Platinum(II) complexes with tetradentate schiff bases as ligands: Synthesis, Characterization and detection of DNA interaction by differential pulse voltammetry

Article abstract of DOI:10.1155/2012/634572

Five sterically hindered platinum(II) complexes with tetradentate schiff bases as ligands, [Pt(L)] (L= N,N'-bisalicylidene-1,2-ethylenediamine (L ¹), N,N'-bisalicylidene-1,2-cyclohexanediamine (L²), N,N'-bis(5-hydroxylsalicylidene)-1,2-cyclohexanediamine (L³), N,N'-bisalicylidene-1,2-diphenylethylenediamine (L⁴) and N,N'-bis(3-tert-butyl-5-methyl-salicylidene)-1,2- diphenylethylenediamine (L⁵) ) have been synthesized and characterized by IR spectroscopy and elemental analysis. The sterical hindrance of antitumor drug candidates potentially makes them less susceptible to deactivation by sulphur containing proteins and helping to overcome resistance mechanisms. The interaction of these metal complexes with fish sperm single-stranded DNA (ssDNA) was studied electrochemically based on the oxidation signals of guanine and adenine. Differential pulse voltammetry was employed to monitor the DNA interaction in solution by using renewable pencil graphite electrode. The results indicate that ligands with different groups can strongly affect the interaction between [Pt(L)] complexes and ssDNA due to sterical hindrances and complex [Pt(L ¹)] has the best interaction with DNA among the five complexes.

Full text of DOI:10.1155/2012/634572

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
http://www.ejchem.net
2012, 9(3), 1422-1430
Platinum(II) Complexes with
Tetradentate Schiff Bases as Ligands:
Synthesis, Characterization and Detection of DNA
Interaction by Differential Pulse Voltammetry
*
LIJUN LI , CHAO TIAN, CHENG WANG,
GUANGYUAN WANG, LIANZENG WANG and JIANLONG DU
College of Chemistry & Environmental Science
Chemical Biology Key Laboratory of Hebei Province
Hebei University, Baoding 071002, China
Received 12 July 2011; Accepted 20 September 2011
Abstract: Five sterically hindered platinum(II) complexes with tetradentate
schiff bases as ligands, [Pt(L)] (L= N,N’-bisalicylidene-1,2-ethylenediamine
1
2
(
L ), N,N’-bisalicylidene-1,2-cyclohexanediamine (L ), N,N’-bis(5-hydroxyl-
3
salicylidene)-1,2-cyclohexanediamine (L ), N,N’-bisalicylidene-1,2-diphenyl-
ethylenediamine (L ) and N,N’-bis(3-tert-butyl-5-methyl-salicylidene)-1,2-
diphenylethylenediamine (L ) ) have been synthesized and characterized by IR
4
5
spectroscopy and elemental analysis. The sterical hindrance of antitumor drug
candidates potentially makes them less susceptible to deactivation by sulphur
containing proteins and helping to overcome resistance mechanisms. The
interaction of these metal complexes with fish sperm single-stranded DNA
(
ssDNA) was studied electrochemically based on the oxidation signals of
guanine and adenine. Differential pulse voltammetry was employed to monitor
the DNA interaction in solution by using renewable pencil graphite electrode.
The results indicate that ligands with different groups can strongly affect the
interaction between [Pt(L)] complexes and ssDNA due to sterical hindrances
1
and complex [Pt(L )] has the best interaction with DNA among the five
complexes.
Keywords: Platinum(II) complexes, Synthesis, DNA interaction, Differential pulse voltammetry.
Introduction
Schiff bases are used as substrates in the preparation of a lot of industrial compounds via
1
ring closure, cycloaddition and replacement reactions . Schiff bases are also important class
2,3
4,5
of compounds in medicinal and pharmaceutical fields such as antimicrobial , antifungal
6
,7
and antitumor activituy . The landmark discovery of cisplatin by Rosenberg in 1965
8
heralded a new era of anticancer drug research based on metallopharmaceuticals . However,
it has several limitations including toxicity (nephrotoxicity, neurotoxicity, ototoxicity and

Platinum(II) Complexes with Tetradentate Schiff Bases as Ligands 1423
9
emetogenesis) and intrinsic or acquired resistance , for instance, Pt(II) compounds have a
strong thermodynamic preference for binding to sulfur donor ligands, hence, before
antitumor platinum drugs reach DNA in the nucleus of tumor cells, they may interact with
various compounds, including sulfur-containing molecules, these interactions are generally
thought to play a primary mechanism underlying tumor resistance to platinum compounds,
1
0
their inactivation and their side effects . Specific chemical and structural features can be
incorporated into new Pt compounds so that they are able to circumvent a specific drug
11
resistance mechanism, such as sterically hindered Pt complexes . There also have been
efforts directed at the design of unconventional complexes that violate the original structure-
1
2
13
activity relationships, such as trans Pt compounds and binuclear Pt complexes . There has
1
4
also been interest in Pt(IV) complexes for their potential as orally active agents. It is hoped
that they will overcome Pt drug resistance in tumors and be applicable to a broader range of
cancers.
In recent years, there has been a gradually attempt in the application of
1
5,16
electrochemical techniques
to understand interactions between DNA and moleculers
due to cheapness, simplicity, fast detection and require small amount of sample with
1
7
respect to the generally used spectroscopic methods . Keeping the above knowledge in
mind, the present paper involves preparing and characterizing five new tetradentate
sterically hindered platinum(II) complexes with schiff bases as ligands which have more
thermodynamic stabilities. In continuation of the study, special attention has been paid to
the application of electrochemical measurements based on the interaction of these metal
complexes with ssDNA via differential pulse voltammetry using disposable pencil
graphite electrode.
Experimental
Reagent grade chemicals were used as received unless otherwise stated. Elemental analysis
were determined on a Elemental Vario EL III elemental analyzer. The IR spectra were
1
recorded using KBr pellets and a Perkin-Elmer Model-683 spectrophotometer. The H NMR
spectra were recorded on a Bruker AVIII 600 NMR spectrometer. Electrochemical
experiments are carried on a PC driven PARC 273A potentiostat: galvanostat running with
mode 270 electrochemical analysis software or on a CHI 660 workstation. A three-
compartment cell contains a working electrode (pencil graphite), a counter electrode
(
Pt plane) and a calomel reference electrode.
1
5
18
Schiff bases ligands (L ~L ) were synthesized according to a published procedure . To
a solution of the amine (1 equiv.) in ethanol was added the relevant aldehyde derivatives
1 equiv.). The resulting yellow/orange solution was refluxed for 1.5 h. After cooling to
(
room temperature the solution was concentrated in vacuo to yield a yellow solid product.
1
Synthesis of N,N’-bisalicylidene-1,2-ethylenediamine (L )
-
1
Yellow solid product (406 mg, 91%): mp 120-122 ºC. IR(KBr, pellet)υ/cm : 1632, 1578,
1
1
7
CH
498, 1283, 1149, 1042, 1021, 857, 749, 741. H NMR (600M Hz, DMSO-d ), δ: 6.850-
6
.438 (m, 8 H, Ar-H), 8.600 (s, 2 H, -CH=N-), 13.380 (s, 2 H, -OH), 3.932 (s, 4H, -CH
-). Anal. Calc. for C16 (268.31): C, 71.62; H, 6.01; N, 10.44. Found: C, 71.54;
H, 6.13; N, 10.41.
2
-
2
16 2 2
H N O
2
Synthesis of N,N’-bisalicylidene-1,2-cyclohexanediamine (L )
Yellow solid product (195 mg, 93%): mp 118-119 ºC. IR(KBr, pellet)υ/cm : 1629, 1579,
-
1
1
1
501, 1280, 1148, 1095, 1045, 767, 758. H NMR (600M Hz, DMSO-d ), δ: 13.325 (s, 2 H,
6
-
OH), 8.490 (s, 2 H, -CH=N-), 6.790-7.350 (m, 8 H, Ar-H), 3.400-3.450 (m, 2 H, -CH-),

1
1
424 LIJUN LI et al.
.440-1.910 (m, 8 H, -CH -CH -). Anal. Calc. for C H N O (322.40): C, 74.51; H, 6.88;
2
2
20 22
2
2
N, 8.69. Found: C, 74.43; H, 6.75; N, 8.62.
3
Synthesis of N,N’-bis(5-hydroxyl-salicylidene)-1,2-cyclohexanediamine (L )
To a 100 mL three-neck flask, equipped with a reflux condenser, thermometer, a nitrogen
source and magnetic stirrer was added hydroquinone (2.0 g, 0.018 mol), sodium hydroxide
(4.0 g, 0.10 mol), distilled water 40 mL, and chloroform 8.0 mL (98 mmol). The mixture
was heated to reflux for 8 h. After cooling, the reaction mixture was acidified to PH 2~3
with 2N hydrochloric acid, and extracted with ethyl acetate. The ethyl acetate extract was
treated with vacuum distillation, dried and obtained crude 5-hydroxylsalicylaldehyde (1.7 g).
The crude product was purified by column chromatography gave yellow solid product (a )
2
-
1
(
1
6
0.41 g, 32.6 %): mp: 94-97 ºC; IR(KBr, pellet)υ/cm : 3441, 1660, 1631, 1582, 1486, 1398,
278, 1151, 1039, 943, 881, 801, 769, 641,484. H NMR (600M Hz, DMSO-d ), δ: 6.812-
1
6
.974(m, 3H, Ar-H), 10.199(s, 1H, -CHO).
-
1
Yellow solid product (159 mg, 90%): mp 216-218 ºC. IR(KBr, pellet)υ/cm : 3329,
641, 1630, 1483, 1300, 1157, 1047, 804, 788. H NMR (600M Hz, DMSO-d ), δ: 12.460
1
1
6
(
1
s, 2 H, -OH), 8.365 (s, 2 H, -CH=N-), 8.930 (s, 2H, -OH), 6.662-6.728 (m, 6H, Ar-H),
.430-1.880 (m, 8 H, -CH -CH -). Anal. Calc. for C H N O (354.40): C, 67.78; H, 6.26;
2
2
20 22
2
4
N, 7.90. Found: C, 67.85; H, 6.13; N, 8.11.
Synthesis of N,N’-bisalicylidene-1,2-diphenylethylenediamine (L )
Yellow solid product (195.1 mg, 93%): m.p. 201~202 ºC; IR(KBr, pellet)υ/cm : 1623,
4
-
1
1
1
5
8
576, 1496, 1279, 1211, 1151,1052, 859,760. H NMR (600M Hz, DMSO-d ), δ: ppm:
6
.0513 (s, 2H, Benzyl-H), 6.8181-6.8650 (m, 8 H, Ar-H), 7.1947-7.3197 (m, 10H, Ph-H),
.4195 (s, 1H, -CH=N-), 8.4244 (s, 1 H, -CH=N-), 13.1777 (s, 2 H, -OH). Anal. Calc. for
C H N O (420.18): C, 79.98; H, 5.75; N, 6.66. Found: C, 79.93; H, 5.86; N,6.47.
28
24
2
2
Synthesis of N,N’-bis(3-tert-butyl-5-methyl-salicylidene)-1,2- diphenylethylenediamine
5
(
L )
The reaction mixture with p-methylphenol (10.8 g, 0.1 mol) and tert-butyl alcohol (8.9 g,
.12 mol) was stirred on a 50 ºC oil bath for 6.5 hour, then 50 mL water was added, the oil
0
layer was separated, and the water layer was extracted with ether. The combined organic
layer was washed with water, Na CO /H O and H O. The products were separated by silica
2
3
2
2
1
gel chromatography to give 2-t-butyl-2-methylphenol (10.3618 g, 71%): H NMR (600 M
Hz, DMSO-d ), δ: ppm: 1.3981 (s, 9 H, t-Bu-H), 2.2699 (s, 3 H, Me-H), 4.2456 (br, 1 H, -
6
OH), 6.5568 (d, 1H, Ar-H), 6.8696 (d, 1H, Ar-H), 7.0654 (s, 1 H, Ar-H).
To a 50 mL three-neck flask, equipped with a reflux condenser, thermometer, a nitrogen
source and magnetic stirrer was added anhydrous toluene 4 mL, 2-tert-butylcresol (1.6456 g,
1
0 mmol), tin(IV) tetrachloride 0.6003 g and 2,6-lutidine 0.547 g. The reaction was
exothermic. The mixture was stirred for 20 min at room temperature, then paraformaldehyde
0.66 g, 22 mmol) was added. The mixture was heated to about 100 ºC for 5 h. After
(
cooling, the reaction mixture was poured into water, acidified to pH 2~3 with 2N
hydrochloric acid and extracted with ether. The ether extract was washed with a saturated
sodium chloride solution, dried (Na SO ) and concentrated to leave crude 3-t-butyl-5-
2
4
methylsalicylaldehyde. Purification by column chromatography (ethyl acetate/petroleum
1
ether) gave the light yellow solid product (a ) (1.1535 g, 60%): mp 67-69 ºC. H NMR
1
(
600M Hz, DMSO-d
H, Ar-H), 7.3308 (d, 1 H, Ar-H), 9.8246 (s, 1 H, -CHO), 11.6025 (s, 1 H, -OH).
Yellow solid product (122.9 mg, 88%): m.p. 179-181 ºC; IR(KBr, pellet)υ/cm : 2957,
6
), δ: ppm: 1.4109 (s, 9 H, t-Bu-H), 2.3240 (s, 3 H, Me-H), 7.1781 (d, 1
-
1
1
1
6
625, 1601, 1440, 1263, 1165, 1047, 862, 788. H NMR (600M Hz, DMSO-d ), δ: ppm:

Platinum(II) Complexes with Tetradentate Schiff Bases as Ligands 1425
1
.4252 (s, 18 H, t-Bu), 2.2170 (s, 6 H, -CH ), 4.8339 (s, 2 H, Benzyl-H), 6.7873 (d, 2H,
3
2
1
-Ar-H), 7.1183 (d, 2H, 4-Ar-H), 7.2187-7.3744 (m, 10H, Ph-H), 8.0995 (s, 2H, -CH=N-),
2.3400 (br, 2H, -OH). Anal. Calc. for C H N O (560.34): C, 81.39; H, 7.91; N, 5.00.
3
8
44
2
2
Found: C, 81.25; H, 7.83; N,4.82.
1
Synthesis of [Pt(L )]
1
2 4
K PtCl (15 mg, 0.036 mmol) was dissoved in 1 mL distilled water, then L (9 mg, 0.034 mmol)
dissolving in absolute methanol was added. The reaction mixture was stired in room
1
temperature for 72 h. The complex [Pt(L )] was purificated by column chromatography
(
ethanol/petroleum ether) gave the yellow solid product (12 mg, 77.5% ):m.p. ＞300 ºC;
IR(KBr, pellet)υ/cm : 1625, 1129, 563,485. Anal. Calc. for C16H C O Pt (461.37): C,
14 2 2
-
1
4
1.65; H, 3.06; N, 6.07. Found: C, 40.97; H, 2.59; N, 6.41.
2
Synthesis of [Pt(L )]
2
1
The synthesis of [Pt(L )] was carried out in an identical manner to [Pt(L )] starting from
2
K
2
PtCl
4
(15 mg, 0.036 mmol) and L (12 mg, 0.037 mmol). Yellow solid (13 mg, 70.12%).
-
1
IR(KBr, pellet)υ/cm : 1620, 1124, 566, 468. Anal. Calc. for C H N O Pt (530.50): C,
23
21
2
2
4
7.54; H, 4.37; N, 5.28. Found: C, 47.35; H, 4.31; N, 5.19.
3
Synthesis of [Pt(L )]
3
1
The synthesis of [Pt(L )]was carried out in an identical manner to [Pt(L )] starting from
3
K PtCl (13 mg, 0.031 mmol) and L (11 mg, 0.031 mmol). Yellow solid.(13 mg, 76.5%)
2
4
-
1
20 2 4
IR(KBr, pellet)υ/cm : 1620, 1125, 560, 462. Anal. Calc. for C20H N O Pt (547.46): C,
4
3.88; H, 3.68; N, 5.21. Found: C, 43.81; H, 3.52; N, 5.37.
4
Synthesis of [Pt(L )]
4
1
The synthesis of [Pt(L )] was carried out in an identical manner to [Pt(L )] starting from
4
K PtCl (15 mg, 0.036 mmol) and L (13mg, 0.031mmol). Yellow solid (14 mg, 73.4%).
2
4
-
1
IR(KBr, pellet)υ/cm : 1619, 1121, 527, 474. Anal. Calc. for C H N O Pt (628.60): C,
29
25
2
2
5
5.41; H, 4.01; N, 4.46. Found: C, 55.24; H, 4.13; N, 4.37.
5
Synthesis of [Pt(L )]
5
1
The synthesis of [Pt(L )]was carried out in an identical manner to [Pt(L )] starting from
K
IR(KBr, pellet)υ/cm : 1619, 1121, 534, 484. Anal. Calc. for C H N O Pt (696.72): C,
5
2
PtCl
4
(12 mg, 0.036 mmol) and L (18 mg, 0.036 mmol). Yellow solid (16 mg, 64%).
-
1
34
33
2
2
5
8.61; H, 4.77; N, 4.02. Found: C, 58.44; H, 4.53; N, 4.21.
DNA interaction procedure
Three replicate measurements were carried out for each electrochemical experiment. All
data were obtained at room temperature.
Interaction of DNA with metal complexes: Metal complex in the concentration level of
1
00 μg/mL (unless otherwise indicated) was added to supporting electrolyte containing 100
μg/mL DNA. A pencil graphite electrode was first pre-treated as described above and
subsequently immersed into the mixture solution. The accumulation of the mixture was
performed for 3 min while holding the potential at +0.50 V under stirred conditions. The
electrode was then washed with a clean supporting electrolyte for 8 s.
Signal transduction: The oxidation signals of guanine and adenine were measured by
using differential pulse voltammetry with the following parameters: amplitude 50 mV, step
potential 8 mV, pulse width 0.06 s, pulse period 0.2 s, setting time 4 s, between +0.45 and
+1.40 V in a fresh supporting electrolyte. Successive measurements were carried out by
repeating the above assay protocol.

1
426 LIJUN LI et al.
Results and Discussion
Chemistry
1
5
The symmetric schiff bases ligands L -L and their complexes were prepared as shown in
1
5
Scheme 1. The platinum complexes [Pt(L )]~[Pt(L )] have been prepared by the reaction of
PtCl with symmetric schiff bases in a mixture of CH OH/H O. Unfortunately, there is no
clear NMR data of the complex due to the low intensity of the signals.
K
2
4
3
2
R3
R4
N
R3
R4
CHO
OH
N
H N
2
NH2
R2
R2
OH HO
R2
R1
R1
R1
1
L : R =R =R =R =H
1
2
3
4
a :R =tert-butyl R =CH
4
1
1
2
3
L : R =R =H R =R =ph
1 2 3 4
5
L : R =tert-butyl R =CH R =R =ph
1
2
3
3
4
R3
N
R4
N
O
Pt
K PtCl4
2
R2
O
R2
R1
R1
CHO
OH
a : R =OH
N
N
H N
NH2
2
R5
R5
OH HO
R5
2
2
5
L : R =H
5
3
L : R =OH
5
N
O
N
O
Pt
K PtCl4
2
R5
R5
1
5
Scheme 1. Synthesis of L -L and Pt complexes.
Main IR absorptions of ligands and complexes were shown in Table 1. Comparison of
the IR spectra of the free ligands with that of their Pt(II) complexes, the (CH=N)
stretching frequencies were found in free ligand at 1632, 1629, 1630, 1623 and 1625 cm ,
while in complexes shifted to low wavenumbers at 1625, 1620, 1620, 1619 and 1619 cm .
On the other hand, in the spectra of a metal complexes, the bands for the phenolic group (C-O)
imine
-
1
-
1

Platinum(II) Complexes with Tetradentate Schiff Bases as Ligands 1427
-
1
-1
shifted from 1149, 1148, 1157, 1151 and 1165 cm to 1129, 1124, 1125, 1121 and 1121 cm ,
-
1
comparing to the free ligands. New bands appeared at about 460-485 and 530-565 cm and
were may assigned to υPt-O and υPt-N, respectively. All of these indicated that nitrogen atoms
of the imine groups and oxygen atoms of the phenolic groups are coordinated to the metal
ion. Elemental analysis also confirms the named stoichiometries of all the complexes.
-
1
Table 1. Main IR absorptions of ligands and complexes (cm ).
ν (C=N)
1632
1629
1630
1623
1625
1625
1620
1620
1619
1619
ν (C-O)
1149
1148
1157
1151
1165
1129
1124
1125
1121
1121
ν (Pt-N)
ν (Pt-O)
1
2
3
4
5
L
L
L
L
L
1
Pt(L )
563
566
560
527
534
485
468
462
474
484
2
Pt(L )
Pt(L )
3
4
Pt(L )
5
Pt(L )
DNA interaction of the complexes
The oxidation peaks of dsDNA are virtually absent in differential pulse voltammetry, on the
contrary, the well-developed voltammetric signals of ssDNA can be readily obtained. The
large difference in the oxidation signals of dsDNA and ssDNA was due to the distinctness of
19
accessibility and flexibility of two kinds of DNA . Denaturation of DNA is performed by
thermal heat up to 100 °C for about 15 min, following by quick cooling in an ice bath. The
redox behavior of tested complexes was investigated by differential pulse voltammetry in
0.5 M acetate buffer pH=4.6 containing 20 mM NaCl, Voltammograms, which were monitored
in blank supporting electrolyte (transfer voltammetry), obtained before/after interaction
-1
-1
between 100 μg/mL Pt(II) complex and 100 μg/mL ssDNA were shown in Figure 1~5.
Potential, (V)
1
1
Figure 1. Interaction of ssDNA with [Pt(L )]. (—) DNA blank. (—) [Pt(L )] + DNA stirring
1
after 0.5 h. (—) [Pt(L )] + DNA stirring after 12 h.

1
428 LIJUN LI et al.
Potential, (V)
2
2
Figure 2. Interaction of ssDNA with [Pt(L )]. (—) DNA blank. (—) [Pt(L )] + DNA stirring
2
after 0.5 h. (—) [Pt(L )] + DNA stirring after 12 h.
Potential, (V)
3
3
Figure 3. Interaction of ssDNA with [Pt(L )]. (—) DNA blank. (—) [Pt(L )] + DNA stirring
3
after 0.5 h. (—) [Pt(L )] + DNA stirring after 12 h.
Potential, (V)
4
4
Figure 4. Interaction of ssDNA with [Pt(L )]. (—) DNA blank. (—) [Pt(L )] + DNA stirring
4
after 0.5 h. (—) [Pt(L )] + DNA stirring after 12 h.

Platinum(II) Complexes with Tetradentate Schiff Bases as Ligands 1429
Potential, (V)
5
5
Figure 5. Interaction of ssDNA with [Pt(L )]. (—) DNA blank. (—) [Pt(L )] + DNA stirring
5
after 0.5 h. (—) [Pt(L )] + DNA stirring after 12 h.
Under the conditions of the experiment, the redox behavior of original ssDNA exhibited
one positive peak at around +1.10 V due to the oxidation of guanine residues, mean response
0
.011± 0.00025 mA (n =3) and the second at around +1.34 V due to the oxidation of adenine
residues, mean response 0.032 ±0.00036 mA (n =3). In the blank supporting electrolyte, we
can see one clearly positive peak around +1.50 V, mean response 0.486 mA, which is
-
1
attributed to the oxidation of Cl . But unfortunately we could not see any positive peak
singles about Pt(II) complexes.
Firstly, we reacted with five ligands and ssDNA in the room temperature in solution, and
found no change of redox signal values of guanine and adenine residues. After the interaction
of complexes and ssDNA in solution, redox signal values of guanine and adenine were shown
1
in Table 2. Complex [Pt(L )] had strong bonding with guanine and adenine residues after
stirring 0.5 h at room temperature, the redox peaks of guanine and adenine residues decreased
by 2.3 and 3.2 μA, from 0.0119 and 0.0333 mA to 0.0096 mA and 0.0301 mA. When
2
1
,2- ethylenediamine was replaced by the large ring planar steric 1,2-cyclohexanediamine (L ),
2
the bond formation of complex [Pt(L )] with ssDNA significantly reduced, decreasing by 0.3
and 0.9μA after the stirring of 0.5 h. 1,2-Cyclohexanediamine planar structure might hamper
the interaction between Pt complex and ssDNA. In order to improve the water-solubility of
complex, we introduced hydroxyl group in aromatic ring (L ), expecting to enhance
coordination of Pt complex [Pt(L )] with ssDNA. However, we found the result had almost no
3
3
change, the redox peaks of guanine and adenine residues only decreased by 0.9 and 2 μA after
0.5 h stirring. To validate whether it was planar structure or not hindering coordination of
complexes and DNA, we substituted 1,2-cyclohexanediamine to non-coplanar 1,2-diphenyl-
4
2
4
ethylenediamine (L ). Compared to [Pt(L )], [Pt(L )] had better interaction with ssDNA after
stirring 0.5 h, decreasing by 1.2 and 3.3μA. On the other hand, we discussed the effect of
interaction between aromatic substituents of complex and DNA. We joined tert-butyl and
5
methyl to o- and p- of phenolic hydroxyl group respectively, synthesizing complex [Pt(L )],
and found that redox peak values of guanine and adenine had no change after 0.5 h stirring.
Symmetrical tert-butyl on benzene ring effectively prevented attacking of Pt ion to ssDNA. We
also observed the interactions between complexes and ssDNA after 12 h stirring, which were
1
4
5
consistent to those after 0.5 h: [Pt(L )]~[ Pt(L )] continued to interact with ssDNA. [Pt(L )]
almost had no coordination to guanine residues, but had better coordination to adenine
residues. So we concluded that substituents on ligands can effectively influence the interaction
between Pt complexes and DNA, bulky substituents on ligands can effectually embarrass the
coordination of Pt ion to guanine and adenine residues.

1
430 LIJUN LI et al.
Table 2. Redox signal values of guanine and adenine (mA).
Stirring after 0.5 h Stirring after 12 h
Guanie
0.0119
0.0096
0.0116
0.0110
0.0107
0.0120
Adenine
0.0333
0.0301
0.0324
0.0313
0.0300
0.0329
Guanie
Adenine
DNA blank
1
Pt(L ) + DNA
0.0092
0.0096
0.0095
0.0108
0.0118
0.0293
0.0308
0.0294
0.0288
0.0299
2
Pt(L ) + DNA
3
Pt(L ) + DNA
4
Pt(L ) + DNA
5
Pt(L ) + DNA
Conclusion
20
Rare-earth platinum complexes have proved their effectiveness in tumor cells . In this study five
platinum complexes with symmetric tetradentate schiff base as ligands were synthesized and
characterized. Compounds were tested for their DNA interaction ability with the fish sperm
ssDNA using differential pulse voltammetry at pencil graphite electrode. The determined DNA
1
binding levels for platinum complexes showed that [Pt(L )] had the best interaction with DNA,
substituents on ligands can effectively influence the interaction between Pt complexes and DNA,
bulky substituents on ligands can effectually embarrass the coordination of Pt ion to guanine
and adenine residues. However, these are preliminary observations and a more extensive
study would be necessary in order to assert that the complexes act as cleavage agents.
Acknowledgement
This work was kindly supported by the fund from the Natural Science Foundation of Hebei
Province (No. B2010000223) and Doctoral fundation of Hebei University (No. 2009-164).
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