Synthesis, characterization, crystal structure, and biological activities of transition metal complexes with 1-phenyl-3-methyl-5-hydroxypyrazole-4- methylene-8′-quinolineimine

Article abstract of DOI:10.1002/zaac.201200475

The Schiff base ligand, 1-phenyl-3-methyl-5-hydroxypyrazole-4-methylene- 8′-quinolineimine, and its Cu^II, Zn^II, and Ni ^II complexes were synthesized and characterized. The crystal structure of the Zn^II complex was determined by single-crystal X-ray diffraction, indicating that the metal ions and Schiff base ligand can form mononuclear six-coordination complexes with 1:1 metal-to-ligand stoichiometry at the metal ions as centers. The binding mechanism and affinity of the ligand and its metal complexes to calf thymus DNA (CT DNA) were investigated by UV/Vis spectroscopy, fluorescence titration spectroscopy, EB displacement experiments, and viscosity measurements, indicating that the free ligand and its metal complexes can bind to DNA via an intercalation mode with the binding constants at the order of magnitude of 105-106 M^-1, and the metal complexes can bind to DNA more strongly than the free ligand alone. In addition, antioxidant activities of the ligand and its metal complexes were investigated through scavenging effects for hydroxyl radical in vitro, indicating that the compounds show stronger antioxidant activities than some standard antioxidants, such as mannitol. The ligand and its metal complexes were subjected to cytotoxic tests, and experimental results indicated that the metal complexes show significant cytotoxic activity against lung cancer A 549 cells. Copyright

Full text of DOI:10.1002/zaac.201200475

ARTICLE
DOI: 10.1002/zaac.201200475
Synthesis, Characterization, Crystal Structure, and Biological Activities of
Transition Metal Complexes with 1-Phenyl-3-methyl-5-hydroxypyrazole-4-
methylene-8Ј-quinolineimine
Xiao-Ying Cheng,[a] Ming-Fang Wang,[a] Zheng-Yin Yang,*[a] Yong Li,[a,b] Zeng-
Chen Liu,[a] and Qiao-Xia Zhou[a]
Keywords: Schiff bases; Metal complexes; Crystal structure; DNA binding; Antioxidants
Abstract. The Schiff base ligand, 1-phenyl-3-methyl-5-hydroxypyr-
azole-4-methylene-8Ј-quinolineimine, and its CuII, ZnII, and NiII com-
DNA via an intercalation mode with the binding constants at the order
of magnitude of 105–106 m–1, and the metal complexes can bind to
plexes were synthesized and characterized. The crystal structure of DNA more strongly than the free ligand alone. In addition, antioxidant
the ZnII complex was determined by single-crystal X-ray diffraction, activities of the ligand and its metal complexes were investigated
indicating that the metal ions and Schiff base ligand can form mononu- through scavenging effects for hydroxyl radical in vitro, indicating that
clear six-coordination complexes with 1:1 metal-to-ligand stoichiome-
try at the metal ions as centers. The binding mechanism and affinity
of the ligand and its metal complexes to calf thymus DNA (CT DNA)
were investigated by UV/Vis spectroscopy, fluorescence titration spec-
troscopy, EB displacement experiments, and viscosity measurements,
indicating that the free ligand and its metal complexes can bind to
the compounds show stronger antioxidant activities than some standard
antioxidants, such as mannitol. The ligand and its metal complexes
were subjected to cytotoxic tests, and experimental results indicated
that the metal complexes show significant cytotoxic activity against
lung cancer A 549 cells.
the most important one, because small molecules binding to
DNA via intercalation often have potential anticancer activi-
ties. Such complexes have been investigated during the past
several decades.[11]
Introduction
Cisplatin (cis-diamminedichloroplatinum(II)) is currently
the most widely used and effective anticancer drug against a
variety of human tumors.[1] Unfortunately, the development of
a resistance in tumor cells and its significant side effects have
greatly limited its general use in the biomedical field.[2,3] The
anticancer effect of drugs such as cisplatin are caused by their
affinity and strength to interact with DNA, and the design of
metal complexes with low toxicity, improved therapeutic prop-
erties and strong interaction with DNA has quickly devel-
oped.[4,5] DNA contains all the genetic information for cellular
function.[6]. Metal complexes are known to bind to DNA via
both covalent and non-covalent interactions. In covalent bind-
ing, ligands of the metal complexes are replaced by nitrogen
bases of DNA such as guanine N6.[7,8] Non-covalent DNA in-
teractions include intercalative, electrostatic and groove (sur-
face) binding of cationic metal complexes along the outside of
Pyrazolone and its derivatives have attracted scientific atten-
tion because of their structures and application in diverse
areas.[12–15] A great number pyrazolone-based complexes were
synthesized since they were easy to prepare and known to dis-
play diverse pharmacological properties, such as antibacterial,
antitumor, antiseptic,[16–18] and inhibition of human te-
lomerase.[19] In addition, Schiff-bases are able to inhibit the
growth of several animal tumors, so it is necessary and valu-
able to design and prepare a pyrazolone derivative Schiff base
ligand.[20] Furthermore, reactive oxygen species (ROS) are
generated by normal cellular metabolism and by exogenous
agents. Even though ROS may serve as cell signaling or bacte-
ricidal agents, excess ROS can cause damage to cellular mac-
the DNA helix.[9,10] Among these interactions, intercalation is romolecules such as polyunsaturated lipids, protein, and DNA,
leading to a process called oxidative stress.[21] Oxidative stress
* Prof. Dr. Z.-Y. Yang
is implicated in the development of many diseases such as
Fax: +86-931-8912582
E-Mail: yangzy@lzu.edu.cn
macular degeneration, cardiacdisease, drug-associated toxicity,
inflammation, atherogenesis, and premature aging.[22–24] The
potential value of antioxidants has already prompted scientists
to search for the cooperative effects of compounds for im-
proving antioxidant activity and cytotoxicity.
Herein, the pyrazolone-based Schiff base ligand, 1-phenyl-
3-methyl-5-hydroxypyrazole-4-methylene-8Ј-quinolineimine
and its CuII, ZnII, and NiII complexes were synthesized and
[a] State Key Laboratory of Applied Organic Chemistry
College of Chemistry and Chemical Engineering
Lanzhou University
Lanzhou 730000, P. R. China
[b] Faculty of Material Science and Chemistry
China University of Geosciences
Wuhan 430074,China
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201200475 or from the au-
thor.
832
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 639, (5), 832–841

Transition Metal Complexes with a Schiff base ligand
–
characterized. Comparative studies of the free ligand and its the coordinated NO3 ion in the transition metal complexes is
transition metal complexes binding to DNA were investigated. a bidentate ligand.[28]
Furthermore, antioxidant activities of the ligand and its transi-
The study of the electronic spectra in the ultraviolet and
tion metal complexes were studied by the scavenging hydroxyl visible ranges of the free ligand and its transition metal com-
radical method. The cytotoxic activities were also evaluated by plexes were carried out in tris-HCl buffer solution. The elec-
cytotoxic tests on lung cancer A 549 cells. Our research should tronic spectra of free ligand have a strong band at 380 nm. For
be valuable for seeking and designing new antitumor drugs the transition metal complexes, a new absorption band at about
and antioxidants, as well as for understanding the mechanism 320 nm yields and the band at 380 nm are red-shifted to
of compounds binding to DNA and helical conformation of 394 nm. This indicates that the transition metal complexes
nucleic acids.
were formed by the reaction of the ligand and transition metal
ions.
Crystals of 2 were obtained by slow vapor diffusion of
CH3OH/Et2O at room temperature. Compound 2 crystallizes
in the monoclinic lattice with space group P21/n. Each unit
cell contains four molecules. The X-ray diffraction data for 2
are given in Table 1 and selected bond lengths and angles are
summarized in Table 2. The crystal structure of 2 is shown in
Figure 1. In 2, the zinc atom is hexacoordinated by the ligand,
one nitrate ion, and one coordinated water molecule. The
Schiff base ligand acts in a tridentate fashion, binding to the
zinc atom through the oxygen atom from the hydroxyl group,
two nitrogen atoms from the C=N group and the quinoline
group, forming a five- and a six-membered chelate ring with
N1–Zn1–N2 and O1–Zn1–N2 bite angles of 171.97(12)° and
94.49(10)°, respectively. The dihedral angle of the O1–Zn–N2
plane and N1–Zn–N2 plane is 174.51°, which is approximately
Results and Discussion
Characterization of Metal Complexes
The transition metal complexes [Cu(L)(H2O)(NO3)] (1),
[Zn(L)(H2O)(NO3)] (2) and [Ni(L)(H2O)(NO3)] (3) were pre-
pared with the ligand, 1-phenyl-3-methyl-5-hydroxypyrazole-
4-methylene-8Ј-quinolineimine (HL), and equimolar amounts
of M(NO3)2·nH2O (M = Cu, n = 3; M = Zn, n = 6; M = Ni,
n = 3).The complexes were easily soluble in DMF and DMSO;
slightly soluble in ethanol, acetone, methanol, and chloroform;
insoluble in water, benzene, and ethyl ether. The melting points
of the three transition metal complexes all exceed 300 °C. The
molar conductivities of the transition metal complexes in DMF
solution were in the range of 6.3–13.6 S·cm2·mol–1, indicating
that all compounds are non-electrolytes.[25] Elemental analyses
indicate that the complexes are of 1:1 metal-to-ligand
stoichiometry.
Table 1. Crystal data and experimental data of 2.
ZnL·NO3·H2O
IR spectroscopy usually provides valuable information on
the coordination modes of the ligand and metal ions. The IR
spectra of the transition metal complexes indicate similarity of
the structures of the complexes. In the ZnII complex, the zinc
ion is coordinated with the free ligand, a water molecule, and
a nitrate ion. The complex must be neutral, whereas the zinc
ion is divalent and the nitrate is a negative univalent ion, so
the OH group must be deprotonated. The ν(OH) of the free
ligand can be observed at 3441 cm–1, whereas for the transition
metal complexes the bands were around 3433cm–1 (for 3 it
was 3413 cm–1), showing that there was a water molecule
bonded and coordinated to the metal cation. In addition, the
weak bands at about 691 cm–1 for the metal complexes were
assigned to ν(M–O), indicating that the oxygen atom from OH
group coordinated with the metal ions.[26] The band at
1670 cm–1 for the free ligand is assigned to ν(C=N) stretch,
which shifted to 1630 cm–1 or so for the transition metal com-
plexes. In addition, the band at 1633 cm–1 for the free ligand
is assigned to the C=N vibration of quinoline group, and for
the metal complexes, the vibration is shifted to about
1596 cm–1. Weak bands at ca. 511 cm–1 are caused by the
ν(M–N) vibrations, indicating that the metal ions is coordi-
nated with nitrogen atoms from the C=N group.[27] The
stretches at 603 cm–1 for the metal complexes are assigned to
the coordinated water molecules. The absorption bands of the
coordinated nitrates were observed at about 1498 (νas) and
831 (νs) cm–1. The separation of the two highest frequency
bands |ν4 – ν1| is at approximately 190 cm–1 and accordingly
Chemical formula
Formula weight
Crystal color
Crystal size /mm
Temperature /K
Wavelength /Å
Radiation
Crystal system
Space group
Z
C20H17N5O5Zn
472.76
colorless
0.25ϫ0.24ϫ0.21
296(2)
0.71073
Mo-Kα
monoclinic
P21/n
4
a /Å
b /Å
c /Å
α /°
β /°
γ /°
9.036(2)
13.917(4)
15.964(4)
90.00
100.265(3)
90.00
1975.4(9)
1.590
1.288
Volume /Å3
D (Calc) /g·cm–3
μ /mm–1
F (000)
θmin/max /°
Index ranges
968
2.42–24.34
–10 Յ h Յ 10
–16 Յ k Յ 10
–19 Յ l Յ 19
10512
3649(Rint = 0.0532)
0.7389 and 0.7737
Full matrix least-squares on F2
2350 / 0 / 289
1.037
Reflections collected
Independent reflections
Max. and min. transmission
Refinement method
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [IϾ2σ (I)]
R indices (all data)
R1 = 0.0422, wR2 = 0.0893
R1 = 0.0884, wR2 = 0.0748
Z. Anorg. Allg. Chem. 2013, 832–841
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
833

Z.-Y. Yang et al.
ARTICLE
Table 2. Selected bond lengths /Å and angles /° for 2.
equal to 180°, indicating that N1,N2,O1 are almost in the same
plane. We conclude that the complex owns a good planarity.
The bond lengths of Zn1–O1, Zn1–N1, Zn1–N2 were
2.008(2) Å, 2.104(3) Å, and 2.053(3) Å, respectively. In ad-
dition, the nitrate ion was coordinated with the zinc atom as a
bidentate ligand and the free water molecule was coordinated
with the zinc atom as a monodentate ligand. The distances of
Zn1–O3 and Zn1–O4 were 2.148(3) and 2.485(4) Å, respec-
tively, and the bond angle of O3–Zn1–O4 was 54.03(11)°. In
addition, the bond length of Zn1–O2 is 2.049(3) Å. According
to the above crystal data, we found the bond lengths of the
zinc atom with the coordinated nitrogen atoms or oxygen
atoms were almost similar, indicating their coordinating abili-
ties differs subtlety.
Zn1–O1
2.008(2)
Zn1–O2
2.049(3)
2.104(3)
2.053(3)
91.11(13)
91.54(10)
149.26(12)
94.49(10)
91.29(11)
99.82(12)
54.03(11)
Zn1–O4
2.485(4)
Zn1–N1
Zn1–O3
2.148(3)
Zn1–N2
N1–Zn1–O4
N2–Zn1–N1
O2–Zn1–O3
O1–Zn1–N1
O2–Zn1–N2
N2–Zn1–O3
O1–Zn1–O4
O2–Zn1–N1
91.51(12)
79.61(12)
95.94(12)
171.97(12)
110.84(13)
152.38(12)
84.09(11)
96.07(14)
O1–Zn1–O2
O1–Zn1–O3
O2–Zn1–O4
O1–Zn1–N2
N1–Zn1–O3
N2–Zn1–O4
O3–Zn1–O4
On the basis of the single crystal structure, elemental analy-
ses, molar conductivities, mass spectrometry, as well as
UV/Vis and IR spectroscopy, the structures of the CuII, ZnII
and NiII complexes were identified as ML·NO3·H2O (M = Cu,
Zn, and Ni).
DNA Binding Properties
Before reacting the ligand and its transition metal complexes
interacting with CT DNA, its solution behavior in Tris-HCl
buffer solution at room temperature was monitored by UV/Vis
spectroscopy for 24 h. Liberation of the ligand and its transi-
tion metal complexes was not observed under these conditions.
These suggest that the ligand and its transition metal com-
plexes are stable under the conditions studied.
Figure 1. ORTEP view of 2 showing the atom numbering of scheme
and 30% thermal ellipsoids probability for the non-hydrogen atoms.
Figure 2. Electronic absorption spectra of HL (a), 1 (b), 2 (c), and 3 (d) (10 μM) in the absence (top spectrum) and presence of increasing
amounts of CT DNA (2.5, 5.0, 7.5, 10.0, 12.5, 15.0, 17.5, and 20.0 μM; subsequent spectra). Arrows show the absorbance changes upon
increasing DNA concentration.
834
www.zaac.wiley-vch.de
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 832–841

Transition Metal Complexes with a Schiff base ligand
Electronic Absorption Spectroscopy
mechanism, ethidium bromide (EB) was employed into the re-
lated experiments, because EB usually interacts with DNA as
a typical indicator of intercalation.[30] Figure 3 shows the elec-
tronic absorption spectra of the free ligand and its metal com-
plexes when EB was employed. As seen from Figure 3, the
absorbance of Tris-HCl buffer solution is highest when there
is only EB alone. After adding CT DNA into Tris-HCl buffer
solution, the absorbance decreases and is the lowest one. How-
ever, when HL and its metal complexes were added into the
above mixture solution, the absorbance increased to a certain
level. Figure 3 shows that the maximal absorption of EB in
Tris-HCl buffer solution at 479 nm decreased and shifted to
494 nm in the presence of CT DNA, which was characteristic
of intercalation binding mode. Curve (B) in Figure 3 was the
absorption of a mixture solution of EB, DNA, and the free
ligand or its metal complexes. It was found that the absorption
at 495 nm increased comparing with curve (C). This could re-
sult from two reasons: (1) EB bound to the free ligand or metal
complexes strongly, resulting in the decreased amount of EB
intercalated into DNA base pairs; (2) there exists a competitive
intercalation between the free ligand or its metal complexes
and EB with DNA, so releasing some free EB from DNA-EB
system. We found that there were no other new absorption
peaks appearing in the experiments, and we think that the for-
mer reason can be precluded.
As shown in Figure 2, the titration of CT DNA into the free
ligand and its three transition metal complexes aroused some
spectral changes, respectively. As shown in Figure 2a, for the
free ligand HL, the absorption band at 380 nm showed a hy-
pochromism of 3.13% with the increasing concentrations of
CT DNA. For the transition metal complexes 1–3, the absorp-
tion bands at about 398 nm exhibited the hypochromism of
39.22%, 16.71%, and 22.41%, respectively. In addition, the
hypochromisms observed for the absorption bands of the free
ligand and its transition metal complex are accompanied by a
small red shift by less than 4 nm. The application of electronic
absorption spectroscopy in investigating DNA binding mecha-
nism and affinity is one of the most effective techniques. If the
compound interacts with DNA via the intercalation binding
mode, the π* orbital of the intercalated ligand can couple with
the π orbital of the DNA base pairs, thus, decreasing the πǞπ*
transition energy and resulting the hypochromism. In addition,
the binding of compound to DNA is accompanied by hypo-
chromism and significant red-shift (bathochromism) in the
electronic absorption spectra due to the strong stacking interac-
tion between the aromatic chromophore of the ligand and DNA
base pairs with extent of hypochromism and bathochromism
commonly consistent with the strength of intercalative intercal-
ation.[29] From the experimental results of the electronic ab-
sorption spectra of the free ligand and its transition metal com-
plexes with CT DNA, we conclude that the studied free ligand
and its metal complexes can interact with DNA via the inter-
calation mechanism and the metal complexes can intercalate
with DNA more strongly than the free ligand alone.
Fluorescence Spectra
As shown in Figure 4, the steady state emission spectra at
about 450 nm of 10 μM solutions of the free ligand and its
In order to further test if the free ligand and its metal com- metal complexes in Tris-HCl buffer solution show an increase
plexes could bind to CT DNA via the intercalation binding in the emission intensity with the successive addition of CT
Figure 3. UV/Vis absorption spectra of 1ϫ10–5 m EB (A); (A) + 2.5ϫ10–5 m DNA (C); (C) + 2.5ϫ10–5 m HL (a), 1 (b), 2 (c), and 3 (d) in
Tris-HCl buffer (pH 7.10) solution.
Z. Anorg. Allg. Chem. 2013, 832–841
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
835

Z.-Y. Yang et al.
ARTICLE
DNA at ambient temperature. The results of the emission ti- mode and their binding affinities are 6.88ϫ104 m–1 and
trations implies that the free ligand and its metal complexes 7.62ϫ103 m–1[36]. In addition, the Schiff bases ligand derived
can strongly interact with DNA and can be protected by DNA from dapsone and 8-formyl-7-hydroxy-4-methylcoumarin/
efficiently, since the hydrophobic environment inside the DNA 5-formyl-6-hydroxycoumarin and their CoII, NiII, and CuII
helix reduces the accessibility of solvent molecules to the com- complexes were synthesized and their biological activities,
pound and the compound mobility is restricted at the binding such as anthelmintic activity, anti-inflammatory activity, and
site, leading to the decrease of the vibrational modes of relac- antibacterial activity were investigated, indicating that they
ation. The binding of the compounds to DNA leading to a have better biological activities.[37] From above experimental
significantly increase of emission intensity also agrees with results, we can find that the DNA bind affinities of the Schiff
those observed for other typical intercalators.[31] According to base ligand and transition metal complexes we synthesized are
the Scatchard equation, a plot of r/Cf vs. r gave the binding higher, indicating that they have better antitumor activity.
constants (Kb) from the fluorescence titration data for HL, 1,
The experimental results indicated that the free ligand and
2, and 3, respectively (Figure 4). The experimental results were its three transition metal complexes can bind to DNA via the
compared with those of similar complexes with a Schiff base intercalation binding mode and the metal complexes can in-
ligand, obtained by condensation of isatin monohydrazone tercalate into DNA base pairs more strongly and deeply than
with 2,3,5-trichlorobenzaldehyde[32] such as: [Cu(L)(phen)Cl], the free ligand. The higher binding affinity of the metal com-
[Cu(L)(bpy)Cl], [Zn(L)(phen)Cl], and [Zn(L)(bpy)Cl],[33] plexes is probably attributed to the extension of the π system
Ni(HAdr)2, Ni(NaLH)2,[34] [MC18H16N4O8] (M = cobalt(II), of the intercalated ligand and the coordination of the metal
nickel(II), copper(II), and zinc(II)).[35] Their values are ions, which leads to a planar area greater than that of the free
5.72ϫ104 m–1,
1.55ϫ104 m–1,
2.06ϫ104 m–1,
and ligand. The coordinated ligand penetrates more deeply into and
0.98ϫ104 m–1, (3.22Ϯ0.09)ϫ105 m–1, (5.92Ϯ0.07) ϫ104 m–1, stacks more strongly with DNA base pairs.
1.58ϫ104 m–1, 1.65ϫ104 m–1, 2.70ϫ104 m–1, 1.83ϫ104 m–1,
The DNA binding modes and affinities were further moni-
2.54Ϯ0.20ϫ104 m–1,3.99Ϯ0.32ϫ104 m–1,6.94Ϯ0.36ϫ104 m–1, tored by a fluorescent EB displacement assay, and the experi-
and 3.62Ϯ0.28ϫ104 m–1, respectively. Further studies also ments were carried out in Tris-HCl buffer solution by keeping
confirm that the different Schiff base ligands and their metal [DNA]/[EB] = 25/2 ([DNA] = 4 μM, [EB] = 0.32 μM) and
complexes can intercalate into DNA base pairs and the com- varying the concentration of the free ligand and its transition
pounds all interact with DNA via intercalation binding metal complexes (2.5–30.0 μM). EB (= 3,8-diamino-5-ethyl-6-
mode. We also found that [Zn(ox)(en)]n(H2O)2n and phenyl-phenanthridinum bromide) is a phenenthridine fluores-
[Cu2(dmeo)(N3)2]n interact with DNA in a groove binding cence dye and is a typical indicator of intercalation binding
Figure 4. Emission enhancement spectra of HL (a), 1 (b), 2 (c), and 3 (d) (10 μM) in the absence (bottom spectrum) and presence of increasing
amounts of CT DNA (2.5, 5.0, 7.5, 10.0, 12.5, 15.0, and 17.5 μM; subsequent spectra). Arrows show the emission intensity changes upon
increasing DNA concentration. Inset: Scatchard plot of the fluorescence titration data of the HL, 1, 2, and 3, Kb (HL) = (8.50Ϯ0.14)ϫ105 m–1,
Kb (1) = (1.92Ϯ0.30)ϫ106 m–1, Kb (2) = (1.02Ϯ0.141)ϫ106 m–1, and Kb (3) = (1.03Ϯ0.10)ϫ106 m–1.
836
www.zaac.wiley-vch.de
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 832–841

Transition Metal Complexes with a Schiff base ligand
mode. It can form soluble complexes with nucleic acids and Viscosity Measurements
emitting intense fluorescence in the presence of CT DNA due
Hydrodynamic measurements that are sensitive to length
to the intercalation of the planar phenenthridinium ring be-
tween the adjacent base pairs on the double helix. When some
compounds, such as the free ligand and metal complexes, in-
teract with DNA, they would complete the binding site of EB,
and then some EB would release from the DNA-EB system,
which would result in the decrease of fluorescence intensity
of DNA-EB system. This is the characteristic of intercalation
binding mechanism, and the changes observed in the spectra
of DNA-EB system on its binding to CT DNA are often used
for the intercalation study between DNA and other com-
pounds, such as the free ligand and metal complexes.
Figure 5 shows the emission spectra of DNA-EB system
with the increasing amounts of the free ligand and its three
transition metal complexes. The addition of free ligand and
metal complexes into DNA-EB system caused the marked de-
crease of fluorescence intensity and the quenching plots illus-
trated that the quenching of EB bound to DNA by the com-
plexes and free ligand is in good agreement with the linear
Stern-Volmer equation. In the plots of F0/F vs. [Q], Kq is given
by the ratio of the slope to the intercept (Figure 5). The experi-
mental data show that the interaction of the free ligand and its
metal complexes can interact with DNA via the intercalation
binding mode, and the metal complexes bind to DNA more
strongly and deeply than the free ligand, which is consistent
with the above electronic absorption spectral results.
change (i.e. viscosity and sedimentation) are regarded as the
least ambiguous and the most critical tests to investigate the
binding mode of compounds to DNA in solution in the absence
of crystallographic or NMR structural data.[38] A classical in-
tercalation mode demands that the DNA helix lengthens as
the DNA base pairs are separated to accommodate the bound
compound, thus leading to the increase of CT DNA viscosity,
as known for other typical DNA intercalators.[10] In contrast,
a partial, non-classical intercalation of compound could bend
(or kink) the DNA helix, reduce its effective length and, con-
comitantly, its viscosity.[28] In addition, some compounds such
as [Ru(bpy)3]2+ interact with DNA by an electrostatic binding
mode, which have no influence on DNA viscosity.[10] To fur-
ther confirm the interaction mode of compounds with DNA,
the viscosity measurements were conducted in Tris-HCl buffer
solution (Figure 6). The viscosity measurements were based on
the flow rate of the DNA solution through a capillary viscome-
ter. The specific viscosity contribution (η) due to the DNA in
the presence of a binding agent was obtained. The experimen-
tal results clearly showed that the absence and presence of the
free ligand and its metal complexes have a marked effect on
the viscosity of DNA, and the increase ration of the studied
compounds is in the order of 1 Ͼ 3 Ͼ 2 Ͼ HL. The specific
viscosity of the DNA sample increases greatly with the ad-
dition of free ligand and its metal complexes. Viscosity mea-
Figure 5. Emission spectra of DNA-EB system, λex = 525 nm, λem = 589 nm, in the presence of 0, 2.5, 5, 7.5, 10, 12.5, 15, 17.5, 20.0, 22.5,
25, 27.5, 30.0, 32.5, 35.0, 37.5, 40, 42.5, 45, 47.5 and 50.0 μM HL (a), 1 (b), 2 (c), and 3 (d). Arrows show the emission intensity changes
upon increasing ligand. Inset: Stern-Volmer plot of the fluorescence titration data of HL, 1, 2, and 3, Kq (HL) = (1.77Ϯ0.04)ϫ104 M–1, Kq (1)
= (4.82Ϯ0.01)ϫ104 M–1, Kq (2) = (2.18Ϯ0.02)ϫ104 M–1, and Kq (3) = (2.81Ϯ0.11)ϫ104 M–1.
Z. Anorg. Allg. Chem. 2013, 832–841
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
837

Z.-Y. Yang et al.
ARTICLE
surements obviously indicated that the free ligand and its metal during the metabolizable process of biological systems. Hy-
complexes interact with DNA via the intercalation binding droxyl radical (·OH) is presumed to play an important role in
mode, and the metal complexes can intercalate into the DNA a number of biological phenomena such as aging, coronary
base pairs more strongly and deeply than the free ligand alone. heart disease, rheumatoid arthritis, cancer, and other pathologi-
The viscosity experimental results also validate the above cal conditions. The hydroxyl radical is by far the most potent
spectroscopic results and discussions.
and therefore the most dangerous oxygen metabolite, elimi-
nation of this radical is one of the major aims of antioxidant
administration.[39] Schiff base metal complexes are always
known to show various biological activities, such as antioxi-
dant activities. In view of this, we can predict that the Schiff
base ligand we prepared and its transition metal complexes
may have better antioxidant activity. In this paper, the antioxi-
dant activity of the ligand and its metal complexes was investi-
gated by measuring the scavenging ration of hydroxyl radical
in KH2PO4-Na2HPO4 buffer solution in vitro.
The data of the suppression ratio for HO· are listed in
Table 3. We find that the inhibitory effect of the compounds
tested on HO· is also concentration dependent and the suppres-
sion ratio increases with increasing sample concentrations in
the range tested (Figure 8). The average suppression ratio of
the free ligand (IC50 = 29.65 μM) for HO· is the least and 3
(IC50 = 3.96 μM) is the most effective in all the compounds.
The order of the suppression ratio of the tested compounds for
HO· is 3 Ͼ 2 Ͼ 1 Ͼ HL. Values of IC50 of ligand and LnIII
complexes for HO· are 143.1 and 2.344–13.33 μmol·L–1,
respectively.[40] The IC50 values of the synthesized compounds
are all in the magnitude of 10–6 m–1, and they are all effective
antioxidants.[41] The IC50 values toward superoxide anions of
the ternary copper(II) complexes with a tridentate NNO donor
Schiff base ligand are in the range of 38–44 M–1.[42] We found
that the metal complexes exhibit better antioxidant activity
than the free ligand alone, and it may be attributed to chelating
Figure 6. Effects of increasing amounts of the ligand and its metal
complexes on the relative viscosity of CT DNA at 25.0Ϯ0.1 °C.
On the basis of all the spectroscopic studies together with
the viscosity measurements, we find that the free ligand and
its three transition metal complexes can bind to CT DNA via
an intercalative mode (Figure 7) and the metal complexes bind
to CT DNA more strongly and deeply than the free ligand.
Figure 7. Molecular mode for the ligand and its metal complexes (via
an intercalation binding mode).
Antioxidant Activity
The free ligand and its metal complexes exhibit strong anti-
tumor activity through binding to DNA via intercalation bind-
ing mode, it is worthwhile to investigate their antioxidant ac-
Figure 8. Scavenging effects of the ligand and its metal complexes on
tivities. It has been reported that various oxygen species occur HO·.
Table 3. Influence of the investigated compounds on HO·.
Compound
Average inhibition /% for HO· /μM
Equation
IC50 /μM
R2
1.0
2.0
3.0
4.0
5.0
6.0
HL
1
2
13.11
24.08
21.34
23.17
16.46
27.13
23.78
34.45
19.82
30.79
27.43
41.77
24.08
33.54
33.23
49.68
29.57
36.89
39.63
55.79
35.36
39.63
44.21
60.06
y = 27.01x + 10.22
y = 19.82x + 22.57
y = 29.11x + 17.74
y = 47.77x + 21.41
29.65
24.15
12.82
3.96
0.932
0.972
0.925
0.993
3
838
www.zaac.wiley-vch.de
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 832–841

Transition Metal Complexes with a Schiff base ligand
effects between the organic molecules and the metal ions, complexes with 1:1 metal-to-ligand stoichiometry at the metal
which exert different and selective effects on scavenging radi- ions as centers, and one water molecule and one nitrate ions
cals of the biological system. We also found that 3 showed the were acted as the coordinated molecules. Experimental results
more efficient antioxidant agent than mannitol (10.19 μM)[43] indicate that the ligand and its metal complexes can bind to
which are usually used as the hydroxyl radical scavenging DNA via intercalation with the binding constants at the order
agent. In summary, the studied ligand and its metal complexes of magnitude of 105–106 M–1. In addition, the ligand and its
all showed the strong antioxidant activity, and the complexes, transition metal complexes show the stronger antioxidant ac-
especially 3, showed the stronger antioxidant activity. It is be- tivities. Experimental results also indicated that the metal com-
lieved that the information we have obtained from the experi- plexes inhibited significant cytotoxic activities against lung
ments would be useful to pursue more efficient antitumor and cancer A 549 cells.
antioxidant agent for some certain diseases.
Experimental Section
Cytotoxic Study
Materials and Instrumentation: Ethidium bromide (EB) and calf
The ligand and its transition metal complexes were evalu- thymus DNA (CT DNA) were purchased from Sigma Chemical Co.
Ethylenediaminetetraaceticacid (EDTA), safrain, 8-aminoquinoline,
M(NO3)2·nH2O [M = CuII, n = 3; ZnII, n = 6; and NiII, n = 6] were
produced in China. All chemicals used were of analytical grade.
EDTA-FeII and KH2PO4-K2HPO4 buffers were prepared with doubly
distilled water.
ated for their cytotoxic activity in vitro against lung cancer A
549 cells, and the experimental results were summarized in
Figure 9.
All the experiments involved with the interaction of the ligands and
complexes with CT DNA were carried out in doubly distilled water
buffer containing 5 mM Tris [tris(hydroxymethyl)-aminomethane] and
50 mM NaCl and adjusted to pH 7.1 with hydrochloric acid. Solution
of CT DNA in the buffer gave ratios of UV absorbance of about 1.8–
1.9:1 at 260 and 280 nm, indicating that the CT DNA was sufficiently
free of protein.[45] The CT DNA concentration per nucleotide was de-
termined spectrophotometrically by employing an extinction coeffi-
cient of 6600 m–1 cm–1 at 260 nm.[46] The ligands and metal complexes
were dissolved in a solvent mixture of 1% DMF and 99% Tris-HCl
buffer solution (pH 7.10) at the concentration 1.0ϫ10–5 m.
Contents of carbon, hydrogen, and nitrogen were determined with an
Elemental Vario EL analyzer. The metal contents of the complexes
were determined by titration with EDTA (xylenol orange tetrasodium
salt used as an indicator and hexamethylidynetetraimine as buffer).
The melting points of the compounds were determined with a Beijing
XT4-100X microscopic melting point apparatus. The IR spectra were
obtained in KBr discs with a Thermo Mattson FTIR spectrophotometer
Figure 9. Cytotoxic activity of the ligand and its metal complexes
against lung cancer A 549 cells.
As shown in Figure 9, the ligand and its transition metal
complexes showed the same inhibitions of the growth of lung
cancer A 549 cells. With the increase of concentrations of the
investigated compounds, the cell survival rates became lower
and lower, indicating that the cytotoxic abilities of the com-
pounds are concentration dependent. In addition, the IC50 val-
ues of 1–3 were 3.67 μM, 7.74 μM, and 166.80 μM, respec-
tively, whereas the IC50 value of the free ligand is more than
300 μM. It is clear that the lower IC50 values of the compounds
are due to the chelation effects of the free ligand and metal
ions. In addition, we noticed that IC50 values of 1 and 2 are
lower than that of cisplatin (25.0 μM), indicating that the two
metal complexes are more efficient anticancer drugs than cis-
platin.[44]
1
in the 4000–400 cm–1 region. H NMR spectra were recorded with a
Varian VR 200 MHz spectrometer in CDCl3 with TMS (tetramethylsil-
ane) as internal standard. Mass spectra were performed with a APEX
II FT-ICR MS instrument using methanol as mobile phase. All conduc-
tivity measurements were performed in N,N-dimethylformamide
(DMF) with a DDS-11C conductometer at 25.0 °C. The UV/Vis spec-
tra were recorded with a Shimadzu UV-240 spectrophotometer. Fluo-
rescence measurements were recorded with a Hitachi RF-4500 spectro-
fluorophotometer at room temperature. Measurement of the antioxi-
dant activity was performed in DMF solution with a 721-E spectropho-
tometer.
DNA Binding Properties
Electronic Absorption Spectroscopy: Electronic absorption titration
experiments were performed with fixed concentration drugs (10 μM),
while gradually increasing the concentration of CT DNA. When meas-
uring the absorption spectra, an equal amount of CT DNA was added
to both the compounds solutions and the reference solution to eliminate
the absorbance of CT DNA itself. Each sample solution was scanned
Conclusions
We have prepared and characterized a novel Schiff base li-
gand, 1-phenyl-3-methyl-5-hydroxypyrazole-4-methylene-8Ј-
quinolineimine, and its three transition metal complexes. The
ligand and metal ions can form mononuclear six-coordination in the range of 190–500 nm.
Z. Anorg. Allg. Chem. 2013, 832–841
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
839

Z.-Y. Yang et al.
ARTICLE
Fluorescence Spectra: Fixed amounts (10 μM) of compounds were
x was the tested compound concentration in μM and y was percent
titrated with increasing amounts of CT DNA, over a range of DNA inhibition of the tested compounds.
concentrations from 2.5 to 20.0 μM. Excitation wavelengths of the
samples were about 322 nm, scan speed was 480 nm·min–1, and slit
width was 10 nm. All experiments were conducted at constant room
temperature in Tris-HCl buffer solution. The intrinsic binding con-
stants (Kb) of the compounds with DNA were obtained through
fluorescence spectra according to the following equation:[47]
Cytotoxic Study: Cytotoxic effect of the free ligand and its metal
complexes on lung cancer A 549 cells were assayed by the 3-(4,5-
dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide (MTT) assay.
Lung cancer A 549 cells were plated in 96-well plates, and the lung
cancer cells were treated with varied concentration of the studied com-
pounds. The culture medium was removed from the plates after 48 h
of culture, well treated with MTT (5 mg·mL–1 PBS), and incubated at
37 °C for 24 h. The color development was assayed at 570 nm in a
micro plate reader. Cell survival was expressed as an absorbance (A)
percentage defined by [(Adrug – Ablank ) / (Acontrol – Ablank)]ϫ100.
r/Cf = Kb ϫ(n – r),
Cb = Ct[(F – F0)/(Fmax – F0)],
where Ct is the total compound concentration, F is the observed fluo-
rescence emission intensity at given DNA concentrations, F0 is the
intensity in the absence of DNA and Fmax is the fluorescence of the
totally bound compound. Binding data were cast into the form of a
Scatchard plot of r/Cf vs. r, where r is the binding ratio Cb/[DNA]t,
Cf is the free compound concentration and n is the binding site number.
Synthesis of the Ligand (HL): 1-Phenyl-3-methyl-4-formyl-2-pyr-
azolin-5-one (PMFP) was synthesized according to the previous litera-
ture.[52] As shown in Scheme 1, the ethanol solution of 8-aminoquinol-
ine (0.14 g, 1 mmol) was added into the ethanol solution of PMFP
(0.202 g, 1 mmol). The mixture solution was stirred and refluxed for
24 h, and a great amount of yellow precipitate was formed. After that,
the yellow solid was filtered off and dried in a vacuum. Yield: 78.6%.
Mp.: 189–191 °C. C20H16N4O: calcd. C 73.15; H 4.91; N 17.06%;
found: C 73.21; H 4.92; N 17.09%. IR (KBr): ν˜ = 3441 ν(OH), 1670
ν(C=N, a), 1633 ν(C=N, b) cm–1. λmax (nm): 380 nm. ESI mass
spectrometry: m/z 329([HL+H]+) 351([HL+Na]+). 1H NMR
(200 MHz,CDCl3, ppm) (Figure S1, Supporting Information): δ =
12.853 (d, 1 H, –OH), 9.053 (d, 1 H, –CH=N), 8.199 (d, 2 H, H9, H11,
J = 7.8 Hz), 8.098 (d, 2 H, H6, H8, J = 8 Hz), 7.610 (d, 2 H, H1, H5,
J = 3.8 Hz), 7.424 (t, 2 H, H2, H4, J = 8 Hz, J = 16Hz), 7.165 (t, 1 H,
H3, J = 8 Hz, 16 Hz), 7.533 (dd, 1 H, H10), 7.637 (dd, 1 H, H7), 2.383
(s, 3 H, CH3-pyrazole) ppm.
Further support for the mode of the ligand and complexes binding to
DNA is given through the emission quenching experiments. A 2.0 mL
solution of 4 μM DNA and 0.32 μM EB (at saturating binding levels)
was titrated by 2.5–30.0 μM the complexes and ligand at a constant
room temperature in Tris-HCl buffer solution. Quenching data were
analyzed according to the Stern-Volmer equation, which could be used
to determine the fluorescent quenching mechanism:
Fo/F = 1 + Kq [Q],
Where Fo and F are the fluorescence intensity in the absence and pres-
ence of drug at [Q] concentration respectively; Kq is the quenching
constant and [Q] is the quencher concentration. Plots of Fo/F vs. [Q]
appear to be linear and Kq depends on temperature.[48]
Viscosity Measurements: Viscosity experiments were conducted on
an Ubbelodhe viscometer, immersed in a thermostatted water-bath
maintained to 25.0Ϯ0.1 °C. Titrations were performed for the com-
plexes (0.5–4 μM), and each compound was introduced into a DNA
solution (5 μM) present in the viscometer. Data were presented as
(η/η0)1/3 vs. the ratio of the concentration of the compound and DNA,
where η is the viscosity of DNA in the presence of the compound and
η0 is the viscosity of DNA alone.[49,50]
Scheme 1. Synthetic route of the novel ligand (HL).
Synthesis of the Transition Metal Complexes 1–3: The ligand
(32.8 mg, 10 mmol) was dissolved in ethanol (20 mL, and the solution
became clear. After 5 min, ZnII nitrate (29.7 mg, 10 mmol) was added
into the above solution and the solution was stirred and refluxed in a
water bath for 12 h. After a while, a large amount of yellow solid, 2,
was obtained from the solution by filtration, purified by washing with
ethanol twice and dried in a vacuum for 24 h (yield 93.5%). Com-
plexes 1 (yield 88.3%), and 3 (yield 72.8%) were obtained by the
same way.
Antioxidant Activity: In antioxidant activity experiments the hy-
droxyl radical (HO·) in aqueous media was generated through the Fen-
ton reaction.[51] The solution of the tested compounds was prepared
with DMF. The reaction mixture contained phosphate buffer (2.5 mL
0.15 m, pH = 7.4), safranin (0.5 mL, 114 μM), EDTA-FeII (1 mL,
945 μM), H2O2 (1 mL, 3%), and the tested compound solution (30 μL)
[the final concentration: Ci (i = 1–6) = 1.0, 2.0, 3.0, 4.0, 5.0 μM]. The
sample without the tested compound was used as the control. The
reaction mixtures were incubated at 37 °C for 60 min in a water-bath.
Absorbances (Ai, A0, Ac) at 520 nm were measured. The suppression
ratio for HO· was calculated from the following expression:
1: C20H18N5O5Cu: calcd. C 50.90; H 3.84; N 14.84; Cu 13.47%;
found: C 50.83; H 3.82; N 15.89; Cu 13.44%. ESI mass spectra: m/z
392([1–NO3–H2O]+), 595([1+2C2H5OH+CH3OH+H]+). IR (KBr): ν˜ =
3433 ν(OH), 1624 ν(C=N, a), 1597 ν(C=N, b), 603 δ(H2O), 1498
ν(NO3), 1384, 1055, 831, 758, 691 ν(M–O), 511 cm–1. λmax (nm): 320,
394 nm. Λm (S·cm2·mol–1): 11.7. 2: C20H18N5O5Zn calcd. C 50.70; H
3.83; N 14.78; Zn 13.80%; found: C 50.73; H 3.75; N 14.71; Cu
13.84%. ESI mass spectra: 489 [2+H2O], 391 [2-NO3–H2O]+. IR
(KBr): ν˜ = 3432 ν(OH), 1630 ν(C=N, a), 1596 ν(C=N, b), 596 δ(H2O),
1497 1384, 1012, 827, 758, 682 ν(M–O), 513 ν(M–N) cm–1.
λmax (nm): 320, 398 nm. ESI-MS peaks: 615, 489, and 391.
Suppression ratio (%) = [(Ai – A0)/(Ac – A0)]ϫ100%
where Ai = the absorbance in the presence of the tested compound; A0
= the absorbance in the absence of the tested compound; Ac = the
absorbance in the absence of the tested compound, EDTA-FeII, and
H2O2.
The antioxidant activity was expressed as the 50% inhibitory concen-
tration (IC50). IC50 values were calculated from regression lines where: Λm(S·cm2·mol–1): 13.6. 3: C20H18N5O5Ni calcd. C 51.43; H 3.88; N
840
www.zaac.wiley-vch.de
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 832–841

Transition Metal Complexes with a Schiff base ligand
[18] D. Costa, A. P. Marques, R. L. Reis, J. Lima, E. Fernandes, Free
Radical Biol. Med. 2006, 40, 632–640.
[19] Y. Kakiuchi, N. Sasaki, M. Satoh-Masuoka, H. Murofushi, K.
Murakami-Murofushi, Biochem. Biophys. Res. Commun. 2004,
320, 1351–1358.
[20] M. M. B. Pessoa, G. F. S. Andrade, V. R. P. Monteiro, M. L. A.
Temperini, Polyhedron 2001, 20, 3133–3141.
[21] B. Halliwell, Annu. Rev. Nutr. 1996, 16, 33–50.
[22] B. N. Ames, M. K. Shigenaga, T. M. Hagen, Proc. Natl. Acad.
Sci. USA 1993, 90, 7915–7922.
[23] A. A. Horton, S. Fairhurst, Critical Rev. Toxicology 1987, 18, 27–
79.
[24] H. L. Wang, Z. Y. Yang, B. D. Wang, Transition Met. Chem.
2006, 31, 470–474.
[25] W. J. Geary, Curr. Contents/Phys. Chem. Earth Sci. 1981, 18–18.
[26] Y. Li, Z. Y. Yang, M. F. Wang, Eur. J. Med. Chem. 2009, 44,
4585–4595.
[27] Y. Li, Z. Y. Yang, M. F. Wang, J. Fluoresc. 2010, 20, 891–905.
[28] J. G. Liu, Q. L. Zhang, X. F. Shi, L. N. Ji, Inorg. Chem. 2001, 40,
5045–5050.
14.99; Ni 12.57%; found: C 51.32; H 3.83; N 14.91; Ni 12.67%. ESI
mass spectra: 404([3-NO3]+), 388([3-NO3–H2O]+). IR (KBr): ν˜ = 3413
ν(OH), 1630 ν(C=N, a), 1590 ν(C=N, b), 611 δ(H2O), 1497 ν(NO3),
1385, 1015, 827, 759, 693 ν(M–O), 507 ν(M–N) cm–1. λmax (nm):
320, 400 nm. Λm(S·cm2·mol–1): 6.3.
Determination of Crystal Structures: X-ray diffraction data for the
crystal were performed with graphite-monochromated Mo-Kα radiation
(0.71073 Å) with a Bruker Smart-1000 CCD diffractometer and col-
lected by the φ/ω scan technique at 296(2) K. The crystal structure was
solved by direct methods. The positions of non-hydrogen atoms were
determined from successive Fourier syntheses. The hydrogen atoms
were placed in their geometrically calculated positions. The positions
and anisotropic thermal parameters of all non-hydrogen atoms were
refined on F2 by full-matrix least-squares techniques with the SHELX-
97 program package. Absorption correction was employed using Semi-
empirical methods from equivalents.
Crystallographic data (excluding structure factors) for the structure in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK.
Copies of the data can be obtained free of charge on quoting the
depository number CCDC-879337 (Fax: +44-1223-336-033; E-Mail:
deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk).
[29] Y. Li, Z. Y. Yang, J. C. Wu, Eur. J. Med. Chem. 2010, 45, 5692–
5701.
[30] W. D. Wilson, L. Ratmeyer, M. Zhao, L. Strekowski, D. Boykin,
Biochemistry 1993, 32, 4098–4104.
[31] H. Xu, K. C. Zheng, L. J. Lin, H. Li, Y. Gao, L. N. Ji, J. Inorg.
Biochem. 2004, 98, 87–97.
[32] N. Raman, K. Pothiraj, T. Baskaran, J. Coord. Chem. 2011, 64,
3900–3917.
[33] K. Pothiraj, T. Baskaran, N. Raman, J. Coord. Chem. 2012, 65,
Supporting Information (see footnote on the first page of this article):
1H NMR of HL (200 MHz, in CDCl3).
2110–2126.
[34] P. S. Guin, P. C. Mandal, S. Das, J. Coord. Chem. 2012, 65, 705–
721.
[35] N. Raman, K. Pothiraj, T. Baskaran, J. Coord. Chem. 2011, 64,
Acknowledgements
4286–4300.
This work is supported by the National Natural Science Foundation of
China (20975046, 81171337 and J1103307).
[36] M. Jiang, Y. T. Li, Z. Y. Wu, J. Coord. Chem. 2012, 65, 1858–
1871.
[37] M. Manjunatha, V. H. Naik, A. D. Kulkarni, S. A. Patil, J. Coord.
Chem. 2011, 64, 4264–4275.
[38] S. Satyanarayana, J. C. Dabrowiak, J. B. Chaires, Biochemistry
1993, 32, 2573–2584.
[39] N. Udilova, A. V. Koziova, W. Bieberschulte, K. Frei, K. Ehren-
berger, H. Nohl, Biochem. Pharmacol. 2003, 65, 59–65.
[40] Y. C. Liu, K. J. Zhang, R. X. Lei, J. N. Liu, T. L. Zhou, Z. Y.
Yang, J. Coord. Chem. 2012, 65, 2041–2054.
[41] A. Ramadan, J. Coord. Chem. 2012, 65, 1417–1433.
References
[1] J. Reedijk, Inorg. Chim. Acta 1992, 198, 873–881.
[2] S. E. Sherman, S. J. Lippard, Chem. Rev. 1987, 87, 1153–1181.
[3] J. Reedijk, Pure Appl. Chem. 1987, 59, 181–192.
[4] C. Marzano, M. Pellei, F. Tisato, C. Santini, Anti-Cancer Agents
Med. Chem. 2009, 9, 185–211.
[5] G. Gasser, I. Ott, N. Metzler-Nolte, J. Med. Chem. 2011, 54, 3– [42] R. N. Patel, A. Singh, K. K. Shukla, V. P. Sondhiya, D. K. Patel,
25. Y. Singh, R. Pandey, J. Coord. Chem. 2012, 65, 1381–1397.
[6] J. Liu, Z. H. Wang, G. A. Luo, Q. W. Li, H. W. Sun, Anal. Sci. [43] Y. Li, Z. Y. Yang, T. R. Li, Chem. Pharm. Bull. 2008, 56, 1528–
2002, 18, 751–755. 1534.
[7] S. Delaney, M. Pascaly, P. K. Bhattacharya, K. Han, J. K. Barton, [44] E. Ramachandran, S. P. Thomas, P. Poornima, P. Kalaivani, R.
Inorg. Chem. 2002, 41, 1966–1974.
[8] H. T. Chifotides, K. R. Dunbar, Acc. Chem. Res. 2005, 38, 146–
156.
Prabhakaran, V. V. Padma, K. Natarajan, Eur. J. Med. Chem.
2012, 50, 405–415.
[45] Y. Z. Cai, Q. Luo, M. Sun, H. Corke, Life Sci. 2004, 74, 2157–
[9] S. M. Hecht, J. Nat. Prod. 2000, 63, 158–168.
2184.
[10] J. G. Liu, B. H. Ye, H. Li, Q. X. Zhen, L. N. Ji, Y. H. Fu, J. Inorg. [46] K. E. Heim, A. R. Tagliaferro, D. J. Bobilya, J. Nutr. Biochem.
Biochem. 1999, 76, 265–271. 2002, 13, 572–584.
[11] X. Sheng, X. Guo, X. M. Lu, G. Y. Lu, Y. Shao, F. Liu, Q. Xu, [47] M. Howe-Grant, K. C. Wu, W. R. Bauer, S. J. Lippard, Biochem-
Bioconjugate Chem. 2008, 19, 490–498. istry 1976, 15, 4339–4346.
[12] F. Marchetti, C. Pettinari, A. Cingolani, R. Pettinari, M. Rossi, F. [48] M. R. Eftink, C. A. Ghiron, Anal. Biochem. 1981, 114, 199–227.
Caruso, J. Organomet. Chem. 2002, 645, 134–145.
[13] B. H. Peng, G. F. Liu, L. Liu, D. Z. Jia, K. B. Yu, J. Mol. Struct.
2004, 692, 217–222.
[14] C. H. Chen, F. I. Wu, C. F. Shu, C. H. Chien, Y. T. Tao, J. Mater.
Chem. 2004, 14, 1585–1589.
[49] M. Eriksson, M. Leijon, C. Hiort, B. Norden, A. Graeslund, Bio-
chemistry 1994, 33, 5031–5040.
[50] Y. Xiong, X. F. He, X. H. Zou, J. Z. Wu, X. M. Chen, L. N. Ji,
R. H. Li, J. Y. Zhou, K. B. Yu, J. Chem. Soc. Dalton Trans. 1999,
19–23.
[15] J. M. You, X. Sheng, C. X. Ding, Z. W. Sun, Y. R. Suo, H. L.
Wang, W. Li, Anal. Chim. Acta 2008, 609, 66–75.
[16] Z. Y. Yang, R. D. Yang, F. S. Li, K. B. Yu, Polyhedron 2000, 19,
2599–2604.
[51] C. C. Winterbourn, Biochem. J. 1981, 198, 125–131.
[52] H. G. Li, Z. Y. Yang, D. D. Qin, Inorg. Chem. Commun. 2009,
12, 494–497.
[17] A. Kimata, H. Nakagawa, R. Ohyama, T. Fukuuchi, S. Ohta, T.
Suzuki, N. Miyata, J. Med. Chem. 2007, 50, 5053–5056.
Received: October 27, 2012
Published Online: March 25, 2013
Z. Anorg. Allg. Chem. 2013, 832–841
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
841