Crystal structure, DNA-binding ability and cytotoxic activity of platinum(II) 2,2′-dipyridylamine complexes

Article abstract of DOI:10.1016/S0020-1693(03)00389-X

Two platinum(II) complexes, [Pt(dpa)Cl₂] (1) and [Pt(dpa)CBDCA] (2), where DPA=2,2′-dipyridylamine and CBDCA=1,1-cyclobutanedicarboxylate, were synthesized and characterized by elemental analysis, IR spectroscopy, ES-MS and X-ray diffraction. Intermolecular hydrogen bonds were observed in both complexes (N-H?Cl for complex 1 and N-H?O for complex 2), which may play a role in formation of hydrogen bonding in metal-DNA adducts. Complex 2 adopts a boat conformation so that the cyclobutane ring and bipyridyl groups are on the same side of the platinum square. The interactions of complexes 1 and 2 with DNA were studied by UV and Fluorescence Spectroscopy, which indicated that both complexes could interact with DNA through groove binding or intercalation. The in vitro cytotoxic activity against melanoma B16-BL6 cells and human Jurkat T-cells was also reported.

Full text of DOI:10.1016/S0020-1693(03)00389-X

Inorganica Chimica Acta 357 (2004) 95–102
www.elsevier.com/locate/ica
Crystal structure, DNA-binding ability and cytotoxic
activity of platinum(II) 2,20-dipyridylamine complexes
a
Chao Tu , Xuefeng Wu , Qin Liu , Xiaoyong Wang , Qiang Xu , Zijian Guo
b
a
a
b
a,
*
a
State Key Laboratory of Coordination Chemistry, Coordination Chemistry Institute, Nanjing University, 210093 Nanjing, PR China
b
State Key Laboratory of Pharmaceutical Biotechnology, Nanjing University, 210093 Nanjing, PR China
Received 27 April 2003; accepted 14 June 2003
Abstract
Two platinum(II) complexes, [Pt(dpa)Cl2] (1) and [Pt(dpa)CBDCA] (2), where DPA ¼ 2,20-dipyridylamine and CBDCA ¼ 1,1-
cyclobutanedicarboxylate, were synthesized and characterized by elemental analysis, IR spectroscopy, ES-MS and X-ray diffraction.
Intermolecular hydrogen bonds were observed in both complexes (N–Hꢀ ꢀ ꢀCl for complex 1 and N–Hꢀ ꢀ ꢀO for complex 2), which
may play a role in formation of hydrogen bonding in metal–DNA adducts. Complex 2 adopts a boat conformation so that the
cyclobutane ring and bipyridyl groups are on the same side of the platinum square. The interactions of complexes 1 and 2 with
DNA were studied by UV and Fluorescence Spectroscopy, which indicated that both complexes could interact with DNA through
groove binding or intercalation. The in vitro cytotoxic activity against melanoma B16-BL6 cells and human Jurkat T-cells was also
reported.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Platinum(II) complex; 2,20-Dipyridylamine; Crystal structure; DNA binding; Cytotoxic activity
1. Introduction
demonstrated certain degree of activity against tumor
cell lines [12–15].
There is a huge scope in the design of novel Pt(II)-
based anticancer complexes which possess improved
clinical efficacy and undesired side effects [1–6]. One of
the key strategies aimed at overcoming the drawbacks is
to design platinum(II) complexes that interact with
DNA in a different fashion from that of the currently
used drugs [5,6]. Early structure–activity relationships
(SAR) have defined the necessity of at least one NH
moiety which is believed to be important for H-bonding
interactions toward DNA [7], although the role of such
NH groups is not completely clarified [8–11].
There is an increasing number of platinum com-
pounds which contain no NH moiety but display sig-
nificant antitumor activity [12–15]. Examples include
Pt(II) complexes containing bipyridyl crown ethers,
pyridine, bis(imidazole), bismethylimidazolecarbinol
and 2-phenylpridine ligands. All these complexes have
The 2,20-dipyridylamine (DPA) is an aromatic amine
sharing some similarity to 2,20-bipyridine (BPY), how-
ever the central amine unit introduces several differ-
ences: the two pyridine rings of DPA are flexible in their
coordination to metal centers, adopting either nearly
coplanar or tilted pyridyl ring planes [16]. In contrast to
the detailed studies on the platinum(II)–BPY complexes,
little is known about the complexes of DPA ligand [17–
19]. Pt(II) and Pd(II) complexes with the formulas of
[MII(DPA)(AA)] and [MII(DPA)(pyc)]þ (AA, amino
acid anion; pyc, pyridine-2-carboxylate; MII, PdII and
PtII) have been reported [18,19], and some of them have
shown potential antitumor activity [18,19]. However, the
structure of these complexes is unknown.
In this work, we have synthesized and structurally
characterized in the solid state two Pt(II)–DPA com-
plexes with both chloride or 1,1-cyclobutanedicarbox-
late (CBDCA) as leaving groups (complexes 1 and 2,
shown in Fig. 1). The potential DNA-binding property
of the complexes was investigated using the model
* Corresponding author. Tel.: +86-25-3594549; fax: +86-25-3314502.
E-mail address: zguo@netra.nju.edu.cn (Z. Guo).
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0020-1693(03)00389-X

96
C. Tu et al. / Inorganica Chimica Acta 357 (2004) 95–102
[Pt(dmso)2Cl2] in 50 ml methanol. The mixture was
refluxed overnight and the solvent was removed under
reduced pressure. The resulting [Pt(dpa)Cl2] was washed
three times with 20 ml water and 5 ml acetone and dried
in vacuo. The yield was 0.355 g for compound 1 (81%).
Anal. Calc. for C10H9Cl2N3Pt (437.18): C, 27.47; H,
2.07; N, 9.61. Found: C, 27.51; H, 2.05; N, 9.59%. Se-
lected IR data (cmꢁ1): 3474 (w), 3281 (s), 3088 (m), 1633
(s), 1584 (s), 1476 (s), 1234 (s), 766 (s), 533 (s). ES-MS m/
z: 436 [Mꢁ], 873 [2M]ꢁ.
Fig. 1. Schematic representation of [Pt(dpa)Cl2] (1) and [Pt(dpa)CBD-
CA] (2).
compound guanosine-50-monophosphate (50-GMP) and
calf thymus (CT) DNA. The cytotoxic activity against
melanoma B16-BL6 cells and human Jurkat T-cells was
also reported.
2.2.2. Pt(dpa)CBDCA (2)
This was synthesized in a way similar to 1, and
[Pt(dmso)2Cl2] was replaced by 0.493 g (1 mmol) of
[Pt(dmso)2CBDCA]. Yield: 83%. Anal. Calc. for
C16H15N3O4Pt (508.39): C, 37.80; H, 2.97; N, 8.27.
Found: C, 37.82; H, 2.98; N, 8.28%. Selected IR data
(cmꢁ1): 3473 (w), 3027 (m), 1654 (s), 1604 (m), 1487 (s),
1369 (s), 1116 (s), 765 (m), 535 (m). ES-MS m/z: 509
[Mþ], 531 [M + Naþ], 1039 [2M + Naþ].
2. Experimental
2.1. Starting materials and physical methods
Solvents such as methanol and acetone were all an-
alytical reagents and used as received. The K2[PtCl6]
was purchased from the First Reagent Factory of
Shanghai, 2,20-dipyridylamine (DPA) from Fluka, di-
sodium salt of 50-GMP and CT DNA from Sigma. The
K2[PtCl4] was synthesized by the reduction of K2[PtCl6]
using hydrazine following the standard procedure [20].
[Pt(dmso)2Cl2] and [Pt(dmso)2CBDCA] were prepared
according to the literature procedures [21,22].
2.2.3. Pt(dpa)(NO3)2 (3)
To a suspension of 0.200 g (0.46 mmol) [Pt(dpa)Cl2]
in 15 ml water was added 0.153 g (0.9 mmol) AgNO3.
After the suspension has been stirred for 8 h at 50 °C in
the dark, the solution was cooled to room temperature.
The resulting AgCl precipitate was removed by centri-
fugation and the filtrate was lyophilized overnight.
2.3. Reaction of complex 3 with 50-GMP
The infrared spectra were recorded on a Bruker
VECTOR22 spectrometer as KBr pellets (4000–500
cmꢁ1). Elemental analysis was performed on a Perkin–
Elmer 240C analytical instrument.
The [Pt(dpa)(NO3)2] with 2 mol equiv. of 50-GMP
(0.005 mmol) were added to 0.5 ml aqueous solution, the
mixture was incubated at 37.8 °C in the dark for 24 h
before the ES-MS spectra being recorded.
Electrospray mass spectra were recorded using an
LCQ electron spray mass spectrometer (ES-MS, Finni-
gan) by loading 1.0 ll of solution into the injection valve
of the LCQ unit and then injecting into the mobile phase
solution (50% of aqueous methanol) that was carried
through the electrospray interface into the mass analyzer
at a rate of 200 ll minꢁ1. The voltage employed at the
electrospray needles was 5 kV, and the capillary was
heated to 200 °C. A maximum ion injection time of 200
ms along with 10 scans was set. Positive and negative ion
mass spectra were obtained. The predicted isotope dis-
tribution patterns for each of the complexes were cal-
culated using the Isopro 3.0 program [23].
2.4. DNA-binding studies
Solutions of CT DNA in 50 mM NaCl/5 mM Tris–
HCl (pH 7.3) gave a ratio of UV absorbance at 260 and
280 nm, A260/A280, of 1.8–1.9, indicating that the DNA
was sufficiently free of protein [24]. Concentrated stock
solution of DNA was prepared in 5 mM Tris–HCl/50
mM NaCl in water, pH 7.3, and the concentration of
DNA was determined by UV absorbance at 260 nm
after 1:100 dilutions. The molar absorption coefficient
was taken as 6600 Mꢁ1 cmꢁ1 [25]. Stock solutions were
stored at 4 °C and used after no more than 4 days.
Complex 1 was dissolved in a mixed solution of 50%
DMSO and 50% buffer (5 mM Tris–HCl/50 mM NaCl)
at a concentration of 1.7 ꢂ 10ꢁ3 M and incubated for 2 h
at room temperature before the DNA was added. The
concentration of complex 1 was eventually reduced to
10ꢁ5 M while adding the calculated amounts of DNA
(10ꢁ5 M, r ¼ 0:5) and the final volume of the solutions
were fixed to 3 ml. The UV–Vis spectra was recorded
UV–Vis spectra were recorded on a UV-3100 spec-
trometer. Fluorescent spectra were recorded on a AM-
INCO Bowman Series 2 Luminescence Spectrometer.
2.2. Preparation of compounds
2.2.1. Pt(dpa)Cl2 (1)
A solution of 0.171 g (1 mmol) DPA in 10 ml of
methanol was added to a solution of 0.422 g (1 mmol)

C. Tu et al. / Inorganica Chimica Acta 357 (2004) 95–102
97
after 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 h, respectively. It has
been verified that the low DMSO percentage added to
the DNA solution would not interfere with the nucleic
acid [26].
The fluorescent spectra (kex ¼ 526 nm, kem ¼ 600 nm)
were also recorded at room temperature and the samples
of complexes 1 and 2 were prepared in a similar way
described above. The experiments were carried out by
titrating the solution of platinum complexes (20 ll per
scan) to the samples containing 2.45 ꢂ 10ꢁ5 M of DNA
and 2.45 ꢂ 10ꢁ5 M EB (ethidium bromide).
full-matrix least-squares method on F2obs by using
the SHELXTL [30] software package. All non-H at-
oms were anisotropically refined. The molecular
graphics were created using SHELXTL. Atomic scat-
tering factors and anomalous dispersion correction
were taken from the International Table for X-ray
Crystallography [31].
3. Results and discussion
3.1. X-ray structure of complexes 1 and 2
2.5. Cytotoxicity assays
The crystal data, data collection, structural solution
and refinement parameters for complexes 1 and 2 are
summarized in Table 1. Selected bond distances and
angles are listed in Tables 2 and 3, respectively.
Fig. 2 shows an ellipsoid plot with the numbering
scheme of the complex 1. The platinum is square-planar
and coordinated by two nitrogen atoms from the che-
lating bidentate ligand (DPA) and two chloride atoms.
The mean deviation from the best PtN2Cl2 plane is
Melanoma B16-BL6 tumor cells and human Jurkat
T-cells were grown in RPMI 1640 medium supple-
mented with 10% freshly inactivated fetal calf serum
(FCS) and antibiotics. The solutions of complexes 1 and
2 were freshly prepared with the RPMI 1640 medium,
and diluted to the required concentration with culture
medium when used. The cells harvested from exponen-
tial phase were planted equivalently into a 96-well plate
(2 ꢂ 105 per ml, 100 ll per well); then the compounds
studied were added in a concentration gradient to give
ꢀ
ꢀ
0.0167 A. The average Pt–Cl distance is 2.2968 A (Pt1–
ꢀ
ꢀ
Cl1 2.3010 A; Pt1–Cl2 2.2925 A). The bond length of
Pt–N is in the expected region for a Pt(II)–pyridyl ni-
trogen bond [32]. In the coordination sphere all angles
are near the idealized value of 90°. The largest deviation
appears for the angle N2–Pt1–N3 which is 88.68(18)°.
The angle of C1–N1–C6 is 127.3(5)° and the dihedral
angle between the two best least-squares planes through
the two pyridyl rings amounts to 147.6°. Intermolecular
hydrogen bonds (N–Hꢀ ꢀ ꢀCl, symmetry code ½x ꢁ 1=2;
ꢁy þ 1=2; z ꢁ 1=2ꢃ) were observed in the crystal, with
final concentrations at 1 ꢂ 10ꢁ4, 1 ꢂ 10ꢁ5, 1 ꢂ 10ꢁ6
,
1 ꢂ 10ꢁ7 and 1 ꢂ 10ꢁ8 M, respectively. The plates were
kept at 37 °C in a humidified atmosphere of 5% CO2 and
incubated for 72 h respectively; then MTT [3-(4,5-di-
methyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium
bro-
mide] solution of an appropriate concentration (2 mg/
ml) was added to each well (40 ll) and the plates incu-
bated at 37 °C for 4 h. The measurements of absorbance
of the solutions related to the number of live cells were
performed on an ELISA spectrophotometer at 540 nm
[27].
ꢀ
the hydrogen bond length being 2.421 A. The angle
between N–Hꢀ ꢀ ꢀCl is 168.77°.
As can be seen from Fig. 3, the platinum in complex 2
is coordinated by two equivalent pyridyl nitrogen atoms
[N2 and N3] of DPA and two carboxyl oxygen atoms
[O5 and O6] of CBDCA. The Pt(II) has the expected
square planar geometry exhibiting the usual structure
parameters. The mean deviation of the best PtN2O2
2.6. Crystallization
Crystallization of [Pt(dpa)Cl2] and [Pt(dpa)CBDCA]
were achieved by slow evaporation of their mother so-
lution. After 3 days, yellow crystals (for compound 2,
colorless) suitable for X-ray structure analysis were
obtained.
ꢀ
plane is 0.0296 A. The CBDCA ligand displays similar
features to those described in the literature [33–36]. The
two six-membered chelate rings which the ligand DPA
and CBDCA formed with the Pt(II) atom adopts the
boat conformation (Fig. 4) and the cyclobutane ring is
nearly perpendicular to the Pt(II) coordination plane.
The cyclobutane ring can adopt either a planar geome-
try or can have a puckered conformations. In the case of
carboplatin, a large thermal parameters for C16 (0.101)
was observed, which was attributed to the dynamic
puckering between two conformations [37]. The angle of
C1–N1–C6 is 130.3(8)° and the dihedral angle between
the two best pyridyl rings is 159.2° which is 11.6° larger
than that appeared in complex 1. The bonds lengths
between Pt(II) and oxygen atoms of CBDCA, in
2.7. Crystal structure determination
The raw data of complexes 1 and 2 were collected
on a Siemens SMART CCD diffractometer. Reflection
data were measured at 20 °C using graphite mono-
ꢀ
chromated Mo Ka (k ¼ 0:71073 A) radiation with a
detector distance of 4 cm and swing angle of )35°.
The collected data were reduced using the program
SAINT [28] and empirical absorption correction was
carried out using SADABS [29] program. The structure
was solved by direct methods that revealed the posi-
tion of all non-hydrogen atoms and refined using the

98
C. Tu et al. / Inorganica Chimica Acta 357 (2004) 95–102
Table 1
Crystal data and structure refinement for complexes 1 and 2
Complex 1
10H9Cl2N3Pt
437.19
Complex 2
Empirical formula
Formula weight
Temperature (K)
Crystal size (mm)
Crystal habit/color
Crystal system
C
C16H15N3O4Pt
508.40
293(2)
293(2)
0.20 ꢂ 0.18 ꢂ 0.18
block/yellow
monoclinic
P2ð1Þ=n
0.18 ꢂ 0.16 ꢂ 0.15
block/colorless
triclinic
Space group
ꢀ
P-1
a (A)
9.9720(11)
10.1771(12)
1.7846(13)
90
9.1181(15)
9.6844(17)
10.0948(17)
68.377(3)
ꢀ
b (A)
ꢀ
c (A)
a (°)
b (°)
c (°)
94.239(2)
90
67.353(3)
70.401(3)
745.1(2)
3
ꢀ
V (A )
1192.7(2)
4
2.435
Z
2
2.266
Calculated density (Mg mꢁ3
)
Absorption coefficient (mmꢁ1
)
12.186
808
9.444
484
F ð000Þ
h range for data collection (°)
Limiting indices
2.58–27.06
ꢁ10 6 h 6 12, ꢁ13 6 k 6 10,
ꢁ15 6 l 6 13
6687
2.27–28.07
ꢁ11 6 h 6 12, ꢁ12 6 k 6 10,
ꢁ13 6 l 6 13
4524
Reflections collected
Independent reflections
Absorption correction
Data/restraints/parameters
Goodness-of-fit on F 2
2589
3339
empirical
empirical
2589/0/145
0.970
3339/0/217
0.941
0.0361
a
Rint
0.0410
Final R indices ½I > 2rðIÞꢃ
R1 ¼ 0:0326b
wR2 ¼ 0:0736c
R1 ¼ 0:0387, wR2 ¼ 0:0750
2.815 and )1.614
R1 ¼ 0:0477,
wR2 ¼ 0:0873
R1 ¼ 0:0638, wR2 ¼ 0:0904
2.967 and )1.642
R indices (all data)
Largest difference peak and hole (e A )
3
ꢀ
P
P
a Rint
¼
jFo2 ꢁ Fo2ðmeanÞj= ½Fo2ꢃ.
P
P
b R ¼ jFoj ꢁ jFcj= jFoj.
P
P
2
2 1=2
c Rw ¼ ½ wðjFoj ꢁ jFcjÞ = wðjFojÞ ꢃ
.
Table 2
3.2. ES-MS study
ꢀ
Selected bond lengths (A) and angles (°) of complex 1
Bond lengths
The ES-MS spectrum for the reaction of complex 3
with 2 mol equiv. of 50-GMP was recorded after 24 h at
37.8 °C in aqueous solution (Fig. 5). As can be seen
from Fig. 5, apart from some unreacted 50-GMP which
give rise to peaks at 724.9 [2GMP]ꢁ and 746.9
[2GMP + Na]ꢁ, the major peaks at 1088.8 and 1452.7
can be assigned to [Pt(dpa)(GMP)2]ꢁ and [Pt(dpa)
(GMP)2 + GMP]ꢁ. The calculated molecular masses and
the isotopic distribution of these peaks matched per-
fectly with the corresponding formulas. The formation
of [Pt(dpa)(GMP)2 + GMP]ꢁ may be due to the high
temperature and pressure in the capillary of the spec-
trometer, and similar association of GMP has been
observed previously [32].
Pt(1)–N(2)
Pt(1)–N(3)
Pt(1)–Cl(2)
Pt(1)–Cl(1)
2.010(4)
2.012(4)
2.2925(15)
2.3010(15)
Bond angles
N(2)–Pt(1)–N(3)
N(2)–Pt(1)–Cl(2)
N(3)–Pt(1)–Cl(2)
N(2)–Pt(1)–Cl(1)
N(3)–Pt(1)–Cl(1)
Cl(2)–Pt(1)–Cl(1)
C(6)–N(1)–C(1)
88.68(18)
177.35(12)
90.87(14)
90.95(13)
177.02(13)
89.37(6)
127.3(5)
ꢀ
ꢀ
complex 2, are 2.005(6) A [Pt1–O2] and 2.011(6) A [Pt1–
O1], respectively.
3.3. UV monitored time-dependent reaction of complex 1
with CT DNA
The intermolecular hydrogen bonds (N–Hꢀ ꢀ ꢀO,
symmetry code ½x; y ꢁ 1; zꢃ) are also found in the
crystal of complex 2, the hydrogen bond length is 2.163
The time-dependent absorption spectra of complex 1
(2.27 ꢂ 10ꢁ5 M) in the absence and presence of CT DNA
ꢀ
A and the angle between N–Hꢀ ꢀ ꢀO is 139.54°.

C. Tu et al. / Inorganica Chimica Acta 357 (2004) 95–102
99
Table 3
ꢀ
Selected bond lengths (A) and angles (°) of complex 2
Bond lengths
Pt(1)–N(2)
Pt(1)–N(3)
Pt(1)–O(2)
Pt(1)–O(1)
O(1)–C(11)
O(2)–C(12)
O(3)–C(11)
O(4)–C(12)
C(13)–C(15)
C(13)–C(14)
C(14)–C(16)
C(15)–C(16)
1.978(7)
1.997(7)
2.005(6)
2.011(6)
1.291(11)
1.327(11)
1.209(10)
1.220(11)
1.560(13)
1.559(12)
1.500(14)
1.510(15)
Fig. 3. Molecular structure and labeling of complex 2. Ellipsoids are
drawn at the 30% probability level.
Bond angles
N(2)–Pt(1)–N(3)
N(2)–Pt(1)–O(2)
N(3)–Pt(1)–O(2)
N(2)–Pt(1)–O(1)
N(3)–Pt(1)–O(1)
O(2)–Pt(1)–O(1)
C(11)–O(1)–Pt(1)
C(12)–O(2)–Pt(1)
C(6)–N(1)–C(1)
C(1)–N(2)–Pt(1)
C(5)–N(2)–Pt(1)
C(6)–N(3)–Pt(1)
C(10)–N(3)–Pt(1)
C(15)–C(13)–C(14)
C(16)–C(14)–C(13)
C(16)–C(15)–C(13)
C(14)–C(16)–C(15)
91.4(3)
177.1(3)
90.3(3)
88.6(3)
178.3(3)
89.8(3)
122.8(6)
121.4(6)
130.3(8)
123.9(6)
120.8(6)
122.5(6)
118.2(6)
88.4(7)
Fig. 4. Two possible relative orientations for the CBDCA and the dpa
ligand in complex 2. The conformation on the left (cis) is adopted in
complex 2.
89.7(8)
89.3(8)
92.5(8)
interaction between complex 1 and DNA. A similar
behavior was previously observed for copper complexes
[38–40], where the hyperchromism was attributed to the
dissociation of ligand aggregates and the breakage of
intermolecular hydrogen bonds when bound to DNA.
The exact mode of interaction remains to be defined.
Complex 2 does not show significant time-dependent
changes in the presence of DNA.
3.4. Fluorescence spectroscopic studies
The fluorescent emission of EB bound to DNA in the
absence and the presence of complexes 1 and 2 are
shown in Fig. 7. The emission band at 600 nm of the
DNA–EB system decreased in intensity with the increase
of the concentration of the two Pt(II) complexes, which
indicated that the complexes can replace EB from the
DNA–EB system. Such a characteristic change is often
observed in the intercalative DNA interaction [40]. The
data suggest that intercalation may be an alternative
binding mode for complexes 1 and 2 due to the planarity
of the DPA rings.
Fig. 2. Molecular structure and labeling of complex 1. Ellipsoids are
drawn at the 30% probability level.
(5.67 ꢂ 10ꢁ5 M) is shown in Fig. 6. It is interesting to
find that the intensity of the absorption band at 301.5
nm which is attributed to the metal to the ligand charge
transfer absorption (MLCT) does not change signifi-
cantly with the time while the absorption around 272 nm
increased dramatically upon addition of CT DNA until
it reached a plateau after 3 h and a new band at 283 nm
appeared. This phenomenon can be an indication of the
3.5. Cytotoxic activity
The effects of both complexes 1 and 2 on Mela-
noma B16-BL6 tumor cells and human Jurkat T-cells

100
C. Tu et al. / Inorganica Chimica Acta 357 (2004) 95–102
Fig. 5. The ES-MS spectrum showing the reaction adducts of complex 4 with 50-GMP. The peaks at 1088.8 and 1452.7 were assigned to
[Pt(dpa)(GMP)2]ꢁ and [Pt(dpa)(GMP)2 + GMP]ꢁ, respectively. The solid line peaks on top right corner are calculated peaks for the two species.
8
1.5
(a)
6
1.0
283nm
301.5nm
4
2
0.5
275nm
272nm
270
0.0
240
560
580
600
620
640
660
680
300
330
360
390
Wavelength (nm)
Wavelength (nm)
Fig. 6. Time-dependent absorption spectra of complex 1 (5.7 ꢂ 10ꢁ5
mol lꢁ1) in the absence (dashed line) and presence (solid lines, repre-
sent 0.5, 1, 1.5, 2, 2.5 and 3 h, respectively) of a fixed amount of CT
DNA (2.3 ꢂ 10ꢁ5 mol lꢁ1) at room temperature.
8
6
4
2
(b)
proliferation after 72 h are reported in Fig. 8. Both
complexes exhibited considerable inhibition rates only
at high concentration (10ꢁ4 M). The change of leaving
groups (chloride or CBDCA) had no impact on the
activity. The data should be interpreted with care be-
cause at such a high concentration the cytotoxic effect of
the solvent (for 1, 0.67% DMSO; for 2, 1% DMF) began
to become relevant.
560
580
600
620
640
660
680
Wavelength (nm)
Fig. 7. Fluorescence emission spectra (excited at 526 nm) of EB bound
to CT DNA in the absence (dashed line) and presence (solid lines) of
increasing amounts of 1.7 ꢂ 10ꢁ3 mol lꢁ1 complex 1 (a) and 1.48 ꢂ 10ꢁ3
mol lꢁ1 complex 2 (b) (20 ll per scan).
4. Conclusion
This work provided two of the very few crystal
structures of Pt(II)–DPA complexes. It is shown that
changing the leaving group (chloride or CBDCA) on
Pt(II)–DPA system had little impact on the ring con-
formation of DPA. The pyridyl amine proton in com-
plexes 1 and 2 may favor their hydrogen bonding to
DNA and thus stabilizes the metal–DNA adducts
[18,19]. The DNA-binding mode of these complexes is

C. Tu et al. / Inorganica Chimica Acta 357 (2004) 95–102
[2] J. Reedijk, Chem. Commun. (1996) 801.
101
4
3
2
1
0
[3] Y. Kidani, K. Inagaki, R. Saito, S. Tsukagoshi, J. Clin. Hematol.
Oncol. 7 (1977) 197.
[4] V. Boudny, O. Vrana, F. Gaucheron, V. Kleinwachter, M. Leng,
V. Brabec, Nucleic Acids Res. 20 (1992) 267.
[5] Z. Guo, P.J. Sadler, Angew. Chem., Int. Ed. Engl. 38 (1999)
1512.
(a)
[6] E. Wong, C.M. Giandomenico, Chem. Rev. 99 (1999) 2451.
[7] J. Reedijk, Inorg. Chim. Acta 198 (1992) 873.
[8] G. Admiraal, J.L. van der Veer, R.A.G. de Graaff, J.H.J. den
Hartog, J. Reedijk, J. Am. Chem. Soc. 109 (1987) 592.
[9] S.E. Sherman, D. Gibson, A.H. Wang, S.J. Lippard, J. Am.
Chem. Soc. 110 (1988) 7368.
[10] S.T. Sullivan, A. Ciccarese, F.P. Fanizzi, L.G. Marzilli, J. Am.
Chem. Soc. 38 (2001) 9345.
1
2
4
-5
5
-6
6
-78
-34
-7
SOL
CTL
[11] M.J. Bloemink, R.J. Heetebrij, K. Inagaki, Y. Kidani, J. Reedijk,
Inorg. Chem. 31 (1992) 4656, and references therein.
[12] A. Gund, B.K. Keppler, Angew. Chem., Int. Ed. Engl. 33 (1994)
186.
Concentration of the Complexes ( lg M )
4
3
2
1
0
[13] L.K. Webster, G.B. Deacon, D.P. Buxton, B.L. Hillcoat, A.M.
James, I.A.G. Roos, R.J. Thomson, L.P.G. Wakelin, T.L.
Williams, J. Med. Chem. 35 (1992) 3349.
[14] M.J. Bloemink, H. Engelking, S. Karentzpoulos, B. Krebs, J.
Reedijk, Inorg. Chem. 35 (1996) 619.
(b)
[15] T. Okada, I.M. El-Mehasseb, M. Kodaka, T. Tomohiro, K.
Okamoto, H. Okuno, J. Med. Chem. 44 (2001) 4661.
[16] R.E. Shepherd, Y. Chen, R.A. Kortes, M.S. Ward, Inorg. Chim.
Acta 303 (2000) 30.
[17] R. Romeo, N. Nastasi, L.M. Scolaro, M.R. Plutino, A. Albinati,
A. Macchioni, Inorg. Chem. 37 (1998) 5460, and references
therein.
[18] A.K. Paul, H. Mansuri-Torshizi, T.S. Srivastava, S.J. Chavan, M.
Chitnis, J. Inorg. Biochem. 50 (1993) 9.
1
2
4
-5
5
-6
6
-34
-7
-78
SOL
CTL
Concentration of the Complexes ( lg M )
[19] A.K. Paul, T.S. Srivastava, S.J. Chavan, M.P. Chitnis, S. Desai,
K.K. Rao, J. Inorg. Biochem. 61 (1996) 179.
Fig. 8. Cytotoxic activity of complexes 1 (j) and 2 (N) against selected
tumor cell lines: Melanoma B16-BL6 tumor cells (a) and human Jurkat
T-cells (b). The solvent contains the maximum concentration of
DMSO/DMF used to dissolve tested compounds.
[20] G.B. Kaufmann, D.O. Cowan, Inorg. Synth. 7 (1963) 240.
[21] J.H. Price, A.N. Williamson, R.F. Shramm, B.B. Wayland, Inorg.
Chem. 11 (1972) 1280.
[22] P. Bitha, G.O. Morton, T.S. Dunne, E.F. Delos Santos, Y. Lin,
S.R. Boone, R.C. Haltiwanger, C.G. Pierpont, Inorg. Chem. 29
(1990) 645.
currently uncertain, spectroscopic data suggest that the
compounds may be able to interact with DNA by
groove binding or intercalation, although ES-MS study
indicated the formation of covalent binding adduct of
complex 1 and 50-GMP. The in vitro tests show that the
cytotoxicity of these complexes against Melanoma B16-
BL6 tumor cells and human Jurkat T-cells does not
warrant further biological testing. We are currently
carrying out studies on other novel heterocyclic Pt(II)
complexes so as to find more active species of the type.
[23] J.A. Yergey, Int. J. Mass Spec. Ion Phys. 52 (1983) 337.
[24] J. Marmur, J. Mol. Biol. 3 (1961) 208.
[25] M.E. Reichmann, S.A. Rice, C.A. Thomas, P. Doty, J. Am.
Chem. Soc. 76 (1954) 3047.
[26] M. Baldini, M. Belicchi-Ferrai, F. Bisceglie, G. Pelosi, S. Pinelli,
P. Tarasconi, Inorg. Chem. 42 (2003) 2049.
[27] T. Mosmann, Immunol. Methods 65 (1983) 55.
[28] G.M. Sheldrick, SAINT v4 Software Reference Manual, Siemens
Analytical X-Ray Systems, Madison, WI, 1996.
[29] G.M. Sheldrick, SADABS, Program for Empirical Absorption
Correction of Area Detector Data, University of Gottingen,
Germany, 1996.
[30] G.M. Sheldrick, SHELXTL, v5 Reference Manual, Siemens Ana-
lytical X-Ray Systems, Madison, WI, 1996.
Acknowledgements
[31] A.J. Wilson, International Table for X-Ray Crystallography, vol.
C, Kluwer Academic Publishers, Dordrecht, 1992 (Tables 6.1.1.4
(p.500) and 4.2.6.8 (p.219), respectively).
We are grateful for the financial support of the Na-
tional Natural Science Foundation of China (Grant
Nos. 29925102, 20231010 and 20228102).
[32] Z. Guo, A. Habtemariam, P.J. Sadler, R. Palmer, B.S. Potter,
New J. Chem. 22 (1998) 11.
[33] J.Y. Zhang, Q. Liu, C. Duan, Y. Shao, J. Ding, Z. Miao, X.-Z.
You, Z. Guo, J. Chem. Soc., Dalton Trans. (2002) 591.
[34] M.S. Ali, J.H. Thurston, K.H. Whitmire, A.R. Khokhar, Poly-
hedron 21 (2002) 2659.
References
[35] A.D.Q. Ferreira, A. Bino, D. Gibson, Inorg. Chim. Acta 265
(1997) 155.
[36] S. Neidle, I.M. Ismail, P.J. Sadler, J. Inorg. Biochem. 13 (1980) 205.
[1] B. Lippert (Ed.), Cisplatin: Chemistry and Biochemistry of a
Leading Anticancer Drug, Wiley-VCH, Weinhein, 1999.

102
C. Tu et al. / Inorganica Chimica Acta 357 (2004) 95–102
[37] B. Beagley, D.W.J. Cruickshank, C.A. McAuliffe, R.G. Pritchard,
A.M. Zaki, R.L. Beddoes, R.J. Cernik, O.S. Mills, J. Mol. Struct.
130 (1985) 97.
[39] J. Liu, T.X. Zhang, T.B. Lu, L.H. Qu, H. Zhou,
Q.L. Zhang, L.N. Ji, J. Inorg. Biochem. 91 (2002)
269.
[40] C.V. Kumar, J.K. Barton, N.J. Turro, J. Am. Chem. Soc. 107
(1985) 5518.
[38] F. Liu, K.A. Meadows, D.R. McMillin, J. Am. Chem. Soc. 115
(1993) 6699.