Design, spectral characterization and biological studies of transition metal(II) complexes with triazole Schiff bases

Article abstract of DOI:10.1016/j.saa.2012.11.077

A new series of three biologically active triazole derived Schiff base ligands L¹-L³ have been synthesized in equimolar reaction of 3-amino-1H-1,2,4-triazole with pyrrol-2-carboxaldehyde, 4-bromo-thiophene-2- carboxaldehyde, and 5-iodo-2-hydroxy benzaldehyde. The prepared Schiff bases were used for further complex formation reaction with different metal elements like Co(II), Ni(II), Cu(II) and Zn(II) as chlorides by using a molar ratio of ligand:metal as 2:1. The structure and bonding nature of all the compounds were identified by their physical, spectral and analytical data. All the metal(II) complexes possessed an octahedral geometry except the Cu(II) complexes which showed a distorted octahedral geometry. All the synthesized compounds, were studied for their in vitro antibacterial, and antifungal activities, against four Gram-negative (Escherichia coli, Shigella sonnei, Pseudomonas aeruginosa and Salmonella typhi) and two Gram-positive (Bacillus subtilis and Staphylococcus aureus) bacterial strains and against six fungal strains (Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani and Candida glabrata) by using agar-well diffusion method. It has been shown that all the synthesized compounds showed moderate to significant antibacterial activity against one or more bacterial strains. In vitro Brine Shrimp bioassay was also carried out to investigate the cytotoxic properties of these compounds. The data also revealed that the metal complexes showed better activity than the ligands due to chelation/coordination.

Full text of DOI:10.1016/j.saa.2012.11.077

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 468–476
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Design, spectral characterization and biological studies of transition metal(II)
complexes with triazole Schiff bases
⇑
Muhammad Hanif, Zahid H. Chohan
Department of Chemistry, Bahauddin Zakariya University, Multan 60800, Pakistan
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
"
"
"
"
Novel series of triazole derived Schiff
bases and their transition metal
complexes are studied.
Characterization is made on the
basis of their physical, spectral and
analytical data.
Antibacterial and antifungal
correlation with the metal ions is
established.
In vitro antibacterial and antifungal
activity is enhanced upon
coordination.
a r t i c l e i n f o
a b s t r a c t
A new series of three biologically active triazole derived Schiff base ligands L1–L3 have been synthesized
in equimolar reaction of 3-amino-1H-1,2,4-triazole with pyrrol-2-carboxaldehyde, 4-bromo-thiophene-
2-carboxaldehyde, and 5-iodo-2-hydroxy benzaldehyde. The prepared Schiff bases were used for further
complex formation reaction with different metal elements like Co(II), Ni(II), Cu(II) and Zn(II) as chlorides
by using a molar ratio of ligand:metal as 2:1. The structure and bonding nature of all the compounds
were identified by their physical, spectral and analytical data. All the metal(II) complexes possessed an
octahedral geometry except the Cu(II) complexes which showed a distorted octahedral geometry. All
the synthesized compounds, were studied for their in vitro antibacterial, and antifungal activities, against
four Gram-negative (Escherichia coli, Shigella sonnei, Pseudomonas aeruginosa and Salmonella typhi) and
two Gram-positive (Bacillus subtilis and Staphylococcus aureus) bacterial strains and against six fungal
strains (Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani
and Candida glabrata) by using agar-well diffusion method. It has been shown that all the synthesized
compounds showed moderate to significant antibacterial activity against one or more bacterial strains.
In vitro Brine Shrimp bioassay was also carried out to investigate the cytotoxic properties of these com-
pounds. The data also revealed that the metal complexes showed better activity than the ligands due to
chelation/coordination.
Article history:
Received 20 September 2012
Received in revised form 8 November 2012
Accepted 23 November 2012
Available online 4 December 2012
Keywords:
Triazole Schiff bases
Metal(II) complexes
Antibacterial
Antifungal activities
Ó 2012 Elsevier B.V. All rights reserved.
Introduction
commonly incorporated into compounds of pharmaceutical inter-
est [1]. Triazole compounds such as fluconazole is a broad spec-
Triazoles and their derivatives occupy a central position in
modern heterocyclic chemistry due to their biologically active
nature. These compounds constitute heterocyclic groups that are
trum antifungal [2], trazodone is used as an antidepressant [3]
vorozole, anastrozole and letrozole are potentially used to inhibit
breast cancer [4]. It is evident that the azomethine linkage (C@N)
is an essential structural requirement for biological activity [5].
Several azomethine group containing compounds have been re-
ported to possess remarkable antibacterial [6], antifungal [7] and
⇑
Corresponding author. Tel.: +92 3006802791.
E-mail address: dr.zahidchohan@gmail.com (Z.H. Chohan).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.11.077

M. Hanif, Z.H. Chohan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 468–476
469
were recorded in DMSO-d6 using TMS as internal standard on a
Bruker Spectrospin Avance DPX-500 spectrometer. Electron impact
mass spectra (EIMS) were recorded on JEOL MS Route Instrument.
In vitro antibacterial, antifungal and cytotoxic properties were
studied at HEJ Research Institute of Chemistry, International Centre
for Chemical Sciences, University of Karachi, Pakistan and Depart-
ment of Chemistry, The Islamia University, of Bahawalpur,
Pakistan.
General procedure for synthesis of triazole Schiff bases ligands L1–L3
N-[(E)-1H-pyrrol-2-ylmethylidene]-1H-1,2,4-triazol-3-amine L1
Pyrrole-2-carboxaldehyde (0.95 g, 10 mmol) in methanol solu-
tion (20 ml) was added to magnetically stirred methanol solution
(20 ml) of 3-amino 1,2,4 triazole (0.84 g, 10 mmol) and mixture
was refluxed for 5 h through monitoring by TLC. After comple-
tion of the reaction, the resultant mixture was cooled to room
temperature, filtered and reduced nearly half of its volume by
rotary evaporator. It was then allowed to stay at room tempera-
ture for 3 h which resulted in the formation of a light-brown
solid product. It was filtered, washed with methanol and recrys-
tallized with a mixture of ethanol:methanol (1:1). The same pro-
cedure was used for the synthesis of ligands L2 and L3. However
the ligand L3 was precipitated during refluxing, filtered and
washed with hot methanol and recrystallized with a mixture
of ethanol:methanol (1:1). The purity of product was checked
by TLC.
Scheme 1. Preparation of the ligands L1–L3 and their metal complexes 1–12.
anticancer activities [8]. In view of above mention, biological
behavior of triazole and azomethine linkage (C@N) many triazole
based Schiff bases have also been reported to possess antibacterial
[9], antifungal [10], antitumor [11], plant growth regulating [12]
and cytotoxic [13] activities. It is also known that N and S atoms
play a key role in the coordination of metals at the active sites of
numerous biomolecules. Metallo-organic chemistry is becoming
an emerging area of research due to the demand for new metal-
based antibacterial and antifungal compounds [13–15]. Various
investigations have proved that binding of a drug to a metalloele-
ment enhances its activity and in some cases, the complex pos-
sesses even more healing properties than the parent drug [16]. In
the present studies metalloelement such as copper, cobalt, nickel
and zinc have been focused due to their smaller size and compar-
atively higher nuclear charge and thus have a great affinity to form
coordination compounds. A bulk of literature [17–20] reveals that
upon coordination with these metalloelements biologically inac-
tive compounds become active and less biologically active com-
pounds become more active.
In view of the significant structural and biological applications
of triazole compounds, we wish to report the synthesis of a new
class of triazole Schiff base derivatives L1–L3, from the condensa-
tion reaction of 3-amino-1,2,4-triazole with 1H-pyrrole-2-carbox-
aldehyde, 4-bromo-thiophene-2-carboxaldehyde and 5-iodo-2-
hydroxybenzaldehydes respectively, and their cobalt(II), nickel(II),
copper(II) and zinc(II) metal complexes 1–12 (Scheme 1). These
compounds have been investigated for in vitro antibacterial activ-
ity against four Gram-negative (Escherichia coli, Shigella sonnei,
Pseudomonas aeruginosa, Salmonella typhi) and two Gram-positive
(Staphylococcus aureus, Bacillus subtilis) bacterial strains, and anti-
fungal activity against six fungal strains (Trichophyton longifusus,
Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium
solani and Candida glabrata). In vitro Brine Shrimp bioassay has also
been carried out to study the cytotoxic properties of these
compounds.
N-[(E)-1H-pyrrol-2-ylmethylidene]-1H-1,2,4-triazol-3-amine L1
Yield: 76% (1.22 g). Color (light-brown). M.p. 190–192 °C. IR
(KBr, cmÀ1): 3185 (NH), 3120 (NH, pyrrole), 1631 (HC@N), 1610
(C@N, triazole), 1570, 1540 (C@C), 1025 (NAN). 1H NMR (DMSO-
d6, d, ppm): 6.24 (dd, 1H, J = 4.6, 4.0 Hz, pyrrole C4AH), 6.86 (d,
1H, J = 4.0 Hz, pyrrole C3AH), 7.11 (d, 1H, J = 4.6 Hz, pyrrole
C5AH), 8.30 (s, 1H, triazole CAH), 8.89 (s, 1H, azomethine CAH),
11.92 (s, 1H, pyrrole NH), 13.69 (s, 1H, triazole NH). 13C NMR
(DMSO-d6, d, ppm): 114.5 (C4), 116.6 (C3), 120.7 (C5), 131.5 (C2),
153.7 (C triazole), 155.8 (C triazole), 159.9 (C azomethine). Anal.
Calcd. for C7H7N5 (161.16): C: 52.17; H: 4.38; N: 43.45; Found:
C: 52.39; H: 4.46; N: 43.72%. Mass spectrum (ESI) [M]+ = 161.16.
N-[(E)-(4-bromothiophen-2-yl)methylidene]-1H-1,2,4-triazol-3-
amine L2
Yield: 75% (1.93 g). Color (off-white). M.p. 215–217 °C. IR (KBr,
cmÀ1): 3184 (NH), 1630 (HC@N), 1608 (C@N, triazole), 1570,
1545 (C@C), 1025 (NAN), 965 (CAS), 670 (CABr). 1H NMR
(DMSO-d6, d, ppm): 7.85 (s, 1H, thienyl C3AH), 8.0 (s, 1H, thienyl
C5AH), 8.55 (s, 1H, triazole CAH), 9.30 (s, 1H, azomethine CAH),
14.00 (s, 1H, triazole NH). 13C NMR (DMSO-d6, d, ppm): 116.7
(C4), 123.9 (C5), 125.2 (C3), 144.6 (C2), 153.4 (C triazole), 156.2 (C
triazole), 159.5 (C azomethine). Anal. Calcd. for C7H5N4SBr
(257.11): C: 32.70; H: 1.96; N: 21.79; S: 12.47; Br: 31.08; Found:
C: 33.06; H: 1.89; N: 22.10; S: 12.34; Br: 30.94%. Mass spectrum
(ESI) [M]+ = 257.0.
4-Iodo-2-[(E)-(1H-1,2,4-triazol-3-ylimino)methyl]phenol L3
Experimental
Yield: 76% (2.40 g). Color (light-yellow). M.p. 255–257 °C. IR
(KBr, cmÀ1): 3270 (OH), 3182 (NH), 1630 (HC@N), 1610 (C@N, tri-
azole), 1030 (NAN). 1H NMR (DMSO-d6, d, ppm): 6.86 (d, 1H,
J = 8.3 Hz, phenyl C6AH), 7.7 (dd, 1H, J = 8.3, 2.5 Hz, phenyl
C5AH), 8.19 (d, 1H, J = 2.5 Hz, phenyl C3AH), 8.48 (s, 1H, triazole
CAH), 9.4 (s, 1H, azomethine CAH), 12.3 (s, 1H, OH), 14.1 (s, 1H, tri-
azole NH). 13C NMR (DMSO-d6, d, ppm): 114.7 (C4), 119.9 (C6),
122.5 (C2), 138.5 (C3), 141.1 (C5), 153.4 (C triazole), 156.6 (C tria-
zole), 161.4 (C azomethine), 163.1 (C1). Anal. Calcd. for C9H7IN4O
Materials and methods
All chemicals used were of analar grade. All metal salts were
used as chloride. Melting points were recorded on Fisher Johns
melting point apparatus. Infrared spectra were recorded on SHI-
MADZU FT-IR spectrometer. The C, H and N analyses was carried
out using a Perkin Elmer, USA model. The 1H and 13C NMR spectra

470
M. Hanif, Z.H. Chohan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 468–476
Table 1
Physical measurements and analytical data of the metal(II) complexes.
No.
Molecular mass/molecular formula
M.P (dec.) yield
(°C)
Found (calc.) %
(%)
61
C
H
N
M
1
[Co(L1–H)2] [379.2]
239–241
43.99
3.19
37.25
(36.93)
36.60
(36.96)
36.49
(36.49)
36.54
15.49
(15.54)
15.45
(15.49)
16.62
(16.55)
16.95
(16.95)
9.19
C
14H12N10Co
[Ni(L1–H)2] [379.0]
14H12N10Ni
[Cu(L1–H)2] [383.8]
14H12N10Cu
[Zn(L1–H)2] [385.7]
14H12N10Zn
[Co(L2)2]Cl2 [644.06]
(44.34)
44.09
(44.37)
43.43
(43.81)
43.90
(43.59)
25.84
(26.11)
26.37
(17.19)
26.18
(25.92)
26.05
(25.85)
31.34
(31.56)
31.60
(31.57)
31.35
(31.35)
31.43
(31.36)
(3.19)
3.06
(3.19)
3.15
(3.15)
3.02
(3.14)
1.39
(1.56)
1.74
(1.57)
1.43
(1.55)
1.61
(1.55)
1.65
(1.77)
1.69
(1.77)
1.69
(1.75)
1.84
(1.75)
2
248–250
245–247
253–255
245–247
251–253
258–260
266–268
279–281
274–276
284–286
293–295
63
60
59
60
59
58
59
64
62
65
63
C
3
C
4
C
(36.31)
17.19
5
C
14H10N8S2Br2Cl2Co
(17.40)
17.57
(9.15)
9.07
6
[Ni(L2)2]Cl2 [643.81]
C14H10N8S2Br2Cl2Ni
[Cu(L2)2]Cl2 [648.67]
(17.40)
17.41
(9.12)
9.84
7
C
14H10N8S2Br2Cl2Cu
(17.27)
17.08
(17.22)
16.45
(9.80)
10.08
(10.05)
8.57
8
[Zn(L2)2]Cl2 [650.52]
C
14H10N8S2Br2Cl2Zn
9
[Co(L3–H)2] [685.08]
C18H12N8O2I2Co
(16.36)
16.48
(16.36)
16.29
(16.25)
16.14
(8.60)
8.58
(8.60)
9.17
(9.21)
9.18
10
11
12
[Ni(L3–H)2] [684.84]
C
18H12N8O2I2Ni
[Cu(L3–H)2] [689.69]
18H12N8O2I2Cu
[Zn(L3–H)2] [691.55]
18H12N8O2I2Zn
C
C
(16.20)
(9.21)
(314.08): C: 34.42; H: 2.25; N: 17.84; I: 40.40; Found: C: 34.24; H:
2.18; N: 18.04; I: 40.27%. Mass spectrum (ESI) [M]+ = 314.0.
C5AH), 8.33 (d, 2H, J = 2.5 Hz, phenyl C3AH), 8.81 (s, 2H, triazole
CAH), 9.81 (s, 2H, CAH azomethine), 14.13 (s, 2H, triazole NH);
13C NMR of Zn(II) complex (DMSO-d6, d, ppm): 115.1 (C4), 120.32
(C6), 122.78 (C2), 138.86 (C3), 141.4 (C5), 154.72 (C triazole),
158.30 (Ctriazole), 162.59 (C azomethine), 164.25 (C1).
General procedure for the synthesis of complexes 1–12
Preparation of cobalt (II) complex with N-[(E)-1H-pyrrol-2-
ylmethylidene]-1H-1,2,4-triazol-3-amine L1 (1).
Biological activity
A hot ethanol solution (20 mL) of Co(II) Cl2.6H2O (0.952 g,
4 mmol) was added drop wise to a magnetically stirred solution
of N-[(E)-1H-pyrrol-2-ylmethylidene]-1H-1,2,4-triazol-3-amine L1
(1.29 g, 8 mmol) in ethanol (25 mL). The resultant mixture was re-
fluxed for 2 h. During refluxing, a solid product precipitated out
which was filtered, washed with ethanol and then with diethyl
ether and dried. Recrystallization from hot aqueous ethanol (1:2)
gave TLC pure product. The same method was used for the prepa-
ration of other complexes (Scheme 1). Physical, analytical and
spectral data is given in Tables 1 and 2.
Antibacterial studies
The entire newly synthesized Schiff base L1–L3 and their respec-
tive metal(II) complexes 1–12 were tested against four Gram-neg-
ative (E. coli, S. sonnei, P. aeruginosa, S. typhi) and two Gram-
positive (S. aureus, B. subtilis) bacterial strains by the disk diffusion
method [21]. The test compounds (ligand/complex) were dissolved
in DMSO to get 10 mg/mL solution. A known volume (10 lL) of the
solution was applied with the help of a micropipette onto the ster-
ilized filter paper disks. The disks were dried at room temperature
overnight and stored in sterilized dry containers. Disks soaked with
NMR data of Zn (II) complexes
10 lL of DMSO and dried in air at room temperature were used as
[Zn (L1-H)2] (4)
the negative control. The standard antibiotic disks used as positive
control were prepared as mention above in the laboratory by
applying a known concentration of the standard antibiotic solu-
tion. Ampicillin was used as standard antibiotic. Bacterial culture
was grown in nutrient broth medium at 37 °C overnight and
spread onto solidified nutrient agar medium in Petri plates using
sterilized cotton swabs. Test and control disks were then applied
to the medium surface with the help of sterilized forceps. The
plates were incubated at 37 °C for 24–48 h. The results were re-
corded by measuring the zone of inhibition in mm against each
compound. The experiments were carried out in triplicate and
the values obtained were statistically analyzed.
1H NMR of Zn (II) complex (DMSO-d6, d, ppm): 6.36 (dd, 2H,
J = 4.6, 4.0 Hz, pyrrole C4AH), 6.97 (d, 2H, J = 4.0 Hz, pyrrole,
C3AH), 7.46 (d, 2H, J = 4.6 Hz, pyrrole, C5AH), 8.67 (s, 2H, triazole,
CAH), 9.34 (s, 2H, CAH azomethine), 13.81 (s, 2H, triazole NH). 13
NMR of Zn(II) complex (DMSO-d6, d, ppm): 114.9 (C4), 116.95 (C3),
121.96 (C5), 132.70 (C2), 154.86 (C triazole), 157.37 (C triazole),
161.6 (C azomethine).
C
[Zn (L2)2] (8)
1H NMR of Zn (II) complex (DMSO-d6, d, ppm): 7.97 (d, 2H,
J = 3.5 Hz, furanyl C3AH), 8.35 (d, 2H, J = 3.5 Hz, furanyl C5AH),
8.89 (s, 2H, triazole CAH), 9.69 (s, 2H, CAH azomethine), 14.10
(s, 2H, triazole NH). 13C NMR of Zn(II) complex (DMSO-d6, d,
ppm): 116.89 (C4), 125.27 (C5), 125.44 (C3), 145.7 (C2), 154.73
(Ctriazole), 157.94 (C triazole), 161.2 (C azomethine).
Antifungal activity (in vitro)
Antifungal activities of all compounds were studied against six
fungal strains (T. longifusus, C. albicans, A. flavus, M. canis, F. solani
and C. glabrata) according to literature protocol [18]. Sabouraud
dextrose agar (Oxoid, Hampshire, England) was seeded with
105 (cfu) mLÀ1 fungal spore suspensions and transferred to petri
[Zn (L3-H)2] (12)
1H NMR of Zn (II) complex (DMSO-d6, d, ppm): 7.02 (d, 2H,
J = 8.3 Hz, phenyl C6AH), 7.86 (dd, 2H, J = 8.3, 2.5 Hz, phenyl

M. Hanif, Z.H. Chohan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 468–476
471
Table 2
Conductivity, magnetic and spectral data of metal(II) complexes.
No.
X
XM
B.M (leff
)
kmax (cmÀ1
)
IR (cmÀ1
)
À1 cm2 molÀ1
1
14.4
18.7
15.8
17.5
87.6
88.4
85.0
89.5
11.5
13.7
18.2
11.6
4.34
3.47
1.57
Dia
8892, 17,759, 30,150
10,085, 16,105, 29,635
14,876, 25,800
3185 (NH), 1618 (HC@N), 1594 (C@N), 1025 (NAN),
540 (MAN), 520 (MAN)
3185 (NH), 1617 (HC@N), 1597 (C@N), 1025 (NAN),
545 (MAN), 525 (MAN)
3185 (NH), 1616 (HC@N), 1596 (C@N), 1025 (NAN),
540 (MAN), 523 (MAN),
3185 (NH), 1616 (HC@N), 1598 (C@N), 1025 (NAN),
535 (MAN), 520 (MAN)
3184 (NH), 1615 (HC@N), 1591 (C@N), 1025 (NAN),
945 (CAS), 670 (CABr), 520 (MAN), 462 (MAS)
3184 (NH), 1614 (HC@N), 1594 (C@N), 1025 (NAN),
948 (CAS), 670 (CABr), 525 (MAN), 465 (MAS)
3184 (NH), 1617 (HC@N), 1592 (C@N), 1025 (NAN),
945 (CAS), 670 (CABr), 521 (MAN), 460 (MAS)
3184 (NH), 1616 (HC@N), 1596 (C@N), 1025 (NAN),
950 (CAS), 670 (CABr), 529 (MAN), 466 (MAS)
3182 (NH), 1618 (HC@N), 1595 (C@N), 1380 (CAO),
1030 (NAN), 532 (MAN), 462 (MAO)
2
3
4
28,778
5
4.62
3.41
1.51
Dia
8786, 17,334, 29,889
10,180, 16,775, 29,440
14,975, 25,267
6
7
8
28,763
9
4.44
3.27
1.67
Dia
8823, 17,677, 29,726
10,156, 16,075, 29,210
14,822, 25,717
10
11
12
3182 (NH), 1618 (HC@N), 1595 (C@N), 1380 (CAO),
1030 (NAN), 526 (MAN), 452 (MAO)
3182 (NH), 1615 (HC@N), 1598 (C@N), 1384 (CAO),
1030 (NAN), 528 (MAN), 459 (MAO)
3182 (NH), 1616 (HC@N), 1596 (C@N), 1390 (CAO),
1030 (NAN), 524 (MAN), 456 (MAO)
28,749
plates. Disks soaked in 20 ml (200 lg/mL in DMSO) of test com-
Results and discussion
pounds were placed at different positions on the agar surface.
The plates were incubated at 32 °C for 7 days. The results were re-
corded as % of inhibition and compared with standard drugs mico-
nazole and amphotericin B [22].
Chemistry
The Schiff base ligands L1–L3 were prepared by the condensa-
tion reaction of 3-amino1H-1,2,4-triazole with a 1H-pyrrole-2-car-
boxaldehyde, 4-bromo-thiophene-2-carboxaldehyde and 5-iodo-
2-hydroxybenzaldehydes, respectively, under reflux as shown in
Scheme 1. All the synthesized derivatives of triazole were soluble
in ethanol, dioxane, DMF and DMSO at room temperature and in
methanol on heating only. The composition of ligands was consis-
tent with their micro-analytical and mass spectral data. The metal
complexes 1–12 of these ligands were prepared by the reaction of
corresponding ligands with metal (Co(II), Ni(II), Cu(II) and Zn(II)) as
chlorides in a (1:2) (metal:ligand) molar ratio. All the metal com-
plexes were air and moisture stable at room temperature. They
were insoluble in common organic solvents and only soluble in
DMF and DMSO. Physical measurements and analytical data of
the complexes 1–12 are given in Tables 1 and 2.
Minimum inhibitory concentration (MIC)
Compounds containing significant antibacterial activity (over
80%) were selected for minimum inhibitory concentration (MIC)
studies. The minimum inhibitory concentration was determined
using the disk diffusion technique by preparing disks containing
10, 25, 50 and 100
the protocol.
lg/mL of the test compounds and applying
In vitro Cytotoxicity
In vitro cytotoxic activity of all synthesized ligands L1–L3 and
their metal(II) complexes 1–12 were studied using the protocol
of Meyer et al. Brine shrimp (Artemia salina leach) eggs were
hatched in a shallow rectangular plastic dish (22 Â 32 cm), filled
with artificial seawater, which was prepared with commercial salt
mixture and double distilled water [20]. An unequal partition was
made in the plastic dish with the help of a perforated device.
Approximately 50 mg of eggs were sprinkled into the large com-
partment, in dark while the matter compartment was opened to
ordinary light. After 2 days nauplii were collected by a pipette from
the side in ordinary light. A sample of the test compound was pre-
pared by dissolving 20 mg of each compound in 2 mL of DMSO.
IR spectra
The characteristic bands of IR spectra of ligands L1–L3 and their
metal(II) complexes are reported in experimental section and in
Table 2. All the ligands possessed potential donor sites like azome-
thine linkage (AC@N), triazole ring nitrogen (AC@N), hydroxyl
(AOH), thienyl (ACAS) and pyrrole (NAH) groups which have ten-
dency to coordinate with the metal ions. The IR spectra of all the
ligands showed [21–23] the peaks at 3182–3185, 1608–1610 and
1025–1030 cmÀ1 respectively due to vibration of (NAH), (C@N)
and (NAN) of triazole moiety. Originally, 3-amino-1,2,4-triazole
and aldehydes showed peaks at 3325 and 1715 cmÀ1 respectively,
due to aldehydic (CHO) and amino (NH2) group vibrations. In the
spectra of the ligands L1–L3, the peaks at 1715 and 3325 cmÀ1
due to aldehydic (CHO) and amino (NH2) groups of the original
moieties are completely disappeared and in turn, a new sharp band
appeared at 1630–1631 cmÀ1 assigned to the azomethine (AC@N)
linkage [23]. The spectrum of ligand L1 showed peak at 3120 cmÀ1
assigned [22] the (NH) group of pyrrole ring. Similarly, the ligand
From this stock solutions 500, 50 and 5 lg/mL were transferred
to 9 vials (three for each dilutions were used for each test sample
and Ld60 is the mean of three values) and one vial was kept as con-
trol having 2 mL of DMSO only for determine its any participating
role. The solvent was allowed to evaporate overnight. After 2 days,
when shrimp larvae were ready, sea water (1 mL) and 10 shrimps
were added to each vial (30 shrimps/dilution) and the volume was
adjusted with sea water to 5 mL per vial. After 24 h the number of
survivors was counted. Data were analyzed by Finney computer
program to determine the LD50 values [23].

472
M. Hanif, Z.H. Chohan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 468–476
L2 showed bands at 965 and 670 cmÀ1 assigned [23] the thienyl
(CAS) and (CABr) groups. Moreover, the ligand L3 showed broad
spectral band at 3270 cmÀ1 due to vibrations of intramolecular
hydrogen bonded [22] hydroxyl (AOH) group with azomethine
(AC@N) group. The comparison of the IR spectra of Schiff base li-
gands with corresponding metal complexes gave clue the different
modes of absorption in complexation of ligands with the metal
ions. All the Schiff base ligands showing IR spectral bands at
1630–1631 cmÀ1 due to azomethine-N shifted to lower frequency
(13–17 cmÀ1) at 1614–1618 cmÀ1 representing the involvement of
the azomethine-N in the complex formation. Similarly, the triazole
ring (C@N) band originally appearing at 1608–1610 cmÀ1 in the
spectra of the ligands shifted to lower frequency at 1591–
1598 cmÀ1 in spectra of metal complexes by 12–19 cmÀ1 indicative
[25] of the coordination of triazole ring nitrogen in the complexes.
The overall conclusions drawn from the comparison of the spectra
of the metal(II) complexes with the ligands are as below
12.3 ppm. The strong experienced down field shifting of hydroxyl
proton indicated [29] its participation in intramolecular hydrogen
bonding with the azomethine group. The ligand L3 displayed C3AH
and C6AH protons of phenyl group as doublet at 8.19 and 6.86 ppm
respectively and the same ligands showed C5AH proton of phenyl
as double of the doublet at 7.7 ppm. A broad singlet was displayed
[26] at 13.69–14.1 ppm due to the NH proton of triazole in all the
ligands observing tautomerism. The coordination of the azome-
thine (CH@N) and (C@N) of triazole nitrogen are assigned [27] by
the downfield shifting of azomethine (ACH@N) and triazole
(CAH) protons signals present at 8.89–9.40 and 8.30–8.55 ppm in
the free ligands to 9.34–9.81 and 8.67–8.81 ppm in the spectra of
their zinc(II) complexes, respectively. Furthermore, signal of pyr-
role (NH), and hydroxyl (OH) protons appearing at 11.92 and
12.30 ppm in the spectra of ligands, L1 and L3 respectively, disap-
peared in spectra of their corresponding zinc complexes indicating
deprotonation and coordination of the nitrogen and oxygen with
the zinc metal atom. The coordination of thienyl-S was justified
by the downfield shifting of C5AH proton of ligand L2 downfield
from 8.0 to 8.35 ppm in their Zn(II) complexes due to deshielding
effect. All other protons overall underwent downfield shift by
0.11–0.25 ppm due to the increased conjugation [29] in the spectra
of the Zn(II) complexes.
1. In all the metal(II) complexes, a new band appeared [26] at
520–532 cmÀ1 due to
m(M–N) vibrations indicating the coordi-
nation of nitrogen of triazole ring with the metal ions. However,
the band appearing at 1025–1030 cmÀ1 in triazole ring assigned
to m(N–N) mode remained unchanged in the spectra of all the
metal(II) complexes thus indicating the non-involvement of
nitrogen of (N-N) of triazole ring.
13C NMR spectra
2. The IR spectra of ligand, L1 showed a band at 3120 cmÀ1 due to
NH vibrations, this band disappeared in spectra of their meta-
l(II) complexes, 1–4 due to the deprotonation of the NH moiety
during coordination. The appearance of a weak band at 535–
The 13C NMR spectra of the Schiff base ligands L1–L3 and their
Zn(II) complexes were taken in DMSO-d6. The 13C NMR spectral
information are reported along with their possible assignments
in the experimental section and all the carbons were found in
the expected region [25–28]. The 13C NMR spectra of all the Schiff
base ligands L1–L3 displayed [26] the azomethine carbon (ACH@N)
at 159.5–161.4. The spectra of ligands L1 and L2 displayed [25] pyr-
role and thienyl carbons in the region at 114.5–131.5 and 116.7–
144.6 ppm respectively. All carbons of phenyl group in ligand L3
appeared [26] at 114.7–163.1 ppm. The carbon C1 in this ligand
L3 was observed downfield at 163.1 ppm due to attachment of hy-
droxyl (OH) group at the same position. However the carbon (C4) of
ligand L3 was observed upfield at 114.7 ppm due to attachment of
lesser electronegative iodo group. All the Schiff base ligands L1–L3
displayed [27] the triazole carbon at 153.4–156.6 ppm. The conclu-
sion obtained from these studies provided further support to the
mode of bonding explained in the IR and 1H NMR spectral data.
The spectra of Zn(II) complexes of all Schiff base ligands exhibited
[28] downfield shifting of azomethine carbon (ACH@NA) and tria-
zole carbon (C@N) from 159.5 to 161.4 and 153.4 to 156.6 ppm in
the spectra of ligands to 161.2–162.59 and 154.72–158.30 ppm in
the spectra of their zinc(II) complexes respectively, indicating the
coordination of azomethine and triazole nitrogen to the zinc metal
ion. Similarly, the phenyl carbon (C1) of ligand L3 existing near the
coordination sites (C1AOAM) showed [28] downfield shift from
163.1 ppm in the spectra of free ligands to 164.25 ppm in the
spectra of the zinc(II) complexes. In the same way, the spectra of
Zn(II) complexes of ligands L1 and L2 exhibited downfield shifting
by 0.8–1.7 ppm in all the carbons which were attached with hetero
atom like sulpher and nitrogen of thienyl and pyrrole respectively.
All other carbons of the ligands in the spectra of the Zn(II)
complexes underwent downfield shifting by 0.24–0.8 ppm due to
the increased conjugation [29] and coordination with the metal
atoms.
545 cmÀ1 due to
dence of the metal–nitrogen (M–N) linkage.
3. The disappearance [25] of broad band of
(OH) at 3270 cmÀ1 in
m(M–N) vibrations, further supported the evi-
m
spectra of metal complexes 9–12 and in turn appearance of new
band assigned to (CAO) at 1380–1390 cmÀ1 revealed deproto-
nation and coordination of hydroxyl-O to the metal atom. The
coordination of metal to oxygen is further justified by the
appearance of a new band at 452–462 cmÀ1 due to MAO.
4. The bands appearing at 965 cmÀ1 in the spectra of the ligands,
L2 due to (CAS) vibration is shifted to lower frequency at
945–950 cmÀ1 by 15–20 cmÀ1 in the spectra of the metal(II)
complexes, 5–8 indicating participation and coordination of thi-
enyl-S ring in the complexation phenomenon. This coordination
is further justified by the appearance [25] of new band at 460–
466 cmÀ1 due to M–S.
5. All other bands remain unchanged in the spectra of all ligands
and their corresponding metal complexes.
6. The IR spectra of all ligands and their metal(II) complexes con-
clusively shown that all the ligands are coordinated to the metal
atoms tri-dentately via the azomethine-N, triazole-N, thio-
phene-S/pyrrolyl-N or hydroxyl-O groups.
1H NMR spectra
The 1H NMR spectral data of the ligands L1–L3 and their diamag-
netic Zn(II) complexes are recorded in the experimental part. The
appeared signals of all the protons of Schiff bases ligands and Zn(II)
complexes due to heteroaromatic/aromatic groups were found [26]
as to be in their expected region. The spectra of all the ligands L1–
L3 displayed [27] azomethine (ACH@N) and triazole CAH protons
as a singlet at 8.89–9.40 and 8.30–8.55 ppm respectively. The
peaks appearing in the spectrum of ligand L1 at 6.86–7.11 ppm
were assigned to C3AH and C5AH protons as a doublet and at
6.24 ppm were assigned to C4AH as double of the doublet. The
spectrum of ligand L1 also displayed a peak of pyrrole-NH proton
at 11.92 ppm. The Schiff base ligand L2 exhibited C3AH and
C5AH protons as singlet at 7.85 and 8.0 ppm. The ligand L3 dis-
played [28] proton of hydroxyl group (AOH) as a singlet at
Mass spectra
The mass spectral data and fragmentation pattern of all the
Schiff base ligands L1–L3 clearly justify [30,31] the formation of
the ligands possessing proposed structures and their bonding pat-
tern. The spectra of ligand L1 showed molecular ion peak m/z 161

M. Hanif, Z.H. Chohan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 468–476
473
higher molar conductance values are indicative of the electrolytic
nature of the metal(II) complexes and lower values as non-electro-
lytic nature [32]. The molar conductance values of the metal com-
plexes 5–8 fall in the range 85.0–89.5
X
À1 cm2 molÀ1 assigned to
their electrolytic nature. However, the molar conductance data of
the metal complexes 1–4 and 9–12 showed their molar conduc-
tance values in the range 11.5–18.7
X
À1 cm2 molÀ1 indicative of
their non-electrolytic nature [32]. The determine magnetic mo-
ment (B.M) values of all the metal(II) complexes, 1–12 at room
temperature were recorded in Table 2. The magnetic moment val-
ues of Co(II) complexes were found in the range of 4.34–4.62 B.M
suggesting the Co(II) complexes as high-spin with three unpaired
electrons in an octahedral [33] environment. The Ni(II) complexes
exhibited magnetic moment values in the range of 3.27–3.47 B.M
representative of two unpaired electrons per Ni(II) ion suggesting
these complexes to have octahedral [34] geometry. The obtained
magnetic moment values 1.51–1.67 B.M for Cu(II) complexes are
indicative of one unpaired electron per Cu(II) ion for d9-system
suggesting spin-free distorted octahedral geometry. All the Zn(II)
complexes were found to be diamagnetic [35] as expected .
Fig. 1. Proposed mass fragmentation pattern of L1.
Electronic spectra
Table 3
Antibacterial bioassay (concentration used 1 mg/mL of DMSO) of ligands and metal(II)
complexes.
The electronic spectral values of Co(II), Ni(II), Cu(II) and Zn(II)
complexes 1–12 are recorded in Table 2. The electronic spectra of
Co(II) complexes generally showed three absorption bands in the
region at 8786–8892, 17,334–17,759 and 29,726–30,150 cmÀ1
which assigned to transitions 4T1g ? 4T2g(F), 4T1g ? 4A2g(F) and
4T1g ? 4Tg(P), showing an octahedral geometry [36] around the
Co(II) ion. The electronic spectral data of Ni(II) complexes showed
d-d bands in the region 10,085–10,180, 16,075–16,775 and
29,210–29,635 cmÀ1 respectively, to assigned the transitions
Compounds
Zone of inhibition (mm)
Gram-negative Gram-positive
SA
Average
(a)
(b)
(c)
(d)
(e)
(f)
L1
L2
L3
1
2
3
4
5
6
7
8
9
10
11
12
A
14
14
14
18
18
17
19
19
16
17
18
18
16
17
16
08
26
16
12
13
20
17
18
20
13
17
16
17
17
18
16
17
11
24
15
14
15
20
19
18
21
17
18
15
17
19
18
20
18
13
32
14
15
13
17
16
17
16
19
17
17
19
18
17
19
17
10
28
12
14
14
14
16
14
16
17
19
18
16
19
19
16
18
10
27
13
13
13
16
17
17
14
19
24
19
19
15
17
16
16
10
29
1.41
1.03
0.82
2.34
1.17
1.47
2.73
2.34
2.88
1.41
1.21
1.50
1.05
1.75
0.89
1.63
2.73
14.0
13.7
13.7
17.5
17.1
16.8
17.7
17.7
18.5
17.0
17.7
17.7
17.5
17.3
17.0
10.3
27.7
3A2g(F) ? 3T2g(F), A2g(F) ? 3T1g(F) and A2g(F) ? 3T2g(F), which
are characteristic of Ni(II) in octahedral geometry . The electronic
spectra of Cu(II) complexes exhibited low-energy absorption band
at 14,822–14,975 cmÀ1 assigned to the transitions 2Eg ? 2T2g. The
high-energy band at 25,267–25,800 cmÀ1 is due to forbidden li-
gand ? metal charge transfer. On the basis of which a distorted
octahedral geometry is suggested for Cu(II) complexes [37]. The
diamagnetic Zn(II) complexes did not show any d–d transitions
and their spectra were dominated [36] only by the charge transfer
3
3
band at 28,749–28,778 cmÀ1
.
SD
Average of ligands L1–L3 = 13.8 mm; average of complexes 1–12 = 17.45 mm;
(a) = E. coli (b) = S. sonnei (c) = P. aeruginosa (d) = S. typhi (e) = S. aureus (f) = B. sub-
Biological activity
tilis. Activity < 10 = weak; >10 = moderate;
1,2,4-triazole and SD = standard drug (ampicillin). SA = Statistical analysis.
> 16 = significant: A = 3-amino-1H-
Antibacterial bioassay
The antibacterial activity of Schiff base ligands, L1–L3 and their
metal(II) complexes, 1–12 were studied against four Gram-nega-
tive (E. coli, S. sonnei, P. aeruginosa, S. typhi) and two Gram-positive
(S. aureus, B. subtilis) bacterial strains according to the literature
protocol and their results were recorded in Table 3. The obtained
results were compared with standard drug, ampicillin and simple
triazole moiety, 3-amino-1H-1,2,4-triazole (Fig. 2). The Schiff base
ligands L1–L3 exhibited varying degree of inhibitory effects on the
growth of different tested strains and their metal(II) complexes
showed moderate to significant inhibitory effects on the growth
of different tested bacterial strains. The antibacterial activity data
of Schiff base ligand L1 showed significant activity (66%) against
(b) and moderate activity (44–50%) against (a) and (c)–(f) bacterial
strains. The Schiff base ligands, L2 and L3 showed moderate activity
(43–53%) against all the tested bacterial strains. The activity data of
metal(II) complexes exhibited that the complexes 2, 6, 8, 10, 11
and 12 showed significant activity (54–82%) against all the tested
bacterial strains, while the complexes 4 and 9 showed significant
(Calcd. 161.16) of [C7H7N5].+ which loses a hydrogen (H) as radical
to give most stable fragment at m/z 160 of [C7H6N5]+. The molecu-
lar mass of ligand, L2 C7H5N4SBr was found as 257 (Calcd. 257.11)
and its base peak [C7H5N4S]+ was observed at m/z 177. The molec-
ular ion peak of ligand L3 was found as 313.9 (Calcd. 314.08) of [C9-
H7N4OI].+ and its most stable fragment [C9H6IN4]+ was observed at
m/z 297. The fragmentation pattern followed the cleavage of C@N
(exocyclic as well as endocyclic), CAI, CAO, CAC and CAN bonds.
Fragmentation pattern of ligand L1 is shown as Fig. 1 in supple-
mentary material.
Conductance and magnetic susceptibility measurements
The molar conductance values of all the metal(II) complexes
were obtained in DMF as a solvent at room temperature and their
results in (X
À1 cm2 molÀ1) are recorded as in Table 2. Generally,

474
M. Hanif, Z.H. Chohan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 468–476
Fig. 2. Comparison of antibacterial activity.
M. canis, F. solani and C. glabrata fungal strains and their results re-
corded in Table 4. The obtained results were compared with the
standard drugs miconazole and amphotericin B. The ligand L1
showed significant activity (55–61%) against (b) and (f) and mod-
erate activity (39–49%) against (a), (d) and (e) and weak activity
against (c) fungal strains. However, the same ligand showed weak
activity (23%) against (c) fungal strain. Similarly, the ligand, L2 pos-
sessed significant activity (56–59%) against (c) and (f), and moder-
ate activity (34–43%) against (b), (d) and (e) and weaker activity
(28%) against (a) fungal strains. The ligand L3 alsoshowed signifi-
cant activity (62%) against (b) and moderate activity (34–52%)
against (a), (c), (d) and (f) and weaker activity (25%) against (e)
fungal strains. From the antifungal activity data it was observed
that the metal(II) complexes, 1–4 possessed significant activity
(55–73%) against (b) and (f) and moderate activity (38–47%)
against (a) and (e) and weaker activity (21–29%) against (c) fungal
strains. The complexes, 1 and 4 also showed significant activity
(55–60%) and complexes, 2 and 3 possessed moderate activity
(50–52%) against fungal strain (b). It was also observed that the
metal complexes, 5–8 showed significant activity (54–62%) against
(c) and (f) and moderate activity (34–50%) against (a), (b), (d) and
(e) fungal strains. However, only the complex 8 showed weaker
activity (31%) against (a) fungal strain. Similarly, the metal com-
plexes, 9–12 showed significant activity (54–69%) against (b) and
(d), moderate (36–53%) against (a), (c) and (f) and weaker activity
(28–31%) against (e) fungal strains. Furthermore, the comparative
studies of average activity value of Schiff base ligands (44.33%)
and the average activity value of their metal(II) complexes
(47.06%) exhibited [39] that the antifungal activity of the metal(II)
complexes is increased upon coordination with metal ions. The
comparative activity data of the Schiff base ligands and their meta-
l(II) complexes is presented in Fig. 3.
Table 4
Antifungal bioassay (concentration used 200
complexes.
l
g/mL) of ligands and metal(II)
Compounds
% Inhibition (mm)
SA
Average
(a)
(b)
(c)
(d)
(e)
(f)
L1
L2
L3
1
2
3
4
5
6
7
8
9
10
11
12
SD
39
28
34
43
38
44
40
41
39
34
31
39
36
38
45
A
55
43
62
57
58
60
55
46
45
44
48
65
69
65
67
B
23
59
43
29
21
25
29
54
55
54
59
44
39
46
48
C
49
41
52
55
50
52
60
43
50
42
39
57
61
56
54
D
43
34
25
47
45
46
45
34
35
40
38
28
26
31
24
E
61
56
44
67
73
64
62
61
61
54
62
49
46
44
53
F
13.38
12.11
13.02
13.12
17.69
13.88
12.81
10.04
8.86
10.99
12.38
13.13
16.14
12.26
14.11
46.2
43.5
43.3
49.7
47.5
48.7
48.5
46.0
47.5
44.3
44.3
47.0
46.2
46.7
48.3
Average of activity ligands L1–L3 = 44.33%; average activity of complexes 1–
12 = 47.06%. (a) = T. longifucus (b) = C. albicans (c) = A. flavus (d) = M. canis (e) = F.
Solani (f) = C. glabrata, SD = standard drugs MIC
l
g/mL; A = miconazole (70
l
l
g/
mL:1.6822 Â 10À7 M/mL), B = miconazole (110.8
g/mL:2.6626 Â 10À7 M/mL),
C = amphotericin
B
(20
l
g/mL:2.1642 Â 10À8 M/mL), D = miconazole (98.4
l
g/
mL:2.3647 Â 10À7 M/mL), E = miconazole (73.25
l
g/mL: 1.7603 Â 10À7 M/mL),
F = miconazole (110.8
l
g/mL: 2.66266 Â 10À7 M/mL). SA = Statistical analysis.
activity (57–83%) against (a)–(e), and moderate activity (48–52%)
against (f) bacterial strains. Similarly, the metal(II) complexes, 1
and 3 showed significant activity (55–83%) against (a)–(d) and
(f) and moderate activity (52%) against (e) bacterial strains. The
complex 5 possessed significant activity (54–73%) against (a) and
(c)–(f) and moderate activity (52%) against (b) bacterial strains.
In the same way, the metal(II) complex 7 also showed significant
activity (61–66%) against (a), (b) and (d)–(f) and moderate activity
(46%) against (c) bacterial strains. The comparison of the average
activity value (13.8 mm) of Schiff base ligands and the average
activity value (17.45 mm) of their corresponding metal(II) com-
plexes revealed [37,38] that the activity of the metal(II) complexes
is increased upon coordination with metal ions.
Minimum inhibitory concentration (MIC)
The preliminary screening results of all the synthesized com-
pounds showed that the metal complexes 1 and 6 were found to
be the most active (above 80%) compounds. Therefore, these two
compounds were selected for minimum inhibitory concentration
(MIC) studies (Table 5). The MIC values of these compounds 1
and 6 fall in the range 1.18 Â 10À7 to 1.82 Â 10À7 M. The MIC re-
sults showed that the compound 6 is the most active showing
maximum inhibition 1.18 Â 10À8 M against bacterial strain B.
Subtilis.
Antifungal bioassay
The Schiff base ligands L1–L3 and their metal(II) complexes, 1–
12 were studied against, T. longifusus, Candida albican, A. flavus,

M. Hanif, Z.H. Chohan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 468–476
475
Fig. 3. Comparison of antifungal activity.
octahedral geometry. The findings of biological studies indicated
that the Schiff base ligands possessed mostly moderate activity
and metal(II) complexes mostly possessed moderate to significant
activities against different bacterial and fungal strains which might
be due to azomethine (AHC@NA) linkage and/or heteroatoms
present in these compounds. The biological activity results showed
that majority of the Schiff base ligands possessed increased activity
upon coordination with different metalloelements. The improve-
ment in biological activity upon coordination may be explained
on the basis of Overtone’s concept and chelation theory.
Table 5
Minimum inhibitory concentration (M/mL) of the selected compounds 1, and
against selected bacteria.
6
Bacterial strains
1
6
Gram-negative
S. sonnei
1.82 Â 10À7
–
Gram-positive
B. subtilis
–
1.18 Â 10À7
Table 6
Brine shrimp bioassay data of the ligands L1–L3 and their metal(II) complexes 1–12.
Acknowledgements
Compounds
LD50 (M/mL)
Compounds
LD50 (M/mL)
The authors are grateful to Higher Education Commission
(HEC), Government of Pakistan for the award to carry out this re-
search. We are also thankful to HEJ research Institute of Chemistry,
University of Karachi, Pakistan, for providing help in taking NMR,
mass spectral and antibacterial/antifungal data.
L1
L2
L3
1
2
3
>1.48 Â 10À3
>1.54 Â 10À3
>8.24 Â 10À4
>2.64 Â 10À3
>9.54 Â 10À4
>9.66 Â 10À4
>1.15 Â 10À3
>5.39 Â 10À4
6
7
8
9
10
11
12
>5.45 Â 10À4
>5.80 Â 10À4
>5.33 Â 10À4
>7.88 Â 10À4
>8.18 Â 10À4
>6.63 Â 10À4
>8.55 Â 10À4
4
5
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The synthesized ligands L1–L3 and their metal complexes 1–12
were screened for their cytotoxicity (Brine Shrimp bioassay) using
the protocol of Meyer et al. [24]. The cytotoxic data recorded in Ta-
ble 6 revealed that all compounds were considered as almost inac-
tive in this assay. It was interesting to note that the metal
complexes showed potent cytotoxicity as compared to the ligands.
This activity relationship may serve as a basis for future develop-
ment of certain cytotoxic agents in clinical practices.
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All the newly synthesized Schiff bases ligands L1–L3 act as
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All the synthesized metal(II) complexes possessed an octahedral
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