Synthesis, spectral characterization, and antimicrobial activities of schiff base complexes derived from 4-aminoantipyrine

Article abstract of DOI:10.1080/00387010.2013.820196

Novel cobalt (II), nickel (II), copper (II), and zinc (II) complexes were synthesized from Schiff base ligand derived from 4-aminoantipyrine, vanillin, and o-anisidine. The structural features were derived from their elemental analysis, molar conductance,

Full text of DOI:10.1080/00387010.2013.820196

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Synthesis, Spectral Characterization and Antimicrobial
Activities of Schiff Base Complexes Derived From 4-
Aminoantipyrine
B. Manjula a , S. Arul Antony a & C. Justin Dhanaraj b
a PG and Research Department of Chemistry , Presidency College , Chennai , Tamil Nadu ,
India
b Department of Chemistry , Anna University College of Engineering , Nagercoil , Tamil
Nadu , India
Accepted author version posted online: 22 Jul 2013.
To cite this article: Spectroscopy Letters (2013): Synthesis, Spectral Characterization and Antimicrobial Activities of Schiff
Base Complexes Derived From 4-Aminoantipyrine, Spectroscopy Letters: An International Journal for Rapid Communication,
DOI: 10.1080/00387010.2013.820196
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SYNTHESIS, SPECTRAL CHARACTERIZATION AND ANTIMICROBIAL
ACTIVITIES OF SCHIFF BASE COMPLEXES DERIVED FROM 4-
AMINOANTIPYRINE
B. Manjula1, S. Arul Antony1,*, C. Justin Dhanaraj2
1PG and Research Department of Chemistry, Presidency College, Chennai, Tamil Nadu,
India, 2Department of Chemistry, Anna University College of Engineering, Nagercoil,
Tamil Nadu, India
E-mail: aruantsam@gmail.com
Abstract
Novel cobalt(II), nickel(II), copper(II) and zinc(II) complexes were synthesized from
Schiff base ligand derived from 4-aminoantipyrine, vanillin and o-anisidine. The
structural features were derived from their elemental analysis, molar conductance,
magnetic measurements, and various spectroscopic techniques such as infrared,
ultraviolet visible, nuclear magnetic resonance and electron paramagnetic resonance
spectroscopy. Antimicrobial screening tests were performed against bacteria and fungi.
The comparative study of the minimum inhibitory concentration values of the Schiff base
and its metal complexes indicate that the metal complexes exhibit greater antimicrobial
activity than the free ligand.
KEYWORDS: Schiff base, 4-Aminoantipyrine, Vanillin, o-Anisidine, Ultraviolet visible
INTRODUCTION
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Schiff bases are widely designed and prepared for its high yield and one-step procedure
via condensation of amines and aldehydes.[1] The various classes of Schiff bases that can
be prepared by condensation of different types of amines and carbonyl compounds are
very popular due to diverse chelating ability.[2] Schiff bases are widely used as analytical
reactants since they allow simple and inexpensive determination of several organic and
inorganic substances.[3] They also form stable complexes with metals that perform
important role in biological systems.[4-7] The booming application of metal complexes in
the treatment of numerous human diseases is vigorously expanding area in biomedical
and inorganic chemistry.[8,9] In recent years,
4-aminoantipyrine transition metal
complexes and their derivatives have been extensively examined due to their wide
applications in various fields.[10, 11] Schiff bases of 4-aminoantipyrine and its complexes
have a variety of applications in biological, clinical, analytical and pharmacological
areas.[12, 13] Studies of a new kind of chemotherapeutic Schiff bases are now attracting
the attention of biochemists.[14, 15] The coordinating properties of 4-aminoantipyrine have
been modified to give a flexible ligand system, formed by condensation with a variety of
reagents like aldehydes, ketones, thiosemicarbazide and carbazide etc.[16-27] Here in we
report the synthesis, characterization and antimicrobial studies of Schiff base derived
from vanillin,
4-aminoantipyrine and o-anisidine.
MATERIALS AND METHODS
All the chemicals, 4-aminoantipyrine, vanillin, o-anisidine and cobalt(II), nickel(II),
copper(II) and zinc(II) acetates are Analar grade and were purchased from E-Merck and
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Loba Chemie, India. The solvents like ethanol, methanol, etc were purified and dried by
the standard procedures.[28, 29]
Molar conductance of the complexes was measured using a coronation digital
conductivity meter. Magnetic moments were measured by Gouy method and corrected
for the diamagnetism of the component using Pascal’s constants. Infrared (IR) spectra
were recorded on Schimadzu FT IR 8400S spectrometer in 4000-400 cm-1 range using
KBr pellet. The ultraviolet visible(UV-Vis.) spectra were recorded on a Schimadzu UV
spectrometer in the wavelength range 200-800 nm. The electron paramagnetic resonance
(EPR) spectrum was recorded by using Bruker EMX EPR instrument at 300 & 77 K. The
nuclear magnetic resonance (1H-NMR) spectra were recorded on a Bruker NMR 300
MHz spectrometer using DMSO d6 as solvent and TMS as internal standard. The
antimicrobial activity was determined with disc diffusion method. Stock solutions were
prepared by dissolving the compounds in DMSO and serial dilutions of the compounds
were prepared in sterile distilled water to determine the minimum inhibitory
concentration (MIC).
PREPARATION OFTHE LIGAND
An ethanolic solution of 4-aminoantipyrine (2.03 g, 0.01 mol, 20 mL) was taken in a
dropping funnel and added drop wise to the ethanolic solution of vanillin (1.52 g, 0.01
mol,
20 mL) with constant stirring for 3 h. The yellow compound formed was filtered
and recrystallised from ethanol. The ethanolic solution of the solid product (3.373 g, 0.01
mol) was added to an ethanolic solution of o-anisidine (1.2 mL, 0.01 mol). The mixture
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was refluxed for about 30 h. The contents were poured into crushed ice, the dark yellow
solid was separated, filtered and recrystallised from ethanol (Scheme 1).
PREPARATION OF THE COMPLEXES
A solution of metal acetate in ethanol (0.01 mol) was refluxed with hot ethanolic solution
of Schiff base (0.01 mol) with few drops of glacial acetic acid on a water bath for 5 h.
Then the solution was reduced to one third of its volume and cooled. The precipitated
complex was filtered, washed with ethanol and dried in vacuum.
ANTIMICROBIAL ACTIVITY
Test Organisms
The bacterial species Pseudomonas aeruginosa (P. aeruginosa), Proteus mirabilis
(P. mirabilis) and Escherichia coli (E. coli) and fungal species Aspergillus niger (A.
niger), Aspergillus fumigatus (A. fumigatus) and Candida albicans (C. albicans) were
used as test organisms and they are maintained on Mueller Hinton Agar solid media
(MHA) and Sabouraud’s dextrose (SDA) media.[30-32]
Assay Of Antimicrobial Activity
Agar diffusion assay was carried out to evaluate the antimicrobial activity of some
synthesized compounds. The plates were incubated at 37 oC for 24 h during which
activity was evidenced by the presence of a zone of inhibition surrounding the well and
antibacterial and antifungal activity was expressed as mean of diameter of inhibition
zones (mm) produced by the synthesized compounds when compared to controls. The
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MIC(minimum inhibitory concentration) value was recorded as the lowest concentration
of drug in the medium that showed no microbial growth by visual observation.
EXPERIMENTAL
MHA and SDA were prepared with lawn culture using desired test organisms. The
inoculated plates were kept aside for few minutes. Using well cutter two wells were made
in the plates at required distance. In each step of well cutting, the well cutter was
thoroughly wiped with alcohol. Using sterilized micropipette, 20 µL of compound extract
was added into one well and to another well the same volume of corresponding control
was added. After diffusion, the plates were incubated at 37 ºC for 24 h. After incubation,
the growth of inhibition was analyzed and the results were recorded.
RESULTS AND DISCUSSION
All the metal complexes were coloured solids, stable towards air and moisture. They get
decomposed at higher temperature and were insoluble in common organic solvents and
soluble in DMSO and DMF. The elemental analysis data (Table 1) of the ligand (L) and
its metal complexes are consistent with the calculated results from the empirical formula
of each compound. The purity of the Schiff base and its metal complexes was confirmed
by TLC. The low conductance values of the complexes (Table 2) support the non-
electrolytic nature.[33] The observed magnetic moment value of cobalt(II) complex is 4.71
BM, which is the expected range for tetrahedral cobalt(II) complexes. For tetrahedral
nickel(II) complexes, µ expected is in the range 2.9-3.9 B.M. In the present case, the
nickel(II) complex has the magnetic moment of 3.1 B.M. in accordance with tetrahedral
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geometry. The square planar copper(II) complexes exhibit magnetic moments from 1.8-
2.1 B.M. The magnetic moment obtained for the present copper(II) complex is 1.95 B.M.
The magnetic moments obtained are in accordance with the proposed geometries. zinc(II)
complex with d10 electronic configuration is diamagnetic[34] and would have tetrahedral
geometry. The proposed structure of the complexes is given in Fig. 1.
In order to study the binding mode of the Schiff base to the metal in the complexes, the
IR spectrum of the free ligand was compared with the spectra of the complexes. The IR
spectra of ligand (2a) and its copper(II) complex (2b) are given in Fig. 2a, b. The IR
spectrum of the ligand shows a strong band at 3104 cm-1 assigned to OH group. The
phenolic OH stretching appear at 3104 cm-1 and does not undergo any appreciable change
in the spectra of complexes, indicates that phenolic OH group does not participate in the
bond formation with the metal. The spectrum of the ligand shows the characteristic –C=N
band at 1628 cm-1 which is shifted to lower frequencies in the spectra of complexes
(1585-1579 cm-1) indicates the coordination of azomethine nitrogen atom with metal ion.
The spectra of the metal complexes also show some new bands in the 500-482 cm-1 and
474-449 cm-1 which are probably due to the formation of M-O and M-N bonds
respectively.[35, 36] Two bands were observed at 1625 cm-1 and 1397- 1378 cm-1
assigned to υasym(COO-) and υsy(COO-) in complexes.[37] The vibrational frequencies of
the free ligand and the metal complexes are given in Table 3.
The electronic spectral measurements were used for assigning the stereochemistry of
metal ions in the complexes based on the positions and number of d-d transition peaks.
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The electronic absorption spectral data of the Schiff base ligand and its complexes were
recorded in DMF in the range of 200-800 nm is presented in Table 4. The absorption
spectrum of free ligand consists of an intense band centered at 345 nm attributed to n-π*
transitions of the azomethine group. Another intense band in higher energy region of the
spectrum of the free ligand was related to π-π* transitions of benzene rings. These
transitions are also found in the spectra of the complexes, but they are shifted towards
lower frequencies confirming the coordination of the ligand with the metal ion. Further
the d-d transition of the complex showed a broad band centered at 535-542 nm for
cobalt(II), nickel(II) and copper(II) complexes. The spectra of cobalt(II) complex shows
band at 542 nm, which can be attributed to 4A2(F)→4T1(P) transition for the tetrahedral
geometry. The electronic spectra of nickel(II) complex shows d-d transition at 540 nm,
due to 3T1(F) → 3T1(P) transition for tetrahedral nickel(II) complex. The copper(II)
complex shows broad band at 535 nm, due to 2B1g → 2A1g transition[38, 39] suggesting
square planar geometry. The zinc(II) complex does not show any d-d transitions. In
general four coordinate zinc(II) complexes would have tetrahedral geometry.
The EPR spectrum of copper(II) complex (Fig. 3a, b) provide information about the
extent of the delocalization of unpaired electron. In the present study the EPR spectrum
of the copper(II) complex were recorded at liquid nitrogen temperature (77 K) and room
temperature (300 K). From the spectra of copper(II) complex gll, g┴, gave and G have
been calculated as 2.1418, 2.0057, 2.0497 and > 4 respectively. EPR spectra of the
copper(II) complex revealed the trend gll>g┴ shows that the unpaired electron is
2
delocalized in dx -y2 orbital in the ground state of metal and spectra are characteristics of
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axial symmetry. The parameter gave was obtained by equation [gave=1/3(gll+2g┴)].
Kivelson and Neiman have reported that gll>2.3 are the characteristics of an ionic
environment and g11<2.3 indicate a covalent character in metal ligand bonding. Applying
this criterion gll (2.1418) indicate the prevalence of covalent character in metal ligand
bond.[40, 41] The exchange coupling interaction has been explained by Hathaway
expression G = gll-2.0023/g┴ – 2.0023. According to Hathaway if the value of G is
greater than four (G>4) the exchange interaction is negligible whereas when the value of
G is less than four (G<4), a considerable exchange interaction is indicated in the
complex. It is observed that G value of the complex is greater than four (G>4) indicating
the exchange interaction is negligible.[42, 43] When the complex is frozen to liquid
nitrogen temperature, four well resolved peaks are obtained. This shows square planar
geometry of the copper(II) complex.
The 1H-NMR spectra of the ligand (Fig. 4a) and its zinc(II) complex (Fig. 4b) were
recorded in DMSO d6. The 1H-NMR shows peak at δ 5.9 to the aromatic OH. The
presence of this peak noted for the zinc(II) complex confirms the –OH proton free from
complexation. The peak for benzene rings appears in the region δ 6.9-7.4. The peaks for
O-CH3, C-CH3 and N-CH3 appear in region δ 3.1 (O-CH3 for vanillin moiety), δ 3.9 (O-
CH3 for o-anisidine moiety), δ 1.61 and δ 2.4 respectively. The azomethine proton signal
at δ 9.531 in the spectrum of zinc(II) complex is shifted to downfield compared to the
free ligand, suggesting deshielding of azomethine group due to the coordination with
metal ion. The rest of the peaks appear in the same region.[44]
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The reactivity of the synthesized compounds towards the biological systems is important
features of the current research and Schiff bases of transition metal complexes. All the
synthesized compounds (Tables 5 & 6) showed a remarkable biological activity against
all the bacterial and fungal species under investigation. Among the synthesized
compounds nickel(II) complex showed very good antibacterial and antifungal activity.
The toxicity of the complexes was found to be better than the ligand owing to the theory
of Tweedy.[45-50] This is probably due to the greater lipophilic nature of the complexes.
Such increased activity of the metal chelates can be explained on the basis of Overtone’s
concept of cell permeability. The lipid membrane that surrounds the cell favors the
passage of lipid soluble materials due to which liposolubility is an important factor which
controls the antimicrobial activity. On chelation, the polarity of the metal ion will be
reduced to a greater extent due to the overlap of the ligand orbital and partial sharing of
positive charge of the metal ion with donor groups. Further, it increases the delocalization
of π electrons over the whole chelate ring and enhances the lipophilicity of the
complexes. This increased lipophilicity enhances the penetration of the complexes into
lipid membrane and blocks the metal binding sites on enzymes of microorganisms.
CONCLUSION
Cobalt(II), nickel(II), copper(II) and zinc(II) complexes with Schiff base derived from
vanillidene-4-aminoantipyrine and o-anisidine have been synthesized and characterized.
Elemental analysis and low molar conductance values indicate mono nuclear and non
electrolytic nature of the complexes. The Schiff base acts as a bidentate ligand and the
possible coordination sites are two azomethine nitrogen atoms. Spectral data and
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magnetic moment studies suggest that cobalt(II), nickel(II), and zinc(II) complexes have
tetrahedral geometry while the copper(II) complex has square planar geometry.
Antimicrobial studies show that the complexes are more active than the ligand.
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TABLE 1. Physical characterization and analytical data of ligand and complexes
Compound
Mol. Formula Mol. Wt Found (Calcd.) %
(Colour)
(Yield
%)
C
H
N
O
M
-
L
C26H26O3N4
(Yellow)
442 (85) 70.31 5.35 12.18 10.67
(70.59 (5.88 (12.67 (10.86
)
)
)
)
[CoL(OAc)2 C30H32O7N4Co 618.9
(Pink) (53)
57.93 5.38 8.95
18.01 9.13
]
(58.17 (5.17 (9.05) (18.10 (9.52)
)
)
)
[NiL(OAc)2 C30H32O7N4Ni 618.7
(Green) (57)
58.01 5.10 9.01
18.10 9.09
]
(58.18 (5.17 (9.05) (18.10 (9.49)
)
)
)
[CuL(OAc)2 C30H32O7N4Cu 623.5
(Brown) (54)
57.31 5.03 8.48
17.35 10.05
]
(57.74 (5.13 (8.98) (17.96 (10.18
)
)
)
)
[ZnL(OAc)2 C30H32O7N4Zn 625.3
(Brown) (68)
57.15 5.0
8.56
17.48 10.06
]
(59.37 (5.12 (8.96) (17.91 (10.46
)
)
)
)
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TABLE 2. Molar conductance data of metal complexes
Compound
Molar conductance (Ω-1cm2 mol-1)
[CoL(OAc)2]
[NiL(OAc)2]
[CuL(OAc)2]
[ZnL(OAc)2]
5.20
7.50
10.20
11.25
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TABLE 3. IR spectral data of ligand and complexes
Compound
L
OH(Phenolic) C = N
M-O
-
M-N
-
3104
3104
3112
2923
3150
1628
1579
1579
1585
1581
[CoL(OAc)2]
[NiL(OAc)2]
[CuL(OAc)2]
[ZnL(OAc)2]
482
495
500
490
453
449
474
464
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TABLE 4. UV-Vis. spectral and molar conductance data of ligand and complexes
Compound
L
d-d π-π*
n→π* Geometry
-
260, 253
345
347
-
[CoL(OAc)2]
542 245, 279
Tetrahedral
[NiL(OAc)2]
[CuL(OAc)2]
540 249, 289
535 241, 27
348
349
Tetrahedral
Square Planar
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TABLE 5. Antibacterial activities of ligand and its complexes (Diameter of inhibition
zone in mm)
Compound
L
P. Aeruginosa
P. mirabilis E. coli
-
-
-
[CoL(OAc)2]
[NiL(OAc)2]
[CuL(OAc)2]
[ZnL(OAc)2]
Ciprofloxacina
aStandard
-
-
-
18
7
20
5
20
25
-
-
-
18
23
17
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TABLE 6. Antifungal activities of ligand and its complexes (Diameter of inhibition zone
in mm)
Compound
L
A. niger
A. fumigatus
C. albicans
-
-
-
[CoL(OAc)2]
[NiL(OAc)2]
[CuL(OAc)2]
[ZnL(OAc)2]
-
-
-
11
9
-
8
-
21
27
-
-
Amphoterecin-Ba 20
aStandard
21
-
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Scheme 1. Synthetic route of Schiff base ligand
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Figure 1. Proposed structure of metal complexes
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Figure 2. IR spectra of (a) ligand and its (b) copper(II) complex
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Figure 3. EPR spectra of copper(II) complex at (a) 77 K and (b) 300 K
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Figure 4. NMR spectra of (a) ligand and its (b) zinc(II) complex
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