Synthesis and spectral studies of acetophenone schiff bases and evaluation of their antimicrobial activities

Article abstract of DOI:10.14233/ajchem.2013.15146

Seven acetophenone derived Schiff bases with different amines were synthesized including, (Z)-2-[(1-phenylethylidene)amino]benzoic acid (HL ¹), (Z)-4-[(1-phenylethylidene)amino]benzoic acid (HL²), (E)-N-(1-phenylethylidene)naphthalen

Full text of DOI:10.14233/ajchem.2013.15146

Asian Journal of Chemistry; Vol. 25, No. 14 (2013), 8105-8110
http://dx.doi.org/10.14233/ajchem.2013.15146
Synthesis and Spectral Studies of Acetophenone Schiff
Bases and Evaluation of their Antimicrobial Activities
*
HIRA MIR, DILDAR AHMED and HAFIZ MUHAMMAD ADEEL SHARIF
Department of Chemistry, Forman Christian College (A Chartered University), Ferozpur Road, Lahore, Pakistan
*Corresponding author: E-mail: dildarahmed@fccollege.edu.pk
(Received: 17 January 2013;
Accepted: 5 August 2013)
AJC-13883
Seven acetophenone derived Schiff bases with different amines were synthesized including, (Z)-2-[(1-phenylethylidene)amino]benzoic
acid (HL1), (Z)-4-[(1-phenylethylidene)amino]benzoic acid (HL2), (E)-N-(1-phenylethylidene)naphthalen-2-amine (HL3), (E)-1-phenyl-2-
(1-phenylethylidene)hydrazine (HL4), N1,N2-bis(1-phenylethylidene)ethane-1,2-diamine (HL5), N1(Z),N2(Z)-N1,N2-bis(1-
phenylethylidene)benzene-1,2-diamine (HL6) and N1,N4-bis(1-phenylethylidene)benzene-1,4-diamine (HL7) and characterized by spectral
studies (IR, MS and NMR) and elemental analysis. Their antimicrobial activity was extensively investigated against 20 Gram-negative
and 10 Gram-positive bacterial strains. Schiff bases HL1-5 showed good antibacterial activity against almost all bacterial strains. HL3
showed remarkable activity against Enterococcus sp., Citrobacter freundii, Salmonella typhi and Pseudomonas aurantiaca. HL4 gave
incredible inhibition against Enterobacter aerogenes. HL7 demonstrated notable activity against Staphylococcus aureus. (E)-N-(1-
phenylethylidene)naphthalen-2-amine (HL3) is reported for the first time.
Key Words: Acetophenone, Schiff bases, Spectroscopic, Antimicrobial activity.
acetophenone and different primary amines including mono-
and diamines of both aromatic and aliphatic nature. According
to our knowledge, acetophenone derived Schiff base with β-
naphthylamine is being reported for the first time. Spectral
studies including 1H NMR, 13C NMR, IR and MS were carried
out to characterize the compounds. Synthesised Schiff bases
were then screened for the first time ever against thirty different
bacterial strains including gram positive and gram negative
bacteria, pathogenic as well as non-pathogenic.
INTRODUCTION
Growing pathogenic resistance to existing antibiotic drugs
is one of the most baffling challenges to human health in the
modern times and necessitates constant efforts to discover more
effective and safer therapeutic agents1-3. The infectious diseases
are, in fact, one of the main causes of deaths the world over4.
The screening of both the natural products and the synthetic
compounds against different pathogenic microorganisms has
thus emerged to be one of the most active fields of research today.
The Schiff bases5-8, or substances with azomethine func-
tionality, comprise a major class of organic compounds being
investigated for multifarious applications including their
possible development into therapeutic agents. They have been
found to possess antibacterial9,10,antifungal11,antiviral12, anti-
inflammatory13, analgesic14, anti- tumour15, anticonvulsant16,
anti HIV17 and antileishmanial18 activities. They are also good
ligands19 and can coordinate with metals in vitro as well as in
vivo.
EXPERIMENTAL
All the reagents and solvents were of analytical-grade
quality purchased from Aldrich Co and were used without
further purification. Melting points were found on Gallenkamp
(Electronic) melting point apparatus and were uncorrected.
The reactions were monitored by thin-layer chromatography
(TLC) on silica gel plates (Sigma-Aldrich).A mixture of ethanol
and ethyl acetate (1:1) was employed as mobile phase and
UV lamp, Model UVLS-225 D, was used for detection.
The IR spectra of the compounds were taken using KBr
disks on Varian 640-IR spectrometer (cm-1). UV-VIS absor-
ption spectra were recorded with Spectro UV-VIS Double PC
8 Auto Cell with variable bandwidth of 0.5, 1.0, 2.0 and 5.0
nm, Model UVD-3200 spectrometer. Both 1H and 13C NMR
spectra were recorded on a Bruker 300 MHz NMR spectrometer
Acetophenone, a ketone having both an aliphatic and an
aromatic moiety, has been shown to form Schiff bases exhibi-
ting considerable antibacterial20,21 and antifungal22,23 activities
along with other useful applications24-28
.
As part of our ongoing search for new therapeutic agents,
seven different Schiff bases were synthesized from unsubstituted

8106 Mir et al.
Asian J. Chem.
(H.E.J. Research Institute of Chemistry, Karachi, Pakistan),
with chemical shift in ppm downfield from TMS as an internal
reference. High resolution mass spectra were captured on
Varian MAT 312 mass spectrometer (H.E.J. Research Institute
of Chemistry, Karachi, Pakistan).
aurantiaca , Salmonella typhi (1), Stenotroph maltophilia,
Enterobacter cloacae, Enterobacter aerogenes, Klebsiella
pneumoniae, Staphylococcus epidermidis, Bacillus subtilis and
Bacillus megaterium. Thirteen different microbial colonies
were attained from biotechnology laboratory, Forman
Christian College, Lahore, Pakistan including two strains of
E. coli [Escherichia coli (3) and Escherichia coli (4)] and single
strain each of Pseudomonas aeruginosa (3), Pseudomonas sp.,
Salmonella typhi (2), Salmonella sp., Achromobacter
xylosoxidans, Azospirillum lipoferum, Rhizobium sp., Citrobacter
freundii, Staphylococcus aureus (3), Bacillus sp.(3) and
Enterococcus sp.All strains were stored at -20 ºC until utilized.
Determination of zones of inhibition (ZI): Agar well
diffusion method29,30 was employed for antimicrobial screening
in terms of the zones of inhibition.
Synthesis of Schiff bases
Schiff bases HL1 to HL4: Acetophenone (1.16 mL, 10
mmol) with o-aminobenzoic acid (1.37 g, 10 mmol) (for HL1),
p-aminobenzoic acid (1.37 g, 10 mmol) (for HL2), β-naph-
thylamine (1.43 g, 10 mmol) (for HL3) and phenylhydrazine
(0.99 mL, 10 mmol) (for HL4) in different round bottom flasks
were refluxed in 20 mL methanol at 40 ºC for 3 h in the presence
of 1 mL glacial acetic acid. In each case, the precipitated base
was filtered off, recrystallized from absolute ethanol and dried
in vacuum desiccator. The structure of the synthesized schiff
bases are given in Fig. 1.
Preparation of standard dilutions: In each case, 2 mg
of a synthesized compound was dissolved per mL of DMSO
to yield stock solution, which was serially diluted to 0.5-1
mg/mL. Three antibiotic drugs levofloxacin, cefixime and
amoxylin were used as standard with final concentration of 2
mg/mL in DMSO.
Preparation of inoculums: All microbial cultures were
re-isolated thrice successively on Mueller-HintonAgar, MHA
(Merck) with incubation period of 24 h at 37 ºC and identity
confirmed by standard bacteriological methods.A loop full of
bacterial suspension was then diluted with sterile physio-
logical solution to standardize inoculum density up to 108 CFU/
mL of bacterial cells (equivalent to turbidity of McFarland,
barium sulphate standard 0.5) followed by 24 h incubation at
37 ºC.
Antimicrobial screening (zones of inhibition): The
bacterial inoculums were uniformly swabbed on prepared
Mueller-Hinton Agar plate followed by a session of drying,
after which three wells of 7 mm diameter each were dug in
the agar gel 33 mm apart from one another using a sterile cork
borer. A 100 µL volume of test compound dilutions were
pipetted into the triplicate wells and allowed to stand for an
hour for diffusion to take place. Finally, plates were incubated
at 37 ºC for 24 h after which zones of inhibition were recorded
to the nearest mm.
Fig. 1. Structures of synthesized Schiff bases
Determination of minimum inhibitory concentration
(MIC): Minimum inhibitory concentration (MIC) is defined
as the lowest concentration of an anti-microbial agent requisite
to inhibit bacterial growth. The agar dilution method31,32 was
executed to evaluate MICs of synthesized compounds and
antibiotics. Briefly, 0.004 g/mL stock solution of each of the
test compounds was prepared in DMSO, from which graded
concentrations were made to achieve final concentrations (mg/
mL) of 0.02, 0.04, 0.08, 0.12, 0.16, 0.20, 0.24, 0.28, 0.32,
0.36 and 0.40 in total 20 mL of Mueller-Hinton Agar plates
by varying the volume of agar and test stock solutions. The
plates were spotted with 0.1 mL overnight activated cultures
of the microbes and incubated at 37 ºC for 24 h.
Schiff bases HL5 to HL7: In different experiments,
acetophenone (2.33 mL, 20 mmol) with ethylene diamine (0.66
mL, 10 mmol) (for HL5), o-amino aniline (1.08 g, 10 mmol)
(for HL6) and p-amino aniline (1.08 g, 10 mmol) (for HL7)
was refluxed at 40 ºC for 3 h in 20 mL of methanol in the
presence of 1 mL glacial acetic acid. The resultant ligands
were filtered, recrystallized from absolute ethanol and dried
in vacuum desiccator. The structures of proposed ligands are
shown in Fig. 1.
Antimicrobial analysis
Test microbes: Seventeen different bacterial cultures were
acquired from The Children Hospital, Lahore, Pakistan
including two strains of E. coli [Escherichia coli (1) and
Escherichia coli (2)], two strains of S. aureus [Staphylococcus
aureus (1) and Staphylococcus aureus (2)], two strains of P.
aeruginosa [Pseudomonas aeruginosa (1) and Pseudomonas
aeruginosa (2)], two unidentified Bacillus species [Bacillus
sp.(1) and Bacillus sp.(2)] and one strain each of Pseudomonas
RESULTS AND DISCUSSION
In the present study, seven different Schiff bases of the
ketone acetophenone were synthesized with different amines
using the conventional reflux method. The structures (Fig. 1)

Vol. 25, No. 14 (2013)
Synthesis and Spectral Studies of Acetophenone Schiff Bases 8107
of the bases were elucidated on the bases of elemental analysis
and spectroscopic data. The bases were then subjected to
antimicrobial screening against different bacterial strains.
(Z)-2-((1-Phenylethylidene)amino)benzoic acid (HL1):
Orange yellow; yield (%): 86; m.p. 233 ºC; anal. calcd. (%)
for C15H13NO2: 75.31, C; 5.43, H; 5.85, N; 13.38, O. Found
(%): 75.30, C; 5.42, H; 5.83, N; 13.35, O. Selected IR (KBr,
(N1(Z),N2(Z)-N1,N2-Bis(1-phenylethylidene)benzene-
1,2-diamine(HL6): Earth brown; yield (%): 88; m.p. 238 ºC;
anal. calcd. (%) for C22H20N2: 84.61, C; 6.41, H; 8.98, N. Found
(%): 84.58, C; 6.40, H; 8.97, N. Selected IR (KBr, νmax, cm-1):
1
1632 (-C=N-). H NMR (CD3OD, 300 MHz) δ 1.98 (s, 6H,
CH3), 6.92-7.11 (m, 4H, Arb=b’, e), 7.15-7.30 (m, 4H, ArHd=d’),
3
7.43 (d, 4H, ArHc=c’, J = 7.5 Hz), 7.59 (d, 4H, ArHa=a’, 3J =
ν
max, cm-1) 1627 (-C=N-), 2900-3100 (O-H), 1721 (C=O), 1290
7.5Hz); 13C NMR (CD3OD, 75 MHz) δ 22.2 (2C, CH3), 121.9
(2C), 122.7 (2C), 126.9 (4C), 127.7 (4C), 128.4 (2C), 129.0
(2C), 129.1 (2C), 169.7 (2C, C=N); MS: m/z 312 [M+].
N1,N4-Bis(1-phenylethylidene)benzene-1,4-diamine
(HL7): Earth brown; yield (%): 88; m.p. 238 ºC; anal. calcd.
(%) for C22H20N2: 84.61, C; 6.41, H; 8.98, N. Found (%): 84.60,
C; 6.39, H; 8.95, N. Selected IR (KBr, νmax, cm-1): 1631
(-C=N-). 1H NMR (CD3OD, 300 MHz) δ 2.28 (s, 6H, CH3),
6.88 (s, 4H, Ara=a’=b=b’), 7.47(m, 6H, ArHd=d’, e), 7.92 (dd, 4H,
ArHc=c’, 3J = 7.2 Hz, 4J = 2.5 Hz); 13C NMR (CD3OD, 75 MHz)
δ 18.2 (2C, CH3), 121.7(4C), 128.4(4C), 129.2(4C), 131.7(2C),
141.0(2C), 148.5(2C), 169.8(2C, C=N); MS: m/z 312 [M+].
The IR spectra of the synthesized Schiff bases showed a
strong band in the region of 1610-1640 cm-1, which is charac-
teristic of the azomethine group (C=N)33. Moreover, O-H
stretch in 3300-2500 cm-1 , C=O stretch in 1760-1690 cm-1
and C-O stretch in 1320-1210 cm-1 was noticed in HL1 and
(C-O). 1H NMR (CD3OD, 300 MHz) δ 2.28 (s, 3H, CH3), 6.82
(m, 3H, ArHf=f’, g), 7.25(d, 1H, ArHd, 3J = 7.2 Hz), 7.52 (t, 1H,
ArHc, 3J = 7.2Hz), 7.74(d, 2H, ArHe=e’, 3J = 7.5 Hz), 7.85(t,
1H, ArHb, 3J = 7.2Hz), 8.12(d, 1H,ArHa, 3J = 7.2 Hz), 11.9 (s,
1H, COOH); 13C NMR (CD3OD, 75 MHz) δ 18.3 (1C, CH3),
111.2 (1C), 122.3 (1C), 125.0 (1C), 126.7 (3C), 127.8 (1C),
133.1 (1C), 135.2 (1C), 137.8 (1C), 150.2 (1C, C-N), 165.3
(1C, C=N), 171.0 (1C, C=O); MS: m/z 239 [M+].
(Z)-4-((1-Phenylethylidene)amino)benzoic acid (HL2):
Lime yellow; yield (%): 82; m.p. 227 ºC; anal. calcd. (%) for
C15H13NO2: 75.31, C; 5.43, H; 5.85, N; 13.38, O. Found (%):
75.31, C; 5.42, H; 5.84, N; 13.36, O. Selected IR (KBr, νmax
,
cm-1): 1629 (-C=N-), 2900-3100 (O–H), 1720 (C=O), 1293
(C–O). 1H NMR (CD3OD, 300MHz) δ 2.27 (s, 3H, CH3), 6.86
(m, 3H, ArHd=d’, e), 7.34(d, 2H, ArHb=b’, 3J = 7.5 Hz), 7.52(d,
2H, ArHc=c’, 3J = 7.5Hz), 8.0(d, 2H, ArHa=a’, 3J = 7.5Hz), 11.8
(s, 1H, COOH); 13C NMR (CD3OD, 75 MHz) δ 24.2(1C, CH3),
112.2 (2C), 120.3(2C), 126.0(1C), 130.8(2C), 133.1(2C),
135.4(4C), 137.8(1C), 152.1(1C, C-N), 163.4(1C, C=N),
171.1(1C, C=O); MS: m/z 239 [M+].
1
HL2, together with H NMR signal between 11.8-12.5 ppm
1
confirming the presence of a carboxylic group in them. H
NMR signal in 12-14 ppm and an IR band in 3400-3200 cm-1
indicating presence of (NH) group was observed in HL4.
Antimicrobial activities: The Schiff bases in general
showed moderate activity against most of the tested microbes.
In some cases, however, the activity was very good while some
compounds exhibited no appreciable activity against diffe-
rent microorganisms. Notably, bases with single azomethine
group were more active than those having two azomethine
functionalities (Table-1). HL4 and HL3 proved to be most
versatile antimicrobial agents combating all 30 strains with
medium to high lethality, while HL5 was least active. As the
Table-1 displays, HL3 showed remarkable activity against
Enterococcus sp., Citrobacter freundii, Salmonella typhi and
Pseudomonas aurantiaca. HL4 exhibited remarkable activity
against Enterobacter aerogenes, while HL7 was notably potent
against Staphylococcus aureus.
(E)-N-(1-Phenylethylidene)naphthalen-2-amine (HL3):
Faded pink; yield (%): 84; m.p. 239 ºC; anal. calcd. (%) for
C18H15N: 88.16, C; 6.12, H; 5.72, N. Found (%): 88.08, C;
6.11, H; 5.71, N. Selected IR (KBr, νmax, cm-1): 1631 (-C=N-).
1H NMR (CD3OD, 300 MHz) δ 2.28 (s, 3H, CH3), 7.23(d, 1H,
ArHj, 3J = 7.2 Hz), 7.32 (m, 3H,ArHb=b’, c), 7.42(m, 2H,ArHg,f,),
7.72(d, 2H,ArHa=a’), 7.88(m, 4H,ArHd,e,h,i); 13C NMR (CD3OD,
75MHz) δ 18.3(1C, CH3), 110.2(1C), 115.3(1C), 120.0(2C),
123.3(1C), 125.1(2C), 125.3(2C), 125.6(2C), 126.2(1C),
127.4(1C), 128.2(1C), 134.2(1C), 135.2(1C, C-N), 146.3(1C,
C=N); MS: m/z 245 [M+].
(E)-1-Phenyl-2-(1-phenylethylidene)hydrazine (HL4):
Chocolate brown; yield (%): 90; m.p. 64 ºC; anal. calcd. (%)
for C14H14N2: 80.00, C; 6.66, H; 13.37, N. Found (%): 79.92,
C; 6.64, H; 13.34, N. Selected IR (KBr, νmax, cm-1): 1637
(-C=N-), 3350 (NH). 1H NMR(CD3OD, 300 MHz) δ 2.28 (s,
3H, CH3), 6.68 (t, 1H, Arc), 7.27(m, 3H, ArHb=b’, c), 7.02 (t, 2H,
ArHb=b’, 3J = 7.2 Hz), 7.25 (d, 2H, ArHa=a’, 3J = 7.5Hz), 7.52
(t, 3H, ArHe=e’, f), 12.96 (s, 1H, NH); 13C NMR (CD3OD, 75
MHz) δ 18.3 (1C, CH3), 115.2(2C), 115.4(1C) 116.5.2 (2C),
116.9 (2C), 118.6 (2C), 136.6 (1C), 138.7 (1C), 168.2 (1C,
C=N); MS: m/z 210 [M+].
HL1 was weakly active against Escherichia coli (2),
Salmonella typhi (1), Staphylococcus aureus (3) and Entero-
coccus sp. with zones of inhibition between 10-11 mm and
MIC between 200-240 µg/mL. It was moderately active against
Escherichia coli (4), Pseudomonas aeruginosa (1) and (2), Staphy-
lococcus aureus (2), Bacillus sp. (3), Staphylococcus epidermidis
and Salmonella sp. with zones of inhibition in the range of
16-19 mm and MIC value between 120-160 µg/mL (Table-2).
HL2 was moderately active against Escherichia coli (3)
and (4), Pseudomonas aeruginosa (2) and (3), Pseudomonas
aurantiaca, Salmonella typhi (1), Salmonella sp., Rhizobium
sp., Citrobacter freundii, Staphylococcus aureus (2), Bacillus
subtilis, Bacillus sp. (3) and Enterococcus sp. with zones of
inhibition between 17-24 mm and MIC between 80-160 µg/mL
(Table-2).
N1,N2-Bis(1-phenylethylidene)ethane-1,2-diamine
(HL5): Pale yellow; yield (%): 80; m.p. 120 ºC; anal. calcd.
(%) for C18H20N2: 81.20, C; 7.15, H; 10.17, N. Found (%):
81.81, C; 7.57, H; 10.60, N. Selected IR (KBr, νmax, cm-1):
1
1635 (-C=N-). H NMR (CD3OD, 300 MHz) δ 2.26 (s, 6H,
CH3), 4.24 (s, 2H, -CH2-), 7.27(m, 6H, ArHb=b’, c), 7.54 (d, 4H,
ArHa=a’, 3J = 7.2Hz); 13C NMR (CD3OD, 75 MHz) δ 18.0 (2C,
CH3), 54.1 (2C, -CH2-), 127.2 (4C), 128.1 (6C), 128.6 (2C),
142.7 (2C), 168.3 (2C, C=N); MS: m/z 264 [M+].
HL3 was weakly active against Klebsiella pneumonia and
Bacillus sp. (1) with zones of inhibition of 10 and 11 mm,

8108 Mir et al.
Asian J. Chem.
TABLE-1
ZONES OF INHIBITION (MM) OF ACETOPHENONE DERIVED SCHIFF BASES IN THREE DIFFERENT CONCENTRATIONS AGAINST
THIRTY DIFFERENT BACTERIAL STRAINS AND THEIR COMPARISON WITH THREE STANDARD ANTIBIOTICS
Zones of inhibition (mm)
HL1 (mg/mL)
HL2 (mg/mL)
HL3 (mg/mL)
S. No.
Bacterial strains
Antibiotics (2 mg/mL)
L
C
A
2
–
1
–
0.5
–
2
1
0.5
7
2
1
0.5
7
1
Escherichia coli (1)
38
40
40
40
40
38
38
24
32
28
32
33
38
32
33
38
38
35
30
32
35
37
35
35
37
38
42
35
36
28
20
23
25
21
20
19
16
10
20
16
15
16
27
21
16
30
22
28
16
16
22
11
28
20
22
17
28
25
20
21
16
20
20
20
15
22
10
13
12
10
10
17
24
10
14
15
15
20
15
11
16
9
12
11
19
17
11
17
17
15
20
16
15
20
14
15
13
12
13
12
16
22
8
10
7
10
24
10
21
24
28
27
22
33
32
33
29
22
27
24
10
21
23
24
32
27
32
9
9
2
Escherichia coli (2)
Escherichia coli (3)
Escherichia coli (4)
Pseudomonas aeruginosa (1)
Pseudomonas aeruginosa (2)
Pseudomonas aeruginosa (3)
Pseudomonas sp.
12
–
9
–
–
20
9
17
8
3
–
–
15
13
7
11
10
–
4
18
16
18
9
15
11
14
7
11
8
16
19
24
21
17
28
26
27
24
17
24
19
8
11
15
20
18
13
23
22
21
19
11
20
15
–
5
6
11
–
11
13
10
17
11
12
17
10
9
7
7
10
8
8
–
–
–
9
Pseudomonas aurantiaca
Salmonella typhi (1)
Salmonella typhi (2)
Salmonella sp.
7
–
–
14
8
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
11
–
7
–
–
–
8
18
–
13
–
9
13
8
Stenotroph maltophilia
Enterobacter cloacae
Enterobacter aerogenes
Klebsiella pneumonia
Achromobacter xylosoxidans
Azospirillum lipoferum
Rhizobium sp.
–
–
–
–
7
8
–
–
11
10
9
8
–
–
–
7
–
–
–
–
17
19
20
26
24
24
7
12
16
17
21
19
20
–
7
–
–
8
–
–
–
–
12
16
–
9
Citrobacter freundii
Staphylococcus aureus (1)
Staphylococcus aureus (2)
Staphylococcus aureus (3)
Bacillus subtilis
7
–
–
12
–
–
–
–
19
11
–
11
7
8
19
14
16
14
15
15
24
17
24
16
11
12
10
13
11
20
13
19
12
7
10
18
26
20
18
14
16
17
–
–
–
9
18
20
11
20
30
31
30
15
18
9
10
14
7
Bacillus megaterium
Bacillus sp.(1)
9
–
–
7
–
–
–
9
Bacillus sp.(2)
Bacillus sp.(3)
–
–
–
7
16
27
27
25
13
21
22
20
19
17
11
14
14
8
10
9
14
10
14
Staphylococcus epidermidis
Enterococcus sp.
–
HL4 (mg/mL)
HL5 (mg/mL)
HL6 (mg/mL)
HL7 (mg/mL)
1
Escherichia coli (1)
Escherichia coli (2)
Escherichia coli (3)
Escherichia coli (4)
Pseudomonas aeruginosa (1)
Pseudomonas aeruginosa (2)
Pseudomonas aeruginosa (3)
Pseudomonas sp.
21
13
10
25
17
15
21
14
23
13
22
19
26
19
28
15
22
14
15
20
20
19
18
14
16
16
13
35
20
21
18
10
8
16
7
–
–
–
–
–
–
–
–
–
–
–
–
7
–
–
–
7
–
8
–
–
–
–
7
17
–
–
14
–
–
9
2
3
7
–
–
–
12
–
10
–
–
4
21
14
12
19
11
20
9
18
11
9
–
–
–
16
18
–
14
15
–
10
9
5
–
–
–
–
–
6
–
–
–
–
–
–
7
16
8
22
–
19
–
16
–
16
–
12
–
11
–
7
–
8
–
–
9
Pseudomonas aurantiaca
Salmonella typhi (1)
Salmonella typhi (2)
Salmonella sp.
18
7
20
–
17
–
15
–
15
–
10
–
15
9
11
–
8
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
–
19
18
23
15
24
10
18
12
12
16
18
17
16
11
11
13
10
30
18
17
16
16
19
11
21
7
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
Stenotroph maltophilia
Enterobacter cloacae
Enterobacter aerogenes
Klebsiella pneumonia
Achromobacter xylosoxidans
Azospirillum lipoferum
Rhizobium sp.
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
16
9
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
8
–
–
–
–
–
–
–
–
–
Citrobacter freundii
Staphylococcus aureus (1)
Staphylococcus aureus (2)
Staphylococcus aureus (3)
Bacillus subtilis
13
15
13
15
8
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
35
–
30
–
24
–
16
–
11
–
–
–
–
–
–
–
–
–
22
9
18
–
13
–
–
–
–
–
–
–
Bacillus megaterium
Bacillus sp.(1)
7
–
–
–
–
–
–
11
10
–
9
–
9
–
–
–
–
–
–
8
–
Bacillus sp.(2)
8
–
–
–
–
–
–
–
–
Bacillus sp.(3)
Staphylococcus epidermidis
Enterococcus sp.
27
14
15
26
–
21
–
18
–
17
–
13
–
10
–
31
–
26
–
20
–
–
–
–
21
17
13
20
16
11
Where L = Levofloxacin, C = Cefixime and A = Amoxylin; the blank boxes show no appreciable activity.

Vol. 25, No. 14 (2013)
Synthesis and Spectral Studies of Acetophenone Schiff Bases 8109
respectively. It was strongly active against Pseudomonas
aeruginosa (2) and (3), Pseudomonas aurantiaca, Pseudomonas
aurantiaca, Salmonella typhi (1) and (2), Salmonella sp.,
Enterobacter cloacae, Citrobacter freundii, Staphylococcus
aureus (1) and (2), Bacillus sp. (3), Staphylococcus epidermidis
and Enterococcus sp. with zones of inhibition between 27-33
mm and MIC values between 20-40 µg/mL. It was moderately
active against rest of microbes with MIC values in the range
80-120 µg/mL (Table-2).
HL4 was weakly active against Escherichia coli (3) with
zone of inhibition of 10 mm and MIC value of 200 µg/mL. It
was strongly active against Stenotroph maltophilia, Enterobacter
aerogenes and Bacillus sp. (3) with zones of inhibition between
26-33 mm and MIC values between 20-40 µg/mL. It was
moderately active against the rest with MIC values 80-160
µg/mL (Table-2).
MIC values between 120-160 µg/mL. It was inactive against
rest microbes (Table-2).
HL7 was weakly active against Pseudomonas aeruginosa
(3), Bacillus megaterium and Bacillus sp. (1) with zones of
inhibition between 10-11 mm and MIC value of 200 g/mL
each. It was moderately active against Escherichia coli (2)
and (4), Pseudomonas aeruginosa (1), Staphylococcus aureus
(3) and Enterococcus sp. with zones of inhibition in between
17-22 mm and MIC range between 80-160 µg/mL. It showed
strong activity against Staphylococcus aureus (1) and Bacillus
sp. (3) with zones of inhibition 35 and 31, respectively and
MIC value of 20 µg/mL each (Table-2).
Comparing the screening results of HL1 and HL2 and HL6
and HL7 gave a trend proving that p-substitution of benzene
with azomethine group is more effective than o-substitution
and hence are better antimicrobial agents.
HL5 was moderately active against Pseudomonas
aeruginosa (3), Pseudomonas aurantiaca, Staphylococcus aureus
(2) and Bacillus sp. (3) with zones of inhibition between 16-
25 mm and MIC values between 80-160 µg/mL. It was totally
inactive against rest of microbes (Table-2).
HL6 was weakly active against Escherichia coli (3) with
zone of inhibition of 12 mm and MIC value of 200 µg/mL. It
showed moderate activity against Pseudomonas aeruginosa
(3), Pseudomonas aurantiaca, Bacillus sp. (3) and Entero-
coccus sp. with zones of inhibition in between 15-21 mm and
HL4 was strongly active against Escherichia coli (1)
and (4), Pseudomonas aeruginosa (3), Pseudomonas
aurantiaca, Stenotroph maltophilia, Enterobacter aerogenes,
Achromobacter xylosoxidans and Bacillus sp. (3) even in 0.5
mg/mL concentration with zones of inhibition between 16-27
mm.
HL5 was strongly active against Bacillus sp. (3) and
Pseudomonas aeruginosa (3) in its lowest concentration with
zones of inhibition 18 mm and 16 mm, respectively whereas
HL7 was strongly active against Staphylococcus aureus (1)
TABLE-2
MIC (MINIMUM INHIBITORY CONCENTRATION) VALUES OF ACETOPHENONE DERIVED
SCHIFF BASES AGAINST GRAM NEGATIVE AND GRAM POSITIVE BACTERIAL STRAINS
MIC (µg/mL)
S. No.
Bacterial strains
HL1
240
200
240
120
160
120
200
240
240
200
240
160
240
240
240
240
240
200
240
200
240
120
200
240
200
240
240
120
160
200
HL2
200
240
120
160
200
160
120
240
120
120
240
120
240
200
200
200
200
200
160
120
240
120
240
160
200
240
200
80
HL3
200
80
HL4
120
160
200
80
HL5
240
280
240
240
240
240
120
160
120
240
280
280
240
240
280
280
240
280
240
240
240
160
240
280
280
240
240
80
HL6
320
240
200
320
280
200
160
280
160
320
280
360
280
320
320
320
320
360
280
280
280
360
360
280
360
280
320
160
360
120
HL7
200
120
240
160
120
240
200
240
160
200
240
320
400
240
280
200
360
240
240
320
20
1
Escherichia coli (1)
Escherichia coli (2)
Escherichia coli (3)
Escherichia coli (4)
Pseudomonas aeruginosa (1)
Pseudomonas aeruginosa (2)
Pseudomonas aeruginosa (3)
Pseudomonas sp.
2
3
200
80
4
5
80
160
160
120
160
120
160
120
120
40
6
40
7
40
8
80
9
Pseudomonas aurantiaca
Salmonella typhi (1)
Salmonella typhi (2)
Salmonella sp.
20
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
40
20
40
Stenotroph maltophilia
Enterobacter cloacae
Enterobacter aerogenes
Klebsiella pneumoniae
Achromobacter xylosoxidans
Azospirillum lipoferum
Rhizobium sp.
80
40
120
40
80
200
80
160
120
160
160
120
120
120
120
160
160
160
160
20
80
80
Citrobacter freundii
Staphylococcus aureus (1)
Staphylococcus aureus (2)
Staphylococcus aureus (3)
Bacillus subtilis
20
40
20
320
80
200
120
120
200
120
40
200
200
200
240
20
Bacillus megaterium
Bacillus sp.(1)
Bacillus sp.(2)
Bacillus sp.(3)
Staphylococcus epidermidis
Enterococcus sp.
160
80
20
120
120
280
280
280
120
40

8110 Mir et al.
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