DNA cleavage, antimicrobial, spectroscopic and fluorescence studies of Co(II), Ni(II) and Cu(II) complexes with SNO donor coumarin Schiff bases

Article abstract of DOI:10.1016/j.saa.2009.10.039

A series of Co(II), Ni(II) and Cu(II) complexes of the type ML₂ have been synthesized with Schiff bases derived from methylthiosemicarbazone and 5-formyl-6-hydroxy coumarin/8-formyl-7-Hydroxy-4-methylcoumarin. The complexes are insoluble in common organic solvents but soluble in DMF and DMSO. The measured molar conductance values in DMF indicate that, the complexes are non-electrolytes in nature. In view of analytical, spectral (IR, UV-vis, ESR, FAB-mass and fluorescence), magnetic and thermal studies, it has been concluded that, all the metal complexes possess octahedral geometry in which ligand is coordinated to metal ion through azomethine nitrogen, thione sulphur and phenolic oxygen atom via deprotonation. The redox behavior of the metal complexes was investigated by using cyclic voltammetry. The Schiff bases and their complexes have been screened for their antibacterial (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Salmonella typhi) and antifungal activities (Aspergillus niger, Aspergillus flavus and Cladosporium) by Minimum Inhibitory Concentration method. The DNA cleavage is studied by agarose gel electrophoresis method.

Full text of DOI:10.1016/j.saa.2009.10.039

Spectrochimica Acta Part A 75 (2010) 347–354
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
DNA cleavage, antimicrobial, spectroscopic and fluorescence studies of Co(II),
Ni(II) and Cu(II) complexes with SNO donor coumarin Schiff bases
a,∗
a
a
b
Sangamesh A. Patil , Vinod H. Naik , Ajaykumar D. Kulkarni , Prema S. Badami
a
P.G. Department of Chemistry, Karnatak University, Pawate Nagar, Dharwad 580 003. 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:
Received 7 May 2009
Received in revised form 10 October 2009
Accepted 26 October 2009
A series of Co(II), Ni(II) and Cu(II) complexes of the type ML2 have been synthesized with Schiff
bases derived from methylthiosemicarbazone and 5-formyl-6-hydroxy coumarin/8-formyl-7-Hydroxy-
4
-methylcoumarin. The complexes are insoluble in common organic solvents but soluble in DMF and
DMSO. The measured molar conductance values in DMF indicate that, the complexes are non-electrolytes
in nature. In view of analytical, spectral (IR, UV–vis, ESR, FAB-mass and fluorescence), magnetic and
thermal studies, it has been concluded that, all the metal complexes possess octahedral geometry in
which ligand is coordinated to metal ion through azomethine nitrogen, thione sulphur and phenolic
oxygen atom via deprotonation. The redox behavior of the metal complexes was investigated by using
cyclic voltammetry. The Schiff bases and their complexes have been screened for their antibacterial
(Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Salmonella typhi) and antifungal
activities (Aspergillus niger, Aspergillus flavus and Cladosporium) by Minimum Inhibitory Concentration
method. The DNA cleavage is studied by agarose gel electrophoresis method.
Keywords:
Antimicrobial
DNA
Fluorescence
Formyl coumarin
Transition metal complexes
Spectroscopic studies
©
2009 Elsevier B.V. All rights reserved.
1
. Introduction
class of sulphur and nitrogen donor ligands specifically for transi-
tion metal ions [11–13]. These compounds exhibit a great variety of
biological activities ranging from antitumour, fungicidal, bactere-
ocidal, antibacterial, antifungal, anti-inflammatory and antiviral
activities [14–20]. It has been suggested that thiosemicarbazone
drugs may act to inhibit viruses by binding to copper ions, which
are the constituents of the virus as long ago [21]. We have reported
spectroscopic, electrochemical and biological studies of a number
of metal complexes with various Schiff bases [22–25]. The interac-
tion of transition metal complexes with DNA have been extensively
studied for their usage as probes for DNA structure and their poten-
tial application in chemotherapy. One of the most important DNA
related activity of the transition metal complexes is that, some of
the complexes show the ability to cleave DNA. Very recently, Cu(II)
complexes have been reported to be active in DNA strand scission
[26–28].
Thus, the available literature encouraged us to synthesize
and characterize the Co(II), Ni(II) and Cu(II) metal com-
plexes with newly synthesized Schiff bases derived from
3-methylthiosemicarbazone and 5-formyl-6-hydroxycoumarin/8-
formyl-7-hydroxy-4-methylcoumarin. The electron transfer mech-
anism is investigated by the aid of cyclic voltammetry. The Schiff
bases and their metal complexes are screened for their antimi-
crobial activity. DNA cleavage property of the complexes is also
studied.
The chemistry of transition metal complexes of Schiff bases
has played an important role in the development of coordina-
tion chemistry as a whole. Multidentate Schiff bases have been
widely used as ligands, because they can easily attached to metal
ions due to the formation of high stability of coordination com-
pounds. Metal complexes of S-, N-, and O-chelating ligands have
attracted the considerable attention because of their interesting
physico-chemical properties, pronounced biological activities, and
as models of metalloenzyme active sites [1,2]. Schiff bases and their
transition metal complexes have been used as anticancer, antitu-
berculer, antibacterial, antifungal, hypertensive and hypothermic
reagents [3–5]. Transition metal complexes are used as catalysts
for many organic reactions [6,7]. Coumarin and its derivatives have
been a subject of numerous investigations due to their diverse
biological activities [8,9], interesting photophysical, photochemical
and metal binding properties. It has been found that, the binding
of a metal to the coumarin moiety retains or even enhances its bio-
logical activity [9,10]. Also thiosemicarbazones are an important
∗ Corresponding author.
E-mail address: patil1956@rediffmail.com (S.A. Patil).
1
386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2009.10.039

3
48
S.A. Patil et al. / Spectrochimica Acta Part A 75 (2010) 347–354
Scheme 1. Synthesis of Schiff bases I–II.
2
. Experimental
coumarin [32,31] have been synthesized according to the published
procedure.
2.1. Analysis and physical measurements
2
.2.1. Synthesis of 3-methyl thiosemicarbazone
Freshly distilled methyl amine (3.42 ml) was dissolved in ammo-
Carbon, hydrogen and nitrogen were estimated by using Ele-
mental Analyzer Carlo Erba EA1108 analyzer. 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. 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
nia (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 carbon disulphide was com-
pletely dissolved. The reaction mixture was then allowed to stand
for 2–3 h. An aqueous sodium chloroacetate (0.1 m) solution was
added followed by hydrazine hydrate (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 recrystal-
lized from hot ethanol.
were recorded in D -DMSO on a BRUKER 300 MHz spectrome-
6
ter at room temperature using TMS as an internal reference. The
fluorescence studies of Schiff bases and their metal complexes
were recorded on HITACHI F-7000 Fluorescence Spectrophotome-
−3
ter (made in Japan). The solutions of 10 M concentration were
prepared in HPLC grade DMF and DMSO solvents and the experi-
ment was carried out at room temperature. FAB-mass spectra were
recorded on a JEOL SX 102/DA-6000 mass spectrometer/data sys-
tem using Argon/Xenon (6 kV, 10 A) as the FAB gas. The accelerating
voltage was 10 kV and the spectra were recorded at room temper-
ature and m-nitrobenzyl alcohol was used as the matrix. The mass
spectrometer was operated in the +ve ion mode. The electrochem-
istry of the complexes was studied on CHI1110A-electrochemical
analyzer (made in U.S.A.) in dimethyl formamide (DMF) containing
2.2.2. Synthesis of Schiff bases [I–II]
The synthesis of Schiff bases is presented in Scheme 1.
The Schiff bases have been synthesized by refluxing the
reaction mixture of hot ethanolic solution (30 ml) of 3-
methylthiosemicarbazone (0.01 mol) and hot ethanolic solution
(30 ml) of 5-formyl-6-hydroxycoumarin/8-formyl-7-hydroxy-4-
methylcoumarin (0.01 mol) for 4–5 h with addition of 4–5 drops
of hydrochloric acid. The precipitate formed during reflux was fil-
tered, washed with cold EtOH and recrystallized from hot EtOH.
0
.05 M n-Bu NClO as the supporting electrolyte. The ESR spectrum
4 4
2
.2.3. Synthesis of Co(II), Ni(II) and Cu(II) complexes [1–6]
An alcoholic solution (45 ml) of Schiff base (2 mmol)
was recorded on Varian-E-4X-band EPR spectrometer and the field
set is 3000 G at modulation frequency of 100 kHz under room tem-
perature and liquid nitrogen temperature using TCNE as g marker.
Thermogravimetric analyses data were measured from room tem-
perature to 1000 C at a heating rate of 10 C/min. The data were
obtained by using a PerkinElmer Diamond TG/DTA instrument.
Molar conductivity measurements were recorded on ELICO-CM-
was mixed with an alcoholic solution (5 ml) of 1 mmol of
CoCl ·6H O/NiCl ·6H O/CuCl ·2H O and refluxed on water
2
2
2
2
2
2
bath for 2 h. Then, to the reaction mixture 2 mmol of sodium
acetate was added and reflux was continued for 3 h. The separated
complex was filtered, washed thoroughly with water, ethanol,
ether and finally dried in vacuum over fused CaCl2.
◦
◦
8
2 T Conductivity Bridge with a cell having cell constant 0.51 and
magnetic moment was carried out by using faraday balance.
2.3. Pharmacology
2.2. Methods
2.3.1. DNA cleavage experiment
.3.1.1. Preparation of culture media. DNA cleavage experiments
2
All the chemicals used were of reagent grade. 7-hydroxy-
-methylcoumarin [29], 6-hydroxy coumarin [29], 8-formyl-
-hydroxy-4-methyl coumarin [30,31] and 5-formyl-6-hydroxy
were done according to the method [33]. Nutrient broth [peptone,
10; yeast extract, 5; NaCl, 10; in (g/l)] was used for culturing of
Escherichia coli and potato dextrose broth [potato, 250; dextrose,
4
7

S.A. Patil et al. / Spectrochimica Acta Part A 75 (2010) 347–354
349
Table 1
Elemental analyses of Schiff bases and their Co(II), Ni(II) and Cu(II) complexes along with molar conductance and magnetic moment data.
Molar conductance (ꢀ cm2 mol
−
1
−1
)
ꢁeff (BM)
Comp. no. Empirical formula Color/yield %
M%
Obsd. Calcd. Obsd. Calcd. Obsd. Calcd. Obsd. Calcd.
C%
H%
N%
I
C12H11N3O3S
C13H13N3O3S
Co(C12H10N3O3S)2 Brown/71%
74%
76%
–
–
9.56
9.02
9.22
9.34
–
–
51.76 51.98 3.56
53.60 53.81 5.26
3.97
5.82
3.27
3.75
3.27
3.76
3.25
3.73
15.02 15.16
14.65 14.43
–
–
–
–
II
1
2
3
4
5
6
9.65 47.25 47.13 3.67
9.23 48.22 48.82 3.13
9.50 47.29 47.21 3.37
9.09 48.99 49.90 3.26
13.23 13.74 23.8
13.03 13.14 17.25
13.24 13.77 22.88
13.04 13.16 29.64
13.35 13.65 18.4
13.71 13.06 21.11
4.88
4.62
3.51
3.42
1.77
1.79
Co(C13H12N3O3S)2 Brown/69%
Ni(C12H10N3O3S)2 Yellowish green/68%
Ni(C13H12N3O3S)2 Yellowish green/69%
Cu(C12H10N3O3S)2 Dark green/66%
Cu(C13H12N3O3S)2 Dark green/69%
10.29 10.24 46.34 46.82 3.77
9.56 9.79 48.34 48.52 3.12
2
0; in (g/l)] was used for the culture of Aspergillus niger. The 50 ml
common organic solvents but soluble in DMF and DMSO. The ele-
mental analyses show that, the Co(II), Ni(II) and Cu(II) complexes
◦
media was prepared, autoclaved for 15 min at 121 C under 15 lb
pressure. The autoclaved media were inoculated with the seed cul-
ture. E. coli is incubated for 24 h and A. niger for 48 h at 37 C.
have 1:2 stoichiometry of the type ML , where L stands for a depro-
2
◦
tonated ligand (Scheme 1). The molar conductance values are too
low to account for any dissociation of the complexes in DMSO,
indicating the non-electrolytic nature of the complexes in DMSO
2.3.1.2. Isolation of DNA. The fresh bacterial culture (1.5 ml) is cen-
(Table 1).
trifuged to obtain the pellet which is then dissolved in 0.5 ml of lysis
buffer (100 mM Tris pH 8.0, 50 mM EDTA, 10% SDS). To this 0.5 ml of
saturated phenol was added and incubated at 55 C for 10 min. Then
centrifuge at 10,000 rpm for 10 min and to the supernatant, equal
volume of chloroform:isoamyl alcohol (24:1) and 1/20th volume of
3
1
◦
3.1. IR spectral studies
The prominent infrared spectral data of Schiff bases and their
M sodium acetate (pH 4.8) was added. Then, again centrifuged at
0,000 rpm for 10 min and to the supernatant, 3 volumes of chilled
Co(II), Ni(II) and Cu(II) complexes are presented in Table 2.
The IR spectra of the Schiff bases exhibited a characteristic band
absolute alcohol was added. The precipitated DNA was separated by
centrifugation and the pellet was dried and dissolved in TAE buffer
−
1
due to ␯(NH) in the region 3144–3105 cm [35]. In addition, the
−
1
characteristic high intensity band in the region 1616–1607 cm
is assigned to ␯(C N) and a band around 1065–1040 cm
(
10 mM Tris pH 8.0, 1 mM EDTA) and stored in cold condition.
−
1
is
assigned to ␯(C S) respectively [36] in the IR spectra of the Schiff
2
.3.1.3. Agarose gel electrophoresis. Cleavage products were ana-
lyzed by agarose gel electrophoresis method [32]. Test samples
1 mg/ml) were prepared in DMF. The samples (25 ␮g) were added
−1
bases. A high intensity band in the 1256–1220 cm region and a
−1
band around 1732–1729 cm are assigned to phenolic ␯(C–O) and
(
␯
(C O) [37], respectively.
to the isolated DNA of E. coli and A. niger. The samples were incu-
bated for 2 h at 37 C and then 20 ␮l of DNA sample (mixed with
In comparison with the spectra of the Schiff bases, all the Co(II),
◦
Ni(II) and Cu(II) complexes exhibited the band of ␯(C N) in the
bromophenol blue dye at 1:1 ratio) was loaded carefully into the
electrophoresis chamber wells along with standard 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. Then 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 and the
results are compared with standard DNA marker.
−1
region 1593–1579 cm showing the shift to lower wave numbers
indicating that, the nitrogen of azomethine group is coordinated to
the metal ion [36,38,39]. The ␯(C S) stretching vibration has been
−1
shifted towards lower frequency and occurred at 1039–1018 cm
in metal complexes indicating the coordination of thione sulphur
to metal ion [36]. A medium to high intensity band appeared in the
−1
region 1299–1267 cm due to phenolic ␯(C–O) [37] indicates the
coordination of phenolic oxygen via deprotonation. The higher side
shift of ␯(C–O) in the metal complexes is may be due to the expected
high mesomeric interaction in the complex that is probably acti-
vated by the presence of the metal ion. The new bands appeared
2.3.2. In vitro antibacterial and antifungal assay
−
1
The biological activities of synthesized Schiff bases and their
in the region of 472–460 and 348–336 cm in the spectra of the
complexes are assigned to stretching frequencies of (M–N) bonds
[40] and metal-sulphur bond formation [41] respectively. The unal-
tered position of a band due to ␯(NH) and ␯(C O) in all the metal
complexes indicates the non-involvement of these groups in the
coordination.
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 10, 30, 50 and 100 ␮g/ml concentrations
in DMF solvent by using four bacteria (E. coli, Staphylococcus aureus,
Pseudomonas aeruginosa and Salmonella typhi) and three fungi (A.
niger, Aspergillus flavus and Cladosporium) by the MIC method [34].
◦
These bacterial stains were incubated for 24 h at 37 C and fun-
gal stains were incubated for 48 h at 37 C. Standard antibacterial
Table 2
◦
The important infrared frequencies (in cm−1) of Schiff bases and their metal
complexes.
(
Gentamycin) and antifungal drug (Fluconazole) was used for com-
parison under similar conditions.
Compound
␯(N–H) ␯(C N) ␯(C 0) ␯(C S) ␯(C–O) ␯(M–N) ␯(M–S)
C12H11N3O3S
C13H13N3O3S
3144
3105
1616
1607
1592
1580
1593
1579
1588
1584
1732
1729
1730
1725
1731
1726
1730
1728
1065
1040
1035
1022
1039
1018
1032
1026
1256
1220
1288
1273
1295
1267
1299
1268
–
–
–
–
3
. Results and discussion
Co(C12H10N3O3S)2 3141
Co(C13H12N3O3S)2 3108
Ni(C12H10N3O3S)2 3149
Ni(C13H12N3O3S)2 3105
Cu(C12H10N3O3S)2 3140
Cu(C13H12N3O3S)2 3101
471
465
460
472
463
469
347
336
345
341
348
339
The Schiff bases (I and II) form octahedral complexes (1–6)
(
Table 1) with CoCl ·6H O/NiCl ·6H O/CuCl ·2H O in ethanol. All
2
2
2
2
2
2
the Co(II), Ni(II) and Cu(II) complexes are colored, (Table 1), stable
and non-hygroscopic in nature. These complexes are insoluble in

3
50
S.A. Patil et al. / Spectrochimica Acta Part A 75 (2010) 347–354
Fig. 1. FAB-mass spectrum of Schiff base I.
3
.2. 1H NMR spectral study of Schiff bases
is not observed because of its proximity to strong ␯3 transition.
The ligand field parameters calculated is presented in Table 3. The
lower ˇ values (0.681 and 0.689) indicate considerable covalence in
metal–ligand bonding. The magnetic measurement for Co(II) com-
plexes exhibit magnetic moment values of 4.88–4.62 which are
well agree with the octahedral range of 4.3–5.2 BM [44] this further
supports the electronic spectral results.
1
In the HNMRspectrum of the Schiff base I, the NHproton exhib-
ited signal at 9.23 ppm (s, 1H) [42]. A characteristic proton signal at
.48 ppm (s, 1H) and a signal at 10.43 ppm (s, 1H) are assigned to
CH N and phenolic –OH respectively. In addition the signals in the
region 6.95–7.81 ppm (m, 8H) and a sharp signal at 3.47 ppm (s, 3H)
are due to aromatic and CH3 protons respectively. In case of Schiff
base II, the signal observed at 9.28 ppm (s, 1H) is attributed to the
NH and a signal at 8.45 ppm (s, 1H) is ascribed to –CH N. The signal
observed as a multiplet in the region 7.01–7.87 (m, 8H) and singlet
8
–
The greenish Ni(II) complex (3) exhibited three bands at 10,612,
−
1
3
3
16,326 and 26,476 cm which are attributed to the A2g → T2g
(␯1); 3A2g → T1g (F) (␯2) and 3A2g → T1g (P) (␯3) transitions
respectively, which indicate an octahedral geometry around Ni(II)
ion [45]. The value of ␯2/␯1 is found to be around 1.54 and the ꢁeff
value is around 3.166 which are within the range of 2.8–3.43 BM,
suggesting the octahedral environment around Ni(II) ion. The
values of the nephelauxetic parameter, ˇ, indicate low covalent
character of the metal–ligand ␴ bonds [46,47]. Ni(II) complexes
showed the magnetic moment values of 3.51–3.42 within the range
of 2.8–3.5 BM suggesting [48] consistency with their octahedral
environment. Hence the ligand field parameters correlate the elec-
tronic spectral and magnetic properties.
3
3
at 3.46 ppm are due to aromatic and CH protons, respectively. And
a signal at 10.45 is due to phenolic–OH.
3
3
.3. Electronic spectral and magnetic studies
The Co(II) complex exhibited electron spectral bands in the
region 8000–10,000 and 18,000–20,000 cm corresponding to ␯1
and ␯ transitions respectively, which are attributed to the transi-
−1
3
4
4
4
4
tions T1 (F) → T (F) (␯ ); T g (F) → T g (P) (␯ ). In the present
g
2g
1
1
1
3
study, the brownish Co(II) complexes show the absorption bands
The electronic spectra of Cu(II) complexes display two promi-
−1
−1
at 9378–9384 and 18,213–18,311 cm
and ␯3 transitions, respectively. These bands are the characteris-
tic of high spin octahedral Co(II) complex [43]. However, ␯2 band
are corresponding to ␯1
nent bands. A low intensity broad band around 16,582 cm
is
assignable to 2Eg → T2g transition and another high intensity
2
−
1
band at 25,642 cm is due to symmetry forbidden ligand → metal
Fig. 2. FAB-mass spectrum of Ni(II) complex (3).

S.A. Patil et al. / Spectrochimica Acta Part A 75 (2010) 347–354
351
Fig. 3. TG/DTA spectrum of Ni(II) complex (3).
charge transfer. On the basis of electronic spectra distorted octa-
3.5. ESR spectrum of Cu(C12H10N O S) complex
3 3 2
hedral geometry around Cu(II) ion is suggested [49]. The Cu(II)
complexes showed magnetic moment 1.77–1.79 BM, which are
slightly higher than the spin-only value 1.73 BM expected for one
unpaired electron, which offers possibility of an octahedral geom-
etry [50].
The ESR spectral studies of Cu(II) complex provides informa-
tion of the metal ion environment. The ESR spectra of the Cu(II)
complexes were recorded in DMSO at liquid nitrogen temperature
(LNT) and at room temperature (RT). The ESR spectrum of one rep-
resentative Cu(C12H10N O S) complex has been discussed here.
3
3
2
The spectrum at RT shows one intense absorption band in the high
field region and is isotropic due to the tumbling motion of the
molecules. However, this complex at LNT shows four well resolved
peaks in low field region. The g|| and g⊥ values have been found to
be 2.03 and 2.02, respectively. The trend g|| > g⊥ > 2.0023 observed
for the complex indicates that the unpaired electron is localized in
3
.4. FAB-mass spectral studies of Schiff bases and their metal
complexes
Representative FAB-mass spectrum of Schiff base I is depicted
in Fig. 1. The spectrum showed a molecular ion peak at m/z 277
which is equivalent to its molecular weight. In addition to this the
fragment ion peaks observed at m/z 260 and 103 are due to the
cleavage of OH and C10H5O5, respectively. In case of Schiff base II
the molecular ion peak is observed at m/z 291 which is ascribed to
C13H13N O S.
the d
2
2
orbital of the Cu(II) ion and which are characteristic for
x –y
the axial symmetry [51]. The gav was calculated to be 2.02. Thus,
the results confirmed that, the Cu(II) complexes possess distorted
octahedral geometry.
3
3
The FAB-mass spectra of Co(C12H10N O S) , Ni(C12H N O S)
3
3
2
10
3
3
2
3.6. Thermal studies of metal complexes
and Cu(C12H10N O S) complexes of Schiff base I showed a molec-
3
+
3
2
ular ion peak M at m/z 611, 610, and 615 which is equivalent of
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, only the representa-
tive Co(C12H10N O S) , Ni(C12H10N O S) and Cu(C12H10N O S)
+
their molecular weight. All the fragments of the species [MHL]
+
undergoes demetallation to form the species [L+H] gave fragment
ion peak at m/z 277. Representative FAB-mass spectrum of Ni(II)
complex (3) is depicted in Fig. 2. In case of Co(II), Ni(II) and Cu(II)
complexes of Schiff base II, the FAB-mass spectra showed a molec-
ular ion peak at m/z 639, 638 and 643 respectively equivalent of
their molecular weight. The complexes undergo demetallation to
3
3
2
3
3
2
3
3
2
complexes have been discussed here.
Fig. 3represents the TG/DTGspectrum of Ni(C12H10N O S) . The
thermal decomposition of Co(C12H10N O S) , Ni(C12H10N O S)
3
3
2
3
3
2
3
3
2
and Cu(C12H10N O S) complexes takes place in one step as indi-
3
3
2
+
form the species [L+H] and gave the fragment ion peak at m/z 291.
◦
cated by DTG peaks around 222–260 C. This shows the mass loss
Table 3
Ligand field parameters of Co(II) and Ni(II) complexes.
Transitions (cm 1
−
)
␯2 Calcd. (cm
−1
)
Dq (cm
−1
)
B1 (cm−1
)
% Distortion
␯2/␯1
LSFE
ꢁeff Calcd. (BM)
ˇ
◦
ˇ (%)
Complex no.
␯
1
␯2
␯3
18,213
18,311
26,476
26,342
Co(C12H10N3O3S)2
Co(C13H12N3O3S)2
Ni(C12H10N3O3S)2
Ni(C13H12N3O3S)2
9,378
9,384
–
–
19,829
19,848
16,658
16,545
1045.19
1046.40
1061.20
1052.10
660.59
667.13
753.26
754.94
–
–
2.11
2.11
1.54
1.61
23.89
23.91
36.38
36.07
–
–
0.681
0.689
0.713
0.715
31.68
31.00
28.67
28.50
10,612
10,521
16,326
16,963
1.994
2.501
3.166
3.169

3
52
S.A. Patil et al. / Spectrochimica Acta Part A 75 (2010) 347–354
Table 4
Thermogravimetric data of Co(II), Ni(II) and Cu(II) complexes.
◦
Empirical formula
Decomposition temperature ( C)
% Weight loss
Obsd.
Metal oxide (%)
Obsd.
Inference
Calcd.
Calcd.
Co(C12H10N3O3S)2
Ni(C12H10N3O3S)2
Cu(C12H10N3O3S)2
222–240
235–260
220–250
34.55
34.64
33.84
34.16
34.21
33.60
12.37
12.07
12.66
12.27
12.13
12.40
Loss due organic moiety
Loss due organic moiety
Loss due organic moiety
of the Schiff base moiety. Finally, the metal complexes decom-
pose gradually with the formation of metal oxide above 900 C. The
3.8. Electrochemistry
◦
nature of proposed chemical change with the temperature range
and the percentage of metal oxide are presented in Table 4.
All the complexes were studied for their electrochemical
behavior. Both the Cu(II) complexes exhibited similar electro-
3.7. Fluorescence spectral studies—emission spectroscopy
The Schiff base I is characterized by an emission band at 413 nm
in DMF. Upon addition of 2–3 drops of aqueous alkali (2% NaOH) to
the Schiff base I, we observed the ꢂmax value at 391 nm in DMF due
to the formation of phenoxide anion [52]. The Co(II), Ni(II) and Cu(II)
complexes of Schiff base I exhibited the emission band at 447, 448
and 429 nm respectively in DMF. The red shift of the ꢂmax value of
the complexes compared with the Schiff base I is may be due to the
deprotonation of the hydroxyl group (Fig. 4). This indicates that, the
Schiff base I and its complexes are fluorescent in nature. The fluo-
rescence emission intensity of Schiff base I decrease upon complex
formation with metal ion in the order: Ni(II) < Cu(II) < Co(II).
Fig. 4. Emission spectrum of Co(II) (a), Ni(II) (b) and Cu(II) (c) complexes.
Table 5
Antimicrobial results of Schiff bases and their metal complexes.
Conc. (␮g ml 1
−
)
% Inhibition against bacteria
E. coli S. aureus
17 23
% Inhibition against fungi
Compound
P. aeruginosa
17
56
68
74
S. typhi
13
28
75
87
A. flavus
Cladosporium
A. niger
C12H11N3O3S
10
55
59
68
79
75
81
88
93
65
69
85
88
3
5
0
0
21
37
53
39
51
59
1
1
1
1
1
1
1
1
00
C13H13N3O3S
10
19
27
41
65
25
39
57
68
19
56
65
73
23
30
69
88
48
59
69
77
66
77
85
94
59
70
78
89
3
5
0
0
00
Co(C12H10N3O3S)2
Co(C13H12N3O3S)2
Ni(C12H10N3O3S)2
Ni(C13H12N3O3S)2
Cu(C12H10N3O3S)2
Cu(C13H12N3O3S)2
10
69
78
83
94
54
67
78
90
80
82
86
99
77
86
89
95
81
84
85
97
75
85
89
94
82
85
92
95
3
5
0
0
00
10
65
77
84
93
57
59
69
81
68
85
84
96
75
79
88
97
76
80
87
98
74
79
88
95
80
85
90
96
3
5
0
0
00
10
47
58
68
78
56
66
78
84
63
71
78
83
63
76
75
83
64
76
79
89
90
93
94
99
72
75
87
90
3
5
0
0
00
10
45
53
69
78
57
68
74
89
56
70
78
89
59
67
73
83
58
68
72
86
82
86
88
90
66
78
80
90
3
5
0
0
00
10
50
53
61
73
36
74
83
93
54
63
72
75
50
65
68
69
64
72
79
99
74
79
91
93
64
85
91
92
3
5
0
0
00
10
84
93
96
98
83
89
94
98
81
85
92
96
82
85
89
95
75
80
86
95
89
92
94
96
87
90
94
97
3
5
0
0
00
Gentamycin
Fluconazole
100
100
100
–
100
–
100
–
100
–
–
–
–
100
100
100

S.A. Patil et al. / Spectrochimica Acta Part A 75 (2010) 347–354
353
3
3
.9. Pharmacological results
.9.1. In vitro antibacterial and antifungal activity
The antibacterial studies inferred that, the Schiff bases (I–II)
were highly active against P. aeruginosa and S. typhi, where as
moderately active against S. aureus and E. coli. All the Co(II), Ni(II)
and Cu(II) metal complexes shown potential antibacterial activ-
ity against all the bacterial strains (Table 5) than the respective
Schiff bases. In case of antifungal activity, the Schiff bases and their
Co(II), Ni(II) and Cu(II) complexes were found to be highly active.
All the metal complexes possess higher antifungal activity than the
Schiff bases. This higher antimicrobial activity of the metal com-
plexes compared to Schiff bases is may be due to the change in
structure due to coordination and chelating tends to make metal
complexes act as more powerful and potent bactereostatic agents,
thus inhibiting the growth of the microorganisms [54,55]. More-
over, coordination reduces the polarity of the metal ion mainly
because of the partial sharing of its positive charge with the donor
groups within the chelate ring system formed during the coordi-
nation. This process, in turn, increases the lipophilic nature of the
central metal atom, which favors its permeation more efficiently
through the lipid layer of the microorganism, thus destroying them
more aggressively.
The minimum inhibitory concentration (MIC) of some selected
compounds, which showed significant activity against selected
bacterial and fungi species, were determined. The results indi-
cated that, these compounds were the most active in inhibiting
the growth of the tested organisms at a 10 ␮g/ml concentration
(Table 6).
3
.9.2. DNA cleavage activity
The representative
Co(C12H10N O S) Ni(C12H10N O S) and Cu(C12H10N O S)
2
Schiff
base
C12H11N O S
and
3
3
Fig. 5. Structure of metal complexes.
3
3
2,
3
3
2
3
3
complexes were studied for their DNA cleavage activity by agarose
gel electrophoresis method against DNA of A. niger.
chemical properties. A cyclic voltammogram of Cu(C12H10N O S)
2
3
3
DNA-binding studies are important for the rational design and
construction of new and more efficient drugs targeted to DNA [56].
The electrophoresis clearly revealed that, the Schiff base I and their
metal complexes 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 lanes D1–D4 compared to
the control DNA of A. niger (Supplementary material Fig. S1). This
shows that, the control DNA alone does not show any apparent
cleavage where as Schiff base and its complexes shown. However,
the nature of reactive intermediates involved in the DNA cleav-
age by the complexes has not been clear. The results indicated the
important role of metal in these isolated DNA cleavage reactions.
As the compound was observed to cleave the DNA, it can be con-
cluded that the compound inhibits the growth of the pathogenic
organism by cleaving the genome.
displays a reduction peak at Epc = 0.25 V with a correspond-
ing oxidation peak at Epa = 0.75 V. The peak separation of this
couple (ꢃEp) is 0.50 V at 0.1 V and increases with increase
in scan rate. The most significant feature of the Cu(II) com-
plex is the Cu(II)/Cu(I) couple. The difference between forward
and backward peak potentials can provide a rough evalua-
tion of the degree of the reversibility of one electron transfer
reaction. The analyses of cyclic voltametric responses with
the scan rate varying 50–300 mV/s gives the evidence for
quasi-reversible one electron transfer process. The ratio of
cathodic to anodic peak height was less than one. How-
ever, the peak current increases with the increase of the
square root of the scan rates. This establishes the electrode
process as diffusion controlled [53]. The separation in peak
potentials increases at higher scan rates. These characteristic fea-
tures are consistent with the quasi-reversibility of Cu(II)/Cu(I)
couple.
4. Conclusions
The newly synthesized Schiff bases act as tridentate ligands
Table 6
coordinating to metal ion through azomethine nitrogen, thione sul-
phur and phenolic oxygen atom via deprotonation. The emission
spectral studies revealed that, the Schiff bases and their com-
plexes are fluorescent in nature. The Schiff bases and their metal
complexes were found to be highly active against some of the
antibacterial and antifungal species. The activity is significantly
increased on coordination. The DNA cleavage studies revealed that,
the complexes shown non-specific cleavage of DNA.
Minimum inhibitory concentration results in (␮g/ml).
Compound
E. coli P. aeruginosa S. typhi A. flavus Cladosporium A. niger
C12H11N3O3S
C13H13N3O3S
25
25
10
10
10
10
10
10
>100
>100
25
25
10
25
10
10
–
25
25
10
10
10
10
25
>100
10
25
10
10
10
10
>100
>100
>100
>100
10
10
10
25
>100
>100
Co(C12H10N3O3S)2 10
Co(C13H12N3O3S)2 10
Ni(C12H10N3O3S)2 10
Ni(C13H12N3O3S)2 10
Cu(C12H10N3O3s)2 25
Cu(C13H12N3O3S)2 25
All these observations put together lead us to propose the fol-
lowing structure (Fig. 5a and b).
–

3
54
S.A. Patil et al. / Spectrochimica Acta Part A 75 (2010) 347–354
Appendix A. Supplementary data
[28] P.R. Reddy, K.S. Rao, B. Satyanarayana, Tetrahedron Lett. 47 (2006) 7311.
[
29] V.K. Ahluwalia, P. Bhagat, R. Aggarwal, R. Chandra, Intermediates for Organic
Synthesis, I.K. International Pvt. Ltd, Delhi, 2005.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2009.10.039.
[
30] E. Spath, M. Pailer, Chem. Ber. 68 (1935) 940.
[31] A.D. Kulkarni, G.B. Bagihalli, S.A. Patil, P.S. Badami, J. Coord. Chem. 62 (18) (2009)
060–3072.
3
[
[
[
32] R.M. Naik, V.M. Thakor, Curr. Sci. 22 (1957) 1626.
33] T.A. Brown, Molecular biology—a practical approach, 1 (1990) 51–52.
34] A.K. Sadana, Y. Miraza, K.R. Aneja, O. Prakash, Eur. J. Med. Chem. 38 (2003)
533–536.
References
[
[
[
[
1] P.K. Mascharak, Coord. Chem. Rev. 225 (2002) 201.
2] P.H. Wang, J.G. Keck, E.J. Lien, et al., J. Med. Chem. 33 (1990) 608.
3] J.R. Merchant, G. Martsyen, N.S. Venkatesh, Ind. J. Chem. Sect. B 20 (1981) 493.
4] R.P. Kapoor, M.K. Rastogi, R. Khanna, C.P. Garg, Ind. J. Chem. Sect. B 20 (1981)
[35] E.M. Saad, M.S. El-Shahwai, H. Saleh, A.A. El-Asmy, Trans. Met. Chem. 32 (2007)
155–162.
[36] R. Garg, N. Fahmi, R.V. Singh, Russ. J. Coord. Chem. 34 (2008) 198–203.
[37] B.S. Shyamala, P.V. Ananthalakshmi, V.J.T. Raju, P.N. Rao, P.U.M. Reddy, Biomet-
als 5 (1992) 23–27.
[38] M. Wang, L.F. Wang, Y.-Z. Li, Q.-X. Li, Z.-D. Xu, D.-M. Qu, Trans. Met. Chem. 26
(2001) 307–310.
[39] S. Chandra, S. Raizada, M. Tyagi, A. Gautam, Bioinorg. Chem. Appl. 2007 (2007)
1–7, Article ID 51483.
3
90.
[
[
[
[
5] P.K. Radhakrishanan, P. Indrasen, C.G.R. Nair, Polyhedron 18 (1998) 67.
6] J. Lopez, S. Liang, X.R. Bu, Tetrahedron Lett. 39 (1998) 4199.
7] W. Zhang, E.N. Jacobsen, J. Org. Chem. 56 (1991) 2296.
8] G. Kokotos, V. Theodorou, C. Tzougraki, D. Deforce, E. Vanden Eeckhout, Bioorg.
Med. Chem. Lett. 7 (1997) 2165–2168.
[9] A. Karaliota, O. Kretsi, C. Tzougraki, J. Inorg. Biochem. 84 (2001) 33–37.
[40] S. Chandra, L.K. Gupta, Spectrochim. Acta Part A 61 (1–2) (2005) 269–275.
[41] K. Nakamoto, Infrared Spectra of Inorganic and Coordination Compounds,
Wiley-Interscience, New York, 1970.
[10] I. Kostova, I. Manolov, I. Nicolova, S. Konstantinov, M. Karaivanova, Eur. J. Med.
Chem. 36 (2001) 339–347.
[
[
[
[
11] S.B. Padhye, G.B. Kauffman, Coord. Chem. Rev. 63 (1985) 127–160.
12] D.X. West, S.B. Padhye, P.B. Sonawane, R.C. Chikte, Struct. Bonding 76 (1991) 1.
13] M.B. Ferrari, S. Capacchi, G. Pelosi, Inorg. Chim. Acta 286 (1999) 134–141.
14] A.K. Nandi, S. Chaudhri, S.K. Mazumdah, S. Ghosh, J. Chem. Soc. Perkin Trans. 2
[42] A.A.E. Adel, M.I.A. Omima, Trans. Met. Chem. 32 (2007) 889.
[43] K. Singh, M.S. Barwa, P. Tyagi, Eur. J. Med. Chem. 41 (2006) 147.
[44] S.S. Konstantinovic, B.C. Radovanovics, S.P. Sovilj, S. Stanojevic, J. Serb. Chem.
Soc. 73 (1) (2008) 7–13.
(
11) (1984) 1729–1733.
[45] K.E.M. Saied, Ind. J. Chem. 33 (1994) 830.
[
[
15] M.A. Ali, D.A. Chowdhary, M. Nazir Uddin, Polyhedron 3 (5) (1984) 595–598.
16] J.P. Scovill, D.L. Klayman, C.F. Franchino, J. Med. Chem. 25 (10) (1982)
[46] A.K. El-Sawaf, D.X. West, F.A. El-Saied, R.M. El-Bahnasawy, Trans. Met. Chem.
23 (1998) 649–655.
[47] N. Saha, N. Mukherjee, Polyhedron 3 (1984) 1135.
1
261–1264.
[
[
17] N.K. Singh, S.B. Singh, Ind. J. Chem. 40 (2001) 1070–1075.
18] R.K. Agarwal, L. Singh, D.K. Sharma, Bioinorg. Chem. Appl. 2006 (2006) 1–9,
Article ID 59509.
19] M.E. Hussain, M.N. Alam, J. Begum, Inorg. Chim. Acta 249 (2) (1996) 207–213.
20] P. Bindu, M.R.P. Kurup, T.R. Satyakeerty, Polyhedron 18 (3–4) (1999) 321–331.
21] C.L. Hoagland, S.M. Ward, L.E. Smadel, T.M. Rivers, J. Exp. Med. 74 (1941) 69.
22] G.B. Bagihalli, P.G. Avaji, S.A. Patil, P.S. Badami, Eur. J. Med. Chem. 43 (2008)
[48] L.K. Gupta, S. Chandra, Spectrochim. Acta Part
796.
A 65 (2006) 792–
[49] H. Liu, H. Wang, F. Gao, D. Niu, Z. Lu, J. Coord. Chem. 60 (24) (2007) 2671–
2678.
[
[
[
[
[50] D.P. Singh, R. Kumar, V. Malik, P. Tyagi, Trans. Met. Chem. 32 (2007) 1051–1055.
[51] S. Chandra, S. Verma, Russ. J. Coord. Chem. 34 (7) (2008) 499–503.
[52] K.N. Thimmaiah, W.D. Lloyd, G.T. Chandrappa, Inorg. Chim. Acta 106 (1985) 81.
[53] A.J. Bard, L.R. Faulkner, Electrochemical Methods, 2nd ed., John Wiley, New
York, 2001.
2
639–2649.
[
[
23] G.B. Bagihalli, P.G. Avaji, S.A. Patil, P.S. Badami, J. Coord. Chem. 61 (2008) 2793.
24] A. Kulkarni, P.G. Avaji, G.B. Bagihalli, S.A. Patil, P.S. Badami, J. Coord. Chem. 62
[54] Z.H. Chohan, M. Arif, M.A. Akhtar, C.T. Supuran, Bioinorg. Chem. Appl. 2006
(2006) 1–13, Article ID 83131.
(
3) (2009) 481–492.
[
[
25] A.D. Kulkarni, S.A. Patil, P.S. Badami, J. Sulfur Chem. 30 (2) (2009) 145–159.
26] J. Liu, T. Zhang, T. Lu, L. Qu, H. Zhou, Q. Zhang, L. Ji, J. Inorg. Biochem. 91 (2002)
[55] Z.H. Chohan, A. Scozzafava, C.T. Supuran, J. Enzyme Inhib. Med. Chem. 18 (2003)
259.
[56] M.J. Waring, in: G.C.K. Roberts (Ed.), Drug Action at the Molecular Level,
Maemillar, London, 1977, p. 167.
2
69.
[
27] V.G. Vaidyanathan, B.U. Nair, J. Inorg. Biochem. 93 (2003) 271.