Synthesis and spectral and antibacterial studies of bivalent transition metal ion macrocyclic complexes

Article abstract of DOI:10.1134/S1070328409100054

A new series of the macrocyclic complexes of type [M(C₁₈H ₁₆N₄O₂)X₂], where M = Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and X = Cl^-, NO ₃ ^-, CH₃COO_-

Full text of DOI:10.1134/S1070328409100054

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2009, Vol. 35, No. 10, pp. 740–745. © Pleiades Publishing, Ltd., 2009.
Synthesis and Spectraland Antibacterial Studies of Bivalent
Transition Metal Ion Macrocyclic Complexes1
D. P. Singha,*, V. Malika, R. Kumara, K. Kumara, and J. Singhb
a Department of Chemistry, National Institute of Technology, Kurukshetra 136119, India
b D.M. Division, National Dairy Research Institute, Karnal 132001, India
*e-mail: dpsinghchem@yahoo.co.in
Received November 17, 2008
Abstract—A new series of the macrocyclic complexes of type [M(C18H16N4O2)X2], where M = Co(II), Ni(II),
Cu(II), Zn(II), Cd(II) and X = Cl–, NO3–, CH3COO–, has been synthesized by the condensation of succinyldihy-
drazide with benzil in the presence of bivalent metal ions. The complexes have been characterized with the aid
of elemental analyses, conductance measurements, and electronic, NMR, and infrared spectral studies. On the
basis of these studies, a six-coordinate distorted octahedral geometry in which two nitrogen and two carbonyl
oxygen atoms are suitably placed for coordination toward metal ion has been proposed for all the complexes.
The complexes were tested for their in vitro antibacterial activity. Some of the complexes showed remarkable
antibacterial activity against some selected bacterial strains.
DOI: 10.1134/S1070328409100054
1
INTRODUCTION
EXPERIMENTAL
Synthesis of complexes. All the reported MCC were
prepared by the template method. To a stirring methan-
olic solution (~50 cm3) of succinyldihydrazide
(10 mmol) was added bivalent cobalt, nickel, copper,
zinc, and cadmium salts (10 mmol) dissolved in a min-
imum quantity of methanol (20 cm3). The resulting
solution was refluxed for 0.5 h. After that benzil
(10 mmol) dissolved in ~20 cm3 of methanol was
added, and the mixture was again refluxed for 6–8 h. On
overnight cooling light colored complexes were
formed, which were filtered, washed with methanol,
acetone, and ether, and dried in vacuo (the yield was
65%). The complexes were soluble in DMF and DMSO
but insoluble in common organic solvents and water.
They were found to be thermally stable up to ~250°C
and then decomposed.
Research on diverse aspects of new macrocyclic
compounds has evoked considerable worldwide inter-
est in recent years. The condensation reaction between
diketones and primary diamines in the presence of
metal ion has played a vital role in the development of
macrocyclic complexes (MCC). MCC are thermody-
namically more stable and more selective ion bindes
than open-chain analogs. The multifarious role is
played by the naturally occurring macrocycles in bio-
logical systems. The chemistry of synthetic MCC is
also of great importance due to their use as dyes and
pigments, MRI contrast agents, and models for natu-
rally occurring macrocycles [1–4]. Macrocyclic nickel
complexes find use in DNA recognition and oxidation
[5], while macrocyclic copper complexes find use in
DNA-binding and cleavage [6]. Some MCC have been
reported as showing antibacterial, antifungal, and anti-
inflammatory activities [7–9]. Macrocyclic metal
chelating agents are useful to detect tumor lesions [10].
Prompted by these, in the present paper a new series of
macrocyclic complexes of Co(II), Ni(II), Cu(II), Zn(II),
and Cd(II) obtained by the template condensation reac-
tion of succinyldihydrazide and benzil has been
reported. The complexes have been characterized with
the help of various physicochemical techniques like
elemental analyses, IR, NMR, magnetic susceptibili-
ties, electronic spectra, and molar conductance. These
macrocyclic complexes were also screened for their in
vitro antibacterial activity.
The template syntheses of the complexes may be
represented by the scheme.
Analytical and physical measurements. The
microanalyses of C, H, and N were carried out at the
Sophisticated Analytical Instrument Facility (CDRI,
Lucknow). The metal contents were determined by
standard EDTA methods. Electronic spectra (DMF)
were recorded on a Cary 14 spectrophotometer. The
magnetic susceptibility measurements were carried at
the IIT Roorkee. The IR spectra were recorded on a
infrared spectrophotometer in the range 4000–200 cm–1
using Nujol mulls. The NMR spectra were recorded on
a Bruker NMR spectrometer (300 MHz). The conduc-
tivity was measured on a digital conductivity meter
(HPG System, G-3001).
1
The article is published in the original.
740

SYNTHESIS AND SPECTRAL AND ANTIBACTERIAL STUDIES
741
H
N
H2C
H2C
C
C
N
N
C6H5
C6H5
C6H5
O
O
X
M
X
O
C
O
C
O
O
Methanol
(6–8 h)
+
NH NH2
+ MX2
H2N HN
CH2 CH2
C6H5
N
H
where M = Co(II), X = Cl– (I),
Co(II), X = NO–3 (II),
Cu(II), X = Cl– (V),
Cu(II), X = NO–3 (VI),
Co(II), X = CH3COO– (III),
Ni(II), X = CH3COO– (IV),
Zn(II), X = CH3COO– (VII),
Cd(II), X = CH3COO– (VIII).
Scheme
Biological ‡ssay. Some of the synthesized macrocy- bition zone of DMSO. Negative control (with no com-
clic complexes were tested for in vitro antibacterial pound) was also observed.
activity against some bacterial strains using spot-on-
lawn on Muller Hinton Agar [11].
RESULTS AND DISCUSSION
Four test pathogenic bacterial strains viz., Bacillus
The analytical data suggest the formula of macrocyclic
complexes as [M(C18H16N4O2)X2], where M = Co(II),
Ni(II), Cu(II), Zn(II), and Cd(II) and X = Cl–, NO3–, and
CH3COO–. The test for anions is positive after decompos-
ing the complexes with concentrated HNO3, indicating
their presence inside the coordination sphere. Conductiv-
ity measurements in DMSO indicate them to be nonelec-
trolytic in nature [12] (10–20 Ohm–1 cm2 mol–1).All com-
pounds give satisfactory elemental analyses results as
shown in Table 1.
A close perusal of IR spectra exhibits a pair of
strong bands at ~3200 and ~3250 cm–1 corresponding to
ν(N–H), which is present in the spectrum of succi-
nyldihydrazide but absent in the spectra of all the com-
plexes [13]. However, a broad peak at ~3350–3400 cm−1
observed in the spectra of all the complexes is due to
ν(NH) stretching vibrations [14, 15]. A strong peak at
~1665 cm–1 in the spectrum of succinyldihydrazide is
attributed to the CO group of the CONH moiety. This
peak is shifted to a lower frequency (~1625–1640 cm–1)
in the spectra of all the complexes [16], suggesting the
coordination of oxygen of the carbonyl group with the
metal. Further no strong absorption band was observed
near 1690 cm–1 in the IR spectra of the complexes as
observed in the spectrum of benzil. This indicates the
absence of the >C=O group of the benzil moiety. This
confirms the condensation of the carbonyl group of
benzil and the amino group of succinyldihydrazide [17,
18]. This fact is also supported by the appearance of a
new strong absorption band in the region ~1590–
1610 cm–1, which may be attributed to ν(C=N) stretch-
ing vibrations [19, 20]. These results provide strong
evidence for the formation of macrocyclic frame [21].
cereus (MTCC 1272), where MTCC – Microbiol Type
Culture Collection, Salmonella typhi (MTCC 733),
Escherichia coli (MTCC 739) and Staphylococcus
aureus (MTCC 1144), were considered for determina-
tion of minimum inhibitory concentration (MIC) of
selected complexes.
The test pathogens were subcultured aerobically
using Brain Heart Infusion Agar (HiMedia, Mumbai,
India) at 37°C/24 h. Working cultures were stored at
4°C in Brain Heart Infusion (BHI) broth (HiMedia,
Mumbai, India), while stock cultures were maintained
at –70°C in BHI broth containing 15% (v/v) glycerol
(Qualigens, Mumbai, India) an organism was grown
overnight in 10 ml BHI broth, and centrifuged at
5.000 g for 10 min and the pellet was suspended in
10 ml of a phosphate saline buffer (PBS, pH 7.2). The
optical density at 545 nm (OD-545) was adjusted to
obtain 108 cfu/ml followed by plating serial dilution
onto plate count agar (HiMedia, Mumbai, India).
The MIC is the lowest concentration of the antimi-
crobial agent that prevents the development of viable
growth after overnight incubation. Antimicrobial activ-
ity of the compounds was evaluated using spot-on-lawn
on Muller Hinton Agar (MHA, HiMedia, Mumbai,
India). Soft agar was prepared by adding 0.75% agar in
Muller Hinton Broth (HiMedia, Mumbai, India). Soft
agar was inoculated with 1% of 108 cfu/ml of the test
pathogen and 10 ml was overlaid on MHA. From
1000X solution of the compound (1 mg/ml of DMSO)
1, 2, 4, 8, 16, 32, 64, and 128X solutions were prepared.
Dilutions of standard antibiotics (Linezolid and Cefa-
clor) were also prepared in the same manner: 5 µl of the
appropriate dilution was spotted on the soft agar and The lower values of ν(C=N) indicate coordination of
incubated at 37°C for 24 h. The zone of inhibition of azomethine nitrogen to metal [22]. The bands present at
compounds as considered after subtraction of the inhi- ~1350–1000 cm–1 may be assigned due to the ν(C–N)
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 35 No. 10 2009

742
SINGH et al.
Table 1. Analytical data of the bivalent cobalt, nickel, copper, zinc, and cadmium complexes derived from succinyldihy-
drazide and benzil
Contents (found/calcd), %
Complex
Color
F.w.
C
H
N
M
[Co(C18H16N4O2)Cl2] (I)
48.19/48.00
42.80/42.94
3.73/3.55
3.13/3.18
4.19/4.42
4.33/4.43
3.59/3.52
3.25/3.15
4.23/4.37
3.93/3.99
12.52/12.44 13.16/13.11 Bluish green
16.95/16.69 11.79/11.72 Orange
11.29/11.26 11.89/11.87 Dark red
11.27/11.29 11.27/11.69 Dark gray
12.35/12.32 13.69/13.97 Bluish green
16.64/16.55 12.62/12.51 Brown
11.27/11.13 12.99/12.92 White
10.10/10.17 20.56/20.42 Off white
450
503
497
496
455
507
503
550
[Co(C18H16N4O2)(NO3)2] (II)
[Co(C18H16N4O2)(OAc)2] (III) 53.19/53.11
[Ni(C18H16N4O2)(OAc)2] (IV)
[Cu(C18H16N4O2)Cl2] (V)
53.31/53.22
46.86/46.70
42.69/42.56
[Cu(C18H16N4O2)(NO3)2] (VI)
[Zn(C18H16N4O2)(OAc)2] (VII) 52.51/52.48
[Cd(C18H16N4O2)(OAc)2] (VI-
II)
47.88/47.96
vibration. The bands present at ~2900–3130 cm–1 may appears approximately at half an energy of the visible
be assigned to ν(C–H) vibrations of the benzil moiety band [31].
and methylene moiety. The far-infrared spectra show
The nickel complexes show magnetic moments in
bands in the region ~420–460 cm–1 corresponding to
the 2.85–2.88 µB range at room temperature showing an
ν(M–N) vibrations in all the complexes [23–25]. The
octahedral environment around the divalent nickel ion
presence of bands in all the complexes in the region
in all complexes. The solution spectra of the nickel
complexes exhibit a well discernable band with a shoul-
der on the low-energy side. The other two bands
observed in the region at ~16760–17030 (ν2), and
~420–460 cm–1 originates from (M–N) azomethine
vibration modes and gives an idea about coordination
of azomethine nitrogen [26]. The bands present at
~300–310 cm–1 may be assigned to ν(M–Cl) vibrations
[23, 25]. The bands present at ~210–230 cm–1 in all
nitrato complexes are assignable to ν(M–O) vibrations
of the nitrato group [23].
26800–28100 cm–1 (ν3), are assigned to 3A2g
3T1g (F)
3
(ν2), and A2g
3T1g (P) (ν3), respectively. The first
two bands result from the splitting of one band ν1, and
are in the range at ~9700–10200 and 11800–
1
The H NMR spectrum of the zinc(II) complex
12500 cm−1, which can be assigned to 3B1g
3Eg and
shows a broad singlet at 8.45 ppm due to protons of the
CONH moiety [14, 27]. A singlet peak at 2.43 ppm may 3B1g
3B2g, assuming the effective symmetry to be
3
be due to CH2 protons [28]. The multiplets in the region
6.9–7.5 ppm may be assigned to aromatic protons [29].
D4h (component of T2g in Oh symmetry) [31]. The
intense higher-energy band at ~34550 cm–1 may be due
to a π–π∗ transition of the (C=N) group. Various bands
do not follow any regular pattern and seem to be anion-
independent. The spectra are consistent with the dis-
torted octahedral nature of these complexes.
The magnetic moments of the cobalt complexes at
room temperature were found to be in a range of 4.87–
4.92 µB. These data correspond to three unpaired elec-
trons. The electronic spectra of the cobalt complexes
show bands at ~8110–9000 (ν1), 12400–15450 (ν2), and
The magnetic moments of the copper complexes lie
in the range 1.77–1.79 µB. The electronic spectra of the
copper complexes exhibit bands in the region ~17550–
19500 cm–1 with a shoulder on the low-energy side at
~14500–16200 cm–1 and show that these complexes are
distorted octahedral [30, 31]. Assuming tetragonal dis-
tortion in the molecule, the d-orbital energy level
18700–20220 cm–1 (ν3), respectively. The spectral data
resemble to those reported to be octahedral [30]. Thus,
assuming the effective symmetry to be D4h, the various
bands can be assigned to 4T1g
4A2g (F), (ν2), and 4T1g
appears that the symmetry of these complexes is not
4T2g (F), (ν1), 4T1g
4T1g (P), (ν3), respectively. It
ideally octahedral but is D4h. The assignment of the first sequence for these complexes may be x2 – y2 > z2 > xy >
spin-allowed band seems plausible, since the first band xz > yz and the shoulder can be assigned to z2 x2 –
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 35 No. 10 2009

SYNTHESIS AND SPECTRAL AND ANTIBACTERIAL STUDIES
743
y2 (2B1g
xy
2B2g) and the broad band contains both
x2 – y2 (2B1g 2Eg) and xz, yz x2 – y2
2A2g) transitions [32]. The band separation of
Table 2. Minimum inhibitory concentration (MIC) shown
by the complexes against test bacteria by using agar dilution
assay
(2B1g
the spectra of the complexes is about 2520 cm–1, which
is consistent with the proposed geometry of the com-
plexes [32]. Therefore, it may be concluded that all the
copper complexes are distorted octahedral.
MIC (µg/ml)*
Complex
a
b
c
d
[Co(C18H16N4O2)Cl2] (I)
[Co(C18H16N4O2)(NO3)2] (II)
[Co(C18H16N4O2)(OAc)2] (III)
[Ni(C18H16N4O2)(OAc)2] (IV)
[Cu(C18H16N4O2)Cl2] (V)
[Cu(C18H16N4O2)(NO3)2] (VI)
[Zn(C18H16N4O2)(OAc)2] (VII)
[Cd(C18H16N4O2)(OAc)2] (VIII)
Cefaclor
64 128 >128 32
Based on elemental analyses, conductivity, mag-
netic, electronic, NMR, and IR spectral studies, the
structure may be proposed for all the complexes:
32
64
32
8
16 64
16 64
64 128
64 64
64
H
N
128
32
8
H2C
H2C
C
C
N
N
C6H5
C6H5
X
M
X
O
O
64 128
16
8
16
8
32 32
16 64
N
H
8
2
8
16
where M = Co(II), Ni(II), Cu(II), Zn(II), Cd(II);
X = Cl–, NO−3, CH3COO–.
Linezolid
4
4
16 32
* a – Bacillus cereus (MTCC 1272); b – Staphylococcus aureus
(MTCC 1144); c – Escherichia coli (MTCC 739); d – Salmonella
typhi (MTCC 733). Cefaclor and Linezolid are standard antibiotics.
The synthesized macrocyclic complexes were tested
for their in vitro antibacterial activity against four test
bacteria Bacillus cereus (MTCC 1272), Salmonella typhi
(MTCC 733), Escherichia coli (MTCC 739), and Sta-
phylococcus aureus (MTCC 1144), the MIC shown by
the complexes against these bacterial strains was com-
pared with MIC shown by standard antibiotics Linezolid
and Cefaclor (Table 2, figure). Complex I showed
remarkable MIC only against Salmonella typhi. It
showed a MIC of 32 µg/ml against bacterial strain Sal-
shown by standard antibiotic Linezolid against the same
bacterial strain. The MIC of complexes II, III, andVIII
against Escherichia coli (MTCC 739) was found to be
16 µg/ml, which is equal to the minimum inhibitory
concentration shown by standard antibiotic Linezolid
monella typhi (MTCC 733), which is equal to MIC against the same bacterial strain. Complex VII showed
70
a
60
b
50
40
30
20
10
0
c
d
1
2
3
4
5
6
7
8
Linezolid Cefaclor
Complexes/Antibiotics
Comparison of MIC of the complexes with standard antibiotics up to a concentration of 64 µg/ml: a – Bacillus cereus (MTCC 1272),
b – Staphylococcus aureus (MTCC 1144), c – Escherichia coli (MTCC 739), d – Salmonella typhi (MTCC 733). Cefaclor and Lin-
ezolid are standard antibiotics
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 35 No. 10 2009

744
SINGH et al.
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a MIC of 32 µg/ml against bacterial strain Salmonella
typhi (MTCC 733), which is equal to MIC shown by
standard antibiotic Linezolid against the same bacterial
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centration of 8 µg/ml against bacterial strain Bacillus
cereus (MTCC 1272), which is equal to MIC shown by
standard antibiotic Cefaclor against the same bacterial
strain.Among the series under testing for determination
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was found to be most potent complex as showing MIC
equal to that of standard antibiotic Cefaclor and Line-
zolid against Bacillus cereus (MTCC 1272) and Escher-
ichia coli (MTCC 739), respectively. However, com-
plexes IV and VI showed poor antibacterial activity or
no activity against all bacterial strains among the whole
series (Table 2, figure).
Thus, based on elemental analyses, conductivity,
magnetic, electronic, NMR, and IR spectral studies, the
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It has been suggested that chelation/coordination
reduces the polarity of the metal ion mainly because of
partial sharing of its positive charge with the donor
group within the whole chelate ring system. This pro-
cess of chelation thus increases the lipophilic nature of
the central metal atom, which, in turn, favors its perme-
ation through the lipoid layer of the membrane thus
causing the metal complex to cross the bacterial mem-
brane more efficiently thus increasing the activity of the
complexes. In addition, from this many other factors,
such as solubility, dipole moment, and conductivity,
influenced by metal ion may be possible reasons for
remarkable antibacterial activities of these complexes
[33–36]. It also has been observed that some moieties,
such as azomethine linkage or heteroaromatic nucleus
introduced into such compounds, exhibit extensive bio-
logical activities that may be responsible for the
increase in hydrophobic character and liposolubility of
the molecules in crossing the cell membrane of the
microorganism and enhance the biological utilization
ratio and activity of the complexes [37–39].
21. Mohamed, A.K., Islam, K.S., Hasan, S.S., and Shakir, M.,
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ACKNOWLEDGMENTS
D.P. Singh thanks the University Grants Commis-
sion (New Delhi) for financial support in the form of the
Major Research Project (MRP-F no. 32–196/2006
(SR)). Thanks are also due to authorities of NIT Kuruk-
shetra for providing necessary facilities.
28. Pavia, D.L., Lampman, G.M., and Kriz, G.S., Introduc-
tion to Spectroscopy, New York: Harcourt College Pub-
lishers, 2001.
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Chem., 2006, vol. 31, p. 970.
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