Spectral, optical, and cytotoxicity studies on N-(2-isonicotinoylhydrazine-carbonothioyl)benzamide and its metal complexes

Article abstract of DOI:10.1002/hc.21415

The ligand N-(2-isonicotinoylhydrazine-carbonothioyl)benzamide (H₃L) and its metal complexes with Co(II), Ni(II), Cu(II), and Zn(II) acetates have been synthesized. The synthesized compounds have been characterized by elemental analyses, FT-IR,

Full text of DOI:10.1002/hc.21415

Received: 15 February 2018
DOI: 10.1002/hc.21415
Revised: 25 April 2018
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R E S E A R C H A R T I C L E
Spectral, optical, and cytotoxicity studies on N-(2-
isonicotinoylhydrazine-carbonothioyl)benzamide and its metal
complexes
Nasser Mohammed Hosny1
Heba M. Mahmoud1
Mohamed H. Abdel-Rhman2
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1Chemistry Department, Faculty of
Science, Port-Said University, Port-Said,
Egypt
2Chemistry Department, Faculty of
Science, Mansoura University, Mansoura,
Egypt
Abstract
The ligand N-(2-isonicotinoylhydrazine-carbonothioyl)benzamide (H3L) and its
metal complexes with Co(II), Ni(II), Cu(II), and Zn(II) acetates have been synthe-
sized. The synthesized compounds have been characterized by elemental analyses,
FT-IR, UV-Visible spectra, 1H-NMR, 13C-NMR, ESR, MS, effective magnetic mo-
ments, molar conductance, and thermal analyses. The free organic ligand exists in
the keto form, but in the metal complexes, it forms chelates with the metal ions in the
enol form. The measured optical band gap (Eg) values confirmed the presence of di-
rect electronic transition and the semiconductivity of the current compounds. The
ligand and its Zn(II) complex were examined as cytotoxic agents against HePG-2
and HCT-116 and showed. H3L exhibited strong cytotoxicity, while Zn complex
showed moderate activity.
Correspondence
Nasser Mohammed Hosny, Chemistry
Department, Faculty of Science, Port-Said
University, Port-Said, Egypt.
Email: Nasserh56@yahoo.com
and
Mohamed H. Abdel-Rhman, Chemistry
Department, Faculty of Science, Mansoura
University, Mansoura, Egypt.
Email: mhassan2371@yahoo.com
that, replacement of the sulfur atom of the thiocarbonyl group
by oxygen leads to decreasing the activity whereas, selenium
1
INTRODUCTION
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To face the increasing challenge of antimicrobial drug-
resistant microorganisms, many researches are performed to
design and synthesize new compounds with potent therapeu-
tic activity.[1] Isoniazid has attracted much more attention due
to its anti-tuberculostatic, anti-bacterial, and anti-depressant
properties. These properties have attracted further research
on isoniazid and its derivatives.[2]
Thiosemicarbazides are among the most interesting
compounds in biological chemistry due to their high activi-
ties as biocidal, antifungal, antibacterial, anticonvulsant,[3-6]
and antitumor.[7,8] Also, thiosemicarbazides could be con-
sidered important class in different branches of chemistry.
It is used as analytical agents for the analysis of different
metal ions.[9]
It was found that the antitumor activity of some thiosemi-
carbazides increases by coordinating to certain metal ions.[10]
To obtain efficient chemotherapeutic agents, much more
effort has been direct to modify structure and to the inter-
pretation of the structure-activity relationships. For example,
in the pyridyl derivatives of thiosemicarbazide, it was found
maintains the activity. Also, the position of the attached sub-
stituents to the pyridyl ring is very effective factor in deter-
mining the antitumor activity.[11]
The main transition metal ions as cobalt, nickel, and cop-
per are essential for both animals and plants. They incor-
porate as cofactor in many oxidative enzymes and vitamins
as lactase, hydrogenase, tyrosinase, vitamin B12, and cyto-
chrome oxidase.[12]
The phenyl, p-methylphenyl, p-methoxyphenyl, and
p-chlorophenyl isothiocyanate derivatives of isonicotinic
acid hydrazide were synthesized and characterized.[13,14]
On continuation to our previous efforts on the metal com-
plexes of isonicotinic thiosemicarbazide derivatives, ethyl,
and benzoyl thiosemicarbazide derivatives have been
reported.[15,16]
This work aims to synthesize and characterize a new li-
gand N-(2-isonicotinoylhydrazine-carbonothioyl)benzamide
and its complexes with some divalent metal ions. To shed
light on the possible activity of the present compounds the cy-
totoxicity activity of these compounds has been investigated.
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Heteroatom Chemistry. 2018;e21415.
https://doi.org/10.1002/hc.21415
wileyonlinelibrary.com/journal/hc
© 2018 Wiley Periodicals, Inc.
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HOSNY et al.
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ν(N4H), and ν(N2H),[16] respectively. The region 1750-
1400 cm−1 displayed overlapped bands and so decon-
volution analyses were applied to resolve these bands
(Table 3; Figure 3). The data showed weak band in
2
RESULTS AND DISCUSSION
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The elemental analyses and some physical properties of the
isolated ligand and its metal complexes are presented in
Table 1. The results indicated that the isolated complexes
have (1:1) (M:L) stoichiometry. They have high melting point
(>300°C) and insoluble in most common organic solvents
but soluble in DMF and DMSO. The molar conductance val-
ues of all complexes are in the range 5.0-9.0 Ω−1 cm2 mol−1
indicating their non-electrolytic nature.
the range 1702-1688 cm−1 and a strong one in the
range 1645-1620 cm−1 assigned to ν(C=O)Ph
and
[15]
ν(C=N)Py,[20] respectively. In addition, a new band
observed at 1640-1665 cm−1 range, attributed to
ν(C=N*)[16] vibration and two bands in the 1534-1511
and 1390-1365 cm−1 regions, assigned to νas(OAc) and
νs(OAc) vibrations, respectively. It was suggested that
acetate group coordinates in bidentate fashions where
the difference between the asymmetric and symmetric
vibrations is ≈ 150 cm−1.[23–25] Furthermore, the spec-
tra displayed new bands at 585-525 and 465-435 cm−1
which may be due to the ν(M-O) and ν(M-N)[26] vibra-
tions, respectively. In comparison with the ligand spec-
trum, it could be concluded that the H3L coordinates
to the metal ions as mononegative bidentate (Figure 4)
where: The disappearance of ν(N1H) and ν(C=O)Py
bands with appearance of new ν(C=N*) band indicates
2.1
IR spectra
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The infrared spectra of H3L, as KBr disk, showed sharp band
at 3211 cm−1 with shoulders at 3243 and 3147 cm−1 as-
signed to ν(N2H), ν(N4H), and ν(N1H) vibrations,[16] respec-
tively. Moreover, three sharp bands appear at 1691, 1672,
and 1640 cm−1 attributed to ν(C=O)Ph,[17-19] ν(C=O)Py,[16]
[20]
and ν(C=N)Py
vibrations, respectively. The spectrum
displayed four bands in the range 1550-1450 cm−1 due
to amide II, amide III, thioamide I, and thioamide II[15]
(Figure 1). Furthermore, the band at 844 cm−1 was assigned
to ν(C=S),[21] while those at 777 and 757 cm−1 were attrib-
uted to ρ(NH)[21] vibration.
Thus, the above-mentioned spectral data clarify that
H3L exists in the keto-form where, NH, carbonyl, and thio-
carbonyl vibrations appear. On comparison with isonico-
tinic hydrazide spectrum, it is observed that the ν(C=O)Py
vibration band shifted to higher position which may be due
to involvement of carbonyl oxygen in intermolecular hydro-
gen bond with N2H group where a new band at ~1965 cm−1
were observed and attributed to intermolecular hydrogen
bond.[22]
On the other hand, the spectral data of H3L metal
complexes (Table 2; Figure 2), indicate that all com-
plexes have three bands in the ranges 3410-3398, 3265-
3245, and 3185-3140 cm−1 attributed to ν(OH)solvent
[23]
FIGURE 1 Infrared spectra of H3L
TABLE 1 Color, melting points and elemental analyses of the ligand and its metal complexes
Elemental analyses % found (Calcd.)
Compound (Mol. Wt.)
Color
m.p. (°C)
C
H
M
H3L
Yellow
206
56.69 (55.99)
4.50 (4.03)
-
(Calcd., 300.34; MS, 300)
[Cu(H2L)Ac] 3H2O
Black
>300
>300
>300
>300
40.43 (40.37)
43.90 (43.29)
43.53 (43.31)
41.60 (41.78)
4.81 (4.24)
5.55 (4.84)
5.10 (4.85)
4.10 (3.91)
13.67 (13.35)
11.90 (11.80)
11.81 (11.76)
12.90 (12.28)
(Calcd., 475.99; MS, 477)
[Co(H2L)Ac] 2H2O EtOH
Dark green
Dark brown
Green
(Calcd., 499.40; MS, 500)
[Ni(H2L)Ac] 2H2O EtOH
(Calcd., 499.16; MS, 500)
[Zn(H2L)Ac] 2H2O EtOH
(Calcd., 505.47; MS, 506)

HOSNY et al.
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TABLE 2 Infrared spectral data of
Vibration
H3L
Cu(II)-H2L
Co(II)-H2L
Ni(II)-H2L
Zn(II)-H2L
H3L and its isolated metal complexes
ν(OH)solvent
ν(N4H)
-
3398
3245
3176
-
3407
3251
3170
-
3407
3245
3185
-
3411
3261
3145
-
3243
3211
3147
1672
-
ν(N2H)
ν(N1H)
ν(C=O)Py
ν(C=N)a
Amide II
Amide III
Thioamide I
Thioamide II
Thioamide III
ν(C=S)
ρ(NH)
νas(OAc)
νs(OAc)
ν(M-O)
ν(M-N)
-
-
-
-
1665a
1557a
1218
1517a
1421
1272
848
1643a
1567a
1213
1515a
1423
1292
840
1642a
1558a
1216
1519a
1421
1288
844
1643a
1565a
1213
1519a
1439
1292
842
1560
1218
1502
1452
1278
844
777, 757
-
784, 709
1527a
1374
588, 539
437
782, 700
1528a
1365
576, 524
443
790, 717
1511a
1374
576, 526
466
798, 707
1534a
1390
574, 514
440
-
-
-
aValues estimated by deconvolution analyses.
FIGURE 2 Infrared spectra of [Cu(H2L)Ac(H2O)]2H2O and [Co(H2L)Ac]2H2O·EtOH
the existence of the ligand in the enol form. The absence
2.2
1H and 13C NMR spectra
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of the band due to ν(OH) clarifies the deprotonation of
the newly formed hydroxyl group on reaction with metal
ion. The positions of the bands due to carbonyl group
and the azomethine of the pyridyl ring did not change
and so they are not involved in coordination. The ap-
pearance of ν(C=S) vibration band approximately at
the same position as in the ligand spectrum, indicates
the inertness of thione sulfur toward coordination to the
metal ions.
1H-NMR of H3L, in DMSO-d6, exhibits several singlet signals
corresponding to the protons of N4H, N2H, and N1H at 11.78,
10.73,and8.80 ppm,respectively.[16] Theappearanceofthesesig-
nals confirms the existence of the H3L in the keto form. Multiplet
signals observed in the region 7.98-7.21-7.31 ppm were assigned
to the protons of the phenyl group (Table 4).[20] The pyridyl ring
showed two doublet signals at 8.82 and 7.83 ppm, due to protons
at (2 and 6) and (3 and 5) positions,[21] respectively.

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HOSNY et al.
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TABLE 3 Deconvolution analyses data of complexes infrared spectra in 1710-1400 cm−1 range
Co(II) complex (R2 = 0.9999)
Ni(II) complex (R2 = 0.9978)
Cu(II) complex (R2 = 0.9990)
Peak
Center
FWHM
% Area
Center
FWHM
% Area
Center
FWHM
% Area
1
2
3
4
5
6
7
8
1460
1475
1515
1528
1567
1604
1643
1703
16.48
25.77
37.51
22.50
34.69
35.54
44.47
28.25
2.11
8.07
22.12
4.16
18.63
7.79
35.18
1.92
1451
1483
1519
1558
1571
1606
1642
1701
10.23
25.82
24.81
12.09
19.10
20.81
38.86
32.37
1.99
10.07
19.92
3.05
3.11
5.63
1507
1527
1557
1572
1620
1665
1699
41.05
20.88
17.29
32.65
50.02
27.42
30.43
14.36
5.347
3.23
17.01
49.22
4.36
50.85
5.34
6.44
TABLE 4 The NMR (13C and 1H) spectral data of ligands and
Zn(II)-HL2 complex
1H-NMR
C-atoms
H3L
Protons
H3L
Zn(II)
2,6-pyridyl
3-pyridyl
5-pyridyl
4-pyridyl
2,6-phenyl
3,5-phenyl
4-phenyl
1-phenyl
(C=O)Py
(C=O)Ph
(C=S)
150.32
121.52
121.52
139.34
128.46
128.72
131.84
133.18
163.13
167.71
181.03
-
N4H
11.78
11.43
8.80
8.82
7.83
7.98
7.60
7.75
11.44
-
N2H
N1H
-
2,6-pyridyl
3,5-pyridyl
2,6-phenyl
3,5-phenyl
4-phenyl
7.73
7.60
7.40
7.30
7.30
CH2
FIGURE 3 Deconvulsion analysis of [Zn(H2L)Ac] 2H2O EtOH
1H-NMR of [Zn2(HL)Ac]2H2OEtOH shows singlet signal at
11.34 ppm assigned to the proton of N4H group. In comparison
with the ligand spectrum, it is clear that N2H signal has disap-
peared. The absence of N2H signal from the spectrum of Zn(II)
complex confirms the coordination of the ligand in the enol form
with liberation of hydrogen ion.[21] The singlet at 8.64 ppm was
attributed N1H proton. The multiplet signals in the ring 7.45-
8.52 ppm were attributed to the phenyl and pyridyl protons.
13C-NMR spectrum of H3L, in DMSO-d6, shows number
of signals represent the number of chemically non-equivalent
carbon atoms of H3L. The signal due to the carbonyl carbon
adjacent to the pyridyl ring appears at 163.13 ppm, while the
thiocarbonyl carbon was observed at ≈ 182 ppm.[21] The pyr-
idyl ring carbons at 3-, 4-, and 5-positions were observed at
≈ 121, 139, and 120 ppm, respectively, while those at 2- and
6-positions were at ≈ 150 ppm. The phenyl group carbon’s
displayed signals in the range 127.06-139.27 ppm (Table 4;
Figure 5).[21]
O
S
Ph
N
H
N
NH
M
Py
nH2O mEtOH
O
O
O
M = Co n = 2 m = 1
M = Cu n = 3 m = 0
M = Ni n = 2 m = 1
M = Zn n = 2 m = 1
FIGURE 4 Suggested structure of the metal complexes

HOSNY et al.
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650 nm attributed to 2B1g→2E1g transition of a square planar
geometry.[28-30] A band was observed also at 420 nm due to
LMCT (Figure 6). The magnetic moment value of was 1.80
B.M. which lies in the normal range of Cu(II) complexes re-
gardless of their stereochemistry (1.75-2.20 B.M.).
2.3
Electronic spectra and
|
magnetic moments
The electronic spectrum of the ligand, in DMSO, showed two
bands in the region 292-298 nm were attributed to (π→π*)
transitions of pyridine or phenyl, and carbonyl groups, re-
spectively. Two shoulders locate at ≈ 341 and 365 nm due
to (π→π*) of thiocarbonyl and (n→π*) of pyridine ring,[21]
respectively. In addition, two bands were observed at 380
and ≈ 390 nm assigned to (n→π*) transitions of carbonyl and
thiocarbonyl groups,[21] respectively.
Thespectrumof[Co(H2L)Ac]2H2OEtOHinDMSOshowed
only one band at 606 nm, attributed to 4A2→4T1(P) transition
which suggests the tetrahedral geometry around the Co(II).[27]
Another band at ≈ 417 nm was observed and assigned to the li-
gand to metal charge transfer transition (LMCT). Moreover, the
spectral data of this complex in Nujol mull (Table 5) showed
the d-d transition band at 615 nm confirming the tetrahedral
structure of this solid complex and indicating that the use of
DMF as solvent did not alter the geometrical structure. The
magnetic moment of this complex was found to be 4.50 B.M.,
supporting the suggested tetrahedral stereochemistry.[27]
Moreover, [Cu(H2L)Ac] 3H2O spectrum (Figure 6) re-
corded in DMSO and Nujol mull exhibited a broadband at
Furthermore, the spectrum of [Ni(H2L)Ac] 2H2O EtOH,
in DMSO, displayed two strong band at 422 and 500 nm
attributed to the ligand to metal charge transfer transitions
(LMCT). In addition, a broadband centered at 570 nm
and a shoulder band at 700 nm assigned to T1→1T1 and
3
3T1→3T1(P) transitions, respectively. The position of these
bands suggests tetrahedral geometry around Ni(II) ion.[27]
Moreover, the Nujol mull spectrum displayed the LMCT
transitions at 450 and 540 nm, while two other transitions
were observed at 550 and 707 cm−1 due to T1→1T1 and
3
3T1→3T1(P) transitions, respectively. These transitions con-
firm the suggested tetrahedral structure of the Ni(II) complex
in solid state. Furthermore, the magnetic moment value of the
Ni(II) complex confirmed the tetrahedral geometry, where it
were found to be 3.4 B.M. which lies in the range of tetrahe-
dral structure (3.4-4.2 B.M.).[27]
Finally, the electronic spectral data of [Zn(H2L)Ac] 2H2O
EtOH in DMSO displayed intra-ligand transition as shown in
Table 5. Three bands were observed at 306, 357, and 386 nm
FIGURE 5 The 13C-NMR spectra of H3L
TABLE 5 Electronic spectral and
Compound
H3L
Band position (nm)
Assignment
μeff (B.M.)
magnetic moment data of ligands and its
complexes
298, 306, 318, 352,
380, 388
(π→π*)Py, (π→π*)C=S, (π→π*)C=O
(n→π*)Py, (n→π*)C=S, (n→π*)C=O
,
-
,
Cu complex
300 (296), 316, 350
(356), 362. 390
(404), 438 (460),
670 (632)
(π→π*)Ph, (π→π*)C=O, (n→π*)Py,
(n→π*)C=S, (n→π*)C=O, LMCT
2B1 g→2E1 g
1.8
Co complex
Ni complex
296, 310 (304), 356
(360), 400 (386),
(π→π*)Py, (π→π*)C=S, (n→π*)Py,
(n→π*)C=O, LMCT 4A2→4T1(P)
4.50
3.14
500 (498), 606 (615)
302, 308 (316), 348,
356 (374), 396, 422
(450), 500 (504),
(π→π*)Ph, (π→π*)C=S, (n→π*)Py,
(n→π*)C=S, (n→π*)C=O, LMCT,
3T1→1T1, 3T1→3T1(P)
570 (550), 700 (708)
Zn complex
282, 302, 318, 340,
364, 390, 470
(π→π*)Py, (π→π*)Ph, (π→π*)C=O
,
-
(n→π*)Py, (n→π*)C=S, (n→π*)C=O
,
LMCT
Value between brackets was from Nujol mull spectrum.

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HOSNY et al.
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FIGURE 6 Electronic spectrum of [Cu(H2L)Ac]3H2O
FIGURE 7 ESR spectra of [Cu(H2L)Ac]2H2O
g⟂ − 2.0023
attributed to (π→π*)Ph, (n→π*)Py, and (n→π*)C=N*, respec-
tively. In addition to LMCT bands at 434 and 504 nm. The
obscure of the bands due to π→π* and n→π* transitions of
carbonyl was taken as an additional evidence for enolization
of this group.
K2 =
× d − d transition
⟂
2 × λ
◦
K2 +2K2
⟂
∣∣
K2 =
2.4
ESR spectra of Cu(II) complex
|
3
ESR is important technique for determining the stereochem-
istry of Cu(II) complexes. The ground state is dz2 in octahedral
or a trigonal bipyramidal Cu(II) complexes with 2A1g ground
state. The ESR can distinguish the ground states according to
the values of the g-tensor. Thus, when 2B1g is the ground state
The pure σ-bonding K|| ≈ K⊥ ≈ 0.77 and for in-plane π-
bonding K|| < K⊥, while for out-of-plane π-bonding K|| > K⊥.
The obtained data are shown Table 6. The results indicated
that Cu(II) complex has K < 1 and K|| < K⊥, so they have co-
valent environment and in-plane π-bonding.
Finally, the magnetic moment for the Cu(II) complexes,
μeff, can be calculated using the ESR data, g-values, by the fol-
lowing expression.[30] The data indicated that it is very close
to obtained value from magnetic susceptibility measurements
(1.80 B.M.) and found to be 1.84 B.M., respectively.
2
the g|| > g⊥ > 2.0023, while in case of A1g ground state the
g⊥ > g|| > 2.0023.[31]
From ESR spectrum of Cu(II) complex (Figure 7), it was
found that, g|| = 2.20 and g⊥ = 2.08. From these observed val-
ues it could be deduced that; g|| is less than 2.3 suggesting a
significant covalent character of metal-ligand bonds.[32] The
obtained g-values are g|| > g⊥ > 2.0023 which means that the
Cu(II) has a dx2−y2 ground state characteristic for square pla-
nar geometry.[33] The exchange interaction between Cu(II)
centers may be expressed by the axial symmetry parameter,
G, where G = (g|| − 2)/(g⊥ − 2). The G value was found to be
2.41, suggesting considerable copper-copper exchange inter-
actions in the solid state.[28]
ꢀ
1
μeff
=
g2 +2g2
⟂
∣∣
2
2.5
Mass spectra
|
The mass spectrum of the H3L ligand shows the molecular
ion peak at m/z = 300 (60.0%), which matches with the sug-
gested formula (Figure 8). The ligand loses HO− ion giving
a peak at m/z = 283 (2.5%) which undergoes two different
fragmentation pathways to base peak at m/z = 77 (100.0%)
corresponding to either pyridyl or phenyl ring (Scheme 1).
The spectrum showed peak at m/z = 268 (3.0%) resulted
from loss of oxygen from the peak at m/z = 283. The latter
peak may lose sulfur to give another peak at m/z = 251 (1.3%)
or loses C7H7N fragments to give a third peak at m/z = 178
(0.3%).
The orbital reduction factor, K, was used as a measure of
covalency, where for ionic environment K = 1, and for cova-
lent K < 1. The orbital reduction factor is calculated using
the following expressions[29] where K||, K⊥, parallel, perpen-
dicular components of orbital reduction factor and λ° is the
spin-orbit coupling constant.
g∣∣ −2.0023
K∣2∣ =
× d−d transition
8 × λ
◦

HOSNY et al.
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TABLE 6 ESR and orbital reduction
Complex
g∣∣
g⊥
G
μeff
K2∣∣
K2
K2
K∣∣
K⊥
K
⟂
parameters of Cu(II) complexes
Cu-H3L
2.20 2.09
2.41
1.84
0.49
0.82
0.71
0.70
0.90
0.84
FIGURE 8 Mass spectrum of H3L
steps of each complex were listed. The TG data indicated that:
In general the first step, water and/or ethanol molecules out the
coordination sphere were lost in temperature range 20-170°C.
In the second stage ranged from 101 to 400°C, the acetate
molecules were lost.
2.6
Thermal analyses
|
Thermal gravimetric analysis (TGA) for the obtained solid
complexes were carried out to clarify their thermal stability
and to help in characterization. In Table 7, the decomposition
O
O
H
H
N
H
N
-
N
N
-
HO
N
H
N
H
N
S
O
N
S
=
=
m/z 283
m/z 300
(2.5%)
(60.0%)
=
2S
+
H12
N O
300.34
C14
=
H11
N
283.33
C14
4OS
4
-
O
H
N
N
N
N
S
=
H11
m/z 267
(50.2%)
•+
=
-
N
267.33
H
N
4
-
C14
4S
C7
3S
H
N
C8
2S
6
-
CHN
N
-
CHN
HN
N
N
=
H
77
=
m/z
C5
m/z 105
C6
=
77
m/z
(100.0%)
=
(49.5%)
=
m/z 105
(100.0%)
(50.2%)
105.06
•
•+
•
4N 78.09
=
H N•+
C7
H
5N2
105.12
=
H
C6
77.04
=
5
7
SCHEME 1 Fragmentation pattern of H3L

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HOSNY et al.
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The kinetics and thermodynamic parameters, acti-
vation energy (Ea), enthalpy (ΔH*), entropy (ΔS*), and
free energy (ΔG*) change of decomposition are evaluated
graphically by employing Coats-Redfern[34] and Horowitz-
Metzger[35] methods. The data obtained were collected in
Table 8. The results indicated the following remarks:
For all complexes, these methods were applicable on the first
decomposition stage corresponding to loss of solvent molecules
outside the coordination sphere, which clarifies that it is simple
and has moderate rate. Other decomposition stages do not fit the
requirements for applying the calculation methods, due to the
overlapped stages, except in case of Ni(II) and Zn(II) complexes.
The Ea values for the first step obtained from Coats-
Redfern method are considerably close to those from
Horowitz-Metzger method. For all complexes, the ob-
tained Ea values of the first step were close and in the range
25-57 kJ.
The negative values of ΔS* indicate that the activated
fragments have more ordered structure than the undecom-
posed complexes and/or the decomposition reactions are
slow. The positive sign of ΔH* reveals that the decomposi-
tion stages are endothermic processes.[36]
The positive sign of ΔG* indicates that the free energy
of the resulting formula is higher than that of the initial
TABLE 7 Thermal gravimetry analysis data of metal complexes
Complex
Temp. range
Wt. loss %
Fragment loss
Fragment %
[Cu(H2L)Ac]3H2O
20-120
101-283
283-415
415-1000
Residue
20-150
151-395
395-575
530-1000
Residue
20-160
260-595
595-1000
Residue
20-170
277-372
372-550
550-1000
Residue
11.47
13.03
35.30
9.58
30.31
16.38
18.01
30.47
9.62
24.52
17.03
32.87
14.06
36.04
17.74
25.76
19.63
7.92
3H2O
C2H3O2
C11H11N
NS
CuC3HNO2
EtOH and 2H2O
C2H4O2S
C11H11N
11.34
12.39
35.76
9.66
30.81
16.41
18.66
31.08
8.81
25.23
16.42
32.69
15.45
35.41
16.22
26.90
20.57
8.70
(475.99)
[Co(H2L)Ac]2H2O EtOH
(499.40)
CO2
CoC2HN3
EtOH and 2H2O
C8H5N2O2
C6H5
NiC2H2N2O2S
EtOH and 2H2O
C2H3O2 and C6H5
C7H6N
[Ni(H2L)Ac]2H2O EtOH
(499.16)
[Zn(H2L)Ac]2H2O EtOH
(505.47)
CS
ZnN3O2
29.45
30.35
TABLE 8 Thermodynamic parameters data of metal complexes
Thermodynamic parameters
ΔS*
Complex
Temp. range
Ea (kJ)
(J mol−1 K−1
)
ΔH* (kJ)
ΔG* (kJ)
A
R
[Cu(H2L)Ac]3H2O
[Co(H2L)Ac]2H2O EtOH
[Ni(H2L)Ac]2H2O EtOH
20-215
20-135
20-120
120-369
277-372
372-550
550-1000
48.78 (57.79)
41.51 (46.44)
44.06 (49.92)
33.05 (45.77)
72.24 (85.79)
72.08 (83.08)
73.94 (97.19)
−201.87
−232.40
−219.13
−301.41
−234.42
−259.52
−303.46
46.01
37.46
41.21
28.74
67.28
65.94
65.41
113.42
150.64
116.54
185.16
207.34
257.63
376.93
198.44
0.973 (0.953)
0.970 (0.957)
0.980 (0.964)
0.985 (0.966)
0.971 (0.974)
0.966 (0.971)
0.973 (0.981)
7.35
25.62
0.002
7.08
0.427
0.003
[Zn(H2L)Ac]2H2O
Values in brackets obtained by Horowitz-Metzger.

HOSNY et al.
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|
compound, and hence all the decomposition steps are non-
spontaneous processes. Moreover, the values of ΔG* in-
crease significantly for the subsequent decomposition stages
of a given compound. This observation is a result of increas-
ing of TΔS, which reflects the lower rate of removal of the
subsequent species compared with the precedent one.[37]
2.7
Optical band gap
|
Molecular materials can be used in molecular electronics
due to their conducting and semi-conducting nature.[38-41]
To have an idea on the conductivity of the current metal
complexes, the optical band gaps (Eg) have been meas-
ured from the electronic spectra. Tauc’s relation (1) has
been applied: αhν = A (hν − Eg)m (1), where m is equal
to 2 for direct electronic transition, A is a constant.[42,43]
Representative examples of the optical band gap (Eg) curves
of the ligand and its metal complexes are represented in
Figure 9. The results indicated that Eg values of H3L and
its metal complexes are in the range 3.82-3.85 eV. These
values are in good agreement with some semi-conducting
materials.[44-48]
2.8
Cytotoxic effect
|
The in vitro cytotoxicity activities of H3L and its Zn(II) com-
plex are studied as representative examples of the present
compounds.
The cytotoxicity activity against human tumor cells
and the relative viability are collected in Tables 9 and 10
(Figure 10). The results indicated that the minimum inhibi-
tory concentration of H3L found to be 11.32 and 7.80 μg/mL
against HCT-116 and HEPG-2 cell lines, respectively. On the
other hand, the minimum inhibitory concentration of Zn(II)
complexes was found to be 30.60 and 25.9 μg/mL against
HCT-116 and HEPG-2 cell lines.
The cytotoxicity tests showed that the H3L has very strong
cytotoxic effect against HePG-2 while, it shows strong cyto-
toxicity against HCT-116. The Zn(II) complex showed mod-
erate cytotoxicity against the two cell lines.
FIGURE 9 Energy gap plots of H3L (A) and (B) Cu(II) complex
TABLE 9 Cytotoxic activity of some compounds against human
tumor cells
In vitro Cytotoxicity IC50 (μg/mL)a
Compounds
HCT116
HePG2
DOX
H3L
Zn complex
5.23 0.3
11.32 1.1
34.60 2.0
4.50 0.2
8.90 0.8
26.20 1.7
Compared with other isonicotinic derivative (2-isonicoti
noyl-N-phenylhydrazine-1-carboxamide),[16] H3L has higher
cytotoxicity activity than 2-isonicotinoyl-N-phenylhydraz
ine-1-carboxamide. The structure of H3L has thione group
(C=S) in place of carbonyl group in the compound under
comparison. It could be concluded that the higher activity of
H3L resulted from the presence of the thione group.
DOX, Doxorubicin.
aIC50 (μg/mL): 1-10 (very strong), 11-20 (strong), 21-50 (moderate), 51-100
(weak), and above 100 (non-cytotoxic).
Ni(II), and Zn(II) in the enol form. H3L reacts with metal
ions as mononegative bidentate via the nitrogen atom of
NH group, deprotonated oxygen of the enolized carbonyl.
The electronic spectra and magnetic data of the isolated
solid complexes indicated the formation of tetrahedral
stereochemistry with all metal ions, except Cu(II) which
forms square planar structure. The optical band gap meas-
urements indicated that the ligand and its metal complexes
3
CONCLUSION
|
The free ligand, 4-benzyl-thiosemicarbazide (H3L) ex-
ists in keto-thioketo form. H3L chelates to Cu(II), Co(II),

10 of 12
HOSNY et al.
|
TABLE 10 Relative viability of cells
DOX
H3L
Zn(II)
(%)
Conc. (μg/mL)
HCT116
HePG2
HCT116
HePG2
HCT116
HePG2
100
50
25
12.5
6.25
3.125
1.56
7.1
6.3
11.3
18.9
30.7
43.8
61.2
82.3
98.6
7.8
16.3
24.5
38.4
55.1
78.3
94.2
30.6
41.9
53.8
67.2
86.5
99.4
100
25.9
37.8
48.1
62.3
75.2
94.7
100
13.9
18.7
31.4
47.9
60.5
73.8
11.2
14.1
28.3
45.8
57.6
71.2
4
EXPERIMENTAL
Reagents
|
4.1
|
Isonicotinic hydrazide (99.0%) and benzoylisothiocyanate
(98.0%) were purchased from Sigma-Aldrich. All the other
used reagents are AR grade and used as it is.
Cell lines, Colorectal (HCT-116), and Hepatocellular
(HePG-2) carcinoma were obtained from ATCC via
(VACSERA), Cairo, Egypt. The reagents RPMI-1640 me-
dium, MTT, and 5-fluorouracil (Sigma Co., St. Louis, USA),
Fetal Bovine serum (GIBCO, UK).
4.2
Measurements
|
The elemental analyses (C, H, and N) were determined on
CHN analyzer (Perkin-Elmer model 2400). The metal con-
tent was determined by direct titration against EDTA using
suitable indicators for the analyzed metal ions.[49] The
FT-IR spectra were recorded, as KBr disks, on a Thermo-
Nicolet IS10 spectrometer. TGA was carried out on a
Shimadzu model 50 instrument with heating rate 10°C/min
and 20 cm3/min nitrogen flow rate. The UV-Visible meas-
urements were taken by Unicamy UV/Vis spectrometer
UV2, with 1 cm silica cells. The NMR (1H and 13C) spectra
were recorded on Bruker Ascend 400 MHz. Electron spin
resonance (ESR) was recorded at room temperature on
Brucker E 500 ESR spectrometer operating at 9.808 GHz,
100 kHz field. Modulation from 480 to 6480 Gauss in a
2 mm quartz capillary. Magnetic measurements were meas-
ured on a Sherwood Scientific magnetic balance. Molar
conductivity was carried out on a conductivity bridge YSI
model 32.
FIGURE 10 In vitro cytotoxic activities of H3L (A) and its
4.3
Deconvolution analysis of infrared
|
Zn(II) complexes compared with the standard doxorubicin (B)
spectral data
Deconvolution analysis of the infrared spectra were calcu-
lated by the Peak Fit program to determine the hidden peaks
at wavenumber different from local maximum in the data
are semiconductors and could be used in solar cell applica-
tions. The ligand showed higher anti-cancer activity than
its Zn(II) complex.

HOSNY et al.
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O
O
H
N
2
H
N
4
NH2
1
benzoyl isothiocyanate
N
H
N
H
N
N
S
O
N-(2-isonicotinoylhydrazine-carbonothioyl)benzamide
isonicotinic hydrazide
H3L
SCHEME 2 Preparation of the ligand
stream.[50] The spectra were corrected for the dark current
noises and background firstly. Spectral Gaussian peaks were
used to obtain the best-fitted data. The intensity, full width
at half maximum (FWHM) and position of each band were
adjusted automatically by the program, on the basis of the
minimization of the deviations between experimental and
simulated spectrum.[51,52]
100 μL dimethyl sulfoxide (DMSO) was added to each well
to dissolve the purple color of the formed formazan. The
readings were taken at 570 nm by a plate reader (EXL 800,
USA). The relative cell viability in percentage was calculated
as (A570 of treated samples/A570 of untreated sample) × 100.
For comparison, Doxorubicin was used as a standard antican-
cer drug.[53,54]
4.4
Synthesis of the ligand (H3L)
ORCID
|
Isonicotinic hydrazide (0.01 mol) was dissolved in 25 mL
ethanol and to which benzoylisothiocyanate (0.01 mol)
was added dropwise. The reaction mixture was refluxed for
1 hour. After cooling to room temperature, white crystals
were precipitated. After filtration the precipitate was washed
with ethanol and dried in air (m.p.: 232°C). The formation
reaction of the ligand is shown in Scheme 2.
Nasser Mohammed Hosny
org/0000-0003-1035-1480
http://orcid.
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