a VARIAN CARY Eclipse Fluorescence
Spectrophotometer. The pH titration measurements were made
using a Model PHS-3C meter.
The host–guest interaction between DSMI and CB[7]
DSMI has an absorption maximum at 450 nm and a fluores-
cence peak at 605 nm in aqueous solution. As shown in Fig. 2,
the absorption maximum changed from 450 nm to 469 nm and
the A value decreased from 0.30 to 0.12 with the addition of 10
equiv. of CB[7] in a phosphate buffer solution (pH = 7.4).
Another absorption peak aroused by the protonated form of
DSMI appeared at B330 nm, suggesting that part of DSMI was
protonated even at pH = 7.4 after the dye included CB[7]. The
fluorescence intensity at the maximum emission wavelength
was increased by B10 times, and the fluorescence peak had a
The absorption and fluorescence spectra of DSMI with CB[7]
were measured in distilled water. The fluorescence titration experi-
ments were performed as follows: 25 mL of 1.0 ꢀ 10ꢁ3 mol Lꢁ1 stock
solution of DSMI and a different amount of 1.0 ꢀ 10ꢁ3 mol Lꢁ1
CB[7] aqueous solution were transferred into a 5 mL volumetric
flask, then the volumetric flask was filled to the final volume with
distilled water. Fluorescence and absorption spectra were measured
after 3 minutes of ultrasonic agitation. The NMR spectra were
obtained in D2O with DSS (3-(trimethyl-silyl)-1-propanesulfonic acid
sodium salt) as the internal standard; the ratio of dye versus CB[7]
was calculated by the ratio of their integral areas for special peaks;
the protonated form of DSMI and D2 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.
Synthesis
The synthetic route for preparation of D2 is illustrated in
Scheme 1:
Compound 1 (4-dimethylamino-benzol-1,3-dicarbaldehyde).
Compound 1 was synthesized according to the literature with
Fig. 2 The absorption and fluorescence (lex = 450 nm) spectra of DSMI
along with the addition of CB[7], from (1) to (14), 0, 0.2, 0.6, 1.0, 1.4, 1.8, 2.2,
2.6, 3.0, 4.0, 5.0, 6.0, 8.0, 10.0 ꢀ 10ꢁ5 M of CB[7] was added, the
concentration of the dye was 1 ꢀ 10ꢁ5 M, pH = 7.4.
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blue shift from 605 nm to 592 nm, demonstrating the inter-
action of the dye with CB[7]. The dye was confined in the
nonpolar cavity of CB[7], decreased the nonradiative decay of
the excited state and hindered the formation of the twisted
intramolecular charge transfer (TICT) state, leading to a
fluorescence enhancement. The fluorescence enhancement
mechanism by CB[7] was similar to that of CB[6] demonstrated
in our previous work.11 However, the fluorescence intensity was
less enhanced by CB[7] because of its relative large cavity size
compared with that of CB[6].
The fluorescence pH titration of the complexed dye (DSMI/
CB[7]) was performed under conditions of virtually quantitative
complexation29 (5 mM DSMI, 100 mM CB[7], corresponding to
499% dye complexation, Fig. S4, ESI†), permitting a direct estima-
Fig. 3 Job’s plot of DSMI/CB[7] complexes in an alkaline environment,
Asymmetric plot with maximum at B0.35 mol fraction indicating a 1 : 2
inclusion.
0
tion of the pKa value 5.6 for the complexation, while the pKa of
DSMI was 3.1. The pKa shift of 2.5 units may be caused by the more
stable complex of DSMIH+/CB[7] compared with DSMI/CB[7].
The interaction between DSMI and CB[7] was investigated by
1H NMR spectroscopy (Fig. S5, ESI†). Because of the pKa shift
from 3.1 to 5.6, the protonated form of DSMI could be formed
when the pH was below 8, so the 1H NMR titration experiment
was performed in D2O with a pH value of B10. When less than
1 equiv. CB[7] was added into the alkaline solution of DSMI in
D2O, all the protons shifted to the upfield, and all the signals
became broader. This indicated that DSMI and CB[7] formed a
loosely bonded complex and the bonded CB[7] shifted back and
forth on the DSMI molecule to undergo a fast exchange
process.12,30,31 All the protons were in the shielding/deshield-
ing microenvironment, and formed a dynamic balance between
the free and complexed states, leading to broader signals.
When more than 1 equiv. of CB[7] was added, the signals of
DSMI were difficult to observe due to the precipitation of the
complex formed between DSMI and CB[7].
conditions. However, the stoichiometry of DSMI and CB[7] was
not certain in alkaline solution. Therefore, for the complexation
of DSMI and CB[7], the stoichiometry was determined by a
continuous variation technique (Job’s plot)32 based on the
fluorescence intensity of DSMI in the presence of CB[7]. Differ-
ent concentration of DSMI and CB[7] solutions were prepared
and mixed and the sum of the concentrations was kept constant.
The typical plot for the DSMI/CB[7] complex is shown in Fig. 3.
The maximum fluorescence intensity was observed at x = 0.35,
indicating that the dye/CB[7] inclusion complex in aqueous
solution was mainly formed with 1 : 2 stoichiometry.
The binding constant values for 1 :1 and 1 : 2 were evaluated
by considering the following complexation equilibrium according
to the literature,33 where K1 and K2 are the binding constants for
the formation of the corresponding 1: 1 and 1: 2 complexes.
K1
Ð
CB½7ꢂ þ Dye
CB½7ꢂ ꢃ Dye
K2
The interaction between the protonated form of DSMI
(1)
1
(DSMIH+) and CB[7] was also investigated by H NMR titration
CB½7ꢂ ꢃ Dye þ CB½7ꢂ
Ð
ðCB½7ꢂÞ2 ꢃ Dye
(Fig. S6, ESI†). A trace amount of acid was added together with
CB[7] to ensure the formation of the DSMIH+/CB[7] complex
(pH = 3). When less than 1 equiv. of CB[7] was added, a stable
DSMIH+/CB[7] complex was formed, and separated signals of
the free DSMI and DSMIH+/CB[7] complex were observed. H8
was kept fixed at 3.32 ppm and H1, H2 and H7 moved down-
field, while H3, H4, H5 and H6 moved upfield, indicating that
CB[7] included DSMIH+ in the aniline ring and the double bond
part. When 1 equiv. of CB[7] was added, the free DSMI signal
disappeared. When more than 1 equiv. of CB[7] was added into
the solution, the unchanged H8 and downfield shifted H7
shifted to the upfield, and H3, H4, H5, and H6 continued to
shift to the upfield, while H1 and H2 shifted to the more
downfield. This result suggested that the second CB[7] included
DSMI from the pyridium ring part and the two CB[7] included
DSMI around H1 and H2. ESI-MS confirmed the formation of
the (CB[7]/DSMI + H+)2+ (1 : 1) complex (Fig. S7, ESI†): m/z calcd
At any stage, the observed fluorescence intensity If corre-
sponds to the sum of the fluorescence intensities from dyes,
CB[7]ꢃdye and (CB[7])2ꢃdye, and is directly proportional to their
corresponding concentrations in the solution. Therefore, one
can write the following eqn (2):
½Dyeꢂeq
½Dyeꢂ0
½CB7 ꢃ Dyeꢂeq
½Dyeꢂ0
If ¼ If0
þ ICB7ꢃDye
(2)
½ðCB7Þ2 ꢃ Dyeꢂeq
þ I
ðCB7Þ2ꢃDye
½Dyeꢂ0
Eqn (2) can be rearranged to a modified Benesi–Hildebrand
eqn (3).33
2
0
I0 þ ICB7ꢃDyeK1½CB7ꢂ þ I
K1K2½CB7ꢂ
ðCB7Þ2ꢃDye
1 þ K1½CB7ꢂ0 þ K1K2½CB7ꢂ0
f
0
If ¼
(3)
2
701.2531, and found 701.2911, but the signal of the 2CB[7]/ where I0f is the fluorescence intensity in the absence of CB[7],
DSMI complex was not found. ICB7ꢃDye is the fluorescence intensity when all the dye molecules
From the NMR titration experiments, the stoichiometry of interact with CB[7] as a 1 : 1 complex, and I(CB7)2ꢃDye is the
DSMIH+ and CB[7] can be determined to be 1 : 2 under acidic fluorescence intensity when all the dye molecules are complexed
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with CB[7] forming a 2 : 1 complex. And finally [Dye]0 and [CB7]0
are the total concentrations of the dye and the CB[7] used.
Applying eqn (3) to fit the experimental data presented in
Fig. S8 (ESI†), the K1 and K2 values were estimated to be (1.35 ꢄ
0.05) ꢀ 105 Mꢁ1 and (3.2 ꢄ 0.4) ꢀ 103 Mꢁ1. The higher value of
the first order binding constant and the lower value of the
second order binding constant indicated that the first com-
plexation was caused by the strong ion–dipole interaction
between the carbonyl laced portals of CB[7] and the positive
charge centered on DSMI. The second interaction was caused
by the hydrophobic nature of the dye.33 The smaller value of K2
could be one of the main reasons why the MS signal for the 1 : 2
complex was not found.
Scheme 2 The competitive binding of DSMI with DNA and CB[7].
peak at 393 nm exhibited a hypochromic shift of 57 nm com-
pared with that of DSMI. It is reasonable to attribute the
hypochromic shift to the reduced electron density on the aniline
ring when the electron-withdrawing substituent (pyridium vinyl
group) anchored.34 The decreased electron-donating ability of
the aniline ring weakened the TICT process of the parent dye. D2
exhibited an enlarged Stokes shift up to 230 nm with very low
background fluorescence (Ff o 0.001), and the emission
maximum was located at 623 nm with a red shift of 18 nm
compared with that of DSMI.
Incremental addition of CB[7] to the D2 solution resulted in
a gradual decrease in the absorbance with B6 nm and B16 nm
bathochromic shifts for the absorption peaks at 345 nm and
393 nm, respectively (Fig. 5). Meanwhile, the emission peak
shifted to 615 nm with B8 nm red shift and the fluorescence
monitored at 623 nm was enhanced about 5-fold with the
gradual addition of 10 equiv. of CB[7]. All these can be ascribed
to CB[7] can include D2 around the two pyridium rings, and
inhibit the torsional motion of the pyridium groups.
Competitive interaction of DSMI with DNA and CB[7]
DSMI could bind to the double helical DNA with high affinity
through a groove binding mode.19 The groove binding inhibits
the non-radiative deactivation of the excited state of DSMI,
and results in enhanced fluorescence intensity, owing to the
geometric restriction imposed by the narrow minor groove of
the DNA helix. About 43-fold of fluorescence enhancement and
no shift in emission maximum were observed with the addition
of 300 equiv. of ct-DNA (Fig. 4a).
As shown in Fig. 4b, when CB[7] was gradually added into
the solution of 1000 equiv. of ct-DNA and DSMI, the fluores-
cence intensity decreased dramatically to 21% of the initial
fluorescence with a B8 nm blue shift of the emission peak.
Both the fluorescence intensity and the emission peak became
similar to the state of DSMI in the presence of CB[7]. These
results show that CB[7] could bind with DSMI competitively
although DSMI bonded with ct-DNA at first. Therefore, it is easy
to deduce that CB[7] has a larger binding affinity with DSMI
than that of ct-DNA. The competitive process is suggested in
Scheme 2.
The 1H NMR titration experiments were carried out in pH 10
(Fig. S9, ESI†) solution to ensure that the dye was not to be
protonated. H9 and H90 remained almost unchanged with the
addition of CB[7], while H8, H80, H1 and H2 moved to the
downfield, and the proton of the vinyl group moved upfield.
The signal changes indicated that the double bond was
included in the CB[7] cavity and H1 and H2 were located
outside the portal of CB[7].
Host–guest interaction between D2 and CB[7]
The interaction between the protonated form of D2 and
CB[7] was also investigated by 1H NMR titration (Fig. S10, ESI†).
A trace amount of acid was added together with CB[7] to ensure
the formation of the D2H+/CB[7] complex (pH = 3). The signals
at down field became broader and difficult observe with the
To make a comparison with DSMI, we introduced another
pyridium vinyl group into the aniline ring of DSMI to generate
a novel fluorescent dye D2. Two absorption peaks at 345 and
393 nm were observed in aqueous solution and the absorption
Fig. 4 The fluorescence spectra of DSMI with the addition of DNA (a),
from (1) to (21), 0, 0.4, 0.8, 1.2, 1.6, 2.0, 3.0, 4.0, 6.0, 8.0, 10.0, 15.0, 20.0,
30.0, 40.0, 60.0, 80.0, 100.0, 150.0, 200.0, 300.0 equiv. of DNA was
added; and the fluorescence spectra of DSMI in the presence of 1000
equiv. DNA with the addition of CB[7] (b), from (1) to (15), 0, 0.4, 0.8, 1.2,
2.0, 3.0, 4.0, 6.0, 8.0, 10.0, 12.0, 15.0, 20.0, 25.0 equiv. of CB[7] was added,
the concentration of DSMI was 1.0 ꢀ 10ꢁ5 M, pH = 7.4.
Fig. 5 The absorption and fluorescence spectra of D2 with the addition of
CB[7], from (1) to (16), 0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.4, 1.8, 2.2, 2.6, 3.0, 4.0, 5.0,
6.0, 8.0, 10.0 ꢀ 10ꢁ5 M of CB[7] was added, the concentration of D2 was
1 ꢀ 10ꢁ5 M, pH = 7.4.
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addition of CB[7]. However, it was clear H1 shifted downfield
until 2 equiv. of CB[7] was added, and H2 and H20 shifted
upfield. These changes indicated that CB[7] interacted with
D2 around each pyridium ring. The MS spectrum further
confirmed this result (Fig. S11, ESI†), m/z found: 506.7834
(calculated for (D2H+ + CB[7])3+: 506.8543), 759.6782 (calculated
for (D2 + CB[7])2+: 759.7814), 894.5886 (calculated for (D2H+ +
2CB[7])/3: 894.3021).
The stoichiometry of 1 : 2 for the D2/CB[7] complex allowed Fig. 6 (a) The fluorescence spectra of D2/DNA with the addition of CB[7],
from (1) to (18), 0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.6, 2.0, 3.0, 4.0, 6.0, 8.0, 10.0,
the binding constant to be calculated according to the above
mentioned method for DSMI. Applying eqn (3) to fit the
experimental data presented in the fluorescent titration spectra
(Fig. S12, ESI†), the K1 and K2 values were estimated to be (8.4 ꢄ
0.4) ꢀ 104 Mꢁ1 and (2.3 ꢄ 0.3) ꢀ 104 Mꢁ1 for the D2/CB[7]
complex. The difference between K1 and K2 of D2 is not much,
which is different from that of DSMI, suggesting that the first and
second complexations are caused by a similar ion–dipole inter-
action. The pKa shift of 1 unit (Fig. S4, ESI†) with and without the
presence of CB[7] can provide some further information.
12.0, 15.0, 20.0, 25.0 equiv. of CB[7] was added, the concentration of D2
was 1 ꢀ 10ꢁ5 M and DNA was 100 equiv. (b) The fluorescence spectra of
D2/CB[7] with the addition of 60 equiv. of DNA, CB[7] was 10.0 equiv.
of D2, the concentration of D2 was 1.0 ꢀ 10ꢁ5 M, pH = 7.4.
Competitive interaction of D2 with DNA and CB[7]
The fluorescence response of D2 to DNA was investigated
through optical measurements. When 30 equiv. of DNA was
added into the dye solution, the absorption maxima of D2 at
345 nm and 393 nm exhibited a first hypochromism (with the
concentration ratio [DNA]/[D2] o 2) and then hyperchromism
(with [DNA]/[D2] 4 2) with bathochromic shifts of 7 nm and
35 nm, respectively (Fig. S13, ESI†). The absorption spectra
changes related to the concentration ratio ([DNA]/[D2]) demon-
strate that the binding mode of D2 with DNA was different. As
suggested in the literature, D2 may be aggregated on the
surface of the DNA helix at a low ratio and intercalated into
DNA base pairs at a high ratio.35 Moreover, D2 exhibited a
significant fluorescence increase with the addition of DNA. The
fluorescence intensity at 623 nm was enhanced by ca. 35-fold
with a red shift of 8 nm in the presence of 100 equiv. of DNA
(Fig. S13, ESI†). This may be caused by the restriction on the
torsional motion of vinyl groups derived from the interactions
between the cationic pyridium unit and the anionic phosphate
backbone of DNA;36 together with the water prohibiting effect
in the hydrophobic environment offered by the higher-order
structure of DNA.
In the presence of D2, the denaturation temperature of
ct-DNA was increased, 17.5 1C, while, only 6.8 1C was increased
in the case of DSMI (Fig. S14, ESI†), suggesting that D2
interacted with DNA through an intercalation mode, while
DSMI interacted with DNA through a grove binding mode.19
Competitive interaction among D2, CB[7] and DNA was
performed and the results are shown in Fig. 6. After titration
of 25 equiv. CB[7] into D2 and 100 equiv. DNA solution (Fig. 6a),
a 20% decrease was observed in the fluorescence intensity. In
Scheme 3 The schematic diagram for the formation of the ternary
complex among D2, CB[7] and DNA.
proposed that one pyridium vinyl of D2 was included into the
cavity of CB[7] and the other intercalated into DNA to form a
ternary complex as shown in Scheme 3.
Conclusion
In summary, the interaction between DSMI and CB[7] was
investigated through UV-Vis, fluorescence, 1H NMR and MS
spectrometry. It was found that DSMI can be included by CB[7]
with a 1 : 2 stoichiometry. When another pyridium vinyl group
was introduced into the aniline ring of DSMI to get a hemi-
cyanine derivative D2, a ternary complex among D2, CB[7] and
DNA was formed. D2 interacted with DNA through a intercala-
tion mode, while DSMI interacted with DNA through a grove
binding mode. All these provide new insights to investigate the
interaction of organic dyes, CB[7] and DNA.
Acknowledgements
comparison, about a 7.5-fold fluorescence increase was observed This work was financially supported by the State Key Laboratory
along with the addition of 60 equiv. of DNA into the solution of of Fine Chemicals, Dalian University of Technology, the
D2 and 10.0 equiv. of CB[7] (Fig. 6b). It should be noted that a National Natural Science Foundation of China (No. 21272030,
quite similar result was reached for the two different procedures. 21072024), the Open Project Program of the Key Laboratory of
Taking account of the symmetric structure of D2, it can be ECO-Textiles (Jiangnan University), the Ministry of Education
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