Synthesis, characterization, DNA cleavage and in vitro antimicrobial studies of La(III), Th(IV) and VO(IV) complexes with Schiff bases of coumarin derivatives

Article abstract of DOI:10.1016/j.ejmech.2008.12.012

A series of La(III), Th(IV) and VO(IV) complexes have been synthesized with Schiff bases derived from 8-formyl-7-hydroxy-4-methylcoumarin and o-phenylenediamine/ethylenediamine. The structure of the complexes has been proposed in the light of analytical, spectral (IR, UV-vis, ESR and FAB-mass), Magnetic and thermal studies. The complexes are soluble in DMF and DMSO. The measured molar conductance values indicate that, the complexes are non-electrolytes in nature. The redox behavior of the complexes was investigated by electrochemical method 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 activity of La(III) and VO(IV) metal complexes is studied by agarose gel electrophoresis method.

Full text of DOI:10.1016/j.ejmech.2008.12.012

European Journal of Medicinal Chemistry 44 (2009) 2904–2912
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis, characterization, DNA cleavage and in vitro antimicrobial studies of
La(III), Th(IV) and VO(IV) complexes with Schiff bases of coumarin derivatives
,
b
Ajaykumar Kulkarni a, Sangamesh A. Patil a , Prema S. Badami
*
a P.G. Department of Chemistry, Karnatak University, Dharwad-580 003, Karnataka, India
b Department of Chemistry, Shri Sharanabasaveswar College of Science, Gulbarga-585102, Karnataka, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of La(III), Th(IV) and VO(IV) complexes have been synthesized with Schiff bases derived from 8-
formyl-7-hydroxy-4-methylcoumarin and o-phenylenediamine/ethylenediamine. The structure of the
complexes has been proposed in the light of analytical, spectral (IR, UV–vis, ESR and FAB-mass), Magnetic
and thermal studies. The complexes are soluble in DMF and DMSO. The measured molar conductance
values indicate that, the complexes are non-electrolytes in nature. The redox behavior of the complexes
was investigated by electrochemical method using cyclic voltammetry. The Schiff bases and their
complexes have been screened for their antibacterial (Escherichia coli, Staphylococcus aureus, Pseudo-
monas aeruginosa and Salmonella typhi) and antifungal activities (Aspergillus niger, Aspergillus flavus and
cladosporium) by Minimum Inhibitory Concentration method. The DNA cleavage activity of La(III) and
VO(IV) metal complexes is studied by agarose gel electrophoresis method.
Received 27 June 2008
Received in revised form
6 November 2008
Accepted 8 December 2008
Available online 24 December 2008
Keywords:
Coumarin
Cyclic voltammetry
DNA
Microbial
Spectral
Ó 2009 Elsevier Masson SAS. All rights reserved.
Synthesis
1. Introduction
hydroxy-4-methylcoumarin)-ethylenediamine [18,19] and coumarin-
3-carboxylic acid [20] have been reported. Recently some transition
Coumarin (1,2-benzopyrone) is structurally the least complex
member of a large class of compounds known as benzopyrones [1]. The
biological activities of coumarin derivatives are multiple and include
antithrombotic [2], antimicrobial [3], antiallergic [4], anti-inflamma-
tory [5], antitumor [6] and anticoagulants [7]. Recently, coumarin
derivatives have been evaluated in the treatment of human immuno-
deficiency virus, due to their ability to inhibit human immunodefi-
ciency virus integrase [8,9]. The coumarin nucleus is also present in the
antibiotics such as novobiocin, clorobiocin and coumermycin A1. These
antibiotics are potent catalytic inhibitors of DNA gyrase. In addition to
that, these antibiotics have been shown to be active against Gram-
positive bacteria, especially against methicillin-resistant Staphylo-
coccus aureus [3]. Further it is evident from the literature [10–13] that,
the transition and rare earth complexes of hydroxycoumarin deriva-
tives are also subjects of increasing interest in bioinorganic and coor-
dination chemistry [14,15]. Lanthanides(III) show antitumor activity
[16]. Some interesting lanthanide complexes of coumarin derivatives
like bis(4-hydroxy-3-coumarinyl)-acetic acid [17], N,N0-bis(8-aceto-7-
metal complexes with coumarin Schiff bases have been reported from
our laboratory [13,21].
Thus, the aim of present work is to synthesize and characterize
La(III), Th(IV) and VO(IV) metal complexes with newly synthesized
Schiff bases derived from 8-formyl-7-hydroxy-4-methylcoumarin
and o-phenylenediamine/ethylenediamine. The electron transfer
mechanism of the Schiff bases and their complexes is investigated
by the aid of cyclic voltammetry. The Schiff bases and their metal
complexes are screened for their in vitro antimicrobial activity. DNA
cleavage property of the complexes is also studied.
2. Chemistry
2.1. Methods
All the chemicals used were of reagent grade. 7-Hydroxy-4-meth-
ylcoumarinwas synthesized according to the literature procedure [22].
2.1.1. Synthesis of 8-formyl-7-hydroxy-4-methylcoumarin
8-Formyl-7-hydroxy-4-methylcoumarin is prepared by the
known method [18] with slight modification. 7-Hydroxy-4-meth-
ylcoumarin (5.28 g, 0.03 mol) and hexamine (9.8 g, 0.07 mol) in
* Corresponding author. Fax: þ91 0836 2771275.
E-mail address: patil1956@rediffmail.com (S.A. Patil).
0223-5234/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2008.12.012

A. Kulkarni et al. / European Journal of Medicinal Chemistry 44 (2009) 2904–2912
2905
O
OC2H5
HO
C
OH
O
HO
O
Conc. H2SO4
O°C
+
CH2
O
C
CH3
CH3
Recorcinol
Ethylacetoacetate
Hydroxy
methylcoumarin
4
7
Hexamine,
At 70-80°C
HO
HCl + Water
CHO
N
HC
CH
N
O
O
o-phenylene diamine
Reflux 4-5 Hr
O
O
O
O
OH
HO
CH3
CH3
CH3
Reflux 4-5 Hr
2HC
ethylene diamine
Schiff base I
CH2
HC
CH
N
N
O
O
O
O
OH
HO
CH3
CH3
Schiff base II
Schiff base I = H2LI; Schiff base II = H2LII.
Scheme 1. Synthesis of Schiff bases H2LI and H2LII.
glacial acetic acid (50 mL) were heated for 6–7 h, then, 20% HCl
(75 mL) was added and further heated for 45 min, then cooled to
20–25 ꢀC and extracted with ether. Ether is evaporated and the
remaining solution is poured into ice with constant stirring, pale
yellow colored solid of 8-formyl-7-hydroxy-4-methylcoumarin
formed was filtered and was recrystalized from hot ethanol.
bases (4.8/4.3 g, 0.01 mol) in super-dry alcohol (40 mL). The reac-
tion mixture was refluxed for 4–5 h. After cooling, the pH of the
reaction mixture was adjusted to ca. 7 by adding dilute ammonia
with constant stirring. The precipitate of the complex formed
during the addition of dilute ammonia was filtered, washed thor-
oughly with super-dry alcohol and ether and finally dried over
fused CaCl2 in vacuum (yield: 61–65%).
2.1.2. Synthesis of Schiff bases [H2LI–H2LII]
The Schiff bases have been synthesized by refluxing the reaction
mixture of hot ethanol solution (30 mL) of o-phenylenediamine/eth-
ylenediamine (1.08/0.6 g, 0.01 mol) andhotethanol solution (30 mL) of
8-formyl-7-hydroxy-4-methylcoumarin (4.08 g, 0.02 mol) for 4–5 h
with addition of a 3–4 drops of concentrated hydrochloric acid. The
precipitate formed during refluxion was filtered, washed with cold
EtOH and recrystallized from hot EtOH (yield: 72.5%).
3. Pharmacology
3.1. DNA cleavage experiment
3.1.1. Preparation of culture media
DNA cleavage experiments were done according to the literature
[23]. 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, 20; in (g/l)] was used for the culture of
Aspergillus niger. The 50 mL media was prepared, autoclaved for
15 min at 121 ꢀC under 15 lb pressure. The autoclaved media were
2.1.3. Synthesis of La(III), Th(IV) and VO(IV) complexes [1–6]
The La(III)/Th(IV) nitrate and vanadyl sulphate (4.3/5.7/1.81 g,
0.01 mol) in super-dry alcohol (10 mL) were treated with Shciff
Table 1
Elemental analyses of Schiff bases and their La(III), Th(IV) and VO(IV) complexes along with molar conductance and magnetic moment data.
Comp. No.
Empirical formula
M%
C%
H%
N%
Molar conductance Ohmꢁ1 cmꢁ2 moleꢁ1
meff (BM)
Obsd
Calcd
Obsd.
Calcd
Obsd.
Calcd
Obsd.
Calcd
H2LI
C28H20N2O6
C24H20N2O6
–
–
–
–
69.994
66.742
48.271
44.440
37.829
34.291
61.659
57.941
70.0
66.66
4.161
4.634
2.877
3.081
2.709
2.851
3.306
3.626
4.166
4.629
2.873
3.086
2.702
2.857
3.302
3.621
5.841
6.479
6.035
6.483
6.305
6.664
5.139
5.639
5.83
–
–
–
–
–
–
–
–
1.73
1.72
H2LII
6.481
6.034
6.481
6.306
6.666
5.137
5.633
1
2
3
4
5
6
[La(H2LI)(NO3)].H2O
[La(H2LII)(NO3)].H2O
[Th(H2LI)(NO3)2].3H2O
[Th(H2LII)(NO3)2].3H2O
[VO(H2LI)]
19.821
21.289
26.120
27.625
12.299
13.488
19.827
21.296
26.126
27.619
12.293
13.481
48.275
44.444
37.837
34.285
61.651
57.947
21.3
22.6
19.8
23.5
22.9
24.1
[VO(H2LII)]

2906
A. Kulkarni et al. / European Journal of Medicinal Chemistry 44 (2009) 2904–2912
Table 2
The important infrared frequencies (in cmꢁ1) of Schiff bases and their metal complexes.
Compound
Lattice water
n
(OH)
Lactonyl
n
(C]O)
n
(C]N)
H-bonded –OH Stretching
Phenolic
n
(C–O)
n
(M–N)
n
(M–O)
H2LI
–
–
1735
1720
1736
1724
1733
1723
1736
1724
1613
3062
3051
1306
1305
1397
1371
1390
1389
1395
1392
–
–
–
–
H2LII
1632
1602
1622
1604
1624
1603
1626
1
2
3
4
5
6
3447
3430
3402
3442
3438
3439
–
–
–
–
–
–
516
510
524
513
486
480
378
375
410
405
395
398
inoculated with the seed culture. E. coli is incubated for 24 h and A.
niger for 48 h at 37 ꢀC.
10 mL of solvent instead of stock solution with sterilized distilled
water.
The bacteria were subcultured in agar medium. The petridishes
were incubated for 24 h at 37 ꢀC. Standard antibacterial drug,
Gentamycine was also screened under similar conditions for
comparison. The fungi were subcultured in potato dextrose agar
medium. Standard antifungal drug, Fluconazole was used for
comparison. The petridishes were incubated for 48 h at 37 ꢀC.
Sterile disks were used in the agar media. Activity was determined
by measuring the diameter of the zone showing complete inhibi-
tion. Compounds showing promising antibacterial/antifungal
activity were selected for minimum inhibitory concentration (MIC)
studies [24].
3.1.2. Isolation of DNA
The fresh bacterial culture (1.5 mL) is centrifuged 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 M
sodium acetate (pH 4.8) was added. Then, centrifuge at 10,000 rpm
for 10 min and to the supernatant, 3 volumes of chilled absolute
alcohol was added. The precipitated DNA was separated by
centrifugation and the pellet was dried and dissolved in TAE buffer
(10 mM tris pH 8.0, 1 mM EDTA) and stored in cold condition.
4. Results and discussion
The synthesis of Schiff bases H2LI and H2LII is schematically
presented in Scheme 1. All the La(III), Th(IV) and VO(IV) complexes
are colored, stable and non-hygroscopic in nature. The complexes
are insoluble in common organic solvents but soluble in DMF and
DMSO. The elemental analyses show that, the La(III), Th(IV) and
VO(IV) complexes have 1:1 stoichiometry. 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
(Table 1).
3.1.3. Agarose gel electrophoresis
Cleavage products were analyzed by agarose gel electrophoresis
method [23]. Test samples (1 mg/mL) were prepared in DMF. The
samples (25
m
g) were added to the isolated DNA of E. coli and A.
niger. The samples were incubated for 2 h at 37 ꢀC and then 20
mL of
DNA sample (mixed with 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. Removed the gel
and stained with 10.0 mg/mL ethidium bromide for 10–15 min and
4.1. Infrared spectra
the bands observed under Vilberlourmate Gel documentation
system and photographed to determine the extent of DNA cleavage.
Then the, results are compared with standard DNA marker.
The prominent infrared spectral data of Schiff bases and their
La(III), Th(IV) and VO(IV) complexes are presented in Table 2.
The IR spectra of the Schiff bases exhibit characteristic high
intensity band at 1613–1632 cmꢁ1 which is attributed to the
3.2. In vitro antibacterial and antifungal assays
n
(C]N) vibration. Another strong band at 1735–1720 cmꢁ1 is
The biological activities of synthesized Schiff bases and their
La(III), Th(IV) and VO(IV) complexes have been studied for their
antibacterial and antifungal activities by agar and potato dextrose
agar diffusion method respectively in DMF solvent against E. coli, S.
aureus, Pseudomonas aeruginosa and Salmonella typhi bacterial and
A. niger, Aspergillus flavus and cladosporium fungi species [24]. The
stock solution (1 mg mLꢁ1) of the test chemical was prepared by
dissolving 10 mg of the test compound in 10 mL of dimethyl
formamide (DMF) solvent. The stock solution was suitably diluted
with sterilized distilled water to get dilution of 100, 50 and
assigned to n(C]O), lactonyl carbon of the coumarin moiety. In
addition to this, the broad band around 3062 cmꢁ1 is assigned to
phenolic H-bonded –OH stretching; a high intensity band in the
1306–1305 cmꢁ1 region with an additional band around 1500 cmꢁ1
is assigned to the phenolic
n(C–O) vibrations and a medium
intensity band at 1585 cmꢁ1 is regarded as an aromatic C]C
stretching vibrations.
In comparison with the spectra of the Schiff bases, all the
complexes exhibit the band of
n(C]N) in the region 1602–
1626 cmꢁ1; showing the shift of band to lower wave numbers [25]
indicating that, the azomethine nitrogen is coordinated to the
25 m
g mLꢁ1. Control for each dilution was prepared by diluting
Table 3
The 1H NMR and 13C NMR data of Schiff bases.
Schiff base
H2LI
1H NMR (CDCL3) (ppm)
13C NMR (CDCL3) (ppm)
14.7 (s, 2H, OH), 9.42 (s, 2H, HC]N), 6.1–7.6
(m, 10H, Ar-H), 2.4 (s, 6H, Ar-CH3)
14.3 (s, 2H, OH), 9.1 (s, 2H, HC]N), 6.1–7.7 (m, 6H, Ar-H),
2.5 (s, 6H, Ar-CH3), 2.1 (t, 4H, CH2–CH2)
111.3, 118.6, 123.6, 125.5, 126.7, 131.5, 133.6, 138.2,
148.6, 152.2, 158.6 (aromatic carbon), 144.3 (C]N), 172.8 (C]O), 38.4 (CH3)
113.1, 123.6, 125.5, 126.7, 131.5, 133.6, 138.2, 148.6 (aromatic carbon),
142.3 (C]N), 165.6 (C]O), 36.8 (CH3), 21.4 (CH2)
H2LII

A. Kulkarni et al. / European Journal of Medicinal Chemistry 44 (2009) 2904–2912
2907
Fig. 1. FAB-mass spectrum of H2LI.
metal ion. The high intensity band due to phenolic C–O appeared at
4.2. 1H NMR spectra
1306–1305 cmꢁ1 in the Schiff bases appeared as a medium to high
intensity band in the 1371–1397 cmꢁ1 region in the complexes.
These observations support the formation of M–O bonds via
deprotonation.
The Schiff bases have been characterized by 1H, 13C NMR spectra
and also by 2D 1H–1H HOMOCOSY to ensure ligand purity in solu-
tion and elucidate the differently positioned proton and carbon. The
1H NMR and 13C NMR spectral data are produced in Table 3.
In 1H NMR spectrum of the Schiff base H2LI, signals at 14.7 and
2.4 ppm are ascribed to phenolic –OH and Aromatic-CH3 respec-
tively. A characteristic singlet proton signal at 9.42 ppm is assigned
to –CH]N. In addition to this the multiplet signals around
6.1–7.6 ppm are due to aromatic protons. In case of Schiff base H2LII,
the singlet at 14.3, 9.1 and 2.5 ppm are attributed to phenolic –OH,
–CH]N and Aromatic-CH3 respectively. In addition to this the
multiplet signals around 6.1–7.7 ppm and triplet around 2.1 ppm is
due to aromatic and CH2–CH2 protons respectively. In both the
Schiff bases, phenolic –OH proton signals disappeared after the
addition of D2O [29].
The broad band of medium intensity occurring in the 3447–
3402 cmꢁ1 region is due to the symmetric and antisymmetric O–H
stretching vibrations of the lattice water [26]. The new bands in the
region of 410–375 and 524–480 cmꢁ1 in all the complexes are
assigned to stretching frequencies of (M–O) and (M–N) bonds
respectively.
The La(III) and Th(IV) nitrato complexes (1–4) contain bands
characteristic of both coordinated and ionic nitrates. The bands
around 1481 cmꢁ1 and around 1330 cmꢁ1 are due to the
n
(N]O)(n1) and nasym (NO2) (n5) respectively, of the coordinated
nitrate. The nsym (NO2) vibration (n2) at 1020 cmꢁ1 is characteristic
of bi-dentate chelating nitrate. The separation (Dn) of the nitrate
stretching fundamentals (n1
–
n5) has been used as a criterion to
In 13C NMR spectra of the Schiff bases, the signals appeared in
the region 111.3–158.6 ppm are assigned to aromatic carbons. The
signals at 172.8–165.6, 144.3–142.3 and 38.4–36.8 ppm are due to
C]O, C]N and CH3 respectively. In case of Schiff base (II) an
additional signal at 21.4 ppm is ascribed to CH2–CH2.
distinguish between mono- and bi-dentate chelating nitrates [27],
increasing as the coordination changes from mono- to bi-dentate
and bridging. The magnitude of this separation (Dn]151) is
inductive of bi-dentate coordination of the nitrate ion.
In the VO(IV) complexes (5–6), a characteristic medium to high
The two dimensional 1H–1H homocosy NMR spectra of Schiff
bases clearly includes all the protons of the aromatic region
observed as a cross peaks in the region 6.1–7.7 ppm. The peaks
due to CH]N, CH3, and CH2–CH2 are well resolved from the
spectrum.
intensity band in the region 944–936 cmꢁ1 is attributed to the
n
(V]O) vibrations [28].
Thus, the IR spectral data provide strong evidence for the
complexation of the tetradentate Schiff bases with ONNO sequence.
Fig. 2. FAB-mass spectrum of La(III) (1) complex.

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A. Kulkarni et al. / European Journal of Medicinal Chemistry 44 (2009) 2904–2912
La(III) (1) complex (Fig. 2) the molecular ion peak Mþ is observed at
m/z 696 which is equivalent to its molecular weight. This molecular
ion undergoes fragmentation with the loss of one water molecule,
gave a species [La(H2LI)(NO3)]þ at m/z 678. Further, the fragment
ion by the loss of one nitrate molecule gave a fragment ion at m/z
616. In case of the Th(IV) (3) complex, the spectrum shows
a molecular ion peak Mþ at m/z 888 which is equivalent to its
molecular weight [Th(H2LI)(NO3)2]$3H2O. This species gave a frag-
ment ion at m/z 834, by the loss of three water molecules. This
fragment ion lost the two nitrate molecules and gave a fragment
ion [Th(H2LI)]þ at m/z 710. Finally, these complexes undergoes
demetallation to form the species [LI þ 2H]þ gave a fragment ion at
m/z 480. All these fragmentation patterns are well observed in the
FAB-mass spectra.
In the spectrum of VO(IV) (5) complex (Fig. S1) the molecular
ion peak Mþ, which is equivalent to its molecular weight is
observed at m/z 545. This molecular ion undergoes demetallation
to give fragment ion peak at m/z 480 which corresponds to the
[LI þ 2H]þ species.
Fig. 3. ESR spectrum of VO(IV) (5) complex.
In 1H NMR spectra of the La(III) and Th(IV) complexes, the signal
due to azomethine proton of Schiff bases (9.42–9.1 ppm) appears in
the region 10.2–9.8 ppm indicating the coordination of the azo-
methine nitrogen to the metal ion. This downfield shift is due to
deshielding of the N]CH proton. Also the slight downfield shift is
observed for aromatic and aliphatic protons. The resonance due to
phenolic –OH around 14.7–14.3 ppm in the Schiff bases disappears
in the spectrum of complexes; this confirms that, the hydroxyl
group reacted with metal ion via deprotonation. All these obser-
vations supported the IR inferences.
4.4. Electronic spectra and magnetic studies
The electronic absorption spectra of the complexes were
recorded for freshly prepared solution in DMF at room temperature.
Electronic absorption spectra of oxovanadium complexes show
two d–d bands around ca. 11.710 and 18.100 cmꢁ1 corresponding to
2B2 / 2E and 2B2 / 2B1 transitions, respectively, which is in
consistent with that of square pyramidal geometry [30,31]. The
magnetic moment values (Table 1) are found to be 1.72–1.73
slightly less than the spin only value.
4.3. FAB-mass spectral studies of Schiff bases and its complexes
The La(III) and Th(IV) complexes exhibited a broad band around
31000 cmꢁ1 which was assigned to L / M charge transfer transi-
tion. All the La(III) and Th(IV) complexes are found to be diamag-
netic in nature.
The FAB-mass spectrum of H2LI has been depicted in Fig. 1. The
spectrum showed a molecular ion peak at m/z 480 which is
equivalent to its molecular weight. In addition, the fragment peaks
at m/z 465 and 292 are due to the cleavage of CH3 and C10H8O3
respectively. In case of H2LII the molecular ion peak at m/z 432 is
ascribed to C24H20N2O6. The peaks at 417 and 241 are assigned to
the cleavage of CH3 and C10H8O3 respectively.
4.5. ESR spectroscopy
The ESR spectrum of VO(IV) (5) complex has been studied under
liquid nitrogen temperature using TCNE as a g marker. The spec-
trum (Fig. 3) is a typical eight-line pattern, which shows that
The FAB-mass spectra of La(III), Th(IV) and VO(IV) complexes
with Schiff base H2LI have also been studied. In the spectrum of
Fig. 4. Thermogram of La(III) (1) complex.

A. Kulkarni et al. / European Journal of Medicinal Chemistry 44 (2009) 2904–2912
2909
Table 4
Thermogravimetric data of La(III) (1), Th(IV) (3) and VO(IV) (5) complexes.
Empirical formula
Metal oxide%
Decomposition temperature
ꢀC
% Weight loss
Obsd.
Inference
Obsd.
Calcd.
Calcd.
[La(H2LI)(NO3)]$H2O
22.122
22.126
50–60
355–375
505–565
45–95
310–340
505–585
300–345
460–535
2.572
8.901
68.672
6.075
13.966
53.821
2.931
2.586
8.908
68.678
6.081
13.964
53.829
2.935
Loss of lattice water
Loss of coordinated nitrate
Decomposition of organic part
loss of lattice water
Loss of coordinated nitrate
Decomposition of organic part
Loss of oxygen atom
[Th(H2LI)(NO3)2]$3H2O
27.923
12.290
27.928
12.293
[VO(H2LI)]
87.701
87.706
Decomposition of organic part
a single vanadium is present in the molecule, i.e., it is a monomer.
chemical change with the temperature range and the percentage of
metal oxide obtained are given in Table 4.
The g and gt values have been found to be 2.0093 and 2.0294
k
respectively. The gav was calculated to be 2.0227. The parameter G,
is found to be 0.3163. The A and At values have been found to be
k
4.7. Electrochemistry
144.79 ꢂ 10ꢁ4 cmꢁ1 and 46.1035 ꢂ10ꢁ4 cmꢁ1 respectively. The Aav
was calculated to be 78.99 ꢂ 10ꢁ4 cmꢁ1. The observed order of the
Electrochemical behaviour of the VO(IV) (5–6) complexes was
studied on a CHI1110A-Electrochemical analyzer in dimethyl form-
amide (DMF) containing 0.05 M n-Bu4NClO4 as the supporting
electrolyte. The nature of cyclic voltammogram is similar for both
the complexes. Hence the representative VO(IV) (5) is discussed
here. A cyclic voltammogram of VO(IV) (5) (Fig. 5) displays one
reduction peak at Epc ¼ 0.6553 V with a corresponding oxidation
parameters (A > At and gt > g ) indicates that the complexes are
k
k
of square-pyramidal geometry, characteristic of the oxovanadiu-
m(IV) complexes [32,33].
4.6. Thermal studies
The thermal behavior studies of all the complexes are almost
same. Hence, the representative La(III) (1), Th(IV) (3) and VO(IV) (5)
complexes have been discussed. The representative thermogram of
La(III) (1) is depicted in Fig. 4.
The La(III) (1) and Th(IV) (3) complexes decompose gradually
with the formation of respective metal oxide above 600 ꢀC. In the
thermograms of the La(III) (1) complex and Th(IV) (3) complexes,
the lattice water molecules decomposed between 50–60 and
45–95 ꢀC respectively; coordinated nitrate decomposes in the
region 355–375 and 310–340 ꢀC respectively. The La(III) (1)
complex decomposed significantly from 505 to 565 ꢀC centered at
524 ꢀC and Th(IV) (3) complex from 505 to 585 ꢀC centered at
540 ꢀC due to the loss of organic part.
The thermal decomposition of VO(IV) (5) complex took place
from 300–345 ꢀC corresponding to the decomposition of oxygen
atom. The organic part decomposed from 460 to 535 ꢀC in two steps
centered at 466 and 510 ꢀC corresponding to the loss of amino-
phenol and formyl coumarin moieties respectively. Finally the
metal oxide formed above 720 ꢀC. The nature of the proposed
peak at Epa ¼ 0.7926. The peak separation (
DEp) is 0.1373 V at
100 mV/s. The most significant feature of the VO(IV) complex is the
one electron transfer redox process corresponding to the VO(IV)/
VO(III) couple. The analyses of cyclic voltametric responses with the
varying scan rates from 100 to 400 mV/s give the evidence for quasi-
reversible nature (Fig. S2). [Cyclic voltammetric figures of VO(IV) (6)
is presented in Supplementary information; Figs S3 and S4].
4.8. Pharmacological results
4.8.1. In vitro antibacterial and antifungal activities
The antibacterial and antifungal studies suggested that, both the
Schiff bases were found to be biologically active and some of their
metal complexes showed significantly enhanced antibacterial and
antifungal activities. It is, however, known [34,35] that, chelating
tends to make the Schiff bases act as more powerful and potent
bactereostatic agents, thus inhibiting the growth of bacteria and
fungi more than the parent Schiff bases.
In case of antibacterial studies it was observed that, both the
Schiff bases were found to be potentially active against E. coli and
Sa. typhi. La(III), Th(IV) and VO(IV) metal complexes shown much
enhanced activity against E. coli, P. aeruginosa and Sa. typhi and
some of these complexes shown almost similar activity as that of
standard drug (Table 5, Fig. 6). Most interesting finding is both the
Schiff bases and their complexes shown higher activity compared
to standard drug against S. aureus however the activity is less.
Both the Schiff bases and their La(III), Th(IV) and VO(IV)
complexes are found to possess high antifungal activity than the
antibacterial activity. Antifungal activity of synthesized Schiff bases
and some of their complexes is almost nearer to the standard drug
Flucanozole (Table 5, Fig. 7).
The minimum inhibitory concentration (MIC) of some selected
compounds, which showed significant activity against selected
bacterial and fungi species, was also determined (Table 6). The MIC
of these compounds varies from 10–100
cated that these compounds were the most active in inhibiting the
growth of the tested organisms at a 10 g/mL concentration.
mg/mL. The results indi-
m
The ligands generally showed moderate antibacterial activity
against one or two species. However, they showed good antifungal
Fig. 5. Cyclic voltammogram of VO(IV) (5) complex at scan rate 100 mV/s.

2910
A. Kulkarni et al. / European Journal of Medicinal Chemistry 44 (2009) 2904–2912
Table 5
Antimicrobial results of Schiff bases and their metal complexes.
Compound Conc. ( % Inhibition against bacteria
g mLꢁ1
Escherichia coli Staphylococcus aureus Pseudomonas aeruginosa Salmonella typhi Aspergillus flavus Cladosporium Aspergillus niger
m
)
% Inhibition against fungi
H2LI
25
50
100
25
50
100
25
50
100
25
50
100
25
50
100
25
50
100
25
50
100
25
50
100
25
6.97
23.25
95.34
8.26
25.36
92.55
27.9
17.14
23.52
38.2
16.35
25.36
44.26
5.88
10.29
16.17
9.36
25.63
29.35
16.17
22.05
25.00
14.59
21.03
22.36
23.52
27.94
35.29
25.96
35.89
44.56
5.88
2.63
44.73
50.00
6.35
26.19
45.23
59.52
28.96
44.96
61.59
42.85
69.04
80.71
44.59
67.83
80.49
54.76
64.28
76.19
44.89
61.55
76.36
61.9
69.04
71.42
55.96
68.35
74.59
61.9
71.4
80.95
–
84.31
92.15
96.07
82.64
88.96
94.56
86.27
90.19
98.03
83.69
91.59
94.86
72.53
78.43
84.31
68.96
72.36
78.99
39.34
50.81
54.09
44.59
55.87
61.59
–
53.84
76.92
87.17
52.86
71.56
82.94
58.97
64.01
74.35
56.95
66.79
78.19
56.41
74.35
79.48
55.76
68.96
80.97
53.84
79.48
97.43
55.86
82.57
96.38
–
47.61
76.19
88.09
54.36
75.93
83.67
78.57
83.33
92.85
79.38
81.37
94.59
42.85
69.04
71.42
44.85
68.97
74.55
80.95
88.09
95.23
82.67
86.96
94.67
–
H2LII
41.98
52.63
55.26
65.76
94.73
53.67
71.48
91.35
46.39
66.05
78.06
40.59
65.98
74.89
18.42
71.05
73.68
26.43
67.89
72.99
81.57
86.84
89.47
–
1
67.44
81.39
29.63
65.32
84.23
44.66
70.69
78.34
43.59
71.29
79.29
37.20
48.83
76.74
41.26
55.63
81.32
86.04
88.37
88.37
–
2
3
4
5
6
Gentamycin
Flucanozole
Control
50
100
25
50
100
100
7.35
14.7
–
84.31
94.1
96.08
92.3
94.87
97.43
88.09
92.85
97.61
100
100
100
100
100
100
100
activity against most of the species. It was evident from the data
that this activity significantly increased on coordination. This
enhancement in the activity of both the Schiff bases may be
rationalized on the basis that their structures mainly possess C]N
bond. It has been suggested that the ligands with nitrogen and
oxygen donor systems inhibit enzyme activity, since the enzymes
which require these groups for their activity appear to be especially
more susceptible to deactivation by metal ions on coordination.
Moreover, coordination reduces the polarity [36,37] of the metal
ion mainly because of the partial sharing of its positive charge with
the donor groups [38–40] within the chelate ring system formed
during coordination. 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 micro-organism [41–44]
thus destroying them more aggressively.
4.8.2. Electrophoretic analysis
The La(III) (1) and VO(IV) (5) complexes were studied for their
DNA cleavage activity by agarose gel electrophoresis method and
presented in Fig. 8.
The gel after electrophoresis clearly revealed that, both the
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 complexes (Lane 1–4)
compared to the control DNA of E. coli and A. niger. This shows that
the control DNA alone does not show any apparent cleavage where
as complexes shown. However, the nature of reactive intermediates
involved in the DNA cleavage 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
Fig. 6. Antibacterial results of H2L1 and its complexes.
Fig. 7. Antifungal results of H2L1 and its complexes.

A. Kulkarni et al. / European Journal of Medicinal Chemistry 44 (2009) 2904–2912
2911
Table 6
the DNA, it can be concluded that the compound inhibits the
growth of the pathogenic organism by cleaving the genome.
Minimum inhibitory concentration (
bacteria.
mg/mL) of selected compounds against selected
Compound E. coli P. aeruginosa Sa. typhi A. Flavus Cladosporium A. Niger
5. Conclusions
H2LI
10
10
10
10
30
50
10
15
22
24
15
20
20
40
20
30
10
10
15
10
50
40
20
10
10
10
10
15
30
30
15
10
10
10
20
20
50
40
15
25
10
10
10
15
20
15
10
10
H2LII
The newly synthesized Schiff bases act as tetradentate ligands.
The metal ion is coordinated through the azomethine nitrogen and
phenolic oxygen atoms via deprotonation. The bonding of ligand to
metal ion is confirmed by the analytical, spectral, magnetic and
thermal studies.
The electrochemical properties of the metal complexes, inves-
tigated in DMF shown the most significant feature of the VO(IV)
complex is the VO(IV)/VO(III) couple.
1
2
3
4
5
6
Antibacterial study reveals that, Schiff bases and some metal
complexes were found to be highly active against E. coli, P. aerugi-
nosa and Sa. typhi. In case of antifungal studies, both Schiff bases
and some of their complexes are found to be highly active. The DNA
cleavage studies revealed that, the La(III) (1) and VO(IV) (5)
complexes shown non-specific cleavage of DNA.
All these observations put together lead us to propose the
following structure (Figs. 9–11).
6. Experimental
Carbon, hydrogen and nitrogen were estimated by using C, H, N
analyzer. The IR spectra of the Schiff bases and their La(III), Th(IV)
and VO(IV) complexes were recorded on a HITACHI-270 IR spec-
trophotometer in the 4000–250 cmꢁ1 region in KBr disc. The
electronic spectra of the complexes were recorded in DMF and
DMSO on a VARIAN CARY 50-BIO UV-spectrophotometer in the
Fig. 8. DNA cleavage activity of La(III) (1) and VO(IV) (5) complexes.
Fig. 9. Proposed structure of La(III) (1,2) complexes.
Fig. 10. Proposed structure of Th(IV) (3,4) complexes.

2912
A. Kulkarni et al. / European Journal of Medicinal Chemistry 44 (2009) 2904–2912
Fig. 11. Proposed structure of VO(IV) (5,6) complexes.
region of 200–1100 nm. The 1H NMR, 13C NMR and two dimen-
sional homocosy spectra of the Schiff bases were recorded in CDCl3
and 1H NMR spectra of La(III), Th(IV) complexes were recorded in
DMSO-d6 on a BRUKER 300 MHz spectrometer at room tempera-
ture using TMS as an internal reference. The ESR spectrum was
recorded on Varian-E-4X-band EPR spectrometer and the field set is
3200 G at modulation frequency of 100 kHz under liquid nitrogen
temperature 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 A) as the FAB gas. The accel-
erating voltage was 10 kV and the spectra were recorded at room
temperature and m-nitrobenzyl alcohol was used as the matrix. The
mass spectrometer was operated in the positive ion mode. The
electrochemistry of VO(IV) complexes was studied on CHI1110A-
electrochemical (HCH Instruments) analyzer (Made in U.S.A).
Thermogravimetric analyses data were measured from room
temperature to 1000 ꢀC at a heating rate of 10 ꢀC/min. The data
were obtained by using a PERKIN–ELMER DIAMOND TG/DTA
instrument. Molar conductivity measurements were recorded on
ELICO-CM-82T Conductivity Bridge with a cell having cell constant
0.51 and magnetic moment was carried out by using Faraday
balance.
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