Characterization and thermal studies of nano-synthesized Mn(II), Co(II), Ni(II) and Cu(II) complexes with adipohydrazone ligand as new promising antimicrobial and antitumor agents

Article abstract of DOI:10.1002/aoc.3885

New seven complexes of N₁,N₆-bis((2-hydroxynaphthalin-1-yl)methinyl))adipohydrazone (H₂L) with MnCl₂?4H₂O, CoCl₂?6H₂O, NiCl₂?6H₂O, CuCl₂?2H₂O, Cu(NO₃)₂?3H₂O, CuSO₄?5H₂O, and Cu(OAc)₂?2H₂O have been prepared and characterized by the aid of elemental and thermal analyses, spectra (FT-IR, ¹H NMR, MS, UV-Vis, ESR, X-ray powder diffraction), molar conductance and magnetic moment measurements. The XRD results unambiguously confirmed the nano-sized particles of the complexes. The results showed that H₂L behaves as dibasic tetra-dentate ligand towards the metal ions of interest. The low molar conductance values revealed the non-electrolytic nature for the chelates. The magnetic moment data, UV-Vis and ESR spectra denoted the formation of octahedral geometries for Mn(II) and Ni(II) complexes, whereas Co(II), Cu(II) complexes exhibited tetrahedral arrangement. The activation parameters for the thermal decomposition stages were calculated from TGA curves using Coats-Redfern and Horowitz–Metzger methods. The obtained data were confirmed by 3-D molecular modeling of the ligand and some complexes. The investigated compounds were screened for their antimicrobial activities against different types of organisms and antitumor activities towards human liver Carcinoma (HEPG2) cell to access their potential chemotherapeutic use. The free ligand (H₂L) exhibited a weak inhibition of cell viability with IC₅₀ of 11.80 μg/ml, complexes 4, 6 and 7 showed a moderate activity with IC₅₀ of 5.56, 7.71 and 5.67 μg/ml, whereas complexes 1, 2, 3, and 5 displayed a strong anticancer activity with IC₅₀ of 4.65, 3.97, 3.30 and 4.84 μg/ml, compared with IC₅₀ value of 4.73 μg/ml for the doxorubicin (standard cytotoxin drug).

Full text of DOI:10.1002/aoc.3885

Received: 6 February 2017
DOI: 10.1002/aoc.3885
Revised: 7 April 2017
Accepted: 15 April 2017
F U L L PA P E R
Characterization and thermal studies of nano‐synthesized Mn(II),
Co(II), Ni(II) and Cu(II) complexes with adipohydrazone ligand as
new promising antimicrobial and antitumor agents
Mohamed Gaber1 | Abdalla M. Khedr1,2
| Mohsen Elsharkawy1
1 Chemistry Department, Faculty of Science,
Tanta University, Tanta, Egypt
2 Department of Chemistry, Faculty of
Applied Science, Umm Al‐Qura University,
Makkah, Saudi Arabia
New seven complexes of N1,N6‐bis((2‐hydroxynaphthalin‐1‐yl)methinyl))
adipohydrazone (H2L) with MnCl2•4H2O, CoCl2•6H2O, NiCl2•6H2O,
CuCl2•2H2O, Cu(NO3)2•3H2O, CuSO4•5H2O, and Cu(OAc)2•2H2O have been
prepared and characterized by the aid of elemental and thermal analyses, spectra
(FT‐IR, 1H NMR, MS, UV‐Vis, ESR, X‐ray powder diffraction), molar conductance
and magnetic moment measurements. The XRD results unambiguously confirmed
the nano‐sized particles of the complexes. The results showed that H2L behaves as
dibasic tetra‐dentate ligand towards the metal ions of interest. The low molar
conductance values revealed the non‐electrolytic nature for the chelates. The
magnetic moment data, UV‐Vis and ESR spectra denoted the formation of
octahedral geometries for Mn(II) and Ni(II) complexes, whereas Co(II), Cu(II)
complexes exhibited tetrahedral arrangement. The activation parameters for the
thermal decomposition stages were calculated from TGA curves using Coats‐
Redfern and Horowitz–Metzger methods. The obtained data were confirmed by
3‐D molecular modeling of the ligand and some complexes. The investigated com-
pounds were screened for their antimicrobial activities against different types of
organisms and antitumor activities towards human liver Carcinoma (HEPG2) cell
to access their potential chemotherapeutic use. The free ligand (H2L) exhibited a
weak inhibition of cell viability with IC50 of 11.80 μg/ml, complexes 4, 6 and 7
showed a moderate activity with IC50 of 5.56, 7.71 and 5.67 μg/ml, whereas
complexes 1, 2, 3, and 5 displayed a strong anticancer activity with IC50 of 4.65,
3.97, 3.30 and 4.84 μg/ml, compared with IC50 value of 4.73 μg/ml for the
doxorubicin (standard cytotoxin drug).
Correspondence
Abdalla M. Khedr, Chemistry Department,
Faculty of Science, Tanta University, Tanta,
Egypt; Department of Chemistry, Faculty of
Applied Science, Umm Al‐Qura University,
Makkah, Saudi Arabia.
Email: abkhedr2010@yahoo.com
KEYWORDS
antimicrobial, antitumor, hydrazone derivatives, nano‐metal complexes, spectral
1 | INTRODUCTION
emulsions. It is used for preparation of active forms of
primarily neutral mannans from pathogenic yeasts (Candida
Adipodihydrazide is a symmetrical molecule with a two
CONHNH2 as reactive groups and C4 backbone. It offers
amido‐ and amino functionality at both ends of the molecules
which makes it splendid cross‐linking agent for water based
glabrata, Candida tropicalis, Candida albicans). Exalted
cross‐linking influence of ADH was detected, despite the
high surplus of ADH involved in the reaction.[1] Also, it is
used as an excellent hardener for certain epoxy resins, in
Appl Organometal Chem. 2017;e3885.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3885

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GABER ET AL.
coating, adhesive and other manufacturing applications.[2]
Schiff bases are a serious category of compounds reported
to own nitrogen carbon double bond which is answerable
for various biological activities,[3] including anticancer,[4]
antipyretic,[5] antitumor,[6] anti‐inflammatory activities.[7]
They possess chelatogenic properties, so form interesting
ligands in coordination chemistry.[8–10] Transition metal
complexes of hydrazones have many applications such as
antibacterial, antifungal, antiviral, and anticancer agents and
they are considered as important model for several biological
systems.[11] Hydrazones and their complexes accentuate a
multilateral class of compounds in organic chemistry. These
compounds have engaging biological properties such as
antitumor, anti‐inflammatory, antituberculous, analgesic,
antimicrobial and anticonvulsant activity.[12,13] Hydrazones
are interesting compounds for drug design and the syntheses
of heterocyclic compounds, organo‐catalysis and also as
possible ligands in metal complexes.[14] Manganese is a
substantial element for human health, essential for antioxi-
dant system, metabolism, and development. The classes of
enzymes that have manganese cofactors are large and
involves transferases, oxidoreductases, lyases, hydrolases,
isomerases, integrins, lectins and ligases.[15] Cobalt is an
important element to the metabolism of all animals. It is a
key constituent of cobalamin, also known as vitamin B12,
the primary biological reservoir of cobalt as an ultratrace
element. Proteins depend on cobalamin apply corrin to grasp
the cobalt.[16] Nickel plays an essential role in the biology of
many plants, fungi, archaebacteria, and eubacteria. Enzymes
of nickel such as urease are considered virulence factors in
many organisms. Urease catalyses the hydrolysis of urea to
compose carbamate and ammonia. The [NiFe]‐hydrogenases
catalyses the oxidation of H2 to form electrons and protons,
also it catalyzes the reverse reaction, formation of hydrogen
gas through the reduction of protons.[17] Copper is biostatic,
touching of copper‐alloy surfaces have natural properties
which destroy a floppy range of microorganisms (e.g., adeno-
virus, influenza A virus, fungi, methicillin‐resistant Staphylo-
coccus aureus (MRSA), E. coli O157:H7, Staphylococcus
and Clostridium difficile). Copper proteins have diversified
roles in biological oxygen transportation and electron
transport, processes that take advantage of the cushy inter‐
conversion of Cu(I) and Cu(II).[18] Also, it has been reported
that different salts of the same metal with the ligand gives
complexes of different stereochemistry.[19,20] Hence, our goal
was to synthesize a new series of bioactive nano‐sized
Mn(II), Co(II), Ni(II) and Cu(II) chelates with N1,N6‐bis(2‐
hydroxynaphthalin‐1‐yl)methinyl)adipohydrazone for phar-
maceutical applications. The subsistence of metal chelates
in nanosized form expedites the absorption of such
compounds by the human body and displays a towering
efficiency of their vitality in treatment of diversified human
diseases. The structural formulae of the complexes are
investigated using analytical and spectral techniques. The
molecular modeling was performed for the ligand and some
complexes to assert their structural formula.
2 | EXPERIMENTAL
Adipodihydrazide, hydrazine hydrate, triethylamine, ethanol,
diethylether, DMSO, DMF, MnCl2•4H2O, CoCl2•6H2O,
NiCl2•6H2O, CuCl2•2H2O, Cu(NO3)2•3H2O, CuSO4•5H2O,
and Cu(OAc)2•2H2O were of analytical grade and used
without further purification.
2.1 | Synthesis of the organic ligand
Ligand
N1,N6‐bis((2‐hydroxynaphthalin‐1‐yl)methinyl))
adipohydrazone (H2L) was synthesized using a procedure
reported in the literature,[21] by condensation of
adipodihydrazide (1 mM, 0.1742 g) and 2‐hydroxy‐1‐
naphthaldehyde (2 mM, 0.34436 g) in ethanol (30 mL). The
reaction mixture was refluxed on a water bath for 20 h, with
constant stirring in presence of four drops of acetic acid. The
mixture was cooled to room temperature and the precipitated
product was filtered off and was recrystallized from ethanol
in order to get a pure sample. The scheme for the preparation
of the free ligand (H2L) is presented in Scheme 1. The purity
of ligand was checked by TLC and melting point constancy.
2.2 | Synthesis of the nano‐sized metal
complexes
The nano‐sized metal complexes were synthesized by mixing
hot ethanolic solution of 1 mM (0.4820 g) of ligand (H2L)
with 1 mM of the metals salts [MnCl2•4H2O (0.1979 g),
CoCl2•6H2O (0.2379 g), NiCl2•6H2O (0.2377 g),
CuCl2•2H2O (0.1705 g), Cu(NO3)2•3H2O (0.2416 g),
CuSO4•5H2O (0.2379 g), and Cu(OAc)2•2H2O (0.2497 g)]
dissolved in ethanol (40 ml) in the presence of five drops of
triethylamine as basic medium. The resulting solution was
SCHEME 1 Preparation of N1,N6‐bis((2‐hydroxynaphthalin‐1‐yl)
methinyl))adipohydrazone (H2L)

GABER ET AL.
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gently refluxed for 18 h. Both contentious heating and the
presence of triethylamine as basic medium enhance the
formation of nano‐sized particles. After cooling, the resulting
precipitate was filtered off, washed several times with ethanol
and finally dried in a vacuum dessicator over anhydrous
CaCl2. The scheme for synthesis of nano‐sized metal
complexes (1–7) is given in Scheme 2. The solids complexes
were subjected to different analytical and spectroscopic tools.
T80 + UV–Vis spectrometer. Room temperature magnetic
susceptibilities were measured using a Sherwood scientific
magnetic susceptibility balance. Experimental magnetic
susceptibility values have been corrected for diamagnetism
of the constituent atoms by the use of Pascal's constants.[22]
EPR spectra of some Cu(II) complexes as powders were
obtained on a Jeol JES‐RE1X EPR spectrometer working
in the X‐band (9.435 GHz). A spectrum was obtained in a
2‐mm quartz capillary at room temperature at Alexandria
University. XRD patterns of the samples were recorded on
X‐ray diffractometer (GNR, APD2000PRO, Italy) at Central
Laboratory, Tanta University, Egypt. All patterns were
obtained using Cu/Kα1 radiation with a graphite monochro-
mator at 0.03° min−1 scanning rate. The thermal gravimetric
analysis (TGA) of the solid complexes was measured via a
Shimadzu TG‐50 thermal analyser from ambient temperature
up to 800οC under nitrogen as atmosphere with 10οC/min
heating rate.
2.3 | Analysis and instrumentations
C, H and N contents were determined micro‐analytically at
the Micro‐Analytical Center, Cairo University by Perkin‐
Elmer 2400 CHN Elemental Analyzer. The metal content
was determined using inductively coupled plasma (ICP)
technique after decomposition of the metal complexes using
nitric acid. The molar conductivities of the metal complexes
were measured in DMF (10−3 mol L−1) by the aid of a con-
ductivity meter JENWAY model 4070 Conductance Bridge
at room temperature. Infrared spectra of the ligand and its
metal complexes in KBr disks were recorded on a Jasco
FT‐IR–4100 (made in Japan) within 4000–200 cm−1 range
at Central Laboratory, Tanta University, Egypt.1HNMR spec-
tra were investigated using a Mercury Oxford NMR 300 Hz
spectrophotometer using tetramethylsilane (TMS) as internal
standard after dissolving the samples in DMSO‐ d6 (EI‐MS).
Standard electron impact mass spectra (E.I) of the free ligand
and its metal complexes were performed by a Finnigan MAT
8222 Spectrometer at 70 eV at Micro‐Analytical Unit of
Cairo University. Electronic absorption spectra were taken
in freshly prepared DMF solution from 200 to 800 nm with
2.4 | Antimicrobial activity (sensitivity) tests
Antimicrobial activity of the free ligand and its metal
complexes was tested using a modified Kirby‐Bauer disc
diffusion method,[23] at Micro‐Analytical Center, Cairo
University. Standard discs of Ampicillin (antibacterial agent),
Norfloxacin (antibacterial agent) and Amphotericin B
(antifungal agent) served as positive controls but filter discs
impregnated with 10 μL of solvent (distilled water, chloro-
form, DMSO) were used as a negative control. 100 μL of
the test bacteria/fungi were grown in 10 ml of fresh media
until they reached a count of 108 cells/ml for bacteria and
105 cells/ml for fungi,[24] approximately. 100 μl of microbial
suspension was spread onto agar plates corresponding to the
broth in which they were preserved. Isolated colonies of each
organism that might be playing a pathogenic role should be
elected from primary agar plates and tested for susceptibility
by disc diffusion method.[25] NCCLS recommends Mueller‐
Hinton agar of the many media available, because it results
in good batch‐to‐batch reproducibility. For evaluating the
susceptibilities of filamentous fungi to antifungal agents, disc
diffusion method for filamentous fungi tested by using
approved standard method (M38‐A) developed by the
NCCLS, 2002.[26] Disc diffusion method for yeasts expanded
by using approved standard method (M44‐P) by the NCCLS,
2003.[27] Plates inoculated with filamentous fungi as
Aspergillus flavus at 25 °C for 48 h; Gram (−) bacteria as,
Escherichia coli; Gram (+) bacteria as Staphylococcus
aureus; they were incubated at 35‐37 °C for 24–48 h and
yeast as Candida albicans incubated at 30 °C for 24–48 h
and, then the diameters of the inhibition zones were mea-
sured in millimetres.[23] Meuller‐Hinton agar is used as agar
that is rigorously tested for composition and pH. Further-
more, the depth of the agar in the plate is a factor to be
SCHEME 2 Synthesis of synthesis of nano‐sized metal complexes
(1–7), where MX2 is Mn(II), co(II), Ni(II), and cu(II) with different
anions

4 of 14
GABER ET AL.
considered in the disc diffusion method. This method is well
documented and standard zones of inhibition have been
measured for susceptible and resistant values. Blank paper
disks (Schleicher & Schuell, Spain) with a diameter of
8.0 mm were impregnated 10 μL of tested concentration of
the stock solutions. The chemical will diffuse from the disc
into the agar, when a filter paper disc impregnated with a
tested chemical is placed on agar. This diffusion will place
the chemical in the agar only around the disc. The molecular
size of the chemical and its solubility will determine the size
of the area of chemical infiltration around the disc. If an
organism is placed on the agar it will not grow in the area
around the disc if it is susceptible to the tested material. This
area of no growth around the disc is known as a clear zone or
zone of inhibition. The zone diameters were measured with
slipping calipers of the National Committee for Clinical
Laboratory Standards,[28] for the disc diffusion. Agar‐based
methods such as E‐test and disk diffusion can be good
alternatives because they are faster and simpler than broth‐
based methods.[29,30]
as 100% proliferation and the percentage of viability was
calculated as (1‐(ODT/ODC)*100% where ODC is the mean
optical density of untreated cells and ODT is the mean opti-
cal density of the cells treated with the tested sample.[31–33]
3 | RESULTS AND DISCUSSION
3.1 | Stoichiometry and nature of the
complexes
The ligand and its metal complexes with their molecular and
empirical formulae, molecular weight, colour, melting point,
conductance and analytical data are compiled in Table 1. All
complexes (1–7) are air‐stable, coloured, insoluble in water
and most common organic solvents such as, ethanol, metha-
nol, acetone but they dissolve in DMF and DMSO. The
intense colour of the complexes can be attributed to a charge
transfer or a defect of crystal.[34] The analytical data prove
that H2L forms complexes which agree well with 1:1 metal
to ligand stiochiometry with MnCl2•4H2O, CoCl2•6H2O,
NiCl2•6H2O, Cu(NO3)2•3H2O, CuSO4•5H2O, and
Cu(OAc)2•2H2O, but forms complex within 1:2 metal to
ligand stiochiometry with CuCl2•2H2O. The yield for the
synthesized complexes was 75.5–90.4%. The molecular for-
mulae of all the complexes were confirmed by spectral data.
The measured molar conductance values for the complexes
lie within 6.80–12.70 ohm−1 cm2 mol−1 range (Table 1).
These values indicate their non‐electrolytic nature.[35]
2.5 | Potential cytotoxicity measurements
2.5.1 | Cell line
The cell lines were obtained from the American type culture
collection (ATCC, Rockville, MD). The cells were
maintained at 37 °C in humidified atmosphere with 5%
CO2 and were sub‐cultured two to three times a week. The
cells were grown as mono layers on RPMI‐1640 medium
supplemented with 10% inactivated fetal calf serum and
50 μg/L gentamycin.
3.2 | 1H NMR and FT‐IR spectra
1H NMR spectrum of H2L displayed a signal at 12.6 ppm can
be attributed to δOH. In comparison, the stretching vibration
band of OH (νOH) appeared at 3475 cm−1 in IR spectrum of
H2L. The –CH = N– proton appeared as a singlet at 9.2 ppm
2.5.2 | Evaluation of the antitumor activity
1
The antitumor activity was screened on Carcinoma cell lines
at the Regional Center for Microbiology and Biotechnology,
Al‐Azhar University, Cairo, Egypt. The minelayers of 10.000
cells adhered at the bottom of the wells in a 96‐wellmicrotiter
plate Falcon, NJ, USA) incubated at 37 °C for 24 h., in a
humidified incubator with 5% CO2. The monolayer was then
washed with sterile phosphate buffered saline (0.01 M
pH 7.2) and simultaneously the cells were treated with
100 μL from different dilutions of tested sample in fresh
maintenance medium and incubated at 37 °C. A control of
untreated cells was made in the absence of the tested sample.
Three wells were used from each concentration of the test
sample. Every 24 h, the observation was made under inverted
microscope. The number of the surviving cells was
determined by staining the cells with crystal violet followed
by cell lysing using 33% glacial acetic acid. After well
mixing, read the absorbance at 590 nm using ELISA reader.
The absorbance values from untreated cells were considered
in H NMR spectrum of the ligand. This is supported by
appearance of νC = N band appeared at 1620 cm−1 in its
IR spectrum.[36] The multiplet signals that appeared at
7.2–7.6 ppm are assignable to aromatic protons.[37] FT‐IR
spectra of Mn(II), Co(II) and Ni(II) and Cu(II) complexes
(1–7) were compared with that of H2L in order to elucidate
the mode of bonding in the formed complexes (Table 2).
νC = N band appeared at 1620 cm−1 in H2L spectrum,
displayed average shift to lower frequency by 3–22 cm−1
indicating coordination of C = N group to the metal cen-
tre.[19] H2L spectrum exhibited a strong band at 1659 cm−1
due to νC = O which confirm that H2L is stable in its keto‐
form. This band has no or a slight small average frequency
shifts in case of metal complexes (1–7) ruling out the
possibility of coordination of carbonyl oxygen atom to the
metal centre.[34] This originates from coordination of both
the naphtholate oxygen atoms and azomethine nitrogen
atoms of the same ligand molecule to the same metal centre.

GABER ET AL.
5 of 14
TABLE 1 Physical characteristics, microanalysis, and molar conductance data of H2L and its metal complexes (1‐7)
Microanalysis
Found (Calc.) %
Molecular formula
(Empirical formulae)
M.Wt. Found
(Calc.)
Colour
(Λm)
Comp. No.
%C
%H
%N
%M
Ligand
H2L
482.21
Milky
70.00
4.81
11.28
__
(C28H26N4O4)
(482.54)
(‐‐‐)
(69.70)
(5.43)
(11.61)
(‐‐‐)
Complex 1
Complex 2
Complex 3
Complex 4
Complex 5
Complex 6
Complex 7
[MnL]•H2O
(C28H26MnN4O5)
553.49
(553.47)
brown
(8.2)
61.02
(60.76)
5.19
(4.73)
10.22
(10.12)
9.94
(9.93)
[CoL]•C2H5OH
(C30H30CoN4O5)
585.11
(585.52)
D. brown
(12.7)
61.98
(61.54)
6.87
(5.16)
9.72
(9.57)
10.00
(10.07)
[NiL]•C2H5OH
(C30H30N4NiO5)
585.51
(585.28)
F. yellow
(6.8)
62.62
(61.57)
5.74
(5.17)
9.65
(9.57)
10.03
(10.03)
[CuL2]•C2H5OH
(C58H56CuN8O9)
1071.00
(1072.67)
Green
(7.5)
66.37
(64.94)
5.46
(5.26)
10.44
(10.95)
5.42
(5.92)
[CuL]•H2O
(C28H26CuN4O5)
562.01
(562.08)
Green
(10.3)
58.79
(59.83)
4.43
(4.66)
9.81
(9.97)
11.18
(11.30)
[CuL]•2H2O
(C28H28CuN4O6)
580.10
(580.09)
Green
(11.5)
57.29
(57.98)
4.55
(4.86)
9.65
(9.66)
10.50
(10.95)
[CuL]•½H2O
(C28H25.5CuN4O4.5
553.74
(553.07)
Green
(9.5)
60.37
(60.80)
3.82
(4.65)
10.56
(10.13)
11.41
(11.45)
)
M. Wt is the molecular weight obtained from mass spectra and Λm is the molar conductance (Ω‐1 cm2 mol‐1)
This should introduce steric crowding in the complex
3.3 | Mass spectral analysis
molecule. So, one dihydrazone arm remains in the equatorial
plane while the other hydrazone arm attains axial position.[38]
Complexes1–7displayedbroadbandswithin3450–3424cm−1
range, which can be attributed to ν(OH) of water or ethanol
molecules associated with complexes. The presence of water
and ethanol molecules renders it difficult to confirm the
deprotonation of the OH groups on complex formation from
the stretching vibration.[39] All these observations are
supported by appearance of new non‐ligand bands at
655–638 and 546–531 due to ν (M–O) and ν(M–N),
respectively.[36]
Mass spectra are used to confirm the constitutions and
purities of the prepared ligand and its chelates (Figure 1).
The free ligand fragmentation exhibits the molecular ion
peak (calc.) at 482.21 (482.53), which is matched with its
theoretical value. Mass spectra of [MnL]•H2O, [CoL]
•C2H5OH, [NiL]•C2H5OH, [CuL]•H2O, [CuL]•2H2O and
[CuL]•½H2O displayed accurate molecular ion peaks (calc.)
at 553.49 (553.47), 585.11 (585.52), 585.51 (585..28),
562.01 (562.08), 580.10 (580.09), 553.74 (553.07), respec-
tively, corresponding to the parent ion [ML]+. Also,
TABLE 2 Assignments of IR spectral bands (cm−1) of diagnostic
importance for the free ligand (H2L) and its metal complexes (1‐7).
Compound νOH
νNH νC=O νC=N νC‐O νM‐O νM‐N
H2L
3475 3045 1659 1620 1320
‐‐
3424 3047 1671 1607 1347 655
3432 3051 1658 1610 1329 653
3450 3041 1668 1608 1348 651
3444 3046 1662 1609 1334 649
3434 3048 1659 1617 1335 640
3457 3043 1659 1610 1348 650
3439 3050 1660 1598 1334 638
‐‐
Complex 1
Complex 2
Complex 3
Complex 4
Complex 5
Complex 6
Complex 7
534
546
531
540
538
539
544
FIGURE 1 Mass spectrum of [CuL]•H2O (5)

6 of 14
GABER ET AL.
appearance of different peaks due to various fragments
during successive degradation of the target compound is a
perfect support for the suggested molecular structure.[40]
New idealistic evidence support the proposed structure of
the complexes comes from the decomposition of metal
complexes (1–7) via abstraction of H2L, which give rise to
the presence of a molecular ion peak attributable to the free
ligand. This is prevalent demeanour for metal chelates
containing different ligands (ML) that decompose through
cleavage of the metal–ligand bond during the ionization
process.[41]
complex showed two bands in DMF at 438 and 550 nm,
corresponding to 3A2g ! T2g(P) and 3A2g ! T2g(F) transi-
tions, respectively, in an octahedral geometry.[47] Ni(II)
complex displayed magnetic moment value equals 3.16 BM
supporting the octahedral environment around Ni(II) cen-
ter.[48] The electronic spectra of Cu(II) complexes (4–7)
displayed two new bands within 430–440 and 545–600 nm
3
3
2
2
ranges which can be attributed to T2 ! E2 and charge
transfer transitions in tetrahedral Cu(II) complexes.[49] The
subnormal μeff value of Cu(II) complexes (1.72–2.10 BM)
in some cases reveals the Cu‐Cu interaction.[50]
3.4 | Electronic spectra and magnetic moment
measurements
3.5 | ESR spectra of cu(II) complexes
The X‐band ESR spectra of the powder Cu(II) complexes
(4–7) at room temperature showed a broadened feature with-
out hyperfine splitting due to the dipolar interaction from the
ESR spectrum of a set of magnetic parameters. Two aniso-
tropic signals were observed in ESR spectra of all Cu(II)
complexes under interest (Figure 2). The profile of ESR spec-
tra is characteristic of tetrahedral geometry around Cu(II)
center which support and agree with the data obtained from
electronic spectral results. The geff‐values (2.1189–2.1380)
of Cu(II) complexes (4–7) have a positive contribution from
the value of the free electron (2.0023) due to the measurable
covalent character in the bonding between the ligand and
Cu(II) ion. So, we can conclude that the metal ligand bonding
in these complexes has essentially covalent character.[51]
The UV–Vis spectrum of the free ligand (H2L) showed three
bands in DMF at 270, 324 and 372 nm which can be assigned
to π—π* transition of the aromatic moiety, π—π* transition
of CH = N group and charge transfer (CT) interaction within
the whole molecule. These bands displayed obvious shifts in
the spectra of metal complexes supporting the coordination
of the ligand to the central metal ions.[42] The electronic
spectrum of Mn(II) complex showed two non‐ligand bands
4
4
at 436 and 530 nm assignable to 6A1g ! Eg and 6A1g ! T2g
transitions, respectively, in an octahedral configuration.[43]
The observed magnetic moment value of Mn(II) complex
equals 5.67 BM (Table 3). denotes Mn(II) complex is in the
high–spin state in an octahedral geometry.[44] Co(II) complex
displayed two electronic absorption bands at 436 and 625 nm
4
4
4
4
due to A2 ! T1(P) and A2 ! T1(F)transitions, respec-
tively, in a tetrahedral arrangement.[45] Co(II) complex gave
magnetic moment value (4.36 BM) which is higher than
theoretical spin only value referring to orbital contribution
of Co(II) complex.[46] The UV–Vis spectrum of Ni(II)
TABLE 3 UV‐Vis, ESR spectral data and magnetic moment values
of the free ligand (H2L) and metal complexes (1‐7).
Electronic spectra
(λmax ; nm) in DMF
Ligand
bands
Non‐ligand μeff (magnetic
geff
Compound
bands
moment; BM) ─values
Ligand
270, 324, 372
—, —
—
—
—
Complex 1 268, 332, 412
Complex 2 288, 318, 336
Complex 3 272, 326, 370
Complex4 276, 324, 374
Complex 5 275, 332, 374
Complex 6 274, 324, 372
Complex 7 276, 344, 372
436, 530
436, 625
438, 550
438, 545
440, 600
430, 570
435, 580
5.67
4.36
3.16
2.10
1.72
2.00
2.03
—
—
2.1380
2.1240
2.1189
2.1222
FIGURE 2 X‐band ESR spectrum of cu(II) complex (6)

GABER ET AL.
7 of 14
(J mol−1 k−1), ΔG* is the Gibbs free energy (kJ mol−1), K is
the Boltzmann constant and h is the Plank constant.
3.6 | Thermo‐gravimetric analysis
The TGA‐DTG curves of the metal complexes under investi-
gation were recorded from ambient temperature up to 800 °C
at heating rate of 10 °C/min under N2 gas flow as shown in
(Figure 3). From TGA curves, the mass loss was determined
for the different thermal decomposition steps and compared
with those theoretically calculated for the suggested formula
based on the data of elemental analyses. In most cases,
TGA denoted the formation of metal oxide as the final prod-
uct from which the metal content is calculated and found to
be in satisfying agreement with that acquired from analytical
measurements.[52] The obtained data revealed that all metal
chelates decomposed in two steps for complex (4), four steps
for 1, 3, 5 and 7 and five steps for 2 and 6. The stages of
decomposition, temperature ranges, theoretical calculated,
and found mass losses as well as final products observed in
each step are given in Table 4.
The kinetic and thermodynamic activation parameters of
thermal decomposition stages of the metal complexes are
given in Tables 5 and 6. ΔH* values are positive which reveals
that the decomposition processes are endothermic. ΔS*
values for complexes were found to be positive. This reveals
that the activated complex is less ordered than the reactants
and/or the reactions are fast.[56] ΔG* values increase in a suf-
ficiently great or important way for the subsequently decom-
position stages due to increasing TΔS* values of one step to
another which override ΔH*values. This reflects that the rate
of removal of the subsequent ligand parts will be lower than
that of the precedent.[57] This can be assigned to the structural
rigidity of the remaining complex after the expulsion of one or
more ligand part, as compared with the precedent complex,
which requires more energy for its rearrangement before
undergoing any compositional change.
3.7 | Thermodynamic and kinetic parameters
3.8 | XRD studies
The mechanism, activation energy (E), reaction order (n) and,
frequency factor (A), for different stages of thermal decompo-
sition of the complexes (1–7) were determined applying inte-
gral method proposed by Coats‐Redfern (Figure 4).[53] and
the approximation method proposed by Horowitz–
Metzger.[54] The thermodynamic activation parameters
namely, enthalpy (ΔH*), entropy (ΔS*) and free energy
change (ΔG*) of different decomposition steps were calcu-
lated applying the following relationships.[55]
Serious structural information about microcrystalline sam-
ples of H2L and its metal complexes can be provided by
XRD (powder technique).[58] The diffraction patterns were
recorded within 2θ (scattering angle) from 10 to 90°. XRD
patterns of free ligand H2L are different compared with those
of each metal complex (Figures 5 and 6). Also, the inter‐pla-
nar spacing d (Å) and relative intensities (I/I0) of each com-
pound are different from each other. The XRD patterns
declare crystalline nature for the compounds under investiga-
tion. This behaviour may probably be due to the incorpora-
tion of the water or ethanol molecules. A comparative study
in the patterns indicates the absence of smearing or contami-
nation with starting materials. A shift in diffraction peaks of
complexes was observed, suggesting a contribution of the
ligand groups. All these observations support the formation
of single phase metal complexes. The inter‐planar distance
d (the volume average of the crystal dimension normal to
diffracting plane) is calculated from 2θ values applying
Bragg's law, which describes the condition on θ for the con-
structive interference to be at its strongest:[59]
ΔHꢀ ¼ Eꢀ−RT
ΔSꢀ ¼ R½ lnðAh=KBTÞ−1ꢁ
ΔGꢀ ¼ ΔHꢀ−TΔSꢀ
(1)
(2)
(3)
Where T is the observed peak temperature, ΔH* is the
activation enthalpy (kJ mol−1), ΔS* is the activation entropy
2d sinθ ¼ nλ;
where, n is a positive integer and λ is the wavelength of inci-
dent wave.The values of θ, d, β [the line broadening at half
the maximum intensity (FWHM)] of prominent intensity
peak, and particle size of the investigated compounds are
given in Table 7. The size of particle or crystallite size was
calculated from XRD patterns by applying the Scherrer equa-
tion.[60] It is a formula that relates the size of sub‐micrometre
particles, or crystallites, in a solid to the broadening of a peak
FIGURE 3 TGA curves of complexes 1, 3 and 5
in
a
diffraction pattern, in X‐ray diffraction and

8 of 14
GABER ET AL.
TABLE 4 Thermo‐gravimetric analysis (TGA) of the metal complexes (1‐7).
Mass loss %
Molecular
formula
Temp. range
(°C)
Found
Calc.
Assignment
Loss of hydrated H2O molecule.
Removal of (‐CH2‐CH2‐CH2‐CH2‐)
Elimination of 2(C=O), (N2H2).
Decomposition of the organic ligand and formation of MnO as final product.
[MnL]•H2O (1)
35‐95
95‐290
290‐350
350‐590
3.15
10.12
15.5
3.25
10.11
15.53
61.17
61.10
[CoL]•C2H5OH (2)
25‐125
125‐200
200‐300
300‐360
360‐560
7.50
14.11
14.80
14.30
39.00
7.85
14.34
14.68
14.00
39.04
Loss of C2H5OH molecule.
Removal of (‐CH2‐CH2‐CH2‐CH2‐), C=O.
Elimination of (C=O), (N4H2).
Elimination of C2H2, 2(C‐O).
Decomposition of the organic ligand and formation of CoO as final product.
[NiL]•C2H5OH (3)
32‐95
95‐295
295‐365
365‐420
7.25
14.00
14.82
52.90
7.86
14.35
14.69
53.07
Loss of C2H5OH molecule.
Removal of (‐CH2‐CH2‐CH2‐CH2‐), C=O.
Elimination of C=O, N2H2, 2N.
Decomposition of the organic ligand with formation of NiO as final product.
[CuL2]•C2H5OH (4)
[CuL]•H2O (5)
40‐140
140‐400
3.82
80.12
4.28
80.54
Loss of C2H5OH molecule.
Decomposition of the organic ligand with formation of CuO + 8C
50‐125
125‐270
270‐355
355‐470
3.04
14.34
29.50
40.50
3.20
14.94
29.88
40.66
Loss of hydrated H2O molecule.
Removal of (‐CH2‐CH2‐CH2‐CH2‐), C=O.
Elimination of C=O, N2H2, 2N, 2(C‐O).
Decomposition and formation of Cu as final product.
[CuL]•2H2O (6)
[CuL]•½H2O (7)
30‐118
118‐193
193‐293
293‐312
312‐600
6.18
9.27
5.15
10.30
57.73
6.20
9.65
5.17
10.68
57.33
Loss of hydrated 2H2O molecule.
Removal of (‐CH2‐CH2‐CH2‐CH2‐).
Elimination of N2H2.
Elimination of 2C=O.
Decomposition of the organic ligand with formation of CuO as final product.
30‐70
70‐230
230‐360
360‐690
2.06
15.46
11.34
59.79
1.62
15.18
10.88
59.76
Loss of hydrated 1/2H2O molecule.
Removal of (‐CH2‐CH2‐CH2‐CH2‐), C=O.
Elimination of C=O, N2H2.
Decomposition of the organic ligand and formation of Cu as final product.
where, λ is the x‐ray wavelength, τ is the mean size (crystal-
lite size) of the ordered (crystalline) domains, which may be
smaller or equal to the grain size, K is a dimensionless shape
factor, with a value close to unity (the shape factor has a
typical value of about 0.9, but varies with the actual shape
of the crystallite), β is the line broadening at half the maxi-
mum intensity (FWHM), after subtracting the instrumental
line broadening, in radians (this quantity is also sometimes
denoted as Δ(2θ) and θ is the Bragg angle. The average
particle size calculated from different diffraction peaks of
H2L, 1, 2, 3, 4, 5, 6, and 7, compounds were found to be
31.26, 38.79, 19.88, 88.99, 6.21, 26.52, 7.98 and 18.38 nm,
respectively.
FIGURE 4 Coats‐Redfern plot for cu(II)‐complex (6); (a) first step,
(b) second step, (c) third step and (d) fourth step, where, Y = [1‐
(1‐α)1‐n] / (1‐n) T2 for n ≠ 1 or Y = [−ln(1‐ α)] / T2 for n = 1
crystallography.[61] This equation is used to determine the
size of particles of crystals in the form of powder. Scherrer
equation can be written as:
3.9 | Molecular modeling studies
Molecular orbital geometry optimization allows a quantita-
tive discussion of the geometrical properties of the inspected
complexes. Geometric structures of H2L and complexes (1, 2,
3 and 5) were computed by optimization of their bond
Kλ
τ ¼
β cosθ

GABER ET AL.
9 of 14
TABLE 5 Thermodynamic and kinetic parameters of Mn(II), Co(II), Ni(II) and Cu(II) complexes (1‐7) calculated from TGA curves using Coats‐
Redfern method.
Comp.
1
n
Step
r
T (K)
E*
Δ H*
A
‐ΔS*
Δ G*
1
1
0.33
1
1st
0.9991
0.9984
0.9970
0.9998
338
434
592
779
19.50
8.67
132.50
57.98
15.31
1.23
169.02
55.25
3605689
8.41×108
3.43×10‐5
6688068
0.1321
0.0923
0.2742
0.1234
81.77
67.72
336.22
95.84
2nd
3rd
4th
2
3
1
0.66
0.5
1
1st
0.9866
0.9938
0.9978
0.9965
0.9966
333
425
498
618
718
52.31
162.58
87.73
191.77
102.16
49.65
158.67
84.42
188.46
97.61
53.27
5.64×10‐10
39.82
0.2208
0.4341
0.2250
0.3546
0.1905
120.21
362.95
174.11
329.80
201.79
2nd
3rd
4th
5th
6.78×10‐6
3482.53
1
1
1
1
1
1st
0.9965
0.9966
0.9998
0.9999
315
437
605
663
64.75
20.82
488.68
136.09
59.66
15.73
481.35
133.36
0.2226
46005859
2.1×10‐3
1.53
0.2717
0.1125
0.8495
0.2505
225.79
84.52
1230.22
215.42
2nd
3rd
4th
4
5
0
1
1st
0.9929
0.9915
379
599
9.77
81.64
4.32
75.48
1.31×109
3669.33
1.17×10‐6
58.56
0.09
1278.714
0.0852
0.1926
60.18
218.08
2nd
1
1st
0.9991
0.9993
0.9999
0.9995
326
477
577
683
95.62
80.301
132.47
104.40
92.89
74.91
129.15
101.09
0.3485
0.2258
0.2753
0.1962
207.54
221.35
238.97
179.34
0.66
0.66
0.33
2nd
3rd
4th
6
7
1
0.66
1
1
0.33
1st
0.9907
0.9860
0.9990
0.9953
0.9999
334
421
470
570
777
26.13
46.63
163.59
257.03
23.94
23.37
43.87
160.82
254.27
21.18
623462.5
44629.18
3.91×10‐8
5.09×10‐13
6.81×108
0.1432
0.1651
0.3960
0.4895
0.0850
70.98
98.77
292.48
417.02
49.45
2nd
3rd
4th
5th
1
0.5
0.5
1
1st
0.9428
0.9921
0.9872
0.9855
315
448
586
840
41.72
30.34
43.64
82.62
38.95
27.58
40.87
79.86
978.26
4795514
4209989
815686.60
0.1969
0.1262
0.1273
0.1410
104.41
69.55
83.21
2nd
3rd
4th
126.73
E*: the activation energy (kJ mol‐1), ΔH*: the activation enthalpy (kJ mol‐1), ΔS*: the entropy (J K‐1 mol‐1), A: the pre‐exponential factor (s‐1), ΔG*: the free energy
(KJ mol‐1).
lengths, bond angles and dihedral angles applying the hyper
chem. 8.03 molecular modelling program.[62] The optimized
molecular structures with minimum energies obtained from
the quantum chemical calculations are presented in Figures 7
and S1‐S4. Selected bond angles and bond lengths are given
in Tables S1‐S5. As shown in Figure 7, the investigated ligand
has a planner form. The bond lengths of atoms in the two che-
lation centres are N(35)‐C(36) = 1.295, N(33)‐C(34) = 1.317,
N(30)‐N(35) = 1.389, N(29)‐N(33) = 1.397, C(26)‐
O(28) = 1.221, C(25)‐O(27) = 1.218, C(26)‐N(30) = 1.440,
C(12)‐O(37) = 1.366, C(25)‐N(29) = 1.453 and C(8)‐
O(39) = 1.354 Å. Upon complexation, the bond lengths of
the ligand molecules are somewhat altered, especially for
atoms in direct contact with the metal ion centres. The other
bond lengths within the ligand are slightly or not affected by
the coordination to the metal ion. The calculations showed
that Mn‐complex attains an octahedral geometry which agrees
with the proposed experimental octahedral geometry. The
bond lengths of the chelating atoms with the central metal
atom are Mn(37)‐O(39) = 1.891, Mn(37)‐O(38) =1.892,
O(36)‐Mn(37) = 1.904, O(35)‐Mn(37) = 1.906, N(33)‐
Mn(37) = 1.908, N(31)‐Mn(37) = 1.902 Å. Also, the quan-
tum chemical calculations donated that Ni‐complex has an
octahedral geometry in good agreement with the obtained
experimental results. The bond lengths of the chelating atoms
with Ni atom are Ni(37)‐O(39)
= 1.872, Ni(37)‐
O(38) = 1.872, O(36)‐Ni(37) = 1.884, O(35)‐Ni(37) = 1.886,
N(33)‐Ni(37) = 1.889 and N(31)‐Ni(37) = 1.882 Å. The bond
angles around Mn and Ni atoms (Tables S2 and S4) are quite
near to an octahedral arrangement,[63] indicating sp3d2
hybridization. Mn(II) and Ni(II) ions are coordinated to the
ligand through the two N‐atoms, oxygens of carbonyl groups
and naphtholate O‐atoms. Co(II) and Cu(II) complexes are
found to be distorted tetrahedral structure where the two
naphtholate O‐atoms and two N‐atoms atoms are coordinated
to the metal center. The bond lengths between Co and chelat-
ing atoms are O(38)‐Co(39) = 1.884, O(37)‐Co(39) = 1.7517,
N(35)‐Co(39) = 1.901 and N(33)‐Co(39) = 1.845 Å. In Cu(II)

10 of 14
GABER ET AL.
TABLE 6 Thermodynamic and kinetic parameters of Mn(II), Co(II), Ni(II) and Cu(II) complexes (1‐7) calculated from TGA curves using Horo-
witz–Metzger method.
Comp.
1
n
Step
r
T (K)
E*
Δ H*
A
‐ΔS*
Δ G*
2
0
1
1
1th
2nd
3rd
4th
0.927
0.964
0.920
0.933
337.5
434.25
592.5
779.5
17.470
1.495
1.552
0.624
14.876
1.098
1.041
1.969
146.73
0.041
0.024
0.008
0.203
0.271
0.275
0.285
78.465
87.149
85.884
90.994
2
3
2
1
0
2
2
1th
2nd
3rd
4th
5th
1th
2nd
3rd
4th
0.942
0.963
0.935
0.949
0.947
333
425.5
498
618
718
31.999
4.209
1.220
2.565
0.604
29.405
1.615
1.373
0.028
1.989
77486.08
0.197
0.151
0.258
0.276
0.262
0.284
76.731
82.346
87.564
81.869
90.639
0.024
0.129
0.009
9.37×105
0.080
0.019
0.009
2
2
0
0
0.998
0.964
0.922
0.918
314.75
437
605.25
663
95.804
4.011
1.135
0.559
93.210
1.417
1.457
2.034
0.060
0.266
0.277
0.283
112.079
84.480
88.156
90.552
4
5
2
0
1th
0.935
0.927
378.75
603.5
5.149
0.521
2.555
2.072
0.171
0.010
0.259
0.283
83.652
90.487
2nd
1
0
2
2
1th
2nd
3rd
4th
0.934
0.923
0.942
0.928
325.5
477
576.5
682.5
28.242
1.698
1.916
1.769
25.648
0.895
0.677
0.824
8200.320
0.022
0.170
0.276
0.270
0.273
78.801
87.235
85.047
86.078
0.048
0.034
6
7
2
1
0
2
2
1th
2nd
3rd
4th
5th
1th
2nd
3rd
4th
0.982
0.905
0.923
0.921
0.959
334.12
421
469.75
569.87
789.37
29.301
3.764
1.777
2.464
0.883
26.707
1.170
1.213
0.129
1.710
9801.40
0.072
0.022
0.059
0.020
0.168
0.267
0.276
0.268
0.277
79.397
84.505
87.141
83.978
88.341
2
0
2
0
0.992
0.986
0.986
0.955
315.37
448
586.25
840.25
72.804
1.752
2.158
0.222
70.210
0.841
0.435
2.371
7.76×1011
0.029
0.057
0.005
0.017
0.274
0.269
0.289
75.723
86.516
84.375
92.587
E*: the activation energy (kJ mol‐1), ΔH*: the activation enthalpy (kJ mol‐1), ΔS*: the entropy (J K‐1 mol‐1), A: the pre‐exponential factor (s‐1), ΔG*: the free energy
(KJ mol‐1).
FIGURE 6 XRD spectral patterns of co(II) complex 2
FIGURE 5 XRD spectral patterns of the free ligand (H2L)
complex (5), the bond lengths between Cu and chelating
atoms are O(38)‐Cu(39) = 1.893, O(37)‐Cu(39) = 1.893,
N(35)‐Cu(39) = 1.899 and N(33)‐Cu(39) = 1.892 Å. The
bond angles of ligand moiety are changed upon chelation with
Co(II) and Cu(II) ions. The largest changes occur for those
including the two nitrogen atoms and two naphtholate
oxygens supporting their coordination to the metal centre
(Tables S3 and S5). For example, the computed bond angles
around Co atom are O(38)‐Co(39)‐O(37) = 102.899, O(38)‐
Co(39)‐N(35) = 90.122, O(38)‐Co(39)‐N(33) = 116.504
and N(35)‐Co(39)‐N(33) 116.097 Å, which confirms the
distorted tetrahedral geometry of the complex. The calculated

GABER ET AL.
11 of 14
TABLE 7 XRD spectral data of the highest value of intensity of H2L and its metal complexes (1‐7).
Comp.
Size of particles (nm)
θ
Intensity
d‐spacing (Å)
FWHM
H2L
29.5601
22.4460
42.8741
88.8330
6.3139
12.6150
3.6550
6.2350
4.6200
12.575
3.8650
4.1900
3.96
1564
171
500
190
264
439
127
328
3.5275
12.0912
7.0899
5.3410x10‐3
6.8780x10‐3
3.6157×10‐3
1.7400x10‐3
0.0250
Complex 1
Complex 2
Complex 3
Complex 4
Complex 5
Complex 6
Complex 7
9.5662
3.5378
13.7870
9.8393
11.4308
10.5500
11.1610
0.0112
0.0157
0.0243×10‐3
6.3814
FIGURE 7 Computational structure of
the free ligand (H2L)
bond angles around Cu atom are O(38)‐Cu(39)‐
O(37) = 112.548, O(38)‐Cu(39)‐N(35) = 103.022, O(37)‐
Cu(39)‐N(33) = 101.684, N(35)‐Cu(39)‐N(33) = 112.213 Å,
supporting the distorted tetrahedral geometry around Cu
centre. The degree of distortion from perfect tetrahedral
arrangement can be detected from the difference between the
minimum and maximum angles around Co(II) and Cu(II)
ions.[64] The disappearance of O—H bonds alongside the
appearance of new M—O bonds revealed the participation of
phenolic hydroxyl groups in chelation via de‐protonation
process.[65] In most cases, the M–N bond length differ than that
of M–O. This can be assigned to the electronegativity
difference between the nitrogen and oxygen atoms.[66,67]
theory.[68] This theory states that a decrease in the polariz-
ability of the metal could enhance the lipophilicity of the
metal chelates. This leads up to a breakdown of the perme-
ability of the cells, resulting in intervention with normal cell
processes. So, the chelation tends to make the Schiff bases
act as more powerful and potent antimicrobial agents,
inhibiting the growth of bacteria more than the parent
ligand.[69] Hence, it is claiming that the chelation process of
significantly influences the activity of compounds that are
potent against microbial strains. All metal chelates under
interest do not have any antifungal activities against the tested
organisms. E. coli was selected as the backbone of Gram‐
negative bacteria, S. aureus was chosen to represent Gram‐
positive bacteria, whereas. C. albicans represented the
unicellular fungi. So, the selected organisms represent a
broad spectrum of test organisms. The obtained results prove
the effectiveness of most investigated complexes as broad
spectrum antimicrobial agents.
3.10 | In‐Vitro antibacterial and antifungal
assay studies
The in‐vitro antimicrobial activities of H2L and the synthe-
sized complexes (1–7) were screened toward E. coli, S.
aureus, C. albicans and A. flavus applying the modified
Kirby–Bauer disc diffusion method.[24] The obtained results
are presented in Table 8. The free ligand under study does
not have any antibacterial or antifungal activities against the
tested organisms. Complexes 3–7 displayed moderate to high
activities toward E. coli. Also, complexes 1, 4, 5, 6, and 7
visualized temperate to elevated activities against S. aureus.
This behaviour can be illustrated on the basis of chelation
3.11 | Antitumor activity studies
New anticancer agents are desperately needed to ameliorate
the outcome for the great number of patients who relapse
after receiving the presently available cancer therapies.[70]
The anticancer activity of H2L and its metal chelates (1–7)
was detected in vitro against human liver Carcinoma cell line
(HEPG2). We chose the particular cell line of liver

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GABER ET AL.
TABLE 8 Antimicrobial activities of H2L and its metal complexes
(1‐7).
Inhibition zone diameter
(mm / mg sample)a
E.
S.
A.
C.
coli aureus flavus
albicans
(G—
)
(G+) (Fungus) (Fungus)
Sample
Control: DMSO
0.0
0.0
0.0
0.0
Standard Ampicillin
Antibacterial
agent
22.0 18.0
30.0 31.0
‐‐
‐‐
Norfloxacin
Antibacterial
agent
‐‐
‐‐
FIGURE 8 In‐vitro cytotoxicity of H2L and complexes 1–7 against
human liver Carcinoma cell line (HEPG2)
Amphotericin
B
‐‐
‐‐
17.0
19.0
Antifungal
agent
activity). Complexes 4, 6 and 7 displayed a moderate activity
and gave IC50 values of 5.56, 7.71 and 5.67 μg/ml, respec-
tively. Complexes 1, 2, 3, and 5 showed a strong anticancer
activity against human liver Carcinoma cell line (HEPG2)
and gave IC50 values of 4.65, 3.97, 3.30 and 4.84 μg/ml,
respectively.
H2L
0.0
13
0.0
10
10
10
13
12
0.0
14
0.0
0.0
13
11
13
13
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
Complex 1
Complex 2
Complex 3
Complex 4
Complex 5
Complex 6
Complex 7
4 | CONCLUSION
aEach experiment is conducted at least three times.
Seven new nano‐sized Mn(II), Co(II), Ni(II) and Cu(II) com-
plexes with N1,N6‐bis((2‐hydroxynaphthalin‐1‐yl)methinyl))
adipohydrazone (H2L) were synthesized. The complexes
were characterized using spectral (FT‐IR, 1H NMR, MS,
UV–Vis, ESR), elemental and thermal analyses. The XRD
studies asserted the nano‐sized nature of the complexes.
H2L coordinated as dibasic tetra‐dentate ligand towards
Mn(II), Co(II), Ni(II) and Cu(II) ions. Mn(II) and Ni(II) com-
plexes have octahedral geometries while Co(II) and Cu(II)
complexes have distorted tetrahedral configuration. Molecu-
lar modelling was performed by the molecular mechanic cal-
culations applying the hyper chem. 8.03 molecular modelling
programme to display the most stable structural formulas.
The most probable mechanism, E*, H*, A, S*, and G*
values were determined from TGA curves applying Coats‐
Redfern and Horowitz–Metzger methods. Mn(II) complex,
Co(II) complex, Ni(II) complex, and Cu(II) complex (5)
exhibited a strong anticancer activity with IC50 of 4.65,
3.97, 3.30 and 4.84 μg/ml, Cu(II) complexes 4, 6 and 7
displayed a moderate activity with IC50 of 5.56, 7.71 and
5.67 μg/ml, while H2L showed a weak inhibition of cell via-
bility with IC50 of 11.80 μg/ml, compared with IC50 value of
4.73 μg/ml for the doxorubicin. The resulting data confirm
great viability of the investigated compounds as new promis-
ing anticancer agents.
Carcinoma because liver Carcinoma is the most common
disease among other different types of Carcinomas in our
country. Doxorubicin (Dox) was applied as a reference drug
(IC50 = 4.73) and untreated cells were used as a control. Each
data point is determined as the average of three independent
experiments and expressed as M
SD. Growth inhibition
of 50% (IC50) is determined as the compound concentrations,
which caused a 50% reduction in cell proliferation during the
sample incubation.[71] The mean IC50 is the concentration of
compound that minifies cell growth by 50% under the exper-
imental conditions. From the obtained results (Figure 8). it is
clear that the growth inhibition of the tested cells strongly
affected by type of metal ion and increases in the order;
H2L < Cu(II) complexes < Mn(II) complex < Co(II) com-
plex < Ni(II) complex. This reveals that the type of metal
ion play an important role in anticancer activity.[72] Accord-
ing to Shier,[73] the compounds exhibiting IC50 value below
5.00 μg/ml are considered strong anticancer agents,
compounds display IC50 value between 5.00–10.00 μg/ml
are moderate while those within 10.00–25.00 μg/ml range
are weak anticancer agents. H2L showed an inhibition of cell
viability and gave IC50 value 11.80 μg/ml (weak antitumor

GABER ET AL.
13 of 14
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Reference Method for Broth Dilution Antifungal Susceptibility
Testing of Conidium‐Forming Filamentous Fungi: Proposed Stan-
dard M38‐A. NCCLS, Wayne, PA, USA.
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SUPPORTING INFORMATION
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Additional Supporting Information may be found online in
the supporting information tab for this article.
[62] HyperChem Version 8.03 Hypercube, Inc.
How to cite this article: Gaber M, Khedr AM,
Elsharkawy M. Characterization and thermal studies
of nano‐synthesized Mn(II), Co(II), Ni(II) and Cu(II)
complexes with adipohydrazone ligand as new
promising antimicrobial and antitumor agents. Appl
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