Syntheses, characterization and antimicrobial screening of N-(benzothiazol-2-yl)-4-methylbenzenesulphonamide and its Cu(I), Ni(II), Mn(II), Co(II) and Zn(II) complexes

Article abstract of DOI:10.14233/ajchem.2013.13226

N-(Benzothiazol-2-yl)-4-methylbenzenesulphonamide (PTS2ABT) was synthesized by the condensation of 2-aminobenzothiazole and 4- methylbenzenesulphonylchloride in acetone at 160 °C. The resulting crude precipitates were recrystallized in acetone/ethanol mix

Full text of DOI:10.14233/ajchem.2013.13226

Asian Journal of Chemistry; Vol. 25, No. 5 (2013), 2369-2376
http://dx.doi.org/10.14233/ajchem.2013.13226
Syntheses, Characterization and Antimicrobial Screening of N-(benzothiazol-2-yl)-4-
methylbenzenesulphonamide and Its Cu(I), Ni(II), Mn(II), Co(II) and Zn(II) Complexes
1,*
1
1
2
L.N. OBASI , C.O.B. OKOYE , P.O. UKOHA and K.F. CHAH
1Department of Pure and Industrial Chemistry, University of Nigeria, Nsukka, Enugu State, Nigeria
2Department of Veterinary Pathology and Microbiology, University of Nigeria, Nsukka, Nigeria
*Corresponding author: E-mail: nnamdi.obasi@unn.edu.ng;obasinl@yahoo.com
(Received: 10 December 2011;
Accepted: 5 November 2012)
AJC-12362
N-(Benzothiazol-2-yl)-4-methylbenzenesulphonamide (PTS2ABT) was synthesized by the condensation of 2-aminobenzothiazole and
4-methylbenzenesulphonylchloride in acetone at 160 ºC. The resulting crude precipitates were recrystallized in acetone/ethanol mixture.
Five metal complexes of copper(I), nickel(II), manganese(II), cobalt(II) and zinc(II) of PTS2ABT were synthesized. The compounds
were characterized using magnetic susceptibility measurements, UV/visible spectrophotometry, elemental microanalysis, infra red, 1H
NMR and 13C NMR spectroscopies. The antimicrobial tests of the ligands and its metal complexes were carried out on both multi-resistant
bacterial strains isolated under clinical conditions and cultured species using agar-well diffusion method. The multi-resistant bacterial
strains used were Escherichia coli, Proteus species, Pseudomonas aeroginosa and Staphylococcus aureus, which were isolated from
dogs. The culture species were Pseudomonas aeruginosa (ATCC 27853), Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC
25923) and the fungi, Candida krusei (ATCC 6258) and Candida albicans (ATCC 90028). The tests were both in vitro and in vivo. Thus
the inhibition zone diameter, the minimum inhibitory concentration and the lethal and effective concentrations (LC50 and EC50) were
determined. The antimicrobial activities of the compounds were compared with those of ciprofloxacin and trimethoprim-sulphamethoxazole
as antibacterial agents and fluconazole as an antifungal drug. All the compounds showed varying activities against the cultured typed
bacteria and fungi used. However, they were less active than the standard drugs used except fluconazole which did not show any activity
against Candida krusei (ATCC 6258) but the ligand, PTS2ABT was very active against it. The lethal concentration (LC50) ranged from
12.16 1.3 to 495.30 86.81 ppm. These are within the permissible concentrations.
Key Words: N-(Benzothiazol-2-yl)-4-methylbenzenesulphonamide, Metal complexes, Antimicrobial.
which causes sepsis and also diarrhea in humans. Obasi et al.9
worked on some sulfonyl derivatives of 2-aminothiazole and
INTRODUCTION
Interest in the coordination chemistry of thiazole and its
derivatives with metal ions has risen due to the important role
they play in biological systems1. Thiazole are known to posses
antitubercular2, hypotensive and hypothermic3 activities. It is
known that metal chelates of ligands with sulphur or nitrogen
the results obtained showed that the compounds were signifi-
cantly active against Staphylococcus aureaus and Escherichia
coli. Some novel N-(benzothiazol-2-yl)ethanamides were also
synthesized and characterized by Obasi et al.10 and were
screened in vitro and in vivo for antibacterial activity. The
donor atoms have interesting physicochemical properties as
compounds were very stable and showed high antibacterial
activities against both gram-positive and gram-negative
well as physiological activities4,5. Studies have shown that the
metal complexes of sulfa drugs promote rapid healing of skin
bacteria tested. The present work is aimed at synthesizing new
disorder, for instance, silver(I)sulfadiazine complex is used
derivative of 2-aminobenzothiazole and its metal(II) comp-
for human burnt treatment and zinc(II)sulfadiazine in preventing
lexes, characterizing them and investigating how their
structural differences affects antimicrobial activities when
bacterial infections in burnt animals6.
Mercury(II) and copper(II) complexes of 6-methyl-2-
compared with conventional sulfonamides.
aminobezothiazole have equally been discovered to show high
activity against Aspergillus niger, Alternaria alternate,
EXPERIMENTAL
Curvularia plunata and Penicillium fumculorus7. Furthermore,
mercury(II) complex of sulfathiazole has been discovered to
show high antibacterial activity against Escherichia coli8,
The ligand, N-(benzothiazol-2-yl)-4-methylbenzenesul-
phonamide (PTS2ABT) was prepared based on our modified
method from that by Sprague et al.11. All the reagents were of

2370 Obasi et al.
Asian J. Chem.
analytical grade and were used as supplied except otherwise
stated. UV-visible spectra of the ligand and complexes were
obtained on UV-2550 UV-VIS spectrophotometer, (SHIMADZU).
FTIR spectra of the compounds were run as Nujol mulls on
FTIR-84005 FTIR Spectrophotometer, (SHIMADZU). 13C and
1H NMR spectra were recorded on Bruker-BioSpin 500 MHz
NMR Spectrometer (UK) using DMSO and CDCl3 as solvents
respectively. The proton NMR peaks were observed at 400
MHz whereas the carbon-13 spectra were observed at about
200 MHz. Elemental analysis was done using LECO-CHNS
932 microanalysis apparatus and the magnetic susceptibility
of the complexes were determined using Sherwood scientific
magnetic susceptibility balance, Mk1 model (Cambridge, UK)
both at Department of Pure andApplied Chemistry, University
of Strathclyde, Scotland, UK.
during which a white crystalline solid was formed. This was
filtered and dried in a stream of air and stored in desicator
(Scheme-III).
S
NH
2
O
NiCl .6H O
+
N
S
2
2
O
120 °C
DMF
CH
3
N-(benzothiazol-2-yl)-4-methylbenzenesulfonamide
2+
S
NH
O
S
N
O
H C
3
2Cl-
Synthesis of N-(benzothiazol-2-yl)-4-methylbenzene-
sulphonamide (PTS2ABT): To a solution of 2-aminobenzo-
thiazole (6.0 g; 40 mmol) in acetone (25 mL) was added a
solution of 4-methylbenzenesulphonylchloride (7.7 g; 41
mmol) in acetone (25 mL) with stirring. The mixture was
refluxed for 1 h at 160 ºC. During the refluxing, a white
precipitate was formed. The precipitate was recrystallized in
acetone/ethanol mixture (Scheme-I).
Ni
CH
3
O
S
N
S
O
NH
Bis [N-(benzothiazol-2-yl)-4-methylbenzenesulphonamide]nickel(II) chloride
Scheme-II: Synthesis of bis-[N-(benzothiazol-2-yl)-4-methylben-
zenesulphonamide] nickel(II) chloride (Ni(II)PTS2ABT)
O
Cl
N
S
S
S
+
H N
NH
2
+
MnCl .4H O
O
2
2
2
O
N
S
O
H C
3
2-aminobenzothiazole
DMF
120 °C
4-methylbenzenesulfonyl chloride
CH
3
N-(benzothiazol-2-yl)-4-methylbenzenesulfonamide
acetone
160 °C
S
N
NH
S
N
O
S
NH
O
O
HCl
+
S
O
H C
3
Cl
Mn
CH
3
Cl
O
N
S
S
CH
3
N-(benzothiazol-2-yl)-4-methylbenzenesulfonamide
O
NH
Scheme-I:Synthesis of N-(benzothiazol-2-yl)-4-methylbenzenesul-
phonamide
Bis [N-(benzothiazol-2-yl)-4-methylbenzenesulphonamide]dichloromanganese(II)
Scheme-III: Synthesis of bis-[N-(benzothiazol-2-yl)-4-methylbenzene-
sulphonamide] dichloromanganese(II) (Mn(II)PTS2ABT)
Synthesis of bis-[N-(benzothiazol-2-yl)-4-methyl-
benzenesulphonamide] nickel(II) chloride (Ni(II)PTS
2ABT): To a solution of N-(benzothiazol-2-yl)-4-methyl-
benzenesulphonamide (0.61 g; 2.00 mmol) in DMF (10 mL)
was added aqueous solution of nickel(II) chloride hexahydrate
(0.30 g; 1 mmol). This was refluxed for 0.5 h at 120 ºC during
which a white precipitate was formed. This was filtered and
dried in a stream of air and stored in desicator (Scheme-II).
Synthesis of bis-[N-(benzothiazol-2-yl)-4-methyl-
benzenesulphonamide] dichloromanganese(II) (Mn(II)PTS
2ABT): To a solution of N-(benzothiazol-2-yl)-4-methyl-
benzenesulphonamide (0.61 g; 2 mmol) in DMF (10 mL) was
added aqueous solution of manganese(II) chloride tetrahydrate
(0.25 g; 1.00 mmol). This was refluxed for 0.5 h at 120 ºC
Synthesis of bis-[N-(benzothiazol-2-yl)-4-methyl-
benzenesulphonamide]dichlorocobalt(II) (Co(II)
PTS2ABT): To a solution of N-(benzothiazol-2-yl)-4-methyl-
benzenesulphonamide (0.61 g; 2.00 mmol) in DMF (10 mL)
was added aqueous solution of cobalt(II) chloride hexahydrate
(0.30 g; 1 mmol). This was refluxed for 0.5 h at 120 ºC. On
refluxing a blue crystalline solid was formed. This was filtered
and dried in a stream of air and stored in desicator (Scheme-
IV).
Synthesis of bis-[N-(benzothiazol-2-yl)-4-methyl-
benzene-sulphonamide]zinc(II) chloride (Zn(II)PTS2ABT):
To a solution of N-(benzothiazol-2-yl)-4-methylbenzene-

Vol. 25, No. 5 (2013)
Syntheses of N-(benzothiazol-2-yl)-4-methylbenzenesulphonamide and Its Metal Complexes 2371
sulphonamide (0.61 g; 2 mmol) in DMF (10 mL) was added
aqueous solution of zinc(II) acetate dihydrate (0.26 g; 1 mmol).
This was refluxed for 0.5 h at 120 ºC during, which a white
precipitate was formed. This was filtered and dried in a stream
of air and stored in desicator (Scheme-V).
g; 1.00 mmol). This was refluxed for 0.5 h at 120 ºC during
which a brown precipitate was formed. This was filtered and
dried in a stream of air and stored in desicator (Scheme-VI).
S
NH
2
CuCl .2H O
+
O
2
2
S
N
S
O
NH
2
O
+
CoCl .6H O
2 2
N
S
O
DMF
120 °C
CH
3
N-(benzothiazol-2-yl)-4-methylbenzenesulfonamide
DMF
120 °C
CH3
N-(benzothiazol-2-yl)-4-methylbenzenesulfonamide
+
S
N
NH
O
S
N
S
NH
O
O
S
O
H C
3
Cl-
Cu
CH
3
H C
Cl
3
Co
CH
O
3
Cl
N
S
S
O
NH
O
N
S
O
NH
Bis [N-(benzothiazol-2-yl)-4-methylbenzenesulphonamide]copper(I) chloride
S
Scheme-VI: Synthesis of bis-[N-(benzothiazol-2-yl)-4-methylbenze-
nesulphonamide] copper(I) chloride (Cu(I)PTS2ABT)
Bis [N-(benzothiazol-2-yl)-4-methylbenzenesulphonamide]dichlorocobalt(II)
Scheme-IV: Synthesis of bis-[N-(benzothiazol-2-yl)-4-methylbenzene-
sulphonamide] dichlorocobalt(II) (Co(II)PTS2ABT)
Antimicrobial properties
In vitro Tests: Multi-resistant bacterial strains isolated
under clinical conditions and typed strains (ATCC cultures)
were used in the study. The bacterial strains used were
Escherichia coli strains (E. coli Strain 1 and E. coli Strain 15),
Proteus species strains (Proteus spp strains 25, Proteus spp
strains 26), Pseudomonas aeroginosa strains 34 and multi-
resistant Staphylococcus aureus (SR) strain. The bacteria typed
strains (ATCC cultures) used were Pseudomonas aeruginosa
(ATCC 27853), Escherichia Coli (ATCC 25922), Staphylo-
coccus aureus (ATCC 25923). Fungi typed strains (ATCC
cultures) used were Candida krusei (ATCC 6258) and Candida
albicans (ATCC 90028). The typed strains were obtained from
bioresources development and conservation program (BDCP),
international centre for ethnomedicine and drug development
(IntaceEED), Nsukka, Nigeria.
S
NH
2
Zn(CH COO)
+
3
2
O
S
N
O
120 °C
DMF
CH
3
N-(benzothiazol-2-yl)-4-methylbenzenesulfonamide
2+
S
N
NH
O
S
O
H C
3
2Cl-
The antibacterial and antifungal activities of ligand,
PTS2ABT and its metal complexes e.g., Ni(II)PTS2ABT,
Mn(II)PTS2ABT, Co(II)PTS2ABT, Zn(II)PTS2ABT,
Cu(I)PTS2ABT against these multi-resistant bacteria were
determined using the agar well diffusion method as described
by Chah et al12. Mueller-Hinton agar plates were inoculated
with 0.1 mL of 3 h broth culture of the test bacteria. Using a
cork borer, wells (7 mm in diameter and 2.5 mm deep) were
bored into the inoculated agar. The test compounds were solu-
bilized in 20 % v/v dimethyl sulfoxide (DMSO) and 0.05 mL
of each compound at a concentration of 20 mg/mL were delivered
into the wells. One of the wells contained 20 % v/v DMSO and
served as control. The plates for antibacterial screening were
incubated at 37 ºC for 24 h while the fungi were incubated at
30 ºC for 48 h and assessment of activity was based on the measu-
rement of the diameter of inhibition zone around the wells. The
Zn
CH
3
O
S
N
O
NH
S
Bis [N-(benzothiazol-2-yl)-4-methylbenzenesulphonamide]zinc(II) chloride
Scheme-V: Synthesis of bis-[N-(benzothiazol-2-yl)-4-methylbenzene-
sulphonamide] zinc(II) chloride (Zn(II)PTS2ABT)
Synthesis of bis-[N-(benzothiazol-2-yl)-4-methyl-
benzenesulphonamide] copper(I) chloride (Cu(I)PTS
2ABT): To a solution of N-(benzothiazol-2-yl)-4-methyl-
benzenesulphonamide (0.61 g; 2 mmol) in DMF (10 mL) was
added aqueous solution of copper(II) chloride dihydrate (0.22

2372 Obasi et al.
Asian J. Chem.
TABLE-1
PHYSICAL PROPERTIES OF THE LIGAND, PTS2ABT AND OF ITS METAL COMPLEXES, THE MAGNETIC
PROPERTIES OF THE COMPLEXES AND ELEMENTAL MICROANALYSIS OF THE LIGAND
S. No
Samples
m.p. (ºC)
Colour
Texture
m.w.
Properties
µeff (BM)
1
2
3
4
5
6
PTS2ABT
144-146
201-203
203-205
204-206
200-202
199-201
White
White
White
Blue
Crystalline
Crystalline
Crystalline
Crystalline
Amorphous
Crystalline
304.00
666.69
733.94
737.93
673.39
707.05
-
-
Ni(II)PTS2ABT
Mn(II)PTS2ABT
Co(II)PTS2ABT
Zn(II)PTS2ABT
Cu(I)PTS2ABT
4.06
2.50
2.77
1.07
1.34
Paramagnetic
Paramagnetic
Paramagnetic
Diamagnetic
Diamagnetic
White
Brown
Elemental microanalysis (%) of the ligand, PTS2ABT
C
H
N
Calc.
55.26
Found
49.26
Calc.
3.95
Found
3.95
Calc.
9.21
Found
11.27
PTS2ABT
test was performed in triplicates, mean inhibitory zone diameter
was recorded to the nearest whole millimetre.
of the ligand, PTS2ABT is 144-146 ºC while those of the
complexes range from 199-206 ºC. The ligand and its metal
complexes are white except the cobalt and copper complexes,
which are blue and brown respectively. The ligand, PTS2ABT
and its complexes are crystalline except the zinc complex which
is amorphous.
The minimum inhibitory concentrations of the test
compounds were determined using the agar dilution method
as described by Ojo et al13. Two-fold serial dilutions of test
compounds were made in 20 % v/v DMSO. One millilitre of
each serial dilution was added to 19 mL of sterile Mueller-
Hinton agar maintained at 45 ºC, thoroughly mixed and poured
into a sterile plate and the medium allowed to solidify. The
final concentrations of the compounds ranged from 20 mg/mL
to 1.25 mg/mL. Amended media were incubated overnight at
37 ºC to check for sterility. Overnight nutrient broth cultures
of the test bacteria were adjusted to contain approximately
108 cfu/mL and 0.025 mL of each of the test organisms was
spot-inoculated on the amended culture media. Inoculated
plates were incubated at 37 ºC for 24 h and observed for presence
of visible growth. The minimum inhibition concentration was
determined as the value of the lowest concentration that comp-
letely suppressed growth of the organisms.
The result of the elemental microanalysis is recorded in
Table-1. The amount of carbon, hydrogen and nitrogen of the
ligand calculated theoretically correspond to a large extent
with the experimental result. The % carbon for PTS2ABT
calculated (55.26) and that found (49.26), was an indication
that the compound may have little amount of some solvents
used in the synthesis and recrystallization.
Electronic spectra: The electronic transition result of the
compounds synthesized are recorded (Table-2). Two bands
were observed for the ligand at 285.6 nm and 370.0 nm. They
are due to π→π* and n→π* transitions.
Nickel complex of the ligand: For most octahedral and
tetrahedral Ni(II) complexes, three bands are expected, how-
ever for some tetrahedral Ni(II) complexes like [NiI4]2- two
broad bands may be found15,16. Thus three bands were observed
for Ni(II) complex of PTS2ABT (13, 620 cm-1, 20, 490 cm-1
and 24, 040 cm-1) and the transitions are assigned as follows;
ν1 = 3T2 (F) ← 3T1 (F); ν2 = 3A2 (F) ← 3T1 (F) and ν3 = 3T1 (P) ←
3T1 (F) transitions.
In vivo tests [Brine Shrimps Lethality Test (BSLT)]:
The method of McLaughlin and coworkers was used to study
the bioactivity of the synthesized compounds14. Artemia salina
eggs obtained from a pet shop in Davis California was incubated
in natural sea water (from Bar Beach, Lagos, Nigeria) in a
dam-well under room condition. About ten (10) 48 h- shrimp
nauplii in 1 mL of autoclaved sea water were put into Bijou
bottles using a Pasteur pipette under a stereo-microscope with
a light source. They were separated into 7 groups in triplicate.
Increasing concentrations (10, 100, 1000 ppm) of the synthe-
sized compounds were added into each of the triplicate and
distilled water was added into the control group. The nauplii
were incubated at room temperature (37 ºC) for 24 h after
which the survivors in each well were counted. The results
were analyzed using Finney probit analysis (MS-DOS-
computer-program) to determine the LC50 at 95 % confidence
interval. Weak nauplii were noted as an indication of central
nervous system depression.
Manganese complex of the ligand: Three bands were
observed for the Mn(II) complex synthesized (13, 630 cm-1,
20, 410 cm-1 and 31, 750 cm-1), the transitions are assigned:
2
2
2
2
ν1 = T1g (H) ← A1g and ν2 = Eg (H) ← Alg transitions of
octahedral geometry.
Cobalt complex of the ligand: In a cubic field, three
spin-allowed transitions are anticipated because of the splitting
of the free- ion ground 4F term and the accompanying 4P term.
Of course it is essentially a 2-electron transition from t2g5 eg2 to
3
4
t2g eg . Three bands were observed for the cobalt complex
(11460, 13620 cm-1 and 32150 cm-1), it is assigned:
ν1 = 2T2g(H) ← 2T1g(H); ν2 = 2A2g(H) ← 2T1g(H) and ν3 = LMCT
transitions.
RESULTS AND DISCUSSION
Zn(II) complexes of the ligand: Three bands were
observed for the Zn(II) complex synthesized, they are probably
due to metal-ligand charge transfer (MLCT) transition. We
deduced a tetrahedral geometry for the Zn(II) complex.
Cu(I) complexes of the ligand: Two bands were observed
for the Cu(I) complex of the ligand synthesized (13620 cm-1
and 33000 cm-1). Based on the fact that the Cu(II) complex
The equations of reactions for the syntheses of the ligand,
PTS2ABT and its metal complexes are represented in Schemes
I-VI.
Physical properties of the compounds and elemental
microanalysis of the ligand: Table-1 shows some physical
properties of both ligand and its complexes. The melting point

Vol. 25, No. 5 (2013)
Syntheses of N-(benzothiazol-2-yl)-4-methylbenzenesulphonamide and Its Metal Complexes 2373
TABLE-2
UV/VISIBLE SPECTRAL RESULT OF PTS2ABT AND ITS COMPLEXES
ν1 (cm-1) ν 2 (cm-1) ν 3 (cm-1)
10-3 ∈1
10-4 ∈2
10-5 ∈3
Samples
Assignments
λmax (nm)
PTS2ABT
285.6
370.0
3.04
4.68
π → π*
n→ π*
ν1 = 3T2 (F) ← 3T1 (F)
ν2 = 3A2 (F) ← 3T1 (F)
ν3 = 3T1 (P) ← 3T1 (F)
ν1 =2T1g(H) ← 2A1g
ν2 =2Eg (H) ← 2Alg
Ni(II)PTS2ABT
734.0
488.0
416.0
13 620
20 490
24 040
13.0
1.37
0.15
Mn(II)PTS2ABT
Co(II)PTS2ABT
733.5
490.0
315.0
872.5
734.0
311.0
13 630
11 460
20 410
13 620
31 750
32 150
13.6
22.1
1.47
2.18
15.5
14.9
ν1 =2T2g(H) ← 2T1g(H)
ν2 =2A2g(H) ← 2T1g(H)
ν3 = LMCT
Zn(II)PTS2ABT
Cu(I)PTS2ABT
299.5
293.5
288.0
734.5
303.0
33 390
13 620
34 070
34 700
33 000
1683
15.4
167
16.7
16.4
MLCT
MLCT
TABLE-3
IR SPECTRA OF THE PTS2ABT AND OF ITS COMPLEXES IN cm-1
PTS2ABT
1590 m
1553 s
1312 s
1300 m
959 sh
717 sh
584 s
Ni(II) PTS2ABT Mn(II) PTS2ABT
Co(II) PTS2ABT
Zn(II) PTS2ABT Cu(I) PTS2ABT
Assignments
1555 s
1464 s
1550 s
1463 s
1555 s
1465 s
1555 s
1464 s
1378 s
1316 s
960 s
1558 s
1464 s
1377 s
1315 s
960 s
C=N stretching vibration
of benzothiazole ring
1377 s
1315 s
960 s
1378 s
1316 s
960 s
1315 s
1275 m
960 s
SO2 stretching vibration
C-H bending vibration in
substituted benzene ring
813 m
673 s
875 m
673 s
813 m
673 s
590 s
835 m
679 s
835 m
673 s
C-S-C stretching
vibration of thiazole ring
390 s
350 s
351 s
384 s
347 s
375 s
350 m
M-N and M-Cl stretching
vibrations
was reduced to Cu(I) in this synthesis, there are no d-d transi-
tions17. With this fact, coupled with the colour of the complex,
it is presumed that the bands observed are as a result of charge
transfer transitions. We therefore proposed tetrahedral geometry
for the copper complex synthesized. The molar absorptivities of
the ligand and its metal complexes are also shown in Table-2.
IR Spectra of the PT2ABT and of its metal complexes:
Table-3 gives the main peaks of the ligand and metal complexes
and presents a scheme for determining the mode of ligation of
the ligand. The broad bands 3427, 3399, 3350, 3400, 3410
and 3400 cm-1 were assigned N-H stretching vibration for the
ligand, PTS2ABT, its Ni(II), Mn(II) Co(II), Zn(II) and Cu(I)
complexes reactively. It was also inferred that there was a
coordination through the exocyclic N since there was a shift
to lower frequencies in the ligand bands up to >17 cm-1 when
compared with the complexes. As in the case of the ligand
BS2ABT, two peaks observed around 2840-2968 cm-1 in all
the compounds are assigned to C-H stretching vibration. The
medium peaks observed between 1654-1603 cm-1 were assigned
to C=C stretching vibration of aromatic ring. Two strong peaks
each were observed between 1590-1463 cm-1. These were
assigned to C=N stretching vibration of benzothiazole ring.
We also observed a reduction in the ligand up to >87 cm-1
compared to the complexes. It is inferred that C=N was
involved in the coordination. Two medium to strong peaks
observed between 1378-1275 cm-1 in the compounds are
assigned SO2 stretching vibration. The shoulder to strong peaks
between 961-718 cm-1 were assigned C-H bending vibration
of substituted benzene ring. The strong peaks between 584-
680 cm-1 in both the ligand and the metal complexes were
assigned C-S-C stretching vibration of benzothiazole ring. The
strong peaks between 391-347 cm-1 in the metal complexes
were assigned metal-nitrogen (M-N) and M-Cl stretching
vibrations.
1H and 13C NMR spectral data: 1H and13C NMR spectra
data of the ligand and its complexes are shown on Tables 4
and 5 respectively. The 1H NMR spectral results of PTS2ABT
and its metal complexes are shown in Table-4, 6b. The peaks
at 10.07 ppm (1H, s) for PTS2ABT, 13.17 ppm (1H, s) for
Zn(II)PTS2ABT and Cu(I)PTS2ABT are assigned to N-H
protons. The peaks at 7.11 ppm (4H, d) for PTS2ABT, 7.30
ppm (4H, m) for Zn(II)PTS2ABT and 7.35 ppm (4H, m) for
Cu(I)PTS2ABT are assigned to phenyl protons. The peaks at
7.90 ppm (4H, t) for PTS2ABT, 7.79 ppm (2H, d) and 8.32
ppm (2H, d) for Zn(II)PTS2ABT and 7.76 ppm (4H, m) for
Cu(I)PTS2ABT are assigned to benzothiazole protons. The
peaks at 2.30 ppm (3H, s) for PTS2ABT, 3.36 ppm ((3H, s)
for Zn(II)PTS2ABT and 3.34 ppm (3H, s) for Cu(I)PTS2ABT
are assigned to CH3- (methyl) protons. Some other peaks
observed at 2.34 ppm and 2.35 ppm in Zn(II)PTS2ABT and
2.31 ppm and 2.35 ppm in Cu(I)PTS2ABT are due to inter-
ference of magnetic field from the metal ions in the complexes.

2374 Obasi et al.
Asian J. Chem.
TABLE-4
1H NMR SPECTRA OF THE PTS2ABT AND OF ITS COMPLEXES IN ppm
PTS2ABT
Ni(II)PTS2ABT Mn(II)PTS2ABT Co(II)PTS2ABT Zn(II)PTS2ABT
Cu(I)PTS2ABT Assignments
10.07(1H, s)
7.11 (4H, d)
7.90 (4H, t)
2.30 (3H, s)
-
-
-
-
-
-
-
-
-
-
-
-
13.17(1H, s)
13.17(1H, s)
7.35(4H, d)
7.76(4H, m)
3.34(3H, s)
N-H protons
7.30(4H, d)
Phenyl protons
8.32(2H, d) 7.79(2H, d)
3.36(3H, s)
Benzothiazole protons
H3 C- (methyl) protons
TABLE-5
13C NMR SPECTRA OF THE PTS2ABT AND OF ITS COMPLEXES IN ppm
7
S
2
6
NH
1
O
5
3
S
N
4
O
8
9
10
9
11
10
12CH3
PTS2ABT Ni(II)PTS2ABT Mn(II)PTS2ABT Co(II)PTS2ABT Zn(II)PTS2ABT
Cu(I)PTS2ABT Assignments
130.1
130.5
137.9
129.1
127.9
123.4
22.0
126.4
130.1
136.8
125.3
124.2
123.3
21.5
125.3
127.8
136.5
124.2
123.3
113.3
21.5
126.4
130.1
136.8
125.3
124.2
123.3
21.5
126.4
128.6
136.8
125.3
124.2
123.3
21.5
-
Benzothiazole carbon (C6)
Benzothiazole carbon (C7)
Phenyl carbon (C8)
125.3
127.8
-
Phenyl carbon (C9)
123.3
113.3
21.5
Phenyl carbon (C10)
Phenyl carbon (C11)
Methyl carbon (C12)
The complexes, Ni(II)PTS2ABT, Mn(II)PTS2ABT and
Co(II)PTS2ABT are paramagnetic and as such the spectra were
not included since they made little or no sense.
Magnetic Properties of the Complexes: The result of
the magnetic properties of the complexes is shown in Table-1.
The result gave an interesting data. It was generally observed
that the metal complexes were of low spin. This is an indication
that the ligand is a strong field and thus was able to cause
pairing of the electrons.As expected the zinc complex investi-
gated gave very small effective magnetic moment, µeff (1.07
BM). Therefore the zinc complex is diamagnetic and have sp3
hybridized geometry, thus tetrahedral structure. Ni(II)PTS
2ABT complex showed effective magnetic moment of 4.06
BM. This showed high spin configuration and correspond to
two unpaired electrons, indicating paramagnetism. It has sp3
hybridized geometry, thus tetrahedral structure. Co(II)PTS
2ABT showed effective magnetic moment of 2.77 BM. This
is an indication of low spin paramagnetism corresponding to
one unpaired electron. We proposed sp3d2 hybridization of
octahedral geometry. The manganese complex investigated
showed effective magnetic moment of 2.50 BM. This is indica-
tion of low spin paramagnetism corresponding to an unpaired
electron. We proposed d2sp3 hybridization of octahedral
geometry. The Cu(I) complex investigated showed diamag-
netism, indicating no unpaired electrons in the metal d-orbitals.
Since there is no possibility of electron pairing in the d-orbitals,
we are presuming that the ligand may have induced reduction
of the Cu2+ to Cu+. This is also confirmed by the brown colour
of the complex formed. We also proposed sp3 hybridization of
tetrahedral geometry for all the Cu(I) complex investigated.
Antimicrobial activity of the ligand and of its metal
complexes: The antimicrobial activities of the ligand and of
its metal complexes are recorded in Tables 6a and 6b.
Peaks at 167.5 ppm in the ligand, 143.2 ppm for the copper
complex and 167.4 ppm in the rest of the other metal comp-
lexes are assigned benzothiazole ring carbon (C1), peaks at
the 139.7 ppm in the complexes except the copper complex
which showed at 130.1 ppm and 139.8 ppm in the ligand are
assigned benzothiazole ring carbon (C2). Peaks at 143.3 ppm
in the ligand, 139.7 ppm in the copper complex and at 143.2
ppm in the other metal complexes are assigned benzothiazole
ring carbon (C3). Peaks at 136.9 ppm in the ligand and the
range of 126.4-130.1 ppm in the metal complexes are assigned
benzothiazole ring carbon (C4). Peaks at 130.3 ppm in the
ligand and the range of 124.2-127.8 ppm in the metal complexes
are assigned benzothiazole ring carbon (C5). Peaks at 130.1
ppm in the ligand and the range of 125.3-126.4 ppm in the
metal complexes are assigned benzothiazole ring carbon (C6).
Peaks at the range of 125.3-130.5 ppm in the ligand and its
metal complexes are assigned benzothiazole ring carbon (C7).
Peaks at the range of 127.8-137.9 ppm in the ligand and its
metal complexes are assigned phenyl ring carbon (C8). Peaks
at the range of 124.2-129.1 ppm in the ligand and its metal
complexes are assigned phenyl ring carbon (C9). Peaks at the
range of 123.3-127.9 ppm in the ligand and its metal complexes
are assigned phenyl ring carbon (C10). Peaks at the range of
113.3-123.4 ppm in the ligand and its metal complexes are
assigned phenyl ring carbon (C11). More still, peaks at the
range of 21.5-22.0 ppm are assigned methyl carbon (C12) in
the ligand, PTS2ABT and its metal complexes.

Vol. 25, No. 5 (2013)
Syntheses of N-(benzothiazol-2-yl)-4-methylbenzenesulphonamide and Its Metal Complexes 2375
TABLE-6a
ANTIMICROBIAL ACTIVITY OF THE LIGAND AND OF THEIR METAL COMPLEXES AGAINST
MULTI-RESISTANT BACTERIAL STRAINS ISOLATED UNDER CLINICAL CONDITIONS
Multi-resistant bacterial strains isolated from clinical conditions
Escherichia coli strains
E. coli
Strain 1
Proteus species strains
Pseudomonas
aeroginosa strains
34
Multi-resistant
Staphylococcus
aureus (SR) strain
Samples
E. coli
Strain 15
Proteus spp
strains 25
Proteus spp
Strains 26
IZD
(mm)
00
MIC
(mg/mL)
IZD
(mm)
10
MIC
(mg/mL)
IZD
(mm)
00
MIC
IZD
MIC
IZD
MIC
(mg/mL) (mm) (mg/mL) (mm) (mg/mL)
IZD
(mm)
00
MIC
(mg/mL)
PTS2ABT
00
00
10
00
00
00
00
00
00
00
00
25
00
00
10
00
00
00
00
00
27
10
00
00
00
Ni(II)PTS2ABT
Mn(II)PTS2ABT
Co(II)PTS2ABT
Zn(II)PTS2ABT
Cu(I)PTS2ABT
Ciprofloxacin
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
0.05
0.025
00
0.05
0.025
00
0.05
0.025
0.05
0.025
0.05
0.025
00
0.05
0.025
Trimethoprim-
sulphamethoxazole
TABLE-6b
ANTIMICROBIAL ACTIVITY OF THE COMPOUNDS AGAINST TYPED STRAINS (ATCC CULTURES) MICROORGANISMS
Typed strains (ATCC cultures)
Samples
Pseudomonas aeruginosa Escherichia coli Staphylococcus
Candida krusei
aureus (ATCC 25923) (ATCC 6258)
Candida albicans
(ATCC 90028)
(ATCC 27853)
IZD (mm)
(ATCC 25922)
IZD MIC
(mg/mL) (mm) (mg/mL)
MIC
IZD (mm)
MIC MIC
(mg/mL) (mm) (mg/mL) (mm) (mg/mL)
IZD
MIC
IZD
PTS2ABT
10
00
10
11
10
9
10
00
00
00
00
00
00
00
18
00
00
9
5
10
11
00
00
00
00
00
-
10
00
00
00
00
00
-
10
00
00
00
00
00
-
10
00
00
00
00
00
-
Ni(II)PTS2ABT
Mn(II)PT`S2ABT
Co(II)PTS2ABT
Zn(II)PTS2ABT
Cu(I)PTS2ABT
12
13
00
00
12
17
10
00
10
10
00
00
10
00
00
10
00
10
Ciprofloxacin
25
0.005
0.025
-
0.005
0.025
-
0.005
0.025
-
Trimethoprim-sulphamethoxazole
Fluconazole disk
-
-
-
-
-
-
-
00
00
20
10
Table-6a showed the activities against multi-resistant bacte-
rial strains isolated under clinical conditions. The inhibitory
zone diameter in mm and minimum inhibitory concentration
in mg/mL of the compounds were determined. Two strains
each of E. coli (E. coli strain 1 and E. coli strain 15) and Proteus
species (Proteus spp strains 25 and Proteus spp strains 26),
Pseudomonas aeroginosa strains 34 and multi-resistant
Staphylococcus aureus (SR) strain, all isolated from dogs at
clinical conditions were used. Ciprofloxacin and trimethoprim-
sulphamethoxazole were used as the standard drugs. We deter-
mined the minimum inhibitory concentration on the concen-
tration range 0.125-10 mg/mL. We discarded concentrations
above 10 mg/mL. Based on this, only the ligand showed
activity against the tested microbes- E. coli strain 15 and
Pseudomonas aeroginosa strains 34 with minimum inhibitory
concentration of 10 mg/mL and inhibitory zone diameter of
10 mm. The complexes showed no detectable activity against
the multi-resistant bacteria tested.
were determined. Ciprofloxacin and trimethoprim-sulphame-
thoxazole were used as the antibacterial standard drugs while
Fluconazole disk was used as antifungal standard drugs.
The minimum inhibitory concentration were determined
majorly on the concentration range of 0.125-10 mg/mL. Based
on this, all the compound synthesized showed activity against
at least one of the tested microbes. We adjudged that as in the
case of the activity against the multi-resistant bacteria, PTS2ABT
showed the highest of activity in that it was active against all of
the typed strains used-both the bacteria except Escherichia coli
(ATCC 25922) and the fungi with minimum inhibitory concen-
tration of 5 mg/mL and inhibitory zone diameter of 9 mm against
Staphylococcus aureus (ATCC 25923). Nickel and manganese
complexes showed activity only against Staphylococcus aureus
(ATCC 25923) with minimum inhibitory concentration of 10
mg/mL and inhibitory zone diameters of 12 and 13 mm respec-
tively. None of the complexes of PTS2ABT was active against
the fungi, Candida krusei (ATCC 6258) and Candida albicans
(ATCC 90028) tested. All the compounds synthesized did not
show activity against Escherichia Coli (ATCC 25922).
Table-6b showed activities of the compounds against typed
strains (ATCC Cultures) microorganisms. The bacteria cultures
used are Pseudomonas aeruginosa (ATCC 27853), Escherica
coli (ATCC 25922) and Staphylococcus aureus (ATCC 25923).
The fungi, Candida krusei (ATCC 6258) and Candida albicans
(ATCC 90028) were also used. As with the multi-resistant
bacteria strains, the inhibitory zone diameter (IZD) in mm and
minimum inhibitory concentration in mg/mL of the compounds
As with the case of the fungus, Candida krusei (ATCC
6258), the ligand synthesized was active against Candida
albicans (ATCC 90028) with minimum inhibitory concen-
tration 10 mg/mL and inhibitory zone diameter of 10 mm.
Like also the case with C. krusei, none of the metal complexes
showed activity against the C. albicans typed strain used,

2376 Obasi et al.
Asian J. Chem.
showing that the ligand has more active antifungal properties
than the synthesized complexes. Fluconazole is primarily
fungistatic but can be fungicidal against certain organisms in
dose-dependent manner. Fluconazole was only active against
the typed strain Candida albicans (ATCC 90028) but not
against C. Krusei tested strains. This was confirmed from
literature18. It is concluded that the compounds showed some
degree of activity against the tested microorganisms which to
a large extent can be compared with the standard drugs used.
Since the standard antifungal drug used did not show activity
against the Candida krusei (ATCC 6258), we can say that the
ligand, PTS2ABT wase more active that the fluconazole.
Lethal concentration (LC50) and effective concentration
(EC50): The result of the cytotoxic tests viz; Lethal concen-
tration (LC50) and effective concentration (EC50) is recorded
in Table-7.
microbial activities of the compounds were compared with
those of ciprofloxacin and trimethoprim-sulphamethoxazole
as antibacterial agents and Fluconazole as an antifungal drug.
N-(benzothiazol-2-yl)-4-methylbenzenesulphonamide,
showed activities against multi-resistant Escherichia coli and
Pseudomonas aeroginosa.All the compounds showed varying
activities against the cultured typed bacteria and fungi used.
However, they were less active than the standard bacterial drugs
used and since the standard antifungal drug (fluconazole) used
did not show activity against the Candida krusei (ATCC 6258),
we can conclude that the compound, PTS2ABT which showed
activity against it was more active than the fluconazole and
can be recommended for preclinical screening. The lethal
concentrations (LC50) were within the permissible concen-
trations.
ACKNOWLEDGEMENTS
TABLE-7
One of the authors, Dr. L.N. Obasi is grateful to Prof. J.
Reglinski, Department of Pure and Applied Chemistry, University
of Strathclyde, Scotland, UK for useful discussions, and
allowing to use some equipments in the course of this work.
The authors are also grateful to Prof. Alexander Gray and his
team at SIPBS, also at the University of Strathclyde, Scotland,
UK for hosting him, and to the University of Nigeria and the
ETF for sponsorship to the UK for a research visit.
LETHAL CONCENTRATION (LC50) AND EFFECTIVE
CONCENTRATION (EC50) RESULTS IN ppm
(CYTOTOXIC TEST)
SAMPLES
LC50 (ppm)
12.16 1.3
EC50 (ppm)
1.2
PTS2ABT
Ni(II)PTS2ABT
Mn(II)PTS2ABT
Co(II)PTS2ABT
Zn(II)PTS2ABT
Cu(I)PTS2ABT
316.70 21.8
101.00 18.2
281.00 18.0
318.00 37.8
495.30 86.81
31.7
10.1
28.1
31.8
49.5
REFERENCES
1. J.D. Edward, M.N. Hughes and K.J. Rutt, J. Chem. Soc. (A), 2101
(1969).
The result showed that all the synthesized compounds
showed high levels of bioactivity against 48 h-nauplii.
PTS2ABT showed the highest bioactivity (12.16 1.3 ppm)
with EC50 of 1.2 ppm while Cu(I) PTS2ABT showed the lowest
bioactivity (495.30 86.81 ppm) with EC50 of 49.5 ppm.
Comparing the complexes, the level of bioactivity is in the
order Mn(II)PTS2ABT > Co(II)PTS2ABT > Ni(II)PTS2ABT
> Zn(II)PTS2ABT > Cu(I)PTS2ABT.
2. M. Tsuruoka and I. Seikutsugaka, Med. Biol., 10, 296 (1947).
3. R.P. Kapoor, M.K. Rastogi, R. Khanna and C.P. Garg, Indian J. Chem.,
23B, 390 (1984).
4. O.R. Rolin, J.H. Williams, P.S. Winnek and J.P. English, J. Am. Chem. Soc.,
62, 2002 (1940).
5. K.D. Karlin and J. Zubieta, Polish J. Chem., 75, 29 (1983).
6. A. Garcia-Raso, J.J. Fiol, G. Martorell, A. Lopez-Zafra and M. Quiros,
Polyhedron, 16, 613 (1997).
7. M.R. Chaurasia, P. Shukla and N.K. Singh, Def. Sci. J., 2, 75 (1982).
8. S. Bellu, E. Hure, T. Marcela, E. Sutich, V. Moreno and R. Marcela,
Quim Nova, 26, 9 (2003).
Brine shrimps lethality test is a rapid, inexpensive and
single bioassay for testing bioactivity of natural and synthetic
products, which in most cases correlates reasonably well with
cytotoxicity and antitumor properties of the products. The
results of brine shrimps lethality test (BSLT) established that
the ligand and the complexes are very potent bioactive comp-
ounds. EC50 value for general bioactivity is approximately one
tenth of the value is the LC50 in brine shrimps lethality test.
The surviving nauphii were dull and inactive, which may be a
sign of central nervous system (CNS) depression.
9. N.L. Obasi, P.O. Ukoha and K.F. Chah, J. Chem. Soc. Nigeria, 35, 190
(2010).
10. N.L. Obasi, P.O. Ukoha, K.F. Chah and A.O. Anaga, Asian J. Chem.,
23, 2043 (2011).
11. M.J. Sprague and L.W. Kissinger, J. Am. Chem. Soc., 63, 578 (1941).
12. K.F. Chah, C.A. Eze, C.E. Emuelosi and C.O. Esimone, J. Ethnopharm.,
104, 164 (2006).
13. O.O. Ojo, A.O. Ajayi and I.I. Anibjuwon, J. Zhejiang Univ. Sci., 8, 189
(2007).
14. J.L. McLaughlin, C.J. Chang and D. Smith, in ed.: Atta-ur-Rahman,
Bench-Top Bioassays for the Discovery of Bioactive Natural Products:
An update In: Studies in Natural Product Chemistry, Elsevier Sci. Publ.
BV, Amsterdam, pp. 383-408 (1991).
Conclusion
N-(Benzothiazol-2-yl)-4-methylbenzenesulphonamide
and its metal complexes were synthesized. The compounds
were characterized using magnetic susceptibility, UV/visible
spectrophotometer, elemental microanalysis, infra red, proton
and 13C NMR. The spectral analyses confirmed the structures
of the compounds synthesized. The antimicrobial tests of the
ligand and their metal complexes were carried out on both
multi-resistant bacterial and fungal strains isolated under clinical
conditions and cultured species using agar-well diffusion
method. The tests were both in vitro and in vivo. The anti-
15. A. Giusti and G. Peyronel, Spectrochim. Acta A, 38, 975 (1982).
16. Z.M. Zaki, S.S. Hagga and A.A. Soayed, Spectrosc. Lett., 31, 757
(1998).
17. F.A. Cotton, G. Wilkinson, C.A. Murillo and M. Bochmann, Advanced
Inorganic Chemistry, John Wiley & Sons, New York, edn. 6, pp. 758-
876 (1999).
18. S. Sweetman, Martindale, The Complete Drug Reference, Pharmaceu-
tical Press, London, edn 34; ISBN 0-85369-550-4 (2004).