Dicarbohydrazide based chemosensors for copper and cyanide ions: Via a displacement approach

Article abstract of DOI:10.1039/c8nj00230d

Ligands attached to pyridine dicarbohydrazide were synthesized and characterized by NMR, FT-IR, elemental analysis, UV-visible spectroscopy, mass spectrophotometry, emission spectra and single crystal X-ray diffraction. These ligands were found to recognize copper ions over other metal ions and cyanide ions by a copper complex performing an in situ experiment with turn on-off-on behaviour over different anions in a CH₃OH:H₂O (9:1, v/v solution) medium. These ligands displayed a red shift in their absorption spectra and quenching in their emission spectra when exposed to copper ions via a PET mechanism and a further copper complex was applied for cyanide detection among the other anions. The 1:2, 1:3, 1:2 and 1:2 stoichiometric ratios of the ligands (L₁-L₄, respectively) with copper ions were calculated from a Job plot based on the UV-visible spectra. The S-V plot represents the linearity of the ligands with copper ions. The limits of detection (LOD) of copper ions along with the ligands (L₁-L₄) were calculated to be 0.12, 0.10, 0.097 and 0.098 μM using emission spectra, respectively. The binding affinities of the ligands with copper ions were determined by various characterization techniques such as FTIR, mass spectrophotometry and electrochemical and optical studies. Furthermore, an in situ experiment was performed for cyanide detection via a metal displacement approach. L₁ and L₄ with Cu²⁺ ions showed an affinity towards cyanide ions, with detection limits of 0.31 and 0.53 μM.

Full text of DOI:10.1039/c8nj00230d

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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Dicarbohydrazide based chemosensors for copper ion and
Cyanide ion via displacement approach
Neetu Yadav and Ashok Kumar Singh
Received 00th January 20xx,
Accepted 00th January 20xx
Pyridine dicarbohydrazide appended ligands were synthesized and characterized by NMR, FT-IR, elemental analysis, UV-
Visible, mass spectrophotometry, emission spectra and X-ray single crystal. These ligands found to recognize copper ion
over other metal ions and cyanide ion by copper complex performing in-situ experiment with turn on-off-on behaviour
over different anions in CH3OH:H2O (9:1, v/v solution) medium. These ligands have shown the red shift in absorption
spectra and quenching in the emission spectra with copper ion via. PET mechanism and further copper complex applied for
cyanide detection among the other anions. The 1:2, 1:3, 1:2 and 1:2 stoichiometry of ligands (L1-L4) with copper ion were
calculated respectively from Job’s plot based on UV-Visible spectra. The S-V plot represents the linearity of ligands with
copper ion. The limit of detection (LOD) of copper ion along with ligands (L1-L4) is 0.12, 0.10, 0.097 and 0.098 µM by
emission spectra, respectively. The binding affinity of ligands with copper ion was determined by the various
characterizations such as FTIR, mass spectrophotometry, electrochemical and optical studies. Further, the in-situ
experiment was performed for cyanide detection via metal displacement approach. The L1 and L4 with Cu2+ ion shows the
DOI: 10.1039/x0xx00000x
www.rsc.org/
affinity
towards
cyanide
ion
with
the
detection
limit
0.31
and
0.53
µM.
block the electron transfer chain in mitochondria18,19. The
extensive use of copper in daily life is the prime reason of
copper pollution in the environment although copper is
essential metal ion but its disorder in concentration is harmful
for living systems. Same as with cyanide ion its frequent use in
industries to make environment polluted. According to World
Health Organization (WHO) the permissible limit of copper ion
and cyanide ion in drinking water is 2 ppm (30 μM) and 0.2
ppm20,21 respectively. In blood the maximal concentration of
copper ion should not surpass22,23 from 100-150 μg-dL-1. The
Environment protection Agency has provided the secure limit
of copper in drinking water 1.3 ppm (ca. 20 μM)24.
1. Introduction
Transition metal plays an important role in the living systems
such as iron, zinc, magnesium and copper. In all transition
metals copper is the third most essential trace metal, which
performs a foremost role in human nervous system as
cofactors of many metalloenzymes1,2. It is an essential part for
wide range of physiological channels such as bone growth,
haemoglobin biosynthesis, dopamine production, nerve
function regulations, functional and structural augmentation
of protein and enzymatic functions. It generates cellular
energy, induced signal transduction and diminished molecular
oxygen3. While unregulated copper and disrupted copper ion
homeostasis4 i.e. related to numerous neurogenerative
diseases such as Menkes, Alzheimer, Wilson5, Amyotrophic
lateral sclerosis, Parkinson’s and Prion diseases6,7. Menkes
diseases8 are due to copper deficiency while Wilson diseases
are due to copper toxicosis conditions are two human genetic
disorders9-12. Similarly, cyanide ion is more toxic ion among
other anions although cyanide is very vital reagent for many
industrial processes in different areas like mining, synthetic
There are many sensors, which was performed for sensing of
copper ion with different mechanism. Apart from this, the
multidentate chemosensors has ability to sense some specific
metal ions. In this context, the multidentate ligands have been
synthesized and apply as chemosensor. Presented work has
the ligands, which have large number of donor atom and
hydroxyl group, in despite of, these ligands are highly sensitive
and selective for copper ion. The presented work
demonstrates four ligands i.e. appended with different
molecule has common backbone pyridine dicarbohydrazide.
These all four ligands were highly selective and sensitive
towards copper ion among pool of metal ions. The
complexation occurred via. PET (photoinduced electron
transfer) mechanism. Further, the anion sensing was
performed with L+ Cu2+ and result shown that the ligands with
copper ion can sense cyanide ion with good limit of detection
via. metal displacement path.
fibre production and electroplating13-16
. The "excessive"
utilization of cyanide17 in these factories and its fundamental
transportation, expands the likelihood of human exposure. Its
acute toxicity destroys body’s central respiratory system and
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1416, C-O: 1118, N-H: 1527 (ESI: Fig. S3). UV-Visible (MeOH,
1
λmax/nm): 339 nm (n-π*) (ESI: Fig. S6), H-NMR (DMSO, 400
2. Experimental Section
2.1 Materials and Measurements
MHz, δ/ppm) 12.042 (s, 2H), 11.659 (s, 2H), 8.535 (s, 2H),
8.322 (d, 2H), 8.252 (t, 1H), 6.983 (s, 1H), 6.607 (s, 1H), 6.190
(s, 1H) (ESI: Fig. S13). 13C-NMR (DMSO, 100MHz, δ/ppm)
159.36, 148.91, 143.36, 140.31, 127.30, 125.53, 123.49,
114.57, 109.98 (ESI: Fig. S14). ESI-mass of L2 m/z 372.4048,
(M+Na)+ (ESI: Fig. S20).
The acetate and chloride salts used were of analytical grade
purchased from Merck and used without further purification.
All chemicals were purchased from Sigma-Aldrich and distilled
solvents were used in whole experiments. The elemental
analysis (CHNS) was performed by Verio MICROV3.1.1
instrument. The vibrational spectrum acquired from Perkin
Elmer FT-IR 1000 spectrophotometer. Specord 600 thermo
scientific PC double beam spectrophotometer (path length
3cm) used for absorption spectra and the emission spectra
obtained by using horiba RF-5301PC with standard quartz cell
(path length 3cm). JEOL 400 MHz spectrometer was used to
obtain the NMR spectra. CHI760E Electro-analyser was used
for obtaining electrochemical studies with three electrode as
pyrolytic graphite used as working electrode, Ag/AgCl2 as
reference electrode, and Pt wire used as counter electrode
Synthesis of ligand L3 bis((2-hydroxynaphthalen-1-
yl)methylene)pyridine-2,6-dicarbohydrazide
Yield (60%), Calc. for C29H21N5O4: C, 58.45; H, 4.33; N, 28.07; O,
9.16 and found: C, 57.59; H, 4.841; N, 26.45; O, 11.19. FT-IR
data (KBr, νmax/cm−1): -N-H: 3389, C-H: 3208, C=O: 1652, C-N:
1416, C-O: 1118, N-H: 1527. UV-Visible (MeOH, λmax/nm ): 317,
1
330 (n-π*), 372 nm (n-π*) (ESI: Fig. S7), H-NMR (DMSO, 400
MHz, δ/ppm) 12.59 (s, 2H), 12.51 (s, 2H), 9.81 (s, 2H), 8.53 (d,
J = 8.6 Hz, 2H), 8.40 (d, J = 6.9 Hz, 2H), 8.36 – 8.31 (m, 1H), 7.99
(d, J = 9.0 Hz, 2H), 7.94 (d, J = 7.9 Hz, 2H), 7.68 (t, J = 7.6 Hz,
2H), 7.47 (t, J = 7.4 Hz, 2H), 7.29 (d, J = 8.9 Hz, 2H) (ESI: Fig.
S15). 13C-NMR (DMSO, 100MHz, δ/ppm) 159.39, 158.81,
149.72, 148.36, 133.78, 132.27, 129.62, 128.50, 128.39,
126.10, 124.29, 121.66, 119.41, 109.17 (ESI: Fig. S16). ESI-mass
of L3 m/z 526.1512, (M+Na)+ (ESI: Fig. S21).
and 0.1
M
tetrabutylammonium hexafluorophosphate
(nBu4NPF6) as supporting electrolyte. The mass spectrum
gleaned via Bruker micrOTOFTM-Q II mass spectrometry.
2.2 Synthesis of precursor (1)
The pyridine-2,6-diester obtained by the refluxing of pyridine-
2,6-dicarboxyclic acid with thionyl chloride in the presence of
solvent methanol for 6hr. Then pyridine-2,6-dicarbohydrazide
Synthesis of ligand L4 bis(anthracen-9-ylmethylene)pyridine-
2,6-dicarbohydrazide
Yield (50%), Calc. for C35H25N5O2: C, 77.74; H, 4.41; N, 12.25; O,
5.60 and found: C, 77.59; H, 4.31; N, 12.05; O, 11.19. FT-IR
data (KBr, νmax/cm−1): -N-H: 3449, C-H: 3047, C=O: 1679, C-N:
1533, C-O: 1165, (ESI: Fig. S4). UV-Visible (MeOH, λmax/nm ):
386 nm (n-π*) (ESI: Fig. S8), 1H-NMR Spectra: NMR (DMSO, 400
MHz) δ(ppm) 12.64 (s, 2H), 9.97 (s, 2H), 8.91 (d, J = 8.8 Hz, 4H),
8.74 (s, 2H), 8.44 (d, J = 7.3 Hz, 2H), 8.39 – 8.33 (m, 1H), 8.15
(d, J = 8.3 Hz, 4H), 7.66 – 7.60 (m, 4H), 7.60–7.54 (m, 4H) (ESI:
Fig. S17). 13C-NMR (DMSO, 100MHz) δ(ppm) 159.91, 149.96,
148.86, 131.51, 130.64, 130.37, 129.64, 127.90, 126.20,
125.55, 125.40 (ESI: Fig. S18). ESI-mass of L4 m/z 594.1910,
(M+Na)+ (ESI: Fig. S22).
(1) was synthesized by stirring of hydrazine (4.4 mmol, 0.223 g)
with pyridine ester (2 mmol, 0.390 g) in the presence of
ethanol lead to the formation of pyridine amine.
Yield: (95%). FT-IR data (KBr, νmax/cm−1): -NH2: 3440 and 3277,
1
C=O: 1681, N-H: 1516 and 1640, C-N: 1442, (ESI: Fig. S1). H
NMR Spectra: NMR (DMSO, 400 MHz) δ(ppm) 10.64 (s, 2H),
8.105 (d, 2H), 8.152 (t, 1H), 4.621 (s, 4H) (ESI: Fig S9). 13C-NMR
(DMSO,100 MHz): The δ(ppm) 124, 139, 148, 162 (ESI: Fig S10).
Synthesis of Ligand L1 [Bis(4-hydroxy-3,5-
dimethoxybenzylidene)pyridine-2,6-dicarbohydrazide]:
Pyridine-2,6-dicarbohydrazide(1) (1mmol, 0.196 g) was
refluxed with syringaldehyde (2 mmol, 0.364 g) for 6hr in the
presence of methanol lead to the formation of ligand L1.The
light yellow coloured precipitate was obtained.
2.3 X-ray Crystallography
Structural measurement of single crystal of L3 and L4 were
performed on a Bruker Kappa Apex four circle- 5 CCD
diffractometer. Single crystal of L3 and L4 compounds, which
was suitable for X-ray diffraction, was developed in DMSO that
mounted on nylon 7 Cryoloop. SMART/SAINT software was
used for data reduction. Graphite monochromatic MoKα
radiation (0.7107 Aº) at 298 K was used in intensity data
collection. Structure solution, refinement and data collection
were collected with SHELXTL program by using direct method.
Images and hydrogen bonding interaction were constructed in
the crystal lattice with mercury software. Refinement
parameters of L3 and L4 are shown in table 1. Crystallographic
data for both compounds have been deposited with
Cambridge Crystallographic Data Centre (deposition no. of L3
and L4 is CCDC No. 1577825 and CCDC No. 1552443
respectively).
Yield: (74%). Calc. for C25H25N5O8: C, 57.73; H, 4.81; N,13.38; O,
24.45 and found: C, 55.73; H, 4.784; N,12.17; O, 27.31. FT-IR
data (KBr, νmax/cm−1): -N-H: 3279, O-H: 3495, C-H: 2938, C=O:
1678, C-N: 1456, C-O: 1113, N-H: 1588 (ESI: Fig. S2). UV-Visible
1
(MeOH:H2O, λmax/nm): 337 nm (n-π*), (ESI: Fig. S5) H-NMR
(DMSO, 400 MHz, δ/ppm) 12.239 (s, 2H), 9.045 (s, 2H), 8.663
(s, 2H), 8.334 (d, 2H), 8.280 (t, 1H), 7.102 (s, 4H), 3.847 (s, 12H)
(ESI: Fig. S11). 13C-NMR (DMSO, 100 MHz, δ/ppm) 159, 151.37,
151.29, 148.93, 148.73, 138.81, 124, 105.49, 105.34, 56.10
(ESI: Fig. S12). ESI-mass of L1 m/z 546.1865, (M+Na)+ (ESI: Fig.
S19).
Synthesis of Ligand L2 Bis((1H-pyrrol-2-yl)methylene)pyridine-
2,6-dicarbohydrazide
Yield (50%), Calc. for C17H15N7O2: C, 58.45; H, 4.33; N, 28.07; O,
9.16 and found: C, 57.59; H, 4.841; N, 26.45; O, 11.19. FT-IR
data (KBr, νmax/cm−1): -N-H: 3389, C-H: 3208, C=O: 1652, C-N:
2 | J. Name., 2012, 00, 1-3
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Fig 1. Synthesis of L1 to L4.
Fig 2(b). ORTEP diagram of L4 molecule with hydrogen bonding interaction.
Fig 2 (a). ORTEP diagram of L3 and L4 molecule with hydrogen bonding interaction.
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Table 1. Crystal data and structure refinement parameters.
copper ion showed the 1:3 stoichiometry i.e. 570.86 (ESI: Fig.
S28). Similarly, L3 also displayed 1:2 stoichiometry in mass
spectrum which was 701.41 (ESI: Fig. S29). Likewise, L4 also
exposed 1:2 stoichiometry with Cu2+ ion, the mass was 815
(ESI: Fig. S30).
L3
L4
Empirical formula
Formula weight
Crystal system
Space group
a/Å
C31 H27 N5 O5 S
581.64
C39 H31 N5 O3 S
649.75
monoclinic
C 2/c
monoclinic
P 21
3.2 Photo-physical properties
30.297
10.0344
The photophysical properties of all four ligands L1, L2, L3 and L4
were recorded via. UV-vis absorption and emission
spectroscopy in MeOH: H2O (9:1) as a solvent. Ligand L1
displayed one broad absorption band at 337 nm due to π - π*
transition from the conjugated system of the ligand. Similarly,
L2 showed a broad absorption peak at 339 nm that was most
likely again π - π* transition. L3 shows three absorption band at
316, 330, 372 nm and were associated to n - π* and π - π*
transition. Similarly, L4 also displayed two bands at 379 and
386 nm corresponding to n - π* and π - π* transition. The
binding of L1, L2, L3 and L4 with the puddle of different metal
ions such as Mg2+, Fe3+, Na+, Li+, Ca2+, Ba2+, Cr3+, Mn2+, Co2+,
Ni2+, Cu2+, Cu+, Zn2+, Al3+, Hg+, Hg2+, V5+ display the most
expressive binding with Cu2+ ion as recognized from the
modulation of absorption spectrum. On addition of Cu2+ (5
mM) salt in L1 (20 μM) the absorption profile was shifted from
337 to 399 nm towards red shift due to the d-d transition
between Cu2+ and Ligand. Similarly, the absorption spectrum
of L2 was also shifted to red shift from 339 to 450 nm on
addition of copper salt among other metal salt. Likewise, the
absorption profile of L3 and L4 was shifted from 372 to 447 nm
and 386 to 395 nm respectively after interaction with Cu2+ ion,
but with L4 there was a new band appears at 322 nm which
demonstrate the interaction with Cu2+ ions because of d-d
transition of Cu2+ ions with ligands and π-π interaction
between the aromatic rings (Fig. 3). The stoichiometry of Cu2+
ion with L1 was determined by the addition of mole fraction of
Cu2+ ion in the ligand L (L1, L2, L3, L4) by plotting Job’s plot. The
1:2, 1:3, 1:2, 1:2 stoichiometry was presented for L1, L2, L3, L4
respectively (ESI: Fig. S31 (a), (b), (c), (d)).
b/Å
c/Å
12.301
16.640
112
8.1177
20.1951
97.782
1629.87
2
β/Å
V/Å3
5750
Z
8
Dcalc(g cm-3)
μ/mm-3
Θ range/º
1.344
1.324
0.162
0.147
0.926 - 29.158
7191
2.408 – 28.314
8135
Reflections collected
Independent
reflections
3666
2584
Parameters
GOF (F2)
403
449
1.040
0.954
R1; wR2[I>2 sigma(I)]
R1; wR2 (all data)
0.0863 – 0.2384
0.1561 – 0.2939
0.0599 – 0.1784
0.0953– 0.1096
3. Result and Discussion
3.1 The binding mode of Ligands with Copper Ion
The binding of copper with these four ligands have supported
by the FT-IR spectra and mass spectra. The FT-IR spectra of L1
and L1 with Cu2+ ion showed that the fingerprint reason was
changed then L1 vibrational spectra. There were some bands at
3506 for –NH, 3279, 1678 for C=O, 1511 and other bands are
disappeared on the complexation with Cu2+ ion. Some new
bands generated at 1627, 1434, 1328 cm-1 that supports the
complexation occurred with C=O, -NH (ESI: Fig. S23). Similarly,
the vibrational spectrum of L2 with Cu2+ ion was different from
L2. In vibrational spectra of complexed and decomplexed L2,
the bands disappeared was at 3221 (pyrrole -NH), 3383 (-NH),
1652 (-C=O), 1641, 1528 and band at 1418 was shifted to 1441
cm-1 new bands were generated at 1609, 1035 cm-1 that
confirmed the complexation with Cu2+ ion (ESI: Fig. S24). The
vibrational spectra of L3 also manifested that some bands were
vanished on metalation with Cu2+ ion i.e. 3232, 3062, 1680,
1666, 1578 cm-1 and some were shifted like 1624 shifted to
1618 cm-1, 1598 shifted to 1602 cm-1, 1548 shifted to 1537 cm-
1 was due to Cu2+ion combined with –NH, -C=O and hydroxyl
group of the ligands. There were new bands at 3451, 1454 cm-1
appeared in case of binding with Cu2+ ion (ESI: Fig. S25). Same
as with L4 ligand, the FT-IR spectra of L4 with Cu2+ ion the
obscured bands were at 3445 (-NH), 3247, 1682 (-C=O),
1538,1450 cm-1 and new bands was visible at 3448, 1632,
1561, 1425 cm-1 that affirmed metalation of all four ligands
with Cu2+ ion (ESI: Fig. S26). The binding of Cu2+ ion with
ligands was also confirmed by mass spectrum25. Mass of L1
with Cu2+ ion is 926.68 which represented 1:2 stoichiometry
i.e. 2 Cu2+ with one L1 (ESI: Fig. S27). The mass of L2 with
Further, the titration experiment of four ligands with 20 μM
concentration was performed with gradual addition of Cu2+ ion
and absorption spectra were recorded after each addition. The
consecutive addition of Cu2+ ion to L1 get to increase in the
absorbance at 399 nm with two isosbestic point at 295 and
370 nm. The new absorption band originate at 399 nm was
due to d-d transition of copper complex as shown in fig 4.
Likewise, the L2 was check with the same metal ion which was
used for L1 the significant change in absorbance was observed.
Titration experiment with L2 was implemented to validate the
reproducibility of the binding of Cu2+ ion with L2. Addition of
consecutive amount of Cu2+ to L2 leads to increase in
absorbance band at 450 nm. The absorbance band at 450 nm
correlates to d-d transition of the copper complex that
represents in fig. 4. Similarly, the titration experiment was
also implemented to confirm the binding of Cu2+ with L3 and L4.
It was confirmed by the graph that the intensity of absorbance
band at 447 nm with L3 was increased by subsequent addition
of Cu2+ to ligand solution and with L4 the absorbance band was
4 | J. Name., 2012, 00, 1-3
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also increased at 395 nm and 322 nm with consecutive
addition of Cu2+ ion (Fig. 4).
Fig 3. Selectivity spectra of L1 to L4 with 20 μM solution of ligand with 5mM of metal ion solutions by absorption spectra in that was selective for copper ion among other metal ion.
The selectivity and sensitivity of Cu2+ ion among various metal
ions was also confirmed by emission studies of all four ligands.
The Cu2+ ion was selective for all four ligands and there was
quenching in the fluorescence intensity due to photoinduced
electron transfer mechanism which was represented in ESI:
Fig. S32. Further, titration experiment performed on gradual
addition of Cu2+ to the 10 μM solution of all four ligands
respectively that shows the interaction of copper ion (10μM)
with all ligands respectively, the quenching in fluorescence
intensity was prominent in titration experiment due to the
photoinduced electron transfer from nitrogen atom that was
shown in fig. 5. Further, the competitive experiment was also
performed with Cu2+ ion in the presence of other metals ions
with all four ligands that showed there was no interference of
other metal ions in selectivity of Cu2+ ion. The competitive
study with Cu2+ in which blue bar represents the ligand + metal
ions and red bar shows ligand+ Cu2++ other metal ion
represented by ESI: Fig. S33 (a), (b), (c), (d). By the emission
Fig 4. Titration experiment of L1, L2, L3 and L4 (20 μM) with gradual addition of Cu2+ ion.
spectra, the S-V plot show the static nature of quenching by
addition of Cu2+.
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Fig 5: These all figures represents the titration experiment by emission spectra of L1 to L4 with copper ion at excitation wavelength 340 nm, 348 nm, 383nm and 394 nm
respectively and inset shows the S-V curve of L1 to L4.
The Hill plot26 has been plotted between log(Cu2+) and
log(I-Imin)/(Imax-I) for binding constant where I, Imin and Imax
represents I for intensity by the gradual addition of Cu2+ ion,
Imin represents intensity without adding Cu2+ ion and Imax shows
the intensity on complete addition of copper ion in the
solution of ligands and value of association constant (Ka) for L1,
L2, L3, L4 (log β) was 8.866, 17.645, 11.145, and 6.45
respectively (ESI: Fig. S34.). The limit of detection (LOD) of L1 to
L4 was 0.12, 0.10, 0.097 and 0.098 μM respectively, which was
less than the permissible limit of copper ion given by WHO, all
data was summarized in table 2. The fig. 6(a), (b) (c) (d) shows
the plot of limit of detection. The comparison with previous
reported data was summarized in the given table 3.
Fig 6(a): Limit of detection plot for copper ion with L1.
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data abridged in the table 4. All the copper complexes have
shown one quasi-reversible peak in the range -0.9 to -1.2 V.
The Cu2(L1) complex display a cathodic peak (Epc) at -1.194 and
an anodic peak (Epa) at 0.57 V as represented in the figures,
that attributed to the Cu2+/Cu The other copper complexes
with other ligands L2, L3 and L4 also display cathodic peaks at -
1.190, -1.080 and -1.003 and anodic peaks at 0.57, 0.57, 0.67,
0.935 V, respectively. Apart from these potentials, the current
was also increased simultaneous in the anodic region. The
redox potential of all copper complexes among negative was
due to the presence of conjugated aromatic ring27. In the
positive potential of all copper complexes, oxidation peak in
the range of 0.57 to 1.49 V, represented Cu/Cu2+. Although, all
four ligands showed the positive potential in the range of
0.0922 to 1.54 V and negative potential in the range of -0.58 to
1.50 V which was diminished after complexation with copper
ion. The new potential peaks were raised apart from other
potentials due to complexation of copper ion with ligands. The
figures 7(a), 7(b), 7(c), 7(d) represented the all changes with
Cu2+ ion from decomplexation to complexation.
Fig 6(b): Limit of detection plot for copper ion with L2.
Fig 6(c): Limit of detection plot for copper ion with L3.
Fig 7(a). electrochemical behaviour of L1 and L1 +Cu2+
.
Fig 6(d): Limit of detection plot for copper ion with L4.
Fig 7(c). Electrochemical behaviour of L3 and L3+ Cu2+
.
3.3 Electrochemical behaviour
The redox demeanour of all four ligands and their metal
complex with copper ions were measured in distilled methanol
in the potential range of +2.0 to -2.0 V and electrochemical
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Table 2: Photophysical properties, binding constant and limit of detection.
Binding constant (log
Absorbance maxima
Emission maxima
Stoichiometry
Stock shift
LOD
β)
-
L1
L2
337(π-π*)
339 (π-π*)
316, 330, 372
(π-π*) &
(n-π*)
494 nm
514 nm
-
-
-
-
-
-
-
L3
L4
485 nm
499 nm
-
-
-
-
-
-
-
-
379, 386
(π-π*) &
(n-π*)
Cu2(L1)
Cu3(L2)
Cu2(L3)
Cu2(L4)
399
Fluorescence quenching at 494 nm
Fluorescence quenching at 514 nm
Fluorescence quenching at 485 nm
Fluorescence quenching at 499 nm
1:2
1:3
1:2
1:2
62 nm
111 nm
72 nm
16 nm
8.866
17.645
11.145
6.45
0.12 μM `
0.10 μM
450
447
0.097 μM
0.098 μM
395
Table 3: Comparison table with previously reported data.
Previous literature
Chemosensor
Detection limit
of copper ion
Applications
Binding
L+Cu2+ As Anion sensor
constant
Sensors and Actuators B
211 (2015) 498–506.28
Tetrahedron letters 48
(2007) 5525-5529.29
Maleonitrile based
7.3 μM
-
-
2.8×104 M−1
-
-
Dioxotetraamine and 1,8-
naphthalimide based
0.3 μM
-
Tetrahedron 70 (2014)
2822-2828.30
Quinolin based
1.4 × 10-5
1.8 × 10−7
M
M
-
3.3×103 M-1
Selective for CN- ion with
0.57 μM detection limit
Sensors and Actuators B
211 (2015) 325–331.31
Rhodamine B-based
Real water
analysis, Paper
strips test
2.28 × 105 M−1
1.18×105 M-1
-
Tetrahedron 68 (2012)
9076-9084.32
Acenaphthene based
2 μM
Selective for CN- ion with 1
μM detection limit
Anal. Methods, 9 (2017)
618-624.33
Picolinamide based
0.67 μM
Real Water
analysis
-
-
present work
Pyridine dicarbohydrazided
based
0.09 to 0.12 μM
Logic gate
6.45 to 17.645
Selective for CN- ion with
0.31 and 0.53 μM
detection limit
behaviour, real
water analysis
Table. 4: Electrochemical behaviour of all ligands and their copper complexes.
I
II
I
II
Oxidation peak
Oxidation peak
Reduction Peak
Reduction peak
L1
L2
1.056
1.06
0.122
0.092
0.57
0.57
-
1.54
-
-0.985
-0822
-0.58
-0.935
-0.82
-
-
-
L3
0.182
1.13
-
-0.79
-1.500
-1.194
-1.190
-1.08
-1.003
L4
Cu2(L1)
Cu3(L2)
Cu2(L3)
Cu2(L4)
1.06
0.325
1.49
-0.67
-
0.63
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showed the 4-11 pH range was more convenient for all four ligands
(ESI: Fig. S35)
.
3.5 In-situ photophysical study with different anions
As indicated by the displacement approach of all four ligands
whose fluorogenic activity was completely quenched by the
complexation with copper ion34-36. On exposure with CN- [Cu2+
with chelating ligands], CN− can facilitate with Cu2+ to frame
the extremely stable species [Cu(CN)x]n- bringing about the
arrival of a free ligand among other anions (Cl-, Br-, F-, CN-,
NO3 , SO2 , SO42-, SO32-, S2-, H2PO4 , HPO42-, SCN-, CO32-, Cys)
(ESI: Fig. S36). In this manner, this incited to estimate that the
L (L1-L4)-Cu2+ gathering is a potential sensor for cyanide ion
among other anions. The in-situ CN- induced decomplexation
were investigated by UV-Vis studies. The results shown that in-
situ L1 and L4 with copper ion has the affinity towards cyanide
ion among other anions due to decomplexation of L1 and L4
from copper ion but L2 and L3 has not shown any interference
with different anions by virtue of high affection against Cu2+
ion. As a result, the study shown that in case of L1 and L4, CN-
ion occurred decomplexation with Cu2+ ion whereas in L2 and
L3 has not developed the ligand as before after in-situ reaction
with CN- ion. The figures 8(a) and 8(b) shown the changes in
absorption spectra on gradual addition of cyanide ion with
L1+Cu2+ and L4+Cu2+ respectively. By the plot between log(CN-)
and A0-A/Amax-A0. The limit of detection of cyanide for L1 and L4
was 0.31 μM and 0.53 μM respectively, that was very less than
the permissible limit of cyanide ion prescribed by world Health
Organization (WHO). Fig. 9(a) and 9(b) expressed the detection
limit graph for cyanide ion.
-
-
-
Fig 7(b). Electrochemical behaviour of L2 and L2 +Cu2+
.
Fig 7(d). Electrochemical behaviour of L4 and L4+ Cu2+
.
3.4 pH study of ligands
The efficiency of all four ligands with or without copper ion at
different pH depicted that at acidic pH the intensity of the ligand
not change as much more as at basic pH. pH study represented that
the intensity was increased at basic pH because of ligands are
enriched with sensitive proton donor sites. At high pH,
deprotonation occurred simultaneously fluorescence intensity
increased. This study revealed that ligands was stable between 4-10
pH apart from this pH the ligands properties was changed. The
same experiment was performed with L (L1-L4) + Cu2+ and found
that in case of L1+Cu2+ the compound was stable between 4-11 pH
after this pH the compound became turbid and intensity was
changed. In case L2+Cu2+ 4- 11 pH range was suitable apart from this
pH the compound became degrade. From the pH study, the
relevant pH range for L3 and L4 with Cu2+ is 3-10 pH aside from this
pH the properties of compounds were changed. So, the results
Fig 8(a). Titration graph of L1+Cu2+(20 µM) in-situ by gradual addition of CN- (20 to 200
μM).
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water from Roorkee and known amount of copper was added
to the water samples. The assessment was determined by
impaling the known amount of standard copper ion solutions
followed by calculating its recovery. The recovery of different
known amounts of copper ion added was collected from 94%
to 99% for tap water and 99.4% to 103% for Ganga river water.
This result shows that the application of ligands for real water
analysis was quite achievable. Table 5 represents the real
water analysis. Same as experiment was performed for CN- ion
in water samples, which was represented in table 6. The in-situ
experiment was executed with CN- ion. This experiment was
analysed only for L1 and L4 because only these two ligands
show metal displacement approach. As the results reveals that
the recovery of CN- ion for tap water lie between 99% to 99.7%
and from 93% to 96% for Ganga river water.
Fig 8(b). Titration graph of L4+Cu2+(20 µM) in-situ by gradual addition of CN- (20 to 200
μM).
Table 5: Determination of Copper ion in different water samples by using L1, L2, L3 and
L4 ligand.
Samples
Spiked Cu2+
(M)
Found aCu2+ ± SD
(M)
Recovery
(%)
L1
Tap water
5 × 10-5
4.95 ± 0.1 × 10-5
99 %
Ganga River
water
5 × 10-5
5.00 ± 0.2 × 10-5
100 %
L2
Tap water
5 × 10-5
5 × 10-5
4.73 ± 0.3 × 10-5
5.1 ± 0.1 × 10-5
94.6 %
102 %
Ganga River
water
L3
L4
Tap water
5 × 10-5
5 × 10-5
4.94 ± 0.1 × 10-5
5.15 ± 0.5 × 10-5
98.8 %
103 %
Ganga River
water
Tap water
5 × 10-5
5 × 10-5
4.89 ± 0.2 × 10-5
4.97 ± 0.1 × 10-5
97.8 %
99.4 %
Fig 9(a). Limit of detection graph of L1+Cu2+ with CN-(20 to 200 μM).
Ganga River
water
a Standard deviation was calculated for three measurements.
Table .6: Determination of Cyanide ion in different water samples by using L1 and L4
ligand.
Samples
Spiked CN-
Found CN- ± SD
Recovery
Tap
4 × 10-5
4 × 10-5
4 × 10-5
4 × 10-5
3.96 ± 0.1 × 10-5
3.87 ± 0.2 × 10-5
3.99 ± 0.1 × 10-5
3.75 ± 0.3 × 10-5
99%
96.7%
99.7%
93%
water
L1+Cu2+
River
water
Tap
water
L4+ Cu2+
Fig 9(b). Limit of detection graph of L4+Cu2+ with CN-(20 to 200 μM).
River
water
a Standard deviation was calculated for three measurements.
4. Applications
4.1 Real sample analysis
To evaluate the potential use of synthesized ligands (L1-L4), the
ligands were applied in analysis of different water samples.
The water samples used was tap water and the Ganga river
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showed that L1 and L4 sense cyanide ion in presence of copper
ion. The data was also applied in molecular switch and
represents INHIBIT logic gate.
Conflicts of Interest
There are no conflicts to declare.
Acknowledgement
Neetu Yadav is grateful to Ministry of Human Resources of
Development (MHRD) for providing funding for this work.
Fig 10. Change in absorbance of L1 at four different input conditions: inset shows
implicated logic diagram.
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Multidentate dicarbohydrazide based ligands was successfully
synthesized and characterized well through NMR, FTIR,
elemental analysis, crystal structure, mass spectrometry and
photophysical properties. These ligands show high selectivity
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