Co(II), Ni(II) and Cu(II) complexes with coumarin-8-yl Schiff-bases: Spectroscopic, in vitro antimicrobial, DNA cleavage and fluorescence studies

Article abstract of DOI:10.1016/j.saa.2011.04.032

A new series of Co(II), Ni(II) and Cu(II) complexes of the type ML·2H₂O of Schiff-bases derived from m-substituted thiosemicarbazides and 8-acetyl-7-hydroxy-4-methylcoumarin have been synthesized and characterized by spectroscopic studies. Schiff-bases exhibit thiol-thione tautomerism wherein sulphur plays an important role in the coordination. The coordination possibility of the Schiff-bases towards metal ions have been proposed in the light of elemental analyses, spectral (IR, UV-vis, FAB-mass, ESR and fluorescence), magnetic and thermal studies. The low molar conductance values in DMF indicate that, the metal complexes are non-electrolytes. The cyclic voltammetric studies suggested that, the Cu(II) and Ni(II) complexes are of single electron transfer quasi-reversible nature. The Schiff-bases and its metal complexes have been evaluated for their in vitro antibacterial (Escherichia coli, Staphilococcus aureus, Bascillus subtilis and Salmonella typhi) and antifungal activities (Candida albicans, Cladosporium and Aspergillus niger) by MIC method. The Schiff-base I and its metal complexes exhibited DNA cleavage activity on isolated DNA of A. niger.

Full text of DOI:10.1016/j.saa.2011.04.032

Spectrochimica Acta Part A 79 (2011) 1128–1136
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Co(II), Ni(II) and Cu(II) complexes with coumarin-8-yl Schiff-bases:
Spectroscopic, in vitro antimicrobial, DNA cleavage and fluorescence studies
a,∗
a
a
a
b
Sangamesh A. Patil , Shrishila N. Unki , Ajaykumar D. Kulkarni , Vinod H. Naik , Prema S. Badami
a
P.G. Department of Chemistry, Karnatak University, Dharwad 580003, Karnataka, India
Department of Chemistry, Shri Sharanabasaveswar College of Science, Gulbarga 585102, Karnataka, India
b
a r t i c l e i n f o
a b s t r a c t
Article history:
A new series of Co(II), Ni(II) and Cu(II) complexes of the type ML·2H O of Schiff-bases derived from m-
2
Received 3 November 2010
Received in revised form 7 April 2011
Accepted 15 April 2011
substituted thiosemicarbazides and 8-acetyl-7-hydroxy-4-methylcoumarin have been synthesized and
characterized by spectroscopic studies. Schiff-bases exhibit thiol–thione tautomerism wherein sulphur
plays an important role in the coordination. The coordination possibility of the Schiff-bases towards
metal ions have been proposed in the light of elemental analyses, spectral (IR, UV–vis, FAB-mass, ESR and
fluorescence), magnetic and thermal studies. The low molar conductance values in DMF indicate that, the
metal complexes are non-electrolytes. The cyclic voltammetric studies suggested that, the Cu(II) and Ni(II)
complexes are of single electron transfer quasi-reversible nature. The Schiff-bases and its metal com-
plexes have been evaluated for their in vitro antibacterial (Escherichia coli, Staphilococcus aureus, Bascillus
subtilis and Salmonella typhi) and antifungal activities (Candida albicans, Cladosporium and Aspergillus
niger) by MIC method. The Schiff-base I and its metal complexes exhibited DNA cleavage activity on
isolated DNA of A. niger.
Keywords:
Antimicrobial
Coumarin
Thiosemicarbazides
Spectroscopic studies
Schiff-bases
Transition metal complexes
©
2011 Elsevier B.V. All rights reserved.
1
. Introduction
by inserting suitable aldehyde or ketone possessing a further donor
atom to render the ligand polydentate [21]. On the other hand,
Schiff-bases derived from coumarin and its metal complexes have
been found to exhibit biological activities and plant regulating
activities [16,22]. The interaction of transition metal complexes
with DNA has extensively been studied for their usage as probes
for DNA structure and their potential application in chemother-
apy. The characteristics common to these complexes are that the
molecule has a high affinity for double-stranded DNA and that the
molecule binds a redox-active metal ion cofactor. The interaction
of a variety of d6 Ru(II) and Rh(III) complexes of polypyridine or
1,10-phenanthroline (phen) ligand with DNA has been extensively
studied [23–25]. They showed that transition metal complexes
can interact noncovalently with DNA by intercalation, groove-face
binding or external electrostatic binding. Sigman et al. found that
a mixture of phen, Cu2+ and thiol depolymerises poly[d(A-T)] solu-
tions under aerobic conditions [26]. Subsequent work has been
focused on a number of copper complexes of phenanthroline-based
ligands. Very recently, Cu(II) complexes have been reported to be
active in DNA strand scission [27–29].
Schiff-bases have often been used as chelating ligands in coordi-
nation chemistry [1,2]. Schiff-bases with donors (N, O, S, etc.) have
structure similarities with neutral biological systems and due to
presence of imine group are utilized in elucidating the mechanism
of transformation of rasemination reaction in biological system
[
3–5]. Thiosemicarbazide and its derivatives as ligands with poten-
tial sulphur and nitrogen bands are interesting and have gained
special attention not only the structural chemistry of their mul-
tifunctional coordination modes but also of their importance in
medicinal and pharmaceutical field. They show biological activities
including antibacterial antifungal [6–10], antidiabetic [11], anti-
tumor [12], antiproliferative [13], anticancer [14], herbicidal [15],
anticorrosion and anti-inflammatory activities [8–10]. Schiff-bases
represent an important class of compounds because they are uti-
lized as starting materials in the synthesis of industrial products
[
16]. Moreover, Schiff-bases are regarded as privileged ligands [17].
Due to their capability to form complexes with different transition
metals can act as catalysts for many different reactions [18–20]. The
structure of the thiosemicarbazide moiety confers a good chelating
capacity and this property can be increased in thiosemicarbazone
Thus, in continuation of our earlier work on coumarin Schiff-
bases [30–34], herein we report the antimicrobial and DNA
cleavage studies of Co(II), Ni(II) and Cu(II) metal complexes with
coumarin-8-yl Schiff-bases. The structural features of the Schiff-
bases and their metal complexes have been studied by various
spectral and analytical techniques.
∗ Corresponding author. Tel.: +91 836 2770290.
E-mail address: patil1956@rediffmail.com (S.A. Patil).
1
386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.04.032

S.A. Patil et al. / Spectrochimica Acta Part A 79 (2011) 1128–1136
1129
Scheme 1. Synthesis of Schiff-bases.
2
. Experimental
2.2.1. Synthesis of 7-hydroxy-4-methylcoumarin [35]
7
-Hydroxy-4-methyl coumarin was synthesized according to
◦
2.1. Analysis and physical measurements
the literature procedure. [m.p. 185–186 C.]
Carbon, nitrogen and sulphur were estimated by using Ele-
2
.2.2. Synthesis of 7-Hydroxy-4-methyl-8-acetylcoumarin [36]
A mixture of 7-hydroxy-4-methyl coumarin (0.1 mol), acetic
mental Analyzer Truspec (Leco Corporation, USA). The IR spectra
of the Schiff-bases and their Co(II), Ni(II) and Cu(II) complexes
were recorded on a HITACHI-270 IR spectrophotometer in the
anhydride (0.1 mol) and anhydrous aluminum chloride (0.15 mol)
was heated in an oil bath at 160–165 C for 4 h. The mass, after
cooling, was decomposed with ice cold hydrochloric acid and the
product was taken into ether. It was washed well with water and
dried. The product obtained was recrystallized twice with aqueous
◦
−1
4
000–250 cm
region in KBr disc. The electronic spectra of the
complexes were recorded in HPLC grade DMF and DMSO solvent
on a VARIAN CARY 50-BIO UV-spectrophotometer in the region
of 200–1100 nm. The 1H NMR spectra of ligands were recorded in
◦
methanol. [m.p. 161–163 C.]
DMSO-d6 on a BRUKER 300 MHz spectrometer at room tempera-
ture using TMS as an internal reference. The fluorescence studies of
Schiff-bases and their metal complexes were recorded on HITACHI
F-7000 Fluorescence Spectrophotometer (Made in Japan). The solu-
2.2.3. Synthesis of m-substituted thiosemicarbazide
Freshly distilled m-chloroaniline/m-nitroaniline (0.1 mol) was
−3
tions of 10 M concentration were prepared in HPLC grade DMF
and DMSO solvents and the experiment was carried out at room
temperature. The electrochemistry of the metal complexes was
recorded on CHI1110A-electrochemical analyzer (Made in USA)
dissolved in ammonia (20 ml) and carbon disulphide (8 ml) was
added to it gradually with stirring in ice bath. Ethanol (30 ml) was
added to it gradually with constant stirring in ice bath till car-
bon disulphide was completely dissolved. The reaction mixture
was then allowed to stand for 2–3 h. An aqueous sodium chloroac-
etate (0.1 mol) solution was added followed by hydrazine hydrate
in dimethyl formamide (DMF) containing 0.05 M n-Bu NClO4 as
4
the supporting electrolyte. The ESR spectrum was recorded on
Varian-E-4X-band EPR spectrometer and the field set is 3000 G at
modulation frequency of 100 kHz under liquid nitrogen temper-
ature using TCNE as ‘g’ marker. FAB-Mass spectra were recorded
on a JEOL SX 102/DA-6000 mass spectrometer/data system using
argon/xenon (6 kV, 10 Am) as the FAB gas. The accelerating voltage
was 10 kV and the spectra were recorded at room temperature and
m-nitrobenzyl alcohol was used as the matrix. Thermogravimetric
(10 ml). The reaction mixture was stirred for 2–3 h and allowed to
stand overnight. The crystals separated were filtered washed with
cold ethanol and recrystallized from hot ethanol. [m.p. 192–193 C.]
◦
2.2.4. Synthesis of Schiff-bases [I–II]
The Schiff-bases were synthesized by the condensation of m-
◦
substituted thiosemicarbazide (0.01 mol) and 8-acetyl-7-hydroxy-
4-methylcoumarin (0.01 mol), dissolved in 30 ml alcoholic medium
containing few drops of concentrated HCl. The resulting mixture
was refluxed for 3–4 h. The solid product separated on evaporation
of the solvent was filtered, washed with alcohol and then finely
recrystallized from EtOH.
analyses data were measured from room temperature to 1000 C
◦
at a heating rate of 10 C/min. The data were obtained by using TA
Instruments Water LLC, New castel, Delware, USA. Model; DCS Q 20,
009. Molar conductivity measurements were recorded on ELICO-
CM-82 T Conductivity Bridge with a cell having cell constant 0.51
and magnetic moment of the complexes was carried out by using
faraday balance.
2
(
SB I): (E)-N-(3-chlorophenyl)-2-(1-(7-hydroxy-4-methyl-2-oxo-
2H-chromen-8-yl)ethylidene)hydrazinecarbothioamide. Yield: 69%.
◦
+
1
M.p: 229 C. FAB MS: m/z 401 M , m/z 403 (M+2). H NMR (d6
2.2. Methods
DMSO) (ppm): 11.15 (s, 1H, OH), 10.50 (s, 1H, NH), 9.93 (s, 1H, NH),
6
.31–7.61 (m, 8H, Ar–H), 3.67 (s, 1H, SH), 2.51 (s, 3H, CH ), 2.81
3
13
All chemicals and solvents used were of AR grade. All metal(II)
(s, 3H, CH ). C NMR (d6 DMSO) (ppm): 88.41–142.04 (aromatic
3
salts were used as their chlorides.
carbon), 155.68 (C N), 161.16 (C O), 19.5 (CH ), 21.90 (CH ).
3
3

1
130
S.A. Patil et al. / Spectrochimica Acta Part A 79 (2011) 1128–1136
(SB II): (E)-2-(1-(7-hydroxy-4-methyl-2-oxo-2H-chromen-8-
yl)ethylidene)-N-(3-nitrophenyl)hydrazinecarbothioamide.
Yield:
◦
+ 1
7
1
8
1%. M.p: 224 C. FAB MS: m/z 412 M . H NMR (d6 DMSO) (ppm):
1.11 (s, 1H, OH), 10.56 (s, 1H, NH), 9.89 (s, 1H, NH), 6.13–7.63 (m,
13
H, Ar–H), 3.74 (s, 1H, SH), 2.22 (s, 3H, CH ), 2.37 (s, 3H, CH ).
C
3
3
NMR (d6 DMSO) (ppm): 88.41–139.93 (aromatic carbon), 155.68
N), 161.01 (C O), 18.98 (CH ), 22.48 (CH ).
(
C
3
3
2.2.5. Synthesis of Co(II), Ni(II) and Cu(II) complexes [1–6]
A general method has been used for the preparation of
complexes using reaction of metal salts and the corresponding
Schiff-bases in molar ratio (M:L = 1:1). An alcoholic solution (45 ml)
of Schiff-bases (1 mmol) was refluxed with an alcoholic solution
(
5 ml) of 1 mmol of CoCl ·6H O/NiCl ·6H O/CuCl ·2H O on steam
2
2
2
2
2
2
bath for 3 h. The separated complexes were filtered off, washed
several times with 50% (v/v) ethanol–water mixture to remove any
traces of unreacted starting materials, then washed with diethyl
ether and dried in a vacuum desiccator over fused CaCl2.
3
. Pharmacology
3.1. DNA cleavage studies
Preparation of culture media and DNA isolation of Aspergillus
niger microbial strains were done according to the literature pro-
cedure [34,37]. Potato dextrose broth [potato, 250; dextrose, 20; in
(
g/l)] was used for the culture of A. niger.
3.2. Agarose gel electrophoresis
Cleavage products were analyzed by agarose gel electrophore-
sis method [37]. Test samples (1 mg/ml) were prepared in DMF.
The samples (25 ␮g) were added to the isolated DNA of A niger.
◦
The samples were incubated for 2 h at 37 C and then 20 ␮l of DNA
sample (mixed with bromophenol blue dye at 1:1 ratio) was loaded
carefully into the electrophoresis chamber wells along with stan-
dard DNA marker containing TAE buffer (4.84 g Tris base, pH 8.0,
0.5 M EDTA/1 l) and finally loaded on agarose gel and passed the
constant 50 V of electricity for around 30 min. Removed the gel and
stained with 10.0 ␮g/ml ethidium bromide for 10–15 min and the
bands observed under Vilberlourmate Gel documentation system
and photographed to determine the extent of DNA cleavage. Then
the, results were compared with standard DNA marker.
3.3. In vitro antibacterial and antifungal assay
The biological activities of synthesized Schiff-bases and their
Co(II), Ni(II) and Cu(II) complexes have been studied for their
antibacterial and antifungal activities by agar and potato dextrose
agar diffusion method respectively. The antibacterial and antifun-
gal activities were done at 25, 50 and 100 ␮g/ml concentrations in
DMSO solvent by using four bacteria (Escherichia coli, Staphilococ-
cus aureus, Bascillus subtilis and Salmonella typhi) and three fungi (A.
niger, Candida albicans and cladosporium) by the reported method
◦
[
38]. These bacterial strains were incubated for 24 h at 37 C and
◦
fungal strains were incubated for 48 h at 37 C. Standard antibac-
terial (Gentamycine) and antifungal drug (Flucanazole) were used
for comparison under similar conditions.
3.4. Minimum inhibitory concentration (MIC)
Compounds showing promising antibacterial/antifungal activ-
ity were selected for minimum inhibitory concentration studies.
The minimum inhibitory concentration was determined by assay-
−1
ing at 100, 50 and 25 ␮g ml concentrations along with standards
at the same concentrations.

S.A. Patil et al. / Spectrochimica Acta Part A 79 (2011) 1128–1136
1131
Table 2
The important infrared frequencies (in cm−1) of Schiff-bases and their metal complexes.
Compound No.
H-bonded
OH
Co-ordinated water
␯(OH)
␯(C O)
␯(C N)
␯(SH)
␯(C S)
Phenolic
␯(C-O)
␯(C–S)
␯(M–N)
␯(M–S)
–
Streching
I
3303
3294
–
–
1703
1706
1682
1687
1680
1681
1684
1691
1616
1628
1601
1615
1596
1610
1600
1605
2759
2785
1154
1156
1279
1273
1315
1317
1318
1326
1314
1320
–
–
–
–
–
–
II
1
2
3
4
5
6
–
–
–
–
–
–
3424
3428
3442
3438
3446
3433
–
–
–
–
–
–
–
–
–
–
–
–
752
753
750
750
751
749
495
491
498
488
468
478
352
341
357
349
350
353
4
. Results and discussion
The presence of coordinated water molecules in the metal com-
plexes are indicated by the appearance of broad band in the region
−
1
The synthesis of Schiff-bases is schematically represented in
Scheme 1. The Schiff-bases (I and II) form octahedral complexes
3424–3446 cm and two weak bands in the region 750–790 and
−
1
710–735 cm due to ␯(–OH) rocking and wagging modes of vibra-
(
1–6) with CoCl ·6H O/NiCl ·6H O/CuCl ·2H O in ethanol. All the
tions respectively [41].
2
2
2
2
2
2
The new bands in the region of 345–368 and 478–498 cm 1 in all
−
Co(II), Ni(II) and Cu(II) complexes are colored, stable and non-
hygroscopic in nature. All the metal complexes are thought to be
polymeric in nature. These complexes are insoluble in common
organic solvents but soluble in DMF and DMSO. The elemental anal-
yses show that, all the Co(II), Ni(II) and Cu(II) complexes have 1:1
the complexes are assigned to stretching frequencies of (M–O) and
(M–N) bonds respectively. The band in the region 341–353 cm is
due to metal–sulphur bond formation.
On the basis of IR data, it is concluded that, all the metal ions are
coordinated to the azomethine nitrogen, phenolic oxygen, sulphur
atom and lactone oxygen. Thus, the IR spectral data results provide
strong evidences for the complexation of Schiff-bases with metal(II)
ions.
−
1
stoichiometry of the type ML·2H O where ‘L’ stands for a depro-
2
tonated ligand and exhibits thiol–thione tautomerism. The molar
conductance values are too low to account for any dissociation of
the complexes in DMF, indicating the non-electrolytic nature of the
complexes in DMF (Table 1).
4.2. NMR spectral studies of Schiff-bases
4
.1. IR spectral studies
The spectral data of 1H and 13C NMR of all the Schiff-bases are
1
13
given in Section 2. The H and C NMR of Schiff-base II is discussed
here.
The prominent infrared spectral data of Schiff-bases and their
metal complexes are presented in Table 2.
In the 1H NMR spectra of the Schiff-bases II, the NH proton
exhibited two singlet signals at 10.56 ppm (s, 1H) and 9.89 ppm
The IR spectra of the Schiff-bases exhibited two characteristic
−
1
band in the region 3166–3107 and 3174–3050 cm correspond-
ing to two ꢂ(NH) groups. Practically no effect on these frequencies
after complexation indicates non involvement of these groups in
coordination. A characteristic strong band at 2759–2785 cm is
ascribed to ꢂ(SH) and another band around 1156–1154 cm
assigned to ꢂ(C S). These observations suggest that, the Schiff-
bases exhibit thiol–thione tautomerism (Fig. 1). The broad band
at 3294–3303 cm , strong band at 1703–1706, 1616–1628 and
1
(
1
s, 1H) respectively. A characteristic proton signal at 11.11 ppm (s,
H) is assigned to –OH. In addition to this, the multiplet signals in
−
1
the region 6.13–7.63 ppm (m, 8H) are due to aromatic protons. A
sharp singlet signal at 3.74 ppm (s, 1H) is attributed to the SH group.
The singlet observed at 2.22 ppm (s, 3H) and at 2.37 (s, 3H) ppm is
due to CH3 and acetyl CH3 respectively. Hence, NMR results sup-
port the IR inferences and confirms the thiol–thione tautomerism
of the Schiff bases.
−
1
is
−1
−1
273–1279 cm
assigned to H-bonded –OH stretching, ꢂ(C O)
In the representative 13C NMR spectrum of the Schiff-base II, the
signal observed at 162.01 ppm is ascribed to lactonyl carbon (C O)
of the coumarin moiety. A characteristic signal at 155.68 ppm is
assigned to (C N). In addition to this the characteristic signals in
the region 88.41–139.93 ppm are assigned to aromatic carbon and
lactonic carbonyl, ꢂ(C N) and phenolic ꢂ(C–O) vibrations respec-
tively.
In comparison with the IR spectra of the Schiff-bases, all the
−
1
metal complexes exhibit downward shift 13–23 cm
of ꢂ(C N)
indicating the participation of azomethine nitrogen in the coor-
dination to the metal ion. The deprotonation of the thiol group
is indicated by the absence of a band in the metal complexes at
Table 3
−1
2
759–2785 cm , which is due to ꢂ(SH) of Schiff-bases, indicating
Electronic absorption spectral data (in DMF) of Co(II), Ni(II) and Cu(II) complexes.
that, the Schiff bases are coordinated to the metal ion through the
thiolate sulphur atom. This is further supported by the lower fre-
quency band appeared in the region 749–753 cm in the metal
Complex No. ꢃmax in nm (cm−1)
Band assignments
Geometry
−
1
4
4
4
4
3
3
3
3
3
3
2
4
1
2
3
1057 (9460)
44 (18,382)
1048 (9541)
49 (18,214)
931 (10,741)
609 (16,420)
382 (26,178)
925 (10,810)
T1g(F) → T2g(F) (ꢂ1)
Octahedral
4
5
T1g (F) → T1g (P) (ꢂ3)
complexes due to ꢂ(C–S). The high intensity band due to phe-
4
−
1
T1g(F) → T2g(F) (ꢂ1)
Octahedral
Octahedral
nolic ꢂ(C–O) appeared in the region at 1273–1279 cm
in the
4
5
T1g(F) → T1g(P) (ꢂ3)
Schiff-bases appeared as a medium to high intensity band in the
A2g(F) → T2g(F) (ꢂ1)
−1
1
315–1326 cm region in the complexes. These observations sup-
A
2
(F) → T (F) (ꢂ )
g
1g
2
port the formation of M–O bonds via deprotonation. So, the –OH
groups have been bonded to the metal ion via deprotination.
The most notable change in the spectral features of Schiff-
bases when coordinated to metal ion is the lower shift of lactone
A2g(F) → T1g(P) (ꢂ3)
A2g(F) → T2g(F) (ꢂ1)
A2g(F) → T1g(F) (ꢂ2)
A2g(F) → T1g(P) (ꢂ3)
4
Octahedral
6
3
01 (16,638)
78 (26,455)
2
5
6
613 (16,313)
395 (25,316)
621 (16,103)
Tg ← Eg
Distorted
octahedral
Distorted
octahedral
−1
ꢂ(C O) to the extent of about 15–25 cm , suggesting that, the
metal is coordinated to the lactone oxygen [39]. This further sup-
ported by downward shift in ꢂ(O–C–O) of the coumarin ring [40].
L → M
2
Tg ← 2Eg
397 (25,188)
L → M

1
132
S.A. Patil et al. / Spectrochimica Acta Part A 79 (2011) 1128–1136
Fig. 1. Structure of Schiff-bases: thiol–thione tautomerism.
the signals at 18.98 and 22.48 ppm are due to CH3 and acetyl CH3
group attached to coumarin ring respectively.
slightly higher than the spin-only value of 1.73 BM expected for
one unpaired electron, which offers possibility of an octahedral
geometry [47].
4.3. Electronic spectra
4.5. ESR spectrum of Cu(II)complex
The electronic absorption spectra of the complexes in DMF
were recorded at room temperature and the band positions of the
absorption band maxima assignments and the proposed geom-
etry are listed in Table 3. The Co(II) complexes exhibited two
distinct absorptions in the region 1048–1057 nm and 544–549 nm
The ESR spectral studies of Cu(II) complex provides information
of the metal ion environment. The ESR spectrum of the Cu(II) com-
plex was recorded in DMSO at liquid nitrogen temperature (LNT)
and at room temperature (RT). The Cu(II) complex (5) exhibits the
g|| value of 2.0932 and g⊥ value of 2.0665. These values g|| > g⊥ indi-
corresponding to 4T1g(F) → T (F) (ꢂ ) and T1g(F) → T1g(P) (ꢂ3)
4
4
4
2g
1
transitions respectively which suggests high spin octahedral geom-
etry around the cobalt(II) ion [42]. The ꢂ2 band that involves a
two-electron transition is not observed in spectra because of its
proximity to strong ꢂ3 transition. The ligand field parameters cal-
culated are presented in Table 4.
cate that, the unpaired electron lies predominantly in the d
2
2
x
−y
orbital [48]. The trend g|| > g⊥ > 2.0023 observed for the complexes
indicate that, the unpaired electron is localized in the d orbital
2
2
x
−y
of the Cu(II) ion and are characteristic of the axial symmetry. The
gav value was calculated to be 2.0754. The deviation of the gav from
that of the free electron (2.0023) is due to the covalence property
[49]. This was supported by Kivelson and Neiman [50] where g|| is
less than 2.3 indicates covalent environment; metal–ligand bond-
ing in Cu(II) is therefore regarded as covalent. Thus, ESR studies
suggests that, the Cu(II) complex may possess distorted octahedral
geometry.
The Ni(II) complex (3) (Table 4) exhibited three bands at 931,
3
3
3
3
6
(
09 and 382 nm attributed to the A2g → T (ꢂ ), A2g → T (F)
2g
1
1g
3 3
ꢂ2) and A2g → T (P) (ꢂ ) transitions respectively, which indi-
1g
3
cate an octahedral geometry around Ni(II) ion. The value of ꢂ /ꢂ is
2
1
found to be around 1.529 and the ꢁeff value is around 3.162 which
are with in the range of 2.8–3.5 BM, suggesting the octahedral envi-
ronment. The values of the nephelauxetic parameters, ␤, indicate
low covalent character of the metal-ligand ␴ bonds [43]. Hence,
the ligand field parameters correlate the electronic spectral and
magnetic properties.
4
.6. Thermal studies of metal complexes
The thermal behavior of Co(II), Ni(II) and Cu(II) complexes has
been studied as a function of temperature. The thermal behavior of
all the complexes is almost same. Hence, the representative Co(II)
1). Ni(II) (3) and Cu(II) (5) complexes have been discussed.
The Co(II) (1) complex has been represented in Fig. 2. The ther-
The electronic spectra of Cu(II) complexes showed low intensity
2
2
broad band around 613–621 nm assignable to Eg → T transition.
2g
Another high intensity band at 395–397 nm is due to symmetry for-
bidden ligand → metal charge transfer. On the basis of electronic
spectra, distorted octahedral geometry around Cu(II) ion is sug-
gested [44].
(
mal decomposition of Co(II) (1) complex took place in three steps as
◦
indicated by DTG curves around 185–195, 250–270 and 310–325 C
corresponding to the mass loss of coordinated water molecules,
thiosemicarbazide and acetyl coumarin moieties respectively. In
case of Co(II) (3) and Ni(II) (5) complexes decomposition took
place in three steps corresponding to the loss of coordinated
water molecules, thiosemicarbazide and acetyl coumarin moieties
around 175–195, 200–235 and 315–335 respectively. Both the
water molecules of all the complexes depart in a considerably nar-
row (∼45 K) one-step process. This may be due to an easier diffusion
of water molecules through the crystal lattice of the complexes.
Finally, the metal complexes decompose gradually with the forma-
4
.4. Magnetic studies
The magnetic moments obtained at room temperature are listed
in Table 1. The magnetic measurement for Co(II) complexes showed
magnetic moment value of 4.72–4.81 which is well within the
range of 4.3–5.2 BM and Ni(II) complexes showed the magnetic
moment value of 3.49–3.51 within the range of 2.8–3.5 BM sug-
gesting [45,46] consistency with their octahedral environment.
The Cu(II) complexes showed magnetic moment 1.76–1.78 BM, is

S.A. Patil et al. / Spectrochimica Acta Part A 79 (2011) 1128–1136
1133
Table 4
Ligand field parameters of Co(II) and Ni(II) complexes.
Transitions (cm 1
−
)
␯2 Calcd.
Dq (cm
−1
)
B1 (cm−1
)
% Distortion
ꢂ2/ꢂ1
LFSE
(kcal/mol)
ꢁeff calcd.
(BM)
ˇ
ˇ%
Complex No.
−
1
(
cm
)
␯
1
␯2
␯3
18,382
18,214
26,178
26,455
1
2
3
4
9460
9541
–
–
20,003
20,154
16,636
16,785
1054.39
1061.36
1074.10
1081.00
667.06
649.70
706.11
720.72
–
–
2.114
2.112
1.529
1.539
24.100
24.259
36.826
37.063
–
–
0.689
0.671
0.669
0.683
31.017
32.811
33.133
31.750
10,741
10,810
16,420
16,638
1.303
0.881
3.162
3.160
Table 5
Thermogravimetric data of Co(II), Ni(II) and Cu(II) complexes.
Complex No.
Decomposition
temperature ( C)
%Weight loss
Obsd.
Metal oxide %
Inference
◦
Calcd.
Obsd.
15.11
Calcd.
15.18
1
3
5
185–195
7.22
7.28
Loss due to co-ordinated water molecules
Loss due to thiosemicarbazide
Loss due to acetyl coumarin
Loss due to co-ordinated water molecules
Loss due to thiosemicarbazide
Loss due to acetyl coumarin
Loss due to co-ordinated water molecules
Loss due to thiosemicarbazide
Loss due to acetyl coumarin
2
3
50–270
10–325
40.15
40.77
7.22
40.23
40.81
7.20
40.08
40.68
7.30
40.16
40.77
7.22
175–185
14.93
15.79
14.97
15.86
2
3
00–230
15–340
180–195
2
3
10–235
20–345
39.81
40.43
39.75
40.36
◦
tion of metal oxide above 575 C. The nature of proposed chemical
change with the temperature range and the percentage of metal
oxide obtained are given in Table 5.
dent for other complexes. All these fragmentation patterns were
well observed in the FAB-mass spectra.
4.8. Electrochemistry
4.7. FAB-mass spectral studies
All the complexes were studied for their electrochemical behav-
ior. Both the Cu(II) complexes exhibited similar electrochemical
properties. A cyclic voltammogram of Cu(II) complex (5) (Fig. 3)
displays a reduction peak at Epc = 0.312 V with a corresponding
oxidation peak at Epa = 0.300 V. The peak separation of this couple
The FAB-mass spectrum of Schiff-base showed a molecular ion
peak M at m/z 401, 403 (M+2) which is equivalent to its molecular
weight. In addition to this the fragment peaks observed at m/z 366,
+
2
02 and 185 are due to the cleavage of Cl, C7H N S and OH respec-
6 3
(ꢄEp) is 0.012 at 200 mV/s and increases with increasing scan rate.
tively. In case of Schiff-base II the molecular ion peak is observed
+
The most significant feature of the Cu(II) complex is the Cu(II)/Cu(I)
couple. The difference between forward and backward peak poten-
tials can provide a rough evaluation of the degree of the reversibility
of one electron transfer reaction. The analyses of cyclic voltamet-
M
at m/z 412 which is ascribed to C19H16N O5S.
4
The FAB-mass spectra of Co(II), Ni(II), and Cu(II) complexes of
+
Schiff-base II showed a molecular ion peak M at m/z 505, 504
and 509 respectively, equivalent to their molecular weights. All
−
1
+
ric responses with the scan rate varying from 50 to 250 mV s give
the evidence for quasi-reversible one electron transfer process. The
ratio of cathodic to anodic peak height was less than one. However,
the peak current increases with increasing square root of the scan
rates. This establishes the electrode process as diffusion-controlled
the fragments of the species [ML·2H O] undergo demetallation
2
+
to form the species [L+H] giving a fragmentation at m/z 412. The
fragmentation peak observed in the case of Co(II) complex (1)
at 469 correspond to the loss of two water molecules. Also, the
+
species [ML·2H O] undergoes demetallation to form the species
2
+
[
L+H] giving a fragment ion at m/z 412. Similar features are evi-
Fig. 2. Thermogravimetric (TGA/DTG) curves of Co(II) (1) complex.
Fig. 3. Cyclic voltammogram of Cu(II) (5) complex at scan rate at 200 mV/s.

1
134
S.A. Patil et al. / Spectrochimica Acta Part A 79 (2011) 1128–1136
Table 6
Antimicrobial results of Schiff-bases and their metal complexes.
Conc. (␮g ml 1
−
)
% Inhibition against bacteria
% Inhibition against fungi
Compound No.
S. typhi
S. aureus
B. subtilis
E. coli
C. albicans
Cladosporium
A. niger
I
25
5.91
21.33
92.14
8.17
26.38
89.22
6.02
11.91
61.34
–
11.31
69.56
–
18.3
41.2
–
38.67
54.45
61.79
66.56
82.78
79.27
90.71
91.23
86.46
85.27
89.67
–
18.22
21.55
50.20
15.68
27.24
42.21
–
8.51
10.82
–
11.43
22.44
31.66
35.56
45.03
17.13
21.64
30.13
–
11.23
25.67
19.91
22.22
37.81
6.71
–
24.39
46.13
57.12
27.91
45.06
60.0
81.31
89.56
94.27
79.64
85.96
91.16
75.57
79.39
88.33
71.96
84.76
91.47
–
49.75
75.91
88.67
51.21
69.3
82.9
–
23.21
45.75
–
35.57
50.82
65.66
72.62
81.48
62.91
75.65
80.94
49.02
57.64
91.3
51.91
74.49
87.21
56.66
76.53
80.17
54.54
65.04
78.81
65.63
76.81
79.09
15.33
28.57
56.00
26.39
44.66
63.32
32.57
55.14
85.83
71.89
76.66
80.65
–
5
1
0
00
41.73
49.56
–
44.78
58.63
–
21.45
31.32
12.69
15.08
26.06
–
7.08
7.91
–
II
25
5
1
0
00
1
25
11.98
31.33
60.12
22.76
43.76
68.03
34.65
69.89
81.23
39.59
73.71
86.13
14.28
22.87
42.85
57.14
64.28
69.04
61.92
71.4
5
1
0
00
2
25
5
1
0
00
3
25
5
1
0
00
–
39.21
21.11
33.86
50.16
55.16
64.11
73.13
81.27
92.11
94.44
–
4
25
5
1
0
00
–
21.76
51.76
62.11
73.15
25.11
25.41
75.94
79.27
83.85
84.57
–
5
25
5
1
0
00
6
25
34.53
67.86
75.45
–
5
1
0
00
Gentamycin
Flucanozole
Control
25
5
1
0
00
8.29
15.0
–
80.95
–
25
83.22
92.98
93.21
100
91.98
93.47
96.13
100
89.19
93.15
97.6
5
1
0
00
100
100
100
100
100
100
[
51]. The separation in peak potentials increased at higher scan
rates.
The Ni(II) complex (3) exhibited a reduction peak at Epc = 0.332 V
were found to be potentially active against E. coli, S. typhi and S.
aureus. All the Co(II), Ni(II) and Cu(II) metal complexes showed
much enhanced activity against S. typhi and Cu(II) complexes exhib-
ited promising results against S. typhi. Both the Schiff-bases and
their Co(II), Ni(II) and Cu(II) complexes are found to possess high
antifungal activity than antibacterial activity. Antifungal activity
of synthesized Schiff-bases and some of their complexes is almost
nearer to the standard drug Flucanozole. It has been reported in past
that; the metal complexes with Schiff-bases of coumarin deriva-
tives possess high antimicrobial activity [30–34].
with a direct oxidation peak at Epa = 0.280 V corresponding to the
formation of Ni(II)/Ni(I) couple. The peak separation of this cou-
ple (ꢄEp) is 0.052 V at 0.1 V and increases with scan rate. These
characteristic features are consistent with the quasi-reversibility
of Ni(II)/Ni(I) couple.
4
.9. Fluorescence studies
The antibacterial and antifungal studies suggested that, all the
Schiff-bases were found to be biologically active and some of their
metal complexes showed significantly enhanced antibacterial and
antifungal activity. It is, however, known [54,55] that, chelating
tends to make the Schiff-bases act as more powerful and potent
The emission spectra of the Schiff-bases and its complexes are
studied in DMF and DMSO.
The Schiff-bases I is characterized by an emission band around
4
61 nm in DMF and 473 nm in DMSO is due to the formation of
phenoxide anion. Upon addition of 2–3 drops of aqueous alkali
2% NaOH) to the Schiff-base solution, we observed ꢃmax values at
42 nm in DMF and 449 nm in DMSO. The shift in ꢃmax values after
(
4
addition of 2–3 drops of aqueous alkali (2% NaOH) in the Schiff-
bases clearly indicates that the proton transferred (H-bonded ion
pair) species exist in equilibrium [52,53].
Fig. 4 shows that, the Co(II), Ni(II) and Cu(II) complexes of
Schiff-base I exhibited the emission bands at 445, 437 and 441 nm
respectively in DMF. It is evident that, fluorescence emission inten-
sity of Schiff-base I decreased dramatically on complex formation
with transition metal ions. Decrease in emission maxima were in
the order of Co(II) > Cu(II) > Ni(II) complexes of Schiff-base I.
5
. Pharmacology results
5.1. In vitro antibacterial and antifungal activity
The microbial results are systematized in Table 6. In case of
antibacterial studies it was observed that, both the Schiff-bases
Fig. 4. Emission spectrum of Schiff-base I and its metal complexes in DMF solution.

S.A. Patil et al. / Spectrochimica Acta Part A 79 (2011) 1128–1136
1135
Table 7
Minimum inhibitory concentration (␮g/ml) results of selected compounds.
Compound No.
S. typhi
P. aeruginosa
E. coli
C. albicans
Cladosporium
A. Niger
I
II
1
2
3
4
5
6
10
10
10
15
25
10
10
10
10
–
10
15
10
15
10
25
10
10
10
–
15
25
10
25
10
10
15
25
10
–
10
15
10
10
25
25
10
10
–
15
10
10
10
10
15
10
25
–
10
10
25
10
10
25
10
15
–
Gentamycin
Flucanozole
10
10
10
bactereostatic agents, thus inhibiting the growth of bacteria and
fungi more than the parent Schiff-bases. It is suspected that, factors
such as solubility, conductivity, dipole moment and cell permeabil-
ity mechanism (influenced by the presence of metal ions) may be
the possible reasons for the increase in activity.
CH3
R
H O
2
O
H O
2
O
N
The minimum inhibitory concentration (MIC) of some selected
compounds, which showed significant activity against selected
bacterial and fungi species, was also determined and presented in
Table 7. The MIC of these compounds varies from 10 to 100 mg/ml.
The results indicated that these compounds were the most active
in inhibiting the growth of the tested organisms at a 10 mg/ml
concentration.
S
CH3
O
HN
M
N
N
O
M
HN
CH3
S
N
O
H O
2
O
H O
2
R
5.2. DNA cleavage studies
CH3
n
The representative SC-I, Co(II) (1), Ni(II) (3) and Cu(II) (5) com-
plexes were studied for their DNA cleavage activity by agarose gel
electrophoresis method and presented in Fig. 5.
The gel after electrophoresis clearly revealed that, all the com-
plexes have acted on DNA as there was molecular weight difference
between the control and the treated DNA samples. The difference
was observed in the bands of Schiff-base I and its complexes (Lanes
R = Cl, NO2
M = Co(II), Ni(II) and Cu(II)
Fig. 6. Structure of metal complexes.
6. Conclusion
1
–4) compared to the control DNA of A. niger. This shows that, the
The synthesized Schiff-bases act as tetradentate ligands and
exhibit thiol–thione tautomerism. The metal ion is coordinated
through the azomethine nitrogen, phenolic oxygen, sulphur atom
and lactone oxygen. The bonding of ligand to metal ion is con-
firmed by the analytical, spectral, magnetic and thermal studies.
The complexes are soluble in DMF and DMSO, fusible at higher tem-
peratures and are polymeric in nature. Representative structure of
Co(II), Ni(II) and Cu(II) complexes are presented in Fig. 6. The Schiff-
bases and their metal complexes were found to be highly active
against some of the antibacterial and antifungal species. The DNA
cleavage studies revealed that, the complexes shown non-specific
cleavage of DNA isolated of A. niger.
control DNA alone does not show any apparent cleavage where as
Schiff-base I and its complexes shown. The results indicated the
important role of metal in these isolated DNA cleavage reactions.
However, the nature of reactive intermediates involved in the DNA
cleavage by the complexes has not been clear. As the compound
was observed to cleave the DNA, it can be concluded that the com-
pound inhibits the growth of the pathogenic organism by cleaving
the genome.
Acknowledgements
The authors are grateful to the Chairman, Department of Chem-
istry, Karnatak University, Dharwad for the facilities. One of the
authors, S.N. Unki is thankful to Karnatak University, Dharwad for
grant of Research Fellowship in Science for Meritorious Students of
UGC.
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