Download RESEARCH ARTICLE Coordination Chemistry of Cadmium

RESEARCH ARTICLE
Coordination Chemistry of Cadmium Complexes with
Bioactive Schiff Bases: Synthesis, Spectral and
Biocidal Aspects
prepared 10−3M solutions in DMF at room
temperature
with
model-1601
microprocessor based conductivity meter
with a dip type cell.
Manju1*, Dinesh Kumar1
Biological Activity
Antibacterial screening In vitro antibacterial
activity of the compounds against E. coli, B.
Subtilis and fungi A. niger, A. Flavus were
carried out using agar media. The activity
was carried out using paper disc method [3032] shown in Table 1. Base plates were
prepared by pouring 10 ml of autoclaved
agar into sterilized petri dishes and allowing
them to settle. Molten autoclaved agar media
that had been kept at 48 ◦C was incubated
with a broth culture of the microbial species
and then poured over the base plate. The
discs were air dried and placed on the top of
agar layer. The plates were incubated for 24–
30 h and the inhibition zones (mm) were
measured around each disc. As the organism
grows, it forms a turbid layer, except in the
region where the concentration of
antimicrobial agent is above the minimum
inhibitory concentration, and a zone of
inhibition is seen. The size of the inhibition
zone depends upon the culture medium,
incubation conditions, rate of diffusion and
the concentration of the antimicrobial agent.
All schiff bases and their metal complexes
individually exhibited varying degree of
inhibitory effects on growth of tested
microbial species. The results evidently show
the activity of Schiff base compounds become
more pronounced when coordinated to the
metal its due to the increase their lipophilic
nature. Inhibition zone diameter mm (%
inhibition): +, (6-10); ++, (10-12), +++, (1316); ++++, (16-20).
Abstracts: 7-methyl carbazole-4-one undergoes condensation reactions with semicarbazide
hydrochloride, thiosemicarbazide, 2-aminothiazole and 2-aminobenzthiazole to give bidentate
N,O and N,S donor (E)-N-(6-methyl-2,3,4,9-tetrahydro-1H-carbazole-1-ylidene) thiazole-2amine [MCT], (E)-N-(6-methyl-2,3,4,9-tetrahydro-1H-carbazole-1-ylidene) benzthiazole-2amine [MCB], (E) - 2 - (6-methyl- 2, 3, 4, 9-tetrahydro - 1H-carbazole-1-ylidene) hydrazine
carbothioamide [MCCT], (E) – 2 - (6-methyl - 2, 3, 4, 9-tetrahydro - 1H – carbazole – 1 ylidene)hydrazine carboxamide [MCCX] Schiff base ligands. These bidentate Schiff bases
formed complexes by reacting with cadmium salt. Structures of these Schiff bases and their
complexes have been determined on the basis of their physical, analytical and spectral data.
The screening result of these compounds indicates that they possess excellent antibacterial as
well as antifungal activity against tested pathogenic organisms E. coli, B. Subtilis, A. niger and A.
Flavus. However in comparison their metal chelates have been shown to possess more
antibacterial and antifungal activities than the uncomplexed Schiff bases.
Key Words: Condensation, Screening, Uncomplexed, Schiff bases, Metal salt.
INTRODUCTION
Reaction between primary amines and
aldehydes, forming with called as Schiff base
ligands that have a huge area in inorganic
and organic chemistry. Functionalized Schiff
base ligands and their metal complexes have
increasingly become important in catalytic
synthesis of organic compounds because of
their improved chemical and physical
properties [1–5]. Schiff base ligands had a rich
history, beginning with the preparation of
the first examples, the pyridinal hydrazones,
by Stoufer and Busch [6], who were motivated
by the current interest in the π-back-bonding
by unsaturated nitrogen donors. Continuing
interest in the chemistry of Schiff bases and
their complexes because of their ability as
biologically active substances, liquid crystals,
dyes, luminophores and polymer stabilizers
[7-9] applications such as antidepressants,
antimicrobial, antitumor, antiphlogogistic,
nematocidal, and other medicinal agents
have been reported based on these
compounds [10-11] have played a major role in
the
development
of
the
inorganic
coordination chemistry providing the effects
of steric interactions on coordination
geometries. Recently metal complexes, which
contain a stable d10 electronic configuration,
have received a lot of attention in the fields
of inorganic chemistry, biochemistry and
environmental chemistry [12-20]. Also d10
complexes
have
been
considerably
investigated as potential luminescent
materials [21-23]. Cadmium belongs to a
category of heavy metal ions and is a nonessential metal [24-25]. It is very toxic even at
low concentrations, although the basis for its
toxicity it not clearly understood. The
concern arises because it accumulates in
particular food species, with potential
Department
of
Chemistry,
University, P.O. – Banasthali
Rajasthan-304022, India.
E-mail: [email protected]
*Corresponding author
1
Banasthali
Vidyapith,
Inventi Rapid: Med Chem Vol. 2012, Issue 2
[ISSN 0976-3821]
consequences for human health (renal
tubular dysfunction, hypertensive disorders,
respiratory problems and others). According
to the literature, one general mechanism for
cadmium detoxification is the chelation of
the metal [26-28].
EXPERIMENTAL
Analytical
Methods
and
Physical
Measurements
Reagents and solvents were dried and
purified by standard methods [29]. The
cadmium salt purchased from Merck. All the
chemicals employed for syntheses were of
analytical grade and were used as supplied
without further purification. FT-IR spectra
with KBr pellets were recorded on FTIR8400 S infrared spectrometer (Shimadzu) in
the 4000–400 cm−1 range. Electronic spectra
were recorded in DMF solutions double
beam spectrophotometer-2101 (Systronics)
with quartz cells of 0.5 cm path length. 1H
NMR spectra were obtained using a Brucker
FT-NMR spectrometer at 500MHz with the
samples dissolved in DMSO-d6 mixture using
TMS as internal standard. MS (m/z) spectra
of the ligands were recorded on Shimadzu
model GC–MS QP5050 [29]. X-ray powder
diffraction spectra of the compound were
obtained on the Bruckers diffractometer
using Cu (Kα) target with Ni filter at room
temperature. The wavelength used was
1.540600 Å and the reflections from 20–80◦
was recorded. Nitrogen and sulphur were
estimated using Kjeldahl’s and fusion
methods respectively [29]. Carbon, hydrogen
and oxygen of dried samples were performed
at the microanalytical laboratory of the
Department of Chemistry, Delhi University,
Delhi. Melting points were recorded on
microtech instrument of melting point
apparatus. Cadmium was estimated by
gravimetrically [29]. Magnetic susceptibilities
at room temperature were measured using a
Sherwood
Scientific
MSB
magnetic
susceptibility
balance
(MK1).
Molar
conductivity of the ligands and their
complexes were measured by freshly
Preparation of Hetroaryl Ketone
A solution of p-toluidine (0.76 g, 0.050 mol)
in aq. HCl (1.92 ml conc. HCl in 3.85 ml of
water) was treated with the cold saturated
solution of sodium nitrite (0.7g in 1.42 ml
water) while the temperature was kept at
00C. The solution was kept aside for 10 min.
it was then added portion wise to an ice
cooled mixture containing 2-hydroxy
methylidene cyclohexanone (1.26 gs, 0.05
mol), sodium acetate trihydrate (1.78 gs),
methanol (10.7 gs) and water (5.7 ml) over a
period of 0.5 hrs with stirring. The contents
was allowed to stand for further 0.5 hrs and
the resulting solid was filtered, washed with
water, dried and recrystallized from ethanol.
Now recrystallized solid product (0.36 g,
0.01 mol) in mixture of acetic acid (2.8 ml)
and HCl (0.714 ml) was refluxed on oil bath
preheated to 125-1300C for 0.5 hrs. The
content was cooled and then poured into
cold water with stirring. Brown solid i.e.
heteroaryl ketone was separate out.
Preparation of (E)-N-(6-methyl-2, 3, 4, 9tetrahydro-1H-carbazole-1-ylidene)
Thiazole-2-amine (MCT)
To a solution of heteroaryl ketone (1 g, 0.005
mol) in dry methanol (10mL) was added a
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RESEARCH ARTICLE
Table 1: Antimicrobial and antifungal activity data of ligands and their complexes investigated
Microbial species
Schiff base/Complex
E. coli
B. Subtilis
MCCX
++
+++
MCCT
++
++
MCT
+
++
MCB
++
++
Cd[MCCX]2Cl2
+++
+++
Cd[MCCT]2 Cl2
++++
+++
Cd[MCT]2 Cl2
++
++++
Cd[MCB]2 Cl2
+++
++++
Fungal species
A. Niger
C. Flavus
++
++
++
+
+
+
+
++
+++
++++
++
+++
++++
+++
+++
++++
Table 2: Analytical and physical properties of schiff base ligands and their cadmium(II) complexes
Λm
Analysis %, Found (Calc.)
Colour
M.P.
Yield
-1cm2
Compound
Ω
0C
State
%
Cd
C
H
N
O/S
mol-1
Greenish
13065.43
6.19
21.75
6.29
MCCX
90
11.5
brown
32
(65.61) (6.29) (21.86)
(6.24)
12461.79
5.82
20.50
11.79
MCCT
Light pink
91
17
28
(61.74) (5.92) (20.57)
(11.77)
Orange
15568.9
5.79
14.56
MCT
89
23.9
yellow
60
(68.30) (5.37) (14.93)
24072.91
5.79
12.56
MCB
Brown
85
22
44
(72.48) (5.17) (12.68)
19516.59
48.81
4.16
16.82
4.07
Cd(MCCX)2Cl2
Dark red
87
20
98
(16.15) (48.32) (4.63) (16.10)
(4.60)
29715.32
46.18
4.9
15.50
8.92
Cd(MCCT)2 Cl2
Yellow
89
15
80
(15.44) (46.19) (4.43) (15.39)
(8.81)
29515.23
51.93
4.48
11.45
8.50
Cd(MCT)2 Cl2
Cream
93
19
97
(15.07) (51.52) (4.05) (11.26)
(8.60)
20513.05
56.97
4.42
9.02
7.79
Cd(MCB)2 Cl2
Green
82
21
10
(13.28) (56.78) (4.05)
(9.93)
(7.58)
Table 3: Vibrational (υ cm-1) spectral data of Schiff bases and their cadmium(II) complexes
Compound
CHstr. (aliph.)
C-Cstr.
C=Cstr.
C=Nthiazole. C=Nstr.
NHstr.
MCCX
2989
1489
1450, 1511
1717
3250
MCCT
2945
1487
1444,1578
1678
3350
MCT
2990
1478
145,1610
1575
1700
3232
MCB
2945
1475
1455, 1612
1500
1678
3348
Cd(MCCX)2 Cl2
2935
1486
1455, 1525
1656
3215
Cd(MCCT)2 Cl2
2946
1485
1460,1540
1635
3311
Cd(MCT)2 Cl2
2934
1481
1444,1520
1548
1655
3220
Cd(MCB)2 Cl2
2946
1480
1455, 1540
1490
1635
3330
C-Sstr.
1310
1145
1154
1305
1144
1155
M.Wt.
Found/Calc.
g mol-1
µeff.
BM
241/256
-
267/272
-
286/281
-
327/331
636/695
752/728
740/746
881/846
Cd-Nstr.
525
527
525
535
Dia
magnetic
Dia
magnetic
Dia
magnetic
Dia
magnetic
Cd-Sstr. Cd-Ostr
466
470
-
Table 4: 1HNMR chemical shifts (δ ppm) of the ligand and its cadmium complexes
Schiff base/ Complex
Proposed assignment of protons
MCCX
12.1(NH pyrole), 7.3-7.6 ( ArCH), 2.5-1.1(CH2), 6.20 (2H,s,NH2),8.02(CH=N), 10.9 (NH)
MCCT
12.1(NH pyrole), 7.3-7.6 ( ArCH), 2.5-1.1(CH2), 6.20 (2H,s,NH2),8.02(CH=N), 10.9 (NH)
MCT
12.1(NH pyrole), 7.3-7.6 ( ArCH), 2.5-1.1(CH2), 8.02(CH=N)
MCB
12.1(NH pyrole), 7.3-7.6 ( ArCH), 2.5-1.1(CH2), 8.02(CH=N)
Cd(MCCX)2 Cl2
12.1(NH pyrole), 7.3-7.6 ( ArCH), 2.5-1.1(CH2), 6.8 (2H,s,NH2),8.20 (CH=N), 11.2 (NH)
Cd(MCCT)2 Cl2
12.1(NH pyrole), 7.3-7.6 ( ArCH), 2.5-1.1(CH2), 6.8 (2H,s,NH2),8.24 (CH=N), 11.3 (NH)
Cd(MCT)2 Cl2
12.1(NH pyrole), 7.3-7.6 ( ArCH), 2.5-1.1(CH2), 8.02(CH=N), 8.26 (CH=N)
Cd(MCB)2 Cl2
12.1(NH pyrole), 7.3-7.6 ( ArCH), 2.5-1.1(CH2), 8.02(CH=N), 8.27 (CH=N)
solution of 2-aminothiazole in dry methanol
(10mL) and irradiated under microwave
irradiations till the completion of reaction.
After completion of the reaction, the solvent
of brown solution was reduced using rotary
evaporator to give the Schiff base ligand. For
purification, brown precipitate of Schiff base
obtained was recrystallized with absolute
ethanol and dried under vacuum to obtain
the ligand with good purity with yield of
72%. The Schiff base is soluble in
dichloromethane,
chloroform,
acetone,
dimethylsulfoxide, dimethylformamide. Same
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procedure was employed for the preparation
of [MCB], [MCCT] and [MCCX] ligands by
using the corresponding reagents in the
same molar ratio.
Preparation of CdL2 (L = [MCT], [MCB],
[MCCT] and [MCCX]) Complexes
The cadmium (II) complexes were prepared
by stepwise addition of the respective ligand
[MCT], [MCB], [MCCT] or [MCCX] (0.002
mol) in dry methanol (15mL) to the 0.001
mol of cadmium(II) chloride in dry methanol
(15mL) and irradiated under microwave for
4-5 min. The complexes, [CdL2X2] so obtained
were filtered off, washed with ethanol twice
and dried under vacuum. The precipitates
were recrystallized from ethanol and dried
under vacuum and were kept in a desiccator
over fused calcium chloride. The yields are as
in table 2.
RESULTS AND DISCUSSIONS
Physical Data
The analytical and physical data of the Schiff
base ligand and its complexes are given in
Table 2. The analytical data show that the
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CH3
O
NH2-C-NHNH2
N
H
HN
N
C
MCCX
O
NH2
CH 3
S
NH2 -C-NHNH2
N
H
HN
N
MCCT
CH3
C
S
NH2
N
N
H
CH 3
NH2
O
S
N
H
S
N
MCT
N
CH 3
N
H
N
S
NH 2
S
N
N
Figure 1: Synthetic route of different ligand, (L= [MCCX], [MCCT], [MCT] and [MCB])
MCB
N
H
N
H
N
N
HN
Cd
Cl
N
H2N
Cd
Cl
S
XCl
X
NH2
N NH
H
N
N
S
Cl
N
H
N
Figure 2: Proposed structures of the complexes
metal halides to ligand ratio are 1:2 in all the
complexes. All of the isolated complexes are
soluble in organic solvents such as
chloroform,
dichloromethane,
dimethylformamide and dimethylsulfoxide
and insoluble in alcohols. The melting points
of the complexes were at 140–240 ◦C. The
complexes can be presented by the general
formula of [CdL2X2] (L= [MCCX], [MCCT],
[MCT] and [MCB]) as shown in Figure 2. All
of the newly synthesized metal complexes
were air and moisture stable. The low molar
conductivities of 10−3M solutions of all
complexes in DMF solvent at room
temperature were in the range of 13.77–
23.74 cm2 Ω−1 mol−1 which shows them to be
Inventi Rapid: Med Chem Vol. 2012, Issue 2
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non-electrolytes so that the complexes are
not dissociated in DMF solution and the
anions are also coordinated to the metal ion.
Electronic Spectra
The electronic absorption spectra are often
very helpful in evaluation of results
furnished by other method of structural
investigation.
Electronic
spectral
measurements were used for assigning the
stereochemistry of metal ion in the
complexes. The UV-VIS spectra of ligands, a
band arising from C=N chromospheres at
370 nm shifted to a shorter wavelength for
complexes such a shift is due to the donation
of lone pair of electron by nitrogen of the
ligand to the central metal ion. A band at
medium intensity 270 and 275 nm remains
unchanged in the spectra of the complexes.
These bands assigned to -* (benzenoid)
electronic transitions.
FT-IR Spectra
In order to study the binding mode of ligand
to metal in the complexes, the ir spectrum of
free ligand was compared with the spectra of
metal complexes. The most characteristic
absorptions of the bidentate Schiff base
ligands and their complexes are summarized
in Table 3. The corresponding cadmium (II)
complexes exhibit ligand absorptions at
different
frequencies
indicating
the
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RESEARCH ARTICLE
coordination of the ligand. The band due to
the imine group C=N mode of free ligand at
1678 cm−1 [33-43] is shifted by 17–20 cm−1 to
lower frequencies in the spectra of the
complexes indicating coordination through
the iminic nitrogen of the Schiff base. In the
spectra of the complexes, the absorption at
470-510 cm−1 regions that are absent in the
spectrum of the ligand may be due to
symmetrical and asymmetrical vibration
modes of Cd–N [44-47] supporting the
coordination of iminic nitrogen’s. A band at
1145 cm-1 due to the C-S in thiazole ligand
was a remains unchanged on complexation
indicates
un-involvement
of
S
in
coordination to metal center [48]. While in
case of carbothioamide peak at 1310 cm-1
shifts to a lower frequency showing
involvement in coordination.
Mass Spectral Investigation
The mass spectrum of the ligand in presents
the peak corresponding to the molecular ion
(M+) peak at 281 lends support to the
formula shown in Figure. 1 and also indicates
stability of ligand. The complexes are
monomers as revealed by their formula
weight determinations.
1H NMR Spectra
The 1H spectra were recorded using DMSO-d6
as solvent at and their data were
summarized in Tables 4. The NMR spectra of
the ligands and its cadmium complexes show
well-resolved signals as expected and
strongly support the geometry of the
compounds, suggesting well coordination of
the iminic nitrogen’s to metal ions.
X-ray Spectral Studies
Cell dimensions of the complex [Cd (MCT) 2]
were successfully calculated, which were
found to be a = 16.10349 Å, b = 10.41570 Å, c
= 9.58846 Å, α = β = γ =90◦ and ɵ range for
data collection (degree) 1.33–23.06. All
these data agree with the orthorhombic
system of the complex.
CONCLUSIONS
The Cd(II) metal template condensation of
four ligands MCT, MCB, MCCX, MCCT starting
from
semicarbazide
hydrochloride,
thiosemicarbazide, 2-aminothiazole and 2aminobenzthiazole with ketone moiety have
been successfully achieved. Cd (II)
coordinated to the N and S/O atoms and form
octahedral geometry. Metal chelates have
Inventi Rapid: Med Chem Vol. 2012, Issue 2
[ISSN 0976-3821]
been shown to possess more antimicrobial
activities than the uncomplexed ligands. The
complexes are monomers as revealed by
their formula weight determinations.
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Acknowledgements: We are thankful to Professor
Aditya Shastri, Vice Chancellor of Banasthali
University for kindly extending the facilities of
‘‘Banasthali Centre for Education and Research in
Basic Sciences” sanctioned under CURIE
programme of the Department of Science and
Technology, New Delhi.
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