Antibacterial Co(II), Ni(II), Cu(II) and Zn(II) complexes with biacetyl-derived Schiff bases

Article abstract of DOI:10.2298/JSC091026098I

The condensation reactions of biacetyl with ortho-hydroxyaniline and 2-aminobenzoic acid to form bidendate NO donor Schiff bases were studied. The prepared Schiff base ligands were further utilized for the formation of metal chelates having the general formula [ML ₂(H ₂O) ₂] where M = Co(II), Ni(II), Cu(II) and Zn(II) and L = HL ¹ and HL ². These new compounds were characterized by conductance measurements, magnetic susceptibility measurements, elemental analysis, and IR, ¹H-NMR, ¹³C-NMR and electronic spectroscopy. Both Schiff base ligands were found to have a mono-anionic bidentate nature and octahedral geometry was assigned to all metal complexes. All the complexes contained coordinated water which was lost at 141-160°C. These compounds were also screened for their in vitro antibacterial activity against four bacterial species, namely: Escherichia coli, Staphylococcus aureus, Salmonella typhi and Bacillus subtilis. The metal complexes were found to have greater antibacterial activity than the uncomplexed Schiff base ligands.

Full text of DOI:10.2298/JSC091026098I

J. Serb. Chem. Soc. 75 (8) 1075–1084 (2010)
JSCS–4032
UDC 542.9+547.571+547.551+547.442.2+
546.732’742’472:615.281–188
Original scientific paper
Antibacterial Co(II), Ni(II), Cu(II) and Zn(II) complexes
with biacetyl-derived Schiff bases
1
2
1
1
*
MUHAMMAD IMRAN , LIVIU MITU , SHOOMAILA LATIF , ZAID MAHMOOD ,
IMTIAZ NAIMAT1, SANA S. ZAMAN1 and SURRYA FATIMA1
1Institute of Chemistry, University of the Punjab, Lahore-Pakistan and 2Department of Phy-
sics and Chemistry, Faculty of Science, University of Pitesti, Pitesti, 110040, Romania
(Received 26 October 2009, revised 1 March 2010)
Abstract: The condensation reactions of biacetyl with ortho-hydroxyaniline and
2-aminobenzoic acid to form bidendate NO donor Schiff bases were studied.
The prepared Schiff base ligands were further utilized for the formation of me-
tal chelates having the general formula [ML2(H2O)2] where M = Co(II), Ni(II),
Cu(II) and Zn(II) and L = HL1 and HL2. These new compounds were charac-
terized by conductance measurements, magnetic susceptibility measurements,
1
elemental analysis, and IR, H-NMR, 13C-NMR and electronic spectroscopy.
Both Schiff base ligands were found to have a mono-anionic bidentate nature
and octahedral geometry was assigned to all metal complexes. All the
complexes contained coordinated water which was lost at 141–160 °C. These
compounds were also screened for their in vitro antibacterial activity against
four bacterial species, namely: Escherichia coli, Staphylococcus aureus,
Salmonella typhi and Bacillus subtilis. The metal complexes were found to
have greater antibacterial activity than the uncomplexed Schiff base ligands.
Keywords: Schiff base; biacetyl; metal ion; antibacterial activity.
INTRODUCTION
The promising bacterial resistance to the currently available antibiotics has
forced the exploration for new prokaryotic targets as well as novel molecules to
inhibit their activity. Among such novel derivatives, metal complexes of biologi-
cally active ligands may represent an attractive approach for designing new anti-
microbial compounds, due to the dual possibility of both ligands and metal ions
1–3
interacting with different steps in the life cycle of pathogens.
Much work has
been realized by bioinorganic as well as medicinal chemists to launch the rela-
tionship between the metal ions and their complexes as antitumor and antibac-
4–8
terial agents.
It is however noteworthy that some biologically active com-
*Corresponding author. E-mail: ktm7ro@yahoo.com
doi: 10.2298/JSC091026098I
1075
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1076
IMRAN et al.
9
pounds may become more carcinostatic and bacteriostatic upon chelation. Ke-
tones and amines are versatile reactive organic compounds due to presence of
C=O and NH groups, respectively. The nucleophilic addition reactions of these
2
compounds result in an important class of compounds known as Schiff bases,
which are considered to be the best candidates for coordination with metal ions.
A number of studies have reported the ligational aspects and biological role of
10–23
Schiff bases and their metal complexes.
A comprehensive search through
the literature revealed that no work has been realized on the preparation and
characterization of metal complexes of Schiff bases derived from biacetyl, ortho-
-hydroxyaniline and 2-aminobenzoic acid. Consequently, an attempt has been
made to synthesize and characterize some novel metal complexes of these Schiff
base ligands. The prepared ligands as well as their metal complexes were also
investigated for their in vitro activity against some bacterial species. The purpose
of the work was to understand the coordination as well as the biological che-
mistry of these novel synthesized compounds.
EXPERIMENTAL
Analytical reagent grade ethanol was used after distillation. All other chemicals and
solvents were of reagent grade and procured from Sigma Aldrich or Merck. Metal chlorides
were used as the metal(II) salts for synthetic purposes. The IR spectra were recorded on Phi-
lips Analytical PU 9800 FT-IR spectrometer. The UV/Vis spectra were obtained on a Spe-
cord-200 spectrometer using Software Acuta710, while the 1H-NMR spectra were recorded on
a Bruker 250 MHz NMR spectrometer in DMSO-d6. The conductance of the metal complexes
was determined in DMF on a Hitachi YSI-32 model conductometer. The magnetic measure-
ments were realized on solid complexes using the Gouy method. Melting points were deter-
mined using a Gallenkamp apparatus.
Preparation of the Schiff bases
An ethanolic solution of biacetyl (0.010 mol, 20 ml) was mixed with an ethanolic solu-
tion of 2-aminobenzoic acid (0.010 mol, 20 ml) and o-hydroxyaniline (0.010 mol, 20 ml)
separately, then 2–3 drops of glacial acetic acid were added and the mixture was refluxed for
four hours. The resulting solution was concentrated and cooled. The obtained colored products
were filtered off, washed with ethanol and dried. Recrystallization with warm ethanol gave the
desired products HL1 and HL2 (Scheme 1).
(a)
(b)
Scheme 1. Numbering of the C atoms in the a) HL1 and b) HL2 ligands.
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Co(II), Ni(II), Cu(II) AND Zn(II) COMPLEXES WITH BIACETYL-DERIVED SCHIFF BASES
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Preparation of metal complexes
Metal chloride (0.0010 mol) was dissolved in distilled water (30 ml ) and the resulting
solution was stirred magnetically. To this magnetically stirred solution was added 0.0020 mol
of each Schiff base ligand in an ethanolic solution (25 ml). The mixture was refluxed for 2–3
h and cooled to room temperature. After cooling, the formed precipitates were filtered,
washed with water, ethanol and dried.
Antibacterial studies
All the synthesized metal complexes were tested for their in vitro antibacterial activity
against some bacterial strains using the spot on Mueller–Hinton agar by following the re-
ported method.24 Four test pathogenic bacterial strains, viz. Staphylococcus aureus (MTCC
1144), Bacillus subtilis (MTCC 2423), Salmonella typhi (MTCC 733) and Escherichia coli
(MTCC 739), were considered for the determination of the minimum inhibitory concentration
(MIC). The minimum inhibitory concentrations were determined by the microbroth dilution
technique using Mueller–Hinton broth. Serial two-fold dilutions ranging from 5000 to 4.8 μg
ml-1 were prepared in Mueller–Hinton broth. The inoculum was prepared with a 4–6 h broth
culture of each strain adjusted to a turbidity equivalent to 0.5 McFarland standard, diluted in
Mueller–Hinton broth to give a concentration of 50 CFU L-1 in the test tray. The trays were
covered and placed in plastic bags to prevent drying; incubation was at 37 °C for 18–20 h. The
MIC was defined as the lowest concentration of a compound giving complete inhibition of
visible growth.
RESULTS AND DISCUSSION
1
2
The physico-analytical data for the Schiff base ligands HL and HL are
given in Table I. These Schiff bases were prepared by refluxing an appropriate
amount of o-hydroxyaniline and 2-aminobenzoic acid with biacetyl in absolute
ethanol. The prepared Schiff base ligands were further reacted with Co(II), Ni(II),
Cu(II) and Zn(II) ions to form the respective metal complexes. These metal com-
plexes were soluble in polar organic solvents, such as MeOH, CHCl , DMF and
3
EtOH, but less soluble in non-polar solvents, such as 1-hexane, 1-heptane and
toluene. These air-stable complexes were obtained in excellent yields (Table I).
TABLE I. Physico-analytical data of the ligands and their metal complexes
b
M.p.
°C
180
Λm
Yield
%
S. No.
Compounda
Color
μeff / μB
Ω-1 cm2 mol-1
1
2
3
4
5
6
7
8
9
HL1
Yellowish brown
Pale Yellow
Sky blue
Light blue
Tea pink
Brown
Greenish blue
Dirt green
Colorless
–
–
–
–
75
67
70
56
62
43
55
44
65
54
HL2
176
[Cu(L1)2(H2O)2]
[Cu(L2)2(H2O)2]
[Co(L1)2(H2O)2]
[Co(L2)2(H2O)2]
[Ni(L1)2(H2O)2]
[Ni(L2)2(H2O)2]
[Zn(L1)2(H2O)2]
[Zn(L2)2(H2O)2]
≈290
≈291
≈285
≈267
≈218
≈212
1.86
1.78
4.18
4.21
3.42
3.26
11
13
8
14
12
18
17
15
≈255 Diamagnetic
≈243 Diamagnetic
10
Colorless
a
b
HL1, HL2 = Schiff base ligands; 10-3 M solution in DMF
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IMRAN et al.
All the metal complexes 3–10 (Table I) of these Schiff bases were prepared at a
mole ratio of the appropriate metal to ligand of 1:2. The low values of the molar
–1
2
–1
conductivity (8–18 Ω cm mol ) of the resulting complexes in DMF showed
25
that they were non-electrolytic in nature. The elemental analysis data (Table II)
support the proposed structures of the synthesized compounds (Figs. 1 and 2).
Fig. 1. Proposed structures of metal
complexes with HL1; M = Co(II),
Ni(II), Cu(II) and Zn(II).
Fig. 2. Proposed structures of metal
complexes with HL2; M = Co(II),
Ni(II), Cu(II) and Zn(II).
TABLE II. Elemental analysis data (Calcd. (Found) %) of the ligands and their metal com-
plexes
S. No.
1
2
3
4
5
6
7
8
Compound
C
H
N
M
–
–
HL1
64.12 (64.39)
67.22 (67.42)
51.78 (52.02)
52.90 (53.15)
52.17 (52.49)
53.55 (53.70)
52.09 (52.52)
53.56 (53.74)
51.59 (51.82)
52.78 (52.93)
5.02 (5.37) 6.55 (6.82)
6.26 (6.74) 7.68 (7.87)
4.60 (4.73) 5.50 (5.52)
5.12 (5.32) 6.02 (6.20)
4.12 (4.77) 5.43 (5.56)
5.13 (5.37) 6.12 (6.27)
4.56 (4.76) 5.23 (5.58)
5.10 (5.37) 6.12 (6.30)
4.44 (4.71) 5.34 (5.50)
5.15 (5.29) 6.11 (6.18)
HL2
[Cu(L1)2(H2O)2]
[Cu(L2)2(H2O)2]
[Co(L1)2(H2O)2]
[Co(L2)2(H2O)2]
[Ni(L1)2(H2O)2]
[Ni(L2)2(H2O)2]
[Zn(L1)2(H2O)2]
[Zn(L2)2(H2O)2]
12.12 (12.52)
13.79 (14.07)
11.45 (11.72)
13.01 (13.19)
11.55 (11.66)
13.01 (13.13)
12.65 (12.84)
14.09 (14.43)
9
10
IR Spectroscopy
The assignment of the characteristic IR frequencies for the Schiff base li-
gands and their resulting complexes are tabulated in Table III and can be discus-
sed as follows. The IR spectra of the Schiff base ligands do not show any band in
–1
the region 3400–3150 cm which could be assigned to –NH vibrations; instead,
2
–1
new bands at 1638 and 1631 cm appeared that can be assigned to (>C=N) lin-
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Co(II), Ni(II), Cu(II) AND Zn(II) COMPLEXES WITH BIACETYL-DERIVED SCHIFF BASES
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TABLE III. Selected IR data (cm-1) of the ligands and their metal complexes
COO- COO-
νC–O νC=O
S.
No.
-
-
Compound
νOH νH O νa
νs
COO COO
∆νa νC=N νM–O νM–N
2
1
2
3
4
5
6
7
8
9
HL1
–
–
3415
–
–
–
–
–
–
–
–
1638
1631
–
–
–
–
HL2
1242 1724
–
–
–
–
–
–
–
–
–
[Cu(L1)2(H2O)2]
[Cu(L2)2(H2O)2]
[Co(L1)2(H2O)2]
[Co(L2)2(H2O)2]
[Ni(L1)2(H2O)2]
[Ni(L2)2(H2O)2]
[Zn(L1)2(H2O)2]
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
3456 1607 1388 219 1619 438 349
3478 1594 1377 217 1607 453 363
3488 1591 1367 224 1622 459 370
3508 1582 1375 207 1609 434 378
3567 1588 1379 209 1634 456 359
3477 1590 1389 201 1623 450 377
3456 1567 1295 272 1610 427 345
3523 1578 1344 234 1608 478 367
10 [Zn(L2)2(H2O)2]
a
∆ν = νaCOO- – νsCOO
-
26
kages. In addition to this characteristic (>C=N) absorption, the Schiff base li-
1
–1
gand HL also exhibited bands at 3415 cm , which can be assigned to phenolic
2
(O–H) group vibrations, while Schiff base ligand HL showed two characterristic
bands at 1724 and 1242 cm , assigned to asymmetric and symmetric vibrations
of the carboxylic acid group. A comparison of the IR spectra of Schiff base
–1
26
ligands with their metal complexes reveals that they are coordinated mainly in
two ways with the metal ions, thus representing their bidentate nature. Both the
–1
Schiff base ligands showed a lower shift (1634–1607 cm ) in the >C=N
stretching frequency (Table III), indicating their coordination with metal ions
1
through the nitrogen atom. In the metal complexes of the Schiff base ligand HL ,
–1
the bands at 3415 cm assigned to (O–H) vibrations are absent, thus indicating
2
chelating of oxygen to the metal atoms after deprotonation. Similarly, in HL
–1
complexes, the absence of bands at 1724 and 1242 cm showed that the –COOH
group was deprotonated on complexation. It is well recognized by some au-
27
–1
thors that ionic carboxylato groups do not have any peak around 1700 cm
–1
due to the C=O group but show two peaks in the region 1610–1550 cm and
1400–1280 cm , assigned to asymmetric and symmetric vibrations of the COO
group, respectively. It is also well recognized in the literature
–1
–
28,29
that this group
can act as monodentate, bidentate or as a bridging ligand and differentiation of
these binding states can be made from the frequency separation (∆ν = ν (COO) –
a
– ν (COO)) between the symmetric and the asymmetric stretching of this group.
s
By probing the symmetric and the asymmetric stretching vibrations of large num-
ber of carboxylato complexes with known crystal structure, a criteria was establi-
shed by Deacon and Phillips29 that can be used to discriminate between these
three binding states of carboxylate complexes. These criteria are: a) monodentate
carboxylato complexes display ∆ν values which are much larger than those of the
–1
ionic salts (∆ν > 200 cm ), b) bidentate carboxylato complexes demonstrate ∆ν
–1
values significantly smaller than the ionic values (∆ν < 100 cm ) and c) brid-
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1080
IMRAN et al.
ging complexes demonstrate ∆ν values comparable to the ionic values (∆ν ≈ 150
–1
cm ). The ∆ν values for the prepared complexes (3–10) were in the range 201–
–1
–272 cm , which suggests that the carboxylato group is acting as monodentate.
–1
Furthermore, the presence of peak at 1702 cm in the IR spectra of the ligands
with no change in the spectra of complexes rejects the possibility for coordina-
tion of the second, uncondensed carbonyl group. In all metal complexes some
new low frequency bands in the region 478–427, 378–345 and > 3450 and 893–
–1
–878 cm were also observed and can be assigned to ν(M–O), ν(M–N) and co-
26
ordinated water modes, respectively.
1H- and 13C-NMR spectroscopy
1
13
The assignments of the H- and C-NMR chemical shifts are tabulated in
1
2
Table IV. In the H-NMR spectrum of the Zn-complex of HL , a signal assign-
nable to carboxylic group proton was absent, indicating that deprotonation of car-
boxylic group occurred and that coordination through this group took place.
TABLE IV. NMR data (δ / ppm) of ligands and their Zn complexes
S. No.
1
Compound
HL1
1H-NMR
10.9 (1H, s, OH), 6.7–7.1
13C-NMR
197.5 (C-2’), 164 (C-3’),137 (C-1),
(4H, m, H2-H5), 2.20 (3H, s, 122.7 (C-3), 117.2 (C-5), 128.7 (C-4),
H-1’), 1.90 (3H, s, H-4’) 123.7 (C-2), 151.5 (C-6), 24.1 (C-1’),
10.1 (C-4’)
2
HL2
11.1 (1H, s, OH), 7.5–8.1
197.5 (C-2’), 164 (C-3’),149 (C-1),
(4H, m, H2-H5), 2.30 (3H, s, 135.3 (C-3), 131.6 (C-5), 127.2 (C-4),
H-1’), 1.92 (3H, s, H-4’) 122.2 (C-2), 116.4 (C-6), 24.1 (C-1’),
10.1 (C-4’), 169.4 (C-1’’)
9
Zn-complex (HL1) 6.6–7.4 (4H, m, H2-H5),
2.22 (3H, s, H-1’), 1.91
197.5 (C-2’),164 (C-3’),137.9(C-1),
122.7 (C-3), 118.5 (C-5), 128.7 (C-4),
123.7 (C-2), 152.3 (C-6), 24.1 (C-1’),
10.1 (C-4’)
197.5 (C-2’), 164 (C-3’), 150 (C-1),
135.3 (C-3), 132.2 (C-5), 127.2 (C-4),
122.2 (C-2), 117.7 (C-6), 24.1 (C-1’),
10.1 (C-4’), 173.2 ( C-1’’)
(3H, s, H-4’)
10
Zn-complex (HL2) 7.4–8.0 (4H, m, H2-H5),
2.32 (3H, s, H-1’), 1.92
(3H, s, H-4’)
13
The Zn-complex of this ligand was also characterized by means of C-
-NMR spectroscopy. The higher values of the chemical shift of C-1”, C-1, C-6
and C-5 atom signals in the Zn-complex in comparison with those of the signals
30
in the respective non-coordinated ligand strongly suggest that coordination
through the carboxylate groups had occurred. On the other hand, the absence of a
change of the chemical shift of the uncondensed carbonyl moiety C-2’ indicates
that this group did not participate in the coordination. A similar pattern of the
1
1
change in the chemical shift was found with ligand HL . Thus, both the H- and
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Co(II), Ni(II), Cu(II) AND Zn(II) COMPLEXES WITH BIACETYL-DERIVED SCHIFF BASES
1081
13
C-NMR spectroscopic data support the proposed structures of the ligands and
their coordination behavior as well.
Electronic absorption spectra
In the electronic spectra, the Co(II) complexes exhibited two low energy
–1
–1
peaks at 7275, 7260 cm ; 17234, 17224 cm and a strong high energy peak at
–1
31
4
20482, 20172 cm , which can be assigned to the transitions T (F) →
1g
4
4
4
4
4
→ T (F), T (F) → A (F) and T (F) → T (P) for a high spin octa-
2g
1g
2g
1g
2g
–
hedral geometry, respectively. The final high intensity band at 27145, 27123 cm
1
is assigned to charge transfer (Table V). The electronic spectra of the Ni(II)
complexes showed d–d transition at 10213, 10110; 15597, 15654 and 26360,
–1
31
3
3
3
3
26197 cm . These are assigned to A (F) → T (F), A (F) → T (F) and
2g
2g
2g
1g
3
3
A
2g
(F) → T (P) transitions, respectively. These are consistent with a well-
2g
-defined octahedral geometry. The Zn(II) complexes exhibited only a high in-
–1
tensity band at 28251, 28231 cm , which is assigned to ligand–metal charge
transfer. In case of the Cu(II) complexes, a broad band at 16644, 16612 cm was
observed that is assigned to the E → T transition, which confirms its
–1
2
2
g
2g
octahedral geometry.
TABLE V. Electronic spectroscopic data of the metal complexes
S. No.
Complex
λ
max / cm-1
16644
16612
7260
17234
20482
27123
7275
17224
20172
27145
10213
15654
26360
10110
15597
26197
28251
28231
Assignments
3
4
5
[Cu(L1) (H2O)2]
[Cu(L2)2(H2O)2]
[Co(L1)2(H2O)2]
2Eg → 2T2g
2Eg → 2T2g
4T1g(F) → 4T2g(F)
4T1g(F) → 4A2g(F)
4T1g(F ) → 4T2g(P)
Charge transfer
4T1g(F) → 4T2g(F)
4T1g(F) → 4A2g(F)
4T1g(F) → 4T2g(P)
Charge transfer
3A2g(F) → 3T2g(F)
3A2g(F) → 3T1g(F)
3A2g(F) → 3T2g(P)
3A2g(F) → 3T2g(F)
3A2g(F) → 3T1g(F)
3A2g(F) → 3T2g(P)
Charge transfer
Charge transfer
6
[Co(L2)2(H2O)2]
7
8
[Ni(L1)2(H2O)2]
[Ni(L2)2(H2O)2]
9
10
[Zn(L1)2(H2O)2]
[Zn(L2)2(H2O)2]
Magnetic susceptibility measurement
The magnetic moment value 4.18; 4.21 μB (Table I) for the solid Co(II) com-
32
plexes suggests an octahedral environment, indicating three unpaired electrons.
The magnetic moment value of the Cu(II) complexes 1.86; 1.78 μB suggests dis-
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IMRAN et al.
33
torted octahedral geometry. The magnetic moment value of the Ni(II) com-
33
plexes 3.42; 3.26 μB, showing two unpaired electrons, suggests an octahedral
geometry for the Ni(II) complexes. The Zn(II) complexes were found to be dia-
10
magnetic, as expected for d configuration.
Antibacterial activity
–1
The antimicrobial activity (MIC, μg ml ) of the metal complexes/ligands
are given in Table VI, from which it can be seen that the complexes had variable
1
–1
antimicrobial activities. The Cu(II)L complex showed an MIC of 4 μg ml against
the bacterial strain B. subtilis which is equal to the MIC shown by the standard
2
antibiotic cefaclor against the same bacterial strain. The Cu(II)L complex exhi-
bited an MIC of 9 μg ml against the bacterial strain S. aureus which is the same
–1
as the MIC shown by standard antibiotic cefaclor against the same bacterial strain.
Furthermore, complexes of Co(II)L1 and Co(II)L2 showed a minimum inhibitory
–1
concentration of 5 μg ml against the bacterial strain B. subtilis, which is the
same as the MIC shown by the standard antibiotic linezolid against the same bac-
2
terial strain. The MIC of the complex Ni(II)L against S. typhi was found to be 18
–1
μg ml , which is equal to the MIC shown by the standard antibiotic linezolid
2
against the same bacterial strain. Similarly, the complex Zn(II)L registered an
–1
MIC of 5 μg ml against the bacterial strain B. subtilis, which is the same as the
MIC shown by the standard antibiotic linezolid against the same bacterial strain.
TABLE VI. Minimum inhibitory concentration (MIC) exhibited by the ligands and their metal
complexes against test bacteria
MIC / μg ml-1
S. No.
Compound
S. aureus
B. subtilis
S. typhi
7
E. coli
15
12
118
149
10
14
15
12
13
–
–
1
2
3
4
5
6
7
8
9
10
Cefaclor
Linezolid
9
6
–
–
18
9
23
11
15
56
11
13
4
5
–
–
4
9
5
5
18
110
–
HL1
HL2
[Cu(L1)2(H2O)2]
[Cu(L2)2(H2O)2]
[Co(L1)2(H2O)2]
[Co(L2)2(H2O)2]
[Ni(L1)2(H2O)2]
[Ni(L2)2(H2O)2]
[Zn(L1)2(H2O)2]
[Zn(L2)2(H2O)2]
15
7
11
16
22
18
22
7
24
33
7
19
12
16
5
Among the series under test for the determination of the MIC, complexes 1
and 3 were found to be the most potent as compared to the other complexes. This
effect can be logically explained by the fact that the Schiff base derivatives must
be activated by the metal ions in some way. This enhancement in antibacterial ac-
34
tivity of these metal complexes can be explained based on the chelation theory.
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Co(II), Ni(II), Cu(II) AND Zn(II) COMPLEXES WITH BIACETYL-DERIVED SCHIFF BASES
1083
When a metal ion is chelated with a ligand, its polarity will be reduced to a grea-
ter extent due to the overlap of ligand orbital and the partial sharing of the posi-
tive charge of the metal ion with donor groups. Furthermore, the chelation pro-
cess increases the delocalization of the π-electrons over the whole chelate ring,
which results in an increase in the lipophilicity of the metal complexes. Conse-
quently, the metal complexes can easily penetrate into the lipid membranes and
block the metal binding sites of enzymes of the microorganisms. These metal
complexes also affect the respiration process of the cell and thus block the syn-
thesis of proteins, which restrict further growth of the organism.
CONCLUSIONS
The complexes of Co(II), Ni(II), Cu(II) and Zn(II) with biacetyl-derived Schiff
bases have been described. They were characterized by their physico–analytical
and spectral data. The Schiff base ligands were found to have mono-anionic bi-
dentate nature and octahedral geometry was assigned to all the metal complexes.
All the metal complexes were found to have appreciable antimicrobial activity
against some bacterial strains.
И З В О Д
АНТИБАКЕТРИЈСКА АКТИВНОСТ КОМПЛЕКСА Co(II), Ni(II), Cu(II) И Zn(II)
КОЈИ КАО ЛИГАНДЕ САДРЖЕ ДЕРИВАТЕ ШИФОВИХ БАЗА
MUHAMMAD IMRAN1, LIVIU MITU2, SHOOMAILA LATIF1, ZAID MAHMOOD1, IMTIAZ NAIMAT1,
SANA S. ZAMAN1 и SURRYA FATIMA1
1Institute of Chemistry, University of the Punjab, Lahore-Pakistan и 2Department of Physics and Chemistry,
Faculty of Science, University of Pitesti, Pitesti, 110040, Romania
Испитивана је кондензациона реакција биацетилa са о-хидроксианилином и 2-амино-
бензоевом киселином, у којој настају бидентатни лиганди типа Шифових база које као до-
норе садрже атоме азота и кисеоника. Ови лиганди су употребљени за грађење хелатних
комплекса опште формуле [ML2(H2O)2] (M = Co(II), Ni(II), Cu(II) и Zn(II); L = HL1, HL2). За
карактеризацију комплекса употребљена су кондуктометријска и магнетна мерења, као и ре-
1
зултати елементарне микроанализе, IR, H-NMR, 13C-NMR и електронске спектроскопије.
На основу ових мерења нађено је да ови лиганди граде моноанјонске комплексе октаедарске
геометрије. Добијени комплекси садрже координовани молекул воде, који се губи из коорди-
национе сфере при температури од 140–160 °C. Испитивана је in vitro антибактеријска актив-
ност изолованих комплекса на следећим врстама бактерија: Escherichia coli, Staphylococcus
aureus, Salmonella typhi и Bacillus subtilis. Добивени резултати ових испитивања су показали
да је активност комплекса метала већа од активности некоординованих лиганада.
(Примљено 26. октобра 2009, ревидирано 1. марта 2010)
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