Biological Activity Studies on Metal Complexes of Macrocyclic Schiff Base Ligand: Synthesis and Spectroscopic Characterization

Abstract

In this study, we prepared the macrocyclic Schiff base ligand (L) derived from 1,4-dicarbonylphenyl-dihydrazide and pentane-2,4-dione (2:2) and its CoII, CuII and NiII complexes. The compounds were characterized by the analytical and spectroscopic methods like elemental analysis, molar conductance measurements, mass spectrometry, 1H nuclear magnetic resonance (NMR), and Fourier transform infrared (FTIR) spectroscopy. The ligand behaves as a tetradentate ligand and coordinates to the metal ions via the nitrogen atoms and the complexes have the mononuclear structures. The analytical and spectroscopic results indicated that the complexes are non-electrolytes in nature and may be formulated as [M(C26H28N8O4)X2], where M = CoII, CuII and NiII and X = Cl– .The antimicrobial activities of the ligand and its complexes, as growth inhibiting agents, have been screened in vitro against different species of bacteria and fungi and the results concluded that the metal complexes are effective drugs against the tested strains as compared to the macrocyclic ligand.

Full text

Article
J. Braz. Chem. Soc., Vol. 26, No. 7, 1331-1337, 2015.
Printed in Brazil - ©2015 Sociedade Brasileira de Química
0103 - 5053 $6.00+0.00 A
http://dx.doi.org/10.5935/0103-5053.20150099
*e-mail: parveezgull@gmail.com
Biological Activity Studies on Metal Complexes of Macrocyclic Schiff Base Ligand:
Synthesis and Spectroscopic Characterization
Parveez Gull* and Athar Adil Hashmi
Department of Chemistry, Jamia Millia Islamia,110025 New Delhi, India
In this study, we prepared the macrocyclic Schiff base ligand (L) derived from 1,4-dicarbonyl-
phenyl-dihydrazide and pentane-2,4-dione (2:2) and its CoII, CuII and NiII complexes. The
compounds were characterized by the analytical and spectroscopic methods like elemental analysis,
molar conductance measurements, mass spectrometry, 1H nuclear magnetic resonance (NMR),
and Fourier transform infrared (FTIR) spectroscopy. The ligand behaves as a tetradentate ligand
and coordinates to the metal ions via the nitrogen atoms and the complexes have the mononuclear
structures. The analytical and spectroscopic results indicated that the complexes are non-electrolytes
in nature and may be formulated as [M(C26H28N8O4)X2], where M = CoII, CuII and NiII and X = Cl–.
The antimicrobial activities of the ligand and its complexes, as growth inhibiting agents, have been
screened in vitro against different species of bacteria and fungi and the results concluded that the
metal complexes are effective drugs against the tested strains as compared to the macrocyclic ligand.
Keywords: tetradentate, non-electrolyte, antimicrobial activity, macrocycle
Introduction
Macrocyclic compounds have attracted increasing
interest owing to their mixed soft-hard donor character,
versatile coordination behavior and in the understanding of
molecular processes.1,2 Macrocyclic metal complexes are of
significant attention in terms of structural and coordination
chemistry. The study of metal complexes of macrocyclic
ligands appears to be fascinating in view of the possibility
of obtaining coordination compounds of unusual structure
and stability. Transition metal macrocyclic complexes
have received exceptional consideration because of their
active part in metalloenzymes and as biomimetic model
compounds due to their closeness to natural proteins and
enzymes. Synthetic tetraaza macrocycle (N4) molecules are
considered typically good models for oxygen carriers due to
the presence of four nitrogen donor sites confined to a single
four-fold or a slightly four-fold plane in a ring structure,
appropriate for metal ligand binding. The research field
dealing with macrocyclic metal complexes is very broad
due in part to their potential interest for a number of
interdisciplinary areas that include bioinorganic chemistry,
catalysis, and magneto chemistry.3-5 A number of important
macrocyclic molecules which show biological activities
including antibacterial, antifungal,6-15 antidiabetic,16
antitumor,17-19 antiproliferative,20,21 anticancer,20,21
herbicidal,22 and anti-inflammatory activities13 have been
reported. Due to their capability to form complexes with
different transition metals, macrocyclic metal complexes
can act as catalysts for different reactions.23-27 Synthetic
macrocycles are emerging class of compounds with
varying chemistry, different molecular topologies and
sets of donor atoms. It is known fact that N atom plays a
key role in the coordination of metals at the active sites of
numerous metallobiomolecules.9 Due to the demand of
new metal based antibacterial and antifungal compounds,
metallorganic chemistry is becoming an emerging area of
research.28,29 Important characteristics that can be correlated
with good antimicrobial activities are the lipophilicity and
penetration of complexes through the lipid membrane.
A survey of the literature reveals that no work has been
carried out on the synthesis of metal complexes with
macrocyclic hydrazone Schiff base ligand derived from
1,4-dicarbonyl-phenyl-dihydrazide with pentane-2,4-dione.
The coordination abilities of Schiff base have attracted
our attention and aroused our interest in elucidating the
structure of CoII, CuII and NiII.
The present study describes the coordination behavior
of macrocyclic system derived from the condensation
of 1,4-dicarbonyl-phenyl-dihydrazide with pentane-2,4-
dione towards some transition elements. For this purpose
the complexes of CoII, CuII and NiII ions with ligand were

Biological Activity Studies on Metal Complexes of Macrocyclic Schiff Base Ligand J. Braz. Chem. Soc.
1332
studied and the structure of the complexes were elucidated
using elemental analyses, infrared (IR), 1H nuclear
magnetic resonance (NMR), magnetic moment, molar
conductance, and thermal analysis measurements. Besides
the characterization of complexes by physicochemical
technique, biological activities of the synthesized
complexes were examined against some microbial strains
for evaluation of antibacterial and antifungal activities.
Experimental
Materials and methods
All chemicals used were of AnalaR grade. Pentane-
2,4-dione was purchased from Sigma Aldrich and diethyl
terephthalate was purchased from Loba Chemie India.
Hydrazinhydrate and metal(II) chlorides were obtained
from Merck and were used as received without any
further purification. All necessary precautions were taken
to exclude moisture during the synthesis and handling
of the compounds. Elemental analysis of ligand and its
metal complexes were carried out using Perkin-Elmer
elemental analyzer. Molar conductance of the complexes
was measured using a coronation digital conductivity meter.
Fourier transform infrared (FTIR) spectra of the ligand and
its metal complexes were recorded in the spectral range
4000-400 cm-1 (using KBr) with a Perkin-Elmer Series
2400 apparatus and FTIR/far infrared (FIR) Perkin Elmer
(Frontier) spectrometer in the range 700-30 cm-1 (using
CsI), respectively. Electronic spectra were recorded on a
Perkin-Elmer spectrophotometer. Magnetic susceptibility
measurements were done using Gouy balance. 1H NMR
spectra were run at Bruker 300 MHz spectrometer in
dimethylsulfoxide (DMSO) against tetramethylsilane
(TMS) as internal reference. Thermal analysis data was
studied under nitrogen atmosphere using an A63000 SII
technology instrument.
Synthesis of 1,4-dicarbonyl-phenyl-dihydrazide
To 2.22 g of diethyl ester of terephthalic acid (1) in
20 mL of ethanol was added hydrazine hydrate (2) (98%,
2 mL) in ethanol. The solution was refluxed for 3-4 h.
The reaction mixture was allowed to cool to the room
temperature and then poured onto ice cold water. The
terephthalohydrazide (3) thus obtained, was filtered and
recrystallized from ethanol.
1,4-dicarbonyl-phenyl-dihydrazide (3)
Yield: 68%; buff color; IR (KBr) nmax / cm-1 3432, 1716;
1H NMR (300 MHz, DMSO-d6) d 7.25-8.01 (m, 4H, J 4.24,
1.72 Hz, Ar–H), 7.87 (t, 1H, J 8.0, 4.0 Hz, N–H), 1.98 (d,
2H, NH2); MS (ESI) calcd. for C8H10N4O2 [M]+: 194.19;
found: 194.08.
Synthesis of macrocyclic ligand (L)
Pentane-2,4-dione (0.324 g, 2 mmol) in ethanol (20 mL)
was added to a solution of terephthalohydrazide (3)
(0.388 g, 2 mmol) in ethanol (20 mL) containing a few
drops of concentrated HCl as depicted in Scheme 1.
The reaction mixture was refluxed for 4 h. The mixture
was cooled to room temperature and the solvent
removed in vacuo until a solid product was formed
that was washed with cold ethanol and dried under
vacuum.
Macrocyclic ligand L (C26H28N8O4)
Yield: 72%; brown solid; IR (KBr) nmax / cm-1 3336,
1625; 1H NMR (300 MHz, DMSO-d6) d 7.18-8.76 (m, 4H,
J 4.25, 1.73 Hz, Ar–H), 7.84 (t, 1H, J 8.0, 4.0 Hz, N–H),
0.8-1.0 (s, 12H, J 8.0, 4.0 Hz, –CH3), 1.0-1.4 (s, 4H, J 8.0,
4.0 Hz –CH2); MS (ESI) calcd. for C26H28N8O4 [M]+: 516;
found: 517 [M + H+]+.
N
N
N
N
O
O
HN NH
OO
NH
HN
OO
O
OO
O
O
NHNH
O
NH2
H2N
()1()2
()3
()L
C2H5OH
HCl
2NH2NH2.H2O
Scheme 1. Synthesis of macrocyclic Schiff base ligand (L).

Gull and Hashmi 1333Vol. 26, No. 7, 2015
Synthesis of the CoII, CuII and NiII complexes
CoII, CuII and NiII complexes were prepared by the
general method. To a solution of 1 mmol of the appropriate
M(Cl)2 metal salts in 20 mL of ethanol was slowly added
with stirring a solution of 1 mmol of L in 20 mL of
ethanol and the reaction mixture was refluxed for 3 h.
The precipitate was filtered off, washed with ethanol and
dried under vacuum over anhydrous CaCl2; yield 60-65%
(Scheme 2).
[Cu(C26H28N8O4)Cl2]
Yield: 72%; dark brown; IR (KBr) nmax / cm-1 3342,
1610, 446, 235; 1H NMR (300 MHz, DMSO-d6) d 7.25-8.01
(m, 4H, J 4.25, 1.73 Hz, Ar–H), 7.87 (t, 1H, J 8.0, 4.0 Hz,
N–H), 0.8-0.98 (s, 12H, J 8.0, 4.0 Hz, –CH3), 1.0-1.4 (s, 4H,
J 8.0, 4.0 Hz, –CH2); MS (ESI) calcd. for [Cu(C26H28N8O4)
Cl2] [M]+: 651; found: 650.
[Co(C26H28N8O4)Cl2]
Yield: 65%; reddish brown; IR (KBr) nmax / cm-1 3343,
1620, 433, 232; 1H NMR (300 MHz, DMSO-d6) d 7.25-8.15
(m, 4H, J 4.22, 1.71 Hz, Ar–H), 7.87 (t, 1H, J 8.1, 4.3 Hz,
N–H), 0.8-0.9 (s, 12H, J 8.1, 4.2 Hz, –CH3), 1.0-1.4 (s, 4H,
J 8.1, 4.2 Hz, –CH2); MS (ESI) calcd. for [Co(C26H28N8O4)
Cl2] [M]+: 647; found: 648 [M + H+]+.
[Ni(C26H28N8O4)Cl2]
Yield: 68%; brown; IR (KBr) nmax ∕ cm-1 3346, 1613,
457, 237; 1H NMR (300 MHz, DMSO-d6) d 7.25-8.10 (m,
4H, J 4.25, 1.73 Hz, Ar–H), 7.89 (t, 1H, J 8.0, 4.0 Hz, N–H),
0.8-0.98 (s, 12H, J 8.0, 4.0 Hz, –CH3), 1.0-1.4 (s, 4H, J 8.0,
4.0 Hz, –CH2); MS (ESI) calcd. for [Ni(C26H28N8O4)Cl2]
[M]+: 646; found: 647[M + H+]+.
Antimicrobial activity
The antimicrobial activities of the synthesized
compounds (macrocyclic ligand and its metal complexes)
have been screened in vitro, as growth inhibiting agents.
The antibacterial and antifungal screening were carried out
using disc diffusion method against some strains of bacteria
like Escherichia coli, Bacillus subtilis, Pseudomonas
aeruginosa, and Staphylococcus aureus and fungal species,
including Candida albicans, Fusarium sp, Trichosporon sp.
and Aspergillus flavus. The compounds were dissolved in
1% DMSO to get the required test solutions. The nutrient
agar and potato dextrose agar (PDA) were used as a required
medium for these activities. After incubation for 24 h at
27 °C in the case of bacteria and for 48 h at 27 °C in the
case of fungi, inhibition of the organisms was evidenced
by clear zone surrounding each disk, which was measured.
Results and Discussion
The two dione groups of pentane-2,4-dione were used
for the condensation of two amino groups of 1,4-dicarbonyl-
phenyl-dihydrazide to synthesize the macrocyclic Schiff
base ligand. The condensation between 1,4-dicarbonyl-
phenyl-dihydrazide and pentane-2,4-dione lead to the
formation of a tetradentate macrocyclic ligand. It is stable
in air and is partially soluble in ethanol, methanol and
completely soluble in chloroform, tetrahydrofuran (THF),
dimethylformamide (DMF) and DMSO. The metal(II)
complexes are non-hygroscopic, soluble in DMSO,
DMF and sparingly soluble in methanol and ethanol. The
elemental analysis data of ligand and its metal complexes
along with molar conductance values are given in Table 1.
Molar conductance
The metal(II) complexes of macrocyclic Schiff base
ligand (10-3 mol dm-3) were dissolved in DMF and molar
conductivities of the solutions at room temperature were
N
N
N
N
O
O
HN NH
OO
NH
HN
CH3
CH3
H
3C
H
3C
N
N
N
N
O
O
HN NH
OO
NH
HN
CH
3
CH3
H3C
H3C
M
Cl
Cl
M(II)salt
Scheme 2. Formation of macrocyclic metal complexes (M = Cu, Co and
Ni; X = Cl).

Biological Activity Studies on Metal Complexes of Macrocyclic Schiff Base Ligand J. Braz. Chem. Soc.
1334
measured. The conductance data (Table 1) indicate that
all the metal complexes are having conductivity values in
accordance with non-electrolytes.30,31
IR spectra
The IR spectra of the macrocyclic ligand and its metal
complexes were obtained on a Perkin-Elmer Series (2400)
apparatus in the range 4000-400 cm-1and FTIR/FIR Perkin
Elmer (Frontier) spectrometer in the range 700-30 cm-1.
The peak observed at 1690 cm-1 in pentane-2,4-dione
is assigned for >C=O group. 1,4-Dicarbonyl-phenyl-
dihydrazide has strong bands at 3432 cm-1 corresponding
to the –NH2 stretching frequency. In macrocyclic Schiff
base ligand these peaks are absent, the imine >C=N band
is superimposed with the >C=O group and appears as
a strong band at 1625 cm-1,32 confirming the formation
of macrocyclic ligand (Supplementary Information
Figure S1). The strong band observed at 1625 cm-1 is
shifted to lower wavenumber by 16-8 cm-1 in the spectra
of metal(II) complexes. This indicates the coordination of
imino (>C=N) groups to the metal atom in complexes. In
the spectra of macrocyclic ligand and its complexes the
band due to ring n(NH) is observed at 3340-3330 cm-1. In
the spectra of the complexes, appearance of new bands in
the region 460-420 and 220-240 cm-1 has been attributed
to M–N and M–Cl bonds, respectively.33 From the IR
spectral data it is concluded that macrocyclic ligand acts
as a tetradentate ligand in CoII, CuII and NiII complexes,
coordinating through imino nitrogen atoms. Important
IR spectral bands of macrocyclic ligand and its metal
complexes are summarized in Table 2.
Mass spectra
The mass spectra of ligand and its CoII, CuII and
NiII complexes were recorded and their stoichiometric
compositions were compared. The mass spectrum of
macrocyclic ligand (C26H28N8O4) shows a well-defined
molecular ion peak at m/z 517 which coincides with the
formula weight of the Schiff base. The mass spectra of all the
synthesized macrocyclic complexes displayed molecular ion
peaks [M + H]+ at m/z 650, 648 and 647 a.m.u. corresponding
to their molecular formulae [Cu(C26H28N8O4)Cl2],
[Co(C26H28N8O4)Cl2] and [Ni(C26H28N8O4)Cl2], respectively.
The mass spectrum of macrocyclic CoII complex shows a
molecular ion peak at m/z 648, which corresponds to
[Co(C26H28N8O4)Cl2 + H+]+ as the calculated mass is 647.
The series of peaks have been observed at m/z 516, 420, 270,
162, and 147 a.m.u., corresponding to various fragments.
The mass spectra of CoII, CuII and NiII macrocyclic
complexes have been recorded (Table 3, Figures S2-S4).
This data is in good agreement with the proposed molecular
formula for these complexes. In addition to the peaks due
to the molecular ion, the spectra exhibit peaks assignable
to various fragments arising from the thermal cleavage of
the complexes.
1H NMR
A survey of literature reveals that the NMR spectroscopy
has been proved useful in establishing the structure and
nature of many Schiff base ligands and its metal complexes.
The 1H NMR spectra of Schiff base ligand was recorded
in DMSO-d6 solution using TMS as internal standard
Table 1. Analytical data of the CuII, CoII, and NiII complexes
Complex Elemental analysis calculated (found) / % μeff (BM) Molar conductivity /
(Ω-1 cm2 mol-1)
C H N O M
C26H28N8O4 (L) 60.45 (60.40) 5.46 (5.38) 21.69 (21.60) 12.39 (12.29) – – –
[Cu(C26H28N8O4)Cl2] 47.97 (47.84) 4.34 (4.29) 17.21 (17.18) 9.83 (9.78) 9.76 (9.70) 1.94 2.4
[Co(C26H28N8O4)Cl2] 48.31 (48.25) 4.37 (4.28) 17.34 (17.26) 9.90 (9.81) 9.12 (9.08) 4.95 3.8
[Ni(C26H28N8O4)Cl2] 48.33 (48.29) 4.37 (4.28) 17.34 (17.25) 9.90 (9.83) 9.08 (9.01) 3.1 6.3
BM: Bohr Magneton.
Table 2. IR spectral data of CoII, CuII and NiIIcomplexes
Compound n(N–H) n(C=N) n(C=O) n(M–N)
C26H28N8O4(L) 3336 1625 1630 –
[Cu(C26H28N8O4)Cl2] 3342 1610 1635 446
[Co(C26H28N8O4)Cl2] 3343 1620 1640 433
[Ni(C26H28N8O4)Cl2] 3346 1613 1635 457
Table 3. Mass spectral data of the macrocyclic metal complexes
Complex Molecular weight Molecular ion peak [M]+
C26H28N8O4 (L) 516.55 [M]+ = 517
[Cu(C26H28N8O4)Cl2] 651 [M]+ = 650
[Co(C26H28N8O4)Cl2] 647 [M + H+]+ = 648
[Ni(C26H28N8O4)Cl2] 646 [M + H+]+ = 647

Gull and Hashmi 1335Vol. 26, No. 7, 2015
(Figure S5). The 1H NMR data for all complexes show
a multiplet in the 6.70-7.00 ppm region which may be
assigned to the secondary amide protons (C–NH; 4H). A
multiplet in the 1.0-1.4 ppm region may be assigned34 to the
methylene protons (–CH2–; 4H). However, a multiplet in
the region 7.18-8.76 ppm may be assigned to aromatic ring
protons,35,36 while a singlet at 0.8-1.0 ppm may be ascribed
to the methyl protons of the pentane moiety (–CH3; 12H).
Electronic spectral studies and magnetic measurements
The electronic spectrum of the macrocyclic Schiff
base CuII complex recorded at room temperature, in
DMF solution, shows broad band absorption in the range
14,220-14,492, 20,398-20,610 and 22,725-23,252 cm-1,
which may be assigned to 2B1g → 2A1g, (dx
2
–y
2 → dz
2)
(n1), 2B1g → 2B2g, (dx
2
–y
2 → dzy)(n2), and 2B1g → 2Eg,
(dx
2
‑y
2 → dzy,dyz)(n3) transitions, respectively, which
confirms the octahedral geometry of the complex.37
The most probable geometric configuration indication
of the synthesized metal complexes is their magnetic
moment value, which lies at 1.98 BM for CuII complex
corresponding to the presence of one unpaired electron
and it supports an octahedral geometry.38
The electronic spectrum of the macrocyclic CoII complex
exhibits absorption bands in the range 12,656-12,901,
15,382-15,745 and 22,219-22,725 cm-1, which may be
assigned to 4T1g (F) → 4T2g (F)(n1), 4T1g → 4A2g (n2) and
4T1g (F) → 4T1g (P)(n3) transitions, respectively, confirm an
octahedral geometry around a CoII ion, in the complexes
under study. The geometry of the complex is supported
by the magnetic moment measurements which lie at 4.98
BM.39
The magnetic moment of the macrocyclic NiII complex
at room temperature lies at 2.97 BM which shows the
presence of an octahedral environment around the NiII
ion. The electronic spectra of the NiII complexes exhibit
three absorption bands, in the range of 10,200-11,109,
15,149-15,382 and 26,313-27,395 cm-1 which may be assigned
to three spin allowed transitions: 3A2g (F) → 3T2g (F)(n1),
3A2g (F) → 3T1g (F)(n2), and 3A2g (F) → 3T1g (P)(n3),
respectively.39
Thermal analysis
The thermal stabilities of the metal complexes were
investigated using thermogravimetric analysis (TGA) under
nitrogen atmosphere with a heating rate of 20 °C min-1 from
35 to 800 °C. The thermograms of all the complexes do not
show any weight loss up to 225 °C indicating the absence
of water molecules in these complexes. The CoII complex
started to decompose at 315 °C and gradual decrease in the
weight loss occurs up to 580 °C. After that a straight line is
obtained indicating the formation of cobalt as residue. The
NiII complex gradually decreases its weight from 355 °C
and forms the metal oxide at 625 °C. The CuII complex was
stable below 335 °C, after that it gradually decomposes
to form the corresponding metal oxide at 700 °C. The
gradual decrease of the weight loss in the complexes may
be due the removal of chlorine atoms as HCl gas, carbon
and nitrogen in the organic moiety as their oxides. From
the data it is confirmed that all the complexes are stable at
ordinary temperature and NiII complex is more stable than
the other complexes (Figure 1).
Antimicrobial activity
The macrocyclic ligand and its CoII, CuII and NiII
complexes were tested in vitro against the bacterial
species Escherichia coli (MTCC 1687), Bacillus subtilis
(MTCC 441), Pseudomonas aeruginosa (MTCC 424),
and Staphylococcus aureus (MTCC 96); and fungal
species Candida albicans (MTCC 183), Fusarium sp.
(MTCC 3326), Trichosporon sp. (MTCC 6179) and
Aspergillus flavus (MTCC 2206) by the disc diffusion
method. The standards used were amikacin and nystatin.
The minimum inhibitory concentration (MIC) was
determined by the Clinical and Laboratory Standards
Institute recommended broth microdilution method
M27-A3.40 The test tubes containing 5 mL of sterile
nutrient/Sabouraud broth were inoculated with 0.02 mL
of 24 h old culture of bacteria and fungi. Different amount
of compounds in DMSO were aseptically added with the
help of sterile pipettes from the stock solution 200 μg mL-1
to 5 mL quantities of respective media so as to reach
the concentration from 1 μg mL-1 to 50 μg mL-1. All test
0 100 200 300 400 500 600 700
800
0
20
40
60
80
100
Temperature / °C
wt.% loss
Figure 1. TGA curves of NiII metal complexes.

Biological Activity Studies on Metal Complexes of Macrocyclic Schiff Base Ligand J. Braz. Chem. Soc.
1336
tubes were incubated at 37 °C and at room temperature
for bacteria and fungi, respectively. Test tubes inoculated
with organisms were observed for presence of turbidity
after 24 and 48 h, respectively. The lowest concentrations
of compounds inhibiting the growth of organisms were
determined as MIC value (Tables S1 and S2).
From the results of the antibacterial and antifungal
activity of metal complexes, it is apparent that the metal
complexes show greater antimicrobial activity than that
of the free macrocyclic ligand; this advanced antibacterial
activity of the metal complexes, compared with that
of Schiff bases, is conceivably owing to modification
in structure due to coordination, and chelating tends
to make metal complexes act as more influential and
powerful bacteriostatic agents, thus inhibiting the growth
of the microorganisms. Overtone’s concept and chelation
theory41 explains the increased antimicrobial effect as
the chelation has a tendency to make the ligand a more
powerful and potent bacterial agent. On chelation, the
polarity of the metal ion will be reduced to a better range
due to the overlap of the ligand orbital and partial sharing
of the positive charge of the metal ion with donor groups.
Further, it increases the delocalization of π-electrons over
the whole chelate ring and enhances the penetration of
the complexes into lipid membranes and blocking of 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.42 In general,
metal complexes are more active than the ligands
because metal complexes may serve as a vehicle for
activation of ligands as the principle cytotoxic species.43
The synthesized compounds exhibit moderate to strong
antimicrobial activity. The CuII complex exhibits a
higher activity than the other metal complexes towards
fungal species. CoII, CuII and NiII complexes have low
activity compared to the standard. In the case of fungal
species, NiII complex shows remarkable activity against
Fusarium sp. and C. albicans compared to the standard drug
(Figures 2 and 3).
Conclusions
The ligand and its CoII, CuII and NiII complexes were
synthesized, characterized and tested for their antimicrobial
inhibition potential. The outcome of antimicrobial studies
showed that the macrocyclic ligand possessed mild activity
and metal(II) complexes possessed moderate to significant
activities against different bacterial and fungal strains
which might be due to azomethine (–C=N–) linkage
and/or heteroatoms present in these compounds. The
biological activity findings exhibited that majority of the
macrocyclic ligands possessed increased activity upon
coordination with different metal ions. The enhancement
in biological activity upon coordination may be elucidated
on the basis of Overtone’s concept and chelation theory.
The cytotoxicities values designate that metal complexes
present significant cytotoxic activities that might help in
the development of potent antimicrobial drugs. Further
structural optimization revisions might thus represent a
rationale for further investigation.
Supplementary Information
Supplementary data are available free of charge at
http://jbcs.sbq.org.br as PDF file.
Ligand(L
)
[Cu(L)Cl
2
]
[Co(L)Cl
2
]
[Ni(L)Cl
2
]
Copper(II)
Cobalt(II)
Nickel(II
)
Amikacin
0
20
40
60
80
100
MIC
Compound
E. coli
B. subtilis
P. aeruginosa
S. aureus
Figure 2. Antibacterial activity of macrocyclic ligand and its metal
complexes.
Ligand(L)
Cu(L)Cl
2
Co(L)Cl
2
Ni(L)Cl
2
Copper(II)
Cobalt(II)
Nickel(II)
Nystatin
0
20
40
60
80
100
MIC
Compound
C. albicans
Fusarium sp.
Trichosporon .sp
A. avus
Figure 3. Antifungal activity of macrocyclic ligand and its metal
complexes.

Gull and Hashmi 1337Vol. 26, No. 7, 2015
Acknowledgments
The authors are grateful to the University Grants
Commission (UGC), New Delhi, for providing financial
assistance in the form of meritorious (UGC-RFSMS)
fellowship.
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Submitted: January 29, 2015
Published online: April 24, 2015