Synthesis, spectroscopic characterization and biological evaluation of a novel chemosensor with different metal ions

Article abstract of DOI:10.1002/aoc.5133

A novel chemosensor, namely 3-(4-chlorophenyl)-1-(pyridin-2-yl)prop-2-en-1-one, CPPEO, and its metal complexes have been synthesized and characterized by using sets of chemical and spectroscopic techniques, such as elemental analysis, mass, Fourier transform-infrared and UV–Vis spectral analysis. The thermal properties of the metal complexes have been investigated by thermogravimetric techniques. The decomposition mechanism of the titled complexes was suggested. The results showed that the Co²⁺ and Mn²⁺ complexes have an octahedral geometry, while Zn²⁺ and Cd²⁺ complexes have tetrahedral geometry. The kinetic and thermodynamic parameters of the thermal decomposition stages have been evaluated using the Coats–Redfern method. The optical sensing response of the investigated chemosensor to the different metal ions was investigated. It responds well to the tested metal ions as reflected from the significant change in both absorption and emission spectra upon adding different concentrations of the metal salts, confirming the intramolecular charge transfer of the chemosensor upon effective coordination with the used metal ions. This leads to enhancing ICT interaction, causing a significant shift in the presence of strongly complexing metal ions. This was fully reversible, where the solution of dye-metal ion complex was decomplexed by adding an EDTA solution to revert the original spectrum of the dye. The stability constants, K, for the complexes of the investigated chemosensor with the mentioned metal ions were calculated, indicating that Co²⁺ is the most effectively detected, and the potential of the novel dye was highly efficient switchers for Co²⁺ ions. Additionally, the molecular modeling was carried out for the chemosensor and its metal complexes. Finally, the solid complexes have been tested for their in vitro antimicrobial activities against some bacterial strains (Gram +ve and Gram ?ve bacteria), as well as antifungal strains.

Full text of DOI:10.1002/aoc.5133

Received: 24 January 2019
DOI: 10.1002/aoc.5133
Revised: 19 June 2019
Accepted: 21 June 2019
F U L L P A P E R
Synthesis, spectroscopic characterization and biological
evaluation of a novel chemosensor with different metal ions
M. Gaber1
Mohammed M. El‐Gamil2
| Tarek A. Fayed1
| Marwa N. El‐Nahass1
| H.A. Diab1 |
1 Department of Chemistry, Faculty of
Science, Tanta University, 31527 Tanta,
Egypt
2 Department of Toxic and Narcotic Drug,
Forensic Medicine, Mansoura Laboratory,
Medico Legal Organization, Ministry of
Justice, Egypt
A novel chemosensor, namely 3‐(4‐chlorophenyl)‐1‐(pyridin‐2‐yl)prop‐2‐en‐1‐
one, CPPEO, and its metal complexes have been synthesized and characterized
by using sets of chemical and spectroscopic techniques, such as elemental
analysis, mass, Fourier transform‐infrared and UV–Vis spectral analysis. The
thermal properties of the metal complexes have been investigated by thermo-
gravimetric techniques. The decomposition mechanism of the titled complexes
was suggested. The results showed that the Co2+ and Mn2+ complexes have an
octahedral geometry, while Zn2+ and Cd2+ complexes have tetrahedral geome-
try. The kinetic and thermodynamic parameters of the thermal decomposition
stages have been evaluated using the Coats–Redfern method. The optical sens-
ing response of the investigated chemosensor to the different metal ions was
investigated. It responds well to the tested metal ions as reflected from the sig-
nificant change in both absorption and emission spectra upon adding different
concentrations of the metal salts, confirming the intramolecular charge trans-
fer of the chemosensor upon effective coordination with the used metal ions.
This leads to enhancing ICT interaction, causing a significant shift in the pres-
ence of strongly complexing metal ions. This was fully reversible, where the
solution of dye‐metal ion complex was decomplexed by adding an EDTA solu-
tion to revert the original spectrum of the dye. The stability constants, K, for
the complexes of the investigated chemosensor with the mentioned metal ions
were calculated, indicating that Co2+ is the most effectively detected, and the
potential of the novel dye was highly efficient switchers for Co2+ ions. Addi-
tionally, the molecular modeling was carried out for the chemosensor and its
metal complexes. Finally, the solid complexes have been tested for their
in vitro antimicrobial activities against some bacterial strains (Gram +ve and
Gram −ve bacteria), as well as antifungal strains.
Correspondence
Tarek A. Fayed, M. Gaber and Marwa N.
El‐Nahass, Department of Chemistry,
Faculty of Science, Tanta University,
31527, Tanta, Egypt.
Email: tfayed2013@science.tanta.edu.eg;
mabuelazm@science.tanta.edu.eg;
marwa.elnahas@science.tanta.edu.eg
KEYWORDS
antimicrobial activities, chemosensor, molecular modeling, optical sensing
Appl Organometal Chem. 2019;e5133.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
1 of 16
https://doi.org/10.1002/aoc.5133

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GABER ET AL.
bacterial strains, also their biological activities were
screened against Gram‐positive, Gram‐negative bacteria
and antifungal strains.
1 | INTRODUCTION
Fluorescent push‐pull dyes have received considerable
attention owing to a growing interest in different
fields.[1,2] They are known as effective photosensitive
materials, and have exhibited considerable photophysical
and photochemical properties.[3] They are extensively
used as non‐linear optical materials,[4] photorefractive
polymers,[5] and in the study of the photo‐alignment layer
of liquid crystal displays.[6] Also, they can be used as
chemosensor probes for toxic metal ion detection. Among
these metal ions, Co (II), Mn (II), Zn (II) and Cd (II) were
the most commonly found ones in wastewater. Their high
degree of toxicity rank among the priority metals that are
of public health significance, so their removal from
2 | EXPERIMENTAL
2.1 | Materials
All the chemicals used in the present study were of pure
grade available from BDH, Aldrich or Sigma. They
include 2‐acetyl pyridine, 4‐chlorobenzaldehyde and
metal chlorides (CoCl2·6H2O, MnCl2.4H2O, ZnCl2.4H2O
and CdCl2.H2O). The solvents used for the spectral study
were spectroscopic grade from Aldrich.
wastewater has become
a major task for many
scientists.[7–11] Additionally, chalcones are of interest
chemotypes for both chemists and physicists, due to the
high natural abundance of them and their easy synthesis.
Also, they are well known for biological activities, such as
antitumor, anti‐inflammatory, immunomodulatory, anti-
bacterial, antimalarial, anti‐leishmanial, trypanocidal
and nitric oxide inhibitory activity.[12,13] Diverse
chalcone‐like compounds have been found to be potent
anticancer agents against human cancer cell lines with
different mechanisms of actions.[14] All the synthesized
chalcones were screened for in vitro anti‐proliferative
activities.[15] Chalcones are interesting chemical entities
from a medicinal chemistry perspective with a wide
variety of applications, although their ease of isomeriza-
tion and Michael‐acceptor potential may hamper some
of these applications.[16] The development of new
chalcone‐based therapeutics against ADs are promising
lead compounds for future research in anti‐AD drugs
discovery and development.[17] The results suggest that
chalcones could represent good strategies for the control
of acute and chronic pain, without significant side‐
effects.[18]
In light of these considerations, our work aimed at
synthesis, structural characterization and optical studies
of a novel chemosensor, namely 3‐(4‐chlorophenyl)‐1‐
(pyridin‐2‐yl)prop‐2‐en‐1‐one, CPPEO, and its metal com-
plexes. Their structures were elucidated by using sets of
chemical and spectroscopic techniques. The thermal
properties of the metal complexes have been investigated
using thermogravimetric (TG) techniques. The optical
sensing responses of the investigated chemosensors to dif-
ferent metal ions such as Co2+, Mn2+, Zn2+ and Cd2+
have been investigated. Also, the reversibility of the
chemosensor response has been elucidated using EDTA
solution. Additionally, molecular modeling was carried
out. Finally, the solid complexes have been tested for
their in vitro antimicrobial activities against some
2.2 | Physical measurements
Perkin‐Elmer 2400 CHN Elemental Analyzer was used
for the elemental microanalysis of the prepared com-
pounds. The Perkin‐Elmer 1430 IR spectrophotometer
was used for recording the infrared (IR) spectra (as KBr
discs) within the range 4000–200 cm−1. The magnetic sus-
ceptibility of the solid complexes was carried out at room
temperature by the Gouy's technique for the magnetic
susceptibility instrument. Mass spectra of metal com-
plexes were carried out on a Varian Mat 311 with start‐
end (m/z) (40–1000) and ionization mode (EI). The
Schimadzu TG‐50 TG analyzer was used for the TG anal-
ysis (TGA) of the solid complexes with a heating rate of
10°C/min under nitrogen atmosphere, in the range 25–
800°C. Electron spin resonance (ESR) spectra of solid
manganese complex at room temperature were obtained
on a JEOL EPR spectrometer working in the X‐band
(9.435 GHz) with a modulation frequency of 100 kHz,
and the microwave power was adjusted to 5 mW.
Steady‐state absorption and emission spectral measure-
ments were carried out using a Shimadzu UV‐3101PC
scanning spectrophotometer and an Agilent Cary Eclipse
Fluorescence Spectrophotometer using matched quartz
cuvettes, respectively. In all experiments, 2 × 10−5 M solu-
tions were used, and were handled under dim light at
room temperature. The samples were excited at 430 nm,
while recording the fluorescence spectra.
2.3 | Synthesis of the chemosensor,
CPPEO
The chemosensor (Figure 1), was prepared and character-
ized as previously described.[19] The purity of the pre-
pared compound was checked by melting point, Fourier
transform (FT)‐IR and UV–Vis spectral measurements.

GABER ET AL.
3 of 16
positive bacteria (Staphylococcus aureus, Enterobacter clo-
acae) and fungi (Candida albicans, Candida dubliniensis,
Candida glabrata, Candida krusei, Candida tropicalis and
Trichophyton mentagrophytes). Freshly prepared spore sus-
pension of different test microorganisms (0.5 ml of about
106 cells/ml) was mixed with 9.5 ml of melting sterile
Sabouraud's dextrose medium (for fungi) or nutrient agar
medium (for bacteria) at 45°C, poured on sterile Petri
dishes, and left to solidify at room temperature. Regular
cellulose filter paper discs of 6 mm diameter were prepared
under aseptic conditions. Each disc was saturated with
20 mg of each tested suspended material. For each test
three replicas were made. All plates were incubated at
27°C for 48 hr for fungi, and at 32°C for 24 hr for bacteria.
The average diameters of inhibition zones were recorded
in millimeters. All experiments were carried out in
triplicate and the mean results were evaluated.
FIGURE 1 The structure of the investigated chemosensor,
CPPEO
2.4 | Synthesis of the metal complexes
To a hot methanolic solution of CPPEO (0.01 mol in
20 ml), a hot methanolic solution (0.01 mol in 20 ml) of
the hydrated metal chlorides [Co2+, Mn2+, Zn2+ and
Cd2+ ions] was added. The resulting solutions were
refluxed under stirring for 4 hr. The solid products were
thus separated out, filtered off, washed several times with
methanol and finally dried in a vacuum desiccator over
anhydrous calcium (II) chloride. The analytical data are
collected in Table 1.
2.5 | Quantum chemical computations
3 | RESULTS AND DISCUSSION
The density functional theory (DFT) computations with
periodic boundary environments were accomplished uti-
lizing the well‐known DMol3 code,[20] by means of Mate-
rials Studio set.[21] The tasks were utilized as part of a
combination together with the specific dual mathematical
and polarization premise set DNP that is precisely
Gaussian basis sets.[22–24] The RPBE (GGA) functions[25]
is up to now the greatest exchange‐correlation func-
tion,[26] and is applied to consider the exchange proper-
ties of the electrons.
The structures of the investigated chemosensor and its
metal complexes were elucidated by means of their ele-
mental, molar conductivity and IR spectral data. The
results of elemental analysis and molar conductance are
collected in Table 1. The isolated solid complexes are sta-
ble in air, and soluble in DMF and DMSO. The melting
points of the metal complexes were found to be over
300°C The low molar conductance values of Zn2+ and
Cd2+ complexes revealed that these complexes are non‐
electrolytes in DMF. The presence of Cl− ions outside
the coordination sphere was confirmed by the chemical
reaction with AgNO3, where the white precipitate of AgCl
was observed. The molar conductance values were 77 and
88 ohm−1 cm2 mol−1 for Co2+ and Mn2+ complexes,
respectively, indicating the electrolyte nature of these
complexes and the presence of the anion outside the coor-
dination sphere.[28]
2.6 | Antimicrobial activity
For screening the antimicrobial activity of organic ligand
and its metal complexes, the agar diffusion technique
was used.[27] The tested organisms are Gram‐negative bac-
teria (Escherichia coli, Pseudomonas aeruginosa, Klebsiella
pneumoniae, Proteus vulgaris and Acinetobacter), Gram‐
TABLE 1 Elemental analysis and molar conductance of the investigated chemosensor, CPPEO, and its metal complexes
Elemental analysis % (found)
Melting
Complex
Color yield Mol. Wt point
C
H
N
Metal content Λm
C1 [CoL2·(H2O)2](Cl)2. (H2O) Dark brown 671.19
> 300°C
50.14 (50.10)
4.13 (3.87) 4.14 (4.17)
8.06 (8.78)
11.60 (11.50)
14.87 (15.35)
24.22 (23.75)
77
88
7
C28H26Cl4Co N2O5 78%
C2 [MnL·(H2O)4](Cl)2.2(H2O) Dark brown 477.52
> 300°C
35.82 (35.21)
4.41 (4.63) 3.17 (2.93)
C14H22Cl3Mn NO7
83%
C3 [ZnL·(Cl)2]·(C2H5OH)
C16H16Cl3Zn NO2
Dark brown 426.108 > 300°C
77%
45.39 (45.099) 4.66 (3.78)
2.9 (3.28)
C4 [CdL·(Cl)2]·(C2H5OH)
Dark brown 473.129 > 300°C
40.71 (40.61)
4.20 (3.40) 3.25 (2.95)
13
C16H16Cl3CdNO2
72%

4 of 16
GABER ET AL.
(1:2). The molecular ion peak for C1 at m/z = 670.72
(20.22%) corresponding to (C28H26Cl4CoN2O5). Further-
more, the mass spectrum of C2, C3 and C4 exhibited a
good indication for the proposed molecular formula of
C2, C3 and C4 (MW 477.52, 426.108 and 473.129, respec-
tively), indicating that the ligand coordinates with metal
ions with a M:L ratio of (1:1). Moreover, the molecular
3.1 | FT‐IR analysis
Assignment of the IR diagnostic bands is depicted in
Table 2. The IR spectrum of the free chemosensor showed
that the υC=O band at 1675 cm−1 is shifted to a lower
frequency (48–85 cm−1) in all complexes, indicating the
participation of the oxygen atom of the carbonyl group
in all complex formation. The stretching vibration of the
υC=N linkage of the pyridine ring, which appeared at
1496 cm−1 in free chemosensor, was shifted to a lower
or higher frequency (8–60 cm−1), indicating the involve-
ment of C=N in the coordination process, confirming
the participation of the carbonyl oxygen and pyridine
nitrogen atom in complexation with the appearance of
new bands in the spectra of the complexes within the
range 525–550 and 442–487 cm−1 for υM → O[29] and
υM → N[30] stretching vibrations, respectively. A very
broad band in the range 3417–3441 cm−1 in the spectra
of the complexes is associated with coordinated and/or
hydrated water molecules.[31] The presence of coordina-
ion peaks for C2 [m/z
= 477.51 36.41%)], C3
[m/z = 426.48 (15.58%)] and C4 [m/z = 473.36 (57.49%)]
correspond to (C14H22Cl3MnNO7), (C16H16Cl3ZnNO2)
and (C16H16Cl3CdNO2), respectively.
3.3 | Magnetic and electronic absorption
measurements
The electronic spectra of ligands and isolated chelates
were illustrated in Table 3. The values of the observed
magnetic moment of the Co2+ complex (μeff = 5.66 BM)
show the presence of three unpaired electrons in the d‐
orbital. On the other hand, the observed magnetic
moment of the Mn2+ complex (μeff = 6.94 BM) shows
the presence of five unpaired electrons in the d‐orbital.
It was found that complexes C1 and C2 have octahedral
geometry with sp3d2 hybridization.[33–35]
tion water molecules has been confirmed on the basis of
−1
a medium intensity band at 693–780 cm
(υOH‐
rocking).[32]
The absorption spectra of Co (II) complex show bands
3.2 | Mass analysis
4
4
at 16 420 and 19 230 cm−1, corresponding to T1g → A2g,
Figures S1–S4 show the mass spectra of the investigated
metal complexes. As can be seen, the mass spectrum of
C1 provided good evidence for its molecular formula:
[CoL2(H2O)2](Cl)2·(H2O) (MW 671.19), indicating that
the ligand coordinates with Co2+ ion with M:L ratio
4T1g → 4T1g (P) transition, indicating the octahedral struc-
ture. The spectra of Mn (II) complex show bands at 27 855
6
and 21 645 cm−1, corresponding to A1g
→
4T2g and
6A1g
→
4Eg transition, also indicating the octahedral
structure.[36]
TABLE 2 The important bands in the IR spectra of the investigated chemosensor, CPPEO, and its metal complexes
Wave number (cm−1
)
ꢀ
No.
νHOH crystalline
υC=O
υM → N
υM → O
υC=N
Ligand CPPEO
–
1675
1590
1627
1605
1595
–
444
482
442
477
–
534
525
532
533
1496
1556
1518
1519
1504
C1
C2
C3
C4
3418–779
3425, 779
3424, 780
3417, 774
TABLE 3 The electronic absorption spectral data and magnetic moment of the investigated metal complexes
No.
μfound BM
CT band (cm−1
)
d‐d spectral band (cm−1
)
geff
C1
C2
C3
C4
5.66
6.94
–
28 011, 26 246
19 230
16420,15082,13192
–
30 864, 27 855, 26 315
21 645
17857, 14492,13157
1.909
35 971, 29 239, 26 881
–
–
–
–
–
–
–
33 003, 30 581, 28 409, 26 595

GABER ET AL.
5 of 16
3.4 | ESR spectra
3.5 | Thermal analysis
The X‐band ESR spectra of the powdered Mn (II) com-
plex (C2) were recorded at room temperature (25°C).
The ESR spectra of Mn2+ complex showed a negative
deviation from the geff values of the free electron
(2.0023). This may be due to the partial ionic character
of the covalent bond between the Mn (II) ion and the
ligand molecules.[37] The spectra of Mn2+ complex
showed a broad signal that indicates an octahedral
geometry around the Mn2+ ion. The g‐value of Mn2+
complex is shown in Table 3 and Figure 2.
The thermal behavior of metal complexes was studied by
means of TGA techniques. The data, including the stages
of decomposition, temperature ranges, peak tempera-
tures, decomposition product loss, found and the calcu-
lated mass loss percentages are listed in Table 4 and
Figure 3.
The obtained data indicated that all the metal com-
plexes underwent thermal decomposition within three
or four steps. Complexes C1 went through four stages of
decomposition processes. The first step of decomposition
appeared within the temperature range 17–120°C and
FIGURE 2 X‐band electron spin resonance (ESR) spectra of
complex C2
FIGURE 3 Thermogravimetric analysis (TGA) curves of the
investigated metal complexes
TABLE 4 Thermal decomposition data of the investigated metal complexes
Mass loss %
o
Complex
Temp. C
Estimate
Calcd
Assignment
C1
C2
C3
C4
[CoL2·(H2O)2](Cl)2. (H2O)
C28H26Cl4Co N2O5
17–120
120–299
299–735
7.24
20.97
60.76
11.00
8.04
21.12
59.66
11.16
Loss of 3H2O molecules
Loss of 4Cl
Dissociation of the organic ligand in two steps
CoO
[MnL·(H2O)4](Cl)2.2(H2O)
C14H22Cl3Mn NO7
23–199
199–444
444–730
22.61
13.99
29.15
35.27
21.58
14.84
27.52
34.95
Loss of 6 H2O molecules in two steps
Loss of 2Cl ions
Dissociation of the organic ligand with formation of
MnO + 8C as final products
[ZnL·(Cl)2].(C2H5OH)
C16H16Cl3Zn NO2
24–159
159–392
392–718
9.83
17.46
55.46
17.01
10.79
16.63
53.46
19.1
Loss of ethanol molecule
Loss of coordinated 2Cl ion
Dissociation of the organic ligand
ZnO
[CdL·(Cl)2]. (C2H5OH)
C16H16Cl3CdNO2
26–149
149–436
436–663
8.79
21.70
41.82
27.67
9.72
22.47
40.62
27.14
Loss of ethanol molecule
Loss of 3Cl
Dissociation of the organic ligand
CdO

6 of 16
GABER ET AL.
was assigned to the loss of water molecules. The second
step appeared within the temperature ranges 120–299°C,
corresponding to the loss of four chlorides atoms for C1.
The third and fourth steps of decomposition appeared at
temperature ranges 299–735°C for complex C1 corre-
sponding to the loss of the organic ligand, and the final
product of decomposition left behind was assigned as
the thermally stable CoO.
Complex C2 decomposed in four successive decompo-
sition steps. The first and second steps appeared within
the temperature range 23–199°C, which were assigned
to the loss of six water molecules. The third step of
decomposition appeared within the ranges 199–444°C,
corresponding to the loss of two chloride anion. The last
step of decomposition (444–730°C) corresponded to
further decomposition of the organic ligand. The final
product of decomposition left behind was assigned as
the thermally stable MnO + 8C.
Complexes C3 and C4 gave three stages of decomposi-
tion processes. The first step of decomposition appeared
within the temperature ranges 24–159 and 26–149°C,
respectively, and was assigned to the loss of ethanol mol-
ecule. The second step appeared within the temperature
ranges 159–392 and 149–436°C for complexes C3 and
C4, respectively, corresponding to the loss of three
chloride atoms for C4. The last step of decomposition
was at 392–718 and 436–663°C for complexes C3 and
C4, respectively, corresponding to the further decomposi-
tion of the organic ligand. The final product of decompo-
sition left behind was assigned as the thermally stable
ZnO and CdO.
3.6 | The kinetic parameters of the
decomposition processes of the complexes
The activation energy (E*), enthalpy (ΔH*), entropy (ΔS*)
and free energy of the decomposition (ΔG*) as well as the
order (n) is evaluated graphically by using the Coats–
Redfern[38] equation:
"
#
1−n
1 − ½1−∝ꢀ
M
T
ln
¼
¼
þ B for n ≠ 1
þ B for n ¼ 1
(1)
(2)
½1 − nꢀT2
ꢀ
ꢁ
− ln½1 − ∝ ꢀ
M
T
ln
T2
where M = −E/R and B = ln (ZR/φE), where E, R, Z and
φ are the activation energy, gas constant, pre‐exponential
factor and heating rate, respectively, n = 0, 0.33, 0.5, 0.66,
1. The order (n) and thermokinetic parameters of the
decomposition steps for the chosen complexes are listed
in Table 5. From the obtained data, the following
observations were made.
1. The ΔS* values for complexes were found to be posi-
tive. This indicates that the activated complex is less
ordered than the reactants and/or the reactions are
fast.[39]
2. The values of ΔG* increase and decrease signifi-
cantly for subsequent decomposition stages due to
increasing or decreasing the values of TΔS* from
one step to another, which override the values of
TABLE 5 Temperatures of decomposition and activation parameters (kJ/mol) of decomposition for the investigated metal complexes
Coats–Redfern
Complex
Steps
T(K)
n
r
E*
ΔH*
−ΔS*
ΔG*
C1
1
2
3
4
353
1
1
1
1
−0.9917824
−0.9918643
−0.9999019
−0.9816343
9.6045809
6.6697389
0.0873084
0.0922166
0.1111245
0.1405206
37.48962
498.5
674.25
794.75
14.404004
31.218162
73.226897
10.259475
25.612447
66.619345
56.22945
100.5381
178.2981
C2
1
2
3
4
329
415.75
612
1
1
0
1
−0.9913327
−0.9902433
−0.9949615
−0.9925623
45.974145
24.6492
14.026481
115.89734
43.238839
21.192655
8.9383133
108.40019
0.2019277
0.1170319
0.0857255
0.0773851
109.673
69.84867
61.402323
178.1822
901.75
C3
C4
1
2
3
371.25
546.25
908.75
1
1
1
−0.9958815
−0.9905973
−0.9964788
2.9269016
19.216575
211.04678
0.1596709
14.675053
203.49143
0.0847936
0.0972558
0.1958555
31.63929
67.80103
381.4751
1
2
3
364.75
578
868.25
1
1
0
−0.9754141
−0.9805662
−0.99972
15.050419
13.690393
42.56595
12.017887
8.8849015
35.347323
0.0940093
0.0821868
0.100569
46.3078
56.38887
122.6661

GABER ET AL.
7 of 16
ΔH*. This increase or decrease reflects that the
3.7 | Molecular modeling
3.7.1 | IR analysis
rate of removal of the subsequent chemosensor will
be lower/higher than that of the precedent
chemosensor.[40] This may be attributed to the
structural rigidity of the remaining complex after
the expulsion of one or more ligands, as compared
with the preceding complex, which requires more
energy for its rearrangement before undergoing
any compositional change.
The theoretical IR spectrum was estimated to produce the
spectroscopic signs of the ligand, and exhibits the υC=O
band (measured: 1675 cm−1; predicted: 1628 cm−1
)
and υC=N band (measured: 1496 cm−1; predicted:
1474 cm−1). The small differences between the predicted
and measured frequencies are illustrated in Figure 4.
The fundamental purpose behind the distinction is that
the count was performed in a vacuum, while the
measurements were refined for solid state. The lower
symmetry is the main reason for the complexity of the
vibrational modes of the investigated chemosensor. All
plane modes are difficult to assign, due to the ring modes
besides the imitative, especially torsion. Regardless, the
presence of some supportive vibrations is in a good agree-
ment with the obtained graph.
3. The positive values of ΔH* mean that the decomposi-
tion processes are endothermic[41] (data shown in
Table 5 and Figures S5a–d).
3.7.2 | Geometry optimization and
chemical reactivity
The optimized structural models are shown in Figures 5–9.
Inspection of the bond distances and angles is shown in
Tables S1 and S2, and the subsequent observations
were made.
FIGURE 4 Comparison of experimental and theoretical infrared
(IR) spectra of ligand
1. The active groups (C=O and C=N) are elongated
upon coordination with the metal ion. This refers to
the formation of M‐N and M‐O bonds,[42] which
enable the C=N and C=O bonds to become weaker.
2. The M‐N and M‐O band distances are in agreement
with the sum of covalent radii for M and N or O
atoms, and are similar to values reported earlier.[43]
3. In C3 and C4, the two axial positions are occupied by
chloride ions, exhibiting that the bond distances of
M‐Cl are longer than M‐N and M‐O.
4. The bond angles are similar to those reported for
octahedral C1 and C2 complexes with d2sp3 or sp3d2
FIGURE 5 Computational structure of the ligand
FIGURE 6 Computational structure of
complex C1

8 of 16
GABER ET AL.
We can demonstrate from computation that the oxygen
of the C=O group has the largest values of molecular
orbital coefficients, showing that it is a suitable site of
complexation.
The energy gap (ΔE = EHOMO − ELUMO), chemical
descriptors such as softness (S), hardness (η), electroneg-
ativity (χ), chemical potential (μ) and electrophilicity (ω)
and softness (σ) for the isolated compounds were shown
in Table S3. These descriptors can be estimated using
the following equations:[45–48]
FIGURE 7 Computational structure of complex C2
χ ðelectronegativityÞ ¼ −1=2 ðELUMO þ EHOMO
μ ðpotentialÞ ¼ −χ ¼ 1=2 ðELUMO þ EHOMO
Þ
(3)
(4)
Þ
η ðhardnessÞ ¼ 1=2 ðELUMO − EHOMO
Þ
(5)
S ðsoftnessÞ ¼ 1=2η
(6)
(7)
ω ðelectrophilicityÞ ¼ μ2=2η
FIGURE 8 Computational structure of complex C3
The inverse value of the global hardness is designed as
the softness σ as follows:
σ ¼ 1=η
(8)
According to calculation results in Table S3, the
following were shown.
i. The EHOMO and ELUMO are almost negative, showing
the stability of the isolated compounds.[49,50]
ii. Gutmann's variation rules, “the bond strength
increases as the neighboring bonds become weaker”,
such as found by Linert and Taha.[51] This interpre-
tation agrees well with the result, as the increase of
the EHOMO is conveyed by a weakness (elongation)
of the metal–ligand bond, which prompts a reinforc-
ing (shortness) of the sites next to the metal–ligand
centers.
FIGURE 9 Computational structure of complex C4
hybrid orbitals; while C3 and C4 exhibit tetrahedral
geometry with sp3 hybrid orbitals.
The highest occupied molecular orbital (HOMO) level is
defined as the one that essentially shows electron dona-
tion behavior. And the lowest unoccupied molecular
orbital (LUMO) is the one that significantly acts as an
electron acceptor. Both named frontier molecular orbitals
(FMOs; Figures S6–S10) estimate electric optical proper-
ties, electronic transitions and kinetic stability.[44] The
FMOs hypothesis anticipates sites of coordination (elec-
trophilic attack) on an aromatic compound. The interac-
tion between the HOMO of one moiety with the LUMO
on another is a major reason in most of the reactions.
iii. A hard molecule is represented by a large HOMO
− LUMO difference, while a soft and more active
framework has a small energy difference. The
chemical potential ‘μ’ that estimates the escaping
capability of electrons from its equilibrium frame-
work diminishes as follows: C2 (−3.248) > C1
(−3.499) > ligand (−4576) > C3 (−4.895) = C4
(−4.895).
iv. The importance of η and σ are to measure the molec-
ular stability and reactivity. In a complex formation
system, metal ions are Lewis acids (soft acids), and

GABER ET AL.
9 of 16
thus Lewis base (soft base) ligands are most effective
interaction energy between the electrical charge pro-
duced from the electrons, nuclei and protons placed at
r.[57] Calculation of the electrostatic potential is feasible
for atoms utilizing the Γ‐point and various k‐points. In
the current investigation, 3D plots of MEPs of ligands
and their metal complexes (Figures S11–S15) have been
produced. The largest negative part, which is the desired
for complex formation. Accordingly, it is concluded
that the investigated ligand with a proper σ
value has a good tendency to chelate metal ions
effectively.[52]
The calculations of the total energy (Table 6) revealed
that the increase in the value of the calculated binding
energy of complexes compared with that of the ligand
indicates that the stability of the formed metal complexes
is higher than that of the ligand. The dipole moment
values of the complexes are larger than the ligand value,
except the dipole moment of Co2+ complex (C1) has a
lower value than that of the ligand. The lowest value of
the dipole moment of Co2+ complex may be due to the
trans‐isomer of both ligand moieties, which are equal
and opposite.[53]
The structure–activity relationship studies were
investigated to correlate the antimicrobial properties of
the studied compounds related to physicochemical
properties. The dipole moments are the property of
interest that gives some insight into the degree of
hydrophobicity/hydrophilicity of the compounds. As the
dipole moment decreases, the polarity decreases. Thus,
the lipophilic nature of the compound increases, which
favors its permeation through the lipid layer of the micro-
organism, then destroying them.
3.7.3 | Molecular electrostatic potential
(MEP)
Molecular electrostatic potential is graphed based on the
electron density surface. It is additionally exceptionally
valuable in the research of sub‐atomic structure with its
physiochemical property association and hydrogen bond-
ing interactions.[54–56] The electrostatic potential V(r) at a
given point r (x, y, z) is characterized as a function of the
SCHEME 1 The structure of the formed complexes
TABLE 6 Some energy of the investigated chemosensor, CPPEO, calculated by D‐Mol3 method using DFT‐calculation
Compound
Free chemosensor
C1
C2
C3
C4
Sum of atomic energies (kcal/mol)
Kinetic energy (kcal/mol)
−7.06 × 1005
−4.99 × 1003
−4.82 × 1002
1.18 × 1003
9.12 × 1002
−7.09 × 1005
−3.37 × 1003
3.4128
−1.61 × 1006
−8.69 × 1003
−3.51 × 1003
2.69 × 1003
2.03 × 1003
−1.62 × 1006
−7.48 × 1003
1.3896
−9.73 × 1005
−4.19 × 1003
−3.38 × 1003
1.65 × 1003
1.38 × 1003
−9.78 × 1005
−4.54 × 1003
11.2473
−1.44 × 1006
−5.88 × 1003
9.74 × 1001
1.27 × 1003
9.29 × 1002
−1.45 × 1006
−3.59 × 1003
5.3146
−1.34 × 1006
−4.97 × 1003
−7.52 × 1002
1.24 × 1003
9.08 × 1002
−1.34 × 1006
−3.58 × 1003
7.8108
Electrostatic energy (kcal/mol)
Exchange‐correlation energy (kcal/mol)
Spin polarization (kcal/mol)
Total energy (kcal/mol)
Binding energy (kcal/mol)
Dipole moment (Debye)

10 of 16
GABER ET AL.
site for electrophilic attack, is indicated by red shading;
the largest positive region, which is the desired site for
nucleophilic attack, is indicated by the blue color. The
potential decreases as follows: red < green < blue, where
blue demonstrates the most preferred site for the attrac-
tion and red reveals the best site for the repulsion. The
areas with negative potential are over the electronegative
molecules, while the districts with positive potential are
over the hydrogen atoms.
3.8 | Optical sensing of metal ions using
the investigated chemosensor, CPPEO
In order to evaluate the metal‐binding potential, the opti-
cal properties of the investigated 3‐(4‐chlorophenyl)‐1‐
(pyridin‐2‐yl)prop‐2‐en‐1‐one (CPPEO) were investigated
using absorption and emission techniques in the presence
of metal ions such as Mn2+, Cd2+, Zn2+ and Co2+. As can
be seen in Figure 10, the investigated CPPEO exhibited a
broad band at λmax = 321 nm with an extinction coeffi-
−1
cient ε ≈ 3.9 ×104
M
cm−1 in MeOH. Addition of
Mn2+ and Co2+ ions resulted in marked changes both
in the energy and the shape of the absorption spectra of
the investigated CPPEO. More dramatic changes occurred
within the ranges 4–28 ×10−4 M, which produced intense
new bands at 357 and 367 nm, respectively. However, for
the interaction of the investigated CPPEO with Cd2+ and
Zn2+ ions in MeOH, the band shifts only to a small
extent. Additionally, well‐defined isosbestic points appear
at 337, 338, 341 and 345 nm for Mn2+, Cd2+, Zn2+ and
Co2+, respectively. These results confirm the existence
of two species in equilibrium, and imply the presence of
ground‐state complexation between the investigated
CPPEO and the studied metal ions via the nitrogen of
the pyridine moiety and the oxygen of the carbonyl
3.7.4 | Mulliken atomic charges
Mulliken atomic charge estimation of ligands and their
complexes (Figure S16; Tables S4–S8) shows a signifi-
cant role in the procedure of theoretical approximation
of the molecular framework. Figure S16 elucidates the
charge distribution of ligand. Both nitrogen and oxygen
atoms have negative values due to their donating ability.
On the other hand, hydrogen atoms and most of the
carbon atoms displayed positive values because of their
accepting ability. Based on the above results, the struc-
tures of the mentioned complexes were shown in
Scheme 1.
FIGURE 10 Absorption spectra of 2 × 10–5 M CPPEO in the absence and presence of different concentrations of the used metal ions in
MeOH

GABER ET AL.
11 of 16
group. This leads to enhancing the ICT interaction,
which causes a significant shift in the presence of
strongly complexing metal ions.
where the metal ion chelator restored the original
absorbance and the nano‐sensor exists largely in the
switched‐off state.
For the synthesized chemosensor, recognition revers-
ibility is an important requirement for continuous recy-
The ground‐state binding constants of Mn2+, Cd2+
,
Zn2+ and Co2+ complexes with the investigated dye were
determined by employing the Benesi Hildebrand
equation[58] as follows:
clability and reusability. Its optical response to Mn2+
,
Cd2+, Zn2+ and Co2+ ions was found to be fully reversible
on adding EDTA to the formed complex (Figure 11),
½Loꢀ
1
1
¼
þ
(9)
A − Ao
ε
ML − εL ðεML − εLÞK½Mꢀ
where Ao and A are the absorbance values of the free dye
solution and with the metal complex at a given wave-
length; εL and εML are the molar extinction coefficients
of the investigated dye and its metal complex, [M] is the
concentration of the studied metal ions, [Lo] is the
initial concentration of the investigated dye, and K is
the binding constant for the interaction, which is
½Loꢀ
determined from the plots of
against 1/[M]
A − Ao
(Figure 12). The binding constants, K, for the complexes
of the investigated dyes with the mentioned metal
ions were calculated, and are summarized in Table 7.
The obtained data indicate that Co2+ is the strongest
binding metal ion with the investigated chemosensor
compared with the other tested metal ions, indicating
that Co2+ is the most effectively detected and the
potential of the novel dye as highly efficient switchers
for Co2+ ions.
FIGURE 11 The absorption spectra of the reversible interaction
of dye/metal ions complexes in the presence of EDTA
A much greater effect has been observed on record-
ing the emission spectra of the investigated CPPEO in
the presence of methanolic solutions of Zn2+, Cd2+
,
Co2+ and Mn2+, as shown in Figure 13. The fluores-
cence of the investigated CPPEO appears as a broad
and structureless band with a maximum at about
456 nm in MeOH. Upon adding different concentrations
of Zn2+, Cd2+, Co2+ and Mn2+ ions within the ranges
(0.2–35) × 10−4 M, the fluorescence intensities of the
chemosensor increase gradually with pronounced
FIGURE 12 Benesi–Hildebrand plots for the binding of CPPEO
with the used metal ions
hypsochromic
shifted
bands.
The
continuous
TABLE 7 Spectroscopic parameters, absorption (a) and fluorescence (f) maxima, the binding constants, K (M−1), in the ground and excited
states for the studied metal ions with the investigated chemosensor, CPPEO
−1
−1
Metal ion
λmaxa, nm
Isosbestic point
λ
maxf, nm
Kb1 (M
Kb2*
(M
)
)
Cd2+
Zn2+
Co2+
Mn2+
321*, 328
329
338
341
345
337
457*, 450
463
123.46
306.32
534.80
169.3
115.05
359.47
901.87
249.48
367
402
357
402, 446
aabsorption.
ffluorescence.
*the binding constant calculated in the excited state.

12 of 16
GABER ET AL.
FIGURE 13 Fluorescence spectra of CPPEO upon addition of different metal ions in MeOH
enhancement in the fluorescence intensities suggests the
optical chemosensor as a potential design for the off–on
sensitive sensing of metal ions and confirming their role
in the semi‐quantitative detection of these metal ions.
The binding constants of the formed complexes
between the investigated chemosensor and the used
metal ions were also calculated from the emission spectra
using the Benesi–Hildebrand equation:[58]
ꢂ
ꢃꢂ
ꢃ
1
1
1
1
¼
þ
(10)
nþ
ΔF ΔF max
ΔF max
K½Mꢀ
where Δ F = F x − F o and Δ F max = F ∞ − Fo, and
where F o, F x and F ∞ are the emission intensities of
the nano‐sensors, considered in the absence of metal
ions, at certain metal ions concentrations, and at the con-
centration of complete interaction, respectively. [M]n+ is
the concentration of the metal ions and K is the binding
constant for the interaction, which is determined from
the plots of 1/Δ F against1/[M]n+. Typical linear recipro-
cal plots were obtained. The binding constants, K, were
calculated from the intercept and the slope ratio
(Table 7). As can be seen in Figure 14, the binding con-
FIGURE 14 Benesi–Hildebrand plots for the binding of CPPEO
with the used metal ions
electrostatic energy, the total intermolecular energy, fre-
quency of binding, and interacting surface area parame-
ters were evaluated to estimate the favorable binding of
the ligand to the protein. Table S9 shows the complete
profile of these parameters of the ligand for its interaction
with receptor of P. vulgaris (4mcx‐toxin) and secreted
from C. albicans (5kbk‐ oxidoreductase).
One of the most favorable bindings of the ligand was
its binding with 5kbk protein with the estimated free
energy of binding −4.78 kcal/mol, and total intermolecu-
lar energy of −5.63 kcal/mol. The ligand showed the inhi-
bition constant (Ki) of 314.91 mM. Figure S17 shows the
binding of the ligand to the protein 5kbk. The ligand
stant values increase in the order Co2+ > Zn2+
Mn2+ > Cd2+ complexes.
>
3.9 | Docking analysis
The free energy of binding, inhibition constant (Ki), total
estimated energy of vdW + Hbond + desolv (EVHD),

GABER ET AL.
13 of 16
was bound with 4mcx protein with an estimated free
energy of binding −4.93 kcal/mol, and the total intermo-
lecular energy was −5.80 kcal/mol. The ligand showed
the inhibition constant (Ki) of 241.43 mM. Figure S18
shows the binding of the ligand to the protein 4mcx. A
HB plot[42,59] was generated to mention interactions with
different amino acids of the proteins (Figures S19 and
S20). A 2D plot was generated where ligand bond, non‐
ligand bond and hydrogen bonds along with their length
were mentioned (Figures S21 and S22). Table S9 exhib-
ited the clustering results obtained from the docking of
the ligand into 5kbk and 4mcx proteins. Based on the
results of docking studies, it has been clearly expressed
that the ligand possibly showed favorable binding with
5kbk and 4mcx. Hence, the ligand can be a potential
inhibitor to the pathogenic microorganisms like bacteria
and fungi. This interaction could deactivate or kill the
microorganisms. The characteristic feature of the ligand
was represented in the presence of several active sites
available for hydrogen bonding interaction. This theoret-
ical analysis proposes the high biological activity of the
organic ligand towards different bacteria or fungi.
FIGURE 15 Antimicrobial assay for the investigated metal
complexes
In the present case, the activity is dependent on the
central metal ion and its ability to diffuse into the cell
membrane of the organism.
The variation in the activity of different complexes
against different microorganisms depends either on the
impermeability of the cells of the microbes or differences
in ribosomes in microbial cells.[60] The data listed in
Table 8 indicated that all the tested compounds showed
a moderate to good antimicrobial activity against the
tested microorganisms when compared with the standard
drugs, except for Acinetobacter.
3.10 | Biological screening
Co (II) complex was more active against Gram‐positive
than other complexes, while Mn (II) complex was inac-
tive against Gram‐negative bacteria such as E. coli only.
It may be concluded that the antimicrobial activity of
the compounds is related to the cell wall structure of
the bacteria. It is possible because the cell wall is essential
to the survival of bacteria and some antibiotics are able to
kill bacteria by inhibiting a step in the synthesis of pepti-
doglycan. Gram‐positive bacteria possess a thick cell wall
containing many layers of peptidoglycan and teichoic
3.10.1 | Antimicrobial activity
The screening results of antimicrobial activity for metal
complexes in comparison with the free chemosensor are
summarized in Table 8 and represented in Figure 15. The
chemosensor showed activity towards P. vulgaris only.
Generally, the investigated chemosensor has lower activ-
ity than the complexes, and complexes showed the
highest activity towards Gram‐positive bacteria and
Gram‐negative bacteria.
TABLE 8 Antimicrobial activity data of the investigated metal complexes
Inhibition zone diameter (mm/mg sample)
Gram (+)‐bacteria
Gram (−)‐bacteria
Fungus
Staphylococcus Enterococcus Escherichia Pseudomonas Klebsiella
Proteus
pneumoniae vulgaris
aureus
cloacae
coli
aeruginosa
Acinetobacter
Trichophyton
Sample
1
2
3
4
5
6
7
mentagrophytes
C1
C2
C3
C4
14.33 1.25
13.66 0.76
14.83 1.04
0
14.5
12
1
14.66 0.76 14.33 1.15
0
0
0
0
13
0
1
21
1
0
0
0
9.33 1.25
10.5
9.33 1.15
9.5
10
1
1
1
23.83 0.76
22.66 0.76
15.33 1.25
12.33 1.25
15
1
13 1.25
12 0.76
13
9.5
Mean SD = standard deviation.

14 of 16
GABER ET AL.
TABLE 9 Diameters of inhibition zones (mm) of the metal complexes against different test Candida types
Types of Candida
Candida albicans
Candida dubliniensis
Candida glabrata
Candida krusei
Candida tropicalis
N.O.
1
2
3
4
5
Free chemosensor
11.66
11
13
10
13
11
11
10
0
12
10
10
11
14
14
11
13
12
12
C1
C2
C3
C4
13
10
13
14
11
11
4 | CONCLUSION
Co (II), Mn (II), Zn (II) and Cd (II) complexes of the titled
chemosensor have been synthesized and characterized by
analytical and spectral methods. The data indicated that
the investigated ligand acts as a bidentate ligand coordi-
nated to the metal ions via the O and N atoms of the
C=O and C=N groups, respectively. The spectral and
magnetic data revealed the formation of octahedral com-
plexes for Co (II), Mn (II), Zn (II) and Cd (II) complexes,
while Cu (II) complex has a tetrahedral geometry. The
thermal properties of the metal complexes have been
investigated using the TG technique. The kinetic and
thermodynamic parameters of the decomposition steps
have been calculated. The optical sensing responses of
the investigated chemosensor to the different metal ions
were investigated. It responds well to the tested metal
ions as reflected from the significant change in both
absorption and emission spectra upon adding different
concentrations of the metal salts, confirming the intramo-
lecular charge transfer of the chemosensor upon effective
coordination with the used metal ions. This leads to
enhancing ICT interaction, causing a significant shift in
the presence of strongly complexing metal ions. They
were fully reversible on adding EDTA to the formed com-
plexes. Also, the solution of dye‐metal ion complex was
decomplexed by adding a solution of EDTA to revert the
original spectrum of the dye, thus demonstrating the
reversibility of the sensing. Molecular orbital calculations
have been performed for the ligand and its complexes.
Finally, the antibacterial and antifungal activities of the
ligand and its complexes have been tested.
FIGURE 16 Antifungal assay for the investigated metal
complexes
acids but, in contrast, Gram‐negative bacteria have a
relatively thin cell wall consisting of a few layers of pepti-
doglycan surrounded by a second lipid membrane
containing lipopolysaccharides and lipoproteins. These
differences in cell wall structure can produce differences
in antibacterial susceptibility, and some antibiotics can
kill only Gram‐positive bacteria and are infective against
Gram‐negative pathogens.[61]
3.10.2 | Antifungal activity (different
Candida types)
For the sensitive organisms C. albicans, C. dubliniensis, C.
glabrata, C. krusei and C. tropicalis, the diameter of the
inhibition zone (mm) was used to compare the antifungal
activity of the complexes with that of the free
chemosensor (Table 9; Figure 16).
The free chemosensor and its complexes were biologi-
cally active against all Candida types, except Co (II) was
inactive towards C. glabrata. In addition to chemosensor,
Cu (II) and Mn (II) complexes were biologically inactive
against T. mentagrophytes.
ORCID
M. Gaber https://orcid.org/0000-0003-2315-5710
Tarek A. Fayed https://orcid.org/0000-0001-6353-6978
Marwa N. El‐Nahass
https://orcid.org/0000-0002-7464-
404X

GABER ET AL.
15 of 16
[27] (a) R. E. Cooper in Analytical Microbiology (Ed.: F. W.
Kavanageh), Vols 1 & 11, Academic Press, New York, 1972;
(b)T. Pridham, L. Lindenfelser, O. Shotwell, F. Stodola, R. Ben-
edict, C. Foley, P. Jacks, W. Zaumeyer, W. Perston, J. Mitchell,
Phytopathology 1956, 46, 568.
Mohammed M. El‐Gamil
5605-2844
https://orcid.org/0000-0001-
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