Synthesis, characterization and DNA interaction of copper (II) complexes with Schiff base ligands derived from 2-pyridinecarboxaldehyde and polyamines

Article abstract of DOI:10.1016/j.inoche.2010.08.006

A series of copper (II) complexes a-d with Schiff bases ligands derived from the condensation reactions between 2-pyridinecarboxaldehyde and different polyamines (ethylenediamine, diethylenetriamine, triethylenetetramine and tetraethylenepentamine) were synthesized and characterized by elemental analysis, FT-IR spectroscopy, HRMS, molar conductance and molecular modeling studies. The interactions of the copper complexes a-d with DNA were investigated by the UV spectra, viscosity measurements and gel electrophoresis under physiological conditions. The experimental results indicated that four complexes could bind to DNA via an intercalative mode and showed a different DNA cleavage activity with the sequence: d > c > a > b.

Full text of DOI:10.1016/j.inoche.2010.08.006

Inorganic Chemistry Communications 13 (2010) 1421–1424
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Synthesis, characterization and DNA interaction of copper (II) complexes with Schiff
base ligands derived from 2-pyridinecarboxaldehyde and polyamines
a,
b
c
a
a
Xin-Bin Yang ⁎, Yu Huang , Jin-Sheng Zhang , Shu-Kai Yuan , Ren-Quan Zeng
a
Department of Basic Science, Rongchang Campus, Southwest University, Chongqing 402460, PR China
Pharmacy College, Ningxia Medical University, Yinchuan 750004, PR China
School of Chemistry and Material Science, Guizhou Normal University, Guiyang 550001, PR China
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of copper (II) complexes a–d with Schiff bases ligands derived from the condensation reactions
between 2-pyridinecarboxaldehyde and different polyamines (ethylenediamine, diethylenetriamine,
triethylenetetramine and tetraethylenepentamine) were synthesized and characterized by elemental
analysis, FT-IR spectroscopy, HRMS, molar conductance and molecular modeling studies. The interactions
of the copper complexes a–d with DNA were investigated by the UV spectra, viscosity measurements and gel
electrophoresis under physiological conditions. The experimental results indicated that four complexes could
bind to DNA via an intercalative mode and showed a different DNA cleavage activity with the sequence:
dNcNaNb.
Received 25 April 2010
Accepted 3 August 2010
Available online 10 August 2010
Keywords:
Schiff base
Copper (II) complexes
DNA binding
DNA cleavage
© 2010 Elsevier B.V. All rights reserved.
Investigations on the interaction between transition metal com-
plexes and DNA has attracted many interests due to their importance
in cancer therapy and molecular biology [1–9]. Among them, Schiff
base metal complex is a kind of attractive reagent due to their special
activities in pharmacology and physiology [10–16]. During the last
decade, transition metal complexes of Schiff base derived from 2-
pyridinecarboxaldehyde and different amines have received consid-
erable attention on the part of synthetic and biological activities of
DNA binding and cleavage with high sequence and structure
selectivity [17–20]. However, to the best of our knowledge, less
attention was paid on the interaction of DNA and Schiff base metal
complexes derived from 2-pyridinecarboxaldehyde and polyamines
such as ethylenediamine, diethylenetriamine, triethylenetetramine
and tetraethylenepentamine. In this communication we describe the
synthesis, DNA binding and cleavage abilities of a series of copper (II)
complexes with Schiff base ligands derived from 2-pyridinecarbox-
aldehyde and different polyamines (Scheme 1).
through elemental analyses, HRMS, IR spectra and molar conductivity
measurements. Since no single crystals suitable for X-ray determination
could be isolated, structural information for these complexes were
obtained from the B3LYP/6-311G** optimization calculations as shown
in Fig. 1. The lengths of coordination bonds are labeled in the figure.
The mode of the four complexes bound to DNA was investigated by
absorption spectra. Hyperchromic effect and hypochromic effect are the
spectra features of DNA concerning its double-helix structure. This
spectra change process reflects the changes of DNA in its conformation
and structures after the complex binds to DNA [25,26]. Hypochromism
results from the contraction of DNA in the helix as well as from the
conformation on DNA, while hyperchromism results from the damage
of the DNA double-helix structure. The absorption spectra of DNA in the
absence and the presence of copper (II) complexes a–d were given in
Fig. 2 respectively. The addition of copper (II) complexes to DNA caused
appreciable increase in the absorption intensity, which was a typical
hyperchromic effect. These results suggested that the binding of copper
(II) complexes with DNA was an intercalative mode.
Spectroscopic data are necessary, but not sufficient to support a
binding mode. Hydrodynamic methods such as viscosity measurements
which are sensitive to length increase of DNA are regarded as the most
effective means of studying the binding mode of complexes to DNA in the
absence of crystallographic structural data and NMR [27]. For further
clarification of the binding mode, viscosity measurements were carried
out. A classical intercalative mode causes a significant increase in
viscosity of DNA solution due to an increase in separation of base pairs at
intercalation site and hence an increase in overall DNA length. However, a
partial and/or nonclassical intercalation of complex may bend (or kink)
the DNA helix, resulting in the decrease of its effective length
and, concomitantly, its viscosity [28,29]. The effect of the copper (II)
The copper (II) complexes a–d were prepared by a typical procedure.
Polyamine (0.12 g, 2 mmol) was added to 2-pyridinecarboxaldehyde
(
0.43 g, 4 mmol) and refluxed in methanol for 4 h. Copper (II) chloride
dehydrate (0.34 g, 2 mmol) dissolved in methanol was added to
this solution and refluxing was continued for another 1 h. Then the
mixture was concentrated under reduced pressure. The resulting green
solid was filtered off, washed with diethyl ether and dried in vacuo. We
1 2 2 2
got the likely composition of complexes: [CuL ] Cl ·2H O (a), [CuL ]
Cl ·2H O (b), [CuL ] Cl ·H O (c) and [CuL ] Cl
2
2
3
2
2
4
2
·H O (d) [21–24]
2
⁎
Corresponding author.
E-mail address: yangxbqq@126.com (X.-B. Yang).
1387-7003/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2010.08.006

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X.-B. Yang et al. / Inorganic Chemistry Communications 13 (2010) 1421–1424
control DNA without any additives. It is obvious that copper (II)
complex d (lane 5) catalyzed the cleavage of plasmid DNA (pUC 19)
much more efficiently than copper (II) complex a (lane 2), b (lane 3)
and c (lane 4) under physiological conditions. Electrophoresis and
densitometry indicated that the copper (II) complexes a–d resulted in
3
5%, 4%, 54% and 82% of nicked DNA respectively. Therefore, our
Scheme 1. Schiff base ligands derived from 2-pyridinecarboxaldehyde and different
polyamines.
subsequent efforts focus on the reactivity of the copper (II) complex d.
The cleavage of DNA by different concentrations of the copper (II)
complex d was studied for 24 h. The intensity of the nicked DNA
(Form II) band increased apparently with the increase of the complex
concentration as shown in Fig. 5. Increasing the concentration of
complex d in the order of 0.25, 0.75, 1.25 and 1.75 mM resulted in 24%,
55%, 76% and 97% nicked DNA, respectively.
In summary, a series of the copper (II) complexes a–d with Schiff
base ligands derived from 2-pyridinecarboxaldehyde and polyamines
were synthesized and characterized. The interactions of complexes a–
d with DNA were studied by UV spectra, viscosity and gel
electrophoresis under physiological conditions. The results indicate
that the Schiff base copper (II) complexes a–d are capable of binding
DNA by an intercalative mode and cleaving DNA without the use of
any exogenous agents. Moreover, complex d shows the considerably
high binding and cleavage abilities. The results revealed that the
structure difference on the polyamine might lead to obvious
complexes on the viscosity of CT-DNA solution is given in Fig. 3. The plots
show that the relative viscosity of DNA increased with the addition of the
copper (II) complexes, which are ascribed to classical intercalative
binding mode. From the relative viscosity values, it is clear that complex d
shows much higher binding affinity than the complex a, b and c.
Besides the above methods, interactions between the copper (II)
complexes and DNA were also investigated by the cleavage assay of
plasmid DNA (pUC 19). The cleavage of the plasmid DNA was
analyzed by monitoring the conversion of supercoiled circular DNA
(
Form I) to nicked DNA (Form II). The amounts of strand scission were
assessed by agarose gel electrophoresis.
First we compared the cleavage abilities of the copper (II)
complexes a–d at a concentration of 1.25 mM and an incubation
time of 12 h. Fig. 4 showed the results. Lane 1 in the figure showed the
A
B
C
D
Fig. 1. The optimized structures of the complexes a–d with lengths of coordination bonds. The red ball stands for copper atom, the blue balls for nitrogens, the grey balls for carbons
and the white balls for hydrogens.

X.-B. Yang et al. / Inorganic Chemistry Communications 13 (2010) 1421–1424
1423
A
B
C
D
Fig. 2. Absorption spectra of CT-DNA in the absence and presence of copper complex a (i), b (ii), c (iii) and d (iv). [DNA]=0.9×10−4 mol/L, [CuL]2+=0, 0.5, 1.0, 1.5, 2.0, and 2.5 μM
respectively. The arrow shows the intensity changes on increasing the copper complex concentration.
difference of DNA binding and cleavage abilities of the complexes. The
–NH– of polyamine might play a key role in the DNA recogni-
tion process. More in-depth studies about binding and cleavage
mechanisms will be continued in our laboratory.
Fig. 4. Effect of different copper (II) complexes a–d (1.25 mM) on the cleavage reactions of
pUC 19 DNA (12.5 μg/mL) in a Tris–HCl buffer (100 mM, pH 7.4) at 37 °C for 12 h. (A)
Agarose gel electrophoresis diagram: lane 1, DNA control; lane 2, a; lane 3, b; lane 4, c; lane
5, d. (B) Quantitation of % plasmid relaxation (Form II%) relative to plasmid DNA per lane.
Fig. 3. Effects of increasing amount of copper complexes a (■), b (●), c (▲) and d (▼)
on the viscosity of CT-DNA, [DNA]=1.0×10− mol/L.
4

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X.-B. Yang et al. / Inorganic Chemistry Communications 13 (2010) 1421–1424
[
[
10] A.S. Sitlani, E.C. Long, A.M. Pyle, J.K. Barton, J. Am. Chem. Soc. 114 (1992) 2303.
11] D.C. Crans, A.D. Keramidas, H.H. Lity, O.P. Anderson, M.M. Miller, L.M. Lemoine, S.P.
Williams, M. Vandenberg, A.J. Rossomando, L.J. Sweet, J. Am. Chem. Soc. 119 (1997)
5447.
[
[
12] V.W.W. Yam, S.W.K. Choi, K.K.W. Lo, W.F. Dung, R.V.C. Kong, J. Chem. Soc., Chem.
Commun. (1994) 2379.
13] L.Z. Li, C. Zhao, T. Xu, H.W. Ji, Y.H. Yu, G.Q. Guo, H. Chao, J. Inorg. Biochem. 99 (2005)
1076.
[
[
14] S. Dhar, M. Nethaji, A.R. Chakravarty, Inorg. Chem. 45 (2006) 11043.
15] K. Dhara, J. Ratha, M. Manassero, X.Y. Wang, S. Gao, P. Banerjee, J. Inorg. Biochem.
101 (2007) 95.
[
16] X.B. Yang, L. Wang, J. Zhang, Z.W. Zhang, H.H. Lin, L.H. Zhou, X.Q. Yu, J. Enzym.
Inhib. Med. Chem. 24 (2009) 125.
[
[
17] Vleck Jr., Coord. Chem. Rev. 230 (2002) 225.
18] G. Garcia-Friaza, A. Fernandez-Botello, M. Perez, J. Prieto, V. Moreno, J. Inorg.
Biochem. 100 (2006) 1368.
[
[
[
19] V. Uma, A. Castineiras, B.U. Nair, Polyhedron 26 (2007) 3008.
20] M. Shakir, M. Azam, Y. Azim, S. Parveen, A.U. Khan, Polyhedron 26 (2007) 5513.
21] Preparation of complex a: ethylenediamine (0.12 g, 2 mmol) was added to 2-
pyridinecarboxaldehyde (0.43 g, 4 mmol) and refluxed in methanol for 4 h.
Copper (II) chloride dehydrate (0.34 g, 2 mmol) dissolved in methanol was added
to this solution and refluxing was continued for another 1 h. Then the mixture
was concentrated under reduced pressure. The resulting green solid was filtered
−
1
off, washed with diethyl ether and dried in vacuo: Yield: 72%, IR (KBr, cm ):
416; 2921, ν(CH ); 1604, ν(C N); 774, γ(C–H); 647, ν(Cu–N). Anal. Calcd. for
14CuN ]Cl ·2H O: C, 41.14; H, 4.44; N, 13.71%. Found: C, 41.64; H, 4.54; N,
3.77%. HRMS-ESI: m/z calcd for C14
00.0544. Conductance: CuCl 239 S cm mol
3
2
[
C
14
H
4
2
2
+
1
3
2
4 1
H13CuN [CuL - H] : 300.0514, found:
2
− 1
2
:
4 2 2
, [C14H14CuN ]Cl ·2H O:
2
−1
46 S cm mol
.
[
[
[
22] Preparation of complex b: this complex was prepared by a similar procedure to that
of complex a by taking diethylenetriamine (0.21 g, 2 mmol), 2-pyridinecarboxalde-
hyde (0.43 g, 4 mmol) and copper (II) chloride dehydrate (0.34 g, 2 mmol). The
resulting dark brown solid was obtained. Yield: 65%, IR (KBr, cm− ): 3419; 2927,
1
Fig. 5. Effect of concentration of complex d on the cleavage of pUC 19 DNA (12.5 μg/mL)
in a Tris–HCl buffer (100 mM, pH 7.4) at 37 °C for 24 h. (A) Agarose gel electrophoresis
diagram: lane 1, DNA control; lanes 2–5, [complex d]=0.25, 0.75, 1.25 and 1.75 mM.
ν(CH
Cl ·2H
m/z calcd for C16
2
); 1604, ν(C N); 772, γ(C–H); 647, ν(Cu–N). Anal. Calcd. For [C16
5
H19CuN ]
2
2
O: C, 42.53; H, 5.13; N, 15.50%. Found: C, 42.21; H, 5.20; N, 15.74%. HRMS-ESI:
+
H
19ClCuN
5
[CuL
2
- H] : 343.0936, found: 343.0974. Conductance:
(B) Quantitation of% plasmid relaxation (Form II%) relative to plasmid DNA per lane.
2
−1
2
−1
CuCl
2
: 239 S cm mol , [C16
5 2 2
H19CuN ]Cl ·2H O: 229 S cm mol
.
23] Preparation of complex c: this complex was prepared by a similar procedure to that
of complex a by taking triethylenetetramine (0.30 g, 2 mmol), 2-pyridinecarbox-
aldehyde (0.43 g, 4 mmol) and copper (II) chloride dehydrate (0.34 g, 2 mmol). The
resulting dark brown solid was obtained. Yield: 81%, IR (KBr), cm− : 3418; 2928,
Acknowledgements
1
This work was financially supported by the Natural Science
Foundation Project of CQ CSTC (No. 2009BB5300) and the doctoral
program of Southwest University.
ν(CH
Cl ·H
m/z calcd for C18
2
); 1604, ν(C N); 773, γ(C–H); 646, ν(Cu–N). Anal. Calcd. For [C18
6
H24CuN ]
2
2
O: C, 45.33; H, 5.50; N, 17.62%. Found: C, 45.19; H, 5.56; N, 16.68. HRMS-ESI:
+
H
23CuN
6
[CuL
3
–H] : 386.1358, found: 386.1362. Conductance:
2
−1
2
−1
CuCl
2
: 239 S cm mol , [C18
6 2 2
H24CuN ]Cl ·H O: 220 S cm mol
.
24] Preparation of complex d: This complex was prepared by a similar procedure to
that of complex by taking tetraethylenepentamine (0.38 g, 2 mmol), 2-
pyridinecarboxaldehyde (0.43 g, 4 mmol) and copper (II) chloride dehydrate
a
References
(
(
0.34 g, 2 mmol). The resulting dark brown solid was obtained. Yield: 78%, IR
[
[
[
[
[
[
[
1] D.B. Hall, R.E. Holmlin, J.K. Barton, Nature 382 (1996) 731.
2] K.E. Erkkila, D.T. Odom, J.K. Barton, Chem. Rev. 99 (1999) 2777.
3] B. Lippert, Coord. Chem. Rev. 200 (2000) 487.
4] C. Liu, M. Wang, T. Zhang, H. Sun, Coord. Chem. Rev. 248 (2004) 147.
5] G. Pratvicl, J. Bernadou, B. Mcunicr, Adv. Inorg. Chem. 45 (1998) 251.
6] M. Shionoya, T. Ikeda, E. Kimura, M. Shiro, J. Am. Chem. Soc. 116 (1994) 3848.
7] D.M. Epstein, L.L. Chappell, H. Khalili, R.M. Supkowski, W.D. Horrocks, J.R. Morrow,
Inorg. Chem. 39 (2000) 2130.
8] X.Y. Wang, J. Zhang, K. Li, N. Jiang, S.Y. Chen, H.H. Lin, Y. Huang, L.J. Ma, X.Q. Yu,
Bioorg. Med. Chem. 14 (2006) 6745.
9] X.B. Yang, J. Feng, J. Zhang, Z.W. Zhang, H.-H. Lin, L.H. Zhou, X.Q. Yu, Bioorg. Med.
Chem. 16 (2008) 3871.
−
1
KBr, cm ): 3424; 2926, ν(CH
29CuN ]Cl ·H O: C, 46.20; H, 6.01; N, 18.86%. Found: C, 47.06; H,
.27; N, 18.74. HRMS-ESI: m/z calcd for C20
29.1851. Conductance: CuCl 239 S cm mol
2
); 1632, ν(C N); 775, γ(C–H); 616, ν(Cu–N). Anal.
Calcd. For [C20
H
7
2
2
+
6
4
2
H
28CuN
7
[CuL
,
4
–H] : 429.1780, found:
[C20 29CuN ]Cl ·H O:
2
− 1
2
:
H
7
2
2
2
−1
10 S cm mol
.
[
[
[
[
[
25] Q.S. Li, P. Yang, H.F. Wang, M.L. Guo, J. Inorg. Biochem. 64 (1996) 181.
26] C.Y. Zhou, J. Zhao, Y.B. Wu, C.X. Yin, P. Yang, J. Inorg. Biochem. 101 (2007) 10.
27] B.C. Baguley, M. LeBret, Biochemistry 23 (1984) 937.
28] S. Satyanarayana, J.C. Dabrowiak, J.B. Chairs, Biochemistry 32 (1993) 2573.
29] S. Shi, J. Liu, J. Li, K.C. Zheng, X.M. Huang, C.P. Tan, L.M. Chen, L.N. Ji, J. Inorg.
Biochem. 100 (2006) 385.
[
[