Single crystal X-ray structurally characterized palladium(II) selective fluorescence and colorimetric indicator for human breast cancer cell imaging

Article abstract of DOI:10.1016/j.ica.2015.07.015

Abstract Condensation of rhodamine B hydrazide with 4-formylbenzonitrile generates a Pd²⁺ selective probe (RDHDNB) that allows its naked eye and fluorescence recognition. Moreover, RDHDNB is useful to detect Pd²⁺ in human breast cancer cells MCF7, under normal and fluorescence microscope.

Full text of DOI:10.1016/j.ica.2015.07.015

Accepted Manuscript
Single crystal X-ray structurally characterized palladium(II) selective fluores-
cence and colorimetric indicator for human breast cancer cell imaging
Abhijit Ghosh, Sandip Nandi, Archya Sengupta, Ansuman Chattopadhyay, Sisir
Lohar, Debasis Das
PII:
S0020-1693(15)00349-7
http://dx.doi.org/10.1016/j.ica.2015.07.015
ICA 16608
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
24 March 2015
26 May 2015
9 July 2015
Please cite this article as: A. Ghosh, S. Nandi, A. Sengupta, A. Chattopadhyay, S. Lohar, D. Das, Single crystal X-
ray structurally characterized palladium(II) selective fluorescence and colorimetric indicator for human breast
cancer cell imaging, Inorganica Chimica Acta (2015), doi: http://dx.doi.org/10.1016/j.ica.2015.07.015
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0
Graphical Abstract
Single crystal
characterized
X-ray
palladium(II)
structurally
selective
Leave this area blank for abstract info.
fluorescence and colorimetric indicator for
human breast cancer cell imaging
a
Abhijit Ghosh , Sandip Nandy , Archya Sengupta , Ansuman Chattopadhyay , Sisir Lohar* and Debasis Das
a
b
b
a
a*

1
Inorganica Chimica Acta
journal homepage: www.elsevier.com
Single crystal X-ray structurally characterized palladium(II) selective
fluorescence and colorimetric indicator for human breast cancer cell
imaging
a
a
b
b
a
Abhijit Ghosh , Sandip Nandi , Archya Sengupta , Ansuman Chattopadhyay , Sisir Lohar* and Debasis
Das
a*
a
Department of Chemistry, The University of Burdwan, Golapbag, Burdwan, India, Fax: +91-342-2530452; Tel: +91-342-
2
533913 (ext. 424); E-mail: ddas100in@yahoo.com
Department of Zoology, Visva Bharati University, Santiniketan, West Bengal, India
b
ARTICLE INFO
ABSTRACT
2
+
Article history:
Received
Condensation of rhodamine B hydrazide with 4-formylbenzonitrile generates a Pd
selective probe (RDHDNB) that allows its naked eye and fluorescence recognition.
2
+
Revised
Moreover, RDHDNB is useful to detect Pd in human breast cancer cells MCF7, under
normal and fluorescence microscope.
Accepted
Available online
2
009 Elsevier Ltd. All rights reserved.
Keywords:
Fluorescence, Naked eye,
Palladium, Rhodamine b, Hydrolysis, Single crystal
X-ray structure
15
1. Introduction
electrophoresis.
However, these methods suffer from
complicated, time consuming sample preparation techniques or
require sophisticated expensive equipment along with suitably
trained analysts. Fluorescence sensing protocol is desirable for its
easier and cost-effective methodology, good sensitivity and
Platinum group metals, specially palladium and its
compounds, are widely used as catalysts in numerous chemical
transformations applied for the synthesis of natural products, fine
1
-4
chemicals, therapeutic drugs, and polymers.
Innumerable
16
selectivity with high throughput fashion. Most of the reported
Pd sensors are based on fluorescence quenching while a few
organic reactions including Buchwald–Hartwig, Heck,
Sonogashira, and Suzuki–Miyaura reactions are usually
palladium catalyzed and have significant role in medicinal
2+
17
18
are “off–on” type. Among the limited fluorescence “on”
5
-7
receptors reported in the literature reaction based
2+
chemodosimeter enabling Pd promoted hydrolytic cleavage of
chemistry. However, despite frequent and fruitful use of such
reactions, resulting high level residual palladium in the product,
8
even after purification, may lead to health hazard. Additionally,
specific bonds as sensing mechanism are rare.
Herein, single crystal X-ray structurally characterized, new
rhodamine B hydrazide derived probe, RDHDNB (Scheme 1)
frequent release of large quantity palladium to the environment
occurs due to its extensive use in numerous commercial
applications such as automobile catalytic converters, jewellery,
dental alloys, fuel cells, medical instruments and electronics.
2+
can detect trace level Pd both naked-eye and under UV light
through recovery of rhodamine B by hydrolysis. Factors insist to
select rhodamine as fluorophore include excellent photo-stability,
impressive extinction coefficient and quantum yield with longer
emission wavelength, favoring easy visualization. In presence of
2
+
Moreover, Pd can bind thiol-containing amino acids, proteins
(
casein, silk fibroin, and many enzymes), DNA, macromolecules
and bio-chemicals (vitamin B6), possibly impairing various
cellular processes. Hence, palladium in environment can cause
serious health problems like memory loss, dizziness, migraine
headaches, allergies, immune system impairment and facial
2+
Pd , colorless RDHDNB turns pink with significant fluorescence
2+
enhancement. To compare the Pd selectivity of this rhodamine-
based probe, RDHDNB, respective fluorescein compound
(FLHDNB) have been synthesized as a model as shown in
Scheme 2.
2. Experimental
2.1. Apparatus and reagents
A Shimadzu Multi Spec 1501 spectrophotometer is used
for recording UV-Vis spectra. FTIR spectra are recorded on
a PerkinElmer FTIR (model RX1) spectrophotometer. Mass
spectra have been performed using a QTOF 60 Micro YA
9
paralysis.
2
So, trace level selective detection and estimation of Pd is
+
2
+
highly demanding. Traditional analytical methods for Pd
determination include atomic absorption spectrometry,
inductively coupled plasma atomic emission spectrometry,
1
0
1
1
1
2
inductively coupled plasma mass spectrometry, solid-phase
1
3
14
microextraction,
X-ray
fluorescence
and
capillary

2
1
2
63 mass spectrometer in ES positive mode. H NMR
spectra of RDHDNB and FLHDNB are recorded using
Bruker Avance DPX 600 (600 MHz) in CDCl and DPX
00 (300 MHz) in DMSO-d respectively. The steady state
2.4. Synthesis of fluorescein hydrazide
Fluorescein hydrazide is prepared in high yield by
reacting fluorescein with hydrazine hydrate in ethanol
3
3
6
2
1
fluorescence emission and excitation spectra are recorded
with a Hitachi F-4500 spectrofluorimeter. Systronics digital
pH meter (model 335) is used for pH measurement of the
solutions. Dilute HCl or NaOH (50 µM) are used for pH
according to the literature.
2.5. Synthesis of FLHDNB
FLHDNB is synthesized in a similar way to that of
RDHDNB where an ethanol solution of fluorescein
hydrazide (0.1 g, 0.2890 mmol) is used instead of
rhodaminehydrazone (Scheme 2). H NMR (300 MHz,
DMSO-d ) (Fig.S4, ESI); QTOF-MS ES+ (Fig.S5, ESI): [M
+
+ Na] = 482.31; FTIR/ cm
adjustment. High purity rhodamine B
cyanobenzaldehyde, hydrazine hydrate and PdCl
,
fluorescein, 4-
are
1
2
purchased from Sigma-Aldrich (India). Solvents used are of
spectroscopic grade. All the metal salts used are either
nitrate or chloride forms. Other analytical reagent grade
chemicals are used without further purification. Milli-Q
6
-1
(
Fig.S6, ESI): υ(O-H) 3278,
N) 2225.
υ(C=O) 1680, υ(CH=N) 1610, υ(C
≡
®
−1
Millipore 18.2 M
Ω cm water is used whenever required.
2
.2. Synthesis of rhodaminehydrazone
N-(rhodamine-B) lactam-hydrazine is prepared by
1
9
refluxing rhodamine B and hydrazine hydrate in ethanol.
2
.3. Synthesis of RDHDNB
N-(rhodamine-B) lactam-hydrazine (0.1 g, 0.2193
mmol), dissolved in 5 mL ethanol, added drop-wise to
ethanol solution of 4-formylbenzonitrile (0.0287 g, 0.2193
mmol, 5 mL) under stirring condition. The reaction mixture
is refluxed for 5h (Scheme 1), filtered and kept at room
temperature. After 4 days, pink color rectangular crystals
1
suitable for single crystal X-ray diffraction are collected. H
NMR (600 MHz, CDCl3) (Fig.S1, ESI); QTOF-MS ES+
+
Fig. S2, ESI): [M + H] = 570.18; FTIR/ cm−1 (Fig. S3
(
,
Fig.1 ORTEP view of RDHDNB (50% thermal ellipsoid probability)
ESI): υ(C=O) 1697, υ(CH=N) 1610, υ(C
Single crystals of RDHDNB are grown from ethanol
solution and characterized by X-ray crystallography (Fig.1).
The selected structural parameters are presented in Table
S1 (ESI). The crystal structure clearly shows that two planes
of the spiro compound are almost mutually vertical position.
≡N) 2227.
2
0
2.7. In vitro cell imaging
Human breast cancer cell line MCF7 is grown in DMEM
(
Sigma, St. Louis, USA) supplemented with 10% fetal
bovine serum (Sigma, St. Louis, USA), 2 mM glutamine,
00 m/L penicillin-streptomycin solution (Gibco,
Invitrogen, USA) in the presence of 5% CO at 37°C. For in
1
U
2
vitro imaging studies, cells are seeded in 6 well culture
5
plates with a seeding density of 10 cells per well. After
reaching 60–70% confluence, the previous media is replaced
2
+
with serum free media, supplemented by Pd
and
RDHDNB at 50 µM and 20 µM, and incubated for 2 h to
2
+
facilitate the Pd or RDHDNB uptake by the cells. Then the
cells were placed under an inverted microscope (Dewinter,
Italy) at different magnifications to examine any adverse
effect on cellular morphology. RDHDNB treated cells are
2
+
then incubated with Pd for 15–30 min and observed under
an inverted fluorescence microscope at different
magnifications with a blue filter.
Scheme1 Synthesis of RDHDNB
3
3
. Result and discussion
.1. Emission and absorption studies
In aqueous-acetonitrile (1: 4, v/v) medium, very weak
emission of RDHDNB (λem, 586 nm; λ 2e x+ , 525 nm, Ф = 0.08)
increases 212 fold in presence of Pd (Ф = 0.41) (Fig.2,
(
Fig.S7, ESI),). Very weak absorbance of RDHDNB (at 560
2
+
nm) increases with gradual addition of Pd and the colorless
solution of free RDHDNB turns pink (Fig.3, Fig.S8). The
linear region of both the emission and absorption spectra
(
Fig.S7a and S8a, ESI) are useful for determination of
2
+
unknown concentration of Pd .
Plausibly, RDHDNB initially coordinates Pd through
imine nitrogen and carboxamide oxygen followed by
2
+
Scheme 2 Synthesis of FLHDNB

3
hydrolysis of the amide bond, releasing rhodamine B.
Interestingly, these changes of optical properties are time
dependent, ~40 min are required to reach a stable signal.
Hence, all spectra are recorded after 40 min of mixing the
ingredients. Optimization of pH is carried out to find the
spectra of RDHDNB in presence of equimolar amount of
common cations and anions separately (Fig.6).
Corresponding color changes observed under UV light and
naked eye are shown in Fig.S12 (ESI). To demonstrate the
practical application of RDHDNB, paper strips coated with
sensor is prepared by soaking the filter paper into the
solution of RDHDNB (25 µM) followed by drying in air.
Next, the so prepared paper strips are soaked in solutions
2
+
optimum pH for sensing Pd . Fig.4 indicates that the entire
studies can be performed at physiological pH, 7.4 (using 0.1
M HEPES buffer solution). Job’s plot (Fig.S9, ESI)
indicates 1: 1 (mole ratio) binding mode of RDHDNB with
2
+
-5
having different Pd concentration, viz. 0 M, 1.0 ×10 M,
2
+
2+
-5
-4
-4
5.0 ×10 , 1.0 ×10 M and 3.0 ×10 M. Fig.S13 shows the
Pd . The lowest detection limit of RDHDNB for Pd is 5.7
×
-8
10 M (Fig.S10, ESI).
colors of the test strips that changes from colorless to pink
2
+
and deepens gradually with the increasing Pd
concentration. This technique may be useful as a simple tool
2
for detecting Pd in environmental samples.
+
Although the reference compound, FLHDNB contains same
2
+
chelating sites remain silent towards Pd , monitored using both
absorption and emission spectroscopy (Fig.S14, ESI). Probably,
weak electron donation ability of –OH group of fluorescein than
2
the –N(Et) of rhodamine B is responsible for the difference.
Fig.2 Changes in the emission spectra of RDHDNB (25 µM, aqueous-
2+
acetonitrile (1: 4, v/v) upon gradual addition of Pd (0-300 µM, after 40
min of addition of Pd ). Inset pictures show the naked colors under UV
2+
2+
light of pure RDHDNB solution and upon addition of Pd to RDHDNB
solution. λex, 525 nm
2+
Fig.5 Emission intensities of [RDHDNB + Pd ] system (after 40 mins
2+
of addition of Pd ) in presence of competing cations
Fig.3 Changes in the absorbance of RDHDNB (25 µM, aqueous-
2+
acetonitrile (1: 4, v/v) upon gradual addition of Pd (0- 300 µM, after
2
+
4
0 mins of addition of Pd ). Inset pictures show the naked colors of
2+
pure RDHDNB solution and upon addition of Pd to RDHDNB
solution.
Fig.6 Emission spectra of RDHDNB (25 µM, λex,525 nm) in aqueous-
acetonitrile (1: 4, v/v) solution in presence of different ions (12 equiv.,
after 40 mins of addition of different ions)
4
. Plausible sensing mechanism
Mass spectrum of the [RDHDNB - Pd ] system
Fig.S15, ESI) provides a reasonable evidence for plausible
2
+
(
2
+
Fig.4 Effect of pH on the emission intensity of free RDHDNB (25 µM) and
[
ratio, λex, 525 nm; λem, 586 nm)
Pd sensing mechanism of RDHDNB. The molecular ion
peak at m/z = 443.40 corresponds to rhodamine-B, also
corroborated from its FTIR spectrum (Fig.S16, ESI) having
2
+
2+
RDHDNB + Pd ] system (after 40 min of addition of Pd ) (1 : 12, mole
−
1
2+
υ(C─O), 1336 cm . These clearly indicate Pd assisted
hydrolysis of RDHDNB (Fig.7). The breaking of amide
bond releases the corresponding hydrazone of 4-
formylbenzonitrile, C H N , which remains complexed with
3
.2. Interference and selectivity studies
No significant interference of common cations on the
8
7
3
2
+
2
+
emission intensity of the [RDHDNB - Pd ] system has been
observed (Fig.5). It is found that RDHDNB can work for
2
visualizing Pd well also when we use tap water as a co-
2 4
Pd along with other coligands like hydrazine (N H ) and
-
+ +
chloride ions (m/z, 361.52 ([C
hydrazone unit further raptures at imine functionality to
release 4-formylbenzonitrile (C NO, m/z, 132.16
8 7 3 2 4
H N +N H +2Cl +Li ] ). The
+
solvent with acetonitrile (Fig.S11, ESI). Further, selectivity
2
of RDHDNB towards Pd is established from the emission
8
H
5
+

4
+
2+
(
8 5
[C H NO+H] ). Thus, Pd is not released in the solution,
thus cannot be termed as catalyst. .
Time dependent NMR spectra before and after 40 min of
2
+
addition of Pd to RDHDNB show a new peak at 9.9 ppm
corresponding to the aldehyde proton of 4-
formylbenzonitrile appears (Fig. 8). All the other protons of
2
+
RDHDNB downfield shifted after interaction with Pd .
Additionally, to examine any reversibility of the
emission spectral signals, excess disodium salt of
ethylenediamine tetraacetic acid (EDTANa ) is added as
2
2
Pd chelating agent to the color solution of [RDHDNB -
+
2
+
Pd ] system. However, no change of color and emission
intensity of the solution is observed that indicates the
irreversible feature of the recognition process.
1 2+
Fig.8 H NMR spectra of RDHDNB (1) and [RDHDNB - Pd ] system
2+
3
recorded after 40 min of addition of Pd (2) in CDCl .
2
+
A control experiment for sensing of Pd in anhydrous
acetonitrile medium instead of aqueous-acetonitrile (1: 4,
v/v, 0.1 M HEPES buffered, pH, 7.4) solution is carried out
without success. This indicates that presence of water is
2
+
essential for Pd recognition event which further hints
2
+
hydrolysis event. All these results affirm the proposed Pd
sensing mechanism as portrayed in Fig. 7.
Fig.9 Fluorescence microscope images of MCF7 cells: (a) and (b) are
2+
2
The kinetics of the Pd recognition event suggests a
+
images of cells after 2 h incubation with Pd (50 µM) and RDHDTNB
25 µM) respectively, while (c) shows cells after 2 h incubation with 50
(
two-step reaction mechanism. The first step i.e., the
2+
µM Pd followed by addition of 20 µM RDHDNB solution and (d) is
the bright field image of the cells after incubation with 20 µM
2
chelation of Pd is fast (k = 3.65 × 10 ) and the second
+
-3
1
2+
-4
RDHDNB for 2h followed by the addition of 50 µM Pd
step i.e., the hydrolysis step is slow (k = 3.10 × 10 )
2
(
Fig.S17, ESI). These results are also in line to our proposed
2
Pd sensing mechanism.
+
6. Conclusion
Rhodamine B hydrazide derived probe, RDHDNB
functions as an excellent colorimetric and fluorescence
2
+
−8
probe for trace level determination of Pd up to 5.7 × 10
M. Chelation followed by hydrolysis of the amide bond
2
releases the rhodamine B unit, responsible for Pd sensing
+
2
+
at physiological pH. The probe can detect intracellular Pd
in human breast cancer cells, MCF7 under fluorescence
microscope.
Acknowledgement
AG is grateful to BU for fellowship. Assistance from CAS,
B.U. is gratefully acknowledged. We sincerely thank Dr. S.
Karmakar, USIC, BU for XRD analysis.
CCDC number of RDHDNB is 948697. ESI is available.
References
2+
Fig.7 Proposed Pd sensing mechanism
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2
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2
+
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(

Graphical Abstract
4
-Benzonitrile appended rhoda mm ine B hydrazide derivative (RDHDNB) sele cc tively detects
2
Pd both naked eye and under
+
2+
UU V light. Moreover, RDHDNB easily detects PP d in human
breast cancer cells MCF7, under normal and fluorescence microscope.

Highlights
2
+
1
.
Visible light excitable, single crystal X-ray structurally characterized Pd
selective fluorescence probe.
-
8
2
3
.
.
Lowest detection limit for 5.7 × 10 M
2
RDHDNB is useful to detect Pd in human breast cancer cells MCF7, under
+
normal and fluorescence microscope.
2
+
4
5
.
.
To the best of our knowledge, this is the first report on Pd assisted
hydrolysis of a rhodamine based fluorescence probe, RDHDNB for its
colorimetric and fluorescence detection.
Common ions do not interfere.