Synthesis of coumarin-pillar[5]arene as a selective fluorescent probe for methyl-parathion

Article abstract of DOI:10.1002/cjoc.201400675

A novel coumarin-pillar[5]arene derivative (P5C10) was prepared. Fluorescence spectroscopy indicates that P5C10 shows good selectivity towards methyl-parathion. A combination of NMR spectra, MALDI-TOF spectra and computational calculations reveals the for

Full text of DOI:10.1002/cjoc.201400675

FULL PAPER
DOI: 10.1002/cjoc.201400675
Synthesis of Coumarin-Pillar[5]arene as a Selective
Fluorescent Probe for Methyl-Parathion
Fan Zhang, Xianliang Cao, Demei Tian,* and Haibing Li*
Key Laboratory of Pesticide and Chemical Biology of the Ministry of Education, College of Chemistry,
Central China Normal University, Wuhan, Hubei 430079, China
A novel coumarin-pillar[5]arene derivative (P5C10) was prepared. Fluorescence spectroscopy indicates that
P5C10 shows good selectivity towards methyl-parathion. A combination of NMR spectra, MALDI-TOF spectra
and computational calculations reveals the formation of a host-guest complex driven by π-π stacking interactions.
Keywords fluorescent probe, pillar[5]arene, methyl-parathion, host-guest
Introduction
fluorescent probe for methyl-parathion (3d). By intro-
ducing the coumarin moieties with high fluorescence
Methyl-parathion is a highly toxic pesticide and
widely used as an insecticide and acaricide on agricul-
[21]
quantum yield to the pillar[5]arene via alkyl chain,
we can get the fluorescent pillar[5]arene derivative
[1]
tural crops. Due to improper use of pesticides, it has
caused serious problems in the environment and food
safety, which has posed a severe threat to human
(P5C10), which shows good selectivity and sensitivity
to methyl-parathion on the fluorescence spectra. The
1
prepared P5C10 was characterized by H NMR, MS,
[2]
health. Therefore, the development of efficient detec-
tion of methyl-parathion is in urgent demand. To meet
this requirement, a large number of methyl-parathion
detection methods have been developed, such as chro-
and elemental analysis. The fluorescence of P5C10 was
strongly quenched by methyl-parathion, which indicated
that receptor P5C10 can serve as a sensor for me-
thyl-parathion.
[
3-5]
[6]
matography,
acetylcholinesterase biosensor, fluo-
[
7]
rescence polarization immunoassay (FPIA) and so
forth. Among these methods of detecting methyl-para-
thion, the fluorescent chemosensor detection is the most
widely applied due to its high sensitivity and efficiency.
To our knowledge, design and synthesis of high effi-
cient and sensitive fluorescent sensors for the selective
recognition of methyl-parathion remains a challenging
task, and it is also the focus of our current study.
Experimental
Apparatus and reagents
1
H NMR spectra were recorded on Varian Mercury
Plus600 instrument at ambient temperature with TMS as
the internal standard. Chemical shifts are expressed in
parts per million and J values are given in hertz. MALD
I-TOF-MS were recorded on matrix assisted laser desor-
ption ionization/time of flight MS. Melting point was
recorded on METTLER TOLEDO FP62 instrument.
The absorption spectra were recorded on UV-2501. All
fluorescence measurements were carried out on a Cary
Eclipse FL10 08M018 instrument. Computational cal-
culations were recorded at HF/6-31G levels using Gaus-
sian 03. The guests are pesticide of methomyl, carbofu-
ran, isoprocarb, methyl-parathion, tsumacide, iprodione,
dichlorvos, profenofos, malathion, purchased from
Germany Dr. Ehrenstorfer Company. All chemicals
were A.R. grade and purified by standard procedures.
Pillararenes as the new generation of macrocyclic
host molecules in supramolecular chemistry have drawn
[
8-10]
considerable attention during the past few years.
With good host-guest properties, pillararene can further
self-assemble and be applied in the artificial transmem-
brane proton channels, fluorescent sensors, or other
[11-14]
[15]
functional materials.
Huang et. al. have reported
the pillar[5]arene can recognize paraquat derivatives by
the cation-π-electron interactions. For the highly sym-
metrical and rigid structure, and being easier to func-
tionalize with different substituents on all of the benzene
[16-20]
rings,
we can introduce the special fluorophore to
Synthesis of P5C10
afford high selective binding to guests.
Herein, in this paper we design and synthesize a
novel coumarin-pillar[5]arene (P5C10) as a selective
As shown in Scheme 1, the P5C10 was synthesized
in two steps. Compounds 1 and 2 were prepared ac-
*
E-mail: hbing@mail.ccnu.edu.cn
Received October 7, 2014; accepted November 21, 2014; published online XXXX, 2014.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201400675 or from the author.
Chin. J. Chem. 2015, XX, 1—5
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1

Zhang et al.
FULL PAPER
cording to the literature reported.
monomer 1 (1.9 g, 5 mmol) in 1,2-dichloroethane (35
mL) was added paraformaldehyde (0.45 g, 15 mmol)
under nitrogen atmosphere. Then boron trifluoride di-
[22]
To a solution of
20H), 3.91 (s, 10H), 3.79 (s, 10H), 2.34 (s, 30H), 2.03 (d,
J＝24.6 Hz, 40H); C NMR (100 MHz, CDCl ) δ:
3
161.95, 161.36, 155.08, 152.41, 149.75, 128.43, 125.54,
114.93, 113.64, 112.87, 111.80, 101.24, 77.27, 76.95,
76.63, 68.19, 29.45, 26.34, 26.03, 25.35, 18.46.
1
3
3 2 5 2
ethyl etherate (BF •(OC H ) , 0.65 mL, 5 mmol) was
added to the solution and the mixture was stirred at
room temperature for 30 min. Methanol (20 mL) was
poured into the reaction mixture and the solution was
concentrated and dissolved in dichloromethane (60 mL).
After the solvent was removed, the obtained solid was
purified by column chromatography on silica gel with
petroleum ether/dichloromethane (V∶V＝1∶1) as the
MALDI-TOF-MS calcd for m/z: 2914.1, found m/z:
2937.0, [M＋Na] . Anal. calcd for C175H O40: C 72.16,
170
H 5.84; found C 72.38, H 5.70.
＋
General procedure of fluorescent detection
P5C10 was dissolved in DMSO as the stock solution
−6
with a concentration of 5.0×10 mol/L for UV-vis
spectroscopy and fluorescent spectroscopy analysis.
And the pesticides (3a－3i) were dissolved in acetoni-
trile to prepare stock solutions with a concentration of
1
eluent to get a white powder 2, 1.3 g, yield 66.1%. H
NMR (CDCl
3
, 600 MHz, TMS) δ: 6.87 (s, 10H), 3.96 (s,
2
2
1
0H), 3.75 (s, 10H), 3.51 (s, 20H), 2.13－2.10 (m, 20H),
−5
.00－1.95 (m, 20H); MALDI-TOF-MS calcd for m/z:
8.0×10 mol/L. The fluorescent spectra were recorded
＋
960.6, found: m/z 1961.6 [M＋H] . Anal. calcd for
on Cary Eclipse FL1008 M018.
75
C H100Br10O10: C 45.92, H 5.10, Br 40.82; found C
4
5.70, H 5.33, Br 40.65.
Compound 2 (0.2 g, 0.1 mmol) and anhydrous potas-
Results and Discussion
The molecular recognition behavior of the P5C10
was studied toward pesticides 3a－3i by fluorescence
spectroscopy. Figure 1 shows the fluorescence response
of P5C10 to 16 equiv. of pesticides (3a－3i), including
methomyl, carbofuran, isoprocarb, methylparathion,
tsumacide, iprodione, dichlorvos, profenofos and mala-
thion. With the 310 nm excitation wavelength, there is a
significant fluorescence quench of P5C10 upon addition
of 3d, but other organic pesticides have little effects on
the fluorescence (Figure 1b). To better elucidate the se-
lective recognition of pesticide compounds, column
chart showed the variation of the fluorescence quench-
ing intensity at 391 nm (Figure 1c). When 3d was added
to the system, the intensity of fluorescence quenching
sium carbonate (0.22 g, 1.6 mmol) were stirred in ace-
tone for 30 min, then coumarins (0.27 g, 1.5mmol) was
added. The mixture was refluxed for 12 h, then cool to
room temperature, the product was collected by vacuum
filtration, with 30 mL dichloromethane dissolved, thor-
oughly washed with saturated salt water (50 mL) and
pure water. After removing the aqueous layer, the or-
ganic layer was collected, and dried over anhydrous
2 4
Na SO , then purified by column chromatography with
methylene chloride/methanol (V∶V＝100∶2) as elu-
ent, giving P5C10 (1.5 g, yield 51.7%). m.p. 129.6－
1
1
31.4 ℃; H NMR (CDCl
3
, 600 MHz, TMS) δ: 7.43 (d,
J＝8.9 Hz, 10H), 6.90 (s, 10H), 6.79 (d, J＝8.7 Hz,
0H), 6.65 (s, 10H), 6.06 (s, 10H), 4.08 (s, 10H), 4.02 (s,
1
Scheme 1 Synthetic route to P5C10
O
O
Br
Br
O
O
O
O
(HCHO)n
BF O(C H )
O
O
3
2
5 2
HO
K CO /CH COCH
3
O
O
ClCH CH Cl
2
2
2
3
3
O
5
5
Br
Br
O
1
2
O
O
2
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Chin. J. Chem. 2015, XX, 1—5

Synthesis of Coumarin-Pillar[5]arene as a Selective Fluorescent Probe for Methyl-Parathion
was 85% of the original. The results indicated that
P5C10 could be employed to distinguish 3d from the
other pesticide compounds by its fluorescence “on-off”.
The fluorescence spectra of P5C10 (5×10−6 mol/L)
at increasing concentrations of 3d are depicted in Figure
2. It was found that while no shift in the fluorescence
maximum was observed, the fluorescence intensity of
P5C10 decreased with increasing concentrations of 3d.
−
6
Figure 1 (a) The structures of the guests. (b) Fluorescence intensity changes for P5C10 (5×10 mol/L) in CH CN/DMSO (V/V＝1/1)
3
−5
0 0 0
upon addition of 3a－3i (8×10 mol/L). (c) (I −I)/I (λem＝391 nm). I is the fluorescent emission intensity of the host, and I is the fluo-
rescent intensity after adding 3a－3i. It shows that P5C10 appeared an obvious selectivity of 3d.
Figure 2 (a) Fluorescence spectra titration of P5C10 (5×10− mol/L) with various equivalents of 3d (0, 2, 4, 8, 12, 16, 20, 24, 28, 32,
6
3
6, 40, 44, 48, 52 equiv., λex＝310 nm). (b) Benesi-Hildebrand analysis of the fluorescence changes for the complexation between P5C10
−
5
and 3d. (c) Job’s plots of P5C10 toward 3d at an invariant total concentration of 1×10 mol/L (λ ＝391 nm, slit＝5). It illustrates the
em
host-guest fluorescence quenching occurs in 1∶1 complexation.
Chin. J. Chem. 2015, XX, 1—5
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3

Zhang et al.
FULL PAPER
Simultaneously, the association constant of P5C10 for
3
d was evaluated using the Benesi-Hildebrand equation
4
and was found to be 2.38×10 L/mol, which indicated
an important feature of P5C10 is the high binding affin-
ity toward 3d over other pesticides. In the Job plot, a
maximum fluorescence change was observed when the
molar fraction of P5C10 versus 3d was 0.5, indicating
1
∶1 complexation (Figure 2). Meanwhile, the compu-
tational calculations revealed the formation of a host-
guest complex driven by π-π stacking interactions which
formed a 1∶1 inclusion complex.
To seek more detailed information on the binding
properties of P5C10 with 3d, the H NMR spectra of
1
Figure 4 The possible complexation mode of host-guest.
mixtures of P5C10 and 3d were investigated as depicted
in Figure 3. Because of the reciprocity, the signals from
aromatic guest was included in the π-rich cavity of the
host pillar[5]arene within a 1∶1 complex mode, which
induces the fluorescence quenching. The P5C10 shows
excellent selectivity and sensitivity to methyl-parathion,
which can be developed as pesticide-detecting sensor in
our life.
the aromatic ring protons of 3d shifted upfield (H
a
, δ
0
.02; H , δ 0.01) and the signals of the protons on the
b
benzene ring skeleton of pillar[5]arene (P5C10) were
downfield shifted (ArH, δ 0.01). Possible mechanism of
host-guest interaction was proposed in Figure 4, and the
computational calculations were carried out at the
[23]
HF/6-31G (d) levels using Gaussian 03. It shows that
due to π-π stacking interactions between 3d and P5C10,
the electron-poor compound of methyl-parathion pene-
trated into the rich-electron cavity of P5C10, which
causes the fluorescence quenching for the electron
transfer.
Acknowledgement
This work was financially supported by the National
Natural Science Foundation of China (Nos. 21372092,
2
1102051), the Natural Science Foundation of Hubei
Province (Nos. 2013CFA112, 2014CFB246) and the
Self-determined Research Funds of CCNU from the
Colleges Basic Research and Operation of MOE (Nos.
CCNU13F005, CCNU14Z01001).
Supporting Information
Available experimental details, MALDI-TOF-MS,
NMR spectra of all of the components, fluorescence
spectra and other data mentioned in above paragraphs.
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