A new two dimensional copper (II) coordination complex with sulphonamide: Synthesis, crystal structure and DNA binding study

Article abstract of DOI:10.1016/j.inoche.2012.05.006

A novel copper (II) complex, [Cu(HL)₂] (where, HL = 3-(4-(sulphonamine)phenylimino)-1-phenylbut-1-en-1-ol) has been synthesized and characterized by IR, UV-vis, magnetic susceptibility measurement and single crystal X-ray crystallographic studies. The crystal data confirm the square planarity of the prepared complex having an orthorhombic space group Pca2 (1). Molecular packing of the complex is stabilized by N - H...O hydrogen bonding and weak N - H...O, C - H...Cg π-ring intermolecular interactions, hence forming a two dimensional supramolecular network structure. CT-DNA binding studies have been carried out by monitoring electronic absorption titrations, luminescence titrations, a DNA melting, cyclic voltametry and viscosity measurement studies. An intercalative mode of DNA binding is suggested for the prepared copper (II) complex.

Full text of DOI:10.1016/j.inoche.2012.05.006

Inorganic Chemistry Communications 21 (2012) 163–167
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
A new two dimensional copper (II) coordination complex with sulphonamide:
Synthesis, crystal structure and DNA binding study
b
b
W. Bembee Devi a, R.K. Bhubon Singh a, , J.P. Jasinski , J.A. Golen
⁎
a
Department of Chemistry, Manipur University, Imphal, Manipur, India
Department of Chemistry, Keene State College, 299 Main Street, Keene, NH, 03435, USA
b
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel copper (II) complex, [Cu(HL)2] (where, HL=3-(4-(sulphonamine)phenylimino)-1-phenylbut-1-en-1-ol)
has been synthesized and characterized by IR, UV–vis, magnetic susceptibility measurement and single crystal
X-ray crystallographic studies. The crystal data confirm the square planarity of the prepared complex having
an orthorhombic space group Pca2 (1). Molecular packing of the complex is stabilized by N―H…O hydrogen
bonding and weak N―H…O, C―H…Cg π-ring intermolecular interactions, hence forming a two dimensional
supramolecular network structure. CT-DNA binding studies have been carried out by monitoring electronic
absorption titrations, luminescence titrations, a DNA melting, cyclic voltametry and viscosity measurement
studies. An intercalative mode of DNA binding is suggested for the prepared copper (II) complex.
© 2012 Elsevier B.V. All rights reserved.
Received 24 December 2011
Accepted 1 May 2012
Available online 8 May 2012
Keywords:
Sulphonamide imine
Absorption titration
DNA binding
Hydrogen bonding
2D supramolecular network
Intercalation
Sulphonamide imines are Schiff base compounds which contain a
carbon–nitrogen double bond (C N) and a sulphonamide (―SO2―NH―)
functional group in the parent structural unit. Systems containing both
azomethine (C N) and a sulphonamide (―SO2―NH―) groups are related
to potential biological and pharmaceutical compounds that display anti-
cancer [1], anti-tubercular [2], anti-inflammatory and anti-microbial [3]
activities. However, their biological activity can be altered depending
upon the substituent present on the parent structural unit or by complex-
ation with a metal ion. The coordination chemistry of sulphonamide
imine complexes has undergone noticeable development in recent
years due to the interesting properties of these substances, such as the
presence of artificial chemical nucleases in a DNA binding study which
plays a major role as a molecular tool in biochemistry [4]. The importance
of metal–DNA interactions in living systems, and their potential applica-
tions, especially in the treatment and diagnosis of diseases, has stimulated
considerable recent interest in this area. Understanding how metal com-
plexes interact with DNA has become an active area of research at the in-
terface between chemistry, molecular biology and medicine. In this paper
we report a synthesis, crystallographic, spectroscopic and DNA binding
study of a new sulphonamide imine Schiff base copper (II) complex,
The electronic spectrum of the copper (II) complex in DMF shows
a broad absorption band ca. 640 nm which may be assigned to the
2A1g→2B1g transition and a square planar geometry (Fig. S2), similar
to that suggested around the copper (II) ion [6] with the sulphonamide
imine ligand as an N, O-donor. In the IR spectrum of the complex the
ν(C N) band was observed ca. 1586 cm−1 (Fig. S3), which shows a mar-
ked shift (Δν=34 cm−1) as compared to the free ligand (1620 cm−1
)
(Fig. S4), suggesting coordination of the azomethine N-atom to the
Cu(II) ion [7]. It has been observed that the lowering of the frequency
of the enolic ν(O―H) band of the ligand (ca. 3346–3062 cm−1) is a re-
sult of intra-molecular (―OH....N―) hydrogen bonding within the re-
spective ligand molecules [8]. The presence of observed bands in the
region, ca. 1321–1332 and 1163–1162 cm−1, may be assigned to the
νa(SO2) and νs(SO2), respectively, for the ligand and the complex [9].
In the title complex, the ν(Cu―N) and ν(Cu―O) vibration modes are
assigned to bands in the region at 516 cm−1 and 463 cm−1, respective-
ly. In the thermal analysis data of the complex, a loss of two ligand mol-
ecules started at ca. 220 °C and was completed ca. 620 °C which was
accompanied by an exotherm ca. 500 °C (Fig. S5).
The square planarity of the title copper (II) complex has been con-
firmed by single crystal X-ray crystallography. The copper (II) ion is
coordinated by a N2O2-donor set of the two sulphonamide imine ligand
molecules (Fig.1). It crystallizes in an orthorhombic, Pca2(1) space
group with one monomeric C32H30CuN4O6S2 group in the asymmetric
unit and maintains a slightly distorted square planar geometry. The
six-membered chelate rings are nearly planar, while the N2―C19
(1.34(1) Å) and N1―C3 (1.33(1) Å) bonds retain their double bond
C32H30CuN4O6S2.
Preparation of the ligand (Fig. S1) and complex along with elemen-
tal analyses, magnetic measurements and crystal data are described [5].
⁎
Corresponding author at: Department of Chemistry, Manipur University, Imphal-
795003, India. Tel.: +91 385 2435093; fax: +91 3852435145.
E-mail address: bhubonsingh@gmail.com (RK.B. Singh).
1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2012.05.006

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W.B. Devi et al. / Inorganic Chemistry Communications 21 (2012) 163–167
surrounding the Cu1-atom (Cu1/O1/C1/C2/C3/N1/O2/C17/C18/C19/
N2) and the substituted benzene rings (C11―C16 (32.8(0)°);
C27―C32 (31.6(6)°)), and the sulphonamide (―SO2―NH―) substitut-
ed benzene rings (C5―C10 (86.0 (8)°); C21―C25 (85.9 (2)°)) shows a
significant twisting of these rings relative to the 11-membered, square
planar ring system. Intra-molecular hydrogen bonds (N3―H3B....O4
(2.38 (4) Å) and N4―H4B....O5(2.24 (17) Å)) are observed. Crystal
packing is stabilized by N―H....O hydrogen bonds and weak N―H....O,
C―H…Cg π-ring intermolecular interactions forming a 2D supramolec-
ular network which displays one molecule of the complex surrounded
by six additional molecules (Fig. 2).
A DNA binding study with the free ligand and complex has been
carried out by monitoring electronic absorption titrations, lumines-
cence titrations, a thermal behavior study, cyclic voltammetry and vis-
cosity measurement studies. Electronic absorption titrations were
carried out on a Perkin Elmer UV–vis Lambda 35 spectrophotometer.
By maintaining a constant concentration of the free ligand and complex
(7.2×10−5 M) and varying the concentration of a CT-DNA solution (ap-
proximately 2.9 to 8.9×10−6 M) which was added, the absorbance for
each addition of the DNA concentration was subsequently recorded.
The intrinsic binding constant was determined from the absorption
spectral data by application of the equation [10],
½DNAꢀ=ðεa−εf Þ ¼ ½DNAꢀ=ðεb−εf Þ þ 1=Kbðεb−εf Þ
ð1Þ
where, εa, εf, and εb correspond to extinction coefficients of the apparent,
free and bound ligand or metal complex, respectively. [DNA] is the molar
concentration of DNA and was measured by electronic absorption spec-
troscopy using the molar absorption coefficient (6600 M−1 cm−1) at
258 nm. The solution of CT-DNA was prepared by using a 5 mM, Tris–
HCl buffer (pH=7.1). The ratio of UV-absorbance at 260 nm and
280 nm, A260/A280, was found to be ca.1.88, indicating that the DNA
was satisfactorily free of protein [11]. A graph of [DNA]/(εb−εf) vs.
[DNA] was plotted with Kb calculated by a ratio of the slope to the
y-intercept. The absorption spectrum of the complex and free ligand in
presence of increasing concentration of the CT-DNA (approximately
Fig. 1. An ortep view of the copper (II) complex with 50% ellipsoidal probability, showing
the atom numbering scheme. Some selected bond lengths (Å) and angles (°): Cu―O1,
1.906(4); Cu―O2, 1.894(4); Cu―N1, 1.991(5); Cu―N2, 1.973(5); O1―Cu1―O2,
179.4(3); O1―Cu1―N1, 92.63(19); O1―Cu1―N2, 87.81(19); O1―Cu1―O2, 87.35(19);
N1―Cu1―N2, 179.5(2).
character. The bond lengths of Cu1―N (1.973 (4) Å; 1.991 (5) Å) and
Cu1―O (1.894 (4) Å; 1.906 (4) Å) are similar to each other. The dihedral
angle between the mean planes of the 11-membered chelate group
Fig. 2. Molecular packing structure of the copper (II) complex viewed along the b axis. Dashed lines indicate N―H....O hydrogen bonds forming a 2D supramolecular network where
one molecule of the complex is surrounded by six molecules of the complex.

W.B. Devi et al. / Inorganic Chemistry Communications 21 (2012) 163–167
165
Fig. 5. Emission spectrum of ethidium bromide bound CT-DNA in the absence (topmost
curve) and in the presence (subsequent curves) of increasing concentration of the
copper (II) complex. The arrow shows the reduction in emission intensity with increasing
concentration of the complex.
Fig. 3. Absorption spectrum of the copper (II) complex in the presence of different
concentrations of CT-DNA. The arrow indicates the increase in absorbance of the
complex with increasing CT-DNA concentration. Inset: plot of [DNA]/(εa −εf) vs.
[DNA] and a linear fit of the titration curve.
and complex were found non-emissive, ethidium bromide (EB) bound
DNA adduct was used to study the luminescence titrations method. Fluo-
rescence emission intensities of EB at 595 nm with an excitation slit
274 nm were measured with different concentrations of the complex
and free ligand. The fluorescence quenching of EB bound to DNA by the
complex and free ligand is in good agreement with the classical linear
Stern–Volmer equation [14].
2.9, 4.5, 5.9, 7.5, 8.9×10−6 M) showed a considerable amount of
hyperchromism with a slight red shift (Fig. 3 and S6). Hyperchromism
in the spectrum might be the result of damage of the double stranded
DNA helix through an intercalative mode of binding of the complex
with DNA molecules [12]. The intrinsic binding constant (Kb) of the com-
plex and free ligand was found to be 5.55×105 and 2.57×105 M−1 re-
spectively. A thermal behavior study of DNA was performed by
measuring the absorption intensity of CT-DNA at 258 nm at a tempera-
ture range 25–100 °C, both in the absence and presence of the complex
and free ligand. The thermal denaturation behavior in the presence of
the copper (II) complex provides insight into conformational changes
when the temperature is raised. The strength of interaction between
the ligand/complex and the DNA can also be monitored. As the temper-
ature of the solution increases, the double stranded DNA tends to disso-
ciate into a single strand thereby displaying a hyperchromic effect on the
absorption spectra of DNA, which was observed. The DNA melting tem-
perature, Tm, where half of the total base pairs becomes non-bonded, was
determined experimentally and found to be 75 °C which increases to 81°,
82°, 86 °C and 80, 81, 82 °C with increasing ratio of DNA to complex and
ligand concentrations (0, 0.1, 0.2 and 0.4), respectively (Fig. 4 and S7).
These results both suggest and provide support for the presence of an
intercalative effect with DNA. The observed mode of DNA stabilization
is similar to that seen in chlorobenzylidine [13]. As the prepared ligand
Io=I ¼ 1 þ Ksv½Qꢀ
ð2Þ
where Io and I are the emission intensity in the absence and presence of
the complex/free ligand, respectively. Ksv is the linear Stern–Volmer
quenching constant and Q is the ratio of the total concentration of the
complex/free ligand to that of DNA. The Ksv value for the complex and
free ligand were found to be 3.31 and 2.33 respectively which is given
by the slope to y-intercept value from the plot of Io/I versus [Q] (Fig. S8).
The apparent binding constant (Kapp) was also calculated by the
equation,
KEB½EBꢀ ¼ Kapp½Complexꢀ
ð3Þ
where the concentration of the complex and ligand was determined by
the value at a 50% reduction of the fluorescence intensity of ethidium
bromide (EB) and KEB =1×107 M−1 ([EB]=1.3×10−6 M). Ethidium
bromide (EB) emits an intense fluorescent light when intercalated be-
tween two DNA base pairs. In presence of an additional DNA binding
Fig. 4. Thermal denaturation profiles of CT-DNA (i) in the absence and presence of different
Fig. 6. Cyclic voltammogram of the copper (II) complex (A) in absence and (B) presence of
concentrations of the complex (ii) 0.1, (iii) 0.2 and (iv) 0.4, respectively.
CT-DNA.

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W.B. Devi et al. / Inorganic Chemistry Communications 21 (2012) 163–167
Acknowledgments
One of the authors W. Bembee Devi is grateful to UGC, New Delhi for
the financial support under the scheme of UGC-BSR Research Fellowship
in Science 2010–2011 (vide order no. 233/MU/8-50/2010/UGC (Pt. I)).
J.P.J. acknowledges the NSF-MRI program (grant no. CHE1039027) for
funds to purchase the X-ray diffractometer.
Appendix A. Supplementary material
Supplementary data to this article can be found online at http://
dx.doi.org/10.1016/j.inoche.2012.05.006.
References
Fig. 7. Effect of increasing amount of the ligand (filled square) and the complex (filled
circle) on the relative viscosity of CT-DNA in a Tris–HCl buffer. [DNA]=77 μM, [Ligand]
or [Complex]=0–100 μM at 20 0.1 °C.
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Å, V=3093.4 93) Å- 3, Z=4, Dc=1.491 Mg m- 3, F(000)=1436, R1 =0.0757,
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