Hydrazone Based Dual – Responsive Colorimetric and Ratiometric Chemosensor for the Detection of Cu2+/F? Ions: DNA Tracking, Practical Performance in Environmental Samples and Tooth Paste

Article abstract of DOI:10.1007/s10895-020-02488-0

Colorimetric sensors have attracted wide scope of attentions due to its fascinating advantages, like handy, equipment-free and naked eye detections. In this investigation, a new and novel hydrazone based dual-responsive ratiometric/colorimetric chemosenso

Full text of DOI:10.1007/s10895-020-02488-0

Journal of Fluorescence
https://doi.org/10.1007/s10895-020-02488-0
ORIGINAL ARTICLE
Hydrazone Based Dual – Responsive Colorimetric and Ratiometric
2
+ −
Chemosensor for the Detection of Cu /F Ions: DNA
Tracking, Practical Performance in Environmental Samples and Tooth
Paste
1
1
Willsingh Anbu Durai & Andy Ramu
Received: 12 December 2019 /Accepted: 13 January 2020
Springer Science+Business Media, LLC, part of Springer Nature 2020
#
Abstract
Colorimetric sensors have attracted wide scope of attentions due to its fascinating advantages, like handy, equipment-free and naked
eye detections. In this investigation, a new and novel hydrazone based dual-responsive ratiometric/colorimetric chemosensor have
2+
−
been developed for highly selective and sensitive detection of Cu and F ions in dimethyl sulfoxide (DMSO) solvent. The probe
2+
−
showed highly selective sensing towards Cu and F ions by exhibiting a color change from pale yellow to yellowish green and
pale yellow to yellowish brown respectively., in DMSO without any interference of other ions at same concentration. These
experimental results have also substantiated by the NMR, HR-MS, UV-Vis spectroscopic, cyclic voltammetry, differential pulse
2+
−
voltammetry techniques and DFT calculations. The detection limits are found to be 5.8 μM for Cu and 0.025 μM for F ions
which is far below to the values recommended by WHO. The stoichiometric ratios between NAPCBH and Cu2+/ F- ions were
1
confirmed from the Job’s plots and H NMR titration experiments which are found to be 2:1 and 1:1 respectively. The tracking
2+
ability of the DNAwith NAPCBH-Cu was studied by UV-Vis titration and Cyclic voltammetry measurements. It shows efficient
2+
affinity towards DNA with NAPCBH-Cu . The probe can also quantitatively determine the Copper and fluoride ions present in
environmental samples & toothpaste. The NAPCBH was promptly recovered by utilizing very low concentration of HCl, showing
2+
−
that was found feasible and re-usable sensor for the convenient detection of Cu and F ions.
.
.
.
Keywords Colorimetric sensor Ratiometric sensor Selective/sensitive probe Naked eye detection
Highlights
•
A new hydrazone based chemosensor NAPCBH was synthesized via
Introduction
simple synthetic process.
•
2
+
-
Dual-response of NAPCBH towards Cu and F ions in an organic
medium was developed.
Recent developments in colorimetric chemosensors showed
special interests due to their utilization in analytical, environ-
mental, therapeutic fields, as well as in industry based sectors
[1–3]. This detection technique was identified to be cost-ef-
fective, rapid and facile with wide range of applications [4, 5].
In comparison to fluorescent chemosensors, the colorimetric
sensors have promising features in the detection of metal ions
and anions. The precise and expedient discovery for the de-
2+
-
•
•
The Cu and F ions detection are highly selective and sensitive.
2+
-
ICT mechanism was confirmed for both NAPCBH with Cu and F
1
ions through Job’s plot, H NMR titration and DFT studies.
2+
•
•
DNA tracking ability was also studied for NAPCBH-Cu successively.
The probe can also quantitatively determine the Copper and fluoride
ions present in environmental samples & toothpaste.
•
The NAPCBH was readily regenerated at lower concentration of HCl,
showing its feasibility to be a re-usable sensor for the convenient detec-
2+
-
tion of Cu and F ions.
2
+
tection of Cu ion using hydrazone based Schiff base by the
naked eye without utilizing massive instruments were created.
Among all, copper ion is one of the important micronutrients
for human existence. It serves as a vital cofactor via constitut-
ing the lively element in a huge variety of enzymes along with
superoxide dismutase, cytochrome c oxidase and tyrosinase
Electronic supplementary material The online version of this article
(https://doi.org/10.1007/s10895-020-02488-0) contains supplementary
material, which is available to authorized users.
*
Andy Ramu
ramumku@yahoo.co.in
[
6–8]. Therefore, day by day ingestion of copper is integral for
1
Department of Inorganic Chemistry, School of Chemistry, Madurai
Kamaraj University, Madurai, Tamil Nadu 625 021, India
human health [9]. However, unregulated overloading of

J Fluoresc
copper ions can result in extreme neurodegenerative illness
inclusive of alzheimer’s, parkinson’s, prion, stomach and
gastro intestinal disturbance, liver or kidney damage, loss of
cognition, Wilson’s disease and etc. [10–15] On the other
hand, copper deficiency is associated with myelopathy [16].
Furthermore, copper ion is a considerable environmental pol-
lutant due to its great usage. The World Health Organization
which allows the naked eye detection of the color change
without using the luxurious methods [43–45] and on other
hand, it offers many advantages such as high sensitivity, spec-
ificity, simplicity, low cost, rapid monitoring of analytes in
biological, toxicological and environmental samples [42,
46–48]. Therefore, the development of a simple and efficient
2
+
−
colorimetric sensor for the detection Cu and F ions might
be useful for chemists and biologists.
(
WHO) has set the safe restriction of copper in drinking water
at 2 ppm (31.5 μM) [17]. Thus, the advancement of detecting
copper ion with higher sensitivity, low detection limit and
quick response is an extraordinary process in high demand.
DNA is a giant cellular target of several metallodrugs for the
treatment of various pathologies, including cancer, and it as-
sumes a vast role in revealing the capability of metal binding
destinations with either electron rich nucleobases or phosphate
oxygen of the DNA [18, 19]. Typical nucleic acid probes dis-
tinguish and identify nucleic acids on the basis of intercalation
Schiff bases possessing π electrons in the imine group and
nitrogen analogues in the aromatic rings provide an opportu-
nity for chelation with the metal ions and anions. The chela-
tion could decorate intramolecular charge transfer (ICT) tran-
sition or cause the ligand to metal charge transfer (LMCT)
transition which will be used for the detection of metal ions
and anions [44, 49]. Although several studies have been re-
ported for the colorimetric detection of copper ion and fluoride
ion in various media they suffer from many complications like
involving tedious synthetic processes, complicated structure
and etc. [50–52]
[20], groove binding [21], electrostatic interaction [22] and hy-
drogen bonds [23]. Thus, DNA tracking is essential in the ad-
vancement of chemical tools for the biologically relevant me-
tallic ions. Very recently there are a number of DNA tracking
strategies for the fluorescent probes with metal ions [24, 25]. To
the best of our knowledge and understanding very few reports
on the tracking of DNA in colorimetric sensor particularly for
In view of the above necessities, we endeavored to design
an easy and efficient probe based on the conjugation of 2-
hydroxy-1-naphthaldehyde and chlorobenzylidene hydrazine
which leads to the formation of hydrazone moiety. Hydrazone
probe are one of the best and promising agents in preventing
many diseases. In addition, NAPCBH possess hydroxyl and
imine moieties which can facilitate metal ions, anions binding
and DNA tracking [53, 54]. The sensing capability of
NAPCBH was examined towards diverse cations and anions.
The experimental results have shown that the probe shows an
2+
Cu ions [26]. It appears strongly that such applications will
bloom in the forthcoming months and years for sure.
Furthermore, biological and environmental strategies have
been given the importance of anions and triggered interests.
Among the anions, some of the features of fluoride ions are
exhibits unique chemical properties, extensively used in tooth
paste, pharmaceutical dealers use them for the prevention of
dental carriers, teeth demineralization at the same time as car-
rying orthodontic appliances and remedy for osteoporosis [27,
2
+
−
effective and colorimetric detection of Cu and F ions in
organic medium without involving any complicated process-
es. The applications and potential of the developed sensor
were examined by DNA tracking, practical performance in
environmental samples and tooth paste.
2
8]. It has been shown that fluoride ions can cause dental,
bone fluorosis and sickness including gastric and kidney is-
sues, urolithiasis and even loss of life [29–31]. Therefore, the
detection of fluoride ions in ingesting water and dwelling or-
gans attracted a great attention in chemistry and bio-inorganic
chemistry [32–34]. Hence, many chemical sensors have
Materials and Methods
Materials
−
been reported towards the detection of F ions [35, 36].
In addition, variety of fluorescent and chemical sensors
based on hydrogen bonding interactions and fluoride ion
induced chemical reactions have also been reported for
fluoride ion sensors [37, 38].
In recent years, plenty of analytical techniques are commer-
cially employed to recognize metal ions and anions such as
atomic absorption spectroscopy [39], inductively-coupled
plasma mass spectroscopy [40] and fluorescence techniques
4-Chlorobenzaldehyde, hydrazine hydrate, 2-hydroxy-1-
naphthaldehyde, tetrabutylammonium perchlorate, metal
salts, all solvents and reagents (analytical grade and
spectroscopic grade) were obtained from Sigma-
Aldrich, Merck respectively and used as obtained with-
out any purification.
Instrumentation
[
41], however, these methods are costly [42], require sophis-
1
13
ticated instrumentation set up, tedious sample preparative
methods and trained operators [5]. Therefore, efforts are being
devoted by researchers to develop most attractive and effec-
tive over other techniques based on colorimetric sensors
H NMR and C NMR were recorded on a BRUKER 300
and 400 MHz. Chemical shifts are mentioned in ppm,
Tetramethylsilane as standard and DMSO-d used as solvent.
Electronic absorption spectral measurements were recorded in
6

J Fluoresc
Scheme 1 Synthetic procedure of
NAPCBH
solution using JASCO V-550 UV-Visible spectrophotometer
with a quartz cuvette (cell length 1 cm). Cyclic voltammetry,
Differential pulse voltammetry studies were carried out at
room temperature using a CH Instruments Electrochemical
Workstation (Model-760D), HR-MS was analyzed in Q –
Tof mass spectrometer and DFT calculations were also per-
formed using Gaussian 09 software.
solution of anions were prepared from their tetra-n-butyl am-
−2
monium and sodium salts in the concentration of 1 × 10
M
using double distilled water. The stock solution of NAPCBH
(30 μl) was diluted with 2 ml DMSO to a final concentration
of 15 μM which was further used for all the experiments
carried out at room temperature.
Synthesis of CBH
Preparation of Stock Solutions
A methanolic solution of 4-chlorobenzaldehyde (100 mg,
1 mmol) was refluxed in an excess amount of hydrazine hy-
drate for 3 h. The white solid product (E)-(4-
chlorobenzylidene)hydrazine (CBH) was obtained from ice
cold water and recrystalized from the hot methanolic solution.
S t o c k s o l u t i o n o f p r o b e ( 1 - ( ( E ) - ( ( ( E ) - 4 -
chlorobenzylidene)hydrazono)methyl)naphthalen-2-ol)
NAPCBH was prepared in the concentration of 1 × 10 M in
DMSO and the solution of metal ions were prepared from
their chloride salts except silver nitrate, lead nitrate and the
−3
1
(Yield 97%) H NMR (300 MHz, DMSO) δ 5.17 (s, 1H), 4.91
Fig. 1 a UV-Vis spectra of
NAPCBH (15 μM) in the pres-
ence of various metal ions in
DMSO; b The color changes of
NAPCBH (15 μM) upon addition
of various metal ions (15 μM) in
DMSO

J Fluoresc
Fig. 2 UV-Vis spectral changes
of NAPCBH (15 μM) upon ad-
2+
dition of Cu ion in DMSO.
Insert zoomed UV-Vis spectral
changes from 350 nm -500 nm
(
1
1
(
dd, J = 36.3, 8.4 Hz, 1H), 4.39 (s, 1H), 0.99 (s, 1H), −0.00 (s,
H) (Fig. S1). C NMR (75 MHz, DMSO) δ 137.65, 136.19,
32.39, 129.33, 127.50, 41.10, 40.99–40.14, 39.86, 39.45,
Fig. S2). HR-MS (calculated 154.60, Found 155.07)
Fig.S5).
10.53 (s, 1H), 7.27 (s, 1H), 6.40 (s, 1H), 6.05 (d, J = 8.6 Hz,
1H), 5.55–5.37 (m, 2H), 5.11 (d, J = 8.4 Hz, 1H), 4.94 (d, J =
7.2 Hz, 1H), 4.75 (d, J = 9.0 Hz, 1H), 0.87 (s, 5H). (Fig. S3).
1
3
1
3
C NMR (75 MHz, DMSO) δ 162.21, 161.53, 160.43,
138.15, 135.15, 133.18, 132.54, 130.31, 129.76, 128.55,
28.32, 123.86, 120.37, 119.59, 108.75(Fig. S4).HR-MS (cal-
(
1
Synthesis of NAPCBH
culated 308.77, found 309.08) (Fig.S6).
A methanolic solution of 2-hydroxy-1-naphthaldehyde
Colorimetric Response of NAPCBH
(
50 mg, 0.2 mmol) was refluxed with CBH (30 mg, 0.2 mmol)
for 2 h. A yellow color solid product 1-((E)-(((E)-4-
chlorobenzylidene)hydrazono)methyl)naphthalen-2-ol
The colorimetric response of NAPCBH dissolved in DMSO
to a final concentration of 15 μM in the presence of diverse
cations and anions dissolved in double distilled water and
DMSO respectively was seen through naked eye detection.
(
NAPCBH) was obtained and recrystalized from the hot meth-
1
anolic solution. (yield 96%). H NMR (300 MHz, DMSO) δ
2+
Fig. 3 a Linear fit and (b) Benesi-Hilderbrand plot obtained from the UV-Vis titration of Cu ions

J Fluoresc
2+
2+
Fig. 4 a Cyclic voltammetry titration of NAPCBH with Cu ions and (b) Differential pulse voltammetry titration of NAPCBH with Cu ions
2
+
After mixing them for few seconds, UV-Vis spectra were re-
corded at room temperature. Further, UV-Vis spectra were
also recorded to determine the selectivity, sensitivity and com-
petitive sensing studies.
Electrochemistry Measurements of NAPCBH with Cu
and F Ions
−
Cyclic voltammetry and differential pulse voltammetry
measurements were measured for the probe NAPCBH at
concentration of 10 M. Copper and fluoride ion concen-
2
+
−4
UV-Vis Titration Measurements of NAPCBH with Cu
Ions
−
4
trations of 10 M were gradually added to NAPCBH and
their electrochemical changes were monitored at room
temperature. In addition, the diverse cations and anions
changes were monitored. The glassy carbon, Ag/AgCl
electrode and platinum electrode were used as working,
reference and counter electrode respectively.
Tetrabutylammonium perchlorate was used as supporting
electrolyte.
The probe NAPCBH concentration of 15 μM was prepared
and to this solution an aqueous copper solution of 10− M was
gradually added and UV-Vis spectral changes were monitored
at room temperature after each addition.
2
−
UV-Vis Titration Measurements of NAPCBH with F
Ions
Calculation of the Limit of Detection and Binding
Constant
The probe NAPCBH final concentration of 15 μM was mea-
−2
sured and fluoride ions of 10 M in DMSO was gradually
added to this solution and UV-Vis spectral changes were mon-
itored at room temperature after each addition.
The limit of detection was calculated using the formula, 3σ/s,
where σ is the standard deviation of the blank titration curve.
2+
2+
Fig. 5 a Absorption spectra for DNA tracking of NAPCBH-Cu (b) Cyclic voltammetry spectra for DNA tracking of NAPCBH-Cu

J Fluoresc
Fig. 6 a UV-Vis spectra of
NAPCBH (15 μM) in the pres-
ence of various anions in DMSO
and (b) The color changes of
NAPCBH (15 μM) upon addition
of various anions in DMSO
The binding constant was calculated from the absorbance data
using Benesi-Hinderbrand equation,
constant could be determined from the slope of the straight
line of the plot of 1/A -A against 1/C.
0
1
=ðA0−AÞ ¼ 1=k fðAmax−A0Þ ðCÞg þ 1=ðAmax−A0Þ;
2+
−
Job’s Plot Measurement for NAPCBH with Cu and F
Ions
where A is the absorbance of the probe in the absence of
0
cation/anion, A is the absorbance recorded in the presence of
cation/anion and Amax is the absorbance maximum recorded
in the presence of cation/anion and K is the association
2
+
−
Job’s plot measurements for NAPCBH with Cu and F ions
were prepared in double distilled water and DMSO respective-
−4
2+
−
ly in the concentration of 10 M. The probe and Cu /F ratio
of 2:2, 1.8:2, 1.6:4, 1.2:8, 1:1, 8:1.2,6:1.4, 4:1.6, 2:1.8 and 0:2
were prepared in an appropriate procedure and the color
changes were monitored using UV-Vis spectrophotometer at
room temperature.
1
2+
−
H NMR Titration Studies of Cu and F Ions
Five NMR tubes consisting of NAPCBH dissolved in DMSO-
6
d were prepared and five different equivalents (0, 0.25, 0.50,
0
.75, 1.0) of respective copper and fluoride salts were dis-
6
solved in DMSO-d were added to NAPCBH separately.
After shaking them for a minute, H NMR spectrum was
1
performed.
Computational Calculations
DFT calculations based on the hybrid exchange correlation
functional B3LYP were performed using Gaussian 09
Fig. 7 UV-Vis spectral changes of NAPCBH (15 μM) upon addition of
F ion in DMSO
−

J Fluoresc
−
Fig. 8 a Linear fit and (b) Benesi-Hilderbrand plot obtained from the UV-Vis titration of F ions
1
13
programme. The 6-31G basis set was used for the probe
NAPCBH, and the LANL2DZ was the basis set employed
for copper and fluoride ions.
probe was confirmed by H and C-NMR and HR-MS spec-
troscopic techniques.
UV-Vis Spectral and Colorimetric Response of NAPCBH
2
+
Towards Cu
Results and Discussion
The colorimetric selective sensing capabilities of NAPCBH
with diverse metal ions in DMSO were monitored using
Synthesis and Characterization of Precursor
and Probe
2
+
UV-Vis electronic spectra. Upon addition of Cu , the probe
caused distinguishable spectral changes while other metal ions
showed either no or small spectral changes (Fig. 1a and b).
This phenomenon was seen from the UV-Vis electronic spec-
trum changes and on other hand the color changes was also
The precursor CBH was prepared by a known synthetic pro-
cedure. The probe NAPCBH was synthesized by the conden-
sation reaction of 2-hydroxy-1-naphthaldehyde with the pre-
cursor in methanol (Scheme 1). The structure of CBH and the
2
+
monitored by naked eye while adding Cu solution to the
−
−
Fig. 9 a Cyclic voltammetry titration of NAPCBH with F ions and (b) Differential pulse voltammetry titration of NAPCBH with F ions

J Fluoresc
1
Fig. 10 H6 NMR titration studies
−
of F in d DMSO
Fig. 11 a UV-Vis spectra of re-
versibility and regeneration of
NAPCBH; b color changes of
NAPCH upon addition of copper,
fluoride and HCl

J Fluoresc
2+
−
Fig. 12 Optimized structure, LUMO, HOMO of the NAPCBH with Cu , F ions
probe from pale yellow to yellowish green indicating that the
absorbance bands at 271 and 331 nm were significantly in-
probe, NAPCBH can efficiently behave for a “naked-eye”
chemosensor of Cu (Fig. S7).
creased and altogether fashioned a single band at 290 nm by
exhibiting a new band at 447 nm, observable ratiometric
changes were also seen [55–57]. From these spectral measure-
ments, three isobestic points were located at 366, 416 and
473 nm which imply that only one product was generated
2
+
In order to investigate the binding ability of NAPCBH with
2
+
Cu ion, UV-Vis titration experiments were performed at
room temperature. The absorption spectrum of NAPCBH
shows three bands at 271, 331 and 384 nm. Upon addition
2
+
from NAPCBH upon binding with Cu (Fig. 2). The sensing
2
+
2+
of Cu to a solution of NAPCBH, the intensities of
mechanism of NAPCBH with Cu might be explained by
2+
Table 1 Determination of Cu
ions in water samples
2
+
2+
Water sample
Cu estimated (μL)
Cu found (μL)
Recovery (%)
Thamirabarani River water collected
from Tirunelveli
0
0
13
22
32
0
–
1
2
3
0
0
0
0
0
0
0
0
0
0
0
130
110
106
–
RO processed drinking water from
Author department
1
2
3
15
26
31
0
150
130
103
–
tap water collected from Madurai corporation
1
2
3
15
22
35
150
110
116

J Fluoresc
−
Table 2 Determination of F ions
in water samples
Water sample
F− estimated (μL) F− found (μL) Recovery (%)
Thamirabarani River water collected from Tirunelveli
0
0
0
0
0
0
0
0
0
0
0
0
0
11
22
31
0
–
1
2
3
110
110
103
–
RO processed drinking water from Author department
tap water collected from Madurai corporation
1
2
3
14
29
33
0
140
145
110
–
1
2
3
12
23
32
120
115
106
ICT and LMCT mechanisms due to the red shift of about
0 nm and decreases band at 384 nm which indicates ICT
mechanism and the appearance of new band at 447 nm upon
Electrochemical Measurements of NAPCBH Towards
Cu Ion
2
+
2
2+
the addition of Cu ion showing the operation of LMCT
mechanism [58]. (Scheme. S1).
The electrochemical response of NAPCBH was investigated
using cyclic voltammetry and differential-pulse voltammetry
2
+
−4
The stoichiometry between the NAPCBH with Cu ion
was determined by the Job’s plot method. From the job’s plot
results (Fig.S9), the stoichiometric ratio was identified as 2:1
techniques at the concentration of 10 M. The measurement
was performed at room temperature using the glassy carbon,
Ag/AgCl electrode and platinum electrode were used as work-
ing, reference and counter electrode respectively. Tetrabutyl
ammonium perchlorate was used as supporting electrolyte.
The electrochemical selective response of NAPCBH
with the diverse metal ions in DMSO was tested using
cyclic voltammetry in the potential window of 0 V to
1
which is further substantiated from H NMR titration and
theoretical calculations. From these evidences, the binding
2
+
structure between NAPCBH and Cu ion was proposed as
:1. The binding constant was calculated by using Benesi-
2
4
Hilderbrand equation k value to be 1.2 x 10 M. (Fig. 3a and
b) The detection limit was calculated from the formula DL =
2
+
−1.4 V, scan rate at 50 mV/s. Upon addition of Cu
3
σ/k where σ is the relative standard deviation from the blank
ion, the appearance of new cathodic peak at −0.21 V
and − 0.65 V was observed which indicates that a quasi-
reversible reduction due to the interaction with Cu
titration, k is the slope of the calibration curve and it is to be
5
3
2
+
.8 μM which is far below to the recommended value
1.5 μM in drinking water [59, 60].
ions whilst the other cations were showed no consider-
able changes (Fig.S10). This observation is strongly
substantiating the detection copper ion [61, 62].
To investigate further the binding ability of NAPCBH with
2
+
Cu , competitive measurements were performed in the pres-
ence of diverse metal cations. The observed experimental data
indicate that there are no significant changes for other metal
2
+
Titration experiments for Cu ion were also conducted
in cyclic voltammetry and differential pulse voltammetry
which showed substantial decrease in the new cathodic
peaks. It is signifying the interaction of NAPCBH with
2
+
ions except Cu ion (Figs. S8 (a) and (b)).
2
+
Cu ions [63] (Fig. 4a and b).
−
Table 3 Determination of F ions in tooth paste samples
2
+
DNA Tracking Towards NAPCBH-Cu Ion
Tooth paste
F− estimated (μL) F− found (μL) Recovery (%)
Copper is the essential metal and have attracted tremendous
interest due to their capability of interacting with DNA/
nuclear protein. The strong affinity of the DNA with many
fluorescent probes with metal ions was reported so far using
fluorescence techniques. In this investigation, we deliberate to
undertake a similar study to demonstrate DNA tracking ability
A concentration
0
0
0
0
0
0
0
0
0
16
24
35
0
–
1
2
3
160
120
116
–
B concentration
1
2
3
14
25
34
140
125
113
2
+
of NAPCBH-Cu which is the colorimetric probe. Therefore
the titration experiments were performed using absorption
2
+
spectra using a fixed concentration of NAPCBH-Cu

J Fluoresc
(
(
50 μL in 2 ml dmso) to which increasing amounts of DNA
10 M in CT-DNA in 5 mM Tris HCl/50 mM NaCl buffer,
DL = 3σ/k where σ is the relative standard deviation from the
blank titration, k is the slope of the calibration curve and it is to
be 0.025 μM which is very low to the permissible value
[65–68] (Fig. 7a and b).
−4
pH 7.2) were gradually added. The binding of the DNA with
NAPCBH-Cu which led to decrease in the absorption with
slight red shift. This output indicating that the binding affinity
of the NAPCBH-Cu to the DNA is efficaciously. Further to
substantiate the effective mode of binding the cyclic
voltammery have been achieved. The electrochemical result
indicates on addition of DNA (10 M in buffer) to the
NAPCBH-Cu (100 μL in 10 ml dmso) decrease with slight
shift at −0.12 Vand 0.13 V was observed. It is also indicating
the effective binding of DNA with NAPCBH-Cu This en-
ables the probe, NAPCBH-Cu can be used as an efficient
DNA tracker [64].
2
+
−
In addition to the binding ability of NAPCBH with F ions,
2
+
competitive measurements were also studied with a series of
anions shown in Fig. 5. The experimental data indicate that
−
there are no significant changes with other anions than for F
−
4
ion (Fig. S12a-b) (Fig. 8).
2
+
Electrochemical Measurements of NAPCBH Towards
2
+.
−
F Ion
2
+
The electrochemical response of NAPCBH was investigated
using cyclic voltammetry and differential-pulse voltammetry
−4
UV-Vis Spectral and Colorimetric Response of NAPCBH
Towards F
techniques at the concentration of 10 M. The electrochem-
ical selective responses of NAPCBH with the diverse anions
in DMSO were tested using cyclic voltammetry in the poten-
tial window of 0.5 V to −1.4 Vat scan rate 50 mV/s. Upon the
−
The colorimetric selective sensing capabilities of NAPCBH
with diverse anions in DMSO were performed using UV-Vis
electronic spectra. The addition of fluoride ion only showed a
significant color change from pale yellow to yellowish brown
when compared with other anions and the observed results are
shown in Fig. 5a–b and Fig. S11.
−
addition of F ion, the appearance of new cathodic peak at
0.11 Vand − 0.62 V was noticed which indicates that a quasi-
reversible reduction due to the formation of fluoride complex
whilst the other anions showed no considerable changes [69,
−
70] (Fig. S14). Further, the titration experiment for F ion was
−
To explore the interaction between NAPCBH with F ion,
performed in cyclic voltammetry and differential pulse volt-
ammetry which shows a steady decrease in the new cathodic
peaks. This observation is strongly supporting the detection of
fluoride ion. Furthermore, differential pulse voltammetry
measurements have also been executed for the additional con-
firmation of the formation of fluoride complex (Figs. 9a-b and
10).
absorption spectral changes of NAPCBH was monitored by
the titration method. Absorption spectra showed a clear
ratiometric response with a slight red shift and the appearance
of new band at 482 nm (Fig. 6). This indicates the negative
charge on the phenolate oxygen might be a probable reason
suggesting the operation of ICT mechanism (Scheme. S2).
The stoichiometric ratio was found to be 1:1 from the Job’s
1
1
2+
−
plot (Fig. S13) which is further supported by H NMR titra-
H NMR Titration Studies of Cu and F Ions
tion, DFT calculations. The binding constant was calculated
1
by using Benesi-Hilderbrand equation k value to be 1.7 ×
H NMR titration studies was performed to confirm the 2:1
4
2+
6
1
0 M. The detection limit was calculated from the formula
stoichiometric between NAPCBH with Cu in DMSO-d .
−
Fig. 13 Absorption spectra of NAPCBH in tooth paste samples for the determination of F ions

J Fluoresc
2
+
2+
−
Upon addition of Cu (0.25 equivalent) to a solution of
NAPCBH, the phenolic OH peak, imine peak notably de-
creased due to the interaction with the NAPCBH. Further
spiked with the standard Cu and F ions and determined
by a well known addition approach with the NAPCBH in
UV-Vis spectra. A satisfactory recovery of the spiked samples
was acquired. The result suggested that the NAPCBH effi-
2
+
additions of Cu led to a complete disappearance of OH peak
and decreased imine peak additionally confirming the partic-
ipation of these groups in the interaction. Moreover, it is note-
worthy to indicate that a well resolved H NMR spectrum for
NAPCBH-Cu couldn’t be acquired because of the paramag-
netic character of the Cu ions (Fig.S15). The H NMR titra-
tion experiments were also conducted for NAPCBH with F
ions to confirm the 1:1 stoichiometric between NAPCBH with
F ions in DMSO-d . The addition of F ions to a solution of
NAPCBH showed a decrease in the phenolic OH peak inten-
sity and further increasing the additions, the O-H peak became
disappeared due to the hydrogen bonding which disclosed the
2
+
−
ciently quantifies the amount of Cu and F ions in the envi-
ronmental samples [78]. (Tables 1 and 2) and (Fig. S 16 & 17).
In addition, the realistic application of NAPCBH for detec-
1
2
+
−
tion of F ions in oral care item has also been tried.
2
+
1
Commercially available toothpaste used in the water sample.
The toothpaste have been weighed and extracted with two
specific amounts of water (A and B). The combinations had
been centrifuged and filtered to get clean extracts. A certain
quantity of every extract added into the NAPCBH solution
one after the other and response of the sensor become moni-
tored. The estimated fluoride ion concentration was calculated
in line with the fluoride content material listed in the aspect
label of toothpaste and the dilutions. The observed fluoride
ion concentrations were received in line with absorbance ratio
response. It is located that the decided fluoride concentrations
had been steady with the anticipated information as given in
Table 3 and Fig. 13 which displaying that the NAPCBH can
quantitatively determine the fluoride ions from toothpaste
samples [79].
−
−
6
−
−
interaction of F with NAPCBH [71, 72] (Fig. 9).
Reversibility and Regeneration of NAPCBH
A realistic sensor probe may be significant beneficial if a
probe may be readily recovered and subsequently reusable
for sensing ions. In order to study the reversibility and regen-
eration of NAPCBH, an absorption spectrum of the recovered
probe was measured. The spectral results and color changes
clearly demonstrated that NAPCBH can be readily regenerat-
ed by utilizing an appropriate reagent like HCl at a concentra-
tion of 15 μM. The absorption spectrum is almost reversible
after the addition of HCl with copper and fluoride consisting
NAPCBH (Fig. 11a, b). Such reversibility and regeneration
are significant for the fabrication of chemosensors to sense
Conclusions
In the present work, a new dual responsive colorimetric,
ratiometric chemosensor was developed with a probe bearing
hydrazone moiety for the detection of copper and fluoride
ions. These detections were possible with very high selectivity
and sensitivity due to facile color changes from pale yellow to
yellowish green for copper ions and pale yellow to yellowish
Cu and F− ions as an environmental solution [73]
2+
(
Fig. 11a-b).
2
+
Computational Calculations
brown for fluoride ions. The detection limits for Cu
5.8 μM) and for F (0.025 μM) was observed and these
−
(
Density Functional Theory has played a significant role in
understanding sensing mechanism theoretically. In order to
confirm and rationalize the spectroscopic results, DFT calcu-
lations studies were performed, as shown in Fig. 12, the ge-
ometry of NAPCBH was optimized using DFT-B3LYP 6-31G
basis set, the HOMO-LUMO energy gap is decreased when
compared with the free NAPCBH. These results were also
confirmed and well correlation with the proposed binding
mode, and mechanism [74–77].
values are far below than the value recommended by WHO.
The colorimetric recognition was confirmed by various tech-
niques like NMR, HR-MS, UV-Vis, cyclic voltammetry,
differential pulse voltammetry. The DNA tracking ability
2
+
of the NAPCBH-Cu was investigated by absorption
and cyclic voltammetry techniques which shown effi-
cient affinity towards DNA. Hence, it can be used as
a DNA tracking agent. The sensing mechanism was
proposed from these results and color changes. The stoi-
2
+
−
chiometric ratio of NAPCBH with Cu , F ions were con-
firmed to be 2:1 and 1:1 complex, respectively as evidenced
2
+
−
Practical Performance of Cu and F Ions
1
from the Job’s plot and H NMR titration studies. All the
In order to examine the practical applicability of NAPCBH,
real sample analyses have been performed to determine the
Cu and F ions. Three distinct water samples had been col-
lected from thamirbarani, Tirunelveli, drinking water in the
author department and tap water from Madurai residential area
were used for the analysis. The water samples have been
spectroscopic results were significantly substantiated by the
theoretical calculations. The NAPCBH was readily regenerat-
ed with HCl, thus showing its feasibility to be utilized as a re-
usable sensor for the convenient detection of Cu and F
ions. The UV-Vis experiments confirmed the NAPCBH fea-
sibility and quantitatively determine the Copper and fluoride
2
+
−
2
+
−

J Fluoresc
1
1
4. Zhou Y, Wang F, Kim Y, Kim S-J, Yoon J (2009) Cu2+-selective
Ratiometric and “off-on” sensor based on the Rhodamine derivative
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MM, Hudspeth M, Sykes AG (2014) Selective fluorescence sens-
ing of copper(II) and water via competing imine hydrolysis and
alcohol oxidation pathways sensitive to water content in aqueous
acetonitrile mixtures. Inorg Chem 53:2953–2962
ions in environmental and toothpaste samples. Thus, the pres-
ent results may become highly useful for the development of
commercial dual responsive colorimetric recognition for cop-
per and fluoride ions.
Acknowledgements The author A.R and W. AD thankful to the school of
chemistry, Madurai Kamaraj University for providing instrument facili-
ties funded by DST-IRHPA, FIST, DST-PURSE and UGC-UPE.
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