Synthesis, spectral, antimicrobial and antitumor assessment of Schiff base derived from 2-aminobenzothiazole and its transition metal complexes

Article abstract of DOI:10.1016/j.saa.2011.04.064

N-(thiophen-2-ylmethylene)benzo[d]thiazol-2-amine Schiff base (L) derived from 2-aminobenzothiazole and 2-thiophenecarboxaldehyde was synthesized and characterized using elemental analysis, IR, mass spectra, ¹H NMR and UV-vis spectra. Its complexes with Cu(II), Fe(III), Ni(II) and Zn(II) were prepared and isolated as solid products and characterized by elemental and thermal analyses, spectral techniques as well as magnetic susceptibility. The IR spectra showed that the Schiff base under investigation behaves as bidentate ligand. The UV-vis spectra and magnetic moment data suggested octahedral geometry around Cu(II) and Fe(III) and tetrahedral geometry around Ni(II) and Zn(II). In view of the biological activity of the Schiff base and its complexes, it has been observed that the antimicrobial activity of the Schiff base increased on complexation with the metal ion. In vitro antitumor activity assayed against five human tumor cell lines furnished the significant toxicities of the Schiff base and its complexes.

Full text of DOI:10.1016/j.saa.2011.04.064

Spectrochimica Acta Part A 79 (2011) 1331–1337
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, spectral, antimicrobial and antitumor assessment of Schiff base
derived from 2-aminobenzothiazole and its transition metal complexes
a
a,∗
b
a
Safaa Eldin H. Etaiw , Dina M. Abd El-Aziz , Eman H. Abd El-Zaher , Elham A. Ali
a
Department of Chemistry, Faculty of Science, Tanta University, Tanta, Egypt
Department of Botany, Faculty of Science, Tanta University, Tanta, Egypt
b
a r t i c l e i n f o
a b s t r a c t
Article history:
N-(thiophen-2-ylmethylene)benzo[d]thiazol-2-amine
Schiff
base
(L)
derived
from
2-
Received 25 January 2011
Received in revised form 17 March 2011
Accepted 27 April 2011
aminobenzothiazole and 2-thiophenecarboxaldehyde was synthesized and characterized using
1
elemental analysis, IR, mass spectra, H NMR and UV–vis spectra. Its complexes with Cu(II), Fe(III), Ni(II)
and Zn(II) were prepared and isolated as solid products and characterized by elemental and thermal
analyses, spectral techniques as well as magnetic susceptibility. The IR spectra showed that the Schiff
base under investigation behaves as bidentate ligand. The UV–vis spectra and magnetic moment data
suggested octahedral geometry around Cu(II) and Fe(III) and tetrahedral geometry around Ni(II) and
Zn(II). In view of the biological activity of the Schiff base and its complexes, it has been observed that the
antimicrobial activity of the Schiff base increased on complexation with the metal ion. In vitro antitumor
activity assayed against five human tumor cell lines furnished the significant toxicities of the Schiff base
and its complexes.
Keywords:
Schiff base
Benzothiazole
Thiophenecarboxaldehyde
Biological activity
In vitro antitumor activity
©
2011 Elsevier B.V. All rights reserved.
1
. Introduction
nitrogen, sulfur and/or oxygen as ligand atoms are of interest as
simple structural models of more complicated biological systems
[12]. In the present work, we report the synthesis, characterization
and biological activities of Cu(II), Fe(III), Ni(II) and Zn(II) com-
plexes containing N-(thiophen-2-ylmethylene)benzo[d]thiazol-
2-amine Schiff base derived from 2-aminobenzothiazole and
2-thiophenecarboxaldehyde. The antimicrobial assessment against
the fungal and the bacterial microorganisms were studied. The
cytotoxicities against five human cancer cell lines were examined.
Schiff bases form an interesting class of ligands that has enjoyed
popular use in the coordination chemistry of transition, inner-
transition and main group elements [1,2]. Schiff bases have been
reported to show a variety of biological actions by virtue of the
azomethine linkage, which is responsible for various antibacterial,
antifungal, herbicidal and clinical activities [3–5]. Polyfunctional
ligands based on benzazole derivatives as 2-aminobenzothiazole,
2
-aminothiazole and 2-aminobenzoxazole are relevant due to their
biological activity as fungicides, antibiotics, pesticides and neu-
roprotectors [6–8]. Thiazole derivatives are widely used in the
synthesis of the medicinal products such as sulphathiazole [9].
Thiazole and its derivatives play significant part in the animal
kingdom. Vitamin B1, Penicillin and coenzyme cocarboxylase con-
tain the thiazole ring. Benzothiazole ring is present in various
marine or terrestrial natural compounds which have useful bio-
logical activities [10]. Transition metal ions play a vital role in a
vast number of widely different biological processes [11]. More-
over, the activity can be enhanced when the biologically active
ligand is coordinated to a transition metal ion. Metal complexes
of Schiff bases derived from heterocyclic compounds containing
2
. Experimental
2.1. Materials and instrumentation
All chemicals used in this study were of the purest grade
and purchased from Aldrich and used without further purifica-
tion. Elemental analyses were performed on a Perkin-Elmer 2400
automatic elemental analyzer. Mass spectra were recorded using
Finnigan MAT 8200 mass spectrophotometer. Infrared spectra were
recorded on a Bruker vector 22 spectrophotometer applying KBr
discs in the range of 4000–400 cm . Electronic absorption spectra
in the visible and ultraviolet regions were measured on a Shi-
madzu 3101 PC spectrophotometer as a Nujol mull matrix. The
magnetic susceptibility was determined with a Magnetic suscepti-
−
1
bility balance 436 Devon Park Drive (USA) using Hg[Co(SCN) ] as
calibrant. Nuclear magnetic resonance spectra were carried out on a
Bruker DPX 200 spectrometer, using deuterated dimethylsulfoxide
∗ Corresponding author. Tel.: +20 105084742; fax: +20 403350804.
4
E-mail addresses: dina.mohamed2@science.tanta.edu.eg,
drdinamoh@yahoo.com (D.M. Abd El-Aziz).
1
386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.04.064

1
332
S.E.H. Etaiw et al. / Spectrochimica Acta Part A 79 (2011) 1331–1337
(
DMSO-d ) as a solvent. The thermogravimetric analysis (TGA) was
0.1 mL of each solution was spread onto agar plates of correspond-
ing media. Controls without the compounds were prepared and the
plates were incubated at proper temperature (as mentioned above)
for 24 h, and then the numbers of colony forming units (CFU) were
recorded. The surviving ratio (M/C) was calculated for each chosen
organism at different compound concentrations against that of the
control, where M is the number of organisms in presence of differ-
ent compound concentrations and C is the number of organisms in
absence of compound (control).
6
◦
performed on Shimadzu AT-50 thermal analyzer in the range 25 C
up to 800 C with heating rate 10 C/min in a nitrogen atmosphere.
◦
◦
2
.2. Synthesis of
N-(thiophen-2-ylmethylene)benzo[d]thiazol-2-amine Schiff base
and their complexes
The Schiff base (L) was prepared by the condensation
reaction of 2-aminobenzothiazole (0.15 g; 1 mmol) and 2-
thiophenecarboxaldhyde (0.12 g; 1.1 mmol) dissolved in 30 mL
absolute EtOH, in the presence of few drops of piperidine. The
resulting mixture was stirred well, refluxed for 7 h. The mixture
was concentrated to its half volume then cooled. Petroleum ether
was added to the reaction mixture dropwise until a product began
to precipitate. The formed product was filtered off, washed several
times with EtOH, recrystalized from EtOH.
2.5. Antitumor activity
In vitro potential cytotoxicity of the complexes was tested using
the method of Skehan et al. [14]. Cells were plated in 96-multiwell
4
plate (10 cells/well) for 24 h before treatment with the complexes
to allow attachment of cell to the wall of the plate. Different con-
centrations of the compounds under test (0, 1, 2.5, 5, 10, 15, 20
and 50 ␮g/mL) were added to the cell monolayer, triplicate wells
were prepared for each individual dose. Monolayer cells were incu-
2
.3. Synthesis of metal complexes
◦
bated with the compounds for 48 h at 37 C and in atmosphere of
5
% CO . After 48 h, cells were fixed, washed and stained with Sulfo-
2
Cu(II) and Fe(III) complexes were prepared by mixing an ethano-
lic (20 mL) solution of L (2 mmol) with metal salts (1 mmol), namely,
Rhodamine-B stain. Excess stain was washed with acetic acid and
attached stain was recovered with Tris EDTA buffer. Color intensity
was measured in an ELISA reader. The relation between surviving
fraction and drug concentration is plotted to get the survival curve
of each tumor cell line after the specified compound.
CuCl ·2H O and FeCl ·6H O in EtOH (10 mL) with continuous stir-
2
2
3
2
ring. The mixture was then refluxed for 6–8 h. The solution was
concentrated. The solid products obtained were filtered, washed
with cold ethanol and dried in vacuum. Ni(II) and Zn(II) complexes
were prepared by mixing the Schiff base (2 mmol) with metal salts,
namely, Ni(AcO) ·4H O and Zn(AcO) , in the solid state and melted
3
. Results and discussion
2
2
2
in oil bath for 6–8 h. After cooling, the solid was finely ground and
washed with diethyle ether.
The level of the purity of L has been checked by running TLC on a
silica gel coated plate using EtOAc–EtOH (6:4, v/v) as the eluent. The
elemental analysis data of the Schiff base and its metal complexes
agree well with the proposed composition of the Schiff base and its
metal complexes, Table 1.
2
.4. Antimicrobial assessment
The fungal microorganisms chosen to test the antimicrobial
activity of the synthesized compounds were Candida albicans,
Aspergillus flavus, Asperigllus niger and Fusarium oxysporum. On the
other hand, Escherchia coli, Klebsielia pneumoniae and Staphylo-
coccus aureus were used as the bacterial microorganism. Nutrient
agar was used for growing bacterial cultures. On the other hand,
Sabouraud dextrose agar was used for the growth of C. albicans
and Cazpek’s dox agar was used for the growth of A. flavus and A.
niger. The tested compounds were water insoluble; the cut plug
method was employed to determine the antimicrobial activity of
the synthesized compounds. A 0.5 mL spores or cell suspension
were prepared and counted, then mixed with 9.5 mL of the cor-
responding sterilized melted media, and left to solidify at room
temperature. Wells are made in seeded agar plate with different
organisms under investigation by cork borer with diameter 8 mm
and each one was filled with 5 mg of the tested compounds. All the
3
.1. Mass spectra
The mass spectrum of L, supplementary material, exhibits the
+
molecular ion peak [M ] at m/z = 244 (80%). This molecular ion
undergoes two major fragmentation pathways (Scheme 1). The first
one includes the elimination of H to give ion-peak at m/z = 243
•
(base peak). This fragment undergoes cleavage to give ion peak at
m/z = 135 (66%). This can be attributed to fragment ion of benzoth-
iazole moiety. This fragment ion undergoes further fragmentation
to give ion peak at m/z = 77 (6%) which can be attributed to the
phenyl radical ion. The second fragmentation pathway includes ion
peak at m/z = 110 (6%) resulting from the elimination of benzoth-
iazole moiety. Also, thiophene radical ion was observed at m/z = 82
(26%). This fragment ion undergoes fragmentation by elimination
•
+•
of HS radical to give fragment ion radical [HC C–C C] at m/z = 50
9%). Analysis by mass spectroscopy for the metal complexes occurs
◦
plates were incubated at proper temperature (37 C for S. aureus,
(
◦
E. coli, K. pneumonia, C. albicans and 27 C for A. niger and A. flavus)
mainly via initial loss of chlorine atoms and solvent molecules, fol-
lowed by losing the metal ion. After losing the metal, the ligand
molecular ion peak appeared at m/z = 244.
for 24 h in case of bacteria and 72 h in case of fungi plates, and then
the inhibition zone diameters were measured [13]. Nystatin used
as antifungal control and ceftriaxone used as antibacterial control
for comparing the results with nystatin and ceftriaxone inhibition
zone.
.2. 1H NMR
3
The formation of L was supported by the 1H NMR spectrum,
2
.4.1. Measuring the organisms surviving ratio
A suspension of each standard organism (0.5 mL) was mixed
supplementary material, by the appearance of a sharp singlet at
9.40 ppm, corresponding to the azomethine proton. The multisig-
nals within the range 7.32–7.58 ppm are assigned to the aromatic
protons of benzothiazole ring. Moreover, the multisignals within
the range 7.93–8.10 ppm are attributed to the protons of the thio-
phene ring. The 1H NMR spectrum of the Zn(II) complex was
compared with that of the parent Schiff base. The –CH N– pro-
ton resonance appeared at 9.40 ppm as a sharp singlet is shifted to
with 9.5 mL of the 10-fold diluted corresponding media broth in
a sterile test tube containing the tested compound. The amount
of compound present was such to give 5, 10, 15, and 20 mg/mL in
the final solution. The seeded tubes were then shaken at 250 rpm
(
round/minute) at shaker incubator and incubated at proper tem-
perature overnight. The solutions were then diluted 2-fold and

S.E.H. Etaiw et al. / Spectrochimica Acta Part A 79 (2011) 1331–1337
1333
Table 1
Analytical and physical data for the Schiff base and its complexes.
ꢁm (ꢂ 1 mol cm2)
−
−1
Compounds
Empirical formula
Color
Elemental analysis Found(Calc.)%
ꢀeff (BM)
%
C
%H
%N
L
C12H8N2S2
Yellow
Green
Orange
Green
58.57(58.99)
33.70(33.30)
38.19(38.54)
45.05(45.63)
44.08(44.92)
3.44(3.30)
3.20(3.30)
4.40(4.04)
3.60(3.35)
3.57(3.30)
11.28(11.47)
6.90(6.50)
5.99(5.62)
6.70(6.65)
6.60(6.55)
–
1.82
3.48
4.15
–
70
98.5
9.3
8.5
[
[
[
[
CuLCl (H2O)3]Cl
FeLCl2(EtOH)2]Cl
NiL(OAc)2]
CuC12H14N2S2O3Cl2
FeC16H24N2S2O4Cl3
NiC16H14N2S2O4
ZnC16H14N2S2O4
ZnL(OAc)2]
Orange
diamagnetic
9
.3 ppm in the Zn(II) complex with dramatic decrease in intensity
3.4. IR spectra
suggest that the azomethine nitrogen is involved in coordination
with Zn(II) in the complex. A new signal at 3.7 ppm may be assigned
to the proton of the water molecules. The multisignals within the
range of 2.4–2.5 ppm are assigned to the protons of the acetate
groups in the complex.
Preliminary identification regarding the formation of L was
obtained from the absence of the IR bands characteristic for the
amino group of 2-aminobenzothiazole and the carbonyl group
of 2-thiophenecarboxaldehyde. This is further confirmed by the
−
1
appearance of new bands at 1642 and 1014 cm
characteristic
of ꢃC N and ꢄCH N of the azomethine group, Table 2. The bands
−
1
3
.3. Molar conductivity measurements
observed at 1572 and 710 cm are attributed to ꢃC N and ꢃ
C–S–C
−
1
of thiazole ring [16]. The bands located at 1530 and 1445 cm
can be assigned to the ꢃC C of the aromatic ring. The two bands
at 3056 and 2980 cm are due to the asymmetric and symmetric
The molar conductivities of 10−3 M solution of the metal com-
◦
−1
plexes in DMF were measured at 25 C. Table 1 shows the molar
conductance (ꢁm) values of the metal complexes. It is concluded
from the results that Cu(II) and Fe(III) complexes were found to
have molar conductance values of 70 and 98.5 ꢂ mol cm ,
respectively, indicating the ionic nature of these complexes [15].
Ni(II) and Zn (II) complexes were found to have molar conductance
stretching vibrations of the CH group of the aromatic ring. The com-
plexation of L with Cu(II), Fe(III), Ni(II) and Zn(II) leads to small shift
in the bands assigned to ꢃC N of the azomethine group and ꢃC–S–C
of thiazole ring. This is probably due to the coordination proper-
ties of the ligand and suggesting the involvement of sulfur atom
in the bonding with the metal ions [17]. Also, the IR bands near
430, 500 and 555 cm are ascribed to ꢃM–S, ꢃM–O and ꢃM–N [18],
respectively. This presents a good evidence for the participation of
thiophene sulfur atom in bond formation. Moreover the IR spec-
tra of Cu(II) and Fe(III) complexes exhibit a medium band around
−
1
−1
2
−1
−1
2
values of 9.3 and 8.5 ꢂ mol cm , respectively, supporting the
non-electrolytic nature.
−
1
−
1
2
80 cm , which are assigned to ꢃ
bands near 3400 cm , which are assigned to ꢃOH of the water or
[19]. All complexes display
H
C
N
M–Cl
−
1
N
S
S
ethanol molecules [20].
m/z = 244 (80%)
Molecular ion peak
3.5. Thermal analysis
The weight loss of thermal gravimetric analysis (TGA) for L
N
H
and its complexes was calculated, Table 3, for the different steps
and compared with those of theoretically calculated for the sug-
gested formula based on the results of elemental analysis and mass
spectra. Differential thermal analysis (DTA) curve of L shows an
S
H
C
N
◦
endothermic peak at 125 C. TG curve exhibits no mass loss at that
N
C
N
temperature range. This DTA peak can be assigned to the lattice
or chemical rearrangement of the compound. The endothermic
S
S
S
m/z = 110 (6%)
m/z = 243 (100%)
Base peak
◦
peak observed at 280 C, with mass loss (100%) is assigned to the
complete decomposition of L. The thermograms of the complexes
◦
exhibit thermal stability from room temperature up to 155 C (Cu),
-
(HCN + H)
CN
◦
◦
◦
S
70 C (Fe), 175 C (Ni) and 158 C (Zn), indicating that no water of
crystallization are present in the complexes. TGA and DTA curves
suggest that the complexes loss the coordinated water or ethanol
molecules followed by chlorine atoms and acetate anions. The
+
+
N
S
S
◦
exothermic decomposition for all complexes began at ca. 260 C
m/z = 82 (26%)
m/z = 135 (66%)
by the elimination of thiophene moiety followed by benzothiazole
moiety and finally the formation of the residue.
-
HS
- NCS
+
3
.6. Electronic spectra and magnetic moments
+
The electronic spectrum of the L, as Nujol mull matrix, Fig. 1,
HC C - C
C
−
1
exhibits absorption bands at ca. 210 nm (47 619 cm ) and 265 nm
m/z= 50 (9%)
−
1
(37,735 cm ), which are corresponding to ␲–␲* transitions of
the benzenoid system of benzothiazole moiety which are due to
m/z= 77 (6%)
1
1
1
1
(
La ← A) and ( L ← A) states, respectively [21]. The absorp-
b
−
1
Scheme 1. Proposed fragmentation route of Schiff base L.
tion band at 230 nm (43,478 cm ) is due to the ␲–␲* transitions

1
334
S.E.H. Etaiw et al. / Spectrochimica Acta Part A 79 (2011) 1331–1337
Table 2
IR spectral bands (cm−1) of the Schiff base and its metal complexes.
Compounds
L
ꢃCH Aromatic
ꢃC N thiazole
ꢃC
C
ꢃC N azomethine
ꢄHC
N
ꢃC–S–C
ꢃM–N
ꢃM–O
ꢃM–S
ꢃM–Cl
3056, 2980
3103, 2984
3057, 2970
3000, 2983
3100, 2998
1572
1576
1581
1615
1588
1530, 1445
1540, 1463
1467
1547, 1454
1532, 1458
1642
1647
1653
1638
1649
1015
1013
1014
1019
1014
710
706
707
721
721
–
555
586
547
559
–
502
482
502
502
–
426
417
430
435
–
288
263
–
[
[
[
[
CuLCl(H2O)3]Cl
FeLCl2(EtOH)2]Cl
NiL(OAc)2]
ZnL(OAc)2]
–
Table 3
Thermal gravimetric analysis data for the investigated complexes.
◦
Compound
Temperature ( C)
Weight loss % Found(Calc.)
Weight of residue % Found(Calc.)
Assignment
[CuLCl (H2O)3]Cl
27–155
–
Thermally stable
1
4
6
55–470
50.0(48.34)
3 coordinated water, 2 chlorine and
thiophene moiety
Complete decomposition and elimination
of benzothiazole moiety
70–655
35.6(34.70)
55–800
27–70
14.4(14.7)
Residue: Cu metal
[FeLCl2(EtOH)2]Cl
–
Thermally stable
7
0–160
9.98(9.24)
31.42(30.60)
17.00(16.87)
30.35(29.92)
1 coordinated ethanol
1
2
3
60–255
55–370
70–500
1 coordinated ethanol and 3 chlorine
Elimination of thiophene moiety
Complete decomposition and elimination
of benzothiazole moiety
5
00–800
11.25(10.44)
14.62(13.77)
22.22(22.78)
Residue: Fe metal
[
NiL(OAc)2]
ZnL(OAc)2]
27–175
75–250
50–370
70–700
–
Thermally stable
1
2
3
28.10(28.02)
19.20(19.80)
32.00(32.10)
2 coordinated acetate groups
Elimination of thiophene moiety
Elimination of benzothiazole +
HCN
6.08(6.41)
7
00–800
Residue: Ni metal
[
27–158
58–245
45–350
50–580
–
Thermally stable
1
2
3
27.45(27.58)
19.65(19.67)
24.74(24.11)
2 coordinated acetate groups
Elimination of thiophene moiety
Elimination of benzothiazole +
HCN
5.94(6.32)
580–800
Residue: ZnS
Fig. 1. Nujol mull electronic spectra of L and its metal complexes (a) L, (b) [CuLCl(H2O)3]Cl, (c) [FeLCl2(EtOH)2]Cl, (d) [NiL(OAc)2], and (e) [ZnL(OAc)2].

S.E.H. Etaiw et al. / Spectrochimica Acta Part A 79 (2011) 1331–1337
1335
(1
2
L ← A) state of the thiazole moiety [22]. The two bands at
1
b
− −1
15 nm (46,512 cm ) and 255 nm (39,215 cm ) are attributed to
1
(a)
1
1
the ␲–␲* transition of the thiophene moieties due to ( La ← A) and
1
1
(
(
L ← A) states, respectively [23]. The shoulder band at 335 nm
b
−1
29,851 cm ) may be assigned to the ␲–␲* transition [18,24]. This
0
1000
2000
3000
4000
5000
6000
band was found in the spectra of all complexes with small shift.
This may be attributed to the donation of the lone pairs of electron
of nitrogen atom of Schiff base to the metal ion [8]. While the broad
−1
band at 375 nm (26,667 cm ) can be attributed to the transition
within the molecule, essentially an intramolecular charge transfers
interaction. The electronic absorption spectrum of Cu(II) com-
plex exhibits three broad, low intensity band centered at 655 nm
− −1 −1
1
(
15,267 cm ), 625 nm (16,000 cm ) and 581 nm (17,211 cm ).
These bands may reasonably be assigned to Cu(II) d–d transitions
2
2
2
2
–dxy) and 2B1g → Eg
2
B1g → A (d
–dz2), B1g → B (d
1g
x2−y2
2g
x2−y2
(b)
(
d
–dxz, dyz) transitions, respectively. These d–d transitions are
x2−y2
2
normally close in energy [18]. These transitions are due to the Eg
and T states of the octahedral Cu(II) ion (d ) split under the influ-
2
9
2
g
ence of the asymmetric filling causing the tetragonal distortion. The
energy level sequence will depend on the amount of tetragonal dis-
tortion due to the ligand field and the Jahn–Teller effect [25]. The
magnetic moment of 1.82 BM, is slightly higher than the spin-only
value 1.73 BM expected for one unpaired electron, which offers pos-
sibility of an octahedral geometry [26]. A shoulder band observed
0
1000
2000
3000
4000
5000
6000
−1
at 460 nm (21,739 cm ) is due to ligand–metal change transfer
LMCT) [18]. The electronic spectrum of Fe (III) complex displays
(
−
1
absorption bands of low intensity at 655 nm (15,267 cm ), 625 nm
(
−1
−1
16,000 cm ) and 581 nm (17,211 cm ). These bands are assigned
Fig. 2. X-band ESR spectra of (a) [CuLCl(H2O)3]Cl and (b) [FeLCl2(EtOH)2]Cl.
to octahedral geometry around Fe(III) [20]. The magnetic moment
value of 3.50 BM is lower than that of high spin d5 configuration,
indicating the probability of equilibrium between high and low spin
states [20]. The electronic spectrum of the green Ni(II) complex
is consistent with tetrahedral geometry showing d–d transition
shows broad signal with of axial symmetry with g value at 2.1 cor-
responds to low spin iron (III) [36,37]. In addition to a weak signal at
3
.9, this is known to be characteristic of distorted high spin iron (III)
38]. These two signals confirm the probability of the equilibrium
between high and low spin states.
[
at 581 nm (17,211 cm ) assignable to 3T1(F) → T
−
1
3
ꢃ3 [27]. The
1(P)
weaker bands on either side of this transition being assigned to
spin forbidden bands [28]. These transitions suggest the tetrahe-
dral geometry around the Ni(II) ion. The shoulder band observed
3.8. Antimicrobial assessment
−
1
at 440 nm (22,727 cm ) corresponds to the excited state derived
The results of antimicrobial assessment, Table 4, exhibit that L
1
from the G term [29]. The magnetic moment value (4.15 BM) is
has a high antifungal activity against A. niger with 17 mm inhibition
zone. Cu(II), Ni(II) and Zn(II) complexes have high antimicrobial
activity against E. coli, the inhibitions zones are 18, 14 and 11 mm,
respectively. Zn(II) complex has antibacterial activity against Kleb-
sielia sp. with 16 mm inhibition zone. L and its Cu(II) and Zn(II)
complexes exhibit large effect on bacterial and fungal species
because they show large clear inhibition zones with the tested bac-
teria and fungi on solid agar media: the diameters of inhibition
zones ranged between (18–25 mm) by the end of incubation. L had
no antiyeast activity against C. albicans. It was observed that antimi-
crobial activity increased when tested compound is coordinated
with Cu, Zn and Ni. Moreover, Zn(II) complex had antifungal activ-
ity against A. niger more than nystatin which was used as control. On
other hand, Cu(II) complex had high antibacterial activity against
near to the value expected for tetrahedral Ni(II) [30]. The elec-
tronic spectrum of the orange Zn(II) complex shows broad band
at 550 nm (18,182 cm ) corresponds to LMCT. On the other hand,
the Zn(II) complex is found to be diamagnetic as expected for d10
configuration. It has been reported that for tetracoordinated Zn(II)
complexes, tetrahedral is the most preferred one [31].
−1
3.7. EPR
The EPR spectrum of Cu(II) complex at room temperature
300 K), Fig. 2, exhibits an axial pattern with no obvious hyperfine
(
structure. The absence of hyperfine structure at room temperature
may be attributed the strong dipolar and exchange interactions
between the Cu(II) ions [32]. The g|| (2.09) and g⊥ (2.05) values sug-
1
.2
1
gest that d
may be the ground state as g|| > g⊥ > 2.04, which is
x2−y2
Aniger
E. coli
consistent with elongated tetragonally distorted octahedral Cu(II)
complexes [33]. Also, the trend g|| > g⊥ > ge (2.0023) observed for
this complex indicated that the unpaired electron is most likely in
0
0
.8
.6
the d
orbital and the spectral features are of axial symmetry
x2−y2
[
30]. It has been reported that g|| value of Cu(II) complex can be used
0.4
0.2
0
as a measure of the covalent character of the metal-ligand bond.
The g|| < 2.3 in agreement with the covalent character of the metal
ligand bond [34]. The axial symmetry parameter G, determined as
G = (g|| − 2)/(g⊥ − 2). The parameter G is found to be much less than
Control
5
10
15
20
Ratio of Surviving
4
suggesting considerable exchange interaction in the solid state
Cu(II) complex [33,35]. The EPR spectrum of Fe(III) complex, Fig. 2,
Fig. 3. Growth inhibition of different concentration of Zn(II) complex.

1
336
S.E.H. Etaiw et al. / Spectrochimica Acta Part A 79 (2011) 1331–1337
Fig. 4. Survival curves of some tumor cell lines.
Table 4
Diameters of inhibition zone (mm) of tested compounds against different species of microorganisms.
Compounds
Inhibition zone/mm
E. coli
Staphylococcus aureus
Klebsiella sp.
Candida albicans
A. niger
A. flavus var. coulmnaris
Fusarium oxysporum
L
0
18
0
14
11
0
0
0
0
0
0
0
0
9
14
16
0
0
0
0
0
0
0
0
17
20
0
0
0
0
0
0
0
0
0
0
0
[
[
[
[
CuLCl (H2O)3]Cl
FeLCl2(EtOH)2]Cl
NiL(OAc)2]
0
ZnL(OAc)2]
25
20
0
Nystatin
Ceftriaxone
0
13
20
0
13
0
21
17

S.E.H. Etaiw et al. / Spectrochimica Acta Part A 79 (2011) 1331–1337
1337
Table 5
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the online version, at doi:10.1016/j.saa.2011.04.064.