Synthesis, characterization, and antibacterial activities of Cr(III), Co(III), Ni(II), and Mn(III) complexes of heptadentate Schiff base ligand derived from tris(2-aminoethyl)amine

Article abstract of DOI:10.1134/S1070363215070312

This is the first study of the antibacterial activity of heptadentate Schiff base ligand (trensal) and its Cr(III), Co(III), Ni(II), and Mn(III) complexes that have been synthesized from the heptadentate Schiff base ligand derived from salicylaldehyde and

Full text of DOI:10.1134/S1070363215070312

ISSN 1070-3632, Russian Journal of General Chemistry, 2015, Vol. 85, No. 7, pp. 1763–1767. © Pleiades Publishing, Ltd., 2015.
Synthesis, Characterization, and Antibacterial Activities
of Cr(III), Co(III), Ni(II), and Mn(III) Complexes
of Heptadentate Schiff Base Ligand Derived
1
from Tris(2-aminoethyl)amine
S. J. Matin and R. R. Khojasteh
Department of Chemistry, North Tehran Branch, Islamic Azad University, Tehran, Iran
e-mail: s.jalalimatin@yahoo.com
Received April 5, 2015
Abstract—This is the first study of the antibacterial activity of heptadentate Schiff base ligand (trensal) and its
Cr(III), Co(III), Ni(II), and Mn(III) complexes that have been synthesized from the heptadentate Schiff base
ligand derived from salicylaldehyde and tris(2-aminoethyl)amine. Heptadentate Schiff base ligand and its
1
13
complexes were characterized by elemental analysis, H and C NMR, IR, and UV–Vis spectroscopy. The
products were tested in vitro against the bacterial species, Staphylococcus aureus, Escherichia coli,
Pseudomonas aeruginosa, and Bacillus cereus by disc diffusion and micro-broth dilution methods. All
compounds demonstrated potent antibacterial activity higher than the Schiff base ligand. Staphylococcus aureus
was the most susceptible bacterial species to Co(III) complex while Escherichia coli and Pseudomonas
aeruginosa required a relatively higher minimum inhibition concentrations of Cr(III) and Ni(II) complexes.
Co(III) complex was the most potent inhibitor against Pseudomonas aeruginosa. Mn(III) complex was active
against Pseudomonas aeruginosa.
Keywords: heptadentate Schiff base complexes, antibacterial effects, tris(2-aminoethyl)amine, salicylaldehyde
DOI: 10.1134/S1070363215070312
INTRODUCTION
salicylaldehyde were synthesized [8]. Potential
applications of macrocyclic Schiff base as supra-
molecular devices are contrast agents in magnetic
resonance imaging (MRI), radiopharmaceuticals and as
models for biological systems [9–12]. Over recent
years the increasing microbial resistances to antibiotics
initiated considerable interest in synthesis of new
compounds with potential effects against pathogenic
bacteria and fungi [13, 14]. Biological activities of
Schiff bases are attributed to formation of stable
chelating complexes with the transition metals present
in the cells. The present study is devoted to the
synthesis and characterization of some new complexes
of trensal potentially heptadentate Schiff base formed
by condensation of salicylaldehyde and tris(2-
aminoethyl)amine. Structures of the products have
been elucidated on the basis of analytical and spectral
data. The complexes have been screened for biological
Schiff bases condensation reactions are used in
synthesis of a wide range of macrocyclic compounds.
The Schiff bases can be coordinated to a metal center
by N atom of imine or a substituent in the aromatic
ring (e.g., O, S,) and form a stable complex [1, 2].
Among synthesized heptadentate Schiff base
complexes are Cryptate [3], Cu(II) N Schiff base [4]
and two In(III) complexes [5]. Heptadentate (N O )
7
4
3
Schiff base potential ligands derived from condensa-
tion reactions of tris(2-aminoethyl)amine (tren) with
various ring substituted salicylaldehydes have been
prepared and their coordination chemistry with
lanthanide ions has been extensively studied [6, 7]. In
the complexes each tripodal heptadentate Schiff base
ligand (trensal) effectively encapsulated the lanthanide
ion and enforces a seven-coordination geometry.
+
–
Complexes of fully condensed potentially hepta-
dentate (N O ) Schiff base ligands derived from
activity against some kinds of bacteria (G and G ).
4
3
condensation of tris(3-aminopropyl) amine and
RESULTS AND DISCUSSION
Physical measurements. The macrocyclic ligand
was synthesized by condensation of salicylaldehyde
1
The text was submitted by the authors in English.
1
763

1
764
MATIN, KHOJASTEH
Scheme 1. Synthesis of the ligand.
5
6
1
4
3
H
O
NH2
+ 3
7
2
EtOH
H N
N
2
9
OH
N
N
8
3
H N
2
with tris(2-aminoethyl)amine in ethanol (Scheme 1).
The reaction proceeded smoothly to give the
corresponding Schiff base ligand in high yield. The
ligand was soluble in common organic solvents. The
Schiff base and Co(III) and Mn(III) complexes were
prepared according to the slightly modified methods
presented in publications [15–17]. All complexes
Electronic spectra of the Schiff base ligand and its
complexes were recorded in DMSO. The absorption
bonds at 257, 313, and 420 nm were attributed to the
transitions π → π* (aromatic ring), n → π* (C–O), and
n → π* (C=N) respectively. In the metals complexes
the bands were shifted to some extent due to
involvement of the imine nitrogen in coordination with
the metals ions.
(
Scheme 2) were stable at room temperature and
insoluble in water but soluble in DMSO. Purity of the
Schiff base ligand and its complexes was monitored by
TLC. IR spectrum of the free ligand demonstrated the
1
H NMR spectrum of the ligand demonstrated the
signal at 13.65 ppm of phenolic OH that was not
recorded in the spectra of complexes which indicated
the coordination bond formation between metal ion
and oxygen due to its deprotonation. Formation of the
complexes was also confirmed by the characteristic
peak of the imine hydrogen. The phenolic C–OH
signal observed at 161.33 ppm in C NMR spectrum
of the ligand had the different shift in the spectra of
complexes.
–
1
characteristic C=N band at 1637 cm that was shifted
to lower frequencies in the spectra of the metal
–
1
complexes (1612–1597 cm ), indicating the bonding
of nitrogen of the azomethine group to the metal ion
via electrons donation from nitrogen to the vacant d-
orbital of the metal ion. The ligand spectrum band at
1
3
–
1
3
450 cm (stretching and deformation of the phenolic
OH) was not recorded in the spectra of complexes
indicating deprotonation of the hydroxyl group and
coordination via oxygen. Participation of oxygen in
formation of the C–O–M bond was confirmed by the
Biological activity. Disc diffusion method. The
Schiff base and its complexes demonstrated
antibacterial activity against some bacterial strains
(Table 1). Co(III) complex demonstrated the highest
antibacterial activity against the Bacillus cereus and
Ni(II) complex was the least active against the
Pseudomonas aeruginosa. A comparative study of the
ligand and its complexes (inhibition zones values, mm)
indicated that complexes exhibited higher anti-
microbial activity than the free ligand. The data
revealed that the effect of products on gram-positive
bacteria was higher than gram-negative bacteria.
Gram-negative organisms have an outer membrane
which provides an efficient control over the uptake of
toxic substances, hence, generally are more resistant to
antibacterial agents [18].
–
1
shift of the ligand spectrum Ph–OH band (1247 cm )
in the spectra of complexes. Therefore, IR spectra
provided strong evidence for complexation of the
potentially heptadentate ligand.
Scheme 2. The proposed chemical structure of the complexes.
N
N
N
N
M
Micro-broth
dilution
minimum
inhibition
O
O
concentration. The MICs (minimum inhibition
concentrations) of the compounds were also
determined because the comparison of sizes of the
inhibition zones was not trustworthy. The antibacterial
activity data (Table 2) indicated that all complexes
O
M = Cr(III), Co(III), Ni(II), or Mn(III).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 85 No. 7 2015

SYNTHESIS, CHARACTERIZATION, AND ANTIBACTERIAL ACTIVITIES
1765
Table 1. Inhibition zones (mm) of complexes and the ligand against bacterial strains
Diameter of inhibition zone D, mm
Compound
Pseudomonas aeruginosa
Escherichia coli
Bacillus cereus
Staphylococcus aureus
Ligand (L)
Cr–L
7
10
8
8
12
14
20
25
14
–
9
12
10
17
21
15
25
–
13
10
20
11
14
20
8
Ni–L
Co–L
17
11
8
Mn–L
Chloramphenicol
Imipeneme
Cephradine
Ampicilin
DMSO
–
20
–
–
–
11
0
–
14
0
0
0
Table 2. Minimum inhibition concentration
Concentration, mg/mL
Compound
Pseudomonas aeruginosa
Escherichia coli
Bacillus cereus
Staphylococcus aureus
Ligand (L)
Cr–L
1.25
1.25
1.25
0.15
0.62
0.62
0.62
0.62
0.15
0.15
0.31
0.31
0.15
0.15
0.31
0.62
0.31
0.31
0.07
0.31
Ni–L
Co–L
Mn–L
exhibited a slightly different antimicrobial activity
compared to that of the control drugs. The lowest MIC
was detected for Co(III) complex against
Staphylococcus aureus and the highest was measured
for Cr(III) and Ni(II) complexes against Pseudomonas
aeruginosa. Overall, the complexes exhibited higher
antibacterial activity than the free ligand.
microorganisms. To the best of our knowledge this is
the first study of the antibacterial activity of
heptadentate Schiff base ligand complexes.
EXPERIMENTAL
Materials and spectral measurements. All
starting materials were purchased from Aldrich and
Merck and used without further purification. IR spectra
were recorded in KBr discs on a Perkin-Elmer 78
spectrophotometer. UV–Vis spectra were recorded in
DMSO on a Shimadzu UV-1601 spectrophotometer.
CHN analysis was carried out on a Heraeus instrument
It can be explained on the basis of chelation theory
[19], according to which the surrounding cell wall is
composed of the lipid membrane that allows only
lipid-soluble substances to enter the cell. Due to
interaction of the ligand orbitals and the metal ions and
the presence of donor groups in a complex polarity of
the metal ions is decreased. Such factors increase the
interaction between a complex and lipid cells promoting
the penetration of complexes into a cell. LPSs are the
main components of cells walls of gram-negative
bacteria. The Schiff base can penetrate the bacterial
cell membrane by coordination of the metal ion via
oxygen or nitrogen donor atom to LPS which damages
the outer cell membrane and inhibits growth of the
bacteria. So, the synthesized Schiff base ligand has
moderate inhibitory effects on the growth of tested
(
Vario EL). Melting point was determined on a Buchi
1
13
SMP-20 capillary melting point apparatus. H and C
NMR spectra were measured in DMSO-d solution by
6
a Brucker AMX 250 MHz spectrometer with TMS as
an internal standard. Metals were determined using a
Shimadzu (A.A) 680 G atomic absorption spectro-
photometer. Isolated bacteria were purchased from
Persian Type Culture Collection(PTCC).
Synthesis of tris[2-(salicylaldeneimino)ethyl]-
amine. Tris[2-(salicylaldeneimino)ethyl]amine (trensal)
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 85 No. 7 2015

1
766
MATIN, KHOJASTEH
1
3
was prepared according to the method presented in the
publication [15]. To a solution of salicylaldehyde
6.50–7.48 m (aromatic ring). C NMR spectrum, δ ,
C
9
8
7
ppm: 54.95 (C ), 59.89 (C ), 166.11 (C ), 116.22,
118.61, 121.15, 132.67, 133.97,159.64 (C to C ).
Found, %: C 62.02; H 5.4; N 10.83. Co C H N O .
1
6
(
0.06 mol, 7.3 g) in absolute ethanol (25 mL) was
added tris(2-aminoethyl)amine (0.02 mol, 2.92 g) in
absolute ethanol (25 mL). The solution was refluxed
for 1 h. The bright yellow microcrystals were filtered
off and dried in vacuum (Scheme 1). Yield 89.12%,
2
7
27
4
3
Calculated, %: C 63.04; H 5.25; N 10.89.
[
Tris(2-(salicylaldeneimino)ethyl)amine]–Cr(III)
–
1
(III). Yellow green solid, yield 72.61%, mp 341–
mp 191–193ºC. IR spectrum, ν, cm : 3450.32 (O–H),
–
1
3
43ºC. IR spectrum, ν, cm : 3070 C–H)arom, 2950
2
1
939.49 (C–H), 1637.24 (C=N), 1068.53 (N–C),
(
C–H)aliph, 1596 (C=N), 1524, 1460 (C=C), 1075
(C–O), 1290 (C–N), 537 (M–N), 410 (M–O). UV–Vis
spectrum, λmax, nm: 257, 307, and 404. H NMR
spectrum, δ, ppm: 1.03 t (6H, H ), 2.64 t (6H, H ), 8.20
247.06 (C–O), 1573.31 (C=C). UV–Vis spectrum,
1
λmax, nm: 254, 338, and 414. H NMR spectrum, δ,
ppm: 2.84 t (6H, H ), 3.59 t (6H, H ), 8.23 s (3H, H ),
6
1
9
8
7
9
8
6
5
4
.87 s (3H, H ), 6.74 t (3H, H ), 7.30 t (3H, H ), 6.84 d
7
6
5
3
13
(3H, H ), 7.55 br (3H, H ), 7.01 br (3H, H ), 7.68 br
(
3H, H ), 13.65 s (3H, OH). C NMR spectrum, δ ,
C
4
3
13
9
8
7
(3H, H ), 6.94 br (3H, H ). C NMR spectrum, δ ,
C
ppm: 55.33 (C ), 57.39 (C ), 166.62 (C ), 116.96,
1
9
8
7
1
6
ppm: 50.86 (C ), 51.36 (C ), 170.72 (C ), 112.56,
18.76, 122.52, 133.53, 135.48, 169.70 (C to C ).
Found, %: C 63.62; H 5.61; N 10.91. Cr C H N O .
Calculated, %: C 63.90; H 5.32; N 11.04.
18.75, 118.84, 131.97, 132.60, 161.33 (C to C ).
1
6
1
Found, %: C 70.68; H 6.63; N 12.21.C H N O .
27
30
4
3
2
7
27
4
3
Calculated, %: C 70.74; H 6.55; N 12.22.
Synthesis of the complexes (general procedure).
To a solution of the ligand (3 mmol) in 20 mL of
ethanol was added hydrated metal nitrate (3 mmol) and
sodium acetate (3 mmol) in 20 mL of ethanol. The
reaction mixture was stirred at room temperature
overnight followed by refluxing for 5 h. The reaction
solution was left in refrigerator overnight. The
precipitate was filtered off and washed with cold
absolute ethanol and dried in vacuum. Co(III) and
Mn(III) complexes were synthesized according to the
method presented in publications [16, 17] with slight
modifications.
[
Tris(2-(salicylaldeneimino)ethyl)amine]–Mn(III)
(
IV). Olive drab solid, yield 92.72%, mp 299–301ºC.
IR spectrum, ν, cm : 3052 C–H)arom, 2946 (C–H)aliph,
612 (C=N), 1546, 1469 (C=C), 1022 (C–O), 1295
C–N), 461 (M–N), 405 (M–O). UV–Vis spectrum,
λmax, nm: 256, 317, and 410. H and C NMR data
were not obtained because the complex was para-
magnetic. Found, %: C 63.51; H 5.4; N 10.97. Mn
–
1
1
(
1
13
C H N O . Calculated, %: C 63.53; H 5.29; N 10.98.
27 27
4
3
Bacterial species. In the study we used two gram-
negative bacteria and two gram-positive bacteria. The
standard strains of the following microorganisms were
used as test organisms: Staphylococcus aureus (PTCC
1112), Escherichia coli (PTCC 1330), Pseudomonas
aeruginosa (PTCC 1074), and Bacillus cereus (PTCC
1015).
Sodium[tris(2-(salicylaldeneimino)ethyl)amine]–
Ni(II) (I). Light yellow solid, yield 70%, mp 339–
–
1
3
(
1
41ºC. IR spectrum, ν, cm : 3060 (C–H)arom, 2949
C–H)aliph, 1597 (C=N), 1524, 1460 (C=C), 1075 (C–O),
291 (C–N), 537 (M–N), 418 (M–O). UV–Vis
1
spectrum, λmax, nm: 257, 317, and 375. H NMR
spectrum, δ, ppm: 2.64 t (6H, H ), 3.00 t (6H, H ), 8.18
t (3H, H ), 7.47 br (3H, H ), 7.09 br (3H, H ), 7.61 br
9
8
Preparation of cultures for antimicrobial
susceptibilities. Two types of media were used
(Müller-nutrient broth and Müller–Hinton agar).
Bacterial isolates were grown in each medium for 24 h
at 37ºC. The inoculum density of each bacterial isolate
was standardized with 0.5 McFarland turbidity
7
6
5
4
3
13
(
3H, H ), 6.91 br (3H, H ). C NMR spectrum, δ ,
C
9
8
7
ppm: 50.61 (C ), 56.84 (C ), 166.27 (C ), 116.61,
1
6
1
18.33, 118.44, 131.63, 132.27, 161.01 (C to C ).
Found, %: C 63.05; H 6.3; N 10.6. Ni C H N O .
2
7
27
4
3
standard. The suspension had a final inoculum of 5 ×
Calculated, %: C 63.07; H 5.25; N 10.9.
Tris(2-(salicylaldeneimino)ethyl)amine]–Co(III)
II). Dark green solid, yield 70.29%, mp 297–299ºC.
8
1
0 cfu/mL (colony-forming unit).
[
(
Antimicrobial activity. The in vitro antibacterial
–
1
IR spectrum, ν, cm : 3055 C–H)arom, 2946 (C–H)aliph
634 (C=N), 1545, 1470 (C=C), 1051 (C–O), 1288
C–N), 540 (M–N), 420 (M–O). UV–Vis spectrum,
,
screening of the Schiff base ligand and its complexes
dissolved in DMSO has been carried out against four
bacteria. We determined antimicrobial activity of
compounds by disc diffusion and micro-broth dilution
methods.
1
(
1
λmax, nm: 265, 310, and 370. H NMR spectrum, δ,
ppm: 1.04 t (6H, H ), 3.45 t (6H, H ), 8.10 (3H, H ),
9
8
7
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 85 No. 7 2015

SYNTHESIS, CHARACTERIZATION, AND ANTIBACTERIAL ACTIVITIES
Disc diffusion method (Table 1). Müller–Hinton
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 85 No. 7 2015