Development of hydrazide based fluorescence probe for detection of Al3+ ions and application in live cell image

Article abstract of DOI:10.1016/j.jphotochem.2020.112921

Development of highly specific and susceptible sensors for aluminium (Al³⁺ ions) determination in water medium is still a remarkable task. Herein, a fluorescence probe (SCH) is derived from the condensation of salicyaldehyde and carbohydrazide

Full text of DOI:10.1016/j.jphotochem.2020.112921

Journal of Photochemistry & Photobiology, A: Chemistry 405 (2021) 112921
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Journal of Photochemistry & Photobiology, A: Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Development of hydrazide based fluorescence probe for detection of Al3
ions and application in live cell image
+
D. Anu, P. Naveen*, R. Rajamanikandan, M. V. Kaveri*
Department of Chemistry, Bharathiar University, Coimbatore-, 641046, India
A R T I C L E I N F O
A B S T R A C T
Development of highly specific and susceptible sensors for aluminium (Al3 ions) determination in water me-
+
Keywords:
Schiff base hydrazide probe
dium is still a remarkable task. Herein, a fluorescence probe (SCH) is derived from the condensation of sali-
3
+
Al detection
3+
cyaldehyde and carbohydrazide in 2:1 M ratio and promising chemical sensing of Al ions is investigated.
DFT calculations
Examinations of the emission features of SCH in CH
3
OH:H
2
O (1:2, v/v) solution showed excellent turn on
Fluorescence life time decay and bio imaging.
3
þ
3þ
behaviour of Al
ions, which is due to 1:1 complex formation between SCH and the Al
ions at ambient
conditions. The lowest limit of detection was estimated by emission titration experiments and found to be 32 nM
which is much more 1000-fold lower than that WHO suggested maximum tolerable concentration. The present
3
þ
probe SCH was highly specific for the detection of Al ions over other potential interfering metal cations. Based
3
þ
on the reversible emission behaviour, an INHIBIT logic gate was assembled with EDTA and Al ions as two
3
þ
inputs. In addition, prospective application of SCH as cellular imaging sensor of Al ions in MCF-7 cells was
monitored using optical fluorescence microscopic images and real water samples.
1
. Introduction
attention has been rewarded to develop the helpful method and to
determine the concentration of Al3 ions in water samples.
+
In recent decade, development and design of super specific and
The various analytical procedures existing for sensitive detection of
Al3 ions such as atomic absorption spectroscopy, high performance
liquid chromatography, electrochemical sensing, inductively coupled
plasma mass spectrometry and etc [10–13]. Conversely, the operation of
these tactics are basically restricted by time consuming and tedious
dealings occupies the usage of high cost instrumentation and not suit-
able for on time monitoring in live cell imaging [10]. Therefore, it is
essential to expand the chemical compounds for choosy determination
+
highly susceptible chemosensors for determination of important metal
ions has received significant consideration owing to their probable
functions in environment and clinical biochemistry. The metal ions are
released into the eco settings as results of human actions which preserve
source in brutal effects for environment and human health [1–3].
3
+
Among the different metal ions, aluminium (Al ) ions were considered
as one of the hazardous metal ions [4,5]. Al3 ions were extensively
related with our everyday life in the type of water purification, food
packaging, pharmaceuticals, cooking utensils and etc [6,7]. The higher
amounts of Al3 ions in microorganism can cause a variety of physio-
logical syndromes, including osteoporosis and Alzheimer’s disease [6].
Even though, the discriminating concern for biologically and environ-
+
of Al3 ions in physiological, analytical and environmental samples.
Small organic molecule based chemosensors by fluorescence spectral
technique has offered chemist’s admittance to a capable substitute de-
vice that specifically identifies particular analytes. In addition, optical
spectral detection method offering excellent selectivity, high sensitivity,
easy visualization, low technical complexity, rapid response and on-site
tracking of bio-imaging in cancer cells [14].
+
+
mentally appropriate moieties of Al3 has stimulated vital to explore on
+
the prospective impact of its poisonous outcomes [3,8]. Due to the toxic
nature of the Al3 ions, World Health Organization (WHO) has sug-
+
Generally, Al ions exhibit hard-acid behaviour, it has been estab-
3+
gested the highest value of Al3 concentration as 7.41
+
μ
M in drinking
lished that Al desires to bind a coordination sphere holding oxygen
3+
water [9]. Moreover, poor coordination ability and a lack of spectro-
scopic characteristics attributed to the quantification of Al3 ions
compose still a most important challenge. Therefore, an important
(O) and nitrogen (N) as hard-base donor sites. Schiff bases (imines,
-C = N) were recognized as excellent ligands for the preparation of metal
complexes. The composition of Schiff base contains N-O-rich
+
*
Corresponding author.
E-mail addresses: naveen.chem011@gmail.com (N. P.), mvkaveri@gmail.com (V.K. M.).
https://doi.org/10.1016/j.jphotochem.2020.112921
Received 24 June 2020; Received in revised form 9 September 2020; Accepted 12 September 2020
Available online 15 September 2020
1
010-6030/© 2020 Elsevier B.V. All rights reserved.

A. D. et al.
Journal of Photochemistry & Photobiology, A: Chemistry 405 (2021) 112921
coordination background which present hard-base behaviour for the
spectroscopic techniques like UV–vis, 1H-NMR and 13C-NMR spec-
trometry. The crude product was recrystallized with ethanol and the
structure of SCH was confirmed by single crystal X-ray crystallography.
The new probe SCH was soluble in common organic solvents such as
dichloromethane, chloroform, ethanol, methanol, dimethylformamide
and dimethylsulfoxide.
binding of Al3 ions (hard-acid) [7,10,15]. Particularly, Schiff base
compounds integrated with a fluorescence molecule are elegant imple-
ments for the quantification of various metal ions [15,16]. In light of this
objective, we have projected a novel Schiff-base probe (SCH), which was
synthesized by simple condensation reaction of carbohydrazide with
salicyaladehyde in 1:2 ratios.
+
◦
ꢀ 1
Light yellow Yield: 78 %. m.p: 165 C. FT-IR (cm ) in KBr disk: 1534
1
In this paper, we reported a Schiff-base probe (SCH) synthesized by
simple condensation reaction and fluorescence based “turn-on’’ probe
(ʋC = N), 3348 (ʋOH), 3436 (ʋNH). H NMR (DMSO-d
6
, ppm) 11.36 (s,
OH), 7.21 (s, NH), 8.71 (s, ꢀ HC = N) and 6.92–7.38 (m, aromatic
3
+
for the detection of Al in Methanol/water, which is due to chelation
induced enhanced fluorescence (CHEF) process. The sensing mechanism
was examined by different spectroscopic experiments and applied for
protons).
2.4. Optical detection of Al3 ions using SCH
+
quantification of Al3 in semi-aqueous media. In addition, potential
+
3
+
usage of SCH as intracellular detection of Al ions in MCF-7 cells was
also examined by fluorescence microscopy and further applied for
environmental water samples.
To prepare requisite stock solutions, at first 2 mM concentration of
each metal salt solution were prepared in DD water and chronological
strength was made to acquire required amount of metal ion solution.
Similarly, the preliminary stock solution (1 mM) of SCH was prepared in
2
. Experimental section
methanol (CH OH). The compound (1.0
μ
M) was assorted with various
3
metal ions concentrations in CH OH:H O (1:2, v/v) in a 1 cm cuvette.
3 2
2
.1. Materials and methods
Then, this solution was stirred well for 5 min. After 5 min, fluorescence
spectra of the mixtures were measured at photo excitation wavelength at
365 nm. The fluorescence intensity of the SCH enhanced within 5 min
after the addition Al3 ions (Figure S1 (a)). After 5 min, no notable
change in the relative fluorescence intensity was examined, which in-
dicates the most favourable incubation time of this probe to the sensing
The metal salts were collected from Sigma-Aldrich and Loba Chemie
+
and are of at least analytical reagent (AR grade) grade. The precursor’s
salicylaldehyde and carbohydrazide utilized for the preparation of Schiff
base probe (SCH) was purchased from Sigma-Aldrich. All the solvents
were obtained from SD fine chemicals (AR grade) and used as received.
Doubly distilled (DD water) water was used throughout the experiments.
of Al3 ions were selected as 5 min. The effect of pH of this probe was
investigated and SCH probe displays maximum intensity in the pH range
from 6 to 8 (Figure S1 (b)). The fluorescence features of the present
probe SCH shows good sensitivity at neutral pH range (6–8) (Figure S1
+
2
.2. Instruments
(
b)), representing that this SCH is useful in a physiologically applicable
UV–vis absorption and steady state fluorescence spectral studies
pH range for bio-imaging applications. All the experiments were done at
◦
were monitored on a JASCO V-730 spectrophotometer and JASCO 7300
spectrofluorometer, respectively. 1 cm quartz cell cuvettes were used
both titration experiments. Infrared spectra were measured as KBr pel-
ambient temperature (25 C) and minimum thrice.
2.5. In vitro cellular imaging
ꢀ 1
1
lets on a Jasco FT-IR 400- 4100 cm range. H-NMR spectrum of probe
SCH were recorded on a 400 MHz ADVANCE Bruker NMR spectrometer
using tetramethylsilane as an internal standard. Fluorescence lifetime
decay analysis were performed using time correlated single photon
counting (TCSPC) method in a Horiba Scientific equipped with NL-C2
pulsed diode excitation source of 390 nm. Single crystal data collec-
tions and corrections for the probe SCH were done at 100 K and the
structure was showed by using SHELXL-2014.
3
þ
MCF-7 cells were incubated with the SCH and SCH þ Al in PBS
buffer (pH = 7.4) for 30 min. Then the cells were centrifuged and
washed with PBS buffer three times. The treated cells were incubated
with probe (10 M) for 10 min and again the cells were washed with PBS
μ
buffer. After washing, the cells were imaged by using inverted phase
contrast fluorescent microscope.
3
þ
The electronic structures of SCH and SCH ¡ Al were optimized via
density functional theory (DFT) on a hybrid B3LYP exchange ꢀ corre-
lation function. Small-core relativistic efficient core prospective was
measured for the Al atom with basis input was considered for H, C, N,
and O atoms. The energized state structures were examined using time-
dependent DFT (TD-DFT) on DFT-optimized geometries [17,18]. All the
energy computations were employed by the Gaussian 09 program.
3. Results and discussion
The new probe SCH was synthesized by condensation of salicy-
laldehyde with carbohydrazide in ethanol in 2:1 ratio under reflux
conditions (Scheme 1). The new probe SCH was characterized by
1
13
various spectroscopic techniques like UV–vis, H NMR and C-NMR
spectrometry. The crude product was recrystallized with ethanol and the
structure of SCH was confirmed by single crystal X-ray crystallography.
The characteristic IR bands of the probe SCH provide significant infor-
(
M06ꢀ 2X/LANL2DZ).
2
.3. Synthesis and characterization SCH
mation of functional groups. A broad band corresponding to
υ
OH and
ꢀ 1
ꢀ 1
υ
NH vibration which was appeared at 3348 cm
and 3436 cm
,
ꢀ 1
The probe SCH was prepared by condensation of salicylaldehyde
respectively. A strong band appeared at 1534 cm are corresponding to
with carbohydrazide in ethanol under reflux in 2:1 ratio (Scheme 1). The
reaction was monitored by thin layer chromatography until the
completion of reaction. After 6 h light yellow colour product precipi-
azomethine nitrogen (ꢀ CH = N) of the probe which was shifted into
1
lower frequency indicating the coordination to metal ion. The H-NMR
6
spectrum of the probe SCH have been recorded in DMSO-d with the
◦
tated was filtered and washed with petroleum ether (60ꢀ 80 C) and
frequency of 400 MHz is shown in Figure S2. In the spectrum of probe
SCH, a singlet corresponding to the phenolic ꢀ OH and –NH protons
dried under vacuum. Probe SCH was characterized by various
Scheme 1. Synthetic route of Probe SCH.
2

A. D. et al.
Journal of Photochemistry & Photobiology, A: Chemistry 405 (2021) 112921
appeared at δ 11.36 ppm and δ 7.21 ppm respectively. Further, a singlet
hydroxyl group oxygen atom of salicylaldehyde are in coordination to
1
3
3þ
appeared at δ 8.71 ppm was assigned to azomethine nitrogen. Then, C-
NMR spectrum of the probe SCH has been recorded in DMSO- d are
shown in Figure S3. The resonance observed at δ 152.40 and δ
57.08 ppm assigned to the azomethine (ꢀ CH = N) carbon of the probe
SCH). The resonances in the range of δ 116.63–133.72 ppm are corre-
form SCH-Al complex. In other words, the rotation about the -C = N
3
þ
6
bond become controlled after the chelation of Al ions which supports
in the observed enhanced fluorescence via CHEF process [21,22].
The lowest limit of detection (LOD) was computed on account of the
emission titration experiments. LOD value was calculated by IUPAC
criteria [14,23]. To estimate the LOD of the present method, the fluo-
1
(
sponding to the aromatic carbons of probe. Further, carbonyl carbon
signal of the probe observed at δ 159.13 and 163.25 ppm. In order to
confirm the exact structure of the probe, X-ray crystallographic analyses
have been done Fig. 1. Probe SCH crystallized in the Orthorhombic with
space group C2c 2. The crystallographic data, selected bond distances
and angles are listed in Tables S1 and S2.
3
þ
rescence intensity values were plotted against the concentration Al
ions, and observed calibration curve displays a well fitted linear rela-
M (Fig. 4). From the slope of
tionship in the concentrations range 2–28
μ
calibration curve, the LOD value is calculated to be 32 nM, which is
much more 1000-fold lower than that WHO suggested maximum
tolerable concentration. The achieved LOD value for Al3 ions in the
present work was compared with earlier documented organic molecules
based fluorometry methods [3,24–33] and is listed in Table S3. The LOD
value of this method was comparable to/better than some reported
methods without using sophisticated instrument techniques. In addition,
the present method was shows simple, rapid, highly specific, good linear
range, low cost with fine sensing performance compared to other
fluorophores.
+
.1. Spectroscopic detection Al3+ ions using SCH
3
The synthesized probe SCH were further applied in the field of
chemosensors was great interest. Hence, we are focusing this probe for
detection of metal cations [7,10,16]. Initially, steady state emission
3
+
+
+
+
3+
spectral studies of probe with various metal ions (Al , Ag , Na , K ,
2
+
2+
2+
2+
2+
2+
2+
2+
2+
2+
Ca , Hg , Mg , Co , Mn , Cu , Ni , Cd , Zn , Pb , Fe ,
To certify the ligand-to-metal stoichiometry of the SCH-Al3 com-
plex, conventional Job’s plot analysis was investigated by steady state
emission spectra [34]. Job’s plot was plotted between the mole fraction
þ
3
+
3+
3 2
Ga and Cr ) in CH OH:H O (1:2, v/v) were monitored and typical
equilibrium process were shown in Fig. 2. SCH Probe alone displayed
very weak fluorescence peak at 443 nm when exciting wavelength at
of Al3 ions and relative emission intensity of probe SCH with the
+
3
65 nm is due to the lower intra-molecular charge transfer (ICT) char-
addition of Al3 ions and presented in Figure S5. As illustrated in
þ
acter and rotation concerning the (-C = N) imine group [10]. Moreover,
upon mixing of Al3+ ions to probe SCH, emission intensity of compound
Figure S5, the maximum intersection point was noted at 0.5 mol frac-
tion of Al3 ions. The observed higher intersection point sturdily pro-
+
enhanced 10-fold at a wavelength of 443 nm. In contrast, addition of
+
2+
+
2+
+
2+
2+
3+
poses that the formation of 1:1 stoichiometry of metal-to-ligand
various significant metal ions including Ag , Na , K , Ca , Hg
,
,
1
2
+
2+
2+
2+
2+
2+
3+
complex. To know the better binding mode of the present work, H-NMR
Mg , Co , Mn , Cu , Ni , Cd , Zn , Pb , Fe
and Cr
3
+
6
titration analysis were recorded in DMSO-d and displayed all the ex-
reasoned nearly no emission enhancement. Interestingly, Ga which
belongs to the similar group on the periodic table also did not generated
increasing emission intensity of compound. It looks that the emission
intensity enhancement behaviour was imitative from the further
pected signals as shown in Figure S6. In the spectra of the probe (SCH),
a doublet appeared around δ11.93ꢀ 11.95 ppm and one singlet appeared
at δ11.64 ppm is corresponding to OH proton. A two sharp singlets
appeared at δ9.01 and 9.41 ppm are assigned to NH protons. The singlet
due to azomethine (ꢀ CH = N-) proton observed atδ 8.51 ppm in the
probe (SCH). As per NMR titration analysis, the addition of 0.5 equiv-
alent of Al3 salts (chloride) into SCH probe led to the decrease in the
intensity field of OH proton (11.93–11.95), NH proton (9.41), which
confirms the coordination of Aluminium metal to probe(SCH). Further,
extensive construction of the
π
-conjugation structure in Schiff base
probe SCH leading to metal binding ability, and the emission features
were highly specific to particular metal cations [6]. The specificity for
+
3
+
Al ions with compound was plotted as a bar diagram were shown in
3
+
Figure S4. As described in Figure S4, Al ions only stimulated in an
articulated emission enhancement comparative to the other cations.
the addition of 1equivalent of Al3 salts (chloride) into SCH probe, the
+
completely disappearance of peaks of one OH proton and NH protonin
1
3
.2. Sensitivity of the probe
the H-NMR spectra, indicating the aluminium metal strongly coordi-
nated. In addition, decrease in the intensity (ꢀ CH = N-) protonfrom
8.51 ppm to 8.43 ppm supports the coordination of azomethine nitrogen
to the Aluminium ion. Further, we have proposed plausible mechanism
In order to understand the identification capability, the steady state
fluorescence spectra for the probe SCH with incremental addition of
3
+
3+
1
Al ions were executed and collected emission spectral profile is pre-
of Al ions by SCH probe with the support of H-NMR spectral data and
theoretical studies (DFT) outcomes. Then, this result was further vali-
dated by mass spectral analysis (Figure S7). The obtained mass spectral
3
+
sented in Fig. 3. Before the addition of Al ions, probe SCH exhibits
weak fluorescence peak at 443 nm. Upon the sequential addition of Al3
ions from 2 to 28 M to probe SCH, the fluorescence intensity was
enhanced 6-fold with slight bathochromic shift were observed. In the
+
+
μ
value m/z = (M+H) 357.20, which indicates the formation of 1:1 probe
SCH-Al3 complex. (Scheme 2)
þ
3
þ
meantime, fluorescence colour of probe SCH with Al
ions also
Furthermore, TCSPC analysis were performed to investigate the
pathway of the “turn-on” chemosensor responses of probe SCH with
3
+
monitored under UV light illumination. After the adding of Al ions to
probe SCH, fluorescence colour changes from colourless to cyan blue
colour (inset of Fig. 3). Quantum yield (ɸ) of Schiff base probe SCH with
and without Al3 ions was calculated to be 0.08 and 0.36, respectively
14,19,20]. The observed result proposed that probe SCH contains
electron providing capability of (-C = N) imine nitrogen atom and
3
þ
Al ions and results are shown in Fig. 5. In accordance with the sub-
sequent equations: 1//<
τ
f>
=k +k , k =Φ
r
nr
r
f/<
τ
f>, where,
τ
f
is average
þ
fluorescence lifetime, knr is non-radiative rate constant and k is radia-
r
3
+
[
tive rate constant of probe SCH in the absence and presence of Al ions
were estimated. The mean fluorescence decay value (τf = 1.13 ns) of
probe SCH with the addition Al3 ions was higher (
þ
τf = 2.85 ns) than
probe SCH due to rising stability of Al3 ions coordinated complex.
þ
Moreover, the enhanced
τ
f
values vitally due to the increase in radiative
ꢀ 1
ꢀ 1
decay process (0.07 S to 0.126 S ) which convey in sustain for the
diminishing order of estimated non-radiative constant rate value (12.43
ꢀ
1
ꢀ 1
S
1
to 2.43 S ) [20,23]. In addition, the relation of knr/k
r
reduces from
77.57 for probe SCH to 19.28 for SCH-Al3 , which is in well accor-
þ
dance with the CHEF process [35]. These outcomes further supported
3
þ
Fig. 1. ORTEP diagram of SCH probe.
with the enhancement of fluorescence intensity for compound with Al
3

A. D. et al.
Journal of Photochemistry & Photobiology, A: Chemistry 405 (2021) 112921
Fig. 2. Emission spectra (a) and (b) colour response under UV-lamp of SCH with various metal ions in CH
3
OH:H
2
O (1:2, v/v). (λex = 365 nm).
Fig. 3. Steady state emission spectral profile for SCH with different concen-
3
þ
3þ
trations (2-28
μ
M) of Al
ions and inset shows emission colour (under UV-
Fig. 4. Calibration curve for the determination of Al ions by SCH in CH
3
OH:
3
þ
light) of SCH and SCH with Al ions in CH
3
OH:H
2
O (1:2, v/v). (λex = 365 nm).
H
2
O (1:2, v/v). The error bars correspond to the standard deviations founded on
three individual experiments.
4

A. D. et al.
Journal of Photochemistry & Photobiology, A: Chemistry 405 (2021) 112921
electrophilic attack, while the dark blue indicated the active regions for
nucleophilic attack. According to ESP maps in Figure S8 (b), there are
red regions on the environment of nitrogen atoms and these atoms are
appropriate for any interaction. Whereas, blue regions of map indicated
low interaction.
The reversibility of the fluorescence spectral reaction of SCH-Al3
þ
was examined using mixing a most efficient chelating agent ethylene-
diaminetetraacetate (EDTA). Due to the larger stability constant value of
the Al3 -EDTA complex, it was probable that EDTA can preferentially
þ
coordinate with Al3 ions discharged probe SCH from the SCH ¡ Al
þ
3þ
3
þ
complex. (Fig. 7) The emission intensity of the SCH ¡ Al probe was
reduced by addition of EDTA and concurrently the emission intensity of
SCH was enhanced after the successive mixing of Al3 ions, which
+
3
þ
clearly indicates that the coordination ability of SCH with Al ions was
reversible process. This result clearly points out that the recycle features
of probe SCH towards sequential detection of Al3 ions and EDTA
þ
(
Figure S9). Hence, probe SCH was ecological after the treatment with
3
+
Scheme 2. Plausible mechanism for Al ions.
EDTA.
3
.4. Binding constant and free energy
Binding constant for the present system can be calculated by using
following double logarithmic equation (Eqn. 1) [38,39] (Figure S10)
[
]
[ ]
F ꢀ F
0
log
= log Ka + n log
Q
(1)
F
þ
where, F and F
probe SCH, “K
ions and “n” is the number of binding sites. The values of n and K
determined from the slope and intercept of the double logarithmic plot.
0
is the emission intensity in the presence of Al3 ions into
3
þ
a
” is the binding constant, “Q” is the concentration of Al
were
a
4
The value of K
strong binding between the probe SCH and Al ions. The free energy
) [39]
a
is calculated to be 1.09 × 10 L/mol, recommending a
3
þ
change (ΔG, determined by the equation ΔG = ꢀ 2.303RT log K
a
was estimated to be ꢀ 22.99 kJ. The negative value of free energy
changes undoubtedly indicates that the spontaneous process of probe
SCH with Al3 ions [14,39].
þ
Fig. 5. Fluorescence life time decay profile for probe SCH in the absence and
3
þ
presence of Al ions in CH
3
OH:H
2
O (1:2, v/v).
3+
3
.5. Selectivity of Al ions over other relevant metal ions
ions.
Emission spectral studies of the Schiff base probe SCH (20 M) in the
μ
3
+
+
+
+
2+
2+
presence of various metal ions such as Al , Ag , Na , K , Ca , Hg ,
2
+
2+
2+
2+
2+
2+
2+
2+
3+
3+
3+
Mg , Co , Mn , Cu , Ni , Cd , Zn , Pb , Fe , Ga and Cr
30 M) in CH OH:H O (1:2, v/v) were performed. Upon examining the
spectra, it is clear that the probe SCH has first-rate selectivity for Al
3
.3. Density functional theory DFT calculations
The orientation of molecular structure and geometry of the probe
(
μ
3
2
3
þ
,
3
þ
which has exhibited a fluorescence enhancement, whereas the other
competent metal ions did not result in a color change and the emission
spectra did not experience any enhancement or suppression of fluores-
cence intensity. This result revealed the favour of probe SCH towards
SCH and SCH þ Al complex was done by using Density Functional
Theory (DFT) with M06ꢀ 2X/LANL2DZ level of theory on Gaussian 09
programme. The optimized electronic structure showed the probe SCH
3
þ
and Al complex in 1:1 stoichiometry as shown in Fig. 6 and Figure S8
a). The results of DFT studies showed two nitrogen atoms with bond
3
þ
Al
ions over other metal ions (Fig. 8). In addition, to check the
(
specificity of the probe SCH to Al3 ions, we performed twin metal
competitive analysis, as shown in Fig. 8. In this case, the emission
spectral response was recorded with the addition of equal concentra-
þ
distance of 1.897 Å and 1.999 Å and one oxygen atom with bond dis-
tance of 1.773 Å exhibited interaction with aluminium ions [36,37].
Furthermore, the structural parameters and planarity of the probe and
+
+
+
2+
2+
2+
2+
2+
3
+
tions of all the metal ions (Ag , Na , K , Ca , Hg , Mg , Co , Mn ,
Al complex are found to be parallel with minimal structural fluctua-
tions observed at the above level of theories. Furthermore, the obtained
negative interaction energies (ꢀ ΔEint) indicated that the complexation
2
+
2+
2+
2+
2+
3+
3+
3+
Cu , Ni , Cd , Zn , Pb , Fe , Ga and Cr in CH
3
OH:H
2
O (1:2,
3
þ
v/v)) to the probe SCH pretreated with Al ions. Both single and dual
3
þ
process is exothermic and the addition of Al3+ ions leads to stable
metal analysis confirmed the excellent selectivity of the probe to Al
ions.
configuration due to large HOMO-LUMO bandgap. The donating ability
of molecules were characterised by HOMO values. The high HOMO
energy values implied more tendency to drop electrons from molecular
system. The electron density comes from the azomethine nitrogen atom,
which chelates with the metal ion. Electrostatic potential (ESP) maps are
correlated to charges on surface. This map helps to predict the active
regions for nucleophilic or electrophilic attack. ESP maps of probe SCH
3.6. Logic gate behaviour
To build the molecular logic gate behaviour of the present system, we
have checked the fluorescence “turn on” process of the probe SCH using
sequence-reliant fluorescence output between EDTA and Al ions as
chemical inputs [40,41]. In the present case, the easy Schiff base mo-
lecular system SCH associates extremely fine with an INHIBIT logic gate
3
þ
3
þ
and SCH þ Al are done at same level of theory and shown in
Figure S8 (b). The red color corresponded to the active regions for
5

A. D. et al.
Journal of Photochemistry & Photobiology, A: Chemistry 405 (2021) 112921
3
þ
Fig. 6. The energy levels of HOMO-LUMO and the interfacial plots of the orbitals for probe SCH and SCH-Al complex calculated from B3LYP and M062x level of
theories where calculated electronic properties are same for both level of theories.
3
þ
Fig. 7. Emission reversible response for SCH with Al
ions and EDTA and
Fig. 8. Emission intensities of SCH in CH
3
OH:H
2
O (1:2, v/v) with 30
μ
M of
OH:
3
+
3þ
inset shows emission colour of SCH (i), SCH þ Al ions (ii) and SCH þ Al
ions + EDTA (iii) solutions. (λex = 365 nm).
3þ
Al ions in H
2
O in the existence of different cations. Pink bar: SCH in CH
3
3+
H
2
O (1:2, v/v) with 30
μ
M of Al ions in aqueous medium. Blue bar: SCH in
3
þ
CH OH:H O (1:2, v/v) with 30
3
2
μ
M Al ions +30
μ
M of potentially interfering
behaviour. In this concern, the INHIBIT logic gate features of probe SCH,
cations. (λex = 365 nm). The error bars correspond to the standard deviations
EDTA and Al3 ions work as inputs, whereas intensity of fluorescence
þ
founded on three individual experiments.
′′
peak at 440 nm is the output. (Fig. 9) If the output is “1 , it means the
logic gate is ON and this behaviour only observed in the existence of
3.7. Analytical application
3
þ
′′
Al ions. If the output is “0 , it means the logic gate is OFF and this
The probe SCH was effectively utilized for the quantification of Al3
þ
result happens in three different settings such as, when the presence of
3
þ
EDTA, in the existence of both EDTA and Al ions, and in the absence
of EDTA and Al3 ions. Therefore, probe SCH works as an INHIBIT logic
ions in tap water and drinking water samples. Standard addition pro-
þ
3þ
cedure was applied to detect the Al ions in real water samples [22,42].
Initially, Al3 ions were not detected in the drinking and tap water
þ
gate behaviour [41].
samples. However, spiking the Al3 ions into real water samples
þ
6

A. D. et al.
Journal of Photochemistry & Photobiology, A: Chemistry 405 (2021) 112921
3
þ
Fig. 9. Logic gate behaviour of SCH with Al ions/EDTA and truth table.
3
þ
reasoned a noteworthy increase in emission intensity for triplicate
measurements. The obtained real water investigation observations are
represented in Table S4. An excellent recovery between 94.8 and 97.2 %
was noted with tap and drinking water samples added with Al3 ions.
The lowest relative standard deviation value suggested the high accu-
racy of the present method.
materials. The sensitivity of SCH and SCH þ Al in living MCF-7 cells
were measured by fluorescent microscope. The MCF-7 cells were incu-
3
þ
bated with SCH and SCH þ Al (10.0
μ
M) in PBS (pH = 7.4) buffer at
þ
◦
37 C for 30 min and imaged through fluorescent microscope as shown
in Fig. 9. It is found that the cells incubated only with SCH displayed
3
þ
very low intense fluorescence, whereas the SCH fused with Al metal
ions showed very strong fluorescence intensity [43]. The cells were
viable throughout the imaging experiments proved by bright and
3
.8. Fluorescence imaging of MCF-7 cells
3
þ
dark-field transmission images of cells treated with SCH and Al ions.
So far, it is accomplished that the Al3 ions fused with SCH could have
applicability to induce viable nuclear fragmentation in living samples.
Fig. 10
þ
MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bro-
mide) assay was carried out to check the cytotoxic nature of the probe
3
þ
SCH and SCH þ Al on MCF-7 cells. The corresponding IC50 values are
shown in Table S5. Cisplatin was used as a positive control. Further, live
4
. Conclusion
3
þ
cell bioimaging were done for the probe SCH and SCH þ Al . To have
convenient suitability, the sensor must be capable of imaging the analyte
specifically in living cells without the interference of other intracellular
In summary, a new type of fluorescent sensor probe SCH has been
3
þ
Fig. 10. Bright field and fluorescence image of MCF-7 cells. (A and B) control Bright field images of SCH and SCH þ Al treated MCF-7 cells. (C and D) Fluorescence
◦
images of MCF-7 cells incubated with SCH (5
μ
M) for 30 min and subsequent addition of (5
μ
M) AlCl
3
for 10 min at 37 C.
7

A. D. et al.
Journal of Photochemistry & Photobiology, A: Chemistry 405 (2021) 112921
synthesized and characterised by various spectroscopic techniques and
structure of probe SCH was confirmed through single crystal X-ray
crystallography. The probe SCH showed strong fluorescent response
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Declaration of Competing Interest
The authors report no declarations of interest.
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