Polarographic determination and antimicrobial activity of Cu(II) complex with 4-chlorobenzylidene-4-aminoacetanilide

Article abstract of DOI:10.1155/2012/656598

The electrochemical behaviour of the complex of Cu(II) with 4-chlorobenzylidene-4-aminoacetanilide (CAA) was studied. It was observed that CAA forms 1:1 complex with Cu(II) in between pH 6.5 to 7.1. It was found that the reduction process of Cu(II)-CAA co

Full text of DOI:10.1155/2012/656598

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
http://www.ejchem.net
2012, 9(2), 749-755
Polarographic Determination and
Antimicrobial Activity of Cu(II) Complex
with 4-Chlorobenzylidene-4-aminoacetanilide
RIYAZ AHMAD DAR and KRISHNA KUMAR RAJ
Chemical Technological Laboratory
Department of Chemistry, Dr. H.S. Gour University, Sagar (M.P.), India
riyazabid.2008@rediffmail.com
Received 18 August 2011; Accepted 4 October 2011
Abstract: The electrochemical behaviour of the complex of Cu(II) with
4-chlorobenzylidene-4-aminoacetanilide (CAA) was studied. It was observed
that CAA forms 1:1 complex with Cu(II) in between pH 6.5 to 7.1. It was
found that the reduction process of Cu(II)- CAA complex is two electron
reversible reduction process at D.M.E. The logarithm value of stability
constant of Cu(II)-4-Chlorobenzylidene-4-aminoacetanilide (CAA) complex
has been found to be 4.85. The redox properties of the complex was
extensively investigated by electrochemical method using cyclic voltammetry
(CV).The Cu(II) complexes exhibited quasi-reversible single electron transfer
process. The Schiff base and its complex has been screened for their in-vitro
antibacterial (Escherichiacoli, Staphylococcus aureus, Vibrio cholerae and
Bacillus subtilis) and antifungal (Aspergillus niger and Penicillium liliacinum)
activities by minimum inhibitory concentration (MIC) method.
Keywords: 4-Chlorobenzaldehyde, Polarography, Cu(II)-CAA complex, MIC.
Introduction
The coordination chemistry of the metal complexes has been widely studied because of their
interesting pharmacological properties specifically the coordination chemistry of metal
complexes of Schiff bases have been studied extensively1-5 owing to their adequate
flexibility and enough selectivity towards the central metal atom. In recent years the
electrochemical techniques have led to the advancement in the field of analysis because of
their sensitivity, low cost and relatively short analysis time when compared with other
techniques. Additional application of electroanalytical techniques includes the determination
of reaction mechanisms. Redox properties of a drug can give insights into its metabolic fate
or pharmaceutical activity6-8. Thus, the aim of present work is to synthesize and characterize
Cu(II) metal complex with newly synthesized Schiff base derived from 4-Chlorobenzal-
dehyde and 4-aminoacetanilide (CAA), possessing donor sites of carbonyl oxygen and
azomethine nitrogen. The complex formation of Cu(II) with 4-Chlorobenzylidene-4-

750 RIYAZ AHMAD DAR et al.
aminoacetanilide (CAA) has been studied polarographically at D.M.E in aqueous/alcoholic
medium. Overall stability constant of Cu(II)-CAA complex was determined. The electron
transfer mechanism of the metal complex was investigated by the aid of cyclic voltammetry.
The Schiff base and its metal complexes were screened for their antimicrobial activity. The
study has been extended to compare action of ligand v/s its Cu(II) complex and thus an
overall mechanism of drug action has been attempted.
Experimental
Carbon, hydrogen and nitrogen were estimated by using Elemental Analyzer Carlo Erba
EA1108 analyzer.FTIR spectral analysis was carried out on a Shimadzu Corporation FTIR-
spectrometer, model-8400S in KBr disc and electronic sperctra (in MeOH) were recorded on
Perkin-Elmer Spectrophotometer at Department of Chemistry at Sagar University,Madhya
Pradesh,India.Molar conductivity measurements were recorded at room temperature by
ELICO-CM-82 T Conductivity Bridge with a cell having cell constant 0.51 and magnetic
moment was carried out by Gouy’s method. Electrochemical behavior of the metal
complexes was investigated by Ω Metrohm 797 VA Computrace (ion analyzer,
Switzerland.) through electrochemical software version 3.1. A three-electrode cell was
employed incorporating a dropping mercury electrode as working electrode, an Ag/AgCl
(saturated KCl) reference electrode and a platinum wire counter electrode. Mass transport
was achieved with a teflon-coated bar at approximately 400 rpm using a magnetic stirrer
(KIKA Labortechinik, Germany). A systronics digital µpH meter model-361 was used for
pH measurements.All experiments were performed at room temperature and dissolved
oxygen was removed by passing pure nitrogen through the solutions. Metal solution (0.01M)
was prepared using CuSO4 .5H2O and ligand solution was prepared by dissolving CAA
(0.01 M) in ethanol containing citric acid and Na2HPO4 solution as buffer to maintain pH.
Ionic strength was kept constant by using KCl as supporting electrolyte and gelatin (0.002%)
was used as maximum suppressor. The Polarographic study of Cu(II)-CAA has been done at
D.M.E in aqueous/ethanolic medium.ESR spectra were recorded at RSIC, I.I.T, Mumbai on
an X-band at a frequency of 9.07 GHz at a magnetic field strength of 2000±4000 Gauss at a
temperature of 300 K.
Materials
All the chemicals used were of reagent grade.
Synthesis of 4-Chlorobenzylidene-4-aminoacetanilide (CAA)
The ligand 4-Chlorobenzylidene-4-aminoacetanilide (CAA) has been synthesized by
refluxing together the 4-chlorobenzaldehyde and 4-aminoacetanilide in methanol in
equimolar ratio. The reaction mixture was refluxed on a waterbath for about 5-7 h. The
coloured condensation product was re-crystallized with methanol. Purity was monitored by
TLC using silicagel.
Synthesis of Cu(II)-4-Chlorobenzylidene-4-aminoacetanilide (CAA) complex
The metal complex has been synthesized by refluxing the methanolic solution of the copper
salt CuCl2 (0,01 mole) with the methanolic solution of the Schiff base (CAA) in 1:1 ratio on
a water bath for 3-5 h. The refluxate was kept overnight. The coloured precipitate that appeared
on cooling the solution, was washed with methanol and petroleum ether, successfully. The
resulting metal complex was re-crystallized and then dried under reduced pressure over
anhydrous CaCl2 in a desicsator. The complex is air stable and slightly soluble in ethanol,
methanol and acetone.

Polarographic Determination and Antimicrobial Activity 751
In vitro antibacterial and antifungal assay
The biological activities of synthesized Schiff base and its Cu(II) metal complex have been
studied for their antibacterial and antifungal activities by agar and potato dextrose agar
diffusion method respectively. The antibacterial and antifungal activities were done at 100,
200 and 500 μg/mL concentrations in DMF solvent by using four bacteria (E. coli, S. aureus,
V. cholerae and Bacillus subtilis) and two fungi (A. niger and P.liliacinum) by the minimum
inhibitory concentration (MIC) method9. These bacterial strains were incubated for 24 h at
37 ºC and fungi strains were incubated for 48 h at 37 ºC. Standard antibacterial
(Streptomycin) and antifungal drug (Nyastatin) was used for comparison under similar
conditions. Activity was determined by measuring the diameter of the zone showing
complete inhibition (mm).
Results and Discussion
The formation of complex of CuCl2.2H2O with Schiff base in MeOH is presented in the
following reaction.
CuCl2.nH2O + CAA → Cu(CAA)(H2O)n(Cl)n.nH2O,
where in L acts as a bidentate ligand. The metal complex is stable and hygroscopic in nature.
The complex is insoluble in common organic solvents but soluble in DMF and DMSO. The
elemental analyses shows that, the Cu(II) complex has 1:1 stoichiometry of the type ML2Cl2.
The molar conductance values are too low to account for any dissociation of the complex in
DMF, indicating the non-electrolytic nature of the complex in DMF (Table 1).
Table 1. Analytical and physical data of ligand and metal comple.
Mol.& Empirical Formula
of compound
Mol.Weight/ Yield
Ω,
μm
(B.M)
Colour
M.P, 0C
%
79
77
ohm1cm3mol-1
CAAC11H11N3ClO
[Cu(CAA)Cl2(H2O)]
Brown
Black
272.7(166)
886.4(328)
-
-
57.3
2.02
Spectral studies
A sharp band at 1625 cm-1 in the IR spectrum of the Schiff base ligand (>C=N) shifts
downward by about 10-15 cm-1 in the complex indicating coordination through azomethine
nitrogen10. The band in Schiff base ligand at 1650 cm-1 due to C=O vibration, appears at
1635±5 cm-1 in the complex. This shows chelation of C=O group with metal ion. The
spectra of complex exhibited new bands around 3445±20 cm-1 and 755±10 cm-1, which are
assignable to stretching and rocking mode of water molecules11.The new bands in the
spectra of complex at 520±5 cm-1 and 460±10 cm-1 may be due to ʋ M-O and ʋ M-N
vibrations, respectively12.
Electronic, ESR spectral and magnetic studies
The electronic spectra of CuII Complex gives a band at 12295 cm-1.The nature of the band
2
corresponds to transition Eʋ -2T2ʋ .The values of ligand field parameters 10Dq,λ and LFSE
comes to be 12295 cm-1 ,(-) 731 and 146.83kJmol-1 , respectively. This favours an octahedral
geometry of the complex13,14. The values of ESR parameters viz. gII, g, gav, G and Δg are
2.1934,2.1353,2.1546,1.4358 and 0.0581 for [Cu(CAA)Cl2(H2O)] complex. The magnetic

752 RIYAZ AHMAD DAR et al.
moment of Cu(II) complex is expected for one unpaired electron, which offers possibility of
an octahedral geometry15.
Electrochemical Studies
Determination of half wave potential of Cu(II) with CAA
A 1×10-2 M Cu(II) solution in M/10 KCl has been used to obtain polarograms of Cu(II).This
showed an E1/2 at 0.225 Vs. Ag/Agl. Polarographic study was done on Cu(II) with various
concentration of CAA. The polarograms showed that half wave potential values shifted
towards more negative value with increasing concentration of ligand indicating complex
formation, further diffusion current was found to decrease regularly with increase of CAA
concentration. Slope of the linear plots of log (i/id-i) vs. Ede was found to be in the range of
30-32 mV, thereby showing the reversible nature of reduction process involving two
electrons. The plot of half wave potential E1/2 vs. log Cx (where Cx = concentration of
complex in m mole lit1-1) have been found to be a straight line showing the formation of
most stable complex. The coordination no. (j) of the metal complex is obtained from the
slope of this plot, as may be expressed by:
d(E1/2 )/d log Cx = -j.0591/n,
where n = no. of electrons involved (here n =2). The value of j was found to be 2. This
shows that composition of the complex is 1:1 (metal: ligand). The tentative structure of 1:1
complex of Cu(II)-CAA has been given in Figure 1.
Figure 1. The tentative structure of 1:1 complex of Cu (II)-CAA.
Determination of stability constant
The stability constant of the Cu(II)-CAA complex has been determined by classical method
of Lingane, as the method is applicable for maximum coordination number and for the
stability constant of highest complex formed. The E1/2 has a linear correlation with ligand
concentration; which shows that there is only complex formed. The following equation has
been used to calculate the stability constant of the complex studied. Δ (E1/2) = 0.0591/n log β
+ j 0.0591/n log Cx. Here, Δ (E1/2) =Difference of half wave potentials of simple metal ion
and complexed ion, n =number of transferred electron, log β = Stability constant of complex
formed, j = Coordination number, Cx = concentration of ligand. Thus the average value of
log β has been found to be 4.84. Polarographic data of Cu(II)-CAA are given in Table 2.

Polarographic Determination and Antimicrobial Activity 753
Table 2. Polarographic characterstics of Cu (II)-CAA.
S.No.
Cx
0.00
0.01
LogCx
0.00
-2.00
-E1/2
0.24
Logß
-
1
2
3
4
5
6
7
8
9
0.280
0.300
0.295
0.305
0.315
0.330
0.350
0.355
5.35
5.67
3.55
3.80
4.06
5.95
5.12
5.23
0.015
0.020
0.025
0.030
0.035
0.04
-1.8239
-1.6987
-1.6020
-1.5228
-1.4559
-1.3979
-1.3467
0.045
A cyclic voltammogram of Cu(II) complex is presented in Figure 2. Voltammogram
displays a reduction peak at Epc= -1.4V with an associated oxidation peak at Epa= -0.6V at a
scan rate of 50 mV/s.The peak separation of this couple (ΔEp) is 0.8V and increases with
scan rate. The ΔEp is 1.1 and 1.4 at scan rates 100 mV/s and 200 mV/s respectively. Thus,
the analyses of cyclic voltammetric responses at different scan rate give the evidence for
quasi-reversible one electron reduction. The most significant feature of the Cu(II) complex
is the Cu(II)/Cu(I) couple. The ratio of cathodic to anodic peak height was less than one.
However, the peak current increases with the increase of the square root of the scan rates.
This establishes the electrode process as diffusion controlled16.
Potential/V
Figure 2. Cyclic voltammogram of Cu(II) complex.
In-vitro antimicrobial assay
The antimicrobial results are systematized in Table 3. From the antibacterial studies it is
inferred that, the Schiff base was found to be potentially active against S. aureus and B.
subtitles at higher concentrations. Some of the complexes showed high antibacterial activity
against S. aureus and B. subtilis than the parent ligands. In case of antifungal activity, the
Schiff base was found to be inactive at low concentrations and their complexes were found to
be active at higher concentrations. It is evident from the results that, the biological activity of
all the metal complexes is higher than the ligands. This enhancement in the activity of the

754 RIYAZ AHMAD DAR et al.
metal complexes can be explained on the basis of chelation theory17. It is, however, known that
the chelating tends to make the Schiff base act as more powerful and potent bactereostatic
agents, thus inhibiting the growth of bacteria and fungi more than the parent Schiff base18-20
.
Table 3. Antimicrobial results of Schiff base and its metal complexes.
Growth Inhibition against Bacteria in
mm
S.aureus B.subtilis V.cholerae E. coli A.Niger P. liliacinum
Growth Inhibition
against Fungi in mm
Conc.
μg/mL
Compound
100
200
500
100
200
500
500
500
11
13
18
12
15
22
28
27
10
12
19
11
13
23
30
29
11
12
15
11
13
17
29
27
12
15
17
14
17
19
27
24
11
13
20
12
16
22
25
25
11
14
18
13
15
22
24
25
C11H11N3ClO
[Cu(CAA)
Cl2(H2O)]
Streptomycin
Nyastatin
1 mL
-
-
-
-
-
-
DMF
Note: Less than 12mm - inactive; 12–16mm - moderately active; above 16mm - highly active.(-) means
no activity.
Conclusion
In this study, complex of Cu(II), with Schiff base derived from 4-Chlorobenzaldehyde and
4-aminoacetanilide was synthesized and characterized. The Schiff base act as versatile
bidentate ligand.The work has also opened up possibility of studying Cu(II)-CAA complex
by D.C polarographic method. The value of log β has been found to be 11.72. This proves
the validity of polarographic techniques for studies of 4-Chlorobenzylidene-4-aminoac-
etanilide (CAA) metal complex. The electrochemical properties of the metal complexes
revealed the quasi-reversible one electron/two electron transfer redox process. The Schiff
base and some of the metal complexes were found to be active against some of the
representative bacterial and fungal strains.
Acknowledgment
The authors are thankful to the Head, department of chemistry, Dr.Hari Singh Gour
University Sagar (M.P) India, for providing necessary laboratory facilities and to the
MPCST-Bhopal for financial support.
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