Development and structure elucidation of new VO2+, Mn2+, Zn2+, and Pd2+ complexes based on azomethine ferrocenyl ligand: DNA interaction, antimicrobial, antioxidant, anticancer activities, and molecular docking

Article abstract of DOI:10.1002/aoc.6154

An organometallic azomethine ferrocenyl ligand (FCAP) and its transition metal complexes ([M (FCAP)₂], where M = VO²⁺, Mn²⁺ cations, and [M (FCAP) (CH₃COO^? or NO^3?)], where M = Zn²⁺

Full text of DOI:10.1002/aoc.6154

Received: 13 October 2020
DOI: 10.1002/aoc.6154
Revised: 19 December 2020
Accepted: 28 December 2020
F U L L P A P E R
2
+
2+
Development and structure elucidation of new VO , Mn ,
2
+
2+
Zn , and Pd complexes based on azomethine ferrocenyl
ligand: DNA interaction, antimicrobial, antioxidant,
anticancer activities, and molecular docking
1
2
3
Enas T. Aljohani
| Mohamed R. Shehata
| Fatmah Alkhatib
4,5
|
4
Seraj Omar Alzahrani
| Ahmed M. Abu-Dief
1
Chemistry Department, College of
An organometallic azomethine ferrocenyl ligand (FCAP) and its transition
Science, Majmaah University, Majmaah,
Saudi Arabia
2+
2+
metal complexes ([M (FCAP) ], where M = VO , Mn
cations, and
2
2
Chemistry Department, Faculty of
−
3−
2+
2+
[
M (FCAP) (CH COO or NO )], where M = Zn and Pd cations) were
3
Science, Cairo University, Giza, Egypt
prepared. Their structures were confirmed via various spectral and physico-
chemical studies performed. The crystallinity of the investigated metal chelates
was confirmed by X-ray diffraction data. The spectral data of the FCAP
azomethine ligand and its metal chelates were explained concerning the struc-
tural changes due to complex formation. From the electronic spectra and the
magnetic moments, the information about geometric structures can be con-
cluded. The activation thermodynamic parameters of the thermal degradation
for FCAP complexes were calculated utilizing the method of Coats–Redfern.
in vitro antimicrobial, anticancer, and antioxidant activities of FCAP
azomethine ligand and its complexes were screened. All the investigated metal
chelates exhibited superiority on the free FCAP ligand in successful treatment.
Moreover, the binding nature of the investigated complexes with calf thymus
DNA (ctDNA) was examined by various methods such as spectrophotometry,
viscosity, and, gel electrophoresis. Their binding feature to ctDNA was pro-
posed to be electrostatic, intercalation, or replacement mode. Furthermore,
molecular docking inspection has been conducted to clarify the nature of the
binding and binding affinity of protein synthesized compounds (PDB:3hb5).
3
Chemistry Department, Faculty of
Applied Science, Umm Al-Qura
University, Makkah, Saudi Arabia
4
Chemistry Department, College of
Science, Taibah University, Madinah,
Saudi Arabia
5
Chemistry Department, Faculty of
Science, Sohag University, Sohag, Egypt
Correspondence
Ahmed M. Abu-Dief, Chemistry
Department, College of Science, Taibah
University, Madinah, P.O. Box 344, Saudi
Arabia.
Email: ahmed_benzoic@yahoo.com;
amamohammed@taibahu.edu.sa
K E Y W O R D S
computational studies, ferrocene-derived azomethine ligand, metal (II) chelates, molecular
docking, organometallic-based antimicrobials
1
| INTRODUCTION
in cells in one way or more. As a result, designing novel
anticancer drugs with high efficacy and low toxicity is
[
1–5]
Cancer is deemed as a large class of diseases that includes
the growth of abnormal cell that may be dispersed to
other parts of the body. Many medications used for can-
cer remediation are now cytotoxic, affecting DNA activity
the most critical challenge these days.
For their lipo-
philic, non-toxic, and reversible redox properties and
their stability in a biological medium, ferrocene deriva-
[
6]
tives are of importance among metallocenes. These
Appl Organomet Chem. 2021;35:e6154.
wileyonlinelibrary.com/journal/aoc
© 2021 John Wiley & Sons, Ltd.
1 of 24
https://doi.org/10.1002/aoc.6154

2
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ALJOHANI ET AL.
compounds have many material science applications,
including electroactive materials, catalysts, sensors, and
aerospace materials, because of the favorable electronic
properties of ferrocene derivatives and their simple
used to acquire the electronic spectra of the investigated
compounds. Infrared (IR) spectra on a Perkin Elmer
−
1
FT-IR spectrophotometer in the 400–4,000 cm area
were registered in KBr. The molar conductivity of solid
complex solutions was measured using the Jenway 4010
conductivity meter. Thermogravimetric (TGA) analyses
of solid complexes were carried out using a thermal ana-
lyzer of Shimadzu TG-50H from room temperature to
[7–10]
functionalization.
Ferrocenyl transition metal com-
pounds have recently been found in molecular sensors,
molecular switches, molecular ferromagnets, electro-
[11–14]
chemical agents, and liquid crystals.
Bio-
ꢁ
organometallic chemistry has therefore gained a great
deal of research attention as a new field. A connection
between organometallic chemistry and molecular bio-
technology is established by ferrocenyl linked to transi-
tional metal compounds. In the development of new
therapeutic reagents and DNA molecular probes, binding
studies of small molecules to DNA are very
1,000 C.
2.2 | Ligand preparation method
Organometallic azomethine FCAP ligand was prepared
by using the homogeneous solution of 2-amino phenol
(2 mmol, 0.218 g) with ferrocene carboxaldehyde
(2 mmol, 0. 428 g). These compounds were separately
dissolved in absolute ethanol, stirred on hot magnetic
hot plate for 45 min, and refluxed using a water con-
denser for 1 h. After complete reflux, the reaction
mixture is cooled at room temperature and kept over-
night in a dark place, the solid separated, and the yield of
product is 88%.
[15–18]
important.
DNA binding potential is the dominant
attitude tested in pharmacology to speculate on the anti-
cancer potential of novel compounds. Consequently, it is
important to design tiny compounds that bind and inter-
act strongly with DNA. In the interaction of complexes
with DNA molecules, the nature of the ligand and metal
ion is of vital importance, which helps to design novel
drugs and create new selective, effective DNA recognition
and cleaving agents. The relationship between the transi-
tion metal complexes and DNA has therefore been thor-
[19–23]
oughly investigated.
2.3 | Azomethine FCAP metal chelate
We wish to report here FCAP ferrocene azomethine
ligand and its use in the preparation, of V (IV)O, Mn
preparation
(
II), Pd (II), and Zn (II) ferrocene azomethine chelates
FCAP azomethine complexes were prepared by mixing
equimolar of ethanolic solution of FCAP azomethine
ligand (2 mmol, 0.610 g) with 2 mmol of Zn (NO ) .4H O
Moreover, we will make structure elucidation for the
prepared compounds utilizing different physicochemical
and analytical tools. In addition, we will check the pos-
sibility of DNA interaction of the investigated ferrocene
azomethine chelates. Furthermore, their application as
a class of organometallic-based antimicrobial, antican-
cer, and antioxidant agents will be screened.
3
2
2
(0.58 g), Pd (CH COO) (0.448 g) or 1 mmol of VO (acac)
2
3
2
(0.54 g) or MnCl .4H O (0.19 g). The resulted mixtures
2
2
were refluxed for 2 h, and then, the reaction mixture is
cooled at room temperature. By filtration, the solid com-
pounds have been separated, washed several times with
hot ethanol and ether, and dried over CaCl . In monitor-
2
ing the developed compounds' purity, thin layer chroma-
tography (TLC) was used. Synthetic pathway of the
azomethine FCAP ligand and its complexes are given in
Scheme 1.
2
2
| PROTOCOLS OF EXPERIMENTS
.1 | Materials and methods
All solvents used were of a chromatographic grade.
Organic compounds such as ferrocene carboxaldehyde
and 2-amino phenol and metal salts such as
manganese chloride (MnCl ꢀ4H O), zinc (II) nitrate
2.4 | Computational studies for
molecular optimization
2
2
(
Zn (NO ) ꢀ4H O), vanadyl acetylacetonate (V (acac) ),
The lowest energy geometries, using the density func-
tional theory (DFT) and the Gaussian09 software,
were measured. The DFT/B3LYP/LANL2DZ theory
level was used. For the optimization of geometry to
achieve the lowest energy structures for FCAP ferrocenyl
3
2
2
2
and palladium acetate (Pd (CH COO) ) were purchased
3
2
from Sigma-Aldrich. C, H, and N contents were deter-
mined using a CHNS-932 (LECO) Vario elemental ana-
1
13
lyzer. DMSO-d reported H and C NMR spectra on a
6
2+
2+
2+
2+
JEOL AL-300 FT-NMR multinuclear spectrometer. The
Shimadzu UV-3600 UV–vis–NIR spectrophotometer was
imine ligand and its VO , Mn , Zn , and Pd
complexes.

ALJOHANI ET AL.
3 of 24
SCHEME 1 Diagrammatic scheme
for pathway of synthesis of the
investigated FCAP imine ligand and its
metal chelates
2.5 | Reactivity with ctDNA
spectrophotometrically
(
determined
at
480
nm
5,860 mol− cm ). Stock solutions of metal complexes
1
−1
Calf thymus DNA (ctDNA) stock solution was freshly
prepared in Tris-HCl (Tris(hydroxymethyl)aminomethane
hydrochloride) (5.0 mM) and NaCl (50.0 mM) in aqueous
(FCAPZn, FCAPPd, FCAPMn, and FCAPVO) were pre-
pared in fresh dimethyl sulfoxide (DMSO). ctDNA inter-
action with FCAPZn, FCAPPd, FCAPMn, or FCAPVO
complex was monitored by the control of pH with the
progressive addition of 1.0 × 10 mol dm from ctDNA
at pH = 7.5.
ꢁ
media and then adjusted at pH = 7.5 and stored at 4 C
[
3,4,19]
−3
−3
for 4 days according to the standard method.
absorbance of ctDNA stock solution was detected at
60 nm (UV region) and the molar absorptivity coefficient
The
2
−1
−1
(
ε) was found to be 6,600 mol cm . Consequently, for
the stock solution of ctDNA, it is important that the ratio
of UV absorbance at 260 and 280 nm, A260/A280, be >1.8
because it is indicative that the ctDNA solution is suffi-
2.5.1 | UV–vis spectrophotometric
titration
[24,25]
ciently free of protein.
Ethidium bromide (EB) was
UV–vis spectra were obtained at different [ctDNA] con-
centrations added to given [FCAPZn], [FCAPPd],
used as standard and its concentration was
a

4
of 24
ALJOHANI ET AL.
[
FCAPMn], or [FCAPVO] concentrations in fresh DMSO
where t is the fluidity time for the compounds and
[3,4,19]
ꢁ
according to known method.
of ctDNA were measured concerning blank solution that
includes all additions except the tested compound. The
The absorbance values
ctDNA, whereas t is the total time of fluidity of complex.
ꢁ
The relative values of viscosity (η/η ) were estimated
from plot of viscosity against 1/R. R values could be
binding constant (K ), which represents interaction
deduced from Equation 5:
b
strength of each tested compound with ctDNA, was
obtained from Equation 1. 24–27]:
[
½DNAꢂ
R =
:
ð5Þ
½Compoundꢂ
½
DNAꢂ ½DNAꢂ
1
=
+ Â
À
ÁÃ,
ð1Þ
ε −ε
a
ε −ε
Kb εb −εf
[DNA] is the molar concentration of ctDNA,
whereas [compound] is the molar concentration of the
complex.
f
b
f
where the molar absorptivity of unreacted, partial, and
complete reacted binding of ctDNA with checked com-
pounds (FCAPZn, FCAPPd, FCAPMn, or FCAPVO) are
ε , ε , and ε , respectively. The molar absorptivities
2.5.3 | Electrophoresis of agarose gel
f
a
b
(
εa and ε ) were extracted from plots of A
aganist
b
abs
[
compound] or ctDNA concentrations [DNA], respec-
Electrophoresis of agarose gel is considered an efficient
tively. Kb values were estimated from intercept/slope
ratio of the plots. ΔG ≠b (standard Gibb's free energy) that
assigned for interaction of ctDNA with FCAPZn,
FCAPPd, FCAPMn, or FCAPVO complex was deter-
method for studying the degradation effect of the com-
[30]
pound tested in ctDNA.
A stock solution of 20.0 mg of
FCAPZn, FCAPPd, FCAPMn, or FCAPVO complex in
dimethylformamide (DMF; 20.0 ml) was prepared. The
25.0-μM complex was then combined with extracted
[28]
mined from Equation 2
:
ꢁ
DNA (from ctDNA) and kept for 1 h at 37 C for incuba-
≠
ΔG = −RTlnK :
ð2Þ
tion. A mixture sample (30.0 μl) was then taken and
poured into an equimolar ratio of 1:1 bromophenol blue
dye and then moved to the electrophoresis chamber
wells. This is in parallel with the regular pure DNA
marker sample in the TBE buffer solution, that is, 50-mM
Tris-base at pH 7.2 combined with 1.0-mM
ethylenediaminetetraacetic acid (EDTA)/1.0 L. Gel run-
ning was tracked by adding 60 V to the electrophoresis
b
b
The chromism values could be determined through
Equation 3:
Afree −Abonding
chromism,% =
,
ð3Þ
Afree
where Afree is the absorbance of free compounds
FCAPZn, FCAPPd, FCAPMn, or FCAPVO) and Abonding
is the absorbance of each complex with alternative
ctDNA concentrations at λmax
[
18,30]
(
chamber for ꢃ45 min.
By taking images with the
Panasonic DMC-LZ5 Lumix genius 3, the agarose gel is
[
18,30]
.
recorded in ctDNA gel.
2
.5.2 | Hydrodynamic reactions
2.6 | Biological assay: Antibacterial and
antifungal activities
(viscosity method)
The Oswald microviscometer was used to evaluate the
relative viscosities of interacted compounds. Hence, eval-
uation for hydrodynamic interaction between current
compounds (FCAPZn, FCAPPd, FCAPMn, or FCAPVO)
with ctDNA at room temperature was performed
As discussed in our previous publications, in vitro anti-
fungal and antibacterial activities of FCAP ligand and its
metal chelates were evaluated by the well diffusion
[
21–25]
method.
Antifungal action of the investigated
ferrocenyl azomethine chelates was tested for the
inhibition of Aspergillus flavus, Getrichm candidum, and
Fusarium oxysporum fungi, and antibacterial activity was
checked on Serratia marcescence, Escherichia coli, and
Micrococcus luteus bacteria. Ofloxacin and fluconazole
have been taken as a standard for the testing of bacterial
and fungal action. To ensure precision, all the measure-
ments were reported in duplicate for the ligand and the
complexes.
[17–19]
according to reported method.
In the presence and
absence of ctDNA under inert N gas bubbling condi-
2
tions, the fluidity time (s) for different complex concen-
trations (from 5.0 to 50.0 μM) could be calculated by
[29]
applying it in Equation 4
:
ꢁ
t−t
t
η =
,
ð4Þ
ꢁ

ALJOHANI ET AL.
5 of 24
2.6.1 | MIC and index of activity (A)
and serial dilutions were applied by using tested com-
pounds. Cells were incubated at 37 C for 48 h under 15%
ꢁ
A number of different FCAP, FCAPZn, FCAPPd,
FCAPMn, and FCAPVO concentrations were tested for
minimum inhibitory concentration (MIC) determination
of their antimicrobial potential. Clear inhibition zones
were appeared and measured in millimeter, and the
activity index percent were calculated as from
(v/v) CO -humidified atmosphere, and then, SRB was
2
applied. Vinblastine was used as the standard and the
corresponding IC50 values were determined in
[
32]
Equation 8
:
ControlOD −CompoundOD
IC50ð%Þ =
× 100:
ð8Þ
[31]
Equation 6
:
ControlOD
A = inhibition zone ðmmÞ=standard drug inhibition zone
ðmmÞ × 100:
ð6Þ
3
| FINDINGS AND DISCUSSION
2.7 | DPPH activity of free radical
3.1 | Description
scavenging
The traditional condensation method was used to synthe-
size the ferrocinyl complexes studied. Physicochemical
properties of the titled azomethine organometallic ligand
and its V (IV)O, Mn (II), Pd (II), and Zn (II) chelates
were given in Table 1. All of the complexes are colored
and thermally stable at room temperature. The titled
azomethine organometallic compounds were soluble in
absolute alcohol, DMF, and DMSO but were insoluble in
organic solvents like on non-polar organic solvents such
as benzene and toluene.
The free radical scavenging screening of FCAP, FCAPZn,
FCAPPd, FCAPMn, and FCAPVO compounds was exam-
ined with the scavenging of DPPH radical. The decay in
the purple color of the methanolic solution of DPPH to
pale yellow color was followed spectroscopically.
A 2.40-ml methanol of 0.1-mM DPPH was dropewisely
poured to an aqueous solution of 100-μM FCAP,
FCAPZn, FCAPPd, FCAPMn, or FCAPVO. The resulted
mixed solution was vortexed in a dark atmosphere for a
ꢁ
half hour (25 C). Measuring of the molar absorptivity of
the resulted solution at λ = 517 nm was achieved spectro-
1
photometrically. Involving vitamin C, that is, ascorbic
3.2 | H NMR spectra and vibrational
[4]
acid, was important for a positive control. Methanol
and a blank sample (without DPPH) were also performed
for comparative negative monitoring. The capacity of
DPPH radical screening percentages was predestined
within Equation 7:
properties data
The FCAP ligand HNMR spectrum shows a proton signal
of CH N at 9.60 ppm. Ferrocene protons may be associ-
ated with multiple signals observed in the 4.80–4.27 ppm
[
33]
range.
These signals appeared almost in the same
%
Reduction of absorbance = ½ða−bÞ=aꢂ × 100,
ð7Þ
range in the FCAPPd and FCAPZn complexes. The aro-
matic protons of the benzene ring were allocated to mul-
[34]
where a is the blank sample absorption and b is the
checked sample absorption.
tiple signals within the range of 6.00–7.11 ppm.
At
8.75 ppm, a single signal appeared linked to the phenolic
proton that disappeared in the complexes of FCAPPd and
FCAPZn. The free ligand IR spectra vary from those of
their complexes and provide important indications about
the ligand binding sites. In comparison with its FCAPPd,
FCAPZn, FCAPMn, and FCAPVO complexes, the experi-
mentally observed IR (Fourier transform [FT]-IR) peaks
of the organometallic ferrocenyl FCAP imine ligand are
recorded in Table 1. The IR spectra of the FCAP ligand
and its FCAPPd complex are given in Figure S1, as typi-
cal examples. The change in the functional groups' wave-
length range indicates that complexes are formed with
metal ions and ligand. It was inferred from the data that
all complexes showed a substantial shift in the ν(C N)
2
.8 | Anticancer activity
Anticancer properties of newly synthesized FCAP,
FCAPZn, FCAPPd, FCAPMn, or FCAPVO were evalu-
ated spectrophotometrically against hepatocellular carci-
noma (HepG-2), breast adenocarcinoma (MCF-7), and
colon carcinoma (HCT-116) cell lines. Such was done by
employing sulforhodamine B (SRB) stain assay according
to reported method.
assay (ELISA) microplate reader (Meter tech.
60, “USA”) was used to record absorbance at 564 nm.
[10]
Enzyme-linked immunosorbent
Σ
9
4
−1
Cells were seeded in 96-multiwell plates, 10 cells/well,
(azomethine) band from higher (1,593 cm ) to lower

6
of 24
ALJOHANI ET AL.
−
1
(
1,570–1,579 cm ) frequencies, confirming its coordina-
[35]
tion with metal ion.
The observed peaks in the spectra
–1
of the complexes in the region between 558–588 cm
and 436–468 cm– belong M-O, M-N vibrational modes
1
and confirms the coordination of the azomethine group
to the investigated cations.
[
36]
In the FCAPZn complex, the characteristic frequen-
cies of the coordinated nitrate group have three non-
−
1
−1
degenerate modes at 1,461 cm (NO )asy, 1,348 cm
(
2
−
1
NO )sy, and 845 cm (NO). The difference between the
2
two highest frequency bands (ν = νasy_ ν ) is 113 cm ,
−
1
sy
implying that nitrate ion (NO ) in the solid complex coor-
3
[22]
dinates to Zn (II) ion in a unidentate manner.
The
FCAPVO complex displays an additional band at
1
9
39 cm− due to the V = O frequency, in addition to the
[
2]
other bands. Two strong to medium bands were identi-
fied at 1,540 and 1,320 cm− for the prepared FCAPPd
complex that could be assigned (asyCOO ) and (syCOO )
vibrations of the acetate group carboxylate ion. The
difference between the vibrations of asymmetric and
symmetric stretching vibration [(asyCOO ) − (syCOO )]
was found to be 210 cm , which corresponds to mono-
dentate ligation.
1
−
−
−
−
−
1
[
5]
3.3 | Elemental analyses and molar
conductivity measurements
The physical characterization data, microanalytical data,
and values of molar conductance for the investigated
complex samples are entered in Table 1. Each value cor-
responds to the above samples found to be in good agree-
ment with the deduced molecular composition including
FCAP ligand and its complexes. Due to the synthesized
complexes being non-electrolytic, the DMF solution of
these metal complexes shows lower molar conductance
−
1
−1
2
values (8.45–14.20 Ω mol cm ) that represent the
absence of anion in the outer sphere of the
[
37,38]
complexes.
3.4 | Electronic spectra and magnetic
moment measurements
The FCAP UV–vis absorption spectra in EtOH are com-
patible with most ferrocenyl chromophores in which they
demonstrate two charge transfer bands (cf. Figure 1 and
Table S1). For the investigated compounds, the spectra
contain a prominent absorption band with a maximum
of 237–252 nm that can be ascribed to a high-energy
ligand-based electronic transition п-п*. In addition, the
absorption band in the visible region is observed at
352 nm, which is assigned to the intraligand band of

ALJOHANI ET AL.
7 of 24
The magnetic moment (μ ) of titled metal azome-
eff
thine chelates, shown in Table 1, is 1.81 for V (IV)O. This
value indicates that the FCAPVO complex with a square
[
40]
pyramidal geometry is paramagnetic,
where the
FCAPMn complex is paramagnetic with μeff of 5.43, indi-
cating octahedral structure. Diamagnetic behavior with
zero μeff value of FCAPZn and FCAPPd complexes
suggests that they have tetrahedral and square planar
[
41]
geometry, respectively.
3.5 | Powder X-ray diffraction analysis
for the investigated FCAP complexes
Single crystal growth of synthesized compounds from dif-
ferent solvents, including ethanol, methanol, chloroform,
acetonitrile, and DMF, does not achieve single crystal
growth. However, the subtle crystalline nature of com-
pounds is obtained, which is not sufficient for single crys-
tal studies and is thus used to measure the degree of
compound crystallinity. In order to gain more information
about the formation of complexes and the structure of
complexes, X-ray diffraction was carried out. The X-ray
diffractogram of synthesized complexes (see Figure 2) was
FIGURE 1 Comparable spectral electronic scans of FCAP
ligand and its FCAPZn, FCAPPd, FCAPMn, and FCAPV complexes
ꢁ
in ethanol media at 25 C
FCAP compound. In addition, the absorption band
observed within the region of 413–426 nm could be
ascribed to the metal–ligand charge transfer (MLCT) pro-
[39]
cess.
The weak d-d transitions in the Schiff bases were
ꢁ
observed within the region of 485–493 nm.
scanned at wavelength 1.5406 Å in the range 5–100 (θ),
FIGURE 2 Powder X-ray pattern for the prepared FCAP complexes

8
of 24
ALJOHANI ET AL.
which gives the essence of their crystallinity. The powder
XRD patterns display the crystalline character of the
complexes, as shown in Figure 2. The presence of crystal-
linity in the organometallic Schiff base complexes is due
4. The positive ΔG sign points to the non-spontaneous
nature of decomposition steps. Also, increasing the
negative value of TΔS leads to a sequenced increase in
[
44]
ΔG values.
[
42]
to the metallic compounds' intrinsic crystalline nature.
3
.7 | Stoichiometry and formation
3.6 | TGA and its kinetic aspects of the
constants of complexes
investigated organometallic FCAP
complexes
The stoichiometry of new complexes that developed in
solution between FCAP and each metal salt (V (IV)O,
Mn (II), Pd (II), and Zn (II)) was evaluated by continuous
variations and molar ratio routes. The curves obtained
from continuous variation and molar methods
(cf. Figures 3 and S3) show maximum absorbance at mole
fraction equal to 1 M:1 L in the molar ratio for Pd
(II) and Zn (II) and 1 M:2 L for V (IV)O and Mn (II).
Although the acceptable difference in complex composi-
tion is prepared in either solid state or solution, congru-
ence gives an enhancement to the composition proposed
The thermal decomposition method of the metal com-
plexes was analyzed using the TGA technique, and the
thermokinetic parameters were estimated. The tempera-
ture ranges, number of stages, stages of degradation, deg-
radation product loss, the calculated and found weight
loss percentage, and finally, the residues of all com-
pounds were given in Table 4. On heating of the
FCAPMn complex within the temperature range
ꢁ
3
5–120 C, two hydration molecules of water with a mass
[
45]
loss = 4.93% (calc. = 4.90%) (cf. Figure S2) were liberated.
The second step was the loss of two coordinated water
for solid complexes.
Also, the formation constant (Kf)
of each complex was calculated from the continuous vari-
ation method (cf. Table 3). Accordingly, the order of sta-
bility of the complexes was proposed as follows:
FCAPMn > FCAPVO > FCAPPd > FCAPZn complex.
Furthermore, Gibbs free energy values were additionally
ꢁ
molecules at 122–180 C with a mass loss = 4.86%
(
calc. = 4.90%). The third and fourth steps were observed
ꢁ
within the range 182–370 C, corresponding to the loss of
part of the ligand with a formula C H with a mass
20
18
loss = 35.06% (calc. = 35.14%). The fifth and six stages
obtained to indicate the spontaneous nature of complex
ꢁ
[46]
were carried out within the range 372–535 C,
formation.
Based on the spectral and physical data of
corresponding to the loss of C H N O fragment leav-
the complexes discussed above, it can be derived that
through the deprotonated oxygen and the azomethine
molecule, metal ions were attached to the Schiff base
ligand, and the structure representation of the complexes
was delineated in Scheme 1.
14
10 2 2
ing mixture of MnO + 2FeO as residue. The same behav-
ior was observed for the rest of the complexes as shown
in Table 2. The data obtained from TGA were correlated
with CHN and confirmed the suggested formula for the
prepared complexes.
Kinetic and thermodynamic parameters were calcu-
lated for all tested complexes over all degradation steps.
The obtained values were aggregated (Table 2) and reveal
the following notices.
3.8 | pH stability range of complexes
The pH profile of the complexes displayed typical dissoci-
ation curves (cf. Figure 4), and the stability range is high
up to pH = 4–9. A noticeable wide steady range of pHs
reflects stability complexes than their free ligand. So, the
different applications on such complexes over the
pH = 4–9 range may happen without affection.
1
. The higher the activation energy values, the higher the
stability of the compound except the first step. Such a
step has the lowest activation energy in agreement
with the easiest removal of crystal water molecules.
. The negative ΔS sign suggests a degradation via an
abnormal pathway for those steps, and the degrada-
tion processes are undesirable. It is also evidence for a
more ordered and organized activated complex. This
can occur through the chemisorption of oxygen and
other decomposition products. The more organized
nature will refer to the activated state's bond polariza-
2
3.9 | DFT calculations
3.9.1 | Molecular DFT ligand FCAP
calculation
[
43]
tion that takes place during electronic transitions.
The optimized FCAP structure is described in Figure 5 as
the lowest energy configurations. The natural charges
obtained from the natural bond orbital (NBO) analysis
3
. The positive ΔH sign indicates the endothermic state
of decomposition steps.

ALJOHANI ET AL.
9 of 24

10 of 24
ALJOHANI ET AL.
FIGURE 3 The curves of Job's method of synthesized FCAP
complexes in DMF at [M] = [FCAPM] = 10−3 M at 298 K
FIGURE 4 Impact of pH on FCAPZn, FCAPPd, FCAPMn, and
ꢁ
FCAPV complexes at 25 C in aqueous media
indicate that O9(−0.625) > N2(−0.581) and Fe(0.218) are
the more negative active sites. Therefore, bidentate coor-
dination is preferred by metal ions to O9 and N2, forming
a stable five-membered ring.
3.9.2 | Molecular DFT complex FCAPVO
calculation
The optimized structure of the complex FCAPVO is
shown in Figure 6 as the lowest energy configurations. In
a distorted square pyramidal geometry, where the atoms
ꢁ
N2, O9, N54, and O56 deviate from the plane by −13.31 ,
FIGURE 5 The optimized structure of FCAP by density
the vanadium atom is five-coordinate (Table 4).
V(+0.881), O56(−0.687), O9(−0.662), O31(−0.430), N54
function B3LYP/LANL2DZ
(
−0.485), and N9(−0.483) are the natural charges com-
puted from the NBO analysis on the coordinated atoms.
In a distorted octahedral geometry, the manganese atom
is six-coordinate, where the atoms (N2, O9, N61, and
O61), (O9, O36, O64, and O68) and (N2, O36, N61, and
O68) are deviated by −10.23, −7.750, and −11.64 from
the plane, respectively (Table 4). From the NBO analysis,
the natural charges calculated on the coordinated atoms
are Mn(+0.644), O9(−0.671), O64(−0.598), O68(−0.885),
O61(−0.855), N61(−0.514), and N2(−0.478).
3.9.3 | Molecular DFT complex FCAPMn
calculation
The optimized structure of the complex FCAPMn is pres-
ented in Figure 6 as the lowest energy configurations.
ΔG (KJmol−1)
*
TABLE 3 The formation and
Complex
FCAPMn
FCAPZn
FCAPPd
FCAPVO
Type of complex
K
f
Log K
7.88
f
stability constants and Gibbs free
7
4
4
7
1:2
1:1
1:1
1:2
7.62 × 10
2.71 × 10
4.31 × 10
5.15 × 10
−44.97
*
energy Δ(G ) values of the investigated
4.43
−25.29
FCAP metal chelates at 298 K
4.63
−26.44
7.71
−43.99

ALJOHANI ET AL.
11 of 24
FIGURE 6 The optimized structure of (a) FCAPVO, (b) FCAPMn, (c) FCAPPd, and (d) FCAPZn complexes using B3LYP/LANL2DZ
ꢁ
TABLE 4 Significant optimized bond angles ( ) and bond lengths (Å) of the prepared FCAP metal chelates
ꢁ
ꢁ
Angle ( )
Complex
Bond type
V=O31
V-O9
Bond length (Å)
1.610
Angle type
O31-V-N2
Angle ( )
100.9
100.4
115.9
117.4
158.6
173.6
83.91
89.35
76.29
89.16
94.96
86.34
173.1
171.3
160.2
Angle type
O9-V-N2
FACPVO
79.55
80.90
1.905
O31-V-N54
O31-V-O9
O56-V-N54
O9-V-N54
V-O56
V-N2
1.913
92.01
2.133
O31-V-O56
O56-V-N2
88.45
V-N54
2.144
N2-V-N54
O9-V-O56
126.6
Fe20-V-Fe45
O64-Mn-N61
O64-Mn-N2
O68-Mn-O9
O68-Mn-O64
O68-Mn-N2
O68-Mn-N61
N2-Mn-N61
O36-Mn-O68
Fe20-Mn-Fe50
N2-O9-N54-O56
O9-Mn-N2
−13.31*
80.68
FACPMn
Mn-O9
Mn-O54
Mn-O36
Mn-N2
1.919
1.872
1.980
2.064
2.031
2.119
O9-Mn-N61
106.2
O36-Mn-O9
95.23
O36-Mn-O64
O36-Mn-N2
99.54
Mn-N61
Mn-O68
85.48
O36-Mn-N61
O9-Mn-O61
94.26
161.5
N2-O9-N61-O64
O9-O36-O64-O68
N2-O36-N61-O68
O36-Pd-O37
O9-Pd-O36
−10.23*
−7.750*
−11.64*
73.14
FACPPd
Pd-O9
Pd-O36
Pd-N2
1.991
2.050
2.057
2.181
N2-Pd-O9
N2-Pd-O37
N2-Pd-O36
83.13
105.1
177.2
98.53
O9-Pd-O37
171.0
Pd-O37
O9 N2-O37-O36
1.114*
(
Continues)

12 of 24
ALJOHANI ET AL.
TABLE 4 (Continued)
ꢁ
ꢁ
Complex
Bond type
Bond length (Å)
1.965
Angle type
N2-Zn-O9
Angle ( )
Angle type
O37-Zn-O40
Angle ( )
FACPZn
Zn-O9
Zn-N2
84.66
116.0
126.5
109.5
90.72
125.8
2.081
N2-Zn-O40
N2-Zn-O37
O9-Zn-O37
O9-Zn-O40
FIGURE 7 Molecular electrostatic potential (MEP) surface of FCAP and complexes FCAPVO, FCAPMn, FCAPPd, and FCAPZn
TABLE 5 Estimated energies of FCAP ligand and its metal chelates at B3LYP/LANL2DZ
E (a.u.)
−910.10
−1198.10
−2075.16
−1341.17
−1331.90
HOMO (eV)
−5.6885
LUMO (eV)
−1.8683
E
g
(eV)
Dipole moment (Debye)
FCAP
3.8202
3.2567
0.6193
2.9887
3.1571
4.7194
11.950
11.8283
9.6167
6.7733
FCAPVO
FCAPMn
FCAPPd
FCAPZn
−8.5940
−5.3373
−3.6915
−3.0722
−5.5152
−2.5265
−5.4883
−2.3312
Note. E is the total energy (a.u.). E
g
= ELUMO − EHOMO.
Abbreviations: HOMO, highest occupied molecular orbital; LUMO, lowest unoccupied molecular orbital.

ALJOHANI ET AL.
13 of 24
3
.9.4 | Molecular DFT complex FCAPPd
a distorted tetrahedral geometry, the zinc atom is four-
coordinate. From the NBO analysis, the natural charges
computed on the coordinated atoms are Zn(+1,398),
O9(−0.876), N2(−0.641), O40(−0.608), and O37(−1.001).
The surface of the molecular electrostatic potential
(MEP) to locate the positive (blue color) and negative
(red color, excess electrons or loosely bound) charged
electrostatic potential in the molecule is shown in
Figure 7. The computed total energy, the lowest
unoccupied molecular orbital (LUMO) energies, the
highest occupied molecular orbital (HOMO) energies,
and the dipole moment for the FCAP ferrocenyl imine
ligand and its metal chelates were calculated (Figure S4
and Table 5). The complexes' more negative total energy
values than those of free FCAP ligand suggest that they
are more stable than free FCAP ligand.
calculation
The optimized structure of the FCAPPd complex is
shown in Figure 6 as the lowest energy configurations. In
a distorted square planar geometry, the palladium atom
is four-coordinate, where the atoms O9, N2, O37, and
ꢁ
O36 are deviated by 1.114 from the plane (Table 4).
From the NBO analysis, the natural charges computed
on the coordinated atoms are Pd(+0.727), O9(−0.616),
N2(−0.478), O36(−0.797), and O37(−0.937).
3.9.5 | Molecular DFT complex FCAPZn
calculation
The optimized structure of the complex FCAPZn is
shown in Figure 6 as the lowest energy configurations. In
3
.10 | DNA binding studies for the
investigated complexes
3.10.1 | Absorbance spectral studies
UV–vis absorbance is the most valuable tool to evaluate
the mode of the interaction and the binding ability of
interesting small molecules and their corresponding
M-complexes with ctDNA. The latter interaction with
complexes is derived either from hypochromism or
bathochromism, as the binding usually includes a strong
interaction between the DNA nitrogen bases and the
ligand (e.g., aromatic moiety). Furthermore, the metal
chelate could bind to the double-stranded DNA within
different interaction modes depending on its charge,
[
16]
structure, and nature of the molecule.
Generally, shifts
and/or changes in the absorbance characteristic bands of
the M-chelate could be observed, when it interacts with
FIGURE 8 FCAPMn complex absorption spectra at
−3
0
.01 mol dm Tris buffer (pH 7.5, 298 K) after addition of ctDNA
[
18,30]
in absence (lower) and ctDNA presence (top) at
DNA.
The strength of such interaction could be cor-
3
[
FCAPMn] = 10− mol dm−3 and [ctDNA] (0–50) μm
related with the magnitude of such shift and/or change
TABLE 6 Spectral parameters for the interaction of the investigated FCAP metal chelates with DNA
*
λ
max
λ
max
Chromism
Δn (%)
Type of
chromism
Binding constant
10 (K )
b
ΔG
4
(KJmol−1)
Complex free (nm)
bound (nm)
FCAPMn
426
38
420
435
9
2
3
2
1
2
9
1
9
2
25.00
4.76
Hypo
Hypo
Hypo
Hypo
Hypo
Hypo
Hypo
Hypo
Hypo
Hypo
3.26
−25.75
2
236
FCAPPd
423
22.47
19.05
8.85
6.80
−27.60
3
2
2
20
47
39
318
248
237
6.60
FCAPVO
FCAPZn
426
39
424
38
435
32.22
4.27
2.20
5.70
−24.80
−27.10
2
238
433
29.91
3.32
2
236

14 of 24
ALJOHANI ET AL.
in the absorbance. For the covalent binding, a labile coor-
dinated ligand in the M-complex could be replaced by the
nitrogen base of DNA such as guanine N7 (e.g., solvent
and DNA in solution. Hydrodynamic measurements are
sensitive to the change of the DNA molecule nature, that
is, the length and bending, which may take place as a
result of its different binding modes with the complex
compounds.
[47]
molecules).
On the other hand, all the electrostatic
interaction, the intercalative action, and groove (surface)
binding of the M-chelating complexes outside the DNA
helix, along the minor or major groove, could be consid-
From Figure 9, the plotting of the relative viscosity
1/3
(η/η) against r = the ratio of [complex]/[DNA] (form
0–0.5 mM) assigned a significant enhancement in the rel-
ative viscosity of DNA with improving the M-complex
concentration. Each probe is similar to that positive inter-
[27]
ered as non-covalent interactions.
Within the inter-
calative interaction mode, the π* orbital of the intercalated
ligand in its M-complex could couple with the π orbital of
the DNA base pairs, causing a decrease in the π ! π* tran-
[
48]
calator reference EB.
Therefore, the overall increase in
[18,20]
sition energy and resulting in hypochromism.
DNA length and viscosity may be due to the intercalation
between the DNA base pairs and the M-complexes. Col-
lectively, the viscosity results and the molecular docking
studies are in good agreement and suggest base pair
intercalation mode.
Accordingly, the binding capability of FCAPZn,
FCAPPd, FCAPMn, and FCAPVO complexes with
ctDNA was investigated by measuring their electronic
spectral variation during the DNA interaction (Figures 8
and S5). The representative spectra show that the absorp-
tion bands of each investigated complex were affected
upon increasing amounts of DNA. This points to a hypo-
chromic effect derived from the interaction of the investi-
gated complexes with ctDNA. On the other hand, the
hyperchromic shift suggests electrostatic interaction
between negatively charged DNA and electropositive
3.10.3 | Gel electrophoresis for the
interaction between the complexes
investigated and DNA
Gel electrophoresis is an important technique for exam-
ining the nature of the binding of compounds with
nucleic acids of DNA. Comparing the DNA gels before
and after its mixing with the investigated current com-
plexes, it could be observed that the staining intensity of
molecules. The intrinsic binding constants (K ) calculated
b
from Figure S4 for the current M-complexes, as shown in
Table 6, are in the following order: FCAPZn >
FCAPPd > FCAPMn > FCAPVO complex.
3.10.2 | Viscosity measurements
Viscosity measurements were progressed to investigate
the binding mode between the synthesized complexes
FIGURE 10 The interaction of the investigated complexes
with ctDNA was studied by agarose gel electrophoresis. Lane 1:
DNA ladder, Lane 2: ctDNA + FCAPZn, Lane 3:
ctDNA + FCAPVO, Lane 4: ctDNA + FCAPPd, Lane 5:
ctDNA + FCAPMn, and Lane 6: FCAPPd complex and FCAPMn
complex
FIGURE 9 The effect of increasing the amount of the
synthesized complexes on the relative viscosities of ctDNA at
[
DNA] = 0.5 mM at 298 K

ALJOHANI ET AL.
15 of 24
the gel was slightly reduced for the mixed one with the
titled metal chelates. Particularly, with the FCAPPd com-
plex, the DNA staining intensity reduced, referring to the
strong DNA interaction with this complex, as shown in
Figure 10. Consequently, the effect of such current metal
imine chelates on the growth of the pathogenic organism
FCAPPd, FCAPMn, and FCAPVO) and DNA, alternative
binding interaction modes could be proposed. The inves-
tigated complexes interact with DNA most likely
through an electrostatic or hydrophobic interaction
mode. For example, the replacement of the FCAPZn
complex acetate group by water molecules by DNA
interaction results in a positive charge on the complex.
An electrostatic binding (see Scheme 2) was then pro-
posed in addition to intercalation and substitution in the
case of that complex. The FCAPMn complex has replace-
[
18,30]
could be attributable to their genomic interaction.
3.10.4 | The proposed mechanism for the
DNA interaction
able coordinated H O molecules. Removal of these coor-
2
dinated water molecules will lead to a flat part in the
middle of the FCAPMn complex. Therefore, the pro-
posed interaction of the FCAPMn complex, for example,
Taking together the spectral investigations and hydrody-
namic obtained between the current reagents (FCAPZn,
SCHEME 2 Suggested mechanism for FCAPZn complex interaction with DNA through (a) electrostatic and (b) minor groove binding

16 of 24
ALJOHANI ET AL.
with DNA, could be via intercalation or replacement as
presented in Scheme 3.
against M. luteus G (+) bacteria and two G (−) bacteria,
namely, S. marcescence and E. coli as well as A. flavus,
G. candidum, and F. oxysporum fungal strains. The
results are shown in Table 7, and Figure 11 is compared
with the standard antibiotics, ofloxacin (for bacteria), and
amphotericin B (for fungi). The clear zones around the
discs are the inhibition zones, measured in millimeter,
and their respective percent activity index was also tabu-
lated (Table S2).
[49]
3.11 | Antimicrobial activity of the
newly synthesized compounds
The interesting DNA binding studies of the newly synthe-
sized complexes encouraged us to further investigate
their corresponding antimicrobial activities. Mounting
reports have shown that transition metal complexes pos-
sess good antimicrobial activity. Therefore, the antimicro-
bial activity of FCAPZn, FCAPPd, FCAPMn, and
FCAPVO complexes and their uncoordinated ligand
As expected, the free ligand FCAP exhibited lower
antimicrobial activity than their corresponding com-
plexes. The antimicrobial activity of the M (II) complexes
compared with their respective uncoordinated ligand
might be interpreted employing Overtone's and Tweedy's
[
4,5,19]
[4,5,19,50]
FCAP was tested within the well diffusion method
concept.
SCHEME 3 Suggested mechanism for FCAPMn complex interaction with DNA through (a) intercalation binding and (b) replacement

ALJOHANI ET AL.
17 of 24
The microdilution method (MIC) results are in good
agreement with the well diffusion assay, and data are
given in Table S3 and presented in Figure 12. It is clear
from the data that the FCAPPd complex (MIC: 2.75, 3.25,
and 2.25 μM) has shown the best bacterial activity against
S. marcescence, E. coli, and M. luteus in comparison with
other complexes. Upon complexation, the lipophilicity of
the transition metal ions is increased due to the delocali-
zation of the π-electrons among the complex sphere. This
in turn improves the diffusion through the cell mem-
brane. Although chelation plays a significant role in the
determination of the antimicrobial behavior of the com-
plexes, other factors may also enhance and control the
antimicrobial activity of metal complexes compared with
the free ligand. These include size, dipole moment, solu-
bility, complexation sites, the redox potential of metal
ion, solubility, the bond length between the ligand and
metal, complexes geometry, steric, pharmacokinetic, con-
[
30,51]
centration, and hydrophobicity.
In addition, the var-
iation in the behavior of the metal complexes against
different microbes can also depend on the preferential
difference in the microbes' cell wall permeability. On
comparing the antimicrobial activity with other related
[52]
ferrocenyl Schiff base complexes in literature,
we
found that our compounds show potent activity than
these compounds against E. coli bacteria considering vari-
ation of the concentration of the tested compounds in the
investigation.
The anticancer activity of FCAP, FCAPZn, FCAPPd,
FCAPMn, and FCAPVO samples was examined against
three different human cancer cells, namely, HCT-116,
MCF-7, and HepG-2 cells. Doxorubicin was used as the
standard, and the corresponding IC50 values were deter-
mined and recorded in Table S4. In general, the cancer
cells' (MCF-7, HepG-2, and HCT-116) growth decreased
in a concentration-dependent manner upon treatment
with tested compounds; however, the antiproliferative
activity was less than vinblastine. Furthermore, the inves-
tigated FCAP metal chelates were more cytotoxic than
the corresponding free FCAP ligand. This might be due
[53,54]
to the presence of the metal redox-active center.
Moreover, the cytotoxicity was more pronounced against
MCF-7 compared with the other cancer cells (HepG-2
and HCT-116). Interestingly, the FCAPPd complex
exhibited superior cytotoxicity against all the three appli-
cable cell lines compared with other complexes and the
free Schiff base ligands (cf. Figure 13). These results were
in excellent agreement with that obtained from the
antimicrobial screening. On comparing the anticancer
activity with other related ferrocenyl Schiff base com-
[
52]
plexes in literature,
we found that our compounds
show potent activity than these compounds against breast
tumor cells.

18 of 24
ALJOHANI ET AL.
FIGURE 11 Histogram indicating antibacterial comparable activities of the prepared FCAP ligand and its FCAPZn, FCAPPd,
FCAPMn, and FCAPV complexes against Microccus luteus bacteria
FIGURE 12 Histogram showing minimum inhibitory concentration for the investigated compounds against the investigated bacteria
and fungi
FIGURE 13 IC50 values
against human colon carcinoma
cells (HCT-116 cell line), breast
carcinoma cells (MCF-7
cell line), and hepatic cellular
carcinoma cells (HepG-2
cell line) of the FCAP mine
ligand and its complexes

ALJOHANI ET AL.
19 of 24
FIGURE 14 Trends in the inhibition of DPPH˙ radical by the FCAP ferrocenyl FCAP imine ligand and its metal chelates
TABLE 8 The docking interaction
Receptor
Interaction
Distance (Å)
E (kcal/mol)
data calculations of FCAP, FCAPMn,
FCAPPd, FCAPZn, and FCAPVO with
the active site of the receptor of breast
cancer oxidoreductase (PDB ID: 3HB5)
FCAP
N 2
NZ LYS 248
H-acceptor
2.83 (1.85)
−13.1
FCAPPd
N 2
OE1 GLU 100
OE2 GLU 100
OE1 GLU 100
OD1 ASP 208
OE1 GLU 100
OD1 ASP 208
H-donor
H-donor
H-donor
H-donor
Ionic
3.12 (2.17)
3.14 (2.24)
2.91 (1.93)
2.95 (2.00)
2.91
−10.5
−7.9
N 2
O 38
−12.8
−17.4
−5.1
O 38
O 38
O 38
Ionic
2.95
−4.8
FCAPZn
N 2
OE1 GLU 100
OE2 GLU 100
OE1 GLU 100
OD1 ASP 208
OG1 THR 211
OE1 GLU 100
OD1 ASP 208
H-donor
H-donor
H-donor
H-donor
Metal
3.42 (2.49)
3.19 (2.28)
2.71 (1.82)
2.75 (1.89)
2.58
−2.8
−6.3
N 2
O 38
−16.3
−17.0
−0.9
O 38
FE 21
O 38
Ionic
2.71
−6.7
O 38
Ionic
2.75
−6.4
FCAPMn
O 36
OE1 GLU 235
OE1 GLU 235
OE1 GLU 235
OE1 GLU 235
H-donor
Metal
Ionic
2.83 (1.92)
2.45
−22.3
−3.3
−3.3
−5.7
FE 20
N 2
3.20
O 36
Ionic
2.83
FCAPVO
N 2
OE1 GLU 100
OD1 ASP 208
OE1 GLU 100
OE2 GLU 100
H-donor
H-donor
Metal
2.85 (1.92)
2.83 (1.91)
2.72
−6.3
−7.4
−0.9
−5.4
O 32
FE 21
FE 21
Metal
2.12
Note. The lengths of H-bonds are in brackets.

20 of 24
ALJOHANI ET AL.
3
.12 | Antioxidant activity of the
The antioxidant potential of the novel synthesized
complexes was further evaluated via the DPPH assay.
The assay relies on the decolorization (at 517 nm) of the
1,1-diphenyl-2-picryl-hydrazine radical violet color upon
the reaction of DPPH with free radical scavengers
prepared compounds via DPPH assay
Collectively, the DNA binding, antimicrobial, and anti-
cancer studies point to a potential activity of the newly
synthesized compounds. These encourage us to further
investigate their corresponding redox properties, which
may also take part in their interesting activities.
[
55,56]
(i.e., antioxidants).
The numbers of scavenged elec-
trons were stoichiometric to the reaction. Ascorbic acid
was used as a (+) control. The (−) control sample consists
FIGURE 15 2D plot of the interaction between FCAP (a) and its complexes: FCAPPd (b), FCAPZn (c), (FCAP)2Mn (d), and FCAPVO
e) with the active site of the receptor of breast cancer (PDB ID: 3hb3). With dotted curves, hydrophobic interactions with amino acid
residues are shown
(

ALJOHANI ET AL.
21 of 24
FIGURE 16 Molecular docking
simulation studies of the interaction
between FCAP (a) and its complexes:
FCAPPd (b), FCAPZn (c), FCAPMn (d),
and FCAPVO (e) with the active site of
the receptor of breast cancer (PDB ID:
3
hb3). The compound's docked
conformation is shown in the ball and
stick representation

22 of 24
ALJOHANI ET AL.
of a methanolic solution of DPPH, whereas the blank
sample is only methanol. The scavenging activity per-
centage of the investigated complexes (%) demonstrated
moderate free radical-scavenging activity compared with
ascorbic acid, as depicted in Figure 14.
groups, ligand behaved as a bidentate ligand and was
bound to metal ions. Correlation of all physicochemical
properties for the prepared complexes with DFT calcula-
tions confirms the suggested structure of the prepared
complexes. UV–vis absorption spectroscopy and hydrody-
namic and gel electrophoreses measurements were per-
formed to detect the interaction and binding mode of the
newly synthesized complexes with DNA. Collectively, the
results show that the absorption bands, as well as DNA
length and viscosity, were affected. These indicate that
the interaction of the complexes with DNA could be via
intercalation or replacement, which was further
supported by molecular docking studies. The antimicro-
bial activity of FCAPZn, FCAPPd, FCAPMn, and
FCAPVO complexes and their free ligand FCAP was eval-
uated against A. flavus, G. candidum, and F. oxysporum
fungal strains as well as M. luteus Gram-positive bacteria
and two Gram-negative bacteria, namely, S. marcescence
and E. coli. Furthermore, the antiproliferative activity of
the investigated compounds and their free ligand FCAP
was also evaluated against different cancer cells such as
3.13 | Molecular docking studies
Docking studies are regarded as a very efficient tool that
can be used to assess the Schiff base ligand's mul-
tireceptor interaction to design the resistance of drug
[
57]
against various effects that occur in our bodies.
The
2+
2+
2+
structure of the FCAP ligand and its VO , Mn , Zn ,
2+
and Pd complexes were created in PDB file format from
the output of Gaussian09 software. The crystal structures
of the receptor of breast cancer (PDB ID: 3HB5) were
downloaded from the protein data bank (http://www.
rcsb.org./pdb). The molecular docking studies were per-
formed using MOA2014 software, to find the possible
binding modes of the most active site of the receptor of
breast cancer oxidoreductase (PDB ID: 3HB5) (Table 8
and Figures 15 and 16). From the findings, it was shown
that the ligand's main interaction force was H-acceptor,
whereas some binding interaction also occurred in com-
plexes alongside the ligand's main interaction, such as
H-donor and ionic. The more negative the energy values,
the more stable (stronger interaction). Thus, the order of
binding of the prepared compounds towards the
receptor is as follows: FCAPPd > FCAPZn > FCAPVO
2
+
HCT-116, MCF-7, and HepG-2 cells. In general, the M
complexes exhibited better antimicrobial and anticancer
activities than FCAP ligand, which might be due to the pres-
ence of the metal redox-active center. Moreover, the
FCAPPd complex was the most active and inhibited the
multiplication of the bacterial and fungal strains as well as
the tested cancer cells. Additionally, the redox properties of
the synthesized complexes were also evaluated via the
DPPH assay. The tested compounds showed moderate–
good antioxidant activities, particularly against the superox-
ide anion radicals, compared with ascorbic acid.
>
FCAPMn > FCAP compound. The obtained data are
correlated with anticancer data against the breast cancer
cell line and found to be in good agreement.
CONFLICT OF INTEREST
All authors agreed to state not any conflict of interest
regarding any content or publication of this work in the
form of a manuscript.
4
| CONCLUSION
Herein, we report the synthesis of ferrocene azomethine
ligand (FCAP) and a series of its V (IV)O, Mn (II), Zn
AUTHOR CONTRIBUTIONS
(
II), and Pd (II) transition metal ions. Accordingly, differ-
Enas Aljohani: Funding acquisition; investigation;
methodology; software. Mohamed Shehata: Formal
analysis; software; supervision; validation. Fatmah
Alkhatib: Funding acquisition; methodology; resources.
Seraj Alzahrani: Data curation; funding acquisition;
investigation; methodology; resources. Ahmed Abu-
Dief: Formal analysis; funding acquisition; investigation;
methodology; resources; supervision; validation.
2+
ent M
Schiff base complexes (FCAPZn, FCAPPd,
FCAPMn, and FCAPVO) were synthesized in good yields
up to 85%) via the reaction with the corresponding
(
metal. The respective chemical structures of all the syn-
thesized compounds (FCAP, FCAPZn, FCAPPd,
FCAPMn, and FCAPVO) were in excellent agreement
with the obtained analytical data (NMR, IR, UV–vis, EA
and TGA analyses, conductance measurements, and
magnetic susceptibility). The data of elemental analysis
confirmed that the FCAP ligand reacted with metal ions
in 1:1 M ratio in the case of Zn (II) and Pd (II) and 1:2 M
ratio for V (IV)O and Mn (II). IR spectra demonstrated
that through deprotonated phenolic and azomethine
ORCID
Enas T. Aljohani https://orcid.org/0000-0001-9476-
0892
Mohamed R. Shehata https://orcid.org/0000-0003-1289-
0285

ALJOHANI ET AL.
23 of 24
Fatmah Alkhatib https://orcid.org/0000-0003-1268-
[27] L. H. Abdel-Rahman, A. A. Abdelhamid, A. M. Abu-Dief,
M. R. Shehata, M. A. Bakhe, J. Mol. Struct. 2020, 1, 127.
3
075
Seraj Omar Alzahrani https://orcid.org/0000-0001-
996-6593
Ahmed M. Abu-Dief https://orcid.org/0000-0003-3771-
011
[
28] D. Sabolova, M. Kozurkova, T. Plichta, Z. Ondrusova, D.
Hudecova, M. Simkovic, H. Paulıkova, A. Valent, Int. J. Biol.
Macromol. 2011, 48, 319.
7
[29] L. H. Abdel-Rahman, R. M. El-Khatib, L. A. E. Nassr, A. M.
Abu-Dief, M. Ismael, A. S. Amin, Spectrochim. Acta a 2014,
9
117, 366.
REFERENCES
[30] L. H. Abdel-Rahman, A. M. Abu-Dief, E. F. Newair, S. K.
Hamdan, J. Photochem. Photobiol. B 2016, 160, 18.
31] A. D. M. Mohamad, M. J. A. Abualreish, A. M. Abu-Dief,
J. Mol. Liq. 2019, 290, 162.
32] A. M. Abu-Dief, L. H. Abdel-Rahman, A. A. Abdelhamid,
A. A. Marzouk, M. R. Shehata, M. A. Bakheet, O. A.
Almaghrabi, A. Nafady, Spectrochim. Acta a 2020, 228, 700.
33] Y. H. Zhang, J. C. Yuan, W. J. Lao, Y. Q. Yin, Z. X. Huang,
J. J. Wu, J. Organomet. Chem. 2001, 628, 123.
34] M. Bal, G. Ceyhan, B. Avar, M. Kose, A. Kayraldiz, M.
Kurtoglu, Turk. J. Chem. 2014, 38, 222.
35] a) I. Kashar, Thermochim. Acta 2010, 507–508, 66;
b) A. Elshafaie, L. H. Abdel-Rahman, A. M. Abu-Dief, S. K.
Hamdan, A. M. Ahmed, E. M. M. Ibrahim, Nano 2018, 13,
[
[
[
1] T. Thirunavukkarasu, H. A. Sparkes, K. Natarajan, V. G.
Gnanasoundari, Inorg. Chem. Acta 2018, 437, 255.
[
[
2] L. H. Abdel-Rahman, A. M. Abu-Dief, M. O. Aboelez, A. A. H.
Abdel-Mawgoud, J. Photochem. Photobiol.B. 2017, 170, 271.
3] L. H. Abdel-Rahman, M. S. Adam, A. M. Abu-Dief, H.
Moustafa, M. Basha, A. H. Aboria, B. S. Al-Farhan, H.
El-Sayed Ahmed, Appl. Organomet. Chem. 2018, 32, e4527.
4] A. M. Abu-Dief, H. M. El-Sagher, M. R. Shehata, Appl.
Organomet. Chem. 2019, 33, e4943.
[
[
[
[
[
[
[
5] A. M. Abu-Dief, L. H. Abdel-Rahman, A. A. Hassan
Abdel-Mawgoud, Appl. Organomet. Chem. 2020, 34, e5373.
6] T. K. Goswami, B. V. S. K. Chakravarthi, M. Roy, A. A.
Karande, A. R. Chakravarty, Inorg. Chem. 2011, 50, 8,452.
7] M. Topçu Sulak, Ö. Gökdogan, A. Gülce, H. Gülce, Biosens.
Bioelectron. 2006, 21, 1719.
1850074; c) E. M. M. Ibrahim, L. H. Abdel-Rahman, A. M.
Abu-Dief, A. Elshafaie, S. K. Hamdan, A. M. Ahmed, Phys.
Scr. 2018, 93, 055801.
[
8] C. Ornelas, New J. Chem. 2011, 35, 1973.
[
[
36] N. Gupta, S. Chandra, Spectrochim. Acta a 2005, 61, 1175.
37] I. Ali, W. A. Wani, K. Saleem, Synth React Inorg Met Org Chem
[
9] F. Zhao, Z. Q. Liu, J. Phys. Org. Chem. 2009, 22, 791.
[
10] A. M. Abu-Dief, I. F. Nassar, W. H. Elsayed, Appl. Organomet.
Chem. 2016, 30, 917.
11] O. N. Kadkin, G. Yu, Russ, Chem. Rev. 2012, 81, 675.
12] C. Bizzarri, V. Conte, B. Floris, P. Galloni, J. Phys. Org. Chem.
011, 24, 327.
13] Y. Yuanyuan, Synth. React. Inorg. Met. Org. Chem. 2015, 45,
788.
14] B. Delavaux-Nicot, R. Mathieu, D. Montauzon, G. Lavigne,
J. P. I. Majoral, Inorg. Chem. 1994, 33, 434.
2013, 43, 1,162.
[
38] a) L. H. Abdel-Rahman, A. M. Abu-Dief, M. S. S. Adam, S. K.
Hamdan, Catal. Lett. 2016, 146, 73; b) L. H. Abdel-Rahman,
N. M. Ismail, M. Ismael, A. M. Abu-Dief, E. A.-H. Ahmed,
J. Mol. Struct. 2017, 1134, 851.
[
[
2
[
[
[
[
[
39] V. S. Elanchezhian, M. Kandaswamy, Inorg. Chem. Commun.
1
2009, 12, 16.
[
[
40] N. A. El-Wakiel, Appl. Organomet. Chem. 2016, 30, 664.
41] M. Gaber, H. A. El-Ghamry, S. K. Fathalla, Spectrochim. Acta
a 2015, 139, 396.
42] V. P. Tamilenthi, Arch. Appl. Sci. Res. 2010, 1, 57.
43] H. Katouah, A. M. Hameed, A. Alharbi, F. Alkhatib, R. Shah,
S. Alzahrani, R. Zaky, N. M. El-Metwaly, ChemistrySelect 2020,
15] K. Tamas, B. Péter, S. Daniele, M. Giovanni, D. Patrick, Inorg.
Chim. Acta 1995, 239, 145.
16] S. A. Mohd Sukri, L. Y. Heng, N. H. Abd Karim, J. Fluoresc.
[
[
2
017, 27, 1,009.
[
[
17] A. M. Abu-Dief, L. A. E. Nassr, J. Iran. Chem. Soc. 2015, 12, 943.
18] L. H. Abdel-Rahman, A. M. Abu-Dief, R. M. El-Khatib, S. M.
Abdel-Fatah, J. Photochem. Photobiol. B 2016, 162, 298.
19] L. H. Abdel-Rahman, A. M. Abu-Dief, M. R. Shehata, F. M.
Atlam, A. A. H. Abdel-Mawgoud, Appl. Organomet. Chem.
5
, 10256.
[
44] M. Montazerozohori, S. MojahediJahromi, A. Masoudiasl, P.
McArdle, Spectrochim. Acta a 2015, 5, 517.
[
[
[
45] S. S. Shah, R. G. Parmar, Pharma Chem. 2011, 3, 318.
46] a) L. H. Abdel-Rahman, R. M. El-Khatib, L. A. E. Nassr, A. M.
Abu-Dief, Arab J Chem 2017, 10, S1835; b) S. I. Al-Saeedi,
L. H. Abdel-Rahman, A. M. Abu-Dief, S. M. Abdel-Fatah,
T. M. Alotaibi, A. M. Alsalme, A. Nafady, Catalysts 2018,
2
019, 33, e4699.
[
[
[
[
[
[
[
20] A. M. Abu-Dief, L. H. Abdel-Rahman, M. R. Shehata, A. A.
Hassan Abdel-Mawgoud, J. Phys. Org. Chem. 2019, 32, e4009.
21] L. H. Abdel-Rahman, A. M. Abu-Dief, M. Ismael, M. A. A.
Mohamed, N. A. Hashem, J. Mol. Struct. 2016, 1, 232.
22] L. H. Abdel-Rahman, A. M. Abu-Dief, H. Mostafa, S. K.
Hamdan, Appl. Organomet. Chem. 2017, 31, e3555.
23] L. H. Abdel-Rahman, A. M. Abu-Dief, H. Moustafa, A. A. H.
Abdel-Mawgoud, Arab J Chem 2020, 13, 649.
24] L. H. Abdel-Rahman, A. M. Abu-Dief, R. M. El-Khatib, S. M.
Abdel-Fatah, Bioorg. Chem. 2016, 69, 140.
8
, 452.
47] M. S. S. Adam, O. M. El-Hady, F. Ullah, RSC Adv. 2019, 9,
4311.
[
[
[
3
48] E. M. Zayed, M. A. Zayed, A. M. M. Hindy, G. G. Mohamed,
Appl. Organomet. Chem. 2018, 32, e4603.
49] L. H. Abdel-Rahman, M. S. Adam, A. M. Abu-Dief, H. E.-S.
Ahmed, A. Nafady, Molecules 2020, 25, 5089.
25] L. H. Abdel-Rahman Ahmed, M. Abu-Dief, R. M. El-Khatib,
S. M. Abdel-Fatah, Int. J. Nano. Chem. 2018, 4, 1.
26] L. H. Abdel-Rahman, R. M. El-Khatib, L. A. E. Nassr, F. E. D.
Lashin, Spectrochim. Acta a 2013, 111, 266.
[50] L. H. Abdel-Rahman, A. M. Abu-Dief, N. M. Ismail, M.
Ismael, Inorg. Nano-Met. Chem. 2017, 47, 467.
[51] L. H. Abdel-Rahman, A. M. Abu-Dief, S. K. Hamdan, A. A.
Seleem, Int. J. Nano. Chem. 2015, 1, 65.

24 of 24
ALJOHANI ET AL.
[
[
[
[
52] W. H. Mahmoud, R. G. Deghadi, G. G. Mohamed, Arab.
J. Chem. 2020, 13, 5390.
53] S. Terpilowska, A. K. Siwicki, Chem. Biol. Interact. 2019,
How to cite this article: Aljohani ET,
Shehata MR, Alkhatib F, Alzahrani SO, Abu-
Dief AM. Development and structure elucidation
2
98, 43.
54] A. Palanimurugan, A. Dhanalakshmi, P. Selvapandian, A.
Kulandaisamy, Heliyon 2019, 5, e02039.
55] S. Shaaban, A. Negm, A. M. Ashmawy, D. M. Ahmed, L. A.
Wessjohann, Eur. J. Med. Chem. 2016, 122, 55.
56] S. Chacko, S. Samanta, Biomed. Pharmacother. 2017, 89, 162.
57] F. Arjmand, S. Parveen, RSC Adv. 2012, 2, 6354.
2+
2+
2+
2+
of new VO , Mn , Zn , and Pd complexes
based on azomethine ferrocenyl ligand: DNA
interaction, antimicrobial, antioxidant, anticancer
activities, and molecular docking. Appl Organomet
Chem. 2021;35:e6154. https://doi.org/10.1002/
aoc.6154
[
[
SUPPORTING INFORMATION
Additional supporting information may be found online
in the Supporting Information section at the end of this
article.