Synthesis and antibacterial activity of Zn(II) Schiff base complexes derived from 3-acetyl-2H-chromen-2-one

Article abstract of DOI:10.14233/ajchem.2015.18720

Zn(II) Schiff base complexes viz., bis[(E)-3-(1-(p-tolylimino)ethyl)-2H-chromen-2-one]zinc(II), bis[(E)-3-(1-((4-chlorophenyl)- imino)ethyl)-2H-chromen-2-one]zinc(II) and bis[(E)-3-(1-((2-nitrophenyl)imino)-ethyl)-2H-chromen-2-one]zinc(II) derived from 3-

Full text of DOI:10.14233/ajchem.2015.18720

Asian Journal of Chemistry; Vol. 27, No. 9 (2015), 3440-3444
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2015.18720
Synthesis and Antibacterial Activity of Zn(II) Schiff Base
Complexes Derived from 3-Acetyl-2H-chromen-2-one
1,*
1
2
1
3
1
HABIB HUSSAIN , SYEDA RUBINA GILANI , FARKHANDA JABEEN , ZULFIQAR ALI , HAJIRA REHMAN and IMDAD HUSSAIN
1Department of Chemistry, University of Engineering and Technology, Lahore, Pakistan
2Department of Botany, University of Punjab, Lahore, Pakistan
3Department of Chemistry, University of Punjab, Lahore, Pakistan
*Corresponding author: Tel: +92 321 4618681; E-mail: hbubak@gmail.com
Received: 9 September 2014;
Accepted: 29 December 2014;
Published online: 26 May 2015;
AJC-17271
Zn(II) Schiff base complexes viz., bis[(E)-3-(1-(p-tolylimino)ethyl)-2H-chromen-2-one]zinc(II), bis[(E)-3-(1-((4-chlorophenyl)-
imino)ethyl)-2H-chromen-2-one]zinc(II) and bis[(E)-3-(1-((2-nitrophenyl)imino)-ethyl)-2H-chromen-2-one]zinc(II) derived from 3-acetyl-
2H-chromen-2-one and p-toluidine, p-chloro aniline and 2-nitroaniline, respectively, have been synthesized and characterized. Physical
properties like, infrared spectroscopy and λmax are recorded and presence of metal is confirmed by atomic absorption spectroscopy.
Infrared spectra reveal complex formation of Zn(II) with synthesized ligands. Both free Schiff bases and their Zn(II) complexes have been
screened for antibacterial activity against Gram-positive Bacillus subtilis, Staphylococcus aureus, Methicillin-resistant Staphylococcus
aureus (MRSA) and Gram-negative E. coli, P. aeruginosa, S. typhi by Agar plate diffusion method. All Schiff bases and their metal
complexes appeared promising as antibacterial agents. Minimum inhibition concentrations were determined for each bacterial strain.
Keywords: Zn(II) complexes, 3-Acetyl-2H-chromen-2-one, p-Toluidine, p-Chloroaniline, 2-Nitroaniline, Antibacterial activity.
3-acetyl-2H-chromen-2-one (4) with p-toluidine (5), 4-chloro-
aniline (7) and 2-nitroaniline (9). Schiff bases were then reacted
with Zinc(II) metal ion and metal complexes were synthesized.
All the synthesized Schiff bases and their complexes were
characterized by physical techniques including infra-red
spectroscopy, UV-visible spectroscopy and atomic absorption
spectroscopy. Both Schiff base ligands and zinc metal comp-
lexes were then investigated and found effective against diffe-
rent bacteria including both Gram-positive and Gram-negative
strains.
INTRODUCTION
Compounds containing -C=N- (imine group) are known
as Schiff bases and are synthesized by condensing primary
amines with active carbonyl groups. Schiff bases are famous
for their biological applications1-3.Antibacterial agents inhibit
the bacterial growth or distinguish bacteria4. Schiff bases which
have chloro and cyano groups at C-2 are found very effective
against a number of bacterial strains5,6. Nitrogen, oxygen and
sulphur containing Schiff base ligands have shown a number
of biological activities and have found of great interest because
of its binding with metal ions. It has been reported that existence
of metals in many biological active compounds increases their
activity7. Schiff base metal complexes have shown infinite
biological activities as antifungal8-12, anti-HIV13, anticonvulsant14,
antimicrobial15-20, antiviral and anticancer21 and antibacterial
agents22. bis-Schiff bases form chelate rings after coordinating
with a metal ion23. Copper(II) complexes synthesized from
Schiff base ligands derived from isatin24 have played very active
role for oxidation of carbohydrates. Similarly, bis-Schiff base
metal complexes are also used as inhibitors of human α-thrombin25.
The present study aims the synthesis, characterization and
study of antibacterial activity of bis-Schiff base metal com-
plexes. We synthesized different Schiff bases by reacting
EXPERIMENTAL
Salicylaldehyde, ethyl acetoacetate, p-toluidine, p-chloro-
aniline, 2-nitroaniline bacteriological agar, Tryptone (Fluka),
yeast extract, sodium chloride, DMSO, ethanol and chloroform
used in this work were purchased from Sigma Aldrich and
were used as such as received. Zn(CH3COO)2.H2O was of the
analytical grade from Fluka dried over phosphorous pentaoxide
(P2O5).All bacterial strains were collected from the department
of microbiology, University of Punjab Lahore, Pakistan.
Perkin-Elmer FT-IR 783 spectrophotometer was used to
take IR spectra for all the synthesized ligands and complexes.
1H NMR and 13C NMR were recorded on Jeol ECS 300 NMR

Vol. 27, No. 9 (2015)
Synthesis and Antibacterial Activity of Zn(II) Schiff Base Complexes 3441
spectrometer. Chemical shifts for protons were measured in
comparison to tetramethylsilane (TMS) at δ = 0 ppm.
Synthesis of 3-acetyl-2H-chromen-2-one (4): 3-Acetyl-
2H-chromen-2-one was prepared according to the reported
method26. To a mixture of salicylaldehyde (1) (12.2 g, 0.1 mol)
and ethylacetoacetate (2) (13 g, 0.1 mol) in 10 mL of ethyl
alcohol few drops of piperidine (3) were added and stirred for
(1C,ArCH), 128.2 (1C,ArCH), 125.0 (1C,ArCH), 122.0 (2C,
2 × ArCH), 118.3 (1C, ArC), 116.0 (1C, ArCH), 113.5 (1C,
ArC), 21.6 (1C, ArCH3) 19.9 (1C, CCH3), IR (film, νmax, cm-1):
3031 (sp2 C-H stretch), 2901 (sp3 C-H stretch), 1677 (C=O
stretch), 1558 (C=N), 1209 (C-O stretch) m.p.: 125 °C.
Synthesis of (E)-3-(1-((4-chlorophenyl)imino)ethyl)-
2H-chromen-2-one (8): 3-Acetyl-2H-chromen-2-one (4)
8 h at room temperature. Yellow coloured solid was formed
and collected by filtration, washed with excess of chilled alcohol,
dried and crystallized as silky needles of 3-acetyl-2H-chromen-
2-one (4) (71.9 %) (Fig. 1).
(1.88 g; 0.0l mol, 1 eq) was reacted with 4-chloroaniline (7)
(1.27 g; 0.0l mol, 1 eq) to synthesize (E)-3-(1-((4-chloro-
phenyl)imino)-ethyl)-2H-chromen-2-one (8) as light yellow
crystalline solid (Yield 76.5 %) (Fig. 3).
CH3
Cl
CH3
O
CH3
CHO
NH2
O
O
O
(3)
Piperidine
+
N
O
+
OH
O
O
(4)
O
O
(1)
(2)
O
O
(8)
Cl
(7)
Fig. 1. Synthesis of 3-acetyl-2H-chromen-2-one
(4)
Fig. 3. Synthesis of (E)-3-(1-((4-chlorophenyl)imino)ethyl)-2H-chromen-
1H NMR (400 MHz, CDCl3) δ ppm 8.51 (1H, s, ArH),
7.86 (1H, d, J = 7.16 Hz, ArH), 7.71 (1H, t, J = 8.19 Hz,ArH),
7.43-7.39 (2H, m, 2 ×ArH), 2.71 (3H, s, CH3). 13C NMR (75.5
MHz, CDCl3) δ ppm 198.8 (1C,ArCOCH3), 159.4 (1C, COO),
153.1 (1C, CO), 136.9 (1C, ArCH), 131.1 (1C,ArCCO), 128.3
(1C, ArCH)), 127.6 (1C,ArCH), 125.4 (1C, ArCH), 118.1 (1C,
ArC), 116.0 (1C, ArCH), 29.6 (1C, CH3), IR (film, νmax, cm-1):
3056 (sp3 C-H), 1725 (C=O), 1200 (C-O); m.p.:120 °C.
2-one
1H NMR (400 MHz, CDCl3) δ ppm 7.81 (1H, d, ArH, J =
8.3), 7.65-7.61 (1H, m, ArH), 7.53 (1H, s, ArH), 7.32-7.25
(4H, m, 4 × ArH), 6.99 (2H, d, 2 × ArH, J = 7.6), 2.10 (3H, s,
CH3). 13C NMR (75.5 MHz, CDCl3) δ ppm 175.4 (1C, C=N),
159.4 (1C, C=O), 153.0 (1C, ArC-O), 148.8 (1C, ArC-N),
132.0 (1C, ArCCl), 131.9 (1C, ArCH), 130.4 (2C, 2 × ArCH),
128.4 (1C,ArCH), 128.1 (1C,ArCH), 125.2 (1C,ArCH), 122.0
(2C, 2 × ArCH), 118.3 (1C, ArC), 116.0 (1C, ArCH), 113.5
(1C, ArC), 19.9 (1C, CCH3), IR (film, νmax, cm-1): 3085 (sp2
C-H stretch), 2940 (sp3 C-H Stretch), 1683 (C=O stretch), 1558
(C=N), 1228 (C-O stretch), m.p.: 131 °C.
Synthesis of (E)-3-(1-((2-nitrophenyl)imino)ethyl)-2H-
chromen-2-one (10): (E)-3-(1-((2-nitrophenyl)imino)ethyl)-
2H-chromen-2-one (10) was synthesized by reacting 3-acetyl-
2H-chromen-2-one (4) (1.88 g; 0.0l mol, 1 eq) with 2-nitro-
aniline (9) (1.27 g; 0.0l mol, 1 eq) as golden yellow crystalline
solid (Yield 77.1 %) (Fig. 4).
Synthesis of ligands
General procedure: The Schiff bases (6, 8, 10) were
synthesized by stirring a mixture of 25 mL of 3-acetyl-2H-
chromen-2-one (4) ethanolic solution (0.0l mol, 1 eq) with
aniline (5, 7, 9) (0.0l mol, 1 eq) in 25 mL of ethanol at 60-
70 °C for 3 h. Progress of reaction was monitored by TLC.
From the resulting solution, solvent was removed by evapo-
ration under vacuum. The crystalline product was separated
by filtration, washed several times with ethanol.After recrysta-
llizing with hot ethanol, product was dried under vacuum. Its
purity was confirmed by TLC technique27.
Synthesis of (E)-3-(1-(p-tolylimino)ethyl)-2H-chromen-
2-one (6): Schiff base (E)-3-(1-(p-tolylimino)ethyl)-2H-
chromen-2-one (6) was synthesized from 3-acetyl-2H-chromen-
2-one (4) (1.88 g; 0.0l mol, 1 eq) and p-toluidine (5) (1.07 g;
0.0l mol, 1 eq) as bright yellow crystalline solid (Yield 71.9 %)
(Fig. 2).
CH3
O
CH3
NH2
O2N
+
N
NO2
O
O
O
O
(10)
(4)
(9)
Fig. 4. Synthesis of (E)-3-(1-((2-nitrophenyl)imino)ethyl)-2H-chromen-2-
one
CH3
O
CH3
N
NH2
1H NMR (400 MHz, CDCl3) δ ppm 8.07 (1H, d, ArH, J =
8.1), 7.85-7.81 (2H, m, 2 ×ArH), 7.72-7.68 (3H, m, 3 ×ArH),
7.58 (1H, s, ArH), 7.37-7.29 (2H, m, 2 × ArH), 2.13 (3H, s,
CH3), 13C NMR (75.5 MHz, CDCl3) δ ppm 175.6 (1C, C=N),
159.3 (1C, C=O), 153.2 (1C, ArC-O), 145.2 (1C, ArC-NO2),
142.2 (1C, ArC-N), 132.6 (1C, ArCH), 131.3 (1C, ArCH),
130.0 (1C,ArCH), 128.5 (1C,ArCH), 128.4 (1C,ArCH), 128.2
(1C,ArCH), 124.8 (1C,ArCH), 124.7 (1C,ArCH), 118.4 (1C,
ArC), 115.9 (1C, ArCH), 113.2 (1C, ArC), 19.9 (1C, CCH3),
IR (film, νmax, cm-1): 3057 (sp2 C-H stretch), 2927 (sp3 C-H
stretch), 1684 (C=O stretch), 1556 (C=N), 1200 (C-O stretch)
m.p.: 127 °C.
+
O
O
(6)
O
O
(5)
(4)
Fig. 2. Synthesis of (E)-3-(1-(p-tolylimino)ethyl)-2H-chromen-2-one
1H NMR (400 MHz, CDCl3) δ ppm 7.83 (1H, d, ArH, J =
8.3), 7.67-7.63 (1H, m, ArH), 7.55 (1H, s, ArH), 7.31-7.27
(2H, m, 2 × ArH), 7.21 (2H, d, 2 × ArH, J = 8.3), 7.12 (2H, d,
2 × ArH, J = 8.2), 2.18 (3H, s, ArCH3), 2.08 (3H, s, CH3), 13C
NMR (75.5 MHz, CDCl3) δ ppm 175.5 (1C, C=N), 159.4 (1C,
C=O), 153.1 (1C, ArC-O), 148.7 (1C, ArC-N), 136.7 (1C,
ArCCH3), 132.1 (1C, ArCH), 130.4 (2C, 2 × ArCH), 128.3

3442 Hussain et al.
Asian J. Chem.
Synthesis of Schiff base metal complexes
and agar (1.5-2 g) were weighed and each component was
dissolved in 1 L Erlenmeyer flask.After maintaining the volume
up to 1 L, solution was autoclaved to ensure that LB was
sterilized of all foreign matter and contaminants. LB medium
was used for bacterial culture growth in solution and bacterial
growth on petri plates. After adding 25-30 mL of LB medium
in petri-dish, it was allowed to solidify; then 1 mL of bacterial
suspension was transferred to plate at 27 °C for 24 h. With the
help of autoclaved pasture pipette, wells were made in plates
and were then filled with solution of ligands/complexes (50
µg/mL) in DMSO. Inhibition zone were measured for both
ligands and complexes. Each synthesized ligands and complexes
were investigated according to pre mentioned concentrations
dissolved in DMSO, while DMSO itself was used as control
for comparison. Results are given in Table-2 and 3. For the
determination of minimum inhibition concentrations values
guidelines given in NCCLS document M27-A29 were followed.
100 µg/mL solutions of ligands and complexes were made in
DMSO and serial dilutions 50, 40, 30, 20, 10, 5 µg/mL were
prepared to determine the minimum inhibition concentrations.
Concentrations of test ligands/complexes: 2 mg of each
ligand and complex was dissolved in 1 mL of DMSO. From
this stock three concentrations 0.2 mg/0.1 mL, 0.02 mg/0.1
mL and 0.002 g/0.1 mL were prepared and used for investi-
gation of antibacterial activities.
General procedure: The metal salt solution (0.005 mol)
made in methanol (10 mL) was slowly added to a solution of
the salicylaldehyde (0.01 mol) in methanol (10 mL). The reaction
mixture was refluxed for 15 min at 60-70 °C with continuous
stirring. After 15 min a solution of aromatic amine derivative
(0.01 mol) was added into the reaction mixture dropwise with
continuous stirring and was refluxed for 4 h at 60-70 °C with
stirring. After cooling precipitates were formed, they were
collected by filtration then washed several times with cold
methanol and recrystallized from methanol.
Synthesis of bis[(E)-3-(1-(p-tolylimino)ethyl)-2H-
chromen-2-one]zinc(II) (11): After refluxing zinc acetate
solution (1.09 g, 0.005 mol, 1 eq) and 3-acetyl-2H-chromen-
2-one (1.88 g, 0.01 mol, 2. eq) in methanol, p-toluidine (1.07 g,
0.01 mol, 2 eq) was added dropwise in the reaction mixture to
obtain desired product as yellow precipitates (66 %). IR (film,
ν
max, cm-1) 3045 (sp2 C-H stretch), 2960 (sp3 C-H stretch), 1663
(C=O stretch), 1557 (C=N), 1232 (C-O stretch), 458 (Zn-N),
340 (Zn-O).
Synthesis of bis[(E)-3-(1-((4-chlorophenyl)imino)-
ethyl)-2H-chromen-2-one]Zinc(II) (12): Zinc acetate
solution (1.09 g, 0.005 mol, 1 eq) made in methanol (10 mL)
was slowly added to the solution of 3-acetyl-2H-chromen-2-
one (1.88 g, 0.01 mol, 2 eq) in methanol (10 mL). The reaction
mixture was refluxed for 15 min at 60-70 °C with continuous
stirring and p-chloroaniline (1.27 g, 0.01 mol, 2 eq) was added
dropwise according to the method in section 2.4 and yellow
RESULTS AND DISCUSSION
Schiff bases ligands (4CH3I2C (6), 4ClI2C (8), 2NO2I2C
(10) were prepared in good yields by reacting 3-acetyl-2H-
chromen-2-one (4) with different derivatives of aniline (5, 7,
9). Yields of the Schiff bases 4CH3I2C and 4ClI2C were 71.9
% and 76.5 %, respectively while yield (77.1 %) for 2NO2I2C
remained maximum among them (Table-1, entry 1, 2, 3). Zinc
metal complexes gave lesser yields when compared with their
respective ligands.Yields for zinc complexes, bis4CH3I2CZn
(11), bis4ClI2CZn (12) and bis2NO2I2CZn (13) were 66, 69.8
and 62.2 %, respectively (Table-1, entry 4, 5, 6). Table-1 shows
precipitates of product were obtained (69.8 %). IR (film, νmax
,
cm-1): 3038 (sp2 C-H stretch), 2938 (sp3 C-H stretch), 1604
(C=O stretch), 1525 (C=N), 1248 (C-O stretch), 453 (Zn-N),
342 (Zn-O).
Synthesis of bis[(E)-3-(1-((2-nitrophenyl)imino)ethyl)-
2H-chromen-2-one]zinc(II) (13): According to procedure in
section 2.4, zinc acetate solution (1.09 g, 0.005 mol, 1 eq) in
methanol (10 mL) was slowly added to the solution of 3-acetyl-
2H-chromen-2-one (1.88 g, 0.01 mol, 2 eq) in methanol (10
mL). After refluxing for 15 min at 60-70 °C, a solution of
2-nitroaniline (1.38 g, 0.01 mol, 2 eq) was added dropwise to
obtain desire product as lemon yellow solid (62.2 %). IR (film,
λ
max (nm), d.p of zinc complexes and m.p of ligands.
Schiff base ligands were characterized by spectroscopic
studies including IR, 1H and 13C NMR while structures of zinc
complexes were estimated by physical characterization.
Presence of zinc metal was confirmed by atomic absorption
spectroscopy (AAS).
ν
max, cm-1): 3036 (sp2 C-H stretch), 2931 (sp3 C-H stretch),
1609 (C=O stretch), 1555 (C=N), 1209 (C-O stretch), 444 (Zn-
N), 343 (Zn-O).
The infrared spectral data of the Schiff bases and their
complexes with Zn(II) ion are found in the expected range.
Band in the range of 1557-1525 cm-1 is attributed to C=N
Antibacterial activity assay procedure: Agar plate diffu-
sion technique28 was used to develop L.B nutrient medium.
Yeast extract (0.5 g), tryptone (1 g), sodium chloride (0.5 g)
TABLE-1
PHYSIOCHEMICAL DATA OF SYNTHESIZED LIGANDS/COMPLEXES
m.p/d.p Yield
Abbreviations
Zn
(ppm)
λmax
S. no.
Ligands/complexes
m.f.
used
(°C)
125
131
127
155
210
(%)
71.9
76.5
77.1
66.0
69.8
(nm)
1
2
3
4
5
(E)-3-(1-(p-tolylimino)ethyl)-2H-chromen-2-one
(E)-3-(1-((4-chlorophenyl)imino)ethyl)-2H-chromen-2-one
(E)-3-(1-((2-nitrophenyl)imino)ethyl)-2H-chromen-2-one
bis[(E)-3-(1-(p-tolylimino)ethyl)-2H-chromen-2-one]zinc(II) C36H30N2O4Zn
bis[(E)-3-(1-((4-chlorophenyl)imino)ethyl)-2H-chromen-2-
C18H15NO2
C17H12ClNO2
C17H12N2O4
4CH3I2C
4ClI2C
2NO2I2C
bis4CH3I2CZn
bis4ClI2CZn
--
--
--
425
425
--
--
--
20.68
19.43
C34H24Cl2N2O4Zn
one]zinc(II)
6
bis[(E)-3-(1-((2-nitrophenyl)imino)ethyl)-2H-chromen-2-
one]zinc(II)
C34H24N4O8Zn
bis2NO2I2CZn
215
62.2
485
18.80

Vol. 27, No. 9 (2015)
Synthesis and Antibacterial Activity of Zn(II) Schiff Base Complexes 3443
TABLE-2
ANTIBACTERIAL ACTIVITY OF Zn(II) COMPLEXES
Diameter of zone of inhibition (mm)
Metal complexes
(50 µg)
S. no.
Gram positive
Gram negative
MRSA
Bacillus subtilis
S. aureus
P. aeruginosa
E. coli
S. typhi
1
2
3
4
5
6
4CH3I2C
4ClI2C
2NO2I2C
bis4CH3I2CZn
bis4ClI2CZn
bis2NO2I2CZn
-
-
10
35
-
-
-
10
25
-
75
75
25
30
75
-
-
10
-
-
15
10
-
55
-
25
-
-
25
-
15
-
115
15
15
20
Note: Mean inhibition zones are measured in mm
TABLE-3
MIC DATA OF Zn(II) COMPLEXES
Metal
complexes
Gram positive
Gram negative
Sr. #
MRSA
Bacillus subtilis
S. aureus
P. aeruginosa
E. coli
S. typhi
10
-
-
-
-
1
2
3
4
5
6
4CH3I2C
4ClI2C
2NO2I2C
bis4CH3I2CZn
bis4ClI2CZn
bis2NO2I2CZn
-
10
-
-
15
10
-
55
-
25
-
-
25
-
15
10 µg
20 µg
20 µg
15 µg
-
20 µg
15 µg
-
20 µg
20 µg
-
-
115
15
10 µg
20 µg
vibration in metal complexes.According to IR spectra, shifting
of C=N group towards lower frequency when compared with
free Schiff base (1558-1556 cm-1) suggests the attachment of
Zn(II) ion through nitrogen atom of imine. The bands in the
range of 1663-1604 cm-1 are assigned to C=O stretching frequency
which were found at 1684-1677 cm-1 in free Schiff base spectra.
New bands at 343-340 cm-1 and 458-444 cm-1 assigned to Zn-O
and Zn-N respectively vibrations in metal complexes were
absent in free Schiff base spectra, it confirmed the involvement
of oxygen and nitrogen atoms in complex formation.
minimum inhibition concentrations was little higher 20 µg
(Table-3, entry 2). Ligand 4CH3I2C was effective against only
two bacterial species S. aureus and S. typhi with minimum
inhibition concentrations 10 and 15 µg, respectively (Table-3,
entry 1).
Zinc(II) complexes were also screened against mentioned
bacterial strains. Complex bis4ClI2CZn was very effective
against E.coli with zone of inhibition 115 mm. Similarly the
zones of inhibition for S. aureus and P. aeruginosa were,
respectively 75 and 15 mm for complex bis4ClI2CZn and had
no effect on S. typhi (Table-2, entry 5). Complex bis4CH3I2CZn
was more active against Gram-positive bacterias than Gram-
negative bacteria. Zones of inhibition against Gram-positive
bacteria MRSA, Bacillus subtilis and S. aureus of bis4CH3I2CZn
were 35, 25 and 30 mm and for Gram-negative bacteria S. typhi
the zone of inhibition was 25 mm while it had no effect on
P. aeruginosa and E. coli (Table-2, entry 4). For bis2NO2I2CZn,
zones of inhibition for MRSA, Bacillus subtilis, E.coli, P.
aeruginosa and S. typhi were 15, 20, 10, 15 and 15 mm while
it was found inactive against S. aureus (Table- 2, entry 6).
Complex bis4ClI2CZn showed minimum inhibition
concentrations 10 µg against P. aeruginosa; and for S. aureus
and E. coli; minimum inhibition concentrations were 15 and
20 µg (Table-3, entry 5). Complex bis4CH3I2CZn was found
equally effective for both MRSA and S. typhi with minimum
inhibition concentrations 15 µg while its minimum inhibition
concentrations values for Bacillus subtilis and S. aureus were
20 µg each (Table-3, entry 4). bis2NO2I2CZn complex showed
good activity against many bacterial strains. Minimum inhi-
bition concentrations for bacteria MRSA, P. aeruginosa and
E. coli were found 10 µg while for Bacillus subtilis and S.
typhi minimum inhibition concentrations were 20 and 15 µg,
respectively (Table-3, entry 6).
The Schiff base ligands and zinc metal complexes have
been screened for their antibacterial activities against different
pathogenic bacteria including Gram-positive and Gram-
negative strains. The results of anti-bacterial activity for both
ligands and complexes are presented in Table-2. All ligands
were found active against different experimental pathogens.
Ligand 2NO2I2C was found very active against Gram-positive
bacterias as it showed zones of inhibition with diameter of 10,
10 and 25 mm for MRSA, Bacillus subtilis and S. aureus,
respectively. While this ligand 2NO2I2C was found passive
against Gram-negative bacteria (Table-2, entry 3). Ligand
4ClI2C was not active against MRSA, Bacillus subtilis and S.
typhi but it (4ClI2C) was found exceptionally active against
S. aureus, P. aeruginosa and E. coli with zones of inhibition
75, 10 and 55 mm, respectively (Table-2, entry 2). Like ligand
4ClI2C, ligand 4CH3I2C was also inactive against Gram-
positive bacteria MRSA and Bacillus subtilis. On the other
hand, it (4CH3I2C) showed opposite behaviour towards
P. aeruginosa and E. coli while it was quite active against
S. aureus with inhibition zone of 75 mm and S. typhi with 25
mm zone of inhibition (Table-2, entry 1). When minimum
inhibitory concentrations (MIC) were determined, ligand
2NO2I2C showed the same minimum inhibition concentrations
for MRSA, Bacillus subtilis and S. aureus (Table-3, entry 3).
4ClI2C was found very active against S. aureus and E. coli with
minimum inhibition concentrations 10 µg while for P. aeruginosa
Conclusion
Schiff base ligands were synthesized by reacting 3-acetyl-
2H-chromen-2-one with different anils. Zinc metal chelates

3444 Hussain et al.
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were then prepared. Both ligands and metal complexes were
screened for antibacterial activity and were found effective.
Among the synthesized ligands, 4CH3I2C showed minimum
activity against selected bacterial strains with good minimum
inhibition concentrations; 4ClI2C was effective against some
of Gram-positive and Gram-negative bacteria with good mini-
mum inhibition concentrations while 2NO2I2C was only effec-
tive against Gram-positive strains.Among zinc(II) Schiff base
complexes bis2NO2I2CZn was found most effective against
Gram-negative and Gram-positive bacterial strains with exce-
llent minimum inhibition concentrations while bis4ClI2CZn
remained least effective. Complex bis4CH3I2CZn has been
found fairly well against Gram-positive and only one of the
Gram-negative strains with good minimum inhibition concen-
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Supporting information: 1H NMR, 13C NMR and IR data
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ACKNOWLEDGEMENTS
The authors are thankful to Chemistry Department, U.E.T.
Lahore, Pakistan; Department of Botany, University of Punjab
for guidance, research and laboratory facilities. Thanks are
also due to Higher Education Commission of Pakistan for
providing research funds.
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