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

Article abstract of DOI:10.1016/j.ejmech.2010.06.016

The two new mononuclear complexes were prepared by reacting symmetric Schiff base, containing pyrimidine rings and the metal chlorides of Pd(II) and Pt(II) in methanol. The mononuclear structure of the complexes was confirmed on the basis of elemental analyses, magnetic susceptibility, IR, UV-Vis, NMR, DTA/TGA and API-ES mass spectral data. The interaction of these metal complexes with fish sperm double-stranded DNA (dsDNA) was studied electrochemically based on the oxidation signals of guanine and adenine. Differential pulse (DP) voltammetry by using renewable pencil graphite electrode was employed to monitor the DNA interaction at the surface or in solution. The results indicate that Pd(II) and (Pt) complexes with Schiff base ligand having pyrimidine rings strongly interacted with DNA. New Pd(II) and Pt(II) complexes of a symmetric Schiff base containing pyrimidine rings have been synthesized and characterized. All the compounds were tested for their DNA interaction ability with the fish sperm DNA. The effect of Pd(II) complex upon the DP voltammetric response of guanine (A) and adenine (B) after interaction of solution-phase DNA.

Full text of DOI:10.1016/j.ejmech.2010.06.016

European Journal of Medicinal Chemistry 45 (2010) 4215e4220
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
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
,
b
c
c
Mehmet Sönmez a , Metin Çelebi , Yavuz Yardım , Zühre S¸ entürk
*
a Department of Chemistry, Faculty of Science and Letters, Gaziantep University, Gaziantep 27310, Turkey
b Department of Inorganic Chemistry, Faculty of Science and Letters, Yüzüncü Yıl University, Van 65080, Turkey
c Department of Analytical Chemistry, Faculty of Science and Letters, Yüzüncü Yıl University, Van 65080, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The two new mononuclear complexes were prepared by reacting symmetric Schiff base, containing
pyrimidine rings and the metal chlorides of Pd(II) and Pt(II) in methanol. The mononuclear structure of
the complexes was confirmed on the basis of elemental analyses, magnetic susceptibility, IR, UVeVis,
NMR, DTA/TGA and API-ES mass spectral data. The interaction of these metal complexes with fish sperm
double-stranded DNA (dsDNA) was studied electrochemically based on the oxidation signals of guanine
and adenine. Differential pulse (DP) voltammetry by using renewable pencil graphite electrode was
employed to monitor the DNA interaction at the surface or in solution. The results indicate that Pd(II) and
(Pt) complexes with Schiff base ligand having pyrimidine rings strongly interacted with DNA.
Ó 2010 Elsevier Masson SAS. All rights reserved.
Received 23 February 2010
Received in revised form
8 June 2010
Accepted 10 June 2010
Available online 17 June 2010
Keywords:
Pd(II) and Pt(II) complexes of
N-aminopyrimidine Schiff base
Synthesis
Characterization
DNA interaction
Voltammetry
Guanine and adenine oxidation
1. Introduction
biological target of drugs, are of great importance. Development of
novel clinical drugs involving metal complexes has been facilitated
During the last few decades there has been great interest in the
chemistry of transition metals associated with nitrogen, oxygen
and sulfur donor ligands, for instance, both five and six membered
heterocyclic pyrazoles, pyridazines and pyrimidines [1e4].
Although extensive studies have been made on various pyridine-
derived ligands [5e8], comparatively less research has centered on
the transition metal chemistry with the Schiff base ligands having
by the extensive knowledge of inorganic chemists about the metal
coordination compounds.
The investigation of the interaction between DNA and other
molecules is helpful to understand the action mechanism of some
DNA-targeted drugs and toxic agents as well as the origins of some
diseases like gene mutation [14e20]. Basically, a molecule may bind
to DNA via covalent and/or noncovalent interactions (intercalative,
electrostatic and groove binding) [21e24]. In recent years, there is
a growing interest in the application of electrochemical techniques
[25e30] to understand such interactions due to simplicity, cheap-
ness, fast detection and require small amount of sample with
respect to the commonly used spectroscopic methods [31e34].
Keeping the above knowledge in mind, the aim of this study is to
prepare and characterize two new palladium(II) and platinum(II)
complexes of Schiff base ligand derived from N-aminopyrimidine
and 2,6-diformyl-4-methylphenol. In continuation of the study,
special attention will be given to the application of electrochemical
measurements based on the interaction of these metal complexes
with DNA via differential pulse voltammetry using disposable
pencil graphite electrode.
pyrimidine as the heterocyclic part. However, the higher p-acidity
and presence of more than one hetero atom in pyrimidine play an
important role in its coordination chemistry compared to that of
pyridine bases and serve as better models in biological systems
[9e12].
For over 40 years, the studies of metal complexes have attracted
much attention due to their potential applications as anticancer,
antitumor, antimutagenic and antiviral agents [13] Therefore, the
researches on their interaction with DNA, that is the primary
* Corresponding author. Fax: þ90 3423601032.
E-mail address: vansonmez@hotmail.com (M. Sönmez).
0223-5234/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2010.06.016

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M. Sönmez et al. / European Journal of Medicinal Chemistry 45 (2010) 4215e4220
2. Results and discussion
bands in the spectra of both complexes remain almost at the same
position (w1270 cmꢀ1) suggesting that (CeO) phenolic group does
not take part in complexation. This behavior may support bidentate
coordination for Schiff base ligand through the carbonyl oxygen
atoms to Pd(II) or Pt(II) ions (Fig. 1). This is also supported by the
2.1. Chemistry
This work is an extension of recently studied symmetric Schiff
base containing pyrimidine rings and its Fe(II), Cu(II), Ni(II) and Co
(II) complexes in our laboratory [35]. The ligand and two complexes
[Cu(II) and Co(II)] were found to show good biological activity
against all tested bacteria and yeast strains. The report presented in
this study includes synthesis and spectral characterization of two
new palladium and platinum complexes of the formula [PdCl2(HL)]
and [PtCl2(HL)]$4H2O with the same Schiff base, and their inter-
action with DNA. As shown below, it was observed a square planar
geometry around the both complexes, in which the ligand acts as
a neutral bidentate one, coordinating through oxygen atoms of
carbonyl groups.
The proposed structures of the mononuclear Schiff base
complexes, [PdCl2(HL)] and [PtCl2(HL)]$4H2O, synthesized in the
present study are given in Fig. 1. Both complexes were found to be
very stable at room temperature in the solid state, and generally
soluble in DMF and DMSO.
The corresponding data for the ligand and its complexes were
presented in the Experimental section. This Schiff base had donor
sites with the ONONO sequence and varied coordination abilities.
This nature of the Schiff base attracted our attention and aroused
our interest in elucidating the structure of metal complexes.
The metal-to-ligand ratio of bidentate Pd(II) and Pt(II)
complexes was found to be 1:1 and the two additional chloride
ligands were coordinated to metal ions. Molar conductance values
presence of n(OeH) peak in the IR spectra and the appearance of
the phenol proton peak in the 1H NMR spectra of the complexes,
which confirm that the ligand did not have lost phenolic proton.
In the spectra of the complexes, the bands observed in the
445e470 cmꢀ1 region might be due to
n
(MeO) [35,36]. The IR
spectra of the complexes were characterized by the appearance of
a broad band in the region 3240e3350 cmꢀ1 due to the
(OeH)
y
frequency of water of crystallization. This water was also identified
by the elemental analyses. The Pt(II) complex had four additional
water of crystallization and thermogravimetric analyses showed
a percentage weight loss of 6.87 for this complex in the tempera-
ture range 65e95 ꢁC.
DMSO-d6 was used as a solvent to measure the 1H NMR spectra
of the ligand and its metal complexes. The 1H NMR spectrum of the
ligand showed signal at 2.35 ppm corresponding to the signals of
CH3. The sharp singlet observed at about
phenolic proton of the ligand [35]. The singlet at
d
11.33 ppm due to
9.54 ppm and
d
8.85 ppm were due to azomethine and pyrimidine ring (CeH)
protons in the spectrum of the ligand, respectively. The multisignals
corresponding aromatic protons appeared between at
d 7.31 and
7.88 ppm. The 1H NMR spectra of Pd(II) and Pt(II) complexes
showed approximately the same peaks identical to those of the free
ligand. The signal for the azomethine proton in the Pd(II) and Pt(II)
complexes appears at 9.58 and 9.63 ppm, respectively. The aromatic
of the Pd(II) and Pt(II) complexes were 42.8 and 31.9
U
ꢀ1 cm2 molꢀ1
,
protons due to phenyl rings have resonated in region d 7.50e8.10 as
respectively. The complexes which contain coordinated chloride
ions are non-conducting or show an increasing degree of conduc-
tivity with time which would be due to their replacements by DMF
solvent molecules.
a multiplet in complexes and these are shifted downfield with
respect to the corresponding signal in the free ligand, indicating
that the metaleoxygen bond is retained in solution.
The electronic spectra of complexes showed three ded spin
Comparison of the IR spectra of the free ligand with that of its Pd
(II) and Pt(II) complexes, showed a approximately the same bands
for stretching of (C]O)benzoyl, (OH)phenolic and (CH]N)azomethine
groups. These carbonyl stretching were found in free ligand at 1652,
1687 cmꢀ1 while in the complexes at 1654 cmꢀ1. The absence of
a band at 1687 cmꢀ1 in the spectra of the complexes, in comparison
to the free ligand, confirms the coordination through the carbonyl
(C]O) group. On the other hand, in the spectra of a metal
complexes, the band at 1273 cmꢀ1 for the phenolic group (CeO) did
not shift, suggesting that this oxygen atom of the phenolic group is
allowed transitions from the three lower lying ‘d’ levels to the
1
empty dx2 ꢀ y2 orbital. The bands are attributed to A1g
/ ,
1A2g
1
1A1g
/
1B1g and to A1g
/
1Eg transitions [37] (see Experimental
section).
In the mass spectra of the ligand and its metal complexes, peaks
were attributable to the molecular ions; m/z: 711.1 [L]þ, m/z: 885.0
[PdCl2 þ LH]þ, m/z: 1029.0 [PtCl þ LH þ 3H2O]þ. The spectrum of
the Pd(II) complex was shown in Fig. 2.
2.2. DNA interaction of the complexes
not coordinated to the metal ion [35,36]. The
n
(OeH)phenolic
The redox behavior of tested compounds was investigated by DP
voltammetry in 0.5 M acetate buffer pH 4.8. Voltammograms,
which were monitored in blank supporting electrolyte (transfer
CH3
voltammetry), obtained before/after interaction between 10
mg/
mLꢀ1 Pd(II) complex and 10 g/mLꢀ1 dsDNA are shown in Fig. 3
m
and those of Pt(II) complex and dsDNA, under similar conditions,
in Fig. 4.
CH
N
CH
N
O
O
Pd(II) complex produced split oxidation peaks at around
þ0.81and þ0.99 V, average two peak mean response
OH
M
N
Ph
N
Ph
0.262 ꢂ 0.012 A (n ¼ 3) with a pre-concentration step on pre-
m
treated PG electrode at open circuit condition for 300 s at pH 4.8 as
presented in Fig. 3-C. In the case of Pt(II) complex, a single oxidation
O
N
Ph
N
O
Ph
peak appeared at around þ0.88 V, mean response 0.167 ꢂ 0.009
mA
(n ¼ 3) (Fig. 4-C).
The voltammetric measurements were also performed for free
ligand and its metal complexes synthesized in reported work [35].
Ligand and its Cu(II), Ni(II) and Fe(II) complexes displayed similar
DP voltammetric behavior, as shown by the Pd(II) complex while
DP voltammograms of Co(II) were almost similar to those obtained
for Pt(II) complex.
Cl
Cl
Fig. 1. Supposed structure of the Pd(II) and Pt(II) complex.

M. Sönmez et al. / European Journal of Medicinal Chemistry 45 (2010) 4215e4220
4217
Fig. 2. API-ES spectrum of Pd(II) complex.
Under the conditions of the experiment, the redox behavior of
original dsDNA exhibited one positive peak at around þ1.03 V due
to the oxidation of guanine residues, mean response
11.59% for adenine after interaction of Pd(II) and Pt(II) complexes,
respectively.
The dependence of the complex concentration (in the range
0.92 ꢂ 0.054
þ1.29 V due to the oxidation of adenine residues, mean response
0.393 ꢂ 0.036 A (n ¼ 3) (Figs. 3- and 4-BA).
m
A (n ¼ 3) (Figs. 3- and 4-BG) and the second at around
0e10 mg/mL) on guanine and adenine signals is shown in Figs. 5
and 6. In the presence of both complexes, guanine and adenine
oxidation peak heights decreased gradually in the percentage of
peak current ratio with concentration up to 10 mg/mL, and the
signals (in special the adenine signal) almost disappeared at more
concentrated solutions.
m
After interaction of complexes in solution, redox signals of
guanine and adenine were decreased to ca. 75 and 88% for Pd(II)
(Fig. 3-AG and AA) and 80 and 90% for Pt(II) (Fig. 4-AG and AA),
respectively, comparing to the results obtained for dsDNA control
solutions. On the other hand, after interaction of complexes at
electrode surface corresponding peak currents were changed to ca.
50% for Pd(II) and 55% for Pt(II). The results obtained by the inter-
action in solution-phase were found to be much suitable for this
study because of the stronger interaction (bigger bases signal
changes). Thus, the assay protocol in solution-phase was chosen for
remaining parts.
Using electrochemical DNA-based biosensors it is not possible to
investigate the mode of binding of complexes to DNA. However,
this method could be very useful for quick, comparative analyses
of DNA interactions. Our results clearly show that the attracting
ability of the Pd(II) and Pt(II) complexes to DNA is quite strong (the
significantly decrease on bases oxidation signals). Moreover,
guanine and adenine oxidation signal changes were almost the
same for both Pd(II) and Pt(II) complexes. That is why we concluded
that these complexes had the similar influence on double helix
of DNA. It is well known that platinum complexes can react with
DNA, by coordinating to N7 of guanine, forming the classical intra-
strand and inter-strand Pt-DNA cross-links that are responsible for
the cellular damage [29,38e43]. In recent years, researchers also
were focused on the palladium complexes owing to their similar
coordination geometry and character to that for platinum
complexes [44e46].
When the experiments were demonstrated for ligand and its
other complexes in the assay conditions, the changes of all analyzed
signals were negligible the compounds did not interact with DNA.
The reproducibility of DNA biosensor protocol was also evalu-
ated based on guanine and adenine signals from three repetitive
measurements for the concentration 10 mg/mL DNA and 10 mg/mL
of complex. Measurements yielded reproducible results with rela-
tive standard deviations of 7.97 and 6.61% for guanine, and 12.2 and
Fig. 3. DP voltammograms in supporting electrolyte pH 4.8 of (C) Pd(II) complex at
bare PG electrode, and control dsDNA (B) before and (A) after interaction with Pd(II)
complex in solution. G, guanine; A, adenine. See Section 4.4, for details.
Fig. 4. DP voltammograms in supporting electrolyte pH 4.8 of (C) Pt(II) complex at
bare PG electrode, and control dsDNA (B) before and (A) after interaction with Pt(II)
complex in solution. G, guanine; A, adenine. See Section 4.4, for details.

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M. Sönmez et al. / European Journal of Medicinal Chemistry 45 (2010) 4215e4220
Fig. 5. The effect of Pd(II) complex upon the DP voltammetric response of guanine (A) and adenine (B) after interaction of solution-phase DNA The average values of the peak
current ratio are presented in the histograms with the error bars See Section 4.4, for details.
It has been previously reported that DNA binding levels of
[PdCl2(HL)] [47] and [PtCl2(HL)] [48] complexes were higher than
those for [Pd(L)2] and [Pt(L)2] complexes. The former complexes,
having labile chloride ligands could probably interact with DNA
becoming activated through equation and reacting with nucleo-
philic DNA bases. Due to the planar motive contained in the
[MCl2(HL)] complexes, intercalation could also be possible.
be a suitable strategy to develop novel therapeutic tools for the
medical treatment [51].
4. Experimental
4.1. Materials
All common laboratory chemicals used in the synthesis of
ligand and its metal complexes were purchased from
commercial sources and used without further purification. The
compounds 1-amino-5-benzoyl-4-phenyl-1H-pyrimidine-2-one
(N-aminopyrimidine, N-AP) and 2,6-diformyl-4-methylphenol
(dfp) were prepared using previously published methodologies
[52,53].
Complexes were tested for their DNA interaction ability using
double-stranded fish sperm DNA (dsDNA) which was kindly
provided by Sigma. The stock solution of the dsDNA (1000
mg/mL)
3. Conclusion
Palladium and platinum complexes have proven their effect
on tumor cells and their ability to bind DNA as main antitumoral
mechanism of action [49,50]. Taking into consideration the simi-
larities between platinum and palladium, in this study two new
palladium and platinum complexes with a phenol based Schiff base
bidentate symmetric ligand which was recently reported, were
synthesized and characterized. Compounds were tested for their
DNA interaction ability with the fish sperm DNA using DP
voltammetry at PG electrode. The determined DNA binding levels
for platinum complex were found to be similar to those of palla-
dium one, showing the strong interaction with DNA. However,
these are preliminary observations and a more extensive study
would be necessary in order to assert that the complexes act as
cleavage agents.
was prepared in TE solution (10 mM TriseHCl, 1 mM EDTA, pH
8.00), and stored at þ4 ꢁC. The solutions were then diluted to the
desired concentration by mixing buffer supporting electrolyte. The
stock solutions (1000
mg/mL) of ligand and its metal complexes
were prepared daily in DMSO. Solutions of different concentrations
of either ligand or its metal complexes were freshly prepared before
each experiment by dilution of the appropriate quantity in sup-
porting electrolyte. The supporting electrolyte solutions were 0.5 M
acetate buffer pH 4.8 containing 20 mM NaCl. All aqueous solutions
were prepared using analytical grade reagents and purified water
Bearing in mind that the structures of several antitumor agents
contain pyrimidine rings, results of this work can show that the
approach of coordinating pyrimidine derivatives with pharmaco-
logically interesting metals such as palladium and platinum could
from a Millipore Milli-Q system (p > 18 M
U
cmꢀ1).
Fig. 6. The effect of Pt(II) complex upon the DP voltammetric response of guanine (A) and adenine (B) after interaction of solution-phase DNA The average values of the peak current
ratio are presented in the histograms with the error bars. See Section 4.4, for details.

M. Sönmez et al. / European Journal of Medicinal Chemistry 45 (2010) 4215e4220
4219
4.2. Instrumentation
was added to this [PdCl4]2ꢀ solution. The mixture was refluxed for
30 h. The precipitated brown compound was removed by filtration,
washed with diethyl ether and followed by cold methanol/water
and dried in vacuum desiccators. Yield: 0.279 g (63%); mp: 300 ꢁC.
Anal. Calc. for C43H30Cl2N6O5Pd (886.07): C, 58.16; H, 3.40; N, 9.46.
The elemental analyses (C, H, N, S) were performed by using
a Leco CHNS model 932 elemental analyzer. The IR spectra were
obtained using KBr pellets (4000e400 cmꢀ1) on a Bio-Rad-Win-IR
Spectrophotometer. The electronic spectra in the 200e900 nm
range were recorded in DMF on a Unicam UV2-100 UVeVis spec-
trophotometer. Magnetic measurements were carried out by the
Gouy method using Hg[Co(SCN)4] as a calibrant. Molar conductance
of the Schiff base ligand and its transitionemetal complexes were
determined in DMF at a room temperature by using a Jenway model
4070 conductivity meter. Thermogravimetric (TGA) measurements
were obtained by a Shimadzu-50 thermal analyzer. The 1H NMR
and 13C NMR spectra of the Schiff base were carried out using
a Bruker 300 MHz Ultrashield TM NMR instrument. LC/MS-API-ES
mass spectra were recorded with an Agilent model 1100 MSD mass
spectrophotometer.
Found: C, 58.60; H, 3.71; N, 9.30%. Selected IR data (
(OeH)phenolic, 1654
(PheCO), 1599 (C]N). 1H NMR (d6-DMSO,
ppm),
n
, cmꢀ1): 3400
n
d
11.32 (s, 1H, OH), 9.63 (s, 1H, HC]N), 9.06 (s, 1H, C(6)H,
7.54e8.10 (m, 7H, Harm); 2.39 (s, 3H, CH3). meff: Dia. LM (10ꢀ3 M, in
DMF, S cm2 molꢀ1): 42.8. UVeVis (in DMF, nm): 239, 254, 278, 294,
347, 460, 616. API-ES, m/z: 885 [M]þ 106Pd isotope).
(
The complex, [PtCl2HL]$4H2O, was synthesized in an identical
manner as that described above using PtCl2 (0.5 mmol, 0.133 g).
[PtCl2HL]$4H2O is orange-brown color compound. Yield: 0.150 g
(51%); mp: 235 ꢁC. Anal. Calc. for C43H38Cl2N6O9Pt (1047.17): C,
49.24; H, 3.65; N 8.01. Found: C, 48.86; H, 3.54; N, 7.67%. Selected IR
data (
n
, cmꢀ1): 3406
n
(OeH/H2O), 1654
n
(ePheC]O), 1597, 1578
n
Differential pulse (DP) voltammograms were recorded with the
(C]N). 1H NMR (d6-DMSO, ppm),
d 12.03 (s, 1H, OH), 9.58
aid of a
m
Autolab type III electrochemical analyzer with GPES
(s, 1H, HC]N), 8.97 (s, 1H, C(6)H, 7.51e8.27 (m, 7H, Harm); 2.33
4.9 software package (Eco-Chemie, The Netherlands). The raw data
were also treated in all DP voltammetric measurements by using
Savitzky and Golay filter (level 2) of the GPES software, followed by
the moving average baseline correction with a peak width of 0.01 V.
Measurements were carried out in a home-made 5-mL glass cell
using the pencil graphite (PG) electrode (active electrode area:
15.9 mm2), with platinum wire counter electrode, and a Ag/AgCl
(3 M NaCl) (Model RE-1, BAS, USA) as reference. For PG electrode,
a mechanical pencil Model T 0.5 (Rotring, Germany) was used as
a holder for pencil lead (Tombo, Japan), which were purchased from
a local stationary. The details of its preparation have been described
in our previous study [54]. Before use, glass cell was soaked
into 3 M HNO3, and rinsed several times with water and acetate
buffer. The convective transport was provided with a magnetic
stirring of 300 rpm.
(s, 3H, CH3). meff: Dia. L (10ꢀ3 M, in DMF, S cm2 molꢀ1): 31.9.
M
UVeVis (in DMF, nm): 229, 281, 309, 355, 389, 451. API-ES, m/z:
1029 [M þ 3H2O]þ
(
194Pt isotope).
4.4. DNA biosensor procedure
The biosensing protocol at the DNA-modified electrode con-
sisted of the electrode pre-treatment, DNA immobilization, inter-
action with metal complexes, and its DP voltammetric
transduction. The guanine and adenine oxidation peaks were used
as the transduction signals. DP voltammograms were recorded
after the transfer of the electrode into a blank supporting electro-
lyte. Three replicate measurements were carried out for each
experiment. All data were obtained at room temperature.
Electrode pre-treatment: The PG electrode surface was pre-
treated by applying a potential of þ1.40 V for 1 min in the blank
supporting electrolyte without stirring, in order to increase the
hydrophilic properties of the electrode surface through introduc-
tion of oxygenated functionalities, accomplished with an oxidative
cleaning.
4.3. Preparation of compounds
4.3.1. Preparation of the ligand (HL)
The Schiff base ligand (HL), [1-((E)-((E)-3-((E)-(5-benzoyl-2-oxo-
4-phenylpyrimidine-1(2H)-yl imino) methyl)-2-hydroxyl-5-meth-
ylbenzilidin)amino)-5-benzoyl-4-phenylpyrimidine-2(1H)-on] was
prepared by condensation between N-AP and dfp and characterized
according to the literature method [35], but its synthesis is here
briefly described. To a solution of 0.164 g (1 mmol) of dfp in hot
ethanol (25 mL) was added 0.582 g (2 mmoL) of N-AP dissolved in
25 mL of hot ethanol and then mixed slowly with constant stirring.
This mixture was refluxed on a water bath at 3 h and cooled. The
precipitate was filtered, washed with hot ethanol and diethyl ether,
and then dried in vacuum over P2O5. The product yielded yellow
precipitate of HL (0.462 g, 65%); mp: 273 ꢁC. Anal. Calc. for
C43H30N6O5 (710): C, 72.67; H, 4.25; N, 11.82. Found: C, 72.20; H,
DNA immobilization: The dsDNA was immobilized onto the pre-
treated PG electrode surface by adsorptive accumulation for 5 min
at þ0.50 V in supporting electrolyte containing 10
mg/mL of DNA
under stirred conditions. The following washing step involved
dipping the electrode in a clean supporting electrolyte for 5 s
(control dsDNA-modified PG electrode).
Interaction of surface-confined DNA with metal complexes: After
the DNA immobilization step described above, the dsDNA-modified
PG electrode was transferred to the stirred supporting electrolyte
containing metal complex concentration of 10 mg/mL. The adsorp-
tion, at open circuit conditions, was allowed to proceed for 5 min.
The biosensor was then rinsed for 5 s in a clean supporting
electrolyte.
4.36; N, 11.66%. Selected IR data, (
O)pyrimidine 1652 (PheCOe), 1608 (HC]N); 1H NMR (d6-DMSO,
ppm), 11.33 (s, 1H, OH), 9.54 (s, 1H, HC]N), 8.85 (s, 1H, C(6)H,
7.31e7.88 (m, 7H, Harm); 2.35 (s, 3H, CH3); 13C NMR (d6-DMSO,
ppm), 192.06 (OCeAr), 179.31 (C]O, pyrimidine), 163.64 (-C6,
n
, cmꢀ1): 3400 (OH), 1687 (eC]
Interaction of solution-phase DNA with metal complexes: Metal
d
complex in the concentration level of 10
mg/mL (unless otherwise
indicated) was added to supporting electrolyte containing 10
m
g/mL
d
DNA. A PG electrode was first pre-treated as described above and
subsequently immersed into the mixture solution. The accumula-
tion of the mixture was performed for 5 min while holding the
potential at þ0.50 V under stirred conditions. The electrode was
then washed with a clean supporting electrolyte for 5 s.
Signal transduction: The oxidation signals of guanine and
adenine were measured by using DP voltammetry with the
following parameters: amplitude 50 mV, step potential 8 mV, scan
rate16 mV/s, between þ0.45 and þ1.40 V in a fresh supporting
electrolyte. Successive measurements were carried out by
pyrimidine ring),157.38 (HC]N),151.54e116.20 (C, aromatic), 20.22
(CH3). LC-MS, m/z 711.1 [M þ 1].
4.3.2. Preparation of the complexes [PdCl2HL] and [PtCl2HL]$4H2O
[PdCl2HL] was prepared according to the following procedure.
First, a solution of [PdCl4]2ꢀ was made by boiling PdCl2 (0.5 mmol,
0.090 g) in concentrated HCl (5 mL), cooling and then diluting with
distilled water (15 mL). Second, a hot solution of HL (0.5 mmol,
0.355 g) in the mixture of chloroform and acetone (100 mL; 1:1, v/v)

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M. Sönmez et al. / European Journal of Medicinal Chemistry 45 (2010) 4215e4220
[28] Y. Cao, X.W. He, Spectrochim. Acta A 54 (1998) 883e892.
[29] E.J. Gao, H.X. Yin, M.C. Zhu, Y.G. Sun, X.F. Gu, Q. Wu, L.X. Ren, J. Struct. Chem.
49 (2008) 1048e1054.
repeating the above assay protocol on a new PG electrode surface
using a new stripping solution and cell.
[30] R.F. Pasternack, C. Bustamante, P.J. Collings, A. Giannetteo, E.J. Gibbs, J. Am.
Chem. Soc. 115 (1993) 5393e5399.
References
[31] R.F. Pasternack, P.G. Coollings, Science 269 (1995) 935e939.
[32] C.Z. Huang, Y.F. Li, X.L. Hu, N.B. Li, Anal. Chim. Acta 395 (1999) 187e197.
[33] J.K. Barton, Comments Inorg. Chem. 3 (1985) 321e348.
[34] M.A.A.F.de C.T. Carrondo, M. Coll, J. Aymami, A.H.J. Wang, G.A. van der Marel,
J.H. van Boom, A. Rich, Biochemistry 28 (1989) 7849e7859.
[1] M. Viciano-Chumillas, S. Tanase, G. Aromí, J.M.M. Smits, R. de Gelder,
X. Solans, E. Bouwman, J. Reedijk, Eur. J. Inorg. Chem. (2007) 2635e2640.
[2] S. Roy, T.N. Mandal, A.K. Barik, S. Pal, S. Gupta, A. Hazra, R.J. Butcher,
A.D. Hunter, M. Zeller, S.K. Kar, Polyhedron 26 (2007) 2603e2611.
[3] N.A. Salih, Turk. J. Chem. 32 (2008) 229e235.
_
[35] M. Sönmez, M. Çelebi, I Berber, Eur. J. Med. Chem. 45 (2010) 1935e1940.
[36] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds. Wiley, New York, 1986.
[37] A.B.P. Lever, Inorganic Electronic Spectroscopy, second ed.. Elsevier, Amster-
dam, 1984.
[38] A.M. Oliveria Breet, H.P. Serrano, A. Macedo, D. Raimundo, M.H. Marques,
M.A. La-Scalea, Electroanalysis 8 (1996) 992e995.
[39] V. Brabec, Electrochim. Acta 45 (2000) 2929e2932.
[40] A. Erdem, B. Kosmider, R. Osiecka, E. Zyner, J. Ochocki, M. Ozsoz, J. Pharm.
Biomed. Anal. 38 (2005) 645e652.
[41] A.M.J. Fichtinger-Schepman, J.L. Van der Veer, J.H.J. Den Hartog, P.H.M. Lohman,
J. Reedijk, Biochemistry 24 (1985) 707e713.
[42] D.Z. Yang, S.S.G.E. Van Boom, J. Reedijk, H.J. Van Boom, A.H.-J. Wang,
Biochemistry 34 (1995) 12912e12920.
[43] J.-M. Malinge, M.-J. Giraud-Panis, M. Leng, J. Inorg. Biochem. 77 (1999) 23e29.
[44] G. Zhao, H. Lin, Y. Ping, H. Sun, S. Zhu, S. Xunchenge, Y. Chen, J. Inorg. Biochem.
73 (1999) 145e149.
[4] S. Roy, J.A. Westmaas, F. Buda, J. Reedijk, J. Inorg. Biochem. 103 (2009)
1278e1287.
[5] M. Sönmez, I. Berber, E. Akbas¸ , Eur. J. Med. Chem. 41 (2006) 101e105.
[6] J.G. Tojal, B. Donnadieu, J.P. Costes, J.L. Serra, L. Lezama, T. Rojo, Inorg. Chim.
Acta 333 (2002) 132e137.
[7] P.F. Rapheal, E. Manoj, M.R.P. Kurup, E. Suresh, Polyhedron 3 (2007) 607e616.
[8] K.A. Ketcham, J.K. Swearingen, A. Castineiras, I. Garcia, E. Bermejo, D.X. West,
Polyhedron 20 (2001) 3265e3273.
[9] F. Zamora, M. Kunsman, M. Sabat, B. Lippert, Inorg. Chem. 36 (1997)
1583e1587.
[10] M. Louloudi, Y. Deligiannakis, J.P. Tuchagues, B. Donnadien, N. Nadjiliadis,
Inorg. Chem. 36 (1997) 6335e6342.
[11] F. Jolibois, J. Cadet, A. Grand, R. Subra, N. Raga, V. Barone, J. Am. Chem. Soc. 120
(1998) 1864e1871.
[12] A.R. Katritzky, C.W. Pees, A.J. Boulton, C. Mckillop, J. Heterocycl. Chem. 3
(1984) 57e68.
_
[45] G.B. Onoa, V. Moreno, E. Freisinger, B. Lippert, J. Inorg. Biochem. 89 (2002)
237e247.
[13] B. Rosenberg, L. VanCamp, T. Krigas, Nature 222 (1969) 385e386.
[14] K.M. Millan, S.R. Mikkelsen, Anal. Chem. 65 (1993) 2317e2323.
[15] J.J. Gooding, Electroanalysis 14 (2002) 1149e1156.
[16] T.G. Drummond, M.G. Hill, J.K. Barton, Nat. Biotechnol. 21 (2003) 1192e1199.
[17] J. Wang, Anal. Chim. Acta 469 (2002) 63e71.
[18] D. Pang, H.D. Abruna, Anal. Chem. 70 (1998) 3162e3169.
[19] B. Jin, X. Ji, T. Nakamura, Electrochim. Acta 50 (2004) 1049e1055.
[20] D.E. Thurston, Brit. J. Cancer 80 (1999) 65e85.
[21] R.F. Pasternack, E.J. Gibbs, J.J. Villafranca, Biochemistry 22 (1983) 2406e2414.
[22] K.E. Erkkila, D.T. Odom, J.K. Barton, Chem. Rev. 99 (1999) 2777e2795.
[23] L.S. Ling, Z.K. He, F. Chen, Y.E. Zeng, Talanta 59 (2003) 269e275.
[24] X.Q. He, Q.Y. Lin, R.D. Hu, X.H. Lu, Spectrochim. Acta A 68 (2007) 84e190.
[25] J. Pastor, J.G. Siro, J.L. Garcia Navio, J.J. Vaquero, J. Alvarez Builla, F. Gago, B. de
Pascual Teresa, M. Pastor, M.M. Rodrigo, J. Org. Chem. 62 (1997) 5476e5483.
[26] C.G. Coates, L. Jacquet, J.J. McGarvey, S.E.J. Bell, A.H.R. Alobaidi, J.M. Kelly,
J. Am. Chem. Soc. 119 (1997) 7130e7136.
[46] A.G. Quiroga, J.M. Perez, I. Lopez-Solera, E.I. Montera, J.R. Masaquer, C. Alonso,
C. Navarro-Ranninger, J. Inorg. Biochem. 69 (1998) 275e281.
[47] L. Otero, M. Vieites, L. Boiani, A. Denicola, C. Rigol, L. Opazo, C. Olea-Azar,
J.D. Maya, A. Morello, R.L. Krauth-Siegel, O.E. Piro, E. Castellano, M. González,
D. Gambino, H. Cerecetto, J. Med. Chem. 49 (2006) 3322e3331.
[48] V. Brabec, Prog. Nucl. Acid Res. Mol. Biol. 71 (2002) 1e68.
[49] A.S. Abu-Surrah, H.H. Al-Sa’doni, M.Y. Abdalla, Cancer Ther. 6 (2008) 1e10.
[50] A.S. Abu-Surrah, Mini. Rev. Med. Chem. 7 (2007) 203e211.
[51] E. Wong, C.M. Giandomenico, Chem. Rev. 99 (1999) 2451e2466.
[52] Y. Akçamur, B. Altural, E. Sarıpınar, G. Kollenz, O. Kappe, K. Peters, E. Peters,
H. Schering, J. Heterocylic Chem. 25 (1988) 1419e1422.
[53] R.R. Gagne, C.L. Spiro, T.J. Smith, C.A. Hamann, W.R. Thies, A.K. Shiemke, J. Am.
Chem. Soc. 103 (1981) 4073e4081.
[54] Y. Yardım, E. Keskin, A. Levent, M. Özsöz, Z. S¸ entürk, Talanta 80 (2010)
1347e1355.
[27] S. Lecomte, M.H. Baron, Biospectroscopy 3 (1997) 31e45.