Synthesis, structure, DNA-binding properties and antioxidant activity of a nickel(II) complex with bis(N-allylbenzimidazol-2-ylmethyl)benzylamine

Article abstract of DOI:10.1016/j.jphotobiol.2011.11.010

A V-shape ligand bis(N-allylbenzimidazol-2-ylmethyl)benzylamine (babb) and its nickel complex, [Ni(babb)₂](pic)₂ (pic = picrate), have been synthesized and characterized by physico-chemical and spectroscopic methods. Single-crystal X

Full text of DOI:10.1016/j.jphotobiol.2011.11.010

Journal of Photochemistry and Photobiology B: Biology 107 (2012) 65–72
Contents lists available at SciVerse ScienceDirect
Journal of Photochemistry and Photobiology B: Biology
journal homepage: www.elsevier.com/locate/jphotobiol
Synthesis, structure, DNA-binding properties and antioxidant activity
of a nickel(II) complex with bis(N-allylbenzimidazol-2-ylmethyl)benzylamine
⇑
Huilu Wu , Jingkun Yuan, Ying Bai, Guolong Pan, Hua Wang, Xingbin Shu
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A
V-shape ligand bis(N-allylbenzimidazol-2-ylmethyl)benzylamine (babb) and its nickel complex,
Received 9 November 2011
Received in revised form 23 November 2011
Accepted 30 November 2011
Available online 21 December 2011
[Ni(babb)2](pic)2 (pic = picrate), have been synthesized and characterized by physico-chemical and spec-
troscopic methods. Single-crystal X-ray revealed that the coordination sphere around Ni(II) is distorted
octahedral with a N6 ligand set, in which six nitrogen atoms were afforded by two tridentate ligand babb.
The DNA-binding properties of the free ligand babb and Ni(II) complex have been investigated by elec-
tronic absorption, fluorescence, and viscosity measurements. The results suggest that babb and Ni(II)
complex both bind to DNA via an intercalative binding mode, and the affinity for DNA is more strong
in case of Ni(II) complex when compared with babb. The intrinsic binding constants (Kb) of the Ni(II) com-
plex and ligand with DNA were 3.65 ꢀ 104 Mꢁ1 and 2.26 ꢀ 103 Mꢁ1, respectively. Additionally, Ni(II)
complex also exhibited potential antioxidant properties in vitro studies.
Keywords:
Benzimidazole
Nickel(II) complex
Crystal structure
DNA-binding property
Antioxidant property
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
application areas [15,16], which gives the possibility for further re-
search, such as design of structural probes and the development of
The benzimidazole moiety is part of the chemical structure of
vitamin B12 which is one of the biologically relevant natural com-
pounds [1]. Benzimidazole and its derivatives have attracted
continuing interest over the years because of their varied biological
activities viz. anticancer [2], antihypertensive [3], antiviral [4],
anti-inflammatory [5], vasodilator [6] and antimicrobial [7–9].
Moreover, as a typical heterocyclic ligand, the large benzimidazole
rings not only can provide potential supramolecular recognition
novel therapeutics.
In the framework of our research project, mainly focus on deal-
ing with the transition metal complexes containing benzimid-
azole-based ligand and exploring the reaction mechanism with
DNA. In preceding reports [17–21], we have investigated the coor-
dinating ability of various benzimidazole ligands and the corre-
sponding transition metal complexes. In this paper, the synthesis,
characterization and DNA-binding activities of Ni(II) complex with
a V-shape ligand are presented. Moreover, We also conducted an
investigation to explore whether the Ni(II) complex has the antiox-
idant property.
sites for p–p stacking interactions, but also act as hydrogen bond
acceptors and donors to assemble multiple coordination geometry
[10].
Transition metal complexes are currently being used to bind
and react at specific sequences of DNA in a search for novel chemo-
therapeutics and probing DNA, and for the development of highly
sensitive diagnostic agents [11–13]. Therefore, an understanding
that how these small molecules bind to DNA will potentially be
useful in the design of such new compounds, which can recognize
specific sites or conformations of DNA [12–14]. As both the spec-
troscopic tags and functional models for the active centers of pro-
teins, metal complexes have helped to elucidate the mechanisms
by which metalloproteins function [12]. However, transition metal
complexes containing benzimidazole-based ligand are a subject of
intensive researches not only owing to their rich coordination
chemistry but also due to a number of established and potential
2. Experimental section
2.1. Materials and methods
All chemicals and solvents were reagent grade and were used
without further purification. C, H and N elemental analyses were
determined using a Carlo Erba 1106 elemental analyzer. Electro-
lytic conductance measurements were made with a DDS-307 type
conductivity bridge using 3 ꢀ 10ꢁ3 mol Lꢁ1 solutions in DMF at
room temperature. The IR spectra were recorded in the 4000–
400 cmꢁ1 region with a Nicolet FT-VERTEX 70 spectrometer using
KBr pellets. Electronic spectra were taken on a Lab-Tech UV
Bluestar spectrophotometer. The fluorescence spectra were pre-
formed on a LS-45 spectrofluorophotometer. The absorbance was
measured with Spectrumlab 722sp spectrophotometer at room
⇑
Corresponding author. Tel.: +86 13893117544.
E-mail address: wuhuilu@163.com (H. Wu).
1011-1344/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotobiol.2011.11.010

66
H. Wu et al. / Journal of Photochemistry and Photobiology B: Biology 107 (2012) 65–72
temperature. 1H NMR spectra were recorded on
a
Varian
2.3. X-ray crystallography
VR300 MHz spectrometer with TMS as an internal standard.
The stock solution of babb and Ni(II) complex were dissolved in
DMF at the concentration 3 ꢀ 10ꢁ3 M. Calf thymus DNA (CT-DNA)
and ethidium bromide (EB) were purchased from Sigma. All the
experiments involving interaction of the ligand and the complexes
with CT-DNA were carried out in doubly distilled water buffer con-
taining 5 mM Tris and 50 mM NaCl and adjusted to pH 7.2 with
hydrochloric acid. A solution of CT-DNA gave a ratio of UV absor-
bance at 260 and 280 nm of about 1.8–1.9, indicating that the
CT-DNA was sufficiently free of protein [22]. The CT-DNA concen-
tration per nucleotide was determined spectrophotometrically by
employing an extinction coefficient of 6600 Mꢁ1 cmꢁ1 at 260 nm
[23].
A suitable single crystal was mounted on a glass fiber, and the
intensity data were collected on a Bruker Smart CCD diffractometer
with graphite-monochromated Mo-K radiation (k = 0.71073 Å) at
a
296 K. Data reduction and cell refinement were performed using
the SMART and SAINT programs [25]. The structure was solved
by direct methods and refined by full-matrix least-squares against
F2 of data using SHELXTL software [26]. All H atoms were found in
difference electron maps and subsequently refined in a riding-
model approximation with CAH distances ranging from 0.93 to
0.97 Å and Uiso(H) = 1.2 Ueq(C).
2.4. DNA-binding experiments
Synthetic routine of ligand babb is showed in Scheme 1.
2.4.1. Electronic absorption titration
2.2. Synthesis
Absorption titration experiments were performed with fixed
concentrations of the complexes, while gradually increasing the
concentration of CT-DNA. To obtain the absorption spectra, the re-
quired amount of CT-DNA was added to both the compound and
reference solutions, in order to eliminate the absorbance of CT-
DNA itself. From the absorption titration data, the binding constant
(Kb) was determined using the equation [27]:
2.2.1. Synthesis of ligand: babb
The precursor bis(2-benzimidazol-2-ylmethyl)benzylamine
(bbb) was synthesized following a slight modification of the proce-
dure in Ref. [24], bbb (7.34 g, 20 mmol) and potassium (1.56 g,
40 mmol) were put in tetrahydrofuran (150 mL), the solution was
refluxed on a water bath for 4 h with stirring. Then, allylbromide
(4.84 g, 40 mmol) was added to this solution. With the dropping
of allylbromide, the solution gradually becomes cream yellow.
After that, the resulting solution was concentrated and cooled, a
pale yellow solid separating out and the pale yellow precipitate
was filtered, washed with massive water, and recrystallized from
ethanol to give the ligand.
½DNAꢂ=ðea
ꢁ
ef Þ ¼ ½DNAꢂ=ðeb
ꢁ
ef Þ þ 1=Kbðeb
ꢁ
ef
Þ
where [DNA] is the concentration of CT-DNA in base pairs,
e
a corre-
sponds to the observed extinction coefficient (Aobsd/[M]), ef corre-
sponds to the extinction coefficient of the free compound, eb is the
extinction coefficient of the compound when fully bound to CT-
DNA, and Kb is the intrinsic binding constant. The ratio of slope to
Yield: 5.46 g (61%); m.p.: 113–115 °C. Found (%): C, 78.02; H,
6.35; N, 15.71. Calcd. (%) for C29H29N5: C, 77.82; H, 6.53; N,
intercept in the plot of [DNA]/(ea
of Kb.
ꢁ
ef) versus [DNA] gave the value
15.65. Km(DMF, 297 K): 1.97 S cm2 molꢁ1 1H NMR (DMSO-d6
.
400 MHz) d/ppm: 3.45 (m, 2H, ACH2AAr), 3.85 (s, 4H, ACH2Aben-
zimidazol), 4.87–5.68 (m, 10H, ACH2ACH@CH2), 7.22 (m, 5H, H-
benzene ring), 7.27–7.64 (m, 8H, H-benzimidazol ring). UV–vis
2.4.2. Fluorescence studies
The enhanced fluorescence of EB in the presence of DNA can be
quenched by the addition of a second molecule [28,29]. The extent
of fluorescence quenching of EB bound to CT-DNA can be used to
determine the extent of binding between the second molecule
and CT-DNA. Competitive binding experiments were carried out
in the buffer by keeping [DNA]/[EB] = 1 and varying the concentra-
tions of the compounds. The fluorescence spectra of EB were mea-
sured using an excitation wavelength of 520 nm, and the emission
range was set between 550 and 750 nm. The spectra were analyzed
according to the classical Stern–Volmer equation [30]:
(k, nm): 279, 286. FT–IR (KBr
(CAN); 1461, (C@N); 1643, (C@C).
m m(oAAr); 1265,
/cmꢁ1): 737,
m
m
m
2.2.2. Synthesis of complex: [Ni(babb)2](pic)2
To a stirred solution of babb (223.5 mg, 0.50 mmol) in hot EtOH
(10 mL) was added Ni(pic)2 (128.73 mg, 0.25 mmol) in EtOH
(2 mL). A yellow crystalline product formed rapidly. The precipi-
tate was filtered off, washed with EtOH and absolute Et2O, and
dried under vacuum. The crude product was dissolved in MeCN
to form a pale yellow solution into which Et2O was allowed to dif-
fuse at room temperature. Yellow crystals of it suitable for X-ray
measurement were obtained after two weeks.
I0=I ¼ 1 þ KSV½Qꢂ
Yield: 164.7 mg (62%). Found (%): C, 51.41; H, 3.29; N, 16.13.
Calcd. (%) for C66H58N18O15Zn: C, 51.17; H, 3.46; N, 16.01. Km(DMF,
297 K): 91.09 S cm2 molꢁ1. UV–vis (k, nm): 279, 282, 381. FT–IR
where I0 and I are the fluorescence intensities at 599 nm in the ab-
sence and presence of the quencher, respectively, Ksv is the linear
Stern–Volmer quenching constant, and [Q] is the concentration of
the quencher. In these experiments [CT-DNA] = 2.5 ꢀ 10ꢁ3 mol/L,
[EB] = 2.2 ꢀ 10ꢁ3 mol/L.
(KBr
m
/cmꢁ1): 746,
m(C@N); 1633,
m(oAAr); 1272,
(C@C).
m(CAN); 1365, m(OANAO);
1490,
m
Scheme 1. Synthetic routine of ligand babb.

H. Wu et al. / Journal of Photochemistry and Photobiology B: Biology 107 (2012) 65–72
67
2.4.3. Viscosity titration measurements
3.2. X-ray structures of the complexes
Viscosity experiments were conducted on an Ubbelodhe vis-
cometer, immersed in a water bath maintained at 25.0 0.1 °C.
Basic crystal data, description of the diffraction experiment, and
details of the structure refinement are given in Table 1. Selected
bond distances and angles are presented in Table 2.
Titrations were performed for the complexes (3–30
l
M), and each
M) present
versus the ratio
of the concentration of the compound to CT-DNA, where is the
compound was introduced into CT-DNA solution (42.5
in the viscometer. Data were analyzed as (g/g0)
l
1/3
g
3.2.1. The crystal structure of complex: [Ni(babb)2](pic)2
viscosity of CT-DNA in the presence of the compound and g0 is
the viscosity of CT-DNA alone. Viscosity values were calculated
from the observed flow time of CT-DNA-containing solutions cor-
The crystal structure of Ni(II) complex consists of a discrete
[Ni(babb)2]2+ cation, two picrate anions. The ORTEP structure (30%
probability ellipsoids) of the [Ni(babb)2]2+ with atom-numberings
is shown in Fig. 1.
rected from the flow time of buffer alone (t0),
g
= (t ꢁ t0) [31].
The central Ni(II) atom is six-coordinated with a N6 ligand set,
in which six nitrogen atoms afforded by two tridentate ligand
babb. The coordination geometry of the Ni(II) may be best de-
scribed as distorted octahedral with (N1, N3, N7, N9) providing
the equatorial plane. The maximum deviation distance (N3) from
the least squares plane calculated from the four coordination atom
atoms is 0.241 Å, and the nickel atom is out of this plane by only
0.133 Å. The distance between the axial atom N5, N6 and the equa-
torial plane are 2.138 Å, 2.075 Å, respectively. The bond angle of
the two atoms (N5ANiAN6) in axial positions is 167.76(12)°.
Therefore, compared with a regular octahedron, it reflects a rela-
tively distorted coordination octahedron around central Ni(II)
atom [42–45].
2.5. Antioxidant property
Hydroxyl radicals were generated in aqueous media through
the Fenton-type reaction [32,33]. The aliquots of reaction mixture
(3 mL) contained 1.0 mL of 0.10 mmol aqueous safranin, 1 mL of
1.0 mmol aqueous EDTA–Fe(II), 1 mL of 3% aqueous H2O2, and a
series of quantitative microadditions of solutions of the test com-
pound. A sample without the tested compound was used as the
control. The reaction mixtures were incubated at 37 °C for
30 min in a water bath. The absorbance was then measured at
520 nm. All the tests were run in triplicate and are expressed as
the mean and standard deviation (SD) [34]. The scavenging effect
for OHꢃ was calculated from the following expression:
3.3. DNA binding properties
Scavenging ratio ð%Þ ¼ ½ðAi ꢁ A0Þ=ðAc ꢁ A0Þꢂ ꢀ 100%
3.3.1. Absorption spectroscopic studies
where Ai is the absorbance in the presence of the test compound; A0
is absorbance of the blank in the absence of the test compound; Ac is
the absorbance in the absence of the test compound, EDTA–Fe(II)
and H2O2.
The application of electronic absorption spectra in DNA-binding
studies is one of the most useful techniques. The binding of interca-
lative drugs to DNA has been characterized classically through
absorption titrations, following the hypochromism and red shift
associated with binding of the colored complex to the helix [27].
The absorption spectra of the ligand babb and Ni(II) complex in the
absence and presence of CT-DNA (at a constant concentration of
compounds) are given in Fig. 2. With increasing DNA concentrations,
the hypochromism reaches as high as 18.32% at 275 nm for free li-
3. Results and discussion
Ligand babb and its Ni(II) complex are very stable in the air.
Ni(II) complex is remarkably soluble in polar aprotic solvents such
as DMF, DMSO and MeCN; slightly soluble in ethanol, methanol,
ethyl acetate and chloroform; insoluble in water, Et2O, and petro-
leum ether. The molar conductivities in DMF solution indicate that
babb is a nonelectrolyte while Ni(II) complex is a 1:2 electrolyte
compound [35].
Table 1
Crystal data and structure refinement for [Ni(babb)2](pic)2.
Complex
[Ni(babb)2](pic)2
Molecular formula
Molecular weight
Color
C70H62N16NiO14
1410.07
Yellow
3.1. IR and electronic spectra
Crystal size, mm3
Crystal system
Space group
a (Å)
0.36 ꢀ 0.34 ꢀ 0.30
The IR spectra of the Ni(II) complex is closely related to that of
the free ligand babb. One of the most diagnostic changes occurs in
the region between 1650 and 1250 cmꢁ1. The spectra of babb show
a strong band at 1461 cmꢁ1 and weak bands at 1643 cmꢁ1. By anal-
ogy with the assigned bands of imidazole, two bands are attributed
Triclinic
P-1
13.877(3)
13.945(3)
19.172(4)
70.138(2)
88.891(2)
74.189(2)
3346.3(12)
2
b (Å)
c (Å)
a
(°)
to the
m
(C@N) and
m
(C@C) frequencies of the benzimidazole group,
(C@N) undergo a blue shift (about
b (°)
respectively [36–38]. The band
m
c
(°)
V (Å3)
29 nm) in the complex as compared to free ligand indicating the
participation of the imine nitrogen atoms in coordination to the
metal ion [39]; these are the preferred nitrogen atom for coordina-
tion, as found in other metal complexes with benzimidazoles [40].
Moreover, Information regarding the possible bonding modes of
the picrate and benzimidazole rings may also be obtained from
the IR spectra [41].
Z
T (K)
293(2)
1.399
1468
Dcalcd (g cmꢁ3
F (000) (e)
)
h range for data collection (°)
hkl range
2.27–25.00
ꢁ16 6 h 6 13, ꢁ16 6 k 6 16,
ꢁ22 6 l 6 22
20973
11596 [Rint = 0.0328]
Full-matrix least-squares on F2
11596/35/910
0.0598/0.1526
0.0998/0.1811
1.018
Reflections collected
Independent reflections
Refinement method
DMF solutions of ligand and Ni(II) complex show, as expected,
almost identical UV spectra. The UV bands of babb (286, 279 nm)
are only marginally red-shifted about 4 nm for Ni(II) complex,
which is evidence of C@N coordination to the metal center. These
Data/restraints/parameters
Final R1/wR2 indices [I P 2
R1/wR2 indices (all data)a
Goodness-of-fit on F2
r
(I)]a
bands are assigned to
p ?
pꢄ (imidazole) transitions. The picrate
bands (observed at 381 nm) are assigned to
[17,18].
p ?
pꢄ transitions
Largest diff. peak and hole (e Åꢁ3
)
0.852 and ꢁ0.616

68
H. Wu et al. / Journal of Photochemistry and Photobiology B: Biology 107 (2012) 65–72
Table 2
affinity for DNA [48]. (ii) The charge transfer of coordinated babb
ligands caused by the coordination of the central Ni(II) atom, lead
to the reduce of the charge density of the plane conjugate system,
which is conducive to insert. (iii) This difference in their DNA bind-
ing ability also could be attributed to the presence of an electron
deficient center in the charged Ni(II) complex where an additional
interaction between the complex and phosphate rich DNA back
bone may occur [49,50].
Selected bond distances (Å) and angles (°) in [Ni(babb)2](pic)2.
Complex [Ni(babb)2](pic)2
Bond distances Ni(1)–N(1)
Ni(1)–N(3)
2.405(3) Ni(1)–N(6)
2.142(3) Ni(1)–N(7)
2.048(3) Ni(1)–N(9)
2.310(3)
2.127(3)
2.082(3)
Ni(1)–N(5)
Bond angles
N(5)–Ni(1)–N(9) 99.88(13) N(7)–Ni(1)–N(6) 75.14(11)
N(5)–Ni(1)–N(7) 93.86(12) N(3)–Ni(1)–N(6) 91.50(12)
N(9)–Ni(1)–N(7) 104.60(12) N(5)–Ni(1)–N(1) 76.74(12)
N(5)–Ni(1)–N(3) 100.72(13) N(9)–Ni(1)–N(1) 166.23(11)
N(9)–Ni(1)–N(3) 94.79(13) N(7)–Ni(1)–N(1) 89.02(11)
N(7)–Ni(1)–N(3) 153.35(12) N(3)–Ni(1)–N(1) 73.02(12)
N(5)–Ni(1)–N(6) 167.76(12) N(6)–Ni(1)–N(1) 107.89(11)
N(9)–Ni(1)–N(6) 78.21(12)
3.3.2. Fluorescence spectroscopic studies
In order to further study the binding properties of the com-
plexes with DNA, competitive binding experiment was carried
out. Relative binding of babb and Ni(II) complex to CT-DNA was
studied by the fluorescence spectral method using ethidium bro-
mide (EB) bound CT-DNA solution in Tris–HCl/NaCl buffer
(pH = 7.2). As a typical indicator of intercalation, EB is a weakly
fluorescent compound. But in the presence of DNA, emission inten-
sity of EB is greatly enhanced because of its strong intercalation be-
tween the adjacent DNA base pairs [29]. In general, measurement
of the ability of a complex to affect the intensity of EB fluorescence
in the EB-DNA adduct allows determination of the affinity of the
complex for DNA, whatever the binding mode may be. If a complex
can displace EB from DNA, the fluorescence of the solution will be
reduced due to the fact that free EB molecules are readily quenched
by the solvent water [51]. For babb and Ni(II) complex, no emission
were observed either alone or in the presence of CT-DNA in the
buffer. The fluorescence quenching of DNA-bound EB by ligand
babb and complex are shown in Fig. 3. The behavior of babb and
Ni(II) complex are in good agreement with the Stern–Volmer equa-
tion, which provide further evidence that them bind to DNA. The
Ksv values are 1.44 ꢀ 104 Mꢁ1 (R = 0.97 for 13 points) for babb,
5.26 ꢀ 104 (R = 0.98 for 10 points in the linear part) for Ni(II) com-
plex, respectively. It may be due to ligand babb and Ni(II) complex
both can interact with DNA in an intercalation mode, and releasing
gand babb; 43.90% at 273 nm for complex Ni(II) complex. The kmax
for babb and Ni(II) complex have a slight red shifts of about
1–2 nm under identical experimental conditions. The hypochro-
mism and red shift suggested that the babb and Ni(II) complex have
strong interaction with DNA [46]. The Kb values of babb and Ni(II)
complex are 2.26 ꢀ 103 Mꢁ1 (R = 0.98 for 15 points), 3.65 ꢀ 104
Mꢁ1 (R = 0.99 for 16 points) for Ni(II) complex, respectively. There-
fore, compare with the classic DNA-intercalative reagent, such as
Ethidium bromide (EB), acridine orange (AO), methylene blue (MB)
[47], in the light of the hypochromism and red shift mentioned
above, we speculate that ligand babb and Ni(II) complex most possi-
bly binds to DNA in an intercalation mode, which may due to the
large coplanar aromatic rings in two compound that facilitate it
intercalating to the base pairs of double helical DNA.
However, the affinity for DNA is more strong in case of Ni(II)
complex when compared with the ligand. For this difference, we
attributed to three possible reasons. (i) By comparison of the
molecular structure of the ligand and Ni(II) complex, we find the
greater number of coplanar aromatic rings may lead to higher
Fig. 1. Molecular structure and atom numberings of [Ni(babb)2]2+ with hydrogen atoms were omitted for clarity.

H. Wu et al. / Journal of Photochemistry and Photobiology B: Biology 107 (2012) 65–72
69
Fig. 2. Electronic spectra of (a) babb, (c) Ni(II) complex in Tris–HCl buffer upon addition of CT-DNA. [Compound] = 3 ꢀ 10ꢁ5 Mꢁ1, [DNA] = 2.5 ꢀ 10ꢁ5 Mꢁ1. Arrow shows the
emission intensity changes upon increasing DNA concentration. Plots of [DNA]/(ea
ꢁ
ef) versus. [DNA] for the titration of (b) babb, (d) Ni(II) complex with CT-DNA.
some free EB from the EB-bound CT-DNA complex system and that
DNA-binding of Ni(II) complex is stronger than that of babb, which
is consistent with the above absorption spectroscopic results. The
Kq values for the ligand babb and the Ni(II) complex are
1.44 ꢀ 1012 Mꢁ1 Sꢁ1 and 5.26 ꢀ 1012 Mꢁ1 Sꢁ1, respectively, indicat-
ing they are static quenching [52].
steadily with the increment of them, and it is further illustrated
that two compounds can intercalates with CT-DNA. The result of
the viscosity experiments confirms the mode of babb and Ni(II)
complex intercalate into DNA base pairs already established
through absorption and fluorescence spectral titration studies.
3.3.3. Viscosity titration measurements
3.4. Antioxidant property
Optical photophysical techniques are widely used to study the
binding model of the ligand, metal complexes and DNA, but do
not give sufficient clues to support a binding model. Hydrodynamic
measurements that are sensitive to the length change (i.e., viscos-
ity and sedimentation) are regarded as the least ambiguous and
the most critical tests of a binding model in solution in the absence
of crystallographic structural data [22,53]. Therefore, viscosity
measurements were carried out to further clarify the interaction
of metal complexes and DNA. In classical intercalation, the DNA
helix lengthens as base pairs are separated to accommodate the
bound ligand leading to increased DNA viscosity whereas a partial,
while nonclassical ligand intercalation causes a bend (or kink) in
DNA helix reducing its effective length and thereby its viscosity
[22].
According to relevant reports in the literature [54–56], some
transition metal complexes may exhibit antioxidant activity. We
therefore also conducted an investigation to explore whether the
Ni(II) complex has the hydroxyl radical scavenging property. We
compared the abilities of one present compounds to scavenge
hydroxyl radicals with those of the well-known natural antioxidants
mannitol and vitamin C, using the same method as reported in a pre-
vious paper [57]. The 50% inhibitory concentration (IC50) value of
mannitol and vitamin C are about 9.6 ꢀ 10ꢁ3 and 8.7 ꢀ 10ꢁ3 Mꢁ1
,
respectively. As shown in Fig. 5, according to the antioxidant exper-
iments, the IC50 values of Ni(II) complex is 6.73 ꢀ 10ꢁ5 Mꢁ1, which
implies that Ni(II) complex has the preferable ability to scavenge hy-
droxyl radical. In view of the observed IC50 values, the Ni(II) complex
can be considered as a potential drug to eliminate the hydroxyl
radical.
The effects of babb and Ni(II) complex on the viscosity of
CT-DNA is shown in Fig. 4. The viscosity of CT-DNA is increased

70
H. Wu et al. / Journal of Photochemistry and Photobiology B: Biology 107 (2012) 65–72
Fig. 3. Emission spectra of EB bound to CT-DNA in the presence of (a) babb and (c) Ni(II) complex; [Compound] = 3 ꢀ 10ꢁ5 M; kex = 520 nm. The arrows show the intensity
changes upon increasing concentrations of the complexes. Fluorescence quenching curves of EB bound to CT-DNA by (b) ligand and (d) Ni(II) complex. (Plots of I0/I versus
[Complex]).
Fig. 4. Effect of increasing amounts of (a) babb and (b) Ni(II) complex on the relative viscosity of CT-DNA at 25.0 0.1 °C.

H. Wu et al. / Journal of Photochemistry and Photobiology B: Biology 107 (2012) 65–72
71
alkylbenzimidazoles bearing a N-phenylpyrrole moiety as novel angiotensin
II AT1 receptor antagonists, Bioorg. Med. Chem. Lett. 17 (2007) 2921–2926.
[4] P.D. Patel, M.R. Patel, N. Kaushik-Basu, T.T. Talele, 3D QSAR and molecular
docking studies of benzimidazole derivatives as hepatitis
polymerase Inhibitors, J. Chem. Inf. Model. 48 (2008) 42–55.
C virus NS5B
[5] K. Taniguchi, S. Shigenaga, T. Ogahara, T. Fujitsu, M. Matsuo, Synthesis and
antiinflammatory and analgesic properties of 2-amino-1H-benzimidazole and
1,2-dihydro-2-iminocycloheptimidazole derivatives, Chem. Pharm. Bull. 41
(1993) 301–309.
[6] S. Estrada-Soto, R. Villalobos-Molina, F. Aguirre-Crespo, J. Vergara-Galicia, H.
Oreno-DÍaz, M. Torres-Piedra, G. Navarrete-Vázquez, Relaxant activity of 2-
(substituted phenyl)-1H-benzimidazoles on isolated rat aortic rings: design
and synthesis of 5-nitro derivatives, Life Sci. 79 (2006) 430–435.
[7] Ö.Ö. Guven, T. Erdoꢀgan, H. Göker, S. Yildiz, Synthesis and antimicrobial activity
of some novel phenyl and benzimidazole substituted benzyl ethers, Bioorg.
Med. Chem. Lett. 17 (2007) 2233–2236.
[8] Z. Ates-Alagoz, S. Yildiz, E. Buyukbingol, Antimicrobial activities of some
tetrahydronaphthalene-benzimidazole derivatives, Chemotherapy 53 (2007)
110–113.
[9] B.G. Mohamed, A.A. Abdel-Alim, M.A. Hussein, Synthesis of 1-acyl-2-alkylthio-
1,2,4-triazolobenzimidazoles with antifungal, anti-inflammatory and analgesic
effects, Acta Pharm. 56 (2006) 31–48.
[10] H.Y. Liu, H. Wu, J. Yang, Y.Y. Liu, B. Liu, Y.Y. Liu, J.F. Ma, pH-Dependent assembly
of 1D to 3D octamolybdate hybrid materials based on a new flexible bis-
[(pyridyl)-benzimidazole] ligand, Cryst. Growth Des. 11 (2011) 2920–2927.
[11] M.S. Diaz-Cruz, J. Mendieta, A. Monjonelli, R. Tauler, M. Esteban, Specific
interactions of bovine and human b-casomorphin-7 with Cu(II) ions, J. Inorg.
Biochem. 70 (1998) 91–95.
Fig. 5. The inhibitory effect of Ni(II) complex on OH radicals; the suppression ratio
increases with increasing concentration of the test compound.
[12] K.E. Erkkila, D.T. Odom, J.K. Barton, Recognition and reaction of
metallointercalators with DNA, Chem. Rev. 99 (1999) 2777–2796.
[13] L.N. Ji, X.H. Zou, J.G. Lin, Shape- and enantioselective interaction of Ru(II)/
Co(III) polypyridyl complexes with DNA, Coord. Chem. Rev. 216–217 (2001)
513–536.
[14] B.M. Zeglis, V.C. Pierre, J.K. Barton, Metallo-intercalators and metallo-insertors,
Chem. Commun. 44 (2007) 4565–4579.
[15] J.A. Cowan, Metal activation of enzymes in nucleic acid biochemistry, Chem.
Rev. 98 (1998) 1067–1088.
[16] C.L. Liu, M. Wang, T.L. Zhang, H.Z. Sun, DNA hydrolysis promoted by di- and
multi-nuclear metal complexes, Coord. Chem. Rev. 248 (2004) 147–168.
[17] H.L. Wu, X.C. Huang, J.K. Yuan, F. Kou, F. Jia, B. Liu, K.T. Wang, A V-shaped
ligand 2,6-bis(2-benzimidazolyl)pyridine and its picrate Mn(II) complex:
Synthesis, crystal structure and DNA-binding properties, Eur. J. Med. Chem.
45 (2010) 5324–5330.
[18] H.L. Wu, K. Li, T. Sun, F. Kou, F. Jia, J.K. Yuan, B. Liu, B.L. Qi, Synthesis, structure,
and DNA-binding properties of manganese(II) and zinc(II) complexes with
tris(N-methylbenzimidazol-2-ylmethyl)amine ligand, Transition. Met. Chem.
36 (2011) 21–28.
4. Conclusion
In this work, a new ligand bis(N-allylbenzimidazol-2-ylmethyl)-
benzylamine and its Ni(II) complex have been synthesized and
characterized. The crystal structure of [Ni(babb)2](pic)2 is six-coor-
dinated adopting a distorted octahedral geometry. The DNA-binding
experimental results suggest that ligand babb and Ni(II) complex
bind to DNA in an intercalation mode, and the Ni(II) complex has
higher binding ability than free ligand. In addition, the Ni(II) com-
plex can be considered as a potential drug to eliminate the hydroxyl
radical. These findings indicate that the Ni(II) complex has many
potential practical applications for the development of nucleic acid
molecular probes and new therapeutic reagents for diseases on the
molecular level and warrant further in vivo experiments and
pharmacological assays.
[19] H.L. Wu, R.R. Yun, K.T. Wang, K. Li, X.C. Huang, T. Sun, Synthesis, crystal
structure, and spectrum properties of cobalt(II) complexes based on tridentate
1, 3-bis(benzimidazol-2-yl)-2-oxopropane ligand and derivative, Z. Anorg.
Allg. Chem. 636 (2010) 629–633.
[20] H.L. Wu, X.C. Huang, J.K. Yuan, K. Li, J. Ding, R.R. Yun, W.K. Dong, X.Y. Fan, A
Acknowledgments
five-coordinate
copper(II)
perchlorate
complex
with
tris(N-
methylbenzimidazol-2-ylmethyl)amine and salicylate, J. Coord. Chem. 62
(2009) 3446–3453.
The authors acknowledge the financial support and grant from
‘Qing Lan’ Talent Engineering Funds by Lanzhou Jiaotong University.
The grant from ‘Long Yuan Qing Nian’ of Gansu Province also is
acknowledged.
[21] H.L. Wu, J.K. Yuan, Y. Bai, F. Kou, F. Jia, B. Liu, Synthesis crystal structure and
spectra properties of the cadmium (II) complex with bis(N-allylbenzimidazol-
2-ylmethyl)benzylamine, Bioinorg. Chem. Appl. 2011 (2011) 705989.
[22] S. Satyanarayana, J.C. Dabrowiak, J.B. Chaires, Tris(phenanthroline)-
ruthenium(II) enantiomer interactions with DNA: mode and specificity of
binding, Biochemistry 32 (1993) 2573–2584.
[23] M.E. Reichmann, S.A. Rice, C.A. Thomas, P. Doty, A further examination of the
molecular weight and size of desoxypentose nucleic acid, J. Am. Chem. Soc. 76
(1954) 3047–3051.
[24] K. Takahashi, Y. Nishida, S. Kida, Crystal structure of copper(II) complex with N,
N-bis(2-benzimidazolylmethyl)benzylamine, Polyhedron 3 (1984) 113–116.
[25] Bruker, Smart saint and sadabs, Bruker Axs, Inc., Madison, WI, 2000.
[26] G.M. Sheldrick, SHELXTL, Siemens Analytical X-ray Instruments, Inc., Madison,
Wisconsin, USA, 1996.
[27] A.M. Pyle, J.P. Rehmann, R. Meshoyrer, C.V. Kumar, N.J. Turro, J.K. Barton,
Mixed-ligand complexes of ruthenium(II): factors governing binding to DNA, J.
Am. Chem. Soc. 111 (1989) 3051–3058.
[28] A. Wolf, G.H. Shimer, T. Meehan, Polycyclic aromatic hydrocarbons physically
intercalate into duplex regions of denatured DNA, Biochemistry 26 (1987)
6392–6396.
[29] B.C. Baguley, M.L. Bret, Quenching of DNA-ethidium fluorescence by amsacrine
and other antitumor agents: a possible electron-transfer effect, Biochemistry
23 (1984) 937–943.
[30] J.R. Lakowicz, G. Webber, Quenching of fluorescence by oxygen Probe for
structural fluctuations in macromolecules, Biochemistry 12 (1973) 4161–
4170.
Appendix A. Supplementary material
Crystallographic data (excluding structure factors) for the struc-
tures reported in this paper have been deposited with the
Cambridge Crystallographic Data Center with reference number
CCDC 848157. Copies of the data can be obtained, free of charge,
on application to the CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK. Tel.: +44 01223 762910; fax: +44 01223 336033; e-mail: de-
posit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk. Supplemen-
tary data associated with this article can be found, in the online
version, at doi: 10.1016/j.jphotobiol.2011.11.010.
References
[1] J.B. Wright, The chemistry of the benzimidazoles, Chem. Rev. 48 (1951) 397–
541.
[2] S.Y. Hong, K.W. Kwak, C.K. Ryu, S.J. Kang, K.H. Chung, Antiproliferative effects
of 6-anilino-5-chloro-1H-benzo[d]imidazole-4,7-dione in vascular smooth
muscle cells, Bioorg. Med. Chem. 16 (2008) 644–649.
[31] C.P. Tan, J. Liu, L.M. Chen, S. Shi, L.N. Ji, Synthesis, structural characteristics,
DNA binding properties and cytotoxicity studies of
complexes, J. Inorg. Biochem. 102 (2008) 1644–1653.
a series of Ru(III)
[32] C.C. Winterbourn, Hydroxyl radical production in body fluids. Roles of metal
ions, ascorbate and superoxide, Biochem. J. 198 (1981) 125–131.
[3] J.Y. Xu, Y. Zeng, Q. Ran, Z. Wei, Y. Bi, Q.H. He, Q.J. Wang, S. Hu, J. Zhang, M.Y.
Tang, W.Y. Hua, X.M. Wu, Synthesis and biological activity of 2-

72
H. Wu et al. / Journal of Photochemistry and Photobiology B: Biology 107 (2012) 65–72
[33] C.C. Winterbourn, Comparison of superoxide with other reducing agents in the
biological production of hydroxyl radicals, Biochem. J. 182 (1979) 625–628.
[34] Z.Y. Guo, R.E. Xing, S. Liu, H.H. Yu, P.B. Wang, C.P. Li, P.C. Li, The synthesis and
antioxidant activity of the Schiff bases of chitosan and carboxymethyl
chitosan, Bioorg. Med. Chem. Lett. 15 (2005) 4600–4603.
[46] J. Liu, T.X. Zhang, L.N. Ji, DNA-binding and cleavage studies of macrocyclic
copper(II) complexes, J. Inorg. Biochem. 91 (2002) 269–276.
[47] S. Nafisi, A.A. Saboury, N. Keramat, J.F. Neault, H.A. Tajmir-Riahi, Stability and
structural features of DNA intercalation with ethidium bromide, acridine
orange and methylene blue, J. Mol. Struct. 827 (2007) 35–43.
[35] W.J. Geary, The use of conductivity measurements in organic solvents for the
characterization of coordination compounds, Coord. Chem. Rev. 7 (1971) 81–
122.
[48] H.L. Wu, J.K. Yuan, Y. Bai, F. Jia, B. Liu, F. Kou, J. Kong, Synthesis, structure, DNA-
binding properties, and antioxidant activity of copper(II) and cobalt(II)
complexes
with
bis(N-allylbenzimidazol-2-ylmethyl)benzylamine,
[36] C.Y. Su, B.S. Kang, C.X. Du, Q.C. Yang, T.C.W. Mak, Formation of mono-, bi-, tri-,
and tetranuclear Ag(I) complexes of C3-symmetric tripodal benzimidazole
ligands, Inorg. Chem. 39 (2000) 4843–4849.
[37] T.J. Lane, I. Nakagawa, J.L. Walter, A.J. Kandathil, Infrared investigationof
certain imidazole derivatives and their metal chelates, Inorg. Chem. 1 (1962)
267–276.
Transition. Met. Chem. 36 (2011) 819–827.
[49] S. Yellappa, J. Seetharamappa, L.M. Rogers, R. Chitta, R.P. Singhal, F. D’Souza,
Binding, electrochemical activation, and cleavage of DNA by cobalt(II)tetrakis-
N-methylpyridyl porphyrin and its b-pyrrole brominated derivative,
Bioconjug. Chem. 17 (2006) 1418–1425.
[50] M. Shakir, M. Azam, M.-F. Ullah, S.-M. Hadi, Synthesis, spectroscopic and
[38] E.K. Chec, M. Kubiak, T. Glowiak, J.J. Ziolkowski, Synthesis, crystal and
molecular structure of the novel complex [dinitrato{N, N-bis(1–
methylbenzimidazol-2–ylmethyl)methylamine}]cobalt(II), Transition. Met.
Chem. 23 (1998) 641–644.
[39] M. McKee, M. Zvagulis, C.A. Reed, Further insight into magnetostructural
correlations in binuclear copper(II) species related to methemocyanin: x-ray
crystal structure of 1, 2-.mu.-nitrito complex, Inorg. Chem. 24 (1985) 2914–
2919.
[40] K. Nakamoto (Ed.), Infrared and Raman Spectra of Inorganic and Coordination
Compounds, Wiley, New York, 1978, p. 305.
[41] H.L. Wu, K.T. Wang, R.R. Yun, X.C. Huang, Studies on copper(II), cobalt (II) and
nickel (II) picrate complexes with the ligand 1,3-bis(2-benzimidazyl)-2-
thiapropane, Synth. React. Inorg., Met.-Org., Nano-Met. Chem. 39 (2009)
629–632.
[42] L.E. Xiao, M. Zhang, W.H. Sun, Synthesis, characterization and ethylene
oligomerization and polymerization of 2-(1H–2-benzimidazolyl)-6-(1-
(arylimino)ethyl)pyridylchromium chlorides, Polyhedron 29 (2010) 142–147.
[43] D. Kang, J. Seo, S.Y. Lee, J.Y. Lee, First dicadmium(II) complex of tripodal amide
ligand with one edge-sharing monocapped octahedral geometry, Inorg. Chem.
Commun. 10 (2007) 1425–1428.
[44] N. Yoshikawa, S. Yamabe, N. Kanehisa, Y. Kai, H. Takashima, K. Tsukahara,
Synthesis, characterization, and DFT investigation of Ir(III) tolylterpyridine
complexes, Eur. J. Inorg. Chem. 13 (2007) 1911–1919.
electrochemical
studies
of
N,
N-bis[(E)-2-thienylmethylidene]-1,8-
naphthalene -diamine and its Cu(II) complex: DNA cleavage and generation
of superoxide anion, J. Photoch. Photobio. B 104 (2011) 449–456.
[51] J.B. LePecq, C. Paoletti, A fluorescent complex between ethidium bromide and
nucleic acids: Physical–Chemical characterization, J. Mol. Biol. 27 (1967) 87–
106.
[52] Q.H. Zhou, P. Yang, Synthesis, crystal structure and DNA binding studies of
Zn(II) complex with 1,3-bis(benzimidazol-2-yl)-2-oxapropane, Acta Chim.
Sinica 64 (2006) 793–798.
[53] S. Satyanarayana, J.C. Dabroniak, J.B. Chaires, Neither.DELTA.- nor.LAMBDA.-
tris(phenanthroline)ruthenium(II) binds to DNA by classical intercalation,
Biochemistry 31 (1992) 9319–9324.
[54] S.B. Bukhari, S. Memon, M. Mahroof-Tahir, M.I. Bhanger, Synthesis,
characterization and antioxidant activity copper–quercetin complex,
Spectrochim. Acta A. Mol. Biomol. Spectrosc. 71 (2009) 1901–1906.
[55] F.V. Botelho, J.I. Alvarez-Leite, V.S. Lemos, A.M.C. Pimenta, H.D.R. Calado, T.
Matencio, C.T. Miranda, E.C. Pereira-Maia, Physicochemical study of floranol,
its copper(II) and iron(III) complexes, and their inhibitory effect on LDL
oxidation, J. Inorg. Biochem. 101 (2007) 935–943.
[56] Q. Wang, Z.Y. Yang, G.F. Qi, D.D. Qin, Synthesis, crystal structure, antioxidant
activities and DNA-binding studies of the Ln(III) complexes with 7-
methoxychromone-3-carbaldehyde-(40-hydroxy) benzoyl hydrazone, Eur. J.
Med. Chem. 44 (2009) 2425–2433.
[45] J.P. Collin, I.M. Dixon, J.P. Sauvage, J.A.G. Williams, F. Barigelletti, L. Flamigni,
Synthesis and photophysical properties of Iridium(III) bisterpyridine and its
homologues: a family of complexes with a long-lived excited state, J. Am.
Chem. Soc. 121 (1999) 5009–5016.
[57] T.R. Li, Z.Y. Yang, B.D. Wang, D.D. Qin, Synthesis, characterization, antioxidant
activity and DNA-binding studies of two rare earth(III) complexes with
naringenin-2-hydroxy benzoyl hydrazone ligand, Eur. J. Med. Chem. 43 (2008)
1688–1695.