Impact of metal on the DNA photo-induced cleavage activity of a family of Phterpy complexes

Article abstract of DOI:10.1016/j.jinorgbio.2013.01.010

A family of Phterpy complexes, [Mn(Phterpy)₂][N(CN) ₂]₂·0.5H₂O (1), [Fe(Phterpy) ₂](NO₃)₂ (2), [Ni(Phterpy)₂](NO ₃)₂ (3), [Ni(Phterpy)₂]Cl₂· 10H₂O (4), [Cd(Phterpy)₂](NO₃) ₂·2H₂O (5) and [Zn(Phterpy)Cl₂] (6) (Phterpy = 4′-phenyl-2,2′:6′,2″-terpyridine), have been synthesized and structurally characterized, and their DNA binding and photo-induced DNA cleavage activities have been investigated. These complexes display binding propensity to the CT-DNA giving a relative order: 1 > 4 > 3, 5, 2, 6. Under dark or ambient lighting conditions, all complexes show no efficient DNA cleavage activity to pBR322 DNA. While on irradiation with UV-A light of 365 nm, complexes of 1, 3 and 4 exhibit significant cleavage activities. In the presence of H₂O₂ as a revulsant or an activator, the cleavage ability of complex 2 is obviously enhanced. Complexes 5 and 6 do not exhibit any apparent chemical nuclease activities under irradiation conditions or with the addition of H₂O₂. The DNA photo-induced cleavage activities are consistent with the number of single-electron in the central metal ion of complexes and singlet oxygen and hydroxyl radical are found as the reactive oxygen species.

Full text of DOI:10.1016/j.jinorgbio.2013.01.010

Journal of Inorganic Biochemistry 122 (2013) 49–56
Contents lists available at SciVerse ScienceDirect
Journal of Inorganic Biochemistry
journal homepage: www.elsevier.com/locate/jinorgbio
Impact of metal on the DNA photo-induced cleavage activity of a family of
Phterpy complexes
b,
Gong-Jun Chen a,b, Zhi-Gang Wang b, Ying-Ying Kou b, Jin-Lei Tian b, , Shi-Ping Yan
⁎
⁎
a
College of Chemistry, Chemical Engineering and Materials Science, Shandong Normal University, Jinan, 250014, PR China
b
Department of Chemistry and Key Laboratory of Advanced Energy Materials Chemistry (MOE) and TKL of Metal and Molecule Based Material Chemistry,
Nankai University, Tianjin 300071, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 October 2012
Received in revised form 12 January 2013
Accepted 16 January 2013
Available online 26 January 2013
A family of Phterpy complexes, [Mn(Phterpy)2][N(CN)2]2·0.5H2O (1), [Fe(Phterpy)2](NO3)2 (2), [Ni(Phterpy)2]
(NO3)2 (3), [Ni(Phterpy)2]Cl2·10H2O (4), [Cd(Phterpy)2](NO3)2·2H2O (5) and [Zn(Phterpy)Cl2] (6) (Phterpy=
4′-phenyl-2,2′:6′,2″-terpyridine), have been synthesized and structurally characterized, and their DNA binding
and photo-induced DNA cleavage activities have been investigated. These complexes display binding propensity
to the CT-DNA giving a relative order: 1>4>3, 5, 2, 6. Under dark or ambient lighting conditions, all complexes
show no efficient DNA cleavage activity to pBR322 DNA. While on irradiation with UV-A light of 365 nm, complexes
of 1, 3 and 4 exhibit significant cleavage activities. In the presence of H2O2 as a revulsant or an activator, the cleavage
ability of complex 2 is obviously enhanced. Complexes 5 and 6 do not exhibit any apparent chemical nuclease activ-
ities under irradiation conditions or with the addition of H2O2. The DNA photo-induced cleavage activities are con-
sistent with the number of single-electron in the central metal ion of complexes and singlet oxygen and hydroxyl
radical are found as the reactive oxygen species.
Keywords:
Crystal structures
DNA binding
Photo-induced DNA cleavage
© 2013 Elsevier Inc. All rights reserved.
1. Introduction
different transition metals. In attempt to obtain more insight on the se-
lectivity and efficiency of DNA cleavage with different transition metal
Photo-induced DNA cleavage involves the simultaneous presence
of light, oxygen, and photosensitizing drugs to achieve the photo cy-
totoxic effect, among which electron transfer and energy transfer are
the two most prevalent processes. Transition metal complexes that
are capable of cleaving DNA under physiological conditions are of
current interest in the development of metal-based anticancer agents
[1–7]. It inspires inorganic chemists to develop more effective, less
toxic, target specific, and preferably noncovalently bound anticancer
drugs [8–18]. Photo-induced DNA cleavage as a nontoxic and high
selective modality for treatment of solid tumors has attracted increas-
ing attention [19–26]. The methodology based on irradiation with
UV-A light has achieved much success for its potential in the treatment
of tumor combined with light and a photosensitizing drug among many
methodologies used for oxidative cleavage of DNA [27]. Complexes
based on the planar heterocyclic ligands have been well investigated
due to their unusual electronic properties, diverse chemical reactivity
and peculiar structure [19–26,28–47]. The ligand 4′-phenyl-2,2′:6′,
2″-terpyridine (Phterpy) has a larger aromatic ring used to generate
photo-induced 3(n–π) and/or 3(π–π) states that can transfer its excited
state energy to molecular oxygen in a type-II process forming singlet
oxygen with oxidative damage to cells. Moreover, less report has fo-
cused on the photo-induced DNA cleavage with the influence of the
complexes, herein we prepared a series of mononuclear d-metal com-
plexes and investigated their DNA cleavage activities.
2. Experimental
2.1. Materials and measurements
The ligand Phterpy was synthesized according to a previous reported
procedure [48,49]. Ethidium bromide (EB), calf thymus DNA (CT-DNA)
and pBR322 plasmid DNA were purchased from Sigma. A Tris–HCl buffer
solution was prepared using deionized sonicated and triple-distilled
water. All other reagents and chemicals were purchased from commer-
cial sources and used as received. Elemental analyses for C, H and N were
obtained on a Perkin-Elmer analyzer model 240. The electronic spectra
were measured on a JASCO V-570 spectrophotometer. The CD spectra
of CT-DNA in the presence or absence of a complex were collected in a
5 mM Tris–HCl buffer (pH=7.2) containing 50 mM NaCl. All CD exper-
iments were performed on a JASCO-J715 spectropolarimeter at room
temperature.
2.2. Synthesis of [Mn(Phterpy)2][N(CN)2]2·0.5H2O (1)
An acetonitrile solution (10 mL) of MnCl2·6H2O (0.2 mmol, 43 mg)
was added to a 10 mL methanol/H2O (1:1) mixture of Phterpy
(0.2 mmol, 62.6 mg) and NaN(CN)2 (0.2 mmol, 18 mg). The resulting
⁎
Corresponding authors. Tel.: +86 22 23509957; fax: +86 22 23502779.
E-mail addresses: tiant@nankai.edu.cn (J.-L. Tian), yansp@nankai.edu.cn (S.-P. Yan).
0162-0134/$ – see front matter © 2013 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.jinorgbio.2013.01.010

50
G.-J. Chen et al. / Journal of Inorganic Biochemistry 122 (2013) 49–56
mixture was stirred for 3 h at room temperature and then filtered.
Several weeks later, the yellow block crystals suitable for X-ray dif-
fraction were obtained by slow evaporation of the filtrate. Yield: 24%
(based on the MnCl2·6H2O solution). Elemental analysis data: calcd.
(%) for C46H31MnN12O0.50: C, 67.81; H, 3.84; N, 20.63; found (%): C,
67.82; H, 3.85; N, 20.61.
applied to raw intensities [51]. The structures were solved by direct
methods (SHELX-97) and refined with full-matrix least-squares tech-
nique on F2 using the SHELX-97 [52,53]. The hydrogen atoms were
added theoretically, and riding on the concerned atoms and refined
with fixed thermal factors. The details of the crystallographic data and
structure refinement parameters are summarized in Table 1. The crys-
tallographic data for complexes 1–6 have been deposited with the
Cambridge Crystallographic Data Centre with the corresponding CCDC
numbers of 632172 (1), 294395 (2), 288966 (3), 632171 (4), 292420
(5) and 675399 (6). Copy of the data can be obtained free of charge
on application to CCDC, e-mail: deposit@ccdc.cam.ac.uk or http://
www.ccdc.cam.ac.uk.
2.3. Synthesis of [Fe(Phterpy)2](NO3)2 (2)
An acetonitrile solution (10 mL) of Fe(NO3)2·6H2O (0.2 mmol,
57 mg) and ascorbic acid (0.3 mmol, 53 mg) were added to a 10 mL
methanol/H2O (1:1) mixture of Phterpy (0.2 mmol, 62.6 mg). The
resulting mixture was stirred for 2 h at room temperature and then
filtered. Green block crystals suitable for X-ray diffraction were obtained
by slow evaporation of the filtrate after several weeks. Yield: 35% (based
on the Fe(NO3)2·6H2O solution). Elemental analysis data: calcd. (%) for:
C42H30FeN8O6: C, 63.17; H, 3.79; N, 14.03; found (%): C, 63.17; H,3.82; N,
14.01.
2.9. DNA-binding and cleavage experiments
The UV absorbance at 260 nm and 280 nm of the CT-DNA solution
in 18 mM NaCl/50 mM Tris–HCl buffer (pH=7.2) gives a ratio of
1.8–1.9, indicating that the DNA was sufficiently free of protein. The
concentration of CT-DNA was determined from its absorption inten-
sity at 260 nm with a molar absorptivity of 6600 M−1 cm−1 [54,55].
DNA binding experiments were done in Tris–HCl/NaCl buffer
(50 mM Tris–HCl, 18 mM NaCl, pH=7.2) using the aqueous solution
of the complexes. Absorption titration experiments were made by
varying the concentration of CT-DNA while keeping the metal com-
plex concentration constant. Each spectrum of the complexes binding
to DNA was recorded after equilibration of the sample for 5 min at
25 °C.
The relative bindings of the complexes to CT-DNA were studied
with an EB–DNA solution in Tris–HCl/NaCl buffer (pH=7.2). The exper-
iment was carried out by titrating complexes into the EB–DNA solution
containing 4.0×10−6 M of EB and 8.0×10−6 M of DNA. The fluores-
cence spectra were recorded at room temperature with excitation at
510 nm and emission at 602 nm.
2.4. Synthesis of [Ni(Phterpy)2](NO3)2 (3)
Complexes 3 and 4 were prepared according to the literature
methods [49,50]. An acetonitrile solution (10 mL) of Ni(NO3)2·6H2O
(0.2 mmol, 58 mg) was added to a 10 mL methanol/H2O (1:1) mixture
of Phterpy (0.2 mmol, 62.6 mg). The resulting mixture was stirred for
2 h at room temperature and then filtered. Green block crystals suitable
for X-ray diffraction were obtained by slow evaporation of the filtrate
after several weeks. Yield: 50% (based on the Ni(NO3)2·6H2O solution).
Elemental analysis data: calcd. (%) for C42H30NiN8O6: C, 62.94; H, 3.77;
N, 13.98; found (%): C, 62.95; H, 3.79; N, 13.96.
2.5. Synthesis of [Ni(Phterpy)2]Cl2·10H2O (4)
Complex 4 was prepared similar to 3, but 0.2 mmol NiCl2·6H2O
instead of Ni(NO3)2·6H2O was added to the reaction mixture. Then
green block crystals suitable for X-ray diffraction were obtained by
slow evaporation of the filtrate after several months. Yield: 43% (based
on the NiCl2·6H2O solution). Elemental analysis data: calcd. (%) for:
The DNA cleavage experiments were done by agarose gel electro-
phoresis, which was performed by incubation at 37 °C as follows:
pBR322 DNA in a 50 mM Tris–HCl/18 mM NaCl buffer (pH=7.2)
was treated with the complexes in the absence of additives. The sam-
ples were incubated with light irradiation, and then a loading buffer
was added. Then the samples were electrophoresed for 3 h at 80 V
on 0.8% agarose gel using a Tris–boric acid–EDTA buffer. After electro-
phoresis, bands were visualized by UV-A light and photographed.
Quantification of cleavage products was performed by UVIpro soft-
ware, version 10.03. Supercoiled plasmid DNA values were corrected
by a factor of 1.3, based on the average literature estimate of lowered
binding of ethidium [56–58].
Cleavage mechanistic investigations of pBR322 DNA were done by
adding different reagents such as DMSO, NaN3, SOD, KI, EDTA, EtSH,
histidine, D2O and catalase to pBR322 DNA prior to the addition of the
complexes. Deoxygenated solutions were prepared by four freeze–
pump–thaw cycles. Before each cycles the solutions were equilibrated
with nitrogen to aid the deoxygenation process. The deoxygenated
solutions were stored under a nitrogen atmosphere prior to use.
C42H50N6NiCl2O10: C, 54.33; H, 5.43; N, 9.05; found (%): C, 54.34; H,
5.45; N, 9.08.
2.6. Synthesis of [Cd(Phterpy)2](NO3)2·2H2O (5)
Complex 5 was prepared similar to 3, but 0.2 mmol Cd(NO3)2·6H2O
instead of Ni(NO3)2·6H2O was added to the reaction mixture. Then
colorless block crystals suitable for X-ray diffraction were obtained
by slow evaporation of the filtrate after several months. Yield: 35%
(based on the Cd(NO3)2·6H2O solution). Elemental analysis data: calcd.
(%) for: C42H34CdN8O8: C, 56.60; H, 3.85; N, 12.57; found (%): C, 56.55;
H, 3.87; N, 12.60.
2.7. Synthesis of [Zn(Phterpy)Cl2] (6)
Complex 6 was prepared similar to 3, but 0.2 mmol ZnCl2·6H2O
instead of Ni(NO3)2·6H2O was added to the reaction mixture. Then
colorless block crystals suitable for X-ray diffraction were obtained
by slow evaporation of the filtrate after several months. Yield: 35%
(based on the ZnCl2·6H2O solution). Elemental analysis data: calcd.
(%) for: C21H15Cl2N3Zn: found (%): C, 56.59; H, 3.39; N, 9.43; found
(%): C, 56.57; H, 3.44; N, 9.40.
3. Results and discussion
3.1. Crystal structures
Complexes 1–6 can be divided into three groups according to the
space group: (i) P-1 triclinic (1–4), (ii) Pbca orthorhombic (5) and
(iii) P2(1)/n monoclinic (6). The bond lengths and angles for the
coordination spheres are given in Table 2. For 1–5, all M(II) centers
adopt distorted octahedron coordination environments and each
Phterpy ligand coordinates the M(II) center in a mer fashion defining
essentially tetragonally compressed [MN6] octahedrons. The M\N
axial bonds involving the pyridine rings are markedly shorter than
the M\N equatorial bonds collectively denoted as M\Ncentral and
2.8. X-ray crystallography
Diffraction data for 1–6 were collected at 293 (2) K, with a Bruker
Smart 1000 CCD diffractometer using Mo-Kα radiation (λ=0.71073 Å)
with the ω-2θ scan technique. An empirical absorption correction was

Table 1
Data collection and processing parameters for complexes 1–6.
Complex
1
2
3
4
5
6
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
(Å)
a (Å)
b (Å)
c (Å)
α (°)
C
46H31MnN12O0.50
C42H30N8NiO6
801.45
293(2)
0.71073
Triclinic
P-1
C42H50Cl2N6NiO10
928.49
113(2)
0.71073
Triclinic
P-1
C42H30FeN8O6
798.59
293(2)
0.71073
Triclinic
P-1
C42H34CdN8O8
891.17
293(2)
0.71073
Orthorhombic
Pbca
C21H15Cl2N3Zn
445.63
113(2)
0.71073
Monoclinic
P2(1)/n
814.77
113(2)
0.71073
Triclinic
P-1
8.767(3)
9.0410(15)
11.0427(19)
20.198(3)
94.444(3)
100.745(3)
106.380(3)
10.190(2)
12.154(2)
19.783(5)
74.728(9)
87.303(11)
67.009(7)
9.095(3)
10.7823(13)
16.9764(19)
42.788(5)
90
90
90
11.963(2)
9.5370(19)
17.124(3)
90
108.56(3)
90
13.821(4)
16.501(5)
86.217(12)
76.567(7)
89.172(11)
10.968(4)
20.236(6)
94.647(6)
101.033(5)
106.389(6)
β (°)
γ (°)
V (Å3)
1940.4(10)
1882.6(5)
2171.6(8)
1881.2(10)
7832.1(16)
1852.2(6)
Z
2
2
2
2
8
4
ρ (mg/m3)
1.395
0.394
840
1.414
0.576
828
1.420
0.634
972
1.410
0.462
824
1.512
0.623
3632
1.598
1.625
904
μ (mm−1
F (000)
)
θ range (°) for data collection
Limiting indices
1.48 to 26.00
−10≤h≤10, −17≤k≤16,
−20≤l≤20
1.94 to 25.01
−10≤h≤5, −11≤k≤13,
−24≤l≤23
1.89 to 26.00
−12≤h≤12, −14≤k≤14,
−24≤l≤16
1.96 to 25.01
−10≤h≤10, −7≤k≤13,
−24≤l≤20
0.95 to 26.42
−13≤h≤13, −12≤k≤21,
−52≤l≤53
1.83 to 25.02
−14≤h≤14, −11≤k≤6,
−20≤l≤20
Reflections collected/unique
Max. and min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
21,611/7613 [R(int)=0.0552]
0.9397 and 0.9184
7613/97/590
9592/6551 [R(int)=0.0283]
1.000 and 0.7073
6551/54/550
1.011
17,953/8463 [R(int)=0.0299]
0.9393 and 0.8837
8463/0/552
9426/6494 [R(int)=0.0482]
1.0000 and 0.7745
6494/136/568
1.038
42,329/8021 [R(int)=0.0747]
0.833 and 0.799
8021/136/594
1.030
10,962/3274 [R(int)=0.0390]
0.8284 and 0.804
3274/0/244
1.070
1.040
1.044
Final R indices [I>2θ(I)]
R indices (all data)
R1=0.0732, wR2=0.1996
R1=0.1002, wR2=0.2220
0.851 and −0.401
R1=0.0699, wR2=0.1765
R1=0.1143, wR2=0.2120
1.086 and −0.496
R1=0.0571, wR2=0.1521
R1=0.0699, wR2=0.1649
1.085 and −0.855
R1=0.0833, wR2=0.1927
R1=0.1645, wR2=0.2415
1.003 and −0.611
R1 =0.0637, wR2=0.1309
R1 =0.1346, wR2=0.1589
0.557 and −0.432
R1=0.0277,wR2=0.0682
R1=0.0313, wR2=0.0708
0.263 and −0.314
Largest diff. peak and hole (e·Å−3
)

52
G.-J. Chen et al. / Journal of Inorganic Biochemistry 122 (2013) 49–56
Table 2
Selected bonds lengths (Å) and angles (deg) for complexes 1–6.
1
Mn1\N1
Mn1\N3
Mn1\N5
N1\Mn1\N2
N1\Mn1\N4
N2\Mn1\N4
N3\Mn1\N5
Fe1\N1
2.244(3)
2.253(3)
2.185(3)
72.7(1)
Mn1\N2
Mn1\N4
Mn1\N6
N1\Mn1\N3
N1\Mn1\N5
N2\Mn1\N5
N3\Mn1\N6
Fe1\N2
2.184(4)
2.221(3)
2.244(3)
145.1(1)
113.3(1)
170.1(1)
92.1(1)
1.871(5)
1.978(5)
1.993(5)
162.0(2)
100.3(2)
177.5(2)
161.3(2)
1.987(4)
2.099(4)
2.119(5)
103.1(2)
100.9(2)
92.0(2)
1.982(3)
2.105(3)
2.105(3)
156.7(1)
99.7(1)
156.5(1)
2.287(4)
2.341(5)
2.355(5)
139.6(2)
121.4(2)
69.9(2)
98.8(1)
115.0(1)
101.3(1)
1.961(5)
1.969(5)
1.883(5)
81.3(2)
90.1(2)
97.5(2)
80.6(2)
2.121(4)
2.116(4)
1.996(4)
156.0(2)
177.4(2)
99.6(2)
2.098(3)
2.106(3)
1.977(2)
78.7(1)
2
Fe1\N3
Fe1\N5
Fe1\N4
Fe1\N6
Fig. 2. Perspective view of 1 cation with the atom-numbering scheme. Hydrogen atoms
and environmental anions are omitted for clarity.
N1\Fe1\N
N1\Fe1\N4
N2\Fe1\N4
N4\Fe1\N5
Ni1\N1
Ni1\N3
Ni1\N5
N1\Ni1\N3
N2\Ni1\N5
N3\Ni1\N5
Ni1\N
Ni1\N3
Ni1\N5
N1\Ni1\N2
N1\Ni1\N4
N2\Ni1\N5
Cd1\N1
N1\Fe1\N3
N1\Fe1\N5
N2\Fe1\N5
N4\Fe1\N6
Ni1\N2
Ni1\N4
Ni1\N6
N2\Ni1\N4
N2\Ni1\N6
N3\Ni1\N6
Ni1\N2
Ni1\N4
Ni1\N6
N1\Ni1\N3
N1\Ni1\N5
N4\Ni1\N6
Cd1\N2
3
4
5
is 2.222(4)Å, which is slightly shorter than the average Mn(II)\N
bond length of 2.27 Å observed for the monocationic [Mn(py5)Cl]+
unit [59], but still consistent with a high-spin Mn(II) center [60].
3.1.2. [Fe(Phterpy)2](NO3)2 (2)
The structure of complex 2 is shown in Fig. 3. Complex 2 has a
distorted octahedral geometry; two terpyridines are tilted 2.5° close
to perfect orthogonality. The Fe\N(2) and Fe\N(5) axial bonds in-
volving the pyridine rings are markedly shorter than the equatorial
bonds [Fe\N(1), Fe\N(3), Fe\N(4) and Fe\N(6)]. The metal–nitrogen
distances are obviously shorter than in complex 1 with an average Fe\N
bond length of 1.942(5)Å within the range of 1.938(2)–2.042(2)Å [61].
The shorter bond lengths may result from the low-spin state of the metal
ion [62]. The shorter bond to the central pyridine nitrogens also allows
for cis N–Fe–N angles that are much closer to the idealized octahedral
values. Moreover, there are strong intermolecular π–π interactions be-
tween ligand layers (π-stacking overlap), while there are no intramo-
lecular π–π interactions.
94.1(1)
178.1(1)
2.333(5)
2.376(5)
2.307(4)
70.5(2)
Cd1\N3
Cd1\N5
Cd1\N4
Cd1\N6
N1\Cd1\N2
N1\Cd1\N4
N1\Cd1\N6
N2\Cd1\N4
Zn1\N1
Zn1\N3
Zn1\Cl2
N1\Zn1\N3
N1\Zn1\Cl1
N2\Zn1\Cl1
N1\Cd1\N3
N1\Cd1\N5
N2\Cd1\N3
N2\Cd1\N5
Zn1\N2
96.1(2)
100.0(2)
120.9(2)
2.1886(19)
2.1913(18)
2.2686(7)
149.20(7)
96.97(5)
124.60(5)
164.4(2)
2.0940(19)
2.2650(7)
74.55(7)
74.67(7)
99.10(5)
118.74(5)
6
Zn1\Cl1
N1\Zn1\N2
N2\Zn1\N3
N1\Zn1\Cl2
N2\Zn1\Cl2
3.1.3. [Ni(Phterpy)2](NO3)2 (3) and [Ni(Phterpy)2]Cl2·10H2O (4)
The Ni\N (axial) and Ni\N (equatorial) bond lengths of 4 are
markedly shorter than that of 3. The average Ni\N bond lengths of
3 and 4 are 2.073(1) and 2.062(2)Å, respectively. The axial positions
are occupied by the atoms of N(5) and N(2) with the angles of N2–
Ni1–N5 equal to 177.42° (3) and 178.03° (4). For 4, two terpyridines
are tilted 1.97° and can be seen at an almost perfect orthogonality.
The structure of complexes 3 and 4 contains layers of the 2D-Phterpy
embrace, each of which interacts with neighboring layers only through
edge-to-face interactions between phenyl groups (Figs. 4, 5.) [63]. In
addition, there are complicated hydrogen bonding interactions in 4,
which enhance the stability of the crystal structure.
N\Ndistal, respectively. It is worthwhile mentioning that complex 6
has distorted trigonal bipyramidal geometry. In all complexes, aro-
matic Phterpy ligands tend to self-assemble via intermolecular π–π
interactions as shown in Fig. 1.
3.1.1. [Mn(Phterpy)2][N(CN)2]2·0.5H2O (1)
The Mn(II) center is in a distorted octahedral geometry owing to
the rotation of pyridine rings within a Phterpy ligand. The angle of
N(2)\Mn\N(5) is 170.14°, thus the two terpyridines are tilted 9.86°
away from perfect orthogonality. The Mn\N(2) and Mn\N(5) axial
bonds involving the pyridine rings are markedly shorter than the equa-
torial bonds [Mn\N(1), Mn\N(3), Mn\N(4) and Mn\N(6)]. The
crystal structure of 1 is shown in Fig. 2. The average bond of Mn(II)\N
3.1.4. [Cd(Phterpy)2](NO3)2·2H2O (5)
The coordination sphere for 5 is also a distorted octahedron with
the average Cd\N bond length of 2.333(2)Å.
M
M
N
N
N
N
N
N
M
N
N
N
N
N
N
M
N
N
N
N
N
N
M
M
Fig. 1. Some of the possible crystal packing interactions for complexes with Phterpy ligands.

G.-J. Chen et al. / Journal of Inorganic Biochemistry 122 (2013) 49–56
53
the equatorial plane and N(1) and N(3) in the axial positions. For a tri-
gonal bipyramid, the equatorial plane is formed by two Cl anions and
N(2), consequently the two angles are close to the theoretical value of
120°. The Zn–N distances are averaged with the value of 2.189(9)Å. A
section of the overall 3D hydrogen bonded network is shown in
Fig. S1. The 3D structure has chlorine ions interspersed with the hydro-
gen of benzene. There is one type of face-to-face π–π stacking interac-
tion apparent at a ring centroid separation of 3.382 Å.
3.2. Circular dichroism studies
CD spectroscopy is useful in monitoring the conformational varia-
tions of DNA in a solution and provides detailed information about
the binding of the complex with DNA. The CD spectrum of CT-DNA
exhibits a positive band at 275 nm due to base stacking and a nega-
tive band at 245 nm due to helicity, which is characteristic of DNA in
the right-handed B form [64]. Fig. S2 displays the CD spectra of CT-DNA
in the absence and presence of complexes 1–6. Both the positive
(~275 nm) and negative (~245 nm) bands decrease significantly in
intensity with redshift with the addition of the complex. This suggests
that the DNA-binding of the complexes induces certain conformational
changes, such as the conversion from a more B-like to a more Z-like
structure within the DNA molecule [65]. The CD spectroscopic results
reveal that the complexes bind to CT-DNA effectively.
Fig. 3. Packing diagram within the layer of 2 and face-to-face of the ligand interactions
in 2.
3.1.5. [Zn(Phterpy)Cl2] (6)
The molecular structure of 6 is shown in Fig. 6. It crystallizes in the
monoclinic space group P2(1)/n. The geometry of the complex is best
described as trigonal bipyramidal with N(2), Cl(1) and Cl(2) occupying
Fig. 4. The π-stacking overlap packing diagram of 3. Hydrogen atoms and environmental anions are omitted for clarity.
Fig. 5. Packing diagram of 4. Hydrogen bonding network of Cl–H–C and ligand interactions.

54
G.-J. Chen et al. / Journal of Inorganic Biochemistry 122 (2013) 49–56
fully DNA-bound form, respectively. The intrinsic binding constant
(Kb) values are given in Table 3.
½DNAꢀ=ða−εf Þ ¼ ½DNAꢀ=ðb−f Þ þ 1=½Kbðb−εf Þꢀ
ð1Þ
The Kb values follow the order 1>4>3, 5, 2, 6. The high-spin com-
plex 1 of the d5 metal shows comparatively higher binding propensity
to CT-DNA possibly due to an extended more unpaired d electrons than
the other metals.
The binding of the complexes to the CT-DNA has also been studied
by a fluorescence spectral method using the emission intensity of EB
as a probe. EB in a buffer medium shows reduced emission intensity
due to quenching by the solvent molecules. However, it shows signif-
icantly enhanced emission intensity when bound to DNA. Binding of
the complex to DNA either displaces EB thus decreasing its emission
intensity or quenching could take place due to the metal complexes
in a DNA bound form. We have measured the reduction of the emis-
sion intensity of EB at different complex concentrations. According
to the classical Stern–Volmer equation I0/I=1+K [Q]; I0 and I are the
fluorescence intensities in the absence and presence of the quencher,
respectively. K is a linear Stern–Volmer quenching constant. [Q] is the
concentration of the quencher. The quenching plots (ESI Fig. S4.) illus-
trate that the quenching of EB bound to DNA by complexes is in agree-
ment with the linear Stern–Volmer equation [69], which also indicates
that the complexes bind to DNA. In the plot of I0/I vs. the concentrations
of complexes, K is given by the ratio of the slope to the intercept.
According to the equation KEB [EB]=Kapp [complex], where the com-
plex concentration was the value at a 50% reduction of the fluorescence
intensity of EB and KEB =1.0×107 M−1, ([EB]=4.0 μ M). The Kapp value
is calculated to be 2.00×105, 2.75×105, 1.43×105, 1.37×105, 3.68×105
and 2.74×105 M−1 for complexes 1–6, respectively, less than the
binding constant of the classical intercalators and metallointercalators
(107 M−1), which suggests that the interaction of those complexes
with DNA is a moderate intercalative mode.
Fig. 6. Perspective view of 6 cation with the atom-numbering scheme.
3.3. UV–visible spectra
The complexes have a strong charge transfer absorption band in
282 nm assigned as intra-ligand electronic spectral transitions as shown
in Fig. 7. The absorption intensity is consistent with the number of
single-electron in the complexes.
3.4. DNA binding studies
The binding of the complexes to CT-DNA has been studied by
an electronic absorption spectral technique. Binding of a complex to
DNA through intercalation usually results in hypochromism and
redshift (bathochromic shift) due to the intercalative mode involving
a strong stacking interaction between the planar aromatic chromo-
phore and the base pairs of DNA [66]. The extent of the hypochromism
in the charge transfer band is commonly consistent with the strength of
intercalative binding interaction. The absorption spectral traces of the
complexes with increasing concentration of CT-DNA are shown in
Fig S3. We have observed a minor bathochromic shift along with signif-
icant hypochromicity. When the amount of CT-DNA is increased, a
decrease of about 30% in the intensity of the charge transfer band is ob-
served. In order to compare the binding strength of the complexes,
their intrinsic binding constants (Kb) with CT-DNA have been deter-
mined from the decay of the spectral band absorbance using Eq. (1)
[67,68], where εa, εb and εf are the apparent absorption coefficient, εa
of the metal complex in its free form and εa of the complex in its
3.5. pBR322 DNA cleavage activity by the complexes
Control cleavage experiments using pBR322 supercoiled DNA with
the six complexes show no efficient DNA cleavage activity in the dark
or in ambient light but show cleavage activity in UV-A light (365 nm)
for 1, 3, and 4. Complex 2 shows DNA cleavage activity in the pres-
ence of H2O2. Complexes 5 and 6 show no DNA photocleavage activity
even in the presence of the UV-A light of 365 nm and hydrogen per-
oxide (H2O2). The concentration-dependent DNA cleavage in UV-A
light shows that the cleavage activity increases with increasing com-
plexes 1–4 and the percentage of undamaged binding sites has almost
no change for 5 and 6 (Fig. S5). The Mn(II) complex (1) (a 10 μM
solution) in UV-A light (ESI Fig. S5) for 3 h exhibits 97% cleavage
of SC DNA (Fig. S5, (1) lane 6). The Ni(II) complexes 3 and 4 show
moderate DNA photocleavage activity of 62% and 88%, respectively
(Fig. S5, (3) lane 6 and (4) lane 6). The Fe(II) complex (2) is a relatively
poor cleaver of DNA in UV-A light.
3.0
(1)
2.5
(2)
(3)
2.0
To verify if reactive oxygen species (ROS) may be formed in the
DNA cleavage reaction, the photo-induced DNA cleavage reactions of
the complexes have been studied in the presence of an additive under
(4)
1.5
(5)
(6)
Table 3
1.0
Change in spectral features of the complexes on interaction with CT-DNA in 50 mM
Tris–HCl/18 mM NaCl buffer (pH=7.2).
0.5
Complex Change in absorptivity λmax (nm) Δλmax (nm) Δε (%) Kb
1
2
3
4
5
6
Hypochromism
Hypochromism
Hypochromism
Hypochromism
Hypochromism
Hypochromism
206
206
208
208
206
212
2
8
10
8
10
6
58.65
34.80
30.49
22.32
31.72
38.90
1.91×105
4.13×103
7.64×103
3.22×104
7.42×103
1.60×103
0.0
200
250
300
350
400
Wav./nm
Fig. 7. UV–visible spectrum of 1–6 in DMF (5%) and H2O (95%).

G.-J. Chen et al. / Journal of Inorganic Biochemistry 122 (2013) 49–56
55
Fig. 8. Agarose gel showing cleavage of pBR322 DNA (0.1 μg/μL) incubated with complex 1 in Tris–HCl/NaCl buffer (pH=7.2) at 37 °C for 30 min with irradiation at 365 nm. Lane 1:
DNA control; lane 2: DNA+1 (15 μM); lane 3: DNA+1 (15 μM)+DMSO (100 μM); lane 4: DNA+1 (15 μM)+NaN3 (100 μM); lane 5: DNA+1 (15 μM)+SOD (100 μM); lane 6:
DNA+1 (15 μM)+catalase (100 μM); lane7: DNA+1 (15 μM)+KI (100 μM); lane 8: DNA+1 (15 μM)+EDTA (100 μM); lane 9: DNA+1 (15 μM)+D2O (100 μM); lane 10:
DNA+1 (15 μM)+EtSH (100 μM); lane 11: DNA+1 (15 μM)+histidine (100 μM).
UV-A light (365 nm). A series of control experiments were carried out
using reagents like sodium azide and histidine as singlet oxygen (1O2)
quencher; DMSO, EtSH, catalase and KI as hydroxyl radical scavengers;
EDTA as chelating agent and superoxide dismutase (SOD) as an O2−
radical scavenger. The mechanistic cleavage active in UV-A light is
essentially the same for 1–4. The present complexes are cleavage inac-
tive in the dark indicating no apparent hydrolytic cleavage of DNA.
Enhancement of the DNA cleavage in D2O and inhibition in the presence
of sodium azide or histidine suggest the possible involvement of singlet
oxygen as the reactive species, and hydroxyl radical scavengers like
DMSO, EtSH or KI also show partial inhibition in the DNA cleavage.
The results suggest the involvement of both singlet oxygen and hy-
droxyl radicals as ROS. The chelating agent EDTA shows inhibition in
the DNA cleavage (Figs. 8–11). The mechanistic data thus exclude the
photoredox pathway superoxide radical (O2• −) in the photocleavage
reaction. The high spin d5-Mn(II) complex (1) shows significant
photo-induced DNA cleavage. The paramagnetic d8-Ni(II) complexes
(3) and (4) display moderate DNA cleavage activity in UV-A light.
Low spin d6-Fe(II) complex (2) shows poor DNA cleavage in the presence
of hydrogen peroxide (H2O2) in UV-A light. Diamagnetic d10-Zn(II) and
d10-Cd(II) complexes show inactive DNA cleavage even in the presence
of hydrogen peroxide (H2O2) in UV-A light. The DNA photo-induced
cleavage activity is consistent with the absorption intensity and the
number of single-electron in metal of complexes.
activity in the dark or in ambient light for the six complexes but show
cleavage activity in UV-A light (365 nm) for high spin 1 d5-Mn(II), 3
d8-Ni(II), and 4 d8-Ni(II) and show chemical nuclease activity in the
presence of hydrogen peroxide (H2O2) for low spin 2 d6-Fe(II). The 5
d10 Zn(II) and 6 Cd(II) complexes show inactive DNA photocleavage
activity even in the light of 365 nm in the presence of hydrogen peroxide
(H2O2). The mechanistic pathway involved the formation of singlet oxy-
gen and hydroxyl radical as the reactive species. DNA cleavage activity
studies show that the complexes examined here may be capable of pro-
moting DNA cleavage with the selection of different metals. This work
sets a good example of rational design of efficient photo-induced DNA
cleavage nucleases.
5. Abbreviations
Phterpy 4′-phenyl-2,2′:6′,2″-terpyridine
DMF
EB
N,N-dimethylformamide
Ethidium bromide
CT-DNA Calf thymus DNA
SOD
MTT
Superoxide dismutase
3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium
bromide
Acknowledgments
4. Conclusions
This work was supported by the National Natural Science Foun-
dation of China (nos. 21001066 and 21171101) and Reward Fund
for Outstanding Young and Middle Aged Scientists of Shandong
Province (no. 2012BSB01101) and Tianjin Science Foundation (no.
12JCYBJC13600).
In summary, a series of Phterpy complexes are prepared. Those
complexes display binding propensity to the calf thymus DNA in the
order: 1>4>3, 5, 2, 6. Control DNA cleavage experiments using
pBR322 DNA with those complexes show no efficient DNA cleavage
Fig. 9. Agarose gel showing cleavage of pBR322 DNA (0.1 μg/μL) incubated with complex 2 in Tris–HCl/NaCl buffer (pH=7.2) at 37 °C for 30 min with irradiation at 365 nm. Lane 1:
DNA control; lane 2: DNA+H2O2; lane 3: DNA+2 (15 μM)+H2O2; lane 4: DNA+2 (15 μM)+DMSO (100 μM)+H2O2; lane 5: DNA+2 (15 μM)+NaN3 (100 μM)+H2O2; lane 6:
DNA+2 (15 μM)+SOD (100 μM)+H2O2; lane 7: DNA+2 (15 μM)+catalase (100 μM)+H2O2; lane8: DNA+2 (15 μM)+KI (100 μM)+H2O2; lane 9: DNA+2 (15 μM)+EDTA
(100 μM)+H2O2; lane 10: DNA+2 (15 μM)+D2O (100 μM)+H2O2; lane 11: DNA+2 (15 μM)+EtSH (100 μM)+H2O2; lane 12: DNA+2 (15 μM)+histidine (100 μM)+H2O2.
Fig. 10. Agarose gel showing cleavage of pBR322 DNA (0.1 μg/μL) incubated with complex 3 in Tris–HCl/NaCl buffer (pH=7.2) at 37 °C for 30 min with irradiation at 365 nm. Lane
1: DNA control; lane 2: DNA+3 (15 μM); lane 3: DNA+3 (15 μM)+DMSO (100 μM); lane 4: DNA+3(15 μM)+NaN3 (100 μM); lane 5: DNA+3 (15 μM)+SOD (100 μM); lane 6:
DNA+3 (15 μM)+catalase (100 μM); lane7: DNA+3 (15 μM)+KI (100 μM); lane 8: DNA+3 (15 μM)+EDTA (100 μM); lane 9: DNA+3 (15 μM)+D2O (100 μM); lane 10:
DNA+3 (15 μM)+EtSH (100 μM); lane 11: DNA+3 (15 μM)+histidine (100 μM).

56
G.-J. Chen et al. / Journal of Inorganic Biochemistry 122 (2013) 49–56
Fig. 11. Agarose gel showing cleavage of pBR322 DNA (0.1 μg/μL) incubated with complex 4 in Tris–HCl/NaCl buffer (pH=7.2) at 37 °C for 30 min with irradiation at 365 nm. Lane
1: DNA control; lane 2: DNA+4 (15 μM); lane 3: DNA+4 (15 μM)+DMSO (100 μM); lane 4: DNA+4 (15 μM)+NaN3 (100 μM); lane 5: DNA+4 (15 μM)+SOD (100 μM); lane
6: DNA+4 (15 μM)+catalase (100 μM); lane7: DNA+4 (15 μM)+KI (100 μM); lane 8: DNA+4 (15 μM)+EDTA (100 μM); lane 9: DNA+4 (15 μM)+D2O (100 μM); lane 10:
DNA+4 (15 μM)+EtSH (100 μM); lane 11: DNA+4 (15 μM)+histidine (100 μM).
Appendix A. Supplementary data
[27] J.P. Nathan, Annu. Rep. Prog. Chem., Sect. A 104 (2008) 498–528.
[28] T.K. Goswami, M. Roy, M. Nethaji, A.R. Chakravarty, Organometallics 28 (2009)
1992–1994.
[29] M. Roy, T. Bhowmick, S. Ramakumar, M. Nethaji, A.R. Chakravarty, Dalton Trans.
(2008) 3542–3545.
[30] P.K. Sasmal, A.K. Patra, A.R. Chakravarty, J. Inorg. Biochem. 102 (2008) 1463–1472.
[31] S. Roy, A.K. Patra, S. Dhar, A.R. Chakravarty, Inorg. Chem. 47 (2008) 5625–5633.
[32] M. Roy, B. Pathak, A.K. Patra, E.D. Jemmis, M. Nethaji, A.R. Chakravarty, Inorg.
Chem. 46 (2007) 11122–11132.
[33] P.K. Sasmal, S. Roy, A.R. Chakravarty, Inorg. Chim. Acta 362 (2009) 1591–1599.
[34] S. Mondal, M. Mukherjee, K. Dhara, S. Ghosh, J. Ratha, P. Banerjee, A.K. Mukherjee,
Cryst. Growth Des. 7 (2007) 1716–1721.
[35] S. Saha, A.K. Patra, M. Nethaji, A.R. Chakravarty, Inorg. Chem. 46 (2007) 4368–4370.
[36] M. Tanaka, K. Ohkubo, S. Fukuzumi, J. Am. Chem. Soc. 128 (2006) 12372–12373.
[37] M. Tanaka, K. Ohkubo, S. Fukuzumi, J. Phys. Chem. A 110 (2006) 11214–11218.
[38] F.S. Mackay, J.A. Woods, H. Moseley, J. Ferguson, A. Dawson, S. Parsons, P.J. Sadler,
Chem. Eur. J. 12 (2006) 3155–3161.
[39] S. Dhar, M. Nethaji, A.R. Chakravarty, Inorg. Chem. 44 (2005) 8876–8883.
[40] P. Yang, Q. Yang, X.H. Qian, J.N. Cui, Bioorg. Med. Chem. 13 (2005) 5909–5914.
[41] S. Shi, J. Liu, J. Li, C. Kang, C.P. Tan, L.M. Chen, L.N. Ji, Dalton Trans. (2005) 2038–2046.
[42] A. Mukherjee, S. Dhar, M. Nethaji, A.R. Chakravarty, Dalton Trans. (2005) 349–353.
[43] M. Rajendran, R. Gandhidasan, R. Murugesan, J. Photochem. Photobiol. A 168
(2004) 67–73.
Electronic supplementary information (ESI) available
Packing diagram of [Zn(Phterpy)Cl2] (6), hydrogen bonding network
of Cl–H–C and ligand interactions (Fig. S1); the CD spectra of CT-DNA in
the buffer solution (Fig. S2); absorption spectra of complexes 1–6 in the
absence (dashed line) and presence (solid line) of increasing amounts
of CT-DNA at room temperature in 50 mmol Tris–HCl/18 mmol NaCl
buffer (pH=7.2) (Fig. S3); fluorescence quenching curves and plots of
I0/I vs. [complex] of EB bound to DNA by complexes 1–6 (Fig. S4); gel
electrophoresis diagrams showing the cleavage of pBR322 DNA at dif-
ferent concentrations (Fig. S5). Supplementary data associated with
this article can be found, in the online version, at http://dx.doi.org/10.
1016/j.jinorgbio.2013.01.010.
References
[1] H.T. Chifotides, K.R. Dunbar, Acc. Chem. Res. 38 (2005) 146–156.
[2] P.M. Bradley, A.M. Angeles-Boza, K.R. Dunbar, C. Turro, Inorg. Chem. 43 (2004)
2450–2452.
[3] P.J. Bednarski, F.S. Mackay, P.J. Sadler, Anticancer Agents Med Chem. 7 (2007) 75–93.
[4] P.J. Dyson, M.J. Rose, N.L. Fry, R. Marlow, L. Hinck, P.K. Mascharak, J. Am. Chem.
Soc. 130 (2008) 8834–8846.
[5] P. Heringova, J. Woods, F.S. Mackay, J. Kasparkova, P.J. Sadler, V. Brabec, J. Med.
Chem. 49 (2006) 7792–7798.
[6] E. Meggers, Chem. Commun. (2009) 1001–1010.
[44] H.P. He, T. Tian, P. Wang, L. Wu, J.J. Xu, X. Zhou, X.L. Zhang, X.P. Cao, X.J. Wu,
Bioorg. Med. Chem. Lett. 14 (2004) 3013–3016.
[45] F.L. Tang, G. Yuan, J. Wang, Photochem. Photobiol. 78 (2003) 175–179.
[46] K. Toshima, R. Takano, T. Ozawa, S. Matsumura, Chem. Commun. (2002) 212–213.
[47] E.T. Farinas, J.D. Tan, P.K. Mascharak, Inorg. Chem. 35 (1996) 2637–2643.
[48] E.C. Constable, A.M.W. Cargill Thompson, D.A. Tocher, M.A.M. Daniels, New
J. Chem. 16 (1992) 855–872.
[49] E.C. Constable, J. Lewis, M.C. Liptrot, P.R. Raithby, Inorg. Chim. Acta 178 (1990)
47–54.
[50] Y.Y. Kou, W. Gu, H. Liu, X.F. Ma, D.D. Li, S.P. Yan, Nankai Daxue Xuebao, Ziran
Kexueban 41 (2008) 19–25.
[51] G.M. Sheldrick, Correction Software, University of Götingen, Germany, 1996.
[52] G.M. Sheldrick, SHELXS 97, Program for the Solution of Crystal Structures, University
of Götingen, Germany, 1997.
[53] G.M. Sheldrick, SHELXL 97, Program for the Refinement of Crystal Structures,
University of Götingen, Germany, 1997.
[54] J. Marmur, J. Mol. Biol. 3 (1961) 585–594.
[55] M.E. Reichmann, S.A. Rice, C.A. Thomas, P. Doty, J. Am. Chem. Soc. 76 (1954)
3047–3053.
[56] R.P. Herzberg, P.P. Derwan, J. Am. Chem. Soc. 104 (1982) 313–315.
[57] C.K. Mirabelli, C.H. Huang, S.T. Crooke, Cancer Res. 40 (1980) 4173–4177.
[58] C.A. Detmer, F.V. Pamatong, J.R. Borcarsly, Inorg. Chem. 35 (1996) 6292–6298.
[59] R.J.M. Klein Gebbin, R.T. Jonas, C.R. Goldsmith, T.D.P. Stack, Inorg. Chem. 41
(2002) 4633–4641.
[60] C.R. Goldsmith, A.P. Cole, T.D.P. Stack, J. Am. Chem. Soc. 127 (2005) 9904–9912.
[61] P. Guionneau, M. Marchivie, G. Bravic, J.F. Létard, D. Chassesu, Top. Curr. Chem.
234 (2004) 97–128.
[62] E.C. Constable, G. Baum, E. Bill, R. Dyson, R. Van Eldik, D. Fenske, S. Kaderli, D. Morris,
A. Neubrand, M. Neuburger, D.R. Smith, K. Wieghardt, M. Zehnder, A.D. Zuberbuhler,
Chem. Eur. J. 5 (1999) 498–508.
[63] J. McMurtriea, I. Dance, CrystEngComm 11 (2009) 1141–1149.
[64] A. Rajendran, B.U. Nair, Biochim. Biophys. Acta 1760 (2006) 1794–1801.
[65] A.D. Richards, A. Rodger, Chem. Soc. Rev. 36 (2007) 471–483.
[66] V.A. Bloomfield, D.M. Crothers, I.J. Tinocco, Physical Chemistry of Nucleic Acids,
Harper & Row, New York, 1974, p. 432.
[7] V. Rajendiran, M. Palaniandavar, P. Swaminathan, L. Uma, Inorg. Chem. 46 (2007)
10446–10448.
[8] B. Rosenberg, L. VamCamp, J.E. Trosko, V.H. Mansour, Nature 222 (1969) 385–386.
[9] E.R. Jamieson, S.J. Lippard, Chem. Rev. 99 (1999) 2467–2498.
[10] F. Arnesano, G. Natile, Coord. Chem. Rev. 253 (2009) 2070–2081.
[11] A.V. Klein, T.W. Hambley, Chem. Rev. 109 (2009) 4911–4920.
[12] R. Gust, W. Beckb, G. Jaouenc, H. Schenberger, Coord. Chem. Rev. 253 (2009)
2742–2759.
[13] M. Skander, P. Retailleau, B. Bourri, L. Schio, P. Mailliet, A. Marinetti, J. Med. Chem.
53 (2010) 2146–2154.
[14] Z. Wu, Q. Liu, X. Liang, X. Yang, N. Wang, X. Wang, H. Sun, Y. Lu, Z. Guo, J. Biol.
Inorg. Chem. 14 (2009) 1313–1323.
[15] Y. Jung, S.J. Lippard, Chem. Rev. 107 (2007) 1387–1407.
[16] K.S. Soppimath, L.H. Liu, W.Y. Seow, S.Q. Liu, R. Powell, P. Chan, Y.Y. Yang, Adv.
Funct. Mater. 17 (2007) 355–362.
[17] Y. Xie, G.G. Miller, S.A. Cubitt, K.J. Soderlind, M.J. Allalunis-Turner, J.W. Lown,
Anti-Cancer Drug Des. 12 (1997) 169–179.
[18] M. Shi, K. Ho, A. Keating, M.S. Shoichet, Adv. Funct. Mater. 19 (2009) 1689–1696.
[19] A. Hussain, D. Lahiri, B.M.S. Ameerunisha, S. Saha, R. Majumdar, R.R. Dighe, A.R.
Chakravarty, Inorg. Chem. 49 (2010) 4036–4045.
[20] B.M.S. Mmeerunisha, S. Saha, M. Nethaji, A.R. Chakravarty, J. Inorg. Biochem. 104
(2010) 477–484.
[21] D. Lahiri, S. Roy, S. Saha, R. Majumdar, R.R. Dighe, A.R. Chakravarty, Dalton Trans.
(2010) 1807–1816.
[22] P.K. Sasmal, S. Saha, R. Majumdar, R.R. Dighe, A.R. Chakravarty, Inorg. Chem. 49
(2010) 849–859.
[23] N. Raman, R. Jeyamurugan, A. Sakthivel, L. Mitu, Spectrochim. Acta, Part A 75A
(2010) 88–97.
[24] S. Roy, S. Saha, R. Majumdar, R.R. Dighe, A.R. Chakravarty, Inorg. Chem. 48 (2009)
9501–9509.
[25] M. Roy, T. Bhowmick, R. Santhanagopal, S. Ramakumar, A.R. Chakravarty, Dalton
Trans. (2009) 4671–4682.
[26] H.J. Yu, S.M. Huang, L.Y. Li, H.N. Jia, H. Chao, Z.W. Mao, J.Z. Liu, L.N. Ji, J. Inorg.
Biochem. 103 (2009) 881–890.
[67] J. Qian, W. Gu, H. Liu, F.X. Gao, L. Feng, S.P. Yan, D.Z. Liao, P. Cheng, Dalton Trans.
(2007) 1060–1067.
[68] M. Navarro, C. Hernández, I. Colmenares, P. Hernández, M. Fernández, A.
Sierraalta, E. Marchan, J. Inorg. Biochem. 101 (2007) 111–116.
[69] J.R. Lakowicz, G. Webber, Biochemistry 12 (1973) 4161–4170.