Synthesis, characterization, biological and catalytic applications of transition metal complexes derived from Schiff base

Article abstract of DOI:10.1016/j.bmcl.2014.05.046

A novel series of Cu(II), Ni(II), Zn(II), Co(II), and Cd(II) complexes have been synthesized from the Schiff base. Structural features were determined by analytical and spectral techniques like IR, ¹H NMR, UV-vis, elemental analysis, molar electric conductibility, magnetic susceptibility and thermal studies. The complexes are found to be soluble in dimethylformamide and dimethylsulfoxide. Molar conductance values in dimethylformamide indicate the non-electrolytic nature of the complexes. Binding of synthesized complexes with calf thymus DNA (CT DNA) was studied. There is significant binding of DNA in lanes 2, 3, and 5. Lanes 4 and 6 are showing more florescence when compared to the control indicating that these molecules are strongly bound to the DNA by inserting themselves between the two stacked base pairs and exhibiting their original property of fluorescence. Angiogenesis study has revealed that the compounds B-2, B-4 and B-5 have potent antitumor efficacy and activation of antiangiogenesis could be one of the possible underlying mechanisms of tumor inhibition.

Full text of DOI:10.1016/j.bmcl.2014.05.046

Bioorganic & Medicinal Chemistry Letters xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis, characterization, biological and catalytic applications
of transition metal complexes derived from Schiff base
A. Bushra Begum a,b, N. D. Rekha c, B. C. Vasantha Kumar d, V. Lakshmi Ranganatha a,
Shaukath Ara Khanum a,
⇑
a Department of Chemistry, Yuvaraj’s College (Autonomous), University of Mysore, Mysore 570 005, Karnataka, India
b Department of Chemistry, D.Banumaiah’s P U Science College, Mysore 570 024, Karnataka, India
c Department of Studies in Biotechnology, JSS College of Arts, Commerce and Science, Mysore, India
d Department of Chemistry, University of Mysore, Mysore, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel series of Cu(II), Ni(II), Zn(II), Co(II), and Cd(II) complexes have been synthesized from the Schiff
base. Structural features were determined by analytical and spectral techniques like IR, 1H NMR, UV–vis,
elemental analysis, molar electric conductibility, magnetic susceptibility and thermal studies. The com-
plexes are found to be soluble in dimethylformamide and dimethylsulfoxide. Molar conductance values
in dimethylformamide indicate the non-electrolytic nature of the complexes. Binding of synthesized
complexes with calf thymus DNA (CT DNA) was studied. There is significant binding of DNA in lanes 2,
3, and 5. Lanes 4 and 6 are showing more florescence when compared to the control indicating that these
molecules are strongly bound to the DNA by inserting themselves between the two stacked base pairs
and exhibiting their original property of fluorescence. Angiogenesis study has revealed that the com-
pounds B-2, B-4 and B-5 have potent antitumor efficacy and activation of antiangiogenesis could be
one of the possible underlying mechanisms of tumor inhibition.
Received 11 March 2014
Revised 30 April 2014
Accepted 15 May 2014
Available online xxxx
Keywords:
Schiff base ligand
Binding/cleavage of DNA
Angiogenesis
Ó 2014 Published by Elsevier Ltd.
A significant rising interest in the design of metal compounds as
drugs and diagnostic agents is currently observed in the area of sci-
entific inquiry appropriately termed medicinal inorganic chemis-
try.1 Investigations in this area focus mostly on the speciation of
metal species in biological media, based on possible interactions
of these metal ions with diverse biomolecules, in an effort to con-
tribute to future development of new therapeutics or diagnostic
agents.2–4 A wide range of metal complexes are already in clinical
use,5 and encourage further studies for new metallodrugs, such as
metal-mediated antibiotics, antibacterial, antiviral, antiparasitic,
radiosensitizing agents, and anticancer compounds.6
During recent years coordination compounds of biologically
active ligands have received much attention. Chelation causes a
drastic change in the biological properties of the ligands and also
the metal moiety. It has been reported that chelation is the cause
and cure of many diseases including cancer.7
important to emphasize the structural similarity between Schiff
bases possessing different donor atoms (N, O, S, etc.) and biologi-
cally active compounds found in natural biological systems.8 Schiff
bases are potential anticancer drugs and, when administered as
their metal complexes, the anticancer activity of these complexes
is enhanced in comparison to the free ligand.9
Schiff bases of o-phenylenediamine and its complexes have a
variety of applications including biological,10 clinical11 and analyt-
ical.12 Earlier work has shown that some drugs showed increased
activity when administered as metal chelates rather than as
organic compounds,13 and that the coordinating possibility of
o-phenylenediamine has been improved by condensing with a
variety of carbonyl compounds.
Schiff base and their metal complexes have been extensively
investigated due to their wide range of applications as catalysts.14
Several research groups have developed different catalytic meth-
ods for oxidation of benzyl alcohol to benzaldehyde. Among the
various methods, transition metal Schiff base complex catalyzed
oxidation is worth mentioning.15 Copper(II) complexes have been
found to show excellent catalytic activity toward different oxida-
tion reactions.16
Schiff base complexes play an important role in designing metal
complexes related to synthetic and natural oxygen carriers. The
compounds of this type can be greatly modified by introducing dif-
ferent substituents providing very useful model compounds for
investigation of different chemical processes and its effects. It is
Angiogenesis is a feature of embryonal development and in sev-
eral physiological and pathological conditions, including rheuma-
toid arthritis, psoriasis, tumor growth and metastasis, diabetic
⇑
Corresponding author. Tel.: +91 99018 88755; fax: +91 821 2419239.
E-mail address: shaukathara@yahoo.co.in (S.A. Khanum).
http://dx.doi.org/10.1016/j.bmcl.2014.05.046
0960-894X/Ó 2014 Published by Elsevier Ltd.
Please cite this article in press as: Bushra Begum, A.; et al. Bioorg. Med. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.bmcl.2014.05.046

2
A. Bushra Begum et al. / Bioorg. Med. Chem. Lett. xxx (2014) xxx–xxx
retinopathy and age-related macular degeneration.17 It appears to
depend on the balance of several stimulating and inhibiting fac-
tors,18 Angiogenesis-dependent diseases are controlled by using
chemotherapy, immunotherapy and radiation therapy to inhibit
the stimulating or stimulate the inhibiting factors.19 It is a complex
process encompassing endothelial cell migration, proliferation and
tube formation. These are well-regulated processes involving a
number of stimulators. Inhibition of angiogenesis is considered to
be one of the promising strategies in the development of novel
antineoplastic therapies.20
DNA is an important drug target and it regulates many bio-
chemical processes that occur in the cellular system. The different
loci present in the DNA are involved in various regulatory pro-
cesses such as gene expression, gene transcription, mutageneis,
carcinogenesis, etc. Many small molecules exert their anticancer
activities by binding with DNA, thereby altering DNA replication
and inhibiting the growth of tumor cells. DNA cleavage reaction
is also considered of prime importance as it proceeds by targeting
various constituents of DNA viz., the nucleic bases, deoxyribose
sugar moiety and phosphodiester linkage.21 Survey of literature
demonstrates that interest in the design of novel transition metal
complexes capable of binding and cleaving duplex DNA with high
sequence and structure selectivity22,23 increases continuously.
Additionally, the metal ion type and different functional groups
of ligands, which are responsible for the geometry of complexes,
also affect the affinity of metal complexes to DNA. In addition, as
small molecules, a great many Schiff-base complexes with transi-
tion metals have provoked wide interests because of their diverse
biological and pharmaceutical activities.24
alcohol was carried out in a 50 mL two necked RB flask fitted with
a water cooled condenser. In a typical reaction, benzyl alcohol
(3.11 mL, 30 mmol) and 30% H2O2 (4.8 mL, 45 mmol) were mixed
and the reaction mixture was heated in an oil bath with continuous
stirring. An appropriate amount of catalyst (30 mmol) was added
to the hot mixture and the reaction was continued. The progress
of the reaction was determined by analyzing the reaction mixture
by withdrawing small aliquots of the reaction mixture at specific
intervals of time.
To carry out biological activities fertilized eggs were obtained
from IVRI, Bangalore, India. CT DNA was purchased from Sigma.
All chemicals and solvents were of reagent grade and purchased
from Merck, DNA stock solution was prepared by dilution of CT
DNA to buffer (containing 150 mM NaCl and 15 mM trisodium
citrate at pH 7.0) followed by exhaustive stirring at 4 °C for three
days, and kept at 4 °C for no longer than a week. The stock solution
of CT DNA gave a ratio of UV absorbance at 260 and 280 nm (A260
/
A280) of 1.89, indicating that the DNA was sufficiently free of
protein contamination. The DNA concentration was determined
by the UV absorbance at 260 nm after 1:20 dilution using
e
= 6600 Mꢀ1 cmꢀ1
.
Antiangiogenic effect of the Schiff base and their metal complex
was studied according to the method of Auerbach et al.,25 briefly,
fertilized hens eggs were surface sterilized using 70% alcohol. The
eggs were incubated in fan assisted humidified incubator at 37 °C.
On the 4th day, the eggs were cracked out into thin films of ham-
mock within a laminar flow cabinet and were further incubated.
On the 5th day when blood vessels were seen proliferating from
the center of the eggs within the hammock, filter paper disk loaded
In this Letter, we report the synthesis of metal(II) complexes of
Schiff base tetradentate ligand (N2O2) formed by the condensation
of o-phenylenediamine with carbonyl compounds and subjected to
biological and catalytic activity.
with 100 lg of the Schiff base and its metal complexes were placed
over the proliferating blood vessels and the eggs were returned to
the incubator. Results for antiangiogenic effect of the compound
were observed after 24 h.
All the reagents used in the preparation of schiff bases and their
metal complexes were of reagent grade(Merck).The solvents used
for the synthesis of schiff bases and metal complexes were distilled
before use. All other chemicals were of AR grade and used without
further purification. The elemental analysis of the compounds was
performed on a Perkin Elmer 2400 Elemental Analyser. The FT-IR
spectra were recorded using KBr disks on FT-IR Jasco 4100 infrared
spectrophotometer. The 1H NMR spectra were recorded using Bru-
ker DRX 400 spectrometer at 400 MHz with TMS as the internal
standard and DMSO-d6 as solvent. The magnetic moments were
measured out using Gouy balance. Purity of the compounds was
checked by TLC.
The Schiff base was synthesized by the condensation of o-phen-
ylenediamine and ortho-toluic acid (1:1 M ratio), dissolved in
dichlromethane. The resulting reaction mixture was stirred for half
an hour with lutidine. To the above reaction mixture TBTU
(O-(benzotriazol-1-yl)-N,N,N0,N0-tetramethyl uronium tetrafluoro-
borate) is added and stirred for 8 h at 0 °C. The volume of the solu-
tion was reduced to one third or till the liquid becomes syrupy and
10 mL of diethyl ether was added with constant stirring. The solid
obtained was treated with an equimolar volume of benzaldehyde
in ethanol and stirred over night with few drops of glacial acetic
acid. The yellow solid precipitate of Schiff base obtained was
filtered, washed with distilled water dried, recrystallized from
ethanol (Scheme 1).
For the gel electrophoresis experiment, the solution of com-
plexes in DMF (1 mg/mL) was prepared and these test samples
(1 lg) were added to the CT-DNA samples and incubated for 2 h
at 37 °C. Agarose gel was prepared in TAE buffer (4.84 Tris base,
pH 8.0, 0.5 M EDTA/1. pH 7.3); the solidified gel attained at approx-
imately 55 °C was placed in electrophoresis chamber flooded with
TAE buffer. After that 20 lL of each of the incubated complex-DNA
mixtures (mixed with bromophenol blue dye at 1:1 ratio) was
loaded on the gel along with standard DNA marker and electropho-
resis was carried out under TAE buffer system at 50 V for 2 h. At the
end of electrophoresis, the gel was carefully stained with EtBr
(Ethidium bromide) solution (10 mg/mL) for 10–15 min and visu-
alized under UV light using a Bio-Rad Trans illuminator. The illumi-
nated gel was photographed by using a Polaroid camera (a red
filter and Polaroid film were used). Both the experiments were
repeated thrice and obtained results were concordant.
All the metal(II) complexes were obtained upon reaction
between metal ions and ligand at 1:2 [M:L] molar ratio. The syn-
thesized complexes are very stable at room temperature. All the
metal complexes are colored and insoluble in water and many
common organic solvents but soluble in DMF and DMSO, decom-
posed at higher temperature. The yield, elemental analysis and
molar conductance data of metal complexes are presented in
Table 1. The analytical data are in a good agreement with the pro-
posed stoichiometry of the complexes. The metal-to-ligand ratio in
the metal(II) complexes was found to be 1:2 ratios. Elemental anal-
ysis is in good agreement with the proposed formula. The purity of
ligand and their metal complexes has been checked by TLC.
The metal complexes discussed herein were dissolved in DMF
and the molar conductivities of their 10ꢀ3 M solutions at room
temperature were measured to establish the charge of the metal
complexes. The conductance values of each metal complex are
listed in Table 1, which indicates that all the metal complexes have
Aqueous ethanolic solution of metal chloride of Co(II), Ni(II),
Cu(II), Cd(II) and Zn(II) was added to the hot ethanolic solution
of the ligand in 1:2 M ratios. The mixture was then refluxed with
stirring for ca. 5 h, which resulted in the precipitation of metal
derivatives in all the cases. The product formed was filtered,
washed and dried in vacuum desiccators.
Further the synthesized complexes were subjected for catalytic
study. The catalytic activity study toward the oxidation of benzyl
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A. Bushra Begum et al. / Bioorg. Med. Chem. Lett. xxx (2014) xxx–xxx
3
Table 1
Elemental analysis of Schiff base and its metal(II) complexes and their molar conductance data
Compound
Molecular formula Color
Yield%
Found (calcd) in %
N
Molar conductance (X )
ꢀ1 cm2 molꢀ1
C
H
M
—
L
C
21H18N2
O
Pale yellow
80
80.03 (80.23) 5.72 (5.72) 8.78 (8.76)
—
[Co(L)2]Cl2ꢂ2H2O (6a) C42H38CoN4 O4
Light brown 65%
Dark yellow 75
69.50 (69.90) 5.30 (5.31) 7.55 (7.76) 8.01 (8.17)
73.54 (73.60) 4.93 (5.00) 8.12 (8.17) 8.52 (8.56)
73.01 (73.08) 4.89 (4.96) 8.09 (8.12) 9.15 (9.21)
72.82 (72.88) 4.90 (4.95) 8.03 (8.09) 9.42 (9.45)
21.2
15.3
17.4
18.9
[Ni(L)2]Cl2 (6b)
[Cu(L)2]Cl2 (6c)
[Zn(L)2]Cl2 (6d)
[Cd(L)2]Cl2 (6e)
C42H34N4 NiO2
C42H34CuN4O2
C42H34N4 O2Zn
C42H34CdN4 O2
brown
60
70
50
White
Pale yellow
68.20 (68.25) 4.61 (4.64) 7.52 (7.58) 15.19 (15.21) 14.7
non-electrolytic nature due to no counter ions in the proposed
structures of the Schiff base metal complexes.26
and Cd(II) complexes were recorded in DMF solution in the range
of 200–800 nm region and data are presented in Table 3.
The electronic transitions due to the organic ligand in the metal
The formation of Schiff base ligand was studied by 1H NMR
spectra. In 1H NMR spectra the appearance of peak at d 2.4 indi-
cates ACH3 attached to the aromatic ring and disappearance of
ANH2, ACHO, ACOOH and appearance of NH and NACH peak at
d 9.7 and d 8.7, respectively, clearly indicates the formation of
Schiff base ligands and further the increase in aromatic protons
evidenced the formation of Schiff base.
complexes, showed the absorption bands of the
p?
p⁄ and n?p⁄
transitions results from the C@N and C@O groups and appeared
at 315–278 and 409–375 nm regions, respectively. These values
are lower than the corresponding absorption bands for the ligand,
which were observed at 317–285 and 413–409 nm, respectively
for C@N and C@O groups. This may be due to the coordination of
the nitrogen and oxygen atoms of the ligand to the metal ions.
The functional groups of the Schiff base ligand and their metal
complexes have been detected by infrared spectra. The IR spectral
bands of metal(II) complexes are listed in Table 2. In the IR spec-
trum of o-phenylenediamine, a pair of bands corresponding to
The effective magnetic moment (leff) of copper(II) complex is
1.72 BM which is consistent with the presence of one unpaired
electron.40 The lower value of magnetic moment at room temper-
ature is consistent with square planar geometry around the metal
m
(NH2) was present at ꢁ3210 and ꢁ3270 cmꢀ1 but was absent in
the IR spectra of all the complexes.27 However, a single broad med-
ions. For a square planar copper(II) complex with dx
ground
2
2
ꢀy
ium band at ꢁ3360–3450 cmꢀ1 was observed in the spectra of all
state, three transitions are possible viz, dx 2 ? dz2, dx 2 ? dxy
,
2
2
ꢀy
ꢀy
2
the complexes, which may be assigned to
m
(NH).28,29 A strong peak
and dx 2 ? dxy, dyz (2B1g ? 2A1g 2B1g ? 2B2g 2B1g ? 2Eg) Since the
ꢀy
at ꢁ1660 cmꢀ1 in the IR spectrum of benzamide was assigned to
four d orbitals lie very close together, each transition cannot be dis-
tinguished by their energy and hence it is very difficult to resolve
the bands into separate components. The broad band observed at
500–550 nm in the electronic spectrum of the complex is assigned
to 2Eg ? 2T2g transition.41,42
the ˜C@O group of the CONH moiety. This peak was shifted to a
lower frequency (ꢁ1620–1640 cmꢀ1 30,31
)
in the spectra of all the
complexes, suggesting the coordination of the oxygen of the car-
bonyl group with the metal. Furthermore, no strong absorption
band was observed near 1700 cmꢀ1 in the IR spectra of all com-
plexes as was observed in spectrum of benzylaldehyde. These facts
confirm the condensation of carbonyl groups of benzylaldehyde
and the amino groups of Benzamide moiety.32,33 The IR spectra of
the complexes showed a new strong absorption band in the region
At room temperature these complexes show the diamagnetic
behavior, indicating the square planar environment around the
Ni(II) ion.43 The electronic spectrum of Ni(II) complex shows
absorption bands at 769, 600 and 425 corresponding to square pla-
nar geometry. These bands may be assigned to 1A1g ? 1A2g (dxy
?
)
ꢁ1595–1610 cmꢀ1, which may be attributed due to
m
(C@N).34,35
dx 2), 1A1g ? 1B2g (dz2 ? dx 2) and 1A1g ? 1E1g (dxy, dyz ? dx
2
2
2
2
ꢀy
ꢀy
ꢀy
These results provide strong evidence for the formation of the mac-
transitions, respectively.
rocyclic frame.36 The lower value of
m
(C@N) indicates coordination
The effective magnetic moments (leff) of cobalt(II) complex are
of the nitrogens of azomethine to the metal.37 The bands present at
found in the range 4.49–4.37 BM. These values are in accordance
with high spin d7 complexes44 which are higher than the spin only
value (3.87) due to the orbital angular momentum contribution in
d7 system and close to the value required for an octahedral struc-
ture.45 The electronic spectrum of cobalt complex displays absorp-
tion bands at 730, 590 and 360 nm corresponding to 4T1g ? 4A2g
ꢁ1300–1000 cmꢀ1 were assigned to
m(CAN) vibrations. The bands
presents at ꢁ3080 cmꢀ1 may be assigned to
m(C–H) vibrations. The
far IR spectra showed bands in the region ꢁ420–450 cmꢀ1
corresponding to
m
(MꢀN) vibrations in all the complexes.38 The
presence of these bands supports the fact concerning the coordina-
tion of the azomethine nitrogen with the metal.39 The bands
(F), T1g (F) ? 4T1g (P), and T1g (F) ? 4T2g (F), transition, respec-
4
4
present at ꢁ510–540 cmꢀ1 in all complexes were due to
m
(MꢀO).38
tively for an octahedral geometry.46
The UV–visible spectra are often very useful in the evaluation of
results furnished by other methods of structural investigation. The
electronic spectral measurements were used for assigning the ste-
reochemistry of metal ions in the complexes based on the positions
and number of d–d transition peaks. The electronic absorption
spectra of the Schiff base ligand and its Cu(II), Ni(II) Zn(II), Co(II),
Zn and Cd(II) ion with d10 electronic configuration permits a
wide range of symmetries and coordination numbers. Since d10
configuration affords no crystal field stabilization, the stereochem-
istry of a particular compound depends on the size and polarizing
power of the M(II) cation and the steric requirement of the ligands.
Zn and Cd(II) have no d–d transition.
Mass spectrometry is an important tool widely applied to the
characterization of coordination compounds.47 The mass spectra
of all the M(II) complexes have been recorded. All the spectra exhi-
bit parent peaks due to molecular ions (M+). The proposed molec-
ular formula of these complexes was confirmed by comparing their
molecular formula weights with m/z values. In addition to the
peaks due to the molecular ions, the spectra exhibit peaks assign-
able to various fragments arising from the thermal cleavage of the
complexes. The peak intensity gives an idea of the stability of the
fragments.
Table 2
Important infrared frequencies of Schiff bases and their metal complexes
Compound
m
(NAH)
m
(C@O)
m
(C@N)
m
(MAN)
m
(MAO)
L
3360
3450
3440
3380
3415
3360
1660
1635
1640
1625
1620
1640
1665
1610
1595
1600
1605
1605
—
—
6a
6b
6c
6d
6e
420
450
425
440
435
290
310
320
240
310
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A. Bushra Begum et al. / Bioorg. Med. Chem. Lett. xxx (2014) xxx–xxx
Table 3
results in a mass loss of 86.02% (calcd 86.83%) corresponding to a
loss of organic moiety in the 175–395 °C temperature range, and
finally results in the formation of the metal oxide above 400 °C.
The thermogravimetric curves show complexes 6(b–e) start to
decompose at 300 °C and stop around 500 °C in a single or two suc-
cessive steps, corresponding to the loss of two Schiff base moieties,
thereby leading to the formation of metal oxides. This sequence
specifies the absence of water molecules in 6(b–e) complexes.
Schiff base transition metal complexes have been extensively
studied because of their potential as catalysts in a wide range of
reactions. However, not all complexes are catalytically active. The
formation of octahedral complexes with no vacant coordination
sites or absence of labile ligands could be a possible reason. In this
study, of the five metal(II) complexes synthesized from the Schiff
base ligands, four were found to have square planar geometry
while one had an octahedral geometry with two coordinated water
molecules. This favorable geometry could render the complexes
catalytically active and hence we have made an attempt to study
the efficiency of these mononuclear metal(II) complexes toward
the oxidation of benzyl alcohol to benzaldehyde with H2O2 as an
oxidant. Benzyl alcohol on oxidation gives benzaldehyde with little
benzoic acid.
Electronic absorption bands and magnetic values of ligand and their metal(II)
complexes
Complexes
Electronic absorption bands and
their assignments (nm)
Magnetic
moment
leff BM
p
–
p⁄ n–p⁄ Charge-transfer d–d
transition
transition
Ligand
6a
6b
6c
6d
317
315
298
284
294
295
410
409
402
396
406
403
—
—
—
542
375
430
—
730, 590, 360 nm 4.49–4.37
769, 600, 425
450
—
—
2.54
1.72–2.47
—
—
6e
—
H3C
NH
COOH
NH2
CH3
+
O
NH2
3
NH2
CHO
4
2
1
The catalytic activity depends on various reaction conditions
like temperature, amount of catalyst, time, oxidant to substrate
ratio etc. Initially we have tried only one complex with different
amount of catalyst and different temperature range. The percent-
age of conversion was found to increase with increase in amount
of catalyst and only little change with increase in temperature,
so that a temperature of 343 K was considered to be optimum.
The amount of catalyst has a significant effect on the oxidation
of benzyl alcohol. Four different amounts of catalyst viz., 10, 20, 30
and 40 mmol were used, keeping all the other parameters fixed:
namely benzyl alcohol, H2O2, temperature and reaction time. The
results obtained are given in Table 5 indicating conversion corre-
sponding to the amount of catalyst used, respectively.
H3C
H3C
N
NH
N
O
O
CH
N
M
CH
HC
N
CH3
O
N
5
6a-e
Scheme 1.
Tumor growth and metastasis are dependent on angiogenesis as
demonstrated in many in vivo experiments.48 Increased neovascu-
lature may allow not only an increase in tumor growth but also
enhances haematogenous tumor remobilization. Thus inhibiting
tumor angiogenesis may arrest the tumor growth and decrease
the metastatic potential of tumors. The current study has revealed
that the compounds B-2(Zn complex), B-4(Cu complex) and B-5(Cd
complex) have potent antitumor efficacy and activation of antian-
giogenesis could be one of the possible underlying mechanisms of
tumor inhibition. Angioprevention effect was assessed by the CAM
assay which is a reliable model for angiogenesis studies.49 A clear
avascular zone around the implanted disk with compounds B-2,
B-4 and B-5 indicates the inhibition of angiogenesis in CAM
(Fig. 2). This angioprevention effect of the compounds B-2, B-4
and B-5 may be due to the presence of different central metal
atoms like zinc, copper and cadmium, respectively.
Further the stability of complexes was studied by thermal anal-
yses Thermogravimetric analyses of the Schiff base ligand, and
their chelates are used to: (i) get information about the thermal
stability of these new complexes, (ii) decide whether the water
molecules (if present) are inside or outside the inner coordination
sphere of the central metal ion, and (iii) suggest a general scheme
for thermal decomposition of these chelates. In the present inves-
tigation, heating rates were suitably controlled at 10 °C minꢀ1
under nitrogen atmosphere, and the weight loss was measured
from the ambient temperature up to 800 °C. The data are provided
in Table 4. The TGA and DTG curves of complexes 6a and 6c are
presented in Figure 1. The weight loss for each chelate was calcu-
lated within the corresponding temperature ranges.
The TGA indicated that complex 6a lose 06.10% (calcd 4.99%) of
the total weight in the 98–171 °C temperature range. This weight
loss corresponds to the release of lattice, as well as coordinated
water molecules. When the temperature increases, complex 6a
Further this potentiality of the compounds was further re-
confirmed by DNA fragmentation assay (Fig. 3). After binding to
DNA, synthetic molecule can induce several changes in DNA
Table 4
Stepwise thermal degradation data obtained from TGA curves and their composition
Complex
Process
Temp. range (°C)
Degradation products
% Weight loss
No. of moles
% Residue
Nature
CoO
Calcd
Expt
Calcd
Expt
6a
I
II
I
I
I
98–171
H2O
4.99
4.50
2
2
2
2
2
2
10.38
09.44
175–375
370–480
380–490
300–410
320–450
ligand
Ligand
Ligand
Ligand
Ligand
86.83
91.36
90.72
90.48
84.72
84.45
89.60
88.20
87.25
83.98
6b
6c
6d
6e
10.89
11.50
11.75
17.37
09.78
10.35
11.22
15.35
NiO
CuO
ZnO
CdO
I
Please cite this article in press as: Bushra Begum, A.; et al. Bioorg. Med. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.bmcl.2014.05.046

A. Bushra Begum et al. / Bioorg. Med. Chem. Lett. xxx (2014) xxx–xxx
5
Figure 1. TG curves of metal complexes (a) 6a, (b) 6c.
Table 5
The influence of the amount of catalyst (Schiff base Cu complex)
Catalyst
wt (mmol)
Time
(h)
Temp
(K)
Benzyl alcohol
(mmol)
H2O2
(mmol)
Conversion
(%)
10
20
30
40
3
3
3
3
343
343
343
343
30
30
30
30
45
45
45
45
17.68
30.55
39.50
40.30
Figure 3. Photograph showing the effects of synthetic molecules on calf thymus
DNA. Lane C: Untreated DNA, Lane 1: B1, Lane 2: B2, Lane 3: B3, Lane 4: B4, Lane5:
B5. Lane 6: B6.
an electric field. DNA is negatively charged and when it is placed
in an electric field, it migrates toward the anode; the extent of
migration of DNA is decided by strength of electric field, buffer,
and density of agarose gel and size of the DNA. Generally it is seen
that mobility of DNA is inversely proportional to its size. Gel elec-
trophoresis picture is shown in Figure 1. The photographs show the
bands with different band widths and brightnesses compared to
the control. The difference observed in the band width and inten-
sity is the criterion for the evaluation of binding/cleavage ability
of synthetic molecule with calf thymus DNA. Figure 1 shows the
bands with different band widths and brightnesses compared to
control. There is a significant binding/cleavage of DNA in lanes 2,
3, and 5. Lanes 4 and 6 are showing more florescence when com-
pared to the control indicating that these molecules are strongly
bound to the DNA by inserting themselves between the two
stacked base pairs and exhibiting their original property of fluores-
cence. Lanes 2, 3 and 5 (treated with synthetic molecule: B2, B3
Figure 2. Suppression of angiogenesis in vivo by synthetic novel B2, B4 and B5 in
shell less CAM assay. Decreased vasculature was observed in treated groups
compared to control.
conformation. Synthetic molecules, which could induce DNA defor-
mations, such as bending, ‘local denaturation’ (over winding and
under winding), intercalation, micro loop formation and subse-
quent DNA shortening lead to a decrease in the molecular weight
of DNA. Gel electrophoresis is an extensively used technique for
the study of binding of compounds with nucleic acids: in this
method segregation of the molecules will be on the basis of their
relative rate of movement through a gel under the influence of
Please cite this article in press as: Bushra Begum, A.; et al. Bioorg. Med. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.bmcl.2014.05.046

6
A. Bushra Begum et al. / Bioorg. Med. Chem. Lett. xxx (2014) xxx–xxx
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The analytical and physico-chemical techniques confirmed the
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We the authors express our sincere gratitude to the University
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One of the authors S.A. Khanum gratefully acknowledged the finan-
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Department of Information Technology, Biotechnology and Science
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Please cite this article in press as: Bushra Begum, A.; et al. Bioorg. Med. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.bmcl.2014.05.046