Molecular docking, DNA binding, thermal studies and antimicrobial activities of Schiff base complexes

Article abstract of DOI:10.1016/j.molliq.2016.02.072

Metal(II) complexes of 3-[(2-hydroxy-3-methoxybenzylidene)hydrazo]-1,3-dihydroindol-2-one (HL) were prepared, their compositions and physicochemical properties were characterized on the basis of elemental analysis, molar conductivity,¹H NMR, UV

Full text of DOI:10.1016/j.molliq.2016.02.072

Journal of Molecular Liquids 218 (2016) 434–456
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Molecular docking, DNA binding, thermal studies and antimicrobial
activities of Schiff base complexes
a
b
a
A.Z. El-Sonbati a, M.A. Diab a, , A.A. El-Bindary , M.I. Abou-Dobara , H.A. Seyam
⁎
a
Chemistry Department, Faculty of Science, Damietta University, Damietta, Egypt
b
Botany Department, Faculty of Science, Damietta University, Damietta, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Metal(II) complexes of 3-[(2-hydroxy-3-methoxybenzylidene)hydrazo]-1,3-dihydroindol-2-one (HL) were pre-
pared, their compositions and physicochemical properties were characterized on the basis of elemental analysis,
molar conductivity, 1H NMR, UV–Vis, IR, mass spectroscopy, X-ray, magnetic measurements and thermogravi-
metric analysis (TGA). All results confirm that the novel complexes have 1:1 metal-to-ligand stoichiometric for-
mulae [M(HL)(OAc)2(OH2)2] (M_Cu(II)(1), Co(II)(2), Ni(II)(3) and Cd(II)(4)), octahedral configuration and the
ligand behaves as a neutral bidentate forming six-membered chelating ring towards the metal ions, bonding
through azomethine nitrogen and ketonic oxygen atoms. The molecular structures of the ligand and its metal
complexes were also studied using quantum chemical calculations and shows that the keto form with hydrogen
bond is more stable than other forms. The coordination geometry around all complexes (1–4) exhibits an octa-
hedral geometry. The XRD studies show that both the ligand and Cu(II) complex show polycrystalline with Tri-
clinic crystal system. The activation thermodynamic parameters, such as activation energy (Ea), enthalpy (ΔH),
entropy (ΔS), and Gibbs free energy change of the decomposition (ΔG) are calculated using Coats–Redfern
and Horowitz–Metzger methods. The ligand and its metal complexes (1–4) showed antimicrobial activity against
bacterial species, Gram positive (Staphylococcus aureus), Gram negative (Escherichia coli) bacteria and yeast
(Candida albicans), the ligand exhibited higher activity than the complexes. All investigated compounds were
screened in vitro for their antioxidant, cytotoxic and antitumor activity. Molecular docking was used to predict
the binding between HL ligand and the receptors of crystal structure of E. coli (3T88), crystal structure of
S. aureus (3q8u) and crystal structure of C. albicans (1Q40).
Received 24 January 2016
Received in revised form 7 February 2016
Accepted 22 February 2016
Available online xxxx
Keywords:
Schiff base
Molecular docking
DNA binding
Molecular structure
Thermodynamic parameters
Antioxidant and antitumor activity
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
cytotoxicity antioxidant activity [13–20]. Isatin derivatives have been
used as important intermediates in organic synthesis [21]. Isatin is an
Schiff bases form an important class of organic compounds with a
wide variety of biological properties [1–5]. Schiff bases, derived from
various heterocycles, were reported to possess cytotoxic [6], antican-
cer, and antifungal activities [7]. Isatin (1H-indole-2,3-dione) was
first discovered by Erdmann and Laurent in 1840 as a product of in-
digo oxidation [8,9]. Isatin have also been recognized in natural
products, such as in humans as it is a metabolic derivative of adren-
aline, marine molluscs, fungal metabolites [10–12]. Isatin and its an-
alogs are versatile substrates, which can be used for the synthesis of
numerous heterocyclic compounds. The synthetic ingenuity of isatin
has led to the wide use of this compound in organic synthesis which re-
ported to possess a variety of pharmacological properties such as antivi-
ral activities, antibacterial, anticancer activities, anticonvulsant activity,
important component of many alkaloids [22], drugs [23], dyes [24], pes-
ticides, and analytical reagents.
Although metal complexes of monohydrazones derived from isatin
have been extensively investigated, those formed from bishydrazones
have received comparatively less attention so far [25–27].
Thereby, in the present study, we report the synthesis of 3-[(2-
hydroxy-3-methoxy-benzylidene)-hydrazono]-1,3-dihydro-indol-
2-one and its metal [Cu(II), Co(II), Ni(II) and Cd(II)] complexes. Also
we report the structure characterization by different spectroscopic
techniques. Antimicrobial activities, antioxidant and antitumor
activity were studied. The calf thymus DNA binding activity of the li-
gand and its metal complexes were studied by absorption spectra.
The thermogravimetric analysis (TGA) studies were done for the in-
vestigated compounds. In addition to the activation thermodynamic
parameters are calculated using Coats–Redfern and Horowitz–
Metzger methods. Study the molecular structures of the investigated
compound. Study the docking of Schiff base ligand. In our laboratories,
⁎
Corresponding author.
E-mail address: m.adiab@yahoo.com (M.A. Diab).
http://dx.doi.org/10.1016/j.molliq.2016.02.072
0167-7322/© 2016 Elsevier B.V. All rights reserved.

A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
435
Scheme 1. Synthetic route of Schiff base ligand (A) keto form, (B) keto form with hydrogen bond, (C) enol form, (D) enol form with hydrogen bond and (E) enol form with hydrogen bond.
the chemical equilibria and although the coordination complexes of
HL (Scheme 1) has been extensively investigated [28–31], no atten-
tion has been paid to the HL or to the metal complexes of the HL.
standard anticancer drug for comparison. The reagents RPMI-1640 me-
dium, MTT, DMSO and 5-fluorouracil (sigma co., St. Louis, USA), Fetal
Bovine serum (GIBCO, UK).
2. Experimental
2.2. Preparation of Schiff base ligand (HL)
2.1. Materials
Schiff base was prepared from ethanolic solutions of isatin and hy-
drazine hydrate in equimolar amount and were refluxed together for
30 min to afford hydrazone. Then condensation of hydrazine with 2-
hydroxy-3-methoxy-benzaldehyde in equimolar amount in ethanol
under reflux for 3 h, the excess solvent was removed by evaporation
and the concentrated solution was cooled and filtration the powder of
Schiff base was collected, then washed with ethanol. Recrystallization
from ethanol afforded pure crystals. 3-[(2-hydroxy-3-methoxy-
benzylidene)-hydrazono]-1,3-dihydro-indol-2-one. Yield: 80%. The
All reactants (Isatin, Metals acetate, Hydrazine and aldehyde) were
purchased from Aldrich, and were used without any further purifica-
tion. CT-DNA was purchased from SRL (India). Double distilled water
was used to prepare all buffer solutions. Cell line Hepatocellular carcino-
ma (HepG-2) and mammary gland breast cancer (MCF-7). The cell line
was obtained from ATCC via Holding company for biological products
and vaccines (VACSERA), Cairo, Egypt. 5-Fluorouracil was used as a

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A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
using the following equation [34]:
½DNAꢀ
½DNAꢀ
1
¼
þ
ð1Þ
ðεa–εf Þ ðεb–εf Þ Kbðεa–εf Þ
where [DNA] is the concentration of CT-DNA in base pairs, єa is the ex-
tinction coefficient observed for the Aobs/[compound] at the given
DNA concentration, єf is the extinction coefficient of the free compound
in solution and єb is the extinction coefficient of the compound when
fully bond to DNA. In plots of [DNA]/(єa–єf) versus [DNA], Kb is given
by the ratio of the slope to the intercept.
2.5. Antimicrobial activity
Chemical compounds were individually tested against a Gram positive
(Staphylococcus aureus), Gram negative (Escherichia coli) bacteria and
yeast (Candida albicans). Each of the compounds was dissolved in
DMSO and solution of the concentration 1 mg/mL were prepared sepa-
rately and paper disks of Whatman filter paper were prepared with stan-
dard size (5 cm) were cut and sterilized in an autoclave. The paper disks
were soaked in the desired concentration of the complex solution and
were placed aseptically in the petri dishes containing nutrient agar
media (agar 20 g, beef extract 3 g and peptone 5 g) seeded with
S. aureus, E. coli and C. albicans. The petri dishes were incubated at 36 °C
and the inhibition zones were recorded after 24 h of incubation. Each
treatment was replicated three times. The antibacterial activity of a com-
mon standard antibiotic ampicillin and antifungal Clotrimazole was also
recorded using the same procedure as above at the same concentration
and solvents. The % activity index for the complex was calculated by the
formula as under [35]:
Fig. 1. The structure of the metal complexes (1–4).
purity of ligand was checked by TLC. Our synthetic route of Schiff base
ligand is shown in Scheme 1.
2.3. Preparation of the complexes
The solid complexes (1–4) of the different metal ions under study
were prepared and purified by recrystallization when possible (Fig. 1).
The following synthetic has been employed.
Ethanolic solution of copper, cobalt, nickel or cadmium acetate
(0.01) was added slowly to the stirred ligand mixture and the reaction
mixture was further refluxed. The colored precipitates were filtered
through sintered glass crucible and washed several times with hot eth-
anol, ether and finally dried in vacuum desiccator for 1 week.
Zone of inhibition by test compoundðdiameterÞ
% activity index ¼
:
Zone of inhibition by standardðdiameterÞ x 100
ð2Þ
2.4. DNA binding experiments
2.6. Antioxidant assay
The binding properties of the ligand and complexes (1–4) to CT-DNA
have been studied using electronic absorption spectroscopy. The stock
solution of CT-DNA was prepared in 5 mM Tris–HCl/50 mM NaCl buffer
Antioxidant activity determined by screening assay ABTS method.
For each of the investigated compounds (2 mL) of ABTS solution
(60 μM) was added to 3 mL MnO2 solution (25 mg/mL), all prepared
in (5 mL) aqueous phosphate buffer solution (pH 7, 0.1 M).The mixture
was shaken, centrifuged, filtered and the absorbance of the resulting
green blue solution (ABTS radical solution) at 734 nm was adjusted to
approx. ca. 0.5. Then, 50 μl of (2 mM) solution of the tested compound
in spectroscopic grade MeOH/phosphate buffer (1:1) was added. The
absorbance was measured and the reduction in color intensity was
expressed as inhibition percentage. L-ascorbic acid was used as stan-
dard antioxidant (Positive control). Blank sample was run without
ABTS and using MeOH/phosphate buffer (1:1) instead of tested com-
pounds. Negative control was run with ABTS and MeOH/phosphate
buffer (1:1) only [36–38].
(pH = 7.2), which a ratio of UV absorbances at 260 and 280 nm (A260
/
A280) of ca. 1.8–1.9, indicating that the DNA was sufficiently free of pro-
tein [32], and the concentration was determined by UV absorbance at
260 nm (Ɛ = 6600 M−1 cm−1) [33]. Electronic absorption spectra
(300–700 nm) were carried out using 1 cm quartz cuvettes at 25 °C
by
fixing
the
concentration
of
ligand
or
complex
(1.00 × 10−3 mol L−1), while gradually increasing the concentration
of CT-DNA (0.00 to 1.30 × 10−4 mol·L−1). An equal amount of CT-
DNA was added to both the compound solutions and the references
buffer solution to eliminate the absorbance of CT-DNA itself. The intrin-
sic binding constant Kb of the compound with CT-DNA was determined
Table 1
Energy values obtained in docking calculations of ligand (HL) with receptors of crystal structure of E. coli (3T88), crystal structure of S. aureus (3q8u) and crystal structure of C. albicans
(1Q40).
Receptors
Est. inhibition constant (Ki)
(μM)
vdW + bond + desolve energy
(kcal/mol)
Electrostatic energy
(kcal/mol)
Total intercooled energy
(kcal/mol)
Interact
surface
3T88
3q8u
1Q40
25.34
88.45
128.65
−7.03
−6.50
−6.24
−0.06
−0.15
−0.08
−7.09
−6.65
−6.32
746.35
824.09
624.06

A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
437
2.7. Cytotoxicity assay
cultured in RPMI-1640 medium with 10% fetal bovine serum. Antibi-
otics added were 100 units/mL penicillin and 100 μg/mL streptomy-
cin at 37 °C in a 5% CO2 incubator. The cell lines were seeded in a 96-
well plate at a density of 1.0 × 104 cells/well at 37 °C for 48 h under
5% CO2, followed by 24 h incubation with the indicated drug doses
[41]. In the end of drug treatment, 20 μl of MTT solution at
5 mg/mL was added and incubated for 4 h. Dimethylsulfoxide in
The cell lines mentioned above were used to determine the inhib-
itory effects of compounds on cell growth using the MTT assay [39,
40]. This colorimetric assay is based on the conversion of the yellow
tetrazolium bromide (MTT) to a purple formazan derivative by mito-
chondrial succinate dehydrogenase in viable cells. Cell lines were
Fig. 2. The ligand HL (green in (a) and blue in (b)) in interaction with receptors of crystal structure of E. coli (3T88), crystal structure of S. aureus (3q8u) and crystal structure of C. albicans
(1Q40). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article).

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A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
Fig. 3. HB plot of interaction between ligand HL and receptor (a) crystal structure of E. coli (3T88), (b) crystal structure of S. aureus (3q8u) and (c) crystal structure of C. albicans (1Q40).
volume of 100 μl is added into each well to dissolve the purple
formazan formed. The colorimetric assay is measured and recorded
at absorbance of 570 nm using a plate reader (EXL 800). The relative
cell viability in percentage was calculated as (A570 of treated sam-
ples/A570 of untreated sample) × 100.
2000 spectrophotometer. The 1H NMR spectrum was obtained with a
Bruker WP 300 MHz using DMSO-d6 as a solvent containing TMS as
the internal standard. Mass spectra were recorded by the EI technique
at 70 eV using MS-5988 GS–MS Hewlett-Packard. The magnetic moment
of the prepared solid complexes was determined at room temperature
using the Gouy's method. Mercury(II) (tetrathiocyanato)cobalt(II),
[Hg{Co(SCN)4}], was used for the calibration of the Gouy tubes. Diamag-
netic corrections were calculated from the values given by Selwood [43]
and Pascal's constants. Magnetic moments were calculated using the
2.8. Measurements
Elemental microanalyses of the separated ligand and solid chelates
for C, H, and N were performed on Perkin-Elmer (2400) CHNS analyzer.
The analyses were repeated twice to check the accuracy of the analyzed
data. The metal content in the complexes was estimated by standard
methods [42]. Spectroscopic data were obtained using the following in-
struments: Ultraviolet–Visible (UV–Vis) spectra of the compounds were
recorded using a Perkin-Elmer AA 800 spectrophotometer model AAS.
Infrared spectra were recorded as KBr disks using a Pye Unicam SP
equation, μeff. = 2.84 [TχMcoor. 1/2
. X-ray diffraction analysis of the li-
]
gand and its Copper complex powder forms was recorded on X-ray
diffractometer in the range of diffraction angle 2θ° = 5–80°. This
analysis was carried out using Cu Kα radiation (λ = 1.540598 Å).
The applied voltage and the tube current are 40 kV and 30 mA, re-
spectively. The diffraction peaks in powder spectra are indexed and
the lattice parameters are determined with the aid of CRYSFIRE

A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
439
Fig. 4. 2D plot of interaction between ligand HL and receptor (a) crystal structure of E. coli (3T88), (b) crystal structure of S. aureus (3q8u) and (c) crystal structure of C. albicans (1Q40).
computer program [44]. The value of interplanar spacing, d, and Mill-
er indices, hkl, for each diffraction peak are determined by using
CHEKCELL program [45]. Thermal studies were computed on Simul-
taneous Thermal Analyzer (STA) 6000 system using thermogravi-
metric analysis (TGA) method. Thermal properties of the samples
were analyzed in the temperature range up to 800 °C at the heating
rate of 10 °C/min under dynamic nitrogen atmosphere. The molecular
structures of the ligands were optimized by HF method with 3–21G
basis set. The molecules were built with the Perkin Elmer ChemBioDraw
and optimized using the Perkin Elmer ChemBio3D software [46,47].
Table 2
Elemental analyses data of metal complexes.
Compounds
Yield (%)
Exp. (Calcd.) (%)
C
μeff (B.M.)
H
N
M
[Cu(HL)(OAc)2(OH2)2] (1)
[Co(HL)(OAc)2(OH2)2] (2)
[Ni(HL)(OAc)2(OH2)2] (3)
[Cd(HL)(OAc)2(OH2)2] (4)
52.67
66.17
65.50
85.50
46.64 (46.83)
47.18 (47.25)
47.15 (47.27)
42.64 (42.75)
4.38 (4.49)
4.37 (4.53)
4.33 (4.53)
3.98 (4.10)
7.88 (8.19)
7.89 (8.27)
7.87 (8.27)
7.19 (7.48)
12.26 (12.40)
11.46 (11.60)
11.37 (11.56)
19.88 (20.02)
1.83
4.46
3.35
Dia.

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A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
Table 3
IR spectral bands of the ligand and its metal complexesa.
(HL)
(1)
(2)
(3)
(4)
Assignments
3436
3180
1714
1617
1251
–
3444
3185
1645
1604
1248
464
3440
3183
1660
1589
1246
460
3441
3186
1660
1605
1245
455
3443
3182
1660
1607
1249
495
ν(OH)
ν(NH)
ν(C_O)
ν(C_N)
ν(C–O)
ν(M–O)
ν(M–N)
–
426
430
440
420
a
Numbers given in Table 2.
In the study simulates the actual docking process in which the ligand–
protein pair-wise interaction energies are calculated using Docking Server
[48]. The MMFF94 Force field was for used energy minimization of ligand
molecule using Docking Server. Gasteiger partial charges were added to
the ligand atoms. Non-polar hydrogen atoms were merged, and rotatable
bonds were defined. Docking calculations were carried out on crystal
structure of E. coli (3T88), crystal structure of S. aureus (3q8u) and crystal
structure of C. albicans (1Q40) model Essential hydrogen atoms, Kollman
united atom type charges, and solvation parameters were added with the
aid of AutoDock tools [49]. Auto Dock parameter set- and distance-
dependent dielectric functions were used in the calculation of the van
der Waals and the electrostatic terms, respectively.
3. Results and discussion
3.1. Characterization of ligand
The structure elucidation of the prepared Schiff base (HL) is carried
out by using different techniques namely elemental analyses, UV–vis,
IR, 1H NMR X-ray and mass spectroscopy, in addition to geometrical
calculations.
HL ligand was a dark orange colored solid compound, m.p. 190–
192 °C and was soluble in common organic solvents. The data of C, H
and N content of HL referred to (C16H13N3O3) are shown in C, 65.09;
H, 4.41; N, 14.24, Found: C, 64.89; H, 4.24; N, 13.80 and found to be in
good accordance with the calculated value based on the synthetic and
proposed structure.
Inspection of IR spectrum of HL revealed that IR spectrum of HL was
associated to the aromatic ring system. The absorption band of ligand
exhibit a broad band at 3436 cm−1 which can be attributed to the
υ(OH) group. A medium intensity band at 3180 cm−1 is due to the
υ(NH) vibrations of the indole ring and two bands at 1714 and
1617 cm−1 due to υ(C_O) of isatin moiety and υ(C_N), respectively.
The bands observed at 1540, 1251 and 950 cm−1 corresponds to the ar-
omatic ring, phenolic (C–O) and (N–N) stretching vibrations, respec-
tively [50].
The 1H NMR spectra of the ligand show two signals at 11.9 and
11.0 ppm corresponding to the N–H and O–H, respectively. The previous
two protons disappear in the presence of D2O. Signal appearing at
8.9 ppm can be attributed to the N_CH. Aromatic proton signals are ob-
served as multiplet in the range 6.9–7.5 ppm. Signal at 3.8 ppm corre-
sponding to the OCH3.
Molecular docking is a key tool in computer drug design [51]. The
focus of molecular docking is to simulate the molecular recognition
process. Molecular docking aims to achieve an optimized conforma-
tion for both the protein and drug with relative orientation between
them such that the free energy of the overall system is minimized. In
this context, we used molecular docking between ligand (HL) and
crystal structure of E. coli (3T88), crystal structure of S. aureus
(3q8u) and crystal structure of the C. albicans (1Q40). The results
showed a possible arrangement between ligand (HL) and receptors
(3T88, 3q8u and 1Q40). The docking study showed a favorable
Fig. 5. Molecular structures with atomic numbering for ligand.
interaction between ligand (HL) and the receptors (3T88, 3q8u and
1Q40) as shown in Fig. 2 and the calculated energy is listed in
Table 1. According to the results obtained in this study, HB plot
curve indicates that the ligand HL binds to the proteins with

A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
441
Fig. 6. Molecular structures with atomic numbering for complexes (1–4).
hydrogen bond interactions and decomposed interaction energies in
kcal/mol were exist between ligand (HL) with 3T88, 3q8u and 1Q40
receptors as shown in Fig. 3 (a, b and c). 2D plot curves of docking
with ligand (HL) are shown in Fig. 4 (a, b and c). The ligand (HL)
shows best interaction with 1Q40 receptor than other receptors.
M(CH3COO)2·nH2O + HL → [M(HL)(OAc)2(OH2)2]
where M_Cu(II), Co(II), Ni(II) or Cd(II).
For the last reaction the ligand behaves as a neutral and contains
two anions (complexes with equivalent anions). The metal(II) com-
plexes were dissolved in DMSO and the molar conductivities of
10−3 M of their solution at room temperature were measured. The
lower conductance values of the complexes support that non-
electrolytic nature of the compounds.
3.2. Metal complexes
The IR spectra of the metal complexes were similar to each other, ex-
cept for some slight shift and intensity changes of few vibration peaks
caused by different metal(II) ions, indicating that the metal complexes
had similar structure.
IR spectra of the complexes clearly indicate the bonding association
of the ligand with the metal ion.
In comparison of the spectrum of the free ligand with that of
[Cu(HL)(OAc)2(OH2)2], [Co(HL)(OAc)2(OH2)2], [Ni(HL)(OAc)2(OH2)2]
and [Cd(HL)(OAc)2(OH2)2] complexes, we found that there are nega-
tive shift of both υ(C_O) and υ(C_N), vibrations. While, the υ(OH)
The isolated complexes having general formula [M(HL)(OAc)2(OH2)2]
are paramagnetic except Cd(II) is diamagnetic. All Schiff base complexes
are highly colored, stable in air, non-hygroscopic in nature and soluble
in DMF and DMSO.
The data of elemental analysis for the metal complexes are in
good agreement with the calculated values (Table 2) showing that
the complexes have 1:1 metal-to-ligand stoichiometry of the
[M(HL)(OAc)2(OH2)2]. Formation of the complexes can be obtainable
in the following reaction.

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Table 4
Selected geometric bond lengths, bond angles and torsional angles of the HL form (B).
Bond lengths (Å)
Bond angles (°)
C(23)–H(35)
C(23)–H(34)
C(23)–H(33)
C(17)–H(32)
C(16)–H(31)
C(15)–H(30)
C(13)–H(29)
N(7)–H(28)
C(6)–H(27)
C(5)-H(26)
C(2)–H(25)
C(1)–H(24)
C(3)–C(4)
C(9)–C(4)
C(5)–C(4)
C(6)–C(5)
C(1)–C(6)
C(2)–C(1)
C(3)–C(2)
N(7)–C(3)
C(8)–N(7)
1.112
1.112
1.113
1.104
1.102
1.102
1.103
1.044
1.103
1.101
1.101
1.103
1.340
1.342
1.339
1.344
1.345
1.344
1.337
1.266
1.266
1.364
1.037
0.998
1.376
1.377
1.355
1.354
1.349
1.340
1.338
1.339
1.351
1.276
1.260
1.212
1.266
1.407
N(12)–H(21)–O(20)
H(35)–C(23)–H(34)
H(35)–C(23)–H(33)
H(35)–C(23)–O(22)
H(34)–C(23)–H(33)
H(34)–C(23)–O(22)
H(33)–C(23)–O(22)
C(18)–O(22)–C(23)
H(21)–O(20)–C(19)
O(20)–C(19)–C(14)
O(20)–C(19)–C(18)
C(14)–C(19)–C(18)
O(22)–C(18)–C(19)
O(22)–C(18)–C(17)
C(19)–C(18)–C(17)
H(32)–C(17)–C(18)
H(32)–C(17)–C(16)
C(18)–C(17)–C(16)
H(31)–C(16)–C(17)
H(31)–C(16)–C(15)
C(17)–C(16)–C(15)
H(30)–C(15)–C(16)
H(30)–C(15)–C(14)
C(16)–C(15)–C(14)
C(19)–C(14)–C(15)
C(19)–C(14)–C(13)
C(15)–C(14)–C(13)
H(29)–C(13)–C(14)
H(29)–C(13)–N(12)
C(14)–C(13)–N(12)
H(21)–N(12)–C(13)
Torsional angles
166.849
112.743
107.411
110.548
107.903
110.414
107.605
120.513
101.103
115.642
124.485
119.870
126.622
116.717
116.630
118.599
117.914
123.485
120.389
120.147
119.463
120.144
121.470
118.385
122.152
114.494
123.350
122.033
119.087
118.851
103.028
H(28)–N(7)–C(3)
H(28)–N(7)–C(8)
C(3)–N(7)–C(8)
H(27)–C(6)–C(5)
H(27)–C(6)–C(1)
C(5)–C(6)–C(1)
H(26)–C(5)–C(4)
H(26)–C(5)–C(6)
C(4)–C(5)–C(6)
C(3)–C(4)–C(9)
C(3)–C(4)–C(5)
C(9)–C(4)–C(5)
C(4)–C(3)–C(2)
C(4)–C(3)–N(7)
C(2)–C(3)–N(7)
H(25)–C(2)–C(1)
H(25)–C(2)–C(3)
C(1)–C(2)–C(3)
H(24)–C(1)–C(6)
H(24)–C(1)–C(2)
C(6)–C(1)–C(2)
N(7)–C(8)–O(11)
C(9)–C(8)–O(11)
H(21)–N(12)–N(10)
C(13)–N(12)–N(10)
N(12)–N(10)–C(9)
C(4)–C(9)–C(8)
C(4)–C(9)–N(10)
C(8)–C(9)–N(10)
N(7)–C(8)–C(9)
125.092
124.371
110.535
119.442
119.565
120.992
121.218
120.780
118.001
107.242
120.814
131.943
121.590
108.608
129.800
121.305
120.926
117.768
119.675
119.491
120.833
121.827
129.066
113.439
110.496
119.636
104.508
123.146
132.345
109.104
C(9)–C(8)
H(21)–N(12)
O(20)–H(21)
C(18)–O(22)
C(19)–O(20)
C(19)–C(14)
C(18)–C(19)
C(17)–C(18)
C(16)–C(17)
C(15)–C(16)
C(14)–C(15)
C(13)–C(14)
N(12)–C(13)
N(10)–N(12)
C(8)–O(11)
C(9)–N(10)
O(22)–C(23)
C(4)–C(9)–N(10)–N(12)
C(2)–C(3)–C(4)–C(9)
H(26)–C(5)–C(4)–C(3)
H(27)–C(6)–C(5)–C(4)
H(24)–C(1)–C(6)–C(5)
H(25)–C(2)–C(1)–C(6)
C(8)–N(7)–C(3)–C(2)
N(10)–C(9)–C(8)–N(7)
C(4)–C(9)–C(8)–O(11)
O(20)–H(21)–N(12)–N(10)
179.076
179.917
179.952
179.997
179.985
179.994
179.885
179.891
179.269
116.193
H(29)–C(13)–C(14)–C(19)
C(17)–C(18)–O(22)–C(23)
C(18)–C(19)–C(14)–C(13)
O(20)–C(19)–C(14)–C(15)
O(22)–C(18)–C(19)–C(14)
H(32)–C(17)–C(18)–C(19)
H(30)–C(15)–C(16)–C(17)
C(13)–C(14)–C(15)–C(16)
N(12)–C(13)–C(14)–C(15)
177.168
167.388
179.505
179.335
179.198
178.996
179.950
179.781
179.607
and υ(NH) vibrations remain at more or less at the same position
Table 3, which indicates that they do not participate in coordination
to the metal ion. So, the HL acts as a neutral bidentate coordination
via υ(C_O) and azomethine nitrogen (C_N) atoms. This observa-
tion is further supported by a new bands were observed in 455–
495 and 420–440 cm−1 regions which assigned to υ(M–O) and
υ(M–N), respectively. Coordination of the Schiff base to the metal(II)
ion through the azomethine nitrogen atom is expected to reduce the
electron density in the azomethine frequency. The band due to
azomethine nitrogen υ(C_N) showed a modest decrease in the
stretching frequency for the complexes and is shifted to lower fre-
quencies (Table 3) after complexation (bathochromic shift) indicat-
ing the coordination of the azomethine [28]. This is further
substantiated by shift of a 1H NMR signal for HC_N group. In
comparing the position of proton signal in the Cd(II) complex
with those of the ligand signal, it can be concluded that all signals
are in the expected region and shift only slightly due to the coordina-
tion of the ligand to the metal ion. Signal at 4.3 ppm in complex
corresponding to water molecules and disappear in the presence of
D2O.
ρw(H2O), respectively. This is supported by results of Ryde [53]. More-
over, strong evidence for the presence or absence of water of crystalliza-
tion and/or coordinated water supported by the thermogram of all
complexes.
3.3. Geometrical structures of the ligand and its metal complexes
Geometrical structure of the ligand (HL) and its metal complexes
(1–4) were calculated by optimizing their bond lengths, bond angels
and torsional angles. The geometrical structures of ligand and its
metal complexes (1–4) are presented in Figs. 5 and 6. Selected geomet-
ric parameters bond lengths and bond angles and torsional angles of HL
and its metal complexes (1–4) are tabulated in Tables 4–6 (Tables S1–S3
in the supplementary). Both the highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO) are the
main orbital takes part in chemical stability. The HOMO represents the
ability to donate an electron, LUMO as an electron acceptor represents
the ability to obtain an electron. Molecular orbital structures (HOMO
& LUMO) for HL and its metal complexes (1–4) are presented in
Figs. 7 and 8. Primary calculations reveal that the keto form with hydro-
gen bond (B) is more stable and reactive than other forms (A and C). The
existence of hydrogen bond in the optimized structures is observed in
the O20–H21–N12 portion. The bond distances, and bond angle values
are 0.998, 1.037 Å and 166.849°, respectively. This hydrogen bonding
In metal acetate complexes, the acetate group coordinates to the
metal ions in a mondentate manner where the difference between the
two acetate bands is Δυ N 180 cm−1 [52]. Also, the bands of coordinated
were observed at ~855 and ~597 cm−1, are assigned to ρr(H2O) and

A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
443
Table 5
Selected geometric bond lengths and bond angles of the complex (1).
Bond lengths (Å)
Bond angles (°)
C(33)–H(56)
C(33)–H(55)
C(33)–H(54)
C(29)–H(53)
C(29)–H(52)
C(29)–H(51)
C(25)–H(50)
C(25)–H(49)
C(25)–H(48)
O(23)–H(47)
O(23)–H(46)
O(22)–H(45)
O(22)–H(44)
O(20)–H(43)
C(17)–H(42)
C(16)–H(41)
C(15)–H(40)
C(13)–H(39)
N(7)–H(38)
C(6)–H(37)
C(5)–H(36)
C(2)–H(35)
C(1)–H(34)
C(14)–C(19)
C(18)–C(19)
C(17)–C(18)
C(16)–C(17)
C(15)–C(16)
C(14)–C(15)
O(23)–Cu(21)
O(22)–Cu(21)
O(11)–Cu(21)
N(12)–Cu(21)
Cu(21)–O(30)
Cu(21)–O(26)
C(18)–O(24)
C(19)–O(20)
C(13)–C(14)
N(12)–C(13)
N(10)–N(12)
C(8)–O(11)
C(9)–N(10)
C(9)–C(4)
1.11
1.11
1.11
1.11
1.11
1.11
1.11
1.11
1.11
1.02
1.02
1.04
1.03
0.96
1.10
1.10
1.10
1.11
1.04
1.10
1.10
1.10
1.10
1.35
1.35
1.34
1.33
1.33
1.34
1.85
1.85
1.84
1.36
1.82
1.82
1.37
1.35
1.35
1.28
1.27
1.22
1.26
1.33
1.35
1.26
1.26
1.34
1.34
1.33
1.34
1.41
C(2)–C(3)
C(1)–C(2)
1.33
1.34
1.51
1.21
1.36
1.51
1.21
1.36
H(56)–C(33)–H(55)
H(56)–C(33)–H(54)
H(56)–C(33)–C(32)
H(55)–C(33)–H(54)
H(55)–C(33)–C(32)
H(54)–C(33)–C(32)
C(33)–C(32)–O(31)
C(33)–C(32)–O(30)
O(31)–C(32)–O(30)
Cu(21)–O(30)–C(32)
H(53)–C(29)–H(52)
H(53)–C(29)–H(51)
H(53)–C(29)–C(28)
H(52)–C(29)–H(51)
H(52)–C(29)–C(28)
H(51)–C(29)–C(28)
C(29)–C(28)–O(27)
C(29)–C(28)–O(26)
O(27)–C(28)–O(26)
Cu(21)–O(26)–C(28)
H(50)–C(25)–H(49)
H(50)–C(25)–H(48)
H(50)–C(25)–O(24)
H(49)–C(25)–H(48)
H(49)–C(25)–O(24)
H(48)–C(25)–O(24)
C(18)–O(24)–C(25)
H(47)–O(23)–H(46)
H(47)–O(23)–Cu(21)
H(46)–O(23)–Cu(21)
H(45)–O(22)–H(44)
H(45)–O(22)–Cu(21)
H(44)–O(22)–Cu(21)
O(23)–Cu(21)–O(22)
O(23)–Cu(21)–O(11)
O(23)–Cu(21)–N(12)
O(23)–Cu(21)–O(30)
O(23)–Cu(21)–O(26)
O(22)–Cu(21)–O(11)
O(22)–Cu(21)–N(12)
O(22)–Cu(21)–O(30)
O(22)–Cu(21)–O(26)
O(11)–Cu(21)–N(12)
O(11)–Cu(21)–O(30)
O(11)–Cu(21)–O(26)
N(12)–Cu(21)–O(30)
N(12)–Cu(21)–O(26)
O(30)–Cu(21)–O(26)
H(43)–O(20)–C(19)
C(14)–C(19)–C(18)
C(14)–C(19)–O(20)
108.02
107.97
110.64
109.24
110.43
110.44
124.34
110.77
124.87
119.38
107.86
109.13
110.69
107.84
110.51
110.70
124.41
111.19
124.37
119.15
110.15
109.13
109.89
109.02
110.40
108.18
113.64
70.02
103.10
96.46
161.22
103.39
95.27
77.53
73.33
172.33
81.68
80.11
150.31
107.60
79.63
91.88
100.86
90.55
H(41)–C(16)–C(15)
C(17)–C(16)–C(15)
H(40)–C(15)–C(16)
H(40)–C(15)–C(14)
C(16)–C(15)–C(14)
C(19)–C(14)–C(15)
C(19)–C(14)–C(13)
C(15)–C(14)–C(13)
H(39)–C(13)–C(14)
H(39)–C(13)–N(12)
C(14)–C(13)–N(12)
Cu(21)–N(12)–C(13)
Cu(21)–N(12)–N(10)
C(13)–N(12)–N(10)
Cu(21)–O(11)–C(8)
N(12)–N(10)–C(9)
N(10)–C(9)–C(4)
N(10)–C(9)–C(8)
C(4)–C(9)–C(8)
O(11)–C(8)–C(9)
O(11)–C(8)–N(7)
C(9)–C(8)–N(7)
H(38)–N(7)–C(8)
H(38)–N(7)–C(3)
C(8)–N(7)–C(3)
H(37)–C(6)–C(1)
H(37)–C(6)–C(5)
C(1)–C(6)–C(5)
H(36)–C(5)–C(6)
H(36)–C(5)–C(4)
C(6)–C(5)–C(4)
C(9)–C(4)–C(5)
C(9)–C(4)–C(3)
C(5)–C(4)–C(3)
N(7)–C(3)–C(4)
N(7)–C(3)–C(2)
C(4)–C(3)–C(2)
H(35)–C(2)–C(3)
H(35)–C(2)–C(1)
C(3)–C(2)–C(1)
H(34)–C(1)–C(6)
H(34)–C(1)–C(2)
C(6)–C(1)–C(2)
C(17)–C(18)–O(24)
H(42)–C(17)–C(18)
H(42)–C(17)–C(16)
C(18)–C(17)–C(16)
H(41)–C(16)–C(17)
C(19)–C(18)–C(17)
C(19)–C(18)–O(24)
C(18)–C(19)–O(20)
120.60
119.14
116.25
121.99
121.74
118.02
125.10
116.86
112.61
115.50
131.65
114.49
114.90
105.86
110.24
116.89
132.69
121.06
105.99
125.70
125.02
108.78
124.96
125.21
109.80
119.62
119.41
120.96
121.43
121.10
117.45
132.37
105.77
121.84
109.54
129.68
120.75
120.84
121.25
117.89
119.54
119.37
121.07
119.63
119.69
119.23
121.07
120.24
118.91
121.03
117.00
C(32)–C(33)
O(31)–C(32)
O(30)–C(32)
C(28)–C(29)
O(27)–C(28)
O(26)–C(28)
C(8)–C(9)
N(7)–C(8)
C(3)–N(7)
C(6)–C(1)
C(5)–C(6)
C(4)–C(5)
C(3)–C(4)
O(24)–C(25)
88.67
93.52
105.06
161.20
111.72
120.88
122.09
can be named as medium strength hydrogen bonding according
to Jeffrey's classification [54] on basis of geometrical parameters. The
M–N bond length values for complexes (1–4) are 1.36, 1.95, 2.13, 2.33
A°, the M–O bond length values for complexes (1–4) are 1.84, 1.17,
0.60, 0.60 A° and bond angle values for complexes (1–4) are 100.86,
108.96, 71.01, 62.46°, respectively. Quantum chemical parameters of
the ligand and its metal complexes (1–4) are obtained from calculations
such as energies of the highest occupied molecular orbital (EHOMO) and
the lowest unoccupied molecular orbital (ELUMO) as listed in Tables 7
−ðEHOMO−ELUMO
Þ
χ ¼
η ¼
:
ð4Þ
2
ELUMO−EHOMO
:
ð5Þ
2
σ ¼ 1=η:
Pi ¼ −χ:
1
ð6Þ
ð7Þ
⁎
and 8. Additional parameters such as HOMO–LUMO energy gap, ΔE ,
absolute electronegativities, χ, chemical potentials, Pi, absolute
hardness, η, absolute softness, σ, global electrophilicity, ω, global
softness, S, and additional electronic charge, ΔNmax, are calculated
using the following equations [46,55]:
S ¼
:
ð8Þ
2η
ω ¼ Pi2=2η:
ð9Þ
ΔNmax ¼ −Pi=η:
ð10Þ
ΔE ¼ ELUMO−EHOMO
:
ð3Þ

444
A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
Table 6
Selected geometric torsional angles of the complexes (1–4).
Complex
Torsional angles
Complex
Torsional angles
(1)
C(13)–C(14)–C(19)–C(18)
C(15)–C(14)–C(19)–O(20)
O(24)–C(18)–C(19)–C(14)
H(42)–C(17)–C(18)–C(19)
C(13)–C(14)–C(15)–C(16)
H(46)–O(23)–Cu(21)–O(30)
H(47)–O(23)–Cu(21)–O(22)
H(44)–O(22)–Cu(21)–N(12)
H(45)–O(22)–Cu(21)–O(11)
H(45)–O(22)–Cu(21)–O(23)
C(8)–O(11)–Cu(21)–O(30)
N(10)–N(12)–Cu(21)–O(22)
C(13)–N(12)–Cu(21)–O(11)
C(13)–N(12)–Cu(21)–O(23)
N(12)–Cu(21)–O(26)–C(28)
N(12)–C(13)–C(14)–C(15)
H(39)–C(13)–C(14)–C(19)
N(10)–N(12)–C(13)–C(14)
N(7)–C(8)–O(11)–Cu(21)
C(4)–C(9)–N(10)–N(12)
N(10)–C(9)–C(4)–C(3)
177.3074
177.143
(2)
C(13)–C(14)–C(19)–C(18)
C(15)–C(14)–C(19)–O(20)
O(32)–C(18)–C(19)–C(14)
H(42)–C(17)–C(18)–C(19)
H(40)–C(15)–C(16)–C(17)
C(13)–C(14)–C(15)–C(16)
H(46)–O(23)–Co(21)–N(12)
H(46)–O(23)–Co(21)–O(22)
H(47)–O(23)–Co(21)–O(24)
H(44)–O(22)–Co(21)–N(12)
H(45)–O(22)–Co(21)–O(11)
H(45)–O(22)–Co(21)–O(23)
N(10)–N(12)–Co(21)–O(22)
N(10)–N(12)–Co(21)–O(23)
O(28)–Co(21)–O(24)–C(26)
N(12)–Co(21)–O(24)–C(26)
N(12)–Co(21)–O(28)–C(30)
N(12)–C(13)–C(14)–C(15)
H(39)–C(13)–C(14)–C(19)
N(10)–N(12)–C(13)–C(14)
C(9)–N(10)–N(12)–C(13)
N(7)–C(8)–O(11)–Co(21)
C(4)–C(9)–N(10)–N(12)
N(7)–C(8)–C(9)–N(10)
179.2946
176.5612
177.9381
175.3166
179.6585
177.9113
145.6082
156.1262
146.9765
119.7913
138.8026
124.6037
139.4419
150.1092
126.8878
116.8185
108.7413
179.4755
164.287
117.6696
176.5038
175.1364
164.4297
174.0666
172.6193
179.8633
178.1654
179.068
178.3012
175.7959
179.6539
136.5789
146.7857
134.2274
149.2302
138.0423
119.4586
130.9215
179.5357
139.3141
102.5065
176.3601
169.3097
124.5002
174.2405
160.0564
176.8675
169.2884
178.8576
179.9162
179.8442
179.9445
179.1768
179.0815
179.8064
179.9188
175.7019
116.1123
124.5563
169.7626
110.5536
123.9927
179.8117
176.1238
172.5622
175.4981
179.7002
175.9201
171.6678
179.0184
118.1466
124.6884
106.4722
142.8327
171.5554
112.8263
107.9752
176.7941
156.3195
118.6603
105.4409
152.4023
103.701
O(11)–C(8)–C(9)–C(4)
C(2)–C(3)–N(7)–C(8)
H(37)–C(6)–C(1)–C(2)
C(4)–C(5)–C(6)–H(37)
C(3)–C(4)–C(5)–H(36)
C(2)–C(3)–C(4)–C(9)
N(7)–C(3)–C(4)–C(5)
H(35)–C(2)–C(3)–C(4)
O(11)–C(8)–C(9)–C(4)
C(4)–C(3)–N(7)–H(38)
C(5)–C(6)–C(1)–H(34)
H(37)–C(6)–C(1)–C(2)
C(2)–C(3)–C(4)–C(9)
N(7)–C(3)–C(4)–C(5)
C(1)–C(2)–C(3)–N(7)
C(6)–C(1)–C(2)–H(35)
176.0945
179.7081
179.0951
179.804
177.6676
124.1538
133.6777
H(34)–C(1)–C(2)–C(3)
O(30)–C(32)–C(33)–H(56)
O(31)–C(32)–C(33)–H(54)
Cu(21)–O(30)–C(32)–C(33)
O(26)–C(28)–C(29)–H(52)
O(27)–C(28)–C(29)–H(53)
Cu(21)–O(26)–C(28)–C(29)
C(18)–O(24)–C(25)–H(48)
C(15)–C(14)–C(19)–O(20)
O(32)–C(18)–C(19)–C(14)
H(42)–C(17)–C(18)–C(19)
H(41)–C(16)–C(17)–C(18)
H(40)–C(15)–C(16)–C(17)
C(13)–C(14)–C(15)–C(16)
H(46)–O(23)–Ni(21)–O(28)
H(47)–O(23)–Ni(21)–O(24)
H(45)–O(22)–Ni(21)–O(23)
C(8)–O(11)–Ni(21)–O(22)
N(10)–N(12)–Ni(21)–O(22)
C(13)–N(12)–Ni(21)–O(11)
N(12)–Ni(21)–O(24)–C(26)
N(12)–Ni(21)–O(28)–C(30)
O(11)–Ni(21)–O(28)–C(30)
H(39)–C(13)–C(14)–C(19)
N(10)–N(12)–C(13)–C(14)
Ni(21)–N(12)–C(13)–H(39)
C(9)–N(10)–N(12)–C(13)
N(7)–C(8)–O(11)–Ni(21)
C(4)–C(9)–N(10)–N(12)
C(8)–C(9)–C(4)–C(5)
C(18)–O(32)–C(33)–H(54)
O(29)–C(30)–C(31)–H(53)
O(25)–C(26)–C(27)–H(49)
(3)
(4)
C(15)–C(14)–C(19)–O(20)
O(32)–C(18)–C(19)–C(14)
H(42)–C(17)–C(18)–C(19)
H(41)–C(16)–C(17)–C(18)
H(40)–C(15)–C(16)–C(17)
C(13)–C(14)–C(15)–C(16)
H(46)–O(23)–Cd(21)–O(28)
H(47)–O(23)–Cd(21)–O(24)
H(44)–O(22)–Cd(21)–N(12)
C(8)–O(11)–Cd(21)–O(22)
N(10)–N(12)–Cd(21)–O(22)
C(13)–N(12)–Cd(21)–O(11)
N(12)–Cd(21)–O(24)–C(26)
O(11)–Cd(21)–O(28)–C(30)
C(19)–C(18)–O(32)–C(33)
N(12)–C(13)–C(14)–C(15)
H(39)–C(13)–C(14)–C(19)
N(10)–N(12)–C(13)–C(14)
Cd(21)–N(12)–C(13)–H(39)
C(9)–N(10)–N(12)–C(13)
C(4)–C(9)–N(10)–N(12)
C(8)–C(9)–C(4)–C(5)
172.8237
167.5563
175.6287
178.9144
173.5522
168.6457
154.7782
169.8892
108.2902
122.2247
149.781
140.5029
137.9811
174.9852
100.3046
175.3075
148.3114
138.3203
140.9462
175.7117
173.6821
175.0561
179.8703
157.8418
178.3991
179.4311
176.6988
176.8517
178.5285
175.8518
178.2484
177.4826
163.286
169.3799
175.357
N(7)–C(8)–C(9)–N(10)
C(3)–N(7)–C(8)–O(11)
C(4)–C(3)–N(7)–H(38)
C(5)–C(6)–C(1)–H(34)
C(4)–C(5)–C(6)–H(37)
C(3)–C(4)–C(5)–H(36)
C(2)–C(3)–C(4)–C(9)
C(1)–C(2)–C(3)–N(7)
172.6868
148.8826
176.1996
176.9551
175.9867
176.7826
173.2048
174.0119
176.8316
176.9101
170.3058
102.7679
138.2227
104.8072
N(7)–C(8)–C(9)–N(10)
C(3)–N(7)–C(8)–O(11)
C(4)–C(3)–N(7)–H(38)
C(5)–C(6)–C(1)–H(34)
C(4)–C(5)–C(6)–H(37)
C(3)–C(4)–C(5)–H(36)
C(2)–C(3)–C(4)–C(9)
C(1)–C(2)–C(3)–N(7)
C(6)–C(1)–C(2)–H(35)
C(6)–C(1)–C(2)–H(35)
C(18)–O(32)–C(33)–H(54)
O(28)–C(30)–C(31)–H(52)
O(29)–C(30)–C(31)–H(53)
O(25)–C(26)–C(27)–H(49)
Ni(21)–O(24)–C(26)–C(27)
C(18)–O(32)–C(33)–H(54)
O(28)–C(30)–C(31)–H(52)
O(29)–C(30)–C(31)–H(53)
O(25)–C(26)–C(27)–H(49)
102.8081
142.2531

A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
445
Fig. 7. Molecular orbital structures (HOMO & LUMO) for ligand (HL).
The HOMO and LUMO energy gap, which is an important stability
index. The smaller is the value of Eg, the more is the reactivity of the
compound [46,55]. It was found that the complex (1) is more stable
and highly reactive than the other complexes, where the value of ΔE
for complexes (1–4) was found 0.239, 1.540, 2.074 and 4.140 eV,
respectively.
Co(II) complex confirms that the complex has octahedral geometry
[56].
The magnetic moment value of the Ni(II) complex is 3.35 B.M. and
corresponding to two unpaired electrons. The magnetic moment value
is in tune with high spin configuration of octahedral Ni(II) complex [56].
The Cu(II) complex exhibits the magnetic moment value of 1.83 B.M.
corresponding to one unpaired electron. This value is higher
than the spin-only value, i.e. 1.73 B.M. for one unpaired electron. This
reveals that this complex is monomeric in nature without any of
metal–metal interaction [56] but with some orbital contribution at
room temperature.
3.4. Magnetic moment
The magnetic moment value of the Co(II) complex measured at
room temperature is found to be 4.46 B.M. This high spin value of

446
A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
Fig. 8. Molecular orbital structures (HOMO & LUMO) for complexes (1–4).
3.5. Electronic spectra
24,630–20,325 cm−1 that could be attributed to the π → π* and
n → π* transitions in the aromatic ring or azomethine (–C_N)
groups for free ligand. In the electronic spectra of the ligand and its
metal complexes, the wide range bands were observed due to either
The electronic spectra of the free ligand in DMF showed strong
absorption band in the region at 28,900 cm−1 and shoulder at
Table 7
The calculated quantum chemical parameters of the ligand (HL).
Form
EHOMO (eV)
ELUMO (eV)
ΔE (eV)
X (eV)
η (eV)
σ (eV)−1
Pi (eV)
S (eV)−1
Ω (eV)
ΔNmax
Keto (A)
Keto hydrogen bond (B)
Enol (C)
Enol hydrogen bond (D)
Enol hydrogen bond (E)
−5.741
−6.225
−6.224
−6.123
−5.151
−3.183
−4.123
−2.659
−1.973
−1.310
2.558
2.102
3.565
4.15
4.462
5.174
4.441
4.048
3.230
1.279
1.051
1.782
2.075
1.920
0.781
0.951
0.561
0.481
0.520
−4.462
−5.174
−4.441
−4.048
−3.230
0.390
0.475
0.280
0.240
0.260
7.783
12.735
5.533
3.948
2.717
3.488
4.922
2.491
1.950
1.682
3.841

A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
447
Table 8
The calculated quantum chemical parameters of the complexes (1–4).
Complexa
EHOMO (eV)
ELUMO (eV)
ΔE (eV)
X (eV)
4.6535
3.228
−3.449
−7.278
η (eV)
σ (eV)−1
Pi (eV)
S (eV)−1
ω (eV)
ΔNmax
(1)
(2)
(3)
(4)
−4.773
−3.998
2.412
−4.534
−2.458
4.486
0.239
1.54
2.074
4.14
0.119
0.77
1.037
2.07
8.368
1.298
0.964
0.483
−4.653
−3.228
3.449
4.184
0.649
0.482
0.241
90.606
6.766
5.735
38.941
4.192
−3.325
−3.515
5.208
9.348
7.278
12.794
a
Numbers given in Table 2.
Fig. 9. Mass spectrum of ligand (HL).
the π–π* and n → π* of C_N chromophore or charge-transfer transi-
tion arising from π electron interactions between the metal and li-
gand, which involved either a metal-to-ligand or ligand-to-metal
electron transfer [57].
The electronic spectrum of Cu(II) complex exhibits an intense broad
band in the range 15,375 cm−1 which is attributed to 2T2g → 2Eg transi-
tion, suggesting distorted octahedral geometry [58]. The observed mag-
netic moment of Cu(II) complex is 1.83 B.M. with the presence of one
Scheme 2. Fragmentation patterns of ligand (HL).

448
A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
Fig. 10. Mass spectrum of complex (1).
Scheme 3. Fragmentation patterns of complex (1).
h
i
ꢀ
ꢁ
1=2
2
2
B ¼ 1=30 –ðυ1–υ3Þ ꢁ –υ1 þ υ3 þ υ1υ3
:
unpaired electron [56]. The magnetic moment of Co(II) is 4.46 B.M. sug-
gesting a high-spin octahedral configuration [56]. The high value may
be due to the orbital contribution.
The Co(II) complex exhibits three bands at 11,760, 18,190 and
26,655 cm−1 in the electronic spectrum. The bands can be assigned to
4T1g → 4T2g(F), 4T1g → 4A2g and 4T1g(F) → 4T2g(P) transitions respective-
ly, which are in accordance with its high-spin octahedral geometry [59].
For calculating the Racah parameters, the following equations are used
[60].
10Dq ¼ 1=2ð2υ2–υ3Þ þ 15B:
h
i
1=2
B ¼ 1=510½7ðυ3–2υ2Þ ꢁ 3 81υ32–16υ2ðυ2–v3Þ
:
The magnetic moment value of Ni(II) complex is 3.35 B.M. The elec-
tronic spectrum exhibits bands at 8.520, 14,520 and 25,000 attributable
to 3A2g(F) → 3T2g(F), 3A2g(F) → 3T1g(F) and 3A2g(F) → 3T1g(P) transitions,
respectively. These data together with the magnetic moment value are
10Dq ¼ 2υ1–υ3 þ 15B:

A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
449
of covalency which is evaluated by the expression:
α2 ¼ All=0:036 þ ðgll–2:0023Þ þ 3=7ðgl–2:0023Þ þ 0:04:
β2 ¼ ðgll–2:0023ÞE=‐8λα2:
where λ = −829 cm−1 for the free copper ion and E is the electronic
transition energy. The covalency of the in-plane σ-bonding, α2 = 1 in-
dicate the complete ionic character, whereas α2 = 0.55 denotes 100%
covalent bonding. The β2 parameter gave an indication of the covalency
of the in-plane π-bonding. The smaller the β2, the larger is the covalency
of the bonding. For the copper(II) complex, the high value of β2 (1.0)
compared to α2 indicated that the in-plane σ-bonding was more cova-
lent than the in-plane π-bonding.
3.6. Mass spectra
The electron impact mass spectrum of ligand and its metal com-
plexes are recorded and investigated at 70 eV of electron energy. It is ob-
vious that, the molecular ion peaks are in good agreement with their
suggested empirical formula as indicated from elemental analysis. The
mass spectrum fragmentation mode of ligand (HL) shows the exact
mass of 295 corresponding to the formula C16H13N3O3 (Fig. 9). The ion
of m/z = 295 undergoes fragmentation to a stable peak at m/z = 267
by losing CO atoms (structure I) as shown in Scheme 2. The loss of
NH2 leads to the fragmentation with m/z = 252 (structure II). The
loss of C7H5N atoms leads to the fragmentation with m/z = 150 (struc-
ture III). The loss of OCH3 atoms leads to the fragmentation with m/z =
118 (structure IV). A breakdown of the backbone of ligand gives the
fragment (structure V). The mass spectrum fragmentation mode of
complex (1) shows the exact mass of 512.4 corresponding to the
formula C20H23N3O9Cu (Fig. 10). The ion of m/z = 512.4 undergoes
fragmentation to a stable peak at m/z = 295.16 by losing C4H10O6Cu
atoms (structure I) as shown in Scheme 3. The loss of NH leads to the
fragmentation with m/z = 281.2 (structure II). The loss of CO atoms
leads to the fragmentation with m/z = 253.1 (structure III). The
loss of C7H5N atoms leads to the fragmentation with m/z = 150.1
(structure IV). A breakdown of the backbone of complex gives the frag-
ment (structure V).
Fig. 11. X-ray diffraction patterns for (a) HL ligand and (b) [Cu(HL)(OAc)2(OH2)2]
complex.
suggestive of an octahedral geometry of the complex [59]. The complex
of Cd(II) is diamagnetic. In analogy with this described for Cd(II) con-
taining N–O donor Schiff base and according to the empirical formula
of this complex. We proposed an octahedral geometry for the Cd(II)
complex.
The ESR spectrum of the solid copper(II) complex at room tempera-
ture exhibits gll(2.240) N gl(2.060) N 2.0023, indicating dx2–y2 ground
state for tetragonal copper(II) complexes [61]. The value of gav.(2.12),
suggests the high covalence property of complex with distorted sym-
metry [58]. In axial symmetry, the g-value was related to the G-factor
by the expression, G = (gll − 2)/(gl − 2) = 4.12, which measured the
exchange interaction between copper centers in the solid. According
to Hathaway and Billing [62]. If the value of G is greater than 4, the ex-
change interaction between copper(II) centers is negligible, whereas
when it is less than 4, a considerable exchange interaction exists in
the solid complex. The factor α2 and β2 are usually taken as measure
Table 9
Crystallographic data for HL and [Cu(HL)(OAc)2(OH2)2].
(HL)
[Cu(HL)(OAc)2(OH2)2]
Sys. triclinica
a = 17.079 Å
α = 92.84°
Peak no.
S.G. p2b
Sys. triclinica
a = 13.585 Å
α = 56.06°
Peak no.
S.G. p1b
b = 18.915 Å
β = 96.93°
2θ (°)
c = 11.370 Å
γ = 94.63°
(hkl)
b = 14.557 Å
β = 103.28°
2θ (°)
c = 9.232 Å
γ = 104.82°
(hkl)
d (Å)
d (Å)
1
6.675
7.460
13.23
11.84
7.42
6.54
6.07
5.17
4.93
3.94
3.54
3.36
3.25
3.04
2.84
1
2
6.809
7.448
12.97
11.85
9.55
8.88
8.38
6.88
5.96
4.86
4.45
4.00
3.68
3.28
3.22
110
110
021
220
130
311
022
331
341
100
011
2
3
11.910
13.511
14.565
17.120
17.945
22.518
25.110
26.457
27.354
29.351
31.440
3
9.250
110
011
4
4
9.951
5
5
10.543
12.846
14.850
18.210
19.930
22.178
24.150
27.158
27.657
111
101
020
6
6
7
7
8
8
111
022
9
9
10
11
12
13
10
11
12
13
032
430
123
331
410
221
511
423
a
Sys.: System.
S.G.: Space group.
b

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A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
Fig. 12. TGA graph for ligand (HL).
Fig. 13. TGA curves for complexes (1–4).
3.7. X-ray diffraction analysis
30.16%). The second stage in the temperature range 350–759 °C
corresponding to loss of C5H8NO (Found 31.36%; calc. 33.22%).
After 759 °C corresponding to loss of carbon atoms (found 39.59%;
calc. 36.61%).
The X-ray diffraction (XRD) patterns of the HL and
[Cu(HL)(OAc)2(OH2)2] powder are shown in Fig. 11. The XRD patterns
of the HL and [Cu(HL)(OAc)2(OH2)2] show that both of HL and complex
are polycrystalline with Triclinic crystal system and structure with
space group p2 and p1, respectively. The estimated lattice parameters
(a, b, c, α, β and γ), interplanar spacing, d, and Miller indices hkl, for
the HL and complex are listed in Table 9.
3.8.2. Thermal analysis of complexes (1–4)
The TGA of the isolated complexes was taken as a proof for the
existing of water molecules as well as the anions in the coordination
sphere. The thermal analyses data for the [M(HL)(OAc)2(OH2)2]
where (M_Cu(II), Co(II), Ni(II) and Cd(II)) complexes are summa-
rized in Table 10. The TGA curves for complexes are shown in
Fig. 13. It can be seen that the TGA curves of the complexes
[M(HL)(OAc)2(OH2)2] show loss of masses up to 120 °C above which
the dehydration begins. In the first stage, all the complexes (1–4) loss
of the two coordinated water molecules as well as the loss of two ace-
tate groups. The second and third stages are related to decomposition
of a parts of the ligand. The final weight losses are due to the decompo-
sition of the rest of the ligand and metal oxides residue.
3.8. Thermal analysis
3.8.1. Thermogravimetric analysis of ligand (HL)
The thermal properties of ligand were characterized on the
basis of thermogravimetric analysis (TGA) and (DTG) methods in
the temperature range 30–800 °C. The TGA curve for ligand is
shown in Fig. 12. The temperature intervals and the percentage
of loss of masses are listed in Table 10. Ligand shows two decom-
position steps, the first stage occur in the temperature range 205–
350 °C is attributed to Loss of C2H5N2O2 (Found 30.69%; calc.
3.8.3. Calculation of activation thermodynamic parameters
The thermodynamic activation parameters of decomposition pro-
cesses of the ligand and its metal complexes (1–4) namely activation en-
ergy (Ea), enthalpy (ΔH*), entropy (ΔS*), and Gibbs free energy change
of the decomposition (ΔG*) are evaluated graphically by employing the
Coast–Redfern [63] and Horowitz–Metzger [64] methods.
Table 10
Weight losses percentage of ligand and its metal complexesa.
Compound Temp. range Found mass loss (calc.) Assignment
3.8.3.1. Coast–Redfern equation. The Coast–Redfern equation, which is a
typical integral method, can represent as:
(°C)
%
HL
205–350
350–759
N759
128–309
309–394
394–795
N795
138–323
323–575
575–763
N763
138–344
344–540
540–758
N758
30.69 (30.16)
31.36 (33.22)
39.59 (36.61)
28.02 (30.05)
7.67 (8.78)
19.68 (19.90)
44.63 (41.25)
27.45(30.3)
27.85 (27.36)
13.5 (11.02)
31.20 (31.28)
27.05 (30.3)
18.97 (17.3)
17.83 (16.35)
36.15 (35.97)
19.35 (16.92)
18.32 (21.55)
12.5 (15.14)
49.83 (46.38)
Loss of C2H5N2O2
Loss of C5H8NO
Loss of carbon atoms
Loss of C4H10O6
Loss of HN2O
Loss of C5H12NO
Loss of carbon atoms + CuO
Loss of C4O6H10
Loss of C6O2H7N2
Loss of C3H6N
Loss of carbon atoms + CoO
Loss of C4H10O6
Loss of C3H8N2O
Loss of C4H5NO
Loss of carbon atoms + NiO
Loss of C2O4H7
Loss of C4H11NO3
Loss of C3H5N2O
Loss of carbon atoms + CdO
ꢂ
ꢃ
Z
Z
a
T2
T1
(1)
dx
A
φ
Ea
RT
¼
exp
−
dt
ð11Þ
n
0 ð1−αÞ
(2)
(3)
(4)
For convenience of integration, the lower limit T1 usually taken as
zero. This equation on integration gives:
ꢄ
ꢅ
ꢄ
ꢅ
lnð1−αÞ
Ea
RT
AR
φEa
ln −
¼ −
þ ln
ð12Þ
T2
120–211
211–446
446–761
N761
A plot of left-hand side (LHS) against 1/T was drawn (Fig. 14). Ea is
the energy of activation in J mol−1 and calculated from the slope and
Numbers given in Table 2.
A in (s−1) from the intercept value. The entropy of activation (ΔS ) in
a
⁎

A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
451
Fig. 14. Coats–Redfern (CR) of the ligand and its metal complexes (1–4).
(J·mol−1·K−1) calculated by using the equation:
write in the form:
ꢄ
ꢂ
ꢃꢅ
ꢄ
ꢂ
ꢃꢅ
Wα
Wγ
Eaθ
2:303RT2S
Ah
kBTS
ASꢂ ¼ 2:303 log
R
ð13Þ
log log
¼
− log2:303
ð15Þ
where θ = T − Ts, wγ = wα − w, wα = mass loss at the completion re-
action; w = mass loss up to time t. The plot of log [log (wα/wγ)] vs. θ
was drawn and found to be linear from the slope of which Ea was calcu-
lated. The pre-exponential factor, A, calculated from equation:
Where kB is the Boltzmann constant, h is the Plank's constant and Ts
is the TG peak temperature.
3.8.3.2. Horowitz–Metzger equation. The Horowitz–Metzger equation is
an illustrative of the approximation methods. These authors derived
the relation:
Ea
RT2S
A
ꢄ
ꢂ
ꢃꢅ
¼
ð16Þ
Ea
RTS
ϕ exp
−
"
#
1−n
1−ð1−αÞ
1−n
Eaθ
2:303RT2S
⁎
log
¼
forn≠1
ð14Þ
The entropy of activation, ΔS , is calculated from the equation.
⁎
⁎
The enthalpy activation, ΔH , and Gibbs free energy, ΔG , calculated
from:
when n = 1, the LHS of equation would be log[−log(1 − α)] (Fig. 15).
For a first order kinetic process, the Horowitz-Metzger equation may
ΔHꢂ ¼ Ea−RT
ð17Þ

452
A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
Fig. 15. Horowitz–Metzger (HM) of the ligand and its metal complexes (1–4).
ΔGꢂ ¼ ΔHꢂ−TΔSꢂ
ð18Þ
3.9. DNA binding studies
Electronic absorption spectroscopy is one of the most universally
employed methods to study the binding modes and binding extent of
compounds to DNA. DNA usually exhibits hypochromism as a conse-
quence of the intercalation mode, which involves a strong stacking
interaction between an aromatic chromophore and the base pairs
⁎
⁎
⁎
The calculated values of Ea, A, ΔS , ΔH and ΔG for the decomposi-
tion steps for ligand and its metal complexes (1–4) are summarized in
Table 11.
Table 11
Kinetic parameters of the ligand and its metal complexesa.
Compound
Decomposition temperature
(°C)
Method
Parameters
a (kJ mol−1
Correlation coefficient (r)
E
)
A (s−1
)
ΔS* (J mol−1 K−1
)
ΔH* (kJ mol−1
)
ΔG* (kJ mol−1
)
(HL)
(1)
(2)
(3)
(4)
205–350
128–309
138–323
138–344
120–211
CR
HM
CR
HM
CR
HM
CR
HM
CR
HM
57.1
67.7
23.0
31.3
31.4
40.1
29.8
38.8
38.6
47.0
1.31 × 103
9.33 × 104
1.25 × 101
9.98
−1.90 × 102
−1.54102
52.9
63.5
19.0
27.3
27.4
36.1
25.7
34.7
35.0
43.4
148
141
147
138
142
138
146
141
121
120
0.982
0.985
0.988
0.995
0.998
0.994
0.992
0.996
0.947
0.949
−2.66 × 102
−2.30 × 102
−2.36 × 102
−2.10 × 102
−2.42 × 102
−2.15 × 102
−2.01 × 102
−1.79 × 102
4.76
1.08 × 102
2.26
5.93 × 101
2.70 × 102
4.11 × 103
a
Numbers given in Table 2.

A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
453
Fig. 16. Absorption spectra of ligand and its metal complexes (1–4) in buffer pH 7.2 at 25 °C in the presence of increasing amount of CT-DNA. Inset: plot of [DNA]/(εa–εf) × 10–8 M2 cm
versus [DNA] × 10–6 M for titration of DNA with ligand and its metal complexes (1–4).
of DNA. This strong stacking interaction is due to the contraction of
calf thymus (CT)-DNA in the helix axis and its conformational chang-
es [65–67]. Absorption titration experiments were performed with
fixed concentrations of the ligand (40 μM) and complexes (1–4)
while gradually increasing the concentration of DNA (10 mM) at
25 °C. While measuring the absorption spectra, an equal amount of
Table 12
Effect of ligand and its metal complexesa on S. aureus, E. coil and C. albicans.
Compound
(mg/ml)
E. coli
S. aureus
C. albicans
Diameter of inhibition
zone (mm)
% activity index
Diameter of inhibition
zone (mm)
% activity index
Diameter of inhibition
zone (mm)
% Activity index
(HL)
(1)
(2)
(3)
10
NA
8
NA
5
41.7
–
33.3
–
20.8
100
–
14
8
10
7
16
22
NA
63.6
36.4
45.4
31.8
72.7
100
–
25
13
19
18
21
NA
26
96.1
50.0
73.1
69.2
80.8
–
(4)
Ampicillin
Colitrimazole
24
NA
100
Each value was replicated three time.
NA → no activity.
a
Numbers given in Table 1.

454
A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
DNA was added to both the compound solution and the reference so-
lution to eliminate the absorbance of DNA itself. We have deter-
mined the intrinsic binding constant to CT-DNA by monitoring the
absorption intensity of the charge transfer spectral bands 345, 351,
321, 348, 341 nm for the ligand and Cu(III), Co(II), Ni(II) and Cd(II)
complexes, respectively. The absorption spectra of these ligand and
complexes (1–4) with increasing concentration of CT-DNA in the
range 300–700 nm are shown in Fig. 16.
DNA interaction study by UV–Visible Spectroscopy Electronic ab-
sorption spectra were initially used to examine the interaction be-
tween ligand and CT-DNA. After interaction with increasing
amount of DNA, the absorption spectra of ligand and its metal com-
plexes (1–4) display clear hypochromism with slight blue shift
(~1–2 nm). After the intercalation of the compounds into the base
pairs of DNA, the π* orbital of the intercalated compounds are able
to couple with the π orbitals of the base pairs, thereby decreasing
the π → π* transition energies. These interactions result in the ob-
served hypochromism [68].
tested to increase the chance of detection of their antimicrobial activi-
ties. The used organisms in the present investigations included Gram
positive (S. aureus), Gram negative (E. coli) bacteria and yeast
(C. albicans). The results of the antimicrobial activities of the synthe-
sized compounds were recorded in Table 12. The zone of inhibition
was measured in mm and was compared with a standard drug. DMSO
was used as a blank and ampicillin was used as the antibacterial stan-
dard and colitrimazole was used as the yeast standard. The results indi-
cate that, these compounds are active in inhibiting the growth of the
bacterial and fungal species [70]. All the compounds were tested at
1 mg/mL concentration. The data show that the ligand is the most active
than complexes against E. coli, with % activity index 41.7. The ligand and
Cd(II) complex display good inhibitory properties against the tested
S. aureus and C. albicans with % activity index 63.6 and 72.7 for
S. aureus and 96.1 and 80.8 for C. albicans, respectively.
3.12. Antioxidant assay
The intrinsic binding constant (Kb) of ligand and its metal complexes
(1–4) with DNA was obtained by observing the changes in absorbance
of the complexes with increasing concentration of DNA. Kb values for li-
gand and Cu(II), Co(II), Ni(II) and Cd(II) complexes were found to be
In vitro antioxidant activities of all the synthesized compounds
were evaluated by 2,2-azinobis-3-ethylbenzothiazoline-6-sulfonic
acid (ABTS) cation radical assay as stable free radical which is a con-
ventional and excellent model for assessing the antioxidant activities
of hydrogen donating and chain breaking antioxidants [71]. Radical
scavenging ability and percentage of inhibition (%) expressed as:
2.99 × 106, 1.34 × 105, 1.19 × 105, 1.10 × 105 and 1.26 × 105 M−1
respectively.
,
AðcontrolÞ−AðtestÞ
3.10. Structural interpretation
% Inhibition ¼
ꢃ
100
AðcontrolÞ
The structures of the complexes of Schiff base HL, with Cu(II), Co(II),
Ni(II) and Cd(II) ions are confirmed by elemental analysis, molar con-
ductivity, 1H NMR, UV–vis, IR, mass spectroscopy, X-ray, magnetic mea-
surements and thermal analysis data. Therefore, from the IR spectra, it is
concluded that HL behaves as a neutral bidentate ligand with NO sites
and coordinated to the metal ions via the azomethine N and carbonyl
O. From the molar conductance data of the complexes, it is concluded
that the complexes are considered as non-electrolytes. The 1H NMR
spectra of the free ligand and its diamagnetic Cd(II) complex shows
that the azomethine signal participate in chelation, without proton NH
and OH signals of HL and complex displacement and/or coordinated.
On the basis of the above observations and from the magnetic and spec-
tral measurements, octahedral geometry is suggested for the investigat-
ed complexes are shown in Fig. 1.
The results of the antioxidant activities of the synthesized com-
pounds were recorded in Table 13. The ligand exhibited a potent radical
scavenging ability with % inhibition value 83.3% which comparable to
that of Ascorbic-acid 89%. Compound having –OH (phenolic) group in
the phenyl ring as in ligand was found to be the most potent antioxi-
dants [72]. On the other hand, Cd(II) and Co(II) complexes showed
moderate antioxidant activity. All complexes of HL represented a
lower antioxidant activity compared to its un-complexed compound.
In accordance with the cytotoxicity testing results, the complexation de-
creases the biological activity of the synthesized compound.
3.13. Cytotoxicity assay
The synthesized compounds ligand and its metal complexes (1–4)
were first evaluated with two cancer cell lines (Hepatocellular carcino-
ma (HepG-2) and mammary gland breast cancer (MCF-7) in vitro by the
standard 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium
3.11. Antimicrobial activity
The antibacterial activity of the Schiff bases may arise from the pres-
ence of imine groups and also from the presence of the hydroxyl groups
because of their capacity of hydrogen bonding interactions with cellular
compartment [69].
The antimicrobial activity of (HL) and metal complexes (1–4) were
tested against bacteria and yeast. More than one test organism was
Table 14
Evaluation of cytotoxicity of Ligand (HL) and their metal complexes (1–4) against HepG-2
and MCF-7 cells.
Cell lines
HepG-2
Sample conc.
Compound
5-FU
HL
(1)
43.6
55.8
67.2
79.3
93.6
100
100
100
(2)
38.3
50.4
62.7
75.0
89.6
100
100
100
(3)
33.9
45.8
58.1
68.7
90.3
100
100
100
(4)
20.8
27.3
38.1
51.7
72.6
91.5
100
100
37.9
49.5
61.4
75.8
91.7
100 μg/ml
50 μg/ml
25 μg/ml
12.5 μg/ml
6.25 μg/ml
3.125 μg/ml
1.56 μg/ml
0 μg/ml
100 μg/ml
50 μg/ml
25 μg/ml
12.5 μg/ml
6.25 μg/ml
3.125 μg/ml
1.56 μg/ml
0 μg/ml
8.6
17.1
24.0
33.1
56.8
70.6
88.7
100
16.3
25.1
36.7
48.2
67.5
88.9
100
100
33.3
Table 13
Antioxidant assay for the prepared ligand and its metal complexesa.
Method compounds
ABTS
Abs(control) − Abs(test) / Abs(control) × 100
Absorbance of samples
% inhibition
MCF-7
5.8
45.6
41.3
47.3
Control of ABTS
Ascorbic-acid
0.520
0.057
0.087
0.315
0.281
0.321
0.172
0%
10.3
16.2
28.5
48.4
62.8
81.6
100
46.2
58.4
69.8
90.5
100
100
100
57.3
71.4
82.5
97.1
100
100
100
52.7
64.1
77.5
91.3
100
100
100
58.5
71.7
82.9
96.8
100
100
100
89.0%
83.3%
39.4%
46.0%
38.3%
66.9%
(HL)
(1)
(2)
(3)
(4)
100
100
100
a
Numbers given in Table 2.

A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
455
bromide (MTT) method. 5-FU used as positive control for comparison.
4. Conclusion
Inhibitory activity against HepG-2 and MCF-7 cell lines was detected
by using different concentrations of the tested compounds (i.e., 1.56,
3.125, 6.25, 12.5, 25, 50 and 100 μg/ml) and viability cells (%) were de-
termined by the colorimetric method, data presented in Table 14. The
half-inhibitory concentration (IC50) values were calculated from
Fig. 17 and summarized in Table 15.
The evaluated compounds were observed to exhibit favorable
growth inhibitory activities against tested cell lines in comparison
with 5-FU. The ligand and Cd(II) complex exhibited strong cytotoxicities
against HepG2 cells IC50 values 14.9 1.30 and 17.3 1.28, respective-
ly. Also they exhibited moderate cytotoxicities against MCF-7 cells IC50
values 41.4 3.62 and 50 3.72, respectively. Ni(II) complex exhibited
moderate cytotoxicity against HepG2 cells IC50 values 41.1 3.11. From
the above results the ligand and its metal complexes (1–4) have a better
cytotoxic and antitumor activity against (HepG-2) than (MCF-7).
The Schiff base derived from isatin, hydrazine hydrate and 2-
hydroxy-3-methoxy-benzaldehyde acts as neutral bidentate ligand.
Bonding through azomethine nitrogen and oxygen atoms. On the
basis of all the spectral data, it is observed that all complexes (1–4) pos-
sess an octahedral geometry. The XRD studies show that both the ligand
and copper(II) complex show polycrystalline with Triclinic crystal sys-
tem. The calf thymus DNA binding activity of the ligand (HL) and its
complexes (1–4) were studied by absorption spectra measurements.
The molecular structures of the investigated compounds have been
discussed. The thermal properties of the ligand and its complexes (1–
4) were investigated by thermogravimetry analysis (TGA) and different
thermodynamic parameters are calculated using Coats–Redfern
and Horowitz–Metzger methods. The ligand and its metal complexes
(1–4) were tested against bacterial species, Gram positive (S. aureus),
Fig. 17. Cytotoxic and antitumor activity of ligand (HL) and its metal complexes (1–4) against HePG2 and MCF-7.

456
A.Z. El-Sonbati et al. / Journal of Molecular Liquids 218 (2016) 434–456
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Table 15
Evaluation of cytotoxicity of the prepared ligand and its metal complexesa against HePG2
and MCF-7 cell.
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