Photo-physical aspects of BODIPY-coumarin conjugated sensor and detection of Al3+ in MCF-7 cell

Article abstract of DOI:10.1080/10610278.2019.1659267

BODIPY azine bearing chemosensor R1 has been synthesised for selective detection of Al³⁺with visual colour change from red-purple to purple and photo-physical studies were explained through F?rster Resonance Energy Transfer (FRET) mechanism. Chemosensor showed good sensing capability with high binding constant and lower Limit of Detection (LOD) towards Al³⁺. Cell viability and fluorescence microscopic experiments illustrated about the cytocompatibily of the sensor in presence of Al³⁺ in living cells (MCF-7).

Full text of DOI:10.1080/10610278.2019.1659267

Supramolecular Chemistry
ISSN: 1061-0278 (Print) 1029-0478 (Online) Journal homepage: https://www.tandfonline.com/loi/gsch20
Photo-physical aspects of BODIPY-coumarin
conjugated sensor and detection of Al3+ in MCF-7
cell
Kumari Somlata Kashyap, Sumit Kumar Hira & Swapan Dey
To cite this article: Kumari Somlata Kashyap, Sumit Kumar Hira & Swapan Dey (2019): Photo-
physical aspects of BODIPY-coumarin conjugated sensor and detection of Al3+ in MCF-7 cell,
Supramolecular Chemistry, DOI: 10.1080/10610278.2019.1659267
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SUPRAMOLECULAR CHEMISTRY
https://doi.org/10.1080/10610278.2019.1659267
ARTICLE
Photo-physical aspects of BODIPY-coumarin conjugated sensor and detection
of Al3+ in MCF-7 cell
Kumari Somlata Kashyapa, Sumit Kumar Hirab and Swapan Deya
b
aDepartment of Chemistry, Indian Institute of Technology (ISM), Dhanbad, India; Department of Zoology, The University of Burdwan,
Burdwan, India
ABSTRACT
ARTICLE HISTORY
Received 22 March 2019
Accepted 5 August 2019
BODIPY azine bearing chemosensor R1 has been synthesised for selective detection of Al3+with
visual colour change from red-purple to purple and photo-physical studies were explained
through Förster Resonance Energy Transfer (FRET) mechanism. Chemosensor showed good
KEYWORDS
sensing capability with high binding constant and lower Limit of Detection (LOD) towards Al3+
.
Chemosensor; FRET; Al3+
and cell image
Cell viability and fluorescence microscopic experiments illustrated about the cytocompatibily of
the sensor in presence of Al3+ in living cells (MCF-7).
1. Introduction
Recently, few publications were appeared describ-
ing the metal ion sensors with different photo-physi-
cal responsive moieties such as rhodamine (12, 13),
coumarin (14), naphthyridine (15), boradiazaindacane
(BODIPY) (16), etc. Among these, BODIPY (4,4-
difluoro-4-bora-3a,4a-diaza-s-indacene) moiety exhib-
ited exceptionally superior photo-physical properties,
like strong absorption and emission in the visible
region, high fluorescence quantum yield, high molar
absorption coefficients, etc. In addition to these, the
photochemical stability also makes BODIPY an excel-
lent candidate in designing of artificial sensors (17)
for the detection of toxic metal ions (18). Keeping
maximum observations and literature survey in
mind, a simple BODIPY bearing 3-acetyl coumarin
chemosensor (R1) has been synthesised and
employed for metal ion recognition in association
As far as the environmental concern, the improvement of
highly selective and sensitive chemosensors for the detec-
tion of metal ions has been concentrated, now-a-days (1).
Among all the metals, aluminium is the third most pre-
valent metallic element in the earth and it is also an
important component to use in food packing, paper,
colour, deodorants and pharmaceutical industry (2–6).
Higher as well as lower, both concentrations of aluminium
in the human being can cause various diseases like osteo-
malacia and breast cancer. Similar to other harmful metal
ions, it can also damage brain and kidney (7–11). All the
adverse effects make the utmost importance to develop a
highly selective and sensitive chemosensor for detection
of Al3+as to serve both environmental and human health
purpose.
CONTACT Swapan Dey
swapan@iitism.ac.in
Department of Applied Chemistry, Indian Institute of Technology (ISM), Dhanbad 826004, India
Supplemental data for this article can be access here
© 2019 Informa UK Limited, trading as Taylor & Francis Group

2
K. S. KASHYAP ET AL.
with cell viability and cytotoxicity test in MCF-7
(breast adenocarcinoma) cells.
Reagents and conditions: (i) DMF, POCl3, DCE 60°C
(ii)N2H4.H2O, ethanol, 25°C, 6.0 h (iii) Piperidine, acetic
acid, r.t. 2.0 h.
spectrometer. All metal perchlorate salts such as
LiClO4, Mg(ClO4)2, Mn(ClO4)2, Cu(ClO4)2, Zn(ClO4)2, Co
(ClO4)2, Ni(ClO4)2, Fe(ClO4)2, Cd(ClO4)2, CsClO4, AgClO4,
Hg(ClO4)2, Pb(ClO4)2 and Bi(ClO4)3 were prepared from
corresponding metal carbonates.
Reagents and conditions: (i) Dry methanol, reflux,
24.0 h.
2.2. Synthesis of compound2
The synthetic steps of sensor are presented in Schemes
1 and 2. In this context, Vilsmeier–Haack reaction has
been performed to get compound 1 (19). Accordingly,
R1 has been synthesised from the reaction of compound
2 and 3 under refluxing condition. The afforded products
Compound 1 (19) (300.0 mg, 1.02 mmol) and hydrazine
hydrate (excess 400.0 mL, 10 mmol) were taken in
ethanol (50.0 mL) and stirred for 6 h at room tempera-
ture to get reddish solid compound. After that it was
filtered and washed several times with ethanol until rest
of starting material was removed. Finally pure solid
compound 2 was isolated (56% yield, m.p.116°C).
1H NMR (400MHz, CDCl3): δ7.82 (s, 1H), 6.09 (s, 1H),
5.42 (s, 2H), 2.66 (s, 3H), 2.63 (s, 3H), 2.54 (s,3H), 2.52
(s,3H), 2.43(s,3H). 13CNMR (100 MHz, CDCl3): δ167.68,
156.29, 154.07, 152.95, 142.40, 133.35, 131.62, 123.48,
122.66, 25.29, 17.62, 16.99, 14.71, 14.64, 13.87. LC-MS:
calculated For C23H25BF2N4: 304.5; found: 303.1[M-H].
1
were confirmed by Fourier-Transform Infrared (FTIR), H
and 13C-NMR and MS spectroscopic analysis.
2. Experimental
2.1. Reagents and conditions
All solvents and chemical reagents were obtained from
commercial sources and used as received without
further purification. UV–Vis and fluorescence spectra
were recorded on a SHIMADZU UV-1800 and a Perkin-
Elmer LS55 spectrophotometer at room temperature,
respectively. NMR spectra were obtained on a Bruker
AV400, BrukerAV-500 NMR. FTIR data were obtained on
2000 Perkin-Elmer Spectrometer. ESI-MS measurements
were carried out using a microTOF-Q II 10,330 mass
2.3. Synthesis of 7-(N,N-diethyl amino)-3-acetyl
coumarin (compound 3)
A mixture of 4-(diethyl amino)-2-hydroxybenzaldehyde
(300.0 mg, 1.50 mmol), ethylacetoacetate (3.0 ml,
2.25 mmol), piperidine (1.0 mL) and few drop of acetic
Scheme 1. Synthesis of compounds 1, 2 and 3.
Scheme 2. (Colour online) Synthetic procedure of R1.

SUPRAMOLECULAR CHEMISTRY
3
acid were mixed at room temperature and stirred for
2.0 h. Then, the yellow precipitation of compound 3
was filtered off and washed with water for several
times. (yield: 60%, m. P. 120–124°C).
was used to measuring the absorbance at 570 nm for
each well. The viability of cells was calculated according
to the following equation:
ꢀ
ꢁ
Experimental OD570
Control OD570
1H NMR (400 MHz, CDCl3): δ8.44(s, 1H), 7.41 (s, 1H),
7.36(s, 1H), 6.67(d, J = 7.2 1H) 6.47 (s, 1H), 4.43 (q,
J = 1.2, 3H), 2.26 (s, 3H) 1.24 (t, J = 1.2, 6H).
%Cell Viability ¼
ꢀ 100
2.7. Fluorescence imaging
2.4. Synthesis of R1
Firstly, stock solution of chemosensor R1 was pre-
pared (9/1, v/v) in H2O/ethanol. MCF-7 Cells were
plated in a 48 well cell culture plate and allowed to
adhere for 48 h. Experiment to assess Al3+ uptake
was performed in phosphate-buffered saline (PBS) in
the presence of Al(NO3)3. The cells were treated
with 10 µM Al(NO3)3, dissolved in sterile PBS
(pH = 7.4) and incubated at 37°C for 60 min. The
treated cells were washed with PBS to remove the
remaining metal ions. In case of Al(NO3)3, culture
medium (0.2 mL) was added to the cell culture,
which was then treated with a 10 µM solution of
chemosensor R1. The samples were incubated at
37°C for 30 min. The culture medium was removed,
and the treated cells were washed with PBS before
observation. Fluorescent images of the cells were
obtained using EVOS® FL Cell Imaging System (21).
Similar procedures were adopted for the competi-
tive metal ion sensing experiments.
Compound 2 (200 mg, 0.65 mmol) was taken in dry
methanol under N2 atmosphere. Then compound 3
(170 mg, 0.65 mmol) was added to it and the reaction
mixture was kept refluxing for 24 h. After cooling at
room temperature, the red precipitate was filtered and
washed with methanol to get pure R1 (60% yield, m.p.
250°C).
1H NMR (500 MHz, CDCl3): δ 8.64 (s, 1H), 8.15 (s,
1H), 7.37 (d, J = 8.0 Hz, 1H), 6.62 (d, J = 8.0 Hz, 1H),
6.52 (s, 1H), 6.17 (s, 1H), 3.46 (m, 4H), 2.83 (s, 3H),
2.71 (d, J = 11.9 Hz, 6H), 2.57 (s, 6H), 2.48 (s, 3H), 1.29–
1.25 (m, 6H). 13C NMR (125 MHz, d6-DMSO): δ 159.51
(s), 156.02 (s), 148.84 (s), 148.26 (s), 146.68–146.52
(m), 143.03 (s), 137.95 (s), 134.28 (s), 127.13
(s), 125.39 (s), 117.92 (s), 110.88 (s), 104.56 (d,
J = 18.1 Hz), 103.53 (s), 91.51 (s), 45.07 (s), 40.08 (s),
34.76 (s), 25.60 (s), 12.11 (s), 9.87 (s). HRMS (EI+):
calcd. For C30H34BF2N5O2: 545.2771; found:
546.2871 [M + H].
3. Results and discussions
2.5. Cell culture
3.1. Photo-physical studies
MCF7 (ATCC® HTB-22™) cells were grown in Dulbecco’s
Modified Eagle’s Medium (DMEM) supplemented with
10% Fetal Bovine Serum (FBS) at 37°C and 5% CO2. Cells
were plated in a 48 or 96 well culture plate and allowed
to adhere for 48 h before experimentation.
The complexation studies of sensor has been inves-
tigated in the presence of a series of metal salts
such as Li+, Mg2+, Al3+, Fe3+, Ni2+, Co2+, Cu2+, Zn2+
,
Cd2+
,
Hg2+ and Pb2+
.
Red-purple colour of
R1 solution was quickly turned to purple in presence
of Al3+ ion, whereas other metal ions did not show
any notable response. It exhibited pink fluorescent
colour under long wave length UV light at 365 nm,
(Figure 1).
2.6. Cell viability assay
Methyl thiazolyl tetrazolium (MTT) assay (20) was used
to measure the cytotoxicity of R1 in MCF-7 cells. MCF-7
cells were seeded in a 96-well cell-culture plate. In this
experiment, different concentrations (0, 5, 10, 25, 50
and 100 µM) of sensor were added to the cells. The
cells were incubated at 37°C under 5% CO2 for 24 h.
MTT (5 mg mL−1, 10 µL) was added to each well and
incubated at 37°C under 5% CO2 for 4 h. The MTT
solution was removed, and yellow precipitates (forma-
zan) observed in plates were dissolved in 200 µL of
acidic isopropanol. BiotekSynergyHT microplate reader
The absorption spectrum of R1 (2.3 × 10−5 M) was
exhibited λmax at 518 nm, where the peak was
decreased with increasing concentration of Al3+
(3.0 × 10−4) ion. Consequently, a new peak at
λmax = 566 nm was appeared with purple colouration
due to the complexation of R1:Al3+. The peak (407 nm)
responsible for coumarin moiety was diminished slowly
(Figure 2(a)). It was also mentioned that no significance
change was observed in presence of other metal ions
(Figure 2(b)).

4
K. S. KASHYAP ET AL.
Figure 1. (Colour online) Visual colour change (top) and fluorescence change (bottom) of R1 with different metal ions in CH3CN.
Figure 2. (Colour online) UV-Vis titration spectra in CH3CN (a) R1 with Al3+ ion (3.0 × 10−4) (b) R1 (2.3 × 10−5 M) with different
metal ions.
BODIPY hydrazone chemosensor (R1) exhibited
weak fluorescence due to intramolecular charge
transfer (ICT) and non-radiative decay process in
between BODIPY core and hydrazine moiety (22).
However, the fluorescence titration was completed
with a similar procedure as described in UV-vis. The
investigation for the selectivity of R1 towards Al3+
ion was carried out with an emission peak observed
at λem = 568 nm, when the sensor was excited at
514 nm. Gradual addition of Al3+ ion created a
significant decrease in the emission intensity at
568 nm and consequently, a new emission peak
appeared at 604 nm (Δλ = 36.0 nm) was due to
complexation (Figure 3(a)). No such changes were
recorded on performing same experiments with
other metal ions (up to 20 equivalents).
3.2. Proposed mechanism of complexation
The possible mode of binding of R1 was discussed on
the basis of photo-physical properties and 1H-NMR
spectra. Al3+ is a hard acid it prefers N and O as
hard-base donor sites in the coordination sphere
(23). Therefore, the two N atom of imine and one O
atom of coumarin moiety coordinate with Al3+ ion to
form stable complex. In absence of Al3+, FRET process
has not occurred as compound 2 was non-fluores-
cent. Absorption spectra of acceptor (BODIPY) and
emission spectra of donor probe (coumarin) recorded
at 568 nm. When R1 (N,N,O atoms) coordinates with
Al3+ ion the resonance energy was transferred from
coumarin moiety to BODIPY hydrazine and restored
the FRET process. As a result, pink fluorescence colour

SUPRAMOLECULAR CHEMISTRY
5
Figure 3. (Colour online) Fluorescence spectra in CH3CN (a) R1 with Al3+ ion (3.0 × 10−4 M) (λex = 518 nm), (b) R1 (2.3 × 10−5) with
different metal ions.
Figure 4. (Colour online) (a) Spectral overlap (FRET) in R1 between coumarin (emission, blue line) and BODIPY hydrazone
(absorption, red line). (b) Possible mode of sensing of R1 with Al3+.
was developed (Figure 4) (24). In the absence of Al3+
ion R1 can rotate around N-N bond and after com-
plexation with Al3+ ion free rotation inhibited
resulted pink fluorescence. Al3+ ion made the com-
plex rigid as possibly it brought two fluorophore
moieties in close proximity.
IR spectra provide useful information on coordi-
nation spectra. In IR spectra, the value of ѵC = O,
vibrations appeared at 1722, after complexation
with Al3+ ion the peak appeared at 1635 which
confirmed the complex (R1:Al3+) formation. In the
complex, the band at 593 cm−1 and was assigned to
was further proved by mass spectrum analysis,
where a peak was obtained at m/z 590.3 for R1
+ Al+H2O (Figure S10).
The extent of fluorescent enhancement was
explained by the calculation of quantum yield (Ф).
R1 exhibited weak fluorescence as the quantum
yield (Ф = 0.09) was very low. After formation of
metal complex R1:Al3+, the quantum yields were
accordingly increased by 8.0 (Ф = 0.78) fold. Good
sensing behaviour was projected estimating limit of
detection (4.1x10−7 M) by plotting fluorescence
titration data (26). A Job plot obtained from emis-
sion data showed 1:1 stoichiometric complexation
between R1 and Al3+ (Figure S15). In addition to
that, the binding efficiency (Ka) was investigated
and found 4.6 × 104 M−1 from Benesi–Hildebrand
linear regression analysis (27).
From the above spectral analysis, it was confirmed
that the metal ion was totally encapsulated in the
optimum cavity of sensor molecule which was created
in association to two N atoms of imine linkage and one
O atom of the coumarin moiety. This brings both
BODIPY and coumarin moieties to come closure leading
to the enhanced FRET.
ѵ
(Al-O), which demonstrated formation of a coordi-
native bond between aluminium and oxygen.
Correspondingly, the ѵ(Al-N) was at 446 cm−1
(Figure S12) (25).
Accordingly, in 1H-NMR the proton signal of –
HC=N– and –N=CCH3– were appeared at δ 8.63
and
δ
2.82 ppm, respectively (Figure 5).
Interestingly, both the protons were getting down
field shifted to δ 8.78 and 2.84 ppm, respectively,
upon complexation with Al3+. The proton present in
the lactone ring of coumarin also shifted from δ 8.14
to 8.47 ppm (Δδ 0.33ppm). The complex formation

6
K. S. KASHYAP ET AL.
1
Figure 5. H-NMR spectra of R1:Al3+ in CDCl3.
(E = −2055 a.u.) This confirmed that complex was
more stable than R1.
3.3. Quantum chemical (DFT) calculation
Quantum chemical (DFT) calculation was carried out by
using Gaussian 09 and Gauss-view 5.0 visualisation pro-
gramme for supporting experimental work (28). The
DFT calculation was carried out for energy optimised
structure including molecular modelling. Accordingly,
the electronic property of sensor and its complex
were determined by using the B3LYP method and 6-
311G basis sets.
3.5. Bio-imaging studies
The potential of BODIPY hydrazine bearing chemosen-
sor (R1) for sensing Al3+ in living cells was investigated.
In this process, MTT assay for MCF-7 (breast adenocar-
cinoma) cells was used to determine the cyto-compat-
ibility of R1. The cell viability was greater than 80%,
following treatment (0–100 µM) with the sensor for
24 h (Figure 7). Hence it was concluded that R1 was
safe and induced low cytotoxicity even at higher
concentration.
Bio-imaging analysis was performed for demonstrat-
ing bio-distribution of the metal ions (Al3+) in living
cells using EVOS® FL Cell Imaging System. MCF-7 cells
were incubated with sensor (R1) only and the chemo-
sensor did not produce any fluorescence signals in the
The HOMO and LUMO of R1 and R1:Al3+ in
Figure 6 represent that, electron density of R1
mainly located on the BODIPY hydrazine moiety.
The energy difference of HOMO and LUMO was
0.09426 a.u. Upon complexation, the electron den-
sity was transferred to aluminium ion and N and O
atoms of coumarin. The energy gap between HOMO
and LUMO of R1: Al3+ ion was found 0.02390 a.u.
which was lower than R1. The total energy of R1
(E = −1812 a.u.) is higher than its complex R1:Al3+

SUPRAMOLECULAR CHEMISTRY
7
Figure 6. (Colour online) Optimised structure of (a) R1 (b) R1:Al3+ and HOMO and LUMO diagrams of (c) R1, and complex R1:Al3+
by DFT/B3LYP/6-311G method.
images (Figure 8(c)) showed that the fluorescence sig-
nals were localised in the intracellular areas, indicating
the subcellular distribution of Al3+ besides effective
cell-membrane permeability for R1. Specificity of R1
towards Al3+ was demonstrated by performing similar
experiments using competing ions in the absence of
selective ions.
4. Conclusions
In conclusion, BODIPY-azine bearing chemosensor R1
has been reported for the visual detection of Al3+and
Figure 7. (Colour online) MTT assay of MCF-7 cells treated in
the presence of R1 (0–100 µM) incubated at 37°C for 24 h.
produced switch on response upon complexation. The
photo-physical properties of R1 and R1:Al3+ were
explained through FRET mechanism. In addition to
that, bio-imaging studies of R1 was exhibited a turn-on
response both in vitro and in live cell. The sensor has the
potential application in selective identification of Al3+
absence of Al3+ ion. However, after treatment with Al3+,
bright red fluorescence was observed in the MCF-7 cells
(Figure 8(b)). Overlaying of fluorescence and bright-field
Figure 8. (Colour online) Fluorescence images of MCF-7 cells treated with R1 and Al3+ (a–c). (a) Bright field image; (b) fluorescence
image and (b) merged image.

8
K. S. KASHYAP ET AL.
ion and cyto-compatibility in the living cells. Hence, the
chemosensor may be proposed as a good marker for
advanced ions sensing and cell imaging studies.
Kumari, C.; Sain, D.; Kumar, A.; Nayek,H. P.; Debnath,S.;
Saha, P.; Dey, S., Sens. Actuators B: 2017, 243, 1181-1190.
(14) (a) Kumar, A.; Mondal, S.; Kayshap, K. S.; Hira,S. K.;
Manna, P. P.; Dehaen,W.; Dey, S. New J. Chem. 2018,
42, 10983-10988; (b) Kumari,C.; Sain,Dr. D.; Kumar, A.
Nayek, Dr. H. P.; Debnath, Dr. S. Saha, Prof. P.; Dey, Dr.
S.; Chemistry Select 2017, 2, 8270-8277.
Acknowledgments
SD acknowledges SERB-DST, Govt. of India, for financial assis-
tance (project no. EMR/2016/002183) and DST- FIST (project
no. SR/FST/CSI-256/2013). KSK are thankful to IIT (ISM),
Dhanbad for providing fellowship. SKH acknowledges DST-
SERB, New Delhi, (project No. ECR/2016/0105), USIC, DST-
FIST & DST-PURSE for providing research facilities.
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Disclosure statement
No potential conflict of interest was reported by the authors.
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