A turn-on fluorescent and colorimetric chemodosimeter for selective detection of Au3+ ions in solution and in live cells: Via Au3+-induced hydrolysis of a rhodamine-derived Schiff base

Article abstract of DOI:10.1039/d0nj01273d

A chromogenic and off-on fluorogenic chemodosimeter (L) based on a naphthalene-rhodamine B derivative was designed, synthesized and characterized for the selective and sensitive detection of Au³⁺ ions in mixed acetonitrile aqueous medium in the presence of other competitive analytes. Probe L displayed a 696-fold turn-on fluorescence signal enhancement toward Au³⁺ ions with the detection limit of Au³⁺ of about 1.51 μM. In the presence of Au³⁺ ions, probe L also exhibited a visible color change from colorless to pink that could be easily identified by the naked eye. This colorimetric and fluorometric changes were mainly due to the Au³⁺ ion-triggered imine bond (CN) hydrolysis sensing mechanism. Moreover, theoretical calculations were performed to explain the experimental results. In addition to these features, the off-on probe was successfully used to monitor intracellular Au³⁺ ions in living MC3T3 cells through fluorescence imaging.

Full text of DOI:10.1039/d0nj01273d

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10.1039/D0NJ01273D.
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A “turn-on” fluorescent and colorimetric chemodosimeter for
selective detection of Au3+ ions in solution and in live cells via
Au3+-induced hydrolysis of rhodamine-derivative Schiff base
Received 00th January 20xx,
Accepted 00th January 20xx
Sanchita Mondal,* a Saikat Kumar Manna, b Sudipta Pathak,b Aritri Ghosh,c Pallab Datta,c Debasish
DOI: 10.1039/x0xx00000x
Mandal,d and Subrata Mukhopadhyaya
A chromogenic and “off-on” fluorogenic chemodosimeter (L) based on naphthalene-rhodamine B derivative was designed,
synthesized and characterized for the selective and sensitive detection of Au3+ ions in mixed acetonitrile aqueous media in
presence of other competitive analytes. Probe L displayed a 696-fold “turn-on” fluorescence signal enhancement toward
Au3+ ions with the detection limit of Au3+ about 1.51 µM. In the presence of Au3+ ions, probe L also exhibited a visible color
change from colorless to pink that could be easily identified by naked eye. This colorimetric and fluorometric changes were
mainly due to the Au3+ ions-triggered imine bond (C=N) hydrolysis sensing mechanism. Moreover, theoretical calculations
were performed to explain the experimental results. In addition to these features, the “off-on” probe was successfully
employed to monitor intracellular Au3+ ions in living MC3T3 cells through fluorescence imaging.
cancer, asthma, malaria, HIV, brain lesions, and asthma.7,8 Again,
gold ions serve as inhibitors of macrophages and
polymorphonuclear leucocytes.9 In spite of its fascinating medicinal
and chemical properties, gold ions especially, Au3+ ions impact
Introduction
Exploration of the chemistry of gold have attracted tremendous
attention to the scientific community owing to their chemical,
analytical, biological, environmental and medicinal importance.1
Gold, one of the most significant noble metals, is widely used in the
area of synthetic chemistry, nanomaterial science, surface
chemistry, theoretical investigations, gold plating, sensing materials
and electrical contacts.2,3 For instance, gold nanoparticles have
been extensively employed in drug carriers, gene delivery systems,
bioimaging substances, biosensors, water purification system,
medicines and additives in cosmetics, and soap.4,5 Besides, ionic
gold species (Au3+ ions), in contrast to its elemental form, are
commonly used as efficient catalysts in selective oxidation reactions
and several organic chemical transformations, in particular for
activating alkyne bond towards nucleophilic addition.6 In addition to
its catalytic properties, gold ions also have anti-inflammatory
properties and are applied as pharmaceuticals for the treatment of
various human diseases including tuberculosis, rheumatic arthritis,
human health and the environment in an adverse manner as Au3+
ions can strongly bind to DNA, enzymes and other biomolecules,
thereby causing severe damage to the kidneys, liver and the
nervous system.10,11 Thus, there is
a critical need for the
development of selective, sensitive, efficient and convenient
analytical techniques to monitor Au3+ ions in the environment and
in the living system. Until now, various conventional analytical
methods have been reported for the detection of gold ions such as
inductively coupled plasma atomic emission spectrometry (ICP-
AES), electrochemical assay inductively coupled plasma mass
spectrometry (ICP-MS), flame atomic absorption spectrometry
(FAAS), anodic stripping voltammetry and graphite furnace atomic
absorption spectrometry (GFAAS) but these techniques often
require sophisticated and costly instrumentation, time consuming,
complicated sample preparation steps and skilled individuals,
making them unsuitable for real-time and in-field analysis.12,13
Hence, chromogenic and fluorogenic method of the spectral field
have recently emerged as a highly proficient, reliable and desirable
approach for quick detection of gold ions due to their high
selectivity, sensitivity, cost-effectiveness, easy sample preparation,
speediness, nondestructive nature, reproducibility and real-time
monitoring of the biological samples.14 Therefore, some fluorescent
probes for Au3+ ions have been developed with a variety of
fluorophores including naphthalimide,15 boron-dipyrromethene
(BODIPY),16 coumarin,17 rhodamine,18 and fluorescein,19 during the
last decades. These fluorescent probes detect Au3+ ions through
a. Department of Chemistry, Jadavpur University, Kolkata 700032, India
b. Department of Chemistry, Haldia Government College, Debhog, Purba Medinipur,
West Bengal 721657, India
c. Centre for Health Care Science, Indian Institute of Engineering Science and
Technology, Shibpur, Howrah 711103, India
d. School of Chemistry and Biochemistry, THAPAR Institute of Engineering and
Technology, Patiala 147004, Punjab, India
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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different sensing mechanisms such as activation of alkyne bond,20 Compound 2 was synthesized through the Schiff baseVcieownAdrteicnlesaOtniloinne
hydrolysis reaction,21 desulfurization reaction,22 and coordination reaction of rhodamine B hydrazide and 4-hydroxy-1-napthaldehyde
DOI: 10.1039/D0NJ01273D
based approaches.23 However, only a scarce number of rhodamine- in 89% yield. Finally, probe L was synthesized by the reaction
based fluorescent probes have been made available to date for the between compound 2 and 1-fluoro-2,4-dinitrobenzene with 85%
detection of Au3+ ions via Au3+ promoted C=N bond (Schiff base) yield. The structure of L was fully characterized by 1H NMR,
hydrolysis mechanism.24 The rhodamine framework are commonly 13C NMR, FT-IR, and mass spectroscopy (Figs. S1-S5, ESI†). The
employed to construct “off-on” fluorescent probes because of its spirolactam form of L was confirmed by the presence of a
outstanding photophysical properties such as great fluorescence characteristics peak near at 67.91 ppm in the 13C NMR spectrum of
quantum yield, large absorption coefficient, high photo stability and L (Fig. S4, ESI†).
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relatively long absorption and emission wavelength. Additionally,
the spirolactam ring of rhodamine-based probes is colorless and
(a)
L + Au3+
L
non-fluorescent, but its ring-opened spirolactam form gives rise to
strong fluorescence emission intensity and a pink color in presence
of specific metal cations, enabling “naked eye” detection of metal
ions.25 Considering the above criteria in mind, herein, we present a
rhodamine-naphthalene based colorimetric and “turn-on”
fluorescent chemodosimeter L which can selectively and sensitively
detect Au3+ ions through spirolactam ring opening followed by
hydrolysis reaction. Probe
L exhibits superb selectivity and
sensitivity for Au3+ ions over other competitive interferences.
Moreover, the comparison between the present probe (L) and a
few previously reported probes for Au3+ ions detection has been
shown in the Table S1 (ESI†). Our probe (L) shows its efficacy and
superiority over other reported probes in terms of its easy synthetic
scheme, good synthetic yield, selectivity, sensitivity, dual sensing
techniques (fluorescence and naked eye detection) and good
detection limit. Additionally, bioimaging experiments indicated that
chemodosimeter L can be utilized as a fluorescent probe for
monitoring Au3+ ions in living cells.
(b)
Results and discussion
Chemodosimeter L was synthesized in three steps as shown in
Scheme 1. Rhodamine B hydrazide (1) was prepared following
literature procedure.26
O
N
NH2
COOH
Fig. 1 (a) UV−vis absorption spectra of L (1.0 × 10−5 M) in the
presence Au3+ ions (1.0 × 10−4 M) in CH3CN/H2O (1: 1, v/v, 10 mM
HEPES buffer, pH 7.4) solution. Inset: Photographs for color changes
of probe L upon addition of Au3+ ions under visible light. (b) UV−vis
absorption spectra of L in the presence of various metal ions in
CH3CN/H2O (1: 1, v/v, 10 mM HEPES buffer, pH 7.4) solution.
NH2NH2.H2O
Ethanol, Reflux,
4 hrs
N
O
N
1
N
O
N
Cl-
CHO
Ethanol, Reflux,
12 hrs
OH
F
NO2
O
O
The UV-vis and fluorescence spectral response of the probe L
O
OH
NO2
N
N
N
N
toward various metal cations (Au3+, Cr3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+,
CH3CN, K2CO3,
KI, Reflux
O2N
Zn2+, Cd2+, Pb2+, Hg2+, Pt2+, Pd2+, Al3+ and Ag+), anions ( S2-, HSO4 ,
-
NO2
N
O
N
N
O
N
HSO3 , and SO32-), amino acid (Cys) and reactive oxygen species
-
2
L
(ClO- , H2O2) were examined in CH3CN/H2O (1: 1, v/v, 10 mM HEPES
buffer, pH 7.4) solution. As shown in Fig. 1, the UV-vis spectrum of
probe L displayed no noticeable absorption band above 500 nm,
signifying the presence of spirolactam form of L. Upon gradual
Scheme 1 The synthetic route of chemosensor L.
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addition of Au3+ to the solution containing chemodosimeter L, a solution of probe L, an amazing enhancement ofViefwluAorrtieclsecOennlicnee
DOI: 10.1039/D0NJ01273D
remarkable increase in absorbance at 560 nm was observed, which spectra at 588 nm was observed (quantum yield ϕ =0.689, ESI†),
indicated the ring-open delocalized spirocyclic structure of L accompanied by an emission color change from colorless to orange
became the major species in the inspected solution. In presence of (Fig. 2a). The fluorescence intensity reached its maximum after
Au3+ ions, the organo aqueous solution CH3CN/H2O (1: 1, v/v, addition of 1.5 equivalent of Au3+ ion and it was increased up to
10 mM HEPES buffer, pH 7.4) of L turned from colorless to pink (Fig. 696-fold which was higher than the result obtained from the
1, inset), thus enabling ‘naked eye’ detection of Au3+ in previously reported Au3+ sensors.27 Moreover, as shown in Fig. 2b,
environmental samples. Under the similar condition, no apparent the observed emission intensity in presence of Au3+ ions was
absorption and color changes happened in the presence of other gradually enhanced in Au3+ concentration-dependent manner. The
interfering species (Fig. 1b and Fig. S7), representing the high above results suggested that the spirocyclic ring of probe L was
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selectivity of L toward Au3+.
opened and conjugated structure was formed in the solution. In
particular, the detection limit is an important factor for
chemosensing applications. Now, the detection limit of L for Au3+
was estimated to be 1.51 µM using fluorescence titration spectra
based on the technique employed in the earlier literature (Fig. S8,
ESI†).28 Moreover, time dependent fluorescence studies revealed
that the chemodosimetric reaction of probe L with Au3+ ions were
very fast. As illustrated in Fig. S9 (ESI†), upon addition of Au3+ ions
to the probe solution, a remarkable increase in fluorescence signal
was found within seconds and the complete enhancement of
emission intensity at 588 nm was observed in 1.5 minute,
demonstrating that chemodosimeter L could be employed for real-
time monitoring of Au3+ in biological specimens.
(a)
L+Au3+
L
(b)
Fig. 3 Fluorescence emission spectra of L (1.0 × 10−5 M) in the
presence of various metal ions in CH3CN/H2O (1: 1, v/v, 10 mM
HEPES buffer, pH 7.4) solution. λext = 560 nm.
Fig. 2 (a) Fluorescence intensity changes of L (1.0 × 10−5 M) upon
addition of Au3+ ions (1.0 × 10−4 M) in CH3CN/H2O (1: 1, v/v, 10 mM
HEPES buffer, pH 7.4) solution. λext = 560 nm. Inset: Fluorescence
photographic images of L and L+ Au3+. (b) Change of emission
intensity at 588 nm with incremental addition of Au3+ (λext= 560
nm).
To study the selectivity of probe L in practice, the fluorescence
response of L toward various competitive analytes were examined
in CH3CN/H2O (1: 1, v/v, 10 mM HEPES buffer, pH 7.4) solution. As
represented in Fig. 3 and Fig. S10, no obvious fluorescence
enhancement and color change observed upon addition of
10 equiv. of different metal ions, anions, amino acid and reactive
oxygen species, whereas the emission intensity was increased
meaningfully after treatment with Au3+ ions. Moreover, the
competitive experiments were performed in the presence of
1.5 equiv. of Au3+ ions mixed with 10 equivalent of other metal
cations stated above, respectively. The increase in fluorescence
The fluorometric titration of the Au3+ ion was also performed under
similar working conditions. The chemodosimeter L exhibited almost
no obvious emission signal upon excitation at 560 nm (quantum
yield ϕ =0.001, ESI†). However, upon addition of Au3+ ion to the
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intensity arising from the mixing of Au3+ and other metal ions was Taken the above observations together, a reasonable reaction
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3+
analogous to that caused only by Au3+ ions, suggesting Au3+-induced mechanism was proposed in Scheme 2. Initially, Au ions rapidly
DOI: 10.1039/D0NJ01273D
fluorescence enhancement was not affected by other interfering coordinated to one oxygen and two nitrogen atoms in probe L and
metal ions (Fig. S11, ESI†). Hence, the above outcomes confirm the promoted the spirocyclic ring opening of the L to form the
high selectivity of L for Au3+ ions.
intermediate I1. Then, fast hydrolysis of the intermediate (I1) C=N
bond by the attack of water first formed rhodamine hydrazide (I2)
which further hydrolyzes to rhodamine B (P), thus generating the
emission color of the solution.
To get insight into the sensing mechanism of chemodosimeter L
with Au3+, we first examined whether the sensing process is
reversible or irreversible. In order to verify this, an excess amount
of Au3+ chelator tetra butyl ammonium cyanide (20 equiv.)
(tBu4NCN) was added to the solution of L pre-treated with Au3+ ions.
As shown in Fig. S12 (ESI†), the absorption and fluorescence spectra
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A
complementary computational investigation30,31 has been
performed to further verify the experimental outcomes and the
possible reasons behind the red-shift absorptions of probe L in
presence of Au3+. As proposed in the mechanistic section that probe
L decomposed in presence of Au3+ and form rhodamine hydrazide
(I2) and then rhodamine B (P) after hydrolysis (Scheme 2 and Fig. 4).
So, we have done a rigorous time dependent density functional
theory investigations of L, I2 and P. The results indicate the
presence of main peak in case of L, I2 and P are at 375 nm, 481 nm
and at 491 nm (Table S2, ESI†), respectively.
induced by Au3+ did not vary after addition of Bu4NCN, suggesting
t
the irreversible chemical reaction of this sensing process. Now, the
result of the suggested reaction based sensing process could be
simply analyzed by Thin Layer Chromatography (TLC) plate. After
the reaction of L with Au3+, a pink colored and orange fluorescent
spots was appeared on the TLC plate, indicating the formation of
new rhodamine derivative (Fig. S13, ESI†). To confirm the sensing
mechanism, the ESI-MS analysis was carried out. As shown in
(a)
(b)
Fig. S5, probe L without Au3+ ions displayed peak only at m/z =
777.3034 (calcd = 776.2958) which corresponded to [L+H]
+
.
However, when 2 equiv. of Au3+ ion was added into the solution of
L, the peak of L (m/z = 777.3034) totally disappeared and two new
peaks were appeared at m/z 457.2900 and 443.2640, assigned to
rhodamine hydrazide (I2) and rhodamine B (P), respectively (Fig. S6,
ESI†). These results supported our assumption that the overall
sensing mechanism was associated with Au3+-promoted ring
opening hydrolysis process. To further validate this hydrolysis
reaction, the FT-IR study of L was performed before and after the
addition of Au3+ ions. Fig. S14 (ESI†) displayed the FT IR spectra of L
and there was no stretching band in the region 3000-3500 cm-1.
Moreover, the FT-IR spectra of L upon reaction with Au3+ exhibited a
strong frequency band at 3370 cm-1 attributable to the –OH group
of the newly formed rhodamine B which was comparable with FTIR
spectra of pure rhodamine B.29 Therefore, the spectral studies
confirmed that the interaction of Au3+ ions with probe L occurred
through a reaction based chemodosimetic approach.
(c)
Fig. 4 The energy optimized structures of (a) L, (b) rhodamine
hydrazide (I2) and (c) rhodamine B (P).
NO2
The experimental observed absorption maxima of L and after
addition of Au3+ were found at 315 nm and 560 nm, respectively
(Fig. S15, ESI†). From the aforementioned values it is quite clear
that the theoretical results are in good agreement with the
experimental observation which can completely able to justify the
insights into the proposed Au3+ sensor mechanism of L. The
computed energies of HOMO and LUMO and their differences are
also presented in the Fig. S16 (ESI†). Apparently, the HOMO, LUMO
gaps looks unusual as it is higher for I2 and P than L though a clear
red shift has been observed (Table S3, ESI†). The anomaly can be
explained by careful observation of the transition orbitals
responsible for the absorption. In case of I2 and P, the major
contributing transitions are HOMO to LUMO whereas for L these
transitions have no role in absorption.
NO2
O
N
Au3+
O
Au3+
O
N
N
N
NO2
O
NO2
N
O
N
N
O
N
I1
L
NO2
H2O
OHC
O
NO2
H2O
COOH
CONHNH2
[M]+:457.2900
N
O
N
N
O
N
P
I2
[M]+:443.2640
Scheme 2 Proposed Au3+-promoted C=N bond hydrolysis reaction
mechanism of probe L.
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Due to the fluorescence ‘turn-on’ behavior of probe L for Au3+ ions, Au3+ ions are also highly selective as the hydrolysis reaction cannot
View Article Online
DOI: 10.1039/D0NJ01273D
probe L was then effectively employed to fluorescence microscopy be facilitated or interfered by a number of biologically important
images of Au3+ ions in living cells. First, MC3T3 cells were treated competitive analytes, achieving the selective necessities for any
with different concentrations of probe L (0.25, 0.5, 1, 1.5, 2 µM) for practical application. In addition, the theoretical calculations
30 min at 37 °C and then washed with PBS buffer (pH 7.4) to authenticate our experimental outcomes. Moreover, cell imaging
eliminate the extra probes. Afterward, the treated cells were studies have shown that the cell membrane permeable
9
supplemented with 0.25, 0.5, 1, 1.5, 2 µM AuCl3 solution and then chemodosimeter
L can be excellently employed to detect
incubated in the culture medium for 30 min at 37 °C. After washing intracellular Au3+ ions in living MC3T3 cells. We believe that this
with the PBS buffer, the incubated cells were successively imaged chemodosimeter will be of potential attractions to the researchers
using a fluorescence microscope. As shown in Fig. 5, the MC3T3 for studying the various functions of Au3+ ions in the biological
cells loaded with both probe L and Au3+ ions showed a substantial systems.
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red fluorescence from the intracellular area, while the cells when
treated with either probe L or Au3+ ions did not exhibit any
perceptible fluorescence. However, the fluorescence intensity of
Experimental Section
the cells increased with increasing concentration of Au3+ ions. In
addition, there were no noteworthy gross morphological changes in
bright-field images of cells, signifying that the cells were viable
throughout the cell imaging experiments. The overlay of
fluorescence and bright-field images established that the emission
signals were located in the perinuclear region of the cytosol,
showing a subcellular distribution of Au3+ ions. The above results
confirmed that the probe L was cell permeable and could be
employed for monitoring intracellular Au3+ ions in living cells.
Moreover, an MTT assay showed that probe L had low cytotoxicity
to the living MC3T3 cells (Fig. S17, ESI†).
Materials and instruments
All the reagents for synthesis, solvents (analytical and spectroscopic
grades) and cationic salts (chlorides salts of Au3+, Cr3+, Fe3+, Zn2+,
Cd2+, Pb2+, Hg2+, Pt2+, Pd2+, perchlorates of Mn2+, Co2+, Ni2+, Cu2+,
and, nitrate salts of Ag+, and Al3+), anionic salts ( sodium salts of S2-,
HSO4 , HSO3- , and SO32-), amino acid (Cysteine) and reactive oxygen
-
species ( NaOCl, H2O2) were purchased from commercial suppliers
and used without any extra purification. All solvents were dried
according to standard processes. All reactions were examined by
thin layer chromatography (TLC) plates with detection by UV
cabinet and column chromatography was completed by using
60−120 mesh silica gel. Elix Millipore water was employed
2 µM probe +
2 µM Au3+
0.25 µM probe + 0.5 µM probe +
0.25 µM Au3+ 0.5µM Au3+
1 µM probe +
1 µM Au3+
1.5 µM probe +
1.5 µM Au3+
Control
1
throughout the all analytical experiments. The H NMR spectra and
13C NMR were measured on Bruker 400 MHz spectrometer (at
400MHz for 1H and 100MHz for 13C) with chemical shifts reported as
ppm (δ) units (in CDCl3 solvent, TMS as an internal standard). Mass
spectra were collected from a HRMS QTOF Micro YA263 mass
spectrometer. UV-visible and fluorescence spectrum were recorded
on a SHIMADZU UV-1800 spectrophometer and a Perkin Elmer LS-
55 spectrofluorimeter, respectively. FT-IR spectra were recorded on
a Perkin Elmer FTIR spectrometer. The following abbreviations are
utilized in 1H NMR spectrum to define spin multiplicities: s = singlet;
d = doublet; t = triplet; and m = multiplet.
32
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Fluorescence
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Fig.5 Bright-field, fluorescence and overlay images of MC3T3 cells
treated with L and Au3+ ions.
Detection limit calculation
The detection limit of L for Au3+ was calculated using the following
equation:28
Conclusions
Detection limit = 3Sb1/S
In summary, we have devised naphthalene-rhodamine B derivative
L as a colorimetric and ‘‘turn-on’’ chemodosimeter for Au3+ ions
based on Au3+-promoted C=N bond (Schiff base) hydrolysis of the
probe L in organo-aqueous solution. Probe L causes high sensitivity
and selectivity toward Au3+ ions in CH3CN/H2O (1: 1, v/v, 10 mM
HEPES buffer, pH 7.4) media with significantly increased absorption
spectra and emission intensity (696-fold), accompanied by a color
change from colorless to strong orange fluorescence. From the
fluorescence titration spectra, the detection limit of
chemodosimeter L for Au3+ ions was found to be 1.51 µM. More
prominently, the fluorescence response of the probe in presence of
where Sb1 is the standard deviation of the blank solution and S is
the slope of the calibration curve.
General method for UV–vis and fluorescence titration experiments
All titrations were performed in CH3CN/H2O (CH3CN/H2O = 1: 1, v/v,
10 mM HEPES buffer, pH = 7.4) solution. Stock solutions of the
probe L (1 × 10-5 M) was prepared in organo aqueous solution.
Again, stock solutions of the analytes (1 × 10-4 M) were prepared in
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Millipore water. During titration, probe L solutions were positioned
every time in a quartz optical cell (1.00 cm optical path length) and
then analyte solutions were gradually added to it by using a
micropipette.
View Article Online
DOI: 10.1039/D0NJ01273D
Where, T= treatment and C = Control.
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Computational details
Imaging studies
9
For imaging studies, 5 × 104 cells were seeded on 18 mm sterile
glass coverslips and culture overnight at 37°C and 5% CO2 in a
humidified incubator (Esco-AC2-4S8). The cells were treated with
different concentrations of probe L and AuCl3 (0.25, 0.5, 1, 1.5, 2
µM) using the same protocol such as cell viability assay. The cells
were washed with 1X PBS after treatment and images in DIC and
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The geometries are fully optimized by employing density functional
theory (DFT) using Becke’s three-parameter hybrid exchange
functional and the Lee−Yang−Parr correlation functional (B3LYP)
with the Pople’s spilt-valence basis set 6-31+G (d, p) basis set.30 The
frequency calculations have also been carried out to verify exact
minima of the complex. TDDFT calculation has been performed in
the same level of theory. All the calculations have been conducted
using Gaussian 16 program.31
fluorescence mode were acquired using
a Nikon inverted
fluorescence microscope (Nikon eclipse Ti, Japan) under 20X
objectives (DIC and S-Plan Fluo).
Cell imaging experiments
Cell culture protocol
Synthesis
Preparation of compound 2
MC3T3, a mouse precursor osteoblast cell line derived from
Musmusculus (mouse) calvaria were used in this study. The cells
were maintained in T25 polystyrene flask (Corning, USA) in
complete α-MEM media (Gibco, Invitrogen Life Science
Technologies, USA) with 10% FBS (Gibco, Invitrogen Life Science
Technologies, USA) and 1% anti-biotic & anti-mycotic solution
(Gibco, Invitrogen Life Science Technologies, USA) at 37°C and 5%
CO2 in a humidified incubator (Esco-AC2-4S8). When the flask
reached 70%-80% confluency, cells were trypsinized with 0.05%
Trypsin-EDTA (Gibco, Invitrogen Life Science Technologies, USA) and
used for in vitro studies.
Rhodamine B hydrazide (1, 0.40 g, 0.88 mmol) was dissolved in
7 ml ethanol with continuous stirring and then 0.15 g 4-hydroxy-1-
naphthaldehyde (0.88 mmol) in 5 ml ethanol was added to the
solution and heated to reflux for 12 h. The precipitate which
appeared was filtered, washed with ethanol, and the residue left
was crystallized from ethanol to give yellow colored solid
1
compound 2 in 89% yield. H NMR (DMSO- d6, 400 MHz) δ(ppm):
1.06 (t, 12H, J= 6.88 Hz, -NCH2CH3), 3.29 (t, 8H, J= 11.36 Hz,-
NCH2CH3), 6.35 (dd, 2H, J= 7.84 Hz & 5.76 Hz), 6.45 (d, 4H, J= 9.68
Hz), 6.86 (d, 1H, J= 8 Hz), 7.15 (d, 1H, J= 7.08 Hz), 7.38 (t, 1H, J= 7.84
Hz), 7.45 (t, 1H, J= 6.92 Hz), 7.50 (d, 1H, J= 8.08 Hz), 7.56-7.64 (m,
2H), 7.91 (d, 1H, J= 6.96 Hz), 8.14 (d, 1H, J= 8.44 Hz), 8.24 (d, 1H, J=
8.48 Hz), 9.27 (s, 1H, -CH=N), 10.74 (s, 1H, -OH). MS (LCMS), m/z =
611.2 [M+H] +; calculated for C39H38N4O3 = 610.29.
Cell viability assay
For assessing the viability of the cells upon treatment with probe L
solubilized in DMSO and AuCl3, MTT assay was executed. In a 96
well plate MC3T3 cells at seeding density of ~104 cells/well were
seeded and cultured overnight at 37°C and 5% CO2 in a humidified
incubator (Esco-AC2-4S8). Different concentrations of probe L and
AuCl3 were used for the study (0.25, 0.5, 1, 1.5, 2 µM). The cells
were incubated with probe L first for 30 min in incomplete medium,
washed with 1 X PBS and then again re-incubated with AuCl3
solution in incomplete medium for 30 min at 37°C and 5% CO2.
After the incubation, 10% (v/v) MTT reagent (MTT assay kit-
Himedia-CCK003) were added with fresh incomplete medium and
further incubated for 4 hr. Following this, the media with MTT
reagent were discarded and solubilization buffer provided with the
kit was used to solubilize the formazan crystals formed within cell,
and absorbance was read at 570 nm using a microplate reader
(Thermo Scientific, USA). A reference measurement was also taken
at the wavelength of 670 nm from all the wells. Cells without any
treatment were kept as control. The percentage cell viability was
calculated as per following equation.
Preparation of chemodosimeter L
To a stirred solution of compound 2 (0.25 mg, 0.41 mmol) in dry
acetonitrile (10 ml), K2CO3 (1.5 equiv.) and catalytic amount of KI
were
added.
After
30
min,
2,4-dinitrofluorobenzene
(0.076 mg, 0.41 mmol) was added drop wise to the stirred
suspension, and the resulting mixture was then refluxed for 8h.
After the completion of the reaction (TLC monitored), solvent was
evaporated in vacuum and the residue was extracted with
dichloromethane/water. The organic layer was dried over
anhydrous sodium sulfate and then evaporated in vacuum. Then
residue was chromatographed on silica gel (60-120 mesh) to give
1
pure compound L as a yellow solid in 85% yield; m.p. > 250°C. H-
NMR (CDCl3, 500 MHz) δ(ppm): 1.16 (t, 12H, J= 8.5 Hz, -NCH2CH3),
3.33 (t, 8H, J= 8.5 Hz, -NCH2CH3), 6.30 (d, 2H, J = 9 Hz), 6.49 (s, 2H),
6.61 (d, 2H, J = 10.5 Hz), 6.82 (t, 1H, J = 11.5 Hz), 7.13-7.19 (m, 3H),
7.47-7.55 (m, 3H), 7.89 (s, 2H), 8.06 (t, 2H, J = 8.5 Hz), 8.19 (dd, 1H,
J = 2.5 Hz & 11.5 Hz), 8.87 (d, 1H, J = 3 Hz), 9.33 (s, 1H, -CH=N). 13C
NMR (CDCl3, 75 MHz) δ(ppm): 12.48, 44.58, 67.91, 98.02, 108.32,
6 | J. Name., 2012, 00, 1-3
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116.84, 121.78, 122.78, 122.84, 124.01, 124.89, 127.22, 128.31,
128.66, 128.94, 129.30, 129.75, 130.07, 131.02, 131.35, 134.12,
138.32, 148.89, 148.98, 149.10, 149.51, 154.51, 166.10. MS
(HRMS): (m/z, %): 777.3034[(M + H+), 100%]; calculated for
C45H40N6O7 = 776.2958.
Am. Chem. Soc., 2006, 128, 11332-11333; (d) Z. Li, C.
Brouwer and C. He, Chem. Rev.,2008, 108, 3239-V3ie2w6A5r.ticle Online
DOI: 10.1039/D0NJ01273D
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Conflicts of interest
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There are no conflicts to declare.
9
C. J. Fleming, E. L. Salisbury, P. Kirwan, D. M. Painter and R. S.
Barnetson, J. Am. Acad. Dermatol., 1996, 34, 349–351.
Acknowledgements
SM would like to give special thanks to UGC, New Delhi, India for
the DSK Postdoctoral fellowship (award No. F.4-2/2006
(BSR)/CH/17-18/0097). SKM and SP thank Haldia Government
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College for partial laboratory facility. DM is very much grateful to
the DST, Government of India, for providing the INSPIRE Faculty
Fellowship (DST/INSPIRE/04/2016/001948).
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DOI: 10.1039/D0NJ01273D
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A “turn-on” fluorescent and colorimetric chemodosimeter for selective
detection of Au3+ ions in solution and in live cells via Au3+ -induced hydrolysis
of rhodamine-derivative Schiff base
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Sanchita Mondal,*,a Saikat Kumar Manna,b Sudipta Pathak,b Aritri Ghosh,c Pallab Datta,c
Debasish Mandal,d and Subrata Mukhopadhyaya
aDepartment of Chemistry, Jadavpur University, Kolkata 700032, India
bDepartment of Chemistry, Haldia Government College, Debhog, Purba Medinipur, West Bengal
721657, India
c Centre for Health Care Science, Indian Institute of Engineering Science and Technology, Shibpur,
Howrah 711103, India
dSchool of Chemistry and Biochemistry, THAPAR Institute of Engineering and Technology,
Patiala 147004, Punjab, India
NO2
O
Au3+
COOH
N
N
O
NO2
N
O
N
N
O
N