Synthesis, characterization and DNA photocleavage study of a novel dehydroacetic acid based hydrazone Schiff's base and its metal complexes

Article abstract of DOI:10.1007/s00044-014-0911-6

A series of some novel colored complexes of Co(II), Ni(II), Cu(II), Mn(II) and Zn(II) with a novel dehydroacetic acid based hydrazone Schiff's base has been synthesized and evaluated for their DNA photocleavage potential. The ligand utilized in the present investigation was synthesized via a condensation reaction between cyanoacetic acid hydrazide and dehydroacetic acid. Further, the ligand was treated with different metal acetates of first transition series in 1:1 and 1:2 (metal to ligand) ratios, respectively, to obtain metal complexes with different ligand to metal stoichiometry. Ligand as well as all the synthesized metal complexes were characterized on the basis of data obtained from the techniques like ¹H and ¹³C NMR, IR spectroscopy, mass spectrometry, UV visible spectroscopy, elemental analysis and molar conductance. ¹H NMR spectrum of Zn(II) complexes showed the coordination of enolic oxygen atom without deprotonation, but in case of DLCu, the deprotonation of enolic proton was occurred prior to coordination. IR data revealed the participation of a carbonyl oxygen atom of ligand in coordination with metal ions. UV visible data confirmed the square-planar and octahedral geometry of the complexes. Mass spectrum showed the formation of both 1:1 and 1:2 metals to ligand stoichiometry. Most of metal complexes exhibited very good DNA photocleavage activities.

Full text of DOI:10.1007/s00044-014-0911-6

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2014) 23:3327–3335
DOI 10.1007/s00044-014-0911-6
ORIGINAL RESEARCH
Synthesis, characterization and DNA photocleavage study
of a novel dehydroacetic acid based hydrazone Schiff’s base
and its metal complexes
•
R. Pal V. Kumar A. K. Gupta V. Beniwal
•
•
Received: 22 October 2013 / Accepted: 7 January 2014 / Published online: 23 January 2014
Ó Springer Science+Business Media New York 2014
Abstract A series of some novel colored complexes of
Co(II), Ni(II), Cu(II), Mn(II) and Zn(II) with a novel de-
hydroacetic acid based hydrazone Schiff’s base has been
synthesized and evaluated for their DNA photocleavage
potential. The ligand utilized in the present investigation
was synthesized via a condensation reaction between cy-
anoacetic acid hydrazide and dehydroacetic acid. Further,
the ligand was treated with different metal acetates of first
transition series in 1:1 and 1:2 (metal to ligand) ratios,
respectively, to obtain metal complexes with different
ligand to metal stoichiometry. Ligand as well as all the
synthesized metal complexes were characterized on the
basis of data obtained from the techniques like 1H and 13C
NMR, IR spectroscopy, mass spectrometry, UV visible
spectroscopy, elemental analysis and molar conductance.
1H NMR spectrum of Zn(II) complexes showed the coor-
dination of enolic oxygen atom without deprotonation, but
in case of DLCu, the deprotonation of enolic proton was
occurred prior to coordination. IR data revealed the par-
ticipation of a carbonyl oxygen atom of ligand in coordi-
nation with metal ions. UV visible data confirmed the
square-planar and octahedral geometry of the complexes.
Mass spectrum showed the formation of both 1:1 and 1:2
metals to ligand stoichiometry. Most of metal complexes
exhibited very good DNA photocleavage activities.
Keywords Dehydroacetic acid ꢀ Cyanoacetic hydrazide ꢀ
Schiff’s base ꢀ Metal complexes ꢀ DNA photocleavage
Introduction
In past decades, intensive studies in the field of Schiff’s
bases and their metal complexes were carried out due to
their flexible chelating capabilities, pharmaceutical appli-
cations and biological activities (Teotia et al., 1973; Can
et al., 2012; Walsh et al., 1996). The presence of azome-
thine functionality particularly is known to be responsible
for their antibacterial (Pandeya et al., 1999; Karthikeyan
et al., 2006), antifungal (Singh et al., 2008), antitumor
(Ainscough et al., 1998; Rajendran et al., 2010), antitu-
berculosis (Patila et al., 2011), anticancer (Osowole et al.,
2012), antihelminthics (Husain et al., 1979), DNA binding
(Patel et al., 2011; Chan and Wong, 1995) and DNA
cleavage (Kulkarni et al., 2011; Sigman et al., 1993; Bharti
et al., 2010) properties. Many of such ligands were used in
analytical chemistry where the applications are due to their
complexation ability with different metal ions (Ganjali
et al., 2007) and in organic chemistry as catalysts to
accelerate the reactions like polymerization and oxidation
etc. (Gupta and Sutar, 2008). The biological activity of
complexes mainly depends upon a large extent to their
molecular structure and the types of metal ions. Dehydro-
acetic acid, a versatile starting material, has been used to
construct a large number of heterocyclic derivatives that
are known to possess potent antifungal and antimicrobial
properties (Jednacak et al., 2011). Owing to promising
chelating properties, a number of Schiff’s bases containing
DHA moiety and their metal complexes with various metal
ions have already been synthesized and found to possess
R. Pal ꢀ V. Kumar (&) ꢀ A. K. Gupta (&)
Department of Chemistry, Maharishi Markandeshwar
University, Mullana, Ambala, India
e-mail: vinodbatan@gmail.com
A. K. Gupta
e-mail: akhileshkumargupta@gmail.com
V. Beniwal
Department of Biotechnology, Maharishi Markandeshwar
University, Mullana, Ambala, India
123

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Med Chem Res (2014) 23:3327–3335
good in vitro antibacterial and antifungal activities (Shelke
et al., 2011; Saini et al., 2013).
Affinity in 4,000–400 cm-1 range using KBr pellet
method. The electronic spectra were recorded using Shi-
madzu UV 1800 instrument in DMSO as a solvent. Mass
spectra were recorded on Agilent mass spectrometer.
Carbon, nitrogen and hydrogen contents were analyzed
using LECO 9320 analyzer. All the melting points were
uncorrected and determined using an open capillary
method.
Some Schiff’s bases were found to act as potential
anticancer drugs, and anticancer activity of such com-
pounds was found to be improved many folds in compar-
ison with the free ligand particularly when administered as
their metal complexes. Biological experiments have
already been demonstrated that DNA is the primary
receptor of most of the anticancer drugs. The DNA mole-
cule of a cancer cell can be damaged as a result of inter-
action with small molecules, which in turns block the cell
division and finally cause the death of cancer cells (Ku-
rdekar et al., 2011). In recent years, studies on the inter-
actions between metal ions and DNA have gained
importance in urge to search of novel and potential che-
motherapeutic agents. Because of specific binding abilities
of these molecules, they can be used as photo cleaving,
non-radioactive probe for DNA structure as well as
potential antitumor agents (Erkkila et al., 1999; Chan and
Wong, 1995; Liang et al., 2004). The design of small
complexes of transition metals which can interact or bind
specifically with DNA molecules of tumor cells has
became an important area of research because of their
biocompatibility and possibility of improvement in their
binding and cleaving ability by changing the ligand envi-
ronment of a metal complexes (Sigman et al., 1993; Va-
idyanathan and Nair, 2003) and therefore can draw
significant structural information in the host. In the torch
light of the above mentioned facts and our continued
interest in the synthesis of Schiff’s base of DHA and its
metal complexes with first transition series (Saini et al.,
2013), in the present study, we report the synthesis of a
novel Schiff’s base and its metal complexes of first tran-
sition series. All synthesized compounds were screened for
their DNA photocleavage potential.
Synthesis of cyanoacetic hydrazide (1)
Cyanoacetic hydrazide was synthesized according to the
literature (Bondock et al., 2006) procedure. Added hydra-
zine hydrate (0.1 mol) drop wise to ethyl cyanoacetate
(0.1 mol) taken in 100-ml round-bottom flask at 5–10 °C
under stirring. The resulting reaction mixture was contin-
ued to stir at 5–10 °C for 30 min. Filtered and washed the
obtained product twice with 20 ml chilled ethanol and
dried in a hot air oven at 60 °C for 2 h.
Synthesis of 2-cyano-N0-(1-(4-hydroxy-6-methyl-2-oxo-2H-
pyran-3-yl)ethylidene)acetohydrazide (DLH1)
Cyanoacetic hydrazide (1) (0.01 mol) was dissolved in
30 ml aqueous ethanol (70 %) in 100-ml round-bottom
flask. The temperature of the reaction mixture rose to 70 °C.
Added hot ethanolic solution of DHA (2) (0.01 mol) to the
above reaction mixture under stirring. The progress of the
reaction was monitored by thin layer chromatography. On
completion, the reaction mixture was allowed to cool at
room temperature. Colorless crystals of the product thus
obtained were filtered and washed with excess of ethanol.
The product was recrystallized from ethanol and dried
(Scheme 1). Colorless solid, Yield: 73 %. M.p: 184 °C.
Molar conductance: 7.3 X-1 cm-2 mol-1. IR (KBr, cm-1
3527(w), t(OH); 1640(s), t(C=N); 3209(s), t(N–H);
)
Experimental
O
O
O
N
C
NH2
NH
Materials and methods
H3C
+
O
O
2
CH3
Dehydroacetic acid was purchased from Merck and used as
such without purification. All other chemicals including
solvents were of LR grade and were used as supplied
without any purification or distillation. All the reactions
were performed on magnetic stirrer equipped with hot plate
under stirring. Double-distilled water was used in the
present investigation. The ligand was purified from ethanol
1
N
C
O
HO
CH3
N
O
N
H
before preparing metal complexes. The H and 13C NMR
1
CH3
O
spectra of the ligand and the complexes were recorded on
Bruker 400 MHz instrument at frequencies of 400 and
100 MHz, respectively, using TMS as an internal reference
standard. IR spectra were recorded on Shimadzu IR
Enol form
DLH1
Scheme 1 Synthesis of the ligand
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Med Chem Res (2014) 23:3327–3335
3329
Table 1 1H and 13C NMR values of ligand and their metal complexes
1
CH3
N
11
3
C
HO
10
4
2
9
N
O
7
6
5
O
N
H
CH3
8
O
Protons
DLH1
DLZn
DL2Zn
DLCu
d (1H)
d (13C)
d (1H)
d (1H)
d (1H)
CH3-
2.13
3.10
3.91
5.93
11.52
16.12
–
16.68(C1)
2.05
2.49
3.71
5.72
11.86
15.89
2.4
2.06, 2.10
2.40, 2.50
3.67, 3.75
5.73, 5.84
11.69
-2.46
2.09
3.73
5.82
12.35
–
–N=C–CH3
NC–CH2–
C3–H
115.31(C3), 19.32(C8)
24.20(C10), 94.90(C11
)
160.49(C7)
–CONH–
O–H
167.97(C9)
180.29(C4)104.90(C5), 163.62(C6),162.62(C2),
–
15.88
CH3–COO
–
2.5
1679(s), t(C=O); 1226(s), t(C–O). Electronic spectra (kmax
nm) in DMSO: 243, 321. H NMR (DMSO-d6, 400 MHz)
O). Electronic spectra (kmax nm) in DMSO: 240, 310, 534,
580. MS: m/z [M?1]? 367.1. Anal. calcd. for
C13H14N3O6Co: C 542.64, H 4.45, N 11.47, M 16.09;
found C 42.61, H 3.55, N 11.44.
1
(ppm): 2.13 (s, 3H, CH3); 3.10 (s, 3H, N=C–CH3); 3.91 (s,
2H, –CH2–CN); 5.93 (s, 1H, ring proton); 11.15 (s, 1H,
CONH); 16.12 (s, 1H, enolic). 13C NMR (DMSO-d6
100 MHz) (ppm): 16.68 (C-1); 162.62 (C-2); 115.31(C-3);
180.29 (C-4); 104.90 (C-5); 163.62 (C-6); 160.49 (C-7);
19.32 (C-8); 167.97 (C-9); 94.90 (C-10) (Table 1). MS: m/z
[M ? 1]? 250.1. Anal. calcd. for C11H11N3O4: C 53.01, H
4.45, N 16.86; found C 52.96, H 4.46, N 16.85.
(C13H13N3O6)Ni (DLNi)
Blue solid yield: 58 %. M.p: 286 °C. Molar conductance:
6.9 X-1 cm-2 mol-1 IR (KBr, cm-1) 1623(s), t(C=N);
3161(s), t(N–H); 1676(s), t(C=O); 1247(s), t(C–O);
466(s), t(M–N); 534(s), t(M–O). Electronic spectra (kmax
nm) in DMSO: 230, 311, 582. 1H NMR (DMSO-d6,
400 MHz) (ppm):2.13 (s, 3H, CH3); 3.10 (s, 3H, N=C–
CH3); 3.91 (s, 2H, –CH2–CN); 5.93 (s, 1H, ring proton);
11.15 (s, 1H, CONH); 16.12 (s, 1H, enolic). MS: m/z
[M?1]? 338.3. Anal. calcd. for C13H13N3O6Ni: C 42.67, H
3.58, N 11.48, M 16.04; found C 42.64, H 3.56, N 11.47, M
16.02.
Synthesis of metal complexes
Charged the ligand (0.1 mol) into a round-bottom flask
containing 50 ml of methanol and raised the temperature to
80 °C to get a clear reaction mass. An appropriate transi-
tion metal acetates (0.1 or 0.05 mol) was dissolved in
20 ml methanol and added to the above reaction mixture.
The resulting reaction mixture was refluxed for 2 h. The
solid metal complexes precipitated out were filtered and
washed with methanol followed by petroleum ether to
remove the traces of impurities. Complexes were dried in a
hot air oven for 4 h to obtain the colored complexes except
that of Mn(II) and Zn(II).
(C13H13N3O6)Cu (DLCu)
Greenish solid, Yield: 74 %. M.p: 292 °C. Molar conduc-
tance: 7.1 X-1 cm-2 mol-1 IR (KBr, cm-1) 1620(s),
t(C=N); 3087(s), t(N–H); 1669(s), t(C=O); 1249(s), t(C–
O); 490(s), t(M–N); 555(s), t(M–O). Electronic spectra
1
(C13H14N3O6)Co (DLCo)
(kmax nm) in DMSO: 243, 319, 658. H NMR (DMSO-d6,
400 MHz) (ppm): -2.46 (s, 3H, CH3); 2.09 (s, 3H, N=C–
CH3); 3.731 (s, 2H, –CH2–CN); 5.82 (s, 1H, ring proton);
12.35 (s, 1H, CONH). MS: m/z [M?1]? 338.3. Anal. calcd.
for C13H13N3O6Cu: C 42.11, H 3.53, N 11.33, M 17.14;
found C 42.06, H 3.51, N 11.31, M 17.13.
Reddish solid, Yield: 62 %. M.p: 281 °C. Molar conduc-
tance: 6.2 X-1 cm-2 mol-1. IR (KBr, cm-1) 3548(w),
t(OH); 1622(s), t(C=N); 3158(s), t(N–H); 1675(s),
t(C=O); 1246(s), t(C–O); 459(s), t(M–N); 533(s), t(M–
123

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Med Chem Res (2014) 23:3327–3335
(C13H13N3O6)Mn (DLMn)
Electronic spectra (kmax nm) in DMSO: 236, 320, 655. MS:
m/z [M?1]? 560.0. Anal. calcd. for C22H20N6O8Co: C
47.19, H 3.60, N 15.01, M 11.35; found C 47.05, H 3.57, N
14.95, M 11.63.
Yellow solid, Yield: 71 %. M.p: 310 °C. Molar conduc-
tance: 5.9 X-1 cm-2 mol-1 IR (KBr, cm-1) 1614(s),
t(C=N); 3036(s), t(N–H); 1661(s), t(C=O); 1245(s), t(C–
O); 467(s), t(M–N); 527(s), t(M–O). Electronic spectra
(kmax nm) in DMSO: 241, 312, 560. MS: m/z [M?1]?
363.0. Anal. calcd. for C13H13N3O6Mn: C 43.11, H 3.62, N
11.33, M 15.17; found C 43.10, H 3.62, N 11.60, M 17.14.
(C22H20N6O8)Zn (DL2Zn)
Colorless solid, Yield: 71 %. M.p: 273 °C. Molar con-
ductance: 6.6 X-1 cm-2 mol-1. IR (KBr, cm-1) 3550(w),
t(OH); 1626(s), t(C=N); 3161(s), t(N–H); 1675(s),
t(C=O); 1246(s), t(C–O); 456(s), t(M–N); 531(s), t(M–
O). Electronic spectra (kmax nm) in DMSO: 239, 320, 719.
1H NMR (DMSO-d6, 400 MHz) (ppm): 2.06 and 2.10 (s,
6H, CH3); 2.40 and 2.50 (s, 6H, N=C–CH3); 3.67 and 3.75
(s, 4H, –CH2–CN); 5.73 and 5.84 (s, 2H, ring proton);
11.69 (s, 1H, CONH); 15.88 (s, 1H, enolic). MS: m/z
[M?1]? 561.0. Anal. calcd. for C22H20N6O8Zn: C 47.03,
H 3.59, N 14.96 M 11.64; found C 47.05, H 3.57, N 14.95,
M 11.63.
(C13H14N3O6)Zn (DLZn)
Colorless solid, Yield: 73 %. M.p: 262 °C. Molar con-
ductance: 8.2 X-1 cm-2 mol-1 IR (KBr, cm-1) 3549(w),
t(OH); 1626(s), t(C=N); 3163(s), t(N–H); 1674(s),
t(C=O); 1247(s), t(C–O); 455(s), t(M–N); 532(s), t(M–
O). Electronic spectra (kmax nm) in DMSO: 239, 322, 533.
1H NMR (DMSO-d6, 400 MHz) (ppm): 2.05 (s, 3H, CH3);
2.99 (s, 3H, N=C–CH3); 3.72 (s, 2H, –CH2–CN); 5.72
(s, 1H, ring proton); 11.86 (s, 1H, CONH); 15.89 (s, 1H,
enolic). MS: m/z [M?1]? 373.0. Anal. calcd. for
C13H14N3O6Zn: C 41.90, H 3.52, N 11.28, M 17.55; found
C 41.85, H 3.50, N 11.26, M 17.53.
DNA photocleavage studies
DNA photocleavage experiment was performed in a volume
of 10 ll containing the plasmid DNA in TE (tris 10 mM,
EDTA 0.01 mM, pH 8.0) buffer in the presence of 40 lg of
the synthesized compound. The reaction volumes were held
in caps of polyethylene microcentrifuge tubes, which were
placed directly on the surface of a transilluminator
(8000 mW cm-1) at 360 nm. The samples were irradiated
for 30 min at room temperature and then incubated at 37 °C
for 1 h. Irradiated samples were mixed with 69 loading dye
containing 0.25 % bromophenol blue and 30 % glycerol.
The samples were then analyzed by electrophoresis on a
0.8 % agarose horizontal slab gel in tris–acetate EDTA
buffer (40 mM tris, 20 mM acetic acid, 1 mM EDTA, pH:
8.0). Untreated plasmid DNA was considered as a control in
each run of gel electrophoresis, which was carried out at
5 V cm-1 for 2.0 h. The gel was stained with ethidium
bromide (1 lg ml-1) and photographed under UV light.
(C22H20N6O8)Ni (DL2Ni)
Blue solid Yield: 61 %. M.p: 281 °C. Molar conductance:
6.9 X-1 cm-2 mol-1 IR (KBr, cm-1) 3530(w), t(OH);
1634(s), t(C=N); 3175(s), t(N–H); 1678(s), t(C=O);
1241(s), t(C–O); 449(s), t(M–N); 539(s), t(M–O). Elec-
tronic spectra (kmax nm) in DMSO: 239, 322, 794. MS: m/z
[M?1]? 555.1. Anal. calcd. for C22H20N6O8Ni: C 43.05, H
3.28, N 13.69, M 19.12; found C 42.98, H 3.26, N 13.68 M
19.12.
(C22H20N6O8)Co (DL2Co)
Reddish solid, Yield: 58 %. M.p: 295 °C. Molar conduc-
tance: 7.4 X-1 cm-2 mol-1 IR (KBr, cm-1) 3549(w),
t(OH); 1622(s), t(C=N); 3158(s), t(N–H); 1675(s),
t(C=O); 1246(s), t(C–O); 458(s), t(M–N); 533(s), t(M–
O). Electronic spectra (kmax nm) in DMSO: 240, 314, 788,
784. MS: m/z [M?1]? 556.0. Anal. calcd. for
C22H20N6O8Co: C 47.58, H 3.63, N 15.53, M 10.61; found
C 47.56, H 3.61, N 15.10, 10.14.
Results and discussion
Chemistry
Ligand as well as all the synthesized metal complexes were
stable at room temperature, freely soluble in DMF/DMSO,
non-hygroscopic in nature, colored except ligand, Mn(II)
and Zn(II) complexes. All the synthesized complexes were
analyzed on the basis of various spectroscopic techniques
in order to determine their structure, type and mode of
bonding between ligand and metal ions.
(C22H20N6O8)Cu (DL2Cu)
Green solid, Yield: 74 %. M.p: 292 °C. Molar conduc-
tance: 6.0 X-1 cm-2 mol-1. IR (KBr, cm-1) 3541(w),
t(OH); 1651(s), t(C=N); 3170(s), t(N–H); 1692(s),
t(C=O); 1238(s), t(C–O); 459(s), t(M–N); 533(s), t(M–O).
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Med Chem Res (2014) 23:3327–3335
3331
Conductance and elemental analysis
assigned to the methyl protons of the coordinated acetate
ions. In 13C NMR spectrum of ligand, a signal appeared at
24.20 ppm was assigned to CN carbon. The signals due to
C=O, CH3, C–OH and C=N were appeared at 163.62,
The conductance of all the synthesized metal complexes
was recorded in 10-4 M DMSO solution at room temper-
ature in order to determine their electrolytic nature. The
observed low conductance values suggested their non-
electrolytic nature. The results of elemental analysis were
in close agreement with that of the proposed structure of
synthesized compounds.
1
16.68, 180.29 and 167.97 ppm, respectively. The H and
13C chemical shift values of the ligand and its metal
complexes are listed in Table 1.
IR spectrum
1H and 13C NMR
FTIR spectrum of metal complexes was compared with
that of free ligand in order to investigate the mode and
nature of chelation of metal ions with ligand. The charac-
teristic FTIR frequencies of free ligand along with their
metal complexes are listed in Table 2. In FTIR spectrum,
free ligand showed some characteristic bands at 3527,
3209, 2970, 2265, 1679, 1640, 1226 and 1002 cm-1 due to
OH (intramolecular hydrogen bonding), N–H (stretch),
C–H (stretch), CN (stretch), C=O (carbonyl), C=N (azo-
methine), C–O (enolic) and N–N stretching, respectively
(AnouEl Enein et al., 2007). The disappearance of band
centered at 3,527 cm-1 in case of DLMn, DLNi and DLCu
complexes suggests the deprotonation of enolic proton,
hence involvement of the enolic oxygen atom in the
coordination with metal ion. This observation was further
strengthened by the fact that there was a 20–22 cm-1
upward shift in tC–O stretch in the spectra of these metal
complexes. However, the presence of a band at 3527 cm-1
in the IR spectrum of DLZn, DLCo, DL2Co, DL2Ni,
DL2Cu and DL2Zn suggested the involvement of enolic
oxygen atom in coordination with metal ion without de-
protonation of OH group which was further supported by
1H NMR spectra of DLZn and DL2Zn. The decrease in
frequency of the C=N band in the spectrum of all metal
complexes as compared to that of free ligand indicates the
involvement of azomethine in coordination with metal ions
1
The H NMR spectrum of ligand displayed six signals at
2.13 (singlet, 3H) due to –CH3 proton, 3.10 (singlet, 3H)
due to –N=C–CH3, 3.91 (singlet, 2H) due to NC–CH2–,
5.93 (singlet, 1H) due to olefinic proton of heterocyclic
DHA ring at 11.52 (singlet, 1H) due to –CONH– and a
broad signal at 16.12 ppm (singlet, 1H) due to enolic
proton (AnouEl Enein et al., 2007; Chalaca and Figueroa
Villar, 2000). In 1H NMR spectrum, Zn(II) complexes
(DLZn and DL2Zn) showed a signal due to enolic proton
which suggests the involvement of enolic oxygen atom in
coordination with metal ion without deprotonation of the
OH group. In case of DL2Zn, enolic proton of one of the
ligands did not participate in coordination with metal ion
due to which a singlet at 16.12 ppm was appeared in the 1H
NMR spectrum. However, in case of DLCu, there is a no
signal corresponding to the enolic proton, hence suggested
the involvement of oxygen atom of the enolic group in
coordination with metal ion with the subsequent deproto-
nation of OH proton. These findings were consistent with
those suggested by Mass and IR data. A signal due to
methyl protons of DHA ring was appeared at -2.46 ppm
could be due to the paramagnetic nature of Cu(II) ions
(Kim and So, 1999). The presence of a singlet at 2.4 ppm
in case of DLZn and at 2.5 ppm in case of DLCu was
Table 2 IR and UV visible data of ligand and metal complexes
Compound
IR band frequency (cm-1
)
kmax (cm-1
)
t (OH)
t (C=O)
t (CN)
t (C=N)
t (C–O)
t (M–N)
t (M–O)
DLH1
DLCo
DLMn
DLCu
DLNi
3,527
3,548
–
1,679
1,675
1,661
1,669
1,676
1,674
1,678
1,692
1,655
1,649
2,265
2,262
2,263
2,254
2,262
2,262
2,263
2,258
2,261
2,262
1,640
1,622
1,614
1,620
1,623
1,626
1,634
1,651
1,626
1,622
1,226
1,246
1,245
1,249
1,247
1,247
1,241
1,238
1,246
1,246
–
–
243, 321
533
527
555
534
532
539
544
531
533
459
467
490
466
455
449
477
456
458
240, 310, 574, 580
241, 312, 560
243, 319, 658
238, 311, 582
239, 322, 533
233, 318, 794
236, 320, 655
239, 320, 719
240, 314, 788, 784
–
–
DLZn
DL2Ni
DL2Cu
DL2Zn
DL2Co
3,549
3,530
3,541
3,550
3,549
123

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Med Chem Res (2014) 23:3327–3335
Fig. 1 Proposed structure for
metal complexes
N
C
NH
CH3
O
N
C
O
M
O
O
H
O
O
CH3
N
C
CH3
Where M = Zn(II) Co(II)
NH
CH3
N
O
N
C
O
H3C
C
H
O
O
M
O
O
CH3
NH
O
O
N
C
O
O
CH3
C
N
O
O
M
H3C
N
O
O
CH3
C
CH3
N
Where M = Cu(II) Ni(II), Mn(II)
Where M = Ni(II), Co(II), Cu(II), Zn(II)
Table 3 Mass fragmentation
data of DLH1 and selected metal
complexes
DLH1
DLCu
DLNi
DL2Co
DL2Zn
250.1, 205, 166.1 338.3, 328.0, 311.0, 363.9, 345.9,
and 151.1 m/z 279.1, 260.2, 304.8, 255.1,
250.1 174.2, 129.2 248.1, 181,
556.0, 489.1, 338.8, 561.0, 492.9, 391.3,
307.0, 279.1, 311.1, 279.2, 272.1,
250.2, 229.9, 166.1 250.2, 166.1, 141.1
and 151.1 m/z and 114.1 m/z
and 114.1 m/z
164.0 and
199.0 m/z
(Mohammedshafi et al., 2011). In case of free ligand, the
band appeared at 1679 cm-1 due to carbonyl carbon was
shifted to lower frequency in the spectrum of metal com-
plexes, suggesting that metal ion coordinate through car-
bonyl oxygen atom (AbouEl-Enein et al., 2008). Moreover,
the spectrum of all metal complexes consists of two non-
ligand bands at 466–490 and 635–645 cm-1, which can be
assigned to tM–O and tM–N vibrations, respectively (Na-
kamoto, 1986). The proposed structures of the metal
complexes are presented in Fig. 1.
bands at 574 and 580 nm, while DLCu and DLNi showed
bands due to d–d transitions at 658 and 582 nm, respec-
tively. The observed bands suggested the square-planar
geometry around the mentioned metal ions (Osman, 2006;
Bharti et al., 2010). Moreover, in case of DLZn and DLMn,
very weak bands were observed at 533 and 560 nm due to
spin-forbidden nature of these transitions. DL2Ni and
DL2Co showed bands at 794, and 788, 784 nm, respec-
tively, suggesting the octahedral geometry around these
metal ions. DL2Cu showed a broad band at 655 nm which
suggested the distorted octahedral geometry around the
Cu(II) ion due to Jahn–Teller distortion.
UV visible spectroscopy
The electronic spectra of the ligand as well as all synthe-
sized complexes were recorded in 10-4 M DMSO solution
at room temperature. The ligand showed the following two
signals centered at 243 and 321 nm, respectively. These
absorption bands were appearing due to p–p* and n-p* of
carbonyl or the azomethine moiety (Rajevel et al., 2008).
These bands were appeared in metal complexes too but
with a blue shift which suggests the involvement of the
azomethine group in coordination. DLCo showed two
Mass spectrum
The mass spectrum of the ligand showed an intense
molecular ion peak at m/z 250.1 which indicates the for-
mation of a desired compound as suggested in Table 3.
Other prominent peaks in the mass spectrum were observed
at m/z 205, 166 and 151, respectively. The mass spectrum
of DLNi exhibited molecular ion peak at m/z 363.9 and that
of DLCu at m/z 369.0 along with the fragments present in
123

Med Chem Res (2014) 23:3327–3335
3333
N
N
C
C
N
NH
N C
NH CH3
N C
CH3
C
O
O
O
H
O
O
H3C
M
M
NH CH3
N C
O
O
O
O
O
H
O
O
O
O
O
CH3
C
H3C
N
O
O
CH3
M
CH3
N
O
3
O
C
N
O
1
2
CH3
CH3
- CH3COOM
-4
M
-C11H10N3O4
O
O
C
H3
C
-
+H
H3C
N
H
O M
HO
N
C
C
O
HO
CH3
O
-HCO2
-M
O
C
H3C
N
N
N
O
N
O
N
O
N
+H
H
H
CH3
CH3
m/z 249.1
O
-C3HNO
CH2
m/z 204.0
6
4
C
N
5
HO
CH3
-C2HN
N
O
HO
H2N
CH3
O
m/z 182.0
N
N
O
9
H
CH3
CH2
-NH3
m/z 165.1
7
HO
CH3
-O
N
O
CH2
O
HO
m/z 165.1
10
N
N
-NH
CH3
CH2
m/z 150.1
HO
CH3
8
O
O
m/z 150.1
11
Scheme 2 Proposed mass fragmentation pattern of ligand as well as metal complexes
the mass spectrum of ligand. The above observations pro-
vided strong evidence for the formation of complex in 1:1
metal to ligand stoichiometry along with the coordination
of acetate ion in both cases. The mass spectra of DL2Co
and DL2Zn was consisted of molecular ion peaks (M??1)
at 555.9 and 560.0, respectively. The observed values for
DL2Co and DL2Zn supported the confirmation of the
ligand to metal 2:1 stoichiometry. The proposed general
mass fragments of ligand as well as metal complexes are
given in Scheme 2.
DNA photocleavage study
There has been a great deal of interest in transition metal
complexes-mediated DNA photocleavage reactions (Liu
et al., 2005). Photocleavage study on plasmid DNA was
123

3334
Med Chem Res (2014) 23:3327–3335
Fig. 2 DNA photocleavage study. Lane C (DNA?DMSO), lane 1
(DNA?ligand), lane 2 (DNA?DLCo), lane 3 (DNA?DLNi), lane 4
(DNA?DLCu), lane 5 (DNA?DLMn), lane 6 (DNA?DLZn), lane 7
(DNA?DL2Co), lane 8 (DNA?DL2Ni), lane 9 (DNA?DL2Co), lane
10 (DNA?DL2Mn), lane 11 (DNA?DL2Zn)
performed by agarose gel electrophoresis. The results of
cleavage study are presented in Fig. 2. Whenever electro-
phoresis is performed on plasmid DNA, the fastest
migration will be observed for the super-coiled form (SC)
as compared to another. If one strand of super-coiled form
is cleaved, the super-coiled form will relax to produce a
slower moving open-circular form (OC). If both strands of
super-coiled form are cleaved, a nicked form (NC) will be
generated that migrates in between the super-coiled and
open-circular form (Patel et al., 2011). It was clear from
Fig. 2 that control (lane C) consists of the super-coiled and
circular coiled forms of plasmid DNA. In case of the ligand
(lane 1), DLCo (lane 2) and DLNi (lane 3), there was
almost complete transformation of the super-coiled form
into an OC form which indicates the cleavage of one strand
of the super-coiled form of plasmid DNA. In all the
remaining cases (lane 4–11), conversion of super-coiled
form into open-circular as well as nicked-coiled form was
suggesting the cleavage of both strands of the super-coiled
form of plasmid DNA. Moreover, there was a formation of
smear in the case of all synthesized compounds (lane 1–11)
where DNA was broken into small fragments. Therefore, it
was concluded that the synthesized complexes are good
DNA photo-cleaving agents. However, there was a
remarkable increase in cleaving ability in case of metal
complexes as compared to free ligand due to non-covalent
interactions of metal complexes with DNA which results in
the binding and finally cleavage of DNA. There were no
observed difference in the DNA photo-cleaving activity of
1:1 and 1:2 complexes, only DL2Co was found to be more
active as compared to DLCo. The difference in the cleav-
age potential was due to the different degree of binding
capabilities of different metal complexes.
prepare novel metal complexes. It was found that metal
complexes possess very good DNA photo-cleaving activi-
ties as compared to free ligand and may serve as the basis
of same novel and efficient antitumor agent in future.
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