Crystal structure, dna-binding, and fluorescence properties of cadmium(II) complex with N-(2-acetic acid)salicyloyl hydrazone and imidazole

Article abstract of DOI:10.1134/S107032841002003X

A novel cadmium(II) complex with N-(2-acetic acid)salicyloyl hydrazone (C₉H₈N₂O₄, H₃L) and imidazole (Im) was prepared and characterized. The crystal structures of ligand H₃L and cadmium(II) complex were determined by X-ray single-crystal diffractometry. The complex consists of three binuclear neutral unattached units. One of Cd²⁺ is six-coordinated by the carboxylic O atom, acylic O atom, and azomethinic N atom of one ligand H₃L (HL ²-form), carboxylic O atom from the other ligand H₃L by the μ₂-bridging form and N atoms from two imidazoles, but the other five Cd²⁺ ions all are seven-coordinated more than an O atom from coordinated water molecule compared with six-coordinated Cd²⁺. HL²-acts as tridentate ligand forming two stable five-numbered rings and sharing one side in the keto form for each ligand, and the carboxyl groups of two HL^2- ligands are coordinated via the μ₂-bridging form. The coordination polyhedron around Cd²⁺ was described as a octahedron or pentagonal bipyramidal. The inter-and intramolecular hydrogen bonds resulted in a three-dimensional network and provided extrastability for the structure. The complex exhibits good fluorescence properties. The complex was also searched for the interaction with CT-DNA by electronic absorption titration and emission titration. The results show that the complex is bound to calf thymus DNA mainly by intercalation. Pleiades Publishing, Ltd., 2010.

Full text of DOI:10.1134/S107032841002003X

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2010, Vol. 36, No. 2, pp. 105–112. © Pleiades Publishing, Ltd., 2010.
Crystal Structure, DNAꢀBinding, and Fluorescence Properties
of Cadmium(II) Complex with Nꢀ(2ꢀAcetic Acid)Salicyloyl
Hydrazone and Imidazole1
F. Liua, b, W. P. Zhanga, and S. Y. Hea
a College of Chemistry and Material Science, Northwest University and Key Laboratory of Synthetic and Natural Functional
Molecule Chemistry of Ministry Education, Xi’an, Shanxi 710069, P.R. China
b Quality Administer Management Shaanxi Heavy Duty Automobile Co., Ltd, Xi’an, Shaanxi 710200, P.R. China
eꢀmail: xdchemistry411@126.com
Received June 15, 2009
Abstract—A novel cadmium(II) complex with Nꢀ(2ꢀacetic acid)salicyloyl hydrazone (C9H8N2O4, H3L) and imiꢀ
dazole (Im) was prepared and characterized. The crystal structures of ligand H3L and cadmium(II) complex were
determined by Xꢀray singleꢀcrystal diffractometry. The complex consists of three binuclear neutral unattached
units. One of Cd2+ is sixꢀcoordinated by the carboxylic O atom, acylic O atom, and azomethinic N atom of one
ligand H3L (HL2– form), carboxylic O atom from the other ligand H3L by the μ2ꢀbridging form and N atoms from
two imidazoles, but the other five Cd2+ ions all are sevenꢀcoordinated more than an O atom from coordinated
water molecule compared with sixꢀcoordinated Cd2+. HL2– acts as tridentate ligand forming two stable fiveꢀnumꢀ
bered rings and sharing one side in the keto form for each ligand, and the carboxyl groups of two HL2– ligands are
coordinated via the μ2ꢀbridging form. The coordination polyhedron around Cd2+ was described as a octahedron
or pentagonal bipyramidal. The interꢀ and intramolecular hydrogen bonds resulted in a threeꢀ dimensional netꢀ
work and provided extrastability for the structure. The complex exhibits good fluorescence properties. The complex
was also searched for the interaction with CTꢀDNA by electronic absorption titration and emission titration. The
results show that the complex is bound to calf thymus DNA mainly by intercalation.
DOI: 10.1134/S107032841002003X
1
INTRODUCTION
plexes have attracted considerable interest due to
potential applications of their special fluorescence
properties [13].
Hydrazones are a versatile class of ligands having
great physiological and biological activities and findꢀ
ing use as insecticides, anticoagulants, antitumour
agents, antioxidants, and plant growth regulators [1],
Their metal complexes have found applications in varꢀ
ious chemical processes like nonlinear optics, sensors,
medicine, etc. [2]. Hydrazone derivatives and their
complexes have been studied for their antifungal and
antibacterial activity and as antiviral drugs [3]. Moreꢀ
over, they have been the subject of extensive investigaꢀ
tion due to their versatile chelating behavior for which
In prevenient work, we have reported synthesis,
crystal structure, and properties of Nꢀ(2ꢀpyruvic
acid)salicyloyl hydrazone (H3L') and its complexes
[14–17]. There are three radicals for the ligand H3L'
(HL'–, HL'2–, HL'3– form) that can participate in coorꢀ
dination (carboxyl group, imide group, and carbonyl
group). This ligand has strong ability and can form staꢀ
ble complexes, which possess excellent biological
activities, fluorescence properties, and novel crystal
they are widely used in analytical chemistry as selecꢀ structures. Ligands H3L and H3L' are homologs;
tive metal extracting agents, as well as in spectroscopic
determination of certain transition metals. Besides,
some hydrazones have been applied as iron chelator
drugs in the therapy of anemias and genetic disorders
such as thalassemia [4]. At the same time, there are
three coordination forms for the ligand of acyl hydraꢀ
zone: ketoꢀform, enolic form, and dehydrogenation
conjugation form [5–7]. Moreover, its valence is
diverse [8–11]. In addition, luminescent metal comꢀ
plexes are found use as labels and sensors for natural
and medical science [12]. Cadmium(II)ꢀbased comꢀ
hence, we forecast that the complexes with H3L should
possess various eximious properties.
To gain an insight into the conformational aspects
of the title ligand and in order to study its coordination
behavior toward transition metal ions, we have
designed and synthesized a complex by condensing
two biologically active moieties, namely H3L and imiꢀ
dazole. In the present work, we report the synthesis,
crystal structure, fluorescence properties, DNAꢀbindꢀ
ing, and coordination chemistry of H3L and its novel
binuclear Cd(II) complex with imidazole for the first
time.
1
The article is published in the original.
105

106
LIU et al.
EXPERIMENTAL
crystal was obtained from the mother solution after a
month of standing. The yield is 65%.
Glyoxylic acid (50%) and calf thymus DNA (CTꢀ
DNA) were purchased from Sigma (USA). All chemiꢀ
cals used were of analytical grade.
For C60H68Cd4N24O24
anal. calcd., %: C, 36.79;
Found, %: C, 36.52;
H, 3.50;
H, 3.98;
N, 17.16.
N, 17.52.
The C, H, and N analyses were taken with a Perkin
Elmer model 2400 elemental analyzer. The Xꢀray data
for the crystal were collected on a Bruker Smartꢀ1000
CCD Xꢀray singleꢀcrystal diffractometer. Fluoresꢀ
cence measurements were made on a Hitachi Fꢀ4500
spectrophotometer.
RESULTS AND DISCUSSION
The crystal data and structure refinement parameꢀ
ters are listed in Table 1, where all the calculation was
performed with the SHELXTLꢀ97 program. Selected
bond lengths and bond angles of the crystal are listed
in Table 2. The molecule structure is shown in Fig. 1,
and the crystal packing diagram is depicted in Fig. 2.
Full crystallographic details have been deposited
with the Cambridge Crystallographic Data Centre
(nos. 663157 (H3L) and 663158 (Cd(II) complex);
deposit@ccdc.cam.ac.uk).
Synthesis of H3L was carried out according to literaꢀ
ture [18], but we revised the traditional synthesis method
and selected glacial acetic acid as solvent in the second
step. A solution (2 ml) of glyoxylic acid was added slowly
dropwise to glacial acetic acid (15 ml) with dissolved salꢀ
icyloyl hydrazide (0.015 mol). The resulting mixture was
The Xꢀray singleꢀcrystal analysis revealed that the
complex consists of three binuclear neutral unatꢀ
tached units. It is interesting that the central ions of
the two have the same coordination environment;
however, the other is different. That is, one of Cd2+ is
sixꢀcoordinated by carboxylic O atom, acylic O atom,
and azomethinic N atom of one ligand HL2–, carboxꢀ
stirred for 1 h in 50°C water bath. The yield is 75%.
ylic O atom from the other ligand HL2– by the μ2
ꢀ
For C9H8N2O4
anal. calcd., %: C, 51.93;
Found, %: C, 51.70;
bridging form and N atoms from two imidazoles in the
unit, but the other five Cd2+ ions all are sevenꢀcoordiꢀ
nated more than a coordinated water molecule comꢀ
pared with sixꢀcoordinated Cd2+. Thus, two fiveꢀ
membered chelate rings sharing one edge are formed
for each ligand HL2–. One of three neutral units has a
asymmetric binuclear structure formed by carboxylic
oxygens of two HL2– connecting two metals with the
μ2ꢀbridging form in which sixꢀcoordinated Cd2+ has a
H, 3.87;
H, 3.65;
N, 13.46.
N, 13.61.
IR (KBr pellet;
UVꢀVis (DMF; , nm): 278.9, 298.6.
ν
cm–1): 3232, 1531, 1738, 1640;
λ
The H3L (0.1 mmol) was dissolved in 20 ml of hot
water and filtered after cooling. The white cubic single
crystal was obtained from the mother solution after 15
days of standing. The synthesis scheme of ligand H3L
is as follows:
{
CdN3O3} environment as shown in Fig. 1. Within the
equatorial plane (0(3),0(6),N(4),0(8)), the sum of
related angles around unique Cd2+ is 359.79
, while
°
two nitrogen atoms of the two imidazole ligands
occupy the axial sites, the angle of the axial
OH
N(11)Cd(2)N(7) is 157.70
°, which deviates from a linꢀ
ear angle of 180
°
. These data indicate that Cd2+ is in
COOCH3
distorted octahedron geometry. The other five Cd2+
ions all are sevenꢀcoordinated by linking one tridenꢀ
tate HL2–, two imidazoles and a water molecule
(Fig. 1). The linkage of the tridentate ligand HL2– to
Cd2+ ion is accomplished through the acylic oxygen,
carboxylic oxygen, and imidic nitrogen. At the same
time, the atoms O(2), N(2), O(3), O(8), and O(9) are
coplanar approximately for Cd(1) and form the equaꢀ
torial plane. While two nitrogen atoms of two imidaꢀ
zoles also occupy the axial sites, the axial angle
OH
NH2NH2H2O
EtOH
NHNH2
O
OH
H
H
O
H
O
H
N
OH
OH
N
N(9)Cd(1)N(5) is 174.99
°, which is close to a linear
CH COOH
3
angle of 180
°
. These data indicate that Cd2+ is in penꢀ
O
O
tagonal bipyramidal geometry. The other two unatꢀ
Synthesis of Cd(II) complex. The Cd(NO3)2
⋅
5H2O, tached units have a centrosymmetric binuclear strucꢀ
imidazole, and H3L in 1 : 2 : 1 stoichiometry were disꢀ ture, and the coordination environment of central ions
solved in a mixed solution of ethanol and then stirred. is the same as that of the aboveꢀmentioned sevenꢀ
The pH of the mixture was adjusted to about 6 using triꢀ coordinated Cd2+. The atoms of two HL2– are almost
ethylamine. Then the resultant solution was refluxed in located on the same plane in each unit, and the two
80°C water bath for 3 h. Brilliant yellow rhombus single planes are approximately coplanar. Imidazole is vertiꢀ
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 36
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2010

CRYSTAL STRUCTURE, DNAꢀBINDING, AND FLUORESCENCE PROPERTIES
107
Table 1. Crystal data and Xꢀray experiment details for the Cd(II)
cal compared with the acylhydrazone ligands. Noncoꢀ
ordinated five water molecules are found in the crystal
lattice. Comparing the distances to CꢀO (1.43 Å) and
C=0 (1.22 Å) [15], the bond lengths of O(6)ꢀC(16),
and O(2)ꢀC(7) are 1.237 and 1.286 Å, respectively,
indicating that these bonds are double and the ligand
functions in the keto form. In the complex, the mean
bond lengths of OꢀC (1.328 Å) of phenolic hydroxyl in
the ligand HL2– is shorter than that of OꢀC (1.359 Å)
in the free ligand, showing that the bond intensity of
OꢀC is increased because of loss of the hydrogen atom
connected with the O atom. So, H3L was coordinated
with Cd(II) by the negative bivalent (HL2– form), and
imidazole is neutral in the complex.
complex
Value
Parameter
H3L
Complex
Formula weight
Temperature, K
Wavelength, A
Crystal system
208.17
291(2)
1958.97
296(2)
0.71073
0.71073
Triclinic
Monoclinic
Space group
P21/n
P
1
There are abundant hydrogen bonds in the comꢀ
plex molecule (Fig. 2, Table 3).
Unit cell dimensions:
The intramolecular hydrogen bonds were formed
between the imido and hydroxyl groups. The intermoꢀ
lecular hydrogen bonds were formed by N(8)···H–
O(23), N(6)···H–O(22), O(21)···H–O(6), O(22)···H–
O(14), and O(21)···H–O(20) and so on. These interꢀ
and intramolecular hydrogen bonds resulted in a
threeꢀdimensional network and provide extrastability
for the structure.
a
, Å
, Å
, Å
, deg
, deg
, deg
1.274(2)
6.5735(14)
12.851(3)
103.754(3)
10.3987(14)
17.410(2)
21.285(3)
101.009(2)
96.712(2)
95.432(2)
3729.4(9)
4
b
c
α
β
γ
For compound H3L, the bond lengths of acyl C=O
1.217 Å) are typical of double bonds, showing its keto
V
Z
, Å3
925.1(3)
4
(
form in the free ligand. Moreover, the benzene ring
and the C(2), O(2), N(1), N(2), C(8), C(9), O(3), and
O(4) atoms are almost coplanar. At the same time,
there are also many hydrogen bonds in the ligand molꢀ
ecule. The intramolecular hydrogen bonds were
formed between the imido and hydroxyl groups. The
intermolecular hydrogen bonds were formed between
the hydroxyl group O atoms, acylic O atoms, and carꢀ
boxylic O atoms, respectively. In addition, there is
oneꢀdimensional single helical chain formed by
hydrogen bonds in the structure (Fig. 3). Furtherꢀ
more, there is also a twoꢀdimensional reticulation
formed by hydrogen bonds along the x axis, and each
gridding is formed by four H3L molecules sharing the
same edge with each other (Fig. 4).
ρcalcd, mg/m3
1.495
0.120
1.730
Absorption coefficient,
mm–1
1.217
F
(000)
Crystal size, mm
range for data collecꢀ
432
1928
0.33
×
0.09
×
0.07 0.38
× 0.26 × 0.13
θ
3.26 to 25.50
1.70 to 25.10
tion, deg
Limiting indices
–13
–7
–15
≤
≤
≤
h
k
l
≤
≤
≤
34
7
15
–12
–20
–25 ≤ l
≤
≤
h
k
≤
≤
≤
12
17
2
The emission spectrum of the ligand H3L and
Cd(II) complex was measured in the solid state at
room temperature. The excitation wavelength is
300 nm. The fluorescence spectrum of the ligand H3L
and complex is shown in Fig. 5. The free ligand H3L
shows two broad bands around 407 and 453 nm, but
the emission peak of the ligand H3L at 407 nm disapꢀ
peared in the complex, and the emission peak at
453 nm is redꢀshifted to 516 nm, which may be
assigned to intraligand fluorescence emission band
[19–23]. In addition, it is evident that the intensity of
Reflections collectꢀ
ed/unique
5284/1691
18929/13067
(
Rint = 0.0320)
(Rint = 0.0207)
Completeness to θ, %
98.8
98.2
Refinement method
Fullꢀmatrix leastꢀ Fullꢀmatrix leastꢀ
squares on F2
squares on F2
Data/restraints/parameꢀ
ters
1691/0/138
13067/0/1013
GOOF
1.027
1.043
Final R indices
R1 = 0.0435,
R1 = 0.0393,
the complex is much stronger than that of ligand H3L
.
(
I
> 2σ(I))
wR2 = 0.0977
wR2 = 0.1098
The fluorescence enhancement of the Cd(II) complex
reflects the efficient energy transfer from the Tiꢀelecꢀ
tron conjugated system of the ligand to the Cd2+.
These observations suggest that the Cd(II) complex
could be anticipated as a potential fluorescent mateꢀ
rial.
R
indices (all data)
R1 = 0.0717,
R1 = 0.0620,
wR2 = 0.1302
wR2 = 0.1130
Largest diff. peak and
hole,
Å–3
0.154
and –0.176
0.840
and –0.596
e
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 36
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108
LIU et al.
Table 2. Selected bond lengths and bond angles for the Cd(II) complex
Bond
d
, Å
Bond
d
, Å
Bond
d, Å
Cd(1)–N(9)
Cd(1)–N(2)
Cd(1)–O(3)
Cd(2)–N(4)
Cd(2)–O(6)
Cd(3)–O(13)#1
Cd(3)–O(11)
Cd(4)–N(23)
Cd(4)–O(16)
2.257(4)
2.400(4)
2.520(3)
2.323(4)
2.475(3)
2.357(3)
2.489(3)
2.294(4)
2.451(3)
Cd(1)–N(5)
Cd(1)–O(8)
Cd(2)–N(7)
Cd(2)–O(3)
Cd(3)–N(15)
Cd(3)–N(14)
Cd(3)–O(13)
Cd(4)–O(18)#2
Cd(4)–O(18)
2.258(5)
2.410(3)
2.223(4)
2.350(3)
2.256(4)
2.381(4)
2.491(3)
2.337(3)
2.468(3)
Cd(1)–O(9)
Cd(1)–O(2)
Cd(2)–N(11)
Cd(2)–O(8)
Cd(3)–N(17)
Cd(3)–O(14)
Cd(4)–N(21)
Cd(4)–N(20)
Cd(4)–O(19)
2.394(4)
2.426(3)
2.234(5)
2.413(3)
2.281(4)
2.458(4)
2.285(4)
2.392(4)
2.485(4)
Angle
ω
, deg
Angle
ω
, deg
Angle
ω, deg
N(9)Cd(1)N(5)
N(9)Cd(1)N(2)
N(9)Cd(1)O(8)
N(2)Cd(1)O(8)
O(9)Cd(1)O(2)
N(9)Cd(1)O(3)
N(2)Cd(1)O(3)
N(7)Cd(2)N(11)
N(7)Cd(2)O(3)
N(7)Cd(2)O(8)
O(3)Cd(2)O(8)
N(4)Cd(2)O(6)
175.03(16)
89.37(16)
86.48(14)
138.51(13)
77.08(14)
85.31(14)
65.69(12)
157.70(18)
84.86(14)
97.23(14)
75.84(12)
65.27(13)
N(9)Cd(1)O(9)
N(5)Cd(1)N(2)
N(5)Cd(1)O(8)
N(9)Cd(1)O(2)
N(2)Cd(1)O(2)
N(5)Cd(1)O(3)
O(8)Cd(1)O(3)
N(7)Cd(2)N(4)
N(11)Cd(2)O(3)
N(11)Cd(2)O(8)
N(7)Cd(2)O(6)
O(3)Cd(2)O(6)
92.06(17)
93.12(17)
88.81(15)
95.46(14)
65.90(13)
91.79(15)
72.82(11)
99.75(15)
89.31(14)
102.18(15)
85.28(14)
150.41(12)
N(5)Cd(1)O(9)
O(9)Cd(1)N(2)
O(9)Cd(1)O(8)
N(5)Cd(1)O(2)
O(8)Cd(1)O(2)
O(9)Cd(1)O(3)
O(2)Cd(1)O(3)
N(11)Cd(2)N(4)
N(4)Cd(2)O(3)
N(4)Cd(2)O(8)
N(11)Cd(2)O(6)
O(8)Cd(2)O(6)
88.55(18)
142.90(14)
78.55(13)
89.48(15)
155.60(12)
151.35(13)
131.57(11)
97.58(16)
144.07(13)
68.23(12)
89.34(14)
133.15(12)
Before reacting the Cd(II) complex with CTꢀ other hand, the coupled
π* orbital is partially filled
DNA, its solution behavior in a buffer solution at with electrons, thus decreasing the transition probaꢀ
room temperature was monitored by UVꢀVis spectrosꢀ bilities. Thus, these effects result in hypochromism
copy for 24 h. No liberation of the ligand was observed [24]. Large hypochromism of an aromatic dye in the
under these conditions. This suggests that the complex presence of double helical DNA is usually characterisꢀ
is stable under the conditions studied.
tic of intercalation into DNA base pairs for the dye due
to the strong stacking interaction between the aroꢀ
matic chromophore and the base pairs [25, 26]. So,
the above phenomena imply that the complex interꢀ
acts with calf thymus DNA quite probably by intercaꢀ
lating the ligand into the base pairs.
The absorption spectra of the Cd(II) complex in
the absence and presence of DNA are shown in Fig. 6.
With increasing DNA concentrations, the absorption
bands at 275 and 329 nm for the Cd(II) complex show
hypochromism of 8.99 and 17.09%, respectively. The
hypochromism observed for the
π
π*
transition
We used [DNA] = 0, 10 × ×
10–6 and 20 10–6 mol/1.
bands of the Cd(II) complex at 329 nm is accompaꢀ Arrow shows the absorbance changes upon increasing
nied by less than 1ꢀnm redꢀshift. On the one hand, DNA concentration The Cd(II) complex can emit
after the Cd(II) complex binds to the base pairs of strong luminescence in Tris buffer with a maximum
DNA, the
couple with the
decreasing the
π
*
orbital of the intercalated ligand could wavelength of about 412 nm. The emission spectra of
orbital of the base pairs, thus Cd(II) complex in the absence and presence of DNA
transition energies. On the are illustrated in Fig. 7. It is evident that the emission
π
π
π*
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 36
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2010

CRYSTAL STRUCTURE, DNAꢀBINDING, AND FLUORESCENCE PROPERTIES
109
O(2)
O(4)
C(5)
C(7)
N(2)
(a)
C(4)
C(6)
C(1)
C(9)
N(1)
C(8)
C(3)
O(3)
C(2)
O(1)
O(20)
C(29)
N(12)
C(48)
O(21)
N(11)
C(30)
(b)
O(15)
C(47)
C(23)
C(22)
C(49)
C(50)
C(13)
C(12)
C(46)
C(45)
C(14)
C(15)
O(4)
N(19)
C(52)
O(17)
C(53)
N(10)
O(6)
Cd(2)
N(9)
C(9)
O(3)
C(54)
C(51)
O(16)
C(24)
N(7)
C(8)
N(1)
C(6)
C(5)
O(1)
C(55)
C(11)
O(5)
C(10)
N(3)
Cd(1)
N(2)
N(4)
N(21)
O(16)
Cd(3)
C(58)
C(59)
C(57
O(8) C(18)
N(23)
C(60)
C(17)
C(4)
C(3)
N(22)
C(56)
C(57)
O(23)
O(2)
N(8)
O(24)
O(19)
C(54
O(17
C(52
O(7)
O(9)
C(26)
O(18)
A)
C(1)
C(19)
N(5)
C(2)
C(21)
Cd(4A)
N(24)
N(21)
O(16
)
A)
N(22
A)
A)
N(6)
A)
C(56A
C(20)
C(55
A
)
A)
C(53A)
C(51A)
C(20
C(19
C(50
A)
C(46
A
)
A
)
A
)
C(47
A)
O(15A)
C(48A)
C(49A)
Fig. 1. Perspective view of H L (a) and complex (b), where H in the complex are omitted for clarity.
3
intensity increases by about 1.27 times with increasing is restricted at the binding site, decreasing the vibraꢀ
tional modes. The binding of the Cd(II) complex to
DNA leads to a marked increase in the emission intenꢀ
sity, which also agrees with those observed for the UV
spectra.
concentrations of CTꢀDNA for the Cd(II) complex.
The results of the emission titrations also indicate that
the complex is protected from solvent water molecules
by the hydrophobic environment inside the DNA
helix. This implies that the complex can insert between
DNA base pairs. Since the hydrophobic environment
inside the DNA helix reduces the accessibility of solꢀ
vent water molecules into the complex, the compound
The emission quenching spectra of the Cd(II)
complex in the absence and presence of DNA are
shown in Fig. 8. With increasing K4[Fe(CN)6]
quencher concentrations, the system of the complex
Fig. 2. Packing diagram of the complex, where H atoms are
omitted for clarity.
Fig. 3. Oneꢀdimensional single helical chains of H L
3
formed by hydrogen bonds.
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110
LIU et al.
Table 3. Geometric parameters of hydrogen bonding in the Cd(II) complex*
d
, Å
⋅⋅⋅
Contact D–H⋅⋅⋅
A
Angle DHA, deg
D–H
H
A
D⋅⋅⋅A
O(22)–H(17w)⋅⋅⋅O(11)
O(21)–H(11w)⋅⋅⋅O(6)
O(23)–H(5w)⋅⋅⋅O(22)
O(19)–H(3w)⋅⋅⋅O(24)
O(9)–H(2w)⋅⋅⋅O(7)
0.83
0.83
0.83
0.83
0.83
0.86
0.86
0.83
0.83
0.83
0.83
0.83
0.83
0.83
0.83
0.82
2.36(3)
1.923(17)
2.11(7)
2.085(16)
1.870(15)
1.90
3.135(6)
2.726(5)
2.811(6)
2.896(6)
2.669(5)
2.583(5)
2.482(6)
2.597(5)
3.081(6)
2.795(7)
2.787(6)
2.868(6)
2.752(5)
2.654(6)
2.912(6)
2.742(6)
155(7)
162(5)
143(10)
166(6)
161(4)
135.8
N(19)–H(19)⋅⋅⋅O(15)
N(13)–H(13)⋅⋅⋅O(10)
O(14)–H(19w)⋅⋅⋅O(12)#1
O(14)–H(13w)⋅⋅⋅O(5)#1
O(20)–H(9w)⋅⋅⋅O(4)#3
O(24)–H(8w)⋅⋅⋅O(10)#4
O(24)–H(7w)⋅⋅⋅O(21)#1
O(23)–H(6w)⋅⋅⋅O(2)#5
O(19)–H(4w)⋅⋅⋅O(17)#2
O(9)–H(1w)⋅⋅⋅O(23)#6
O(15)–H(15)⋅⋅⋅O(22)#7
1.78
137.8
2.03(8)
2.28(3)
2.22(7)
1.971(15)
2.13(5)
1.955(18)
1.843(12)
2.18(2)
1.95
126(8)
162(9)
127(8)
168(6)
147(9)
161(5)
165(5)
146(4)
162
#1
#2
#3
#4
* Symmetry transformations used to generate equivalent atoms: –x + 1, –y + 1, –z + 1; –x, –y + 2, –z + 1; –x + 1, –y, –z + 2; x, y + 1,
z; x + 1, y, z – 1; x – 1, y, z + 1; x – 1, y, z.
#5
#6
#7
1000
800
600
400
200
0
Complex
Ligand
400
300
350
450
500
550
Wavelength, nm
Fig. 4. Twoꢀdimensional net structure of H L formed by
Fig. 5. Fluorescence spectra of H L (a) and complex (b) in
3
3
hydrogen bonds.
the solid state.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 36
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CRYSTAL STRUCTURE, DNAꢀBINDING, AND FLUORESCENCE PROPERTIES
111
2
1
0
220
200
180
160
140
120
100
80
60
40
20
0
–20
+DNA
+DNA
300 350 400 450 500 550 600
Wavelength, nm
300
Wavelength, nm
400
Fig. 6. Electronic spectra of the Cd(II) complex
Fig. 7. Emission enhancement spectra of the complex
3
0.1 ×
10⎯ mol/1) in the presence of CTꢀDNA.
–3
–6
(
(
0.1
×
10 mol/1) in the presence of 0,10 10 × 10 , 20 ×
–6
–6
10 , and 30
× 10 mol/1 CTꢀDNA. Arrow shows the
emission intensity changes upon increasing the DNA conꢀ
centration.
400
300
200
100
0
Complex
1.6
1.5
+K4[Fe(CN)6]
Complex
1.4
1.3
1.2
Complex
3
⎯
DNA
4
1.1
1.0
350
400
450
Wavelength, nm
500
550
1
2
С ([K4Fe(CN)6]), 10–3 mol/l
Fig. 8. Emission quenching spectra of the complex
–3
(
0.1 × 10 mol/1) and complexꢀDNA with increasing the
Fig. 9. Emission quenching curve of the complex with the
increasing concentration of K [Fe(CN) ] quencher. is
the fluorescence intensity of the complex in the absence of
DNA, and F is the fluorescence intensity of the complex in
the presence of DNA.
concentration of K [Fe(CN) ] quencher. [K [Fe(CN) ]] =
4
6
4
6
–3
10⎯ mol/1. Arrow shows the emission intensities changes
F
0
0, 0.5, 1, 1.5, and
2 × 10 mol/1. [DNA] = 40 ×
4
6
6
upon increasing the K [Fe(CN) ] quencher concentraꢀ
4
6
tion.
the same after bonding to DNA, which suggests that
there is only a bonding mode between the complex and
DNA. That is, the Cd(II) complex is possibly bound to
calf thymus DNA mainly by intercalation.
and complexꢀDNA causes obvious reduction in the
emission intensity, but the emission intensity of comꢀ
plex in the absence of DNA is lower than that in the
presence of DNA under the same K4[Fe(CN)6]
quencher concentration, indicating that the Cd(II)
complex binds to DNA and is protected from
K4[Fe(CN)6] quencher in the presence of DNA. In
addition, it is evident that the emission quenching curꢀ
vilinear slope in the absence of DNA is bigger than
that in the presence of DNA (Fig. 9). Furthermore,
ACKNOWLEDGMENTS
The work was supported by the Program of the
Technology and Plan (project no. 2007K02ꢀ11) and
the Shaanxi Provincial Science and Technology
the emission quenching curve is close to a beeline all (project no. ZDKGꢀ268).
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 36
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112
LIU et al.
13. Lu, Y.C., An, C.X., Zhang, Z.H., et al., Chin. J. Inorg.
Chem., 2007, vol. 20, no. 4, p. 645.
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