Rare earth complexes with 3-carbaldehyde chromone-(benzoyl) hydrazone: Synthesis, characterization, DNA binding studies and antioxidant activity

Article abstract of DOI:10.1007/s10895-009-0561-0

A new ligand, 3-carbaldehyde chromone-(benzoyl) hydrazone (L), was prepared by condensation of 3-carbaldehyde chromone with benzoyl hydrazine. Its four rare earth complexes have been prepared and characterized on the basis of elemental analyses, molar conductivities, mass spectra, ¹H NMR spectra, UV-vis spectra, fluorescence studies and IR spectra. The Sm(III) complex exhibits red fluorescence under UV light and the fluorescent properties of Sm(III) complex in solid state and different solutions were investigated. In addition, the DNA binding properties of the ligand and its complexes have been investigated by electronic absorption spectroscopy, fluorescence spectra, ethidium bromide displacement experiments, iodide quenching experiments, salt effect and viscosity measurements. Experimental results suggest that all the compounds can bind to DNA via an intercalation binding mode. Furthermore, the antioxidant activities of the ligand and its complexes were determined by superoxide and hydroxyl radical scavenging methods in vitro. The rare earth complexes were found to possess potent antioxidant activities that are better than those of the ligand alone.

Full text of DOI:10.1007/s10895-009-0561-0

J Fluoresc (2010) 20:329–342
DOI 10.1007/s10895-009-0561-0
ORIGINAL PAPER
Rare Earth Complexes with 3-Carbaldehyde Chromone-
(Benzoyl) Hydrazone: Synthesis, Characterization, DNA
Binding Studies and Antioxidant Activity
Yong Li & Zheng-yin Yang
Received: 31 May 2009 /Accepted: 12 October 2009 /Published online: 24 October 2009
#
Springer Science + Business Media, LLC 2009
Abstract A new ligand, 3-carbaldehyde chromone-(benzoyl)
hydrazone (L), was prepared by condensation of 3-
carbaldehyde chromone with benzoyl hydrazine. Its four rare
earth complexes have been prepared and characterized on the
basis of elemental analyses, molar conductivities, mass
spectra, 1H NMR spectra, UV-vis spectra, fluorescence
studies and IR spectra. The Sm(III) complex exhibits red
fluorescence under UV light and the fluorescent properties of
Sm(III) complex in solid state and different solutions were
investigated. In addition, the DNA binding properties of the
ligand and its complexes have been investigated by electronic
absorption spectroscopy, fluorescence spectra, ethidium bro-
mide displacement experiments, iodide quenching experi-
ments, salt effect and viscosity measurements. Experimental
results suggest that all the compounds can bind to DNA via
an intercalation binding mode. Furthermore, the antioxidant
activities of the ligand and its complexes were determined by
superoxide and hydroxyl radical scavenging methods in vitro.
The rare earth complexes were found to possess potent
antioxidant activities that are better than those of the ligand
alone.
Introduction
DNA plays an important role in the life process since it
contains all the genetic information for the cellular
function. However, DNA molecules are prone to be
damaged under various conditions such as interactions with
some small molecules. This damage may lead to various
pathological changes in living organisms. The interaction of
metal complexes with DNA is of great interest in design
and development of synthetic restriction enzymes, chemo-
therapeutic drugs and DNA foot printing agents [1–4].
Metal complexes can bind to DNA in non-covalent ways
such as electrostatic effect, groove binding and intercala-
tion. However, considerable useful applications of the metal
complexes require that the complexes can bind to DNA via
an intercalation mode which could induce cellular degra-
dation [5]. It was reported the ability of metal complexes
intercalating into DNA will increase with the planarity of
the ligand [6, 7]. The coordination geometry and ligand
donor atom type also play key roles in determining the
binding extent of complexes to DNA [8, 9]. Additionly,
both the metal ion type and its valence also play important
roles in deciding extent of complexes to DNA [10]. Among
all the metal complexes, rare earth complexes are widely
investigated since the rare earth complexes with tetracy-
cline, phenanthroline [11], adriamycin and pyridine [12–14]
have been synthesized as a probe to study nucleic acids.
Chromones (1-benzopyran-4-one) are a group of natu-
rally and widely distributed compounds that are ubiquitous
in nature, especially in the plant kingdom [15]. These
compounds have attracted a great deal of attention and
many synthesized chromone derivatives have been widely
studied due to their biological activities including anti-
mycobacterial, antifungal, anticonvulsant, antimicrobial and
mushroom tyrosinase inhibition activities [16, 17]. These
.
Keywords 3-carbaldehyde chromone-(benzoyl) hydrazone
.
.
Rare earth complexes Fluorescence spectra DNA binding
.
properties Antioxidant activity
:
Y. Li Z.-y. Yang (*)
College of Chemistry and Chemical Engineering and State Key
Laboratory of Applied Organic Chemistry, Lanzhou University,
Lanzhou 730000, People’s Republic of China
e-mail: yangzy@lzu.edu.cn

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J Fluoresc (2010) 20:329–342
derivatives also serve as intermediates to many products of
fine chemical industries such as pharmaceuticals, agro-
chemicals and dyestuffs [18]. In this regard, as a further
research, a new Schiff-base ligand, 3-carbaldehyde
chromone-(benzoyl) hydrazone (L) and its rare earth
complexes were synthesized and their DNA binding
properties were investigated systematically. In addition,
the antioxidant activities of the ligand and its complexes
were determined by superoxide and hydroxyl radical
scavenging methods in vitro. Furthermore, the Sm(III)
complex can emit intrinsic spectra under excitation both
in solid state and organic solvents, which may provide more
advantages to be applied as a candidate of anticancer drugs
and nucleic acid probe.
Shimadzu UV-240 spectrophotometer. Fluorescence spectra
were recorded on a Hitachi RF-4500 spectrofluorophotom-
eter at a constant room temperature. Its measuring wave-
length range (on both EX and EM) is from 200 to 730 nm,
and the spectral resolution is 1.0 nm. In addition, its light
source and detector are 150 W xenon lamp and R3788
photomultiplier tube, respectively. Quantum yields of the
ligand and its complexes were determined by an absolute
method using an integrating sphere on FLS-920 of
Edinburgh instrument with coumarin 307 as the reference
sample. The FLS-920 is equipped by a pulsed xenon lamp
as the excitation source, a raster as the detector and with
spectral resolution of 0.05 nm.
DNA binding studies
Experimental section
Electronic absorption spectroscopy
Materials and instrumentation
Electronic absorption titration experiments were performed
with fixed concentration drugs (10 µM), while gradually
increasing the concentration of CT DNA. When measuring
the absorption spectra, an equal amount of CT DNA was
added to both the complex solutions and the reference
solution to eliminate the absorbance of CT DNA itself. Each
sample solution was scanned in the range of 190–500 nm.
Ethidium bromide (EB) and calf thymus DNA (CT DNA)
were purchased from Sigma Chemical Co.. All chemicals
and solvents used were of analytical reagent grade and used
without further purification unless otherwise noted.
All the experiments involved with the interaction of the
ligand and complexes with CT DNA were carried out in
doubly distilled water buffer containing 5 mM Tris [Tris
(hydroxymethyl)-aminomethane] and 50 mM NaCl and
adjusted to pH 7.1 with hydrochloric acid. Solution of CT
DNA in the buffer gave ratios of UV absorbance of about
1.8–1.9:1 at 260 and 280 nm, indicating that the CT DNA
was sufficiently free of protein [19]. The CT DNA
concentration per nucleotide was determined spectrophoto-
metrically by employing an extinction coefficient of 6,600
M−1 cm−1 at 260 nm [20]. The ligand and complexes were
dissolved in a solvent mixture of 1% DMF and 99% Tris-
HCl buffer (pH 7.1) at the concentration 1.0×10−5 M.
Carbon, hydrogen and nitrogen were determined using
an Elemental Vario EL analyzer. The metal contents of the
complexes were determined by titration with EDTA
(xylenol orange tetrasodium salt used as an indicator and
hexamethylidynetetraimine as buffer). The melting point of
the ligand was determined on a Beijing XT4-100X
microscopic melting point apparatus (the thermometer was
not corrected). The IR spectra were obtained in KBr discs
on a Therrno Mattson FTIR spectrophotometer in the 4,000
Fluorescence spectra
Fixed amounts (10 μM) of compounds were titrated with
increasing amounts of CT DNA, over a range of DNA
concentrations from 2.5 to 15 μM. Excitation wavelengths
of the samples were about 345 nm, scan speed was 480 nm/
min, slit width was 5 nm. All experiments were conducted
at a constant room temperature in a buffer solution
containing 5 mM Tris-HCl (pH 7.1) and 50 mM NaCl
concentrations. The intrinsic binding constants (Kb) of the
compounds with DNA were obtained through fluorescence
spectra according to the following equation [21]:
r=Cf ¼ Kb ꢀ ðn ꢁ rÞ
ÂÀ
ÁꢀÀ
ÁÃ
Cb ¼ Ct F ꢁ F0
Fmax ꢁ F0
;
where Ct is the total compound concentration, F is the
observed fluorescence emission intensity at given DNA
concentrations, F0 is the intensity in the absence of DNA
and Fmax is the fluorescence of the totally bound com-
pound. Binding data were cast into the form of a Scatchard
plot of r/Cf versus r, where r is the binding ratio Cb/
[DNA]t, Cf is the free compound concentration and n is the
binding site number.
1
−400 cm−1 region. H NMR spectra were recorded on a
Varian VR 300 MHz spectrometer in DMSO-d6 with TMS
(tetramethylsilane) as an internal standard. Mass spectra
were performed on a APEX II FT-ICR MS instrument using
DMF as mobile phase. Conductivity measurements were
performed in DMF solution with a DDS-11C conductom-
eter at 25.0 °C. The UV-vis spectra were recorded on a
Further support for the mode of the ligand and
complexes binding to DNA is given through the emission
quenching experiments. A 2.0 mL solution of 4 µM DNA

J Fluoresc (2010) 20:329–342
331
and 0.32 µM EB (at saturating binding levels) was titrated
by 2.5–50 µM the complexes and ligand at a constant room
temperature in a buffer solution containing 5 mM Tris-HCl
(pH 7.1) and 50 mM NaCl concentrations. Quenching data
were analyzed according to the Stern-Volmer equation
which could be used to determine the fluorescent quenching
mechanism:
calculated by measuring the absorbance at 560 nm, because
NBT can be reduced quantitatively to blue formazan by
O2•−. The solution of MET, VitB2 and NBT were prepared
with 0.067 M phosphate buffer (pH=7.8) at the condition
of avoiding light. The tested compounds were dissolved in
DMF. The reaction mixture contained MET (0.01 mol L−1),
NBT (4.6×10−5 mol L−1), VitB2 (3.3×10−6 mol L−1),
phosphate buffer solution (0.067 mol L−1) and the tested
compound (the final concentration: Ci (i=1–6)=0.4, 1.0, 2.0,
4.0, 6.0, 8.0 µM). After incubating at 30 °C for 10 min and
illuminating with a fluorescent lamp for 3 min, the
absorbance (Ai) of the samples were measured at 560 nm.
The sample without the tested compound and avoiding light
was used as the control. The suppression ratio for O2•− was
calculated from the following expression:
ꢀ
Fo F ¼ 1 þ Kq½Qꢂ;
Where Fo and F are the fluorescence intensity in the
absence and presence of drug at [Q] concentration
respectively; Kq is the quenching constant and [Q] is the
quencher concentration. Plots of Fo /F versus [Q] appear to
be linear and Kq depends on temperature [22].
Iodide quenching experiments were done according to the
below methods: fluorescence intensities were recorded in the
absence and presence of DNA in the mixture solution of each
compound and KI. The fluorescence quenching efficiency is
evaluated by Stern-Volmer Ksv, which varies with the
experimental conditions. Quenching plots were constructed
according to the following Stern-Volmer equation.
Suppression ratio ð%Þ ¼ ½ðA ꢁ A Þ A ꢂ ꢀ 100%
=
0
i
0
where Ai = the absorbance in the presence of the ligand or
its complexes, A0 = the absorbance in the absence of the
ligand or its complexes.
In antioxidant activity experiments the hydroxyl radical
(HO•) in aqueous media was generated through the Fenton
reaction [27]. The solution of the tested compounds was
prepared with DMF. The reaction mixture contained 2.5 mL
0.15 M phosphate buffer (pH=7.4), 0.5 mL 114 µM
safranin, 1 mL 945 µM EDTA-Fe(II), 1 mL 3% H2O2 and
30 µL the tested compound solution (the final concentra-
tion: Ci (i=1–6)=1.0, 2.0, 3.0, 4.0, 5.0, 6.0 µM). The sample
without the tested compound was used as the control. The
reaction mixtures were incubated at 37 °C for 60 min in a
water-bath. Absorbances (Ai, A0, Ac) at 520 nm were
measured. The suppression ratio for HO· was calculated
from the following expression:
Fo=F ¼ 1 þ Ksv½Iꢁꢂ;
Where Fo and F are the fluorescence intensity in the absence
and presence of iodide at [I-] concentration, respectively; Ksv
is the quenching constant and [I-] is the concentration of
iodide. Plots of Fo /F versus [I−] appear to be linear and Ksv
was evaluated by linear least-squares analysis of the data
according to the equation [23].
Fluorescence intensities were also recorded in the
absence and presence of DNA in the mixture solution of
each compound and NaCl to investigate the salt effects of
compounds to DNA.
Suppression ratio ð%Þ ¼ ½ðAi ꢁ A0Þ=ðAc ꢁ A0Þꢂ ꢀ 100%
Viscosity measurements
Where Ai = the absorbance in the presence of the tested
compound; A0 = the bsorbance in the absence of the tested
compound; Ac = the absorbance in the absence of the
tested compound, EDTA-Fe(II) and H2O2.
The antioxidant activity was expressed as the 50%
inhibitory concentration (IC50). IC50 values were calculated
from regression lines where: x was the tested compound
concentration in mM and y was percent inhibition of the
tested compounds.
Viscosity experiments were conducted on an Ubbelodhe
viscometer, immersed in a thermostated water-bath main-
tained to 25.0 0.1 °C. Titrations were performed for the
complexes (0.5–4 µM), and each compound was introduced
into a DNA solution (5 µM) present in the viscometer. Data
were presented as (η/η0)1/3 versus the ratio of the
concentration of the compound and DNA, where η is the
viscosity of DNA in the presence of the compound and η0
is the viscosity of DNA alone [24, 25].
Preparation of the ligand (L)
Antioxidant activity
Scheme of the synthesis of the ligand is shown in Fig. 1. 3-
carbaldehyde chromone was prepared according to the
literature methods [28]. An ethanol solution containing
benzoyl hydrazine (1.36 g, 10 mmol) was added dropwise
In antioxidant activity experiments the superoxide radicals
(O2•−) were produced by the system MET/VitB2/NBT [26].
The amount of O2 and suppression ratio for O2 can be
•−
•−

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J Fluoresc (2010) 20:329–342
Fig. 1 Scheme of the synthesis
of the ligand (L)
to another ethanol solution containing 3-carbaldehyde
chromone (1.74 g, 10 mmol). The mixture was refluxed
on an oil bath for 4 h with stirring and a yellow precipitate
formed. The yellow precipitate was filtered, washed several
times with ethanol and recrystallized from DMF and water
to give the ligand (L), which was dried in a vacuum. Yield:
82.16%. Mp 176–178 °C. Anal. Calcd for C17H12N2O3: C,
69.86; H, 4.14; N, 9.58. Found: C, 69.92; H, 4.174; N,
17.10. Found: C, 43.82; H, 2.73; N, 10.67; Tb, 17.15. IR
νmax (cm−1): ν(carbonyl)C=O: 1,639, ν(hydrazonic)C=O: 1,614,
νC=N: 1,563, νNO : 1,489, 1,384, 1,317, 1,194, 822, νM-O
:
3
639, νM-N: 429 cm−1. Umax (nm): 276, 307 nm. Λm (S cm2
mol−1): 102.
Results and discussion
9.49. IR νmax (cm−1): ν(carbonyl)C=O: 1,679, ν(hydrazonic)C=O
1,639, νC=N: 1,600 cm−1. Umax (nm): 273, 303 nm.
:
The complexes were prepared by direct reaction of the
ligand with appropriate mole ratios of Ln(III) nitrate in
ethanol. The yields were good to moderate. The complexes
are stable in atmospheric conditions for extended periods
and easily soluble in DMF and DMSO; slightly soluble in
ethanol, methanol and acetone; insoluble in benzene, water
and diethyl ether. The molar conductivities of the com-
plexes are around 99 – 117 in DMF solution and in accord
with them being formulated as 1:1 electrolytes [29]. The
structures of the complexes were characterized on the basis
of elemental analyses, molar conductivities, mass spectra,
1H NMR spectra, UV-vis spectra, fluorescence studies and
IR spectra. The elemental analyses and molar conductivities
show that formulas of the complexes conform to [Ln L2•
(NO3)2]•NO3 [Ln(III) = La, Sm, Nd and Tb; L is the ligand
3-carbaldehyde chromone-(benzoyl) hydrazone].
Preparation of the complexes
The ligand (1.0 mmol, 0.292 g) and the La(III) nitrate
(1.0 mmol, 0.434 g) were added together in ethanol
(20 mL). The mixture solution was refluxed on an oil bath
for 2 h with stirring and a white precipitate, the La(III)
complex, was separated from the solution by suction
filtration, purified by washing several times with ethanol
and dried for 24 h in a vacuum. Sm(III), Nd(III) and Tb(III)
complexes were prepared by the same way. Anal. Calcd for
La(III) complex C34H24N7O15La: C, 44.90; H, 2.66; N,
10.78; La, 15.27. Found: C, 44.82; H, 2.61; N, 10.75; La,
15.30. IR νmax (cm−1): ν(carbonyl)C=O: 1,643, ν(hydrazonic)C=O
1,620, νC=N: 1,569, νNO : 1,482, 1,385, 1,327, 1,185, 819,
:
3
ν
M-O: 605, νM-N: 418 cm−1. Umax (nm): 277, 308 nm. Λm
(S cm2 mol−1): 117. Anal. Calcd for Sm(III) complex
C34H24N7O15Sm: C, 44.34; H, 2.63; N, 10.65; Sm, 16.33.
Found: C, 44.52; H, 2.69; N, 10.54; Sm, 16.38. IR νmax
Structure of the complexes
IR spectra
(cm−1): ν(carbonyl)C=O: 1,642, ν(hydrazonic)C=O: 1,618, νC=N
:
1,574, νNO : 1,481, 1,384, 1,322, 1,185, 817, νM-O: 610,
The IR spectra of the complexes are similar and IR spectra
usually provide a lot of valuable information on coordina-
tion reaction. All the spectra are characterized by vibra-
tional bands mainly due to the C = O, C = N and NO3
groups. The ν(carbonyl)C=O and ν(hydrazonic)C=O vibrations of
the free ligand appear at 1,679 and 1,639 cm−1, respective-
ly; for the complexes these peaks shift to 1,642 and
1,618 cm−1 or so, Δν(ligand-complexes) is equal to 37 and
21 cm−1. In the complexes, the band at 610 cm−1 or so is
assigned to νM-O. It demonstrates that the oxygen of
3
ν
M-N: 421 cm−1. Umax (nm): 277, 307 nm. Λm (S cm2
mol−1): 100. Anal. Calcd for Nd(III) complex
C34H24N7O15Nd: C, 44.64; H, 2.64; N, 10.72; Nd, 15.77.
Found: C, 44.62; H, 2.71; N, 10.77; Nd, 15.65. IR νmax
(cm−1): ν(carbonyl)C=O: 1,639, ν(hydrazonic)C=O: 1,618, νC=N
:
1,574, νNO : 1,483, 1,382, 1,320, 1,187, 818, νM-O: 609,
3
ν
M-N: 420 cm−1. Umax (nm): 277, 308 nm. Λm (S cm2
mol−1): 99. Anal. Calcd for Tb(III) complex
C34H24N7O15NTb: C, 43.93; H, 2.60; N, 10.55; Tb,

J Fluoresc (2010) 20:329–342
333
carbonyl has formed a coordinative bond with the rare earth
ions [30]. The different shifts of the wavenumbers indicate
that the Ln-O (carbonyl) bond is stronger than the Ln-O
(hydrazonic) bond. The band at 1,600 cm−1 for the free
ligand is assigned to the νC=N stretch, which shifts to about
1,574 cm−1 for the complexes, Δν(ligand-complexes) is equal to
26 cm−1. Weak bands at 420 cm−1 or so are assigned to
νM-N in the complexes. These shifts and new bands further
confirm that the nitrogen of the imino-group bonds to the
rare earth ions [31]. The absorption bands of the coordi-
nated nitrates were observed at about 1,481 (νas) and 820
(νs) cm−1. The ν3 (E’) free nitrates appear at 1,384 cm−1 in
the spectra of the rare earth complexes. In addition, the
separation of the two highest frequency bands jv4 ꢁ v1j is
approximately 165 cm−1, and accordingly the coordinated
Fluorescence studies
The emission spectra of the ligand and Sm(III) complex in
solid state (both the excitation and emission slit widths were
1.5 nm) were recorded at room temperature. The Sm(III)
complex exhibits red fluorescence and the emission is readily
observed with naked eyes under UV light, whereas, the
fluorescence intensities of other rare earth complexes are much
too weak in the solid state, which are not discussed in our
present work. Fluorescence spectra of the ligand and Sm(III)
complex in solid state are shown in Fig. 2. Based on the
theory of antenna effect [33, 34], the intensity of lumines-
cence of Ln(III) complexes is related to the efficiency of the
intramolecular energy transfer between the triple level of the
ligand and the emitting level of the metal ions, which
depends on the energy gap between the two levels. In the
solid state, probably the energy gap between the ligand’s
triplet levels and the emitting levels of the Sm(III) favors the
energy transfer process for samarium, which makes Sm(III)
complex show the most intense red fluorescence. However,
other rare earth complexes do not exhibit fluorescence,
indicating that energy transfer process between the ligand’s
triplet levels and the emitting levels of other rare earth ions is
not favored. Furthermore, the excitation and emission spectra
of the rare earth complexes were obtained and their relative
fluorescence intensities are very low comparing with the Sm
(III) complex under the same conditions (the excitation and
emission slit widths are both 1.5 nm). The excitation and
emission wavelengths are 343, 421 nm (La(III) complex),
344, 559 nm (Sm(III) complex), 393, 489 nm (Nd(III)
complex) and 390, 482 nm (Tb(III) complex), respectively.
Because La(III) ion has no 4f electrons and La(III) complex
shows no characteristic fluorescence, it is not necessary to
discuss its luminescent properties. In order to clarify the
-
NO3 anion in the complexes is a bidentate ligand [32].
UV-vis spectra
The study of the electronic spectra in the ultraviolet and
visible (UV-vis) ranges for the rare earth complexes and
ligand was carried out in a buffer solution containing 5 mM
Tris-HCl (pH 7.1) and 50 mM NaCl concentrations. The
electronic spectra of the free ligand have a strong band at
U
max=273 nm and a medium band at Umax=303 nm. The
complexes also yield two bands and the two bands are
shifted to 277 and 308 nm or so. These indicate that the rare
earth complexes are formed.
Mass spectra
The electrospray ionization (ESI) mass spectra of La (III)
complex were made. The mass spectra of La (III) complex
show peaks at 847, 784, and 721 which can be assigned to
the fragments [La(III) complex–NO3]+, [La(III) complex–
2NO3–H]+ and [La(III) complex–3NO3–2H]+, respectively.
4G5/2
6H7/2
250
200
150
100
50
1H NMR spectra
6H5/2
4G5/2
The 1H NMR spectra of the ligand and its La (III)
complex are assigned as follows: L (DMSO-d6 300 MHz):
δ 11.96 (1H, s, = NNH, exchangeable with D2O), 8.85
(1H, s, 2-H), 8.65 (1H, s, 9-H), 8.15 (1H, dd, J=1.2,
8.1 Hz, 7-H), 8.14-7.85 (3H, m, PhH, 5, 8, 12-H), 7.75
(1H, dd, J=1.2, 8.1 Hz, 6-H), 7.57-7.53 (4H, m, PhH, 10,
11-H). [La L2•(NO3)2]•NO3 (DMSO-d6 300 MHz): δ
11.91 (2H, s, = NNH), 8.84 (2H, s, 2-H), 8.63 (2H, s, 9-H),
8.11 (2H, dd, J=0.8, 7.2 Hz, 7-H), 8.06-7.90 (6H, m, PhH, 5,
8, 12-H), 7.83 (2H, dd, J=0.8, 7.2 Hz, 6-H), 7.71-7.59 (8H,
m, PhH, 10, 11-H). The hydrogen of the = NNH- group is
still detected in the complexes and there were no hydrogens
displaced by metal, which is also supported by the above
investigations.
4G5/2
6H9/2
b
a
0
500
550
600
650
Wavelength (nm)
Fig. 2 Solid state emission spectra of the ligand a (λex=343 nm, λem
449 nm) and Sm(III) complex b (λex=344 nm, λem=559 nm)
=

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J Fluoresc (2010) 20:329–342
ligand’s triplet level, a new coordination compound, [Gd L2•
(NO3)2]•NO3 was prepared according to the previous method
and its phosphorescence spectrum was measured at 77K in
DMF solution (1×10−5 mol/L). The lowest triplet-state level
energy (T) of the ligand was calculated by the shortest
wavelength transition in the phosphorescence spectrum to be
21,008 cm−1 (476 nm) [35]. This energy level is above the
the oscillatory motions of the entering solvent molecules
may consume more energy. All these indicate that the
polarity of the solvents affects the fluorescence of Sm(III)
complex. In addition, the detailed differences in the optical
measurement conditions also affect the influence of
solvents. The solid emission spectrum of the Sm(III)
complex was determined on a Hitachi RF-4500 spectro-
fluorophotometer, whereas its emission spectra and quan-
tum yields in different organic solvents were determined on
FLS-920 of Edinburgh instrument. The two instruments
have different detectors, resolutions and so on, so the
different instruments also exert certain influence on the
fluorescence intensities. Furthermore, the fluorescence
quantum yields of Sm(III) complex are significantly higher
than the free ligand, indicating that Sm(III) complex will be
a good candidate for biological use and red emitter in
electroluminescence devices.
4
5
4
resonance level G5/2 of Sm(III), D4 of Tb(III) and F3/2 of
Nd(III) ions. Thus the absorbed energy could be transferred
from the ligand to Sm(III), Tb(III) or Nd(III) ion. However,
the intramolecular transfer efficiency depends chiefly on two
energy transfer processes: one is from the lowest triplet level
(T) of ligand to the resonance level of Sm(III) ion (4G5/2) by
resonant exchange interaction, and the other is just an inverse
energy transfer by the thermal de-excitation mechanism [36,
37]. Established on this theory, the conclusion can be drawn
that energy gap between T and 4G5/2 is of opposite influence
on the two energy transfer processes and an optimal value
can be assumed to exist. In addition, based on the view of
numerical point, the strong fluorescence of the Sm(III)
complex is due to the optimal (∆ν=3,119 cm-1), and it
should be better than that of Tb(III) complex (∆ν=261 cm-1)
and Nd(III) complex (∆ν=558 cm-1) [38]. Too large or
small energy gap affects the energy transfer from the ligand
and rare earth ions and then the fluorescence of the
complexes would be quenched. That is why Sm(III)
complex can emit characteristic fluorescence, whereas other
investigated rare earth complexes can not exhibit their
characteristic luminescence [39].
Since the crystal structures of the rare earth complexes
have not been obtained yet, we characterized the complexes
and determined its possible structure by elemental analyses,
1
molar conductivities, IR spectra, mass spectra, H NMR
spectra, fluorescence studies and UV-vis spectra. The likely
structure of the rare earth complexes is [Ln L2•(NO3)2]•NO3
[Ln(III) = La, Sm, Nd and Tb; L is the ligand 3-carbaldehyde
chromone-(benzoyl) hydrazone].
DNA binding studies
Electronic absorption spectroscopy
The influence of solvents on the fluorescence intensities
of the ligand and Sm(III) complex was also investigated. As
shown in Table 1, the fluorescence intensities of Sm(III)
complex in organic solvents are obviously weaker than that
of the powder. This may be due to the quenching process of
solvent molecules in the solution. The energy transfer from
the triplet excited state of the ligand to the emitting level of
the samarium ion could not be carried out perfectly because
Before reacting the ligand and its rare earth complexes
interacting with CT DNA, their solution behavior in buffer
solution at room temperature was monitored by UV-vis
spectroscopy for 24 h. Liberation of the ligand and its
complexes was not observed under these conditions. These
suggest that the ligand and its complexes are stable under
the conditions studied.
Table 1 Fluorescecne spectra and fluorescecne quantum yields ∅f of the ligand and Sm(III) complex in different solutions at room temperature.
All the emission and excitation slit widths were 3 nm
Compound
L
Solvent
λex (nm)
λem (nm)
Emission intensity
∅
f
Ethanol
Methanol
DMF
395
405
374
396
371
409
405
374
357
361
489
489
431
503
498
497
496
432
489
452
41.344
9.739
0.1213
0.1254
0.2356
0.0869
0.0754
0.0223
0.0154
0.0312
0.0112
0.0123
30.337
0.793
CH3CN
THF
1.203
Sm(III) complex
Ethanol
Methanol
DMF
16.746
10.625
24.158
1.757
CH3CN
THF
3.022

J Fluoresc (2010) 20:329–342
335
The binding abilities of the ligand and rare earth
complexes with CT DNA can be characterized by measur-
ing their effects on the UV-vis spectroscopy. Complexes
binding to DNA via an intercalation mode usually results in
hypochromism and bathochromism due to intercalative
mode involving a strong stacking interaction between an
aromatic chromophore and the base pairs of DNA [40]. In
the present investigation, the interaction of complexes with
DNA has been studied. The binding of complexes to DNA
led to decrease in the absorption intensities with a small
amount of red shifts in the UV-vis absorption spectra. After
intercalating the base pairs of DNA, the π* orbital of the
intercalated ligand can couple with the π orbital of the
DNA base pairs, thus, decreasing the π→π* transition
energy and resulting in the bathochromism. On the other
hand, the coupling π orbial is partially filled by electrons,
thus, decreasing the transition probalities and concomitantly
resuting in the hypochromism [41]. Therefore, in order to
obtain evidence for the possibility of binding mode of each
compound to CT DNA, spectroscopic titration of a solution
of compounds with CT DNA should be performed.
Tb(III) complexes at about 308 nm exhibited hypochrom-
ism of about 34.5%, 44.2%, 35.2%, 51.0% and 36.9%,
respectively. The hypochromism observed for the rare earth
complexes are all accompanied by a small red shift by
about 3 nm. All these results suggest that the complexes
can interact with CT DNA quite probably by intercalating
the compounds into DNA base pairs, so we can conclude
that the free ligand and its metal complexes can interact
with CT DNA via a same mode (intercalation).
EB (a typical indicator of intercalation) quenching assay
was performed to further test the binding modes of DNA to
these investigated compounds [42]. Figure 4 shows the
electronic absorption spectra when EB was employed. The
absorbance of the buffer solution is highest when there is
EB alone. After adding CT DNA into the buffer solution,
the absorbance decreases. However, it increases when the
ligand and metal complexes were added dropwise into the
buffer solution. In addition, the maximal absorption of EB
at 479 nm decreases and shiftes to 494 nm in the presence
of CT DNA, which is characteristic of intercalation mode.
Curve (B) in Fig. 4 shows the absorption of a mixture
solution of EB, DNA and Sm(III) complex. It is also found
that the absorption at 494 nm has increased comparing with
curve (C). These may result from two reasons: (1) EB
bound to the free ligand and metal complexes strongly,
The electronic absorption spectra of the free ligand and
its complexes in the absence and presence of CT DNA are
given in Fig. 3. As shown, in the presence of DNA, the
absorption bands of the ligand, La(III), Sm(III), Nd(III) and
(a)
(b)
0.30
(c)
0.30
0.5
0.25
0.20
0.15
0.10
0.05
0.00
0.25
0.20
0.15
0.10
0.05
0.00
0.4
0.3
0.2
0.1
0.0
250
300
350
400
450
250
300
350
400
450
250
300
350
400
450
Wavelength (nm)
Wavelength (nm)
Wavelength (nm)
(d)
(e)
0.75
0.50
0.25
0.00
0.5
0.4
0.3
0.2
0.1
0.0
250
300
350
400
450
250
300
350
400
450
Wavelength (nm)
Wavelength (nm)
Fig. 3 Electronic absorption spectra of the ligand a, La(III) b, Sm(III)
c, Nd(III) d and Tb(III) e complexes (10 µM) in the absence (top
spectrum) and presence of increasing amounts of CT DNA (2.5, 5.0, 7.5,
10.0, 12.5, 15.0, 17.5, 20.0 and 22.5 µM; subsequent spectra). Arrow
shows the absorbance changes upon increasing DNA concentration

336
J Fluoresc (2010) 20:329–342
0.05
0.04
0.03
0.02
0.01
0.00
compounds to DNA leading to a significantly increase in
emission intensity also agrees with those observed for other
intercalators [43]. The fluorescence spectra show that the
rare earth complexes can bind to DNA more strongly and
deeply than the free ligand alone, The higher binding
affinities of the complexes are probably attributed to the
extension of the π system of the intercalated ligand due to
the coordination of rare earth ions, which also leads to a
planar area greater than that of the free ligand and the
coordinated ligand penetrating more deeply into and
stacking more strongly with the base pairs of DNA.
A
B
C
EB is one of the most sensitive fluorescence probes that
can bind to DNA and the fluorescence of EB increases after
intercalating into DNA base pairs [44]. If the complexes
intercalate into the DNA base pairs, leading to a decrease in
the binding sites of DNA available for EB and resulting in
the decrease in the fluorescence intensity of the DNA-EB
system. The reduction of the fluorescence emission inten-
sity gives a criteria to investigate the DNA binding
propensity of the complexes and the stacking interaction
(intercalation) between the adjacent DNA base pairs [45].
Figure 6 shows the emission spectra of the DNA–EB
system with increasing amounts of the rare earth complexes
and free ligand. The addition of the compounds to the
DNA-bound EB solutions caused obvious reduction in
emission intensities and the quenching of EB bound to
DNA by the rare earth complexes is in good agreement
with the linear Stern-Volmer equation. In the plots of F0/F
versus [Q], Kq is given by the ratio of the slope to the
intercept and Kq values for the ligand, La(III), Sm(III), Nd
(III) and Tb(III) complexes are (1.39 0.01)×104 M-1, (5.66
0.07)×104 M-1, (5.16 0.04)×104 M-1, (2.42 0.05)×104 M-1
and (4.62 0.04)×104 M-1. The results show that all the
compounds can bind to DNA and the complexes bind to
DNA more strongly than the free ligand, which also validate
the electronic absorption spectral results. Since these changes
indicate only one kind of quenching process, it may be
concluded that the complexes and free ligand can bind to
DNA via the same mode (intercalation).
In the aqueous solution, iodide and ferrocyanide anions
quench the fluorescence of complexes very efficiently, and
we used potassium iodide as the quencher to determine the
relative accessibilities of the free and bound Sm(III)
complex. Emission spectra for the Sm(III) complex and
potassium iodide with absence and presence of CT DNA
are illustrated in the titration curves (Fig. 7). Compared to
the emission spectra of Sm(III) complex in Tris-HCl buffer
solution alone, fluorescence intensities decrease with the
addition of potassium iodide regardless whether the buffer
solution contains CT DNA and the quenching plots
illustrated that the quenching studies of the Sm(III)
complex are in good agreement with the linear Stern–
Volmer equation and the slopes were calculated by the
400
500
600
Wavelength (nm)
Fig. 4 The ultraviolet visible absorption spectra of 1×10-5 M EB (A);
(A)+2.5×10-5 M DNA (C); (C)+2.5×10-5 M Sm(III) complex in Tris-
HCl buffer (5 mM Tris–HCl, 50 mM NaCl, pH 7.1) solution
resulting in the decrease of the amount of EB intercalated
into DNA; (2) there exists competitive intercalation
between the free ligand and metal complexes and EB with
DNA, so releasing some free EB from DNA–EB system.
However, the former reason could be precluded because
there were no new absorption peaks appearing. Thus, we
can come to a conclusion that Sm(III) complex can displace
EB from its DNA-EB system. Quite similar results are also
observed for other rare earth complexes.
Fluorescence spectra
The steady-state emission spectra of 10 μM solutions of the
rare earth complexes in Tris-HCl buffer show an increase in
the emission intensity with successive addition of CT DNA
at room temperature (Fig. 5). According to the Scatchard
equation, a plot of r/Cf versus r gave Kb values of (7.39
0.48)×105, (2.02 0.91)×106, (1.42 0.74)×106, (7.39
0.48)×106, (1.21 0.60)×106 M-1 from the fluorescence
data for the ligand, La(III), Sm(III), Nd(III) and Tb(III)
complexes, respectively. Results obtained from fluores-
cence spectra suggest that all the compounds are protected
from solvent water molecules by the hydrophobic environ-
ment inside the DNA helix and that the metal complexes
can be protected more efficiently than the free ligand alone.
This implies that all the metal complexes and free ligand
can insert between DNA base pairs deeply and the metal
complexes can bind to DNA more strongly than the free
ligand alone. Since the hydrophobic environment inside the
DNA helix reduces the accessibility of solvent water
molecules to the compound and the compound mobility is
restricted at the certain binding site, a decrease of the
vibrational modes of relaxation results. The binding of the

J Fluoresc (2010) 20:329–342
337
Fig. 5 The emission enhance-
ment spectra of the free ligand a
(λex=451 nm, λem=342 nm), La
(a)
160
12
10
8
140
120
100
80
Kb = (7.39 0.48)X105 M-1
(III) b (λex=454 nm, λem
342 nm), Sm(III) c (λex=455 nm,
em=347 nm), Nd(III) d (λex
456 nm, λem=345 nm) and Tb
(III) e (λex=457 nm, λem
=
Kb = (7.39 0.48)X105 M-1
λ
=
=
6
60
347 nm) complexes (10 µM) in
the absence (bottom spectrum)
and presence of increasing
amounts of CT DNA (2.5, 5.0,
7.5, 10.0, 12.5 and 15.0 µM;
subsequent spectra). Arrows
show the emission intensity
changes upon increasing DNA
concentration. Inset: Scatchard
plot of the fluorescence
4
40
20
2
0
350
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
400
450
500
550
600
Wavelength (nm)
r
(b)
250
200
150
100
50
14
12
10
8
Kb = (2.02 0.91)X106 M-1
Kb = (2.02 0.91)X106 M-1
titration data of ligand and
rare earth complexes,
Kb (a)=(7.39 0.48)×105; Kb
(b)=(2.02 0.91)×106 M-1; Kb
(c)=(1.42 0.74)×106 M-1;
Kb (d)=(7.39 0.48)×106 M-1;
Kb (e)=(1.21 0.60)×106 M-1
6
4
2
0
0
350
400
450
500
550
600
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
Wavelength (nm)
r
(c)
7
6
5
4
3
2
350
300
250
200
150
100
50
Kb = (1.42 0.74)X106 M-1
Kb = (1.42 0.74)X106 M-1
0
0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05
400
450
500
550
600
Wavelength (nm)
r
(d)
400
350
300
250
200
150
100
50
12
10
8
Kb = (7.39 0.48)X105 M-1
Kb = (7.39 0.48)X105 M-1
6
4
2
0
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
400
450
500
550
600
Wavelength (nm)
r
(e)
500
400
300
200
100
0
9
8
7
6
5
4
3
2
Kb = (1.21 0.60)X106 M-1
Kb = (1.21 0.60)X106 M-1
400
450
500
550
600
0.6
0.7
0.8
0.9
1.0
1.1
1.2
Wavelength (nm)
r

338
J Fluoresc (2010) 20:329–342
Fig. 6 The emission spectra of
DNA-EB system λex=525 nm,
(a)
600
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
λem=550-650 nm, in the pres-
-1
Kq = (1.93 0.01)X104
M
ence of 0, 25.0, 50.0, 75.0,
100.0, 125.0, 150.0 and
Kq = (1.93 0.01)X104 M-1
450
300
150
0
175.0 µM free ligand a and 0,
2.5, 5, 7.5, 10, 12.5, 15, 17.5,
20.0, 22.5, 25, 27.5, 30.0, 32.5,
35.0, 37.5, 40, 42.5, 45, 47.5
and 50.0 µM La(III) b, Sm(III)
c, Nd(III) d and Tb(III) e com-
plexes. Arrows show the emis-
sion intensity changes upon
increasing ligand. Inset: Stern
Volmer plot of the fluorescence
titration data of ligand and
complexes, Kq (a)=(1.39
2
4
6
8
10 12 14 16 18 20
550
600
600
600
650
Wavelength (nm)
700
750
750
750
[Compound]X106
M
(b)
4.0
3.5
3.0
2.5
2.0
1.5
1.0
600
500
400
300
200
100
0
Kq = (5.66 0.07)X104 M-1
Kq = (5.66 0.07)X104 M-1
0.01)×104 M-1; Kq
(b)=(5.66 0.07)×104 M-1; Kq
(c)=(5.16 0.04)×104 M-1;
Kq (d)=(2.42 0.05)×104 M-1;
Kq (e)=(4.62 0.04)×104 M-1
0
10
20
30
40
50
550
650
Wavelength (nm)
700
[Compound]X106 M
(c)
4.0
3.5
3.0
2.5
2.0
1.5
1.0
600
500
400
300
200
100
0
Kq = (5.16 0.04)X104 M-1
Kq = (5.16 0.04)X104 M-1
0
10
20
30
40
50
550
650
Wavelength (nm)
700
[Compound]X106
M
(d)
600
500
400
300
200
100
0
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
Kq = (2.42 0.05)X104 M-1
Kq = (2.42 0.05)X104 M-1
0
10
20
30
40
50
550
600
650
Wavelength (nm)
700
750
[Compound]X106
M
(e)
3.5
3.0
2.5
2.0
1.5
1.0
600
500
400
300
200
100
0
Kq = (4.62 0.04)X104 M-1
Kq = (4.62 0.04)X104 M-1
0
10
20
30
40
50
550
600
650
700
750
[Compound]X105
M
Wavelength (nm)

J Fluoresc (2010) 20:329–342
339
Fig. 7 a Fluorescence spectra
of Sm(III) complex (10 µM)
(λex=446 nm, λem=674 nm)
with increasing concentration of
KI (5, 10, 15, 20, 25, 30 and
35 mM). b Fluorescence spectra
of Sm(III) complex (10 µM)
(λex=442 nm, λem=664 nm) and
DNA (20 µM) system with
increasing concentration of KI
(5, 10, 15, 20, 25, 30 and
35 mM). c Inset: Stern Volmer
plot of the fluorescence titration
data of Sm(III) complex. Effect
of KI concentration (1: Sm(III)
complex + KI; 2: Sm(III) com-
plex + KI + CT DNA). Ksv (1)=
41.96 0.07 M-1, Ksv (2)=5.41
0.01 M-1
(a)
(b)
900
800
Ksv (1) = 41.96 0.07 M-1
Ksv (2) = 5.41 0.01 M-1
600
400
200
0
600
300
0
400
450
500
550
600
400
450
500
550
600
Wavelength (nm)
Wavelength (nm)
(c)
2.2
2.0
1.8
1.6
1.4
1.2
1.0
Ksv (1) = 41.96 0.07 M-1
Ksv (2) = 5.41 0.01 M-1
0.00
0.01
0.02
0.03
0.04
0.05
[KI]
linear least-squares method. The observed quenching
constants (Ksv) were 5.41 0.01 and 41.96 0.07 M-1 with
and without CT DNA, respectively. The quenching of the
Sm(III) complex fluorescence was in fact enhanced by a
factor of about 8 when the Sm(III) complex was bound to
the DNA helix. The values of Ksv were used to deduce the
interaction mode of the fluorescence probe with DNA.
Higher binding constants should correspond to the better
protection by the DNA and a stronger inhibition of
quenching by anionic species. Similar results can be
obtained for other complexes and then we can conclude
that the metal complexes are intercalated into the DNA
helix and they should be protected from the anionic
quencher, owning to the base pairs above and below the
intercalators [46].
The effect of the ionic strength on the complexes
fluorescence intensity was tested by the addition of a strong
electrolyte, such as NaCl, instead of potassium iodide.
Cations of the salts can neutralize the negatively charged
phosphate. If the compound binds to DNA through an
electrostatic interaction mode, the surface of DNA will be
surrounded by the sodium ions with the increase of ionic
strength. Then the compound has difficulty to approach
DNA molecules and the strength of compounds binding to
DNA decreases, then the degrees of fluorescence quenching
also decreases [21]. As seen from Fig. 8, addition of NaCl
2.0
1.8
1.6
1.4
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
L
La(III) complex
Sm(III) complex
Tb(III) complex
Nd(III) complex
1.2
1
1.0
2
0.8
0.6
0.4
0.2
0.0
0
2
4
6
8
10
12
14
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
[NaCl] (mol L-1)
[M]/[DNA]
Fig. 9 Effects of increasing amounts of the ligand and its rare earth
Fig. 8 Effect of NaCl concentration (1: Sm(III) complex + NaCl; 2:
complexes on the relative viscosity of CT DNA at 25.0 0.1 °C
Sm(III) complex + NaCl + CT DNA)

340
J Fluoresc (2010) 20:329–342
binding mode, have no influence on DNA viscosity [49]. To
further elucidate the binding mode of the present com-
plexes, viscosity measurements were carried out by keeping
[DNA]=5 μM and varying the concentration of the
compounds.
The changes in relative viscosity of CT DNA in the
presence of the ligand and complexes are shown in Fig. 9.
As seen from Fig. 9, upon increasing amounts of the ligand
and complexes, the relative viscosities of DNA increase
steadily with increasing concentrations of ligand and
complexes. The increased degree of viscosity, which may
depend on the binding affinity of compounds to DNA,
following the order of La(III) complex >Sm(III) complex
>Tb(III) complex >Nd(III) complex >L. These results
suggest that all the title complexes and ligand intercalate
between the DNA base pairs and the binding affinities of
the complexes are higher than that of the free ligand, which
is consistent with the above experimental results.
Fig. 10 Molecular mode for the rare earth complexes (via an
intercalative mode)
to the Sm(III) complex in the absence and presence of CT
DNA had little or no effects on the fluorescence intensity,
showing that the interaction of the Sm(III) complex with
CT DNA is not through an electrostatic interaction. Similar
results also can be gained for other complexes. Hereby, we
can conclude that the compounds interact with DNA is not
via an electrostatic mode.
On the basis of all the spectroscopic studies together
with the viscosity measurements, we find that the rare earth
complexes and free ligand can bind to CT DNA via an
intercalative mode (Fig. 10) and the complexes bind to CT
DNA more strongly and deeply than the free ligand alone.
Viscosity measurements
Hydrodynamic measurements sensitive to length changes,
as reflected in viscosity 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 [47]. A classical intercalation model
demands that the DNA helix must lengthen as base pairs
are separated to accommodate the binding complexes,
leading to the increase of DNA viscosity, as for the
behaviors of the known DNA intercalators [48]. In contrast,
a partial and/or non-classical intercalation of the complex
could bend (or kink) the DNA helix, reducing its viscosity
concomitantly [47]. In addition, some compounds such as
[Ru(bpy)3]2+, which interacts with DNA by an electrostatic
Antioxidant activity
Since the synthesized ligand and its rare earth complexes
exhibit good DNA binding affinity, it is considered
worthwhile to investigate their other biological activities,
such as antioxidant activity. The antioxidant activity of
chromones and their derivatives has attracted increasing
interests and been extensively investigated, mainly in the
vitro system [50]. It has been reported that over production
of free radicals may induce some oxidative damages to
(a)
(b)
75
L
L
40
35
30
25
20
15
10
5
La(III) complex
Sm(III) complex
La(III) complex
Sm(III) complex
Tb(III) complex
Nd(III) complex
Nd(III) complex
Tb(III) complex
60
45
30
15
0
0
3
6
9
12
15
18
1
2
3
4
5
6
Concentration (µM)
Concentration (µM)
Fig. 11 Scavenging effect of the ligand and its rare earth complexes on O2 a and HO• b
•-

J Fluoresc (2010) 20:329–342
341
Acknowledgements This work is supported by the National Natural
Science Foundation of China (20475023) and Gansu NSF
(0710RJZA012).
biomolecules such as carbohydrates, proteins, lipids and
DNA, thus accelerating aging, cancer, cardiovascular dis-
eases, inflammation and so on [51]. So, in this paper, the
ligand and its rare earth complexes were studied to
investigate their antiradicals ability by comparing their
scavenging effects on hydroxyl radical (HO•) and superoxide
References
•-
radical (O2 ).
1. Kelland LR (2005) Overcoming the immortality of tumour cells
by telomere and telomerase based cancer therapeutics-current
status and future prospects. Eur J Cancer 41(7):971–979
2. Uma V, Kanthimath M, Weyhermuller T, Nair BU (2005)
Oxidative DNA cleavage mediated by a new copper (II)
terpyridine complex: crystal structure and DNA binding studies.
JInorgChem 99(12):2299–2307
3. Erkkila KE, Odom DT, Barton JK (1999) Recognition and reaction
of metallointercalators with DNA. Chem Rev 99(9):2777–2795
4. Arockiasamy DL, Radhika S, Parthasarathi R, Nair BU (2009)
Synthesis and DNA-binding studies of two ruthenium(II) com-
plexes of an intercalating ligand. Eur J MedChem 44(5):2044–2051
5. Wang BD, Yang ZY, Crewdson P, Wang DQ (2007) Synthesis,
crystal structure and DNA-binding studies of the Ln(III) complex
with 6-hydroxychromone-3-carbaldehyde benzoyl hydrazone. J
Inorg Biochem 101(10):1492–1504
6. Kumar CV, Barton JK, Turro NJ (1985) Photophysics of
ruthenium complexes bound to double helical DNA. J Am Chem
Soc 107(19):5518–5523
7. Xu H, Zheng KC, Chen Y, Li YZ, Lin LJ, Li H, Zhang PX, Ji LN
(2003) Effects of ligand planarity on the interaction of polypyridyl
Ru(II) complexes with DNA. Dalton Trans 3(11):2260–2268
8. Mahadvan S, Palaniandavar M (1997) Spectroscopic and voltam-
metric studies of copper(II) complexes of bis(pyrid-2-yl)-di/trithia
ligands bound to calf thymus DNA. Inorg Chim Acta 254(2):291–
302
9. Xu H, Zheng KC, Deng H, Lin LJ, Zhang QL, Ji LN (2003)
Effects of the ancillary ligands of polypyridyl ruthenium(III)
complexes on the DNA-binding behaviors. New J Chem 27
(8):1255–1263
10. Asadi M, Safaei E, Ranjbar B, Hasani L (2004) Thermodynamic and
spectroscopic study on the binding of cationic Zn(II) and Co(II)
tetrapyridinoporphyrazines to calf thymus DNA: the role of the
central metal in binding parameters. New J Chem 28(10):1227–1234
11. Bisi CC, Carugo O (1989) Studies on fluorescent lanthanide
complexes. New complexes of lanthanides(III) with coumarinic-3-
carboxylic acid. Inorg Chim Acta 159(2):157–161
Figure 11a shows the plots of superoxide radical
scavenging effect (%) for the ligand and complexes. We find
•-
that the inhibitory effect of the compounds tested on O2 is
concentration dependent and the suppression ratio increases
with increasing sample concentrations in the range tested.
The average suppression ratio of the free ligand (IC50=
58.48 µM) for O2•- is the least in all compounds. The La(III)
complex (IC50=5.00 µM) is the most effective one in the rare
earth complexes, which may be induced by the metal ions.
Figure 11b shows the plots of hydroxyl radical scavenging
effect (%) for the ligand and complexes. The inhibitory effect
of the compounds is marked and the average suppression
ratio for HO• increases with the increaseing compound
concentration. The order of the suppression ratio of the
tested compounds for HO is La(III) complex >Tb(III)
complex >Nd(III) complex >Sm(III) complex >L. The
average suppression ratio of the rare earth complexes is
better than the free ligand alone. It is clearly shown that
metal complexes exhibit considerable scavenging abilities
due to the chelation of organic molecules to rare earth ions
and the rare earth ions such as La(III), Tb(III), Nd(III), Sm
(III) exert differential and selective effects on scavenging
radicals of the biological system. In order to prepare more
effective and lower poisonous antioxidants, the metal
complexes we studied in this paper deserve to be further
researched.
Conclusions
12. Ci YX, Li YZ, Chang WB (1991) Fluorescence reaction of
terbium(III) with nucleic acids in the presence of phenanthroline.
Anal Chim Acta 248(2):589–594
13. Horne DA, Dervan PB (1990) Recognition of mixed-sequence
duplex DNA by alternate-strand triple-helix formation. J Am
Chem Soc 112(6):2435–2437
In summary, a new ligand, 3-carbaldehyde chromone-
(benzoyl) hydrazone, and its four rare earth complexes
have been prepared and characterized. The Sm(III) complex
is red-fluorescent in the solid state and its emission
intensity are highly solvent-dependent. In addition, their
DNA binding properties and antioxidant activities were
studied systematically. Experimental results indicate that
the ligand and its complexes can bind to DNA via an
intercalation mode and the complexes have better DNA
binding affinity than the free ligand alone. Furthermore, the
complexes have more active scavenging effects on O2•- and
HO•. Our work clearly indicates that rare earth-based
complexes have many potential practical applications, such
as understanding the mechanisms of interaction between
compounds and DNA, the development of potential acid
molecular probes and new therapeutic reagents for diseases.
14. Moser HE, Dervan PB (1987) Sequence-specific cleavage of double
helical DNA by triple helix formation. Science 238(4827):645–650
15. Sosnovskikh VY (2003) Synthesis and reactions of halogen-
containing chromones. Russ Chem Rev 72(6):489–516
16. Athanasellis G, Melagraki G, Afantitis A, Makridima K, Markopoulou
OI (2006) A simple synthesis of functionalized 2-amino-3-cyano-4-
chromones by application of the N-hydroxybenzotriazole methodol-
ogy. Arkivoc 10:28–34
17. Singh G, Singh R, Girdhar NK, Ishar MPS (2002) A versatile
route to 2-alkyl-/aryl-amino-3-formyl- and hetero-annelated-
chromones, through a facile nucleophilic substitution at C2 in 2-(N-
methylanilino)-3-formylchromones. Tetrahedron 58(12):2471–2480
18. Piao LZ, Park HR, Park YK, Lee SK, Park JH, Park MK (2002)
Mushroom tyrosinase inhibition activity of some chromones.
Chem Pharm Bull 50(3):309–311

342
J Fluoresc (2010) 20:329–342
19. Cai YZ, Luo Q, Sun M, Corke H (2004) Antioxidant activity and
phenolic compounds of 112 traditional Chinese medicinal plants
associated with anticancer. Life Sci 74(17):2157–2184
20. Heim KE, Tagliaferro AR, Bobilya DJ (2002) Flavonoid
antioxidants: chemistry, metabolism and structure-activity rela-
tionships. J Nutr Biochem 13(10):572–584
21. Howe GM, Wu KC, Bauer WR, Lippard SJ (1976) Binding of
platinum and palladium metallointercalation reagents and antitumor
drugs to closed and open DNAs. Biochem 15(19):4339–4346
22. Eftink MR, Ghiron CA (1981) Fluorescence quenching studies
with proteins. Anal Biochem 114(2):199–227
36. Sato S, Wada M (1970) Relations between intramolecular energy
transfer efficiencies and triplet state energies in rare Earth β-
diketone chelates. Bull Chem Soc Jpn 43(7):1955–1962
37. Wua WN, Tang N, Yan L (2008) Rare earth complexes with a
novel ligand N-(naphthalen-2-yl)-N-phenyl-2-(quinolin-8-yloxy)
acetamide: preparation and spectroscopic studies. Spectrochim
Acta Part A 71(4):1461–1465
38. Tang Y, Tang KZ, Liu WS, Tan MY (2008) Assembly, crystal
structure, and luminescent properties of three-dimensional (10,3)-
a netted rare earth coordination polymers. Sci China, Ser B 51
(7):614–622
23. Kumar CV, Turner RS, Asuncion EH (1993) Groove binding of a
styrylcyanine dye to the DNA double helix: the salt effect. J
Photochem Photobiol A: Chem 74(2–3):231–238
24. Eriksson M, Leijon M, Hiort C, Norden B, Graeslund A (1994)
Binding of Δ- and Δ-[Ru(phen)3]2+ to [d(CGCGATCGCG)]2
studied by NMR. Biochem 33(17):5031–5040
25. Xiong Y, He XF, Zou XH, Wu JZ, Chen XM, Ji LN, Li RH, Zhou
JY, Yu KB (1999) Interaction of polypyridyl ruthenium(II)
complexes containing non-planar ligands with DNA. J Chem
Soc, Dalton Trans: Inorg Chem 1:19–24
26. Winterbourn CC (1979) Comparison of superoxide with other
reducing agents in the biological production of hydroxyl radicals.
Biochem J 182(2):625–628
27. Winterbourn CC (1981) Hydroxyl radical production in body
fluids. Roles of metal ions, ascorbate and superoxide. Biochem J
198(1):125–131
28. Nohara A, Umetani T, Sanno Y (1973) Facile synthesis of
chromone-3-carboxaldehyde, chromone-3-carboxylic acid, and 3-
hydroxymethylchromone. Tetrahedron Lett 14(22):1995–1998
29. Geary WJ (1971) Use of conductivity measurements in organic
solvents for the characterization of coordination compounds.
Coord Chem Rev 7(1):81–122
30. Marchetti F, Pettinari C, Pettinari R, Cingolani A, Leonesi D,
Lorenzotti A (1999) Group 12 metal complexes of tetradentate
N2O2-Schiff-base ligands incorporating pyrazole: synthesis, char-
acterisation and reactivity toward S-donors, N-donors, copper and
tin acceptors. Polyhedron 18(23):3041–3050
31. Narang KK, Singh VP (1993) Synthesis and characterization of
cobalt(II), nickel(II), copper(II) and zinc(II) complexes with
acetylacetone bis-benzoylhydrazone and acetylacetone bis-
isonicotinoylhydrazone. Transition Met Chem 18(3):287–290
32. Wang BD, Yang ZY, Zhang DW, Wang Y (2006) Synthesis,
structure, infrared and fluorescence spectra of new rare earth
complexes with 6-hydroxy chromone-3-carbaldehyde benzoyl
hydrazone. Spectrochim acta Part A 63(1):213–219
39. Latva M, Takalo H, Mukkala VM, Matachescu C, Rodríguez-Ubis
JC, Kankare J (1997) Correlation between the lowest triplet state
energy level of the ligand and lanthanide(III) luminescence
quantum yield. J Lumin 75(2):149–169
40. Gao F, Chao H, Zhou F, Yuan YX, Peng B, Ji LN (2006) DNA
interactions of a functionalized ruthenium(II) mixed-polypyridyl
complex [Ru(bpy)2 ppd]2+. J Inorg Biochem 100(9):1487–1494
41. Pyle AM, Rehmann JP, Meshoyrer R, Kumar CV, Turro NJ, Barton
JK (1989) Mixed-ligand complexes of ruthenium(II): factors
governing binding to DNA. J Am Chem Soc 111(8):3051–3058
42. Wilson WD, Ratmeyer L, Zhao M, Strekowski L, Boykin D
(1993) The search for structure-specific nucleic acid-interactive
drugs: effects of compound structure on RNA versus DNA
interaction strength. Biochem 32(15):4098–4104
43. Xu H, Zheng KC, Lin LJ, Li H, Gao Y, Ji LN (2004) Effects of
the substitution positions of Br group in intercalative ligand on the
DNA-binding behaviors of Ru(II) polypyridyl complexes. J Inorg
Biochem 98(1):87–97
44. Le-Pecq JB, Paoletti C (1967) A fluorescent complex between
ethidium bromide and nucleic acids. J Mol Biol 27(1):87–106
45. Lee M, Rhodes AL, Wyatt MD, Forrow S, Hartley JA (1993) GC
base sequence recognition by oligo(imidazolecarboxamide) and
C-terminus-modified analogues of distamycin deduced from
circular dichroism, proton nuclear magnetic resonance, and
methidiumpropylethylenediaminetetraacetate-iron(II) footprinting
studies. Biochem 32(16):4237–4245
46. Lerman LS (1961) Structural considerations in the interaction of
deoxyribonucleic acid and acridines. J Mol Biol 3:18–30
47. Satyanarayana S, Dabrowiak JC, Chaires JB (1993) Tris(phenan-
throline)ruthenium(II) enantiomer interactions with DNA: mode
and specificity of binding. Biochem 32(10):2573–2584
48. Liu JG, Zhang QL, Shi XF, Ji LN (2001) Interaction of [Ru
(dmp)2(dppz)]2+ and [Ru(dmb)2(dppz)]2+ with DNA: effects of
the ancillary ligands on the DNA-binding behaviors. Inorg Chem
40(19):5045–5050
33. Lehn JM (1990) Perspectives in supramolecular chemistry: from
molecular recognition to molecular information processing and
self organization. Angew Chem Int Ed Engl 29(11):1304–1319
34. Latva M, Takalo H, Simberg K, Ankare KJ (1995) Enhanced EuIII
ion luminescence and efficient energy transfer between lanthanide
chelates within the polymeric structure in aqueous solutions. J
Chem Soc, Perkin Trans 2(5):995–999
35. Wu SL, Wu YL, Yang YS (1992) Rare earth(iii) complexes with
indole-derived acetylacetones II. luminescent intensity for europium
(iii) and terbium(iii) complexes. J Alloys Compd 180(2):399–402
49. Liu JG, Ye BH, Li H, Zhen QX, Ji LN, Fu YH (1999) Polypyridyl
ruthenium(II) complexes containing intramolecular hydrogen-
bond ligand: syntheses, characterization, and DNA-binding
properties. J Inorg Biochem 76(3–4):265–271
50. Wang Q, Yang ZY, Qi GF, Qin DD (2009) Synthesis, crystal
structure, antioxidant activities and DNA-binding studies of the
Ln(III) complexes with 7-methoxychromone-3-carbaldehyde-(4'-
hydroxy) benzoyl hydrazone. Eur J Med Chem 44(6):2425–2433
51. Proctor PH, Reynolds ES (1984) Free radicals and disease in man.
Physiol Chem Phys Med NMR 16(3):175–195