Synthesis of novel macrocyclic Schiff's-base and its complexes having N2O2 group of donor atoms. Characterization and anticancer screening are studied

Article abstract of DOI:10.1002/aoc.3694

Novel Schiff base [N′,N′″-(((ethane-1,2-diylbis(oxy))bis(2,1-phenylene))bis(methanylylidene))di(benzohydrazide)] was formed by the condensation reaction of benzohydrazide with 2,2′-(ethane-1,2-diylbis(oxy))dibenzaldehyde. Its reaction with various metal i

Full text of DOI:10.1002/aoc.3694

Received: 16 October 2016
DOI 10.1002/aoc.3694
Accepted: 29 October 2016
F U L L PA P E R
Novel macrocyclic Schiff base and its complexes having N2O2
group of donor atoms: Synthesis, characterization and anticancer
screening
Ehab M. Zayed1 | Mohamed A. Zayed2 | Asmaa M. Fahim1 | Fatma A. El‐Samahy1
1 Green Chemistry Department, Research Centre,
Novel Schiff base [N′,N′″‐(((ethane‐1,2‐diylbis(oxy))bis(2,1‐phenylene))bis(metha-
nylylidene))di(benzohydrazide)] was formed by the condensation reaction of
benzohydrazide with 2,2′‐(ethane‐1,2‐diylbis(oxy))dibenzaldehyde. Its reaction with
various metal ions was studied and the structures of the new products were charac-
terized using common analytical and spectroscopic methods. All the metal com-
plexes have pronounced anticancer activities. The antimicrobial activities against
33 EL Bohouthst (former EL Tahrirst), Dokki,
12622 Giza, Egypt
2 Chemistry Department, Faculty of Science, Cairo
University, 12613 Giza, Egypt
Correspondence
M. A. Zayed, Chemistry Department, Faculty of
Science, Cairo University, 12613 Giza, Egypt.
Email: mazayed429@yahoo.com
Gram‐negative and Gram‐positive bacteria were investigated.
Funding information
KEYWORDS
Chemistry Department at Cairo University and
Green Chemistry Department
anticancer screening, antimicrobial activities, complexes, kinetic, metal ions, novel
Schiff’s base, spectroscopic analysis, thermal analysis
1
|
INTRODUCTION
development of resistance during therapy.[6,18,19] To avoid
these disadvantages, current strategies for the development of
The physicochemical and pharmacological properties of het-
erocyclic compounds such as benzimidazoles are improved
upon reaction with transition metal chlorides to give com-
plexes.[1–4] Positively charged metal centre combined with
heteroaromatic periphery forms well‐defined geometries,
which facilitate the interaction with biomolecules and trans-
port across membranes in biological systems.[5,6]
Thiosemicarbazone heterocyclic compounds and their metal
complexes have attracted considerable attention due to their
coordination chemistry and broad range of pharmacological
properties.[7,8] Hydrazones are characterized by the presence
of azomethine group (─CH═N─); they are good polydentate
chelating agents that can form a variety of complexes with
various transition metals and inner transition metals.[9–17]
Metal complexes containing improved organic ligands are
widely used in cancer chemotherapy. The great success in
the clinical treatment of human malignancies has stimulated
research in the area of inorganic antitumor agents, the appli-
cation of which can be hampered by severe toxicity and
novel metallo drugs have focused on the use of transition metal
complexes.[11,20] Various coordination compounds have
been synthesized and the effects of metal, ligand and substitu-
ent on biological and anticancer activities have been investi-
gated.[21–23] However, side effects, toxicity, cancer specificity
and especially acquired resistance are still significant problems.
The main goal of the research reported here was to pre-
pare and characterize a biologically active heterocyclic
ligand. This was reacted with metal chlorides to yield com-
plexes having anticancer and other biological activities.
2
| EXPERIMENTAL
2.1 | Materials and reagents
All chemicals used in this study were of analytical reagent
grade and of the highest purity available. They included
Cu(II) chloride (Sigma), Co(II) chloride hexahydrate and
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DOI 10.1002/aoc.3694

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ZAYED ET AL.
(20 ml min−1) with a heating rate of 10 °C min−1 using a
DTG‐60 H Shimadzu simultaneous DTA/TG apparatus.
2.3 | Synthesis of metal complexes 5
The metal complexes 5 were prepared by the addition of a hot
solution (60 °C) of the appropriate metal chloride 4 in abso-
lute ethanol (15 ml) to a hot solution (60 °C) of the organic
ligand 3 (0.3 g) in ethanol and DMF (15 ml). The resulting
mixture was heated with stirring to evaporate all the solvents
to afford a precipitate. The precipitate was dried and weighed
to calculate the yield. All the above steps were repeated for all
the selected transition metal complexes.
2.4 | Biological activity
Testing was done using the diffusion agar technique. Spore
suspension (0.5 ml, 106–107 spores ml−1) of each of the
investigated organisms was added to a sterile agar medium
just before solidification, then poured into sterile Petri dishes
(9 cm in diameter) and left to solidify. Using a sterile cork
borer (6 mm in diameter), three holes (wells) were made into
each dish, and then 0.1 ml of the test compound dissolved in
DMF (100 mg ml−1) was poured into these holes. The dishes
were incubated at 37 °C for 48 h where a clear or inhibition
zone was detected around each hole. DMF (0.1 ml) was used
as a control under the same conditions. By subtracting the
diameter of the inhibition zone resulting from DMF from that
obtained from each metal complex or the free Schiff base,
antibacterial activities were calculated as a mean of three rep-
licates. MIC50 was determined, defined as the lowest com-
pound concentration that inhibits growth by 50%.
SCHEME 1 Synthesis of metal complexes 5
Ni(II) chloride hexahydrate (BDH), ferric chloride hexahy-
drate (Prolabo), zinc chloride (Ubichem) and Cd(II)
chloride (Aldrich). The other materials included 2,2′‐(eth-
ane‐1,2‐diylbis(oxy))dibenzaldehyde, salicylaldehyde, 1,2‐
dibromoethane (Sigma) and benzohydrazide (Aldrich).
Organic solvents used included absolute ethyl alcohol and
dimethylformamide (DMF). These solvents were spectro-
scopically pure from BDH. Double‐distilled water collected
using all‐glass equipment was used in all preparations.
2.2 | Instrumentation
Elemental microanalyses of the separated solid chelates for C,
H, N and Cl were performed at the Microanalytical Centre,
Cairo University, using a CHNS‐932 (LECO) Vario elemen-
tal analyser. The analyses were repeated twice to check the
accuracy of the data. The molar conductance of solid chelates
in DMF was measured using a Jenway 4010 conductivity
meter. Fourier transform infrared (FT‐IR) spectra were
recorded with a PerkinElmer FT‐IR type 1650 spectropho-
tometer in the wavenumber region 400–4000 cm−1. The
spectra were recorded as KBr pellets. Solid reflectance spec-
tra were measured with a Shimadzu 3101pc spectrophotome-
ter. The molar magnetic susceptibility was measured with
powdered samples using the Faraday method. Diamagnetic
corrections were made using Pascal’s constant and
Hg[Co(SCN)4] was used as a calibrant. Mass spectra were
recorded with the EI technique at 70 eV using an MS‐5988
GS‐MS Hewlett‐Packard instrument at the Microanalytical
2.5 | Pharmacology materials and methods
MCF‐7 breast cancer cell line was obtained from the National
Cancer Institute (Cairo, Egypt). MCF‐7 cells were grown in
RPMI‐1640. Media were supplemented with 10% heat‐
inactivated foetal bovine serum, 50 U ml−1 penicillin and
50 g ml−1 streptomycin and maintained at 37 °C in a humid-
ified atmosphere containing 5% CO2. The cells were main-
tained as ‘monolayer culture’ by serial sub‐culturing.
Cytotoxicity was determined using the sulforhodamine B
(SRB) method as previously described.[21] Exponentially
growing cells were collected using 0.25% trypsin–EDTA
and seeded in 96‐well plates at 1000–2000 cells per well in
RPMI‐1640 supplemented medium. After 24 h, cells were
incubated for 72 h with various concentrations of the test
compounds as well as doxorubicin as reference drug. Follow-
ing 72 h of treatment, the cells were fixed with 10% trichlo-
roacetic acid for 1 h at 4 °C. Wells were stained for 10 min
at room temperature with 0.4% SRB stain dissolved in 1%
acetic acid. The plates were air‐dried for 24 h and the dye
was solubilized with Tris–HCl for 5 min on a shaker at
1600 rpm. The optical density of each well was measured
spectrophotometrically at 564 nm with an ELISA microplate
1
Centre, Cairo University. H NMR spectra were recorded
using a 300 MHz Varian‐Oxford Mercury. The solvent used
was deuterated dimethylsulfoxide (DMSO‐d6) and the spectra
extended from
0
to 15 ppm. Thermal analyses
(thermogravimetry (TG) and differential thermogravimetry
(DTG)) were carried out in a dynamic nitrogen atmosphere

ZAYED ET AL.
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reader (ChroMate‐4300, FL, USA). The IC50 values were cal-
culated according to the equation for Boltzmann sigmoidal
concentration–response curve using nonlinear regression
fitting models (GraphPad Prism, Version 5).
the other hand, the Fe(III) complex has a molar conductance
value of 250 Ω−1 mol−1 cm2, indicating its ionic nature and it
is considered as a 1:3 electrolyte.[29–31]
3.3 | FT‐IR spectra and mode of bonding
3
| RESULTS AND DISCUSSION
The FT‐IR spectra of all complexes 5 show absorption bands
ν(C═N) at 1586–1656 cm−1 which are shifted by 50–52 cm−1
to lower energy regions compared to compound 3.[32–35] This
is due to the coordination of azomethine nitrogen to metal
ion.[36,37] Also, a broad ν(H2O) band of 5 is found at
3.1 | Characterization of metal complexes
Ligand 3 was formed by the condensation reaction of
dibenzaldehyde derivative 1 with benzohydrazide (2)[24]
(Scheme 1). The reactions of ligand 3 with metal ions 4 in
equal molar ratio afforded metal complexes 5 (Scheme 1);
their elemental analyses, yields and melting points are pre-
3260 cm−1 [38,39]
The stretching band of ν(C─O─C) is
.
observed at 1226 cm−1 in the spectrum of 3 which is shifted
to higher wavenumbers (1253–1261 cm−1) in the spectra of
5 due to the participation of the oxygen atom in chelation.
New absorption bands appear in the spectra of complexes cor-
responding to stretching vibrations ν(M─O) and ν(M─N) in
the regions 505–609 and 435–484 cm−1, respectively.[40]
1
sented in Table 1. The H NMR spectra of metal complexes
5 show the absence of a signal of NH group in the free ligand
at 8.71 ppm due to the chelating process with metal. The char-
acteristic signals of the 13C NMR spectrum for complex 5b as
an example show that metal ions influence the electronic
charge distribution around particular carbons which appear
at 72.2 ppm (CH2) and 150.4 ppm (CH═), and slightly change
that of other carbons at 113.2 (CH), 117 (CH), 121.3 (CH),
125 (CH), 127 (CH), 134.7 (CH), 135.1 (CH), 157 (C─O)
and 162 ppm (C═O). This means that the electron densities
around the referred carbons are affected by the ligand interac-
tion with metal cations to form their metal complexes.[25–28]
3.4 | Electronic spectral and magnetic susceptibility
studies (Table 2)
Electronic spectra of complexes 5b and 5f show bands at
26 000 and 24 500 cm−1, respectively, which may be due to
ligand–metal charge transfer. Molar conductivities of 5b
and 5f are over 100 Ω−1 cm2 mol−1 as expected for 1:2 elec-
trolytes of Zn(II) and Cd(II) complexes.[41–44]
3.2 | Molar conductance measurements
3.5 | Thermal analyses (TG and DTG) and
Conductivity measurement of metal chelates in non‐aqueous
solutions has been used in structural studies within the limits
of their solubility. This method gives the degree of ionization
of compounds 5, the molar conductivity increasing with
increasing amount of ions that a complex liberates in solu-
tion. The molar conductivities of 10−3 molar solutions of
the metal chelates at 25 2 °C are given in Table 1. From
the molar conductance values (108–150 Ω−1 mol−1 cm2) of
Co(II), Ni(II), Cu(II), Mn(II), Cd(II) and Zn(II) complexes,
it is concluded that these complexes are 1:2 electrolytes. On
thermodynamic calculations
TG analysis of the ligand shows two successive steps of
decomposition. The first mass loss of 16% (15.41%) in the
temperature range 50–250 °C may be due to the decomposi-
tion of benzene molecule. At 250–400 °C the mass loss of
34% (34.13%) may be for the decomposition of C8H7N3O2
molecule. In the final stage from 400 to 600 °C, the estimated
mass is loss of 50% (50.30%) is due to C16H13NO2 molecule
with complete decomposition.
TABLE 1 Analytical and physical data of metal complexes 5
% Found (calcd)
μeff
(BM)
Λm (Ω−1 mol−1 cm2)
Complex
Colour (% yield)
M.p. (°C)
C
H
N
O
M
C30H30Cl2CuN4O6
[Cu(L).2H2O].Cl2 (5a)
Brown (77)
220
53.22 (53.11) 4.47 4.25) 8.28 (8.13) 14.18 (13.78)
9.39
1.5
Dia.
3.8
108
120
250
118
130
125
150
C30H30Cl2ZnN4O6
[Zn(L).2H2O].Cl2 (5b)
Yellowish white (80)
Brown (75)
215
284
255
280
265
250
53.08 (52.89) 4.45 (4.55) 8.25 (8.12) 14.14 (13.98)
9.63
C30H30 FeCl2N4O6
[Fe(L).2H2O].Cl3 (5c)
47.37 (47.21) 3.98 (3.54) 7.37 (7.26) 12.62 (12.52) 14.68
C30H30Cl2NiN4O6
Greenish yellow (88)
Dark red (78)
53.60 (53.42) 4.50 (4.23) 8.34 (8.22) 14.28 (14.16)
53.59 (53.58) 4.50 (4.26) 8.33 (7.89) 14.28 (13.87)
8.73
8.76
2.4
[Ni(L).2H2O].Cl2 (5d)
C30H30Cl2CoN4O6
[Co(L).2H2O].Cl2 (5e)
3.06
C30H30Cl2CdN4O6
[Cd(L).2H2O].Cl2 (5f)
Pale yellow (80)
Pale yellow (86)
49.64 (49.32) 4.17 (4.56) 7.72 (7.48) 13.22 (13.54) 15.49 Dia.
53.91 (53.28) 4.52 (4.31) 8.38 (8.26) 14.36 (14.12) 8.22 3.69
C30H30Cl2MnN4O6
[Mn(L).2H2O].Cl2 (5 g)

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ZAYED ET AL.
TABLE 2 Electronic spectral data and magnetic susceptibility of complexes 5a, 5c–e and 5 g
Compound
5a
Bands (cm−1
)
Transitions
Magnetic moment (BM)
Geometry
15 331
16 588
21 188
2B1g → 2B2g
2B1g → 2Eg
2B1g → 2A1g
1.5
Octahedral[45,46]
5c
22 754
16 550–18 321
13 822–17 436
6A1g → T2 g(G)
6A1g → 5T1g
3.8
Octahedral[42]
Octahedral[43,44]
Octahedral[43,44]
Octahedral[41]
5d
5e
15 785
17 406
19 588
3A2g → 3T2g
3A2g → 3T1g (F)
3A2g → 3T1g (P)
2.4
17 452
19 569
24 459
4T1g(F) → 4 T2 g(F)
4T1g(F) → 4A2g(F)
4T1g(F) → 4 T2 g(P)
3.06
3.69
5 g
15 810
17 513
4T1g → 6A1g
4 T2 g(G) → 6A1g
4T1g(D) → 6A1g
The TG analysis of complex 5a as an example shows
decomposition at 44–800 °C (Table 3). At 44–193 °C the
complex loses 2HCl, O2 and NO molecules with a mass loss
of 20% (20.08%) as a first step. The second step corresponds
to 2H2O, N2 and 4CH4 molecules with a mass loss of 18%
(18.9%) within the range 196–364 °C. The third step of
decomposition occurs at 366–457 °C for loss of C2H5
molecule with a mass loss of 4% (4.28%). The final stage
within the range 457–715 °C shows loss of C24H3N with
a mass loss of 45% (45.79%) leaving CuO as a residue.
Three decomposition steps appear in the thermal
analysis of complex 5c as an example of trivalant com-
plex (Table 3). The first one corresponds to 2H2O and
1/2O2 molecules at 24–194 °C with mass loss of 7%
(6.84%). The second (198–407 °C) corresponds to the
loss of some of organic ligand, 3HCl and CH4 mole-
cules with mass loss of 16% (16.31%). The final stage
at 407–699 °C corresponds to the loss of C29H19N4
molecule with mass loss of 56% (56.18%) and Fe2O3
as a residue.
TABLE 3 Thermal analysis (TG and DTG) results for complexes 5
Mass loss, calcd Total mass loss, calcd
Compound
TG range (°C) DTGmax (°C) n*
(estim.) (%)
(estim.) (%)
Assignment
Residue
[Cu(L).2H2O]Cl2 (5a)
44–193
196–364
366–457
457–715
84
301
406
561
1
1
1
1
20.08 (20)
18.9 (18)
4.28 (4)
88.37 (88)
Loss of 2HCl,O2 and NO
Loss of 2H2O, N2 and 4CH4
Loss of C2H5
CuO
11.7 (11)
45.79 (45)
Loss of C24H3N
[Zn(L).2H2O]Cl2 (5b)
37–108
75
1
5.30 (5)
87.58 (87)
Loss of 2(H2O)
ZnO
12.42 (12)
Loss of 2(HCl) and 1/2O2
Loss of 2(C2H5) and NO
Loss ofC26H14N3O
112–229
231–429
431–997
170
307
615
1
1
1
12.97 (13)
13.56 (14)
55.75 (55)
[Fe(L).2H2O]Cl3 (5c)
[Ni(L).2H2O]Cl2 (5d)
24–194
198–407
407–699
138
308
499
1
1
1
6.84(7)
16.31(16)
56.18 (56)
79.33(79)
89.71 (89)
Loss of 2(H2O) and 1/2O2
Loss of 3(HCl) and CH4
Loss of C29H19N4
Fe2O3
20.67 (21)
23–97
98–354
355–452
453–654
56
286
401
518
1
1
1
1
5.35 (6)
Loss of 2(H2O)
Loss of 2(HCl) and 2(NO)
Loss of C2H5, N2O and CH4
NiO
11.11 (11)
20.23 (20)
13.69 (13)
50.44 (50)
[Co(L).2H2O]Cl2 (5e)
26–115
74
1
4.76 (5)
88. 86 (88)
Loss of 2(H2O)
Loss of HCl
CoO
11.14 (12)
117–204
206–393
395–710
155
294
517
1
1
1
5.35 (5)
14.77 (14)
63.98 (64)
Loss of HCl and NO
Loss of C30H24N2O
[Cd(L).2H2O]Cl2 (5f)
[Mn(L).2H2O]Cl2 (5 g)
23–238
152
1
4. 95 (5)
82.94 (82)
89. 8 (89)
Loss of 2(H2O)
Loss of 2(HCl), 2(NO) and 2(CH4) 17.06 (18)
Loss of C28H16N2O
CdO
240–461
461–792
341
605
1
1
23. 17 (23)
54.82 (54)
24–204
79
1
5.38 (5)
Loss of C2H4N4S2
Loss of 2(HCl) and 1/2O2
Loss of C4H10O2N2
MnO
C12H8
204–386
387–658
311
514
1
1
17.81 (18)
66.61 (66)
10.2 (11)

ZAYED ET AL.
5 of 7
3.6 | Calculation of activation thermodynamic
TABLE 5 Antibacterial activity data for compounds 3 and 5
Inhibition zone (mm mg−1 sample)/MIC50 (mg ml−1
)
parameters
Gram negative
Gram positive
The activation energies of decomposition of the new com-
pounds are found to be in the range 80.01–964.90 kJ mol−1
,
Proteus
Bacillus
subtilis
Streptococcus
pyogenes
Sample
Escherichia coli
vulgaris
these high values of the activation energies reflecting
the thermal stability of the complexes (Table 4). On the
other hand, the entropy of activation has a negative value
for all the complexes, which indicates that the decompo-
sition reactions proceed with a lower rate than the normal
ones.
3
25
26
25
25
5a
5b
5c
5d
5e
5f
30/>100
25/>100
18/>100
32/>100
20/>50
28/>100
24/>100
31/>100
28/>100
19/>100
30/>100
22/>50
29/>100
22/>100
31/>100
29/>100
20/>100
31/>100
23/>25
27/>100
23/>100
34/>100
27/>100
22/>100
34/>100
25/>50
25/>100
21/>100
3.7 | Biological activity
5 g
The Schiff base 3 and its metal complexes 5 were tested in
terms of antibacterial activity using the diffusion agar
method.[45–52] The reference compound for antibacterial
activities was streptomycin and more than one test organism
was used. The antibacterial activity data for compounds 3
and 5 have a wide degree of variation (Table 5).
and 5f are found to possess slightly inhibited significant
activity. Fe (III) compound 5c shows comparatively weak
inhibition against Gram‐positive bacterium S. pyogenes at
MIC50 (>100 mg ml−1).
The bis‐Schiff base ligand 3 has more sensitivity towards
Gram‐positive than Gram‐negative bacteria and has high
MIC50 (>100 mg ml−1) for both types of bacteria. It is found
that Cu(II) compound 5a and Ni(II) compound 5d have the
3.8 | In vitro cytotoxic activity and anticancer screening
studies
highest inhibition zones and high MIC50 (>100 mg ml−1
)
against Gram‐negative bacteria (E. coli and P. vulgaris). On
the other hand, complex 5e has moderate inhibitory activity
(20 and 22 mm) for E. coli and P. vulgaris, respectively, but
lowest MIC50 (>50 mg ml−1) for both microorganisms. Mn
(II) compound 5 g poorly inhibits E. coli and P. vulgaris
against two Gram‐negative bacteria; whereas forms 3, 5b
The results are reported in Table 6 for three separate experi-
ments. Statistical differences were analysed according to
one‐way ANOVA tests wherein the differences were consid-
ered to be significant at p < 0.05.
Anti‐proliferative activities of the new metal complexes
of Co, Cu, Zn, Cd, Fe, Ni and Mn were examined in MCF‐
TABLE 4 Thermodynamic data for complexes 5a
Decomposition
temp. (°C)
E
ΔS
ΔH
ΔG
Complex
A (s−1
)
(kJ mol−1
)
(J K−1 mol−1
)
(kJ mol−1
)
(kJ mol−1
)
[Cu(L).2H2O]Cl2 (5a)
44–193
196–364
366–457
457–715
4.10 × 105
9.02 × 106
7.46 × 108
7.56 × 107
52.86
28.72
98.35
79.51
−107.26
−244.18
−82.95
46.46
280.82
97.71
128.97
92.96
104.94
80.01
−101.98
155.12
[Zn(L).2H2O]Cl2 (5b)
37–108
112–229
231–429
431–997
4.68 × 106
1.93 × 107
9.46 × 108
1.57 × 105
229.16
278.90
385.32
711.82
−39.18
−34.61
−34.05
15.33
222.76
272.08
378.92
647.82
786. 83
569.73
117.16
182.74
[Fe(L).2H2O]Cl3 (5c)
[Ni(L).2H2O]Cl2 (5d)
24–197
198–407
407–699
2.87 × 106
2.96 × 107
6.57 × 106
1.17 × 105
6.36 × 106
2.81 × 107
4.84 × 108
307.53
469.44
134.81
−44. 52
−48. 37
−64.85
301.13
46.30
128.41
413. 78
908.69
178.31
23–97
98–354
355–452
453–654
308.29
918.06
803.99
689.79
−64.83
−136. 37
−90.47
301.89
858.68
797.59
497.36
196.91
183. 56
101.60
817.96
−105.67
[Co(L).2H2O]Cl2 (5e)
26–115
117–204
206–393
395–710
6. 81 × 106
1.54 × 107
1.35 × 108
1.91 × 1011
608.29
485.92
390.11
127.61
−131. 40
−76. 55
−32.40
−36.90
601.76
479.52
383.71
636.66
409. 12
109.40
134.39
347.47
[Cd(L).2H2O]Cl2 (5f)
[Mn(L).2H2O]Cl2 (5 g)
23–238
240–461
461–792
1.91 × 106
9.63 × 107
6.36 × 108
1.68 × 107
4.09 × 108
7.22 × 109
53.80
96.55
144.60
39.68
72.35
77.71
537.97
965.45
144.60
537.67
964.90
144.60
24–204
204–386
387–658
110.48
246.79
523.47
195.53
21.84
35.71
104.08
240.39
517.07
890.39
723.64
242.307
aE, activation energy; H, enthalpy; S, entropy; G, Gibbs free energy.

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ZAYED ET AL.
TABLE 6 In vitro anti‐proliferative activities of the newly prepared deriv-
atives against various cell lines
IC50 (μg μl−1 b
)
Compounda
MCF‐7
HepG2
HCT
5e
14.8 0.02
10.3 0.01
4.8 0.007
4.4 0.006
11.9 0.017
12.2 0.018
4.4 0.006
4.6 0.008
ND
10.6 0.01
4.7 0.007
3.1 0.004
3.3 0.004
9.4 0.014
5.3 0.007
10.5 0.015
ND
8.2 0.012
3.7 0.005
11.2 0.016
5.9 0.008
8.6 0.013
3.9 0.005
5.7 0.008
ND
5a
5b
5f
5c
5d
5 g
DOX
DOX
DOX
FIGURE 2 The growth inhibitory IC50 values [μM] of metal (II) complexes
5 at the concentration of 20 μM for HEPG‐2 (liver cancer cells)
1.2 0.002
ND
ND
ND
4.69 0.008
aDOX, doxorubicin (standard drug)
bIC50 values are mean SD of three separate experiments. ND, not detected.
7 (breast cancer) cell line (Figure 1), HepG2 (perpetual) cell
line and HCT (colon cancer) cell line using doxorubicin col-
orimetric assay as described previously.[53]
Doxorubicin was used as a reference cytotoxic compound
for the MCF‐7, HepG2 and HCT cell lines. The growth inhib-
itory concentration (IC50) values, which refer to the concen-
tration of compound required to produce a 50% inhibition
of cell growth after 72 h of incubation compared to untreated
controls, are summarized in Table 6. The complexes for
which cell growth was inhibited by more than 50% are
assigned as active. Almost all heterocyclic transition
metal(II) complexes did not show cytotoxic activity and did
not enter the secondary screening. Transition metal com-
plexes with Zn, Cd and Mn show high specificity and are
more potent for MCF‐7 cell line compared with doxorubicin
analogue with IC50 = 4.6 μM. This is due to chelation of
Schiff bases of our heterocyclic compounds containing an
azomethine group (─CH═N─) bond.
FIGURE 3 The growth inhibition IC50 values [μM] of metal (II) complexes
5 at the concentration of 20 μM for HCT (colony cancer cells)
possesses the ability to inhibit the growth of cancer cell
lines at 20 μM.
Finally the transition metal(II) complexes were tested
against HCT cell line (Figure 3). The Cu(II) complex
shows higher activity at IC50 = 3.7 μM compared with
doxorubicin analogue at IC50 = 4.69 μM, which indicates
that the Cu(II) complex exhibits cytotoxic activity against
HCT cell line.
Also, the heterocyclic transition metal complexes were
screened against HepG2 cells (Figure 2). The results show
moderate activity for the Zn metal complex at
IC50 = 3.1 μM compared with doxorubicin analogue with
IC50 = 1.2 μM. This means that none of the complexes
4
| CONCLUSIONS
In this study a novel Schiff base and novel synthesized het-
erocyclic transition metal complexes were developed via a
delivery system emulated by self‐assembly of doxorubicin.
Their biological, in vitro cytotoxic and anticancer activities
were investigated. The Cu(II) complex increased the accumu-
lation of doxorubicin in tumour cells (HCT). The Cd, Zn and
Mn complexes increased the efficacy in breast cancer cells
(MCF‐7). The metal complexes have greater antimicrobial
effect than the free ligand.
ACKNOWLEDGMENTS
The authors acknowledge the support of this research given
by the Chemistry Department at Cairo University and Green
Chemistry Department and National Research Centre Egypt.
FIGURE 1 The growth inhibitory IC50 values [μM] of metal (II) complexes
5 at the concentration of 20 μM for MCF‐7 (breast cancer cells)

ZAYED ET AL.
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of Cairo University at which all analyses were made.
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How to cite this article: Zayed EM, Zayed MA,
Fahim AM, El‐Samahy FA. Novel macrocyclic Schiff
base and its complexes having N2O2 group of donor
atoms: Synthesis, characterization and anticancer
screening. Appl Organometal Chem. 2017;e3694.
doi: 10.1002/aoc.3694
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