Transition Metal (II) Complexes with a Novel Azo-azomethine Schiff Base Ligand: Synthesis, Structural and Spectroscopic Characterization, Thermal Properties and Biological Applications

Article abstract of DOI:10.1007/s10895-017-2166-3

The pyrimidine based azo-linked Schiff base ligand, 5-benzoyl-1-((E)-(2-hydroxy-3-methoxy-5-((E)phenyldiazenyl)benzylidene)amino)-4-phenylpyrimidin-2(1H)-one (HL), and its transition metal (II) complexes were synthesized and defined by using ¹H-NMR, ¹³C-NMR, Elemental analysis, FT-IR, MS, UV–vis, molar conductance, magnetic susceptibility and thermal analysis techniques. According to the conductance data obtained indicate all of the metal complexes have non-electrolytic nature. Square pyramidal geometry for Pd(II) and octahedral geometry for all the other complexes synthesized was concluded from the electronic absorption spectra and magnetic susceptibility measurements of the complexes. Investigation of the significant infrared bands of the active groups in the ligand and the solid complexes alludes that HL is coordinated to the metal ions ONO tridentate manner. Moreover, the absorption and emission properties of the azo-azomethine based ligand and its complexes were investigated. The results obtained show that fluorescence emissions of the ligand and its metal (II) complexes depend on the type of transition metal ions and the derivatives displayed moderate Stokes’ shift values between 44 and 107?nm. All the compounds exhibited superb photostability. Further, antioxidant, antimicrobial and pBR322 plasmid DNA cleavage activities were investigated. All compounds showed good DPPH? (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity and complexes of [MnL₂]?H₂O and [NiL₂]?H₂O exhibited excellent metal chelating activity. All the compounds tested demonstrated two strand DNA cleavage activities.

Full text of DOI:10.1007/s10895-017-2166-3

J Fluoresc
DOI 10.1007/s10895-017-2166-3
ORIGINAL ARTICLE
Transition Metal (II) Complexes with a Novel Azo-azomethine
Schiff Base Ligand: Synthesis, Structural and Spectroscopic
Characterization, Thermal Properties and Biological Applications
1
1
2
2,3
Gökhan Yeğiner · Mehmet Gülcan · Sema Işık · Gülsiye Öztürk Ürüt
·
4
5
Sadin Özdemir · Mükerrem Kurtoğlu
Received: 21 April 2017 / Accepted: 10 August 2017
Springer Science+Business Media, LLC 2017
©
Abstract The pyrimidine based azo-linked Schiff base ligand,
and its complexes were investigated. The results obtained show
that fluorescence emissions of the ligand and its metal (II)
complexes depend on the type of transition metal ions and the
derivatives displayed moderate Stokes’ shift values between 44
and 107 nm. All the compounds exhibited superb photostability.
Further, antioxidant, antimicrobial and pBR322 plasmid DNA
cleavage activities were investigated. All compounds showed
good DPPH• (1,1-diphenyl-2-picrylhydrazyl) radical scaveng-
ing activity and complexes of [MnL ]•H O and [NiL ]•H O
5-benzoyl-1-((E)-(2-hydroxy-3-methoxy-5-((E)phenyldiazenyl)
benzylidene)amino)-4-phenylpyrimidin-2(1H)-one (HL), and
its transition metal (II) complexes were synthesized and defined
1
13
by using H-NMR, C-NMR, Elemental analysis, FT-IR, MS,
UV–vis, molar conductance, magnetic susceptibility and ther-
mal analysis techniques. According to the conductance data
obtained indicate all of the metal complexes have non-electro-
lytic nature. Square pyramidal geometry for Pd(II) and octa-
hedral geometry for all the other complexes synthesized was
concluded from the electronic absorption spectra and magnetic
susceptibility measurements of the complexes. Investigation of
the significant infrared bands of the active groups in the ligand
and the solid complexes alludes that HL is coordinated to the
metal ions ONO tridentate manner. Moreover, the absorption
and emission properties of the azo-azomethine based ligand
2
2
2
2
exhibited excellent metal chelating activity. All the compounds
tested demonstrated two strand DNA cleavage activities.
Keywords Azo-azomethine · Transition metal complex ·
Fluorescence · Biological application
Introduction
Electronic supplementary material The online version
of this article (doi:10.1007/s10895-017-2166-3) contains
supplementary material, which is available to authorized users.
The condensation of primary amines with carbonyl com-
pounds produces Schiff bases which were named after Hugo
Schiff in 1864 [1]. These compounds common structural
property is the azomethine group which has a general for-
mula of R-HC=N-R. Schiff bases are used as ligands in the
coordination chemistry. These ligands and their transition
metal complexes have increased extremely and comprise an
extensive field of organometallic compounds and diverse
appearance of bioinorganic chemistry. Schiff base ligands
were studied to exhibit different biological actions by merit
of the azomethine linkage, which gives opportunity for many
applications like antibacterial, antifungal and analytical
activities [2–5]. On the other hand, metal complexes with
oxygen and nitrogen donor Schiff bases gain special concern,
due to their capability to have unusual geometry [3, 6–9].
Azo dyes are one of the significant classes of organic col-
orants, which consist of at least a conjugated azo (-N=N-)
*
Mehmet Gülcan
mehmetgulcan65@gmail.com
*
Gülsiye Öztürk Ürüt
gulsiye.ozturk@deu.edu.tr; gulsiyeozturk@yahoo.com
1
2
3
4
Department of Chemistry, Science Faculty, University
of Van Yüzüncü Yıl, Van, Turkey
Department of Chemistry, Science Faculty, University
of Dokuz Eylül, Tınaztepe, Izmir, Turkey
Department of Chemistry, Faculty of Sciences, Dokuz Eylül
University, Tinaztepe Campus, 35160, Buca, Izmir, Turkey
Food Processing Programme, Technical Science Vocational
School, Mersin University, TR-33343, Yenisehir, Mersin,
Turkey
5
Department of Chemistry, Science Faculty, University
of Kahramanmaraş Sütçü İmam, Kahramanmaraş, Turkey
Vol.:(0
1
123456789)
3

J Fluoresc
chromophore, and are the major and most sophisticated class of
dyes [10]. Owing to their effective physico-chemical properties
azo compounds have gained substantial interest. These deriva-
tives have been intensively investigated for nonlinear optics,
optical information storage and switching [11]. In addition to
them, azo-azomethines were broadly utilized as coloring matter
for wool, synthetic fabrics and leather due to their remarkable
dyeing features and also in components of optical communi-
cation systems, photonic devices and electro-optic modulators
because of their second-order nonlinear optical features [12, 13].
In last years the research for new organic stuff which is
applicable in light emitting devices has gained considerable
interest [14–17]. For instance, especially blue region emit-
ting organic polymers at low driving voltages are very inter-
esting for flat panel display applications [18, 19]. Besides,
rare earth complexes with low molecular weight organic
ligands were also investigated to produce materials with high
fluorescence for electroluminescent instruments [20, 21] and
laser framework [22]. Additionally, many aromatic amines
and polymeric arylamines were prepared as hole transport
layers in organic electroluminescent investigation.
azo-azomethine dye and its metal(II) complexes were examined.
Also, the free radical scavenging features of the derivatives have
been rated by using diverse methods, such as the DPPH• scav-
enging activity, metal chelating assay and reducing power and
were evaluated. In addition, antimicrobial and pBR322 plasmid
DNA cleavage activities were investigated.
Experimental
Materials and Instrumentation
All of chemicals utilized in this work were purchased from
Aldrich or Merck and used without any purification. Solvents
used for the synthesis were purified and dried by usual methods
[25]. Elemental analyses (C, H, N and S) were performed on a
Leco CHNS model 932 automatic elemental analyzer. FT-IR
spectra were recorded on a Bio-Rad-Win-IR spectrophotometer
−
1
applying KBr discs in the range of 4000–400 cm . Electronic
absorption spectra in the visible and ultraviolet regions were
measured on a Shimadzu 1601 PC spectrophotometer (Tokyo,
Japan). The magnetic susceptibility was determined with a mag-
netic susceptibility balance 436 Devon Park Drive (USA) using
Oxygen is essential for the aerobic organisms to survive.
Unfortunately, various reactive oxygen species (ROS) such as
hydrogen peroxide, superoxide anions, nitric oxide and hydroxyl
radicals occurs in the course of the oxygen metabolism. These
free radicals must be reduced as they have toxic effects on cells
and tissues. Antioxidant agents play an important role in the
prevention of human diseases by free radical mediated toxic-
ity [23]. A new trend in the area of antioxidant improvement
focuses on multipotent antioxidant substances that can avoid
biological organisms from oxidative damage. However, these
synthesized antioxidant substances should have no toxic effects.
For this reason, there is a growing demand and concern for safer
antioxidants in pharmaceutical and food applications. On the
other hand, there is also an increasing interest in developing new
compounds that can interact with DNA for application in chem-
otherapy. These compounds, specifically their metal complexes
can be also used as chemotherapeutic agents to cure a diversity
of illnesses such as AIDS, cancer etc. These metal complexes
can interact with DNA duplex through a diversity of binding
modes including DNA intercalation, covalent and non-covalent
binding and DNA cleavage [23, 24].
1
13
Hg[Co(SCN) ] as a calibrant. H-NMR and C-NMR spectra
4
were carried out on a Bruker 300 MHz Ultrashield TM NMR
instrument, using deuterated dimethyl sulfoxide (DMSO-d )
6
as a solvent. All fluorescence measurements were undertaken
by using Varian-Carry Eclipse spectrofluorimeter (Mulgrave,
Australia). Thermogravimetric analysis (TG and DTG) and dif-
ferential thermal analysis (DTA) experiments were performed
using a SII Exstar TG/DTA 6300 in the temperature range
−
1
25–1000 °C with a heating rate of 40 °C min under flowing
−
1
nitrogen atmosphere (30 ml min ).
Synthesis of the Precursors
Azo-coupled salicylaldehyde precursor, 2-hydroxy-3-meth-
oxy-5-(phenyldiazenyl)benzaldehyde [26, 27] and a pyrim-
idine-based primary amine derivative, N-aminopyrimidine-
2-one [28], were synthesized by the well-known literature
procedures.
From perspective of the above-mentioned inquiry and the
sustained concern to coordination compounds, the present work
deals with the synthesis and features of a new azo-azomethine
based fluorescent dye having ONO donor set of atoms obtained
by the condensation reaction of N-Aminopyrimidine-2-one with
Synthesis of the Azo-azomethine Based Ligand (HL)
The pyrimidine-based azo-azomethine ligand (HL) was
prepared by 1:1 condensation reaction between 2-hydroxy-
3-methoxy-5-(phenyldiazenyl)benzaldehyde and N-amino-
pyrimidine-2-one (Scheme 1). A hot anhydrous ethanolic
solution of N-aminopyrimidine-2-one (1 mmol; 291 mg)
and 2-hydroxy-3-methoxy-5-(phenyldiazenyl)benzaldehyde
(1 mmol; 256 mg) was refluxed for 3 h. Then the hot mix-
ture was filtered and the solid obtained was washed with hot
ethanol (three times) and then with diethyl ether.
2-hydroxy-3-methoxy-5-(phenyldiazenyl)benzaldehyde, along
with its metal(II) complexes (Schemes 1 and 2). The newly pre-
pared compounds were characterized by structurally. Thermal
properties of the prepared azo-linked Schiff base ligand and
its metal(II) complexes have been further investigated by ther-
mal analysis techniques. Moreover, fluorescent properties of
1
3

J Fluoresc
Scheme 1 Synthetic route of the ligand (HL)
Yellow powder, yield 79%, Mp 252 °C. Anal. Calc. for
C H N O (529.55 g/mol): C, 70.31; H, 4.38; N, 13.23.
Ni(CH COO) •4H O; 124.5 mg Co(CH COO) •4H O;
3 2 2 3 2 2
122.5 mg Mn(CH COO) •4H O; 112.5 mg Pd(CH COO) ]
3
1
23
5
4
3
2
2
3
2
Found: C, 70.33; H, 4.32; N, 13.18%. FTIR data (KBr,
in MeOH (25 mL) was added dropwise to a stirred solu-
tion of 5-benzoyl-1-((E)-(2-hydroxy-3-methoxy-5-((E)-
phenyldiazenyl)benzylidene)amino)-4-phenylpyrimidin-
2(1H)-one (HL) (1 mmol, 530 mg) in a mixture of MeOH/
−
1
cm ): 3433 ν(OH), 3054 ν(C-H
), 2970 ν(C-H
),
aliphatic
aromatic
1
662 ν(C=O), 1608 ν(CH=N
), 1474 ν(N=N), 1261
azomethine
ν(C-O
), 1122, 1006, 733, 690. UV–Vis (λ , nm):
phenolic
max
1
5
02, 462, 365, 285, 265, 220. H NMR (300 MHz, DMSO-
CHCl 1:1 (30 mL, V:V) as solvent at room temperature
3
d ): δ = 9.58 (s, 1H), 8.74 (s, 1H), 8.11 (s, 1H, Ar-H),
(Scheme 2). The mixture was stirred and heated to reflux
for 1 h at 80 °C and then concentrated in a rotary evapora-
tor to a volume of approximately 15 mL. The precipitate
obtained was filtered and washed with hot methanol and
diethyl ether. The final solid was dried under vacuum at
80 °C overnight.
6
7
3
.87–7.84 (m, 4H, Ar-H), 7.63–7.31 ppm (m, 13H, Ar-H),
1
3
.96 (s, 3H, OCH ) ppm. C NMR (75 MHz, DMSO-d ):
3
6
δ=191.6, 170.5, 162.5, 151.9, 151.3, 149.7, 148.9, 143.8,
1
1
29.7, 129.4, 128.6, 128.2, 122.2, 118.4, 118.1, 115.6,
05.2, 56 ppm. ESI-MS (m/z): 530.5 [M+H].
General Process for the Synthesis of Metal Complexes
[CuL ]•2H O
2
2
A solution of the metal salt M(CH COO) •xH O
The amber product is soluble in dimethylsulfoxide,
3
2
2
(
0.5 mmol) [99.75 mg Cu(CH COO) •H O; 124.5 mg
N,N′-dimethylformamide. Yield 76%; Mp: 214 °C.
3
2
2
1
3

J Fluoresc
Scheme 2 Synthetic route and suggested possible structures of the metal complexes
Anal. Calc. for C H CuN O (1156.65 g/mol): C,
[NiL ]•H O
2 2
6
2
50
10 11
6
1
4.39; H, 4.18; N, 12.11. Found: C, 64.36; H, 4.21; N,
−
1
2.04%. FTIR data (KBr, cm ): 3429 ν(OH/H O), 3059
The dark blue product is soluble in dimethylsulfoxide,
N,N′-dimethylformamide. Yield 56%; Mp: 283 °C. Anal.
Calc. for C H NiN O (1133.78 g/mol): C, 65.68; H,
2
ν(C-H
), 2831 ν(C-H
), 1658 ν(C=O), 1604
aromatic
aliphatic
ν(CH=N
), 1474 ν(N=N), 1251 ν(C-O
),
azomethine
phenolic
62 46
10
9
5
5
20 ν(Cu-O), 439 ν(Cu-N). UV–Vis (λ , nm): 511,
4.09; N, 12.35. Found: C, 65.45; H, 4.08; N, 12.31%. FTIR
max
2
− 1
02, 438, 403, 285, 241, 216. µ : 1.53 BM, Λo (S cm
data (KBr, cm ): 3448 ν(OH/H O), 3059 ν(C-H
),
),
eff
2
aromatic
−
1
mol ): 2.66. ESI-MS (m/z): 1060 [M-2H O-2CH O- +
2835 ν(C-H
), 1654 ν(C=O), 1600 ν(CH=N
2
3
aliphatic azomethine
1477 ν(N=N), 1253 ν(C-O
2
H].
), 513 ν(Ni-O), 416
phenolic
1
3

J Fluoresc
ν(Ni-N). UV–Vis (λ , nm): 521, 422, 283, 264, 237. µ ,
Elemental Analysis
max
eff
2
− 1
2
.67 BM, Λo (S cm mol ): 2.34. ESI-MS (m/z): 1085
−
+3
[
M-H O-2CH O ] .
Elemental analysis indicates that the found and calculated values
were within acceptable limits (± 0.5). The elemental analysis
data verifies that the composition of the complexes under inter-
est is 1:2 metal:ligand stoichiometry and is in agreement with
2
3
[
CoL2]
The dark blue product is soluble in dimethylsulfoxide, N,N′-
dimethylformamide. Yield 52%; Mp: 262 °C. Anal. Calc.
for C H CoN O (1116.01 g/mol): C, 66.73; H, 3.97;
the suggested formula of [ML ] type for Cu(II), Ni(II), Co(II)
2
and Mn(II) complexes and has the 1:1 metal:ligand stoichiom-
etry [M(HL)] for Pd(II) complex (Scheme 2).
6
2
44
10
8
N, 12.55. Found: C, 66.65; H, 3.87; N, 12.51%. FTIR data
−
1
(
KBr, cm ): 3059 ν(C-H
), 2831 ν(C-H
), 1654
aliphatic
FT-IR Results
aromatic
ν(C=O), 1597 ν(CH=N
), 1477 ν(N=N), 1253 ν(C-
azomethine
O
), 513 ν(Co-O), 451 ν(Co-N). UV–Vis (λ , nm):
The bonding of the azo-azomethine ligand to the metal was
investigated via the comparison of Fourier transform-infrared
spectrum of the ligand with the spectra of the metal chelates.
Useful data was obtained concerning the structure of the func-
tional groups attached to the metal ions. The primary infrared
bands and their definitions are presented in the experimental
phenolic
max
2
−1
5
1
15, 442, 264, 252, 218. µ , 3.63 BM. Λo (S cm mol ):
eff
+
2
.46. ESI-MS (m/z): 1113.95 [M] .
[
MnL ]•H O
2 2
−
1
The claret red product is soluble in dimethylsulfoxide, N,N′-
dimethylformamide. Yield 79%; Mp: 277 °C. Anal. Calc.
for C H MnN O (1111.27 g/mol): C, 66.97; H, 3.99;
part. A strong band at 1608 cm at the spectrum of the ligand
in Fig. 1, can be referred to the -CH=N group. The shift of this
band to a lower frequency due to a shift of lone pair density
toward the metal ion, reveals the coordination of azomethine
nitrogen to the metal center. The spectrum of the azo-azome-
6
2
44
10
8
N, 12.60. Found: C, 66.90; H, 3.92; N, 12.55%. FTIR data
(
KBr, cm− ): 3445 ν(OH/H O), 3062 ν(C-H
1
), 2920
aromatic
2
−
1
ν(C-H
ν(C-O
), 1600 ν(CH=N
), 1477 ν(N=N), 1253
thine ligand displays a broad band at 3433 cm because of
phenolic structure and water [29]. The FT-IR spectra of Cu(II),
Ni(II) and Mn(II) metal chelates given in Fig. 1. They demon-
aliphatic
azomethine
), 501 ν(Mn-O), 412 ν(Mn-N). UV–Vis (λ
,
phenolic
max
2
−1
nm): 514, 419, 284, 265. µ , 6.01 BM. Λo (S cm mol ):
eff
−
+2
−1
3
.19. ESI-MS (m/z): 1062[M-H O-CH O ] .
strated broad bands at 3448−3429 cm that belong to -OH
2
3
group of the crystal water molecules in the structure of complex
molecules (the presence of water was also verified by elemental
and thermal analyses) [29, 30].
[
Pd(HL)(Ace)2]
−
1
The orange product is soluble in dimethylsulfoxide, N,N′-
dimethylformamide. Yield 70%; Mp: 281 °C. Anal. Calc. for
C H PdN O (754.05 g/mol): C, 55.75; H, 3.88; N, 9.29.
The carbonyl vibration of the pyrimidine ring at 1662 cm
−
1
shifted to 1658−1651 cm after complexation, verifying
the generation of a bond between the carbonyl oxygen and
the metal. A comparison of infrared spectra of azo-azome-
thine based ligand and the metal(II) complexes also indicates
3
5
29
5
8
−
1
Found: C, 56.01; H, 3.90; N, 9.33%. FTIR data (KBr, cm ):
3
055 ν(C-H
), 2835 ν(C-H
), 1651 ν(C=O), 1604
aromatic
aliphatic
−
1
ν(CH=N
), 1473 ν(N=N), 1261 ν(C-O
), 520
phenolic
that a band, characteristic of ν(C-O) at 1261 cm , is shifted
azomethine
−
1
ν(Pd-O), 439 ν(Pd-N). UV–Vis (λ , nm): 400, 286, 264,
to 1253−1251 cm , because of C-O-M bond formation
[11]. Asymmetric and symmetric stretching vibrations of
methyl group in the structure of the ligand were observed at
max
2
− 1
2
6
21, 211. µ : D. Λo (S cm mol ): 2.44. ESI-MS (m/z):
eff
−
−
07 [M-2CH COO -CH O ].
3
3
−
1
2
970−2831 cm . In addition, all the metal complexes reveal
−
1
two new bands at 520−501 and 451−412 cm which can be
attributed to formation of M-O and M-N bonds, further verifying
formation of coordination complexes [29]. However, the ν(C-O)
band in the spectrum of the Pd(II) complex maintained at nearly
Results and Discussion
The azo-azomethine ligand, HL, and its transition metal(II)
complexes were prepared and characterized structurally as
explained in the experimental section. All the derivatives are
stable at room temperature and retained fine storage grade.
The azo-azomethine ligand is soluble in common organic
−
1
the same value of 1261 cm , proposing the C-O group does not
take a part in complexation and showing bidentate coordination
for the azo-azomethine ligand through the phenolic oxygen and
nitrogen of the azomethine to the Pd (II) ion [3]. In the FT-IR
solvents such as EtOH, MeOH, THF, CHCl while its tran-
spectrum of [Pd(HL)(Ace) ], the new carbonyl (C=O) stretch
3
2
−
1
sition metal(II) complexes are partially soluble in common
organic solvents and well soluble in DMF and DMSO. The
analytical and physical features of the complexes are dedi-
cated in the experimental section.
of the acetate ligand occurred at 1705 cm (Fig. 1). In addi-
tion, the vibration band of the azo chromogen group both in the
−
1
ligand and the complexes was observed at around 1474 cm .
Although the azo chromogen group has a donor character and
1
3

J Fluoresc
Fig. 1 FT-IR spectra of the
azo-azomethine ligand and its
transition metal (II) complexes
can form coordination compounds, the constant value of its
vibration both in the ligand and the complexes shows that there
is no coordination between the azo chromogen group and the
metal ions [31]. All the vibrational data proposes that the metal
ions are bonded to the azo-azomethine ligand through the phe-
nolic oxygen, carbonyl oxygen of the pyrimidine ring and the
imino nitrogen atoms.
attributed to the phenolic proton (-OH). Another singlet signal
at 8.74 ppm is considered as the signal of the proton related to
1
the azomethine group (-CH=N-) proton [7, 30]. The H-NMR
spectrum of the ligand demonstrates other signals at 8.11 (bs,
1H, Ar-H), 7.87–7.84 (m, 4H, Ar-H), 7.63–7.31 ppm (m, 13H,
Ar–H) ppm for aromatic protons and 3.96 (s, 3H) for methoxy
protons [7, 17]. Moreover, there is also water protons of the sol-
13
vent ((CD ) S=O), observed at 3.47 ppm [32]. The C-NMR
3
2
NMR Spectroscopy
spectrum of the ligand (Fig. S1b) revealed characteristic signals
at 191.6, 170.5, and 162.5 ppm because of (OC–Ar), (C=O,
pyrimidine), and (−C6, pyrimidine ring) of the azo-azomethine
base ligand, respectively. The peak at δ=151.9 ppm was due to
azomethine carbon of the ligand. Additionally, the spectrum of
the ligand displayed peaks between 151.3 and 105.2 ppm (151.3,
149.7, 148.9, 143.8, 129.7, 129.4, 128.6, 128.2, 122.2, 118.4,
1
13
The H and C-NMR spectra of the ligand were taken at
room temperature in deuterated dimethylsulfoxide solution
(
(CD ) S=O) using TMS as an internal standard and the data
3 2
1
are given in the experimental part. The H-NMR spectrum
of the ligand displays singlet signal in the 9.58 ppm which is
1
3

J Fluoresc
1
18.1, 115.6 and 105.2 ppm) because of aromatic carbon atoms.
Also, the peak at 56 ppm was due to aliphatic methoxy carbon
7, 30, 33].
dependable knowledge concerning the ligand arrangement in
transition metal complexes. The electronic spectra of the free
ligand shows absorption bands at 220 and 265 nm, because of
intraligand π-π* transitions and these bands remained nearly the
same in the spectra of the complexes [26]. Absorptions in the
285 and 365 nm are attributed to the n-π* transition related to
azomethine and the red shift of this absorption via complexation
can be attributed to the donation of a lone pair of electrons to the
metal ion, displaying the coordination of azomethine nitrogen of
azo-azomethine ligand [33]. The band at 462 nm can be attrib-
uted to the transition within the molecule, actually an intramo-
lecular charge transfer interaction [8, 33]. The Cu(II) complex
[
Magnetic Susceptibility, Absorption Spectroscopy
and Fluorescence Features
The general structural formula of the complexes are given in
Scheme 2. It was specified that Cu(II), Ni(II), Co(II), and Mn(II)
complexes are paramagnetic. The magnetic moment values (μ )
eff
are in the 1.53–6.01 B.M. range for metal complexes at room
temperature. Pd(II) complexes did not display any magnetism,
as it was expected. All the compounds electronic absorption
exhibits a µ value of 1.53 B.M., corresponding to one unpaired
eff
−
3
spectra were obtained in 10 M DMF solution between 200
and 800 nm at room temperature. In Table 1, the UV–Vis spec-
tral data of the synthesized azo-azomethine ligand and its metal
complexes are given. The electronic absorption spectra provide
electron [34]. Ni(II) shows a magnetic moment of 2.67 BM,
coherent with octahedral geometry [7–9]. Co(II) and Mn(II)
complexes possess magnetic moments of 3.63 BM and 6.01 BM,
which agree with values given for three unpaired electrons in an
octahedral environment [35]. Moreover, the electronic spectra
of the Cu(II), Ni(II), Co(II) and Mn(II) complexes demonstrated
bands at 502, 511, 521, 515 and 514 nm, respectively. These
bands are assigned to d-d transition in the complexes and are
characteristics of octahedral complexes. The electronic spectra
of the palladium(II) complex comprise intense bands at 476 and
Table 1 UV–Vis. (nm) data of the synthesized azo-azomethine
ligand and its metal complexes in DMF
Compound
Absorption
π–π*
λmax(nm)
n-π*/CT
n–π*
d–d
Ligand (HL)
220, 265
216, 241
237
285, 365
285
264, 283
264
462
403, 438
422
–
4
00 nm, attributed to charge transfer and spin allowed transition
[
[
[
[
[
CuL ]•2H O
NiL ]•H O
CoL2]
MnL ]•H O
502, 511
521
515
2
2
for Pd(II) with a square planar stereochemistry [30, 33, 36].
Moreover, the absorption and emission properties of the azo-
azomethine ligand and its complexes were investigated in freshly
prepared solutions of toluene, ethylacetate and tetrahydrofuran
2
2
218
442
265
211, 221
284
264, 286
419
400
514
476
2
2
Pd(HL)(Ace)2]
(Figs. 2 and 3). The data obtained are given in Table 2.
Fig. 2 Absorption spectra
−
5
of the ligand (─) (1×10
M), [CuL ]·2H O(− − −)
2
2
−
5
(
0,9538×10 M), [CoL ]
2
−5
(
······) (0,9578×10
M), [NiL ]·H O (− · −)
2
2
−
5
(
(
0,9591×10 M), [MnL ]·H O
2 2
−5
− ·· −) (0,9911×10 M)
__
and [Pd(HL)(Ace) ] ( )
2
−
5
(
0,5880×10 M) in ethylac-
etate
1
3

J Fluoresc
Fig. 3 Fluorescence spectra
1000
800
600
400
−
5
of the ligand (1) (1×10
M), [CuL ]·2H O (2)
6
2
2
5
−
5
(
(
(
[
0,9538×10 M), [CoL ] (3)
2
−5
3
2
1
0,9578×10 M), [NiL ]·H O
2
2
−
5
4
4) (0,9591×10 M),
1
−
5
MnL ]·H O (5) (0,9911×10
2
2
2
M) and [Pd(HL)(Ace) ] (6)
2
−
5
(
0,5880×10 M) in THF
5
6
200
4
3
0
500
600
700
Wavelength (nm)
−
1
−1
Table 2 Absorption and emission maxima, λ (nm), molar extinction coefficients, ε (l mol cm ), Stokes’ shifts, Δλ (nm) and singlet energies,
−
1
Es (kcal.mol ) of HL, [CuL ]·2H O, [CoL ], [NiL ]·H O, [MnL ]·H O and [Pd(HL)(Ace) ] in toluene, tetrahydrofuran and ethyl acetate
2
2
2
2
2
2
2
2
1
λabs
2
εmax1
εmax2
λems.max1
λems.max2
Es1
Es2
Compound
HL
Solvent
λabs
Δλ
max
max
Toluene
286
283
288
284
285
283
287
277
285
290
277
282
290
280
284
287
278
281
367
373
375
387
397
370
414
418
415
420
420
417
365
363
413
400
399
395
19,000
27,180
21,770
124,764
66,419
25,425
79,338
149,593
62,341
34,929
103,138
62,788
53,890
154,374
87,519
86,684
261,905
95,646
20,700
22,800
20,650
75,152
59,750
26,442
43,224
65,556
67,582
36,962
46,825
52,716
70,629
61,548
83,715
76,446
87,415
87,772
421
419
422
459
459
414
474
473
474
477
476
475
471
470
472
447
447
446
575
585
567
652
514
730
651
503
647
651
504
651
649
648
651
650
649
784
54
67.7
68.2
67.6
62.1
62.1
68.9
60.1
60.3
60.1
59.8
59.9
60.0
60.5
60.7
60.4
63.8
63.8
63.9
49.6
48.7
50.3
43.7
55.5
39.0
43.8
56.7
44.0
43.8
56.6
43.8
43.9
44.0
43.8
43.8
43.9
36.3
Tetrahydrofuran
Ethylacetate
Toluene
Tetrahydrofuran
Ethylacetate
Toluene
Tetrahydrofuran
Ethylacetate
Toluene
Tetrahydrofuran
Ethylacetate
Toluene
Tetrahydrofuran
Ethylacetate
Toluene
Tetrahydrofuran
Ethylacetate
46
47
72
62
44
60
55
59
57
56
58
106
107
59
47
48
51
[
[
[
[
[
CuL ]·2H O
2
2
CoL2]
NiL ]·H O
2
2
MnL ]·H O
2
2
Pd(HL)(Ace)2]
The azo-azomethine ligand and its complexes with
displayed two emission maxima; the first one between 419
and 476 nm and the second one between 503 and 784 nm
(Table 2). In general both the first and second emission max-
ima of the Cu(II), Co(II), Ni(II), Mn(II) and Pd(II) com-
plexes is red shifted in comparison to the azo-azomethine
ligand. The longest emission maxima was obtained for Pd(II)
complex in ethylacetate. The compounds exhibited moderate
Stokes’ shift values ranging from 44 to 107 nm, which con-
fers to the advantage of better spectral resolution in emission
based studies. The biggest Stokes’ shift value was observed
for Mn(II) complex in tetrahydrofuran.
Cu(II), Co(II), Ni(II), Mn(II) and Pd(II) have two absorption
maxima in all the solvents studied; the first one is between
2
4
77 and 290 nm and the second one is between 365 and
20 nm, designated as π→π* and n→π* transitions, respec-
tively (Table 2). The first absorption maxima of the azo-
azomethine ligand and its transition metal (II) complexes
are in the same region, but the second absorption maxima of
transition metal(II) complexes are red shifted in comparison
to the azo-azomethine ligand, and the biggest red shift was
obtained for its [NiL ]•H O complex.
2
2
The molar extinction coefficients of the complexes are
higher than the molar extinction coefficients of azo-azome-
thine ligand. This is because the complexation of the ligands
to metal ion increases their rigidity and thus reduces the loss
of energy by thermal vibration decay. All the compounds
The photostabilities of the compounds in toluene, tetrahy-
drofuran and ethylacetate were identified with a steady-state
spectrofluorimeter in time-based mode. Considering the data
collected after 1 h, there was no considerable change in the
fluorescence intensities of the compounds (Fig. 4).
1
3

J Fluoresc
Fig. 4 Photostability test results
of the ligand (1), [CuL ]·2H O
2
2
(
(
[
2), [MnL ]·H O (3), [Pd(HL)
2 2
Ace) (4), [NiL ]·H O (5) and
2
2
2
CoL ] (6) in THF after 1 h of
2
monitoring
Molar Conductance
whereas the coordinated water molecule is lost at high tem-
peratures (150–200 °C) [38]. On heating, mass losses corre-
The molar conductance data of the transition metal(II) com-
plexes obtained in 0.001 M solutions of DMF are shown in
the experimental part. The data vary between 1.46 and 3.19
sponded to H O, Ph–CO–, and the other organic moieties in
2
the first, second, third, fourth, and fifth stages of decomposi-
tion. The Cu(II), Ni(II) and Mn(II) complexes suffered loss
−
1
2
− 1
Ω
cm mol , which is the expected range for the com-
of H O in the first stage, the complexes contained 2, 1 and
2
plexes to behave as non-electrolytes [37].
1 moles of water of crystallization per complex molecule,
respectively. The thermogram of the complexes of Co(II)
and Pd(II) did not display any peak below 200 °C which
revealed that there was no water molecule inside or outside
the coordination sphere. The thermogravimetric curves of
the [CuL ]•2H O and [NiL ]•H O complexes are shown in
Mass Spectroscopy
Mass spectra of synthesized compounds provides an impor-
tant clue for elucidating the structure of azo-azomethine
ligand and its transition metal(II) complexes. The mass spec-
tra of the azo-azomethine ligand and its transition metal(II)
complexes recorded at room temperature were used to com-
pare their stoichiometry (Table 3).
2
2
2
2
Supplementary data (Figure S2).
Biological Applications
Antioxidant Activity
Each synthesized compound was consistent with the
molecular ion fragment and support the proposed structure
of the complexes (Schemes 1 and 2). The spectra of the azo-
azomethine ligand and its Co(II) complex are shown in the
Supplementary data (Fig. S3(a–b)).
DPPH Radical Scavenging Ability The application of the
DPPH process provides a simple and rapid way to measure
antioxidants by spectrophotometry. The compounds free rad-
ical scavenging ability is presented in Fig. 5. In the presence
of 10, 25, 50, 100, 200 and 500 mg/L, all tested compounds
demonstrated nearly the same radical scavenging ability.
The DPPH scavenging effect increased with the increas-
ing concentrations of the compounds studied. At concen-
Thermal Analysis
The analyses were taken to examine the nature of the water
molecules in the complexes and their thermal stabilities. In
general, two kinds of water molecules are associated with
the complexes which are lattice water and coordinated water.
The lattice water is lost at low temperature (60–120 °C),
tration of 5 mg/L, Pd(HL)(Ace) demonstrated higher free
2
Table 3 Mass spectral data of
Compound
Calculated mass
Obtained mass m/z
Peak assigned
[M+H]
the azo-azomethine ligand and
its metal complexes
Ligand (HL)
529.55
1156.65
1133.78
1116.01
1111.27
754.05
530.5
1060
1085
1113.95
1062
574
−
[
[
[
[
[
CuL ]·2H O
[M-2H O-2CH O + 2H]
2
2
2 3
−
+3
NiL ]·H O
[M-H O-2CH O ]
2 3
2
2
+2
CoL2]
[M]
[M-H O-CH O ]
−
+2
MnL ]·H O
2
2
2
3
−
−
Pd(HL)(Ace)2]
[M-2CH COO -2CH O ]
3
3
1
3

J Fluoresc
Fig. 5 Free radical scavenging
1
00
90
80
abilities of the ligand (HL) (1);
[
[
(
CoL ] (2); [CuL ]•2H O (3);
2 2 2
MnL ]•H O (4); [NiL ]•H O
1
2
3
4
5
6
2
2
2
2
5); [Pd(HL)(Ace) ] (6)
2
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
Ascorbic acid
Trolox
5
10
25
50
100
Concentration (mg/L)
radical scavenging ability than Ascorbic Acid and Trolox.
The free radical scavenging ability was in the following
order [MnL ]•H O > [Pd(HL)(Ace) ] > [CoL ] > HL >
[NiL ]•H O showed extremely significant chelating activity
2 2
with standard substance EDTA.
2
2
2
2
[
NiL ]•H O > [CuL ]•2H O at 100 mg/L.
Reducing Power The reducing power has been applied
as one of the antioxidant ability indicators [40]. The exist-
ence of reductants in the studied compounds causes the
2
2
2
2
2
+
Ferrous Chelating Activity Fe initiates free radicals
3
+
through the Fenton and Haber–Weiss reaction. Fenton Weiss
reduction of the Fe /ferricyanide complex to the ferrous
2
+
2+
reaction is a reaction between Fe and H O which gener-
form (Fe ) in the reducing power process. The quantity
2
2
2
+
ates extremely reactive •OH implicated in various illnesses
of Fe complex can therefore be observed by measuring
the formation of Perl’s Prussian Blue at 700 nm [41]. Fig-
ure 7 indicates the reducing power of the compounds. The
experimental results exhibited that the reducing power was
dependent on concentration. Especially, the reducing power
of [NiL ]•H O and Pd(HL)(Ace) were strong and raised
2+
[
39]. Percentage of Fe chelating activity was demonstrated
2
+
in Fig. 6. All tested compounds were able to chelate Fe
ions. Metal chelating activities of the compounds were found
to be concentration dependent and linearly raised up with
the compound concentration rise. When the concentration
of HL, CoL , [CuL ]•2H O, [MnL ]•H O, [NiL ]•H O,
2
2
2
steadily with rising concentrations of them. The reductive
capability of tested compounds and Alpha-Tocopherol (AT)
exhibited the following order: AT > [NiL ]•H O > [Pd(HL)
2
2
2
2
2
2
2
and [Pd(HL)(Ace) ] increased from 25 to 100 mg/mL, the
2
chelating activities increased from 21.3 to 68.8%, from 11.1
to 29.7%, from 25.2 to 69.7%, from 48.6 to 87.5%, from 49.7
to 93.3%, and from 11.9 to 36.1%, respectively. As seen in
Fig. 6, the compounds HL and [CuL ]•2H O showed sig-
2
2
(Ace) ] > [MnL ]•H O > [CuL ]•2H O > HL > [CoL ].
2
2
2
2
2
2
As a result, these newly synthesized compounds were good
electron and hydrogen donors and could finish the radical
series reaction, turning free radicals into more harmless
2
2
nificant chelating activity while compound [MnL ]•H O and
2
2
Fig. 6 Iron(II) chelating
100
abilities of the ligand (HL) (1);
90
[
[
(
CoL ] (2); [CuL ]•2H O (3);
2 2 2
MnL ]•H O (4); [NiL ]•H O
80
2
2
2
2
1
5); [Pd(HL)(Ace) ] (6)
2
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
2
3
4
5
6
Ascorbic acid
5
10
25
50
100
Concentration (mg/L)
1
3

J Fluoresc
Fig. 7 Reducing power
0
.6
abilities of the ligand (HL) (1);
[
[
(
CoL ] (2); [CuL ]•2H O (3);
2 2 2
0.5
0.4
MnL ]•H O (4); [NiL ]•H O
2
2
2
2
1
5); [Pd(HL)(Ace) ] (6)
2
2
0
.3
.2
3
0
4
0
.1
0
5
6
5
1
0
25
Ascorbic acid
50
100
Concentration (mg/L)
products. Our results based on the DPPH scavenging activ-
ity, ferrous chelating activity and reducing power of com-
pounds recommended that they were likely to contribute
significantly towards the antioxidant effect.
Staphylococcus aureus (ATCC 6538), Legionella pneu-
mophila subsp. pneumophiia (ATCC 33152), Bacil-
lus subtilis (6051), and Candida albicans. However, all
test compounds showed moderate antibacterial activ-
ity (zone inhibition diameter ranging from 14 to 17 mm)
DNA Cleavage Studies
against to Bacillus cereus. Also, ligand (HL) and its CoL ,
2
[
CuL ]•2H O, and [NiL ]•H O complexes exhibited mod-
2
2
2
2
It is well known that, when pBR 322 plasmid DNA is
exposed to gel electrophoresis to assess the quantity of
strand cleavage, Form I displays the fastest running com-
pared to Form II and Form III. If one strand is cut, Form
I will relax to produce a slower moving nicked Form II.
If both strands are cut, Form III is generated between the
positions of Form I and Form II [42, 43]. The results of
DNA cleavage abilities of ligand and its metal complexes
are represented in Fig. 8. As seen in Lane 1, control study
using pBR 322 plasmid DNA alone does not demonstrate a
cleavage during the cleavage process. On the other hand, all
tested compounds showed two strand DNA cleaving proper-
ties. These compounds can be used as anticancer drugs after
various anticancer and toxicity test systems.
erate antibacterial activity to E. coli (ATCC 10536) in 15,
14 and 18 zone inhibition diameter, respectively. Finally,
ligand (HL), CoL , [CuL ]•2H O and [MnL ]•H O com-
2
2
2
2
2
pounds demonstrated moderate antibacterial activity 14, 17
and 19 mm against E. hirae (ATCC 10541), respectively.
Conclusion
The novel azo-azomethine ligand, was synthesized by con-
densation of N-aminopyrimidine-2-one with 2-hydroxy-3-
methoxy-5-(phenyldiazenyl)benzaldehyde. The reactions of
the azo-azomethine ligand with Cu(II), Ni(II), Co(II), Mn(II)
and Pd(II) metal acetates yielded colored complexes. The
synthesized compounds have been defined on the basis of
1
13
Antibacterial Activity
Elemental analysis, FT-IR, H NMR, C NMR, UV–Vis,
MS and thermal analysis (TGA/DTA) as well as the mag-
netic susceptibility and molar conductivity measurements
indicating ONO tridentate donors. Due to physicochemical
and spectroscopic results given above, the complexes may be
The synthesized compounds were examined for antimi-
crobial activity by using disc diffusion process. All tested
compounds did not exhibit any antimicrobial activity to
Fig. 8 The DNA cleavage pattern of pBR 322 DNA by newly syn-
thesized of compounds. Lane 1, pBR 322 DNA; Lane 2, pBR 322
DNA+50 μg/mL of HL; Lane 3, pBR 322 DNA+50 μg/mL of
5, pBR 322 DNA+50 μg/mL of [MnL ]•H O; Lane 6, pBR 322
2
2
DNA+50 μg/mL of [NiL ]•H O; Lane 7, pBR 322 DNA+50 μg/mL
2
2
of [Pd(HL)(Ace) ]
2
[
CoL ]; Lane 4, pBR 322 DNA+50 μg/mL of [CuL ]•2H O; Lane
2 2 2
1
3

J Fluoresc
proposed to have octahedral geometry around Cu(II), Ni(II),
Co(II) and Mn(II) complexes, and square planar geometry
for Pd(II) complex. All the synthesized metal complexes
were determined to be mononuclear. Furthermore, the inves-
tigation of absorption and emission properties of the azo-
azomethine ligand and its corresponding metal complexes
were evaluated in different solvents. The compounds dissi-
pated moderate Stokes’ shift values between 44 and 107 nm,
which provides the benefit of better spectral resolution in
emission related investigations. All derivatives exhibited
excellent photostability in tetrahydrofuran, ethylacetate and
toluene. The free radical scavenging features of prepared
derivatives were interpreted by application of different meth-
ods, like the DPPH• scavenging activity, the metal chelating
assay along with the reducing power. In addition, antimi-
crobial and pBR 322 plasmid DNA cleavage activities were
investigated. All compounds showed good DPPH• scaveng-
ing activity and [MnL ]•H O and [NiL ]•H O compounds
and antimicrobial activity of Co(II), Ni(II), Zn(II), Fe(III) and
VO(IV) complexes with 4-aminoantipyrine Schiff base of ortho-
vanillin. J Fluoresc 24:1067–1076
8
9
.
.
Bitmez Ş, Sayin K, Avar B, Köse M, Kayraldız A, Kurtoglu M
(2014) Preparation, spectral, X-ray powder diffraction and compu-
tational studies and genotoxic properties of new azo–azomethine
metal chelates. J Mol Struct 1076:213–226
Anitha C, Sheela CD, Tharmaraj P, Sumathi S (2012) Spectro-
scopic studies and biological evaluation of some transition metal
complexes of azo Schiff-base ligand derived from (1-phenyl-
2,3-dimethyl-4-aminopyrazol-5-one) and 5-((4-chlorophe-
nyl)diazenyl)-2-hydroxybenzaldehyde. Spectrochim Acta A
9
6:493–500
1
0. Marmion DM (1991) Handbook of U.S. colorants. 3rd ed. Wiley,
New York
11. Bal M, Ceyhan G, Avar B, Köse M, Kayraldız A, Kurtoglu M
(
2014) Synthesis and X-ray powder difraction, electrochemical,
and genotoxic properties of a new azo-Schiff base and its metal
complexes. Turk J Chem 38:222–241
12. Kamel M, Galil F, Abdelwahab L, Osman A (1971) Some rela-
tions between chemical structure and light fastness of monoazo
dispersed dyes. J Prakt Chem 313:1011–1021
2
2
2
2
1
3. Gopal J, Srinivasan M (1986) Preparation and properties of pol-
yazo Schiff-bases. J Polym Sci Polym Chem Ed 24:2789–2796
exhibited excellent metal chelating activity. All tested com-
pounds demonstrated two strand DNA cleavage activities.
The results of the present study reveals that these deriva-
tives are especially powerful scavengers of free radicals
and chelating agents. They can also exhibit DNA cleavage
activities. However, further studies are needed to identify the
compounds’ toxic effects on living organisms and to develop
their applications as food or drugs.
14. Wang H, Song N, Li H, Li Y, Li X (2005) Synthesis and charac-
terization of a partial-conjugated hyperbranched poly(p-phenylene
vinylene) (HPPV). Synth Met 151:279–284
1
5. Gulcan M, Zengin H, Çelebi M, Sönmez M, Berber İ (2013)
2
,6-Bis((E)-((5-benzoyl-2-thioxo-4-phenylpyrimidin-1(2 H)-yl)
imino)methyl)-4-(methyl)phenol and its metal(II) complexes: syn-
thesis, spectroscopy, biological activity, and photoluminescence
features. Z Anorg Allg Chem 639:2282–2289
1
1
6. Gulcan M, Doğru Ü, Öztürk G, Levent A, Akbaş E (2014) Fluo-
rescence properties and electrochemical behavior of some Schiff
bases derived from N-aminopyrimidine. J Fluoresc 24:389–396
7. Gulcan M, Karataş Y, Işık S, Öztürk G, Akbaş E, Şahin E (2014)
Transition metal(II) complexes of a novel symmetrical benzothi-
azole-based ligand: synthesis, spectral/structural characterization
and fluorescence properties. J Fluoresc 24:1679–1686
Acknowledgements This work was supported by University of Van
Yüzüncü Yıl [FYL-2016-5334].
References
1
8. Carrard M, Goncalves-Conto S, Si-Ahmed L, Ades D, Siove A
(
1999) Improved stability of interfaces in organic light emitting
1
.
Schiff H (1864) Mitteilungen aus dem universitatslaboratorium in
Pisa: Eineneue reihe organischer basen. Justus Liebigs Ann Chem
diodes with high Tg materials and self-assembled monolayers.
Thin Solid Films 352:189–194
1
31:118–119
19. Feng L, Chen Z (2005) Synthesis and photoluminescent proper-
ties of polymer containing perylene and fluorene units. Polymers
46:3952–3956
2
.
Abdel-Nasser MA, Alaghaz YA, Ammar HA, Bayoumi A, Sharah
A (2014) Synthesis, spectral characterization, thermal analysis,
molecular modeling and antimicrobial activity of new potentially
N2O2 azo-dye Schiff base complexes. J Mol Struct 1074:359–375
Gulcan M, Sönmez M, Berber İ (2012) Synthesis, characteriza-
tion, and antimicrobial activity of a new pyrimidine Schiff base
and its Cu(II), Ni(II), Co(II), Pt(II), and Pd(II) complexes. Turk J
Chem 36:189–200
20. Fang Q, Tanimoto A, Yamamoto T (2005) Synthesis and chemical
properties of new photoluminescent poly(p-phenyleneethynylene)
containing an electron-accepting benzothiadiazole unit and an
electron-donating dialkoxybenzene unit: effect of twisting of the
main chain on photoluminescence. Synth Met 150:73–78
21. Qin C, Wang X, Wang E, Hu C, Xu L (2004) Synthesis and
characterization of a novel three-dimensional photoluminescent
coordination polymer generated from unsymmetrically bridging
ligand. Inorg Chim Acta 12:3683–3688
3
4
5
.
.
.
Alghool S, Abd El-Halim HF, Dahshan A (2010) Synthesis,
spectroscopic thermal and biological activity studies on azo-
containing Schiff base dye and its cobalt(II), chromium(III) and
strontium(II) complexes. J Mol Struct 983:32–38
22. Heller A, Wasserman E (1965) Intermolecular energy transfer
from excited organic compounds to rare-earth ions in dilute solu-
tions. J Chem Phys 42:949–956
Sönmez M, Çelebi M, Yardım Y, Sentürk Z (2010) Palladium(II)
and platinum(II) complexes of a symmetric Schiff base derived
from 2,6,diformyl-4-methylphenol with N-aminopyrimidine:
synthesis, characterization and detection of DNA interaction by
voltammetry. Eur J Med Chem 45:4215–4220
23. Prakash CR, Raja S, Saravanan G, Kumar PD, Selvam TP (2011)
Synthesis and evaluation of antioxidant activities of some novel
isatin derivatives and analogs. Asian J Res Pharm Sci 1:140–143
24. Dar AM, Manzoor S, Gatoo A (2015) Synthesis of new steroidal
imidazo [1,2-a] pyridines: DNA binding studies, cleavage activity
and in vitro cytotoxicity. Steroids 104:163–175
6
7
.
.
Borisova NE, Reshetova MD, Ustynyuk YA (2007) Metal-free
methods in the synthesis of macrocyclic Schiff bases. Chem Rev
1
07:46–79
Anupama B, Sunita M, Shiva Leela D, Ushaiah B, Kumari CG
2014) Synthesis, spectral characterization, DNA binding studies
25. Chai CLL, Armarego WLF (2009) Purification of laboratory
chemicals. Sixth ed. Elsevier, Oxford
(
1
3

J Fluoresc
2
2
6. Lever ABP (1984) Inorganic electronic spectroscopy. Elsevier,
Amsterdam
35. Naik KHK, Selvaraj S, Naik N (2014) Metal complexes of ONO
donor Schiff base ligand as a new class of bioactive compounds;
synthesis, characterization and biological evolution. Spectrochim
Acta A 131:599–605
7. Cabir B, Avar B, Gülcan M, Kayraldız A, Kurtoglu M (2013)
Synthesis, spectroscopic characterization, and genotoxicity of a
new group of azo-oxime metal chelates. Turk J Chem 37:422–438
8. Altural B, Akçamur Y, Sarıpınar E, Yıldırım I, Kollenz G (1989)
Reactions of cyclics oxalyl compounds, part 29 [1] a simple
synthesis of functionalized 1 H-pyrimidines. Monatsh Chem
36. Tas E, Kilic A, Durgun M, Kupecik L, Yilmaz İ, Arslan S (2010)
Cu(II), Co(II), Ni(II), Mn(II), and Fe(II) metal complexes con-
taining N,N′-(3,4-diaminobenzophenon)-3,5-But2-salicylaldimine
ligand: synthesis, structural characterization, thermal properties,
electrochemistry, and spectroelectrochemistry. Spectrochim Acta
A 75:811–818
2
1
20:1015–1020
2
3
9. Nakamoto K (1997) Infrared and Raman spectra of inorganic and
coordination compounds. Wiley, New York
37. Geary WJ (1971) The use of conductivity measurements in
organic solvents for the characterisation of coordination com-
pounds. Coord Chem Rev 7:81–122
0. Gulcan M, Sönmez M (2011) Synthesis and characterization
of Cu(II), Ni(II), Co(II), Mn(II), and Cd(II) transition metal
complexes of tridentate Schiff base derived from o-vanillin
and N-aminopyrimidine-2-thione. Phosphorus Sulfur Silicon
38. Nikolaev AV, Myachina LI, Logvinenko VA (1969) Thermo-
graphic study of the structures of some simple, mixed and binu-
clear chelates of EDTA. Therm Anal 2:779–791
1
86:1962–1971
3
1. Sarigul M, Deveci P, Kose M, Arslan U, Dagi HT, Kurtoglu M
39. Lloyd RV, Hanna PM, Mason RP (1997) The origin of the
hydroxyl radical oxygen in the Fenton reaction. Free Radic Biol
Med 22:885–888
(
2015) New tridentate azo–azomethines and their copper(II) com-
plexes: synthesis, solvent effect on tautomerism, electrochemical
and biological studies. J Mol Struct 1096:64–73
40. Bhandari MR, Kawabata J (2004) Organic acid, phenolic content
and antioxidant activity of wild yam (Dioscorea spp.) tubers of
Nepal. Food Chem 88:163–168
3
3
2. Gottlieb HE, Kotlyar V, Nudelman A (1997) NMR chemical shifts
of common laboratory solvents as trace impurities. J Org Chem
6
2:7512–7515
41. Chung SK, Osawa T, Kawakishi S (1997) Hydroxyl radical scav-
enging effects of spices and scavengers from brown mustard
(Brassica nigra). Biosci Biotech Biochem 61:118–123
42. Kumar H, Devaraji V, Prasath R, Jadhao M, Joshi R, Bhavana P,
Ghosh SK (2015) Groove binding mediated structural modulation
and DNA cleavage by quinoline appended chalcone derivative.
Spectrochim Acta A 151:605–615
3. Alaghaz AMA, Bayoumi HA, Ammar YA, Aldhlmani SA (2013)
Synthesis, characterization, and antipathogenic studies of some
transition metal complexes with N,O-chelating Schiff’s base
ligand incorporating azo and sulfonamide moieties. J Mol Struct
1
035:383–399
3
4. Patil SA, Prabhakara CT, Halasangi BM, Toragalmath SS, Badami
PS (2015) DNA cleavage, antibacterial, antifungal and anthelmin-
tic studies of Co(II), Ni(II) and Cu(II) complexes of coumarin
Schiff bases: synthesis and spectral approach. Spectrochim Acta
A 137:641–651
43. Parveen S, Arjmand F, Ahmad I (2014) Enantiomeric in vitro
DNA binding, pBR322 DNA cleavage and molecular docking
studies of chiral L- and D-ternary copper(II) complexes of histi-
dine and picolinic acid. J Photochem Photobiol B 130:170–178
1
3