Synthesis, characterization and antibacterial activities of novel mixed ligands (azo anils and oxalate ion) copper(II) complexes

Article abstract of DOI:10.4314/bcse.v29i3.7

Three azo anils ligands; 4-[(4-nitrophenyl)diazenyl]-2-[(phenylimino)met-hyl]phenol (L1), 2- {[(2-methylphenyl)-imino]-methyl}-4-[(4-nitrophenyl)diazenyl]phenol (L2) and 2-[(naphthalen-1-ylimino)- methyl]-4-[(4-nitrophenyl)diazenyl]-phenol (L3) were synthesized and characterized using elemental analysis, FT/IR spectroscopy, ¹³C and ¹H NMR spectroscopy and UV-Vis spectroscopy. Similarly three mixed ligand complexes, {(L1)Cu(II)(OX)}, {(L2)Cu(II)(OX)} and {(L3)Cu(II)(OX)} constituting of azo anils and oxalate ion were also synthesized and characterized using elemental analysis, atomic absorption spectroscopy, FT/IR spectroscopy and UV-Vis spectroscopy and square planner geometry was suggested for Cu(II) complexes. Antibacterial activities of free ligands (azo anils and oxalate) and Cu(II) complexes were determined. Gram positive (Bacillus subtilis and Staphylococcus aureus) and Gram negative (Enterobacter aerogenes and Escherichia coli) bacteria were used for antibacterial study. The results have shown that Cu(II) complexes have privileged antibacterial activities compared to free ligands. The enhancement in antibacterial activities of transition metal complexes compared to corresponding free ligands may be attributed to structural symmetry of transition metal. The order of antibacterial activities of transition metal complexes, {(L1)Cu(II)(OX)} > {(L2)Cu(II)(OX)} > {(L3)Cu(II)(OX)}.

Full text of DOI:10.4314/bcse.v29i3.7

Bull. Chem. Soc. Ethiop. 2015, 29(3), 399-406.
Printed in Ethiopia
DOI: http://dx.doi.org/10.4314/bcse.v29i3.7
ISSN 1011-3924
 2015 Chemical Society of Ethiopia
SYNTHESIS, CHARACTERIZATION AND ANTIBACTERIAL ACTIVITIES OF
NOVEL MIXED LIGANDS (AZO ANILS AND OXALATE ION) COPPER(II)
COMPLEXES
Muhammad Ameen1*, S.R. Gilani1, Amina Naseer1, Ishrat Shoukat1 and S.D. Ali2
1Department of Chemistry, University of Engineering and Technology, Lahore-54890, Pakistan
2Nano Science and Catalysis Division, National Centre for Physics, Islamabad-45320, Pakistan
(Received October 20, 2014; revised September 7, 2015)
ABSTRACT. Three azo anils ligands; 4-[(4-nitrophenyl)diazenyl]-2-[(phenylimino)met-hyl]phenol (L1), 2-
{[(2-methylphenyl)-imino]-methyl}-4-[(4-nitrophenyl)diazenyl]phenol (L2) and 2-[(naphthalen-1-ylimino)-
methyl]-4-[(4-nitrophenyl)diazenyl]-phenol (L3) were synthesized and characterized using elemental analysis,
FT/IR spectroscopy, 13C and 1H NMR spectroscopy and UV-Vis spectroscopy. Similarly three mixed ligand
complexes, {(L1)Cu(II)(OX)}, {(L2)Cu(II)(OX)} and {(L3)Cu(II)(OX)} constituting of azo anils and oxalate ion
were also synthesized and characterized using elemental analysis, atomic absorption spectroscopy, FT/IR
spectroscopy and UV-Vis spectroscopy and square planner geometry was suggested for Cu(II) complexes.
Antibacterial activities of free ligands (azo anils and oxalate) and Cu(II) complexes were determined. Gram
positive (Bacillus subtilis and Staphylococcus aureus) and Gram negative (Enterobacter aerogenes and
Escherichia coli) bacteria were used for antibacterial study. The results have shown that Cu(II) complexes have
privileged antibacterial activities compared to free ligands. The enhancement in antibacterial activities of
transition metal complexes compared to corresponding free ligands may be attributed to structural symmetry of
transition metal. The order of antibacterial activities of transition metal complexes, {(L1)Cu(II)(OX)} ˃
{(L2)Cu(II)(OX)} ˃ {(L3)Cu(II)(OX)}.
KEY WORDS: Azo anils, Oxalate ion, Mixed ligands Cu(II) complexes, Spectroscopic study, Antibacterial
activities
INTRODUCTION
Schiff bases are gaining a centre of attention for biochemist due to their medicinal properties
and are being used in medicinal products [1]. Schiff bases with azo group and their transition
metal complexes have displayed antibacterial and antifungal activities [2]. The azomethine
(-C=N-) group in azo Schiff bases introduced an exposure to biochemical mechanism in
biological system [3-4]. It has been described earlier that biochemically active compounds
proved higher antibacterial activities when coordinated to central metal atom in compared to
free ligand [5]. Biomedicinal characteristic of free azo Schiff base ligands upon coordination to
central metal atom led the complexes for numerous biomedicinal functions such as
therapeutically energetic analgesic properties [6], anti-inflammatory [7], antiviral [8] and
antibacterial [9].
Here we are reporting antibacterial activities of three newly synthesized azo anils ligands
and their three mixed ligands complexes with Cu(II) complexes using oxalate ion as second
ligand. The azo anils ligands are: 4-[(4-nitrophenyl)diazenyl]-2-[(phenylimino)methyl]phenol
(L1), 2-{[(2-methylphenyl)imino]-methyl}-4-[(4-nitrophenyl)diazenyl]phenol (L2) and 2-
[(naphthalen-1-ylimino)methyl]-4-[(4-nitrophenyl)-diazenyl]-phenol (L3). The antibacterial
activities of azo anils ligands were enhanced after coordination with Cu(II) ion. This is due
square planner geometry of synthesized copper(II) complexes.
__________
*Corresponding author. E-mail: ch.ameen86@gmail.com

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Muhammad Ameen et al.
Scheme 1. Steps involved in the synthesis of azo anils ligands.
Table 1. Physical and analytical data of ligands and complexes.
Elemental anal. calcd./found
Compounds
Color
C
H
N
Cu(II)
m.p. (°C)
205-207
240-245
270-275
˃ 350
L1: C19H14N4O3.H2O Reddish brown 62.63/62.60 4.43/4.45 15.38/15.45
-
-
-
L2: C20H16N4O3.H2O
L3: C23H16N4O3.H2O
{(L1)Cu(II)(OX)}
{(L2)Cu(II)(OX)}
{(L3)Cu(II)(OX)}
Bright brown 63.48/63.49 4.79/4.79 14.81/14.78
Yellow green 66.66/66.65 4.38/4.39 13.52/13.52
Brown
50.76/50.74 2.64/2.62 11.28/11.30 12.79 / 12.81
Yellow brown 51.72/51.70 2.96/2.93 10.97/10.98 12.44 / 12.46
Light brown 54.90/54.93 2.76/2.73 10.24/10.23 11.62 / 11.65
˃ 350
˃ 350
EXPERIMENTAL
Chemicals
Analytical grade chemicals; CuCl2.2H2O, DMSO, methanol and ethanol were purchased from
Aldrich chemicals. The other chemicals such as aniline, methyl aniline, 1-naphthylamine and
oxalic acid were purchased from BDH. All chemicals were used without any further
purification, except vacuum dried over calcium chloride.
Instrumentations
C H, N contents in synthesized azo anils ligands and in Cu(II) complexes were found using
CHNS technique (Costech international-4100). Metal contents in synthesized complexes were
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Synthesis, characterization and antibacterial activities of novel copper(II) complexes
401
determined using Varian atomic absorption spectroscopy. The electronic spectra of azo anils and
that of corresponding complexes was determined using Perkin-Elmer lambda-25 UV-Vis
spectrophotometer and DMSO was used as solvent as well as reference. Jasco FT/IR (4100-
typeA) was used to determine FT/IR spectra (4000-400 cm-1) using KBr disk. Bruker 300 MHz
spectrometer was used to determine 13C and 1H NMR spectra.
Synthesis of azo dye
An azo dye, 2-hydroxy-5-[(4-nitrophenyl)diazenyl]benzaldehyde has been synthesized
according to standard procedure [10]. In 4.14 g (30 mmol) of 4-nitroaniline, 40 mL of
concentrated Hydrochloric acid and 20 mL of distilled water were added and heated up to 87 oC
o
until p-nitro aniline dissolved completely. Diazotization occurred below 5 C when solution of
p-nitro aniline was added to aqueous solution of sodium nitrite (2.1 g, 30 mmol). Cooled
diazonium solution was slowly poured to the salicyladehyde solution which was prepared by
adding 3.2 g (30 mmol) of salicyladehyde in 65 mL H2O, which also contain 1.2 g of NaOH and
11.1 g of Na2CO3. The mixture was continuously stirred for 35 min within ice bath. The azo dye
was obtained using gooch crucible. The obtained azo dye was washed with 20% sodium
chloride solution. To salicyladehyde, diazonium occurred at (4-position from hydroxyl group).
The end product was broadly washed with water and then with ethanol to remove any organic
o
impurities. Formula, C13H9N3O4, solid: yellow, yield: 78%; m.p. 186-188 C; UV-Vis (DMSO)
λmax/nm: 390 and 542; The FT/IR (KBr, cm−1): 3105 (-OH stretching of phenolic proton), 1660
(-CHO stretching of aldehydic group), 1475 (N=N stretching of azo group), 1335 (NO2
stretching of nitro group) and 1288 (C-O stretching of aromatic carbon and phenolic oxygen).
Synthesis of azo anils ligands
Azo anils ligands has been synthesised in accordance with published method [11]. Absolute
ethanol (60 mL) was added to 4 mmol of azo dye and stirred for 30 min. Then ethanolic
solutions of aniline, 2-methyl aniline and 1-naphthylamine each (4 mmol) were added to stirred
solution of azo dye respectively and azo anils ligands (L1, L2 and L3) were obtained in
consistent way. The whole reaction mixture was refluxed for 3 h.
4-[(4-Nitrophenyl)diazenyl]-2-[(phenylimino)methyl]phenol (L1)
o
Reddish brown solid; yield: 75%; m.p. 205-207 C; UV-Vis (DMSO) λmax/nm: 292 and 337;
FT/IR (KBr, cm−1): 3270-3370 (-OH stretching of phenolic proton), 3640-3740 (H2O, stretching
of coordinated water), 3053 (C-H, stretching of aromatic hydrogen), 1660 (-C=N, stretching of
azomethine group), 1608 (-C=C-, stretching of aromatic ring), 1435 (-N=N-, stretching of azo
1
group), 1257 (C-O, stretching of aromatic carbon and phenolic oxygen); H NMR (DMSO-d6)
/ppm: 12.50 (S, 1H), 8.50 (S, 1H), 8.40 (S, 2H), 8.0 (S, 2H), 7.80 (S, 2H), 7.50 (S, 2H), 7.20
(S, 1H), 7.25 (S, 2H), 6.95 (S, 1H); 13C NMR (DMSO-d6) /ppm: 163.20 (C-10), 160.0 (C-5),
152.40 (C-14), 151.50 (C-6), 150.40 (C-15), 129.20 (C-22), 126.10 (C-13) ,125.50 (C-4),
124.50 (C-12), 123.40 (C-23), 118.50 (C-8), 113.2 (C-3). Elemental analysis: calcd. mass
fractions of elements, w/w% for C19H14N4O3.H2O (MW = 364.35) are: C 62.63, H 4.43, N
15.38, O 17.56; found: C 62.60, H 4.45, N 15.40, O 17.53.
Figure 1. Structure of 4-[(4-nitrophenyl)diazenyl]-2-[(phenylimino)methyl]phenol.
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Muhammad Ameen et al.
2-{[(2-Methylphenyl)imino]methyl}-4-[(4-nitrophenyl)diazenyl]phenol (L2)
Bright brown solid, yield: 73%, m.p. 240-245 oC; UV-Vis (DMSO) λmax/nm: 291 and 338; FTIR
(KBr, cm−1): 3275-3380 (-OH, stretching of phenolic proton), 3650-3750 (H2O, stretching of
coordinated water), 3060 C-H, stretching of aromatic hydrogen), 1655 (-C=N, stretching of
azomethine group), 1615 (-C=C-, stretching of aromatic ring), 1430 (-N=N-, stretching of azo
1
group), 1255 (C-O, stretching of aromatic carbon and phenolic oxygen); H NMR (DMSO-d6)
/ppm: 12.60 (S, 1H), 8.55 (S, 1H),, 8.40 (S, 2H), 7.90 (S, 2H), 7.80 (S, 1H), 7.70 (S, 1H), 7.60
(S, 1H), 7.40 (S, 1H), 7.20 (S, 1H), 6.92 (S, 2H), 2.10 (S, 1H). 13C NMR (DMSO-d6) /ppm:
163.30 (C-11), 160.20 (C-6), 153.10 (C-15), 127.20 (C-23), 126.80 (C-14), 125.60 (C-18),
124.70 (C-5), 123.20 (C-13), 119.40 (C-8), 118.80 (C-24), 118.20 (C-1), 112.30 (C-4).
Elemental analysis: calcd. mass fractions of elements, w/w% for C20H16N4O3.H2O (MW =
378.38) are: C 63.48, H 4.79, N 14.81, O 16.91; found: C 63.49, H 4.78, N 14.82, O 16.87.
Figure 2. Structure of 2-{[(2-methylphenyl)imino]methyl}-4-[(4-nitrophenyl)diazenyl]phenol.
2-[(Naphthalen-1-ylimino)methyl]-4-[(4-nitrophenyl)diazenyl]phenol (L3)
o
Yellowish green solid; yield: 71%; m.p. 270-275 C; UV-Vis (DMSO) λmax/nm: 290 and 338;
FTIR (KBr, cm−1): 3272-3375 (-OH, stretching of phenolic proton), 3643-3740 (H2O, stretching
of coordinated water), 3048 C-H, stretching of aromatic hydrogen), 1655 (-C=N, stretching of
azomethine group), 1616 (-C=C-, aromatic), 1432 (-N=N-, stretching of azo group), 1360 (C-O,
phenolic); 1H NMR (DMSO-d6) /ppm: 12.40 (S, 1H), 8.60 (S, 1H), 8.50 (S, 3H), 8.10 (S, 1H),
7.90 (S, 2H), 7.85 (S, 2H), 7.70 (S, 1H), 7.60 (S, 2H), 7.55 (S, 1H), 7.10 (S, 1H); 13C NMR
(DMSO-d6) /ppm: 162.50 (C-10), 160.20 (C-5), 152.60 (C-14), 150.20 (C-6), 148.40 (C-15),
147.40 (C-25), 135.30 (C-26), 130.50 (C-27), 126.40 (C-22), 125.50 (C-13), 124.90 (C-17),
124.80 (C-24), 124.50 (C-4), 123.0 (C-12), 122.30 (C-16), 118.90 (C-8), 113.50 (C-23), 112.50
(C-3). Elemental analysis: calcd. mass fractions of elements, w/w% for C23H16N4O3.H2O (MW =
414.41) are: C 66.66; H 4.38; N 13.52, O 15.44; found: C 66.65, H 4.39, N 13.51, O 15.46.
Figure 3. Structure of 2-[(naphthalen-1-ylimino)methyl]-4-[(4-nitrophenyl)diazenyl]phenol.
Synthesis of copper(II) complexes
The stirred ethanolic solution of CuCl2.2H2O (1 mmol) was added to stirred solution of oxalic
acid (1 mmol) and azo anils (1 mmol). A colour change was observed after addition of
CuCl2.2H2O solution. To ensure completion of reaction, the reaction mixture was refluxed for 4
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Synthesis, characterization and antibacterial activities of novel copper(II) complexes
403
h. Gooch crucible was used to obtain precipitated product and washed again and again with
ethanol.
[4-[(4-Nitrophenyl)diazenyl]-2-[(phenylimino)methyl]phenolCu(II)(OX)]
o
Brown solid; yield: 45%; m.p. ˃ 350 C; UV-Vis (DMSO) λmax/nm: 287 and 333; FTIR (KBr,
cm−1): 1638 (C=N, stretching of azomethine group), 1425 to (N=N, stretching of azo group),
1333 (C-O, stretching of aromatic carbon and phenolic oxygen). The band such as 458, 588
correspond to Cu-N and Cu-O bonds, respectively. Elemental analysis: calcd. mass fractions of
elements, w/w% for C21H13CuN4O7 (MW = 496.89) are: C 50.76, H 2.64, N 11.28, Cu(II),
12.79; found: C 50.74, H 2.62, N 11.30, Cu(II), 12.81.
[2-{[(2-Methylphenyl)imino]methyl}-4-[(4-nitrophenyl)diazenyl]phenolCu(II)(OX)]
o
Yellowish brown solid; yield: 50%; m.p. ˃ 350 C; UV-Vis (DMSO) λmax/nm: 289 and 331;
FTIR (KBr, cm−1): 1625 (C=N, stretching of azomethine group), 1430 (N=N, stretching of azo
group), 1333 (C-O, stretching of aromatic carbon and phenolic oxygen). The band such as 460,
590 correspond to Cu-N and Cu-O bonds, respectively. Elemental analysis: calcd. mass
fractions of elements, w/w% for C22H15N4O7Cu (MW = 510.92) are: C 51.72, H 2.96, N 10.97,
Cu(II), 12.44; found: C 51.70, H 2.93, N 10.98, Cu(II), 12.45.
[2-[(Naphthalen-1-ylimino)methyl]-4-[(4-nitrophenyl)diazenyl]phenolCu(II)(OX)]
o
Light brown solid; yield: 47%; m.p. ˃ 350 C; UV-Vis (DMSO) λmax/nm: 287 and 330; FTIR
(KBr, cm−1): 1625 (C=N, stretching of azomethine group), 1430 (N=N, stretching of azo group),
1333 (C-O, stretching of aromatic carbon and phenolic oxygen). The band such as 462, 592
correspond to Cu-N and Cu-O bonds, respectively. Elemental analysis: calcd. mass fractions of
elements, w/w% for C25H15N4O7Cu (Mr = 546.96) are: C 54.90, H 2.76, N 10.24, Cu, 11.62;
found: C 54.93, H 2.73, N 10.23, Cu, 11.65.
Antibacterial activities
The diffusion disc method was used for determination of antibacterial activities of azo anils and
their mixed ligands Cu(II) complexes [12-17]. The glass wares were sterilized for 1 h at 170 oC.
The agar medium was prepared by the addition of nutrient agar (2.8 g) and agar technical (1 g)
in 100 mL water (distilled). The homogeneous mixture was boiled for ½ h, followed by cooling.
Dil. HCl and dil. NaOH were used for the adjustment of pH at 7.4. The agar medium was
o
autoclaved for 15 min at 121 C [18]. Agar medium (30-35 mL) was spread on Petri dishes
o
using glass spreader and incubated at 37 C for a period of 24 h. A measured quantity of test
compound was added in DMSO to attain a concentration of 1000 mg/L. In two Petri dishes (9
cm, diameter), the agar medium was spread using sterilized spreader and after solidifying the
medium, 0.2 mL of Gram positive (Bacillus subtilis and Staphylococcus aureus) and Gram
negative (Enterobacter aerogenes and Escherichia coli) bacteria were spread respectively over
it and incubated. The discs (6.00 mm, diameter) of Whatmann filter paper were soaked in the
solution of test compound and located on Petri dishes which were incubated for 48 hours at 37
oC. The area of inhibition was evaluated in millimetres.
A given amount of DMSO (0.2 mL) under same conditions was also taken as a standard for
Gram positive (Bacillus subtilis and Staphylococcus aureus) and Gram negative (Enterobacter
aerogenes and Escherichia coli) bacteria. The thickness of inhibition zone originating from
DMSO was subtracted from the inhibition zone originating from test compounds and means of
three replicate reading determined antibacterial activities.
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Table 2. Measurement of antibacterial activities of test compounds against gram positive and gram negative
bacteria.
Name of
compound
Diameter of inhibition zone measured (mm)
Bacterial species
Volume of
compound
(μL)
Gram positive
Gram negative
Escherichia
Bacillus Staphylococcus Enterobacter
Subtilis
4±1.0
2±1.0
5±1.0
8±1.0
9±1.0
14±1.0
10±1.0
14±1.0
5±1.0
aureus
4±1.0
3±1.0
8±1.0
8±1.0
8±1.0
14±1.0
13±1.0
12±1.0
7±1.0
aerogenes
coli
CuCl2.2H20
Oxalic acid
20
20
20
20
20
20
20
20
20
4±1.0
4±1.0
4±1.0
5±1.0
3±1.0
4±1.0
8±1.0
8±1.0
7±1.0
10±1.0
14±1.0
14±1.0
10±1.0
C19H14N4O3.H2O (L1)
C20H16N4O3.H2O (L2)
C23H16N4O3.H2O (L3)
{(L1)Cu(II)(OX)}
{(L2)Cu(II)(OX)}
{(L3)Cu(II)(OX)}
*2Streptomycin
8±1.0
12±1.0
14±1.0
13±1.0
8±1.0
These values are expressed as a mean of three replicate reading (±SD).
RESULTS AND DISCUSSION
FTIR spectra
FTIR spectra of synthesized azo anils and mixed ligands complexes (azo anils and oxalate ion)
were performed over KBr (4000-400, cm-1). FT/IR bands in the range 1645-1655, correspond to
coordinated oxalate group, verified from similar complexes [19]. FT/IR spectra comparison
revealed that the absorption bands in the region 3270-3380 due to –OH (phenolic group) was
not appeared in mixed ligands complexes, an indication for the loss of phenolic proton upon
formation of complexes. The new absorption band in Cu(II) spectra at 588-590 correspond to
Cu-O bond. In azo anils ligands the absorption bands at 1655-1660 was assigned to azomethine
(-C=N) group, which upon complexation shifted toward lower stretching frequency 1630-1625.
Lessened double bond character of (-C=N) azomethine was caused due to coordination between
metal and nitrogen of azomethine group. The absorption band at 458-462 was consigned to Cu-
N bond which was confirmed from similar complexes [20-22]. The band at 758 correspond to
(–OCO) group as reported earlier [19].
Electronic spectra of azo anils ligands and Cu(II) complexes
The electronic spectra of all three azo anils ligands (L1, L2 and L3) displayed two absorption
bands at 290 nm and 335 nm which were assigned to π→π* (phenyl rings) and n→π* (H-C=N
and azomethine group) transitions respectively as reported earlier [23]. Electronic spectra
regarding mixed ligands (azo anils and oxalate) complexes of copper(II) exhibited two
2
2
absorption bands at 288 nm and 330 nm which were corresponded to d-d and B1g  Eg,
transitions and square planner geometry was suggested for Cu(II) complexes as reported earlier
[24].
13C-1H-NMR spectra of azo anils
1
13C and H-NMR spectra of azo anils were recorded in (DMSO-d6) solvent. 1H-NMR exhibited
peaks at 12.60-12.40 ppm and 8.40-8.10 ppm which could be assigned to phenolic and
azomethine protons respectively. In 13C-NMR, the peaks appeared in the range of 113.60-160.40
ppm which could be assigned to aromatic carbon and signal at 163.30 ppm to azomethine group.
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Synthesis, characterization and antibacterial activities of novel copper(II) complexes
405
Antibacterial activities evaluation
The strain of Gram positive (Bacillus subtilis and Staphylococcus aureus) and Gram negative
(Enterobacter aerogenes and Escherichia coli) bacteria were used for the measurement of
antibacterial activities of copper chloride dihydrate, oxalic acid, azo anils and copper(II)
complexes. Streptomycin an antibacterial drug, under same conditions was used to compare
antibacterial activities of azo anils and respective Cu(II) complexes. The observations given in
Table 3 showed that Cu(II) complexes exhibited sky-scraping antibacterial activities as
compared CuCl2.2H2O, azo anils and oxalate ion. The Tweedy’s chelation theory and Searl’s
idea described, why antibacterial activities of metal complexes enhanced [25].
Table 3. Results of antibacterial activities test compounds against gram positive and gram negative
bacteria*.
Gram positive
Gram negative
E. aerogenes
Compounds
B.
S. aureus
E.coli
subtilis
CuCl2.2H20
+++
+++
+++
+++
+++
+++
+++
+++
+++
Oxalic acid
+++
C19H14N4O3.H2O (L1) (Ligand # L1)
C20H16N4O3.H2O (L2) (Ligand # L2)
+++
++++
++++
++++
++++
+++
C23H16N4O3.H2O (L3) (Complex-1)
{(L1)Cu(II)(OX)} (Complex-2)
{(L2)Cu(II)(OX)}
++++
+++++
+++++
+++++
++++
++++
+++++
+++++
+++++
++++
++++
+++++
+++++
+++++
++++
+++
++++
++++
+++++
+++
{(L3)Cu(II)(OX)}
*2Streptomycin
*Antibacterial activity was measured using disc diffusion method: disc diameter = 6 mm; inhibition zone = 1-5
mm beyond control limit = +++ (less active); inhibition zone = 6-10 mm beyond control limit = ++++ (moderately
active); inhibition zone = 11-15 mm beyond control limit = +++++ (highly active); inhibition zone = 0 (resistant to
bacteria). *2 Streptomycin: standard antibacterial drug.
The results showed that antibacterial activities of azo anils enhance, when these free azo
anils ligands were coordinated to transition metal atom. The antibacterial activities of mixed
ligands Cu(II) complexes were higher than corresponding ligands due to their structural
symmetry or structural features, i.e. electron withdrawing group (nitro and azomethine)
connected to benzene ring. It has been believed that azo anils (or Schiff base) having nitrogen
and oxygen system retard enzymatic activities of bacteria later than coordination to transition
metal atom.
CONCLUSION
Here we are reporting, three mixed ligands Cu(II) complexes, synthesized from azo anils
namely, 4-[(4-nitrophenyl)diazenyl]-2-[(phenylimino)methyl]phenol (L1), 2-{[(2-methyl-
phenyl)imino]methyl}-4-[(4-nitrophenyl)diazenyl]phenol
(L2)
and
2-[(naphthalen-1-
ylimino)methyl]-4-[(4-nitrophenyl)diazenyl]phenol (L3) and oxalate ligands, respectively.
Elemental analysis, AAS, FT/IR and UV-Vis spectroscopy determined square planner geometry
for these copper(II) complexes. Copper chloride dihydrate, azo anils, oxalic acid and Cu(II)
complexes were screened out for their antibacterial activities against Gram positive (Bacillus
subtilis and Staphylococcus aureus) and Gram negative (Enterobacter aerogenes and
Escherichia coli) bacteria. The results showed that Cu(II) complexes exhibit higher antibacterial
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Muhammad Ameen et al.
activities as compared to free ligands and metal salt due to structural geometry and electron
withdrawing group (nitro and azomethine) connected to benzene ring. The order of antibacterial
activities of Cu(II) complexes was {L1Cu(II)(OX)}˃{L2Cu(II)(OX)}˃{L3Cu(II)(OX)}.
In future an effort could be made to prepare Ni(II), Zn(II), Cd(II) mixed ligands complexes
using these azo anils ligands and oxalate ion because these transition metals and copper(II) have
similar chemical characteristics.
ACKNOWLEDGMENT
The author is thankful to Department of Microbiology, PCSIR, Lahore, Pakistan for their
cooperation in the biological study of synthesized ligands and complexes.
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