Complexes of some 3d-metals with a Schiff base derived from 5-acetamido-l,3,4-thiadiazole-2-sulphonamide and their biological activity

Article abstract of DOI:10.2298/JSC110111118M

Using a bidentate ligand, a Schiff base of 5-acetamido-l,3,4-thiadiazole-2- sulphonamide, complexes of transition metals having the general formula ML ₂, where M = Mn(II), Fe(II), Ni(II) and Cu(II), were synthesized. The complexes were characterized by elemental analysis, molar conductivity, magnetic moment, electronic, ESR and IR spectroscopy, and particle size analysis. The conductivity data of the complexes suggests their non-electrolytic nature. The stability constants and free energy change for the complexes were calculated. Spectral studies and magnetic susceptibility measurements revealed an octahedral geometry for all the complexes. The ligand and its complexes were screened for their fungicidal activity against Aspergillus niger and A. flavus. 2011 Copyright (CC) SCS.

Full text of DOI:10.2298/JSC110111118M

J. Serb. Chem. Soc. 76 (10) 1387–1394 (2011)
JSCS–4213
UDC 542.9+547.571+547.551+537.311.35:
546.712’722’742’562:66.022.362
Original scientific paper
Complexes of some 3d-metals with a Schiff base derived from
5-acetamido-1,3,4-thiadiazole-2-sulphonamide
and their biological activity
1
1
2
*
SUMAN MALIK , SUPARNA GHOSH and LIVIU MITU
1Department of Chemistry, Sadhu Vaswani College, Bairagarh, Bhopal – 462030, India and
2Department of Physics and Chemistry, University of Pitesti, Pitesti – 110040, Romania
(Received 11 January, revised 29 March 2011)
Abstract: Using a bidentate ligand, a Schiff base of 5-acetamido-1,3,4-thiadiazole-
-2-sulphonamide, complexes of transition metals having the general formula ML2,
where M = Mn(II), Fe(II), Ni(II) and Cu(II), were synthesized. The complexes were
characterized by elemental analysis, molar conductivity, magnetic moment, elec-
tronic, ESR and IR spectroscopy, and particle size analysis. The conductivity data
of the complexes suggests their non-electrolytic nature. The stability constants and
free energy change for the complexes were calculated. Spectral studies and mag-
netic susceptibility measurements revealed an octahedral geometry for all the
complexes. The ligand and its complexes were screened for their fungicidal activity
against Aspergillus niger and A. flavus.
Keywords: Schiff base; conductivity; non-electrolytic; stability constant; fungicidal
activity.
INTRODUCTION
5-Acetamido-1,3,4-thiadiazole-2-sulphonamide (acetazolamide) is a diuretic
drug. Diuretics are described as medicines that help to reduce the amount of wa-
ter in the body. In the present day scenario, diseases such as high blood pressure,
renal failure, diabetes, etc. have become very common. Hence, diuretic drugs were
chosen for the present study. Schiff base metal complexes played a central role in
the development of coordination chemistry. Schiff bases are widely applicable
because of their industrial and biological importance and hence were well studied
1–4
in the past.
It was established that the biological activity of a Schiff base is
5–7
altered many fold on its coordination with suitable metal ions.
The introduc-
tion of nitrogen atoms into the structure of organic compounds often resulted in
important changes in their behaviour towards metal ions. Many investigations
*Corresponding author. E-mail: ktm7ro@yahoo.com
doi: 10.2298/JSC110111118M
1387
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MALIK, GHOSH and MITU
were undertaken of the interaction of metal ions with ligands containing oxygen
8,9
and nitrogen as donor atoms. In the present study, metal complexes of Mn(II),
Fe(II), Ni(II) and Cu(II) with a Schiff base derived from 5-acetamido-1,3,4-thia-
diazole-2-sulphonamide (acetazolamide) and salicylaldehyde were synthesized
10–12
and characterized in view of their importance in biological systems.
EXPERIMENTAL
All the chemicals used in this work were of analytical reagent grade (anhydrous) and
purchased from Merck (USA).
Synthesis of Schiff base
Equimolar (0.01 M) solutions of pure drug (3.26 g) (provided by Shalaks’ Pharmaceu-
ticals, Mumbai, India) and salicylaldehyde (1.04 ml) were separately dissolved in a methanol–
–water mixture (1:1). The mixture was refluxed for four hours and kept for a day. Pale yellow
crystals of acetazolamide Schiff base formed in the reaction mixture (Fig. 1), which were
filtered and washed thoroughly with 50 % methanol–water mixture, dried under vacuum and
weighed. The colour of the solid product was pale yellow (yield 54 %). Melting point of the
Schiff base was recorded.
Fig. 1. The structure of the Schiff base.
Synthesis of complexes
For the synthesis of the complexes, 0.02 mol acetazolamide–salicylaldimine ligand
solution (AZM–SA) was prepared in 60 % acetone–water solvent and then the required metal
salt (0.01mol) was added. The resulting solution was refluxed for 4–5 h. The refluxed solu-
tions were kept for some days whereby solid crystalline compounds appeared in the solution,
which were filtered, washed with 60 % acetone–water mixture, dried and weighed. The melt-
ing points of the complexes were recorded.
Methods and apparatus applied
Elemental analyses were performed on a model 240 Perkin–Elmer elemental analyzer
(USA) at CDRI Lucknow, India. The metal contents were determined gravimetrically.13 Mag-
netic susceptibility measurements of the complexes in the solid state were determined on a
vibrating sample magnetometer (PAR, model 155, USA) at room temperature. Molar conduc-
tance measurements were realized in anhydrous DMF on a Systronics model 305 (India) con-
ductivity bridge. The electronic spectra of the metal complexes in dimethylformamide (DMF)
were recorded on a Shimadzu UV-160A UV–Vis (USA) spectrophotometer (5815–32573 cm-1).
The infrared spectra were measured on a Nicolet 400 D FT-IR (USA) spectrophotometer in
the wave number range 4000–400 cm-1 using KBr pellets. The electron spin resonance (ESR)
spectra were recorded on a Bruker DRX-300 (Germany) spectrophotometer and an X-E-4
bands spectrometer (Bruker, Germany) at LNT (liquid nitrogen temperature) and RT (room
temperature), respectively. Particle size analysis was performed at Sicart, Gujarat (India)
using a laser diffraction particle size analyzer (Cilas, model 1064 L/D, France). The melting
points of the ligand and complexes were recorded in open capillaries on a capillary melting
point apparatus (EI, model 934, IndiaLine no. 60, India).
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COMPLEXES OF SOME 3d-METALS WITH SCHIFF BASE LIGANDS
1389
Antifungal activity
The antifungal activities of the newly synthesized compounds and ligand were evaluated
by the agar growth food poison technique14 at 500 and 1000 ppm concentrations against As-
pergillus niger and A. flavus. The disc diffusion method was used for the standard drug neta-
mycin against A. niger and A. flavus using Czapek’s agar medium. The fungi were grown at
25±1 °C on dextrose agar medium. All the microbial plates were incubated for 48 h at 35 °C.
The antifungal activity of all the synthesized compounds was evaluated by percentage zone of
growth inhibition. Three replicates were performed for each dilution of the test compounds
from the screening results. All the fungal species were procured from the Microbial Type
Collection and Gene Bank, Institute of Microbial Technology (IMTECH), Chandigarh, India.
RESULTS AND DISCUSSION
Based on the physicochemical characteristics (Table I), it was found that all
the complexes were non-hygroscopic, stable at room temperature and insoluble
in water but fairly soluble in dimethyl sulfoxide (DMSO). The magnetic moment
data indicated all the complexes to be paramagnetic in nature. The molar conduc-
–1
2
–1
tance values for the complexes were found between 13–17 Ω cm mol in
15
DMSO, which indicates their non-electrolytic nature. The elemental analysis
data, formula weights and melting points are given in Table II.
TABLE I. Synthesis and physico–chemical characteristics of the complexes
Stability
Yield constant
a
Ligand–
–metal ratio
ΔF
Λm
μeff
Ligand/complex
Colour
%
log K kJ mol-1 Ω-1 cm2 mol-1 μB
L mol-1
AZM-SA
–
Pale
54
–
–
–
–
yellow
[Mn(AZM-SA)2(H2O)2]
2:1
Brown 35
11.16
–64.58
15.3
5.38
[Fe(AZM-SA)2(H2O)2]
[Ni(AZM-SA)2(H2O)2]
2:1
2:1
Black 69
11.15
10.84
–64.62
–65.12
16.4
13.0
5.78
3.18
Pale
65
green
[Cu(AZM-SA)2(H2O)2]
2:1
Dark 42
green
12.08
–71.26
14.6
1.83
a
-3
10 M solution in DMSO
TABLE II. Analytical data of the ligand and complexes
Elemental analysis, found (calcd.), %
Ligand/complex
C11H10N4O4S2
M.p., °C
242
C
H
N
S
Metal
–
39.01
(40.46)
38.46
(37.13)
37.36
(37.00)
4.08
(3.06)
2.63
(2.53)
2.53
(2.91)
18.21
(17.26)
15.69
(15.75)
15.53
(15.67)
19.50
(19.61)
18.10
(18.00)
18.18
(18.50)
(C11H9N4O4S2)2Mn⋅2H2O
(C11H9N4O4S2)2Fe⋅2H2O
3.38
(3.52)
6.88
355
360
(7.91)
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MALIK, GHOSH and MITU
TABLE II. Continued
Elemental analysis, found (calcd.), %
Ligand/complex
M.p., °C
260
C
H
N
S
Metal
7.96
(7.91)
8.86
(C11H9N4O4S2)2Ni⋅2H2O
35.00
(35.45)
36.98
(36.00)
2.80
(2.41)
2.50
14.93
(15.03)
15.69
(16.67)
17.14
(17.18)
17.93
(17.50)
(C11H9N4O4S2)2Cu⋅2H2O
199
(2.91)
(8.91)
Magnetic measurements
The magnetic moment data are presented in Table I. The Mn(II) complex
showed a value of 5.38 μ , which is slightly lower than the spin only value of
B
16
5.92 μ for high spin octahedral Mn(II) complexes. The magnetic moment of
B
the Fe(II) complex was 5.78 μ , which supports its high spin octahedral geo-
B
17
metry. The observed magnetic value of Ni(II) complex was 3.18 μ , which is
in good agreement with a spin free octahedral geometry. The Cu(II) complex
exhibited a value of 1.83 μ , which suggests an octahedral geometry around
B
18
19
B
the central metal ion.
Electronic spectra
The electronic spectra of the complexes were recorded in the solution state.
The energies of the observed spin allowed bands in all the complexes agreed with
the octahedral geometry. The electronic spectrum of Mn(II) complex shows four
–1
weak bands at bands at 16000, 19810, 20746 and 26740 cm , which can be
6
6
6
4
6
4
6
4
assigned to A → T , A → T , A → E and A → T , respec-
1g
1g
1g
2g
1g
g
1g
1g
20
tively, for an Mn(II) ion in an octahedral field. The electronic spectrum of the
–1
Fe(II) complex showed two bands. The band at 10820 cm may be assigned to
5
5
21
–1
22
the T → E transition and the other at 20490 cm to charge transfer.
2g
g
23
Similar types of transitions were reported for octahedral Fe(II) complexes. The
electronic spectrum of the Ni(II) complex displayed three bands at 12500, 18900
–1
3
3
3
3
and 26400 cm , assigned to A (F) → T (F), T (F) and T (P) transitions,
respectively, which indicate octahedral geometry of the Ni(II) complex. The
electronic spectrum of the Cu(II) complex showed two ligand field bands at
2g
2g
1g
24
1g
–1
2
2
13700 and 18000 cm , assigned to the transitions E → T and charge trans-
g
2g
fer, respectively. The electronic spectrum of the Cu(II) complex suggests an octa-
hedral geometry.25
Infrared spectra
–1
The IR spectrum of the Schiff base showed a sharp band near 1610 cm ,
26–28
which may be due to the azomethine linkage,
which was shifted to lower
frequencies in the metal complexes, indicating coordination of the metal ions
29
–1
through the azomethine linkage. The ligand showed a strong band at 3410 cm
30
due to the phenolic –OH group. This band was absent in the spectra of all the
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COMPLEXES OF SOME 3d-METALS WITH SCHIFF BASE LIGANDS
1391
metal complexes, indicating involvement of this group in the formation of the
31
–1
complexes. The bands observed at 1176, 1174, 1178, 1175 and 1173 cm are
characteristics of SO –N linkages in the Schiff base and the Mn(II), Fe(II), Ni(II)
2
32
and Cu(II) complexes, respectively. The appearance of the M–N bands at 411,
–1
–1
409, 412 and 415 cm and the M–O bands at 505, 508, 511 and 550 cm in the
complexes indicate that AZM-SA was coordinated through an O and a N
33,34
–1
atom.
The absorption bands at 3410, 3592, 3621 and 3547 cm show the
presence of coordination water in the complexes. The weak bands observed at
1280, 1286, 1282, 1288 and 1290 cm are characteristics of ν
in the Schiff base and the metal complexes, respectively. The medium frequen-
cies observed in the region 674 cm in the ligand and the respective metal com-
plexes are assigned to ν
ments are given in Table III.
35
–1
36
(phenolic)
C–O
–1
37
.
The IR spectral data and their tentative assign-
C–S
TABLE III. Infrared spectral data (cm–1) and their tentative assignments (vs – very strong, s –
strong, m – medium, w – weak)
Ligand/complex
ν(HC=N) ν(SO2N) ν(N–H) ν(M–N) ν(M–O) ν(H2O)
AZM-SA
1610 vs 1176 vs
3301 s
3300 s
3304 s
3300 s
–
–
–
[Mn(AZM-SA)2(H2O)2]
[Fe(AZM-SA)2(H2O)2]
[Ni(AZM-SA)2(H2O)2]
[Cu(AZM-SA)2(H2O)2]
1578 s
1581 s
1590 s
1174 vs
1178 s
1175 vs
505 m
508 s
511 m
550 s
411 s
409 w
412 s
415 w
3410 vs
3592 vs
3621 vs
3547 vs
1593 s 1173.5 s 3300 s
ESR spectra
The ESR spectra of the Fe(II) and Cu(II) complexes were recorded in DMSO
at LNT (liquid nitrogen temperature) and RT (room temperature). The spectrum
of the Cu complex at RT shows one intense absorption band in the high field. At
LNT, the Cu(II) complex shows four well-resolved peaks in the low field region.
The g║ and g┴ components were calculated respectively from the low and high
intensity envelopes. The values obtained for Cu(II) complex were g║ > g┴ > 2, in-
38
2
2
dicating that the Cu(II) lies predominantly in the dx –y orbital. The observed
2
2
2
values of α , β and γ of the Cu(II) complex are less than unity, which indicates
that the complex has some covalent character in the ligand environment. The
39
ESR spectrum of the Fe(II) complex at both RT and LNT, consisted of a single
broad peak of high intensity, explaining its paramagnetic character that is also
supported by the value of the magnetic moment (Table I). The values of g║ = g┴
and g were less than two, which predicts the presence of vacant energy shells in
av
40
Fe(II) ion to accept an electron pair from the ligand.
Particle size analysis
The pure acetazolamide drug (5-acetamido-1,3,4-thiadiazole-2-sulphonami-
de), its Schiff base and the Mn(II) and Cu(II) complexes derived from the Schiff
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MALIK, GHOSH and MITU
base were evaluated for their particle size distribution and average particle dia-
meter using the laser diffraction method. The average particle size of the Mn(II)
and Cu(II) complexes were found to be 2.93 and 2.76 μm, respectively, which is
smaller than that of the Schiff base (AZM-SA) with an average diameter of 4.01
μm and that of the pure drug with an average diameter of 4.16 μm. The smaller
41
particle size of the complexes results in an enhanced solubility of the drug.
Fungicidal activity
Above synthesized compounds and the ligand (Schiff base) were screened
against A. niger and A. flavus by the agar growth food poison technique to assess
their potentials as fungicidal agents. The disc diffusion method was used for the
standard drug gentamycin against A. niger and A. flavus using Sabouraud agar
medium. The percentage growth by an inhibitor at different dilutions is deter-
mined as 100(C – T)/C (where C is the diameter of the fungus colony in the
control plate and T is the diameter of fungus colony in the test plate). The zone of
inhibition based on the size around the disc was measured. The inhibition zone
percentages are recorded in Table IV. From the results, it can be observed that
the complexes showed greater activity as compared to the Schiff base. The im-
proved activities of some of the metal complexes as compared to the ligand can
be explained by the chelation theory. This theory explains that a decrease in the
polarizability of the metal could enhance the lipophilicity of the complexes, which
leads to a breakdown of the permeability of the cells, resulting in interference
42
with normal cell processes. This indicates that chelation increases the fungi-
43
cidal activity.
TABLE IV. Antifungal activity (inhibition zone, %) of Schiff base and complexes; medium:
Czapek’s agar; time: 5 days; temperature: 25±1 °C, dose = 500 ppm
Compound
A. niger
A. flavus
AZM-SA
51.23
66.38
72.25
81.46
81.45
55.23
59.47
71.23
81.78
95.67
98.55
45.53
(AZM-SA)2Mn
(AZM-SA)2Fe
(AZM-SA)2Ni
(AZM-SA)2Cu
Netamycin
CONCLUSIONS
Based on elemental analysis, magnetic moment data, conductivity measure-
ments and spectral studies, an octahedral structure for the complexes is proposed
(Fig. 2.). All the synthesized metal complexes showed biological activities
against the tested pathogenic fungal species by the well agar method. To counter
increased fungal disease to their rapid growth in the population, investigation of
the fungicidal activities of ligands and their metal complexes would be very use-
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COMPLEXES OF SOME 3d-METALS WITH SCHIFF BASE LIGANDS
1393
ful to control this harmful disease. The present work will be extended to the syn-
thesis of other metal complexes and their biological activities.
Fig. 2. The proposed structure of the complexes: M = Mn(II), Fe(II), Ni(II), Cu(II).
Acknowledgements. The authors are thankful to the Principal of Sadhu Vaswani College,
India, for providing all laboratory facilities. The authors also owe their sincere thanks to UGC
for sanctioning a UGC Research Award to Dr Suman Malik, one of the co-authors. The au-
thors are also indebted to CDRI Lucknow, India, for providing the facilities for the elemental
analysis, SICART Gujrat, India, for the electronic and ESR spectra and Vikram University
Ujjain, India, for recording the IR spectra.
И З В О Д
КОМПЛЕКСИ НЕКИХ 3d-МЕТАЛА СА ШИФОВИМ БАЗАМА КОЈЕ СУ ДОБИЈЕНЕ ИЗ
5-АЦЕТАМИДО-1,3,4-ТИЈАДИАЗОЛ-2-СУЛФОНАМИДА И ЊИХОВА БИОЛОШКА
АКТИВНОСТ
SUMAN MALIK1, SUPARNA GHOSH1 и LIVIU MITU2
1Department of Chemistry, Sadhu Vaswani College,Bairagarh, Bhopal – 462030, India и 2Department of
Physics and Chemistry,University of Pitesti, Pitesti – 110040, Romania
Полазећи од бидентатног лиганда, Шифове базе 5-ацетамидо-1,3,4-тијадиазол-2-сул-
фонамида, синтетизовани су комплекси неких прелазних метала, опште формуле ML2 (где је
M = Mn(II), Fe(II), Ni(II) и Cu(II)). За карактеризацију комплекса употребљени су елемен-
тална микроанализа, мерења моларне проводљивости и магнетног момента, електронска,
ESR и IR спетроскопија, као и метода анализе прахова. На основу мерења моларне про-
водљивости претпостављено је да су испитивани комплекси електронеутрални. Израчунате
су вредности константи стабилности, као и вредности промене слободне енергије. На основу
измерених вредности магнетних момената за све испитиване комплексе претпостављена је
октаедарска геометрија. Испитивана је антифунгална активност за лиганд и одговарајуће
комплексе на сојевима Aspergillus niger и A. flavus.
(Примљено 11. јануара, ревидирано 29 марта 2011)
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