A novel coumarin-based pyrazoline fluorescent probe for detection of Fe3+ and its application in cells

Article abstract of DOI:10.1016/j.ica.2021.120469

A novel coumarin-based pyrazoline fluorescent probe A was synthesized through a four-step reaction. The structure was characterized by ¹H NMR(Nuclear magnetic resonance), ¹³C NMR and HR-ESI-MS(High resolution electrospray ionization mass spectrometry). The optical properties of the fluorescent probe was investigated by UV–vis absorption and fluorescence emission spectra. The results showed that the addition of Fe³⁺ makes the fluorescence emission spectra of A quenched and displayed a linear fluorescence response to Fe³⁺ with a detection limit of 1.01 × 10^?7 M. It also shows good reversibility upon addition of EDTA(Ethylene diamine tetraacetic acid). The structure of the fluorescent probe was optimized by DFT(Density functional theory) calculations, and the binding mechanism between the fluorescent probe and the recognition ion was explained. Moreover, the probe also has practical application in cell imaging.

Full text of DOI:10.1016/j.ica.2021.120469

Inorganica Chimica Acta 525 (2021) 120469
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Research paper
A novel coumarin-based pyrazoline fluorescent probe for detection of Fe3+
and its application in cells
,
,
Ying-Peng Zhanga *, Qi Tenga, Yun-Shang Yanga *, Hui-Chen Guob, Ji-Jun Xuec
a School of Petrochemical Engineering, Lanzhou University of Technology, Lanzhou 730050, China
b State Key Laboratory of Veterinary Etiological Biology and National Foot and Mouth Disease Reference Laboratory, Lanzhou Veterinary Research Institute, Chinese
Academy of Agricultural Sciences, Lanzhou 730046, China
c State Key Laboratory of Applied Organic Chemistry & College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
A novel coumarin-based pyrazoline fluorescent probe A was synthesized through a four-step reaction. The
structure was characterized by 1H NMR(Nuclear magnetic resonance), 13C NMR and HR-ESI-MS(High resolution
electrospray ionization mass spectrometry). The optical properties of the fluorescent probe was investigated by
UV–vis absorption and fluorescence emission spectra. The results showed that the addition of Fe3+ makes the
fluorescence emission spectra of A quenched and displayed a linear fluorescence response to Fe3+ with a
detection limit of 1.01 × 10ꢀ 7 M. It also shows good reversibility upon addition of EDTA(Ethylene diamine
tetraacetic acid). The structure of the fluorescent probe was optimized by DFT(Density functional theory) cal-
culations, and the binding mechanism between the fluorescent probe and the recognition ion was explained.
Moreover, the probe also has practical application in cell imaging.
Coumarin
Pyrazoline
Fe3+
Fluorescent probe
Cell imaging
1. Introduction
benzene rings connected around it to form a star-shaped structure.
Because of its special structure, it has larger steric hindrance and higher
Recently, fluorescent chemosensors for transition metal ions has
been attached considerable attentions due to their potential applications
in chemical and biological processes [1]. As we know, iron is an essential
micronutrient element for most organisms, it plays essential role in ox-
ygen transport and oxygen storage in blood and muscles, and has
become an important component of various enzymes and hemoglobin
[2]. However, overloaded iron was responsible for cell damage, organ
dysfunction and cancer through the abnormal production of reactive
oxygen species, hepatitis, Alzheimer’s disease [3,4].
hole transport rate [16]. Although the fluorescence emission efficiency
of triphenylamine was not high, the modified triphenylamine de-
rivatives were used in fluorescent probes [17–20], organic electrolu-
minescent materials [21,23] and organic solar cell materials [24] and
other aspects have been widely used. Pyrazoline was widely used in
molecular fluorescent probes and other fields due to its excellent blue
luminescence properties and strong fluorescence performance [25–33].
Taking all these into account, we have synthesized a new coumarin-
based pyrazoline fluorescent probe A. The probe A showed good selec-
tivity to Fe3+ over other metal ions. And this probe could be suitable for
imaging in living cells.
Organic small molecule fluorescent probes have the characteristics of
low toxicity and high sensitivity, and were widely studied and applied
by scientific researchers. Coumarin compound was a lactone compound
with benzopyrone structure. Because of its high fluorescence quantum
yield, large Stokes shift, good light stability, and easy modification of the
structure, its derivatives were widely used in antibacterial, water envi-
ronment, anti-tumor and other fields [5]. At present, the coumarin-
based fluorescent probes mainly include Schiff bases [6–11]and bio-
logical thiols [12,13], and there were few reports on coumarin-based
pyrazoline fluorescent probes[14,15].
2. Materials and methods
The raw materials required for the experiment such as triphenyl-
amine, phosphorusvoxychloride, N,N-dimethylformamide, piperidine,
sodium hydroxide, ethanol, and chloroform, Ethyl acetoacetate, 4-
(diethylamino) Salicylaldehyde were purchased from commercial
channels without further purification. The salts used in stock aqueous
solutions of metal ions were KCl, NaCl, AgNO3 , Cu(NO3)2, HgCl2, Mg
Triphenylamine was a molecule with a central N atom and three
* Corresponding authors.
E-mail addresses: yingpengzhang@126.com (Y.-P. Zhang), yangyunshang@tom.com (Y.-S. Yang).
https://doi.org/10.1016/j.ica.2021.120469
Received 24 February 2021; Received in revised form 23 April 2021; Accepted 19 May 2021
Available online 23 May 2021
0020-1693/© 2021 Elsevier B.V. All rights reserved.

Y.-P. Zhang et al.
Inorganica Chimica Acta 525 (2021) 120469
(NO3)2, Ba(NO3)2, Ca(NO3)2, CoCl2, Zn(NO3)2, CdCl2, Fe(NO3)3, Al
(NO3)3, Fe2(SO4)3, FeCl3, Fe(NO3)2, Ni(NO3)2 . 1H and 13C NMR spectra
were recorded on a Avance 400 spectrometer in CDCl3 with TMS as an
internal standard. Mass spectrum was recorded on the Thermo Q-
Exactive mass spectrometer. The melting point was measured on the
Zn2+, Pb2+, Fe2+, Cu2+, Fe3+, Na+, Ag+, K+ metal ions as the test objects.
As shown in Fig. S4, after adding 10 equiv. of the above mentioned ions
to the THF solution of probe A, only the addition of Fe3+ made the ab-
sorption spectrum curve change significantly, the addition of other
metal ions did not cause significant changes in the UV–vis absorption
XRC-1
μ
melting point instrument. The ultraviolet absorption was
spectrum, indicating that the probe A can selectively recognize Fe3+
.
recorded on Cary50. The fluorescence test was recorded on the FE06CN-
IF171(ZB) LD/LM luminescence spectrophotometer. The cells were
imaged under Leica TCS SP8 MP multiphoton microscopy, HeLa cells
was provided by the Lanzhou veterinary research institute, Chinese
academy of agricultural sciences.
4.2. Fluorescence spectra of probe A for selective and anti-interference
detection
In order to verify whether the selectivity of probe A in the fluores-
cence spectrum was consistent with that in the ultraviolet absorption
spectrum, use the same buffer solution used in the UV–vis absorption
experiment to test its effect on the fluorescence spectrum by adding 10
equiv. of different metal cations. As shown in Fig. 1, the probe A shows a
strong fluorescence emission band at 523 nm (fluorescence quantum
yield 0.326). When Fe3+ was added to the probe A system, the
3. Experimental section
The synthesis route of A was depicted in Scheme 1. Compound 1 and
2 were easily synthesized according to the literature reported methods
[34,35]. According to the literature [36], compound 3 was readily
prepared from compound 1 and 2 in 65% yield. A mixture of compound
3 (0.5140 g,1.0 mmol) and 85% hydrazine hydrate (0.6123 g, 10.0
mmol) were taken in a 100 mL reaction flask in the presence of glacial
acetic acid (15 mL) and refluxed at 118℃ for 7 h. After completion of
reaction, it was cooled and poured into crushed ice. The pure product
was obtained by silica gel column chromatography (petroleum/ethyl
acetate = 1:1) in 60% yield. Melting point(M.p.) 198-202℃. 1H NMR
(CDCl3, 400 MHz) (Fig. S1):δH ppm 8.29(s, 1H), 7.35(d, J = 8 Hz, 1H),
7.20(t, J = 12 Hz, 5H), 7.06(t, J = 12 Hz, 5H), 6.98(t, J = 8 Hz, 3H), 6.96
(s, 1H), 6.01(d, J = 8 Hz, 1H), 6.47(s, 1H), 5.51(d, J = 8 Hz, 1H), 3.87
(dd, J = 8, 12 Hz, 1H), 3.44(t, J = 8 Hz, 4H), 2.41(s, 3H), 1.22(t, J = 12
Hz, 7H).13C NMR(CDCl3, 100 MHz) (Fig. S2):δC ppm 168.56, 160.43,
157.22, 151.70, 146.95, 141.56, 135.96, 129.12, 124.20, 124.06,
122.63, 109.55, 108.44, 96.92, 59.55, 44.98, 44.53, 22.03, 12.46.HR-
ESI-MS (Fig. S3) calculated for [M + H]+ 571.2700 , found 571.2703.
4. Results and discussion
4.1. UV–vis absorption of a to Fe3+
Fig. 1. Fluorescence spectra of probe A(10 μM) in THF solution in the pre-
In order to explore the selectivity of probe a to different metal cations
scence of various metal ions.
in THF solution, select Al3+, Ni2+, Ba2+, Co2+, Cd2+, Ca2+, Mg2+, Hg2+
,
Scheme 1. Synthesis routes of probe A.
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Y.-P. Zhang et al.
Inorganica Chimica Acta 525 (2021) 120469
fluorescence intensity was quenched to 45%(fluorescence quantum
yield 0.108), and the fluorescence quantum yield was calculated by Φ =
Φs(ІА /І А)(η2
/
η2s). The addition of Al3+, Ni2+, Ba2+, Co2+, Cd2+, Ca2+
,
s
s
Mg2+, Hg2+, Zn2+, Pb2+, and Fe2+, Cu2+, Na+, K+, Ag+ metal ions did
not cause significant changes in the fluorescence spectrum. It shows that
probe A has high selectivity to Fe3+
.
Meanwhile, considering the interference of other metal cations in
practical applications, different metal cations were successively added
to the A-Fe3+ system to investigate their influence on the fluorescence
selectivity. As shown in Fig. 2, the presence of other metal cations failed
to cause a significant change in the intensity of the fluorescence spec-
trum, indicating that the presence of other metal cations will not
interfere with the selectivity of probe A.
In order to further explore the selectivity of probe A to Fe3+ and its
strong anti-interference ability, the fluorescence spectra test was carried
out in the presence of iron sulfate, chloride and nitrate in THF solution.
It can be seen from Fig. 3 that the fluorescence spectra in the presence of
different iron salts have not changed significantly, indicating that the
anion will not affect the selective recognition of Fe3+ by probe A.
Fig. 3. Fluorescence spectra of probe A(10 μM) in the prescence of different
iron salts in THF solution.
4.3. Titration experiment of probe A to Fe3+
In order to understand the sensitivity of probe A to Fe3+, the fluo-
rescence titration experiment under different Fe3+ concentrations was
studied. As shown in Fig. 4, with the continuous addition of Fe3+, the
fluorescence intensity of probe A gradually decreased. As shown in
Fig. 5, a straight line was obtained by the Benesi-Hildebrand equation
fitting. It can be found that the binding constant of A- Fe3+ complex was
3.5 × 103 Mꢀ 1, and the detection limit was 1.01 × 10ꢀ 7 M calculated
using 3σ/Ka [37].
4.4. Binding of probe A with Fe3+
In order to study the stoichiometry of probe A and Fe3+, the job’s plot
experiment was carried out in THF solution. Keeping the total concen-
tration of probe A and Fe3+ for 10
μM, and the concentration ratio of 1:9,
2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2 and 9:1 between probe A and Fe3+ was
titrated [38]. As shown in Fig. 6, the maximum mole fraction of A ap-
pears at 0.5, which supporting a 1:1(A: Fe3+) binding stoichiometry.
Fig. 7.
Fig. 4. Fluorescence emission spectra of probe A was titrated with Fe3+ (0–12
In order to fully understand the response of probe A to Fe3+, EDTA
was added to the A-Fe3+ complex to investigate its influence on the
fluorescence intensity. With the addition of EDTA into the A-Fe3+
complex, the fluorescence intensity was basically restored. It shows that
the complexation between probe A and Fe3+ was reversible.
equiv.) in THF solution.
Fig. 5. Benesi-Hildebrand plot of A (10
Fe3+ (0–12 equiv.).
μM) in THF solution in the presence of
Fig. 2. Fluorescence spectra of probe A(10
μ
M) and Fe3+(10 equiv.) in the
prescence of various metal ions in THF solution.
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Y.-P. Zhang et al.
Inorganica Chimica Acta 525 (2021) 120469
respectively. After 24 h, the cell proliferation did not change signifi-
cantly, and the cell survival rate was greater than 85%. These data
indicate that probe A has very low toxicity.
4.6. Imaging of intracellular Fe3+
In order to study the application of probe A in the biological field,
fluorescence microscopy imaging technology was used to study its
fluorescence imaging in HeLa cells. As shown in Fig. 9, the cells remain
intact in the bright field, and green fluorescence appears in the fluo-
rescence field. When the bright field and the fluorescent field overlap, it
indicates that the probe A has good cell permeability and can enter the
cell. When Fe3+ was added to the above system, the fluorescence in-
tensity of probe A in the cell decreased. Therefore, the fluorescence in-
tensity signal of the probe can be used to detect Fe3+ in the cell. It also
provides a possible method for detecting Fe3+ in biological systems in
the future.
Fig. 6. Job’s plot for A with Fe3+ in THF solution.
4.7. Proposed mechanism of A to Fe3+
As shown in Fig. S5, the absorption peak at 1699 cmꢀ 1 was the
characteristic absorption peak of the carbonyl group of α-pyrone. The
absorption peak at 1667 cmꢀ 1 was the characteristic absorption peak of
the benzene ring in the coumarin matrix, and the absorption peak at
1621 cmꢀ 1 was the characteristic absorption peak of the double bond
conjugated with the α-pyrone carbonyl group.
The characteristic absorption peak of the carbonyl group in the
acetyl group attached to the pyrazole ring was at 1586 cmꢀ 1. The ab-
sorption peak around 1260 cmꢀ 1 to 1280 cmꢀ 1 was the characteristic
–
absorption peak of the C O bond connected to the carbonyl group of
α
-pyrone. The absorption peak at 1511 cmꢀ 1 was the characteristic
–
absorption peak of the C N double bond on the pyrazole ring.
–
After adding Fe3+, the characteristic absorption peak of the carbonyl
group of
α
-pyrone shifted from 1699 cmꢀ 1 to 1738 cmꢀ 1, and the
characteristic absorption peak of the carbonyl group in the acetyl group
connected to the pyrazole ring shifted from 1586 cmꢀ 1 to 1589 cmꢀ 1
.
–
–
The characteristic absorption peak of the C N double bond on the
pyrazole ring shifted from 1511 cmꢀ 1 to 1515 cmꢀ 1. It shows that Fe3+
coordinated with probe A at three positions, which changed the char-
acteristic absorption peak wavenumber.
Fig. 7. Reversible study of A to Fe3+ with EDTA.
4.5. Cytotoxicity of the probe A
4.8. DFT calculation
In order to study the biocompatibility of the probe, the MTS method
was used to detect the toxicity of probe A to HeLa cells [39]. As shown in
Combined with the results of infrared spectroscopy, B3LYP/6–31(G)
d and B3LYP/LANL2DZ were used to optimize the structure of probe A
before and after the ion was added [40]. As shown in Fig. 10, before ion
was added, the electron cloud with the highest molecular orbital of
probe A was mainly distributed in the triphenylamine part. The electron
cloud with the lowest unoccupied molecular orbital was mainly
Fig. 8, HeLa cells were incubated with 5, 10, 25, 50, and 100 μL probe A,
distributed in the coumarin and pyrazole ring part. After adding Fe3+
,
the electron cloud distribution has changed. And the energy level dif-
ference of the orbital was reduced from 3.3945 eV to 1.1291 eV. It shows
that the addition of Fe3+ makes the system stable.
4.9. Speculated mechanism of fluorescence
In order to further understand the binding behavior of probe A and
Fe3+
,
1H NMR titration experiment was studied (Fig. S6). Through ex-
periments, it was found that due to the paramagnetic influence of Fe3+
,
it has caused serious interference to the peak shape of the compound.
However, it can be seen from the figure that the hydrogen protons on the
–
C
N bond on the pyrazole ring (5.40–5.43 ppm) and the hydrogen
protons on the –CH3 on the acetyl group (2.27 ppm) have slightly
moved. As shown in Scheme 2, according to the results of infrared
titration and DFT, it was speculated that the carbonyl group of benzo-
–
–
Fig. 8. Cytotoxicity of the probe A in HeLa cells.
pyrone in the probe A molecule, CH = N and C O on the pyrazole ring
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Y.-P. Zhang et al.
Inorganica Chimica Acta 525 (2021) 120469
Fig. 9. Fluorescence images of HeLa cells. (a) fluorescence images of HeLa cells incubated with probe A(10
μ
M); (b) fluorescence images after prescence of
Fe3+(100
μM).
Fig. 10. The HOMO-LUMO energy gaps for probe A and A-Fe3+
.
were involved in the coordination of Fe3+ in a 1:1 mode. It was because
of the coordination of Fe3+ that the charge or energy in the molecule was
transferred and the fluorescence intensity decreased.
5. Conclusion
In summary, we have designed a novel coumarin-based fluorescent
probe A as an analytical tool for detecting Fe3+. The fluorescence was
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Y.-P. Zhang et al.
Inorganica Chimica Acta 525 (2021) 120469
Scheme 2. Proposed binding mode of A with Fe3+
.
quenched when Fe3+ was added. And the complex process was revers-
ible with Fe3+. The probe A has low toxicity and outstanding cell
permeation, which laid the foundation for practical application for
fluorescence detection.
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CRediT authorship contribution statement
Ying-Peng Zhang: Conceptualization, Methodology, Supervision.
Qi Teng: Data curation, Writing - original draft. Yun-Shang Yang:
Investigation, Writing - review & editing. Hui-Chen Guo: Data curation.
Ji-Jun Xue: Software, Validation.
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[17] B. Dumat, E. Faurel-Paul, P. Fornarelli, N. Saettel, G. Metge, C. Fiorini
Declaration of Competing Interest
Debuisschert, F. Charra, F. Mahuteau-Betzer, M.P. Teulade-Fichou, Influence of the
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The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
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