Antioxidation and DNA-binding properties of binuclear lanthanide(III) complexes with a schiff base ligand derived from 8-hydroxyquinoline-7- carboxaldehyde and benzoylhydrazine

Article abstract of DOI:10.1002/cbdv.201100322

8-Hydroxyquinoline-7-carboxaldehyde (8-HQ-7-CA), Schiff-base ligand 8-hydroxyquinoline-7-carboxaldehyde benzoylhydrazone, and binuclear complexes [LnL(NO₃)(H₂O)₂]₂ were prepared from the ligand and equivalent molar amounts of Ln(NO₃)·6 H ₂O (Ln=La³⁺, Nd³⁺, Sm³⁺, Eu ³⁺, Gd³⁺, Dy³⁺, Ho³⁺, Er ³⁺, Yb³⁺, resp.). Ligand acts as dibasic tetradentates, binding to Ln^III through the phenolate O-atom, N-atom of quinolinato unit, and C=N and -O-C=N- groups of the benzoylhydrazine side chain. Dimerization of this monomeric unit occurs through the phenolate O-atoms leading to a central four-membered (LnO)₂ ring. Ligand and all of the Ln^III complexes can strongly bind to CT-DNA through intercalation with the binding constants at 10⁵-10⁶ m^-1. Moreover, ligand and all of the Ln^III complexes have strong abilities of scavenging effects for hydroxyl (HO^.) radicals. Both the antioxidation and DNA-binding properties of Ln^III complexes are much better than that of ligand. Copyright

Full text of DOI:10.1002/cbdv.201100322

CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
1533
Antioxidation and DNA-Binding Properties of Binuclear Lanthanide(III)
Complexes with a Schiff Base Ligand Derived from 8-Hydroxyquinoline-7-
carboxaldehyde and Benzoylhydrazine
by Yongchun Liu*, Kejun Zhang, Yun Wu, Junying Zhao, and Jianning Liu
College of Chemistry and Chemical Engineering, Key Laboratory of Longdong Biological Resources in
Gansu Province, Longdong University, Qingyang, Gansu 745000, P. R. China
(phone: 86-934-6466862; e-mail: ychliu001@163.com)
8-Hydroxyquinoline-7-carboxaldehyde (8-HQ-7-CA), Schiff-base ligand 8-hydroxyquinoline-7-
carboxaldehyde benzoylhydrazone, and binuclear complexes [LnL(NO3)(H2O)2]2 were prepared from
the ligand and equivalent molar amounts of Ln(NO3)·6 H2O (Ln¼La3þ, Nd3þ, Sm3þ, Eu3þ, Gd3þ, Dy3þ
,
Ho3þ, Er3þ, Yb3þ, resp.). Ligand acts as dibasic tetradentates, binding to LnIII through the phenolate O-
atom, N-atom of quinolinato unit, and C¼N and ꢀOꢀC¼Nꢀ groups of the benzoylhydrazine side chain.
Dimerization of this monomeric unit occurs through the phenolate O-atoms leading to a central four-
membered (LnO)2 ring. Ligand and all of the LnIII complexes can strongly bind to CT-DNA through
intercalation with the binding constants at 105 –106 mꢀ1. Moreover, ligand and all of the LnIII complexes
.
have strong abilities of scavenging effects for hydroxyl (HO ) radicals. Both the antioxidation and DNA-
binding properties of LnIII complexes are much better than that of ligand.
Introduction. – DNA is one of the primary intracellular targets of anticancer drugs
due to the interaction of small molecules with it, causing DNA damage in cancer cells,
inhibiting the division of cancer cells, and resulting in cell death [1]. Some DNA binders
are effective inhibitors of the formation of a DNA/TBP complex or topoisomerases.
Adding a reactive entity endowed with oxidative properties should improve the
efficiency of inhibitors [2].
Previously, we investigated the biological properties of lanthanide(III) complexes
with Schiff base ligands derived from 8-hydroxyquinoline-2-carboxaldehyde and some
aroylhydrazines. It was found that all these ligands and rare earth metal complexes
showed strong antioxidation and DNA-binding properties, and they might be used as
potential anticancer drugs [3]. In this study, the Schiff base ligand derived from 8-
hydroxyquinoline-7-carboxaldehyde with benzoylhydrazine and its LnIII complexes
were prepare to investigate their antioxidation and DNA-binding properties.
Results and Discussion. – 8-Hydroxyquinoline-7-carboxaldehyde (8-HQ-7-CA)
was prepared according literature procedures with small modifications [4]. The Schiff
base ligand 8-hydroxyquinoline-7-carboxaldehyde benzoylhydrazone (H2L; 1) was
prepared from equivalent molar amounts of 8-HQ-7-CA and benzoylhydrazine
(Scheme). Then, its nine LnIII complexes 2–10 were prepared from the ligand and
equivalent molar amounts of Ln(NO3)·6 H2O (Ln¼La3þ, Nd3þ, Sm3þ, Eu3þ, Gd3þ
,
Dy3þ, Ho3þ, Er3þ, Yb3þ, resp.). All the LnIII complexes are yellow powders, stable in
ꢀ 2012 Verlag Helvetica Chimica Acta AG, Zꢁrich

1534
CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
air, and soluble in DMF and DMSO, but slightly soluble in MeOH, EtOH, MeCN,
AcOEt and acetone, THF and CHCl3. They are 1:1 metal-to-ligand (stoichiometry)
complexes and act as non-electrolytes [5].
Scheme 1. The Synthetic Route to Ligand 1
The characteristic IR bands (cmꢀ1) at 3328, 3206, 1641, 1597, 1571, and 1288 of
ligand can be assigned to ˜n(NH), ˜n(OH), ˜n(CO), ˜n(C¼N, azomethine), ˜n(C¼N,
pyridine), and n(CꢀOH), respectively. Careful comparison with the characteristic IR
bands of the ligand and LnIII complexes led to the following conclusions: 1) Bands at
3412–3387 (br.) assigned to ˜n(OH) of H2O, at 965–960w assigned to 1r(H2O), and at
642–633w assigned to 1w (H2O) indicate that coordinated H2O molecules participate in
the LnIII complexes. 2) Bands at 1099–1094 assigned to ˜n(CꢀOM) indicate that the
binding of every metal ion to ligand through an OꢀM linkage takes place [6]. 3) Bands
at 1641s assigned to ˜n(CO) and at 3328vs assigned to ˜n(NH) of benzoylhydrazine side
chain of ligand have disappeared in the IR spectra of LnIII complexes, indicating that
they participate in the LnIII complexes with the O¼CꢀNHꢀ group, possibly undergoing
enolization and deprotonation toꢀOꢀC¼Nꢀ. 4) Bands at 1603–1590 assigned to ˜n(CN)
of azomethines of the LnIII complexes were shifted by 6–4 cmꢀ1, and bands at 1564–
1558 assigned to ˜n(CN) of pyridines of the LnIII complexes were shifted by 7–13 cmꢀ1
in comparison with those of the ligand, indicating that both N-atoms of azomethines
and pyridines participate in the complexes. 5) Bands at 537–531w assigned to ˜n(MO)
and at 447–428w assigned to ˜n(MN) of the LnIII complexes further indicate that the O-
and N-atoms participate in complexes. 6) All the LnIII complexes exhibit bands at
1469–1465 (n1), 1326–1317 (n4), 1036–1031 (n2), 838–836 (n3), 726–716 (n5), and
Dn(n1 –n4) 149–144 cmꢀ1, indicating that nitrate ions bidentately participate in the LnIII
complexes [7].
The results of elemental analyses, molar conductance, IR spectra, and ESI-MS data
indicate that ligand acts as a dibasic tetradentate, binding to LnIII through the phenolate
O-atom, N-atom of quinolinato unit, and C¼N group and ꢀOꢀC¼Nꢀ groups (enolized
and deprotonated from O¼CꢀNHꢀ) of the benzoylhydrazine side chain. Dimerization
of this monomeric unit may occur through the phenolate O-atoms leading to a central
four-membered (LnO)2 ring. All the metal complexes are structurally similar to each
other, and the suggested binuclear composition is [LnL(NO3)(H2O)2]2 (Fig. 1).
However, the m/z data (Mþ ; DMF solution) of complexes indicate that the
coordinated H2O molecules of powder LnIII complex can be replaced by DMF
molecules, when it is dissolved in DMF solution, and that the composition of binuclear
complex in DMF solution is of [LnL(NO3)(DMF)2]2. Additionally, the m/z data ([M/

CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
1535
Fig. 1. The suggested binuclear structures of LnIII complexes
2]þ ; DMF solution) of complex can also be found, indicating that there exists a
monomeric unit in DMF solution.
Hydrodynamic measurements that are sensitive to length change of DNA (i.e.,
viscosity and sedimentation) are regarded as the least ambiguous and the most critical
criteria for binding modes in solution in absence of crystallographic structural data [8].
Viscosity measurements are very sensitive to changes in the length of DNA, as viscosity
is proportional to L3 for rod-like DNA of length L. Intercalation involves the insertion
of a planar molecule between DNA base pairs, resulting in a decrease in the DNA
helical twist and lengthening of the DNA; therefore, intercalators cause the unwinding
and lengthening of DNA helix, as base pairs become separated to accommodate the
binding compound [9]. Whereas agents bound to DNA through groove binding do not
alter the relative viscosity of DNA, agents bound to DNA through electrostatic binding
will bend or kink the DNA helix, reducing its effective length and its viscosity,
concomitantly [10]. With the increasing ratios of the investigated compounds to DNA
(base pairs, bps), the relative viscosities of DNA increase steadily (Fig. 2), indicating
that intercalation takes place between the investigated compounds and DNA helix. In
addition, the increases of relative viscosities of DNA for complexes are more than that
for ligand, indicating the extent of the unwinding and lengthening of DNA helix by
compounds, and the affinities of compounds binding to DNA.
The UV/VIS spectra of the ligand have two types of absorption bands of lmax at 246
(e¼2.58ꢁ104 mꢀ1 cmꢀ1) and 348 nm (e¼2.11ꢁ104 mꢀ1 cmꢀ1), which can be assigned
to p–p* transition of aromatic rings and p–p* of conjugated aromatic rings,
respectively. The UV/VIS spectra of LnIII complexes exhibit two typical bands of lmax
in the range of 247–263 (e¼1.93–3.68ꢁ104 mꢀ1 cmꢀ1) and 343–350 nm (e¼1.44–
32.76ꢁ104 mꢀ1 cmꢀ1), which can be assigned to p–p* transition of aromatic rings and
p–p* of conjugated aromatic rings, respectively. However, compared with ligand, the
new bands of lmax at 401–406 nm for complexes can be assigned to the charge transfer
from ligand to metal ions (L!Ln3þ ) [3]. Additionally, isosbestic point at 385 nm for
ligand and isosbestic points at 460–468 nm for LnIII complexes are observed, indicating
that the equilibrium of reaction takes place between compound and DNA. Upon
successive addition of CT-DNA (bps), the UV/VIS absorption band of ligand shows a
progressive hypochromism of 24.1% at 246 nm and another progressive hypochromism
of 31.4% at 348 nm at approximately saturated titration end point with CDNA/Cligand

1536
CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
Fig. 2. Effects of increasing amounts of the investigated compounds on the relative viscosity of CT-DNA.
The concentration of CT-DNA was 50 mm (bps).
1.4 :1. Similarly, the UV/VIS bands of complexes show a progressive hypochromism of
15.2–72.2% at 247–263 nm and another progressive hypochromism of 12.5–62.5% at
343–350 nm with CDNA/Ccomplex 1.0–1.6 :1. The obvious hypochromism further indicate
the non-covalently intercalative binding of compounds to DNA helix, due to the strong
stacking interaction between the aromatic chromophores of the compound and base
pairs of DNA [11]. The magnitude of hypochromism is parallel to the intercalative
strength and the affinity of a compound binding to DNA [8]. From the UV/VIS
titration data, the binding constant (Kb) was determined [12], and the values of Kb are
compiled in the Table. Figs. 3–5 show the plots of the UV/VIS titration, the plot of
[DNA]/(ef –ea) vs. [DNA] for DyIII complex 7, and the plot of Kb vs. 4f electron number
of metal ions, respectively. It is found that EuIII complex 5 presents the strongest
binding ability to DNA (Kb ¼26.13ꢁ105 mꢀ1) among the investigated compounds (Kb
in the range of 26.13–2.938ꢁ105 mꢀ1), and that from GdIII to ErIII complexes, 6–9,
respectively, the values of Kb decrease gradually, while YbIII complex 10 presents higher
binding ability, which may be related to the 4f electron effect and the size of metal ions.
Additionally, Kb values of DNA binding to ligand and EB (ethidium bromide, classical
intercalative agent) are 1.397ꢁ105 and 0.3068ꢁ105 mꢀ1, respectively, indicating that all
of the LnIII complexes present higher binding abilities to DNA than that of either ligand
or EB.
The fluorescence emission intensity of DNAꢀEB system decreased dramatically
upon increasing the amounts of both ligand and LnIII complexes. SternꢀVolmer
equation was used to determine the fluorescent quenching mechanism [9]. Plots of Fo/F
vs. [Q] are shown in Fig. 6, and the quenching data collected and calculated from the
good linear relationship when P<0.05 are compiled in the Table. The KSV values are in
the range of 0.8908–2.694ꢁ105 mꢀ1 for ligand and LnIII complexes; accordingly, the

CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
1537
Fig. 3. Plot of the UV/VIS titration for DyIII complex (7) by DNA. Both of the molar concentration of
DyIII complex and DNA (bps) are 10.0 mm at approximately saturated titration end point.
Fig. 4. Plot of [DNA]/(ef ꢀea) vs. [DNA] for DyIII complex (7)
corresponding calculated data of Kq are in the range of 4.949–14.97ꢁ1012 mꢀ1 sꢀ1
where the value of to is taken as 1.8ꢁ10ꢀ9 s. All of the current Kq values for the
investigated compounds are much greater than Kq(max) (2.0ꢁ1010 mꢀ1 sꢀ1), the
maximum quenching rate constant of bimolecular diffusion collision, which is
indicative of a static type of quenching mechanism arising from the formation of dark
complex between the fluorophore and quenching agent [13]. The loss of fluorescence
,

1538
CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
Fig. 5. Plots of Kb and KSV vs. 4f electron number of metal ions
.
Table 1. Parameters Kb, KSV, Kq, FC50, and SC50 (OH ) for Ligand and LnIII Complexes
.
Kb ꢁ105 [mꢀ1
]
KSV ꢁ105 [mꢀ1
]
Kq ꢁ1012 FC50 [mm]
SC50 [mm] for HO
[mꢀ1 sꢀ1
]
(Ccompound/CDNA,nucleotides)
Ligand 1
2
3
4
5
6
7
8
9
1.397ꢂ0.011 0.8908ꢂ0.0145
6.708ꢂ0.015 1.240ꢂ0.025
4.949
6.889
10.69
8.467
8.122
9.578
7.122
10.04
9.906
14.97
12.35 (3.088)
8.791 (2.198)
6.393 (1.598)
7.358 (1.839)
7.323 (1.831)
6.913 (1.728)
8.030 (2.008)
6.436 (1.609)
6.571 (1.643)
5.724 (1.431)
21.33ꢂ2.51
5.675ꢂ0.307
5.415ꢂ0.147
5.824ꢂ0.194
5.515ꢂ0.095
6.149ꢂ0.212
7.568ꢂ0.347
2.499ꢂ0.222
4.206ꢂ0.026
4.841ꢂ0.030
16.86ꢂ0.15
14.40ꢂ0.15
26.13ꢂ0.13
11.33ꢂ0.15
1.925ꢂ0.105
1.524ꢂ0.052
1.462ꢂ0.036
1.724ꢂ0.056
6.294ꢂ0.015 1.282ꢂ0.020
4.236ꢂ0.010 1.808ꢂ0.041
2.938ꢂ0.010 1.783ꢂ0.068
10
10.56ꢂ0.13
2.694ꢂ0.293
intensity at the maximum wavelength indicates that most of the EB molecules have
been displaced from DNAꢀEB complex by every quencher at the approximately
saturated end point, and that the intercalative binding modes take place between the
investigated compounds with DNA [10]. Furthermore, the SternꢀVolmer dynamic
quenching constants, KSV, can also be interpreted as binding affinities of the
complexation reaction [14]. The KSV data present the order that is slightly deviating
from that of Kb determined by UV/VIS titration (Fig. 5), indicating that the interaction
mechanism is determined not only by complex formation but also by some weak
interactions such as hydrophobic force, Van der Waals force, and electrostatic force
[15]. More importantly, DNA intercalators have been used extensively as antitumor,
antineoplastic, antimalarial, antibiotic, and antifungal agents [9]. There is a criterion
for screening out antitumor drugs from others by DNAꢀEB fluorescent tracer method,

CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
1539
Fig. 6. The SternꢀVolmer plots for ligand and LnIII complexes in EBꢀDNA systems. The molar
concentrations of DNA and EB are 4.0 mm (nucleotides) and 0.32 mm, respectively. lex ¼525 nm, lem
¼
587 nm.
i.e., a compound may be used as potential antitumor drug, if it causes a 50% loss of
DNAꢀEB fluorescence intensity by fluorescent titrations before the molar concen-
tration ratio of the compound to DNA (nucleotides) does not exceed 100 :1 [16]. The
FC50 value is introduced to denote the molar concentration of a compound that causes a
50% loss in the fluorescence intensity of DNAꢀEB system. According to the FC50 data
and the molar ratios of compounds to DNA (Table), it is interesting to note that at
FC50, all the molar concentration ratios of the investigated compounds to DNA (1.431–
3.088 :1) are significantly under 100 :1, indicating that all these investigated compounds
can be considered as potential antitumor drugs, and the antitumor activities of LnIII
complexes are probably better than that of ligand. However, their pharmacodynamical,
pharmacological, and toxicological properties should be further studied in vivo.
.
Fig. 7 shows the plots of HO radical-scavenging effects [%] vs. molar concentration
of the tested complexes. The SC50 value, calculated from the regression line of the log
(concentration of the tested compound) vs. the scavenging effect [%] of the compound,
is introduced to denote the molar concentration of the tested compound which causes a
.
50% scavenging effect on HO radicals. The SC50 values of ligand and LnIII complexes
.
for HO are 21.33 and 2.499–6.149 mm, respectively (Table). Apparently, the scaveng-
.
ing effects of LnIII complexes on HO are much higher than that of ligand, possibly in
.
that the larger conjugated metal complexes can react with HO to form larger stable
macromolecular radicals by the typical H-abstraction reaction than the ligand [17]. The
.
SC50 value of mannite for HO tested under the same conditions is 14.41 mm. However,
.
the scavenging effects of LnIII complexes and ligand on HO are much better than that
.
of either mannite or ascorbic acid (the value of SC50 for HO is 1.537 mg mlꢀ1, i.e.,
8.727 mm), standard antioxidative agents for nonenzymatic reaction [18]. Endowed

1540
CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
.
Fig. 7. Plots of HO radical-scavenging effects [%] vs. the molar concentrations of the tested complexes
with antioxidative properties, these DNA binders may be effective inhibitors of the
formation of a DNAꢀTBP (¼ TATA binding protein) complex topoisomerases.
Conclusions. – 8-Hydroxyquinoline-7-carboxaldehyde (8-HQ-7-CA) and its Schiff
base ligand 8-hydroxyquinoline-7-carboxaldehyde benzoylhydrazone (H2L; 1) were
prepared. Then, the nine binuclear complexes [LnL(NO3)(H2O)2]2, 2–10, were
prepared from the ligand and equivalent molar amounts of Ln(NO3)·6 H2O (Ln¼
La3þ, Nd3þ, Sm3þ, Eu3þ, Gd3þ, Dy3þ, Ho3þ, Er3þ, Yb3þ, resp.). Ligand acts as a dibasic
tetradentate, binding to LnIII through the phenolate O-atom, N-atom of quinolinato
unit, and C¼N group and ꢀOꢀC¼Nꢀ groups (enolized and deprotonated from
O¼CꢀNHꢀ) of the benzoylhydrazine side chain. Dimerization of this monomeric unit
may occur through the phenolate O-atoms leading to a central four-membered (LnO)2
ring. However, the composition changes to [LnL(NO3)(DMF)2]2 when the complex is
dissolved in DMF solution.
In addition, ligand and all of the LnIII complexes can bind to CT-DNA through
intercalation with the binding constants at 105 –106 mꢀ1, but LnIII complexes present
stronger affinities to DNA than the ligand. Ligand and all of the LnIII complexes may be
considered as potential anticancer drugs; however, their pharmacodynamical, phar-
macological and toxicological properties should be further studied in vivo.
Moreover, ligand and all of the LnIII complexes exhibit strong scavenging effects on
.
HO radicals, but LnIII complexes show stronger scavenging effects than the ligand.
Endowed with anti-oxidative properties, these DNA binders may be effective inhibitors
of the formation of a DNAꢀTBP complex topoisomerases, which should be studied
further in vivo. Furthermore, the LnIII complexes of 8-hydroxyquinoline-7-carbox-
aldehyde benzoylhydrazone are similar not only in structures but also in antioxidation
and DNA-binding properties with the LnIII complexes of 8-hydroxyquinoline-2-
carboxaldehyde benzoylhydrazone.

CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
1541
Experimental Part
General. Materials. Calf thymus DNA (CT-DNA) and ethidium bromide (EB) were obtained from
SigmaꢀAldrich Biotech. Co., Ltd. The stock soln. (1.0 mm) of the investigated compound was prepared by
dissolving the powdered material into appropriate amounts of DMF soln. Deionized doubly distilled
H2O and anal. grade reagents were used throughout. CT-DNA Stock soln. was prepared by dissolving the
solid material in 5 mm Tris·HCl buffer (pH 7.20) containing 50 mm NaCl and kept over 48 h at 48. The
CT-DNA concentration in terms of base pair lꢀ1 was determined spectrophotometrically by employing
an extinction coefficient of e¼13,200 mꢀ1 cmꢀ1 (base pair)ꢀ1 at 260 nm, and its concentration in terms of
nucleotide lꢀ1 was also determined spectrophotometrically by employing an extinction coefficient of
6600 mꢀ1 cmꢀ1 (nucleotide)ꢀ1 at 260 nm [19]. The stock soln. was stored at ꢀ208, until it was used.
Working standard soln. of CT-DNA was obtained by appropriate dilution of the stock soln. in 5 mm Tris·
HCl buffer (pH 7.20) containing 50 mm NaCl. EB was dissolved in 5 mm Tris·HCl buffer (pH 7.20), and
its concentration was determined assuming a molar extinction coefficient of 5600 mꢀ1 cmꢀ1 at 480 nm [9].
Methods. M.p.: XT4–100X Microscopic melting-point apparatus (Beijing, P. R. China). IR Spectra:
Nicolet Nexus 670 FT-IR spectrometer using KBr discs in the 4000–400-cmꢀ1 region. 1H-NMR Spectra:
Bruker Advance DRX 200-MHz spectrometer with tetramethylsilane (TMS) as an internal standard.
ESI-MS (ESI-Trap/Mass) spectra: Bruker Esquire6000 mass spectrophotometer; HCOOH as the proton
source. Elemental analyses of C, N and H: Elemental Vario EL analyzer. The metal ion content was
determined by complexometric titration with EDTA after destruction of the complex in the conventional
manner.
Viscosity titration experiments were carried out on an Ubbelohde viscometer in a thermostated
water bath maintained at 25.00ꢂ0.018. Data were presented as (h/h0)1/3 vs. the ratio of the compound to
DNA, where h is the viscosity of DNA in the presence of the compound corrected from the solvent effect,
and h0 is the viscosity of DNA alone [9].
UV/VIS Spectra were recorded using a PerkinꢀElmer Lambda UV/VIS spectrophotometer. The
UV/VIS spectra of the investigated compounds in the absence and in the presence of the CT-DNA were
obtained in DMF/Tris·HCl buffer (5 mm, pH 7.20) containing 50 mm NaCl of 1:100 solns., resp. The
binding constant (Kb) was determined according to the Eqn. 1 [12]:
½DNAꢃ ½DNAꢃ
1
¼
þ
(1)
ef ꢀ ea
ef ꢀ eb Kbðef ꢀ ebÞ
where [DNA] is the molar concentration of DNA in base pairs, ea [mꢀ1 cmꢀ1] is the extinction coefficient
observed, ef [mꢀ1 cmꢀ1] is the extinction coefficient of the free compound, eb [mꢀ1 cmꢀ1] is the extinction
coefficient of the compound when fully bound to DNA, and Kb is the intrinsic binding constant. The ratio
of slope to intercept in the plot of [DNA]/(ef ꢀea) vs. [DNA] gives the value of Kb.
Fluorescence spectra were recorded with a RF–5301PC spectrofluorophotometer (Shimadzu,
Japan) using a 1-cm quartz cell. Both the excitation and emission band widths were 10 nm. DNAꢀEB
Quenching assay was performed as described in [3][20]. Measurements were conducted at a constant r.t.,
298 K. SternꢀVolmer equation was used to determine the fluorescent quenching mechanism [15]:
Fo/F¼1þKqto[Q]¼1þKSV[Q]
(2)
where Fo and F are the fluorescence intensity in the absence and in the presence of a compound at [Q]
concentration, resp., KSV is the SternꢀVolmer dynamic quenching constant, Kq is the quenching rate
constant of bimolecular diffusion collision, and to is the lifetime of free EB.
.
The HO radicals in aq. media were generated through the Fenton-type reaction [3][21]. The 5-ml
mixtures contained 2.0 ml of 100 mm phosphate buffer (pH 7.4), 1.0 ml of 0.10 mm aq. safranin, 1 ml of
1.0 mm aq. EDTAꢀFeII, 1 ml of 3% aq. H2O2, and a series of quantitatively microadding solns. of the
tested compound. The mixtures were incubated at 378 for 60 min in a water-bath. Absorbance at 520 nm
was measured, and the solvent effect was corrected throughout. The scavenging effect of compound on
.
HO was calculated from the following expression [22]:

1542
CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
AsampleꢀAblank
Scavenging effect [%]¼
ꢁ 100
(3)
AcontrolꢀAblank
where Asample is the absorbance of the sample in the presence of the tested compound, Ablank is the
absorbance of the blank in the absence of the tested compound, and Acontrol is the absorbance in the
absence of the tested compound and EDTAꢀFeII. The data for antioxidation activities are presented as
means ꢂSD of three determinations and followed by Studentꢂs t-test. Differences were considered to be
statistically significant if P<0.05.
Preparation of 8-Hydroxyquinoline-7-carboxaldehyde. Chloropicrin (32 ml, 0.4 mol) was dropped
into the EtOH soln. of 14.5 g (0.1 mol) of 8-hydroxyquinoline and 40% aq. NaOH (1 mol) soln.
Refluxing the mixtures for 4 h at 65–708, the crude product was obtained after acidification to pH 5.0–
5.5 with 0.1m HCl. Salmon-pink crystals were obtained by chromatographic separation (eluent, Vpetroleum
/
VAcOEt 40 :1). Then, recrystallization afforded pale-orange needle-like crystals were obtained after drying
in vacuum. Yield: 18% (3.1 g), M.p. 1788.
Preparation of 8-Hydroxyquinoline-7-carboxaldehyde Benzoylhydrazone (1). Refluxing and stirring
the mixture of a 10-ml EtOH soln. of 8-hydroxyquinoline-7-carboxaldehyde (0.519 g, 3 mm) and a 10-ml
90% EtOH aq. soln. of benzoylhydrazine (0.408 g, 3 mm) for 8 h, and cooling to r.t. afforded a precipitate,
which was filtered, recrystallized from 80% MeOH aq. soln., and dried in vacuum over 48 h. Pale-yellow
powder. Yield: 73.4% (0.641 g). M.p. 257–2598. UV/VIS (lmax [nm], eꢁ104 [mꢀ1 cmꢀ1]): 246 (2.58), 348
1
(2.11). IR (KBr): 3328, 3205, 1641, 1597, 1571, 1288. H-NMR ((D6)DMSO, 200 MHz): 9.63–9.60 (dd,
J(2,3)¼7.2, J(2,4)¼1.8, HꢀC(2)); 8.83 (s, C(11)H¼N); 8.96–8.95 (d, J¼2.4, HꢀC(4)); 7.97–7.95 (d, J¼
6.6, HꢀC(16), HꢀC(20)); 7.80–7.78 (d, J¼7.5, HꢀC(6)); 7.76–7.73 (m, HꢀC(18)); 7.62–7.53 (m, HꢀC(3),
HꢀC(17), HꢀC(19)); 7.19–7.16 (d, J¼7.5, HꢀC(5)). ESI-TRAP-MS (DMF): 292.1 ([MþH]þ ). Anal.
calc. for C17H13N3O2: C 70.09, H 4.50, N 14.42; found: C 37.05, H 4.54, N 14.41.
Preparation of Complexes 2–10. Each complex was prepared by refluxing and stirring the mixtures
of a 40-ml MeOH soln. of compound 1 (0.058 g, 0.2 mm) and equimolar amounts of Ln(NO3)·6 H2O
(Ln¼La3þ, Nd3þ, Sm3þ, Eu3þ, Gd3þ, Dy3þ, Ho3þ, Er3þ, Yb3þ, resp.) on a water bath. After refluxing for
30 min, Et3N (0.020 g, 0.2 mm) was added dropwise into the mixtures to deprotonate the phenolic OH
substituent of 8-hydroxyquinolinato unit. Then, the mixtures were refluxed and stirred continuously for
8 h. Cooled to r.t., the precipitate was centrifuged, washed with MeOH soln., and dried in vacuum over
48 h. All the LnIII complexes were yellow powders, and their melting points exceeded 3008.
Complex 2. Yield: 86.4% (0.091 g). UV/VIS (lmax [nm], eꢁ104 [mꢀ1 cmꢀ1]): 247 (3.68), 349 (2.76).
IR (KBr): 3399, 3229, 1645, 1601, 1558, 960, 633, 1094, 1386, 1465, 1317, 1031, 836, 716, 531, 428. ESI-
TRAP-MS (DMF): 1278.4 ([MþH]þ ), 639.7 ([M/2þH]þ ), 638.2 ([M/2]þ ). Anal. calc. for C34H30La2-
N8O14: C 38.80, H 2.87, N 10.65, La 26.40; found: C 38.71, H 2.85, N 10.69, La 26.48. Lm (cm2 Wꢀ1 molꢀ1
;
DMF): 49.0.
Complex 3. Yield: 86.6% (0.092 g). UV/VIS: 247 (2.55), 350 (1.96). IR (KBr): 3392, 3226, 1644,
1602, 1560, 963, 633, 1095, 1386, 1466, 1320, 1034, 838, 719, 533, 436. ESI-TRAP-MS (DMF): 1283.9
([MþH]þ ), 1283.0 (Mþ ), 642.7 ([M/2þH]þ ). Anal. calc. for C34H30N8Nd2O14: C 38.41, H 2.84, N 10.54,
Nd 27.14; found: C 38.32, H 2.82, N 10.46, Nd 27.02. Lm: 42.3.
Complex 4. Yield: 81.7% (0.088 g). UV/VIS: 262 (2.98), 348 (2.27). IR (KBr): 3402, 3227, 1645, 1603,
1561, 962, 634, 1096, 1386, 1466, 1322, 1033, 837, 720, 533, 438. ESI-TRAP-MS (DMF): 1296.9 ([MþH]þ ),
1295.3 (Mþ ), 649.3 ([M/2þH]þ ). Anal. calc. for C34H30N8O14Sm2: C 37.97, H 2.81, N 10.42, Sm 27.96;
found: C 38.13, H 2.80, N 10.37, Sm 27.81. Lm: 40.5.
Complex 5. Yield: 82.8% (0.089 g). UV/VIS: 261 (3.67), 348 (2.55). IR (KBr): 3387, 3230, 1643,
1602, 1562, 964, 642, 1098, 1388, 1468, 1321, 1001, 836, 721, 533, 436. ESI-TRAP-MS (DMF): 1301.1
([MþH]þ ), 649.0 ([M/2]þ ). Anal. calc. for C34H30Eu2N8O14: C 37.86, H 2.80, N 10.39, Eu 28.18; found: C
37.83, H 2.80, N 10.44, Eu 28.26. Lm: 58.2.
Complex 6. Yield: 86.4% (0.094 g). UV/VIS: 263 (3.26), 347 (2.34). IR (KBr): 3398, 3223, 1646,
1603, 1561, 962, 634, 1097, 1385, 1467, 1323, 1031, 837, 722, 532, 441. ESI-TRAP-MS (DMF): 1310.7 ([Mþ
H]þ ), 655.4 ([M/2þH]þ ), 654.4 ([M/2]þ ). Anal. calc. for C34H30Gd2N8O14: C 37.49, H 2.78, N 10.29, Gd
28.88; found: C 37.38, H 2.77, N 10.23, Gd 28.97. Lm: 58.1.
Complex 7. Yield: 83.9% (0.092 g). UV/VIS: 262 (2.16), 347 (1.60). IR (KBr): 3399, 3223, 1653, 1602,
1562, 962, 634, 1096, 1386, 1467, 1319, 1034, 836, 723, 535, 441. ESI-TRAP-MS (DMF): 1320.3 ([MþH]þ ),

CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
1543
660.9 ([M/2þH]þ ), 659.6 ([M/2]þ ). Anal. calc. for C34H30Dy2N8O14: C 37.14, H 2.75, N 10.29, Dy 29.55;
found: C 37.24, H 2.75, N 10.22, Dy 29.64. Lm: 40.6.
Complex 8. Yield: 83.7% (0.092 g). UV/VIS: 262 (2.37), 345 (1.72). IR (KBr): 3399, 3224, 1650,
1590, 1563, 962, 634, 1097, 1386, 1467, 1320, 1033, 836, 724, 535, 443. ESI-TRAP-MS (DMF): 1325.2
([MþH]þ ), 1324.3 (Mþ ), 663.8 ([M/2þH]þ ), 662.9 ([M/2]þ ). Anal. calc. for C34H30Ho2N8O14: C 36.97,
H 2.74, N 10.15, Ho 29.86; found: C 37.00, H 2.75, N 10.10, Ho 29.94. Lm: 45.0.
Complex 9. Yield: 84.8% (0.094 g). UV/VIS: 262 (1.93), 345 (1.44). IR (KBr): 3409, 3226, 1649,
1592, 1562, , 964, 634, 1098, 1385, 1468, 1326, 1032, 837, 724, 534, 443. ESI-TRAP-MS (DMF): 1330.5
([MþH]þ ), 1329.1 (Mþ ), 665.5 ([M/2þH]þ ). Anal. calc. for C34H30Er2N8O14: C 36.82, H 2.73, N 10.10,
Er 30.16; found: C 36.74, H 2.71, N 10.03, Er 30.12. Lm: 31.2.
Complex 10. Yield: 83.8% (0.094 g). UV/VIS: 263 (3.23), 343 (2.37). IR (KBr): 3412, 3226, 1654,
1591, 1564, 965, 634, 1099, 1385, 1469, 1320, 1036, 836, 726, 537, 447. ESI-TRAP-MS (DMF): 1341.7 (Mþ ),
671.5 ([M/2þH]þ ), 670.0 ([M/2]þ ). Anal. calc. for C34H30N8O14Yb2: C 36.44, H 2.70, N 10.00, Yb 30.88;
found: C 36.27, H 2.70, N 10.07, Yb 30.97. Lm: 39.1.
This study was supported by China NNSF (No. 20975046) and Gansu Educational Fund SRP
(No. 1010B-04).
REFERENCES
[1] G. Zuber, J. C. Quada Jr., S. M. Hecht, J. Am. Chem. Soc. 1998, 120, 9368; V.-S. Li, D. Choi, Z.
Wang, L. S. Jimenez, M.-S. Tang, H. Kohn, J. Am. Chem. Soc. 1996, 118, 2326.
[2] S.-Y. Chiang, J. Welch, F. J. Rauscher III, T. A. Beerman, Biochemistry 1994, 33, 7033; J. M.
Woynarowski, M. McHugh, R. D. Sigmund, T. A. Beerman, Mol. Pharmacol. 1989, 35, 177; A. Y.
Chen, C. Yu, B. Gatto, L. F. Liu, Proc. Natl. Acad. Sci. U.S.A. 1993, 90, 8131.
[3] Y.-C. Liu, Z.-Y. Yang, Biometals 2009, 22, 733; Y.-C. Liu, Z.-Y. Yang, J. Organomet. Chem. 2009,
694, 3091; Y.-C. Liu, Z.-Y. Yang, J. Inorg. Biochem. 2009, 103, 1014; Y.-C. Liu, Z.-Y. Yang, Inorg.
Chem. Commun. 2009, 12, 704; Y.-C. Liu, Z.-Y. Yang, Eur. J. Med. Chem. 2009, 44, 5080.
[4] A. A. El-Asmy, A. Z. El-Sonbati, A. A. Ba-Issa, M. Mounir, Transition Met. Chem. 1990, 15, 222;
T. M. A. Ismail, J. Coord. Chem. 2005, 58, 141; Z. Zeng, L.-M. Jin, X.-Y. Jiao, C.-C. Guo, Jingxi
Huagong Zhongjianti 2004, 34, 17; R.-X. Lei, Y.-C. Liu, Baoji Wenli Xueyuan Xuebao 2008, 28, 206;
C. Hamada, Y. Hirano, T. Iida, Nippon Kagaku Zassi 1956, 77, 1107; R.-X Lei, J. Cheng, Y.-Y. Jia, C.-
F. Liu, Y.-C. Liu, Baoji Wenli Xueyuan Xuebao 2010, 30, 24.
[5] W. J. Geary, Coord. Chem. Rev. 1971, 7, 81.
[6] J.-M. Ou-Yang, Z.-H. Tai, Wuji Huaxue Xuebao 1997, 13, 315.
[7] X.-H. Lu, Q.-Y. Lin, L.-C. Kong, X.-Q. He, Huaxue Yanjiu Yu Yingyong 2006, 18, 1380.
[8] D. S. Sigman, A. Mazumder, D. M. Perrin, Chem. Rev. 1993, 93, 2295.
[9] D. Suh, J. B. Chaires, Bioorg. Med. Chem. 1995, 3, 723; R. Palchaudhuri, P. J. Hergenrother, Curr.
Opin. Biotechnol. 2007, 18, 497.
[10] S. Satyanarayana, J. C. Dabrowiak, J. B. Chaires, Biochemistry 1992, 31, 9319; B.-D. Wang, Z.-Y.
Yang, P. Crewdson, D.-Q. Wang, J. Inorg. Biochem. 2007, 101, 1492.
[11] J. K. Barton, A. T. Danishefsky, J. M. Goldberg, J. Am. Chem. Soc. 1984, 106, 2172; H.-L. Lu, J.-J.
Liang, Z.-Z. Zeng, P.-X. Xi, X.-H. Liu, F.-J. Chen, Z.-H. Xu, Transition Met. Chem. 2007, 32, 564.
[12] A. Wolfe, G. H. Shimer Jr., T. Meehan, Biochemistry 1987, 26, 6392; P.-X. Xi, Z.-H. Xu, X.-H. Liu,
F.-J. Cheng, Z.-Z. Zeng, Spectrochim. Acta, Part A 2008, 71, 523.
[13] Y.-C. Liu, Z.-Y. Yang, J. Du, X.-J. Yao, R.-X. Lei, X.-D. Zheng, J.-N. Liu, H.-S. Hu, H. Li,
Immunobiology 2008, 213, 651.
[14] L. A. Bagatolli, S. C. Kivatinitz, G. D. Fidelio, J. Pharm. Sci. 1996, 85, 1131; M.-M. Yang, P. Yang, L.-
W. Zhang, Chin. Sci. Bull. 1994, 9, 31.
[15] A. Ayar, B. Mercimek, Process Biochem. 2006, 41, 1553.
[16] Z.-L. Li, J.-H. Chen, K.-C. Zhang, M.-L. Li, R.-Q. Yu, Sci. China, Ser. B: Chem. 1991, 11, 1193.
[17] J. Ueda, N. Saito, Y. Shimazu, T. Ozawa, Arch. Biochem. Biophys. 1996, 333, 377.

1544
CHEMISTRY & BIODIVERSITY – Vol. 9 (2012)
[18] R. Xing, H. Yu, S. Liu, W. Zhang, Q. Zhang, Z. Li, P. Li, Bioorg. Med. Chem. 2005, 13, 1387.
´
[19] F. Zsila, Z. Bikadi, M. Simonyi, Org. Biomol. Chem. 2004, 2, 2902.
[20] A. G. Krishna, D. V. Kumar, B. M. Khan, S. K. Rawal, K. N. Ganesh, Biochim. Biophys. Acta – Gen.
Subj. 1998, 1381, 104.
[21] C. C. Winterbourn, Biochem. J. 1979, 182, 625; C. C. Winterbourn, Biochem. J. 1981, 198, 125.
[22] Z. Guo, R. Xing, S. Liu, H. Yu, P. Wang, C. Li, P. Li, Bioorg. Med. Chem. Lett. 2005, 15, 4600.
Received September 28, 2011