Cobalt, nickel, copper and zinc complexes with 1,3-diphenyl-1H-pyrazole-4- carboxaldehyde Schiff bases: Antimicrobial, spectroscopic, thermal and fluorescence studies

Article abstract of DOI:10.1016/j.ejmech.2012.02.053

Two new Schiff bases of 1,3-diphenyl-1H-pyrazole-4-carboxaldehyde and 4-amino-5-mercapto-3-methyl/H-1,2,4-triazole [HL^1-2] and their Cobalt, Nickel, Copper and Zinc complexes have been synthesized and characterized by elemental analyses, spectr

Full text of DOI:10.1016/j.ejmech.2012.02.053

European Journal of Medicinal Chemistry 52 (2012) 313e321
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Short communication
Cobalt, nickel, copper and zinc complexes with 1,3-diphenyl-1H-pyrazole-4-
carboxaldehyde Schiff bases: Antimicrobial, spectroscopic, thermal and
fluorescence studies
,
a
a
a
b
Kiran Singh a , Yogender Kumar , Parvesh Puri , Mahender Kumar , Chetan Sharma
*
a Department of Chemistry, Kurukshetra University, Kurukshetra, Haryana 136 119, India
b Department of Microbiology, Kurukshetra University, Kurukshetra, Haryana 136 119, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new Schiff bases of 1,3-diphenyl-1H-pyrazole-4-carboxaldehyde and 4-amino-5-mercapto-3-
methyl/H-1,2,4-triazole [HL1e2
and their Cobalt, Nickel, Copper and Zinc complexes have been
Received 30 September 2011
Received in revised form
22 February 2012
Accepted 27 February 2012
Available online 3 March 2012
]
synthesized and characterized by elemental analyses, spectral (UVevis, IR, 1H NMR, Fluorescence)
studies, thermal techniques and magnetic measurements. A square planar geometry for Cu(II) and
octahedral geometry for Co(II), Ni(II) and Zn(II) complexes have been proposed. In order to evaluate the
biological activity of Schiff bases and to assess the role of metal ion on biological activity, the pyrazole
Schiff bases and their metal complexes have been studied in vitro antibacterial against Staphylococcus
aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa and antifungal against Aspergillus niger,
and Aspergillus flavus. In most of the cases higher activity was exhibited upon coordination with metal
ions.
Keywords:
1,3-Diphenyl-1H-pyrazole-4-
carboxaldehyde
Antimicrobial activity
Thermal studies
1,2,4-Triazole
Ó 2012 Elsevier Masson SAS. All rights reserved.
Fluorescence
1. Introduction
portion of chemical entities, which are part of many natural
products, fine chemicals and biologically active pharmaceuticals
Finding new species, with a wide spectrum of biological activity
(antimicrobial, antiviral) and also low cytotoxicity represents a very
important aspect in the biochemical research area. This is due the
fact that the pathogens agents continuously undergo mutations
and also the drugs used to treat the viral disease develop in time
a certain resistance to a particular antibiotic [1e3].
Recently, there has been considerable amount of progress in 1,3-
diarylpyrazole chemistry because of the recognition of importance
of the pyrazole structure in biological processes as antimicrobial
[4], anti-inflammatory [5], antitubercular [6], antitumor [7], anti-
angiogensis [8], antiparasitic [9], antiviral [10] and also possesses
analgesic and anxiolytic activity [11]. 4-Amino-3-mercapto-1,2,4-
triazole derivative is an ideal heterocyclic by virtue of its vicinal
nucleophiles amino and mercapto groups constitutes a ready-made
building block for construction of various organic heterocycles [12].
Nitrogen containing heterocyclic molecules constitutes the largest
vital for enhancing the quality of life [13]. Schiff bases derived from
3-substituted-4-amino-5-mercapto-1,2,4-triazoles show analgesic,
antimicrobial, antidepressant and anti-inflammatory activities [14].
When bioorganic molecules or drugs are bound to metal ions, there
is drastic change in their biomimetic properties, therapeutic effects
and pharmacological properties. Essential metal ions and their
complex are found to be antitumor active, catalytic active, antimi-
crobial and cytotoxic [15e18].
Keeping in view biological and medicinal properties of triazoles,
pyrazoles and the potential chemistry of transition metals, we find
it vital to join the chemistry of both moieties in search of designing
metal based biological active compounds that could aggressively
work against resistant bacterial species. For this accomplishment,
1,3-diphenyl-1H-pyrazole-4-carboxaldehyde was reacted with 4-
amino-5-mercapto-1,2,4-triazole [HL1] and 4-amino-5-mercapto-
3-methyl-1,2,4-triazole [HL2] to form a new series of biologically
active Schiff bases [HL1e2] and their metal complex with Co(II),
Ni(II), Cu(II) and Zn(II) ions. The synthesized ligands and their metal
complexes were characterized by different techniques like
elemental analyses, spectral studies (UVevis, IR, 1H NMR, Fluores-
cence), TGA, magnetic and conductance measurements.
* Corresponding author. Tel.: þ91 9812137734.
E-mail address: kiransinghkuk@yahoo.co.in (K. Singh).
0223-5234/$ e see front matter Ó 2012 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2012.02.053

314
K. Singh et al. / European Journal of Medicinal Chemistry 52 (2012) 313e321
2. Pharmacology
NHNH2
COCH3
C2H5OH
Reflux
2.1. Antibacterial activity (in vitro)
+
NHN
C
CH3
All the newly synthesized ligands [HL1e2] and their metal
complexes were screened in vitro for their antibacterial
activity against two Gram-positive (Staphylococcus aureus
MTCC 96, Bacillus subtilis MTCC 121) and two Gram-negative
(Escherichia coli MTCC 1652, Pseudomonas aeruginosa MTCC
741) bacterial strains by agar well diffusion method as reported
in our previous paper [19]. DMSO was used as a negative control
whereas Ciprofloxacin was used as positive control. All the
bacterial cultures were procured from Microbial Type Culture
Collection (MTCC), IMTECH, Chandigarh and subcultured on
nutrient agar.
50-600C
POCl3/DMF
N
N
N
+
R
SH
N
N
NH2
C2H5OH
Reflux
CHO
N
2.2. Antifungal activity (in vitro)
N
SH
All the newly synthesized ligands [HL1e2] and their metal
complexes were screened in vitro for their antifungal activity
against two fungi, Aspergillus niger and Aspergillus flavus, the ear
pathogens isolated from the patients of Kurukshetra [20] and
evaluated by poisoned food technique [19]. The molds were grown
on Sabouraud dextrose agar (SDA) at 25 ꢀC for 7 days and used as
inocula. DMSO was used as the negative control whereas Fluco-
nazole was used as the positive control. The experiments were
performed in triplicates. Diameters of fungal colonies were
measured and expressed as percent mycelial inhibition.
N
R
H
C
N
N
N
R = H (HL1), CH3 (HL2)
Fig. 1. Scheme for the synthesis of Schiff bases [HL1e2].
Percent inhibition of mycelial growth ¼ ðdc ꢁ dtÞ=dc ꢂ 100
3.1. IR spectral studies
Where dc average diameter of fungal colony in negative control sets
and dt average diameter fungal colony in experimental sets.
The mode of binding of ligands to the metal ions was elucidated
by recording the IR spectra of the complexes as compared with the
spectra of free ligands (Table 1). The formation of ligands is
confirmed by the absence of stretching vibrations due to aldehyde
2.3. Determination of minimum inhibitory concentration (MIC)
n
(CHO) and amino
new band appeared at 1615e1618 cmꢁ1 corresponding to the
azomethine (HC]N) group [15,18,19]. After complexation, the
n(NH2) moiety of triazole and instead, a strong
MIC is the lowest concentration of an antimicrobial compound
that will inhibit the visible growth of a microorganism after
overnight incubation. MIC of the various compounds against
bacterial strains was tested through a modified agar well diffusion
method [21]. In this method, a twofold serial dilution of each
synthesized compound was prepared by first reconstituting the
compound in DMSO followed by dilution in sterile distilled water
n
band due to azomethine vibration shifted to lower frequency
(15e20 cmꢁ1), thus indicating the coordination of the azomethine-
N to the metal ion. A characteristic strong band at 2739e2762 cmꢁ1
is ascribed to n(SH), disappeared in the spectra of metal complexes,
to achieve a decreasing concentration range 256e0.5
100 l volume of each dilution was introduced into wells (in
m
g mLꢁ1. A
m
triplicate) in the agar plates already seeded with 100
ml of
Table 1
The important IR frequencies of the ligands and their metal complexes (cmꢁ1).
standardized inoculum (106 cfu mLꢁ1) of the test microbial
strain. All test plates were incubated aerobically at 37 ꢀC for
24 h and observed for the inhibition zones. Ciprofloxacin was
used as positive control.
Compound
n
n
n
n
n
n
n
(N]CH) (CeS) (SeH) (OOCCH3) (H2O/OH) (MeS) (MeN)
HL1
1615
e
756
755
753
753
756
756
750
752
e
2739
e
e
e
e
e
Co(L1)(OAc)$3H2O 1597
1728
e
3356
3350
3348
3300
3318
e
352
351
348
350
338
340
352
356
e
487
491
502
508
488
488
503
511
e
Co(L1)2$2H2O
Ni(L1)(OAc)$3H2O 1592
Ni(L1)2$2H2O
1592
Cu(L1)(OAc)$H2O 1595
Cu(L1)2
1593
1598
e
3. Results and discussion
e
1720
e
e
The synthesis of Schiff bases [HL1e2] is schematically repre-
sented in Fig. 1. Analytical data indicated the formation of 1:1 and
1:2 metal complexes of HL1e2 with Co(II), Ni(II), Cu(II) and Zn(II)
metal ions. The molar conductance values of the complexes
(measured in 10ꢁ3 M DMF) are in the range 3.4e8.2 Uꢁ1 cm2 molꢁ1
indicating the non electrolytic nature [22,23]. The low conductivity
values are in agreement with low solubility of metal complexes in
water, ethanol, chloroform, acetone and most organic solvents. On
the other hand, they are soluble in DMSO, DMF and decomposed
at higher temperature. The purity of ligands and their metal
complexes has been checked by TLC.
e
1726
e
e
Zn(L1)(OAc)$3H2O 1598
e
1719
e
3388
3397
e
Zn(L1)2$2H2O
1597
1618
e
HL2
2762
e
e
Co(L2)(OAc)$3H2O 1598
756
758
764
756
758
754
765
764
1723
e
3348
3310
3310
3310
3412
e
338
342
340
339
353
350
347
349
499
503
495
509
515
520
487
488
Co(L2)2$2H2O
Ni(L2)(OAc)$3H2O 1597
Ni(L2)2$2H2O
1597
Cu(L2)(OAc)$H2O 1593
Cu(L2)2
1595
Zn(L2)(OAc)$3H2O 1594
Zn(L2)2$2H2O
1597
1600
e
e
1729
e
e
e
1727
e
e
e
1730
e
3388
3387
e

K. Singh et al. / European Journal of Medicinal Chemistry 52 (2012) 313e321
315
confirming deprotonation and coordination of thiol group [24]. This
%) have also been calculated (Table 3) for Co(II) complexes by using
Band-fitting equation [26]. The Rachah parameter (B) is found to be
764e810 cmꢁ1 (<971 cmꢁ1), suggesting an overlapping of ligand
metal orbital’s. The nephelauxetic ratio (b) for the 1:1 and 1:2
cobalt complexes is less than one suggesting partial covalency in
the metal ligand bond.
is further supported by the lower frequency band appeared at
750e765 cmꢁ1 in the metal complexes due to
n
(CeS). The new
band in the region of 335e355 and 485e520 cmꢁ1 in all metal
complexes are assigned to vibrations of (MeS) and (MeN) bonds,
n
n
respectively [22,23]. In the spectra of metal complexes a broad
band in the region 3300e3415 cmꢁ1 indicated the presence of
The electronic spectra of Ni(II) complexes show three absorption
coordinated water molecules.
A strong band in the region
band in the region 9999e10,123 cmꢁ1, 16,380e17320 cmꢁ1 and
1718e1730 cmꢁ1 has been assigned to
n
(OOCCH3) in 1:1 metal
24,885e24,993 cmꢁ1, which were assigned to A2g(F) / T2g(F)
(
3
3
3
3
3
3
complexes [19].
n1), A2g(F) / T1g(F) (n2) and A2g(F) / T1g(P) (n3) transitions
[25]. These are the characteristic bands of octahedral environment
around Ni(II) ion. The ligand field parameters (Dq, B, %) indicate
b, b
3.2. 1H NMR spectra of Schiff bases and Zn(II) complexes
significant covalent character of the metal ligand bonds. The
magnetic moments of the complexes are in the region 3.0e3.5 BM,
which agrees with the presence of Ni(II) ion in an octahedral
geometry [27].
The 1H NMR spectral data of Schiff bases and Zn(II) complexes
have been given in Table 2. Upon comparison with the free ligands,
the signal observed at w14 ppm can be assigned to the eSH protons
[22,23]. This signal disappears in the spectra of metal complexes,
which confirms the coordination of ligand to metal ion through the
deprotonated thiol group. The ligands [HL1e2] showed character-
Cu(II) complexes show absorption band at 18,600e19,020 cmꢁ1
are due to the 2B1g/2A1g
(n1) transition. It is a characteristic band
of square planar geometry around the Cu(II) [26,28]. The square
planar geometry of Cu(II) in the complexes is confirmed by the
measured magnetic moment values, 1.73e1.81 BM.
istic azomethine proton signal at d 9.67 and d 9.99, respectively (see
Supplementary materials). The characteristic signal due to azo-
methine proton deshielded in the spectra of metal complexes,
suggests coordination of azomethine nitrogen atom to metal ion.
The aromatic protons present in the ligands (HL1e2) are found as
3.4. Fluorescence properties
two multiplets at
8.03 ppm, respectively, show a slight shift upon coordination. The
triazole-H and pyrazole-H of HL1 appeared as singlet at
8.80 and
9.24 ppm, respectively, and pyrazole-H of HL2 at 9.29 ppm. In the
d
7.42, 7.55 and double doublets at 7.85 and
The fluorescence emission spectra of the Schiff bases HL1e2 and
their 1:2 metal complexes were recorded in DMF with excitation
wavelength 265 nm at room temperature. The fluorescence emis-
sion spectrum of HL1 with its 1:2 metal complexes is depicted in
Fig. 2. HL1 exhibits a strong fluorescence emission at 382 nm,
contrast to this partial fluorescence quenching phenomena are
observed in its metal complexes with weak fluorescence emission
at 393, 400, 367 and 376 nm for Co(II), Ni(II), Cu(II) and Zn(II),
respectively. HL2 shows strong fluorescence band at 376 nm and its
Co(II), Ni(II), Cu(II) and Zn(II) complexes exhibit weak emission
bands at 402, 390, 380, and 378 nm, respectively. The maximum
emission wavelength of Schiff bases is red-shifted about 5e20 nm
owing to the formation of complex. It is evident from the fluores-
cence spectra that, fluorescence emission intensity of Schiff bases
decreased dramatically on complex formation with transition
metal ions. The decrease in fluorescence intensity with formation
of metal complexes is due to decrease in electron density on Schiff
bases [15,29]. The decrease in emission maxima were in the order
of Zn(II) > Cu(II) > Co(II) > Ni(II).
d
spectra of 1:1 Zn complexes singlet at
of acetate ion.
d 1.82 is due to methyl group
3.3. Magnetic measurements and electronic spectra
The electronic spectra and magnetic moments data of the metal
complexes are listed in Table 3. The electronic spectra provided
enough information regarding the arrangements of the ligands
around the metal ions. The magnetic moments of the Co(II)
complexes of HL1e2 at room temperature are in the range
4.65e4.75 BM [15]. These values are in good agreement with those
reported for octahedral Co(II) complexes. For high spin octahedral
complexes of Co(II), two transitions are expected in the electronic
spectra; they are 4T1g(F) / 4T2g(F) (n1); 4T1g(F) / 4T1g(P) (n3), n2 is
not observed, but it can be calculated [25,26] by using relation
n2
¼ n1 þ10Dq, which is very close to (n3) transition. Also the ratio of
second to first transition [26] should lie in the range of 2.1e2.2.
3.5. Thermal analyses
Co(II) complexes exhibits two absorption bands in the region
11,240e11,390 cmꢁ1
tion energy ratio of second to first is 2.11, corresponding to high
spin octahedral complexes. The ligand field parameters (Dq, B, b, b
(
n1) and 21,575e22,225 cmꢁ1
(
n3) and transi-
The thermogravimetric analysis were carried out for
Co(L1)2$2H2O, Ni(L1)2$2H2O, Cu(L2)(OAc)$H2O and Zn(L2)(OAc)$
3H2O and are shown in Fig. 3. The decomposition of all the
Table 2
1H NMR spectral data of Schiff bases and Zn(II) metal complexes.
Compound
1H NMR (DMSO-d6) (ppm)
HL1 [C18H14N6S]
7.42 (m, 1H, AreH), 7.54 (m, 5H, AreH), 7.85 (d, 2H, AreH), 8.03 (d, 2H, AreH), 8.80 (s, 1H, triazole-H), 9.24
(s, 1H, pyrazole-H), 9.67 (s, 1H, eN]CHe), 14.0 (s, 1H, eSH)
Zn(L1)(OAc)$3H2O [C20H22N6O5SZn]
Zn(L1)2$2H2O [C36H30N12O2S2Zn]
HL2 [C19H16N6S]
7.43 (m, 1H, AreH), 7.53 (m, 5H, AreH), 7.84 (d, 2H, AreH), 8.02 (d, 2H, AreH), 8.94 (s, 1H, triazole-H), 9.21
(s, 1H, pyrazole-H), 9.99 (s, 1H, eN]CHe), 1.82 (s,3H, CH3COO)
7.43 (m, 2H, AreH), 7.64 (m, 10H, AreH), 7.83 (d, 4H, AreH), 7.99 (d, 4H, AreH), 8.71 (s, 2H, triazole-H), 9.33
(s, 2H, pyrazole-H), 9.99 (s, 2H, eN]CHe)
2.34 (s, 3H, eCH3), 7.42 (m, 1H, AreH), 7.55 (m, 5H, AreH), 7.86 (d, 2H, AreH), 8.03 (d, 2H, AreH), 9.29
(s, 1H, pyrazole-H), 9.99 (s, 1H, eN]CHe), 13.88 (s, 1H, eSH)
2.27 (s, 3H, eCH3), 7.40 (m, 1H, AreH), 7.54 (m, 5H, AreH), 7.74 (d, 2H, AreH), 8.19 (d, 2H, AreH), 9.23
(s, 1H, pyrazole-H), 10.12 (s, 1H, eN]CHe), 1.81(s, 3H, CH3COO)
Zn(L2)(OAc)$3H2O [C21H24N6O5SZn]
Zn(L2)2$2H2O [C38H34N12O2S2Zn]
2.33 (s, 6H, eCH3), 7.40 (m, 2H, AreH), 7.54 (m, 10H, AreH), 7.85 (d, 4H, AreH), 8.23 (d, 4H, AreH), 9.24
(s, 2H, pyrazole-H), 10.14 (s, 2H, eN]CHe)

316
K. Singh et al. / European Journal of Medicinal Chemistry 52 (2012) 313e321
Table 3
Electronic spectra, magnetic data and ligand field parameters of metal complexes.
Compound
Transitions (cmꢁ1
)
Dq (cmꢁ1
)
B (cmꢁ1
)
n2
/n1
b
b
%
meff (BM)
n1
n2
n3
Co(L1)(OAc)$3H2O
Co(L1)2$2H2O
Ni(L1)(OAc)$3H2O
Ni(L1)2$2H2O
Cu(L1)(OAc)$H2O
Cu(L1)2
11,248
11,376
9980
23,767a
24,021a
15,479
15,458
21,584
21,578
23,584
23,680
1251.9
1264.5
998.0
989.9
e
773.8
764.7
608.2
629.4
e
2.11
2.11
1.55
1.56
e
0.796
20.4
21.3
41.6
39.6
e
4.73
4.65
3.32
3.29
1.78
1.73
4.82
4.78
3.11
3.09
1.80
1.81
0.787
0.584
0.604
e
9899
18,999
19,011
11,389
11,275
9920
9935
18,583
18,610
e
e
e
e
e
Co(L2)(OAc)$3H2O
Co(L2)2$2H2O
Ni(L2)(OAc)$3H2O
Ni(L2)2$2H2O
Cu(L2)(OAc)$H2O
Cu(L2)2
24,088a
23,848a
15,174
15,230
22,222
22,010
24,883
24,887
1269.9
1257.3
992.0
988.7
e
809.5
802.2
686.4
687.4
e
2.11
2.11
1.52
1.53
e
0.833
0.826
0.659
0.660
e
16.7
17.4
34.1
34.0
e
e
e
e
e
e
a
Calculated.
complexes ended with oxide formation [18,19,22,23]. The deter-
mined temperature ranges, percentage mass losses, and thermal
effects accompanying the changes in the coordination compounds
on heating revealed the following finding (Table 4). In case of
Co(L1)2$2H2O complex, the first step 80e200 ꢀC, results in a mass
loss of 4.6% (calcd. 4.6%) corresponding to loss of two water
molecules. The second step in the temperature range 200e300 ꢀC
corresponding to loss of pyrazole moieties with mass loss 57.7%
(calcd. 59.0%) and third steps (300e700 ꢀC) correspond to removal
of two triazole molecules with mass loss of 26.7% (calcd. 28.7%) of
the ligand leaving metal oxide as residue. The thermal decompo-
sition of Ni complex took place in three steps as indicated by TG
curve around 80e197, 197e392 and 392e700 ꢀC corresponding to
mass loss of water molecules, pyrazole and triazole moieties,
respectively. In case of Cu complex decomposition took place in
three steps corresponding to loss of coordinated water molecule,
organic (acetate group and pyrazole) and triazole moiety around
80e175, 175e305 and 305e700 ꢀC, respectively. The decomposi-
tion of Zn complex also takes place in three major stages. The first
and second stage is consisting of loss of water molecules and
organic (acetate group and pyrazole) moiety in temperature range
80e408 ꢀC. The third step corresponds to decomposition of triazole
molecule at 408e700 ꢀC in the TG curve. The results show good
agreement with the formulae suggested from the analytical data.
3.5.1. Determination of degradation activation energy
CoatseRedfern equation [30] (equation (1)) is used to evaluate
thermal degradation activation energy (E, kJ molꢁ1) and degrada-
tion mechanism for Co(L1)2$2H2O, Ni(L1)2$2H2O, Cu(L2)(OAc)$H2O
and Zn(L2)(OAc)$3H2O.
ꢀ
ꢁ
ꢀ
ꢁ
gð
a
T2
Þ
AR
E
RT
ln
¼ ln
ꢁ
(1)
E
b
In above equation,
b
is the heating rate (ꢀC minꢁ1), T is
temperature, R is the universal gas constant, A is the pre-
exponential factor (minꢁ1),
a
is the degree of conversion and g(a)
100
80
60
40
20
0
Zn complex
Ni complex
Cu complex
Co complex
100
200
300
400
500
600
700
Temperature (OC)
Fig. 2. Fluorescence emission spectra of Schiff base [HL1] and its metal complexes.
Fig. 3. Thermogravimetric curves of metal complexes.

K. Singh et al. / European Journal of Medicinal Chemistry 52 (2012) 313e321
317
Table 4
Thermogravimetric characteristics of metal complexes.
Zn complex
Cu complex
Ni complex
Co complex
-5.4
-5.6
-5.8
-6.0
-6.2
-6.4
Compound
Decomposition stages
& assignment
Temp. (ꢀC) % Weight loss
found (calcd.)
Co(L1)2$2H2O
1, Water molecules
80e200
200e300
300e700
80e197
197e392
392e700
80e175
4.6(4.6)
57.7(59.0)
26.7(28.7)
4.8(4.6)
58.4(59.1)
25.8(28.9)
3.5(3.6)
58.5(58.2)
22.3(25.4)
10.0(10.1)
52.1(54.3)
21.0(23.6)
[C36H30CoN12O2S2] 2, Organic moiety
3, Triazole moiety
Ni(L1)2$2H2O
1, Water molecules
2, Organic moiety
3, Triazole moiety
1, Water molecules
[C36H30N12NiO2S2]
Cu(L2)(OAc)$H2O
[C21H20CuN6O3S]
2, eOAc & organic moiety 175e305
3, Triazole moiety
305e700
80e263
263e408
408e700
Zn(L2)OAc$3H2O
[C21H24N6O5SZn]
1, Water molecules
2, eOAc, organic moiety
3, Triazole moiety
is degradation mechanism defined by various models as given in
Table 5. E can be calculated from the slope of the graph between
1.65 1.70 1.75 1.80 1.85 1.90 1.95 2.00
1000/T (K-1)
ln½gð
a
Þ=T2ꢃ and 1/T. Table 5 presents the activation energy values
produced using equations of various models with CoatseRedfern
method. To choose the best mechanism among the various
models, two conditions are imposed on the results i.e. firstly,
models resulting into negative values and secondly, models
producing values corresponding to low regression coefficients (r2)
Fig. 4. CoatseRedfern plots for the four compounds using second order mechanism.
Tested compounds showed zone of inhibition ranging
16 mme28 mm against the Gram-positive bacteria and between
13 mm and 24 mm against Gram-negative bacteria. The ligands
(HL1e2) show zone of inhibition ranging 17.6 mme19.6 mm against
Gram-positive bacteria and 13.3 mme15.6 mm against Gram-
negative bacteria. It has been observed that the metal complexes
showed increased zone of inhibition against the bacterial strains
(Table 6) as compared to ligands ranging 13.0e27.6 mm. On the
basis of zone of inhibition produced against the test bacterium,
compound 9 was found to be most effective against S. aureus,
B. subtilis, E. coli and P. aeruginosa with zone of inhibition of
27.6 mm, 25.6 mm, 24.0 mm and 21.0 mm, respectively (Table 6).
However, some of the compounds in this series were not effective
against any Gram-negative bacteria. The MIC results suggest that
the ligands and their complexes (Table 7) showed a moderate
activity against the bacterial strains as compared to the standard
drug (Ciprofloxacin). In the whole series, the MIC of synthesized
in either degradation stage are summarily neglected. Noticeably,
ꢁ1
the second order mechanism with g(
a) ¼ (1 ꢁ
a)
ꢁ 1, results
positive E values for the complexes and with best r2 data among all
models producing positive E values (Table 5) and the corresponding
plots are shown in Fig. 4. Based on the E2 (second stage) values as
deduced using second order model, following stability order is
suggested: Cu > Co > Zn > Ni complex.
3.6. Antimicrobial discussion
The ligands (HL1e2), metal complexes, standard drugs and DMSO
solvent were screened separately for their antibacterial activity
againstGram-positive (S. aureus, B. subtilis)andGram-negative(E.coli,
P. aeruginosa) bacteria and antifungal activity against A. niger and
A. flavus. The microbial results are summarized in Tables 6e8. The
antimicrobial studies suggested that the Schiff bases are biologically
active and their metal complexes showed significantly enhanced
antibacterial and antifungal activity against microbial strains in
comparison to the free ligands. Positive controls (Standard drug)
produced significantly sized inhibition zones against the tested
bacteria and fungi; however, negative control (DMSO) produced no
observable inhibitory effect against any of the test organisms.
compounds ranged 10.0e481.7
mM against Gram-positive bacteria
and 19.5e710.2 M against Gram-negative bacteria. MIC results
m
revealed that the metal complexes are more effective against the
antibacterial strains as compared to the Schiff bases. Compound 9
was found to be best antibacterial agent exhibited the lowest MIC
mM against S. aureus and B. subtilis (Table 7). The results of our
study are in accordance with the reports of earlier workers
10.0
Table 5
Activation energy values calculated using CoatseRedfern method.
Model
Cu complex
Ni complex
Zn complex
Co complex
E2(r2)a
E3(r2)a
E2(r2)
E3(r2)
E2(r2)
E3(r2)
E2(r2)
E3(r2)
Power law, a1/4
17.8(0.993) ꢁ8.2(0.99)
26.0(0.995) ꢁ7.4(0.98)
6.7(0.93)
11.9(0.96)
ꢁ8.7(0.998)
ꢁ7.8(0.996)
7.6(0.941) ꢁ9.9(0.998)
13.2(0.965) ꢁ9.5(0.997)
28.1(0.958) ꢁ8.6(0.99)
13.0(0.964) ꢁ8.2(0.994)
20.4(0.974) ꢁ7.5(0.987)
10.5(0.975)
17.1(0.984) ꢁ8.25(0.999)
ꢁ8.7(0.999)
Power law, a1/3
Power law, a1/2
44.6(0.96)
ꢁ6.1(0.96)
22.5(0.976) ꢁ6.5(0.986)
9.7(0.978) ꢁ6.0(0.963)
15.9(0.986) ꢁ4.5(0.88)
30.1(0.988)
15.0(0.998)
23.3(0.989)
39.2(0.997)
147.4(0.992)
80.8(0.997)
162.4(0.997)
87.1(0.998)
ꢁ7.2(0.999)
ꢁ6.7(0.994)
ꢁ5.5(0.983)
ꢁ3.2(0.884)
1.9(0.651)
0.6(0.105)
7.4(0.81)
3.8(0.694)
17.2(0.883)
0.8(0.264)
0.6(0.105)
AvramieErofeev, [ꢁln(1 ꢁ
AvramieErofeev, [ꢁln(1 ꢁ
AvramieErofeev, [ꢁln(1 ꢁ
a
a
a
)]1/4
)]1/3
)]1/2
22.8(0.999) ꢁ5.6(0.97)
33.3(0.999) ꢁ4.1(0.93)
54.9(0.999) ꢁ1.1(0.33)
28.6(0.99)
117.3(0.97)
61.8(0.996)
127.7(0.99)
66.0(0.993)
ꢁ1.2(0.189)
35.5(0.98)
ꢁ5.6(0.948)
One dimensional diffusion, a2
205.0(0.997)
111.4(0.999)
6.1(0.71)
3.8(0.689)
7.0(0.797) 140.5(0.973) ꢁ1.1(0.16)
1/3
2
Diffusion control (Janders), [1 ꢁ (1 ꢁ
a
)
]
4.3(0.565)
74.8(0.98)
ꢁ2.5(0.62)
3.16(0.45)
0.1(0.001)
2/3
Diffusion control (Crank) 1 ꢁ (2/3)
a
e(1 ꢁ
a)
222.6(0.999) 12.9(0.88)
118.4(0.999) 8.0(0.87)
141.5(0.999) 24.3(0.98)
14.3(0.856) 152.7(0.7)
8.5(0.718)
Mampel (first order), ꢁln(1 ꢁ
a)
74.1(0.994)
96.7(0.993)
ꢁ1
Second order, (1 ꢁ
a)
ꢁ 1
79.8(0.995) 25.3(0.82)
59.8(0.98)
61.8(0.996)
9.6(0.737) 108.3(0.998)
1/2
Contracting cylinder, 1 ꢁ (1 ꢁ
a
)
107.9(0.99)
111.4(0.999)
2.2(0.42)
3.8(0.68)
2.5(0.387)
4.3(0.565)
72.5(0.978) ꢁ3.6(0.82)
77.8(0.996)
80.8(0.997)
1/3
Contracting Sphere, 1 ꢁ (1 ꢁ
a)
74.9(0.98)
ꢁ2.5(0.65)
a
2 & 3 stands for second & third stage, r2 stands for regression coefficient.

318
K. Singh et al. / European Journal of Medicinal Chemistry 52 (2012) 313e321
Table 6
Table 8
Antibacterial activity of chemical compounds through agar well diffusion method.
Antifungal activity of Schiff bases and their metal complexes.
Sr. No. Compounds
Diameter of growth of inhibition zone (mm)a
Sr. No.
Compounds
Mycelial growth inhibition (%)
S. aureus
B. subtilis
E. coli
P. aeruginosa
A. niger
A. flavus
1
2
3
4
5
6
7
8
HL1
17.6
18.3
18.6
18.3
22.6
19.6
17.6
18.3
24.6
25.6
19.6
19.3
21.6
19.3
19.6
19.3
17.0
19.6
18.3
24.0
13.3
e
14.3
13.0
e
1
2
3
4
5
6
7
8
HL1
45.5
48.8
50.0
55.5
48.8
45.5
51.1
58.8
60.0
57.7
51.1
55.5
48.8
45.5
52.5
43.3
41.1
42.5
81.1
42.5
44.4
43.3
52.5
44.4
41.1
47.7
55.5
63.3
61.1
52.5
58.8
51.1
48.8
50.0
45.5
44.4
47.7
77.7
Co(L1)(OAc)$3H2O 18.3
Co(L1)(OAc)$3H2O
Co(L1)2$2H2O
Ni(L1)(OAc)$3H2O
Ni(L1)2$2H2O
Cu(L1)(OAc)$H2O
Cu(L1)2
Co(L1)2$2H2O
17.3
15.3
18.3
17.6
14.3
e
Ni(L1)(OAc)$3H2O 21.6
16.3
16.6
16.6
e
Ni(L1)2$2H2O
Cu(L1)(OAc)$H2O
Cu(L1)2
20.6
16.3
17.6
Zn(L1)(OAc)$3H2O 22.6
19.3
24.0
17.3
e
17.6
21.0
15.6
e
Zn(L1)(OAc)$3H2O
Zn(L1)2$2H2O
HL2
9
Zn(L1)2$2H2O
27.6
18.6
9
10
11
12
13
14
15
16
17
18
19
HL2
10
11
12
13
14
15
16
17
18
19
Co(L2)(OAc)$3H2O 16.3
Co(L2)(OAc)$3H2O
Co(L2)2$2H2O
Ni(L2)(OAc)$3H2O
Ni(L2)2$2H2O
Cu(L2)(OAc)$H2O
Cu(L2)2
Co(L2)2$2H2O
22.6
17.3
16.6
17.6
14.3
16.2
13.3
17.6
25.0
16.3
16.4
15.6
14.3
14.3
14.3
17.0
22.0
Ni(L2)(OAc)$3H2O 16.3
Ni(L2)2$2H2O
Cu(L2)(OAc)$H2O
Cu(L2)2
20.0
17.3
15.6
Zn(L2)(OAc)$3H2O 17.3
Zn(L2)(OAc)$3H2O
Zn(L2)2$2H2O
Fluconazole
Zn(L2)2$2H2O
Ciprofloxacin
17.6
26.6
e No activity.
a
Values, including diameter of the well (8 mm), are means of three replicates.
over the whole chelate ring is increased and lipophilicity of the
complexes is enhanced. The increased lipophilicity enhances the
penetration of the complexes into the lipid membranes and blocks
the metal binding sites in the enzymes of microorganisms. These
complexes also disturb the respiration process of the cell and thus
block the synthesis of proteins, which restricts further growth of
the organism. In general, metal complexes are more active than
ligands as they may serve as principal cytotoxic species. Thus
exhibiting their broad spectrum nature and can be further used in
pharmaceutical industry for mankind, as an antimicrobial agent,
after testing its toxicity to human beings.
[17,18,31], which also showed that the antibacterial activity of
ligands is greatly enhanced when it is coordinated to metal ions.
Both of the Schiff bases showed activity against fungal species.
However, metal complexes of these Schiff bases show enhanced
activity as compared to the uncoordinated compounds, especially
with A. niger. Of the 18 chemical compounds screened for their
antifungal activity, three compounds 8, 9 and 10 showed more than
55% inhibition of mycelial growth against A. niger whereas two
compounds 9 and 10 showed more than 60% inhibition of mycelial
growth against A. flavus (Table 8). The overtone’s concept [32] and
Tweedy’s chelation theory [33] can be used to explain the enhanced
in antimicrobial activity of the metal complexes. According to the
Overtone’s concept of cell permeability, the lipid membrane
surrounding the cell favors the passage of only lipid-soluble
materials; therefore, liposolubility is an important factor which
controls the antimicrobial activity. On chelation, polarity of the
metal ion is reduced to a greater extent due the overlapping of the
ligand orbital and partial sharing of the positive charge of the metal
4. Conclusions
The synthesized Schiff bases act as bidentate ligands and coor-
dinated to metal ion through nitrogen and sulphur of thiol group.
The bonding of ligand to metal ion is confirmed by elemental
analyses, spectral studies (UVevis, IR, 1H NMR, Fluorescence), TGA,
magnetic and conductance measurements. The ligand field
parameters (Dq, B, b, b%) indicated significant covalent character of
ion with donor groups. Moreover, delocalization of the p-electrons
the metal ligand bonds. The proposed structures of metal
complexes are presented in Fig. 5. The antimicrobial studies sug-
gested that the Schiff bases were found to be biologically active and
their metal complexes show significantly enhanced antibacterial
and antifungal activity against microbial strains in comparison to
the free ligands. Thus, exhibiting their broad spectrum nature and
can become a new antimicrobial agent, after further biological
studies.
Table 7
Minimum inhibitory concentration (MIC) (
mM) of compounds.
Sr. no. Compound Staphylococcus Bacillus Escherichia Pseudomonas
aureus
subtilis coli
aeruginosa
1
2
3
4
5
6
7
8
HL1
184.7
369.5
123.6
162.8
30.9
162.9
131.6
169.6
30.5
739.0
e
369.9
162.9
e
Co(L1)(OAc)$3H2O 123.6
Co(L1)2$2H2O
81.4
61.8
40.7
81.4
247.4
162.9
263.3
e
Ni(L1)(OAc)$3H2O
Ni(L1)2$2H2O
494.9
325.8
526.7
e
Cu(L1)(OAc)$H2O 263.3
5. Experimental protocols
Cu(L1)2
84.4
Zn(L1)(OAc)$3H2O 61.0
244.3
40.3
355.1
e
244.3
80.7
710.2
e
5.1. Materials and methods
9
Zn(L1)2$2H2O
10.0
177.5
10.0
88.7
240.8
10
11
12
13
14
15
16
17
18
19
HL2
Co(L2)(OAc)$3H2O 481.7
All the chemicals used in the present investigation were of
Analytical grade and used without further purification. The
elemental analyses (C, H, and N) were carried out at SAIF, Punjab
University, Chandigarh by using PerkineElmer 2400 Elemental
Analyzer. The metal contents were determined using standard
gravimetric methods; cobalt was estimated as cobalt pyridine
thiocyanate, nickel as nickel dimethylglyoximate, copper as
cuprous thiocyanate, and zinc as zinc ammonium phosphate [34].
The FT-IR measurements of neat samples were performed on a MB-
Co(L2)2$2H2O
Ni(L2)(OAc)$3H2O 120.4
Ni(L2)2$2H2O
39.3
Cu(L2)(OAc)$H2O 127.9
Cu(L2)2
327.1
39.32
39.32 314.5
78.6
240.9
314.6
255.9
40.8
59.4
39.0
15.1
120.4
157.3
255.9
163.5
59.4
240.9
157.3
511.9
81.7
118.9
19.5
Zn(L2)(OAc)$3H2O 118.9
Zn(L2)2$2H2O
Ciprofloxacin
156.0
15.1
156.0
15.1
15.1
e Not tested.

K. Singh et al. / European Journal of Medicinal Chemistry 52 (2012) 313e321
319
Ph
Ph
N
N
N
N
H2O
CH
CH
Ph
Ph
COCH3
COCH3
O
N
N
O
R
R
M
Cu
N
N
S
S
H2O
H2O
H2O
N
N
N
N
Ph
1:1
N
N
N
N
H2O
CH
N
R
S
Ph
N
N
N
M
N
R
S
Ph
CH
H2O
N
N
Ph
N
1:2
N
Ph
N
N
N
CH
N
R
S
Ph
N
N
N
Cu
N
R
S
Ph
CH
N
N
N
R = H (HL1), -CH3 (HL2)
M = Co(II), Ni(II), Zn(II)
Ph
Fig. 5. Proposed structures of metal complexes.
3000 ABB Spectrometer in the range 4000e250 cmꢁ1
.
The
SHIMADZU RF-5301PC spectrophotometer. The solutions of 10ꢁ3 M
concentration were prepared in HPLC grade DMF and the experi-
ment was carried out at room temperature.
UVevisible absorption spectra of solid complexes were recorded on
T 90 (PG Instruments ltd) UV/vis spectrometer in the region
1100e200 nm. Proton NMR spectra were recorded in DMSO-d6 on
a Bruker ACF 300 spectrometer at 300 MHZ using “tetramethyl
silane” as the internal standard. Magnetic moments were measured
at Institute Instrumentation Centre, IIT Roorkee on vibrating
sample magnetometer (Model 155). The PerkineElmer (Pyris Dia-
mond) instrument was used to carry out thermal analysis of metal
complexes in atmospheric air (80e700 ꢀC) at a heating rate of
10 ꢀC minꢁ1 using a reference to alumina powder. The Perfit elec-
trical melting point apparatus is used to record melting points of
the synthesized complexes and are uncorrected. The fluorescence
studies of Schiff bases and their metal complexes were recorded on
5.2. Syntheses
4-Amino-5-mercapto-1,2,4-triazole [35], 4-amino-5-mercapto-
3-methyl-1,2,4-triazole [35] and 1,3-diphenyl-1H-pyrazole-4-
carboxaldehyde [36] were prepared by reported literature method.
5.2.1. 4-[(1,3-Diphenyl-1H-pyrazol-4-ylmethylene)-amino]-5-
mercapto-1,2,4-triazole [HL1]
To a hot ethanolic (20 mL) solution of 4-amino-5-mercapto-
1,2,4-triazole (1.08 g, 9.28 mmol), 1,3-diphenyl-1H-pyrazole-4-

320
K. Singh et al. / European Journal of Medicinal Chemistry 52 (2012) 313e321
carboxaldehyde (2.30 g, 9.28 mmol) in ethanol (20 mL) was added
with constant stirring and refluxed for 6 h after cooling the mixture
to room temperature, the precipitated product thus formed was
filtered off, washed with ice cooled ethanol and recrystallized from
same solvent. Finally the product dried under vacuum.
Dull white. Yield (60%); m.p. 258e260 ꢀC; Anal. calcd. for
C18H14N6S: C, 62.41; H, 4.07; N, 24.26; found: C, 62.38; H, 4.07; N,
24.11%.
which resulted in the immediate precipitation of metal complexes.
The solid complexes were filtered off, washed thoroughly with
warm water, with aqueous ethanol to remove unreacted metal
acetates or ligands and finally with acetone and vacuo dried.
Co(L2)OAc$3H2O: Anal. calcd. for C21H24CoN6O5S: C, 47.46; H,
4.55; N,15.21; Co,11.09; found: C, 47.42; H, 4.38; N,15.20; Co,11.00%.
Ni(L2)OAc$3H2O: Anal. calcd. for C21H24N6NiO5S: C, 47.48; H,
4.55; N, 15.82; Ni, 11.05; found: C, 47.43; H, 4.48; N, 15.21; Ni,
10.98%.
5.2.2. 4-[(1,3-Diphenyl-1H-pyrazol-4-ylmethylene)-amino]-5-
mercapto-3-methyl-4H-1,2,4-triazole [HL2]
Cu(L2)OAc$H2O: Anal. calcd. for C21H20CuN6O3S: C, 50.44; H,
4.03; N, 16.81; Cu, 12.71; found: C, 50.40; H, 4.01; N, 16.38; Cu,
12.38%.
A
solution of 4-amino-5-mercapto-3-methyl-1,2,4-triazole
(1.2 g, 9.23 mmol) in ethanol (40 mL) was treated with 1,3-
diphenyl-1H-pyrazole-4-carboxaldehyde (2.28 g, 9.23 mmol). The
reaction mixture was refluxed for 5 h and the solid crude was
filtered off and washed with cold ethanol, dried and recrystallized
from the same solvent.
Zn(L2)OAc$3H2O: Anal. calcd. for C21H24N6O5SZn: C, 46.89; H,
4.50; N,15.62; Zn,12.16; found: C, 46.74; H, 4.50; N,15.61; Zn,12.16%.
5.2.6. Metal complexes of HL2 (1:2)
The aqueous ethanolic solutions of acetates of Co(II) (0.15 g,
0.60 mmol), Ni(II) (0.15 g, 0.60 mmol), Cu(II) (0.12 g, 0.60 mmol)
and Zn(II) (0.13 g, 0.60 mmol) were treated with the hot ethanolic
solutions of the HL2 (0.43 g, 1.20 mmol). The products formed were
filtered and purified by washing thoroughly with warm water, with
aqueous ethanol to remove unreacted metal acetates or ligands and
finally with acetone and dried.
Creamish white. Yield (68%); m.p. 227e230 ꢀC; Anal. calcd. for
C19H16N6S: C, 63.31; H, 4.47; N, 23.32; found: C, 63.24; H, 4.32; N,
23.31%.
5.2.3. Metal complexes of HL1 (1:1)
The solid complexes were prepared by mixing hot ethanolic
solutions of the HL1 (0.35 g, 1.03 mmol) with aqueous ethanolic
solutions of acetates of Co(II) (0.26 g, 1.03 mmol), Ni(II) (0.26 g,
1.03 mmol), Cu(II) (0.21 g,1.03 mmol) and Zn(II) (0.23 g,1.03 mmol),
which resulted in the immediate precipitation of metal complexes.
The solid complexes were filtered off, washed thoroughly with
warm water, with aqueous ethanol to remove unreacted metal
acetates or ligands and finally with acetone and vacuo dried.
Co(L1)OAc$3H2O: Anal. calcd. for C20H22CoN6O5S: C, 46.42; H,
4.29; N, 16.24; Co, 11.39; found: C, 46.42; H, 4.22; N, 16.23; Co,
11.36%.
Co(L2)2$2H2O: Anal. calcd. for C38H34CoN12O2S2: C, 56.08; H,
4.21; N, 20.65; Co, 7.24; found: C, 56.03; H, 4.20; N, 20.63; Co, 7.23%.
Ni(L2)2$2H2O: Anal. calcd. for C38H34N12NiO2S2: C, 56.10; H,
4.21; N, 20.66; Ni, 7.21; found: C, 55.00; H, 3.82; N, 21.40; Ni, 7.22%.
Cu(L2)2: Anal. calcd. for C38H30CuN12S2: C, 58.33; H, 3.86; N,
21.48; Cu, 8.12; found: C, 58.33; H, 3.85; N, 21.46; Cu, 8.12%.
Zn(L2)2$2H2O: Anal. calcd. for C38H34N12O2S2Zn: C, 55.64; H,
4.18; N, 20.49; Zn, 7.97; found: C, 55.63; H, 4.15; N, 20.46; Zn, 7.96%.
Acknowledgements
Ni(L1)OAc$3H2O: Anal. calcd. for C20H22N6NiO5S: C, 46.45; H,
4.29; N, 16.25; Ni, 11.35; found: C, 46.43; H, 4.23; N, 16.21; Ni,
11.31%.
Yogender Kumar is highly thankful to University Grant
Commission, New Delhi for providing Senior Research Fellowship
(SRF) and Department of Chemistry, Kurukshetra University Kur-
ukshetra, for providing facilities to carry out this research work.
Cu(L1)OAc$H2O: Anal. calcd. for C20H18CuN6O3S: C, 49.43; H,
3.73; N, 17.29; Cu, 13.08; found: C, 49.40; H, 3.71; N, 17.28; Cu,
13.00%.
Zn(L1)OAc$3H2O: Anal. calcd. for C20H22N6O5SZn: C, 45.85; H,
4.23; N, 16.04; Zn, 12.48; found: C, 45.82; H, 4.18; N, 16.00; Zn,
12.43%.
Appendix A. Supplementary material
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.ejmech.2012.02.053.
5.2.4. Metal complexes of HL1 (1:2)
The aqueous ethanolic solutions of acetates of Co(II) (0.12 g,
0.50 mmol), Ni(II) (0.13 g, 0.50 mmol), Cu(II) (0.10 g, 0.50 mmol)
and Zn(II) (0.10 g, 0.50 mmol) were treated with the hot ethanolic
solutions of the HL1 (0.35 g, 1.00 mmol). The products formed were
filtered and purified by washing thoroughly with warm water, with
aqueous ethanol to remove unreacted metal acetates or ligands and
finally with acetone and dried.
References
[1] N. J. Thumar, M. P. Patel, Med. Chem. Res. doi 10.1007/s00044-011-9693-2.
[2] J. Peto, Nature 411 (2001) 390e395.
[3] I. Chopra, C. Schofield, M. Everett, A. O’Neill, K. Miller, M. Wilcox, J.M. Fre`re,
M. Dawson, L. Czaplewski, U. Urleb, P. Courvalin, Lancet Infect. Dis. 8 (2008)
133e139.
[4] I. Damljanovic, M. Vukicevic, N. Radulovic, R. Palic, E. Ellmerer, Z. Ratkovic,
M.D. Joksovic, R.D. Vukicevic, Bioorg. Med. Chem. Lett. 19 (2009) 1093e1096.
[5] A.A. Bekhit, H.M.A. Ashour, Y.S.A. Ghany, A.E.A. Bekhit, A.M. Baraka, Eur. J.
Med. Chem. 43 (2008) 456e463.
[6] P.T. Chovatia, J.D. Akabari, P.K. Kachhadia, P.D. Zalawadia, H.S. Joshi, J. Serb.
Chem. Soc. 71 (2007) 713e720.
[7] M.D. Joksovic, V. Markovic, Z.D. Juranic, T. Stanojkovic, L.S. Jovanovic,
I.S. Damljanovic, K.M. Szecsenyi, N. Todorovic, S. Trifunovic, R.D. Vukicevic,
J. Organomet. Chem. 694 (2009) 3935e3942.
[8] A.H. Abadi, A.A.H. Eissa, G.S. Hassan, Chem. Pharm. Bull. 51 (2003) 838e844.
[9] P. Rathelot, N. Azas, H. El-Kashef, F. Delmas, C.D. Giorgio, P. Timon-David,
J. Maldonado, P. Vanelle, Eur. J. Med. Chem. 37 (2002) 671e679.
[10] A.I. Hashem, A.S.A. Youssef, K.A. Kandeel, W.S.I. Abou-Elmagd, Eur. J. Med.
Chem. 42 (2007) 934e939.
Co(L1)2$2H2O: Anal. calcd. for C36H30CoN12O2S2: C, 55.03; H,
3.85; N, 21.39; Co, 7.50; found: C, 55.00; H, 3.84; N, 21.33; Co, 7.45%.
Ni(L1)2$2H2O: Anal. calcd. for C36H30N12NiO2S2: C, 55.04; H,
3.85; N, 21.40; Ni, 7.47; found: C, 55.00; H, 3.82; N, 21.40; Ni, 7.22%.
Cu(L1)2: Anal. calcd. for C36H26CuN12S2: C, 57.32; H, 3.47; N,
22.48; Cu, 8.42; found: C, 57.30; H, 3.41; N, 22.20; Cu, 8.38%.
Zn(L1)2$2H2O: Anal. calcd. for C36H30N12O2S2Zn: C, 54.58; H,
3.82; N, 21.22; Zn, 8.25; found: C, 54.55; H, 3.75; N, 21.18; Zn, 8.20%.
5.2.5. Metal complexes of HL2 (1:1)
[11] S.C. Shetty, V.C. Bhagat, Asian J. Chem. 20 (2008) 5037e5045.
[12] X. Collin, A. Sauleau, J. Coulon, Bioorg. Med. Chem. Lett. 13 (2003) 2601e2605.
[13] B. Kalluraya, B. Lingappa, N.S. Rai, Phosphorus, Sulfur Silicon Relat. Elem. 182
(2007) 1393e1401.
The solid complexes were prepared by mixing hot ethanolic
solutions of the HL2 (0.36 g, 1.01 mmol) with aqueous ethanolic
solutions of acetates of Co(II) (0.25 g, 1.01 mmol), Ni(II) (0.25 g,
1.01 mmol), Cu(II) (0.20 g,1.01 mmol) and Zn(II) (0.22 g,1.01 mmol),
[14] O. Bekircan, H. Bektas, Molecules 11 (2006) 469e477.

K. Singh et al. / European Journal of Medicinal Chemistry 52 (2012) 313e321
321
[15] S.A. Patil, S.N. Unki, A.D. Kulkarni, V.H. Naik, P.S. Badami, Spectrochim. Acta
Part A 79 (2011) 1128e1136.
[25] F.A. Cotton, G. Williknson, C.A. Murillo, M. Bochman, Advanced Inorganic
Chemistry, sixth ed. Wiley, New York, 2003.
[16] H.A. El-Boraeya, R.M. Abdel-Rahmanb, E.M. Atia, K.H. Hilmy, Cent. Eur. J.
Chem. 8 (2010) 820e833.
[17] Z.H. Chohan, S.H. Sumrra, M.H. Youssoufi, T.B. Hadda, Eur. J. Med. Chem. 45
(2010) 2739e2747.
[26] A.B.P. Lever, Inorganic Spectroscopy, Elsvier, Amsterdam, 1968.
[27] K.A. Mehla, J. Enz. Inhib. Med. Chem. 23 (2008) 285e295.
[28] A.H. Osman, M.S. Saleh, M.M. Sanaa, Synth. React. Inorg. Met.-Org. Chem. 34
(2004) 1069e1085.
[18] K. Singh, M.S. Barwa, P. Tyagi, Eur. J. Med. Chem. 41 (2006) 147e153.
[19] K. Singh, Y. Kumar, P. Puri, C. Sharma, K.R. Aneja, Med. Chem. Res. (2011).
doi:10.1007/s00044-011-9683-4.
[20] K.R. Aneja, C. Sharma, R. Joshi, Inter. J. Otorhinolaryngol. 74 (2010) 604e607.
[21] M.I. Okeke, C.U. Iroegbu, E.N. Eze, A.S. Okoli, C.O. Esimone, J. Ethnopharmacol.
78 (2001) 119e127.
[29] Q.H.Wang, W.Weng, J.M. Liu,L.Z. Cai, G.C.Guo, J.Coord.Chem. 59(2006)485e492.
[30] A.W. Coats, J.P. Redfern, Nature 201 (1964) 68e69.
[31] V.P. Singh, A. Katiyar, S. Singh, Biometals 21 (2008) 491e501.
[32] N. Raman, A. Kulandaisamy, K. Jayasubramanian, Polish J. Chem. 76 (2002)
1085e1094.
[33] B.G. Tweedy, Phytopathology 55 (1964) 910.
[22] K. Singh, D.P. Singh, M.S. Barwa, P. Tyagi, Y. Mirza, J. Enz. Inhib. Med. Chem. 21
(2006) 557e562.
[34] A.I. Vogel, Text Book of Quantitative Chemical Analysis Longmans, Addison
Wesley, London, 1999.
[23] K. Singh, D.P. Singh, M.S. Barwa, P. Tyagi, Y. Mirza, J. Enz. Inhib. Med. Chem. 21
(2006) 749e755.
[35] S. Bala, R.P. Gupta, M.L. Sachdeva, A. Singh, H.K. Pujari, Indian J. Chem. Sect. B.
16 (1978) 481e483.
[24] A.D. Kulkarni, S.A. Patil, V.H. Naik, P.S Badami, Med. Chem. Res. 20 (2011)
346e354.
[36] A.Q. Ather, M.N. Tahir, M.A. Khan, K. Mehmood, F. Chaudhary, Acta Cryst. E66
(2010) 3170.